Hand in Hand: Experimental and Theoretical Investigations into the Reactions of Copper(I) Mono‐ and Bis(guanidine) Complexes with Dioxygen

Abstract

Mono-and bis(guanidine) ligands stabilise bis-μ-oxido dicopper(III) complexes. Here, the formation of these complexes has been investigated in detail by means of lowtemperature stopped-flow techniques for the monoguanidine 2-[3-(dimethylamino)propyl]-1,1,3,3-tetramethylguanidine (TMGdmap) and the related bis(guanidine) 1,3-bis(N,N,N′,N′-tetramethylguanidino)propane (btmgp). Low-temperature IR studies in solution support the formation of bis-μ-oxido complexes. For both systems, no intermediates on the pathways to the bis-μ-oxido complexes could be detected; this has been explained through extensive DFT calculations. In the first step,

Oxygen Activation by Copper Complexes with an Aromatic Bis(guanidine) Ligand

“…An explanation for this phenomenon could be the already decaying Cu III intermediate because of the very fast decay rate of the complexes, even at temperatures below 223 K. When comparing the formation rates of both complexes, it appears that the formation of O1 is faster at 193 K, but this trend is not confirmed through measurements at other temperatures. Compared to the O species of the bis(guanidine) btmgp (0.88 s –1 ), the O species formation of O1 and O3 is considerably faster …”

“…The formation of the Cu III species from a bis(guanidine) ligand follows a multistep process. With btmgp the reduction of oxygen to a superoxide is rate‐determining and a reaction of first order . In this case, the formation (vide supra) is so fast, that no conclusion on the mechanism can be drawn.…”

“…Bis(guanidine) ligands are particularly interesting because of their flexibility in the synthesis of different structures by combining guanidine units with different spacers . Bis(tetramethylguanidino)propane (btmgp) is a basic bis(guanidine) ligand, which has been studied in its structural parameters and oxygen activation abilities in many studies , . Most bis(guanidine)copper complexes form a bis(µ‐oxido) species, and some are active in oxidation catalysis , .…”

“…Most bis(guanidine)copper complexes form a bis(µ‐oxido) species, and some are active in oxidation catalysis , . To understand the mechanism and efficiency of the bis(guanidine)–oxido intermediate species, the formation and decay rates are evaluated with different spectroscopic methods, such as UV/Vis, stopped‐flow and fluorescence spectroscopy , . An extremely stabile Cu 2 O 2 species, based on a sterically highly demanding bis(guanidine) ligand system, was synthesised and analysed accordingly.…”

Catalytic Aerobic Phenol Homo‐ and Cross‐Coupling Reactions with Copper Complexes Bearing Redox‐Active Guanidine Ligands

“…[53,54] For prolongedr eaction times the bands vanished again, signaling decompositiono ft his complexe ven at À80 8C. The evolution of an intense band at 406 nm (e = 3300 Lmol À1 cm À1 )w as observedi nt he UV/Vis spectra,w ith the maximum absorbance being reached after 290 s. The wavelength and the high extinction coefficient are characteristic for Cu 2 O 2 complexes,a nd especially comparable to previously reported Cu 2 O 2 complexes with guanidinel igands.…”