Breaking New Ground: MBene Route toward Selective Vinyl Double Bond Hydrogenation in Nitroarenes

Doping, or incremental substitution of one element for another, is an effective way to tailor a compound's structure as well as its physical and chemical properties. Herein, we replaced up to 30% of Ni with Co in members of the family of layered LiNiB compounds, stabilizing the high-temperature polymorph of LiNiB while the room-temperature polymorph does not form. By studying this layered boride with in situ high-temperature powder diffraction, we obtained a distorted variant of LiNi_0.7Co_0.3B featuring a perfect interlayer placement of [Ni_0.7Co_0.3B] layers on top of each other─a structural motif not seen before in other borides. Because of the Co doping, LiNi_0.7Co_0.3B can undergo a nearly complete topochemical Li deintercalation under ambient conditions, resulting in a metastable boride with the formula Li_0.04Ni_0.7Co_0.3B. Heating of Li_0.04Ni_0.7Co_0.3B in anaerobic conditions led to yet another metastable boride, Li_0.01Ni_0.7Co_0.3B, with a CoB-type crystal structure that cannot be obtained by simple annealing of Ni, Co, and B. No significant alterations of magnetic properties were detected upon Co-doping in the temperature-independent paramagnet LiNi_0.7Co_0.3B or its Li-deintercalated counterparts. Finally, Li_0.01Ni_0.7Co_0.3B stands out as an exceptional catalyst for the selective hydrogenation of the vinyl C═C bond in 3-nitrostyrene, even in the presence of other competing functional groups. This research showcases an innovative approach to heterogeneous catalyst design by meticulously synthesizing metastable compounds.