Structural and Electronic Properties of Iron(0) PNP Pincer Complexes

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Inorganic Synthesis

Background:

• Low-valent iron complexes are crucial in catalysis and materials science.
• Understanding the electronic and structural properties of iron(0) carbonyls is key to advancing their applications.
• Previous studies on iron complexes often focus on higher oxidation states.

Purpose of the Study:

• To synthesize and fully characterize novel iron(0) carbonyl complexes of the type [Fe(PNP)(CO)2].
• To investigate the influence of ligand structure on the geometry and electronic properties of these iron(0) complexes.
• To compare the spectroscopic properties, particularly Mössbauer spectra, with related iron(I) systems.

Main Methods:

• Synthesis of iron(0) complexes via reduction of iron(II) precursors ([Fe(PNP)(Cl)2]) using KC8 in the presence of carbon monoxide.
• Full characterization including X-ray crystallography (implied by geometry determination) and Mössbauer spectroscopy.
• Density Functional Theory (DFT) calculations to complement experimental data.

Main Results:

• Successful preparation of [Fe(PNP)(CO)2] complexes.
• Trigonal bipyramidal geometry observed for [Fe(PNP^NMe-iPr)(CO)2] and [Fe(PNP^NEt-iPr)(CO)2].
• Square pyramidal geometry favored for the bulkier [Fe(PNP^NH-tBu)(CO)2].
• Mössbauer isomer shifts near 0 mm/s, characteristic of Fe(I) systems.
• Distinct quadrupole splitting values (2.2–2.7 mm/s) compared to Fe(I) complexes (∼0.6 mm/s).

Conclusions:

• The steric and electronic properties of the PNP ligand significantly influence the geometry of the resulting iron(0) complexes.
• Mössbauer spectroscopy reveals unique electronic characteristics of these iron(0) complexes, differentiating them from Fe(I) analogues.
• The study provides valuable data for understanding bonding and structure in low-valent organoiron compounds.