E-CONTENT ON ORGANO METALIC COMPOUND BY DR. SEJAL S. NAIK, ASSISTANT PROFESSOR, V.S.PATEL COLLEGE OF ARTS & SCIENCE, BILIMORA

ORGANOMETALIC COMPOUND
DEFINATION
CLASSIFICATION

1. DR . SEJAL SOHAM NAIK Assistant professor Chemistry Department V . S. Patel College of Arts & Science , Bilimora

2. ORGANOMETALIC COMPOUND

3. ORGANOMETALIC COMPOUNDS

4. “Organic compounds that contain carbon-metal bond are called organometalic compounds.” or “The compound containing at least one direct metal-carbon bond are called organo metalic compounds and the branch of chemistry which deals with such compound is called organo-metalic chemistry.” General structure of compounds is represented by R M . The nature of carbon metal bond varies widely , ranging from ionic to covelent ORGANOMETALIC COMPOUNDS

5. Ionic character of carbon-metal bond maimly depends on the electro positive character of the metal. More will be the electropositive character of metal, higher will be the ionic character between carbon-metal bond. C-Na, C-Li bonds are largely ionic in chaeacter and C-Zn, C- Pb , C-Cu and C-Hg bonds are essaentially covelent . In organometalic compounds carbon is bonded with electro positive atom hance carbon bears negative charge and metal bears positive charge thus carbon-metal bond is polarised -  R M + 

6. Organic part of organometalic compounds thus always behaves as necleophile as well as base. Reactivity of organometalic compounds as nucleophile and as base depends mainly on electropositive character of metal more will be electropositive character higher will be reactivity of organometalic compounds. Organolithium and organomagnesium have highest ionic character and behave as weak nucleophiles in their reactions.

7. This type of compounds named by prefixing the name of the names of organometalic compounds are as under. CH 3 Li ---- Methyl Lithium (CH 3 ) 3 Al ---- Trimethyl Aluminium (CH 3 CH 2 ) 2 Zn ---- Diethyl Zinc (CH 3 CH 2 ) 3 B ---- Triethyl Boran (CH 3 ) 3 Si ---- Trimethyl Silane (CH 3 CH 2 ) 2 Cd ---- Diethyl Cadminum C 6 H 5 Li ---- Phenyl Lithium CH 3 MgBr ---- Methyl Magnesium Bromide. Most of the organometalic compounds are liquid and soluble in organic solvent. They react with oxygen and moisture

8. Organometalic compounds can be classify into two types Organometalic Compounds Simple Organometalic Mixed organometalic Compounds Compounds Classification based on bonding : on the basis of bonding between metal atom and carbon organometalic compounds they can be classified into three classes. 1. Ionic organometalic Compounds 2. Covalent organometalic Compounds 3. Complex organometalic Compounds CLASSIFICATION

9. 1. Ionic organometalic Compounds : In this type carbon bonded to metal with ionic bond. M C (nature of bond is ionic) e.g. C 10 H 8 Na 2. Covalent organometalic Compounds : In this type carbon bonded to metal with covalent bond or in this type non transition metal is bonded to carbon with covalent bond M C (nature of bond is Covalent) e.g. Al(CH 3 ) 3, Bi(CH 3 ) 4 3. Complex organometalic Compounds : Which consist of centrally located metals and perpheral organic compounds called Ligands . M C e.g. K [C 2 H 4 PbCl 2 ]

10. C-Li, C-Na bonds are largely ionic in character. Organolithium and organomagnesium have highest ionic character and behave as strong nucleophiles in their reactions and they react with any acid stronger than alkane . Method of preparation The organolithium compounds(R-Li) can be prepared by the following methods: ORGANOLITHIUM

11. By reaction of alkyl or aryl halide with metallic lithium By metal-halogen exchange method By metal-hydrogen exchange [ metallation ] By metal-metal exchange [Trans- metallation ]. (1) By reaction of alkyl or aryl halide with metallic lithium:- Zigher (1930) prepared organolithium compounds by the reaction of alkyl halide with metallic lithium. 2Li + C 2 H 5 Cl C2H5Li + LiCl ethyl lithium lithium chloride 2Li + -Br -Li + LiBr phenyl lithium Lithium alkyl are generally obtained by the interaction of alkyl or aryl chloride in ether at -20°C temperature because of high reactivity of both the reactant and the product. The order of the reactivity of alkyl halide in this reaction is, R-I > R-Br > R- Cl > R-F

12. (2) By metal-halogen exchange:- This type of reaction can be represented by the general reaction. Phenyl lithium is made conveniently prepared by this method. CH 3 -Li + -X -Li + CH 3 X Methyl phenyl phenyl methyl Lithium halide lithium halide This type of reaction is usually fast at room temperature and also below the room temperature. The metal become preferentially attack on the more electro negative organic radical. n-Bu-Li + -Br -Li + n-Bu-Br phenyl lithium(95%) n-Bu-Li + 3-Bromo 3- Lithium Pyridine Pyridine

13. (3)By metal-hydrogen exchange( metallation ):- This is the reaction between organolithium compound(R-Li) and a hydrocarbon(R’-H). R-Li + R’-H R’-Li + R-H Ph-Li + Ph-C=CH Ph-C=C-Li + Ph-H phenyl phenyl phenyl benzene lithium acetylene acetelene lithium n-butyl lithium forms a complex with tetra methylene ethylene diamine (TMEDA). This complex is a powerful metaliting agent.

14. (4) By metal-metal exchange[trans metallation ]:- This reaction are quite fast at room temperature and particularly when compound of an equilibrium product is sparingly soluble. * 4Ph-Li +(CH 2 =CH 2 ) 4 Sn Ph 4 Sn +4(CH 2 =CH 2 )Li Phenyl tetra alkene alkene lithium stanus lithium The reaction between metallic Li and organic compounds of more electronegative metals are not really called trans metallisation , byt they are used in preparing the compound by Alkylation. *4 Li + (CH 2 =CH 2 ) 4 Pb 4 (CH 2 =CH 2 ) Li + Pb tetra alkene alkene lead lithium ether

15. SYNTHETIC APPLICATION 1] Preparation of alcohol: 1° alcohol= When formaldehyde reacts with R-Li, it produces 1° alcohol. O R R || | | H-C-H + R-Li H-C-H H-C-H or R-CH 2 OH | | 1° alcohol O-Li OH 2. 2° alcohol= when higher aldehyde is treated with R-Li then it will give 2° alcohol. O R R R || | | | R’-C-H + R-Li R’-C-H R’-C-H or R’-CH- OH | | 2° alcohol O-Li OH H 2 O - LiOH H 2 O - LiOH

16. 3. 3°alcohol= When ketone is treated with R-Li then it will give 3°alcohol. O O -Li OH || | | R’-C-R” + R-Li R’-C-R” R’-C-R” | | R R 2] preparation of Acid and ketone : when R-Li reacts with CO 2 in benzene gives ketone and acid as under. * R-Li + O=C=O R-C- OLi || O * R-C- OLi H 2 O R-C-OH || - LiOH || O O Acid H 2 O - LiOH

17. O OLi O || | || R-C- OLi R’-H R-C-OH - LiOH R-C-R’ | R’ In below reactions, ketone is produce as Final product when the acid is used as starting material. O O -Li O || | || C-OH C-OH C-CH 3 +CH 3 Li | Cyclohexane CH 3 1-cyclohexyl Carboxylic acid ethanone 3].To increase polarity :- The polarity of Li-C bond is greatly increase by the co-ordination of TMEDA. Hence TMEDA-n-Bu-Li complex added into ethylene under pressure gives polymer. This polymer reacts with benzene and gives another polymer with phenyl. This is known as Tolemer .

18. n-Bu-Li-TMEDA + C 6 H 6 PhLi -TMEDA PhLi -TMEDA + nCH 2 =CH 2 Ph-(CH 2 –CH 2 ) n –Li-TMEDA Ph-(CH 2 –CH 2 ) n –Li-TMEDA + C 6 H 6 PhLi -TMEDA + Ph-(CH 2 –CH 2 ) n Tolemer similarly reaction between alkyl lithium(R-Li) and congugated diene (like isoprene) give synthetic rubber known as “ Haved Rubber”. CH 2 CH 2 --- H 2 C CH 2 ---- || || | | C - C +R-Li C = C | | | | H 3 C H CH 3 H n Isoprene or 2-methyl Buta 1,3 diene Haved rubber or Poly isoprene or neoprene 4]. Preparation of aldehyde & ketone : organo lithium compound has in the system of C-N bond. The reaction of R-Li with substituted amide gives aldehyde and ketone as under. O O || || R-Li + H- C-N (CH 3 ) 2 R-C-H + Li-N (CH 3 ) 2 DMF Aldehyde ..

19. O O || || R-Li + R’- C-N (CH 3 ) 2 R-C-R’ + Li-N (CH 3 ) 2 Ketone .. ( 5) Preparation of hydrocarbon:- Reaction with compound containing active hydrogen ( water ,alcohol , amine , etc.) gives hydrocarbon. R-Li + H-OH R-H + LiOH Hydrocarbon R-Li + H-OR’ R-H + LiOR ’ R-Li + H-NHR’ R-H + LiNHR ’ (6) Reaction with alkyl cyanide:- R-C = N + R’-Li R-C=N-Li R-C=NH R-C=O | | | R’ R’ R’ Hydrolysis - LiOH Hydrolysis H 2 O/ H⁺

20. (7) Reaction with epoxide R- CH – CH 2 + CH 3 –Li R-CH-CH 2 – OLi R-CH-CH 2 –OH | | CH 3 CH 3 (8) Reaction with α , β - unsaturarted carbonyl compound:- Ph-C-CH=CH-Ph + Ph-Li (Ph) 2 C–CH= CH-Ph (Ph) 2 C–CH= CH-Ph || | | O O -Li OH (9) Nucleophilic displacement:- Hydrolysis - LiOH + Ph-Li Ph⁻ Ph⁻ - LiCl Cl Li ph + 1-phenyl naphthalene 2-phenyl naphthalene Cl Ph O

21. 9]. Electrophilic displacement: CH 2 =CH-Br + n- BuLi CH 2 =CH-Li +n-Bu Br Bromo ethylene

22. Organoborane compounds can be prepared by two methods. 1. By using another organometallic compounds 2. By hydroboration reaction (1) By using another organometallic compounds :- This method includes a reaction between borane halide ether with other organometallic compound preferentially R-Mg-X or R 3 Al to produce organo borane compounds. ORGANO BORANES

23. 3 R-Mg-X + BF 3 O(C 2 H 5 ) 2 R 3 B + F-Mg-x Grignard reagent Boron halide ether Trialkyl borane 3CH 3 MgCl + BF 3 O(C 2 H 5 ) 2 (CH 3 ) 3 B + F-Mg- Cl The most satisfactory method is to use triethyl aluminium and triethyl ortho borate. (C 2 H 5 ) 3 Al + B(0C 2 H 5 ) 3 Triethyl Triethyl Aluminium orthoborate (C 2 H 5 ) 3 B + Al(OC 2 H 5 ) 3 Triethyl Borane

24. (2) By hydroboration reaction : - Addition of diborane to alkene or olefine (double bond) is known as “Hydroboration” . The addition takes place as per Anti Marcownikoff rule. Hydroboration is the reaction in which borane of the type R 2 BH react with olefine.

25. H R-CH=CH 2 + B+ H H H R-CH 2 -CH 2 -B+ R-CH=CH 2 R-CH 2 -CH 2 -B-CH 2 -CH 2 -R H H Mono alkyl borane dialkyl borane R-CH=CH 2 R-CH 2 -CH 2 -B-CH 2 -CH 2 -R CH 2 -CH 2 -R Trialkyl borane

26. (2) 3CH 3 -CH=CH-CH 3 + BH 3 0ċ THF CH 3 CH 3 -CH 2 -CH B Trialkyl borane (3) 3NaBH 4 + 4BF 3 3NaBF 4 + 2B 2 H 6 Diborane 3

27. Hydroboration oxidation is stereospecific reaction. The reaction of alkene with H 2 O 2 gives alcohols according to Anti-markownikoff’s rules,it is cis addition. The reaction indicates that the reaction is initiated by addition of peroxide ion (HOO ) to boron and then migration of alkyl group from boron to oxygen. When all the alkyl group migrated , the resulting borone is hydrolysed and give alcohol. R 3 B + H 2 O 2 OH 3ROH + B(OH) 3 25 ċ Mechanism Of Hydroboration Oxidation

28. Mechanism

29. (1) Disiamyl Borane :- Dialkyl borane is known as disiamyl borane. CH 3 -C = CH + BH 3 CH 3 - CH- CH BH CH 3 CH 3 CH 3 CH 3 2 Trisubstituted Disiamyl borane alkene PREPARATION

30. (2) Texyl borane:- Mono alkyl borane is known as Texyl borane. CH 3 -C = C- CH 3 + BH 3 CH 3 CH 3 Tetra substituted alkene CH 3 CH 3 -CH-C-BH 2 CH 3 CH 3 Texyl borane

31. (3) 9 BBN = 9 bicyclo borononane or 9 boro bicyclo [3,3,1] nonane When cyclo octadiene is react with BH 3 in presence of THF at oċ then 9 BBN is produced which is stereoselective and stereospecific reagent. It is crystalline solid which is stable to both therally and atmosphare.

32. (1) Preparation of ketone or oxidation by chromic acid :- Chromic acid oxidise organoborane compound to directly ketone. CH 3 CH 3 H B H 3 B Na 2 CrO 4 + H 2 SO 4 H (o) 25-30ċ CH 3 O 1-methyl cyclohexene 2-methyl cyclohexanone SYNTHETIC APPLICATIONS :-

33. CH 3 H CH 3 H 3 C-C=C-CH 3 + BH 3 0ċ CH 3 - C - C- BH 2 CH 3 THF CH 3 CH 3 Mono alkyl borane H CH 3 H 2 O 2 /OH CH 3 -C - C - OH CH 3 CH 3 Tertiary alcohol (2)Preparation Of alcohol:- Tertiary alcohol:-

34. (3) Preparation of Amines:- CH 3 CH 3 B 3 + B H 3 3NH 2 OSO 3 H CH 3 3 Trialkyl NH 2 borane B( OSO 3 H) 3 + 3 1-Methyl 2-amino cyclohexane