Dissertations / Theses on the topic '030204 Main Group Metal Chemistry'

This thesis focuses on the design and development of novel versatile diamido ligands for transition metal and main group element chemistry. The central concept of this work deal relied on the design of N, N'-disubstituted-1,8-diaminonaphthalene (H2RR’-DAN) as proligands to dianionic diamido ligand scaffolds. These ligands would then be employed for stabilization of main group element (e.g. Li, B, Al) and transition metal (e.g. Ti, Zn) compounds.

Structural studies on solvated adducts of bismuth (III) chloride have demonstrated the ability of the main group element to form multiple bonding contacts, giving "hypervalent" complexes. Similar interactions are observed in almost all aspects of the chemistry of the heavy main group elements. The reaction of $\rm \lbrack Bi\sb2Co\sb4(CO)11\rbrack\sp{1{-}}$ with $\rm Mo(CO)\sb3(\eta\sp6$-$\rm C\sb6H\sb5Me)$ in tetrahydrofuran yields an unidentified cluster product which, upon slow oxidation with molecular dioxygen or mild metal-organic oxidants yields the two large cluster species, $\rm \lbrack Bi\sb4CO\sb9(CO)\sb8(\mu$-$\rm CO)\sb8\rbrack\sp{2{-}}$ and $\rm \lbrack Bi\sb8Co\sb{14}(CO)\sb{12}(\mu$-$\rm CO)\sb8\rbrack\sp{2{-}}.$ These cluster products contain arrays of metal atoms in the cluster framework which are reminiscent of close-packed solid-state intermetallics. Halogenation of the bismuth-iron cluster $\rm \lbrack Bi\sb4Fe\sb4(CO)\sb{13}\rbrack\sp{2{-}}$ has been performed using the phosphine halide reagent, MePCl$\sb2.$ With the addition of one equivalent of the reagent, two compounds are produced in an approximately 3:1 ratio, respectively: $\rm \lbrack Fe\sb2(CO)\sb6(\mu$-$\rm H)Bi\sb2\{\mu$-$\rm Fe(CO)\sb4\}\rbrack\sp-$ and $\rm \lbrack Bi\sb3Cl\sb4(\mu$-$\rm Cl)\sb4\{\mu\sb3$-$\rm Fe(CO)\sb3\}\rbrack\sp{3{-}}.$ Upon the addition of a second equivalent of reagent, the latter compound apparently decomposes; however the former is converted into the related dichloro-cluster, $\rm \lbrack Fe\sb2CO)\sb6(\mu$-$\rm H)Bi\sb2(\mu$-$\rm Cl)\sb2\rbrack\sp-.$ Addition of yet more reagent results in the formation of the bismuth chloride-iron carbonyl adduct $\rm \lbrack Bi\sb2Cl\sb4(\mu$-$\rm Cl)\sb2\{ \mu$-$\rm Fe(CO)\sb4\}\rbrack\sp{2{-}}$ at the expense of the dichloride cluster. This latter complex may also be produced quantitatively by reaction of $\rm \lbrack Fe(CO)\rbrack\sp{2{-}}$ with two equivalents of BiCl$\sb3$ in MeCN. The reaction of the tellurium-iron cluster $\rm Te\sb2Fe\sb3(CO)\sb9$ with SO$\sb2$Cl$\sb2$ yields a variety of products, depending on the reaction stoichiometry and the solvent employed in the synthesis. In CH$\sb2$Cl$\sb2$ at a ratio of 1:2, respectively, the large dimeric complex $\rm \lbrack Fe\sb2(CO)\sb6(\mu$-$\rm Cl)(\mu$-$\rm TeCl)\sb2\rbrack\sb2\lbrack Te\sb2Cl\sb{10}\rbrack$ is formed, which decomposes in solution to the Zintl-ion complex $\rm \lbrack Fe\sb2(CO)\sb6(\mu$-$\rm TeCl\sb2)(\eta\sp2$-$\mu\sb2$-$\mu\sb2$-Te$\sb4 )\rbrack.$ In MeCN at a ratio of 1:1, the previously reported tetrahedral cluster Te$\sb2$Fe$\sb2$(CO)$\sb6$ is produced, which reacts with additional reagent to yield a complex thought to be $\rm \lbrack Fe\sb2(CO)\sb6(\mu$-$\rm TeCl)\sb2(\mu$-$\rm Cl)\rbrack$ from spectroscopic evidence. This cluster in turn decomposes in solution to $\rm \lbrack Fe\sb2(CO)\sb6(\mu$-$\rm TeCl\sb2)(\eta\sp2$-$\mu\sb2$-$\mu\sb2$-Te$\sb4)\rbrack$ like the first compound. Different products result if the solvent system is again changed to SO$\sb2$/Me$\sb2$CO at $-$30$\sp\circ$C. Although these unstable products have not been structurally characterized, a fair amount of other analytical and spectroscopic data have been obtained. The bromination of Te$\sb2$Fe$\sb3$(CO)$\sb9$ with CBr$\sb4$ has also been performed in MeCN, giving initially Te$\sb2$Fe$\sb2$(CO)$\sb6;$ however, upon reaction with more CBr$\sb4$ over a few weeks time at 0$\sp\circ$C, the novel cubane-like cluster $\rm \lbrack Fe\sb3(CO)\sb9Te\sb4(\mu\sb3$-$\rm CTeBr\sb4)\rbrack$ results in low to moderate yields of 30-65% based on Te. Theoretical calculations by the extended Huckel method have been performed on some model systems, and have provided valuable insight into the underlying bonding arrangements giving rise to the sometimes-unexpected stability and structural features of these products.

Thermoelectric energy (TE) conversion can be used to create electricity from temperature gradients. Hence power can be generated from waste heat using TE materials, e.g. from the exhaust in automotives. This power in turn may lead to a reduction of gas consumption by reducing the alternator load on the engine. Because of the increasing demand and limited availability of energy sources, there is strong and renewed interest in advancing thermoelectric materials. Past research shows that the best TE materials are narrow band gap semiconductors composed of heavy elements, exhibiting a large Seebeck coefficient, S, combined with high electrical conductivity, σ, and low thermal conductivity, κ. Various research projects have been attempted during the past four years of my Ph.D. studies. These include the synthesis, crystal structure studies, electronic structure calculations and thermoelectric properties of transition metal oxides and thallium main group chalcogenides. Because of the good thermal stability, lack of sensitivity to the air, and non-toxicity, transition metal oxides are potential candidates for commercial thermoelectric applications. During the investigation of oxides for thermoelectric application, several interesting features of different transition metal oxides have been discovered: 1. A new quaternary layered transition-metal oxide, Na2Cu2TeO6, has been synthesized under air using stoichiometric mixtures of Na2CO3, CuO and TeO2. Na2Cu2TeO6 crystallizes in a new structure type, monoclinic space group C2/m with a = 5.7059(6) Å, b = 8.6751(9) Å, c = 5.9380(6) Å,  = 113.740(2)°, V = 269.05(5) Å3 and Z = 2, as determined by single crystal X-ray diffraction. The structure is composed of[Cu2TeO6] layers with the Na atoms located in the octahedral voids between the layers. Na2Cu2TeO6 is a green nonmetallic compound, in agreement with the electronic structure calculation and electrical resistance measurement. 2. An n-type narrow band gap semiconductor, LaMo8O14, exhibiting the high Seebeck coefficient of -94 μVK-1 at room temperature has been investigated. 3. Pb0.69Mo4O6 with a new modulated structure and stoichiometry was determined from single-crystal X-ray diffraction data. The compound crystallizes in the tetragonal super space group, P4/mbm(00g)00ss, with a = 9.6112(3) Å, c = 2.8411(1) Å, q = 0.25c*, which is different from the previously reported structure. As for the research of thermoelectric properties of thallium main group chalcogenides, three new ternary thallium selenides, Tl2.35Sb8.65Se14, Tl1.97Sb8.03Se13 and Tl2.04Bi7.96Se13, have been discovered. All three compounds crystallize in the same space group P21/m with different cell parameters, and in part different Wyckoff sites, hence different structure types. The three selenides with similar structures are composed of distorted edge-sharing (Sb,Bi)Se6 octahedra, while the distorted Tl/(Sb, Bi) sites are coordinated by 8 - 9 Se atoms. Electronic structure calculations and physical property measurements reveal they are semiconductors with high Seebeck coefficient but low electrical conductivity, and therefore not good thermoelectrics. On the other hand, our transport property measurements on the unoptimized Tl2SnTe3 sample show interesting thermoelectric properties of this known compound. Advanced thermoelectrics are dominated by antimonides and tellurides so far. The structures of the tellurides are mostly composed of NaCl-related motifs, hence do not contain any Te–Te bonds. All of the antimonide structures containing Sb–Sb bonds of various lengths are much more complex. The Sb atom substructures are Sb24– pairs in β-Zn4Sb3, linear Sb37– units in Yb14MnSb11, planar Sb44– rectangles in the skutterudites, e.g., LaFe3CoSb12, and Sb8 cubes interconnected via short Sb–Sb bonds to a three-dimensional network in Mo3Sb5Te2. The results of electronic structure calculations suggested that these interactions have a significant impact on the band gap size as well as on the effective mass around the Fermi level, which represent vital criteria for advanced thermoelectrics. The crystal structure and electronic structure investigation for the unique T net planar Sb–Sb interactions in Hf5Sb9 will be also presented, although Hf5Sb9 is metallic compound with poor thermoelectric performances.

This thesis explores the synthesis, characterization, and reactivity of main group and transition metal complexes that feature ligands with carbon, sulfur, and selenium donor atoms. Specifically, the carbon donor ligands explored include the carbodiphosphorane, (Ph3P)2C, and the analytical reagent, nitron, which behaves like an N-heterocyclic carbene in solution. The sulfur ligands include the amino acids cysteine and glutathione, and the tripodal tris(2-mercapto-1-t-butylimidazolyl)hydroborato ligand, of which the latter provides an [S3] coordination environment. Finally, the selenium donor ligands explored comprise the phenylselenolate, [PhSe]–, and the selenobenzimidazole, H(sebenzimMe). Chapter 1 investigates the chemistry of two-coordinate mercury alkyl complexes supported by sulfur and selenium ligands. The first part of Chapter 1 examines the structure of the amino acid complexes, (Cys)HgMe and (GS)HgMe, which indicate that both complexes possess linear geometries. Additionally, 1H NMR studies confirm the labile nature of the cysteinato ligand in (Cys)HgMe. More specifically, in the presence of excess cysteine, exchange is observed, a result that is of relevance to mercury toxicity and detoxification. The second part of Chapter 1 examines the exchange reactions of the phenylselenolate mercury alkyl complexes, PhSeHgR (R = Me, Et), as well as their propensity to undergo protolytic Hg–C bond cleavage. The results from these experiments indicate that coordination by selenium promotes protolytic cleavage of Hg–C bonds more rapidly than compared to the sulfur analogues. Expanding the metal centers to include the lighter group 12 metals, Chapter 2 investigates ligand exchange between zinc, cadmium, and mercury in a sulfur-rich coordination environment as provided by the [S3] tris(2-mercapto-1-t-butylimidazolyl)hydroborato ligand. Similar to the Schlenk equilibrium, alkyl group exchange between the same metal center is observed as demonstrated by the formation of [TmBut]MMe via treatment of [TmBut]2M with Me2M (M = Zn, Cd). Additionally, alkyl group exchange between different metals centers is also possible. For example, a mixture of [TmBut]ZnMe and Me2Cd form an equilibrium mixture with [TmBut]CdMe and Me2Zn. Furthermore, transfer of the [TmBut] ligand between the metal centers is possible too. This is demonstrated by the transfer of [TmBut] from mercury to zinc in the methyl system, [TmBut]HgMe/Me2Zn. Additionally, transfer of [TmBut] from zinc to mercury is also observed upon treatment of [TmBut]2Zn with HgI2 to afford [TmBut]HgI and [TmBut]ZnI, thereby indicating that the nature of the co-ligand has a profound effect on the thermodynamics of ligand exchange. Chapter 3 explores the coordination chemistry of the selenium donor ligand, H(sebenzimMe). H(sebenzimMe) is able to coordinate metal centers through the selenium atom in a dative fashion, and, depending upon the metal center, up to four H(sebenzimMe) ligands can coordinate the same metal. Additionally, H(sebenzimMe) can be deprotonated to form [sebenzimMe]–, allowing for the potential of an LX coordination mode, which results in bridging complexes for the metal compounds investigated. In regards to the metal centers investigated in Chapter 3, H(sebenzimMe) has been demonstrated to be an effective ligand for Pd, Ni, Zn and Cd. Chapter 4 investigates the various structural polymorphs of the carbodiphosphorane, (Ph3P)2C. More specifically, previous crystal structures of (Ph3P)2C have demonstrated that the P–C–P bond angle is highly bent. This is consistent with simple VSEPR theory, which predicts a bent geometry for compounds possessing a coordination number of two and two lone pairs of electrons. However, Chapter 4 details the characterization of a new linear form of (Ph3P)2C. DFT calculations indicate that the energy required to bend the P–C–P bonds of (Ph3P)2C over the range of 130˚-180˚ is less than 1.0 kcal mol–1. Analysis of the Natural Localized Molecular Orbitals (NLMOs) indicates that upon bending of the P–C–P bond angle, the -type lone pair NLMO on the central carbon atom is stabilized, while the two P–C bonding orbitals NLMOs are destabilized. The differential behavior of the lone-pair and bonding orbitals upon bending is one component that provides a simple rationalization for the flexibility of (Ph3P)2C. In view of the fact that carbodiphosphoranes possess two lone pairs of electrons on the central carbon atom, (Ph3P)2C is an effective ligand for a variety of metals and nonmetals. Chapter 5 investigates the reactivity of (Ph3P)2C towards the main group alkyl metal complexes, Me3E (E = Al, Ga), Me2M (M = Mg, Zn, Cd), and MeHgI, as well as Mg[N(TMS)2]2. Additionally, the reactivity of (Ph3P)2C towards transition metal complexes was also investigated. (Ph3P)2C is capable of coordinating in several different ways, a couple of which include forming a Lewis acid/base adduct, and ortho metalation of one of the phenyl groups. Lastly, Chapter 6 expands the coordination chemistry of nitron. Nitron, which is used as a quantitative analytical reagent, has recently been shown to behave like an NHC in solution. This is attributed to the presence of the carbenic tautomer of nitron when placed in solution. Thus, nitron effectively coordinates metal centers through the central carbon atom. Chapter 6 outlines (i) the synthesis and structural characterization of nickel, palladium, and iridium complexes that feature nitron as a ligand, and (ii) the ability of the corresponding iridium complexes to serve as catalysts for the dehydrogenation of formic acid and the hydrosilylation of aldehydes.

This thesis reports on the applications of a particular N-heterocyclic silylene, Dipp2NHSi (1), as an ambiphilic reagent in main group chemistry and as a ligand in transition metal chemistry. One focus of the work lies in the evaluation of the differences in the reactivity of N-heterocyclic silylenes in main group element and transition metal chemistry in comparison with the in these areas nowadays ubiquitous N-heterocyclic carbenes. The first chapter gives an insight into the reactivity of Dipp2NHSi with respect to different types of main group element compounds. Silylene 1 was reacted with group 13 compounds. Adduct formation was observed with AlI3, Al(C6F5)3 and B(C6F5)3 which led to isolation of Dipp2NHSi·AlI3 (2), Dipp2NHSi·Al(C6F5)3 (3) and Dipp2NHSi·B(C6F5)3 (4). Furthermore, the reactivity of Dipp2NHSi (1) with respect to different elementhalide bonds was investigated. The reaction with elemental bromine and iodine leads to the dihalosilanes Dipp2NHSiBr2 (5) and Dipp2NHSiI2 (6). Utilizing methyl iodide, benzyl chloride and benzyl bromide, the insertion products Dipp2NHSi(I)(Me) (10), Dipp2NHSi(Cl)(benzyl) (11) and Dipp2NHSi(Br)(benzyl) (12) are obtained. Thus, insertion is preferred to reductive coupling with formation of RH2C–CH2R (R = H, Ph) and the corresponding dihalosilane. The reaction of 1 with Me3SnCl leads to the diazabutene {(Me3Sn)N(Dipp)CH}2 (9). The reaction of 1 with Ph2SnCl2 gives exclusively Dipp2NHSiCl2 (8) and cyclic polystannanes (Ph2Sn)n. The reactivity of 1 towards selected 1,3-dipolar compounds was also examined and Dipp2NHSi was reacted with azides of different size. The reaction with adamantyl azide led to the formation of the tetrazoline 13. For the reaction with the sterically less demanding trimethylsilyl azide the azido silane Dipp2NHSi(N(SiMe3)2)(N3) (14) and the degradation product 14* was isolated. The cyclosilamine 15 was formed from the reaction of 1 with 2,6-(diphenyl)phenyl azide. The bonding situation and ligation properties of Dipp2NHSi in transition metal complexes was assessed in the second part of the thesis by means of theoretical calculations and experimental investigations. Calculations on the main electronic features of Me2Im/Me2NHSi and Dipp2NHSi/Dipp2Im revealed significant differences in the frontier orbital region of these compounds, which affect the ligation properties of NHSis in general. It was demonstrated that NHSis show significantly different behaviour concerning their coordination chemistry. In particular, one energetically low lying π-acceptor orbital seems to determine the coordination chemistry of these ligands. To provide experimental support for these calculations, the silylene complexes [M(CO)5(Dipp2NHSi)] (M = Cr 16, Mo 17, W 18) were synthesized from Dipp2NHSi and [M(CO)6] (M = Cr, Mo, W) and the tungsten NHSi complex 18 was compared to the NHC complexes [W(CO)5(iPr2Im)] (19), [W(CO)5(iPr2ImMe)] (20) and [W(CO)5(Me2ImMe)] (21). The bonding of Me2Im and Me2NHSi (= L) to transition metal complexes has been assessed with DFT calculations for the model systems [Ni(L)], [Ni(CO)3(L)], and [W(CO)5(L)]. These studies revealed some common features in the difference between M–NHSi and M–NHC bonding which largely affect the bonding situation in transition metal complexes. NHSis show a propensity for bridging two metal atoms which was demonstrated on three different examples. Dipp2NHSi reacts with [Ni(CO)4] to form the dinuclear silylene-bridged complex [{Ni(CO)2(μ-Dipp2NHSi)}2] (22) upon CO elimination. The reduction of [Ni(η5-C5H5)2] with lithium naphthalenide in the presence of Dipp2NHSi yielded the NHSi-bridged Ni(I) dimer [{(η5 C5H5)Ni(µ-Dipp2NHSi)}2] (23). The dimeric half-sandwich complex [{(η5-C5H5)Fe(CO)2}2] led upon reaction with Dipp2NHSi to the formation of the dinuclear, NHSi-bridged complex [{(η5-C5H5)Fe(CO)}2(µ-CO)(µ-Dipp2NHSi)] (24). The insertion of Dipp2NHSi into metal halide bonds was investigated in a series of manganese complexes [Mn(CO)5(X)] (X = Cl, Br, I). The reaction of Dipp2NHSi with [Mn(CO)5(I)] led to substitution of two carbonyl ligands with Dipp2NHSi (1) to afford the tricarbonyl complex [Mn(CO)3(Dipp2NHSi)2(I)] (25). In 25, the iodide ligand is aligned in the {Mn(CO)3} plane, located between both NHSi silicon atoms. Treatment of [Mn(CO)5(Br)] with two equivalents of Dipp2NHSi afforded the complex [Mn(CO)3(Dipp2NHSi)2(Br)] (26), in which the bromide ligand is distorted towards one of the NHSi ligands. The reaction of the silylene ligand with [Mn(CO)5(Cl)] at room temperature afforded a mixture of two products, [Mn(CO)3(Dipp2NHSi)2(Cl)] (27*) and the insertion product [Mn(CO)4(Dipp2NHSi)(Dipp2NHSi-Cl)] (27). Complete transfer of a halide to the silylene was achieved for the reaction of Dipp2NHSi with [(η5-C5H5)Ni(PPh3)(Cl)] to yield [Ni(PPh3)(η5-C5H5)(Dipp2NHSi-Cl)] (28). Similarly, the reaction with [(η5-C5H5)Fe(CO)2(I)] led to the formation of [(η5 C5H5)Fe(CO)2(Dipp2NHSi-I)] (29)
Diese Arbeit beschäftigt sich mit den Anwendungen des N-heterocyclischen Silylens Dipp2NHSi (1) als ambiphiles Reagenz in der Hauptgruppenchemie und als Ligand in der Übergangsmetallchemie. Ein Schwerpunkt dieser Arbeit ist die Beurteilung der Unterschiede in der Reaktivität von N-heterocyclischen Silylenen in der Hauptgruppen- und Übergangsmetallchemie im Vergleich zu den heutzutage allgegenwärtigen N heterocyclischen Carbenen. Im Verlauf dieser Studie wurde Silylen 1 mit Verbindungen der Gruppe 13 umgesetzt und die Addukte Dipp2NHSi·AlI3 (2), Dipp2NHSi·Al(C6F5)3 (3) und Dipp2NHSi·B(C6F5)3 (4) isoliert. Weiterhin wurde die Reaktivität von Dipp2NHSi (1) in Bezug auf ElementHalogen-Bindungen verschiedener Hauptgruppenelement-Verbindungen untersucht. Die Umsetzung mit elementarem Brom und Iod führt zu den Dihalogensilanen Dipp2NHSiBr2 (5) und Dipp2NHSiI2 (6). Unter Verwendung von Methyliodid, Benzylchlorid und Benzylbromid konnten die Insertionsprodukte Dipp2NHSi(I)(Me) (10), Dipp2NHSi(Cl)(benzyl) (11) und Dipp2NHSi(Br)(benzyl) (12) gebildet werden. Die Insertion ist gegenüber der reduktiven Kupplung unter Ausbildung von RH2C–CH2R (R = H, Ph) und dem Dihalosilan bevorzugt. Die Umsetzung von 1 mit dem Zinnchlorid Me3SnCl führt Bildung des Diazabutens {(Me3Sn)N(Dipp)CH}2 (9). Die Reaktion mit Ph2SnCl2 hingegen ergibt das Dichlorsilan Dipp2NHSiCl2 (8) sowie cyclische Polystannane der Form (Ph2Sn)n. Außerdem wurde Dipp2NHSi mit Aziden unterschiedlichen sterischen Anspruchs umgesetzt. Die Reaktion mit Adamantylazid führt zur Bildung des Tetrazolins 13. Das sterisch weniger anspruchsvolle Trimethylsilylazid reagiert mit Dipp2NHSi unter Bildung des Silylazids Dipp2NHSi(N(SiMe3)2)(N3) (14). Das Cyclosilamin 15 wird durch die Reaktion von 1 mit 2,6-(Diphenyl)phenylazid gebildet. Im zweiten Teil der Arbeit wurden die Bindungssituation und die Ligandeneigenschaften von Dipp2NHSi (1) in Übergangsmetallkomplexen mithilfe von theoretischen Rechnungen und experimentellen Untersuchungen beleuchtet. DFT-Rechnungen zu den grundlegenden elektronischen Eigenschaften von Me2Im/Me2NHSi und Dipp2Im/Dipp2NHSi ergaben signifikante Unterschiede im Bereich der Grenzorbitale, welche die Bindungssituation von NHSis im Allgemeinen beeinflussen. Insbesondere ein energetisch tiefliegendes π-Orbital scheint die Koordinationschemie dieser Liganden zu bestimmen. Zur Unterstützung der theoretischen Befunde wurden die Silylen-Komplexe M(CO)5(Dipp2NHSi)] (M = Cr 16, Mo 17, W 18) durch Umsetzung von Dipp2NHSi und [M(CO)6] (M= Cr, Mo, W) dargestellt und der Wolframkomplex 18 mit den NHC-Komplexen [W(CO)5(iPr2Im)] (19), [W(CO)5(iPr2ImMe)] (20) und [W(CO)5(Me2ImMe)] (21) verglichen. Die Bindung von Me2Im und Me2NHSi (= L) und Übergangsmetallkomplexen wurde für die verschiedenen Modellverbindungen [Ni(L)], [Ni(CO)3(L)] und [W(CO)5(L)] mittels DFT Rechnungen untersucht, wobei einige Unterschiede zwischen den M–NHSi und M–NHC Bindungen festgestellt wurden, welche die Bindungssituation in Übergangsmetallkomplexen stark beeinflussen. Im Unterschied zu NHCs zeigen N-heterocyclische Silylene eine Neigung zur Verbrückung zweier Metallzentren und dieses Verhalten konnte anhand dreier Beispielen belegt werden. Dipp2NHSi (1) reagiert mit [Ni(CO)4] zum Silylen-verbrückten Nickelkomplex [{Ni(CO)2(μ-Dipp2NHSi)}2] (22). Die Reduktion von Nickelocen mit Lithiumnaphthalid in der Gegenwart von Dipp2NHSi (1) führt zur Bildung des NHSi verbrückten, Ni(I)-Dimers [(η5-C5H5)Ni(µ-Dipp2NHSi)]2 (23). Ähnlich hierzu reagiert der dimere Komplex {[(η5-C5H5)Fe(CO)2]2} mit Dipp2NHSi zum Silylen-verbrückten dinuklearen Komplex [{(η5 C5H5)Fe(CO)}2(µ-CO)(µ-Dipp2NHSi)] (24). Weiterhin wurde die Insertion von Dipp2NHSi (1) in MetallHalogen-Bindungen anhand einer Reihe von Mangankomplexen der Form [Mn(CO)5(X)] (X = Cl, Br, I) untersucht. Die Reaktion von zwei Äquivalenten des Silylens 1 mit dem Iodokomplex [Mn(CO)5(I)] führt zur Bildung des Tricarbonylkomplexes [Mn(CO)3(Dipp2NHSi)2(I)] (25), in dem der Iodidligand symmetrisch zwischen den beiden Siliciumatomen der Silylenliganden in der {Mn(CO)3}-Ebene liegt. Ähnlich hierzu wird der Bis-Silylenkomplex [Mn(CO)3(Dipp2NHSi)2(Br)] (26) durch Umsetzung von [Mn(CO)5(Br)] mit 1 erhalten, wobei eine Wechselwirkung des Bromidliganden mit einem Silylenliganden beobachtet wird. Die Reaktion von Dipp2NHSi 1 mit [Mn(CO)5(Cl)] bei Raumtemperatur resultiert in der Bildung zweier Reaktionsprodukte, dem Bis-Silylenkomplex [Mn(CO)3(Dipp2NHSi)2(Cl)] (27*) und dem Insertionsprodukt [Mn(CO)4(Dipp2NHSi)(Dipp2NHSi-Cl)] (27). Die vollständige Übertragung des Halogenidoliganden auf das Siliciumatom von 1 kann auch für den Halb-Sandwich-Komplex [(η5-C5H5)Ni(PPh3)(Cl)] beobachtet werden, wobei der Komplex [Ni(PPh3)(η5-C5H5)(Dipp2NHSi-Cl)] (28) isoliert wird. Ähnlich hierzu führt die Reaktion von [(η5-C5H5)Fe(CO)2(I)] mit dem Silylen 1 ebenfalls zur Bildung des Insertionsproduktes [(η5 C5H5)Fe(CO)2(Dipp2NHSi-I)] (29)

As levels of carbon dioxide continue to increase in the atmosphere, it is appealing to consider the prospect of utilizing CO2 as a C1 building block for the synthesis of value-added organic chemicals. Such transformations offer potential to directly counteract environmental concerns, and could also enhance the recyclability of current materials. To meet this challenge, the development of metal catalysts capable of promoting the functionalization of carbon dioxide is necessary. Furthermore, there is great interest in employing main group metals for these transformations, particularly those metals that are earth-abundant, non-toxic and affordable. To address these needs and others, the research herein has been driven by the synthesis and characterization of main group metal hydride, alkyl and fluoride complexes with the ultimate aim of developing catalysts for CO2 functionalization. Chapter 1 investigates the synthesis of magnesium, zinc and calcium complexes supported by the tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl)]methyl ligand, [TismPriBenz]. Most significantly, the magnesium carbatrane compound, [TismPriBenz]MgH, which possesses a terminal hydride ligand, has been synthesized and structurally characterized. The corresponding magnesium methyl derivative, [TismPriBenz]MgMe, was also prepared, and the reactivity of these compounds with respect to both metathesis and insertion is explored in great detail. The synthesis and characterization of the corresponding zinc hydride complex, [κ3 TismPriBenz]ZnH, is also described, as well as the preparation of a rare example of a monomeric calcium benzyl compound, [TismPriBenz]CaCH2Ph. Some reactivity of the zinc and calcium derivatives is also described. In Chapter 2, the aforementioned magnesium and zinc compounds and their reactivity towards CO2 is described in detail. Systems comprised of [TismPriBenz]MH (M = Mg, Zn) and tris(pentafluorophenyl)borane are highly effective for the room temperature reduction of CO2 with R3SiH to afford sequentially the bis(silyl)acetal, H2C(OSiR3)2, and CH4 (R3SiH = PhSiH3, Et3SiH and Ph3SiH). Notably, the selectivity of the catalytic system may be controlled by the nature of the silane. Catalytic intermediates were isolated and structurally characterized, including an interesting magnesium formatoborate complex, which has helped elucidate an understanding of the mechanism of the catalysis. Most significantly, it was found that H2C(OSiPh3)2 can be prepared on a multi-gram scale as a crystalline solid and can be converted directly into formaldehyde (CH2O), which is an important industrial chemical. Thus, H2C(OSiPh3)2 can serve as a formaldehyde surrogate and its ability to provide a means to incorporate CH and CH2 moieties into organic molecules is described. Isotopologues of H2C(OSiPh3)2, namely D2C(OSiPh3)2, H213C(OSiPh3)2, and D213C(OSiPh3)2, may be synthesized from the appropriate combinations of (12C/13C)O2 and Ph3Si(H/D), thereby providing a direct and convenient means to use carbon dioxide as a source of isotopic labels in complex organic molecules. In Chapter 3, details pertaining to other transformations catalyzed by [TismPriBenz]MgR (R = H, Me) are provided and their mechanisms are discussed. Notably, [TismPriBenz]MgR is a catalyst for hydrosilylation and hydroboration of styrene to afford exclusively the Markovnikov products, Ph(Me)C(H)SiH2Ph and Ph(Me)C(H)Bpin; the magnesium alkyl intermediate in the catalytic process, [TismPriBenz]MgCH(Me)Ph, has been isolated and structurally characterized, providing the first structural evidence for the insertion of an olefin into a magnesium hydride bond. Other catalytic transformations are described, including hydroboration of carbodiimides to form N-boryl formamidines and hydroboration of pyridine to provide N-boryl 1,4- and 1,2-dihydropyridines. Additionally, the ability for the magnesium hydride and methyl complexes to catalyze dehydrocoupling reactions is discussed. Finally, the ability for [TismPriBenz]MgMe to catalyze the isomerization of a terminal alkyne is reported. Chapter 4 outlines the chemistry of magnesium and zinc compounds supported by a different scaffold, namely, the tris(3-tert-butyl-5-methylpyrazolyl)hydroborato, [TpBut,Me], ligand. The magnesium methyl compound, [TpBut,Me]MgMe, was used as a precursor to prepare [TpBut,Me]MgF via metathesis with Me3SnF, and is the first example of a structurally characterized monomeric magnesium fluoride complex. The reactivity of [TpBut,Me]MgF is described, including its ability to serve as a hydrogen bond and halogen bond acceptor, such that it forms adducts with indole and C6F5I. Corresponding zinc chemistry was studied, including interesting reactivity of [TpBut,Me]ZnH and [TpBut,Me]ZnF. Finally, new heterobimetallic compounds containing magnesium or zinc supported by the [TpBut,Me] ligand and tungsten were synthesized and structurally characterized.

This thesis entitled “Electronic Structure and Bonding in Metallaboranes and Main Group Compounds” consists of five chapters. Chapter 1 gives an exposition of concepts and techniques used in understanding the electronic structure and bonding in some chemically interesting molecules. Heuristics concepts like isolobal analogy and electron counting rules are used in analyzing and predicting some novel chemical systems. A brief description of computational techniques such as density functional theory (DFT) based methods are used to quantitatively examine the structures and energies of these systems. In chapter 2 we present a critical analysis of bonding in neutral and dianionic stannadiphospholes and compare the potential energy surfaces with the isoelectronic Cp+ and Cp- species. The analysis indicates that Sn can be a better isolobal analogue to P+ than to BH or CH+. In chapter 3 we present new strategy to stabilize B2H4 in planar configuration using transition metal fragments. This requires the metal to donate two electrons into the empty B-B π orbital. Such complexes present a unique case study to the classical DCD model of metal-π complex. In chapter 4 we study the bonding in some recently synthesized metallaboranes which does not follow conventional electron counting rules. The complex and non-canonical nature of these metallaboranes feature some unique bonding patterns which are elucidated using theoretical techniques. In the final chapter we present new approach to build metal coated boron fullerenes. We use electron counting rules to device new structures which show enhanced metal boron bonding.

Chapter 1 focuses on the computational study of Zr(CH2Ph)4 and chapter 2 discusses synthesis, characterization and density functional study of 2-imidazolethione. Chapters 3 - 6 describe the synthesis, structural characterization several multidentate tripodal ligands, namely tris(mercaptoimidazolyl)-hydroborato ligand, [TmR], tris(2-pyridylseleno)methyl ligand, [Tpsem], bis(2-pyridonyl)(pyridine-2-yloxy)methyl ligand, [O-poBpom] and allyl-tris(3-t-butylpyrazolyl)borato ligand, [allylTpBut], and their application to main group and transition metals. Chapter 1 describes the analysis of a monoclinic modification of Zr(CH2Ph)4 by single crystal X-ray diffraction, which reveals that the Zr-CH2-Ph bond angles in this compound span a range of 25.1°; that is much larger than previously observed for the orthorhombic form (12.1°;). In accord with this large range, density functional theory calculations demonstrate that little energy is required to perturb the Zr-CH2-Ph bond angles in this compound. Furthermore, density functional theory calculations on Me3ZrCH2Ph indicate that bending of the Zr-CH2-Ph moiety in the monobenzyl compound is also facile, thereby demonstrating that a benzyl ligand attached to zirconium is intrinsically flexible, such that its bending does not require a buffering effect involving another benzyl ligand. Chapter 2 describes the structure of 1-t-butyl-1,3-dihydro-2H-benzimidazole-2-thione which has been determined by X-ray diffraction. The compound exists in the chalcogenone form instead of chalcogenol form, which is similar to its oxo and selone counterparts. Comparison of 2-imidazolone, 2-imidazolethione and 2-imidazoleselone compounds shows that two N-C-E bond angles in the chalcogenone forms are not symmetric. This trend can be reproduced by density functional theory calculations. Additionally, H(mbenzimBut) has intermolecular hydrogen bonding interactions, whereas its selenium counterpart does not. The C-E bond lengths of 2-imidazolone, 2-imidazolethione and 2-imidazoleselone compounds are intermediate between those of formal C-E single and double bonds, which is in accord with the notion that zwitterionic structures that feature single C+-E- dative covalent bonds provide an important contribution in such molecules. Furthermore, NBO analysis of the bonding in H(ximBut) derivatives demonstrates that the doubly bonded C=E resonance structure is most significant for the oxygen derivative, whereas singly bonded C+-E- resonance structures dominate for the tellurium derivative. This result appears to be counterintuitive, based on the fact that it opposes the trend that one would expect on the basis of electronegativity difference, however, studies on XC(E)NH2 derivatives provide solid support for it. In this regard, the C~E bonding in these compounds is significantly different to that in chalcogenoformaldehyde derivatives for which the bonding is well represented by a H2C=E double bonded resonance structure. Chapter 3 describes the computational study on [TmMeBenz] anion and the synthesis and characterization of [TmButBenz]Na, [TmButBenz]Tl and [TmButBenz]Tl. It is worth noting that the two thallium compounds are the first structurally characterized monovalent monomeric [TmR]Tl complexes. Chapter 4 describes the synthesis and characterization of a few [TmR]M (M = Ti, Zr, Hf) complexes, including (i) Cp[TmBut]TiCl2 and Cp[TmBut]ZrCl2, which are analogues of Cp2TiCl2 and Cp2ZrCl2; (ii) [TmBut]Zr(CH2Ph)3 and (iii) [TmBut]Hf(CH2Ph)3 and [TmAd]Hf(CH2Ph)3, which are the first structurally characterized [TmR]Hf complexes. Chapter 5 describes two multidentate, L3X type ligands, which feature [CN3] and [CNO2] donors, namely tris(2 pyridylseleno)methane, [Tpsem]H, and bis(2-pyridonyl)(pyridin-2-yloxy)methane, [O-poBpom]H. They have been synthesized, characterized, and employed in the synthesis of zinc and cadmium complexes. Chapter 6 describes the synthesis and structural characterization of a new [Tp] ligand featuring an allyl substituent on the central boron atom, namely [allylTpBut]Li is reported. The compound reacts steadily with CH3CH2SH under 350 nm UV light via a thiol-ene click reaction. The resulting [CH3CH2S(CH2)3TpBut]Li complex can further react with metal halide. For example, the reaction of [CH3CH2S(CH2)3TpBut]Li with ZnI2 produced [CH3CH2S(CH2)3TpBut]ZnI at room temperature. This study provides a simple model on the immobilization of [Tp] metal complexes to the polymer chains with -SH terminals.

Alkylation of the compounds (PPN) $\sb2\lbrack$EFe$\rm\sb3(CO)\sb9\rbrack$ (E = S, Se, Te) was performed using methyl triflate and methyl iodide. The S-cluster yielded the novel compound (PPN) (Fe$\sb3$(CO)$\sb9$SMe), whereas the Se and Te-cluster alkylated at the Fe$\sb3$-base yielding (PPN) (MeFe$\sb3$(CO)$\sb9$E). For comparison, the clusters (PPN) $\sb2\lbrack$HE$\rm\{Fe(CO)\sb4\}\sb3\rbrack$ (E = Sb, As) were alkylated as well. Reaction of the Sb-cluster with MeI yielded (PPN) (MeSb(I)$\rm\{Fe(CO)\sb4\}\rbrack,$ whereas the reaction with EtI yielded (PPN) $\sb2\lbrack$ISb$\rm\{Fe(CO)\sb4\}\sb3\rbrack$ and ethane. The possibility of a radical chain reaction for the latter was ruled out by performing the reaction in the presence of a radical scavenger as well as in the dark. The compounds $\rm\lbrack Cat\rbrack\sb{2-x}\lbrack H\sb{x}M\sb3(CO)\sb9E\rbrack\ (cat=Et\sb4N\sp+,\ PPN\sp+;$ x = 0, 1; M = Fe, Ru; E = S, Se, Te) were shown to mediate the catalytic formation of methyl formate from methanol and CO. The reaction is pseudo first order in catalyst and the initial rate is independent of the pressure. NaAsO$\sb2$ reacts with Mo(CO)$\sb6$ in refluxing methanol or ethanol to form $\rm\lbrack Et\sb4N\rbrack\sb2\lbrack(OC)\sb5MoAsMo\sb3(CO)\sb9(\mu\sb3$-$\rm OR)\sb3Mo(CO)\sb3\rbrack$ (R=Me, Et). The compounds are electron rich, and extended Huckel calculations have shown that the extra electron pair resides in an a$\sb2$ orbital, equally delocalized over three molybdenum atoms. A $\sp{205}$Tl NMR study has been conducted on the following compounds with Tl-transition metal bonds: $\rm Tl\{CO(CO)\sb4\}\sb3,\ \lbrack BnMe\sb3N\rbrack\sb3\lbrack Tl\{Fe(CO)\sb4\}\sb3\rbrack,\ Tl\{M(CO)\sb3Cp\}\sb3$ (M = Cr, Mo, W), TlFp$\sb3,$ Fp = CpFe(CO)$\rm\sb2),\ \lbrack PPN\rbrack\sb2\lbrack Tl\sb2Fe\sb6(CO)\sb{24}\rbrack,\ \lbrack Et\sb4N\rbrack\sb2\lbrack Tl\sb2Fe\sb4(CO)\sb{16}\rbrack,\ \lbrack Et\sb4N\rbrack\lbrack LTl\{Fe(CO)\sb4\}\sb2\rbrack$ (L = bipy, en, phen, tmeda, dien), and $\rm\lbrack Et\sb4N\rbrack\sb4\lbrack Tl\sb4Fe\sb8(CO)\sb{30}\rbrack,$ as well as $\rm TlCo(CO)\sb4.$ The possibility of formation of carbonylate anion adducts was also investigated by $\sp{205}$Tl NMR. This technique was used to probe the dynamic behavior of the Tl-metal cluster complexes in solution, and it was shown that most larger Tl-Fe clusters dissociate into simpler fragments in solution.

Open–framework inorganic materials are an important class of compounds because of their many applications in the areas of ion–exchange, separation and catalysis. Ever since the discovery of microporous aluminophosphates by Flanigen and co–workers in the early 80’s, the field of open–framework compounds has witnessed explosive growth. It is now established that the open–framework compounds comprise of almost all the elements of the periodic table. In addition, it has been shown that the inorganic anions in the open–framework compounds can be partially substituted by rigid organic linkers such as the oxalate. The resulting inorganic–organic hybrid structures are interesting due to the variable nature of the binding properties of the organic and inorganic moieties. The present thesis consists of systematic studies on the formation of amine–templated inorganic open–framework structures and inorganic–organic hybrid compounds based on the main group, transition metal and actinide elements. In Chapter 1 of the thesis an overview of inorganic open-framework materials is presented, with an emphasis on the elements that have been employed in the present study. Chapter 2 has two parts (Parts A and B) describing the synthesis and structure of open-framework tin(II) containing compounds. In Part A, the syntheses and structures of amine–templated tin(II) phosphates are presented, and in Part B, the syntheses and structures of a family of tin(II) oxalate compounds are discussed. Weak intermolecular forces such as hydrogen-bond interactions, π•••π interactions, and lone-pair–π interactions have been observed in these compounds, and appear to lend structural stability. As part of this study, efforts have been made to evaluate the energies associated with the π•••π interactions and the lone-pair–π interactions using suitable theoretical models. In Chapter 3, a new family of organically templated hybrid materials based on indium, synthesized by partially substituting the inorganic anion (phosphite/phosphate/suphate) by the oxalate group, is presented. These compounds exhibit a wide range of structures in which the oxalates play a variety of roles. The observation of the first zero-dimensional molecular hybrid structure and the isolation of concomitant polymorphic compounds is noteworthy. The molecular hybrid structure is reactive and undergoes transformation reactions under both acidic and basic conditions. In Chapter 4, the synthesis and structural studies of five new open–framework phosphate and phosphite compounds of gallium are presented. All the compounds have three-dimensional structures, and the formation of a gallium phosphate based on only one type of building unit (spiro–5) is noteworthy. While a large number of organically templated transition metal phosphates have been synthesized, studies on transition metal phosphites are not many. In Chapter 5, the synthesis, structure and magnetic properties of a family of transition metal (cobalt, vanadium, manganese) phosphite structures templated by the organic amines are presented. A previously known vanadyl phosphite has also been isolated and investigated by temperature dependent ESR and magnetic susceptibility studies. All the transition metal compounds exhibit antiferromagnetic behavior. In Chapter 6, the synthesis, structure, and transformation reactions in amine-templated actinide phosphonoacetates are presented. The compounds, which are based on uranium and thorium, are built up from the connectivity between the metal polyhedra and the phosphonoacetate/oxalate units, forming two– and three–dimensional structures. It has been shown that the two–dimensional uranyl phosphonoacetate–oxalate compound can be prepared by two different synthetic approaches: (i) solvent–free solid state reaction at 150˚C and (ii) room temperature mechanochemical (grinding) route. The formation of oxalate hybrids using the phosphonocarboxylate ligand is a new approach in the synthesis of multi-component hybrid compounds.

Recently, the Parkin group has synthesized tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methane, [Tismᴾʳⁱᴮᵉⁿᶻ]H, a bulky tetradentate tripodal ligand, which upon deprotonation can coordinate to metal centers via three nitrogen donor atoms and a carbon bridgehead to form metal atrane compounds. The [Tismᴾʳⁱᴮᵉⁿᶻ] ligand has been previously shown to stabilize metal hydride complexes, for example [Tismᴾʳⁱᴮᵉⁿᶻ]MgH [Tismᴾʳⁱᴮᵉⁿᶻ]ZnH. However, no attempts had been previously made to employ this ligand to stabilize heavier Group 12 analogues of these complexes, namely the cadmium and mercury hydride derivatives. In addition, all [Tismᴾʳⁱᴮᵉⁿᶻ] complexes previously reported have employed metals in the first or second oxidation states. In this work, an investigation is undertaken to use the [Tismᴾʳⁱᴮᵉⁿᶻ] ligand to stabilize rare examples of cadmium and mercury hydrides, as well as survey how this ligand binds to Group 13 and transition metals in a variety of oxidation states. In Chapter 1, a series of [Tismᴾʳⁱᴮᵉⁿᶻ] cadmium complexes are reported, including the novel cadmium hydride species [Tismᴾʳᴮᵉⁿᶻ]CdH, which is only the third terminal cadmium hydride species to be structurally characterized by X-ray diffraction. The reactivity of this complex has been probed, revealing the first detailed report of reactivity for a Cd-H bond, as well as the first comparison in relative reactivity between an analogous Cd-H and Zn-H bond. This reactivity of [Tismᴾʳⁱᴮᵉⁿᶻ]CdH includes the ability to insert CO₂ and CS₂, and the resulting cadmium formate and dithioformate complexes have been characterized and discussed, with the latter being the first structurally characterized example of a cadmium dithioformate complex. In addition, [Tismᴾʳⁱᴮᵉⁿᶻ]CdH can undergo hydride extraction to yield the ion pair {[Tismᴾʳⁱᴮᵉⁿᶻ]Cd}[HB(C6F5)₃], a rare example of trigonal monopyramidal cadmium complex. Finally, [Tismᴾʳⁱᴮᵉⁿᶻ]CdMe was synthesized, revealing a different coordination mode of the [Tismᴾʳⁱᴮᵉⁿᶻ] ligand than in the analogous [Tismᴾʳⁱᴮᵉⁿᶻ]ZnMe. In Chapter 2, a series of [Tismᴾʳⁱᴮᵉⁿᶻ] mercury complexes are reported and compared with their cadmium analogues. This comparison revealed several notable differences between [Tismᴾʳⁱᴮᵉⁿᶻ] mercury and cadmium complexes, most notably that the M-O-Si bond angle in [Tismᴾʳⁱᴮᵉⁿᶻ]HgOSiPh₃ is bent, as opposed to the linear [Tismᴾʳⁱᴮᵉⁿᶻ]CdOPh₃ derivative. The synthesis and characterization of [Tismᴾʳⁱᴮᵉⁿᶻ]HgH, the first mercury hydride complex to be structurally characterized by X-ray diffraction, is also reported. This complex has been crystallized in both the κ⁴ and κ³-coordination mode of the [Tismᴾʳⁱᴮᵉⁿᶻ] ligand, representing the first example of a [Tismᴾʳⁱᴮᵉⁿᶻ] compound to be structurally characterized in two coordination modes. In Chapter 3, the synthesis of Group 13 and transition metal [Tismᴾʳⁱᴮᵉⁿᶻ] complexes are reported. These compounds include the first examples of [Tismᴾʳⁱᴮᵉⁿᶻ]M(III) complexes, which reveal that trivalent Group 13 [Tismᴾʳⁱᴮᵉⁿᶻ]M halide compounds form charged ion pairs, whereas trivalent transition metal chloride compounds form six-coordinate octahedral complexes. The investigation into Group 13 [Tismᴾʳᴮᵉⁿᶻ] complexes also led to the structural characterization of [Tismᴾʳⁱᴮᵉⁿᶻ]In→InI₃, the first example of a [Tismᴾʳⁱᴮᵉⁿᶻ] compound with a metal-metal bond. A series of [Tismᴾʳⁱᴮᵉⁿᶻ]MCl (M = Mn, Fe, Co, Cu) complexes are reported and their metrical data compared, along with an investigation into the reactivity of [Tismᴾʳⁱᴮᵉⁿᶻ]NiBr, which led to spectroscopic evidence for a [Tismᴾʳⁱᴮᵉⁿᶻ]NiH complex. Finally, the gold complex [κ1-Tismᴾʳⁱᴮᵉⁿᶻ]AuPPh₃ is reported, which adopts a novel κ1-coordination of the [Tismᴾʳⁱᴮᵉⁿᶻ] ligand.

In Chapter 1, I discuss the synthesis and characterization of lithium tris(pyrazolyl)hydroborato complexes, [TpR1,R2]Li. Group 1 [TpR1,R2]M complexes serve as key starting points to access many other main group and transition metal complexes; however, the synthesis and crystal structures of [Tp R1,R2]Li has not been reported. Molecular structures of [TpBut]Li and [TpBut,Me]Li show these complexes are trigonal pyramidal, an unusual geometry for lithium. These complexes are also able to bind small molecules to form four-coordinate pseudo-tetrahedral complexes, [Tp]Li-L (L = MeCN, pzButH, and H2O). The binding constants for the association of acetonitrile to [TpBut]Li and [TpBut,Me]Li are 0.84M-1 and 0.96M-1, respectively, indicating that the dissociation of MeCN is facile in solution. In addition, [TpBut,Me]Li serves as transmetallating agent to yield the cadmium halide complexes, [TpBut,Me]CdX (X = Cl, Br, I). In Chapter 2, I discuss the synthesis and characterization of organometallic cadmium complexes supported by the nitrogen-rich multidentate ligands, tris(pyridylthio)methane, [Tptm]H; tris(1-methyl-imidazolylthio)methane, [TitmMe]H; and tris(1-methyl-benzimidazolylthio)methane, [TitmiPrBenz]H. These ligands are in the nascent stages of development and there are only a few metal [Tptm] and [TitmMe] complexes in the literature. An investigation of the reactivity of [L]CdN(SiMe3)2, [L]CdOSiMe3, and [L]CdOSiPh3 ([L] = [Tptm], [TitmMe], [TitmiPrBenz]) shows these complexes provide access to a variety of organometallic cadmium complexes, [L]CdX, (X = OAc, Cl, Br, O2CH, NCO). The characterization of cadmium acetate and formate complexes is significant due to their structural similarity with the metal bicarbonate intermediate formed by zinc and cadmium-substituted carbonic anhydrase. In addition, the synthesis and characterization of cadmium methyl complexes, [L]CdMe, is discussed. The application of heat to a mixture of [TitmiPrBenz]H and CdMe2 results in isomerization of the ligand to [S3-TitmiPrBenz]CdMe. This sulfur-rich [S3-TitmiPrBenz] ligand is not reported in the literature and is ripe for further investigation. The solid state structures of these compounds provide a comparison with biologically relevant [Tp] or [Tm] cadmium methyl complexes in the literature. In Chapter 3, I describe the synthesis and structural characterization of [BmButBenz]M (M = Na, K) and [BmRBenz]Ca(THF)2 (R = Me, But) are discussed. The sulfur-rich tripodal ligand tris(imidazolylthio)hydroborato, [Tm], was previously designed to serve as a softer version of the [Tp] ligand. Metal [Tm] complexes are prevalent in the literature and have often been used as molecular mimics of sulfur-rich enzyme active sites. Recently, the benzannulated [TmRBenz]M complexes were reported and were found to promote k3 coordination toward the metal center. To allow for an in-depth investigation of the newly synthesized [BmRBenz] class of ligand, the [BmButBenz]M (M = Na, K, Ca) complexes were synthesized and compared to previously reported metal [BmMeBenz]M complexes. Additionally, the [BmMeBenz]2Ca(THF)2 was synthesized and characterized via X-ray diffraction. The molecular structure of [BmMeBenz]2Ca(THF)2 shows the complex is monometallic with an uncommon eight-coordinate dodecahedral calcium center. [BmMeBenz]2Ca(THF)2 is the first molecular structure of calcium coordinated to the [Tm] or [Bm] ligand class. In Chapter 4, I discuss the synthesis and characterization of mercury alkyl complexes supported by the [TmMe], [BmR], [TmRBenz] and [BmRBenz] ligands (R = Me or But). As previously mentioned, [Tm]M complexes are considered biologically relevant molecular models of enzyme active sites. With this in mind, [TmBut]HgR (R = Me,Et) complexes have served as mimics for the mercury detoxification enzyme MerB. A previous study by our group showed that the adoption of multiple coordination modes of the ligand in [TmBut]HgR plays a significant role in the activation of the Hg-C bond toward protonolysis. The molecular structures of the [TmR], [BmR], [TmRBenz], and [BmRBenz] mercury alkyl complexes show that they adopt various coordination modes, ranging from k1 to k3. Preliminary competition experiments in which benzenethiol was added to [TmR]HgEt and [TmRBenz]HgEt indicate that the Hg-C bond in [TmMeBenz]HgEt was cleaved faster than that in [TmMe]HgEt. Conversely, the Hg-C bond in [TmBut]HgEt was cleaved faster than that in [TmButBenz]HgEt, indicating that benzannulation and the size of the R-group on the [Tm] ligand play important roles in Hg-C bond cleavage.

碩士
國立中正大學
化學暨生物化學研究所
102
This thesis consists of three chapters. In chapter 1, we applied the multi-coefficient density functional theory (MC-DFT) to a few recent Minnesota functionals. In chapter 2, we have developed a new method using mixed functionals and we tested it on 70 bond energies of 3d transition-metal-containing molecules. In chapter 3, we investigated the kinetic isotope effects and tunneling effects of noble-gas exchange reactions. 　　 　　In chapter 1, we have applied MC-DFT method to four recent Minnesota functionals, including M06-2X, M08-HX, M11, and MN12-SX on the performance of thermochemical kinetics. The results indicated that the accuracy can be improved significantly by using two or three basis sets. We further included the SCS-MP2 energies into MC-DFT, and the resulting mean unsigned errors (MUE) decreased by ~0.3 kcal/mol for the most accurate basis set combinations. The M06-2X functional with the simple [6-311+G(d,p)/6-311+G(2d,2p)] combination gave the best performance/cost ratios for the MC-DFT and MC-SCS-MP2 | MC-DFT methods with MUE of 1.58 and 1.22 kcal/mol, respectively. 　　 　　In chapter 2, we have developed a new method using mixed functionals for transition metals. This method was tested against a database including 70 bond energies of 3d transition-metal-containing molecules with small experimental uncertainties. The best mixed functional method was the τ-HCTHhyb/mPW2-PLYP combination, and it yielded an MUE of 5.49 kcal/mol. In comparison, the single τ-HCTHhyb and mPW2-PLYP functional gave MUEs of 6.14 and 12.88 kcal/mol, respectively. We also applied the MC-DFT approach into the mixed functional and it yielded an MUE of 4.94 kcal/mol. We further added the MP2 and CCSD energies into the new method, and obtained MUE of 4.75 kcal/mol and 4.51 kcal/mol, respectively. 　　 　　In chapter 3, we used VTST/MT method to investigate four noble-gas exchange reactions: Ng’ + HNBNg+ (Ng, Ng’ = He, Ne, and Ar). The barrier heights of these four reactions were predicted to be 5－9 kcal/mol. The calculated results showed significant tunneling effects even at room temperature, especially for the He + HNBHe+ reaction. All reactions showed very significant tunneling effects at low temperature. For helium exchange reactions, the internal helium atom (in the cation) contributed more in the tunneling effects than the external helium atom (the neutral reactant) at low temperature.