The crystallographic and quantum mechanical analysis of some rhodium(I) n-heterocyclic carbene complexes

In this thesis, molecular and crystal structures of [1,3 ? bis(2 ? methyl ? 4 ? diethylaminophenyl) imidazolidin ? 2 ? ylidene] chloro (1,5 ? cyclooctadiene) rhodium(I), [1,3 ? bis(methoxyethyl) ? 4,5 ? bis(2,4,6 ? trimethylphenyl) ? imidazolidin ? 2 ? ylidene] chloro (1,5 ? cyclooctadiene) rhodium(I) and [1,3 ? bis(metoxyethyl) ? 4,5 ? bis(4 ? methylphenyl) imidazolidin ? 2 ? ylidene] iodo (1,5 ? cyclooctadiene) rhodium(I) were determined by the single crystal X-ray diffraction technique. Bonding situations in the compounds have been examined by quantum mechanical principles in the framework of Density Functional Theory (DFT) with the aid of Natural Bond Orbital (NBO) and Fragment Approach analyses. It has been experimentally and theoretically showed that the dominant factor stabilizing the N-Heterocyclic Carbene (NHC) ligands is the electron donation from the nitrogen lone pairs into the formally empty p(pi) orbitals of the carbene carbon atoms. Not only are the NHC ligands in the complexes under discussion contributed to sigma-donation process, but also they are participated in pi-donation and pi-back donation mechanisms. In addition, it is shown that the presence of bulky substituents on the carbon atoms at 4 and 5 positions of the imidazolidin rings affects negatively sigma-donation properties of NHC ligands.