Click chemistry on surfaces: 1,3-dipolar cycloaddition reactions of azide-terminated monolayers on silica

Monolayers of 11-azido-undecylsiloxane were prepared on powdered silica and on silicon wafers by the substitution of 11-bromo-undecylsiloxane and were subsequently coupled with three substituted acetylenes R-C drop C-R' (R, R' = C6H13, H (1); COOCH3, H (2); COOC2H5, COOC2H5 (3)) to yield 1,2,3 triazoles via the Huisgen 1,3-dipolar cycloaddition reaction. The pathway and yield of the surface reactions were monitored by infrared spectroscopy and ellipsometry. No reaction was observed with 1, whereas 2 and 3 react quantitatively both on powdered silica and on flat wafer surfaces at a temperature of 70 degreesC without catalytic activation. Thus, the unique properties of this reaction in solution (high selectivity, quantitative yields, no by products, simple reaction conditions) seem to be transferable to surface-bound reactants and might provide access to a range of novel, functionalized surfaces by analogy to the Sharpless click chemistry concept for solution-phase synthesis.