The History of Main Group Chemistry
Jones, Cameron
Jerabek, Paul
Hegemann, Julian
Authmann, Andreas
Prof. Jones (Monash University, Australia) gives a short historical overview over the developments in main group chemistry.
 Today I've been asked to give you a little bit of an idea of some areas of chemistry that we're involved with and I thought it would be nice to give you a bit of a general rundown of the advances that have been made in the field of main group chemistry, specifically over the last 20 to 30 years or so. These advances have been very rapid and so rapid in fact that this change in main group chemistry since the early 80s has been termed the renaissance of main group chemistry. It's developed into an area now that I like to call a modern main group chemistry and so today I wanted to give you an idea of why these changes have occurred and what potentials there are for the future of main group chemistry. But I think to do this it would be nice to have a little bit of a look at the historical aspects of main group chemistry and I've looked into this a little bit and I've found that there are some direct and indirect links with the chemistry department here at Marburg and so maybe we can talk about those as well. So main group organometallic chemistry obviously involves the chemistry of compounds containing a bond, chemical bond between a main group element and carbon and this field began actually 250 years ago this year. So the first main group organometallic compound that was prepared in 1760 and this is in fact the first example of an organometallic compound itself if you consider arsenic as a metal. It's actually a semi-metal I suppose but this was prepared by a French chemist called Catae de Gassicourt and he for whatever reason decided to react potassium acetate with arsenic oxide and this generated a deep red foul smelling liquid that fumed on exposure to air and this is commonly called Catae's fuming liquid and it was later found that this liquid comprised several components two of which were tetramethyl diarsane so that is a compound containing an arsenic-arsic bond with two arsenic centers bonded by two methyl groups. The other component or main component was the oxide of this compound and these were called cacodil and cacodil oxide respectively and these names came not surprisingly from the foul stench of these very poisonous compounds and there's actually a fairly direct link between cacodil and cadae's fuming liquid with the chemistry department here at Marburg because in the mid 19th century a very famous professor from Marburg University Robert Bunsen was looking into the components of this fuming liquid trying to understand what the components of this liquid were and I think Bunsen's well-known chemistry and notoriety attracted researchers from around Europe to come and work with him and one of those researchers was a young English chemist called Edward Franklin who many of you will know that name and Franklin came to Marburg to carry out his PhD which he did in 1849 I think and before he came to Marburg he was carrying out his own research and he was looking at a related research he was looking at the interaction of methyl zinc and ethyl zinc with zinc metal and he found that these reactions generated in both cases mobile liquids which were pyrophorics that they spontaneously combusted in air. He didn't really know what these compounds were but during his time at Marburg I think and after he realized what they were and he found that they were actually diethyl zinc and dimethyl zinc and if any of you have used these compounds or zinc alkyls in general you will know how remarkably pyrophoric they are as soon as they see air they burst into flames and I suppose as an undergraduate chemist I was always amazed that in the mid 19th century people could handle these compounds and study them. We deal with pyrophoric compounds all the time we have to handle them under inert atmospheres we have general techniques for doing this using oxygen free nitrogen for example or oxygen free argon and Franklin himself had to use inert gas as well and that was another thing I found remarkable about this era of history was that the inert gas that he used was dihydrogen so you can imagine the potential here for explosions in his laboratory and I'm not sure if he actually had any. So this was in my view during my undergraduate days was an interesting era in the history of main group chemistry if you want to call it that if you consider zinc a main group element which many people do. So these compounds were really the forerunners of Grignard reagents and we all know that Grignard reagents are formed from the reaction of alkyl or aryl halides with magnesium metal, they are magnesium organometallic compounds they've had vast importance over the last 120 or 110 years and they were developed by Victor Grignard in France and I think he won the Nobel Prize for this chemistry in about 1912. And again in my undergraduate days I carried out a undergraduate research project on the trying to develop polygrignard reagents so I was quite heavily involved in Grignard reagents and their synthesis and it surprised me at the time and it still does that the mechanism of formation of these incredibly important reagents is still pretty much unknown. There are a lot of theories out there on how they're formed and some evidence but the definite mechanism of the formation of Grignard reagents is unknown at this stage. But one theory suggests that intermediates in the formation of these compounds contain magnesium-magnesium bonds so they're alkyl, magnesium-magnesium halides and so formally these compounds contain magnesium in the plus one oxidation state. And so this is how we became involved with our interests in low oxidation state magnesium compounds 25 odd years later. So that's a side and I'll talk about that in a minute but the chemistry of the main group elements was becoming to be developed up to this stage the early part of the 20th century and then it was rapidly developed in the first half of the 20th century. And I think by the third quarter of the 20th century it was pretty well understood what main group chemists can do, how they behave, what their properties are and they became perhaps a little bit boring I would say. All of their properties were known. There was no surprises on offer that the compounds containing the S and the P block elements contain those elements in either one or two oxidation states depending on whether the valence S and P electrons were involved in bonding or just the valence P electrons were involved in bonding. You could predict the coordination numbers of these compounds very well and a whole range of rules were developed or written if you like to pigeonhole the properties of main group or especially P block compounds. And one of these rules was the so-called double bond rule which told us reassuringly that you could not form compounds containing multiple bonds between the second and subsequent row P block elements. And I think a general belief in this rule led to a stagnation in the chemistry of P block element compounds in the mid to later part of the 20th century. And that was in contrast to the chemistry of transition metals which really rapidly developed in the second half of the 20th century. Main group compounds are nearly always colorless. They have one or two oxidation states. They really don't behave in any catalytic behavior whereas transition metals have nice colors. They have variable oxidation states. And we know that these properties are derived from their partial filling of their valence D orbitals and the close energy spacing of these D orbitals allows these compounds and led to these compounds being useful in for example catalysis which is a hugely important area of chemistry where transition metal compounds have been used. So this belief that main group compounds had perhaps not very interesting chemistry persisted until the 80s. And then I think in 1981 in my view anyway this is where the change, this renaissance in main group chemistry occurred. And three important discoveries were made in that year. They were firstly the development or the preparation of the first compound to contain a phosphorus-carbon triple bond and these are called phosphoryl kind. And this work was carried out by two German chemists, Verne Ull and Gerd Becker. I think both of whom have associations or have had past associations with the chemistry department here at Marbeau. There was the development of a compound containing a phosphorus-carbon double bond. This is called a diphosphene. Formally has phosphorus in the plus one oxidation state and this was prepared by a Japanese chemist Yoshifuge. And finally the first example of a compound containing a silicon-silicon double bond was made in 1981. So this is the silicon analogue if you like of the well-known alkenes. And this was prepared by a US chemist Bob West. So I think once these compounds had hit the literature if you like, the general belief that a low oxidation state and a low coordination number, main group compounds, they couldn't be formed, was thrown out the window and there was an explosion in the area of the development of these compounds. And obviously these species are very reactive. They're generally, they shouldn't exist thermodynamically. They should either oligomerize, they should disproportionate, they should react with oxygen etc. So to prepare these compounds and to stabilize them kinetically, generally a whole range of very bulky alkyl, aryl, amido ligands were developed to attach these ligands to the metal centers in these compounds to stop them oligomerizing or disproportionating, for example. And this allowed the development of a vast range of metal-metal bonded compounds, element-element bonded compounds, huge clusters containing in some cases up to 84 gallium atoms, chemistry developed by Schnerkel's group at Karlsruhe and very fascinating compound types. And I suppose some people see these as mere chemical curiosities, but I think they have, obviously their high reactivity will lend them to having a number of applications. And this is starting to develop now and I might talk about that in a minute. But because all of these new compound types were being developed, for example compounds with silicon-silicon triple bonds, germanium-germanium double bonds, iron or formally, well not formally, but what were described as iron-gallium triple bonds, new theoretical methods and bonding models needed to be developed to try and understand the bonds between the elements in these compounds. And a whole range of theoretical techniques have been developed to analyze the bonding in such compounds. And this has really developed quite well, except it's not fully developed yet and the analysis or the interpretation of the bonding in a lot of these systems has led to some vigorous debate in the literature, let's say. So it's very interesting to read a number of papers, some people have views on some compounds and the bonding in these compounds. And one example is this iron-gallium triple bonded species that I mentioned. I won't go into the specifics of the compound, but some people see it, for example, as having an iron-gallium triple bond, some as an iron-gallium double bond and some as an iron-gallium single bond. So you can see how controversy can be generated in these systems. And again, here there is a direct link with Marburg in that one of your current professors, Gernot Franking, is I would say one of the world leaders in analyzing the bonding in multiple bonded P-block compounds using theoretical methods. So as I said, the chemistry of these systems has developed rapidly over the last 20, 25 years or so. And also, as I said, they're probably viewed by the chemical community as largely being just chemical curiosity. It's very interesting compounds, but not with much use. And that has really changed a lot over the last, I would say, three years. There are a number of groups showing that these compounds or the high reactivity of these compounds can be used for useful purposes. And I would say some of those groups are Phil Powers group at UC Davis, Doug Steffens group in Toronto, and Guy Bertrand's group in UC Riverside. And these groups are looking at using low-coordinate, low-oxidation state main group compounds to activate small molecules, for example, dihydrogen, ammonia, and ethylene. And this has never been done before for hydrogen and ammonia. The first activations of these important molecules with P-block or low-oxidation state P-block compounds really only occurred in the last three or four years. And it's now been shown that in some cases these activations are actually reversible. So I think it's quite obvious that such low-oxidation state P-block compounds might find use in catalysis. And indeed, someday they might even be able to replace transition metals in catalytic processes. And we all know that most of the transition metals used in catalysis are the very expensive ones, so if we can replace those with extremely cheap P-block element compounds, then there's a definite use for such compounds.
 Today I've been asked to give you a little bit of an idea of some areas of chemistry  that we're involved with and I thought it would be nice to give you a bit of a general  rundown of the advances that have been made in the field of main group chemistry, specifically  over the last 20 to 30 years or so. These advances have been very rapid and so rapid  in fact that this change in main group chemistry since the early 80s has been termed the renaissance  of main group chemistry. It's developed into an area now that I like to call a modern main  group chemistry and so today I wanted to give you an idea of why these changes have occurred  and what potentials there are for the future of main group chemistry. But I think to do  this it would be nice to have a little bit of a look at the historical aspects of main  group chemistry and I've looked into this a little bit and I've found that there are  some direct and indirect links with the chemistry department here at Marburg and so maybe we  can talk about those as well. So main group organometallic chemistry obviously involves  the chemistry of compounds containing a bond, chemical bond between a main group element  and carbon and this field began actually 250 years ago this year. So the first main group  organometallic compound that was prepared in 1760 and this is in fact the first example  of an organometallic compound itself if you consider arsenic as a metal. It's actually  a semi-metal I suppose but this was prepared by a French chemist called Catae de Gassicourt  and he for whatever reason decided to react potassium acetate with arsenic oxide and this  generated a deep red foul smelling liquid that fumed on exposure to air and this is commonly  called Catae's fuming liquid and it was later found that this liquid comprised several components  two of which were tetramethyl diarsane so that is a compound containing an arsenic-arsic  bond with two arsenic centers bonded by two methyl groups. The other component or main  component was the oxide of this compound and these were called cacodil and cacodil oxide  respectively and these names came not surprisingly from the foul stench of these very poisonous  compounds and there's actually a fairly direct link between cacodil and cadae's fuming liquid  with the chemistry department here at Marburg because in the mid 19th century a very famous  professor from Marburg University Robert Bunsen was looking into the components of this fuming  liquid trying to understand what the components of this liquid were and I think Bunsen's  well-known chemistry and notoriety attracted researchers from around Europe to come and  work with him and one of those researchers was a young English chemist called Edward  Franklin who many of you will know that name and Franklin came to Marburg to carry out  his PhD which he did in 1849 I think and before he came to Marburg he was carrying out his  own research and he was looking at a related research he was looking at the interaction  of methyl zinc and ethyl zinc with zinc metal and he found that these reactions generated  in both cases mobile liquids which were pyrophorics that they spontaneously combusted in air.  He didn't really know what these compounds were but during his time at Marburg I think  and after he realized what they were and he found that they were actually diethyl zinc  and dimethyl zinc and if any of you have used these compounds or zinc alkyls in general you  will know how remarkably pyrophoric they are as soon as they see air they burst into flames  and I suppose as an undergraduate chemist I was always amazed that in the mid 19th century  people could handle these compounds and study them.  We deal with pyrophoric compounds all the time we have to handle them under inert atmospheres  we have general techniques for doing this using oxygen free nitrogen for example or  oxygen free argon and Franklin himself had to use inert gas as well and that was another  thing I found remarkable about this era of history was that the inert gas that he used  was dihydrogen so you can imagine the potential here for explosions in his laboratory and  I'm not sure if he actually had any.  So this was in my view during my undergraduate days was an interesting era in the history  of main group chemistry if you want to call it that if you consider zinc a main group  element which many people do.  So these compounds were really the forerunners of Grignard reagents and we all know that Grignard  reagents are formed from the reaction of alkyl or aryl halides with magnesium metal, they  are magnesium organometallic compounds they've had vast importance over the last 120 or  110 years and they were developed by Victor Grignard in France and I think he won the  Nobel Prize for this chemistry in about 1912.  And again in my undergraduate days I carried out a undergraduate research project on the  trying to develop polygrignard reagents so I was quite heavily involved in Grignard reagents  and their synthesis and it surprised me at the time and it still does that the mechanism  of formation of these incredibly important reagents is still pretty much unknown.  There are a lot of theories out there on how they're formed and some evidence but the definite  mechanism of the formation of Grignard reagents is unknown at this stage.  But one theory suggests that intermediates in the formation of these compounds contain  magnesium-magnesium bonds so they're alkyl, magnesium-magnesium halides and so formally  these compounds contain magnesium in the plus one oxidation state.  And so this is how we became involved with our interests in low oxidation state magnesium  compounds 25 odd years later.  So that's a side and I'll talk about that in a minute but the chemistry of the main group  elements was becoming to be developed up to this stage the early part of the 20th century  and then it was rapidly developed in the first half of the 20th century.  And I think by the third quarter of the 20th century it was pretty well understood what  main group chemists can do, how they behave, what their properties are and they became  perhaps a little bit boring I would say.  All of their properties were known.  There was no surprises on offer that the compounds containing the S and the P block elements  contain those elements in either one or two oxidation states depending on whether the  valence S and P electrons were involved in bonding or just the valence P electrons were  involved in bonding.  You could predict the coordination numbers of these compounds very well and a whole range  of rules were developed or written if you like to pigeonhole the properties of main  group or especially P block compounds.  And one of these rules was the so-called double bond rule which told us reassuringly that  you could not form compounds containing multiple bonds between the second and subsequent row  P block elements.  And I think a general belief in this rule led to a stagnation in the chemistry of P block  element compounds in the mid to later part of the 20th century.  And that was in contrast to the chemistry of transition metals which really rapidly  developed in the second half of the 20th century.  Main group compounds are nearly always colorless.  They have one or two oxidation states.  They really don't behave in any catalytic behavior whereas transition metals have nice  colors.  They have variable oxidation states.  And we know that these properties are derived from their partial filling of their valence  D orbitals and the close energy spacing of these D orbitals allows these compounds and  led to these compounds being useful in for example catalysis which is a hugely important  area of chemistry where transition metal compounds have been used.  So this belief that main group compounds had perhaps not very interesting chemistry persisted  until the 80s.  And then I think in 1981 in my view anyway this is where the change, this renaissance  in main group chemistry occurred.  And three important discoveries were made in that year.  They were firstly the development or the preparation of the first compound to contain  a phosphorus-carbon triple bond and these are called phosphoryl kind.  And this work was carried out by two German chemists, Verne Ull and Gerd Becker.  I think both of whom have associations or have had past associations with the chemistry  department here at Marbeau.  There was the development of a compound containing a phosphorus-carbon double bond.  This is called a diphosphene.  Formally has phosphorus in the plus one oxidation state and this was prepared by a Japanese  chemist Yoshifuge.  And finally the first example of a compound containing a silicon-silicon double bond was  made in 1981.  So this is the silicon analogue if you like of the well-known alkenes.  And this was prepared by a US chemist Bob West.  So I think once these compounds had hit the literature if you like, the general belief  that a low oxidation state and a low coordination number, main group compounds, they couldn't  be formed, was thrown out the window and there was an explosion in the area of the development  of these compounds.  And obviously these species are very reactive.  They're generally, they shouldn't exist thermodynamically.  They should either oligomerize, they should disproportionate, they should react with oxygen  etc.  So to prepare these compounds and to stabilize them kinetically, generally a whole range  of very bulky alkyl, aryl, amido ligands were developed to attach these ligands to  the metal centers in these compounds to stop them oligomerizing or disproportionating,  for example.  And this allowed the development of a vast range of metal-metal bonded compounds, element-element  bonded compounds, huge clusters containing in some cases up to 84 gallium atoms, chemistry  developed by Schnerkel's group at Karlsruhe and very fascinating compound types.  And I suppose some people see these as mere chemical curiosities, but I think they have,  obviously their high reactivity will lend them to having a number of applications.  And this is starting to develop now and I might talk about that in a minute.  But because all of these new compound types were being developed, for example compounds  with silicon-silicon triple bonds, germanium-germanium double bonds, iron or formally, well not formally,  but what were described as iron-gallium triple bonds, new theoretical methods and bonding  models needed to be developed to try and understand the bonds between the elements in these compounds.  And a whole range of theoretical techniques have been developed to analyze the bonding  in such compounds.  And this has really developed quite well, except it's not fully developed yet and the  analysis or the interpretation of the bonding in a lot of these systems has led to some  vigorous debate in the literature, let's say.  So it's very interesting to read a number of papers, some people have views on some  compounds and the bonding in these compounds.  And one example is this iron-gallium triple bonded species that I mentioned.  I won't go into the specifics of the compound, but some people see it, for example, as having  an iron-gallium triple bond, some as an iron-gallium double bond and some as an iron-gallium single  bond.  So you can see how controversy can be generated in these systems.  And again, here there is a direct link with Marburg in that one of your current professors,  Gernot Franking, is I would say one of the world leaders in analyzing the bonding in  multiple bonded P-block compounds using theoretical methods.  So as I said, the chemistry of these systems has developed rapidly over the last 20, 25  years or so.  And also, as I said, they're probably viewed by the chemical community as largely being  just chemical curiosity.  It's very interesting compounds, but not with much use.  And that has really changed a lot over the last, I would say, three years.  There are a number of groups showing that these compounds or the high reactivity of these  compounds can be used for useful purposes.  And I would say some of those groups are Phil Powers group at UC Davis, Doug Steffens  group in Toronto, and Guy Bertrand's group in UC Riverside.  And these groups are looking at using low-coordinate, low-oxidation state main group compounds to  activate small molecules, for example, dihydrogen, ammonia, and ethylene.  And this has never been done before for hydrogen and ammonia.  The first activations of these important molecules with P-block or low-oxidation state P-block  compounds really only occurred in the last three or four years.  And it's now been shown that in some cases these activations are actually reversible.  So I think it's quite obvious that such low-oxidation state P-block compounds might find use in  catalysis.  And indeed, someday they might even be able to replace transition metals in catalytic  processes.  And we all know that most of the transition metals used in catalysis are the very expensive  ones, so if we can replace those with extremely cheap P-block element compounds, then there's  a definite use for such compounds.
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Today I've been asked to give you a little bit of an idea of some areas of chemistry that we're involved with and I thought it would be nice to give you a bit of a general rundown of the advances that have been made in the field of main group chemistry, specifically over the last 20 to 30 years or so. These advances have been very rapid and so rapid in fact that this change in main group chemistry since the early 80s has been termed the renaissance of main group chemistry. It's developed into an area now that I like to call a modern main group chemistry and so today I wanted to give you an idea of why these changes have occurred and what potentials there are for the future of main group chemistry. But I think to do this it would be nice to have a little bit of a look at the historical aspects of main group chemistry and I've looked into this a little bit and I've found that there are some direct and indirect links with the chemistry department here at Marburg and so maybe we can talk about those as well. So main group organometallic chemistry obviously involves the chemistry of compounds containing a bond, chemical bond between a main group element and carbon and this field began actually 250 years ago this year. So the first main group organometallic compound that was prepared in 1760 and this is in fact the first example of an organometallic compound itself if you consider arsenic as a metal. It's actually a semi-metal I suppose but this was prepared by a French chemist called Catae de Gassicourt and he for whatever reason decided to react potassium acetate with arsenic oxide and this generated a deep red foul smelling liquid that fumed on exposure to air and this is commonly called Catae's fuming liquid and it was later found that this liquid comprised several components two of which were tetramethyl diarsane so that is a compound containing an arsenic-arsic bond with two arsenic centers bonded by two methyl groups. The other component or main component was the oxide of this compound and these were called cacodil and cacodil oxide respectively and these names came not surprisingly from the foul stench of these very poisonous compounds and there's actually a fairly direct link between cacodil and cadae's fuming liquid with the chemistry department here at Marburg because in the mid 19th century a very famous professor from Marburg University Robert Bunsen was looking into the components of this fuming liquid trying to understand what the components of this liquid were and I think Bunsen's well-known chemistry and notoriety attracted researchers from around Europe to come and work with him and one of those researchers was a young English chemist called Edward Franklin who many of you will know that name and Franklin came to Marburg to carry out his PhD which he did in 1849 I think and before he came to Marburg he was carrying out his own research and he was looking at a related research he was looking at the interaction of methyl zinc and ethyl zinc with zinc metal and he found that these reactions generated in both cases mobile liquids which were pyrophorics that they spontaneously combusted in air. He didn't really know what these compounds were but during his time at Marburg I think and after he realized what they were and he found that they were actually diethyl zinc and dimethyl zinc and if any of you have used these compounds or zinc alkyls in general you will know how remarkably pyrophoric they are as soon as they see air they burst into flames and I suppose as an undergraduate chemist I was always amazed that in the mid 19th century people could handle these compounds and study them. We deal with pyrophoric compounds all the time we have to handle them under inert atmospheres we have general techniques for doing this using oxygen free nitrogen for example or oxygen free argon and Franklin himself had to use inert gas as well and that was another thing I found remarkable about this era of history was that the inert gas that he used was dihydrogen so you can imagine the potential here for explosions in his laboratory and I'm not sure if he actually had any. So this was in my view during my undergraduate days was an interesting era in the history of main group chemistry if you want to call it that if you consider zinc a main group element which many people do. So these compounds were really the forerunners of Grignard reagents and we all know that Grignard reagents are formed from the reaction of alkyl or aryl halides with magnesium metal, they are magnesium organometallic compounds they've had vast importance over the last 120 or 110 years and they were developed by Victor Grignard in France and I think he won the Nobel Prize for this chemistry in about 1912. And again in my undergraduate days I carried out a undergraduate research project on the trying to develop polygrignard reagents so I was quite heavily involved in Grignard reagents and their synthesis and it surprised me at the time and it still does that the mechanism of formation of these incredibly important reagents is still pretty much unknown. There are a lot of theories out there on how they're formed and some evidence but the definite mechanism of the formation of Grignard reagents is unknown at this stage. But one theory suggests that intermediates in the formation of these compounds contain magnesium-magnesium bonds so they're alkyl, magnesium-magnesium halides and so formally these compounds contain magnesium in the plus one oxidation state. And so this is how we became involved with our interests in low oxidation state magnesium compounds 25 odd years later. So that's a side and I'll talk about that in a minute but the chemistry of the main group elements was becoming to be developed up to this stage the early part of the 20th century and then it was rapidly developed in the first half of the 20th century. And I think by the third quarter of the 20th century it was pretty well understood what main group chemists can do, how they behave, what their properties are and they became perhaps a little bit boring I would say. All of their properties were known. There was no surprises on offer that the compounds containing the S and the P block elements contain those elements in either one or two oxidation states depending on whether the valence S and P electrons were involved in bonding or just the valence P electrons were involved in bonding. You could predict the coordination numbers of these compounds very well and a whole range of rules were developed or written if you like to pigeonhole the properties of main group or especially P block compounds. And one of these rules was the so-called double bond rule which told us reassuringly that you could not form compounds containing multiple bonds between the second and subsequent row P block elements. And I think a general belief in this rule led to a stagnation in the chemistry of P block element compounds in the mid to later part of the 20th century. And that was in contrast to the chemistry of transition metals which really rapidly developed in the second half of the 20th century. Main group compounds are nearly always colorless. They have one or two oxidation states. They really don't behave in any catalytic behavior whereas transition metals have nice colors. They have variable oxidation states. And we know that these properties are derived from their partial filling of their valence D orbitals and the close energy spacing of these D orbitals allows these compounds and led to these compounds being useful in for example catalysis which is a hugely important area of chemistry where transition metal compounds have been used. So this belief that main group compounds had perhaps not very interesting chemistry persisted until the 80s. And then I think in 1981 in my view anyway this is where the change, this renaissance in main group chemistry occurred. And three important discoveries were made in that year. They were firstly the development or the preparation of the first compound to contain a phosphorus-carbon triple bond and these are called phosphoryl kind. And this work was carried out by two German chemists, Verne Ull and Gerd Becker. I think both of whom have associations or have had past associations with the chemistry department here at Marbeau. There was the development of a compound containing a phosphorus-carbon double bond. This is called a diphosphene. Formally has phosphorus in the plus one oxidation state and this was prepared by a Japanese chemist Yoshifuge. And finally the first example of a compound containing a silicon-silicon double bond was made in 1981. So this is the silicon analogue if you like of the well-known alkenes. And this was prepared by a US chemist Bob West. So I think once these compounds had hit the literature if you like, the general belief that a low oxidation state and a low coordination number, main group compounds, they couldn't be formed, was thrown out the window and there was an explosion in the area of the development of these compounds. And obviously these species are very reactive. They're generally, they shouldn't exist thermodynamically. They should either oligomerize, they should disproportionate, they should react with oxygen etc. So to prepare these compounds and to stabilize them kinetically, generally a whole range of very bulky alkyl, aryl, amido ligands were developed to attach these ligands to the metal centers in these compounds to stop them oligomerizing or disproportionating, for example. And this allowed the development of a vast range of metal-metal bonded compounds, element-element bonded compounds, huge clusters containing in some cases up to 84 gallium atoms, chemistry developed by Schnerkel's group at Karlsruhe and very fascinating compound types. And I suppose some people see these as mere chemical curiosities, but I think they have, obviously their high reactivity will lend them to having a number of applications. And this is starting to develop now and I might talk about that in a minute. But because all of these new compound types were being developed, for example compounds with silicon-silicon triple bonds, germanium-germanium double bonds, iron or formally, well not formally, but what were described as iron-gallium triple bonds, new theoretical methods and bonding models needed to be developed to try and understand the bonds between the elements in these compounds. And a whole range of theoretical techniques have been developed to analyze the bonding in such compounds. And this has really developed quite well, except it's not fully developed yet and the analysis or the interpretation of the bonding in a lot of these systems has led to some vigorous debate in the literature, let's say. So it's very interesting to read a number of papers, some people have views on some compounds and the bonding in these compounds. And one example is this iron-gallium triple bonded species that I mentioned. I won't go into the specifics of the compound, but some people see it, for example, as having an iron-gallium triple bond, some as an iron-gallium double bond and some as an iron-gallium single bond. So you can see how controversy can be generated in these systems. And again, here there is a direct link with Marburg in that one of your current professors, Gernot Franking, is I would say one of the world leaders in analyzing the bonding in multiple bonded P-block compounds using theoretical methods. So as I said, the chemistry of these systems has developed rapidly over the last 20, 25 years or so. And also, as I said, they're probably viewed by the chemical community as largely being just chemical curiosity. It's very interesting compounds, but not with much use. And that has really changed a lot over the last, I would say, three years. There are a number of groups showing that these compounds or the high reactivity of these compounds can be used for useful purposes. And I would say some of those groups are Phil Powers group at UC Davis, Doug Steffens group in Toronto, and Guy Bertrand's group in UC Riverside. And these groups are looking at using low-coordinate, low-oxidation state main group compounds to activate small molecules, for example, dihydrogen, ammonia, and ethylene. And this has never been done before for hydrogen and ammonia. The first activations of these important molecules with P-block or low-oxidation state P-block compounds really only occurred in the last three or four years. And it's now been shown that in some cases these activations are actually reversible. So I think it's quite obvious that such low-oxidation state P-block compounds might find use in catalysis. And indeed, someday they might even be able to replace transition metals in catalytic processes. And we all know that most of the transition metals used in catalysis are the very expensive ones, so if we can replace those with extremely cheap P-block element compounds, then there's a definite use for such compounds.
group chemistry, specifically over the last 20 to renaissance in main group chemistry occurred. And