试剂 介绍

1. Tris(dibenzylideneacetone)dipalladium(0)

Tris(dibenzylideneacetone)dipalladium(0) or Pd2(dba)3 is an organometallic complex based on

palladium and dibenzylideneacetone used in organic chemistry. It was discovered in 1970.

Preparation and structure:

It is prepared from dibenzylideneacetone and sodium tetrachloropalladate.[2] The complex has a

dark purple/brown color, and, because it is commonly recrystalized from chloroform, it often as

the adduct Pd2(dba)3.CHCl3.

In tris(dibenzylideneacetone)dipalladium(0) the pair of Pd atoms are separated by 320 pm but are

tied together by dba units.[3] The Pd(0) centres are bound to the alkene parts of the dba ligands.

Applications:

Pd2(dba)3 is used as a source of soluble Pd(0), particularly as a catalyst for various coupling

reactions in which it undergoes oxidation to Pd(II). Examples of reactions using this reagent are

the Negishi coupling, Suzuki coupling, Carroll rearrangement, Trost asymmetric allylic alkylation,

as well as Buchwald–Hartwig amination.[4] A related Pd(0) complex is

tetrakis(triphenylphosphine)palladium(0).

References1.

1.^ Takahashi, Y.; Ito, Ts.; Sakai, S.; Ishii, Y. (1970). "A novel palladium(0) complex;

bis(dibenzylideneacetone)palladium(0)". Journal of the Chemical Society D: Chemical

Communications: 1065. doi:10.1039/C29700001065.

2.^ Encyclopedia of Reagents for Organic Synthesis, L.A. Paquette, Ed.: J. Wiley and Sons:

Sussex, England, 1996

3.^ Pierpont, Cortlandt G.; Mazza, Margaret C. (1974). "Crystal and molecular structure of

tris(dibenzylideneacetone)dipalladium(0)". Inorg. Chem. 13: 1891. doi:10.1021/ic50138a020.

4.^ Hartwig, J. F. (2010). Organotransition Metal Chemistry, from Bonding to Catalysis. New

York: University Science Books. ISBN 189138953X.

The Negishi coupling is a cross coupling reaction in organic chemistry involving an organozinc

compound, an organic halide and a nickel or palladium catalyst creating a new carbon-carbon

covalent bond:[1][2]

The halide X can be chloride, bromine or iodine but also a triflate or acetyloxy group with as the organic residue R alkenyl, aryl, allyl, alkynyl or propargyl. The halide X' in the organozinc compound can be chloride, bromine or iodine and the organic

residue R' is alkenyl, aryl, allyl or alkyl.

The metal M in the catalyst is nickel or palladium

The ligand L in the catalyst can be triphenylphosphine, dppe, BINAP or chiraphos

Palladium catalysts in general have higher chemical yields and higher functional group tolerance.

The Suzuki reaction is the organic reaction of an aryl- or vinyl-boronic acid with an aryl- or

vinyl-halide catalyzed by a palladium(0) complex.[1][2] It is widely used to synthesize

poly-olefins, styrenes, and substituted biphenyls, and has been extended to incorporate alkyl

bromides.[3] Several reviews have been published

The reaction also works with pseudohalides, such as triflates (OTf), instead of halides, and also

with boron-esters instead of boronic acids.

Relative reactivity: R2-I > R2-OTf > R2-Br >> R2-Cl

First published in 1979 by Akira Suzuki, the Suzuki reaction couples boronic acids (containing an

organic part) to halides. The reaction relies on a palladium catalyst such as

tetrakis(triphenylphosphine)palladium(0) to effect part of the transformation. The palladium

catalyst (more strictly a pre-catalyst) is 4-coordinate, and usually involves phosphine supporting

groups.

The 2010 Nobel Prize in Chemistry was awarded to Suzuki for his discovery and development of

this reaction. In many publications this reaction also goes by the name Suzuki-Miyaura reaction. It

is also often referred to as "Suzuki Coupling".

Reaction mechanism

The mechanism of the Suzuki reaction is best viewed from the perspective of the palladium

catalyst. The first step is the oxidative addition of palladium to the halide 2 to form the

organopalladium species 3. Reaction with base gives intermediate 4, which via transmetalation[7]

with the boron-ate complex 6 forms the organopalladium species 8. Reductive elimination of the

desired product 9 restores the original palladium catalyst 1.

Oxidative addition

Oxidative addition proceeds with retention of stereochemistry with vinyl halides, while giving inversion of stereochemistry with allylic and benzylic halides.[8] The oxidative addition initially

forms the cis-palladium complex, which rapidly isomerizes to the trans-complex.[9]

Reductive elimination

Using deuterium-labelling, Ridgway et al. have shown the reductive elimination proceeds with

retention of stereochemistry.[10] Relative reactivity of different metal complexes in the C-C

reductive elimination was established: Pd(IV), Pd(II) > Pt(IV), Pt(II), Rh(III) > Ir(III), Ru(II),