Neutral N−O Chelated Palladium(II) Complexes: Syntheses, Characterization, and Reactivity

A series of neutral salicylaldiminato Pd(II) complexes, Pd(Me)(Ph-CHN-R‘)[3-tBu-2-(O)C6H3-CHN-2,6-di-iPr-C6H3] (R = CH3, n-Pr, tert-Bu, Ph, benzyl) (3a−3e) and Pd(Me)[2-(CHN-t-Bu)-Py][3-tBu-2-(O)C6H3-CHN-2,6-di-iPr-C6H3] (4), have been synthesized and
characterized. The structures of complexes 3a, 3c−3e, and 4 have been confirmed by X-ray
analysis. NMR studies utilizing 3c indicate that the insertion of CO into the Pd−Me bond
occurs through a five-coordinate intermediate. The acyl compounds in turn undergo imine
insertion. The neutral complexes 3a−3e show moderate catalytic activity for the polymerization of methyl acrylate at ambient temperature. However, a radical rather than vinyl
insertion mechanism appears to be operative.