Rearrangement of Metallabenzynes to Chlorocyclopentadienyl Complexes

Abstract

Treatment of the osmabenzyne complex Os{≡C-C(SiMe3)═C(CH3)-C(SiMe3)═CH−}Cl2(PPh3)2 with Mo(CO)6 in refluxing benzene produced the η5-chlorocyclopentadienyl complex Os{η5-C5HCl(CH3)(SiMe3)2}Cl(CO)(PPh3) and Mo(CO)5(PPh3). A computational study suggests that the chlorocyclopentadienyl complex is most likely produced via the carbene intermediate Os{═C(C(SiMe3)═C(CH3)-C(SiMe3)═CH−)}Cl2(CO)(PPh3) formed by a migratory insertion reaction of the osmabenzyne complex Os{≡C-C(SiMe3)═C(CH3)-C(SiMe3)═CH}Cl2(CO)(PPh3). DFT calculations show that the relative thermal stability of metallabenzynes Os(≡C-CH═CHCH═CH)Cl2(L)2 and the corresponding isomeric carbene complexes Os{═C(−CH═CHCH═CH−)}Cl2(L)2 as well as the chlorocyclopentadienyl complexes Os(η5-C5ClH4)Cl(L)2 (L = CO, phosphine, pyridine, amine) is strongly dependent on ligand L.