Boron Functionalization and Unusual B–C Bond
Activation in Rhodium(III) and Iridium(III) Complexes with Diphenylbis(pyrazolylborate)
Ligands (Ph<sub>2</sub>Bp)
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Abstract
The
Rh(III) and Ir(III) pentamethylcyclopentadienyl compounds [M(Cp*)(κ<sup>2</sup>-Ph<sub>2</sub>Bp)Cl] (M = Rh, <b>1</b>; M = Ir, <b>4</b>) were readily prepared from interaction of the salt K[Ph<sub>2</sub>Bp] (Ph<sub>2</sub>Bp = diphenylbis(pyrazolyl)borate) and
the [M(Cp*)Cl<sub>2</sub>]<sub>2</sub> 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){κ<sup>2</sup>-(pz)(OH)BPh<sub>2</sub>}]
(<b>2</b>). In contrast, in the case of Ir only B–N hydrolysis
was observed and the ionic species [Ir(Cp*)(Hpz){κ<sup>2</sup>-(pz)(OH)BPh<sub>2</sub>}]Cl (<b>5</b>) was obtained, upon
coordination of the liberated Hpz. Additionally, by reaction of <b>1</b> with AgClO<sub>4</sub> in acetonitrile, the ionic [Rh(Cp*)(Ph){κ<sup>2</sup>-(pz)(OH)B(OH)}]ClO<sub>4</sub> (<b>3</b>) was isolated.
Complexes <b>1</b>–<b>3</b> and <b>5</b> 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
