Cobalt, chelates

The title cobalt chelate exploded at 175°C during DTA studies, 30° lower than the Co chelate of dicupferron . 

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxy-carbonyl groups are cyclopropanated selectively. No such reaction occurs with alkyl-substituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetylene95). The cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a r 33%) with ethyl diazoacetate deserve notice, as these components usually... 

It has already been mentioned that prochirality of the olefin is not necessary for successful enantioselective cyclopropanation with an alkyl diazoacetate in the presence of catalysts 207. What happens if a prochiral olefin and a non-prochiral diazo compound are combined Only one result provides an answer to date The cyclopropane derived from styrene and dicyanodiazomethane shows only very low optical induction (4.6 % e.e. of the (25) enantiomer, catalyst 207a) 9S). Thus, it can be concluded that with the cobalt chelate catalysts 207, enantioface selectivity at the olefin is generally unimportant and that a prochiral diazo compound is needed for efficient optical induction. As the results with chiral copper 1,3-diketonates 205 and 2-diazodi-medone show, such a statement can not be generalized, of course. 

Friedel-Crafts acylations of the metal acetylacetonate rings are much slower than the electrophilic substitutions described above, probably because of the considerable steric bulk at the reaction site. Furthermore, the strongly acidic conditions during the reaction and subsequent hydrolysis step give rise to considerable degradation, particularly in the case of the more sensitive chromium and cobalt chelates. This consideration places severe limitations on the reaction conditions that can be employed. 

Rhodium acetylacetonate differed considerably from the other metal chelates in the acetylation reaction (26). Under the same conditions that had given extensive acetylation of the cobalt and chromium acetylacetonates, the rhodium chelate reacted very slowly and formed only a small amount of the monoacetylated compound (XX). Fortunately, the hydrolytic stability of rhodium acetylacetonate is such that the Friedel-Crafts reaction can be carried out under vigorous conditions that would rapidly degrade the chromium and cobalt chelates. Thus treatment of rhodium acetylacetonate with acetyl chloride and aluminum chloride in dichloroethane afforded the mono- and diacetylated chelates (XX and XXI). No triacetylated chelate was isolated from this reaction. In a similar manner butyryl-and benzoyl-substituted rhodium chelates (XXIII and XXIV) have been prepared. These and other experiments indicate that the rhodium acetylacetonate ring is less reactive than the cobalt or chromium rings. 

The partially resolved cobalt acetylacetonate was found to be optically stable in solution or in the solid state for long periods. However, slow crystallization of this substance always produced racemic crystals (14). Several of the optically active substituted cobalt chelates exhibited the same strange phenomenon. Removal of the solvent from solutions of optically active cobalt acetylacetonate with a slow stream of air yielded a solid which showed little apparent crystalline character under a polarizing microscope but dissolved to form a solution of about the same specific rotation as the starting solution. 

Synthesis of a typical cobalt chelated styrene derivative [7] is illustrated in Fig. 3. 

As expected, azide addition to dimethyl maleate is very sluggish, and a triazoline is not isolated32 because the LUMOfumarale < LUMOmaleale.304a Recently, however, it has been found that azide coordinated in a cobalt chelate complex [N3Co(DH)2NH3] is sufficiently reactive to add to diethyl maleate, and 25% of the pure triazoline has been obtained (Scheme 80).30 5... 

A convenient method for carrying out the reaction of a high cis-1,4-polybutadiene with PVC was to polymerize butadiene using a suitable catalyst system—e.g., Et2AlCl-cobalt stearate-terf-butyl chloride or Et3Al-cobalt chelate-benzyl chloride, and then to add an appropriate quantity of the resultant polybutadiene solution to a suspension of PVC in chlorobenzene. Additional Et2AlCl could then be added to the reaction mixture, although this was unnecessary if the initial concentration was adequate. 

Calculate (3 for this column, and for both the beryllium and the cobalt chelates calculate the following parameters Vr, VN, k, Rr, K, n, and H. For the unresolved mixture of chromium and ruthenium chelates, calculate the resolution, Rs, assuming that the peaks are of equal height. 

G. Costa Pure Appl. Chem. 30, 335 (1972) The effect of the nature of ligands on the reactivity of the metal-carbon bond in cobalt chelates 18 (61)... 

G. Costa Coord. Chem. Rev. 8, 63 (1972) Recent developments in the field of organometallic derivatives of cobalt chelates 13 (47)... 

The importance of cobalt in the physiology and ecology of cyanobacteria is underscored by evidence showing that they produce strong, specific cobalt chelators. Production of such cobalt... 

It is clear that cobalt catalysts 10—44 are much less active than cobaloximes, generally by 2 orders of magnitude. It is concluded that the hydrogen transfer reaction is not diffusion controlled in their case. This difference in reactivity also suggests that some of the trends found for cobaloximes may not work for other cobalt chelates. Unfortunately, there have been few studies to this end. Most of the values of Cc in Table 4 were calculated having only one or two points on the Mayo dependence. For cases when Cc < 50, it is usually necessary to carry out ad-... 

Hydrides of cobalt chelates are well documented in inorganic chemistry,89 163 and cobaloximes received particular attention in the I960—70s because their chemical behavior was somewhat similar to that of vitamin Bi2.85,86,164 171 Although the hydrides of cobaloximes are very reactive, two instances in which (DH)2CoH was isolated have been reported.88172 It is believed that in the absence of radicals or monomer, the main mode of decomposition of (DH)2CoH... 

The ratio between the rates of parallel eqs 18 and 19 is an issue of practical importance. Cobalt chelates may be good capping agents in living radical polymerization, LRP.206-207 This requires that eq 19 be reversible and the forward and backward (eq 20) rates be approximately equal. 

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