Ligand and environmental influences on the formation, dynamic behavior, and reactivity of dicopper-dioxygen adducts.

摘要

The reaction of CuI and O2 has proven to be quite diverse in terms of the various types of dioxygen adducts that can form. A multitude of copper-dioxygen species (i.e. superoxo, peroxo, hydroperoxo, etc) have been isolated and fully spectroscopically characterized, and certain structural types are now known for having specific substrate reactivity. One particular subtopic of great interest within the dioxygen chemistry of copper(I), has been the equilibrium between the two isoelectronic structures: mu-eta 2:eta2-"side-on"-peroxo dicopper(II) species ([Cu II2(O2)]2+) and the bis(mu-oxo) dicopper(III) species ([CuIII2(O)2] 2+). Experimental observations and theoretical calculations demonstrate that both species are energetically comparable and have a very low barrier for interconversion.; In Chapter 2, employing a new tridentate ligand, PYAN (N-[2-(pyridin-2-yl)ethyl]- N,N',N'-trimethyl-propane-1,3-diamine), we discuss the solvent influences on the dioxygen reactivity of [Cu(PYAN)(MeCN)][B(C6F5) 4] (1). Depending on the reaction solvent, varying mixtures of side-on peroxo (2Peroxo) and bis(mu-oxo) (2Oxo) species form the reaction of 1 with O2. UV-visible absorption and resonance Raman spectroscopic signatures demonstrate that the equilibrium is highly solvent dependent whereby coordinating solvents increase the ratio of bis(mu-oxo) species formed. Thermodynamic parameters for the equilibrium between 2Peroxo and 2Oxo were found to be, THF: Delta H° = -15.8 kJ/mol, DeltaS° -83 J/K·mol; acetone: DeltaH° ∼ -15.7 kJ/mol, Delta S° ∼ -76 J/K·mol.; In Chapters 3 and 4, we probe the electronic effects on the equilibrium between a mu-eta2:eta2-(side-on)-peroxo [Cu2II(O22-)]2+ and bis(mu-oxo) [Cu2III(O2-) 2] species by variation of ligand para-substituents on pyridyl donor groups of the PYAN ligand.; This study shows that the equilibrium between [Cu2 II(O22-)]2+ and [Cu 2III(O2-)2] can be tuned by ligand design - specifically, more electron donating ligands favor the formation of the bis(mu-oxo) dicopper(III) isomer. We also probe the exogenous substrate reactivity of [Cu2II(O2 2-)]2+ and [Cu2III(O 2-)2] and discover different mechanistic pathways for the oxidative N-dealkylation of dimethylaniline. These substrate reactivity studies implicate the existence of a new type of copper-dioxygen species that is responsible for substrate oxidation.; In Chapter 5, we describe the synthesis of tetradentate ligands comprised of three nitrogen donors and one thioether donor: L1 (2-ethylthio-N,N-bis(pyridin-2yl)methylethanamine) and L2 (2-ethylthio-N,N-bis(pyridin-2-yl)ethylethanamine) and compared their dioxygen chemistry to that of the analogous [Cu(TMPA)(MeCN)]+ and [Cu(PMAP)]+ complexes (TMPA = tris(2-pyridylmethyl)amine; PMAP = bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine). (Abstract shortened by UMI.)