Three-center-four-electron halogen bond enables non-metallic complex catalysis for Mukaiyama-Mannich-type reaction

Shunya Oishi; Takeshi Fujinami; Yu Masui; Toshiyasu Suzuki; Masayuki Kato; Naoya Ohtsuka; Norie Momiyama

doi:10.1016/j.isci.2022.105220

Three-center-four-electron halogen bond enables non-metallic complex catalysis for Mukaiyama-Mannich-type reaction

iScience. 2022 Sep 27;25(10):105220. doi: 10.1016/j.isci.2022.105220. eCollection 2022 Oct 21.

Authors

Shunya Oishi^{1

2}, Takeshi Fujinami¹, Yu Masui^{1

2}, Toshiyasu Suzuki¹, Masayuki Kato^{1

2}, Naoya Ohtsuka^{1

2}, Norie Momiyama^{1

2}

Affiliations

¹ Institute for Molecular Science, Okazaki, Aichi 444-8787, Japan.
² SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan.

Abstract

The three-center-four-electron halogen bond (3c4e X-bond) presents a fundamental design concept for catalysis. By integrating halogen(I) (X⁺: I⁺ or Br⁺), the bis-pyridyl ligand NN, and a non-nucleophilic counteranion Y, we developed non-metallic complex catalysts, [N···X···N]Ys, that exhibited outstanding activity and facilitated the Mukaiyama-Mannich-type reaction of N-heteroaromatics with parts-per-million-level catalyst loading. The high activity of [N···X···N]SbF₆ was clearly demonstrated. NMR titration experiments, CSI-MS, computations, and UV-vis spectroscopic studies suggest that the robust catalytic activity of [N···X···N]Y can be attributed to the unique ability of the 3c4e X-bond for binding chloride: i) the covalent nature transforms the [N···X···N]⁺ complexation to sp² CH as a hydrogen-bonding donor site, and ii) the noncovalent property allows for the dissociation of [N···X···N]⁺ for the formation of [Cl···X···Cl]^-. This study introduces the application of 3c4e X-bonds in catalysis via halogen(I) complexes.

Keywords: Chemistry; Organic chemistry.