Transfer hydrogenation of aldehydes catalyzed by silyl hydrido iron complexes bearing a [PSiP] pincer ligand.

The synthesis and characterization of a series of silyl hydrido iron complexes bearing a pincer-type [PSiP] ligand (2-R 2 PC 6 H 4 ) 2 SiH 2 (R = Ph (1) and i Pr (5)) or (2-Ph 2 PC 6 H 4 ) 2 SiMeH (2) were reported. Preligand 1 reacted with Fe(PMe 3 ) 4 to afford complex ((2-Ph 2 PC 6 H 4 )SiH)Fe(H)(PMe 3 ) 2 (3) in toluene, which was structurally characterized by X-ray diffraction. ((2- i Pr 2 PC 6 H 4 )SiH)Fe(H)(PMe 3 ) (6) could be obtained from the reaction of preligand 5 with Fe(PMe 3 ) 4 in toluene. Furthermore, complex ((2- i Pr 2 PC 6 H 4 )Si(OMe))Fe(H)(PMe 3 ) (7) was isolated by the reaction of complex 6 with 2 equiv. MeOH in THF. The molecular structure of complex 7 was also determined by single-crystal X-ray analysis. Complexes 3, 4, 6 and 7 showed good to excellent catalytic activity for transfer hydrogenation of aldehydes under mild conditions, using 2-propanol as both solvent and hydrogen donor. α,β-Unsaturated aldehydes could be selectively reduced to corresponding α,β-unsaturated alcohols. The catalytic activity of penta-coordinate complex 6 or 7 is stronger than that of hexa-coordinate complex 3 or 4.