N-heterocyclic bis-carbene palladium complexes derived from functionalized naphthalimides – Synthesis, Structure elucidation and DFT study

Abstract Two new bis-carbene (Pd(NHC)2Cl2 and Pd(NHC)(NHC`)Br2) complexes derived from substituted 1,8-naphthalimides were synthesized. All complexes were fully characterized by NMR spectra, which indicate trans orientation of the NHC ligands. 1H and 13C NMR spectra of complex Pd(NHC)2Cl2 are influenced by existence of trans-syn and trans-anti rotamers. The dynamic behaviour in solution of the complex Pd(NHC)2Cl2 was studied by 1H NMR spectra in the temperature range of 293–403 K. The rotational barrier is experimentally estimated to 20 kcal/mol at 298 K. The DFT calculations reproduce the experimental data very well. The analysis of DFT calculations suggests electronic origin of the restricted rotation around Pd-Ccarbene bond. The electron-donating properties of reported system are situated between unsaturated and saturated five-membered ring NHC ligands.