Synthesis of aryl cobalt and iron complexes and their catalytic activity on hydrosilylation of alkenes

Abstract

Four aryl cobalt and iron complexes, [(F₄C₅N)Co(Cl)(PMe₃)₃] (1), [(F₄C₅N)Fe(PMe₃)₄] (2), [(F₅C₆)Co(Cl)(PMe₃)₃] (3) and [(F₅C₆)Fe(Cl)(PMe₃)₃] (4), were synthesized from the reactions of 3-chloro-2,4,5,6-tetrafluoro-pyridine and chloropentafluorobenzene with Co(PMe₃)₄ and Fe(PMe₃)₄, respectively. Under similar reaction conditions, the reaction of 3-chloropyridine with Co(PMe₃)₄ afforded CoCl(PMe₃)₃ as a single-electron oxidative addition product. Complexes 1–4 were used as catalysts for alkene hydrosilylation. It was found that cobalt(II) complex 1 is the best catalyst for hydrosilylation of alkenes with Markovnikov selectivity for aryl alkenes and anti-Markovnikov selectivity for aliphatic alkenes. Using HCOONa or NaBHEt₃ as an additive, the catalytic reaction could be promoted. In particular, with NaBHEt₃, the catalytic reaction could be carried out under mild conditions (40 °C) with high conversion and good selectivity for most substrates selected. Using 1 mol% 1 as a catalyst, the gram-scale reaction of styrene with Ph₂SiH₂ gave rise to the product in 93% yield with excellent selectivity (b/l = 97 : 3). Complexes 1 and 3 reacted with phenylethynyl lithium to afford alkynyl cobalt complexes 6 and 7, respectively. Complex 2 was stable in CH₃I. Complexes 1, 2, 4, 6 and 7 are new complexes and the molecular structures of them were determined by single crystal X-ray diffraction analysis.