The Phenoxy/Phenol/Copper Cation: A Minimalistic Model of Bonding Relations in Active Centers of Mononuclear Copper Enzymes

Abstract

The "bare" complex [Cu(PhOH)(PhO)](+) with a phenol (PhOH) and a phenoxy (PhO) ligand bound to copper is studied both experimentally and computationally. The binding energies and structure of this complex are probed by mass spectrometry, infrared multi-photon dissociation, and DFT calculations. Further, the monoligated complexes [Cu(PhO)](+) and [Cu(PhOH)](+) are investigated for comparison. DFT calculations on the [Cu(PhOH)(PhO)](+) complex predict that a phenolate anion interacts with copper(II) preferentially through the oxygen atom, and the bonding is associated with electron transfer to the metal center resulting in location of the unpaired electron at the aromatic moiety. Neutral phenol, on the other hand, interacts with copper preferentially through the aromatic ring. The same arrangements are also found in the monoligated complexes [Cu(PhO)](+) and [Cu(PhOH)](+). The calculations further indicate that the bond strength between the copper atom and the oxygen atom of the phenoxy radical is weakened by the presence of neutral phenol from 2.6 eV in bare [Cu(PhO)](+) to 2.1 eV in [Cu(PhOH)(PhO)](+).

Molecular Complexes of Simple Anions with Electron‐Deficient Arenes: Spectroscopic Evidence for Two Types of Structural Motifs for Anion–Arene Interactions

“…Relative abundances of fragment ions display an energy dependence that can be modeled by a sigmoid function and phenomenological appearance energies may be derived from linear extrapolation of the rise of the sigmoid curves to the baseline. [65,[70][71][72] The curves were found not to be affected to any significant degree by varying the pressure in q2 (1.5-5.5 10 À5 mbar), which suggests that the CID experiments are not perturbed by multiple collision events.…”

Theory meets experiment: Gas-phase chemistry of coinage metals

“…In this case, tyrosine takes an active role in the electron-transfer processes and is present as a radical, which can serve as an electron shuttle. The investigation of bonding relations between copper and phenolate, as a model for tyrosinate, revealed that phenolate interacts with copper via the oxygen atom, as expected [166][167][168][169]. Interestingly, the gas-phase study shows that the formation of the Cu O bond is associated with electron transfer from phenolate to copper so that the resulting complex (PhO)Cu + corresponds to copper(I) bound to the phenoxy radical [166,170].…”

“…Interesting to note in this context is that the bonding between copper(I) and neutral phenol moiety does not take place via the oxygen atom, but copper is rather bound to the aromatic ring [176][177][178][179][180]. This remarkable feature was proved by calculations using density functional theory and infrared multiphoton dissociation (IRMPD) spectra of mass-selected ions [166], where the combination of these two modern techniques which is one of the most powerful tool available for the structural elucidation of gaseous ions [15,[181][182][183][184].…”

Mechanistic Studies on the Copper‐Catalyzed Hydrosilylation of Ketones

“…Moreover, recent calculations performed for various isomers of [Cu(PhOH)] + did not reveal severe discrepancies with the results obtained at the DFT and CCSD(T) levels. [27] As far as the reaction mechanism is concerned, we checked (for 1a) our previous suggestion that a pentacoordinate silicon intermediate of type B or a copper(III) intermediate like C might be involved (Scheme 4). We did not succeed in optimizing such intermediates.…”