Ferrocenylethynyltin Compounds – Characterization and Reactivity towards Triethylborane

Ferrocenylethynyl(trimethyl)tin (1), bis(ferrocenylethynyl)dimethyltin (2), tetrakis(ferrocenylethynyl)tin (3), and chloro(ferrocenylethynyl)dimethyltin (4) have been prepared and characterized in solution by 1H, 13C, and 119Sn NMR spectroscopy. Solid‐state MAS 13C and 119Sn NMR spectra were measured for 2 and 3, and the molecular structure of one of the modifications of 2 was determined by X‐ray analysis. The reactivity of 1–4 towards triethylborane has been explored. 1,1‐Organoboration takes place in all cases, and the reactions are stereoselective for 1 and 4 to give the alkenes 5 and 6, respectively, in which the stannyl and the boryl groups are in cis‐positions at the C=C bond. In the case of 2, the final products are the 1‐stannacyclopenta‐2,4‐diene 7a and the 1‐stanna‐4‐boracyclohexa‐2,5‐diene 8a, whereas the reaction of 2 with triisopropylborane leads selectively to the six‐membered ring 8b. Zwitterionic intermediates 9a,b, in which the tin atom is coordinated side‐on to the C≡C bond of an alkynylborate, have been detected by NMR spectroscopy. Compound 3 reacts with triethylborane to give a mixture of three spirotin compounds 10–12 as the final products, where the tin atom connects five‐ and six‐membered rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)