Isomeric commo-Ferracarboranes: meso-, dd/ll-[PPh3R][commo-Fe(2,4-closo-C2B8H10)2] and Their Bimetal Ferra–Copper Zwitterion Derivatives

The reaction of [Na][C2B8H11] with anhydrous FeCl2 in THF affords a mixture of dd/ll and meso isomers of anionic paramagnetic commo-ferracarborane [Ph3PR][commo-1,1′-Fe(closo-2,4-C2B8H10)2] (meso, R = Me: 1a; meso, Et: 1b; dd/ll, R = Me: 2a; dd/ll, R = Et: 2b) with unusual closo geometry. Both dd/ll and meso isomers were successfully isolated and their structures were determined using single-crystal X-ray diffraction studies. Their paramagnetic properties were confirmed with EPR spectra and their oxidative–reductive properties were investigated using cyclic voltammetry. It was shown that facile dd/ll → meso and meso → dd/ll transformations, leading to equilibrium in CH2Cl2 solution, occur. Quantum-chemical calculations of the isomer-to-isomer transformations were performed. Ferra–copper zwitterionic complexes [3,3′,6,7′-exo-{Ph3PCu}-3,3′,6,7′-(µ-H)4-commo-1,1′-Fe(2,4-C2B8H8)2] and [3,3′,6,6′-exo-{Ph3PCu}-3,3′,6,6′-(µ-H)4-commo-1,1′-Fe(2,4-C2B8H8)2] were synthesized and their structures were determined by single-crystal X-ray diffraction studies. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim