Si-C and Si-N activation at a single nickel center via amido group transfer reactions

Abstract

Group transfer reactions have been one of the major research topics in recent years due to its potential applications in chemical industry to generate high-value chemicals. Among the generation of various products by group transfer reactions reported in the literature, the production of isocyanates might be one of the crucial applications. Isocyanates are widely utilized in various organic reactions and it is currently produced over 4.4 Mt annually. In modern industry, TDI and MDI as the major products in the global isocyanate production are synthesized by hydrogenation of nitro aromatic species followed by phosgenation of resulting amines. However, utilizing the poisonous phosgene and producing hydrochloric acid as a byproduct have been pointed out as drawbacks of the reaction. Therefore, it is attractive to study the alternative synthesis of such isocyanates without toxic reagent(s) or any hazardous byproduct. As our own synthetic methodology, group transfer reactions utilizing $1^{st}$ row transition metal supported by $RSiP_2^{-} (RSiP_2^{-} = Si(2-(P(i-Pr)_2R)_2^{-} , R = Me, Ph)$ were studied. Two different nickel(II) amido species, ($MeSiP_2$)Ni(NHAr) vs. $(PhSiP_2)Ni(NHAr) revealed the different reactivity in their group transfer reactions. Nickel(II) amido complexes (PhSiP_2)Ni(NHAr)$ (Ar = Mes, Trip) showed unusual group transfer reaction revealing the formation of (ArHNSiP2)NiPh via Si-C and Ni-N bond activation. Interestingly, the reaction of ($MesHNSiP_2$)NiPh with $CO-2$ occurred revealing the formation of the nickel(II) carbamate species, ($PhSiP_2$)Ni(OC(O)NHMes). The corresponding backward reaction should involve the Si-N and Ni-C bond activation.