Pentaphenylcyclopentadienes that are para-substituted at each phenyl group prove to be valuable new ligands. They are easily prepared in good yield and high purity from pentaphenylcyclopentadiene by acetylation and subsequent acetalation. Owing to the ease with which the electronic properties of these ligands can be modified and due to the solubility and the facile characterization of their complexes it is now possible to explore the whole field of decaatylmetallocenes. The first soluble decaaryhnetallocenes with tin and lead as the metal atom are described.

transferred to a separatory funnel containing brine (10 mL). The mixture was extracted with chloroform (6X10 mL), and then the combined extracts were dried over MgSQ4. The solvent was evaporated and the residue was purified by reverse-phase chromatography (Water Delta Prep, 30 cm X 30 mm Clg Delta Pak column, 80% water/methanol to 40% water/methanol over 10 min, 40% water/methanol to 100% methanol over 15 min) to provide syn oxime 28 (10 mg, 6% yield) and the desired anti oxime 29 (82 mg, 53% yield) as colorless oils: 'H NMR (200

Zr-Me). Die Anionen in 1 und 3 zeigen jeweils ihnliche Resonanzsignale wie die in 2 bzw. 4.

2H-Tetrazolium ions of type 2 are part of the tetrazolium/ formazanide redox system, which is distinguished by an excellent charge stabilization within both the cationic and the anionic oxidation state. As a consequence, the 2H-tetrazolio substituent should facilitate redox umpolung."] We have examined nucleophilic reagents for the introduction of the 2H-tetrazolio group into electrophilic substrates ['] and report trapping reactions of the 5-lithiotetrazolium ion 3 and its spectroscopic detection by ' 3C NMR spectroscopy. 2a-cArN::pY'H NMR spectra show that tetrazolium salts 2, dissolved in tetrahydrofuran, are deprotonated quantitatively at -90 "C by n-or rert-butyllithium. The 5-lithiotetrazolium salts 3 thus formed can be considered as car be no id^.^^] At -100°C they are sufficiently stable for their 13C NMR spectra to be recorded.[41 The 13C NMR spectrum of 2 b had no signals between 6 = 165 and 250, whereas, after lithiation, a single unstructured multiplet appeared at 6 = 202.4 and vanished when the solution was heated up to room temperature. IGLO/DZ//6-31G* calculations[51 indicate that this multiplet is the 13C NMR signal of the solvated carbenoid's tetrazolium ring.16] According to the calculations, this shift of 48 ppm to lower field upon lithiation of 2 b can be explained mainly by the decrease of n-electron density at the tetrazolium C atom and by the weakening of the two N-C 0 bonds to this atom. ['] The new tetrazolium salts 6 and 9 b thus formed had not been accessible before, among other reasons because the reactivity'"] of 1,5-diarylformazans towards 5 is too low. On the other hand, this sole method to derivatize tetrazolium ions of type 2 failed when strongly oxidizing electrophiles like chlorine (or bromine) were used. In this case not the desired product but ion 2 as its chloride (bromide) was isolated in a yield of 67% (79%). We assume that 3 was oxidized by the halogen to the corresponding radical cation which abstracted an H atom from the solvent THF to re-form 2. ['']The azide 9 b was identified spectros~opically['~~ and by its reduction with iodide to amine 10 b and subsequent diazotization to the known['4] tetrazolium-5-diazotate 8 b. Reduction of 9 b with triphenylphosphane/water led to fission of the C-N bond. In contrast to Balli's azidinium salts,''s1 9 b did not react with azide ions. Thus, from the intensely yellow, shock-insensitive tetraphenylborate salt 9b, the corresponding colorless chloride or azide salt could be prepared with tetrabutylammonium chloride or azide, respectively. Experimental Procedure 9b: To Zb (4.64 mmol) dissolved in 50 mL of THF, n-butyllithium (5.1 mmol, 1.6 molar in hexane) and then tosyl azide (10 mmol) were added dropwise at -90°C. The initially dark brown solution turned dark red within a few minutes. After warming to 20°C over 10 h the solvent was evaporated. The green brown residue, which contained a small amount of 7b according to mass spectrometry, waschromatographed with dichloromethane/methanol (1 : 0 to 10 : 1) on silica gel. From acetonitr...

No Absract.