Controlled Ring Opening of a Tetracyclic Tetraphosphane with Twofold Metallocene Bridging

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Materials Science

Background:

• Ferrocene derivatives are crucial in organometallic chemistry, offering unique electronic and structural properties.
• Tetraphosphanes represent an intriguing class of inorganic compounds with potential applications in catalysis and materials science.
• Controlled synthesis and functionalization of polyphosphorus compounds remain a significant challenge.

Purpose of the Study:

• To develop a direct synthetic route to a doubly ferrocene bridged tetracyclic tetraphosphane.
• To investigate the selective P-P bond activation and reactivity of the synthesized tetraphosphane.
• To explore the potential of this tetraphosphane in polymerization reactions.

Main Methods:

• Reductive coupling of Fe(CpPCl2)2 (2a) to form the target tetraphosphane.
• Reactions with elemental selenium and [Cp*Al]4 for P-P bond activation and heteroatom insertion.
• Methylation with MeOTf to study functionalization pathways.
• Spectroscopic characterization (NMR, Mass Spectrometry) and Single-Crystal X-ray Diffraction (SC-XRD).
• Density Functional Theory (DFT) calculations to rationalize reactivity.

Main Results:

• Successful synthesis of a doubly ferrocene bridged tetracyclic tetraphosphane (1) via reductive coupling.
• Identification of a chlorine-terminated linear P4-compound (3) as an intermediate.
• Regioselective insertion of Se and Al atoms into P-P bonds, yielding ferrocenylene-bridged [P4Se] (4) and [P4Al] (7) moieties.
• Transformation of compound 7 to a hydrogen-terminated linear P4 species (8).
• Methylation of compound 1 leads to a dimethylated dicationic species (6) with a linear P4-unit.
• Determination of the solid-state structures of key compounds (1, 4, 6, 8) via SC-XRD.
• Demonstration of ring-opening polymerization of tetraphosphane 1 to a linear polyphosphane (9).

Conclusions:

• A novel and direct synthetic pathway to a unique ferrocene-bridged tetraphosphane has been established.
• The tetraphosphane exhibits versatile reactivity, allowing for selective P-P bond cleavage and heteroatom incorporation.
• The compound serves as a precursor for linear polyphosphanes, opening avenues for new phosphorus-based materials.