5-Coordination cobalt

At the time of the first volume of CCC(1987), the biological chemistry of cobalt was almost exclusively concerned with the cobalamins. The field has expanded and developed markedly since then. New cobalt-containing proteins have been characterized and applications of traditional cobalt coordination compounds in biology developed. These developments are illustrated below in some detail, as the field was not reviewed in the first edition. 

In the presence of all the other catalysts shown in Table II, acrylonitrile and VP react further to give appreciable amounts of activated olefins which can compete with the acetylene for cobalt coordination sites and therefore act as a catalyst poison. 

Vitamin Bjj (8.50, cobalamin) is an extremely complex molecule consisting of a corrin ring system similar to heme. The central metal atom is cobalt, coordinated with a ribofuranosyl-dimethylbenzimidazole. Vitamin Bjj occurs in liver, but is also produced by many bacteria and is therefore obtained commercially by fermentation. The vitamin is a catalyst for the rearrangement of methylmalonyl-CoA to the succinyl derivative in the degradation of some amino acids and the oxidation of fatty acids with an odd number of carbon atoms. It is also necessary for the methylation of homocysteine to methionine. 

In 2003, Torre and his co-workers prepared new terpene-aromatic hybrids 47 in high yields in the reactions of cobalt-coordinated propargylic compounds, derived from commercial (7iJ)-myrtenal, with a variety of aromatic compounds (Equation (23)). Interestingly, any terpene-aromatic hybrids are not produced from propargylic compounds without cobalt coordination. 

Examples of carbanion additions to cobalt-coordinated imines will be considered in the next section (7.4.3.2) as chelate ring formation is a consequence in some cases. 

Cobalt-coordinated amide nucleophiles have also been observed to attack coordinated phosphate esters (equation 38),148 disulfides (Scheme 47)149 150 and nitriles (Scheme 48).151>152 Chelated amides can also be formed by intramolecular attack of cobalt hydroxides.153... 

Fig. 8.11. 600 MHz NOESY spectra of the four-cobalt cluster of cobalt-substituted metalloth-ionein. The spectra have been recorded with tm = 7 ms using a specially built probe featuring a 90° pulse of 3.7 p,s. (A) Spectrum obtained with a 125 kHz 16 bit ADC by folding the spectrum in both dimensions cross peaks g-b and c-i are folded. (B) Spectrum recorded using a fast ADC over a 250 kHz spectral width. The nine observed connectivities between geminal protons of cobalt-coordinated cysteine P-CH2 are summarized in the inset. Cross peaks marked with numbers are EXSY cross peaks to a minor species labeled Y in the inset [12].

Supplementary information on the cobalt coordination can be derived from the XANES region. The near-edge structure of the samples is shown in Figure 2 The spectra all show a weak absorption peak near threshold which has been identified as a 1s —> 3d transition (17,18). This transition has been observed to be more intense in te-... 

Corroles are tetrapyrrole macrocycles that are closely related to porphyrins, with one carbon atom less in the onter periphery and one NH proton more in their inner core. They may also be considered as the aromatic version (identical skeleton) of the only partially conjugated corrin, the cobalt-coordinating ligand in Vitamin B. Two potential application of corroles are in tumor detection and their use in photovoltaic devices. Selective snbstitntion of corroles via nitration, hydroformylation, and chlorosulfonation for the gallinm were studied in detail and the respective mechanistic pathways and spectroscopic data were reported, (an example is shown in Fignre 27). Overall, over 139 varions corroles were synthesized and the effect of various metal complexation pertaining to their selective reactivity examined. ... 

The experiments by Werner and his associates on cobalt coordination compounds accomplished two things they increased the chemical knowledge in this extensive area (more than 700 compounds) and helped Werner develop his ideas on coordination theory and stereochemistry. It was only after he had received the Nobel Prize (191S) and after his death (1919) that his ideas of primary and secondary valence were confirmed. Unfortunately, Werner s span of active life was short (1893-1915). A listing is given of his co-workers who researched cobalt compounds. These resulted in 52 papers by Werner, 75 with co-authors, and at least 10 unpublished theses. Research to 1960 on cobalt coordination compounds has been summarized in Gmelins Handbuch der anorganischen Chemie (1963). 

A Ifred Werner (December 12, 1866-November 15, 1919) during his professionally active life (1893-1915) contributed extraordinarily to the knowledge of cobalt coordination compounds. These compounds, no doubt, helped him develop his ideas that resulted in the two theories that made him a leader in two phases of twentieth century chemistry coordination theory and stereochemistry. 

S. Konig, J.A. Leary, Evidence for linkage position determination in cobalt coordinated pentasaccharides using ion trap MS, J. Am. Soc. Mass Spectrom., 9 (1998) 1125. 

EXPERIMENT 2.3 ANALYSIS OF COBALT COORDINATION COMPOUNDS I SPECTROPHOTOMETRIC DETERMINATION OF COBALT1-5... 

Each student must dry his/her sample of cobalt coordination compound in a weighing bottle (top ajar) for about 1 h at 120 °C and cool to room temperature in a desiccator. It is recommended that this be carried out during a pre-lab lecture or at the start of Procedure 2.2.a. 

Procedure 2.3.b Preparation of the Cobalt Coordination Compound Sample Solution—Decomposition and Reduction of Cobalt(lll) to Cobalt(ll). 

Remove your dried and cooled sample of cobalt coordination compound from the desiccator, and immediately weigh (by difference, using an analytical balance)... 

EXPERIMENT 2.4 ANALYSIS OF COBALT COORDINATION COMPOUNDS II—ACID-BASE TITRIMETRIC DETERMINATION OF AMMONIA16 Level 2... 

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