Amidoamine-based dendrimers with end-grafted Pd–Fe units: Synthesis, characterization and their use in the Heck reaction

Diaqua-β-octaferrocenyltetraphenylporphyrin: a multiredox-active and air-stable 16π non-aromatic species

Herein the synthesis and properties of the first β-octaferrocenyltetraphenylporphyrin, {TPPFc₈(H₂O)₂}, in its extraordinary stable and non-aromatic 16π form are reported, showing seven separate reversible redox events.

Synthesis of unsymmetrical multi-aroyl derivatives of ferrocene using palladium catalysed oxidative C–H aroylation

Palladium catalysed oxidative C–H aroylation of ferrocene: accessing the multi-aroyl derivatives of ferrocene.

Fabrication of a label-free electrochemical immunosensor using a redox active ferrocenyl dendrimer

An amperometric immunosensor based on a redox active ferrocenyl end-grafted PAMAM dendrimer provides highly sensitive detection of immunoglobulin, down to 2 ng mL⁻¹.

CuII bis(oxamato) end-grafted poly(amidoamine) dendrimers

“Magneto-dendrimers” comprising up to ten endgrafted {Cu₃(3,4-bopb)(pmdta)₂}²⁻ complex fragments have been synthesized to determine their magnetic properties.

1,3,5-Triferrocenyl-2,4,6-tris(ethynylferrocenyl)-benzene--a new member of the family of multiferrocenyl-functionalized cyclic systems

The consecutive synthesis of 1,3,5-triferrocenyl-2,4,6-tris(ethynylferrocenyl)benzene (6c) is described using 1,3,5-Cl3-2,4,6-I3-C6 (2) as starting compound. Subsequent Sonogashira C,C cross-coupling of 2 with FcC≡CH (3) in the molar ratio of 1:4 afforded solely 1,3,5-Cl3-2,4,6-(FcC≡C)3-C6 (4c) (Fc = Fe(η(5)-C5H4)(η(5)-C5H5)). However, when 2 is reacted with 3 in a 1:3 ratio a mixture of 1,3,5-Cl3-2-(FcC≡C)-4,6-I2-C6 (4a) and 1,3,5-Cl3-2,4-(FcC≡C)2-6-I-C6 (4b) is obtained. Negishi C,C cross-coupling of 4c with FcZnCl (5) in the presence of catalytic amounts of [Pd(CH2C(CH3)2P(tC4H9)2)(μ-Cl)]2 gave 1,3-Cl2-5-Fc-2,4,6-(FcC≡C)3-C6 (6a), 1-Cl-3,5-Fc2-2,4,6-(FcC≡C)3-C6 (6b) and 1,3,5-Fc3-2,4,6-(FcC≡C)3-C6 (6c) of which 6b is the main product. Column chromatography allowed the separation of these organometallic species. The structures of 4a,b and 6a in the solid state were determined by single crystal X-ray diffractometry showing a π–π interacting dimer (4b) and a complex π–π pattern for 6a. The electrochemical properties of 4a–c and 6a–c were studied by cyclic voltammetry (=CV) and square wave voltammetry (=SWV). It was found that the FcC≡C-substituted benzenes 4a–c show only one reversible redox event, indicating a simultaneous oxidation of all ferrocenyl units, whereby 4c is most difficult to oxidise (4a, E°′1 = 190, ΔEp = 71; 4b, E°′1 = 195, ΔEp = 59; 4c, E°′1 = 390, ΔEp = 59 mV). In case of 4c, the oxidation states 4c(n+) (n = 2, 3) are destabilised by the partial negative charge of the electronegative chlorine atoms, which compensates the repulsive electrostatic Fc+–Fc+ interactions with attractive electrostatic Fc+–Cl(δ−) interactions. When ferrocenyl units are directly attached to the benzene C6 core, organometallic 6a shows three, 6b five and 6c six separated reversible waves highlighting that the Fc units can separately be oxidised. UV-Vis/NIR spectroscopy allowed to determine IVCT absorptions (=Inter Valence Charge Transfer) for 6c(n+) (n = 1, 2) (n = 1: νmax = 7860 cm(−1), εmax = 405 L mol(−1) cm(−1), Δν1/2 = 7070 cm(−1); n = 2: νmax = 9070 cm(−1), εmax = 620 L mol(−1) cm(−1), Δν1/2 = 8010 cm(−1)) classifying these mixed-valent species as weakly coupled class II systems according to Robin and Day, while for 6a,b only LMCT transitions (=ligand to metal charge transfer) could be detected.

Multivalency as a key factor for high activity of selective supported organocatalysts for the Baylis-Hillman reaction

The polystyrene-supported N-alkylimidazole-based dendritic catalysts for the Baylis-Hillman reaction exhibit one of the strongest beneficial effects of multivalent architecture ever reported for an organocatalyst. The yields in the model reaction of methyl vinyl ketone with p-nitrobenzaldehyde are more than tripled when a non-dendritic catalyst is replaced by a second- or third-generation analogue. Moreover, the reaction of the less active substrates will not occur with the non-dendritic catalyst and will proceed to a significant extent only with the analogous catalysts of higher generations. A substantial additional enhancement of the reaction yield could be achieved by increasing the content of water in the reaction solvent. The plausible cause of the dendritic effect is the assistance of the second, nearby imidazole moiety in the presumably rate-determining proton transfer in the intermediate adduct, after the first imidazole unit induced the formation of the new carbon-carbon bond.