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⋮C−R‘ (R, R‘ = C 6 H 13, H ( 1 ); COOCH 3, H ( 2 ); COOC 2 H 5, COOC 2 H 5 ( 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 °C without catalytic activation. Thus, the unique properties of this reaction in solution (high selectivity, quantitative yields, no byproducts, 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.