Establishing the Role of Triflate Anions in H Activation by a Cationic Triorganotin(IV) Lewis Acid.

Cationic Lewis acids (LAs) are gaining interest as targets for frustrated Lewis pair (FLP)-mediated catalysis. Unlike neutral boranes, which are the most prevalent LAs for FLP hydrogenations, the Lewis acidity of cations can be tuned through modulation of the counteranion; however, detailed studies on such anion effects are currently lacking in the literature. Herein, we present experimental and computational studies which probe the mechanism of H activation using PrSnOTf (-OTf) in conjunction with a coordinating (quinuclidine; qui) and noncoordinating (2,4,6-collidine; col) base and compare its reactivity with {PrSn·base}{Al[OC(CF)]} (base = qui/col) systems which lack a coordinating anion to investigate the active species responsible for H activation and hence resolve any mechanistic roles for OTf in the PrSnOTf-mediated pathway.

Enantioselective reduction of N-alkyl ketimines with frustrated Lewis pair catalysis using chiral borenium ions.

Enantioselective reduction of ketimines was demonstrated using chiral N-heterocyclic carbene (NHC)-stabilised borenium ions in frustrated Lewis pair catalysis. High levels of enantioselectivity were achieved for substrates featuring secondary N-alkyl substituents. Comparative reactivity and mechanistic studies identify key determinants required to achieve useful enantioselectivity and represent a step forward in the further development of enantioselective FLP methodologies.

Fe-Catalyzed Conversion of N to N(SiMe) via an Fe-Hydrazido Resting State.

The catalytic conversion of N to N(SiMe) by homogeneous transition metal compounds is a rapidly developing field, yet few mechanistic details have been experimentally elucidated for 3 d element catalysts. Herein we show that Fe(PP)(N) (PP = RPCHCHPR; R = Me, 1; R = Et, 1) are highly effective for the catalytic production of N(SiMe) from N (using KC/MeSiCl), with the yields being the highest reported to date for Fe-based catalysts. We propose that N fixation proceeds via electrophilic N silylation and 1e reduction to form unstable Fe(NN-SiMe) intermediates, which disproportionate to 1 and hydrazido Fe[N-N(SiMe)] species (3); the latter act as resting states on the catalytic cycle.

Cationic silyldiazenido complexes of the Fe(diphosphine)(N) platform: structural and electronic models for an elusive first intermediate in N fixation.

The first cationic Fe silyldiazenido complexes, [Fe(PP)(NN-SiMe)][BAr] (PP = dmpe/depe), have been synthesised and thoroughly characterised. Computational studies show the compounds to be useful structural and electronic surrogates for the more elusive [Fe(PP)(NN-H)], which are postulated intermediates in the H/e mediated fixation of N by Fe(PP)(N) species.