Electrocatalytic cleavage of a carbon–chlorine bond by Re(IV)–chloro complex: a mechanistic insight from DFT

• Published in: Journal of applied electrochemistry Vol. 51; no. 12; pp. 1689 - 1703
• Main Authors: Shakeri, Jamaladin, Hadadzadeh, Hassan, Farrokhpour, Hossein, Weil, Matthias, Joshaghani, Mohammad
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-12-2021; Springer Nature B.V
• Subjects: Acetonitrile; Carbon; Chemistry; Chemistry and Materials Science; Chlorine; Cleavage; Crystallography; Dechlorination; Density functional theory; Dichloroethane; Dichloromethane; Electrochemical Processes; Electrochemistry; Electrolysis; Gas chromatography; Industrial Chemistry/Chemical Engineering; Mass spectrometry; Physical Chemistry; Research Article; Rhenium; Solvents; Density functional theory; Mechanistic insight; C–Cl bond cleavage; Electrocatalytic reaction
• ISSN: 0021-891X; 1572-8838
• DOI: 10.1007/s10800-021-01607-4

A new mononuclear hexachlororhenate complex salt ((2-ppyH)
2
[ReCl
6
], where 2-ppyH
+
 = 2-phenylpyridinium cation) was synthesized and structurally characterized by X-ray crystallography. The hexachlororhenate complex ([ReCl
6
]
2
¯
) was utilized as an efficient catalyst for the electrocatalytic dechlorination of dichloromethane (CH
2
Cl
2
). The cyclic voltammograms (CVs) in the presence of CH2Cl2 show catalytic cathodic currents in place of the reversible wave for the redox pair Re(IV)/Re(III). The controlled potential electrolysis was also employed to study the catalytic carbon–chloride (C–Cl) bond cleavage of CH
2
Cl
2
in the presence of [ReCl
6
]
2
¯
. The major electrolysis product was characterized as 1,2-dichloroethane (EDC), determined by gas chromatography–mass spectrometry (GC–MS). According to the cyclic voltammetry data, an electrocatalytic mechanism was proposed using the density functional theory (DFT, M06-L) to investigate the cleavage of the C–Cl bond in the presence of hexachlororhenate(IV). The optimized structures and the Δ
G
° changes (Δ
G
°
g
and Δ
G
°
sol
) for the proposed mechanism were calculated. Accordingly, the electrochemical pathway was thermodynamically feasible in both gas and solvent (acetonitrile) phases. The DFT studies suggest that the chlorine elimination proceeds through an interaction between the chlorine atom of CH
2
Cl
2
and the five-coordinated unsaturated rhenium (III) intermediate. The transition state for the transfer of chlorine to the Re center was located with the assessed barrier energy of + 16.53 kJ mol
−1
in the solvent phase.
Graphic abstract