The reactivity of the anion 7,8-(ethane-1′,2′-dithiolato-SS′)-dicarba-nido-undecaborate is reported. It reacts easily with salts of transition metals, replaces phosphines in complexes where these are ligands, and stabilizes low oxidation states. The molecular structure of 1,4-dithiabutane-7′,8′-dicarbaundecaborate(12)bis(triphenylphosphine)rhodium(I) has been resolved. The compound crystallizes in space group P1 with 2 formula units per cell. The cell dimensions are a=10.165(2), b=14.665(3), c=14.951(3) Å with α=81.21(4), β=87.68(4) and γ= 72.20°. © 1990.