Enabling enelike reactions on Si(111)-7x7 through tuning organic molecular structures.

We previously demonstrated that acetonitrile (N[triple bond]C-CH(3)) binds to the adjacent adatom-rest atom pair of Si(111)-7x7 through a [2+2]-like cycloaddition reaction, forming a (Si)N=C(Si)-CH(3)-like surface species [Tao et al., J. Phys. Chem. B 106, 3890 (2002)]. Current investigation clearly showed that chloroacetonitrile (N[triple bond]C-CH(2)Cl), propargyl chloride (HC[triple bond]C-CH(2)Cl), and 3-chloropropionitrile (N[triple bond]C-CH(2)-CH(2)Cl) react with the surface via enelike reactions, concurrently involving N[triple bond]C/C[triple bond]C as well as the breakage of the C-Cl/C-H bond. Further separation of the unsaturated bond (C[triple bond]C) from the C-Cl bond using CH(2) spacers in 5-chloro-1-pentyne (CH[triple bond]C-CH(2)CH(2)CH(2)Cl) would direct the reaction to a [2+2]-like cycloaddition. These experimental results clearly suggest the possibility of controlling the surface reaction pathways by tuning the organic molecular structures. This strategy can be useful in designing and fabricating functional molecular templates on Si(111)-7x7.