Signet-Ring-Shaped Octaphosphorus-Cobalt Complexes: Synthesis, Structure, and Functionalization Reactions with...

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Catalysis

Background:

• Low-valent metal activation of white phosphorus (P4) typically yields small phosphorus molecules (Pn, n ≤ 4).
• Metal-mediated synthesis of large polyphosphorus clusters from P4 remains underdeveloped.
• N-heterocyclic carbene (NHC)-metal complexes are increasingly explored for small molecule activation.

Purpose of the Study:

• To investigate P4 activation using NHC-cobalt(0)-alkene complexes for the synthesis of larger polyphosphorus structures.
• To characterize the resulting P8 complexes and explore their reactivity.
• To demonstrate the potential for selective functionalization of these novel polyphosphorus cages.

Main Methods:

• Reaction of white phosphorus with three-coordinate NHC-cobalt(0)-alkene complexes.
• Isolation and characterization of the resulting cobalt-P8 complexes using spectroscopic and crystallographic techniques.
• Subsequent functionalization reactions of the P8 ligand with various reagents (e.g., N-heterocyclic silylenes, organic azides).

Main Results:

• High-yield synthesis of cobalt-P8 complexes, [(NHC)2Co2(μ-η6:η6-P8)], featuring a unique signet-ring P8 ligand structure.
• Theoretical studies indicate a Co0–[P8]0–Co0 formulation with a Co-Co σ-bond and significant back-donation.
• Demonstration of selective cage functionalization of the P8 ligand, yielding diverse P8X, RNPPP6, and cyclo-P4P3 structures, while P4 remains inert.

Conclusions:

• NHC-cobalt complexes effectively mediate the coupling of P4 to form unprecedented P8 clusters.
• The synthesized P8 ligand exhibits enhanced reactivity compared to P4, allowing for diverse electrophilic and nucleophilic functionalizations.
• This work opens new avenues for constructing complex polyphosphorus architectures with potential applications in materials science and catalysis.