Amines, as cobalt complex ligand

The sorption processes for cobalt complexes can be complicated by hydrolysis reactions of the complex in solution, surface induced ligand loss processes, sorption of hydrolysis products of either amine, protonated amine, or mixed amine/aquo cobalt complexes, and oxidation/reduction processes associated with cobalt. The principal objective of the XPS studies was to evaluate, the chemical state of cobalt and amine ligands, the surface concentration of the respective elements, and the ligand to cobalt ratio as indicated by the surface nitrogen to cobalt atomic ratio. 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

Both acyclic and cyclic amines, as well as ammonia, can act as ligands, primarily in cobalt(II) and cobalt(III) complexes, so as to produce systems that react with and/or activate dioxygen. With some inevitable overlap, we have separated these topics into distinct sections to aid in the clarity of presentation. 

The alleged preparation of the supposed cobaltdD complex Na[Co(Et2dtc)3] described by D Ascenzo and Wendlandt (305) has been repeated by Holah and Murphy (306), who identified the product as [CofEtjdtcla]. Complexes of cobalt(III), nickel(II), and palladiumdl) salts with cationic, dithiocarbamate ligands have been synthesized (307). Reaction of the secondary amine (Et2N(CH2)2>2NH with CS2 produces... 

Co(in) complexes promote similar reactions. When four of the six octahedral positions are occupied by amine ligands and two cis positions are available for further reactions, it is possible to study not only the hydrolysis itself, but the steric preferences of the complexes. In general, these compounds catalyze the hydrolysis of N-terminal amino acids from peptides, and the amino acid that is removed remains as part of the complex. The reactions apparently proceed by coordination of the free amine to cobalt, followed either by coordination of the carbonyl to cobalt and subsequent reaction with OH or H2O from the solution (path A in Figure 12-15) or reaction of the carbonyl carbon with coordinated hydroxide (path B). As a result, the N-terminal amino acid is removed from the peptide and left as part of the cobalt complex in which the a-amino nitrogen and the carbonyl oxygen are bonded to the cobalt. Esters and amides are also hydrolyzed by the same mechanism, with the relative importance of the two pathways dependent on the specific compoimds used. 

Kinetically inert low-spin cobalt (III) clathrochelates are reversibly reduced by accepting one electron to yield kinetically labile cobalt(II) complexes. In the case of the usual amines (for instance, ammonia), the reduction is, as a rule, accompanied by irreversible decay of the amine cobalt complex. This reaction is slower for chelating amines macrocyclic and especially macrobicyclic amines produce complexes with cobalt(II) ion that are stable over a long time. This fact facilitates the study of the reduction of cobalt(III) complexes to cobalt(II) ones. In most cases, the reactions of macrobicyclic ligands do not interfere with this process. 

Linear and cyclic polyamine complexes of mthenium(III) have been little studied relative to those of first-row transition elements such as cobalt(III) and nickel(II), presumably due to a lack of general routes of syntheses. A convenient and reproducible method for the syntheses of trans-[RuLCl2], where L is any multidentate aliphatic ligand with a four-amine donor combination, has been developed. Procedures for the preparation of trans-[RuLCl2] [L = (en)2,J 2,3,2,-tet,f and cyclamj] are described here. The literature method is closely followed except that the much safer hexafluorophosphate(l — ) anion is employed in place of perchlorate. 

Oxidative carbonylation of amines to carbamates and ureas in the presence of cobalt complexes was recently reported (24-25), We have found that Co(II) complexes bearing nitrogen and oxygen-donor ligands such as carboxylates, acetylacetonates and Schiff bases produce DMC with high selectivity in methanol under CO and Oj. (Table VII) (26-27),... 

PPO is generally prepared by oxidative polymerization of 2,6-dimethylphenol in toluene solution in the presence of oxygen over an catalyst. Copper-amine catalysts are undoubtedly the most studied systems whereas other metal systems including manganese chloride (12), cobalt complex (13) have also shown to be effective in bench scale. Various amines including mono-dentate and biden-tate amines have been used as ligand for copper (I) complex which shows a wide range of activity as indicated in Table 2.4 (2,14-16). 

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