 Hello everyone, once again I welcome you all to MSP lecture series on Transmittal Chemistry. We have been discussing in length about the classification of ligands by donor atoms. In the middle of discussion about phosphorus donor ligands and we came to know I did mention about how phosphines can be tuned both electronically and sterically to make ideal candidates for the application of the complexes containing phosphines in coordination chemistry, ergonomatically chemistry and catalysis. So when we talk about ligands they are the most important components of chemistry especially coordination chemistry, ergonomatically chemistry and ultimate use in catalysis. And among all ligands the so called we know how to classify them as classical and non-classical. So these non-classical type of ligands stand out as most important class of anserative ligands or silent ligands or supporting ligands compared to any other donor system essentially because of their remarkable flexibility in tuning their electronic and steric properties and also the remarkable flexibility in the ligand design process. So from that point of view especially phosphines offer a great deal of flexibility in designing a several types of phosphines of course that goes with our imagination. One can make mono dented to poly dented with different linkers, linkers can be alkyl groups aryl groups or any other hetero donor atoms or any other hetero atoms for that matter. And another important thing I am highlighting here is about steric and electronic properties they can be easily tuned and once when you tune and use them they offer remarkable flexibility to the geometries around central metal atoms. And another advantage with phosphines is phosphorus 31P phosphorus is 100% abundant and has nuclear spin I equals half very easy to analyze and record spectra. With this let us continue to show about with this let us talk little bit more about phosphines. This is a simple phosphine it is very similar to ammonia we have and once when you start replacing this hydrogen atoms with alkyl groups aryl groups we will be having secondary phosphines and eventually tertiary phosphines this are all with carbon linkers you can see here one carbon is there are two carbons are there and even chiral is there as I mentioned it goes with our imagination we have several starting compounds are there at our disposal and to hook on these phosphorus mites. So this is an interesting chiral phosphorus lead called duphos and of course this is quite well known this called DPPF bisadiphenylphosphinoferosine and widely used in catalysis I have shown one palladium complex of this one and this is a stereogenic complex here we have binab and of course one can also have bulky groups on top position and also one can have cyclohexyl groups on phosphorus and also a bulky group here so that we can stabilize with low coordination number and these are some of the phosphines that we made in our group we have been working with phosphorus chemistry since 25 years we have been focused on making a variety of phosphines with an intention of using them in catalysis we can see we have made also octophosphine and also we have other donor atoms are they like triazole is there or you can have some other oxygen donors and also one can also make very bulky phosphines here they show interesting properties these are some of very interesting phosphines generated from this cyclo-diphosphazine you can see having a different structure some of them are macro cycles you can see we have as many as 8 phosphorus atoms are there this is ferrocene based one shows very interesting chemistry and this is the one I have shown here so this has something like this structure and using these phosphines we have been carrying out lot of catalytic reactions most of the catalytic reactions we perform are listed here you can go through it if you are interested in whenever you get time when we started again making phosphines we also looked into adding some of these functional groups with donor atoms as I mentioned earlier they have a very totally different and interesting chemistry and only this one was known having a phosphine on one of the triazole carbon but these two are not known so then when we started digging we understood the synthetic problems people came across for example the best way to put a phosphorus moiety on a carbon is by lithiation and then replacing that lithium with chlorophosphines you know for example when this bromodorivity was taken and treated with n-butyl lithium at minus 78 degree centigrade lithium goes here through halogen exchange and then at minus 78 degree centigrade maintain for couple of hours or even 8 hours and then add chlorodiphenylphosphine it gives this one as expected in contrast of lithiation if you warm the lithiated compound to room temperature and add chlorodiphenylphosphine it does not go to ortho position of phenyl ring instead it goes to triazole carbon that means when you warm it what happens lithium halogen exchange takes place okay this requires small energy for the cn rotation and it should come here it should interact and then lithium exchange takes place and as a result now when you add later chlorodiphenylphosphine we get phosphinated on triazole carbon okay so these things we came to know when one of my students was working on this system and eventually we investigated in detail using spectroscopic and means and other kinetics and we concluded that yes this is very temperature dependent reaction once we did this one and we generated a series of phosphines here and also we also immobilized on a heterogeneous surface such as graphene oxide so now it is very easy to perform catalysis here this system can be called as homogenized heterogeneous surface okay that means homogenized heterogeneous system so in this case what happened this portion okay of course graphene oxide is insoluble in any organic solvent but when you attach these things like here and we have put a metal and now this entire moiety is soluble in organic solvents that means if you just soak it in organic solvent what happens this will remain but on the other this goes into the solution if it goes into the solution you can carry out homogeneous catalysis and the interesting thing is once the product is formed if you just do filtration along with this heterogeneous surface it comes out so that means contamination of organic product with complex and a tedious job of its separation does not exist here that is the advantage so one can conveniently fix some of this organic soluble ligand systems especially this phosphine and then complexation you can do with whatever the metals of your choice and in a particular oxygen state and then one can perform homogeneous catalysis this is the advantage of homogenizing heterogeneous surface by phosphines or any other ligands for that matter so now with this one you can see the versatility of this kind of ligands this phosphines are there besides that we also have at least two nerds are not of that can coordinate to metals and these are also called hemilabial ligands because what happens either phosphorous and nerds can coordinate or with C and rotation both the peak can come on to the same side to form PP coordination you can see all these things are happening here and also in isobaration also happens in case of valve dirham and tungsten complexes you can see PN coordination is there whereas here PP coordination is there and in this one again P coordination is there and here PP coordination is there along with another phenanthonyligand PP coordination this is an interesting 16 electron species in palladium zero state this is a wonderful catalyst for lot of organic reactions so that means as I mentioned it goes with your imagination but you should know the basics and very nicely these factors like electronic and steric property should be imbibed into the design so that you can make desired phosphines and attached to right kind of transient metals to explore their catalytic activities and as I mentioned here you can see initially if you take this phosphine and treat with tungsten tetra carbonyl with two labile ligands such as papyridine they can be replaced at room temperature in dichloromethane to initially form a PN compound on standing this one in solution for 72 hours it undergoes isomerization to form PP compound whereas in case of malmdenum also same thing happens but this PN coordinated compound is relatively unstable compared to tungsten complex and in on keeping in solution of the completion of the reaction within two hours it isomerization from PN to PP compound whereas here it takes 72 hours so why that happens one can also do DFT calculations to understand the energy profile and to conclude that why malmdenum is much faster whereas in case of tungsten it takes little longer time. You can see here this conversion was monitored using phosphor cinema as I mentioned phosphor cinema comes very handy in characterizing the component also in understanding the reaction sequence for example you take here before the reaction started we have two distinct chemical shifts for two phosphorus atoms which are very different they are chemically and magnetically non-equivalent I shall tell you little bit more about NMR then you will understand these terms magnetically and chemically non-equivalent and all those things if you have already studied it is very easy so once you add a metal immediately what happens one of the phosphorus is coordinated that is shifted here other one is uncoordinated it does not change with very few PPM changes there that is expected and with time what happens this one would start diminishing here you can see this the chemical shift due to uncoordinated is diminishing because simultaneously formation of this that has started here at the end of two hours in case of malmdenum everything is converted this phosphine from PN coordination to PP coordination and same thing is also carried out same experiment was also carried out with Nungsten compound whereas here it takes 72 hours you can say after 72 hours we have these two these two corresponds to both coordinated one whereas here this corresponds to one coordinated that is shifted another one is not shifted it is still in the ligand free ligand region that is for this one so that means you can see now how important phosphorus NMR in diagnosing the reaction sequence in coordination chemistry and of course as I mentioned since we know the strategy of performing reactions we can conveniently carry out and make all kind of phosphines here and of course temperature is very critical you can see here at what temperature what is added and what you get at the end you go through this sequence of reactions to get to know about the synthetic strategies usually planned by people who design ligands and again when you perform this reaction you never know which product is formed but however when you just look into the 31 PNMR it can guide you yes that nature of product that is formed in a particular reaction even if all these three are formed in a reaction in various proportions again by looking into the intensity you should be able to tell the percentage of formation of these compounds I shall show you more interesting reactions that were monitored using phosphorus NMR when I go to the interpretive part after completing all aspects of coordination chemistry so you can see here this trisolic hydrogen is there that one is coupled with two phosphorus atoms as a result it can show triplet that can also be seen here and also once if it is replaced can and a metal comes here through CH activation disappearance of this hydrogen can also be seen in one HMR so that concludes that yes this hydrogen has been replaced and probably this ligand is acting as a tridentate where we have a carbon to metal covalent bond and when we have carbon to metal covalent bond the chemical shift of carbon in a in its 13 C NMR spectrum will also vary so that means NMR is an important tool in characterizing metal complexes or organometallic compounds we make so this is another interesting reaction I was just telling about phosphorus to carbon bond activation on a coordinated phosphine in my last lecture so this one we observed in our own reaction for example this is a very interesting ligand prepared by one of my students and when it was treated with palladium and platinum you can see what happens if you take this one and treat in prints of a base forms a compound like this pincer compound it is called because N H is there H is gone HCl is eliminated because we started with a palladium chloride having some labile ligand such as chord that is gone with base and whereas in this case even without base it forms a compound and then with base usually this HCl is eliminated and you can see this ligand acting as a tridentate ligand another interesting feature of this ligand system is this one you can see here in this one without base when you add palladium to palladium to complex to this one okay there is interesting a pc bond is broken here and pc bond is broken that phenyl fragment has abstracted H from N to come out as benzene and then that resulted in formation of a five-membered azafospholene ring and now phosphorus is still in trivalent this lone pair comes to palladium so now we have some sort of unsymmetrical phosphate very rarely seen probably this is the first example we have reported and then in this case what happened this phenyl group comes out it binds to the metal very interesting whether we can use this in in alkylation or a reaction yes there is an answer okay we are still our group is working on to see whether we can see a catalytic reaction emerging out of it one interesting thing is all compounds can be nicely crystallized and assess it by performing single crystal X-ray analysis most of the complexes we make we always try to crystallize and look into single crystal structure to understand the bonding features and how the reactions were carried out systematically is shown through this reaction sequence here of course I am not going to elaborate all those things when you get time just look into it and try to understand how these intermediates have been formed and what is the reason the another interesting thing is here you can see now platinum is just a 12 electron species with platinum is 0 it is a 12 electron species formed as a transient species and then this phosphonium salt what happens one of the phenyl group is now added oxidative to platinum to form this kind of compound here and then PTCL bond is established here so now it comes back from platinum 0 to platinum 2 some sort of oxidative addition of course I shall elaborate more about oxidative addition of the completion of this topic I am discussing at present once after making this one initially we did not had this kind of ligand we had NH was there and we have PPH2 but during this time azophosphoryl in ring formation took place whether we can get free ligand that is the next step of course one can do it but reading with bisadiphenyl phosphinobenzene what happens this has more affinity to palladium to chelate as a result this is chelated and this was freed from the metal this is some sort of electrophilic substitution you can see this ligand is freed so that means very interesting chemistry one can carry out with phosphine ligands and why we make as I mentioned we are using several catalytic reactions one such reaction I have shown here this is called N-alkylation of benzene alcohol N-alkylation of benzyl alcohol here these three compounds were used we formed this compound is much more superior in terms of its catalytic activity in forming both of these compounds and initially both the compounds are formed and then again this H can go as H2 and then that can also give this one that means we can control the formation of either this one or this one by changing the reaction conditions and this is a consolidation I have shown this is very interesting result one is breaking of PC bond and then formation of N this PN bond is formed in fact PN bond is much more reactive but however PC bond is less reactive and more stable but it is against that one so PC bond is broken and less stable PN bond is formed so always unusual and interesting chemistry emerges that you can see here that means R can be taken out and then whatever the R- comes out as carbon anion it binds to the metal migration takes place so very interesting result this was with this we shall move on to classification of ligands by donor atom center so now we shall move on to halogen based ligands so far we completed and this is the last ligand series the halogens group 16 elements so when we talk about group 16 elements usually they are denoted by term X in coordination chemistry and we know that halides are very good sigma donors and very good pi donors because they have low energy field sigma orbitals and low energy field pi orbitals and when they interact with metal especially when the metals are there in high valence state metals are electron deficient in that case what happens these ligands not only perform as sigma donors they can also perform as pi donors because pi orbitals on metals are empty and they can readily pass on electrons from halogens to metal orbitals so these ligands usually terminal but often they can act as bridging ligands when they act as bridging ligands they can bridge two metal centers they can bridge three metal centers interestingly they can also bridge four metal centers we have several examples in our own laboratory I shall show you later due to their pi basicity the halide ligands are weak field ligands of course when you look into spectrochemical series you know where these halides stand among rest of the ligands if you just look into spectrochemical series it can be broadly classified into again three categories in the beginning what we have is pure sigma donor and pi donor ligands and later we have only sigma donor ligands at the end where strong field ligands emerge there we have sigma donor and pi acceptor ligands and due to a smaller crystal field splitting energy I have shown clearly in a more diagram how the crystal field splitting energy decreases shrinks when we have halogens because of their donor properties and as a result what happens halide complexes are very labile in most of the reactions we use anhydrous halogen complexes for performing substitution reaction to generate other coordination compounds and also argumentary compounds and most of the halide complexes are high spin complexes and hexahalide that means homolyptic halides are also known with most of the metals and when you have six halogen atoms or six halides are there they adopt preferably octahedral geometry whereas four coordination they prefer tetrahedral geometries but in some cases especially with platinum metals they are still form squab and are complexes and due to the presence of field p pi orbitals due to the presence of field p pi orbitals halide ligands and trans metals are able to reinforce pi back bonding on to pi acid that means those metals which are oxophilic and oxohalic we call them especially early metals in their high valent state high oxo state they are electron deficient in that case what happens metals conveniently drift electrons from halogens of course if you take any halogen for example if I take Cl minus if I take we know that we have 8 electrons are there and out of 8 electrons this electrons may go for making metal to covalent bond still we will be left with strictly speaking still it can coordinate all known pairs but most common ones are something like this just I have taken chloride it can also be in general it can also be X so that any halide so this is the one now basically if this is covalent bond you should remember this is a coordinate bond this lone pair is coming if another is there this can also come like this always if it is a triply bridging one is covalent bond other two are coordinate bonds so let me stop at this and maybe continue discussing more interesting chemistry of halogens in my next lecture until then have an excellent time