E versus Z isomers of Fischer aminocarbene complex [Mo(CO)4(PPh3){C(NHCy)(2-furyl)}]: NH⋯O versus CH⋯O intramolecular hydrogen bonds

• DFT conformation analysis yields 12 possible structural conformations.
• Crystal structure shows syn conformation for the two heteroatoms.
• Crystal structure shows Z conformation for cyclohexyl group relative to Mo.
• Crystal structure shows cis isomer for PPh3 relative to the carbene ligand.
• Calculated NBO donor–acceptor interactions show intramolecular H-bond interactions.

A density functional theory (DFT) calculated conformation analysis of the twelve possible conformations of [Mo(CO)4(PPh3){C(NHCy)(2-furyl)}], 1, utilizing different DFT methods, showed that both the cis-syn,Z (2), 1-Z, and the cis-syn,Z (2), 1-E, conformations of this aminocarbene complex have similar electronic and Gibbs free energies. The solid-state crystal structure of the 1-Z is presented in this study and compared to the structure of the 1-E conformation. The stability of 1-Z, versus the previously published solid-state structure of conformer 1-E, is ascribed to stabilization of the NH⋯OFu intramolecular bond. This is evidenced by a shorter H⋯O intramolecular bond in the experimental crystal structure of 1-Z. The stability of the 1-Z and 1-E conformations were analyzed and compared by density functional theory, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) methods. The NBO analysis reveals similar but stronger donor–acceptor interactions in 1-Z than in 1-E. QTAIM calculations indicate 6 and 5 bond critical points related to intramolecular bonds stabilizing the orientation of 2-furyl and NHCy in 1-Z and 1-E respectively.

X-ray, NBO and QTAIM analysis of the E and Z isomers of a Fischer Mo-aminocarbene complex.Figure optionsDownload as PowerPoint slide