Normal-to-Abnormal Rearrangement and NHC Activation in Three-Coordinate Iron(II) Carbene Complexes

Abstract

The 'normal' three-coordinate iron-NHC complex [(IPr)Fe(N'')2] (N″ = N(SiMe3)2) rearranges to its abnormal NHC analogue [(aIPr)Fe(N″)2] (6) on heating, providing a rare abnormal iron-aNHC complex, and the first such three-coordinate complex. The tert-butyl-substituted complex [(I(t)Bu)Fe(N″)2] (4) undergoes a thermal decomposition that has not previously been observed in iron-NHC chemistry, resulting in the bis(imidazole) complex [((t)BuIm)2Fe(N″)2] (7). A mechanism that involves consecutive C-H and C-N activation is proposed to account for the formation of 7.

Palladium‐Catalyzed Direct C2‐Arylation of an N‐Heterocyclic Carbene: An Atom‐Economic Route to Mesoionic Carbene Ligands

“…[15,16] Moreover, isolation of a thermally stable MIC(B) species has remained a challenge until very recently. [17] Bertrand and co-workers reported the first metal-free MIC (II, Scheme 1) in 2009, synthesized by deprotonating a 1,2,3,4-tetraarylated imidazolium chloride.…”

NHC adducts of tantalum amidohalides: the first example of NHC abnormally coordinated to an early transition metal

“…However, with the more crowded precursor, Ga(CH 2 SiMe 3 ) 3 , IPr shows fast nNHC to aNHC conversion, whereas ItBu forms only the aNHC complex but not the nNHC complex. 23 In our case, complex 3 is formed under mild conditions (toluene, rt), implying that the steric hindrance around the Ta center is the main driving force for the aNHC coordination. A solution of the less sterically hindered 1a in C 6 D 6 remained intact upon heating at 70°C for 5 days, showing no changes in its NMR spectra.…”

Coordination chemistry of ditopic carbanionic N-heterocyclic carbenes

“…5) [41]. This reaction clearly demonstrates the potential for "abnormal" bonding in NHC complexes to be thermodynamically controlled.…”