AbstractVinyl complexes [Ru{η2‐C(=CH2)CPh(R)OH(Ru–O)}P4]BPh4 (1) [P = P(OEt)3; R = Ph, Me] were prepared by allowing the RuH2P4 hydride to react first with HBF4·Et2O and then with propargylic alcohol HC≡CCPh(R)OH at low temperature. The complexes were characterised spectroscopically (IR, NMR) and by X‐ray crystal structure determination of the [Ru{η2‐C(=CH2)CPh2OH(Ru–O)}{P(OEt)3}4]BPh4 (1a) derivative. Related osmium complexes [Os{η2‐C(=CH2)CPh(R)OH(Os–O)}P4]BPh4 (2) and [Os{η2‐CH=C(H)CPh(R)OH(Os–O)}P4]BPh4 (3) [P = P(OEt)3; R = Ph, Me] were obtained by treating the OsH2P4 hydride first with methyl triflate(MeOTf) and then with propargylic alcohol [HC≡CCPh(R)OH]. Spectroscopic data (1H, 31P, 13C NMR) suggest the presence of two isomers with four‐ and five‐membered chelate rings of the vinyl ligands. Treatment of vinyl complexes 1 and 2+3 with terminal alkynes R1C≡CH yielded enynyl derivatives [M{η3‐R1C3C(H)R1}P4]BPh4 (M = Ru, Os). The allenylidene complex [Os(=C=C=CPh2)P5](BPh4)2 was also prepared by allowing the triflate cation [Os(κ2‐OTf)P4]+ to react with propargylic alcohol in CH2Cl2 solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)