Facile Method to Obtain Functionalised η6-Bound Arenes in Ru(II) and Os(II) Half-Sandwich Complexes.

Half-sandwich Ru(II)- and Os(II)-arene complexes have great potential for catalytic and biological applications. The possibility of fine-tuning their chemical reactivity by including modifications in the ligands around the metal adds to their many advantages. However, structural modifications at the n6-bound arene have had significant synthetic limitations, particularly in the design of Os(II)-tethered complexes. For the first time, we have employed a practical C(sp3)-C(sp2) coupling to obtain 28 new Ru(II) and Os(II) η6-arene half-sandwich complexes with a wide variety of arene functionalities, including those that enable the formation of tether rings, such as quinoline and coumarin. The introduction of novel functional groups at the arene in Ru(II)- and Os(II) half-sandwich complexes can broaden the synthetic scope of this type of organometallic complexes, and help to take full advantage of their structural diversity, especially in intracellular catalysis.

Chemotherapeutic Activities of New η6-p-Cymene Ruthenium(II) and Osmium(II) Complexes with Chelating SS and Tridentate SNS Ligands.

A series of new chelating bidentate (SS) alkylimidazole-2-thione-Ru(II)/Os(II) complexes (3ai, 3aii, 3aiii, 3bii/4aiii, 4bi, 4bii), and the tridentate (SNS) pyridine-2,6-diylimidazole-2-thione-Ru(II)/Os(II) complexes (5bi, 5civ/6bi, 6ci, 6civ) in the forms [MII(cym)(L)Cl]PF6 and [MII(cym)(L)]PF6 (M = Ru or Os, cym = η6-p-cymene, and L = heterocyclic derivatives of thiourea) respectively, were successfully synthesized. Spectroscopic and analytical methods were used to characterize the complexes and their ligands. Solid-state single-crystal X-ray diffraction analyses revealed a "piano-stool" geometry around the Ru(II) or Os(II) centers in the respective complexes. The complexes were investigated for in vitro chemotherapeutic activities against human cervical carcinoma (HeLa) and the non-cancerous cell line (Hek293) using the MTT assay. The compounds 3aii, 5civ, 5bi, 4aiii, 6ci, 6civ, and the reference drug, 5-fluorouracil were found to be selective toward the tumor cells; the compounds 3ai, 3aiii, 3bii, 4bi, 4bii, and 6bi, which were found not to be selective between normal and tumor cell lines. The IC50 value of the tridentate half-sandwich complex 5bi (86 ± 9 µM) showed comparable anti-proliferative activity with the referenced commercial anti-cancer drug, 5-fluorouracil (87 ± 15 µM). The pincer (SNS) osmium complexes 6ci (36 ± 10 µM) and 6civ (40 ± 4 µM) were twice as effective as the reference drug 5-fluorouracil at the respective dose concentrations. However, the analogous pincer (SNS) ruthenium complex 5civ was ineffective and did not show anti-proliferative activity, even at a higher concentration of 147 ± 1 µM. These findings imply that the higher stability of the chelating (SS) and the pincer (SNS) ligand architectures in the complexes improves the biological (anti-proliferative) activity of the complexes by reducing the chance of ligand dissociation under physiological conditions. In general, the pincer (SNS) osmium complexes were found to be more cytotoxic than their ruthenium analogues, suggesting that the anti-proliferative activity of the imidazole-2-thione-Ru/Os complexes depends on the ligand's spatial coordination, the nature of the metal center, and the charge of the metal complex ions.

Germaaluminocenes-Masked Heterofulvenes.

Germaaluminocenes are formed by salt metathesis reactions of dipotassium germacyclopentadienediides with pentamethylcyclopentadienylaluminum dichloride. The reactivity pattern of these sandwich complexes is determined by the electrophilic central aluminum atom and by the nucleophilic dicoordinated germanium center. Surprisingly, the products formed by reactions with Lewis acids, Lewis bases, amphiphiles and compounds with polar double bonds are those expected from the reaction of a hypothetical aluminagermapentafulvene with these types of reagents. This suggests that germaaluminocenes are synthetic equivalents to these pentafulvenes.

Selective Construction and Structural Transformation of Homogeneous Linear Metalla[4]catenane and Metalla[2]catenane Assemblies.

Although the synthesis of mechanically interlocked molecules has been extensively researched, selectively constructing homogeneous linear [4]catenanes remains a formidable challenge. Here, we selectively constructed a homogeneous linear metalla[4]catenane in a one-step process through the coordination-driven self-assembly of a bidentate benzothiadiazole derivative ligand and a binuclear half-sandwich rhodium precursor. The formation of metalla[4]catenanes was facilitated by cooperative interactions between strong sandwich-type π-π stacking and non-classical hydrogen bonds between the components. Moreover, by modulating the aromatic substituents on the binuclear precursor, two homogeneous metalla[2]catenanes were obtained. The molecular structures of these metallacatenanes were unambiguously characterized by single-crystal X-ray diffraction analysis. Additionally, reversible structural transformation between metal-catenanes and the corresponding metallarectangles could be achieved by altering their concentration, as confirmed by mass spectrometry and NMR spectroscopy studies.

Stereocontrolled Synthesis of Chiral Helicene-Indenido ansa- and Half-Sandwich Metal Complexes and Their Use in Catalysis.

Despite recent tremendous progress in the synthesis of nonplanar chiral aromatics, and helicenes in particular, their conversion to half-sandwich or sandwich transition metal complexes still lags behind, although they represent an attractive family of modular and underexplored chiral architectures with a potential catalytic use. In this work, starting from various chiral helicene-indene proligands, we prepared the enantio- and diastereopure oxa[6]- and oxa[7]helicene-indenido half-sandwich RhI and RhIII complexes and oxa[7]helicene-bisindenido ansa-metallocene FeII complex. To document their use, oxahelicene-indenido half-sandwich RhIII complexes were employed as chiral catalysts in enantioselective C-H arylation of benzo[h]quinolines with 1-diazonaphthoquinones to afford a series of axially chiral biaryls in mostly good to high yields and in up to 96 : 4 er. Thus, we developed stereocontrolled synthesis of chiral helicene-indenido ansa- and half-sandwich metal complexes, successfully demonstrated the first use of such helicene Cp-related metal complexes in enantioselective catalysis, and described an unusual sequence of efficient central-to-helical-to-planar-to-axial chirality transfer.

Efficient and Selective Construction of 41 2 Metalla-links Using Weak C-H⋠⋠⋠Halogen Interactions.

Through a coordination-driven self-assembly method, four 4 1 2 ${4_1^2 }$ metalla-links and one tetranuclear monocycle were constructed with high selectivity and yield by adjusting the substituent species of the building blocks, as evidenced using X-ray crystallographic analysis, electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), elemental analysis and detailed solution-state nuclear magnetic resonance (NMR) spectroscopy. Based on X-ray crystallographic analysis and independent gradient model analysis, a significant factor leading to the formation of 4 1 2 ${4_1^2 }$ metalla-links was the introduction of F, Cl, Br and I atoms, which generated additional weak C-H⋅⋅⋅X (X=F, Cl, Br and I) interactions. Furthermore, the dynamic conversion of 4 1 2 ${4_1^2 }$ metalla-links to monocyclic rings in methanol solution was systematically investigated using quantitative 1H NMR techniques.

Fulleride-metal η5 sandwich and multi-decker sandwich complexes: A DFT prediction.

The (C60 CN)- formed by the reaction of CN- with fullerene shows high electron rich character, very similar to C60 ˙- , and it behaves as a large anion. Similar to Cp- , the bulky anion, (C60 CN)- , acts as a strong η5 ligand towards transition metal centers. Previous studies on η5 coordination of fullerene cage are reported for pseudo fullerenes whereas the present study deals with sandwich complexes of (C60 CN)- with Fe(II), Ru(II), Cr(II), Mo(II), and Ni(II) and multi-decker sandwich complexes of CN-fullerides with Fe(II). The structural parameters of these complexes and the corresponding Cp- complexes showed very close resemblance. Analysis of the metal-to-carbon bonding molecular orbitals showed that sandwich complex [Fe(η5 -(C60 CN)- )2 ] exhibit bonding features very similar to that of ferrocene. Also, a 6-fold decrease in the band gap energy is observed for [Fe(η5 -(C60 CN)- )2 ] compared to ferrocene. The energy of dissociation (ΔE) of the ligand (C60 CN)- from [Fe(η5 -(C60 CN)- )2 ] is slightly lower than the ΔE of a Cp* ligand from a ferrocene derivative wherein each cyclopentadienyl unit is substituted with four tertiary butyl groups. The (C60 CN)- ligand behaved as one of the bulkiest ligands in the chemistry of sandwich complexes. Further, the coordinating ability of the dianion, (C60 (CN)2 )2- is evaluated which showed strong coordination ability simultaneously with two metal centers leading to the formation of multi-decker sandwich and pearl-necklace type polymeric structures.

Computational study of ground-state properties of µ2 -bridged group 14 porphyrinic sandwich complexes.

The structural properties of µ2 -bridged porphyrinic double-decker complexes are investigated and the influence of various ligands, metals, substituents, and bridging atoms on the dominant structural motif is elucidated. A variety of quantum chemical methods including semiempirical (SQM) methods and density functional theory (DFT) is assessed for the calculation of ecliptic and staggered conformational energies. Local coupled cluster (DLPNO-CCSD(T1)) data are generated for reference. The r2 SCAN-3c composite scheme as well as the B2PLYP-D4/def2-QZVPP approach are identified as reliable methods. Energy decomposition analyses (EDA) and localized molecular orbital analyses (LMO) are used to investigate the bonding situation and the nature of the inter-ligand interaction energy underlining the crucial role of attractive London dispersion interactions. Targeted modification of the bridging atom, e.g., by replacing O2- by S2- is shown to drastically change the major structural features of the investigated complexes. Further, the influence of different substituents of varying size at the phthalocyanine ligand regarding the dominant conformation is described.

Dynamic Magnetic Properties of Germole-ligated Lanthanide Sandwich Complexes.

The first germole-ligated single-molecule magnets are reported, with contrasting properties found for the near-linear sandwich complexes [(η8 -COT)Ln(η5 -CpGe ]- , where Ln=Dy (1Dy ) or Er (1Er ), COT is cyclo-octatetraenyl and CpGe is [GeC4 -2,5-(SiMe3 )2 -3,4-Me2 ]2- . Whereas 1Er has an energy barrier of 120(1) cm-1 in zero applied field and open hysteresis loops up to 10 K, the relaxation in 1Dy is characterized by quantum tunneling within the ground state.

Unexpectedly Large Structural Variations in Benzyl-Substituted Sila[1]ferrocenophanes.

A set of four planar-chiral sila[1]ferrocenophanes equipped with a benzyl group in the α-position, either on one or both Cp rings, and substituted on the bridging silicon atom, either by methyl or phenyl groups, were prepared. While NMR, UV/Vis, and DSC measurements did not show anything uncommon, single crystal X-ray analyses revealed unexpectedly large variations of the dihedral angles between both Cp rings (α tilt angle). While DFT calculations predicted α between 19.6 and 20.8°, measured values were found between 16.6(2) and 21.45(14)°. However, experimentally determined conformers differ significantly from those calculated for the gas phase. For the sila[1]ferrocenophane with the largest mismatch between the experimental and predicted α angle, it was shown that the orientation of benzyl groups have a significant influence on the ring-tilted structure. Packing of molecules in the crystal lattice forces benzyl groups into unusual orientations, resulting in a significantly reduced α angle through steric repulsions.

[Ni(CO)4 ]+ as NiI Synthon: Synthesis and Characterization of NiI Half-Sandwich and Sandwich Cations.

The stable, easily accessible salt [Ni(CO)4 ]+ [F{Al(ORF )3 }2 ]- (RF =C(CF3 )3 ) was used as a NiI synthon to generate the novel half-sandwich complexes [Ni(arene)(CO)2 ]+ (arene=C6 H6 , o-dfb=1,2-F2 C6 H4 ). By irreversible removal of CO from the equilibrium, even the rather endergonic reaction to a [Ni(o-dfb)2 ]+ salt was successful (Δr G°(solv) =+78 kJ mol-1 ). The latter displays an unprecedented slipped η3 ,η3 -sandwich structure and is the ultimate synthon to NiI -chemistry.

Organometallic Ionic Liquids Containing Sandwich Complexes: Molecular Design, Physical Properties, and Chemical Reactivities.

Ionic liquids (ILs) are salts with low melting points and are useful as electrolytes and solvents. We have developed ILs containing cationic metal complexes, which form a family of functional liquids that exhibit unique physical properties and chemical reactivities originating from metal complexes. Our study explores the liquid chemistry in the field of coordination chemistry, where solid-state chemistry is currently the main focus. This review describes the molecular design, physical properties, and reactivities of organometallic ILs containing sandwich or half-sandwich complexes. This paper mainly covers stimuli-responsive ILs, whose magnetic properties, solvent polarities, colors, or structures change by the application of external fields, such as light, heat, and magnetic fields, or by reaction with coordinating molecules.

Bonding and Reactivity in Terminal versus Bridging Arenide Complexes of Thorium Acting as ThII Synthons.

Thorium redox chemistry is extremely scarce due to the high stability of ThIV . Here we report two unique examples of thorium arenide complexes prepared by reduction of a ThIV -siloxide complex in presence of naphthalene, the mononuclear arenide complex [K(OSi(Ot Bu)3 )3 Th(η6 -C10 H8 )] (1) and the inverse-sandwich complex [K(OSi(Ot Bu)3 )3 Th]2 (µ-η6 ,η6 -C10 H8 )] (2). The electrons stored in these complexes allow the reduction of a broad range of substrates (N2 O, AdN3 , CO2 , HBBN). Higher reactivity was found for the complex 1 which reacts with the diazoolefin IDipp=CN2 to yield the unexpected ThIV amidoalkynyl complex 5 via a terminal N-heterocyclic vinylidene intermediate. This work showed that arenides can act as convenient redox-active ligands for implementing thorium-ligand cooperative multielectron transfer and that the reactivity can be tuned by the arenide binding mode.

Anticancer Water-Soluble Organoruthenium Complexes: Synthesis and Preclinical Evaluation.

The synthesis, characterisation, and evaluation of the in vitro cytotoxicity of five maleonitriledithiolate-based ruthenium metal complexes bearing various phosphine ligands towards two ovarian cancer cell lines (A2780 and A2780cisR), one non-small-cell lung cancer cell line (H460) and one normal prostate cell line (PNT2) are presented herein. These 18-electron complexes were designed with four water-soluble phosphine ligands to increase the water-solubility character of the corresponding electron-deficient ruthenium complex which showed great in vitro promises, and triphenylphosphine for comparison. The complexes with triphenylphosphine-3,3',3''-trisulfonic acid and triphenylphosphine present similar cytotoxicity compared to the 16-electron precursor, with equal cytotoxicity to both A2780 and A2780cisR. Hints at the mechanism of action suggest an apoptotic pathway based on reactive oxygen species (ROS) production. No toxicity was observed in preliminary in vivo pilot studies for these two complexes in subcutaneous A2780 and A2780cisR xenograft models, with some evidence of tumour growth delay.

Naphthalene Exchange in [Re(η6 -napht)2 ]+ with Pharmaceuticals Leads to Highly Functionalized Sandwich Complexes [M(η6 -pharm)2 ]+ (M=Re/99m Tc).

Bis-arene sandwich complexes are generally prepared by the Fischer-Hafner reaction, which conditions are incompatible with most O- and N- functional groups. We report a new way for the synthesis of sandwich type complexes [Re(η6 -arene)2 ]+ and [Re(η6 -arene)(η6 -benzene)]+ from [Re(η6 -napht)2 ]+ and [Re(η6 -napht)(η6 -benzene)]+ , with functionalized arenes and pharmaceuticals. N-methylpyrrolidine (NMP) facilitates the substitution of naphthalene with the incoming arene. A series of fully characterized rhenium sandwich complexes with simple arenes, such as aniline, as well as with active compounds like lidocaine and melatonin are presented. With these rhenium compounds in hand, the radioactive sandwich complexes [99m Tc(η6 -pharm)2 ]+ (pharm=pharmaceutical) can be unambiguously confirmed. The direct labelling of pharmaceuticals with 99m Tc through η6 -coordination to phenyl rings and the confirmation of the structures with the rhenium homologues opens a path into molecular theranostics.

Rational Design and Integrative Assembly of Heteromeric Metalla[2]Catenanes Featuring Cp*Ir/Rh Fragments.

We report a design strategy for integrative assembly of heteromeric [2]catenanes. The design focuses on the shape and functional group match of two different metalla-rectangles. A series of dipyridyl ligands with different lengths, widths and functional groups were designed and used for assembly experiments. Six heteromeric [2]catenanes were obtained both by direct mixture of two pre-assembled metalla-rectangles and one-pot three-component self-assembly. Multiple analytic methods were employed to characterize the catenanes, including single crystal X-ray diffraction analysis, NMR spectroscopy, mass spectroscopy and elemental analysis.

Isolation and Characterization of the Homoleptic Nickel(I) and Nickel(II) Bis-benzene Sandwich Cations.

A stable salt of the metalloradical [Ni(C6 H6 )2 ]+ hitherto unknown in the condensed phase was synthesized from [Ni(CO)4 ]+ [WCA]- and benzene ([WCA]- =[F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ). Single crystal XRD reveals a remarkable asymmetrically η3 ,η6 -slipped sandwich structure. The magnetic properties of the [Ni(C6 H6 )2 ]+ cation were determined in solution and in the gas phase. Oxidation with the synergistic Ag+ /0.5 l2 system led to the salt [Ni(C6 H6 )2 ]2+ ([WCA]- )2 . All products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.

Easy Access to Versatile Catalytic Systems for C-H Activation and Reductive Amination Based on Tetrahydrofluorenyl Rhodium(III) Complexes.

On the basis of the 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C-C and C-N bonds. The halide compounds [(η5 -tetrahydrofluorenyl)RhX2 ]2 (2 a: X=Br; 2 b: X=I) were synthesized by treatment of the bis(ethylene) derivative (η5 -tetrahydrofluorenyl)Rh(C2 H4 )2 (1 a) with halogens. An analogous reaction of the cyclooctadiene complex (η5 -tetrahydrofluorenyl)Rh(cod) (1 b) with I2 is complicated by the side formation of [(cod)RhI]2 . The reaction of 2 b with 2,2'-bipyridyl leads to cation [(η5 -tetrahydrofluorenyl)Rh(2,2'-bipyridyl)I]+ (3). The halide abstraction from 2 a,b with thallium or silver salts allowed us to prepare sandwich compounds with incoming cyclopentadienyl, dicarbollide and mesityleneligands [(η5 -tetrahydrofluorenyl)RhCp]+ (4), (η5 -tetrahydrofluorenyl)Rh(η-7,8-C2 B9 H11 ) (5), and [(η5 -tetrahydrofluorenyl)Rh(η-mesitylene)]2+ (6). The structures of 1 b, 2 b ⋅ 2I2 , 3PF6 , 4TlI4 , 5, and [(cod)RhI]2 were determined by X-ray diffraction. Compounds 2 a,b efficiently catalyze the oxidative coupling of benzoic acids with alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature. Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation. Compound 2 b also effectively catalyzes the reductive amination of aldehydes and ketones in the presence of carbon monoxide and water via water-gas shift reaction, giving amines in high yields (67-99 %).

Emerging Spacers-Based Ligands for Supramolecular Coordination Complexes.

The design and self-assembly of supramolecular coordination complexes (SCCs) i. e., discrete cyclic metalloarchitectures such as cycles, cages, mesocates, and helicates with desired size, shape, and properties have been increasing exponentially owing to their potential applications in molecular sensors, molecular cargos, molecular recognition, and catalysis. The introduction of the organic motifs and metal complexes as a spacer provides functionality to the metalloarchitecture. This review mainly focusses on newly evolving spacer based ligands employed to yield simple to high-order metallosupramolecular assemblies using straight-forward approaches. The new spacers including corannulene, organic cyclic framework, bicyclic organic motifs, aliphatic chain, metalloligands, triarylboron, BODIPY, azaphosphatrane, phosphine, and thio/selenophosphates offer a great set of properties and in-built functionalities to the metalloarchitectures which are discussed in this review.

Rhodocenium Functionalization Enabled by Half-Sandwich Capping, Zincke Reaction, Diazoniation and Sandmeyer Chemistry.

In continuation of our exploration of metallocenium chemistry we report here on innovative ways toward monofunctionalized rhodocenium salts applying half-sandwich capping reactions of cyclopentadienyl rhodium(III) halide synthons with cyclopentadienyl ylides containing pyridine, phosphine or dinitrogen leaving groups, followed by Zincke and Sandmeyer reactions. Thereby amino, diazonio, bromo, azido and iodo rhodocenium salts containing valuable functional groups are accessible for the first time. Target compounds were characterized by spectroscopic (1H/13C/103Rh-NMR, IR, HR-MS), structural (single crystal XRD) and electrochemical (CV) methods and their properties were compared to those of isoelectronic cobaltocenium compounds. These new functionalized rhodocenium complexes significantly expand the so far extremely limited chemical space of rhodocenium salts with promising options for the future development in the area of rhodocenium chemistry.