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 ΣX-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.