C—S Bond-Breaking and Bond-Making Reactions in Molybdenum and Tungsten Complexes

Abstract

Selected C-S bond-breaking and bond-making reactions from our work are discussed that have implications to the modeling of both industrial and biological processes. The complexes WCl5(SR) were found to be subject to elimination of RCl, with concomitant formation of WCl4S via a carbonium ion mechanism. Attempts to emulate the C-S bond cleavage step of hydrodesulfurization by introduction of hydride into the coordination sphere, or by reaction with a second transition metal hydride, resulted in the synthesis of a variety of homonuclear and heteronuclear complexes, with elimination of the appropriate alkane. The synthesis of complexes of the type Cl 3 W(µ-R 2 S) 3 WCl 3 led to the discovery of the reactivity of the C-S bonds toward nucleophiles, including hydride. A computational study provides an explanation for this lability. Reactions of the [MoS4]2-and [WS4]2-ions with organic halides, have been reinvestigated.[PPh4][WS 3 (SR)] (R = Et, i Pr, t Bu) and [PPh4][MoS3(S t Bu)] have been characterized crystallographically. These complexes undergo reductive elimination reactions forming polynuclear sulfidometalates such as W3S92-. The synthetic potential and possible biological significance of these reactions is discussed.The rich chemistry of molybdenum and tungsten with sulfide and organosulfur ligands has been recognized for more than two decades. It is punctuated by complicated redox behavior of both metal and ligands, and also by unexpected reactions of the coordinated ligands. In this regard the metal-assisted cleavage of C-S bonds has been of particular interest, since this process is believed to be involved in the catalytic hydrodesulfurization of fossil fuels. The reverse process, namely the formation of C-S bonds has attracted less attention, but it is interesting to speculate as to the possible importance of this process in the biosynthesis of metalloenzymes.

Synthesis and Reactivity Aspects of the Bis(dithiolene) Chalcogenide Series [WIVQ(S2C2R2)2]2-(Q = O, S, Se)

“…The series [WQ(S 2 C 2 Ph 2 ) 2 ] 2- presents the possibilities of alkylation at the terminal chalcogenide and/or the dithiolene sulfur atoms which, from bond distances, are incorporated in chelate rings with considerable eneditholate character. At the outset, we note examples of alkylation of coordinated thiolate and selenolate by methyl iodide in strictly analogous molecules in the rate order Co III SR < Co III SeR, the same as that of free PhS - and PhSe - toward methyl iodide, and alkylation of terminal Mo VI O, M VI S (in MS 3,4 species, M = Mo, W), − and SMo IV S groups with retention of the alkoxide or alkanethiolate ligand. None of the latter reactions involved species with terminal oxo or sulfido and thiolate ligands.…”

Trithiotungsten(VI) Complexes Having Phosphine-Thiolate Hybrid Ligands: Synthesis and Cluster Forming Reactions with CuBr, FeCl2, and [Fe(CH3CN)6](ClO4)2

“…Anal. Calcd for C 42 H 43 Br 1 -Cu 2 N 1 P 3 W 1 S 4 : C,42.98;H,3.69;N,1.19;S,10.93. Found: C,43.01;H,3.80;N,1.31;S,11.18.…”

“…Another interesting family of this class are monoalkylated tetrathiotungstates (PPh 4 )[(RS)W(S) 3 ] (R = Et, i Pr, i Bu, t Bu, benzyl, allyl, n -hexyl), which have been isolated first by Boorman et al and later by us. , The analogous trithio(thiolato) complexes of niobium and tantalum, (Et 4 N) 2 [( t BuS)M(S) 3 ] (M = Nb, Ta), were prepared from the reactions of NbCl 5 and TaCl 5 with NaS t Bu in the presence of elemental sulfur . A unique aspect of these complexes is that they are electronically/coordinatively unsaturated, as one multiple MS bond of tetrathiometalates is replaced by a single MSR bond.…”

“…Anal. Calcd for C 42 H 42 O 1 P 2 W 1 S 4 :C, 53.85; H, 4.52; S, 13.69. Found: C, 53.52; H, 4.61; S, 13.91.…”

C−S Bond Cleavage by Chloride in a Thioether N2S2 Complex of Platinum

“…Such reactions may lead to cyclometalation, rearrangement or C−S bond cleavage . These reactions have implications for a variety of fields in chemistry such as organic synthesis, biological chemistry, and HDS processes .…”