MECHANISM OF ACETYLENE AND OLEFIN INSERTION INTO PALLADIUM-CARBON sigma BONDS.

Article abstract of DOI:10.1021/ja00331a019

The intramolecular acetylene insertion reactions of C1L//2PdCO//2(CH//2)//nC EQUVLNT CCH//3 (1a, L equals Ph//3P, n equals 2; 1b, L equals p-tol//3P, n equals 2; 2, L equals Ph//3P, n equals 3) and the intramolecular olefin insertion reaction of C1L//2PdCO//2CH//2CH//2CH equals CH//2 (3, L equals Ph//3P) have been investigated. The acetylene insertion reactions give stable vinyl complexes 5a, 5b, and 6; the olefin insertion reaction gives an unsaturated lactone by beta -hydrogen elimination from the initially formed insertion product. Kinetic and **3**1P NMR studies show that, as predicted by Thorn and Hoffmann, the reactions proceed by a four-coordinate mechanism, with the triple or double bond displacing a phosphine ligand in a rapidly maintained equilibrium prior to insertion. The triple bond in 2, with the longer carbon chain, is more easily coordinated than that in 1a but inserts less rapidly after coordination.