Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

Ojo, J. Folorunso; Ige, Jide; Ogunlusi, Grace O.; Owoyomi, Olanrewaju; Olaseni, Esan S.

doi:10.1007/s11243-005-6398-8

Cited by 5 publications

(12 citation statements)

References 14 publications

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“…Similar observations have been reported in our earlier studies [24] as well as in both the aminolysis of sulfamate esters in chloroform [41] and in the reactions of Co(II) protoporphyrins IX dimethyl ester with pyridine and related compounds [34,37]. Such saturation kinetics is also typical of the formation of a precursor complex prior to electron transfer as observed in the electron transfer reactions of halopentacyanocobaltate(III) complexes [42]. The above observation fits well with the following mechanism:…”

Section: Cobaltsupporting

confidence: 90%

Substitution and Redox Properties of Some Organoisocyanide Cobalt(II) Complexes

Oyetunji¹,

Tatolo²,

Paphane³

et al. 2017

Cobalt

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The reactions of four tetrakis(arylisocyanide)cobalt(II) complexes, [Co(CNR) 4 (ClO 4 ) 2 ] {R = 2,6-Me 2 C 6 H 3 (A), 2,4,6-Me 3 C 6 H 2 (B), 2,6-Et 2 C 6 H 3 (C), and 2,6-iPr 2 C 6 H 3 (D)}, with two pyridines, 4-CNpy and 4-Mepy, have been kinetically studied in trifluoroethanol medium. Each of the reactions, which was monitored over a temperature range of 293 to 318 K, exhibited two distinct processes proposed to be an initial fast substitution process followed by a slow reduction process. For each pyridine, steric hindrance was observed to play a significant role in the rates of the reactions, which decrease with increasing size of the arylisocyanide ligand in the order k(A)>k ( B)>k (C)>k ( D). Addition of each of three triarylphosphines, PR 3 (R = Ph, C 6 H 4 Me-p, C 6 H 4 OMe-p), to solutions of pentakis (t-octylisocyanide)cobalt(II), [Co(CNC 8 H 17 -t) 5 ](ClO 4 ) 2 , resulted in a shift in the λ max of the electronic spectrum accompanied by a change in color of the solutions. The shift is attributed to ligand substitution. The reactions of the cobalt(II) complex [Co(CNC 8 H 17 -t) 5 ] 2+ with the triarylphosphines are proposed to proceed via a combination of substitution, reduction, and disproportionation mechanisms with final formation of disubstituted Co (I) complexes. The order of reactivity of the complex with the triarylphosphines was found to be P(C 6 H 4 OMe-p) 3 >P ( C 6 H 4 Me-p) 3 >P P h 3 . This order is explained in terms of the electron donating/π-acceptor properties of the phosphines.

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Section: Cobaltsupporting

confidence: 90%

Substitution and Redox Properties of Some Organoisocyanide Cobalt(II) Complexes

Oyetunji¹,

Tatolo²,

Paphane³

et al. 2017

Cobalt

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“…The ion-pair formation process is a necessary pre-equilibrium to give a reactive intermediate in the two redox systems studied. Plots of k obs versus [oxidant] are similar to those obtained previously for the halopentacyanocobaltate(III) complexes [6]. Both Fe(II) complexes are known to be inert to substitution due to the non-availability of a co-ordination site for inner-sphere precursor complex formation.…”

Section: Discussionsupporting

confidence: 79%

“…Both Fe(II) complexes are known to be inert to substitution due to the non-availability of a co-ordination site for inner-sphere precursor complex formation. Outer-sphere mechanisms have been established for reactions of some polypyridyliron(II) complexes with Cr(IV) [19] and Co(III) [6,[20][21][22]. The first-order aquation rate constants obtained for Fe(phen) 3 2? and Fe(bipy) 3 2?…”

Section: Discussionmentioning

confidence: 99%

“…In our earlier papers [6,7], we reported the formation of ion-pairs in the reactions of Co(CN) 5 X 3-(X = Cl, Br, I) with Fe(phen) 3 2? in aqueous acidic medium and the protonation of these halo-pentacyanocobaltate(III) complexes.…”

Section: Introductionmentioning

confidence: 99%

“…in aqueous acidic medium and the protonation of these halo-pentacyanocobaltate(III) complexes. So far, our investigations on the reactions of these halo-pentacyanocobaltate(III) complexes have presented very interesting results [6,7] because of the relatively high protonation constants and ion-pairing constants of the cobalt complexes with the polypyridyl iron(II) complexes. The chemical reactions of the pentaamine complex, Co(NH 3 ) 5 N 3 2?…”

Section: Introductionmentioning

confidence: 99%

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Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium

Ogunlusi

Ige

Oyetunji

et al. 2009

Transition Met Chem

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The kinetics of the reactions between azidopentacyanocobaltate(III), Co(CN) 5 N 3 3-, and iron(II) polypyridyl complexes, Fe(LL) 3 2? (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm -3 NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL) 3 2? was kept constant, and the second-order rate constants obtained for the reactions at 35°C were within the range of 0.156-0.219 dm 3 mol -1 s -1 for LL = bipy and 0.090-0.118 dm 3 mol -1 s -1 for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied in the range [H ? ] = 0.001-0.008 mol dm -3 . The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed outerand inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k 5 ) is slower than through the outer-sphere path (k 4 ).

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Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

Ojo

Ige

Ogunlusi

et al. 2006

Transition Met Chem

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The kinetics of the reactions between Fe(phen) 3 2+ [phen = tris-(1,10) phenanthroline] and Co(CN) 5 X 3À (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm )3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H + ] = 0.01 mol dm )3 ) and the second-order rate constants for the reactions at 25°C were within the range of (0.151-1.117) dm 3 mol )1 s )1 . Ion-pair constants K ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 Â 10 4 , 3.00 Â 10 2 and 4.02 Â 10 4 mol )1 dm )3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: DH* (kJ K )1 mol )1 ) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; DS* (J K )1 ) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; DG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm 3 mol )1 s )1 ) = (7.079 ± 0.035) Â 10 16 , (1.413 ± 0.011) Â 10 17 , and (9.772 ± 0.027) Â 10 20 for X = Cl, Br, and I respectively. An outer -sphere mechanism is proposed for all the reactions.

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Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

Cited by 5 publications

References 14 publications

Substitution and Redox Properties of Some Organoisocyanide Cobalt(II) Complexes

Substitution and Redox Properties of Some Organoisocyanide Cobalt(II) Complexes

Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

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