C(arenium)-C(alkyl) bond making and breaking: key process in the platinum-mediated C(aryl)-C(alkyl) bond formation. Analogies to organic electrophilic aromatic substitution.

The reaction of cationic platinum aqua complexes 2 [Pt(C(6)H(2)[CH(2)NMe(2)](2)-E-4)(OH(2))](X') (X' = SO(3)CF(3), BF(4)) with alkyl halides RX gave various air-stable arenium complexes 3-5 containing a new C-C bond (R = Me, 3; Et, 4; Bn, 5). Electron-releasing oxo-substituents on the aromatic ligand (E = e.g., OH, b; OMe, c) enhance the reactivity of the aqua complex 2 and were essential for arenium formation from alkyl halides different from MeX. This process is initiated by oxidative addition of alkyl halides to the platinum(II) center of 2, which affords (alkyl)(aryl) platinum(IV) complexes (e.g., 9, alkyl = benzyl) as intermediates. Spectroscopic analyses provided direct evidence for a subsequent reversible 1,2-sigmatropic shift of the alkyl group along the Pt-C(aryl) bond, which is identical to repetitive C(arenium)-C(alkyl) bond making and breaking and concerted metal reduction and oxidation. Temperature-dependent NMR spectroscopy revealed DeltaH degrees = -1.3 (+/- 0.1) kJ mol(-1), DeltaS degrees = +3.8 (+/- 0.2) J mol(-1) K(-1), and DeltaG degrees (298) = -2.4 (+/- 0.1) kJ mol(-1) for the formation of the arenium complex 5b from 9 involving the migration of a benzyl group. The arenium complexes were transformed to cyclohexadiene-type addition products 7 or to demetalated alkyl-substituted arenes, 8, thus completing the platinum-mediated formation of a sp(2)-sp(3) C-C bond which is analogous to the aromatic substitution of a [PtX](+) unit by an alkyl cation R(+). The formation of related trimethylsilyl arenium complexes 6 suggests arenium complexes as key intermediates, not only in (metal-mediated) sp(2)-sp(3) C-C bond making and breaking but also in silyl-directed cyclometalation.

Multiple use of soluble metallodendritic materials as catalysts and dyes.

Different sizes of core-functionalized metallodendritic wedges were prepared by anchoring sensor-active arylplatinum(II) sites at the focal point of Fréchet-type polyether dendritic wedges of various generations. The strong color of these metallodendrimers in the presence of SO2 was used to assess the permeability of nanofiltration membranes (molecular weight cut-off of 400 dalton) at ambient pressure. A primary result of these studies is that dendrimers do not have to be exceptionally large for successful retention. Hence, nanofiltration, membrane-capped. immersion vials were developed, which operate as sensor devices when loaded with metallodendrimers with good retention properties. Appropriate substitution of the dye site at the focal point of these metallodendritic wedges by a catalytically active group afforded dendritic catalysts that exhibit essentially the same physical properties (shape, retention) as the corresponding dyefunctionalized dendritic wedges. When this homogeneous catalyst is compartmentalized in membrane-capped vials, a unique and convenient method for its retrieval from product solutions is available. Moreover, such immobilized metallodendritic catalysts can be regenerated and stored for months without losing their activity; this provides access for the development of novel sustainable homogeneous catalysts.

Selective liquid-phase semihydrogenation of functionalized acetylenes and propargylic alcohols with silica-supported bimetallic palladium-copper catalysts.

Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated.

Polycationic (mixed) core-shell dendrimers for binding and delivery of inorganic/organic substrates.

The convergent synthesis of a series of polycationic aryl ether dendrimers has been accomplished by a convenient procedure involving quantitative quaternarization of aryl(poly)amine core molecules. The series has been expanded to the preparation of the first polycationic, mixed core-shell dendrimer. All these dendrimers consist of an apolar core with a peripheral ionic layer which is surrounded by a less polar layer of dendritic wedges. These cationic, macromolecular species have been investigated for their ability to form assemblies with (anionic) guest molecules. The results obtained from UV/Vis and NMR spectroscopies, and MALDI-TOF-MS demonstrate that all the cationic sites throughout the dendrimer core are involved in ion pair formation with anionic guests giving predefined guest/host ratios up to 24. The large NMR spectroscopic shifts of resonances correlated with the groupings located in the core of the dendrimers, together with the relaxation time data indicate that the anionic guests are associated with the cationic core of these dendrimers. The X-ray molecular structure of the octacationic, tetra-arylsilane model derivative [Si(C6H3[CH2NMe3](2)-3,5)4]8+. 8I- shows that the iodide counterions are primarily located near the polycationic sphere. The new polycationic dendrimers have been investigated for their catalytic phase-transfer behavior and substrate delivery over a nanofiltration membrane.

Platinum- and palladium-catalysed Kocheshkov redistribution of dialkyltin dichlorides or tetraalkyltins with tin tetrachloride.

The Kocheshkov redistribution reaction of tetraalkyltin or dialkyltin dichlorides with tin tetrachloride is effectively catalysed by platinum(II) or palladium(II) phosphine complexes, yielding alkyltin trichlorides in high yield and with high selectivity.

Detection of ppm quantities of gaseous SO2 by o9rganoplatinum dendritic sites immobilised on a quartz microbalance.

Sensor devices for the detection of low quantities of SO2 gas have been constructed which comprise organoplatinum receptor sites for the selective recognition of SO2 and a quartz crystal microbalance for the detection of small mass changes at the receptor sites.

New peptide labels containing covalently bonded platinum(II) centers as diagnostic biomarkers and biosensors.

[reaction: see text] Water- and acid-resistant arylplatinum(II) complexes have been covalently bonded to the N-terminus of L-valine, thus providing organometallic biomolecules with excellent stability properties. Owing to the (195)Pt nucleus (I = (1)/(2)), these building blocks are potentially versatile biomarkers (e.g., MRI). Moreover, they display efficient in vitro biosensor characteristics since they detect SO(2) gas selectively and fully reversibly by an instantaneous change of the spectroscopic properties including a diagnostic (195)Pt NMR signal.

Functionalized carbosilane dendritic species as soluble supports in organic synthesis.

A new methodology, which is compatible with the use of reactive organometallic reagents, has been developed for the use of carbosilane dendrimers as soluble supports in organic synthesis. Hydroxy-functionalized dendritic carbosilanes Si[CH2CH2CH2SiMe2(C6H4CH(R)OH)]4 (G0-OH, R = H or (S)-Me) and Si[CH2CH2CH2Si[CH2CH2CH2SiMe2(C6H4CH(R)OH)]3]4 (G1-OH, R = H or (S)-Me) were prepared and subsequently converted into the esters Si[CH2CH2CH2SiMe2(C6H4CH(R)OC(O)CH2Ph)]4 (R = H or (S)-Me) and Si[CH2CH2CH2Si[CH2CH2CH2SiMe2(C6H4CH(R)OC(O)CH2C6H4 R')]3]4 (R = H and R' = H or R = (S)-Me and R' = H or R = H and R' = Br). As an example the latter compound was functionalized under Suzuki conditions. The functionalized carboxylic acid was obtained in high yield after cleavage from the dendritic support. Moreover, the ester functionalized dendrimers were converted to the corresponding zinc enolates followed by a condensation reaction with an imine to a beta-lactam in excellent yield and purity. Furthermore, it was demonstrated that a small combinatorial library of beta-lactams could be prepared starting from a carbosilane dendrimer functionalized with different ester moieties. These results show that carbosilane dendrimers can be applied as soluble substrate carriers for the generation of low molecular weight organic molecules. In combination with nanofiltration techniques, separation and recycling of the dendrimers can be realized.

Organoplatinum crystals for gas-triggered switches

Considerable effort is being devoted to the fabrication of nanoscale devices. Molecular machines, motors and switches have been made, generally operating in solution, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion-reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches.

Diagnostic organometallic and metallodendritic materials for SO2 gas detection: reversible binding of sulfur dioxide to arylplatinum(II) complexes

A series of square-planar platinum(II) complexes of the N,C,N'-terdentate-coordinating monoanionic "pincer" ligand, [PtX(4-E-2,6-[CH2NRR']2-C6H2](X=Cl, Br, I, tolyl; R, R'=Et, Me; E=H, OH, OSiMe2tBu) has been prepared. In the presence of sulfur dioxide, these complexes spontaneously adsorb this gas to form penta-coordinated adducts. Solid-state crystal-structure analyses of the SO2 adducts 8c (X=I, R=R=Me, E=OSiMe2tBu) and 11 (X=Cl, R=R'=Me, E=OH) show a square-pyramidal geometry around the metal center with SO2 in the apical position. Most interestingly. the adduct 11 forms similar Pt-Cl... H-O hydrogen-bonded alpha-type networks as the corresponding SO2-free complex 5. The conservation of the supramolecular information (hydrogen-bonded self-assembly) throughout a reaction (SO2 adsorption) is unprecedented in crystal engineering. Adduct formation in the solid state or in solution is fast and reversible and is indicated by a characteristic color change of the material from colorless to bright orange. Since facile methods have been developed to remove SO2 from the adducts and to regenerate the square-planar starting complexes, these complexes fulfill several essential prerequisites of sensor materials for repeated diagnostic SO2 detection. The platinum sensors have been found to be highly selective for sulfur dioxide and particularly sensitive for submilimolar to molar gas quantities. Their response capacity is tuneable by electronic and steric modifications of the ligand array by introduction of, for example, different substituents on the nitrogen donors. The periphery of dendrimers is shown to be an appropriate macromolecular support for anchoring the detection-active sites, thus allowing full recovery of the sensor materials for repeated use. By using this concept, metallo-dendrimers 3 and 15 have been prepared. Owing to the dendritic connectivity, these sensors are suitable for repetitive qualitative and quantitative detection of small amounts of SO2.

Synthesis of periphery-functionalized dendritic molecules using polylithiated dendrimers as starting material

A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction.

Synthesis and properties of a novel family of fluorous triphenylphosphine derivatives

A novel approach to the preparation of perfluorotail-functionalized triarylphosphines using a p-silyl substituent as the branching point has been developed. This approach enabled the attachment of between three and nine perfluorotails per phosphorus atom, resulting in the production of highly fluorous tris[p-(1H,1H,2H, 2H-perfluoroalkylsilyl)aryl]phosphines, P[C(6)H(4)-p-SiMe(3)(-)(n)()(CH(2)CH(2)C(x)()F(2)(x)()(+1))(n)()](3) (n = 1, 2, 3; x = 6, 8), containing between 50 and 67 wt % fluorine. (31)P NMR studies indicate that the phosphorus atoms, and consequently the sigma-donor and pi-acceptor properties of these phosphines, are not influenced by the electron-withdrawing perfluoroalkyltails. The fluorous triarylphosphines are readily soluble in fluorous solvents and display fluorous phase preference in several fluorous biphasic systems. The phase partitioning of these fluorous ligands, as well as their donor properties, is discussed in relation to their potential for fluorous biphasic catalyst separation.

The "Dendritic Effect" in Homogeneous Catalysis with Carbosilane-Supported Arylnickel(II) Catalysts: Observation of Active-Site Proximity Effects in Atom-Transfer Radical Addition.

Advantages of homo- and heterogeneous catalysts are united in metallodendritic molecules where nickel-based catalysts are bound to carbosilane dendrimers. The first direct indication of a "dendritic effect" in the redox catalysis behavior is described: variation of the dendrimer support controls the proximity of the Ni(II) centers, which in turn controls catalytic activity. Catalyst deactivation, by means of Ni(III) formation, can be avoided by a larger separation of the Ni(II) centers (see picture).

Phosphino carboxylic acid ester functionalized carbosilane dendrimers: nanoscale ligands for the Pd-catalyzed hydrovinylation reaction in a membrane reactor

Phosphino carboxylic acid ester terminated G(0) compounds Si(CH(2))(3)SiMe(2)(C(6)H(4)CH(2)OC(O)(CH(2))(n)()CH(2)PPh(2)(4) (9a and 9b; n = 1, 2) and the carbosilane dendrimers Si(CH(2))(3)Si((CH(2))(3)SiMe(2)(C(6)H(4)CH(2)OC(O)(CH(2))(n)()CH(2) PPh(2))(3)(4) (10a and 10b; n = 1, 2) have been prepared as hemilabile nanoscale ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was carried out in a continuously operated nanofiltration membrane reactor. Under continuous conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II) precursor.

Vanadium(IV) and -(V) complexes with O,N-chelating aminophenolate and pyridylalkoxide ligands.

Two different monoanionic O,N-chelating ligand systems, i.e., [OC6H2(CH2NMe2)-2-Me2-4,6]- (1) and [OCMe2([2]-Py)]- (2), have been applied in the synthesis of vanadium(V) complexes. The tertiary amine functionality in 1 caused reduction of the vanadium nucleus to the 4+ oxidation state with either [VOCl3], [V(=NR)Cl3], or [V(=NR)(NEt2)3] (R = Ph, (3a, 5a), R = p-Tol (3b, 5b)), and applying 1 as a reducing agent resulted in the synthesis of the vanadium(IV) complexes [VO(OC6H2(CH2NMe2)-2-Me2-4,6)2] (4) and [V(=NPh)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (6). In the case of [V(=N-p-Tol)(NEt2)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (7b), the reduction was sufficiently slow to allow its characterization by 1H NMR and variable-temperature studies showed it to be a five-coordinate species in solution. Although the reaction of 1 with [V(=N-p-Tol)(O-i-Pr)3] (9b) did not result in reduction of the vanadium nucleus, vanadium(V) compounds could not be isolated. Mixtures of the vanadium(V) (mono)phenolate, [V(=N-p-Tol)(O-i-Pr)2(OC6H2(CH2NMe2)-2-Me2-4,6)] (10), and the vanadium(V) (bis)phenolate, [V(=N-p-Tol)(O-i-Pr)(OC6H2(CH2NMe2)-2-Me2-4,6)2] (11), were obtained. With the pyridylalkoxide 2, no reduction was observed and the vanadium(V) compounds [VOCl2(OCMe2([2]-Py))] (12) and [V(=N-p-Tol)Cl2(OCMe2([2]-Py)] (13) were obtained. 51V NMR showed 7b and 12 to be five-coordinate in solution, whereas for 10, 11, and 13 a coordination number of 6 was found. Compounds 12 and 13 showed decreased activity compared to their nonchelated vanadium(V) analogues when applied as catalysts in ethene polymerization. Two polymorphic forms with a difference in the V-N-C angle of 12.5 degrees have been found for 6. Crystal data: 6.Et2O, triclinic, P1, a = 11.1557(6) A, b = 12.5744(12) A, c = 13.1051(14) A, alpha = 64.244(8) degrees, beta = 70.472(7) degrees, gamma = 87.950(6) degrees, V = 1547(3) A3, Z = 2; 6.C6H6, triclinic, P1, a = 8.6034(3) A, b = 13.3614(4) A, c = 15.1044(5) A, alpha = 98.182(3) degrees, beta = 105.618(2) degrees, gamma = 107.130(2) degrees, V = 1551.00(10) A3, Z = 2; 12, orthorhombic, Pbca, a = 11.8576(12) A, b = 12.6710(13) A, c = 14.722(2) A, V = 2211.9(4) A3, Z = 8.

Design of Novel Hexametallic Cartwheel Molecules from Persubstituted Benzene Compounds.

The cartwheel complexes A are novel, nano-sized hexametallic species available from persubstituted benzenes C(6)[3,5-(CH(2)Y)(2)C(6)H(3)] (Y=NMe(2), P(O)Ph(2), PPh(2), SPh). The molecular structure of A (Y=SPh, ML(n)=PdCl) shows C(3) symmetry with adjacent radial Pd-Pd separations of 7.339(2) and 8.006(2) Å and a diametrically opposed Pd-Pd separation of 15.340(2) Å. Because of their size hexametallic species such as A are potential homogeneous catalysts in organic reactions which can be recovered by nanomembrane filtration techniques.