Unusual Activation of 1,1-Diphenyl-2-propyn-1-ol Mediated by the Os(η5-C5H5) Unit

Os(η 5 -C 5 H 5 )Cl(P i Pr 3 ) 2 ( 2 ) reacts with thallium acetate in CH 2 Cl 2 to give Os(η 5 -C 5 H 5 ){κ 1 -OC(O)CH 3 }(P i Pr 3 ) 2 ( 3 ). Reaction of the latter with 1,1-diphenyl-2-propyn-1-ol affords the π-alkyne derivative Os(η 5 -C 5 H 5 ){κ 1 -OC(O)CH 3 }{η 2 -HC⋮CC(OH)Ph 2 }(P i Pr 3 ) ( 4 ). In solution, complex 4 is unstable above −40 °C and rapidly changes into the 2-{( Z )-3-acetoxy-1-hydroxy-1-phenyl-2-propenyl}aryl complex Os(η 5 -C 5 H 5 ){C 6 H 4 [C(OH)(Ph)CH CHOC(O)CH 3 ]}(P i Pr 3 ) ( 5 ), whose structure was determined by X-ray diffraction analysis.