Bis(imino)carbazolide complexes of rhodium: Highly nucleophilic ligands exerting a dramatic accelerating effect on MeI oxidative addition

Rhodium(I) complexes bearing a bis(imino)carbazolide ligand L and an additional neutral donor [LRh(C2H4), 2; LRh(CO), 3] have been prepared via a salt metathesis reaction between NaL and the dimeric rhodium precursors [RhCl(C2H4)(2)](2) and [RhCl(CO)(2)](2), respectively. Complex 3 was also prepared by reaction of the free ligand with [RhCl(CO)(2)](2), whereas a related reaction with [RhCl(C2H4)(2)](2) afforded the dinuclear Rh-I-Rh-III ethyl complex 4. The X-ray crystal structure of 4 showed octahedral [bis(imino)carbazolide]Rh-III(Cl)Et linked to square-planar bis(ethylene)(RhCl)-Cl-I via chloride bridges. Kinetic studies on the oxidative addition of MeI to 3 to form the (LRhI)-I-III(CO)Me complex 5 revealed a second-order rate constant of 1.66 M-1 s(-1) in CH2Cl2 at 25 degreesC, which corresponds to a reaction rate approximately 50 000 times faster than that observed for [RhI2(CO)(2)](-).