Main-Group Element, Organic, and Organometallic Derivatives of Polyoxometalates

Synthesis, characterization and catalytic activity of a Wilkinson's type metal-organic–polyoxometalate hybrid compound

A metal-organic-polyoxometalate hybrid compound with two functional centers consisting of a rhodium(I)bis(diphenylphospine) unit connected through two alkylene bridging groups to a lacunary Keggin type polyoxometalate was synthesized and used as an effective, recyclable hydrogenation catalyst in monophasic and aqueous biphasic reaction modes.

Structure and properties of the dendron-encapsulated polyoxometalate (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], a first generation dendrizyme

Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins.

Interplay of cubic building blocks in (et6-arene)ruthenium-containing tungsten and molybdenum oxides

A series of molybdenum and tungsten organometallic oxides containing [Ru(arene)]2+ units (arene =p-cymene, C6Me6) was obtained by condensation of [[Ru(arene)Cl2]2] with oxomolybdates and oxotungstates in aqueous or nonaqueous solvents. The crystal structures of [[Ru(eta6-C6Me6]]4W4O16], [[Ru(eta6-p-MeC6H4iPr]]4W2O10], [[[Ru-(eta6-p-MeC6H4iPr)]2(mu-OH)3]2][[Ru(eta6-p-MeC6H4iPr)]2W8O28(OH)2[Ru(eta6-p-MeC6H4iPr)(H2O)]2], and [[Ru(eta6-C6Me6)]2M5O18[Ru(eta6-C6Me6)(H2O)]] (M = Mo, W) have been determined. While the windmill-type clusters [[Ru(eta6-arene)]4(MO3)4(mu3-O)4] (M = Mo, W; arene =p-MeC6H4iPr, C6Me6), the face-sharing double cubane-type cluster [[Ru(eta6-p-MeC6H4iPr)]4(WO2)2(mu3-O)4(mu4-O)2], and the dimeric cluster [[Ru(eta6-p-MeC6H4iPr)(WO3)3(mu3-O)3(mu3-OH)Ru(eta6-pMeC6H4iPr)(H2O)]2(mu-WO2)2]2- are based on cubane-like units, [(Ru(eta6-C6Me6)]2M5O18[Ru(eta6-C6Me6)(H2O)]] (M = Mo, W) are more properly described as lacunary Lindqvist-type polyoxoanions supporting three ruthenium centers. Precubane clusters [[Ru(eta6-arene)](MO3)2(mu-O)3(mu3-O)]6- are possible intermediates in the formation of these clusters. The cluster structures are retained in solution, except for [[Ru(eta6-p-MeC6H4iPr)]4Mo4O16], which isomerizes to the triple-cubane form.

Robust, Alkali-Stable, Triscarbonyl Metal Derivatives of Hexametalate Anions, [M6O19{M‘(CO)3}n](8-n)- (M = Nb, Ta; M‘ = Mn, Re; n = 1, 2)

Ten 1:1 and 2:1 complexes of [Mn(CO)(3)](+) and [Re(CO)(3)](+) with [Nb(6)O(19)](8)(-) and [Ta(6)O(19)](8)(-) have been isolated as potassium salts in good yields and characterized by elemental analysis, (17)O NMR and infrared spectroscopy, and single-crystal X-ray structure determinations. Crystal data for 1 (t-Re(2)Ta(6)): empirical formula, K(4)Na(2)Re(2)C(6)Ta(6)O(35)H(20), monoclinic, space group, C2/m, a = 17.648(3) A, b = 10.056(1) A, c = 13.171(2) A, beta = 112.531(2) degrees, Z = 2. 2 (t-Re(2)Nb(6)): empirical formula, K(6)Re(2)C(6)Nb(6)O(38)H(26), monoclinic, space group, C2/m, a = 17.724(1) A, b = 10.0664(6) A, c = 13.1965(7) A, beta = 112.067(1) degrees, Z = 2. 3 (t-Mn(2)Nb(6)): empirical formula, K(6)Mn(2)C(6)Nb(6)O(37)H(24), monoclinic, space group, C2/m, a = 17.812(2) A, b = 10.098(1) A, c = 13.109(2) A, beta = 112.733(2) degrees, Z = 2. 4 (c-Mn(2)Nb(6)): empirical formula, K(6)Mn(2)C(6)Nb(6)O(50)H(50), triclinic, space group, P1, a = 10.2617(6) A, b = 13.4198(8) A, c = 21.411(1) A, alpha = 72.738(1) degrees, beta = 112.067(1) degrees, gamma = 83.501(1) degrees, Z = 2. 5 (c-Re(2)Nb(6)): empirical formula, K(6)Re(2)C(6)Nb(6)O(54)H(58), monoclinic, space group, P2(1)/c, a = 21.687(2) A, b = 10.3085(9) A, c = 26.780(2) A, beta = 108.787(1) degrees, Z = 4. The complexes contain M(CO)(3) groups attached to the surface bridging oxygen atoms of the hexametalate anions to yield structures of nominal C(3)(v)() (1:1), D(3)(d)() (trans 2:1), and C(2)(v)() (cis 2:1) symmetry. The syntheses are carried out in aqueous solution or by aqueous hydrothermal methods, and the complexes have remarkably high thermal, redox, and hydrolytic stabilities. The Re-containing compounds are stable to 400-450 degrees C, at which point CO loss occurs. The Mn compounds lose CO at temperatures above 200 degrees C. Cyclic voltammetry of all complexes in 0.1 M sodium acetate show no redox behavior, except an irreversible oxidation process at approximately 1.0 V vs. Ag/AgCl. In contrast to the parent hexametalate anions that are stable only in alkaline (pH >10) solution, the new complexes are stable, at least kinetically, between pH 4 and pEta approximately 12.

Organic-Inorganic Hybrids Based on Polyoxometalates. 5.(1) Synthesis and Structural Characterization of Bis(organophosphoryl)decatungstosilicates [gamma-SiW(10)O(36)((RPO)(2)](4)(-)

Organophosphoryl polyoxotungstate derivatives [gamma-SiW(10)O(36)(RPO)(2)](4)(-) (R = H (1), Et (2), n-Bu (3), t-Bu (4), C(2)H(4)COOH (5), Ph (6)) have been obtained by reaction of the divacant [gamma-SiW(10)O(36)](8)(-) anion with organophosphonic acids RPO(OH)(2) in acetonitrile. These new heteropolyanions have been characterized by elemental analysis, infrared spectroscopy, multinuclear ((1)H, (29)Si, (31)P, and (183)W) NMR, and X-ray crystallography. Crystals of (NBu(4))(2)(NEt(4))H[gamma-SiW(10)O(36)(C(6)H(5)PO)(2)] (anion 6) are monoclinic, space group P2(1), with lattice constants a = 16.489(4) Å, b = 14.016(3) Å, c = 18.542(8) Å, beta = 91.30(3) degrees, and Z = 2. The hybrid anion has a structure of virtual C(2v)() symmetry with two phenylphosphonate groups grafted to the surface of the divacant tungstosilicate. (183)W and (31)P NMR spectra of NBu(4) salts in DMF solution agree with the solid-state structure and the virtual C(2)(v)() symmetry.

Synthesis, Structure, and Magnetic Properties of (n-Bu(4)N)(2)[{Ni(MeOH)(2)}(2){Mo(NO)}(2)(&mgr;(3)-OH)(2)(&mgr;-OMe)(4){Mo(5)O(13)(OMe)(4)(NO)}(2)], a New Type of Polyoxometalate Incorporating a Rhomb-like Cluster

The oxo-nitrosyl compound (n-Bu(4)N)(2)[{Na(MeOH)}Mo(5)O(13)(OMe)(4)(NO)].3MeOH reacts with various nickel(II) salts in methanol to give (n-Bu(4)N)(2)[{Ni(MeOH)(2)}(2){Mo(NO)}(2)(&mgr;(3)-OH)(2)(&mgr;-OMe)(4){Mo(5)O(13)(OMe)(4)(NO)}(2)], which has been characterized by single-crystal X-ray diffraction analysis and magnetic susceptibility measurements. This reaction shows the dual behavior of the defect Lindqvist-type species [Mo(5)O(13)(OMe)(4)(NO)](3)(-), which can act both as a ligand and as a source of the {Mo(NO)}(3+) unit. Furthermore, the reaction is reminiscent of the dissolution-precipitation of oxide supports in the preparation of supported catalysts and provides a novel illustration of the potential of polyoxometalates for probing the reactivity of oxides. The new polyoxomolybdate is made of a central rhomb-like {Ni(2)Mo(2)} cluster linked to two terminal [Mo(5)O(13)(OMe)(4)(NO)](3)(-) units, each terminal cluster being linked to a molybdenum center of the central unit through two oxo ligands. The two Ni(II) ions are coupled in a ferromagnetic way (J = 13.1 cm(-)(1)).