Synthesis of Aryl-Terminated Polyenaldehydes and Polyenetriethoxysilanes for Preparation of Self-Assembled Monolayers on Silicon Surfaces

Abstract

The synthesis of α,ω-terminally functionalized polyenes with arenes or hetarenes at one end and either an aldehyde or a triethoxysilyl function at the other end, capable of reacting with H-terminated or oxidized silicon surfaces, is described. Analogous to known Wittig reactions, polyenedialdehydes 1 and 3, the latter derived from 1 and phosphonium chloride 2 in a twofold Wittig olefination, were converted with phosphonium bromides 4 to give the (all-E)-arylpolyenaldehydes 5 and 6. A terminal alkyl chain was introduced in dialdehydes 1a and 3a by reaction with P,P-didecyldibenzophospholium bromide 8, resulting in polyenals 9. Wittig olefination of 5c and 9a with phosphonium chloride 2 afforded the (2-thienyl)tridecahexaenal 7 and the docosahexaenal 10. With respect to monolayer formation on oxidized Si(100) surfaces, (9-anthryl)- and (2-thienyl)-ω-functionalized polyenetriethoxysilanes 16 and 17 were prepared in a reaction sequence involving the introduction of a terminal triple bond with [3-(trimethylsilyl)prop-2-ynyl]triphenylphosphonium bromide (11), desilylation of the resulting arylpolyeninetrimethylsilanes 12, 13 with Bu4NF3H2O, and subsequent hydrosilylation of the arylpolyenines 14, 15 using triethoxysilane under dichlorocyclooctadienylplatinum(II) catalysis.