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DiPasquale AG, Kaminsky W, Mayer JM. Oxygen-oxygen bond homolysis in a novel titanium(IV) alkylperoxide complex, Cp2Ti(OOtBu)Cl. J Am Chem Soc 2002; 124:14534-5. [PMID: 12465953 DOI: 10.1021/ja028500a] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Cp2TiCl2 reacts with NaOOtBu to form the new titanium peroxide complex, Cp2Ti(OOtBu)Cl (1), which has been characterized both in solution and in the solid state. This complex is surprisingly unreactive towards olefins and phosphines, as it does not directly transfer an oxygen atom. Instead, decomposition occurs via initial homolysis of the oxygen-oxygen bond, yielding a tert-butoxyl radical. Decomposition of 1 in the presence of phosphines yields either phosphine oxides (e.g., OPPh3) or phosphinites (e.g., tBuOPEt2), products that result from tBuO* + PR3. O-O bond homolysis is surprising because the Ti(IV) center is d0 and cannot be oxidized, where all previous clear examples of homolytic cleavage of metal peroxide complexes are facilitated by oxidation of the metal center.
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Mayer JM, Hrovat DA, Thomas JL, Borden WT. Proton-coupled electron transfer versus hydrogen atom transfer in benzyl/toluene, methoxyl/methanol, and phenoxyl/phenol self-exchange reactions. J Am Chem Soc 2002; 124:11142-7. [PMID: 12224962 DOI: 10.1021/ja012732c] [Citation(s) in RCA: 273] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Degenerate hydrogen atom exchange reactions have been studied using calculations, based on density functional theory (DFT), for (i) benzyl radical plus toluene, (ii) phenoxyl radical plus phenol, and (iii) methoxyl radical plus methanol. The first and third reactions occur via hydrogen atom transfer (HAT) mechanisms. The transition structure (TS) for benzyl/toluene hydrogen exchange has C(2)(h)() symmetry and corresponds to the approach of the 2p-pi orbital on the benzylic carbon of the radical to a benzylic hydrogen of toluene. In this TS, and in the similar C(2) TS for methoxyl/methanol hydrogen exchange, the SOMO has significant density in atomic orbitals that lie along the C-H vectors in the former reaction and nearly along the O-H vectors in the latter. In contrast, the SOMO at the phenoxyl/phenol TS is a pi symmetry orbital within each of the C(6)H(5)O units, involving 2p atomic orbitals on the oxygen atoms that are essentially orthogonal to the O.H.O vector. The transferring hydrogen in this reaction is a proton that is part of a typical hydrogen bond, involving a sigma lone pair on the oxygen of the phenoxyl radical and the O-H bond of phenol. Because the proton is transferred between oxygen sigma orbitals, and the electron is transferred between oxygen pi orbitals, this reaction should be described as a proton-coupled electron transfer (PCET). The PCET mechanism requires the formation of a hydrogen bond, and so is not available for benzyl/toluene exchange. The preference for phenoxyl/phenol to occur by PCET while methoxyl/methanol exchange occurs by HAT is traced to the greater pi donating ability of phenyl over methyl. This results in greater electron density on the oxygens in the PCET transition structure for phenoxyl/phenol, as compared to the PCET hilltop for methoxyl/methanol, and the greater electron density on the oxygens selectively stabilizes the phenoxyl/phenol TS by providing a larger binding energy of the transferring proton.
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203
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Larsen AS, Wang K, Lockwood MA, Rice GL, Won TJ, Lovell S, Sadílek M, Turecek F, Mayer JM. Hydrocarbon oxidation by Bis-mu-oxo manganese dimers: electron transfer, hydride transfer, and hydrogen atom transfer mechanisms. J Am Chem Soc 2002; 124:10112-23. [PMID: 12188675 DOI: 10.1021/ja020204a] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Described here are oxidations of alkylaromatic compounds by dimanganese mu-oxo and mu-hydroxo dimers [(phen)(2)Mn(IV)(mu-O)(2)Mn(IV)(phen)(2)](4+) ([Mn(2)(O)(2)](4+)), [(phen)(2)Mn(IV)(mu-O)(2)Mn(III)(phen)(2)](3+) ([Mn(2)(O)(2)](3+)), and [(phen)(2)Mn(III)(mu-O)(mu-OH)Mn(III)(phen)(2)](3+) ([Mn(2)(O)(OH)](3+)). Dihydroanthracene, xanthene, and fluorene are oxidized by [Mn(2)(O)(2)](3+) to give anthracene, bixanthenyl, and bifluorenyl, respectively. The manganese product is the bis(hydroxide) dimer, [(phen)(2)Mn(III)(mu-OH)(2)Mn(II)(phen)(2)](3+) ([Mn(2)(OH)(2)](3+)). Global analysis of the UV/vis spectral kinetic data shows a consecutive reaction with buildup and decay of [Mn(2)(O)(OH)](3+) as an intermediate. The kinetics and products indicate a mechanism of hydrogen atom transfers from the substrates to oxo groups of [Mn(2)(O)(2)](3+) and [Mn(2)(O)(OH)](3+). [Mn(2)(O)(2)](4+) is a much stronger oxidant, converting toluene to tolyl-phenylmethanes and naphthalene to binaphthyl. Kinetic and mechanistic data indicate a mechanism of initial preequilibrium electron transfer for p-methoxytoluene and naphthalenes because, for instance, the reactions are inhibited by addition of [Mn(2)(O)(2)](3+). The oxidation of toluene by [Mn(2)(O)(2)](4+), however, is not inhibited by [Mn(2)(O)(2)](3+). Oxidation of a mixture of C(6)H(5)CH(3) and C(6)H(5)CD(3) shows a kinetic isotope effect of 4.3 +/- 0.8, consistent with C-H bond cleavage in the rate-determining step. The data indicate a mechanism of initial hydride transfer from toluene to [Mn(2)(O)(2)](4+). Thus, oxidations by manganese oxo dimers occur by three different mechanisms: hydrogen atom transfer, electron transfer, and hydride transfer. The thermodynamics of e(-), H(*), and H(-) transfers have been determined from redox potential and pK(a) measurements. For a particular oxidant and a particular substrate, the choice of mechanism is influenced both by the thermochemistry and by the intrinsic barriers. Rate constants for hydrogen atom abstraction by [Mn(2)(O)(2)](3+) and [Mn(2)(O)(OH)](3+) are consistent with their 79 and 75 kcal mol(-)(1) affinities for H(*). In the oxidation of p-methoxytoluene by [Mn(2)(O)(2)](4+), hydride transfer is thermochemically 24 kcal mol(-)(1) more facile than electron transfer; yet the latter mechanism is preferred. Thus, electron transfer has a substantially smaller intrinsic barrier than does hydride transfer in this system.
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204
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Bryant JR, Taves JE, Mayer JM. Oxidations of hydrocarbons by manganese(III) tris(hexafluoroacetylacetonate). Inorg Chem 2002; 41:2769-76. [PMID: 12005502 DOI: 10.1021/ic025541z] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mn(hfacac)(3) is an easily prepared and reactive oxidant (hfacac = hexafluoroacetylacetonate). It forms stable solutions in benzene and methylene chloride but is rapidly reduced in acetonitrile, DMSO, acetone, and ethers. It is reduced by ferrocene to give the Mn(II) complex [Cp(2)Fe][Mn(hfacac)(3)], which has been structurally characterized. Mn(hfacac)(3) also rapidly oxidizes 1-acetylferrocene, 1,1'-diacetylferrocene, and tris(4-bromophenyl)amine. Based on an equilibrium established with tris(2,4-dibromophenyl)amine, a redox potential of 0.9 +/- 0.1 V vs Cp(2)Fe(+/0) is calculated. Mn(hfacac)(3) oxidizes 9,10-dihydroanthracene (DHA) cleanly to anthracene, with a bimolecular rate constant of 6.8 x 10(-4) M(-1) s(-1) at 25 degrees C in benzene solution. In the presence of small amounts of water, the manganese(II) product is isolated as cis-Mn(hfacac)(2)(H(2)O)(2), which has also been structurally characterized. Mn(hfacac)(3) also oxidizes xanthene to 9,9'-bixanthene, 1,4-cyclohexadiene to benzene, and 2,4-di-tert-butylphenol to the phenol dimer. Toluene and substituted toluenes are oxidized to tolylphenylmethanes. Product analyses and relative rates--for instance that p-methoxytoluene reacts much faster than toluene--indicate that the more electron rich substrates react by initial electron transfer to manganese. For the less electron rich substrates, such as 1,4-cyclohexadiene, a mechanism of initial hydrogen atom transfer to Mn(hfacac)(3) is suggested. The ability of Mn(hfacac)(3) to abstract H* is reasonable given its high redox potential and the basicity of [Mn(hfacac)(3)](-). In CH(2)Cl(2) solution, oxidation of DHA is catalyzed by chloride ion.
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205
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Cook GK, Mayer JM. C-H Bond Activation by Metal Oxo Species: Oxidation of Cyclohexane by Chromyl Chloride. J Am Chem Soc 2002. [DOI: 10.1021/ja00084a029] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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206
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Bryan JC, Stenkamp RE, Tulip TH, Mayer JM. Oxygen atom transfer among rhenium, sulfur, and phosphorus. Characterization and reactivity of Re(O)Cl3(Me2S)(OPPh3) and Re(O)Cl3(CNCMe3)2. Inorg Chem 2002. [DOI: 10.1021/ic00261a024] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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207
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Conry RR, Mayer JM. Oxygen atom transfer reactions of cationic rhenium(III), rhenium(V), and rhenium(VII) triazacyclononane complexes. Inorg Chem 2002. [DOI: 10.1021/ic00349a010] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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208
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Bryan JC, Mayer JM. Oxidative addition of cyclopentanone to WCl2(PMePh2)4 to give a tungsten(VI) oxo-alkylidene complex. J Am Chem Soc 2002. [DOI: 10.1021/ja00257a064] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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209
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Atagi LM, Over DE, McAlister DR, Mayer JM. On the mechanism of oxygen-atom or nitrene-group transfer in reactions of epoxides and aziridines with tungsten(II) compounds. J Am Chem Soc 2002. [DOI: 10.1021/ja00003a021] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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210
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Mayer JM, Tulip TH, Calabrese JC, Valencia E. Associative ligand substitution reactions of low-valent rhenium-oxo compounds. Crystal and molecular structures of [ReO(MeC.tplbond.CMe)2L]SbF6, L = pyridine and 4,4'-dimethyl-2,2'-bipyridine. J Am Chem Soc 2002. [DOI: 10.1021/ja00235a024] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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211
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Jang S, Atagi LM, Mayer JM. Deoxygenation of alcohols and desulfurization of thiols by WCl2(PMePh2)4. J Am Chem Soc 2002. [DOI: 10.1021/ja00173a048] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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212
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Hall KA, Mayer JM. Reactions of ML4Cl2 (M = Mo, W; L = PMe3, PMePh2) with epoxides, episulfides, carbon dioxide, heterocumulenes, and other substrates: a comparative study of oxidative addition by oxygen atom, sulfur atom, or nitrene group transfer. J Am Chem Soc 2002. [DOI: 10.1021/ja00052a041] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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213
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Brock SL, Mayer JM. Oxygen atom transfer from a phosphine oxide to tungsten(II) compounds. Inorg Chem 2002. [DOI: 10.1021/ic00009a034] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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214
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Atagi LM, Critchlow SC, Mayer JM. Reactivity of the tungsten carbyne W(.tplbond.CCH3)Cl(PMe3)4: double carbonylation, carbyne-alkyne complexes, and stoichiometric acetylene metathesis. J Am Chem Soc 2002. [DOI: 10.1021/ja00049a085] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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215
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Mayer JM, Wolczanski PT, Santarsiero BD, Olson WA, Bercaw JE. X-ray crystal structure determination of [.eta.5-C5(CH3)5]Ta[P(CH3)3]2H4 and high-field NMR studies of phosphine derivatives of (pentamethylcyclopentadienyl)tantalum(V) hydrides. Inorg Chem 2002. [DOI: 10.1021/ic00150a001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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216
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Erikson TKG, Bryan JC, Mayer JM. Low-valent oxo compounds. 5. Low-valent rhenium oxo alkoxide complexes. Synthesis, characterization, structure, and ligand exchange and carbon monoxide insertion reactions. Organometallics 2002. [DOI: 10.1021/om00099a006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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217
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Hall KA, Mayer JM. .mu.-Sulfido and .mu.-Oxo Dimers M2(.mu.-E)(.mu.-Cl)Cl3(PMe3)5 Obtained by Conproportionation of MCl2(PMe3)4 and M(E)Cl2(PMe3)3 (M = Mo, W; E = O, S): Complete vs Incomplete Intermetal Atom Transfer. Inorg Chem 2002. [DOI: 10.1021/ic00093a016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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218
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Helgeson RC, Weisman GR, Toner JL, Tarnowski TL, Chao Y, Mayer JM, Cram DJ. Host-guest complexation. 18. Effects on cation binding of convergent ligand sites appended to macrocyclic polyethers. J Am Chem Soc 2002. [DOI: 10.1021/ja00511a024] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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219
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Brown SN, Mayer JM. Self-Assembly of a Complex Fluorinated Metallacycle from Hexafluoroacetone and Acetonitrile on Aerobic Photolysis of (HB(pz)3)ReO(C2O4). Inorg Chem 2002. [DOI: 10.1021/ic00117a030] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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220
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Spaltenstein E, Erikson TKG, Critchlow SC, Mayer JM. Low-valent oxo compounds. 7. Low-valent rhenium-oxo alkyl and -oxo hydride complexes. The stabilizing influence of the oxo ligand. J Am Chem Soc 2002. [DOI: 10.1021/ja00184a032] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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221
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222
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Bryan JC, Arterburn JB, Cook GK, Mayer JM. Deoxygenative coupling of ketones and alkenes by tungsten(II) compounds. Organometallics 2002. [DOI: 10.1021/om00060a010] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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223
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Cook GK, Mayer JM. C-H Bond Activation by Metal Oxo Species: Oxidation of Cyclohexane by Chromyl Chloride. [Erratum to document cited in CA120:163174]. J Am Chem Soc 2002. [DOI: 10.1021/ja00098a077] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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224
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Helgeson RC, Timko JM, Moreau P, Peacock SC, Mayer JM, Cram DJ. Models for chiral recognition in molecular complexation. J Am Chem Soc 2002. [DOI: 10.1021/ja00828a039] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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225
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Bryan JC, Mayer JM. Oxidative addition of carbon-oxygen and carbon-nitrogen double bonds to WCl2(PMePh2)4. Synthesis of tungsten metallaoxirane and tungsten oxo- and imido-alkylidene complexes. J Am Chem Soc 2002. [DOI: 10.1021/ja00162a034] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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