Amine Attack on the Carbonyl Ligands of the Protonated Dicyclopentadienyl-Bridged Diruthenium Complex [{(η⁵-C₅H₃)₂(SiMe₂)₂}Ru₂(CO)₄(μ-H)]⁺

Complexes [{(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 4 (μ-H)] + ( 1 H + BF 4 -, 1 D + TfO - ), with a protonated Ru−Ru bond, were prepared by protonation of {(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 4 ( 1 ) with HBF 4 ·Et 2 O or CF 3 SO 3 D. The bridging proton in 1 H + is removed only very slowly by amine bases even though it is thermodynamically acidic (p K a AN = 6.5 (±0.2)). This remarkable kinetic inertness of the bridging proton allows amines (NH 3, NH 2 CH 3, NH(CH 3 ) 2, morpholine, piperidine, pyrrolidine) to react with 1 H + by attacking the CO ligand to give a formamide (HC( O)NR 2 ) and the CO-substituted product {(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 3 (NHR 2 ) ( 2 ). Thus, protonation of the metal−metal bond in 1 H + promotes reactions of the CO ligand that are not possible in the unprotonated 1 . A proposed mechanism for these reactions is supported by kinetic studies of the reaction of 1 D + TfO - with morpholine in nitromethane at 20.0 °C, as well as by deuterium-labeling experiments. The molecular structure of {(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 3 (NH 2 CH 3 ) ( 2f ), as determined by an X-ray diffraction investigation, is also presented.