INTRAMOLECULAR AND INTERMOLECULAR HYDROGEN-BONDING IN TRIPHENYLPHOSPHINE DERIVATIVES OF COPPER(I) CARBOXYLATES, (PH(3)P)(2)CUO2C(CH2)(N)COOH - ROLE OF COPPER(I) IN THE DECARBOXYLATION OF MALONIC-ACID AND ITS DERIVATIVES

The air-sensitive copper(l) hydrogen dicarboxylate complexes (Ph(3)P)(2)CuO2C(CH2)(n)COOH (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 is discussed. Crystal data for 1: space group P ($) over bar 1, a 12.949(6) Angstrom A, b = 13.162(7) Angstrom A, c 13.253(6) Angstrom A, alpha = 60.73(3)degrees, beta = 85.26(4)degrees, gamma = 68.62(4)degrees, Z = 2, R = 5.80%. Crystal data for 2: space group P2(1)/n, a = 13.141(2) Angstrom A, b =13.0070(10) Angstrom A, c = 20.814(3) Angstrom A, beta = 100.300(10)degrees, Z = 4, R = 4.00%.