Remarkable, sterically induced rate enhancement in the insertion of allenes into palladium-methyl bonds

The rate of insertion of methyl-substituted allenes into the Pd-Me bond in chelate pyridine-thioether complexes [PdCl(Me)(R'N-SR)] (R'N-SR = 6-R'-C5H3 N-2-CH2SR) to give 2-methylallyl derivatives is remarkably enhanced by the presence of a methyl group in position 6 of the pyridine ring, which induce s distortion, on the main coordination plane, resulting in a metal substrat e more prone to allene insertion. The flexibility of the sulfur-donor chela te ligand appears to be a paramount requisite.