Attempted synthesis of ortho -phenylene phosphino-tritylium cations

Abstract

With the synthesis of -phenylene phosphino-tritylium cations as an objective, we generated (2-lithiophenyl)diphenylphosphine and (2-lithiophenyl)di-isopropylphosphine and allowed these organolithium reagents to react with benzophenone. The resulting phosphino-triarylcarbinols were allowed to react with HBF in the presence of trifluoroacetic anhydride in order to generate the corresponding cations. Instead of the targeted -phenylene phosphino-tritylium, the cations formed in these reactions were identified as the four-membered phosphonium species 7,7-bis(phenyl)-8,8-bis(phenyl)-7-phosphoniabicyclo[4.2.0]octa-1,3,5-triene () and 7,7-bis(phenyl)-8,8-bis(isopropyl)-7-phosphoniabicyclo[4.2.0]octa-1,3,5-triene (), which were both isolated as tetrafluoroborate salts. The structure of these compounds has been confirmed by X-ray analysis. These new cations are thermally unstable and isomerize into the corresponding 5,10-dihydro-5,5-diphenyl-10-phenyl-acridophosphinium () and 5,10-dihydro-5,5-di(isopropyl)-10-phenyl-acridophosphinium () as tetrafluoroborate salts. These reactions suggest the involvement of -phenylene phosphino-tritylium cations, which would be obtained by dissociation of the RP-CAr bonds in andThis article is part of the themed issue 'Frustrated Lewis pair chemistry'.

Stabilized Carbenium Ions as Latent, Z‐type Ligands

“…In other words,acarbenium ion should be am ore potent s-acceptor ligand, leading to ag reater enhancement in the hardness and Lewis acidity of the metal atom. Carbenium ions,which have already received interest as ligands for transition metals, [9] may also present ah igher chemical resilience,i np articular to oxidative conditions.W ith av iew to capitalize on these attributes,w e thus decided to reengage in carbenium chemistry [10] and explore the synthesis and properties of carbenium-based analogues [11] of known L/Z ambiphilic boron-containing ligands ( Figure 1C). [3a] Thec arbenium-based systems described herein bear similarities with phosphine ligands functionalized by carbon-based redox non-innocent moieties [12] while also adding to ongoing efforts in the chemistry of cationic phosphines as ligands for late-transition-metal catalysts.…”

Frustrated Lewis pair chemistry

“…Gowda & Chen [7] apply FLPs in selective polymerizations of butyrolactones. Gabbaï and co-workers [8] report on efforts to combine carbon-Lewis acids with phosphines, while Stephan and co-workers [9] describe the use of gallium and indium Lewis acids in FLP chemistry. The issue is concluded with an article by Ashley and co-workers [10] in which they describe the activation of H 2 by a tin-based Lewis acid.…”

Carbocations as Secondary Coordination Sphere Z-Type Ligands – Anion-Induced Au(I)/Au(III) Oxidation and Impact on Reactivity

“…Our original efforts toward the synthesis of such species focused on cations such as [o-Ph2P(C6H4)CPh2] + . 18 We found that this formulation actually existed as four-membered phosphonium species as a result of an intramolecular cyclization resulting from nucleophilic attack of the methylium carbon atom by the phosphino group. To disfavor phosphonium ion formation, we have now decided to pursue the introduction of methylium units where the carbocation is substantially stabilized as in the case of acridinium and xanthylium derivatives.…”