Base metal complexes featuring a new pyrazole-derived PCP pincer ligand

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Ligand Design

Background:

• Pincer ligands are versatile scaffolds in coordination chemistry, offering unique steric and electronic properties.
• Pyrazole-based ligands are increasingly explored for their tunable coordination modes and potential applications.

Purpose of the Study:

• To synthesize and characterize a new pyrazole-derived PCP pincer ligand (PCP-iPr).
• To investigate the coordination behavior of PCP-iPr with group six and transition metal carbonyl complexes.
• To explore the postfunctionalization of the synthesized metal-PCP complexes.

Main Methods:

• Synthesis of the pyrazole-derived PCP pincer ligand (PCP-iPr).
• Reactions of PCP-iPr with various metal carbonyl precursors ([M(CO)6], [Mn2(CO)10], [Fe2(CO)9], [Co2(CO)8], [Ni(COD)2]).
• Characterization of resulting complexes using NMR (1H, 13C, 31P), IR spectroscopy, HR-MS, and X-ray crystallography.
• Density Functional Theory (DFT) calculations were employed to understand bonding interactions.

Main Results:

• A new pyrazole-derived PCP pincer ligand (PCP-iPr) was successfully prepared.
• Complexes with group six metals ([M(κ2PN-PCP-iPr)(CO)4]) and transition metals ([Mn(κ3PCP-PCP-iPr)(CO)3], [Fe(κ3PCP-PCP-iPr)(H)(CO)2], [Co(κ3PCP-PCP-iPr)(CO)2], [Ni(κ3PCP-PCP-iPr)(H)]) were synthesized, showcasing different coordination modes.
• Molybdenum complexes exhibited a κ3PCP coordination with a weak Mo-C bond at higher temperatures.
• Postfunctionalization via N-methylation yielded cationic PCP pincer complexes.

Conclusions:

• The pyrazole-derived PCP pincer ligand demonstrates versatile coordination capabilities with a range of metal centers.
• The ligand can adopt different binding modes (κ2PN and κ3PCP) depending on the metal and reaction conditions.
• Postfunctionalization offers a route to modify the electronic properties and charge of the resulting metal complexes.