Zhongshu Li

Sodium Phosphaethynolate as a Building Block for Heterocycles

Phosphorus-containing heterocycles have evolved from laboratory curiosities to functional components, such as ligands in catalytically active metal complexes or molecular constituents in electronic devices. The straightforward synthesis of functionalized heterocycles on a larger scale remains a challenge. Herein, we report the use of the phosphaethynolate (OCP)(-) anion as a building block for various sterically unprotected and functionalized hydroxy substituted phosphorus heterocycles. Because the resulting heterocycles are themselves anions, they are building blocks in their own right and allow further facile functionalization. This property may be of interest in coordination chemistry and material science.

N-Heterocyclic Carbenes as Promotors for the Rearrangement of Phosphaketenes to Phosphaheteroallenes: A Case Study for OCP to OPC Constitutional Isomerism.

The concept of isomerism is essential to chemistry and allows defining molecules with an identical composition but different connectivity (bonds) between their atoms (constitutional isomers) and/or a different arrangement in space (stereoisomers). The reaction of phosphanyl ketenes, (NHP)-P=C=O (NHP=N-heterocyclic phosphenium) with N-heterocyclic carbenes (NHCs) leads to phosphaheteroallenes (NHP)-O-P=C=NHC in which the PCO unit has been isomerized to OPC. Based on the isolation of several intermediates and DFT calculations, a mechanism for this fundamental isomerisation process is proposed.

(L)2C2P2: dicarbondiphosphide stabilized by N-heterocyclic carbenes or cyclic diamido carbenes

Carbon phosphides, Cn Pm , may have highly promising electronic, optical, and mechanical properties, but they are experimentally almost unexplored materials. Phosphaheteroallenes stabilized by N-heterocyclic carbenes undergo a one-electron reduction to yield compounds of the type (L)2 C2 P2 with diverse structures. The use of imidazolylidenes as ligands L give complexes with a central four-membered ring C2 P2 , while more electrophilic cyclic diamidocarbenes (DAC) give a compound with an acyclic π-conjugated CP-PC unit. Cyclic C2 P2 compounds are best described as non-Kekulé molecules that are stabilized by coordination to the NHC ligands NHC→(C2 P2 )←NHC. These species can be easily oxidized to give stable radical cations [(NHC)2 C2 P2 ]+. . The remarkably stable molecules with an acylic C2 P2 core are best described with electron-sharing bonds (DAC)=C=P-P=C=(DAC).

L3C3P3: Tricarbontriphosphide Tricyclic Radicals and Cations Stabilized by Cyclic (alkyl)(amino)carbenes

Alkynes usually oligomerize to give rings with a conjugated π-electron system. In contrast, phosphaalkynes, R-C≡P, frequently give compounds with polycyclic structures, which are thermodynamically more stable than the corresponding π-conjugated isomers. The syntheses of the first C3 P3 tricyclic compounds are reported with either radical or cationic ground states stabilized by cyclic (alkyl)(amino)carbenes (CAACs). These compounds may be considered as examples of tricarbontriphosphide coordinated by carbenes and are likely formed via trimerization of the corresponding mono-radicals CAAC-CP. . The mechanism for the formation of these tricarbontriphosphide radicals has been rationalized by a combination of experiments and DFT calculations.

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.

Multidentate Phosphanyl Phosphinines: Synthesis and Properties

With respect to the well-developed chemistry of pyridines, that of phosphinines is in its infancy. There are still challenges to be overcome with respect to the development of simple syntheses and the application of phosphinine derivatives. Here, we show that sodium phosphinin-2-olate is a valuable building block to prepare multidentate phosphinine ligands, which in turn can be employed for the preparation of metal complexes. These PdII and RhI complexes were fully characterized, including by NMR spectra and single-crystal X-ray diffraction studies, which clearly demonstrate that molecules R3-x P(O-phosphinine)x with one, two, and three phosphinines (x=1, 2, 3) can be tethered to a central phosphorus donor center to give bis-, tris-, and tetradentate ligands.

Biradicaloid and Zwitterion Reactivity of Dicarbondiphosphide Stabilized with N-Heterocyclic Carbenes

Organic biradicals are usually very short lived species under standard laboratory conditions, which makes their experimental studies difficult. In contrast, heteroatom-substituted analogues of these biradicals show enhanced stability due to π-electron delocalization, which is why main group biradicals (or biradicaloids) of archetypical heterocyclobutanediyls have been thoroughly investigated. Herein, N-heterocyclic carbene (NHC)-stabilized dicarbondiphosphide compounds of the type (L2 )C2 P2 (L=NHC) were utilized to activate both single and multiple bonds in small molecules with a feasible concerted mechanism. This reactivity is explicable by considerable biradicaloid character of the dicarbondiphosphide compounds, which is further corroborated by theoretical studies. Furthermore, the dicarbondiphosphide compounds also exhibited Lewis base properties towards Lewis acids, such as borane and metal halides.

Bismesitoylphosphinic Acid (BAPO‐OH): A Ligand for Copper Complexes and Four‐Electron Photoreductant for the Preparation of Copper Nanomaterials

Bismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO-OH), is an efficient photoinitiator for free-radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO-OH as the ligand. The complex CuII (BAPO-O)2 (H2 O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO-OH, which serves as a four-electron photoreductant.