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

The reaction of hydrazones with bis(π-η⁵:σ-η¹-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 κ²N,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 κ¹N 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═N double bond into the Ti-C_exo bond of the pentafulvene moiety. Using 2-pyridinecarboxaldehyde phenylhydrazone, a formal κ³N,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 κ³N,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 κ²N,O coordination mode of the hydrazido ligand.