Carbonyl nickel catalysis

A-methoxy-carbonyl-2-pyrroline 235 Michael reactions, nickel catalysis 97-8 monophospholanes with pendant f-BuS group 17,19... 

Keywords Allylation Carbonyl compound Dienes Homoallylation Nickel catalysis Reductive coupling... 

Similarly, allenes [32] and alkynols [33] were used as starting materials and their carbonylation provides /3,y-unsaturated acids and unsaturated diacids, respectively. The specific reactivity of alkynols is explained by three formal steps during nickel catalysis (i) carbonylation of the triple bond leading to an acid containing an allylic alcohol moiety (ii) second carbonylation of the double bond to provide a hydroxydiacid and (iii) a dehydration step giving the corresponding unsaturated diacid (Scheme 2). 

Multiple-component difunctionalization reactions of a,/ -unsaturated carbonyl systems have been achieved by catalytic conjugate addition/aldol sequences. As Scheme 8.13 illustrates, an efficient method reported by Montgomery [46] allows regioselective addition of an aryl iodide to the /i-position of an unsaturated ester under nickel catalysis and subsequent trapping with an aldehyde to give / -hydroxyesters (e.g. 33). Significantly, premature termination of the sequence by the /Miydride elimination process that is usually observed in Pd-catalyzed Heck reactions does not occur here. 

The stereochemistry of the metallo-ene cyclization step plays a crucial role in the accessibility of subsequent reaction steps. Thus, only the civ-isomer of the cyclization product can undergo further carbonylative cyclization to form the bicyclic products, while the fram-isorner can Only undergo linear carboxylation 65. Product distribution also depends on the catalyst used. Thus, for selective carbonylative bicyclizations, nickel catalysis, especially Ni(cod)2/1,4-bis(diphenylphos-phino)butane, are more effective than palladium systems, such as Pd(dba)2/triphenylphosphane55. 

Isocyanide complexes have found numerous applications in organic synthesis and catalysis. Isocyanides undergo polymerization in the presence of many transition metal complexes, for instance, metal carbonyls, metallocenes, cyclopentadienyl carbonyls, nickel(II), palladium(II), and cobalt(II) complexes. Exceptionally high activity is exhibited by nickel and cobalt carbonyls. The resulting polymers are Schiff bases ... 

In addition to benzyl zincates, thymidine derivatives bearing carbonyl functionalities were successfully employed in this reaction. However, according to a recent report, nickel catalysis might be superior to palladium catalysis for such coupling reactions. ... 

Scheme 3.5 Domino carbonyl ylide formation-l,3-dipolar cycloaddition reaction catalysed by a combination of rhodium catalysis and chiral nickel catalysis.

The nickel-catalyzed Suzuki-Miyaura-type C-O bond arylation has been successfully applied to steroidal architecture (Scheme 4). A hydroxyl moiety in estrone can readily be substituted by an array of aryl groups under nickel catalysis via conversion into pivalate instead of the typically used triflate [38]. The carbonyl moiety in estrone also serves as a suitable precursor for an alkenyl C-O electrophile. Treatment of estrone with 2-propenyl acetate affords the compounds bearing two acetate groups, both of which are potentially reactive toward nickel-catalyzed cross-coupling. However, selective arylation took place at the alkenyl position, and... 

Allyl chlorides and bromides are readily carbonylated to unsaturated acids using nickel cyanide and phase transfer catalysis conditions. Mechanistic studies revealed that the key catalytic species in this reaction is the cyanotricarbonylnickelate ion(20). 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Nickel and other transition metal catalysts, when modified with a chiral compound such as (R,R)-tartaric acid 5S), become enantioselective. All attempts to modify solid surfaces with optically active substances have so far resulted in catalysts of only low stereoselectivity. This is due to the fact that too many active centers of different structures are present on the surface of the catalysts. Consequently, in asymmetric hydrogenations the technique of homogeneous catalysis is superior to heterogeneous catalysis56). However, some carbonyl compounds have been hydrogenated in the presence of tartaric-acid-supported nickel catalysts in up to 92% optical purity55 . 

In either the acid catalysis or the nickel carbonyl (or other metallic catalyst) method, if alcohols, thiols, amines, etc. are used instead of water, the product is the corresponding ester, thiol ester, or amide, instead of the carboxylic acid. 

The copper(II)-promoted hydrolysis of glycylglycine has been studied in some detail.120 Copper(II) ions catalyze the hydrolysis of glycylglycine in the pH range 3.5 to 6 at 85 °C.120 The pH rate profile has a maximum at pH 4.2, consistent with the view that the catalytically active species in the reaction is the carbonyl-bonded complex. The decrease in rate at higher pH is associated with the formation of a catalytically inactive complex produced by ionization of the peptide hydrogen atom. This view has subsequently been confirmed by other workers,121 in conjunction with an IR investigation of the structures of the copper(II) and zinc(II) complexes in D20 solution.122 Catalysis by cobalt(II),123 and zinc(II), nickel(II) and manganese(II) has also been studied.124-126... 

---