Protonation and H2 Heterolysis Reactions of Electrophilic (η5-C5R5)Ru(dfepe)(X) (R = H, Me; X = H, OTf) Complexes

Addition of excess HOSO 2 CF 3 (HOTf) to CpRu(L)H ( 1 ) (L = dfepe = PR 2 CH 2 CH 2 PR 2, R = C 2 F 5 ) in CD 2 Cl 2 under N 2 produces a mixture of [CpRu(L)(H) 2 ] + ( 2a ), [CpRu(L)(H 2 )] + ( 2b ), and CpRu(L)(OTf) ( 3 ) in a ratio of 1:5:2. Salts of the acid [HOEt 2 ] + are not strong enough to protonate 1 . Complexes 2 slowly eliminate H 2 to give 3; this reaction is slowed by adding excess HOTf. Of all such complexes [CpRu(PR 2 CH 2 CH 2 PR 2 )(H 2 )] +, R = alkyl and aryl, the dihydrogen complex 2b has the greatest acidity (similar to that of HOTf) and the related HD complex has the greatest J HD (29.1 Hz) because of the electron-withdrawing substituents R = C 2 F 5 . The reaction of 3 with 1 atm H 2 (g) proceeds much faster in the presence than in the absence of 1 equiv of HOTf to produce 1 and HOTf. This is a rare example of the production of a strong acid from H 2 (g) where the intermediate dihydrogen complex has been characterized. Reaction of Cp*Ru(L)Cl ( 4 ), Cp* = C 5 Me 5, in dry CH 2 Cl 2 at −78 °C with AgX salts under H 2 (g) (1 atm) gives mixtures of Cp*Ru(L)H ( 5 ) and [Cp*Ru(L)(H) 2 ] + ( 6 ), which have been identified by 1 H NMR. 6 is deprotonated by traces of water or by PPh 3 to give Cp*Ru(L)H ( 5 ). The addition of excess HOTf to mixtures of 5 and 6 under H 2 (g) produces 6 . Complexes 3, 4, and 5 have been characterized by single-crystal X-ray diffraction. Complexes CpRu(L)Cl, 1, 4, and 5 have very positive redox potentials that indicate that the dfepe ligand has the electron-withdrawing power close to that of two carbonyl ligands.