含dppm桥的双核过渡金属配合物中金属─金属间的相互作用

应用ＥＨＭＯ法研究了一系列含ｄｐｐｍ双二苯基膦甲烷桥的双核过渡金属配合物［ＰｄＢｒ（ｄｐｐｍ）］_２，Ｍ_２Ｃｌ_２（μ－ＣＯ）（ｄｐｐｍ）_２（Ｍ＝Ｐｄ，Ｒｈ），［ＲｈＣｌ（ＣＯ）（ｄｐｐｍ）］_２，Ｍ_２－（μ－Ｃｌ）_２Ｃｌ_４（ｄｐｐｍ）_２（Ｍ＝Ｎｂ、Ｔａ、Ｒｅ、Ｒｕ）的电子结构。根据配合物的成键特征，对其金属－金属的相互作用进行了分析。计算结果可以作为解释这类配合物的某些物理化学性质的理论依据。     

含dppm桥的双核过渡金属配合物中金属─金属间的相互作用

应用ＥＨＭＯ法研究了一系列含ｄｐｐｍ双二苯基膦甲烷桥的双核过渡金属配合物［ＰｄＢｒ（ｄｐｐｍ）］_２，Ｍ_２Ｃｌ_２（μ－ＣＯ）（ｄｐｐｍ）_２（Ｍ＝Ｐｄ，Ｒｈ），［ＲｈＣｌ（ＣＯ）（ｄｐｐｍ）］_２，Ｍ_２－（μ－Ｃｌ）_２Ｃｌ_４（ｄｐｐｍ）_２（Ｍ＝Ｎｂ、Ｔａ、Ｒｅ、Ｒｕ）的电子结构。根据配合物的成键特征，对其金属－金属的相互作用进行了分析。计算结果可以作为解释这类配合物的某些物理化学性质的理论依据。     

Bandgap Engineering of Titanium–Oxo Clusters: Labile Surface Sites Used for Ligand Substitution and Metal Incorporation

Through the labile coordination sites of a robust phosphonate‐stabilized titanium–oxo cluster, 14 O‐donor ligands have been successfully introduced without changing the cluster core. The increasing electron‐withdrawing effect of the organic species allows the gradual reduction of the bandgaps of the {Ti₆} complexes. Transition‐metal ions are then incorporated by the use of bifunctional O/N‐donor ligands, organizing these {Ti₆} clusters into polymeric structures. The coordination environments of the applied metal ions show significant influence on their visible‐light adsorption. Both the above structural functionalizations also tune the photocatalytic H₂ production activities of these clusters. This work provides a systematic bandgap engineering study of titanium–oxo clusters, which is important not only for their future photocatalytic applications, also for the better understanding of the structure–property relationships.     

Metal Recognition Driven by Weak Interactions: A Case Study in Solvent Extraction

Tuning the affinity of a medium for a given metallic cation with the sole modification of weak interactions is a challenge for molecular recognition. Solvent extraction is a key technique employed in the recovery and purification of valuable metals, and it is facing an increased complexity of metal fluxes to deal with. The selectivity of such processes generally relies on the use of specific ligands, designed after their coordination chemistry. In the present study, we illustrate the possibility to employ the sole control of weak interactions to achieve the selective extraction of Pd^II over Nd^III: the control over selectivity is obtained by tuning the self‐assembly of the organic phase. A model is proposed, after detailed experimental analysis of molecular (XRD, NMR) and supra‐molecular (SAXS) features of the organic phases. We thus demonstrate that Pd^II extraction is driven by metal coordination, whereas Nd^III extraction requires aggregation of the extractant in addition to metal coordination. These results are of general interest for the applications which rely on the stabilization of metals in organic phases.     

Yldiide Ligands as Building Blocks for Polynuclear Coinage Metal Complexes: Metal Squares,Triangles and Chains

Yldiides have unique electronic properties and donor abilities, but as ligands in transition metal complexes they are scarcely represented in the literature. Here, the controlled synthesis of a series of polynuclear gold yldiide complexes derived from triphenyl(cyanomethyl)phosphonium bromide, [Ph₃PCH₂CN]Br, under mild conditions is described. Anionic dinuclear NBu₄[(AuX)₂{C(CN)PPh₃}] (X=Cl, C₆F₅) or trinuclear derivatives NBu₄[Au₃X₂{C(CN)PPh₃}] bearing terminal chloride or pentafluorophenyl groups and bridging yldiide ligands have been prepared. These compounds evolve in solution giving rise to the formation of an unprecedented tetrameric gold cluster, [Au₄{C(CN)PPh₃}₄], by the loss of the gold complex NBu₄[AuX₂]. This gold cluster can also be prepared in high yield by a transmetalation reaction from the analogous tetrameric silver cluster, and two geometric isomers have been characterised, their formation dependent on the synthetic route. The triphenylphosphonium cyanomethyldiide ligand has also been used to build different dinuclear and trinuclear cationic complexes bearing phosphine or diphosphine ancillary ligands and bridging yldiide moieties. Further coordination through the cyano group of the yldiide ligand gives heterometallic trinuclear or pentanuclear derivatives. Structural characterisation of many of these compounds reveals the presence of complex molecular systems stabilised by gold⋅⋅⋅gold interactions and bridging yldiide ligands.     

Shedding Light on the Interactions of Hydrocarbon Ester Substituents upon Formation of Dimeric Titanium(IV) Triscatecholates in DMSO Solution

The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The ¹H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n-alkyls, n-Ω-alkenyls or n-Ω-alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation.     

Noncovalent Interactions at Lanthanide Complexes

Lanthanide complexes have attracted a widespread attention due to their structural diversity, as well as multifunctional and tunable properties. The development of lanthanide based functional materials has often relied on the design of the secondary coordination sphere of the corresponding lanthanide complexes. For instance, usually simple lanthanide salts (solvento complexes) do not catalyze effectively organic reactions or provide low yield of the expected product, whereas the presence of a suitable organic ligand with a noncovalent bond donor or acceptor centre (secondary coordination sphere) modifies the symmetry around the metal centre in lanthanide complexes which then successfully can act as catalysts in both homogenous and heterogenous catalysis. In this minireview, we discuss several relevant examples, based on X-ray crystal structure analyses, in which the hydrogen, halogen, chalcogen, pnictogen, tetrel and rare-earth bonds, as well as cation-π, anion-π, lone pair-π, π–π and pancake interactions, are used as a synthon in the decoration of the secondary coordination sphere of lanthanide complexes.     

Metal–Metal Interactions in Heterobimetallic Complexes with Dinucleating Redox‐Active Ligands

The tuning of metal–metal interactions in multinuclear assemblies is a challenge. Selective P coordination of a redox‐active PNO ligand to Au^I followed by homoleptic metalation of the NO pocket with Ni^II affords a unique trinuclear Au–Ni–Au complex. This species features two antiferromagnetically coupled ligand‐centered radicals and a double intramolecular d⁸–d¹⁰ interaction, as supported by spectroscopic, single‐crystal X‐ray diffraction, and computational data. A corresponding cationic dinuclear Au–Ni analogue with a stronger d⁸–d¹⁰ interaction is also reported. Although both heterobimetallic structures display rich electrochemistry, only the trinuclear Au–Ni–Au complex facilitates electrocatalytic C?X bond activation of alkyl halides in its doubly reduced state. Hence, the presence of a redox‐active ligand framework, an available coordination site at gold, and the nature of the nickel–gold interaction appear to be essential for this reactivity.     

Coinage Metal Complexes of a Tellurium Diimide: cis→trans Isomerization and Metal–Metal Interactions

The different coordination behavior of the ligand tBuN=Te(μ-NtBu)₂Te=NtBu (L) towards Cu⁺ and Ag⁺ results from a cis→trans isomerization. The two Cu⁺ ions in [Cu₂L₃]²⁺ (shown schematically) bridge trans and cis isomers of the ligand, whereas the Ag⁺ ions in [Ag₂L₂]²⁺ link two trans ligands and exhibit a weak Ag⋅⋅⋅Ag interaction.     

The Tetracyanopyrrolide Anion as Ligand in Transition Metal Complexes

Two isotypic mononuclear discrete complexes [Co(MeCN)₄(tcp)₂] · 2MeCN ( 1 ) and [Ni(MeCN)₄(tcp)₂] · 2MeCN ( 2 ) containing the tetracyanopyrrolide anion [C₄(CN)₄N]^– (tcp) were synthesized from [Me₄N]tcp and the respective metal perchlorates in acetone/acetonitrile. Tcp coordinates to the transition metal atoms in η¹ fashion via the nitrogen atom of the pyrrole ring. No coordination via the cyano groups is observed. Both complexes show nearly ideal paramagnetic behavior according to the Curie law with magnetic moments of 4.98 μ_B for 1 and 3.09 μ_B for 2 . In the presence of Cu²⁺ ions tcp reacts with traces of water under hydrolysis of one cyano group to tricyanopyrrole‐2‐carboxamide (NC₄(CN)₃C(O)NH₂)^– (tcpc). From solutions in DMF the complex [Cu(tcpc)₂(DMF)₂] ( 3 ) is isolated.     

Ligand Bridged Heterodinuclear Transition Metal Complexes – Syntheses,Structures and Electrochemical Investigations

The syntheses of the homo‐ and hererobimetallic compounds [L_n¹M(η⁵‐C₅H₄)CMe₂(η⁵‐C₉H₆)²ML_n] ( 2a‐5d ), [(C₉H₇)CMe₂(η⁵‐C₅H₄)Fe(η⁵‐C₅H₄)CMe₂(η⁵‐C₉H₆)²ML_n] ( 6a‐c ), and [(η⁵‐C₅H₄)CMe₂(η⁵‐C₉H₆)²ML_n]₂Fe ( 7a‐b ) are reported with ¹ML_n = Rh(cod) 2 , Ir(cod) 3 , Mn(CO)₃ 4 and FeCp 5 , ²ML_n = Rh(cod) a , Ir(cod) b , Mn(CO)₃ c and FeCp d , respectively. Crystal structures of 3a, 3b and 5c are described showing two different ligand conformations in form of two rotamers. The energetic difference between these both rotamers is insignificant small in the gas phase according to DFT calculations. The rotation barrier for the species has been determined to 23 kJ/mol. According to the absence of intermolecular interactions in the solid state, the preference for one of the conformers is deduced from packing effects. All complexes are investigated by cyclic voltammetry. The shift of the redox potentials with respect to the mononuclear reference systems is a suitable tool to determine intermetallic electronic interaction. For some compounds, the normal behaviour with an increasing separation of the redox potentials is observed. A second group of complexes shows the opposite behaviour with a decreasing in the potential differences. A mechanism of intramolecular catalytic oxidation is supposed for that species.