Redox behavior and structural characterization of nitrosyl pincer-type PNP rhodium complexes

JUAN PELLEGRINO; CARINA GAVIGLIO; FABIO DOCTOROVICH

Otro; LatinXChem 2020; 2020

A topic of interest consists on exploring the combination ofrobust bulky pincer ligands that present high stability and steric protectionwith redox active ligands like NO in the reactivity of {RhNO}n complexes.Nitrosyl complexes are described as {MNO}n where n stands for the number ofelectrons in the metal d and π* NO orbitals. In a previous work the activationof carbon-halogen bonds by a paramagnetic complex {RhNO}9 with a PCP pincertype ligand was reported [1]. Herein the synthesis and characterization of anew paramagnetic complex {RhNO}9 1+. with a PNP pincer type ligand ispresented.Reaction of {RhNO}8 1++ with 1 equivalent of Co(Cp)2 intrifluorotoluene resulted in quantitative formation of 1+. and [Co(Cp)2][BF4].The paramagnetic nature of the one-electron reduced {RhNO}9 species 1+. wasconfirmed by EPR and by the broad resonances occurring in 1H NMR. Also by FTIRthe expected change was observed in the NO stretching frequency upon the{RhNO}8/9 conversion from 1++ to 1+. (1911 to 1650 cm-1).The molecularstructure of both compounds 1++ and 1+. was confirmed by X-ray diffraction. Inboth structures the rhodium atom is located in the center of a square-planargeometry with the nitrosyl group occupying the position trans to the ipsocarbon. In 1++ the Rh-N-O angle is 176.1(3)º while in 1+. is 145.5(2)º. Thisconsiderable change in the MNO angle is expected for a {RhNO}8/9 conversion insquare-planar complexes.Further reduction to the putative {RhNO}10 form wasaccomplished. This higly reduced species is not indefinitely stable insolution, and slowly decomposed to a paramagnetic {RhNO}9 complex with adearomatized PNP ligand, through formal loss of an H radical.[1] J. Pellegrino,C. Gaviglio, D. Milstein, F. Doctorovich, Organometallics, 32 (2013) 6555?6564.