Optimizing Group Transfer Catalysis by Copper Complex with Redox-Active Ligand in an Entatic State

Abstract

Metalloenzymes use earth-abundant non-noble metals to perform high-fidelity transformations in the biological world. To ensure chemical efficiency, metalloenzymes have acquired evolutionary reactivity-enhancing tools. Among these, the entatic state model states that a strongly distorted geometry induced by ligands around a metal center gives rise to an energized structure called entatic state, strongly improving the reactivity. However, the original definition refers both to the transfer of electrons or chemical groups, whereas the chemical application of this concept in synthetic systems has mostly focused on electron transfer, therefore eluding chemical transformations. Here we report that a highly strained redox-active ligand enables a copper complex to perform catalytic nitrogenand carbon-group transfer in as fast as 2 min, thus exhibiting a strong increase in reactivity compared with its unstrained analogue. This report combines two reactivity-enhancing features from metalloenzymes, entasis and redox cofactors, applied to group-transfer catalysis.

Copper catalysis with redox-active ligands

“…Among these tools, the entatic state model relies on the fact that a strong steric distortion induced by ligands in the coordination sphere around a metal center produces an energized and highly reactive structure. Our recently published study revealed, that use of a highly-strained redox-active ligand facilitates a transfer of nitrogen-and carbon-containig group by copper complex 22 in as fast as two minutes, and therefore, it exhibits a strong increase in reactivity when compared to its unstrained analogue [40]. This example of a bioinspired small-molecule synthetic system combines two reactivity-enhancing features from metalloenzymes: entasis and redox cofactors.…”

Carbene Radicals in Transition-Metal-Catalyzed Reactions

“…Although the formation of a catalytically competent carbene radical is often accomplished by SET from the metal to the carbene, the group of Desage-El Murr employed the use of a redox-active ligand in combination with a copper metal center ( Scheme 8 ). 53 Copper has already been used to great effect in contemporary carbene transfer catalysis but generally has been observed to operate via two-electron concerted mechanisms. 54 Through use of two redox-active o -aminophenolate moieties bridged by a chiral binaphthyl group, the Desage-El Murr group has shown that their Cu-catalyzed cyclopropanation of styrenes likely operates via a stepwise radical mechanism.…”

Optically active bis(aminophenols) and their metal complexes

“…24 Recently, an optically active bis(aminophenol) based on commercially available 1,1′-binaphthyl-2,2′-diamine has been prepared and complexed to copper. 25 Here we report the preparation of an optically active version of the EganH 4 ligand, (R,R)-BdanH 4 , using commercially available (R,R)-2,3-butanediol as starting material. Both this ligand and the bis(aminophenol) derived from (R)-1,1′-binaphthyl-2,2′-diamine, (R)-BiniqH 4 , are metalated stereoselectively to give group 10 bis(iminoxolene) complexes as single stereoisomers.…”

“…24 Recently, an optically active bis(aminophenol) based on commercially available 1,1′-binaphthyl-2,2′-diamine has been prepared and complexed to copper. 25…”