A new tridentate N ligand (TMGtach) consisting of cis,cis-1,3,5-triaminocyclohexane (tach) and three N,N,N',N'-tetramethylguanidino (TMG) groups has been developed to prepare copper complexes with a tetrahedral geometry and a labile coordination site. Treatment of the ligand with CuX (X = Cl and Br) gave copper(II)-halide complexes, [Cu(TMGtach)Cl] (2) and [Cu(TMGtach)Br] (2), the structures of which have been determined by X-ray crystallographic analysis. The complexes exhibit a four-coordinate structure with C symmetry, where the labile halide ligand (X) occupies a position on the trigonal axis. 2 was converted to a methoxido-copper(II) complex [Cu(TMGtach)(OMe)](OTf) (2), also having a similar four-coordinate geometry, by treating it with an equimolar amount of tetrabutylammonium hydroxide in methanol. The methoxido-complex 2 was further converted to the corresponding phenolato-copper(II) (2) and thiophenolato-copper(II) (2) complexes by ligand exchange reactions with the neutral phenol and thiophenol derivatives, respectively. The electronic structures of the copper(II) complexes with different axial ligands are discussed on the basis of EPR spectroscopy and DFT calculations.

At etrahedral Cu II alkylperoxidoc omplex [Cu II (TMG 3 tach)(OOCm)] +(1 OOCm )( TMG 3 tach = {2,2',2''-[(1s,3s,5s)-cyclohexane-1,3,5-triyl]tris-(1,1,3,3-tetramethyl guanidine)}, OOCm = cumyl peroxide) is prepared and characterized by UV/Vis, cold-sprayi onization mass spectroscopy( CSI-MS), resonanceR aman, and EPR spectroscopic methods. Producta nalysis of the self-decomposition reaction of 1 OOCm in acetonitrile (MeCN)i ndicates that the reaction involves OÀOb ond homolytic cleavageo ft he peroxidem oiety with concomitant CÀHb ond activation of the solventm olecule. When an external substrate such as 1,4-cyclohexadiene (CHD)i sa dded, the OÀOb ond homolysis leads to CÀHa ctivationo ft he substrate. Furthermore, the reaction of 1 OOCm with 2,6-di-tert-butylphenol derivatives produces the corresponding phenoxyl radical species (ArOC)t ogether with aC u I complex through ac oncerted proton-electron transfer (CPET)m echanism.D etails of the reactionm echanismsa re explored by DFT calculations.

Structures, physicochemical properties, and reactivity of the whole series of copper(II)−halide complexes (1 X ; X = F, Cl, Br, and I) were examined using a TMG 3 tach tridentate supporting ligand consisting of cis,cis-1,3,5-triaminocyclohexane (tach) and N,N,N′,N′-tetramethylguanidine (TMG). The tach ligand framework with the bulky and strongly electron-donating TMG substituents enforces the copper(II) complexes to take a tetrahedral geometry, as inferred from the electron paramagnetic resonance (EPR) spectra, exhibiting relatively large g z and small A z values. The electronic absorption spectra of 1 X agreed with the simulation spectra obtained by time-dependent density functional theory (TD-DFT) calculations on a slightly distorted tetrahedral geometry. 1 I and 1 Br gradually decomposed to generate the corresponding copper(I) complex and halide radical X • , and in the case of 1 Br , intramolecular hydroxylation of a methyl group of the TMG substituent took place under aerobic conditions, which may be caused by the reaction of the generated copper(I) complex and dioxygen (O 2 ), generating a reactive oxygen species. 1 X except 1 I showed hydrogen atom abstraction (HAA) reactivity toward 1,4-cyclohexadiene (CHD), where 1 F exhibited the highest reactivity with a second-order rate constant as 1.4 × 10 −3 M −1 s −1 at 25 °C. Such an HAA reactivity can be attributed to the higher basicity of F − and/or large bond dissociation free energy of conjugate acid H−F as well as the unstable copper(II) electronic state in the tetrahedral geometry.