Synthesis, structures and reactivity of novel metallocyclotriphosphazenes

Abstract

Phosphazenes, inorganic hetero ring and chain compounds containing alternate phosphorus and nitrogen atoms in their skeleton, are unique carriers for various metals owing to their ability to serve as versatile multifuctional ligands and templates. The chemistry of metallophosphazenes, which spans the overlapped area of three materials science fields of polymers, ceramics, and metals, has been the subject of increasing research interest in conjunction with the potential opportunities for discovering new materials. In particular, cyclotriphosphazenes are excellent models for exploratory reactions that can be applied subsequently at the high polymer level. In this dissertation, synthesis, structures and reactivity of lanthanide, transition and main group metal complexes of hexakis(3,5-dimethylpyrazolyl)cyclotriphosphazene (1) are reported. The reaction of the ligand 1 with 1.5~3 equiv of lanthanide (Ⅲ) chloride $LnCl_{3}$ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) in dichloromethane affords new mononulear lanthanidocyclotriphosphazene complexes $[1ㆍLnCl_3]$ (Ln = La, 4; Ce, 5; Pr, 6; Nd, 7; Sm, 8; Eu, 9; Gd, 10) with hendecahedral coordination polyhedron in which the ligand 1 employs an unprecedented $κ^5N$ binding core consisting of one cyclotriphosphazene ring nitrogen atom and four pyridinic nitrogen atoms of two sets of geminal pyrazolyl groups. The complex 8 which is soluble in dichloromethane shows the catalytic activity for the syndio-rich polymerization of MMA in the presence of MMAO cocatalyst. The reaction of the ligand 1 with 3 equiv. of metal (Ⅱ) chloride $MCl_2$ (M = Fe, Co) in dichloromethane affords dinuclear metallophosphazenes $[1ㆍ(MCl_2)_{2}]$ (M = Fe, 11; Co, 12). The coordination mode of 11 is $κ^3N-κ^2N$ type. One iron metal is bound to two non-geminal pyrazolyl nitrogens and a phosphazene skeletal nitrogen and the other is coordinated to only two geminal pyrazolyl nitrogens. Accordingly, the coordination spheres around two Fe metal centers have dist...