Synthesis of Dinuclear Cobalt Silylene Complexes and Their Catalytic Activity for Alkene Hydrosilylation Reactions.

A novel dinuclear silylene cobalt complex [((Me3P)2Co)(PMe2)(CoCl(PMe3))(Si(NCH2PPh2)2C6H4)] (1) supported by the [PSi(silylene)P] ligand was prepared through the reaction of N-heterocyclic [PSiP] pincer ligand L1 (HSiCl(NCH2PPh2)2C6H4) with Co(PMe3)4. Complex [((Me3P)2Co)2(Si(NCH2PPh2)2C6H4)] (2) was formed through the reaction of complex 1 with MeLi. To the best of our knowledge, complexes 1 and 2 are the first examples of dinuclear silylene cobalt complexes supported by the [PSi(silylene)P] ligand. A new preligand L2 (SiCl2(NCH2PPh2)2C6H4) was synthesized, and the reaction of preligand L2 with Co(PMe3)4 afforded silyl cobalt complex [((Me3P)2Co)(SiCl(NCH2PPh2)2C6H4)] (3). The reaction of 3 with CO delivered cobalt carbonyl complex [((Me3P)(CO)Co)(Si(NCH2PPh2)2C6H4)]2O (4). The catalytic activity of cobalt complexes 1-4 on the hydrosilylation of alkenes was explored. Among the four complexes, complex 1 has the best catalytic activity. The catalytic process could be promoted with NaBHEt3 as an additive, and a complete conversion with an excellent selectivity of 98:2 (b/l) could be reached at 120 °C within 8 min for aryl alkenes. A possible catalytic cycle was proposed on the basis of the experimental results and literature reports, with a cobalt hydride complex as an active intermediate. The molecular structure of complexes 1-4 was determined by single-crystal X-ray diffraction analysis.

Toward Molecular Textiles: Synthesis and Characterization of Molecular Patches.

This works describes a new step into the assembly of molecular textiles by the use of covalent templating. To establish a well-founded base and to tackle pre-mature obstacles, expected during the fabrication of the desired 2D-material, we opted to investigate the in-solution synthesis of molecular patches e. g. cut-outs of a textile. A bi-functional cross-shaped monomer was designed, synthesized and was in-detail characterized by means of 1H-NMR and chiro-optical spectroscopy. In addition, x-ray structure crystallography was used to assess the absolute configuration. The monomer was used in an in-solution oligomerization to assemble the molecular patches via imine condensation, which revealed the formation of predominately dimeric patches. The imine-oligomer mixtures were further analyzed by reduction and cleaved to investigate the conditions required post mono-layer assembly. All reaction stages were followed by FT-IR and 1H-NMR analysis. Finally, we address the adsorption of the cross-shaped monomer onto a Au(111) surface, via high vacuum electrospray deposition. The subsequent annealing of the interface induced the on-surface imine condensation reaction, leading to unidimensional oligomers co-adsorbed with clusters of cyclic-dimers. Nc-AFM analysis revealed the tridimensional molecular structures, and together with electrospray deposition technique showed to be a promising pathway to investigate potential monomer candidates.

Circularly Polarized Luminescence of Thiophene-Bridged Macrocyclic pseudo-meta [2.2]Paracyclophanes.

Chiral organic molecules possessing high quantum yields, circular dichroism, and circularly polarized luminescence values have great potential as optically active materials for future applications. Recently, the identification of a promising class of inherently chiral compounds was reported, namely macrocyclic 1,3-butadiyne-linked pseudo-meta[2.2]paracyclophanes, displaying high circular dichroism and related gabs values albeit modest quantum yields. Increasing the quantum yields in an attempt to get bright circularly polarized light emitters, the high-yielding heterocyclization of those 1,3-butadiyne bridges resulting in macrocyclic 2,5-thienyls-linked pseudo-meta [2.2]paracyclophanes is herein described. The chiroptical properties of both, the previously reported 1,3-butadiyne, and the novel 2,5-thienyl bridged macrocycles of various sizes, are experimentally recorded, and theoretically described using density-functional theory.

Ion-Selective Assembly of Supertetrahedral Selenido Germanate Clusters for Alkali Metal Ion Capture and Separation.

Supertetrahedral chalcogenido (semi)metalate cluster-based frameworks possess high selectivity for alkali metal cations, matching the specific charge density of their inner surfaces, which enables their use as ion-exchange materials. Aggregates of the supertetrahedral chalcogenido metalate cluster offer even new perspectives for metal ion capture and separation. Herein, we report on ionothermal preparation of two corresponding model compounds, (C2C1Im)7[Cs@GeII4(GeIV4Se10)4] (1) and (C2C1Im)10[Na5(CN)6@Cu6(Ge4Se10)4(Cu)] (2). Their formation is reliant on one specific cation type each, Cs+ for 1 and Na+ for 2, thus providing promising separation potential during crystallization. Compound 1 is based on the largest discrete binary selenido germanate cluster reported to date and the first mixed-valent chalcogenido germanate(II/IV) supertetrahedron. Moreover, it adds to the few examples of chalcogenides capable of capturing Cs+ ions. Its high selectivity for Cs+ compared to that of Li+, Na+, K+, and Rb+ was confirmed by single-crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, and electrospray ionization mass spectrometry. Quantum chemical studies indicate that smaller ions, K+ and Rb+, could also be embedded in an isolated cluster assembly, but as the cluster aggregate slightly distorts for crystallization, the selectivity for Cs+ becomes exclusive in the salt. The anionic substructure of compound 2 is based on a two-dimensional network of supramolecular assemblies and exhibits an exclusive preference for Na+. This work thus provides the first comprehensive insight into the selective incorporation of specific alkali metal ions into supramolecular aggregates of supertetrahedral chalcogenide clusters, as a promising basis for new ion trapping techniques─especially for heavy alkali metal ions that pose environmental challenges.

Intense Molar Circular Dichroism in Fully Conjugated All-Carbon Macrocyclic 1,3-Butadiyne Linked pseudo-meta [2.2]Paracyclophanes.

Invited for the cover of this issue is the group of Marcel Mayor at the University of Basel with co-workers Olaf Fuhr and Dieter Fenske from Karlsruhe Institute of Technology. The image depicts the studied all-carbon polygon shaped macrocycles along with their intense circular dichroism spectra in the background. The bright light within the macrocycles displays its efficient conjugation. Read the full text of the article at 10.1002/chem.202201764.

Intense Molar Circular Dichroism in Fully Conjugated All-Carbon Macrocyclic 1,3-Butadiyne Linked pseudo-meta [2.2]Paracyclophanes.

The synthetic access to macrocyclic molecular topologies with interesting photophysical properties has greatly improved thanks to the successful implementation of organic and inorganic corner units. Based on recent reports, we realized that pseudo-meta [2.2]paracyclophanes (PCPs) might serve as optimal corner units for constructing 3D functional materials, owing to their efficient electronic communication, angled substituents and planar chirality. Herein, we report the synthesis, characterization and optical properties of four novel all-carbon enantiopure macrocycles bearing three to six pseudo-meta PCPs linked by 1,3-butadiyne units. The macrocycles were obtained by a single step from enantiopure, literature-known dialkyne pseudo-meta PCP and were unambiguously identified and characterized by state of the art spectroscopic methods and in part even by x-ray crystallography. By comparing the optical properties to relevant reference compounds, it is shown that the pseudo-meta PCP subunit effectively elongates the conjugated system throughout the macrocyclic backbone, such that already the smallest macrocycle consisting of only three subunits reaches a polymer-like conjugation length. Additionally, it is shown that the chiral pseudo-meta PCPs induce a remarkable chiroptical response in the respective macrocycles, reaching unprecedented high molar circular dichroism values for all-carbon macrocycles of up to 1307 L mol-1  cm-1 .

Nitro-Decorated Microporous Covalent Organic Framework (TpPa-NO2) for Selective Separation of C2H4 from a C2H2/C2H4/CO2 Mixture and CO2 Capture.

A nitro-decorated microporous covalent organic framework, TpPa-NO2, has been synthesized in a gram scale with a one-pot reaction. It can effectively selectively separate C2H4 from a C2H2/C2H4/CO2 mixture and capture CO2 from CO2/N2 based on ideal adsorption solution theory calculations and transient breakthrough experiments. Theoretical calculations illustrated that the hydrogen atoms of imine bonds, carbonyl oxygen, and nitro group show high affinity toward C2H2 and CO2, playing vital roles in efficient separation.

Geländer Molecules with Orthogonal Joints: Synthesis of Macrocyclic Dimers.

Orthogonal joints, understood as connections with an angle of 90°, were introduced in the design of the "Geländer" model compounds 1 and 2. The banister, consisting of a conjugated carbazole dimer linked by either 1,3-butadiyne (2) or a single thiophene (1), wraps around an axis composed of a phthalimide dimer due to the dimensional mismatch of both subunits, which are interconnected by phenylene rungs. The "Geländer" structure was assembled from a monomer comprising the 1,4-diaminobenzene rung with one amino substituent as part of a 4-bromo phthalimide subunit forming the orthogonal junction to the axis, and the other as part of a masked 2-ethynyl carbazole as orthogonal joint to the banister. The macrocycle was obtained by two sequential homocoupling steps. A first dimerization by a reductive homocoupling assembled the axis, while an oxidative acetylene coupling served as ring-closing reaction. The formed butadiyne was further derivatized to a thiophene, rendering all carbons of the model compound sp2 hybridized. Both helical structures were fully characterized and chirally resolved. Assignment of the enantiomers was achieved by simulation of chiroptical properties and enantiopure synthesis.

A Rare Flexible Metal-Organic Framework Based on a Tailorable Mn8 -Cluster Showing Smart Responsiveness to Aromatic Guests and Capacity for Gas Separation.

The design and creation of soft porous crystals combining regularity and flexibility may promote potential applications for gas storage and separation due to their deformable framework's responsiveness to external stimuli. The flexibility of metal-organic frameworks (MOFs) relies on alterable degrees of freedom that are mainly provided by organic linkers or the junctions linking organic and inorganic building units. Herein, we report a new dynamic MOF whose flexibility originates from an unprecedented tailorable Mn8 O38 -cluster and shows simultaneous coordination geometry changes and ligand migration that are reversibly driven by guest exchange. This provides an extra degree of freedom to the framework's deformation, resulting in three-dimensional variations in the framework that subtly respond to varied aromatic molecules. The gas adsorption behavior of this flexible MOF was evaluated, and the selective separation of light hydrocarbons and Freon gases is achieved.

Synthesis of silyl iron dinitrogen complexes for activation of dihydrogen and catalytic silylation of dinitrogen.

Three novel iron dinitrogen hydrides, [FeH(iPr-PSiMeP)(N2)(PMe3)] (1), [FeH(iPr-PSiPhP)(N2)(PMe3)] (2), and [FeH(iPr-PSiPh)(N2)(PMe3)] (3), supported by a silyl ligand are synthesized for the first time by changing the electronic effect and steric hindrance of the ligands through the reaction of ligands L1-L3 with Fe(PMe3)4 in a nitrogen atmosphere. The ligands containing an electron-donating group with large steric hindrance on the phosphorus atom are beneficial for the formation of dinitrogen complexes. A penta-coordinate iron hydride [FeH(iPr-PSiPh)(PMe3)2] (4) was formed through the reaction of ligand L3 with Fe(PMe3)4 in an argon atmosphere under the same conditions. The reactions between complexes 1-3 with an atmospheric pressure of dihydrogen gas resulted in Fe(II) dihydrides, [(iPr-PSiMe(µ-H)P)Fe(H)2(PMe3)] (5), [(iPr-PSiPh(µ-H)P)Fe(H)2(PMe3)] (6) and [(iPr-PSiPh(µ-H))Fe(H)2(PMe3)2] (7), with an η2-(Si-H) coordination. The isolation of dihydrides 5-7 demonstrates the ability of the dinitrogen complexes 1-3 to realize the activation of dihydrogen under ambient temperature and pressure. The molecular structures of complexes 1-7 were elucidated by single crystal X-ray diffraction analysis. The iron dinitrogen hydrides 1-3 are effective catalysts for the silylation of dinitrogen under ambient conditions and among them 3 is the best catalyst.

Selectivity Reverse of Hydrosilylation of Aryl Alkenes Realized by Pyridine N-Oxide with [PSiP] Pincer Cobalt(III) Hydride as Catalyst.

Six silyl cobalt(III) hydrides 1-6 with [PSiP] pincer ligands having different substituents at the P and Si atoms ([(2-Ph2PC6H4)2MeSiCo(H)(Cl)(PMe3)] (1), [(2-Ph2PC6H4)2HSiCo(H)(Cl)(PMe3)] (2), [(2-Ph2PC6H4)2PhSiCo(H)(Cl)(PMe3)] (3), [(2-iPr2PC6H4)2HSiCo(H)(Cl)(PMe3)] (4), [(2-iPr2PC6H4)2MeSiCo(H)(Cl)(PMe3)] (5), and [(2-iPr2PC6H4)2PhSiCo(H)(Cl)(PMe3)] (6)) were synthesized through the reactions of the ligands (L1-L6) with CoCl(PMe3)3 via Si-H bond cleavage. Compounds 1-6 have catalytic activity for alkene hydrosilylation, and among them, complex 3 is the best catalyst with excellent anti-Markovnikov regioselectivity. A silyl dihydrido cobalt(III) complex 7 from the reaction of 3 with Ph2SiH2 was isolated, and its catalytic activity is equivalent to that of complex 3. Complex 7 and its derivatives 10-12 could also be obtained through the reactions of complexes 3, 1, 4, and 5 with NaBHEt3. The molecular structure of 7 was indirectly verified by the structures of 10-12. To our delight, the addition of pyridine N-oxide reversed the selectivity of the reaction, from anti-Markovnikov to Markovnikov addition. At the same time, the reaction temperature was reduced from 70 to 30 °C on the premise of high yield and excellent selectivity. However, this catalytic system is only applicable to aromatic alkenes. On the basis of the experimental information, two reaction mechanisms are proposed. The molecular structures of cobalt(III) complexes 3-6 and 10-12 were determined by single crystal X-ray diffraction analysis.

Synthesis and Transport Studies of a Cofacial Porphyrin Cyclophane.

Porphyrin cyclophane 1, consisting of two rigidly fixed but still movable cofacial porphyrins and exposing acetate-masked thiols in opposed directions of the macrocycle, is designed, synthesized, and characterized. The functional cyclophane 1, as pioneer of mechanosensitive 3D materials, forms stable single-molecule junctions in a mechanically controlled break-junction setup. Its reliable integration in a single-molecule junction is a fundamental prerequisite to explore the potential of these structures as mechanically triggered functional units and devices.

The Effect of Substituents on the Formation of Silyl [PSiP] Pincer Cobalt(I) Complexes and Catalytic Application in Both Nitrogen Silylation and Alkene Hydrosilylation.

Four different [PSiP]-pincer ligands L1-L4 ((2-Ph2PC6H4)2SiHR (R = H (L1) and Ph (L2)) and (2-iPr2PC6H4)2SiHR' (R' = Ph (L3) and H (L4)) were used to investigate the effect of substituents at P and/or Si atom of the [PSiP] pincer ligands on the formation of silyl cobalt(I) complexes by the reactions with CoMe(PMe3)4 via Si-H cleavage. Two penta-coordinated silyl cobalt(I) complexes, (2-Ph2PC6H4)2HSiCo(PMe3)2 (1) and (2-Ph2PC6H4)2PhSiCo(PMe3)2 (2), were obtained from the reactions of L1 and L2 with CoMe(PMe3)4, respectively. Under similar reaction conditions, a tetra-coordinated cobalt(I) complex (2-iPr2PC6H4)2PhSiCo(PMe3) (3) was isolated from the interaction of L3 with CoMe(PMe3)4. It was found that, only in the case of ligand L4, silyl dinitrogen cobalt(I) complex 4, [(2-iPr2PC6H4)2HSiCo(N2)(PMe3)], was formed. Our results indicate that the increasing of electron cloud density at the Co center is beneficial for the formation of a dinitrogen cobalt complex because the large electron density at Co center leads to the enhancement of the π-backbonding from cobalt to the coordinated N2. It was found that silyl dinitrogen cobalt(I) complex 4 is an effective catalyst for catalytic transformation of dinitrogen into silylamine. Among these four silyl cobalt(I) complexes, complex 1 is the best catalyst for hydrosilylation of alkenes with excellent regioselectivity. For aromatic alkenes, catalyst 1 provided Markovnikov products, while for aliphatic alkenes, anti-Markovnikov products could be obtained. Both catalytic reaction mechanisms were proposed and discussed. The molecular structures of complexes 1-4 were confirmed by single-crystal X-ray diffraction.

The periodic law of the chemical elements: 'The new system of atomic weights which renders evident the analogies which exist between bodies' [1].

The historical roots, the discovery and the modern relevance of Dmitri Mendeleev's remarkable advance have been the subject of numerous scholarly works. Here, with a brief overview, we hope to provide a link into the contents of this special issue honouring the great scientist. Mendeleev's advance, announced in March 1869, as he put it in 1889, to the '…then youthful Russian Chemical Society…', first set out the very basis of the periodic law of the chemical elements, the natural relation between the properties of the elements and their atomic weights. This was, and still is, the centrepiece of a historical journey for chemistry to today's position as a pre-eminent science. This article is part of the theme issue 'Mendeleev and the periodic table'.

Correction: Pyridine N-oxide promoted hydrosilylation of carbonyl compounds catalyzed by [PSiP]-pincer iron hydrides.

Correction for 'Pyridine N-oxide promoted hydrosilylation of carbonyl compounds catalyzed by [PSiP]-pincer iron hydrides' by Guoliang Chang et al., Dalton Trans., 2020, 49, 9349-9354, DOI: 10.1039/D0DT00392A.

Pyridine N-oxide promoted hydrosilylation of carbonyl compounds catalyzed by [PSiP]-pincer iron hydrides.

Five [PSiP]-pincer iron hydrides 1-5, [(2-Ph2PC6H4)2HSiFe(H)(PMe3)2 (1), (2-Ph2PC6H4)2MeSiFe(H)(PMe3)2 (2), (2-Ph2PC6H4)2PhSiFe(H)(PMe3)2 (3), (2-(iPr)2PC6H4)2HSiFe(H)(PMe3) (4), and (2-(iPr)2PC6H4)2MeSiFe(H)(PMe3)2 (5)], were used as catalysts to study the effects of pyridine N-oxide and the electronic properties of [PSiP]-ligands on the catalytic hydrosilylation of carbonyl compounds. It was proved for the first time that this catalytic process could be promoted with pyridine N-oxide as the initiator at 30 °C because the addition of pyridine N-oxide is beneficial for the formation of an unsaturated hydrido iron complex, which is the key intermediate in the catalytic mechanism. Complex 4 as the best catalyst shows excellent catalytic performance. Among the five complexes, complex 3 was new and the molecular structure of complex 3 was determined by single crystal X-ray diffraction. A proposed mechanism was discussed.

Novel double functional protection of cephalostatin analogues using a gas-free chlorination method.

Herewith, we report on a method that allows to simultaneously protect both the ∆14,15 bond and the carbonyl group of the symmetrical bis-steroidal diketone 2. We found that environmentally friendly and gas-free chlorination is ideally suited to achieve this goal. This method was discovered during our efforts to methoxylate 2 in a solution of dichloromethane and basic methanol in the presence of diacetoxy iodobenzene. Unexpectedly, the ∆14,15 bonds were chlorinated once as well as twice in a statistical manner. Interestingly, the singly dichlorinated desymmetrized product is an ideal precursor for conduction a series of position selective transformations. Importantly, the carbonyl group present in the nonchlorinated hemisphere can be selectively reduced, olefinated or oximated, while the other carbonyl group stays unaltered. A structurally related "monomeric" steroid derivative undergoes ∆14,15 chlorination and 11-position methoxylation under same conditions. These findings represent a powerful entry for preparing new nonsymmetrical cephalostatin derivatives.

Low-valent homobimetallic Rh complexes: influence of ligands on the structure and the intramolecular reactivity of Rh-H intermediates.

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. Their reaction with hydrogen rapidly forms Rh hydrides that undergo an intramolecular semihydrogenation of two C[triple bond, length as m-dash]C bonds of the trop ligand. This reaction is chemoselective and converts C[triple bond, length as m-dash]C bonds to a bridging carbene and an olefinic ligand in the first and the second semihydrogenation steps, respectively. Stabilization by a bridging diphosphine ligand allows characterization of a Rh hydride species by advanced NMR techniques and may provide insight into possible elementary steps of H2 activation by interfacial sites of heterogeneous Rh/C catalysts.

The coordination behavior of 2,3-bis(diphenylphosphino)maleic-N-phenylimide towards copper, silver, gold and palladium.

The bidentate phosphine bis(diphenylphosphino)-N-phenyl-maleimide (L1) is used to synthesize a series of complexes from coinage metals and palladium. Some of them are mononuclear species where one metal atom is coordinated by two phosphine ligands. Three of these complexes have been investigated in detail because they contain the initial ligand in an anionic, radical form (L1') i.e. [Cu(L1L1')] (1), [Ag(L1L1')] (7), [Pd(L1')2] (11). L1' in 1, 7 and 11 shows significant differences in its bonding parameters compared to free or coordinating L1. By magnetic measurements the radical nature of these three compounds could be verified. Quantum chemical calculations prove the existence of either one (1 and 7) or two (11) unpaired electrons localized on the ligand. Furthermore these calculations can explain that 1 and 7 show an asymmetric structure in solid state where one can clearly differ L1 from L1'.

[Pb{Mn(CO)5}3][AlCl4]: a lead-manganese carbonyl with AlCl4-linked PbMn3 clusters.

[Pb{Mn(CO)5}3][AlCl4] containing a trigonal planar PbMn3 cluster was obtained by the reaction of PbCl2 and Mn2(CO)10 in the ionic liquid [BMIm][AlCl4]. The title compound is composed of [Pb{Mn(CO)5}3]+ carbonyl cations and [AlCl4]- anions that are connected to infinite zig-zag chains. The [Pb{Mn(CO)5}3]+ cation exhibits a central PbMn3 cluster with three equal Pb-Mn single bonds, resulting in an almost equilateral triangle of three manganese atoms with a formal Pb+I in its center. Such a cluster and compound were identified for the first time. In addition to single-crystal structure analysis, the composition, structure and properties were further characterized by density functional theory (DFT) calculations, energy dispersive X-ray spectroscopy (EDXS), and Fourier-transform infrared spectroscopy (FT-IR), as well as optical spectroscopy (UV-Vis).