Zinc dihydride - NHC marriage

21 April 2013 - Orgo

In the category of binary compounds of hydrogen a large group of metals is conspicuously absent or are unwilling partners. Zinc dihydride is one of them: dimeric in nature and very prone to decomposition. Luckily Rit et al. have recently demonstrated a novel way to tame the compound: with an N-heterocyclic carbene (DOI).

All it takes is combining solid zinc dihydride with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene in THF for the complex the crystallize. In this complex each zinc atom in the dimer is stabilized by a NHC ligand. The crystals only decompose with temperatures in excess of 170°C. In toluene above 40°C the molecule is fluxional of an uncertain origin.
Whereas zinc dihydride itself does not react with carbon dioxide, the corresponding complex is converted to the formate. The complex is also found the catalyse the reaction of phenylsilane and methanol to trimethoxyphenylsilane and hydrogen.