Exclusive C-C activation and an apparent α-H elimination with a rhodium phosphinite pincer complex

Exclusive C-C bond activation involving the new bisphosphinite ligand {C6H3(CH3)[OP(Pr-i)(2)](2)} (1) was observed at room temperature, upon reaction with the cationic complex [Rh(COE)(2)(THF)(2)]BF4 (COE = cyclooctene) in THF, yielding the Rh(RI) complex [(POCOP)Rh(Me)]BF4 (2) (POCOP = C6H3[OP(Pr-i)(2)](2)). No parallel C-H activation was observed. This preference is assumed to be governed by the better directed phosphinite-bound metal center toward the C-C bond. A single-crystal X-ray diffraction analysis of complex 2 revealed a square pyramidal geometry with the BF4- ion coordinated to the metal center. Complex 2 reacted with H-2 at room temperature in THF to yield the Rh(Ill)-hydrido complex 3 and methane. Deprotonation of 3 with KO'Bu yielded the Rh(I) dinitrogen complex [(POCOP)Rh](2)(mu-N-2) (4), which upon reaction with 1 equiv of CO or ethylene formed (POCOP)Rh(CO) (5) or (POCOP)Rh-(C2H4) (6), respectively. Complex 4 readily underwent oxidative addition of Mel, benzyl chloride, and benzyl bromide, forming complexes 7, 8, and 9, respectively. Halide abstraction from complex 9 with AgBF4 led to the cationic benzyl complex 12, bearing a coordinated BF4- ion as observed by a singlecrystal X-ray diffraction analysis. Finally, we report an apparent alpha-H elimination from Rh(III)-Me, which takes place upon heating of the C-C activation product 2 at 150 degrees C in the solid state, yielding the hydride complex 3 and ethylene.