Addition of Isocyanides at Diiron μ-Vinyliminium Complexes: Synthesis of Novel Ketenimine−Bis(alkylidene) Complexes

Abstract

Reactions of the vinyliminium complexes [Fe2{μ-η1:η3-Cγ(R′)Cβ(H)CαN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Xyl, R′ = Me, 1a; R = Xyl, R′ = CO2Me, 1b; R = 4-C6H4OMe, R′ = CO2Me, 1c; Xyl = 2,6-Me2C6H3) with isocyanides (CNR′′), in the presence of NaH, lead to abstraction of the Cβ−H proton and to isocyanide addition with formation of a carbon−carbon double bond. The observed products are the ketenimine−bis(alkylidene) complexes [Fe2{μ-η1:η2-Cγ(R′)Cβ(CNR′′)CαN(Me)(R)}(μ-CO)(CO)(Cp)2] (R = Xyl, R′ = Me, R′′ = Xyl, 2a; R = Xyl, R′ = CO2Me, R′′ = Xyl, 2b; R = Xyl, R′ = CO2Me, R′′ = But, 2c; R = Xyl, R′ = CO2Me, R′′ = 4-C6H4CN, 2d; R = 4-C6H4OMe, R′ = CO2Me, R′′ = But, 2e), obtained in 60−70% yields. Conversely, the vinyliminium complex [Fe2{μ-η1:η3-Cγ(CO2Me)Cβ(H)CαN(Me)2}(μ-CO)(CO)(Cp)2][SO3CF3] (1d) undergoes double isocyanide addition. Reactions of 1d with a 2-fold excess of CNXyl or CNBut, in the presence of NaH, afford [Fe(CO)(Cp)Cα(NMe2)Cβ(CNXyl)Cγ(CO2Me)C(NXy)Fe(CO)(Cp)] (3) and [Fe(CO)(Cp)C(NBut)Cα(NMe2)CβCγ(CO2Me)Fe(Cp)(CO)CNBut] (4), respectively. Finally, the vinyliminium complex [Fe2{μ-η1:η3-Cγ(H)Cβ(H)CαN(Me)2}(μ-CO)(CO)(Cp)2][SO3CF3] (1e), treated with with CNBut and NaH, yields a mixture of the diiron aminocarbyne complexes [Fe2{μ-CN(Me)2}(μ-CO)(CO)(Cp)(C5H5CH2CN)(CNBut)], (6) and [Fe2{μ-CN(Me)2}(μ-CO)(CO)(Cp)2(CNBut)] (5). The molecular structures of 2a,b, 3·1.5CH2Cl2, 4, and 6·0.5Et2O have been ascertained by X-ray diffraction studies.

Assembly and incorporation of a CO2Me group into a bridging vinyliminium ligand in a diiron complex

“…Fe(1)-Fe (2) 2.5614(10) Fe(3)-Fe (4) 2.5511(10) Fe(1)-C (11) 1.907 (5) Fe (3)-C(41) 1.895(5) Fe(2)-C (11) 1.899 (5) Fe (4)-C(41) 1.901(5) Fe(1)-C (12) 2.096 (4) Fe (3)-C(42) 2.110(4) Fe(2)-C (12) 1.940 (5) Fe (4) C]C]CH 2 )(CO) 6 ], that undergoes amine addition to terminal CO, with consequent migration of the resulting amide to the allenyl moiety [12]. A closer analogy is represented by the reaction shown in Scheme 4, involving a vinyliminium complex very similar to 1.…”

“…A further distinctive feature, that is consequence of the bridging coordination, is the a CeH activation, which cannot be accomplished in conjugated iminium species [5]. Removal of the a CeH proton generates very reactive intermediate, which can be trapped upon reactions with a variety of reagents, such as arylisocyanides [6], diazoacetates, [7], disulfides [8], and group 16 elements [9]. These reactions, resulting in the formation of CeC or C-heteroatom bonds, lead to the transformation of the bridging frame into more complex structures of potential synthetic interest.…”

C–H Activation in Diiron Bridging Vinyliminium Ligands: Reaction with CS2 to Form New Zwitterionic Complexes Acting as Organometallic Ligands

“…[5] The double nature of the intermediate has been exploited to generate new single and double bonds. Examples of both possibilities are shown in Scheme 1: reactions with aryl isocyanides (CNR) [6] or diazoacetates [7] lead to bis-alkylidene complexes (V and VII, respectively) bearing a double bond at C 2 . On the other hand, intermediates can be oxidized by treatment with S 8 [8] or PhSSPh [9] to afford vinyliminium complexes (VI and IV, respectively) with a C 2 -S single bond.…”

“…[10] Moreover, CS 2 and other heteroallenes are known to be reactive towards diiron complexes under appropriate conditions, leading to the fragmentation and incorporation of the heteroallenes in the metal-ligand framework. Examples include the reactions with [Fe 2 (CO) 9 ], [11] [Fe 2 (μ-RCCNEt 2 )(CO) 7 ], [12] [Fe 2 (μ-CO)(μ-dppm)(CO) 6 ], [13] [Fe 2 (μ-SR) 3 Cp 2 ], [14] [Fe 2 (μ-SR)(μ-CO)(CO) 6 ] -and related species, [15] which provide effective routes for the transformation of these small molecules. …”

γ‐Deprotonation of Bridging Vinyliminium Ligands: New Route to Aminobutadienylidene Diiron and Diruthenium Complexes

“…[7] In the light of these considerations, the reactivity of α,β-unsaturated iminium ions as bridging ligands appears unique in that they undergo α C-H abstraction upon treatment with NaH, leading to the formation of reactive intermediates. [8] These can be combined with a variety of reagents, (e.g., elemental sulfur or selenium, [9] diazoacetates, [10] arylisocyanides, [11] and phenyldisulfides [12] ), re- Scheme 2. sulting in the replacement of the α C-H with a range of functional groups (α-functionalization). As an example, some of the complexes obtained by replacing the C-H with C-S bonds are shown in Scheme 1.…”