Potassium Aluminyl Promoted Carbonylation of Ethene

Abstract

The potassium aluminyl [K{Al(NON^Dipp )}]₂ ([NON^Dipp ]^2- =[O{SiMe₂ NDipp}₂ ]^2- , Dipp=2,6-iPr₂ C₆ H₃ ) activates ethene towards carbonylation with CO under mild conditions. An isolated bis-aluminacyclopropane compound reacted with CO via carbonylation of an Al-C bond, followed by an intramolecular hydrogen shift to form K₂ [Al(NON^Dipp )(μ-CH₂ CH=CO-1κ² C^1,3 -2κO)Al(NON^Dipp )Et]. Restricting the chemistry to a mono-aluminium system allowed isolation of [Al(NON^Dipp )(CH₂ CH₂ CO-κ² C^1,3 )]^- , which undergoes thermal isomerisation to form the [Al(NON^Dipp )(CH₂ CH=CHO-κ² C,O)]^- anion. DFT calculations highlight the stabilising influence of incorporated benzene at multiple steps in the reaction pathways.

Keywords: Aluminyl Anions; Bimetallic Complexes; Carbonylation; Hydrogen-Shift; Metallacycles.

Scheme 1

Metal‐promoted carbonylation reactions involving ethene and CO.

Figure 1

Structurally characterised aluminacyclopropanes.

Scheme 2

Synthesis of [1⋅C₆H₆]₂ and 2.

Figure 2

Displacement ellipsoid plot of [1⋅C₆H₆]₂ ⋅C₆H₆ (ellipsoids 30 %; benzene solvate and H‐atoms except C₂ H₄ omitted; peripheral C‐atoms represented as spheres). Selected bond lengths [Å]: C29−C30 1.587(2), C59−C60 1.596(2), Al1−C29 1.9669(18), Al1−C30 1.9510(17), Al2−C59 1.9473(16), Al2−C60 1.9632(18).

Figure 3

Displacement ellipsoid plot of 2 (ellipsoids 30 %; H‐atoms except AlEt and AlC₃ H₃ O omitted; peripheral C‐atoms represented as spheres. ′=−x, y, $1/2$ −z). Selected bond lengths [Å]: Al−O2′ 1.802(2), Al−C29 2.0144(19), C29−C30 1.578(5), Al′−C31′ 2.0144(19), Al′−C33′ 2.089(4), C31′−C32′ 1.636(4), C32′−C33′ 1.353(6), C33′−O2′ 1.384(4).

Figure 4

DFT‐calculated free energy profile at the BP86‐D3(BJ)−C₆H₆/6‐311++G**//BP86/BS1 level (in kcal mol⁻¹) for the conversion of [1⋅C₆H₆]₂ to 2. Inset: Conversion of 3 to 4.

Scheme 3

Synthesis of 3, 4 and 5 (18‐c‐6=18‐crown‐6).

Figure 5

Displacement ellipsoid plots of 4⋅THF (ellipsoids 20 %) and 5⋅THF (ellipsoids 30 %). Disordered atoms, THF solvate and H‐atoms except AlC₃ H₄ O omitted; peripheral C‐atoms represented as spheres). Selected bond lengths [Å]: a) Al−C29 2.020(3), Al−C31 2.048(4), C29−C30 1.481(6), C30−C31 1.576(6), C31−O2 1.183(5). b) Al−C29 1.975(2), Al−O2 1.8095(16), C29−C30 1.523(4), C30−C31 1.317(5), C31−O2 1.432(3).