Dative versus electron-sharing bonding in N-imides and phosphane imides R₃ENX and relative energies of the R₂EN(X)R isomers (E = N, P; R = H, Cl, Me, Ph; X = H, F, Cl)^*

* This paper is dedicated to the memory of Dieter Cremer.

ABSTRACT

Quantum chemical calculations using density functional theory BP86 and M06-2X functionals in conjunction with def2-TZVPP basis sets have been carried out on the title molecules. The calculation results reveal that the N-imides R₃NNX are always clearly higher in energy than the imine isomers R₂NN(X)R. In the case of phosphane imides R₃PNX and the isomers R₂PN(X)R, the substituent R plays a critical role in determining their relative stabilities. When R is hydrogen or phenyl group, R₃PNX are always higher in energy than R₂PN(X)R but the former are more stable than the latter when R = Cl. Interestingly, the Me₃PNX and Me₂PN(X)Me are quite close in energy. The energy decomposition analysis suggests that the P–N bond in the phosphane imides R₃PNX (R = H, Cl, Me, Ph; X = H, F, Cl) should be described in terms of an electron-sharing single bond between two charged fragments R₃P⁺-NX⁻ that is supported by (R₃P)⁺←(NX)⁻ π-backdonation. The π-bond contributes 14–21% of the total orbital interactions while the σ-bond provides 60–68% of ΔE_orb.

GRAPHICAL ABSTRACT

KEYWORDS:

• Chemical bond
• N-imides
• phosphane imides
• energy decomposition analysis
• DFT

Acknowledgements

T. Y. thanks the Alexander von Humboldt Foundation for a postdoctoral fellowship. This work was supported by the Deutsche Forschungsgemeinschaft.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Gernot Frenking http://orcid.org/0000-0003-1689-1197

Notes

* This paper is dedicated to the memory of Dieter Cremer.