Boron Functionalization and Unusual B–C Bond Activation in Rhodium(III) and Iridium(III) Complexes with Diphenylbis(pyrazolylborate) Ligands (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.