To read the articles go to:
Why chemists are pushing C–C bonds to their limits, by Laura Howes. March 9, 2019. Volume 97, Issue 10.
What is a carbon-carbon bond? You might think this is a question with a simple answer, but chemists are still working to figure it out. To do so, they are pushing carbon-carbon bonds to their very limits. Amid claims about who holds the record for longest bond, a more detailed story of bonding is emerging.
In 2002, a team including Clara Viñas of the Institute of Materials Science of Barcelona (ICMAB-CSIC) described a 2.022 Å long carbon-carbon bond in an inorganic cluster (Inorg. Chem. 2002, DOI: 10.1021/ic011285z
). Like Xiao’s 1.931 Å bond, mentioned in our original story, this bond is found in a carborane cluster. Unlike Xiao’s bond, though, this one is part of a carborane within a larger organometallic compound. The compound features a negatively charged dicarbollide coordinated to a pyrrolyl anion via a cobalt(III) ion. As discussed in our story, the bonds in carborane clusters are more diffuse than a simple two-center, two-electron bond, and this holds true for Viñas’s bond as well. When asked to describe their bond, Viñas and group leader Francesc Teixidor describe how a combination of sterics and back electron donation to an antibonding orbital create a long carbon-carbon distance that has fewer electrons than a simple single bond between carbons. Viñas also mentions an even older paper, from 1987, in which Ken Wade, then at Durham University, and colleagues reported a carbon-carbon distance of around 2.001 Å in a carborane (J. Chem. Soc., Chem. Commun. 1987, DOI: 10.1039/c39870000889
). This find in the literature shows that investigations pushing carbon-carbon bonds to their extremes have been going on for longer than our article indicated.
April 20, 2019. Appeared in Volume 97, Issue 16.
Letters to the editor by Clara Viñas (Barcelona, Spain) and Joel S. Miller (Salt Lake City).