Synthesis, characterization and properties of some organozinc hydride complexes

Abstract

The synthesis and characterization of the monopyridine complexes of ethylzinc hydride and phenylzinc hydride are described. On treatment with TMED these complexes are converted into R2Zn3H4. TMED species through a combination of ligand-exchange and disproportionation. The formation of organozinc hydrides from ω-functionally-substituted diorganozinc compounds is only successful when the intramolecular coordination in these starting materials is weak and easily broken by pyridine. The results of these investigations are used as a basis for a discussion of the factors governing the formation of stable organozinc hydrides. The RZnH.py complexes easily reduce ketones and aldehydes, but no unusual stereoselectivity was observed in the reduction of substituted cyclohexanones. EtZnH.py reacts with an excess of pyridine with formation of the bis pyridine complex of ethyl(1,4-dihydro-1-pyridyl)zinc, a soluble compound, which is monomeric in benzene. The corresponding phenylzinc complex, however, cannot be isolated; disproportionation to Ph2Zn .2py and the bis pyridine complex of bis(1,4-dihydro-1-pyridyl)zinc occurs.