 Hello everyone, welcome you all to MSP lecture series on transformative chemistry. I have been discussing in the last couple of lectures about the classification of ligands by donor atoms and I completed discussion on hydrogen and we are midway with respect to carbon as donor atom. Let me continue from where I had stopped in my previous lecture I had initiated discussion about the CO analog CS. Let me start about the chemistry of carbon thio monoxide complexes. As I mentioned unlike carbon monoxide, carbon thio monoxide is not stable and polymerizes above minus 160 degree centigrade. So that means free CS does not exist in a stable form and however CS compounds can be made using appropriate CS precursors and then very similar to carbon monoxide CS can be incorporated. There are examples of homolyptic CS complexes also. Let me show you preparation of few carbon thio monoxide complexes. Before I start writing about the thio monoxide preparation let me show you the coordination modes. Coordination modes are pretty similar to what we come across among carbon monoxide complexes. It can comfortably act as a terminal ligand very similar to carbon monoxide and since SC soft here it can readily bind to another soft metal in bridging fashion like this. On the other hand this carbon can also donate its loan paid to two metal centers with or without metal metal bond and it can also bridge three metal centers and also one can anticipate this kind of coordination also in a trimetallic system where sulfur loan paid goes to one metal and carbon takes another metal and whereas this double bond can bind to another metal and of course you can have carbon functioning as a bridged bidentate and then sulfur can go to another one or one of this fashion. There are examples in each case. Let me show you a few examples or representative examples. Further when you look into carbon disulfide very similar to carbon dioxide it also shows following coordination modes you can see simple one when it binds this is how it is going to bind breaking one of the CS double bonds and then it can also bridge two metal centers in this fashion eta 2 and mu and it can also show this kind of coordination and where you can also come across trimetallic system in this way or one can also have something like this or this or this one. So these are some of standard and well-known coordination modes are binding modes of carbon disulfide. Let us look into the preparation of CS complexes. There are at least two to three very useful precursors are there that can be conveniently used to prepare CS complexes. The simplest one is using carbon disulfide. I deliberately taken two different type of tertiary phosphine here when you take this iridium tritry tertiary phosphine chloride compound iridium in plus one state and treat this one with carbon disulfide. So now if you see here now it is giving a compound very similar to Vasca's compound this is a trans compound and here why the sulfur is not abstracted by triphenyl phosphine rather tritracibutyl phosphine because here the one that is more basic so that would leave to form disulfide you should remember if you have two different type of tertiary phosphines the one that is better sigma donor will readily get oxidized as a result. So here forminion butyl phosphine sulfide and it is abstracting sulfur from CS2 and of course if you consider another reaction for example something like this similar reaction now it does not have any option other than eliminating one of the triphenyl phosphine as triphenyl phosphine sulfide. But when choice is there the most basic one leaves this is one method of making CS complexes. Another important method is so this is thioacetate so this one also can give so this can also form a compound like this so this is very much similar to FeCO3 Pme3 twice a 18 electron complex it is in 0 valence state. So let us look into another example here so di anionic complex so here the cation can be sodium so if that is the case I can also see here Na2 FeCO4 for example you take this one and treat this one with this is thiophosphate gene okay phosphine we know it is COCl2 so we are using thiophosphate in CSCl2 this one can also give a compound very similar to FeCO5 so this one is very similar to FeCO5 so this comes along with so if it is 2 sodium or NaCl will come out this is a neat reaction only thing is one has to be extremely careful while handling phosphine or thiophosphate they are very poisonous gases so this is the second method and third method in fact we use thiophosphate we use carbon disulfate we use it and also we use thiophosphate in another method carbon disulfate can also be used for example let us consider for variety a half sandwich compound of manganese suppose we do not have a phosphine here so we start with the reaction in which we do not have a phosphine to abstract sulfur from carbon disulfate in that case later one can also add a suitable tertiary phosphine to abstract yes from CS2 to form CS complexes so initially if we add CS2 for this one one of the ligands would come out and it forms an intermediate compound of this type this gives you some idea how CS2 would initially bind to the metal center and eventually it cleaves one of the CS bond if phosphine is there it will abstract that sulfur to form phosphine sulfide and hence you get the corresponding CS compound initially it forms a compound like this now we will add a tertiary phosphine it abstract the sulfur to form so this is how one can conveniently use one of the available methods to make these compounds let me write one more method of preparation using sodium amalgam in a state complex if you treat this complex with sodium amalgam this is again an electron species so these are the few methods that one can conveniently use to make thio-carbon monoxide complexes and as I mentioned again thio monoxide is a relatively good sigma donor and a better pi acceptor compared to carbon monoxide before I go I did mention about orthometallation this is another important reaction we come across in case of carbon donor ligands especially when we have phenyl groups are there on a donor atom that is in close proximity to the metal you can see CH activation and then there can be some elimination or it can be added oxidatively to form orthometallated compound the first orthometallated compound was made in 1960 from this reaction let me write show you the first example of orthometallated compound that was with palladium with this diazo benzene so when this organic compound was reflected in ethanol with potassium tetrachloropalladium so it resulted in the elimination of two equivalents of HCl to form a compound like this you can see palladium is in plus one state a plus two state here in both this is the first compound which shows orthometallation and later several orthometallated compounds were made and also in fact people planned orthometallation reactions and one disadvantage with this orthometallation is there sometime when you are using some tertiary phosphines especially having aromatic groups with not having any substituents at ortho position they can leads to orthometallation and also they can deactivate the catalyst and one such example is seen with Wilkinson catalyst for example if you take Wilkinson catalyst here with rhodium triphenylphosphine complex so this can readily form oxidatively added compound through orthometallation and rhodium is getting oxidized from rhodium 1 to rhodium 3 just I have shown one of the phenyl groups expanded so that orthometallation can be seen here other two triphenylphosphines remain so something like this so now you can see okay through the CH is added to rhodium we have rhodium in plus 3 state and however there can be reductive elimination this HCl like very similar to concerted elimination that can also happen and that can leads to the formation of this compound. So this is a typical orthometallation reaction one can see especially with triphenylphosphine or any bisphosphine having phenyl substituents and due to the steel problem if the phenyl groups comes very close to the metal center and there can be CH activation that can leads to either oxidative addition and that compound can also be stable or can be stabilized or eventually if you leave it or if you heat it little bit the HCl elimination can be seen or even the elimination can be speeded up by adding a base such as triethylamine so triethylamine can abstract HCl to form triethylamine chloride and this reaction can proceed and to give eventually orthometallated product. So one has to be extremely careful for this kind of reactions and especially when we are using triphenylphosphine with platinum metals for catalytic purpose these reactions are quite common and does can deactivate the catalyst so that your rate of reaction decreases dramatically. Now let us look into another interesting ligand system isocyanates and isocyanates I have shown the binding mode so you can have either linear fashion it can bind or it can also show this bent mode here and the difference can be seen from the bond angle here it is 165 to 179 we can consider as linear and if it is in the range of 130 to 135 it will be bent. So then let us see how this isocyanate compounds are prepared isocyanate are again neutral ligands very similar to carbon monoxide or tertiary phosphines so some simple substitution reaction can be performed this is a general reaction I am going to write that means by choosing appropriate reaction condition one can substitute all carbon monoxide on a metal center to form homolyptic isocyanate complexes you take this again 0 valent complex treat with CNR one can make homolyptic complex this is very similar to CRCO6 in 18 electron species so one can also make this compound one can also start with a dinitrogen compound of course you may be curious to know how dinitrogen compounds are there once I complete the carbon ligands I shall move on to nitrogen there I would be elaborating more about nitrogen preparation of dinitrogen compounds and their reactivity and all those things if you take this dinitrogen complex of molybdenum or tungsten of course here 2 and 2 comes out these are some of the important methods of preparation of isocyanate complexes and let us look into the reactions of isocyanate that means the reactions of bound isocyanates what are the reactions one can perform when an isocyanate ligand is coordinated to a metal center so 3 reactions one can think of one is coupling reaction one is nucleophilic reaction and other one is electrophilic reaction so let us look into first coupling reaction let us take a molybdenum complex treat this one with zinc and wet THF THF will take care of this one I am just writing 4 isocyanates on one side to show the coupling reaction this is a dimeric complex of neobium when it is treated with the isocyanate of course excess of isocyanate and now you should remember they have lone pairs intact these lone pairs will be donated to the other neobium that has 4 chlorides on it so these are the examples for coupling reactions one can perform on bound isocyanates just take this one and treat this one with methyl iodide this is another interesting example for this coupling reaction here it gives metalated compound of this type these are the few examples to understand the coupling reactions of isocyanates with various trans-metalous one I showed you with molybdenum and another one I showed you with neobium and one I showed with homolyptic iron complex pent isocyanate iron so let us look into reactivity more reactivity of bound isocyanates in my next lecture thank you.