Cobalt amine complexes synthesis

It was also reported by PruP et al. [31] that in situ formed cobalt(III) complexes of pyridine-4-ylmethyl-propyl-amine (PYPA) on preformed organomodified HMS are active as catalysts in the aerobic oxidation of styrene and also 1-decene (Figure 3). Incorporation of PYPA may be achieved by following several routes viz. sol-gel synthesis, post modification of sol-gel AMP-HMS, and grafting. The authors proposed that all materials are able to act as... 

Coordinated a-amino amides can be formed by the nucleophilic addition of amines to coordinated a-amino esters (see Chapter 7.4). This reaction forms the basis of attempts to use suitable metal coordination to promote peptide synthesis. Again, studies have been carried out using coordination of several metals and an interesting early example is amide formation on an amino acid imine complex of magnesium (equation 75).355 However, cobalt(III) complexes, because of their high kinetic stability, have received most serious investigation. These studies have been closely associated with those previously described for the hydrolysis of esters, amides and peptides. Whereas hydrolysis is observed when reactions are carried out in water, reactions in dimethyl-formamide or dimethyl sulfoxide result in peptide bond formation. These comparative results are illustrated in Scheme 91.356-358 The key intermediate (126) has also been reacted with dipeptide... 

A consequence of the addition of coordinated OH- to alkenes is that other nucleophilies, for example a coordinated aminate ion, should also be active. This type of reaction is seen with the chloropentaammine complex [Co(NH3)500CCH=CHC02Bu,]2+ in aqueous base533 (Scheme 49). The reaction of the f-butyl maleate complex occurs to the extent of ca. 50% and is complicated by hydrolysis of the maleate ester and some decomposition of the cobalt(III) complexes. Reactions of this type have recently been exploited in the synthesis of j3-carboxyaspartic acid in the coordination sphere of cobalt(III).53... 

A novel synthesis of benzosultam 164 involves a Co-based catalytic system for intramolecular C-H animation with azides <07OL4889>. The commercially available cobalt tetraphenylporphyrin complex, Co(TPP) 163, is an effective catalyst for catalyzing C-H animation with arylsulfonyl azides 162 leading to benzosultams 164 in excellent yields. In addition to benzylic C-H bond, non-benzylic C-H bonds can also be intramolecularly aminated. For example, reaction of arylsulfonyl azides 165 with Co catalyst 163 results in a mixture of 5- and 6-membered ring products, 166 and 167. 

The cobalt complex, Co(NO)[S2CN(CH3)2]2, is well characterized. - However, direct synthesis of itfrom the reaction between NO and Co[S2CN(CH3)2]2 leads to impure materials which are very difficult to purify. The ethylenedi-amine complex, Co(NO)(C2H4N2H4)2(Cl04)2, can readily be prepared in good yields and is easily converted into the dithiocarbamate derivative. The products from these reactions are obtained in a relatively pure form and can easily be further purified. 

From the viewpoints of reaction mechanism and efficiency in organic synthesis, oxidation of phenols with dioxygen catalyzed by cobalt-, manganese- and related metal-amine complexes has been studied . In particular, much effort has been directed toward constructing new efficient catalysts by a combination of metals with... 

In chapter 6 we described the use of the remarkable Pauson-Khand reaction for the synthesis of cyclopentenones. If the components (CO, alkene and alkyne) are tethered by a nitrogen atom, a heterocycle will also be formed. The first stage in this process is to couple the cobalt carbonyl complex, e.g. 236, of ahalo-alkyne with an amine containing the alkene in the side chain. The best way to do this is to react 234 with Co2(CO)9 to give 235 and then 236 and to capture this complex with the amine without isolation of intermediates.34... 

A.S. Abu-Surrah, B. Rieger, R. Fawzi, M. Steiman, Synthesis of chiral and C2-S5nnmetric iron (II) and cobalt(II) complexes bearing a new tetradentate amine ligand system. J. OrganomeL Chem. 497, 73-79 (1995)... 

In a series of papers, Siddiqi et al. detail the synthesis of purported cobalt(lI) complexes, [Co(S2CNR2)2], derived from a range of amines including succi-nimide and phthalimide (49), p-naphthylamine (1125), and chloroanilines (1423). Others have claimed the preparation of those containing benzyl (506) and benzylpiperazine (1126), substituted piperidines (1116,1424,1425), and 1,3,4-thiaxolyl dithiocarbamate (1426). In none of this work was oxygen rigorously excluded. 

Alkyne-nitrile cyclotrimerization is a powerful synthetic methodology for the synthesis of complex heterocyclic aromatic molecules.118 Recently, Fatland et al. developed an aqueous alkyne-nitrile cyclotrimerization of one nitrile with two alkynes for the synthesis of highly functionalized pyridines by a water-soluble cobalt catalyst (Eq. 4.62). The reaction was chemospecific and several different functional groups such as unprotected alcohols, ketones, and amines were compatible with the reaction.119 In addition, photocatalyzed [2+2+2] alkyne or alkyne-nitrile cyclotrimerization in water120 and cyclotrimerization in supercritical H2O110121 have been reported in recent years. 

Sargeson and his coworkers have developed an area of cobalt(III) coordination chemistry which has enabled the synthesis of complicated multidentate ligands directly around the metal. The basis for all of this chemistry is the high stability of cobalt(III) ammine complexes towards dissociation. Consequently, a coordinated ammonia molecule can be deprotonated with base to produce a coordinated amine anion (or amide anion) which functions as a powerful nucleophile. Such a species can attack carbonyl groups, either in intramolecular or intermolecular processes. Similar reactions can be performed by coordinated primary or secondary amines after deprotonation. The resulting imines coordinated to cobalt(III) show unusually high stability towards hydrolysis, but are reactive towards carbon nucleophiles. While the cobalt(III) ion produces some iminium character, it occupies the normal site of protonation and is attached to the nitrogen atom by a kinetically inert bond, and thus resists hydrolysis. 

Interest in these ligands stems from a desire to synthesize improved analogues of the cobalamines 100). With this in mind, 2,6-diacetylpyridine was condensed with N,N,N- f ra(aminopropyl)amine in the presence of nickel(II) or eopper(II) to afford the complex of 105, Cobalt(II) and zinc(II) have also been employed as templating agents in the synthesis of 105 101). The reaction of the nickel(II) complex of 105 with acetone results in a dimeric complex, 106101), by a process that is well established for primary amines 102). 

This precedents prompted several groups to develop reaction protocols that lead exclusively to the reduced products (the reductive PKR), in order to use them in synthesis. Thus, Becker obtained diazabicyclooctanones like 208 from amines (207) as the only reaction product when they used DSAC conditions under an inert atmosphere. The nitrogen atmosphere was essential as in air they obtained mixtures of the cyclopentanones and the cyclopentenones. This group has used this methodology for the synthesis of azaadamantanes like 209 as part of the structure of certain antagonists (Scheme 59) [ 182-184], Addition of TFA to the reaction favors the formation of reduced products. A series of alkynes produced cyclopentanones as the major product when reacted with norbornene, Co2(CO)8 and TFA. The authors think TFA reacts with the cobalt complex 210, prior to the reductive elimination that gives the final product 211 (Scheme 60) [185]. 

Another important example of COj-hydrogenation is the synthesis of form-amides. In 1970, Haynes c/tf/. of Shell Development Co. discovered the reaction of carbon dioxide, hydrogen and certain amines, when catalyzed under mild conditions by cobalt, rhodium, iridium and palladium complexes [ I70. ... 

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