 Welcome to this lecture on transition metal organometallics in catalysis and biology. We have been discussing olefin metathesis in continuation with the previous discussion of ReP reactions in which we have looked at the utility of acetylene to various chemical feedstock and how it was overcome using elegant organometallic synthesis. We had also observed in the previous lectures that both academia as well as industry had been in the forefront while contributing to the expansion of the field and in that context we have noted that ReP synthesis had been a development which has exclusively or significantly happened at the industry whereas the next one olefin metathesis reactions that we have taken up in the previous class there we have noted that both academic world as well as the industrial world had been equally serious about the development of olefin metathesis reaction. In the previous discussion we have also noted that both olefin metathesis as well as olefin polymerizations these are two seminal discoveries in the field of polymers and both have been awarded with a Nobel prize in 1953 whereas for the other one in 2005 about 50 years apart and both have been reorganized as important development in the area of polymers. They have also noted in the previous discussion that even though both the olefin polymerization as well as olefin metathesis had its origin in mid 1900s to 1950s, their elucidation and understanding staggered a bit with olefin polymerization being understood first followed by olefin metathesis and subsequently the application aspects of these two Nobel prize award-winning discoveries were taking place in the chemical world. So with these we are going to focus more on today's topic which is on olefin metathesis and I am going to give an early perspective, early developmental of this discovery and this is best given by an article in Chemical and Engineering News 2002 volume 80 page 34 238. So this article provides fantastic description about the development of olefin metathesis in 1950s how this was taken up around at that time. So continuing further on our discussion on olefin metathesis let me begin by saying that initial discovery had happened in the laboratories of industry particularly at a famous chemical industry laboratory which is at Dupont and it is worth mentioning that olefin metathesis discoveries happened by chance by exploring the conditions for olefin polymerization reactions. So it is sort of like the research in olefin polymerization accidentally had led to the discovery of olefin metathesis. So olefin metathesis sort of can be seen as an offshoot of olefin polymerization with that said let me just talk about how olefin metathesis was born and it goes back to 1956 at Dupont. Dupont is a well known chemical industry which is being and being more than about 200 years old and they have had some wonderful chemists which have contributed to new research and development of important compounds have come out of laboratories of Dupont. The famous nylon was also developed in Dupont and there are many other important products which have transformed the world have also had its origin tracking back to Dupont laboratories. So in 1956 at Dupont a researcher Euletro while polymerizing propylene in molybdenum catalyst observed ethylene propylene polymer. So this was a surprising result because if the propylene was polymerized then the polymer obtained should have been a propylene polymer whereas this formation of the ethylene was a big surprise that how could ethylene propylene copolymer was obtained. Now to investigate that what Calderon discovered further that this output feed of this propylene gas actually consisted of propylene ethylene butene which eventually was polymerizing to give this ethylene propylene copolymer. So that was kind of interesting observation which at that point remained unexplained and also what was unexplained over here at the formation of other gases like ethylene and propylene butene how they were formed from the feed which had only propylene to start with. So this at that point of time this was observation which was completely perplexing and subsequently again in another industrial setting in standard oil and company of Indiana this is in 1960s scientist Wolzer Peters and Everings observed that when propylene was passed over molybdenum catalyst in presence of aluminum compound then they were obtaining ethylene plus butene and this is aluminum tri-isobutyl in presence of aluminum tri-isobutyl propylene was giving ethylene and butene and this again was a result which was at that point of time unexplained that how could one get these two olefins from propylene and they had filed a US patent regarding this discovery because they thought this might be something very interesting subsequently again another observation was reported in another industrial company which is Philips Petrolium in 1964 where the disproportionation of propylene to ethylene plus butene were reported on molybdenum hexacarbonyl compound. So what was observed over here that there has been observations which remain unexplained as how other olefins were forming from propylene and then in some cases that these olefins were even went got further polymerized to give ethylene propylene or ethylene butene copolymers. So this was a very perplexing discoveries and people in the industrial world as well as in the academic world were trying to figure out as to what was happening in conversion of olefin to other kinds of olefin. It seemed to them as if somebody had stitched cut open the olefin from the middle with the scissor and stitched end with the other fragments in a very neat fashion. So this at that time was very complex and intriguing observation which when the scientists at that time were unable to explain indeed the name of olefin metathesis was coined at industry and this was given in 1967 about three more years later in Goodyear tires where the researchers coined the term olefin metathesis first introduced. So this is an interesting thing that nomenclature the nomenclature of this type of reaction was happened about 10 years about 15 years from this initial observation of what this reaction was meant to be. The results of the term is first traced back to a tetrahedron later publication in 1967 when the Goodyear first coined the term olefin metathesis. Now once a name has been given to this olefin metathesis the mystery still remained as to how the reaction was happening or sort of what is the mechanism of this reaction. So the next focus of research was diverted towards understanding the mechanism of olefin metathesis. Now and what is interesting to see that a lot of effort and lot of attempts and speculations were made as to arrive at the correct mechanisms with and people as usual tried different things starting from isotope leveling experiments and so on and so forth trying to arrive at the mechanism. The most important interesting bit about it is that much of the speculative mechanism which was proposed at that time and where published got accepted in premier journals however did not turn out to be true whereas a very non descriptive whereas a mechanism in a very non descriptive foreign language finally turned out to be the correct and went on to win the Nobel Prize. So one can see the excitement and unpredictability that science has to offer. In this effort the first set of experiments were indeed done at the Goodyear tyre using a homogeneous catalysis where they experimented with butene Goodyear tyres. Research was done with butene and deuterated butene. The combinations of isotope leveling experiments were performed to see the formation of olefins and what is interesting is the fact that they could see the various kinds of labeling where half of it is deuterated, other half remains protonated and so on and so forth depending on the type of the isotope leveling olefins that they took they could arrive at this and this was published in Journal of American Chemical Society in 1968 4133. So this is an interesting paper contribution from Goodyear tyres where they took on the path to elucidate the mechanism and the first thing they tried is to take butene an isotope leveled butene and to see what kind of isotope distribution happened in the olefin that is formed and then based on that they had come up with the mechanism. The second interesting effort also on labeling experiments with C14 labeled propylene was used by a research group in Netherlands where they looked at the distribution of the C14 fragments and to describe the experiment this is the labeled C14 carbon so two of these gave the products and this was published in an important journal of royal society which is chemical communication in the year 1968 volume 633. So what is worth noting is the time of publication for these two references both are in 1968 one happened in jacks another happened in chemcom one was from US the other one was from Netherlands this also highlights how competitive or how intense was the efforts research efforts at that point of time towards elucidating this mechanism as to how this olefin metathesis reactions were happening and in this way we see a the same approach of isotope labeling studies one with deuterated olefins the other with carbon 13 labeled olefins were studied to come out at the possible mechanism for these two types of reaction and indeed all of these studies led to the various kinds of hypothesis which were going to be a looking at it and what would be surprising to see that even though a number of hypothesis had been proposed for the mechanism only and they had appeared in very many important journals however the ones that have that appeared in not so famous journal had was later proven to be correct and was recognized with mobile prize. So that sort of brings us to the perspective that you know the work is important and it does not really matter where it gets published so long it gets published it will see the light of the day if it is a good effort. So the intense speculation as to how the reaction was proceeding led to the discoveries in various pathways that was resulting in the metathesis reaction with regard to the mechanism of metathesis what was more interesting to the community was how does or how is the metathesis reaction proceeding. What the researchers were sort of perplexed at was this cotton stitch phenomenon observing at the time so what was perplexing what was perplexing was the observation of stitching of olefins under metathesis conditions. So this is something which was really intriguing at that point of time and this is what consumed much of the effort in obtaining an understanding of these reactions. Now once that was obtained its full potential was explored with regard to developing various kinds of metathesis reaction for further development. Now with this I would conclude to the conclude today's lecture where we have looked into this olefin metathesis particularly from the time of its origin and how it was observed first in industry which led to baffling interpretations with regard to the formation of this. We had also observed that the term olefin metathesis was indeed a kind in industry particularly at good wear tires where they have termed the coin olefin metathesis to this set of reactions. We have also seen that this baffling observation of cutting and stitching of olefins was observed as an offshoot of while studying or developing the olefin polymerization chemistry using propylene substituted olefin feeds under molybdenum catalyst in presence or in absence of aluminum alkyls. So this is an interesting thing to note that olefin metathesis has its birth in olefin polymerization and which has both of which has developed into their own field duly recognized with noble prizes by their own right and merit. We had also seen in this discussion as to how industry has helped in first observing this reaction this new reaction and then getting started on it and trying to name and then understand this reaction with regard to what they were observing. So more of this discussion as we continue in the next class we look into the interesting aspect of the next phase of focus on metathesis reaction which is trying to sort of trying to elucidate the mechanism in which such cutting and stitching of olefins were effortlessly being done in under the gamut of this reaction. So what we would see that intense effort across America and Europe at that time led to the development of this interesting reaction and more on how this happened as we meet in the next class. Till that I thank you for being with me in this lecture where we are looking up a very interesting topic of olefin metathesis more on olefin metathesis as we meet next where we look at the development of this reaction what has happened till today. So with this I conclude today's lecture and I look forward to being with you in the next lecture till then goodbye and thank you.