ISSN:
1572-9001
Keywords:
Thermochemistry
;
oxidative addition
;
indium
;
extended Hückel
;
X-ray structure
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The energetics of the oxidative additive of I2 to [Ir(Μ-L)(CO)2]2 [L =t-buthylthiolate (S t Bu), 3,5-dimethylpyrazolate (3,5-Me2pz), and 7-azaindolate (7-aza)] complexes was investigated by using the results of reaction-solution calorimetric measurements, X-ray structure determinations, and extended Hückel (EH) molecular orbital calculations. The addition of 1 mol of iodine to 1 mol of [Ir(Μ-L)(CO)2]2, in toluene, leads to [Ir(Μ-L)(I)(CO)2]2, with the formation of two Ir-I bonds and one Ir-Ir bond. The following enthalpies of reaction were obtained for this process: −125.8±4.9 kJ mol−1 (L = S t Bu), −152.0±3.8 kJ mol−1 (L=3,5-Me2pz), and −205.9±9.9 kJ mol¹ (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 suggested by the results of EH calculations. The calculations also indicate a slightly stronger Ir-Ir bond for L = 3,5-Me2pz than for L= S t Bu despite the fact that the Ir-Ir bond lengths are identical for both complexes. The reaction of 1 mol of [Ir(Μ-S t Bu)(CO)2]2 with 2 mol of iodine to yield [Ir(Μ-S t Bu)(I)2(CO)2]2 was also studied. In this process four Ir-I bonds are formed, and from the corresponding enthalpy of reaction (−186.4±2.7 kJ mol−1) a solution phase Ir-I mean bond dissociation enthalpy in [Ir(Μ-S t Bu)(I)2(CO)2]2, $$\overline {DH} _{\sin } (Ir - I) = 122.2 \pm 0.7 kJ mol^{ - 1} $$ , was derived. This value is lower than most $$\overline {DH} _{\sin } (Ir - I)$$ values reported for octahedral mononuclear Ir111 complexes. New large-scale syntheses of the [Ir(Μ-L)(CO)2]2 complexes, with yields up to 90%, using [Ir(acac)(CO)2] as starting material, are also reported. The X-ray structures of [Ir(Μ-L)(I)(CO)2]2 (L=StBu and 3,5-Me2pz) complexes have been determined. For L=StBu the crystals are monoclinic, space group P2l/c,a=10.741(2) å,b= 11.282(3) å,c=18.308(3) å,Β=96.71(1)
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02275160
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