A comparative study of the speciation in methanol solution and activity in the oxidative coupling of 2,6-di-tert-butylphenol presented by the complexes: Copper(II)-N,N 0 -di-tert-butylethylenediamine-halogen and some copper(II)-diamine-halogen complexes José J.N. Segoviano-Garﬁas a , Guillermo Mendoza-Díaz b , Rafael Moreno-Esparza c,⇑ a Departamento de Ingeniería Bioquímica, Instituto Tecnológico Superior de Irapuato (ITESI), Carretera Irapuato-Silao km. 12.5, Irapuato, Gto. 36821, Mexico b Departamento de Ingeniería Química, Electrónica y Biomédica, División de Ciencias e Ingenierías, Campus León, Universidad de Guanajuato, Lomas del Bosque No. 103, Col. Lomas del Campestre, León, Gto. 37150, Mexico c Facultad de Química (UNAM), Ediﬁcio B. Av. Universidad 3000, Coyoacán, México D. F. 04510, Mexico article info Article history: Received 14 September 2013 Received in revised form 27 November 2013 Accepted 6 December 2013 Available online 15 December 2013 Keywords: Copper(II) complexes Catalysis Oxidative coupling Speciation Solution equilibria Nonaqueous solvents abstract The oxidative coupling of 2,6-di-methylphenol is an industrial reaction catalyzed by the copper(II)-di- tert-butylethylenediamine-dibromo complex. In order to get more insight about the behavior of the N,N 0 -dialkyl-diamine cupric complexes and the halide effect on the catalyic activity, a spectrophotomet- ric study of the speciation in methanol of copper(II) coordinated with N,N 0 -di-tert-butylethylenediamine or 1,5-pentanediamine and their respective halides chloride and bromide, was carried out at 303 K. Formation constants and individual calculated electronic spectra of all species, were obtained. With the purpose to compare the catalytic activity of these complexes with other diamine complex systems in the oxidative coupling of 2,6-di-methylphenol, the oxidative coupling of 2,6-di-tert-butylphenol was used as a catalytic model system. Solutions with the most abundant complexes were tested and correlated to their catalytic activity. These data are compared with several studies of the copper(II) diamine complexes, with or without chlo- ride or bromide ions. The catalytic activity in the oxidation of 2,6-di-tert-butylphenol was monitored in methanol solution, following the corresponding quinone formation, at 418 nm (e = 3.95x10 4 L mol 1 - cm 1 at 303 K). The obtained formation constants of the copper(II)-di-tert-butylethylenediamine system are: log b 110 = 4.13 ± 0.12, log b 120 = 6.56 ± 0.12. For the ternary copper(II)-di-tert-butylethylenediamine chloro or bromo systems are: log b 111 = 6.10 ± 0.09 and log b 111 = 6.69 ± 0.04, respectively. While of the copper(II)-1,5-pentanediamine system are log b 110 = 3.32 ± 0.11, log b 210 = 5.73 ± 0.10. Kinetic studies of the oxidative coupling of 2,6-di-tert-butylphenol catalyzed by the copper(II)-diamine systems indicate that the copper(II)-1,5-pentanediamine presents low activity, while the copper(II)-N, N 0 -di-tert-butylethylenediamine shows a very similar activity to the copper(II)-1,4-butanediamine system reported earlier. Further studies are needed in order to explain the reasons why the complexes generated with this two different diamines display such similar activity. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Due to their important industrial applications, the oxidative polymerization of phenols has been a reaction widely studied [1]. This reaction is especially important, when 2,6-di-methylphenol is used as substrate, to obtain the poly(2,6-di-methyl-1,4-pheny- lene oxide). This polymer, when blended with polystyrene, gener- ate the noryl resin. This blend is widely used as engineering plastics. In 2003 were reported sales approaching at one billion dollar per year [1]. Several complexes has been used as catalysts in this reaction, and copper(II)-di-tert-butylethylenediamine-di- bromo complex was found to be the best [2–4]. Nevertheless, the reasons why this complex is so active remain unclear. After these developments, several reaction paths has been pro- posed for the oxidative coupling of 2,6-di-methylphenol. Although the mechanism which drives this reaction is not well understood, most of the research groups consider that a phenoxyl radical is pro- duced in a mononuclear copper species, followed by their coupling [1,5]. However in contrast, few other groups believe that a biomi- metic dinuclear copper species (with an active site like a laccase or tyrosinase) is involved in the oxidative coupling [5,6]. Supporting this last mechanism, Stack and co-workers have re- ported that [(dbed)Cu II (l-g 2 :g 2 -O 2 )Cu II (dbed)] 2+ (dbed = N,N’-di- 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.12.009 ⇑ Corresponding author. Tel.: +52 (55)5622 3793; fax: +52 (55)5616 2010. E-mail addresses: moresp@unam.mx, rmorenoe@me.com (R. Moreno-Esparza). Inorganica Chimica Acta 411 (2014) 148–157 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica