Me,Si)
,CH) the differences between the Sb-Sb bond lengths (282.2-286.6 pm) are considerably smaller. The bond angles at the antimony atoms of 1 range between 84.66(9)O and 113.2(7)". A similar wide range of Sb-Sb bond lengths and bond angles has also been observed in other antimony clusters, such as the anions Sb:-[2d1 or [Sb,M(C0),I3-(M = CrfZb1, MorZa1). The differences in the distances and angles of 1 cause some deviations from the geometry of the realgar structure. This is apparent for the antimony atoms Sb(l), Sb(4), Sb(8), and Sb(6) bearing alkyl substiuents. They are not exactly situated in a plane; the deviations from the best plane are between -39.1 and 38.6 pm. The nonbonding distances between the antimony atoms without alkyl substituents [Sb(2)-Sb(5), Sb(2)-Sb(7), Sb(3)-Sb(5), Sb(3)-Sb( 7)] vary only little between 429.0 and 432.3 pm. This corresponds quite well to the idealized geometry of the realgar type. A detailed examination of the structure of the five-membered rings reveals some deviations from an ideal envelope conformation. The atoms Sb(2), Sb(3), Sb(4), and Sb(5), for example, are not exactly in a plane either; the deviations from the best plane vary from -21.4 to 20.9 pm.
Apart from crystallographic analysis, mass spectrometry is also suitable for detecting the novel polycycles. In the chemical ionization mass spectrum, in addition to 1, Sb,R, (2, R = (Me,Si),CH) was also detected through the intensive group of signals of the molecular ion. Attempts to determine the structure of 2 by X-ray structure analysis or NMR spectroscopy have not yet been successful. Analogous phosphorus compounds of the type P7R5 have the bicyclic norbornane structure.r31
Experimental Section
All operations were carried out with strict exclusion of air in an argon atmosphere. AI,O, was heated under reduced pressure and loaded under argon. A solution of RSbCl, [R = (Me,Si),CH] [6] (1.58 g, 4.5 mmol) in THF (20 mL) was added dropwise within 30 min with stirring to magnesium filings (0.1 5 g, 6 mmol) in THF ( 5 mL) activated with BrCH,CH,Br. The dark brown mixture was stirred for 1 h, the solvent was removed at reduced pressure, and the residue was washed three times with portions of petroleum ether (100mL). The extracts were combined, concentrated to a volume of IOmL, and separated by chromatography with petroleum ether on A1,0, (A1,0, neutral according to Brockmann, activity Super I, particle size 0.063-0.200mm; column 8 x 1.5cm). The first, intensely orange fraction contained (SbR), (yield 0.76 g, 60%). The second, less intensely colored fraction was concentrated to a volume of 10 mL under reduced pressure. It contained (SbR), as main component as well as SbR, and the polycycles 1 and 2. Small yellow crystals of 1 were obtained when the concentrated solution was stored at -27°C for two months (MS (CI, positive-ion mode, NH,): 1: m/z :1608-1612 [Mi]; 2. mjz: 1643-1658 [M'H]).