The Os(CO)(PiPr3)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(C 2 Ph) 2 (CO)(P i Pr 3 ) 2 ( 1 ) can be broken by water to give Os(CH 2 Ph)(C 2 Ph)(CO) 2 (P i Pr 3 ) 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 H 2 18 O yields Os(CH 2 Ph)(C 2 Ph)(C 18 O)(CO)(P i Pr 3 ) 2 ( 2- 18 O ), and the reaction of 1 with water in the presence of deuterated 2-propanol ( i PrOD- d 8 ) affords Os(CD 2 Ph)(C 2 Ph)(CO) 2 (P i Pr 3 ) 2 ( 2- d 2 ). In methanol and in the presence of trifluoroacetic acid, complex 2 isomerizes into the osmaindene 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 CF 3 COOD to ( 3- d 1 ) and 3 in a 2.5:1 molar ratio. Complex 2 also reacts with HBF 4 . The reaction leads to a mixture of 3 and the π-allyl complex [Os{η 3 -CH(Ph)CHCHPh}(CO) 2 (P i Pr 3 ) 2 ]BF 4 ( 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 HBF 4 to give a mixture and [Os{η 3 -CD(Ph)CDCHPh}(CO) 2 (P i Pr 3 ) 2 ] BF 4 ( 4- d 2 ). On the basis of the isotope labeling experiments, the mechanisms of the above-mentioned transformations are discussed.