Preorganized Frustrated Lewis Pairs

Abstract

Geminal frustrated Lewis pairs (FLPs) are expected to exhibit increased reactivity when the donor and acceptor sites are perfectly aligned. This is shown for reactions of the nonfluorinated FLP tBu(2)PCH(2)BPh(2) with H(2), CO(2), and isocyanates and supported computationally.

Boron-mediated activation of carbon dioxide

“…The same year, Slootweg, Lammertsma et al used an intramolecular FLP system with a methylene linker between a phosphine and a non-fluorinated borane moieties. Interestingly, despite a less Lewis acidic borane, CO 2 is activated and compound 14 isolated [33]. A similar structure was also found with an alane moiety in place of the borane [34].…”

Frustrated Lewis Pair Chemistry: Development and Perspectives

“…Lammertsma and co-workers [99] prepared the geminal phosphine-borane species t Bu 2 PCH 2 BPh 2 and demonstrated the formation of the CO 2 adduct t Bu 2 PCH 2 BPh 2 (CO 2 ) (113; Scheme 45) despite the dramatic reduction in Lewis acidity. Tamm and co-workers [100] prepared the intramolecular N/B FLP based on the pyrazolyl-borane (C 3 H t Bu 2 N 2 )B(C 6 F 5 ) 2 and showed binding of CO 2 to give, in a strongly exothermic reaction, (C 3 H t Bu 2 N 2 )B(C 6 F 5 ) 2 (CO 2 ) (114).…”

Structurally simple complexes of CO2

“…104 Because of this stability, reactions at the CO2 center can be accomplished without its release, facilitating its reduction to, for example, carbon monoxide 105,106 Many borane-based FLPs also bind CO2 to form stable adducts, requiring the use of forcing conditions (typically high temperature and vacuum) to release the CO2. 109,110 Again, the fact that these complexes are so stable is not necessarily a disadvantage, depending on their ultimate use. Easily-reversible binding of carbon dioxide requires the formation of weak interactions between the Lewis acid and the base, and there are already examples of FLPs that bind CO2 and release it at remarkably low temperatures (~ −20°C).…”