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Australian Journal of Chemistry Australian Journal of Chemistry Society
An international journal for chemical science
RESEARCH ARTICLE

Saturated N,X-Heterocyclic Carbenes (X = N, O, S, P, Si, C, and B): Stability, Nucleophilicity, and Basicity

Zahra Azizi A E , Mehdi Ghambarian B , Mohammad A. Rezaei C and Mohammad Ghashghaee D
+ Author Affiliations
- Author Affiliations

A Department of Chemistry, Karaj Branch, Islamic Azad University, PO Box 31485-313, Karaj, Iran.

B Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemical Institute, PO Box 14975-112, Tehran, Iran.

C Biophysics Graduate Program, Ohio State University, Columbus, OH 43210, USA.

D Faculty of Petrochemicals, Iran Polymer and Petrochemical Institute, PO Box 14975-112, Tehran, Iran.

E Corresponding author. Email: Zahra.Azizi@kiau.ac.ir

Australian Journal of Chemistry 68(9) 1438-1445 https://doi.org/10.1071/CH14715
Submitted: 17 December 2014  Accepted: 4 March 2015   Published: 15 April 2015

Abstract

Various saturated five-membered N,X-heterocyclic carbenes (X = N, O, S, P, Si, C, and B) have been studied by ab initio and density functional theory (DFT) methods. The substitutions alter the properties of the reference carbene from the viewpoint of electronic structure, stability, nucleophilicity, and basicity. Our study shows that the oxygen containing carbene (X = O) induces the highest HOMO–LUMO energy gap (ΔEHOMO–LUMO), while carbene with X = N has the widest singlet–triplet energy difference (ΔEs–t). The nucleophilicity of the carbene derivatives increased upon replacement of C, Si, and B, with the effect of the boron substituent being more pronounced. In addition, the basicity of the structure increased for the carbene derivatives with X = C and B with the latter substitution imposing a remarkably higher effect. Moreover, the substitution of boron at the α-position of the carbene increased the nucleophilicity and basicity, while inducing a reduction in the values of ΔEs–t and ΔEHOMO–LUMO.


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