Density functional study of N-heterocyclic and diamino carbene complexes: Comparison with phosphines

Ming Tsung Lee, Ching Han Hu

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Abstract

In this study we have examined 27 Cr(CO)5L complexes, ligands including N-heterocyclic carbenes (NHCs), acyclic diaminocarbenes, Fischer- and Schrock-type carbenes, and phosphines. We found that NHC-metal bonds are significantly stronger than those of phosphines. Imidazol-2-ylidenes (1a-g) and their C-C saturated imidazolin-2-ylidene counterparts (2a-g) demonstrate similar ligand-metal binding and gas-phase proton affinity (PA). CO exchange from Cr(CO)6 by NHCs and carbenes is energetically favorable, while CO exchange for phosphines is unfavorable. NHC ligands facilitate carbonyl dissociation from the complexes to a larger extent than phosphines. It was found that the geometrical parameters and force constants of trans C-O in Cr(CO)5L complexes are closely related to ligand properties such as PA, electronegativity (χ), and charge transfer (ΔN). In general, NHCs and phosphines are nucleophilic and soft ligands, while the nucleophilicity and softness of NHCs are slightly larger. Among them, acyclic diaminocarbenes, imidazolin-2-ylidenes with large substituent groups on nitrogens, and PCy3 and PPh3 are ligands that are the softest and most nucleophilic. The nucleophilicity of ligands decrease in the order: :C(N(i-Pr)2)2 > :C(NMe2)2 > PCy3, :C(Me)(NMe2) > PPh3, 2c-g > 1c-g, :C(Me)(OMe), P(alkyl)3 > PH3, :C(OH)2 > :CH2 > PF3 > :CF2.

Original languageEnglish
Pages (from-to)976-983
Number of pages8
JournalOrganometallics
Volume23
Issue number5
DOIs
Publication statusPublished - 2004 Mar 1

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Phosphines
carbenes
phosphines
Carbon Monoxide
Ligands
ligands
affinity
Protons
Metals
Electronegativity
softness
protons
carbene
imidazoles
metals
Charge transfer
Nitrogen
Gases
charge transfer
dissociation

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

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abstract = "In this study we have examined 27 Cr(CO)5L complexes, ligands including N-heterocyclic carbenes (NHCs), acyclic diaminocarbenes, Fischer- and Schrock-type carbenes, and phosphines. We found that NHC-metal bonds are significantly stronger than those of phosphines. Imidazol-2-ylidenes (1a-g) and their C-C saturated imidazolin-2-ylidene counterparts (2a-g) demonstrate similar ligand-metal binding and gas-phase proton affinity (PA). CO exchange from Cr(CO)6 by NHCs and carbenes is energetically favorable, while CO exchange for phosphines is unfavorable. NHC ligands facilitate carbonyl dissociation from the complexes to a larger extent than phosphines. It was found that the geometrical parameters and force constants of trans C-O in Cr(CO)5L complexes are closely related to ligand properties such as PA, electronegativity (χ), and charge transfer (ΔN). In general, NHCs and phosphines are nucleophilic and soft ligands, while the nucleophilicity and softness of NHCs are slightly larger. Among them, acyclic diaminocarbenes, imidazolin-2-ylidenes with large substituent groups on nitrogens, and PCy3 and PPh3 are ligands that are the softest and most nucleophilic. The nucleophilicity of ligands decrease in the order: :C(N(i-Pr)2)2 > :C(NMe2)2 > PCy3, :C(Me)(NMe2) > PPh3, 2c-g > 1c-g, :C(Me)(OMe), P(alkyl)3 > PH3, :C(OH)2 > :CH2 > PF3 > :CF2.",
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Density functional study of N-heterocyclic and diamino carbene complexes : Comparison with phosphines. / Lee, Ming Tsung; Hu, Ching Han.

In: Organometallics, Vol. 23, No. 5, 01.03.2004, p. 976-983.

Research output: Contribution to journalArticle

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