Dalton Transactions Blog

This Hot Article from the University of Western Ontario by Laura C. Pavelka and Kim M. Baines details some interesting cycloaddition reactions of phosphaalkenes with alkynes.

Reactions of this type have not been well studied and typically require electron rich alkynes and quite specialised phosphoalkenes for the reaction to proceed. Here the authors have developed a much simpler approach to the syntheses using readily available reagents and a more direct route, allowing them to produce a variety of 1,2-dihydrophosphinines in good yields.

To find out how, you can download their article which is free to access for the next 4 weeks

Facile synthesis of luminescent benzo-1,2-dihydrophosphinines from a phosphaalkene
Laura C. Pavelka and Kim M. Baines
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT11690A

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The need for a hydrogen storage material that can store hydrogen reversibly, with little or no kinetic barrier, and at ambient conditions remains a great challenge for researchers in this field. In order to progress towards a future hydrogen economy, hydrogen storage materials must also be practical for mobile applications and of course be economically viable.

Many different materials have been proposed for hydrogen storage. These range from physisorption materials such as activated carbons, zeolites and Metal Organic Frameworks (MOFs) to materials based on chemisorption such as metal hydrides, ammonia boranes and alanates. The hydrogen binding mechanism of chemisorption materials is through the formation of strong covalent bonds with hydrogen and so even though they have high hydrogen storage capacities, the drawback is that due to their high hydrogen binding enthalpies, the materials must be heated to remove H₂.

To improve the unfavorable thermodynamics and poor kinetics of complex hydrides, researchers have successfully applied a ‘multicomponent’ strategy whereby  two compounds are mixed together to form a multinary phase.  The mixed LiNH₂–MgH₂ system is a successful example of the employment of the ‘multicomponent’ strategy to improve the characteristics of complex hydrides for hydrogen storage. Applying this method to metal amidoborane systems is an exciting prospect.

With this in mind, Chen et al. synthesized a Li–Na mixed amidoborane, Na[Li(NH₂BH₃)₂] using a wet-chemical method. Using first-principles techniques, the team were able to explore the likelihood of the existence of multicomponent Li–Na amidoboranes with varying  Li/Na ratios. They discovered that the dehydrogenation temperature of Na[Li(NH₂BH₃)₂] is lower than that of lithium or sodium amidoboranes and determined that this could be due to a stronger dihydrogen bond interaction and  a moderate hydrogen atom removal energy. They also proposed the mechanism for the first-step dehydrogenation.

To find out more, read the Dalton Transactions full paper…

Li–Na ternary amidoborane for hydrogen storage: experimental and first-principles study

Wen Li, Ling Miao, Ralph H. Scheicher, Zhitao Xiong, Guotao Wu, C. Moysés Araújo, Andreas Blomqvist, Rajeev Ahuja, Yuanping Feng and Ping Chen

DOI: 10.1039/C2DT11819J

Zinc alkyl complexes have an interesting role in a wide variety of stoichiometric and catalytic transformations and understanding how the ligands affect reactivity is important in understanding these structures and their reactivity. This Hot Article from Andrew Wheatley and Janusz Lewinski et al. details experiments involving the reactions of Et₂Zn with a bicyclic guanidine.

Exposure of the produced complex (EtZn(hpp)) to undried air alters the composition depending on whether THF or CH₂Cl₂ is used as the solvent (displayed above). You can read the full details of the teams investigation by downloading their article below, which is free to access for 4 weeks.

Synthesis, structure and unique reactivity of the ethylzinc derivative of a bicyclic guanidine
Karolina Zelga, Michał Leszczyński, Iwona Justyniak, Arkadiusz Kornowicz, Maciej Cabaj, Andrew E. H. Wheatley and Janusz Lewiński
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT11959E

Most metal organic frameworks are based on 3-d or 4-f elements such as Zn, Cu, Co, Ni and there are notably fewer containing lighter metals such as Li, Be, B, Mg, and Al. This Hot Communication by Pingyun Feng and Xianhui Bu et al. reports the first Mg-MOF example constructed from the [Mg₃(μ₃-OH)(CO₂)₆] trimer and opens up the possibility of further Mg-MOF systems.

The porous crystal shows relatively high H₂ uptake (1.37% at 77 K and 1 atm) showing that Mg-MOF systems may have great potential. The applications of MOFs include gas storage, separation, purification and catalysis, undoubtedly developing these applications requires the design and improvement of new MOFs.

You can download this Dalton Transactions Hot Article below, which is free to access for 4 weeks.

Induction of trimeric [Mg3(OH)(CO2)6] in a porous framework by a desymmetrized tritopic ligand
Quanguo Zhai, Qipu Lin, Tao Wu, Shou-Tian Zheng, Xianhui Bu and Pingyun Feng
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT12215D

Despite the fact that the catalytic activity of Cr and W imido complexes in ethylene dimerization processes has been studied by various authors, to date the analogous Mo catalysts have not been studied.  In this HOT article, Dyer et al. set out to fill this gap in our knowledge and several molybdenum bis(imido) complexes were tested for ethylene dimerization catalysis in combination with EtAlCl₂, showing moderate activity when bulky aryl substituents at the imido ligand are employed. In contrast, when MeAlCl₂ is used the activity of the catalyst decreases considerably. To understand the role of the activator in these processes the authors have determined the molecular structures of several complexes derived of the reaction of bis(imido) molybdenum compounds with different aluminium halide reagents.

Read more for FREE about the role of the activator in dimerization catalysis until 20th February 2012 at:

Application of molybdenum bis(imido) complexes in ethylene dimerisation catalysis
William R. H. Wright, Andrei S. Batsanov, Antonis M. Messinis, Judith A. K. Howard, Robert P. Tooze, Martin J. Hanton and Philip W. Dyer
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT12061E

In this HOT article, several new Ti(IV) complexes bearing aryloxy or alkoxy ligands have been prepared and evaluated as catalysts for the oligomerization/polymerization of ethylene. Obviously, polyethylene is the major product but ethylene oligomers also result, ranging from dimers to higher oligomers. The results indicate a number of different active species are formed upon activation, with oligomers likely arising through a metallacyclic mechanism.

Read more about the possible mechanism for FREE until 20th February 2012 at:

Preparation and structures of aryloxy- and alkoxy-Ti(IV) complexes and their evaluation in ethylene oligomerisation and polymerisation
James A. Suttil, David S. McGuinness, Markus Pichler, Michael G. Gardiner, David H. Morgan and Stephen J. Evans
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT11737A

See also the authors previous work providing further evidence for metallocyclic mechanisms at work at:

J. A. Suttil, D. S. McGuinness and S. J. Evans, Dalton Trans., 2010, 39,
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