Facile C-H bond cleavage via a proton-coupled electron transfer involving a C-H...Cu(II) interaction.
The present study provides mechanistic details of a mild aromatic C-H activation effected by a copper(II) center ligated in a triazamacrocylic ligand, affording equimolar amounts of a Cu(III)-aryl species and Cu(I) species as reaction products. At low temperatures the Cu(II) complex 1 forms a three-center, three-electron C-H...Cu(II) interaction, identified by pulse electron paramagnetic resonance spectroscopy and supported by density functional theory calculations. C-H bond cleavage is coupled with copper oxidation, as a Cu(III)-aryl product 2 is formed. This reaction proceeds to completion at 273 K within minutes through either a copper disproportionation reaction or, alternatively, even faster with 1 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), quantitatively yielding 2. Kinetic studies of both reactions strongly implicate a rate-limiting proton-coupled electron transfer as the key C-H activation step, a mechanism that does not conform to the C-H activation mechanism in a Ni(II) analogue or to any previously proposed C-H activation mechanisms.
Ribas
Xavi
X
Departament de Química, Universitat de Girona, Campus de Montilivi, E-17071 Girona, Catalonia, Spain. xavi.ribas@udg.edu
Calle
Carlos
C
Poater
Albert
A
Casitas
Alicia
A
Gómez
Laura
L
Xifra
Raül
R
Parella
Teodor
T
Benet-Buchholz
Jordi
J
Schweiger
Arthur
A
Mitrikas
George
G
Solà
Miquel
M
Llobet
Antoni
A
Stack
T Daniel P
TD
D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004583:Electrons; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D008024:Ligands; D047028:Macrocyclic Compounds / Q000737:chemistry; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011522:Protons; D013696:Temperature
D006841:Hydrocarbons, Aromatic; D008024:Ligands; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D011522:Protons; D003300:Copper