The stepwise interaction of [(phen)(Ph 3P)Cu(O 2COH)] with pyrazoles and CO 2: Synthesis and reactivity of copper(I) pyrazolecarboxylates

Abstract

Reactions between [(phen)(Ph 3P)Cu(O 2COH)] ( A, phen = 1,10-phenanthroline) and 3,5-dimethyl- pyrazole (pzH) or pyrazole (PzH) in acetone afford the insoluble copper(I) pyrazolates [Cu(pz)] n or [Cu(Pz)] n and red solutions. The action of CO 2 on these suspensions at low temperature yields new copper(I) pyrazolecarboxylates of formula [(phen)(Ph 3P)Cu(O 2Cpz)(H 2O)] ( 1a) or [(phen)(Ph 3P)Cu(O 2CPz)(H 2O)] ( 1b) respectively. When heated at 80 °C under vacuum as solid, 1a gives [(phen)(Ph 3P)Cu(pz)] ( 2). The latter can be also obtained by N 2 bubbling at 0 °C through suspensions of 1a. At higher temperatures the decarboxylation reaction of 1a is accompanied by the loss of phen and PPh 3, [Cu(pz)] n being recovered as the final product. By stirring an acetone suspension of 1a under a CO 2 atmosphere, free pzH and an orange product analysing as [(phen)(Ph 3P)Cu(O 2COH)] ( 3) were isolated. Complex 3, although having the same stoichiometry as A, was shown to exhibit spectroscopic and some chemical properties quite different from those of A. The action of pzH under an inert atmosphere on 3 (molar ratio pzH/ 3 = 1), allowed the isolation of 1a, without carbon dioxide evolution. Excess phen on polymeric [Cu(pz)] n causes the formation of [(phen)Cu(pz)] 2 ( 4), probably containing a bridging pyrazolate group. The latter has been reacted with CO 2 in the presence of pzH (molar ratio pzH/ 4>1) obtaining the pyrazolecarboxylato complex 5, [(phen)(pzH)Cu(O 2Cpz)]. The neutral pyrazole ligand present in 5, weakly bound to the metal center, can be easily displaced by triphenyl- phosphine, with formation of 1a, or by cyclohexyl- isocyanide. In the latter case, displacement of both pzH and phen has been observed, and the new pyrazolyl complex 6 [(CyNC)Cu(pz)] 2, formed. Gas volumetric and thermogravimetric measurements and IR spectra are reported and discussed. A plausible mechanism by which complexes 1 are formed, is also reported.