Publications (43)1.3 Total impact
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Dataset: Eur. J. Inorg. Chem. 2007, 2105-2109 (front cover)
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Article: Synthesis, structure, and catalytic performance of diastereopure five-coordinated NCN-pincer palladium(II) complexes bearing bulky amino acid substituents
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ABSTRACT: New chiral NCN-pincer palladium complexes containing bulky diphenylhydroxymethyl pyrrolidinyl moieties as chiral auxiliaries have been synthesized. Oxidative palladium addition to ligand 2 (2 = 2,6-bis{[(S)-2-(diphenylhydroxymethyl)-1-pyrrolidinyl]methyl}-1-bromobenzene) initially yielded neutral arylpalladium bromide complex 3 in a moderate yield as a consequence of the bulky pyrrolidinyl functional groups. Performing the palladation reaction under microwave irradiation for only 5 min gave 3 in 79% yield. Abstraction of the bromide ion from 3 subsequently yielded the cationic complexes [4]PF6 and [4]BF4. Palladium complexes 3, [4]PF6, and [4]BF4 are all formed as single diastereoisomers with an RNRNSCSC configuration. X-ray crystal structure determinations of [4]PF6 and [4]BF4 revealed an unusual κ5-N,C,N,O,O coordination around palladium, in which the normal meridional κ3-coordination mode of the pincer framework is complemented by two rather long Pd−O interactions (2.622(2)–2.649(2) Å). Theoretical calculations (Mulliken population analysis and “atoms in molecules” analysis) confirmed that there is a coordinative interaction between the palladium and the oxygen atoms of both hydroxyl groups despite the long Pd−O distance. Complexes [4]PF6 and [4]BF4 catalyze the aldol condensation between α-methyl isocyanoacetate and various aromatic aldehydes with enhanced regio- (up to 70%) and stereoselectivity (up to 42% ee) for the cis-oxazolines. These observations are in contrast to prior literature results on other pincer systems, where the trans-oxazolines were the main product, and point to a deeper chiral cavity pointing away from palladium toward the coordinated isocyanoacetate substrate.05/2008; -
Article: Luminiscent and Electronic Properties of Stilbenoid NCN-Pincer Pt(II) Compounds
Eur.J.Inorg.Chem. 01/2007; -
Article: Synthesis and Catalytic Properties of Di- and Trinuclear Palladium Complexes with PCP-Pincer Ligands
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ABSTRACT: Linear and branched conjugated pincer ligands having Ph2P groups were synthesized: 3,3',5,5'- tetrakis(diphenylphosphinomethyl)diphenylacetylene, 3,3',5,5'-tetrakis(diphenylphosphinomethyl)diphenyldi- acetylene, 1,3,5-tris[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene, and hexakis[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene. Palladation of these ligands by heating with Pd(BF4)2(MeCN)4 in boiling acetonitrile gave the corresponding di- and trinuclear ionic pincer palladium complexes. No individual complex was obtained from hexakis[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene. The ionic com- plexes were converted into the corresponding chloride complexes by treatment with sodium chloride in a mixture of water with methylene chloride. The structure of the ionic palladium complex with 3,3',5,5'-tetrakis(diphenylphosphinomethyl)diphenylacetylene was established by X-ray analysis. The obtained palladium complexes exhibited a considerable catalytic activity in the Heck reaction of iodobenzene with ethyl acrylate and in the Michael addition of ethyl cyanoacetate with methyl vinyl ketone. The catalytic activity per palladium atom decreases as the number of palladium atoms in the complex increases.Russian Journal of Organic Chemistry 08/2003; 39(9):1268-1281. · 0.65 Impact Factor -
Article: Template-Directed Synthesis of Macroheterocycles by Ring-Closing Metathesis of Olefin-Substituted Pyridines in the Coordination Sphere of a Triplatinum Complex
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ABSTRACT: Mono- and tris-3,5- and 2,6-pyridinediyl-containing macroheterocycles were synthesized by metathesis of olefin-substituted pyridines in the coordination sphere of mono- and tris-platinum complexes, respectively. Tris(2,6-pyridinediyl)-containing macroheterocycles were hydrogenated over palladium catalyst. The hydrogenated macrocycle was used as ligand for the triplatinum template. The structure of the resulting complex was established by X-ray analysis.Russian Journal of Organic Chemistry 02/2003; 39(3):422-429. · 0.65 Impact Factor -
Article: Protagonists in Chemistry
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Article: Bis(ortho-)Chelated Monoanionic Bisphosphinoaryl Ruthenium(II) Complexes: Synthesis, Characterization and Reactivity
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ABSTRACT: Bisphosphinoaryl ruthenium(II) compounds are synthezed using two distinct synthetic routes. One route, direct cycloruthenation, consists of the reaction of the parent arene compound R-PCHP with [ RuCL₂ (PPH₃)₃] in chlorinated solvents. However, this route suffers from major drawbacks because HCI is formed as well as free triphenylphodine. The other route, the transcyclometalation reaction , involves the interconversion of one cyclometalated ligand metal complex, [RuCl(NCN) ( PPH₃ )] , into another complex, [RuCl(RPCP)(PPH₃)] , with concomitant consumption and formation of the corresponding arenes R-PCHP and NCHN, respectively. -
Article: Organic Transformations on σ-Aryl Organometallic
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ABSTRACT: This work reviews recent developments in the field of organic transformations on σ-aryl organometallic complexes. The general notion that M-C bonds are kinetically labile, highly reactive, and incompatible with typical reaction conditions met in organic synthesis has limited the use of these synthetic strategies thus far. However, organic transformations on metal-bound σ-aryl fragments are being used more and more by chemists in both industry and academia. In this Review, emphasis is put on the synthetic methods applied in this field up to now. The simplicity and generally good yields of these methods are very attractive for the construction of functionalized organometallic building blocks that are potentially useful as photochemical molecular devices, biosensors and -conjugates, or molecular switches. Thus, this Review has been tailored for a broader audience with the aim of encouraging the application of these strategies. -
Article: 2-Carboxy-4-(hydroxymethyl)pyridinium chloride hemihydrate
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ABSTRACT: The title compound, C7H8NO3+·Cl-·0.5H2O, features inter- and intramolecular O-HCl and N-HO hydrogen bonds, linking the molecules into a three-dimensional network. The water molecule is located on a crystallographic twofold rotation axis. -
Article: Metal-chelating capacities attached to fullerenes
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ABSTRACT: This review describes the synthesis, properties and application of fullerenes covalently attached to metal-chelating groups. The application of these structures in artificial photosynthetic systems and their reaction on external stimuli, such as light or electrons is described. urthermore, the use of fullerene organometallic building blocks in macromolecular synthesis and catalysis has been highlighted. -
Article: A Ruthenium(II) Complex Stabilized by a Highly Fluorinated PCP Pincer Ligand
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Article: Construction of Supported Organometallics Using Cycloplatinated Arylamine Ligands
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ABSTRACT: The preparation of ortho-chelating aminoaryl ligands ([C6H3(CH2NMe2)-2-R-4]-, abbreviated as C,N) containing a pendant hydroxymethyl group is described. These ligands have been cycloplatinated with cis-PtCl2(DMSO)2, yielding the corresponding C,N-platinum(II) complexes. The pendant hydroxymethyl substituent is a versatile group for attachment of the organometallic moiety to macromolecules, which has been demonstrated by attaching the C,N-platinum complexes to a dendritic wedge and to C60. -
Article: Ring closing metathesis employing organometallic substrates and the templated synthesis of macrocycles
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Article: Electron-Poor Pentafluorophenyl-substituted PCP-Palladium Pincer Complexes
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Article: (P-Bis(pentafluorophenyl) substituted) PCP-pincer Ru(II) complexes: A theoretical study of the molecular structure and electronic properties
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ABSTRACT: The differences between the molecular struturs of the PCP-pincer complex [RuCl{C6H3(CH2P(C6H5)2)2- 2,6}(PPh3)] ([RuCl(PCP H)(PPh3), 1) and its tetrakis-pentafluorophenyl substituted analogue [RuCl{C6H3(CH2P(C6F5)2)2- 2,6}(PPh3)] (RuCl(PCP F20)(PPh3)], 2) have been rationalised by performing calculations on the cations [Ru(PCP H)(PPh3)]+ (1cat) and [Ru(PCP F20)(PPh3)]+ (2cat). The molucular interactions between the chloride ligand and the axial rings, as found in 1 and 2, respectively, have been studied computationally in the model system [(C6X5PH2)2CL-](X = H, F). The calculations on 2cat show that in 2 it is most likely the attractive electrostatic interaction between the chloride ligand and the fluorinated phenyl rings that forces the C ipso atom to occupy an axial postion rather than an equatorial one in the observed (X-ray of 2) square pyramidal arrangement. In 1, however, repulsive steric hinderance forces the PPh3 ligand to take the apical postion. The applicability of the TD-DFT method for the calculation of the electronic spectra of the PCP-pincer compounds 1 and 2 has been tested. The results indicate that the excitation energies calculated for both complexes are in a reasonable agreement with the experimental absorption maxima. However, for 1, all the calculated transition energies are underestimated. -
Article: 2,6-Bis(oxazolinyl)phenylnickel(II) Bromide and 2,6-Bis(ketimine)phenylnickel(II) Bromide: Synthesis, Structural Features, and Redox Properties
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ABSTRACT: 2,6-Bis(oxazolinyl)phenylnickel bromide complexes [NiBr(R,R'-Phebox)] (2) were synthesized via two synthetic routes (A and B). In route A, selective bis-ortho lithiation of [R,R'-PheboxBr], followed by a transmetalation reaction with [NiBr2(PEt3)2], yielded not only complexes 2 with an 3-mer-N,C,N'-bonded Phebox ligand but also [NiBr(R,R'-Phebox)(PEt3)2], 7, where the nickel center is 1-C bonded to the intra-annular Cipso of the Phebox ligand. Coordination of two PEt3 ligands completes the square-planar coordination sphere of the Ni center in 7. When R = t-Bu, R' = H, only complex 7c was formed. Alternatively, when route B (oxidative addition with [Ni(cod)2], cod = cyclooctadiene) was followed, selective formation of complexes 2 was observed. X-ray crystal structures were obtained for [NiBr-(i-Pr,H-Phebox)] (2b) and [NiBr(bis(ketimine)phenyl)] (3). The Ni centers have square-planar geometries with a planar, 3-mer-N,C,N' coordination of the terdentate ligand systems. Complexes 2 were found to be inactive as catalysts in the atom-transfer radical polymerization (ATRP) reaction of methyl methacrylate (MMA) and in the atom-transfer radical addition (ATRA, Kharasch addition) reaction of CCl4 to MMA. This is ascribed to the relatively high oxidation potential of NiII-Phebox complexes, which excludes the (reversible) formation of a d7-NiIII-Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)4NBr as supporting electrolyte) showed no electrochemical waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)4NBr as supporting electrode). Theoretical calculations showed that the energy (Eox) needed for the oxidation reaction occurring during the CV experiments is considerably higher for [NiBr(Me,Me-Phebox)] (1.87 eV) and [NiBr(bis(ketimine)phenyl)] (1.90 eV) than for [NiBr(NCN)] (1) (1.45 eV). -
Article: Metathesis of olefin-substituted pyridines: the metalated NCN-pincer complex in a dual role as protecting group and scaffold.
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ABSTRACT: Pincer-palladium(II) and -platinum(II) cations, YCY-M (YCY=[2,6-(YCH2)2C6H3]; Y=NMe2, SPh; M=PdII, PtII), bound to diolefin-substituted pyridines (3,5- or 2,6-substitution) were successfully synthesized, and subsequently used in olefin metathesis (RCM) as a model study for template-directed synthesis of macrocycles. Especially a 3,5-disubstituted pyridine bound to a NCN-PtII-center (5a) gave a fast metathesis reaction, while the same reaction with the PdII analogue (4a) was much slower and less selective (isomerization products were formed). Furthermore, it was found that 2,6-diolefin-substituted pyridines (4b, 5b, 5c) gave slow metathesis reactions, which is mainly ascribed to steric hindrance during the ring-closing step. In all cases where prolonged reaction times were required an isomerization process, most likely assisted by cationic pincer-MII species, was observed as a competing reaction. 1H NMR spectroscopy experiments revealed that pyridines are stronger bound to a cationic NCN-PtII-center than to its PdII-analogue. This aspect is of crucial importance when these pincer-pyridine complexes are applied in metathesis, since free pyridine in solution deactivates the Ru-metathesis catalyst. For the templated construction of macrocycles, a strong M-N(py) bond is also important since it determines the selectivity for the desired product. In addition, these results open a new research field in which organometallic (pincer) complexes are used as protecting groups for strong Lewis-basic groups in catalysis. From failed attempts to prepare macrocycles using hexakis[SCS-PdII-(1a)] complex 14, and from the results obtained with the monometallic pincer complexes in RCM, it can be concluded that the most suitable candidate for constructing macrocycles should comprise 2,6-diolefin-substituted pyridines bound to a multi-(NCN-PtII)-template. In such a system, intrapyridine metathesis (steric hindrance) as well as isomerization reactions (strong M-N(py) bond) are suppressed. -
Article: Electronic Effects in PCP-Pincer Ru(II)-Based Hydrogen Transfer Catalysis
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ABSTRACT: The synthesis and characterization of novel cyclometalated ruthenium(II) complexes [RuCl(PCPOMe)(PPh3)] and [RuCl(PCPCF3)(PPh3)] containing monoanionic, tridentate coordinating PCP-pincer ligands [C6H3{CH2P(p-MeOC6H4)2}2-2,6]- (PCPOMe) and [C6H3{CH2P(p-CF3C6H4)2}2-2,6]- (PCPCF3) are reported. These compounds have been tested as catalyst precursors in the hydrogen transfer reaction of cyclohexanone to cyclohexanol in 2-propanol using NaOH as a base. The initial rate of the hydrogen transfer reaction appeared to depend on the electronic character of the Ar2P- groups of the PCP-pincer ligand. Among the catalyst precursors studied, the complex [RuCl(PCPCF3)(PPh3)] was found to exhibit the highest activity and the initial TOF exceeded that observed for the Ph2P analogue [RuCl(PCPPh)(PPh3)]. Most importantly, catalysis performed with [RuCl(PCPCF3)(PPh3)] does not require pretreatment of the precursor in the absence of substrate. Conversely, a different catalytic profile and a low activity were observed when either the electron-poor [RuCl{C6H3(CH2P(C6F5)2)2-2,6}(PPh3)] ([RuCl(PCPF20)(PPh3)]) complex or its triflate analogue was used as catalyst precursors. NMR studies and ESI-MS measurements provided information concerning the catalytically active species formed during the pretreatment of the precursor complexes. The results indicate that during the pretreatment period a monoanionic, monohydride ruthenium(II) species, Na[Ru(H)(PCPiPr)(OiPr)(PPh3)], is selectively formed. The latter hydride complex was also obtained via an independent synthetic route. On the basis of both the present results and those previously reported in literature, a mechanism is proposed. -
Article: A Bis(ortho-amine)aryl-Gold(I) Compound as an Efficient, Nontoxic, Arylating Reagent
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ABSTRACT: A novel strategy for the synthesis of bis(ortho-amine)chelated monoanionic bisaminoaryl-metal complexes is presented. This method constitutes the exchange of a monoanionic, NCN-pincer ligand (NCN = [C6H3(CH2NMe2)2-2,6]-) between a stable arylgold(I) phosphine, [Au(1-C-NCN)(PPh3)] (2), and a transition metal halide. This transmetalation results in the quantitative formation of [M(NCN)] organometallic compounds (M = AuIII, NiII, PdII, PtII, TiIV, and FeIII) and [AuCl(PPh3)] as the only coproduct that can be recovered. -
Article: Comment on “Theoretical studies on the ground states in [M(terpyridine)2]2+ and [M(4-(4-(t-butyl)phenyl)terpyridine)2]2+ (M = Fe, Ru, Os) and excited states in [Ru(terpyridine)2]2+ using density functional theory”
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ABSTRACT: The nature of the first excited state of [Fe(terpyridine)2]2+ has been reinvestigated. In contrast to previous findings, it is metal-to-ligand charge transfer in nature, thus fitting in the series of the Ru and Os complexes.
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2003
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Universiteit Utrecht
Utrecht, Provincie Utrecht, Netherlands
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