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Silicon, the most abundant heavier main-group element in our solar system, naturally occurs as silicate minerals, which are basically tetravalent polyoxyanions of silicon containing strong, covalent Si−O single bond. Total mass of silicon in the Earth is almost twelve times the mass of the Moon. Despite it´s elemental abundance silicon does not occur naturally as organosilanes, the inorganic analogue of alkanes, featuring Si−C bonds. The first organosilicon compound Si(C2H5)4 was synthesized by Friedel and Crafts almost 150 years ago and not surprisingly reactivity studies of many functional organosilanes revealed that silicon, being more electropositive, differs greatly from it´s sister element carbon in many respect. For example, silicon, being a heavier main-group element, is reluctant to form multiple bonds. This notion remained true until 1981 when Brook and West concurrently synthesized the first stable low-oxidation state organosilicon compound, namely, silaethene and disilene derivatives containing Si=C and Si=Si double bonds, respectively, using bulky organyl substituents to kinetically stabilize the reactive multiple bonds.[1,2] A further impetus to this rapidly growing field of research was provided by Robinson, Filippou and Roesky, who have independently shown that highly reactive inherently Lewis-acidic low-valent silicon containing species can be stabilized by “donor-acceptor-interaction” using bulky N-heterocyclic carbene (NHC) as a donor ligand.[3-5] For example, dihalosilylenes (SiX2, X = Cl, Br), which have been invoked as highly reactive intermediates in the Siemens and Direct processes, could be isolated as room temperature stable adduct SiX2(NHC).[4,5]
In this presentation chemical properties of the adduct A will be compared with B (scheme 1). It will be shown that their chemical behavior in solution and coordination chemistry towards Lewis-bases and organo-lithium reagents are surprisingly different. The reactivity studies of A and B will be also presented leading to the isolation of several interesting classes of molecular silicon compounds in lowoxidation states, such as NHC-stabilized disilavinylidene (II) and silacyclopentadien-1-ylidene (III), silenide (IV), and titaniumsilylidyne complex (V) (scheme 1).[6,7]
References: 1) A. G. Brook, F. Abdesaken, B. Gutekunst, G. Gutekunst, R. K. Kallury, Chem. Commun., 1981, 191; 2) R. West, M. J. Fink, J. Michl, Science, 1981, 214, 1343; 3) Y. Wang, Y. Xie, P. Wei, R. B. King, H. F. Schaefer III, P. v. R. Schleyer, G. H. Robinson, Science, 2008, 321, 1069; 4) A. C. Filippou, O. Chernov, G. Schnakenburg, Angew. Chem. Int. Ed. 2009, 48, 5687; 5) R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn, D. Stalke, Angew. Chem. Int. Ed. 2009, 48, 5683; 6) P. Ghana, M. I. Arz, U. Das, G. Schnakenburg, A. C. Filippou, Angew. Chem. Int. Ed. 2015, 54, 9980; 7) Y. N. Lebedev, U. Das, O. Chernov, G. Schnakenburg, A. C. Filippou, Chem. Eur. J, 2014, 20, 9280.
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