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The Ullmann coupling has been used extensively as a synthetic tool for the formation of C-C bonds on surfaces. Thus far, most syntheses made use of aryl bromides or aryl iodides. We investigated the applicability of an aryl chloride in the bottom-up assembly of graphene nanoribbons. Specifically, the reactions of 10,10'-dichloro-9,9'-bianthryl (DCBA) on Au(111) were studied. Using atomic resolution non-contact AFM, the structure of various coupling products and intermediates were resolved, allowing us to reveal the important role of the geometry of the intermediate aryl radicals in the formation mechanism. For the aryl chloride, cyclodehydrogenation occurs before dehalogenation and polymerization. Due to their geometry, the planar bisanthene radicals display a different coupling behavior compared to the staggered bianthryl radicals formed when aryl bromides are used. This results in oligo- and polybisanthenes with predominantly fluoranthene-type connections., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A system of three coupled catalytic cycles enabling the one-pot transformation of epoxides to amines via Meinwald rearrangement, imine condensation, and imine reduction is described. This assisted tandem catalysis is catalyzed by B(C6F5)3 resulting in the first tandem Meinwald rearrangement-reductive amination protocol. The reaction proceeds in nondried solvents and yields β-functionalized amines. In particular, β-diarylamines are obtained in high yields.

Bulky iron complexes are described that catalyze the site-selective oxidation of alkyl C-H bonds with hydrogen peroxide under mild conditions. Steric bulk at the iron center is introduced by appending trialkylsilyl groups at the meta-position of the pyridines in tetradentate aminopyridine ligands, and this effect translates into high product yields, an enhanced preferential oxidation of secondary over tertiary C-H bonds, and the ability to perform site-selective oxidation of methylenic sites in terpenoid and steroidal substrates. Unprecedented site selective oxidation at C6 and C12 methylenic sites in steroidal substrates is shown to be governed by the chirality of the catalysts., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A range of silanes was synthesized by the reaction of HSiCl3 with iminopyrrole derivatives in the presence of NEt3 . In certain cases, intramolecular hydrosilylation converts the imine ligand into an amino substituent. This reaction is inhibited by factors such as electron-donating substitution on Si and steric bulk. The monosubstituted ((Dipp) IMP)SiHMeCl ((Dipp) IMP=2-[N-(2,6-diisopropylphenyl)iminomethyl]pyrrolide), is stable towards hydrosilylation, but slow hydrosilylation is observed for ((Dipp) IMP)SiHCl2 . Reaction of two equivalents of (Dipp) IMPH with HSiCl3 results in the hydrosilylation product ((Dipp) AMP)((Dipp) IMP)SiCl ((Dipp) AMP=2-[N-(2,6-diisopropylphenyl)aminomethylene]pyrrolide), but the trisubsitituted ((Dipp) IMP)3 SiH is stable. Monitoring the hydrosilylation reaction of ((Dipp) IMP)SiHCl2 reveals a reactive pathway involving ligand redistribution reactions to form the disubstituted ((Dipp) AMP)((Dipp) IMP)SiCl as an intermediate. The reaction is strongly accelerated in the presence of chloride anions., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An iron complex with a C1-symmetric tetradentate N-based ligand catalyzes the asymmetric epoxidation of cyclic enones and cyclohexene ketones with aqueous hydrogen peroxide, providing the corresponding epoxides in good to excellent yields and enantioselectivities (up to 99% yield, and 95% ee), under mild conditions and in short reaction times. Evidence is provided that reactions involve an electrophilic oxidant, and this element is employed in performing site selective epoxidation of enones containing two alkene sites.

A series of Grubbs-type catalysts that contain lipase-inhibiting phosphoester functionalities have been synthesized and reacted with the lipase cutinase, which leads to artificial metalloenzymes for olefin metathesis. The resulting hybrids comprise the organometallic fragment that is covalently bound to the active amino acid residue of the enzyme host in an orthogonal orientation. Differences in reactivity as well as accessibility of the active site by the functionalized inhibitor became evident through variation of the anchoring motif and substituents on the N-heterocyclic carbene ligand. Such observations led to the design of a hybrid that is active in the ring-closing metathesis and the cross-metathesis of N,N-diallyl-p-toluenesulfonamide and allylbenzene, respectively, the latter being the first example of its kind in the field of artificial metalloenzymes., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first shape-persistent macrocycle 1 offering a Brønsted pair functionalized interior is described. Via postcyclization transformation, this heterosequenced compound can be obtained from its corresponding ester 2. The macrocycles differ dramatically in their characteristics such as solubility and appearance. Theoretical investigations suggest that those contrasts might originate from conformational changes due to the formation of a strong O-H-N hydrogen bond in 1.

A Rh(NHC) phosphonate complex reacts with the lipases cutinase and Candida antarctica lipase B resulting in the first (soluble) artificial metalloenzymes formed by covalent active site-directed hybridization. When compared to unsupported complexes, these new robust hybrids show enhanced chemoselectivity in the (competitive) hydrogenation of olefins over ketones.

Reaction of [PdClMe(P^N)2] with SnCl2 followed by Cl-abstraction leads to apparent Pd-C bond activation, resulting in methylstannylene species trans-[PdCl{(P^N)2SnClMe}][BF4] (P^N = diaryl phosphino-N-heterocycle). In contrast, reaction of Pt analogues with SnCl2 leads to Pt-Cl bond activation, resulting in methylplatinum species trans-[PtMe{(P^N)2SnCl2}][BF4]. Over time, they isomerise to methylstannylene species, indicating that both kinetic and thermodynamic products can be isolated for Pt, whereas for Pd only methylstannylene complexes are isolated. Oxidative addition of RSnCl3 (R = Me, Bu, Ph) to M(0) precursors (M = Pd or Pt) in the presence of P^N ligands results in diphosphinostannylene pincer complexes trans-[MCl{(P^N)2SnCl(R)}][SnCl4R], which are structurally similar to the products from SnCl2 insertion. This showed that addition of RSnCl3 to M(0) results in formal Sn-Cl bond oxidative addition. A probable pathway of activation of the tin reagents and formation of different products is proposed and the relevancy of the findings for Pd and Pt catalysed processes that use SnCl2 as a co-catalyst is discussed., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of new chiral pyridinyl prolinate (RPyProR) ligands and their corresponding Fe(II) triflate and chloride complexes are reported. The ligands possess an NN'O coordination motif, as found in the active site of non-heme iron enzymes with the so-called 2-His-1-carboxylate facial triad. The coordination behaviour of these ligands towards iron turned out to be dependent on the counter ion (chloride or triflate), the crystallization conditions (coordinating or non-coordinating solvents) and the presence of substituents on the ligand. In combination with Fe(II)(OTf)2, coordinatively saturated complexes of the type [Fe(L)2](OTf)2 are formed, in which the ligands adopt a meridional coordination mode. The use of FeCl2 in a non-coordinating solvent leads to 5-coordinated complexes [Fe(L)(Cl)2] with a meridional N,N',O ligand. Crystallization of these complexes from a coordinating solvent leads to 6-coordinated [Fe(L)(solv)(Cl)2] complexes (solv = methanol or acetonitrile), in which the N,N',O ligand is coordinated in a facial manner. For RPyProR ligands bearing a 6-Me substituent on the pyridine ring, solvent coordination and, accordingly, ligand rearrangement are prevented by steric constraints. The complexes were tested as oxidation catalysts in the epoxidation of alkene substrates in acetonitrile with hydrogen peroxide as the oxidant under oxidant limiting conditions. The complexes were shown to be especially active in the epoxidation of styrene type substrates (styrene and trans-beta-methylstyrene). In the best case, complex [Fe(6-Me-PyProNH2)Cl2] (15) allowed for 65% productive consumption of hydrogen peroxide toward epoxide and benzaldehyde products.

The title compound, [(C2H5)4N][FeCl4], has at room temperature a disordered structure in the high-hexagonal space group P63mc. At 230 K, the structure is merohedrally twinned in the low-hexagonal space group P63. The volume has increased by a factor of 9 with respect to the room-temperature structure. At 170 and 110 K, the structure is identical in the orthorhombic space group Pca21 and twinned by reticular pseudomerohedry. The volume has doubled with respect to the room-temperature structure. All three space groups, viz. P63mc, P63 and Pca21, are polar and the direction of the polar axis is not affected by the twinning. In the P63 and Pca21 structures, all cations and anions are well ordered.

A one-pot method has been developed for the oxidative cleavage of internal alkenes into aldehydes by using 0.5 mol% of the nonheme iron complex [Fe(OTf)2(mix-bpbp)] (bpbp=N,N'-bis(2-picolyl)-2,2'-bipyrrolidine) as catalyst and 1.5 equivalents of hydrogen peroxide and 1 equivalent of sodium periodate as oxidants. A mixture of diastereomers of the chiral bpbp ligand can be used, thereby omitting the need for resolution of its optically active components. The cleavage reaction can be performed in one pot within 20 h and under ambient conditions. Addition of water after the epoxidation, acidification and subsequent pH neutralization are crucial to perform the epoxidation, hydrolysis, and subsequent diol cleavage in one pot. High aldehyde yields can be obtained for the cleavage of internal aliphatic double bonds with cis and trans configuration (86-98%) and unsaturated fatty acids and esters (69-96%). Good aldehyde yields are obtained in reactions of trisubstituted and terminal alkenes (62-63%). The products can be easily isolated by a simple extraction step with an organic solvent. The presented protocol involves a lower catalyst loading than conventional methods based on Ru or Os. Also, hydrogen peroxide can be used as the oxidant in this case, which is often disproportionated by second- and third-row metals. By using only mild oxidants, overoxidation of the aldehyde to the carboxylic acid is prevented., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Rhenium-based complexes are powerful catalysts for the dehydration of various alcohols to the corresponding olefins. Here, we report on both experimental and theoretical (DFT) studies into the mechanism of the rhenium-catalyzed dehydration of alcohols to olefins in general, and the methyltrioxorhenium-catalyzed dehydration of 1-phenylethanol to styrene in particular. The experimental and theoretical studies are in good agreement, both showing the involvement of several proton transfers, and of a carbenium ion intermediate in the catalytic cycle., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A bulky cyclopentadienyl (Cp)-based trioxorhenium compound was developed for the catalytic deoxydehydration of vicinal diols to olefins. The 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium (2) catalyst was synthesised in a two-step synthesis procedure. Dirhenium decacarbonyl was converted into 1,2,4-tri(tert-butyl)cyclopentadienyl tricarbonyl rhenium, followed by a biphasic oxidation with H2 O2 . These two new three-legged compounds with a 'piano-stool' configuration were fully characterised, including their single crystal X-ray structures. Deoxydehydration reaction conditions were optimised by using 2 mol % loading of 2 for the conversion of 1,2-octanediol into 1-octene. Different phosphine-based and other, more conventional, reductants were tested in combination with 2. Under optimised conditions, a variety of vicinal diols (aromatic and aliphatic, internal and terminal) were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. A high turnover number of 1400 per Re was achieved for the deoxydehydration of 1,2-octanediol. Furthermore, the biomass-derived polyols (glycerol and erythritol) were converted into their corresponding olefinic products by 2 as the catalyst., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of mononuclear Fe(II) triflate complexes based on the 3,3-bis(1-alkylimidazole-2-yl)propionate ester (BAIP) ligand scaffold are reported. In these complexes, the tripodal N,N,O-BAIP ester ligand is varied by (i) changing the ester moiety (i.e., n-Pr, tert-Bu esters, n-Pr amide), (ii) changing the methylimidazole moieties to methylbenzimidazole moieties, and (iii) changing the methylimidazole moieties to 1-ethyl-4-isopropylimidazole moieties. The general structure of the resulting complexes comprises two facially capping BAIP ligands around a coordinatively saturated octahedral Fe(II) center, with either a transoid or cisoid orientation of the N,N,O-donor manifold that depends on the combined steric and electronic demand of the ligands. In the case of the sterically most encumbered ligand, a four-coordinate all N-coordinate complex is formed as well, which cocrystallizes with the six-coordinate complex. In combination with the catalytic properties of the new complexes in the epoxidation/cis-dihydroxylation of cyclooctene with H2O2, in terms of turnover number and cis-diol formation, these studies provide a number of insights for further ligand design and catalyst development aimed at Fe-mediated cis-dihydroxylation.

This paper describes a mechanistic study of the SCS-pincer Pd(II)-catalyzed auto-tandem reaction consisting of the stannylation of cinnamyl chloride with hexamethylditin, followed by an electrophilic allylic substitution of the primary tandem-reaction product with 4-nitrobenzaldehyde to yield homoallylic alcohols as the secondary tandem products. As it turned out, the anticipated stannylation product, cinnamyl trimethylstannane, is not a substrate for the second part of the tandem reaction. These studies have provided insight in the catalytic behavior of SCS-pincer Pd(II) complexes in the auto-tandem reaction and on the formation and possible involvement of Pd(0) species during prolonged reaction times. This has led to optimized reaction conditions in which the overall tandem reaction proceeds through SCS-pincer Pd(II) -mediated catalysis, that is, true auto-tandem catalysis. Accordingly, this study has provided the appropriate reaction conditions that allow the pincer catalysts to be recycled and reused., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this work, the complexation of the bapbpy ligand to zinc dichloride is described (bapbpy = 6,6′-bis(2-aminopyridyl)-2,2′-bipyridine). The water-soluble, colorless complex [Zn(bapbpy)Cl]Cl·2H2O (compound 2·H2O) was synthesized; its X-ray crystal structure shows a mononuclear, pentacoordinated geometry with one chloride ligand in apical position. Upon excitation of its lowest-energy absorption band (375 nm) compound 2 shows intense emission (Φ = 0.50) at 418 nm in aqueous solution, and an excited state lifetime of 5 ns at room temperature. Photophysical measurements, DFT, and TD-DFT calculations prove that emission arises from vibronically coupled Ligand-to-Ligand Charge Transfer singlet excited states, characterized by electron density flowing from the lone pairs of the non-coordinated NH bridges to the π* orbitals of the pyridine rings. Monofunctionalization of the ligand with one long alkyl chain was realized to afford ligand 3, which can be inserted into dimyristoylphosphatidylglycerol (DMPG) or dimyristoylphosphatidylcholine (DMPC) unilamellar vesicles. For negatively charged DMPG membranes the addition of a zinc salt to the vesicles leads to an enhancement of the fluorescence due to zinc coordination to the membrane-embedded tetrapyridyl ligand. No changes were observed for the zwitterionic DMPC lipids, where binding of the Zn ions does not take place. A modest binding constant was found (5 × 10(6) M(−1)) for the coordination of zinc cations to bapbpy-functionalized DMPG membranes, which allows for the detection of micromolar zinc concentrations in aqueous solution. The influence of chloride concentration and other transition metal ions on the zinc binding was evaluated, and the potential of liposome-supported metal chelators such as ligand 3 for zinc detection in biological media is discussed.

Hexa-ammonium functionalized Dendriphos ligands and mono-sulfonate functionalized metal complexes have been used as building blocks for the preparation of multimetallic dendritic assemblies. These metallodendrimers consist of a single metal centre surrounded by an oligocationic shell formed by the coordinated Dendriphos ligands and multiple associated anionic organometallic complexes.

The newly synthesized dinuclear complex [Fe(III)(2)(μ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) Å) and Fe-O distances (1.941(2)/1.949(2) Å) compared to other unsupported Fe(III)(2)(μ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mössbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 Å, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 Å) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions.

The SO(2)-binding properties of a series of η(6),η(1)-NCN-pincer ruthenium platinum complexes (NCN = 2,6-bis[(dimethylamino)methyl]phenyl anion) have been studied by both UV-visible spectroscopy and theoretical calculations. When an electron-withdrawing [Ru(C(5)R(5))](+) fragment (R = H or Me) is η(6)-coordinated to the phenyl ring of the NCN-pincer platinum fragment (cf. [2](+) and [3](+), see Scheme 1), the characteristic orange coloration (pointing to η(1)- SO(2) binding to Pt) of a solution of the parent NCN-pincer platinum complex 1 in dichloromethane upon SO(2)-bubbling is not observed. However, when the ruthenium center is η(6)-coordinated to a phenyl substituent linked in para-position to the carbon-to-platinum bond, i.e. complex [4](+), the SO(2)-binding property of the NCN-platinum center seems to be retained, as bubbling SO(2) into a solution of the latter complex produces the characteristic orange color. We performed theoretical calculations at the MP2 level of approximation and TD-DFT studies, which enabled us to interpret the absence of color change in the case of [2](+) as an absence of coordination of SO(2) to platinum. We analyze this absence or weaker SO(2)-coordination in dichloromethane to be a consequence of the relative electron-poorness of the platinum center in the respective η(6)-ruthenium coordinated NCN-pincer platinum complexes, that leads to a lower binding energy and an elongated calculated Pt-S bond distance. We also discuss the effects of electrostatic interactions in these cationic systems, which also seems to play a destabilizing role for complex [2(SO(2))](+).

The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX(2)(L)(2) (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1](6+) and [2](6+), two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX(2)(L)(2), while for the tri-para-ammoniomethyl-substituted ligand [7](3+), the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI(2)(1)(2)]I(12), the geometrical parameters of the phosphine ligand [1](6+) are very similar to those found in the analogous complex of the benchmark ligand PPh(3), i.e. trans-PtI(2)(PPh(3))(2), indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.

The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric and electronic effects, the presence of charged groups often leads to additional, supramolecular interactions that occur in the second coordination sphere of the metal complex, such as intramolecular, interligand hydrogen bonding and Coulombic repulsion. These interactions can significantly alter the behavior of the phosphine ligand in question. Such effects have been observed in phosphine-metal association/dissociation equilibria, ligand substitution reactions, and stereoisomerism in phosphine-metal complexes. By drawing general conclusions, this review offers an insight into the coordination and catalytic behavior of phosphine ligands containing ionic functionalities and their corresponding metal complexes., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis and catalytic properties of ditopic mono-pincer-mono-porphyrin complexes were investigated. The statistical Adler condensation reaction of 3,5-bis(methoxymethyl)-4-bromo-benzaldehyde, p-tolylaldehyde, and pyrrole, furnished an AB(3)-type tetraphenylporphyrin, containing three meso-p-tolyl groups and one meso-3,5-bis(methoxymethyl)-4-bromophenyl group. This material was converted into the ditopic ligand [2H(Br)], which comprises one porphyrin site and an NCN-pincer type ligand moiety. In order to metalate this compound in a stepwise, site-selective manner, two distinct synthetic routes were followed. Route A relies on the introduction of a metal in the porphyrin cavity followed by pincer metalation and a reversal of this order is employed for route B. For the hetero-bimetallic pincer-porphyrin target compounds, route A invariably proved to be the highest yielding alternative, giving pincer-porphyrin hybrids of general formula [M(1)(M(2)X)] (M(1) = 2H, Mg, Co, Ni, Zn; M(2) = Pd, Br; X = Cl, Br). (195)Pt NMR spectroscopy revealed that the porphyrin metal has a modest influence on the electron density on the NCN-pincer Pt site. When the analogous cationic Pd complexes were used as Lewis acid catalysts for the double Michael addition between methyl vinyl ketone and ethyl alpha-cyanoacetate, it was noted that the catalytic activity did not depend on the central metal for M(1) = 2H, Ni, and Zn. However, when Mg occupied the porphyrin cavity, the rate of the reaction increased by a factor of six. Although a rate enhancement was observed when catalysis was conducted with a mixture of the two constituents of [Mg(PdOH(2))]BF(4) (i.e. MgTTP and [PdOH(2)(NCN)]BF(4)) this could not fully account for the rate enhancement. We believe that the rationale for this behaviour is dual, consisting of "cooperative dual catalysis" and supramolecular aggregation of two or more catalyst-substrate complexes.

The synthesis of an S,NH,S-pincer ligand possessing a pyrrole core and two O,O-diethylthiophosphonyl groups to design P=S lateral coordination sites is reported. The synthetic procedure to produce this ligand makes use of the nitrogen atom of the pyrrole heterocycle to successively functionalize the ortho-positions with the two O,O-diethylthiophosphonyl moieties. The ortho-functionalization arises from a repetition of a [1,2] base-induced rearrangement allowing the transformation of O,O-diethyl-N-pyrollylthiophosphoramidate to ortho-thiophosphonate. The coordination properties of this tridentate S,NH,S-ligand have been investigated with silver and palladium metals. Reaction of the monoanionic S,N,S-pincer ligand 4 (O,O,O,O-tetraethylpyrrol-2,5-yl-dithiophosphonate) with PdCl(2)(MeCN)(2) at room temperature in the presence of triethylamine gives rise to the formation of the eta(3)-complex [Pd(eta(3)-4')Cl] 5. Ligand 4 also reacts with silver oxide in dichloromethane to produce complex which, in the solid state, exists as a tetramer involving an almost linear arrangement of four silver atoms.

The reaction of tin dichloride with catalytically-relevant group 10 metal precursors [M(Cl)(X)(2-PyPPh(2))(2)] (M = Ni, Pd, Pt; 2-PyPPh(2) = 2-pyridyldiphenylphosphine; X = Cl, Me) provides easy access to unprecedented cationic dichlorostannylene complexes [M(X)(2-PyPPh(2))(2)(SnCl(2))](+) where the M-Sn bond is bridged by two head-to-head coordinated 2-PyPPh(2) ligands. The formation of such species instead of the classical neutral trichlorostannyl derivatives [M(X)(SnCl(3))(2-PyPPh(2))(2)] offers a new insight on the specific effect of the SnCl(2) cocatalyst in group 10 metal catalyzed transformations.

Several heteromultimetallic pincer-porphyrin hybrids have been prepared in excellent yields by stepwise metalation of a general precursor, [2H(Br(NCN))(4)], which was designed in such a way so as to guarantee selectivity for either the porphyrin or pincer sites during the metalation steps. First, a metal was introduced in the porphyrin cavity using a metal(II) salt, followed by metalation of the pincer units through oxidative addition to an appropriate metal(0) complex. The resulting multimetallic complexes show an appreciable amount of intramolecular communication between the meso-pincer metal groups and the central metalloporphyrin component. This was manifested in changes of the optical and ligand-binding properties of the metalloporphyrin part upon reactions at the peripheral pincer sites.

The title compound, [Mn(CF(3)SO(3))(2)(CH(3)CN)(2)](n), has an Mn(II) cation on an inversion centre in an octahedral environment. The trifluoromethanesulfonate anions act as bridging ligands and form a one-dimensional coordination polymer in the direction of the a axis. The F atoms of the trifluoromethanesulfonate anions form layers parallel to the ab plane, but despite short intermolecular distances, no stabilizing F...F interactions are detected. The Mn-N and C-C bonds of the acetonitrile ligand are analyzed according to the Hirshfeld rigid-bond test. Renninger effects in the reflection data are considered, explored and discussed.

The combination of Pd(2)dba(3) x CHCl(3) and hexacationic triarylphosphine-based Dendriphos ligands (1-3) leads to a highly active catalytic system in the Suzuki-Miyaura cross-coupling reaction. Under relatively mild reaction conditions, nonactivated aryl bromides and activated aryl chlorides can be coupled at a low Pd loading (0.1 mol %). The observed activity of this catalytic system, in particular in coupling reactions of aryl chlorides, is dramatically higher than that of conventional Pd catalysts employing triarylphosphine ligands. Through control and poisoning experiments, it is concluded that a homogeneous Pd(0)-Dendriphos complex is the active species in this catalytic system. Despite their triarylphosphine-based structure, Dendriphos ligands behave as very bulky phosphine ligands and lead to a preferential formation of coordinatively unsaturated and catalytically active Pd(0) species, which explains the observed high catalytic activity for these systems. The presence of six permanent cationic charges in the backbone of this class of ligands is proposed to result in a significant interligand Coulombic repulsion and plays a crucial role in their bulky behavior. In the coupling reactions of activated aryl chlorides, a positive dendritic kinetic effect was observed among the different Dendriphos generations, indicating an increased ability of the higher ligand generations to stabilize the active species due to steric effects. For aryl bromides, no dendritic effect was observed due to a shift in the rate-determining step in the catalytic cycle, from oxidative addition for aryl chlorides to transmetalation for aryl bromides.

Feel the pinch! Planar-chiral, cationic, ruthenium-palladium complexes based on eta(6),eta(1)-coordinated ECE' pincer ligands are synthesized as racemic mixtures by reacting ECE'-palladium complexes and [Ru(C(5)R(5))(MeCN)(3)](+) arenophiles (R=H or Me). Chiral resolution of the cationic complexes was achieved by using the chiral counterion [Delta-TRISPHAT](-), and solving the X-ray crystal structure of one diastereoisomer (shown here).

The first crystal structures of lipases that have been covalently modified through site-selective inhibition by different organometallic phosphonate-pincer-metal complexes are described. Two ECE-pincer-type d(8)-metal complexes, that is, platinum (1) or palladium (2) with phosphonate esters (ECE = [(EtO)-(O=)P(-O-C(6)H(4)-(NO(2))-4)(-C(3)H(6)-4-(C(6)H(2)-(CH(2)E)(2))](-); E = NMe(2) or SMe) were introduced prior to crystallization and have been shown to bind selectively to the Ser(120) residue in the active site of the lipase cutinase to give cut-1 (platinum) or cut-2 (palladium) hybrids. For all five presented crystal structures, the ECE-pincer-platinum or -palladium head group sticks out of the cutinase molecule and is exposed to the solvent. Depending on the nature of the ECE-pincer-metal head group, the ECE-pincer-platinum and -palladium guests occupy different pockets in the active site of cutinase, with concomitant different stereochemistries on the phosphorous atom for the cut-1 (S(P)) and cut-2 (R(P)) structures. When cut-1 was crystallized under halide-poor conditions, a novel metal-induced dimeric structure was formed between two cutinase-bound pincer-platinum head groups, which are interconnected through a single mu-Cl bridge. This halide-bridged metal dimer shows that coordination chemistry is possible with protein-modified pincer-metal complexes. Furthermore, we could use NCN-pincer-platinum complex 1 as site-selective tool for the phasing of raw protein diffraction data, which shows the potential use of pincer-platinum complex 1 as a heavy-atom derivative in protein crystallography.

Iron-containing enzymes are one of Nature's main means of effecting key biological transformations. The mononuclear non-heme iron oxygenases and oxidases have received the most attention recently, primarily because of the recent availability of crystal structures of many different enzymes and the stunningly diverse oxidative transformations that these enzymes catalyze. The wealth of available structural data has furthermore established the so-called 2-His-1-carboxylate facial triad as a new common structural motif for the activation of dioxygen. This superfamily of mononuclear iron(ii) enzymes catalyzes a wide range of oxidative transformations, ranging from the cis-dihydroxylation of arenes to the biosynthesis of antibiotics such as isopenicillin and fosfomycin. The remarkable scope of oxidative transformations seems to be even broader than that associated with oxidative heme enzymes. Not only are many of these oxidative transformations of key biological importance, many of these selective oxidations are also unprecedented in synthetic organic chemistry. In this critical review, we wish to provide a concise background on the chemistry of the mononuclear non-heme iron enzymes characterized by the 2-His-1-carboxylate facial triad and to discuss the many recent developments in the field. New examples of enzymes with unique reactivities belonging to the superfamily have been reported. Furthermore, key insights into the intricate mechanistic details and reactive intermediates have been obtained from both enzyme and modeling studies. Sections of this review are devoted to each of these subjects, i.e. the enzymes, biomimetic models, and reactive intermediates (225 references).

The use of 2,2':6',2''-terpyridine-4'-thiol (tpySH) was explored as a bridging ligand for the formation of stable assemblies containing both [4Fe-4S] clusters and single metal ions. Reaction of tpySH (2 equiv) with (NH4)2Fe(SO4)(2).6H2O generated the homoleptic complex [Fe(tpySH)2](2+), which was isolated as its PF6(-) salt. The compound could be fully deprotonated to yield neutral [Fe(tpyS)2], and the absorption spectrum is highly dependent on the protonation state. Reaction of [Fe(tpySH)2](PF6)2 with the new 3:1 site-differentiated cluster (n-Bu4N)2[Fe4S4(TriS)(SEt)] yielded the first metal-bridged [4Fe-4S] cluster dimer, (n-Bu4N)2[{Fe4S4(TriS)(mu-Stpy)}2Fe]. Electrochemical studies indicate that the [4Fe-4S] clusters in the dimer act as independent redox units, while UV-vis spectroscopy provides strong evidence for a thioquinonoid electron distribution in the bridging tpyS(-) ligand. TpySH thus acts as a directional bridging ligand between [4Fe-4S] clusters and single metal ions, thereby opening the way to the synthesis of larger, more complex assemblies.

The photosynthetic apparatus of green sulfur bacteria, the chlorosome, is generally considered as a highly efficient natural light-harvesting system. The efficient exciton transport through chlorosomes toward the reaction centers originates from self-assembly of the bacteriochlorophyll molecules. The aim of the present work is to realize a long exciton diffusion length in an artificial light-harvesting system using the concept of self-assembled natural chlorosomal chromophores. The ability to transport excitons is studied for porphyrin derivatives with different tendencies to form molecular stacks by self-assembly. A porphyrin derivative denoted as ZnOP, containing methoxymethyl substituents ({meso-tetrakis[3,5-bis(methoxymethyl)phenyl]porphyrinato}zinc(II)) is found to form self-assembled stacks, in contrast to a derivative with tert-butyl substituents, ZnBuP ({meso-tetrakis[3,5-bis(tert-butyl)phenyl]porphyrinato}zinc(II)). Exciton transport and dissociation in a bilayer of these porphyrin derivatives and TiO2 are studied using the time-resolved microwave conductivity (TRMC) method. For ZnOP layers it is found that excitons undergo diffusive motion between the self-assembled stacks, with the exciton diffusion length being as long as 15 +/- 1 nm, which is comparable to that in natural chlorosomes. For ZnBuP a considerably shorter exciton diffusion length of 3 +/- 1 nm is found. Combining these exciton diffusion lengths with exciton lifetimes of 160 ps for ZnOP and 74 ps for ZnBuP yields exciton diffusion coefficients equal to 1.4 x 10(-6) m2/s and 1 x 10(-7) m2/s, respectively. The larger exciton diffusion coefficient for ZnOP originates from a strong excitonic coupling for interstack energy transfer. The findings show that energy transfer is strongly affected by the molecular organization. The efficient interstack energy transfer shows promising prospects for application of such self-assembled porphyrins in optoelectronics.

Reactive phosphonates are important probes to target the active site of serine hydrolases, one of the largest and most diverse family of enzymes. Developing such inhibitory probes is of special importance in activity based protein profiling, a strategy that is increasingly used to gain information about a certain class of enzymes in complex proteosomes. Therefore, gaining detailed information about these inhibition events on the individual protein level is important since it affords information that can be used to fine-tune the probe for a specific task. Here, we report a novel and versatile synthesis protocol to access a variety of functionalised p-nitrophenyl phosphonate (PNPP) inhibitors from a common azide functionalised precursor using click chemistry. The obtained PNPPs were successfully used to covalently label serine hydrolases in their active sites with molecular tags. Furthermore, a model study is described in which we developed straightforward protocols that can be used to study protein inhibition events. Kinetic studies using UV-Vis and fluorescence spectroscopy techniques revealed that these PNPPs possess different inhibition rates for various proteins and were shown to be suitable probes to discriminate between various lipases. Additionally, we demonstrate that PNPPs are highly selective for serine hydrolases, making these probes very interesting as diagnostic or affinity probes for studying proteins in complex proteosomes.

The cation of the title compound, C(13)H(18)N(3)S(+).NO(3)(-), consists of two subunits, viz. a planar indole moiety and a nonplanar thiouronium moiety. An isolated intermolecular hydrogen bond connects the cation with the nitrate anion. The crystal packing is additionally characterized by short intermolecular contacts between parallel indole systems. A topological analysis of the electron density revealed C-S single bonds and partial double bonding in the N-C-N group.

The synthesis and catalytic applications of a new aryl-based unsymmetrical PCS-pincer complex are reported. Preparation of the robust air- and moisture-stable PCS-pincer palladium complex 5[X] started from the symmetrical alpha,alpha'-dibromo-meta-xylene and involved the selective substitution of one bromide by PPh(2)(BH(3)), followed by substitution of the second bromide by SPh and subsequent introduction of the palladium. The new PCS complexes (5[X]) were employed as catalysts in two important organic transformations. Firstly, complex 5[Cl] displays high catalytic activity in aldol reactions but enters the catalytic cycle as a precatalyst. Secondly, complex 5[BF(4)] displays tandem catalytic activity in the coupling of allyl chlorides with aldehydes and imines in the presence of hexamethylditin. In these tandem catalytic reactions the first process is the conversion of allyl chlorides into trimethylallyltin (and trimethyltin chloride) with Sn(2)Me(6), which is followed by catalytic allylation of aldehyde and sulfonimine substrates. In addition, we present a new catalytic process for the one-pot allylation of 4-nitrobenzaldehyde with vinyloxirane. The catalytic performance of the novel PCS-pincer palladium complex was compared to those of its symmetrical PCP- and SCS-pincer complex analogues. It was concluded that the unsymmetrical PCS complex advantageously unifies the attractive catalytic features of the corresponding symmetrical pincer complexes including both (pi-) electron-withdrawing (such as phosphorus) or (sigma-) electron-donating (such as sulfur and nitrogen) heteroatoms. Thus, in the aldol reaction the PCS-pincer palladium complex 5[X] provides a high turnover frequency, while in the tandem process both reactions are catalysed with sufficiently high activity.

The coordination chemistry of porphyrins has traditionally involved the ability of the porphyrin's tetrapyrrolic core to accommodate metal ions of varying charges and sizes, and on the organometallic chemistry of the resulting metalloporphyrins. However, the organometallic chemistry of porphyrins is not necessarily restricted to the metal bound in the porphyrin core, but can also be extended to the porphyrin periphery, be it through direct metalation of the porphyrin macrocycle at the meso or beta position, or by attachment to or merger of the porphyrin skeleton with ligands, followed by metalation. This Review focuses on the synthetic strategies used for porphyrins with peripheral metal-carbon bonds. The exciting results that have been produced underscore the importance and future potential of this field.

The Rieske dioxygenases are a group of non-heme iron enzymes, which catalyze the stereospecific cis-dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3-bis(1-methylimidazol-2-yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [Fe(II)(PrL1)(2)](BPh(4))(2) (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [Fe(II)(PrL1)(2)(MeOH)(2)](OTf)(2) (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non-heme iron(II) enzyme apocarotenoid-15-15'-oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non-heme iron complexes [Fe(II)(PrL1)(2)](OTf)(2) (2) and [Fe(II)(PrL1)(2)](BPh(4))(2) (3) were tested in olefin oxidation reactions with H(2)O(2) as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis-dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.

Copper(II) complexes of the potentially tripodal N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its conjugate acid HL1 have been synthesised and structurally and spectroscopically characterised. The reaction of equimolar amounts of ligand and CuII resulted in the complexes [Cu(L1)]n(X)n (X=OTf-, PF6(-); n=1,2), for which a new bridging coordination mode of L1 is inferred. Although these complexes showed moderate catecholase activity in the oxidation of 3,5-di-tert-butylcatechol, surprising reactivity with the pseudo-substrate tetrachlorocatechol was observed. A chloranilato-bridged dinuclear CuII complex was isolated from the reaction of [Cu(L1)]n(PF6)n with tetrachlorocatechol. This stoichiometric oxidative double dehalogenation of tetrachlorocatechol to chloranilic acid by a biomimetic copper(II) complex is unprecedented. The crystal structure of the product, [Cu2(ca)Cl2(HL1)2], shows a bridging bis-bidentate chloranilato (ca) ligand and ligand L1 coordinated as its conjugate acid (HL1) in a tridentate fashion. Magnetic susceptibility studies revealed weak antiferromagnetic coupling (J= -35 cm(-1)) between the two copper centres in the dinuclear complex. Dissolution of the green complex [Cu2(ca)Cl2(HL1)2] resulted in the formation of new pink-purple mononuclear compound [Cu(ca)(HL1)(H2O)], the crystal structure of which was determined. It showed a terminal bidentate chloranilato ligand and N,N-bidentate coordination of ligand HL1, which illustrates the flexible coordination chemistry of ligand L1.

In the title compound, C(9)H(10)N(3)S(+)·I(-), the indole ring system and the thiouronium group are essentially perpendicular, with a dihedral angle of 89.87 (8)°. By inter-molecular hydrogen bonding, a three-dimensional network is formed, which is additionally supported by inter-molecular C-H⋯π inter-actions.

In the title compound, C(9)H(10)N(3)S(+)·NO(3) (-), the indole ring system and the thiouronium group are nearly perpendicular, with a dihedral angle of 88.62 (6)°. Hydrogen bonding generates two-dimensional networks which are linked to each other via π stacking inter-actions of the indole groups [average inter-planar ring-ring distance of 3.449 (2) Å].

The coordination chemistry of the 2-His-1-carboxylate facial triad mimics 3,3-bis(1-methylimidazol-2-yl)propionate (MIm(2)Pr) and 3,3-bis(1-ethyl-4-isopropylimidazol-2-yl) propionate (iPrEtIm(2)Pr) towards ZnCl(2) was studied both in solution and in the solid state. Different coordination modes were found depending both on the stoichiometry and on the ligand that was employed. In the 2:1 ligand-to-metal complex [Zn(MIm(2)Pr)(2)], the ligand coordinates in a tridentate, tripodal N,N,O fashion similar to the 2-His-1-carboxylate facial triad. However, the 1:1 ligand-to-metal complexes [Zn(MIm(2)Pr)Cl(H(2)O)] and [Zn(iPrEtIm(2)Pr)Cl] were crystallographically characterized and found to be polymeric in nature. A new, bridging coordination mode of the ligands was observed in both structures comprising N,N-bidentate coordination of the ligand to one zinc atom and O-monodentate coordination to a zinc second atom. A rather unique transformation of pyruvate into oxalate was found with [Zn(MIm(2)Pr)Cl], which resulted in the isolation of the new, oxalato bridged zinc coordination polymer [Zn(2)(MIm(2)Pr)(2)(ox)].6H(2)O, the structure of which was established by X-ray crystal structure determination.

A series of meso-tetrakis-(ERE donor) zinc(II) porphyrins nZn (ERE donor = 4-R-3,5-bis[(E)-methyl]phenyl; 1Zn: E = NMe2, R = Br; 2Zn: E = NMe2, R = H; 3Zn: E = OMe, R = Br; 4Zn: E = OMe, R = H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of nZn self-assemble to form one-dimensional porphyrin polymers [nZn](infinity) in the solid state, as confirmed for 1Zn and 3Zn by X-ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E = N, O) provided by the EBrE donor groups of adjacent nZn molecules. Complexes 2Zn and 4Zn did not form single crystals, but solid-state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and 1H NMR spectroscopy indicated that interactions between 1Zn and 2Zn monomers in the polymers are stronger than between 3Zn and 4Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the nZn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc-zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.

The potential of "click" 1,2,3-triazoles to act as mono-dentate ligands in late transition metal complexes is explored relative to other commonly-used Lewis bases and it is shown that their coordination strength, determined by their 1- and 4-substituents, is easily tunable.

This work reviews recent developments in the field of organic transformations on sigma-aryl organometallic complexes. The general notion that M--C sigma 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 sigma-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.

Ionic core-shell dendrimers with an octacationic core have been applied as noncovalent supports for homogeneous catalysts. Catalytically active arylpalladium complexes, which bear a tethered sulfato group, were noncovalently attached to the ionic core-shell dendritic supports via a straightforward ion-exchange reaction under mild conditions. Diagnostic shifts in (1)H NMR and Overhauser contacts show that the sulfato groups of the catalysts are located close to the octacationic core of the dendritic support in the resulting assemblies. The location of the catalytic Pd(II) sites has been varied via two strategies: by increasing the dendrimer generation and/or by shortening of the sulfato tether. In addition, a metallodendritic assembly was prepared, which bears an alternative shell of apolar dodecyl groups. Both the dendrimer size and the nature of the dendritic shell have no influence on the binding properties of the dendritic supports, i.e., the octacationic dendrimers of generations 1-3 form discrete 1:8 assemblies with the arylpalladium complexes. The structural aspects and the nature of the metallodendritic assemblies have been studied by means of pulse gradient spin-echo NMR diffusion methods, Overhauser spectroscopy, and electron microscopy (TEM). These techniques showed that the dendritic supports and arylpalladium complexes are strongly associated in solution to give unimolecular assemblies of nanoscopic dimensions. Membrane dialysis can recover these metallodendritic assemblies due to their nanoscopic size. The catalytic performances of the metallodendritic assemblies are comparable, but slightly lower than the performance of the unsupported catalyst.