The Reaction Pattern of the MoCl₅-Mediated Oxidative Aryl-aryl Coupling

Abstract

The oxidative coupling of electron rich aryls by molybdenum pentachloride is reported. The stoichiometry of the coupling reaction reveals that MoCl₅ is a single electron acceptor. Interestingly, the 1,2-dialkoxy substitution pattern is pivotal for the aryl-aryl coupling.

Key words

biaryls - coupling - dimerizations - electron transfer - molybdenum

References

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4

All reactions were strictly performed under inert atmosphere using anhydrous solvents. Different grades of molybdenum pentachloride from various suppliers were tested having minor alternations on yield and the reaction outcome.

13

14: Mp: 126 °C(methanol); ¹H NMR (CDCl₃, 300 MHz): δ = 7.26-7.19 (m, 4 H); 7.03 (s, 2 H), 7.01-6.93 (m, 2 H), 6.85-6.81 (m, 4 H), 6.62 (s, 2 H), 3.81 (s, 6 H), 3.73 (s, 6 H); ¹³C NMR (CDCl₃, 75 MHz): δ = 158.7, 149.0, 146.2, 146.0, 129.4, 129.3, 121.7, 116.8, 116.5, 115.8, 114.4, 105.3, 55.9, 55.8; MS (EI, 70 eV): m/z (%) = 458(100) [M⁺]; HRMS (EI): m/z calcd for C₂₈H₂₆O₆ [M⁺]: 458.1729; found: 458.1736.

14

16: Mp: 143 °C (hexanes/CHCl₃); ¹H NMR (CDCl₃, 300 MHz): δ = 6.89-6.83 (m, 2 H), 6.75-6.67 (m, 2 H), 3.89 (s, 6 H), 3.85 (s, 6 H); ¹³C NMR (CDCl₃, 75 MHz): δ = 154.0 (d, ² J (F, C) = -240 Hz), 149.6, 145.2, 114.0, 113.8, 100.2, 56.5, 56.1; ¹⁹F NMR (CDCl₃, 282 MHz): δ = -122.3; MS (EI, 70 eV): m/z (%) = 310(100) [M⁺]. Elemental analysis: calcd for C₁₆H₁₆F₂O₄ (310.30): C, 61.92; H, 5.20. Found: C, 61.94; H, 5.28.