Preparation, Characterization, and Reactions of [(EDBP)Al(μ-O i Pr)] 2 , a Novel Catalyst for MPV Hydrogen Transfer Reactions

The reaction of [(μ-EDBP)AlMe] 2 (EDBP-H 2 = 2,2‘-ethylidenebis(4,6-di- tert -butylphenol) with 2 mol equiv of 2-propanol at ambient temperature yields [(EDBP)Al(μ-O i Pr)] 2 ( 1 ), which has shown excellent catalytic activities toward hydrogen transfer reactions between aldehydes and 2-propanol (Meerwein−Ponndorf−Verley (MPV) reactions). The addition of 4 mol equiv of benzaldehyde, 4-methoxybenzaldehyde, or 4-chlorobenzaldehyde to [(EDBP)Al(μ-O i Pr)] 2 yields [(EDBP)Al(μ-OBz- p -X)(O CHC 6 H 4 - p -X)] 2 ( 2, X = H; 3, X = OMe; 4, X = Cl). However, in the reaction of 1 with excess 4-nitrobenzaldehyde, only the four-coordinated complex [(EDBP)Al(μ-OBz-p-NO 2 )] 2 ( 5 ) was obtained. Complex 1 further reacts with 2 mol equiv of OPPh 3 or hexamethylphosphoramide (HMPA), yielding the four-coordinated monomeric complex [(EDBP)Al(O i Pr)(S)] ( 6, S = OPPh 3; 7, S = HMPA). Compounds 1, 3, 6, and 7 have been characterized by X-ray crystal structure determinations, enabling us to describe the intermediate of the MPV reactions.