Syntheses, Characterization, and Multifaceted Coordination Chemistry of Hydrazonido Titanium Complexes

The reaction of hydrazones with bis(pi-eta(5):sigma-eta(1)-pentafulvene)titanium complexes leads to both hydrazonido and hydrazido complexes depending on the interaction of the hydrazone with the fulvene ligand of the metal complex. The molecular structures mostly reveal kappa N-2,N side-on coordination of the hydrazonido ligand due to the deprotonation of the N-H bond by one of the fulvene moieties. Instead of deprotonation, the reaction of the bis(adamantylidene fulvene)titanium complexes with cinnamon aldehyde phenylhydrazone leads to kappa N-1 coordination. By using donating groups in the backbone of the hydrazone ligands, there are exceptions to this coordination mode due to the insertion of the C & boxH;N double bond into the Ti-C-exo bond of the pentafulvene moiety. Using 2-pyridinecarboxaldehyde phenylhydrazone, a formal kappa N-3,N,N ligand system is formed by the coordination of the pyridine nitrogen atom to the metal center via consecutive N-H deprotonation and insertion. Finally, the use of salicylaldehyde phenylhydrazone ultimately produces a complex with the kappa N-3,N,O coordination mode by double deprotonation of the hydrazone N-H and O-H functions. Because of its slow conversion to the final product, the intermediate was isolated as an insertion product with consecutive O-H deprotonation, showing a kappa N-2,O coordination mode of the hydrazido ligand.