Cationic Half-Sandwich Iron(II) and Iron(III) Complexes with N-Heterocyclic Carbene Ligands

Abstract

The cationic piano-stool iron complexes containing the N-heterocyclic carbene ligand tethered to a tetramethylcyclopentadienyl ring [(Cp*-NHC)Fe(CO)(L)]-[X] (L = NCMe, DMSO; X = BF 4 , OTf) have been prepared and analyzed by spectroscopic, electrochemical, and crystallographic methods. Oxidation reactions of the cationic complex [(Cp*-NHC)Fe(CO)(NCMe)][BF 4 ] (2) with silver tetrafluoroborate and tert-butyl hydroperoxide in acetonitrile yield the dicationic iron(III) complexes [(Cp*-NHC)Fe(NCMe) 2 ][BF 4 ] 2 and [(Cp*-NHC)Fe(H 2 O)][BF 4 ] 2 , respectively. When the reaction of 2 with AgBF 4 is performed in dichloromethane, the cationic complex [(Cp*-NHC)FeCl][BF 4 ] is obtained. These new iron(III) complexes have been characterized by Mossbauer spectroscopy and in one case by X-ray diffraction studies. DFT calculations were used to rationalize experimental results. The cationic complex [(Cp*-NHC)Fe(CO)(NCMe)][OTf] is catalytically active toward the reduction of benzaldehyde and acetophenone using phenylsilane under neat conditions and in the absence of visible light irradiation.

Asymmetric binuclear Ni(ii) and Cu(ii) Schiff base metallopolymers

“…The redox potentials can be estimated as the difference between the energies of the initial complex (1 or 2) and its oxidation product (1 + and 2 + ), in their optimised geometries, both in gas phase and in dichloromethane, as reported in previous studies of cyclopentadienyl complexes. 17 The calculated values (V relative to SCE) were calculated as 1.47 in gasphase and 0.68 (dichloromethane) for 1, and 1.53 in gasphase and 0.36 (dichloromethane) for 2, reproducing the trends observed in the experimental ones, although with a shi of $0.5 V.…”

“…58 The molecular structure and 3-d orbital representations were obtained with Molekel. 59,60 Redox potentials were estimated via DFT calculations, 17 according to the equation: E ¼ [(G Ox,solv. À G Red,solv. )…”

Pseudo electron-deficient organometallics: limited reactivity towards electron-donating ligands

“…1 They are also known to be extremely unstable and most organometallics follow the 18-electron rule. Some stable coordinatively unsaturated 16-electron (16-e) complexes have been isolated in particular by the groups of Koelle, Tilley, Suzuki, among others, [2][3][4][5][6][7][8][9][10][11][12] but little is known about the reactivity of air and moisture stable 16-e complexes and about their properties in solution. Half-sandwich metal complexes are a particular class of organometallics which has attracted an enormous attention for the design of catalysts, 13 anticancer drug candidates, [14][15][16][17][18][19][20][21][22]23,24 and as building blocks for supramolecular chemistry.…”

Iron N‐Heterocyclic Carbenes in Reduction Reactions

“…Moreover, treatment of 5 with stoichiometric amounts of AgBF 4 yielded the corresponding cationic complex [(Cp‐NHC)Fe(CO)][BF 4 ], which was active in the reduction of ketones and sulfoxides, affording full conversions at 100 °C (Scheme ). These results demonstrated that smooth changes in the coordination sphere of iron have interesting implications on the catalytic activity of the metal complexes.…”