Oxidations of (R(3)tach)M(CO)(3) Complexes [M = Cr, Mo, W; R(3)tach = 1,3,5-Trialkyl-1,3,5-triazacyclohexane (R = t-Bu, Bn)]. Crystal Structures of (t-Bu(3)tach)MO(3).15H(2)O (M = Mo, W)

Stable Cr, Mo, and W complexes having a metal in oxidation state II, III, or VI, and possessing a facially coordinated 1,3,5-trialkyl-1,3,5-triazacyclohexane (R(3)tach) ligand, can be prepared by oxidation of (R(3)tach)M(CO)(3) with a variety of oxidizing agents. The reaction of the chromium or molybdenum complexes (R(3)tach)M(CO)(3) (M = Cr, R = Bn (benzyl), t-Bu and M = Mo, R = t-Bu) with bromine or thionyl chloride at reflux affords a series of monomeric M(III) trihalide complexes. More controlled oxidation of (t-Bu(3)tach)M(CO)(3) (M = Mo, W) with either bromine or iodine yields the 7-coordinate M(II) cations [(t-Bu(3)tach)M(CO)(3)X](+) (X = Br, I); protonation with trifluoromethanesulfonic acid affords the isolable [(t-Bu(3)tach)M(CO)(3)H](+) cations as their trifluoromethanesulfonate salts. Exhaustive oxidation of (t-Bu(3)tach)M(CO)(3) (M = Mo, W) with hydrogen peroxide affords the monomeric M(VI) trioxo complexes (t-Bu(3)tach)MO(3). The facial complexes (t-Bu(3)tach)MO(3) (M = Mo, W) have been characterized by room-temperature single-crystal X-ray diffraction studies. The complexes both crystallize with 15 waters of hydration and lie on the 3-axes of rhombohedral R3c cells of dimensions a = 21.026(3) Å and c = 13.418(2) Å for M = Mo and a = 21.011(3) Å and c = 13.390(3) Å for M = W. The array is a superlattice on a quasi-R3m structure (c halved) with successive molecules along c slightly staggered and with a small perturbation on the molecular symmetry, degrading it from 3m to 3. The Mo=O (W=O) bond distances are 1.724(3) Å (1.745(4) Å), and the Mo-N (W-N) bond distances are 2.374(3) Å (2.355(6) Å). The O-Mo-O (O-W-O) angles are 107.1(2) degrees (106.4(3) degrees ), and the N-Mo-N (N-W-N) angles are 58.8(1) degrees (59.0(3) degrees ). The high solvent component is associated with a hydrogen-bonded array, with the substrate molecules lying in axial tunnels in an ice-like structure.