Synthesis and Reactivity of Silicon- and Germanium-Bridged<i>ansa</i>-Cycloheptatrienyl−Cyclopentadienyl Titanium Complexes

Abstract

A new type of ansa-cycloheptatrienyl−cyclopentadienyl complex with germanium as a bridging atom has been synthesized. Using the established route for the formation of [(η-C5H4)Me2Si(η-C7H6)Ti], [1]silatroticenophane 1, the analogous germylene-bridged derivative [(η-C5H4)Me2Ge(η-C7H6)Ti] (2) has been isolated from the reaction of [(η-C7H7)Ti(η-C5H5)] (troticene) with n-butyllithium/N,N,N‘,N‘-tetramethylethylenediamine (tmeda) in hexane and subsequent treatment of the intermediate dilithio complex with dimethyl(dichloro)germane. [1]Germatroticenophane 2 has been isolated in yields up to 15−20% and was characterized by means of 1H, 13C NMR spectroscopy, elemental analysis, and mass spectrometry. In addition, an X-ray diffraction study on a single crystal of 2 has been performed, and the structural characteristics are discussed in comparison to related ansa-compounds. The differential scanning calorimetry trace of 2 shows a strong exotherm at about 130 °C, which is the result of a thermally induced ring-opening polymerization reaction, and a strain energy of about 45 kJ mol-1 has been determined. The reaction of 2 with equivalent amounts of tris(triethylphosphine)platinum(0) involves a regioselective insertion of a [Pt(PEt3)2] moiety into the germanium−carbon bond at the C7H6 site, yielding the [2]platinasilagermatroticenophane [(η-C5H4)Me2GePt(PEt3)2(η-C7H6)Ti] (10), which was characterized by 1H, 13C, 31P, and 195Pt NMR spectroscopy. In addition, the reactivity of 1 toward protic acids such as HCl and HBF4 has been investigated, yielding complexes of the type [(η-C7H7)Ti(η-C5H4SiMe2X)] (X = Cl, F) by exclusive cleavage of the Si−C7H6 silicon−carbon bond and protonation of the cycloheptatrienyl ipso-carbon atom.