Fluorinated antimony(v) derivatives: strong Lewis acidic properties and application to the complexation of formaldehyde in aqueous solutions

Coordination of a stibine oxide to a Lewis acidic stiborane at the upper rim of the biphenylene backbone

The biphenylene backbone is used to support a stibine oxide stabilized intramolecularly by a SbO → Sb(v) donor–acceptor interaction.

Hydrogen activation using a novel tribenzyltin Lewis acid

Over the last decade there has been an explosion in the reactivity and applications of frustrated Lewis pair (FLP) chemistry. Despite this, the Lewis acids (LAs) in these transformations are often boranes, with heavier p-block elements receiving surprisingly little attention. The novel LA Bn₃SnOTf (1) has been synthesized from simple, inexpensive starting materials and has been spectroscopically and structurally characterized. Subtle modulation of the electronics at the tin centre has led to an increase in its Lewis acidity in comparison with previously reported R₃SnOTf LAs, and has facilitated low temperature hydrogen activation and imine hydrogenation. Deactivation pathways of the R₃Sn⁺ LA core have also been investigated.This article is part of the themed issue 'Frustrated Lewis pair chemistry'.

Attempted synthesis of ortho-phenylene phosphino-tritylium cations

With the synthesis of ortho-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 HBF₄ in the presence of trifluoroacetic anhydride in order to generate the corresponding cations. Instead of the targeted ortho-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 (3⁺) and 7,7-bis(phenyl)-8,8-bis(isopropyl)-7-phosphoniabicyclo[4.2.0]octa-1,3,5-triene (4⁺), 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 (5⁺) and 5,10-dihydro-5,5-di(isopropyl)-10-phenyl-acridophosphinium (6⁺) as tetrafluoroborate salts. These reactions suggest the involvement of ortho-phenylene phosphino-tritylium cations, which would be obtained by dissociation of the R₃P⁺-CAr₃ bonds in 4⁺ and 5⁺This article is part of the themed issue 'Frustrated Lewis pair chemistry'.

Activation of an Au-Cl Bond by a Pendent SbIII Lewis Acid: Impact on Structure and Catalytic Activity

With the objective of identifying new coordination modes of ambiphilic ligands, we have investigated the bidentate Sb/P ligands (o-(Ph₂ P)C₆ H₄ )SbCl₂ (L^Cl ) and (o-(Ph₂ P)C₆ H₄ )SbPh₂ (L^Ph ). Reaction of these ligands with (tht)AuCl affords the monoligated species L^Cl AuCl (1) and L^Ph AuCl (2), respectively, in which the antimony centers are only weakly engaged with the coordinated gold atom. Treatment of 1 with PPh₃ induces an intramolecular transfer of a chloride ligand from gold to antimony to form the zwitterionic species o-(Cl₃ Sb)C₆ H₄ (Ph₂ P)Au(PPh₃ ) (3). Natural bond orbital (NBO) calculations show that the antimony and gold centers are involved in weak Sb→Au and Au→Sb interactions, the latter reflecting the Lewis acidity of the pendent antimony group. Finally, we demonstrate that the ability of the antimony center in 1 to abstract a gold-bound chloride in the presence of a Lewis basic substrate may be utilized to activate the gold center for the electrophilic cycloisomerization of propargylic amides.