Synthesis and electrochemistry of 2,2′-bipyridyl complexes of dioxorhenium(V)

M. S. Ram, Christopher S. Johnson, Robert L. Blackbourn, Joseph T Hupp

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Abstract

The rhenium(V) bipyridyl (bpy) complexes [(bpy)(py)2Re(O)2](ClO4) and [(bpy)(3-pySO3)2Re(O)2](Na)·2H 2O have been prepared by reaction of 2,2′-bipyridine with trans-[(py)4Re(O)2](Cl) and trans-[(3-pySO3)4Re(O)2](Na)3 in methanol or methanol/water solutions (py = pyridine, 3-pySO3 = 3-pyridinesulfonate). Despite the seemingly trivial change in coordination environment, the bpy-containing complexes were found to behave very differently from the corresponding tetrapyridyl complexes. For example, the pH-independent formal potential for reduction of Re(VI) to Re(V) was lowered by some 600 mV. On the other hand, the pH-dependent potential for the Re(V/III) couple increased by ca. 200 mV upon bpy coordination. The V/III couple also became considerably more reversible (kinetically) in its electrochemical response. The Re(III/II) potential was also shifted in the positive direction. At high pH's, the V/III and III/II couples coalesced to yield the first example of three-electron redox behavior in rhenium chemistry. By analogy with known dioxoosmium complexes, both the thermodynamic and kinetic electrochemical effects were attributed to a relative stabilization of the inaccessible Re(IV) oxidation state following bpy coordination. It was proposed that the destabilization is induced by trans to cis isomerization. The cis-dioxo configuration has only rarely been seen in d2 coordination chemistry, and never for hexacoordinate rhenium. Nevertheless, circumstantial evidence from IR, NMR, and Raman experiments supported the assignment. Unfortunately, proof was not possible by these methods since both cis- and trans-(bpy)(py)2Re(O)2+ would possess C symmetry. Very recent X-ray investigations (to be reported elsewhere) have now confirmed the cis assignment.

Original languageEnglish
Pages (from-to)238-244
Number of pages7
JournalInorganic Chemistry
Volume29
Issue number2
Publication statusPublished - 1990

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2,2'-Dipyridyl
Electrochemistry
electrochemistry
rhenium
Rhenium
synthesis
methyl alcohol
chemistry
destabilization
Methanol
isomerization
stabilization
thermodynamics
nuclear magnetic resonance
oxidation
Isomerization
oligomycin sensitivity-conferring protein
kinetics
symmetry
configurations

ASJC Scopus subject areas

  • Inorganic Chemistry

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Synthesis and electrochemistry of 2,2′-bipyridyl complexes of dioxorhenium(V). / Ram, M. S.; Johnson, Christopher S.; Blackbourn, Robert L.; Hupp, Joseph T.

In: Inorganic Chemistry, Vol. 29, No. 2, 1990, p. 238-244.

Research output: Contribution to journalArticle

Ram, MS, Johnson, CS, Blackbourn, RL & Hupp, JT 1990, 'Synthesis and electrochemistry of 2,2′-bipyridyl complexes of dioxorhenium(V)', Inorganic Chemistry, vol. 29, no. 2, pp. 238-244.
Ram, M. S. ; Johnson, Christopher S. ; Blackbourn, Robert L. ; Hupp, Joseph T. / Synthesis and electrochemistry of 2,2′-bipyridyl complexes of dioxorhenium(V). In: Inorganic Chemistry. 1990 ; Vol. 29, No. 2. pp. 238-244.
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abstract = "The rhenium(V) bipyridyl (bpy) complexes [(bpy)(py)2Re(O)2](ClO4) and [(bpy)(3-pySO3)2Re(O)2](Na)·2H 2O have been prepared by reaction of 2,2′-bipyridine with trans-[(py)4Re(O)2](Cl) and trans-[(3-pySO3)4Re(O)2](Na)3 in methanol or methanol/water solutions (py = pyridine, 3-pySO3 = 3-pyridinesulfonate). Despite the seemingly trivial change in coordination environment, the bpy-containing complexes were found to behave very differently from the corresponding tetrapyridyl complexes. For example, the pH-independent formal potential for reduction of Re(VI) to Re(V) was lowered by some 600 mV. On the other hand, the pH-dependent potential for the Re(V/III) couple increased by ca. 200 mV upon bpy coordination. The V/III couple also became considerably more reversible (kinetically) in its electrochemical response. The Re(III/II) potential was also shifted in the positive direction. At high pH's, the V/III and III/II couples coalesced to yield the first example of three-electron redox behavior in rhenium chemistry. By analogy with known dioxoosmium complexes, both the thermodynamic and kinetic electrochemical effects were attributed to a relative stabilization of the inaccessible Re(IV) oxidation state following bpy coordination. It was proposed that the destabilization is induced by trans to cis isomerization. The cis-dioxo configuration has only rarely been seen in d2 coordination chemistry, and never for hexacoordinate rhenium. Nevertheless, circumstantial evidence from IR, NMR, and Raman experiments supported the assignment. Unfortunately, proof was not possible by these methods since both cis- and trans-(bpy)(py)2Re(O)2+ would possess C2υ symmetry. Very recent X-ray investigations (to be reported elsewhere) have now confirmed the cis assignment.",
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N2 - The rhenium(V) bipyridyl (bpy) complexes [(bpy)(py)2Re(O)2](ClO4) and [(bpy)(3-pySO3)2Re(O)2](Na)·2H 2O have been prepared by reaction of 2,2′-bipyridine with trans-[(py)4Re(O)2](Cl) and trans-[(3-pySO3)4Re(O)2](Na)3 in methanol or methanol/water solutions (py = pyridine, 3-pySO3 = 3-pyridinesulfonate). Despite the seemingly trivial change in coordination environment, the bpy-containing complexes were found to behave very differently from the corresponding tetrapyridyl complexes. For example, the pH-independent formal potential for reduction of Re(VI) to Re(V) was lowered by some 600 mV. On the other hand, the pH-dependent potential for the Re(V/III) couple increased by ca. 200 mV upon bpy coordination. The V/III couple also became considerably more reversible (kinetically) in its electrochemical response. The Re(III/II) potential was also shifted in the positive direction. At high pH's, the V/III and III/II couples coalesced to yield the first example of three-electron redox behavior in rhenium chemistry. By analogy with known dioxoosmium complexes, both the thermodynamic and kinetic electrochemical effects were attributed to a relative stabilization of the inaccessible Re(IV) oxidation state following bpy coordination. It was proposed that the destabilization is induced by trans to cis isomerization. The cis-dioxo configuration has only rarely been seen in d2 coordination chemistry, and never for hexacoordinate rhenium. Nevertheless, circumstantial evidence from IR, NMR, and Raman experiments supported the assignment. Unfortunately, proof was not possible by these methods since both cis- and trans-(bpy)(py)2Re(O)2+ would possess C2υ symmetry. Very recent X-ray investigations (to be reported elsewhere) have now confirmed the cis assignment.

AB - The rhenium(V) bipyridyl (bpy) complexes [(bpy)(py)2Re(O)2](ClO4) and [(bpy)(3-pySO3)2Re(O)2](Na)·2H 2O have been prepared by reaction of 2,2′-bipyridine with trans-[(py)4Re(O)2](Cl) and trans-[(3-pySO3)4Re(O)2](Na)3 in methanol or methanol/water solutions (py = pyridine, 3-pySO3 = 3-pyridinesulfonate). Despite the seemingly trivial change in coordination environment, the bpy-containing complexes were found to behave very differently from the corresponding tetrapyridyl complexes. For example, the pH-independent formal potential for reduction of Re(VI) to Re(V) was lowered by some 600 mV. On the other hand, the pH-dependent potential for the Re(V/III) couple increased by ca. 200 mV upon bpy coordination. The V/III couple also became considerably more reversible (kinetically) in its electrochemical response. The Re(III/II) potential was also shifted in the positive direction. At high pH's, the V/III and III/II couples coalesced to yield the first example of three-electron redox behavior in rhenium chemistry. By analogy with known dioxoosmium complexes, both the thermodynamic and kinetic electrochemical effects were attributed to a relative stabilization of the inaccessible Re(IV) oxidation state following bpy coordination. It was proposed that the destabilization is induced by trans to cis isomerization. The cis-dioxo configuration has only rarely been seen in d2 coordination chemistry, and never for hexacoordinate rhenium. Nevertheless, circumstantial evidence from IR, NMR, and Raman experiments supported the assignment. Unfortunately, proof was not possible by these methods since both cis- and trans-(bpy)(py)2Re(O)2+ would possess C2υ symmetry. Very recent X-ray investigations (to be reported elsewhere) have now confirmed the cis assignment.

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