Cobalt reaction with Lewis bases

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

Supported Cobalt Catalysts. Experiments were conducted with [Co(PC)]/Si02 at 340°C to determine the important variables for the catalysis of a typical [M(PC)]. Table IV gives the results for runs which were conducted for varying periods of time. It is seen that even at 100 hr. the conversion only reached 36%. The equilibrium conversion at 342°C can be estimated to be 97%. (9) Thus, the reaction is quite far from equilibrium even at long times. This may be taken as evidence for product inhibition of the catalysis. This might be expected since tetrahydroquinoline is a stronger Lewis base than quinoline. Thus, the product could bind to the metal center and prevent activation of the substrate and/or hydrogen. One important conclusion is that the reaction is not over in 24 hours and it can be assumed that the difference in conversions noted in Table I with different [M(PC)] are due to differences in inherent activity of the [M(PC)]. 

The cobalt-silicon compounds described here undergo reactions with protonic molecules such as hydrogen chloride, Lewis bases such as trimethylamine, and oxidizing agents. 

Transition metals have a particular tendency to form complex ions because they have more than one oxidation state. This property allows them to act effectively as Lewis acids in reactions with many molecules or ions that serve as electron donors, or as Lewis bases. For example, a solution of cobalt(II) chloride is pink because of the presence of the Co(H20)6 ions (Figure 16.8). When HCl is added, the solution turns blue as a result of the formation of the complex ion CoCl4 ... 

A test first described by Parri in 1924 in which the barbiturate gives a colored complex with cobalt(II) has been adapted by the pharmacopoeia. The test parameters of the determination have been modified several times through the years, but the presence of a number of elements constitutes the essence of the procedure a ion, normally cobalt(II) or copper(II) an organic solvent, preferably one with a Lewis base character and an alkaline reaction and the absence of water in the test solution. Furthermore ammonia, or an organic amine, is sometimes added. 

The cobalt carbonyls are prepared by the disproportionation reaction of [Co2(CO)g] in the presence of Lewis bases or by the reduction of cluster cobalt carbonyls with the alkali metals. The iridium compounds are obtained during reduction of [Ir4(CO)i2] with sodium in ether solution. The rhodium carbonyls are usually synthesized by reduction of [Rh2Cl2(CO)4] or [RhClg] " with carbon monoxide in basic medium or by nucleophilic attack of bases on the carbonyl group of carbonyl clusters (see preparation of [M4(CO)i2] and [M6(CO)i6]). 

Cobalt exhibits a characteristic tendency to form clusters of the formula RCCo3(CO)9, which have trigonal-pyramidal structures. The cobalt atoms occupy the three positions at the base of the pyramid, and the carbon group lies at its top vertex. These cobalt-carbon clusters are prepared by reactions of RCX3 with Co2(CO)8 or NaCo(CO)4 in the presence of Lewis bases ... 

A remarkable acceleration effect on the ring-opening of various epoxides with HCo(CO)4 was achieved by the addition of small amounts of Lewis bases such as alcohols (ethanol, butanol) [8]. In this maimer, the hydroformylation of propylene oxide was accelerated by a factor of 100. An improvement of conversion was also observed in the presence of acetone, diethyl ether, or THE (tetrahydrofu-ran). Low reaction temperatures stimulated hkewise the selective formation of hydroxy aldehydes. With styrene, mainly isomeric diols were obtained because of the high reducing power of the cobalt catalyst. Epichlorohydrin yielded mainly ethyl y-chloro-P-hydroxypropionate. The relative reactivity of the olefin oxides toward these hydroformylation conditions was found to be in the following order (Figure 6.15). 

The scope of this reaction is similar to that of 10-21. Though anhydrides are somewhat less reactive than acyl halides, they are often used to prepare carboxylic esters. Acids, Lewis acids, and bases are often used as catalysts—most often, pyridine. Catalysis by pyridine is of the nucleophilic type (see 10-9). 4-(A,A-Dimethylamino)pyridine is a better catalyst than pyridine and can be used in cases where pyridine fails. " Nonbasic catalysts are cobalt(II) chloride " and TaCls—Si02. " Formic anhydride is not a stable compound but esters of formic acid can be prepared by treating alcohols " or phenols " with acetic-formic anhydride. Cyclic anhydrides give monoesterified dicarboxylic acids, for example,... 

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