Yttrium Analogue Research Articles

Bis(phosphinimino)methanide Borohydride Complexes of the Rare‐Earth Elements as Initiators for the Ring‐Opening Polymerization of ε‐Caprolactone: Combined Experimental and Computational Investigations

Rare-earth-metal borohydrides are known to be efficient catalysts for the polymerization of apolar and polar monomers. The bis-borohydrides [{CH(PPh2 NSiMe3)2}La(BH4)2(THF)] and [{CH(PPh2NSiMe3)2}Ln(BH4)2] (Ln = Y, Lu) have been synthesized by two different synthetic routes. The lanthanum and the lutetium complexes were prepared from [Ln(BH4)3(THF)3] and K{CH(PPh2NSiMe3)2}, whereas the yttrium analogue was obtained from in situ prepared [{CH(PPh2NSiMe3)2}YCl2]2 and NaBH4. All new compounds were characterized by standard analytical/spectroscopic techniques, and the solid-state structures were established by single-crystal X-ray diffraction. The ring-opening polymerization (ROP) of ε-caprolactone initiated by [{CH(PPh2NSiMe3)2}La(BH4)2(THF)] and [{CH(PPh2NSiMe3)2}Ln(BH4)2] (Ln = Y, Lu) was studied. At 0 °C the molar mass distributions determined were the narrowest values (M(w)/M(n) = 1.06-1.11) ever obtained for the ROP of ε-caprolactone initiated by rare-earth-metal borohydride species. DFT investigations of the reaction mechanism indicate that this type of complex reacts in an unprecedented manner with the first B-H activation being achieved within two steps. This particularity has been attributed to the metallic fragment based on the natural bond order analysis.

Syntheses and structures of bora-amidinate lanthanide(iii) complexes

The use and coordination modes of the dianionic bora-amidinate ligand in lanthanide(III) chemistry is explored. Synthetic routes to complexes of the type (DIPP)NBN-LnR (Ln = lanthanide, (DIPP)NBN = HB[N(2,6-iPr(2)-phenyl)](2), R = an amide or benzylide group) have been developed. The reaction of (DIPP)NBN-H(2) with (DMA)(3)Sm (DMA = 2-Me(2)N-benzyl) gave dark-red crystals of (DIPP)NBN-Sm(DMA) in 68% yield. The yttrium analogue, (DIPP)NBN-Y(DMA), was prepared similarly (yellow crystals, 58% yield). The reaction of (DIPP)NBN-Sm(DMA) with (Me(3)Si)(2)NH gave (DIPP)NBN-SmN(SiMe(3))(2).(THF)(2) (yellow crystals, 54% yield). Crystal structure determinations of (DIPP)NBN-Sm(DMA) and (DIPP)NBN-Y(DMA) revealed dimeric complexes that are held together by LnDIPP interactions. The complex (DIPP)NBN-SmN(SiMe(3))(2).(THF)(2) crystallized as a monomer. NMR investigations of [(DIPP)NBN-Y(DMA)](2) in benzene indicate that it is also dimeric in solution. The addition of THF resulted in its dissociation into monomeric units of (DIPP)NBN-Y(DMA).(THF)(x).

Design Principles and Theory of Paramagnetic Fluorine‐Labelled Lanthanide Complexes as Probes for 19F Magnetic Resonance: A Proof‐of‐Concept Study

The synthesis and spectroscopic properties of a series of CF(3)-labelled lanthanide(III) complexes (Ln=Gd, Tb, Dy, Ho, Er, Tm) with amide-substituted ligands based on 1,4,7,10-tetraazacyclododecane are described. The theoretical contributions of the (19)F magnetic relaxation processes in these systems are critically assessed and selected volumetric plots are presented. These plots allow an accurate estimation of the increase in the rates of longitudinal and transverse relaxation as a function of the distance between the Ln(III) ion and the fluorine nucleus, the applied magnetic field, and the re-rotational correlation time of the complex, for a given Ln(III) ion. Selected complexes exhibit pH-dependent chemical shift behaviour, and a pK(a) of 7.0 was determined in one example based on the holmium complex of an ortho-cyano DO3A-monoamide ligand, which allowed the pH to be assessed by measuring the difference in chemical shift (varying by over 14 ppm) between two (19)F resonances. Relaxation analyses of variable-temperature and variable-field (19)F, (17)O and (1)H NMR spectroscopy experiments are reported, aided by identification of salient low-energy conformers by using density functional theory. The study of fluorine relaxation rates, over a field range of 4.7 to 16.5 T allowed precise computation of the distance between the Ln(III) ion and the CF(3) reporter group by using global fitting methods. The sensitivity benefits of using such paramagnetic fluorinated probes in (19)F NMR spectroscopic studies are quantified in preliminary spectroscopic and imaging experiments with respect to a diamagnetic yttrium(III) analogue.

Cerium(IV) Catalysts for the Ring-Opening Polymerization of Lactide

A rare example of a cerium(IV) alkoxide catalyst for lactide polymerization is reported. The lactide polymerization activity of the new cerium(IV) complex supported by a ferrocene Schiff base ligand, salfen, is compared to the activity of the yttrium analogue and to that of Ce(O(t)Bu)(4)(THF)(2). The complex Ce(salfen)(O(t)Bu)(2) is less active than Ce(O(t)Bu)(4)(THF)(2) and the corresponding yttrium(III) alkoxide, Y(salfen)(O(t)Bu)(THF). The different activity was correlated with the Mulliken charges calculated by density functional theory for the two complexes.

Tetraaquabis(biuret-κ2O,O′)gadolinium(III) trichloride

In the title compound, [Gd(C2H5N3O2)2(H2O)4]Cl3, which is isostrucutural with its yttrium analogue, the Gd3+ ion (site symmetry 2) is bonded to eight O atoms (arising from two O,O′-bidentate biuret mol­ecules and four water mol­ecules) in a distorted square-anti­prismatic arrangement. A network of N—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds helps to establish the packing, leading to a three-dimensional network. One of the chloride ions has site symmetry 2.

Synthesis and characterization of a new three-dimensional lanthanide carboxyphosphonate: Ln(4)(H(2)O)(7)[O(2)C-C(5)H(10)N-CH(2)(-)PO(3)](4)(H(2)O)(5).

The first open-framework lanthanide carboxyphosphonate has been obtained under hydrothermal conditions. The three-dimensional structure of MIL-84(Pr) (MIL = Material Institut Lavoisier) or Pr(4)(H(2)O)(7)[O(2)C-C(5)H(10)N-CH(2)(-)PO(3)](4)(H(2)O)(5) has been solved from X-ray diffraction single-crystal data (a = 23.481(1) A, b = 10.159(1) A, c = 23.006(1) A, beta = 105.63(1) degrees, V = 5284.6(6) A(3), space group Cc (No. 9)). Its framework is built up from chains of edged-sharing eight or nine-coordinated monocapped square antiprism polyhedra and carboxyphosphonate anions, creating a three-dimensional structure with small pores filled with water molecules. The thermal behavior of MIL-84(Pr) has been investigated using TGA and X-ray thermodiffractometry and indicates that MIL-84(Pr) is stable up to 523 K with a reversible hydration-dehydration process. The optical study of its yttrium analogue doped at 3.4% with europium (MIL-84(Y,Eu)) reveals a significant red-orange emission under UV radiation.

Donor-functionalized lanthanide terphenyl complexes: Synthesis and structural characterization of 2,6-di(o-anisol)phenyl compounds of ytterbium, yttrium, and samarium.

The syntheses and molecular structures of a number of 2,6-di(o-anisol)phenyl ([double bond]Danip-) -based bis(amide) and bis(alkoxide) compounds of ytterbium, yttrium, and samarium are reported. Additionally, NMR spectroscopic data are reported for the analogous diamagnetic yttrium compounds. Salt metathesis reaction of equimolar amounts of DanipLi and YbCl(3) in tetrahydrofuran at room temperature followed by addition of 2 equiv of KN(SiMe(3))(2) or KN(SiHMe(2))(2) produces DanipYb[N(SiMe(3))(2)](2) (1) and DanipYb[N(SiHMe(2))(2)](2) (2), respectively. The analogous reaction using SmCl(3) and KN(SiHMe(2))(2) produces DanipSm[N(SiHMe(2))(2)](2) (3). Reaction of DanipLi and YbCl(3) in tetrahydrofuran at room temperature followed by addition of 2 equiv of KO(2,6-diisopropylphenyl) produces DanipYb[O(2,6-diisopropylphenyl)](2) (4). Our attempts to also prepare the yttrium analogue of complex 4 yielded single-crystalline material of the tetrahydrofuran adduct DanipY(THF)[O(2,6-diisopropylphenyl)](2) (5). The molecular structures of the complexes 1-4 feature five-coordinate metal atoms and coordination polyhedra which can be described as distorted square-pyramidal rather than trigonal-bipyramidal, with the ipso carbon atom occupying the apical position. On the other hand, the molecular structure of the tetrahydrofuran-solvated yttrium Danip arylalkoxide compound 5 features a six-coordinate metal atom in a distorted trigonal-prismatic coordination environment. In all cases the Danip ligand system adopts the chiral (racemic) d,l form.

Synthesis, structure and catalytic activity of new iminophenolato complexes of scandium and yttrium

The reaction of equimolar amounts of 2-(2,4,6-Me 3C 6H 2NCH)(6-Bu t )C 6H 3OH (HL 1) with M(CH 2SiMe 3) 3(THF) 3 (M=Sc or Y) under mild conditions gives M(CH 2SiMe 3) 2(THF)(L 1). The trigonal-bipyramidal structure of these dialkyls was confirmed crystallographically for M=Sc. Whereas the scandium complex is stable in solution at room temperature, the yttrium derivative slowly disproportionates to give Y(L 1) 3 which is also accessible from Y(CH 2SiMe 3) 3(THF) 3 and three HL 1. The X-ray structure of Y(L 1) 3 indicates a chiral tris-chelate complex. While the reaction of the related ligand (2-CyNCH)(6-Bu t )C 6H 3OH (HL 2, Cy=cyclohexyl) with Sc(CH 2SiMe 3) 3(THF) 3 gives the expected dialkyl Sc(CH 2SiMe 3) 2(THF)(L 2), the reaction with the yttrium analogue affords the six-coordinate monoalkyl product Y(CH 2SiMe 3)(THF)(L 2) 2. This product is stable in solution towards disproportionation. The reaction of Y[N(SiMe 3) 2] 3 with (2-C 6F 5NCH)(6-Bu t )C 6H 3OH (HL 3) affords Y{N(SiMe 3) 2}(L 3) 2 and Y(L 3) 3. Both complexes are seven-coordinate in the solid state due to Y⋯F co-ordination to the C 6F 5 substituents. The scandium alkyl complexes are efficient catalysts for the ring-opening polymerisation of ε-caprolactone.

Synthesis and characterisation of a new 8 OK superconductor (Y, Gd) Ba 2Ca 3Cu 4O 11

Samples of YBa 2Ca 3Cu 4O 11 - the Yttrium analogue of the 125 K superconductor TlBa 2Ca 3Cu 4O 11 - have been synthesised by the solid state reaction technique. Resistivity and ac susceptibility measurements show the T c to be 80K. Oxygen annealing seems to be ineffective in enhancing the T c of these samples. The oxygen content of the sample is close to 11 as measured by the iodometric titration technique. Powder XRD shows a tetragonal structure, a = 3.85 A ̊ and c = 19.1 A ̊ . GdBa 2Ca 3Cu 4O 11 has been prepared by the total replacement of Tl by Gd to see the effect of rare-earth in this system.

Synthesis, structure and superconducting properties of metastable Y(Ba2−xYx)Cu3O7+δ

The oxygen-deficient orthorhombic oxide YBa2Cu3O7–δ1–3 has been the centre of intense recent interest because of its bulk superconducting properties near 90 K. More recently the closely related oxide, La1.5Ba1.5Cu3O7+δ, is receiving increased attention4–7. The yttrium analogue, Y1.5Ba1.5Cu3O7+δ, has not been successfully synthesized by the usual ceramic routes involving firing at temperatures above 900°C8,9, because of its intrinsic metastability. Here we report on the synthesis and characterization of a majority (90–95%) phase Y1.5Ba1.5Cu3O7+δ(referred to for historical reasons8 as Y 3-3-6), prepared by firing an atomically mixed citrate precursor between 810° and 825 °C for 2 h. X-ray powder diffraction data indicate that Y 3-3-6 is isostructural with its tetragonal La analogue4,7. Electron microprobe and thermogravimetry data yield a unit-cell composition Y(Ba2–xYx)Cu3O7+δ, with x=0.50 and δ=0.1–0.15 for the parent compound. Specimens of Y 3-3-6 with x = 0.50 and 0.375, which were annealed in O2 at 1 atm and >3 atm, displayed semiconducting behaviour. Filamentary superconductivity, detected electrically and magnetically, with transition onsets at 80 and 60 K respectively, is observed in specimens annealed in 3 atm O2 at 520°C.

Studies on organolanthanide complexes: VIII. Synthesis and thermal decomposition of new σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes

1,1′-Trimethylenedicyclopentadienyl-early lanthanide chlorides, [C 5H 4CH 2) 3-C 5H 4]LnCl · THF, in THF at −70°C reacted with aryllithium or alkyllithium, producing seven new THF solvated LnC σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes. The yttrium analogue was also synthesized. Their structures were determined by elemental analysis, infrared spectra, mass spectra, 1H NMR and thermoanalyses. The thermal decomposition of the complexes obtained was studied at ambient temperature or 100°C.