Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

Abstract

In this contribution, we discuss the reactivity of different phosphanes (XPhos (1a), t BuXPhos (1b), and Mes 2 PEt (1c)) and tris(pentafluorophenyl)borane (and in one case, EtB(C 6 F 5 ) 2 ) against small molecules. 1a/B(C 6 F 5 ) 3 , 1b/B(C 6 F 5 ) 3 , and 1c/B(C 6 F 5 ) 3 split dihydrogen heterolytically to yield the phosphonium borate salts 2a, 2b, and 2c, respectively. Control experiments with D 2 gave the respective deuterated phosphonium borates 2a-D 2 , 2b-D 2 , and 2c-D 2 . The FLP systems 1b/ B(C 6 F 5 ) 3 and 1c/B(C 6 F 5 ) 3 underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates 3b and 3c. As well, the Lewis pair EtB(C 6 F 5 ) 2 and Mes 2 PEt reacted with ethene to yield the corresponding 1,2-addition product 3d. At low temperature, the FLP systems 1a/B(C 6 F 5 ) 3 and 1c/B(C 6 F 5 ) 3 coordinated carbon dioxide (4a, 4c). The new compounds 2a, 2b, 3b, 3c, 3d, 4a, and 4c were characterized by X-ray crystal structure analyses.

Carbene‐9‐BBN Ring Expansions as a Route to Intramolecular Frustrated Lewis Pairs for CO2 Reduction

“…This stands in contrast to FLPs derived from strong Lewis acids in which only stoichiometric reductions are observed. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] This situation is analogous to the recently reported work from Fontaine and co-workers, in which they exploited intramolecular FLPs for similar CO 2 reductions. [27] In summary, herein we have reported the insertion of CÀN bonds of an N-heterocyclic carbene into 9-BBN.…”

Reactivity of a Frustrated Lewis Pair and Small‐Molecule Activation by an Isolable Arduengo CarbeneB{3,5‐(CF3)2C6H3}3 Complex

“…Another important issue in FLP chemistry is CO 2 fixation; [38] consequently, the reactivity of compound 4 a towards carbon dioxide was studied. When CO 2 was bubbled through a clear solution of compound 4 a in hot benzene (T = 60 8C), a white precipitate formed instantaneously and the CO 2 adduct (7) could be isolated in 66 % yield by filtration and crystallisation from CH 2 Cl 2 /n-hexane ( Figure 3).…”

Isolation and Reactivity of a Frustrated N‐Heterocyclic Carbene‐Borane

“…The capture of carbon dioxide is a well‐established reaction for many FLP systems,, whereas CO 2 fixation can also be accomplished by N‐heterocyclic carbenes without any additional Lewis acid . For imidazolin‐2‐ylidenes, the stability of the resulting imidazolium‐2‐carboxylates depends strongly on the substitution pattern, and the adduct 1· CO 2 proved significantly less stable than adducts of NHCs with smaller substituents , .…”