We've been involved in low oxidation state main group chemistry probably for 15 years or so now and about three years ago we began to wonder if we could

extend this low oxidation state chemistry of the p-block elements to the s-block elements and this had largely not been done before there were no examples of compounds containing two s-block elements or two s-block

bonded to each other covalently and we wondered if we could perhaps extend the chemistry the well-known chemistry of low oxidation state p-block compounds to this area and I suppose again this harks back to my undergraduate days where where I was looking at the at the formation of new Grignard reagents and

and thinking about the mechanism of formation of Grignard reagents and the fact that magnesium magnesium bonded compounds had been proposed as intermediates in the formation of Grignard reagents so we wanted to see if we could actually make such systems and we drew some inspiration I

suppose from another landmark study in 2004 by a Spanish chemist Ernesto Carmona who managed to prepare the first examples of zinc-zinc bonded compounds so formally compounds containing zinc in the plus one oxidation state okay and surprisingly he made these compounds or this particular

compound which has a zinc-zinc bond the two zinc centers are coordinated each by a pentamethyl cyclopentadienyl ligand a bulky ligand to stabilize this system towards a disproportionate but he made this compound actually by accident and one of the reagents that he used in its

preparation was diethyl zinc the same compound that Franklin made in 1850 okay so given the chemical similarities I suppose between zinc a group 12 metal and magnesium a group 2 metal and the fact that zinc-zinc bonds could be stabilized we then thought well maybe we could use some of these some of our

bulky ligands that we'd developed to stabilize low oxidation state p-block compounds for example gallium 1 compounds and germanium 1 compounds and maybe these compounds could kinetically stabilize magnesium magnesium bonded systems and that's what we set out to do and that the main ligand types

that we used were di or sorry a chelating and enchilating mono anionic ligand systems such as bulky guanidine 8 ligands which we developed in our laboratory and also beta diketenamate ligands which we found had similar stabilizing properties to our bulky guanidine 8 and so we began by

preparing magnesium 2 precursors to our target magnesium 1 compounds and these were magnesium iodide systems containing or incorporating the bulky guanidine 8 or beta diketenamate ligands and we simply started by

trying to reduce these systems with potassium metal at room temperature and to our surprise in early experiments we managed to prepare these magnesium magnesium bonded systems I think if we if we if we didn't have results early on we might have abandoned this study because we thought intuitively that these systems would be pretty hard to stabilize and pretty hard to to

eventually access but that proved not to be the case so we managed to prepare a range of such systems they are quite reactive as you might expect but they're not terribly air and moisture sensitive so these ligands that we've used to stabilize them really do protect them from oxidation and hydrolysis and they're remarkably firmly stable theoretical studies have

suggested that the magnesium magnesium bonds in these systems are quite strong but they're not not remarkably so about 45 kilo cals per mole but these compounds in some cases can be stable at 300 degrees Celsius which to us seemed

really quite remarkable and we once we had prepared these compounds we thought well we we must really prove that we have magnesium one systems this is that'd be quite a big claim and would not look good if we were wrong and so we spent a long time trying to prove that these systems had magnesium magnesium covalent bonds and I'm not going to go into what we did to do that

but we managed to do that and we published the work I think in the last week of 2007 in science and after that time we thought well we we now have these systems we really must look at their further chemistry and their properties and and really this work is still in its infancy but we

have looked in some detail using experimental and theoretical techniques to try and analyze the the metal metal bonding in these systems and again this work is only in its infancy but we've used DFT calculations in the theory

sense and experimental charge density studies in the experimental sense and this technique allows you effectively to see the electrons between the magnesium centers and and this shows that these systems do indeed contain magnesium magnesium covalent bonds albeit with rather a diffuse electron

density between the magnesium centers but there is we believe certainly a covalent bond and so we've also found that this although there is electron density between shared between the two magnesium centers it's really quite diffuse in fact very diffuse and and this has led to some strange properties for these compounds the magnesium magnesium bond is what we call

deformable we can we can stretch it quite significantly for example by coordinating the magnesium centers by other Lewis bases we can stretch the bonds by up to about 8% so we we can elongate them from about 2.85 angstroms in the uncoordinated diamonds to about 3.05 angstroms in the

coordinated diamonds which is which is a remarkable elongation so that's one area that we've been looking at we've also been looking at the use of magnesium one systems as reducing agents obviously with this element in this unusual oxidation state you would expect that these dimeric systems

would be able to deliver electrons to substrates and we are indeed looking at that with respect to their use as what we call bespoke reducing agents in both organic and organometallic synthesis so in organic synthesis we've shown that these dimeric systems can act as very facile to center to electron

reducing agents they can deliver if you like two electrons very easily to unsaturated organic substrates and we've looked at many reactions and we found that we can we can induce carbon-carbon bond forming reactions nitrogen-nitrogen bond forming reactions we can carry out oxidative

insertion reactions we can carry out reductive cleavage reactions and we've seen a whole range of reaction types within organic synthesis if you like using these magnesium one systems and I think most importantly many of the products of these reductions differ from those that you obtain by reducing

the same substrates with more classical reducing agents used in organic synthesis such as samarium 2 reagents and alkali metals and because of this we think that there is a potential use of these systems as selective reducing agents in inorganic synthesis and we are developing that at

the moment in collaboration with with organic chemists with respect to inorganic chemistry we're also investigating the use of these systems to as as reducing agents to access previously unknown examples of low oxidation state p-block complexes so we're using these magnesium one

reagents to try and prepare the systems that got us into this area in the first place and we've had quite a bit of early success and just one example of a compound we've published I think late 2009 we took an n-heterocyclic carbine adduct of germanium dichloride a simple compound

and we reduced it with our magnesium one compound this this worked and this generated a magnesium two chloride system but the byproduct in this system was and was a compound that contained two n-heterocyclic carbines coordinated to a germanium two fragment no other substituents on the germanium so formally

this compound contains germanium in the zero oxidation state so very unusual compound you could think of it as a soluble source of this element so at the moment we're trying to extend it to other elements in the p-block and indeed in the d-block and we can see these NHC adducts of the elements if you

like as soluble sources of those elements that can be delivering those elements to other reactants in synthesis and this is something that we've really only just begun work on there are a number of other groups working on this area of chemistry around the world Greg Robinson's group in Georgia for example who really whose excellent work got us into this area so

that's another area of chemistry that we've been looking out with our magnesium one compounds the other main area that we are looking at is is using these magnesium one compounds as soluble models if you like to examine the mechanisms or potentially examine the mechanisms and the kinetics of the

hydrogenation of magnesium metal so magnesium metal reacts with dihydrogen to give magnesium hydride this is an important reaction it's a reversible reaction and it's important because magnesium dihydride contains about seven point seven percent by weight hydrogen okay and so therefore it's finding use

as a hydrogen storage system in a number of devices such as such as fuel cells etc so it's a reversible hydrogen storage system and in the in the rapidly developing hydrogen economy such systems are quite important but this

hydrogenation of magnesium metal to give magnesium hydride has problems okay it's it has kinetic problems the kinetics are slow and in fact you need a temperature of about 300 degrees Celsius to hydrogenate magnesium metal and to dehydrogenate magnesium hydride you need about 300

degrees or greater than 300 degrees Celsius as well so really it's obvious that you can't use these systems in portable devices and so a lot of work has been carried out to try and improve the kinetics of the hydrogenation of magnesium metal for example by doping it with transition

metals or alloying it with p-block metals for example aluminium and this tends to work in some cases and the hydrogenation temperatures of magnesium alloys have been reduced into the hundreds of degrees which is a usable range but it's not really known what the mechanisms or the reasons

behind this improvement in the kinetics of the hydrogenation of magnesium occur and so we're beginning to wonder if we can use these magnesium one systems as soluble sources of magnesium if you like to try and look at how the magnesium is hydrogenated in the presence of in the

presence of other metals and this is an area that we have looked at in the last six months or so we haven't published anything on it yet but hopefully we will be as soon doing this so I'm not going to not going to dwell on that so really that's all I wanted to talk about today I wanted to

give you just a bit of an overview of this rapid development in main group chemistry over the last 30 years or so I think it's gone from being a rather staid and perhaps boring area of chemistry to what I think is one of the most exciting areas of and rapidly developing areas of inorganic chemistry

that is studied today and I think this this Renaissance in main group chemistry can can tell us one lesson and that is as chemists when we see rules in textbooks maybe we should question those rules because if we do question those rules and we can and we prove that they are they shouldn't be rules then we can access new areas of chemistry very interesting new

compounds which have potential applications and and if they don't well they have enough fundamental fundamental interest to keep us excited