The First Coordination Complexes of Selenones:  A Structural Comparison with Complexes of Sulfones^†

Reactivity of the two classes of very weak donors R₂XO₂ (X = S, R = Me (1) and Ph (2); X = Se, R = Me (3) and Ph (4)) have been studied. Coordination properties of sulfones and selenones in solution and in the gas phase have been compared for the first time using a model bidentate metal complex, [Rh₂(O₂CCF₃)₄]. Two coordination modes, bridging μ₂-O,O‘ and terminal η¹-O, have been detected. These types of binding were realized in two series of sulfone and selenone metal complexes, polymeric mono-adducts {Rh₂(O₂CCF₃)₄·(R₂XO₂)}_∞ (X = S, R = Me (1a); R = Ph (2a); X = Se, R = Ph (4a)) and discrete bis-adducts [Rh₂(O₂CCF₃)₄·(R₂XO₂)₂] (X = S, R = Ph (2b); X = Se, R = Me (3b)). The compositions and structures of new compounds have been confirmed by NMR and IR spectroscopy, chemical analyses, and X-ray diffraction studies. Compounds 3b and 4a are the first crystallographically characterized metal complexes having selenone ligands coordinated to the metal centers. Preparation and X-ray study of analogous metal complexes of sulfone and selenone ligands allow, for the first time, tracking the structural changes induced by metal coordination. In addition, the X-ray structure of dimethyl selenone, Me₂SeO₂ (3), an analogue of Me₂SO₂, has been determined. Geometries of coordinated sulfone and selenones ligands have been compared with those of the corresponding “free” molecules.