Experimentelle und theoretische Studien zu amino- und silylsubstituierten cyclischen Tetrylenen

Verbindungen, in denen Gruppe 14 Elemente zweifach koordiniert sind (Tetrylene), eignen sich gut als Ausgangsstoffe zur Synthese von Mehrfachbindungssystemen, Metallkomplexen und kationischen Verbindungen. Im Rahmen dieser Arbeit wurde speziell der Einsatz amino- sowie silylsubstituierter cyclischer Tetrylene (Silylene, Germylene, Stannylene und Plumbylene) zur Darstellung entsprechender niederkoordinierter Verbindungen der Gruppe 14 Elemente untersucht. In diesem Zusammenhang wurde die Synthese eines bislang unbekannten N-heterocyclischen Stannylens und die Darstellung eines Wolframpentacarbonylsilylenkomplexes vorgestellt. Auf Grundlage experimenteller Ergebnisse konnten die Bindungseigenschaften von N-heterocyclischen Silylenen in Komplexen erklärt werden. Zusätzlich wurde mit Hilfe quantenchemische Rechnungen herausgestellt, dass nicht kovalente Wechselwirkungen einen großen Beitrag zur Bindungssituation in Tetrylendimeren und Tetrylenmetallkomplexen leisten

Coordination Chemistry of Cyclic Disilylated Stannylenes and Plumbylenes to Group 4 Metallocenes

[Image: see text] Reduction of group 4 metallocene dichlorides with magnesium in the presence of cyclic disilylated stannylene or plumbylene phosphine adducts yielded the respective metallocene tetrylene phosphine complexes. Under the same conditions the use of the respective dimerized stannylene or plumbylene gave metallocene ditetrylene complexes. A computational analysis of these reactions revealed for all investigated compounds multiple-bonded character for the M–E(II) linkage, which can be rationalized in the case of the monotetrylene complex with the classical σ-donor/π-acceptor interaction. The strength of the M–E(II) bond increases descending group 4 and decreases going from Sn to its heavier congener Pb. The weakness of the Ti–E(II) bonds is caused by the significantly reduced ability of the titanium atom for d–p π-back-bonding

Coordination Chemistry of Cyclic Disilylated Stannylenes and Plumbylenes to Group 4 Metallocenes

Reduction of group 4 metallocene dichlorides with magnesium in the presence of cyclic disilylated stannylene or plumbylene phosphine adducts yielded the respective metallocene tetrylene phosphine complexes. Under the same conditions the use of the respective dimerized stannylene or plumbylene gave metallocene ditetrylene complexes. A computational analysis of these reactions revealed for all investigated compounds multiple-bonded character for the M–E­(II) linkage, which can be rationalized in the case of the monotetrylene complex with the classical σ-donor/π-acceptor interaction. The strength of the M–E­(II) bond increases descending group 4 and decreases going from Sn to its heavier congener Pb. The weakness of the Ti–E­(II) bonds is caused by the significantly reduced ability of the titanium atom for d–p π-back-bonding

Electrochemistry and MO Computations of Saturated and Unsaturated N-Heterocyclic Silylenes

The results of electrochemical investigations by cyclic voltammetry and density functional computations of new saturated (2, 3) and unsaturated N-heterocyclic silylenes (5, 6) are described and compared with the previously known N-heterocyclic silylenes (1, 4). Good correlations have been found between experimental oxidation potentials of saturated 1−3 and unsaturated 4−6 with those of density functional calculations of the electronic properties of these divalent silicon derivatives

Coordination Chemistry of Disilylated Stannylenes with Group 10 d¹⁰ Transition Metals: Silastannene vs Stannylene Complexation

The coordination behavior of disilylated stannylenes toward zerovalent group 10 transition metal complexes was studied. This was accomplished by reactions of PEt₃ adducts of disilylated stannylenes with zerovalent group 10 transition metal complexes. The thus obtained products differed between the first row example nickel and its heavier congeners. While with nickel stannylene complex formation was observed, coordination of the stannylenes to palladium and platinum compounds led to unusual silastannene complexes of these metals. A computational model study indicated that in each case metal stannylene complexes were formed first and that the disilylstannylene/silastannene rearrangement occurs only after complexation to the group 10 metal. The isomerization is a two-step process with relatively small barriers, suggesting a thermodynamic control of product formation. In addition, the results of the computational investigation revealed a subtle balance of steric and electronic effects, which determines the relative stability of the metalastannylene complex relative to its silastannene isomer. In the case of cyclic disilylstannylenes, the Pd(0) and Pt(0) silastannene complexes are found to be more stable, while with acyclic disilylstannylenes the Ni(0) stannylene complex is formed preferentially

Dispersion Energy Enforced Dimerization of a Cyclic Disilylated Plumbylene

By reaction of 1,4-dipotassio-1,1,4,4-tetrakis­(trimethylsilyl)­tetramethyltetrasilane with PbBr₂ in the presence of triethylphosphine a base adduct of a cyclic disilylated plumbylene could be obtained. Phosphine abstraction with B­(C₆F₅)₃ led to formation of a base-free plumbylene dimer, which features an unexpected single donor–acceptor PbPb bond. The results of density functional computations at the M06-2X and B3LYP level of theory indicate that the dominating interactions which hold the plumbylene subunits together and which define its actual molecular structure are attracting van der Waals forces between the two large and polarizable plumbylene subunits