Assembly of an Allenylidene Ligand, a Terminal Alkyne, and an Acetonitrile Molecule: Formation of Osmacyclopentapyrrole Derivatives

Treatment in acetonitrile at −30 °C of the hydride−alkenylcarbyne complex [OsH(⋮CCHCPh2)(CH3CN)2(PiPr3)2][BF4]2 (1) with tBuOK produces the selective deprotonation of the alkenyl substituent
of the carbyne and the formation of the bis-solvento hydride−allenylidene derivative [OsH(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (2), which under carbon monoxide atmosphere is converted into [Os(CHCCPh2)(CO)(CH3CN)2(PiPr3)2]BF4 (3). When the treatment of 1 with tBuOK is carried out in dichloromethane
at room temperature, the fluoro−alkenylcarbyne [OsHF(⋮CCHCPh2)(CH3CN)(PiPr3)2]BF4 (4) is isolated.
Complex 2 reacts with terminal alkynes. The reactions with phenylacetylene and cyclohexylacetylene afford
[Os{(E)-CHCHR}(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (R = Ph (5), Cy (6)), containing an alkenyl ligand
beside the allenylidene, while the reaction with acetylene in dichloromethane at −20 °C gives the hydride−allenylidene−π-alkyne [OsH(CCCPh2)(η2-HC⋮CH)(PiPr3)2]BF4 (7), with the alkyne acting as a four-electron donor ligand. In acetonitrile under reflux, complexes 5 and 6 are transformed into the
osmacyclopentapyrrole compounds (R = Ph (8), Cy (9)),
as a result of the assembly of the allenylidene ligand, the alkenyl group, and an acetonitrile molecule. The
X-ray structures of 2, 5, and 8 are also reported.