Silaethene: XIII. Erzeugung von SiC-Doppelbindungen in der Koordinationssphäre von Eisencarbonylkomplexen

Abstract

The suitability of the vinylsilyliron complexes [Cp(CO) 2Fe]RSi(Cl)CHCH 2 [R = Me ( 1), Ph ( 2), Bu t ( 3), Fe(CO) 2Cp ( 4)] and of [Cp(CO) 2Fe]MeSi(Cl)CMeCH 2 ( 14) as precursors for the generation of silaethene derivatives has been investigated. The starting compounds 1 to 4 and 14 can be obtained from Me(Vi)SiCl 2, Ph(Vi)SiCl 2, HSiCl 3 and MeSiCl 3, respectively, by judicious combination of published procedures. They have been characterized by analytical and spectroscopic studies as well as by comparison with known data. The generation of the SiC intermediates was attempted by treating the vinylsilyl iron complexes wit LiBu t at low temperatures (−10°C). Only with 1 was a smooth reaction observed with formation of the Z Z dimer 1,3-bis(cyclopentadienyl-dicarbonyliron)-1,3-dimethyl-2,4-dineopentyl-1,3-disilacyclobutane ( 16) of the expected silaethene [Cp(CO) 2Fe]-MeSiCHCH 2Bu t. This intermediate also seems plausible on the basis of trapping experiments, using 2,3-dimethyl-1,3-butadiene, isoprene or 1,3-cyclohexadiene. However, since 16 is formed as the main product even in the presence of an excess of these dienes, the cyclization of the lithiated precursor ClSiMe[Fe(CO) 2Cp]-CH(CH 2Bu t)SiMe[Fe(CO) 2Cp]CH(Li)CH 2Bu t must be regarded as an alternative route to 16. The crystal and molecular structure of 16 indicate a Z Z configuration of the bulky ring substituents. The disilacyclobutane skeleton is nonplanar with a dihedral angle of 18.7°. Similar to other 1,3-disilacyclobutane derivatives, 16 shows a fairly short transannular Si(1)⋯Si(2) distance of 2.641(1) Å. Due to the −I effect of the phenyl substituent reaction of 2 with LiBu t yields oligomeric coupling products, whereas in 3, 4 or 14 for steric reasons LiBu t clearly attacks the carbonyl ligand instead of the CC double bond to give black, pyrophoric solids of low solubility.