Reductive coupling reactions of carbonyl compounds with a low-valent titanium(II) porphyrin complex

The reactions of a low-valent titanium(II) tetratolylporphyrin complex, (TTP)Ti(eta(2)-PhC=CPh) (1), with various aromatic aldehydes or aryl ketones afforded the reductive coupling products Ti(IV) diolato complexes (2a-c, 3a-d). Treatment of I with two different carbonyl compounds selectively produced cross-coupled diolato complexes (4a-d). Interestingly, unreactive aliphatic aldehydes or ketones could be cross-coupled with aryl ketones. Reaction of 1 with benzil produced the enediolato complex (TTP)Ti[OC(Ph)C(Ph)O] (5). Putative eta(2)-carbonyl complexes were observed in the reactions of 1 with benzaldehyde and p-chlorobenzaldehyde, and their implication in reaction mechanisms is discussed.