Metal-centered oxidation decreases nitrile hydration activity of bioinspired (N2S3)Ru-PPh3 precatalysts

Abstract

A series of ruthenium(II) nitrile hydration catalysts based on the pentadentate ligand 4,7-bis(2'methyl-2'-mercaptopropyl)-1-thia-4,7-diazacyclononane and its sulfur-oxidized derivatives have been oxidized at the metal center yielding the ruthenium(III) counterparts. Metal-centered oxidation results in complete loss of nitrile hydration activity for the dithiolato (RS-/RS-) parent complex. The sulfuroxidized thiolato/sulfinato (RS-,RSO 2-) derivative displays a decrease in turnover number from 238 ± 23 to 3 ± 1 upon oxidation of Ru(II) to Ru(III). A similar decrease in turnover number from 242 ± 23 to 7 ± 3 is observed upon metal-centered oxidation of the sulfenato/sulfinato (RSO-,RSO 2-) derivative. The inactive complex [(4,7-bis(2'-methyl-2'-mercaptopropyl)-1-thia-4,7-diazacyclononane)(triphenylphosphine)ruthenium(III)]hexafluorophosphate has been synthesized and characterized by electronic spectroscopy, electron paramagnetic resonance, and single crystal x-ray diffraction studies.

Recent Advances and Promises in Nitrile Hydratase: From Mechanism to Industrial Applications

“…The Oxidation states of the metal ions and cysteine residues at the NHase active site now represent intriguing research hotspots. Studies show that the oxidation states of the metal ions and cysteine residues at the NHase active site could kinetically influence the activity of NHase (Crisóstomo et al, 2010;Swartz et al, 2011;Li et al, 2012;Chang et al, 2015;Kumar et al, 2015;Yano et al, 2015).…”