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'-(mu-H)(4)-commo-1,1'-Fe(2,4-C2B8H8)(2)] and [3,3',6,6'-exo-{Ph3PCu}-3,3',6,6'-(mu-H)(4)-commo-1,1'-Fe(2,4-C2B8H8)(2)] were synthesized and their structures were determined by single-crystal X-ray diffraction studies.