869110-13-4Relevant academic research and scientific papers
Intramolecular trapping of an intermediate in the reduction of imines by a hydroxycyclopentadienyl ruthenium hydride: Support for a concerted outer sphere mechanism
Casey, Charles P.,Clark, Timothy B.,Guzei, Ilia A.
, p. 11821 - 11827 (2008/03/27)
Reduction of imines by [2,5-Ph2-3,4-Tol2(η 5-C4COH)]Ru(CO)2H (1) produces kinetically stable ruthenium amine complexes. Reduction of an imine possessing an intramolecular amine was studied to distinguish between inner sphere and outer sphere mechanisms. 1,4-Bn15NH(c-C6H10)=NBn (12) was reduced by 1 in toluene-d8 to give 85% of [2,5-Ph 2-3,4-Tol2(η4-C4CO)](CO) 2RuNHBn(c-C6H10)15NHBn (16-RuN, 15N), resulting from coordination of the newly formed amine to the ruthenium center, and 15% of trapping product [2,5-Ph2-3,4-Tol 2(η4-C4CO)](CO)2Ru 15NHBn(c-C6H10)NHBn (16-Ru15N,N), resulting from coordination of the intramolecular trapping amine. These results provide support for an outer sphere transfer of hydrogen to the imine to generate a coordinatively unsaturated intermediate, which can be trapped by the intramolecular amine. An opposing mechanism, requiring coordination of the imine nitrogen to ruthenium prior to hydrogen transfer, cannot readily explain the observation of the trapping product 16-Ru15N,N.
Reduction of imines by hydroxycyclopentadienyl ruthenium hydride: Intramolecular trapping evidence for hydride and proton transfer outside the coordination sphere of the metal
Casey, Charles P.,Bikzhanova, Galina A.,Cui, Qiang,Guzei, Ilia A.
, p. 14062 - 14071 (2007/10/03)
Reduction of imines by [2,5-Ph2-3,4-Tol2(η 5-C4COH)]Ru(CO)2H (2) produces kinetically stable ruthenium amine complexes. Reduction of an imine by 2 in the presence of an external amine trap gives only the complex of the newly generated amine. Reaction of 2 with H2N-p-C6H4N=CHPh (11), which contains an intramolecular amine trap, gave a 1:1 mixture of [2,5-Ph 2-3,4-Tol2(η4-C4CO)](CO) 2RuNH(CH2Ph)(C6H4-p-NH2) (8), formed by coordination of the newly generated amine to the ruthenium center, and [2,5-Ph2-3,4-Tol2(η4-C 4CO)](CO)2RuNH2C6H 4-p-NHCH2Ph (9), formed by coordination of the amine already present in the substrate. These results require transfer of hydrogen to the imine outside the coordination sphere of the metal to give a coordinatively unsaturated intermediate that can be trapped inside the initial solvent cage. Amine diffusion from the solvent cage must be much slower than coordination to the metal center. Mechanisms requiring prior coordination of the substrate to ruthenium would have led only to 8 and can be eliminated.
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.
