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A tridentate diphenolate phosphine ligand H2[OPO] (bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine) has been synthesized in high yield. Treatment of H2[OPO] with Ti(OEt)4 in toluene at room temperature produced reddish orange crystalline Ti[OPO]2. The bis-ligand complex Ti[OPO]2 also be obtained from the in situ lithiation of H2[OPO] in THF or toluene followed by addition of TiCl4(THF)2. The reactions of MCl2[N(SiMe3)2]2 (M = Zr, Hf) with H2[OPO] in pentane at room temperature generated cleanly [OPO]2Zr(H2O) and [OPO]2Hf(H2O), respectively, in high yield. Treatment of TiCl4(THF)2 with Ti[OPO]2 in toluene afforded [OPO]TiCl2(THF). The solution and solid-state structures of Ti[OPO]2, [OPO]TiCl2(THF), [OPO]2Zr(H2O) and [OPO]2Hf(H2O) were studied by multinuclear NMR spectroscopy and X-ray crystallography. lithiation of H2[OPO] with n-BuLi in DME solution afforded [OPO]Li2(DME)2. The metathetical reactions of H2[OPO] with NaH or KH in DME solutions, respectively, produced the corresponding complexes [OPO]Na2(DME)2 and {[OPO]K2(DME)2}2. Both [OPO]Li2(DME)2 and [OPO]Na2(DME)2 are highly active catalysts for ring-opening polymerization of caprolactone. A series of tetravalent tin complexes [OPO]SnX2 (X = Cl, Me, n-Bu) also be obtained from the in situ lithiation of H2[OPO] in THF followed by addition of SnCl2X2. A divalent tin complexe [OPO]Sn also be obtained by analogous way from the in situ lithiation of H2[OPO] in pentane followed by addition of SnCl2.

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Here we report the preparation, structure, and spectroscopic properties of an intriguing copper(I) cyclophane-like dimeric complex [Cu2(dppa)2(bpy)2][BF4]2(2)¡B[Cu2(dppa)2(mbpy)2][BF4]2(3)¡B[Cu2(dpbp)2(bpy)2][BF4]2(7)©M[Cu2(dppb)2(bpy)2] [BF4]2(8), containing phenyl phosphine bridge ligands, such as diphenylphosphino acetylene (dppa), 1,4-bis(diphenylphosphino)benzene (dppb) and 4,4'-bis(diphenyl phosphino)biphenyl (dpbp). As a building unit, the complex [Cu2(dpbp)2(NCMe)4] [BF4]2(9) containing labile acetonitrile molecules those can be easily substituted by anionic ligands, is expected to combine with suitable linkers to synthesize supramolecular arrays with shapes of polygons and polyhedra.

We prepared a seties of tridentate amido diphosphine ligands, including symmetrical [N(o-C6H4PR2)2]- ([R-PNP]- ; R = Ph, iPr, Cy) and unsymmetrical [N(o-C6H4PPh2) (o-C6H4PiPr2)]-. Deprotonation of neutral ligands, H[R-PNP] ( R = Ph, iPr, Cy) or H[Ph-PNP-iPr], with n-BuLi in ether solutions at -35oC produced the lithium complexes, [R-PNP]Li(solv)n ( R = Ph, iPr, Cy; solv = THF, OEt2; n = 1,2) or [Ph-PNP-iPr]Li(solv)n (solv = THF, OEt2; n = 1,2), respectively. The reactions of the lithium complexes or neutral ligands with NiCl2(DME) in THF solutions generated nickel(II) chloride complexes, [R-PNP]NiCl ( R = Ph, iPr, Cy) or [Ph-PNP-iPr]NiCl, which was then reacted with a variety of Grignard reagents to afford the corresponding hydrocarbyl complexes. Of particular interest among the compounds isolated are alkyl complexes that contain £]−hydrogen atoms. The metathetical reactions of nickel(II) chloride complexes with LiNHPh, NaOPh, NaSPh, or NaOtBu, respectively, produced the correspounding nickel anilide, nickel phenolate, nickel thiophenolate and nickel tert-butoxide derivatives. Protonolysis studies of nickel(II)-heteroatom complexes revealed the basic reactivity of these £k-donor ligands. The basicity follows the order OtBu > NHPh > OPh > SPh. Treatment of Ni(COD)2 (COD = cycloocta-1,5-diene) with neutral ligands produced the correspounding four-corrdinate nickel hydride complexes, [R-PNP]NiH (R = Ph, iPr, Cy) or [Ph-PNP-iPr]NiH. The olefin insertion reactions of [iPr-PNP]NiH or [Ph-PNP-iPr]NiH with ethylene, 1-hexene, and norbornene, respectively, generated the corresponding ethyl, n-hexyl, and 2-norbornyl complexes. The formation of [iPr-PNP]Ni(n-hexyl) or [Ph-PNP-iPr]Ni(n-hexyl) is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni-H bond of [Ph-PNP-iPr]NiH in an exclusively 2,1-manner to afford [Ph-PNP-iPr]NiCH(Me)Ph. The selective 2,1-insertion products [R-PNP]NiCH(Me)CO2Me (R = Ph, iPr, Cy) or [Ph-PNP-iPr]NiCH(Me)CO2Me were also isolated from the reactions of methyl acrylate with the corresponding nickel hydride complexes. The effects of the phosphorus and olefin substituent on the reactivity and regioselectivity of the olefin insertion reactions are discussed. We also prepared nickel acyl complexes and nickel complexes catalyzed C-N bond formation. In addition to solution NMR spectroscopic data for all new compounds. X-ray diffraction revealed solid structures. A series of five-coordinate aluminum complexes supported by o-phenylene - derived amido diphosphine ligands have been prepared and structurally characterized. Alkane elimination reactions of trialkylaluminum with neutral ligands, H[R-PNP] ( R = Ph, iPr) and H[Ph-PNP-iPr] in toluene solution at -35oC respectively produced the corresponding dialkyl complexes [iPr-PNP]AlR'2, [Ph-PNP]AlR'2 and [iPr-PNP-Ph]AlR'2 (R' = Me, Et, iBu) in high isolated yield. The dihydride complexes [iPr-PNP] AlH2, [Ph-PNP]AlH2 and [iPr-PNP-Ph]AlH2 prepared in one-pot reactions of in situ prepared dichloride precursors with LiAlH4 in THF at room temperature. X-ray diffraction studies revealed a distorted trigonal-bipyramidal structure for these molecules in which the two phosphorus donors are mutually trans. The solution structures of these complexes were all characterized by 1H, 13C, and 31P NMR spectroscopy. The NMR data are indicative of solution C2 symmetry for [iPr-PNP]- and [Ph-PNP]- complexes, whereas they are indicative of C1 for [iPr-PNP-Ph]- derivatives. The 1H NMR spectra of [iPr-PNP]AlR'2, [Ph-PNP]AlR'2 and [iPr-PNP-Ph]AlR'2 (R' = Et, iBu) revealed diastereotopy for the £\-hydrogen atoms in these molecules.

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The carbonylation of methanol to acetic acid is one of the most important applications in homogeneous catalysis. The first chapter comprises a review on the mechanistic studies into the catalytic cycle of the ‘Monsanto process’ and includes some of the most prominent studies into the use of phosphines in the rhodium-catalysed carbonylation of methanol. The second chapter of this thesis reports on an investigation into the application of rhodium complexes containing several C4 bridged diphosphines, namely BINAP, dppb, dppx and dcpb as catalysts for hydrogen tolerant methanol carbonylation. An investigation into the structure, reactivity and stability of pre-catalysts and catalyst resting states of these complexes has also been carried out. The origin of this hydrogen tolerance is explained based on the differing reactivities of the Rh acetyls with hydrogen gas, and by considering the structure of the complexes. In the third chapter I report on an investigation into how electronic properties and coordination mode affect the elimination of phosphonium salts from rhodium complexes. The stability of a range of monodentate, bidentate and tridentate rhodium-phosphine complexes was tested. I also report on the formation of a novel bidentate complex containing a partially quaternised TRIPHOS ligand and investigate the mechanism of formation using 13CH3I. Strong evidence is also presented supporting a dissociative mechanism as the means of phosphine loss from the rhodium centre. In the final chapters I report an investigation into the stability of rhodium-aminophosphine ligand complexes and into increasing the solubility of potential rhodium pre-catalysts through the use of amine-containing phosphine ligands.

The binding of molecular hydrogen to a metal center leads to the elongation of the H−H bond and subsequently to its cleavage along the reaction coordinate for the oxidative addition of H2. There has been considerable interest in the study of the activation of dihydrogen and map out the reaction coordinate for the homolysis of H2 on a metal center. A large number of H2 complexes reported to date possess H−H distances ranging from 0.8 to 1.0 Å. A relatively fewer examples of elongated dihydrogen complexes wherein the H−H distances fall in the range of 1.0 to 1.5 Å, are known. Study of the elongated dihydrogen complexes is of great significance because of its relevance in important catalytic processes such as hydrogenation, hydrogenolysis, and hydroformylation. Objectives The objectives of this work are as follows: (a) Synthesis and characterization of elongated dihydrogen complexes with chelating phosphine coligands by varying the electron donor ability. (b) Trap the various intermediate states in the process of oxidative addition of H2 to a metal center. (c) Map the reaction coordinate for the oxidative addition for the oxidative addition of H2 to a metal center. Results We have synthesized and characterized two new elongated dihydrogen complexes cis-[Ir(H)(η2-S2CH)(η2-H2)(PR3)2][BF4] (PR3 = PCy3, PPh3) wherein hydrogen atom undergoes site exchange between the H2 and the hydride sites. The dynamics of the exchange was studied using NMR spectroscopy. In addition, a series of ruthenium dihydrogen complexes of the type trans-[Ru(Cl)(η2-H2)(PP)][BF4] (PP = 1,2- Synopsis bis(diarylphosphino)ethane) has been synthesized and characterized wherein the aryl group is a benzyl moiety with a substituent (p-fluoro, H, m-methyl, p-methyl, p-isopropyl); in this series of complexes, a small increment in the electron donor ability (decrease in Hammett substituent constants) of the chelating phosphine ligand resulted in an elongation of the H−H bond by a small, yet significant amount. We also synthesized a series of 16-electron dicationic dihydrogen complexes bearing elongated dihydrogen ligand. In addition, we prepared a series of dihydrogen complexes of the type [RuCp/Cp*(PP)(η2-H2)][OTf] (PP = 1,2-bis(diarylphosphino)ethane, 1,2-bis(diarylphosphino)methane, 1,2-bis(dialkylphosphino)methane) bearing elongated H2 ligand (dHH = 1.0 to 1.17 Å); in this series of complexes as well, we found that the H−H bond distances increased as the donor ability of the chelating phosphines increased in small increments, along the reaction coordinate for the oxidative addition of H2 to a metal center. This investigation therefore, has established a very nice correlation between the H−H bond lengths and the Hammett substitutent constants (donor properties) resulting in the construction of dihydrogen complexes along the reaction coordinate for the oxidative addition of H2 to a metal center.