A series of Cu(I) and Cu(II) complexes of a variety of beta-diketiminate ligands (L(-)) with a range of substitution patterns were prepared and characterized by spectroscopic, electrochemical, and, in several cases, X-ray crystallographic methods. Specifically, complexes of the general formula [LCuCl](2) were structurally characterized and their magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-temperature SQUID magnetization measurements on a powder sample. UV-vis spectra indicated reversible dissociation to 3-coordinate monomers LCuCl in solution at temperatures above -55 degrees C. The Cu(I) complexes LCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with E(1/2) values between +300 and +520 mV versus NHE (cyclic voltammetry, MeCN solutions). These complexes were highly reactive with O(2), yielding intermediates that were identified as rare examples of neutral bis(mu-oxo)dicopper complexes on the basis of their EPR silence, diagnostic UV-vis absorption data, and O-isotope-sensitive resonance Raman spectroscopic features. The structural features of the compounds [LCuCl](2) and LCu(MeCN) as well as the proclivity to form bis(mu-oxo)dicopper products upon oxygenation of the Cu(I) complexes are compared to data previously reported for complexes of more sterically hindered beta-diketiminate ligands (Aboelella, N. W.; Lewis, E. A.; Reynolds, A. M.; Brennessel, W. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 10600. Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270). The observed structural and reactivity differences are rationalized by considering the steric influences of both the substituents on the flanking aromatic rings and those present on the beta-diketiminate backbone.

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A series of CuII and ZnII complexes with new ligands having either one or two substituted phenolates appended to the 1,4,7-triazacyclononane frame were prepared and characterized by optical absorption, EPR, NMR, and/or resonance Raman spectroscopy, cyclic voltammetry, and, in eight cases, X-ray crystallography. Features of the active site geometries of the CuII−tyrosinate forms of galactose and glyoxal oxidases (GAO and GLO) were modeled by these complexes, including the binding of a redox-active phenolate and an exogenous ligand (Cl-, CH3CO2 -, or CH3CN) in a cis-equatorial position of a square pyramidal metal ion. The role of the unique ortho S−C covalent bond between a cysteine (C228) and the equatorial tyrosinate (Y272) in the proteins was probed through an examination of the optical absorption and electrochemical properties of sets of similar complexes comprised of phenolate ligands with differing ortho substituents, including thioether groups. The o-alkylthio unit influences the PhO- → CuII LMCT transition and the MII−phenolate/MII−phenoxyl radical redox potential, but to a relatively small degree. Electrochemical and chemical one-electron oxidations of the CuII and ZnII complexes of ligands having tert-butyl protecting groups on the phenolates yielded new species that were identified as novel MII−phenoxyl radical compounds analogous to the active CuII−tyrosyl radical forms of GAO and GLO. The MII−phenoxyl radical species were characterized by optical absorption, EPR, and resonance Raman spectroscopy, as well as by their stoichiometry of formation and chemical reduction. Notable features of the CuII−phenoxyl radical compounds that are similar to their protein counterparts include EPR silence indicative of magnetic coupling between the CuII ion and the bound radical, a band with λmax ≈ 410 nm (ε ≈ 3900 M-1 cm-1) in UV−vis spectra diagnostic for the phenoxyl radical, and a feature attributable to the phenoxyl radical C−O vibration (ν7a) in resonance Raman spectra. Similar Raman spectra and electrochemical behavior for the ZnII analogs, as well as an isotropic signal at g = 2.00 in their X-band EPR spectra, further corroborate the formulations of the MII−phenoxyl radical species.

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).

We have prepared the yttrium(III) alkoxides [(L Me2 )(HL Me2 )Y3(OCH2C6H5)4] (3) and [(S-L Me )Y]2‚2(HOCH2C6H5) (1‚2BnOH) through treatment of two previously developed complexes with benzyl alcohol. Complex 3 possesses a novel cluster structure that appears to be retained in solution and is capable of polymerizing both DL-lactide (LA) and -caprolactone (CL). The polymerizations are controlled as evidenced by the linear nature of molecular weight versus conversion plots and [M]/[3] ratios. The kinetics of LA polymerization using 3 are first-order with respect to the monomer at low [LA]/[Y] ratios. The polymerization of CL is zero-order in monomer. Complex 1‚2BnOH possesses a dimeric structure previously seen in both the solid and solution state. However, the added presence of benzyl alcohol moieties in 1‚2BnOH increases the rate of LA polymerization and allows for control over the molecular weights of isolated polylactide, a feature unseen in earlier reported dimers. The complex 1‚2BnOH is not active for the polymerization of CL.

The reaction of 2,6-diisopropylaniline-based bis-imine ligands (4, 9) with M(CH2Ph)4 (M = Hf, Zr) led to formation of novel imino−amido tribenzyl complexes via migratory insertion of a benzyl group into a CN bond. Imino−amido complexes were found to undergo unprecedented dibenzyl elimination to form ene−diamido complexes. Imino−amido complexes were found to be active ethylene polymerization catalysts.

The Cu(I)-phenolate complexes (1)LCu and (2)LCu and the Cu(I)-phenol complex [H(2)LCu(CNC(6)H(3)Me(2))]BArF(4) were prepared and structurally characterized by X-ray crystallography, where (1)L(-) and (2)L(-) are ligands comprised of a 2,4-di- tert-butylphenolate linked to 1-isopropyl-1,5-diazacyclooctane or 1,4-diisopropyl-1,4,7-triazacyclononane, respectively. The reduced galactose oxidase (GAO) structural models (1)LCu and (2)LCu were found to be highly reactive with O(2), and through combined stopped-flow kinetic and EPR, UV-vis, and resonance Raman spectroscopic studies of the oxygenation of (2)LCu at low temperature, new intermediates relevant to those postulated for the active site oxidation step of the GAO catalytic cycle were identified. The oxygenation was shown by kinetics experiments to proceed via initial binding of O(2) to yield a green, unusually thermodynamically stable 1:1 adduct, (2)LCu(O(2)). Symmetric (eta(2)) binding of a superoxo ligand was indicated by oxygen-isotope-sensitive features in resonance Raman spectra obtained in batch experiments; peaks at nu((16)O(2))=1120 cm(-1), nu((18)O(16)O)=1093 cm(-1), and nu((18)O(2))=1058 cm(-1) were assigned as O-O stretching vibrations. These data represent the first experimental evidence for such superoxide coordination in complexes of tetradentate tripodal ligands and provide new precedent for how O(2) may bind at the reduced GAO active site. The 1:1 Cu/O(2) adduct subsequently evolves into a metastable purple species that is only observable under conditions of substoichiometric O(2). The kinetics of formation of this transient species are second order overall (rate= k'(2)[(2)LCu(O(2))][(2)LCu]). It exhibits an absorption band with lambda(max)=565 nm (epsilon=17900 M(-1) cm(-1)) and multiple oxygen-isotope-sensitive nu(Cu-O) and nu(O-O) features in the respective regions 500-550 cm(-1) and 700-850 cm(-1) in Raman spectra, with excitation-wavelength-dependent intensities that correlate with the 565 nm absorption feature. On the basis of the combined data available, the presence of multiple isomeric peroxodicopper species in the transient purple solution is postulated.

New hafnium and zirconium imino-amido complexes containing trimethylethylidene bridging groups are reported. Investigation into the thermal stability of these complexes revealed that they undergo facile rearrangement of the ligand backbone at 80 °C to produce isomeric imino-amido complexes. Mechanistic experiments and DFT calculations indicate that this isomerization reaction proceeds via a direct 1,2-methyl shift rather than a multistep mechanism involving the metal center. The initial imino-amido complexes (pre isomerization) exhibit high ethylene/1-octene copolymerization activities and generate polymers with very high molecular weights and relatively low comonomer contents. On the other hand, the isomerized complexes display significantly lower polymerization activities and give polymers with lower molecular weights and broad molecular weight distributions, indicative of multisite behavior.