title: A mechanistic investigation of oxidative addition of methyl iodide to [Tp*Rh(CO)(L)].
abstract: Reaction of methyl iodide with square planar [kappa(2)-Tp*Rh(CO)(PMe(3))] 1a (Tp* = HB(3,5-Me(2)pz)(3)) at room temperature affords [kappa(3)-Tp*Rh(CO)(PMe(3))(Me)]I 2a, which was fully characterized by spectroscopy and X-ray crystallography. The pseudooctahedral geometry of cationic 2a, which contains a kappa(3)-coordinated Tp* ligand, indicates a reaction mechanism in which nucleophilic attack by Rh on MeI is accompanied by coordination of the pendant pyrazolyl group. In solution 2a transforms slowly into a neutral (acetyl)(iodo) rhodium complex [kappa(3)-Tp*Rh(PMe(3))(COMe)I] 3a, for which an X-ray crystal structure is also reported. Kinetic studies on the reactions of [kappa(2)-Tp*Rh(CO)(L)] (L = PMe(3), PMe(2)Ph, PMePh(2), PPh(3), CO)] with MeI show second-order behavior with large negative activation entropies, consistent with an S(N)2 mechanism. The second-order rate constants correlate well with phosphine basicity. For L = CO, reaction with MeI gives an acetyl complex, [kappa(3)-Tp*Rh(CO)(COMe)I]. The bis(pyrazolyl)borate complexes [kappa(2)-Bp*Rh(CO)(L)] (L = PPh(3), CO) are much less reactive toward MeI than the Tp* analogues, indicating the importance of the third pyrazolyl group and the accessibility of a kappa(3) coordination mode. The results strengthen the evidence in favor of an S(N)2 mechanism for oxidative addition of MeI to square planar d(8) transition metal complexes.
authors.affiliation: Laboratoire de Catalyse Chimie Fine et Polymères, Ecole Nationale Superieure des Ingénieurs en Arts Chimiques et Technologiques, 118 route de Narbonne, 31077 Toulouse Cedex 4, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Chauby
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Daran
authors.forename: Carole
authors.initials: C
authors.lastname: Serra-Le Berre
authors.forename: François
authors.initials: F
authors.lastname: Malbosc
authors.forename: Philippe
authors.initials: P
authors.lastname: Kalck
authors.forename: Oscar
authors.initials: O
authors.lastname: Delgado Gonzalez
authors.forename: Claire E
authors.initials: CE
authors.lastname: Haslam
authors.forename: Anthony
authors.initials: A
authors.lastname: Haynes