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Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes
Nicole M. Camasso, and Melanie S. SanfordScience
Volume 347(6227):1218-1220March 13, 2015
Presented by- Anubhav RajpootArun KumarAshik Biswas
Instructor-Dr. Swadhin MandalAssociate professor IISER Kolkata
Biologically important
Nature’s antioxidant
Paramagnetic
C C M+ +M
CC
C C + M
Introduction to coupling reactions
C X M
M
XCC X M++ +
C-C Bonds between complex fragments
Carbon-Heteroatom bondsBetween complex fragments
Biologically important
Nature’s antioxidant
Coupling Reaction: Traditional Catalytic Cycle
Oxidative Addition: M(0) M(ii) Addition of Organic halide
to the M
Transmetalation: Transfer of alkyl/aryl group from one metal to another High activation energy Rate determining step Two electron transfer
process
Reductive Elimination: Final Product Regeneration of the
catalyst M(ii) M(0)
Objective
Metal atom having variable Ox. State ie. loose/gain electron relatively easily
Can accelerate many chemical reaction as catalyst
Tune the coordination environment around metal
Can be used in coupling reactions.
Concept of Nickel(IV) Complexes
Pd & Ni share same group so, they should have similar analogy.
Can Ni(IV) be prepared & equally
useful?
Pd(IV) has mediated many important C-X coupling reactions.
Why Ni instead of Pd?
Fig:Price of the elements (in $/kg) Vs. their annual production (in kg/yr).(Chem. Rev. 2016, 116, 3594−3657)
More sustainable and economical
Favourable intrinsic properties
Lower atomic radius
More Number
of oxidation
states.Lesselectronegativity
Does Ni(IV) complex accessible?
Cyclic voltammogram of (bpy)Ni(II)(CH2CMe2-o-C6H4)
study of Ni(ii) complex:
two oxidative waves at –0.61 V and +0.27 V versus Fc/Fc+ (Fc, ferrocene).
NiIII/NiIV NiII/NiIII
Reaction Scheme
(3)
-[Ni]
-[Ni]
VERY TRANSIENT.NO NMR.
At RT or -400 C
Ni(IV) complex is stable due to presence of
strong EWG.
Which oxidant to use ?
Tridentate instead of bidentate ligand
-[NiII]
>Immediate colour chan from dark red to
yellow. >much stable than bidentate ligand Ni
complex.92% yield isolated by recrystallzation
Solid state, Octahedral geometry
How to stabilise Ni(iv) complex
1.2 equiv NMe4OAc
1.2 equiv NMe4 X
X
(78%)X=OPh,SPh
Complicated mixtures of products
Which Ni precursor to use forNucleophiles like OPh and SPh?
Works only with Acetate!
Precursor which gives neutral intermediate
Why?
Due to positive charge on Ni(IV) Intermediate!
Reactivity of NiIV complex
The Ni(IV) intermediate does not have any charge on it
Lesser side product.Good selectivity.
Ni precursor with Tp ligand.(Tp=Trispyrazolylborate)
Application of Ni(IV) complex as catalyst
-N2
Adventitious water-Ni(II)
>Pharmaceuticals
>Chemical industries.
Dimethyl indole (is used as photorefractive material ) can be prepared by using nickel(IV) complex through alkyl azide formation
Conclusion
A series of Organometallic Niiv complexes are designed, synthesized . Niiv complexes undergo highly selective carbon(sp3)-oxygen, carbon(sp3)-nitrogen, and carbon(sp3)-sulfur coupling reactions with exogenous nucleophiles. Observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions.
Reference……… (1.) Yoshinori Aihara and Naoto Chatani, J. Am. Chem. Soc. 2014, 136, 898−901
(2.) Sarah Z. Tasker1*, Eric A. Standley1* & Timothy F. Jamison1,N AT U R E, V O L 5 0 9 ,2 0 1 4
(3.) Xile Hu*, Chem. Sci., 2011, 2, 1867
(4.) RSC Catalysis Series No. 21,New Trends in Cross-Coupling: Theory and Applications
(5.)Shao M, Chang Q, Dodelet J, Chenitz R, Chem. Rev. 2016, 116, 3594−3657
(6.)Wikipedia
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