Cyclometalated ruthenium(II) complexes of benzo[h]quinoline (bzqH)[Ru(bzq)(NCMe)4]+, [Ru(bzq)(LL)(NCMe)2]+, and [Ru(bzq)(LL)2]+ (LL = bpy, phen)

Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η6-C6H6)]2 in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)4]PF6 (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)4]PF6 (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)4]PF6 complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)2]PF6, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)2]PF6 {LL = bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)2]PF6 {LL = bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF6 as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)2]PF6, which lose one and two MeCN ligands for LL = bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4–7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography.

Cyclometalated RuII derivatives of ‘non-flexible’ benzo[h]quinoline [Ru(bzq)(MeCN)4]PF6 show similar reactivity toward ‘non-flexible’ 1,10-phenanthroline and ‘flexible’ 2,2′-bipyridine. Properties of [Ru(bzq)(LL)(MeCN)2]PF6 (LL = bpy and phen) are also similar. This behavior contrasts to that of the corresponding derivatives of ‘flexible’ 2-phenylpyridine.Figure optionsDownload as PowerPoint slide