Preparation and reactivity of dihydrogen complexes [MX(η2-H2)P4]BF4 (M = Ru or Os; X = halogenide or SEt−; P = phosphite)

Abstract

Monohydride complexes MHXP₄ [M = Ru or Os; X = Cl⁻, Br⁻, I⁻, SEt⁻ or N₃⁻; P = P(OEt)₃, PPh(OEt)₂ or PPh₂OEt] were prepared by treating dihydride species MH₂P₄ first with CF₃SO₃Me and then with an excess of the anionic ligand X. In an argon atmosphere, protonation of MHXP₄ with HBF₄·Et₂O gives dihydrogen cations [MX(η²-H₂)P₄]⁺, with X = Cl, Br, I or SEt; the classical dihydride [MH₂(N₃)P₄]⁺ was obtained with the azide ligand. Instead, in a hydrogen atmosphere, protonation of MHXP₄ with HBF₄·Et₂O gives hydride–dihydrogen [MH(η²-H₂)P₄]⁺ species, according to a proposed mechanism involving interaction of Brønsted acid with ligand X. Some [MX(η²-H₂)P₄]⁺ cations were thermally unstable and fully characterised in solution (¹H and ³¹P NMR, variable temperature T₁ measurements), whereas the [OsX(η²-H₂){PPh(OEt)₂}₄]BF₄ complexes were stable and isolated as solids. Treatment of [MX(η²-H₂)P₄]⁺ cations with alkyne PhCCH gave evolution of H₂ and formation of the vinylidene intermediate [MX{CC(H)Ph}P₄]⁺ which, by reaction with base, afforded the final acetylide M(CCPh)XP₄ derivatives. Treatment with propargyl alcohols HCCC(OH)RR′ of the [MX(η²-H₂)P₄]⁺ cations, instead, gave propadienylidene derivatives [MX(CCCRR′)P₄]BPh₄ (M = Ru or Os; R = R′ = Ph or R = Ph, R′ = Me). Hydrazine complexes [MX(NH₂NH₂)P₄]BPh₄ were also prepared by substitution of the dihydrogen ligand in the new η²-H₂ derivatives.