Convenient synthesis of diacyl complexes of platinum(II) via novel stereoselective carbon monoxide-insertion and acyl scrambling of trans acyl alkyl complexes of platinum. A mechanistic model of palladium-catalyzed coupling and carbonylative coupling of acid halides with organometals

The palladium-catalyzed coupling reactions of acid chlorides with organometal reagents are useful for the synthesis of ketones.] Mechanistic studies suggest that the acyl alkyl complex of Pd(11), presumably resulting from transmetalation between the acylhalopalladium and organotin species, serves as a crucial intermediate in these reactions. However, no detection of such complexes or their platinum analogues has been achieved.2 Tanaka reported the carbonylative coupling between diorganozincs and acid halides to yield a-diketones and proposed a mechanism involving a intermediacy of diacyl complexes but without direct e~idence.~ Described herein are the convenient synthesis of trans acyl alkyl complexes of platinum(I1) and the unique carbonylation reactions of such complexes including one with intriguing acyl scrambling, exclusively leading to the cisdiacyl products and finally to the diketones and ketones. It is proposed that these results provide the first good model for the Pd-catalyzed coupling and carbonylative coupling of acid halides with organometals. Treatment of trans-Pt(COR)(X)(PPh3)2 (R = Me, X = Br (la); R = Et, X = CI (lb); R = Ph, X = C1 ( 1 ~ ) ) ~ with ZnR’2 (R’ = Et, Ph) in benzene at 25 OC resulted in the formation of trons-Pt(COR)(R’)(PPh3)2 (R = Me, R’ = Et (2a); R = R’ = Et (2b); R = Ph, R’ = Et (2c); R = Et, R’ = Ph (2c’)) in high yields.5 It had been previously believed that complexes containing ligands of high trans-influence at trans disposition would be unstable, and therefore they have escaped attention.6 To our knowledge, these are the first well-characterized examples of ds square planar acyl alkyl complexes of trans geometry.’ In the presence of CO at 25 OC, complex 2b readily underwent stereoselective carbonylation to yield cis-Pt(COEt)2(PPh3)z (3b) exclusively. In a similar fashion, both complexes 2c and 2c’ were