Syntheses and X-ray Structures of Potassium Derivatives and a Paramagnetic Nickel(II) Complex of a Cyclodiphosph(III/V)azane Monoselenide

The cyclodiphosph(III/V)azane monoselenide [tBu(H)N(Se)P(μ-NtBu)2PN(H)tBu] (6, H2cdppSe where cdpp =
cyclodiphosphazane) is obtained in quantitative yield from the comproportionation reaction of equimolar amounts
of H2cdpp (7) and H2cdppSe2 (3) in toluene at 85 °C. The X-ray structures of 3 and 6 reveal that both the
monoselenide and the diselenide adopt a cis,endo,exo arrangement of the tBuNH groups. Metalation of 6 with 1
equiv of KOtBu or 2 equiv of KCH2Ph in THF produces {(THF)K[HcdppSe]}2 (8) or {[(THF)2K]2[cdppSe]}2 (9),
respectively. The initial deprotonation involves the tBuNH group attached to the P(V) center in 6. In the dimeric
structure of 8, both of the monoanionic ligands are bis-N,Se-chelated to the two K+ cations to give a distorted
K2N2Se2 octahedron. In the centrosymmetric dimer 9, the dianionic ligands adopt two different coordination modes
to the bis-solvated K+ ions, viz., tridentate N,N‘,N‘‘ coordination and N,Se-chelation involving both exo- and endocyclic
nitrogen atoms. The dimer is linked through K−Se interactions. The reaction of 2 equiv of 8 with NiCl2(PMe3)2 in
THF produces [Ni(HcdppSe)2], which has a distorted tetrahedral structure and exhibits anomalous 1H, 13C, and 31P
NMR chemical shifts owing to the proximity of the paramagnetic Ni(II) center.