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A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)2-3,5}-2,2':6',2' '-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)2, and [Ru(TPBr)2](PF6)2, synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)2 (7) and [Ru(TPPdCl)2](PF6)2 (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)2](PF6)2 (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono- and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (1)MLCT (Ru --tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)2]2+ indicates stabilization of the luminescent 3MLCT state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)2, are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)2} chromophoric unit and the (non)metalated NCN-pincer moiety.

The synthesis of the first series of 4-mono and 3,5-bis(dimethylamino)methyl-functionalized triarylphosphanes of the general formula PPh 3 − n Ar n (Ar = 1-C 6 H 3 (CH 2 NMe 2 ) 2 -3,5 (NC(H)N), n = 1 (ligand 2 ) or n = 3 (ligand 4 ); Ar = 1-C 6 H 4 (CH 2 NMe 2 )-4 (NC(H)), n = 3 (ligand 7 )) is described. These phosphanes were used for the construction of complexes of the form [AuCl(P)] and [PtCl 2 (P) 2 ]. In these complexes selective coordination of phosphorus to the metal ion is observed. The 31 P NMR data show the formation of cis -Pt complexes, even in the case of triarylphosphane 4 , which features a tris{3,5-bis(dimethylamino)methyl} substitution pattern. The structure of the gold complex of mono-3,5-functionalized triarylphosphane 2 in the solid state shows a striking resemblance to the structure of the corresponding complex [AuCl(PPh 3 )]. The solid-state structure of the AuCl complex of tris-4-functionalized ligand 7 differs from that of [AuCl(PPh 3 )] in the sign of the torsion angles. The amine functionalities in this class of gold compounds could be reacted selectively with either acid (HCl, H 3 PO 4 ) to generate ammonium salts or with an alkylating agent (benzyl bromide) to afford benzyl ammonium salts, without the violation of the Au–P bond.

One of the greatest challenges of this time is providing the world with the energy it needs to sustain human kind's current standard of living. Solar energy is the most abundant and ubiquitous renewable energy source available, and as such it holds great promises. Traditionally, the field of solar energy conversion has been dominated by solid-state semiconductor technology. However, the need for high-purity materials makes these single junction solar cells expensive and unlikely to reach cost parity with fossil energy in the near future. The dependence on high purity materials can be substantially decreased by physically separating the charge separation and transport functions of the solar cell. This vital insight stands at the cradle of dye-sensitized solar cells (DSSCs), in which a large bandgap semiconductor is sensitized by a sensitizer molecule. Producing a DSSC is a relatively simple and cheap process compared to low bandgap solid-state semiconductor cells based on silicon. Demonstration kits for home-built DSSCs are commercially available which use harmless components and colorants such as berry juices. However, the highest efficiencies, up to 11 % power conversion, are typically reached using polypyridine complexes of ruthenium as sensitizers. Unfortunately, issues related to the efficiency for the conversion of red light as well as long term stability are still associated with these complexes. This thesis describes our efforts towards using cyclometalation as a new design paradigm to address these issues. A two-step upconversion would allow the use of photons below the operational threshold set by the bandgap energy but requires new types of sensitizer. Our efforts in the design and characterization of potential dyes for this process are also described. Cyclometalated complexes contain at least one covalent carbon-to-metal bond in a multidentate ligand. The interaction between the strong sigma-donor carbon atom and the metal center affects the electronic properties of the resulting complexes, red-shifting the absorption characteristics. The red-shift of the absorption features in the standard dyes for DSSCs is typically achieved with monodentate thiocyanate ligands, which are sensitive towards decomposition processes associated with dissociation. In contrast, the polydentate nature of cyclometalated ligands make these complexes inherently long-term stable. This thesis uses experimental and theoretical tools to study the fundamental influence of cyclometalation in polypyridine-type ruthenium complexes on the electronic and photophysical properties, as well as their chemical consequences. It is demonstrated that cyclometalation is a very promising technique in the design of new sensitizer molecules. It is also concluded that extensive knowledge of the complexes' photophysical properties is a prerequisite to the de novo design of efficient systems. Finally, the possibility to use photons of energy below the operational threshold of the DSSC is explored using a two-step upconversion scheme. To study this upconversion scheme several dinuclear redox unsymmetrical ruthenium complexes have been studied in solution as well as incorporated in a DSSC, demonstrating the necessary individual processes.

[4Fe-4S] clusters are one of Nature’s most ubiquitous cofactors, playing vital roles in protein structure stabilization, electron transport, catalysis, and sensing. When an enzymatic active site features a [4Fe-4S] cluster, the coordination environment of the cluster is 3:1 site-differentiated, meaning that the ligand or residue coordinated to one of the four iron atoms is markedly different from those coordinated to the other three iron atoms. To study these intriguing metallosites, biomimetic chemists prepare, study, and compare synthetic [4Fe-4S] clusters to their biological counterparts. 3:1 site differentiation in synthetic clusters is usually achieved by the use of tripodal trithiolate ligands, which chelate three of the four iron sites, leaving one iron atom free for further modification. Chapter 1 of this thesis provides an overview of natural and synthetic 3:1 site-differentiated [4Fe-4S] clusters. Chapter 2 presents a new synthetic route to the promising site-differentiating TriSH3 ligand. The route avoids the use of highly toxic reagents and results in an overall yield that is more than double that in the original procedure. TriSH3 reacts with (n-Bu4N)2[Fe4S4(SEt)4] to yield (n-Bu4N)2[Fe4S4(TriS)(SEt)], which in turn reacts with [Fe(tpySH)2](PF6)2 (tpySH = 2,2':6',2''-terpyridine-4'-thiol) to form the first [4Fe-4S] cluster dimer to be linked by a metal-containing bridge. Chapter 3 presents a series of symmetrically substituted [4Fe-4S] clusters with N-substituted indole-3-thiolate ligands, which are monodentate analogues of TriS3–. The new cluster family undergoes 2–/3– redox transitions at potentials midway between the potential ranges in which clusters fully coordinated by all-aliphatic and all-aromatic thiolates generally display redox transitions, and show electronic transitions that are among the most redshifted known in [4Fe-4S] cluster chemistry. Chapter 4 demonstrates that reaction of (n-Bu4N)2[Fe4S4(TriS)(SEt)] with 4-pyridinethiol results in a 3:1 site-differentiated [4Fe-4S] cluster with a pendant pyridyl group, which can subsequently react with the ruthenium porphyrin [Ru(TTP)(CO)(MeOH)] (TTP = 5,10,15,20-tetra(p-tolyl)porphyrinato dianion) to form a [4Fe-4S]-Ru assembly. Furthermore, 19F NMR indicates that the reaction of (n-Bu4N)2[Fe4S4(TriS)(SEt)] with p-fluorothiophenol forms minor side products stemming from decoordination of TriS3– arms, demonstrating the benefits of using 19F NMR to study the substitution behavior of [4Fe-4S] clusters. Chapter 5 presents a new model for the active site of iron-only hydrogenase. The model is the TriS3– analogue of an earlier, LS33–-based model reported by Pickett and co-workers and the change in tripodal ligand has a profound impact on the properties of the mimic as a whole. 1H NMR spectroscopy and cyclic voltammetry suggest that the [4Fe-4S] and diiron redox entities in the new model are strongly coupled, as also observed in the natural enzyme. Chapter 6 describes the immobilization of [4Fe-4S] clusters on self-assembled monolayers (SAMs). (n-Bu4N)2[Fe4S4(TriS)(SEt)] can react with the thiol groups at the surface of a mixed SAM, resulting in an immobilizing interaction strong enough to resist extensive washing. The immobilization represents a first step towards studies of [4Fe-4S] clusters at controlled solid-liquid interfaces.

The work described in this thesis has demonstrated the application of heterogenised homogeneous catalysts. We have shown that by coupling a homogeneous catalyst to a heterogeneous support we could combine the benefits of two major fields of catalysis: retain the high selectivity of homogeneous catalysts with the ease of separation and cost-efficiency of heterogeneous catalysts. A number of techniques both for the functionalisation of organometallic complexes, and the functionalisation of inorganic support materials have been demonstrated and applied. These techniques are a breakthrough because they demonstrate simple, highly efficient procedures for the desired products. Furthermore, they demonstrate a very simple ‘from lab shelf to reaction vessel’ concept for the immobilisation of homogeneous catalysts and application of such catalytic materials. It was further demonstrated that by compartmentalising heterogenised homogeneous catalysts we could mimic nature’s ability to carry out highly selective multi-step reaction sequences without work-up or intermediate isolation steps. This achievement is a simple, but highly important and distinguished achievement because it brings the field of multi-step catalysis a step closer to being truly efficient, and more importantly, environmentally benign.

Glycerol is considered a potential renewable building block for the synthesis of existing as well as new chemicals. A promising route is the telomerization of 1,3-butadiene with glycerol leading to C8 chain ethers of glycerol with applications in, for example, surfactant chemistry. Recently, we reported a new set of palladium-based homogeneous catalytic systems for the telomerization of 1,3-butadiene with glycerol and found that palladium complexes bearing methoxy-functionalized triphenylphosphine ligands are highly active catalysts capable of converting crude glycerol without any significant loss of activity. Herein, we present a detailed account of these investigations by reporting on the influence of the butadiene/glycerol ratio, temperature, and reaction time on product selectivity and activity allowing further optimization of catalyst performance. Maximum activity and yield were reached for high 1,3-butadiene/glycerol ratios at a temperature of 90 °C, whereas the selectivity for mono- and diethers of glycerol could be optimized by combining high reaction temperatures and short reaction times with low butadiene/glycerol ratios. Variation of the PdII metal precursors and the metal/ligand ratio showed that palladium precursors with halogen ligands gave unsatisfying results, in contrast to precursors with weakly coordinated ligands such as [Pd(OAc)2] and [Pd(acac)2]. [Pd(dba)2], the only Pd0 precursor tested, gave the best results in terms of activity, which illustrates the importance of the ability to form a Pd0 species in the catalytic cycle. Finally, base addition resulted in a shortening of the reaction time and most likely facilitates the formation of a Pd0 species. Based on these results, we were able to realize the first attempts towards a rational ligand design aimed at a high selectivity for mono- and diether formation.

In the title compound, C9H10N3S+·NO3-, 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 [pi] stacking interactions of the indole groups [average inter-planar ring-ring distance of 3.449 (2) Å].

In the title compound, C9H10N3S+·I-, the indole ring system and the thiouronium group are essentially perpendicular, with a dihedral angle of 89.87 (8)°. By intermolecular hydrogen bonding, a three-dimensional network is formed, which is additionally supported by intermolecular C-H ... [pi] interactions.

SCS-pincer metal complexes [MX(SCS)] (SCS = [2,6-(RSCH2)2C6H3]−; R = Ph: PhSCS; R = Me: MeSCS; M = Pd, Pt, Ni) have been synthesized via mild and tolerant oxidative addition procedures. The complexes have been characterized by 1H and 13C NMR spectroscopy and X-ray crystal structure determination. Interestingly, the crystal structures of [NiBr(MeSCS)] 4, [PdBr(MeSCS)] 5, [PtBr(MeSCS)] 6, and [PtBr(PhSCS)] 8 each have a unit cell with a unique set of independent [MBr(RSCS)] molecules; each of these structures has a different conformation of the five-membered ortho-chelate ring (including the configuration of the coordinated S-center) in the solid state. The temperature-dependent 1H NMR resonance patterns of these complexes in solution were related to structural features encountered in the solid state and allowed us to assign all dynamic processes (rac/meso isomerizations) that occurred in solution.

Copper(I)-mediated reactions have recently become the choice for large industrial scale applications, since copper is environmentally friendly and cheaper than other transition metals already explored. However, most organocopper compounds still present several limitations including the sensitivity towards moisture and air, the low solubility in organic solvents and the thermal instability. Many studies were performed trying to improve the activity and selectivity of copper-catalyzed reactions.

The synthesis of O,O-diethyl 2-hydroxyarylthiophosphonate is reported by using a [1,3]-rearrangement. This method is achieved in high yield from ortho-bromophenols derivatives by a two-step process

The application of hexa[(dimethylamino)methyl]-functionalized triphenylphosphine (1) and its benzylammonium salt, Bn-Dendriphos (2), in the Suzuki-Miyaura cross-coupling of aryl bromides with arylboronic acids is described. The 3,5-bis[(benzyldimethylammonio)methyl] substitution pattern in 2 leads to a rate enhancement compared to both the non-ionic parent compound 1 and triphenylphospine (PPh3) itself. At the same time, the resulting catalytic species are stable towards palladium black formation, even at a phosphine/palladium ratio of 1. These observations are attributed to the presence of a total of six ammonium groups in the backbone of the phosphine ligand, which presumably leads to an unsaturated phosphine-palladium complex.

New enantiomerically pure S,N-chelated (R)-Zn(Et)SR complexes, 3a–3c (R = 2-[CHMeN(CH2)4]-5-[SiMe3−n(CH2CH2CxF2x+1)n]C6H3; n = 1, x = 10; n = 2, 3 and x = 8), have been synthesized from the reaction of EtZnCl and the corresponding trimethylsilyl(aminoaryl) thioethers, or lithium aminoarene thiolate 2c. Complexes 3a–3c were successfully used as highly enantioselective catalysts for the 1,2-addition (e.e. up to 92%) of diethylzinc to benzaldehyde in perfluoromethylcyclohexane/n-octane. At 2.5 mol%, catalyst 3c, thanks to its three CH2CH2C8F17 tails, could be reused at least 10 times with retention of its initial high enantioselectivity, thereby significantly increasing the turnover number per unit amount of catalyst in comparison with earlier studies.

A protocol for the copper-catalyzed aryl−sulfur bond formation between aryl iodides and thiophenols is reported. The reaction is catalyzed by a low amount (1−2.5 mol %) of readily available and ligand-free copper iodide salt. A variety of diaryl thioethers are synthesized under relatively mild reaction conditions with good chemoselectivity and functional group tolerance.

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 × 10-6 m2/s and 1 × 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.

The nature of the first excited state of [Fe(terpyridine)2]2+ has been reinvestigated. In contrast to previous findings, it is metal-to-ligand charge transfer in nature, thus fitting in the series of the Ru and Os complexes.

Stable heterobimetallic complexes of the type [MX(NCN)Ru(C5R5)]+ (R = H or Me), where the phenylene ring of an NCN-pincer ligand coordinates first to a platinum or palladium center via a σ-bond, and second to a ruthenium organometallic fragment via a π-bond, are synthesized in a single step involving electrophilic attack of a cationic Ru species on the aryl metal complex. X-ray crystal structures and solution NMR agree on the simultaneous presence of orthogonal η6- and η1-coordination axes. 195Pt NMR and electrochemistry show that the η6-coordinated ruthenium fragment has a strong electron-withdrawing effect on the pincer metal, which leads to a diminished nucleophilicity of the platinum center toward electrophiles such as SO2.

Various para-OH functionalized ECE–pincer metal complexes [MX(ECE–OH)Ln] (ECE–OH = [C6H2(CH2E)2-2,6-OH-4]−, E = NMe2, PPh2 and SPh) were synthesized. The X-ray crystal structures of neutral [PdCl(SCS–OH)], [PdCl(NCN–OH)], and cationic [Pd(PCP–OH)(MeCN)](BF4) are reported. The neutral halide complexes exhibit self-assembly to form polymeric chains via H-bonding involving the para-OH group as donors and the halide ligand on the metal as acceptors. Moreover, the halide ligand can be replaced by a monomeric aryloxy-O ligand leading to the formation of a covalently bonded dimer. The crystal structure of such a dimer derived from [PdI(NCN–OH)] is reported. Furthermore, these pincer–metal complexes were tethered through a carbamate linker to a siloxane functionality with the aim to be immobilized on a silica support. The crystal structure of a siloxane-functionalized [PtI(NCN–Z)] complex exemplifies how other H-bonding interactions not involving the metal–halide groupings can lead to polymeric networks as well.

The synthesis and characterization of homobimetallic palladium and platinum complexes of type [(Me(O)CS-4-NCN–M ← N∩N → M–NCN-4-SC(O)Me](OTf)2 (Me(O)CS-4-NCN = [C6H2(CH2NMe2)2-2,6-SC(O)Me-4]−; N∩N = 4,4′-bipyridine (bipy); M = Pd, 12; M = Pt, 13) is reported. The required bifunctional thio-acetyl NCN pincer starting compound NC(Br)N-4-SC(O)Me (2) has been synthesized by the consecutive reactions of NC(Br)N–I (I-1-C6H2(CH2NMe2)2-3,5-Br-4) (1) with tBuLi, S8 and Me(O)CCl, respectively. Chemoselective metallation at the Caryl–Br bond was achieved by the reaction of 2 with the palladium(0) source [Pd2(dba)3] (3) (dba = dibenzylidene acetone). Treatment of thus formed [Pd(NCN-4-SC(O)Me)(Br)] (4) with [AgOTf] (8) (OTf = triflate, OSO2CF3) gave [Pd(NCN-4-SC(O)Me)(H2O)][OTf] (9) which was further reacted with 0.5 equiv. of 4,4′-bipyridine (11a) to afford rigid-rod structured 12. When [Pt(tol)2(SEt2)]2 (5) (tol = 4-tolyl) was used instead of 3, then 13 was produced via the in situ formation of [PtBr(NCN-4-SC(O)Me)] (7) and [Pt(NCN-4-SC(O)Me)(H2O)][OTf] (10). Another possibility to synthesize 7 relied upon the subsequent reaction of 1 with 0.5 equiv. of 5 to give [PtBr(NCN-4-I)] (6) which further reacted with tBuLi, 1/8 S8 and Me(O)CCl to afford 7. The cyclic voltammograms of 2, 7, and 13 are discussed. Complex 7 was structurally characterized by single crystal X-ray crystallography. Organometallic 7 crystallizes with three independent molecules in the asymmetric unit and displays a monomeric structure as commonly encountered in d8-metal pincer chemistry.

We present the facile immobilisation of a chiral diphosphine ligand, BINAP, on a silica (high pore volume, low surface area). The protected ligand has been immobilised as a phosphine oxide and deprotected on the surface to prevent side reactions of unprotected phosphines with surface silanol groups. The resulting diphosphine ligand on silica was converted to both rhodium and ruthenium complexes. The novel materials were characterised using solid-state IR-DRIFT and 29Si and 31P CP-MAS NMR techniques as well as elemental content measurements. Ruthenium and rhodium catalysed asymmetric hydrogenation of various enamides, -keto-esters and aromatic ketones is presented using immobilised BINAP ligands. The repeated use of the immobilised catalyst in five recycles demonstrates homogeneous catalysis with heterogeneous catalysts, thus reducing solvent waste, and loss of precious metal and or ligand.

Nitrile-functionalized NCN-pincer complexes of type [MBr(NC-4-C6H2(CH2NMe2)2-2,6)] (6a, M = Pd; 6b, M = Pt) (NCN = [C6H2(CH2NMe2)2-2,6]−) are accessible by the reaction of Br-1-NC-4-C6H2(CH2NMe2)2-2,6 (2b) with [Pd2(dba)3 · CHCl3] (5a) (dba = dibenzylidene acetone) and [Pt(tol-4)2(SEt2)]2 (5b) (tol = tolyl), respectively. Complex 6b could successfully be converted to the linear coordination polymer {[Pt(NC-4-C6H2(CH2NMe2)2-2,6)](ClO4)}n (8) upon its reaction with the organometallic heterobimetallic π-tweezer compound {[Ti](μ-σ,π-CCSiMe3)2}AgOClO3 (7) ([Ti] = (η5-C5H4SiMe3)2Ti). The structures of 6a (M = Pd) and 6b (M = Pt) in the solid state are reported. In both complexes the d8-configurated transition metal ions palladium(II) and platinum(II) possess a somewhat distorted square-planar coordination sphere. Coordination number 4 at the group-10 metal atoms M is reached by the coordination of two ortho-substituents Me2NCH2, the NCN ipso-carbon atom and the bromide ligand. The NC group is para-positioned with respect to M.

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 ,-dibromo-meta-xylene and involved the selective substitution of one bromide by PPh2(BH3), 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[BF4] 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 Sn2Me6, 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 (π-) electron-withdrawing (such as phosphorus) or (σ-) 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.

We have developed techniques which allow for covalent tethering, via a “hetero” cyclometallating ligand, of heteroleptic tris-cyclometallated iridium(III) complexes to polymeric supports (for application in light-emitting diode technologies). This involved the selective synthesis and thorough characterization of heteroleptic [Ir(C,N)2(C′,N′)] tris-cyclometallated iridium(III) complexes. Furthermore, the synthesis and characterization of heteroleptic [Ir(C,N)2OR] complexes is presented. Under standard thermal conditions for the synthesis of the facial (fac) isomer of tris-cyclometallated complexes, it was not possible to synthesize pure heteroleptic complexes of the form [Ir(C,N)2(C′,N′)]. Instead, a mixture of homo- and heteroleptic complexes was acquired. It was found that a stepwise procedure involving the synthesis of a pure meridonial (mer) isomer followed by photochemical isomerization of this mer to the fac isomer was necessary to synthesize pure fac-[Ir(C,N)2(C′,N′)] complexes. Under thermal isomerization conditions, the conversion of mer-[Ir(C,N)2(C′,N′)] to fac-[Ir(C,N)2(C′,N′)] was also not a clean reaction, with again a mixture of homo- and heteroleptic complexes acquired. An investigation into the thermal mer to fac isomerization of both homo- and heteroleptic tris-cyclometallated complexes is presented. It was found that the process is an alcohol-catalyzed reaction with the formation of an iridium alkoxide [Ir(C,N)2OR] intermediate in the isomerization process. This catalyzed reaction can be carried out between 50 and 100 °C, the first such example of low-temperature mer−fac thermal isomerization. We have synthesized analogous complexes and have shown that they do indeed react so as to give fac-tris-cyclometallated products. A detailed explanation of the intermediates (and all of their stereoisomers, in particular when systems of the generic formula [M(a,b)2(a′,b′)] are synthesized) formed in the mer to fac isomerization process is presented, including how the formed intermediates react further, and the stereoisomeric products they yield.

A series of 4,4′-disubstituted organic−organometallic stilbenes, i.e., the 4′-substituted stilbenoid-NCN-pincer platinum(II) complexes [PtCl(NCN-R-4)] (NCN-R-4 = [C6H2(CH2NMe2)2-2,6-R-4]− in which R = C2H2C6H4-R′-4′ with R′ = NPh2, NMe2, OMe, SiMe3 H, I, CN, NO2) (1−8), were studied for their electronic, electrochemical, and NLO properties. Complex 7 was also chemically oxidized using Cu(II)Cl2, yielding the [Pt(IV)Cl3(NCN(C2H2C6H4-CN-4′)-4)] complex 11. In contrast to 1 and 7, 11 did not show luminescent properties in solution at room temperature. In the solid state (X-ray crystallography) 11 has an overall bent structure, with the pincer moiety and the cyano group beneath the plane of the central double bond. Stilbenoid pincer complex 1 (R′ = NPh2) was also studied with UV/vis spectroscopy in a series of different solvents. The compound shows an intense low-energy transition band, appearing at a lower energy (λmax = 374–379 nm) than 2 (R′ = NMe2), which contains a stronger donor group. The UV/vis absorption data of a selected series of stilbenoid pincer platinum complexes were interpreted in terms of a qualitative orbital model based on DFT and TD-DFT calculations. The trends observed in the transition energies correlate well with the donor/acceptor properties of the substituents. It was shown that the HOMO–LUMO gap of the stilbenoid pincer platinum compounds decreases when going from an electron-neutral group (R′ = H) toward an electron-donating (R′ = NMe2) or -accepting (R′ = NO2) group. The fluorescence properties of 1 were also investigated using fluorescence and laser spectroscopy, showing that the metal center favors nonradiative decay from the excited state to the ground state. For 7 (R′ = CN), solid-state 13C CP/MAS NMR measurements were performed, and a value of 1J(13C,195Pt) = 1003 ± 15 Hz was obtained for the Cipso carbon, reflecting π-contributions in the carbon−metal bond. The cyclic voltammetry study on the complexes revealed an irreversible oxidation from Pt(II) to Pt(IV). In general the oxidation potential is influenced by the electronic character of the R′ substituent. The influence of the para R′ substituent on the hyperpolarizability of the compound was investigated using the femtosecond (frequency-resolved) HRS technique. For 1−7 good βzzz values were measured (βzzz ranging from (164–1324) × 10−30 esu) with the highest value for 6 (R′ = I). The higher βzzz values were found for the compounds that contain a low-energy UV/vis absorption band and/or a large absorption coefficient. Donor–acceptor complexes 7 and 8 were successfully applied in an organic light-emitting diode (OLED). In the electroluminescence spectrum of 7 (R′ = CN) a low-energy emission band was observed at 643 nm. This band also appeared in the solid-state luminescence spectra of 7, however, only at low temperatures (298–15 K). The emission band was assigned to result from a triplet excited state. The present study shows that the introduction of a NCN-pincer platinum fragment in a donor–acceptor stilbenoid molecule leads to complexes that have promising NLO properties. These compounds can now successfully be applied in OLED devices, although the performances of the devices have to be improved to become interesting for practical applications.

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)(μ-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.

New chiral NCN-pincer palladium complexes containing bulky diphenylhydroxymethyl pyrrolidinyl moieties as chiral auxiliaries have been synthesized. Oxidative palladium addition to ligand 2 (2 = 2,6-bis{[(S)-2-(diphenylhydroxymethyl)-1-pyrrolidinyl]methyl}-1-bromobenzene) initially yielded neutral arylpalladium bromide complex 3 in a moderate yield as a consequence of the bulky pyrrolidinyl functional groups. Performing the palladation reaction under microwave irradiation for only 5 min gave 3 in 79% yield. Abstraction of the bromide ion from 3 subsequently yielded the cationic complexes [4]PF6 and [4]BF4. Palladium complexes 3, [4]PF6, and [4]BF4 are all formed as single diastereoisomers with an RNRNSCSC configuration. X-ray crystal structure determinations of [4]PF6 and [4]BF4 revealed an unusual κ5-N,C,N,O,O coordination around palladium, in which the normal meridional κ3-coordination mode of the pincer framework is complemented by two rather long Pd−O interactions (2.622(2)–2.649(2) Å). Theoretical calculations (Mulliken population analysis and “atoms in molecules” analysis) confirmed that there is a coordinative interaction between the palladium and the oxygen atoms of both hydroxyl groups despite the long Pd−O distance. Complexes [4]PF6 and [4]BF4 catalyze the aldol condensation between α-methyl isocyanoacetate and various aromatic aldehydes with enhanced regio- (up to 70%) and stereoselectivity (up to 42% ee) for the cis-oxazolines. These observations are in contrast to prior literature results on other pincer systems, where the trans-oxazolines were the main product, and point to a deeper chiral cavity pointing away from palladium toward the coordinated isocyanoacetate substrate.

The cation of the title compound, C13H18N3S+·NO3-, 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 first description of a telomerization reaction came from Smutny in 1967 who was studying the oligomerization and dimerization of 1,3-butadiene and its reactions with nucleophiles. Since then, numerous studies have appeared concentrated on monofunctional alcohols and other simple nucleophiles such as ammonia.

The reaction of NCNLi pincers (NCN = [2,6-(R2NCH2)2C6H3]-, R = Me ( 3), Et ( 4)) with various equivalents of nBuLi in non-polar solvent results in the generation of novel mixed alkyl–aryl organolithium hetero-aggregates. The identification (variable temperature 1H, 13C, 7Li and 2D NMR spectroscopy and X-ray crystallography) of multiple, equilibrating mixed-aggregates that form in these reactions has been achieved. Fluxional processes in the parent [NCNLi]2 dimeric homo-aggregates were re-evaluated and Li–N bond rupture was found to be in operation, a prerequisite towards further aggregation chemistry. The crystallized aggregates, with the formula 32·[nBuLi]2 or 42·[nBuLi]2, shows one amine arm from each NCNLi fragment stabilizing a [nBuLi]2 dimer. The core of the aggregates exhibit a roughly cubic Li4C4 configuration with each aryl carbanion 3 coordinated to Li3 triangular faces. Dissolution of microcrystalline powders of 32·[nBuLi]2 or 42·[nBuLi]2 regenerates the observed equilibria. Based on the NMR data, the remaining mixed aggregates are proposed to have the formula 3·[nBuLi]3 and 4·[nBuLi]3, respectively; the solution structure is again based on a Li4C4 cluster. The relative concentration of the constituents in these equilibria was found to vary depending on the steric size of the amine groups. In the case of 3, the predominant species is the 32·[nBuLi]2 aggregate while for 4, the dimer 42 is favoured.

A 3:1 site-differentiated [4Fe-4S] cluster is immobilized on a thiol-functionalized self-assembled monolayer (SAM) on Au(111) by thiol−thiolate exchange chemistry. Fe 2p signals observed by X-ray photoelectron spectroscopy support the presence of [4Fe-4S] clusters at the SAM surface; further evidence comes from the detection of n-Bu4N+ and cluster-derived species by secondary-ion mass spectrometry. The immobilizing interaction is sufficiently strong to allow the study of [4Fe-4S] clusters at solid−liquid interfaces.

The oxime-substituted NCN-pincer molecules HONCH-1-C6H3(CH2NMe2)2-3,5 (2a) and HONCH-4-C6H2(CH2NMe2)2-2,6-Br-1 (2b) were accessible by treatment of the benzaldehydes H(O)C-4-C6H3(CH2NMe2)2-3,5 (1a) and H(O)C-4-C6H2(CH2NMe2)2-2,6-Br-1 (1b) with an excess of hydroxylamine. In the solid state both compounds are forming polymers with intermolecular O–HN connectivities between the Me2NCH2 substituents and the oxime entity of further molecules of 2a and 2b, respectively. Characteristic for 2a and 2b is a helically arrangement involving a crystallographic 21 screw axis of the HONCH-1-C6H3(CH2NMe2)2-3,5 and HONCH-4-C6H2(CH2NMe2)2-2,6-Br-1 building blocks. The reaction of 2b with equimolar amounts of [Pd2(dba)3 · CHCl3] (3) (dba = dibenzylidene acetone) or [Pt(tol)2(SEt2)]2 (4) (tol = 4-tolyl) gave by an oxidative addition of the C–Br unit to M coordination polymers with a [(HONCH-4-C6H2(CH2NMe2)2-2,6)MBr] repeating unit (5: M = Pd, 6: M = Pt). Complexes 5 and 6 are in the solid state linear hydrogen-bridged polymers with O–HBr contacts between the oxime entities and the metal-bonded bromide.

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 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.

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.

A series of N-substituted indole-3-thiols, synthesized by sequential alkylation, thiouronium salt formation, and hydrolysis, are used to generate a novel family of [4Fe–4S] clusters. The redox transitions of the clusters deviate from those of other [4Fe–4S] cluster families, with half-wave potentials lying in a range midway between those of [4Fe–4S] clusters bound by aliphatic thiolate ligands and those bound by thiophenolate-based ligands. In UV–vis spectroscopy, the new cluster family shows absorption maxima that are among the most red-shifted reported thus far in [4Fe–4S] cluster chemistry. The indole-3-thiolate ligand thus leads to a highly specific and uncommon combination of [4Fe–4S] cluster properties, which can be fine-tuned by facile derivatization at the indole nitrogen atom.

Organometallic NCN-pincer complexes, bearing either a p-nitrophenyl phosphonate ester or a phosphonic acid group directly attached to the aromatic ring of the pincer complex, were synthesized. These compounds were tested as covalent inhibitors for the lipase cutinase. In a stoichiometric reaction of the NCN-pincer platinum phosphonate p-nitrophenyl ester 2 with cutinase, a 94 % conversion to the protein-pincer metal complex hybrid was obtained in 48 h. The NCN-pincer metal phosphonic acid derivatives (3, 4) appeared to be inactive as cutinase inhibitors. In contrast to our previous work which entails propyl tethered phosphonate esters connected to pincer metal complexes, the presented strategy allows positioning of metal complexes inside the active site of lipases. This opens up the possibility for fine-tuning the chemical environment (second coordination sphere) around a synthetic metal center inside the pocket of an enzyme for diagnostic and catalytic purposes.

A series of meso-tetrakis(SCS-pincer PdCl)−(metallo)porphyrin hybrids have been synthesized using two distinct synthetic routes. Manganese and nickel were introduced into the porphyrin macrocycle prior to peripheral electrophilic palladation, whereas magnesium was introduced thereafter in light of its acid sensitivity. When these complexes were used as precatalysts in the Heck reaction between iodobenzene and styrene, different catalytic activities were observed for each hybrid complex. The catalytic activity increased for the metalloporphyrin series MnCl

The title compound, C7H8NO3+·Cl-·0.5H2O, features inter- and intramolecular O-HCl and N-HO hydrogen bonds, linking the molecules into a three-dimensional network. The water molecule is located on a crystallographic twofold rotation axis.

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.

In the title compound [Pt(C17H22N3O4)I(I2)]·0.5CH2Cl2, the coordination environment of the PtII centre is distorted square-pyramidal and is defined by two neutral N atoms and an anionic C atom from the mono-anionic ligand, an iodide anion, and an additional η1-coordinated I2 molecule. Intermolecular C—H...O contacts result in a dimeric structure. The asymmetric unit of (I) consists of two independent [PtI(C17H22N3O4)(I2)] molecules and a CH2Cl2 solvent molecule

The structural aspects and host–guest binding properties of ionic core–shell dendrimers [1]Br8 and [2]Br4, which bear a polycationic core and a neutral shell of Fréchet-type poly(benzyl aryl ether) dendrons, have been investigated by means of dendritic wedges [3]Br2 and [4]Br, that resemble one of the four wedges of the dendrimers. Alike the dendrimers, dendritic wedges [3]Br2 and [4]Br form discrete stoichiometric assemblies with Methyl Orange anions to give host–guest assemblies [3][MO]2 and [4][MO], respectively. X-Ray crystal structures of dendritic wedge [3]Br2 and host–guest assembly [4][MO] have been resolved and reveal that besides Coulombic interactions additional interactions, such as weak hydrogen bonds and π–π interactions, can also be present between the dendritic host and substrate molecules. The substrate selectivity of the ionic core–shell dendrimers for sulfonato anions over carboxylato anions, as was observed in preliminary competition experiments, can be attributed to these additional binding interactions. These X-ray structures, furthermore, substantiate earlier speculations in literature on the presence of π–π interactions between Fréchet-type poly(benzyl aryl ether) dendritic wedges and aromatic substrate molecules.

The synthesis and characterization of novel cyclometalated ruthenium(II) complexes [RuCl(PCPOMe)(PPh3)] and [RuCl(PCPCF3)(PPh3)] containing monoanionic, tridentate coordinating PCP-pincer ligands [C6H3{CH2P(p-MeOC6H4)2}2-2,6]- (PCPOMe) and [C6H3{CH2P(p-CF3C6H4)2}2-2,6]- (PCPCF3) are reported. These compounds have been tested as catalyst precursors in the hydrogen transfer reaction of cyclohexanone to cyclohexanol in 2-propanol using NaOH as a base. The initial rate of the hydrogen transfer reaction appeared to depend on the electronic character of the Ar2P- groups of the PCP-pincer ligand. Among the catalyst precursors studied, the complex [RuCl(PCPCF3)(PPh3)] was found to exhibit the highest activity and the initial TOF exceeded that observed for the Ph2P analogue [RuCl(PCPPh)(PPh3)]. Most importantly, catalysis performed with [RuCl(PCPCF3)(PPh3)] does not require pretreatment of the precursor in the absence of substrate. Conversely, a different catalytic profile and a low activity were observed when either the electron-poor [RuCl{C6H3(CH2P(C6F5)2)2-2,6}(PPh3)] ([RuCl(PCPF20)(PPh3)]) complex or its triflate analogue was used as catalyst precursors. NMR studies and ESI-MS measurements provided information concerning the catalytically active species formed during the pretreatment of the precursor complexes. The results indicate that during the pretreatment period a monoanionic, monohydride ruthenium(II) species, Na[Ru(H)(PCPiPr)(OiPr)(PPh3)], is selectively formed. The latter hydride complex was also obtained via an independent synthetic route. On the basis of both the present results and those previously reported in literature, a mechanism is proposed.

Monodisperse magnetizable colloidal silica particles in a stable dispersion have been functionalized with a homogeneous catalyst: a PCP–pincer Pd-complex. In a proof-of-principle experiment we demonstrate the catalytic activity of the colloids in a C–C bond formation reaction. Advantages of the magnetic silica carriers are the large surface-to-volume ratio and the easy recovery by magnetic separation. After magnetic separation, the catalyst-loaded particles are readily redispersed for further use.

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] 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.

A tin(IV) porphyrin was combined with two axial NCN-pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN-pincer platinum derived benzoic acid. The solid-state structure determined by X-ray crystallography revealed some close contacts between the pincer complexes and the meso-p-tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures.

By careful selection of the appropriate preparation parameters we show how it is possible to immobilize transition metal ion complexes within the supercages of zeolite Y to create molecular species, which mimic the active sites of enzymes and their catalytic function. In particular, we demonstrate the use of 3,3-bis(1-methylimidazol-2-yl)propionate (MIm2Pr) combined with Cu2+ to imitate enzyme actives sites based on the 2-His-1-carboxylate facial triad motif and the use of histidine moieties (His) to replicate the active site of galactose oxidase. Characterization of these active site mimics using a variety of advanced spectroscopic techniques, has also been performed in order to understand why they possess this improved catalytic activity.

2,6-Bis(oxazolinyl)phenylnickel bromide complexes [NiBr(R,R'-Phebox)] (2) were synthesized via two synthetic routes (A and B). In route A, selective bis-ortho lithiation of [R,R'-PheboxBr], followed by a transmetalation reaction with [NiBr2(PEt3)2], yielded not only complexes 2 with an 3-mer-N,C,N'-bonded Phebox ligand but also [NiBr(R,R'-Phebox)(PEt3)2], 7, where the nickel center is 1-C bonded to the intra-annular Cipso of the Phebox ligand. Coordination of two PEt3 ligands completes the square-planar coordination sphere of the Ni center in 7. When R = t-Bu, R' = H, only complex 7c was formed. Alternatively, when route B (oxidative addition with [Ni(cod)2], cod = cyclooctadiene) was followed, selective formation of complexes 2 was observed. X-ray crystal structures were obtained for [NiBr-(i-Pr,H-Phebox)] (2b) and [NiBr(bis(ketimine)phenyl)] (3). The Ni centers have square-planar geometries with a planar, 3-mer-N,C,N' coordination of the terdentate ligand systems. Complexes 2 were found to be inactive as catalysts in the atom-transfer radical polymerization (ATRP) reaction of methyl methacrylate (MMA) and in the atom-transfer radical addition (ATRA, Kharasch addition) reaction of CCl4 to MMA. This is ascribed to the relatively high oxidation potential of NiII-Phebox complexes, which excludes the (reversible) formation of a d7-NiIII-Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)4NBr as supporting electrolyte) showed no electrochemical waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)4NBr as supporting electrode). Theoretical calculations showed that the energy (Eox) needed for the oxidation reaction occurring during the CV experiments is considerably higher for [NiBr(Me,Me-Phebox)] (1.87 eV) and [NiBr(bis(ketimine)phenyl)] (1.90 eV) than for [NiBr(NCN)] (1) (1.45 eV).

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

In the title compound, [Zn(C9H12NS)2], the ZnII center is located on a twofold rotation axis and is coordinated in a distorted tetrahedral environment in a bidentate fashion by anionic thiolate S and neutral amino N atoms of two 2-[(dimethylamino)methyl]benzenethiolate ligands. All the molecules are in the form. The chosen crystal can thus be considered enantiomerically pure. Intermolecular C-H...π contacts connect the molecules into a two-dimensional network.