Copper Chemistry of β-Diketiminate Ligands:  Monomer/Dimer Equilibria and a New Class of Bis(μ-oxo)dicopper Compounds

Abstract

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.

Ligand Structural Effects on Cu2S2 Bonding and Reactivity in Side-On Disulfido-Bridged Dicopper Complexes

“…47 We postulate that this congestion is the underlying cause of the relatively longer Cu-S and Cu-Cu distances and the decreased level of S-S bond activation in their disulfido complexes. These steric effects for c and j have precedent in Cu/O 2 chemistry, as reactions of O 2 with Cu(I) complexes of these ligands yield 1:1 adducts 42b,48 instead of bis(μ-oxo) complexes seen with a,b,d-g. 45 Preliminary investigation of the reactivity of one of the disulfido complexes (2h) showed some similarity to that previously reported for 2 (L = Me 2 NPY2), 18 although significant differences also were seen (Scheme 2). Thus, S-atom transfer to PPh 3 with trapping of the resulting Cu(I) sites by excess phosphine was observed for both, but the results with only 2 equiv.…”

Nickel (II) complexes supported by a fluorinated β‐diketiminate backbone ligand: synthesis, catalytic activity toward norbornene polymerization, and the oxygenated species

“…42,43 Our experiments indicate that these nickel complexes offer similar behavior. X-ray analyses indicates the oxygenated species is indeed the bis(µ-OH)dinickel (II, II) of complex 3 (Fig.…”

Heterobimetallic Activation of Dioxygen: Characterization and Reactivity of Novel Cu(I)−Ge(II) Complexes

“…GeCl 2 ·dioxane and benzil were purchased from Aldrich Chemical Corp. and used as received. The complexes L R2 Cu (MeCN) (R = Me, Et, iPr; L R2 = β-diketiminate derived from respective 2-(2,6-di-R-phenyl)amino-4-(2,6-dimethylphenyl)imino-2-pentene), 10 …”