TRANSITION METAL CATALYSIS

TRANSITION METAL CATALYSIS , THE DIFFERENT METALS OF TRANSITION USED AS CATALYTIC REAGENT WITH ITS PROPERTIES , THEIR CHARGE TRANSFER ITS REACTION INCLUDING COPPER, PALLADIUM FOLLWED BY HECKMAN, ULLMAN COUPLING REACTION, GILLMAN REACTION, HECK REACTION

1. TRANSITION METAL CATALYSIS

2. A transition metal as an element whose atom has a partially filled d subshell , or which can give rise to cations with an incomplete d sub-shell . The transition metal ions the outermost d orbitals are incompletely filled with electrons so they can easily give and take electrons. This makes transition metals prime candidates for catalysis. Here transition metals are used as catalysts . INTRODUCTION

3. Zinc, cadmium, and mercury are generally excluded from the transition metals as they have the electronic configuration [ ]d 10s 2 , with no incomplete d shell.

4. The formation of compounds in many oxidation states, due to the relatively low energy gap between different possible oxidation states eg , Fe(II), Fe(III) or switch oxidizing state . Form complexes with reagents by adsorption at active site . Colour in transition-series metal compounds is generally due to electronic transitions of two principal types. Charge transfer transitions d-d transitions PROPERTIES

5. Charge transfer transitions: An electron may jump from a predominantly ligand orbital to a predominantly metal orbital, giving rise to a ligand -to-metal charge-transfer (LMCT) transition. These can most easily occur when the metal is in a high oxidation state. For example, The colour of chromate, dichromate and permanganate ions is due to LMCT transitions. Another example is that mercuric iodide, HgI2, is red because of a LMCT transition . d-d transitions: An electron jumps from one d-orbital to another d-orbital and leads to d-d transitions .

6. The principal reasons why transition metals contribute the essential ingredient in catalyst systems can be summarized as the following headings: (a) Bonding ability (b) Catholic choice of ligands (c) Ligand effects (d) Variability of oxidation state (e) Variablility of co-ordination number

7. Sr.no Transition metal Type of reaction 1 Rhodiam Wilkinson’s reaction 2 Copper Gilman reaction Ullman Coupling Reaction Reactions of organo copper reagent 3 Palladium Heck Reaction Negishi Reaction Stille Reaction Buchwalt-Hartwig amination Suzuki Reaction Sonogashira reaction Hiyama coupling Reaction 4 Nickel Kumada coupling Reaction Transition Metal Catalysed Reaction

8. It is used in the selective hydrogenation of alkenes and alkynes without affecting the functional groups like: C=O, CN, NO2, Aryl, CO2R etc. 1-Rhodium Catalysed Reaction Wilkinsons Reaction

9. A Gilman reagent is a lithium and copper ( diorganocopper ) reagent compound, R2CuLi (Lithium dimethylcuprate ), where R is an alkyl or aryl. They react with organic halides to replace the halide group with an R group . Such displacement reactions allow for the synthesis of complex products from simple building blocks 2-COPPER CATALYSED REACTION Gillman Reaction

10. Generalized chemical reaction showing Gilman reagent reacting with organic halide to form products and showing Cu(III) reaction intermediate In the reaction, the Gilman reagent is a methylating reagent reacting with an alkyne in a conjugate addition forming a cyclic enone

11. Ullmann coupling is a coupling reaction between aryl halides in the presence of copper as a transition metal catalyst to produce Diaryl compounds . A typical example is the coupling of 2 ortho-chloronitrobenzene reactants to form 2,2'-dinitrobiphenyl with a copper - bronze alloy . Ullmann coupling Reaction

12. Carbocupration is a nucleophilic addition of organocopper reagents (R-Cu) to acetylene or terminal alkynes resulting in an alkenylcopper compound (RC=C-Cu).It is a special case of carbometalation and also called the Normant reaction. Substitution Reactions oxidative addition of copper(I) into the carbon-leaving group bond takes place, generating a copper(III) intermediate which then undergoes reductive elimination to generate the coupled product . Reaction of Organocopper Reagent

13. B.Conjugated addition reaction Carbocupration across the carbon-carbon double bond may then generate a copper enolate , Subsequent reductive elimination and protonation leads to the product. C . Enantioselective Variants Diastereoselective conjugate addition reactions of chiral organocuprates provideβ -functionalized ketones in high yield and diastereoselectivity

14. It is the chemical reaction of an alkyl halide with an alkene in the presence of a base and a palladium catalyst (or palladium nanomaterial -based catalyst) to form a substituted alkene . PALLADIUM CATALYSED REACTION Heck Reaction

15. The reaction couples alkyl or aryl halides with organozinc /tin compounds, forming carbon-carbon bonds (c-c) in the process. It involves the coupling of an organotin compound (also known as organostannanes ) with a variety of organic electrophiles via palladium catalyzed coupling reaction . Negishi coupling Stille reaction

16. Used for the synthesis of carbon–nitrogen bonds via the palladium catalyzed cross-coupling of amines with aryl halides . In this coupling occurs between a boronic acid and an organohalide which is catalyzed by a palladium(0) complex . Buchwald Hartwig Amination Suzuki Reaction

17. The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vinyl halide . The Hiyama coupling is a palladium-catalyzed cross-coupling reaction of organosilanes with organic halides used in organic chemistry to form carbon–carbon bonds (C-C bonds) . Sanogishira Coupling Hiyama coupling

18. The Kumada coupling is a type of cross coupling reaction, useful for generating carbon–carbon bonds by the reaction of a Grignardreagent and an organic halide. The procedure uses transition metal catalysts, typically nickel orpalladium , to couple a combination of two alkyl, aryl or vinyl groups NICKEL CATALYSED REACTION Kumada coupling

19. www.wikipeadia.com Textbook of organic chemistry by morrisons and boyd seventh edition pg no 350 Textbook of Organic chemistry by Arun bahl and B.S. bahl Pg no 356 References