Abstract
Reactions of the bis-((R(2)phosphanyl)-methyl)-1H-benzo-[d]-imidazole-3-ium hexafluorophosphate precursors [(PCP-R)-H]-PF(6) (R = iPr, Ph) with zerovalent precursors [Fe(3)(CO)(12)], [Co(2)(CO)(8)], [Ni-(COD)(2)] and [Ni-(PPh(3))(4)], respectively, gave rise to the cationic iron, cobalt and nickel complexes [Fe-(PCP-iPr)-(CO)(2)H]-PF(6) (1), [Co-(PCP-iPr)-(CO)(2)]-PF(6) (2), [Co-(PCP-Ph)-(CO)(2)]-PF(6) (3), [Ni-(PCP-iPr)-(cyclooct-4-en-1-yl)]-PF(6) (4) and [Ni-(PCP-iPr)-H]-PF(6) (5), by oxidative addition of the benzimidazolium CH bond in [(PCP-R)-H]-PF(6). The complexes bearing the bidentate ligand 3-((diisopropylphosphanyl)-methyl)-1-methyl-1H-benzo-[d]-imidazolidene PC-iPr [Fe-(PC-iPr)-(CO)(3)] (6) and [Fe-(PC-iPr)-(CO)(3)H]-BF(4) (7) were also synthesized. All complexes were characterized by NMR and FTIR spectroscopies, high resolution mass spectrometry and selected cases by single-crystal X-ray diffraction. Cobalt complexes 2 and 3 were catalytically active in the hydroboration of styrene with pinacolborane (HBPin) using 1 mol % of precatalyst and 2 mol % of KOtBu in THF at 70 °C for 18 h with yields of 87-93%. In addition, complex 2 also catalyzed the hydroboration of terminal alkenes in good yields (68-88%). Reaction of complex 2 with 5 equivs of HBPin and 2 equivs of KOtBu in THF gave rise to the cobalt-(I) hydride complex [Co-(κ(2)-(P,C)-PCP-iPr)-H-(CO)(2)] (8), indicating that the mechanism of the catalytic process follows a cobalt-(I) hydride pathway.