Structural evidence for non-reactivity towards dehydroralogenation in a bis-t-butylamine-t-butylimido complex of tungsten(V). The preparation and X-ray crystal structure of [W(NCMe3)Cl3(NH2CMe3)2

Abstract

Abstract Reaction of WCl6 with four equivalents of Me3SiNHCMe3 in benzene gives a low yield of [W(NCMe3)Cl3(NH2CMe3)2] for which the IR spectrum indicates a mer arrangement of metal trichlorides. Further dehydrohalogenation to give an amido ligand does not take place. The structure of the complex was determined by single-crystal X-ray diffraction methods. The crystals are monoclinic, space group C2/c with four molecules in a unit cell of dimensions a = 19.701(3), b = 9.674(2), c = 11.430(2) A and β = 116.40(1)°. The structure was solved by Patterson and Fourier methods and refined to an R value of 0.030. The tungsten atom is in a distorted octahedral environment comprising three mer chloro ligands, two trans t-butylamine ligands and a t-butylimido ligand. A crystallographic two-fold axis passes through Cl(1), W and Nt-butylimido. Observed distances are WNt-butylimido = 1.728(5), WNt-butylamine = 2.230(4), WCl(2)=2.407(1) and WCl(1) = 2.473(2)A. The Cl(2)WNt-butylamine bond angle is 99.0(1)°. The t-butylamine quaternary carbon, C(21), lies close to the equatorial plane thereby reducing methyl group contact with the t-butylimido methyls. Rotation about the N(2)C(21) bond positions the methyl groups C(22) and C(24) above and below the equatorial plane. The hydrogens on N(2) also lie above and below the plane. As a consequence of this arrangement the NH and Cl atoms are unfavourably placed for further dehydrohalogenation to occur.