Effect of substituent groups on the interaction of benzene with nickel(111)

Abstract

The adsorption and reaction of aniline, phenol, methoxybenzene, benzonitrile, chlorobenzene, nitrosobenzene, nitrobenzene, and benzaldehyde were studied on Ni(ll1) groups to elucidate the role of substituent groups in adsorption and reaction of substituted benzenes. Temperature-programmed reaction (TPR) and reflection absorption infrared spectroscopy were used to characterize modes of bonding and reaction paths. The absorption bonds were also modeled by using the semiempirical intermediate neglect of differential overlap technique (INDO) with a 19 nickel atom cluster having the symmetry of the (111) surface. The nickel surface acted as an electron acceptor in electrophilic reactions with adsorbates. Chlorobenzene was found to adsorb flat, with the chlorine atom participating in the bond to the surface. With electron-withdrawing groups, the substituents were the site of chemical activity. The CN side group in benzonitrile rehybridized upon adsorption on Ni(lll), resulting in a bonding configuration in which the phenyl ring was tilted away from the surface. Benzaldehyde also apparently interacts mainly through the C 4 bond of the CHO side group. NO bonds were particularly reactive. Nitrosobenzene and nitrobenzene bonded dissociatively through their side group, and NO bond scission was very facile. Electron-donating groups activated the benzene for electrophilic addition reactions. It is postulated that the amine substituent in aniline was activated by electrophilic attack by the surface leading to polymerization. The polyaniline was thermally very stable and did not decompose to above 700 K. Evidence for phenol polymerization was also found. In methoxybenzene, the bulky methyl side group hindered the polymerization, and the molecule decomposed. INDO calculations were found to be useful in identifying charge transfer during adsorption and in elucidating the reaction pathways.

Aniline hydrogenolysis on nickel: effects of surface hydrogen and surface structure

“…Aniline was found to adsorb both molecularly via the n-electrons and dissociatively via an anion formed by the release of a proton from the amino group. On well-defined nickel single crystal surfaces under ultrahigh vacuum (UHV) conditions, adsorbed aniline is thought to form polyaniline, an unreactive aromatic surface polymer which is stable to above 600 K [4,5]. Polymerization is believed to occur when surface activated ring carbon atoms lose their hydrogen and react with the amino groups on adjacent aniline groups.…”

Mechanism study on Raney nickel-catalyzed amination of resorcinol

“…Ni(111) is the main diffraction peak of Raney Ni catalyst. Surface science studies have been performed on well-defined Ni(111) for the chemisorption and hydrogenation of benzene [18][19][20][21][22][23] and phenol [23,24]. The aromatic ring oriented paralled to the Ni(111) surface is adsorbed via the π orbitals [23].…”

Thiolate-Bonded Self-Assembled Monolayers on Ni(111): Bonding Strength, Structure, and Stability

“…This suggests that CN residues are still present, at least to some extent, on the surface at 200 K. This appears plausible, in view of the fact that, on Ni(111), hydrogen cyanide and the dehydrogenated CN fragments are known to dissociate into their atomic constituents at considerably higher temperatures, 95,96 and that, on the same surface, the decomposition of benzonitrile has been shown to proceed preferentially via scission of the C−CN bond rather than by further breakage of the stronger CN bond. 97 Further evidence for the distinct molecule−substrate interaction in the 4-CTP SAMs compared to the 4-FTP counterpart is provided by NEXAFS. Indeed, the intensity contrast (linear dichroism) of the angle-dependent C K-edge absorption spectra of Figure 11 is reversed with respect to the 4-FTP case (Figure 3).…”