Reactions of catecholborane with iridium complexes: molecular structure of trans-IrHCl(CO)(Bcat)(PPh3)2

Abstract

Reactions of certain iridium complexes with catecholborane (HBcat) gave boron-substituent redistribution products ([Bcat2]−, B2cat3) with concomitant formation of a complex mixture of iridium hydrides. While "IrCl(PPh3)(COE)n" generated in situ from [Ir(μ-Cl)(COE)2]2 (COE = cyclooctene) (2) plus 2 equivalents of PPh3 also promoted HBcat degradation, this catalyst system was extremely active and selective for alkene hydroborations. Oxidative addition of HBcat to the metal centre can be the sole reaction pathway, however, with iridium complexes containing electron-rich phosphines. The unsaturated boryl complex IrHCl(Bcat)(PPri3)2 was prepared and isolated in high yield from reaction of HBcat with 2 in the presence of four equivalents of PPri3. Ancillary carbonyl ligands also appear to facilitate oxidative addition of HBcat to an iridium centre. Addition of HBcat to trans-IrCl(CO)(PPh3)2 gives the first structurally characterized metal-carbonyl boryl complex trans-IrHCl(CO)(Bcat)(PPh3)2 (7). Colourless crystals of 7 are triclinic, [Formula: see text] (No.2) with two molecules per unit cell of dimensions a = 12.223(2) Å, b = 12.684(2) Å, c = 14.652(1) Å, α = 70.81(1)°, β = 72.47(1)°, and γ = 71.92(1)°.