Synthesis, characterization, and fluxional behavior in solution of the salts Et4N+[Me2Ga(N2C5H7)(OCH2CH2X)]M(CO)3− (where N2C5H7 = 3,5-dimethylpyrazolyl, X = NMe2 or SEt, and M = Cr, Mo, or W). X-Ray crystal structure of the W complex with X = NMe2

Abstract

The tricarbonyl anions of Cr, Mo, and W incorporating unsymmetrical tridentate chelating pyrazolyl gallate ligands, [Me2Ga(N2C5H7)(OCH2CH2X)]M(CO)3−, have been isolated as their crystalline Et4N+ salts. 1H nmr and solution infrared studies indicate that the octahedral anions display a facial arrangement of the gallate ligand and the three carbonyl groups. This stereochemistry has been proven definitively for the tungsten complex with X = NMe2 by an X-ray structure determination (see below). Fluxional behavior for the anions in d6-acetone solution has been demonstrated by variable temperature 1H nmr studies and is compared to similar behavior displayed by the neutral molybdenum "allyl" complex, [Me2Ga(N2C3H3)(OCH2CH2NMe2)]Mo(CO)2(η3-C4H7). Crystals of tetraethylammonium [dimethyl(3,5-dimethylpyrazol-1-yl)(2-N,N-dimethylaminoethoxy)gallato-N2,N3,O]tricarbonyltungstate are orthorhombic, a = 11.312(9), b = 33.111(9), c = 7.445(6) Å, Z = 4, space group P212121. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.034 for 2508 reflections with I ≥ 3σ(I). The [Me2Ga(N2C5H7)(OCH2CH2NMe2)]W(CO)3− anion has fac-octahedral coordination geometry with W—O = 2.228(7), W—N(pyrazolyl) = 2.299(8), W—N(amine) = 2.37(1), and W—CO = 1.91 (1)–1.92(1) Å. Keywords: pyrazolyl-gallate complexes, fluxional behavior of Ga–W complexes, crystal structure of Ga–W complex, gallate–tungsten complexes.