“Aromatic Carbon–Carbon Bond Cleavage Using Tungsten Complexes. A DFT Computational Study”

The mechanism of aromatic C–C bond cleavage in quinoxaline (QoxH) catalyzed by the tungsten complexes W(PMe3)4(η2-CH2PMe2)H has been theoretically investigated at the DFT level. The mononuclear species (η2(N,C)-Qox)W(PMe3)4H (experimentally isolated and characterized) is directly involved in the formation of the final product [κ2(C2)-C6H4(NC)2]W(PMe3)4, where the aromatic C–C bond of quinoxaline has been broken. The mechanism requires a double insertion of the metal into two quinoxaline C–H bonds, thus affording the “strained” benzyne-type species η2(C2)-C6H4(NCCN)W(PMe3)4H2. After expulsion of H2 the η2(C2) complex leads to the [κ2(C2)-C6H4(NC)2]W(PMe3)4 product, thus relieving the structural strain of the small WCC cycle in η2(C2). Also, the theoretical investigation shows the existence of a stable (η4(C2N2)-QoxH)W(PMe3)3H2 complex (an unprecedented example of η4 coordination), in agreement with its experimental observation and characterization by X-ray diffraction.