Stabilization of NH Tautomers of Quinolines by Osmium and Ruthenium

Complexes OsH2Cl2(PiPr3)2 and RuH2Cl2(PiPr3)2 promote the tautomerization of quinoline and 8-methylquinoline to NH tautomers, which lie about 44 kcal·mol-1 above the usual CH tautomers. The NH tautomers are stabilized by coordination to the metal center and by means of a Cl···HN interaction. As a consequence, the six-coordinate elongated dihydrogen complexes OsCl2{κ-C2-(HNC9H5R)}(η2-H2)(PiPr3)2, the five-coordinate derivatives RuCl2{κ-C2-(HNC9H5R)}(PiPr3)2, and the six-coordinate dihydrogen compounds RuCl2{κ-C2-(HNC9H5R)}(η2-H2)(PiPr3)2 (R = H, Me) have been isolated and characterized.