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Imido Transfer from Bis(imido)ruthenium(VI) Porphyrins to Hydrocarbons:  Effect of Imido Substituents, C−H Bond Dissociation Energies, and RuVI/V Reduction Potentials

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journal contribution
posted on 30.11.2005, 00:00 by Sarana Ka-Yan Leung, Wai-Man Tsui, Jie-Sheng Huang, Chi-Ming Che, Jiang-Lin Liang, Nianyong Zhu
[RuVI(TMP)(NSO2R)2] (SO2R = Ms, Ts, Bs, Cs, Ns; R = p-C6H4OMe, p-C6H4Me, C6H5, p-C6H4Cl, p-C6H4NO2, respectively) and [RuVI(Por)(NTs)2] (Por = 2,6-Cl2TPP, F20-TPP) were prepared by the reactions of [RuII(Por)(CO)] with PhINSO2R in CH2Cl2. These complexes exhibit reversible RuVI/V couple with E1/2 = −0.41 to −0.12 V vs Cp2Fe+/0 and undergo imido transfer reactions with styrenes, norbornene, cis-cyclooctene, indene, ethylbenzenes, cumene, 9,10-dihydroanthracene, xanthene, cyclohexene, toluene, and tetrahydrofuran to afford aziridines or amides in up to 85% yields. The second-order rate constants (k2) of the aziridination/amidation reactions at 298 K were determined to be (2.6 ± 0.1) × 10-5 to 14.4 ± 0.6 dm3 mol-1 s-1, which generally increase with increasing RuVI/V reduction potential of the imido complexes and decreasing C−H bond dissociation energy (BDE) of the hydrocarbons. A linear correlation was observed between log k‘ (k‘ is the k2 value divided by the number of reactive hydrogens) and BDE and between log k2 and E1/2(RuVI/V); the linearity in the former case supports a H-atom abstraction mechanism. The amidation by [RuVI(TMP)(NNs)2] reverses the thermodynamic reactivity order cumene > ethylbenzene/toluene, with k‘(3° C−H)/k‘(2° C−H) = 0.2 and k‘(3° C−H)/k‘(1° C−H) = 0.8.