Synthesis and Photoluminescence Properties of CuIComplexes with Chelating Phosphinito Phosphinine Ligands

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.

So Close, Yet so Different: How One Donor Atom Changes Significantly the Photophysical Properties of Mononuclear Cu(I) Complexes

The manipulation of the photophysical properties of molecular emitters can be realized by composing the close environment of the metal center with the "heavier pnictogen atom" effect. Replacing a nitrogen atom with a heavier phosphorus atom in otherwise isostructural molecular systems results in a significant change of the photophysical parameters. Herein, we report on the synthesis of four pairs of novel phosphinine-based and isostructural diimine-based Cu(I) complexes, which feature peculiar photophysical properties, and show how these parameters depend on the "heavier pnictogen atom" effect. The obtained Cu(I) complexes show triplet luminescence with MLCT character, which was investigated by means of spectroscopic and computational methods. It has been found that the photophysical properties of the coordination compounds show a dependency on the rigidity of the ancillary phosphine ligand in an unexpected manner. Replacing the nitrogen atom with a heavier phosphorus atom in otherwise isostructural molecular systems results in a significant change in emission energy and especially in the lifetime of the excited state. The results obtained demonstrate an efficient approach to the design of emissive molecular materials, which allows the construction of luminescent complexes with controlled photophysical properties.

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.

Synthesis, Electronic Properties and OLED Devices of Chromophores Based on λ5 -Phosphinines

A new series of 2,4,6-triaryl-λ5 -phosphinines have been synthesized that contain different substituents both on the carbon backbone and the phosphorus atom of the six-membered heterocycle. Their optical and redox properties were studied in detail, supported by in-depth theoretical calculations. The modularity of the synthetic strategy allowed the establishment of structure-property relationships for this class of compounds and an OLED based on a blue phosphinine emitter could be developed for the first time.

1,3,4-Azadiphospholides as building blocks for scorpionate and bidentate ligands in multinuclear complexes

Annulated oxy-substituted 1,3,4-azadiphospholides such as the anion in Na[1] are readily accessible phosphorus heterocycles made from the phosphaethynolate anion (OCP)- and 2-chloropyridines. The sodium salt Na[1] reacts with oxophilic element halides such as OPCl3, PhSiCl3, PhBCl2 and CpTiCl3 at room temperature to form exclusively the oxygen bound tris-substituted compounds E(1)3 (with E = OP, PhSi, PhB- or CpTi). Six equivalents of Na[1] with group four metal chlorides MCl4 (M = Ti, Zr, Hf) form cleanly the hexa-substituted dianions (Na2[M(1)6]) which are isolated in excellent yields. The titanium complexes are deeply coloured species due to ligand to metal charge transfer (LMCT) excitations. In all complexes, the phosphorus atoms of the azadiphosphole moieties are able to coordinate to a soft metal center as shown in their reactions with [Mo(CO)3Mes], yielding complexes in which the Mo(CO)3 binds in a fac manner. Functionalization of the oxy group with amino phosphanes allows isolation of tridentate ligands, which have been used as synthons for macrocyclic molybdenum carbonyl complexes.

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.

Photoluminescent Phosphinine Cu(I) Halide Complexes: Temperature Dependence of the Photophysical Properties and Applications as a Molecular Thermometer

Luminescent thermometers have attracted much attention, because of their fast response, high sensitivity, and noninvasive operation, relative to other traditional thermometers. The extensive studies on the temperature-dependent luminescent properties of Cu(I) complexes make this low-cost metal source a promising candidate as a component of thermometers. Herein, we prepared three luminescent phosphinine Cu(I) complexes whose emission lifetimes are precisely dependent on the temperature variations. For practical utilization, sensor films have been fabricated by doping these Cu(I) complexes into the matrices of polyacrylamide. These films not only exhibit excellent linear correlations between the temperature and emission lifetime over the wide range of 77-337 K, but also show high sensitivity (with the best one to -6.99 μs K^-1). These are essential factors for the application in luminescent molecular thermometers. Moreover, the emission mechanism for these Cu(I) complexes are rationalized by the combination of experimental and theoretical results.

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.

Highlights on π-systems based on six-membered phosphorus heterocycles

Herein, we highlight relevant π-systems based on six-membered phosphorus heterocycles as well as their potential in bio- and optoelectronic applications.

Two isomers of a bis(diphenylphosphino)phosphinine, and the synthesis and reactivity of Ru arene/Cp* phosphinophosphinine complexes

Two isomers of a bis(diphenylphosphino)phosphinine have been synthesised, and the Ru coordination chemistry of a 2-phosphinophosphinine extended to include reactions of H₂O across a PC double bond.

A ruthenium(ii) bis(phosphinophosphinine) complex as a precatalyst for transfer-hydrogenation and hydrogen-borrowing reactions

A Ru(ii) complex with 2-phosphinophosphinine ligands activated with KO^tBu catalyses the room temperature transfer hydrogenation of acetophenone and the hydrogen-borrowing reaction of MeOH/EtOH to the advanced biofuel isobutanol.

Neutral copper(i) complexes featuring phosphinesulfonate chelates

The reaction of diphenylphosphinobenzenesulfonic acid with copper(i) oxide resulted in the formation of the new neutral dimeric copper(i) complex {Cu₂(DPPBS)₂·(MeOH)₂}.