Acrylate ligands

K. The rearrangement from 27 to the more stable, primary alkyl regioisomer 29 was shown to be intermolecular. This is thought to occur via the unobserved hydride 28, since addition of unlabeled methyl acrylate leads to the equilibrium distribution of label in 29 (28 exchanges acrylate ligands with the acrylate pool). 

The strongly electron-withdrawing acrylate ligand is responsible for this high regio-selectivity of 1,4-addition. However, it has been demonstrated experimentally (Eq. 268) that the regioselectivity is ligand-dependent. 

Examples of additional procedures for fabrication of ORMOSIL monoliths such as with acrylic ligand group and urea ligand group are presented in Refs [90] and [91], respectively. 

The reaction of iodobenzene with acrylate is a good synthetic method for the cinnamate 17[7]. In the competitive reaction of acrylate with a mixture of 0-and /i-iodoanisoles (18 and 19), the o-methoxycinnamate 20 was obtained selectively owing to the molecular recognition by interlamellar montmorillonite ethylsilyldiphenylphosphine (L) as a heterogenized homogeneous catalyst used as a ligand[28]. 

Benzyl chloride reacts with alkenes bearing an EWG[8], The reaction with acrylate proceeds smoothly to give 7-phenylcrotonate (76) in the presence of BujN without a ligand. No reaction takes place with Pd(Ph,P)4[77]. 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

A cr-aryl-Pd bond is formed by the transfer of an aryl group even from arylphosphines to Pd and alkene insertion takes placefl 17-119], This reaction is slow and it is not a serious problem when triarylphosphine is used as a ligand. The cinnamate 149 is obtained by the reaction of PhsP with acrylate in the presence of Pd(OAc)2 in AcOH. 

Wulff and coworkers have applied their aluminum catalyst 2 containing a vaulted biphenanthrol ligand (VAPOL, Section 2.1) to the Diels-Alder reaction between methyl acrylate and cyclopentadiene [25] (Scheme 1.32). In this Diels-Alder reaction auto-induction is observed, because of a cooperative interaction between the product... 

The use of ionic liquids as reaction media for the palladium-catalyzed Heck reaction was first described by Kaufmann et ak, in 1996 [85]. Treatment of bromoben-zene with butyl acrylate to provide butyl trans-cinnamate succeeded in high yield in molten tetraallcylammonium and tetraallcylphosphonium bromide salts, without addition of phosphine ligands (Scheme 5.2-16). 

These carbonyl chloride-activated carriers are unstable on storage, so ligand coupling to them has to be undertaken immediately after chemisorption of the copolymer. To overcome this drawback, more stable activated carriers have been synthesized by treating aminopropyl-silicas with poly(p-nitrophenyl acrylate) and acetic anhydride. 

Poly (p-nitrophenyl acrylate)-coated wide-pore glass (WPG) was also used as an activated carrier for the immobilization of biospecific ligands and enzymes, A detailed description of properties of these sorbents and catalysts as well as some specific features of their functioning is given in Sect. 6. 

Porous glass (PG) modified with covalently adsorbed poly(p-nitrophenyl acrylate), as described in Sect. 4.1, turned out to be a highly suitable carrier for immobilization of various biospecific ligands and enzymes. When the residual active ester groups of the carrier were blocked by ethanolamine, the immobilized ligands when bound to the solid support via hydrophilic and flexible poly(2-hydroxyethyl acrylamide). The effective biospecific binding provided by the ligands... 

Transition metal salts trap carbon-centered radicals by electron transfer or by ligand transfer. These reagents often show high specificity for reaction with specific radicals and the rates of trapping may be correlated with the nucleophilicity of the radical (Table 5.6). For example, PS radicals are much more reactive towards ferric chloride than acrylic propagating species."07... 

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. 

In recent years, the catalytic asymmetric hydrogenation of a-acylamino acrylic or cinnamic acid derivatives has been widely investigated as a method for preparing chiral a-amino acids, and considerable efforts have been devoted for developing new chiral ligands and complexes to this end. In this context, simple chiral phosphinous amides as well as chiral bis(aminophosphanes) have found notorious applications as ligands in Rh(I) complexes, which have been used in the asymmetric hydrogenation of a-acylamino acrylic acid derivatives (Scheme 43). 

Chiral monodentate carbene complexes of Rh and Ir of the type [MCl(l,5-COD) (NHC)] (M = Rh, Ir) with the ligands 7-9 (Fig. 2.1) have been stndied as catalysts for the enantioselective hydrogenation of methyl-2-acetamido acrylate. Even though the activities were high, the enantiomeric excesses (ee) were poor [7, 8]. 

The use of y-ray induced radical pol5unerization proved to be a successful alternative for the radical co-polymer-ization of metal complexes with ligands containing acrylic C—C double bonds [100-102,129,130]. In particular, the palladium(II) complex cw-[PdCl2(ICPA)2] (1, Scheme 4) was co-polymerized in DMF solution with DMA and MBAA (cross-linker, 4% mol), with no degradation of the metal center [100,101]. 

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