η2 Coordination of Electron-Deficient Arenes with Group 6 Dearomatization Agents

• Published in: Organometallics 2020-07, Vol.39 (13), p.2493-2510
• Main Authors: Smith, Jacob A, Simpson, Spenser R, Westendorff, Karl S, Weatherford-Pratt, Justin, Myers, Jeffery T, Wilde, Justin H, Dickie, Diane A, Harman, W. Dean
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.0c00277

The exceptionally π-basic metal fragments {MoTp­(NO)­(DMAP)} and {WTp­(NO)­(PMe3)} (Tp = tris­(pyrazolyl)­borate; DMAP = 4-(N,N-dimethylamino)­pyridine) form thermally stable η2-coordinated complexes with a variety of electron-deficient arenes. The tolerance of substituted arenes with fluorine-containing electron withdrawing groups (EWG; −F, −CF3, −SF5) is examined for both the molybdenum and tungsten systems. When the EWG contains a π bond (nitriles, aldehydes, ketones, ester), η2 coordination occurs predominantly on the nonaromatic functional group. However, complexation of the tungsten complex with trimethyl orthobenzoate (PhC­(OMe)3) followed by hydrolysis allows access to an η2-coordinated arene with an ester substituent. In general, the tungsten system tolerates sulfur-based withdrawing groups well (e.g., PhSO2Ph, MeSO2Ph), and the integration of multiple electron-withdrawing groups on a benzene ring further enhances the π-back-bonding interaction between the metal and aromatic ligand. While the molybdenum system did not form stable η2-arene complexes with the sulfones or ortho esters, it was capable of forming rare examples of stable η2-coordinated arene complexes with a range of fluorinated benzenes (e.g., fluorobenzene, difluorobenzenes). In contrast to what has been observed for the tungsten system, these complexes formed without interference of C–H or C–F insertion.