Synthesis of 4′-substituted-2,2′:6′,2"-terpyridines

The terdentate ligand 2,2':6',2"-terpyridine (tpy) has increasingly become one of the most popular ligands in coordination chemistry. A variety of substituents are utilised to tailor the properties of its metal complexes. 2,2':6',2"-Terpyridine was reacted with almost all transition metals to form complexes. Among a series of tpy ligand derivatives, those containing substituents at the C(4') position are of especial interest. Metal-bonded tpy ligands with spacers at C(4') provide a means of directionality, and thus a means of linear communication, it means that electronic communication can occur along the coordination axis. In addition, the insertion of a single substituent at the C(4')-position of the tpy ligand results in no enantiomeric derivatives, as the derivative retains its plane of symmetry. The synthetic strategies used to prepare tpy ligands are reviewed comprehensively. 1 Introduction 2 The Configuration of 2,2':6',2"-Terpyridine 3 Methods for the Synthesis of tpy Ligands 3.1 Condensation Methodology 3.2 Pyrolysis of Hydrazonium Salt 3.3 Tohda Methodology 3.4 Metal-mediated Methodologies 3.5 Sauer Methodology 4. Synthesis of Ligands 4.1 4'-Aromatic Substituted-2,2':6',2"-terpyridines 4.2 Synthesis of tpy Ligands Possessing Functional Groups Directly Attached to C(4') 4.2.1 Preparation of Trimethyl Derivatives of 2,2':6',2"-Terpyridine 4.2.2 Carbonyl Derivatives of tpy Ligands 4.2.3 Synthesis of 4'-Carbaldehyde Oxime-2,2':6',2"-terpyridine 4.2.4 Carboxylate Derivatives of tpy Ligands 4.2.5 Synthesis of 4'-Nitro-2,2':6',2"-Terpyridines 4.2.6 Synthesis of 4'-Hydroxy-2,2':6',2"-terpyridines 4.2.7 Synthesis of 4',4'-Bis(2,2':6',2"-terpyridyl)amine 4.2.8 Synthesis of 4'-Thio-substituted 2,2':6',2"-Terpyridines 4.2.9 Synthesis of 2,2':6',2"-Terpyridine-1'-oxides 5 Conclusion.