Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry.

Invited for the cover of this issue are the groups of M. Haas, G. Gescheidt and H. Grützmacher from the Graz University of Technology and the ETH Zürich. The image depicts a phosphorus mine, where the workers are acid chlorides using their shovels and red phosphorus to provide the chemicals necessary to produce novel reagents. Read the full text of the article at 10.1002/chem.202302535.

Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry.

Herein, we present a convenient synthesis for symmetrical and mixed substituted tris(acyl)phosphines (TAPs) starting from red phosphorus. All TAPs exhibit a phosphaalkene-acylphosphine equilibrium, which was investigated in detail by variable-temperature (VT) NMR spectroscopy supported by density-functional theory (DFT) calculations. Depending on the substituents, two phosphaalkene derivatives and ten acylphosphine derivatives could be isolated. NMR spectroscopy and single-crystal X-ray crystallography enabled a clear structural assignment of these compounds. Oxidation of selected TAPs led to the formation of the corresponding tris(acyl)phosphine oxides (TAPOs). Furthermore, their spectroscopic properties as well as their photochemistry was investigated. Especially, the TAPO compounds were evaluated for their suitability as photoinitiators by CIDNP spectroscopy, photobleaching measurements and by storage stability tests.

Bis(acyl)phosphide - Ambidentate Ligands for the Synthesis of Group 14 and 15 Main Group Element Compounds.

The reactivity of the bis(acyl)phosphide ion [P(COR)2 ]- (BAP- , R=Ph, Mes) with silicon halides SiX4 (X=Cl, Br) and pnictogen chlorides ECl3 (E=As, Sb and Bi) was investigated. The reaction with SiX4 leads to the hexacoordinate silanes SiX2 (BAP)2 in which BAP- is coordinated in the chelating κ2 -O,O' mode, analogously to acac- . Unexpectedly, the coordination behaviour of BAP- differs from the one of acac- in the interpnictogen compounds E(BAP)3 (E=As, Sb) in which the formation of E-P bonds is favoured over κ2 -O,O' chelation via the oxygen centres. Finally, the reaction of BiCl3 with three equivalents of Na(BAP) leads to the formation of red, crystalline Bi2 (BAP)4 , an air stable dibismuthine, as product of a redox reaction.

Transient Dipnictyl Analogues of Acrylamides, R-E=E'-CONR2 , and a Related Diphosphadigalletane from Na[OCP] and (R2 N)2 ECl (E, E'=P, As, Ga).

The reaction of Na[OCP] with (R2 N)2 ECl (E=P or As; R=alkyl) granted direct access to transient amine-substituted diphospha- and arsaphospha-acrylamide analogues, (R2 N)E=P(CONR2 ) 1. Their facile formation allowed for a comprehensive reactivity study. Dimerization yielded the four-membered rings (R2 N)2 E2 P2 (CONR2 )2 , whereas in the presence of excess Na[OCP], a stepwise [2+2] cycloaddition occured, leading to the sodium salts of carboxotripnictides [(R2 N)EP2 CO(CONR2 )]- . These salts served as a reservoir of 1, either by extrusion of Na[OCP] or by reaction with the appropriate (R2 N)2 ECl, giving the [4+2]-cycloaddition products (R2 N)EP(C6 H10 )(CONR2 ) in the presence of 2,3-dimethylbutadiene. The formal conjugate addition product K[(tBuO)(R2 N)PP(CONR2 )] was obtained by reaction of Na[(R2 N)PP2 CO(CONR2 )] with tBuOK. In addition, a rare diphosphadigalletane with a ladder-type (R2 N)2 Ga2 P2 (CONR2 )2 core was isolated from the reaction of Na[OCP] with (R2 N)2 GaCl (R=alkyl). The unprecedented pnictogenyl carboxamide compounds were thoroughly characterized, including single-crystal X-ray structure determinations, and mechanisms for their formation were investigated by DFT calculations.

Synthesis of P2C2O2 and P2CO via NHC-mediated coupling of the phosphaethynolate anion.

The reaction of the chloroimidazolium chloride salt, [NHC-Cl][Cl], NHC = C{N(2,6-iPr2C6H3)CH}2 (1) with two equivalents of sodium phosphaethynolate, Na[OCP]·(dioxane)2.5, results in the formation of NHC-{cyclo-(CO)-P2-C(O)} (2) and NHC-P2-C(O)-NHC (3). Notably, in the presence of free NHC ligand, compound 2 converts to compound 3via extrusion of CO at elevated temperatures. The nature of the bonding in these complexes was probed computationally and spectroscopically.

Tris(2-pyridyl)phosphine as a versatile ligand for pnictogen acceptors.

We report cationic complexes of arsenic and antimony with the tris(2-pyridyl)phosphine ligand. Chloride ion abstraction from AsCl3 using TMSOTf in the presence of the ligand gives [P(Pyr)3As][OTf]3, in which the trication adopts a C3v symmetric cage structure. The reaction proceeds via the intermediate [P(Pyr)3AsCl][OTf]2, which undergoes chloride exchange to give [P(Pyr)3As][OTf]3 and [P(Pyr)3AsCl2][OTf]. The rearrangement reaction has been supported by the isolation of the antimony mono fluoride derivative [P(Pyr)3SbF][OTf]2. The asymmetric axial lone pairs in derivatives of [P(Pyr)3Pn]3+ are electronically separated. The HOMO-1 (for arsenic) and HOMO (for antimony) represent the major contribution to the phosphine lone pair indicating the possibility for nucleophilic behaviour despite the +3 charge. Less accessible is the HOMO-7, which represents the lone pair at arsenic or antimony, respectively.