Addition of excess HOSO2CF3 (HOTf) to CpRu(L)H (1) (L = dfepe = PR2CH2CH2PR2, R =
C2F5) in CD2Cl2 under N2 produces a mixture of [CpRu(L)(H)2]+ (2a), [CpRu(L)(H2)]+ (2b),
and CpRu(L)(OTf) (3) in a ratio of 1:5:2. Salts of the acid [HOEt2]+ are not strong enough to
protonate 1. Complexes 2 slowly eliminate H2 to give 3; this reaction is slowed by adding
excess HOTf. Of all such complexes [CpRu(PR2CH2CH2PR2)(H2)]+, 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 = C2F5. The reaction of 3 with 1 atm H2(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 H2(g) where the intermediate dihydrogen complex has been
characterized. Reaction of Cp*Ru(L)Cl (4), Cp* = C5Me5, in dry CH2Cl2 at −78 °C with AgX
salts under H2(g) (1 atm) gives mixtures of Cp*Ru(L)H (5) and [Cp*Ru(L)(H)2]+ (6), which
have been identified by 1H NMR. 6 is deprotonated by traces of water or by PPh3 to give
Cp*Ru(L)H (5). The addition of excess HOTf to mixtures of 5 and 6 under H2(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.
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