Speciation and decomposition pathways of ruthenium catalysts used for selective C–H hydroxylation

Abstract

Mechanistic insight into the C–H hydroxylation reaction catalysed by [(Me3tacn)RuCl3] has been obtained using desorption electrospray ionization mass spectrometry (DESI-MS) to identify reactive intermediates and to determine the fate of the starting metal complex.

A Mixed N‐Heterocyclic Carbene/2,2′‐Bipyridine‐Supported Robust Ruthenium(II) Oxidation Precatalyst for Benzylic C−H Oxidation

“…This result suggested the formation of high‐valent ruthenium‐oxo species in the solution from the reaction with the oxidant . By using desorption electrospray ionization mass spectrometry (DESI‐MS), DuBois and Zare recently demonstrated the generation of Ru VI ‐dioxo and Ru V ‐dioxo species from low‐valent ruthenium precursors on treatment with NaIO 4 . On analysis of a reaction mixture of 1 and NaIO 4 (1:20 molar ratio) in CH 3 CN/H 2 16 O by ESI‐MS, out of several peaks of small intensity, a reasonably intense peak was observed at m / z= 510.05, which might be assigned for similar Ru VI ‐dioxo species, [ 1 −(2 CH 3 CN)−H+( 16 O) 2 ] + (Figure B and the Supporting Information).…”

Going beyond electrospray: mass spectrometric studies of chemical reactions in and on liquids

“…Flender et al determined that the C–H hydroxylation catalyst [(Me 3 tacn)RuCl 3 ] as well as its tribromide equivalent undergo dimerization during catalysis (Me 3 tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane). 34 This process was shown to be a deactivation pathway because adding more substrate did not lead to more product formation. In a separate study utilizing a combined approach of DESI-MS, time-resolved sonic-spray ionization (SSI), and vibrational spectroscopy, Ingram et al examined the activation mechanism of a Cp*Ir precatalyst for catalytic water oxidation with periodate as the terminal oxidant (Cp* = pentamethylcyclopentadienyl).…”

cis-Oxoruthenium complexes supported by chiral tetradentate amine (N4) ligands for hydrocarbon oxidations

“… 20 Using desorption electrospray ionization mass spectrometry (DESI-MS), cis -[(Me 3 tacn)Ru VI (O) 2 (OH)] + was identified to be a plausible reactive hydroxylating agent, but the possible involvement of Ru( v ) and/or Ru( iv ) species could not be discounted. 78 In this work, stoichiometric reactions between 1e and several alkane substrates ( Table 3 ) provided direct evidence that cis -dioxoruthenium( vi ) preferentially oxidizes the tertiary C–H bonds in hydrocarbons. The same selectivity was observed in catalytic experiments.…”