Substituent-element cooperativity for homogeneous catalysis with p-block element compounds
The focus of research in our group is on various aspects of substituent-element cooperativity
in group 13/14 main-group element compounds. The installation of very strained, electron-rich,
electron-poor or photo-addressable substituents around elements in its natural valency states
shall lead to interesting new reactivities and optoelectronic features. The synthetic work is
constantly inspired and supported by modern quantum chemical methods and bonding analyses.
Examples of current research:
Synthesis of electron-rich, planarized silicon(IV) species and the theoretical analysis of dimerizing aminosilanes.
Kramer, N., Jöst, C., Mackenroth, A. and Greb, L., 2017, Chem. Eur. J.. doi:10.1002/chem.201703649
Equipping silicon(IV) with electron-rich, geometrically constrained NNN- and ONO-tridentate substituents leads to aminosilanes with increased Lewis acidity – expressed through the formation of Si2N2 rings by head-to-tail dimerization. Depending on the substituents, the dimerization can be controlled for the first time, yielding monomeric, structurally reversible and dimeric states. The monomeric species display substantial distortions from tetrahedral towards planar geometry at silicon. The dimerization and the Lewis acidiy of aminosilanes are rationalized by (conceptual) DFT, NBO, ETS-NOCV and QTAIM methods. The preorganization at silicon, London dispersion between the substituents and resonance phenomena inside the formed Si2N2 tetracycles are identified as driving forces for the dimerization. Comparison with selected aminosilanes permits general conclusions on the Lewis acidity of silicon species and on the aggregation of amphiphilic compounds.
Bis(perchlorocatecholato)silane - A neutral silicon Lewis super acid
R. Maskey, M. Schadler, C. Legler, L. Greb, 2017, Angew. Chem. Int. Ed. , doi: 10.1002/anie.201712155
No neutral silicon Lewis super acids are known to date. We report on the synthesis of bis(perchlorocatecholato)silane and verify its Lewis super acidity by computation (DLPNO-CCSD(T)) and experiment (fluoride abstraction from SbF6-). The exceptional affinity towards donors is further demonstrated by e.g. the characterization of an unprecedented SiO4F2 dianion and applied in the first hydrodefluorination reaction catalyzed by a neutral silicon Lewis acid. Given the strength and convenient access to this new Lewis acid, versatile applications might be foreseen.