Influence of 1,2,4-Tri--butylcyclopentadienyl Ligand on the Reactivity of the Thorium Bipyridyl Metallocene [η-1,2,4-(MeC)CH]Th(bipy)].

The thorium bipyridyl metallocene (Cp)Th(bipy) (; Cp = η-1,2,4-(MeC)CH) shows a rich reactivity toward a series of small molecules. For example, complex may act as a synthon for the (Cp)Th(II) fragment as illustrated by its reactivity toward to CuI, hydrazine derivative (PhNH), Ph ( = S, Se), elemental sulfur (S) and selenium (Se), organic azides, CS, and isothiocyanates. Moreover, in the presence of polar multiple bonds, such as those in ketones PhCO and (CH)CO, aldehydes -MePhCHO and -ClPhCHO, seleno-ketone (-MeOPh)CSe, nitriles PhCN, PhCHCN, CHCN, and -(NC)Ph, and benzoyl cyanide PhCOCN, C-C coupling occurs to furnish (Cp)Th[(bipy)(PhCO)] (), (Cp)Th[(bipy)((CH)CO)] (), (Cp)Th[(bipy)(-MePhCHO)] (), (Cp)Th[(bipy)(-ClPhCHO)] (), (Cp)Th[(bipy){(-MeOPh)CSe}] (), (Cp)Th[(bipy)(PhCN)] (), (Cp)Th[(bipy)(PhCHCN)] (), (Cp)Th[(bipy)(CHCN)] (), [(Cp)Th]{μ-(bipy)[-Ph(CN)](bipy)} (), and (Cp)Th{(bipy)[PhC(CN)O]} (), respectively.

Homo- and heterobimetallic transition metal cluster derived from [Cp*Fe(η-E)] (E = P, As) - unprecedented structural motifs of the resulting polypnictogen ligands.

A general synthetic procedure to neutral homo- and heterobimetallic cage compounds exhibiting various structural motifs of the polypnictogen ligands starting from [Cp*Fe(η-E)] (E = P (1), As (2); Cp* = CMe) is reported. The impact of the implemented transition metal precursors {Cp'''M} (M = Cr, Mn, Fe, Ni; Cp''' = 1,2,4-BuCH) emphasises the variability of the isolated complexes exhibiting a broad variety of structural motifs of the pnictogen ligands. Spectroscopic, crystallographic, and theoretical investigations provide insight into the structure of the partially unprecedented polypnictogen ligands.

Synthesis and Structure of [η-1,2,4-(MeSi)CH]Th(bipy) and Its Reactivity toward Small Molecules.

Halide exchange of (Cp)ThCl (; Cp = η-1,2,4-(MeSi)CH) with MeSiI furnishes (Cp)ThI (), which is then reduced with potassium graphite (KC) in the presence of 2,2'-bipyridine to give the thorium bipyridyl metallocene (Cp)Th(bipy) () in good yield. Complex was fully characterized and readily reacted with various small molecules. For example, may serve as a synthetic equivalent for the (Cp)Th(II) fragment when exposed to CuI, PhS, organic azides, and CS.

Geometry and electronic structure of Yb(III)[CH(SiMe)] from EPR and solid-state NMR augmented by computations.

Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and - still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-the-art magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe)], a prototypical example, which contains notable structural features according to X-ray crystallography.

Uranium versus Thorium: A Case Study on a Base-Free Terminal Uranium Imido Metallocene.

The structure of and bonding in two base-free terminal actinide imido metallocenes, [η-1,2,4-(MeC)CH]An═N(-tolyl) (An = U (), Th ()) are compared and connected to their individual reactivity. While structurally rather similar, the U(IV) derivative is slightly more sterically crowded. Furthermore, density functional theory (DFT) studies imply that the 5f orbital contribution to the bonding within the individual actinide imido An═N(-tolyl) moieties is significantly larger for than for , which makes the bonds between the [η-1,2,4-(MeC)CH]U and [(-tolyl)N] fragments more covalent.

Experimental and Computational Studies on Uranium Diazomethanediide Complexes.

Uranium diazomethanediide complexes can be prepared and their synthesis, structure and reactivity were explored. Reaction of the uranium imido compound [η -1,2,4-(Me Si) C H ] U=N(p-tolyl)(dmap) (1) or [η -1,3-(Me C) C H ] U=N(p-tolyl)(dmap) (4) with Me SiCHN cleanly yields the first isocyanoimido metal complexes [η -1,2,4-(Me Si) C H ] U(=NNC)(μ-CNN=)U(dmap)[η -1,2,4-(Me Si) C H ] (2) and {[η -1,3-(Me C) C H ] U[μ-(=NNC)]} (5), respectively. Both compounds exhibit remarkable thermal stability and were fully characterized.

Reactivity of a Lewis base-supported uranium terminal imido metallocene towards small molecules.

The Lewis base-supported uranium terminal imido metallocene [η-1,2,4-(MeSi)CH]UN(-tolyl)(dmap) (1) readily reacts with various small molecules such as internal alkynes, isothiocyanates, thioketones, amidates, organic nitriles and imines, chlorosilanes, copper iodide, diphenyl disulfide, organic azides and diazoalkane derivatives. For example, treatment of 1 with PhCCCCPh and PhNCS forms metallaheterocycles originating from a [2 + 2] cycloaddition to yield [η-1-(-tolyl)NC(Ph)CHCC(Ph)CHSi(Me)-2,4-(MeSi)CH][η-1,2,4-(MeSi)CH]U (2) and [η-1,2,4-(MeSi)CH]U[N(-tolyl)C(NPh)S](dmap) (3), respectively. The reaction of 1 with the thioketone PhCS forms the known uranium sulfido complex [η-1,2,4-(MeSi)CH]US(dmap) (4), which reacts with a second molecule of PhCS to give the disulfido compound [η-1,2,4-(MeSi)CH]U(SCPh) (5).

A Comprehensive Study Concerning the Synthesis, Structure, and Reactivity of Terminal Uranium Oxido, Sulfido, and Selenido Metallocenes.

Terminal uranium oxido, sulfido, and selenido metallocenes were synthesized, and their reactivity was comprehensively studied. Heating of an equimolar mixture of [η-1,2,4-(MeSi)CH]UMe () and [η-1,2,4-(MeSi)CH]U(NH--tolyl) () in the presence of 4-dimethylaminopyridine (dmap) in refluxing toluene forms [η-1,2,4-(MeSi)CH]U═N(-tolyl)(dmap) (), which is a useful precursor for the preparation of the terminal uranium oxido, sulfido, and selenido metallocenes [η-1,2,4-(MeSi)CH]U═E(dmap) (E = O (), S (), Se ()) employing a cycloaddition-elimination methodology with PhC═E (E = O, S) or (-MeOPh)CSe, respectively. Metallocenes - are inert toward alkynes, but they act as nucleophiles in the presence of alkylsilyl halides.

Low-Coordinate Iron(II) Amido Half-Sandwich Complexes with Large Internal Magnetic Hyperfine Fields.

The half-sandwich complex [Cp'Fe{N(dipp)(SiMe)}] (; Cp' = 1,2,4-tri--butylcyclopentadienyl and dipp = 2,6-diisopropylphenyl) and the mixed metallocene [Cp'Fe{(η-CHPr)═N(SiMe)}] () formed in the reaction between [{Cp'Fe(μ-I)}] and [Li{N(dipp)(SiMe)}] were characterized by NMR spectroscopy and X-ray diffraction analysis. complements the series of low-coordinate, quasi-linear iron amido half-sandwich complexes [Cp'Fe{N(Bu)(SiMe)}] () and [Cp'Fe{N(SiMe)}] () reported earlier, and all three compounds were characterized in the solid state by zero-field Fe Mössbauer spectroscopy and magnetic susceptibility measurements, confirming their = 2 electronic ground state. Moreover, the Mössbauer absorption spectra reveal slow paramagnetic relaxation at low temperatures with large internal magnetic hyperfine fields of = 96.

Intrinsic reactivity of [η-1,3-(MeSi)CH]U(η-CPh) in small molecule activation.

The uranium metallacyclocumulene, [η-1,3-(MeSi)CH]U(η-CPh) (3) was isolated from the reaction mixture containing [η-1,3-(MeSi)CH]UCl (1), potassium graphite (KC) and 1,4-diphenylbutadiyne (PhCC-CCPh) in good yield. The reactivity of 3 towards various small organic molecules was evaluated. For example, while complex 3 shows no reactivity towards alkynes and 2,2'-bipyridine, it may deliver the [η-1,3-(MeSi)CH]U(II) fragment in the presence of PhE (E = S, Se) and PhCN, or react as a nucleophile in the presence of carbodiimides, isothiocyanates, aldehydes, ketones, and pyridine derivatives, forming five-, seven- or nine-membered heterometallacycles.

Small-Molecule Activation Mediated by [η-1,3-(MeSi)CH]U(bipy).

The uranium bipyridyl metallocene, [η-1,3-(MeSi)CH]U(bipy) (), is readily accessible in good yield by adding potassium graphite (KC) to a mixture of [η-1,3-(MeSi)CH]UCl () and 2,2'-bipyridine. Compound was fully characterized and employed for small-molecule activation. It has been demonstrated that may serve as a synthon for [η-1,3-(MeSi)CH]U(II) fragment in the presence of PhE (E = S, Se), alkynes, and a variety of hetero-unsaturated molecules such as diazabutadienes, azine (PhC═N), -benzoquinone, pyridine -oxide, CS, isothiocyanates, and organic azides.

Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of -lactide.

The alkyl-functionalised scandium complex [(pdl*SiMeNBu)Sc(thf)(CHSiMe)] (2) was synthesised in enantiomerically pure form and characterised by NMR spectroscopy and X-ray diffraction analysis. Complex 2 features a chiral constrained geometry ligand derived from the natural compound (1)-(-)-myrtenal, in which the pentadienyl (pdl*) fragment coordinates in η:η-allyl-en fashion to the scandium atom. Compound 2 catalyses the polymerisation of -lactide at 30 °C and 50 °C yielding amorphous poly(lactide) with slightly heterotactic enchainment ( = 0.

Synthesis and reactivity of the uranium phosphinidene metallocene [η-1,3-(MeSi)CH]U(P-2,4,6-PrCH)(OPMe): influence of the coordinated Lewis base.

This paper describes the synthesis and reactivity of [η-1,3-(MeSi)CH]U(P-2,4,6-PrCH)(OPMe) (6) which is accessible from a ligand exchange reaction between [η-1,3-(MeSi)CH]U(P-2,4,6-PrCH)(OPPh) (2) and MePO at ambient temperature. Phosphinidene 6 exhibits no reactivity towards internal alkynes, but readily reacts with various hetero-unsaturated molecules such as isothiocyanates, aldehydes, nitriles, isonitriles, and organic azides, forming uranium sulfido, oxido, imido, and uranaheterocyclic compounds. Nevertheless, with the bidentate -dicyanobenzene -CH(CN) the zwitterionic species [η-1,3-(MeSi)CH]U[NHC(N){CHCP(2,4,6-PrCH)CHPMeO}] (13) is isolated in good yield.

Crystal structure of potassium tri-ethyl-hydridoborate ('superhydride').

In the title compound, formally K·CHB, the contact sphere of potassium consists of eleven hydrogen atoms from three different anions, assuming an arbitrary cut-off of 3 Å. The shortest inter-action, 2.53 (2) Å, involves the hydridic hydrogen H01, which fulfils a bridging function in the formation of chains of KHBEt units parallel to the axis [K1-H01 2.

Reactivity studies involving a Lewis base supported terminal uranium phosphinidene metallocene [η-1,3-(MeC)CH]U([double bond, length as m-dash]P-2,4,6-PrCH)(OPMe).

The Lewis base supported terminal uranium phosphinidene metallocene [η5-1,3-(Me3C)2C5H3]2U([double bond, length as m-dash]P-2,4,6-iPr3C6H2)(OPMe3) (2) could be isolated from a salt metathesis reaction in toluene at ambient temperature between [η5-1,3-(Me3C)2C5H3]2U(Cl)Me (1) and 2,4,6-iPr3C6H2PHK in the presence of Me3PO, and its structure and reactivity were probed in detail. No reaction of 2 with internal alkynes was observed, but it reacts in the presence of various heterounsaturated molecules such as CS2, isothiocyanates, aldehydes, imines, diazenes, carbodiimides, nitriles, isonitriles, diazoalkane, and organic azides, forming carbodithioates, sulfidos, oxidos, metallaheterocycles, and imido complexes, in good yields. Moreover, on reaction with the diazoalkane derivative Me3SiCHN2 the pseudophosphinimido uranium(iii) complex [η5-1,3-(Me3C)2C5H3]2U(N[double bond, length as m-dash]P-2,4,6-iPr3C6H2)(OPMe3) (20) can be isolated in good yield.

Uranium versus Thorium: Synthesis and Reactivity of [η -1,2,4-(Me C) C H ] U[η -C Ph ].

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η -1,2,4-(Me C) C H ] U=P-2,4,6-tBu C H (1) yields the stable uranium metallacyclopropene, [η -1,2,4-(Me C) C H ] U[η -C Ph ] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U-(η -C=C) moiety increases significantly compared to the related Th compound [η -1,2,4-(Me C) C H ] Th[η -C Ph ], which also results in more covalent bonds between the [η -1,2,4-(Me C) C H ] U and [η -C Ph ] fragments.

Experimental evaluation of the stabilization of the COT orbitals by 4f orbitals in COTCe using a Hubbard model.

Significant orbital mixing is rare in lanthanide complexes because of the limited radial extent of the 4f orbitals, which results in a generally small stabilization due to 4f orbital interactions. Nevertheless, even a small amount of additional stabilization could enhance lanthanide separations. One lanthanide complex in which orbital mixing has been extensively studied both experimentally and computationally is cerocene, COTCe, where COT is cyclooctatetraene.

A Lewis Base Supported Terminal Uranium Phosphinidene Metallocene.

A Lewis base supported terminal uranium phosphinidene, [η-1,3-(MeC)CH]U(═P-2,4,6-BuCH)(OPMe) (), is isolated from the reaction of the uranium methyl chloride [η-1,3-(MeC)CH]U(Cl)Me () with 2,4,6-(MeC)CHPHK in toluene in the presence of MePO. Moreover, the reactivity of uranium phospinidene toward a series of small molecules was comprehensively explored. While no reactivity of with internal alkynes is observed attributed to steric hindrance, it readily reacts in good yields with various small molecules including isothiocyanates, aldehydes, imines, diazenes, carbodiimides, nitriles, isonitriles, and organic azides, yielding uranium sulfidos, oxidos, metallaheterocycles, and imido complexes.

Experimental and Computational Studies on a Base-Free Terminal Uranium Phosphinidene Metallocene.

The first stable base-free terminal uranium phosphinidene metallocene is presented; and its structure and reactivity have been studied in detail and compared to that of the corresponding thorium derivative. Salt metathesis reaction of the methyl iodide uranium metallocene Cp''' U(I)Me (2, Cp'''=η -1,2,4-(Me C) C H ) with Mes*PHK (Mes*=2,4,6-(Me C) C H ) in THF yields the base-free terminal uranium phosphinidene metallocene, Cp''' U=PMes* (3). In addition, density functional theory (DFT) studies suggest substantial 5f orbital contributions to the bonding within the uranium phosphinidene [U]=PAr moiety, which results in a more covalent bonding between the [Cp''' U] and [Mes*P] fragments than that for the related thorium derivative.

Enantiomerically Pure Constrained Geometry Complexes of the Rare-Earth Metals Featuring a Dianionic N-Donor Functionalised Pentadienyl Ligand: Synthesis and Characterisation.

We report the preparation of enantiomerically pure constrained geometry complexes (cgc) of the rare-earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1R)-(-)-myrtenal. The potassium salt 1, [Kpdl*], was treated with ClSiMe NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser-type base KOtPen/nBuLi (tPen=CMe (CH Me)) to yield the dipotassium salt [K (pdl*SiMe NtBu)] (3). However, 3 rearranges in THF solution to its isomer 3' by a 1,3-H shift, which elongates the bridge between the pdl and SiMe NtBu moieties by one CH unit.

NH formation from N and H mediated by molecular tri-iron complexes.

Living systems carry out the reduction of N to ammonia (NH) through a series of protonation and electron transfer steps under ambient conditions using the enzyme nitrogenase. In the chemical industry, the Haber-Bosch process hydrogenates N but requires high temperatures and pressures. Both processes rely on iron-based catalysts, but molecular iron complexes that promote the formation of NH on addition of H to N have remained difficult to devise.

Non-oxidative Methane Coupling over Silica versus Silica-Supported Iron(II) Single Sites.

Non-oxidative CH coupling is promoted by silica with incorporated iron sites, but the role of these sites and their speciation under reaction conditions are poorly understood. Here, silica-supported iron(II) single sites, prepared via surface organometallic chemistry and stable at 1020 °C in vacuum, are shown to rapidly initiate CH coupling at 1000 °C, leading to 15-22 % hydrocarbons selectivity at 3-4 % conversion. During this process, iron reduces and forms carburized iron(0) nanoparticles.

Pogo-Stick Iron and Cobalt Complexes: Synthesis, Structures, and Magnetic Properties.

The synthesis, structures, and magnetic properties of monomeric half-sandwich iron and cobalt imidazolin-2-iminato complexes have been comprehensively investigated. Salt metathesis reactions of [Cp'M(μ-I)] (, M = Fe, Co; Cp' = η-1,2,4-tri--butylcyclopentadienyl) with [ImNLi] (ImN = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) furnishes the terminal half-sandwich compounds [Cp'M(NIm)] (, M = Fe, Co), which can be regarded as models for elusive half-sandwich iron and cobalt imido complexes. X-ray diffraction analysis confirmed the structure motif of a one-legged piano stool.

Synthesis and molecular structure of enantiomerically pure pentadienyl complexes of the rare-earth metals.

The enantiomerically pure pentadienyl (Pdl*) ligand derived from the natural product (1R)-(-)-myrtenal forms with MCl (M = La, Ce, Pr, and Nd) the corresponding homoleptic [(η-U-Pdl*)M compounds (1-M). These complexes were fully characterised by H NMR spectroscopy, elemental analyses and X-ray diffraction. They exhibit in solution and solid state idealized C symmetry, and their molecular structures also reveal that the Pdl* ligand adopts a U-conformation and coordinates exclusively with its less sterically encumbered face to the rare-earth metal atom.