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Atomic XAFS on [PtCl(NCN)-Z] pincer complexes shows it to be a sensitive probe for the determination of the electron density on the metal atom, similar yet complementary to NMR.

The effect of the nature of the anion on the performance of ionic rhodium catalysts has received little attention. Herein it is shown that the use of highly fluorous tetraphenylborate anions can enhance catalyst activity in both conventional and fluorous media. For hydrogenation catalysts of the type [Rh(COD)(dppb)][X] {COD=1,5-cis,cis-cyclooctadiene; dppb=1,4-bis(diphenylphosphino)butane; X=BF4- (1a), [BPh4]- (1b), [B{C6H4(SiMe3)-4}4]- (1c), [B{C6H3(CF3)2-3,5}4]- (1d), [B{C6H4(SiMe2CH2CH2C6F13)-4}4]- (1e), [B{C6H4(C6F13)-4}4]- (1f) and [B{C6H3(C6F13)2-3,5}4]- (1 g)} the activity towards the hydrogenation of 1-octene in acetone increased in the order 1c

A shape-persistent nanosize dodecakis(NCN-PdII-aqua) complex (4b) was applied as a homogeneous catalyst in the double Michael reaction between methyl vinyl ketone and ethyl -cyanoacetate under continuous reaction conditions in a nanofiltration membrane reactor. Due to its macromolecular dimensions, the catalyst is retained in the reactor (R=99.5% determined by ICP-AAS) during catalysis. In addition, the catalyst was found to be stable under the continuous reaction conditions as a constant activity was obtained at prolonged reaction times (26 h, 65 exchanged reactor volumes). The turnover number of the catalyst was thus increased by a factor greater than 40 from 80 (batch) up to >3000 mol/mol Pd. Further development of this technology will allow an increase of the number of (industrial) catalytic processes in which homogeneous catalysts are applied.

Cupric complexes of a novel phenanthroline-phenolate ligand have strongly distorted coordination geometries and electrochemical properties conducive to modeling the spectroscopy and reactivity of the enzyme galactose oxidase.

A series of fluorous derivatives of group 10 complexes MCl2(dppe) and [M(dppe)2](BF4)2 (M = Ni, Pd or Pt; dppe = 1,2-bis(diphenylphosphino)ethane) and cis-PtCl2(PPh3)2 was synthesized. The influence of para-(1H,1H,2H,2H-perfluoroalkyl)dimethylsilyl-functionalization of the phosphine phenyl groups of these complexes, as studied by NMR spectroscopy, cyclovoltammetry (CV), XPS analyses, as well as DFT calculations, points to a weak steric and no significant inductive electronic effect. The steric effect is most pronounced for M = Ni and leads in the case of NiCl2(1c) (3c) and [Ni(1c)2](BF4)2 (7c) (1c = [CH2P{C6H4(SiMe2CH2CH2C6F13)-4}2]2) to a tetrahedral distortion from the expected square planar geometry. The solubility behavior of NiCl2[CH2P{C6H4(SiMe3-b(CH2CH2CxF2x+1)b)-4}2]2 (3: b = 1-3; x = 6, 8) in THF, toluene, and c-C6F11CF3 was found to follow the same trends as those observed for the free fluorous ligands 1. A similar correlation between the partition coefficient (P) of complexes 3 and free 1 was observed in fluorous biphasic solvent systems, with a maximum value obtained for 3f (b = 3, x = 6, P = 23 in favor of the fluorous phase).

The preparation of a series of new ligands, comprising a NCN ligand (C{6}H{2}(CH{2}NMe{2}){2}-2, 6-X-4, X=H, Br, I) substituted on the para position with a [1,2]-methanofullerene group is described. Metallation of these ligands is achieved via an oxidative addition reaction of nickel(0) or palladium(0) complexes. The first step of this reaction comprises the formation of a @p-complex between the metal center and the fullerene moiety of the ligand, which upon heating in a subsequent step is followed by oxidative addition of the NCN-halide bond to the metal center. The nickel(II) complex C{6}{0}@?C(Me)@?NCN.NiBr (9) was isolated in pure form. Low temperature NMR spectroscopy and theoretical calculations showed that the NCN moiety in 9 rotates about the (Me)C@?NCN bond at room temperature. UV-Vis spectroscopic measurements of 9 suggest that binding a metal center via a covalent metal-carbon bond to the NCN moiety does not lead to a substantial change in the electronic structure of the fullerene moiety. The cyclo voltammograms of 9 showed the absence of a Ni(II)/Ni(III) oxidation/reduction process, while the second and fourth C{6}{0} reduction potentials were anodically shifted.

A novel fluorous room-temperature ionic liquid, 1-butyl-3-methyl-imidazolium tetrakis[p-{dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl}phenyl]borate (1), was used as a solvent for the homogeneous hydrosilylation of 1-octene catalyzed by a fluorous version of Wilkinson's catalyst. The catalyst was recycled by biphasic separation with an average retention of catalyst activity of 94%. As opposed to other ionic liquids, 1 exhibits high miscibility with apolar compounds such as alkenes and resembles fluorous solvents in its phase behavior with organic solvents.

Herein we describe a structural characterisation with EXAFS of copper(I) arenethiolate complexes in both the solid and liquid state. Previously noted difficulties in the detection of the CuCu interaction have been attributed to anti-phase behaviour of different CuCu neighbour contributions. A data analysis procedure solely based on EXAFS parameters is presented which resolves these problems. A careful analysis of the individual coordination shells and the use of different k-weightings during the data analysis are shown to be an absolute necessity to obtain reliable results. During R-space fitting, the difference file technique is used to separate, examine and compare the individual contributions. Using this technique their statistical significance and correctness can be determined. Anti-phase behaviour can be detected and accounted for in this way. An additional mixed organocopper aggregate [Cu4(SAr)2(Mes)2] with different Cu sites is analysed, which proves the value of the analysis procedure described above. Moreover, this newly developed EXAFS data analysis procedure is applicable to any other EXAFS spectrum obtained. The structural analysis of these organocopper complexes with EXAFS provides information about their actual structure and dynamic behaviour in solution. The technique can now be used to obtain insights into the reactivity of these complexes and the way in which they form catalytic reaction intermediates.

Hexakis(PCP-pincer) complexes [C6{PtBr(PCP)}6] (5d) and [C6{RuCl(PCP)(PPh3)}6] (5e) were synthesized via the transcyclometalation (TCM) procedure. Mixing the hexakis(PCHP-arene) ligand 7 with six equivalents of [PtBr(NCN)] (1a) or [RuCl(NCN)(PPh3)] (1b), respectively, resulted in the selective metalation of all PCP-ligand sites and the concomitant formation of six equivalents of the NCHN-arene ligand. This procedure was found to be superior over existing metalation procedures. In addition, hexakisruthenium complex 5e was applied as homogeneous catalyst in the hydrogen transfer reactions of cyclohexanone, acetophenone and benzophenone to the corresponding alcohols. In these reactions, the activity per ruthenium center of 5e was found to be of the same order of magnitude as that of the mononuclear analogue [RuCl(PCP)(PPh3)] 3b, indicating that all ruthenium centers act as independent catalytic sites.

Herein we describe a structural characterisation with EXAFS of copper(I) arenethiolate complexes in both the solid and liquid state. Previously noted difficulties in the detection of the CuCu interaction have been attributed to anti-phase behaviour of different CuCu neighbour contributions. A data analysis procedure solely based on EXAFS parameters is presented which resolves these problems. A careful analysis of the individual coordination shells and the use of different k-weightings during the data analysis are shown to be an absolute necessity to obtain reliable results. During R-space fitting, the difference file technique is used to separate, examine and compare the individual contributions. Using this technique their statistical significance and correctness can be determined. Anti-phase behaviour can be detected and accounted for in this way. An additional mixed organocopper aggregate [Cu4(SAr)2(Mes)2] with different Cu sites is analysed, which proves the value of the analysis procedure described above. Moreover, this newly developed EXAFS data analysis procedure is applicable to any other EXAFS spectrum obtained. The structural analysis of these organocopper complexes with EXAFS provides information about their actual structure and dynamic behaviour in solution. The technique can now be used to obtain insights into the reactivity of these complexes and the way in which they form catalytic reaction intermediates.

The complex trans-PtCl(p-Tol)(SEt{2}){2} is obtained from the reaction of [Pt(p-Tol){2}(SEt{2})]{2} with PtCl{2}(SEt{2}){2} and SEt{2} in mole ratio 1:2:2. The mono(p-tolyl)platinum(II) and bis(p-tolyl)platinum(II) complexes of diethylsulfide react with 2, 2'-bipyridine to form the complexes PtX(p-Tol)(bpy) (X=p-Tol, Cl) and are useful reagents for organoplatinum chemistry. X-ray crystal structures are presented for square planar PtCl(p-Tol)(bpy) and the centrosymmetric dimer [Pt(p-Tol){2}(@m-SEt{2})]{2}.

The synthesis of enantiopure (oxo-functionalized) C{2}-symmetric NCN pincer ligands is described. A key step is the symmetric functionalization of the benzylic positions, which was achieved by enantioselective ketone reduction and subsequent stereoselective substitution protocols. The introduction of @a-alkyl substituents has a pronounced effect on the cavity for metal binding. For example, lithiation of the @a-ethyl-functionalized pincer ligand afforded mixed (alkyl)(aryl)lithium aggregates rather than dinuclear bis(aryl) lithium [Li(NCN)]{2} species as usually observed for NCN-lithium complexes. Similar effects were established for the (trans)-metalation reaction, which proceeded significantly slower when the steric demand of the @a-substituent is increased. The potential of the corresponding enantiopure palladium and ruthenium complexes as enantioselective catalyst has been probed in the asymmetric aldol condensation and hydrogen transfer reactions. The low enantiomeric excess of the products of both reactions indicated that face-discrimination of substrates is not induced by these catalysts and that the chiral information must be located in closer proximity to the metal center.

The reaction of cationic platinum aqua complexes 2 [Pt(C6H2{CH2NMe2}2-E-4)(OH2)](X') (X' = SO3CF3, BF4) 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-Caryl bond, which is identical to repetitive Carenium-Calkyl bond making and breaking and concerted metal reduction and oxidation. Temperature-dependent NMR spectroscopy revealed H = -1.3 (± 0.1) kJ mol-1, S = +3.8 (± 0.2) J mol-1 K-1, and G298 = -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 sp2-sp3 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) sp2-sp3 C-C bond making and breaking but also in silyl-directed cyclometalation.

Dit onderzoek beschrijft een serie polykationische arylether-dendrimeren, die in kwantitatieve opbrengst zijn verkregen door reactie van dendritische benzyl bromides met organosilanen die vier aryl(di)amine substituenten bevatten. Deze dendrimeren zijn opgebouwd uit een polykationische kern en een polaire buitenlaag. Tevens wordt de synthese van het eerste gemengde, polykationische dendrimeer beschreven. Dit nieuwe type dendrimeer bestaat achtereenvolgens uit een [G1] carbosilaandendrimeer kern, een poly-ionische tussenlaag en een polaire buitenlaag opgebouwd uit [G1] Fréchet type dendrons. De bindingscapaciteiten van deze dendrimeren ten aanzien van anionische gast-molekulen zijn onderzocht. Spectroscopische metingen (UV/Vis, NMR en MALDI-TOF) wijzen erop dat alle kationische centra in de dendrimeren beschikbaar zijn voor de vorming van ionparen. Zo is het mogelijk om een maximum aantal van 24 anionische gasten te binden. De grote NMR spectroscopische verschuivingen gecombineerd met relaxatiemetingen van de groepen die aanwezig zijn in de kern van de dendrimeren, duiden op een duidelijke associatie van de anionen met de kationische centra van de dendrimeren. De kristalstructuur van de octakationische model-verbinding [Si(C6H3{CH2NMe3}2-3,5)4]8+8 I- laat zien dat de (jodide) anionen zich voornamelijk in de buurt van de kationische centra bevinden. De nieuwe polykationische dendrimeren zijn gebruikt in fase-transfer katalyse en voor het transport van organische substraten door nanofiltratiemembranen. 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+8 I- 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.

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 dye-functionalized 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.

Mono- and binuclear ruthenium(II) complexes containing ligands derived from the meta-bis(phosphanyl)arene ligand 1-R-3,5-(CH2PPh2)2C6H3 [R-PCHP: R = H (5), Br (3), or Si(n-CH2CH2C8F17)3 (4)] have been synthesized and fully characterized. On reaction of equimolar amounts of the ruthenium starting material (e.g. [RuCl2(PPh3)3]) and the meta-bis(phosphanyl)arene, complexes of the type [RuCl{C6H2(CH2PPh2)2-2,6-R-4}(PPh3)] are invariably isolated, which contain only one [C6H3(CH2PPh2)2-2,6]- monoanionic ligand 3-P,C,P-bonded to Ru. Monitoring of this reaction by 1H and 31P NMR has shown it to proceed via intermediate species having an apparently 3-P,C,P-bonded PCP ligand and a second meta-bis(phosphanyl)arene ligand that is either 1-P-bonded or -1-P,1-P-bridging between two [RuCl(PCP)] units. The synthesis of the first PCP pincer-type ligand with a polyfluorinated pony tail is detailed, viz. compound 4 as well as the corresponding ruthenium complex [RuCl{(n-C8F17CH2CH2)3Si-PCP}], 7. The latter compound is soluble in fluorinated solvents and hence represents the first ruthenium pincer complex that may find use in fluorinated biphasic systems.

The concept of fluorous biphasic separation has been applied in the recycling of rhodium-based catalysts for the hydrosilylation of 1-alkenes and fluorinated 1-alkenes by following two approaches. Hydrosilylation of 1-hexene using various silanes and fluorous versions of Wilkinson's catalyst [RhCl{P(C6H4-4-SiMe2Rf)3}3] (1; Rf = CH2CH2C6F13) or [RhCl{P(C6H4-4-SiMe(Rf)2)3}3] (2; Rf = CH2CH2C8F17) in fluorous biphasic solvent systems afforded the corresponding n-hexylsilanes in high yield. The catalyst activities were similar to those obtained using conventional [RhCl(PPh3)3]. The fluorous phase containing the catalyst was recycled at least twice without noticeable loss of activity, despite the fact that 12 and 1.7% of [Rh] was lost for 1 and 2, respectively, in the first cycle. The fluorous hydride intermediate [Rh(H)(Cl)(SiCl3){P(C6H4-4-SiMe2Rf)3}2] (3; Rf = CH2CH2C6F13) was identified by NMR spectroscopy. In a reverse approach, the original Wilkinson's catalyst was used for the hydrosilylation of 1H,1H,2H-perfluoro-1-alkenes in benzene or toluene as solvent. Fluorous extraction of the products enabled recycling of the nonfluorous catalyst.

The synthesis, characterization, and reactivity of various ruthenium(II) complexes [Ru(R-PCP)(R'-PCHP)][OTf] are presented. These complexes are highly dissymmetric and show fluxional behavior in solution. They contain one monoanionic, 3-P,C,P'-tridentate-bonded bisphosphinoaryl ligand (R-PCP = [C6H2(CH2PPh2)2-2,6-R-4]-; R = H or Br) and one neutral, trans-P,P'-bidentate-bonded bisphosphinoarene ligand (R'-PCHP = C6H3(CH2PPh2)2-3,5-R'-1). The C-H bond that is ortho to both CH2PPh2 substituents of the bidentate-bonded ligand is interacting with the metal center (i.e., has an agostic contact with the cationic ruthenium center). The location of the agostic proton in the 1H NMR spectrum as well as the three-dimensional structure of these complexes in solution was obtained by means of several two-dimensional NMR techniques (1H-1H COSY, 31P-1H COSY, 13C-1H COSY, 1H NOESY, 1H ROESY, and 31P EXSY). The 1JHC of the agostic contact amounted to 112 Hz, which represents a reduction of 46 Hz in relation with the same coupling for this C-H bond in the free ligand. Furthermore, the molecular geometry of [Ru(H-PCP)(PCHP)][OTf] in the solid state was established by single-crystal X-ray diffraction techniques, and the structural features corroborate with the observations in solution. In the complex [Ru(H-PCP)(Br-PCHP)][OTf], interconversion of the cyclometalated and neutral bisphosphine ligands via exchange of the agostic hydrogen atom from the neutral to the cyclometalated carbon to yield [Ru(Br-PCP)(H-PCHP)][OTf] was observed. A mechanistic proposal based on an aromatic electrophilic substitution is discussed. Moreover, the reaction of [Ru(OSO2CF3)(NCN)(PPh3)] (NCN = [C6H3(CH2NMe2)2-2,6]-) with the neutral bisphosphinoarene resulted in the quantitative formation of the new cyclometalated species [Ru(R-PCP)(R-PCHP)][OTf] with the net loss of the neutral bisaminoarene ligand NCHN and PPh3.

The preparation and structure of the rigid rod-like platinum monoacetylide {Pt}CC-4-C6H2I-1-(CH2NMe2)2-2,6) ({Pt} = [Pt(C6H3{Me2NCH2}2-2,6)]) are described. Its oxidative addition to Pd(dba)2 yields a heterobinuclear {Pt}CC{Pd}I complex ({Pd} = [Pd(-4-C6H2{Me2NCH2}2-2,6)]+); this provides a new strategy for the controlled and stepwise construction of rigid rod-like metallopolymers.

Novel strategies for the preparation of rigid cartwheel pincer metal complexes have been developed. The aromatic backbone of these materials ensures a high rigidity, which is expected to be important for a high retention when these multimetallic nanosize complexes are applied as homogeneous catalysts in a nanomembrane reactor. The ligand precursors C6[C6H3(CH2Y)2-3,5]6 (10, Y = NMe2; 11, Y = SPh; 12, Y = PPh2; 13, Y = pz = pyrazol-1-yl) have been prepared in high yields from the key intermediate C6[C6H3(CH2Br)2-3,5]6 (9). The hexakis(pincer) palladium(II) complexes C6[(PdX)-4-C6H2(CH2Y)2-3,5]6 (14, Y = SPh, L = Cl; 15, Y = PPh2, L = Cl; 16, Y = pyrazol-1-yl, L = OAc; 17, Y = pyrazol-1-yl, L = Cl) have been prepared via direct electrophilic palladation of the corresponding ligands. The (tris)pincer ligand C6H3[Br-4-C6H3(CH2NMe2)2-3,5]3-1,3,5 (20) was prepared via a triple-condensation reaction of 4-bromo-3,5-bis[(dimethylamino)methyl]acetophenone (19). Reaction of 20 with Pd(dba)2 yielded the tripalladium complex C6H3[(PdBr)-4-C6H3(CH2NMe2)2-3,5]3-1,3,5 (21). The crystal structure of 21 shows a propeller-like structure with D3 symmetry and a fixed bromine-bromine distance of 17.4573(4) Å, approximately forming a triangle with a height of 15.2 Å. These nanosize cartwheel pincer metal complexes based on tridentate Y,C,Y' pincer ligands have been used as homogeneous Lewis-acid catalysts. Moreover, the influence of the donor substituent Y on the catalytic activity of cationic mono-Y,C,Y' PdII complexes as Lewis-acid catalysts in the double Michael reaction between methyl vinyl ketone and ethyl -cyanoacetate, as a model reaction, has been investigated. It was found that cationic N,C,N'-type pincer complexes (1a, Y = NMe2; 1b, Y = pz; 1c, Y = pz* = 3,5-dimethylpyrazol-1-yl; 23) were superior to the P,C,P'- and S,C,S'-pincer complexes (1d, Y = PPh2; 1e, Y = SPh). The nanosize cationic tri-N,C,N' PdII complex 23 was found to have a catalytic activity per catalytic site in the double Michael reaction of the same order of magnitude as the monopincer analogue 1a (k = 279 × 10-6 s-1 for 1a vs k = 232 × 10-6 s-1 for 23). The combination of the nanosize dimensions, the catalytic activity, and the high thermal and air stability makes these complexes excellent candidates for application in a continuous process in a nanomembrane reactor.

A series of cyclopalladated carbosilane dendrimers functionalized with monoanionic [C6H4(CH2NMe2)-4]- (= CN) C,N-chelating ligands via a multiple and selective C-H bond activation process have been prepared. The structure of the support, i.e., the branching degree as well as the nature of the alkanediyl linkers present in the carbosilane dendrimer, was varied to investigate its influence on the dimer formation of the peripheral [CN-PdCl] complexes and on the catalytic performance of these Pd(II)-functionalized dendrimers. Me2Si{(CH2)3SiMe2-CN-PdCl}2 (4) and Si{(CH2)2SiMe2-CN-PdCl}4 (7a) were characterized by a single X-ray crystal structure determination. In both cases a unique intramolecular halide-assisted macrocyclic ring structure was present. Variable-temperature NMR spectroscopic investigations indicated that in solutions of 4 and 7a the cis-bridging mode of the peripheral dimers is predominant. For the two asymmetrically branched [G1] palladodendrimers Si{(CH2)2Si(Me){(CH2)2SiMe2-CN-PdCl}2}4 (10a) and Si{(CH2)3Si(Me){(CH2)3SiMe2-CN-PdCl}2}4 (12a) isomeric forms of the [CN-PdCl] dimeric units were observed. In addition, for the [G2] dendrimer Si{(CH2)3Si{(CH2)3Si{(CH2)3SiMe2-CN-PdCl(pyr)}3}3}4, 15b, appended with a maximum of 36 [CN-PdCl(pyr)] complexes, a cis/trans isomerization of the peripheral [CN-PdCl(pyr)] groups is noted. The applicability of the cationic cyclopalladated carbosilane dendrimers, obtained by halide abstraction with AgBF4, as Lewis acid catalysts in a model aldol condensation reaction was demonstrated. Their catalytic performance was compared to that of the parent mononuclear derivative [Pd(C6H3{CH2NMe2}-2-(SiMe3)-5)(pyr)(H2O)]BF4 (16). The obtained catalytic data showed that up to generation [G2], the selectivity of the reaction is not affected. However, the rate of the reaction decreased with increasing steric congestion at the dendrimer periphery.

Monoanionic, potentially bi- or terdentate aminophenolates, ([OC6H3(CH2NMe2)-2-R-4)]-, R = H (a), Me (b), tBu (c), Cl (d), N=NPh (e), MeO (f) and [OC6H2(CH2NMe2)2-2,6-Me-4]- (g)), have been used in the synthesis of well-defined vanadium-based catalysts for the polymerization of -olefins. The reaction of [Cp2V] with the parent phenol of g resulted in oxidation of the vanadium(II) nucleus to obtain the vanadium(III) (tris)phenolate [V(OC6H2(CH2NMe2)2-2,6-Me-4)3] (1). Vanadium(III) aminophenolates could not be obtained by reaction of [VCl3(THF)3] with the sodium phenolates because of incorporation of NaCl. However, use of the corresponding silyl ether Me3SiOC6H3(CH2NMe2)-2-Me-4 (2) resulted in the formation of the chlorovanadium (bis)phenolate [VCl(OC6H3(CH2NMe2)-2-Me-4)2] (3). Attempts to oxidize 3 to the corresponding dichlorovanadium(IV) (bis)phenolate were not successful. No reaction was observed with CuCl, AgCl and PbCl2. A dark blue compound 4 was obtained with CuCl2, which was tentatively assigned as a VIII/CuII dinuclear species. Treatment of the vanadium(IV) oxo (bis)phenolates 5a-5f with SOCl2 in benzene at room temperature or in toluene at reflux temperature resulted in the formation of dark blue compounds 6a-6f, whose stoichiometries indicated excess chloride. Only when 5a and 5d were reacted with SOCl2 at -70 °C could the desired dichlorovanadium (bis)phenolates [VCl2(OC6H4(CH2NMe2)-2)2] (7a) and [VCl2(OC6H3(CH2NMe2)-2-Cl-4)2] (7d) be obtained. X-ray crystal structure determination of 1 and 3 showed that both compounds have a trigonal bipyramidal geometry with two aminophenolate ligands bound in a bidentate 2-O,N fashion to the vanadium center in similar ways. The compounds 1, 3, 6 and 7 were tested for ethene/propene copolymerization.

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.

A series of cycloplatinated carbosilane dendrimers appended with the monoanionic C, N-bidentate ligand [C{6}H{4}{CH{2}NMe{2}}-2]}-{ (CN) was prepared via a multiple C@?H activation reaction. Ligand exchange in the parent model species [PtCl(C{6}H{3}{CH{2}NMe{2}}-2-SiMe{3}-5)(DMSO)] (1) in the presence of PPh{3} gave the phosphine complex [PtCl(C{6}H{3}{CH{2}NMe{2}}-2-SiMe{3}-5)(PPh{3})] (2). The crystal structure of 2 was also determined, showing a close proximity between one of the Ar@?H of the phosphine ligand and the Ar@?H{o}{r}{t}{h}{o} of the CN ligand.

The application of platinum(II) complexes based on the N,N-dimethylbenzylamine ligand (abbreviated as H-C,N) in macromolecular synthesis was demonstrated. Two cationic C,N-platinum moieties were linked with a 4,4'-bipyridine bridge, giving [{C6H4(CH2NMe2)-2-Pt(PPh3)}2(4,4'-bpy)](BF4)2 (2), the crystal structure of which was determined. To introduce C60 groups into this assembly, [1,2]-methanofullerene-substituted H-C,N ligands were prepared and platinated using cis-PtCl2(DMSO)2. Application of the methanofullerene C,N-platinum complexes in the preparation of macrostructures afforded insoluble compounds. Therefore, phosphine ligands containing perfluoroalkyl groups were introduced into the fullerene-based complexes via a ligand exchange reaction. These fluorous complexes showed enhanced solubility in organic and fluorinated solvents. A soluble bismethanofullerene C,N-platinum(II) structure with a 4,4'-bipyridine bridge was obtained using these fluorinated fullerenes.

Synthetic routes have been developed for the attachment of palladium(II) bis(amino)aryl (NCN or C6H2{CH2NMe2}2-2,6)- complexes to C60. Using diazo and Bingel addition reactions, various methanofullerene NCN-SiMe3 compounds (C60-L-NCN-SiMe3, L = C(Me), C(CO2Et)CO2CH2, and C(Me)C6H4CC) have been prepared and characterized. Electrophilic palladation of these ligands was achieved with Pd(OAc)2, leading to the corresponding C60-L-NCN·PdCl complexes. These were converted into active Lewis acid catalysts for the aldol condensation and the Michael reaction. Catalytic tests show that the activity of cationic methanofullerene NCN-palladium complexes in the aldol reaction between benzaldehyde and methyl isocyanoacetate is comparable to the parent unsupported NCN palladium complex. However, in the Michael reaction of methyl vinyl ketone and ethyl cyanoacetate, the fullerene catalysts are not only significantly slower but also undergo a deactivation/decomposition process during the reaction. Preliminary retention measurements using a nanofiltration membrane have shown 72% retention of the palladium complex C60-C(Me)-(NCN)PdCl.

In search of new possibilities for rendering catalysts soluble in fluorous solvents, the preparation of a sodium derivative of tetrakis{3, 5-bis(perfluorohexyl)phenyl}borate, a new and highly fluorous anion, is described. This weakly coordinating anion exhibits substantial affinity for perfluorinated solvents and is therefore expected to make a broad range of cationic transition-metal catalysts compatible with fluorous biphasic recycling techniques.

Trimethylsilyl- and dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl substituents have been introduced in the para position of tetraphenylborate anions, resulting in enhanced solubility of their complexes n-Bu4N[B(C6H4SiMe2R-4)4] (R = Me, CH2CH2C6F13) and [Rh(dppe)2][B(C6H4SiMe2R-4)4] (dppe = 1,2-bis(diphenylphosphino)ethane, R = Me, CH2CH2C6F13) in apolar organic solvents.

A series of homodinuclear Pt compounds containing the anionic, potentially terdentate NCN ligand (NCN=[C{6}H{3}(Me{2}NCH{2}){2}-2, 6]}-{) or its 4-ethynyl derivative were prepared. The two platinum centres are linked together in two different fashions: (i) directly linked by an ethynyl or diethynylphenyl group (head-to-head) and (ii) indirectly bonded by a ethynyl- or butadiynyl-linked bis-NCN ligand (tail-to-tail). The reaction of the head-to-head @s,@s'-ethynylide complex {Pt}C@8C{Pt} ({Pt}=[Pt(C{6}H{3}{CH{2}NMe{2}}{2}-2,6)]}+{) with [CuCl]{n} yields {Pt}Cl and [Cu{2}C{2}]{n}, while with [Cu(NCMe){4}][BF{4}] a Cu(I) bridged complex was formed: [(@h}2{-{Pt}C@8C{Pt}){2}Cu][BF{4}]. The results of cyclic voltammetry experiments reveal that both connection modes of the two platinum centres lead to electrochemically independent Pt-NCN units. The X-ray crystal structure analysis of the neutral, tail-to-tail bridging butadiyne bis-NCNH ligand [C{6}H{3}(CH{2}NMe{2})-1,3-(C@8C)-5]{2} is reported.

Since the first reports in the late 1970s on transition metal complexes containing pincer-type ligands - named after the particular coordination mode of these ligands - these systems have attracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typically, such a ligand comprises an anionic aryl ring which is ortho,ortho-disubstituted with heteroatom substituents, for example, CH2NR2, CH2PR2 or CH2SR, which generally coordinate to the metal center, and therefore support the M-C bond. This commonly results in a terdentate and meridional coordination mode consisting of two metallacycles which share the M-C bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental understanding of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mechanistic elucidation of fundamental transformations (for example, C-C bond activation), the construction of the first metallodendrimers for sustainable homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous investigations. This review discusses the synthetic methodologies that are currently available for the preparation of platinum group metal complexes containing pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineering of sensors, switches, and catalysts.

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.

Square-planar platinum(II) complexes containing N,C,N terdentate coordinating, anionic 'pincer' ligands reversibly bind gaseous SO2 in the solid state by Pt-S bond formation and cleavage giving five-coordinate adducts. When the starting material is crystalline, exposure to this gas leads to quantitative adduct formation with the unique feature that the product is also crystalline, although the crystal structures of the adduct and the SO2 free complex are significantly different from each other and are both non-porous. Remarkably, the reverse reaction, i.e. the release of SO2 gas, modifies but does not destroy the crystalline ordering in the arylplatinum assemblies. These processes include repetitive expansion and reduction of the crystal lattice without any loss of crystallinity of the material. Variation of the ligand framework revealed that the presence of intermolecular interactions such as - or -type networks is not an essential prerequisite for these crystalline transformations. Consequently, this class of supermolecules provides access to sensitive crystalline switches with 'on' and 'off ' positions which are a direct response to the gaseous environment.

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 have been found for 6. Crystal data: 6·Et2O, triclinic, P, a = 11.1557(6) Å, b = 12.5744(12) Å, c = 13.1051(14) Å, = 64.244(8), = 70.472(7), = 87.950(6), V = 1547(3) Å3, Z = 2; 6·C6H6, triclinic, P, a = 8.6034(3) Å, b = 13.3614(4) Å, c = 15.1044(5) Å, = 98.182(3), = 105.618(2), = 107.130(2), V = 1551.00(10) Å3, Z = 2; 12, orthorhombic, Pbca, a = 11.8576(12) Å, b = 12.6710(13) Å, c = 14.722(2) Å, V = 2211.9(4) Å3, Z = 8.