Insertion Reactions of 1,2-Disubstituted Olefins with an alpha-Diimine Palladium(II) Complex

The migratory insertions of cis or trans olefins CH(X)=CH(Me) (X=Ph, Br, or Et) into the metal–acyl bond of the complex [Pd(Me)(CO)( iPr2dab)] + [B{3,5-(CF3)2C6H3}4]- (1) ( iPr2dab=1,4-diisopropyl-1,4-diazabuta-1,3-diene=N,N’-(ethane-1,2-diylidene)bis[1-methylethanamine]) are described (Scheme1). The resulting five-membered palladacycles were characterized by NMR spectroscopy and X-ray analysis. Experimental data reveal some important aspects concerning the regio- and stereochemistry of the insertion process. In particular, the presence of a Ph or Br substituent at the alkene leads to the formationof highly regiospecific products. Moreover, in all cases, the geometry of the substituents in the formed palladacycle was the same as in the starting olefin, as a consequence of a cisaddition of the Pd–acyl fragment to the C=C bond. Reaction with CO and MeOH of the five-membered complex derived from trans b-methylstyrene (=[(1E)-prop-1-enyl]benzene) insertion, yielded the 2,3-substitutedg-keto ester 9 with an (2RS,3SR)-configuration (Scheme 3)