The Original Coordination Chemistry of 2-Phosphaphenol with Copper(I) and Gold(I) Halides

From phosphanylphosphaalkenes to coordination copper and silver polymers containing P-P bonds

This study was focused on the activation of the CP bond via reactions of Ph2CP-PtBu2 (1) with 1,6-hexanediol and selected dithiols (1,4-butanedithiol, 1,4-benzenedithiol and 1,4-benzenedimethanethiol). These reactions proceed according to a 1,2-addition mechanism, providing new compounds with formulas {(Ph)2(H)C-P-PtBu2}{μ2-(O-(CH2)6-O)}{tBu2P-P-C(H)(Ph)2} (2), {(Ph)2(H)C-P-PtBu2}{μ2-(S-(CH2)4-S)}{tBu2P-P-C(H)(Ph)2} (3a), {(Ph)2(H)C-P-PtBu2}{μ2-(S-C6H4-S)}{tBu2P-P-C(H)(Ph)2} (3b), and {(Ph)2(H)C-P-PtBu2}{μ2-(S-CH2-C6H4-CH2-S)}{tBu2P-P-C(H)(Ph)2} (3c). Next, the reactions of 3a and 3c with metal chlorides led to the growth of desired coordination polymers of copper(I) and silver(I). All the obtained compounds remained stable under atmospheric conditions.

The case of a μ2-P aromatic phosphinine as a 4-electron donor forming σ- and π-three-center-two-electron bonds

Profound insight into the electronic structures of occasionally observed μ2-P bridging phosphinines remains limited. In this work, we present the isolation and X-ray crystallographic characterization of a dimeric Rh(I) phosphinine complex exhibiting both η1-P and μ2-P phosphinine coordination modes. Variable temperature NMR analyses and DOSY spectrum measurement confirmed the presence of two types of fluxional phenomena in solution: η1-P phosphinine bonding and dissociation, and η1-P and μ2-P equilibrium. DFT calculations in conjunction with single crystal X-ray diffraction studies suggest that the μ2-P phosphinines donate four electrons via a σ-lone pair and a high-lying π-type electron pair, instead of two σ-lone pairs, forming σ- and π-three-center-two-electron bonds. The stronger π-type interactions lead to longer P-C bonds and larger negative coordination chemical shifts for μ2-P phosphinines. However, the binding interactions of μ2-P are thermodynamically weaker than those of η1-P. Reactivity studies further confirm the labile nature of the μ2-P phosphinine bonds, which could be easily converted to an η1-P phosphinine.

A dinuclear Rh(-i)/Rh(i) complex bridged by biphilic phosphinine ligands

Bimetallic complexes have enabled precise control of catalysis by accumulating two discrete metal centres. In these complexes, bridging ligands are essential to combine multiple metals into one molecule. Among some bridging modes, an unsymmetric bridging mode will differentiate the electronic structures of the two metal centres. In this study, a dinuclear Rh(-i)/Rh(i) complex bridged by tridentate phosphine-phosphinine-phosphine ligands was prepared by reduction of the corresponding Rh(i) complex. Single-crystal X-ray analysis and DFT calculations suggest that the phosphinine ligands adopt an unsymmetric bridging mode wherein phosphinine accepts d-electrons from one Rh centre and, at the same time, donates lone pairs to the other Rh centre.

Triple dehydrofluorination as a route to amidine-functionalized, aromatic phosphorus heterocycles

An unexpected route to hitherto unknown amidine-functionalized phosphinines has been developed that is rapid and simple. Starting from primary amines and CF₃-substituted λ³,σ²-phosphinines, a cascade of dehydrofluorination reactions leads selectively to ortho-amidinephosphinines. DFT calculations reveal that this unusual transformation can take place via a series of nucleophilic attacks at the electrophilic, low-coordinate phosphorus atom.

Digold Phosphinine Complexes Are Stable with a Bis(Phosphinine) Ligand but Not with a 2-Phosphinophosphinine

The reaction of [bis{3-methyl-6-(trimethylsilyl)phosphinine-2-yl}dimethylsilane] (19) with one and two equivalents of [AuCl(tht)] was attempted in order to selectively form the mono and digold species, respectively. The digold species [(AuCl)2(19)] (21) was synthesized in 32% yield and comprehensibly characterized (multinuclear NMR spectroscopy, elemental analysis, mass spectrometry and single-crystal X-ray diffraction). The monogold species showed no 31P nuclear magnetic resonance at 25 °C but two resonances at −70 °C due to rapid exchange of AuCl between the phosphinine donors at 25 °C and was also susceptible to redistribution reactions to form the digold species. Analogous reactions of [AuCl(tht)] with 2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (22) revealed preferential coordination of the AuCl unit to the PPh2 donor first, with coordination to the phosphinine achieved upon reaction with the second equivalent of [AuCl(tht)]. Unexpectedly, the digold complex was not stable, undergoing decomposition to give an unidentified black precipitate. Structural information could only be obtained on the digold hydrolysis product [(AuCl)2(1-OH-2-PPh2-3-MePC5H4)], which showed an aurophilic interaction.

Understanding the Mechanism of Diels-Alder Reactions with Anionic Dienophiles: A Systematic Comparison of [ECX]- (E = P, As; X = O, S, Se) Anions

While Diels–Alder (DA) reactions involving neutral or cationic dienophiles are well-known, the characteristics of the analogous reactions with anionic dienophiles are practically unexplored. Herein we present the first comparative computational investigations on the characteristics of DA cycloadditions with anionic dienophiles on the basis of the reactions of [ECX]⁻ anions (E = P, As; X = O, S, Se) with 2H-pyran-2-one. All of these reactions were found to be both kinetically and thermodynamically feasible, enabling synthetic access toward 2-phosphaphenolate and arsaphenolate derivatives in the future. This study also reveals that the [ECO]⁻ anions show clear regioselectivity, while for [ECS]⁻ and [ECSe]⁻ anions, the two possible reaction channels have very similar energetics. Additionally, the activation barriers for the [ECO]⁻ anions are lower than those of the heavier analogues. The observed differences can be traced back to the starkly differing nucleophilic character of the pnictogen center in the anions, leading to a barrier-lowering effect in the case of the [ECO]⁻ anions. Furthermore, analysis of the geometries and electron distributions of the corresponding transition states revealed structure–property relationships, and thus a direct comparison of the cycloaddition reactivity of these anions was achieved. Along one of the two pathways, a good correlation was found between the activation barriers and suitable nucleophilicity descriptors (nucleophilic Parr function and global nucleophilicity). Additionally, the tendency of the reaction energies can be explained by the changing aromaticity of the products.

In contrast to the phosphaethynolate [PCO]⁻ anion, the cycloaddition reactivity of the heavier congeners ([ECX]⁻, where E = P, As and X = O, S, Se) is unexplored. In this computational study, the Diels−Alder reaction between the known [ECX]⁻ anions and 2-pyrone was employed to compare the reactivity patterns. The first activation barrier of these reactions correlates with the nucleophilicity of the anions, indicating a barrier-lowering effect. The feasibility of the studied reactions, leading to P and As heterocycles, was also explored.

2-(Dimethylamino)phosphinine: A Phosphorus-Containing Aniline Derivative

The yet unknown 2-amino-substituted λ³ ,σ² -phosphinines are phosphorus-containing aniline derivatives. Calculations show that the strong interaction of the π-donating NR₂  group with the aromatic system results in a high π-density at the phosphorus atom. We could now synthesize 2-N(CH₃ )₂ -functionalized phosphinines, starting from a 3-N(CH₃ )₂ -substituted 2-pyrone and (CH₃ )₃ Si-C≡P. Their reaction with CuBr⋅S(CH₃ )₂ affords Cu^I  complexes with the first example of a neutral phosphinine acting as a rare bridging μ₂ -P-4e donor-ligand between two Cu^I  centers. Our experimental and theoretical investigations show that 2-aminophosphinines are missing links in the series of known 2-donor-functionalized phosphinines.

π-Excess-aromatic and non-aromatic 1,3-azaphospholes – impact of annulation and multiple reactivity

Syntheses, properties, structure aspects and reactivity of non- and aromatically carbo- and heterocyclic annulated1H- and3H-1,3-azaphospholes are compared to illuminate the impact of annulation, substituent effects, aromatic stabilization and π-excess at phosphorus of the1H-isomers, to demonstrate the current knowledge and open questions in this field of research.

Making the unconventional μ2-P bridging binding mode more conventional in phosphinine complexes

As compared to the normal η¹-P σ-complexes or η⁶-phosphinine π-complexes, the rare μ²-P bridging binding mode of phosphinines can be tuned by employing electron donating substitute.

Phosphinines, as aromatic heterocycles, usually engage in coordination as η¹-P σ-complexes or η⁶-phosphinine π-complexes. The μ²-P bridging coordination mode is rarely observed. With the aim to study the effect of different electronic configurations of phosphinines on the coordination modes, a series of anionic phosphinin-2-olates and neutral phosphinin-2-ols were prepared with moderate to high yield. Then the coordination chemistry of these two series was studied in detail towards coinage metals (Au(i) and Cu(i)). It is observed that the anionic phosphinin-2-olates possess a higher tendency to take a bridging position between two metal centers compared to the neutral phosphinin-2-ols. Based on these experimental findings bolstered by DFT calculations, some insight is gained on how the unconventional μ²-P phosphinine bridging coordination mode can be made more conventional and used for the synthesis of polynuclear complexes.

A substituent-tolerant synthetic approach to N/P-“loaded” heteroarenes

Tetrazines react with OCP⁻¹ through a reverse electron demand Diels–Alder process to produce 3,6-disubstituted-1,2,4-diazaphosphinin-5-olates.

Reactivity studies of an imine-functionalised phosphaalkene; unusual electrostatic and supramolecular stabilisation of a σ2λ3-phosphorus motif via hydrogen bonding

Protonation with strong acids at an imine over addition to a phosphaalkene; resulting adducts display hydrogen bonding.

Expanding the chemistry of ring-fused 1,4-diphosphinines by stable mono anion formation

Synthesis of a novel tricyclic 1,4-diphosphinine I and, subsequently, of a stable anionic 1,4-diphosphinine II is reported; while II can be used as precursor for 1,4-disubstitution products, its oxidation leads to the formation of the P–P coupling product III.

[Re(CO)3Cl(C5H4ClP)2] and [Re(CO)2Cl(C5H4ClP)3]: synthesis and characterization of two novel rhenium(i) phosphinine complexes

Two novel rhenium(i) phosphinine complexes [Re(CO)₃Cl(η¹-C₅H₄ClP)₂] (1) and [Re(CO)₂Cl(η¹-C₅H₄ClP)₃] (2) were synthesized and the molecular structure of both was determined by single crystal X-ray diffraction.

π-Excess aromatic σ²-P ligands: synthesis and structure of an unprecedented μ²-P-1,3-benzazaphosphole bridged tetranuclear copper(I) acetate complex

The -P=CH-NR-heterocycle 1-neopentyl-1,3-benzazaphosphole (npBAP) reacts in THF with copper(I) acetate via labile soluble complexes (npBAP)xCuOAc preferably to form the insoluble tetranuclear (npBAP)2(CuOAc)4 complex 1. The crystal structure analysis of 1·2CH2Cl2, grown from CH2Cl2-hexane, reveals two μ(2)-P coordinated ligands, folding the Cu4 ring with each two short distances of the cyclic copper(I) acetate tetramer to a butterfly arrangement. AIM analysis of the ωB97-D/6-31+G* electron density, obtained at the crystal structure geometry, shows bond critical points between the copper atoms indicating covalent bonding interactions between the neighboring Cu atoms.