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

Abstract The reactivity of the geminal frustrated Lewis pair (FLP) (F 5 C 2 ) 3 SnCH 2 P( t Bu) 2 ( 1 ) was explored by reacting it with a variety of small molecules (PhOCN, PhNCS, PhCCH, t BuCCH, H 3 CC(O)CH=CH 2 , Ph[C(O)] 2 Ph, PhN=NPh and Me 3 SiCHN 2 ), 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 ( t Bu) 2 PCH 2 ‐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.