Amino Acid Derivatives of Tungsten Carbonyl. Structure and Reactivity Investigations of Zerovalent Tungsten Glycine Derivatives
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The amino acid derivatives of tongsten(0) [Et4N][W(CO)4(O2CCH2NH2)] (1), [Et4N][W(CO)4(O2CCH2NHMe)] (2), and [Et4N][W(CO)4(O2CCH2NMe2)] (3) have been synthesized from the reaction of W(CO)5THF with the tetraethylammonium salt of the corresponding α-amino acid in a tetrahydrofuran solution. The glycine derivative, complex 1, is highly soluble in water. The complexes have been characterized in solution by infrared and NMR spectroscopies and in the solid state by X-ray crystallography. Complex 1 crystallized in the orthorhombic space group P212121 with a = 10.408(14) Å, b = 13.155(11) Å, c = 13.657(10) Å, V= 1870(3) Å3, and dcalc = 1.777 g cm−3, for Z = 4, from hexane/THF. Complex 2 crystallized in the monoclinic system, space group P21/c, with a = 14.012(5) Å, b = 10.335(2) Å, c = 14.728(4) Å, β = 112.28(2)°, V = 1973.5(8) Å3, and dcalc = 1.731 g cm−3, for Z = 4, from hexane/THF. Complex 3 crystallized in the triclinic space group P1 with a = 11.586(5) Å, b= 11.711(6) Å, and c = 15.068(7) Å, α = 90.01(4)°, β = 96.28(4)°, γ = 90.27(4)°, V = 2032(2) Å3, and dcalc = 1.727 g cm−3, for Z = 4, from a hexane-layered THF solution of 3. The geometry of the anion in each case is that of a slightly distorted octahedral arrangement of four carbonyl ligands and a puckered five-membered glycinate chelate ring. Complexes 1 and 2 exihibit intermolecular hydrogen-bonding interactions with N· ·· distances of 2.746 and 2.826 Å, respectively. Weaker hydrogen-bonding interactions in solution with THF and CH3CN are noted as well. Although the coordination environments about the tungsten centers of the three glycinate derivatives are essentially the same, the CO lability is greatly enhanced in complexes 1 and 2 as compared to complex 3. This CO labilization in complexes 1 and 2 is attributed to a solvent-assisted removal of a proton from the amine ligand leading to a substitutionally labile amide transient species. Deprotonation of the amine ligand is aided by the π-donation of the thus formed amide ligand to the coordinatively unsaturated metal center in the reactive intermediate. © 1994, American Chemical Society. All rights reserved.
author list (cited authors)
Darensbourg, D. J., Atnip, E. V., Klausmeyer, K. K., & Reibenspies, J. H.