Abstract
The osmochrome Os II(OEP)[P(OMe) 3] 2, where OEP is octaethylporphine, undergoes an oxidative photosubstitution reaction in hexane in the presence of chlorinated hydrocarbons (CH 2Cl 2, CHCl 3, CCl 4, CHCl 2CH 3 and CH 2ClCH 2Cl) under steady state photolysis. The product has been identified as Os IV(OEP)Cl 2. Both initial rates of reaction and quantum yields are, within experimental error, independent of whether the hexane-chlorinated hydrocarbon solutions are argon purged, air equilibrated, N 2O purged or oxygen purged. The quantum yields increase with increase in CR 2Cl 2 (R H or Cl) concentration; limiting quantum yields are 0.0017 ± 0.0001 (CH 2Cl 2), 0.25 ± 0.08 (CHCl 3) and 0.93 ± 0.10 (CCl 4). The reactivity of the chlorinated reactants is CCl 4 (280) > CHCl 3 (35) & >; CH 2ClCH 2Cl (1.4) ≈ CHCl 2CH 3 (1.1) ≈ CH 2Cl 2 (1.0) under the experimental conditions used; this order accords with expectations based on the CCl bond strengths. A mechanism is postulated in which the three essential steps are (L P(OMe) 3) (i) Os(OEP)LL ⇌ Os(OEP)L + L (ii) Os(OEP)L + CR 2Cl 2 → products and (iii) Os(OEP)LL + CR 2Cl 2 → products The data are treated using both the conventional kinetic theory and the model of Noyes for the scavenging of photoproduced radical pairs in solution.
Published Version
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