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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.

ChemInform Abstract The compound (V) contains a mixture of (Mo2O2S10)2-and (Mo2O2S9)2-anions. Oxidative coupling of the latter anion affords the Mo(VI) linear tetramer (VIII), which crystallizes in space group P1 with Z=2. Reaction of (V) with NiCl2 yields the new chloro derivative (X) ( P21/n, Z=4) as a result of ligand exchange. The nucleophilicity of (Mo2O2S9)2-is demonstrated in its reaction with MeI, which gives the methanethiolato-bridged derivative (VI). Both (V) and (VI) crystallize in the space group P21/c with Z=4. The structures of (V), (VI), (VIII), and (X) contain Mo(VI) ions with pseudo-pentagonal bipyramidal environments.

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The synthesis of the new dithiolene complexes, [{(MeOOC),C,S2}2Mo(2-S)]; and [OMo(S2C2(COOMe)2)2]2-, is reported. These complexes are obtained by the reaction of dicarbomethoxyacetylene (DMA) with either [(S~)MO(S)(~~-S)~MO(S)(S~)]~-or [(CS~)MO(S)(~~-S)~MO(S)(CS~)]~-and [OMO(S~)~]~-, respectively. The reaction of [(S4)Mo(0)(~2-S)2Mo(O)(S2)]2-with DMA results in the new dithiolene complex [{(MeOOC)2C2S2}M~(0)(~2-S)]~, which is the isomeric form of the vinyl disulfide complex obtained in the reaction of the [(S2)Mo(0)(~2-S)2Mo(O)(S2)]2-complex with DMA. The difference in reactivity between the two complexes that contain the same [Mo202S212+ core is attributed to the intrinsically different reactivity characteristics of the Sg-and S:-ligands. As a result of Mo-S d,-p, bonding an alternation in the S-S bond lengths is observed in virtually all of the structurally characterized Mo-S4 units. The consequent weakening of the S-S bonds adjacent to the Mo-S bonds allows for the ready dissociation of $3 from the MO-coordinated Si-ligands. This weakening also accounts for the facile formation of dithiolenes in cycloaddition reactions of alkynes with the Mo-S, units. By comparison, the S-S bond in side-on MO-coordinated St-ligands is strengthened as a result of depopulation of the ligand x*-orbitals. Reactions of the latter with alkynes do not proceed by cycloaddition. Instead, insertion into the Mo-S bond has been reported for at least one such reaction. The importance of activated polysulfide ligands in the hydrodesulfurization reaction is discussed.

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035ChemInform Abstract The compounds (III), (V), (VI), and (VIII), containing the title anions, are prepared as shown in the scheme. (III) and (VIII) crystallize in the triclinic system, space group P1 with Z=2. Crystals of (V) and (VI) are isostructural and crystallize in the space group P1 with Z=1. In the structure of (V) the thio anions Mo2S72-and Mo2 S62-occupy the same center of symmetry with occupancy factors 0.63 and 0.37, respectively. In (III) and (VIII) the complex assumes a distorted-square-pyramidal arrangement where the terminal sulfido ligand occupies the apical position. One S42-ligand and one MoS24 ligand occupy the equatorial positions in (III) while one S22-ligand and one MoS42-ligand occupy the equatorial positions in (VIII). The Mo2S62-anion in (VI) consists of two slightlydistorted tetrahedral Mo(V)S4 units that share an edge. In contrast to (III) and (VIII) the sym. dimer (VI) shows complete delocalization of charge (general scheme relating the (Mo2(S)n(S2)6-n)2-anions and plausible isomers, electronic and IR spectra).