Organic Synthesis via Transition Metal Complexes. 112.1 Reactivity Enhancement of Group VI Fischer Carbene Complexes by Copper and Rhodium Catalysts: Experimental Proof of a Carbene Rhodium Complex as an Intermediate

Rhodium(I) compounds were found to efficiently catalyze reactions of Fischer carbene complexes. It was shown that the thermally quite unreactive tungstaoctatetraenes 14a − d were readily transformed into spiro-fused vinylcyclopentadienes 15a − d in the presence of catalytic amounts of RhCl 3 ·3H 2 O in MeOH or [(COD)RhCl] 2 . A reactivity enhancement was observed also for the transformation of the tungsten complex 8a into vinylcyclopentadiene 10a . Experimental proof for the intermediacy of carbene rhodium complexes in these reactions was provided by preparation of the rhodaoctatetraene 16c from the reaction of the tungsten compound 14c with a stoichiometric amount of [(COD)RhCl] 2 . The carbene rhodium compound 16c was transformed into the vinylcyclopentadiene 15c thermally in a smooth reaction and showed a catalytic activity similar to [(COD)RhCl] 2 . Not only rhodium but also copper compounds were found to be good catalysts for the π-cyclization of tungstaoctatetraenes.