METALLOCENE SULFIDE CHEMISTRY OF NIOBIUM AND TANTALUM - NEW INSIGHTS INTO THE FORMATION OF NIOBIUM POLYSULFIDO COMPLEXES AND SYNTHESIS, STRUCTURE, AND REACTIVITY OF (CP')2TA(ETA-2-S2)H (CP' = TERT-BUC5H4)

The previously described reaction of Cp'2NbH3 (Cp' = t-BuC5H4) with S8 was investigated with regard to the kinetic stabilization of as yet elusive intermediates during the formation of the polysulfide complex Cp'4Nb2S9 (1). Therefore, the permethylated complex Cp*2NbS3H (2; Cp* = C5Me5) and the Ta complex Cp'2TaS2H (3) were synthesized in a related reaction and structurally investigated. Despite the problematic localization of the hydride atom during X-ray crystallographic studies, the molecules can be described in a proper manner: Characteristic of 2 and 3 are M(eta(2)-S2) cores to which either an SH (2) or a H (3) ligand is attached. Complex 3 is the first known tantalocene sulfide. It readily loses sulfur upon reaction with PR3 (R = C6H5, OCH3) and CH3I to form compounds 4 and 5, which both contain the Ta = S moiety. Attempts to prepare ''classical'' metallocene sulfides by metathesis reaction of Cp'2NbCl2 and Li2S5 gave the polynuclear compounds Cp'3Nb3S10O (6) and Cp'4Nb4S13 (7).