Synthesis of the Quatercyclopentadienyl Ligand and Its Half-Sandwich Tetratungsten Complexes.
Double 3-oxocyclopentenylation of the fulvalene dianion, followed by metalation, results in the four isomeric bis(enones) 1 (e.g. I) which were elaborated via the bis(cyclopentadienes) 2 (e.g. II) to the four regio- and stereoisomeric forms of (quatercyclopentadienyl)tetratungsten (connectivity 1,1',2',1'',3'',1''' (3a,b (e.g. III) and 4a,b (e.g. IV)) and 1,1',3',1'',3'',1''' (3c,d and 4c,d)). The mol. structures of 1a and 1b were detd. by x-ray anal. The tetra-Me complex 5 (shown as V) was obtained from 2d by a metalation-methylation sequence involving deprotonation of the intermediate bis(tungsten hydride) with K+(-OCMe3).
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