Hypervalent organoselenium compounds stabilized by intramolecular coordination: synthesis and crystal structures.

Two novel hypervalent selenium(IV) compounds stabilized by intramolecular interactions, namely 6-phenyl-6,7-dihydro-5H-2,3-dioxa-2aλ-selenacyclopenta[hi]indene, CHOSe, 14, and 5-phenyl-5,6-dihydro-4H-benzo[c][1,2]oxaselenole-7-carbaldehyde, CHOSe, 15, have been synthesized by the reaction of 2-chloro-1-formyl-3-(hydroxymethylene)cyclohexene with in-situ-generated disodium diselenide (NaSe). The title compounds were characterized by FT-IR spectroscopy, ESI-MS, and single-crystal X-ray diffraction studies. For 14, there is whole-molecule disorder, with occupancies of 0.605 (10) and 0.395 (10), a double bond between C and Se, and the five-membered selenopentalene rings are coplanar. The packing is stabilized by π-π stacking interactions involving one of the five-membered Se/C/C/C/O rings [centroid-centroid (Cg...Cg) distance = 3.6472 (18) Å and slippage = 1.361 Å], as well as C-H...π interactions involving a C-H group and the phenyl ring. In addition, there are bifurcated C-H...Se,O interactions which link the molecules into ribbons in the c direction. For 15, the C-Se bond lengths are longer than those of 14. The two five-membered rings are coplanar. There are no π-π or C-H...π interactions; however, molecules are linked by C-H...O interactions into centrosymmetric dimers, with graph-set notation R(16).