Investigating Steric and Electronic Effects in the Synthesis of Square Planar 6d Th(III) Complexes.

The factors affecting the formation and crystal structures of unusual 6d Th(III) square planar aryloxide complexes, as exemplified by [Th(OAr)] (OAr = OCHBu-2,6-Me-4), were explored by synthetic and reduction studies of a series of related Th(IV) tetrakis(aryloxide) complexes, Th(OAr) (OAr = OCHBu-2,6-R-4). Specifically, electronic, steric, and countercation effects were explored by varying the aryloxide ligand, the alkali metal reducing agent, and the alkali metal chelating agent. Salt metathesis reactions between ThBr(DME) (DME = 1,2-dimethoxyethane) and 4 equiv of the appropriate potassium aryloxide salt were used to prepare a series of Th(IV) aryloxide complexes in high yields: Th(OAr) (OAr = OCHBu-2,6), Th(OAr) (OAr = OCHBu-2,4,6), Th(OAr) (OAr = OCHBu-2,6-OMe-4), and Th(OAr) (OAr = OCHBu-2,6-Ph-4).

Perplexing EPR Signals from 5f6d U(II) Complexes.

Metal complexes with unpaired electrons in orbitals of different angular momentum quantum numbers (., f and d orbitals) are unusual and opportunities to study the interactions among these electrons are rare. X-band electron paramagnetic resonance (EPR) data were collected at <10 and 77 K on 10 U(II) complexes with 5f6d electron configurations and on some analogous Ce(II), Pr(II), and Nd(II) complexes with 4f5d electron configurations.

Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium -Metallocene Hydride Complex, [K(crypt)][(μ-Cp)Y(μ-H)] (Cp = MeSi[CH(SiMe)-3]), with a 3.4 Å Yttrium-Yttrium Distance.

The reduction of a bimetallic yttrium -metallocene hydride was examined to explore the possible formation of Y-Y bonds with 4d Y(II) ions. The precursor [CpY(μ-H)(THF)] (Cp = MeSi[CH(SiMe)-3]) was synthesized by hydrogenolysis of the allyl complex CpY(η-CH)(THF), which was prepared from (CH)MgCl and [CpY(μ-Cl)]. Treatment of [CpY(μ-H)(THF)] with excess KC in the presence of one equivalent of 2.

Trimethyltriazacyclohexane coordination chemistry of simple rare-earth metal salts.

Reactions of 1,3,5-trimethyl-triazacyclohexane (Metach) with common rare-earth metal iodide, chloride, and triflate salts were examined to determine the capacity of this inexpensive chelate to provide alternative precursors for THF-free reactions. The reaction of LaI(THF) and CeI(THF) with 1,3,5-trimethyl-triazacyclohexane in THF generated toluene soluble (Metach)LnI, 1-Ln, in which the Ln center has a tri-capped trigonal prismatic geometry with two eclipsed Metach rings. Reaction with NdI(THF) forms the analogous 1-Nd, but a different structure with one outer sphere iodide, [(Metach)NdI][I], 2-Nd, is also accessible and has a structure reminiscent of bent metallocenes.

Synthesis of Trimethyltriazacyclohexane (Metach) Sandwich Complexes of Uranium, Neptunium, and Plutonium Triiodides: (Metach)AnI.

1,3,5-Trimethyl-1,3,5-triazacyclohexane (Metach) readily complexes uranium triiodide to form (Metach)UI. The complex is soluble in THF and arenes and can function as a source of UI to form organometallic U(III) complexes. When dissolved in pyridine (py), (Metach)UI forms (Metach)UI(py).

Reduction of Rare-Earth Metal Complexes Induced by γ Irradiation.

The utility of γ irradiation for generating unstable, low oxidation state molecular species containing rare-earth metal ions in frozen solution has been examined. The method was evaluated by irradiating Ln(III) precursors (Ln = Sc, Y, and La) in a solid matrix of 2-methyltetrahydrofuran at 77 K with a 700 keV Cs source to generate free electrons capable of reducing the Ln(III) species. These experiments yielded EPR and UV-visible spectroscopic data that matched those of the known Ln(II) species [(CHSiMe)Y], [(CHSiMe)La], and {Sc[N(SiMe)]}.

Identification of the U(V) complex (CMe)UI(NSiMe) in the reaction of (CMe)UI(THF) with NSiMe.

The U(V) imido complex (CMe)UI(NSiMe), 1, was crystallographically characterized from the reaction of (CMe)UI(THF) with NSiMe which demonstrates that it can be an intermediate in the reaction which ultimately forms (CMe)U(NSiMe) and (CMe)UI. U(V) intermediates have been proposed in such reactions, but have not been previously observed. The direct observation of 1 provides insight into the reaction mechanisms of U(III) compounds with azide reagents.

Expanding Bismuth Trihalide Coordination Chemistry with Trimethyltriazacyclohexane and Trimethyltriazacyclononane.

1,3,5-Trimethyltriazacyclohexane, Metach, readily adds to bismuth triiodide to form a variety of new coordination compounds depending on the stoichiometry, solvent, and crystallization conditions. X-ray crystallographic evidence has been obtained for both 2:1 and 1:1 Metach:Bi complexes with formulas of [(Metach)BiI][(Metach)BiI], [(Metach)BiI][BiI][I][HMetach]·THF, and (Metach)BiI(py). The related chloride structure (Metach)BiCl(py) forms from BiCl.

Synthesis and Reduction of Heteroleptic Bis(cyclopentadienyl) Uranium(III) Complexes.

Heteroleptic U(III) complexes supported by bis(cyclopentadienyl) frameworks have been synthesized to examine their suitability as precursors to U(II) complexes. The newly synthesized (CMe)U(OCHBu-2,6-Me-4), (CMe)U(OCHAd-2,6-Bu-4) (Ad = 1-adamantyl), (CMe)U(CH), and (CMe)U(CMeH) are compared with (CMe)U[N(SiMe)], (CMe)U[CH(SiMe)], and (CMe)U[N(SiMe)]. An improved synthesis of (CMe)U(μ-Ph)BPh was developed, which was used to synthesize (CMe)U(CMeH).

Anion-induced disproportionation of Th(III) complexes to form Th(II) and Th(IV) products.

A new synthesis of Th(II) complexes has been identified involving addition of simple MX salts (M = Li, Na, K; X = H, Cl, Me, N) to Cp''Th [Cp'' = [CH(SiMe)] in the presence of 18-crown-6 or 2.2.2-cryptand, forming [M(chelate)][Cp''Th] and Cp''ThX.

Isolation and characterization of a californium metallocene.

Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin-orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked.

A Rare-Earth Metal Retrospective to Stimulate All Fields.

Formulating insightful questions and experiments is crucial to the advancement of science. The purpose of this Perspective is to encourage scientists in all areas of chemistry to ask more "What if?" questions: What if we tried this experiment? What if we used these conditions? What if that idea is not correct? To stimulate this thinking, a retrospective analysis of a specific field, in this case rare-earth metal chemistry, is presented that describes the "What if?" questions that could have and should have been asked earlier based on our current knowledge. The goal is to provide scientists with a historical perspective of discovery that exemplifies how previous views in chemistry were often narrowed by predominant beliefs in principles that were incorrect.

Density Functional Theory Analysis of the Importance of Coordination Geometry for 5f6d versus 5f Electron Configurations in U(II) Complexes.

Density functional theory (DFT) calculations on four known and seven hypothetical U(II) complexes indicate the importance of coordination geometry in favoring 5f6d versus 5f electronic ground states. The known [Cp″U], [CpU], and [U(NR)] [Cp″ = CH(SiMe), Cp = CMeH, and R = SiMe] anions were found to have 5f6d ground states, while a 5f ground state was found for the known compound (NHAr)U. The UV-visible spectra of the known 5f6d compounds were simulated via time-dependent DFT and are in qualitative agreement with the experimental spectra.

Evaluating electrochemical accessibility of 4f5d and 4f Ln(II) ions in (CHSiMe)Ln and (CMeH)Ln complexes.

The reduction potentials (reported Fc/Fc) for a series of Cp'Ln complexes (Cp' = CHSiMe, Ln = lanthanide) were determined electrochemistry in THF with [BuN][BPh] as the supporting electrolyte. The Ln(III)/Ln(II) reduction potentials for Ln = Eu, Yb, Sm, and Tm (-1.07 to -2.

Electrochemical studies of tris(cyclopentadienyl)thorium and uranium complexes in the +2, +3, and +4 oxidation states.

Electrochemical measurements on tris(cyclopentadienyl)thorium and uranium compounds in the +2, +3, and +4 oxidation states are reported with CH(SiMe), CHSiMe, and CMeH ligands. The reduction potentials for both U and Th complexes trend with the electron donating abilities of the cyclopentadienyl ligand. Thorium complexes have more negative An(iii)/An(ii) reduction potentials than the uranium analogs.

In search of tris(trimethylsilylcyclopentadienyl) thorium.

Reduction of Cp'ThCl, Cp'ThBr, and Cp'ThI (Cp' = CHSiMe) with potassium graphite generates dark blue solutions with reactivity and spectroscopic properties consistent with the formation of Cp'Th. The EPR and UV-visible spectra of the solutions are similar to those of crystallographically-characterized tris(cyclopentadienyl) Th(iii) complexes: [CH(SiMe)]Th, (CMeH)Th, (CBuH)Th, and (CMe)Th. Density functional theory (DFT) analysis indicates that the UV-visible spectrum is consistent with Cp'Th and not [Cp'ThBr].