Ruthenium complexes that incorporate a chiro-inositol derived diphosphinite ligand as catalysts for asymmetric hydrogenation reactions

Abstract

The diol, 1 d-1,2,5,6-tetra- O-methyl- chiro-inositol ( D-9), can be conveniently prepared from 1 d- chiro-inositol using a series of standard protection/deprotection steps. Treatment of D-9 with Ph 2PCl gives the chiral diphosphinite, 1 d-3,4-bis( O-diphenylphosphino)-1,2,5,6-tetra- O-methyl- chiro-inositol ( D-10). The structure of D-10 has been determined by X-ray crystallography. Using 1 l- chiro-inositol as starting material and following the same synthetic sequence used to produce D-10, the other enantiomer of this diphosphinite, 1 l-3,4-bis( O-diphenylphosphino)-1,2,5,6-tetra- O-methyl- chiro-inositol ( L-10) can also be obtained. Ruthenium complexes of these diphosphinite ligands can be conveniently prepared through ligand substitution reactions with appropriate substrate complexes. Thus, treatment of [RuCl 2(COD)] n with D-10 in the presence of triethylamine produces the bis(diphosphinite) complex, RuHCl{κ 2( P, P)-1 d-3,4-bis( O-diphenylphosphino)-1,2,5,6-tetra- O-methyl- chiro-inositol} 2 ( 11). In addition, reaction between RuCl 2(PPh 3) 3, D-10 and (1 R,2 R)-(+)-1,2-diphenylethylenediamine gives the mono(diphosphinite) complex, RuCl 2{κ 2( P, P)-1 d-3,4-bis( O-diphenylphosphino)-1,2,5,6-tetra- O-methyl- chiro-inositol}{κ 2( N, N)-(1 R,2 R)-(+)-1,2-diphenylethylenediamine} ( 12). The closely related complex RuCl 2{κ 2( P, P)-1 d-3,4-bis( O-diphenylphosphino)-1,2,5,6-tetra- O-methyl- chiro-inositol}{κ 2( N, N)-(1 S,2 S)-(−)-1,2-diphenylethylenediamine} ( 13) can be obtained in a similar manner using (1 S,2 S)-(−)-1,2-diphenylethylenediamine in place of the corresponding (+)-isomer. These new chiral, diphosphinite complexes catalyse the hydrogenation of the ketones acetophenone and 3-quinuclidinone to give the corresponding alcohols with low to moderate enantiomeric excesses. The complexes are not catalytically active for the hydrogenation of the olefin dimethylitaconate or the α-ketoester methyl benzoylformate.