Synthesis and Coordination Ability of a Donor-Stabilised Bis-Phosphinidene

Chelating phosphines have long been a mainstay as efficient directing ligands in transition-metal catalysis. Low-valent derivatives, namely chelating phosphinidenes, are to date unknown, and could lead to chelating complexes containing more than one metal centre due to the intrisic capacity of phosphinidenes to bind two metal fragments at one P-centre. Here we describe the synthesis of the first such chelating bis-phosphinidene ligand, XantP(2) (2), generated by the reduction of a diphosphino xanthene derivative, Xant(PH2)(2) (1) with (NHC)-N-iPr ((NHC)-N-iPr=[:C{N(iPr)C(H)}(2)]). Initial studies have shown that this novel chelating ligand can act as a bidentate ligand towards element dihalides (i.e. FeCl2, ZnI2, GeCl2, SnBr2), forming cationic complexes with the tetryl elements. In contrast, XantP(2) demonstrates an ability to bind multiple metal centres in the reaction with CuCl, leading to a cationic Cu3P3 ring complex, with Cu centres bridged by phosphinidene arms. Density Functional Theory calculations show that 2 indeed holds 4 lone pairs of electrons, shedding further light on the coordination capacity for this novel ligand class through observation of directionality and hybridisation of these electron pairs.

Automated summary

Chelating phosphinidenes have not been previously reported, and the newly synthesized XantP(2) ligand shows a unique ability to form cationic complexes with element dihalides while also demonstrating the capacity to bind multiple metal centers in the presence of CuCl. Density Functional Theory calculations confirm the coordination capacity of 2 through observation of lone pairs of electrons and their directionality and hybridization.