Ligand properties of aromatic azines: C–H activation, metal induced disproportionation and catalytic C–C coupling reactions

The reaction of ortho-halogenated aromatic aldazine ligands with Fe2(CO)9: symmetrical cleavage of the azine and carbon–halogen activation

“…One of the CO ligands at Fe2 shows a semi-bridging coordination mode towards Fe3 leading to a slightly enhanced iron carbon bond length Fe2-C13 compared to the corresponding bond lengths of terminal CO ligands and a bond angle of Fe2-C13-O6 of 164.0°. Similar trinuclear iron carbonyl cluster compounds with a bridging hydride ligand instead of a formal carbanion have been observed from the reaction of carbonylferrates with nitriles in the presence of a proton source and from the iron induced disproportionation reaction of aromatic azines [15,16]. So we think that the formation of 2a is also due to a disproportionation of 1a into a primary imine and a nitrile and 2a being the product of the reaction of the nitrile with Fe 2 (CO) 9 .…”

“…One of them is C-H activation in ortho-position with respect to the exocyclic imine substituent, the other one is a metal induced disproportionation of the azine into a primary imine and a nitrile. The same reaction principles are also observed in catalytic C-C coupling reactions starting from the same substrates [15].…”

“…The resulting azaferra-cyclopentadiene system is apically coordinated by the second Fe(CO) 3 moiety. This coordination mode has quite frequently been observed in the reaction of aromatic imines or azines, respectively [13,15]. In this cases, the formation of the dinuclear product clusters has been rationalized by the reaction sequence of a C-H activation in ortho-position with respect to the exocyclic imine function followed by an intramolecular hydrogen transfer towards the former imine nitrogen atom [13].…”

α,β-Unsaturated diimines as substrates in catalytic C–H activation reactions and as ligands in iron carbonyl complexes

“…There is one reaction reported in the literature, in which an imine derived from p-anisidine and cinnamaldehyde reacts with Fe 2 (CO) 9 to yield a dinuclear iron carbonyl compound, in which the C-H bond in b-position relative to the C-N double bond is activated and the corresponding hydrogen atom is trans ferred to the former imine carbon atom [16,17]. The same reaction sequence on the other hand is typical for aromatic imines [18][19][20][21][22][23][24], although in one case a mononuclear iron tricarbonyl compound has been isolated from the reaction of Fe 2 (CO) 9 with naphthalen-2-ylmethylene-phenyl-amine [21]. Scheme 3 shows the three component reactions of 1, 4 and 6 with carbon monoxide and ethylene in the presence of catalytic amounts of Ru 3 (CO) 12 .…”

The variation of coordination modes of aromatic imines in iron carbonyl complexes: Is there a correlation between bond lengths in organometallic model compounds and the reactivity of the ligands in catalytic C–C bond formation reactions?

“…But it is remarkable that the imines showing very long Fe ap -C b interactions in their iron carbonyl complexes produce heterocyclic products if reacted with carbon monoxide and ethylene (Scheme 5, Fig. 9) [16], whereas the ligands derived from benzaldimines 10-16 or a-naphthylcarbaldimines 18, 19 and 21 either yield the alkene insertion products or acylated compounds by the subsequent insertion of CO and an alkene under similar reaction conditions [16,25,26,36]. The diironhexacarbonyl complexes produced from the latter ligands show Fe ap -C b bond lengths in the range of 228-240 pm.…”