Migratory insertion in N-heterocyclic carbene-containing Fe carbonyl complexes: an experimental and theoretical study

Abstract

The compound [Fe(eta-C5H5)(CO)2(Me)] reacts thermally with N-heterocyclic carbenes (L) to give both alkyl, [Fe(eta-C5H5)(L)(CO)(Me)], and acyl, [Fe(eta-C5H5)(L)(CO)(COMe)], derivatives. The reaction temperature has been shown to affect the product distribution. The alkyl and acyl derivatives exist in an equilibrium that is more easily perturbed than in the tertiary phosphine analogues. DFT studies on the reactivity of [Fe(eta-C5H5)(CO)2(Me)] with PH3 and dihydroimidazole-2-ylidene (IH) have shown that CO exchange is energetically favoured for IH, and energetically disfavoured for PH3. The products of CO-induced migratory insertion, [Fe(eta-C5H5)(L)(CO)(COMe)], are more stable than the parent alkyl, [Fe(eta-C5H5)(L)(CO)(Me)], compounds. This stabilisation is larger when L = IH than when L = PH3. Stabilisation of the transition state by agostic interactions was seen in both instances, but this was significantly more pronounced for L = IH.

N‐Heterocyclic Carbene Piano‐Stool Iron Complexes as Efficient Catalysts for Hydrosilylation of Carbonyl Derivatives

“…A small number of examples of bis‐carbene iron complexes12 has been synthesized. The first examples of mono‐carbene complexes were reported in 2003 by Guerchais13 which was followed by examples from Albrecht14, Llewellyn,15 and more recently the groups of Cesar and Lavigne16 and Ohki andTatsumi 17. Up to now, they were used in only very few examples as catalysts 17,18…”

“…A small number of examples of bis-carbene iron complexes [12] has been synthesized. The first examples of mono-carbene complexes were reported in 2003 by Guerchais [13] which was followed by examples from Albrecht [14] , Llewellyn, [15] and more recently the groups of Cesar and Lavigne [16] and Ohki andTatsumi.[17] Up to now, they were used in only very few examples as catalysts. [17,18] Our interest in iron catalysis [19] and especially hydrosilylation [20,21] prompted us to examine the possibility of using NHC well-defined iron complexes in the hydrosilylation reaction.…”

Piano-stool N-heterocyclic carbene iron complexes: Synthesis, reactivity and catalytic applications

“…12 upon photoinduced cleavage of one Fe-CO bond and coordination of iodide. Following this report, our group [62][63][64][65][66] and others have expanded the scope of this synthesis by varying the wingtip substituents, [67,68] heterocyclic framework, [66,[69][70][71] co-ligands [71] and installing chelating groups to form dicarbene, [72] picolyl-carbene, [62] and pyridine-carbene complexes. [64] We have further demonstrated that bimetallic complexes can be accessed using dicarbene ligands with either flexible (13) electron complex is smoothly converted to the air-stable 18e − species 19 when exposed to a CO atmosphere.…”

1,3-Bis(2,6-diisopropylphenyl)-4,5-dihydro-1H-imidazol-3-ium triiodide

“…For a related structure with a 1,3-(2,6-diisopropylphenyl)imidazolidinium unit, see: Giffin et al (2010). For its synthesis, see: Llewellyn et al (2006). Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.…”