Cyclometalated N,N-dimethylbenzylamine ruthenium(II) complexes [Ru(C6HR1R2R3-o-CH2NMe2)(bpy)(RCN)2]PF6 for bioapplications:: synthesis, characterization, crystal structures, redox properties, and reactivity toward PQQ-dependent glucose dehydrogenase

Cyclometalated derivatives of ring-substituted NN-dimethylbenzylamines with controlled redox potentials as potent mediators of bioelectrochemical electron transport are reported. The cycloruthenation of (RRRC6H2CH2NMe2)-R-1-R-2-C-3 (R-1, R-2, R-3 = H, Me, (BuO)-Bu-t, MeO, NMe2, F, CF3, CN, NO2) by [(eta(6)-C6H6)RuCl(mu-Cl)](2) in the presence of NaOH/KPF6 in acetonitrile or pivalonitrile affords cyclometalated complexes [(eta(6)-C6H6)RU((C6HRRR3)-R-1-R-2-omicron-(CHNMe2)-N-2)(RCN)]PF6 [R = Me (1) and R = CMe3 (2)] in good yields. Reactions of complexes 1 and 2 with 2,2'-bipyridine (bpy) in acetonitrile or pivalonitrile result in dissociation of eta(6)-bound benzene and the formation of [Ru((C6HRRR3)-R-1-R-2-omicron-CH2NMe2)(bpy)(RCN)(2)]PF6 [R = Me (3) and R = CMe3 (4)]. All new compounds have been fully characterized by mass spectrometry, H-1/C-13 NMR, and IR spectroscopy. An X-ray crystal structural investigation of complex 1 (R-1/R-2/R-3 = H/H/H) and two complexes of type 3 (R-1/R-2/R-3 = MeO/H/H, MeO/MeO/H) has been performed. Acetonitrile ligands of 3 are mutually cis and the a-bound carbon is trans to one of the bpy nitrogens. Measured by the cyclic voltammetry in MeOH as solvent, the redox potentials of complexes 3 for the Ru-II/III feature cover the range 320-720 mV (versus Ag/AgCl) and correlate linearly with the Hammett (sigma(p)(+) + sigma(m)) constants. Complexes 3 mediate efficiently the electron transport between the active site of PQQ-dependent glucose dehydrogenase (PQQ = pyrroloquinoline quinone) and a glassy carbon electrode. Determined by P cyclic voltammetry the second order rate constant for the oxidation of the reduced (by D-glucose) enzyme active site by Ru-III derivative of 3 (R-1/R-2/R-3 = H) (generated electrochemically) is as high as 4.8 x 10(7) M-1 s(-1) at 25 degreesC and pH 7. (C) 2004 Elsevier B.V. All rights reserved.