Molecular Design of Hypercoordinated Silacyclophanes

• Published in: Organometallics Vol. 30; no. 21; pp. 5595 - 5603
• Main Authors: Doronina, Evgeniya P, Belogolova, Elena F, Sidorkin, Valery F
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.11.2011
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om200340k

MP2 and DFT (B3LYP, M06-2X) methods using the 6-31G(d) and 6-311++G(d,p) basis sets are applied to the investigation of the structure of a wide series of silacyclophanes XSi[Y(CH2) n ]3C6R3 1–9 (X = t-Bu, Me, NH2, F, OTf; Y = O, NH, CH2; R = H, SiH3, Li; n = 1, 2). The molecules studied exist exclusively in the out-C 3-symmetric form (for X = NH2, OTf the symmetry is not strict). Identification of the presence and estimation of the extent of the hitherto unknown Si···Ar multicenter intramolecular interaction of the tetracoordinate silicon atom with the π-system of the benzene ring in 1–9 was performed by analysis of geometric parameters, using the methods of Δδ 29Si coordination shift, NICS(1) values, and the results of the AIM, NBO, and MO analyses. In molecules XSi[YCH2CH2]3C6R3 1–4, irrespective of the nature of X, Y, and R, the multicenter interaction Si···Ar is weak. This interaction is strongly enhanced in compounds XSi[YCH2]3C6R3 5–9, with side chains shortened by one methylene group. The variation of geometric (d Si–Ar, ΔSi, ηα), electronic (∑δ(Si,C)), orbital (∑ΔE (2)[πC–C→σ*Si‑X]), and NMR (Δδ 29Si) characteristics of the coordination center XSiY3Ar in 5–9, caused by varying the environments of the silicon atom and of the arene fragment, is typical for pentacoordinate silicon compounds.