Cyclopentadienyl-carbonyl-acetylen-methyl-wolfram, eine ausgangsverbindung für neue wolfram—acetylen-komplexe

Abstract

The photochemical reaction of C 5H 5W(C0) 3CH 3 (I) with acetylene (C 2H 2) in solution leads to the formation of the diamagnetic complexes C 5H 5W(CO) 2-(C 2H 2COCH 3) (II) and C 5H 5W(CO)(C 2H 2)CH 3 (III). The adduct II contains a methylvinylketone ligand, in which the C 2H 2 unit is a σ-bonded olefin. The 16 electron system III, however, contains a mobile π-bonded C 2H 2-ligand. III reacts readily with two-electron ligands L; as examples the reactions with carbon monoxide, trimethylphosphite and trimethylphosphane are described. In the new π-acetylene complexes the C 2H 2 ligand shows a hindered rotation around the metal-C 2H 2 bond axis. The free activation enthalpies of the acetylene rotation are surprisingly high (e.g. for C 5H 5W(CO)(C 2H 2)CH 3 ΔG† 364 18.2 kcal mol -1, indicating strong metal→acetylene backbonding.