Tesi sul tema "Ruthenium compounds"

The discovery of the chemical properties related to the physiological and pathophysiological processes of the nitric oxide molecule has advanced scientific research concerning the control of NO availability in the biological environment. Complexes involving ruthenium and other ligands, such as amine and tetraazomacrocycles, have been used as models because they display properties like stability to air oxidation, solubility in water, and low cytotoxicity against host cells. Given the peculiar properties of nitric oxide, we first conducted a computational experiment based on the molecular orbital diagram of NO (Chapter 3). Then, we performed exercises of computational quantum chemistry involving the monocation (NO+) and monoanion (NO-) of NO. These exercises were presented to students at the end of their undergraduate studies or at the beginning of their postgraduate studies. The students started the experiment by exploring the Lewis structures of NO+, NO, and NO- along with the molecular orbital diagram of NO, to obtain a correlation with different properties like bond lengths and atomic charges. Next, they compared the calculated bond lengths and vibrational frequencies with experimental results found in Internet databases, which allowed them to discuss the differences they visualized. In addition, distinct approximations helped to calculate partial atomic charges. The students verified that it is difficult to determine this parameter because it is not physically observable and does not rely on any quantum mechanical operator to determine its quantity. The dipole moment calculated for NO, 0.153 D, by using B3LYP/631+G(d,p) level is close to the most accepted experimental data. This value contrasts with a recent determination of this parameter indicating that the negative charge concentrates on the nitrogen atom. The students finished the experiment by dealing with two topics of relevant interest to computational chemistry: (i) investigation of the behavior of some properties; for instance, atomic charges and spin densities, in relation to the basis set increment, and (ii) calculation of accurate electronic energies from extrapolation of the basis set pcn, n = 2-4, to infinity. Given the relevance of the nitric oxide molecule and the important role of water as solvent in the biological environment, we undertook a computational study of the interaction of NO, NO+, and NO- with H2O: [NO.H2O], 0, [NO.H2O]+, 0+, and [NO.H2O]-, 0- (Chapter 4). The geometries optimized for these clusters indicated that the NO.H2O interaction depends on the total charge: (ON.HOH), (NO-.HOH), and (ON+.OH2). The atomic spin densities along with the frontier molecular orbitals representation demonstrated that NO goes from 0 to 0+ or 0- in the oxidation or reduction processes, respectively, and that both processes occur on the nitrogen atom. The quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and natural bond-bond polarizability (NBBP) methods helped to quantify the electronic delocalization level between NO and H2O: 0+ > 0 > 0-, to show a predominantly ionic character for the intermolecular interactions, but a primarily covalent character for the intramolecular chemical bonds. Energy analyses carried out by the natural bond orbital (NBO) and localized molecular orbital energy decomposition (LMOEDA) methods for the interaction between NO and H2O in the complexes 0, 0+, and 0- demonstrated a more favorable interaction in 0- than in 0+ and 0, as revealed by the former method. However, the latter method indicated more negative total interaction energy for 0+ in relation to 0- and 0 because of its predominantly electrostatic component. Analysis of the electrostatic potential surfaces furnished a clear and direct explanation for the relative position of the monomers. Additionally, this analysis showed that the Coulombic attraction between the water molecule and the charged complexes NO+ and NO- is larger than in the case of the complexes with NO. Accordingly, we investigated the complexes cis-[RuCl(NO)(NH3)4]+, 1; cis-[RuCl(NO)(NH3)4]2+, 2; cis-[RuCl(NO)(NH3)4]3+, 3; trans-[RuCl(NO)(NH3)4]+, 4; trans-[RuCl(NO)(NH3)4]2+, 5; trans-[RuCl(NO)(NH3)4]3+, 6; [Ru(NO)(NH3)5]+, 7; [Ru(NO)(NH3)5]2+, 8; and [Ru(NO)(NH3)5]3+, 9 to improve our understanding of the nature of Ru-NO chemical bond and of the influence of the total charge, nature, and relative position of simple ligands on NO release from these complexes (Chapter 5). According to the analysis of charges conducted by the QTAIM and NBO methods along with the molecular orbital representation, the first chemical reduction of complexes 3 and 6 to complexes 2 and 5, respectively, occurs in the pi orbital of Cl, whereas the second reduction, from complexes 2 and 5 to complexes 1 and 4, respectively, and the overall reduction process complex 9 --> complex 8 --> complex 7 takes place in the pi* orbital of NO. In addition, geometric parameters, wavenumbers related to bond stretching, and analysis of electron density by the QTAIM and NBO methods showed that the thermodynamic stability of the Ru-NO bond in complexes 1-6 increases in the first reduction (on going from total charge 3+ to 2+), but it decreases in the second reduction (on going from 2+ to 1+). For complexes 7-9, the stability of the Ru-NO bond decreases in the first reduction, but it increases in the second reduction. This is because interaction between NO and Ru is more favorable in complex 7 than interaction between NO and Ru in complex 8. For NO, the bond order decreases upon reduction of the total charge in the three classes of complexes: 1-3, 4-6, and 7-9. For the complexes containing the chlorine atom, it is possible to observe that the chloride group increases the electron density and provides a more favorable electrostatic interaction in the Ru-NO bond as compared to the complexes containing amine only. The results also indicate increased stability of the Ru-NO bond in complexes 1-3 as compared to complexes 4-6. As a result, the electrostatic interaction between Cl and NO is larger in complexes 1 and 3 as compared to complexes 4 and 6, respectively. We investigated the influence of the Effective Core Potential (ECP) in relation to the treatment involving all the electrons along the scalar relativistic effects obtained by the secondorder Douglas-Kroll-Hess (DKH2) approximation by analyzing the geometric parameters of complexes 1-9 and trans-[RuCl(NO)(NH3)4], 10. By using the ECP basis set, we determined the energies of reduction (A: 2-->1, B: 3-->2, C: 5-->4, D: 6-->5, E: 8-->7, and F: 9-->8), isomerization (G: 1-->4, H: 2-->5, and I: 3-->6), and Cl negative trans influence (J: 7+Cl- --> 10+NH3, K: 8+Cl- --> 5+NH3, and L: 9+Cl- --> 6+NH3) with the computational methods: RI-MP2, RI-SCS-MP2, OO-RI-MP2, OO-R-ISCS-MP2, M06-L, M06, M06-2X, M06-HF, BP86-D3BJ, BP86, B2PLYP, LC-wPBE, and B3LYP. We adopted the CCSD(T) method as reference (Chapter 6). For the statistical analysis, we used the following parameters: minimal negative deviation, Dneg(Min); maximum positive deviation, Dpos(Max); medium absolute deviation, MAD; and rootmeansquare, RMS. In addition to these results, we used values relative to the computational model used as reference, CCSD(T)/def2TZVP, or even a comparison with the experimental results. The geometric parameters obtained with ECP were very close to the values obtained with DKH2 - we achieved MARD values of 1.4 and 0.4% for the bond lengths and angles, respectively. Besides that, the calculated data had MARD values close to 4% as compared to the X-ray experimental results for bond lengths and MARD values close to 3% for the bond angles. These results are acceptable, despite deviation intervals of (5%) - 9% for r, and (5%) - 7% for <. Concerning the reaction energies, the B2PLYP method gave the closest values in relation to those obtained by CCSD(T) in A-I, whereas B3LYP showed the best performance in the proposed chemical reactions J-L. We also studied the nature of the Ru-NO and Ru-NO2 bonds in the compound fac-[Ru(NO)Cl2(3N4,N8,N11(1-carboxypropyl)cyclam)]+ as well as its derivatives obtained upon changes in pH by the computational model B3LYP/ccpVDZ with pseudopotential ECP28MDF for ruthenium. The electronic structure was analyzed with the aid of the density overlap regions indicator (DORI), QTAIM, ELF, and NBO methods (Chapter 7). The DORI method identified a region where the electron density of Ru and NO or NO2 overlapped, which indicated the presence of the Ru-NO or Ru-NO2 chemical bond. The QTAIM and ELF methods showed that these bonds have low covalent character. Investigation of the electron density demonstrated that the number of electrons shared between Ru and NO increases on going from complex 11 to complex 12, when carboxyl group is deprotonated. However, this number decreases with increasing pH and formation of complex 13, from deprotonation of N(2), and complex 14, with conversion of Ru-NO to Ru-NO2. By using NBO, we also observed interaction between the localized d orbitals of Ru and the pi* orbital of NO or NO2. This interaction is related to the pi backdonation process, which is more favorable to the stabilization of complexes 11-14 than the interaction between the sigma NBOs of NO or NO2 with the d-sigma orbital of Ru, associated with the donation route. Successively, the second order stabilization energy involving the NBOs with symmetry increases on going from complex 11 to complex 12 due to the decreased energy difference and increased overlap between these localized orbitals. The opposite trend is observed on going from complex 12 to complexes 13 and 14, in agreement with previous results. We examined the Ru-NO bond mechanism in the complex trans-[RuCl(NO)(NH3)4]2+ (Chapter 8). Then, we obtained the geometry of this compound and the bond dissociation energy (-Delta-E) of the decompositions trans-[RuCl(NH3)4]+ + NO+, trans-[RuCl(NH3)4]2+ + NO, and trans-[RuCl(NH3)4]3+ + NO by using the computational models ZORA-BP86/TZ2P and BP86/TZ2P, to evaluate how the ZORA approximation influenced treatment of the relativistic effects. Both computational models agreed well with the geometric parameters obtained by X-ray diffraction in the literature. Nevertheless, the values of -Delta-E were significantly different, so we adopted the ZORA-BP86/TZ2P model in the subsequent discussions. The dissociation trans-[RuCl(NH3)4]+ + NO+ gave the lowest -Delta-E, which agreed with a value for the Ru-NO bond angle close to 180º and is typical of trans-[Ru(NO)L(NH3)4]n+ that are EPR silent. We used this decomposition along with the Kohn-Sham molecular orbital theory in combination with the energetic decomposition analysis to highlight some important characteristics of the Ru-NO bond mechanism. Investigation of the negative trans influence of the Cl- group on Ru-NO revealed a favorable interaction energy for the interaction between trans-[RuCl(NH3)4]+ and NO+ - in this structure, the interaction term of the pi orbital counterbalances the electrostatic repulsion and the Pauli repulsion. We also studied the Ru-NO bond in the absence of the Cl- group for trans-[Ru(NH3)4]2+ and NO+. The interaction is repulsive because electrostatic repulsion predominates in relation to the attractive contribution of the interaction of the pi orbital. We also analyzed the RuCl bond in the absence of NO+ for trans-[Ru(NH3)4]2+ and Cl. The interaction is attractive due to the considerable value of the favorable electrostatic term. Investigation of the synergism between the processes of sigma donation and pi backdonation present in Ru-NO showed that this synergism accounts for the increased stability of this bond. The pi component is essential for maintenance of this chemical bond
A descoberta das novas propriedades químicas da molécula de óxido nítrico, relacionadas principalmente a processos fisiológicos e fisiopatológicos, promoveu um avanço nas pesquisas científicas ligada ao controle da disponibilidade desta molécula em meio biológico. Sendo que compostos, que possuem especialmente rutênio e ligantes, tais como, amina e tetraazomacrocíclicos são utilizadas como modelo devido a suas propriedades como, por exemplo, estabilidade frente à oxidação promovida pelo ar, solubilidade em água e baixa citoxicidade contra células hospedeiras. Assim, devido às propriedades peculiares do óxido nítrico, foi realizado em primeiro lugar um experimento computacional baseado no diagrama de orbitais moleculares do NO e em exercícios de química quântica computacional envolvendo também seu monocátion (NO+) e monoânion (NO) (Capítulo 3). Os estudantes iniciaram este experimento explorando as estruturas de Lewis de NO+, NO e NO junto ao diagrama de orbitais moleculares do NO obtendo uma correlação com diferentes propriedades, por exemplo, comprimentos de ligação, e cargas atômicas. Em seguida, os valores dos comprimentos de ligação e frequências vibracionais calculados foram comparados com os dados experimentais encontrados em bancos de dados na internet, permitindo uma discussão a respeito das diferenças observadas. Em seguida, distintas aproximações foram utilizadas para o cálculo das cargas atômicas parciais demonstrando a dificuldade na determinação deste parâmetro, uma vez que este não é uma observável física e, consequentemente, não há um operador mecânico quântico para a obtenção desta grandeza. Além disso, o momento de dipolo calculado do NO, 0,153 D, com B3LYP/631+G(d,p), é próximo ao valor experimental, mais aceito, em contaste a uma recente determinação que indica uma carga negativa concentrada no sentido do átomo de nitrogênio. O experimento termina com dois tópicos de grande interesse para a química computacional. Onde, em primeiro lugar, foi realizada uma investigação de como propriedades, tais como, cargas e densidades de spin atômicas se comportam com o aumento do conjunto de base. E em segundo lugar, o cálculo de energias eletrônicas precisas foi possível com a extrapolação do conjunto de base pcn, n = 24, para n igual a infinito. Dada à relevância da molécula de óxido nítrico e o papel da água como solvente em meio biológico, também foi realizado o estudo computacional da interação entre NO, NO+, e NO com H2O: [NO.H2O], 0, [NO.H2O]+, 0+, e [NO.H2O], 0 (Capítulo 4). Onde, as geometrias otimizadas destes clusters indicam que a interação NO.H2O depende da carga total: (ON.HOH), (NO.HOH) e (ON+.OH2). Sendo que as densidades de spin atômicas e a forma dos orbitais moleculares indicam que a partir de 0 para 0+ ou 0 os processos de oxidação ou redução, respectivamente, ocorrem sobre o NO, ou mais especificamente sobre o átomo de nitrogênio. Logo, os métodos quantum theory of atoms in molecules (QTAIM), electron localization function (ELF) e natural bondbond polarizability (NBBP) permitem quantificar o nível de deslocalização eletrônica entre o NO e o H2O: 0+ > 0 > 0, e mostram um caráter predominantemente iônico para as interações intermoleculares, porém, primariamente covalente para as ligações químicas intramoleculares. Destarte, a analise energética obtida junta aos métodos natural bond orbital (NBO) e localized molecular orbital energy decomposition (LMOEDA) para a interação entre NO e H2O nos complexos 0, 0+, e 0 demostra ser mais favorável em 0 do que 0+, e 0 quanto a influência mútua dos orbitais naturais de ligação, ao passo que o segundo método designa uma energia de interação total mais negativa para 0+ em relação a 0,e 0, devido ao seu componente eletrostático predominante. Para concluir, a análise das superfícies de potenciais eletrostáticos fornece uma explicação direta e clara a respeito da posição relativa dos monômeros. Em seguida, a atração de Coulomb entre a molécula de água e os compostos carregados NO+ e NO é mais favorável frente ao NO. Por conseguinte, considerando compostos capazes de controlar a disponibilidade do NO, foram investigados os seguintes complexos: cis[RuCl(NO)(NH3)4]+, 1, cis[RuCl(NO)(NH3)4]2+, 2, cis[RuCl(NO)(NH3)4]3+, 3, trans[RuCl(NO)(NH3)4]+, 4, trans[RuCl(NO)(NH3)4]2+, 5, trans[RuCl(NO)(NH3)4]3+, 6, [Ru(NO)(NH3)5]+, 7, [Ru(NO)(NH3)5]2+, 8, e [Ru(NO)(NH3)5]3+, 9, de modo estudar a natureza da ligação química RuNO sobre a influência da carga total, bem como, da natureza e posição relativa de ligantes simples (Capítulo 5). Desta forma, em primeiro lugar, a partir da analise das cargas obtidas pelos métodos QTAIM e NBO em conjunto com a representação dos orbitais moleculares, temos que a primeira redução química em 3-->2 e 6-->5 ocorre sobre o orbital do átomo de Cl, ao passo que a segunda redução em 2-->1 e 5-->4, bem como, em 9-->8-->7 é sobre o orbital * do NO. Em seguida, os parâmetros geométricos, números de onda vibracionais de estiramento, e a analise da densidade eletrônica pelos métodos QTAIM e NBO mostram que a estabilidade termodinâmica da ligação RuNO nos compostos 16 aumenta na primeira redução, a partir de 3+ para 2+, contudo, diminuem na segunda redução, a partir de 2+ para +. Para os compostos 79, a estabilidade de RuNO diminui com a primeira redução da carga total, mas, aumenta na segunda redução. Sendo que o último processo é explicado pela interação entre o NO, e o Ru ser mais favorável em 7, do que o NO e o metal em 8. Para NO, uma diminuição da ordem de ligação é visualizada com a redução da carga total nas três classes de complexos: 13, 46 e 79. Em 16, a comparação das moléculas 1 e 4 frente a 8, assim como, 2 e 5 em relação a 9 demonstra que a influência negativa do grupo cloreto relativo a contribuição do ligante amina promove uma maior densidade eletrônica e mais favorável interação eletrostática na ligação RuNO. Adicionalmente, os resultados indicam um aumento da estabilidade em RuNO para 13 comparado a 46, devido à interação eletrostática entre Cl, e NO, apesar da densidade eletrônica nesta ligação química ser maior somente em 1 e 3 frente a 4 e 6, respectivamente. A seguir, foi realizado um estudo da influência do Effective Core Potential (ECP) em relação ao tratamento envolvendo todos os elétrons junto aos chamados efeitos relativísticos escalares por meio da aproximação secondorder DouglasKrollHess (DKH2). Isto foi realizado por meio da analise dos parâmetros geométricos dos complexos metálicos: 19 e trans[RuCl(NO)(NH3)4], 10. A partir das geometrias otimizadas com o conjunto de base com ECP, também foram avaliadas as energias das reações químicas de redução (A: 2-->1, B: 3-->2, C: 5-->4, D: 6-->5, E: 8-->7 e F: 9-->8), isomerização (G: 1-->4, H: 2-->5 e I: 3-->6), e influência trans negativa do Cl (J: 7+Cl --> 10+NH3, K: 8+Cl --> 5+NH3 e L: 9+Cl --> 6+NH3) junto aos seguintes métodos computacionais: RIMP2, RISCSMP2, OORIMP2, OORISCSMP2, M06L, M06, M062X, M06HF, BP86D3BJ, BP86, B2PLYP, LCwPBE, e B3LYP. Sendo que o método CCSD(T) foi adotado como referência (Capítulo 6). Para a análise estatística foram utilizados os seguintes parâmetros: desvio negativo mínimo, Dneg(Mín), desvio positivo máximo, Dpos(Máx), desvio absoluto médio, DAM, e raiz quadrada do erro quadrático médio, RQEQM. Além destes parâmetros, foram empregados também valores relativos ao modelo computacional adotado como referência, CCSD(T)/def2TZVP, ou mesmo frente a resultados experimentais. Agora, os parâmetros geométricos obtidos com ECP frente à DKH2 apresentam valores próximos como pode ser destacado pelos valores do desvio absoluto médio relativo, DAMR, de 1,4 e 0,4% para os comprimentos e ângulos de ligação, respectivamente. Em adição, os dados calculados frente aos resultados experimentais de raiosX apresentam pequenos valores de DAMR, próximos a 4% para os comprimentos de ligação, e 3% para os ângulos de ligação, apesar do intervalo de desvios serem de (5%) 9% para r, e (5%) 7% para <. Para as energias das reações químicas propostas, o método B2PLYP apresentou resultados mais próximos ao obtido pelo CCSD(T) para AI, enquanto que o método B3LYP apresentou as energias mais próximas às obtidas com o método de referência para JL. Também foi estudada a natureza das ligações RuNO e RuNO2 no composto fac[Ru(NO)Cl2(3N4,N8,N11(1carboxipropil)cyclam)]Cl H2O ((1carboxipropil)cyclam) = 3(ácido 1,4,8,11tetraazociclotetradecan1il)propiônico), e em seus derivados junto as modificações do pH, por meio do modelo computacional B3LYP/ccpVDZ com pseudopotencial relativístico ECP28MDF para o Ru. Onde a analise da estrutura eletrônica foi realizada através dos métodos density overlap regions indicator (DORI), QTAIM, ELF e NBO (Capítulo 7). O método DORI permitiu se identificar uma região de recobrimento de densidade eletrônica entre o Ru e NO ou NO2 indicando a presença das ligações químicas RuNO e RuNO2. Os métodos QTAIM e ELF mostraram que estas ligações possuem um baixo caráter covalente. A analise da densidade eletrônica mostrou que o numero de elétrons compartilhados entre Ru e o NO aumenta a partir de 11 para 12, com a desprotonação do grupo carboxílico, porém, diminui com o aumento de pH e formação de 13, a partir da desprotonação de N(2), e 14, com a conversão da ligação RuNO para RuNO2. O método NBO também possibilitou determinar a interação entre os orbitais localizados d do Ru com * do NO ou NO2, relacionada ao processo de retrodoação , como mais favorável para a estabilização dos compostos 1114 frente à interação entre os NBOs do NO ou NO2 com d do Ru, pautada ao processo de doação . Sendo que a energia de estabilização de segunda ordem envolvendo os NBOs de simetria aumenta em 11-->12, devido à diminuição da diferença de energia e o aumento do recobrimento entre estes orbitais localizados. Entretanto, foi observada uma tendência contrária para 12-->13-->14, concordando com os resultados prévios. O mecanismo da ligação RuNO foi analisado a partir do complexo trans[RuCl(NO)(NH3)4]2+ (Capítulo 8). A geometria deste composto e a energia de dissociação de ligação (E) para as decomposições: trans[RuCl(NH3)4]+ + NO+, trans[RuCl(NH3)4]2+ + NO, e trans[RuCl(NH3)4]3+ + NO, foram obtidas junto aos modelos computacionais: ZORABP86/TZ2P e BP86/TZ2P, com o objetivo da avaliar a influência da aproximação ZORA no tratamento dos efeitos relativísticos. Os resultados mostraram que ambos os modelos computacionais apresentam uma boa concordância com os parâmetros geométricos obtidos por difração de raiosX que foram encontrados na literatura. Entretanto, os valores de E apresentaram uma diferença mais acentuada, e o modelo ZORABP86/TZ2P foi adotado nas seções seguintes deste estudo. Outro ponto é que a menor E foi obtida para trans[RuCl(NH3)4]+ + NO+, concordando com o ângulo de ligação RuNO próximo a 180º típico de compostos trans[Ru(NO)L(NH3)4]n+ que não apresentam sinais de EPR. Sendo assim, esta decomposição foi utilizada junto à teoria do orbital molecular de KohnSham em combinação com analise de decomposição energética para destacar algumas características do mecanismo da ligação RuNO. Assim sendo, na ligação RuNO sobre a influência trans negativa do Cl, estudada por meio da interação entre trans[RuCl(NH3)4]+ e NO+, temos uma energia de interação favorável porque, nesta estrutura, o termo de interação orbital contrabalança a repulsão eletrostática e a repulsão de Pauli. Por outro lado, a ligação RuNO na ausência do grupo Cl foi estudada através da interação entre trans[Ru(NH3)4]2+ e NO+, demostrando ser repulsiva devido a predominância da repulsão eletrostática frente a contribuição atrativa da interação orbital . Agora, a ligação RuCl na ausência de NO+, analisada a partir da interação entre trans[Ru(NH3)4]2+ e Cl, é atrativa devido ao considerável valor do termo eletrostático favorável. Ainda, o estudo do sinergismo entre os processos de doação e retrodoação presentes em RuNO mostrou que este é responsável por aumentar a estabilidade desta ligação. Porém, a retrodoação demonstrou não ser somente a mais importante, mas, também fundamental para a manutenção desta ligação química

This study investigated the reduction reaction of ruthenium tetroxide by various aliphatic alcohols in acidic medium. UV-Vis spectroscopy still plays an essential role in the analysis and study of volatile ruthenium tetroxide and was used in this study to collect kinetic data. This data was analyzed using graphical and computational methods, such as Mauser diagrams and kinetic simulation software. From the results obtained it is proposed that the reaction occurs by the following two-step reaction model: Ru(VIII) k1 Ru(VI) Ru(VI) k2 k-2 Ru(III) Molar extinction coefficients and conditional rate constants were calculated using kinetic simulating software and a hydride transfer mechanism was proposed. The temperature dependence of this reduction reaction was also investigated and thermodynamic parameters calculated. Ruthenium concentrations were determined using a method employing UV-Vis spectroscopy. The method proved to be a reliable, sensitive and simple technique.

This thesis describes two projects involving the organometallic chemistry of iron and ruthenium complexes with DMPE ligands [DMPE = 1,2-bis(dimethylphosphino)ethane]. The first study involves an investigation into the kinetics and mechanisms of OH bond activation reactions of [Fe(DMPE)2]. The second project involves an investigation into the synthesis of RuH2(DMPE)2, the formation and properties of trans-[RuH(n2-H2)(DMPE)2]*, and the reactions of RuH2(DMPE)2 with alkyl and aryl thiols. In Part I of this work, the kinetics of the cis/trans isomerization of FeH(C6H5)(DMPE)2 and FeD(C6D5)(DMPE)2 were measured by 31P NMR spectroscopy in pentane and THF. The isomerization reactions follow first-order reversible kinetics. FeH(C6H5)(DMPE)2 and FeD(C6D5)(DMPE)2 also undergo exchange with added arenes in a concerted fashion at the iron centre. The rate of exchange is comparable to the rate of isomerization. From the equilibrium constant for the exchange reaction, it was found that FeH(C6H5)(DMPE)2 is thermodynamically more stable than FeD(C6D5)(DMPE)2 by approximately 3 kJ mol'1 in pentane. FeH(C6H5)(DMPE)2 and FeD(C6D5)(DMPE)2 react with diethyl disulfide to give Fe(SEt)2(DMPE)2. The reaction proceeds via loss of benzene or benzene-d6 followed by addition of [Fe(DMPE)2] to the 8-8 bond of EtSSEt. By following the kinetics of the reactions of EtSSEt with FeH(C6H5)(DMPE)2 and FeD(C6D5)(DMPE)2 in THF separately, the rates of reductive elimination of benzene OH and GD bonds at 283 K were found to be 3.9 x 10‘ s-1 and 6.5 x 104 s-1 respectively. The inverse deuterium isotope effect (k”/kD = 0.6) can be rationalized by the presence of a n-benzene intermediate in the elimination reaction. In solution, the phenyl ring in cis'FeH(C6H5)(DMPE)2 assumes a fixed orientation and is constantly flipping at 240 K. During this work, it was discovered that [Fe(DMPE)2] is capable of catalyzing the hydrogenation of alkenes to alkanes under photochemical conditions. The hydrogenation reaction competes with a significantly slower dehydrogenation reaction. A quantitative analysis of the efficiency of [Fe(DMPE)2] as a hydrogenation catalyst was carried out. The hydrogenation of cyclopentene is faster than that of tenninal alkenes. A reaction cycle is proposed for the hydrogenation-dehydrogenation reactions mediated by Fe(DMPE)2 complexes. Treatment of an irradiated sample of FeH(cyclopenteny1)(DMPE)2 with dibromomethane afforded FeBr2(DMPE)2 and trans-[Fe(cyclopentenyl)Br(DMPE)2]Br.2H20 whose crystal structures are presented. In Part II, a synthesis of Rqu(DMPE)2 from trans-RuC12(DMPE)2 by reduction with sodium/Z-propanol is presented. Protonation of RuH2(DMPE)2 with weak organic acids such as methanol, ethanol and thiols affords the molecular hydrogen complex trans-[RuH(T]2-H2)(DMPE)2]+ which has a nZ-bound H2 ligand and a 6-bound hydride ligand. T1 measurements and 1JHD coupling in nZ-HD ligand confirm the 'non-classical' structure. Between 220 and 300 K, the molecular hydmgen complex continuously undergoes intermolecular exchange with the protonating solvent and all the rutheniumbound hydrides undergo intramolecular exchange. In methanol, a previously unreported five-coordinate ruthenium(II) complex, trans-[RuH(DMPE)2]+, exists in equilibn'um with the molecular hydrogen complex. Reactions of the ruthenium dihydride with alkyl- and arylthiols afford trans-monothiolate hydrides. Aromatic thiols react more rapidly than alkanethiols. The reaction is believed to proceed via protonation of the dihydride (by the acidic thiol group) to give the molecular hydrogen complex, followed by substitution of the 'r12-H2 ligand with the conjugate base of the thiol. The dithiolate complex trans-[Ru(SPh)2(DMPE)2] has been isolated and its X-ray crystal structure is presented. In dithiols, dithiaruthenocycles are not formed, which is in contrast with the formation of the iron analogues. Although protonation of RuH2(DMPE)2 with alcohols is facile, substitution of trans-[RuH(T]2-H2)(DMPE)2]* by alkoxide ions does not take place in the presence of thiolate ions.

The chemistry of homogeneous transition metal systems offer parallels to the reactions on the surfaces of industrial hydrodesulphurization catalysts. The reactions of several ruthenium complexes with sulphur-containing reagents are described, with an emphasis on the kinetics and mechanisms thereof. The complex Ru(CO)₂(PPh₃)₃ (2), for example, reacts quickly with thiols and disulphides, producing cct-RuH(SR)(CO)₂(PPh₃)₂ (9) and cct-Ru(SR)₂(CO)₂(PPh₃)₂ (14), respectively, although 2 fails to react with unstrained thioethers. Reactions of the related complex Ru(CO)₂(PPh₃)(dpm) (dpm=Ph₂PCH₂PPh₂) are complicated by the lability of all of the three different ligands. The two dihydrides cct-RuH₂(CO)₂(PPh₃)₂ (3) and RuH₂(dpm)₂, as a cis/trans mixture (7), react with thiols to produce the hydrido-thiolato complexes 9 and RuH(SR)(dpm)₂ (13). respectively. The mechanisms appear to depend on the basicity of the hydride ligands; the more basic dihydride, 7, is probably protonated by the thiol, giving an unobserved molecular hydrogen intermediate, while 3 reacts by slow reductive elimination of H₂. The same rate constant, rate law, and activation parameters are found for the reaction of 3 with thiols, CO or PPh₃. The reaction of 3 with RSSR produces mostly 9, with small amounts of 14. The complete characterization of several members of the series 9 and 14 is described, including the crystal structure of the p-thiocresolate example of each. The reactions of 9 with other thiols, P(C₆H₄pCH₃)₃, CO, RSSR, HCl, PPh₃, and H₂, are also reported. The first three of these reactions share the same rate law and rate constant, the common rate determining step probably being initial loss of PPh₃. Some equilibrium constants for the exchange reactions of 9d (R=CH₂CH₃) with other thiols were tetermined, the Keq values increasing with the acidity of the incoming thiol. The mercapto hydrogens of 9a and 14a (R=H) exchange with the acidic deuterons of added CD₃OD. The hydridic and ortho-phenyl hydrogens exchange more slowly, presumably by intramolecular processes. Complex 14b (R=C₆H₄pCH₃) is unstable in the presence of light, exchanges phosphines rapidly with added P(C₆H₄pCH₃)₃, exchanges thiolate groups with added thiols, and is converted by high pressures of H₂ to a mixture of 9b and 3. Intermediates proposed for the mechanism of the thiol exchange reactions of 9 and 14 contain two or three thiolate groups sharing a proton. A related complex, [Ru(CO)₂(PPh₃)(μSEt)₂(μ₃SEt)Na(THF)]₂, which contains three thiolate groups on a ruthenium centre sharing a sodium cation, was isolated from the reaction of cct-RuCl₂(CO)₂(PPh₃)₂ with sodium ethanethiolate. In acetone, 9b and 14b can be formed cleanly from cct-RuHCl(CO)₂(PPh₃)₂ and cct-RuCl₂(CO)₂(PPh₃)₂, respectively, by reaction with p-thiocresolate. Complex 3 or cheaper analogues could be used as catalysts for the reduction of disulphides by H₂, or as recyclable reagents for the non-oxidative extraction of thiols from thiol-containing mixtures such as oil fractions. The chemistry described above will help to guide future researchers to systems that more closely parallel the processes occurring on the surfaces of industrial hydrodesulphurization catalysts.
Science, Faculty of
Chemistry, Department of
Graduate

This thesis work reports developments in the coordination chemistry of ruthenium porphyrin complexes, both in terms of the synthesis and chemistry of new compounds, as well as the study of the solution chemistry of some previously reported complexes. The synthesis, characterization and chemistry of ten new Ru(porp) coordination complexes in the oxidation states Ru[superscript]Ⅲ and Ru[superscript]Ⅳ containing halide (Br, CI) and other axial ligands (pyridine, CH₃CN, NH₃ and SbF₆) are described in this thesis. Some additional ten Ru(porp) complexes have been studied in situ. Measurement of the rate constants for forward and reverse reactions and the corresponding equilibrium constant by 'H NMR and UV/visible spectroscopy for the dissociation of PPh₃ ligand from Ru(OEP)L(PPh₃) (OEP is the octaethylporphyrinato dianion; L = CO, PPh₃) in C₇D₈ to generate the previously reported five-coordinate Ru(OEP)L complexes allowed for an estimation of the Ru-P bond strength (64 ± 9 kJ mol⁻¹) in these complexes. A study of PPh₃ dissociation from Ru(OEP)CO(PPh₃) in C₇D₈ and in CDC1₃ indicates that solvation effects play a major role, with CDC1₃ being more capable than C₇D₈ of solvating the Ru(OEP)CO complex. The presence of trace H₂0 in these systems was a major problem, and the coordination of H₂0 to Ru(OEP)L complexes to generate the in situ Ru(OEP)L(H₂0) complexes (L = CO, PPh₃) is described. The formation of Ru(OEP)L(H₂0) and the observed difference in the solvation of Ru(OEP)CO by C₇H₈ and CHC1₃ indicate that truly Five-coordinate species may not exist in solution. The outer-sphere oxidation of Ru [superscript]Ⅳ(OEP)PPh₃ by 0₂ to give [Ru [superscript]Ⅳ(OEP)OH]₂0 was shown to occur only in the presence of H₂0. Mechanistic studies on the previously reported reaction of HCI with [Ru(OEP)]₂ to generate Ru^(OEP)Cl₂ (C. Sishta, M.Sc.Thesis, University of British Columbia, 1986) show that solvent plays a major role in directing this oxidation reaction. A reaction stoichiometry of 4:1 between HCI and [Ru(OEP)]₂ in C₆D₆ or C₇D₈ showed that HCI itself was the oxidant and not trace Cl₂ in HCI, as thought previously. A range of HX acids having pK[subscript]a, values in the range 38 to less than -10 (HX = H₂, MeOH, H₂0, H₂S, CH₃COOH, C₆H₅COOH, HF, CF₃COOH, HN0₃, HBF₄, HCI. HBr, and HSbF₆) were tested for reactivity with [Ru(OEP)]₂in C₆D₆; the data showed that a strong acid (pK[subscript]a < ca. 0) was necessary to initiate reactivity. The complex Ru[superscript]Ⅳ(OEP)(SbF₆)₂ was generated in situ by reacting HSbF₆ with [Ru(OEP)]₂. In CH₂C1₂, a 1:1 stoichiometric reaction between HCI and [Ru(OEP)]₂ was observed, instantly fanning a mixture of products, tentatively formulated as Rura(OEP)H and [Ru[superscript]Ⅲ(OEP)]₂CHCl₂ based on spectroscopic data. The species proved impossible to separate. These same products were formed slowly by the reaction of [Ru(OEP)]₂ with CH₂C1₂ in the absence of HCI, and kinetic studies suggest that a direct reaction of [Ru(OEP)]₂ with CH₂C1₂ is likely, rather than reaction of [Ru(OEP)]₂ with impurities in CH₂C1₂. The product mixture generated Ru(OEP)Cl₂ upon further reaction with HCI, both in the absence and in the presence of air. The complex Ru[superscript]Ⅳ(OEP)(BF₄)₂ was generated in situ by an analogous reaction of aqueous HBF₄ with the product mixture. The required hydrogen-containing co-product from the reaction of HX (X = Br, CI) with [Ru(OEP)|₂ in C₇D₈ or CH₂C1₂ was not detected, but was shown not to be H₂. Oxidation of Ru(porp)(CH₃CN)₂ and Ru(OEP)py₂ (py = pyridine; porp = OEP, TMP (the dianion of tetramesitylporphyrin)) by gaseous HX (X = Br, CI) in the absence of air yielded Ru[superscript]Ⅳ(porp)X₂ complexes. The new compound Ru(TMP)Br₂ was synthesized by this method using the bis(acetonitrile) precursor, and was characterized by spectroscopy; the chloride analogue Ru(TMP)Cl₂ was generated in situ. The magnetic properties (susceptibility and moment) of Ru(OEP)Br₂ from 6 to 300 K are unlike those reported for ruthenium(IV) non-porphyrin complexes, and reveal a significant contribution from temperature-independent paramagnetism. The reaction of Ru(OEP)X₂ (X = Br, CI) with NH₃ gave the complexes Ru[superscript]Ⅲ(OEP)X(NH₃), which upon acidification under an inert atmosphere yielded the Rum(OEP)X compounds. These Ru111 complexes were characterized by spectroscopic techniques, and the solution chemistry of the five-coordinate species Ru(OEP)X was developed: the Ru[superscript]Ⅲ(OEP)X(CH₃CN) species were also characterized. Solvation of the five-coordinate species Ru(OEP)X (X = Br, CI) was observed in coordinating solvents to form the six-coordinate species Ru(OEP)X(solvent) (solvent = py, CH₃CN and MeOH). Estimates of the equilibrium constants for the association of these ligands to Ru(OEP)X were obtained from UV/visible titration experiments in CH₂C1₂. Similarly, the equilibrium constant for the association of Br to Ru(OEP)Br to generate in situ (n-Bu)₄N⁺[Ru[superscript]Ⅲ(OEP)Br⁺₂]", was measured. Disappointingly, the complexes Ru(OEP)X were shown not to catalyze the oxidation of organic substrates such as cyclohexene. Electrochemical and spectroelectrochemical studies of the complexes Ru(OEP)X₂ and Ru(OEP)X (X = Br, CI) showed that the Ru[superscript]Ⅳ/Ru[superscript]Ⅲ couple occurred at 480-460 mV and 950-870 mV vs. NHE, respectively, and that the probable reductant for the reaction of Ru(OEP)X₂ with NH₃ was NH₃ itself. A facile reduction of Ru(OEP)(SbF₆)₂ gave the complex Ru[superscript]Ⅲ(OEP)SbF₆, by a probable homolysis of the Ru-F bond. The outer-sphere oxidation of Ru(OEP)py₂ by air in the presence of HX acids gave the isolated or in situ characterized complexes [Ruin(OEP)py₂]+ X" (X = CI, Br, F, BF₄). Similar oxidation of Ru(OEP)(CH₃CN)₂ formed [Ru(OEP)(CH₃CN)₂]+ Br-. Electrochenucal studies showed that 0₂ in acidic media was capable of oxidizing the Ru(OEP)(solvent)₂ complexes (solvent = py, CH₃CN) to the Ru[superscript]Ⅲ complexes, presumably generating H0₂ .
Science, Faculty of
Chemistry, Department of
Graduate

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.
Includes bibliographical references (leaves 135-146). Also available in electronic version. Access restricted to campus users.

The previously known complexes, RU₂H₄Cl₂(PR₃)₄, have now been correctly reformulated as the η²-H₂ species (η²-H₂)(PR₃)₂Ru(μ-Cl)₂(μ-H)RuH(PR₃)₂ (R = Ph, p-tol), 1a and 1b, and it is confirmed that in solution they are dimeric and undergo no ligand dissociation. Also, a new analogue of complexes of type 1 is reported: the complex (η²-H₂)(isoPFA)Ru(μ-Cl)₂(μ-H)RuH(PPh₃)₂,4, is formed from the reaction of RuCl₂(PPh₃)(isoPFA), 3b, with H₂ in methanol/benzene, and a crystal structure of 4 shows the η²-H₂ ligand; isoPFA and PPFA (see below) are ferrocene based, chelating P-N ligands, with the structures: [Chemical compound diagram omitted] R = Pri and Ph for isoPFA and PPFA, respectively. Complexes 1a, 1b and 4 all react with 1-hexene to give hexane; the main ruthenium phosphine product in the case of 1 is the corresponding RuHCl(PR₃)₃ complex, while 4 reacts to give a complex mixture of ruthenium phosphine complexes, including 3b. The amount of hexane formed from the reaction of 4 with hexene is quantified as 2 mol/mol 4. The hydrogenation of 1-hexene catalyzed by 1a is re-interpreted as occurring via the mechanism: (η²-H₂)(PPh₃)₂Ru(μ-Cl)₂(μ-H)RuH(PPh₃)₂ + hexene K₁→(PPh₃)₂Ru(μ-Cl)₂(μ-H)RuH(PPh₃)₂ + hexane (1) (PPh₃)₂Ru(μ-Cl)₂(μ-H)RuH(PPh₃)₂ + H₂ K₂⇆(η²-H₂)(PPh₃)₂Ru(μ-Cl)₂(μ-H)RuH(PPh₃)₂ (2) Reactions of RuCl₂(PPh₃)(PPFA), 3a, and RuCl₂(PPh₃)(isoPFA), 3b, with H₂ have been further studied, in connection with earlier mechanistic studies on hydrogenation of organic substrates catalyzed by complex 3a. The complex 3a reacts with 2-8 atm H₂ in n-butanol to give ruthenium phosphine products including 1a. The complex 3b reacts with H₂ in methanol/benzene to give 4, as mentioned above, as well as a number of unidentified hydrides; in DMA, the reaction of 3b with H₂ gives 1a, 4, RuHCl(PPh₃)(isoPFA) (7), RuHCl(PPh₃)₃ and other unidentified ruthenium phosphine complexes. The product H₂NMe₂+Cl⁻ was also isolated from the methanol/benzene reaction mixture, and this product provides evidence that the amine functionality of the P-N ligands is involved in the promotion of the heterolytic cleavage of dihydrogen to give a proton and a hydride (H₂→ H⁺ + H⁻). Kinetic studies on the hydrogenation of 1-hexene catalyzed by 3a, and by 3b in the present work, are now interpreted according to the mechanism [Chemical compound diagram omitted] Reactions involving 3b and methanol have also been studied, and 3b is also active for the transfer hydrogenation (from methanol) of ketones and activated olefins. The reaction of 3b with methanol in the absence of base is proposed to occur with the stoichiometry: RuCl₂(PPh₃)(isoPFA) + 2MeOH→ H₂NMe₂⁺Cl⁻ + H₂ + 3b RuHCl(CO)(PPh₃)(isoPOF), 5 (5) where the ligand isoPOF is formed from isoPFA by replacement of the NMe₂ group on isoPFA by a methoxo group; reaction 6 could occur via the following steps: RuCl₂(PPh₃)(isoPFA) + MeOH→ RuHCl(CO)(PPh₃)(isoPFA), 6 3b + H₂ + HCl (6) RuHCl(CO)(PPh₃)(isoPFA) + MeOH→ RuHCl(CO)(PPh₃)(isoPOF), 5 + HNMe₂ (7) HCl + HNMe₂ H₂NMe₂⁺Cl⁻ (8) A mechanism for reaction 7 is presented and invokes reversible attack by MeOH with replacement of Cl⁻, followed by reversible deprotonation of coordinated MeOH to give successively methoxo, formaldehyde and formyl intermediates, and finally the hydrido-carbonyl, 6. The reaction of 3b with methanol in the presence of KOH is proposed to occur according to the stoichiometry: RuCl₂(PPh₃)(isoPFA) + KOH + CH₃OH→ RuHCl(CO)(PPh₃)(isoPFA) + KCI + H₂ + H₂O (9) and two pathways have been identified, one base-independent, identical to that proposed for reaction 7, and one showing a second-order dependence on KOH. The latter pathway invokes initial reversible attack on RuCl₂(PPh₃)(isoPFA), 3b, by MeO⁻, replacing Cl⁻ to give RuCl(OMe)(PPh₃)(isoPFA), and subsequent reversible replacement of PPh₃ by OH⁻, followed by concerted loss of OH⁻ and hydride transfer from coordinated OMe⁻ to give a hydrido-formaldehyde complex RuHCl(η²-CH₂O)(isoPFA). A subsequently formed formyl intermediate reacts via intramolecular hydride transfer from the formyl to the metal, H₂ loss, and phosphine coordination to give the hydrido-carbonyl 6.
Science, Faculty of
Chemistry, Department of
Graduate

Ruthenium (II) polypyridine complexes in general have been extensively studied because of their unique redox and photochemical properties. A typical example of such complexes is tris(2,2’-bipyridyl) ruthenium (II). In this study, this complex was synthesized and then characterized using electronic spectroscopy and cyclic voltammetry. It was also shown that the ruthenium concentration could be accurately determined using ICP-MS. It was found that the complex is very stable in various chemical environments. It was observed from spectrophotometric investigations that persulphate and lead dioxide easily oxidize Ru(bpy)3 2+ to Ru(bpy)3 3+ in the presence of heat and H2SO4, respectively. It was also observed that the oxidation between Ru(bpy)3 2+ and cerium (IV) occurred at approximately 3:2 [Ce(IV)]/[Ru(II)] mole ratio. The resultant Ru(bpy)3 3+ solution was unstable in the presence of light and recovery of Ru(bpy)3 2+ occurred gradually. The regeneration of Ru(bpy)3 2+ from Ru(bpy)3 3+ was found to be a multistep process, which appears to involve the formation of an intermediate species. The following reaction model was found to best explain the kinetic data obtained: Ru(bpy)3 2+ + Ce(IV) → Ru(bpy)3 3+ Ru(bpy)3 3+ → Ru(bpy)3 2+ Ru(bpy)3 3+ → Ru* intermediate Ru* intermediate → Ru(bpy)3 2+ Theoretical rate constants were also calculated for the same process under the experimental conditions. The comparison between the experimental and theoretical results gave good agreement. In addition, the factors that influence the rate of the regeneration of Ru(bpy)3 2+ from Ru(bpy)3 3+ were also discussed.

Ruthenium polypyridyl complexes have long been studied due to their unique photophysical characteristics and their synthetic accessibility. We report here the use of new ruthenium polypyridyl’s in photodynamic chemotherapeutic and solar fuel applications. Nearly half of all chemotherapeutics administered today are derived from platinum-based drugs (platins) which lack specificity and can cause sever side-effects. Photodynamic chemotherapeutics (PDT) circumvent these issues utilizing light activation at the site of cancerous cells to generate a cytotoxic Ru(II) center and eventually trigger cellular apoptosis. The new PDT pro-drugs presented push their metal-to-ligand charge transfer (MLCT) light absorption out into the near-IR which is able to penetrate skin at greater depths than traditional PDT drugs. New Ru(II) hydrogen fuel evolution catalyst for use in dye-sensitized photoelectrosynthesis cells (DSPECs) based off of the extensively explored octahedral tridentate-bidentate coordination motif is also investigated. In particular, pendant bases are oriented toward the active site of the catalyst to increase catalytic rates and lower overpotentials. Preliminary density functional theory calculations show that strategic placement of the pendant amine on the bidentate ligand allows for productive interactions between the base and the active site of the catalyst to evolve hydrogen.

Ruthenium complexes are promising candidates for the treatment of cancers. Two ruthenium(III) complexes have previously completed phase I clinical trials and half-sandwich ruthenium(II) η6-arene complexes are receiving much interest as anti-cancer agents. A range of new ruthenium(II) complexes have been prepared with a κ3-N fac-coordinating six electron donor, cis-1,3,5-triaminocyclohexane (cis-tach), replacing the η6-arene ligand. It is hypothesised that the cis-tach ligand will allow highly active complexes with good water solubility. Initial access to ruthenium(II) cis-tach complexes was established with triphenylphosphane ligands, yielding the complexes [RuCl(cis-tach)(PPh3)2]Cl and [RuCl2(cis-tach)(PPh3)]. The complexes adopt a piano-stool type structure, similar to η6-arene complexes. Use of labile dmso ligands in [RuCl(dmso-S)2(cis-tach)]Cl permitted the preparation of a range of complexes. Those with N–N and P–P bidentate chelating ligands, following the formula [Ru(dmso-S)(N–N)(cis-tach)]2+ and [RuCl(P–P)(cis-tach)]+ were studied. Complexes with N–N chelating ligands were found to be inert to substitution in aqueous solution compared to the bis-dmso complex, and were inactive in tumour growth inhibition. The complexes with chelating diphosphane ligands are highly water-soluble, with excellent in vitro activity in the inhibition of tumor cell growth; two of which were found to exceed that of cisplatin. A structure-activity relationship is discussed, and two compounds were selected for further study for their good water solubility and high activity respectively. The aqueous chemistry and the interaction of two of these complexes with small models of biomolecules and DNA was also investigated.

The previously reported synthesis of dinuclear mixed-valence ruthenium complexes of general formula Ru₂Cl₅(P-P)₂, P-P = DPPP, DPPB, 5,5-CHIRAPHOS, or R.R-DIOP, has been extended to include other diphosphines: P-P = DPPN, DPPH, rac-DPPCP, rac-DPCYCP, S,S-BDPP, R- and S-BINAP, or S-PHENOP. The complexes are prepared by the reaction of RuCl₃P₂(DMA)-DMA, P = PPh₃ or P(p-tolyl)₃, with one equivalent of the appropriate diphosphine. The H₂-reduction of Ru₂Cl₅(P-P)₂ complexes in DMA, or in toluene in the presence of an added base, affords the corresponding dimeric Ru(II) complexes [RuCl(P-P)(µ-Cl)]₂, P-P = DPPN, R- or S-BINAP, or S,S-BDPP, which have been characterised by NMR spectroscopy. The [RuCl(P-P)(µ,-Cl)]₂ complexes (Structure I) show a great propensity to form trichloro-bridged dinuclear species (Structure II) in the presence of neutral coordinating ligands (L). A series of trichloro-bridged complexes of the type [(L)(P-P)Ru-(µ-Cl)₃RuCl(P-P)] (e.g. P-P = DPPB; L = NEt₃, NHBu₂, CO, DMA, PhCN, Mel) have been isolated or studied in situ and characterised spectroscopically. The molecular structure of the DMSO analogue shows an S-bonded DMSO ligand with an unsymmetrical arrangement of the chelating DPPB ligand (cf. Structure II). [ Formulas omitted ] The reaction of [RuCl(DPPB)(µ,-Cl)]₂ with H₂ has been investigated. In benzene or toluene, in the absence of an added base, dihydrogen adds reversibly to the ruthenium dimer to give the remarkably simple molecular hydrogen complex (L = η²-H₂; Structure II); the η²-H₂ ligand (with an H-H distance of 0.86 Å as estimated by ¹H NMR variable temperature spin-lattice relaxation data; T₁(min) - 12 ms at 300 MHz) is replaceable by N2. The reaction of [RuCl(P-P)(µ-Cl)]₂, P-P = DPPB or 5,5-CHIRAPHOS, with H₂ in the presence of NEt₃ as the added base yields the corresponding trinuclear Ru(II) hydride complex, [RuHCl(P-P)]₃, along with [(NEt₃)(P-P)Ru(u-Cl)3RuCl(P-P)]. The hydride complexes had been synthesised previously, albeit in low yields (<10%), and the crystal structure of the CHIRAPHOS derivative obtained. During the present work the original synthetic procedure has been modified to obtain the desired [RuHCl(P-P)]₃ complexes in ∼50% yield. In addition, these species have been characterised completely by NMR spectroscopy. The conversion of [RuCl(P-P)-((µ-Cl)]₂ to the corresponding hydride derivative likely proceeds via deprotonation by NEt₃ of the initially formed molecular hydrogen species. Under hydrogen atmosphere, [RuHClQDPPB)]₃ breaks down to form the dinuclear derivative [(η²-H₂)(DPPB)Ru(µ-H)(µ-Cl)₂RuH(DPPB)] containing a molecular hydrogen ligand, which has been identified by ¹H NMR T₁ measurements; similar complexes, but with a nitrile ligand (MeCN or PhCN) in place of the η²-H₂, have also been observed. Alternative routes to ruthenium complexes containing only one diphosphine per Ru ("RuII(P-P)") have been investigated. Some of the trichloro-bridged derivatives (e.g. L = amine, CO; Structure II, see above) are also accessible through reactions of the mixed-phosphine complex RuCl₂(DPPB)(PPh₃) with amines and aldehydes, respectively. Studies on the reactions of RuCl₂(DMSO)₄ or [RuCl(p-cymene)-(µ,-Cl)]₂ with one equivalent of diphosphines show that the nature and the distribution of product(s) (i.e. RuCl₂(P-P)₂ vs. "RuCl₂(P-P)") are greatly influenced by the chelate size of the diphosphine. The "RuCl₂(P-P)" species is observed only for those phosphines which form at least a six-membered ring upon coordination to the metal. Solid-state ³¹P NMR studies indicate that the structure of RuCl₂(DPPB)(PPh₃) is similar to that of RuCl₂(PPh₃)₃, which has been characterised previously by X-ray crystallography. Reactions of RuCl₂(DPPB)(PPh₃) with chelating ligands afford six-coordinate complexes of the type RuCl₂(DPPB)(L-L), L-L = PPh₂Py, DPPM, or norbornadiene; the corresponding hydridochloro derivatives are obtained when the reactions are conducted under an atmosphere of H₂ in the presence of Proton Sponge®. The dimeric [RuCl(P-P)(µ-Cl)]₂ and the trinuclear [RuHCl(P-P)]₃ complexes described in this study are effective catalyst precursors for the hydrogenation of various alkene, ketone, imine, and nitrile substrates under relatively mild conditions (30-100 °C, 1-12 atm of H₂). A detailed kinetic study on the hydrogenation of styrene catalysed by [RuCl(DPPB)(µ-Cl)]₂ shows a first-order dependence of the maximum rate on catalyst concentration, a first- to zero-order dependence on styrene concentration and a zero- to first-order dependence on the H₂ pressure. A mechanism involving formation of the molecular hydrogen (η²-H₂) complex (see above) followed by hydrogen transfer to the substrate is proposed to account for the observations, and the rate constants at 30 ºC for the various steps have been determined. Preliminary data on acetophenone and benzonitrile hydrogenation shows that the trinuclear hydride complexes are an order of magnitude more effective than the corresponding dimeric precursors.
Science, Faculty of
Chemistry, Department of
Graduate

We have studied the electrostatic and other interactions of the inorganic, hexavalent dye Ruthenium Red (RR) with phospholipid vesicles composed of phosphatidylcholine (PC) and phosphatidylserine (PS) or phosphatidylinositol (Pl) in various mixtures and concentrations. Experiments were based on spectrophotometric absorption measurements which compared RR concentrations in the presence and in the absence of liposomes at different dye concentrations. Multilamellar liposomes were obtained by handshaken preparations. Five freeze-and-thaw cycles of the lipid-RR suspension produced an ion equilibrium distribution at the membrane-water interface. Results are given in terms of the Gouy-Chapman-Stem adsorption theory with the linear partition coefficient and a newly introduced effective ion valency as parameters. Data on the time stability of RR solutions and their interaction with laboratory equipment are given. Furthermore, we characterize the freeze-and-thawing process and present an electron micrograph of liposomes. Two main results were found. First, the Gouy-Chapman-Stem theory correctly describes adsorption of a hexavalent ion to charged phospholipid vesicles if an effective valency is introduced. The effective valency accounts for the finite size of the ions and the repulsion between the ions. Values ranged between 2.9 and 4.1. Effective valencies decrease with increasing membrane surface charge density and are independent of the lipid concentration. Second, Ruthenium Red adsorbs to phospholipids and the adsorption is strongly related to the surface charge density of the membrane. Vesicles made from a mixture of PC and PI adsorb significantly less than vesicles made from a mixture of PC and PS. The second result is of special interest for molecular biology since biological membranes consist to a large extent of phospholipids. Sarcoplasmic reticulum (SR) membranes are discussed as an example. Liposomes (PC:PS 20: 1) with surface charge densities comparable to SR membranes adsorb a maximum of about 9±3nmol RR per mg lipid.