CHEMICAL EVIDENCE FOR THE EXISTENCE OF PERALKYLATED NIOBOCENE IN A FULVENOID FORM BY ITS REACTION WITH SULFUR

Completely reduced Cp(2)() NbCl2 (Cp* = eta(5)-C(5)Me(5)) solutions ( two equivalents of Na-Hg) which were previously supposed to contain tw o isomers A and B of decamethylniobocene react with sulfur to give pro ducts 1-4. Their H-1 and C-13 NMR spectroscopy investigations allow fo r the first time a clear assignment of the structures of A and B. As 1 and 2 are identical with the previously reported Cp(2)() Nb(eta-S-2) L derivatives (L = H (1), SH (2)) a bent niobocene structure follows f or isomer A. Products 3 and 4 are in agreement with structures involvi ng a eta(1):eta(5)-tetramethylfulvene ligand which in the case of 4 is slightly modified by sulfur insertion into the CH2-Nb bond. Thus the structure of isomer B may be derived from bent niobocene by a hydride migration from one CH3 group to Nb.