Divalent Complexes Research Articles

Displacement, reduction, and ligand redistribution reactivity of the cationic mono-C 5Me 5 Ln 2+ complexes (C 5Me 5)Ln(BPh 4) (Ln = Sm, Yb)

The reactivity of the mono(pentamethylcyclopentadienyl) divalent lanthanide tetraphenylborate complexes, (C 5Me 5)Ln(BPh 4) (Ln = Sm, 1; Yb, 2), was investigated to determine how Ln 2+ and (BPh 4) 1− reactivity would combine in these species. The (BPh 4) 1− ligand in (C 5Me 5)Yb(BPh 4) can be displaced with KN(SiMe 3) 2 to form the heteroleptic divalent dimer, {(C 5Me 5)Yb[μ-N(SiMe 3) 2]} 2 ( 3). Both 1 and 2 reduce phenazine to give the bis(pentamethylcyclopentadienyl) ligand redistribution products, [(C 5Me 5) 2Ln] 2(μ-C 12H 8N 2). 2,2-Bipyridine is reduced by 1 to yield the ligand redistribution product, (C 5Me 5) 2Sm(C 10H 8N 2) (4), while 2 does not react with bipyridine. Tert-butyl chloride is reduced by 1 to form the trimetallic pentachloride complex [{(C 5Me 5)(THF)Sm} 3(μ-Cl) 5][BPh 4] ( 6), in a reaction that appears to use the reductive capacity of both Sm 2+ and (BPh 4) 1−.

Isolation of a Chromium Hydride Single-Component Ethylene Polymerization Catalyst

Reaction of the divalent complex [(t-Bu)NPN(t-Bu)]2Cr (1) with different stoichiometric ratios of Al(i-Bu)3 afforded {μ-[(t-Bu)NP(i-Bu)N(t-Bu)]Al(i-Bu)2}2Cr (2) and [{(i-Bu)P{μ-N(t-Bu)}2Al(i-Bu)2}Cr(μ-H)]2 (3) as part of the same reaction sequence. Complex 2 arises from association of alane and the two ligands via alkylation of the P atom and retention of the AlR2 unit. Complex 3 appears to be generated from subsequent dissociation of one alkylated ligand and possible transfer of an i-Bu group to Cr followed by β-H elimination or transfer of a hydride originating from isobutyl elimination of the aluminum-containing residue. Both species are potent ethylene polymerization catalysts with no need for further activation. It is assumed that 2 is transformed in situ into 3 under the influence of ethylene. Reactions with ethylene carried out in the presence of excess of Al(i-Bu)3 switch the selectivity completely toward selective trimerization.

Divalent Lanthanide Complexes: Highly Active Precatalysts for the Addition of N−H and C−H Bonds to Carbodiimides

Various divalent lanthanide complexes with the formula LnL2(sol)x (L = N(TMS)2, sol = THF, x = 3, Ln = Sm (I), Eu (II), Yb (III); L = MeC5H4, sol = THF, x = 2, Ln = Sm (IV); L = ArO(Ar = [2,6-((t)Bu)2-4-MeC6H2]), sol = THF, x = 2, Ln = Sm (V)), especially complexes I- III, serve as excellent catalyst precursors for catalytic addition of various primary and secondary amines to carbodiimides, efficiently providing the corresponding guanidine derivatives with a wide range of substrates under solvent-free condition. The reaction shows good functional groups tolerance. Complexes I- III are also excellent precatalysts for addition of terminal alkynes to carbodiimides yielding a series of propiolamidines. The active sequence of Yb < Eu < Sm for metal and MeC5H4 < ArO < N(TMS)2 for ligand around the metal was observed for both reactions. The first step in both reactions was supposed to include the formation of a bimetallic bisamidinate samarium species originating from the reduction-coupling reaction of carbodiimide promoted by lanthanide(II) complex. The active species is proposed to be a lanthanide guanidinate and a lanthanide amidinate.

Accessing Decaphenylmetallocenes of Ytterbium, Calcium, and Barium by Desolvation of Solvent-Separated Ion Pairs: Overcoming Adverse Solubility Properties

The redox-transmetalation ligand-exchange reaction of ytterbium or calcium metal with 2 equiv of pentaphenylcyclopentadiene (C5Ph5H) and 1 equiv of HgPh2 in thf afforded the solvent-separated ion pairs (SSIPs) [M(thf)6][C5Ph5]2 (M = Yb, Ca), which were characterized by single-crystal X-ray analyses. Addition of toluene to the isolated SSIPs led to the precipitation of the homoleptic sandwich complexes [M(C5Ph5)2] (M = Yb, Ca). In the reaction of barium metal with C5Ph5H and HgPh2 the corresponding SSIP was observed in situ, and only the sandwich complex [Ba(C5Ph5)2] could be isolated. Single-crystal X-ray analyses were carried out for [M(C5Ph5)2] (M = Yb, Ba), which confirmed the highly symmetric structure of these complexes with two parallel cyclopentadienyl ligands. Oxidation and metal-ligand exchange reactions were investigated for the divalent ytterbium complexes.

Photophysical properties, X-ray structures, electrochemistry, and DFT computational chemistry of osmium complexes

We report the synthesis of phosphorescent divalent osmium complexes of the form [Os(N–N) 2(L–L) or Os(L–L) 2(N–N)] 2+ (PF 6) 2 where N–N is a derivative of 1,10-phenanthroline, and L–L is a diarsine or diphosphine ligand: 1,2-bis(dimethylphosphino)ethane, 1,2-bis(dicyclohexylphosphino)ethane, or 1,2-bis(dimethylarseno)benzene. X-ray structures have been determined, luminescent and electrochemical properties have been measured and DFT calculations have been performed on the complexes. The emission lifetime of complexes of structure Os(II)(L–L) 2(N–N) are longer than the those of Os(II)(N–N) 2(L–L). The DFT calculations show that there is significant mixing of the π−π ∗ into the dπ−π ∗ charge-transfer state for the complexes of the form Os(II)(L–L) 2(N–N) resulting in a longer lived excited state. Through DFT calculations we were able to conclude that the HOMO of the complexes is a d orbital on the osmium while the LUMO is the b 1( ψ) π ∗ system of the phenanthroline. However, we found that the HOMO did not have the correct symmetry to enable strong charge transfer to the phenanthroline to be observed, and the strong MLCT transition observed in the spectra is the metal d HOMO(−1) to the b1 π ∗ LUMO of the phenanthroline.

Divalent Ytterbium Boratabenzene Complex (C5H5BNPh2)2Yb(THF)2: Synthesis, Structure, and Solvent-Mediated Redox Transformation

The boratabenzene derivative of divalent ytterbium complex (C5H5BNPh2)2Yb(THF)2 (1) was synthesized and characterized. Reaction of 1 with α-diimine PhNC(Me)C(Me)NPh in toluene afforded a trivalent ytterbium complex, [C5H5BNPh2]2Yb[PhNC(Me)C(Me)NPh] (2), which was characterized by single-crystal X-ray diffraction. The redox process is solvent sensitive and reversible.

Divalent Metal Ion Complexes of S100B in the Absence and Presence of Pentamidine

As part of an effort to inhibit S100B, structures of pentamidine (Pnt) bound to Ca2+-loaded and Zn2+,Ca2+-loaded S100B were determined by X-ray crystallography at 2.15 Å (Rfree=0.266) and 1.85 Å (Rfree=0.243) resolution, respectively. These data were compared to X-ray structures solved in the absence of Pnt, including Ca2+-loaded S100B and Zn2+,Ca2+-loaded S100B determined here (1.88 Å; Rfree=0.267). In the presence and absence of Zn2+, electron density corresponding to two Pnt molecules per S100B subunit was mapped for both drug-bound structures. One Pnt binding site (site 1) was adjacent to a p53 peptide binding site on S100B (±Zn2+), and the second Pnt molecule was mapped to the dimer interface (site 2; ±Zn2+) and in a pocket near residues that define the Zn2+ binding site on S100B. In addition, a conformational change in S100B was observed upon the addition of Zn2+ to Ca2+–S100B, which changed the conformation and orientation of Pnt bound to sites 1 and 2 of Pnt–Zn2+,Ca2+–S100B when compared to Pnt–Ca2+–S100B. That Pnt can adapt to this Zn2+-dependent conformational change was unexpected and provides a new mode for S100B inhibition by this drug. These data will be useful for developing novel inhibitors of both Ca2+- and Ca2+,Zn2+-bound S100B.

Experimental evidences for some unusual divalent cation complexes of valinomycin

From extraction experiments and � -activity measurements, the exchange extraction constants cor- responding to the general equilibrium M 2þ ðaqÞþ 1� Sr 2þ ðnbÞ! 1� M 2þ ðnbÞþSr 2þ ðaqÞ taking place in the two-phase water-nitrobenzene system (M 2þ ¼ Cu 2þ ,Z n 2þ ,C d 2þ ,P b 2þ ,U O 2þ 2 ,F e 2þ ,C o 2þ ,a nd Ni 2þ ; 1¼ valinomycin; aq¼ aqueous phase, nb¼ nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1� M 2þ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Fe 2þ <Cd 2þ ,C o 2þ < Ni 2þ <UO 2þ 2 ,Z n 2þ <Cu 2þ <Pb 2þ .

Coordination behaviour and two-dimensional-network formation in poly[[μ-aqua-diaqua(μ5-propane-1,3-diyldinitrilotetraacetato)dilithium(I)cobalt(II)] dihydrate]: the first example of anMII–1,3-pdta complex with a monovalent metal counter-ion

The title compound, {[CoLi2(C11H14N2O8)(H2O)3].2H2O}n, constitutes the first example of a salt of the [M(II)(1,3-pdta)](2-) complex (1,3-pdta is propane-1,3-diyldinitrilotetraacetate) with a monopositive cation as counter-ion. Insertion of the Li+ cation could only be achieved through application of the ion-exchange column technique which, however, appeared unsuccessful with other alkali metals and the ammonium cation. The structure contains two tetrahedrally coordinated Li+ cations, an octahedral [Co(1,3-pdta)](2-) anion and five water molecules, two of which are uncoordinated, and is built of two-dimensional layers extending parallel to the (010) lattice plane, the constituents of which are connected by the coordinate bonds. O-H(water)...O hydrogen bonds operate both within and between these layers. The crystal investigated belongs to the enantiomeric space group P2(1) with only one (Lambda) of two possible optical isomers of the [Co(1,3-pdta)](2-) complex. A possible cause of enantiomer separation during crystallization might be the rigidification and polarization of the [M(1,3-pdta)](2-) core, resulting from direct coordination of Li+ cations to three out of four carboxylate groups constituting the 1,3-pdta ligand. The structure of (I) differs considerably from those of the other [M(II)(1,3-pdta)](2-) complexes, in which the charge compensation is realized by means of divalent hexaaqua complex cations. This finding demonstrates a significant structure-determining role of the counter-ions.

Electrochemical behaviors of multivalent complexes in room temperature ionic liquids based on quaternary phosphonium cations

A new group of room temperature ionic liquids based on triethylalkyl and tri- n-butylalkylphosphonium cations with a bis(trifluoromethylsulfonyl)imide anion as a novel green solvent is presented. The electrochemical behaviors of trivalent, divalent and neutral complexes such as rare earth, noble metal and ferrocene were investigated in phosphonium based ionic liquids in comparison with the corresponding ammonium type of ionic liquids. The diffusion coefficients of these metal complexes were estimated by cyclic voltammetry, chronoamperometry and chronopotentiometry, because it is important for development of the electrochemical devices to understand the available diffusive properties. The redox potentials of these trivalent lanthanide couples suggested that the donor property of phosphonium based ionic liquids was slightly larger than that of nitrogen based ionic liquids. The palladium complexes were more stabilized in phosphonium ionic liquids due to the relatively strong ligand field. The redox reaction of neutral complex, ferrocene, was reversible electrochemically in triethylalkyl and tri- n-butylalkyl phosphonium based ionic liquids. The multivalent and neutral complexes in phosphonium type of ionic liquids were somewhat movable than that in corresponding ammonium ionic liquids because the interaction between the cation and the anion in phosphonium based ionic liquids is weaker.

Bis-tridentate chelates of an asymmetric ligand: X-ray structures and solution NMR characterization of divalent zinc triad metal ion complexes of N-(2-pyridylmethyl)- N-(2-(methylthio)ethyl)amine

Divalent zinc triad metal ion complexes of type M( L) 2(ClO 4) 2 ( L = N-(2-pyridylmethyl)- N-(2-(methylthio)ethyl)amine) with N 4S 2 metal coordination spheres were isolated and characterized by X-ray crystallography and variable temperature proton NMR. Although bis-tridentate chelates have nine geometric isomers, the crystallographically characterized complexes of all three metal ions had trans facial octahedral coordination geometry with C i symmetry. Despite the low coordination number and geometric preferences of d 10 metal ions, which facilitate inter- and intramolecular exchange processes, dilute solutions of these bis-tridentate chelates exhibited slow geometric isomerization. Symmetry, sterics and shielding arguments supported specific isomeric assignments for the major and minor chemical shift environments observed at low temperature. At elevated temperature, rapid intramolecular exchange occurred for all three complexes but slow intermolecular exchange on the coupling constant time scale was evidenced through detection of J HgH interactions for Hg ( L ) 2 2 + . These unusual observations are discussed in the context of the zinc triad metal ion coordination chemistry of related bis-tridentate chelates.

Nitrogen-directed ortho-arylation and -heteroarylation of aromatic rings catalyzed by ruthenium complexes

The ruthenium-catalyzed direct ortho-arylation reactions of 2-phenylpyridine and 2-aryloxazolines have been successfully expanded to the direct aryl–heteroaryl coupling reactions using heteroaryl bromides. The reaction mechanism involving the Ru II/Ru IV intermediates is proposed from the results of the stoichiometric reaction of a divalent ruthenacycle complex of 2-phenylpyridine with bromobenzene.

Synthesis and structures of new metallocene derivatives of lanthanides. Molecular structures of the complexes (C13H9)2Eu(THF)2 and (C5Me4H)2YbI(THF)

The divalent europium bis-fluorenyl complex (C13H9)2Eu(THF)2 was synthesized by the metathesis reaction of EuI2(THF)2 with two equivalents of fluorenylpotassium and by the protolytic substitution of the naphthalene ligand in the (C10H8)Eu(THF)2 complex using the reaction with fluorene. According to X-ray diffraction data, the complex displays a skewed sandwich structure, in which one fluorenyl ligand is η5-coordinated to the metal atom, whereas the η3-coordination mode makes a great contribution to the coordination of another ligand. The (C5Me4H)2YbI(THF) complex was synthesized by the reaction of YbI3(THF)2 with two equivalents of (C5Me4H)K. The structure of the complex was established by X-ray diffraction.

Small Steric Variations in Ligands with Large Synthetic and Structural Consequences

AbstractThe reaction of ytterbium metal with the aminopyridines2,6‐(diisopropylphenyl)‐[6‐(2,6‐dimethylphenyl)pyridin‐2‐yl]amine (1, Ap′H) and (2,4,6‐trimethylphenyl)‐[6‐(2,4,6‐trimethylphenyl)pyridin‐2‐yl]amine (2, ApMeH) at elevated temperature under vacuum in the presence of mercury gave rise to divalent [Yb(Ap′)2] (3) and trivalent [Yb(ApMe)3] (4), respectively. The single‐crystal X‐ray structure analysis of 3 revealed a four‐coordinate ytterbium atom with two chelating (N,N′) Ap′ ligands inclined to each other at an angle of 126.93(7)° (Cl–Yb–C26). Additionally the complex forms intermolecular CAryl–H agostic interactions [Yb1···C17 2.981(2) Å and Yb1···H17 2.56(3) Å] (all H atoms refined). Complex 4 contains a six‐coordinate ytterbium atom having three chelating (N,N′) ApMe ligands and has distorted octahedral stereochemistry. The reaction of the potassium salts of Ap′H (5) and ApMeH (6) with [YbI2 (thf)4] in thf gave rise to the divalent lanthanoid complexes [Yb(Ap′)2(thf)] (7), and [Yb(ApMe)2(thf)2] (8), respectively, and 7 was also obtained by redox transmetallation/ligand exchange from Yb metal, HgPh2 and Ap′H. X‐ray crystal structures show that 7 and 8 have five‐ and six‐coordinate ytterbium atoms and distorted trigonal‐bipyramidal and distorted octahedral stereochemistry, respectively, the difference in coordination number reflecting the difference in steric demand of the Ap′ and ApMe ligands.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Hydrothermal synthesis of divalent metal pyromellitate/dipyridylamine complexes: From an unprecedented supramolecular three-dimensional topology to an anionic coordination polymer framework with large incipient cation-bearing voids

Hydrothermal synthesis has afforded two divalent metal coordination complexes incorporating both fully deprotonated pyromellitate (pyro) anions and the kinked dipodal organodiimine 4,4′-dipyridylamine (dpa), {[Co(H2O)4(Hdpa)2][pyro]} (1) and {[H2dpa][Zn(pyro)]·2H2O} (2). Both new complexes were characterized by single crystal X-ray diffraction and spectral and thermogravimetric analyses. Complex 1 possesses discrete [Co(H2O)4(Hdpa)2]4+ cations linked into supramolecular 2-D (4,4) rhomboid grid layer motifs by hydrogen bonding between the unligated pyro anions and the aquo ligands. The pendant, monodentate Hdpa+ cations also engage in charge-separated hydrogen bonding to pyro anions in neighboring layers, resulting in a supramolecular 3-D structure with an unprecedented 6-connected 446108 topology. In contrast, 2 is a true coordination polymer, with divalent Zn atoms linked by ligated pyro anions into a binodal 4-connected PtS-type anionic network (4284 topology), which encapsulates H2dpa2+ cations and unligated water molecules within large incipient pores coursing through the structure. Irradiation of a solid sample of 2 with ultraviolet light resulted in blue-light emission, likely indicative of π–π* transitions within the orbital manifolds of both the pyro anions and unligated H2dpa2+ cations.

Facile insertion and halogen migration reactions of the hexaphosphapentaprismane cage P6C4tBu4 with zerovalent and divalent platinum complexes

The hexaphosphapentaprismane P(6)C(4)(t)Bu(4) undergoes specific insertion of the zerovalent platinum fragment [Pt(PPh(3))(2)] into the unique P-P bond between the 5-membered rings to afford [Pt(PPh(3))(2)P(6)C(4)(t)Bu(4)]. A similar reaction with the Pt(ii) complexes [{PtCl(2)(PMe(3))}(2)] and [PtCl(2)(eta(4)-COD)] results in both insertion and chlorine migration reactions. The complexes [Pt(PPh(3))(2)P(6)C(4)(t)Bu(4)], trans-[PtCl(PMe(3))P(6)C(4)(t)Bu(4)Cl], cis-,trans-[{PtCl(2)(PMe(3))}micro-{P(6)C(4)(t)Bu(4)}{PtCl(2)(PMe(3))}], [{PtClP(6)C(4)(t)Bu(4)Cl}(2)] and cis-[PtClP(6)C(4)(t)Bu(4)Cl(P(6)C(4)(t)Bu(4))] have been structurally characterized by single crystal X-ray diffraction and multinuclear NMR studies.

Nickel(II) Complexes Containing Bidentate Amido Phosphine Ligands Derived from α-Iminophosphorus Ylides: Synthesis and Structural Characterization

The reactions of prop-2-ynyltriphenylphosphonium bromide with a series of primary aromatic or aliphatic amines in refluxing acetonitrile generated the corresponding 2-hydrocarbylaminoprop-1-enyltriphenylphosphonium bromide [RNHC(Me)=CHPPh(3)]+Br- (R = 2,6-C(6)H(3)iPr(2) (1a), 2,6-C(6)H(3)Me(2) (1b), Ph (1c), t-Bu (1d)) as crystalline solids. Deprotonation of 1a-d with NaH in THF at -35 degrees C afforded the alpha-iminophosphorus ylides RN=C(Me)CH=PPh(3) (2a-d) in high yield. Spectroscopic and crystallographic data of 2 suggest a strong intramolecular interaction between the imino nitrogen and the phosphorus atom. In contrast to N-arylated 2a-c, the N-tert-butyl-derived 2d is extremely moisture-sensitive. Hydrolysis of 2d led to elimination of benzene and generated concomitantly the phosphine oxide 3d that contains an ene-amine functionality. The reactions of 2a-c with Ni(COD)(2) in the presence of an excess amount of pyridine in toluene produced the divalent nickel complexes of the type [kappa(2)-RNC(Me)=CHPPh(2)]Ni(Ph)(Py) (4a-c). The solution and solid-state structures of these new compounds are presented.

Divalent metal complexes of an amide-appended N3O-donor ligand: synthesis, structural and spectroscopic features, and amide methanolysis reactivity§

Divalent zinc, cobalt, and nickel complexes of an amide-appended N3O-donor ligand (mpppa, N-methyl-N-((6-pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylethyl)amine) have been prepared and characterized. X-ray crystallographic studies indicate that [(mpppa)Zn(CH3CN)](ClO4)2 (1) exhibits a distorted square pyramidal geometry, whereas [(mpppa)M(CH3OH)(H2O)](ClO4)2 (M=Co (2·H2O), Ni (3)) exhibit distorted octahedral structures. Each complex was also characterized by analytical and spectroscopic methods. Treatment of 1 with Me4NOH·5H2O in methanol-containing solutions results in amide methanolysis. This reaction proceeds via the initial formation of a deprotonated amide intermediate, [(mpppa−)Zn]ClO4 (4), which has been isolated and characterized. Kinetic studies performed as a function of the amount of methanol present revealed saturation behavior with respect to the alcohol concentration. Variable temperature kinetic studies yielded activation parameters (ΔH ‡=19.8kcal/mol; ΔS ‡=−3.8(1) eu) that are interestingly different from those exhibited by a zinc complex of an amide-appended N4O-donor ligand. These results are discussed in the context of the overall coordination number and geometry of the zinc center. Treatment of 2 and 3 with Me4NOH·5H2O in methanol-containing solutions does not result in amide methanolysis. §Contribution for Peter Williams issue.

Good linear relationship between logarithms of Eigen’s water exchange constants for several divalent metal ions and activation energies of corresponding metal-catalyzed alkoxysilane hydrolysis in ethylene–propylene copolymer system

Catalytic efficiencies of seven divalent metal acetylacetonate complexes [M(acac) 2; M = Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II)] with respect to the water-crosslinking kinetics of vinyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR- g-VTMS) were investigated to examine the effects of progressive changes in metal ion using ATR–FTIR spectroscopy. The hydrolysis activation energies of EPR- g-VTMS follows the order: No catalyst ≈ Ni(acac) 2 > Co(acac) 2 > Fe(acac) 2 ≈ Zn(acac) 2 > Cd(acac) 2 ≈ Cu(acac) 2 > Pb(acac) 2. Interestingly, the kinetics results revealed that the plots of hydrolysis activation energies of EPR- g-VTMS containing M(acac) 2 complexes and Eigen’s water exchange constants for corresponding metal ions showed a excellent linear relationship, suggesting that the reaction pathway for the silane water-crosslinking with hydrous M(acac) 2 complex in EPR- g-VTMS system may be similar to that for water exchange of the metal ion in an aqueous system. Based on the knowledge of traditional kinetics studies by Eigen and Wilkins and hybrid sol–gel chemistry, the plausible catalytic mechanism for M(acac) 2 complexes in EPR- g-VTMS system was proposed.

Formation of a Sulfur-Atom-Inserted N-Confused Porphyrin Iron Nitrosyl Complex by Denitrosation and C−S Bond Cleavage of an S-Nitrosothiol

The reaction of nitrosothiol, Ph3CSNO, with a divalent iron N-confused porphyrin complex, Fe(HCTPPH)Br, yields a {Fe(NO)}6 iron nitrosyl complex with a sulfur atom inserted in the Fe-C bond. The crystal structure reveals a bent Fe-N-O geometry and an eta2-(C,S) bonding mode between iron and the C-S bond. A reaction mechanism involving a transnitrosation and a nitrosothiol C-S bond cleavage is proposed.