Electron rich and geometrical constrained substituents in molecular silicon compounds - planar(ized) SiIV for bond activation and optoelectronic materials

• Applicant: Professor Dr. Lutz Greb
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 376818922

Homogeneous catalysts and materials for optoelectronic applications have been actively investigated for several decades - with transitions metal complexes in the spotlight of interest. However, an alternative for the often toxic, hard to separate and rare transition metals by abundant main group element compounds is desirable. Moreover, the reactivity of main group compounds in unusual bond situations is of major current interest in fundamental research. The herewith given approach deals with the synthesis and investigation of silicon(IV) compounds equipped with electron rich und geometrically constrained substituents. The nature of the proposed polydentate or macrocyclic amido/phenolato/pyrrolo-substituents gives answer to a series of fundamental as well as applied problems. (Pro)chiral substituents will allow for the elucidation of the planar inversion of tetravalent silicon(IV) - a theoretically long known, but experimentally neglected aspect of stereodynamics in this substance class. The geometrical distortion by the substituents leads to augmented reactivity: the Lewis-acidity increases substantially whereas the nucleophilicity of the electron rich substituents remains high. Small HOMO-LUMO gaps are resulting, leading to new reaction possibilities in the activation of small molecules with strong sigma-bonds. On one hand, the participation of the substituents in redox reactions combined with the ability of hypercoordination at silicon(IV) is plausible, leading to formal oxidative additions at silicon(IV). Alternatively, the strong amphiphilic character of the proposed compounds could provoke heterolytic bond activation of specific substrates. The concept of planarization finally will enable the realization of the first molecular, planar, tetravalent silicon(IV) species, with plenty of interesting structural, reactive and optical features. The proposed structures are synthetically straightforward accessible and quantum theoretical considerations reveal such compounds as highly attractive - with e.g. stronger Lewis-acidity than the reference Lewis acid B(C6F5)3 and considerable absorption of visible light - highly unusual properties of neutral, tetravalent silicon(IV) compounds. The acceptor properties and the modular synthesis offers the easy installation of donor functionalities for the creation of e.g. non-linear optical effects. The proposed concept allows for the integrated examination of the influence of substituents and planarization in silicon(IV)-compounds on stereodynamics, reactivity and photo physics. First promising results in relation to the given objectives are shortly discussed.

• DFG Programme: Research Grants