Effects of metal-centered reduction on the structural, electronic, and coordination properties of nickel and copper octaethylisobacteriochlorins

Mark W. Renner, Lars R Furenlid, Alan M. Stolzenberg

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

The structural properties of nickel and copper complexes of octaethylisobacteriochlorin (OEiBC) are investigated as part of an effort to understand the chemistry of factor 430 (F430), the nickel hydrocorphinoid cofactor of methyl coenzyme-M reductase. Both NiII and CuII(OEiBC) undergo one-electron reductions to yield metal(I) complexes. The nature of the starting materials, the anionic metal(I) reduction products, and their ligand-binding properties are probed with electron paramagnetic resonance (EPR) and X-ray absorption techniques. Comparison between the structures of the isoelectronic NiII and CuII complexes reveals that the marked distortions observed in the NiI-macrocycle core environment, which has two Ni-N distances of 1.91(2) A and two Ni-N distances of 2.07(2) Å, are not apparent for CuII, which has four Cu-N distances of 2.00(2) Å. Thus, the distortion of the NiI environment does not result from an electronic configuration effect such as a Jahn - Teller distortion. X-ray absorption near-edge studies of OEiBC complexes at reduced temperatures demonstrate for the first time that NiI hydroporphyrins can bind a single axial ligand. Optical and EPR spectra are found to be insensitive to the axial binding for these cases. Chemical reduction of CuII(OEiBC), using sodium amalgam, affords a CuI complex that has unchanged Cu-N distances and two sodium ions coordinated on opposite sides of the OEiBC ring at Cu-Na distances of 2.89(4) Å. The sodium ions can be sequestered using the crown ether 18-crown-6. Direct comparison of CuII and the non-ion-paired CuI complexes, which have the same geometry and coordination environment, establishes that the average Cu-N distance increases 0.06 Å upon reduction. The structural differences between the NiI and CuI complexes may account for their different reactivities toward alkyl halides and oxygen.

Original languageEnglish (US)
Pages (from-to)293-300
Number of pages8
JournalJournal of the American Chemical Society
Volume117
Issue number1
StatePublished - Jan 11 1995
Externally publishedYes

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Nickel
Copper
Metals
Sodium
Electron Spin Resonance Spectroscopy
X ray absorption
X-Rays
Ions
Ligands
Crown Ethers
Paramagnetic resonance
Coordination Complexes
Coenzymes
Mercury amalgams
Jahn-Teller effect
Crown ethers
Metal complexes
Electrons
Oxygen
Structural properties

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Effects of metal-centered reduction on the structural, electronic, and coordination properties of nickel and copper octaethylisobacteriochlorins. / Renner, Mark W.; Furenlid, Lars R; Stolzenberg, Alan M.

In: Journal of the American Chemical Society, Vol. 117, No. 1, 11.01.1995, p. 293-300.

Research output: Contribution to journalArticle

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abstract = "The structural properties of nickel and copper complexes of octaethylisobacteriochlorin (OEiBC) are investigated as part of an effort to understand the chemistry of factor 430 (F430), the nickel hydrocorphinoid cofactor of methyl coenzyme-M reductase. Both NiII and CuII(OEiBC) undergo one-electron reductions to yield metal(I) complexes. The nature of the starting materials, the anionic metal(I) reduction products, and their ligand-binding properties are probed with electron paramagnetic resonance (EPR) and X-ray absorption techniques. Comparison between the structures of the isoelectronic NiII and CuII complexes reveals that the marked distortions observed in the NiI-macrocycle core environment, which has two Ni-N distances of 1.91(2) A and two Ni-N distances of 2.07(2) {\AA}, are not apparent for CuII, which has four Cu-N distances of 2.00(2) {\AA}. Thus, the distortion of the NiI environment does not result from an electronic configuration effect such as a Jahn - Teller distortion. X-ray absorption near-edge studies of OEiBC complexes at reduced temperatures demonstrate for the first time that NiI hydroporphyrins can bind a single axial ligand. Optical and EPR spectra are found to be insensitive to the axial binding for these cases. Chemical reduction of CuII(OEiBC), using sodium amalgam, affords a CuI complex that has unchanged Cu-N distances and two sodium ions coordinated on opposite sides of the OEiBC ring at Cu-Na distances of 2.89(4) {\AA}. The sodium ions can be sequestered using the crown ether 18-crown-6. Direct comparison of CuII and the non-ion-paired CuI complexes, which have the same geometry and coordination environment, establishes that the average Cu-N distance increases 0.06 {\AA} upon reduction. The structural differences between the NiI and CuI complexes may account for their different reactivities toward alkyl halides and oxygen.",
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AB - The structural properties of nickel and copper complexes of octaethylisobacteriochlorin (OEiBC) are investigated as part of an effort to understand the chemistry of factor 430 (F430), the nickel hydrocorphinoid cofactor of methyl coenzyme-M reductase. Both NiII and CuII(OEiBC) undergo one-electron reductions to yield metal(I) complexes. The nature of the starting materials, the anionic metal(I) reduction products, and their ligand-binding properties are probed with electron paramagnetic resonance (EPR) and X-ray absorption techniques. Comparison between the structures of the isoelectronic NiII and CuII complexes reveals that the marked distortions observed in the NiI-macrocycle core environment, which has two Ni-N distances of 1.91(2) A and two Ni-N distances of 2.07(2) Å, are not apparent for CuII, which has four Cu-N distances of 2.00(2) Å. Thus, the distortion of the NiI environment does not result from an electronic configuration effect such as a Jahn - Teller distortion. X-ray absorption near-edge studies of OEiBC complexes at reduced temperatures demonstrate for the first time that NiI hydroporphyrins can bind a single axial ligand. Optical and EPR spectra are found to be insensitive to the axial binding for these cases. Chemical reduction of CuII(OEiBC), using sodium amalgam, affords a CuI complex that has unchanged Cu-N distances and two sodium ions coordinated on opposite sides of the OEiBC ring at Cu-Na distances of 2.89(4) Å. The sodium ions can be sequestered using the crown ether 18-crown-6. Direct comparison of CuII and the non-ion-paired CuI complexes, which have the same geometry and coordination environment, establishes that the average Cu-N distance increases 0.06 Å upon reduction. The structural differences between the NiI and CuI complexes may account for their different reactivities toward alkyl halides and oxygen.

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