Sequential Construction of One, Two, or Three Dithiolene Ligands from Alkynes and Sulfur in Dinuclear Cyclopentadienyl Molybdenum Complexes

Abstract

This paper describes the sequential assembly of up to three dithiolene ligands from alkynes and elemental sulfur at a dimetal center. The dimolybdenum mu-alkyne complexes [Mo(2)(mu-R(1)C[triple bond]CR(2))(CO)(4)Cp(2)] (1a-c; Cp = eta-C(5)H(5), R(1) = R(2) = H, CO(2)Me; R(1) = H, R(2) = CO(2)Me) undergo oxidative decarbonylation on reaction with elemental sulfur in refluxing toluene to give good to excellent yields of the terminal dithiolene complexes [Mo(2)(S)(mu-S)(2)(SCR(1)=CR(2)S)Cp(2)] (2a-c). Further reaction of these complexes with 1 equiv of an alkyne R(3)C[triple bond]CR(4) (R(3) = R(4) = H, CO(2)Me; R(3) = H, R(4) = CO(2)Me) followed by oxidation with elemental sulfur produces the bis(dithiolene) complexes [Mo(2)(mu-S)(2)(SCR(1)=CR(2)S)(SCR(3)=CR(4)S)Cp(2)] (4a-d). Two examples, [Mo(2)(mu-S)(2)(S(2)C(2)H(2))(2)Cp(2)] and [Mo(2)(mu-S)(2){S(2)C(2)(CO(2)Me)(2)}(2)Cp(2)], have been structurally characterized. Reaction of 2 with an excess of an activated alkyne R(5)C[triple bond]CR(6) (R(5) = R(6) = CO(2)Me) and sulfur, or of 4 with the alkyne alone, affords good yields of the tris(dithiolene) complexes [Mo(2)(SCR(1)=CR(2)S)(SCR(3)=CR(4)S)(SCR(5)=CR(6)S)Cp(2)] (6a-e). The degree of control over the substituents in these complexes is demonstrated by the synthesis of [Mo(2)(S(2)C(2)H(2)){mu-S(2)C(2)(CO(2)Me)(2)}{mu-S(2)C(2)(CO(2)Et)(2)}Cp(2)] (6e), which contains three different dithiolene ligands, as a single isomer.

Aminobisphenolate supported tungsten disulphido and dithiolene complexes

“…In the studied complexes, the overall geometry around the metal centre is closely similar to those reported for analogous Mo and W dioxo complexes with aminobisphenolates. (7) 73.88 (8) typical for molecular tungsten sulphido complexes used as structural analogues of the oxidized sites in the xanthine oxidoreductase enzyme family. In all these compounds, the WvS bond lengths (2.16-2.17 Å), are Scheme 1 Syntheses of disulphido complexes.…”

“…an unsaturated and potentially non-innocent bidentate dianionic ligand where two donor atoms are both sulphur. [5][6][7][8] In the latter reactions, the formation of the five-membered ring structure is associated with a formally twoelectron reduction of the metal centre. 3,4 Although there are several ways to prepare metal complexes with dithiolene ligands, there are no routine procedures for tungsten dithiolenes.…”

“…5 Alternatively, if there are appropriate metal disulphido complexes available, the metal dithiolenes can be produced readily by the reaction of isolated metal disulphides with activated alkynes such as dimethyl acetylene-dicarboxylate. [5][6][7][8] In the latter reactions, the formation of the five-membered ring structure is associated with a formally twoelectron reduction of the metal centre. The number of tungsten(VI) disulphido complexes which are useful for the dithiolene synthesis is rather limited, obviously due to the lack of suitable disulphide precursors.…”

A radical pathway to synthesise Mo and W dithiolene complexes

“…4 Given the scientific significance of dithiolene complexes, it is important to develop new methods for their synthesis and to produce new examples of these systems. 5 Dithiolene ligands have been synthesised by several methods, including the combination of an alkyne with sulfur in a variety of its chemical forms. 5,6 The reaction of a d-transition metal di-or polysulfide complex with a substituted alkyne has proved to be a very effective route, 7 e.g.…”

“…5 Dithiolene ligands have been synthesised by several methods, including the combination of an alkyne with sulfur in a variety of its chemical forms. 5,6 The reaction of a d-transition metal di-or polysulfide complex with a substituted alkyne has proved to be a very effective route, 7 e.g. [Cp 2 Mo(S 4 )] 8 reacts with the alkynes RC 2 R 0 (R = C(O)Me; R 0 = a C(2)-substituted quinoxaline or a C(6)-substituted pterin) to produce the corresponding [Cp 2 Mo(S 2 C 2 RR 0 )] compound.…”