ADDUCTS OF CARBENES WITH GROUP-II AND GROUP-XII METALLOCENES

The reactions and adducts of 1,3,4,5 -tetramethylimidazol-2-ylidene wi th bis(pentamethylcyclopentadienyl)magnesium, -calcium, -strontium, -b arium, or -zinc are described. A consistent tend in the spectroscopic properties and structures of the alkaline earth metallocenes is observ ed, The adduct between 1,3,4,5-tetramethylimidazol-2-ylidene and bis(p entamethylcyclopentadienyl)zinc shows a structure in which the zinc is only sigma-bonded to the three ligating groups. Among the alkaline ea rth adducts, the sigma-bonded interaction to the former carbene center of the 1,3,4,5-tetramethylimidazol-2-ylidene shows the shortest metal -carbon distances in each of the structures but the difference between the carbene-metal and pentamethylcyclopentadienyl-metal distances dec reases as the atomic number of the metal increases.