Metal Complex Host Research Articles

Facile preparation of Ni/Al2O3 catalytic formulations with the aid of cyclodextrin complexes: Towards highly active and robust catalysts for the direct amination of alcohols

A series of Ni/Al2O3 catalysts with variable Ni loading (2–20 wt%) were prepared by aqueous wet impregnation of a nitrate precursor using native cyclodextrins as metal complex hosts. The impact of β-CD was carefully characterized at different stages of the preparation by a set of complementary techniques including TG-MS analysis, mass spectrometry, X-ray diffraction, temperature-programmed reduction, CO pulse chemisorption, X-ray photoelectron spectroscopy and electron microscopy. It was found that the use of cyclodextrins afforded a much higher Ni dispersion and narrower distribution of Ni particle sizes, as well as a much higher availability of reduced surface Ni species. As a result, the cyclodextrin-assisted catalysts exhibited enhanced catalytic properties in the direct amination of benzyl alcohol with aniline and 1-octanol with ammonia, both operated via the hydrogen borrowing mechanism. Furthermore, the use of cyclodextrins allowed a significant improvement of the robustness of the catalysts by mitigating the nickel leaching during reaction.

Second-sphere interaction of anions with a weakly binding metal complex host: probing the effect of counteranions

The reaction of [Re(OTf)(CO)5] with N-methylimidazole (MeIm) afforded [Re(CO)3(MeIm)3]OTf (1). The reactions of 1 with KPF6, NaBPh4 and NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl) afforded [Re(CO)3(MeIm)3]PF6 (2) [Re(CO)3(MeIm)3]BPh4 (3) and [Re(CO)3(MeIm)3]BAr'4 (4) respectively. An analogous reaction using N-phenylimidazole (PhIm) yielded [Re(CO)3(PhIm)3]BAr'4 (7). These new compounds were characterized by IR and NMR, and the structures of 1 and 2 were determined by X-ray diffraction. Compounds [Re(CO)3(MeIm)3]2[PtCl6] (5), [Re(CO)3(MeIm)3][HSO4] (6), [Re(CO)3(PhIm)3][Br] (8) and [Re(CO)3(PhIm)3][NO3] (9) were crystallized from equimolar mixtures of either 4 or 7 and the tetrabutylammonium salt of the corresponding anion, and their structures were determined by X-ray diffraction. The solution behavior of 1-4, 7 toward several anions was studied spectroscopically, including the quantitative determination of binding constants by 1H NMR. The cationic tris(imidazole)complexes are stable against imidazole-by-anion substitution, and the main hydrogen bonding interactions involve the imidazole NC(H)N groups. The binding constants for compounds 1-4 with several external anions follow the order 1<2<3<4, indicating that the strength of the cationic complex-counteranion interaction follows the order OTf(-) > PF6(-) > BPh4(-) > BAr'4(-).

Nickel(II) and zinc(II) dibenzoylmethanates: molecular and crystal structure, polymorphism, and guest- or temperature-induced oligomerization.

Four forms of nickel(II) and two of zinc(II) dibenzoylmethanates have been isolated and characterized with powder and single-crystal X-ray diffraction analyses, differential scanning calorimetry, magnetic susceptibility measurements, and solid-state 13C cross-polarization/magic angle spinning NMR. Nickel dibenzoylmethanate, Ni(DBM)2 (DBM = PhCOCHCOPh-), forms three polymorphic forms (light-green, brown, and green) and a fourth clathrate form with guest benzene included. The light-green polymorph is metastable. Substituted benzenes induce recrystallization of the polymorph into a stable brown form (C30H22NiO4; a = 26.502(3) A, b = 5.774(1) A, c = 16.456(2) A, beta = 116.03(1) degrees; monoclinic, C2/c; Z = 4). Unlike the other forms, the brown form is diamagnetic and is comprised of monomers of the low-spin [Ni(DBM)2] complex. The Ni(II) is chelated by two DBM ligands in a square planar environment by four donor oxygen atoms. When heated, the brown form transforms to a green form which is stable above 202 degrees C (C90H66Ni3O12; a = 13.819(2) A, b = 16.252(2) A, c = 17.358(2) A, beta = 108.28(1) degrees; monoclinic, P2(1)/n; Z = 2). This polymorph is formed by van der Waals packing of trimers [Ni3(DBM)6] containing linear Ni3 clusters with an Ni-Ni distance of 2.81 A. The cluster is surrounded by six DBM ligands, providing a distorted octahedral environment about each Ni by six oxygen atoms. Benzene stabilizes the trimeric structure at room temperature, forming a [Ni3(DBM)6].2(benzene) inclusion compound (Ni-Ni distance of 2.83 A) with guest benzene molecules located in channels (C90H66Ni3O12 + 2(C6H6); a = 17.670(2) A, b = 20.945(3) A, c=11.209(2) A, beta = 102.57(1) degrees; monoclinic, P2(1)/c; Z = 2). Zinc dibenzoylmethanate has been prepared in two polymorphic forms. The monomeric form contains [Zn(DBM)2] molecules with the zinc center in a distorted tetrahedral environment of four oxygens from the two chelated DBMs (C30H22O4Zn; a = 10.288(2) A, b = 10.716(2) A, c = 12.243(2) A, alpha = 89.19(1) degrees, beta = 75.39(1) degrees, gamma = 64.18(1) degrees; triclinic, P1; Z = 2). Another, dimeric form contains [Zn2(DBM)4] species, with two zinc atoms separated by a distance of 3.14 A and each zinc coordinated by five oxygen atoms (C60H44O8Zn2; a = 25.792(3) A, b = 7.274(1) A, c = 24.307(2) A, beta = 90.58(1) degrees; monoclinic, C2/c; Z = 4). The polymorphic variety of the title complexes and the peculiarities of the Ni(II) and Zn(II) coordination environments are discussed in the context of using the complexes as precursors for new metal complex hosts.

4-Vinylpyridine-Modified Nickel and Cobalt Dibenzoylmethanates as New Hosts: Inclusions with Carbon Tetrachloride and Chlorobenzene

Bis(4-vinylpyridine)bis(dibenzoylmethanato)metal(II), [M(ViPy)2(DBM)2] (M = Ni(II), Co(II); ViPy = 4-Vinylpyridine; DBM = C6H5COCHCOC6H5 −, dibenzoylmethanate) is a new metal-complex host. Its inclusions with carbon tetrachloride (host:guest = 1:2; triclinic, P 1, Z = 1) and chlorobenzene (host:guest = 1:1; monoclinic, P2 1 /c, Z = 4) are consistent with the van der Waals packing of neutral complex (host) and solvent (guest) molecules. In the host unit, four oxygens from two chelate DBM-units provide a square-planar environment around the metal center that is extended to octahedral coordination by two apical nitrogens from two vinylpyridine moieties in the trans-position. In the carbon tetrachloride inclusions, the host traps two guest molecules in large prolate spheroidal cavities. In the chlorobenzene inclusions, guest species are located inside 8-shaped serpentine channels along the y-axis. The nickel and cobalt versions of the inclusion compounds were found to be very similar.

Modified Metal Dibenzoylmethanates and their Clathrates. Part I. Clathration Ability of dipyridinebis(dibenzoylmethanato)nickel(II), a Novel Metal-Complex Host [1

The title complex, [NiPy2(DBM)2] (DBM = C6H5CO CHCOC6H5, dibenzoylmethanate), entraps solvent molecules upon crystallization. Six clathrates of four structural types have been studied by single-crystal X-ray diffraction (guest, host:guest molar ratio, crystal system, space group, formula units per unit cell): (I) carbon tetrachloride, 1:2, orthorhombic, P212121, Z = 4; (II) pyridine, 1:2, monoclinic, C2/c, Z = 8; (III) benzene, 1:1, monoclinic, C2/c, Z = 8; (IV) chlorobenzene, 1:1, monoclinic, C2/c, Z = 8; (V) chloroform, 1:2, monoclinic, P21/n, Z = 2; (VI) tetra-hydrofuran, 1:2, monoclinic, P21/n, Z = 2. A non-clathrate form of the complex (VII) was obtained from acetone; it is triclinic, P1, Z = 1. The compounds I-VII are consistent with van der Waals type of packing. The complex unit is formed by octahedral coordination to nickel of four oxygen and two nitrogen atoms from two chelate DBM and two pyridine molecules, respectively. In all seven compounds the host complex is trans-configured. Complexes of similar composition but with Zn (VIII) and Cd (IX) replacing Ni have been also studied for comparison: they are monoclinic, P21, Z = 2, with a cis-configured complex unit, and they do not form inclusion compounds with above guests.

The metal complex host catena-[(1,2-diaminopropane)-cadmium(II) tetracyanonickelate(II)] which provides channel cavities for straight- and branched-chain aliphatic guests

A number of inclusion compounds [(pn)Cd(CN)4Ni]·nG (pn = 1,2-diaminopropane; n= 0.3–0.5) have been prepared for various straight-and branched-chain aliphatic guest molecules (G), which are accommodated in the three-dimensional structure of the metal complex host. This structure contains channel cavities surrounded by tetracyanonickelate(II) moieties linked alternately to the Cd which is chelated by the pn. The inclusion compounds are grouped into two types, U- and T-type, according to the shape of the channel revealed by their single-crystal structures. In the monoclinic U-type structure the point-symmetric arrangement of the pn chelate rings provides a snake-like channel, analogous to the spiral ones in urea inclusion compounds, for the straight-chain aliphatic guests pentane, hexane, heptane, diethyl ether, ethane-1,2-diol, 1-bromo-butane and -pentane. In the orthorhombic T-type structure the mirror-symmetric arrangement of the pn chelate rings results in nodal channels, similar to those in thiourea inclusion compounds for 1,1,2,2-tetrachloroethane, 2-chlorobutane, 1,2-dichloropropane, PriOH, 1,2-dichloro- and 1,2-dibromo-ethane and 1,3-dichloropropane. For the straight-line dihalogenoalkane guests the halogen atoms appear to contribute to the preference for the nodal channel by formation of hydrogen bonds with the pn-amino group.

Thermoanalytical investigation of the guest-release process in aromatic-guest clathrates of three-dimensional metal complex hosts

The guest-release process was investigated in terms of the activation energy evaluated by thermogravimetry for the en-Td-type clathratescatena-μ-[catena-μ-(ethylenediamine)cadmium(II) tetra-μ-cyanocadmate(II) or -mercurate(II)]-benzene(1/2), -benzene-d6(1/2), and -pyrrole(1/2), the Hofmannen-type clathratescatena-[catena-μ-(ethylenediamine)cadmium(II) tetra-μ-cyanonickelate(Il)]-benzene (1/2) and -pyrrole(1/2), the Hofmann-pn-type clathratecatena-[catena-μ-(dl- orl-propylenediamine (cadmium(II) tetra-μ-cyanonickelate(II)]-pyrrole(2/3), and the pn-Td-type clathratescatena-[catena-μ-(dl-propylenediamine) or -(l-propylenediamine)cadmium(II) tetra-μ-cyanocadmate(II)]-benzene(2/3). Values of the activation energy are correlated with the structural change in the metal complex host accompanied by the release of the guest molecules. The crystal structure ofcatena-[ethylenediaminecadmium tetra-μ-cyanonickelate(II)], the residual host of the Hofmann-en-type, has been analyzed to elucidate the correlation.

Novel series of clathrate compounds of the three-dimensional metal complex hosts (N-methyl-1,3-diaminopropane)cadmium(II) tetracyanonickelate(II), (N, N-Dimethyl-1,3-diaminopropane)cadmium(II) Tetracyanonickelate(II), and (2-Hydroxyethylmethylamine) cadmium(II) Tetracyanonickelate(II)

The clathrate compounds of the title three-dimensional metal complex hosts have been prepared with various aliphatic, alicyclic, and aromatic guest molecules. The typical structure has been demonstrated for a cyclohexane clathrate (N-methyl-1,3-diaminopropane)cadmium(II) tetracyanonickelate(II)-cyclohexane(2/1) by X-ray single crystal analysis. The powder X-ray diffraction data were assigned for the other clathrates to the tetragonal systems isostructural to the cyclohexane clathrate in which the box-like cavity with the approximate dimensions of 7 × 7 × 5 A3 accommodates the guest molecule.

Catena-μ-(1,9-Diaminononane)cadmium(II) Array in the Crystal Structure of catena-[Bis-catena-μ-(1,9-diaminononane)cadmium(II) cis-Di-μ-cyano-dicyanonickelate(II)]-(2,4-Xylidine) (1/2) Different from That in the 2,3-Isomer Analog

Abstract In a novel three-dimensional host framework of the title inclusion compound the ambidentate 1,9-diaminononane (danon) makes a two-dimensional catena-μ-network with Cd atoms in contrast with the catena-bis-μ-danon double-1D chain structure in the 2,3-xylidine analog. The 3D framework of the metal-complex host is accomplished by catena-μ-dicyano linkage of –NCNi(CN)2CN– between adjacent networks.

Novel Three-dimensional Metal-complex Host Structures of catena-[Propylenediaminecadmium(II) Tetra-μ-cyanonickelate(II)] and catena-[Propylenediaminecadmium(II) Tetra-μ-cyanocadmate(II)

Abstract Two novel metal-complex host structures, consisting of the three-dimensional linkages between square-planar tetracyanonickelate(II) or tetrahedral tetracyanocadmate(II) and propylenediamine-chelated octahedral cadmium(II), have been demonstrated for the 1,2-dichloroethane inclusion compounds.

Accommodation of an aliphatic guest molecule in hofmann-diaminooctane-type host. A model structure of a pillared intercalation compound

catena-[catena-μ-(1,8-Diaminooctane)cadmium(II) tetra-μ-cyanonickelate(II)]-(1-hexanol)(1/1) has been prepared as the first example of an aliphatic guest clathrate of the Hofmann-type and analogous metal complex hosts. The clathrate crystallizes in the monoclinic space groupP2/m,a=11.470(2),b=7.782(1), andc=6.945(1) A, β=105.29(1)°,Z=1;R=0.043 for 1865 reflections. The structure presents a model of pillared intercalation compounds formed between layers of metal complex sheets pillared by α,ω-ambidentaten-alkaneskeletal ligands andn-alkyl derivative guests.

The crystal structures of ?,?-diaminoalkanecadmium(II) tetracyanonickelate(II)-aromatic molecule inclusion compounds. IV. (1,6-Diaminohexane)cadmium(II) tetracyanonickelate(II)-m-toluidine(1/1),-p-toluidine(1/1), and-2,4-xylidine(1/1) clathrates, and the coordination complex bis(p-toluidine) (1,6-diaminohexane)cadmium(II) tetracyanonickelate(II)

The crystal structures of the four title compounds have been analyzed by single crystal X-ray diffraction methods at room temperature. Three with a general formula Cd[NH2(CH2)6NH2]Ni(CN)4·G (G=m-toluidine,Im;p-toluidine,Ip; and 2,4-xylidine,Ix) are the inclusion compounds of the respective aromatic molecules in the three-dimensional metal complex host (1,6-diaminohexane)cadmium(II) tetracyanonickelate(II). The remaining one is a coordination complex ofp-toluidine, bis(p-toluidine) (1,6-diaminohexane)cadmium(II) tetracyanonick-elate(II),II, Im, Ix, andII crystallize under similar experimental conditions;Ip is obtained using thep-toluidinemesitylene mixture at higher dilution than that used forII. Im crystallizes in the tri linic space group\(P\bar 1\), witha=9.725(2),b=7.598(1),c=7.177(1) A, α=90.44(1), β=98.80(1), γ=95.70(1)o, andZ=1 (the final conventionalR=0.037 for 3526 reflections);Ip: monoclinic,P2/m,a=9.540(2),b=7.611(1),c=7.120(1) A, β=100.95(1)o, andZ=1 (R=0.027 for 1700 reflections);Ix: monoclinic,P2/m,a=9.628(2),b=7.613(1),c=7.122(1) A, β=100.01(1)o, andZ=1 (R=0.049 for 2704 reflections);II: monoclinic,P21/n,a=12.107(3),b=10.117(2),c=12.471(3) A, β=113.67(2)o, andZ=2 (R=0.037 for 2616 reflections).

Two Novel Metal-complex Host Structures Consisting of Cyanocadmate Coordination Polyhedra. Clay-like and Zeolite-like Structures

Abstract The metal-complex host of a clathrate compound [Cd3{NH(CH3)2(CH2)3NH2}(CN)7]·C6H5F has a layered structure like a clay consisting of the linkage of tetrahedral Cd(CN)4 and Cd(CN)3(NC), and octahedral Cd(NC)5[NH2(CH2)3NH(CH3)2) coordination polyhedra. The host of another clathrate [Cd3(CN)7]·{NH(CH3)2(CH2)3NH2}·(CH2ClCH2Cl) has a three-dimensional structure like a zeolite comprised of the linkage of tetrahedral Cd(CN)4 and Cd(CN)3(NC), and octahedral Cd(NC)6 coordination polyhedra; the 3-(dimethylammonio)propylamine is accommodated as a cationic guest in the cavity formed in the host structure.

Inclusion Selectivity for Aromatic Guests in catena-[Bis-(dimethylamine)cadmium(II) tetra-μ-cyanonickelate(II)] Host Clathrate

Inclusion selectivity has been examined for xylene isomers and benzene in the Hofmann-dma-type Cd[NH- (CH3)2]2Ni(CN) 4 metal complex host. This has a layered structure of a two-dimensionally extended cyanometal complex network with the dimethylamine ligands protruding up and down from the network. The o-isomer is preferentially enclathrated in the metal complex host from the mixtures of xylene isomers, but the presence of benzene in the mixture makes the p-isomer more preferable. Benzene is enriched from the mixtures with xylene isomers at very low concentrations. The selectivity behavior is discussed based on the crystal structures of the relevant clathrates.

Three-dimensional metal complex hosts built of ?,?-(long-carbon-chain)-diaminoalkane ligand bridging two-dimensional cyanometal complex network: Hofmann-diaminoalkane-type clathrates

We have been developing systematically the chemistry of Hofmann-type and related clathrate compounds. Several modifications of the metal complex host structures have been derived from that of the Hofmann-type by replacing the ammine ligands by amines or diamines, and/or the square-planar tetracyanometallate by tetrahedral one [1], However, their structures were substantially similar to that of the Hofmann-type: the volume of cavity was barely large enough to accommodate such small aromatic molecule as those enclathrated in the Hofmann-type host.

Crystal structures of ethylenediaminecadmium(II) tetracyanocadmate(II)-benzene(1/2) and ethylenediaminecadmium(II) tetracyanocadmate(II)

The crystal structure of ethylenediaminecadmium(II) tetracyanocadmate(II)-benzene(1/2),I, has been redetermined based on 1632 reflections collected anew for the crystal coated with epoxy resin, with a final conventionalR=0.038;I crystallizes in space groupP4222, witha=b=8.265(1) andc=15.512(3) A, andZ=2. Ethylenediaminecadmium(II) tetracyanocadmate(II),II, is concluded to be identical with the residual metal complex host ofI, remaining after the liberation of the guest benzene molecules;II crystallizes from an aqueous solution containing bis- or tris-ethylenediaminecadmium(II) tetracyanocadmate(II) in space groupI41/acd, witha=b=14.366(1) andc=23.771(4) A, andZ=16; refinement led to a conventionalR=0.043 for 1181 reflections. The bridging ethylenediamine ligand inI turns to a chelating one inII; dissociation and recombination should occur in the coordination sphere of the six-coordinate cadmium atom, whenII is derived fromI by the liberation of the guest molecules.

INCLUSION OF AROMATIC GUEST MOLECULES WITH BULKY SUBSTITUENTS IN LAYERED METAL COMPLEX HOST trans-BIS(DIMETHYLAMINE)CADMIUM(II) TETRA-catena-μ-CYANONICKELATE(II)

Abstract A novel type of the metal complex host Cd(NH(CH3)2)2Ni(CN)4 derived by replacing the NH3 in Hofmann-type host Cd(NH3)2Ni(CN)4 by NH(CH3)2includes the benzene derivatives with several bulky substituents between the layered structure, the guest molecules which have never been enclathrated into Hofmann-type and the analogous hosts.

Recent developments in the chemistry of hofmann-type and the analogous clathrates

Based on the structural features of Hofmann-type clathraces M(NH 3) 2M'(CN) 4 · 2G (M = a divalent metal in six-coordination, M' = a divalent metal in square-planar coordination, G = a small aromatic guest molecule), several series of the analogous clathrates have been derived by appropriate replacements of the host moieties. These clathrates are designated with a general formula Cd (diam)M'(CN) 4 · n G where diam refers to diammine, an ambident diamine or monoethanolamine (mea), or a pair of unidencate mea's, M'(CN) 4 is a square-planar or a tetrahedral tetracyanometallate(II), and G is a small aromatic guest molecule. The number of guest molecules, n , varies stepwise from 2 through 3 2 to 1 depending on the bulkiness of diam ligand which builds up the host structure. Their structural features are discussed on the two- and three-dimensional networks of the metal complex hosts. The historical background is also reviewed briefly.

Aromatic Guest Molecules Enclathrated in Hofmann‐Type and Analogous Clathrates

AbstractThe structural features of the clathrate compounds with a general formula M(diam)M'(CN)4. 2G (M = a divalent metal in six‐coordination, diam = (NH3)2 or a diamine, M'(CN)4 = a square‐planar or tetrahedral teracyanometallate(II), G = an aromatic guest such as C4H5N, C4H4S, C6H6, C6H5NH2, etc.) are discussed from the viewpoint of the arrangement and orientation of the guest molecules in relation to the structure of the metal complex hosts. The layer structure of the Hofmann‐type host M(NH3)2M'(CN)4 (M'(CN)4 = a square‐planar moiety) enclathrates the guest molecules with a fixed orientation, but the three‐dimensional host structures built up of tetrahedral M'(CN)4 moieties provide considerably flexible and expanded cavities for guest molecules. The cavity in the three‐dimensional host may be seen as a container of a guest molecule with a chemically inactive wall and with a volume slightly larger than that of the molecule; in the container the guest molecule has freedom of motion to a certain extent. It can be expected that appropriate selection of the host constituents will afford the host lattice a stereospecific function and/or a function of keeping chemically‐active species stable in the cavity of the clathrate structure.

Benzene clathrates with a novel kind of metal complex host lattice. Cd(en)Cd(CN)4.2C6H6 and Cd(en)Hg(CN)4.2C6H6

Benzene clathrates with a novel kind of metal complex host lattice. Cd(en)Cd(CN)4.2C6H6 and Cd(en)Hg(CN)4.2C6H6