Proton Transfer in Aminocyclopentadienyl Ruthenium Hydride Complexes

Abstract

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 Å, in excellent agreement with T 1 measurements (1.52 Å). The proposed mechanism for the fluxional process does not involve a proton transfer within the dihydrogen bond.

An Efficient Solvent‐Free Route to Silyl Esters and Silyl Ethers

“…[11] Then, the nucleophilic attack of a substrate (carboxylic acid or alcohol) to the hydride intermediate proceeds to give the corresponding silylated product. [10] The present [RuCl 2 A C H T U N G T R E N N U N G (p-cymene)] 2 -catalyzed dehydrosilylation with an optically active silane proceeded exclusively with inversion of stereochemistry at the chiral silicon center: the silylation of 4b (1.5 equivalents with respect to 2f) with R-(+)-methyl(1naphthyl)phenylsilane (92% ee) (2f) afforded R-(À)butoxymethyl(1-naphthyl)phenylsilane (5s) in 84% ee, for example [Eq. (6)].…”

Pendant bases as proton transfer relays in diiron dithiolate complexes inspired by [Fe–Fe] hydrogenase active site

“…Studies on organometallic complexes have shown that pendant nitrogen bases play an important role in proton/hydride exchange reactions [21][22][23]. An understanding of proton transfer precess will be necessary for developing efficient hydrogen production/hydrogen oxidation catalysts.…”

Cooperative Catalysis by Ru and Pd for the Direct Coupling of a Chelating Aldehyde with Iodoarenes or Organostannanes

“…A greatly improved efficiency was obtained when a Ru catalyst was employed instead of Rh in the presence of the Pd co-catalyst. Among all the Ru catalysts investigated, [Ru 3 (CO) 12 ] was found to be the most effective counterpart when combined with [Pd 2 (dba) 3 ]·CHCl 3 . This combination afforded the ketone product in 83 % yield (5 mol % of each catalyst) in the presence of NaHCO 3 (1.5 equiv) at 135 8C (20 h).…”

“…This result may rule out the possibility that the reaction of aldehyde 1 and iodoarenes proceeds by Rucatalyzed decarbonylation of 1 followed by Pd-catalyzed arylcarbonylation of iodobenzene. [9] In fact, there are several precedents for the [Ru 3 (CO) 12 ]-catalyzed orthometalation of nitrogen-containing heteroaromatic compounds to provide ortho-carbonylated adducts. [10] Aldehydes devoid of a coordinating group were not coupled with iodobenzene, which implies that activation of a formyl CÀH bond of 1 is coordination-directed [Eq.…”

“…[11] When 1 was treated with a stoichiometric amount of [Ru 3 (CO) 12 ] in 1,2-dichloroethane (120 8C, 30 min) the aldehydic proton signal disappeared gradually from the 1 H NMR spectrum, to be replaced by a signal for an acylruthenium hydride (d = À15.9 ppm; singlet in CDCl 3 ). [12] The IR spectrum of the isolated adduct shows an absorbance band at 1846 cm À1 , which is assignable to the stretching band of the speculative RuÀH bond. [13] It should be noted that a stoichiometric activation of 1 has previously been reported with Na 2 PdCl 4 to afford a chloro-bridged Pd dimer.…”