HypCoSi - Hypercoordinated silanes with heavier group 14 element-element bonds

While the chemistry of the lightest group 14 element carbon (organic chemistry) is highly developed, the chemistry of the higher group 14 elements: silicon, germanium, tin, and lead is much simpler and also less developed. However, although the heavier elements lack carbon's ease to hybridize orbitals and thus its amazing structural and functional variety, they have some unique qualities of themselves to offer. These include stable divalent states, electron delocalization along σ-bonds, and a much higher tendency to engage in hyper-coordinate bonding situations. The current proposal aims at investigations combining the last two mentioned features of heavier group 14 elements. In organic chemistry it is long known that in organic molecules with extended π-electron systems the π-electrons are delocalized over more than one (and often many) bonds. This concept of electron delocalization is not only important to understand reactivity of organic molecules, it is also responsible for the property of certain organic molecules to work as conducting material f.i in organic light emitting diodes and other organic circuitry. Not as well known is the fact that catenated heavier analogs of carbon such as polysilanes, -germanes and stannanes also exhibit the feature of electron delocalization. However, electrons in these molecules are not delocalized along an extended π-system but along a number of σ-bonds. For both types of electron delocalization phenomena it is important that the molecule is oriented to allow the involved orbitals to overlap effectively. For polysilanes with comparably long Si-Si bonds the rotational barriers to attain certain spatial orientations are very low. Thus, alignment of the main chain needs to be adjusted by some measures such as the introduction of bulky substituent which force the chain into a specific conformation. Other methods entail inclusion into cyclodextrines, incorporation into bicyclic systems. Another property which distinguishes the heavier group 14 elements from carbon is that of hyper-coordination, meaning that these atoms can accommodate interactions with more than four other atoms. The proposed research intends to study the effect of hyper-coordination on σ-bond electron delocalization. It will be investigated how hyper-coordination can be utilized to control and enhance the conductivity of polysilanes. The involved Austrian and Russian research groups are specialists in the field of polysilanes and hypercoordinated group 14 elements. They will join forces and utilize their respective expertise to study this new area of material science.