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Syntheses of the copper and gold complexes [Cu{Fe(CO)5}2][SbF6] and [Au{Fe(CO)5}2][HOB{3,5‐(CF3)2C6H3}3] containing the homoleptic carbonyl cations [M{Fe(CO)5}2]+ (M=Cu, Au) are reported. Structural data of the rare, trimetallic Cu2Fe, Ag2Fe and Au2Fe complexes [Cu{Fe(CO)5}2][SbF6], [Ag{Fe(CO)5}2][SbF6] and [Au{Fe(CO)5}2][HOB{3,5‐(CF3)2C6H3}3] are also given. The silver and gold cations [M{Fe(CO)5}2]+ (M=Ag, Au) possess a nearly linear Fe‐M‐Fe’ moiety but the Fe‐Cu‐Fe’ in [Cu{Fe(CO)5}2][SbF6] exhibits a significant bending angle of 147° due to the strong interaction with the [SbF6]− anion. The Fe(CO)5 ligands adopt a distorted square‐pyramidal geometry in the cations [M{Fe(CO)5}2]+, with the basal CO groups inclined towards M. The geometry optimization with DFT methods of the cations [M{Fe(CO)5}2]+ (M=Cu, Ag, Au) gives equilibrium structures with linear Fe‐M‐Fe’ fragments and D 2 symmetry for the copper and silver cations and D 4d symmetry for the gold cation. There is nearly free rotation of the Fe(CO)5 ligands around the Fe‐M‐Fe’ axis. The calculated bond dissociation energies for the loss of both Fe(CO)5 ligands from the cations [M{Fe(CO)5}2]+ show the order M=Au (D e=137.2 kcal mol−1)>Cu (D e=109.0 kcal mol−1)>Ag (D e=92.4 kcal mol−1). The QTAIM analysis shows bond paths and bond critical points for the M−Fe linkage but not between M and the CO ligands. The EDA‐NOCV calculations suggest that the [Fe(CO)5]→M+←[Fe(CO)5] donation is significantly stronger than the [Fe(CO)5]←M+→[Fe(CO)5] backdonation. Inspection of the pairwise orbital interactions identifies four contributions for the charge donation of the Fe(CO)5 ligands into the vacant (n)s and (n)p AOs of M+ and five components for the backdonation from the occupied (n‐1)d AOs of M+ into vacant ligand orbitals., Donation of an electron pair from the HOMO of [Fe(CO)5]2 to the 4s LUMO of Cu+ giving the (+,+) component of the Fe‐Cu‐Fe σ bond in [Cu{Fe(CO)5}2]+. The associated charge flow with the direction red→blue is given by the deformation density.

We present the synthesis and coordination chemistry of a bulky, tripodal N,N,O ligand, ImPh2NNO tBu (L), designed to model the 2‐His‐1‐carboxylate facial triad (2H1C) by means of two imidazole groups and an anionic 2,4‐di‐tert‐butyl‐subtituted phenolate. Reacting K‐L with MCl2 (M = Fe, Zn) affords the isostructural, tetrahedral non‐heme complexes [Fe(L)(Cl)] (1) and [Zn(L)(Cl)] (2) in high yield. The tridentate N,N,O ligand coordination observed in their X‐ray crystal structures remains intact and well‐defined in MeCN and CH2Cl2 solution. Reacting 2 with NaSPh affords a tetrahedral zinc thiolate complex, [Zn(L)(SPh)] (4), that is relevant to isopenicillin N synthase (IPNS) biomimicry. Cyclic voltammetry studies demonstrate the ligand's redox non‐innocence, where phenolate oxidation is the first electrochemical response observed in K‐L, 2 and 4. However, the first electrochemical oxidation in 1 is iron‐centred, the assignment of which is supported by DFT calculations. Overall, ImPh2NNO tBu provides access to well‐defined mononuclear, monoligated, N,N,O‐bound metal complexes, enabling more accurate structural modelling of the 2H1C to be achieved., How N,N,O can you go? A new bulky, tripodal N,N,O phenolate ligand provides access to well‐defined mononuclear, monoligated non‐heme iron and zinc complexes that accurately model the 2‐His‐1‐carboxylate facial triad. These complexes are ideal synthons from which to create a range of biomimetic N,N,O‐bound complexes featuring biorelevant cofactors.

Reaction of [Pt(DMSO)2Cl2] or [Pd(MeCN)2Cl2] with the electron‐rich LH=N,N’‐bis(4‐dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL2] (1) but dinuclear [Pd2L4] (2), a paddle‐wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV‐vis‐NIR spectroscopy, magnetic resonance) and TD‐DFT calculations as metal(II) species with noninnocent ligands L−. The reversibly accessible cations [PtL2]+ and [Pd2L4]+ were also studied, the latter as [Pd2L4][B{3,5‐(CF3)2C6H3}4] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [PtII(L−)2] or [Pt.(L )2], [PtII(L0.5−)2]+ or [PtIII(L−)2]+, [(PdII)2(μ‐L−)4] or [(Pd1.5)2(μ‐L0.75−)4], and [(Pd2.5)2(μ‐L−)4]+ or [(PdII)2(μ‐L0.75−)4]+. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL2] with an N‐Pt‐N bite angle of 62.8(2)° in contrast to [Pd2L4], and the dimetal (Pd2 4+→Pd2 5+) instead of ligand (L−→L ) oxidation of the dinuclear palladium compound., Qualitatively different structures and electron transfer behavior have been established for platinum and palladium complexes [PtL2]0/+ and [Pd2L4]0/+ with a redox‐active amidinato ligand L− /L..

Chelating phosphines have long been a mainstay as efficient directing ligands in transition‐metal catalysis. Low‐valent derivatives, namely chelating phosphinidenes, are to date unknown, and could lead to chelating complexes containing more than one metal centre due to the intrisic capacity of phosphinidenes to bind two metal fragments at one P‐centre. Here we describe the synthesis of the first such chelating bis‐phosphinidene ligand, XantP2 (2), generated by the reduction of a diphosphino xanthene derivative, Xant(PH2)2 (1) with iPrNHC (iPrNHC=[:C{N(iPr)C(H)}2]). Initial studies have shown that this novel chelating ligand can act as a bidentate ligand towards element dihalides (i.e. FeCl2, ZnI2, GeCl2, SnBr2), forming cationic complexes with the tetryl elements. In contrast, XantP2 demonstrates an ability to bind multiple metal centres in the reaction with CuCl, leading to a cationic Cu3P3 ring complex, with Cu centres bridged by phosphinidene arms. Density Functional Theory calculations show that 2 indeed holds 4 lone pairs of electrons, shedding further light on the coordination capacity for this novel ligand class through observation of directionality and hybridisation of these electron pairs., It's a P‐P‐Party! A facile synthetic route to a new form of chelating phosphorous ligand, namely the chelating bis‐phosphinidene XantP2, has been developed, allowing for the gram‐scale synthesis of this novel ligand scaffold. Computational investigations corroborate that each P‐centre holds two lone pairs of electrons, allowing for the binding of multiple metal centres. Initial efforts towards the coordination chemistry of XantP2 are reported.

The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene)2]+ (arene = C6H3Me3, C6H5Me) with 16 valence electrons and heteroleptic arene‐carbonyl cations [(CO)Nb(arene)2]+ (arene = C6H3Me3, C6H5Me) and [(arene)M(CO)4]+ (arene = C6H3Me3, C6H6) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(ORF)4]− or [F{Al(ORF)3}2]− (RF = C(CF3)3). The limits of two synthesis routes starting from neutral Nb(arene)2 (arene = C6H3Me3, C6H5Me) or [NEt4][M(CO)6] (M = Nb, Ta) were investigated. All compounds were analyzed by single crystal X‐ray determination, vibrational and NMR spectroscopy. DFT calculations were executed to support the experimental data., A variety of niobium‐sandwich and piano‐stool cations were stabilized by the weakly coordinating anions [Al(OC(CF3)4]− and [F{Al(OC(CF)3)3}2]−. Besides the analysis by single‐crystal X‐ray diffraction, vibrational and NMR spectroscopy, DFT calculations were executed to support the experimental data.

A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ‐η2‐C,C′‐κ2‐S,P‐C2(PPh2)S}Ru(η5‐C5H5)(PPh3)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side‐on carbon P,S‐chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like‐isomer is oxidized at W while the unlike‐isomer is oxidized at Ru, which is proven by IR, NIR and EPR‐spectroscopy supported by spectro‐electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ‐η2‐C,C′‐κ2‐S,P‐C2(PPh2)S}Ru(η5‐C5H5)‐(PPh3)], in which valence trapped WIII/RuII and WII/RuIII cationic species are at equilibrium., Diastereomers differ in physical properties: A case of real metal/metal redox isomerism is observed in a dinuclear complex with a particularly short bridging ligand. The two stereogenic complex moieties at W and Ru, respectively, are linked by an alkyne based phosphine thiolate chelate ligand. Oxidation of the like isomer pertains to tungsten, whereas the unlike isomer is oxidised at ruthenium. The diastereomers show opposite redox behaviour!

Quantum chemical studies using density functional theory and ab initio methods have been carried out for the molecules L‐C3‐L with L=PPh3 (1), NHCMe (2, NHC=N‐heterocyclic carbene), and cAACMe (3, cAAC=cyclic (alkyl)(amino) carbene). The calculations predict that 1 and 2 have equilibrium geometries where the ligands are bonded with rather acute bonding angles at the linear C3 moiety. The phosphine adduct 1 has a synclinal (gauche) conformation whereas 2 exhibits a trans conformation of the ligands. In contrast, the compound 3 possesses a nearly linear arrangement of the carbene ligands at the C3 fragment. The bond dissociation energies of the ligands have the order 1, C3 stabilization: Quantum chemical studies using density functional theory and ab initio methods have been carried out for the molecules L‐C3‐L with L=PPh3 (1), NHCMe (2, NHC=N‐heterocyclic carbene), and cAACMe (3, cAAC= cyclic (alkyl)(amino) carbene). The calculations predict that 1 and 2 have equilibrium geometries where the ligands are bonded with rather acute bonding angles at the linear C3 moiety.

Reduction of [SmIII(COT1,4‐SiiPr3)(BH4)(thf)] (COT1,4‐SiiPr3=1,4‐( i Pr3Si)3C8H6) with KC8 resulted in [SmIII/II/III(COT1,4‐SiiPr3)4], the first example of a homoleptic lanthanide quadruple‐decker. As indicated by an analysis of the bond metrics in the solid‐state, the inner Sm ion is present in the divalent oxidation state, while the outer ones are trivalent. This observation could be confirmed by quantum chemical calculations. Mechanistic studies revealed not only insight into possible formation pathways of [SmIII/II/III(COT1,4‐SiiPr3)4] but also resulted in the transformation to other mixed metal sandwich complexes with unique structural properties. These are the 1D‐polymeric chain structured [KSmIII(COT1,4‐SiiPr3)] n and the hexametallic species [(tol)K(COT1,4‐SiiPr3)SmII(COT1,4‐SiiPr3)K]2 which were initially envisioned as possible building blocks as part of different retrosynthetically guided pathways that we developed., The synthesis of the first well‐defined neutral and homoleptic (same metal, same ligand) all‐carbon‐based quadruple‐decker complexes [SmIII/II/III 3(COT1,4‐SiiPr3)4] (COT1,4‐SiiPr3=1,4‐( i Pr3Si)3C8H6) along with other unique sandwich complexes is shown.

When carbonyl ligands coordinate to transition metals, their bond distance either increases (classical) or decreases (nonclassical) with respect to the bond length in the isolated CO molecule. C−O expansion can easily be understood by π‐back‐donation, which results in a population of the CO's π*‐antibonding orbital and hence a weakening of its bond. Nonclassical carbonyl ligands are less straightforward to explain, and their nature is still subject of an ongoing debate. In this work, we studied five isoelectronic octahedral complexes, namely Fe(CO)6 2+, Mn(CO)6 +, Cr(CO)6, V(CO)6 − and Ti(CO)6 2−, at the ZORA‐BLYP/TZ2P level of theory to explain this nonclassical behavior in the framework of Kohn–Sham molecular orbital theory. We show that there are two competing forces that affect the C−O bond length, namely electrostatic interactions (favoring C−O contraction) and π‐back‐donation (favoring C−O expansion). It is a balance between those two terms that determines whether the carbonyl is classical or nonclassical. By further decomposing the electrostatic interaction ΔV elstat into four fundamental terms, we are able to rationalize why ΔV elstat gives rise to the nonclassical behavior, leading to new insights into the driving forces behind C−O contraction., Classical or nonclassical? We show that there are two competing forces that affect the CO bond length in transition metal complexes, namely electrostatic interactions (favoring CO contraction) and π‐back‐donation (favoring CO expansion). The origin is elucidated by quantitative MO‐theory, leading to new insights into the driving forces behind nonclassical behavior.

The interplay of metal ions with polysaccharides is important for the immune recognition in the lung. Due to the localization of beryllium associated diseases to the lung, it is likely that beryllium carbohydrate complexes play a vital role for the development of berylliosis. Herein, we present a detailed study on the interaction of Be2+ ions with fructose and glucose as well as simpler biomimetic ligands, which emulate binding motives of saccharides. Through NMR and IR spectroscopy as well as single‐crystal X‐ray diffraction, complemented by competition reactions we were able to determine a distinctive trend in the binding affinity of these ligands. This suggests that under physiological conditions beryllium ions are only bound irreversibly in glycoproteins or polysaccharides if a quasi ideal tetrahedral environment and κ4‐coordination is provided by the respective biomolecule. Furthermore, Lewis acid induced conversions of the ligands and an extreme increase in the Brønstedt acidity of the present OH‐groups imply that upon enclosure of Be2+, alterations may be induced by the metal ion in glycoproteins or polysaccharides. In addition the frequent formation of Be‐O‐heterocycles indicates that multinuclear beryllium compounds might be the actual trigger of berylliosis. This investigation on beryllium coordination chemistry was supplemented by binding studies of selected biomimetic ligands with Al3+, Zn2+, Mg2+, and Li+, which revealed that none of these beryllium related ions was tetrahedrally coordinated under the give conditions. Therefore, studies on the metabolization of beryllium compounds cannot be performed with other hard cations as a substitute for the hazardous Be2+., Beryllium chemistry: A detailed study on the interaction of saccharide‐mimicking ligands with Be2+ delivered the first comprehensive knowledge on the preferred binding environment around Be ions in polysaccharides and glycoproteins (see graphic). Additional experiments enabled elucidation of beryllium‐induced alterations in biomolecules, which sheds light on the biochemical mechanisms liable for the development of berylliosis.

Two types of imidazole ligands were introduced both at the end of tetramolecular and into the loop region of unimolecular DNA G‐quadruplexes. The modified oligonucleotides were shown to complex a range of different transition‐metal cations including NiII, CuII, ZnII and CoII, as indicated by UV/Vis absorption spectroscopy and ion mobility mass spectrometry. Molecular dynamics simulations were performed to obtain structural insight into the investigated systems. Variation of ligand number and position in the loop region of unimolecular sequences derived from the human telomer region (htel) allows for a controlled design of distinct coordination environments with fine‐tuned metal affinities. It is shown that CuII, which is typically square‐planar coordinated, has a higher affinity for systems offering four ligands, whereas NiII prefers G‐quadruplexes with six ligands. Likewise, the positioning of ligands in a square‐planar versus tetrahedral fashion affects binding affinities of CuII and ZnII cations, respectively. Gaining control over ligand arrangement patterns will spur the rational development of transition‐metal‐modified DNAzymes. Furthermore, this method is suited to combine different types of ligands, for example, those typically found in metalloenzymes, inside a single DNA architecture., Unimolecular DNA G‐quadruplexes, modified with metallo‐enzyme‐inspired imidazole moieties, can be fine‐tuned to bind a variety of transition‐metal cations in their loop region.

Aldehydes play a key role in the human metabolism. Therefore, it is essential to know their reactivity with beryllium compounds in order to assess its effects in the body. The reactivity of simple aldehydes towards beryllium halides (F, Cl, Br, I) was studied through solution and solid‐state techniques and revealed distinctively different reactivities of the beryllium halides, with BeF2 being the least and BeI2 the most reactive. Rearrangement and aldol condensation reactions were observed and monitored by in situ NMR spectroscopy. Crystal structures of various compounds obtained by Be2+‐catalyzed cyclization, rearrangement, and aldol addition reactions or ligation of beryllium halides have been determined, including unprecedented one‐dimensional BeCl2 chains and the first structurally characterized example of an 1‐iodo‐alkoxide. Long‐term studies showed that only aldehydes without a β‐H can form stable beryllium complexes, whereas other aldehydes are oligo‐ and polymerized or decomposed by beryllium halides.

The noncovalent interactions of heavy pnictogens with π‐arenes play a fundamental role in fields like crystal engineering or catalysis. The strength of such bonds is based on an interplay between dispersion and donor/acceptor interactions, and is generally attributed to the presence of π‐arenes. Computational studies of the interaction between the heavy pnictogens As, Sb and Bi and cyclohexane, in comparison with previous studies on the interaction between heavy pnictogens and benzene, show that this concept probably has to be revised. A thorough analysis of all the different energetic components that play a role in these systems, carried out with state‐of‐the‐art computational methods, sheds light on how they influence one another and the effect that their interplay has on the overall system. Furthermore, the analysis of such interactions leads us to the unexpected finding that the presence of the pnictogen compounds strongly affects the conformational equilibrium of cyclohexane, reversing the relative stability of the chair and boat‐twist conformers, and thus suggesting a possible application of tuneable dispersion energy donors to stabilise the desired conformation., Is it, or is it not π? The interaction of heavy pnictogen compounds with benzene and cyclohexane provides an insightful example of whether such interactions are indeed “π interactions”. High‐level, ab‐initio calculations show that in both cases the interaction is dominated by dispersion and that this contribution is practically the same with or without a π system.

Supramolecular coordination‐based self‐assembled nanostructures have been widely studied, and currently various applications are being explored. For several applications, the stability of the nanostructure is of key importance, and this strongly depends on the metal used in the self‐assembly process. Herein, design strategies and synthetic protocols to access desirable kinetically stable Pt12L24 nanospheres are reported, and it is demonstrated that these are stable under conditions under which the palladium counterparts decompose. Descriptors previously used for palladium nanospheres are insufficient for platinum analogues, as the stronger metal–ligand bond results in a mixture of kinetically trapped structures. We report that next to the dihedral angle, the rigidity of the ditopic ligand is also a key parameter for the controlled formation of Pt12L24 nanospheres. Catalytic amounts of coordinating additives to labilise the platinum‐pyridyl bond to some extent are needed to selectively form Pt12L24 assemblies. The formed Pt12L24 nanospheres were demonstrated to be stable in the presence of chloride, amines and acids, unlike the palladium analogues., Avoiding the unwanted: Robust Pt12L24 assemblies were selectively formed by a combination of thermodynamic tuning, achieved by rigidifying the ligands, and kinetic tuning with catalytic amounts of additives. The described methodology can be applied to prepare a variety of functionalised platinum assemblies that were shown to be kinetically stable against biologically and catalytically relevant substrates.

The behavior of the redox‐active aminotroponiminate (ATI) ligand in the coordination sphere of bismuth has been investigated in neutral and cationic compounds, [Bi(ATI)3] and [Bi(ATI)2Ln][A] (L=neutral ligand; n=0, 1; A=counteranion). Their coordination chemistry in solution and in the solid state has been analyzed through (variable‐temperature) NMR spectroscopy, line‐shape analysis, and single‐crystal X‐ray diffraction analyses, and their Lewis acidity has been evaluated by using the Gutmann–Beckett method (and modifications thereof). Cyclic voltammetry, in combination with DFT calculations, indicates that switching between ligand‐ and metal‐centered redox events is possible by altering the charge of the compounds from 0 in neutral species to +1 in cationic compounds. This adds important facets to the rich redox chemistry of ATIs and to the redox chemistry of bismuth compounds, which is, so far, largely unexplored., Central control: A series of bismuth aminotroponiminate cations are discussed and differences between neutral and cationic compounds in terms of coordination chemistry, Lewis acidity, and redox behavior are pinpointed. Specifically, cationization allows switching from ligand‐centered redox events to metal‐centered redox events, facilitating rare examples of quasi‐reversible electron transfer at bismuth.

Combined experimental and theoretical methods are used to gain fundamental understanding of the redox���properties of iron���vanadium oxo���alkoxide clusters as they related to modification of the heterometal number. The rational control of the electrochemical properties of polyoxovanadate���alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal���functionalized cluster was examined. The redox properties of [V5O6(OCH3)12FeCl] (1���[V5FeCl]) and [V5O6(OCH3)12Fe]X (2���[V5Fe]X; X=ClO4, OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal���functionalized clusters reveals that differences in the redox profiles of 1���[V5FeCl] and 2���[V5Fe]X arise from changes in the number of ligands surrounding the iron center (e.g., 6���coordinate vs. 5���coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed���valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster., publishedVersion

Chemistry - a European journal 26(44), 10133 - 10139 (2020). doi:10.1002/chem.202002653, Lanthanides (Ln) are critical raw materials, however, their mining and purification have a considerable negative environmental impact and sustainable recycling and separation strategies for these elements are needed. In this study, the precipitation and solubility behavior of Ln complexes with pyrroloquinoline quinone (PQQ), the cofactor of recently discovered lanthanide (Ln) dependent methanol dehydrogenase (MDH) enzymes, is presented. In this context, the molecular structure of a biorelevant europium PQQ complex was for the first time elucidated outside a protein environment. The complex crystallizes as an inversion symmetric dimer, Eu$_2$PQQ$_2$, with binding of Eu in the biologically relevant pocket of PQQ. LnPQQ and Ln1Ln2PQQ complexes were characterized by using inductively coupled plasma mass spectrometry (ICP‐MS), infrared (IR) spectroscopy, $^{151}$Eu‐Mössbauer spectroscopy, X‐ray total scattering, and extended X‐ray absorption fine structure (EXAFS). It is shown that a natural enzymatic cofactor is capable to achieve separation by precipitation of the notoriously similar, and thus difficult to separate, lanthanides to some extent., Published by Wiley-VCH, Weinheim

We herein report on new synthetic strategies for the preparation of pyridine and imidazole substituted 2,2’‐dihalo biphenyls. These structures are pre‐ligands suitable for the preparation of respective stannoles. The latter can successfully be transmetalated to K[AuCl4] forming non‐palindromic [(C^C^D)AuIII] pincer complexes featuring a lateral pyridine (D=N) or N‐heterocyclic carbene (NHC, D=C’) donor. The latter is the first report on a pincer complex with two formally anionic sp2 and one carbenic carbon donor. The [(C^C^D)AuIII] complexes show intense phosphorescence in solution at room temperature. We discuss the developed multistep strategy and touch upon synthetic challenges. The prepared complexes have been fully characterized including X‐ray diffraction analysis. The gold(III) complexes’ photophysical properties have been investigated by absorption and emission spectroscopy as well as quantum chemical calculations on the quasi‐relativistic two‐component TD‐DFT and GW/Bethe–Salpeter level including spin–orbit coupling. Thus, we shed light on the electronic influence of the non‐palindromic pincer ligand and reveal non‐radiative relaxation pathways of the different ligands employed., Capture the gold(fish)! Donor‐substituted dihalobiphenyls are suitable pre‐ligands for the preparation of luminescent, non‐palindromic [(C^C^D)AuIII] complexes with a lateral pyridine or carbene donor. Like an anglerfish's rod enmeshes its prey, the lateral donor tunes the gold‘s electronic properties which is hold by the rigid biphenyl mouth. Synthesis, spectroscopy and quantum chemistry draw a comprehensive picture about the new complexes prepared.

The use of a bis(diphenyl)phosphine functionalized β‐diketiminato ligand, [HC{(CH3)C}2{(ortho‐[P(C6H5)2]2C6H4)N}2]− (PNac), as a support for germanium(II) and tin(II) chloride and phosphaketene compounds, is described. The conformational flexibility and hemilability of this unique ligand provide a versatile coordination environment that can accommodate the electronic needs of the ligated elements. For example, chloride abstraction from [(PNac)ECl] (E=Ge, Sn) affords the cationic germyliumylidene and stannyliumylidene species [(PNac)E]+ in which the pendant phosphine arms associate more strongly with the Lewis acidic main group element centers, providing further electronic stabilization. In a similar fashion, chemical decarbonylation of the germanium phosphaketene [(PNac)Ge(PCO)] with tris(pentafluorophenyl)borane affords a “push–pull” stabilized phosphinidene in which one of the phosphine groups of the ligand backbone associates with the low valent phosphinidene center., The synthesis and reactivity of a family of germanium(II) and tin(II) complexes supported by a bis(diphenyl)phosphine functionalized β‐diketiminato ligand is reported, including an intramolecularly stabilized “push–pull” phosphinidene.

Derivatives of 1,2‐dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi‐responsive) molecular switches. Transition‐metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione is described, which reacts with [V(TMEDA)2Cl2] to give a rare non‐oxido vanadium(IV) species 3(M,M/P,P). This blue complex has two bidentate en‐diolato ligands which chelate the VIV center and give rise to two five‐membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P). Both complexes were isolated and structurally characterized by single‐crystal X‐ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution., A rare species: In this work, the redox active ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione is described. Chelation of a vanadium metal center gives rise to an en‐diolate motif in two five‐membered VIV metallacycles with hexatriene DTE backbones bearing axial chirality. Two non‐oxido VIV atropisomeric complexes with metalloradical character were isolated. Their dynamic behavior (reversible cyclization) in solution was studied in a CW EPR spectroscopic study.

ChemistryOpen : including thesis treasury 8(7), 951-960 (2019). doi:10.1002/open.201900203, Published by Wiley-VCH-Verl., Weinheim

The coordination chemistry of the 1,2-BN-cyclohexanes 2,2-R2 -1,2-B,N-C4 H10 (R2 =HH, MeH, Me2 ) with Ir and Rh metal fragments has been studied. This led to the solution (NMR spectroscopy) and solid-state (X-ray diffraction) characterization of [Ir(PCy3 )2 (H)2 (η(2) η(2) -H2 BNR2 C4 H8 )][BAr(F) 4 ] (NR2 =NH2 , NMeH) and [Rh(iPr2 PCH2 CH2 CH2 PiPr2 )(η(2) η(2) -H2 BNR2 C4 H8 )][BAr(F) 4 ] (NR2 =NH2 , NMeH, NMe2 ). For NR2 =NH2 subsequent metal-promoted, dehydrocoupling shows the eventual formation of the cyclic tricyclic borazine [BNC4 H8 ]3 , via amino-borane and, tentatively characterized using DFT/GIAO chemical shift calculations, cycloborazane intermediates. For NR2 =NMeH the final product is the cyclic amino-borane HBNMeC4 H8 . The mechanism of dehydrogenation of 2,2-H,Me-1,2-B,N-C4 H10 using the {Rh(iPr2 PCH2 CH2 CH2 PiPr2 )}(+) catalyst has been probed. Catalytic experiments indicate the rapid formation of a dimeric species, [Rh2 (iPr2 PCH2 CH2 CH2 PiPr2 )2 H5 ][BAr(F) 4 ]. Using the initial rate method starting from this dimer, a first-order relationship to [amine-borane], but half-order to [Rh] is established, which is suggested to be due to a rapid dimer-monomer equilibrium operating.

A high yield preparation, spectroscopic and crystallographic investigation of the crystalline Zn-complex of a di(β,β′-sulfoleno)pyrrin are reported here. In the brightly green fluorescent Zn-complex of the hardly luminescent di(β,β′-sulfoleno)pyrrin, the metal ion is bound by two di(β,β′-sulfoleno)pyrrin ligands, as revealed first by its mass spectra. The crystal structure of this Zn-complex of the di(β,β′-sulfoleno)pyrrin confirmed a regular 2:1 composition of the bidentate di(β,β′-sulfoleno)pyrrin ligand and the metal ion. The latter was coordinated in a distorted tetrahedral fashion, as found in other dipyrrin Zn-complexes. The here studied Zn-complex of a designed di(β,β′-sulfoleno)pyrrin ligand provides insights into the coordination properties of the proposed (2:1)- and (2:2)-complexes of phylloxanthobilin and bilirubin, respectively, which are two abundant natural bilin-type tetrapyrroles. Graphical abstract

A new family of cyclometallated gold(III) thiolato complexes based on pyrazine‐centred pincer ligands has been prepared, (C^Npz^C)AuSR, where C^Npz^C=2,6‐bis(4‐ButC6H4)pyrazine dianion and R=Ph (1), C6H4 tBu‐4 (2), 2‐pyridyl (3), 1‐naphthyl (1‐Np, 4), 2‐Np (5), quinolinyl (Quin, 6), 4‐methylcoumarinyl (Coum, 7) and 1‐adamantyl (8). The complexes were isolated as yellow to red solids in high yields using mild synthetic conditions. The single‐crystal X‐ray structures revealed that the colour of the deep‐red solids is associated with the formation of a particular type of short (3.2–3.3 Å) intermolecular pyrazine⋅⋅⋅pyrazine π‐interactions. In some cases, yellow and red crystal polymorphs were formed; only the latter were emissive at room temperature. Combined NMR and UV/Vis techniques showed that the supramolecular π‐stacking interactions persist in solution and give rise to intense deep‐red photoluminescence. Monomeric molecules show vibronically structured green emissions at low temperature, assigned to ligand‐based 3IL(C^N^C) triplet emissions. By contrast, the unstructured red emissions correlate mainly with a 3LLCT(SR→{(C^Npz^C)2}) charge transfer transition from the thiolate ligand to the π⋅⋅⋅π dimerized pyrazine. Unusually, the π‐interactions can be influenced by sample treatment in solution, such that the emissions can switch reversibly from red to green. To our knowledge this is the first report of aggregation‐enhanced emission in gold(III) chemistry.

(Figure Presented). Methylene-bridged calix[4]arenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calix[4]-arenes and transition metal ions or 3d-4 f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.

As a result of systematic UV–Vis absorption spectroscopy studies in the U(VI) acetate system, the single component spectrum of [UO2CH3COO]+ with characteristic parameters was evaluated and applied in quantitative deconvolution of multicomponent spectra. Free acetate concentrations were obtained by the use of geochemical and probabilistic modelling codes. A total of 51 UV–Vis spectra were collected in a wide range of experimental conditions where coordination of U(VI) by acetate ion was indicated by characteristic variations in the spectra structure as compared to UO2 2+. Using chemometric data analysis, the resulting factor structure was evaluated to obtain a subset of 14 spectra holding only one coordinated species next to UO2 2+ (aq). The molar absorption coefficient for the U(VI) monoaceto species was estimated as e 418 = 17.8 ± 1 dm3 mol−1 cm−1. Spectral deconvolution was used to obtain an estimate of the species concentrations which allowed to calculate for each sample the free acetate concentration, the total U(VI) amount and, eventually, to estimate the formation quotient lg β 11 = 2.8 ± 0.3 of UO2(CH3COO)+.

We report the unprecedented observation and unequivocal crystallographic characterization of the meta-stable ligand loss intermediate solvento complex trans-[Ru(bpy)(κ2-btz)(κ1-btz)(NCMe)]2+ (1 a) that contains a monodentate chelate ligand. This and analogous complexes can be observed during the photolysis reactions of a family of complexes of the form [Ru(equation image)(btz)2]2+ (1 a–d: btz=1,1′-dibenzyl-4,4′-bi-1,2,3-triazolyl; equation image=a) 2,2′-bipyridyl (bpy), b) 4,4′-dimethyl-2,2′-bipyridyl (dmbpy), c) 4,4′-dimethoxy-2,2′-bipyridyl (dmeobpy), d) 1,10-phenanthroline (phen)). In acetonitrile solutions, 1 a–d eventually convert to the bis-solvento complexes trans-[Ru(equation image)(btz)(NCMe)2]2+ (3 a–d) along with one equivalent of free btz, in a process in which the remaining coordinated bidentate ligands undergo a new rearrangement such that they become coplanar. X-ray crystal structure of 3 a and 3 d confirmed the co-planar arrangement of the equation image and btz ligands and the trans coordination of two solvent molecules. These conversions proceed via the observed intermediate complexes 2 a–d, which are formed quantitatively from 1 a–d in a matter of minutes and to which they slowly revert back on being left to stand in the dark over several days. The remarkably long lifetime of the intermediate complexes (>12 h at 40 °C) allowed the isolation of 2 a in the solid state, and the complex to be crystallographically characterized. Similarly to the structures adopted by complexes 3 a and d, the bpy and κ2-btz ligands in 2 a coordinate in a square-planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand.

The mesomeric betaine imidazolium-1-ylphenolate forms a borane adduct with tris(pentafluorophenyl)borane by coordination with the phenolate oxygen, whereas its NHC tautomer 1-(2-phenol)imidazol-2-ylidene reacts with (triphenylphosphine)gold(I) chloride to give the cationic NHC complex [Au(NHC)2][Cl] by coordination with the carbene carbon atom. The anionic N-heterocyclic carbene 1-(2-phenolate)imidazol-2-ylidene gives the complexes [K][Au(NHC−)2], [Rh(NHC−)3] and [Ni(NHC−)2], respectively. Results of four single crystal analyses are presented.

In the context of palladium-catalyzed guanylation of anilines herein, we have been able to characterize and isolate bis(anilino) and bis(guanidino)Pd(II) complexes using reaction conditions under which stoichiometric amounts of palladium salts are used. Characterization of these palladium complexes strongly supports a mechanistic proposal for the catalytic guanylation of anilines using PdCl2 (NCCH3)2 as catalyst that involves the intermediacy of these Pd(II) complexes. © 2013 Grirrane et al.

Racemic boronate–imine and boronate–amine complexes 8 and 10, both featuring a stereogenic boron atom were synthesized from 2-amino-1,1-diphenylethanol (5) and characterized by crystal structure analyses. Proof of enantiomerism at the boron center for the novel boronate–amine complex 10 was established by separation of the enantiomers. Racemization barriers were found to be in the same range for both amine and imine complexes (100–110 kJ/mol).

The synthesis of several symmetrically 4,4″-functionalized 2,2′:6′,2″-terpyridines is reported. In addition to the biscarboxylic acid 4,4″-tpy(CO2H)2 (3), the anthryl esters 4,4″-tpy(CO2CH2Anth)2 (5a) and 4,4″-tpy(CO2CH2CH2OAnth)2 (5b) were synthesized. Furthermore, both anthryl esters were used to synthesize symmetric iron(II)-bis(terpyridine)complexes 6a–b. Irradiation experiments were carried out with both the free ligands and an iron(II)-complex in order to investigate the photochemistry of the compounds.

The synthesis of a perfluorocyclopentene based diarylethene bearing two terpyridine units is reported. Furthermore studies of the free ligand’s photochromism and investigations regarding the influence of various transition metal ions on the photochromic reaction are presented. The photochromism of the central diarylethene unit is strongly dependent on the transition metal present, vice versa the photochromic reaction seems to influence the MLCT transition of a binuclear Ru(II) complex.