A combined experimental and theoretical study of dinitrosyl iron complexes containing chelating bis(diphenyl)phosphinoX (X=benzene, propane and ethylene): X-ray crystal structures and properties influenced by the presence or absence of π-bonds in chelating ligands

• Published in: Polyhedron 2014-03, Vol.70, p.29-38
• Main Authors: Holloway, Lauren R., Clough, Andrew J., Li, Jessica Y., Tao, Emily L., Tao, Fu-Ming, Li, Lijuan
• Format: Article
• Language: English
• Subjects: Chelating bisphosphines; DFT calculations; Dinitrosyl iron complexes; Spectroscopy
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2013.12.019

Dinitrosyl iron complexes with formula [(DPPX)Fe(NO)2], {DPPX=1,2-bis(diphenylphosphino)benzene (1), 1,3-bis(diphenylphosphino)propane (2), and cis-1,2-bis(diphenylphosphino)ethylene (3)} have been prepared and characterized by FT-IR, NMR, UV–Vis, X-ray crystallography, electrochemical techniques, and DFT calculations. The presence of π-bonds between the two phosphorus atoms lowered the HOMO–LUMO gap and caused charge delocalization upon oxidation. Recent discoveries involving the roles of nitric oxide in humans have stimulated intense interest in transition metal nitrosyl complexes. A series of dinitrosyl iron complexes with the formula [(DPPX)Fe(NO)2], {DPPX=1,2-bis(diphenylphosphino)benzene (1), 1,3-bis(diphenylphosphino)propane (2), and cis-1,2-bis(diphenylphosphino)ethylene (3)} has been prepared and characterized through a combination of FT-IR, NMR, UV–Vis, X-ray crystallography, and electrochemical techniques. Infrared spectroscopy showed NO shifts to the region of 1723 and 1674cm−1 for complexes 1 and 3, and 1708 and 1660cm−1 for 2, indicating that ligand 2 acts as a stronger σ-donor. The X-ray crystallographic data showed that 1 and 3 possess the rare repulso conformation while 2 has the attracto conformation. CV studies on compounds 1, 2 and 3 display two quasi-reversible oxidations with the E°1/2 values at 0.101 and 0.186V, 0.121 and 0.184V, and 0.019 and 0.342V, respectively. The larger ΔE value for compound 2 compared with that of 1 and 3 is attributed to the lack of π-bonds between the two phosphorus atoms. Theoretical calculations using density functional theory were carried out on the synthesized compounds and model compounds and the results are consistent with the experimental data. The calculated HOMO–LUMO gaps for compounds 1, 2 and 3 are 3.736, 4.060, and 3.669eV, respectively, which supports the stronger back-donation for compound 2 than that of compounds 1 and 3.