Sustainability in Phosphorus Chemistry :
Contact : Duncan Carmichael
As well as research directed towards the exploitation of sp2 hybridised phosphorus atoms, we are also engaged in more 'classical' phosphorus chemistry involving sp3 hybridised phosphines. This more 'traditional' research strand is principally funded at present through a European Community- sponsored HPRN network "SusPhos". Phosphorus is classed as an "endangered element" by the EU, and principal objective of SusPhos is to promote the responsible use of phosphorus within the Chemical Community. For more information concerning the future of phosphorus and endangered elements in general, please see the site here
Phosphorus remains an essential component of modern chemical processes, and the laboratory's contribution to the SusPhos program is designed to contribute to its improved use in two distinct areas.
a) The preparation of new phosphine ligands through non- anionic routes. White phosphorus (P4) and phosphine (PH3) are two of the most fundamental phosphorus- containing building blocks that are produced by industry. However, many phosphines of commercial importance, such as PPh3, are prepared from halophosphine starting materials such as PCl3. These are undesirable precursors because they consume large volumes of chlorine gas to prepare, require air-sensitive organomagnesium or organosodium coreagents, and generate huge amounts of salt waste. Such syntheses are also inherently multistep in nature, which potentially increases phosphorus waste. In collaboration with a startup, Magpie Polymers, and the University of Bristol, we are engaged in a program to understand and promote the use of hydroxymethylphosphines and their derivatives as ligands and precursors for the preparation of water- soluble catalysts. Such hydroxymethyl phosphines are very convenient to handle and are in principle available conveniently and cheaply from the relatively ecofriendly PH3 and formaldehyde. Catalytic studies employing such ligands are currently being initiated.
b) Improved ligands for high- tonnage industrial processes. The presence of two metal centres within a well- defined chemical space can allow their cooperativity, so that one metal organises part of a catalytic cycle, whilst another provides a centre for activating and/or transferring crucial intermediates. Bimetallic complexes are therefore interesting as homogeneous catalysts and hydroformylation constitutes a well- known example of a process where the intervention of bimetallic species can significantly improve performance.
In this framework, we are collaborating with the (Université Fédérale Toulouse Midi-Pyrénées and the University of St Andrews) to prepare easily accessible ligands that have rigid backbones whose geometry specifically promotes bimetallic interactions between phosphine- bound metal centres. We are currently interested in ligand skeletons such as the phosphorus- containing dibenzodioxocins below. These promote the generation of bimetallic systems wherein the metals are separated by ca 4Å at a distance that is nicely adapted to bimetallic catalysis.
 A. Nijland, S. van Zutphen, D. Carmichael, Phosphorus Sulfur and Silicon and the Related Elements 2015, 190, 720-724. Link
 M. E. Broussard, B. Juma, S. G. Train, W. J. Peng, S. A. Laneman, G. G. Stanley, Science 1993, 260, 1784-1788. Link
 J. M. Lopez-Valbuena, E. C. Escudero-Adan, J. Benet-Buchholz, Z. Freixa, P. W. N. M. van Leeuwen, Dalton Transactions 2010, 39, 8560-8574. Link