 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been talking about non-group for metal based olefin polymerization catalyst. This is indeed a very interesting area that we have been focusing upon and to say the list that this started actually the whole field of olefin polymerization catalysis actually originated from our non-group for metal based phenomenon and this is what is the famous nickel effect that led to identification of group 4 metal based transition metal complexes which are extremely active for olefin catalysis and then subsequently search in areas which are beyond group 4 transition metals they eventually took place and in that context we have spoken about the lanthanum transition metal complexes also we have spoken about iron and then in the last lecture we had seen how palladium took the center stage first nickel and then palladium for nickel the story has been that it has been like coming to a full circle because it is the nickel effect which had indeed led to the start of these polymerization of olefins and then later on it is the brookert we who had developed catalyst which was sort of useful for olefin polymerization. So let me just run it down so we started with nickel in so called nickel effect led to titanium Ziegler natta which led to zirconium as well as titanium metallocene catalyst this was heterogeneous and these were homogeneous that that led to lanthanum metallocene again homogeneous now this is a non group for metal then we went to iron and this was non Cp non Cp ligand and then finally from iron with brookert we went back to nickel which was this famous nickel catalyst that of this type of the ligands which are used are and they mainly are of this type the catalyst represented are or bromides now with the nickel this could produce a long chain linear polymer as well as oligomers depending on the substituents of the the nickel followed by the work by Bazan which we had discussed about in the tandem catalysis where they could produce a ethylene 1-butene copolymer using a single monomer so now there is another interesting discovery which sort of change the field in a dramatic way is that when this metal when the metal bound to this ligand when the metal bound to this ligand is changed from nickel to palladium then there is a startling discovery and the startling discovery is that when this metal is a palladium then one can do polymerization of olefin with functional comonomers so this is a really and very interesting discovery because only things with functional group sort of poisons the catalyst and such kind of copolymerization with olefin with functional monomer absolutely was a real tough challenge at that point of time and this was overcome by substituting nickel which happily did ethylene polymerization or ethylene alpha olefin copolymerization with palladium that sort of could carry out ethylene polymerization with polar functional monomers so this is a very interesting story it was again developed by Brookhart in the JSCS 1988 paper the request the interested students to look this reference up and the copolymerization was shown over here olefin plus vinyl monomers functionalized monomers in presence of the catalyst of this type palladium methyl OET plus and PAR for minus a non coordinating anion in dichromethane 1 to 6 bar pressure 30 degree centigrade almost room temperature reaction could give this much wanted CH CH 2 X OR CH 2 Y CH CH 2 W CH 3 CH 2 Z N so this is amorphous highly branched product with polar ester groups polar ester side groups so this is a very interesting discovery which could copolymerize and that there is a polar functional side group now present on the polymer backbone so this was sort of the breakthrough first provided by Brookhart in being able to carrying out polymerization of polar functional monomer with olefin subsequent that there were other groups like Grubbs and so on and so forth could report some other complexes as well as Bazan report other complexes that could successfully carry out such a polar polymerization now moving on there was another focus was on obtaining being able to actually polymerize ethylene and carbon monoxide CO copolymerization it is important to note that C2H4 homopolymerization is possible however CO homopolymerization is not possible and these would result this polymerization would result in poly ketones which which have very important polymer properties are important for their polymeric properties now for being able to carry out this ethylene CO copolymerization the first report was given by a repi in 1952 who sort of had observed that one if one takes alpha olefin and carbon monoxide in presence of catalyst then one could get a poly ketone poly 3 oxo trimethylene the in presence of a catalyst like a2 ni cn 4 in some product so one could see its formation and that was first reported by repi in 1952 the first breakthrough was however reported by drent about more than 30 years later in 1996 when using a catalyst he could polymerize ethylene and CO using a phosphine based catalyst in HOTS methanol 65 degree centigrade 40 bar pressure he could make poly ketone molecular weight 400 000 Tm equals to 60 degree centigrade and this is a thermoplastic material so the breakthrough actually in being able to make poly ketone successfully in being able to polymerizing came much later in 1996 as a report from drent now there are two aspects to it the first observation was however made by repi in 1952 now there are two aspects to it one is that the alternating addition of CO as well as ethylene to give poly ketone and there were no this poly ketone polymer showed that it was really indeed a alternating polymer where both the groups were inserting one after another and that is what which was confusing because though CO homopolymerization is not known but ethylene homopolymerization is quite known so there were chances that one may see two three ethylene insertion followed by one CO but to everybody's surprise what was found that the polymer really had one is to one incorporation of ethylene and CO which said that it is indeed an alternating insertion of CO and ethylene now based on the catalyst and the proposed mechanism and doing the end group analysis of a polymer so actually this is a very powerful method of finding out the insight about the polymer mechanism is by looking at the end groups which are present in the polymer and what they showed that there were two end groups one is carbonyl compound another is ester compounds and the fact that the two end groups are provided obtained in nearly equal amounts which sort of said that both the polymerization were happening in equal way so this is illustrated by this nice example of the mechanism shown over here so for example the catalyst which is in short is written by PP a palladium acetate or maybe I will draw it nicely this catalyst would give a catalyst precursor which is drawn by losing to acetate the catalyst precursor so now there are two pathways one I am showing in green so it can add CO to give PD CO 2 plus and that can take methanol add methanol giving out H plus and resulting in the compound PD PD CO plus and then once this is formed this can subsequently undergo various coordination insertion of ethylene and CO to give a polymer PD with the polymer with the end group being a ketone so alternating ester end group in polymer whereas the other possibility it might as well be it first takes methanol and gives out H plus to give P CO CH 3 plus and that can eliminate aldehyde CH 2 O giving palladium hydride which again can do CO ethylene polymer to give a polymer which has a ketone end group so alternating ketone end group now this species again can react with CO to give the ester so now the glimpse of the mechanism can be obtained by the fact that one can get a alternating polymer with ketone end group or one can get an alternating polymer with ester end group depending on how in what sequence it reacts with the solvent and these also throws inside as to mechanism of this polymerization reaction and the chain propagation happens through alternating insertion step as it shown over here giving CO now this CO comes and enters over here to give the product to give the product which then binds to an olefin now once the CO has inserted the olefin would also insert over here then the corresponding the inserted product would be again to this another molecule of CO will come which will come and inside over there to give the corresponding CO inserted product and that subsequently will result in poly three oxo cry methylene polymer so these are poly ketones now what is interesting about here is the fact that both CO and ethylene they are undergoing insertion alternatively so for example here here so it is sequential alternating insertion which is happening now to sort of have an insight on this one has to consider the following for example there are chances that instead of having this alternative insertion there can be chances that double insertion of carbonyl can happen to insertion of carbonyl now double insertion of carbonyl is an uphill an impossible task so that is discounted double insertion of CO is an uphill task and hence discounted that means that CO homopolymerization does not happen and it is discounted and hence is not considered so then what is one left with is our homopolymerization of ethylene or alternating polymerization of ethylene propylene now homopolymerization of ethylene is energetically favored so has to be considered or taken into account and the finally the mechanism of this has been illustrated elucidated by brookhardt very elegant example mechanistic study in 2000 which sort of explained provided evidence in favor of this alternative insertion of palladium so what brookhardt did was he showed that this catalyst is present in two forms for example this is the polymer chain where ethylene is coordinated so when that is formed it has two possibilities one is that it can insert to this or the ones maybe I illustrated this with thing one possibility will that this will undergo insertion and what is the this is possibility number one and the other possibility is that this coordinates may be replaced by a carbonyl which is as more stronger binding so this is possibility number two so if carbonyl displaces ethylene which is more fast then and this is a very fast reaction and k a k equilibrium is about 10 to the power 4 10,000 time faster then it produces this palladium co coordinated compound plus ethylene and this co and now then co can insert into this olefinic bond co can insert into this olefinic bond to give the alternate co polymerization as shown over here and the other thing can be a double insertion as we said that this possibility number one where this can insert into this then the double inserted product can also be pd co this is pd plus so what we find over here is that two insertions of olefinic unit has happened one is this another is this now this and this let us say is given by k one dash so the ratio of k one by k one dash is approximately a 10 to the power 200 so overall as let me summarize as this is bigger much greater than this as well as this equilibrium constant is 10 to the power 4 times in favor of this so it is what we see is favored the alternating insertion of ethylene with poly ethylene is what is favored so with these we come to the end of the catalyst development story the non group for the metals and let me just summarize the overall findings of this work which has been discussed so far so there are actually two types of metals first is the early transition metal and we had also this is how we started the story with and then we had seen that the central metal atom metal atom for these early transition metals usually are usually are titanium for zirconium for half-mayan for lanthanum 3 then the ligands which are used for these ligands in pre catalyst usually had been cp-halides counter anion for these case the counter anion had been non coordinating coordination geometry coordination is pseudo octahedral active site is of this geometry and functional group tolerance tolerance and in this case absolutely none and what we saw that as we evolved from early transition metal to something of late transition metal in the course of catalyst development what was found that the metals which really did well are iron 2 then nickel 2 and palladium 2 actually they sort of did the trick whatever was complementary or challenge for these early transition metal they were made by the late transition metal the ligand used by diphos these are non cp type ligands diamine or halide x-type of ligand counter anion however is the same weekly or non coordinating counter anion in terms of active site active site is almost similar what we had seen coordination geometry is probably I will write that first coordination geometry is pseudo square planar mostly a mostly square planar and that is inconsistent with d8 configuration of nickel and palladium and the active site is shown over here there is the vacant site and functional group tolerance yes that is a big yes for late transition metal that they are indeed functional group tolerant so here is the summary which brings out the comparison between the early transition metal and the late transition metal and what sort of differentiates between the two is this functional group tolerance and that sort of helps this late transition metal to carry out copolymerization of ethylene with polar functional monomers so with these we come to the conclusion of today's lecture and hereby in this lecture we complete our discussion on the transition metals in catalysis aspect of this course where we have seen a lot of important industrial large scale processes that are carried out by organometallic catalyst right from repeated synthesis metathesis polymerization so on and so forth and then we move on to another very interesting aspect of organometallic chemistry that is bio organometallics or the applications of organometallic chemistry in biology this aspect actually is still in the developmental stage and we have a few very exciting developments to talk about in the context of applications of organometallic chemistry when we meet next and I once again thank you for being with me in this throughout this course particularly I enjoyed a lot of talking about various important processes of organometallic chemistry kind of showcasing the prowess of organometallic chemistry and the features of organometallic chemistry and we move on to the other aspect of organometallic chemistry particularly a bio organometallic chemistry so with this once again I thank you and I look forward to take up the bio organometallic chemistry in details when we meet next till then goodbye and thank you