Insertion of trivalent uranium in macrocyclic crown-ethers: EXAFS and X-ray structural analyses

The structure of the first U(III) macrocyclic coordinated complex, [U(III)(BH₄)₂ dicyclohexyl-(18-crown-6)]₂U(IV)C1₅(BH₄) (complex I), has been determined from three dimensional X-ray diffraction data. The metal atom in trivalent state is inserted in the crown cavity as a monovalent cation [U(BH₄)₂]⁺. This compound resulted from a partial oxidation in a dichloromethane solution of U₃(III)(BH₄)₉[dicyclohexyl-(18-crown-6)]₂ (complex ^II).EXAFS analysis performed on powdered sample of the homologue of complex II, U₃(BH₄)₉[18-crown-6]₂ (complex III) has shown the presence of carbon atoms in the vicinity of the uranium atom and hence has proved that all the oxygen atoms of the crown-ether are directly coordinated to the metal.In parallel, an EXAFS study on the uranyl complex UO₂(18-crown-6)(C1O₄)2 (complex IV) has verified the insertion of the uranyl ion in the solid state, and given evidence for its partial de-insertion in an acetonitrile solution.     

Bi- and triheteronuclear complexes of uranium and group VI transition metals

The new heterobimetallic compounds Cp₃U[OCM(CO)₂Cp′] containing uranium and group VI transition metals are synthesized from Cp₃UCl and Na[M(CO)₃Cp′] or from Cp₃UCH₃ and H[M(CO)₃Cp′] (M = Mo, W; Cp = C₅H₅; Cp′ = C₅H₅ or C₅Me₅). In a same manner, the trimetallic Cp₂U[OCMo(CO) ₂Cp]₂ is obtained starting from Cp₂U(NEt₂)₂ and H[Mo(CO)₃Cp]. All these complexes exhibit low CO stretching frequencies characteristic of isocarbonyl linkages between uranium and Mo or W atoms.     

Tricyclopentadienyluranium azide complexes

The synthesis and characterization of A(N₃), [Na(18-crown-6)] [A(N₃)], [A(N₃A][BPh₄], [Na(18-crown-6)] [A(N₃)A] and A(N₃)A [A = (C₅H₄SiMe₃)₃U] are reported.     

Metallorganische verbindungen der lanthanoide: XXXI. Synthese und molekülstruktur einiger cyclopentadienyllutetiumhydride

The reaction of alkyl- and aryl-(dicyclopentadienyl)lutetium complexes (1) with H₂ or D₂ gives dimeric dicyclopentadienyllutetiumhydride (2) or -deuteride (3). Dicyclopentadienyllutetiumchloride (4) reacts with sodium in tetrahydrofuran (THF) with formation of [Na(THF)₆][(Cp₂LuH)₃H] (5). Tricyclopentadienyllutetium (6) reacts with NaH or NaD to give the complexes [Na(THF)₆][(Cp₃Lu)₂H]·2(THF) (7) or [Na(THF)₆][(Cp₃Lu)₂D]·2(THF) (8), respectively. The molecular structures of 2 and 7 were determined by single crystal X-ray diffraction.     

Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl complexes of N-B-PTA(BH3): X-ray crystal structures of [CpRhCl2{N-B}-PTA(BH3)] and [CpRh{N-B-PTA(BH3)}(η-CH2 = CHPh)]

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N-B-PTA(BH₃) and [Cp^∗RhCl(μ-Cl)]₂ affords [Cp^∗Rh{N-B-PTA(BH₃)}Cl₂] (3) or [Cp_∗Rh{N-B-PTA(BH₃)}₂Cl]Cl (5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp_∗Rh{N-B-PTA(BH₃)}H₂] (8) was also obtained by reaction of 3 with NaBH₄ and alternatively by direct hydroboration of [Cp^∗Rh(PTA)Cl₂] with excess NaBH₄. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H₃BO₃ and the corresponding PTA derivatives, including the water-soluble dihydride [Cp^∗Rh(PTA)H₂] (9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp^∗Rh{N-B-PTA(BH₃)}(η²-CH₂ = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η²-coordinated to rhodium without affecting the N-BH₃ moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.     

Electron affinities of biscyclopentadienyl and phospholyl uranium(IV) borohydride complexes: Experimental and DFT studies

Electron affinities (EAs) of a series of biscyclopentadienyl and phospholyl uranium(IV) complexes L₂U(BH₄)₂ [L₂ = Cp₂, (tmp)₂, (tBuCp)₂, (Cp*)(tmp) and Cp*₂] related to the U(III)/U(IV) redox system were calculated using relativistic Density Functional Theory (DFT) based methods coupled with the Conductor-like Screening Model for Real Solvents (COSMO-RS) approach. Electrochemical measurements of half-wave potentials in solution (tetrahydrofuran THF) were carried out for all these compounds under the same rigorous conditions. A good correlation (r² = 0.99) is obtained between the calculated EA values, at the ZORA/BP86/TZ2P level, and the half-wave reduction potentials measured by electrochemistry. The investigations bring to light the importance of spin-orbit coupling and solvent effect and the use of a large basis set in order to achieve such a good agreement between theory and experiment. The study confirms the instability of the Cp₂U(BH₄)₂ complex during the reduction process. The influence of the substituted aromatic ligand L₂, namely their electron donating ability, on EA was studied. The role of involved orbitals (singled occupied molecular orbital –SOMO– of anionic species or lowest unoccupied molecular orbital –LUMO– of neutral species) in the redox process was revealed.     

Thorium–ligand multiple bonds via reductive deprotection of a trityl group

Reaction of [Th(I)(NR₂)₃] (R = SiMe₃) (2) with KECPh₃ (E = O, S) affords the thorium chalcogenates, [Th(ECPh₃)(NR₂)₃] (3, E = O; 4, E = S), in moderate yields. Reductive deprotection of the trityl group from 3 and 4 by reaction with KC₈, in the presence of 18-crown-6, affords the thorium oxo complex, [K(18-crown-6)][Th(O)(NR₂)₃] (6), and the thorium sulphide complex, [K(18-crown-6)][Th(S)(NR₂)₃] (7), respectively. The natural bond orbital and quantum theory of atoms-in-molecules approaches are employed to explore the metal–ligand bonding in 6 and 7 and their uranium analogues, and in particular the relative roles of the actinide 5f and 6d orbitals.     

Bis(4-benzhydryl-benzoxazol-2-yl)methane – from a Bulky NacNac Alternative to a Trianion in Alkali Metal Complexes

A novel sterically demanding bis(4-benzhydryl-benzoxazol-2-yl)methane ligand 6 (^4−BzhH2BoxCH₂) was gained in a straightforward six-step synthesis. Starting from this ligand monomeric [M(^4-BzhH2BoxCH)] (M=Na ( 7 ), K ( 8₁ )) and dimeric [{M(^4-BzhH2BoxCH)}₂] (M=K ( 8₂ ), Rb ( 9 ), Cs ( 10 )) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18-crown-6 resulted in the solvent separated ion pair [{(THF)₂K@(18-crown-6)}{bis(4-benzhydryl-benzoxazol-2-yl)methanide}] ( 11 ), including the energetically favoured monoanionic (E,E)-(^4-BzhH2BoxCH) ligand. Further reaction of ^4−BzhH2BoxCH₂ with three equivalents KH and two equivalents 18-crown-6 yielded polymeric [{(THF)₂K@(18-crown-6)}{K@(18-crown-6)K(^4-BzhBoxCH)}]_n (n→∞) ( 12 ) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X-ray analyses identifying the latter as a promising precursor for low-valent main group complexes.     

Reactions of half-sandwich rhodium(III) and iridium(III) compounds with pyridinethiolate ligands: Mono-, di-, and tri-nuclear complexes

Neutral trinuclear metallomacrocycles, [Cp^*RhCl(μ-4-PyS)]₃ (3) and [Cp^*IrCl(μ-4-PyS)]₃ (4) [Cp^* = pentamethylcyclopentadienyl, 4-PyS = 4-pyridinethiolate], have been synthesized by self-assembly reactions of [Cp^*RhCl₂]₂ (1) and [Cp^*IrCl₂]₂ (2) with lithium 4-pyridinethiolate, respectively. In situ reaction of complex 3 with three equivalent of lithium 4-pyridinethiolate resulted in [Cp^*Rh(μ-4-PyS)(4-PyS)]₃ (5) containing both skeleton and pendent 4-PyS groups. Chelating coordination of 2-pyridinethiolate broke down the triangular skeleton to give mononuclear metalloligands Cp^*Rh(2-PyS)(4-PyS) (6) and Cp^*Ir(2-PyS)(4-PyS) (7) [2-PyS = 2-pyridinethiolate], which could also be synthesized from Cp^*RhCl(2-PyS) (10) and Cp^*IrCl(2-PyS) (11) with lithium 4-pyridinethiolate. The coordination reactions of 6 with complexes 1 and 2 gave dinuclear complexes [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*RhCl₂] (8) and [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*IrCl₂] (9), respectively. Molecular structures of 3, 4, 6 and 11 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Crystalline Diuranium Phosphinidiide and μ‐Phosphido Complexes with Symmetric and Asymmetric UPU Cores

Reaction of [U(Tren^TIPS)(PH₂)] ( 1 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃) with C₆H₅CH₂K and [U(Tren^TIPS)(THF)][BPh₄] ( 2 ) afforded a rare diuranium parent phosphinidiide complex [{U(Tren^TIPS)}₂(μ‐PH)] ( 3 ). Treatment of 3 with C₆H₅CH₂K and two equivalents of benzo‐15‐crown‐5 ether (B15C5) gave the diuranium μ‐phosphido complex [{U(Tren^TIPS)}₂(μ‐P)][K(B15C5)₂] ( 4 ). Alternatively, reaction of [U(Tren^TIPS)(PH)][Na(12C4)₂] ( 5 , 12C4=12‐crown‐4 ether) with [U{N(CH₂CH₂NSiMe₂Bu^t)₂CH₂CH₂NSi(Me)(CH₂)(Bu^t)}] ( 6 ) produced the diuranium μ‐phosphido complex [{U(Tren^TIPS)}(μ‐P){U(Tren^DMBS)}][Na(12C4)₂] [ 7 , Tren^DMBS=N(CH₂CH₂NSiMe₂Bu^t)₃]. Compounds 4 and 7 are unprecedented examples of uranium phosphido complexes outside of matrix isolation studies, and they rapidly decompose in solution underscoring the paucity of uranium phosphido complexes. Interestingly, 4 and 7 feature symmetric and asymmetric UPU cores, respectively, reflecting their differing steric profiles.     

Bis-cyclopentadienyl alkoxides and aryl oxides of uranium(IV). Influence of the steric hindrance of the R groups on the stability of the Cp2U(OR)2, Cp2U(OC6H4R)2 and Cp2U(OC6H3R2)2 derivatives

Reactions of Cp₂U(NEt₂)₂ with the moderately acidic agents ROH and ArOH lead to the cleavage of the UNEt₂ bonds and formation of di-cyclopentadienyl dialkoxides and diaryl oxides of uranium(IV). The yields of the new derivatives are strongly dependent on the bulk of the OR or OAr groups; they can undergo disproportionation or decomposition reactions with formation of tris-cyclopentadienyl derivatives of uranium(IV). With the high-sterically crowded 2,6-(Bu^t)₂C₆H₃OH ligand only one UNEt₂ bond is cleaved, with formation of the stable Cp₂U(OAr)(NEt₂) complex. The tris-cyclopentadienyl aryl oxides of uranium(IV) formed in the disproportionation reactions of the bis-cyclopentadienyl diaryl oxides have been also obtained by reaction of Cp₃UNEt₂ with ArOH.     

f-Element Half-Sandwich Complexes: A Tetrasilylcyclobutadienyl–Uranium(IV)–Tris(tetrahydroborate) Anion Pianostool Complex

Despite there being numerous examples of f-element compounds supported by cyclopentadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands (C_5–8), cyclobutadienyl (C₄) complexes remain exceedingly rare. Here, we report that reaction of [Li₂{C₄(SiMe₃)₄}(THF)₂] ( 1 ) with [U(BH₄)₃(THF)₂] ( 2 ) gives the pianostool complex [U{C₄(SiMe₃)₄}(BH₄)₃][Li(THF)₄] ( 3 ), where use of a borohydride and preformed C₄-unit circumvents difficulties in product isolation and closing a C₄-ring at uranium. Complex 3 is an unprecedented example of an f-element half-sandwich cyclobutadienyl complex, and it is only the second example of an actinide-cyclobutadienyl complex, the other being an inverse-sandwich. The U−C distances are short (av. 2.513 Å), reflecting the formal 2− charge of the C₄-unit, and the SiMe₃ groups are displaced from the C₄-plane, which we propose maximises U−C₄ orbital overlap. DFT calculations identify two quasi-degenerate U−C₄ π-bonds utilising the ψ₂ and ψ₃ molecular orbitals of the C₄-unit, but the potential δ-bond using the ψ₄ orbital is vacant.     

Coordination compounds of sodium,potassium, and calcium with benzo-15-crown-5-substituted terpyridines

Sodium and potassium complexes with 4′-(4‴-benzo-15-crown-5)methyloxy-2,2′:6′,2″-terpyridine (L¹) and 4′-(4′-benzo-15-crown-5)oxy-2,2′:6′,2″-terpyridine (L²) and heteronuclear Na, K, Ca, and transition metal complexes with L¹ were synthesized. The structure of the complexes was proposed on the basis of elemental analysis data, IR spectra, and the results of earlier X-ray diffraction studies of L², [NaL¹NCS], and [Na₂{Cu(L¹)₂}(NCS)₃]NCS · CH₃CN.     

The lead(II) complexes with 18-Crown-6, 1,1,1,5,5,5-hexafluoropentane-2,4-dionate and 1,1,1-trifluoropentate-2,4-dionate anions: Synthesis,structure, and thermochemical properties

The complexes trans-[Pb(18-crown-6)(NO₃)₂] (I), trans-[Pb(18-crown-6)(Hfa)₂] (II), and [Pb₂(18-crown-6)(Tfa)₄] (III), where Hhfa is 1,1,1,5,5,5-hexafluoropentane-2,4-dione and Htfa is 1,1,1-trifluoropentane-2,4-dione, were synthesized and identified. The structures of crystals I–III were determined by X-ray diffraction, whereas the melting and decomposition of compounds II, III were studied by the differential scanning calorimetry. The temperature of preparative sublimation of complexes II, III was determined at 10^?2 mm Hg. The semiempirical structural-thermochemical approach was used to analyze the parameters of complex II vaporization.     

(18-Crown-6)sodium tribromide and (18-crown-6)potassium triiodide (with an admixture of bromodiiodide): Synthesis and crystal structure

Two crystalline host-guest complexes are synthesized and studied using X-ray diffraction analysis: (18-crown-6)sodium tribromide [Na(18-crown-6)]⁺ · Br ₃ ^? (I) and (18-crown-6)potassium tribromide (with an admixture of bromodiiodide) [K(18-crown-6)]⁺ · (Br_0.25I_2.75)^? (II). The structures of compound I (space group P2₁/_{n, a} = 8.957 Å, b = 8.288 Å, c = 14.054 Å, β = 104.80°, Z = 2) and compound II (space group Cc, a = 8.417 Å, b = 15.147 Å, c = 17.445 Å, β = 99.01°, Z = 4) are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.098 (I) and 0.036 (II) for all 2311 (I) and 2678 (II) independent measured reflections on a CAD-4 automated diffractometer (λMoK _α). Similar crystalline complexes I and II exist as infinite chains of alternating complex cations and trihalide anions linked to each other through weak Na-Br or K-I coordination bonds. In [Na(18-crown-6)]⁺ and [K(18-crown-6)]⁺ complex cations, the Na⁺ or K⁺ cation (coordination number is eight) is located in the center of the cavity of the 18-crown-6 ligand and coordinated by the six O atoms and two terminal Br or I atoms of two trihalide anions lying on opposite sides of the rms plane of the crown ligand.     

f‐Element Half‐Sandwich Complexes: A Tetrasilylcyclobutadienyl–Uranium(IV)–Tris(tetrahydroborate) Anion Pianostool Complex

Despite there being numerous examples of f‐element compounds supported by cyclopentadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands (C_5–8), cyclobutadienyl (C₄) complexes remain exceedingly rare. Here, we report that reaction of [Li₂{C₄(SiMe₃)₄}(THF)₂] ( 1 ) with [U(BH₄)₃(THF)₂] ( 2 ) gives the pianostool complex [U{C₄(SiMe₃)₄}(BH₄)₃][Li(THF)₄] ( 3 ), where use of a borohydride and preformed C₄‐unit circumvents difficulties in product isolation and closing a C₄‐ring at uranium. Complex 3 is an unprecedented example of an f‐element half‐sandwich cyclobutadienyl complex, and it is only the second example of an actinide‐cyclobutadienyl complex, the other being an inverse‐sandwich. The U?C distances are short (av. 2.513 Å), reflecting the formal 2? charge of the C₄‐unit, and the SiMe₃ groups are displaced from the C₄‐plane, which we propose maximises U?C₄ orbital overlap. DFT calculations identify two quasi‐degenerate U?C₄ π‐bonds utilising the ψ₂ and ψ₃ molecular orbitals of the C₄‐unit, but the potential δ‐bond using the ψ₄ orbital is vacant.     

Homoleptic tris(dithiolene) and tetrakis(dithiolene) complexes of uranium(IV)

Reaction of UCl4 with 3 or 4 mol equiv of Na2dddt (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) in THF afforded the first example of a tetrakis(dithiolene) metal compound, [Na4(THF)8U(dddt)4](infinity) (1). The red crystals of 1 are composed of infinite zigzag chains in which Na2(micro-THF)3 fragments ensure the linking of Na2(THF)5U(dddt)4 moieties; the uranium atom is in a dodecahedral environment of eight sulfur atoms. Treatment of UCl4 with 3 mol equiv of Na2dddt in pyridine gave a mixture of tris- and tetrakis(dithiolene) compounds. After addition of 18c6 (18-crown-6), only the tris(dithiolene) complex was obtained and crystallized as orange crystals of [Na(18c6)(py)2]2[U(dddt)3].2py (2.2py) in which the isolated [U(dddt)3]2- anion adopts a slightly distorted trigonal prismatic configuration. A few red crystals of the unsolvated complex 2 and the trinuclear anionic compound [Na(18c6)(py)2]3[Na{U(dddt)3}2] (3) were also obtained along with orange crystals of 2.2py. All the tris(dithiolene) compounds exhibit large folding of the dddt ligand and significant interaction between the C=C double bond and the metal center.     

Bis(η5‐isopropyltetramethylcyclo­pentadienyl)(tetrahydroborato‐κ3H,H′,H′′)(tetrahydrofuran‐O)‐samarium(III): a lanthanidocene complex with a tridentate tetrahydroborato ligand

The lanthanidocene complex [Sm(BH₄)(C₁₂H₁₉)₂(C₄H₈O)], (I), shows a distorted tetrahedral arrangement around the central Sm^III atom. It consists of two η⁵‐isopropyltetramethylcyclopentadienyl ligands, one tetrahydroborato (BH₄^?) ligand bridging via H atoms to the lanthanide atom and one coordinating tetrahydrofuran (thf) molecule. The BH₄^? unit of (I) coordinates as a tridentate ligand with three bridging H atoms and one terminal H atom [Sm—B—H4 176 (2)°]. The η⁵‐isopropyl­tetra­methylcyclopentadienyl ligands of this bent‐sandwich complex [Cp1—Sm—Cp2 133.53 (1)° where Cp denotes the centroid of the cyclopentadienyl ring] adopt staggered conformations.     

Synthesis,Reactivity and Structural Properties of Trifluoromethylphosphoranides

Phosphoranides are interesting hypervalent species which serve as model compounds for intermediates or transition states in nucleophilic substitution reactions at trivalent phosphorus substrates. Herein, the syntheses and properties of stable trifluoromethylphosphoranide salts are reported. [K(18-crown-6)][P(CF₃)₄], [K(18-crown-6)][P(CF₃)₃F], and [NMe₄][P(CF₃)₂F₂] were obtained by treatment of trivalent precursors with sources of CF₃⁻ or F⁻ units. These [P(CF₃)_4-nF_n]⁻ (n=0–2) salts exhibit fluorinating (n=1–2) or trifluoromethylating (n=0) properties, which is disclosed by studying their reactivity towards selected electrophiles. The solid-state structures of [K(18-crown-6)][P(CF₃)₄] and [K(18-crown-6)][P(CF₃)₃F] are ascertained by single crystal X-ray crystallography. The dynamics of these compounds are investigated by variable temperature NMR spectroscopy.     

(18‐Crown‐6)‐μ‐oxo‐hexa­kis(tetra­hydro­borato)diuranium(IV): an unprecedented asymmetric dinuclear complex

In the title compound, (1,4,7,10,13,16‐hexa­oxacyclo­octa­decane‐1κ⁶O)‐μ‐oxo‐1:2κ²O:O‐hexa­kis(tetra­hydro­borato)‐1κ³H;2κ²H;2κ²H;2κ³H;2κ³H;2κ³H‐diuranium(IV), [U₂(BH₄)₆O(C₁₂H₂₄O₆)], one of the U atoms (U1), located at the centre of the crown ether moiety, is bound to the six ether O atoms, and also to a tridentate tetra­hydro­borate group and a μ‐oxo atom in axial positions. The other U atom (U2) is bound to the same oxo group and to five tetra­hydro­borate moieties, three of them tridentate and the other two bidentate. The two metal centres are bridged by the μ‐oxo atom in an asymmetric fashion, thus giving the species (18‐crown‐6)(κ³‐BH₄)U=(μ‐O)—U(κ³‐BH₄)₃(κ²‐BH₄)₂, in which the U1=O and U2—O bond lengths to the μ‐O atom [1.979 (5) and 2.187 (5) Å, respectively] are indicative of the presence of positive and negative partial charges on U1 and U2, respectively.