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COMMUNICATIONS exchanger (Dowcx 50 WX?. acid form). and subsequently eluted wilh 0.5 M aqueous NH,. The resulting product mixture was separated by chromatography on S-Sepharose and o n Fractogcl TSK HW-40 (monitored with iodine. Rydon Smith. and z-naphthol!sulfuric acid staining. and by UV detection at 210 nm). Total yield of I and 2 was 0.9 g and 1.5 g. respectively. Hexaacelyl dcrivativr of 1: Compound I (10 mg) was dissolved in anhydrous pyridine (3 mL) and acetic anhydride (1 mL). The solution was maintained at rooin temperature for 15 h. Ice was then added. and the rcaction was extracted with CHCI,. After chromatographic purification o n silicn gel wilh CHCI,,'CH,OH (99:l). 5 mg of hexaacct~l-1 was isolated. HR-El MS: iri;: 506.1865 (0.2%).

Although tetrakis(2-tert-butyl-4,5,6-trimethylphenyl)distannene (9), the first tetraaryl-distannene to be reported on, is stable in the solid state, only the monomeric stannylene 8 can b e detected in solution. An X-ray crystal structure analysis of 9 reveals a long tin-tin bond length of 291.0( 1) p m and a trans-bent Sn2C4 framework with different fold angles of 21.4" and 64.4".Lappert's tetraalkyldistannene 1 was the first molecule to be reported on with a homonuclear double bond between heavier elements of the fourth main g r o~p [~,~l . Even though numerous disilene~[~,~] as well as some digermenesL5] -compounds with Si=Si and Ge=Ge double bonds -have been discovered in the meantime, compound 1 has remained as the only structurally characterised distannene. Although 1 is stable in the solid state, it dissociates in solution to two stannylene molecules 2. The distannene 5, accessible from thermal or photochemical reaction of the cyclotristannane 3r61, behaves differently and retains its structural integrity in solution, as evidenced by ' 19Sn-NMR spectroscopy [6] and trapping r e a c t i o n~ [~~~] .However, only the three-membered ring system 2 can be detected in the solid state at room temperature (Scheme l)I6p9I. The apparently promising idea to suppress the formation of the three-membered ring system by replacing the 2,4,6-triisopropylphenyl group in 5 by the even bulkier 2,4,6-tritert-butylphenyl group was not successful since the thus formed bis(2,4,6-tri-tert-butylphenyl)stannylene 6 exists only as the monomer also in the solid state"O1. A weak tintin interaction was observed ["] in one of the crystalline forms of the intramolecular donor atom-stabilised molecule Sn[2,4,6-(CF3)3C6H2]2; however, the separation of 364 pm is much too large for a possible bonding situation['*].Since the steric overcrowding in 6 was obviously too large for distannene formation, we reduced the steric requirements of the substituents and now report on the formation of the stannylene 8 and the distannene 9 which is stable in the solid state. The reaction of the Grignard compound 7 with tin(I1) chloride affords a dark red solution of the stannylene 8, the constitution of which is substantiated by spectral data and trapping reaction with, for example, 3,5-ditert-butylbenzoquinone to yield the [4 + 11 cycloadduct 10. Chem.