Boron Functionalization and Unusual B-C Bond Activation in Rh(III) and Ir(III) Complexes with Diphenylbis(pyrazolylborate) Ligand (Ph2Bp)

The Rh(III) and Ir(III) pentamethylcyclopentadienyl compounds [M(Cp*)(κ2-Ph2Bp)Cl] (M = Rh, 1; M = Ir, 4) were readily prepared from interaction of the salt K[Ph2Bp] (Ph2Bp = diphenylbis(pyrazolyl)borate) and the [M(Cp*)Cl2]2 dimer precursors in dichloromethane under anhydrous conditions. When the same reactions were carried out in non-anhydrous conditions by using acetonitrile as solvent, we observed, in the case of Rh, both B−N bond hydrolysis and Rh−C(Ph) bond activation with the formation of the hydroxy(pyrazolyl)- borate complex [Rh(Cp*)(Ph){κ2-(pz)(OH)BPh2}] (2). In contrast, in the case of Ir only B−N hydrolysis was observed and the ionic species [Ir(Cp*)(Hpz){κ2- (pz)(OH)BPh2}]Cl (5) was obtained, upon coordination of the liberated Hpz. Additionally, by reaction of 1 with AgClO4 in acetonitrile, the ionic [Rh(Cp*)- (Ph){κ2-(pz)(OH)B(OH)}]ClO4 (3) was isolated. Complexes 1−3 and 5 have been structurally characterized by X-ray crystallography. Spectral studies have been performed for all species, together with a computational DFT modeling investigation. A decomposition mechanism for the diphenylbis(pyrazolyl)borate ligand in the different complexes is proposed.