Suzuki Cross-Coupling-百灵威

This Nobel Prize-winning (2010) palladium-catalyzed cross-coupling reaction between organohalides and organoboron compounds is a versatile four-step process, creating carbon-carbon sigma bonds:

(i) Oxidative addition of the organohalide to the Pd⁽⁰⁾ catalyst, creating a halide-Pd^(II)-alkyl complex

(ii) Replacement of the halide attached to the complex with the anion of the base (metathesis)

(iii) The organoboron compound and base form a tetracoordinate borate anion, which increases the nucleophilicity of its alkyl group to exchange with the attached anion of the base, forming a Pd^(II) complex with two alkyl groups (transmetallation)

(iv) Reductive elimination facilitates the formation of a single bond between the alkyl groups, regenerating the Pd⁽⁰⁾ catalyst.

Lab Tips:

Nickel ^[1] or nanocatalysts ^[2] can also be used for this reaction. Moreover, transition-metal-free biaryl coupling has been carried out in water with tetrabutylammonium bromide (TBAB) as an additive. ^[3]
The R group of the organic electrophile may be an alkenyl, aryl, or alkyl. Possible electrophile groups include Cl, Br, I, OTf, and OPO(OR)₂ (enol phosphate). ^[4]
Aryl chlorides generally react sluggishly ^[4] , but improvements to the protocol have been developed. ^[5,6]
Organotrifluoroborates are an alternative to boronic acids, boronate esters, and organoboranes. ^[7]
This coupling reaction is highly stereo- and regioselective. ^[4]
Self-coupling by-products may form because of solvent-dissolved oxygen. ^[4]
Many organic compounds are base-sensitive; choosing the right base and solvent system reduces side reactions and improves yields. ^[8]
Sterically hindered substrates are tolerated. ^[8]
Sp3-hybridized alkyl boranes with β hydrogens that are prone to competitive side reactions can also be coupled via the β-alkyl Suzuki-Miyaura cross-coupling reaction. ^[8]

_{1. Ramgren, S. D., Hie, L., Ye, Y., Garg, N. K. Nickel-catalyzed Suzuki-Miyaura couplings in green solvents. Org. Lett. 2013, 15, 15, 3950-3953.
2. Fihri, A. et al, Nanocatalysts for Suzuki cross-coupling reactions. J. Chem. Soc. Rev. 2011, 40(10), 5181-5203.
3. Leadbeater, N. E., Marco, M. Transition-metal-free Suzuki-type coupling reactions. Angew. Chem. Int. Ed. 2003, 42(12).
4. Kürti, L., Czakó, B. (2005). Strategic Applications of Named Reactions in Organic Synthesis; Background and Detailed Mechanisms. Burlington, MA: Elsevier Academic Press.
5. Littke, A. F., Fu, G. C. A convenient and general method for Pd-catalyzed Suzuki cross-couplings of aryl chlorides and arylboronic acids. Angew. Chem. Int. Ed. Engl. 1999, 37, 3387-3388.
6. Wolfe, J. P., Singer, R. A., Yang, B. H., Buchwald, S. L. Highly active palladium catalysts for Suzuki coupling reactions. J. Am. Chem. Soc. 1999, 121, 9550-9561.
7. Molander, G. A., Ellis, N. Organotrifluoroborates: Protected boronic acids that expand the versatility of the Suzuki coupling reaction. Acc. Chem. Res. 2007, 40, 4, 275-286.
8. Suzuki, Akira. Cross-coupling reactions of organoboranes: an easy way to construct C-C bonds (Nobel Lecture). Angew. Chem. Int. Ed. 2011, 50, 6722-6737.}

Reagents: Catalytic Palladium, Base (NaOH, Ba(OH₂), Na₂CO₃, K₃PO₄, etc.)
Reactant: Organic Electrophile (Organohalide/Triflate, etc.), Organoboron Compound (Alkyl-, Allyl-, Alkenyl-, Alkynyl-, Aryl-Borane, Boronic Acid, or Boronic (Boronate) Ester)
Product: Coupled Product
Type of Reaction: Cross-Coupling
Bond Formation: C-C