The reaction of Me₂PCl₃ with the linear phosphazene [NH₂CPh₂)-PNP(Ph₂)NH₂]⁺Cl⁻ in chlorobenzene gives not only the expected cyclic product gem-N₃P₃Ph₄Me₂, but also significant amounts of (NPPh₂)₄, (NPMe₂)₄ and the new mixed derivative 1,1,3,3-tetramethyl-5,5,7,7-tetraphenylcyclo-tetraphosphazene N₄P₄Me₄Ph₄. The methylphosphazenes, gem-N₃P₃Ph₄Me₂ and N^P^Meg, along with N₃P₃Me₆, can be deprotonated by alkyllithiums. The resulting carbanions, gem-N₃P₃Ph₄Me(CH₂⁻) , N₄P₄Me₄ (CH₂⁻)₄ and N₃P₃Me₃(CH₂⁻)₃ respectively, react with monofunctional electrophiles to form phosphazenes carrying the groups PCH₂R (R = Br, I, PhC(O), and AsMe₂). Two phosphazenyl groups have also been joined by the use of a difunctional halide Me₂SiCl₂ yielding the bridged compound (N₃P₃Ph₄MeCH₂)₂ SiMe₂. The reaction of the tetracarbanion N₃P₃Ph₄MeCH₂⁻)₄ with ethyl benzoate is unique, in that it goes no further than di-substitution. Moreover, the ¹H and ³¹P n.m.r. spectra of the dibenzoyl derivative indicate vicinal substitution, and depend on both solvent and time. By contrast, a tribenzoyl derivative is formed from the tricarbanion N₃P₃Me₃ (CH₂⁻)₃. These results are explained by the aid of simple Hiickel molecular orbital theory, and are informative about conjugation. The preparation of phosphazenes in which the ring is joined to a pyrazole nucleus by a P-N bond has also been undertaken. The chemical, spectroscopic and structural properties of the homogeneously substituted pyrazolylphosphazenes [NP(Pz)₂]₃_₆, [NP(Mepz)₂]₃_₅ and [NP(Me₂pz)₂]₃,₄ (where Pz denotes the 1-pyrazolyl group, Mepz the 3-methyl-1-pyrazolyl group and Me₂pz the 3,5-dimethyl-1-pyrazolyl group) show that the pyrazolyl groups act as strongly electron withdrawing substituents on the phosphazene ring, with at most a minor conjugative contribution to the bonding. These pyrazolylphosphazenes have an added feature, in that the pyridine-type nitrogen in the pyrazole ring is expected to be basic. Thus, their ability to act as donors to transition metal ions, either via the nitrogen atoms in the pyrazole ring or in the phosphazene ring, is an important part of their chemistry. Consequently, the formation of complexes with Mo(0), Co(II), Pd(II), Pt(II), Ag(I), Zn(II) and Cd(II) has been investigated using as ligands N₃P₃(Me₂Pz)₆, gem-N₃P₃Ph₂(Me₂pz)₄ and gem-N₃P₃Ph₄-(Me[sub=x]pz)₂ (x = 1, 2). Reaction of N₃P₃(Me₂pz)₆ with an excess of anhydrous CoCl₂ in THF precipitates the di-cobalt complex N₃P₃(Me₂Pz)₆•2CoCl₂•THF, the crystal structure of which shows the cobalt atoms to be situated in different coordination geometries: tetrahedral and trigonal bipyramidal. The latter configuration involves two Me₂pz groups each on different phosphorus atoms and a nitrogen atom in the phosphazene ring, and is also found in the structure of gem-N₃P₃Ph₂(Me₂pz)₄•ZnCl₂. The former configuration incorporates two Me₂pz groups on the same phosphorus atom, similar to that found in the structure of gem-N₃P₃Ph₄(Me₂pz)₄•CoCl₂. As a comparison, the reaction of N₃P₃(Me₂pz)₆, with an excess of PdCl₂(PhCN)₂ in CH₂Cl₂ gives the tri-palladium complex N₃P₃(Me₂pz)₆•3PDCl₂, ¹H and ³¹P n.m.r. spectra of which indicate that only bonding to Me₂pz groups on the same phosphorus atom is present. / Science, Faculty of / Chemistry, Department of / Graduate

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The electronic structure of substituted cyclic phosphazenes has been investigated using Density Functional Theory (DFT) and Natural Bond Order (NBO) analysis. NBO analysis shows covalent, ionic and negative hyper-conjugation interactions all contribute to the electronic structure of cyclic phosphazenes. The geometric and electronic structural changes that occur when transition metals are coordinated to the nitrogen atom of the phosphazene ring have been analyzed using the NBO model. The bonding of transition metal ions with the ring nitrogen on the phosphazene was investigated by modeling hexakis(2-pyridyloxy)cyclotriphosphazene, hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene and octakis(2- pyridyloxy)cyclotetraphosphazene with different metal ions (Co(II), Ni(II), Cu(II), Zn(II)) in their assorted configurations with DFT as implemented in the Gaussian03 package. First-row transition metals bind to the phosphazene ring with simple s donor behaviour via the ring nitrogen. The lengthening of the PN bonds adjacent to the coordinated metal centre is a result of electron density being removed from the PN bonding orbitals and going into the 4s orbital of the metal ion. Investigating the pyridine substituents on the phosphazene ring showed that these can affect the PN bonds in a similar fashion, although weaker, to the transition metals. This effect is the result of the pyridine nitrogen lone pair affecting the negative hyperconjugation component of the PN bond. Coupling between two metal atoms coordinated to the phosphazene ring was investigated by DFT calculations, which showed molecular orbitals in both the tricyclic and tetracyclic phosphazene capable of providing an ‘electron density bridge’ between the metal centres. These results are in accord with ESR and magnetic susceptibility results, which can be explained in terms of weak antiferromagnetic coupling between metal ions. The cyclic phosphazenes are model compounds for polyphosphazenes and the results obtained from this work will provide insight into the electronic properties of this important class of inorganic polymers.

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