249303-27-3Relevant academic research and scientific papers
Proton transfer in aminocyclopentadienyl ruthenium hydride complexes
Ayllon, José A.,Sayers, Stephen F.,Sabo-Etienne, Sylviane,Donnadieu, Bruno,Chaudret, Bruno,Clot, Eric
, p. 3981 - 3990 (2008/10/08)
A new ruthenium hydride complex of the aminocyclopentadienyl ligand (Cp-N)RuH(PPh3)2 (Cp-N = C5H4CH2CH2NMe2, 1) has been prepared and characterized by X-ray diffraction. Protonation of 1 with excess HPF6 leads to the dicationic derivative [(Cp-NH)RuH2(PPh3)2]-(PF6) 2 (2), in which both the metal and the amino substituent have been protonated. Addition of 1 equiv of HBF4·Et2O to 1 leads to the complex [(Cp-N)Ru(PPh3)2](BF4) (3), containing a chelating amino cyclopentadienyl ligand after elimination of H2. However, using (HNEt3)-(BPh4) or (HPBu3)(BPh4) as protonating agent, it is possible to form [(Cp-NH)RuH(PPh3)2]-(BPh4) (4), which was isolated as yellow crystals of 4·H2O upon addition of undistilled methanol and characterized by X-ray crystallographic analysis. A fluxional process exchanging the ammonium proton and the hydride without changing the thermodynamic state of the system could be established by 1H NMR, and activation energies of 11 kcal·mol-1 were calculated for 4·H2O and the product resulting from in situ addition Of [HNEt3][BPh4] to 1, whereas an activation energy of 10.1 kcal·mol-1 was found for the product resulting from in situ addition of [HPBu3][BPh4] to 1. A density functional study (B3PW91) was carried out, and the dihydrogen bond in the model system for 4 was calculated to be 1.545 A?, in excellent agreement with T1 measurements (1.52 A?). The proposed mechanism for the fluxional process does not involve a proton transfer within the dihydrogen bond.
