Generation and detection of tellurane [10–Te–4(C4)] and selenurane [10–Se–4(C4)] having alkyl and aryl ligands Soichi Sato, * Makoto Matsuo, Tsukasa Nakahodo, Naomichi Furukawa and Tatsuya Nabeshima * Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan Received 2 June 2005; revised 20 September 2005; accepted 22 September 2005 Abstract—Formation of 2,2 0 -biphenylylenedimethylselenurane and -tellurane was observed by the 1 H, 13 C, 77 Se, and 125 Te NMR studies at low temperature, in the reactions of dibenzoselenophene Se-oxide and 2,2 0 -biphenylylenedibromotellurane with methyl- lithium. These hypervalent compounds were unstable and decomposed at room temperature to give the corresponding dibenzo- chalcogenophenes quantitatively. Ó 2005 Elsevier Ltd. All rights reserved. Hypervalent compounds of main group elements have attracted attention as a key compound for generation of new functional molecules. 1 Though r-tetracoordi- nated chalcogen species (chalcogenuranes) [10–M–4, M=S,Se,Te] 2 are in general less stable than usual chal- cogenspecies,whichobeytheoctetrule,chalcogenuranes can be stabilized by the strongly electronegative atoms (oxygen, nitrogen, fluorine, etc.) and electron-withdraw- ing ligands on the apical positions. Five-membered ring also contributes the stabilization due to fixation of the hypervalent structure (TBP configuration). Several chalcogenuranes bearing only carbon ligands have been reported, but most of the corresponding isolable com- pounds have been stabilized by one or two five-mem- bered ring connecting apical and equatorial positions. 3 We have systematically studied the syntheses and char- acterization of organo-chalcogenuranes [10–M–4(C4), M = S, Se, Te], and have succeeded in detection and iso- lation of the new chalcogenuranes having only carbon ligands. 4 However the ligands employed in the prepara- tion of these chalcogenuranes (IV) have been restricted to aryl groups. Gedridge et al. prepared tetramethyl- and tetravinyl-telluranes as a hypervalent organotellu- rium (IV) compound. 5 Hellwinkel et al. and Hori et al. tried to prepare telluranes and sulfuranes bearing biphen- ylylene and alkyl ligands, but they could not succeed even in the detection of such telluranes and sulfur- anes. 6,11 Although hexacoordinated hypervalent chalco- gen (VI) species, pertelluranes having alkyl and/or aryl ligands recently have been reported by Morrison et al. and Akiba et al., 7 the direct detection and isolation of sulfurane and selenurane [10–M–4(C4), M = S, Se] hav- ing at least one alkyl ligand have never been reported. We, therefore, tried to synthesize and characterize the hypervalent chalcogen compounds (IV) having alkyl and aryl ligands. Here we report the first generation of 2,2 0 -biphenylylenedialkylchalcogenuranes and their reactivities. In general, telluranes (IV) are more stable than the cor- responding selenurane (IV) and sulfurane (IV). Thus, we tried first to prepare 2,2 0 -biphenylylenedimethyltellu- rane (2a) [10–Te–4(C4)]. When 2.2 equimolar amounts of MeLi (1.02 M, diethylether solution) were added to a suspension of 2,2 0 -biphenylylenedibromotellurane (1) in anhydrous tetrahydrofuran-d 8 (THF-d 8 ) in an NMR tube (/ 5 mm) under an argon atmosphere at 78 °C, the mixture turned to a yellow homogeneous solution. Structure of the product 2a was identified by the 1 H, 13 C, 125 Te NMR experiments at low temperature 8 (Scheme 1). The 1 H and 13 C NMR spectra of the product 2a in the aromatic region revealed that the two benzene rings on the biphenylylene group are equivalent. In the 1 H 0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2005.09.148 Keywords: Hypervalent; Tellurane; Selenurane; Sulfurane; Ligand coupling reaction; Pseudorotation. * Corresponding authors. Tel./fax: +81 29 853 4527 (S.S.); tel./fax: +81 29 853 4507 (T.N.); e-mail addresses: sato@chem.tsukuba.ac.jp; nabesima@chem.tsukuba.ac.jp Tetrahedron Letters 46 (2005) 8091–8093 Tetrahedron Letters