The tin(II) hydride [ArSn(μ-H)](Ar = CH-2,6(CH-2,4,6-Pr)) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn(Ar)R(R = ethyl or t-butylethyl), which exist either as a symmetric distannene Ar(R)SnSn(R)Ar (2a or 5a) or an unsymmetric stannylstannylene ArSnSnRAr (3a). In contrast, the less crowded Sn(II) hydride [ArSn(μ-H)] (Ar = CH-2,6(CH-2,6-Pr)) (1b) reacts with excess ethylene to give Ar(CHCH)Sn(CHCH)Sn(CHCH)(CHCH)Ar (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, -CH═CH, group. The Ar isomers of 2a and 3a, i.e., [ArSn(CH)] (2b) and ArSnSn(CH)Ar (3b) are obtained by reaction of [ArSn(μ-Cl)] with EtLi or EtMgBr. The isomeric pairs 2a and 3a are separated by crystallization at different temperatures. Variable-temperature H NMR spectroscopy indicates fast ethyl group exchange between Ar(CH)SnSn(CH)Ar (Ar = Ar (2a) or Ar (2b)) and ArSnSn(CH)Ar (Ar = Ar (3a) or Ar (3b)) with ΔG = 14.2 ± 0.65 kcal mol for 2a/3a and 14.8 ± 0.36 kcal mol for 2b/3b. The bulkier distannenes [ArSn(CHCHBu)] (Ar = Ar (5a) or Ar (5b)), obtained from 1a or 1b and t-butylethylene, dissociate to ArSnCHCHBu monomers in solution. At lower temperature, they interconvert with their stannylstannylene isomers with parameters K = 4.09 ± 0.16 for 5a and 6.38 ± 0.41 for 5b and ΔG = -1.81 ± 0.19 kcal mol for 5a and -1.0 ± 0.03 kcal mol for 5b at 298 K. The 1:1 reaction of 1a or 1b with 5a or 5b yields the unknown monohydrido species SnRHAr which has the structure ArSn-Sn(H)(CHCHBu)Ar (6a) or the monohydrido bridged ArS n(μ-H)S n(CHCHBu)Ar (6b). The latter represents the first structural characterization of a monohydrido bridged isomer of a ditetrelene.

The background of the investigation is constituted by reactive moieties and intermediates playing relevant roles on the surfaces of vanadiumoxide-based catalysts during the oxygenation/dehydrogenation of organic substrates. With the aim of modeling such species, a series of mono- and dinuclear charged and uncharged vanadium oxo complexes containing p-tert-butylated calix[4]arene and calix[8]arene ligands (denoted H4B and H8B' ', respectively, in the protonated forms) has been synthesized and characterized: PPh4[O=VB] ((PPh41), O=VB(OAc) (2), PPh4[O2V2HB' '] (3), and [mu-O(O=V(OMe))2B(Me2)] (4), where superscripts OAc and Me2 indicate that one or two protons of H4B are substituted by these residues, respectively. These compounds were analyzed both in solution and by means of single-crystal X-ray crystallography; it turned out that the crystal structures are retained on dissolution (2 changed only from the paco to the cone structure). In the case of 4, it could be shown that the bulk product consists of a mixture of two isomers (4t and 4c) differing in the relative positions of the vanadium-bound methoxy groups. Subsequently, all compounds were tested as catalysts for the oxidation of alcohols with O2. It turned out that the two dinuclear complexes efficiently catalyze the oxidation of 1-phenyl-1-propargyl alcohol and fluorenol; in addition, they even show some activity with respect to the oxidation of dihydroanthracene. This may hint to a higher activity of dinuclear sites on the surfaces of heterogeneous catalysts as well.

A ligand that offers two parallel malonate binding sites linked by a xanthene backbone, namely, Xanthmal2-, has been utilised to synthesise dinuclear FeII complex [Fe2(Xanthmal)2] (1). The reactivity of 1 in contact with O2 was investigated at -40 degrees C and room temperature. After activation of O2 through interaction with both iron centres the ligand is oxidised: at the Calpha position monooxygenation and peroxide formation occur, partially accompanied by C-C bond cleavage to yield alpha-keto ester groups. To reveal mechanistic details investigations concerning 1) peroxide decomposition, 2) the reactivity of a corresponding mononuclear complex, 3) the influence of monooxygenation of the ligand on the reactivity and 4) product formation in dependence on time were carried out. The results can be explained by postulating formation of high-valent Fe intermediates and ligand-to-metal electron transfer, and the mechanistic scheme derived includes several steps that mimic the (suggested) functioning of non-heme iron enzymes. In agreement with this proposal, ligand oxidation can also be performed catalytically. Furthermore, we show that via a competitive route [(Xanthmal)2Fe2O] (2) is formed, which is unreactive towards O2 and thus is a dead end with respect to ligand oxidation. Both compounds 1 and 2 were fully characterised, and their properties are discussed.

With the aim of modeling reactive moieties and relevant intermediates on the surfaces of vanadium oxide based catalysts during oxygenation/dehydrogenation of organic substrates, mono- and dinuclear vanadium oxo complexes of doubly deprotonated p-tert-butylated tetrathiacalix[4]arene (H4TC) have been synthesized and characterized: PPh4[(H2TC)VOCl(2)] (1) and (PPh4)2[{(H2TC)V(O)(mu-O)}2] (2). According to the NMR spectra of the dissolved complexes they both retain the structures adopted in the crystalline state, as revealed by single-crystal X-ray crystallography. Compounds 1 and 2 were tested as catalysts for the oxidation of alcohols with O(2) at 80 degrees C. Both 1 and 2 efficiently catalyze the oxidation of benzyl alcohol, crotyl alcohol, 1-phenyl-1-propanol, and fluorenol, and in most cases dinuclear complex 2 is more active than mononuclear complex 1. Moreover, the two thiacalixarene complexes 1 and 2 are in many instances more active than oxovanadium(V) complexes containing "classical" calixarene ligands tested previously. Complexes 1 and 2 also show significant activity in the oxidation of dihydroanthracene. Further investigations led to the conclusion that 1 acts as precatalyst that is converted to the active species PPh4[(TC)V==O] (3) at 80 degrees C by double intramolecular HCl elimination. For complex 2, the results of mechanistic investigations indicated that the oxidation chemistry takes place at the bridging oxo ligands and that the two vanadium centers cooperate during the process. The intermediate (PPh4)2[{H2TCV(O)}2(mu-OH)(mu-OC13H9)] (4) was isolated and characterized, also with respect to its reactivity, and the results afforded a mechanistic proposal for a reasonable catalytic cycle. The implications which these findings gathered in solution may have for oxidation mechanisms on the surfaces of V-based heterogeneous catalysts are discussed.

Highly dispersed vanadium-doped metal oxides such as VO x /ZrO 2 , VO x /SiO 2 and VO x /TiO 2 /SiO 2 with vanadium contents between 0 and 25 mole% were prepared by special bulk preparation methods (coprecipitation and sol-gel, followed by freeze-drying). Bulk and surface properties of the obtained mixed oxide solid solutions were thoroughly investigated by different analytical methods (Raman and FTIR spectroscopy, TPD, H 2 -TPR, oxygen isotope measurements etc.). Moreover, the catalytic behaviour of the oxides was studied for the example of the oxidative dehydrogenation (ODH) of propane to propylene. Independent of the preparation method, the catalytic behaviour of vanadium-doped ZrO 2 and TiO 2 phases is very similar. Both metal oxide solid solutions are very active in propane ODH whereas the catalytic activity of VO x /SiO 2 is relatively low. On the other hand, the reduction of the catalytic activity is accompanied by an improved selectivity for the formation of propylene. The correlation between the catalytic activity and the acidity of the oxide systems is discussed. Oxidation experiments with 18 O 2 clearly show that the ODH reaction occurs according to the Mars-van Krevelen mechanism. Experimental Sample preparationVanadium-doped metal oxides containing up to 25 mole% VO x were prepared by two different routes.

Reactions of the Sn(II) hydrides [ArSn(μ-H)] (1) (Ar = Ar (1a), Ar (1b); Ar = CH-2,6-(CH-2,6-Pr), Ar = CH-2,6-(CH-2,4,6-Pr)) with norbornene (NB) or norbornadiene (NBD) readily generate the bicyclic alkyl-/alkenyl-substituted stannylenes, ArSn(norbornyl) (2a or 2b) and ArSn(norbornenyl) (3a or 3b), respectively. Heating a toluene solution of 3a or 3b at reflux afforded the rearranged species ArSn(3-tricyclo[2.2.1.0]heptane) (4a or 4b), in which the norbornenyl ligand is transformed into a nortricyclyl group. H NMR studies of the reactions of 4a or 4b with tert-butylethylene indicated the existence of an apparently unique reversible β-hydride elimination from the bicyclic substituted aryl/alkyl stannylenes 2a or 2b and 3a or 3b. Mechanistic studies indicated that the transformation of 3a or 3b into 4a or 4b occurs via a β-hydride elimination of 1a or 1b to regenerate NBD. Kinetic studies showed that the conversion of 3a or 3b to 4a or 4b is first order. The rate constant k for the conversion of 3a into 3b was determined to be 3.33 × 10 min, with an activation energy E of 16.4 ± 0.7 kcal mol.

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A novel β‐diketiminato ligand precursor, LH (II), containing thioether tethers was synthesized by the reaction of acetylacetone and 2‐methylthioaniline. II was deprotonated and used in the synthesis of two iron(II) complexes, [LFeCl] (1), and [LFeOTf] (2), and one nickel(II) complex, [LNiBr] (3). All three compounds were characterized by means of single crystal X‐ray diffraction and their structures are discussed.