Synthesis, structure and spectroelectrochemistry of bis(eta(6)-1,4-tri-tert-butyl-benzene)chromium(0) and bis(eta(5)-1,2,4-tri-tert-butyl-cyclopentadienyl)cobalt(II). Dia- and paramagnetic sandwich complexes derived from sterically highly demanding pi-ligands

Metal atom synthesis gives access to the bis(arene)chromium sandwich of 1,4 di-tert-butyl-benzene (5). 5 displays an axial sandwich structure with a l inear arene-chromium-arene axis and a Cr-arene distance of 1.64 Angstrom. R eduction of [{(eta(5)-1,2,4 tri-tert-butyl-Cp)CoCl}(2)] with the trianion o f decacyclene in THF produces the cobaltocene sandwich [(eta(5)-1,2,4 tri-t ert-butyl Cp)(2)Co] 2 as black crystals in 65% yield. Electrochemistry show s that the monocations 2(+) and 5(+) are able to support reversibly the one -electron reduction to their corresponding neutral congeners. (C) 1999 Else vier Science S.A. All rights reserved.