Ground-state singlet L3Fe-(mu-N)-FeL3 and L3Fe(NR) complexes featuring pseudotetrahedral Fe(II) centers

Pseudotetrahedral iron(II) coordination complexes that contain bridged nitride and terminal imide linkages, and exhibit singlet ground-state electronic configurations, are described. Sodium amalgam reduction of the ferromagnetically coupled dimer, {[PhBP(3)]Fe(mu-1,3-N(3))}(2) (2) ([PhBP(3)] = [PhB(CH(2)PPh(2))(3)](-)), yields the diamagnetic bridging nitride species [{[PhBP(3)]Fe}(2)(mu-N)][Na(THF)(5)] (3). The Fe-N-Fe linkage featured in the anion of 3 exhibits an unusually bent angle of approximately 135 degrees , and the short Fe-N bond distances (Fe-N(av) approximately equal to 1.70 A) suggest substantial Fe-N multiple bond character. The diamagnetic imide complex {[PhBP(3)]Fe(II)(triple bond)N(1-Ad)}{(n)()Bu(4)N} (4) has been prepared by sodium amalgam reduction of its low-spin iron(III) precursor, [PhBP(3)]Fe(III)(triple bond)N(1-Ad) (5). Complexes 4 and 5 have been structurally characterized, and their respective electronic structures are discussed in the context of a supporting DFT calculation. Diamagnetic 4 provides a bona fide example of a pseudotetrahedral iron(II) center in a low-spin ground-state configuration. Comparative optical data strongly suggest that dinuclear 3 is best described as containing two high-spin iron(II) centers that are strongly antiferromagnetically coupled to give rise to a singlet ground-state at room temperature.     

Highly electrophilic (salen)ruthenium(VI) nitrido complexes

A series of cationic ruthenium(VI) nitrido species containing the cyclohexyl-bridged salen ligand (L) and its derivatives, [RuVI(N)(L)]+, have been prepared by treatment of [NBun4][RuVI(N)Cl4] with H2L in methanol. The structure of [RuVI(N)(L)](ClO4) (1a) has been determined by X-ray crystallography, d(RuN) = 1.592 A. In solvents such as DMF or DMSO, [RuVI(N)(L)]+ undergoes a facile N...N coupling reaction at room temperature to produce N2 and [RuIII(L)(S)2]+ (S = solvent). 1a reacts rapidly with secondary amines to produce diamagnetic RuIV-hydrazido(1-) species, [RuIV(N(H)NR2)(L)(HNR2)]+. The reaction with morpholine is first order in RuVI and second order in morpholine with k(CH3CN, 25 degrees C) = 2.08 x 106 M-2 s-1. This rate constant is over 4 orders of magnitude larger than that of the corresponding reaction of the electrophilic osmium nitride, trans-[OsVI(N)(tpy)(Cl)2]+, with morpholine. The structure of [Ru(NHNC4H8)(L)(NHC4H8)](PF6)2 has been determined by X-ray crystallography, the Ru-N(hydrazido) distance is 1.940 A, and the Ru-N-N angle is 129.4 degrees .     

Cationic Copper(I) Complexes as Highly Efficient Catalysts for Single and Double A3‐Coupling Mannich Reactions of Terminal Alkynes: Mechanistic Insights and Comparative Studies with Analogous Gold(I) Complexes

Cationic Cu?L complexes (L=Buchwald‐type phosphane) with N co‐ligands have been characterised by structural and spectroscopic properties. These copper(I) complexes are extremely active catalysts, far more active than analogous gold(I) complexes, to promote the single and double A³ coupling of terminal alkynes, pyrrolidine and formaldehyde. The activity data show the possible ways in which the solvent can influence the catalytic performance by limiting complex solubility, by solvent decomposition or instability of the copper(I) redox state. Isolation of copper(I) complexes that are likely to be the key catalytic species has allowed light to be shed on the reaction mechanism.     

Octahedral Fe(II) and Ru(II) complexes based on a new bis 1,10-phenanthroline ligand that imposes a well defined axis.

A bis-chelating ligand (L1), made of two 7-(p-anisyl)-1,10-phenanthroline (phen) subunits connected with a p-(CH(2))(2)C(6)H(4)(CH(2))(2) spacer through their 4 positions, has been prepared, using Skraup syntheses and reaction of the anion of 4-methyl-7-anisyl-1,10-phenanthroline with alpha,alpha'-dibromo-p-xylene. Its Fe(II) complex, [FeL1(dmbp)](PF(6))(2), was prepared in one step by reaction of L1 with [Fe(dmbp)(3)](PF(6))(2) (dmbp = 4,4'-dimethyl-2,2'-bipyridine). On the other hand, its Ru(II) complex, [RuL1(dmbp)](PF(6))(2), was prepared in two steps from Ru(CH(3)CN)(4)Cl(2) and L1, followed by reaction with dmbp. X-ray crystal structure analyses show that in the two octahedral complexes, ligand L1 coils around the metal by coordination of the axial and two equatorial positions. It defines a 21 A long axis (O.O distance) running through the central metal and the terminal anisyl substituents. The complexes were also characterized by (1)H NMR, mass spectrometry, cyclic voltammetry, electronic absorption, and, in the case of Ru(II), fluorescence spectroscopy.     

Radical (NO) and nonradical (N(2)O) reagents convert a ruthenium(IV) nitride to the same nitrosyl complex

The ruthenium(IV) nitride complex (PNP)RuN (PNP = (tBu2PCH2-SiMe2)2N-) reacts rapidly with 2NO to form (PNP)Ru(NO) and N2O, via no detectable intermediate. The linear nitrosyl complex has a planar structure. In a slower reaction, (PNP)RuN reacts with N2O by O-atom transfer (established by 15N labeling) to give the same nitrosyl complex and N2. Density functional theory (B3LYP) calculations show both reactions to be very thermodynamically favorable. Analysis of possible intermediates in each reaction shows that radical (PNP)RuN(NO) has much spin density on nitride N (hence, N2-), while one 2 + 3 metallacycle, (PNP)RuN3O, has the wrong connectivity to form a product. Instead, an intermediate with a doubly bent N2O (hence, a two-electron reduced N-nitrosoimide form) brings the O atom in proximity to the nitride N on the path to a product.     

Spectroscopic and catalytic characterization of a functional Fe(III)Fe(II) biomimetic for the active site of uteroferrin and protein cleavage

A mixed-valence complex, [Fe(III)Fe(II)L1(μ-OAc)(2)]BF(4)·H(2)O, where the ligand H(2)L1 = 2-{[[3-[((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl](pyridin-2-ylmethyl)amino]methyl]phenol}, has been studied with a range of techniques, and, where possible, its properties have been compared to those of the corresponding enzyme system purple acid phosphatase. The Fe(III)Fe(II) and Fe(III)(2) oxidized species were studied spectroelectrochemically. The temperature-dependent population of the S = 3/2 spin states of the heterovalent system, observed using magnetic circular dichroism, confirmed that the dinuclear center is weakly antiferromagnetically coupled (H = -2JS(1)·S(2), where J = -5.6 cm(-1)) in a frozen solution. The ligand-to-metal charge-transfer transitions are correlated with density functional theory calculations. The Fe(III)Fe(II) complex is electron paramagnetic resonance (EPR)-silent, except at very low temperatures (<2 K), because of the broadening caused by the exchange coupling and zero-field-splitting parameters being of comparable magnitude and rapid spin-lattice relaxation. However, a phosphate-bound Fe(III)(2) complex showed an EPR spectrum due to population of the S(tot) = 3 state (J= -3.5 cm(-1)). The phosphatase activity of the Fe(III)Fe(II) complex in hydrolysis of bis(2,4-dinitrophenyl)phosphate (k(cat.) = 1.88 × 10(-3) s(-1); K(m) = 4.63 × 10(-3) mol L(-1)) is similar to that of other bimetallic heterovalent complexes with the same ligand. Analysis of the kinetic data supports a mechanism where the initiating nucleophile in the phosphatase reaction is a hydroxide, terminally bound to Fe(III). It is interesting to note that aqueous solutions of [Fe(III)Fe(II)L1(μ-OAc)(2)](+) are also capable of protein cleavage, at mild temperature and pH conditions, thus further expanding the scope of this complex's catalytic promiscuity.     

Complexes of 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine: formation of mononuclear complexes, and self-assembly of double helical dinuclear and tetranuclear copper(II) and trinuclear nickel(II) complexes

The potentially pentadentate ligand 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine (H2L1), readily prepared from reaction of a diester of pyridine-2,6-dicarboxylic acid (H2dipic) and 2-aminomethylpyridine (ampy), shows limited tendency to form 1:1 M:L complexes with labile metal ions, although [CuL1] and [NiL1] were observed as minor species, the latter characterized by a crystal structure analysis. A mononuclear complex formed with inert Co(III) was characterized by a crystal structure as the neutral 1:2 complex [Co(L1)(HL1)] with two ligands acting as tridentate ligands, one coordinated by the central pyridine and its two flanking deprotonated amido groups, and the other by the central pyridine, one amido and one terminal pyridine group, with the remaining poorly coordinating protonated amide remaining unbound along with other terminal pyridine groups. Fe(III) is known to form a symmetrical 1:2 complex, but that complex is anionic due to binding of all four deprotonated amido groups; the unsymmetrical neutral Co(III) complex converts into a symmetrical anionic species only on heating for hours in aqueous base in the presence of activated carbon. The most remarkable tendency of H2L1, however, is towards the formation of robust double helical complexes: a dinuclear Cu(II) complex [Cu2L1(2)] forms, as well as a trinuclear Ni(II) complex [Ni(3)(L1)2(OAc)2(MeOH)2]. Moreover, in the presence of added H2dipic, the tetranuclear complex [Cu4(L1)2(dipic)2(OH2)2] is obtained. All helical complexes have been characterized by X-ray crystal structure analyses, and all crystals feature a racemic mixture of left- and right-handed double helices stabilized by inter-ligand pi-stacking (inter-ring distances of 3.2-3.8 A) of ligands which each span several metal ions. Using the chelating ligand pentane-2,4-dione (acac), each of the two pairs of adjacent monodentate ligands in [Ni3(L1)2(OAc)2(OH2)2] have been shown to be available for substitution without destroying the helical structure, to form [Ni3(L1)2(acac)2], also characterized by a crystal structure.     

Intramolecularly Double-Donor-Stabilized Stannylene and Its Coordination towards Ag(I) and Au(I) Centers

The intramolecularly double-donor-stabilized stannylene 1 has been synthesized from the salt-metathesis reaction between two equivalents of lithium pyridine ene-amide L1 and SnCl₂. Compound 1 exhibits dipolar behavior when reacted with B(C₆F₅)₃ leading to the zwitterionic compound 2 . The reaction of 1 with one equivalent and 0.5 equivalent of AgOTf (OTf=trifluoromethane sulfonate) result in the formation of a stannylene-AgOTf complex 3 and a homoleptic distannylene-silver ionic complex 4 , respectively. Analogous to complex 4 , the gold(I) complex 5 has been synthesized from the reaction between two equivalents of 1 and 0.5 equivalent of AuCl.SMe₂/Me₃SiOTf. Complex 5 is the first example of homoleptic stannylene-Au(I) ionic complex among the very scarce reports on stannylene-gold(I) coordination complexes. All compounds have been structurally characterized using single crystal X-ray crystallography. Solution-state characterization have been performed using multinuclear NMR techniques. Detailed DFT calculations on the optimized geometries 1 o , 3 o – 5 o reveal the change in sp- hybridization on the pyramidal Sn(II) center upon metal coordination and their bonding overlaps.     

Photolyse der Chrom(III)-azido-Komplexe und Darstellung des Chrom(V)-nitrido-Komplexes mit N,N′-Ethylen-bis(salicylaldimin)

Photochemical Reactions of Chromium(III) Azido Complexes. Preparation of Nitrido-N, N′-ethylene-bis(salicylideniminato) Chromium(V) Complex The azide to nitride ligand conversion in the coordination sphere of chromium(III) complexes under light of 313 nm excitation has been observed. This photochemical reaction has been used to prepare the nitrido-N, N′-ethylene-bis(salicylideniminato)-chromium(V) complex characterized by an elementar analysis, electron, absorption, IR, and ESR spectra. The results of previous authors that the 313 nm photolysis of Cr(NH₃)₅N₃²⁺ yields Cr²⁺ or coordinated nitrenes are reinterpreted solely by formation of chromium(V) nitrido species.     

Oxidative group transfer to Co(I) affords a terminal Co(III) imido complex

The synthesis of the first terminal imido complex of cobalt, [PhBP3]CoN-p-tolyl, is reported. Its synthesis proceeds by oxidative group transfer from cobalt(I) upon addition of tolyl azide at room temperature. This species and a related eta1-diazoalkane adduct have been structurally characterized. The diamagnetic imido complex [PhBP3]CoN-p-tolyl reacts with CO to liberate isocyanate and the cobalt(I) dicarbonyl complex [PhBP3]Co(CO)2.     

金催化的吲哚与末端炔烃的分子间烷基化反应

尝试了用金(Au)催化吲哚和炔烃的Friedel-Crafts烷基化反应, 具体探讨了金(I)配合物催化吲哚与末端炔烃的烷基化反应的条件, 并制备了一系列尚未见文献报道的双取代β-吲哚烷基化衍生物. 产物的结构经1H NMR, 13C NMR, MS和元素分析确证. 并对其反应机理可能性进行了推测.     

Synthesis, structure and dioxygen reactivity of a bis(micro-iodo)dicopper(I) complex supported by the [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine ligand

The air-sensitive bis(micro-iodo)dicopper(I) complex 1 supported by [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine (L) has been prepared by treating copper(I) iodide with L in anhydrous THF. Compound 1 crystallizes as a dimer in space group C2/c. Each copper(I) center has distorted tetrahedral N2I2 coordination geometry with Cu-N(pyridyl) distances 2.061(3) and 2.063(3) A, Cu-I distances 2.6162(5) and 2.7817(5) and a Cu...Cu distance of 2.9086(8) A. Complex 1 is rapidly oxidized by dioxygen in CH2Cl2 with a 1 : 1 stoichiometry giving the bis(micro-iodo)peroxodicopper(II) complex [Cu(L)(micro-I)]2O2 (2). The reaction of 1 with dioxygen has been characterized by UV-vis, mass spectrometry, EPR and Cu K-edge X-ray absorption spectroscopy at low temperature (193 K) and above. The mass spectrometry and low temperature EPR measurements suggested an equilibrium between the bis(micro-iodo)peroxodicopper(II) complex 2 and its dimer, namely, the tetranuclear (peroxodicopper(II))2 complex [Cu(L)(micro-I)]4O4 (2'). Complex 2 undergoes an effective oxo-transfer reaction converting PPh3 into O=PPh3 under anaerobic conditions. At sufficiently high concentration of PPh3, the oxygen atom transfer from 2 to PPh3 was followed by the formation of [Cu(PPh3)3I]. The dioxygen reactivity of 1 was compared with that known for other halo(amine)copper(I) dimers.     

Syntheses and structures of Ag(I)-containing coordination polymers and Co(II)-containing supramolecular complex based on novel fulvene ligands

Three new rigid conjugated fulvene ligands L1-L3 were synthesized. L1 and L3 have been prepared by an aroylation reaction of cyclohexyl-substituted cyclopentadienyl anions. L2 was prepared by the reaction of L1 with PhNHNH2 in hot enthanol. Six new coordination polymers, namely [Ag(C25H20N2O2)(ClO4)] x 3.5C6H6 (1), [Ag2(mu-C31H24N4)(eta2-C6H6)(H2O)](ClO4)2 x (C6H6) x (H2O)0.5 (3), [Ag(C31H24N4)]SbF6 x solvate (4), [Ag(C31H24N4)](SbF6)2 x 2C6H6 x CH2Cl2 (5), [Ag(C25H20N2O2)2]SbF6 (6), and [Ag(C25H20N2O2)2]SbF6 (7), and one seven-membered cobaltacycle-containing complex, namely Co(C25H20N2O2)2(C2H5OH)2 (2), were obtained through self-assembly based on these three new fulvene lignads. L2-L3 and compounds 1-7 have been fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The results indicate that the coordination chemistry of new fulvene ligands is versatile. They can bind metal ions not only through the terminal N-donors and fulvene carbon atoms into organometallic coordination polymers but also through the two chelating carbonyl groups into unusual seven-membered metallo-ring supramolecular complexes. In the solid state, ligands L1-L3 are luminescent. A blue-shift in the emission was observed between the free ligand L1 and the one incorporated into Co(II)-containing complex 2, and a red-shift in the emission was observed between the free ligand L3 and the one incorporated into Ag(I)-containing polymeric compounds 6 and 7.     

XAS characterization of a nitridoiron(IV) complex with a very short Fe-N bond

X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBPR3]Fe(N) complexes (R=iPr and CyCH2) and obtain direct spectroscopic evidence for a very short Fe-N distance. The distance of 1.51-1.55 A reflects the presence of an FeN triple bond in accord with the observed FeN vibration observed for one of these species (nuFeN=1034 cm(-1)). This highly covalent bonding interaction results in the appearance of an unusually intense pre-edge peak, whose estimated area of 100(20) units is much larger than those of the related tetrahedral complexes with FeI-N2-FeI, FeII-NPh2, and FeIIINAd motifs, and those of recently described six-coordinate FeVN and FeVIN complexes. The observation that the FeIV-N distances of two [PhBPR3]Fe(N) complexes are shorter than the FeIV-O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater pi basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex.     

Spectroscopic characterization of the oxo-transfer reaction from a bis(mu-oxo)dicopper(III) complex to triphenylphosphine

The oxygen-atom transfer reaction from the bis(mu-oxo)dicopper(III) complex [Cu(III)(2)(mu-O)(2)(L)(2)](2+), where L =N,N,N',N' -tetraethylethylenediamine, to PPh(3) has been studied by UV-vis, EPR, (1)H NMR and Cu K-edge X-ray absorption spectroscopy in parallel at low temperatures (193 K) and above. Under aerobic conditions (excess dioxygen), 1 reacted with PPh(3), giving O=Ph(3) and a diamagnetic species that has been assigned to an oxo-bridged dicopper(II) complex on the basis of EPR and Cu K-edge X-ray absorption spectroscopic data. Isotope-labeling experiments ((18)O(2)) established that the oxygen atom incorporated into the triphenylphosphine oxide came from both complex 1 and exogenous dioxygen. Detailed kinetic studies revealed that the process is a third-order reaction; the rate law is first order in both complex 1 and triphenylphosphine, as well as in dioxygen. At temperatures above 233 K, reaction of 1 with PPh(3) was accompanied by ligand degradation, leading to oxidative N-dealkylation of one of the ethyl groups. By contrast, when the reaction was performed in the absence of excess dioxygen, negligible substrate (PPh(3)) oxidation was observed. Instead, highly symmetrical copper complexes with a characteristic isotropic EPR signal at g= 2.11 were formed. These results are discussed in terms of parallel reaction channels that are activated under various conditions of temperature and dioxygen.     

Synthesis and structural characterization of mixed-metal complexes of Cu(I) with MOS3 cores (M = Mo, W) and of an unusual polymeric AgI/mercaptoimidazole complex with five different Ag(I) coordination environments

Reaction of (NH(4))(2)[MO(2)S(2)] (M = Mo or W) with KI, CuCl and 1,3-diazepane-2-thione (Diap) in acetone affords air- and moisture-stable mixed-metal cluster compounds [MOS(3)(CuDiap)(3)]I (1 and 2). Attempts to produce [WS(4)Ag(2)(Mim(Ph))(4)] (Mim(Ph) = 2-mercapto-1-phenylimidazole) led to the unexpected polymeric compound [Ag(5)I(5)(Mim(Ph))(4)](n) (4), subsequently obtained from a rational direct reaction between AgI and Mim(Ph) in chloroform. The complexes have been characterized by IR, (1)H and (13)C NMR spectroscopy, and single-crystal diffraction. 1 and 2 have crystallographic threefold rotation symmetry, with an incomplete distorted cube MS(3)Cu(3) core bearing terminal oxo and Diap ligands on M and Cu, respectively. The cube vertex opposite M is empty, giving an overall +1 cationic cluster and a separate I(-) anion too distant from the three Cu atoms to be considered as covalently bonded and resulting in discrete ion pairs in the crystal structures. This arrangement is different from previously reported related OMS(3)(CuL)(3)X complexes (L = monodentate ligand, X = halide), in which X, when present, is directly bonded to one, two or three Cu atoms. 4 has a one-dimensional polymeric chain structure in which silver displays five different approximately tetrahedral coordination environments, iodide ions serve as μ(2), μ(3) and μ(4) bridges, and the thione ligands are each either terminal or bridging. This unusually complex structure for a relatively simple chemical formula represents only the fifth example of a complex (AgI)(n)L(m) in which L is a neutral S-donor ligand, and the five structures display a wide range of individual features. In all three of the new structures, N-H···S and/or N-H···I hydrogen bonds are found.     

Substitution and hydrogenation reactions on rhodium(I)-ethylene complexes of the hydrotris(pyrazolyl)borate ligands T (T = Tp, TpMe2)

The bis(ethylene) Rh species TpMe2Rh(C2H4)2(1*) (TpMe2 = tris(3,5-dimethyl-1-pyrazol-1-yl)hydroborate) has been obtained from [RhCl(C2H4)2]2 and KTpMe2. Complex 1* easily decomposes in solution to give mainly the butadiene species TpMe2Rh(eta74-C4H6). In the solid state its thermal decomposition follows a different course and the allyl TpMe2RhH(syn-C3H4Me) is cleanly obtained as a mixture of exo and endo isomers. The complexes Tp'Rh(C2H4)2 (Tp' = Tp, TpMe2) afford the monosubstituted species Tp'Rh(C2H4)(PR3) upon reaction with PR3 but react differently with L = CO or CNR: the Tp compound gives dinuclear [TpRh]2(mu-L)3 complexes, while, in the case of 1*, TpMe2Rh(C2H4)(L) species are obtained. The ethylene ligand of complexes TpMe2Rh(C2H4)(PR3) is labile, and several peroxo compounds of composition TpMe2Rh(O2)(PR3) have been isolated by their reaction with O2. All the mononuclear Rh(I) complexes are formulated as 18e- trigonal bipyramidal species on the basis of IR and NMR spectroscopic studies. A series of dihydride complexes of Rh(III) of formulation Tp'RhH2(PR3) have been prepared by the hydrogenation of the corresponding ethylene derivatives. Complexes [TpRh]2(mu-CNCy)3, TpMe2Rh(C2H4)(PEt3), and TpMe2Rh(O2)(PEt3) have been further characterized by X-ray diffraction studies.     

Conversion of {Fe(NO)2}10 dinitrosyl iron to nitrato iron(III) species by molecular oxygen

A new {Fe(NO)(2)}(10) dinitrosyl iron complex possessing a 2,9-dimethyl-1,10-phenanthroline ligand has been prepared. This complex exhibits dioxygenase activity, converting NO to nitrate (NO(3)(-)) anions. During the oxygenation reaction, formation of reactive nitrating species is implicated, as shown in the effective o-nitration with a phenolic substrate.     

Ytterbium(II) complex bearing a diaminobis(phenolate) ligand: synthesis, structure, and one-electron-transfer and epsilon-caprolactone polymerization reactions

The first divalent ytterbium complex supported by a diaminobis(phenolate) ligand, YbL(THF)2.0.5C7H8 (1; THF = tetrahydrofuran), was synthesized in good yield by the amine elimination reaction of Yb[N(SiMe3)2]2(THF)2 with H2L (L = [Me2NCH2CH2N(CH2-2-OC6H2-3,5-But2)2]) in a 1:1 molar ratio. X-ray structural determination shows complex 1 to be a THF-solvated monomer, which adopts a distorted octahedral coordination geometry around the Yb atom. Complex 1 can react with PhNCO and PhCCH, as a single electron-transfer reagent, to give the corresponding reduction coupling product [(YbLOCNPh)(THF)]2.4THF (2) and the alkynide complex YbLCCPh(DME) (3; DME = 1,2-dimethoxyethane). Complexes 2 and 3 have been characterized by X-ray crystal structural analysis. In complex 2, the dianionic oxamide ligand resulting from the reductive coupling of two phenyl isocyanate molecules coordinates to two Yb atoms in a mu,eta4 fashion. Complex 3 has a monomeric structure with a Yb-C(terminal phenylacetynide) bond length of 2.374(3) A. Complex 1 is also a highly efficient catalyst for ring-opening polymerization of epsilon-caprolactone.     

Tri- and tetranuclear copper(II) complexes consisting of mononuclear Cu(II) chiral building blocks with a sugar-derived Schiff's base ligand

A new sugar-derived Schiff's base ligand N-(3-tert-butyl-2-hydroxybenzylidene)-4,6-O-ethylidene-beta-D-glucopyranosylamine (H3L1) has been developed which afforded the coordinatively labile, alcoholophilic trinuclear Cu(II) complex [Cu3(L1)2(CH3OH)(H2O)] (1). Complex 1 has been further used in the synthesis of a series of alcohol-bound complexes with a common formula of [Cu3(L1)2(ROH)2] (R = Me (2), Et (3), nPr (4), nBu (5), nOct (6)). X-ray structural analyses of complexes 2-6 revealed the collinearity of trinuclear copper(II) centers with Cu-Cu-Cu angles in the range of 166-172 degrees . The terminal and central coppers are bound with NO3 and O4 atoms, respectively, and exhibit square-planar geometry. The trinuclear structures of 2-6 can be viewed as the two {Cu(L1)}- fragments capture a copper(II) ion in the central position, which is further stabilized by a hydrogen-bonding interaction between the alcohol ligands and the sugar C-3 alkoxo group. Complex 2 exhibits a strong antiferromagnetic interaction between the Cu(II) ions (J = -238 cm(-1)). Diffusion of methanol into a solution of complex 1 in a chloroform/THF mixed solvent afforded the linear trinuclear complex [Cu(3)(L1)2(CH3OH)2(THF)2] (7). The basic structure of 7 is identical to complex 2; however, THF binding about the terminal coppers (Cu-O(THF) = 2.394(7) and 2.466(7) A) has introduced the square-pyramidal geometry, indicating that the planar trinuclear complexes 2-6 are coordinatively unsaturated and the terminal metal sites are responsible for further ligations. In the venture of proton-transfer reactions, a successful proton transfer onto the saccharide C-3 alkoxo group has been achieved using 4,6-O-ethylidene-d-glucopyranose, resulting in the self-assembled tetranuclear complex, [Cu4(HL1)4] (8), consisting of the mononuclear Cu(II) chiral building blocks, {Cu(HL1)}.