Hydroxymethylcyclopropane on Oxygen-Covered Mo(110):  A Radical Clock on a Surface

Kretzschmar, Ilona; Levinson, Joshua A.; Friend, Cynthia M.

doi:10.1021/ja002769h

“…Molybdenum oxide films have been grown on Mo (110) surfaces by Friend et al [321][322][323][324][325][326], although a detailed structural characterization with atomic detail is still lacking. A number of structural units have been identified by vibrational spectroscopy, in particular molybdenum oxygen double bonds.…”

Section: Molybdenum Oxidementioning

confidence: 99%

Ultrathin Oxide Films

Freund

¹

,

Goodman

²

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Magnesium Oxide Mg O (100)/ Mo (100) Mg O (100)/ Ag (100) Mg O (111)/ Mo (110) Nickel Oxide Ni O (100)/ Ni (100), Mo (100) Ni O (111)/ Ni (111) Alumina Alumina/ Ni Al (110) Alumina/ Ni 3 Al (111) Al 2 O 3 (111)/ Ta (110) Al 2 O 3 (111)/ Mo (110) and Cu / Al 2 O 3 (111)/ Mo (110) Silica Si O 2 / Mo (110) Si O 2 / Mo (211) Cu / Si O 2 / Mo (110) Pd / Si O 2 / Mo (110) Au / Si O 2 / Mo (211) and Au / Ti O 2 / Si O 2 / Mo (211) Titania Ti x O y / Mo (100), Mo (110), Pt (111), Ni (110), W (100) Au / Ti O x / Mo (211) Chromia Cr 2 O 3 (111)/ Cr (11O) Vanadia Vanadium Sesquioxide Iron oxides Fe O / Pt (111), Fe 2 O 3 (0001)/ Pt (111), Fe 3 O 4 (001)/ Pt (111) Pd , Au on Iron Oxides Niobia Molybdenum Oxide Ceria Binary Oxides Ni O / Mg O , Ni O / Ca O , Mg O / Ni O , Ca O / Ni O / Mo (100) Conclusions Acknowledgments

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“…Since the onset of the β 1 -H 2 O peak at 430 K coincides with the maximum of the 410 K product peak, we propose that oxygen in the alkoxide is deposited on the surface prior to water formation. [11][12][13] Similarly, the second hightemperature water peak (β 2 ) at 525 K also lags slightly behind the maximum of the 520 K product.…”

Section: Resultsmentioning

confidence: 94%

“…The broad ν(OH) stretch near 3275 cm -1 is observed only when the surface is covered with multilayers, a behavior commonly observed for alcohols. 11,29 Infrared data provide evidence that O-H bond dissociation occurs upon heating to 250 K, yielding adsorbed 2-methylcyclopropylmethoxide and adsorbed OH. Two new features appear in the infrared spectrum when the 2-methylcyclopropylmethanolcovered surface is heated to 250 K: (i) a broad peak near 900 cm -1 and (ii) a sharp ν(OH) band near 3580 cm -1 (Figure 2ii).…”

Section: Resultsmentioning

confidence: 99%

“…In an ongoing effort to develop tools for the detection of radicals and the determination of the radical lifetimes in the vicinity of surfaces, we have studied various radical-clock precursors and their reactivity on the oxygenmodified Mo(110) surface. Three different precursors (hydroxymethylcyclopropane, 11 bromomethylcyclopropane, 12 and cyclopropyl-methanethiol 13 ) form a cyclopropylmethoxide intermediate on the O/Mo(110) surface. Adsorbed cyclopropylmethoxide subsequently undergoes homolytic C-O bond cleavage at ∼350 K, yielding cyclopropylmethyl radical, 2 (X,Y ) H) in the vicinity of the surface.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Kinetic Control of Surface Reactions: Regioselectivity in the Reaction of 2-Methylcyclopropylmethanol on Mo(110)−(6×1)−O

Kretzschmar

¹

,

Friend

²

2002

Self Cite

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The reactions of a diastereomeric mixture of 2-methylcyclopropylmethanol are investigated on oxygen-modified Mo(110) as a means of probing the influence of lifetime and stability of hydrocarbon radicals formed in a surface reaction on selectivity. 2-Methylcyclopropylmethanol forms 2-methylcyclopropylmethoxide at ∼250 K. The C−O bond of 2-methylcyclopropylmethoxide subsequently breaks near 350 K, yielding the (2-methylcyclopropyl)methyl radical. The (2-methylcyclopropyl)methyl radical can undergo fast rearrangement to two different linear C5 homoallyl radical species. The two different ring-opening pathways are due to the asymmetric methyl substitution of the cyclopropyl unit. Only one pathway results in a surface-bound product: adsorbed 4-penten-2-oxide is formed via rearrangement to 4-penten-2-yl radical and subsequent trapping on surface oxygen. The 4-penten-2-oxide is identified by comparison of infrared and temperature-programmed reaction data for the reaction product to analogous data for the reference compound. Evolution of C5 hydrocarbons competes with trapping at 350 K. Careful analysis of temperature-programmed reaction data indicates that 3-methyl-1-butene, 2-methyl-1,3-butadiene, and 1,2-dimethylcyclopropane contribute to the 410 K product. However, the close resemblance of the fragmentation patterns for all C5 hydrocarbons renders quantitative analysis impossible. At elevated temperatures the C−O bond of 4-penten-2-oxide breaks and C5 hydrocarbon evolution sets in. 1-Pentene and 1,3-pentadiene, as well as propene, are formed in a ratio of 20:70:10 at ∼520 K. Above 900 K CO is formed from recombination of adsorbed carbon and oxygen. Our results are discussed in the context of relative reaction rates for different pathways available to hydrocarbon radicals and their relation to product selectivity.

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“…1,2 As it provides ultrafast mechanistic probes of radical intermediacy and lifetime, its uses span biological systems 3 to surface science. 4 A related but much less assessed system is the vinyl analog (Scheme 1), for which, to the best of our knowledge, no physical data have been reported.…”

mentioning

confidence: 99%