Cycloaddition Reactions of an Active Cyclic Phosphane/Borane Pair with Alkenes, Alkynes, and Carbon Dioxide

Abstract

The active six-membered cyclo-FLP 6 undergoes ar apid P/B addition reaction to carbond ioxide.A te levated temperature, the resultingh eterobicyclo[2.2.2]octane derivedproduct 7 undergoes ring opening and equilibrates with the cyclotetramer (7) 4 .Int he largemacrocyclic structure, four monomeric six-membered cyclo-FLP units are connected by four CO 2 molecules to form the supramolecular ring system.T he P/B cyclo-FLP 6 undergoes a variety of additional cycloadditionreactions.Coexistent pairs of active Lewis acids and bases were shown to undergo av ariety of remarkable reactions. [1] Such frustrated Lewis pairs often bind or activates mall molecules;t he heterolytic cleavage of dihydrogen is ap rominente xample, [2] which has resulted in the developmento fa ctivem etal-free hydrogenation catalysts. [3] Some intramolecular FLPs have shown unusual reactivities beyondt his, such as, for example, uncommon pathways of CO reduction [4] or reactions with nitric oxide to give new persistentn itroxide radicals. [5] The attachment of bulky substituents is mostly used to hindert he Lewis acid/ base pairs from forming inactive Lewis adducts, but geometric factors might become an additional supporting matter of choice. Incorporation of the central heteroatom components into cyclic structures serves to effectively hindert heir internal neutralization reaction. This has surprisingly seldom been used systematically. [6] We had recently devised as imple pathway to preparee xamples of the very active five-membered ring P/B FLP 3 [7] by ah ydroboration sequence (see Scheme 1) [8] .T he preparation of the isomeric six-membered P/B heterocycle 6 required ad ifferent strategy. This was achieved by as equence involving s-bond

Bis(1-bora-4-phosphorinane) ring closure at Cp*M (M = Fe, Co) complexes

“…Further work has exploited this scaffold for use in metal-free bond activation as a frustrated Lewis-Pair. 5,6 In 2020, we began researching the use of diphosphine ligands bearing pendant Lewis acids as moieties primed for metal-ligand cooperative behaviour. 7 In these instances, hydroboration of unsaturated pendant groups revealed boranyl moieties, which have found application in several elementary reactions, such as hydride transfer 7c and iodopyridine oxidative addition.…”

Solid-State NMR Techniques for the Structural Characterization of Cyclic Aggregates Based on Borane–Phosphane Frustrated Lewis Pairs

“…The six-membered cyclic B/P FLP 6 shown in Figure 24 adds carbon dioxide under mild conditions. Upon crystallization, a unique macrocyclic tetramer 7 with bridging CO 2 molecules between the individual cyclo-FLP units was obtained [85]. The spectroscopic features of this macrocycle were compared with those of a closely related monomeric B/B/P FLP adduct 8, which can be stabilized upon addition of one extra equivalent of B(C 6 F 5 ) 3 (BCF) to the starting material (cf.…”

Use of 5,10‐Disubstituted Dibenzoazaborines and Dibenzophosphaborines as Cyclic Supports of Frustrated Lewis Pairs for the Capture of CO2

“…Analogous saturated six-membered rings with the phosphorous and boron groups in 1/4 positions has been shown to react as FLP vs. alkenes, alkynes and CO 2 . [59] In the present study, the corresponding stationary points (minima and TSs) for the reaction between DHA derivatives containing P/B and N/B pairs in positions 9/10 with a variety of substituents and CO 2 have been obtained utilizing quantumchemical computations. Based on these studies, an equation has been developed linking the acid and basic properties of the isolated DHA derivatives to their ability to form CO 2 adducts.…”

“…In all structures, the pnictogen atom is linked to a H atom, a methyl group or an aromatic ring and the B atom is bonded to a substituted aromatic ring, hydroxyl groups, or Cl atoms. Analogous saturated six‐membered rings with the phosphorous and boron groups in 1/4 positions has been shown to react as FLP vs. alkenes, alkynes and CO 2 [59] …”