Dalton Transactions Blog

What we think of as “organic chemistry” doesn’t often focus on the structure and bonding environments of the carbon atom, unlike inorganic chemistry which often does so with heteroatoms.  So I don’t think I’m going far out on a limb when I say that perhaps the key development in the structure and bonding of carbon over the last quarter century has been the isolation and use of the persistent carbene. 

Arduengo carbene

A carbene is a divalent carbon atom possessing two electrons.  Once thought to be unisolable, its history is recent enough that almost all important figures in its development are not only still living to this day, but still working.  Ron Breslow proposed that carbenes could be isolated in 1957, Guy Bertrand isolated a liquid dicarbene in 1989 and, in 1991, Anthony Arduengo reported the first comprehensive solid-state data of the type of carbene that now bears his name (pictured above).  

So why waste the words of a short post blog on historical perspective?

Because the uses of the carbene have fallen almost entirely in one direction.  Primarily, the carbene has been used as a strong s 2-electron donor – attached to many transition metal atoms it forms very stable complexes, and it is relatively easy to vary its size. 

Only recently have the uses of the carbene diverged. 

In a recent Dalton Transactions paper, Arnold, Love and co-workers present work on labile carbenes tethered to rare earth metals by an alkoxy arm.  On rare earth metals – which are much harder Lewis acids than late transition metals – the soft carbene donor and hard metal acceptor are poorer matches.  Thus the carbon-metal bond may break, freeing the carbene for reactivity, while the hard alkoxy arm keeps the ligand tethered to the metal.

Reactivity of tethered alkoxycarbene complexes 

The authors present some examples of reactivity, including co-operative activation of pyrroles and alkynes by the carbene and metal centres, as well as outer-sphere interactions in the form of hydrogen bonding between pyrroles and the metal-bound O atom in solution.   Despite these being small steps, they are nonetheless important if the carbene is to find new roles outside stabilising late transition metal centres.

Interested in finding out more? Read the full paper:

Homo- and heteroleptic alkoxycarbene f-element complexes and their reactivity towards acidic N–H and C–H bonds
Polly L. Arnold, Thomas Cadenbach, Isobel H. Marr, Andrew A. Fyfe, Nicola L. Bell, Ronan Bellabarba, Robert P. Tooze and Jason B. Love
Dalton Trans., 2014, DOI: 10.1039/C4DT01442A

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.

Enzymes function as biological catalysts in a wide array of reactions which are essential for sustaining life. They are almost always large protein molecules which adopt complex three dimensional structures, yet are able to remain structurally dynamic in order to allow the function of the enzyme to be switched on and off.

This feature allows an enzyme’s catalytic activity to be active only when required in the metabolic pathway in which it is involved. For this reason, enzymes have long been a source of inspiration to researchers involved in the design and synthesis of artificial molecular switches and machines.

SARS-CoV 3CLpro is a protease enzyme which is involved in the replication and transcription process of the human coronavirus, the virus which causes severe acute respiratory syndrome (SARS). This enzyme is catalytically inactive as a monomer and only functions as a catalyst when it is bound with another monomer in a complex called a homodimer.

Both crystallographic and mutation studies have implicated several amino acid residues in the dimerization process, however the exact mechanism of dimer formation and how this activates the enzyme’s catalytic activity is still unconfirmed.

 Scheme 1. Switching between open and close conformations of nanoswitch 1 in response to metal ion addition

Drawing inspiration from this monomer-dimer on-off mechanism, Schmittel and co-workers have devised a molecular switch capable of toggling between monomeric and dimeric forms in response to the addition of different metal ions. With no metal ions present, the triangular framework adopts the ‘OPEN-I’ conformation (Scheme 1). Upon the addition of copper(I) ions, the two pyridine-based ligands come into proximity to mutually coordinate the metal.

This changes the conformation of the framework to the ‘CLOSE’ state. Addition of iron(II) ions to the ‘CLOSE’ state again changes the molecular conformation, as the iron(II) ions occupy the terpyridine moiety and the copper(I) ions move to occupy only the shielded phenanthroline ligand.

This both forms a homoleptic dimer, as the iron(II) ions can coordinate two terpyridine moieties simultaneously from two different molecules, and creates a coordinatively unsaturated copper species which acts as a catalyst for a cyclopropanation reaction. The authors impressively demonstrate the reversibility of each step, with the removal of metal ions changing the framework back to its uncoordinated conformation.

In this way, they have successfully made a molecular switch which responds to a metal ion signal (Fe²⁺) and turns a catalytic complex on and off. Like SARS-CoV 3CLpro enzyme, the catalytically active state is the homodimer, with the monomeric form being catalytically inactive.

To find out more, read the full article:

A monomer-dimer nanoswitch that mimics the working principle of the SARS-CoV 3CLpro enzyme controls copper-catalysed cyclopropanation
Soumen De, Susnata Pramanik and Michael Schmittle
Dalton Trans. 2014, DOI:10.1039/c4dt01508h

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.

During the 1st quarter of the year (the months of January, February & March) the top 10 most downloaded Dalton Transactions articles were:

Chloride ion impact on materials for light-emitting electrochemical cells
Gabriel E. Schneider, Henk J. Bolink, Edwin C. Constable, Cathrin D. Ertl, Catherine E. Housecroft, Antonio Pertegàs, Jennifer A. Zampese, Andreas Kanitz, Florian Kessler and Sebastian B. Meier
Dalton Trans., 2014, 43, 1961-1964
DOI: 10.1039/C3DT53229A

Syntheses, topological analyses, and NLO-active properties of new Cd(II)/M(II) (M = Ca, Sr) metal–organic frameworks based on R-isophthalic acids (R = H, OH, and t-Bu)  
Jian-Di Lin, Shu-Ting Wu, Zhi-Hua Li and Shao-Wu Du 
Dalton Trans., 2010, 39, 10719-10728 
DOI: 10.1039/C0DT00390E 

Nitrogen defects from NH₃ in rare-earth sesquioxides and ZrO₂  
Jonathan M. Polfus, Truls Norby and Reidar Haugsrud 
Dalton Trans., 2011, 40, 132-135 
DOI: 10.1039/C0DT01068E  

Recent progress in the synthesis of inorganic nanoparticles  
C. N. R. Rao, H. S. S. Ramakrishna Matte, Rakesh Voggu and A. Govindaraj 
Dalton Trans., 2012, 41, 5089-5120 
DOI: 10.1039/C2DT12266A     
  
Shape-controlled synthesis and catalytic application of ceria nanomaterials  
Dengsong Zhang, Xianjun Du, Liyi Shia and Ruihua Gao 
Dalton Trans., 2012, 41, 14455-14475 
DOI: 10.1039/C2DT31759A     

Organometal halide perovskites as useful materials in sensitized solar cells  
Surya Prakash Singh and P. Nagarjuna 
Dalton Trans., 2014, 43, 5247-5251 
DOI: 10.1039/C3DT53503G  

Synthesis, crystal structure and EPR spectroscopic analysis of novel copper complexes formed from N-pyridyl-4-nitro-1,8-naphthalimide ligands  
Jonathan A. Kitchen, Paulo N. Martinho, Grace G. Morgan and Thorfinnur Gunnlaugsson 
Dalton Trans., 2014, 43, 6468-6479 
DOI: 10.1039/C3DT53323A  

Metal–organic frameworks in mixed-matrix membranes for gas separation  
Harold B. Tanh Jeazet, Claudia Staudt and Christoph Janiak 
Dalton Trans., 2012, 41, 14003-14027 
DOI: 10.1039/C2DT31550E  

A colorimetric organic chemo-sensor for Co²⁺ in a fully aqueous environment  
Gyeong Jin Park, Yu Jeong Na, Hyun Yong Jo, Seul Ah Lee and  Cheal Kim 
Dalton Trans., 2014, 43, 6618-6622 
DOI: 10.1039/C4DT00423J  

Zinc and cobalt complexes based on tripodal ligands: synthesis, structure and reactivity toward lactide  
Mathieu J.-L. Tschan, Jia Guo, Sumesh K. Raman, Emilie Brulé, Thierry Roisnel, Marie-Noelle Rager, Rémi Legay, Guillaume Durieux, Baptiste Rigaud and Christophe M. Thomas 
Dalton Trans., 2014, 43, 4550-4564 
DOI: 10.1039/C3DT52629A

Like what you read? If so, please comment below.

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Researchers in Japan have demonstrated the exceptional potential of a hydrated titanium oxide to extract lithium from salt lake brine collected from Salar de Uyuni in Bolivia, the world’s largest salt flat.  

The high levels of magnesium and sulfate in Uyuni brine would create difficulties if it was processed by conventional techniques © Shutterstock

Demand for lithium is growing alongside the development of lithium ion batteries. This strain on scarce supplies puts the cost and effectiveness of current methods for harvesting lithium into question.

Interested? Read the full article at Chemistry World.

The original article can be read below:

Lithium recovery from salt lake brine by H₂TiO₃
Ramesh Chitrakar, Yoji Makita, Kenta Ooi and Akinari Sonoda
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT00467A

The Royal Society of Chemistry has awarded a National Chemical Landmark blue plaque to the University of Oxford Inorganic Chemistry Laboratory, to celebrate the 50th anniversary of Britain’s first female Nobel Prize winner.

Chief Executive of the Royal Society of Chemistry, Dr Robert Parker, spoke at the plaque presentation and said: “I am delighted to be here again, to honour and celebrate the work of Dorothy Crowfoot Hodgkin. 

“It has been 50 years since she received the Nobel Prize in Chemistry, and so I am delighted to mark the occasion by awarding a new plaque, one that will inspire those that read its message and demonstrate the valuable work that takes place here at the Inorganic Chemistry Laboratory, in Oxford.”

Dorothy Hodgkin won the Nobel Prize “for her determinations by X-ray techniques of the structures of important biochemical substances”.

Amongst her most significant discoveries are the confirmation of the three-dimensional structures of penicillin, Vitamin B12 and insulin.

An award symposium to mark the presentation saw Professors Susan Lea , Paul Raithby and Andrew Goodwin discussing their work in the field of crystallography, and how the field has changed in the 50 years since Hodgkin’s Nobel Prize.

The audience included Professor Philip Mountford, Head of Inorganic Chemistry and Chair of the Dalton Transactions Editorial Board, as well as some of Dorothy’s former students and those they have gone on to teach

2014 is International year of Crystallography and the events at Oxford’s Inorganic Chemistry Laboratory form part of the year-long celebration.