(Disulfido)tris(N,N-Substituted Dithiocarbamato)Mo(V) Complexes

1. Field of the Invention

This invention relates to (disulfido)tris(N,N-substituted dithiocarbamate)Mo(V) complexes. More particularly, this invention relates to compounds of the formula MoS.sub.2 (S.sub.2 CNR.sub.2).sub.3 which are mononuclear, eight-coordinate, neutral Mo(V) complexes containing only eight sulfur atoms in the Mo coordination sphere.

2. Background of the Disclosure

Molybdenum and sulfur each display redox activity which profoundly influences their chemistry. MoS.sub.4.sup.2- and organic disulfides react by a process involving induced internal electron transfer to yield the binary anion [Mo.sub.2 (.mu.-S).sub.2 (S).sub.2 (S.sub.2).sub.2 ].sup.2-. This anion is formally the dimer of the one-electron oxidation product of MoS.sub.4.sup.2- and no atoms are added or removed. The addition of an oxidant RSSR to the hexavalent MoS.sub.4.sup.2- leads to a reduced product, i.e., the dinuclear Mo(V) complex in a reaction involving an induced internal electron transfer.

Miller et al in "Mo.sub.2 S.sub.4.sup.2+ Core: New Syntheses, New Complexes, and Electrochemical Diversity", J.A.C.S., 102, 5102 (1980) reported dinuclear molybdenum compounds containing both sulfide (S.sup.2-) ligands and diethyl dithiocarbamates. A. Nieuwpoort in "New Compounds Containing Molybdenum and Diethyldithiocarbamate", J. Less Common Metals, 36, 271 (1974) disclosed non-neutral, eight-coordinate, N,N-diethyldithiocarbamate Mo(V) cation complexes which do not contain a disulfide ligand in the Mo coordination sphere. Dirand et al, "The Reaction of MoO.sub.2 (S.sub.2 CNPr.sub.2).sub.2 and H.sub.2 S: Preparation and Molecular Structure of a New Disulfur Complex: MoO(S.sub.2)(S.sub.2 CNPr.sub.2).sub.2 ", Inorg. Nucl. Chem. Lett., 11, 661-4 (1975), disclosed a Mo(VI) complex which contains an oxo ligand in addition to two N,N-dipropyldithiocarbamato groups and a disulfide ligand. However, no previously disclosed compound contains both S.sub.2.sup.2- and dithiocarbamate ligands in a Mo(V) coordination sphere with eight sulfur atoms bound to the Mo.

(Disulfido)tris(N,N-substituted dithiocarbamato)Mo(V) complexes have now been prepared. These are new compositions of matter which are mononuclear, eight-coordinate neutral, Mo(V) complexes containing only eight sulfur atoms in the Mo coordination sphere and have the general formula MoS.sub.2 (S.sub.2 CNR.sub.2).sub.3 wherein R is H, an alkyl group, cycloalkyl group, aryl group or mixture thereof and preferably an alkyl group. These new compositions have the following structure: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are the same or different and are H, an alkyl group, aryl group and cycloalkyl group. Preferably R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are the same and will be an alkyl group.

These new compounds have been found to be useful lubricant additives and have been prepared by reacting a substituted ammonium tetrathiomolybdate with a thiuramdisulfide in non-aqueous media under an inert atmosphere.

(Disulfido)tris(N,N-substituted dithiocarbamato)Mo(V) complex compounds of the formula MoS.sub.2 (S.sub.2 CNR.sub.2).sub.3 and of the structure set forth above have now been prepared. These new compounds are mononuclear, eight-coordinate, neutral Mo(V) complexes containing eight sulfur atoms bound to the Mo in the Mo coordination sphere and have been prepared in non-aqueous media by reacting a substituted ammonium tetrathiomolybdate with a thiuramdisulfide in non-aqueous media under an inert atmosphere. In the compound two of the sulfur atoms are bound to the Mo as a disulfide ligand.

The compounds of this invention are an example of induced internal redox in MoS.sub.4.sup.2- wherein a mononuclear Mo(V) complex is formed. Using N,N,N',N'-tetraethylthiuramdisulfide as the oxidant, the product Mo(S.sub.2)[S.sub.2 CN(C.sub.2 H.sub.5).sub.2 ].sub.3 was obtained. This compound is a rare example of a mononuclear Mo(V) species containing eight sulfur donor atoms. The only other Mo(V) mononuclear complexes with eight sulfur donors are the [Mo(S.sub.2 CNR.sub.2).sub.4 ].sup.+ ions reported by Nieuwpoort in 1974. The Mo(V) compounds first reported by Nieuwpoort differ from the compounds of this invention in that they are cations and have no S.sub.2.sup.2- ligand.

As set forth under SUMMARY OF THE INVENTION, the compounds of this invention have the structure: ##STR2## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are the same or different and are H, an alkyl, aryl or cycloalkyl group. Preferably R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are the same and are alkyl groups. These compounds are made by reacting one or more suitable tetrathiomolybdate salts, [Cat].sub.2 MoS.sub.4, wherein cat is a monovalent cation, with a thiuramdisulfide in non-aqueous media and in an inert atmosphere. Those skilled in the art know that thiuramdisulfide is the oxidized form of the dithiocarbamato ligand. The nature of the cation Cat effects both the solubility of the tetrathiomolybdate salt and the reaction rate, but does not form a part of the neutral complex products of the reaction which are the compounds of this invention. Preferably Cat will be an ammonium or substituted ammonium cation NH.sub.a R.sub.4-a wherein a is 0, 1, 2, 3 or 4 and wherein R comprises an alkyl, cycloalkyl or aryl group or mixture thereof. More preferably Cat will be a tetraalkyl ammonium cation, [NR.sub.4 ].sup.+.

Thiuramdisulfides useful for forming the compounds of this invention have the formula: ##STR3## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and are H, alkyl, aryl and cycloalkyl groups. Preferably R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same and are alkyl groups. It should be understood that if the R groups on the thiuramdisulfide are different, then one will obtain an isomeric mixture of the neutral Mo(V) complex compounds of this invention.

Dark brown crystals of Mo(S.sub.2)[S.sub.2 CN(C.sub.2 H.sub.5).sub.2 ].sub.3 were grown by vapor diffusion of diethylether into a CHCl.sub.3 solution of the compound. A crystal was mounted on a diffractometer. Crystal data were obtained on a computer controlled Four Circle Nicolet Autodiffractometer equipped with a graphite-monochromatized MoK (.lambda.=0.71073 .ANG.) radiation source. The crystal was found to be monoclinic with space group C2/C-C.sub.2.sup.6 h. Least squares refinement of 15 computer centered reflections (2.theta.>20.degree.) at ambient temperature of 20.degree..+-.1.degree. C. gave the following lattice constants: a=16.273 .ANG.; b=11.025 .ANG. c=31.219 .ANG.; .beta.=94.57.degree.. Its cell volume of 5584 .ANG..sup.3 and Z=8 gave a calculated density of 1.44 g/ml.

Crystal intensity measurements were made and the structure was solved to R=0.049 using standard procedures.

The structural studies of the Mo(S.sub.2)[S.sub.2 CN(C.sub.2 H.sub.5).sub.2 ].sub.3 showed it to be eight-coordinate with six sulfur donor atoms from three dithiocarbamate ligands and two sulfur donors from a disulfide ligand. The eight sulfur atoms describe a distorted dodecahedron around the molybdenum. The bond lengths about the Mo atoms in the coordination sphere of the Mo(S.sub.2)[S.sub.2 CN(C.sub.2 H.sub.5).sub.2 ].sub.3 are set forth in the Table below. The S-S distance of 2.022 .ANG. reveals the presence of the S.sub.2.sup.2- ligand in this mononuclear complex.

The invention will be further understood by reference to the following Examples.

Acetonitrile (Burdick & Jackson) was refluxed over CaH.sub.2 and distilled before use. Chloroform (Fisher, reagent grade) and ether (MCB, anhydrous) were used as received. N,N,N',N'-tetraethyl thiuramdisulfide (Aldrich) was used as received. (NH.sub.4).sub.2 MoS.sub.4 (SPEX) was also used as received. N,N,N',N'-tetraisobutyl thiuramdisulfide was prepared according to Rothstein, et al., "Note Sur La Preparatione des Tetraalkylthiurames," Recueil. Trav. Chim., 73, 561-2 (1975).

Bis(tetraethylammonium)tetrathiomolybdate(VI) [N(C.sub.2 H.sub.5).sub.4 ].sub.2 MoS.sub.4 was prepared using the following method. All operations were carried out under N.sub.2 except the work-up which was carried out in air. (NH.sub.4).sub.2 MoS.sub.4 (25.6 g) was first ball-milled to a fine powder. [N(C.sub.2 H.sub.5).sub.4 ]OH (25% in methanol, Fluka) (150 g) was added to 250 ml methanol. This solution was added to the (NH.sub.4).sub.2 MoS.sub.4 powder. The resulting mixture was stirred for about 18 h. The orange-red precipitate was filtered, washed with methanol, diethylether and air dried. Further drying was carried out under vacuum. The yield was 40.7 g (85%). The absence of any NH.sub.4.sup.+ in the product was confirmed by its infrared spectrum.

In the following examples all operations were conducted under an inert atmosphere such as argon.

A degassed solution containing 4.0 g (0.0135 mol) of tetraethylthiuram disulfide (Aldrich) in 30 ml of acetonitrile, was added dropwise to a degassed slurry containing 2.58 g (0.0053 mol) of bis(tetraethylammonium)tetrathiomolybdate (TEA.sub.2 MoS.sub.4) in 10 ml acetonitrile. The mixture was stirred under argon for two hours. 0.9 grams of the brown, solid product Mo(S.sub.2)[S.sub.2 CN(C.sub.2 H.sub.5).sub.2 ].sub.3, was then filtered under argon, washed with 50 ml of a diethylether/acetonitrile mixture (5/1 v/v), and recrystallized from chloroform and diethylether.

A degassed solution of 4.10 g (0.010 mol) tetraisobutylthiuram disulfide in a mixture of 15 ml CH.sub.2 Cl.sub.2 and 15 ml acetonitrile was prepared and added dropwise to a slurry of 1.95 g (0.0035 mol) of bis(tetraethyl ammonium)tetrathiomolybdate (TEA.sub.2 MoS.sub.4) in 10 ml acetonitrile. The mixture was stirred under argon at room temperature for one hour. Following the reaction, the solvent was removed by evaporation, and the resultant residue was first washed with hexane, then redissolved in acetonitrile and filtered. 1.1 grams of the brown solid product, Mo(S.sub.2)[S.sub.2 CN(C.sub.4 H.sub.9).sub.2 ].sub.3, was isolated from this filtrate by evaporation and recrystallized.