H–Si(111)-terminated
surfaces were alkenylated via two routes:
through a novel one-step gas-phase hydrosilylation reaction with short
alkynes (C<sub>3</sub> to C<sub>6</sub>) and for comparison via a
two-step chlorination and Grignard alkenylation process. All modified
surfaces were characterized by static water contact angles and X-ray
photoelectron spectroscopy (XPS). Propenyl- and butenyl-coated Si(111)
surfaces display a significantly higher packing density than conventional
C<sub>10</sub>–C<sub>18</sub> alkyne-derived monolayers, showing
the potential of this approach. In addition, propyne chemisorption
proceeds via either of two approaches: the standard hydrosilylation
at the terminal carbon (<i>lin</i>) at temperatures above
90 °C and an unprecedented reaction at the second carbon (<i>iso</i>) at temperatures below 90 °C. Molecular modeling
revealed that the packing energy of a monolayer bonded at the second
carbon is significantly more favorable, which drives <i>iso</i>-attachment, with a dense packing of surface-bound <i>iso</i>-propenyl chains at 40% surface coverage, in line with the experiments
at <90 °C. The highest density monolayers are obtained at
130 °C and show a linear attachment of 1-propenyl chains with
92% surface coverage