Effect of Conformational Constraints on Gated Electron-Transfer Kinetics. A Multifaceted Study on Copper(II/I) Complexes with cis- and trans-Cyclohexanediyl-[14]aneS4

Salhi, Cynthia A.; Yu, Qiuyue; Heeg, Mary Jane; Villeneuve, Nicole M.; Juntunen, Kerri L.; Schroeder, Ronald R.; Ochrymowycz, L. A.; Rorabacher, D. B.

doi:10.1021/ic00128a016

Cited by 42 publications

(82 citation statements)

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“…The copper boron distance is with 2.065(2) Å very similar to the one in [Cu{B(Pn tBu ) 3 }Cl] (2.068(3) Å) but significantly shorter than in triphosphine boratranes. , The S–Cu–B–N torsion angles are in the range of 35.18(13)°–38.47(13)° aligning the heterocycles in a paddlewheel-like twisted fashion around the copper. The copper chlorine bond distance is with 2.2871(6) Å in the typical range for similar complexes. , On the one hand, the crystal structure reveals the methyl groups pointing away from the chlorine atom, so larger substituents would be necessary for a significant steric impact at the metal center. On the other hand, the methyl group shields the sulfur atom to avoid its reaction with electrophiles, which is known for related methimazolyl borate systems …”

Section: Resultsmentioning

confidence: 99%

Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

et al. 2016

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In Z-type ligands the electrons for the coordination bond are formally provided by the metal. They represent an important addition to the much more extensively used L- and X-type σ-donor ligands for the development of transition metal complexes with new reactivities. We report here a new boron Z-type ligand with three tethering thiopyridazinyl donors forming exclusively complexes that feature a metal boron bond. Rational substitution pattern in the backbone of the pyridazinyl heterocycle led to a well-behaved ligand system that allowed preparation of a series of copper boratrane complexes in high yields. They are found to be more soluble in common organic solvents allowing reactivity studies in contrast to previous complexes with this type of ligand. Thus, copper complexes [Cu{B(Pn(Me,tBu))3}X] with X = Cl, OTf, N3, and κN-NCS are reported. Solution behavior was explored, and the molecular structures were determined by single-crystal X-ray diffraction analyses. The thiocyanate ligand is found to coordinate via its nitrogen atom pointing to a high oxidation state of the copper. Density functional theory calculations indicate a high positive charge on copper and a strong copper-boron interaction. Thus, here reported complexes deliver synthetic evidence for the Z-type nature of the ligand. These findings are important for further dissemination of these types of ligands in coordination chemistry.

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Section: Resultsmentioning

confidence: 99%

Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

et al. 2016

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“…These are reflected in the individual rate and equilibrium parameters for these systems as generated from the matching of computer simulations to a huge array of experimental CVs as shown in Table 8. Extensive cross-reaction kinetic studies were also made on these Cu(II/I) systems 136,137 from which it became possible to calculate the selfexchange rate constants for each of the two pathways in Scheme 1, k 11(A) and k 11(B) ( Table 8). The combination of these latter values with the equilibrium constants for the conformational changes, K OQ (i.e., k OQ /k QO ) and K RP (i.e., k RP /k PR ), as determined from the CV measurements, 51 has permitted an estimation of the specific self-exchange rate constants repre- [14]aneS4; L2 ) cis-cyhx- [14]aneS4; L3 ) trans-cyhx- [14]aneS4; L7 ) syn-cis,cis-dicyhx- [14]aneS4; L8 ) anti-cis,cisdicyhx- [14]aneS4; L9 ) meso-trans,trans-dicyhx- [14]aneS4; L10 ) dl-trans,trans-dicyhx- [14]aneS4; L11 ) cis,trans-dicyhx- [14]aneS4 (see Figure 10) sentative of the two stable oxidation states exchanging electrons directly with their metastable counterparts: 137 These latter values are included in Table 8.…”

Section: Thiaether Complexesmentioning

confidence: 99%

Electron Transfer by Copper Centers

2004

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“…Rorabacher recently reviewed ET reactions by Cu(II)/(I) centers, 13 in which he seems to have confirmed that the gated ET reactions exhibited by copper complexes are successfully explained by this scheme. 8- 12 In general, ET reactions of Cu(II)/(I)-polythioether complexes proceed through path A in Scheme 1, and the direction in which the estimated self-exchange rate constant is much smaller than that directly measured by NMR is gated: i.e. the selfexchange rate constant estimated from the non-gated direction is almost identical to that measured directly by the NMR method.…”

Section: Introductionmentioning

confidence: 98%

“…Among investigations carried out to date, intensive and systematic studies by Rorabacher and co-workers seem to have largely improved understandings of the gated phenomena: they examined ET reactions of Cu(II)/(I)-macrocyclic polythioether complexes and found that the coordination structural change takes place essentially at the Cu(I) site while the coordination geometry around the Cu(II) species is not largely altered. [8][9][10][11][12] They related this phenomenon to the biologically important catalytic processes and postulated a dual-pathway Square Scheme described in Scheme 1. Rorabacher recently reviewed ET reactions by Cu(II)/(I) centers, 13 in which he seems to have confirmed that the gated ET reactions exhibited by copper complexes are successfully explained by this scheme.…”

Section: Introductionmentioning

confidence: 99%

Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane

et al. 2005

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[Cu(2,9-dimethyl-1,10-phenanthroline)(2)](2+) and [Cu(6,6'-dimethyl-2,2'-bipyridine)(2)](2+/+) complexes with no coordinated solvent molecule were synthesized and the crystal structures were analyzed: the coordination geometry around the Cu(i) center was in the D(2d) symmetry while a D(2) structure was observed for the four-coordinate Cu(ii) complexes. Coordination of a water or an acetonitrile molecule was found in the trigonal plane of the five-coordinate Cu(ii) complex in the Tbp(trigonal bipyramidal) structure. Spectrophotometric analyses revealed that the D(2) structure of the Cu(ii) complex was retained in nitromethane, although a five-coordinate Tbp species (green in color), was readily formed upon dissolution of the solid (reddish brown) in acetonitrile. The electron self-exchange reaction between D(2d)-Cu(I) and D(2)-Cu(II), observed by the NMR method, was very rapid with k(ex)=(1.1 +/- 0.2) x 10(5) kg mol(-1) s(-1) at 25 degrees C (DeltaH*= 15.6 +/- 1.3 kJ mol(-1) and DeltaS*=-96 +/- 4 J mol(-1) K(-1)), which was more than 10 times larger than that reported for the self-exchange reaction between D(2d)-Cu(I) and Tbp-Cu(II) in acetonitrile. The cross reduction reactions of D(2)-Cu(ii) by ferrocene and decamethylferrocene in nitromethane exhibited a completely gated behavior, while the oxidation reaction of D(2d)-Cu(i) by [Ni(1,4,7-triazacyclononane)(2)](3+) in nitromethane estimated an identically large self-exchange rate constant to that directly obtained by the NMR method. The electron self-exchange rate constant estimated from the oxidation cross reaction in 50% v/v acetonitrile-nitromethane mixture was 10 times smaller than that observed in pure nitromethane. On the basis of the Principle of the Least Motion (PLM) and the Symmetry Rules, it was concluded that gated behaviors observed for the reduction reactions of the five-coordinate Cu(ii)-polypyridine complexes are related to the high-energy C(2v)--> D(2d) conformational change around Cu(ii), and that the electron self-exchange reactions of the Cu(ii)/(i) couples are always adiabatic through the C(2v) structures for both Cu(ii) and Cu(i) since the conformational changes between D(2d), D(2) and C(2v) structures for Cu(i) as well as the conformational change between Tbp and C(2v) structures for Cu(ii) are symmetry-allowed. The completely gated behavior observed for the reduction reactions of D(2)-Cu(ii) species in nitromethane was attributed to the very slow conformational change from the ground-state D(2) to the entatic D(2d) structure that is symmetry-forbidden for d(9) metal complexes: the very slow back reaction, the forbidden conformational change from entatic D(2d) to the ground-state D(2) structure, ensures that the rate of the reduction reaction is independent of the concentration of the reducing reagent.

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Effect of Conformational Constraints on Gated Electron-Transfer Kinetics. A Multifaceted Study on Copper(II/I) Complexes with cis- and trans-Cyclohexanediyl-[14]aneS4

Cited by 42 publications

References 4 publications

Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

Electron Transfer by Copper Centers

Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane

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Effect of Conformational Constraints on Gated Electron-Transfer Kinetics. A Multifaceted Study on Copper(II/I) Complexes with cis- and trans-Cyclohexanediyl-[14]aneS4

Cited by 42 publications

References 4 publications

Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

Electron Transfer by Copper Centers

Syntheses, structural analyses and redox kinetics of four-coordinate [CuL2]2+and five-coordinate [CuL2(solvent)]2+complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)2]2+in nitromethane

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Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane