Biomimetic polyorganosiloxanes: Model compounds for new materials

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 PhMe 2Si(CH2)4C (8) (A = adenine, C = cytosine). Model di- and tri-siloxanes [Br(CH2)4(Me) 2Si]2O (10), Me3SiOSi(Me)2(CH 2)4Br (11), PhMe2SiOSi(Me)2(CH 2)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(CH 2)4T (14), Me3SiO(Me)2Si(CH 2)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-[(CH 2)4(Me)2Si]2O (19) and [T(CH 2)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)(CH 2)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. This journal is © the Partner Organisations 2014