Pincer Ru and Os complexes as efficient catalysts for racemization and deuteration of alcohols

The pincer complexes [MX(CNN)( PP)] ( M = Ru, Os; X = Cl, OTf; HCNN = 1-(6-arylpyridin-2-yl) methanamine; PP = diphosphine) have proven to efficiently catalyze both racemization and deuteration of alcohols in the presence of a base. Chiral alcohols have been racemized at 30-50 degrees C using 1 mol% of Ru or Os pincer complexes and 5 mol% of KOtBu in 2-propanol. Primary and secondary alcohols are efficiently deuterated at the a position, with respect to the OH group, using 2-propanol-d(8) as solvent with Ru or Os pincer complexes and KOtBu at 30-50 degrees C. For secondary alcohols incorporation of deuterium at the b position has also been observed. In 2-propanol-d(8) the pincer complexes catalyze the simultaneous deuteration and racemization of (S)-1-phenylethanol, the two processes being strictly correlated. For both reactions much the same activity has been observed with the Ru and Os complexes. The pincer complexes display a superior activity with respect to the related compounds [MCl2(NN)(PP)] ( NN = bidentate amine or pyridine ligand). The synthesis of the new complexes [MCl(CNN)(PP)] ( M = Ru, 2, 4 and Os, 6, 7; PP = dppb, dppf) and [Ru(OTf)(CNN)(dppb)] (3) is also reported.