Mild and selective Pd-Ar protonolysis and C-H activation promoted by a ligand aryloxide groupElectronic supplementary information (ESI) available: Details of the experimental and spectroscopic properties. X-ray data are available in CIF format. CCDC 1811771-1811773. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt00437d

A bidentate nitrogen-donor ligand with an appended phenol group, C 5 H 4 NCH&z.dbd;N-2-C 6 H 4 OH, H(L1) was treated with a palladium cycloneophyl complex [Pd(CH 2 CMe 2 C 6 H 4 )(COD)], with both Pd-aryl and Pd-alkyl bonds, to give a Pd-alkyl complex, [Pd(CH 2 CMe 2 C 6 H 5 )(κ 3 - N , N ′, O -OC 6 H 4 N&z.dbd;CH(2-C 5 H 4 N))], 1 . The cleavage of the Pd-aryl bond and the deprotonation of the ligand phenol to afford a bound aryloxide, indicates facile Pd-aryl bond protonolysis. Deuterium labelling experiments confirmed that the ligand phenol promotes protonolysis and that the reverse, aryl C-H activation, occurs under very mild reaction conditions (within 10 min at room temperature). An unusual isomerization of the Pd-alkyl complex 1 to a Pd-aryl complex, [Pd(C 6 H 4 (2- t -Bu))(κ 3 - N , N ′, O -OC 6 H 4 N&z.dbd;CH(2-C 5 H 4 N))], 2 , was observed to give an equilibrium with [ 2 ]/[ 1 ] = 9 after 5 days in methanol. The isomerization requires that both aryl C-H activation and Pd-alkyl protonolysis steps occur. The very large KIE value ( k H / k D = ca. 40) for isomerization of 1 to 2 , suggests a concerted S E 2-type mechanism for the Pd-alkyl protonolysis step. A ligand phenol/aryloxide group mediates reversible protonolysis and C-H activation at a Pd( ii ) centre.