Tt-Allyl palladium complex

As mentioned in the introduction, 7T-complexes of conjugated dienes with palladium(II) are not stable enough to be isolated. However, reaction of a conjugated diene with PdCl2 in alcoholic solvents or acetic acid gives a (TT-allyl)palladium complex 27 in which the... 

The reaction starts with an oxidative addition of an allylic compound to palladium(O) and a Tt-allyl-palladium complex forms. Carboxylates, allyl halides, etc. can be used. In practice one often starts with divalent palladium sources, which require in situ reduction. This reduction can take place in several ways, it may involve the alkene, the nucleophile, or the phosphine ligand added. One can start from zerovalent palladium complexes, but very stable palladium(O) complexes may also require an incubation period. Good starting materials are the 7t-allyl-palladium intermediates ... 

TT-allyl palladium complexes through addition-elimination of a palladium hydride. 

The reaction of tt -allyl palladium complexes with hydrogen causes decomposition of the compounds, and produces either alkenes or alkanes, depending on the degree of substitution of the TT-aUyl complex and the reaction conditions. Hydride reagents, such as NaBUi and LiAUTi, also reduce the aUylic group to alkanes or alkenes. 

For the palladium dibenzylideneacetone complex (1), NMR data to support the proposition that the bis-phosphine acts as a bidentate ligand has been reported. A triflate salt of the TT-allyl palladium complex has been isolated and is stable in the solid state. However, no crystals suitable for X-ray analysis were obtained. An X-ray crystal structure of the ligand and a bis-palladium complex has been reported. The palladium complexes are generated just before use under an inert atmosphere exposure to air affords a catalytically inactive tetra-coordinated palladium(II) species. ... 

Abstract Palladium-catalyzed cascade reactions have gained steadily increasing importance over the last decade. The important factor in these reactions is the catalytic generation of Ti-allyl palladium intermediates which further undergo a variety of reactions. TT-Allyl palladium complexes can be easily formed by the treatment of allylic substrates with Pd(0). A 7r-allyl palladium complexes on treatment with allylic metal species produce bis Ti-allyl palladium complex. In this review, the palladium catalyzed cascade reactions involving 7r-allyl palladium chemistry is described. The first part deals with catalytic reactions involving 7r-allyl palladium complexes as an intermediate, while the second part features catalytic reactions involving bis 7r-allyl palladium complex as an intermediate. 

Bis TT-allyl palladium complex Synthetic strategies Heterocycles... 

It is very well known that 7r-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as bisallypalladium complex (also called bis-jr-allylpalladium complex), bis(allyl)palladium complex, 77 77 -bis(allyl)palladium complex, respectively. Bis TT-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis jr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

Scheme 8-8 Stereocontrolled acetate attack on (TT-allyl)palladium complexes.

Palladium-catalyzed oxidation of 1,4-dienes has also been reported. Thus, Brown and Davidson obtained the l,3-diacetate 25 from oxidation of l,4-cyclohexadiene by ben-zoquinone in acetic acid with palladium acetate as the catalyst (Scheme 3). Presumably the reaction proceeds via acetoxypalladation-isomerization to give a Tt-allyl intermediate, which subsequently undergoes nucleophilic attack by acetate. This principle, i.e. rearrangement of a (cr,7r-allyl)- to a (Tt-allyl)palladium complex, has been applied in nonoxidative palladium-catalyzed reactions of 1,4-dienes by Larock and coworkers. Akermark and coworkers have demonstrated the stereochemistry of this process by the transformation of l,4-cyclohexadiene to the (Tr-allyl)palladium complex 26 by treatment... 

Recently an allylic phosphonate has been shown to react as an allylic phosphonate cation by transformation to a TT-allyl-palladium complex, susceptible to attack by nucleophiles such as stabilized carb-anions (Scheme 34). ... 

Furstner has employed the Trost pyrrole synthesis in the first total synthesis of roseophilin, wherein this A-benzylpyirole ring forming step occurred in 70% yield [28]. Backvall has found that primary amines react with dienes under the guidance of Pd(II) to form pyrroles 236 in variable yields [146]. The intermediate tt-allyl-palladium complexes are quite stable. 

Aryl and vinyl haiides can be coupled in reactions catalyzed by palladium or nickel complexes bearing phosphine ligands [253], Allylic derivatives that are precursors of tt-allyl palladium complexes can also be coupled with organomagnesium reagents. Asymmetry can be induced by using chiral phosphines as ligands. 

TT-Allyl palladium complexes may be prepared from alkenes. The resulting complexes are electrophilic (Chapter 9). Nucleophilic attack results in the formation of a functionalized alkene, while the... 

Bakker JM, Besson T, Lemaire J, Scuderi D, Maitre P (2007) Gas-phase structure of a tt-allyl-palladium complex efficient infrared spectroscopy in a 7 T Fourier transform mass spectrometer. J Phys Chem A 111 13415-13424... 

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