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

New Journal of Chemistry Pub Date: 2022-03-15 DOI: 10.1039/D1NJ06133J

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.

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