Synthesis and Spectro‐electrochemical Aspects of [Ru II (trpy)(pdt)(X)] n + (trpy = 2,2′:6′,2″‐Terpyridine, pdt = 5,6‐Diphenyl‐3‐pyridyl‐ as ‐triazine, X = Cl – , CH 3 CN, NO 2 – , NO + , NO · ) – Electrophilicity of {Ru II –NO + } and Photolability of {Ru II –NO · }

Nitrosylruthenium derivatives having NO + and NO · states have been synthesized in a stepwise manner starting from [Ru II (trpy)(pdt)(Cl)](ClO 4 ) {[ 1 ](ClO 4 )} → [Ru II (trpy)(pdt)(CH 3 CN)](ClO 4 ) 2 {[ 2 ](ClO 4 ) 2 } → [Ru II (trpy)(pdt)(NO 2 )](ClO 4 ) {[ 3 ](ClO 4 )} → [Ru II (trpy)(pdt)(NO + )](ClO 4 ) 3 {[ 4 ](ClO 4 ) 3 } → [Ru II (trpy)(pdt)(NO · )](ClO 4 ) 2 {[ 4 ](ClO 4 ) 2 } [trpy = 2,2′:6′,2″‐terpyridine, pdt = 5,6‐diphenyl‐3‐pyridyl‐ as ‐triazine]. The molecular identity of [ 1 ](ClO 4 ) and [ 2 ](ClO 4 ) 2 and the subsequent stereoretentive transformation of [ 1 ](ClO 4 ) → [ 2 ](ClO 4 ) 2 have been authenticated by single‐crystal X‐ray structures. Electrochemical and spectral features are investigated as a function of the monodentate ligands (Cl – , CH 3 CN, NO 2 – , NO + , NO · ). The kinetic and thermodynamic aspects of the reaction of the moderately strong electrophilic {Ru II –NO + } center [ ν (NO): 1944 cm –1 ] in [ 4 ] 3+ with a nucleophile such as OH – have been studied. The nitrosyl species [Ru II (trpy)(pdt)(NO + )] 3+ ([ 4 ] 3+ ) can be selectively reduced to [Ru II (trpy)(pdt)(NO · )] 2+ ([ 4 ] 2+ ) electrochemically as well as chemically by hydrazine hydrate. On exposure to light an acetonitrile solution of [Ru II (trpy)(pdt)(NO · )] 2+ ([ 4 ] 2+ ) undergoes slow photocleavage of the Ru II –NO bond over a period of 4 h, resulting in the corresponding solvated species [Ru II (trpy)(pdt)(CH 3 CN)] 2+ ([ 2 ] 2+ ). The rate of photolability of the Ru II –NO bond in [ 4 ] 2+ has been monitored spectrophotometrically. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)