Kinetics studies of the reaction of the ruthenium porphyrin Ru(OEP)(CO) with the S-nitrosothiol N-acetyl-1-amino-2-methylpropyl-2-thionitrite.

The reaction of the S-nitrosothiol compound N-acetyl-1-amino-2-methylpropyl-2-thionitrite (RSNO) with the model metalloporphyrin complex Ru(II)(OEP)(CO) (OEP = octaethylporphyrinato dianion) gives the addition product trans-Ru(II)(OEP)(NO)(SR). Here we report the details of a stopped flow kinetics investigation which demonstrates the rapid equilibrium formation of an intermediate concluded to be S-bound RSNO complex Ru(II)(OEP)(RSNO)(CO), which undergoes a rate-limiting step, presumably S-NO bond cleavage to give a second intermediate Ru(III)(OEP)(SR)(CO) too short lived for direct observation. Notably, this is different from the nitrogen coordination pathway often proposed and represents an alternative mechanism by which S-nitrosothiols may be formed or decomposed in the presence of redox active metal centers. Also reported is a brief study of the quantitative photochemistry of RSNO, the photodecomposition of which complicates the kinetics studies by spectroscopic techniques.