Syntheses, spectroscopy, and catalysis of (η~4-cod)Rh(I)-complexes with (R or S)-2-(salicylaIdimine)-2-phenylethanol or (rac)-2-(salicylaldimine)-l-phenylethanol

摘要

Condensation of salicyldehyde with (R or S)-2-amino-2-phenylethanol or rac-2-amino-l-phenylethanol gives enantiopure (R or S)-2-(salicylaldimine)-2-phenylethanol (R- or S-H_2L1) or (rac)-2-(salicyIaldimine)-l-phenylethanol (rac-H_2L2). The Schiff bases coordinate to [Rh(η~4-cod)(μ-O_2CCH_3)]2 to afford mononuclear [Rh(η~4-cod){(R or S)-2-(salicylaldiminato)-2-phenylethanol-k~2 N,O}], [Rh(η~4-cod)(R- or S-HL1)] (1 or 2), or [Rh(η~4-cod){(rac)-2-(salicylal-diminato)-l-phenylethanol-K~2 N,O}], [Rh(η~4-cod)(rac-HL2)] (3). The Schiff base and complexes are characterized by IR-, U V/Vis-, ~1H/~(13)C-NMR-, mass-spectroscopy, circular dichroism (CD), and polarimetry. The synthetic and spectroscopic results suggest that deprotonated Schiff base coordinates to [Rh(η~4-cod)] as a six-membered N,O-chelate with distorted square planar geometry at rhodium. CD and polarimetry measurements show the enantiopurity of the Schiff bases as well as the complexes in solution. The in situ system composed of [Rh(η~4-cod)Cl]_2 and S-H_2L1 has been used as a catalyst for the reduction of acetophenone into rac-1-phenylethanol with 85% conversion in diphenylsilane at 0-5°C.