Synthesis and reactivity of [OsH{C<inf>6</inf>H<inf>4</inf>(CH=CHH)}(CO)(PPrⁱ<inf>3</inf>) <inf>2</inf>] and the formato compounds [Os{(E)-CH=CHPh}(η²-O<inf>2</inf>CH)-(CO)(PPrⁱ<inf>3</inf>)<inf>2</inf>] and [OsH(η²-O<inf>2</inf>CH)(CO)(PPrⁱ<inf>3</inf>) <inf>2</inf>]

The complex [OsH{C6H4(CH=CHH)}(CO)(PPri3) 2] has been prepared by reaction of the five-co-ordinate [Os{(E)-CH=CHPh}Cl(CO)(PPri3)2] with LiBun in hexane. It reacts with P(OMe)3 and CO to give [OsH{(E)CH=CHPh}(CO){P(OMe)3}(PPri3) 2] and [OsH{(E)-CH=CHPh}(CO)2(PPri3)2], while under a CO2 atmosphere the formate derivative [Os{(E)-CH=CHPh}(η2-O2CH)(CO)(PPri3)2] is obtained. Carbonylation of the latter leads to the monodentate formato complex [Os{(E)-CH=CHPh} {η1-OC(O)H}(CO)2(PPri3) 2] and under a hydrogen atmosphere it affords styrene and [OsH(η2-O2CH)(CO)(PPri3) 2], which can be also prepared by reaction of [OsH2(η2-CH2=CHEt)(CO)(PPri3)2] with CO2. The complex [OsH(η2-O2CH)(CO)(PPri3) 2] reacts with CO, P(OMe)3 and MeO2CC≡CCO2Me to give [OsH{η1-OC(O)H}(CO)L(PPri3)2] [L = CO, P(OMe)3 or MeO2CC≡ CCO2Me]; the carbon atom of its formate ligand is attacked by NEt2H leading to the carbamato compound [OsH(η2-O2CNEt2)(CO)(PPri3)2] and molecular hydrogen. Similarly treatment of [Os{(E)-CH=CHPh}(η2-O2CH)(CO)(PPri3)2] with NEt2H afforded [Os{(E)-CH=CHPh}(η2-O2CNEt2)(CO)(PPr i3)2]. The former complex also reacts with HBF4·OEt2, giving two different derivatives depending upon the conditions: in diethyl ether as solvent and in the presence of acetonitrile the vinyl complex [Os{(E)-CH=CHPh}(CO)(MeCN)2(PPri3) 2]BF4 is formed, while the carbene derivative [Os(η2-O2CH)(=CHCH2Ph)(CO)(PPr i3)2]BF4 is obtained in chloroform. The products formed by reaction of [OsH(η2-O2CH)(CO)(PPri3) 2] with HBF4·OEt2 also depend upon the reaction conditions: in diethyl ether and in the presence of MeCN the hydrido compound [OsH(CO)(MeCN)2(PPri3)2]BF 4 is obtained; however a mixture of products, mainly dihydrogen derivatives, is formed in CDCl3. On the basis of theoretical calculations and T1 measurements, the nature and structure of these dihydrogen compounds are discussed.