The Os(CO)((PPr3)-Pr-i)(2) unit as a support for the transformation of two alkyne molecules into new organometallic ligands

In 2-propanol, the C-C triple bond of one of the two alkynyl ligands of the complex Os(C2Ph)(2)(CO)((PPr3)-Pr-i)(2) (1) can be broken by water to give Os(CH2Ph)(C2Ph)(CO)(2)((PPr3)-Pr-i)(2) (2). The reaction involves a metal-promoted, hydration-disproportionation of the transformed alkynyl ligand catalyzed by the solvent. Thus, the treatment of 1 with (H2O)-O-18 yields Os(CH2Ph)(C2Ph)((CO)-O-18)(Co)((PPr3)-Pr-i)(2) (2-O-18), and the reaction of 1 with water in the presence of deuterated 2-propanol ((PrOD)-Pr-i-d(8)) affords Os(CD2Ph)(C2Ph)(CO)(2)((PPr3)-Pr-i)2 (2-d(2)). In methanol and in the presence of trifluoroacetic acid, complex 2 isomerizes into the osmaindene derivative Os{C(CH2Ph)=CHC6H4}(CO)(2)(PiPr(3))(2) (3). The structure of 3 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted octahedron with the two triisopropylphosphine Ligands occupying two relative trans positions. The remaining perpendicular plane is formed by the carbonyl ligands mutually cis disposed and the metallacycle, which forms a planar five-membered ring with the osmium atom. In methanol-d(4), complex 2 reacts with CF3COOD to give Os{C(CH2Ph)=CDC6H4}(CO)(2)((PPr3)-Pr-i)(2) (3-d(1)) and 3 in a 2.5:1 molar ratio. Complex 2 also reacts with HBF4. The reaction leads to a mixture of 3 and the pi-allyl complex [Os{eta(3)-CH(Ph)CHCHPh}(CO)(2)((PPr3)-Pr-i)(2)]BF4 (4), which is a result from the addition of the proton from the acid and the carbon-carbon coupling of the benzyl and alkynyl ligands of 2. Similar to 2, complex 2-d(2) reacts with HBF4 to give a mixture of Os{C(CD2Ph)=CHC6H4}(CO)(2)((PPr3)-Pr-i)(2) (3-d(2)) and [Os{eta(3)-CD(Ph)CDCHPh}(CO)(2)((PPr3)-Pr-i)(2)]BF4 (4-d(2)). On the basis of the isotope labeling experiments, the mechanisms of the above-mentioned transformations are discussed.