Exploring the Reactivity of a Frustrated Sn/P Lewis Pair: The Highly Selective Complexation of the cis‐Azobenzene Photoisomer

• Published in: Chemistry : a European journal 2021-02, Vol.27 (11), p.3793-3798
• Main Authors: Holtkamp, Philipp, Poier, Dario, Neumann, Beate, Stammler, Hans‐Georg, Mitzel, Norbert W.
• Format: Article
• Language: English
• Subjects: activation; Adducts; Azo compounds; Benzil; Chemistry; Complexation; fluoroalkyl groups; frustrated Lewis pairs; Magnetic resonance spectroscopy; NMR; NMR spectroscopy; Nuclear magnetic resonance; small molecules; Stereoselectivity; tin
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202004600

The reactivity of the geminal frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 (1) was explored by reacting it with a variety of small molecules (PhOCN, PhNCS, PhCCH, tBuCCH, H3CC(O)CH=CH2, Ph[C(O)]2Ph, PhN=NPh and Me3SiCHN2), featuring polar or non‐polar multiple bonds and/or represent α,β‐unsaturated systems. While most adducts are formed readily, the binding of azobenzene requires UV‐induced photoisomerization, which results in the highly selective complexation of cis‐azobenzene. In the case of benzil, the reaction does not lead to the expected 1,2‐ or 1,4‐addition products, but to the non‐stereoselective (tBu)2PCH2‐transfer to a prochiral keto function of benzil. All adducts of 1 were characterised by means of multinuclear NMR spectroscopy, elemental analyses and X‐ray diffraction experiments. A highly selective complexation of cis‐azobenzene was found when reacting the isomeric compound with the intramolecular frustrated Lewis pair (F5C2)3SnCH2P(tBu)2 under UV‐induced photoisomerization conditions.