333382-69-7Relevant academic research and scientific papers
Hydrogen elimination from a hydroxycyclopentadienyl ruthenium(II) hydride: Study of hydrogen activation in a ligand-metal bifuncfional hydrogenation catalyst
Casey, Charles P.,Johnson, Jeffrey B.,Singer, Steven W.,Cui, Qiang
, p. 3100 - 3109 (2005)
At high temperatures in toluene, [2,5-Ph2-3,4-Tol 2(η5-C4COH)]Ru(CO)2H (3) undergoes hydrogen elimination in the presence of PPh3 to produce the ruthenium phosphine complex [2,5-Ph2-3,4-Tol2- (η4-C4CO)]Ru(PPh3)(CO)2 (6). In the absence of alcohols, the lack of RuH/OD exchange, a rate law first order in Ru and zero order in phosphine, and kinetic deuterium isotope effects all point to a mechanism involving irreversible formation of a transient dihydrogen ruthenium complex B, loss of H2 to give unsaturated ruthenium complex A, and trapping by PPh3 to give 6. DFT calculations showed that a mechanism involving direct transfer of a hydrogen from the CpOH group to form B had too high a barrier to be considered. DFT calculations also indicated that an alcohol or the CpOH group of 3 could provide a low energy pathway for formation of B. PGSE NMR measurements established that 3 is a hydrogen-bonded dimer in toluene, and the first-order kinetics indicate that two molecules of 3 are also involved in the transition state for hydrogen transfer to form B, which is the rate-limiting step. In the presence of ethanol, hydrogen loss from 3 is accelerated and RuD/OH exchange occurs 250 times faster than in its absence. Calculations indicate that the transition state for dihydrogen complex formation involves an ethanol bridge between the acidic CpOH and hydridic RuH of 3; the alcohol facilitates proton transfer and accelerates the reversible formation of dihydrogen complex B. In the presence of EtOH, the rate-limiting step shifts to the loss of hydrogen from B.
Synthesis of ruthenium boryl analogues of the shvo metal-ligand bifunctional catalyst
Koren-Selfridge, Liza,Query, Ian P.,Hanson, Joel A.,Isley, Nicholas A.,Guzei, Ilia A.,Clark, Timothy B.
, p. 3896 - 3900 (2010/12/24)
Metal boryl complexes have received significant attention in the literature in recent years due to their role as key intermediates in a number of metal-catalyzed borylation reactions. The ligand scaffold is known to have a significant impact on the observed reactivity of these metal boryl complexes. A synthetic strategy to access ruthenium boryl analogues of the Shvo metal-ligand catalysts is described. Heating a precursor to Shvos catalyst (1) with bis(catecholato)diboron at 50 °C provided ruthenium boryl complex 3, [2,5-Ph2-3,4-Tol2(η5-C4COBcat) Ru(CO)2Bcat] (Bcat = catecholatoboryl). Addition of bis(catecholato)diboron to complex 1 in the presence of a phenol results in ruthenium boryl complex 5, [2,5-Ph2-3,4-Tol2(η 5-C4COH)Ru(CO)2Bcat], at 22 °C in 30% isolated yield. A single-crystal X-ray analysis of complex 5 confirmed the assigned structure. An improved synthesis of ruthenium boryl complex 5 was developed by the in situ formation of complex 3, [2,5-Ph2-3,4- Tol2(η5-C4COBcat)Ru(CO)2Bcat], followed by addition of the phenol, resulting in a 51% yield.
Isomerization and deuterium scrambling evidence for a change in the rate-limiting step during imine hydrogenation by Shvo's hydroxycyclopentadienyl ruthenium hydride
Casey, Charles P.,Johnson, Jeffrey B.
, p. 1883 - 1894 (2007/10/03)
Hydroxycyclopentadienyl ruthenium hydride 5 efficiently reduces imines below room temperature. Better donor substituents on nitrogen give rise to faster rates and a shift of the rate-determining step from hydrogen transfer to amine coordination. Reduction of electron-deficient N- benzilidenepentafluoroaniline (8) at 11°C resulted in free amine and kinetic isotope effects of kOH/kOD = 1.61 ± 0.08, k RuH/kRuD = 2.05 ± 0.08, and kRuHOH/ kRuDOD = 3.32 ± 0.14, indicative of rate-limiting concerted hydrogen transfer, a mechanism analogous to that proposed for aldehyde and ketone reduction. Reduction of electron-rich N-alkyl-substituted imine, N-isopropyl-(4-methyl)benzilidene amine (9), was accompanied by facile imine isomerization and scrambling of deuterium labels from reduction with 5-RuDOH into the N-alkyl substituent of both the amine complex and into the recovered imine. Inverse equilibrium isotope effects were observed in the reduction of N-benzilidene-tert-butylamine (11) at -48°C (kOH/kOD = 0.89 ± 0.06, kRuH/kRuD = 0.64 ± 0.05, and kRuHOH/kRuDOD = 0.56 ± 0.05). These results are consistent with a mechanism involving reversible hydrogen transfer followed by rate-limiting amine coordination.
The role of a hydroxycyclopentadienyl ruthenium dicarbonyl formate in formic acid reductions of carbonyl compounds catalyzed by Shvo's diruthenium catalyst
Casey,Singer,Powell
, p. 1002 - 1011 (2007/10/03)
Addition of excess HCO2H to {2,5-Ph2-3,4-Tol2(η5-C4CO)] Ru(CO)2}2 (6) at -20°C led to the formation of [2,5-Ph2-3,4-Tol2{η5-C4COH)] Ru(CO)2(η1-OCHO) (5), a proposed intermediate in catalytic transfer hydrogenations developed by Shvo. Hydroxycyclopentadienyl formate 5 undergoes rapid reversible dissociation of HCO2H at -20°C, and undergoes decarboxylation at 1°C to form a 1:10 mixture of {[2,5-Ph2-3,4-Tol2(η5-C4CO)] 2H}Ru2(CO)4(μ-H) (3):[2,5-Ph2-3,4-Tol2(η5-C4 COH)Ru(CO)2H] (4). 5 does not reduce PhCHO below the temperature at which 5 is converted to hydride 4. The catalytic production of benzyl alcohol from 5 and PhCHO in the presence of excess HCO2H is not accelerated by higher concentrations of PhCHO, indicating that 5 does not directly reduce PhCHO. Formate complex 5 is the precursor of hydride 4 which transfers hydrogen to PhCHO. A crucial role for the CpOH proton in the decarboxylation of 5 was indicated by the much slower decarboxylation of the methoxycyclopentadienyl analog [2,5-Ph2-3,4-Tol2(η5-C4COCH 3)]Ru(CO)2(η1-OCHO) (7). A mechanism for decarboxylation of 5 is proposed which involves reversible dissociation of formic acid to form the unsaturated dienone dicarbonyl ruthenium intermediate C, followed by simultaneous transfer of hydride to ruthenium from the formic acid carbon and of proton to the carbonyl of C from the formic acid OH group.
Hydrogen transfer to carbonyls and imines from a hydroxycyclopentadienyl ruthenium hydride: Evidence for concerted hydride and proton transfer
Casey,Singer,Powell,Hayashi,Kavana
, p. 1090 - 1100 (2007/10/03)
Reaction of { [2,5-Ph2-3,4-Tol2(η5-C 4CO)]2H}Ru2(CO)4(μ-H) (6) with H2 formed [2,5-Ph2-3,4-Tol2(η5-C 4COH)Ru(CO)2H] (8), the active species in catalytic carbonyl reductions developed by Shvo. Kinetic studies of the reduction of PhCHO by 8 in THF at - 10 °C showed second-order kinetics with ΔH? = 12.0 kcal mol-1 and ΔS? = -28 eu. The rate of reduction was not accelerated by CF3CO2H, and was not inhibited by CO. Selective deuteration of the RuH and OH positions in 8 gave individual kinetic isotope effects kRuH/kRuD = 1.5 ± 0.2 and kOH/kOD = 2.2 ± 0.1 for PhCHO reduction at 0 °C. Simultaneous deuteration of both positions in 8 gave a combined kinetic isotope effect of kORuH/kODRuD = 3.6 ± 0.3. [2,5-Ph2-3,4-Tol2(η5-C 4COSiEt3) Ru(CO)2H] (12) and NEt4+[2,5-Ph2-3,4-Tol 2(η4-C4CO) Ru(CO)2H]- (13) were unreactive toward PhCHO under conditions where facile PhCHO reduction by 8 occurred. PhCOMe was reduced by 8 30 times slower than PhCHO; MeN=CHPh was reduced by 8 26 times faster than PhCHO. Cyclohexene was reduced to cyclohexane by 8 at 80 °C only in the presence of H2. Concerted transfer of a proton from OH and hydride from Ru of 8 to carbonyls and imines is proposed.
