1,3-Dipolar Cycloaddition Reactions of Low-Valent Rhodium and Iridium Complexes with Arylnitrile N-Oxides

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Organic Synthesis

Background:

• Low-valent metal-carbonyl complexes are known to participate in various chemical transformations.
• 1,3-Dipolar cycloadditions are fundamental reactions in organic synthesis for forming heterocyclic compounds.

Purpose of the Study:

• To investigate the reaction mechanisms between Rh(I)/Ir(I) metal-carbonyls and arylnitrile oxides.
• To elucidate the electronic and structural factors influencing the cycloaddition process and product stability.
• To compare the reactivity of Rh and Ir complexes in these cycloaddition reactions.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the reaction pathways.
• Natural Bonding Orbital (NBO) analysis, including Wiberg index calculations, was used to assess metal-carbonyl bond character.
• Analysis of distortion energies was performed to understand reaction rate control.

Main Results:

• The reactions were characterized as 1,3-dipolar cycloadditions involving M═C bonds, supported by DFT and NBO analyses.
• The stability of the resulting metallaisoxazolin-5-ones was explained through computational modeling.
• Distortion energy was identified as a key factor controlling the rates of metallacycloadduct formation.
• Anionic Ir complexes exhibited higher reactivity than Rh analogues due to enhanced electron density sharing and oxidation state accommodation.

Conclusions:

• The reactions represent a novel class of 1,3-dipolar cycloadditions involving metal-carbonyl complexes.
• DFT calculations provide valuable insights into the mechanism, reactivity, and stability of these organometallic cycloadditions.
• Iridium complexes demonstrate superior reactivity in these cycloaddition reactions compared to rhodium complexes.