Proton transfer to CpRuH(CO)(PCy3) studied by low-temperature IR and NMR spectroscopy

The interaction of the ruthenium hydride complex RuH = CpRuH(CO)(PCy3) (1) with various proton donors AH = CF3CH2OH (2a), (CF3)(2)CHOH (2b), (CF3)(3)C OH (2c), CF3COOH (2d), and HBF4 (2e) has been studied by variable-temperatu re IR spectroscopy using hexane and CH2Cl2 as solvents of different polarit y. A low-temperature NMR study of the interaction of 1 with 2e was performe d using [D-8]methylcyclohexane, CD2Cl2, and a liquefied mixture of CDF2Cl/C DF3 (2:1). The first stage of the proton transfer process was found to be t he formation of hydrogen-bonded complexes of the type RuH PIA. The hydrogen bonds in these complexes are of medium strength (-DeltaH degrees = 5.3-7.6 kcal mol(-1)). The second stage is the slow conversion of the H-complex to a dihydrogen complex to which a hydrogen-bonded ion-pair structure [Ru(eta (2)-H-2)](+)...A(-) was assigned. The kinetics of this unusually Slow prot on transfer reaction was monitored in the case of 2c at 200 K in CH2Cl2. Fa st protonation of 1 by 2d leads additionally to a species assigned as the f ree cationic complex [RU(eta (2)-H-2)](+), whose formation is driven by the formation of the homoconjugated anionic complex [AHA](-). At temperatures above 220 K both the hydrogen-bonded ion pair and the free cationic complex easily release dihydrogen, producing RuA.