Η1 Coordination Mode Research Articles

η3-Allyl Coordination at Pb(II)

Allylmagnesium chloride and methyl-propenyl-magnesium bromide were reacted with bulky substituted organolead and organotin halides (Ar*PbBr)2, (Ar′PbBr)2, (Ar*SnCl)2 (Ar* = 2,6-trip2C6H3-, trip = 2,4,6-triisopropylphenyl, Ar′ = 2,6-mes2C6H3-, mes = 2,4,6-trimethylphenyl). The allyl ligand coordinates in an η3-coordination mode at organoplumbylene fragments. In the solid state as well as in solution, η3-coordination was characterized by crystal structure analysis and Saunders’ isotopic perturbation technique. For the plumbylene Ar*Pb(C3H5), a solid state 207Pb magic angle spinning (MAS) NMR spectrum could be obtained. The isotropic chemical shift is −435 ppm, and the magnitude of the 207Pb chemical shift tensor of 7000(500) ppm is among the greatest observed experimentally. The methylallyl ligand coordinated at a plumbylene fragment exhibits two short and one long Pb–C interaction. In reaction with aniline, the allyl ligand reacts as a leaving group to give amidoplumbylenes.

Neutral Nickel(II) Complexes Bearing Aryloxide Imidazolin-2-imine Ligands for Efficient Copolymerization of Norbornene and Polar Monomers

A series of novel aryloxide imidazolin-2-imine bidentate neutral Ni(II) complexes with different substituents on the imidazolin-2-imine ligand were synthesized and characterized. The complex Ni2 bearing a 2,6-diisopropylphenyl substituent adopted an almost square planar geometry, while the bulkier 2,6-bis(diphenylmethyl)-4-methylphenyl substituent ligated complex Ni3 was obtained in an allyl adduct base-free η3 coordination mode. In the presence of B(C6F5)3, these Ni(II) complexes exhibited remarkably high activity (up to 2.7 × 107 g of PNB (mol of Ni)−1 h–1) and particularly good thermal stability toward the addition polymerization of norbornene. Most importantly, these catalysts were able to promote the direct copolymerization of norbornene with various polar monomers with high activity (∼105 g (mol of Ni)−1 h–1), reasonable comonomer incorporation (0.14–3.08%), and high copolymer molecular weight (Mn up to 2.0 × 105). The strategy of installing a strongly electron donating imidazolin-2-imine ligand on ...

Theoretical study of the mechanism of the manganese catalase KatB.

The mechanism of the H2O2 disproportionation catalyzed by the manganese catalase (MnCat) KatB was studied using the hybrid density functional theory B3LYP and the quantum chemical cluster approach. Compared to the previous mechanistic study at the molecular level for the Thermus thermophilus MnCat (TTC), more modern methodology was used and larger models of increasing sizes were employed with the help of the high-resolution X-ray structure. In the reaction pathway suggested for KatB using the Large chemical model, the O-O homolysis of the first substrate H2O2 occurs through a μ-η1:η1 coordination mode and requires a barrier of 10.9kcal/mol. In the intermediate state of the bond cleavage, two hydroxides form as terminal ligands of the dimanganese cluster at the Mn2(III,III) oxidation state. One of the two Mn(III)-OH- moieties and a second-sphere tyrosine stabilize the second substrate H2O2 in the second-sphere of the active site via hydrogen bonding interactions. The H2O2, unbound to the metals, is first oxidized into HO2· through a proton-coupled electron transfer (PCET) step with a barrier of 9.5kcal/mol. After the system switches to the triplet surface, the uncoordinated HO2· replaces the product water terminally bound to the Mn(II) and is then oxidized into O2 spontaneously. Transition states with structural similarities to those obtained for TTC, where μ-η2-OH-/O2- groups play important roles, were found to be higher in energy.

Iron(II) complexes of dimethyltriazacyclophane.

Treatment of the ortho-triazacyclophane 1,4-dimethyltribenzo[b,e,h][1,4,7]triazacyclonona-2,5,8-triene [(C6H5)3(NH)(NCH3)2, L1] with Fe[N(SiMe3)2]2 yields the dimeric iron(II) complex bis(μ-1,4-dimethyltribenzo[b,e,h][1,4,7]triazacyclonona-2,5,8-trien-7-ido)bis[(μ-1,4-dimethyltribenzo[b,e,h][1,4,7]triazacyclonona-2,5,8-trien-7-ido)iron(II)], [Fe(C20H18N3)4] or Fe2(L1)4 (9). Dissolution of 9 in tetrahydrofuran (THF) results in solvation by two THF ligands and the formation of a simpler monoiron complex, namely bis(μ-1,4-dimethyltribenzo[b,e,h][1,4,7]triazacyclonona-2,5,8-trien-7-ido-κN7)bis(tetrahydrofuran-κO)iron(II), [Fe(C20H18N3)2(C4H8O)2] or (L1)2Fe(THF)2 (10). The reaction is reversible and 10 reverts in vacuo to diiron complex 9. In the structures of both 9 and 10, the monoanionic triazacyclophane ligand L1- is observed in only the less-symmetric saddle conformation. No bowl-shaped crown conformers are observed in the solid state, thus preventing chelating κ3-coordination to the metal as had been proposed earlier based on density functional theory (DFT) calculations. Instead, the L1- ligands are bound in either a η2-chelating fashion through the amide and one amine donor (for one of the four ligands of 9), or solely through their amide N atoms in an even simpler monodentate η1-coordination mode. Density functional calculations on dimer 9 revealed nearly full cationic charges on each Fe atom and no bonding interaction between the two metal centers, consistent with the relatively long Fe...Fe distance of 2.912 (1) Å observed in the solid state.

Robustness, Selective Gas Separation, and Nitrobenzene Sensing on Two Isomers of Cadmium Metal-Organic Frameworks Containing Various Metal-O-Metal Chains.

Poor stability has been one of the major difficulties affecting to the practical application of metal-organic frameworks (MOFs). In this work, we obtained two 3D structurally isomeric Cd-MOFs, {[Cd6(NH2Me2)2(PTB)4(HCOO)2(H2O)]·(DMF)13·(H2O)4} n (FJU-35) and {[Cd6(NH2Me2)2(PTB)4(HCOO)2]·(DMF)6·(H2O)2} n (FJU-36) (H3PTB = pyridine-2,4,6-tribenzoic acid) containing different CdII-O-CdII chains by varying the addition agents. FJU-35 with coordinated solvent and formate in asymmetric μ3-η1:η2 coordination mode within the CdII-O-CdII chains is vulnerable to external attacks and is apt to collapse after activation, while FJU-36 with no coordinated solvent in the CdII-O-CdII chains but fully protected by the carboxylates from the ligands and the symmetric formate in the coordination mode μ3-η2:η2 is stable, and its activated sample shows efficient separation of C2H2/CH4 and C2H2/CO2 mixtures. Conversely, FJU-35 with more vulnerability is more sensitive to the detection of nitrobenzene than FJU-36.

Relevance of Protons in Heterolytic Activation of H2O2 over Nb(V): Insights from Model Studies on Nb-Substituted Polyoxometalates

Nb-monosubstituted Lindqvist-type polyoxometalates (POM), (Bu4N)4[(NbW5O18)2O] (1) and (Bu4N)3[Nb(O)W5O18] (2), catalyze epoxidation of alkenes with hydrogen peroxide and mimic the catalytic performance of heterogeneous Nb-silicate catalysts. Dimer 1 is more active than monomer 2, but the catalytic activity of the latter increases in the presence of acid. Kinetic and spectroscopic studies suggest a mechanism that involves generation of monomer (Bu4N)2[Nb(OH)W5O18] (3), interaction of 3 with H2O2 leading to a protonated peroxo niobium species, (Bu4N)2[HNb(O2)W5O18] (4), followed by oxygen transfer to a C═C bond in alkene. The previously unknown peroxo complex 4 has been isolated and characterized by elemental analysis; UV–vis, FT-IR, Raman, 93Nb, 17O and 183W NMR spectroscopy; cyclic voltammetry; and potentiometric titration. The physicochemical techniques support a monomeric Lindqvist structure of 4 bearing one peroxo ligand attached to Nb(V) in a η2-coordination mode. While the unprotonated peroxo comple...

Are there analogues of the indenyl effect in larger ring systems: a DFT study of hydride attack on [Mn(CO)3(naphthalene)]+ and [Cr(CO)3(benzotropylium)

Two pairs of complexes, [Mn(CO)3(benzene)]+/[Mn(CO)3(naphthalene)]+ and [Cr(CO)3(tropylium)]+/[Cr(CO)3(benzotropylium)]+, have been used as a platform to establish the extent to which the well-known ‘indenyl effect’ translates into other bicyclic ligand systems. Density functional theory (DFT) suggests that the ‘naphthalene effect’ is minimal, the pathway for hydride reduction of [Mn(CO)3(naphthalene)]+ resembling closely that for the benzene analogue. In the benzotropylium system, in contrast, stabilisation of an η5 coordination mode through aromatisation of the six-membered ring plays a similar role to stabilisation of η3 in the indenyl effect. The greater influence of aromatisation in the five- and seven-membered ring systems stems from the presence of formal charge on the ligands in these cases: localisation of this charge on a subset of the available carbon atoms enhances the electrostatic component of the metal-ligand bond. This is particularly dramatic in the benzotropylium case, where the η7–η5 slippage corresponds to a formal 2-electron reduction of the ligand from [C7H7]+ to [C7H7]−.

Scandium complexes with the tetraphenylethylene and anthracene dianions.

The structural study of Sc complexes containing dianions of anthracene and tetraphenylethylene should shed some light on the nature of rare-earth metal-carbon bonding. The crystal structures of (18-crown-6)bis(tetrahydrofuran-κO)sodium bis(η6-1,1,2,2-tetraphenylethenediyl)scandium(III) tetrahydrofuran disolvate, [Na(C4H8O)2(C12H24O6)][Sc(C26H20)2]·2C4H8O or [Na(18-crown-6)(THF)2][Sc(η6-C2Ph4)2]·2(THF), (1b), (η5-1,3-diphenylcyclopentadienyl)(tetrahydrofuran-κO)(η6-1,1,2,2-tetraphenylethenediyl)scandium(III) toluene hemisolvate, [Sc(C17H13)(C26H20)(C4H8O)]·0.5C7H8 or [(η5-1,3-Ph2C5H3)Sc(η6-C2Ph4)(THF)]·0.5(toluene), (5b), poly[[(μ2-η3:η3-anthracenediyl)bis(η6-anthracenediyl)bis(η5-1,3-diphenylcyclopentadienyl)tetrakis(tetrahydrofuran)dipotassiumdiscandium(III)] tetrahydrofuran monosolvate], {[K2Sc2(C14H10)3(C17H13)2(C4H8O)4]·C4H8O}n or [K(THF)2]2[(1,3-Ph2C5H3)2Sc2(C14H10)3]·THF, (6), and 1,4-diphenylcyclopenta-1,3-diene, C17H14, (3a), have been established. The [Sc(η6-C2Ph4)2]- complex anion in (1b) contains the tetraphenylethylene dianion in a symmetrical bis-η3-allyl coordination mode. The complex homoleptic [Sc(η6-C2Ph4)2]- anion retains its structure in THF solution, displaying hindered rotation of the coordinated phenyl rings. The 1D 1H and 13C{1H}, and 2D COSY 1H-1H and 13C-1H NMR data are presented for M[Sc(Ph4C2)2]·xTHF [M = Na and x = 4 for (1a); M = K and x = 3.5 for (2a)] in THF-d8 media. Complex (5b) exhibits an unsymmetrical bis-η3-allyl coordination mode of the dianion, but this changes to a η4 coordination mode for (1,3-Ph2C5H3)Sc(Ph4C2)(THF)2, (5a), in THF-d8 solution. A 45Sc NMR study of (2a) and UV-Vis studies of (1a), (2a) and (5a) indicate a significant covalent contribution to the Sc-Ph4C2 bond character. The unique Sc ate complex, (6), contains three anthracenide dianions demonstrating both a η6-coordination mode for two bent ligands and a μ2-η3:η3-bridging mode of a flat ligand. Each [(1,3-Ph2C5H3)2Sc2(C14H10)3]2- dianionic unit is connected to four neighbouring units via short contacts with [K(THF)2]+ cations, forming a two-dimensional coordination polymer framework parallel to (001).

Synthesis and characterization structural of alkali cations (Li+, Na+, K+, Rb+, Cs+) carboxylate-dithiocarbamate complexes of L-Proline

The alkali metal (Li+, Na+, K+, Rb+, Cs+) carboxylate-dithiocarbamate complexes of L-proline have been prepared from the reaction of L-proline with carbon disulfide in the presence of two equivalents of the corresponding alkali metal hydroxide. The resulting compounds have been characterized by FAB+ mass spectrometry, IR spectroscopy, NMR (1H, 13C) spectroscopy. The X-ray single crystal crystallography analysis of the complexes of K+, Rb+ and Cs+ complexes showed that the coordination modes of dithiocarbamate and carboxylate groups to the alkali metal is modulated by the resonance effect, the ionic radius of the sulfur and oxygen atoms as well as the size, charge-density, and Lewis-acidity of the metal ions. In this way in the solid state polymeric structures in 2D for K+ and Rb+ complexes, and 3D in the case of Cs+ are generated. The distances C···M, M···S1 and M···S2 suggest the existence of cation···π and van der Waals interactions that can be described as a η3 coordination mode of the dtc group to the alkali metal ions.

Unexpected Formation and Structural Characterization of a Dinuclear Sodium Half-Sandwich Complex

Treatment of N,N′-diisopropylcarbodiimide with sodium cyclopentadienide (NaCp) in a molar ratio of 1:1 in THF solution resulted in formation of the unexpected dinuclear sodium half-sandwich complex [NaC5H3{C(NHiPr)(=NiPr)}2-1,2]2 (1) as colorless crystals in low yield. The newly formed ligand, which belongs to the group of 6-aminofulvene-2-aldiminate ligands, coordinates to sodium in an η5-coordination mode via the cyclopentadienyl ring. Dimerization occurs through additional chelating κN,N′-coordination of the amidine substituents. The NMR data of 1 indicated a slow dimer/monomer equilibrium in solution. A serendipitously isolated hydrolysis product, {µ-(iPrNH)2C=O}2[NaC5H3{C(NHiPr)(=NiPr)}2-1,2]2 (2), contains the new 6-aminofulvene-2-aldiminate ligand in the N,N′-chelating coordination mode with the cyclopentadiene ring being uncoordinated. In this case, dimerization occurs through the presence of two bridging neutral N,N′-diisopropylurea ligands. Both compounds have been structurally characterized by single-crystal X-ray diffraction.

Synthesis and molecular structures of YbII and Ca bis(amidinate) complexes containing the tridentate amidinate ligand [2,6-Pri2C6H3NC(But)NC6H4OMe-2

New bis(amidinate) complexes of calcium, [2,6-Pri2C6H3NC(But)NC6H4OMe-2]2Ca(DME) (2), and divalent ytterbium, [2,6-Pri2C6H3NC(But)NC6H4OMe-2]2Yb (4), were synthesized by the transamination of the bis(amide) derivatives [(Me3Si)2N]2M(THF)2 (M = Ca, Yb) with two equivalents of amidine 2,6-Pri2C6H3N=C(But)N(H)C6H4OMe-2, in which one nitrogen atom bears an o-methoxyphenylene moiety capable of coordinating a metalion. An X-ray diffraction study showed that, despite very similar ionic radii of Ca2+ and Yb2+, the amidinate ligands in complexes 2 and 4 bind to these ions in different coordination modes. In the calcium complex, both ligands adopt a κ2-N, O-chelating coordination mode. In the divalent ytterbium compound, one ligand is chelating and binds to the metalion in a κ2-N, O-coordination mode, while the second ligand is coordinated via both the N and O (κ2) atoms and the arene ring of the 2,6-Pri2C6H3 moiety (η6-coordination mode).

E-H Bond Activation and Insertion Processes in the Reactions of the Unsaturated Hydride [W2Cp2(μ-H)(μ-PPh2)(NO)2

The reactions of the title complex (1) with different p-block element (E) molecules was examined. Compound 1 reacted with BH3·THF at room temperature to give the trihydride [W2Cp2(μ-H)H2(μ-PPh2)(NO)2], which formally results from hydrogenation of 1, a reaction that actually does not take place when neat dihydrogen is used. Clean E-H bond oxidative addition, however, took place when 1 was reacted with HSnPh3, to give the related dihydride stannyl derivative [W2Cp2(μ-H)H(μ-PPh2)(NO)2(SnPh3)]. In contrast, the reaction of 1 with HSPh involved H2 elimination to give the thiolate-bridged complex [W2Cp2(μ-SPh)(μ-PPh2)(NO)2], while that with (p-tol)C(O)H resulted in insertion of the aldehyde to yield the related alkoxide complex [W2Cp2{μ-OCH2(p-tol)}(μ-PPh2)(NO)2]. Insertion also prevailed in the reactions of 1 with CNtBu, which, however, involved the competitive formation of new C-H or N-H bonds, to give a mixture of formimidoyl and aminocarbyne derivatives, [W2Cp2(μ-κ1:η2-HCNtBu)(μ-PPh2)(NO)2] (W-W = 3.0177(2) Å) and [W2Cp2{μ-C(NHtBu)}(μ-PPh2)(NO)2] (W-W = 2.9010(4) Å), respectively, even though the latter was thermodynamically preferred, according to density functional theory calculations. The former represents the first structurally characterized complex displaying a formimidoyl or iminoacyl ligand in the alkenyl-like μ-κ1:η2 coordination mode. The reaction of 1 with diazomethane proceeded with N2 elimination and C-H coupling to yield the agostic methyl-bridged complex [W2Cp2(μ-κ1:η2-CH3)(μ-PPh2)(NO)2] (calculated W-W = 2.923 Å), whereas the reaction with N2CH(SiMe3) proceeded with insertion of the diazoalkane to give the corresponding hydrazonide complex [W2Cp2{μ-NH(NCHSiMe3)}(μ-PPh2)(NO)2] (W-W = 2.8608(4) Å). The latter was converted under alkaline conditions to the methyldiazenide derivative [W2Cp2{μ-N(NMe)}(μ-PPh2)(NO)2] (W-W = 2.8730(2) Å), in a process involving hydrolysis of the C-Si bond coupled with a 1,3-H shift from N to C.

Substituent Effects at the β-Positions of the Nonfused Pyrroles in a Quadruply Fused Porphyrin on the Structure and Optical and Electrochemical Properties.

We have synthesized 2, a derivative of zinc(II) quadruply fused porphyrinato (ZnIIQFP) that is tetrabrominated at the β-positions of the two nonfused pyrroles, by treatment of ZnIIQFP with N-bromosuccinimide. X-ray diffraction analysis of a single crystal obtained from a THF solution of 2 by vapor diffusion of ethanol (EtOH) revealed that 2 formed an unprecedented dimeric structure, (2)2-L (L = EtOH), in which one of the brominated QFP ligands acts as a bridging ligand in an unprecedented μ-η3:η1 coordination mode. In the dimeric structure, the two QFP ligands showed a unique η3 coordination mode for both ZnII centers. In (2)2-EtOH, one of the pyrrolic nitrogen atoms of the two nonfused pyrroles dissociates from the ZnII center, and the dissociated pyrrolic nitrogen atom coordinates to the ZnII center of the other molecule in the dimer. The ZnII center having the μ-η3:η1-QFP ligand is coordinated by an EtOH molecule, and the other ZnII center is coordinated by the η3-QFP ligand and one nitrogen atom of the bridging QFP ligand. The dimeric structure is stable and maintained even in a solution of noncoordinating solvents such as dichloromethane. The bromo groups of 2 can be substituted with phenyl groups under Suzuki coupling conditions to afford the tetraphenyl derivative, 3. Furthermore, the effects of the substituents at the β-positions on the optical and electrochemical properties and Lewis acidity of the ZnII centers have been investigated. The redox potentials were positively shifted by introduction of electron-withdrawing groups at the β-positions, and the shift widths exhibited a linear correlation to the Hammett parameters of the substituents.

Ligands’ σ-donation and π-backdonation effects on metal-metal bonding in trinuclear [M3(Tr)2(L)3]2+ (M = Fe, Ni, Pd, Pt, Tr = tropylium and L = CO, HCN and C2H4) sandwich compounds: Theoretical investigation

Abstract DFT calculations with full geometry optimization using GGA BP86 and meta-GGA M06L functionals have been performed on the [M3(Tr)2L3]2+ (M = Fe, Ni, Pd, Pt, Tr+ = C7H7+ and L = CO, HCN and η2-C2H4) sandwich complexes. The M3 triangular core is encapsulated between two tropylium cations which tends to establish M–L bonding with regards to the metal nature and the spin state. It turned out that each tropylium cation is connected to the M3 triangular core through an η2, η2, η2 coordination mode engaging six carbon atoms amongst seven. For the Fe singlet structures, the calculated HOMO–LUMO gaps by both BP86 and M06L are small, thus favouring the triplet one. The [Fe3(Tr)L3]2+ singlet structures are predicted to have two formal Fe Fe single bonds and one formal Fe Fe triple one within the Fe3 triangle based on the bond distances and the Wiberg bond indices (WBIs), while their analogues of triplet state exhibit two formal Fe Fe single bonds and one formal Fe Fe double bond. For the nickel, palladium and platinum d10 metal structures, they display large HOMO–LUMO gaps and adopt three formal metal–metal single bonds within the M3 core, in accordance with the small WBIs. The different binding capabilities of the isoelectronic CO, HCN and C2H4 auxiliary ligands are highlighted by the corresponding MOs’ diagrams and their donation and backdonation amounts.

Synthesis, crystal structure, and properties of a tetrairon cluster based on 2-methyl-8-hydroxyquinoline

The synthesis, structure, and magnetic properties of a tetrairon(III) complex [Fe4(μ2-O)2Cl4(L)4]·0.5H2O (1, L = 2-methyl-8-hydroxyquinoline), which was prepared under solvothermal conditions and characterized by IR spectra, elemental analysis, TG, and single-crystal X-ray crystal diffraction, are presented. Each Fe center adopts a distorted trigonal bipyramid geometry and is coordinated with three oxygen atoms, one nitrogen atom, and one chlorine atom. Each 2-methyl-8-hydroxyquinoline is coordinated to two FeIII ions with μ2-η2:η1 coordination mode. The magnetic properties of the complex are dominated by antiferromagnetic exchange interactions.

A loop chain and a three-dimensional network assembled from a multi-dentate nitronyl nitroxide radical and M(hfac)2 (M = CoII, CuII).

A multi-dentate nitronyl nitroxide radical Nit-Ph-3,5-bIm (Nit-Ph-3,5-bIm = 2-[3,5-bis(1-imidazole)-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) reacted with Co(hfac)2·2H2O or Cu(hfac)2 to yield two novel 3d-radical complexes {[Co(hfac)2]2(Nit-Ph-3,5-bIm)}n1 and {[Cu(hfac)2]7(Nit-Ph-3,5-bIm)3}n2 (hfac- = hexafluoroacetylacetonate). In both compounds, the Nit-Ph-3,5-bIm radical ligand behaves as a tetradentate ligand to link four M(hfac)2 units in a μ4-η1:η1:η1:η1-coordination mode via its two NO groups and two N atoms of imidazole, generating a unique loop chain for 1 and a three-dimensional framework for 2. The magnetic studies revealed a strong antiferromagnetic Co-ON exchange interaction in 1 while a ferromagnetic Cu-ON interaction is observed in 2. The dc magnetic behaviors of two complexes are analyzed by means of appropriate magnetic models. Furthermore, ac magnetic susceptibilities of the Co complex reveal slow relaxation of magnetization.

Lithium Complexes Derived of Benzylphosphines: Synthesis, Characterization and Evaluation in the ROP of rac-Lactide and ε-Caprolactone.

A series of lithium complexes ([Ph2P(o-C6H4-CH2Li·TMEDA)] (1-Li), [PhP(o-C6H4-CH3)(o-C6H4-CH2Li·TMEDA)] (2-Li), [PhP(o-C6H4-CH2Li·TMEDA)2] (2-Li2) and [P(o-C6H4-CH2Li·TMEDA)3] (3-Li3)) was prepared from mono-, di- and tri-benzylphosphines and varying amounts of nBuLi and was characterized extensively by IR and 1H, 7Li, 13C and 31P NMR spectroscopy. The molecular structures of complexes 1-Li and 2-Li were determined by single-crystal X-ray diffraction studies. The two complexes have monomeric structures in the solid state comprising seesaw lithium atoms. In each case, the ligand exhibits an asymmetric C-C η2-coordination mode and an intramolecular P-Li bond interaction. Theoretical calculations at Density functional theory (DFT) level M06/6111+G(2d,p) show that indeed a P-Li bond is established which can be explained as the P lone pair (sp1.26) being partially delocalized on an available sp2 orbital on Li (sp2.04) and additional bonding contribution of the phosphorous atom to Li stems from further delocalization of a σ P-C orbital into the sp2 orbital on Li. The observed short contact distances between an aromatic ipso carbon and Li in the crystal structures of 1-Li and 2-Li are explained as due to the interaction of a σ C-Li orbital into the π* orbital of a C-C aromatic bond. Preliminary tests show compounds 1-Li, 2-Li, 2-Li2 and 3-Li3 are active catalysts in the solvent free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA). High conversions to polycaprolactones were obtained in short periods of time: 1–6 min at 25 °C. Additionally, all four lithium complexes behave as moderately good initiators for the ROP of rac-LA showing high conversions to polylactides at 140 °C in one hour.

Crystal structure of poly[[di-μ3-acetato-tetra-aqua-bis-(μ2-cyclo-hexane-1,4-di-carboxyl-ato)dilanth-an-um(III)] dihydrate

The title compound, {[La2(CH3COO)2(C8H10O4)2(H2O)4]·2H2O} n or [La2(ac)2(e,a-cis-1,4-chdc)2(H2O)4]·2H2O, where ac is acetate and 1,4-chdc is cyclo-hexane-1,4-di-carboxyl-ate anion, is a binuclear lanthanum(III) complex. Each metal atom is deca-coordinated by four O atoms from two distinct 1,4-chdc2- ligands, four O atoms from three acetate groups and two O atoms from coordinated water mol-ecules to form a distorted bicapped square-anti-prismatic geometry. Two non-coordinated water mol-ecules are also present in the formula unit. The most remarkable feature of this compound is that it possesses a only cis conformation for cyclo-hexane-1,4-di-carb-oxy-lic acid, although the raw material consists of a mixture of cis and trans isomers. The μ3-η2:η2 coordination mode of the bridging acetate group and the flexible di-carboxyl-ate fragments of 1,4-chdc2- results in the formation of infinite two-dimensional lanthanide-carboxyl-ate layers within the crystal structure. The directionality of strong inter-molecular O-H⋯O and weak C-H⋯O inter-actions provides robustness to the layers, which leads to the construction of a three-dimensional supra-molecular network. The crystal studied was refined as a two-component twin.

Dual Functionalization of White Phosphorus: Formation, Characterization, and Reactivity of Rare-Earth-Metal Cyclo-P3 Complexes.

The [3+1] fragmentation reaction of rare-earth metallacyclopentadienes 1 a-c with 0.5 equivalents of P4 affords a series of rare-earth metal cyclo-P3 complexes 2 a-c and a phospholyl anion 3. 2 a-c demonstrate an unusual η3 coordination mode with one P-P bond featuring partial π-bonding character. 2 a-c are the first cyclo-P3 complexes of rare-earth metals, and also the first organo-substituted polyphosphides in the category of Group 3 and f-block elements. Rare-earth metallacyclopentadienes play a dual role in the combination of aromatization and Diels-Alder reaction. Compounds 2 a-c can coordinate to one or two [W(CO)5 ] units, yielding 4 a-c or 5 c, respectively. Furthermore, oxidation of 2 a with p-benzoquinone produces its corresponding phospholyllithium and regenerated P4 .

Dual Functionalization of White Phosphorus: Formation, Characterization, and Reactivity of Rare‐Earth‐Metal Cyclo‐P3 Complexes

AbstractThe [3+1] fragmentation reaction of rare‐earth metallacyclopentadienes 1 a–c with 0.5 equivalents of P4 affords a series of rare‐earth metal cyclo‐P3 complexes 2 a–c and a phospholyl anion 3. 2 a–c demonstrate an unusual η3 coordination mode with one P−P bond featuring partial π‐bonding character. 2 a–c are the first cyclo‐P3 complexes of rare‐earth metals, and also the first organo‐substituted polyphosphides in the category of Group 3 and f‐block elements. Rare‐earth metallacyclopentadienes play a dual role in the combination of aromatization and Diels–Alder reaction. Compounds 2 a–c can coordinate to one or two [W(CO)5] units, yielding 4 a–c or 5 c, respectively. Furthermore, oxidation of 2 a with p‐benzoquinone produces its corresponding phospholyllithium and regenerated P4.