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

Addition of excess HOSO{sub 2}CF{sub 3} (HOTf) to CpRu(L)H (1) (L = dfepe = PR{sub 2}CH{sub 2}CH{sub 2}PR{sub 2}, R = C{sub 2}F{sub 5}) in CD{sub 2}Cl{sub 2} under N{sub 2} produces a mixture of [CpRu(L)(H{sub 2})]{sup +} (2a), [CpRu(L)(H{sub 2})]{sup +} (2b), and CpRu(L)(OTf) (3) in a ratio of 1:5:2. Salts of the acid [HOEt{sub 2}]{sup +} are not strong enough to protonate 1. Complexes 2 slowly eliminate H{sub 2} to give 3; this reaction is slowed by adding excess HOTf. Of all such complexes [CpRu(PR{sub 2}CH{sub 2}CH{sub 2}PR{sub 2})(H{sub 2})]{sup +}, R = alkyl and aryl, the dihydrogen complex 2b has the greatest acidity (somilar to that of HOTf) and the related HD complex has the greatest J{sub HD} (29.1 Hz) because of the electron-withdrawing substituents R = C{sub 2}F{sub 5}. The reaction of 3 with 1 atm H{sub 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{sub 2}(g) where the intermediate dihydrogen complex has been characterized. Reaction of Cp{sup *}Ru(L)Cl (4), Cp{sup *} = C{sub 5}Me{sub 5}, in dry CH{sub 2}Cl{submore » 2} at {minus}78 C with AgX salts under H{sub 2}(g) (1 atm) gives mixtures of Cp{sup *}Ru(L)H (5) and [Cp{sup *}Ru(L)(H){sub 2}]{sup +} (6), which have been identified by {sup 1}H NMR. 6 is deprotonated by traces of water or by PPh{sub 3} to give Cp{sup *}Ru(L)H (5). The addition of excess HOTf to mixtures of 5 and 6 under H{sub 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.« less