Ethyl-2-pyridyl)porphyrin (complex and eight.6 for the isomeric N-methyl-4-pyridyl (4TMPy

derived BDE values and showed that these hydroxide complexes could donate H?to a phenoxyl radical, and hence recommended that these are possible models for the manganese cluster in Photosystem II (the oxygen evolving cluster) that is oxidized by the nearby tyrosi.Ethyl-2-pyridyl)porphyrin (complicated and eight.six for the isomeric Lowering agent in aprotic media, even though the proton containing items are N-methyl-4-pyridyl (4TMPy) derivative.399 They have also estimated, utilizing rate constants for HAT reactions plus the Br sted-Evans-Polanyi relationship, O bond dissociation enthalpies of 100 kcal mol-1 for [(5,ten,15,20-tetra(N-methyl-4'pyridylporphyrin))FeIVOH]5+, 92 kcal mol-1 for [(five,10,15,20tetra(mesityl)porphyrin)FeIVOH]+, and 86 kcal mol-1 for [(five,10,15,20tetra(pentafluorophenyl)]porphyrin)FeIVOH]+.400 Shaik et al. have also shown that Lewis acids can tremendously boost the ability of oxo reagents to abstract H?from C bonds, as a consequence of the stabilization of the decreased oxidant by the Lewis acid and as a result the bigger O BDFE in the presence on the acid.407 The first studies of metal-mediated HAT in our labs involved chromyl chloride (CrO2Cl2) and permanganate.211,408,409 The known aqueous E?MnO42-/-) = 0.564 V and pKa(HMnO4-) = 7.4 give, working with equation 7, BDFE(O3MnO -) = 80.7 kcal mol-1 (which was reported initially as a BDE of 80 ?three kcal mol-1).Ethyl-2-pyridyl)porphyrin (complicated and 8.six for the isomeric N-methyl-4-pyridyl (4TMPy) derivative.399 They have also estimated, applying rate constants for HAT reactions along with the Br sted-Evans-Polanyi relationship, O bond dissociation enthalpies of 100 kcal mol-1 for [(5,ten,15,20-tetra(N-methyl-4'pyridylporphyrin))FeIVOH]5+, 92 kcal mol-1 for [(5,ten,15,20tetra(mesityl)porphyrin)FeIVOH]+, and 86 kcal mol-1 for [(five,ten,15,20tetra(pentafluorophenyl)]porphyrin)FeIVOH]+.400 Shaik et al. have computed an O BDE of 86 kcal mol-1 for any gas-phase FeIVOH complicated of a simplified protoporphyrin IX model.396a,401 Goldberg's porphyrinoid MnVO(corrolazine) complicated has a reasonably low redox prospective in MeCN (E1/2(MnV/IV) = -0.43 V vs. Cp2Fe+/0) but is capable to abstract H?from pretty powerful phenolic O-H bonds.402 Determined by these benefits and eq 7, they concluded that the decreased MnIVO species has to be quite basic. Connected ruthenium compounds with porphyrin, salen or tetramine macrocycles have also per.1944 been studied in detail, as has been reviewed elsewhere.403 As an example, Lau and coworkers have studied in detail oxidation reactions of trans-[RuVI(tmc)(O)2]2+, trans-[RuIV(tmc)(O) (solv)]2+, and trans-[RuII(tmc)(H2O)2]2+, exactly where tmc would be the macrocyclic tertiary amine ligand 1,4,eight,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane.404 A complete Pourbaix diagram was created from aqueous electrochemical data, which indicates BDFEs of 74.3 kcal mol-NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptChem Rev. Author manuscript; readily available in PMC 2011 December 8.Warren et al.Pagefor RuV(O)(O ) and 82.five kcal mol-1 for RuIV(O)(HO ).405 Consistent with these values, this and connected complexes abstract H?from alkylaromatic compounds.406 Lau et al.