Amine complexes, of cobalt

Certain octahedral complexes, particularly the acido—amine complexes of cobalt(III), undergo substitution in protonic solvents at rates that are proportional to the concentration of the conjugate base of the solvent (e.g. OH- in water) or inversely proportional to the concentration of the conjugate acid of the solvent (e.g. retardation by H30+ in water or NH4+ in liquid ammonia). Such reactions have received considerable attention since systematic studies of ligand substitution commenced, and figured amongst the earliest kinetic studies in the field.298 The subject has been... 

The cobalt(n) complexes of protoporphyrin-IX dimethylester and mesoporphyrin-IX dimethylester have been reduced polarographically.113 The original study by Stynes and Ibers114 of the oxygenation of the amine complexes of cobalt(n) protoporphyrin-IX dimethylester has been criticized by Guidry and Drago,115 who suggest that the treatment of the data was incorrect and that the system is ill-defined. Ibers et al.116 have reconsidered their data and claim that this substantiates the earlier work and proves that the system is clearly defined. 

Electroreduction and electrooxidation of salene (7V,N -bis(salicylidene)-ethyledi-amine) complexes of cobalt and copper studied by Kapturkiewicz and Behr [147] in eight aprotic solvents obey these conditions. These authors were the first to demonstrate experimentally the significant influence of the dielectric relaxation time of solvents on the electrode kinetics. They found earlier [171] that the mechanism of electrode reactions of salene complexes is independent of the solvents applied. No correlation with the prediction of the Marcus theory was found, but the kinetic data correlated well with the viscosity of the solvents and their dielectric relaxation time. However, because the ohmic drop was not well compensated, their rate constants are likely to be too low, as was shown in DMSO by Lasia and coworkers [172]. 

Lattermann et al. reported the first metallomesogenic dendrimer when they described results on trigonal bipyramidal metal complexes of ethylene-imine dendrimers of the first and second generation, based on derivatives of tris(2-aminoethyl)amine. Complexes of cobalt, nickel, copper, and zinc were prepared and found to exhibit relatively low temperature mesophases, which generally possessed hexagonal columnar structures. These materials therefore provided the first examples of metallomesogenic dendrimers [72,73]. 

As a result of a large number of studies on acido amine complexes of cobalt(lll), it appears that replacement of the acido group by H2O occurs by a process that is primarily dissociative in character. The ligand-cobalt bond must be stretehed to some eritieal distance before a H2O molecule begins to enter the... 

Henderson and Tobe [9] have considered in detail how the stereochemistry of amine complexes of cobalt(lll) influences base hydrolysis rates. These authors concluded that the requirements for high lability towards base hydrolysis are as follows ... 

A more detailed understanding of the conjugate-base mechanism for the hydrolysis of kinetically inert amine complexes of cobalt(III) and rhodium(III) is possible if liquid ammonia is used as a solvent. Such techniques allow the separation of parameters for the pre-equilibrium step ( Tcb) and the rate-determining step. A polyamine complex generally contains more than one potentially acidic proton and each proton is characterized by its own acidity constant (Kcb)- exchange rates for... 

Other aquation reactions give further evidence concerning the most favored mechanism of octahedral substitution reactions. Consider the data for the aquation of various bidentate amine complexes of cobalt(III) as shown in Equation (5.33) and Table 5.3 ... 

The alleged preparation of the supposed cobalt(II) 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 [Co(Et2dtc)3]. Complexes of cobalt(III), nickel(II), and palladium(II) salts with cationic, dithiocarbamate ligands have been synthesized (307). Reaction of the secondary amine (Et2N(CH2)2)2NH with CS2 produces... 

The relative instrumental sensitivity factors for cobalt and nitrogen were determined by measuring core level (Co 2p and N Is) XPS spectra for a series of pure cobalt amine complexes of established stoichiometry. To evaluate the core level photopeak intensities, peak areas, including shake-up satellite intensity were used. The precision for the measurements of the nitrogen to cobalt atomic ratio is 10% while the accuracy is approximately 15%. Additional details of the XPS measurements are contained in the literature (24,25). 

The complexes [LCo(p-02)(p-OH)CoL] [L = en, trien, dien, tetra-ethylenepentamine, or tris-(2-aminoethyl)amine] have been studied, and the new complexes [[Co(imidazole)(gly)2 202],4H20 [ Co2(imidazole)2-(gly)402 0H],3H20, and [Co(imidazole)(gly)2(02)H20] have been prepared The spectroscopic properties of various p-peroxo- and p-superoxo-cobalt(iii) complexes have been examined. The singly-bridged p-peroxo-compounds have a strong band at 300 nm, whereas this falls at 350 nm for p-peroxo-p-hydroxo-complexes and two peaks at 480 and 700 nm are observed for p-superoxo-species. The i.r. spectra of p-peroxo-bridged complexes of cobalt(iii)-cyclam have been reported. ... 

Bosnich, B., Poon, C. K., Tobe, M. L., Complexes of cobalt(III) with a cyclic tetradentate secondary amine. Inorg. Chem. 1965,4, 1102-1109. 

The procedure described here is based on the observation that amine monohydroxo complexes of cobalt(III), rhodium(IIl), and iridium(III) react directly with carbon dioxide to form the corresponding carbonato complexes,2 3 without effect on the configuration of the amine ligands.4 The amine monoaqua complex is allowed to react with lithium carbonate or carbon dioxide gas at room temperature at pH 8.0 for a few minutes, and the carbonato complex is isolated by adding alcohol. The procedure has been used to prepare salts of the following cations pentaammine(carbonato)-cobalt(III),2 ds-ammine(carbonato)bis(ethylenediamine)cobalt(III),5 trans-... 

The rate enhancements observed in amine complexes of metal ions such as cobalt(III) and ruthenium(III) are not universally observed. Water exchange on [Fe(OH2)6l is more rapid in base ( 750-fold) (112), enhanced but less so for [Cr(OH2)6p ( 60-fold) (266), and absent in [V(OH2)6] (227). The trend reflects expectations of increasing associative character in reactions of these metal ions from Fe + to to eventually, the conjugate base may play no significant role in the exchange mechanism. For the type of complexes generally covered in this review, however, hydroxide ion causes a significant increase in lability. 

Studies of redox-active metallointercalation agents in the presence of dsDNA have been done with solutions containing the redox complexes of cobalt, iron and osmium [64,68,72,95]. Osmium tetroxide complexes with tertiary amines (Os, L) have been used as a chemical probe of DNA structure. The simultaneous determination, based on a sufficient peak separation on the potential scale of (Os, L)-DNA adducts and free (Os, L), was obtained by Fojta et al. [96] using a p5Tolytic graphite electrode. 

Syntheses reported for the pentaammine(trifluoromethanesulfonato-O) complexes can be readily adapted for other amine or multidentate amine analogs. Syntheses of coIbalt(III) complexes with 1,2-ethanediamine or A -ethyl-l,2-eth-anediamine ligands have been reported earlier in this series. To exemplify the procedures further, trifluoromethanesulfonato-O complexes of cobalt(III), chro-mium(III), and rhodium(III) with unidentate methylamine ligands based on the readily prepared [M(NH3)5Cl]Cl2 precursors are reported here. The following sections report syntheses of 1,2-ethanediamine complexes of Rh(III) and Irflll) and of Ru(II) and Os(II) diimines with trifluoromethanesulfonato ligands. Such syntheses indicate the diversity of the synthesis technique, and the complexes described are excellent precursors for other compounds. 

Probably, the most widely studied coordination compounds are the ammine complexes of cobalt(III). Their stability, ease of preparation, and slow reactions makes them particularly amenable to kinetic study. 8ince work on these complexes has been done almost exclusively in water, the reactions of the complexes with the solvent water had to be considered first. In general, ammonia or amines coordinated to cobalt(ni) are observed to be replaced so slowly by water that only the replacement of ligands other than amines is usually considered. 

Caged Amine complexes of Co(III) The reduced form of Co(III) complexes such as Co(III)(NH3)5X2+ are substitutionally labile. A number of caged cobalt(II) compounds have been found to be fairly inert to substitution. The sar, sep or the sulfur-containing capten cage complexes have [Co(III)/Co(II)] potentials > -0.2V vs NHE are and efficient quenchers of Ru(bpy)3 [41-43]. Some of them have been found use as relays for water photoreduction. 

Aquation of the chlorito complex [Co(NH3)5(C102)] forms part of the overall substitution and redox reactivity pattern established for this complex. Indeed the mechanism of aquation involves an internal redox process. Rate constants and activation parameters for aquation of this chlorito complex in acidic aqueous solution are k29 = 8.0 x 10 s A// = 105 kJ mol and AS = + 13 J mol Although this complex could hardly be described as robust, the chlorite anion is considerably less fragile when coordinated to cobalt(III) than when bonded to Cobalt(III)-amine complexes of organic carbox-... 

The kinetics of stereoselective deuteration of malonate hydrogens in bis(malonato)-cobalt(III) complexes [Co(mal)2L2] containing L2 = en, pn, N,N -Me2en, phen, c/5 -(NH3)2, or c/5-(py)2 have been monitored. Both acid and base hydrolysis are observed, and there is a reversal of stereoselectivity with solution pH. There are some kinetic differences between the amine ligands on the one hand and py and phen on the other, as competition for OD" between malonate and amine is possible, between malonate and py or phen not. The rate law for deuteration of a hydrogens in a-aminocarboxylato complexes of cobalt(III) containing various combinations of glycine, sarcosine, or alanine with ammonia, ethylenediamine, or diaminopropane is simple second order. 

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