SYNTHESIS OF THE QUATERCYCLOPENTADIENYL LIGAND AND ITS HALF-SANDWICH TETRATUNGSTEN COMPLEXES

Double 3-oxocyclopentenylation of the fulvalene dianion, followed by m etalation, results in the four isomeric bis(enones) 1 which were elabo rated via the bis(cyclopentadienes) 2 to the four regio- and stereoiso meric forms of(quatercyclopentadienyl)tetratungsten (connectivity 1,1' ,2',1 '',3 '', 1''' (3a,b and 4a,b) and 1,1',3',1 '',3 '',1''' (3c,d a nd 4c,d)). The molecular structures of la and Ib have been determined by X-ray analysis. The tetramethyl complex 5 is obtained from 2d by a metalation-methylation sequence involving deprotonation of the interme diate bis(tungsten hydride) with K+((OC)-O--(CH3)(3)).