Ligand properties of N-heterocyclic and Bertrand carbenes

A density functional study

Chun Liang Lai, Wen Hsin Guo, Ming Tsung Lee, Ching Han Hu

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

In order to probe the ligand properties we have examined a series of Cr(CO)5L and Ni(CO)3L complexes using density functional theory (DFT). The ligands included in our study are N-heterocyclic carbenes (NHCs) and Bertrand-type carbenes. Our study shows that the carbene-metal bonds of imidazol-2-ylidenes (1), imidazolin-2-ylidenes (2), thiazo-2-ylidenes (3), and triazo-5-ylidenes (4) are significantly stronger than those of Bertrand-type carbenes (5-7). The force constants of C-O in complexes are related to the property of isolated carbenes such as proton affinity (PA), electronegativity (χ), and charge transfer (ΔN). NHCs and Bertrand-type carbenes are identified as nucleophilic, soft ligands. Carbene stabilization energy (CSE) computations indicate that carbenes 1 and 4 are the most stable species, while 2 and 3 are less stable. In contrast to NHCs, CSE of carbenes 5-7 are much smaller, and their relative stabilities are in the order (amino)(aryl) carbenes 7e-7g > (amino)(alkyl) carbenes 7a-7d > (phosphino)(aryl) 6d-6e, and (phosphino)(silyl) carbenes 5a-5c > no)(alkyl) carbenes 6a-6c.

Original languageEnglish (US)
Pages (from-to)5867-5875
Number of pages9
JournalJournal of Organometallic Chemistry
Volume690
Issue number24-25
DOIs
StatePublished - Dec 1 2005
Externally publishedYes

Fingerprint

carbenes
Ligands
ligands
Stabilization
Electronegativity
Density functional theory
Charge transfer
Protons
Metals
carbene
Carbon Monoxide
stabilization
imidazoles
affinity

Keywords

  • Electronegativity
  • Electrophilicity
  • Hardness
  • N-heterocyclic carbene
  • Nucleophilicity

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Materials Science (miscellaneous)
  • Materials Chemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry
  • Biochemistry

Cite this

Ligand properties of N-heterocyclic and Bertrand carbenes : A density functional study. / Lai, Chun Liang; Guo, Wen Hsin; Lee, Ming Tsung; Hu, Ching Han.

In: Journal of Organometallic Chemistry, Vol. 690, No. 24-25, 01.12.2005, p. 5867-5875.

Research output: Contribution to journalArticle

Lai, Chun Liang ; Guo, Wen Hsin ; Lee, Ming Tsung ; Hu, Ching Han. / Ligand properties of N-heterocyclic and Bertrand carbenes : A density functional study. In: Journal of Organometallic Chemistry. 2005 ; Vol. 690, No. 24-25. pp. 5867-5875.
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N2 - In order to probe the ligand properties we have examined a series of Cr(CO)5L and Ni(CO)3L complexes using density functional theory (DFT). The ligands included in our study are N-heterocyclic carbenes (NHCs) and Bertrand-type carbenes. Our study shows that the carbene-metal bonds of imidazol-2-ylidenes (1), imidazolin-2-ylidenes (2), thiazo-2-ylidenes (3), and triazo-5-ylidenes (4) are significantly stronger than those of Bertrand-type carbenes (5-7). The force constants of C-O in complexes are related to the property of isolated carbenes such as proton affinity (PA), electronegativity (χ), and charge transfer (ΔN). NHCs and Bertrand-type carbenes are identified as nucleophilic, soft ligands. Carbene stabilization energy (CSE) computations indicate that carbenes 1 and 4 are the most stable species, while 2 and 3 are less stable. In contrast to NHCs, CSE of carbenes 5-7 are much smaller, and their relative stabilities are in the order (amino)(aryl) carbenes 7e-7g > (amino)(alkyl) carbenes 7a-7d > (phosphino)(aryl) 6d-6e, and (phosphino)(silyl) carbenes 5a-5c > no)(alkyl) carbenes 6a-6c.

AB - In order to probe the ligand properties we have examined a series of Cr(CO)5L and Ni(CO)3L complexes using density functional theory (DFT). The ligands included in our study are N-heterocyclic carbenes (NHCs) and Bertrand-type carbenes. Our study shows that the carbene-metal bonds of imidazol-2-ylidenes (1), imidazolin-2-ylidenes (2), thiazo-2-ylidenes (3), and triazo-5-ylidenes (4) are significantly stronger than those of Bertrand-type carbenes (5-7). The force constants of C-O in complexes are related to the property of isolated carbenes such as proton affinity (PA), electronegativity (χ), and charge transfer (ΔN). NHCs and Bertrand-type carbenes are identified as nucleophilic, soft ligands. Carbene stabilization energy (CSE) computations indicate that carbenes 1 and 4 are the most stable species, while 2 and 3 are less stable. In contrast to NHCs, CSE of carbenes 5-7 are much smaller, and their relative stabilities are in the order (amino)(aryl) carbenes 7e-7g > (amino)(alkyl) carbenes 7a-7d > (phosphino)(aryl) 6d-6e, and (phosphino)(silyl) carbenes 5a-5c > no)(alkyl) carbenes 6a-6c.

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