The complex trans-RuCl2(dppm)(2) (trans-1) (dppm = Ph2PCH2PPh2) has been converted to the corresponding cis isomer (cis-1) at room temperature in the presence of catalytic CuCl or CuI. The halide-bridged heterotrimetallic [{cis-RuCl2(dppm)(2)}(2)Cu][CuCl2] (2) was isolated when trans-1 or cis-1 was reacted with excess CuCl. Complex 2 was crystallized and characterized by single-crystal X-ray diffraction. Cell parameters for 2 . solvent: a = 11.6059(4) Angstrom, b = 13.8415(5) Angstrom, c = 36.163(1) Angstrom, beta = 95.03(1)degrees with Z = 2 in space group P2/c. The P-31 NMR spectrum of 2 indicates that several complexes are present in solution. Adding a small amount of 2 to a solution of trans-1 results in isomerization to cis-1. Complex 2 was converted quantitatively to cis-1 by reaction with excess [n-Bu4N]Cl or HCl(aq). A mechanism for the catalytic isomerization of trans-1 to cis-1 and the formation of 2 is proposed.