 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. In this course so far, we have been talking about various kinds of olefin metathesis reaction, apart from other industrial processes reactions, which has come out of organometallic chemistry discoveries. In the context of olefin metathesis, we have covered alkene metathesis and alkyne metathesis. And we had seen how there exists a similarity or parallel of reactions for both these kinds of metathesis reaction alkene as well as alkyne metathesis. And today we are going to discuss another interesting topic in more detail, which is called alkyne metathesis reaction alkene, which is called in-ion metathesis reactions. Now in order to understand this reaction, this reaction is kind of a bit different than its predecessors, which is alkyne metathesis or alkyne metathesis. And in order to understand this, we need to reflect on the initial characteristics of these two alkyne metathesis and alkyne metathesis individually. So let me just start with alkyne metathesis, which is the reaction between these two olefins giving this and the catalyst present is a metal carbene species. So this is a metal carbene catalyst. Now the alkyne metathesis is also a similar kind of reaction. It involves two types of alkynes giving two of the mixed alkyne, and the catalyst is a metal carbene catalyst. So this is alkyne metathesis, and the earlier one that we have discussed was alkyne metathesis. So now the question comes, what about the reaction that we are discussing now, which is alkyne alkyne metathesis. So now this has both the substrates, which we will take a look. This has both the substrates, for example, so it has both the substrates and alkyne and as well as an alkene. And the question which comes to mind is, which of the catalyst would be able to carry out such a metathesis, as far as the catalyst is concerned, which of the catalyst metathesis. So this is an intrinsic question. This means that there are possibility of metal carbene versus metal carbene. So the interesting thing to note over here is that the first question is this, which of these two catalysts, the carbene or the carbene would be effective for this in-ion metathesis reaction that involves reaction of alkene and alkyne. Now the next question, which comes to the fourth with regard to this chemistry, is the question number two. It says, even if one of the two is or both of them are effective for carrying out this in-ion mechanism or in-ion metathesis, then the question is, what will be the sequence of metathesis reaction? What would be the sequence of metathesis reaction? By this, whether it will be in-ion and then in-ion metathesis versus in-ion metathesis. So this also is a very relevant and interesting question, is that even if either of the two is effective in carrying out this metathesis of alkene and alkyne, then the question is which one would be the first to undergo metathesis, whether this is in-ion metathesis where the alkyne would undergo metathesis first followed by the alkyne or it is in-ion metathesis, which would be starting with alkyne first and then in-ion alkyne in the order of the metathesis reaction it would go. So, these are important questions like what kind of catalyst, what would be the sequence of reactions as now the substrates contain both unsaturated alkyne as well as alkyne, and then another interesting attribute is that they can be present in the same molecule which can be in thyrmolecular or in thyrmolecular, so both possibilities exist for alkyne metathesis reaction. Now these are the issues that had challenged the people who had been working in the areas and several studies has been done in order to elucidate the exact mechanism or exact active species responsible for this in-ion metathesis reaction and to sum up the finding what is said that it is the metal carbene complexes they are effective for alkyne metathesis reactions. The catalysts are indeed these metal carbene species, the evidence point that the active species are indeed the metal carbene species which is responsible for alkyne alkyne metathesis reaction. Now with respect to the second question that what would be the sequence of metathesis whether it will be a olefin first and then alkyne second metathesis or alkyne first olefin second metathesis the answer to that which the evidence point is that this in-ion metathesis which is supposedly the one which is followed in most of the cases and most popular. So the take home point is that alkyne metathesis or in-ion metathesis is a complex metathesis which has come out of these individual classes of alkyne metathesis and alkyne metathesis and given the complexity that arise regarding the pathway the metal carbene species are supposed to be the active species for this in-ion metathesis and second thing that the mechanism proceeds by in first or in-ion metathesis that olefin gets attacked first and then alkyne undergoes metathesis second. So I am going to now go deep into this the mechanistic aspect of this in-ion mechanism and talk about these in bit more detail. So now of these there can be two variants as I said that this can undergo intermolecular as well as intramolecular and I am showing it by examples catalyst giving R1. So this is an example of intermolecular in-ion metathesis similarly the intramolecular metathesis are also reported which involves a bridging group or substrate containing a linker in which the substrate contains both the alkyne and the alkyne moiety are present and then the catalyst as I mentioned is that in the present case also this is a carbene type of the catalyst which gives the product of the type of the type this is a five membered. So this is an example of intramolecular in-ion metathesis, but in this case as there is a ring closing occurring in place so this mechanism is also popularly called as ring closing in-ion metathesis or RCEYM this is called ring closing in-ion metathesis. So both the possibilities as I mentioned earlier exist for the in-ion mechanism and we are going to take a look at it in bit more detail as we look at individual example in-ion metathesis examples. Now I am going to illustrate this with respect to the intramolecular substrate as is shown over here now this reacts with the ruthenium carbene complex so this will give this metallocyclo propene intermediate that will further rearrange to give this olefin and the substrate activated ruthenium carbene species. Now this then would go through this intermediate as is shown over here to give cyclobutene intermediate of the type this which will then rearrange as is shown over here to give the desired active species on the R. These there are two intermediates being formed metallocyclobutene intermediates this is called metallocyclobutene and this one is called metallocyclobutene intermediate. So a transition state these are the transition state. Now once this is formed of which I will draw it over here the first path is about in first so metathesis what we are observing happens on the olefin that is the first path is the in first and then the second pathway where the metathesis of the ion would happen and for that these species goes and enters into a second cycle as is shown over here. In this the first substrate further acts to give where similar kind of transition state is further formed as is shown over here and then this transition state undergoes rearrangement the product the active species of the ruthenium species of the type this that then undergoes again metathesis with the ion to give this metallocyclobutene as is shown over here and that further undergoes rearrangement to give the species which is this. The driving force of this reaction is the formation of conjugated 1,3 diene formation formation of conjugated 1,3 diene provides driving force for the reaction so the formation of this conjugated diene provides the driving force for this reaction. Now what we had seen that this enyne mechanism is quite complex and actually it involves number of steps number of steps in which the first is that the metal carbene complex proceeds with in first mechanism where it does not attack the alkyne but attacks the olefin first and then it undergoes a metallocyclobutene intermediate once it is formed the metallocyclobutene intermediate with the ruthenium carbene on the substrate then it attacks the alkyne to give a metallocyclobutene intermediate which undergoes rearrangement to again giving the ring closing metathesis so it closes the ring and the active site now resides on the vinyl carbene which is stable now that reacts with the second substrate again to give a metallocyclobutene intermediate butene which undergoes metathesis to give this 1,3 conjugated diene product which is this which provides the driving force and for the reaction and then it undergoes the reaction with the second alkyne moiety to give a metallocyclobutene butene species then and subsequently goes back to the starting product so one thing which is important is to note is that this vinyl carbene species of the substrate these two species are exactly the same species and they get translated from one cycle to the another cycle and carry out this anion metathesis we are going to talk more on the mechanistic aspect of this in first pathway of anion mechanism as we move in the next lecture however we have come to the end of this lecture in which we have just looked into various mechanistic pathways that are possible for anion mechanism we have also looked into the rational that behind this anion mechanism starting with questions like what is the active species whether it is a metal carbene species or a metal carbene species which would be effective for this anion metathesis because anion contains both alkyne and alkyne and what we have found is that it is the carbene species metal carbene species which carries out this anion metathesis we have also looked into other aspects like whether it is going to be the alkene first pathway or alkyne first pathway and in this class we have summarized effectiveness of alkene first pathway which involves two cycles or two different types of pathways combined as is shown by the pink and the green cycles and then we have also looked into the conditions which will which is provides the driving force for this anion in first pathway which is nothing but the formation of this conjugated 1, 3 anions. So, with this I conclude today's discussion on anion metathesis mechanism and we are going to dwell a bit more on the other possibility which is the anion first and the effectiveness of anion mechanism as we meet in the next class. Till then thank you for being with me in this class and I look forward to being with you in more details when we take up this E9 mechanism next in the next lecture. Till then goodbye and thank you.