Themed collection Frustrated Lewis Pairs

In the six short years following our initial report, the areas impacted by the chemistry of “frustrated Lewis pairs” (FLPs) continue to grow most dramatically. The collection of papers presented in this issue of Dalton Transactions reflect the broadening impact and excitement of the new field of FLP chemistry.

Two 2-[bis(pentafluorophenyl)boryl]-N,N-dialkylanilines, exemplifying a new class of intramolecular frustrated B/N Lewis pairs, can activate hydrogen at near ambient conditions; besides, one of them can hydrogenate imines and enamines in a catalytic fashion.

A camphor based chiral phosphonium hydrido borate zwitterion was synthesised and successfully applied in the enantioselective hydrogenation of imines with selectivities up to 76% ee. The high stability of the novel chiral FLP-system enables effective recycling of the metal-free catalyst.

Tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF₁₈) forms a Frustrated Lewis pair with 2,2,6,6-tetramethylpiperidine, which cleaves H₂ to provide the novel bridging borohydride [μ-H(BArF₁₈)₂]⁻.

Explicit solvent molecular dynamics simulations of the (^tBu)₃P/B(C₆F₅)₃ pair in toluene allowed the estimation of the degree of intermolecular association and the population of encounter complex states in solution phase.

Exchange reactions of tBu₃P(CO₂)B(C₆F₅)₂Cl afford tBu₃P(CO₂)B(C₆F₅)₂(OSO₂CF₃), tBu₃P(CO₂)Al(C₆F₅)₃ and [tBu₃P(CO₂)TiCp₂Cl][B(C₆F₅)₄].

Al(C₆F₅)₃-based classical and frustrated Lewis pairs exhibit exceptional activity in Lewis pair polymerization of conjugated polar alkenes and renewable methylene butyrolactones.

The reaction of 4-ethynyl-2,6-lutidine, (2,6-Me₂)(4-HCC)C₅H₂N, with the Lewis acid B(C₆F₅)₃ leads to the zwitterion [(2,6-Me₂)(4-(C₆F₅)₃BCC)-C₅H₂NH], whereas its reactions with MR₃ (M = Al, Ga, In; R = Me, Et) lead exclusively to metallation of the ethynyl group and the products [(2,6-Me₂)(R₂MCC)C₅H₂N].

The reactivity of E–H bonds (E = S, O, Cl) with Pt(II) complexes ligated by an N-heterocyclic phosphido-containing diphosphine ligand have been investigated.

The cooperative nature of small molecule activation with FLPs is analysed in terms of many-body contributions to energy and deformation density.

The synthesis of several electron poor allenes is described and their application as Lewis acids for the formation of organic frustrated Lewis pairs evaluated.

The frustrated Lewis pair B(C₆F₅)₃/PtBu₃ reacts with 2,4-hexadiyne to give mixture of the 1,2- and 1,4-addition products.

Computations show the promise of using the previously designed catalysts to promote intramolecular hydroaminations of non-activated aminoalkenes affording nitrogen heterocycles.

The fixation of carbon dioxide and related small molecules is efficiently accomplished by a bifunctional frustrated pyrazolylborane Lewis pair; CO₂ fixation presumably proceeds via a van der Waals complex with a low energy barrier of approximately 7.2 kcal mol⁻¹.

Several interesting facets of FLP–N₂O complexes were investigated computationally, including the preference for the BONNP core and the trans–trans structure, borane exchange reactions, and possibilities for N₂O derivatization.

The bulky borane tris(2,2,2-perfluorobiphenyl)borane is crystallographically characterised, and is used with nitrogen based Lewis bases to synthesize novel ‘frustrated Lewis pairs’ that activate dihydrogen.

The heterolytic splitting of hydrogen by two types of [2.2]paracyclophane derived bisphosphines (1, 2a and 2b) in combination with tris(pentafluorophenyl)borane (3) at room temperature is described.

Titanium–phosphorus frustrated Lewis pairs (FLPs) based on titanocene–phosphinoaryloxide complexes have been studied..

Al–P-based dimers with coordinatively saturated Al and P atoms act as masked frustrated Lewis pairs by dipolar activation of CO₂ and phenyl isocyanate.