 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. In the first lecture, I am going to give a brief introduction about these advanced levels transition metal organometallics course, and then subsequently we will take up a very interesting topic, which is Repi synthesis, mainly from the perspective of utility and challenges of applications of organometallic chemistry in chemical catalysis. This transition metal organometallics in catalysis and biology is a continuation of the past three courses, which have been offered in this series of NPTEL lecture series. To start with, I had given advanced transition metal organometallic chemistry, followed by transition metal organometallic chemistry from principles to applications, and then introduction to transition metal organometallic chemistry. These are the three courses, which form the basis and prerequisite for these current courses, which are transition metal organometallics in catalysis and biology, and would provide the necessary foundation and platform based on these current courses. The current course focuses mainly on the application aspects of transition metal organometallics in catalysis and biology, and the principles, and all the rationalizations have been covered in the earlier courses, which I have just mentioned so far. In the current time, transition metal organometallic compounds or transition metal organometallic chemistry as a field is going through an exciting time given the fact that over the last century, about nine Nobel Prizes have been awarded to this field of transition metal organometallic chemistry. This is a tremendous achievement for any field or recognition for any field to showcase the potential utility of this very important set of transition metal organometallic compounds. To begin with, the first Nobel Prize went to Victor Grignard and Paul Sabatier for Grignard reagent discovery as early as 1912. Now, this, if one looks at, is a seminal discovery, which allowed the chemist to form carbon-carbon bonds. However, there was a great bit of challenge associated with it, particularly going to the air and moisture sensitivities of this alkaline earth reagent like organomagnetium compounds. Another limitation, as we saw for carrying out these C-C bond formations in the stoichiometric fashion. The next very important discovery in this area came from this Ziegler-Natter catalyst for the discovery of olefin polymerization. Now, this open door to this world of polymers that were synthesized by transition metal organometallic compounds and a lot of applications of polyolefins emerged out of this discovery. This was indeed a discovery, which has broken bounds from the confines of the walls of laboratory to these large scale industries and had a lot of applications in the society at large. Another important and seminal discovery was reported by Fisher and Wilkinson, which is the hydrogenation reaction, followed by Liskom in 1976. They got the Nobel Prize for Structure and Bonding Illucidation of borane compounds, which are very complex in terms of the bonds they formed. They are mainly known to form multi-center electron deficient non-classical bonds, which are beyond the intuition of normal classical two-centered two-electron bonds. Here was the rich world of complex bonding structures about sharing electrons in a non-classical fashion between multi-center for which Liskom was rightfully awarded the Nobel Prize. In 1979, we saw H.C. Brown getting Nobel Prize for developing organoboron reagents. An organoboron reagent, as we say, has a lot of applications in the chemistry of reductions, particularly borohydrides and other reagents. You would also see that the second Nobel Prize was also an offshoot of the discovery of organoboron reagent, particularly that of this palladium mediated cross coupling reaction, which H.C. Suzuki and Negishi gave the Nobel Prize of. What we see is that a field not only getting Nobel Prize for one time, but in many cases has won a second Nobel Prize for subsequent development of the field, as we had seen with H.C. Brown organoboron reagent getting Nobel Prize in 1979, as well as in 2010. The utility of organoboron reagent for palladium mediated cross coupling reaction, H.C. Suzuki and Negishi also getting the Nobel Prize. Incidentally, both H.C. Suzuki and Negishi was a postdoc working for H.C. Brown when the excitement of organoboron chemistry was developed. What we see is that a second generation of Nobel Prize coming to the same junior chemist who had been the advisor as well as the postdoctoral research associate, both ended up getting two different Nobel Prize in a time of about 30 years or so apart. Then in 1981, Professor Rold Hoffman was given Nobel Prize again for explaining a complex set of rules, particularly pertaining to isolability, where metal fragments behaved chemically similar or the reactivity of these metal fragments were very similar to that of their organic counterparts. Then in 2001, Noel's, Nairi and Sharples got a Nobel Prize for asymmetric hydrogenation reaction. Here also we see a trend that this is a second Nobel Prize on the similar discovery with the first one being awarded to Fischer and Wilkinson on hydrogenation in 1973. In 2001, Noel's, Nairi and Sharples getting the second Nobel Prize in asymmetric hydrogenation in more refined techniques for hydrogenation after another 30 years or so. Again, in 2005, another important discovery in the area of organometallic chemistry, namely this metathesis reaction was recognized and given Nobel Prize to Professor Richard Strock, Robert Graves and Professor Chauvin. This also is, in that way one can say, a second Nobel Prize to organometallic polymerization field, the first being that of Karl Ziegler and Julian Nader in 1963, given for polyolefin polymerization. Again after a span of about 40 years, Strock, Graves and Chauvin getting a Nobel Prize for another discovery in the area of olefin polymerization, particularly from the metathesis standpoint. What I intend to highlight through all these discoveries and this correlation is the fact that applications of transition metal organometallics in catalysis and biology have tremendous potential, which are now being realized and also been recognized by the fact that so many Nobel Prizes have been awarded to this particular field in the last 100 years or so. Another thing that I should stress about this course is that this course not only focuses on the applications of transition metal organometallics in catalysis, but also in biology, particularly from the perspective of bio organometallic chemistry. Now if I may point out to all these 9 Nobel Prizes that have been awarded, now all can see that almost all of them have been awarded to the field of catalysis and the area of transition metal organometallics in biology still remains a state in development and has yet to be recognized as a potential area of importance. So, this course also focuses on this particular aspect where one can see that how transition metal organometallics are becoming very important in the area of biology, particularly in bio organometallic chemistry. And the course also is focused in this end. Now, before we just go in, let me recall some of the concepts that we had discussed in the earlier courses as these would be very much essential in appreciating and understanding the content which would be given in these next few lectures. Now, to begin with, we had looked at various kinds of ligand systems which stabilize transition metal organometallic compounds, particularly from their bonding perspective and they include sigma as well as pi donor ligands, pi acceptor ligands. Now, these in the previous courses we have looked into the various orbitals that are involved in engaging in bonding with metal. Now, one interesting concept about transition metal organometallics is that transition metal ligand bond is a two-way traffic. That means that the transition metal accepts a sigma electron from the ligand which is an electron rich entity and also provides a second kind of interaction which is a donation of an electron back from the metal to the ligand. So, this is a unique property of transition metal ligand interaction, where a two-way traffic of electron flow is observed. The first one is the sigma interaction, where the ligand gives an electron to the metal and the second one is the pi interaction, where the metal gives an electron back to the ligand. So, there is an interplay and there is a balance between the type of flow that exists between transition ligand bonding and we had observed this phenomenon to be present in various kinds of ligand starting with the C3 fragments, which are C3 R3+. And then we have looked into the higher homologs of this ligand like cyclobutane C4 H4 or the more common variant C5 H5 and looked into the preparation properties of this kind of ligand which are by nature sigma donating, pi donating or pi accepting ligands. And we have also looked into heteroleptic complexes, where this transition metal is bound to various kinds of different ligands and that are like cyclopentadienyl, carbonyl, nitrocyl hydride and the halide complexes of transition metals. So, in most of these cases, the important take off messages, the dual or two way interaction of metal ligand with respect to the electron flow is evident and important and also they play a crucial role in being able to stabilize the particular kind of interaction. In the past, we had seen that one has looked into the three-fragment interaction with the metal, the four-fragment interaction with the metal, the five-fragment interaction with the metal, then the six-fragment interaction with the metal. Even the seven-fragment interaction with the metal and lastly the eight-fragment interaction with metal. So, there is a wide diversity of range of interaction which is possible between the metal and ligand and in the previous course, we have looked into the type of metal ligand interaction which are possible. The constant thing is that in all of these, there is a metal ligand interaction where there is a sigma bond between the metal and the ligand and there is a back donation which happens from the metal to the ligand. This is a unique feature of organometallic compounds and that is present in various kind of interactions that we have discussed in the previous course. As we moved on from C6 fragment to the cyclohexatrinyl C7H7 and C8H8 fragments looked at the interactions. Then in the previous class, we have also looked at various applications of these transition metal organometallic compounds particularly from C-C cross coupling reactions. As I said that this is a very interesting area which has recently been awarded the Nobel Prize where the C-C coupling has been recognized as an important synthetic tool for constructing various kind of organic targets. This is effortlessly done using palladium, hex, Suzuki and steel coupling and other sets of palladium mediated cross coupling reactions. As I said that when I was highlighting talking about the importance of organometallic chemistry as a field, as I said that in several instances we had observed that the particular discovery being recognized with Nobel Prize not only once but even more than once. To that we had seen the examples of olefin polymerization as well as metathesis polymerization. Both are transition metal mediated polymerization being recognized as an important discovery and being awarded Nobel Prize twice. We had also seen like hydrogenation by Wilkinson as well as Nair's asymmetric hydrogenation getting this Nobel Prize twice. Similarly on the same flow what we saw is this C-C bond forming reaction by Grignard given Nobel Prize in 1912. Again about 100 years later in 2010 again the C-C bond forming reaction particularly the cross coupling reaction winning Nobel Prize as given to Hex, Suzuki coupling. This shows that a field even could achieve significant milestones in terms of discovery even about a century apart since the first major discovery organized by Nobel Prize was. Grignard won in 1912 and then again Suzuki coupling still winning in 2010. Another important thing on this is that this cross coupling reaction which was given Nobel Prize in 2010 is mainly for several improvements on with regard to C-C cross coupling reaction which this Nobel discovery brought in. For example, the Grignard reactions are extremely air and moisture sensitive whereas the current Nobel Prize winning cross coupling reactions are stable in air and these reactions can be performed in open air under Arabic conditions. So there has been a lot of grounds which have been covered in terms of improvements and discovery. Furthermore another important benefit of this more devised way of C-C cross coupling reaction is the fact that these reactions are carried out in with the metal reagent being used in catalytic amounts where large number of turnovers are observed by the same catalyst. Whereas the Grignard discovery had mainly been stoichiometric with respect to the very sensitive Grignard reagents which were used for making these carbon-carbon bonds. And hence again thing is that a lot of grounds have been covered in terms of the discovery in terms of overcoming the challenges and it is becoming more and more evident that the field is really very important. As many of the discoveries or many of the areas of the discoveries have been awarded the Nobel Prize not only once but more than once over a span of as little as 30 years to as high as about 80 or 90 or 100 years to say that this field of organometallic chemistry is really passing through an exciting time and it is alive and kicking. Along with the same flow we had looked into some applications earlier on in our previous courses that involved cross coupling reaction, Sonogashira coupling, hydrocyanation reactions, carbon-heteroatrum coupling, hydroamination reaction. Now some of these are really very interesting problems even industrially from a society point of view given the fact that they pose a lot of challenges when one wants to achieve and one such thing is hydroamination reaction. Hydroamination reactions are reactions which are very clean in the sense that they are atom economic which means that there is no side product which is or by products which are to be produced in the course of the reaction which needs to be discarded. So, these are highly desirable atom economic reaction in the sense that all the reactants get incorporated into the product and there is nothing to discard off. But the major challenge in hydroamination reactions are that both making the two reactant to react because the amines and the substrates unsaturated substrates like olefins, alkynes, all are electron rich entities and they mutually repel each other and they would not participate in reaction with each other. And here what we observe is that the solution has been provided by transition metal chemistry where the transition metal binds to these electron rich species activates them that is make them more electron deficient as a result of binding to transition metal through the metal ligand forward sigma donation and backward pi donation. The type of donation we have just discussed about in the earlier slide making one of the reactant more agreeable to reacting with the other reactant and hence we see how this academic challenge of making two electron rich substrates react becomes possible as a result of intervention of transition metals in transition metal organometallic chemistry. Along the same line we have looked into some other very useful applications of transition metal organometallic chemistry particularly carbon heteroatom coupling, hydroboration reactions, hydro silylation reactions, olefin oxidation reactions. We have also looked at some of the very important industrial processes like water gap shift reaction, fissure drop synthesis, carbonylation of alcohols, we have also in the same breath we have also looked into these hydrogenation reactions, their asymmetric form as a part of the previous course where we discussed some of the applications of transition metal organometallic chemistry. In the world of chemical catalysis now now today given the fact that I have just provided a glimpse of the extent and the utility to which the transition metal organometallic chemistry in the world of catalysis can expand to and also being recognized with noble prices today in this course. I am going to take up another very important applications of transition metal chemistry particularly in the area of repi synthesis, which is nothing but the utility of acetylene in industrial processes. Here I should mention that this development of transition metal organometallic chemistry is kind of unique where we see the development being carried out equally in industry as well as in the laboratory of academia. So, the first topic in this course is repi synthesis, which has been exclusively or extensively developed in industry where and has been done about a century ago by Walter Repi who was a pioneer in acetylene chemistry. Now, we are going to be looking up in this rich applications of acetylene chemistry as developed by Walter Repi and which are popularly known as this repi synthesis in the subsequent lecture from now on. I should also mention that the most of the applications of transition metal organometallics has been by and large in the area of chemical catalysis homogeneous as well as heterogeneous. However, the applications of transition metal organometallics in biology is still an emerging and the new area which is getting importance by the day. With that, I want to emphasize that this course we are going to take up topics not only for the utility of transition metal organometallics in catalysis but also in biology. So, with this I conclude today's lecture where I had given brief introduction about the potential importance and utility of transition metal organometallics in catalysis. I have made grounds for their utility in biology and also introduced an important reaction that I would be talking about which is repi synthesis which has been developed mainly in the industry and had been a contribution from the industry in Germany. In today's lecture, we are going to take up these repi synthesis, repi chemistry in more details in subsequent lecture. Till that, goodbye and look forward to being with you in the next lecture. Thank you.