The tailoring of smart material properties is one of the challenges in materials science. The unique features of polymers with pendant ferrocene units, either as ferrocenyl or ferrocenediyl groups, provide electrochemical, electronic, optoelectronic, catalytic, and biological properties with potential for applications as smart materials. The possibility to tune or to switch the properties of such materials relies mostly on the redox activity of the ferrocene/ferricenium couple. By switching the redox state of ferrocenyl units - separately or in a cooperative fashion - charge, polarity, color (UV-vis range) and hydrophilicity of polymers, polymer functionalized surfaces and polymer derived networks (sol-gel) may be controlled. In turn, also the vicinity of such polymers influences the redox behavior of the pendant ferrocenyl units allowing for sensing applications by using polymer bound enzymes as triggering units. In this review the focus is set mainly on the literature of the past five years.
The new terphenyl trifluorosilanes Mes 2 C 6 H 3 SiF 3 (1) and Tip 2 C 6 H 3 SiF 3 (2) have been synthesized, and their reduction behavior has been investigated in detail. Reduction with sodium in both cases results in insertion of the silicon center into C-C bonds of the substituent. The reactive intermediates giving rise to the C-C insertion most likely involve fluorosilylene or disilyne species. The final product is a bis-silafluorenyl (3) in the case of 1 and a silafluorenyl anion in the case of 2. The anion can be protonated to give a stable silafluorene. The reduction of 1 and 2 with potassium gives a completely different result, and radical species are formed instead. The different reaction pathway is probably caused by the existence of a poorly soluble intermediate [2Mes 2 C 6 H 3 SiF 3 ‚3KF] (10) that lowers the concentration of the starting material and therefore influences the reaction kinetics. Crystal structures are presented for 1, 2, the insertion product 3, and the intermediate adduct 10.
The formation of t-butyl substituted polyhedral silsesquioxanes (POSS) starting from the corresponding silanetriol is reported. Several intermediates involved in this complex condensation process could be identified spectroscopically. In addition, the initial condensation intermediate t-Bu(2)Si(2)O(OH)(4), as well as t-Bu(6)Si(6)O(9) and t-Bu(7)Si(7)O(9)(OH)(3), could be characterized by X-ray crystallography. Owing to the high crystal quality it was possible to experimentally determine the geometric parameters of the unusual cyclic hydrogen bond network in a dimeric POSS trisilanol for the first time. Furthermore, we investigated the structural changes concomitant with dimer formation/dissociation of the t-butyl substituted POSS trisilanol and its methyl analogue.
The rational synthesis of an octahedral coordination capsule in which the triangular faces are covered by single ligands is described herein. Starting with tris(2-hydroxybenzylidene)triaminoguanidinium chloride [H(6)L]Cl, we observed an oxidative cyclization of this ligand in the presence of PPh(4) (+) ions resulting in the complex [Pd(H(2)L')(PPh(3))] (1). The use of 5,5-diethylbarbiturate (bar(2-)) as a bridging ligand in the presence of [Co(en)(3)](3+) (en=ethylenediamine) leads to the formation of a rectangular box with the formula (Et(4)N)(6)[[Co[(PdCl)(Pd)L](2)(mu-bar)](2)] (2). The analysis of the architecture of compounds 1 and 2 enables the development of a self-assembly strategy for the synthesis of an octahedral coordination cage 3 with the formula Na(4)(Et(3)NH)(12)[(Pd(3)L)(8)[mu-(bar)](12)].x H(2)O. Compound 3 was characterized by (13)C-MAS-NMR spectroscopy and single-crystal structure analysis.
An iridium catalysed oxidation was coupled concurrently to an asymmetric biocatalytic reduction in one-pot; thus it was shown for the first time that iridium-and alcohol dehydrogenasecatalysed redox reactions are compatible. As a model system racemic chlorohydrins were transformed to enantioenriched chlorohydrins via an oxidation-asymmetric reduction sequence.Scheme 1 Concurrent transition metal-and biocatalysed redox reactions: a transition metal catalysed oxidation and a biocatalytic asymmetric reduction run simultaneously.Scheme 2 Oxidation of halohydrin 2a via hydrogen transfer.
A series of [3]ferrocenophanes with functional P-E-P motifs (E = group 14 fragments) is reported. Out of these, the silicon compounds with the general formula Fe(C5H4PtBu)2SiXY (XY = Cl2, Br2, I2, H2, HCl) have been characterized by spectroscopic means and the bonding situation was analyzed using X-ray crystallography and quantum chemical calculations. Despite the two stereogenic phosphanyl centers, most of the [3]ferrocenophanes have been obtained as single isomers in the course of stereospecific reactions. The corresponding stannylene Fe(C5H4PtBu)2Sn has been obtained in the form of its dimeric adduct.
Pure 2,3,5,6-tetrafluoroterephthalic acid (H2tfBDC) is obtained in high yields (95%) by reacting 1,2,4,5-tetrafluorobenzene with a surplus (>2 equiv) of n-butyllithium in tetrahydrofuran (THF) and subsequent carbonation with CO2 without any extensive purification procedure. A single crystal X-ray structure analysis of H2tfBDC (1) confirms former data obtained for a deuterated sample (P1̅, Z = 1). Recrystallization from water/acetone leads to single crystals of H2tfBDC·2H2O (2, P21/c, Z = 2), where an extensive hydrogen bonding network is found. By reacting H2tfBDC with an aqueous ammonia solution, single crystals of (NH4)2tfBDC (3, C2/m, Z = 2) are obtained. 3 is thermally stable up to 250 °C and shows an enhanced solubility in water compared to H2tfBDC. Monosubstituted 2,3,5,6-tetrafluorobenzoic acid (H2tfBC, 4) is obtained by reacting 1,2,4,5-tetrafluorobenzene with stoichiometric amounts (1 equiv) of n-butyllithium in THF. Its crystal structure (Fdd2, Z = 16) shows dimeric units as characteristic structural feature.
Controlled
condensation reactions of tertiary silanetriols CH3(CH2)n(CH3)2CSi(OH)3 (1b–f; n = 1–5) in the presence of trifluoroacetic
acid and the hydrolysis of CH3(CH2)6(CH3)2CSiCl3 (3) lead
to the selective formation of the corresponding disiloxane tetrols
[CH3(CH2)n(CH3)2CSi(OH)2]2O (2b–g; n = 1–6) in good
yields. The TBAF-driven condensation reactions of the silanetriols
CH3(CH2)n(CH3)2CSi(OH)3 (1a–c; n = 0–2) as well as of the disiloxane-1,1,3,3-tetrol 2d (n = 3) yield in the selective formation
of the first T8 cages bearing tertiary carbon substituents,
CH3(CH2)n(CH3)2C (4a–d; n = 0–3), which was not possible via the condensation
of their alkoxysilane counterparts so far. The resulting compounds 2b–g and 4a–d have been characterized by multinuclear NMR, MS, and single-crystal
X-ray diffraction.
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