Petr Štěpnička

Heterogeneous Pd catalysts supported on silica matrices

Palladium catalysts deposited over different types of silica (amorphous silica, mesoporous molecular sieves, solids obtained by co-condensation of silicate precursors and many others) modified with suitable donor moieties have gained enormous importance due to their wide application as catalysts for cross-coupling and other synthetically useful organic reactions. This work provides an overview of the chemistry of silica-supported palladium catalysts in different types of organic transformations in order to present the major features, advantages and limitations of various supports and immobilised ligands.

SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF PD(II) AND PT(II) COMPLEXES WITH P-BONDED 1'-(DIPHENYLPHOSPHINO)FERROCENECARBOXYLIC ACID

Abstract The title hybrid phosphine ligand (Hdpf) coordinates to Pt(II) and Pd(II) as a monodentate phosphine. In the absence of deprotonating agents, its carboxyl group remains uncoordinated to metal, but takes part in various types of hydrogen bonding. Using K2MCl4 as the metal ion source, trans-square planar complexes of the M(Hdpf-P)2X2 type (MPd, XCl, Br; MPt, XCl) were obtained. While Pd(Hdpf-P)2Cl2 is formed also from Pd(cycloocta-1,5-diene)Cl2, the analogous Pt(II)–cod complex provides cis-square planar Pt(Hdpf-P)2Cl2. The trans-chlorides behave inconsistently on recrystallization from carboxylic acids. While acetic acid gives single crystals of the solvates M(Hdpf-P)2Cl2·2 AcOH, propionic or formic acid does not form solvates with Pt(Hdpf-P)2Cl2 at comparable conditions. Single crystal X-ray structure determination of the last four complexes revealed remarkable differences in the conformation of the ferrocenyl moiety and in inter- and intramolecular hydrogen bonding. The two isostructural solvates have molecular arrangement with solvent molecules hydrogen-bonded to the carboxyl groups of the ligand, thus saturating their hydrogen-bond capability. As can be expected, the structure of the unsolvated trans-Pt(Hdpf-P)2Cl2 is that of a one-dimensional polymer linked by intermolecular hydrogen bonds. Finally, the cis-complex is dimeric in the crystal, being joined by pairs of the peripheral carboxyls; there is a further bonding π–π interaction between the phenyl groups of the cis-phosphines.

Complexation of Europium(III) by Bis(dialkyltriazinyl)bipyridines in 1-Octanol

The present work focuses on highly selective ligands for An(III)/Ln(III) separation: bis(triazinyl)bipyridines (BTBPs). By combining time-resolved laser-induced fluorescence spectroscopy, nanoelectrospray ionization mass spectrometry, vibronic sideband spectroscopy, and X-ray diffraction, we obtain a detailed picture of the structure and stoichiometry of the first coordination sphere of Eu(III)-BTBP complexes in an octanolic solution. The main focus is on the 1:2 complexes because extraction studies revealed that those are the species extracted into the organic phase. The investigations on europium(III) complexes of BTBP with different triazin alkylation revealed differences in the formed complexes due to the bulkiness of the ligands. Because of the vibronic sidebands in the fluorescence spectra, we were able to detect whether or not nitrate ligands are coordinated in the first coordination sphere of the Eu-BTBP complexes. In solution, less sterically demanding BTBP offers enough space for additional coordination of anions and/or solvent molecules to form 9-coordinated Eu-BTBP 1:2 complexes, while bulkier ligands tend to form 8-fold-coordinated structures. We also report the first crystal structure of a Ln-BTBP 1:2 complex and that of its 1:1 complex, both of which are 10-coordinated.

Phosphino-carboxamides: the inconspicuous gems

Compounds combining phosphine and carboxamide moieties in their molecules have developed virtually unnoticed into a specific class of highly structurally versatile and tuneable donor molecules finding manifold use in various fields, particularly in coordination chemistry, biomedical sciences and in catalysis. In the latter field, some phosphinoamides became the real privileged ligands and an indispensable part of a standard toolbox for synthetic chemists. This critical review aims to give an overview of the multifaceted chemistry of such compounds, paying attention to both the fundamentals and recent developments in this continuously expanding field.

Reduction of Bis[η5-(ω-alkenyl)tetramethylcyclopentadienyl]titanium Dichlorides: An Efficient Synthesis of Long-Chainansa-Bridged Titanocene Dichlorides by Acidolysis of Cyclopentadienyl-Ring- Tethered Titanacyclopentanes

The reduction of symmetric, fully-substituted titanocene dichlorides bearing two pendant ω-alkenyl groups, [TiCl2(η5-C5Me4R)2], RCH(Me)CH=CH2 (1 a), (CH2)2CH=CH2 (1 b) and (CH2)3CH=CH2 (1 c), by magnesium in tetrahydrofuran affords bis(cyclopentadienyl)titanacyclopentanes [TiIV{η1:η1:tlsb&endash;3%>η5:η5-C5Me4CH(Me)CH(Ti)CH2CH(CH2(Ti))CH(Me)C5Me4}] (2 a), [TiIV{η1:η1:η5:η5-C5Me4(CH2)2CH(Ti)(CH2)2CH(Ti)(CH2)2C5Me4}] (2 b) and [TiIV{η1:η1:η5:η5-C5Me4(CH2)2CH(Ti)CH(Me)CH(Me)CH(Ti)(CH2)2C5Me4}] (2 c), respectively, as the products of oxidative coupling of the double bonds across a titanocene intermediate. For the case of complex 1 c, a product of a double bond isomerisation is obtained owing to a preferred formation of five-membered titanacycles. The reaction of the titanacyclopentanes with PbCl2 recovers starting materials 1 a from 2 a and 1 b from 2 b, but complex 2 c affords, under the same conditions, an isomer of 1 c with a shifted carbon-carbon double bond, [TiCl2{η5-C5Me4(CH2CH2CH=CHMe)}2] (1 c′). The titanacycles 2 a-c can be opened by HCl to give ansa-titanocene dichlorides ansa-[{η5:η5-C5Me4CH(Me)CH2CH2CH(Me)CH(Me)C5Me4}TiCl2] (3 a), ansa-[{η5:η5-C5Me4(CH2)8C5Me4}TiCl2] (3 b), along with a minor product ansa-[{η5:η5-C5Me4CH2CH=CH(CH2)5C5Me4}TiCl2] (3 b′), and ansa-[{η5:η5-C5Me4(CH2)3CH(Me)CH(Me)CH=CHCH2C5Me4}TiCl2] (3 c), respectively, with the bridging aliphatic chain consisting of five (3 a) and eight (3 b, 3 b′ and 3 c) carbon atoms. The course of the acidolysis changes with the nature of the pendant group; while the cyclopentadienyl ring-linking carbon chains in 3 a and 3 b are fully saturated, compounds 3 c and 3 b′ contain one asymetrically placed carbon-carbon double bond, which evidently arises from the β-hydrogen elimination that follows the HCl addition.

Synthesis, characterization and diastereoselective coordination of a planarly chiral, hybrid ferrocene ligand, (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid

Hydrolytic cleavage of the dihydrooxazole ring in (Sp)-2-{2-(diphenylphosphino)ferrocenyl}-4-(1-methylethyl)-4,5-dihydrooxazole affords the planarly chiral functionalized phosphine, (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid, (Sp)-Hpfc, in two steps and 65% yield. (Sp)-Hpfc, all intermediates and the corresponding phosphine oxides were characterized by elemental analysis, multinuclear NMR and IR spectroscopy, and by optical rotation measurements. Solid-state structures of the phosphine oxides were further studied by X-ray crystallography to reveal extensive hydrogen bonding of various types. Neutralization of (Sp)-Hpfc with tert-BuOK followed by metathesis of the in situ obtained salt with [{RuCl(μ-Cl)(η6-p-cymene)}2] gives a chelate complex [RuCl(pfc-κ2O,P)(η6-p-cymene)], 5, as a kinetic 1 : 1 mixture of diastereoisomers. Upon standing in solution, the diastereomeric mixture undergoes a spontaneous resolution to yield the thermodynamically preferred diastereoisomer (RRu,Sp)-5 whose configuration was corroborated by X-ray crystallography; the (RRu,Sp)-5 diastereoisomer was obtained in 82% yield by crystallization. The epimerization is likely initiated by a reversible Ru–O bond cleavage and suggests a hemilabile coordination of the (Sp)-pfc− anion. However, according to NMR spectra pure (RRu,Sp)-5 does not undergo diastereoisomer interconversion in a solution, which is in agreement with an unfavourable geometric arrangement of the (SRu)-epimer.

Synthesis, characterization and X-ray structural, electrochemical and Mössbauer study of mercury(II) complexes with 1′-(diphenylphosphino)ferrocenecarboxylic acid

Abstract Reaction of mercury(II) halides with 1′-(diphenylphosphino)ferrocenecarboxylic acid (Hdpf) affords [HgX2(Hdpf-P)2] or [HgX(μ-X)(Hdpf-P)]2 complexes (X=Cl, Br, I) depending on the stoichiometry of the educts. The complexes have been studied by IR, Mossbauer and solution NMR spectroscopy. In dimethyl sulfoxide-d6 solution, 1H- and 31P{1H}-NMR spectra indicate solvolytic cleavage of the mercury(II)–phosphine bond resulting in partial decomplexation of the phosphine ligand. Electrochemical measurements in donor solvents also confirm the presence of a non-coordinated ligand since the electrochemical behavior is the superposition of that of the product of solvolysis and of the ligand. X-ray structural analysis, of the representatives of both types, was carried out: [HgBr2(Hdpf-P)2] ([C46H38Br2Fe2HgO4P2], monoclinic; space group C2/c, a=19.453(1), b=13.704(1), c=17.929(2) A; β=114.953(7)°; Z=4) and [HgBr(μ-Br)(Hdpf-P)]2·2CH3CO2H ([C54H54Br4Fe2Hg2O12P2], triclinic; space group P, a=9.442(1), b=11.7101(9), c=14.806(1) A; α=109.692(7), β=92.494(9), γ=101.883(7)°; Z=1). The P-monodentate coordination of the phosphinocarboxylic ligand was confirmed in both cases, the carboxyl group being involved in hydrogen bonding to carboxyl groups of either neighboring ligand or solvating acetic acid. The expected Br2P2 and Br3P tetrahedral donor sets around Hg(II) are the subject of different degrees of deformation due to steric effects. 57Fe Mossbauer spectra of the complexes also point to the P-coordination of the ferrocenylphosphino ligand, as follows from the decrease of the quadrupole splitting and only a slight variation of the isomer shift on going from ligand to complex.

The coordination behaviour of ferrocene-based pyridylphosphine ligands towards ZnII, CdII and HgII

The reaction of Group 12 metal dihalides MX(2) with the P,N-ligands [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-2-py)] (1) (2-py = pyrid-2-yl), [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-CH(2)-2-py)] (2) and [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-3-py)] (3) (3-py = pyrid-3-yl) was investigated. For a 1 : 1 molar ratio of MX(2) and the respective ligand, three structure types were found in the solid state, viz. chelate, cyclic dimer and chain-like coordination polymer. The M(II) coordination environment is distorted pseudo-tetrahedral in each case. The P-M-N angle is much larger in the chelates (≥119°) than in the ligand-bridged structures (≤109°). 1 prefers the formation of chelates [MX(2)(1-κ(2)N,P)]. 3 forms coordination polymers [MX(2)(μ-3)](n). With the more flexible 2 all three structure types can occur. Dynamic coordination equilibria were observed in solution for the molecular complexes obtained with 1 and 2. NMR data indicate that the N- and P-donor sites interact most strongly with Zn(II) and Hg(II), respectively. While the formation of bis(phosphine)mercury complexes (soft-soft) was easily achieved, no bis(pyridine)zinc complex (borderline-borderline) could be obtained, which is surprising in view of the HSAB principle.

Hydrogen bonding and self-assembly in the crystal structures of ferrocenylmethanol derivatives having different phosphorus substituents on the ferrocene unit

Ferrocenylmethanol derivatives bearing a phosphorus substituent in position two of the ferrocene unit, rac-2-(diphenylphosphino)ferrocenylmethanol (3), rac-2-(diphenylphosphinoyl)ferrocenylmethanol (4), and rac-2-(diphenylthiophosphoryl)ferrocenylmethanol (5), have been synthesized and structurally characterized by single-crystal X-ray diffraction. While the overall molecular geometry does not differ significantly in the whole series, showing only differences in the arrangement at the phosphorus atom owing to a replacement of the lone electron pair (2, 3) with oxygen (4) and sulfur (5), and in the conformation of the hydroxylmethyl group, the compounds form different crystal packing patterns that result from a counterplay of hydrogen bonding of various types and non-polar interactions. Alcohol 3 associates into dimers by double O–H⋯O hydrogen bridges between disordered hydroxy groups of neighbouring molecules. The distribution of molecules in the crystal of 4 appears identical to that of 3. However, the structure of 4 comprises intermolecular O–H⋯OP hydrogen bridges instead. The packing of phosphine sulfide 5 is different, featuring intramolecular O–H⋯S bridges. Although the molecular entities are involved in further interactions such as O–H⋯P and C–H⋯O hydrogen bonding, and π-π stacking interaction of the phenyl rings, which further propagate the molecular network, the principal force towards self-assembly always results in the formation of entropically favoured, closed cyclic systems. The solid state structure of the common precursor, rac-2-(diphenylphosphino)ferrocenylmethyl acetate (2) shows only C–H⋯O intermolecular interactions due to the lack of a better hydrogen bond donor.

Internal ferrocenylalkynes —a comparative electrochemical and mass spectrometric study

Abstract A series of ferrocenylalkynes FcCCY, where Fc is ferrocenyl and Y=H ( 1 ), Me ( 2 ), Ph ( 3 ), EMe 3 [E=C ( 4 ), Si ( 5 ), and Ge ( 6 )], I ( 8 ), CPh 2 (OR) [R=H ( 9 ), Me ( 10 )], CHO ( 11 ), C(O)Me ( 12 ), and CO 2 R [R=H ( 13 ), Et ( 14 )] was synthesized (some representatives for the first time) and subjected to spectroscopic (IR, NMR, UV–vis, MS) and electrochemical study. In electron-impact mass spectra, all alkynes fragment via processes typical for the ferrocene skeleton and the substituent Y. Besides, the molecular ions of alkynes 1 – 3 decompose by a loss of {FeH 2 } affording likely a Y-substituted fulvene as the result of a cyclopentadienyl-ring transfer. The carbonyl group containing alkynes 11 – 14 tend to fragment so that ions isobaric with 1 + are produced. Similarly, the fragmentation of alcohol 10 appears as a superposition of fragmentation pathways due to Ph 2 CO + and 1 + . In cyclic voltammograms, all alkynes exhibit one-electron reversible wave of the ferrocene/ferrocenium couple, whose redox potential correlates linearly with Hammett σ p constants. A similar correlation with inductive σ I constants is less pronounced due to neglecting resonance effects. An influence of the triple bond spacer between the substituent Y and the ferrocene unit is discussed.