Reactivity of electrophilic Cp*Ru(NO) complex towards alcohols

Abstract Treatment of the complex 1 Cp*Ru(NO)(OTf) 2 (OTf = OSO 2 CF 3 , Cp* = η 5 -C(CH 3 ) 5 ) with neat 2- propanolresults in the rapid quantitative formation of the Ru(0) complex [Cp*Ru(μ-NO)] 2 and (CH 3 ) 2 C O. Formation of H 2 and CHDCl 2 is detected when the reaction between 1 and 2- propanoloccurs in CDCl 3 , indicating possible formation of a short-lived metal hydride species. Similar results are observed upon treatment of 1 with ethanol and methanol, with formation of acetaldehyde and formaldehyde, respectively. The kinetics of the oxidation of 2- propanolby complex 1 is studied by 1 H NMR spectroscopy in CH 2 Cl 2 at variable temperatures and the reaction is found to be first-order in complex 1 and in 2- propanol. The kinetic isotope effectfor the reaction of 1 with (CD 3 ) 2 CD-OD at −11 °C is determined to be k H / k D = 2.0 (3). A mechanism for alcohol oxidationby electrophilic ruthenium (II) complexes via a β-hydrogen elimination step is proposed. The pre-equilibrium exchange step between complex Cp*Ru(NO)(OTf) 2 ( 1 ) and alcohol-coordinated species is examined by 19 F and 1 H NMR spectroscopy in CH 2 Cl 2 solution, where triflate substitution is found to be exothermic and entropically unfavorable. The synthesis and solid state structure of the chelate-stabilized complex diol salt [Cp*Ru(NO)(HO–CH 2 CH 2 –OH)][2OTf] are discussed.