Rare-Earth Metal Phosphinidene Complexes: A Trip from Bridging One to Terminal One

Enchanting Realm of Five-Membered Rare-Earth Metallacycles

ConspectusMetallacycles, derivatives of carbocyclic compounds wherein a metal atom replaces at least one carbon center, have been a constant powerhouse in organic synthesis. While metallacycles of main-group, transition, and actinide metals have been extensively studied, those incorporating rare-earth (RE) elements (Sc, Y, and lanthanides) have remained elusive primarily due to synthetic challenges. Nevertheless, the electropositive character of these elements and the resulting polarization of RE-C bonds, along with the intrinsic synergistic effects within metallacycles, endow RE metallacycles with unique properties and a rich, yet largely untapped, reaction chemistry. In this Account, we present the development and applications of five-membered RE metallacycles.Over the past decade, we have successfully synthesized a variety of five-membered all-carbon rare-earth metallacycles using two key synthetic strategies: (i) transmetalation, which has been employed to prepare RE metallacyclopentadienes and spiro-metallacyclopentadienes, which, featuring various ligand systems, provide distinct coordination environments around the RE center, significantly influencing their reactivity, and (ii) transmetalation and reduction, enabling the synthesis of RE spiro-metallacyclopentenes and 2-butene tetraanion (BTA)-bridged dinuclear RE metallacyclopentenes. The reduction process proceeds via either self-disproportionation of metallacyclopentadienes or reduction by divalent RE centers or alkali metals. These metallacycles represent the first instances of such RE-containing metallacyclic ring structures.Our investigations into these metallacycles have uncovered unique reactivities and new reaction modes. The high intrinsic reactivity and multiple reactive sites of rare-earth metallacycles enable them not only to activate small molecules efficiently but also to exhibit distinct activation modes for some small molecules. For instance, reactions of RE metallacyclopentadienes with carbodiimides showcase diverse insertion/rearrangement chemistry, influenced by various factors such as number of equivalents of carbodiimide and the solvent choice. The RE metallacyclopentadiene-mediated [3 + 1] fragmentation of white phosphorus demonstrates an activation mode markedly different from that observed with main-group and transition metal analogs. Moreover, the discovery of cross-carbanion coupling at RE centers and RE-metal-mediated ring-opening metathesis of benzene introduces new reaction modes, demonstrating that, with rational design, RE metals can exhibit properties similar to or even surpassing those of transition metals. These reaction modes have further led to the development of applications for RE metallacycles in synthetic chemistry.Additionally, some novel properties of these rare-earth metallacycles have been uncovered, stemming from their unique geometric and electronic structures. Structural analysis and theoretical calculations have revealed the nonplanar aromaticity of BTA-bridged dinuclear RE metallacyclopentenes, extending the concept of nonplanar aromaticity into the chemistry of carbon-RE metallacycles. Furthermore, benefiting from the redox capabilities of butadiene dianion and BTA ligands, the ligand-based redox chemistry of BTA-bridged dinuclear RE metallacyclopentenes demonstrates diverse and efficient multielectron transfer processes, highlighting the potential of these metallacycles for redox chemistry.The studies of rare-earth metallacycles, encompassing their construction, characterization, properties, reactivity, and synthetic applications, have greatly enriched the field of f-block metallacycles. We hope that this Account will inspire further exploration into the synthesis of new organometallic reagents and metallacycle-mediated transformations, fueling continued progress in rare-earth chemistry.

Rare Earth Complex-Based Functional Materials: From Molecular Design and Performance Regulation to Unique Applications

ConspectusRare earth (RE) elements, due to their unique electronic structures, exhibit excellent optical, electrical, and magnetic properties and thus have found widespread applications in the fields of electronics, optics, and biomedicine. A significant advancement in the use of RE elements is the formation of RE complexes. RE complexes, created by the coordination of RE ions with organic ligands, not only offer high molecular design flexibility but also incorporate features such as a broad absorption band and efficient energy transfer of organic ligands. Through the "antenna effect", organic ligands can transfer energy to RE ions, enhancing their luminescence efficiency. Moreover, the modification of the ligands can influence the local environment of the RE ions, thereby regulating their electronic structures and energy-level distributions. This makes it one of the important avenues for the efficient development and utilization of RE resources.The meticulous design of organic ligands during molecular synthesis enables the precise construction and regulation of RE complex structures, which are essential for probing molecular-level structure-performance relations and developing functional materials in fields such as optoelectronics, sensing, and catalysis/energy. Despite notable advancements, challenges persist in refining synthesis methodologies, innovating RE complex-based materials, enhancing stability, gaining better control over device functionality, and realizing high-value applications. This Account summarizes the recent advancements in molecular design and performance regulation achieved by our research group, particularly focusing on the synthesis and functional regulation of RE complex-based materials. We have employed strategies such as coordination self-assembly, in situ coordination, and microstructural evolution to achieve the precise synthesis and functional modulation of RE complex-based materials. These approaches have allowed us to finely tune properties such as the luminescence, electrical performance, and catalytic performance of various material systems. Consequently, we have made considerable strides in multidimensional optical information storage, the development of intelligent biological probes, the preparation of nanocatalysts, and the enhancement of inorganic-organic hybrid perovskite solar cell devices. Finally, we are committed to conducting an in-depth analysis of the challenges and opportunities that arise from the precise synthesis methods, performance regulation strategies, and innovative applications of RE complex-based functional materials. Additionally, we aim to propose potential solutions to current issues. This Account comprehensively summarizes the developments in RE complex-based materials to stimulate innovative thinking and new research directions and to establish a foundation for function-oriented precise synthesis methods.

A bridging bis-phosphanido-phosphinidene complex of lanthanum supported by a sterically encumbering PN ligand

Synthesis of a bulky anilidophosphine ligand (short PNTerph) and its lanthanum complexes 1 and 3 is reported. When exposed to KPHMes, both complexes form the first example of a bis-phosphanido-phosphinidene complex 2. This complex undergoes Phospha-Wittig type reactions and its reactivity towards strong bases is further investigated.

Panoply of P: An Array of Rhenium-Phosphorus Complexes Generated from a Transition Metal Anion

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (1, BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) to generate several rhenium-phosphorus complexes. Complex 1 reacts in a metathetical manner with chlorophosphines Ph2PCl, MeNHP-Cl, and OHP-Cl to generate XL-type phosphido complexes 2, 3, and 4, respectively (MeNHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad 2, 3, and 4 reveal that increasing the electronegativity of the phosphorus substituent (C < N < O) results in a shortening and strengthening of the rhenium-phosphorus bond. Complex 1 reacts with iminophosphane Mes*NPCl (Mes* = 2,4,6-tritert-butylphenyl) to generate linear iminophosphanyl complex 5. In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine iPr2NPCl2 to afford cationic phosphinidene complex 6+. Complex 6+ may be reduced by one electron to form 6•, a rare example of a stable, paramagnetic phosphinidene complex. Spectroscopic and structural investigations, as well as computational analyses, are employed to elucidate the influence of the phosphorus substituent on the nature of the rhenium-phosphorus bond in 2 through 6. Furthermore, we examine several common analogies employed to understand metal phosphido, phosphinidene, and iminophosphanyl complexes.

Hydrogen-Bonded Complex of the Parent Phosphinidene

The diatomic molecule PH is very reactive, and it serves as the parent compound for phosphinidenes featuring a monovalent phosphorus atom. Herein, we report the characterization and reactivity of a rare hydrogen-bonded complex of PH. Specifically, the molecular complex between PH and HCl has been generated by photolysis of chlorophosphine (H2PCl) at 254 nm in a solid Ar-matrix at 10 K. The IR spectrum of the complex HP⋅⋅⋅HCl and quantum chemical calculations at the UCCSD(T)-F12a/haTZ level consistently prove that the phosphorus atom acts as a hydrogen bond acceptor with a binding energy (D0) of -0.6 kcal mol-1. In line with the observed absorption at 341 nm for the binary complex, the triplet phosphinidene PH undergoes prototype H-Cl bond insertion by reformation of H2PCl upon photoexcitation at 365 nm. However, this hydrogen-bonded complex is unstable in the presence of N2 and HCl, as both molecules prefers stronger interactions with HCl than PH in the observed complexes HP⋅⋅⋅HCl⋅⋅⋅N2 and HP⋅⋅⋅2HCl.

f-Element heavy pnictogen chemistry

The coordination and organometallic chemistry of the f-elements, that is group 3, lanthanide, and actinide ions, supported by nitrogen ligands, e.g. amides, imides, and nitrides, has become well developed over many decades. In contrast, the corresponding f-element chemisty with the heavier pnictogen analogues phosphorus, arsenic, antimony, and bismuth has remained significantly underdeveloped, due largely to a lack of suitable synthetic methodologies and also the inherent hard(f-element)-soft(heavier pnictogen) acid-base mismatch, but has begun to flourish in recent years. Here, we review complexes containing chemical bonds between the f-elements and heavy pnictogens from phosphorus to bismuth that spans five decades of endeavour. We focus on complexes whose identity has been unambiguously established by structural authentication by single-crystal X-ray diffraction with respect to their synthesis, characterisation, bonding, and reactivity, in order to provide a representative overview of this burgeoning area. By highlighting that much has been achieved but that there is still much to do this review aims to inspire, focus and guide future efforts in this area.