Mono- and tetra-nuclear copper complexes bearing bis(imino)phenoxide derived ligands: catalytic evaluation for benzene oxidation and ROP of epsilon-caprolactone

Complexes of the type [Cu(L)2] (1) and [Cu4L2(μ4−O)(OAc)4] (2) have been obtained from the reaction of the phenoxydiimine 1,3-(2,6-R22C6H3N=CH)2-5-R1C6H2OH-2 (LH) (where R1 = Me, tBu, Cl; R2 = Me, iPr) with copper(II) acetate [Cu(OAc)2]; changing the molar ratio of the reactants affords 10 differing amounts of 1 or 2. Reaction of the parent dialdehyde [1,3-(CHO)2-5-MeC6H2OH-2] with [Cu(OAc)2] in the presence of Et3N afforded, following work-up, a polymeric chain (3) comprising {[Cu2(OAc)4]OAc}n, HNEt3 and MeCN. The crystal structures of 1 (R1 = Me, R2 = iPr 1a; R1 = Cl, R2 = iPr 1b), 2 (R1 = Me, R2 = Me 2a; R1 = Me, R2 = iPr 2b; R1 = tBu, R2 = Me 2c; R1 = Cl, R2 = Me 2d; R1 = Cl, R2 = iPr 2e; R1 = tBu, R2 =iPr 2f) and 3 are reported (synchrotron radiation was necessary for 3). The 15 magnetic properties of the cluster 2b are presented. Complexes of type 2 and 3 were screened for the ring opening polymerization (ROP) of ε-caprolactone, with or without benzyl alcohol present, under a variety of conditions, however only trace polymer was isolated. The electrochemistry of all complexes was also investigated, together with their ability to catalyze benzene oxidation (using hydrogen peroxide); although low conversions were observed, the tetra-nuclear complexes exhibited excellent selectivity.