Metallacyclobutane and Cyclopropyl Species on Cu(111) and Cu(110)

Abstract

Low-energy electron bombardment of cyclopropane submonolayers was used to prepare cyclopropyl and metallacyclobutane species on Cu(110) and Cu(111) surfaces. The thermal chemistry of both species was monitored over the 90−450 K range by taking high-resolution electron energy loss (HREELS) and temperature-programmed desorption (TPD) measurements. Cyclization of the metallacyclobutane species, to eliminate cyclopropane, was found to occur at 205 K. The metallacyclobutane species was characterized by CH stretching losses at 2806 and 2839 cm-1 for Cu(110) and Cu(111), respectively. The cyclopropyl species was found to undergo ring opening to yield a propene desorption product at 290 K. The observed surface chemistry of both of these cyclic C3 species is compared with data from the organometallic, catalysis, and surface science literature.

Chemistry of Cyclopropane on Pt(111): Thermal, Electron, and Photon Activation

“…The latter have been reported on copper substrates. 20 The downward energy shift associated with the C-H stretching region is consistent with alterations that increase the sp 3 hybrid character of the bonding at the carbon atoms, e.g., increased C-Pt coupling and larger C-C-C bond angle.…”

“…Ring modes from cyclopropane, cyclopropyl fragments, and C 3 metallacycles do not vary greatly; on Cu, the asymmetric ring deformation at 1034 cm -1 shows a shift to 967 cm -1 , the symmetric ring deformation shifts from 872 to 838 cm -1 , and the ring breathing mode shifts from 1179 to 1177 cm -1 . 37,20 In our case, the intensity that remains in the regions expected for metallacyclobutane ring modes, e.g., 700-1300 cm -1 , is ambiguous, since other intermediates, e.g., η 3 -allyl, have numerous modes that contribute to this region. While there is some intensity at 780 cm -1 , which may have shifted from the strong 840 cm -1 band of c-C 3 H 6 , it is clear that an intact metallacycle fragment is not the dominant product of electron irradiation.…”

“…Both π-allyl and n-propyl species have been proposed as being responsible for propylene formation. 26,34,35 UHV surface science studies of c-C 3 H 6 on Ru, 21 Ni, 17 and Cu, 20,36 but not Pt(111), have been reported. Results on Cu-(111) and Cu(110) 20,37 are related to the work reported here.…”

“…26,34,35 UHV surface science studies of c-C 3 H 6 on Ru, 21 Ni, 17 and Cu, 20,36 but not Pt(111), have been reported. Results on Cu-(111) and Cu(110) 20,37 are related to the work reported here. On low-temperature (e100 K) Cu(110) and Cu(111), c-C 3 H 6 adsorbs molecularly and there are no thermally activated reactions in subsequent thermal desorption.…”

The Thermal Chemistry of 1-Chloro-3-Iodopropane (ClC3H6I) Adsorbed on Pt(111)

“…We have used electron irradiation of adsorbed c-C 3 H 6 at 100 K to synthesize C 3 fragments and have evidence for C 3 H 6 metallacycles based on vibrational spectroscopy and surface reaction processes. A trimethylene species, metallacyclobutane or metallacyclopentane, is widely proposed to account for both hydrogenation and hydrogenolysis products from reactions of cyclopropane over supported metal catalysts. − ClC 3 H 6 I was chosen for study since it provides an alternative route to C 3 intermediates with potential for forming cyclic intermediates and possesses distinguishable halogens.…”