Transformations of aryl isothiocyanates on tetraphosphine tungsten complexes and reactivity of the resulting dithiocarbonimidate ligand

Abstract

Treatment of [WH(4)(κ(4)-P4)] (3: P4 = meso-o-C(6)H(4)(PPhCH(2)CH(2)PPh(2))(2)) with aryl isothiocyanate ArNCS at 50 °C afforded the dithiocarbonimidate-isocyanide complex [W(κ(2)-S(2)CNAr)(CNAr)(κ(4)-P4)] (4) in moderate yields. The reaction also produced ArNHCH(3) and a small amount of ArNH(2). The yield of the hydrodesulfurization product ArNHCH(3) increased when the reaction was conducted under H(2) (up to 0.65 equiv. to 3 for Ar = p-MeC(6)H(4) (Tol)). Complex 4 was proposed to be formed via reductive disproportionation of two ArNCS molecules on a zero-valent W species generated by dissociation of H(2) from 3. The reaction of W(0) complex [W(dppe)(κ(4)-P4)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) with ArNCS also yielded 4 accompanied by free dppe, in contrast to that of [Mo(dppe)(κ(4)-P4)], which had been previously reported to undergo sulfur-atom transfer to phosphine ligands. The dithiocarbonimidate ligands in 4a (Ar = Tol) received the addition of electrophiles [PhMe(2)NH][BF(4)], MeI, and PhCOCl selectively at the N atom to afford the cationic dithiocarbamate complexes [W(κ(2)-S(2)CNHTol)(CNTol)(κ(4)-P4)][BF(4)] (6), [W{κ(2)-S(2)CN(Me)Tol}(CNTol)(κ(4)-P4)]I (7), and [W{κ(2)-S(2)CN(COPh)Tol}(CNTol)(κ(4)-P4)]Cl (8). Complexes 4a, 6, 7, and 8 have been characterized by spectroscopic and crystallographic methods, and the donor strengths of their κ(2)-dithio ligands are discussed.