Dicationic μ‐Diborolyl Arene Triple‐Decker Complexes [CpCo(μ‐1,3‐C3B2Me5)M(arene)]2+ (M = Rh, Ir; Cp = Cyclopentadienyl): Synthesis, Structures, Electrochemistry and Bonding

Abstract

AbstractThe reaction of the bromide complexes [CpCo(μ‐1,3‐C3B2Me5)MBr2]2 [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) μ‐diborolyl triple‐decker complexes [CpCo(μ‐1,3‐C3B2Me5)M(MeCN)3]2+ [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(μ‐1,3‐C3B2Me5)M(MeNO2)3]2+, generated in a similar way, react with benzene and its methylated derivatives to give the arene triple‐decker complexes [CpCo(μ‐1,3‐C3B2Me5)M(arene)]2+ [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5‐Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)2, 5c(BF4)2, 6b(BF4)2 and 6c(BF4)2 were determined by X‐ray diffraction. The electron‐transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one‐electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a η6 → η4 hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh–benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)]2+; however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene.