Design principles in frustrated Lewis pair catalysis for the functionalization of carbon dioxide and heterocycles

Abstract

This is the peer reviewed version of the following article: [Design Principles in Frustrated Lewis KeywordsFrustrated Lewis pairs, Ambiphilic molecules, Boron, Aluminum, Carbon dioxide, Methanol, C-H activation. Highlights 1.Phosphine-aluminum frustrated Lewis pairs (FLPs) can activate CO2 but show significant stability issues. 2.The Lewis acidity and basicity need to be fine-tuned to the desired reactivity for efficient FLP catalysis.3. FLP catalysts need to generate strong hydrides to reduce catalytically carbon dioxide. 4.Transition metal catalysis can serve as an inspiration for the design of metal-free catalysts for many transformations, including the borylation of heteroarenes. Graphical abstract AbstractThis account describes our work on the use of ambiphilic molecules as catalysts for the reduction of carbon dioxide. Starting with the discovery that aluminum ambiphilic species (Me2PCH2AlMe2)2 (1) and Al(C6H4-PPh3)3 (5) could coordinate CO2 but showed significant instability, we found that phosphinoborane Ph2P-2-Bcat-C6H4 (7) was an exceptional catalyst for the hydroboration of CO2 to methoxyboranes, a molecule that can be readily hydrolyzed to methanol. A mechanistic investigation allowed us to outline the similarities between the catalytic activity of frustrated Lewis pairs (FLPs) and that of transition metal complexes. We were able to extrapolate four important guidelines, described in this account, to synthesize efficient metal-free catalysts. We demonstrate that using these concepts it was possible to rationally design FLP catalysts for the C-H borylation of heteroarenes.

Halogenated triarylboranes: synthesis, properties and applications in catalysis

“…Since the first example of CO2 activation by FLPs in 2009, 140 its capture and further utilisation has been an attractive target for chemists. 141 In the case of CO2 activation, the basic phosphine attacks the electrophilic carbon atom, whilst one of the electron rich oxygen atoms donates into the empty p-orbital of the borane (Scheme 21).…”

Aldehyde Carboxylation: A Concise DFT Mechanistic Study and a Hypothetical Role of CO2 in the Origin of Life

“…Based on the precedents outlined in the Introduction, we envisaged that the activation of CO 2 would be critical to mitigate the selectivity of the carboxylation reaction of al-Scheme 1 (A) -Keto acid formation reactions of aldehyde under CO 2 atmosphere, and attempts at (B) CO 2 reduction with aldehydes, (C) carboxylation, and (D) oxidation with water and air. [11][12][13][14] Particularly, nucleophilic catalysts (i.e., NHCs, amidine, diamines, guanidines, and DMAP derivatives) have been employed in CO 2 activation by forming CO 2 -nucleophile adducts. 15,16 For example, a single-crystal structure analysis of TBD-CO 2 (TBD: 1,5,7-triazabicyclodec-5-ene) complex showed that intramolecular hydrogen-bonding may contribute to the stabilization of the complex.…”

Diaminophosphinoboranes: effective reagents for phosphinoboration of CO2

“…Increasingly stringent environmental standards are prompting us to look for clean and efficient methods for the synthesis of organic compounds. In recent years, much attention has been focused on reactions employing simple, nonmetallic P,Bbased [1][2][3][4][5][6] systems that can activate waste gases such as CO, 7,8 CO 2 , [9][10][11][12][13] NO x , 10,14 SO 2 , 14,15 or even H 2 . 5,9,[16][17][18][19] These metal-free reactions not only involve easily accessible and inexpensive gaseous reagents as the feedstock but also enable the straightforward and efficient synthesis of organic compounds through the functionalization of small inorganic molecules.…”