Di- and trinuclear Pd(II) and Pt(II) complexes containing bridging 2,7-disubstituted naphthyridines

Abstract

Dinuclear complex cations of the type cis-[M 2L 2(bpy) 2] 2+ ( 1, 2, M=Pd, L=onp −, monp −; 5, 6, M=Pt, L=onp −, monp −) contain μ-1κ N 1:2κ N 8 bridging monoanionic naphthyridine ligands (Honp=1,8-naphthyridin-2-one, Hmonp=7-methyl-1,8-naphthyridin-2-one) in a head/tail arrangement and exhibit short M⋯M distances in the range 2.794–2.804 Å. The analogous reaction of [MCl 2(bpy)] with the dibasic 2,7-disubstituted naphthyridine H 2donp (1,8-naphthyridin-2,7-dione) in the presence of LiOH leads to the trinuclear complexes cis-[M 3(donp) 2(bpy) 3] 2+ ( 3) (M=Pd) and 9 (M=Pt) with similar short M⋯M distances (2.801–2.807 Å). A head/tail arrangement is once again adopted by the μ 3-1κ O 2:2κ N 1:3κ N 8 bridging donp 2− dianionic ligands. Blue–green coloured 9 exhibits reversible one-electron transfer waves at E 1/2 0.65 and 1.30 V (in CH 3CN versus Ag/AgCl) accompanied by a colour change from blue–green (λ max=725 nm) to violet (λ max=695, 540 nm) and corresponding to oxidation to [Pt 3(donp) 2(bpy) 3] 3+ and [Pt 3(donp) 2(bpy) 3] 4+. 9 can be reduced to green coloured [Pt 3(donp) 2(bpy) 3] + at E 1/2=−0.82 V. The structures of the above compounds and [Pt(mbznnp)(bpy)(H 2O)]ClO 4 ( 4, Hmbznnp=2-benzylamino-7-methyl-1,8-naphthyridine), [Pt(donp)(bpy)] ( 7) and [Pt 2Cl 2(donp)(bpy) 2] ( 8) were established by X-ray structural analysis.