MONONUCLEAR TUNGSTEN(VI) PHENYLIMIDO PHENOXIDE AND ALKOXIDE COMPLEXES WITH INTRAMOLECULAR AMINE COORDINATION - MOLECULAR-STRUCTURE OF WCL3(=NPH)[OC6H2(CH2NME2)2-2,6-ME-4]

Mononuclear tungsten(VI) phenylimido phenoxide and alkoxide chlorides have been synthesized in which a potential intramolecularly coordinating amine donor atom is present. The selected ligands were phenoxides with one or two ortho-(dimethylamino)methyl groups, [OC6H4CH2NMe2-2] (a) and [OC6H2(CH2NMe2)2,6-Me-4] (b), respectively, 8-quinolinolate (8-quin) (c) or alpha-substituted 2-pyridylmethoxides, i.e. 2,4-dimethyl-3-(2-pyridyl)-3-pentoxide (d) and diphenyl-2-pyridylmethoxide (e), respectively. They were attached to the metal center by reaction of their lithium or sodium salts with WCl4(=NPh)(OEt2) in diethyl ether. To establish the influence of a potentially intramolecular coordinating amine function, three methyl-substituted phenoxide complexes have been prepared in which a diethyl ether molecule instead of the tertiary amine function coordinates to tungsten. Variable-temperature NMR spectroscopy as well as cryoscopic molecular weight measurements in benzene indicate that these complexes are six-coordinate monomers in solution. The solid-state structure of WCl3(=NPh)[OC6H2(CH2NMe2)2-2,6-Me4] (2a), a tungsten(VI) phenylimido phenoxide containing two potentially ortho-chelating (dimethylamino)methyl groups, has been determined. Crystals of 2a are monoclinic, space-group P2(1)/c, with unit-cell dimensions a = 6.893(1) angstrom, b = 15.415(2) angstrom, c = 21.334(2) angstrom, beta = 94.53(1)degrees, and V = 2259.7 angstrom3, Z = 4, R = 0.0353, and R(w) = 0.0259 for 3544 observed reflections and 260 parameters. One of the ortho-CH2NMe2 substituents of the ''pincer-phenolate'' ligand intramolecularly coordinates to the tungsten center trans to the phenylimido group, whereas the second ortho-CH2NMe2 group is not coordinated. This octahedral geometry was also found for 2a in solution, and even at elevated temperatures two resonance patterns were observed for two different ortho-CH2NMe2 substituents indicating that intramolecular exchange between the tertiary amine groups does not occur.