Biomimetic polyorganosiloxanes: model compounds for new materials

Abstract

The chemistry of N-organosilylalkyl-substituted heterocyclic bases (thymine, adenine and cytosine) is described, covering the structures of model compounds, the synthesis of substituted oligo-siloxanes and a preliminary report of the synthesis of a poly(organosiloxane) with pendant N-alkyl(heterocycle) functionalities. N-Alkenylthymines CH₂CH(CH₂)_nT (T = thymine, n = 1 (1), 2 (2), 3 (3)) have been prepared and 2 hydrosilylated to form PhMe₂Si(CH₂)₄T (5). Alternatively, 5 was prepared by reaction of PhMe₂Si(CH₂)₄Br (6) with (O,O-SiMe₃)₂T, a method which has also been used to prepare PhMe₂Si(CH₂)₄A (7) and PhMe₂Si(CH₂)₄C (8) (A = adenine, C = cytosine). Model di- and tri-siloxanes [Br(CH₂)₄(Me)₂Si]₂O (10), Me₃SiOSi(Me)₂(CH₂)₄Br (11), PhMe₂SiOSi(Me)₂(CH₂)₄Br (12) and (Me₃SiO)₂(Me)Si(CH₂)₄Br (13) have been prepared by hydrosilylation of H₂CC(H)(CH₂)₄Br with an appropriate hydrosiloxane and used to prepare Me₃SiO(Me)₂Si(CH₂)₄T (14), Me₃SiO(Me)₂Si(CH₂)₄A (15) (both from 11), and (Me₃SiO)₂(Me)Si(CH₂)₄T (16), (Me₃SiO)₂(Me)Si(CH₂)₄A (17) (both from 13). 10 reacts with thymine to give a mixture of the pyrimidocyclophane cyclo-T-N,N-[(CH₂)₄(Me)₂Si]₂O (19) and [T(CH₂)₄Si(Me)₂]₂O (20), while cytosine reacts similarly to form cyclo-C-N,N-[(CH₂)₄(Me)₂Si]₂O (21; as an imine) and [C(CH₂)₄Si(Me)₂]₂O (22); adenine only generates [A(CH₂)₄Si(Me)₂]₂O (18) in an analogous synthesis. Using a related protocol, polymeric {[MeSi(O)(CH₂)₄Br]₂[Me₂SiO]₉₈}_n (23) has been converted to {[MeSi(O)(CH₂)₄T]₂[Me₂SiO]₉₈}_n (24) and {[MeSi(O)(CH₂)₄A]₂[Me₂SiO]₉₈}_n (25). The structures of 4, 5, 8, 19 and 21, along with a 2 : 1 adduct of 5 with Ni(dithiobiuret)₂ (9) are reported.