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Article

Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered

1
Department of Chemistry, University of Kansas, 1567 Irving Hill Road, Lawrence, KS 66045, USA
2
Department of Chemistry & Physics, Clayton State University, 2000 Clayton State Blvd., Morrow, GA 30260, USA
3
Department of Chemistry, Missouri State University, 901 S. National Ave., Springfield, MO 65897, USA
*
Authors to whom correspondence should be addressed.
Academic Editor: Vito Lippolis
Molecules 2021, 26(4), 981; https://doi.org/10.3390/molecules26040981
Received: 19 January 2021 / Revised: 5 February 2021 / Accepted: 9 February 2021 / Published: 12 February 2021
(This article belongs to the Special Issue Recent Advances in Modern Inorganic Chemistry)
Isocyanoazulenes (CNAz) constitute a relatively new class of isocyanoarenes that offers rich structural and electronic diversification of the organic isocyanide ligand platform. This article considers a series of 2-isocyano-1,3-X2-azulene ligands (X = H, Me, CO2Et, Br, and CN) and the corresponding zero-valent complexes thereof, [(OC)5Cr(2-isocyano-1,3-X2-azulene)]. Air- and thermally stable, X-ray structurally characterized 2-isocyano-1,3-dimethylazulene may be viewed as a non-benzenoid aromatic congener of 2,6-dimethyphenyl isocyanide (2,6-xylyl isocyanide), a longtime “workhorse” aryl isocyanide ligand in coordination chemistry. Single crystal X-ray crystallographic {Cr–CNAz bond distances}, cyclic voltametric {E1/2(Cr0/1+)}, 13C NMR {δ(13CN), δ(13CO)}, UV-vis {dπ(Cr) → pπ*(CNAz) Metal-to-Ligand Charge Transfer}, and FTIR {νNC, νCO, kCO} analyses of the [(OC)5Cr(2-isocyano-1,3-X2-azulene)] complexes provided a multifaceted, quantitative assessment of the π-acceptor/σ-donor characteristics of the above five 2-isocyanoazulenes. In particular, the following inverse linear relationships were documented: δ(13COtrans) vs. δ(13CN), δ(13COcis) vs. δ(13CN), and δ(13COtrans) vs. kCO,trans force constant. Remarkably, the net electron withdrawing capability of the 2-isocyano-1,3-dicyanoazulene ligand rivals those of perfluorinated isocyanides CNC6F5 and CNC2F3. View Full-Text
Keywords: chromium pentacarbonyl; isocyanide; azulene; back-bonding; metal-to-ligand charge transfer; voltammetry chromium pentacarbonyl; isocyanide; azulene; back-bonding; metal-to-ligand charge transfer; voltammetry
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MDPI and ACS Style

Hart, M.D.; Meyers, J.J., Jr.; Wood, Z.A.; Nakakita, T.; Applegate, J.C.; Erickson, N.R.; Gerasimchuk, N.N.; Barybin, M.V. Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered. Molecules 2021, 26, 981. https://doi.org/10.3390/molecules26040981

AMA Style

Hart MD, Meyers JJ Jr., Wood ZA, Nakakita T, Applegate JC, Erickson NR, Gerasimchuk NN, Barybin MV. Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered. Molecules. 2021; 26(4):981. https://doi.org/10.3390/molecules26040981

Chicago/Turabian Style

Hart, Mason D., John J. Meyers Jr., Zachary A. Wood, Toshinori Nakakita, Jason C. Applegate, Nathan R. Erickson, Nikolay N. Gerasimchuk, and Mikhail V. Barybin 2021. "Tuning π-Acceptor/σ-Donor Ratio of the 2-Isocyanoazulene Ligand: Non-Fluorinated Rival of Pentafluorophenyl Isocyanide and Trifluorovinyl Isocyanide Discovered" Molecules 26, no. 4: 981. https://doi.org/10.3390/molecules26040981

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