Chiral [Bis(olefin)amine]rhodium(I) Complexes – Transfer Hydrogenation in Ethanol

[Co2(CO)6(Alkynyl)] Complexes of Dibenzosuberyl and Dibenzosuberenyl Carbocations: Dibenzotropylium or Dibenzoheptafulvene?

“…We have already reported X‐ray crystal structures of several Pauson–Khand [Co 2 (CO) 5 (η 2 ‐alkene)(μ‐alkyne)] intermediates 27 , whereby a cobalt carbonyl vertex is coordinated to the C10=C11 double bond in the seven‐membered ring . Moreover, rhodium complexes involving coordination to the corresponding C10=C11 bond in aminodibenzosuberenyl systems have been reported by Grützmacher et al …”

“…Thus, it may not be the exocyclicd oubleb ond of the alkene that coordinates to ac obalt tricarbonyl vertex, as in 31,b ut instead, as depicted in Scheme 10, it could involvec oordination to the C10=C11 double bond within the ring to form 32.W eh ave already reported X-ray crystal structures of several Pauson-Khand [Co 2 (CO) 5 (h 2 -alkene)(m-alkyne)] intermediates 27,w hereby ac obaltc arbonyl vertex is coordinated to the C10=C11d ouble bond in the seven-membered ring. [30,33] Moreover, rhodium complexes involving coordinationt ot he corresponding C10=C11b ond in aminodibenzosuberenyl systemsh ave been reported by Grützmacher et al [35] The NMRs pectra of the possible isomeric cations 31 and 32 are very congested in the aromatic region owing to the pres-ence of the dppm ligand. Consequently,i na na ttemptt os implify the problem,[ Co 2 (CO) 6 {5-ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol}] (28)w as also protonated and 13 CNMR spectroscopy data were acquired on the resulting cation 33.I nt he mirror-symmetric alcohol precursor 28,t he peaks for C4a/C5a and C9a/C11a are found at d = 132.5 and 142.6 ppm, respectively,t he aromatic CH units give rise to four resonancesa td = 124.2, 127.2,1 28.5 and1 29.6 ppm, and the C10=C11s ignal is found at d = 131.5 ppm.…”

Applying Le Chatelier's Principle for a Highly Efficient Catalytic Transfer Hydrogenation with Ethanol as the Hydrogen Source

“…The capturing of the primary oxidation product acetic aldehyde in form of ethyl acetate solves the problem of side reactions caused by the reactive aldehyde. In the following year, the same group published chiral versions of this type of catalyst and could reach up to 58 % ee …”

Bicyclic β-amino acids

“…78 Derivatives of the amino acids 31a and 31c were used in the design of bolaamphiphiles 79 and catalysts for asymmetric transfer hydrogenation. 80 In both cases, no good results were obtained on self-aggregation and enantioselectivity, respectively. …”