An investigation of Ru(II) complexes containing sterically demanding imido ligands : a thesis presented to Massey University in partial fulfilment of the requirements for the degree of Master of Science

Abstract

Monomeric, low oxidation state, ruthenium imido compounds, (η6

-arene) RuN-Ar' (arene= p-cymene and C6 Me6 ; Ar'= 2,4,6-tri-tert-butylphenyl) have been synthesized from [(η6 -arene) RuCl2 ]2 and 4 equiv of LiNHAr' in THF. An X-ray crystal structure of (η6 -p-cymene) Ru=NAr' showed a short Ru-N distance (1.753(3)Ǻ) and a near linear Ru-N-C angle (177.8(4)° ) consistent with ruthenium to nitrogen multiple bonding. Reaction of [(η6 -p- cymene) RuCl2 ]2 with 4 equiv of LiNHR (R= 2,6-dimethylphenyl or 2,6-diisopropylphenyl) in THF afforded the dimeric ruthenium imido compounds [(η6 -p-cymene) Ru(µ-NR)]2. An X-ray crystal structure of [(η6 -p-cymene) Ru(µ-NAr)]2 (Ar= 2,6-diisopropylphenyl) showed an averaged Ru-N distance of 1.974(8)Ǻ and features characteristic of Ru(II) bridging imido complexes. Addition of 2 equiv of LiNHAr to [(η6 -C6 Me6 ) RuCl2 ]2 gave a HCl adduct, (η6 -C6 Me6 ) RuClNHAr, characterisation of the complex was obtained by X-ray diffraction. Reaction of the HC1 adduct with phenylisocyanate gave the ureylene metallacycle, (η6 -C6 Me6 ) RuN(Ar)C(0)N(Ph), indicating the presence of an imido intermediate. This complex was shown to have a υ(CO) band at 1596cm -1 and is comparable with other monomeric ureylene complexes. In addition, the complex [(η6 -p-cymene) Ru(µ-NAr)]2 was made from 2 equiv of the amine, ArNH2 , and [(η6 -p-cymene) RuCl2 ]2 and dehydrochlorinated with KN(SiMe3 )2 providing an alternative route. Further, an X-ray crystal structure of the amine complex, (η6 -p-cymene) RuCl2 (ArNH2 ) was obtained. The reaction of (bpy)2 RuCl2 (bpy= 2,2'-bipyridine) with LiNHAr' in THF afforded the complex, (bpy)2 Ru=NAr', characterised by nmr and elemental analysis.