Cyclopentadienylcobalt 1,4-Diaryltetraazadienes. A Structural, Spectroscopic, and Theoretical Study

Michal E. Gross, William C. Trogler*, James A. Ibers

*Corresponding author for this work

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Unsaturated metallacycles such as (η5-C5H5)Co(R—N=N—N=N—R), where R = alkyl or aryl, offer the possibility of π-delocalized bonding. Xα calculations predict that two dπ electrons on the (η5-C6H5)Co fragment should strongly interact with an empty low-lying π* orbital of the tetraazadiene ligand to yield metallacycle π and π* orbitals. A single-crystal X-ray diffraction study at −150 °C of the R = C6F5 derivative provides direct evidence of the π-acceptor abilities of the RN4R ligand. The [formula omitted] ring is planar and exhibits unusually short Co—N(1) and Co—N(4) distances of 1.802 (2) and 1.819 (2) Å, respectively, indicative of multiple-bond character. The short N(2)—N(3) bond [1.279 (2) Å] and long N(1)—N(2) [1.360 (2) Å] and N(3)—N(4) [1.355 (2) Å] bonds demonstrate that π back-bonding has altered the pattern of unsaturated bonds in the tetraazadiene chelate. Electronic absorption spectra of (η5-C6H5)Co(RN4R) [R = CH3, C6H6, C6F5, 2,4-F2C6H3, 2,6-(CH3)2C6H3] display three bands characteristic of the cobalt-tetraazadiene ring: λmax1 (ϵ), 600–670 nm (300–700); λmax2 (ϵ), 425–470 nm (5000–9000); λmax3 (ϵ), 335–390 nm (<4000). These absorptions are attributed to one-electron transitions that terminate in the low-lying metallacycle π* orbital. Crystals of C17H5CoF10N4· 1/2C6H6 at −150 °C are monoclinic, space group P21/c, with four formula units in a cell of dimensions a = 8.612 (4) Å, b = 22.687 (12) Å, c = 9.820 (6) Å, and β = 91.58 (2). Least-squares refinement of 315 variables has led to a final value of the R index on F2 of 0.047 for 5367 observations; the conventional R index on F is 0.033 for 4313 observations having Fo2 > 3σ(Fo2).

Original languageEnglish (US)
Pages (from-to)732-739
Number of pages8
JournalOrganometallics
Volume1
Issue number5
DOIs
StatePublished - Jan 1 1982

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Ligands
orbitals
ligands
rings
Cobalt
chelates
electronic spectra
Absorption spectra
cobalt
Display devices
fragments
Single crystals
Derivatives
absorption spectra
X ray diffraction
Electrons
single crystals
diffraction
electrons
x rays

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

@article{8eeea7a2af594db19befa3301a02243c,
title = "Cyclopentadienylcobalt 1,4-Diaryltetraazadienes. A Structural, Spectroscopic, and Theoretical Study",
abstract = "Unsaturated metallacycles such as (η5-C5H5)Co(R—N=N—N=N—R), where R = alkyl or aryl, offer the possibility of π-delocalized bonding. Xα calculations predict that two dπ electrons on the (η5-C6H5)Co fragment should strongly interact with an empty low-lying π* orbital of the tetraazadiene ligand to yield metallacycle π and π* orbitals. A single-crystal X-ray diffraction study at −150 °C of the R = C6F5 derivative provides direct evidence of the π-acceptor abilities of the RN4R ligand. The [formula omitted] ring is planar and exhibits unusually short Co—N(1) and Co—N(4) distances of 1.802 (2) and 1.819 (2) {\AA}, respectively, indicative of multiple-bond character. The short N(2)—N(3) bond [1.279 (2) {\AA}] and long N(1)—N(2) [1.360 (2) {\AA}] and N(3)—N(4) [1.355 (2) {\AA}] bonds demonstrate that π back-bonding has altered the pattern of unsaturated bonds in the tetraazadiene chelate. Electronic absorption spectra of (η5-C6H5)Co(RN4R) [R = CH3, C6H6, C6F5, 2,4-F2C6H3, 2,6-(CH3)2C6H3] display three bands characteristic of the cobalt-tetraazadiene ring: λmax1 (ϵ), 600–670 nm (300–700); λmax2 (ϵ), 425–470 nm (5000–9000); λmax3 (ϵ), 335–390 nm (<4000). These absorptions are attributed to one-electron transitions that terminate in the low-lying metallacycle π* orbital. Crystals of C17H5CoF10N4· 1/2C6H6 at −150 °C are monoclinic, space group P21/c, with four formula units in a cell of dimensions a = 8.612 (4) {\AA}, b = 22.687 (12) {\AA}, c = 9.820 (6) {\AA}, and β = 91.58 (2)∘. Least-squares refinement of 315 variables has led to a final value of the R index on F2 of 0.047 for 5367 observations; the conventional R index on F is 0.033 for 4313 observations having Fo2 > 3σ(Fo2).",
author = "Gross, {Michal E.} and Trogler, {William C.} and Ibers, {James A.}",
year = "1982",
month = "1",
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language = "English (US)",
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Cyclopentadienylcobalt 1,4-Diaryltetraazadienes. A Structural, Spectroscopic, and Theoretical Study. / Gross, Michal E.; Trogler, William C.; Ibers, James A.

In: Organometallics, Vol. 1, No. 5, 01.01.1982, p. 732-739.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Cyclopentadienylcobalt 1,4-Diaryltetraazadienes. A Structural, Spectroscopic, and Theoretical Study

AU - Gross, Michal E.

AU - Trogler, William C.

AU - Ibers, James A.

PY - 1982/1/1

Y1 - 1982/1/1

N2 - Unsaturated metallacycles such as (η5-C5H5)Co(R—N=N—N=N—R), where R = alkyl or aryl, offer the possibility of π-delocalized bonding. Xα calculations predict that two dπ electrons on the (η5-C6H5)Co fragment should strongly interact with an empty low-lying π* orbital of the tetraazadiene ligand to yield metallacycle π and π* orbitals. A single-crystal X-ray diffraction study at −150 °C of the R = C6F5 derivative provides direct evidence of the π-acceptor abilities of the RN4R ligand. The [formula omitted] ring is planar and exhibits unusually short Co—N(1) and Co—N(4) distances of 1.802 (2) and 1.819 (2) Å, respectively, indicative of multiple-bond character. The short N(2)—N(3) bond [1.279 (2) Å] and long N(1)—N(2) [1.360 (2) Å] and N(3)—N(4) [1.355 (2) Å] bonds demonstrate that π back-bonding has altered the pattern of unsaturated bonds in the tetraazadiene chelate. Electronic absorption spectra of (η5-C6H5)Co(RN4R) [R = CH3, C6H6, C6F5, 2,4-F2C6H3, 2,6-(CH3)2C6H3] display three bands characteristic of the cobalt-tetraazadiene ring: λmax1 (ϵ), 600–670 nm (300–700); λmax2 (ϵ), 425–470 nm (5000–9000); λmax3 (ϵ), 335–390 nm (<4000). These absorptions are attributed to one-electron transitions that terminate in the low-lying metallacycle π* orbital. Crystals of C17H5CoF10N4· 1/2C6H6 at −150 °C are monoclinic, space group P21/c, with four formula units in a cell of dimensions a = 8.612 (4) Å, b = 22.687 (12) Å, c = 9.820 (6) Å, and β = 91.58 (2)∘. Least-squares refinement of 315 variables has led to a final value of the R index on F2 of 0.047 for 5367 observations; the conventional R index on F is 0.033 for 4313 observations having Fo2 > 3σ(Fo2).

AB - Unsaturated metallacycles such as (η5-C5H5)Co(R—N=N—N=N—R), where R = alkyl or aryl, offer the possibility of π-delocalized bonding. Xα calculations predict that two dπ electrons on the (η5-C6H5)Co fragment should strongly interact with an empty low-lying π* orbital of the tetraazadiene ligand to yield metallacycle π and π* orbitals. A single-crystal X-ray diffraction study at −150 °C of the R = C6F5 derivative provides direct evidence of the π-acceptor abilities of the RN4R ligand. The [formula omitted] ring is planar and exhibits unusually short Co—N(1) and Co—N(4) distances of 1.802 (2) and 1.819 (2) Å, respectively, indicative of multiple-bond character. The short N(2)—N(3) bond [1.279 (2) Å] and long N(1)—N(2) [1.360 (2) Å] and N(3)—N(4) [1.355 (2) Å] bonds demonstrate that π back-bonding has altered the pattern of unsaturated bonds in the tetraazadiene chelate. Electronic absorption spectra of (η5-C6H5)Co(RN4R) [R = CH3, C6H6, C6F5, 2,4-F2C6H3, 2,6-(CH3)2C6H3] display three bands characteristic of the cobalt-tetraazadiene ring: λmax1 (ϵ), 600–670 nm (300–700); λmax2 (ϵ), 425–470 nm (5000–9000); λmax3 (ϵ), 335–390 nm (<4000). These absorptions are attributed to one-electron transitions that terminate in the low-lying metallacycle π* orbital. Crystals of C17H5CoF10N4· 1/2C6H6 at −150 °C are monoclinic, space group P21/c, with four formula units in a cell of dimensions a = 8.612 (4) Å, b = 22.687 (12) Å, c = 9.820 (6) Å, and β = 91.58 (2)∘. Least-squares refinement of 315 variables has led to a final value of the R index on F2 of 0.047 for 5367 observations; the conventional R index on F is 0.033 for 4313 observations having Fo2 > 3σ(Fo2).

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