Ylide-Functionalization via Metalated Ylides: Synthesis and Structural Properties

The α-metallated ylides [Ph₃P−C−Z]⁻M⁺ (with Z=SO₂Tol or CN and M=Na or K) were used as versatile nucleophiles for the facile access to ylide-substituted compounds. Halogenations, alkylations, carbonylations and functionalization reactions with main group element halides were easily accomplished by simple trapping reactions with the appropriate electrophiles. X-ray crystallographic studies of all compounds – including the first structures of α-fluorinated P-ylides – showed remarkable differences in the ylide backbone depending on the substituents. In the fluorinated compounds, a change from a fully planar to a pyramidalized ylidic carbon centre was observed despite the strongly anion-stabilizing ability of the yldiide substituent. π-Donation from the ylide substituent also resulted in geometric restrictions depending on the steric and electronic properties of the introduced substituents.     

Solvent polarity controls the helical conformation of short peptides rich in Calpha-tetrasubstituted amino acids

The two peptides, rich in C(alpha)-tetrasubstituted amino acids, Ac-[Aib-L-(alphaMe)Val-Aib](2)-L-His-NH(2) (1) and Ac-[Aib-L-(alphaMe)Val-Aib](2)-O-tBu (2 a) are prevalently helical. They present the unique property of changing their conformation from the alpha- to the 3(10)-helix as a function of the polarity of the solvent: alpha in more polar solvents, 3(10) in less polar ones. Conclusive evidence of this reversible change of conformation is reported on the basis of the circular dichroism (CD) spectra and a detailed two-dimensional NMR analysis in two solvents (trifluoroethanol and methanol) refined with molecular dynamics calculations. The X-ray diffractometric analysis of the crystals of both peptides reveals that they assume a prevalent 3(10)-helix conformation in the solid state. This conformation is practically superimposable on that obtained from the NMR analysis of 1 in methanol. The NMR results further validate the reported CD signature of the 3(10)-helix and the use of the CD technique for its assessment.     

High Ethene/Ethane Selectivity in 2,2′‐Bipyridine‐Based Silver(I) Complexes by Removal of Coordinated Solvent

Following removal of coordinated CH₃CN, the resulting complexes [Ag^I(2,2′‐bipyridine)][BF₄] ( 1 ) and [Ag^I(6,6′‐dimethyl‐2,2′‐bipyridine)][OTf] ( 2 ) show ethene/ethane sorption selectivities of 390 and 340, respectively, and corresponding ethene sorption capacities of 2.38 and 2.18 mmol g^?1 when tested at an applied gas pressure of 90 kPa and a temperature of (20±1) °C. These ethene/ethane selectivities are 13 times higher than those reported for known solid sorbents for ethene/ethane separation. For 2 , ethene sorption reached 90 % of equilibrium capacity within 15 minutes, and this equilibrium capacity was maintained over the three sorption/desorption cycles tested. The rates of ethene sorption were also measured. To our knowledge, these are the first complexes, designed for olefin/paraffin separations, which have open silver(I) sites. The high selectivities arise from these open silver(I) sites and the relatively low molecular surface areas of the complexes.     

Two Series of Homodinuclear Lanthanide Complexes: Greatly Enhancing Energy Barriers through Tuning Terminal Solvent Ligands in Dy2 Single‐Molecule Magnets

The utilization of 2‐ethoxy‐6‐{[(2‐hydroxy‐3‐methoxybenzyl)imino]methyl}phenol (H₂L) as a chelating ligand, in combination with the employment of alcohols (EtOH and MeOH) as auxiliary ligands, in 4 f‐metal chemistry afforded two series of dinuclear lanthanide complexes of compositions [Ln₂L₂(NO₃)₂(EtOH)₂] (Ln=Sm ( 1 ), Eu ( 2 ), Gd ( 3 ), Tb ( 4 ), Dy ( 5 ), Ho ( 6 ), Er ( 7 )) and [Ln₂L₂(NO₃)₂(MeOH)₂] (Ln=Sm ( 8 ), Eu ( 9 ), Gd ( 10 ), Tb ( 11 ), Dy ( 12 ), Ho ( 13 ), Er ( 14 )). The structures of 1 – 14 were determined by single‐crystal X‐ray crystallography. Complexes 1 – 7 are isomorphous. The two lanthanide(III) ions in 1 – 7 are doubly bridged by two deprotonated aminophenoxide oxygen atoms of two μ₂:η⁰:η¹:η²:η¹:η¹:η⁰‐L²⁻ ligands. One nitrogen atom, two oxygen atoms of the NO₃⁻ anion, two methoxide oxygen atoms of two ligand sets, and one oxygen atom of the terminally coordinated EtOH molecule complete the distorted dodecahedron geometry of each lanthanide(III) ion. Compounds 8 – 14 are isomorphous and their structures are similar to those of 1 – 7 . The slight difference between 1 – 7 and 8 – 14 stems from purposefully replacing the EtOH ligands in 1 – 7 with MeOH in 8 – 14 . Direct‐current magnetic susceptibility studies in the 2–300 K range reveal weak antiferromagnetic interactions for 3 , 4 , 7 , 10 , 11 , and 14 , and ferromagnetic interactions at low temperature for 5 , 6 , 12 , and 13 . Complexes 5 and 12 exhibit single‐molecule magnet (SMM) behavior with energy barriers of 131.3 K for 5 and 198.8 K for 12 . The energy barrier is significantly enhanced by dexterously regulating the terminal ligands. To rationalize the observed difference in the magnetic behavior, complete‐active‐space self‐consistent field (CASSCF) calculations were performed on two Dy₂ complexes. Subtle variation in the angle between the magnetic axes and the vector connecting two dysprosium(III) ions results in a weaker influence on the tunneling gap of individual dysprosium(III) ions by the dipolar field in 12 . This work proposes an efficient strategy for synthesizing Dy₂ SMMs with high energy barriers.     

A structural and computational study of synthetically important alkali-metal/tetramethylpiperidide (TMP) amine solvates

Two heavy alkali-metal salts of the sterically demanding amine, 2,2,6,6-tetramethylpiperidine (TMPH), have been prepared using different methodologies. Complex 1, [((tmeda)Na(tmp))2] (TMEDA=N,N, N',N'-tetramethylethylenediamine), can be synthesized by a deprotonative route. This is achieved by reacting butylsodium with TMPH in the presence of excess TMEDA in hexane. The potassium congener [((tmeda)K(tmp))2] (2), can be prepared by treating KTMP (made using a metathesis reaction between LiTMP and potassium tert-butoxide) with an excess of TMEDA in hexane. In the solid state, 1 and 2 are essentially isostructural. They are discretely dimeric and their framework consists of a four-membered M-N-M-N ring (M=Na or K, N=TMP). Due to the high steric demand of the TMP ligand, the TMEDA molecules bind to the metal centers in an asymmetric manner. In 2, each of the coordination spheres of the metals is completed by an agostic K...CH3(TMP) interaction. DFT calculations at the B3 LYP/6-311G** level give an insight into why 1 and 2 adopt dramatically different structures from their previously reported, "open-dimeric", lithium counterpart. The theoretical work also focuses on the TMEDA-free parent amide complexes and reveals that the energy difference for the formation of [(M(tmp))x] (in which, M=Li or Na, x=3 or 4; and M=K, x=2, 3 or 4) are small.     

Synthesis,Crystal and Electronic Structures of a Thiophosphinoyl- and Amino-Substituted Metallated Ylide

α-Metallated ylides have revealed themselves to be versatile reagents for the introduction of ylide groups. Herein, we report the synthesis of the thiophosphinoyl and piperidyl (Pip) substituted α-metallated ylide [Ph₂(Pip)P=C−P(S)Ph₂]M (M=Li, Na, K) through a four-step synthetic procedure starting from diphenylmethylphosphine sulfide. Metallation of the ylide intermediate was successfully accomplished with different alkali metal bases delivering the lithium, sodium and potassium salts, the latter isolable in high yields. Structure analyses of the lithium and potassium compounds in the solid state with and without crown ether revealed different aggregates (monomer, dimer and hexamer) with the metals coordinated by the thiophosphoryl moiety and ylidic carbon atom. Although the piperidyl group does not coordinate to the metal, it significantly contributes to the stability of the yldiide by charge delocalization through negative hyperconjugation.     

Thermodynamic and Structural Trends in Hexavalent Actinyl Cations: Complexation of Dipicolinic Acid with NpO22+ and PuO22+ in Comparison with UO22+

The complexation of NpO₂²⁺ and PuO₂²⁺ with dipicolinic acid (DPA) has been investigated in 0.1 M NaClO₄ by spectrophotometry, microcalorimetry, and single crystal diffractometry. Formation of 1:1 and 1:2 (metal/ligand molar ratio) complexes of DPA with NpO₂²⁺ and PuO₂²⁺ were identified and the thermodynamic parameters were determined and compared with those of UO₂²⁺. All three hexavalent actinyl cations form strong 1:1 DPA complexes with slightly decreasing but comparable stability constants from UO₂²⁺ to PuO₂²⁺, whereas the stability constants of the 1:2 complexes (log β₂) decrease substantially along the series (16.3 for UO₂L₂^2?, 15.17 for NpO₂L₂^2?, and 14.17 for PuO₂L₂^2? at 25 °C). The enthalpies of complexation for the 1:2 complexes become less exothermic from UO₂L₂^2? (?28.9 kJ mol^?1), through NpO₂L₂^2? (?27.2 kJ mol^?1), and to PuO₂L₂^2? (?22.7 kJ mol^?1). The trends in the thermodynamic parameters are discussed in terms of the effective charge of the cations and the steric constraints in the structures of the complexes. In addition, the features of the absorption spectra, including the wavelength and intensity of the absorption bands, are related to the perturbation of the ligand field and the symmetry of the actinyl complexes.     

Bridging the Gap between Bisylides and Methandiides: Isolation,Reactivity, and Electronic Structure of an Yldiide

Bisylides and methandiides are two unique families of carbon bases that have found a variety of applications in recent years. Metalated ylides (yldiides) are the link between these types of compounds. Yet, only little is known about their properties, reactivities, and particularly their electronic structure. Here, we report the preparation of the metalated ylide [Ph₃P‐C‐SO₂Tol]^? ( 1 ) with different alkali metal counterions. The compounds have been studied by X‐ray diffraction analysis and NMR spectroscopy and the first structures of a sodium and potassium yldiide are presented. The electronic structure of 1 was explored by DFT calculations confirming its relation with other divalent carbon species. Reactivity studies demonstrate the strong nucleophilicity of the yldiide and its capability to act both as a σ‐ and π‐donor.     

Heavy alkaline earth metal pyrazolates: synthetic pathways, structural trends, and comparison with divalent lanthanoids

Two series of heavy alkaline earth metal pyrazolates, [M(Ph(2)pz)(2)(thf)(4)] 1 a-c (Ph(2)pz=3,5-diphenylpyrazolate, M=Ca, Sr, Ba; THF=tetrahydrofuran) and [M(Ph(2)pz)(2)(dme)(n)] (M=Ca, 2 a, Sr, 2 b, n=2; M=Ba, 2 c, n=3; DME=1,2-dimethoxyethane) have been prepared by redox transmetallation/ligand exchange utilizing Hg(C(6)F(5))(2). Compounds 1 a and 2 b were also obtained by redox transmetallation with Tl(Ph(2)pz). Alternatively, direct reaction of the alkaline earth metals with 3,5-diphenylpyrazole at elevated temperatures under solventless conditions yielded compounds 1 a-c and 2 a-c upon extraction with THF or DME. By contrast, [M(Me(2)pz)(2)(Me(2)pzH)(4)] 3 a-c (M=Ca, Sr, Ba; Me(2)pzH=3,5-dimethylpyrazole) were prepared by protolysis of [M[N(SiMe(3))(2)](2)(thf)(2)] (M=Ca, Sr, Ba) with Me(2)pzH in THF and by direct metallation with Me(2)pzH in liquid NH(3)/THF. Compounds 1 a-c and 2 a-c display eta(2)-bonded pyrazolate ligands, while 3 a,b exhibit eta(1)-coordination. Complexes 1 a-c have transoid Ph(2)pz ligands and an overall coordination number of eight with a switch from mutually coplanar Ph(2)pz ligands in 1 a,b to perpendicular in 1 c. In eight coordinate 2 a,b the pyrazolate ligands are cisoid, whilst 2 c has an additional DME ligand and a metal coordination number of ten. By contrast, 3 a,b have octahedral geometry with four eta(1)-Me(2)pzH donors, which are hydrogen-bonded to the uncoordinated nitrogen atoms of the two trans Me(2)pz ligands. The application of synthetic routes initially developed for the preparation of lanthanoid pyrazolates provides detailed insight into the similarities and differences between the two groups of metals and structures of their complexes.     

以硝基对苯二甲酸和4,4'-联吡啶为配体的四个金属Ag配合物的合成、结构多样性和电子光谱

由2-硝基-1,4-对苯二甲酸和4,4'-联吡啶作为起始原料合成了4个金属银的配位聚合物,{[Ag(4,4'-bipy)]·2-Hnbdc·2H₂O·CH₃OH}_n (1),{[Ag(4,4'-bipy)(2-Hnbdc)]}_n (2),{[Ag₂(4,4'-bipy)₂(2-nbdc)]·2H₂O}_n (3),和{[Ag₂(4,4'-bipy)₂(2-nbdc)(H₂O)]·2H₂O}_n (4)。通过IR、元素分析、TG、UV和荧光光谱以及粉末衍射等手段,对配合物进行了表征和性质研究。单晶衍射分析显示,配合物1为1D阴-阳离子型聚合物,配合物2为1D双链结构,且结构中不存在溶剂分子。配合物3和4均为1D链状结构。结构的多样性主要是由配体构象、硝基对苯二甲酸的配位模式以及弱作用(如π-π堆积、Ag…Ag作用以及氢键等)导致的。结构的不同也使得它们的稳定性、紫外吸收以及荧光光谱存在着差异。     

以硝基对苯二甲酸和4,4'-联吡啶为配体的四个金属Ag配合物的合成、结构多样性和电子光谱

由2-硝基-1, 4-对苯二甲酸和4, 4'-联吡啶作为起始原料合成了4个金属银的配位聚合物, {[Ag(4, 4'-bipy)]·2-Hnbdc·2H₂O ·CH₃OH}_n (1), {[Ag(4, 4'-bipy)(2-Hnbdc)]}_n (2), {[Ag₂(4, 4'-bipy)₂(2-nbdc)]·2H₂O}_n (3), 和{[Ag₂(4, 4'-bipy)₂(2-nbdc)(H₂O)]·2H₂O}_n (4)。通过IR、元素分析、TG、UV和荧光光谱以及粉末衍射等手段, 对配合物进行了表征和性质研究。单晶衍射分析显示, 配合物1为1D阴-阳离子型聚合物, 配合物2为1D双链结构, 且结构中不存在溶剂分子。配合物3和4均为1D链状结构。结构的多样性主要是由配体构象、硝基对苯二甲酸的配位模式以及弱作用(如π-π堆积、Ag…Ag作用以及氢键等)导致的。结构的不同也使得它们的稳定性、紫外吸收以及荧光光谱存在着差异。     

A Remarkable cis‐ and trans‐Spanning Dibenzylidene Acetone Diphosphine Chelating Ligand (dbaphos)

A multidentate and flexible diolefin–diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos ( 1 ), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt^II the dbaphos ligand forms cis‐ and trans‐diphosphine complexes and can be defined as a wide‐angle spanning ligand. ¹H NMR spectroscopic analysis shows that the β‐hydrogen of one olefin moiety interacts with the Pt^II centre (an anagostic interaction), which is supported by DFT calculations. At Pd⁰ and Rh^I, the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd⁰ complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other “free” olefin. The Pd⁰ complex of dbaphos reacts with iodobenzene to afford trans‐[Pd^II(dbaphos)I(Ph)]. In the case of Rh^I, dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand (“Lei” ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively.     

Heavy Alkali Metal Manganate Complexes: Synthesis,Structures and Solvent-Induced Dissociation Effects

Rare examples of heavier alkali metal manganates [{(AM)Mn(CH₂SiMe₃)(N^‘Ar)₂}_∞] (AM=K, Rb, or Cs) [N^‘Ar=N(SiMe₃)(Dipp), where Dipp=2,6-iPr₂-C₆H₃] have been synthesised with the Rb and Cs examples crystallographically characterised. These heaviest manganates crystallise as polymeric zig-zag chains propagated by AM⋅⋅⋅π-arene interactions. Key to their preparation is to avoid Lewis base donor solvents. In contrast, using multidentate nitrogen donors encourages ligand scrambling leading to redistribution of these bimetallic manganate compounds into their corresponding homometallic species as witnessed for the complete Li - Cs series. Adding to the few known crystallographically characterised unsolvated and solvated rubidium and caesium s-block metal amides, six new derivatives ([{AM(N^‘Ar)}_∞], [{AM(N^‘Ar)⋅TMEDA}_∞], and [{AM(N^‘Ar)⋅PMDETA}_∞] where AM=Rb or Cs) have been structurally authenticated. Utilising monodentate diethyl ether as a donor, it was also possible to isolate and crystallographically characterise sodium manganate [(Et₂O)₂Na(ⁿBu)Mn[(N^‘Ar)₂], a monomeric, dinuclear structure prevented from aggregating by two blocking ether ligands bound to sodium.