Novel chiral phosphine ligands and complexes from amino acid esters

N-Diphenylphosphinoamino acid methyl/ethyl esters RCH(NHPPh2)CO2R' 1a-1e were prepared in high yield from equimolar amounts of amino acid methyl/ethyl ester hydrochloride and chlorodiphenylphosphine. The reaction proceeds with configurational retention. Oxidation of 1a (R=R'=CH3) with H2O2 or S-8 leads to the N-diphenylphosphinoylalanine methyl ester 2a or N-diphenylthiophosphinoylalanine methyl ester 3a. 1a-1e function as monodentate ligands to [PtCl2(cod)], [RhCl(cod)](2) and [AuCl(tht)] to give cis-[PtCl2(1-P)(2)], [RhCl(cod)(1-P)] and [AuCl(1-P)]. Two equivalents of chlorodiphenylphosphine react with alanine methyl ester hydrochloride in CH2Cl2 to give N,N-bis(diphenylphosphino)alanine methyl ester, bdppal. This is an excellent bidentate ligand, the chelate complexes [MCl2(bdppal-P,P')] (M=Pd or Pt) being prepared and studied by X-ray analysis. Oxidation at one P atom in bdppal with either H2O2 or S-8 gives N-diphenylphosphino-N-diphenylphosphinoylalanine methyl ester, bdppalO, and N-diphenylphosphino-N-diphenylthiophosphinoylalanine methyl ester, bdppalS, respectively. bdppalO is very difficult to isolate but does react in situ with [PdCl2(cod)] to give [PdCl2(bdppalO-O,P)]. bdppalS reacts with [MCl2(cod)] (M=Pd or Pt) giving [MCl2(bdppalS-P,S)]. The dioxidised product N,N-bis(diphenylphosphinoyl)alanine methyl ester, bdppalO(2), does not react with [MCl2(cod)] (M=Pd or Pt), whereas N,N-bis(diphenylthiophosphinoyl)alanine methyl ester, bdppalS(2), reacts with [PdCl2(cod)] to give [PdCl2(bdppal-S,S')]. All the compounds are chiral and have been fully characterised by microanalysis, IR, P-31-{H-1}, H-1 NMR, and FAB(+) mass spectroscopies, and in several cases structures are confirmed by X-ray analysis. The crystal structures described and those previously determined reveal the configurational retention of the reactions.