Pyrrolyl鈥揝ilicon Compounds as Precursors for Donor鈥揂cceptor Systems Stabilized by Noncovalent Interactions

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• 作者：Susana Gonz谩lez-Santana ; Cercis Morera-Boado ; Luis A. Montero-Cabrera ; Monica Trueba ; Stefano P. Trasatti
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：July 9, 2015
• 年：2015
• 卷：119
• 期：27
• 页码：7038-7051
• 全文大小：766K
• ISSN：1520-5215

文摘

Pyrrolyl鈥搒ilicon compounds were investigated by different theoretical approaches. Model monomers consisted of a pyrrole ring N-substituted with silylmethoxy and silylhydroxy end groups through a propyl chain spacer, designated as PySi and PySiOH. Geometrical, vibrational, and electronic properties, as well as chemical reactivity, are discussed and compared with pyrrole (Py) and N-propylpyrrole (N-PrPy) that were studied in parallel for reference purposes and methods validation. The electronic distribution between PySi and PySiOH differs importantly, the former being an electron donor, as Py and N-PrPy. Conversely, PySiOH presents donor鈥揳cceptor character with the LUMO energy level localized on the silanol end group. Global and local reactivity descriptors predict PySiOH more reactive than PySi with two preferential reactive sites: electron-rich Py ring and electron-deficient silanol group. On the basis of experimental studies, oligomers of PySiOH linked 伪鈥撐扁€?via Py rings (伪鈥撐扁€睵y_nSiOH, n = 2, 3) were considered as model molecules of hydrolyzed PySi. The most stable structures were derived from randomly generated 伪鈥撐扁€睵y_nSiOH that were optimized at semiempirical AM1 and refined with M05-2X/6-31G(d,p). Conformational analysis of dimer and trimer structures points to stability enhanced by molecular packing. Nonetheless, NBO and RDG results indicate that oligomer stability is dictated by the cooperative contribution of hydrogen bonding between silanol end groups and dispersive vdW interactions between silanol and the 蟺 system of the Py ring. The latter interaction resulting from electron delocalization induced by an electron-deficient silanol group seems to determine the smaller gap energy of T-shaped OH鈭捪€ arrangements. The theoretical findings support the peculiar chemical behavior revealed by experiment.