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Natural Gas: An Alternative to Petroleum?

. Natural gas reserves: ~ 60 years Petroleum reserves: ~ 40 years. . Combustion of natural gas releases more energy per CO 2 molecule than that of petroleum. . Combustion of natural gas releases more energy per gram than that of petroleum. .

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Natural Gas: An Alternative to Petroleum?

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  1. Natural gas reserves: ~ 60 years Petroleum reserves: ~ 40 years  Combustion of natural gas releases more energy per CO2 molecule than that of petroleum  Combustion of natural gas releases more energy per gram than that of petroleum  Approximately twice the amount of natural gas produced for consumption is vented or burned at its source  Pressurization and refrigeration required for liquefaction (bp -164 °C)  Largest reserves located in remote regions of the world Natural Gas: An Alternative to Petroleum? Crabtree, R. H. Chem. Rev. 1995, 95, 987-1007 American Methanol Institute, 2000

  2. Natural Gas is a Source of Methane

  3. Limitations for the Practical Use of Methane Crabtree, R. H. Chem. Rev. 1995, 95, 987-1007

  4. 10% acetic acid polyethylene terephthalate (PET) 41% methyl t-butylether oxygenated fuels fuel cells 25% formaldehyde resins, urethane plastics, Spandex 27% other cleaning fluid, solvents, refrigerants, chlorine-free bleaches Methanol: a Fuel and a Chemical Feedstock 1995 U.S. Production 2.2 billion gallons www.methanex.com

  5. Direct Conversion of Methane to Methanol thermodynamically favored but the high temperature required to activate the strong C-H bond (439 kJ/mol) leads to overoxidation, i.e. CO2 and H2O Methane Monooxygenase Crabtree, R. H. Chem. Rev. 1995, 95, 987-1007 Periana, R. A. et al. Science1993, 259, 340-343

  6. Conversion of Methane to Methanol via Heterogeneous Catalysis Steam Reforming Substantial capital investment required to implement Crabtree, R. H. Chem. Rev. 1995, 95, 987-1007

  7. Industrial Hydrogen Production

  8. PtCl42- CH3OH + CH3Cl + PtCl42- CH4 + PtCl62- + H2O 120 °C Methane to Methanol Catalyzed by Soluble Pt(II) Salts Gol'dshleger, N. F.; Es'kova, V. V.; Shilov, A. E.; Shteinman, A. A. Zh. Fiz. Khim. (Engl. Transl.)1972, 46, 785-786

  9. Alkane C-H Bond Activation Using Electron Rich Transition Metal Complexes Oxidative Addition Ir(III) Ir(I) Ir(III) Ir(III) Ir(I) Ir(I) Reductive Elimination Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982, 104, 352-354

  10. C-H Bond Activation by an Electron Rich Metal Center

  11. C-H Bond Activation by an Electron Rich Metal Center Oxidative Addition has occurred

  12. C-H Bond Activation Selectivity Radical Process Oxidative Addition by Late Transition Metal Complexes the stronger C-H bond is favored

  13. A Remarkably Stable Pt(IV) Methyl Hydride Tp’PtMe2H in the solid state begins to decompose at 140 °C O'Reilly, S. A.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1996, 118, 5684

  14. Would react similarly? Lewis Acid Generates a Vacant Site at Pt(II) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J. J.Chem. Soc., Dalton Trans. 1996, 1809

  15. C-H Activation at Pt(II) the first stable Pt(IV) alkyl hydride formed by alkane oxidative addition to Pt(II) Wick, D. D.; Goldberg, K. I. J. Am. Chem. Soc.1997, 119, 10235

  16. Proposed Mechanism of C-H Activation

  17. C-H Bond Activation by an Electron Rich Metal Center Arrested State An Alkane Complex Oxidative Addition has occurred

  18. Mechanism of Reductive Elimination Involves Alkane Complexes (0.7)* (0.5)* (0.62)* (0.29)* (0.74) (0.75)* (0.8)* (0.77)*

  19. Pt(IV) Dimethyl Hydride Reacts with Oxygen Wick, D. D.; Goldberg, K. I. J. Am. Chem. Soc.1999, 121, 11900

  20. A Pt(IV) Dialkyl Hydroxide Hydroxide is thermally stable

  21. Catalytic Functionalization of Methane by Pt(II) (bpym)PtCl2 CH4 + 2H2SO4 CH3OSO3H + 2H2O + SO2 220 °C Periana, R. A. et al. Science1998, 280, 560-564

  22. Acknowledgements

  23. Synthesis of Dichloride Precursor 80 % yield 1H-NMR

  24. Structures of Isopropyl and Cyclopropyl Complexes

  25. Methyl Hydride Rearrangement d, 1.225 ppm JRhH = 2 Hz d, 1.236 ppm JRhH = 2 Hz t = 3 h t = 1 h 1H{2H}-NMR t = 0

  26. Reductive Elimination of Methane 1H -NMR d, -14.818 ppm JRhH = 24 Hz t, 0.134 ppm *

  27. Loss of Methane Shows Isotope Effects kH/kD = 0.62(7) Solvent kH/kD = 1.07(6)

  28. Loss of Methane is Dependent on Benzene Concentration

  29. Double Reciprocal Plot Plot is consistent with saturation behavior, i.e. a reversible Keq followed by the rate determining step Plot of 1/kobs vs. 1/[C6D6] is linear

  30. Kinetic Data are Consistent with an Alkane Complex Kinetic Scheme

  31. Reductive Elimination from Pt(IV) a 5-coordinate intermediate is required for both reductive elimination and oxidative addition Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 5961 Hill, G. S.; Rendina, L. M.; Puddephatt, R. J. Organometallics 1995, 14, 4966

  32. Oxidative Addition followed by Deprotonation of a Pt(IV) Alkyl Hydride Deprotonation of a Pt(II) Alkane Complex Mechanism of Shilov Type C-H Bond Activation

  33. C-H Activation at Pt(II) oxidative addition sigma bond metathesis Holtcamp, M. W.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1997, 119, 848

  34. Effect of Radical Initiator/Inhibitor O2, 1 atm Tp’PtMe2H Tp’PtMe2(OOH) C6D6

  35. O2, 1 atm Tp’PtMe2H Tp’PtMe2(OOH) C6D6/RT Reaction of Pt(IV) Dialkyl Hydride with Oxygen is Promoted by Light

  36. Proposed Radical Mechanism

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