Organic synthesis via transition metal complexes. 112. 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 Fische r carbene complexes. It was shown that the thermally quite unreactive tungs taoctatetraenes 14a-d were readily transformed into spiro-fused vinylcyclop entadienes 15a-d in the presence of catalytic amounts of RhCl3. 3H(2)O in M eOH or [(COD)RhCl](2). A reactivity enhancement was observed also for the t ransformation of the tungsten complex 8a into vinylcyclopentadiene 10a. Exp erimental 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 [(CO D)RhCl](2). The carbene rhodium compound 16c was transformed into the vinyl cyclopentadiene 15c thermally in a smooth reaction and showed a catalytic a ctivity similar to [(COD)RhCl](2). Not only rhodium but also copper compoun ds were found to be good catalysts for the pi -cyclization of tungstaoctate traenes.