Che Chi-Ming, Zhang Jun-Long, Zhang Rui, Huang Jie-Sheng, Lai Tat-Shing, Tsui Wai-Man, Zhou Xiang-Ge, Zhou Zhong-Yuan, Zhu Nianyong, Chang Chi Kwong
Department of Chemistry, Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Hong Kong.
Chemistry. 2005 Nov 18;11(23):7040-53. doi: 10.1002/chem.200500814.
beta-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru(VI)(F(28)-tpp)O(2)] [F(28)-tpp=2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(VI)(beta-Br(8)-tmp)O(2)] [beta-Br(8)-tmp=2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(2,4,6-trimethylphenyl)porphyrinato(2-)] were prepared from reactions of [Ru(II)(por)(CO)] [por=porphyrinato(2-)] with m-chloroperoxybenzoic acid in CH(2)Cl(2). Reactions of [Ru(VI)(por)O(2)] with excess PPh(3) in CH(2)Cl(2) gave [Ru(II)(F(20)-tpp)(PPh(3))(2)] [F(20)-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(II)(F(28)-tpp)(PPh(3))(2)]. The structures of [Ru(II)(por)(CO)(H(2)O)] and [Ru(II)(por)(PPh(3))(2)] (por=F(20)-tpp, F(28)-tpp) were determined by X-ray crystallography, revealing the effect of beta-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru(VI)(F(20)-tpp)O(2)] shows a Ru=O bond length of 1.718(3) A. Electrochemical reduction of [Ru(VI)(por)O(2)] (Ru(VI) to Ru(V)) is irreversible or quasi-reversible, with the E(p,c)(Ru(VI/V)) spanning -0.31 to -1.15 V versus Cp(2)Fe(+/0). Kinetic studies were performed for the reactions of various [Ru(VI)(por)O(2)], including [Ru(VI)(F(28)-tpp)O(2)] and [Ru(VI)(beta-Br(8)-tmp)O(2)], with para-substituted styrenes p-X-C(6)H(4)CH=CH(2) (X=H, F, Cl, Me, MeO), cis- and trans-beta-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k(2)) obtained for the hydrocarbon oxidations by [Ru(VI)(F(28)-tpp)O(2)] are up to 28-fold larger than by [Ru(VI)(F(20)-tpp)O(2)]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru(VI)(F(28)-tpp)O(2)] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k(2) values for the oxidation of styrene and ethylbenzene by [Ru(VI)(por)O(2)] increase with E(p,c)(Ru(VI/V)), and there is a linear correlation between log k(2) and E(p,c)(Ru(VI/V)). The small slope (approximately 2 V(-1)) of the log k(2) versus E(p,c)(Ru(VI/V)) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism.
β-卤代二氧钌（VI）卟啉配合物[Ru(VI)(F(28)-tpp)O₂] [F(28)-tpp = 2,3,7,8,12,13,17,18-八氟-5,10,15,20-四（五氟苯基）卟啉二价阴离子]和[Ru(VI)(β-Br(8)-tmp)O₂] [β-Br(8)-tmp = 2,3,7,8,12,13,17,18-八溴-5,10,15,20-四（2,4,6-三甲基苯基）卟啉二价阴离子]由[Ru(II)(por)(CO)] [por = 卟啉二价阴离子]与间氯过氧苯甲酸在二氯甲烷中反应制备。[Ru(VI)(por)O₂]与过量三苯基膦在二氯甲烷中反应得到[Ru(II)(F(20)-tpp)(PPh₃)₂] [F(20)-tpp = 5,10,15,20-四（五氟苯基）卟啉二价阴离子]和[Ru(II)(F(28)-tpp)(PPh₃)₂]。通过X射线晶体学确定了[Ru(II)(por)(CO)(H₂O)]和[Ru(II)(por)(PPh₃)₂]（por = F(20)-tpp, F(28)-tpp）的结构，揭示了卟啉配体的β-氟化对轴向配体与钌原子配位的影响。[Ru(VI)(F(20)-tpp)O₂]的X射线晶体结构显示Ru=O键长为1.718(3) Å。[Ru(VI)(por)O₂]（Ru(VI)到Ru(V)）的电化学还原是不可逆或准可逆的，相对于二茂铁Cp₂Fe⁺/⁰，E(p,c)(Ru(VI/V))范围为 -0.31至 -1.15 V。对各种[Ru(VI)(por)O₂]，包括[Ru(VI)(F(28)-tpp)O₂]和[Ru(VI)(β-Br(8)-tmp)O₂]与对取代苯乙烯p-X-C₆H₄CH=CH₂（X = H, F, Cl, Me, MeO）、顺式和反式β-甲基苯乙烯、环己烯、降冰片烯、乙苯、异丙苯、9,10-二氢蒽、氧杂蒽和芴的反应进行了动力学研究。[Ru(VI)(F(28)-tpp)O₂]氧化烃类得到的二级速率常数（k₂）比[Ru(VI)(F(20)-tpp)O₂]大高达28倍。双参数哈米特相关性表明，[Ru(VI)(F(28)-tpp)O₂]氧化苯乙烯应涉及苄基自由基中间体的限速生成，且自旋离域效应比极性效应更重要。[Ru(VI)(por)O₂]氧化苯乙烯和乙苯的k₂值随E(p,c)(Ru(VI/V))增加，且log k₂与E(p,c)(Ru(VI/V))之间存在线性相关性。log k₂对E(p,c)(Ru(VI/V))图的小斜率（约2 V⁻¹）表明在烃类氧化的速率决定步骤中电荷转移程度较小。速率常数与C-H键解离能相关性良好，支持氢原子夺取机理。
