Preparation, characterization, and heck reaction of siloxane films derived from carbosilane dendrons with a bromophenyl group at the focal point and up to 27 SiCl3 groups at the periphery

Multidentate organosiloxane thin films were prepared on SiO2/Si surfaces by solution phase deposition of carbosilane dendrons containing a bromophenyl group at the focal point and 3 (Br-G0), 9 (Br-G1), and 27 (Br-G2) SiCl3 groups at the periphery. The films were characterized by contact angle goniometry, ellipsometry, and X-ray photoelectron spectroscopy (XPS). The results indicated that about six Br-G0 molecules covered the same surface area as three Br-G1 molecules and one Br-G2 molecule. Hence, the density of the bromophenyl groups in the films could be defined by the size (generation) of the dendron adsorbates. We also demonstrated that the bromophenyl groups on the film surfaces could serve as a handle for attaching conjugated molecules via formation of C-C bonds. Thus, upon treatment of the films with 4-fluorostyrene under Heck reaction conditions, XPS analysis showed that about 90, 66, and 51% of the bromine atoms in the films prepared from Br-G0, Br-G1, and Br-G2 were consumed, and 94, 82, and 58% of the consumed bromine atoms were replaced by fluorostyryl groups. The remaining bromophenyl groups were probably not accessible to the reactants because of their unfavorable orientation. The overall yields for the surface Heck reaction were estimated to be 84, 54, and 30% for the films prepared from Br-G0, Br-G1, and Br-G2, respectively.