Linear uranium metallocenes with polydentate aromatic nitrogen ligands

Treatment of [Cp*(2)U(NCMe)(5)]X(2) [Cp* = C(5)Me(5), X = BPh(4) (1) or I (1')] or Cp*(2)UI(2) in acetonitrile with the polydentate aromatic nitrogen bases phen, terpy and R(4)btbp led to the formation of the linear uranium metallocenes [Cp*(2)U(NCMe)(3)(phen)]X(2) [X = BPh(4) (2), I (2')], [Cp*(2)U(NCMe)(2)(terpy)][BPh(4)](2) (4), [Cp*(2)U(NCMe)(Me(4)btbp)][BPh(4)](2) (5) and [Cp*(2)U(NCMe)(CyMe(4)btbp)][X](2), [X = BPh(4) (6), I (6')], [phen = 1,10-phenanthroline, terpy = 2,2':6,2''-terpyridine, Me(4)btbp = 6,6'-bis-(3,3,6,6-tetramethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine, CyMe(4)btbp = 6,6'-bis-(3,3,6,6-tetramethyl-cyclohexane-1,2,4-triazin-3-yl)-2,2'-bipyridine]. The bent metallocene [Cp*(2)U(phen)(2)][BPh(4)](2) (3) was isolated from the reaction of 1 and two molar equivalents of phen in THF. The X-ray crystal structures of 2.2MeCN, 3.2THF, and 6'.2MeCN were determined.

Easy access to uranium nucleophilic carbene complexes

Metathesis reactions of UCl(4) with Li(2)C(Ph(2)PS)(2) in Et(2)O only afforded the tris-carbene complex [{Li(OEt(2))}(2)U{=C(Ph(2)PS)(2)}(3)] (1), while the bis- and mono-carbene compounds [U{=C(Ph(2)PS)(2)}(2)(THF)(2)] (2) and [{Li(THF)(2)}(2)U{=C(Ph(2)PS)(2)}Cl(4)] (3) were obtained by treatment of UCl(4) with Li(2)C(Ph(2)PS)(2) in a mixture of THF and toluene. The bis-carbene complex 2 was also obtained either from the comproportionation reaction of 1 and UCl(4) or protonolysis reaction of U(NEt(2))(4) with H(2)C(Ph(2)PS)(2) and was transformed into the mono-carbene complex [U{=C(Ph(2)PS)(2)}Cl(2)(THF)(2)] (4) by further reaction with UCl(4). The utility of these complexes as precursors is illustrated by the synthesis of the biscyclopentadienyl derivative [Cp(2)U{=C(Ph(2)PS)(2)}] (5) by treatment of 3 with TlCp. The crystal structures of [U{=C(Ph(2)PS)(2)}(2)(py)(2)].1.5py.0.5THF and 5.toluene are reported.

First 5f-element complexes with the tetradentate BTBP ligand. Synthesis and crystal structure of uranyl(VI) compounds with CyMe4BTBP

Treatment of [UO2(OTf)2] or [UO2I2(thf)3] with 1 equiv. of CyMe4BTBP in anhydrous acetonitrile led to the formation of [UO2(CyMe4BTBP)(OTf)2] (1) and [UO2(CyMe4BTBP)I2] (2) which crystallized as the cationic forms [UO2(CyMe4BTBP)(py)][OTf]2 (3) and [UO2I(CyMe4BTBP)][I] (4) in pyridine and acetonitrile, respectively. These compounds are unique examples of structurally characterized actinide complexes with a BTBP molecule; this ligand adopts a planar conformation in the equatorial plane of the {UO2}2+ ion. In pyridine, 1 is dissociated into [UO2(OTf)2(py)3] and free CyMe4BTBP and the thermodynamic parameters (K, ΔH, ΔS) of this equilibrium have been determined by 1H NMR spectroscopy. The ethoxide derivative [UO2(OEt)(CyMe4BTBP)][OTf] (5) crystallized from a solution of 1 in a mixture of ethanol and acetone under air, and the dinuclear μ-oxo complex [{UO2(CyMe4BTBP)}2(μ-O)][I]2 (6) was obtained from [UO2I(thf)2.7] and CyMe4BTBP. The crystal structures of 6 and of the analogous derivatives [{UO2(py)4}2(μ-O)][I]2 (7) and [{UO2(TPTZ)(py)}2(μ-O)][I3]2 (8) exhibit a flexible [{UO2}–O–{UO2}]2+ moiety.

Extraction of rubidium and caesium from strongly alkaline media

Huge amounts of alkaline liquid waste containing a high sodium salt concentration (and in some cases, a lesser potassium salt concentration) are contaminated by 137caesium. Selective removal of radioactive caesium ions, present in the waste at trace level, requires very selective extractants since the ratio of sodium over caesium exceeds 105. As expected, calix[4]arene-crown-6 is satisfactory for the extraction of caesium from liquid waste containing large amounts of sodium. The presence of potassium, which competes more than sodium with caesium, leads to a drastic caesium distribution coefficient decrease as the concentration of this competing cation increases. On the contrary, calix[4]arene and p-tert-butylcalix[4]arene, efficient extractants in high alkalinity media, display an exceptional selectivity for caesium over other alkaline cations, including rubidium. This selectivity of p-tert-butylcalix[4]arene, and to a lesser extent of calix[4]arene, allows caesium to be extracted from alkaline solutions containing large amounts of sodium and potassium.

The U=C double bond: synthesis and study of uranium nucleophilic carbene complexes

Treatment of U(BH(4))(4) with 1 or 3 equiv of Li(2)(SCS) x 1.5 Et(2)O, 1, afforded the actinide carbene complexes U(mu-SCS)(3)[U(BH(4))(3)](2) (4) and U(mu-SCS)(3)[Li(Et(2)O)](2) (6), respectively [SCS = (Ph(2)P = S)(2)C]. In THF, complex 4 was transformed into the mononuclear derivative (SCS)U(BH(4))(2)(THF)(2) (5). The multiple bond character of the uranium-carbon bond was first revealed by the X-ray crystal structures of the three complexes. The U=C bond in these complexes present a nucleophilic character, as shown by their reaction with a carbonyl derivative. Finally, DFT calculations prove the involvement of both 5f and 6d orbitals in both the sigma and the pi U-C bonds.

Lanthanide(III) and actinide(III) complexes [M(BH4)2 (THF)5][BPh4] and [M(BH4)2(18-crown-6)][BPh4] (M = Nd, Ce, U): synthesis, crystal structure, and density functional theory investigation of the covalent contribution to metal-borohydride bonding

Treatment of [M(BH4)3(THF)3] with NEt3HBPh4 in THF afforded the cationic complexes [M(BH4)2(THF)5][BPh4] [M = U (1), Nd (2), Ce (3)] which were transformed into [M(BH4)2(18-crown-6)][BPh4] [M = U (4), Nd (5), Ce (6)] in the presence of 18-crown-6; [U(BH4)2(18-thiacrown-6)][BPh4] (7) was obtained from 1 and 18-thiacrown-6 in tetrahydro-thiophene. Compounds 1, 3.C4H8S, 4.THF, 5, and 6.THF exhibit a penta- or hexagonal bipyramidal crystal structure with the two terdentate borohydride ligands in apical positions; the BH4 groups in the crystals of 7.C4H8S are in relative cis positions, and the thiacrown-ether presents a saddle shape, with two diametrically opposite sulfur atoms bound to uranium in trans positions. The crystal structures of these complexes, as well as those of previously reported [M(BH4)2(THF)5]+ cations, do not reveal any clear-cut lanthanide(III)/actinide(III) differentiation. The structural data obtained for [M(BH4)2(18-crown-6)]+ (M = U, Ce) by relativistic density functional theory (DFT) calculations are indicative of a small shortening of the U...B with respect to the Ce...B distance, which is accompanied by a lengthening of the U-Hb bonds and an opening of the Hb-B-Hb angle (Hb = bridging hydrogen atom of the eta3-BH4 ligand). The Mulliken population analysis and the natural bond orbital analysis indicate that the BH4 -->M(III) donation is greater for M = U than for M = Ce, as well as the overlap population of the M-Hb bond, thus showing a better interaction between the uranium 5f orbitals and the Hb atoms. The more covalent character of the B-H-U three-center two-electron bond was confirmed by the molecular orbital (MO) analysis. Three MOs represent the pi bonding interactions between U(III) and the three Hb atoms with significant 6d and 5f orbital contributions. These MOs in the cerium(III) complex exhibit a much lesser metallic weight with practically no participation of the 4f orbitals.

Functionalised azetidines as ligands: species derived by selective alkylation at substituent-nitrogen

Selective functionalisation of the tridentate ligand 1-(2-aminoethyl)-3-methyl-3-(2-pyridyl)azetidine at its terminal amino-nitrogen atom can be readily achieved by both reductive alkylation and simple alkylation reactions to give tri-, quadri-, quinque- and sexi-dentate derivatives. Simple alkylation by 2-picolinyl chloride provides the only example of a second reaction pathway where the azetidine ring of the reactant has undergone activation towards ring opening. Structural characterisation of the Cu(II) complexes of these ligands has revealed several remarkable aspects of their solid-state coordination chemistry, including the formation of infinite helical aggregates through pi-stacking and tetramerisation through carboxylate bridging, as well as further examples of the crystallisation of mixed species found to be rather common with complexes of the parent ligand.