Carborane Stabilized "19-Electron" Molybdenum Metalloradical.

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Molybdenum Chemistry

Background:

• Paramagnetic metal complexes are crucial in chemical reactions.
• These complexes often involve 17-electron (17-e) metalloradicals and highly reactive 19-electron (19-e) species.
• Molybdenum (Mo)-centered radicals are of significant interest, though 19-e Mo radicals are rarely detected.

Purpose of the Study:

• To generate and characterize a persistent 19-electron Mo-centered radical.
• To investigate the stabilization mechanisms of such elusive species.
• To explore the role of substituents in stabilizing paramagnetic molybdenum complexes.

Main Methods:

• Photodissociation of the [Cp(CO)3Mo]2 dimer in the presence of phosphines.
• Electron Paramagnetic Resonance (EPR) spectroscopy for radical characterization.
• Mass Spectrometry (MS) and Density Functional Theory (DFT) calculations for structural and electronic analysis.

Main Results:

• The first persistent, formally 19-e Mo radical, Cp(CO)3MoPPh2(o-C2B10H11) (5b), was successfully generated.
• The radical exhibited significant electron density (22%) on the Mo center.
• Stabilization is attributed to the electron-withdrawing effect of the o-carboranyl group on the phosphorus atom.

Conclusions:

• The study reports the first persistent 19-e Mo radical, challenging previous notions of their elusiveness.
• The o-carboranyl substituent plays a key role in stabilizing the 19-e Mo radical.
• This work opens new avenues for designing and utilizing paramagnetic molybdenum complexes.