Three-Coordinate Copper(II)−Phenolate Complexes

Abstract

The reactions of LCuCl (L = 2,4-bis((2,6-diisopropylphenyl)imido)pentane (L(iPr)), 2,4-bis((2,6-diisopropylphenyl)imido)-3-chloropentane (L(CliPr))) with the phenolates TlOAr (Ar = C(6)H(3)Me(2), C(6)H(4)OMe, C(6)H(4)tBu) and NaOC(6)H(3)(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 < Delta < 28 degrees, where Delta = angleN(1)-Cu-O - angleN(2)-Cu-O). The exception is L(iPr)Cu(OC(6)H(4)tBu), for which X-ray structures at -100 and 25 degrees C 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)(v) symmetry (Delta = 0 degrees ), and upon cooling below the phase transition temperature (-8 +/- 5 degrees C) 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 L(iPr)Cu(OC(6)H(4)tBu) corroborated assignment of phenolate --> Cu(II) LMCT character in the UV-vis spectra. Cyclic voltammetry experiments (THF, 0.5 M NBu(4)PF(6)) 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 and 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 L(iPr)CuCl with NaOC(6)H(3)(tBu)(2) no Cu(II)-phenolate was observed. Instead, a Cu(I) complex was generated quantitatively by trapping with added isocyanide, [L(iPr)CuNC(C(6)H(3)Me(2))], 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).

New Cu(II) complexes with polydentate chelating Schiff base ligands: Synthesis, structures, characterisations and biochemical activity studies

“…The UV absorption bands observed at 385, 388 and 395 nm for complexes 1, 2 and 3, respectively can be attributed to the ligand to Cu(II) charge transfer transition (LMCT) [26,27]. Those very weak low-intensity absorption bands associated with d − d transitions at 670, 675 and 676 nm may be assigned for to a Cu(II) d-d transition [26][27][28][29] for 1, 2 and 3, respectively and support the five-coordinated geometry around copper(II) ions with the CuN 4 chromophoric group.…”

Effects of Thioether Substituents on the O2 Reactivity of β-Diketiminate−Cu(I) Complexes: Probing the Role of the Methionine Ligand in Copper Monooxygenases

“…28 Other β-diketiminates with smaller arene and/or backbone substituents yield chloride-bridged dimeric structures, [LCu(μ-Cl)] 2 , in the solid state. 29 The thioether sulfur atom is bound to the Cu(II) center in both complexes, with a Cu-S bond distance of 2.3793(11) Å in Me 2 L iPr,SMe CuCl and 2.5941(9) Å in Me 2 L iPr,SPh CuCl, which contains the more bulky phenyl group on the thioether arm. These Cu(II)-thioether bond distances fall within the range of such distances reported previously (2.28-2.91 Å, avg.…”

Synthesis and Structural Characterization of β-Diketoiminate Complexes Containing Three-Coordinate Zinc and Copper Atoms

“…In contrast, Tolman et al recently reported the preparation of a copper(I) compound with the β-diketoiminate ligand in which the copper formed a six-membered CuN 2 C 3 ring. [35] A possible explanation for this different behaviour might be that the soft Cu I prefers coordination with the soft carbon atom while the harder Cu II prefers coordination with the harder nitrogen atoms. The CuϪC bond length of 2.089(6) Å is similar to those found in the literature.…”