Alkyl cobalt pyridine

Alkyl cobalt(lII)bis(dimethylglyoxime anion)pyridine, [R-Co(l,l)(dmgH)2py,l]... 

As with polybut-l-ene and many other vinyl monomers that contain an asymmetric carbon, isotactic, syndiotactic and atactic stmctures may be drawn. Using co-ordination catalysts such as mixtures of cobalt chlorides, aluminium alkyls, pyridine and water high-1,2 (high vinyl) polymers may be obtained. One product marketed by the Japan Synthetic Rubber Company (JSR 1,2 PBD) is 91% 1,2, and 51-66% of the 1,2 units are in the syndiotactic state. The molecular mass is said to be several hundred thousand and the ratio MJM is in the range 1.7-2.6. 

Duong and Gaudemer studied the alkylation of (presumably) [Co -(DMG)2X], where X is pyridine, aniline, or water, by the cis and trans isomers of )S-bromostyrene (PhCH=CHBr) and the methyl ester of )3-chloroacrylic acid (CHCl=CHCOOMe) in 50% aqueous methanol, and found that the configuration of the double bond remained unchanged, i.e., the halogen had simply been replaced by cobalt. They suggested that the reaction involved the addition of cobalt, followed by the elimination of the halide ion (apparently without rotation around the C—C bond), i.e.. 

The hydrogenations become analogous to those involving HMn(CO)5 (see Section II,D), and to some catalyzed by HCo(CN)53 (see below). Use of bis(dimethylglyoximato)cobalt(II)-base complexes or cobaloximes(II) as catalysts (7, p. 193) has been more thoroughly studied (189, 190). Alkyl intermediates have been isolated with some activated olefinic substrates using the pyridine system, and electronic and steric effects on the catalytic hydrogenation rates have been reported (189). Mechanistic studies have appeared on the use of (pyridine)cobaloxime(II) with H2, and of (pyridine)chlorocobaloxime(III) and vitamin B12 with borohydride, for reduction of a,/3-unsaturated esters (190). Protonation of a carbanion... 

The benzyl ligand of benzylbis(dimethylglyoximato)pyridine cobalt complex has been selectively converted to 3,5-dibenzyl-l,2,4-oxadiazole by a reaction with alkyl nitrite in the presence of light (426). The reaction proceeds by the in situ formation of an oxime and a nitrile oxide (Scheme 1.44). 

More recently, Potthoff and Breitmaier found that alkoxy dienes (83) react with cyanoformate (84) under mild conditions if a cobalt catalyst is used (equation 28). The products of the reaction are py-ridines (85) and/or (86) depending upon the 2-alkyl substituent in the diene. Thus, if R = methyl, only isomer (85) is formed. When R = ethyl, a mixture of pyridines is produced, whereas when R is large only (86) is detected. The origin of these results is not clear. 

This type of reaction could not be effected using alkyl-lithium or alkyl-Grignard reagents. Also, the products represented by 2.225 and 2.227 with presumed divalent cobalt centers as offered by Johnson and coworkers should be considered as being tentative only no conclusive data were actually given in support of the proposed formulations. There is also a discrepancy between the main textual body and the experimental section of the 1973 paper by Johnson and coworkers as to which Co(III) derivative was actually used in these reactions. In the main body, it is stated that the square planar (implying pyridine-free) Co(III) corrole is used, whereas in the experimental section, it is stated that the pyridine derivatives were used. 

Yamazaki s complex (Structure 5) contains two alkyne molecules linked together to form a five-membered metallacycle. Arene-solvated cobalt atoms, obtained by reacting cobalt vapor and arenes, have been used by Italian workers to promote the conversion of a,w-dialkynes and nitriles giving alkynyl-substituted pyridines [20]. -Tolueneiron(0) complexes have also been utilized for the co-cyclotrimerization of acetylene and alkyl cyanides or benzonitrile giving a-substituted pyridine derivatives. However, the catalytic transformation to the industrially important 2-vinylpyridine fails in this case acrylonitrile cannot be co-cyclotrimerized with acetylene at the iron catalyst [17]. 

A [2 + 2 + 2] cobalt(I) cycloaddition between 2,6-di-(trimethylsilylethynyl)-pyridine and 5-hexynenitrile builds up the two distal pyridines to provide (72).79 The chiral tpy (73a) was built up using Krohnke methodology and then stereospecifically alkylated with lithium diisopropylamide and different alkyl iodides to provide derivatives such as (73b).80... 

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