Solvent exchange rates in cobalt(III) complexes measured by N.M.R. spectroscopy

Abstract

The mechanism of substitution reactions in octahedral coba1t(111) complexes of the type [CoXY en,]"+, where en represents 1,2-diaminoethane, and X and Y monodentate ligands, has been extensively re~iewed.l-~ In aquation studies, where studies of oxygen exchange in aquo complexes would have been useful in the interpretation of mechanism, the techniques are difficult, and not a great amount of work has been a t t e m~t e d .~,~ In most of the non-aqueous solvent studies7-10 the differentiation between unimolecular (SN1) and bimolecular solvolytic SOL) mechanisms of substitution has proved difficult because intermediates containing the coordinated solvent have not been isolated.Recent work in dipolar aprotic ~o l v e n t s , l~-~* where stable complexes containing the coordinated solvent have been prepared, has emphasized the need for solvent exchange results, and in these systems n.m.r. spectroscopy will prove a useful technique in that proton resonances in such ligands as dimethyl sulphoxide (DMSO) and NN-dimethylformamide (DMF) are shifted significantly by coordination. 15 We have studied exchange of the solvent DMSO-d, for DMSO in complex ions of the type cis-[CoX(DMSO) en2I2+ where X = C1-, Br-, and NO;, and in the complex ion cis-[Co(DMSO), en,I3+ a t the probe temperature (35") in a Varian A60 analytical n.m.r. spectrometer. (DNSO-d, was used as supplied by Merck, Sharpe & Dohme at 99.9% purity.) Rate constants were calculated from the areas of the methyl proton resonances of the coordinated and free dimethyl sulphoxide molecules.

Second sphere interaction in fluoroanion binding: Synthesis, spectroscopic and X-ray structural study of trans-dichlorobis(ethylenediamine) cobalt(III) terafluoroborate

“…The peak area observed is 8:8 for both types of protons as indicated by the chemical formula of the complex salt and no coupling was observed. But when 1 H NMR is recorded in D 2 O, the singlet at 5.26 ppm is observed due to NH 2 protons and singlet at 2.93 ppm is observed due to CH 2 protons [18]. The peak area observed is again 1:1 for both type of protons and coupling was also observed between protons of -CH 2 -group and -NH 2 -group of the ligand ethylenediammine, which may be due to the exchange of some of the hydrogens by deuterium.…”

Stereochemistry of spontaneous and induced aquation of some resolved cis-bis(ethylenediamine)cobalt(III) complexes - nonretentive spontaneous aquation

“…Equation 2was fitted in the form of eq 12 where the parameter TV is a function e = ec 4-(eA ec + A)e~kat -Ne~hit (12) of eB, the other parameter Zq, and the constant Zq. Thus as Zq -» Zq, eq 12 approximates eq 13 whence N and hence eB e = ec +(eA ~ec)e~kt (13) are undefined. Although eobsd and qaicd agreed and Zq was well-defined with small standard deviations (±3%), eB values so obtained were meaningless.…”

First X-ray crystal structure of cation [cis-Co(en)2(H2O)Cl]2+: Synthesis, spectroscopic and X-ray structural study of [cis-Co(en)2(H2O)Cl](C6H5SO3)2·H2O

“…NMR spectrum of the complex salt was recorded in D 2 [12] group are observed at 2.0 ppm, thus confirming the cis geometry of the complex. The two signals at 7.0 and 7.3 ppm are attributed to the protons of benzene ring, the two protons in the vicinity of SO À 3 group and the three protons far from this group respectively.…”

“…To distinguish between cis and trans isomers, the NMR spectra of ethylenediamine cobalt(III) complexes in deuterium oxide is very diagnostic: the nitrogen protons show different number of signals depending on geometry of complex [12]. The cis-bisethylenediaminecobalt(III) complex has multiple peaks attributed to nitrogen protons, while the trans isomer shows single peak due to nitrogen protons.…”