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

Complex Os(η5-C5H5)Cl{[η2-CH2C(CH3)]PiPr2} (1) reacts with phenylacetylene to give
the dienylphosphine derivative Os(η5-C5H5)Cl{[η2-(E)-PhCHCHCH2C(CH2)]PiPr2} (2). The
reaction of 1 with PhC⋮CD leads to the monodeuterated compound Os(η5-C5H5)Cl{[η2-(E)-PhCHCDCH2C(CH2)]PiPr2} (2-d1). The position of the deuterium atom in 2-d1 is consistent
with the participation of π-alkyne intermediates in the formation of 2 and 2-d1. In agreement
with this, complex 1 reacts with 1,1-diphenyl-2-propyn-1-ol to give initially Os(η5-C5H5)Cl{η2-HC⋮CC(OH)Ph2}{PiPr2[C(CH3)CH2]} (3), which in toluene under reflux evolves into
Os(η5-C5H5)Cl{[η2-(E)-{Ph2(OH)C}CHCHCH2C(CH2)]PiPr2} (4). Treatment of 1 with
lithium phenylacetylide affords the alkynyl derivative Os(η5-C5H5)(C⋮CPh){[η2-CH2C(CH3)]PiPr2} (5). Complex 5 also reacts with 1,1-diphenyl-2-propyn-1-ol. The reaction initially gives
Os(η5-C5H5)(C⋮CPh){η2-HC⋮CC(OH)Ph2}{PiPr2[C(CH3)CH2]} (6), which subsequently affords Os(η5-C5H5)(C⋮CPh){[η2-(E)-{Ph2(OH)C}CHCHCH2C(CH2)]PiPr2} (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(η5-C5H5)Cl(CCHPh){PiPr2[C(CH3)CH2]} (8). The X-ray structures of 2 and 8 are also
reported.