 Today, we will talk about C H bond activation. We have discussed in the past the activation of C X bonds, where X is a heteroatom. But today, we will talk about the C H bond, which is in fact ubiquitous in all organic chemistry. So, the chemistry of the C H bond in the context of organometallic chemistry is quite important. But yet, this has been a major difficulty, a major challenge for organometallic chemistry. One can trace this difficulty to the fact that the C H bond is in fact a thermodynamically stable species, an extremely stable species, which has got one of the highest bond energies that is accessible to carbon with any other element. And in fact, if you look at the name paraffin, which is what is given for long chain alkanes, where there is no other functional group, you realize that it is because of its low affinity for other chemical species. So, if the thermodynamics is working against you, it is in fact difficult to carry out any activation of that particular bond. So, let us take a closer look at why this activation is difficult. Now, if you look at the lowest unoccupied molecular orbital of the C H bond, it would approximately have this shape. Now, we are not particularly concerned with the contribution of carbon and the contribution of hydrogen in this particular molecule orbital. But just schematically, we have represented it here and we show that the anti-bonding orbital will have this symmetry and approximate shape. Even if you match the C H bond, the sigma star bond in terms of symmetry and energy, pumping electrons into this MO becomes a difficult task. The metal in fact has got orbitals of the right symmetry, but not often of the right energy. But if the energy is matched, then indeed pumping electrons would be possible. But even there, you notice that on the carbon side, there are three bonds on the carbon in an sp3 hybridized orbital. There are three bonds on the carbon, which are in fact protecting the lobe that is present on the C H sigma star. So, it is sterically inaccessible. So, this orbital that we are talking about is not accessible to the metal and that is the interaction is shown by the arrow. It would be easier to pump an electron density onto the hydrogen. But if you just push an electron density into the hydrogen, you would have to generate it as a H. You have to dislodge it as a H minus and that would also be an extremely difficult task. On the other hand, we might be able to remove an electron from the C H bond. In fact, the bonding orbitals are low lying. But nevertheless, we could find an empty orbital, which is hopefully lower in energy than the C H bond itself. But if you remove an electron from the C H bond, the form of that is like a simple sigma bond, then it would be possible to find an empty orbital on the metal that would leave it as C H plus dot and it will ionize very readily as H plus. This in fact is a favorable situation and it might be quite feasible. But on the other hand, because the C H bond is ubiquitous, selective functionalization is a major challenge, which has to be countered. So, let us proceed with the outline of today's discussion. We do have some situations where you have both electrophilic substitution and oxidative addition. These are the two major forms by which C H activation occurs. There are a few instances where you do have sigma bond metathesis and one-two addition. Finally, before we close the discussion, we will discuss two important aspects, which is one is the interaction of C H bonds with metal atoms, which have mostly manifested themselves as agnostic interactions. One very recent development, which is an application of C H bond activation, which seems to be very promising. Now, each one of these interesting applications are color coded here in this outline and they will continue to be color coded in the presentation as well. So, let us take up electrophilic substitution. In fact, it is interesting to know that as early as 1966, Shilov in Russia published a paper in a Russian journal in the Russian language, which made it reasonably inaccessible to most of the chemists, because at that time Russia was behind the iron curtain. It was not obvious to many that this very interesting paper on the direct activation of methane had been accomplished and that was accomplished by a simple platinum catalyst, which was a platinum 2, platinum in the platinum 2 oxidation state and it was an exchange of hydrogen for deuterium. This paper triggered a lot of attention later on when it became accessible to many people in the west. Around about a few years later, little later, Shilov himself published a second more significant paper, in which he clearly showed that a platinum 4 species, a platinum 4 species could be used in a stoichiometric fashion to activate methane to give either methanol or methyl chloride depending on the concentration of the chloride ion in the medium. Now, this reaction although it is not extremely useful, because you have to use a stoichiometric amount of platinum 4, platinum 2 is only a catalyst. In spite of this, it turns out that this paves the way for understanding electrophilic aromatic substitution, electrophilic substitution. So, this was published only in 1972, about 6 years after the 1966 paper. The mechanism of this reaction was solved much, much later by workers in the west, but it is interesting to see what is the scheme of things that is going on in this interesting reaction. Platinum 2, we can ignore the ligands which are fairly labile. Platinum 2 can react with this alkane. Apparently, it interacts with the alkane in such a way that you now form a platinum carbon bond. Now, in this case, if methane is involved, R equals CH 3. So, you form a platinum metal bond and release a proton into the medium. Now, these reactions are usually carried out in highly protic solvents and in acidic media. So, the release of this proton is then followed by an oxidation of this platinum metal complex by platinum 4. This step is the stoichiometric reaction. This is a stoichiometric step whereas, the platinum 2 that was used in this reaction is completely regenerated at the end of the cycle. So, the platinum 4 oxidizes this platinum 2 species in what might be considered as a inner sphere to electron transfer. So, two electrons are transferred from the platinum 2 to the platinum 4 and at the same time, a ligand which is an X group, which is usually an anionic group is transferred from the platinum 4 to the platinum 2 species. That we have indicated by this X group here. Initially, the X was present on the platinum 4 species. It has now been transferred to the platinum 2 species and along with that, two electrons have been transferred in an inner sphere way. This results in a platinum 4 complex, which has got an X group and an R group. So, we can now do a reductive elimination from this platinum 4 species by eliminating R X. Now, in case the X is OH and there is not enough chloride and concentration, you would end up eliminating R OH. Otherwise, you would get RCl as the product. This regenerates the platinum 2 complex and so, the catalytic cycle can continue. Now, what you have seen here is a case of electrophilic activation of the CH bond in methane because you have removed an electron from the methane and released the hydrogen as H plus. So, it was this reaction although it was very important. It could not be reproduced by any other catalyst. It was only in 1998 that alternative system was discovered by this company catalytica, which showed that if you have a ligand which on platinum, a nitrogen based ligand on platinum. You could in fact carry out this reaction with extremely high selectivity and that is methane sulfonic acid could be generated with as high as 72 percent conversion efficiency and the oxidant was in fact, sulfuric acid. So, this turns out to be catalytic in platinum and so, it is an extremely important discovery. Platinum is still expensive, but you could recover it at the end of the reaction and so, this turns out to be a valuable contribution. Now, methane is in fact, one of the most inert compounds and if you can activate it and convert it to methane sulfonic acid with such high conversion efficiencies, it is a valuable contribution indeed. You could do this reaction with palladium 2 and that was shown by Rohr Periana in 2003. Unfortunately, palladium is not as efficient as platinum and the reaction only proceeds with 10 percent conversion, but 90 percent of this 10 percent. So, that means a total of 9 percent of the product turns out to be only acetic acid and there are no other side products in this whole reaction. So, conversion of the remaining amount is remaining 90 percent of the methane is recovered unreacted, but it can be recycled in the industrial setup. So, both palladium 2 and platinum 2 have been shown to be very useful as catalysts for activating methane. Now, let us take a look at the key features of this electrophilic substitution. The key feature I feel is the formation of the metal carbon bond. The metal carbon bond is formed in the very first step and release of H plus is the most important and key step in this whole process. In the second step of course, you need an oxidant. The oxidant can could be charged or it could be neutral, but nevertheless it has to remove two electrons and probably provide the X minus group. So, that R X is generated at the end of the reaction. Now, you usually can you can usually do this only with platinum, but there are a few instances where other heavy transition elements are capable of carrying out this reaction. The medium has to be a very polar and ionic medium. Usually, there is an anhydrous or strong acid that is present as well. Now, there is this example that I have shown for you in a box here, which suggests that CH activation can in fact be easier than OH activation. The reaction that you see is an example of a intermolecular CH activation, but interestingly you proceed only from the left to right, which indicates that the CH bond is activated better than the OH bond. If you proceed from right to left, you would have to activate the OH bond. Now, there are a few other examples where this is indeed been shown to hold water. You do have activation of CH bonds in the presence of OH bonds, but nevertheless this is a good way which or a good example which tells us that CH bond activation is difficult, but nevertheless it is not impossible. Now, let us proceed to the next way of CH bond activation and this deals with oxidative addition of the CH bond. Probably the first example of CH activation by oxidative addition was carried out close to Shilov's work as early as 1965. This was done by chat and he reported the generation of a ruthenium zero complex, which underwent CH activation. Interestingly the initial observation was in fact the case where the ligand was oxidized by or oxidatively added to the ruthenium zero. So, here is the ruthenium complex, ruthenium zero complex, which has got four phosphorous atoms ligated to it and it carries out activation of the CH bond of another ligand present in the adjacent molecule. So, you have a CH 3 group becoming a CH 3 group which is present on the metal. The methyl group which is present on the metal one of the methyl groups here is one methyl group. The second methyl group which is present here has oxidatively added and forms a CH 2 H group on the ruthenium. Similarly, the other phosphorous atom which has got two methyl groups one of them forms a CH 2 group and a hydrogen. So, you have a mutual oxidation of the ligand of the adjacent metal complex. Now, if you do not have, if you have the option of an SV 2 CH bond, then the molecule seems to prefer the SV 2 carbon and it can do this in intermolecular fashion. For this time of a molecule that is available in the solution and it oxidatively adds the CH bond which is present on the ring. So, this is a hydrogen which has been oxidatively added, but nevertheless this turns out to be the first example of a CH bond being activated in an intermolecular fashion and the generation of the low oxidation state metal atom seems to be the key requirement for doing or carrying out such an oxidative addition. Now, around about the same time or about 4 or 5 years later, it was discovered by M L H Green who is another pioneer and important contributor in the area of CH bond interactions. He found that if you took this tungsten dihydride, this is a tungsten tungsto scene which has got a two hydrogens attached to it. If you photolyse it in a benzene solution, then you would lose these two hydrogens as H 2 and that gives you a very reactive tungsto scene. Now, this in fact is a co-ordinatively unsaturated molecule and it reacts with the solvent and forms carries out oxidative addition of the CH bond and this was discovered in 1970. Now, going on further, there were other examples which were accessible, but these are mostly reactions that have been carried out in a intramolecular fashion. The ease with which an intramolecular CH activation can take place is in fact tremendously higher. They are much more common than intermolecular CH bond activations. So, here is an example of a CH bond activation which happens with P P H 3 which is extremely commonly and one of the hydrogens of the phenyl group which is there on the phosphorous. Phosphorous has got three phenyl groups and one of the phenyl groups, the hydrogen in that phenyl group has been oxidatively added in order to generate this molecule. So, this was discovered along with this happens along with dissociation of one of the P P H 3 units, but there was another example where white sides found out that you can eliminate a molecule of C Me 4 tetramethyl methane and that can be done by abstraction of a hydrogen from methyl group which is present here. This is a methyl group and so one of the hydrogens on the methyl group can be abstracted and this CH 2 which is present here can abstract this hydrogen and you would end up with C Me 4 as a molecule that would be extruded and you form a cyclic molecule. So, these are intramolecular fashion oxidative additions. So, this is quite common. So, when people observed this oxidative addition on a tungsten 0 species, it was in fact a special observation and so was this observation by chat in 1965. So, Bergman was the first one to thoroughly study this intermolecular CH activation and he did this using isotopic substitution techniques and he did a extremely thorough job which allowed one to understand how these reactions are proceeding. So, here is an example where cyclohexane has been used as a solvent and the same technique of photolysis has been used and cyclohexane has been activated which is also one of the more unreactive molecules that are available in the organic milieu. So, this was done in 1982 and the same system or a similar system was taken by him and it was shown that the intermediacy of an ethylene was not there and in fact it was completely an intramolecular reaction that was going on. What he did was he took ethane and now one of the hydrogens of the ethane was activated to you know oxidatively added to the eridium 1 species and it forms the eridium 3 compound. So, this is the eridium 3 compound that is formed as a result of oxidative addition and after it forms the oxidative addition he showed that the deuterium atoms do not scramble between the two carbons. So, you always end up with CD 3 CH 3 if you start with CD 3 CH 3 you do not get CD 2 H CH 2 D in the end of the reaction. So, this would be possible only if the cycle stuck to this particular reaction cycle which I have indicated when it oxidatively adds a deuterium when it oxidatively adds a deuterium it the interaction is confined to that carbon it goes back to this same carbon as a result of reductive elimination. So, this was shown by Periana and Bergman in 1986. So, there are very few examples in the literature about oxidative addition of 3 D elements. A notable example is the study by L D field in 1986 he showed that you can do this reductive elimination of dihydrogen using a ion complex. He fertilized the same in hexane and he showed that you can have oxidative addition of the paraffin to the ion 0 species which would be generated if you eliminated the two hydrogens which are present. So, the two hydrogens which are present the two hydrogens are here and these two hydrogens are eliminated as H 2 and then you end up with ion 0 species which just like the just like the ruthenium 0 species carries out oxidative addition, but this time it does it with solvent and so you get alkyl hydride as the product. So, this was carried out in 1986 and this was a time and there was a lot of excitement about the possibility and the reality of C H bond activation. So, to summarize oxidative addition the section on oxidative addition just want to show that the metal has to be generated either by a drastic reduction step. You usually use photochemistry or reduction with sodium and that generates a metal complex in a highly electron rich state and this happens with late transition metals and electron rich late transition metal carries out an oxidative addition of the R H bond. It up to now mostly it has been the D 8 group or the platinum group of elements which have been observed for oxidative as being capable of carrying out oxidative addition and here is an example where iridium goes from the plus 1 state to the plus 3 state and or in a this is a example in fact of a situation where you have iridium 3 going to iridium 5, but in general it is iridium 1 going to a iridium 3 complex. So, one other method which has been less commonly observed is a sigma bond metathesis technically or at least in principle one can think of a reaction just like the carbon carbon double bond metathesis where you have a M double bond C reacting with a C double bond C. If one can do that with sigma bonds you could have a transition state where you have a C M C H cyclic 4 membered transition state in which you would end up with an R H bond and an L N R M R bond. Now, this 4 membered transition state is very often referred to as a kite like transition state because you have 4 atoms as if in the corners of the kite. Now, one example of that which has appeared in is with the actinide elements and lanthanides and actinides high oxidation state do not have the possibility of carrying out an oxidative addition step. So, if you want to have a carbon hydrogen bond activation it has to be through some other mechanism either an electrophilic activation or a C H bond metathesis. Now, in this case it has been suggested that this reaction goes through a sigma bond metathesis. In fact, the sigma bond metathesis and the electrophilic activation mechanisms are reasonably close together. So, it would be difficult to distinguish these two, but here is a kite like transition state that we are talking about when you have a carbon ruthenium, a carbon ruthenium, ruthenium carbon hydrogen intermediate which looks like a kite. So, this looks like a kite and that is why it is called a 4 membered sigma, sigma bond metathesis mechanism. Now, you can see that the hydrogen is transferred directly from the carbon to the other carbon which is leaving and the for this slide I have generated a simulated at the transition state for you and you can see that the transition state has got this geometry which I have indicated for you here. The geometry is indicated here and what you have what you see on the slide is the hydrogen shuttling between the benzene ring and the methyl group and the intermediate form as ruthenium hydrogen which is almost within the bonding distance. So, you can calculate the energetics of such a process and it is clear that the interaction of the ruthenium with the methane and with the benzene ring turn out to be low energy forms. So, you have an oxidation you have an intermediate where the hydrogen is transferred directly between the benzene and the methyl group to form the methane complex. So, sigma bond metathesis is in fact one of the possible ways by which you can carry out this reaction. What is different from the electrophilic substitution reaction that we discussed in the beginning is a simple fact that these reactions can be carried out in non polar solvents and you have a direct transfer of this hydrogen. You do not seem to require the highly polar solvents that I use in electrophilic activation, but it is commonly done with high valent transition metal complexes as we saw in the as we saw for the luteatium complex that where we exchange the methyl group. So, at another possibility is a fact that you can have a metathesis reaction between two groups which are unequally bonded. Here is a M double bond X group and if that M double bond X group reacts with an R H this would be similar to the interaction that we observed when we did a metathesis reaction. When we did the metathesis reaction also we had such types of unequal reactions happening and I can add the R H or break the carbon hydrogen bond the carbon hydrogen bond which is present in this case. I could add this across the metal X bond and if you do that you would end up with the two groups adding across the M X bond and this was observed by Berkov for where X is actually nitrogen group and an imine complex reacted with methane to form a zirconium methyl group which is interacting with which is now having a third N H group attached to it or coordinated to the zirconium. So, you have the oxidative addition of a carbon hydrogen bond across the zirconium nitrogen bond. So, you seem to be directly forming the carbon carbon zirconium bond and the hydrogen nitrogen bond in order to generate this particular complex. So, these are extremely rare examples not many of them are known, but nevertheless in the future we can expect these two areas to develop more where you have such types of sigma bond metathesis and metal double bond X groups doing oxidative addition of the carbon hydrogen bond. So, now let us get back to the two common reactions that we observed one was the electrophilic activation the other was the oxidative addition in both instances we are removing an electron or a pair of electrons from the C H bond. So, the metal must be having an empty orbital which is interacting with the C H bond and so you can think of a situation where you have the C H bond shuttling between these two forms before separate carbon hydrogen bonds are formed as in this as shown on the right hand side. So, let us take a look at some of the structures that are being discovered by M L H green where he showed that it is possible to see this interaction of a C H bond with a metal. He described this as a three center two electron interaction the two electrons come from the C H bond and the third center is actually the metal center with zero electrons. So, you end up with a three center two electron interaction where there is an agnostic interaction supposed to be an agnostic interaction between the metal and the C H bond. These covalent interactions between the C H bond and the metal are interesting because they have been structurally characterized and a recent review on this whole interaction is given for you in this slide in coordination chemical reviews. Now, agnostic comes from a term which means to clasp or hold to oneself and the metal is holding ligand close to itself in an agnostic fashion. Many times this is observed only in a intramolecular fashion and so the C H bond is forced to be close to the metal. If this interaction involves not just donation of electron density from the C H bond to the metal empty orbitals as it is shown here. If it involves pumping of electron density into the anti-bonding orbitals of the C H bond you would end up with the oxidative addition and you would end up with the product which will be looking like this. So, this is a spectrum that you would observe. On one hand you would have no interaction between the metal and the C H bond. On the other hand you can have this agnostic interaction between the metal and the C H bond. So, you could have all types of interactions and these are being observed in the literature and we will look at some of these examples. Now, here is an example of a titanium compound which has got an ethyl group and this titanium is in fact in the plus 4 oxidation state and so it is electron deficient. It is electron deficient and it can it can it cannot do an oxidative addition because it does not have 2 extra electrons to pump into the C H sigma star orbital. But on the other hand it can interact with the C H sigma bond in an agnostic fashion and that is what you see here. You find that the bond angle between C C H which is what is listed here will mark it with a different color. So, that you can visualize it easily. Here is the angle that we are talking about C C H that should have been a 109 degrees. What you expect for an sp3 carbon is 109 degrees, but instead what you observe is this very acute angle of 86 degrees. So, that is a significant drop in the bond angle and that is caused by this attractive force that titanium is exerting on this hydrogen. So, one of the hydrogens is bent towards the titanium and not only that the bond distance is remarkably short between the hydrogen and the titanium. It is only about 2.3 angstroms and so this bending is supposed to be rising out of this agnostic interaction. So, the ligands which are relatively small and which would allow for this close approach of the C H bond result in agnostic interactions. Now, you could see a review of this chemistry again by Brukhardt in the proceedings of national academy of sciences in a 2007 article which I have given for you here. Now, alkane C H bonds, alkane C H bonds can coordinate to the metal in a variety of fashion. What we have seen here is the examples that we have seen here are eta 1 type of interaction or eta 2 type of interaction of the C H bond with a metal atom. So, these are the 2 types that we have seen in the previous examples, but it is also possible for 2 hydrogens of this C H methylene group to interact with the metal in the same agnostic fashion. Electron deficient metal accepts electron density from the C H 2 group or even from a C H 3 group. Now, this has been observed for a B H 4 minus group. For example, a B H 4 minus would be analogous to C H 4 and that has been shown to interact with a metal like this in this particular fashion also. So, these type of interactions a weak interaction between an alkane group and the metal reasonably common especially if you look at the crystal structures of these molecules. Now, the other evidences for agnostic interaction are as follows not only can we look at crystal structures, anomalous bond angles and distances. We could also look at time resolved infrared spectroscopy where these intermediates have been noted in the spectrum of molecules generated in a transient way. Anomers spectroscopic studies also show anomalous chemical shifts. The chemical shifts of C H bonds which are interacting with a metal are different from those that do not. And restricted rotation of a methyl group is possible when one of the hydrogens is interacting with a metal. So, finally isotopic labeling studies have also been made all of them point to the fact that they can be weak interaction between the metal and a C H bond. And these interactions are presumably or probably the intermediates which are available for us before the electrophilic substitution is going to happen. Now, can we use C H activation for carrying out any useful reaction? This is in fact a question that would plague you. We have seen several examples where C H activation has happened, but many of these intermediates have been generated at a lot of cost in terms of energy pumped in through light or energy pumped in through a strong reducing agent or for that matter by extreme heating. So, is it possible to use these reactions? And the reason for this difficulty is because we are going thermodynamically uphill. This reaction which I have shown for you here with cyclo octane as an example and a generic metal has undergone oxidative addition in as it has gone from left to right. This is the oxidatively added species where the metal has undergone an oxidation state change of plus 2. So, it is usually true that thermodynamically speaking it is easier for the reaction to go in this direction. In other words energy delta G is negative when you go from left to right rather than from right to left. So, how will we solve this puzzle? How can we utilize this reaction effectively? Similarly, we have seen several hydrogenation reactions activation of dihydrogen was one of the topics that we have covered. And in those cases we have noted that it is possible to go from the right side of this equation to the left side rather easily, but not vice versa. So, if we have to push this reaction from left to right one has to somehow remove this hydrogen from this equation remove this hydrogen from this particular scheme. So, this was done by several workers who found out that if you have a good acceptor for the hydrogen. Now, the good acceptor for hydrogen could be a variety of different ligands, but what they found was tertiary butyl ethylene was a very good acceptor not only does it mop up the hydrogen during the hydrogenation process, but it also it is not a ligand that would poison the catalyst. In these reactions if the ligand which is liberated or ligand which is available if that blocks the coordination site then the reaction will not proceed. So, they found out that tertiary butyl ethylene because of its bulky tertiary butyl group is not a good ligand. And so is capable of taking up the hydrogen and being removed from the reaction as this molecule which have marked with an arrow. So, a catalyst which is capable of carrying out activation of di hydrogen hydrogenation and dehydrogenation is shown here it is a iridium 3 plus catalyst and it carries out hydrogenation of tertiary butyl ethylene provides enough energy and pushes this reaction from left to right. In this particular example that I have shown for you you would need 3 equivalents of tertiary butyl ethylene to give you 3 equivalents of the saturated molecule because you have removed several hydrogens from the cyclopentane which has got converted into the cyclopentadiene molecule which is present on the iridium. So, it was it is to credit of Goldman and Brookhart who have now used this reaction very effectively and the way they have done it is by is as follows. They have carried out what is called an alkane metathesis which involves C H bond activation. Alkanes are paraffins so in essence they are unreactive but if you carry out C H bond activation and convert it to an alkene they become more reactive and in fact they can now carry out a metathesis reaction. After it carries out a metathesis reaction it can be hydrogenated by the same set of catalysts and this amazing reaction was published in science in 2006 and it really is a landmark paper which tells you that C H bond activation has come of age and can now be used in a useful fashion. Now, here is the reaction they took cyclohexane they took hexane they took hexane and converted it into decane and ethane. So, here you have a 6 plus 6 carbon alkane getting converted into a 10 carbon chain and a 2 carbon ethane molecule. So, let us take a look at now at the type of reaction that they are proposing they have carried out. Here is a catalyst which can hydrogenate this tertiary butyl ethylene and ethyl tertiary butyl methane is what you have here and you end up with this molecule which has got no hydrogen which is the reaction active form of the catalyst. This catalyst can remove two hydrogens from another molecule which is a hexane molecule and generate one hexane. It will coordinate to the least sterically hindered carbon and that would be the terminal carbon of the hexane. So, we have a hexane molecule reacting with the iridium center and the iridium center now becomes a iridium 3 center iridium 1 center which is present here. This is the iridium 1 center that becomes the iridium 3 center with abstraction of two hydrogens which have come from the two terminal points of the hexane. So, you have generated an unsaturated form of the hexane, one hexane generated one hexane and the dihydridocomplex. Now, let us see how we can utilize this hexane in a reaction that would allow us to carry out some interesting chemistry. The Goldman and Brookhardt did a metathesis reaction now with the hexane one hexane. So, you would end up with combining these two carbons together and generating ethylene and if these two carbons come together you would form the decane. So, that is a 10 carbon alkene which has got the carbon double bond carbon in the center of the molecule. Now, let us carry out the same reaction which is the dihydride addition of the dihydride to this alkene. So, that will give us the saturated variety of the C 2 H 4. So, the ethylene would get converted to ethane and the decane would get converted to the decane. So, here you have converted the molecule which was a simple C C C. So, C 6 H 14 you took the C 6 H 14 and converted into a decane and ethane by combining two different catalysts. One catalyst which will do C H bond activation and another catalyst which would do the metathesis reaction. Now, not all catalysts are capable of being combined together like this. Very often when you do tandem catalysis as this is called tandem catalysis results in complications because the reactants or the intermediates would sometimes poison one of the catalysts or the two catalysts themselves would interact with one another and cause complications. So, this is an unique example and if you read the paper you will realize that they had to try out many different catalysts, metathesis catalysts before they could arrive at a successful combination of ligands for the alkane metathesis, alkane dehydrogenation and for the Schrocks metathesis reaction. So, let us proceed further now and here I have shown for you what happens when you have this metathesis, alkane metathesis carried out with the Schrocks metathesis catalyst which is at 16 millimoles and a total of 7.6 in this example about 7 moles of hexane were used and this reaction mixture was used in the fact cooked together at 125 degrees in a sealed tube. What they have shown is that after 6 hours of reaction you get close to 123 or close to 0.75 moles that is about 10 percent reaction at the end of the reaction at the end of 6 hours and at the end of 4 days you get only 1.6 moles of the product which means about 5 percent of the reactants have been converted after 4 days. So, this is in fact a very slow catalytic process, you are not having a fast catalysis as a result of this 2 reactions and at the same time another fact is that you have to carry it out at higher temperature in a batch process and also notice that you do not get just decane that is decane is one of the products. You get a variety of alkenes and alkenes in the reaction mixture and this is this is this table gives you a combination of all the alkenes and alkenes that have been formed as a result of this reaction and you also have C 3 products being formed because you have ethane, ethene reacting with other molecules and so you end up with a very complex mixture of products is not necessarily extremely useful chemistry, but nevertheless it is illustrated a key principle that C H bond activation can be used in a very useful fashion for carrying out reactions with paraffins. So, what we have seen today is a fact that electrophilic substitution reactions, electrophilic substitution reactions can be used with alkenes and you need a metal in a high oxidation state the metal has to be in a very high oxidation state. So, we will indicate that with the plus plus metal has to be in the high oxidation state and usually it generates H plus. So, you have a reaction medium which is very polar which will allow for the stabilization of H plus usually it is water and it is an acidic medium that is present. You can also have on the other hand with a low oxidation state metal. So, the low oxidation state metals are can be denoted with M 0 and that can also end up with an oxidation of metal to M 2, M H and M C bonds where oxidative addition of the C H bond can be this is also been observed fairly readily. So, these two are two examples of C H bond activation which is commonly observed the intermolecular variety is very common, but intramolecular species have also been observed in recent times. What is less common though is a fact that you can have sigma bond metathesis. Although the result is the conversion of 1 M R bond is converted into by reacting with an R dash H it gets converted into a M R dashed with with an R H being released. This hydrogen has coming from the reactant that was added into the reaction mixture. A direct transfer of a hydrogen has happened. This is less common although it is been observed in several systems now, but these are again carried out with electrophilic metals where you cannot carry out oxidative additions. The last example the 1 2 addition is again an example which is less common not as common as the electrophilic substitution or activation or the oxidative addition, but 1 2 additions are being observed with M double bond X systems. M double bond X systems where the C and H add on to M C and X H usually the X group is basic. So, it is like a system where you have an external base, you have an internal base in this case which interacts with the proton and mops up the proton that is being liberated. So, in all these cases you the reaction could be preceded by agostic interactions. These agostic interactions are systems where you have a small or weak interaction between the hydrogen C H bond and the metal atom. If you want to have an agostic interaction you would have to have metal in if you want to observe the agostic interaction you should have the metal in a high oxidation state where it is co-ordinatively unsaturated. Finally, conclude with a positive note that there are possible applications of the C H bond. The C H bond can be productively used for doing for example, a metathesis reaction as illustrated by Goldman and his group.