Activation of a C−H Bond in Indene by [(COD)Rh(μ2-OH)]2†

The air- and water-tolerant hydroxy-bridged rhodium dimer [(COD)Rh(μ 2 -OH)] 2 cleanly activates the aliphatic C−H bond in indene to generate [(COD)Rh(η 3 -indenyl)]. The mechanism involves direct coordination of indene to the dimer followed by rate-determining C−H bond cleavage, in contrast to the previously reported analogous reactions of [(diimine)M(μ 2 -OH)] 2 2+ (M = Pd, Pt), for which the dimer must be cleaved before rate-determining displacement of solvent by indene. Another difference is observed in the reactions with indene in the presence of acid: the Rh system generates a stable η 6 -indene 18-electron cation, [(COD)Rh(η 6 -indene)] +, that is not available for Pd and Pt, which instead form the η 3 -indenyl C−H activation products. The crystal structure of [(COD)Rh(η 6 -indene)] is reported.