Materials DPPF

An interesting parallel was found while the microwave-enhanced Heck reaction was explored on the C-3 position of the pyrazinone system [29]. The additional problem here was caused by the capability of the alkene to undergo Diels-Alder reaction with the 2-azadiene system of the pyrazinone. An interesting competition between the Heck reaction and the Diels-Alder reaction has been noticed, while the outcome solely depended on the substrates and the catalyst system. Microwave irradiation of a mixture of pyrazinone (Re = H), ethyl acrylate (Y = COOEt) and Pd(dppf)Cl2 resulted in the formation of a mixture of the starting material together with the cycloaddition product in a 3 1 ratio (Scheme 15). On the contrary, when Pd(OAc)2 was used in combination with the bulky phosphine ligand 2-(di-t-butylphosphino)biphenyl [41-44], the Heck reaction product was obtained as the sole product. When a mixture of the pyrazinone (Re = Ar) with ethyl acrylate or styrene and Pd(dppf)Cl2 was irradiated at 150 °C for 15 min, both catalytic systems favored the Heck reaction product with no trace of Diels-Alder adduct. 

Again a distorted tetrahedral coordination of Hg is achieved in the l,l-bis(diphenylphos-phino)ferrocene (dppf) complex with Hgl2. Both Hg—P in the dppf chelate ring and terminal Hg—I bonds (averages 256.5 pm and 277.6 pm, respectively) are clearly longer than in the previous examples all angles around Hg are close to the value for a tetrahedron. Nonlinear optical properties of the material have been studied.241... 

Suzuki-type coupling protocols were also evaluated as a method to prepare some related tetrahedral stilbenoid molecules and the optimal yields were achieved when using Pd(dppf)Cl2 as the catalyst. The cruciform materials prepared using this strategy are shown in Scheme 3.3. Compounds 5a and b were obtained as a mixture of cis and trans isomers as identified by high-performance liquid chromatographic (HPLC) analysis. Nevertheless, the mixtures were readily converted into the all-trans isomers by irradiating the dissolved samples with a mercury lamp. 

A number of groups have used the palladium chemistry to prepare triarylamines that are relevant to electronic materials. Barlow and Marder showed that N,N-diarylaminoferrocenes can be prepared by this methodology. Aminoferrocene [247] was allowed to react with 4-bromotoluene under rigorously anaerobic palladium-catalyzed conditions with DPPF as the... 

Representative Procedure for the Palladium-Catalyzed Arylation of Amines with Aryl Bromides using DPPF/Pd (Excerpted with permission from [29]. 1996 American Chemical Society) In an inert atmosphere dry box, DPPFPdClj and 3.0 equiv. of DPPF/Pd were added to a solution of 20 equiv of bromoben-zophenone and 25 equiv of sodium ferf-butoxide in 8 ml of anhydrous THF. The reaction tube was sealed with a cap containing a PTFE septum and removed from the dry box. Butylamine (25 equiv) was added to the reaction mixture by syringe, and the mixture was heated to 100 °C for 3 h. The reaction was cooled to room temperature, the volatile materials were removed by rotary evaporation, and the product was isolated by either sublimation or silica-gel chromatography (20 1 hexane/EtOAc or 10 1 hexane/Et20 followed by 4 1 hexane Et20). 

Dialkylzinc is another common substrate in Pd-catalyzed couplings. An efficient ketone synthesis uses acid chlorides as starting material (Scheme 1-9). The use of PdCl2(dppf) offers high yields and is best in restricting the formation of benzaldehyde as a )8-elimination byproduct [117]. A-Aryl aromatic imine 34 can be obtained from aromatic iodides and aryl isocyanide 35 [118]. The proposed intermediate,... 

A-Arylhydrazones are useful agricultural materials. Moreover, they can be cleaved to form A-arylhydrazines for pyrazole synthesis, and the hydrazine portion can be transferred to ketones to serve as substrates for the Fischer indole synthesis.t The reactions of benzophenone hydrazone with aryl halides have been reported, and to date these reactions are best conducted with chelating phosphine ligands such as DPPF and BINAP, as shown in Eq. 22. These catalyst systans have been the only ones reported for hydra-zone arylation. The chemistry of hydrazonato complexes is similar to that of aniUdes and diarylamides.f Thus, the reactions of aryl chlorides with hydrazones should be accessible in the future using alkylphosphine ligands. 

C.iii.c. Preparation of Small Molecules for Materials Science. Pd-catalyzed amination has also been used to prepare small molecules that are useful as hole-transport materials, selective metal-cation detection systems, and dyestuffs. As mentioned briefly in the section on reacting diarylamines with aryl halides, Marder and co-workers used palladium chemistry to form triarylamines, which are useful as hole-transport layers. Reactions of primary arylamines with aryl halides using DPPF-hgated palladium as catalyst allows for the selective addition of one aryl halide, followed by the addition of a second aryl halide to form mixed triarylamines, as shown in Eq. 42. This procedure has been used to generate unsymmetrical triarylamines that are analogs of TPD, as shown in Eq. 43. hi addition, they have used aminoferrocene as a substrate to conduct diarylations to form N, A-diarylaminoferrocenes. ... 

At the time of the work, only two large scale examples of the palladium-catalyzed cyanation had been reported [14, 15], and the standard method consisted of heating an aryl iodide or bromide with Pd(OAc)2, dppf, Zn(CN)2 and Zn (dust) in DMF at 80-120°C [23]. Application of these conditions on 1 g scale in the lab gave high conversion to 2, but during the 50 g scale manufacture, the reaction stopped at incomplete conversion. Even after forced conditions (>10 h at 120°C), only a 35% conversion to product was observed, together with a mixture of equal amounts of unreacted starting material and by-products. 

The robust catalyst systems based on BINAP (1) and DPPF (9) found wide applications in the synthesis of building blocks for pharmaceuticals and new materials. For example, the densely functionalized aryl bromide 51 was coupled with the aniline 51 in quantitative yield (Scheme 13.61) [109]. 

Triarylamines attracted considerable interest because of their potential as novel organic electronic materials [113-115]. Hartwig et al. [116] demonstrated tlie potential of P(tBu)3 (26) or DPPF (9) for such applications in the synthesis of dendrimeric triarylamines. Hole-transporting organic materials were synthesized from poly-brominated arenes and diarylamines using only 0.025 mol% of Pd(OAc)2/P(fBu)3 (26) (Scheme 13.68) [117]. 

Scheme 3 Diastereo- and enantioselective alcohol-mediated hydrohydroxyalkylation of butadienes. Yields are of material isolated by flash chromatography on silica gel. Diastereoselectivity was determined through NMR analysis of crude reaction mixtures. Enantiomeric excess was determined by chiral stationary phase HPLC analysis. DM-SEGPHOS = 5,5 -fots-[di(3,5-xylyl)phosphino]-4,4 -bi-l,3-benzodioxole. dppf = 1,1-(>M-(diphenylphosphino)ferrocene. SEGPHOS = 5,5 -Ws-(diphenylphosphino)-4,4 -bi-l,3-benzodioxole...

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