Aromatic molecules dihapto-bound to a π-basic metal are dearomatized and activated for novel organic reactivity. Research into the Group 6 π-basic fragment {MoTp(DMAP)(NO)} has uncovered the isolatable Mo(Tp)(DMAP)(NO)(η2-benzene) complex. A thermodynamic profile of the molybdenum benzene complex and its precursor Mo(Tp)(DMAP)(NO)(3,4-η2-α,α,α-trifluorotoluene) is examined. Along with dearomatizating benzene, a wide array of electron deficient arenes are found to coordinate to molybdenum in a dihapto-fashion. An emphasis is placed on investigated fluorinated and trifluoromethylated aromatics, given the proliferation of fluorinated compounds in the medicinal chemical community. The metal-arene η2-bond, heavily contingent on the π-back-bonding interaction between metal and aromatic, is enhanced when the benzene ring is made more electron deficient by electron-withdrawing groups (EWGs). The tungsten fragment {WTp(DMAP)(NO)} is also found to activate a wide array of electron-deficient arenes. Additionally, coordination of benzene to tungsten allows for the synthesis of an isolatable η2-benzenium complex under moderately acidic conditions (pKa ~ 0). Selectivity for the initial electrophilic addition is enforced by the metal, an important contribution that allows for control over the final dearomatized product. Reactivity trends for the initial organic chemistry between the parent benzene and electron-deficient arenes upon coordination to the tungsten fragment are examined.

Dearomatization and reactivity of benzene and electron-deficient arenes promoted by π-basic transition metal complexes

255th National Meeting (2018)

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