Search

An isostructural series of four annulated actinocene complexes, M(hdcCOT) 2 (M = Th, U, Np, Pu), is reported. The syntheses proceed through a trivalent starting material when M = U, Np, Pu with subsequent oxidation or, in the case of M = Th, directly from ThCl 4 (DME) 2 . X-ray crystallography shows that each actinocene has C 2h molecular point symmetry in the solid state, with the metal atoms symmetrically bonded to two 10π-aromatic [8]annulene dianion rings. UV-Vis spectroscopy shows bands that were assigned as ligand-to-metal charge transfer (LMCT) transitions with the aid of time-dependent density functional theory (TDDFT) calculations. Compared to the M(COT) 2 analogs, the LMCT transitions for M(hdcCOT) 2 are red-shifted by ∼0.1 eV for all four metals. These actinocenes may be readily synthesized and crystallized even on the milligram scale (≤1 mg of metal ion content), which will enable future studies of the organometallic chemistry of transplutonium elements.

The synthesis of actinide tetrarhenate complexes completes a series of iridate, osmate, and rhenate polyhydrides, allowing for structural and bonding comparisons to be made. Computational studies examine the bonding interactions, particularly between metals, in these complexes. Several factors─including metal oxidation state, coordination number, and dispersion effects─affect metal-metal distances and covalency in these actinide tetrametallates. Related osmium and rhenium octametallic U 2 M 6 clusters are synthesized and described, and subjected to similar structural and electronic analyses.

Lignin, the heterogeneous aromatic macromolecule found in the cell walls of vascular plants, is an abundant feedstock for the production of biochemicals and biofuels. Many valorization schemes rely on lignin depolymerization, with decades of research focused on accessing monomers through C-O bond cleavage, given the abundance of β-O-4 bonds in lignin and the large number of available C-O bond cleavage strategies. Monomer yields are, however, invariably lower than desired, owing to the presence of recalcitrant C-C bonds whose selective cleavage remains a major challenge in catalysis. In this Review, we highlight lignin C-C cleavage reactions, including those of linkages arising from biosynthesis (β-1, β-5, β-β and 5-5) and industrial processing (5-CH 2 -5 and α-5). We examine multiple approaches to C-C cleavage, including homogeneous and heterogeneous catalysis, photocatalysis and biocatalysis, to identify promising strategies for further research and provide guidelines for definitive measurements of lignin C-C bond cleavage., (© 2024. Springer Nature Limited.)

We report the synthesis of a heterobimetallic U(III)-Ir species which reacts with CS 2 to form the novel ethanetetrathiolate fragment via hydride insertion and C-C coupling. Computational studies suggest the formation of a radical intermediate, which may couple with another equivalent to form the final product.

Amidate-based ligands ( N -( tert -butyl)isobutyramide, ITA ) bind κ 2 to form homoleptic, 8-coordinate complexes with tetravalent 237 Np (Np(ITA) 4 , 1-Np ) and 242 Pu (Pu(ITA) 4 , 1-Pu ). These compounds complete an isostructural series from Th, U-Pu and allow for the direct comparison between many of the early actinides with stable tetravalent oxidation states by nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction (SCXRD). The molecular precursors are subjected to controlled thermolysis under mild conditions with the exclusion of exogenous air and moisture, facilitating the removal of the volatile organic ligands and ligand byproducts. The preformed metal-oxygen bond in the precursor, as well as the metal oxidation state, are maintained through the decomposition, forming fully stoichiometric, oxidation-state pure NpO 2 and PuO 2 . Powder X-ray diffraction (PXRD), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDS) elemental mapping supported the evaluation of these high-purity materials. This chemistry is applicable to a wide range of metals, including actinides, with accessible tetravalent oxidation states, and provides a consistent route to analytical standards of importance to the field of nuclear nonproliferation, forensics, and fundamental studies.

A single-source-precursor approach was developed to synthesize uranium-based materials outside of the typically-studied oxides. This approach allows for shorter reaction times, milder reaction conditions, and control over the chemicals present in synthesis. To this end, the first homoleptic uranium thioamidate complex was synthesized as a precursor for US 2 materials. Pyrolysis of the thioamidate results in decomposition via an alkene elimination pathway and formation of γ-US 2 , which has historically been hard to access without the need for a secondary sulfur source. Despite the oxophilicity of uranium, the method successfully forms US 2 without the inclusion of oxygen in the bulk final product. These findings are supported by simultaneous thermal analysis, elemental analysis, powder X-ray diffraction, and uranium L 3 -edge X-ray absorption fine-structure spectroscopy. This work represents the first example of a single-source precursor approach to target and synthesize actinide materials other than the oxides., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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 Ph 2 PCl, Me NHP-Cl, and OHP-Cl to generate XL-type phosphido complexes 2 , 3 , and 4 , respectively ( Me NHP-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-tri tert -butylphenyl) to generate linear iminophosphanyl complex 5 . In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine i Pr 2 NPCl 2 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.

While synthesizing a series of rhenium-lanthanide triple inverse sandwich complexes, we unexpectedly uncovered evidence for rare examples of end-on lanthanide dinitrogen coordination for certain heavy lanthanide elements as well as for uranium. We begin our report with the synthesis and characterization of a series of trirhenium triple inverse sandwich complexes with the early lanthanides, Ln[(μ-η 5 :η 5 -Cp)Re(BDI)] 3 (THF) ( 1-Ln , Ln = La, Ce, Pr, Nd, Sm; Cp = cyclopentadienide, BDI = N , N '-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate). However, as we moved across the lanthanide series, we ran into an unexpected result for gadolinium in which we structurally characterized two products for gadolinium, namely, 1-Gd (analogous to 1-Ln ) and a diazenido dirhenium double inverse sandwich complex Gd[(μ-η 1 :η 1 -N 2 )Re(η 5 -Cp)(BDI)][(μ-η 5 :η 5 -Cp)Re(BDI)] 2 (THF) 2 ( 2-Gd ). Evidence for analogues of 2-Gd was spectroscopically observed for other heavy lanthanides ( 2-Ln , Ln = Tb, Dy, Er), and, in the case of 2-Er , structurally authenticated. These complexes represent the first observed examples of heterobimetallic end-on lanthanide dinitrogen coordination. Density functional theory (DFT) calculations were utilized to probe relevant bonding interactions and reveal energetic differences between both the experimental and putative 1-Ln and 2-Ln complexes. We also present additional examples of novel end-on heterobimetallic lanthanide and actinide diazenido moieties in the erbium-rhenium complex (η 8 -COT)Er[(μ-η 1 :η 1 -N 2 )Re(η 5 -Cp)(BDI)](THF)(Et 2 O) ( 3-Er ) and uranium-rhenium complex [Na(2.2.2-cryptand)][(η 5 -C 5 H 4 SiMe 3 ) 3 U(μ-η 1 :η 1 -N 2 )Re(η 5 -Cp)(BDI)] ( 4-U ). Finally, we expand the scope of rhenium inverse sandwich coordination by synthesizing divalent double inverse sandwich complex Yb[(μ-η 5 :η 5 -Cp)Re(BDI)] 2 (THF) 2 ( 5-Yb ), as well as base-free, homoleptic rhenium-rare earth triple inverse sandwich complex Y[(μ-η 5 :η 5 -Cp)Re(BDI)] 3 ( 6-Y ).

Simple lanthanide cyclopentadienyl (Cp) complexes can photochemically cleave the sp 3 carbon-chlorine bond of unactivated chlorinated hydrocarbons including polyvinyl chloride (PVC). The excited state lifetimes of these simple complexes are among the longest observed for cerium complexes (175 ns for [(Cp Me4 ) 2 Ce(μ-Cl)] 2 ) and the light absorption by the Cp ligand is efficient, so photocatalytic reactivity is enhanced for cerium and now also made possible for neighboring, normally photoinactive, lanthanide congeners.

A novel heavy metal-free and safe synthetic methodology enabling one-step conversion of ketones into corresponding 4,5,6,7-tetrafluorobenzofurans (F 4 BFs) has been developed. The presented approach has numerous advantageous qualities, including utilization of readily available substrates, broad scope, scalability, and good reaction yields. Importantly, some of the benzofurans prepared by this method were heretofore inaccessible by any other known transformation. Importantly, furo[2,3-b]pyrazines and heretofore unexplored difuro[2,3-c:3',2'-e]pyridazine can be prepared using this strategy. Spectroscopic studies reveal that for simple systems, absorption and fluorescence maxima fall within the UV spectral range, while π-electron system expansion red-shifts both spectra. Moreover, the good fluorescence quantum yields observed in solution, up to 96 %, are also maintained in the solid state. Experimental results are supported by density functional theory (DFT) calculations. The presented methodology, combined with the spectroscopic characteristics, suggest the possibility of using F 4 BFs in the optoelectronic industry (i. e., organic light emitting devices (OLED), organic field-effect transistors (OFET), organic photovoltaics (OPV)) as inexpensive and readily available emissive or semiconductor materials., (© 2023 Wiley-VCH GmbH.)

Reaction of the potassium pentamethylcyclopentadienyl iridate tris-hydride K[IrCp*H 3 ] with UCl 4 and ThCl 4 (DME) 2 led to the complete replacement of the halide ligands to generate multimetallic complexes U{(μ-H) 3 IrCp*} 4 (1) and Th{[(μ-H 2 )(H)IrCp*] 2 [(μ-H) 3 IrCp*] 2 } (2), respectively. These analogues feature a significant discrepancy in hydride bonding modes; 1 contains twelve bridging hydrides while 2 contains ten bridging hydrides and two terminal, Ir-bound hydrides. Use of a U(iii) starting material, UI 3 (1,4-dioxane) 1.5 , resulted in the octanuclear complex {U[(μ 2 -H 3 )IrCp*] 2 [(μ 3 -H 2 )IrCp*]} 2 (3). Computational studies indicate significant bonding character between U/Th and Ir in 1 and 2, with f-orbital involvement in the singly-occupied molecular orbitals of the uranium species 1. In addition, these studies attribute the variation in hydride bonding between 1 and 2 to differences in dispersion effects., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We report the synthesis and characterization of rhenium-group 9 heterobimetallic diazenido species (η 5 -Cp)Re(μ-BDI)(μ-N 2 )M(η 4 -COD) ( 1-M , M = Ir or Rh, Cp = cyclopentadienide, BDI = N , N '-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate, COD = 1,5-cyclooctadiene), formed from salt elimination reactions between Na[(η 5 -Cp)Re(BDI)] and [MCl(η 4 -COD)] 2 . Additionally, we find that these same reagents react under an argon atmosphere to instead produce bridging hydride complexes (BDI)Re(μ-η 5 :η 1 -C 5 H 4 )(μ-H)M(η 4 -COD) ( 2 - M ), which undergo rearrangements upon protonation to form the alternative bridging hydrides [(η 5 -Cp)Re(μ-BDI)(μ-H)M(η 4 -COD)][(B( m -C 6 H 3 (CF 3 ) 2 ) 4 )] ( 3-M ). Further, we demonstrate the first example of N-C bond formation at a heterobimetallic dinitrogen complex through reactions of 1-M and methyl triflate, which produces the alkylated species [(η 5 -Cp)Re(μ-N(Me)N)(μ-BDI)M(η 4 -COD)][OTf] ( 4-M , OTf = trifluoromethanesulfonate). A combination of spectroscopic studies, X-ray structural analysis, and computational investigations is discussed as an aid to understanding the modes of dinitrogen activation within these unique heterobimetallic complexes.

Eleven conjoined coumarins possessing a chromeno[3,4- c ]chromene-6,7-dione skeleton have been synthesized via the reaction of electron-rich phenols with esters of coumarin-3-carboxylic acids, catalyzed by either Lewis acids or 4-dimethylaminopyridine. Furthermore, Michael-type addition to angular benzo[ f ]coumarins is possible, leading to conjugated helical systems. Arrangement of the electron-donating amino groups at diverse positions on this heterocyclic skeleton makes it possible to obtain π-expanded coumarins with emission either sensitive to, or entirely independent of, solvent polarity with large Stokes shifts. Computational studies have provided a rationale for moderate solvatochromic effects unveiling the lack of collinearity of the dipole moments in the ground and excited states. Depending on the functional groups present, the obtained dyes are highly polarized with dipole moments of ∼14 D in the ground state and ∼20-25 D in the excited state. Strong emission in nonpolar solvents, in spite of the inclusion of a NO 2 group, is rationalized by the fact that the intramolecular charge transfer introduced into these molecules is strong enough to suppress intersystem crossing yet weak enough to prevent the formation of dark twisted intramolecular charge transfer states. Photochemical transformation of the dye possessing a chromeno[3,4- c ]pyridine-4,5-dione scaffold led to the formation of a spirocyclic benzo[ g ]coumarin.

Low-valent transition metalates─anionic, electronic-rich organometallic complexes─comprise a class of highly reactive chemical reagents that find integral applications in organic synthesis, small-molecule activation, transient species stabilization, and M-E bond formation, among others. The inherent reactivity of such electron-rich metal centers has necessitated the widespread use of strong backbonding ligands, particularly carbonyls, to aid in the isolation and handling of metalate reagents, albeit sometimes at the expense of partially masking their full reactivity. However, recent synthetic explorations into transition-metalate complexes devoid of archetypic back-bonding ligands have led to the discovery of highly reactive metalates capable of performing a variety of novel chemical transformations.Building on our group's long-standing interest in reactive organometallic species, a series of rational progressions in early-to-middle transition-metal chemistry ultimately led to our isolation of a rhenium(I) β-diketiminate cyclopentadienide metalate that displays exceptional reactivity. We have found this Re(I) metalate to be capable of small-molecule activation; notably, the complex reversibly binds dinitrogen in solution and can be utilized to trap N 2 for the synthesis of functionalized diazenido species. By employing isolobal analogues to N 2 (CO and RNC), we were able to thoroughly monitor the mechanism of activation and conclude that the metalate's sodium counterion plays an integral role in promoting dinitrogen activation through a novel side-on interaction. The Re(I) metalate is also used in forming a variety of M-E bonds, including a series of uncommon rhenium-tetrylene (Si, Ge, and Sn) complexes that display varying degrees of multiple bonding. These metal tetrylenes act to highlight deviations in chemical properties within the group 14 elements. Our metalate's utility also applies to metal-metal bond formation, as demonstrated through the synthesis of a heterotetrametallic rhenium-zinc dimer. In this reaction, the Re(I) metalate performs a dual role as a reductant and metalloligand to stabilize a transient Zn 2 2+ core fragment. Finally, the metalate displays unique reactivity with uranium(III) to yield the first transition metal-actinide inverse-sandwich bonds, in this case with three rhenium fragments bound through their Cp moieties surrounding the uranium center. Notably, throughout these endeavors we demonstrate that the metalate displays reactivity at multiple locations, including directly at the rhenium metal center, at a Cp carbon, through a Cp-sandwich mode, or through reversibly bound dinitrogen.Overall, the rhenium(I) metalate described herein demonstrates utility in diverse applications: small-molecule activation, the stabilization of reduced and/or unstable species, and the formation of unconventional M-E/M-M bonds or heterometallic complexes. Moving forward, we suggest that the continued discovery of noncarbonyl, electron-rich transition-metal anions featuring new or unconventional ligands should produce additional reactive organometallic species capable of stabilizing unique structural motifs and performing novel and unusual chemical transformations.