We report and analyze chemoselectivity in the gas phase reactions of cycloalkenes (cyclohexene, cycloheptene, cis-cyclooctene, 1,4-cyclohexadiene) with a non-heme iron(IV)-oxo complex [(PyTACN)Fe(O)(Cl)]+, which models the active species in iron-dependent halogenases. Unlike in the halogenases, we did not observe any chlorination of the substrate. However, we observed two other reaction pathways: allylic hydrogen atom transfer (HAT) and alkene epoxidation. The HAT is clearly preferred in the case of 1,4-cyclohexadiene, both pathways have comparable reaction rates in reaction with cyclohexene, and epoxidation is strongly favored in reactions with cycloheptene and cis-cyclooctene. This preference for epoxidation differs from the reactivity of iron(IV)-oxo complexes in the condensed phase, where HAT usually prevails. To understand the observed selectivity, we analyze effects of the substrate, spin state, and solvation. Our DFT and CASPT2 calculations suggest that all the reactions occur on the quintet potential energy surface. The DFT-calculated energies of the transition states for the epoxidation and hydroxylation pathways explain the observed chemoselectivity. The SMD implicit solvation model predicts the relative increase of the epoxidation barriers with solvent polarity, which explains the clear preference of HAT in the condensed phase.

Departament de Quimica and Institute of Computational Chemistry and Catalysis University of Girona Campus Montilivi 17071 Girona Spain

Department of Organic Chemistry Faculty of Science Charles University Hlavova 2030 8 128 43 Prague 2 Czech Republic

Institute for Molecules and Materials Radboud University Nijmegen Heyendaalseweg 135 6525 AJ Nijmegen Netherlands

J Heyrovsky Institute of Physical Chemistry of the CAS v v i Dolejškova 2155 3 182 23 Prague 8 Czech Republic

School of Chemical Science and Engineering Yachay Tech University 100650 Yachay City of Knowledge Urcuqui Ecuador

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Sono M, Roach MP, Coulter ED, Dawson JH. Heme-containing oxygenases. Chem. Rev. 1996;96:2841–2888. PubMed

Meunier B, de Visser SP, Shaik S. Mechanism of oxidation reactions catalyzed by cytochrome P450 enzymes. Chem. Rev. 2004;104:3947–3980. PubMed

Huang X, Groves JT. Beyond ferryl-mediated hydroxylation: 40 years of the rebound mechanism and C–H activation. J. Biol. Inorg. Chem. 2017;22:185–207. PubMed PMC

Huang X, Groves JT. Oxygen activation and radical transformations in heme proteins and metalloporphyrins. Chem. Rev. 2018;118:2491–2553. PubMed PMC

Groves JT, McClusky GA. Aliphatic hydroxylation via oxygen rebound. Oxygen transfer catalyzed by iron. J. Am. Chem. Soc. 1976;98:859–861.

Bugg TD, Ramaswamy S. Non-heme iron-dependent dioxygenases: unravelling catalytic mechanisms for complex enzymatic oxidations. Curr. Opin. Chem. Biol. 2008;12:134–140. PubMed

Riggs-Gelasco PJ, Price JC, Guyer RB, Brehm JH, Barr EW, Bollinger JM, Krebs C. EXAFS spectroscopic evidence for an FeO unit in the Fe(IV) intermediate observed during oxygen activation by taurine:α-ketoglutarate dioxygenase. J. Am. Chem. Soc. 2004;126:8108–8109. PubMed

Kovaleva EG, Lipscomb JD. Versatility of biological non-heme Fe(II) centers in oxygen activation reactions. Nat. Chem. Biol. 2008;4:186–193. PubMed PMC

Krebs C, Galonić Fujimori D, Walsh CT, Bollinger JM. Non-heme Fe(IV)-oxo intermediates. Acc. Chem. Res. 2007;40:484–492. PubMed PMC

Matthews ML, Chang WC, Layne AP, Miles LA, Krebs C, Bollinger JM. Direct nitration and azidation of aliphatic carbons by an iron-dependent halogenase. Nat. Chem. Biol. 2014;10:209–215. PubMed PMC

Ortiz de Montellano PR. Hydrocarbon hydroxylation by cytochrome P450 enzymes. Chem. Rev. 2010;110:932–948. PubMed PMC

Bordeaux M, Galarneau A, Drone J. Catalytic, mild, and selective oxyfunctionalization of linear alkanes: current challenges. Angew. Chem. Int. Ed. 2012;51:10712–10723. PubMed

Shaik S, De Visser SP, Ogliaro F, Schwarz H, Schröder D. Two-state reactivity mechanisms of hydroxylation and epoxidation by cytochrome P-450 revealed by theory. Curr. Opin. Chem. Biol. 2002;6:556–567. PubMed

Rittle J, Green MT. Cytochrome P450 compound I: capture, characterization, and C-H bond activation kinetics. Science. 2010;330:933–937. PubMed

Green MT. C-H bond activation in heme proteins: the role of thiolate ligation in cytochrome P450. Curr. Opin. Chem. Biol. 2009;13:84–88. PubMed

Bell SR, Groves JT. A highly reactive P450 model compound I. J. Am. Chem. Soc. 2009;131:9640–9641. PubMed PMC

Rohde JU, In JH, Lim MH, Brennessel WW, Bukowski MR, Stubna A, Münck E, Nam W, Que L. Crystallographic and spectroscopic characterization of a nonheme Fe(IV)-O complex. Science. 2003;299:1037–1039. PubMed

Park J, Lee YM, Ohkubo K, Nam W, Fukuzumi S. Efficient epoxidation of styrene derivatives by a nonheme iron(IV)-oxo complex via proton-coupled electron transfer with triflic acid. Inorg. Chem. 2015;54:5806–5812. PubMed

Nam W. Synthetic mononuclear nonheme iron–oxygen intermediates. Acc. Chem. Res. 2015;48:2415–2423. PubMed

Que L. The road to non-heme oxoferryls and beyond. Acc. Chem. Res. 2007;40:493–500. PubMed

Hohenberger J, Ray K, Meyer K. The biology and chemistry of highvalent iron–oxo and iron–nitrido complexes. Nat. Commun. 2012;3:720. PubMed

McDonald AR, Que L. High-valent nonheme iron-oxo complexes: synthesis, structure, and spectroscopy. Coord. Chem. Rev. 2013;257:414–428.

Guo M, Corona T, Ray K, Nam W. Heme and nonheme high-valent iron and manganese oxo cores in biological and abiological oxidation reactions. ACS Cent. Sci. 2019;5:13–28. PubMed PMC

Price, J.C., Barr, E.W., Glass, T.E., Krebs, C., Bollinger, J.M.: Evidence for hydrogen abstraction from C1 of taurine by the high-spin Fe(IV) intermediate detected during oxygen activation by taurine:alpha-ketoglutarate dioxygenase (TauD). J. Am. Chem. Soc. 125, 13008–13009 (2003) PubMed

Hoffart LM, Barr EW, Guyer RB, Bollinger JM, Krebs C. Direct spectroscopic detection of a C-H-cleaving high-spin Fe(IV) complex in a prolyl-4-hydroxylase. Proc. Natl. Acad. Sci. U. S. A. 2006;103:14738–14743. PubMed PMC

Galonić DP, Barr EW, Walsh CT, Bollinger JM, Krebs C. Two interconverting Fe(IV) intermediates in aliphatic chlorination by the halogenase CytC3. Nat. Chem. Biol. 2007;3:113–116. PubMed

Solomon EI, Decker A, Lehnert N. Non-heme iron enzymes: contrasts to heme catalysis. Proc. Natl. Acad. Sci. U. S. A. 2003;100:3589–3594. PubMed PMC

Cho KB, Hirao H, Shaik S, Nam W. To rebound or dissociate? This is the mechanistic question in C–H hydroxylation by heme and nonheme metal–oxo complexes. Chem. Soc. Rev. 2016;45:1197–1210. PubMed

Visser SP. Propene activation by the oxo-iron active species of taurine/α-ketoglutarate dioxygenase (TauD) enzyme. How does the catalysis compare to heme-enzymes? J. Am. Chem. Soc. 2006;128:9813–9824. PubMed

Faponle AS, Quesne MG, Sastri CV, Banse F, Visser SP. Differences and comparisons of the properties and reactivities of iron(III)–hydroperoxo complexes with saturated coordination sphere. Chemistry. 2015;21:1221–1236. PubMed PMC

Schröder, D., Schwarz, H.: C-H and C-C bond activation by bare transition-metal oxide cations in the gas phase. Angew. Chem. Int. Ed. 34, 1973–1995 (1995)

Meunier B. Metalloporphyrins as versatile catalysts for oxidation reactions and oxidative DNA cleavage. Chem. Rev. 1992;92:1411–1456.

Groves JT, Nemo TE. Aliphatic hydroxylation catalyzed by iron porphyrin complexes. J. Am. Chem. Soc. 1983;105:6243–6248.

Suh Y, Seo MS, Kim KM, Kim YS, Jang HG, Tosha T, Kitagawa T, Kim J, Nam W. Nonheme iron(II) complexes of macrocyclic ligands in the generation of oxoiron(IV) complexes and the catalytic epoxidation of olefins. J. Inorg. Biochem. 2006;100:627–633. PubMed

Bae SH, Seo MS, Lee YM, Cho KB, Kim WS, Nam W. Mononuclear nonheme high-spin (S=2) versus intermediate-spin (S=1) iron(IV)–oxo complexes in oxidation reactions. Angew. Chem. Int. Ed. Engl. 2016;55:8027–8031. PubMed

Park J, Lee YM, Ohkubo K, Nam W, Fukuzumi S. Efficient epoxidation of styrene derivatives by a nonheme iron(IV)-oxo complex via proton-coupled electron transfer with triflic. Inorg. Chem. 2015;54:5806–5812. PubMed

Wang B, Lee YM, Seo MS, Nam W. Mononuclear nonheme iron(III)-iodosylarene and high-valent ironoxo complexes in olefin epoxidation reactions. Angew. Chem. Int. Ed. 2015;54:11740–11744. PubMed

Kwon YH, Mai BK, Lee YM, Dhuri SN, Mandal D, Cho KB, Kim Y, Shaik S, Nam W. Determination of spin inversion probability, H-tunneling correction, and regioselectivity in the two-state reactivity of nonheme iron(IV)-oxo complexes. J. Phys. Chem. Lett. 2015;6:1472–1476. PubMed

Ye WH, Ho DM, Friedle S, Palluccio TD, Rybak-Akimova EV. Role of Fe(IV)-oxo intermediates in stoichiometric and catalytic oxidations mediated by iron pyridine-azamacrocycles. Inorg. Chem. 2012;51:5006–5021. PubMed

Nam W, Ho R, Valentine JS. Iron-cyclam complexes as catalysts for the epoxidation of olefins by 30% aqueous hydrogen peroxide in acetonitrile and methanol. J. Am. Chem. Soc. 1991;113:7052–7054.

Engelmann X, Malik DD, Corona T, Warm K, Farquhar ER, Swart M, Nam W, Ray K. Trapping of a highly reactive oxoiron(IV) complex in the catalytic epoxidation of olefins by hydrogen peroxide. Angew. Chem. Int. Ed. Engl. 2019;58:4012–4016. PubMed

Mayer JM. Understanding hydrogen atom transfer: from bond strengths to Marcus theory. Acc. Chem. Res. 2011;44:36–46. PubMed PMC

De Visser SP, Ogliaro F, Sharma PK, Shaik S. What factors affect the regioselectivity of oxidation by cytochrome P450? A DFT study of allylic hydroxylation and double bond epoxidation in a model reaction. J. Am. Chem. Soc. 2002;124:11809–11826. PubMed

Sainna MA, Kumar S, Kumar D, Fornarini S, Crestoni ME, de Visser SP. A comprehensive test set of epoxidation rate constants for iron(IV)–oxo porphyrin cation radical complexes. Chem. Sci. 2015;6:1516–1529. PubMed PMC

Gonzalez-Ovalle LE, Quesne MG, Kumar D, Goldberg DP, de Visser SP. Axial and equatorial ligand effects on biomimetic cysteine dioxygenase model complexes. Org. Biomol. Chem. 2012;10:5401–5409. PubMed PMC

Chantarojsiri T, Sun Y, Long JR, Chang CJ. Water-soluble iron(IV)-oxo complexes supported by pentapyridine ligands: axial ligand effects on hydrogen atom and oxygen atom transfer reactivity. Inorg. Chem. 2015;54:5879–5887. PubMed

Geng C, Ye S, Neese F. Analysis of reaction channels for alkane hydroxylation by nonheme iron(IV)–oxo complexes. Angew. Chem. Int. Ed. 2010;49:5717–5720. PubMed

Ye S, Neese F. Nonheme oxo-iron(IV) intermediates form an oxyl radical upon approaching the C–H bond activation transition state. Proc. Natl. Acad. Sci. 2011;108:1228–1233. PubMed PMC

Saouma CT, Mayer JM. Do spin state and spin density affect hydrogen atom transfer reactivity? Chem. Sci. 2014;5:21–31. PubMed PMC

Kang, Y., Chen, H., Jeong, Y.J., Lai, W., Bae, E.H., Shaik, S., Nam, W.: Enhanced reactivities of iron(IV)-oxo porphyrin π-cation radicals in oxygenation reactions by electron-donating axial ligands. Chem. Eur. J. 15, 10039–10046 (2009) PubMed

Hirao H, Kumar D, Thiel W, Shaik S. Two states and two more in the mechanisms of hydroxylation and epoxidation by cytochrome P450. J. Am. Chem. Soc. 2005;127:13007–13018. PubMed

Kumar D, de Visser SP, Shaik S. Multistate reactivity in styrene epoxidation by compound I of cytochrome p450: mechanisms of products and side products formation. Chem. Eur. J. 2005;11:2825–2835. PubMed

Schröder D, Shaik S, Schwarz H. Characterization, orbital description, and reactivity patterns of transition-metal oxo species in the gas phase. Struct. Bonding (Berlin, Ger.) 2000;97:91–123.

Hirao H, Que L, Nam W, Shaik S. A two-state reactivity rationale for counterintuitive axial ligand effects on the C-H activation reactivity of nonheme FeIV=O oxidants. Chem. Eur. J. 2008;14:1740–1756. PubMed

Ye S, Neese F. Quantum chemical studies of C-H activation reactions by high-valent nonheme iron centers. Curr. Opin. Chem. Biol. 2009;13:89–98. PubMed

Seo MS, Kim NH, Cho KB, So JE, Park SK, Clemancey M, Garcia-Serres R, Latour JM, Shaik S, Nam W. A mononuclear nonheme iron(IV)-oxo complex which is more reactive than cytochrome P450 model compound I. Chem. Sci. 2011;2:1039–1045.

Appleton AJ, Evans S, Smith JRL. Allylic oxidation and epoxidation of cycloalkenes by iodosylbenzene catalysed by iron(III) and manganese(III) tetra(dichlorophenyl)porphyrin: the marked influence of ring size on the rate of allylic oxidation. J. Chem. Soc. Perkin Trans. 1996;2(3):281–285.

Yi W, Yuan L, Kun Y, Zhengwen H, Jing T, Xu F, Hong G, Yong W. What factors influence the reactivity of C–H hydroxylation and C=C epoxidation by [FeIV(Lax)(1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)(O)]n+ J. Biol. Inorg. Chem. 2015;20:1123–1134. PubMed

Kumar D, Latifi R, Kumar S, Rybak-Akimova EV, Sainna MA, De Visser SP. Rationalization of the barrier height for p-Z-styrene epoxidation by iron(IV)-oxo porphyrin cation radicals with variable axial ligands. Inorg. Chem. 2013;52:7968–7979. PubMed

Bernasconi L, Baerends EJ. A frontier orbital study with ab initio molecular dynamics of the effects of solvation on chemical reactivity: solvent-induced orbital control in FeO-activated hydroxylation reactions. J. Am. Chem. Soc. 2013;135:8857–8867. PubMed

Planas O, Clemancey M, Latour JM, Company A, Costas M. Structural modeling of iron halogenases: synthesis and reactivity of halide-iron(IV)-oxo compounds. Chem. Commun. 2014;50:10887–10890. PubMed

Ducháčková L, Roithová J. The interaction of zinc(II) and hydroxamic acids and a metal-triggered Lossen rearrangement. Chem. Eur. J. 2009;15:13399–13405. PubMed

Jašíková L, Roithová J. Interaction of the gold(I) cation Au(PMe3)+ with unsaturated hydrocarbons. Organometallics. 2012;31:1935–1942.

Andris E, Jašík J, Gómez L, Costas M, Roithová J. Spectroscopic characterization and reactivity of triplet and quintet iron(IV) oxo complexes in the gas phase. Angew. Chem. 2016;128:3701–3705. PubMed PMC

Company A, Prat I, Frisch JR, Mas-Ballesté R, Güell M, Juhász G, Ribas X, Münck E, Luis JM, Que L, Costas M. Modelling the cis-oxo-labile binding site motif of non-heme iron oxygenases. Water exchange and remarkable oxidation reactivity of a novel non-heme iron(IV)-oxo compound bearing a tripodal tetradentate ligand. Chem. Eur. J. 2011;17:1622–1634. PubMed PMC

Stephens P, Devlin FJ, Chabalowski CF, Frisch MJ. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem. 1994;98:11623–11627.

Becke AD. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993;98:5648.

Lee C, Yang W, Parr RG. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B. 1988;37:785–789. PubMed

Grimme S, Ehrlich S, Goerigk L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 2011;32:1456–1465. PubMed

Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Scalmani, G., Barone, V., Mennucci, B., Petersson, G.A., Nakatsuji, H., Caricato, M., Li, X., Hratchian, H.P., Izmaylov, A.F., Bloino, J., Zheng, G., Sonnenberg, J.L., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven, T., Montgomery Jr., J.A., Peralta, J.E., Ogliaro, F., Bearpark, M., Heyd, J.J., Brothers, E., Kudin, K.N., Staroverov, V.N., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A., Burant, J.C., Iyengar, S.S., Tomasi, J., Cossi, M., Rega, N., Millam, J. M., Klene, M., Knox, J. E., Cross, J. B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R.E., Yazyev, O., Austin, A. J., Cammi, R., Pomelli, C., Ochterski, J.W., Martin, R. L., Morokuma, K., Zakrzewski, V.G., Voth, G.A., Salvador, P., Dannenberg, J.J., Dapprich, S., Daniels, A. D., Farkas, Ö., Foresman, J.B., Ortiz, J.V, Cioslowski, J., Fox, D.J.: Gaussian 09 Revision D.01, (2013)

Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D.J.: Gaussian 16 Revision A.03, (2016)

Chen H, Lai W, Shaik S. Exchange-enhanced H-abstraction reactivity of high-valent nonheme iron(IV)-oxo from coupled cluster and density functional theories. J. Phys. Chem. Lett. 2010;1:1533–1540.

Andris E, Navrátil R, Jašík J, Terencio T, Srnec M, Costas M, Roithová J. Chasing the evasive Fe═O stretch and the spin state of the iron(IV)-oxo complexes by photodissociation spectroscopy. J. Am. Chem. Soc. 2017;139:2757–2765. PubMed

Reed AE, Weinstock RB, Weinhold F. Natural population analysis. J. Chem. Phys. 1985;83:735–746.

Marenich AV, Cramer CJ, Truhlar DG. Universal solvation model based on solute electron density and on a continuum model of the solvent defined by the bulk dielectric constant and atomic surface tensions. J. Phys. Chem. B. 2009;113:6378–6396. PubMed

Andersson K, Malmqvist PÅ, Roos BO, Sadlej AJ, Wolinski K. Second-order perturbation theory with a CASSCF reference function. J. Phys. Chem. 1990;94:5483–5488.

Andersson K, Malmqvist PÅ, Roos BO. Second-order perturbation theory with a complete active space self-consistent field reference function. J. Chem. Phys. 1992;96:1218–1226.

Andersson K. Different forms of the zeroth-order Hamiltonian in second-order perturbation theory with a complete active space self-consistent field reference function. Theor. Chim. Acta. 1995;91:31–46.

Finley J, Malmqvist P-Å, Roos BO, Serrano-Andrés L. The multi-state CASPT2 method. Chem. Phys. Lett. 1998;288:299–306.

Aquilante F, Autschbach J, Carlson RK, Chibotaru LF, Delcey MG, De Vico L, Galván IF, Ferré N, Frutos LM, Gagliardi L, Garavelli M, Giussani A, Hoyer CE, Manni GL, Lischka H, Ma D, Malmqvist PÅ, Müller T, Nenov A, Olivucci M, Pedersen TB, Peng D, Plasser F, Pritchard B, Reiher M, Rivalta I, Schapiro I, Segarra-Martí J, Stenrup M, Truhlar DG, Ungur L, Valentini A, Vancoillie S, Veryazov V, Vysotskiy VP, Weingart O, Zapata F, Lindh R. MOLCAS 8: new capabilities for multiconfigurational quantum chemical calculations across the periodic table. J. Comp. Chem. 2016;37:506–541. PubMed

Douglas M, Kroll NM. Quantum electrodynamical corrections to the fine structure of helium. Ann. Phys. (Amsterdam, Neth.) 1974;82:89–−155.

Hess BA. Relativistic electronic-structure calculations employing a two-component no-pair formalism with external-field projection operators. Phys. Rev. A: At. Mol. Opt. Phys. 1986;33:3742–3748. PubMed

Jansen G, Hess BA. Revision of the Douglas-Kroll transformation. Phys. Rev. A: At. Mol. Opt. Phys. 1989;39:6016–6017. PubMed

Aquilante F, Malmqvist P-Å, Pedersen TB, Ghosh A, Roos BO. Cholesky decomposition-based multiconfiguration second-order perturbation theory (CD-CASPT2): application to the spin-state energetics of CoIII(diiminato)(NPh) J. Chem. Theory Comput. 2008;4:694–702. PubMed

Schröder D, Shaik S, Schwarz H. Two-state reactivity as a new concept in organometallic chemistry. Acc. Chem. Res. 2000;33:139–145. PubMed

Schlangen M, Neugebauer J, Reiher M, Schröder D, López JP, Haryono M, Heinemann FW, Grohmann A, Schwarz H. Gas-phase C-H and N-H bond activation by a high valent nitrido-iron dication and NH-transfer to activated olefins. J. Am. Chem. Soc. 2008;130:4285–4294. PubMed

Schlangen M, Schwarz H. Effects of ligands, cluster size, and charge state in gas-phase catalysis: a happy marriage of experimental and computational studies. Catal. Lett. 2012;142:1265–1278.

Puri M, Biswas AN, Fan R, Guo Y, Que L., Jr Modeling non-heme iron halogenases: high-spin oxoiron(IV)–halide complexes that halogenate C–H bonds. J. Am. Chem. Soc. 2016;138:2484–2487. PubMed

Rana S, Biswas JP, Sen A, Clémancey M, Blondin G, Latour J-M, Rajaraman G, Maiti D. Selective C–H halogenation over hydroxylation by non-heme iron(IV)-oxo. Chem. Sci. 2018;9:7843–7858. PubMed PMC

Favini G, Buemi G, Raimondi M. Molecular conformation of cyclenes. I. Cyclohexene, cycloheptene, cis- and trans-cyclooctene, cis- and trans-cyclononene. J. Mol. Struct. 1968;2:137–148.

Buemi G, Favini G, Zuccarello F. Molecular conformation of cyclenes: III. Trans-cyclooctene, trans-cyclononene, cis- and trans-cyclo-decene. J. Mol. Struct. 1970;5:101–110.

Jensen FR, Bushweller CH. Conformational preferences and interconversion barriers in cyclohexene and derivatives. J. Am. Chem. Soc. 1969;91:5774–5782.

Allinger NL. Conformational analysis. 130. MM2. A hydrocarbon force field utilizing V1 and V2 torsional terms. J. Am. Chem. Soc. 1977;99:8127–8134.

Leong MK, Mastryukov VS, Boggs JE. Structure and conformation of cyclopentene, cycloheptene and trans-cyclooctene. J. Mol. Struct. 1998;445:149–160.

Neuenschwander U, Hermans I. The conformations of cyclooctene: consequences for epoxidation chemistry. J. Org. Chem. 2011;76:10236–10240. PubMed

Lee YM, Hong S, Morimoto Y, Shin W, Fukuzumi S, Nam W. Dioxygen activation by a non-heme iron(II) complex: formation of an iron(IV)−oxo complex via C−H activation by a putative iron(III)−superoxo species. J. Am. Chem. Soc. 2010;132:10668–10670. PubMed

Bischof P, Heilbronner E. Photoelectron–spectroscopic evidence concerning “homo-aromaticity”. Helv. Chim. Acta. 1970;53:1677–1682.

Blanksby SJ, Ellison GB. Bond dissociation energies of organic molecules. Acc. Chem. Res. 2003;36:255–263. PubMed