Metal-Assisted Opening of Intact P₄ Tetrahedra

The reactivity of ruthenium and manganese complexes bearing intact white phosphorus in the coordination sphere was investigated towards the low-valent transition-metal species [Cp'''Co] (Cp'''=η⁵ -C₅ H₂ -1,2,4-tBu₃ ) and [L⁰ M] (L⁰ =CH[CHN(2,6-Me₂ C₆ H₃ )]₂ ; M=Fe, Co). Remarkably, and irrespective of the metal species, the reaction proceeds by the selective cleavage of two P-P edges and the formation of a square-planar cyclo-P₄ ligand. The reaction products [{CpRu(PPh₃ )₂ }{CoCp'''}(μ,η^1:4 -P₄ )][CF₃ SO₃ ] (5), [{Cp^BIG Mn(CO)₂ }₂ {CoCp'''}(μ,η^1:1:4 -P₄ )] (6) and [{Cp^BIG Mn(CO)₂ }₂ {ML⁰ }(μ,η^1:1:4 -P₄ )] (Cp^BIG =C₅ (C₆ H₄ nBu)₅ ; L⁰ =CH[CHN(2,6-Me₂ C₆ H₃ )]₂ ; M=Fe (7 a), Co (7 b)), respectively, were fully characterized by single-crystal X-ray diffraction and spectroscopic methods. The electronic structure of the cyclo-P₄ ligand in the complexes 5-7 is best described as a π-delocalized P₄ ^2- system, which is further stabilized by two and three metal moieties, respectively. DFT calculations envisaged a potential intermediate in the reaction to form 5, in which a quasi-butterfly-shaped P₄ moiety bridges the two metals and behaves as an η³ -coordinated ligand towards the cobalt center.