Styrenes, hydrocyanation

Enantiomeric excess was obtained by chiral HPLC using a Daicel Chiralcel OB column (styrene hydrocyanation 99 1 hexane/2-propanol 1.0 mL min 40°C. 6-methoxy-vinylnaphthalene hydrocyanation 93 7 hexane/2-propanol 0.5 mL min 40 C). 

Table 2 Structure-property relationships for styrene hydrocyanation. Conditions ... 

Table 10.1. Nickel-catalysed hydrocyanation of styrene, using diphosphine ligands. ...

Leeuwen, P.W.N.M., Vogt D. and Keim, W. (1995) Effect of the bite angle of diphosphine ligands on activity and selectivity in the nickel-catalysed hydrocyanation of styrene. /. Chem. Soc. Chem. Commun., 2177-1778. 

Hydrocyanation of alkenes usually gives anti-Markovnikov products. Interestingly, however, addition of HCN to styrene yields mostly the branched (Marko-vnikov) adduct. This was suggested to result from stabilization of the branched alkylnickel cyanide intermediate by interaction of nickel with the aromatic ring.176... 

Figure 5. The catalytic cycle of hydrocyanation of styrene as example of the vinylarenes.

FIGURE 22 Preparation of supramolecular catalysts for hydrocyanation reactions (82) (A) assembly of heterodimeric chelating ligands (B) structure of the optimal nickel-diphosphine complex for hydrocyanation (other ligands of the metal center are omitted for clarity) and (C) hydrocyanation of functionalized styrenes. (For a color version of this figure, the reader is referred to the Web version of this chapter.)... 

The authors assessed the catalytic activities of these supramolecular nickel complexes for the hydrocyanation of substituted styrenes with... 

Hydrocyanation of styrene 26 (eq. (7)) has been examined in some detail. With Ni[P(0-o-tolyl)3]4 27 the branched nitrile 29 is strongly favored over the linear one, which is explained by the intermediary formation of a detectable alkyl species 28. The stability of this intermediate is attributed to the donation of aromatic ring electrons to the coordinatively unsaturated metal center. Crystal structures of related compounds are reported in the literature [53, 54]. 

In the earliest attempt at the asymmetric hydrocyanation of styrene, Gosser obtained 10% ee in the Ni-DIOP-catalyzed reaction [5]. Our initial studies were... 

The asymmetric hydrocyanation of a series of p-substituted styrene derivatives showed that indeed the electron-deficient catalyst gave the highest ees in every case (e.g. for 4-methylstyrene la - 70% lb - 47% Ic - 1%). Yet the electronic nature of the substrate also seems to play an important role. For example, the following % ees were observed using la for a series of substituted styrenes ... 

The entrance into the catalytic cycle from complex 5 may occur via a small equilibrium concentration of Ni-(la)-(MVN) complex6 (pathA, Schemes) and/or via oxidative addition of HCN to generate the species Ni-[la]-HCN, 7 (pathB). In either event, formation of the hydridoalkene complex Ni-[1]-(MVN)(H)(CN), 8, occurs and is followed by an insertion reaction to produce the (ri -benzyl)nickel cyanide intermediate 9. Although this allyl-type species has not been directly detected, the exclusive formation of the branched nitrile supports its intermediacy. Analogous intermediates have been postulated in the hydrocyanation of 1,3-butadiene with NilPlO-o-tolylljjj or Ni[P(OEt)3]4 and in the hydrocyanation of styrene with Ni[P(0-p-tolyl)3]4. Examples of other nick-el-benzyl complexes exhibiting similar allylic interactions in the solution and solid state are also known. 

In the metal catalyzed hydrocyanation area, the stage is set for major improvements in enantioselectivity for simple styrene derivatives. Asymmetric hydrocyanation of dienes and functionaUzed olefins is another exciting area ripe for further explorations. 

Spectral investigations of the catalytic resting states in both asymmetric hydroformylation and hydrocyanation using bisphosphite 1 were performed. Reaction of Rh(CO)2(acac) with 1 equiv of i under 1 1 CO/H2 led to clean formation of Rh(l)(CO)2H. Infrared spectra of the reaction product exhibited bands at 2069, 2015 and 1984 cm. Extensive characterization of this complex by NMR has been published by van Leeuwen.(4) Under 50 psi l.T CO/H2 in the presence of styrene, identical bands were observed by in situ IR using the ReactIR system. 

The catalyst resting state in asymmetric hydrocyanation using bisphosphite 1 was studied by multinuclear NMR. Reaction of (COD)2Ni with 1 equiv of 1. in 2 1 THF-rfg/styrene was monitored by NMR. A large AB quartet was... 

This pyrolysis technique was used in the analysis of copolymers of acrylonitrile with styrene in a broad range of monomer ratio variations [34]. An ampoule containing a weighed amount (5—10 mg) of the polymer was pre-evacuated down to a residual pressure of 10" mmHg. The pyrolysis was conducted for 20—30 min at 500°C. The composition of the copolymers can be determined from the peaks of hydrocyanic acid and toluene, which are present in the pyrolysis products in amounts proportional to those of acrylonitrile and toluene, respectively, initially present in the copolymer. 

While propylene gives primarily 73, styrene gives exclusively the phenyl-substituted derivative corresponding to 74. It is noteworthy in this connection that hydrocyanation of propylene (using a Ni[P(Ootolyl)3]3 catalyst) gives primarily n-butyronitrile, while styrene gives predominantly the branched product 2-phenyl-propionitrile. ... 

The anti-inflammatory activities of 2-arylpropanoic acids (54) continue to stimulate new methods for their preparation. Hydrocyanation of styrenes and other vinylarenes can be catalysed... 

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