Ni(ii) and Co(ii) bis(acetylacetonato) complexes for alkene/vinylsilane silylation and silicone crosslinking

Abstract

Commercially available Ni(II) and Co(II) complexes – M(acac)₂ (acac = acetylacetonate) and M(tmhd)₂ (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionato) – exhibit catalytic activity for alkene/vinylsilane dehydrogenative silylation (DS) and hydrosilylation (HS) with tertiary silanes without the use of any external reducing agents. Using the model compounds divinyltetramethylsiloxane a.k.a dvtms and vinylpentamethyldisiloxane a.k.a vpmds, different selectivities (HS, DS, undesired non-C–Si bond-forming reactions…) are observed whether nickel or cobalt catalysts are employed, with Ni being DS-selective and Co yielding bothHS and DS products. All four complexes are efficient at thermally inducing silicone-oil crosslinking under a non-inert atmosphere, and promote metal-dependent selectivity that is slightly different from model reactions, which HR-MAS NMR spectroscopy unveils. Additional observations as well as NMR studies of [Ni(tmhd)₂ + reagent] mixtures provide some insights into the possible activation pathways.