Pyridine Ligands

Pyridine is a six-membered heterocyclic compound. It is very similar to the benzene structure in which one benzene-methyl (=CH-) group is occupied by nitrogen atom to form a six-membered aromatic heterocyclic ring of the formula C₅H₅N. Due to its Lewis basic character, pyridine can act as a ligand for transition metals and form metal complexes with metals in the periodic table. It is usually a weak monodentate ligand with the ability to bind metals in different ratios to produce metal complexes.

Figure 1. Pyridine

Applications:

Polymerization: Titanium-pyridine complex [Ti(py)_XCl_Y] can be used as a catalyst for the polymerization of olefins and alkynes. In the Ziegler-Natta catalyzed process, these titanium complexes can be used in combination with various aluminum cocatalysts to catalyze the polymerization. A pyridine complex derived from VCl₃, VCl₄ and VOCl₃ can also be used as an olefin polymerization catalyst.

• Hydrogenation reaction: The [ReCl₄(NO)(py)₂] complex exhibits catalytic activity in the hydrogenation of cyclohexene. In the selective reduction of nitrobenzene to phenylhydroxylamine, the iron(II)-pyridine complex catalyzes the reaction with sodium borohydride.
• Hydroformylation reaction: Some pyridine complexes of Rh(I) and Rh(III) are capable of catalyzing the hydroformylation of ethylene hydrocarbons.
• Hydroamination reaction: The pyridine-titanium complex also functions in the intramolecular hydroamination of the aminoalkene substrate and can be used to synthesize gem-disubstituted 5- and 6-membered ring products.
• Hydroalkylation reaction: The bis(3-phenyl-2-pyridonate)bis(dimethylamido) titanium complex is selective for the hydroalkylation reaction. This reaction can selectively alpha-alkylate a primary amino olefin.
• Thermal reaction battery: Manganese(III)-pyridine complex can be used to develop photographic images. [Mn(py)₄Cl₂] is used in thermal reaction battery, in which the composite is thermally decomposed into conductive salts to form an electrolyte.
• Starting material: Pyridine can be nitrated to give 3-nitropyridine at elevated temperature in [RuCl₃(py)₃],. The iron(II)-pyridine complex is used as a starting material for the synthesis of iron(II) chelate complex with no pyridine ligand.