 Hello everyone, once again I welcome you all to MSP lecture series on transformative chemistry. Ever since I started discussing on classification of ligands by donor atoms, I had no option other than writing lot of equations, probably it may be boring or you may think it is lot of memories needed, now it is not true that is the reason in my previous lecture I showed you how you can see depending upon the lateral movements of electrons between the atoms where electron density resides more, where electron density resides less and how the bond is polarized based on that one when you are using a substance, when you are using a reagent, how again that reagent polarizes before it attacks the coordinated atoms. So, that in order to stress upon those things, I have no option other than writing some of these equations. Let me continue doing that one of course it is inorganic chemistry, inorganic chemistry is incomplete without chemical equations, especially balanced chemical equations and then once we know how to write balanced chemical equations, we should also see the mechanistic path and all those things. For that one understanding the sequence of reactions is very very important. Now let us look into some more reactions of coordinated NO, let us take a simple coordinated NO coordinated complex, pentasino nitrosil complex 2 minus charge, use a base here, this close step and of course if you add H it will come back, it is a reversible reaction 3 minus NO and again add one more. Let us consider the same starting metal complex and add RS minus so that we can make better comparison between these two reactions. With thiols, when you treat nitrosil compound with thiols, it turns red color and that is used for the detection of RS minus species or RS minus anions. From that point of view this is a very important reaction. Let us consider one more reaction here, treat this one with SO3. So reaction of nitroproside with sulfite to form nitrosil sulfito is the first example of a coordinated NO reported by this gentleman Bodecker in 1861 and of course this has a very long NS bond, the NS bond distances around 1.82 m strong units. So now let us look into the electrophilic attacks, example consider H plus or ME, they can attack either N or O on a coordinated nitrosil ligand, let us look into both the cases. This is osmium and treatment of this one with HCl, it forms a compound of this type. Now you know H plus has attacked N. Now let us look into another example, a bipyridyl complex, 22 dash bipyridyl complex of ruthenium. When noting down these reactions you shall also practice electron count probably all reactants and products you should do electron count so that you will be familiar with this electron counting method. And we can also have a bridging nitrosil complexes where N bridges two metal centres. What would happen if electrophilic attack occurs on a bridging NO? Let us consider one example here. So this is derived from RU3CO12, a neutral carbonyl cluster. So now when you are replacing two carbon monoxide with one NO, NO is a three electron donor. So it is in short of one more electron as a result it carries a negative charge here. So when you treat this one with CF3 SO3ME it forms a complex of this type. I think this much information will do about nitrosil ligand and the preparation of nitrosil complexes and their further reactions with various reagents such as electrophiles and nucleophiles. Now let us move on to nitridocomplexes. You consider NH3, NH3 is there and if from NH3 if you remove one proton, one hydrogen then it becomes NH2 minus amide and then if you remove one more then it becomes imide and then if you remove the last hydrogen then it will carry a negative charge and 3 minus then this is called nitride. Nitridocomplexes are also known. In fact nitride is a six electron donor is one of the strongest P donors known and if you just look into M triple bond N distance or in the range of 1.6 to 1.8 anesthetic units and the coordination modes I have shown here it can bridge two metal centers in this fashion or it can also bridge three metals mu3 it can also bridge four metal centers and there are examples where these four metals are arranged in a tetrahedral arrangement something like this. So we come across this kind of mu4 bridging and of course it can also bridge three metal centers in this fashion keeping the lone pair intact so it can go to another one. So if you see here it is typically like a ammonia here it can be nicely compared to ammonia we have covalent bonds two electron covalent bonds are there and then still this lone pair is intact now this can act as a metalloligand. So these are some of the very very important coordinating modes of nitride ligand. Now let us look into the synthetic methods. So for this one usually we are using metals in their high oxygen states. So when this Trescibutax alkoxy derivative is treated with isocyanide it forms two complexes one is nitride complex other one is alkylidine complex and if we take osmium tetroxide and treat with base it can also form a nitride complex. So it is giving three electrons as a result one negative charge is there on this one and of course whenever we write like this you should understand that we have something like this a triple bond between metal and nitrogen. Similarly we can also make nitrides having other ligands such as cyclopentadienyl ligand. So here we have chosen a Cp star Cp star means pentamethyl cyclopentadienyl of course here. This is also called aminolysis reaction. These are some of the important methods of preparation of nitride and as I mentioned here if we can also make anionic compounds of N for example Rn2 minus is there. So this is also very important ligand in some metal complexes that can be used in metathesis and also in some organic reactions. So let me give the preparatory methods of imidocomplexes. If you take tungsten tetrachloride oxytetrachloride and treat with RnCO it forms here we have double bond between tungsten and nitrogen. Treat this one with amide secondary amine. We have on N1 trimethylsilate group and tercibutyl group. So here of course if you keep it for a prolonged time it loses one molecule of water and it forms emethyhexamethyl disiloxane it forms. So here also we have rhenium 2 nitrogen double bond. Take this compound and treat this one with a typical aryl amine. Usually here aryl groups considered are very bulky ones. Let me give one more example here. One can also make imidocomplexes starting from an organic azide such as phenyl azide. Let us consider vanadocein. Here we have Cp's pentamethyl cyclopentadienyl we have chosen. Or in general one can also start with a nitride complex like this. Treatment of this one with reagents such as methyl lithium can give a salt having imidobond. So these are some of important reactions one can use to generate imidocomplexes and also I showed you earlier nitride complexes. So what are the other ligands that we have not touched when it comes to nitrogen donor ligands? We have plenty of macro cycles are there and also having heterodonor atoms are there. For example we have N O ligands are there and we have S and N donor ligands are there. And of course N O P ligands are also there and there are macro cycles where we have donor atoms such as P, N, S as well as O. So it goes with our imagination and also the availability of appropriate reagents to make a variety of macro cyclic ligands having versatility in its coordination behavior having several different donor atoms. And why people work with macro cycles is macro cycles have a marked kinetic stability compared to corresponding monodentate ligands. And also they can stabilize metals in very unusual actual states because of chelate effect or encapsulation. And also they are very thermodynamically stable from this point of view. And also they can be very robust and also when we make macro cycles and we will be having a suitable cavity and the size of cavity is also very, very important. And when we choose a right metal of suitable size that fits into the cavity against stability increases. So from that point of view when we want to make a macro cycle or a cage like structures for a particular metal and encapsulation we have to keep all these things in mind to make sure that optimum size is left for metal to occupy that coordination site. And among amines we have diamine is there ethylene diamine is there triethylene diamine is there like that there are plenty of amines are there. Let me show you a couple of examples here. So a typical nickel complex is there and all are a neutral donor nitrogen. So this is a cationic this plus 2 charge. There are other type of compounds as well where one side the chain is open having NH 2 mighty of course in this case competing the structure should be any problem. So now this is another tetraintate ligand. The advantage of these things are we can do further reactions on bound amine groups and of course we are all familiar with the skew based ligands are very, very important in coordination chemistry. Skew based can have either nitrogen completely or nitrogen and also oxygen donors or sometime they can be anionic complexes also provided we have some proton that can be readily dissociated like OH group is there SH group is there they can act as anionic ligands also. The typical preparation of skew bases involve the condensation of a ketone with amine primary amine. So this is a typical reaction that is used in making a variety of skew bases. Let us look into how one can also generate a skew base with amine ligands bound to the metal center. Let us consider this cationic complex and treat this one with 4 equivalents of ketone. You can see here the formation of a skew base with bound ethylene diamine ligands. What would happen if here both the sides are open one can also perform reaction when the one side is open. Let us consider another example here with couple 2 plus ion. So this one let us treat with the 2 equivalents of ketone here. This results in the condensation of course rest of this part does not participate in any reaction whereas here so this happens here. So like this on bound amine ligands one can also perform skew based reaction to generate the corresponding skew bases. Let me continue talking little bit more about nitrogen donor ligands especially giving some emphasis for macro cyclic ligands in my next lecture before I conclude on nitrogen donor ligands and move on to oxygen donor ligands until then have an excellent time reading coordination chemistry and try to understand the classification of ligands by donor atoms.