Diverse Cooperative Reactivity at a Square Planar Aluminium Complex and Catalytic Reduction of CO₂

Abstract

The use of a sterically demanding pincer ligand to prepare an unusual square planar aluminium complex is reported. Due to the constrained geometry imposed by the ligand scaffold, this four-coordinate aluminium centre remains Lewis acidic and reacts via differing metal-ligand cooperative pathways for activating ketones and CO 2 . It is also a rare example of a single-component aluminium system for the catalytic reduction of CO 2 to a methanol equivalent at room temperature.

Quest for Active Species in Al/B-Catalyzed CO2 Hydrosilylation

“…Like 4, the solid-state structure of 6 exhibits two bridging hydrides between aluminum and boron atoms, having a similar Al−B bond distance of 2.288(3) Å (Figure 5 Contrary to our expectation, the reaction of 1 with the more Lewis acidic B(C 6 F 5 ) 3 led to multiple rearranged products. One of the products, (2-Me 2 NCH 2 C 6 H 4 )Al(C 6 F 5 ) 2 (7), was crystallized from a mixture of toluene and n-pentane (Scheme 3 and Figure 6). X-ray diffraction studies on 7 showed that the aluminum center adopts the coordination number of 4, acquiring a tetrahedral geometry.…”

“…Catalytic reduction of carbon dioxide (CO 2 ) is an attractive route for obtaining C 1 feedstock. − As an alternative to transition metals, main-group elements were employed to prepare catalytically active compounds for CO 2 reduction to obtain formic acid, formaldehyde, methanol, and methane using dihydrogen (H 2 ), boranes, and silanes as hydrogen sources. − Due to its abundance in the earth’s crust and low toxicity, aluminum is a potential metal for designing catalysts for CO 2 reduction. − One of the earliest reports of CO 2 reduction to methanol by aluminum, using LiAlH 4 , appeared in 1948 . This inspired chemists to design molecular aluminum hydrides that could reduce CO 2 in a stoichiometric manner. − With the advent of frustrated Lewis pairs (FLPs), − the Mes 3 P­(AlX 3 ) system converted CO 2 to methanol using ammonia borane as a hydrogen source. ,, While stoichiometric reductions were successfully performed using aluminum compounds, , catalytic conversions are challenging.…”

“…Found: C, 48.97; H, 2.36. 1 H NMR (C 6 D 6 , 500 MHz): δ 7.09 (d, 6H, J = 1.7 Hz, o-C 6 H 3 Cl 2 ),7.17 (t, 3H, J = 1.65 Hz, p-C 6 H 3 Cl 2 ) 13. C{ 1 H} NMR (C 6 D 6 , 126 MHz): δ 132.4 (s, o-C 6 H 3 Cl 2 ), 135.3 (s, p-C 6 H 3 Cl 2 ), 135.5 (s, m-C 6 H 3 Cl 2 ), 144.5 (s, i-C 6 H 3 Cl 2 ).…”

“…Figure7. Computed enthalpy profile (Gibbs free energy provided in parentheses) at room temperature for the reaction of 1 with CO 2 .…”

Accelerating σ-Bond Metathesis at Sn(II) Centers

“…σ-Bond metathesis is the rate-determining step in this catalytic cycle and is similarly rate-determining in many main-group hydride catalytic cycles . The use of main-group hydride catalysis has seen particular application in CO 2 valorization through hydrofunctionalization. − …”