Co salen

In order to make these oxidative reactions of 1,3-dienes catalytic, several reoxidants are used. In general, a stoichiometric amount of benzoquinone is used. Furthermore, Fe-phthalocyanine complex or Co-salen complex is used to reoxidize hydroquinone to benzoquinone. Also, it was found that the reaction is faster and stereoselectivity is higher when (phenylsulflnyl)benzoquinone (383) is used owing to coordination of the sulfinyl group to Pd, Thus the reaction can be carried out using catalytic amounts of PdfOAcji and (arylsulfinyl)benzoquinone in the presence of the Fe or Co complex under an oxygen atmosphere[320]. Oxidative dicyanation of butadiene takes place to give l,4-dicyano-2-butene(384) (40%) and l,2-dicyano-3-butene (385)[32l]. 

To a solution of indoline (20 mM in MeOH) was added Co(salen) (0.10 equiv.) and O2 was bubbled through the suspension at 25°C. After 1 h the suspension became homogeneous and the solvent was removed in vacuo and the product purified by chromatography on silica gel. 

Square planar complexes are also well authenticated if not particularly numerous and include [Co(phthalocyanine)] and [Co(CN)4] as well as [Co(salen)] and complexes with other Schiff bases. These are invariably low-spin with magnetic moments at room temperature in the range 2.1-2.9 BM, indicating 1 unpaired electron. They are primarily of interest because... 

HKR 0.6 equiv H20 relative to epoxide, neat, rt, 15-24 h, yield based on epoxide (50% max) PKR 2.2-2.5 equiv epoxide relative to phenol, 4 °C, CH3CN, <24 h, yield based on phenol AKR 2.2-2.5 equiv epoxide relative to alcohol, 4 °C, CH3CN, <24 h, yield based on alcohol (R,R)-oligomeric Co(salen) OTs 21 catalyst used instead in this entry... 

One way of overcoming these problems is by kinetic resolution of racemic epoxides. Jacobsen has been very successful in applying chiral Co-salen catalysts, such as 21, in the kinetic resolution of terminal epoxides (Scheme 9.18) [83]. One enantiomer of the epoxide is converted into the corresponding diol, whereas the other enantiomer can be recovered intact, usually with excellent ee. The strategy works for a variety of epoxides, including vinylepoxides. The major limitation of this strategy is that the maximum theoretical yield is 50%. 

The formulas and names of these organocobalt complexes are usually given in the form [RCo(L4)X], e.g., [vinyl-Co(salen)py]. 

Change of base (pyridine, aniline, water) had no obvious effect on the steric course of the reaction (59). Rather surprisingly, it appears that the reactions of the cis and trans isomers of 1-bromopropene with the hydride [Co(CN)5H] give different products this eliminates an initial addition of Co—H to the double bond, since this would lead to the same product for the two isomers 105). Vinyl chloride apparently reacts only with [Co salen] , and not with the hydride, to form the CH2=CHCo complex 43) the same may be the case with the BAE complexes 40). 

Catalytic hydrogenation with platinum liberates the hydrocarbon from methylcobalamin (57) and from alkyl-Co-DMG complexes (161), but not from pentacyanides with primary alkyl, vinyl, or benzyl ligands, though the cr-allyl complex yields propylene (109). Sodium sand gives mixtures of hydrocarbons with the alkyl-Co-salen complexes (64). Dithioerythritol will liberate methane from a variety of methyl complexes [cobalamin, DMG, DMG-BF2, G, DPG, CHD, salen, and (DO)(DOH)pn] (156), as will 1,4-butanedithiol from the DMG complex (157), and certain unspecified thiols will reduce DMG complexes with substituted alkyl ligands (e.g., C0-CH2COOH ->CH3C00H) (163, 164). Reaction with thiols can also lead to the formation of thioethers (see Section C,3). 

Asymmetric Ring Opening of Some Terminal Epoxides Catalyzed by Dimeric Type Novel Chiral Co(Salen) Complexes... 

The asymmetric ring opening (ARO) of racemic terminal epoxides with H2O via hydrolytic kinetic resolution provides an efficient synthetic route to prepare optically pure terminal epoxides. The dimeric type chiral Co(salen)AlX3 complex has great potential to catalyze HKR of terminal epoxides in a highly reactive and enantioselective manner in comparison to their monomeric analogy. 

To a solution of hexa hydrated aluminum chloride (1.99g, 8.28 mmol, 1.0 equiv.) in tetrahydrofuran (25 mL), precatalyst (R,R)-salenCo (5.0 g, 8.28 mmol, 1.0 equiv. ) was added and stirred in at open atmosphere at room temperature. As soon as the chiral Co (salen) was added color of the solution changes from brick red to dark olive green. The mixture was stirred for 1 h. The resulting solution was concentrated imder reduced pressure. The crude solid was worked up with H2O and CH2CI2. Yield = 98-99 % as a dark green solid powder. The complex have been analyzed by A1 NMR with reference to [A1(D20)6] and... 

UV visible spectrophotometer. A1 (N03)3.9H20 monomer was prepared in same manner. In case of synthesis of dimer complex, 2 equivalent of the Co(salen) was taken with respect to AlX3.nH20. 

The formation of monomer and dimer of (salen)Co AIX3 complex can be confirmed by Al NMR. Monomer complex la show Al NMR chemical shift on 5=43.1 ppm line width =30.2 Hz and dimer complex lb 5=37.7 ppm line width =12.7 Hz. Further instrumental evidence may be viewed by UV-Vis spectrophotometer. The new synthesized complex showed absorption band at 370 nm. The characteristic absorption band of the precatalyst Co(salen) at 420 nm disappeared (Figure 1). It has long been known that oxygen atoms of the metal complexes of the SchifT bases are able to coordinate to the transition and group 13 metals to form bi- and trinuclear complex [9]. On these proofs the possible structure is shown in Scheme 1. 

Fig. 1. UV-Vis absorption spectra of the precatalyst Scheme 2. Possible working model for the HKR chiral Co(salen) and monomer and dimer complex. of terminal epoxides catalyzed by C0-AIX3...

In the present study the dimer (salen)CoAlX3 showed enhanced activity and enantioselectivity. The catalyst can be synthesized easily by readily commercially available precatalyst Co(salen) in both enantiomeric forms. Potentially, the catalyst may be used on an industrial scale and could be recycled. Currently we are looking for the applicability of the catalyst to asymmetric reaction of terminal and meso epoxides with other nucleophiles and related electrophile-nucleophile reactions. 

Much work has been devoted to the study of Schiff base complexes, in particular M(salen), where M = metal, has been the subject of extensive work 114). The early work by Calvin et al. (section 111(A)) suggested that the 2 1 (M O2) dioxygen adduct, type I, formed by Co(salen) in the solid state, contains a peroxo linkage. An X-ray analysis 115, 116) of the complex (Co Salen)202(DMF)2 supports this hypothesis see Fig. 5 for the pertinent results of this study. 

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