Synthesis and characterization of bifunctional surfaces with tunable functional group pairs

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- Anchored paired functional groups can be generated with organochlorosilanes containing a silyl ester bond.
- Surfaces with carboxylic acid groups paired with organosilanols, secondary amines, pyridines, and phosphines were prepared.
- Evidence of amide formation was presented for carboxylic acid/amine pairs.
- Amines in amine-carboxylic acid pairs were three times more active than free amines for nitroaldol condensation.

Grafting of pairs of functional groups onto a silica surface was demonstrated by tethering both terminals of an organochlorosilane precursor molecule, Cl2(CH3)Si(CH2)4(CO)(OSi(i-Pr)2)(CH2)2Si(CH3)Cl2, that possess a cleavable silyl ester bond, onto a silica surface. Hydrolytic cleavage of the silyl ester bond of the grafted molecule resulted in the generation of organized pairs of carboxylic acid and organosilanol groups. This organosilanol moiety was easily transformed into other functional groups through condensation reactions to form, together with the neighboring acid group, pairs such as carboxylic acid/secondary amine, carboxylic acid/pyridine, and carboxylic acid/phosphine. In the case of carboxylic acid/amine pairing, there was evidence of the formation of amide. A sample grafted with amine-carboxylic acid pairs was three times more active (per free amine) than a sample without such pairs for the nitroaldol condensation of 4-nitrobenzaldehyde and nitromethane.

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