Coffindaffer, TW; Niccolai, GP; Powell, D; Rothwell, IP; Huffmar, JC
The effect of aryloxide ancillary lieands on the chemistry of Mo2 and W2 dinuclear compounds has been investigated by reaction of the compounds M2(NMe2)6(M = Mo and W) and Mo2(O-t-Pr)6 with a variety of phenols. The sterically less demanding ligands 4-methylphenol (HOAr-4-Me) and 3,5-dimethylphenol (HOAr-3,5-Me2) react with Mo2(NMe2)6 to give salt complexes [Me2NH2] [Mo2(OAr)7(HNMe2)2] in good yields. A single-crystal diffraction study shows the anion obtained by using 4-methylphenol to contain a confacial bioctahedral arrangement of ligands in the Mo2O7N2 core, with a metal-metal distance of 2.601 A. Both complexes are slightly paramagnetic in solution at 30 °C, μ= 0.8-0.9 μβ by Evans' method. However, relatively sharp contact shifted 1H NMR spectra are present at 30 °C for both complexes, and in the case of the 4-methylphenoxo derivative, the temperature dependence of the 4-methyl groups indicates that the electrons on the molybdenum atoms are antiferromagnetically coupled. An estimate of the exchange integral, J, gave a value between 230 and 290 cm-1. Using W2(NMe2)6 instead of Mo2(NMe2)6 in the reaction yields only the simple amine adducts W2(OAr-4-Me)6(HNMe2)2 and W2(OAr-3,5-Me2)6(HNMe2)2. Addition of only 4 equiv of 3,5-dimethylphenol to Mo2(NMe2)6 in the presence of a large excess of HNMe2 leads to the formation of a reduced, Mo2 4+-containing species Mo2(OAr-3,5-Me2)4(HNMe2)4 as a blue crystalline solid in good yield. Ligand exchange with trimethylphosphine gives the emerald green Mo2(OAr-3, 5-Me2)4(PMe3)4. The pathway of the reduction is uncertain, but from the reaction mixture an oxidized species Mo2(OAr-3, 5-Me2)6(NMe2)(HNMe2)2 was isolated and structurally characterized. The Mo2 7+ core is surrounded by a confacial bioctahedral arrangement of ligands with a bridging dimethylamido group. The Mo-Mo distance of 2.41 Ã
is consistent with the presence of a bond of order 2.5. Electrochemical one-electron oxidation of the quadruply bonded Mo2(OAr-3,5-Me2)4(PMe3)4leads to the monocation containing an Mo2 5+ core with a formal bond order of 3.5. EPR measurements show the resulting unpaired electron coupled to the four PMe3 nuclei. Crystal data for [Mo2(OAr-4-Me)7(HNMe2)2]-n-hexane at-163 °C are as follows: a = 14.677 (6) Ã
, b = 16.62 (7) Ã
, c = 14.402 (6) Ã
, a = 115.78 (2)°, β = 107.67 (2)°, γ = 77.82 (2)°, Z = 2, dcalcd = 1.281 gem'3 in space group P1Ì
. Crystal data for Mo2(OAr-3, 5-Me2)6(NMe2)(HNMe2)2 at-140 °C are as follows: 29.281 (6) Ã
, b = 12.071 (4) Ã
, c = 14.653 (8) Ã
, β= 92.57 (3)°, Z = 4, dcald= 1.350 g cm-3 in space group P21/n. © 1985, American Chemical Society. All rights reserved.