Three-coordinate copper(II)-phenolate complexes

The re actions of LCuCl (L = 2,4-bis((2,6-diisopropylphenyl)imido)pentane (L-iPr), 2,4-bis((2,6-diisopropylphenyl)iniido)-3-chloropentane (L-CliPr)) with the phenolates TlOAr (Ar = C6H3Me2, C6H4OMe, C(6)H(4)tBu) and NaOC6H3(tBu)(2) were explored. Novel three-coordinate Cu(II)-phenolates, LCuOAr, were isolated from the reactions with the thallium phenolates and were characterized by X-ray crystallography and spectroscopy (UV-vis, EPR). The complexes feature short Cu-O(phenolate) distances (average Cu-O = 1.81 A) and, with one exception, irregular N-Cu-O(phenolate) angles that differ within each compound (15 degrees < Angstrom < 28 degrees, where Delta = <N-I-Cu-O-<N-2-Cu-O). The exception is (LCu)-Cu-iPr(OC(6)H(4)tBu), for which X-ray structures. at -100 and 25 degreesC differed due to an unusual reversible phase change with nonmerohedral twinning (2:1 ratio) in the low-temperature form. The high-temperature form has local C-2 nu, symmetry (Delta = 0 degrees), and upon cooling below the phase transition temperature (-8 +/-5 degreesC), lateral movement of the phenolate ligand (Delta = 17.6 degrees) and rotation of the phenolate plane by 10.7 degrees occurs. Resonance Raman spectroscopic data acquired for (LCu)-Cu-iPr(OC6H4tBu) corroborated assignment of phenolate --> Cu(II) LMCT character in the UV-vis spectra. Cyclic voltammetry experiments (THF, 0.5 M NBu4PF6) revealed negative E-1/2 values for the Cu(II)/Cu(I) couples relative to NHE, consistent with enhanced stabilization of the Cu(II) state by both the strongly electron donating beta -diketiminate ligand an. d the phenolates. Although thermally stable, the Cu(II) -phenolates are unusually reactive with dioxygen, albeit to give product(s) that have yet to be identified. In the reaction of (LCuCl)-Cu-iPr with NaOC6H3(tBu)(2) no Cu(II)-phenolate was observed. Instead, a Cu(I) complex was generated quantitatively by trapping with added isocyanide, [(LCuNC)-Cu-iPr(C6H3Me2)], along with 3,3',5,5'-tetra-tert-butyl-4,4'-dibenzoquinone and 2,6-di-tert-butylphenol in 27 +/- 3% and 46 +/- 6% yields, respectively, corresponding to the overall reaction 4L(iPr)Cu(II)Cl + 4NaOAr --> 4L(iPr)Cu(I) + 4NaCl + dibenzoquinone + 2(phenol).