An inorganic functional group approach to the systematic synthesis and reactivity studies of binuclear Mo/S and Mo/S/O complexes

Abstract

A number of general reactions, based on molybdenum-coordinated sulphido or polysulphido ligands, can account for the synthesis of many members of the [MO: (S),(S&_,]'-, [Mob,,_,]'-and [Mo3l(C?),(S),(S,),_Jl"-homologous series. These reactions include : (a) sulphur addition and sulphur abstraction reactions ; (b) oxidative removal of the Sz-ligands and their replacement by substitutionally labile ligands ; (c) oxidation of coodinated RS-ligands by S," fragments, and in situ generation of S,'-ligands ; (d) oxidative dimerization reactions of molybdenum(IV) complexes ; and (e) reductive elimination of S," fragments. The synthesis of the new [(C~)MO~(O)(~-S)~MO~(O)S~]-and [(Cp)MoV(0)(p-S),MoV(0)S2]-anions has alowed the use of 'H NMR spectroscopy to monitor the solution behaviour and reactivity of the MoV(0)S2 group. The existence of the MoV(0)S2 + S2 F? MoV(0)S4 equilibri? has been unequivocally established. The [(Cp)Mo' (O)(p-S),Mov(0)S2]-complex gives a vinyl disulphide derivative by insertion of dicarbomethoxyacetylene, DMA, into the MO-q2-S2 group. Upon prolonged heating to 70°C the vinyl disulphide ligand is converted quantitatively to a dithiolene ligand. The same conversion takes place swiftly at ambient temperatures when catalytic amounts of Ss are present in the reaction medium. Reaction pathways for both the thermal and catalytic conversions have been suggested by 'H NMR studies. Preliminary studies of the utility of the (J%N)[Mo2W&U, ~i(~~~)61~02~2~~~~1~, (EWdMa@.&l and (Phd%[Mo&l complexes as catalysts for the hydrodesulphurization of thiophene are reported. The Ni/Mo catalyst obtained from ~i(DMF)6][Mo202S,Cl]2 is at least 10 times more effective than a commercial CO/MO catalyst.

Evidence Favoring Molybdenum−Carbon Bond Formation in Xanthine Oxidase Action: 17O- and 13C-ENDOR and Kinetic Studies

“…Such a step was suggested, but not favored, by Turner et al (1989), on the basis of the ab initio calculations of Rappé and Goddard (1982). More recently, Coucouvanis et al (1991) have provided more direct support from the reactions of model compounds and have indeed suggested a mechanism for xanthine oxidase action closely related to that proposed here.…”

“…Current understanding (Bray, 1988;Turner et al, 1989;Pilato & Stiefel, 1993;Hille, 1994) of the catalytic mechanism of the enzyme depends in substantial measure on these studies, supplemented by studies of model compounds and model reactions (Holm, 1990;Coucouvanis et al, 1991;Greenwood et al, 1993;Enemark & Young, 1993).…”

Facets of early transition metal–sulfur chemistry: Metal–sulfur ligand redox, induced internal electron transfer, and the reactions of metal–sulfur complexes with alkynes

“…[114]. Vinyl disulfide complexes have also been observed in Ti (vide supra) [100] and Mo Cp chemistry [115]. Sulfur appears to catalyse the conversion of vinyl sulfide complexes into more stable dithiolene species, e.g., (53), accounting for the rarity of vinyl sulfide complexes.…”

Pterins, Quinoxalines, and Metallo-Ene-Dithiolates

“…A limited number of 1,2-ene-dithiolates can be isolated as the disodium salts and many of these contain electron-withdrawing groups (72-77). However, many 1,2-ene-dithiolates can be prepared as metal complexes where the 1,2-ene-dithiolate is stabilized as a chelating ligand (as is suggested for Moco) (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Synthetic routes to métallo-1,2-ene-dithiolate complexes include the reactions of metal complexes (containing labile ligands) with dithines (26), dithiolium salts (79,29) or ahydroxy ketones in the presence of P4S10 (17), as shown in equations 1, 2, and 3, respectively.…”

“…Synthetic routes to métallo-1,2-ene-dithiolate complexes include the reactions of metal complexes (containing labile ligands) with dithines (26), dithiolium salts (79,29) or ahydroxy ketones in the presence of P4S10 (17), as shown in equations 1, 2, and 3, respectively. Another interesting synthetically useful method for the preparation of dithiolenes is the reaction of a metal polysulfido complex with an alkyne as shown in equation 4 (8,11,18,21,22,24). The previously reported synthesis of C(6)-alkynesubstituted pterin derivatives (such as Form A) (9,70) should, in conjunction with the reaction shown in equation 4, allow die preparation of molybdenum 1,2-ene-dithiolate (dithiolene) complexes that approach the structure of Moco.…”