Ruthenium Tetraammines as a Model of Nitric Oxide Donor Compounds

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Abstract
The nitric oxide liberation fromtrans‐[Ru(NH3)4(L)(NO)]3+(where L = py, 4‐pic, isn, nic,L‐His, 4‐Clpy, imN) after one‐electron‐chemical or electrochemical reduction was investigated through spectroscopic and electrochemical techniques, reaction‐product analysis and quantum‐mechanic calculations. These complexes can be formally viewed as a RuII(NO+) species and the reduction site is located on the NO ligand. TheE° for thetrans‐[RuII(NH3)4(L)(NO+)]3+/trans‐[RuII(NH3)4(L)(NO)]2+redox process ranges from 0.072 V vs. NHE (nic) to −0.118 V vs. NHE (imN). The specific rate constants for NO dissociation fromtrans‐[RuII(NH3)4(L)(NO)]2+, evaluated through double‐step chronoamperometry, range from 0.025 s−1(nic) to 0.160 s−1(ImN) at 25 °C. The [RuIINO+/RuIINO0] redox potential and the specific rate constant (k‐NO),key steps for designing nitrosyl complexes as NO‐donor drug prototypes, proved to be controlled by a judicious choice of the ligand (L) trans to NO. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)