 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been talking about olefin polymerization and in this context we have covered a lot of grounds particularly with respect to homopolymerization. We started off with ethylene homopolymerization using Ziegler-Natta system as also moved on to propylene homopolymerization with the Ziegler-Natta system then to metallocene system then we had seen advent of MAO and boron based reagents metallocene catalyst which were extremely active for ethylene as well as propylene homopolymerization. We had also observed how the stereo specificity of the polypropylene polymerization could be controlled using a variety of metallocene catalyst and then subsequently in the last few lectures we have moved into copolymerization reactions of these olefins and to this extent we have looked into copolymerization of two different kinds of olefins for example diolefins one can be ethylene the other can be alpha olefin as well as we have also looked into copolymerizations of cyclic olefins which could also be used so in this context we have spoken about one type of cyclic olefins which were obtained in the previous class which was obtained using two reactions one is Diels-Alder reaction followed by copolymerization of the cyclic olefin. So, let me just focus on what we had finished in our previous class and then we have moved into the other routes of making this kind of polyolefin polymers. They can be formed by two ways by two methods and these are really a very interesting method. The one we had discussed in the last class involves two reactions this is method one or metallocene catalyst and that could give this polymer of this type. So, we had seen how these polymers are important for magnetic applications and we are going to now take a look at the other pathway using zirconium catalyst the second pathway uses zirconium X2 MAO catalyst and the reaction is shown over here it already has a polymer chain building on it and then this olefin comes the first is the insertion of this olefin on the metal polymer chain length and then that gives this inserted product now then what happens is the first this is called intermolecular insertion and now intermolecular insertion would happen now this will now insert in this bond to give this product and subsequently this insertion would follow through so there are two types of insertions and that would give rise to various kinds of products possible products which are shown here it can be this where the stereochemistry can be a meso within the ring or resmic m m capital M or small m for meso r and smaller for resmic like this so this is a cis isotactic the other possibility can be like this as where it can be r r r r so this is trans isotactic similarly it can be m r m r m this is cis symbiotactic cis symbiotactic and the last can be and this can be r m r m r and this is called trans symbiotactic so these insertion can happen in four ways as is shown over here and these are two types of insertion as has been mentioned in this so one is intermolecular intermolecular the other is intermolecular and these gives optically active polycyclic olefins and the best one which is produced by this method exclusively is trans isotactic so this is the one which is exclusively produced this is the trans isotactic so this is an interesting result we had seen that there are two ways in which polycyclic olefins one can be through copolymerization by dill solder and then using the vanadium catalyst the other can be using a non conjugated diene and doing intermolecular and intermolecular catalyst with chiral answer breached zirconium zirconocene catalyst so that exclusively he gave the trans isotactic products so apart from this there are several efforts were made in trying to diversify the metal learning this regard the emphasis were developed on generating non group 4 catalyst and in these regards the several metals were looked into but what emerged out are these lanthanum lanthanum dcn lanthanum derivatives are called lanthanum dosine and other and other metals other transition metals like iron cobalt nickel and palladium became of interest now so when the quest for other types of metals since were developed then this lanthanum based the catalyst as well as other transition metals like iron cobalt nickel became of interest so developing so begin to focus right now on the first part which is this lanthanum based metallosine catalyst and the question was although there was a nice work by Watson who sort of developed Watson reported reported cp star 2 alium methyl complex for ethylene polymerization so but this is an interesting complex if there is the cp star complex of the the complex could take ethylene and like you know polymerize it fast fast polymerization to give cp star so it could successfully polymerize ethylene very fast but the interesting thing is that it could only do one insertion single insertion with propylene so with propylene it could first give this alkyl complex and then the second ethylene of insertion was surprisingly very slow to give slow complex of this type so and beyond this it did not proceed and then this is a very unusual behavior in terms of the earlier observation that only one ethylene insertion and could take place and the reaction did not proceed so and then the thing which was contrasting is that corresponding metallosine complexes for zirconium could allow several insertion of propylene to give the product and this was finally explained by Ziegler using DFT calculations which sort of said that coordination in the neutral alkene zirconicin cationic zirconicin complex is more favorable for further reaction than in the neutral lanthanium species so this is explained by Ziegler by DFT calculations and DFT showed the isoelectronic species are structurally different that is for lanthanium it is a neutral compound whereas for zirconium there is a approach of olefin that could bite for zirconium because of this cationic nature there is a free site where it could bind favours alkene binding and these for the lanthanium series because it is the isoelectronic species neutral in nature so they are less favorable to alphan binding and favours dimerization favours dimerization with formation of mu R species so there is a fundamental difference between the lanthanium complex as well as the zirconium catalyst which could polymerize with olefin and the reason was finally answered by DFT which sort of showed that this is a neutral complex this is a neutral and this is cationic and being cationic it favours olefin binding whereas this neutral these does not favour olefin burning to a great extent on the other hand there is a decomposition of the catalyst through formation of R alkyl bridges is observed in cases of lanthanium so these was a great difference between the lanthanium lanthanocene chemistry as well as the transient metal zirconium chemistry in case of lanthanocene alkyl compound sigma bond metathesis is also observed another interesting reactivity of lanthanocene catalyst is in case of lanthanodocene alkyl compound instead of polymerization sigma bond metathesis reactions were reported this and of the first in this is the insertion into the alkyl bond as is shown to give to give the corresponding species that in presence of another propylene gave this sigma bond metathesis reaction to give the compound which is this and for yttrium also plays a role and then several metals of this type for example scanrion yttrium lanthanum complexes are also reported to exhibit this polymerization activity however however these catalysts to find practical utility however this complex is yet to find practical utility now these are starkingly different in terms of behavior with respect to the early transition metal zirconium catalyst and the main thing what we had seen that though they may be able to polymerize ethylene these cannot undergo subsequent propylene insertion and in some cases only one insertion of propylene could be obtained and in other cases even that is not observed just after first insertion the second insertion does not happen and just sigma bond metathesis reaction takes place so with this we come to the end of lanthanum chemistry for designing polypropylene catalyst as a part of these non-group for transition metals non-group for metals for polymerization purpose and now we move on to the effort that that describes other non-group for metallocene catalyst and they involve other transition metals for example iron nickel cobalt palladium so on and so forth now the story is sort of first focuses on iron by a catalyst given by gibson brookard and gibson they are fantastic catalyst and then the focus is sort of from lanthanum shifts to iron of polymerization and these are like a very important catalyst is given by where R is a bulky group is equal to isopropyl or bulky group that these with MO and MO greater than 300 equivalents and in ethylene when R equals methyl this is R and R dashed two different substituents this is R dashed R equals methyl R dashed equals hydrogen it could give oligomers alpha olefins c 10 to c 20 and when R equals R dashed equals methyl then it could give H high density HDP high density poly ethylene high density poly ethylene and this is activities the important thing is the activity of is very similar to the activity is comparable to most active Ziegler not catalyst so this is a important discovery in the sense that the iron right now can be used to produce oligomers as well as ethyliens high density poly ethylene of extremely high activity so with this we come to the end of today's discussion where we have looked in to development of non-group for metal based catalyst for olefin polymerization and now we have seen that how the landscape changed on going from lanthanum to iron so more of these non-group for transition metal catalyst as we take up the discussion in the next class in which we will move beyond iron and see other metals like nickel cobalt so on and so forth being present for these developing polyolefin polymers so with this I again thank you for being with me in this class and I look forward to being with you in the next class where we take up this non-group for transition metals in more details thank you