 Welcome to this course on Transition organometallics in catalysis and biology. Today we are going to be talking about oligomerisation of alkene and alkyne. This is an interesting area which has emerged out of Ziegelnatter catalysis and it has its own domain. Now we have discussed these alkene and alkyne oligomerisation reactions earlier in the context of applications of organometallic catalysis in large scale synthesis. In this context, it is worth noting that we have spoken about an important industrial process which is called Shell-Hair-Oliphene polymerisation process, which was developed in the 1950s to make use of various fragments of alkyne oligomers for commercial purpose. Now the story goes back to the 1950s when Shell was trying to develop methods for using alkyne from the range of C8 to C14. We had discussed this in great detail in our earlier lecture on applications of organometallic catalysis, and a nice review of this process Shell-Hair-Oliphene process or shop has been nicely reviewed in this article by William Keim in Angiocam edition in English 2013-52-12492-12496. We have looked into this process whereby alpha olefins were prepared by Zignal Nata method C2H4 ethylene using nickel catalyst produced alpha olefin oligomers, and that had a huge distribution as is shown over here of different fragments mole person from C12 to C18, and this is greater than C18, and this is less than C12, and the distribution goes something like this of which the range of alpha olefins from C12 to C18, this range was used for making detergents, and this was what provided the impetus for looking into use of the other two fragments, which at that point of time were not being used. One is the fragment which was less than C12 and the fragment which is above C12, so these fragments at that point of time were unusable and were trying to find some use to make these unusable fragments. This oligomerization of alpha olefin was produced by this process which is called alkene oligomerization using Zignal Nata catalysis, that means that coordination insertion method, so all these alpha olefins the whole thing was produced by this process of having have to use nickel catalyst for alpha olefins, but of these various fragments only the usable fractions was C12 to C18 was usable. In this shop a parallel development in which they used isomerization reaction as well as metathesis reaction to use these fractions C12 and C18 to convert to around something between C12 to C18 and hence can be utilized. This was done using Zignal Nata catalysis, and a nice example is given over here in the following reaction, for example, one octene this is C8 was isomerized to give the isomerized product which is 4 octene as well as CH217, this is one Eicocene, this is C20 fragment isomerization to give to get 10 Eicocene and these two together was done metathesis to give C10 or 2 tetradicene, so what we have seen that this shop includes two process, three process mainly the first is this coordination insertion process, this is number one process which generates all these range of alpha olefins generated from here and then the two other process one is isomerization process over here as well as over here isomerization process and the second one is metathesis process which is over here, so these two process together would help these fractions which are less than C12 and C18 together to come into a range which is usable, so for mainly a couple of process that came together to look at to find use for this wide range of alpha olefin as a part of the shop process. Now in our discussion so far what we have done is we have already discussed these reactions earlier on isomerization as well as metathesis as well as this distribution curve as a part of olefin metathesis while covering the utility of olefin metathesis industrial scale and however we have not looked into this oligomerization process using nickel catalyst and in today's lecture we are going to focus on this alkene and alkyne oligomerization using Ziegler-Natter catalyst as a part of the shop chemistry and all of it is nicely reviewed by this William Keim article given in anguic KM-52 12492 12496 and I request all the students who are auditing to this course to go through this review which explains the story and the development at that time very elaborately and would benefit the reader very much. So shell higher volition process characteristics one, it involves the formations of C8 to C18 form ethylene based on oligomerization, isomerization and alkyne metathesis reaction. Now this we have discussed in detail in our previous slide where we had shown diagrammatically with example where each of these reactions play a role to produce this C18 to C18 fragments which had application for detergent usage. So these three reactions are to be discussed under the shop shell higher olefin process reaction family of reactions. Now the other characteristics of shop is the shop process is the most successful method in industry under homogeneous conditions and usually this polymerizations are carried out in polar solvent. So this is one of a powerful method in which this oligomerization reactions to produce alpha olefin using Ziegler Nata catalysis is concerned. So shop is a very successful method in industry and it was primarily used for producing alpha olefins from ethylene as alternative method for producing alpha olefins from petroleum or by cracking of natural crude oil. So let us now take a look at the mechanism for this alkyne oligomerization reaction mechanism. Now the rule of thumb is that if it is electron rich metal, then oligomers are preferred whereas if it is an electron deficient metal like early transition metal, then these polymers are preferred. So for Ziegler Nata catalysis, the rule of thumb is for Mxn type catalyst, M equals electron rich late transition metal, then oligomerization is favored giving alpha olefins whereas when M is electron deficient early transition metal, then polymerization is preferred. Now in our first discussion on the extent of the growing of the polymer chain, we had said that the extent of this chain length is very much dependent on the rate in which this propagation step and the termination step occur in a comparative sense. If propagation step is faster than the termination step, then one ends up getting polymers and if the propagation step is comparable or slower than the termination step, then one ends up getting oligomers. And also what we see that this for electron deficient metal, early transition metal polymerization is preferred implying that the propagation rate is higher than that of the termination step whereas for electron rich late transition metal, the propagation rate is comparable or slower than that of the termination rate, one can imply implying that alpha olefin oligomers are formed. Now we are going to take a detailed look at the mechanism of this oligomerization reaction. So, this is the catalyst. So, this loses the hydrogen in a beta hydride elimination process. This is alpha carbon, this is beta carbon. In a beta hydride elimination process giving an active species of nickel hydride along with nickel cod chloride. So, cod is eliminated and the active catalyst is formed. So, this is the active species which then enters the catalytic cycle and this is represented by this carton diagram as is shown here. The nickel hydride then reacts with the olefin by coordination insertion pathway. This is the coordination step, and this is the insertion step as shown here. Now this olefin moiety will insert into the nickel hydride bond giving creating a vacant site as is shown over here, and a nickel ethyl moiety. Now a second olefin will come and bind in the olefin excite coordination followed by insertion as is shown in the previous step. Now this can proceed in two directions from here. The first is that it can beta eliminate as can be shown over here. This is alpha, this is beta. It can beta eliminate to give the catalyst nickel hydride coordinated to the alpha olefin which can eventually give the nickel hydride species and the olefin going away. The other method is over here, another olefin can come in times bind in the vacant site in times and undergo coordination insertion to give a nickel alkyl species. This nickel alkyl species can beta eliminate to give the nickel hydrogen along with alpha olefin long chain alpha olefin. This alpha olefin through isomerization and olefin metathesis is taken for producing the desired fraction by shop process. What it shows is that these oligomerizations are mainly proceed by two methods, which is coordination insertion. In the shop process, the late transition metal nickel is used for olefin oligomerization, and usually the active sites is a nickel hydride species is the active complex. Now nickel hydride species can insert olefin and then coordinate olefin and then undergo insertion. Then it can do the same thing twice over and then there is a possibility in the first possibility it gives one butene and the nickel hydride or it can undergo subsequent olefin insertion to give a long chain nickel alkyl, which can then beta eliminate to give back the nickel hydride as well as alpha olefins. Now these alpha olefins are then fed into the isomerization and olefin metathesis reaction as a part of the shop process. So with this we conclude our discussion of olefin oligomerization as a part of shop process in today's lecture. What we have done is we have looked at the shell higher olefin process in its entirety and we have looked at how three different applications of organometallic chemistry involving this alpha olefin oligomerization reaction using nickel catalyst and second isomerization reaction and third olefin metathesis reaction all come into play in channelizing the various lengths of alpha olefin obtained for producing something which is important commercially particularly the alpha olefins in C8 to C18 fractions which are used commercially. With this we come to the end of today's lecture. We are going to be taking up more on olefin oligomerization when you continue with the discussion in the next lecture. I thank you for being with me in this lecture and I very much look forward to being with you in the subsequent lecture when we talk more on olefin oligomerization reaction in more detail. Till then, goodbye and thank you.