Synthesis, structure, and reactivity of new rhodium and iridium complexes, bearing a highly electron-donating PNP system. Iridium-mediated vinylic C-H bond activation

Reaction of the new highly electron-donating PNP ligand [2,6-bis-(di-tert-butylphosphinomethyl)pyridine] (1) with [Rh(COE)(2)Cl](2) (COE = cyclooctene) at room temperature resulted in formation of the neutral Rh(I) complex [Rh(PNP)Cl] (2). Unsaturated cationic complexes [Rh(PNP)(CH3CN)]BF4 (3) and [Rh(PNP)(C2H4)]SO3CF3 (4) were obtained in reaction of 1 with [(COE)(2)Rh(CH3CN)(2)]BF4 and [(C2H4)(2)Rh(THF)(2)]SO3CF3, respectively. Upon reaction of the PNP ligand 1 with [Ir(COE)(2)Cl]2, facile vinylic C-H activation takes place, yielding the hydrido-vinyl complex [ClIr(PNP)(H)(C8H13)] (5). Also, coordination of ligand 1 to the cationic iridium complex [Ir(COD)(2)]BF4 (COD = cyclooctadiene) in RCN (R = CH3, CH(CH3)(2), C(CH3)(3)) led to iridium insertion into a vinylic C-H bond, resulting in complexes [(RCN)-Ir(PNP)(H)(CF8H11)]BF4 (6a-c). The hydrido-vinyl complexes 6a,c readily react with H-2 (2 atm) at room temperature, affording the iridium dihydride complexes [(RCN)Ir(PNP)(H)(2)]BF4 (R = CH3, C(CH3)(3)) (7a,b).