Preparation of an oxoperoxocyanomolybdate(VI) complex by dioxygen oxidation of an oxocyanomolybdate(IV) anion. Structure and reactivity toward phosphines and olefins

Abstract

Potassium oxopentacyanomolybdate(IV), [Mo(0)(CN)5]K3-2H20, is prepared either through a disproportionation process of the molybdenum(V) cyano intermediate or by controlled hydrolysis of the octacyanomolybdate(IV). The tetraphenylphosphonium salt obtained under phase-transfer conditions reacts readily with dioxygen to give tetraphenylphosphonium oxoperoxotetracyanomolybdate(VI) [Mo(0)(02)(CN)4][PPh4]2, whose structure is determined by an X-ray analysis. The crystalline compound belongs to triclinic space group Pi with a = 10.951 (2) A, b = 22.597 (6) A, c = 10.283 (2) A, a = 97.66 (2)°, /3 = 116.24 (2)°, and y = 84.43 (2)°. The volume of the unit cell is 2260 (2) A3 with Z = 2. The structure was refined to R = 3.1%. The reactivity of the peroxo complex toward triphenylphosphine is studied and is shown to give 1.5 mol of phosphine oxide/mol of peroxo complex. This unusual stoichiometry is rationalized in terms of a classical oxidation of 1 mol of phosphine by the peroxo moiety followed by an oxo transfer involving 2 mol of the dioxomolybdenum(VI) intermediate. The plausible implications that such a process could have on the catalytic oxidation on metal oxide surfaces is given. The poor reactivity of the oxoperoxomolybdenum dianion toward olefins is dramatically increased in the presence of silver salts. A monoanionic species, stabilized by hexamethylphosphoramide, [Mo(0)(02)(CN)3-HMPA] [(PhCH2)Ph3P], is isolated and characterized by an X-ray analysis. The crystalline compound belongs to monoclinic space group P2Jn with a = 9.801 (2) A, b = 13.613 (3) A, c = 27.597 (8) A, and d = 90.56 (2)°. The volume of the unit cell is 3682 (2) A3 with Z = 4. The structure was refined to R = 7.12%.

Dioxygen Activation with Molybdenum Complexes Bearing Amide-Functionalized Iminophenolate Ligands

“…Thus, the possibility to use environmentally benign and cheap dioxygen (or even air) would be highly desirable [22]. Several transition metals, including molybdenum, are known to activate dioxygen [23,24,25,26,27,28,29,30,31,32]. In our group, molybdenum(IV) complexes based on β-ketiminate and iminophenolate ligand systems were investigated regarding their usability in dioxygen activation [33,34,35,36].…”

Activation of Molecular Oxygen by a Molybdenum(IV) Imido Compound

“…Whereas the activation of molecular oxygen by molybdenum(IV) complexes has been established by our group and others, concomitant oxygen atom transfer is restricted to very few substrates. [11][12][13][14][15][16] All molybdenum complexes capable of activating molecular oxygen are of the general structure [MoOLn] and lead to the formation of [MoO(O2)Ln] complexes, with L being either CNor bidentate monoanionic ligands. The oxido ligand renders the metal center electron poor, thus leading to strong σ-bonds but simultaneously inhibiting any π-backbonding to the peroxido unit.…”

95Mo NMR: a useful tool for structural studies in solution

“…The solid-state structures of the monometallic (I-VI) [9,13,14] and bimetallic (IX-XI) [11,16] complexes show a distorted octahedral geometry around the metal atom, while for the heptacoordinated compounds VII and VIII, the ligands are placed around the molybdenum centre giving a pseudopentagonal bipyramidal geometry. [8,15] The chemical shifts observed cover a wide range (ca 1100 ppm, from +500 to −600 ppm), depending on the electronic density on the metal by modulation of the coordinated ligands (Table 1 and Fig. 2(a)).…”

“…An exponential window function was applied with a line broadening of 20-200 Hz before Fourier transform to obtain an optimum signal-to-noise ratio. Ligands 3, [12] (R)-4 and (S)-5, [9] and complexes II, [13] III and XI, [11] IV-V, [9] VI, [14] VII, [15] IX [16] and X [8] were prepared according to published methods. Complexes I [17] and VIII [18] were prepared following the methodology described for related compounds.…”