Protonation and H₂Heterolysis Reactions of Electrophilic (η⁵-C₅R₅)Ru(dfepe)(X) (R = H, Me; X = H, OTf) Complexes

Addition of excess HOSO2CF3 (HOTf) to CpRu(L)H (1) (L = dfepe = PR2CH2CH2PR2, R = C2F5) in CD2Cl2 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 [HOEt2](+) are not strong enough to protonate 1. Complexes 2 slowly eliminate Hz to give 3; this reaction is slowed by-adding excess HOTf. Of all such complexes [CpRu(PR2CH2CH2PR2)(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 R = C2F5. 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* = C5Me5, in dry CH2Cl2 at -78 degrees 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 H-1 NMR. 6 is deprotonated by traces of water or by PPh3 to give Cp*Ru(L)H (5). The addition of excess HOTf 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.