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Non-Classical Bonds to Silicon: Principles of Structure and Reactivity

Ziel

In contrast to carbon, silicon displays pronounced susceptibility to coordination bonding and reluctance to form non-hindered kinetically stable cations and multiply bonded compounds. In last three decades the profound diversity of three, five and six co-ordinate silicon chemistry opened up its opportunities. While tetracoordinate silicon compounds have many commercial applications compounds with non-classical bonds to silicon are a subject of current interest for the development of advanced material science objects, e.g. new polymeric materials, new nanotechnological compounds, new reagents.

The project has as its object the development of the fundamentals of the chemistry of hypervalent, cationic and doubly bonded silicon compounds, namely:
1. To develop synthetic methods for the preparation of "anchor" or "bell-clapper" polychelate silanes and oligosilanes containing the same or different bidentate ligands at the silicon atom(s). Study their aptitude for the formation of donor-stabilized siliconium and doubly bonded silicon species.

2. To gain insight into the molecular and MO structure of the silicon and siliconium chelates, the nature of their coordination bonding, its stabilizing effect and the unprecedented high sensitivity to medium effects. The kinetics and mechanism of ligand-site exchange, flip-flop rearrangement, intermolecular exchange reactions and stereochemistry. The experimental and computational study of the SN2 substitution reaction pathway at tetrahedral and trigonal-bipyramidal silicon.

3. To gain understanding of the effects of substitution and stabilizing-coordination on the molecular and electronic structure and stability of M=X double bonds. Determination of the pi-bond energies in R2Si=X (X = CH2, NR, PR, O, S) hetero-pi-systems. Modelling of the addition reaction to the double bonds formed with the three-coordinate M atoms. Study of the synthetic potential of arylsilenes' thermal rearrangements and their mechanisms. Formation of Si=X double bonds by direct (heterogeneous or redox-mediated) reductive coupling.

4. To develop new approaches to a variety of silicon-containing macromolecules and novel materials based on hypervalent silicon monomers, developed in the course of the cooperative work. The applicants intended to convert hypervalent silicon compounds into potentially useful materials by means of sol-gel reactions, "self assembly" oligomerization, ring-opening polymerisation and co-polymerisation as well as by electrochemical methods.
T
he expected results will be important for a number of currently developing neighbouring fields (organic and organometallic chemistry, physical organic chemistry, structural and macromolecular chemistry, as well as material and life sciences) and will be published in the leading national and international scientific journals. The project involves substantial collaboration among 7 research groups, and provides active exchange of young scientists.

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Ben-Gurion University
EU-Beitrag
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Adresse
Hanessi'im St.
84105 Beer-Sheva
Israel

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Beteiligte (6)