Synthesis of rhodium complexes of an asymmetric η5,η1,η1-cyclo-pentadienyl-bis(phosphine) ligand by regioselective intramolecular dehydrofluorinative CC coupling

The reaction between [{(η5-C5Me4H)RhX2}2] and (C6F5)2PCH2CH2P(C6F5)2 (dfppe) proceeds in refluxing benzene via cleavage of two CF bonds and CH bonds of adjacent methyl groups and formation of two CC bonds to yield selectively the asymmetric cation [{η5,η1,η1-C5HMe2-3,4-[CH2-2-C6F4P(C6F5)CH2]2-1,2}RhX]+. The selectivity for X=Cl was determined to be >90%. Treatment of [(η5-C5Me4H)RhCl(dfppe)]BF4 with proton sponge afforded [{η5,η1,η1-C5HMe2-3,4-[CH2-2-C6F4P(C6F5)CH2]2-1,2}RhCl]BF4 exclusively. The regioselectivity displayed by these reactions is in stark contrast to that in the reaction between [(Cp*RhX2)2] and dfppe, and that between [Cp*RhCl(dfppe)]+ and proton sponge, in which CH bonds of methyl groups in a 1,3 disposition are cleaved to yield the cation [{η5,η1,η1-C5Me3[CH2-2-C6F4P(C6F5)CH2]2-1,3}RhX]+ exclusively. The structure of [{(η5-C5Me4H)RhCl2}2] has been determined by single-crystal X-ray diffraction.