Dihapto-Coordinated Conjugated Carbocycles (η2-CnHn n = 5–8): Blurring the Line Between Aromatic and Antiaromatic Hydrocarbons

The tungsten fragment {WTp(NO)(PMe₃)} (Tp = trispyrazolylborate) is an effective dearomatization agent for benzene and its derivatives. The dihapto-coordination of this system to an arene disrupts its aromatic stability, thereby promoting facile electrophilic additions to the hydrocarbon, which can then be followed by the addition of nucleophiles. This preliminary study endeavors to extend this conceptual approach to other aromatic and antiaromatic carbocycles. Dihapto-coordinated complexes of η²-tropylium, η²-cyclopentadienyl cation, and η²-cyclooctatetraene have been synthesized and characterized using SC-XRD, DFT, CV, and ¹H, ³¹P, and ¹³C NMR (including COSY, NOESY, HSQC, HMBC). Their fluxional behavior and reactivity toward electrophilic/nucleophilic additions, such as protonation and methylation, are also demonstrated.