Dalton Transactions Blog

Posted on behalf of Ian Mallov, web writer for Dalton Transactions

Reading the chemical literature as a synthetic chemist, I can often empathize with the story of the practical challenges which underlies the research story in a paper.  This article from Gunnoe and co-workers certainly left me with an appreciation for the gutsy way in which the researchers overcame significant challenges to the usual synthetic and analytical techniques of the inorganic chemist to present some hard-won gains on the reductive elimination chemistry of rhodium.

The power of reductive elimination – inducing two chemical moieties bonded to a central atom to leave without one of their electrons, resulting in a formal gain of electrons by this central atom – lies in its ability to fuse together the two groups leaving. In this way chemical bonds which are difficult or impossible to form by other means can be created.  When the elimination of one group breaks a metal-carbon bond, the possibility to form a carbon-X bond with the other group reductively-eliminated, and thus functionalize a carbon centre, is particularly attractive.

Such is the technique the Gunnoe group present here.  Much more commonly used in platinum chemistry, they prove this approach to be applicable to rhodium chemistry also, inducing reductive elimination of CH₃ and a range of halides or pseudo-halides.  While the CH₃-X products formed are useful only as a proof of principle, the proof was a result of overcoming significant challenges. 

The Rh-terpyridine complex ultimately coaxed to undergo reductive CH₃-X elimination was so insoluble that they were unable to obtain a NMR spectrum, much less an x-ray crystal structure, and had to trust that a combustion analysis supporting their hypothesized product was evidence enough to proceed.  Then, the hoped-for reductive elimination did not occur until electron-withdrawing NO₂ groups were installed on the terpyridine backbone, the reaction was heated, and the solvent changed to CD₃NO₂ (certainly not the first solvent one would have tried).  Moreover, the CH₃-X products formed were gases, making it very difficult to quantify the amount produced.

Nonetheless, their persistent tweaks of the organometallic complex itself, aided by computational thermodynamic data and the use of second-choice analytical techniques when necessary yielded insight into Rh reductive elimination.

Find out more and download the article now:

Reductive functionalization of a rhodium(III)–methyl bond by electronic modification of the supporting ligand
M. E. O’Reilly, D. R. Pahls, J. R. Webb, N. C. Boaz, S. Majumdar, C. D. Hoff, J. T. Groves, T. R. Cundari and T. B. Gunnoe
Dalton Trans., 2014, DOI: 10.1039/C4DT00234B

Ian Mallov is currently a Ph.D. student in Professor Doug Stephan’s group at the University of Toronto. His research is focused on synthesizing new Lewis-acidic compounds active in Frustrated Lewis Pair chemistry. He grew up in Truro, Nova Scotia and graduated from Dalhousie University and the University of Ottawa, and worked in chemical analysis in industry for three years before returning to grad school.

Posted on behalf of Philip Mountford, Chair, Dalton Transactions Editorial Board

I am writing on behalf of the Editorial Board of Dalton Transactions to let you know that Dr Jamie Humphrey has accepted a new position within the Royal Society of Chemistry as Publisher of Dalton Transactions and as such will no longer be Editor. However, we are delighted to report the appointment of the new Editor for Dalton Transactions, Sarah Ruthven.

Sarah has been a member of Royal Society of Chemistry editorial staff since 2005. Since her time at the organisation, Sarah has overseen the successful development of a number of journals, including Green Chemistry and Food & Function, and in 2011 she launched the Royal Society of Chemistry’s innovative journal, RSC Advances, which in the three years since its launch has grown to be the largest journal that the Royal Society of Chemistry publishes.

As the Journal’s Editor, Sarah brings extensive journal and publishing experience to Dalton Transactions, together with tremendous enthusiasm and a reputation for getting things done. I have every surety that Dalton Transactions will thrive and prosper under her editorship. Sarah will lead the Dalton Transactions editorial team based in Cambridge, UK: Deputy Editor, Fiona McKenzie and Development Editor, Guy Jones, and Editorial Production Manager Andrew Shore and his team of Publishing Editors.

Together with all the authors and readers, and the editorial and advisory board members of Dalton Transactions I am sure you would wish to join me in thanking Jamie for his hugely important role at the Journal during the past 11 years. From 2003 to 2014, the Journal has seen the number of published articles grow substantially from 689 to 1709 per year, with a subsequent increase in issue frequency from 24 to 48 issues per year—making Dalton Transactions the first weekly inorganic journal. Jamie also introduced topic-based themed issues and increased the number of Associate Editors to 7, based in 6 countries worldwide.

During Jamie’s tenure, Dalton Transactions also has seen its impact factor grow from 3.02 to 3.81, maintaining its highly competitive position in comparison to its international counterparts. Jamie has been tireless in promoting and representing the Journal at meetings and conferences throughout the world, and many of us have enjoyed his company in both a professional and personal setting.

We thank you Jamie for all of this and wish you all the best for the future!

Orignally published in Dalton Transactions as an Editorial article

Hypochlorous acid (HOCl) is a weak acid, formed from the reaction of chlorine with water. In addition to its use as a reagent in organic chemistry, it has significant biological relevance. HOCl is generated in biological systems in a reaction between chloride ions and hydrogen peroxide, catalysed by the enzyme myeloperoxidase.

This enzyme is secreted by phagocytes (cells which help protect the body by ‘ingesting’ bacteria) when they are activated during an immune response. Hypochlorite (ClO^–), the conjugate base of HOCl, is extremely toxic to bacteria and plays a vital role in assisting the activated phagocytes with killing a wide range of pathogens.¹

Excess production of HOCl in a living system can have a detrimental effect, as HOCl can react with many different biological molecules, including DNA, cholesterol and proteins, leading to changes in their biological properties. An example of this is the reaction of hypochlorous acid with unsaturated bonds in lipids, which produces a species called a chlorohydrin. This disrupts the formation of the essential lipid by-layers which form around cells.

Excess hypochlorous acid has been implicated in conditions such as inflammatory diseases, neurodegeneration and cancers.² In order to fully understand the role of HOCl in these biological processes, accurate detection methods must be developed to monitor the molecule in living cells.

Several ‘HOCl-recognising’ molecules have been found to be effective sensors of hypochlorous acid. When conjugated with a fluorophore, these probes can successfully ‘recognise’ HOCl by reacting with it, however their application in vivo is still limited due to their excitation wavelengths being in the ultraviolet region of light.³ Sensors with adsorption (or emission) in the visible light range are more desirable for clinical diagnostic applications. 

In one recent paper in Dalton Transactions, Yuan and co-workers combine an excellent HOCl-recognising moiety: 4-amino-3-nitrol phenol) and a ruthenium(II)-2,2-bipyridyl complex, which is well known to exhibit visible light adsorption and emission, into one compound to create a luminescent probe for HOCl.

The resulting complex [Ru(bpy)₂(AN-bpy)][PF₆]₂ is very weakly luminescent but, upon reaction with HOCl in aqueous media, converts to [Ru(bpy)₂(HM-bpy)][PF₆]₂, which has a luminescence signal which is 110-fold stronger.

Impressively, the authors show that when HeLa cells are incubated with [Ru(bpy)₂(AN-bpy)][PF₆]₂ for two hours they remain non-luminescent; when the same cells are subsequently treated with HOCl for thirty minutes, a bright red luminescence is observed, clearly demonstrating the potential for using this ruthenium complex as an in vivo, luminescent detector of hypochlorous acid. 

To find out more, read the article using the link below:

Development of a functional ruthenium(II) complex for probing hypochlorous acid in living cells
Dalton Trans. 2014, DOI:10.1039/C4DT00179F

Dr C. Liana Allen is currently a post-doctoral research associate in the group of Professor Scott Miller at Yale University, where she works on controlling the enantio- or regioselectivity of reactions using small peptide catalysts. Liana received her Ph.D. in organic chemistry at Bath University with Professor Jonathan Williams, where she worked on developing novel, efficient syntheses of amide bonds.

References  

 ¹ J. M. Albrich, C. A. McCarthy, J. K. Hurst, Prot. Nat. Acad. Sci., 1981, 78, 210.
²  T. I. Kim, S. Park, Y. Choi, Y. Kim, Chem.-Asian J., 2011, 6, 1358
³ Y. Xiao, R. Zhang, Z. Ye, Z. Dai, H. An, J. Yuan, Anal. Chem., 2012, 84, 10785.