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The cycloaddition reactions of eleven substituted anthracenes with nosylated quinone imines provides a convenient route to the respective triptycenes. Following re‐aromatization, selective O‐butylation and cleavage of the nosyl‐group the respective triptycene anilines are obtained, which are converted into the respective imidazolium salts according to established procedures. Deprotonation of the imidazolium salts provide new triptycene‐NHC‐metal complexes (M=AuCl, RhCl(cod), IrCl(cod), RhCl(CO)₂, IrCl(CO)₂, PdI₂(py), PtCl₂(py), Pd(allyl)Cl) with unusual ligand sterics.

FRET pairs involving up to three different Bodipy dyes are utilized to provide information on the assembly/disassembly of organometallic complexes. Azolium salts tagged with chemically robust and photostable blue or green or red fluorescent Bodipy, respectively, were synthesized and the azolium salts used to prepare metal complexes [(NHC_blue)ML], [(NHC_green)ML] and [(NHC_red)ML] (ML = Pd(allyl)Cl, IrCl(cod), RhCl(cod), AuCl, Au(NTf2), CuBr). The blue and the green Bodipy and the green and the red Bodipy, respectively, were designed to allow the formation of efficient FRET pairs with minimal cross-talk. Organometallic dyads formed from two subunits enable the transfer of excitation energy from the donor dye to the acceptor dye. The blue, green and red emission provide three information channels on the formation of complexes, which is demonstrated for alkyne or sulfur bridged digold species and for ion pairing of a red fluorescent cation and a green fluorescent anion. This approach is extended to probe an assembly of three different subunits. In such a triad, each component is tagged with either a blue, a green or a red Bodipy and the energy transfer blue green  red proves the formation of the triad. The tagging of molecular components with robust fluorophores can be a general strategy in (organometallic) chemistry to establish connectivities for intermediates in homogeneous catalysis

The close ion-pair of Ir(bdpSO3)(cod)(IMes)] is an efficient photosensitizer, while the solvent-separated anion is highly fluorescent.

The efficient hydrohydrazidation of terminal (6a–r, 18 examples, 0.1–0.2 mol % [(NHC)Au(NTf2)], T = 60 °C) and internal alkynes (7a–j, 10 examples, 0.2–0.5 mol % [(NHC)Au(NTf2)], T = 60–80 °C) utilizing a complex with a sterically demanding bispentiptycenyl-substituted NHC ligand and the benign reaction solvent anisole, is reported.

Three different types of bimetallic NHC-metal complexes were synthesized, whose NHC units are attached at the 4,5-positions of xanthene. The NHC units are in close proximity and are designed such that each carbene coordinates one ML unit, while the chelation of one metal by two NHC is not possible. Several xanthene-((NHC)ML)

The reaction of 2,6-dimethyl-4-(Bodipy-8-yl)aniline with 1,4-dioxane-2,3-diol provides the respective diimine 3, followed by ring closure with paraformaldehyde, resulting in the imidazolium salt 4·HCl containing two fluorophores. The NHC metal complexes ([IrCl(cod)(4)], [Ir(cod)(4)(py)]OTf, [IrCl(CO)2(4)], [PdCl(allyl)(4)], [PdCl2(Clpy)(4)], [AuCl(4)], and [NiCl(Cp)(4)]) were prepared. The complexes with (Au, Pd) are fluorescent. Weakly fluorescent complexes with Ir undergo fluorogenic reactions with CO and H2. The oxidative addition of H2 to [Ir(cod)(4)]OTf leads to a fluorescence gain of 8.2 and is suitable for the detection of hydrogen. Following activation of the diimine complex [PdCl(CH3)(3)] with NaBArF, the formed [Pd(CH3)(3)]BArF is a competent ethene polymerization catalyst. The addition of (pyridine, CH3CN, CO) or olefins (ethene, 1-hexene, styrene) to the activated complex results in a pronounced increase in the fluorescence because of metal–ligand interactions and the modulation of photoinduce...

A number of Ir–N-heterocyclic carbene (Ir–NHC) complexes with asymmetric N-heterocyclic carbene (NHC) ligands have been prepared and examined for signal amplification by reversible exchange (SABRE). Pyridine was chosen as model compound for hyperpolarization experiments. This substrate was examined in a solvent mixture using several Ir–NHC complexes, which differ in their NHC ligands. The SABRE polarization was created at 6 mT and the 1H nuclear magnetic resonance signals were detected at 7 T. We show that asymmetric NHC ligands, because of their favorable chemistry, can adapt the SABRE active complexes to different chemical scenarios.

Ni2+ coordinated within a bowl-shaped diimine ligand with two pentiptycenyl-substituents [(diimine)NiBr2] displays excellent activity for the polymerization of ethene (7 atm) with activities of up to 34 × 103 kg(mol Ni)−1 h–1 following activation with Et2AlCl. The resulting polymer is characterized by high molecular weights (Mn = 150 × 103 g·mol–1), low branching (12/1000 C), and a high melting point (Tm = 133 °C). The polymerization of ethene with polar comonomers leads to the formation of the respective polar polymers with very efficient incorporation of comonomer. The activity of the catalyst critically depends on the molar ratio of Et2AlCl activator and the polar functional group.

The initiation reactions of the three Hoveyda–Grubbs complexes (GH(H), GH(4-NO2), and GH(5-NO2)) with ethene were studied via UV–vis spectroscopy. The unsubstituted complex GH(H) initiates approximately 5 times slower with ethene than with 1-hexene, and the electron-deficient GH(4-NO2) and GH(5-NO2) initiates 1.2 and 1.7 times slower with ethene than with 1-hexene. A detailed multiwavelength analysis of the absorbance–time traces reveals the multistep nature of the reaction of the Hoveyda–Grubbs complexes with ethene. In addition to the established rate constant k1 (being first order in ethene), two additional, c(olefin) independent reactions k2 and k3 were identified: k2 depends on the nature of the GH precatalyst, while k3 is nearly independent of the precatalyst. The reaction associated with k1 precedes the faster k2 leading to low stationary concentration of an intermediate formed from the respective Hoveyda–Grubbs complex and ethene, corresponding to a postinitiation species.

A Grubbs-Hoveyda type catalyst with a N-pentiptycenyl, N-cyclohexyl-NHC ligand provides poly(nbe-alt-coe) with an excellent degree of alternation while lacking significant activity in the homopolymerization of cyclooctene.

A new N,N′-bis(triptycenyl)-NHC ligand with methyl groups in the ortho position has been synthesized starting from 2,3-dimethyltriptycene-1,4-quinone. The respective metal complexes [ML(NHC)] [ML = CuBr, AuCl, PdCl(allyl), RhCl(cod), IrCl(cod), RhCl(CO)2, IrCl(CO)2, and RuCl2(=CHC6H4OiPr)] were obtained by standard procedures. All the complexes were initially mixtures of syn and anti isomers. The ruthenium complex was separated into the syn and anti isomers. The crystal structure of the anti complex [RhCl(cod)(8)] has been determined.

Complexes of the general formula [IrCl(cod)(bdp-NHC-bdp′)] and [IrCl(cod)(bdp-NHC)] (bdp=bodipy=4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, cod=1,5-cyclooctadiene) were synthesized. The substitution reaction of cod with two molecules of CO converts weakly fluorescent into strongly fluorescent complexes [IrCl(CO)2(bdp-NHC-bdp′)] and [IrCl(CO)2(bdp-NHC)]. Bdp and bdp“ form a fluorescence resonance energy transfer (FRET) pair and the excitation of bdp leads to a strong emission from bdp” with a virtual Stokes shift of 98 nm. The fluorescence gain (IFl[Ir(CO)2]]/IFl[Ir(cod)]=1.7) upon reaction with CO in this complex is modest. To increase the fluorescence gain, the quenching capacity of the transition metal was improved by increasing the electron density at iridium. This was achieved by substituting the metal-bound chloride with an electron-rich thiolate RC6H4S. Depending on the nature of the R substituent in [Ir(SC6H4R)(cod)(bdp-NHC-bdp′)], an improved fluorescence gain in the cod/CO substitution reaction of up to 4.3 was observed and up to 26 (from gain=5) in [Ir(SC6H4R)(cod)(bdp-NHC)]. DFT calculations on closely related [Ir(SC6H4R)(cod)(bdp-NHC)] complexes indicate that a photoinduced electron transfer mechanism is the dominant quenching pathway for the iridium thiolates with R=COMe, CF3, Cl, H, Me, tBu, OMe, NEt2. The CO-responsive FRET complex was immobilized on paper, displaying a red fluorescent color upon exposure to CO.

Five different highly fluorescent boron-dipyrromethene (BODIPY)-tagged N-heterocyclic carbene NHC-gold halide complexes were synthesized. The substitution of the halogeno ligand by 4-substituted aryl thiolates leads to a decrease in the brightness of the complexes. This decrease depends on the electronic nature of the thiols, being most pronounced with highly electron-rich thiols (4-R=NMe2 ). The brightness of the gold thiolates also depends on the distance between the sulfur atom and the BODIPY moiety. The systematic variation of the electron density of [(NHC-bodipy)Au(SC6 H4 R)] (via different R groups) enables the systematic variation of the fluorescence brightness of an appended BODIPY fluorophore. Based on this and supported by DFT calculations, a photoinduced electron-transfer quenching appears to be the dominant mechanism controlling the brightness of the appended BODIPY dye.

The control of ionic permselectivity in porous films is an interesting aspect in the context of lab-on-chip devices and μ-electronics. Especially, visible light triggered ionic permselectivity control is of relevance because control by light can be maintained externally without changing internal system parameters. In addition, light is a sustainable energy source if sunlight is used. Here, we present the first mesoporous films modified with two different photochromic homopolymers by surface-initiated ring opening metathesis polymerization (SI-ROMP). Spiropyran- and spirooxazine functionalized norbornene monomers and the corresponding ROMP homopolymers are synthesized in solution and in mesopores and compared concerning their optical properties such as photochromic conversion kinetics, photostability, and the ratio of converted molecules. Optical properties are investigated using UV/VIS spectroscopy and 1H-NMR spectroscopy. Especially, spirooxazine, whose surface functionalization has not been studied in detail, shows fast switching properties and higher ratios of photochromically interconverted molecules. After grafting spiropyran- and spirooxazine norbornene homopolymers into mesopores, a slightly faster photochromic interconversion of polymers located inside the mesopores is observed compared to the solution polymers.

A Crabtree-type Ir(I) complex tagged with a fluorescent dye (bodipy) was synthesized. The oxidative addition of H2 converts the weakly fluorescent Ir(I) complex (Φ=0.038) into a highly fluorescent Ir(III) species (Φ=0.51). This fluorogenic reaction can be utilized for the detection of H2 and to probe the oxidative addition step in the catalytic hydrogenation of olefins.

Two gold complexes with different bodipy-tagged N-heterocyclic carbene ligands, which are a potential FRET pair, were synthesized. It was shown, that the formation of dinuclear intermediates in alkyne transformations (“dual gold catalysis”) are characterized by a FRET signal.

A thin film of poly-([IrCl(cod)(NHC-onbe)]n -(propyl-onbe)m ) (onbe=oxanorbornene) coated on filter paper reacts quantitatively with CO to yield 1,5-cyclooctadiene, the unpleasant smell of which can be detected by the human olfactory system with very high sensitivity. Odorless, but toxic CO is thus "translated" into the distinct smell of 1,5-cyclooctadiene. Based on malodorogenic sensing it is possible to smell the presence of CO.

Several metal complexes with a boron dipyrromethene (BODIPY)-functionalized N-heterocyclic carbene (NHC) ligand 4 were synthesized. The fluorescence in [(4)(SIMes)RuCl2(ind)] complex is quenched (Φ = 0.003), it is weak in [(4)PdI2(Clpy)] (Φ = 0.033), and strong in [(4)AuI] (Φ = 0.70). The BODIPY-tagged complexes can experience pronounced changes in the brightness of the fluorophore upon ligand-exchange and ligand-dissociation reactions. Complexes [(4)MX(1,5-cyclooctadiene)] (M = Rh, Ir; X = Cl, I; Φ = 0.008-0.016) are converted into strongly fluorescent complexes [(4)MX(CO)2] (Φ = 0.53-0.70) upon reaction with carbon monoxide. The unquenching of the Rh and Ir complexes appears to be a consequence of the decreased electron density at Rh or Ir in the carbonyl complexes. In contrast, the substitution of an iodo ligand in [(4)AuI] by an electron-rich thiolate decreases the brightness of the BODIPY fluorophore, rendering the BODIPY as a highly sensitive probe for changes in the coordination sphere of the transition metal.

1,3,5-Tricycloalkylbenzene (cycloalkyl = C5H9, C6H11) was converted into the respective anilines (by means of nitration and reduction) and then into the corresponding diimines (with glyoxal), the cyclization of which with (HCHO)n/ZnCl2 provided the respective 1,3-bis(2,4,6-tricyclopentylphenyl)imidazolium salt in modest yields. An analogous reaction sequence that employed acenaphthene-1,2-dione instead of glyoxal yielded the two azolium salts in good yields, which were converted into the respective N-heterocyclic carbene (NHC) complexes [(NHC)AgCl], [(NHC)AuCl], [(NHC)RhCl(cod)] (cod = cyclooctadiene), and [(NHC)RhCl(CO)2].

The present work establishes a new synthetic route that leads to substituted azolium salts. The base stable 1-(4-bromo-2,6-diisopropylphenyl)-3-(2,6-diisopropylphenyl)imidazolidine and 1,3-bis(4-bromo-2,6-diisopropylphenyl)imidazolidine were synthesized and the 4-Br substituents converted into various functional groups through Br/Li exchange or Pd-catalyzed cross-coupling reactions (Suzuki, Sonogashira, and vinylation). The substituted imidazolidines were oxidized, by using chloranil or N-bromosuccinimide, to provide the respective azolium salts, which are convenient precursors to N-heterocyclic carbenes.

In recent years, the hyperpolarization method Signal Amplification By Reversible Exchange (SABRE) has developed into a powerful technique to enhance Nuclear Magnetic Resonance (NMR) signals of organic substrates in solution (mostly via binding to the nitrogen lone pair of N-heterocyclic compounds) by several orders of magnitude. In order to establish the application and development of SABRE as a hyperpolarization method for medical imaging, the separation of the Ir-N-Heterocyclic Carbene (Ir-NHC) complex, which facilitates the hyperpolarization of the substrates in solution, is indispensable. Here, we report for the first time the use of novel Ir-NHC complexes with a polymer unit substitution in the backbone of N-Heterocyclic Carbenes (NHC) for SABRE hyperpolarization, which permits the removal of the complexes from solution after the hyperpolarization of a target substrate has been generated.

Conversion-time data were recorded for various ring-closing metathesis (RCM) reactions that lead to five- or six-membered cyclic olefins by using different precatalysts of the Hoveyda type. Slowly activated precatalysts were found to produce more RCM product than rapidly activated complexes, but this comes at the price of slower product formation. A kinetic model for the analysis of the conversion-time data was derived, which is based on the conversion of the precatalyst (Pcat) into the active species (Acat), with the rate constant k(act), followed by two parallel reactions: 1) the catalytic reaction, which utilizes Acat to convert reactants into products, with the rate k(cat), and 2) the conversion of Acat into the inactive species (Dcat), with the rate k(dec). The calculations employ two experimental parameters: the concentration of the substrate (c(S)) at a given time and the rate of substrate conversion (-dc(S)/dt). This provides a direct measure of the concentration of Acat and enables the calculation of the pseudo-first-order rate constants k(act), k(cat), and k(dec) and of k(S) (for the RCM conversion of the respective substrate by Acat). Most of the RCM reactions studied with different precatalysts are characterized by fast k(cat) rates and by the k(dec) value being greater than the k(act) value, which leads to quasistationarity for Acat. The active species formed during the activation step was shown to be the same, regardless of the nature of different Pcats. The decomposition of Acat occurs along two parallel pathways, a unimolecular (or pseudo-first-order) reaction and a bimolecular reaction involving two ruthenium complexes. Electron-deficient precatalysts display higher rates of catalyst deactivation than their electron-rich relatives. Slowly initiating Pcats act as a reservoir, by generating small stationary concentrations of Acat. Based on this, it can be understood why the use of different precatalysts results in different substrate conversions in olefin metathesis reactions.

Eight new N-Hoveyda-type complexes were synthesized in yields of 67-92 % through reaction of [RuCl2 (NHC)(Ind)(py)] (NHC=1,3-bis(2,4,6-trimethylphenylimidazolin)-2-ylidene (SIMes) or 1,3-bis(2,6-diisopropylphenylimidazolin)-2-ylidene (SIPr), Ind=3-phenylindenylid-1-ene, py=pyridine) with various 1- or 1,2-substituted ferrocene compounds with vinyl and amine or imine substituents. The redox potentials of the respective complexes were determined; in all complexes an iron-centered oxidation reaction occurs at potentials close to E=+0.5 V. The crystal structures of the reduced and of the respective oxidized Hoveyda-type complexes were determined and show that the oxidation of the ferrocene unit has little effect on the ruthenium environment. Two of the eight new complexes were found to be switchable catalysts, in that the reduced form is inactive in the ring-opening metathesis polymerization of cis-cyclooctene (COE), whereas the oxidized complexes produce polyCOE. The other complexes are not switchable catalysts and are either inactive or active in both reduced and oxidized states.

Redox-responsive polyvinylferrocene-grafted silica nanoparticles have been used for modulating the catalytic activity of surface-attached Grubbs second generation type catalysts for the ring-opening metathesis polymerization (ROMP) of norbornene monomer. A facile and very efficient protocol for the modification of living polyvinylferrocene chains was developed to introduce a suitable functional group for the intended “grafting onto” approach. Grafted particles were characterized by using TEM, SEM/energy dispersive X-ray spectroscopy (EDS), XPS, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and cyclic voltammetry, revealing both the presence of redox-responsive polymers and the presence of Grubbs catalyst in the particle exterior. Chemical oxidation protocols for immobilized polymers were applied to deactivate surface-attached catalysts in ROMP protocols, while chemical in situ reduction immediately led to catalyst’s reactivation.

End-of-life tire granulates were used in olefin metathesis reactions with ethene (ethenolysis); utilizing 0.0074 mmol of a Grubbs type ruthenium complex for 1.0 gram of tire granules leads to the isolation of ca. 0.5 g of organic solubles, which are primarily composed of oligomeric 1,4-cis isoprenes.

The electrochemical behaviour and cation recognition properties of two oxaferrocene cryptand ligands, 1,1′-[(1,4,10-trioxa-7,13-diazacyclopentadecane-7,13-diyl)diethoxy]-3,3′,4,4′-tetraphenylferrocene and 1,1′-[(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)diethoxy]-3,3′,4,4′-tetraphenylferrocene, have been characterized in acetonitrile in the presence of Ba 2+ and Na + by cyclic voltammetry, square wave voltammetry and a rotating disc electrode. The changes in the redox signals for the cryptates at varying concentrations of the target cations are used as a direct measure of the electronic coupling between the two units, leading to the conclusion that the cryptate formation process proceeds in multiple stages and the ligand offers several binding sites in the complex.

The reaction of 1-amino,4-hydroxy-pentiptycene with diacetyl or acenaphthene-1,2-dione gave the respective diimines, followed by alkylation of the hydroxyl groups, and cyclization of the alkylated diimines to the respective bispentiptycene-imidazolium salts NHC·HCl. The azolium salts, being precursors to N-heterocyclic carbenes, were converted into metal complexes [(NHC)MX] (MX = CuI, AgCl, AuCl) and [(NHC)IrCl(cod)] and [(NHC)IrCl(CO)2] in good yields. In the solid state [(NHC)AgCl] displays a bowl-shaped structure of the ligand with the metal center buried within the concave unit.

Based on 1-amino-4-hydroxy-triptycene, new saturated and unsaturated triptycene-NHC (N-heterocyclic carbene) ligands were synthesized from glyoxal-derived diimines. The respective carbenes were converted into metal complexes [(NHC)MX] (M=Cu, Ag, Au; X=Cl, Br) and [(NHC)MCl(cod)] (M=Rh, Ir; cod=1,5-cyclooctadiene) in good yields. The new azolium salts and metal complexes suffer from limited solubility in common organic solvents. Consequently, the introduction of solubilizing groups (such as 2-ethylhexyl or 1-hexyl by O-alkylation) is essential to render the complexes soluble. The triptycene unit infers special steric properties onto the metal complexes that enable the steric shielding of selected areas close to the metal center. Next, chiral and meso-triptycene based N-heterocyclic carbene ligands were prepared. The key step in the synthesis of the chiral ligand is the Buchwald-Hartwig amination of 1-bromo-4-butoxy-triptycene with (1S,2S)-1,2-diphenyl-1,2-diaminoethane, followed by cyclization to the azolinium salt with HC(OEt)3 . The analogous reaction with meso-1,2-diphenyl-1,2-diaminoethane provides the respective meso-azolinium salt. Both the chiral and meso-azolinium salts were converted into metal complexes including [(NHC)AuCl], [(NHC)RhCl(cod)], [(NHC)IrCl(cod)], and [(NHC)PdCl(allyl)]. An in situ prepared chiral copper complex was tested in the enantioselective borylation of α,β-unsaturated esters and found to give an excellent enantiomeric ratio (er close to 90:10).

Reactions of the Grubbs 3rd generation complexes [RuCl(2)(NHC)(Ind)(Py)] (N-heterocyclic carbene (NHC)=1,3-bis(2,4,6-trimethylphenylimidazolin)-2-ylidene (SIMes), 1,3-bis(2,6-diisopropylphenylimidazolin)-2-ylidene (SIPr), or 1,3-bis(2,6-diisopropylphenylimidazol)-2-ylidene (IPr); Ind=3-phenylindenylid-1-ene, Py=pyridine) with 2-ethenyl-N-alkylaniline (alkyl=Me, Et) result in the formation of the new N-Grubbs-Hoveyda-type complexes 5 (NHC=SIMes, alkyl=Me), 6 (SIMes, Et), 7 (IPr, Me), 8 (SIPr, Me), and 9 (SIPr, Et) with N-chelating benzylidene ligands in yields of 50-75 %. Compared to their respective, conventional, O-Grubbs-Hoveyda complexes, the new complexes are characterized by fast catalyst activation, which translates into fast and efficient ring-closing metathesis (RCM) reactivity. Catalyst loadings of 15-150 ppm (0.0015-0.015 mol %) are sufficient for the conversion of a wide range of diolefinic substrates into the respective RCM products after 15 min at 50 °C in toluene; compounds 8 and 9 are the most catalytically active complexes. The use of complex 8 in RCM reactions enables the formation of N-protected 2,5-dihydropyrroles with turnover numbers (TONs) of up to 58,000 and turnover frequencies (TOFs) of up to 232,000 h(-1); the use of the N-protected 1,2,3,6-tetrahydropyridines proceeds with TONs of up to 37,000 and TOFs of up to 147,000 h(-1); and the use of the N-protected 2,3,6,7-tetrahydroazepines proceeds with TONs of up to 19,000 and TOFs of up to 76,000 h(-1), with yields for these reactions ranging from 83-92 %.

The conversion-time data for 168 different Pd/Cu-catalyzed Sonogashira cross-coupling reactions of five arylacetylenes (phenylacetylene; 1-ethynyl-2-ethylbenzene; 1-ethynyl-2,4,6-R(3)-benzene (R = Me, Et, i-Pr)) and Me(3)SiCCH with seven aryl bromides (three 2-R-bromobenzenes (R = Me, Et, i-Pr); 2,6-Me(2)-bromobenzene and three 2,4,6-R(3)-bromobenzenes (R = Me, Et, i-Pr)) with four different phosphines (P-t-Bu(3), t-Bu(2)PCy, t-BuPCy(2), PCy(3)) were determined using quantitative gas chromatography. The stereoelectronic properties of the substituents in the aryl bromides, acetylenes, and phosphines were correlated with the performance in Sonogashira reactions. It was found that the nature of the most active Pd/PR(3) complex for a Sonogashira transformation is primarily determined by the steric bulk of the acetylene; ideal catalysts are: Pd/P-t-Bu(3) or Pd/t-Bu(2)PCy for sterically undemanding phenylacetylene, Pd/t-BuPCy(2) for 2- and 2,6-substituted arylacetylenes or Me(3)SiCCH and Pd/PCy(3) for extremely bulky acetylenes and aryl bromides. Electron-rich and sterically demanding aryl bromides with substituents in the 2- or the 2,6-position require larger amounts of catalyst than 4-substituted aryl bromides. The synthesis of tolanes with bulky groups at one of the two aryl rings is best done by placing the steric bulk at the arylacetylene, which is also the best place for electron-withdrawing substituents.

Grubbs-Hoveyda-type complexes with variable 4-R (complexes 1: 4-R = NEt(2), OiPr, H, F, NO(2)) and 5-R substituents (complexes 2: 5-R = NEt(2), OiPr, Me, F, NO(2)) at the 2-isopropoxy benzylidene ether ligand and with variable 4-R substituents (complexes 3: 4-R = H, NO(2)) at the 2-methoxy benzylidene ether ligand were synthesized and the respective Ru(II/III) redox potentials (ranging from ΔE = +0.46 to +1.04 V), and UV-vis spectra recorded. The initiation kinetics of complexes 1-3 with the olefins diethyl diallyl malonate (DEDAM), butyl vinyl ether (BuVE), 1-hexene, styrene, and 3,3-dimethylbut-1-ene were investigated using UV-vis spectroscopy. Electron-withdrawing groups at the benzylidene ether ligands were found to increase the initiation rates, while electron-donating groups lead to slower precatalyst activation; accordingly with DEDAM, the complex 1(NO(2)) initiates almost 100 times faster than 1(NEt(2)). The 4-R substituents (para to the benzylidene carbon) were found to have a stronger influence on physical and kinetic properties of complexes 1 and 2 than that of 5-R groups para to the ether oxygen. The DEDAM-induced initiation reactions of complexes 1 and 2 are classified as two-step reactions with an element of reversibility. The hyperbolic fit of the k(obs) vs [DEDAM] plots is interpreted according to a dissociative mechanism (D). Kinetic studies employing BuVE showed that the initiation reactions simultaneously follow two different mechanistic pathways, since the k(obs) vs [olefin] plots are best fitted to k(obs) = k(D)·k(4)/k(-D)·[olefin]/(1 + k(4)/k(-D)·[olefin]) + k(I)·[olefin]. The k(I)·[olefin] term dominates the initiation behavior of the sterically less demanding complexes 3 and was shown to correspond to an interchange mechanism with associative mode of activation (I(a)), leading to very fast precatalyst activation at high olefin concentrations. Equilibrium and rate constants for the reactions of complexes 1-3 with the bulky PCy(3) were determined. In general, sterically demanding olefins (DEDAM, styrene) and Grubbs-Hoveyda type complexes 1 and 2 preferentially initiate according to the dissociative pathway; for the less bulky olefins (BuVE, 1-hexene) and complexes 1 and 2 both D and I(a) are important. Activation parameters for BuVE reactions and complexes 1(NEt(2)), 1(H), and 1(NO(2)) were determined, and ΔS(‡) was found to be negative (ΔS(‡) = -113 to -167 J·K(-1)·mol(-1)) providing additional support for the I(a) catalyst activation.

The utility of [(NHC)(PPh 3 )RuCl 2 (CHPh)] for the facile and efficient synthesis of ten complexes of the type [(NHC)(NHC ewg )RuCl 2 (CHR)] with saturated and unsaturated NHC ligands in 85–94% isolated yield via a simple one step synthesis utilizing [AgI(NHC ewg )] as NHC ewg transfer reagents was demonstrated.

Grubbs−Hoveyda and Grubbs III type complexes with ferrocenyl- or −NEt2-substituted NHC ligands were synthesized according to standard procedures. The electron donation of the NHC ligands in the respective ruthenium complexes can be modulated by oxidation of the ferrocenyl moiety or by protonation of the amino group. The neutral and the respective cationic (oxidized or protonated) ruthenium complexes were tested in the ROMP of norbornene. The change in the electron donation of the NHC ligands upon protonation leads to a significant change in the double-bond geometry (from E/Z ratio = 0.78 to E/Z = 1.04) and in the microstructure of the resulting polynorbornene. Consequently, addition of acid and protonation of the living catalyst attached to the polymer chain during the polymerization reaction allows fine-tuning the E/Z ratio of the resulting polynorbornene.

The palladium complex (0.5 mol-%) of a water-soluble sulfonated fluorenylphosphane (cataCXium Fsulf) enables thefacile Suzuki–Miyaura coupling of various (heterocyclic) aryl tosylates and aryl mesylate with various (heterocyclic) boronic acids in excellent yields (> 95 %) using water as the reaction solvent. Retraction: The following article from the European Journal of Organic Chemistry, “Suzuki–Miyaura Coupling of Aryl Tosylates and Mesylates in Water”, published online on April 15, 2010 in Wiley Online Library (www.onlinelibrary.wiley.com, doi: 10.1002/ejoc.201000251) and in print (Eur. J. Org. Chem.2010, 2934–2937), has been retracted by agreement between the corresponding author, the journal Editor, Dr. Haymo Ross, and Wiley-VCH. The retraction has been agreed because several 1H and 13C NMR spectroscopic data listed in the manuscript are incorrect, and the original mass spectra cannot be located. Attempts to repeat the synthesis of several representative products under the conditions reported in this manuscript have failed.

The reactions of the N,N'-diarylimidazolium and N,N'-diarylimidazolinium salts with chlorosulfonic acid result in the formation of the respective disulfonated N-heterocyclic carbene (NHC) precursors in reasonable yields (46-77%). Water-soluble palladium catalyst complexes, in situ obtained from the respective sulfonated imidazolinium salt, sodium tetrachloropalladate (Na 2 PdCl 4 ) and potassium hydroxide (KOH) in water, were successfully applied in the copper-free Sonogashira coupling reaction in isopropyl alcohol/water mixtures using 0.2 mol% catalyst loading. The preformed (disulfonatedNHC)PdCl(cinnamyl) complex was used in aqueous Suzuki-Miyaura reactions at 0.1 mol% catalyst loading. The coupling protocol reported here is very useful for Sonogashira reactions of N- and S-heterocyclic aryl bromides and chlorides with aryl- and alkylacetylenes.

Imidazolium salts (NHC(ewg)HCl) with electronically variable substituents in the 4,5-position (H,H or Cl,Cl or H,NO(2) or CN,CN) and sterically variable substituents in the 1,3-position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)(ewg)] complexes. The reactions of [(NHC)RuCl(2)(CHPh)(py)(2)] with the [AgI(NHC(ewg))] complexes provide the respective [(NHC)(NHC(ewg))RuCl(2)(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring-closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2-0.5 mol % at 80 degrees C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHC(ewg) group with 1,3-Me,iPr and 4,5-Cl,Cl substituents and can be synthesized in 95 % isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL-NHC)(NHC(ewg))RuCl(2)(CHPh)] and [(FL-NHC(ewg))(NHC)RuCl(2)(CHPh)], with a dansyl fluorophore (FL)-tagged electron-rich NHC ligand (FL-NHC) and an electron-deficient NHC ligand (FL-NHC(ewg)) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore-tagged ligand. In this manner, it was shown for ring-opening metathesis ploymerization (ROMP) reactions at room temperature that the NHC(ewg) ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium.

The strong electron-donation and the steric bulk of trialkylphosphines renders them as very useful ligands for palladium-catalyzed cross coupling reactions. This critical review reports on the synthesis of two families of trialkylphosphines (diadamantylalkylphosphines, fluorenyldialkylphosphines) and the properties of the respective palladium complexes in various cross coupling reactions, which evolved as alternatives to the classical Pd/PtBu(3) system. In contrast to the latter phosphine the new classes of ligands are characterized by a highly flexible ligand design, which allows the fine tuning of catalytic properties to the specific needs of certain substrates and also enables the attachment of additional tags to impart certain useful properties onto the respective phosphines (179 references).

NHC with EWGs for RCM: Ruthenium complexes with two N-heterocyclic carbenes (NHCs), one of them substituted with electron-withdrawing groups (EWGs), are highly efficient (pre)catalysts for the synthesis of tetrasubstituted olefins and trisubstituted olefins by ring-closing metathesis reactions (RCM, see scheme).

An enlarged imidazolinium salt with a molecular mass of nearly 800 g/mol was synthesized and the respective N-heterocyclic carbene (NHC= N,N′-bis(2,6-diisopropyl-4-CH2NCy2-phenyl)-4,5-dihydroimidazol-2-ylidene) converted into (NHC)Pd(allyl)Cl and (NHC)Pd(cinnamyl)Cl complexes. The cinnamyl complex displays excellent activities in the Suzuki−Miyaura coupling and the Buchwald−Hartwig amination. The separation of this complex from the coupling products by means of a solvent-resistant nanofiltration using a PDMS (polydimethylsiloxane) membrane on PAN (polyacrylonitrile) was tested, and very high retention of between 97% and 99.9% of the (NHC)Pd complex was observed. The residual Pd content in the cross-coupling products is in the range 3.5−25 ppm.

Twenty-three different Rh complexes of the (NHC)RhCl(cod) and (NHC)RhCl(CO) 2 type were synthesized from [RhCl(cod)] 2 . The electron donating nature of the NHC ligands was changed in a systematic manner. The redox potentials of the various (NHC)RhCl(cod) and the ν (CO) of the various (NHC)RhCl(CO) 2 were determined. A correlation of the Rh redox potentials and the Rh ν (CO), respectively, with the related data from analogous (NHC)IrCl(cod) and (NHC)IrCl(CO) 2 complexes established two linear relationships. The linear regression ( R 2 = 0.993) of the Rh and the Ir redox potentials results in an equation for the redox potential transformation: E 1/2 (Ir) = 1.016 · E 1/2 (Rh) − 0.076 V. The linear regression ( R 2 = 0.97) of the Rh and Ir ν av (CO) results in an equation for the ν av (CO) transformation: ν av (CO)Ir = 0.8695 · ν av (CO)Rh + 250.7 cm −1 . In this manner the Rh and the Ir-scale for the determination of the electron donating properties of NHC ligands are unified.