Bis(μ-oxo) Dicopper(III) Species of the Simplest Peralkylated Diamine: Enhanced Reactivity toward Exogenous Substrates

Peng Kang†, Elena Bobyr†, John Dustman†, Keith O. Hodgson*†‡, Britt Hedman*‡, Edward I. Solomon*†‡, and T. Daniel P. Stack*†
† Department of Chemistry, Stanford University, Stanford, California 94305, United States
‡ Stanford Synchrotron Radiation Lightsource, SLAC, Stanford University, Menlo Park, California 94025, United States
Inorg. Chem., 2010, 49 (23), pp 11030–11038
DOI: 10.1021/ic101515g
Publication Date (Web): October 28, 2010
Copyright © 2010 American Chemical Society
*To whom correspondence should be addressed. E-mail: hodgson@ssrl.slac.stanford.edu (K.O.H.), hedman@ssrl.slac.stanford.edu (B.H.), edward.solomon@stanford.edu (E.I.S.), stack@stanford.edu (T.D.P.S.).
Inorganic Chemicals and Reactions

Abstract

Abstract Image

N,N,N′,N′-tetramethylethylenediamine (TMED), the simplest and most extensively used peralkylated diamine ligand, is conspicuously absent from those known to form a bis(μ-oxo)dicopper(III) (O) species, [(TMED)2Cu(III)2(μ2-O)2]2+, upon oxygenation of its Cu(I) complex. Presented here is the characterization of this O species and its reactivity toward exogenous substrates. Its formation is complicated both by the instability of the [(TMED)Cu(I)]1+ precursor and by competitive formation of a presumed mixed-valent trinuclear [(TMED)3Cu(III)Cu(II)2(μ3-O)2]3+ (T) species. Under most reaction conditions, the T species dominates, yet, the O species can be formed preferentially (>80%) upon oxygenation of acetone solutions, if the copper concentration is low (<2 mM) and [(TMED)Cu(I)]1+ is prepared immediately before use. The experimental data of this simplest O species provide a benchmark by which to evaluate density functional theory (DFT) computational methods for geometry optimization and spectroscopic predictions. The enhanced thermal stability of [(TMED)2Cu(III)2(μ2-O)2]2+ and its limited steric demands compared to other O species allows more efficient oxidation of exogenous substrates, including benzyl alcohol to benzaldehyde (80% yield), highlighting the importance of ligand structure to not only enhance the oxidant stability but also maintain accessibility to the nascent metal/O2 oxidant.

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History

  • Published In Issue December 06, 2010
  • Article ASAPOctober 28, 2010
  • Received: July 28, 2010

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