title: 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 (ONO3-) is explored. Despite their differing reactivity towards nucleophilic substrates with polarised element-hydrogen bonds (e.g., NH3), both the phosphorus(III), P(ONO) (1 a), and arsenic(III), As(ONO) (1 b), compounds exhibit similar reactivity towards charged nucleophiles and electrophiles. Reactions of 1 a and 1 b with KOtBu or KNPh2afford anionic complexes in which the nucleophilic anion associates with the pnictogen centre ([(tBuO)Pn(ONO)]-(Pn=P (2 a), As (2 b)) and [(Ph2N)Pn(ONO)]-(Pn=P (3 a), As (3 b)). Compound 2 a can subsequently be reacted with a proton source or benzylbromide to afford the phosphorus(V) compounds (tBuO)HP(ONO) (4 a) and (tBuO)BzP(ONO) (5 a), respectively, whereas analogous arsenic(V) compounds are inaccessible. Electrophilic substrates, such as HOTf and MeOTf, preferentially associate with the nitrogen atom of the ligand backbone of both 1 a and 1 b, giving rise to cationic species that can be rationalised as either ammonium salts or as amine-stabilised phosphenium or arsenium complexes ([Pn{ON(H)O}]+(Pn=P (6 a), As (6 b)) and [Pn{ON(Me)O}]+(Pn=P (7 a), As (7 b)). Reaction of 1 a with an acid bearing a nucleophilic counteranion (such as HCl) gives rise to a phosphorus(V) compound HPCl(ONO) (8 a), whereas the analogous reaction with 1 b results in the addition of HCl across one of the As-O bonds to afford ClAs{(H)ONO} (8 b). Functionalisation at both the pnictogen centre and the ligand backbone is also possible by reaction of 7 a/7 b with KOtBu, which affords the neutral species (tBuO)Pn{ON(Me)O} (Pn=P (9 a), As (9 b)). The ambiphilic reactivity of these geometrically constrained complexes allows some insight into the mechanism of reactivity of 1 a towards small molecules, such as ammonia and water.
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Robinson
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Siu-Kwan
authors.initials: SK
authors.lastname: Lo
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: De Rosa
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Aldridge
authors.affiliation: Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK. jose.goicoechea@chem.ox.ac.uk.
authors.forename: Jose M
authors.identifier: http://orcid.org/0000-0002-7311-1663
authors.initials: JM
authors.lastname: Goicoechea
keywords: arsenic; phosphorus; reaction mechanism; structure elucidation