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

The diol, 1d-1,2,5,6-tetra-O-methyl-chiro-inositol (D-9), can be conveniently prepared from 1d-chiro-inositol using a series of standard protection/deprotection steps. Treatment of D-9 with Ph2PCl gives the chiral diphosphinite, 1d-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 1l-chiro-inositol as starting material and following the same synthetic sequence used to produce D-10, the other enantiomer of this diphosphinite, 1l-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 [RuCl2(COD)]n with D-10 in the presence of triethylamine produces the bis(diphosphinite) complex, RuHCl{κ2(P,P)-1d-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol}2 (11). In addition, reaction between RuCl2(PPh3)3, D-10 and (1R,2R)-(+)-1,2-diphenylethylenediamine gives the mono(diphosphinite) complex, RuCl2{κ2(P,P)-1d-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol}{κ2(N,N)-(1R,2R)-(+)-1,2-diphenylethylenediamine} (12). The closely related complex RuCl2{κ2(P,P)-1d-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol}{κ2(N,N)-(1S,2S)-(−)-1,2-diphenylethylenediamine} (13) can be obtained in a similar manner using (1S,2S)-(−)-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.

The chiral diphosphinite ligand, 1d-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol (D-10), can be conveniently synthesised from 1d-chiro-inositol, and L-10, the enantiomer of D-10, can also be readily prepared. Ruthenium complexes of D-10 are effective ketone hydrogenation catalysts with conversions of close to 100% and ee’s up to 50% in some cases.Figure optionsDownload as PowerPoint slide