Synthesis, Structures, and Properties of Mixed Dithiolene-Carbonyl and Dithiolene-Phosphine Complexes of Tungsten

Abstract

A new, high yield synthesis of [Ni(S2C2Me2)2] (3) is described using 4,5-dimethyl-1,3-dithiol-2-one, Me2C2S2CO (1), as dithiolene ligand precursor. Reaction of (Me2C2S2)SnnBu2, 2, with WCl6 produces tris(dithiolene) [W(S2C2Me2)3] (6) and demonstrates the potential synthetic utility of this compound in metallodithiolene synthesis. The series of compounds [W(S2C2Me2)x(CO)6−2x] (x = 1−3), obtained as a mixture via the reaction of [Ni(S2C2Me2)2] with [W(MeCN)3(CO)3], has been characterized structurally. A trigonal prismatic geometry is observed for [W(S2C2Me2)(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(S2C2Me2)3] crystallizes in disordered fashion upon a 2-fold axis in C2/c, a different space group than that observed for its molybdenum homologue (P1̅), which is attributed to a slightly smaller chelate fold angle, α, in the former. The reactivity of 4 and [W(S2C2Me2)2(CO)2] (5) toward PMe3 has been examined. Compound 4 yields only [W(S2C2Me2)(CO)2(PMe3)2] (7), while 5 produces either [W(S2C2Me2)2(CO)(PMe3)] (8) or [W(S2C2Me2)2(PMe3)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 π-acidic CO ligands upon the apparent state of reduction of the dithiolene ligand in compounds with ostensibly the same oxidation state