Macrocycles cobalt with oxygen

Suitable halogeno precursors for the cobalt and chromium compounds [PcCoCN] [124] and [PcCrCN] [117] are not known. The reported synthesis of PcCoCl [2b] actually produces impure PCC0CI2 [81] the oxidation product of PcCo with excess of iodine is reported to lead to a species, formulated as [Pc -C o I ] [43,125]. However, in the case of 2,3-TNP as macrocycle chlorination leads to the monomeric pentacoordinated species 2,3-TNPCoCl [14]. This compound exhibits an electrical conductivity of nearly 10 S/cm which, as in the case of the dib-complexes of 2,3-TNPFe, is caused by an additional oxidative doping of the macrocycle with oxygen. 

The impressive sulfur-based reactivity of square planar nickel complexes containing tetradentate N2S2 ligands has been known for many years. Interest has recently resurfaced because of the discovery of similar donor sites in metalloproteins that bind nickel, iron, and cobalt.The iV,iV -bis(mercaptoethyl)-l,5-diazacyclooc-tane ligand H2(BME-D ACO) and its nickel complex have been particularly useful in establishing the scope of S-based reactivity with electrophiles as displayed in the reaction summary shown in Scheme 1." The fundamental features of this reactivity include templated macrocycle production, S-oxygenation as contrasted to oxidation, Lewis acid/base adduct formation, metal-ion capture, and the synthesis of heterodi- and polymetallic complexes. ... 

Carbon dioxide is a linear molecule in which the oxygen atoms are weak Lewis (and Br0nsted) bases and the carbon is electrophilic. Reactions of carbon dioxide are dominated by nucleophilic attacks at the carbon, which result in bending of the O—C—O angle to about 120°. Figure 5.3 illustrates four very different nucleophilic reactions hydroxide attack on CO2 to form bicarbonate the initial addition of ammonia to CO2, which ultimately produces urea the binding of CO2 to a macrocyclic cobalt(I) complex, which catalyzes CO2 reduction and the addition of an electron to CO2 to yield the carbon dioxide radical ion. The first three also exemplify the reactivity of CO2 with respect to nucleophilic attack on the carbon. 

The reaction is regioselective, producing / ara-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain sp C-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products. Kinetic and mechanistic models of the oxidation of phenol with HP, catalysed by a new macrocyclic cobalt(II) complex, have been proposed. The catalytic system displayed high catalytic activity and the catalytic character of a metalloenzyme, although it did not attain the catalytic efficiency of enzymes. 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

Catalysis can be broken down into a number of areas, depending on the substrate and the catalytic reaction. One of the prime areas of the initial effort in catalysis has been small molecule activation, such as oxygen with a number of transition metal ion macrocycles and carbon dioxide, the latter particularly with cobalt(I) and nickel(I) macrocycles. Once the polyanunonium macrocycles were found to be able to recognize substrates other than metal ions, other catalysis applications evolved. For example, phosphoryl transfer catalysis with simple polyanunonium macrocycles has become quite accessible. ... 

There are now several structural studies on cobalt(II) crown ether and cryptand complexes (Table 78), which show the coordination mode to be markedly sensitive to the macrocycle cavity diameter. Both 12-crown-4 and 15-crown-5 (cavity diameters 120-150 pm and 170-220 pm respectively) can include ions to form structures in which every ether oxygen atom is bound to the metal. In contrast Co—O (ether) bonding is destabilized in the larger 18-crown-6 and dicyclohexyl-18-crown 6 polyethers. In the blue complexes obtained from the reaction of these compounds with C0CI2 the role of the cyclic polyether is to solvate discrete [Co(H20)6] cations and [CoC ] " anions and there are no direct Co—O (ether) bonds.A similar effect is seen in the Co" complex of a 27-membered-ring macrocycle where the pentacoordinate structure (267) features only one long Co—O (ether) bond. " ... 

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