Phosphine-catalysed reductive coupling of dihalophosphanes

Area of Science:

• Organophosphorus Chemistry
• Catalysis
• Synthetic Methodology

Background:

• Traditional synthesis of tetraaryl diphosphanes relies on Wurtz-type reductive coupling of halophosphanes or dehydrocoupling of phosphines.
• Existing catalytic dehydrocoupling methods are restricted to specific phosphine substrates (R2PH).
• Access to sterically hindered or functionalized diphosphanes and diphosphenes remains challenging.

Purpose of the Study:

• To develop a novel catalytic reductive coupling method for synthesizing tetraaryl diphosphanes and diphosphenes.
• To explore the scope and limitations of triethylphosphine (PEt3) as a catalyst in these transformations.
• To investigate the synthesis of previously inaccessible diphosphane and diphosphene structures.

Main Methods:

• Catalytic reductive coupling of halophosphanes (TipPBr2, DipPBr2, Ph2PCl, Mes2PX) using triethylphosphine (PEt3) as a catalyst.
• Utilized varying phosphine precursors and reaction conditions to optimize product formation.
• Characterization of synthesized diphosphanes and diphosphenes using spectroscopic techniques and stability studies.

Main Results:

• Selective synthesis of dibromodiphosphane (TipPBr)2 from TipPBr2 using PEt3 catalysis, a compound not accessible via traditional Mg reduction.
• Surprising selective formation of the diphosphene (PDip)2 from DipPBr2 catalyzed by PEt3, featuring a P=P double bond.
• Demonstrated broad applicability by efficiently coupling Ph2PCl and Mes2PX (X = Cl, Br) to yield (Ph2P)2 and (Mes2P)2, respectively, using 10 mol% PEt3.

Conclusions:

• Triethylphosphine (PEt3) effectively catalyzes the reductive coupling of various halophosphanes, offering a versatile route to tetraaryl diphosphanes and diphosphenes.
• The developed protocol provides access to unique diphosphane and diphosphene structures, expanding synthetic possibilities in organophosphorus chemistry.
• The stable diphosphene (PDip)2 can be further utilized, for instance, with N-heterocyclic carbenes (NHCs) to form NHC-phosphinidene adducts.