The syntheses, characterization, and interconversions of (Et(3)P)(2)Ir(C2H4)(2)Cl (1) and (Et(3)P)(2)Ir(C2H4(Cl) (2) as well as the X-ray crystal structure of 1 are reported. In solution complex 1 has a stereochemically rigid trigonal-bipyramidal structure with nonrotating ethylene ligands. Formation of complex 1 from complex 2 and ethylene is thermodynamically favorable; Delta G(298) = -2.12 +/- 0.03 kcal/mol.