Chemical synthesis: Golden wedding for molecules

Date:
April 14, 2022
Source:
Swiss Federal Laboratories for Materials Science and Technology
(EMPA)
Summary:
Chemical syntheses in liquids and gases take place in
three-dimensional space. Random collisions between molecules have
to result in something new in an extremely short time. But there is
another way: on a gold surface under ultrahigh vacuum conditions,
molecules lying still next to each other can be made to combine -
even those that would never 'want' to react with each other in
a liquid. Researchers have now discovered such a reaction. Best
of all, the experts can 'take pictures' and watch every step of
the reaction.



FULL STORY ==========================================================================
In chemistry, there are structures that are particularly stable, such
as the so-called "benzene ring" consisting of six interconnected carbon
atoms. Such rings form the structural basis for graphite and graphene,
but they also occur in many dyes -- such as the jeans dye indigo and in
many drugs such as aspirin.


==========================================================================
When chemists wanted to build such rings in a targeted manner, they
used so- called coupling reactions, which usually bear the name of their inventors: for example, the Diels-Alder reaction, the Ullmann reaction,
the Bergman cyclization or the Suzuki coupling. Now there is another
one that does not yet have a name. It was discovered by a team from Empa together with the Max Planck Institute for Polymer Research in Mainz.

Everything in the dry The Empa researchers omitted liquids in their
chemical synthesis and instead attached the starting materials
to a gold surface in an ultra-high vacuum. The starting material (diisopropyl-p-terphenyl) can be observed resting calmly in the
cooled-down scanning tunneling microscope before the researchers turn
up the heat.

Turn up the heating -- movement on the dance floor At room temperature,
nothing happens yet, but at about 200 degrees Celsius, an amazing reaction occurs that would never happen in liquids: the two isopropyl groups --
which are normally completely inactive from a chemical point of view --
combine to form a benzene ring. The reason: due to the firm "adhesion"
on the gold surface, a hydrogen atom is first loosened and then released
from the molecule. This creates carbon radicals that are waiting for
new partners. And there are many partners on the gold surface. At 200
degrees Celsius, the molecules vibrate and perform rapid pirouettes --
there is a lot of movement on the golden dance floor. So what belongs
together soon gets together.

And once again everything in slow motion Matchmaking on the golden
surface has two advantages. First, there is no need for coercion: the
reaction takes place without mediating boric acids or halogen atoms flying away. It is a coupling involving only saturated hydrocarbons. The starting materials are cheap and easy to obtain, and there are no toxic byproducts.

The second advantage is that the researchers can watch every step of the reaction -- another thing that is not possible with classical, "liquid" chemistry. The Empa team simply turns up the heating of the gold surface gradually. At 180 degrees Celsius, the molecules have only connected
one arm with their neighbors, the second still protrudes freely into
the dance floor.

If one now cools down the gold surface inside a scanning tunneling
microscope, one can view and "photograph" the molecules just before they
are "married off." This is exactly what the researchers did. Thus,
the reaction mechanism can been followed in the form of "snapshots." Opportunities for a "new" chemistry The researchers and their colleagues
expect two kinds of effects to emerge from the current work. First,
the "snapshot method" could also be suitable for elucidating completely different reaction mechanisms. At Empa, instruments are being developed
that use ultrashort laser pulses in a scanning tunneling microscope
to elucidate such chemical reactions step by step. This could provide additional insights into chemical reactions and soon shake up many an
old theory.

However, the research results "from the dry" could also be useful
to further develop "liquid" chemistry. So far, most of the reactions
documented in the literature have come from classical liquid chemistry,
and scanning probe researchers have been able to recreate these
experiments. In the future, certain reactions could also be designed
in the scanning tunneling microscope and later transferred to liquid or
gaseous chemistry.


========================================================================== Story Source: Materials provided by Swiss_Federal_Laboratories_for_Materials_Science_and
Technology_(EMPA). Original written by Rainer Klose. Note: Content may
be edited for style and length.


========================================================================== Related Multimedia:
* Chemical_synthesis_on_a_gold_surface ========================================================================== Journal Reference:
1. Amogh Kinikar, Marco Di Giovannantonio, Jose' I. Urgel, Kristjan
Eimre,
Zijie Qiu, Yanwei Gu, Enquan Jin, Akimitsu Narita, Xiao-Ye
Wang, Klaus Mu"llen, Pascal Ruffieux, Carlo A. Pignedoli, Roman
Fasel. On-surface polyarylene synthesis by cycloaromatization of
isopropyl substituents.

Nature Synthesis, 2022; 1 (4): 289 DOI: 10.1038/s44160-022-00032-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220414110737.htm

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