Chromium(0) and Molydenum(0) Complexes with a Pyridyl-Mesoionic Carbene Ligand: Structural, (Spectro)electrochemical, Photochemical, and Theoretical Investigations

Abstract

This work reports on the synthesis and in-depth electrochemical and photochemical characterization of two chromium(0) and molydenum(0) metal complexes with bidentate pyridyl-mesoionic carbene (MIC) ligands of the 1,2,3-triazol-5ylidene type and carbonyl coligands. Metal complexes with MIC ligands have turned out to have very promising electrocatalytic and photochemical properties, but examples of MIC-containing complexes with early-transition-metal centers remain extremely rare. The electrochemistry of these new MIC complexes was studied by cyclic voltammetry and especially spectroelectrochemistry in the IR region consistent with a mainly metal-centered oxidation, which is fully reversible in the case of the chromium(0) complex. At the same time, the two reduction steps are predominantly ligandcentered according to the observed near-IR absorbance, with the first reduction step being reversible for both systems. The results of the electron paramagnetic resonance studies on the oxidized and reduced species confirm the IR spectroelectrochemistry experiments. The photochemical reactivity of the complexes with a series of organic ligands was investigated by time-resolved (stepscan) Fourier transform infrared (FTIR) spectroscopy. Interestingly, the photoreactions in pyridine and acetonitrile are fully reversible with a slow dark reverse reaction back to the educt species over minutes and even hours, depending on the metal center and reagent. This reversible behavior is in contrast to the expected loss of one or several CO ligands known from related homoleptic as well as heteroleptic M(CO) 4 L 2 α-diimine transition-metal complexes.

Electrochemically Driven Reduction of Carbon Dioxide Mediated by Mono‐Reduced Mo‐Diimine Tetracarbonyl Complexes: Electrochemical, Spectroelectrochemical and Theoretical Studies

“…Remarkably, low‐energy broad bands were detected in the NIR region for 1 .− , 2 .− and 3 .− (1200–2000 nm) (Figure S6). These bands may be ascribed to an intra‐ligand charge‐transfer transition and thus confirm the diimine character of the first cathodic process [20] . Further reduction of the complexes 1–3 until E pc (2) under argon led to a modification of the IR and UV‐Vis spectra.…”

“…These bands may be ascribed to an intra-ligand charge-transfer transition and thus confirm the diimine character of the first cathodic process. [20] Further reduction of the complexes 1-3 until E pc (2) under argon led to a modification of the IR and UV-Vis spectra. On one hand, the four ν CO bands found for the neutral and mono-reduced species evolved towards a 3-bands signature at ca.…”

NIR‐Emissive Chromium(0), Molybdenum(0), and Tungsten(0) Complexes in the Solid State at Room Temperature

“…The visible (VIS) emission spectra of KBr pellets of the three complexes reveal clear emission bands for Mo and W, the [33] and W(0) (top) as well as ORTEP representation of W (bottom). Ellipsoids are drawn with 50 % probability.…”

“…Figure 1. Molecular structure and synthesis of the investigated complexes [M(PyC-NMIC-dipp)(CO) 4 ] with M = Cr(0), Mo(0)[33] and W(0) (top) as well as ORTEP representation of W (bottom). Ellipsoids are drawn with 50 % probability.…”

Bright luminescent lithium and magnesium carbene complexes

“…Despite the fact that they are much less popular than conventional NHCs 42 and less explored in photochemistry, they increasingly attract attention. 52,[78][79][80][81][82][83][84][85][86][87][88][89] During our initial coordination experiments with the 1,2,3-triazolinylidene decorated car-bazolide obtained by deprotonation of 3, we noticed strong luminescence upon deprotonation (vide infra). Intriguingly, Kunz had already noticed luminescence for lithium carbazolyl bridged dicarbenes, however, these systems have not been studied spectroscopically yet (Fig.…”