A. Pires de Matos

Dihydrobis(3,5-dimethylpyrazolyl)borate derivatives of ƒ elements

Abstract The trivalent chlorides of U, Ce, Sm and Yb react readily in THF with KH2B(3,5-Me2Pz)2 to yield the complexes M[H(μ-H)B(3,5-Me2Pz)2]3. The crystal and molecular structures of U[H(μ-H)B(3,5-Me2Pz)2]3 and Sm[H(μ-H)B(3,5-Me2Pz)2]3 have been determined. The compounds are isomorphous with the six nitrogen donor atoms of the bis-chelating ligands arranged in a trigonal prismatic geometry. Each of the three rectangular faces of the trigonal prism is capped by a bridging BH … M three centre bond, leading to compounds where the metal centres are formally nine-coordinate. The synthesis and characterization of the related UIV derivatives UCl2[H2B(3,5-Me2Pz)2]2 and U(OBut)2[H2B(3,5-Me2Pz)2]2 are also reported. The crystal and molecular structure of {UCl[H(μ-H)B(3,5-Me2Pz)2[H(μ-O)B(3,5-Me2Pz)2]2}2, a dimeric complex formed during the recrystallization of UCl2[H2B(3,5-Me2Pz)2]2, is also presented. Each uranium centre is eight-coordinate and displays square antiprismatic geometry, distorted towards the dodecahedron.

Actinide poly(pyrazol-1-yl)borate complexes: synthesis and structure of hydrotris(3,5-dimethylpyrazol-1-yl)boratotrichlorotetrahydrofuran actinide(IV), M[HB(3,5-Me2Pz)3]Cl3(THF) (M=Th and U)

Abstract The reaction of MCl4 with K[HB(3,5-Me2Pz)3] in THF gives the monosubstituted derivatives M[HB(3,5-Me2Pz)3]Cl3(THF) (M=Th (1) and U (2)) in excellent yields. The NMR spectra of the molecules indicate symmetrical structures with equivalent pyrazolyl groups. This has been corroborated by single-crystal X-ray analysis. The uranium center in 2 is seven-coordinate and displays capped octahedral geometry. The tridentate pyrazolylborate moiety and the three Cl atoms define the two staggered triangular faces respectively, the latter is capped by the THF oxygen. The coordination geometry is close to C3v symmetry. The steric congestion imposed by the bulky pyrazolylborate ligand is evidenced by the relative low coordination number and the long U—O bond length, 2.546(4) A. Crystal data 2: monoclinic, P21/n, a=10.195(2), b=14.905(2), c=17.414(4) A, β=100.08(2)°, V= 2605.32 A3 and Z=4. Complex 1 is isomorphous with 2.

Standard enthalpies of formation of sodium alkoxides

Abstract The standard enthalpies of formation of several crystalline sodium alkoxides, Δ H o f (NaOR, cr), have been determined by reaction-solution calorimetry. A linear correlation has been found between Δ H O f (NaOR, cr) and Δ H o f (ROH, 1/cr) for R = n-alkyl, enabling the prediction of data for other sodium alkoxides. The results were also used to derive the lattice energies and the thermochemical radii of the anions OR − .

HYDROCARBYL DERIVATIVES OF UCL2HB(PZ)32 : SYNTHESIS, CHARACTERIZATION AND REACTIVITY STUDIES TOWARDS PROTIC SUBSTRATES AND KETONES

Abstract The reaction of [UCl 2 HB(pz) 3 2 ] ( 1 ) with lithium alkyls LiR (R = Me, CH 2 SiMe 3 , C 6 H 4 - o -CH 2 NMe 2 ) in the 1:1 or 1:2 molar ratio affords the compounds [UCIRHB(pz) 3 2 ] (pz = C 3 H 3 N 2 , R = Me ( 2 ), CH 2 SiMe 3 ( 3 ), C 6 H 4 - o -CH 2 NMe 2 ( 4 )) and [UR 2 HB(pz) 3 2 ] (R = Me ( 5 ), CH 2 SiMe 3 ( 6 )) respectively in 60–80% yield. Complex 2 can also be obtained (60% yield) by redistribution at room temperature between the complexes 1 and 5 . Compounds 2, 3 and 4 react with pzH providing [UCl(pz)HB(pz) 3 2 ] ( 7 ) in almost quantitative yield and 5 and 6 react also with pzH leading to [U(pz) 2 HB(pz) 3 2 ] ( 8 ). The alkoxide [U(OC 6 H 4 - o -OMe) 2 HB(pz) 3 2 ] ( 9 ) was synthesized by reacting 5 or 6 with guaiacol. By reacting the chlorohydrocarbyls 2, 3 or 4 with excess of acetone the aldolate [UCl(OCMe 2 CH 2 (C=O)Me)HB(pz) 3 2 ] ( 11 ) was obtained, due to the activation of α -CH bond of acetone; however, for 3 the reaction is not clean and a mixture of 11 and [UCl(OCMe 2 CH 2 SiMe 3 )HB(pz) 3 2 ] ( 12 ) is always obtained. Stoichiometric amounts of acetone insert into the metal-carbon bonds of 2 and 5 yielding [UCl(O t Bu)HB(pz) 3 2 ] and [U(O t Bu) 2 HB(pz) 3 2 ] respectively, while the insertion product [U(OCMe 2 CH 2 SiMe 3 ) 2 HB(pz) 3 2 ] ( 10 ) can only be obtained when 6 reacts with excess of this substrate. 9 crystallizes from toluene/hexane in the triclinic space group P 1¯ with unit cell dimensions a = 12.295(2) A, b = 12.640(2) A, c = 13.994(2) A, α = 76.10(1)°, β = 72.50(1)°, γ = 80.71(1)°, V = 2004(2) A 3 and Z = 2. Recrystallization of a mixture containing [UCl(O t Bu)HB(pz) 32 ] and 11 led to a decomposition product which has been characterized by X-ray structural analysis as [UCl(Hpz)(O t Bu)(μ-O)B(μ-pz)(pz) 2 ] 2 ( 13 ): monoclinic P 2 1 / n , a = 13.701(3) A, b = 11.337(2) A, c = 14.857(4) A, β = 104.65(2)°, V = 2233(1) A 3 and Z = 2. Extended Huckel molecular orbital calculations provided some information on the bonding capabilities of the [UHB(pz) 3 2 ] fragment compared to [U(C 5 Me 5 ) 2 ] and on the vulnerability of the poly(pyrazolyl)borate ligands to nucleophilic attack.

Synthesis, characterization and reactivity of lantahnide(II) poly(pyrazol-1-yl)borates (LnSm, Eu and Yb); fluorescence studies of [EuL2(THF)2] [LB(pz)4, HB(pz)3]; X-ray crystal structures of [Eu{B(pz)4}2(THF)2] and ]Yb{B(pz)4}3]·(2H5OH

Abstract The reaction [LnI2(THF)x] (Ln - Sm, Eu, Yb) with 2 equiv. of K[B(pz)4] (pz = pyrazolyl) in THF resulted in the formation of [Ln{B(pz)4}2(THF)2] complexes. The molecular structure of [Eu{B(pz)4}2(THF)2] has been determined by single-crystal X-ray diffraction analysis. The [Sm{B(pz)4}2(THF)2] and [Yb{B(pz)4}2(THF)2] complexes are fluxional in solution, as indicated by the equivalence of the pyrazolyl rings in the 1H NMR spectra at room temperature. A static spectrum could be obtained for the Sm compound at -68°C with a pattern that is in accordance with the geometry found for the Eu complex, in the solid state. The complexes [{LnHB(pz)3}2(THF)2] (Ln - Sm, Eu, Yb) have been prepared by the procedure used to synthesize the [Ln{B)pz)4}2(THF)2] complexes. The THF molecules can be replaced by 1,2-dimethoxyethane yielding the compounds [{LnHB(pz)3}2(DME)] (Ln = Sm, Yb. [Sm[B)pz)42(THF2] and [Yb{B)pz)4}2(THF)2] react readily with alkyl halides, alcohols or alkynes to yield LnIII complexes that disproportionate to the [Ln{B(pz)4}3] complexes. The crystal structure of the compound [Yb{B(pz)4}3]·C2H5OH obtained in the reaction of [Yb{B(pz)4}2(THF)2] with ethanol was determined by X-ray diffraction analysis. Fluorescence studies on the Eu compounds are also reported.

Some reactions of hydrotris(3,5-dimethylpyrazolyl)-borato trichloroactinides(IV), MCl3(HBL3)·THF (M ≡ ThIV, UIV; L ≡ 3,5-dimethylpyrazolyl, THF ≡ tetrahydrofuran)☆

Abstract The thorium(IV) and uranium(IV) compounds MCl2(Cp)(HBL3) (Cp ≡ η5-C5H5), MCl2[N(SiMe3)2](HBL3) and M(NPh2)3(HBL3) have been prepared from MCl3(HBL3)·THF. IR, near-IR-visible, 1H NMR and 11B NMR spectra are reported for these compounds.

Experimental aspects of metal vapour synthesis of alkoxides and aryloxides of lanthanides

Abstract The synthesis of metal alkoxides and aryloxides of lanthanides by the metal vapour technique has been investigated. The reactions of Ce, Sm, Eu and Yb with MeOH, EtOH and PriOH were studied. The compound Sm[OC6H3(But)2]3 was obtained from the reaction of samarium with 2,6-di-t-butylphenol.

Uranium poly(pyrazol-1-yl)borate complexes: X-ray crystal structures of UCl2Cp[HB(3,5-Me2Pz)3] and UCl3[HB(3,5-Me2Pz)3]

Abstract The crystal and molecular structures of UCl2Cp[HB(3,5-Me2Pz)3] (1) and UCl3[HB(3,5-Me2Pz)3] (2) have been determined by single crystal X-ray diffraction. Compound 1 crystallizes in space group P 1 , a = 10.770(1), b = 11.146(5), c = 11.820(4) A, α = 114.53(2), β = 91.70(2), γ = 107.45(2)°, V = 1211.77 A3, Z = 2; compound 2 crystallizes in space group P21/c, a = 8.173(1), b = 14.279(3), c 19.167(7) A, β = 100.17(2)°, V = 2201.71 A3, Z = 4. In both compounds the uranium centre is six-coordinate and displays octahedral geometry, close to Cs, symmetry for complex 1 and to C3v symmetry for complex 2. For compound 1 the average UCl, UN and UC(Cp) bond distances are 2.60(1), 2.51(2) and 2.74(1) A; for 2 the average UCl and UN bond distances are 2.56(1) and 2.43(1) A.

Chloro-lanthanide, and plutonium complexes containing the hydrotris (3,5-dimethylpyrazol-1-yl)borate ligand: the crystal and molecular structures of [PrCl (μ-Cl)TpMe2 (3,5-Me2pzH)]2 and YbCl2TpMe2 (THF)

Abstract Reactions of PuCl3 and LnCl3 (Ln=Pr, Nd ) with the stoichiometric amount of KTpMe2 (TpMe2=HB (3,5-Me2pz)3) yielded the dimeric [MCl (μ-Cl)TpMe2 (Me2pzH)]2 compounds (M=Pu (1), Pr (2), Nd (3)). The analogous reaction with YbCl3 afforded the monomeric YbCl2TpMe2 (THF) complex (4). The crystal and molecular structures of 2 and 4 have been assessed by means of single crystal X-ray diffraction analysis. In 2 each Pr atom is seven-coordinate and is linked to the adjacent metal centre by two bridging chlorine ligands. In 4 the Yb atom is six-coordinate and displays octahedral geometry. 4 undergoes intermolecular rearrangement reactions to yield [YbCl2TPMe2 (Me2pzH)]·THF (6) and [YbCl3TpMe2]− [ (Me2pzH2)]+ (7). The molecular structures of 6 and 7 were determined by X-ray diffraction. In 6 the tridentate ligand, the two chlorine atoms and the nitrogen atom of the neutral dimethylpyrazole describe a distorted octahedron. 7 consist of discrete [YbCl3TpMe2]− and [ (Me2pzH2)]+ ions, with the ytterbium atom of the cation coordinated to three pyrazolyl nitrogens and three chlorine atoms.

Tetramethylurea adducts of the tricyclopentadienyl lanthanide complexes

Abstract The tetramethylurea adducts of tricyclopentadienyl lanthanide(III) complexes, Cp3Ln·TMU (Ln = La, Ce, Nd, Sm, Eu and Yb, TMU = 1,1,3,3-tetramethylurea), have been isolated by addition of the stoichiometric amount of (CH3)2NCON(CH3)2 to Cp3Ln·THF, in hexane. The compounds were characterized by standard techniques and the molecular structures of Cp3Ce·TMU and Cp3Nd·TMU were determined by single crystal X-ray diffraction analysis. The two compounds are isomorphous. The metal centre is tetrahedrally coordinated.