Ad imethylxanthene-based phosphine/borane frustrated Lewis pair (FLP) is shown to effect reversible CÀH activation, cleaving phenylacetylene, PhCCH, to give an equilibrium mixture of the free FLP and phosphoniuma cetylide in CD 2 Cl 2 solution at room temperature. This systema lso reacts with BÀHb onds although in ad ifferentf ashion:r eactions with HBpin and HBcatp roceed via CÀB/BÀHm etathe-sis, leading to replacement of the -B(C 6 F 5 ) 2 Lewis acid component by -Bpin/-Bcat, and transfer of HB(C 6 F 5 ) 2 to the phosphine Lewis base. Thist ransformationu nderpins the ability of the FLP to catalyze the hydroboration of alkynes by HBpin: the active species is derived from the HB(C 6 F 5 ) 2 fragment generated in this exchangep rocess.Scheme1.Stoichiometric reactions( a) between 1a and PhCCH;a nd (b) between 1b and PhCCH.

We report two BNB-type frustrated Lewis pairs which feature an acceptor-donor-acceptor functionalized cavity, and which differ in the nature of the B-bound fluoroaryl group (C 6 F 5 vs. C 6 H 3 (CF 3 ) 2 -3,5, Ar f ). These receptor systems are capable of capturing gaseous CO, and in the case of the -BAr f 2 system this can be shown to occur in reversible fashion at/above room temperature. For both systems, the binding event is accompanied by migration of one of the aryl substituents to the electrophilic carbon of the CO guest. Experiments utilizing an additional equivalent of P t Bu 3 allow the initially formed (non-migrated) CO adduct to be identified and trapped (via demethylation), while also establishing the reversibility of the B-to-C migration process. When partnered with the slightly less Lewis acidic -BAr f 2 substituent, this reversibility allows for release of the captured carbon monoxide in the temperature range 40-70 8C, and the possibility for CO sensing, making use of the associated colourless to orange/ red colour change.

We report two BNB-type frustrated Lewis pairs which feature an acceptor-donor-acceptor functionalized cavity, and which differ in the nature of the B-bound fluoroaryl group (C 6 F 5 vs. C 6 H 3 (CF 3 ) 2 -3,5, Ar f ). These receptor systems are capable of capturing gaseous CO, and in the case of the -BAr f 2 system this can be shown to occur in reversible fashion at/above room temperature. For both systems, the binding event is accompanied by migration of one of the aryl substituents to the electrophilic carbon of the CO guest. Experiments utilizing an additional equivalent of P t Bu 3 allow the initially formed (non-migrated) CO adduct to be identified and trapped (via demethylation), while also establishing the reversibility of the B-to-C migration process. When partnered with the slightly less Lewis acidic -BAr f 2 substituent, this reversibility allows for release of the captured carbon monoxide in the temperature range 40-70 8C, and the possibility for CO sensing, making use of the associated colourless to orange/ red colour change.

We present convenient syntheses of a range of PNP‐type phosphines which feature a pair of ortho‐functionalized ArPPh2 moieties linked via a central NMe unit, but which differ in the nature of the additional backbone ‘tether’ linking the aryl groups. These comprise the acyclic system bis(2‐diphenylphosphinophenyl)methylamine, together with related systems centred around 5‐, 6‐ and 7‐membered heterocycles. Structurally, contraction of the backbone tether causes the phosphine centres to be projected further apart, and to be more constrained torsionally to the plane containing the NMe unit. In terms of potential frustrated Lewis pair (FLP) reactivity, the conformationally more flexible systems based on an acyclic linker or a cyclic core featuring a 7‐membered ring, are capable of achieving P−B bond formation and generating a classical Lewis adduct with B(C6F5)3. The less flexible carbazole‐derived compound (featuring a five membered heterocyclic core) gives rise to an FLP at room temperature, and an equilibrium mixture of frustrated and classical Lewis pairs at lower temperatures. Most interestingly, the PNP system based on a central six‐membered acridine ring ‐ which gives rise to the shortest contacts in the solid state between phosphorus and the N‐bound methyl group – undergoes C−H activation in the presence of B(C6F5)3, resulting in the formation of B−H and P−C bonds.

Dedicated to a colleague and friend, Cameron Jones, on the occasion of his 60 th birthdayThe reactivity towards SiÀ H and SnÀ H bonds of a dimethylxanthene-based frustrated Lewis pair featuring À P i Pr 2 and À B(C 6 F 5 ) 2 functions in the 4-, and 5-positions is reported. In the case of silanes, greater steric bulk appears to impede reactivity, with only PhSiH 3 and SiH 4 showing unambiguous evidence for SiÀ H bond activation. In the case of PhSiH 3 , the silylphosphonium borohydride 1 iPr (SiH 2 Ph)(H) is formed by SiÀ H bond activation across the P/B manifold. 1 iPr (SiH 2 Ph)(H) loses PhSiH 3 in hydrocarbon solution and therefore can only be crystallized from the neat silane. On heating, it undergoes a metathesis process leading to installation of the À SiH 2 Ph function at the 5-position of the xanthene scaffold, with accompanying migration of the boryl group (as Piers' borane, HB(C 6 F 5 ) 2 ) to the phosphine. Similar chemistry is observed with SiH 4 (although occurring much more readily), and such processes are thought to be mechanistically similar to related rearrangements occurring with the boranes HBpin and HBcat. By contrast, the activation of the weaker SnÀ H bonds found in stannanes occurs more readily, even for bulkier substrates, and the stannylphosphonium borohydrides 1 iPr (Sn n Bu 3 )(H) and 1 iPr (SnPh 3 )(H) are obtained from the room temperature reactions with n Bu 3 SnH and Ph 3 SnH, respectively.