Vinylidene, allenylidene, cyclic oxycarbene, and η2-alkyne complexes from reactions of (η5-C5Me5)OsCl(PPh3)2 with alkynes and alkynols

Abstract

Reactions of Cp*OsCl(PPh3)2 (Cp* = pentamethylcyclopentadienyl) with alkynes and alkynols are described. Treatment of Cp*OsCl(PPh3)2 with phenylacetylene and trimethylsilylacetylene gave the vinylidene complexes Cp*OsCl(=C=CHPh)(PPh3) and Cp*OsCl(=C=CH2)(PPh3), respectively. Treatment of Cp*OsCl(PPh3)2 with the internal alkyne dimethyl acetylenedicarboxylate produced the η2-alkyne complex Cp*OsCl(η2-MeO2C≡CCO2Me)(PPh3). Treatment of Cp*OsCl(PPh3)2 with the propargylic alcohol HC≡CC(OH)Ph2 gave the osmium allenylidene complex Cp*OsCl(=C = C=CPh2)(PPh3). The outcomes of the reactions of Cp*OsCl(PPh3)2 with ω-alkynols HC≡C(CH2)nOH are dependent on the length of the -(CH2)n- linker. The reaction with 3-butyn-1-ol produced the cyclic oxycarbene complex Cp*OsCl{=C(CH2)3O}(PPh3) exclusively. The reactions with 4-pentyn-1-ol produced a mixture of the hydroxyalkyl vinylidene complex Cp*OsCl{=C=CH(CH2)3OH}(PPh3) and the cyclic oxycarbene complex Cp*OsCl{=C(CH2)4O}(PPh3) in about 10:1 molar ratio. The reaction with 5-hexyn-1-ol gave exclusively the hydroxyalkyl vinylidene complex Cp*OsCl{=C=CH(CH2)4OH}(PPh3).