Intramolecular and intermolecular hydrogen bonding in triphenylphosphine derivatives of copper(I) carboxylates, (Ph3P)2CuO2C(CH2)nCOOH. Role of copper(I) in the decarboxylation of malonic acid and its derivatives
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The air-sensitive copper(I) hydrogen dicarboxylate complexes (Ph3P)2CuO2C(CH2)nCOOH (n = 1,2) and derivatives thereof have been synthesized from 1 equiv of the corresponding dicarboxylic acid and cuprous butyrate. The solid-state structures of these derivatives exhibit quite different hydrogen bonding motifs. That is, the malonate derivative (1) contains a three-coordinate copper(I) center composed of two phosphine ligands and a monodentate carboxylate ligand. The appended carboxylic acid forms a strong intramolecular hydrogen bond with the distal oxygen atom of the carboxylate group bound to copper. On the other hand, the succinate derivative (2) displays a polymeric chain structure in which the carboxylic acid moiety is intermolecularly hydrogen bonded to the neighboring complex. Complex 1 undergoes decarboxylation in tetrahydrofuran solution, whereas complex 2 is stable toward decarboxylation. The phenylmalonic acid analog of complex 1 similarly undergoes carbon dioxide extrusion under milder conditions than 1 and has been shown to proceed via a first-order process. This copper(I) derivative is a very effective catalyst for the decarboxylation of phenylmalonic acid to phenylacetic acid and carbon dioxide. This process has been shown to be first-order in copper(I) complex and zero order in [acid]. The rate constants for CO2 extrusion from the complex and for acid decarboxylation are very similar, an observation consistent with a reaction pathway for the catalytic decarboxylation where the slow step is the extrusion of CO2 from the half-acid copper(I) complex. The role of intra- and intermolecular hydrogen bonding involving complex 1 on the CO2 extrusion process isdiscussed. Crystal data for 1: space group P1, a = 12.949(6) Å, b= 13.162(7) Å, c= 13.253(6) Å, α = 60.73(3)°, β = 85.26(4)°, γ = 68.62(4)°, Z= 2, R = 5.80%. Crystal data for 2: space group P21/n, a = 13.141(2) Å, b = 13.0070(10) Å, c = 20.814(3) Å, β = 100.300(10)°, Z = 4, R = 4.00%. © 1994, American Chemical Society. All rights reserved.
author list (cited authors)
Darensbourg, D. J., Holtcamp, M. W., Khandelwal, B., & Reibenspies, J. H.