Synthesis and Reactivity of Heptamethylcyclohexadienyl Rhodium(III) Complexes

We report the synthesis and reactivity of the half-sandwich rhodium(III) complexes with the fully methylated cyclohexadienyl ligand C6Me7, which is analogous to the classical Cp*. The starting complex [(C6Me7)RhCl2]2 (4) was obtained in high yield (92%) by the reaction of [(cyclooctene)2RhCl]2 with the readily available 6-methylenehexamethylcyclohexadiene-1,4 (C6Me6═CH2) followed by addition of HCl. Reactions of complex 4 with common two-electron ligands L gave the expected adducts (C6Me7)RhCl2L (L = pyridine, P(OEt)3, PPh3) in high yields (80–90%). At the same time, the interaction of 4 with the stronger ligand tBuNC led to the replacement of the C6Me7 ligand. The cationic complex [(C6Me7)Rh(dppe)Cl]PF6 and the dicationic complex [(C6Me7)Rh(C6Me6)](BF4)2 were obtained by abstraction of chlorides from 4 with TlPF6 or AgBF4 in the presence of the corresponding ligands. The reaction of 4 with 2-phenylpyridine in the presence of CsOAc proceeded via CH activation and gave the cyclometalated product (C6Me7)Rh(...