 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been discussing a very important reaction in the context of applications of transition metal organometallics in catalysis, and this is about this repi chemistry or repi reactions, which have been developed by Walter Repi in the early 1900s. And this has been an effort, which has been absolutely developed in industry and has been a great contribution to the rich chemistry of transition metal organometallics catalysis that is being seen today. Now, in this context, in the earlier class, we have looked into various kinds of repi reactions, and to this extent, we have covered nearly three types of repi reactions, starting with vinylization reactions, and examples of this giving vinyl cyanides as well as with HCl and catalyst giving vinyl chlorides. The second reaction that we had covered is this catalytic ethanylation reaction reactions, and in this, we have looked into reactions of aldehydes giving alcohols of the kind shown as well as the same with two equivalents in presence of catalyst giving diols of the type the ones drawn over here. We have also seen the reactions with carbon monoxide and acid giving acrylic acid acrylates. Now, we have discussed these three reactions or type of reactions in great details, and where we had observed that these reactions all require intervention of catalyst and proceeds by a formation of organometallic species, and the catalyst used often involve nickel, copper, mercury, iron, ruthenium shown and so forth in getting the kind of chemistry that have been detailed over here. Now, I must also mention that these products are useful as important monomers for various polymerization reactions, and hence they are sort of very much in industry. Now, in this context, another very important reaction which comes into play, which is developed by Rithi, and this involves the formation of a vinyl pyrrolidone, vinyl production synthesis. This is a reaction which is important from an industrial point of view, and the sequence is shown over here. Calcium carbide in presence of catalyst gives acetylene in presence of formaldehyde catalyst and 300 to 350 PSI gives this diol, which we had just discussed about that upon reduction, and complete reduction gives the 1,4 diol, and using ranonical that we had also discussed about, and this then undergo dehydrogenation of this cyclic lactide, which upon reaction with ammonia at 230 degree centigrade gives the cyclic amide, and that when further reacts with acetylene at 150 degree centigrade gives vinyl pyrrolidone vinyl. This is an important outcome of lepe synthesis, which was formally patented by lepe and was a big draw from outcome of different products, which had come up with the lepe synthesis in the sense that this simple acetylene compound was converted to this pyrrolidone moiety using lepe chemistry. So, this shows that how a very complex molecule, which is also an important feedstock in chemical industry can be synthesized using the conversion of acetylene using lepe chemistry. So, this was one of the big draw of lepe chemistry in overall, and there was a patent which had come out of it, and here is a picture showing lepe explaining the synthesis of polyvinyl pyrrolidone on the board. Now, with this, we come to an very important aspect of lepe chemistry, which involves cyclopolymerization reactions or cycloligomerization reactions using mediation of metal. So, cycloligomerization reactions of acetylene are the fourth type of reaction that the lepe chemistry shows. For example, this also proceeds via the mediation of the metal. The first of it is shown over here with the catalyst gives benzene, and these are called conventional repereaction. The beauty of this synthesis can be seen that aromatic compounds can be obtained from acetylene moiety. There are different kinds of lepe reactions, which are called metallative lepe, which is shown over here, where it involves two different kinds of acetylenes. So, this requires a metal catalyst, and it also gives an aromatic compound with a metal X bond, which can further be functionalized, and these are called metallative lepe. So, what we see in today's lecture is that there is a very important dimension to lepe chemistry, where not only simple functionalized acetylene products in terms of vinylization, ethanylation, as well as hydrocarboxylation of acetylene moiety into simple elephatic compounds, not only can they be formed, but repereaction can be extended more conveniently to produce more complex and intriguing aromatic compounds. So, in the next few minutes, we are going to focus on different kinds of lepe, a cyclo oligomerization reaction, and to begin with, we are going to look at the formation of the benzene from acetylene fragment in a conventional lepe system. The formation of the lepe from this acetylene system is best elaborated by an active species, which is formed from the acetylene adduct of nickel. So, what is suggested that nickel triacetylene species is formed initially as a catalyst, which is the active species for this lepe cyclo oligomerization, and then once this species is formed, it undergoes this cyclicization reaction between these two acetylene to give acetylene bound nickel cyclometallated species. This has been extensively probed using DFT in a paper, which elaborates the pathway, where it says that this is the rate determining step for the reaction. Now, the reference for this study is given in this journal Chemistry European Journal 2004, volume 103081 to 8123090, so one can look up this study in bit more detail, if one were interested in see how this cyclo oligomerization proceeds. Once this is formed, that reacts with another acetylene moiety to give this nickel acetylene cyclometallated species, which then undergoes another insertion of the acetylene to give a 7-membered ring, and that then further undergoes insertion of this acetylene to give a species, which is a nickel bound 9-membered species of the type shown over here, and once this is formed in presence of another acetylene, this species undergoes reductive elimination to give the corresponding cyclo octatetraene bound nickel acetylene species. Now, this in presence of acetylene gives this acetylene species, and which eventually loses this cyclo octatetraene to give the nickel misacetylene species, and that finally in presence of acetylene comes back to give the acetylene active species. So, this is the resting state of the catalyst, and this is formed in this cyclo pathway. So, this is an interesting reaction, and what it seems that the first step of formation of this cyclo metallocyclopentene type complex is the redetermining step of such cyclo oligomerization reaction. Now, proceeding further another interesting thing about this repic chemistry is that when the cyclo oligomerization reactions are performed, the reaction sort of works well for symmetrical or singular substrate for the same substrate. For example, over here the oligomerization happened using the same type of acetylene. So, the repi reaction sort of works very good for the cyclization of similar kind of acetylene. For example, this is going to this. So, there is only one type of acetylene being used, or for the reaction giving in presence of metal catalyst M, where two different kinds of acetylene, one is this, another is this, kind of acetylene produced, but when one goes to use three different kinds of acetylene, for example, then things becomes complicated, becomes very complicated in terms of selectivity, loss of selectivity, and 48 different coupled products, 38 homo and cross coupled products are obtained, 38 homo and cross coupled products obtained. So, this is an inherent difficulty in repi synthesis. So, what we have discussed or seen today is that there is a repi chemistry has a dimension, which is unique and very interesting in terms of being able to use acetylene fragments towards the formation of aromatic compounds, and this is very different from simple vinylization reactions or ethylation reactions or even the reactions with carbon monoxide, where the functionalization of acetylene to various important small molecule functionalized elephatic feedstocks were synthesized, whereas by the fourth reaction that we have discussed today, cyclo oligomerization of acetylene to give aromatic compounds starting from benzene or cyclo octatetraene, what we have found that this indeed is a very interesting aspect of repi chemistry where the cyclo oligomerization has happened. Now, what we have discussed in today's class with regard to cyclo oligomerization, we have looked into the reaction of cyclo trimarization of acetylene to give cyclo octatetraene, and what we have seen that the formation of a tri acetylene nickel zero species is the active species, which is responsible for the catalysis, and what we had also seen the formation of a five membered metallocyclo pentane ring in that catalytic cycle is the red determining step for these. We have also looked into metallative refi, which involve again the formation of aromatic compound, but in this case there are two different kinds of acetylenes which are used in metallative refi, this is metallative refi two different alkynes used, whereas in conventional refi this is conventional refi one type of alkyne, and then we also discussed that as we move from one type of alkyne to two different type of alkyne to even three types of alkyne alkynes, then the gain become even more difficult with loss of selectivity, and a large number of homo and cross coupled products are observed, and then the system for the cyclization of these three different kind of becomes very challenging. Now we are going to take up these in a bit more detail as how this was solved in a nice demonstration of fine organometallic chemistry, where even the rapid coupling of three different alkynes to give highly selective aromatic products could be obtained, and this would be taken up in the next class. So, with this I come to an end to today's discussion, where we had looked into a very interesting aspect of repi chemistry, which are cyclo oligomerization of repi from alkyne producing aromatic compound, and in that we have discussed about the formation of conventional repi, where only one type of alkyne is used or even the metallative repi where two different kinds of alkynes are used, we have also looked at the mechanistic pathway in which the conventional repi towards cyclo tetramerization of alkyne to cyclo octatetraene was obtained using a nickel catalyst, and with this I conclude today's lecture, and in the next lecture we are going to be discussing more about using three different kinds of alkynes, even in the context of repi chemistry to produce highly selective aromatic compounds, which are indeed a challenge for repitence synthesis. So, with this I conclude today's lecture, and I look forward to be seeing you in the next lecture, where we take up this interesting portion of repi chemistry. Till then, goodbye and thank you.