Divalent Complexes Research Articles

Gas-phase reactions of divalent Ni complex ions with acetonitrile: chelate ring size, inductive, and steric effects

Ni(II) complexes of a series of pentadentate polyamine ligands have been reacted with CH 3CN in the gas phase using a modified quadrupole ion trap mass spectrometer. The ligands have structural features such that upon complexation, chelate ring size, sterics, and inductive effects can be evaluated in the gas phase. Rate and equilibrium constants for CH 3CN addition to the metal complexes show that there is a general decrease in the gas-phase reactivity as the chelate ring size is increased. Density functional theory calculations at the B3LYP/LANL2DZ level of theory have been used to obtain minimum energy structures and Mulliken charges for the complexes. The decreased reactivity observed as the chelate ring size is increased correlates with a decrease in the atomic charge on the metal. A larger chelate ring size enhances ligand flexibility and improves the overlap of the ligand's donor atoms with the metal center. Adding methyl groups adjacent to or on the nitrogen donor groups of a ligand also decreases the rate and equilibrium constants for the reactions of a given complex with CH 3CN. Analysis of Mulliken charges for these complexes indicates that both inductive and steric effects are responsible for lower complex reactivity. These results suggest that while the gas-phase reactivity of a metal complex with CH 3CN is very dependent on the functional groups directly bound to the metal, in some cases steric effects can conceal the correlation between reactivity and coordination structure.

Nickel(II) Complexes Containing Bidentate Diarylamido Phosphine Ligands

A series of diamagnetic divalent nickel complexes supported by bidentate diarylamido phosphine ligands have been prepared and characterized. Deprotonation of N-(2-diphenylphosphinophenyl)-2,6-diisopropylaniline (H[iPr-NP]) and N-(2-diphenylphosphinophenyl)-2,6-dimethylaniline (H[Me-NP]) with n-BuLi in THF at −35 °C produced the corresponding lithium complexes, [iPr-NP]Li(THF)2 and [Me-NP]Li(THF)2, respectively. The chloride complex {[iPr-NP]NiCl}2 is accessible from the reaction of NiCl2(DME) with [iPr-NP]Li(THF)2 or H[iPr-NP] in the presence of triethylamine. Addition of PMe3 to {[iPr-NP]NiCl}2 afforded [iPr-NP]NiCl(PMe3), from which [iPr-NP]NiMe(PMe3), [iPr-NP]NiPh(PMe3), and [iPr-NP]Ni(η3-CH2Ph) were prepared from the metathetical reactions with appropriate Grignard reagents. Solution NMR data of [iPr-NP]NiMe(PMe3) revealed two geometric isomers at room temperature with the major species carrying PMe3 cis to the phosphorus donor of the amido phosphine ligand. Interestingly, only one of the possible isomers is observed for [iPr-NP]NiCl(PMe3) and [iPr-NP]NiPh(PMe3), in which the two phosphorus donors in the former are exclusively cis whereas those in the latter are trans. The benzyl complexes [iPr-NP]Ni(η3-CH2Ph) and [Me-NP]Ni(η3-CH2Ph) are prepared directly from the reactions of [iPr-NP]Li(THF)2 and [Me-NP]Li(THF)2, respectively, with Ni(COD)2 in the presence of benzyl chloride. The η3-feature of the benzyl ligand maintained in solution is elucidated by the 1JCH value observed for the benzylic methylene group in the NMR spectroscopy. In addition to the spectroscopic data for all new molecules, X-ray structures of H[iPr-NP], [Me-NP]Li(THF)2, [iPr-NP]NiCl(PMe3), [iPr-NP]NiMe(PMe3), [iPr-NP]NiPh(PMe3), [iPr-NP]Ni(η3-CH2Ph), and [Me-NP]Ni(η3-CH2Ph) are presented.

Synthesis, crystal structure, and chirality of divalent lanthanide reagents containing tri- and tetraglyme

Six new divalent lanthanide complexes using triglyme (trigly) and tetraglyme (tetgly) as achiral ligands have been prepared, using a facile synthetic method, in search for enantioselective solid-state reagents. The crystal structures of cis-[SmI 2(trigly)thf] ( 1), trans-[YbI 2(trigly)thf] ( 2), trans-[SmI 2(trigly)dme] ( 3), trans-[YbI 2(tetgly)] ( 4), trans-[EuI 2(tetgly)thf] ( 5), and [Sm(tetgly) 2][SmI 3(tetgly)]I ( 6) have been determined. All complexes, except 5, are chiral. The 10-coordinate cation in 6 displays a helical chirality since the two tetraglyme ligands are wrapped around the samarium ion. Since trans-[YbI 2(tetgly)] ( 4), which has a chiral arrangement of terminal methyl groups, crystallizes as a conglomerate, preferential crystallization and consequent enantioselective reduction of acetophenone was attempted, but resulted in racemic products, possibly on account of racemic twinning in 4.

Are gas-phase reactions of five-coordinate divalent metal ion complexes affected by coordination geometry?

Five-coordinate metal complex ions of the type [ML](2+) [where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and L= 1,9-bis(2-pyridyl)-2,5,8-triazanonane (DIEN-(pyr)(2)) and 1,9-bis(2-imidazolyl)-2,5,8-triazanonane (DIEN-(imi)(2)] have been reacted with acetonitrile in the gas phase using a modified quadrupole ion trap mass spectrometer. The kinetics and thermodynamics of these reactions show that the reactivity of these complexes is affected by metal electronic structure and falls into three groups: Mn(II) and Ni(II) complexes are the most reactive, Fe(II) and Co(II) complexes exhibit intermediate reactivity, and Cu(II) and Zn(II) complexes are the least reactive. To help explain the experimental trends in reactivity, theoretical calculations have been used. Due to the relatively large size of the metal complexes involved, we have utilized a two-layered ONIOM method to perform geometry optimizations and single point energy calculations for the [ML](2+) and [ML + CH(3)CN](2+) systems. The calculations show that the reactant five-coordinate complexes ([ML](2+)) exhibit structures that are slightly distorted trigonal bipyramidal geometries, while the six-coordinate complexes ([ML + CH(3)CN](2+)) have geometries that are close to octahedral. The Delta G values obtained from the ONIOM calculations roughly agree with the experimental data, but the calculations fail to completely explain the trends for the different metal complexes. The failure to consider all possible isomers as well as adequately represent pi-d interactions for the metal complexes is the likely cause of this discrepancy. Using the angular overlap model (AOM) to obtain molecular orbital stabilization energies (MOSE) also fails to reproduce the experimental trends when only sigma interactions are considered but succeeds in explaining the trends when pi interactions are taken into account. These results indicate that the pi-donor character of the CH(3)CN plays a subtle, yet important, role in controlling the reactivity of these five-coordinate complexes. Also, the AOM calculations are consistent with the experimental data when the [ML](2+) complexes have high-spin trigonal bipyramidal configurations. Generally, these results suggest that ion-molecule reactions can be very sensitive to metal complex coordination geometry and thus may have some promise for providing gas-phase coordination structure.

A Theoretical Study of Divalent Lanthanide (Sm and Yb) Complexes with a Triazacyclononane-Functionalized Tetramethylcyclopentadienyl Ligand

A density functional theory (DFT) study of the divalent lanthanide complexes [C5Me4SiMe2(iPr2-tacn)]LnI (Ln = Sm, Yb; tacn = 1,4-diisopropyl-1,4,7-triazacyclononane) is presented. A methodological study was done with various density functionals that employ large-core ECPs for the lanthanide atoms. The DFT results were compared with recent experimental X-ray structures for the compounds investigated here. The B3PW91 functional was found to give the best description of the complexes at an affordable level of computational effort. The geometry of the [C5Me4SiMe2(iPr2-tacn)]LnI complexes was found to be a distorted trigonal bipyramidal and the essential structural features are correctly reproduced from the DFT calculations. Further model studies show that the computations can be simplified by replacing the methyl groups (which do not interact with the lanthanide center directly) with hydrogen atoms to still provide reasonable predictions for the structure of the complex.

Hydrolysis of p-nitrophenyl picolinate catalyzed by divalent metal ion complexes containing imidazole groups in micellar solution

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by Zn(II), Cu(II) and Co(II) complexes of imidazole groups have been investigated kinetically in the pH range 6.0–8.0 at the presence of three kinds of surfactants and 25.0±0.01°C, respectively. The results indicated that Zn(II) complex exhibit a great catalytic function in micellar solution with higher pH value, but when reactions were performed in weak acid solutions, Cu(II) complex catalyzed the hydrolysis of PNPP more efficiently than Zn(II) and Co(II) complexes did, which may be attributable to the different ionization states of the corresponding complexes in micellar media with different pH values and the different nucleophilic ability of active species in different complexes. In addition, these complexes showed more reactivity in zwitterionic (LSS) and nonionic (Brij35) micelles than that in cationic (CTAB) micelle, which may be explained by the electrostatic interaction between metal ions of these complexes and the head groups of surfactants or the substrate. The relative kinetic and thermodynamic parameters were obtained by kinetic analysis employing ternary complex model for metallomicellar catalysis.

Steric saturation of the ytterbium coordination environment: (Tp tBu, Me )Yb(OMes), a four coordinate, monomeric, base-free divalent lanthanide complex, its solvation with tetrahydrofuran, and comparison to the β-diketonate complex, (Tp tBu, Me )Yb(dpm)

Reaction of (Tp tBu, Me )Yb(I)(THF) with KOMes (Mes=2,4,6-C 6H 2Me 3) in tetrahydrofuran (THF) at −45 °C afforded the monomeric divalent lanthanide aryloxide complex (Tp tBu, Me )Yb(OMes)(THF) ( 1). Reaction of [(Tp tBu, Me )Yb(μ-H)] 2 (Tp tBu, Me =hydrotris(3- tert-butyl-5-methylpyrazolyl)borate) with HOMes in benzene at ambient temperature gave the monomeric solvent free lanthanide aryloxide complex (Tp tBu, Me )Yb(OMes) ( 2). Dissolution of 2 in tetrahydrofuran at ambient temperature resulted in clean transformation to the solvated complex 1. The coordinated THF ligand is persistent in non-ethereal solvents. Reaction of [(Tp tBu, Me )Yb(μ-H)] 2 with dipivaloylmethane (Hdpm) afforded the related β-diketonate complex (Tp tBu, Me )Yb(dpm) ( 3). Complexes 1– 3 have been fully characterized by spectroscopic methods and their structures were confirmed by X-ray crystallographic studies. Crystal data: C 38.5H 62.5BN 6O 2Yb ( 1 · 0.25 C 6H 14): monoclinic, C2/ c, a=21.526(4) Å, b=13.213(2) Å, c=31.403(7) Å, β=105.80(2)°, Z=8; C 33H 51BN 6OYb ( 2): orthorhombic, Pbcm, a=10.5344(5) Å, b=20.3495(7) Å, c=16.3768(6) Å, Z=4; C 35H 59BN 6O 2Yb ( 3): monoclinic, C2/ c, a=13.370(1) Å, b=21.134(2) Å, c=28.242(2) Å, β=97.356(2)°, Z=8.

Divalent molybdenum complexes of the dipyrrolide ligand system. Isolation of a Mo2 unit with a 45 degree twist angle.

The preparation of divalent Mo complexes of dipyrrolide dianions was carried out by reacting Mo(2)(acetate)(4) with the dipotassium salts of Ph(2)C(2-C(4)H(3)NH)(2) and 2-[1,1-bis(1H-pyrrol-2-yl)ethyl]pyridine. The two reactions respectively afforded the diamagnetic [[Ph(2)C(C(4)H(3)N)(2)](2)Mo(2)(OAc)(2)[K(THF)(3)][K(THF)]].THF (1) and [[(2-C(5)H(4) N)(CH(3))C(2-C(4)H(3)N)(2)]Mo(OAc)[K(THF)]](2).THF (2). Both compounds retained two acetate units in the dimetallic structure. Conversely, the reaction of Me(8)Mo(2)Li(4)(THF)(4) with Et(2)C(2-C(4)H(3)NH)(2) afforded the paramagnetic dimer [[Et(2)C(C(4)H(3)N)(2)](4)Mo(2)Li(2)][Li(THF)(4)](2).0.5THF (3). The paramagnetism is most likely caused by the 45 degree rotation of the two Mo(dipyrrolide) units with respect to each other and which, in turn, is caused by the presence of two lithium cations in the molecular structure.

Regional citrate anticoagulation during simulated treatments of sustained low efficiency diafiltration.

Renal replacement therapy is frequently required for critically ill patients with a high risk of bleeding. Conventional heparinization strategies to prevent extracorporeal blood circuit clotting can cause significant haemorrhage in such patients because of systemic anticoagulation. Regional citrate anticoagulation (RCA) is a well-established technique that minimizes this complication by the decalcification of blood in the extracorporeal circuit such that it is incapable of clotting. To date, there are no reports on the use of RCA for sustained low-efficiency dialysis/diafiltration (SLED), a hybrid therapy that involves the use of conventional haemodialysis machinery to deliver lower solute clearances over prolonged periods of time. In preparation for clinical study, an in vitro simulation of SLED was devised (blood substitute flow 250 mL/min, dialysate flow 200 mL/min, predilution haemofiltration 100 mL/min). Blood substitute was decalcified by an infusion of 4% trisodium citrate (TSC) proximally into the extracorporeal blood circuit, with partial restoration of calcium homeostasis from dialysate containing ionized [Ca2+] at 0.9 mmol/L. This simulation was used to establish first the 4% TSC requirement for therapeutic decalcification, and second the associated changes in ionized [Ca2+] and [Mg2+] within the blood substitute from chelation with citrate and subsequent removal of the resulting divalent cation-citrate complex. Serial measurements of blood substitute [Ca2+] from strategic points along the extracorporeal circuit showed therapeutic decalcification was not achieved with 4% TSC infusion rates up to 400 mL/h, and extrapolation of experimental results suggests that 450 mL/h will be required. Under these conditions, ionized [Ca2+] and [Mg2+] in the blood substitute venous return and would be 0.42 and 0.2 mmol/L, respectively, with 0.35 mmol of citrate being returned per minute via the blood substitute venous return. These results were modelled for various changes in SLED operating parameters, and discussed in detail. An appropriate regimen for 4% TSC infusion and divalent cation replacement is proposed for clinical study in the future.

Synthesis of lanthanide(II)–imine complexes and their use in carbon–carbon and carbon–nitrogen unsaturated bond transformation

Ytterbium and samarium metals reduced aromatic ketimines to give directly divalent azalanthanacyclopropane complexes 1 quantitatively, the structure of which was characterized by X-ray analysis. The imine complexes 1 catalyzed dehydrogenative silylation of terminal alkynes, hydrosilylation of imines and alkenes, and intermolecular hydrophosphination of alkynes. Moreover, dehydrogenative double silylation of conjugated dienes was achieved with 1.

Syntheses, crystal structures and characterization of divalent transition metal sulfonate complexes with O-phenanthroline

Two new complexes, [Zn(phen)2(H2O)2]2L·H2O (1) and [Cu(phen)(L)(H2O)2]L·3H2O (2), where HL = 4-aminobenzenesulfonic acid and phen = o-phenanthroline, have been synthesized and their crystal structures determined by X-ray diffraction. In the complexes the Cu(II) and Zn(II) atoms revealed two different coordination environments. Complex 1 consists of a cation [Zn(phen)2(H2O)2]2+, in which Zn(II) is six-coordinated by four nitrogen atoms from two o-phenanthroline molecules and by two water molecules. Complex 2 has two crystallographically unique Cu(II) ions, where Cu(II) ion is five-coordinate with two nitrogen atoms of o-phenanthroline, two water molecules and one sulfonate oxygen atom. The electrochemical behavior and FT-IR of the two compounds have also been studied in detail.

Cytotoxic iron chelators: characterization of the structure, solution chemistry and redox activity of ligands and iron complexes of the di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) analogues

Di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) and a range of its analogues comprise a series of monobasic acids that are capable of binding iron (Fe) as tridentate ( N, N, O) ligands. Recently, we have shown that these chelators are highly cytotoxic, but show selective activity against cancer cells. Particularly interesting was the fact that cytotoxicity of theHPKIH analogues is maintained even after complexation with Fe. To understand the potent anti-tumor activity of these compounds, we have fully characterized their chemical properties. This included examination of the solution chemistry and X-ray crystal structures of both the ligands and Fe complexes from this class and the ability of these complexes to mediate redox reactions. Potentiometric titrations demonstrated that all chelators are present predominantly in their charge-neutral form at physiological pH (7.4), allowing access across biological membranes. Keto-enol tautomerism of the ligands was identified, with the tautomers exhibiting distinctly different protonation constants. Interestingly, the chelators form low-spin (diamagnetic) divalent Fe complexes in solution. The chelators form distorted octahedral complexes with Fe(II), with two tridentate ligands arranged in a meridional fashion. Electrochemistry of the Fe complexes in both aqueous and non-aqueous solutions revealed that the complexes are oxidized to their ferric form at relatively high potentials, but this oxidation is coupled to a rapid reaction with water to form a hydrated (carbinolamine) derivative, leading to irreversible electrochemistry. The Fe complexes of theHPKIH analogues caused marked DNA degradation in the presence of hydrogen peroxide. This observation confirms that Fe complexes from theHPKIH series mediate Fenton chemistry and do not repel DNA. Collectively, studies on the solution chemistry and structure of theseHPKIH analogues indicate that they can bind cellular Fe and enhance its redox activity, resulting in oxidative damage to vital biomolecules.

Syntheses, crystal structures and characterization of divalent transition metal sulfonate complexes with o-phenanthroline

Three new complexes, namely [Cu(phen)(L)(H 2O) 2]L·H 2O 1, [M(phen) 2(H 2O) 2]2L·6H 2O [M=Co( 2), Ni( 3)], where, HL=4-methylbenzenesulfonic acid and phen= o-phenanthroline, have been synthesized. The crystal structures were determined by X-ray diffraction method and refined by full-matrix least-squares methods to R=0.0535 and wR=0.1492 using 3567 reflections with I>2 σ( I) for 1; R=0.0388 and wR=0.1223 using 3844 reflections with I>2 σ( I) for 2; and R=0.0401 and wR=0.1222 using 3425 reflections with I>2 σ( I) for 3. 1 Consists of cationic species [Cu(phen)(L)(H 2O) 2] +, in which Cu(II) ion is five-coordinated by two nitrogen atoms of o-phenanthroline, two water molecules and one sulfonate oxygen atom. The cations and the non-coordinating sulfonate anions are linked by hydrogen bonds to form infinite chains. Complexes 2 and 3 are isostructral compounds. Each of them consists of cationic species [M(phen) 2(H 2O) 2] 2+, in which metal ion is six-coordinated by four nitrogen atoms from two o-phenanthroline molecules and two water oxygen atoms. The sulfonate ions do not coordinate to metal ion. The cations, non-coordinating sulfonate ions and lattice water molecules are linked by hydrogen bonds to form infinite zigzag chains. CV, FT-IR, UV–Vis and TGA were also used to characterize these compounds.

Ring‐opening polymerization and block copolymerization of L‐lactide with divalent samarocene complex

AbstractDivalent samarocene complex [(C5H9C5H4)2Sm(tetrahydrofuran)2] was prepared and characterized and used to catalyze the ring‐opening polymerization of L‐lactide (L‐LA) and copolymerization of L‐LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L‐LA was retained. The structure of the block copolymer of CL/L‐LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)‐b‐P(L‐LA) copolymer were monitored with real‐time hot‐stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL‐b‐P(L‐LA) copolymer was demonstrated through AFM observation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2667–2675, 2003

Synthesis and Structural Characterization of Divalent Ytterbium Complexes Supported byβ-Diketiminate Ligands and Their Catalytic Activity for the Polymerization of Methyl Methacrylate

Three divalent ytterbium complexes supported by a β-diketiminate ligand were synthesized for the first time. The mixed-ligand ytterbium chlorides (CH3C5H4)[(DIPPh)2nacnac]YbCl (1), (C9H7)[(DIPPh)2nacnac]YbCl (2), and (ArO)[(DIPPh)2nacnac]YbCl(THF) (3) ((DIPPh)2nacnac = N,N-diisopropylphenyl-2, 4-pentanediimine anion, ArO = 2,6-di-tert-butyl-4-methylphenoxo), which were obtained in high yield by using [(DIPPh)2nacnac]YbCl2(THF)2 as precursor, were reduced by Na/K alloy in THF to afford the corresponding divalent species (CH3C5H4)[(DIPPh)2nacnac]Yb(THF) (4), (C9H7)[(DIPPh)2nacnac]Yb(THF) (5), and {(ArO)[(DIPPh)2nacnac]Yb(THF)}(THF) (6), respectively. Complexes 2−6 were well characterized, and crystal structures of complexes 4−6 were determined. These divalent complexes exhibit good catalytic activity for the polymerization of methyl methacrylate.

Polymerization of Methyl Methacrylate Initiated by a Divalent Samarium Phenoxide Complex with an Alkyl Aluminium Compound

AbstractA divalent samarium complex that bears two bulky phenoxide ligands promotes the living polymerization of methyl methacrylate in the absence of cocatalyst. The initiation involves a tail‐to‐tail coupling reaction of the samarium‐enolate radical followed by a one‐electron reduction of the monomer with the divalent samarium initiator. The polymerization takes place stereospecifically and the samarium initiator affords highly syndiotactic poly(methyl methacrylate). The stereoregularity of the polymer is variable with the ratio of the samarium initiator to aluminium compound (2,6‐di‐tert‐butyl‐4‐methylphenoxy)2AlMe. The polymer obtained when the [Al]/[Sm] ratio is 4.0 has a unique tacticity, [mm]/[mr]/[rr] = 42:11:47, and the polymer has a melting point at 161 °C, which suggests the formation of a stereocomplex between syndiotactic and isotactic poly(methyl methacrylate).Part of the possible initiation mechanism and equimolar reaction of BHT‐SmII with MMA.magnified imagePart of the possible initiation mechanism and equimolar reaction of BHT‐SmII with MMA.

Quinoline‐Containing Calixarene Fluoroionophores: A Combined NMR, Photophysical and Modeling Study

AbstractThe 8‐alkoxy‐5‐chloroquinoline fluorophore was appended at the lower rim of a calix[4]arene triamide with two different orientations. In ligand 1 the quinoline part is linked to the calixarene skeleton through the pyridine C2 atom, while in 2 it is linked through the phenolic oxygen atom of the chromophore. The binding properties of both ligands, investigated in chloroform and methanol solutions, indicate that they are efficient fluoroionophores, with selectivity for sodium and strontium ions among alkali and alkaline earth metal ions. Combined NMR, photophysical, and modeling studies disclosed the peculiar conformational and coordination features of monovalent and divalent metal ion complexes. Lanthanide metal ion complexes were prepared and studied in acetonitrile solution showing good luminescence in the case of Nd3+, Yb3+, and Er3+ ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthetic, Structural and Biological Studies on Divalent Tin Complexes of Sixteen to Twenty-Four Membered Tetraaza Macrocycles

A new series of 16- to 24-membered macrocycles of tin(II) containing tetraaza groups has been prepared by the template condensation reaction of glutaric acid and phthalic acid with 1,2-phenylenediamine, 2,6-diaminopyridine, and diethylenetriamine in 1:2:2 molar ratios. The reaction products were characterized by elemental analyses, molecular weight determinations, infrared, 1 H NMR, 119 Sn NMR, and mass spectral studies. X-ray powder diffraction spectrum of one representative compound also has been reported. The hexacoordinated state for tin has been confirmed by spectral studies. An octahedral geometry for these complexes has been proposed as the binding sites are the nitrogen atoms of the macrocycle. The formulation of the complexes as [Sn(N 4 MaC n )Cl 2 ] (where N 4 MaCn represent the ligand molecule and n = 1 to 6 has been established on the basis of the chemical composition. All of the complexes are monomeric. The ligands and their complexes also have been screened for their antimicrobial activities and the results are discussed.

The first thorium arene complex: a divalent synthon.

The first thorium arene complex: a divalent synthon.

Di‐ and Trivalent Ytterbium Complexes Containing Linked Amino‐ and Amidocyclopentadienyl Ligands

AbstractReactions of the aminocyclopentadienes (C5Me4H)SiMe2NHR (R = Et, allyl, nPr, tBu) with [YbI2(THF)2] in the presence of two equivalents of potassium 1,2‐diphenylethenide in THF at room temperature gave the diamagnetic half‐sandwich complexes [Yb(η5‐C5Me4SiMe2NHR)Ln(μ‐I)]2 (L = THF, n = 2, L = DME, n = 1). The tert‐butylamido derivative [Yb(η5‐C5Me4SiMe2NHtBu)(THF)2(μ‐I)]2 was characterized by X‐ray structural analysis as a dinuclear complex containing a nonchelating aminocyclopentadienyl ligand. Deprotonation of the aminocyclopentadiene (C5H4tBu)SiMe2NHtBu with two equivalents of potassium 1,2‐diphenylethenide in THF, followed by reaction with [YbI2(THF)2] at 60 °C, gave the trivalent ytterbium ate complex [K(DME)][Yb{(η5:η1‐C5H3tBu‐3)SiMe2NtBu}2]. A single crystal X‐ray diffraction study of this complex shows polymeric chains consisting of trivalent ytterbocene units with two chelating amidocyclopentadienyl ligands coordinated to potassium ions. Metalation of the aminoindene (C9H7)SiMe2NHtBu under the same conditions and treatment with [YbI2(THF)2] in THF at ambient temperature resulted in the formation of the divalent ytterbocene complex [Yb{η5‐(1‐C9H6)SiMe2NHtBu}2(THF)2]. The reaction of ytterbium naphthalenide [Yb(C10H8)(THF)2] with one equivalent of (C9H7)SiMe2NHtBu afforded the bis(indenyl) compound which was isolated as its 2,2′‐bipyridyl adduct [Yb{η5‐(1‐C9H6)SiMe2NHtBu}2(bipy)]. It was shown by single‐crystal structural analysis to exhibit a bent metallocene structure with noncoordinating amino side‐chains. The reaction of (C5Me4H)CH2SiMe2NHtBu, which contains a longer CH2SiMe2 bridge, with [Yb(C10H8)(THF)2] gave the complex [Li0.5][Yb(μ‐η5:η1‐C5Me4CH2SiMe2NtBu)(THF)2(μ‐I)0.5]. Single crystal X‐ray structure analysis revealed the presence of polymeric chains consisting of dinuclear iodo‐bridged [Yb(η5:η1‐C5Me4CH2SiMe2NtBu)] units with a chelating linked amidocyclopentadienyl ligand, intermolecularly bridged by lithium ions. The lithium ions are bonded in an η5‐manner to both units, forming a lithocene structure. When YbCl3 was reacted with Li2[(C5H3tBu‐3)SiMe2NCH2CH2X] (X = NMe2, OMe), heterobimetallic complexes Li[Yb{(η5:η1‐C5H3tBu‐3)SiMe2NCH2CH2X}2] with a helical metallocene structure were isolated. The single crystal structure analysis of one of the three possible diastereomers of Li{Yb[(η5:η1‐C5H3tBu‐3)SiMe2NCH2CH2NMe2]2}, viz. the thermodynamically stable (R,R)/(S,S) epimer was performed. When YbCl3 was reacted with one equivalent of Li2[(C5H3tBu‐3)SiMe2NCH2CH2NMe2] and reduced “in situ” with one equivalent of sodium 1,2‐diphenylethenide in THF, the ytterbium(II) metallocene complex [Li(THF)]2[Yb{(η5‐C5H3tBu‐3)SiMe2NH(CH2CH2NMe2)}2(μ‐Cl)2] was isolated, which exhibits a structure with the two amino functions coordinating to the lithium ions and the chloro ligands bridging both the lithium and ytterbium centers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)