Enantioselective Michael Addition Reaction Catalysed by Enantiopure Binuclear Nickel(II) Close‐Ended Helicates

Abstract

The enantiopure Ni(II) helicates [Ni2L1RR.Cl2] (1), [Ni2L1SS.Cl2] (1′), [Ni2L2RR.Cl2] (2), [Ni2L2SS.Cl2] (2′) were synthesized by one‐pot self‐assembly technique from R‐(+)‐ or S‐(−)‐1,1′‐binaphthyl‐2,2′‐diamine, with 4‐methyl‐2,6‐diformyl phenol or 4‐tert‐butyl‐2,6‐diformyl phenol and nickel salts. This binuclear double stranded Ni(II) helicates were characterized by ESI‐MS, IR and single crystal X‐ray structure wherever applicable. The extensive chiroptical studies suggest that the complexes are enantiopure in nature. The chirality transfer from ligand L1RR & L2RR to Ni(II) metal centre produced ΔΔ geometrical chirality, while their enantiomeric counterpart L1SS & L2SS produced ΛΛ chirality in their respective complexes.These enantiopure helicates were applied as catalysts in asymmetric Michael addition of 1,3‐dicarbonyl compounds with β‐nitrostyrene to produce nitroalkanes in good yield (96–98%) and ee (78–94%).

New Dinuclear Macrocyclic Copper(II) Complexes as Potentially Fluorescent and Magnetic Materials

“…Additionally, in the absorption spectra, the presence of low-intensity bands at 660 nm for K1 and 664 nm for K2 absorption bands from d-d transitions [46] only in the less polar solvent chloroform were noted. This results from the square pyramidal or trigonal bipyramid environment of the copper atoms shifted towards the apical chloride anion [23,47]. The same was observed previously for similar copper(II) compounds [41,48].…”

“…Moreover, the highest fluorescence intensity in most polar solvents such as DMSO and methanol was noted (Figure 10, Table S2). A similar situation also occurred in the case of other metal(II) complexes [23]. When the emission spectra registered in a solution and in the solid state were compared, it was possible to infer that the solvent destroyed the π-π interactions, and thus the transition energy was increased in the solution, as was observed previously [50].…”

“…Cu(II) metal salt was used in these syntheses. The obtained compounds were enantiomerically pure, showed chiroptical properties, and exhibited catalytic activity in many reactions of organic transformations [22][23][24]. Great interest was shown in the design, synthesis, and modification of complexes due to their possible impact on the field of molecular magnetism [25,26].…”

Recent developments in enantioselective nickel(ii)-catalyzed conjugate additions

“…Later in 2020, Subramanian et al described the synthesis of novel binuclear nickel( ii ) helicates through self-assembly of chiral 1,1′-binaphthyl-2,2′-diamine, 4-methyl-2,6-diformyl phenol and nickel salts. 22 These dinuclear double stranded Ni( ii ) helicates were characterized by crystal X-ray diffraction and further investigated as catalysts in asymmetric Michael additions of various 1,3-dicarbonyl compounds and derivatives to nitroalkenes. The optimal catalyst was found to be complex 4 employed at room temperature at 2 mol% of catalyst loading in dichloromethane as solvent.…”