Cycloaddition Chemistry of 1,3-Dienes on the Silicon(001) Surface:  Competition between [4 + 2] and [2 + 2] Reactions

Abstract

The reactions of 1,3-dienes with the Si(001) surface have been investigated using scanning tunneling microscopy (STM) and Fourier transform infrared spectroscopy (FTIR), and the relative efficiencies of [2 + 2] and [4 + 2] reactions have been determined. STM and FTIR studies show that the 2,3-dimethyl-1,3-butadiene molecule has two bonding configurations; 80% of the molecules bond via a [4 + 2] reaction involving both alkene groups with the remaining 20% bonding via a [2 + 2] reaction involving only one alkene group. The molecule 1,3-cyclohaxadiene shows three separate bonding configurations in the STM, and the FTIR shows at least four separate peaks in the alkene stretching region. The [4 + 2] product is found to comprise 55% of the surface species, the [2 + 2] product 35%, and an unknown product 10%. The surface temperature is found to have little affect on the product distribution. The formation of multiple products and the lack of temperature effects indicate that the product distribution is controlled primarily by the kinetics of the adsorption process, not by the thermodynamics. Thus, although [4 + 2] reactions are predicted to be more stable, [2 + 2] reactions occur nearly as frequently.

Partial Hessian Vibrational Analysis of Organic Molecules Adsorbed on Si(100)

“…13 The addition of 2,3-dimethyl-1,3-butadiene to Si(100) was also explored by Hamers and co-workers. 19 The surface species were found to comprise 80% of the Diels-Alder product, with the remaining 20% arising from a [2+2] addition. Okamura et al 20 used IR spectroscopy to investigate the adsorption of naphthalene on Si(100).…”

Adsorption of phenylacetylene on Si(100)-2×1: Reaction mechanism and formation of a styrene-like π-conjugation system

“…This asymmetric approach is of lower symmetry and can occur with a lower energy barrier. Conjugated dienes or multienes [21][22][23][24] can be covalently bonded to Si(100)-2ϫ1 through ͓4ϩ2͔-like or/and ͓2ϩ2͔-like cycloaddition strategies. For six-membered aromatic molecules and their substitutions, [25][26][27][28][29][30][31][32][33][34] their binding mechanisms are…”

Cycloaddition reaction of furan with Si(100)-2×1

“…The (2ϫ1) surface reconstruction obtained by a simple lateral translation of surface Si-atoms to form Si dimers was first suggested by Schlier and Farnsworth 2 in 1959 and further confirmed in the scanning tunneling microscopic ͑STM͒ studies by Hamers et al [3][4][5] Many of the physical and chemical properties of Si͑100͒ can be rationalized by considering a double bond feature of dimer, that is, a strong bond linking the two Si atoms and a rather weak bond. All studies of simple alkenes on Si͑100͒ have shown a facial ͓2ϩ2͔ cycloaddition reaction pathway; [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] despite the fact that, according to Woodward's rule, the analogous reaction of two organic alkenes is forbidden in the high-symmetry suprafacial-suprafacial ͓2 s ϩ2 s ͔ approach. 23 Moreover, experimental evidence has shown that the molecular stereochemistry is preserved through this reaction, thereby ruling out the suprafacialantarafacial ͓2 s ϩ2 a ͔ mechanism.…”