Unprecedented Transformation of a Hydrotris(pyrazolyl)borate Ligand at a Metal Center: Synthesis and Rearrangement of the First Mixed Tp/Cp Lanthanide Complex, Sm(TpMe2)2(Cp)

Reduction chemistry yields stable and soluble divalent lanthanide tris(pyrazolyl)borate complexes

Reduction of the heteroleptic Ln(III) precursors [Ln(Tp)₂(OTf)] (Tp = hydrotris(1-pyrazolyl)borate; OTf = triflate) with either an aluminyl(I) anion or KC₈ yielded the adduct-free homoleptic Ln(II) complexes dimeric 1-Eu [{Eu(Tp)(μ-κ¹:η⁵-Tp)}₂] and monomeric 1-Yb [Yb(Tp)₂]. Complexes 1-Ln have good solubility and stability in both non-coordinating and coordinating solvents. Reaction of 1-Ln with 2 Ph₃PO yielded 1-Ln(OPPh3)2. All complexes are intensely coloured and 1-Eu is photoluminescent. The electronic absorption data show the 4f-5d electronic transitions in Ln(II). Single-crystal X-ray diffraction data reveal first μ-κ¹:η⁵-coordination mode of the unsubstituted Tp ligand to lanthanides in 1-Eu.

Two Novel Sm and La Metal-Organic Frameworks Suggesting the Reductive Coupling of Carbon Dioxide (CO2) to Oxalate (C2O42-): {[Ln(HPIDC)•(μ4-C2O4)0.5·H2O]·2H2O}n.(Ln=Sm or La)

Complexes formulated as {[Ln(HPIDC)(μ4-C2O4)0.5(H2O)]·2H2O}n [Ln=Sm or La; H3PIDC=2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylic acid] have been synthesised under hydrothermal conditions. The complexes are both built up from T-shaped 3-connected HPIDC2- and 4-connected metal nodes and contain bridging oxalate (C2O42-) ligands, which might have been formed by the reductive coupling of CO2 molecules released from the HPIDC2- ligands through C-C bond cleavage.

Versatile scorpionates and new developments in the denticity changes of NNCp hybrid scorpionate/cyclopentadienyl ligands in Sc and Y compounds: from kappa1-Neta5-Cp to kappa2-NNeta5-Cp

Reaction of hybrid scorpionate/cyclopentadienyl ligands in the form of the lithium derivatives [Li(bpzcp)(THF)] [bpzcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl], [Li(bpztcp)(THF)] [bpztcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl], and the in situ-generated "Li(bpzpcp)" [bpzpcp=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-phenylethylcyclopentadienyl] with MCl3(THF)3 afforded the group 3 halide compounds [MCl2(bpzcp)(THF)] (M=Sc, 1; Y, 2), [MCl2(bpztcp)(THF)] (M=Sc, 3; Y, 4), and [MCl2(bpzpcp)(THF)] (M=Sc, 5; Y, 6). The H2O adduct of 4, [YCl2(bpztcp)(H2O)] (7), was formed when a solution of 4 was allowed to stand at room temperature in the presence of moisture. Complexes 1-7 adopt a pseudo-octahedral structure with heteroscorpionate ligands kappa2-NNeta5-Cp coordinated to the metal through the cyclopentadienyl group and two imino nitrogens of pyrazole rings. The alkyl heteroscorpionate scandium and yttrium complexes recently reported by our group, [M(CH2SiMe3)2(bpzcp)], react with 2,6-dimethylphenol and 3,5-dimethylphenol to give the bis(aryloxide) derivatives [M(OAr)2(bpzcp)] (M=Sc, OAr=2,6-dimethylphenoxide, 8; M=Y, OAr=2,6-dimethylphenoxide, 9; M=Y, OAr=3,5-dimethylphenoxide, 10). Complex 9 underwent an interesting hydrolysis process to give the tetranuclear complex [{Y(bpzcp)}(micro-OH)2(micro3-OH){Y(OAr)2}]2 (11). Variable-temperature 1H NMR experiments on 9 and 10 revealed a rapid fluxional exchange between coordinated and noncoordinated pyrazolyl rings, producing interconversion between the two enantiomers in which the scorpionate ligand can be coordinated in a kappa1-Neta5-Cp form. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 2, 7, and 11 were also established. Complexes 1 and 2 are active olefin polymerization catalysts after activation with methylaluminoxane. These compounds gave atactic polystyrenes with narrow molecular weight distribution (Mn/Mw 1.26-1.91) and with low molecular weights.

Uranium (III) Scorpionates: Synthesis and Structure of [(TpMe2)2U{N(C6H5)2}] and [(TpMe2)2U{N(SiMe3)2}]

Reaction of [(Tp(Me)2)(2)UI] with KNR(2) (R = C(6)H(5), SiMe(3)) in tetrahydrofuran (THF) afforded the monomeric trivalent actinide amide complexes [(Tp(Me)2)(2)U[N(C(6)H(5))(2)]], 1, and [(Tp(Me)2)(2)U[N(SiMe(3))(2)]], 2. The complexes have been fully characterized by spectroscopic methods and their structures were confirmed by X-ray crystallographic studies. In the solid state 1 and 2 exhibit distorted pentagonal bipyramidal geometries. The U-NR(2) bond lengths in both complexes are the same but in complex 2 the greater steric demands of the N(SiMe(3))(2) ligand led to elongated U-N(pz) bonds, especially those opposite the amido ligand.

An Unprecedented Hybrid Scorpionate/Cyclopentadienyl Ligand

An efficient method for the preparation of the first hybrid scorpionate/cyclopentadienyllithium compound as a new class of tridentate ligand is described. This compound is an excellent reagent for the introduction of this ligand into transition metal complexes.

Coordination of 2,2‘-Bipyridyl and 1,10-Phenanthroline to Yttrium and Lanthanum Complexes Based on a Scorpionate Ligand

Reaction of yttrium and lanthanum trichloride with 1 equiv of sodium or potassium hydrotris(3,5-dimethylpyrazolyl)borate and 1 equiv of 2,2'-bipyridine gives good yields of the complexes [MCl(2)(Tp(Me2))(C(10)H(8)N(2))] (M = Y (1), La (2)). The analogous compounds with 1,10-phenanthroline, [MCl(2)(Tp(Me2))(C(12)H(8)N(2))] (M = Y (3), La (4)), have been obtained by a similar procedure. The solid-state structures of 2-4 were determined by single-crystal X-ray diffraction and revealed that the compounds are all seven-coordinate with capped octahedral geometry. In contrast, reaction of yttrium trichloride with 1 equiv of sodium hydrotris(3,5-dimethylpyrazolyl)borate in the presence of 1 equiv of neocuproine affords [YCl(3)(Tp(Me2))][Na(neoc)(3))] (5). Compounds 1 and 2 provide an entry for the synthesis of complexes containing the bipyridyl ligand in a radical anionic form or in a dianionic form. Reaction of 1 and 2 with an excess of sodium amalgam gives [Y(Tp(Me2))(bipy)(THF)(2)] (6) and [La(Tp(Me2))(2)(bipy)] (7), respectively. The structures of both compounds have been determined by X-ray crystallography. Compound 7 can be oxidized with iodine to give [La(Tp(Me2))(2)(bipy)]I (8).

Facile pyrazolylborate ligand degradation at lanthanide centers: X-ray crystal structures of pyrazolylborinate-bridged bimetallics

Adventitious hydrolysis of a number of different complexes with the molecular formula Ln(Tp(Me2))(2)X [Tp(Me2) = (HB(dmpz)(3)), where X is a basic anionic ligand] in various solvents, yielded crystals of highly insoluble dimers of the general formula [Ln(Tp(Me2))(mu-BOp(Me2))](2) (1) [Ln = La, Ce, Sm; BOp(Me2) = (HBO(dmpz)(2))(2)(-); dmpzH = 3,5-dimethylpyrazole]. The results of several single-crystal X-ray determinations are reported. One metal nitrogen distance, that lying across from the two negatively charged bridging oxygen atoms, is 0.06 A longer than the others, suggesting an unusual trans influence at a lanthanide center. The formation of 1 is proposed to involve the intermediacy of Ln(Tp(Me2))(2)OH formed by protonolysis with adventitious water.

Solid-state structure and solution behavior of eight-coordinate Sm(III) poly(pyrazolyl)borate compounds

[Sm(Tp(Me2)(2)(kappa(2)-S(2)CNR(2))] compounds (R = Et (1), Me (2); Tp(Me2) = HB(3,5-Me2pz)(3)) have been isolated from reaction of (R(2)NC(S)S)(2) with 2 equiv of [Sm(Tp(Me2)(2)]. Reductive cleavage of 2,2'-dipyridyl disulfide or 2,2'-dipyridyl diselenide by [Sm(Tp(Me2)(2)] afforded good yields of [Sm(Tp(Me2)(2)(kappa(2)-Y)] compounds (Y = 2-SC(5)H(4)N (3), 2-SeC(5)H(4)N (4)). 4 is the first selenopyridine complex of an f-block element. Sm(Tp(Me2)(2)(2-OC(5)H(4)N) (5) has been synthesized by salt metathesis of [Sm(Tp(Me2)(2)Cl] with the sodium salt of the 2-hydroxypyridine. The solid-state structures of 1, 3, 4, and 5 were determined by single-crystal X-ray diffraction analysis and revealed that the compounds are all eight-coordinate with dodecahedral geometry. The samarium atoms are bound in tridentate fashion to two pyrazolylborate ligands and in bidentate fashion by the third ligand. The solution behavior of the compounds was studied by (1)H NMR techniques. (1)H-(1)H exchange spectroscopy experiments give evidence for two distinct dynamic regimes occurring in solution.