Synthesis, kinetics and mechanism of the reaction of a quasi-aromatic copper(II) complex, [Cu(PnAO)-6H](0), with aromatic aldehydes

The quasi-aromatic metal complex (1,1,2,8,9,9-hexamethy]-4,6-dioxa-5-hydro- 3,7,10. 14-tetraazacyclotetradecane-2,7,10,12-tetraene)copper(II), [Cu(PnAO )-6H](0) (AH), was synthesized. Reactions of AH were studied spectrophotome trically in acidic media IpH = 1 similar to 2, EtOH:H2O = 1:4 v/v) with par a-substituted benzaldehydes (ald). The Cu,2N,3C quasi-aromatic heterocyclic ring in AH is highly reactive at the central-aromatic-carbon atom. Cl2, to most aldehydes. A novel parallel, competitive a nd consecutive second-orde r reaction mechanism is proposed, To obtain the rate constants following th is mechanism, the Gauss-Newton-Marquardt and Runge-Kutta methods were emplo yed. Consistent results were obtained. Effects of acidity, solvent, tempera ture and substituent R (R=H, CH3, OCH3, Cl) of the aromatic aldehydes on th e reaction rate constants were studied. The results support the proposed SN 2 mechanism. A linear free energy relationship between the rate constant k( 1), and the Hammett parameters for the substituted benzaldehydes as well th e activation parameters are presented. (C) 2000 John Wiley & Sons, Inc.