Reactivity of some osmium complexes containing a salen ligand

Abstract

The reactivity of some osmium complexes containing salchda ligands (salchda = N,N’-bis(salicylidene)- o-cyclohexyldiamine) has been investigated. The contents are divided into three main parts. In part I, the reactivity of osmium(VI) nitrido complexes containing salchda ligands towards various nucleophiles such as amines and phosphines have been studied. Several osmium(III), (IV) and (VI) complexes was isolated and characterized with IR, ESI-MS and CHN elemental analysis. Two osmium(VI) nitrido complexes, [NnBu4][OsVI(N)Cl4(im)] and [OsVI(N)Cl3(pz)3], were prepared from [NnBu4][Os(N)Cl4]. The cytotoxity of these two complexes were determined and the IC50 value obtained for [OsVI(N)Cl3(pz)3] is at 37μM which implies the complex is rather cytotoxic. The reaction between [OsVI(N)(salchda)(MeOH)PF6] and bis(phenylphosphino)acetylene afforded a phosphoaminato complex [OsIV(NHP(=O)(Ph)2)(salchda)(OMe)] and its structure has been determined by X-ray crystallography. In part II, several osmium(IV) salchda complexes have been prepared from the reaction between trans-[OsVI(salchda)O2] and hydrazine monohydrate. Various alkoxyl group and arylamines were incorporated onto the osmium center and they were characterized by IR, ESI-MS, UV and CHN analysis. Attempts to oxidize the osmium(IV) anilindo complex trans-[OsIV(salchda)(NHC6H5)2] into the osmium(VI) bis(imido) salchda complexes trans-[OsVI(salchda)(NC6H5)2] were unsuccessful. However, the reaction between the dimethoxyosmium(IV) salchda complex trans-[OsIV(salchda)(OMe)2] with FeCl3 led to the formation of the oxo-bridged complex μ-O[OsIV(salchda)Cl]2. The bimetallic structure was determined by X-ray crystallography and the Os-O-Os bond angle was found to be 180∘. In part III, a bis(acetonitrile)osmium(III) salchda complex trans-[OsIII(salchda)(CH3CN)2]PF6 has been synthesized by the reduction of trans-[OsIV(salchda)(OMe)2] in acetonitrile. The complex was characterized by X-ray crystallography. This complex reacts with a variety of amines to form bis(acetamidine)osmium(III) salchda complexes. All the compounds were characterized by ESI-MS, UV, CHN elemental analysis and cyclic voltammetry. The structures of trans-[OsIII(salchda)(NH=C(NC4H4O)CH3)2]PF6 and trans-[OsIII (salchda)(NH=C[N(CH2CH2OH)2]CH3)(NH=C(NH2)CH3)]PF6 have been determined by X-ray crystallography.