Isomerization, Ring Expansion, and Ring Contraction of 1,3-Diphosphete Complexes

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Main Group Chemistry

Background:

• 1,3-Diphosphete complexes are known but less stable than their 1,2-isomers.
• The synthesis and reactivity of strained phosphorus-containing heterocycles are of significant interest.
• Exploring novel reaction pathways for organometallic complexes is crucial for advancing synthetic chemistry.

Purpose of the Study:

• To investigate the reactivity of the 1,3-diphosphete complex [Cp'''Co(η⁴-P₂C₂tBu₂)] (1) with Ag[Al{OC(CF₃)₃}₄].
• To explore conditions leading to isomerization, ring expansion, and ring contraction reactions.
• To synthesize and characterize novel cobalt-phosphorus complexes.

Main Methods:

• Reactions of complex 1 with Ag[pftb] in dichloromethane and n-hexane.
• Diffusion experiments to facilitate reactions between reactants in different solvents.
• Addition of pyridine to a silver complex and thermolysis of complex 1.

Main Results:

• Isolation of an unprecedented 1,2-diphosphete isomerization product (2) in dichloromethane.
• Formation of a triphosphacobaltocenium complex (4) via ring expansion and a phosphirenylium complex (5) via ring contraction under diffusion conditions.
• Synthesis of a new 1,2-diphosphete complex (3) by pyridine addition to complex 2 or thermolysis of complex 1.

Conclusions:

• The reaction conditions significantly influence the outcome, leading to diverse phosphorus-containing cobalt complexes.
• Thermolysis of complex 1 provides a viable synthetic route to the more stable 1,2-diphosphete complexes.
• 1,2-Diphosphete complexes are thermodynamically favored but synthetically challenging, highlighting the significance of these findings.