Oxidation-dependent Lewis acidity in chalcogen adducts of Sb/P frustrated Lewis pairs.

The reactions of the frustrated Lewis pair (F 5 C 2 ) 2 SbCH 2 P( t Bu) 2 with oxygen, sulphur, selenium and tellurium led to the mono-oxidation products (F 5 C 2 ) 2 SbCH 2 P(E)( t Bu) 2 (E = O, S, Se, Te). Further oxidation of these chalcogen adducts with tetrachloro- ortho -benzoquinone ( o -chloranil) gave (F 5 C 2 ) 2 Sb(CH 2 )(μ-E)P( t Bu) 2 ·Cat Cl (Cat Cl = o -O 2 C 6 Cl 4 ) with a central four-membered ring heterocycle for E = O, S, and Se. For E = Te the elimination of elemental tellurium led to an oxidation product with two equivalents of o -chloranil, (F 5 C 2 ) 2 SbCH 2 P( t Bu) 2 ·2Cat Cl , which is also accessible by reaction of (F 5 C 2 ) 2 SbCH 2 P( t Bu) 2 with o -chloranil. The synthesised compounds were characterised by NMR spectroscopy and X-ray structure analyses, and the structural properties were analysed in the light of the altered Lewis acidity due to the oxidation of the antimony atoms.