A Structural Comparison of Organoterminated Selenide, Diselenide, and Triselenide

GRAPHICAL ABSTRACT Abstract A series of organosubstituted mono-, di-, and triselenides has been prepared and structurally characterized. In this series, a novel modification of 1,2,3-triselena-[3]ferrocenophane has been obtained in which intermolecular contacts between the central selenium atoms are below the sum of the van der Waals radii. Moreover, dimesitylselenide has been structurally characterized.


INTRODUCTION
During the Xerox process, light-induced charge separation in amorphous Se/Te alloys takes place. However, undesired residual charges may persist after exposure to light which may be due to formation of chalcogenonium cations and chalcogenolate anions in the solid state (valence-alternation-model). 1,2 In an alternative model, the collapse of such polar defects in Se/Te alloys has been proposed, which involves the interaction of persistent "-onium" and "-ate" functionalities in a nonclassical way. 3 Also in the solid state structures of the elemental forms of α-selenium and α-tellurium, short contacts between atoms of different spiral chains are observed, which are well below the van der Waals radii of the atoms involved and may suggest closed shell interactions. Based on our previous work in organoselenium chemistry, [4][5][6][7] we encountered structures of some organic and organometallic selenides in which similar interactions may or may not take place depending on the substituents and the geometry imposed by the latter. Here, we would like to report the solid state structures of a new modification of 1,2,3-triselena [3]-ferrocenophane in comparison to that of dimesityldiselenide co-crystallized with dimesitylselenide.
When monofunctional organometallic compounds of the type R-M (M = Li, MgBr) are allowed to react with elemental selenium, related organoselenides of the type R 2 Se n can  be expected besides R-SeM. 11 We have performed this reaction starting from MesMgBr (Mes = 2,4,6-trimethylphenyl) and elemental selenium. Besides the primary insertion product, Mes-SeMgBr, the corresponding neutral mono-and diselenides 2 and 3 have been obtained. Although both compounds have been described in the literature before, 16-21 monoselenide 3 has not been structurally characterized so far. Upon extraction of the reaction products with unpolar solvents, 2 and 3 can be separated from magnesium selenides. Protonation of the crude reaction mixture with aqueous hydrochloric acid reveals the formation of Mes 2 Se 2 (2), Mes 2 Se (3), and MesSeH (4) in the relative ratio 1:1:2 according to 77 Se NMR. Recrystallization from toluene gave crystals of co-crystallized 2 and 3 (Fig. 3). According to single crystal X-ray diffraction studies at 100 K, the 1:1 combination of 2 and 3 crystallizes in the monoclinic space group P2 1 /n ( Table 2). The geometrical parameters For dimesitylselenide 3 however, it is the first time that structural data have been obtained outside the coordination sphere of a metal. The Se-C distances are close to 1.93 Å and therefore slightly longer than in 1. The C-Se-C angle is 102 • and slightly larger than the C-Se-Se angles in 1 and 2. Intermolecular Se . . . Se contacts are well beyond the sum of the van der Waals radii and bonding interactions therefore can be excluded.

SUMMARY AND CONCLUSION
In conclusion, we have reported a novel modification of triselena- [3]ferrocenophane 1 in which intermolecular contacts between the central selenium atoms below the sum of the van der Waals radii are evident. Moreover, the structural characterization of dimesitylselenide 3 has been presented. While there are several structural reports on coordination compounds involving 3, 20 this is the first report on the structure of the noncoordinated ligand.

EXPERIMENTAL
All manipulations were carried out under inert argon atmosphere using standard Schlenk technique, if not otherwise stated. 1

Synthesis of Compounds 2 and 3
Magnesium powder (4.87 g, 0.2 mol) was immersed in 40 mL of THF in an argon atmosphere. To this mixture, MesBr (29.13 mL, 0.190 mol) diluted with 20 mL of THF were added dropwise via an additional funnel. Upon complete addition, the mixture was refluxed for 2 h. The mixture was then slowly cooled to room temperature and gray selenium (15 g, 0.190 mol) was added in small portions. Upon complete addition, the mixture was heated to reflux for an additional 2 h. Without heating, stirring was continued for further 10 h. The resulting solid gray mixture was then quenched with 70 mL of aqueous HCl (4 M) under ice cooling. The resulting orange solution was extracted twice with 100 mL of diethylether. The ether phase was evaporated to dryness under vacuum and the resulting product was recrystallized from toluene. Spectral data before recrystallization: 77 Se NMR (C 6

X-Ray Diffraction Studies on Compound 2·3
The measurements were performed with a Bruker APEX-II CCD using graphitemonochromatized Mo K α radiation at 100 K on a yellow needle shaped crystal (0.23 × 0.10 × 0.08 mm): C 18  The structure was solved by direct methods (SHELXS-97) and refined by full-matrix least-square techniques against F 2 (SHELXL-97). 25 The nonhydrogen atoms were refined with anisotropic displacement parameters without any constraints. The H atoms of the phenyl rings were put at the external bisector of the C-C-C angle at a C-H distance of 0.95 Å and common isotropic displacement parameters were refined for the H atoms of the same phenyl group. The H atoms of the methyl group C48 are disordered over two orientations and were refined with site occupation factors of 0.5 at two positions rotated from each other by 60 • with common isotropic displacement parameters for the H atoms and idealized geometry with tetrahedral angles, enabling rotation around the C-C bond and C-H distances of 0.98 Å. The H atoms of the other methyl groups were refined with common isotropic displacement parameters for the H atoms of the same group and idealized geometry with tetrahedral angles, enabling rotation around the C-C bond, and C-H distances of 0.98 Å. For 380 parameters, final R indices of R 1 = 0.0211 and wR 2 = 0.0528 (GOF = 1.046) were obtained. A multiscan-type absorption correction has been applied (Bruker SADABS). The largest peak in a difference Fourier map was 0.447 eÅ −3 .

SUPPLEMENTAL MATERIAL
Supplementary data for this article can be accessed on the publisher's website, www.tandfonline.com/gpss