The reactions of the 16-electron cycloheptatrienyl−cyclopentadienyl−zirconium sandwich complex [(η7-C7H7)Zr(η5-C5H5)] (1) with tert-butyl isocyanide (tBuNC) and 2,6-dimethylphenyl isocyanide (o-XyNC) have been studied. The isocyanide complexes [(η7-C7H7)(η5-C5H5)Zr(CNR)] (R = tBu, 2a; R = o-Xy, 2b) can be isolated in quantitative yield as stable orange (2a) or red (2b) crystalline solids. The CN stretching vibrations are observed at 2156 (2a) and 2134 cm-1 (2b) in KBr, indicating a relatively weak zirconium−isocyanide interaction. Solution NMR studies consequently reveal that the isocyanides quickly exchange on the NMR time scale at room temperature. The equilibrium reaction of 1 with tBuNC has been examined in further detail by dynamic NMR spectroscopy, allowing an enthalpy for the formation of 2a of ΔH° = −39.6 ± 6.6 kJ mol-1 to be established. DFT calculations reveal that the weakness of the zirconium−isocyanide bonds in 2a and 2b can be attributed to the strong and appreciably covalent zirconium−cycloheptatrienyl interaction, leading to highly stabilized frontier orbitals and consequently to a diminishing π-electron release capability and a small propensity to efficiently interact with σ-donor/π-acceptor ligands. The X-ray crystal structures of 1 and 2a are also reported.

On treatment with [Pt(PEt3)3], silicon-bridged ansa-cycloheptatrienyl-cyclopentadienyl Ti and V complexes, [1]silatroticenophane and [1]silatrovacenophane, undergo oxidative addition and regioselective insertion of a Pt(PEt3)2 moiety into the silicon-carbon bond to the seven-membered ring; the resulting complexes, [2]platinasilatroticenophane and [2]platinasilatrovacenophane, can be partly used as single-source catalysts for the ring-opening polymerization (ROP) of the original highly strained sandwich molecules.

Die Einführung der Me2Si‐Brücke und die Verzerrung der Sandwichstruktur erleichtern die Wechselwirkung des 16‐Elektronen‐ansa‐Komplexes (siehe Bild; blau Ti, gelb Si, grau C) mit σ‐Donor/π‐Acceptorliganden wie CO oder Isocyaniden. Dadurch gelang es, die elektronische Struktur dieses stark gebogenen ersten ansa‐Cycloheptatrienyl‐Cyclopentadienyl‐Übergangsmetallkomplexes zu untersuchen. Der Komplex wurde aus [(η‐C7H7)Ti(η‐C5H5)] erhalten.

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-C 5 H 4 )Me 2 Si(η-C 7 H 6 )Ti], [1]silatroticenophane 1, the analogous germylene-bridged derivative [(η-C 5 H 4 )Me 2 Ge(η-C 7 H 6 )Ti] (2) has been isolated from the reaction of [(η-C 7 H 7 )Ti(η-C 5 H 5 )] (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 1 H, 13 C 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(PEt 3 ) 2 ] moiety into the germanium-carbon bond at the C 7 H 6 site, yielding the [2]platinasilagermatroticenophane [(η-C 5 H 4 )Me 2 GePt(PEt 3 ) 2 (η-C 7 H 6 )Ti] (10), which was characterized by 1 H, 13 C, 31 P, and 195 Pt NMR spectroscopy. In addition, the reactivity of 1 toward protic acids such as HCl and HBF 4 has been investigated, yielding complexes of the type [(η-C 7 H 7 )Ti(η-C 5 H 4 SiMe 2 X)] (X ) Cl, F) by exclusive cleavage of the Si-C 7 H 6 silicon-carbon bond and protonation of the cycloheptatrienyl ipso-carbon atom.