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(iPr)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(III) complex [(POCOP)Rh(Me)]BF4 (2) (POCOP = C6H3[OP(iPr)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 H2 at room temperature in THF to yield the Rh(III)-hydrido complex 3 and
methane. Deprotonation of 3 with KOtBu yielded the Rh(I) dinitrogen complex [(POCOP)Rh]2(μ-N2)
(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 MeI, 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 single-crystal X-ray diffraction analysis. Finally, we report an apparent α-H elimination from Rh(III)−Me,
which takes place upon heating of the C−C activation product 2 at 150 °C in the solid state, yielding the
hydride complex 3 and ethylene.