Syntheses and structures of potassium complexes containing bis(diphenylphosphanyl)methanide anions

The reaction of [K{(Ph₂P)₂CH}(Et₂O) _0.5]_n with an excess of tetrahydropyran yields polymeric [K{(Ph₂P)₂CH}(thp)]_∞ (1). Application of neutral bidentate ligands such as dimethoxyethane or N,N,N′N′- tetramethylethylenediamine leads to a splitting of the polymeric starting material into discrete dinuclear entities and the complexes [K{(Ph ₂P)₂CH}(dme)]₂ (3) and [K{(Ph ₂P)₂CH}(tmeda)]₂ (4) were isolated. In compounds 1, 3 and 4, the phosphorus atoms as well as the methanide carbon atom and two of the four phenyl groups of the anionic ligand participate in metal binding. Oligodentate ligands such as diglyme and 18-crown-6 enforce a reduction of the interaction between potassium and the diphosphanylmethanide anion and lead to the mononuclear complexes [K{(Ph₂P)₂CH}(diglyme) ₂] (5) and [{K{(Ph₂P)₂CH}(18C6)}{K{(Ph ₂P)₂CH}(18C6)(thf)}] (6), respectively. In these compounds, only the phosphorus atoms of the diphosphanylmethanide ligands coordinate to the central potassium cation. The related lithium derivative [Li{(Ph₂P)₂CH}(thp)₃] (2) was prepared for comparison. All complexes were characterized by NMR methods and X-ray diffraction measurements. The disaggregation of polymeric potassium bis(diphenylphosphanyl)methanide into discrete mono- or dinuclear entities as well as the resulting changes in coordination mode of the anionic ligand were studied. The process depends on the nature of the mono-, bi- and oligodentate neutral oxygen or nitrogen donor ligand added.