 Welcome to this course on transition metal organ metallics in catalysis and biology. In this regard we have been discussing olefin oligomerisation reactions in the past few lectures and today we are going to finish the discussion on olefin oligomerisation or alkene oligomerisation and if time permits we start with the topic alkene olefin polymerisation as well. So with that let me just give a brief overview of what we have been discussing in the previous lectures. As mentioned earlier that we had started off with ethylene oligomerisation in the context of shop process, cell hire olefin process and then we have looked into ethylene trimerisation using a tantalum catalyst. This was a work by Prof. Rausman Sen, where one could produce one hexene selectively by trimerising ethylene. The third that we have spoken about under this topic is this propylene dimerisation in terms of producing various kinds of branched hexanes. This also is an industrially applicable reaction which is used for application in auto industry, particularly these branched hexanes when hydrogenated are very good anti-nocking agents and are used in petrol for their attributes. So, after dimerisation of propylene producing branched hexanes we then looked at trimerisation of butadiene which gives this cyclo-dodeca triene, which is a cyclic compound ring, with three unsaturated olefinic bonds and each in a trans-trans-trans configuration. And subsequent that we have also looked at the Ziegler-Natta way of preparing this cyclo-dodeca triene using Ziegler-Natta catalyst, titanium catalyst. And today we are going to discuss butadiene dimerisation. The one that we had spoken about earlier was butadiene trimerisation, and today we are going to talk about butadiene dimerisation, cyclo-dimerisation of butadiene. Now in order to take up this topic, we should refer to the earlier discussion of cyclo-trimerisation of butadiene, and this was reported by Wilke in 1960. Now the difference between these two processes is that the earlier one was cyclo-trimerisation process, where the dodeca triene was obtained, and today what we are going to be discussing is the dimerisation process, where we are going to make a cyclic octadiene. So there is the difference in the product, which would be formed because of dimerisation and obviously the trimerisation process, however there is a lot of similarity in the process as well. For example, both involve the substrate butadiene, so today's one is the dimerisation of butadiene, and the earlier one we had discussed the trimerisation of butadiene. The other similarity is that the catalyst precursor is same for both, the catalyst precursor is same for the both, the one which is a dimerisation and the one for the trimerisation as well, and let me just draw the catalyst precursor. So this bis allyl nickel complex is the catalyst for cyclo-trimerisation process, and also the same is true for the butadiene cyclo-trimerisation butadiene process. Now the difference lies in the final product, one is for the dimerisation, the other is the trimerisation, whereas the similarity is that both are of butadiene and both require the same catalyst, the only other difference is that this butadiene dimerisation proceeds in presence of phosphines, and they results in dimerisation. So when phosphine is present with nickel aryl catalyst and with butadiene as a substrate, primarily the dimerisation product of the butadiene is observed, whereas when nickel aryl with butadiene is present exclusively, then the trimerised product is observed. So in this case when phosphines are present, then the dimerised product distribution can be controlled by varying R or the alkyl group of the phosphine, so that gives a useful handle on how this dimerisation process occurs. So now let me just give the scope of this reaction in terms of the different products being formed, and this is shown over here, this reacting with two butadiene in presence of phosphine, we had observed similar reductive elimination, so this over here nickel is in plus two oxidation state, and reductive elimination of these two species occurs to give the diallyl compound as shown over here, and this is quite similar to what had been observed during the cyclotrimerisation of butadiene process, where two diallyl compound was evolved, but please note that this triallyl phosphine was not present during that time, and resulting in this product, this alyl nickel product again with the oxidation state of this plus two, but like last time this reaction can proceed as shown over here, this would go via the formation of this nickel zero, and that in presence of P r3 would give this nickel two compound, that would involve this oxidisation of these two to form this ligand, and then nickel becoming nickel two, this process sort of is a two step process, where a nickel zero is formed followed by that, now once this is formed, then that can reductively eliminate to give cod cyclo octadiene polymer, or these can be in equilibrium to give this compound, so here the alyl moiety has just become a sigma donor, and the other alyl moiety also has become a sigma donor as it is shown here, now this can again undergo reductive elimination to give this six-membered compound, cyclohexane compound as is shown over here, similarly these are the central species can also become this nickel metallacycal as is shown over here, and that undergo reductive elimination to give an interesting compound, cyclobutadiene compound of this type, so what is seen over here that this dimerization of butadiene as is shown over here can occur to give this cyclo octadiene in presence of phosphine, however in presence of the different substituents of phosphine, there can be other products which can be also obtained from the reaction, for example if there is this particular kind of two sigma alyl reagents are formed, sigma bonds to nickel are formed, then one six-membered ring can be obtained, whereas if this nickel cycle five-membered ring is formed, then cyclobutane with two vinyl substituents are obtained, so this is a nice demonstration again of the ability or scope of organometallic catalysis, where a variety of substituents can be obtained depending on the sterics that one uses, so with this now we come to this end of our discussion on cyclo dimerization of butane, and also we conclude our discussion on alkene oligomerization reaction, so to summarize we have looked into variety of alkene oligomerization reactions starting with ethylene oligomerization in the context of shop catalysis, second one is ethylene trimerization to obtain one hexene, third one that we have looked at is propene dimerization, fourth one we had looked at is cyclo trimerization of butadiene, and fifth one again that we have looked at in this context is cyclo dimerization of butadiene, so we have looked at two reactions of butadiene dimerization and trimerization, we have looked at one reaction of propene dimerization, and we have looked at two reactions of ethylene trimerization and oligomerization, it is important to mention that in all of these cases the catalyst which have used is nickel except for ethylene trimerization where tantalum was used for catalysis, so these further rain states nickel plays as a metal of choice for producing oligomers of different degrees cyclic and acyclic from olefins, and that reason being that more electron rich lead transition metal are good for alkene oligomerization whereas early transition metal are good for electron deficient early transition metal are good for olefin polymerization, so with this we move on to another interesting topic which is olefin polymerization, so now we are moving on from low molecular weight oligomers of olefins to high molecular weight polymers of olefins, now olefin polymerization is an important reaction in terms of producing polyolefins and it is very sort of synonymous with synonymous with Ziegler-Natter catalysis, however there is more to olefin polymerization, there is just Ziegler-Natter catalysis and different types of polymerizations that are possible for olefin and Ziegler-Natter though constitute a primary portion of it, so this is an application which has seen the light of the day in terms of the application moving on from the discovery within the confines of laboratory to being practiced large scale in industry, so polyolefins are produced industrially for making macromolecules, polyolefins are scruely produced for making macromolecular materials, now the importance of this polyolefins can be gauged by the extent of production that is required to meet our daily need or the need for these plastics, so the increased production of polyolefins over 70 megaton annually is mainly due to widespread applications of polyolefins, so this is mainly a due to large scale applications of polyolefins, polyolefins are applied for various purposes and the demand for polyolefin is made by increasing the production and really a large amount about 70 megaton of polyolefins are being produced annually to meet the demand, so because of its large scale application, the knowledge about structure property relationship and the development of new catalysts for polymerization is important, the knowledge structure property relationship is important for catalyst development, now this is a important attribute because this is where the mechanism the insights about the mechanism come into play because if one were to know the mechanism fully well then one can come up with modifications which will enhance the catalytic attribute of this catalyst performance for this process and produce improved polymers, so there is the research primarily in this direction are focused in understanding this structure property relationship or structure activity relationship as a function of catalyst structure and another thing about polyolefin is that not only its polymers are important but also the segmental mobility or degree of branching is important with regard to determining what kind of polymeric material it would be, whether it would be a hard brittle kind of polymer or would it be a soft ductile kind of polymer, so important term over here is segmental mobility depends mobility is an important property that depends on the degree of branching of polymer, so what we see that polyolefin is a important area overall this is what the take home message from here in the sense that this has gone big and went on to become as one of the biggest industrial process for making large macromolecules and then the demand for polyolefins or polyolefinic materials are so high that annually of about 7 T megaton that is a huge amount of polymers being produced, now this widespread application of polymers in different applications for example, from furniture to bottles to other devices to utensils to everything that depends on the nature of the polymers and to understand that the mechanism of the polymerization is very important and for obtaining inside some the mechanism the structure property relationship as a function of the catalyst structure is important for developing better catalyst which will produce more controlled and better polymers and lastly the segmental mobility of the polymer is an important property that is dependent on the extent of the branching of the polymer and then the need comes to make polymers which are branched and then exclusively make polymers which are non branched or linear and their overall property would depend on the extent of branching of the linearity for example, if a polymer is branched highly branched then it will be more soft material whereas if the polymer is long chain linear polymer then it will be a very brittle and hard so depending on the application there is a need for producing each of these types of different polymers so with these I come to an end of today's discussion on olefin oligomerization as well as olefin polymerization reactions to begin with we had finished our discussion on the topic of olefin oligomerization by discussing cyclo dimerization of olefin using a nickel allyl catalyst this is very similar the catalyst is very similar to that of the reaction cyclo trimerization of olefin the only difference is that in the cyclo dimerization of olefin phosphines are used and depending on the types of phosphine used of the steric bulk of the phosphine one can not only produce this cyclo octadiene which is the cyclo dimerized part of butadiene but also one can obtain four-membered cyclobutane or six-membered cyclohexane rings depending on the nature of the group of the phosphine we have looked into that and then we have looked into this important process of olefin polymerization we have looked into the need for large scale production of this process and how they are being met by organometallic catalyst we have also noted the importance of the knowledge of structure property relationship in respect to catalyst development and lastly with respect to the polymer properties we have discussed about the importance of branching or segmental mobility of the polymer which sort of defines the very nature of the polymer so with these I come to an end of today's discussion we are going to be talking more on olefin polymerization particularly about various types of polymer and their attributes when we make next and then look into how or what are the various examples and the types of polymers that are there for this under this topic of olefin polymerization so with this I once again like to thank you for being with me in this class and I look forward to be discussing this olefin polymerization in great more detail when we meet next till then goodbye and thank you