A rhodium(I) dicarbonyl complex with a redox-active ferrocenyl phosphine-NHC ligand: Enhanced reactivity of the metal centre through ferrocene oxidation

Abstract

A rhodium(I) dicarbonyl complex bearing a bidentate ferrocenyl phosphine-NHC ligand has been synthesized and characterized by NMR, IR spectroscopy, mass spectrometry and X-Ray diffraction methods. Its behaviour towards oxidation was investigated and revealed that changing the oxidation state of ferrocene can significantly modify the electron density at rhodium. Oxidation of the rhodium(I) dicarbonyl complex in acetonitrile furnished an airstable rhodium(III) complex, stabilized by acetonitrile molecules and with an interesting C-H bond activation at ferrocene. This new rhodium(III) complex is active for the hydrosilylation of acetophenone and its derivatives.

Cooperative Effects in Multimetallic Complexes Applied in Catalysis

“…The use of ferrocene as an electron relay has been further demonstrated with a ferrocenyl phosphine-NHC ligand coordinating a Rh(I) center (Scheme 40). [126,127] Twofold oxidation of 99 gives a Rh(III) complex, which undergoes intramolecular CÀ H activation on the ferrocenyl moiety. Cyclic voltammetry experiments show that ferrocene is oxidized before rhodium.…”

Gold(ii) in redox-switchable gold(i) catalysis

“…39,40 Fully analogously, rhodium(I) complexes bearing a ferrocenyl phosphine-NHC ligand are first oxidised at the Fc unit, while the second oxidation is rhodium centered initiating a further intramolecular electron transfer from rhodium to Fc + . 35 In these examples, the Fc/Fc + redox couple acts as intermediate parking position for a positive charge. DFT calculations suggest that coordination of oxygen nucleophiles such as amides (e.g.…”

“…[26][27][28] Indeed, RSC is a strongly expanding field in homogeneous catalysis. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] The redox-switching event occurs either at a remote redox-active unit, e.g. a Fc unit located on the ligand [26][27][28]30,33,34,[36][37][38] or directly at the catalytic metal centre, e.g.…”

Planar‐Chiral Ferrocene‐Based N‐Heterocyclic Carbene Ligands

“…[52] In as tudy to examine the redox chemistry of Rh complex 63,w hich contains an achiral ferrocenyl phosphine-NHC ligand, Labande and co-workersr eported in 2013 that they accidentally obtained planar-chiral Rh complex 64, which was probably formed by an intramolecularC ÀHa ctivation of af errocene CÀHb ond on Rh triggered by oxidation of the Fe center (Scheme 22). [53] As uniquec omplex 64 was confirmed to act as ac atalyst in such reactions as the hydrosilylation of acetophenones, the future development of 64 in an enantiomerically pure form is expected.…”