A Novel Iron Complex for Cross-Coupling Reactions of Multiple C-Cl Bonds in Polychlorinated Solvents with Grignard Reagents

A novel iron(III) complex (2) of a pincer ligand [1, N2,N6-bis(2,6-diisopropylphenyl)pyridine-2,6-dicarboxamide] was developed and used for remediation of polychlorinated solvents via sp(3)-sp(3) coupling of Grignard reagents with C-Cl bonds. The use of an iron catalyst for such coupling reactions is highly desirable due to its greener and more economical nature. Complex 2 was characterized using various spectroscopic techniques: electrospray ionization mass spectrometer (ESI-MS, m/z 575.1), cyclic voltammetry (E-1/2, 0.03 V and Delta E, 0.97 V), and ultraviolet visible (UV/Vis) spectroscopic techniques. The iron(III) complex showed efficient activation of multiple C-Cl bonds and catalyzing C-C coupling of polychlorinated alkyl halides, such as dichloromethane (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4), with various Grignard reagents under ambient reaction conditions. Complex 2 showed exceptional activity with reactions approaching near completion in about 5 min. With the required catalyst loading as low as 0.2 mol%, considerably high turnover numbers (TON = 483) and turnover frequency (TOF = 5,800 h(-1)) were obtained. None of the products detected during the reaction contained any chlorine, indicating an efficient dechlorination method while synthesizing products of synthetic and commercial interest. Interestingly, the catalyst was capable of replacing all chlorine atoms in each polychlorinated solvent under the investigations with high conversion.