Kuppuswamy Arumugam

Synthesis, structures, and properties of mixed dithiolene-carbonyl and dithiolene-phosphine complexes of tungsten.

A new, high yield synthesis of [Ni(S(2)C(2)Me(2))(2)] (3) is described using 4,5-dimethyl-1,3-dithiol-2-one, Me(2)C(2)S(2)CO (1), as dithiolene ligand precursor. Reaction of (Me(2)C(2)S(2))Sn(n)Bu(2), 2, with WCl(6) produces tris(dithiolene) [W(S(2)C(2)Me(2))(3)] (6) and demonstrates the potential synthetic utility of this compound in metallodithiolene synthesis. The series of compounds [W(S(2)C(2)Me(2))(x)(CO)(6-2x)] (x = 1-3), obtained as a mixture via the reaction of [Ni(S(2)C(2)Me(2))(2)] with [W(MeCN)(3)(CO)(3)], has been characterized structurally. A trigonal prismatic geometry is observed for [W(S(2)C(2)Me(2))(CO)(4)] (4) and confirmed by a DFT geometry optimization to be lower in energy than an octahedron by 5.1 kcal/mol. The tris(dithiolene) compound [W(S(2)C(2)Me(2))(3)] crystallizes in disordered fashion upon a 2-fold axis in C2/c, a different space group than that observed for its molybdenum homologue (P1), which is attributed to a slightly smaller chelate fold angle, alpha, in the former. The reactivity of 4 and [W(S(2)C(2)Me(2))(2)(CO)(2)] (5) toward PMe(3) has been examined. Compound 4 yields only [W(S(2)C(2)Me(2))(CO)(2)(PMe(3))(2)] (7), while 5 produces either [W(S(2)C(2)Me(2))(2)(CO)(PMe(3))] (8) or [W(S(2)C(2)Me(2))(2)(PMe(3))(2)] (9) depending upon reaction conditions. Crystallographic characterization of 5, 8, and 9 reveals a trend toward greater reduction of the dithiolene ligand (i.e., more ene-1,2-dithiolate character) across the series, as manifested by C-C and C-S bond lengths. These structural data indicate a profound effect exerted by the pi-acidic CO ligands upon the apparent state of reduction of the dithiolene ligand in compounds with ostensibly the same oxidation state.

Synthesis, Structures, and Properties of 1,2,4,5-Benzenetetrathiolate Linked Group 10 Metal Complexes

Dimetallic compounds [(P-P)M(S(2)C(6)H(2)S(2))M(P-P)] (M = Ni, Pd; P-P = chelating bis(phosphine), 3a-3f) are prepared from O=CS(2)C(6)H(2)S(2)C=O or (n)Bu(2)SnS(2)C(6)H(2)S(2)Sn(n)Bu(2), which are protected forms of 1,2,4,5-benzenetetrathiolate. Selective monodeprotections of O=CS(2)C(6)H(2)S(2)C=O or (n)Bu(2)SnS(2)C(6)H(2)S(2)Sn(n)Bu(2) lead to [(P-P)Ni(S(2)C(6)H(2)S(2)C=O)] or [(P-P)Ni(S(2)C(6)H(2)S(2)Sn(n)Bu(2))]; the former is used to prepare trimetallic compounds [(dcpe)Ni(S(2)C(6)H(2)S(2))M(S(2)C(6)H(2)S(2))Ni(dcpe)] (M = Ni (6a) or Pt (6b); dcpe = 1,2-bis(dicyclohexylphosphino)ethane). Compounds 3a-3f are redox active and display two oxidation processes, of which the first is generally reversible. Dinickel compound [(dcpe)Ni(S(2)C(6)H(2)S(2))Ni(dcpe)] (3d) reveals two reversible oxidation waves with DeltaE(1/2) = 0.66 V, corresponding to K(c) of 1.6 x 10(11) for the mixed valence species. Electrochemical behavior is unstable to repeated scanning in the presence of [Bu(4)N][PF(6)] electrolyte but indefinitely stable with Na[BArF(24)] (BArF(24) = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), suggesting that the radical cation generated by oxidation is vulnerable to reaction with PF(6)(-). Chemical oxidation of 3d with [Cp(2)Fe][BArF(24)] leads to formation of [3d][BArF(24)]. Structural identification of [3d][BArF(24)] reveals appreciable shortening and lengthening of C-S and C-C bond distances, respectively, within the tetrathioarene fragment compared to charge-neutral 3d, indicating this to be the redox active moiety. Attempted oxidation of [(dppb)Ni(S(2)C(6)H(2)S(2))Ni(dppb)] (3c) (dppb = 1,2-bis(diphenylphosphino)benzene) with AgBArF(24) produces [[(dppb)Ni(S(2)C(6)H(2)S(2))Ni(dppb)](2)(mu-Ag(2))][BArF(24)](2), [4c][BArF(24)](2), in which no redox chemistry has occurred. Crystal structures of bis(disulfide)-linked compounds [(P-P)Ni(S(2)C(6)H(2)(mu-S(2))(2)C(6)H(2)S(2))Ni(P-P)] are reported. Near IR spectroscopy upon cationic [3d](+) and neutral 6a reveals multiple intense absorptions in the 950-1400 nm region. Time-dependent density functional theory (DFT) calculations on a 6a model compound indicate that these absorptions are transitions between ligand-based pi-type orbitals that have significant contributions from the sulfur p orbitals.

A Convergent Approach to the Synthesis of Multimetallic Dithiolene Complexes

Controlled base hydrolysis of one or both of the protected 1,2-dithiolene chelates of 1,3,5,7-tetrathia- s-indacene-2,6-dione (OCS 2C 6H 2S 2CO) enables the stepwise synthesis of di- and trimetallic complexes with 1,2,4,5-benzenetetrathiolate as the connector. Treatment of OCS 2C 6H 2S 2CO with MeO (-), followed by [NiBr 2(dcpe)] [dcpe = 1,2-bis(dicyclohexylphosphino)ethane], yields [(dcpe)Ni(S 2C 6H 2S 2CO)] ( 4). The reaction of 4 with EtO (-), followed by [MX 2(dcpe)] (X = halide), yields [(dcpe)Ni(S 2C 6H 2S 2)M(dcpe)] [M = Ni ( 5a), Pd ( 5b)]. Deprotection of the 1,3-dithiol-2-one group of 4, followed by introduction of (1)/ 2 equiv of MX 2 and then I 2, yields the neutral trimetallic compounds [(dcpe)Ni(S 2C 6H 2S 2)] 2M [M = Ni ( 6a), Pt ( 6b)]. Tetrahedralization at nickel is observed in 5a, which density functional theory calculations attribute to second-order Jahn-Teller effects, while 6a and 6b display an end-to-end folding of approximately 46 degrees . A color darkening is observed in moving from 4 to compounds 6 due to the increasing size of the conjugated metal-organic pi system. Intense, broad absorptions in the near-IR are observed for 6a and 6b.

The dithiolene ligand and tetrathiafulvalene precursor molecules 4,5-bis(bromomethyl)-1,3-dithiol-2-one and 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one

The crystal structures of 4,5-bis(bromomethyl)-1,3-dithiol-2-one, C(5)H(4)Br(2)OS(2), (I), and 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one, C(5)H(8)O(7)P(2)S(2), (II), occur with similar unit cells in the same monoclinic space group. Both molecules reside on a twofold symmetry axis coincident with the C=O bond, so that the substituents in the 4- and 5-positions project above and below the plane of the 1,3-dithiol-2-one ring. In both structures, the molecules align themselves in a head-to-tail fashion along the b axis, and these rows of molecules then stack, with alternating directionality, along the c axis. For (II), an extensive network of intermolecular hydrogen bonds occurs between molecules within the same stack and between adjacent stacks. Each -CH(2)P(O)(OH)(2) group participates in four hydrogen bonds, twice as donor and twice as acceptor.