 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been discussing various types of ring closing inion metathesis as well as inion metathesis reactions, the conditions and the examples and also we had been exploring the scope of this ring closing inion metathesis as well as inion metathesis in terms of applications. In this context, we have discussed about a cycloaddition reaction in inion metathesis reaction in the earlier lecture, and today we are going to take a look at some more examples of this inion metathesis reactions, then try to finish off our discussion on inion metathesis reaction and then take up another very interesting topic, which is alkyne and alkyne oligomerization reactions. In keeping with the main scope of this course, where we had highlighted the important organometallic catalytic reactions, which has made it big in terms of going beyond the confines of the laboratory and reaching the source of industry in terms of large scale utility, this alkyne and alkyne metathesis oligomerization reaction is another such topics, which had been recognized with noble prize and its utility to the mankind is well recognized and well established by now. So, with this, let us come back to our initial topic of inion metathesis examples, which we are going to be taking up now. The reaction is between these and two kinds of substrates, one is this or the other is this substrate. The products formed are now to work out the product one needs to start with the substrate and the catalyst, which would come along as it is shown here to give the metallocyclobutane intermediate that would further generate this alkyne, this active species, which is the metal, then these active species as is shown over here would subsequently go on to react with the substrate as is shown in the next slide would react with the alkyne substrate OBZ to give the first the metallocyclobutane transition state OBZ as is shown over here and that we arrange to give. So, there is a double bond between 5 and 6 and 7. This is a very interesting intermediate and it has two possibilities that it can arise. One is this reacting with the olefin giving the corresponding alkyne regenerating back the olefin that is possibility number one. The other possibility is this undergoing a metathesis between these two olefin in something which is shown over here, this is 1, 2, 3, 5, this is 7. So, this 7 also has OBZ, so this is in this configuration if it comes around, then possibility is this and that this structure is not done properly 3, 4, 5, this is 7. So that would give a structure, this would undergo a metathesis and would give a structure like this 3, 4, 5, 6, 7 as is shown here and then subsequently this would undergo rearrangement to give the product OBZ. So, as mentioned earlier that this was an important intermediate and that can result into two different product number one and the second product number two and that arises because of intramolecular metathesis reaction between two in which occurs between these two or it can give this product. Now these are very interesting reactions where depending on the orientation of the reactant intermolecular as well as the intermolecular reaction may proceed and that can give rise to two different products. This is enyne plus cycloaddition and this is just enyne reaction that is happening. So with that we come to the end of our discussion on enyne metathesis reactions. We have looked into all variants of it to start with, we have looked at intermolecular enyne metathesis followed by entramolecular enyne metathesis and the different products that have been obtained using this metathesis reaction. We have also looked at various complex structures that can be obtained by enyne metathesis reactions, some can be cycloadditions, tandem and with that very complex motifs have been synthesized. So with this we conclude our discussion on olefin metathesis and we are going to move on to another interesting topic of alkene olefin oligomerization and polymerization reactions. Now to move on to these new reactions of olefin oligomerization and polyglomation I must mention that these are also important reactions particularly in terms of large scale synthesis and utility in industry for producing various value added chemicals using these methods. And these are also a part of the Nobel Prize award winning discovery of olefin polymerization. And furthermore this highlights the utility of organometallic chemistry for large scale applications. So with this let us move on to the next topic of oligomerization and polymerization of alkenes and alkynes. One must mention that these reactions oligomerization of alkenes and alkynes and polymerization of alkenes and alkynes they were initially discovered almost at the same time of olefin metathesis reactions. So the first observation happened in late 1950s or early 1960s which had been the case for both olefin metathesis as well as for olefin oligomerization and polymerization reactions. But even though this metathesis reaction as well as polymerization reactions of olefin metathesis were initially observed in and around same time, it is the olefin oligomerization and polymerization reactions were established much earlier with the Nobel Prize coming in in 1960s, mid 60s, 63, 64 for the discovery, whereas for the olefin metathesis the reaction took longer time to incubate and develop and the final recognition came in 2005 so about 30 or 40 more years later. So the olefin oligomerization and polymerization of reactions had seen the light of the day much earlier than the olefin metathesis reactions that we had discussed in our earlier topic. Now one reason for this late recognition of olefin metathesis as in comparison to olefin oligomerization and polymerization is because of the fact that olefin metathesis is much more complex reaction in terms of the mechanism and the pathway it takes in terms of applications. So it is much more complex, much more bigger and hence it took a longer time to elucidate and understand than the olefin polymerization reaction. But this does not take away any credit from the olefin oligomerization and polymerization reactions because they themselves represent a huge field as such and a due credit is given to them as well in presence or absence of any other discoveries. So with this let us start our discussion on oligomerization and polymerization of alkenes and alkynes. One of the things which is common to this oligomerization reaction is that the mechanism in which this oligomerization happens and this usually happens by a pathway called coordination insertion pathway. What it means is that what it means is that the metal must have a vacant site, metal with all these ligands must have a vacant site to which the olefin first binds. This is called coordination step and the next step is this after binding the olefin then inserts into this metal alkyl bond, this vacant site is regenerated to which again an olefin comes and binds and then the process proceeds on. This in short is the mechanism which is aptly followed and this is commonly referred to as coordination insertion. The coordination step is shown over here and the insertion step is shown over here. The first step involves coordination and the second step involves insertion where the olefin inserts into the metal alkyl bond. What is important to note is that this is a common mechanism or common pathway accepted for olefin oligomerization and the polymerization reactions. What is the important step common to the polymerization, oligomerization and polymerization reactions is the insertion of etatoo alkene to the metal alkyl bond and this is exactly what we had referred to as coordination insertion mechanism. The second step for any oligomerization, dimerization, trimerization or non-polymerization is the insertion. First, the coordination of the olefin to the vacant site and then subsequent insertion of the coordinated olefin to the metal alkyl bond. The second important thing is the formation of product depends on the composition of chain growth and chain termination. This is an interesting observation, it says that the extent to which a polymer will grow depends on the comparative rate of chain growth, which is a propagation step as well as the chain termination. If the chain propagation step is faster than the termination step, then longer polymers will form and if the chain termination overtakes chain propagation, then shorter polymers or oligomers will form. This is an interesting observation and in this context, in this slide, we are going to take a look at various examples of alkyl oligomerization and polymerization processes as we move on with the discussion on this topic in the subsequent lectures. With this, we come to the conclusion of today's lecture. To raise the lecture, we have looked into another example of tandem enyne metathesis and cycloidation reaction resulting in formation of two products depending on the orientation of the active species and the olefins and subsequent reaction with alkyl. We have looked into various pros and cons or various important features of this enyne metathesis reaction both in intermolecular as well as in intermolecular fashion. In this lecture, we have finished our discussion on enyne metathesis and then initiated our discussion on another important topic of olefin oligomerization and polymerization reactions. We have noted that these oligomerization and polymerization reactions proceed via coordination insertion pathway, where there is a vacant site to which the olefin binds and subsequent insertion of the bound olefin or coordinated olefin to a metal alkyl bond is crucial to the formation of this oligomerization or polymerization reaction. Another thing that we have noted is that the extent to which a polymer length will grow depends on the rate in which the propagation and the termination step occur and depending on the interplay of the two factors would decide on the length of the oligomer. So, with this, we are coming to an end of today's discussion. We are going to be discussing this new topic of olefin oligomerization and polymerization in more detail as we take up the topic in the subsequent lecture. I once again thank you for being with me in this discussion and I look forward to taking up this discussion on olefin oligomerization and polymerization in much detail when we meet next. Till then, goodbye and thank you.