A NEW ENTRY INTO MOLYBDENUM TUNGSTEN SULFUR CHEMISTRY - SYNTHESIS ANDREACTIONS OF MONONUCLEAR SULFIDE COMPLEXES OF PENTAMETHYLCYCLOPENTADIENYL-MOLYBDENUM(VI) AND PENTAMETHYLCYCLOPENTADIENYL-TUNGSTEN(VI)/

A series of mononuclear thio complexes of pentamethylcyclopentadienyl- molybdenum(VI) and -tungsten-(VT) have been synthesized via C-S bond-c leaving reactions of thiolates. Use of Li2S2 for sulfurization of CpM oCl4 resulted in the known dinuclear complex, anti-CpMo-2(2)(S)(2)(mu -S)(2) (1), while the analogous reaction of CpWCl4 gave rise to anti- CpW-2(2)(S)(2)(mu-S)(2) (2) and (PPh4)[Cp*W(S)(3)] (3), the latter of which was isolated after the subsequent cation exchange reaction with PPh4Br. In contrast, the reaction of CpWCl4 with Li(2)edt (edt = SCH 2CH2S) followed by treatment with PPh4Br generated 3 as the sole isola ble product in high yield. A similar reaction between CpWCl4 and (LiS Bu)-Bu-t afforded CpW(S)(2)((SBu)-Bu-t) (6), which turned out to be t hermally unstable in solution and gradually degraded to 2. In these re actions of CpWCl4 with lithium thiolates, a facile C-S bond cleavage took place and the tungsten atom was oxidized from W(V) to W(VI). On t he other hand, the Mo(IV) thiolate complexes, CpMo((SBu)-Bu-t)(3) (4) and (PPh4)[CpMo(edt)(2)] (5), were formed from the Cp*MoCl4/(LiSBu)- Bu-t and CpMoCl4/Li(2)edt/PPh4Br reaction systems. The complex 4 was readily oxidized by dry O-2 producing CpMo(O)(2)((SBu)-Bu-t) (7) excl usively, while the reactions of 4 with NH2NMe2 and NH2NHPh occurred sl owly to yield CpMo(S)(2)((SBu)-Bu-t) (8). The hydrazines acted as oxi dants, presumably by cleaving the N-N bond, and promoted the C-S bond rupture of tert-butyl thiolate and concomitant oxidation of molybdenum from Mo(IV) to Mo(VI). Elemental sulfur Ss and grey selenium also act ed as oxidants in the reactions with 4, leading to a complex mixture o f products. From the 4 + Ss reaction, the complexes 1, 8, and CpMo(O) (S)((SBu)-Bu-t) (9) were produced, and the 4 + Se reaction lead to 8 a nd anti-CpMo-2(2)(E)(2)(mu-E)(2) (10; E = S, Se). Finally treatment o f 8 with Li2S2 and PPh4Br afforded (PPh4)[CpMo(S)(3)] (11). We found that 11 was synthesized more easily by a one-pot reaction of 4, 1/4 eq uiv of S-8, and Li2S2 in THF. The trithio complexes, 3 and 11, reacted very cleanly with PhC=CPh generating (PPh4)[CpM(S)(S2C2Ph2)] (M = W (12), Mo (13)), respectively. A kinetic study of these reactions showe d that they were first order in PhC=CPh and first order in 3 or 11 wit h appreciable negative entropies of activation and that the activation barrier was higher for the molybdenum reaction. The crystal structure s of 3-8 and 11-13 were determined by the X-ray analysis.