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Title: Structures and reactivities of cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene on Pt(111)

Abstract

The structures and reactivities of various cyclic C{sub 7} hydrocarbons (cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene) adsorbed on Pt(111) have been examined by means of temperature-programmed reaction, reflection-absorption infrared, and Auger electron spectroscopies. At temperatures below 200 K, cycloheptane binds weakly to the surface and exhibits vibrational mode softening consistent with the presence of agostic C-H{hor_ellipsis}M interactions. In contrast, the cyclic alkenes cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene all bind strongly (and largely irreversibly) to the surface principally by means of interactions with their {pi}-systems. The chemistry of these adsorbates at higher temperatures has been mapped out in considerable detail. For cycloheptane, most simply desorbs but about 30% is dehydrogenated; interestingly, cycloheptene is not an intermediate in this process. Cycloheptene first loses two hydrogen atoms to give what the authors propose is an {eta}{sup 3},{eta}{sup 1}-C{sub 7}H{sub 10} product. 1,3-Cycloheptadiene first loses two hydrogen atoms to afford an {eta}{sup 5}-cycloheptadienyl product, which dehydrogenates further to give surface-bound cycloheptatriene in (apparently) high yield. Between 325 and 375 K, all of the cyclic C{sub 7} hydrocarbons dehydrogenate further and eventually yield a planar {eta}{sup 7}-cycloheptatrienyl (C{sub 7}H{sub 7}) species on the surface, although for cycloheptene this conversion is inefficient. The thermolytic decomposition of the {eta}{supmore » 7}-C{sub 7}H{sub 7} species begins at about 425 K and affords surface-bound hydrocarbons that are largely undetectable by RAIR spectroscopy. At higher temperatures (> 800 K), these hydrocarbons are completely dehydrogenated to form a carbonaceous overlayer. Ring contraction products, such as surface-bound benzene, are not observed as intermediates in any of the thermolytic reactions. The RAIR spectra of the {eta}{sup 5}-cycloheptadienyl and cycloheptatriene adsorbates both contain an unusual low-frequency vibrational band near 2,770 cm{sup {minus}1}. This band is not indicative of an agostic C-H{hor_ellipsis}M interaction, but is instead the signature of a methylene C-H bond that has been perturbed by hyperconjugative drain of electron density into the adjacent {pi}-system.« less

Authors:
; ; ;  [1]
  1. Univ. of Illinois, Urbana, IL (United States)
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
691310
DOE Contract Number:  
FG02-91ER45439
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 103; Journal Issue: 32; Other Information: PBD: 12 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; CYCLOALKANES; CYCLOALKENES; PLATINUM; AUGER ELECTRON SPECTROSCOPY; INFRARED SPECTRA

Citation Formats

Manner, W.L., Hostetler, M.J., Girolami, G.S., and Nuzzo, R.G. Structures and reactivities of cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene on Pt(111). United States: N. p., 1999. Web. doi:10.1021/jp990501a.
Manner, W.L., Hostetler, M.J., Girolami, G.S., & Nuzzo, R.G. Structures and reactivities of cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene on Pt(111). United States. doi:10.1021/jp990501a.
Manner, W.L., Hostetler, M.J., Girolami, G.S., and Nuzzo, R.G. Thu . "Structures and reactivities of cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene on Pt(111)". United States. doi:10.1021/jp990501a.
@article{osti_691310,
title = {Structures and reactivities of cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene on Pt(111)},
author = {Manner, W.L. and Hostetler, M.J. and Girolami, G.S. and Nuzzo, R.G.},
abstractNote = {The structures and reactivities of various cyclic C{sub 7} hydrocarbons (cycloheptane, cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene) adsorbed on Pt(111) have been examined by means of temperature-programmed reaction, reflection-absorption infrared, and Auger electron spectroscopies. At temperatures below 200 K, cycloheptane binds weakly to the surface and exhibits vibrational mode softening consistent with the presence of agostic C-H{hor_ellipsis}M interactions. In contrast, the cyclic alkenes cycloheptene, 1,3-cycloheptadiene, and cycloheptatriene all bind strongly (and largely irreversibly) to the surface principally by means of interactions with their {pi}-systems. The chemistry of these adsorbates at higher temperatures has been mapped out in considerable detail. For cycloheptane, most simply desorbs but about 30% is dehydrogenated; interestingly, cycloheptene is not an intermediate in this process. Cycloheptene first loses two hydrogen atoms to give what the authors propose is an {eta}{sup 3},{eta}{sup 1}-C{sub 7}H{sub 10} product. 1,3-Cycloheptadiene first loses two hydrogen atoms to afford an {eta}{sup 5}-cycloheptadienyl product, which dehydrogenates further to give surface-bound cycloheptatriene in (apparently) high yield. Between 325 and 375 K, all of the cyclic C{sub 7} hydrocarbons dehydrogenate further and eventually yield a planar {eta}{sup 7}-cycloheptatrienyl (C{sub 7}H{sub 7}) species on the surface, although for cycloheptene this conversion is inefficient. The thermolytic decomposition of the {eta}{sup 7}-C{sub 7}H{sub 7} species begins at about 425 K and affords surface-bound hydrocarbons that are largely undetectable by RAIR spectroscopy. At higher temperatures (> 800 K), these hydrocarbons are completely dehydrogenated to form a carbonaceous overlayer. Ring contraction products, such as surface-bound benzene, are not observed as intermediates in any of the thermolytic reactions. The RAIR spectra of the {eta}{sup 5}-cycloheptadienyl and cycloheptatriene adsorbates both contain an unusual low-frequency vibrational band near 2,770 cm{sup {minus}1}. This band is not indicative of an agostic C-H{hor_ellipsis}M interaction, but is instead the signature of a methylene C-H bond that has been perturbed by hyperconjugative drain of electron density into the adjacent {pi}-system.},
doi = {10.1021/jp990501a},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
number = 32,
volume = 103,
place = {United States},
year = {1999},
month = {8}
}