| The reactions of [PPh4]2[ME4] (M = Mo, W; E = O, S, Se) with alkyl halides have been investigated and we report the characterization of alkylated intermediates, [PPh4] [ME3(ER)], and their subsequent decomposition processes. 1H, 77 Se and 95Mo NMR spectroscopy have been used to follow these reactions, and 183W NMR spectroscopy has been used to characterize alkylated products from reactions of [PPh4]2 [WS4]. The optimum synthetic conditions for alkylated products have been obtained from time dependent NMR spectroscopic data, allowing isolation of [PPh4][WS3(SR)] (R = iBu, Bz, allyl) and their characterization by X-ray crystallography. In reactions of [PPh 4]2[WS4] with alkyl dihalides, monoalkylation is observed to occur readily but bis-alkylation at the same metal centre is not a predominant process. Instead, novel bridging dithiolate species of the formula [PPh4]2[S3W(SRS)WS3] (R = CH2(C4H6)CH2) are formed and have been isolated and characterized under appropriate conditions.; X-ray crystal structures for the salts [PPh4]2[WO xS4−x] (M = Mo, W; x = 0–2) are reported and include modelling of the rotational disorder observed in the oxothiometallate structures (x = 1, 2). The salts were further characterized by 183 W and 95Mo NMR, elemental analysis and IR spectroscopy, and then pure samples were reacted with alkyl halides. Alkylation of [PPh 4]2[WOxS4−x] (x = 1, 2) was found to initiate O/S ligand exchange resulting in the formation of [PPh4][WS 3(SR)], and alkylation with tBuBr results in the formation of isobutene, presumably by C-S bond cleavage and β-hydrogen transfer, which is not observed in analogous reactions of tetrathio- or tetraselenometallates. Acetonitrile solutions of [PPh4]2[WOxS 4−x] (x = 1–3) were found to be susceptible to aerial oxidation resulting in the formation of [PPh4]2[W6O 19], which was characterized crystallographically, and S8.; Alkylated intermediates, [PPh4][ME3(ER)], were found to decrease in stability moving from M = W to M = Mo and E = S to E = Se, making isolation of [PPh4][MoSe3(SeR)] a difficult task that has not been successfully achieved. [PPh4][MoS3 (SR)] and [PPh4][WSe3(SeR)] show higher, and comparable, stabilities in solution, but only one member has yet been characterized crystallographically. |
