Catalytic asymmetric phosphorus-carbon bond formation with platinum-phosphido complexes

Chapter One. Synthesis and Structure of Chiral Pt(Duphos) Terminal Phosphido Complexes. Treatment of Pt halide precursors with a secondary phosphine in the presence of the base NaOSiMe3 gave the terminal phosphido complexes Pt(Duphos)(Ph)(PMeIs). Low-barrier pyramidal inversion in the phosphido complexes was investigated by 31P NMR spectroscopy. Complexes 1-6, 9, and 11 were structurally characterized by X-ray crystallography; structural and 31P NMR results suggest the trans influence order P(O)MeIs > PMeIs > PHMe(Is).;Chapter Two. Platinum-Catalyzed Asymmetric Alkylation of Secondary Phosphines: I. Enantioselective Synthesis of P-Stereogenic Phosphines. II. Mechanism and Origin of Enantioselectivity. In this chapter, we report Pt-catalyzed asymmetric alkylation of secondary phosphines as a new approach to this useful class of compounds. The absolute configuration of the product phosphine PMeIs(CH2Ph) was determined from the crystal structure of the major diastereomer of its complex, [Pt((R,R)-Me-Duphos)(Ph)(PMeIs(CH 2Ph))][BF4], while the absolute configuration of the major diastereomer of phosphido complex 1 was determined by multinuclear low-temperature NMR spectroscopy. From these observations, we propose that enantioselectivity is determined mainly by the thermodynamic preference for one of the rapidly interconverting diastereomers of 1, although the relative rates of alkylation of the diastereomers of 1 are also important (Curtin-Hammett kinetics).;Chapter Three. A Protic Additive Suppresses Formation of Byproducts in Platinum-Catalyzed Hydrophosphination of Activated Olefins. Evidence for P-C and C-C Bond Formation by Michael Addition. Platinum-catalyzed hydrophosphination of activated olefins yields byproducts derived from more than one alkene. Formation of byproducts is suppressed by adding t-butanol, consistent with a mechanism in which Michael addition of a nucleophilic Pt-PR2 group to the alkene yields a zwitterionic intermediate, which can undergo further conjugate additions.;Chapter Four. Regiochemistry of Pt-catalyzed Hydrophosphination of a Diene. Formation of the Chiral Diphosphine Et2PCH(CN)CH(CH 2CH2CN)PEt2 via Monophosphine Intermediates. Pt-catalyzed addition of diethylphosphine to the diene cis, cis-mucononitrile gave the new diphosphine Et2PCH(CN)CH(CH2CH2CN)PEt 2 as a 3:2 mixture of diastereomers. Two monophosphine-alkene intermediates in the hydrophosphination were characterized by NMR spectroscopy.;Chapter Five. P-C and C-C Bond Formation by Michael Addition in Pt-Catalyzed Hydrophosphination. To test the Michael mechanism proposed in Chapter 3, we tried to trap the proposed carbanion with another electrophile. This led to the development of a Pt-catalyzed three-component coupling of secondary phosphines, t-butyl acrylate, and benzaldehyde. In a second approach, we replaced the hydride with a methyl group, to prevent C-H bond formation. Thus, the reactions of several complexes Pt(diphos)(Me)(PR 2) with t-butyl acrylate and acrylonitrile were examined. More exidence for a Michael mechanism was obtained by studying the chemistry of model compounds which lacked the PR2 group.;Chapter Six. Pt(II) Phosphido Complexes as Metalloligands. Structural and Spectroscopic Consequences of Conversion from Terminal to Bridging Coordination. Treatment of the terminal phosphido complexes Pt(dppe)(Me)(PPh(R)) was converted to [(Pt(Me-Duphos)(Me))2(mu-PPh(i-Bu))][OTf] (63). A fluxional process in 61 and 63, presumably involving hindered rotation about the Pt-PPh(i-Bu) bonds, was observed by NMR spectroscopy; it resulted in two diastereomers for 61 and four for 63 at low temperature.;Chapter Seven. Chiral Pt(Duphos) Terminal Phosphido Complexes: Phosphido Transfer and Ligand Behavior. Reaction of 1 with [Pd(allyl)Cl]2, followed by treatment with dppe, gave Pt((R,R)-Me-Duphos)(Ph)(Cl), PMeIs(allyl) (66) and Pd(dppe)2. Treatment of 1 with Pd[P(o-Tol)3]2 gave an equilibrium mixture containing the two-coordinate palladium complex Pd[P( o-Tol)3](mu- PMeIs)Pt((R,R)-Me-Duphos)(Ph) (67 ), Pd[P(o-Tol)3]2, P( o-Tol)3, and 1. Treatment of 4 with Pd[P(o-Tol)3]2 led to oxidative addition of the Pt-Cl bond to Pd, yielding Pd[P(o-Tol) 3](Cl)(mu-PMeIs)(Pt((R,R)-Me-Duphos)) (68), which deposited red crystals of the tetranuclear [Pt((R,R)-Me-Duphos)(PMeIs)]2(Pd 2(mu-Cl)2) (69). (Abstract shortened by UMI.)...