A (Diborole)cobalt Complex with a C–H···B Bridge, CpCo(1,3‐C3B2Me5H), and Its Thallium Derivative: Synthesis, Structure, and Bonding

Abstract

AbstractThe reaction of CpCo(1,3‐C3B2Me5H) (1) with CpTl affords the thallium derivative CpCo(1,3‐C3B2Me5)Tl (2). The structures of 1 and 2 were determined by X‐ray diffraction at 100 K. An “extra” hydrogen atom in 1 occupies a C–H···B bridging position. According to DFT calculations, 1 exists as a mixture of two enantiomers with an enantiomerization barrier of only 0.5 kcal mol–1. The transition state has Cs symmetry with an endo‐CH hydrogen atom. The isomeric iso‐1with the Co–H···B bridge is less stable than 1 by 10 kcal mol–1.The formation of 1 and iso‐1 from C3B2Me5H and CpCo(C2H4)2 have almost equal activation energies. The isomerization of iso‐1 to 1 was shown to proceed as a two‐step hydrogen transfer. The bonding of the “extra” hydrogen atom in the related CHB‐bridged carborane nido‐2,3,5‐C3B3R5H2 and metallacarboranes M(C5R5)(C3B2R′5H) (R, R′ = H, Me; M = Co, Rh, Ir) as well as their hydridic isomers MH(C5R5)(C3B2R′5) was compared. According to energy decomposition analysis, the bonding of the parent anion [CpCo(1,3‐C3B2H5)]– with metal cations becomes stronger in the following order: K+ < Na+ < Tl+ < Li+ < [RuCp]+. The attractive interactions between the [CpCo(1,3‐C3B2H5)]– and Tl+ fragments are 68 % electrostatic and 32 % covalent.