High-Loading Aminopropyl Silicas as Novel Scavenger Resins for High Throughput Synthesis

Abstract

High loading amino- and diamino-functionalised silicas were prepared by a simple method; the resultant materials have been shown to be excellent high capacity scavengers for three representative types of electrophile with a wide solvent compatibility.

Key words

electrophilic additions - combinatorial chemistry - acylations - silica - scavengers

References

• 1 Ley SV. Baxendale IR. Bream RN. Jackson PS. Leach AG. Longbottom DA. Nesi M. Scott JS. Storer RI. Taylor SJ. J. Chem Soc., Perkin Trans 1  2000,  3815 
• 2 Booth RJ. Hodges JC. Acc. Chem. Res.  1999,  32:  18 
• 3 Cresswell MW. Bolton GL. Hodges JC. Meppen M. Tetrahedron  1998,  54:  3983 
• 4 Parlow JJ. Flynn DL. Tetrahedron  1998,  54:  4013 
• 5 Booth RJ. Hodges JC. J. Am. Chem. Soc.  1997,  119:  4882 
• 6 Sherrington DC. Chem. Commun.  1998,  2275 
• 7 Macquarrie DJ. J. Chem. Soc., Chem. Commun.  1996,  1961 
• 8 Macquarrie DJ. Jackson DB. Mdoe JEG. Clark JH. New J. Chem.  1999,  23:  539 
• 9 Elings JA. Ait-Meddour R. Macquarrie DJ. Clark JH. Chem. Commun.  1998,  2707 
• 10 Lambert A. Elings JA. Macquarrie DJ. Carr G. Clark JH. Synlett  2000,  1052 
• 11 Clark JH. Elings SA. Wilson K. C. R. Acad. Sci.  2000,  3:  399 
• 12 Macquarrie DJ. Green Chem.  1999,  1:  195 

13

The materials prepared were made by the templated co-condensation of tetraethoxysilane (TEOS) and a second functional amine[7], either 3-aminopropyltrimethoxysilane 1 or N-(2′-aminoethyl)-3-aminopropyltrimethoxysilane 2. The proportion of the functional silane was kept as high as possible, commensurate with a high yield of the desired solid product [50 mol% RSi(OMe)₃: 50 mol% TEOS in the case of 1, 33 mol% RSi(OMe)₃: 67 mol% TEOS in the case of 2]. The two silanes were added together but separately (in each case a total of 0.1 mol of silane was added) to a mixture of water, ethanol (50 mL of each) and 1-aminododecane (5.1 g) at room temperature. After stirring for 18 h, the white suspension was filtered and the resultant solid was extracted using a Soxhlet extractor and ethanol as extractant for 12 hours. The extracted solids were dried at 100 °C to remove solvent, and were stored in screwtop jars. Yield is typically 10 g. These procedures gave materials with loadings of 5 mmolg^-1 aminopropyl(3) and 3.7 mmolg^-1 of the diaminosilane respectively(4) (Scheme [1] ).

14

These materials were then evaluated as scavengers by stirring them with an excess (a mole ratio of 2:1 electrophile: amine group was used) of electrophiles (phenyl isocyanate 5, benzenesulfonyl chloride 6, and benzoyl chloride 7) in a range of solvents. For 1 g of scavenger 5 mL of solvent was used. After 5 hours, the solids were removed by filtration, washed with the solvent used in the reaction, and the quantity of electrophile remaining in solution was calculated from GC with n-dodecane as internal standard.