 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been discussing alkene and alkyne oligomerization reaction in the past few lectures. In this context, we have covered two main reactions. One is alkyne, ethylene oligomerization, alkyne and alkyne oligomerization. In this context, we have covered two reactions. First one is ethylene oligomerization. This we have covered from the perspective of shop process. Shop is a shell higher olefin process, and this we have covered using the nickel catalyst. Nickel hydride is an active species is an active species for the catalyst for ethylene oligomerization, and this ethylene oligomerization came into prominence with regard to the shop process, particularly for finding a synthetic root to producing detergents, and this was achieved by oligomerization of ethylene with a nickel catalyst, followed by two other important processes which were added to it. One is ethylene alkene isomerization and alkene metathesis reactions, which together oligomerization, isomerization and metathesis all together constitute the shop process, shell higher olefin process, and this was primarily used for preparing the starting material for synthesis of detergents. This has been discussed in great detail with respect to both ethylene oligomerization as a part of this topic, as well as with respect to olefin metathesis, which was the topic that was discussed in the earlier lectures. We had also discussed ethylene trimarization. This ethylene trimarization is primarily used to produce one hexene, primarily used to produce one hexene using tantalum 3 catalysts, and which was obtained by from tantalum 5 salts by presence of alkylating reagent, and this also we have discussed in great details, particularly the mechanism of its formation, highlighting the main advantage of this process, which is about the selectivity of this reaction. Today, we are going to discuss about two other reactions. One is propene dimarization, and the fourth one is cyclotrimarization of butadiene. These two are very interesting processes that we would be talking about today, and both involve a nickel catalyst that carry out these two trimarization of propene and cyclotrimarization of butadiene reactions. Today's main lecture with this highlight on these two reactions. One is propene dimarization as well as cyclotrimarization of butadiene. Earlier on in a previous two lectures, we have discussed the above two reactions, ethylene oligomerization using again a nickel catalyst, and the second one that we had discussed in the earlier reaction was ethylene trimarization to one hexene using a tantalum catalyst. With this, we are going to focus on the first reaction, which is propene dimarization reaction using nickel. This process in which propene dimarizes to give various types of branched hexenes, this is called dimersol process. The process in which propene dimarizes and gives branched hexene and gives branched hexenes is called dimersol process. The reaction is depicted as follows 2n using a catalyst gives where 2n equals x plus y plus z, x gives x moles of x in of this type plus y moles of plus z moles of. Now, these are important intermediates, as these branched hexenes can be hydrogenated to give high quadrate petrol of antinoch property. Branched hexenes are hydrogenated to give petrol of high antinoch properties. Now, let us take a look at the mechanism for this dimarization of the propene reaction, the mechanism of it, and that is given as follows. The catalyst precursor is of the type nickel Lx type ligand with a allyl. Now, allyl moiety bound to nickel, so this is a nickel 2 complex, and an allyl moiety bound to nickel can be viewed as such given over here, one sigma bond, another pi bond as shown over here that react with a propene to give nickel x sigma pi complex. So, what really happens over here is that this pi bond of the allyl gets replaced by this olefinic pi bond, and this eta 3 becomes sigma and pi over here as is shown over here. So, now this reacts with an olefin to give this nickel 2 complex x, where this olefin first undergoes migratory insertion into the nickel alkyl sigma bond to give the following complex as is shown over here. Actually, to be more accurate, this undergoes migratory insertion, and this comes in coordinate, that is the more accurate representation, and this undergoes this to give this inserted complex, which then beta eliminates, this is alpha and beta and there is a hydrogen over here, beta eliminates to give the corresponding alkene branched x in as is shown over here, and that then reacts with another propene molecule. Again, a similar kind of coordination insertion happens, where this insert into the nickel hydride bond, and this comes in coordinates to give the product as is shown with the nickel bound now to an isopropyl moiety and an alkene. Note that the isopropyl moiety is obtained by insertion of this hydride into this hydride gives you the isopropyl moiety. Now, the reaction of this with propene gives nickel. Again, as was observed in earlier case, this undergoes insertion into the isopropyl moiety, and this olefin coordinates there, giving rise to this compound as is shown here, and this further beta eliminates, give this nickel hydride complex with alkene, and where the product which are formed is this branched alkene as is shown over here. Trimerization of propene then leads to the formation of variety of alkene through this process as is shown over here. Now, to note L for the catalyst is phosphine X is to note over here that L and X are shown here, L is a phosphine, and X is an ethyl tri-aluminum chloride moiety. So, with this, we show how this dimerization of propene gives rise to branching branched hexanes, which when hydrogenation gives this anti-nock grade high petrol, and this involves nickel hydride as the active species that carry out this dimerization of propene process efficiently. So, the actual catalyst is a nickel hydride species, the catalyst is the one which is ethyl, nickel, pcy3, Br, Et, Al, Cl2, this is the active catalyst which displays high turnover number, number 60,000 per second, and these numbers, the high turnover number is comparable to enzyme activity. For example, catalase exhibits high turnover number of 100000 per second. So, this is an interesting compound where nickel is bound to one ethyl, one cycloexyl group, one bromide, and this leusacidic Et3 Al Cl2, and this sort of is an effective species for dimerization of propene, and that gives various kinds of branched hexanes, which upon hydrogenation gives high quality petrol having anti-nock properties. So, today we have looked into the mechanism as to how this branching of propene occurs, and these mainly go through this nickel hydride active species, then forming the coordinated propene, which then goes insertion into the metal alkyl bond to give the branched propene. So, with this we come to the conclusion of today's lecture, which was primarily on this important reaction of dimerization propene. We had also looked at this reaction in context of the other two alkene oligomerization reaction for shop process, as well as this ethylene trimerization reaction to give one hexene. Now, with this we move on to the next reaction, which is cyclotrimerization of butadiene, and we are going to be looking at how this catalyst is used for making this butadiene trimer, when we take up the discussion in the next class. I conclude today's lecture, in which we had discussed about this one particular reaction, which is propene dimerization reaction, and this is called the dimersal process, and is used to make branched hexenes, which upon hydrogenated give high grade anti-knocking and quality of petrol, and has used in automobile industry. So, with this we come to the end of today's lecture, and I thank you for being with me in this lecture, and I look forward to discuss more on this olefin oligomerization reaction as we meet next. Till then, goodbye and thank you.