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A synthetic route has been developed for a series of 3d homobimetallic complexes of Mn, Fe, Co, Ni, and Cu using three different pyridyldiimine and pyridyldialdimine macrocyclic ligands with ring sizes of 18, 20, and 22 atoms. Crystallographic analyses indicate that while the distances between the metals can be modulated by the size of the macrocycle pocket, the flexibility in the alkyl linkers used to construct the macrocycles enables the ligand to adjust the orientation of the PD(A)I fragments in response to the geometry of the [M 2 (μ-Cl) 2 ] 2+ core, particularly with respect to Jahn-Teller distortions. Analyses by UV-vis spectroscopy and SQUID magnetometry revealed deviations in the properties [M 2 (μ-Cl) 2 ] 2+ -containing complexes bound by standard mononucleating ligands, highlighting the ability of macrocycles to use ring size to control the magnetic interactions of pseudo -octahedral, high-spin metal centers.

This study presents the role of 5d orbitals in the bonding, and electronic and magnetic structure of Ce imido and oxo complexes synthesized with a tris(hydroxylaminato) [((2- t BuNO)C 6 H 4 CH 2 ) 3 N] 3- (TriNO x 3- ) ligand framework, including the reported synthesis and characterization of two new alkali metal-capped Ce oxo species. X-ray spectroscopy measurements reveal that the imido and oxo materials exhibit an intermediate valent ground state of the Ce, displaying hallmark features in the Ce L III absorption of partial f-orbital occupancy that are relatively constant for all measured compounds. These spectra feature a double peak consistent with other formal Ce(iv) compounds. Magnetic susceptibility measurements reveal enhanced levels of temperature-independent paramagnetism (TIP). In contrast to systems with direct bonding to an aromatic ligand, no clear correlation between the level of TIP and f-orbital occupancy is observed. CASSCF calculations defy a conventional van Vleck explanation of the TIP, indicating a single-reference ground state with no low-lying triplet excited state, despite accurately predicting the measured values of f-orbital occupancy. The calculations do, however, predict strong 4f/5d hybridization. In fact, within these complexes, despite having similar f-orbital occupancies and therefore levels of 4f/5d hybridization, the d-state distributions vary depending on the bonding motif (Ce[double bond, length as m-dash]O vs. Ce[double bond, length as m-dash]N) of the complex, and can also be fine-tuned based on varying alkali metal cation capping species. This system therefore provides a platform for understanding the characteristic nature of Ce multiple bonds and potential impact that the associated d-state distribution may have on resulting reactivity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A series of 2,6-diiminopyridine-derived macrocyclic ligands have been synthesized via [2+2] condensation around alkaline earth metal triflate salts. The inclusion of a tert -butyl group at the 4-position of the pyridine ring of the macrocyclic synthons results in macrocyclic complexes that are soluble in common organic solvents, thereby enabling a systematic comparison of the physical properties of the complexes by NMR spectroscopy, mass spectrometry, solution-phase UV-Vis spectroscopy, cyclic voltammetry and single-crystal X-ray crystallography. Solid-state structures determined crystallographically demonstrate increased twisting in the ligand, concurrent with either a decrease in ion size or an increase in macrocycle ring size (18, 20, or 22 membered rings). The degree of folding and twisting within the macrocycle can be quantified using parameters derived from the N pyr -M-N pyr bond angle and the relative orientation of the pyridinediimine (PDI) and pyridinedialdimine (PDAI) fragments to each other within the solid state structures. Cyclic voltammetry and UV-Vis spectroscopy were used to compare the relative energies of the imine π* orbital of the redox active PDI and PDAI components in the macrocycle when coordinated to redox inactive metals. Both methods indicate the change from a methyl to hydrogen substitution on the imine carbon lowers the energy of the ligand π* system., Competing Interests: Declaration of Interest. The authors have no known competing interests to declare.

The super electron donor (SED) ability of 2-azaallyl anions has recently been discovered and applied to diverse reactivity, including transition metal-free cross-coupling and dehydrogenative cross-coupling processes. Surprisingly, the redox properties of 2-azaallyl anions and radicals have been rarely studied. Understanding the chemistry of elusive species is the key to further development. Electrochemical analysis of phenyl substituted 2-azaallyl anions revealed an oxidation wave at E 1/2 or E pa = -1.6 V versus Fc/Fc + , which is ∼800 mV less than the reduction potential predicted ( E pa = -2.4 V vs. Fc/Fc + ) based on reactivity studies. Investigation of the kinetics of electron transfer revealed reorganization energies an order of magnitude lower than commonly employed SEDs. The electrochemical study enabled the synthetic design of the first stable, acyclic 2-azaallyl radical. These results indicate that the reorganization energy should be an important design consideration for the development of more potent organic reductants., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

A series of cerium(iv) mixed-ligand guanidinate-amide complexes, {[(Me 3 Si) 2 NC(N i Pr) 2 ] x Ce IV [N(SiMe 3 ) 2 ] 3- x } + ( x = 0-3), was prepared by chemical oxidation of the corresponding cerium(iii) complexes, where x = 1 and 2 represent novel complexes. The Ce(iv) complexes exhibited a range of intense colors, including red, black, cyan, and green. Notably, increasing the number of the guanidinate ligands from zero to three resulted in significant redshift of the absorption bands from 503 nm (2.48 eV) to 785 nm (1.58 eV) in THF. X-ray absorption near edge structure (XANES) spectra indicated increasing f occupancy ( n f ) with more guanidinate ligands, and revealed the multiconfigurational ground states for all Ce(iv) complexes. Cyclic voltammetry experiments demonstrated less stabilization of the Ce(iv) oxidation state with more guanidinate ligands. Moreover, the Ce(iv) tris(guanidinate) complex exhibited temperature independent paramagnetism (TIP) arising from the small energy gap between the ground- and excited states with considerable magnetic moments. Computational analysis suggested that the origin of the low energy absorption bands was a charge transfer between guanidinate π orbitals that were close in energy to the unoccupied Ce 4f orbitals. However, the incorporation of sterically hindered guanidinate ligands inhibited optimal overlaps between Ce 5d and ligand N 2p orbitals. As a result, there was an overall decrease of ligand-to-metal donation and a less stabilized Ce(iv) oxidation state, while at the same time, more of the donated electron density ended up in the 4f shell. The results indicate that incorporating guanidinate ligands into Ce(iv) complexes gives rise to intense charge transfer bands and noteworthy electronic structures, providing insights into the stabilization of tetravalent lanthanide oxidation states., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N-H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N-H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E-H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH 3 in high yield through a reaction that engages the redox-activity of the ligand during PCET., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This report describes an isostructural series of dinuclear iron, cobalt, and nickel complexes bound by a redox-active macrocyclic ligand. The series spans five redox levels (34-38 e - /cluster core), allowing for a detailed investigation into both the degree of metal-metal interaction and the extent of ligand-based redox-activity. Magnetometry, electrochemistry, UV-vis-NIR absorption spectroscopy, and crystallography were used in conjunction with DFT computational analyses to extract the electronic structures of the six homodinuclear complexes. The isoelectronic, 34 e - species [( 3 PDI 2 )Fe 2 (PMe 3 ) 2 (μ-Cl)](OTf) and [( 3 PDI 2 )Co 2 (PMe 3 ) 2 (μ-Cl)](OTf) 3 exhibit metal-metal single bonds, with varying amounts of electron density delocalization into the ligand as a function of the effective nuclear charge of the metal ions. One- and two-electron reductions of [( 3 PDI 2 )Co 2 (PMe 3 ) 2 (μ-Cl)](OTf) 3 lead to isolable products, which show successive increases in both the Co-Co distances and the extent of reduction of the ligand manifold. This trend results from reduction of a Co-Co σ* orbital, which was found to be heavily mixed with the redox-active manifold of the 3 PDI 2 ligand. A similar trend was observed in the 37 and 38 e - dinickel complexes [( 3 PDI 2 )Ni 2 (PMe 3 ) 2 (μ-Cl)](OTf) 2 and [( 3 PDI 2 )Ni 2 (PMe 3 ) 2 (μ-Cl)](OTf); however, their higher electron counts lead to high-spin ground states that result from occupation of a high-lying δ/δ* manifold with significant Ni-N PDI σ* character. This change in ground state configuration reforms a M-M bonding interaction in the 37 e - complex, but formation of the 38 e - species again disrupts the M-M bond alongside the transfer of electron density to the ligand.

The separation of rare-earth ions from one another is challenging due to their chemical and physical similarities. Nearly all rare-earth separations rely upon small changes in ionic radii to direct speciation or reactivity. Herein, we show that the intrinsic magnetic properties of the rare-earth ions impact the separations of light/heavy and selected heavy/heavy binary mixtures. Using TriNOx 3- ([{(2- t BuNO)C 6 H 4 CH 2 } 3 N] 3- ) rare-earth complexes, we efficiently and selectively crystallized heavy rare earths (Tb-Yb) from a mixture with light rare earths (La and Nd) in the presence of an external Fe 14 Nd 2 B magnet, concomitant with the introduction of a concentration gradient (decrease in temperature). The optimal separation was observed for an equimolar mixture of La:Dy, which gave an enrichment factor of EF La:Dy =297±31 for the solid fraction, compared to EF La:Dy =159±22 in the absence of the field, and achieving a 99.7 % pure Dy sample in one step. These results indicate that the application of a magnetic field can improve performance in a molecular separation system for paramagnetic rare-earth cations., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Separation of the rare-earth (RE) elements (Sc, Y, La-Lu) is challenging because of their similar chemical properties, but is necessary for their applications in renewable energy and electronic device technologies. The development of separation processes driven by kinetic factors represents a new area for this field. Herein, we disclose a novel method of separating select rare earths by reacting RE cyclopentadienides with the triradical species tris(2- tert -butylnitroxyl)benzylamine ( 1 ). The key proligand 1 was characterized using a variety of techniques including X-ray crystallography, magnetometry, and EPR spectroscopy. When applied to an equimolar mixture of La:Y cyclopentadienide complexes, different rates of chelation of these organometallic precursors by 1 were observed, affording a separation factor of 26 under the reported conditions.

Correction for 'Synthesis of novel copper-rare earth BINOLate frameworks from a hydrogen bonding DBU-H rare earth BINOLate complex' by Grace B. Panetti, et al., Dalton Trans., 2018, 47, 14408-14410.

A structural modification strategy to improve the photocatalytic performance of a series of cerium(iii) bis(guanidinate) mono(amide) molecular luminophores was demonstrated. Reducing the steric bulkiness of the amide ligand gave rise to two categories of complexes with distinct photophysical and photochemical properties. A structural parameter, the amide cone angle (θ), was applied to differentiate the two categories. Complexes with smaller cone angles (θ < 156°, category B) exhibited more reducing potentials and faster electron-transfer rates than those of complexes with larger cone angles (θ > 173°, category A). And only complexes in the category B could achieve the photocatalytic phenylation of an aryl bromide. These results demonstrated that reducing the steric bulkiness of the amide ligand improved the performance of cerium(iii) bis(guanidinate) mono(amide) photocatalysts in a systematic manner.

A series of uranium(VI)-acetylide complexes of the general formula U VI (O)(C≡C-C 6 H 4 -R)[N(SiMe 3 ) 2 ] 3 , with variation of the para substituent (R = NMe 2 , OMe, Me, Ph, H, Cl) on the aryl(acetylide) ring, was prepared. These compounds were analyzed by 13 C NMR spectroscopy, which showed that the acetylide carbon bound to the uranium(VI) center, U- C≡C-Ar, was shifted strongly downfield, with δ( 13 C) values ranging from 392.1 to 409.7 ppm for Cl and NMe 2 substituted complexes, respectively. These extreme high-frequency 13 C resonances are attributed to large negative paramagnetic (σ para ) and relativistic spin-orbit (σ SO ) shielding contributions, associated with extensive U(5f) and C(2s) orbital contributions to the U-C bonding in title complexes. The trend in the 13 C chemical shift of the terminal acetylide carbon is opposite that observed in the series of parent (aryl)acetylenes, due to shielding effects of the para substituent. The 13 C chemical shifts of the acetylide carbon instead correlate with DFT computed U-C bond lengths and corresponding QTAIM delocalization indices or Wiberg bond orders. SQUID magnetic susceptibility measurements were indicative of the Van Vleck temperature independent paramagnetism (TIP) of the uranium(VI) complexes, suggesting a magnetic field-induced mixing of the singlet ground-state (f 0 ) of the U(VI) ion with low-lying (thermally inaccessible) paramagnetic excited states (involved also in the perturbation-theoretical treatment of the unusually large paramagnetic and SO contributions to the 13 C shifts). Thus, together with reported data, we demonstrate that the sensitive 13 C NMR shifts serve as a direct, simple, and accessible measure of uranium(VI)-carbon bond covalency.

A nickel-catalyzed cross-coupling of toluene derivatives with both aryl bromides and chlorides using a NIXANTPHOS-ligated nickel(II) complex has been developed. The key factor to success is proposed to be the catalyst activation of toluene by a cation-π complex, enabling methyl arenes (p K a ≈ 43) to be deprotonated with the relatively mild base NaN(SiMe 3 ) 2 . This method facilitates access to a variety of sterically and electronically diverse hetero- and nonheteroaryl-containing diarylmethanes.

The preparation of a novel H-bonding DBU-H+ BINOLate Rare Earth Metal complex enabled the synthesis of the first copper-Rare Earth Metal BINOLate complex (CuDBU-REMB). CuDBU-REMB was compared to the analogous Li complex using X-ray crystallography and Exchange NMR spectroscopy (EXSY). The results provide insight into the role of the secondary metal cation in the framework's stabilization.

Uranium complexes in the +3 and +4 oxidation states were prepared using the anionic PN - (PN - = ( N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide) ligand framework. New complexes include the halide starting materials, (PN) 2 U III I (1) and (PN) 2 U IV Cl 2 (2), which both yield (PN) 2 U IV (N 3 ) 2 (3) by reaction with NaN 3 . Compound 3 was reduced with potassium graphite to produce a putative, transient uranium-nitrido moiety that underwent an intramolecular C-H activation to form a rare example of a parent imido complex, [K(THF) 3 ][(PN)U IV (═NH)[ i Pr 2 P(C 6 H 3 Me)N(C 6 H 2 Me 2 CH 2 )]] (4). Calculated reaction energy profiles strongly suggest that a C-H insertion becomes unfavorable when a reductant is present, offering a distinctively different reaction pathway than previously observed for other uranium nitride complexes.

A methoxy-substituted tripodal hydroxylamine ligand, H3TriNOxOMe, was synthesized and coordinated to rare earth cations for separation purposes. Metrics of the resulting complexes were investigated and compared with their parent TriNOx3- counterparts for determination of the molecular basis for the described rare earth separation system. Addition of an electron donating group to the aryl backbone resulted in a more electron rich ligand that increased the equilbrium constant for complex dimerization five-fold. The new separation system yielded efficient Nd/Dy separations in toluene rather than benzene.

A palladium-catalyzed direct arylation of (3-thiophene)S(O)Me derivatives has been developed. This protocol is effective for the selective synthesis of 2-arylated and 2,5-diarylated sulfinylthiophene derivatives with as low as 0.5 mol % catalyst loading. Various functional groups are well tolerated. A method to install two different aryl groups on 3-(methylsulfinyl)thiophenes is also introduced.

Molecular cerium complexes are a new class of tunable and energy-efficient visible- and UV-luminophores. Understanding and controlling the emission brightness and color are important for tailoring them for new and specialized applications. Herein, we describe the experimental and computational analyses for series of tris(guanidinate) (1-8, Ce{(R 2 N)C(N i Pr) 2 } 3 , R = alkyl, silyl, or phenyl groups), guanidinate-amide [GA, A = N(SiMe 3 ) 2 , G = (Me 3 Si) 2 NC(N i Pr) 2 ], and guanidinate-aryloxide (GOAr, OAr = 2,6-di- tert-butylphenoxide) cerium(III) complexes to understand and develop predictive capabilities for their optical properties. Structural studies performed on complexes 1-8 revealed marked differences in the steric encumbrance around the cerium center induced by various guanidinate ligand backbone substituents, a property that was correlated to photoluminescent quantum yield. Computational studies revealed that consecutive replacements of the amide and aryloxide ligands by guanidinate ligand led to less nonradiative relaxation of bright excited states and smaller Stokes shifts. The results establish a comprehensive structure-luminescence model for molecular cerium(III) luminophores in terms of both quantum yields and colors. The results provide a clear basis for the design of tunable, molecular, cerium-based, luminescent materials.

Incorporation of photoresponsive molecules within soft materials can provide spatiotemporal control over bulk properties and address challenges in targeted delivery and mechanical variability. However, the kinetics of in situ photochemical reactions are often slow and typically employ ultraviolet wavelengths. Here, we present a novel photoactive crosslinker Ru(bipyridine) 2 (3-pyridinaldehyde) 2 (RuAldehyde), which was reacted with hydrazide-functionalized hyaluronic acid to form hydrogels capable of encapsulating protein cargo. Visible light irradiation (400-500 nm) initiated rapid ligand exchange on the ruthenium center, which degraded the hydrogel within seconds to minutes, depending on gel thickness. An exemplar enzyme cargo, TEM1 β-lactamase, was loaded into and photoreleased from the Ru-hydrogel. To expand their applications, Ru-hydrogels were also processed into microgels using a microfluidic platform., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first example of the OCPPCO ligand, diisophosphaethynolate, is reported via reductive coupling of a Sc-OCP precursor. Upon reduction with KC 8 , isolation of the dinuclear complex, namely [K(OEt 2 )] 2 [(nacnac)Sc(OAr)] 2 (OCPPCO), is observed, leading to a unique motif [OCPPCO] 4- , stabilized by two scandium centers. Detailed NMR spectra of all complexes as well as IR and single crystal X-ray studies were obtained to fully elucidate the nature of these complexes in solution as well as in the solid state. Theory is combined to probe the electronic structure and orbitals responsible for the bonding interactions in the Sc-OCPPCO-Sc skeleton but also to compare to the linear mode observed in the precursor., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Methyl benzoate, N,N-dimethylbenzamide, and benzophenone were reduced by U III [N(SiMe 3 ) 2 ] 3 resulting in uranium(IV) products. Reduction of benzophenone lead to U IV [OC⋅Ph 2 )][N(SiMe 3 ) 2 ] 3 , (1.1) which forms the dinuclear complex, [N(SiMe 3 ) 2 ] 3 U IV (OCPhPh-CPh 2 O)U IV [N(SiMe 3 ) 2 ] 3 (1.2), through coupling of the ketyl radical species upon crystallization. Reaction of N,N-dimethylbenzamide with U III [N(SiMe 3 ) 2 ] 3 resulted in U IV [OC⋅(Ph)(NMe 2 )][N(SiMe 3 ) 2 ] 3 (2), a uranium(IV) compound and the first example of a charge-separated amide radical. In the case of methyl benzoate, the reduction resulted in U IV (OMe)[N(SiMe 3 ) 2 ] 3 (3) and benzaldehyde as the reduced organic fragment. Compound 2 showed the ability to act as a uranium(III) synthon in its reactivity with trimethylsilyl azide, a reaction that yielded U V (=NSiMe 3 )[N(SiMe 3 ) 2 ] 3 . Additionally, 2 was reduced with potassium graphite resulting in [U(μ-O)[O=C(NMe 2 )(Ph)][N(SiMe 3 ) 2 ] 2 ] 2 (4), a dinuclear uranium compound bridged by oxo ligands. Reduction of 2 in the presence of 15-crown-5 afforded isolation of the mono-oxo compound, [(15-crown-5) 2 K][UO[N(SiMe 3 ) 2 ] 3 ] (5). The results expand the reduction capabilities of U III complexes and demonstrate a strategy for isolating novel metal-stabilized radicals., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Synthetic methods for the coordination of the monoanionic bis[2-(diisopropylphosphino)-4-methylphenyl]amido (PNP) ligand framework to the cerium(III) cation have been developed and applied for the isolation of a series of {(PNP)Ce} and {(PNP) 2 Ce} type complexes. The structures of the complexes were studied by X-ray diffraction and multinuclear NMR spectroscopy. We found that the cerium(III) ion can induce the elimination of one of the iPr groups at phosphorus to yield a new dianionic PNP tridentate framework (PNP -iPr ) featuring a phosphido-donor functionality, which is bound to the cerium ion with the shortest known Ce-P bond of 2.7884(14) Å for molecular compounds. The reaction of the complex [(PNP)Ce{N(SiMe 3 ) 2 } 2 ] (1) with Ph 2 CO gave the Ce-bound product of C-C coupling, - N(SiMe 3 )SiMe 2 CH 2 -CPh 2 O - , through the C-H bond activation of a SiMe 3 group. 31 P NMR spectroscopy was used to estimate the presence of a vacant coordination position at the cerium ion in the Ce III -PNP complexes by the examination of the δ( 31 P) shift recorded both in non-polar (C 6 D 6 ) and polar ([D 8 ]THF) solvents. Moreover, 31 P NMR spectroscopy was also found to be a useful tool for the estimation of the Ce-P bond distances in {(PNP)Ce III } and {(PNP) 2 Ce III } systems. Electrochemical and computational studies for 1 and its lanthanum analogue containing a redox-innocent metal center revealed the stabilization of the Ce III oxidation state by the PNP ligand., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dicobalt complexes supported by flexible macrocyclic ligands were used to target the generation of the bridging nitrido species [( n PDI 2 )Co 2 (μ-N)(PMe 3 ) 2 ] 3+ (PDI=2,6-pyridyldiimine; n=2, 3, corresponding to the number of catenated methylene units between imino nitrogen atoms). Depending on the size of the macrocycle and the reaction conditions (solution versus solid-state), the thermolysis of azide precursors yielded bridging phosphinimido [( 2 PDI 2 )Co 2 (μ-NPMe 3 )(PMe 3 ) 2 ] 3+ , amido [( n PDI 2 )Co 2 (μ-NH 2 )(PMe 3 ) 2 ] 3+ (n=2, 3), and C-H amination [( 3 PDI 2 *-μ-NH)Co 2 (PMe 3 ) 2 ] 3+ products. All results are consistent with the initial formation of [( n PDI 2 )Co 2 (μ-N)(PMe 3 ) 2 ] 3+ , followed by 1) PMe 3 attack on the nitride, 2) net hydrogen-atom transfer to form N-H bonds, or 3) C-H amination of the alkyl linker of the n PDI 2 ligand., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Selectively converting linear alkanes to α-olefins under mild conditions is a highly desirable transformation given the abundance of alkanes as well as the use of olefins as building blocks in the chemical community. Until now, this reaction has been primarily the remit of noble-metal catalysts, despite extensive work showing that base-metal alkylidenes can mediate the reaction in a stoichiometric fashion. Here, we show how the presence of a hydrogen acceptor, such as the phosphorus ylide, when combined with the alkylidene complex (PNP)Ti=CH t Bu(CH 3 ) (PNP=N[2-P(CHMe 2 ) 2 -4-methylphenyl] 2 ), catalyses the dehydrogenation of cycloalkanes to cyclic alkenes, and linear alkanes with chain lengths of C - to C 4 to C 8 to terminal olefins under mild conditions. This Article represents the first example of a homogeneous and selective alkane dehydrogenation reaction using a base-metal titanium catalyst. We also propose a unique mechanism for the transfer dehydrogenation of hydrocarbons to olefins and discuss a complete cycle based on a combined experimental and computational study.

Purification of rare earth elements is challenging due to their chemical similarities. All of the deployed separation methods rely on thermodynamic properties, such as distribution equilibria in solvent extraction. Rare-earth-metal separations based on kinetic differences have not been examined. Herein, we demonstrate a new approach for rare-earth-element separations by exploiting differences in the oxidation rates within a series of rare earth compounds containing the redox-active ligand [{2-(tBuN(O))C 6 H 4 CH 2 } 3 N] 3- . Using this method, a single-step separation factor up to 261 was obtained for the separation of a 50:50 yttrium-lutetium mixture., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel approach to produce chiral diaryl sulfoxides from aryl benzyl sulfoxides and aryl bromides via an enantioselective arylation of aryl sulfenate anions is reported. A (JosiPhos)Pd-based catalyst successfully promotes the asymmetric arylation reaction with good functional group compatibility. A wide range of enantioenriched diaryl, aryl heteroaryl, and even diheteroaryl sulfoxides were generated. Many of the sulfoxides prepared herein would be difficult to prepare via classic enantioselective oxidation of sulfides, including Ph(Ph-d 5 )SO (90% ee, 95% yield). A DFT-based computational study suggested that chiral induction originates from two primary factors: (i) both a kinetic and a thermodynamic preference for oxidative addition that places the bromide trans to the JosiPhos-diarylphosphine moiety and (ii) Curtin-Hammett-type control over the interconversion between O- and S-bound isomers of palladium sulfenate species following rapid interconversion between re- and si-bound transmetalation products, re/si-Pd-OSPh (re/si-PdO-trans).

The complex [(nacnac)Ti(OAr)] 2 (μ 2 :η 2 ,η 2 -P 2 ) (1) is formed via reductive decarbonylation of the phosphaethynolate ion - [OCP], which serves as a P atom source. Complex 1 is the first structurally characterized Group 4 transition metal P 2 complex and its structure reveals the rhombic Ti 2 P 2 core is essentially planar with short bond lengths suggesting some degree of multiple bonding character between the Ti-P and P-P sites. Computational studies of 1 provide an understanding of the Ti 2 P 2 core as well as the origin of the highly downfield 31 P NMR spectroscopic signal., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first example of a structurally characterized titanium methylidene, (PN) 2 Ti[double bond, length as m-dash]CH 2 , has been prepared via one-electron oxidation of (PN) 2 Ti(CH 3 ) followed by deprotonation or by H-atom abstraction using an aryloxyl radical. The Ti[double bond, length as m-dash]C distance was found to be 1.939(3) Å, and variable temperature, multinuclear, and multidimensional NMR spectroscopic experiments revealed the methylidene to engage in long range interactions with protons on the ligand framework. Computational studies showed that the Ti[double bond, length as m-dash]C bond, which until now has eluded structural studies, displays all the hallmarks of a prototypical Schrock-carbene.

A series of alkali metal capped cerium(IV) imido complexes, [M(solv) x ][Ce═N(3,5-(CF 3 ) 2 C 6 H 3 )(TriNOx)] (M = Li, K, Rb, Cs; solv = TMEDA, THF, Et 2 O, or DME), was isolated and fully characterized. An X-ray structural investigation of the cerium imido complexes demonstrated the impact of the alkali metal counterions on the geometry of the [Ce═N(3,5-(CF 3 ) 2 C 6 H 3 )(TriNOx)] - moiety. Substantial shortening of the Ce═N bond was observed with increasing size of the alkali metal cation. The first complex featuring an unsupported, terminal multiple bond between a Ce(IV) ion and a ligand fragment was also isolated by encapsulation of a Cs + counterion with 2.2.2-cryptand. This complex shows the shortest recorded Ce═N bond length of 2.077(3) Å. Computational investigation of the cerium imido complexes using DFT methods showed a relatively larger contribution of the cerium 5d orbital than the 4f orbital to the Ce═N bonds. The [K(DME) 2 ][Ce═N(3,5-(CF 3 ) 2 C 6 H 3 )(TriNOx)] complex cleaves the Si-O bond in (Me 3 Si) 2 O, yielding the [(Me 3 SiO)Ce IV (TriNOx)] adduct. The reaction of the rubidium capped imido complex with benzophenone resulted in the formation of a rare Ce(IV)-oxo complex, that was stabilized by a supramolecular, tetrameric oligomerization of the Ce═O units with rubidium cations.

In this contribution we present reactivity studies of a rare example of a titanium salt, in the form of [μ 2 -K(OEt 2 )] 2 [(PN) 2 Ti[triple bond, length as m-dash]N] 2 ( 1 ) (PN - = N -(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide) to produce a series of imide moieties including rare examples such as methylimido, borylimido, phosphonylimido, and a parent imido. For the latter, using various weak acids allowed us to narrow the p K a range of the NH group in (PN) 2 Ti[triple bond, length as m-dash]NH to be between 26-36. Complex 1 could be produced by a reductively promoted elimination of N 2 from the azide precursor (PN) 2 TiN 3 , whereas reductive splitting of N 2 could not be achieved using the complex (PN) 2 Ti[double bond, length as m-dash]N[double bond, length as m-dash]N[double bond, length as m-dash]Ti(PN) 2 ( 2 ) and a strong reductant. Complete N-atom transfer reactions could also be observed when 1 was treated with ClC(O) t Bu and OCCPh 2 to form NC t Bu and KNCCPh 2 , respectively, along with the terminal oxo complex (PN) 2 Ti[triple bond, length as m-dash]O, which was also characterized. A combination of solid state 15 N NMR (MAS) and theoretical studies allowed us to understand the shielding effect of the counter cation in dimer 1 , the monomer [K(18-crown-6)][(PN) 2 Ti[triple bond, length as m-dash]N], and the discrete salt [K(2,2,2-Kryptofix)][(PN) 2 Ti[triple bond, length as m-dash]N] as well as the origin of the highly downfield 15 N NMR resonance when shifting from dimer to monomer to a terminal nitride (discrete salt). The upfield shift of 15 N nitride resonance in the 15 N NMR spectrum was found to be linked to the K + induced electronic structural change of the titanium-nitride functionality by using a combination of MO analysis and quantum chemical analysis of the corresponding shielding tensors., (This journal is © The Royal Society of Chemistry 2016.)

Rare earth (RE) metals are critical components of electronic materials and permanent magnets. Recycling of consumer materials is a promising new source of rare REs. To incentivize recycling, there is a clear need for the development of simple methods for targeted separations of mixtures of RE metal salts. Metal complexes of a tripodal hydroxylaminato ligand, TriNOx 3- , featured a size-sensitive aperture formed of its three η 2 -(N,O) ligand arms. Exposure of cations in the aperture induced a self-associative equilibrium comprising RE(TriNOx)THF and [RE(TriNOx)] 2 species. Differences in the equilibrium constants K dimer for early and late metals enabled simple separations through leaching. Separations were performed on RE1/RE2 mixtures, where RE1 = La-Sm and RE2 = Gd-Lu, with emphasis on Eu/Y separations for potential applications in the recycling of phosphor waste from compact fluorescent light bulbs. Using the leaching method, separations factors approaching 2,000 were obtained for early-late RE combinations. Following solvent optimization, >95% pure samples of Eu were obtained with a 67% recovery for the technologically relevant Eu/Y separation., Competing Interests: The authors declare the following competing financial interest: Intellectual property pertaining to the technology described in this article is covered by International Patent Application no. PCT/US2015/042703.

The hexachlorocerate(III) anion, [Ce III Cl 6 ] 3- , was found to be a potent photoreductant in acetonitrile solution with an estimated excited-state reduction potential of -3.45 V versus Cp 2 Fe 0/+ . Despite a short lifetime of 22.1(1) ns, the anion exhibited a photoluminescence quantum yield of 0.61(4) and fast quenching kinetics toward organohalogens allowing for its application in the photocatalytic reduction of aryl chloride substrates.

We report the synthesis and structure of a titanium(iv) benzophenone adduct bearing a terminal oxo ligand, (PNP)Ti = O(OTf)(OCPh 2 ) (PNP - = N[2-P i Pr 2 -4-methylphenyl] 2 ) (2). Complex 2 is readily synthesized in 71% yield from the previously reported titanium alkylidene (PNP)Ti[double bond, length as m-dash]CH t Bu(OTf) (1) and two equivalents of benzophenone, by extruding the olefin Ph 2 C[double bond, length as m-dash]CH t Bu. Treatment of benzophenone adduct 2 with a bulky aryloxide salt results in formation of (PNP)Ti[double bond, length as m-dash]O(OAr) (3) (OAr - = 2,6-bis(diphenylmethyl)-4-tert-butylphenoxide), concurrent with salt elimination and displacement of the benzophenone. Complexes 2 and 3 were characterized by single-crystal X-ray diffraction and a variety of spectroscopic techniques, including NMR, UV-Vis-NIR spectroscopies, and TD-DFT calculations.

Structurally authenticated, terminal lanthanide-ligand multiple bonds are rare and expected to be highly reactive. Even capped with an alkali metal cation, poor orbital energy matching and overlap of metal and ligand valence orbitals should result in strong charge polarization within such bonds. We expand on a new strategy for isolating terminal lanthanide-ligand multiple bonds using cerium(IV) complexes. In the current case, our tailored tris(hydroxylaminato) ligand framework, TriNOx(3-), provides steric protection against ligand scrambling and metal complex oligomerization and electronic protection against reduction. This strategy culminates in isolation of the first formal Ce═N bonded moiety in the complex [K(DME)2][Ce═N(3,5-(CF3)2C6H3)(TriNOx)], whose Ce═N bond is the shortest known at 2.119(3) Å.

Two complete mixed-ligand series of luminescent Ce(III) complexes with the general formulas [(Me3Si)2NC(N(i)Pr)2]xCe(III)[N(SiMe3)2]3-x (x = 0, 1-N; x = 1, 2-N, x = 2, 3-N; x = 3, 4) and [(Me3Si)2NC(N(i)Pr)2]xCe(III)(OAr)3-x (x = 0, 1-OAr; x = 1, 2-OAr, x = 2, 3-OAr; x = 3, 4) were developed, featuring photoluminescence quantum yields up to 0.81(2) and lifetimes to 117(1) ns. Although the 4f → 5d absorptive transitions for these complexes were all found at ca. 420 nm, their emission bands exhibited large Stokes shifts with maxima occurring at 553 nm for 1-N, 518 nm for 2-N, 508 nm for 3-N, and 459 nm for 4, featuring yellow, lime-green, green, and blue light, respectively. Combined time-dependent density functional theory (TD-DFT) calculations and spectroscopic studies suggested that the long-lived (2)D excited states of these complexes corresponded to singly occupied 5dz(2) orbitals. The observed difference in the Stokes shifts was attributed to the relaxation of excited states through vibrational processes facilitated by the ligands. The photochemistry of the sterically congested complex 4 was demonstrated by C-C bond forming reaction between 4-fluoroiodobenzene and benzene through an outer sphere electron transfer pathway, which expands the capabilities of cerium photosensitizers beyond our previous results that demonstrated inner sphere halogen atom abstraction reactivity by 1-N.

The synthesis and characterization of two high-valent vanadium-cyclo-P3 complexes, (nacnac)V(cyclo-P3)(Ntolyl2) (1) and (nacnac)V(cyclo-P3)(OAr) (2), and an inverted sandwich derivative, [(nacnac)V(Ntolyl2)]2(μ2-η(3):η(2)-cyclo-P3) (3), are presented. These novel complexes are prepared by activating white phosphorus (P4) with three-coordinate vanadium(II) precursors. Structural metrics, redox behavior, and DFT electronic structure analysis indicate that a [cyclo-P3](3-) ligand is bound to a V(V) center in monomeric species 1 and 2. A salient feature of these new cyclo-P3 complexes is their significantly downfield shifted (by ∼300 ppm) (31)P NMR resonances, which is highly unusual compared to related complexes such as (Ar[(i)Pr]N)3Mo(cyclo-P3) (4) and other cyclo-P3 complexes that display significantly upfield shifted resonances. This NMR spectroscopic signature was thus far thought to be a diagnostic property for the cyclo-P3 ligand related to its acute endocyclic angle. Using DFT calculations, we scrutinized and conceptualized the origin of the unusual chemical shifts seen in this new class of complexes. Our analysis provides an intuitive rational paradigm for understanding the experimental (31)P NMR spectroscopic signature by relating the nuclear magnetic shielding with the electronic structure of the molecule, especially with the characteristics of metal-cyclo-P3 bonding.

The ethylene complex (PNP)Ti(η(2)-H2C═CH2)(CH2(t)Bu) or (PNP)Ti═CH(t)Bu(CH2(t)Bu) (PNP(-) = N[2-P(CHMe2)2-4-methylphenyl]2) reacts with H2CPPh3 to form the κ(2)-phosphinoalkylidene (PNP)Ti═CHPPh2(Ph) (1). Compound 1 activates benzene via the transient intermediate [(PNP)Ti≡CPPh2] (C). By treatment of (PNP)Ti═CH(t)Bu(OTf) with LiCH2PPh2, 1 or its isotopologue (PNP)Ti═CDPPh2(C6D5) (1-d6) can be produced by an independent route involving intermediate C, which activates benzene or benzene-d6 and dehydrogenates cyclohexane-d12. Addition of MeOTf to 1 results in elimination of benzene concomitant with the formation of the phosphonioalkylidyne complex, [(PNP)Ti≡CPPh2Me(OTf) (2). Theoretical studies of 2 suggest a resonance structure having dominant Ti-C triple-bond character with some contribution also from a C-P multiple bond.

Triarylborane Lewis acids bind [Fe2(pdt)(CO)4(CN)2](2-) [1](2-) (pdt(2-) = 1,3-propanedithiolate) and [Fe2(adt)(CO)4(CN)2](2-) [3](2-) (adt(2-) = 1,3-azadithiolate, HN(CH2S(-))2) to give the 2:1 adducts [Fe2(xdt)(CO)4(CNBAr3)2](2-). Attempts to prepare the 1:1 adducts [1(BAr3)](2-) (Ar = Ph, C6F5) were unsuccessful, but related 1:1 adducts were obtained using the bulky borane B(C6F4-o-C6F5)3 (BAr(F)*3). By virtue of the N-protection by the borane, salts of [Fe2(pdt)(CO)4(CNBAr3)2](2-) sustain protonation to give hydrides that are stable (in contrast to [H1](-)). The hydrides [H1(BAr3)2](-) are 2.5-5 pKa units more acidic than the parent [H1](-). The adducts [1(BAr3)2](2-) oxidize quasi-reversibly around -0.3 V versus Fc(0/+) in contrast to ca. -0.8 V observed for the [1](2-/-) couple. A simplified synthesis of [1](2-), [3](2-), and [Fe2(pdt)(CO)5(CN)](-) ([2](-)) was developed, entailing reaction of the diiron hexacarbonyl complexes with KCN in MeCN.

Described are experiments demonstrating incorporation of cyanide cofactors and hydride substrate into [NiFe]-hydrogenase (H2ase) active site models. Complexes of the type (CO)2(CN)2Fe(pdt)Ni(dxpe) (dxpe = dppe, 1; dxpe = dcpe, 2) bind the Lewis acid B(C6F5)3 (BAr(F)3) to give the adducts (CO)2(CNBAr(F)3)2Fe(pdt)Ni(dxpe), (1(BAr(F)3)2, 2(BAr(F)3)2). Upon decarbonylation using amine oxides, these adducts react with H2 to give hydrido derivatives [(CO)(CNBAr(F)3)2Fe(H)(pdt)Ni(dxpe)](-) (dxpe = dppe, [H3(BAr(F)3)2](-); dxpe = dcpe, [H4(BAr(F)3)2](-)). Crystallographic analysis shows that Et4N[H3(BAr(F)3)2] generally resembles the active site of the enzyme in the reduced, hydride-containing states (Ni-C/R). The Fe-H···Ni center is unsymmetrical with r(Fe-H) = 1.51(3) Å and r(Ni-H) = 1.71(3) Å. Both crystallographic and (19)F NMR analyses show that the CNBAr(F)3(-) ligands occupy basal and apical sites. Unlike cationic Ni-Fe hydrides, [H3(BAr(F)3)2](-) and [H4(BAr(F)3)2](-) oxidize at mild potentials, near the Fc(+/0) couple. Electrochemical measurements indicate that in the presence of base, [H3(BAr(F)3)2](-) catalyzes the oxidation of H2. NMR evidence indicates dihydrogen bonding between these anionic hydrides and R3NH(+) salts, which is relevant to the mechanism of hydrogenogenesis. In the case of Et4N[H3(BAr(F)3)2], strong acids such as HCl induce H2 release to give the chloride Et4N[(CO)(CNBAr(F)3)2Fe(Cl)(pdt)Ni(dppe)].

Nuclear inelastic scattering of (57)Fe labeled [NiFe] hydrogenase is shown to give information on different states of the enzyme. It was thus possible to detect and assign Fe-CO and Fe-CN bending and stretching vibrations of the active site outside the spectral range of the Fe-S cluster normal modes., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)