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Proton-Coupled Electron Transfer to a Molybdenum Ethylene Complex Yields a β-Agostic Ethyl: Structure, Dynamics and Mechanism

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/jacs.8b08460· OSTI ID:1478323
 [1];  [2]
  1. Princeton Univ., NJ (United States). Department of Chemistry; Princeton University
  2. Princeton Univ., NJ (United States). Department of Chemistry
+ Show Author Affiliations
In this paper, the interconversion of molybdenum ethylene and ethyl complexes by proton-coupled electron transfer (PCET) is described, an unusual transformation in organometallic chemistry. The cationic molybdenum ethylene complex [(PhTpy)(PPh2Me)2Mo(C2H4)][BArF24] ([1-C2H4]+; PhTpy = 4'-Ph-2,2',6',2"-terpyridine, ArF24 = [C6H3-3,5-(CF3)2]4) was synthesized, structurally characterized, and its electronic structure established by a combination of spectroscopic and computational methods. The overall electronic structure is best described as a molybdenum(III) complex with a metallacyclopropane and a redox neutral terpyridine ligand. Addition of the nonclassical ammine complex [(PhTpy)(PPh2Me)2Mo(NH3)][BArF24] ([1-NH3]+) to [1-C2H4]+ resulted in a net C–H bond-forming PCET reaction to yield the molybdenum ethyl [(PhTpy)(PPh2Me)2Mo(CH2CH3)][BArF24] ([1-CH2CH3]+) and amido [(PhTpy)(PPh2Me)2Mo(NH2)][BArF24] ([1-NH2]+) compounds. The reaction was reversed by addition of 2,4,6-tritert-butylphenoxyl radical to [1-CH2CH3]+. The solid-state structure of [1-CH2CH3]+ established a β-agostic ethyl ligand that is maintained in solution as judged by variable temperature 1H and 13C NMR experiments. A combination of variable-temperature NMR experiments and isotopic labeling studies were used to probe the dynamics of [1-CH2CH3]+ and established restricted β-agostic -CH3 rotation at low temperature (ΔG‡ = 9.8 kcal mol–1 at -86 °C) as well as ethyl isomerization by β-hydride elimination-olefin rotation-reinsertion (ΔH‡ = 19.3 ± 0.6 kcal mol–1; ΔS‡ = 3.4 ± 1.7 cal mol–1 K–1). The β-(C–H) bond-dissociation free energy (BDFE) in [1-CH2CH3]+ was determined experimentally as 57 kcal mol–1 (THF) supported by a DFT-computed value of 52 kcal/mol–1 (gas phase). Comparison of pKa and electrochemical data for the complexes [1-C2H4]+ and [1-NH3]+ in combination with a deuterium kinetic isotope effect (kH/kD) of 3.5(2) at 23 °C support a PCET process involving initial electron transfer followed by protonation leading to the formation of [1-CH2CH3]+ and [1-NH2]+ or a concerted pathway. Lastly, the data presented herein provides a structural, thermochemical and mechanistic foundation for understanding the PCET reactivity of organometallic complexes with alkene and alkyl ligands.
Research Organization:
Princeton Univ., NJ (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0006498
OSTI ID:
1478323
Journal Information:
Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 42 Vol. 140; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

References (83)

Water: The Ideal Hydrogen-Atom Source in Free-Radical Chemistry Mediated by TiIII and Other Single-Electron-Transfer Metals? journal August 2006
Coordination-Number Dependence of Reactivity in an Imidoiron(III) Complex journal October 2006
Agostic NSiH⋅⋅⋅Mo Complexes: From Curiosity to Catalysis journal September 2008
A Cobalt(I) Pincer Complex with an η 2 -C aryl −H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation, Radical Abstraction, and Oxidative Addition journal January 2016
Structure and Isotope Effects of the β‐H Agostic (α‐Diimine)Nickel Cation as a Polymerization Intermediate journal February 2017
Interconversion of Molybdenum Imido and Amido Complexes by Proton-Coupled Electron Transfer journal January 2018
Hydrogen-Atom Transfer Reactions of Transition-Metal Hydrides journal January 1991
Activation of dihydrogen and coordination of molecular H2 on transition metals journal February 2014
Molecular Catalysts for Water Oxidation journal July 2015
Transition-Metal Hydride Radical Cations journal February 2016
Brønsted–Lowry Acid Strength of Metal Hydride and Dihydrogen Complexes journal March 2016
Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins journal June 2016
Homolytic N–H Activation of Ammonia: Hydrogen Transfer of Parent Iridium Ammine, Amide, Imide, and Nitride Species journal July 2015
Terpyridine Molybdenum Dinitrogen Chemistry: Synthesis of Dinitrogen Complexes That Vary by Five Oxidation States journal March 2016
Arene C(sp 2 )-H Metalation at Ni II Modeled with a Reactive PONC Ph Ligand journal July 2016
Iron PCP Pincer Complexes in Three Oxidation States: Reversible Ligand Protonation To Afford an Fe(0) Complex with an Agostic C–H Arene Bond journal June 2018
Nickel-Catalyzed Reductive Cycloisomerization of Enynes with CO 2 journal June 2017
Structural Characterization of β-Agostic Bonds in Pd-Catalyzed Polymerization journal September 2017
Reversible Ligand Protonation of a Mn(I) PCP Pincer Complex To Afford a Complex with an η 2 -C aryl –H Agostic Bond journal June 2018
Absolute Estimates of Pd II (η 2 -Arene) C–H Acidity journal July 2018
Catalytic N 2 -to-NH 3 Conversion by Fe at Lower Driving Force: A Proposed Role for Metallocene-Mediated PCET journal February 2017
Understanding Hydrogen Atom Transfer: From Bond Strengths to Marcus Theory journal January 2011
Climbing Nitrogenase: Toward a Mechanism of Enzymatic Nitrogen Fixation journal May 2009
Proton-Coupled Electron Transfer journal November 2007
Thermochemistry of Proton-Coupled Electron Transfer Reagents and its Implications journal December 2010
Proton-Coupled Electron Flow in Protein Redox Machines journal December 2010
Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds journal November 2010
Introduction: Proton-Coupled Electron Transfer journal December 2010
Synthesis of hexanuclear molybdenum cluster alkyl complexes coordinated with trialkylphosphines: crystal structures of trans-[(Mo6Cl8)Cl4{P(n-C4H9)3}2] and all-trans-[(Mo6Cl8)Cl2(C2H5)2{P(n-C4H9)3}2].cntdot.2C6H5CH3 journal April 1986
Electronic Structure and Reactivity of Isomeric Oxo-Mn(V) Porphyrins:  Effects of Spin-State Crossing and p K a Modulation journal May 2006
Spectroscopic and magnetic properties of heptacyanomolybdate(III). Evidence for pentagonal-bipyramidal and monocapped trigonal-prismatic structures journal April 1973
Molybdenum and Tungsten Structural Differences are Dependent on n d z 2 /( n + 1)s Mixing: Comparisons of (silox) 3 MX/R (M = Mo, W; silox = t Bu 3 SiO) journal July 2008
.beta.-Migratory insertion reactions of (.eta.5-C5R'5)Rh(L)(C2H4)R+BF4- (R' = hydrogen, methyl; R = hydrogen, ethyl; L = P(OMe)3, PMe3). Comparison of the energetics of hydride versus alkyl migration journal December 1992
Effect of the Ligand and Metal on the pKa Values of the Dihydrogen Ligand in the Series of Complexes [M(H2)H(L)2]+, M = Fe, Ru, Os, Containing Isosteric Ditertiaryphosphine Ligands, L journal April 1994
Reaction of [P 2 N 2 ]TaCH 2 (Me) with Ethylene:  Synthesis of [P 2 N 2 ]Ta(C 2 H 4 )Et, a Neutral Species with a β-Agostic Ethyl Group in Equilibrium with an α-Agostic Ethyl Group ([P 2 N 2 ] = PhP(CH 2 SiMe 2 NSiMe 2 CH 2 ) 2 PPh) journal February 2001
Acidity-oxidation-potential (AOP) values as estimates of relative bond dissociation energies and radical stabilities in dimethyl sulfoxide solution journal April 1986
Proton-coupled electron transfer between [Ru(bpy)2(py)OH2]2+ and [Ru(bpy)2(py)O]2+. A solvent isotope effect (kH2O/kD2O) of 16.1 journal May 1981
Preparation and characterization of 1,2-dialkyl compounds of dimolybdenum and ditungsten of formula M2R2(NMe2)4 (M.tplbond.M) journal July 1981
Decacarbonyl(methyl)hydrotriosmium: NMR evidence for a carbon.cntdot..cntdot.hydrogen.cntdot..cntdot.osmium interaction journal November 1978
Nuclear Magnetic Resonance Line-Shape and Double-Resonance Studies of Ring Inversion in Cyclohexane- d 11 journal February 1967
Hydride Donor Abilities and Bond Dissociation Free Energies of Transition Metal Formyl Complexes journal March 2002
Hydrocarbon Oxidation by Bis-μ-oxo Manganese Dimers:  Electron Transfer, Hydride Transfer, and Hydrogen Atom Transfer Mechanisms journal August 2002
Mechanistic Studies of Nickel(II) Alkyl Agostic Cations and Alkyl Ethylene Complexes:  Investigations of Chain Propagation and Isomerization in (α-diimine)Ni(II)-Catalyzed Ethylene Polymerization journal March 2003
Electron and Hydrogen-Atom Self-Exchange Reactions of Iron and Cobalt Coordination Complexes journal March 2003
Monomeric Mn III/II and Fe III/II Complexes with Terminal Hydroxo and Oxo Ligands:  Probing Reactivity via O−H Bond Dissociation Energies journal October 2003
Activation of C−H / H−H Bonds by Rhodium(II) Porphyrin Bimetalloradicals journal July 2004
Imido Transfer from Bis(imido)ruthenium(VI) Porphyrins to Hydrocarbons:  Effect of Imido Substituents, C−H Bond Dissociation Energies, and Ru VI/V Reduction Potentials journal November 2005
Thermodynamics of Rhodium Hydride Reactions with CO, Aldehydes, and Olefins in Water:  Organo-Rhodium Porphyrin Bond Dissociation Free Energies journal November 2005
Room Temperature Dehydrogenation of Ethane to Ethylene journal July 2011
Rapid C–H Bond Activation by a Monocopper(III)–Hydroxide Complex journal November 2011
Four-Coordinate Cobalt Pincer Complexes: Electronic Structure Studies and Ligand Modification by Homolytic and Heterolytic Pathways journal June 2014
Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions journal April 2009
Concerted Proton−Electron Transfer in a Ruthenium Terpyridyl-Benzoate System with a Large Separation between the Redox and Basic Sites journal July 2009
C−H Bond Activation by a Ferric Methoxide Complex:  A Model for the Rate-Determining Step in the Mechanism of Lipoxygenase journal September 1997
Formation of η 2 C−H Agostic Rhodium Arene Complexes and Their Relevance to Electrophilic Bond Activation journal November 1998
Thermodynamics of C−H Activation in Multiple Oxidation States:  Comparison of Benzylic C−H Acidities and C−H Bond Dissociation Energies in the Isostructural 16−20-Electron Complexes [Fe x (η 5 -C 5 R 5 )(η 6 -arene)] n , x = 0−IV, R = H or Me, n = −1 to +3 journal June 1999
Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes journal June 2000
Ammonia Synthesis by Hydrogenolysis of Titanium–Nitrogen Bonds Using Proton Coupled Electron Transfer journal March 2015
Bond-Weakening Catalysis: Conjugate Aminations Enabled by the Soft Homolysis of Strong N–H Bonds journal May 2015
Proton-Coupled Electron Transfer in the Reduction of Arenes by SmI 2 –Water Complexes journal August 2015
Ammonia Synthesis from a Pincer Ruthenium Nitride via Metal–Ligand Cooperative Proton-Coupled Electron Transfer journal April 2017
Effects of .pi.-Coordinated Transition-Metal Groups on Fluorene Acidities and Homolytic Bond Dissociation Enthalpies journal August 1994
.alpha.-Hydride vs. .beta.-hydride elimination. An example of an equilibrium between two tautomers journal March 1982
Organometallic nitrosyl chemistry. 35. Cyclopentadienylethyldinitrosylmolybdate anion, a novel, prototypal 19-electron nitrosyl complex journal February 1988
Studies of molybdenum compounds. 5. Diethyl(2,2'-bipyridyl)dioxomolybdenum(VI) and other higher dialkyl derivatives of dioxomolybdenum(VI) journal December 1986
Measurement of the Barrier to β-Hydride Elimination in a β-Agostic Palladium−Ethyl Complex:  A Model for the Energetics of Chain-Walking in (α-Diimine)PdR + Olefin Polymerization Catalysts journal September 2001
Some Organometallic Chemistry of Molybdenum Complexes that Contain the [HIPTN 3 N] 3 - Triamidoamine Ligand, {[3,5-(2,4,6- i -Pr 3 C 6 H 2 ) 2 C 6 H 3 NCH 2 CH 2 ] 3 N} 3 - journal August 2005
Effects of the Niobium(V) Center on the Energetics of Ligand-Centered Proton and Hydrogen Atom Transfer Reactions in Acyl and Alkoxide Complexes journal July 1997
The roles of the first and second coordination spheres in the design of molecular catalysts for H 2 production and oxidation journal January 2009
Thermodynamics of benzylic C–H activation in 18- and 19-electron iron sandwich complexes: determination of pK a values and bond dissociation energies journal January 1995
Cyclopentadiene-mediated hydride transfer from rhodium complexes journal January 2016
Nuclear magnetic resonance studies on partially deuteriated transition metal–methyl derivatives journal January 1992
New ansa-2,2-bis(η-cyclopentadienyl)propane molybdenum and tungsten compounds and intramolecular hydrogen–deuterium exchange in methyl-hydride and ethyl-hydride derivatives  journal January 1997
The role of proton coupled electron transfer in water oxidation journal January 2012
586. Olefin co-ordination compounds. Part III. Infra-red spectra and structure: attempted preparation of acetylene complexes journal January 1953
Titanium(IV) Isopropoxide-Catalyzed Formation of 1-Substituted Cyclopropanols in the Reaction of Ethylmagnesium Bromide with Methyl Alkanecarboxylates journal January 1991
Agostic interactions in transition metal compounds journal April 2007
Metal-Hydrogen Bond Cleavage Reactions of Transition Metal Hydrides: Hydrogen Atom, Hydride, and Proton Transfer Reactions journal May 1991
The crystal and molecular structures of bent bis-π-cyclopentadienyl–metal complexes: (a) bis-π-cyclopentadienyldibromorhenium(V) tetrafluoroborate, (b) bis-π-cyclopentadienyldichloromolybdenum(IV), (c) bis-π-cyclopentadienylhydroxomethylaminomolybdenum(IV) hexafluorophosphate, (d) bis-π-cyclopentadienylethylchloromolybdenum(IV), (e) bis-π-cyclopentadienyldichloroniobium(IV), (f) bis-π-cyclopentadienyldichloromolybdenum(V) tetrafluoroborate, (g) μ-oxo-bis[bis-π-cyclopentadienylchloroniobium(IV)] tetrafluoroborate, (h) bis-π-cyclopentadienyldichlorozirconium journal October 1974
Application of the Marcus Cross Relation to Hydrogen Atom Transfer Reactions journal December 2001
Cytochrome P450 Compound I: Capture, Characterization, and C-H Bond Activation Kinetics journal November 2010
Coordination-induced weakening of ammonia, water, and hydrazine X–H bonds in a molybdenum complex journal November 2016
Proton-Coupled Electron Transfer in Biology: Results from Synergistic Studies in Natural and Model Systems journal June 2009

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