Ene-Type Reactions between an α-Alkenylphosphine and Terminal Alkynes Promoted by Osmium-Cyclopentadienyl Fragments

Complex Os(η 5 -C 5 H 5 )Cl{[η 2 -CH 2 C(CH 3 )]P i Pr 2 } ( 1 ) reacts with phenylacetylene to give the dienylphosphine derivative Os(η 5 -C 5 H 5 )Cl{[η 2 -( E )-PhCH CHCH 2 C( CH 2 )]P i Pr 2 } ( 2 ). The reaction of 1 with PhC⋮CD leads to the monodeuterated compound Os(η 5 -C 5 H 5 )Cl{[η 2 -( E )-PhCH CDCH 2 C( CH 2 )]P i Pr 2 } ( 2- d 1 ). The position of the deuterium atom in 2- d 1 is consistent with the participation of π-alkyne intermediates in the formation of 2 and 2- d 1 . In agreement with this, complex 1 reacts with 1,1-diphenyl-2-propyn-1-ol to give initially Os(η 5 -C 5 H 5 )Cl{η 2 -HC⋮CC(OH)Ph 2 }{P i Pr 2 [C(CH 3 ) CH 2 ]} ( 3 ), which in toluene under reflux evolves into Os(η 5 -C 5 H 5 )Cl{[η 2 -( E )-{Ph 2 (OH)C}CH CHCH 2 C( CH 2 )]P i Pr 2 } ( 4 ). Treatment of 1 with lithium phenylacetylide affords the alkynyl derivative Os(η 5 -C 5 H 5 )(C⋮CPh){[η 2 -CH 2 C(CH 3 )]P i Pr 2 } ( 5 ). Complex 5 also reacts with 1,1-diphenyl-2-propyn-1-ol. The reaction initially gives Os(η 5 -C 5 H 5 )(C⋮CPh){η 2 -HC⋮CC(OH)Ph 2 }{P i Pr 2 [C(CH 3 ) CH 2 ]} ( 6 ), which subsequently affords Os(η 5 -C 5 H 5 )(C⋮CPh){[η 2 -( E )-{Ph 2 (OH)C}CH CHCH 2 C( CH 2 )]P i Pr 2 } ( 7 ). Triethylamine inhibits the coupling between the isopropenyl group of 1 and phenylacetylene. In the presence of this base, the addition of phenylacetylene to 1 leads to the vinylidene derivative Os(η 5 -C 5 H 5 )Cl( C CHPh){P i Pr 2 [C(CH 3 ) CH 2 ]} ( 8 ). The X-ray structures of 2 and 8 are also reported.