Comparison of the Reactivities of Neutral and Cationic Organopalladium Complexes toward CO, Isocyanides, and Olefins

Cationic solvent-coordinated organopalladium complexes [PdR(solvent)(L)2]+A− 2 (R = organic group, L = tertiary phosphine, A = counter anion such as BF4, PF6, and triflate) have been prepared by removal of the halide ligand X in neutral complexes, [PdR(X)(L)2] 1 with an equimolar amount of silver salt. The cationic complexes 2 show much greater rates of CO insertion than the parent neutral complexes 1. Comparison of the reactivities of 2 and of the other cationic complexes [PdMe(Y)(L)2]+ (Y = strongly coordinating ligand such as tertiary phosphine, pyridine, and isocyanide) toward CO insertion indicates that availability of the site for incoming CO is a dominant factor in determining their reactivities. In contrast, insertion of isocyanides into Pd–C bond is not hindered by occupation of the vacant site in the organopalladium complexes. Successive hetero-insertions of isocyanide and CO into Me–Pd bond, i.e., CO insertion into the 1-iminoalkyl–Pd bond and isocyanide insertion into the acetyl–Pd, were realized. Olefins were found not to undergo the insertion into Pd–Me bond in phosphine-coordinated complexes, whereas insertion of methyl acrylate into the Me–Pd bond in a cationic complex having bipyridine ligand was observed.