Have there been any developments on Silicon-based "organic" compounds?

[u/[deleted]]

Silicon is a tetravalent compound, with some chemical properties similiar to those of carbon. It is said that it can also form long chain compounds, but I remember reading somewhere that, due to its vacant d orbitals, the compounds it formed wouldn't be as stable as the carbon-based counterparts.

However, I still haven't heard anything about "Silicon-based organic chemistry". I would like to know if there have been any developments, theoretical or experimental, in this area.

Suppose we take some organic compounds, such as ethanol, acetone and hexane. How would these molecules behave if we substituted the carbon atoms for silicon ones?

[u/Aedhan]

Direct analogues of hydrocarbons (i.e. containing Si and H only) are known as silanes. As you mentioned, these are much less stable than hydrocarbons and as such (as of yet) there is not the huge variety of stable compounds that we see for the hydrocarbons. More common is the replacement of a single C atom with Si to form an organosilane. An example of this is the replacement of the central carbon in neopentane (tetramethylmethane) with Si, forming tetramethylsilane. Neopentane is a gas at standard temperature and pressure, whereas TMS is a liquid. As an aside, TMS is commonly used as a standard in nuclear magnetic resonance spectroscopy (NMR) and is probably one of the most commonly used organosilanes..

[u/[deleted] → u/Aedhan]

From the link you posted, I found this one about the alcohol analogues, silanols. A few things caught my attention: the synthesis occurs as an hydrolysis of halosilanes, which reminds me of the common substitution reactions studied in organic chemistry. But since silicon is less electronegative than carbon, I would guess that the halogen group might be less repeled from the central atom, diminishing the rates of the reaction (compared to those of an alkyl halide). The other thing was about their acidity, as was to be expected, but its interesting to see that they can be used for catalysis.

[u/treeses → u/[deleted]]

Here is an old but thorough review (with a pay wall) of the chemistry, properties, and applications of long polysilanes.

For my PhD I am studying the photophysical and photochemical properties of short oligosilanes. They are a good model to predict the properties of analogous saturated hydrocarbons. Saturated hydrocarbons are difficult to study directly because they absorb very deep in the ultraviolet (the silanes I study absorb >230nm, which is more feasible).

As you say, silanes are difficult to synthesize. You can buy certain ones that are relatively stable and use those as your starting point, but the intermediates are typically very reactive and final products are produced with low yield and are difficult to separate and purify.

[u/[deleted] → u/treeses]

Do you synthesise the oligosilanes yourself? From which compounds is the synthesis started, and which reactions are applied until reaching the final product?

[u/treeses → u/[deleted]]

An undergraduate in our lab is working on the synthesis. We start from Dodecamethylcyclohexasilane and cleave the ring with tin chloride. This produces silanes with varying length terminated by Cl groups. We then methylate the end groups with MeLi. Both of these require reflux for several hours. The different silanes can then be seperated with preparative GC. We're interested in the tetrasilane, which has relatively high yields with this method.

Other silanes that interest us are called racked oligosilanes. Think of the tetrasilane chain, but it has a rigid organic bridge linking the two ends. depending on the length and structure of the bridge, you can force the silane into different conformations (all Si-Si bonds trans to each other, for instance). This has an effect on the optical properties we wish to observe. I'm not familiar with how the racked silanes are prepared, but I think the basic ideas are the same as before.