Ion-bearing stairs: alkali metal complexes of 1,2-diaza-4-phospholides.

In this work, eight alkali metal complexes with 1,2-diaza-4-phospholide ligands were prepared and characterized by X-ray single-crystal structural analysis and NMR spectroscopy. Their structures showed varied coordination motifs: (i) a dimeric 1,2-diaza-4-phospholide lithium complex with exo -bidentate bridging coordination (4) consists of two lithium atoms that are linked via two μ 2 -bridging, κ N ,κ N' -coordinated ligands; (ii) the polymeric chain 1,2-diaza-4-phospholide potassium complex (5) showed an ion-bearing stair-shaped chain structure running through axis a , where the steps are η 2 interactions, and there is a transition platform between every two stairs; (iii) the polymeric chain 1,2-diaza-4-phospholide potassium complex (6) also presented a polymeric chain structure in the solid state but displayed a head-to-tail arrangement of two 1,2-diaza-4-phospholides; (iv) in comparison to 6, the 1,2-diaza-4-phospholide sodium complex (7) displayed a tetrameric structure, in which the sodium ions are arranged in a distorted tetrahedral fashion and each of them occupies a vertex of the tetrahedron; (v) the polymeric chain 1,2-diaza-4-phospholide potassium complex (8) presented a solvent-free chain structure, in which potassium ions each is η 5 -bonded by two 1,2-diaza-4-phospholides and η 2 -coordinated by another, consisting of a stair-shaped chain structure running through axis a but without significant intermolecular contacts between the adjacent stairs in comparison to that of 5; (vi) the polymeric chain 1,2-diaza-4-phospholide sodium complex (9) presented a solvent-free chain structure, in which sodium ions each is η 1 ( N ),η 2 ( N , N ),η 1 ( P )-bonded by three 1,2-diaza-4-phospholides, consisting of a chain structure running through axis a ; and (vii) the treatment complex 8 with elemental sulphur or selenium in the presence of crown ether gave rare thiophosphonato potassium [η 3 ( S , P , S )-3,5- t Bu 2 dp-(μ-K)(S 2 )([18]crown-6)] (10) or a selenophosphonato potassium [η 3 ( Se , P , Se )-3,5- t Bu 2 dp-(μ-K)(Se 2 )([18]crown-6)] (11). Both of the complexes crystallized in the orthorhombic space group Pnma as pale-yellow (or red) crystals. The X-ray diffraction analysis revealed 10 or 11 as a terminal complex with the η 1 ,η 1 - X , X -coordination mode (X = S and Se). The 1 H DOSY NMR spectroscopy study of the species 8 in DMSO- d 6 suggested that polymeric complexes (4-9) in the solid state should dissociate into the related monomers in the solutions when the donor solvents were used.