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.

Catalytic Production of Isothiocyanates via a Mo(II)/Mo(IV) Cycle for the “Soft” Sulfur Oxidation of Isonitriles

“…The solid-state molecular structure of 8 as determined by single-crystal X-ray analysis is presented in Figure , for which the geometric bond length values (Å) associated with the κ-( S,S )-S 2 CN t Bu fragment are as follows: Mo1–S1, 2.3694(4); Mo1–S2, 2.3763(3); S1–C24, 1.7832(12); S2–C24, 1.7963(12); C24–N3, 1.2631(15) . On the basis of literature precedent, the most likely mechanism for formation of 8 involves SAT from initial coordination of t BuNCS to a Mo­(II) center to form a transient formal Mo­(IV) terminal sulfide through elimination of t BuNC, followed by trapping of this metal sulfide with another 1 equiv of t BuNCS to form the final thermodynamically stable dithiocarbonimidate product . Thus, the fact that 8 is never observed during conversion of t BuNC and S 8 to t BuNCS strongly suggests the absence of competing SAT processes involving the ITC product that might lead to CPAM Mo IV (S) intermediates during catalysis.…”

“…Indeed, as Scheme terminal sulfide through elimination of t BuNC, followed by trapping of this metal sulfide with another 1 equiv of t BuNCS to form the final thermodynamically stable dithiocarbonimidate product. 25 Thus, the fact that 8 is never observed during conversion of t BuNC and S 8 to t BuNCS strongly suggests the absence of competing SAT processes involving the ITC product that might lead to CPAM Mo IV (S) intermediates during catalysis. "On-Demand" ITC Production.…”

The Coordination Chemistry of Imidomethanedithiolate Di-anions: A Structural Comparison with Their Dithiocarbamate Analogs

“…A very similar molecu-lar geometry is noted, and the bond lengths tend to be longer (Mo-S: 2 × 2. 45 [29]. In this case, there are small differences between the W-S bond lengths (W-S: 2.54 and 2.55 Å cf.…”

“…The t-butyl-dithiocarbimate ligand is µ 2 -bridging, as each sulfur atom is connected to both the molybdenum and manganese atoms (Mo-S: 2.46 and 2.47 Å and Mn-S: 2 × 2.33 Å). 4) [29]. The molecular structure of the complex in 3 is represented in Figu 2c.…”

Linear Connection of Four Nitrile Molecules on the Tetraphosphine Complexes of Tungsten and Molybdenum

“…It has also been reported that two or more nitrile molecules are directly combined together on certain metal centers to form metallacyclic structures, ,− some of which are the possible intermediates leading to the above heterocycles or other polyfunctionalized compounds. We have been investigating transformations of unsaturated organic molecules by using the low-valent Mo and W complexes bearing tetradentate phosphine ligands . Here a unique coupling reaction of four nitrile molecules that forms a metallacyclic system on these complexes is described.…”