NHC Effects on Reduction Dynamics in Iron‐Catalyzed Organic Transformations**

Abstract

The high abundance, low toxicity and rich redox chemistry of iron has resulted in a surge of iron‐catalyzed organic transformations over the last two decades. Within this area, N‐heterocyclic carbene (NHC) ligands have been widely utilized to achieve high yields across reactions including cross‐coupling and C−H alkylation, amongst others. Central to the development of iron‐NHC catalytic methods is the understanding of iron speciation and the propensity of these species to undergo reduction events, as low‐valent iron species can be advantageous or undesirable from one system to the next. This study highlights the importance of the identity of the NHC on iron speciation upon reaction with EtMgBr, where reactions with SIMes and IMes NHCs were shown to undergo β‐hydride elimination more readily than those with SIPr and IPr NHCs. This insight is vital to developing new iron‐NHC catalyzed transformations as understanding how to control this reduction by simply changing the NHC is central to improving the reactivity in iron‐NHC catalysis.

Iminium substituent directs cyanide and hydride additions to triiron vinyliminium complexes

“…The formation of 3 from [1c]CF 3 SO 3 (23% yield) is imputable to the alkenyl unit, behaving as a η 2 -ligand towards the iron and thus inducing the extrusion of alkynyl–ferrocene. Although neutral η 2 -ligands generally behave as labile ones towards middle-late transition metal centres, 46–49 3 is stabilized by the multisite coordination of the alkylidene–alkenyl moiety, whereby the alkene portion does not behave as labile. 50…”

“…The formation of 3 from [1c]CF 3 SO 3 (23% yield) is imputable to the alkenyl unit, behaving as a Z 2 -ligand towards the iron and thus inducing the extrusion of alkynyl-ferrocene. Although neutral Z 2 -ligands generally behave as labile ones towards middle-late transition metal centres, [46][47][48][49] 3 is stabilized by the multisite coordination of the alkylidene-alkenyl moiety, whereby the alkene portion does not behave as labile. 50 Our attempts to convert 2c into 3 by thermal treatment failed (no change in the 1 H NMR spectrum of 2c), therefore it is presumable that the formation of 3 is not subsequent to that of 2c but takes place from [1c] + as a parallel process.…”