Half-sandwich manganese complexes Cp(CO)2Mn(NHC) as redox-active organometallic fragments

Oxidation of the half-sandwich Mn-I complexes Cp(CO)(2)Mn(NHC) bearing dialkyl-, arylalkyl- and diarylsubstituted N-heterocyclic carbene ligands (NHC = IMe, IMeMes, IMes) affords the corresponding stable Mn-II radical cations [Cp(CO)(2)Mn(NHC)](BF4) isolated in 92-95% yield. Systematic X-ray diffraction studies of the series of Mn-I and Mn-II NHC complexes revealed the expected characteristic structural changes upon oxidation, namely the elongation of the Mn-CO and Mn-NHC bonds as well as the diminution of the OC-Mn-CO angle. ESR spectra of [Cp(CO)(2)Mn(IMes)](BF4) in frozen solution (CH2Cl2/toluene 1 : 1, 70 K) allowed the identification of two conformers for this complex and their structural assignment using DFT calculations. The stability of these NHC complexes in both metal oxidation states, moderate oxidation potentials and the ease of detection of Mn-II species by a variety of spectroscopic techniques (UV-Vis, IR, paramagnetic H-1 NMR, and ESR) make these compounds promising objects for applications as redox-active organometallic fragments.

Automated summary

The oxidation of half-sandwich Mn-I complexes Cp(CO)(2)Mn(NHC) bearing various N-heterocyclic carbene ligands resulted in the isolation of stable Mn-II radical cations in high yield. Systematic X-ray diffraction studies revealed structural changes upon oxidation, and ESR spectra allowed for the identification of complex conformers and structural assignment using DFT calculations. The promising applications of these redox-active organometallic fragments lie in their stability in both metal oxidation states, moderate oxidation potentials, and ease of detection using various spectroscopic techniques.