Synthesis of zinc hydrazonide complexes.

The zinc hydrazonide complexes ClZn(CH(2)C(Me)=NNMe(2))(py), ClZn(CH(2)C(t-Bu)=NNMe(2)), Zn(CH(2)C(Me)=NNMe(2))(2), Zn(CH(2)C(i-Pr)=NNMe(2))(2), and Zn(CH(2)C(t-Bu)=NNMe(2))(2) were synthesized by salt metathesis reactions, and the coordination polymer EtZn(CH(2)C(Me)=NNMe(2)) was obtained from the reaction between excess ZnEt(2) and Zn(CH(2)C(Me)=NNMe(2))(2). Single crystal X-ray crystallography studies revealed that the hydrazonide ligands were bound to zinc as chelating alkyl ligands. The ligand precursor Li(CH(2)C(i-Pr)=NNMe(2))(THF) was also structurally characterized. In the anion of Li(CH(2)C(i-Pr)=NNMe(2))(THF), the hydrazonide ligand in EtZn(CH(2)C(Me)=NNMe(2)), and the bridging hydrazonide ligands in Zn(CH(2)C(Me)=NNMe(2))(2) and ClZn(CH(2)C(Me)=NNMe(2))(py), there is evidence for three-center charge delocalization. In solution, the dimer Zn(CH(2)C(Me)=NNMe(2))(2) is in equilibrium with the monomer Zn(CH(2)C(Me)=NNMe(2))(2). The thermodynamic parameters DeltaH degrees = 55.8(2.9) kJ/mol, DeltaS degrees = 144(2) J/mol K, and DeltaG degrees (298K) = 13(2) kJ/mol for the equilibrium were obtained from a variable temperature (1)H NMR study.