Academic literature on the topic 'Phosphinoamine'

In a refluxing chloroform solution, the η1-pyrimidinyl {pyrimidinyl = C4H3N2} palladium complex [Pd(PPh3)2(η1-C4H3N2)(Br)], 1 exhibited intermolecular displacement of two triphenylphosphine ligands to form the doubly bridged η2-pyrimidinyl Dipalladium complex [Pd(PPh3)(Br)]2(μ,η2-C4H3N2)2, 3. The treatment of 1 with Hdppa {Hdppa = N,N-bisdiphenyl phosphinoamine} in refluxing dichloromethane yielded the doubly bridged Hdppa dipalladium complex [Pd(Br)]2(μ,η2-Hdppa)2, 4. Complex 1 reacted with the bidentate ligand, NH4S2CNC4H8 and, NaS2COEt, and the tridentate ligand, KTp {Tp = tris(pyrazoyl-1-yl)borate}, to form the η2-dithio η1-pyrimidinyl complex [Pd(PPh3)(η1-C4H3N2)(η2-SS)], (5: SS = S2CNC4H8; 6: SS = S2COEt) and η2-Tp η1-pyrimidinyl complex [Pd(PPh3)(η1-C4H3N2)(η2-Tp)], 7, respectively. Treatment of 1 with AgBF4 in acetonitrile at room temperature resulted in the formation of the doubly bridged η2-pyrimidinyl dipalladium complex [{Pd(PPh3)(CH3CN)}2(μ,η2-C4H3N2)2][BF4]2, 8. All of the complexes were identified using spectroscopic methods, and complexes 3, 4, and 8 were determined using single-crystal X-ray diffraction analyses.

Many major advances in our fundamental chemical knowledge have emerged from novel metal-metal chemistry. Such complexes which exhibit metal-metal interactions, have provided excellent tools for developing our understanding of chemical structure and bonding, catalysis, metal surface chemistry and bioinorganic chemistry. However, whilst metal-metal bonding is now well understood in the p- and d- blocks and to some extent the s-block of the Periodic Table very little is known, in comparison, about that for the f-block and especially the actinide elements. Traditionally the chemistry of molecular f-element compounds has been dominated by the use of carbon, nitrogen, oxygen and halogen based ligands with the implementation of metal-based fragments as ligands considerably less developed. In recent years dinuclear species containing a metal-metal bond between two different transition metal centres bridged by a supporting ligand structure have rapidly been gaining interest, as they would be expected to exhibit different reactivity to those of monometallic or homobimetallic complexes. Early/late heterobimetallic complexes, featuring metal-metal interactions supported by a phosphinoamine ligand system, have received particular attention due to their two very different reaction sites, inherent bond polarity, and synergy between the two centres resulting in unique reactivity. A range of novel phosphinoamines, including MesN(H)PPh2, have been successfully synthesised to accompany the previously reported phosphinoamines DippN(H)PPh2 and MesN(H)PiPr2. All phosphinoamines were successfully deprotonated using nBuLi to afford the corresponding lithium salts as ligand transfer reagents. Reaction of uranium tetrachloride or thorium tetrachloride with three molar equivalents of either [Li(MesNPPh2)(Et2O)2] or [{LiNMes(PiPr2)(Et2O)}2] resulted in the respective tris(phosphinoamide) actinide(IV) chloride complexes [AnCl(MesNPPh2)3] and [AnCl(MesNPiPr2)3] (An = U, Th). Treatment of the tris(phosphinoamide) actinide(IV) halide complexes with Me3SiI afforded the corresponding tris(phosphinoamide) actinide(IV) iodide complexes. The installation of cobalt iodide into the coordination sphere of the uranium was achieved in the presence of zinc powder to afford the two uranium-cobalt complexes [UCl(MesNPPh2)3CoI] and [(MesNPiPr2)U(μ-X)(MesNPiPr2)2CoI] (X = 41% I, 59%Cl). [UCl(MesNPPh2)3CoI] adopts a paddle-wheel structure whereas [(MesNPiPr2)U(μ-X)(MesNPiPr2)2CoI] exhibits a structure with at best C2v symmetry and two bridging phosphinoamides and one bridging halide ligand. These structural differences confer very different magnetic behaviour. At low temperature [UCl(MesNPPh2)3CoI] can be formulated as an S = 1 spin system resulting from a combination of a magnetic singlet uranium(IV) and triplet cobalt(I). However, in contrast [(MesNPiPr2)U(μ-X)(MesNPiPr2)2CoI] is an S = 0 spin system at low temperature with antiferromagnetic exchange between uranium and cobalt proposed. Density functional theory calculations and topological bond analyses support the notion of formally dative Co → U bonds in both complexes. In an attempt to further support the claim of antiferromagnetic exchange between uranium and cobalt the thorium analogues were synthesised. To date, investigations into the respective electronic structures are still on going and conclusions about the exact nature of the cobalt centres cannot be drawn. There is however sufficient evidence which warrants further investigation that would be expected to be very detailed and that is thus unfortunately beyond the timeframe of this PhD. Reaction of the same four tris(phosphinoamide) actinide(IV) chlorides, that resulted in the synthesis of the actinide-cobalt complexes, with [Mo(MeCN)3(CO)3] in dichloromethane afforded the heterobimetallic uranium- and thorium-molybdenum complexes [AnCl(MesNPR2)2(MesNPR2{μ-NCMe})Mo(CO)3] (An = U, R = iPr; An = Th, R = iPr; An = U, R = Ph; An = Th, R = Ph). In contrast treatment of the tris(phosphinoamide) actinide(IV) iodides [IAn(MesNPiPr2)3] (An = Th, U) with [Mo(MeCN)3(CO)3] in toluene resulted in the formation of the complexes [(η2-MesNPiPr2)AnI(MesNPiPr2)({μ-NCMe}MesNPiPr2)Mo(CO)3 (An = U, Th). These compounds show unprecedented acetonitrile insertion as a bridging ligand between the actinide metal and Mo with structural analysis suggests an activation of the nitrile group. To synthesise the analogous actinide-molybdenum paddlewheel complexes to [UCl(MesNPPh2)3CoI], the appropriate tris(phosphinoamide) actinide(IV) halides were treated with [Mo(CO)3(NCMe)3] to afford the heterobimetallic uranium- and thorium-molybdenum complexes [M(X)(MesNPPh2)3Mo(CO)3] (M = U, X = Cl; M = U, X = I; M = Th, X = Cl; M = Th, X = I,). Orbital- and density-based quantum chemical calculations reveal dative MoM σ-interactions in all cases and so these complexes constitute unprecedented actinide-group 6 metal-metal bonds, where before heterobimetallic uranium-metal bonds were restricted to a few group 7-10 metals. With a synthetic route towards actinide-cobalt complexes established future work must look towards the reduction of these complexes to result in highly reactive and polarised early-late heterobimetallic compounds. The subsequent reaction of these compounds with small molecules such as CO, CO2 and H2 etc has the potential to result in novel and unusual chemistry which can help develop our fundamental understanding of the actinides. Although the actinide-molybdenum complexes were relatively straightforward to synthesise, surprisingly, the analogous chromium and tungsten complexes were not accessible by the same method, although it has been anticipated that photolysis could be an alternative synthetic route. Photolysis could also lead to the removal of one or more of the carbonyl groups situated on the group 6 metal and result in the targeted highly reactive and polarised early-late heterobimetallic compounds suitable for the activation of small molecules.

Early transition metal hydrides are currently of great interest; they are intermediates in catalytic processes, and have demonstrated ability to activate small molecules. While these complexes are traditionally supported by cyclopentadienyl-type ancillary ligands, current efforts are focused on alternative architectures. In particular, chelating mixed-donor ancillary ligands are currently employed for the synthesis of metal hydride complexes. Bidentate phosphinoamide ligands ([ArNPiPr₂]¹- where Ar = 3,5-dimethylphenyl) were used herein for the synthesis of scandium, yttrium and zirconium organometallic complexes that were characterized using NMR spectroscopy and X-ray diffraction techniques. Mixed phosphinoamide-alkyl yttrium complexes were generated in solution as a mixture of products from reaction of ArNHPiPr₂ with Y(CH₂SiMe₃)₃(THF)₂. Using the same methodology, (ArNPiPr₂)₂Sc(CH₂SiMe₃)(THF) was prepared and reaction with H₂ or PhSiH₃ gave the ligand redistribution product (ArNPiPr₂)₃Sc(THF), along with insoluble materials. A ferrocene-linked diphosphinoamide ligand was developed ([fc(NPiPr₂)₂]²- where fc = 1,1′-ferrocenyl) and employed for the synthesis of a discandium dihydride complex which is bridged by both hydride and phosphinoamide ligands. Because of the insolubility of this discandium dihydride subsequent attempted reactions with CO, alkenes and alkynes were unsuccessful. Triphosphinoamide zirconium complexes (ArNPiPr₂)₃ZrX (X = Cl, Et, CH₂Ph, BH₄, PHPh) were prepared and proved to be poor precursors for the synthesis of a zirconium hydride complex. The ferrocene-linked diphosphinoamide ligand was used in the synthesis of zirconium organometallic complexes, fc(NPiPr₂)2ZrR₂ (R = Me, CH₂Ph, CH₂tBu, tBu). While these dialkyl zirconium complexes were unreactive with respect to H₂, they have been shown to undergo insertion of (2,6-dimethylphenyl)isocyanide to generate the expected iminoacyl complexes. The reactivity of the iminoacyl complexes has been examined and a thermally induced 1,2-hydrogen shift reaction was observed for the benzyl-substituted iminoacyl, to generate an amidoalkene complex; the kinetics of the transformation were studied and deuterium isotopic labelling experiments revealed a primary isotope effect for the migrating hydrogen. The electrochemical oxidation of ferrocene-linked diphosphinoamide scandium and zirconium complexes was examined using cyclic-voltammetry; irreversible oxidation of the ferrocenyl diphosphinoamide ligand in these complexes was observed.