Mild sp 2 Carbon-Oxygen Bond Activation by an Isolable Ruthenium(II) Bis(dinitrogen) Complex: Experiment and Theory.

The isolable ruthenium(II) bis(dinitrogen) complex [Ru(H)2 (N2 )2 (PCy3 )2 ] ( 1 ) reacts with aryl ethers (Ar-OR, R = Me and Ar) containing a ketone directing group to effect sp2 C-O bond activation at temperatures below 40 °C. DFT studies support a low-energy Ru(II)/Ru(IV) pathway for C-O bond activation: oxidative addition of the C-O bond to Ru(II) occurs in an asynchronous manner with Ru-C bond formation preceding C-O bond breaking. Alternative pathways based on a Ru(0)/Ru(II) couple are competitive but less accessible due to the high energy of the Ru(0) precursors. Both experimentally and by DFT calculations, sp2 C-H bond activation is shown to be more facile than sp2 C-O bond activation. The kinetic preference for C-H bond activation over C-O activation is attributed to unfavorable approach of the C-O bond toward the metal in the selectivity determining step of the reaction pathway.