Synthesis and reactivity of an anionic NHC-borane featuring a weakly coordinating silicate anion

Thomas Deis (1) , Fabrizio Medici (1) , Antoine Poussard-Schulz (1) , Gilles Lemière (1) , Louis Fensterbank (1)

1 IPCM - Institut Parisien de Chimie Moléculaire

We report herein the synthesis of a new NHC-stabilised borane complexe featuring a weakly coordinating anion, namely a pentaorganosilicate, on the NHC backbone. The synthesis can be achieved from a zwitterionic abnormal silicate-imidazolium adduct by deprotonation with a strong base followed by quenching with a borane transfer agent. Alternatively, the IPr-BH 3 complex can also be deprotonated and the resulting vinylanion is trapped by a tetravalent spirosilane. The first structural data on a lithium derivative of an anionic NHC-borane complex functionalized by a silicate have been obtained and reveal an interaction between the three hydrogens of the borane and the lithium cation. Assessment of the reactivity highlights the higher hydridicity of the anionic NHCborane compared to the parent IPr-BH 3. Finally, electronic properties of this new species have been evaluated by means of DFT calculations and the presence of the silicate on the NHC backbone raises the HOMO which can in part explain the high hydride-donor abilities. This is consistent with the smooth reduction of an aldehyde without Lewis acid additive.

Mots clés: NHC-Borane; Anionic NHC; Silicon; Spirosilane; Pentacoordinated compounds; DFT calculations

Domaines: Chimie organique

Thomas Deis, Fabrizio Medici, Antoine Poussard-Schulz, Gilles Lemière, Louis Fensterbank. Synthesis and reactivity of an anionic NHC-borane featuring a weakly coordinating silicate anion. Journal of Organometallic Chemistry, 2021, 956, pp.122120. ⟨10.1016/j.jorganchem.2021.122120⟩. ⟨hal-03414826⟩