Small Organoselenium Molecules. 1. Dimethyl Selenoxide:  Structure, Complexation, and Gas-Phase Transformation

For the first time the structural characterization of dimethyl selenoxide coordinated to metal complexes has been performed confirming the Me₂SeO arrangement assigned by spectroscopic techniques for the molecule in solution and solid state. The structure of Me₂SeO is trigonal pyramidal with Se−O and Se−C bond lengths of 1.70 and 1.92 Å, respectively, and Σ_X-Se-Y = 301°. As a ligand, dimethyl selenoxide was found to bind to the rhodium centers of various Lewis acidity strengths by using only its oxo functionality in both terminal and bridging fashions. This O-directed coordination preference contrasts with an ambidentate (−S and −O) binding character revealed by dimethyl sulfoxide upon formation of analogous donor−acceptor complexes. The study of dimethyl selenoxide in the gas phase at 135−140 °C resulted in a thermal degradation of this molecule. The major decomposition product has been entrapped by a metal complex and identified as dimethyl selenide. The isolation of the coordinated Me₂Se fragment clearly demonstrates that the Me₂SeO molecule is less thermally stable than Me₂SO, which under similar reaction conditions shows no sign of decomposition at temperatures up to 160 °C.