The formation and some substitution chemistry of the bis(ethylene) complexes Bp Rh(C 2 H 4 ) 2 (Bp = Bp * , 1 * ; Bp = Bp, 1) are described. Reaction of 1 * with 1 equiv. of N-donor ligands or monodentate phosphines (L) leads to the isolation of compounds of general formula Bp * Rh(C 2 H 4 )(L). Addition of an excess of amine produces the eighteen electron complexes Bp * Rh(C 2 H 4 )(L) 2 whereas in the case of the PR 3 ligands the second equivalent of the donor gives the disubstituted sixteen electron compounds Bp * Rh(L) 2 . The ethylene groups in 1 * and 1 can also be replaced by carbon monoxide and tert-butyl isocyanide, affording the complexes Bp Rh(L) 2 (L = CO, CN t Bu). The solid state structures of the compounds Bp * Rh(C 2 H 4 ) 2 (1 * ) and BpRh(PPh 3 ) 2 (9) have been determined by X-ray diffraction studies. Crystals of 1 * are monoclinic, space group P2 1 /c, with a = 15.129(3), b = 17.501(3), c = 13.425(8) 9, β = 111.02(4)°, V = 3318(2) 9 3 , and D c a l c = 1.06 g cm - 3 for Z = 8; R = 4.3 and R w = 4.4. Crystals of 9 are triclinic, space group P1, with a = 10.281(2), b = 11.637(2), c = 17.836(8) 9, α = 90.09(2), β = 95.77(2), γ = 108.410(13)°, V = 2013(2) 9 3 , and D c a l c = 1.4 g cm - 3 for Z = 2; R = 0.0302 and wR = 0.0787.