Transmetalation reactions. The role of the stabilizing olefin in determining the overall reaction rate

A systematic study concerning the transmetalation reaction between the palladium butadienyl complexes [PdCl((ZCdouble bond; length as m-dashCZ)2Me)(L-L′)] (Z = COOMe; L-L′ = MeN-SPh (1A), N-SPh (1B), DPPQ-Me (1C), BiPy (1D), DPPE (1E)) and tributyl-phenylethynyl-stannane in the presence of some stabilizing olefins (ma, fn, nq, dmfu, and tmetc) was undertaken. The dependence of the reaction rate on the nature of the ancillary ligand was discussed in terms of the donor capability and steric characteristics of the ligand. It has been noticed that, other things being equal, the joined distorted MeN-SPh ligand imparts the highest reactivity to its derivative (complex 1A). The most surprising issue was however represented by the olefin which seems to affect heavily the reactivity of the starting substrate thereby increasing the overall reaction rate. The most active olefins were ma and fn. In the case of the reaction between the complex 1A and tributyl-phenylethynyl-stannane in the presence of fn an exhaustive kinetic study was carried out and a mechanistic hypothesis was advanced.