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 C(3)N(2) 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...O=Si hydrogen bond as confirmed by single-crystal X-ray diffraction analysis.