Hexacoordinate silicon diols have the potential to act as chiral dual hydrogen bond donors for catalysis. Hydrogen bond donor catalysts are being explored using earth abundant, air and moisture stable alternatives to transition metals. While most of the hydrogen bond donor catalysis field is based on organic catalysts, a few groups have started exploring silicon diols as potential catalysts. Although the chemistries of carbon and its heavier congener silicon are quite similar, two significant differences are the stability of the geminal silicon diol and the ability of silicon to form hexacoordinate coordination complexes. The goal of this research is to develop chiral hexacoordinate bis-bipyridylsilicon(IV) diols as dual hydrogen bond donors for catalysis. The catalysts, [Si(tBu-bpy)2(OH)2](PF6)2, was synthesized by combining 2 equivalents of 4,4’-di-tert-butyl-2,2’-bipyridine with SiI4, followed by slow hydrolysis in air, and metathesis with NH4PF6. The resulting compound is soluble in CH2Cl2. For initial catalyst testing, the Michael addition reaction of N-methylindole with trans-Beta-nitrostyrene in CD2Cl2 was monitored by NMR in various amounts of catalyst. With 5% catalyst loading a 4-fold rate increase was observed, and an 8-fold rate increase was observed at 10% catalyst loading. The resolution of the hexacoordinate bis-bipyridylsilicon(IV) diol is underway. Preliminary results using fractional crystallization with chiral tartrate salts indicate the diol can be resolved and remain enantiomerically pure for at least 24 hours in acetonitrile. The results of catalyst testing of the enantiomerically pure catalyst will be reported.

Bis-bipyridylsilicon(IV) diols as potential dual hydrogen bond donors for chiral catalysis

251st National Meeting (2016)

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