Preparation of Half-Sandwich Alkoxycarbene Complexes of Osmium(II)

Abstract

Alkoxy-alkylcarbene complexes [OsCl{═C(OR′)CH2R′′}(η6-p-cymene)L]BPh4 (1−4) [R′ = Me, Et; R′′ = Ph, p-tolyl, But; L = P(OMe)3, P(OEt)3, PPh(OEt)2, PPh2OEt] were prepared by allowing dichloro compounds OsCl2(η6-p-cymene)L to react with terminal alkyne R′′C≡CH in alcohol. Ethoxy-methylcarbene [OsCl{═C(OEt)CH3}(η6-p-cymene)L]BPh4 (5) was also prepared from reaction with trimethylsilyl acetylene. A reaction path for the formation of compounds 1−5, involving the nucleophilic attack of alcohol on intermediate vinylidene complexes, is discussed. Acetylide derivatives OsCl(C≡CAr)(η6-p-cymene)L (6, 7) [Ar = Ph, p-tolyl; L = P(OMe)3, P(OEt)3, PPh(OEt)2] were prepared by reacting dichloro compounds OsCl2(η6-p-cymene)L with lithium acetylide (Li+[ArC≡C]−) in thf. Protonation reaction with Brønsted acids of 6 and 7 led to vinylidene cations [OsCl{═C═C(H)Ar}(η6-p-cymene)L]+. Complexes OsCl2(η6-p-cymene)L also reacted with both PhC≡CH and (CH3)3SiC≡CH in the presence of H2O to give alkyl-carbonyl derivatives [Os(η1-CH2Ph)(CO)(η6-p-cymene)L]BPh4 (8) and [Os(η1-CH3)(CO)(η6-p-cymene)L]BPh4 (9). The complexes were characterized spectroscopically (IR and 1H, 13C, 31P NMR) and by X-ray crystal structure determinations of [OsCl{═C(OEt)CH2Ph}(η6-p-cymene){PPh(OEt)2}]BPh4 (1c), [OsCl{═C(OEt)CH2Ph}(η6-p-cymene)(PPh2OEt)]BPh4 (1d), and [Os(η1-CH2Ph)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (8c).