Electron transfer behavior of pincer-type {RhNO}8 complexes

Spectroscopic characterization and reactivity of paramagnetic {RhNO}9 complexes

Juan Pellegrino, Carina Gaviglio, David Milstein, Fabio Doctorovich

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The electrochemistry of the {RhNO}8 complexes [Rh(PCP tBu)(NO)][BF4] (1+), [Rh(PCP tBuCH2)(NO)][BF4] (2+), and Rh(PCPtBu)(NO)Cl (3) was studied. Both four-coordinate complexes 1+ and 2+ exhibit a reversible reduction within the CH2Cl2 solvent window. Nevertheless, the chemical or electrochemical reduction of 1+ and 2+ in CH 2Cl2 led to the formation of the five-coordinate {RhNO}8 complexes 3 and Rh(PCPtBuCH2)(NO)Cl (4), respectively, through chloride abstraction from CH2Cl 2 by the one-electron-reduced {RhNO}9 species [Rh(PCP tBu)(NO)] (1) and [Rh(PCP tBuCH2)(NO)] (2), as has been observed for many other 17-electron paramagnetic complexes. The new complex 4 was fully characterized by multinuclear NMR techniques, IR, X-ray diffraction, CV, UV-vis, and elemental analysis. On the other hand, the five-coordinate complexes 3 and 4 show only one irreversible oxidation in CH2Cl2 and two irreversible reductions in THF. The {RhNO}9 complex 1 could be obtained quantitatively by one-electron reduction of 1+ with cobaltocene in nonchlorinated solvents and was characterized by IR, EPR, and 1H NMR in solution. Activation of carbon-halogen bonds by complex 1 was observed by studying the reactivity of 1 with some aryl halides, giving in all cases the {RhNO}8 Rh(PCPtBu)(NO)X (X = Cl -, 3, or X = I-, 6) as the only rhodium complex, while a complex with coordination of the aryl moiety was not observed as a stable final product in any case. The fate of the aryl organic radicals could be determined in some cases. In addition, DFT calculations were performed to elucidate the electronic structure of 1 and to support the observed reactivity.

Original languageEnglish
Pages (from-to)6555-6564
Number of pages10
JournalOrganometallics
Volume32
Issue number21
DOIs
Publication statusPublished - Nov 11 2013

Fingerprint

electron transfer
reactivity
Electrons
nuclear magnetic resonance
electrons
Nuclear magnetic resonance
electrochemistry
rhodium
halogens
Rhodium
Halogens
halides
Electrochemistry
chlorides
Discrete Fourier transforms
activation
methylidyne
electronic structure
Electronic structure
Paramagnetic resonance

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Electron transfer behavior of pincer-type {RhNO}8 complexes : Spectroscopic characterization and reactivity of paramagnetic {RhNO}9 complexes. / Pellegrino, Juan; Gaviglio, Carina; Milstein, David; Doctorovich, Fabio.

In: Organometallics, Vol. 32, No. 21, 11.11.2013, p. 6555-6564.

Research output: Contribution to journalArticle

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abstract = "The electrochemistry of the {RhNO}8 complexes [Rh(PCP tBu)(NO)][BF4] (1+), [Rh(PCP tBuCH2)(NO)][BF4] (2+), and Rh(PCPtBu)(NO)Cl (3) was studied. Both four-coordinate complexes 1+ and 2+ exhibit a reversible reduction within the CH2Cl2 solvent window. Nevertheless, the chemical or electrochemical reduction of 1+ and 2+ in CH 2Cl2 led to the formation of the five-coordinate {RhNO}8 complexes 3 and Rh(PCPtBuCH2)(NO)Cl (4), respectively, through chloride abstraction from CH2Cl 2 by the one-electron-reduced {RhNO}9 species [Rh(PCP tBu)(NO)]• (1•) and [Rh(PCP tBuCH2)(NO)]• (2•), as has been observed for many other 17-electron paramagnetic complexes. The new complex 4 was fully characterized by multinuclear NMR techniques, IR, X-ray diffraction, CV, UV-vis, and elemental analysis. On the other hand, the five-coordinate complexes 3 and 4 show only one irreversible oxidation in CH2Cl2 and two irreversible reductions in THF. The {RhNO}9 complex 1• could be obtained quantitatively by one-electron reduction of 1+ with cobaltocene in nonchlorinated solvents and was characterized by IR, EPR, and 1H NMR in solution. Activation of carbon-halogen bonds by complex 1• was observed by studying the reactivity of 1• with some aryl halides, giving in all cases the {RhNO}8 Rh(PCPtBu)(NO)X (X = Cl -, 3, or X = I-, 6) as the only rhodium complex, while a complex with coordination of the aryl moiety was not observed as a stable final product in any case. The fate of the aryl organic radicals could be determined in some cases. In addition, DFT calculations were performed to elucidate the electronic structure of 1• and to support the observed reactivity.",
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AB - The electrochemistry of the {RhNO}8 complexes [Rh(PCP tBu)(NO)][BF4] (1+), [Rh(PCP tBuCH2)(NO)][BF4] (2+), and Rh(PCPtBu)(NO)Cl (3) was studied. Both four-coordinate complexes 1+ and 2+ exhibit a reversible reduction within the CH2Cl2 solvent window. Nevertheless, the chemical or electrochemical reduction of 1+ and 2+ in CH 2Cl2 led to the formation of the five-coordinate {RhNO}8 complexes 3 and Rh(PCPtBuCH2)(NO)Cl (4), respectively, through chloride abstraction from CH2Cl 2 by the one-electron-reduced {RhNO}9 species [Rh(PCP tBu)(NO)]• (1•) and [Rh(PCP tBuCH2)(NO)]• (2•), as has been observed for many other 17-electron paramagnetic complexes. The new complex 4 was fully characterized by multinuclear NMR techniques, IR, X-ray diffraction, CV, UV-vis, and elemental analysis. On the other hand, the five-coordinate complexes 3 and 4 show only one irreversible oxidation in CH2Cl2 and two irreversible reductions in THF. The {RhNO}9 complex 1• could be obtained quantitatively by one-electron reduction of 1+ with cobaltocene in nonchlorinated solvents and was characterized by IR, EPR, and 1H NMR in solution. Activation of carbon-halogen bonds by complex 1• was observed by studying the reactivity of 1• with some aryl halides, giving in all cases the {RhNO}8 Rh(PCPtBu)(NO)X (X = Cl -, 3, or X = I-, 6) as the only rhodium complex, while a complex with coordination of the aryl moiety was not observed as a stable final product in any case. The fate of the aryl organic radicals could be determined in some cases. In addition, DFT calculations were performed to elucidate the electronic structure of 1• and to support the observed reactivity.

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