 Hello everyone, I welcome you all once again to MSP lecture series on transformative chemistry. We have started discussion on classification of ligands by donor atoms, so far I have completed discussion on hydrogen, carbon and nitrogen I just began in my previous lecture and I gave little information about the donor properties of nitrogen and how the nitrogen behaves very similar to isocyanates and carbon monoxide so that one can do some reactions. If you know little bit more about how we can perform on bound nitrogen, some reactions that might be helpful in those who are working in the nitrogen reduction and carbon dioxide reduction and other such similar reactions from that point of view. Let me continue from where I had stopped, let us look into the reactivity of coordinated nitrogen ligands or nitrogen donor ligands. So how this electrophilic attack by H or any other electrophiles results in new products that we can see in a couple of reactions by choosing very specific examples. Let us consider a simple phosphine and nitrogen complex. So when we have phosphines and when we try to put dinitrogen we should remember we should go for very strong sigma donor ligands among phosphines if we have alkyl groups they are good sigma donors. From that point of view you can see in most of these reactions we are using alkyl bound phosphines not the aryl and of course here to have some moderate sigma donor ability one can also replace one of the alkyl groups with aryl groups such as phenyl. So when this compound is treated with Hx, so in this reaction one of the N2 is liberated whereas the other N2 is reduced to form this kind of product. Diphos is a bidentate ligand I shall show you the structure diphos is nothing but this is the one. 1, 2 bis diphenyl phosphine of benzene. The mechanism of N2 reduction in biological system is not really clear however the reactivity of coordinated N2 is well studied. The reaction involved usually hydrozyto, imido and nitride species the possible reactions one can anticipate or electrophilic, nucleophilic or coupling reactions. So now let us look into the electrophilic attack by H or other electrophiles. The same reaction I am considering again the addition of Rx here can leads to Cx bond cleavage and radical reaction. Now let us look into nucleophilic reaction what would happen if a nucleophile attacks the nitrogen center. A manganese complex is chosen for this purpose having cyclopentadiene ligand and 2 carbon monoxide. When this is treated with methyl lithium initially it forms an intermediate of this type of course here counter cation is lithium. And further treatment with ME3O, BF4 a good methylation agent and when we treat this with a typical alkyl magnesium such as diethyl magnesium it gives an interesting magnesium complex having 2 cobalt moieties. So this ethyl group it abstract hydrogen from cobalt hydrogen bond to give C2H6 and of course here we have this reaction is carried out in THF. So this is another reaction that depicts the nucleophilic reaction of coordinated nitrogen. So with this let us move on to consider another interesting ligand called nitrosil ligand. Nitric oxide we call it as nitrosil NO is a bioregulatory agent produced endogenously disturbances in the production and regulation of NO are known to cause central nervous system disorder and asthma besides many other diseases. Iron nitrosil complexes help to balance the beneficial effects of NO against its potentially fatal effects of course one should remember the fact that NO is also a very toxic gas. Now let us look into the amode diagram of NO before we proceed for preparatory methods and reactivity and other things. You can see here the amode diagram and of course if you count valence electrons in case of NO 6 electrons are coming from oxygen and 5 electrons are coming from nitrogen. So that means we have totally 11 electrons so 2 s electrons can be left for all practical purpose because they are not adding anything to NO bond. So now you consider 3 electrons and of course here 2 electrons are there they form anti-bonding and bonding. What is interesting is about 2p electrons here and 2p electrons here and if you see here we have 4 electrons and here 3 electrons if you start filling in this fashion we will be left 1 electron in anti-bonding orbital that leads to the bond order of 2.5. So that is the reason why NO has a tendency to lose one of the electrons readily is to have bond order 3. So the moment you remove this electron to generate nitrosyl cation we have the bond order 3 and that is stabilized. So because of this reason NO acts as a nitrosyl cation. So let us look into the binding properties and of course nitrogen has a lone pair here and that lone pair can be readily donated to the metal to form a sigma bond and this is sigma donation okay and then in the linear fashion when it is binds the angle should be around 180 or it will be close to 180 and when it binds in bent fashion what happens it can have an MN angle of about 120 degree here and then because of the presence of pi star orbital you can anticipate back donation with NO as well very similar to carbon monoxide and this is how one can show the interaction of filled metal orbital with pi star of nitrosily gantt. This is backbonding that means this also a sigma donor as well as a pi acceptor and the relative strength also I already showed you couple of times earlier in a table you can refer to it if you want once again. So this one again I am bringing to show what would happen when a metal binds so that means this yamad diagram repeats the interaction of NO with metal. So now you can say the focus should be only on this electrons that can go as you know sigma to the metal so you can see here these two electrons are donated to appropriate metal orbital so either dx square minus y square or dz square to establish a sigma bond and then metal has electrons in dxy dxz or dyz so those things what happens they can be shared with pi star of this one. So pi star and metal d orbital having pi symmetry would overlap again to generate pi bonding and pi anti bonding orbital so in which these electrons are placed so this represents back donation from metal to NO and this represent NO to metal sigma bonding. This is a typical yamad diagram for a metal nitrosily complex. Now let us look into the properties of linearly coordinated NO and of course one can also see the similarities between the way I have written the movement of electrons from oxygen to metal through nitrogen here and this can be very similarly compared to what would happen with carbon monoxide with minimum back donation and maximum back donation with of course having sigma bond intact. In the same way one can also write you can see here when there is minimum just sigma donation this would happen when slightly back donation is there this bond is weakened this bond is strengthened so this the three extremes one can think of in case of NO ligand as well. So when it is detached it leaves as a nitrosyl cation so leaving a negative charge on the metal so in that context NO plus is a 2 electron donor. If you just count the electrons we have 10 electrons in NO plus and similarly in case of carbon monoxide also 4 plus 6 10 electrons are there in the valence shell so it is obvious that both are isoelectronic but NO plus needs to coordinate to a metal having one electron more so that means in order to generate nitrosyl cation it has to bind to a metal and it has to give that electron then only it becomes NO plus and then that would be isoelectronic with carbon monoxide. So that means two NO groups are equivalent to three CO groups let us look into the synthetic methods that are available for making NO complexes in the laboratory simplest method is treating directly NO gas for example let us consider CO to CO 8 and treat this one with two equivalents of NO so it is very interesting to analyze this one with the structure of this one half a molecule of this one you know why CO CO 4 cobalt tetracharbonyl exists as a dimer because it is a 17 electron species in order to satisfy 18 electron rule what happens it will establishes CO CO bond and hence becomes attains 18 electron as a result it stabilizes it as a dimeric species whereas in this case when you replace one of the carbon monoxide with NO now NO is a 3 electron donor when it is linear so now it is 3 electron if it is giving cobalt has 9 plus 3 so plus 6 so 18 electrons are there so that is the reason this can be stabilizer simply as a monomeric species you should know the difference why it is stabilizer as monomeric species whereas CO CO 4 is not means that is a 17 electron species and this is an 18 electron species. Let us look into another reaction where we are using a reagent of different type to generate metal to nitrosil bond let us consider FeCO 5 and treat this one with PPN I am not sure whether you are familiar with this cation is a very bulky cation usually use it to stabilize anions I shall write the structure of that one later of completing this equation. So you take this one and treat this with NO 2 salt in isotron nitrile it is a counter cation and what we get is FeCO 3 NO minus plus CO 2 plus CO. So now let us look let us count the electrons here so if you take Fe that is 8 plus 6 plus 3 so 1 negative charge is there so you will understand why negative charge is there on this one because in order to satisfy because we have taken out 2 carbon monoxide and 4 electrons have been taken out and in its place we have only 1 NO there is a 3 electron donor so with this charge it becomes 18 electron species so everything one should you know explain very satisfactory provided we understand this method of electron counting now we must have realized how important it is to know how to do electron counting and PPN what is PPN? PPN is nothing but this bulky cation and NO 2 here is so this is called PPN. Let us look into couple of more methods of preparation of nitrile compounds let us consider now very different one so far we discussed with 2 metal complex in zero valent state now let us go to another metal in high valent state osmium tetraxide in osmium tetraxide osmium is in plus 8 state so when this is treated with NH 2 OH HCl in presence of NCS isocyanide ligand thioisocyanide ligand one can make so this is another way of making nitrosyls with metal in high valent state. Let me write one more another interesting reaction here let us consider rhodium chlorocarbonyl bistrile triphenyl phosphine complex when this is treated with NO BF4 so now let us look let us count electrons here so this one let us go with the neutral method so this is now cationic so this is in plus 3 state if you go with this one 9 plus 1 plus 2 plus I will leave it here and plus 4 so now we see 16 plus now this is 3 and now the charge is now positive so we have a negative so since positive charge is there you subtract one so it goes so it is gating electron species so you can always verify this way to know what kind of donor NO nitrosyl group is since I told you nitrosyl is both it forms bent one electron donor and also when it is linear 3 electron donor so this helps in understanding this one I think these 4 methods are sufficient and if you are interested in looking to more methods always you can go to write kind of textbooks. Now let us look into their reactions of coordinated NO so due to the difference in the electronic structure of linear and bent coordination modes I already mentioned reactivity of coordinated NO can be very different so linear MNO groups can be readily attacked by nucleophiles whereas in bent structure lone pair on nitrogen are susceptible for electrophilic attack but there can be some exceptions and reactions of linear MNOs that is linear metal nitrosyl bonds with nucleophiles such as OH-, OR-, SR- or NH-2R usually occur at the nitrogen autumn you should remember when reaction happens with linear MNO with nucleophiles the reaction usually occurs at N autumn and also can occur at oxygen as well. So well known example is a nitroproside with hydroxide ion to give a nitro complex well known example is of nitroproside with hydroxide ion to give a nitro complex. I think let me continue showing some of these reactions in my next lecture.