The reaction of a naphthalene complex [CpRu(eta(6)-C10H8)]-PF6 (Cp = eta(5)-C5H5) with 8-diphenylphosphinoisoquinoline and sodium acetate in acetonitrile afforded a P-C chelate 1,2-dihydroisoquinolin- 1-ylidene ruthenium complex 2 bearing an NH group at the position beta to the metal. The cationic carbene complex 2 underwent reversible deprotonation of the NH group to give the corresponding 1-isoquinolyl complex 3. The crystal structures of the chelation-stabilized acid-base pair (2 and 3) have been compared in detail as potential metal-ligand cooperating catalysts.