(Cyclopentadienyl)metalladicarbollides 3-(η-C5R5)-3,1,2-MC2B9H11 (M = Co, Rh, Ir): Synthesis, electrochemistry, and bonding

Metallacarboranes 3-(η-C5R5)-3,1,2-MC2B9H11 (1a: M = Co, R = H; 1b: M = Co, R = Me; 2a: M = Rh, R = H; 2b: M = Rh, R = Me; 3a: M = Ir, R = H; 3b: M = Ir, R = Me) were obtained by reactions of Tl[Tl(η-7,8-C2B9H11)] with [(η-C5R5)MX2]2 (X = Cl, I) or [CpM(MeCN)3]2+. The structures of 2a and 3a were determined by X-ray diffraction. The electrochemical investigation of complexes 2a,b and 3a,b shows that they undergo the partially reversible M(III)/M(II) electron addition followed by the irreversible M(II)/M(I) reduction. Such a path is quite reminiscent of that occurring for the isolobal and isoelectronic monocations [(η-C5R5)MCp]+ (M = Rh, Ir; R = H, Me). An electrochemical comparison is made also with respect to the cobalt derivatives 1a,b. DFT calculations of the redox potentials and the respective geometrical changes were performed. Metal–ligand bonding in 1a, 2a and 3a was analyzed by energy decomposition analysis.