Formation of Cationic Half-Sandwich Osmium−Vinylidene Complexes from [Os(η5-C5H5)(PiPr3)2]+ and Terminal Alkynes

Ab initio calculations on the model complexes [Os(η 5 -C 5 H 5 )(η 2 -HC⋮CH)(PH 3 ) 2 ] + ( 1 ), [OsH(η 5 -C 5 H 5 )-(C⋮CH)(PH 3 ) 2 ] + ( 2 ), and [Os(η 5 -C 5 H 5 )( C CH 2 )(PH 3 ) 2 ] + ( 3 ) indicate that the thermodynamic stability of these compounds decreases according to the sequence 3 > 1 > 2 . According to this, the vinylidene complexes [Os(η 5 -C 5 H 5 )( C CHR)(P i Pr 3 ) 2 ]PF 6 (R = Cy ( 8 ), Ph ( 9 )) are prepared by deprotonation of [OsH(η 5 -C 5 H 5 )(C⋮CR)-(P i Pr 3 ) 2 ]PF 6 (R = Cy ( 4 ), Ph ( 5 )) with KOH in methanol and subsequent protonation of the resulting alkynyl derivatives Os(η 5 -C 5 H 5 )(C⋮CR)(P i Pr 3 ) 2 (R = Cy ( 6 ), Ph ( 7 )). The X-ray structure of [Os(η 5 -C 5 H 5 )( C CHPh)-(P i Pr 3 ) 2 ]PF 6 ( 9 ) is also reported.