Syntheses and Structures of Trilithium Cyclotriphosphazenates Equipped with 2‐Halo‐aryl Substituents

Hexakis (2‐halo‐anilino) cyclotriphosphazenes (2‐X‐C₆H₄NH)₆P₃N₃ {X = F ( 1d ), Cl ( 1e ), Br ( 1f )} were prepared by refluxing mixtures of hexachloro cyclotriphosphazene, 2‐haloaniline and triethylamine in toluene and characterized by single crystal X‐ray diffraction. 1d , 1e and 1f were reacted with ⁿBuLi in thf. Reactions were monitored with ³¹P NMR. Addition of three equivalents of ⁿBuLi yields lithium complexes of trianionic phosphazenates [{(thf)₂Li}₃{(2‐X‐C₆H₄N)₃(2‐X‐C₆H₄NH)₃P₃N₃}] {X= F ( 2d ), Cl ( 2e ) and Br ( 2f )}. 2d , 2e and 2f were structurally characterized by X‐ray diffraction, which reveals monomeric cis‐metalated phosphazenates featuring central P₃N₃ ring systems of chair conformation. Lithium ions reside in three N(eq)‐P‐N(endo) chelation sites at one face of the P₃N₃ ring system. Li…X distances are rather long (> 3Å) indicating no Li‐X interactions.     

From neutral iminophosphoranes to multianionic phosphazenates. The coordination chemistry of imino-aza-P(V) ligands

This review deals with the chemistry and coordination behaviour of imino-aza phosphorus(V) ligands focussing on s- and p-block as well as Group 11 and 12 metal complexes. Imino phosphorus(V) ligands contain one or more terminal RNP-units, which include iminophosphoranes R₃PNR′, monoanionic diiminophosphinates [R₂P(NR′)₂]⁻, dianionic triiminophosphonates [RP(NR′)₃]²⁻ and trianionic tetraiminophosphates [P(NR′)₄]³⁻. Aza-phosphorus(V) ligands feature bridging PNP units, which include cyclic and polymeric phosphazenes [R₂PN]_n. Imino-aza- phosphorus(V) ligands containing both imino and aza functions include linear diiminodiphosphazenates [N{R₂P(NR′)₂}₂]⁻ and multianionic poly(imino) cyclophosphazeantes such as [N₄{RP(NR′)}₄]⁴⁻ and [N₃{P(NR′)₂}₃]⁶⁻. Imino-aza phosphorus(V) ligands are assembled of three basic building blocks: the cationic tetravalent phosphonium centre (P), the anionic divalent amido function (N) and the terminally arranged R-group. The overall negative charge Z of the resulting ligand system is equal to the difference between the number of P and the number of N-centres: Z=n(P)n(N). Imino-aza phosphorus(V) ligands are electron rich N-donor ligands which co-ordinate via both N(imino) and N(aza) functions and have been applied in numerous metal complexes in order to stabilise low coordination numbers, unusual oxidation states and bonding modes or serve as ligands in homogeneous catalysis. The R-group provides both steric bulk and solubility in non-polar solvents. Multianionic phosphazenates feature a polydentate ligand surface, which facilitates an extremely high metal load. PN units of iminophosphoranes and phosphazenes have acceptor properties and enhance the acidity of α-alkyl and ortho-aryl protons. Deprotonation of P-alkyl and P-aryl iminophosphoranes give ligand systems featuring C,N chelating sites, which are also discussed.