Lecture 10

[Music] okay uh welcome to the class the uh in the last class I told you that these uh molecules or cryptons there are two aspects of their synthesis one is is called uh strategy and the other is methodology right one is strategy and the other is methodology and I discussed about there are four strategies you know of synthesizing these molecules starting from noncyclic starting materials so about the methodology two aspects about the methodology I will tell you the first is first is template method template method template method okay this is the first method I will describe and I will tell you in terms of a story okay we wanted to make this uh I said that we introduced first the tripodal coupling that is tripod and two tripods will come okay so now why they will come we have to put a template so that the template will bind template because they are far apart so if I put a template if I put a template maybe I will write the if I put a template all right if I put a template I'm writing template as a metal ion so I'm writing like this this is my template fine so if I put a template then both of them will come together both these tripods template will bring them together so template will come here and they will react when they're closed they will react and I will get I will get the desired cryptand so this was the idea so with this idea we made this starting material can be made I'm not telling you how to make it and all that these are available in books and all that but suppose we it's not very difficult to make okay this compound is available in the market alri sells it and so many other companies sells it nh2 okay and this is called T2 Amino ethy Amine in short it is called train and the other one that we made was like this okay I will write here only it'll be easy for me to write is easy for me to write where is it yeah that's why one 2 3 three 1 2 three oxygen and this and then C H [Music] O CH O and C H O Okay this triehy we call it Tri alide so now why they will meet they will M because I will use a metal ion as template followed so metalion has template I we expected that this will come like this like this and then it will come let me draw like this and then amine and aldhy will combine to form a c base they will form a c base double bond double bond then okay and here also it's not I lost it maybe on this side I'll will put it'll be easier so it will form a SE base like that and then upon reduction it will form the upon reduction what will happen I will make this part ular compound NH H and H no it is immediately I made mistake and the third one is also let me finish it with with cartoon so this was our idea so for 2 years we struggled with usually people take when they take template they usually people take uh transition metal ions so he used to take all first row transition metal ions second row transition metal ions and try this reaction and this reaction never got success then suddenly one bright morning we decided to start using alkaly metal and precisely we tried with cesium chloride cesium chloride has some solubility in methanol large quantity of methanol we took and we put cesium chloride and it worked very well we got 40% yield why was that that is you have to know this reaction c h o okay and then nh2 then R say R Prime if they react how they react with aldhy they react like this typical reaction that it will go there and then the lone pair will attack the carbon to form the IM form the IM from the Amin I will get amine and then I will get a stable cryptand so that means it depends upon the availability of the lone pair on nitrogen for the reaction to go forward Ward the reaction did not go forward why because we took always a transition metal ion and a transition metal ion binds with this Prim these Amin pretty well that means binds pretty well it binds that means the lone pair is not available further for for attacking this car this carbonal carbon so reaction did not go therefore when we took alkal metal ions it it binds this both oxygen and nitrogen but very weakly but what it does it brings the two part one part and second part two parts together like this so cium will bring cium plus will bring them and it will go very nicely to imin from imin it will go to Amin and we got our product okay almost 40% yield which was tremendous so since then it is very when you use template all the story was is to tra is to tell you that when you use template you and especially metal ion as a template you should be very very careful which metalon you are taking and what reaction you desire so with that idea with that idea your choice of template should be very very good so that the reaction go pretty well under the in presence of that metal ion so with transition metal this does not work at all but with alkal metal ion it works perfect and we get the Krypton in about 40% yield that can be crystallized as a bright colorless crystals like sugar cubes you have taken this you have seen sugar okay big big uh yeah particle sugar single crystals so here also you get single crystals and we did the X-ray structure of that so that is template method so just remember when you use template method we must use choose a metal ion properly after that high dilution method after template there is another method called high dilution method if you if you high dilution method High dilution method as I told you earlier also when we discussed synthesis of macrocycles high dilution means the intermediate has enough residence time in the mixture so that it can undergo intra desired intr molecular condensation okay intr molecular not intermolecular so to make intr molecular we have to take High dilution and high dilution as I told you I earlier during uh macrocyclic uh synthesis macrocycle synthesis that high dilution means it will go for go for days sometimes more than one week it will go so those things you have to remember after that another new method so this is second method High dilution and we very cleverly made this High dilution how I am going to tell right now what happens is this Tri alide that I told you that I have written here that triehy I am doing cartoon now because otherwise it will take a long time this this Tri alide is not that much soluble in methanol espcially at room temperature okay so when we take it in the solution phase then my meth then concentration of this trial is very small and then from Top we put this train we put train dropwise a dilute solution of train drop wise that means what you have in solution you have very small amount of this trial deide and we put a very dilute solution of amine from Top drop that to drop wise and that not as slow as high dilution technique but here we generate the situation of a high dilution by playing with Sol with solubility so here we do that and drop wise will it falls and then we can get a very good yield of this product this can be done then without using a template while we are playing with this then one group from uh us they show that they show they made this compound I'm showing you nh2 train then glyoxal this is glyoxal is better to use cartoons we can easily illustrate so they took glyoxal dropwise falling glyoxal in methanolic solution and we have a trend whole thing their temperature we there is no they did not do it at room temperature but they did keeping the temperature around 5° C okay so you can easily keep this at 5° cius without using without using any templating ion and you see that there are 12 inter 12 points at 12 reactions will go on the same time 1 2 3 4 5 6 and then uh six means there are 12 units they have to bind like this so at 5° C they got a very high yield so there is another method that is low temperature method and why it worked I will tell you now low temperature method so low temperature in low temperature method what happens this amine this amine let me put suppose this I'm talking care of this amine uh this amine at room temperature if you put in a solution this amine is playing all these three arms but you lower the temperature degrees of freedom of movement of this three will be drastically reduced if you put the temperature at low at 5° around then this amine will not roam around but they will be they they will still roam around but they will be almost fixed in one position because the temperature is so low they low they will not fix there room temperature they are doing this but when the temperature is low they will be like this and that's why two are coming this way and the glyoxal is linear so it is immediately binding we are getting high yield so low temperature is another very very important method therefore in the methodology that we have discussed thus far will be a using a template a template number one and as I told you template the metal Ion must be chosen properly judiciously with lot of thinking should go into choosing a particular metal ion number two will be high dilution but High dilution has its own problem because it takes it requires lots of solvent so you have to recycle the solvent otherwise you'll waste lot of chemicals okay and then another method that we that we use nowadays is the low temperature method so the best method might be you can take a low temperature and a template as well that's what we do you take a metal ion as a template particular metal ion as a template and use low temperature so both when you take both then sometimes we can get the yield as much as 90% if you tell somebody that some reaction like this we got 90% he he he will laugh at us because it is impossible but indeed if you take a good templating iron at say 5° C it is possible to get 90% healed so these are the two aspects of synthesis that I talked about one was the strategy and the other is other is methodology the 90% yield was I will tell you now I will show you the picture uh it will take some uh time but nevertheless let me show it before I end before I end so P all okay so we made this compound I am drawing the other two Bridges identical so I'm writing here writing like this to save time see that so this is a cryptand having a very long cavity and this is you can obtain at low temperature with this we did not use any templating metal ion but at low temperature we used and what did we use we use this alide so this is an aldhy dihy okay this a dhide and reacted with this so we got this particular Krypton at 90% yield H so in some cases really wonders can happen with this kind of molecules okay so that is that is probably ending the class today so therefore I told you that synthesis of this compound and how the some of the structures are now I'll tell you their complexing abilities so there can be monomeric okay I will now use I will always use uh Cartoon now otherwise it will take a very long time but I will one day I will write all the references for you to follow okay so you can take Monon I'll we already discussed about these donor when you have nitrogen donors they are pref so they are preferred by transition metals so if you take a say copper then what will happen copper will go here copper see copper will be here copper binds here okay it's it binds to this nitrogens okay 1 2 3 4 so four nitrogens binds to the is copper and its other here is empty this part is empty there's nothing so that something can come and do some chemistry also that chemistry I will show you another day so what happens is it comes and something can bind here something can bind here some organic Moy and then another can come come here and then it can bind for example when you have a Cobalt Cobalt or copper then they oxidize olenic and benzilic benzilic substrates to their epoxides so epoxides can be formed for example okay this compound with oxygen oxygen from Air in presence of one alide that is sacrificial isob Beed alide sacrificial you can get in very good yield epoxide okay what is the yield yield is quantitative quantitive okay so almost quantitative yield you you can get so therefore there are many other reactions I'm going to talk about that and in a suitable cases that I showed you earlier I showed earlier with the pazo and other cases there more than one metal ion can be inside so that means in a cryptand we can put one metal depending upon its structure we can put mononuclear cryptate that is known as we can put dinuclear crypted and we can put truclear crypted as well so different types of different numbers of metal ions can be put inside the cavity and that depends upon the length of the length of the cavity its environment so on and so forth so thank [Music] you [Music] [Music] [Music]