Ruthenium mediated halogenation of white phosphorus: synthesis and reactivity of the unprecedented P4Cl2 moiety

The transition metal mediated functionalization of P-4 is an approach to develop a more sustainable production of organophosphorus compounds. In this paper a ruthenium complex is presented, in which the P-4 unit can be selectively converted into new P4R2 molecules in a two-step synthesis. The unsaturated 16 electron species [RuX(Cp*)(PCy3)] (Cp* = C5Me5, X = Cl, Br) reacts with a half equivalent of P-4 affording a bimetallic complex bearing a planar P4X2 moiety as a ligand. The latter eliminates chloride anions under reduction with magnesium. In this process the butadiene-like P4Cl2 ligand is converted into two weakly bound P-2 units which bridge the ruthenium centers. In the presence of n-BuLi, the P4Cl2 unit can be selectively alkylated, yielding the planar organophosphorus ligand (P4Bu2)-Bu-n. A detailed analysis of the electronic properties and solid state structures of the compounds combined with DFT calculations and AIM analyses demonstrate that the P-4 unit in all complexes acts as an electronically highly flexible, non-innocent ligand.