An Amphiphilic (salen)Co Complex – Utilizing Hydrophobic Interactions to Enhance the Efficiency of a Cooperative Catalyst

Abstract

An amphiphilic (salen)Co(III) complex is presented that accelerates the hydrolytic kinetic resolution (HKR) of epoxides almost 10 times faster than catalysts from commercially available sources. This was achieved by introducing hydrophobic chains that increase the rate of reaction in one of two ways – by enhancing cooperativity under homogeneous conditions, and increasing the interfacial area under biphasic reaction conditions. While numerous strategies have been employed to increase the efficiency of cooperative catalysts, the utilization of hydrophobic interactions is scarce. With the recent upsurge in green chemistry methods that conduct reactions ‘on water’ and at the oil‐water interface, the introduction of hydrophobic interactions has potential to become a general strategy for enhancing the catalytic efficiency of cooperative catalytic systems.

Synthesis, Characterization, and Study of Catalytic Activity of Chiral Cu(II) and Ni(II) Salen Complexes in the α-Amino Acid C-α Alkylation Reaction

“…Chemical shifts (δ) are reported in parts per million (ppm) relative to tetramethyl silane. Signals were referenced to the residual solvent peak 7.26 (CDCl3), 3.31 (CD3OD), 4.79 (D2O), 2.50 ((CD3)2SO) for 1 H and 77.10 (CDCl3), 49.15 (CD3OD), 39.52 ((CD3)2SO) for 13 C NMR spectra. The 13 C NMR spectra were measured with proton decoupling.…”

“…1 H NMR (300 MHz, CDCl3): δ 7.34 (s, 1H), 7.11 (d, J = 7.1 Hz, 1H), 6.95 (dd, J = 7.9, 1.9 Hz, 1H), 6.54-6.43 (m, 1H), 6.09 (ddt, J = 17.0, 10.0, 6.9 Hz, 1H), 5.20-4.99 (m, 3H), 3.43 (d, J = 6.9 Hz, 2H), 3.23 (s, 1H), 2.40 (s, 1H), 1.91 (s, 1H), 1.37-1.24 (m, 2H) ppm. 13 The ligands for complexes 4, 11 and 6, 13 were synthesized from (S,S)-cyclohexanediamine and the corresponding salicylic aldehyde derivatives. To a (S,S)-cyclohexanediamine solution in 7 mL methanol, the corresponding salicylic aldehyde derivatives with a 1:2 molar ratio were added.…”

“…Their simple synthesis and the versatility in their structural modification have contributed to the current increased interest in the synthesis and characterization of new salen metal complexes [ 5 , 6 , 7 , 8 , 9 , 10 ]. From an applicative perspective, such complexes of the first-row transition metals are known for their attractive catalytic, magnetic and biological properties [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Due to their structural diversity and selectivity in the coordination with metal ions, Schiff bases have found wide application in the asymmetric catalysis as ligands.…”

“…13. Ni(II) complex of (1S,2S)-[N,N-bis(2'-hydroxy-5'-bromo-benzylidene)]-1,2-diaminocyclohexane(13) Chemical yield 99%. Mp dec. 340 °C without melting.…”

“…J = 2.6 Hz, 1H),6.88 (d, J = 2.6 Hz, 1H), 2.97 (s, 1H), 2.46 (s, 1H), 1.93 (s, 1H), 1.42 (s, 8H), 1.33 (d, J = 6.0 Hz, 2H), 1.27 (s, 9H) ppm 13. C NMR (75 MHz, Chloroform-d): δ 157.8, 129.1, 126.3, 96.3, 69.9, 35.9, 33.9, 31.5, 29.8, 29.0, 24.6 ppm.…”