1,4-Diaryl-1-azabuta-1,3-diene-Catalyzed Complexation of Cyclohexa-1,3-diene by the Tricarbonyliron Fragment:  Development of Highly Efficient Catalysts, Optimization of Reaction Conditions, and Proposed Mechanism

Abstract

The 1,4-diaryl-1-azabuta-1,3-diene-catalyzed complexation of cyclohexa-1,3-diene with either nonacarbonyldiiron or pentacarbonyliron is reported to provide high yields of the tricarbonyl(η4-cyclohexa-1,3-diene)iron complex. This procedure enables exploitation of both tricarbonyliron fragments of nonacarbonyldiiron for the complexation of dienes for the first time. Using 12.5 mol % of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene and optimized reaction conditions (nonacarbonyldiiron, dimethoxyethane, reflux, 16.5 h, or pentacarbonyliron, dioxane, reflux, 45 h), a quantitative catalytic complexation of cyclohexa-1,3-diene is feasible with both reagents. An extensive study with a broad range of 1,4-diaryl-1-azabuta-1,3-dienes shows that the efficiency of the catalysts strongly depends on the substituents of the two aryl rings. Remarkably high activities are found for those catalysts deriving from condensation of cinnamaldehyde and ortho-methoxy-substituted arylamines. A hexacarbonyldiiron complex of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene is obtained as a byproduct of the catalytic complexation and is structurally confirmed by X-ray crystallography. A mechanism supported by the experimental findings is proposed.

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

“…The next step in the catalytic cycle would then be the C-H activation reaction in terms of an cyclometalation (Scheme 2). 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].…”

Synthesis of Biologically Active Carbazole Alkaloids Using Selective Transition-metal-catalyzed Coupling Reactions

“…Coordination of cyclohexadienes to the tricarbonyliron fragment is most efficiently achieved by the 1-azadiene-catalyzed complexation developed in our laboratories. [8][9][10] Thus, catalytic complexation of cyclohexa-1,3-diene (3) with pentacarbonyliron quantitatively provides tricarbonyl( 4 -cyclohexa-1,3-diene)iron (6). It is important to note that this process can be applied as well to substituted cyclohexadienes leading to the corresponding substituted irondiene complexes.…”

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?

“…A 360 mg portion Fe 2 (CO) 9 (1 mmol) together with an equimolar amount of the corresponding imines with only one imine function (188 mg 7, 177 mg 8, 201 mg 14) or half an equivalent of the diimines (146 mg 30, 193 mg …”

“…The resulting organometallic compounds therefore consist of an formally six electron donating enyl-amido ligand adopting a l 2 -g 3 -coordination mode (Scheme 1) [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. This reaction sequence has been shown to be the major reaction pathway for a wide variety of carbocyclic and heterocyclic imine ligands.…”