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

Abstract

The reactivity of a geometrically constrained phosphorus(III) complex bearing the N,N-bis(3,5-di-tert-butyl-2-phenolate)amide pincer ligand (P(ONO); 1) towards oxidants and reductants is explored. This compound can be readily oxidized to the phosphorus(V) dihalo-derivatives P(ONO)X where X=Cl (2), Br (3) and I (4). Attempts at isolating the analogous difluoride through oxidation of 1 were unsuccessful yielding only the hydrofluoride P(ONO)(H)F (5), however P(ONO)F (6) can be accessed via a halide exchange reaction of 2 with KF. Compound 2 can be employed as a precursor to novel cationic species through chloride ion displacement using strong Lewis bases. Thus, reaction of 2 with two or three molar equivalents of dimethylaminopyridine (DMAP) affords [P(ONO)(Cl)(DMAP) ] (7) and [P(ONO)(DMAP) ] (8). Reaction of 2 with the weaker bidentate base 2,2'-bipyridine (bipy) affords [P(ONO)(Cl)(bipy)] (9), although this species was only accessible upon addition of a halide abstracting agent. The dicationic tris(pyridine) adduct [P(ONO)(py) ] (10) is also accessible by reaction of 4 with pyridine. Oxidation of 1 using oxygen gas proceeds slowly and allows for the observation of two compounds, a mixed valence dimeric phosphorus(III)/phosphorus(V) compound [P(ONO)(μ -O)(μ :κ ,κ -ONO)P] (11) and the fully oxidized species [P(ONO)(μ -O)(μ :κ ,κ -ONO)P(O)] (12). Finally, reaction of 1 using KC results in the dimerization of the putative radical anion [P(ONO)] through formation of a P-P bond to afford [P(ONO)] (13). Reactions with TEMPO result in the formation of the trigonal bipyramidal species P(ONO)(TEMPO) (14).

Sterically Constrained Bicyclic Phosphines: A Class of Fascinating Compounds Suitable for Application in Small Molecule Activation and Coordination Chemistry

“…The difluoride of compound 6 was obtained in a high yield by direct treatment of the PC 3 phosphine with XeF 2 in acetonitrile at −78 °C ( 12 a , Scheme ) . In contrast, this simple and obvious procedure gave only a mixture of products [PF 2 ( 13 a ) and PHF derivatives] when the PNO 2 phosphine 2 (Scheme ) was applied . The pure difluoride 13 a was finally obtained in a low yield of 11 % by halogen exchange starting with the corresponding dichloride 13 b and potassium fluoride and heating of a suspension in toluene to 80 °C for five days (Scheme ) .…”

“…A dibromide ( 14 c ) was also obtained by an alternative route starting with the diketoamine and PBr 5 . Diiodides were generated by the reaction of 2 with elemental iodine ( 13 d ) or treatment of 12 a with BI 3 ( 12 d ) . The dibromides and diiodides represent rare examples of phosphorus(V) dihalides of the heavier halogens .…”

“…These dihalides are promising starting materials and potentially applicable for the generation of numerous secondary products, but only few reactions have been reported so far in the literature. Addition of nitrogen bases such as dimethylaminopyridine to the dichloro compound 13 b afforded mono‐ or dicationic species by the replacement of one or two chlorine atoms and the coordination of two or three of the nitrogen ligands to phosphorus . One or two isolated chloride anions are present as the counter ions.…”

“…The coordination number of the phosphorus atoms increases in all cationic species from five in the dichloride 13 b to six in the adducts. 2,2′‐Bipyridine reacted with 13 b only in the presence of a chlorine acceptor, Na[BAr F 4 ] (BAr F 4 =tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate), and only one chlorine atom was replaced by the chelating ligand . The starting compound 2 was partially recovered upon treatment of the diiodide 13 d with pyridine .…”

Insertion of a Nontrigonal Phosphorus Ligand into a Transition Metal-Hydride: Direct Access to a Metallohydrophosphorane

“…molecular symmetries C 2v , C s ) express enhanced biphilic reactivity. 33 - 37 For instance, C s -symmetric phosphorous triamide 1 inserts into E–H bonds (E = −OR, −NHR), 38,39 in some cases reversibly. This and related P -centered reactivity have been applied to a variety of stoichiometric and catalytic chemical transformations.…”