On the Ambiphilic Reactivity of Geometrically Constrained Phosphorus(III) and Arsenic(III) Compounds: Insights into Their Interaction with Ionic Substrates

Abstract

The ambiphilic nature of geometrically constrained Group 15 complexes bearing the N,N-bis(3,5-di-tert-butyl-2-phenolate)amide pincer ligand (ONO 3À )i se xplored. Despite their differing reactivity towards nucleophilic substrates with polarised element-hydrogen bonds (e.g.,N H 3 ), both the phosphorus(III), P(ONO)( 1a), anda rsenic(III), As(ONO)( 1b), compounds exhibit similar reactivity towards charged nucleophilesa nd electrophiles. Reactions of 1a and 1b with KOtBu or KNPh 2 afford anionicc omplexes in which the nucleophilic anion associates with the pnictogen centreÀ (Pn = P( 3a), As (3b)).C ompound 2a can subsequentlybe reacted with ap rotons ource or benzylbromide to afford the phosphorus(V) compounds (tBuO)HP(O-NO) (4a)a nd (tBuO)BzP(ONO) (5a), respectively,w hereas analogous arsenic(V) compounds are inaccessible.E lectrophilic substrates, such as HOTf and MeOTf, preferentially associate with the nitrogen atom of the ligand backbone of both 1a and 1b,g iving rise to cationic species that can be rationalised as either ammonium salts or as amine-stabilised phospheniumo ra rsenium complexes( [Pn{ON(H)O}] + (Pn = P (6a), As (6b)) and [Pn{ON(Me)O}] + (Pn = P( 7a), As (7b)). Reactiono f1a with an acid bearing an ucleophilic counteranion (such as HCl) gives rise to ap hosphorus(V) compound HPCl(ONO) (8a), whereas the analogous reaction with 1b results in the addition of HCl across one of the AsÀOb onds to afford ClAs{(H)ONO} (8b). Functionalisation at both the pnictogenc entre and the ligand backbone is also possible by reactiono f7a/7b with KOtBu, which affords the neutral species (tBuO)Pn{ON(Me)O} (Pn = P( 9a), As (9b)).T he ambiphilic reactivity of theseg eometrically constrainedc omplexes allowss omei nsight into the mechanism of reactivity of 1a towardssmall molecules, such as ammonia and water.

On the Redox Reactivity of a Geometrically Constrained Phosphorus(III) Compound

“…Studies by Arduengo, Radosevich, Kinjo, and our own research group, have demonstrated that the distorted T‐shaped phosphorus(III) compounds pictured in Figure are capable of undergoing formal oxidative addition reactions to afford trigonal bipyramidal phosphorus(V) compounds. The reactivity of such species towards common nucleophiles and electrophiles seems to highlight that such reactions are unlikely to proceed in a concerted fashion at the phosphorus centre, but rather that the ligand framework is intimately involved in such reactions . Several theoretical studies have also corroborated this hypothesis …”

“…The reactivity of such species towards common nucleophiles and electrophiles seemst oh ighlight that such reactions are unlikely to proceed in ac oncerted fashion at the phosphorus centre, but rather that the ligand framework is intimately involved in such reactions. [7,8] Severalt heoretical studies have also corroboratedt his hypothesis. [9,10] This class of compounds forms part of ar apidly increasing family of main group element-containing species that have been shown to activate small molecule substrates, [11] the most notable of which are alkyl(amino)c arbenes (AACs), [12] lowo xidationstate compounds of the triel and tetrel elements, [13,14] and frustratedL ewisp airs (FLPs).…”

“…The P−O bond lengths (1.897(1) and 1.932(1) Å) are unsymmetrical and significantly lengthened relative to those of 1 , whereas the P−N bond is very similar to that of the parent complex. This is in analogy to the structures of the tert ‐butoxide and diphenylamide adducts of 1 that have recently been reported . Coupled with the 1 H NMR data recorded for 13 the long P−O bonds suggest lability of one of the phenoxide arms in solution.…”

“…Thermal ellipsoidss et at 50 %p robability;h ydrogen atoms and solvent of crystallisationa re omitted for clarity. Selectedb ond lengths[ ]and angles [8]: 2:P1 ÀN1 1.696(1), P1ÀO1 1.667(1), P1ÀO2 1.667(1), P1ÀCl12.038(1), P1À Cl2 2.047(1); O1-P1-O2 167.91 (5), O1-P1-N188.86(4), O1-P1-Cl1 95.71(4), O1-P1-Cl2 87.52 (3), O2-P1-N18 8.71(4), O2-P1-Cl1 96.21(4), O2-P1-Cl2 87.49(4), N1-P1-Cl1 111.11 (4), N1-P1-Cl2 143.98(4), Cl1-P1-Cl2 104.91 (2). 3:P 1-N1 1.702(4), P1-O1 1.661(3), P1-O21 .663(3), P1-Br1 2.219(2), P1-Br 2.235(2);O 1-P1-O2 165.42 (19), O1-P1-N188.51 (17), O1-P1-Br1 96.98 (13), O1-P1-Br2 86.40 (12),O 2-P1-N18 9.94 (18), O2-P1-Br1 97.…”

“…(6; right). Thermal ellipsoids set at 50 %p robability;hydrogen atoms, with the exception of H1 in 5 and any disordered component omittedf or clarity.Selectedb ond lengths []and angles [8]: 5:P 1 ÀN1 1.689 (3),P 1 ÀO1 1.663 (2), P1ÀO2 1.654 (2), P1ÀF1 1.635 (3), P1ÀH1 1.36 (2);O 1-P1-O2 179.13 (12), O1-P1-N1 89.54 (12), O1-P1-F1 90.11 (10), O1-P1-H189.6 (7), O2-P1-N1 89.59 (11), O2-P1-F1 90.13 (10), O2-P1-H1 91.0 (7), N1-P1-F1106.30 (15), N1-P1-H1141.5 (17), F1-P1-H1112.2 (18). 6:P1 ÀN1 1.681 (3), P1ÀO1 1.655(2) P1ÀO2 1.650(2), 1.538 (2);O1-P1-O2 179.05 (11), O1-P1-N18 9.51 (11), O1-P1-F1 90.25 (8), O2-P1-N1 89.53 (11), O2-P1-F190.34 (8), N1-P1-F1 128.00 (11), F1-P1-F1' 104.0 (2).…”