ENERGETICS OF THE OXIDATIVE ADDITION OF I-2 TO [IR(CL-L)(CO)(2)](2) (L=S(T)BU,3,5-ME(2)PZ,7-AZA) COMPLEXES - X-RAY STRUCTURES OF [IR(MU-S(T)BU)(I)(CO)(2)](2) AND [IR(MU-3,5-ME(2)PZ)(I)(CO)(2)](2)

The energetics of the oxidative additive of I-2 to [Ir(mu-L)(CO)(2)](2 ) [L = t-buthylthiolate (S'Bu), 3,5-dimethylpyrazolate (3,5-Me(2)pz), and 7-azaindolate (7-aza)] complexes was investigated by using the res ults of reaction-solution calorimetric measurements, X-ray structure d eterminations, and extended Huckel (EH) molecular orbital calculations . The addition of 1 mol of iodine to 1 mol of [Ir(mu-L)(CO)(2)](2), in toluene, leads to [Ir(mu-L)(I)(CO)(2)](2), with the formation of two Ir-I bonds and one Ir-Ir bond. The following enthalpies of reaction we re obtained for this process: -125.8 +/- 4.9 kJ mol(-1) (L = S'Bu), -1 52.0 +/- 3.8 kJ mol(-1) (L = 3,5-Me(2)pz), and -205.9 +/- 9.9 kJ mol(- 1) (L = 7-aza). These results are consistent with a possible decrease of the strain associated with the formation of three-, four-, and five -membered rings, respectively, in the corresponding products, as sugge sted by the results of EH calculations. The calculations also indicate a slightly stronger Ir-Ir bond for L = 3,5-Me(2)pz than for L = S'Bu despite the fact that the Ir-Ir bond lengths are identical for both co mplexes. The reaction of 1 mol of [Ir(mu-S'Bu)(CO)(2)](2) with 2 mol o f iodine to yield [Ir(mu-S'Bu)(I)(2)(CO)(2)](2) was also studied. In t his process four Ir-I bonds are formed, and from the corresponding ent halpy of reaction (-186.4 +/- 2.7 kJ mol(-1)) a solution phase Ir-I me an bond dissociation enthalpy in [Ir(mu-S'Bu)(I)(2)(CO)(2)](2), D<(DH) over bar>(sin)(Ir-I) = 122.2 +/- 0.7 kJ mol(-1), was derived. This val ue is lower than most <(DH)over bar>(sin)(Ir-I) values reported for oc tahedral mononuclear Ir-III complexes. New large-scale syntheses of th e [Ir(mu-L)(CO)(2)](2) complexes, with yields up to 90%, using [Ir(aca c)(CO)(2)] as starting material, are also reported. The X-ray structur es of [Ir(mu-L)(I)(CO)(2)](2) (L = S'Bu and 3,5-Me(2)pz) complexes hav e been determined. For L = S'Bu the crystals are monoclinic, space gro up P2(1)/c, a = 10.741(2) Angstrom, b = 11.282(3) Angstrom, c = 18.308 (3) Angstrom, beta = 96.71(1)degrees, and Z = 4. Crystals of the mu-3, 5-Me(2)pz derivative are monoclinic, space group P2(1)/n, a = 14.002(3 ) Angstrom, b = 10.686(1) Angstrom, c = 15.627(3) Angstrom, beta = 112 .406(8)degrees, and Z = 4. In both complexes the overall structure can be described as two square-planar pyramids, one around each iridium a tom, with the iodine atoms in the apical positions, and the equatorial positions occupied by two CO groups and the two sulfur atoms of the S 'Bu ligands, or two N atoms of the pyrazolyl ligands. In the case of L = S'Bu the pyramids share a common edge defined by the two bridging s ulfur atoms and for L = 3,5-Me(2)pz they are connected through the two N-N bonds of the pyrazolyl ligands. The complexes exhibit short Ir-Ir single bonds of 2.638(1) Angstrom for L = S'Bu and 2.637(1) Angstrom for L = 3,5-Me(2)Pz. The oxidative addition of iodine to [Ir(mu-3,5-Me (2)pz)(CO)(2)](2) results in a remarkable compression of 0.608 Angstro m in the Ir-Ir separation.