Bis a-camphorquinone dioximato cobalt

Form Supplied in ligand may be available but the catalyst is sensitive to air and must be prepared just before use. 

Analysis of Reagent Purity a change in color from brown to pale brown or yellow indicates decomposition. Only the soluble part should be used. 

Preparative Methods Co(a-cqd)2 is prepared from Cobalt(II) Chloride hexahydrate and the corresponding isomer of cam-phorquinone dioxime (cqd) (from optically active natural camphor) in ethanol with addition of an aqueous solution of NaOH under nitrogen or argon. This complex is best when freshly prepared before use under nitrogen or preferably under argon. The starting material, L-camphor, is easily obtained in optically pure form. 

Handling, Storage, and Precautions the dry solid must be kept under nitrogen or argon, preferably in the cold. The solution of the catalyst in organic solvents such as benzene, acetone, ethyl acetate, hexanes, or acetophenone deteriorates on standing even under nitrogen. Therefore use just after preparation is recommended. 

Although many chiral cyclopropanation catalysts are known, this class of complexes is superior for the alkenes containing vinyl, phenyl, or alkoxycarbonyl groups. Some relevant examples are shown in eq 1-5. In eq 5, the enantiomeric excess of the product is not known due to the absence of enantiomerically pure isomer. The absolute configuration is not known. 

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R2Zn, cat bis((->camphorquinone-a-dioximato) cobalt(II) or palladium(II)] (enantioselective)... 

Bis(camphorquinone-a-dioximato)cobalt(II) (10) has been developed as a catalyst for enan-tioselective cyclopropanation reactions. It allows selective carbene transfer from diazoacetic esters to terminal C-C double bonds which are in conjugation with vinyl, aryl, alkoxycarbonyl or cyano groups, but not to alkyl-substituted alkenes, cycloalkenes, 1,3-dienes and al-lenes. The unusual chemoselectivity and some other experimental observations make the two mechanistic pathways proposed vide supra) questionable for these special carbene-transfer reactions. In contrast, the cobalt(II) complex 11 allows not only the cyclopropanation of styrene but also of oct-l-ene, a nonactivated alkene (ethyl diazoacetate, 35 °C, 3mol% of catalyst yield 50-60%). ... 

The ability of chiral bis(camphorquinone-a-dioximato)cobalt(Il) complexes (Section 1.2.1.2.4.2.6.3.1.) to catalyze carbene transfer from diazocarbonyl compounds (diazoacetic esters, 2-diazo-l-phenylethan-l-one) to terminal alkenes conjugated with vinyl, aryl, carbonyl, and cyano groups, has already been mentioned. The ee-values are 75-88 /o at best, often lower. The highest values are again obtained with bulky diazoacetic esters. The significance of these catalysts, however, is their ability to promote cyclopropanation of electron-deficient alkenes, such as acrylates and acrylonitriles, in contrast to the rhodium and copper catalysts discussed above. 

Bis[( — )-camphoFquinone-a-dioximato]cobalt(ll) hydrate (1). Mol. wt. 467.42, m.p. 240 241". The chiral complex is prepared by the reaction of CoCIa-OHaO with the a-dioxjme of (— )-camphorquinone. 

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