Activation of Ammonia by a Si=O Double Bond and Formation of a Unique Pair of Sila-Hemiaminal and Silanoic Amide Tautomers

The new silanone complex 3 is accessible in 82% yield and is capable of undergoing addition of ammonia under mild conditions, yielding the sila-hemiaminal 4 and, at the same time, its unique tautomer 5, the first silanoic amide. The unexpected formation of 3 is due to the presence of the basic exocyclic methylene group in the C3N2 ligand backbone. Strikingly, the tautomers 4 and 5 are in equilibrium in solution and can be cocrystallized in benzene or THF solutions having a SiOH center dot center dot center dot O=Si hydrogen bond as confirmed by single-crystal X-ray diffraction analysis.