Transition Metal Coordination Chemistry Research Articles

Reversible Co(II)-Co(III) Transformation in a Family of Metal-Dipyrazolate Frameworks.

Transformation between oxidation states is widespread in transition metal coordination chemistry and biochemistry, typically occurring in solution. However, air-induced oxidation in porous crystalline solids with retention of crystallinity is rare due to the dearth of materials with high structural stability that are inherently redox active. Herein, we report a new family of such materials, four isostructural cobalt-pyrazolate frameworks of face-centered cubic, fcu, topology, fcu-L-Co, that are sustained by Co8 molecular building blocks (MBBs) and dipyrazolate ligands, L. fcu-L-Co were observed to spontaneously transform from Co(II)8 to Co(III)8 MBBs in air with retention of crystallinity, marking the first such instance in metal-organic frameworks (MOFs). This transformation can also be achieved through water vapor sorption cycling, heating, or chemical oxidation. The reverse reactions were conducted by exposure of fcu-L-Co(III) to aqueous hydrazine. fcu-L-Co(II) exhibited high gravimetric water vapor uptakes of 0.55-0.68 g g-1 at 30% relative humidity (RH), while in fcu-L-Co(III) the inflection point shifted to lower RH and framework stability improved. Insight into the transformation between fcu-L-Co(II) and fcu-L-Co(III) was gained from single crystal X-ray diffraction and in situ spectroscopy. Overall, the crystal engineering approach we adopted has afforded a new family of MOFs that exhibit cobalt redox chemistry in a confined space coupled with high porosity.

Borataalkenes, boraalkenes, and the η2-B,C coordination mode in coordination chemistry and catalysis.

Borataalkenes and boraalkenes are the boron-containing isoelectronic analogues of alkenes and vinyl cations respectively. Compared with alkenes, the borataalkene and boraalkene ligand motifs in transition metal coordination chemistry are relatively underexplored. In this review, the synthesis of borataalkene and boraalkene complexes and other transition metal complexes featuring the η2-B,C coordination mode is described. The diversity of coordination modes and geometry in these complexes, and the spectroscopic and structural evidence supporting their assignments is disclosed as well as computational analysis of bonding. The applications of the borataalkene ligand motif in synthetic organic homogeneous catalysis, especially those involving geminal bis(pinacolatoboronates) and 1,4-azaborines, are discussed.

2-Pyridonates: a versatile ligand platform in 3d transition metal coordination chemistry and catalysis

Among the vast family of aminoalcohol ligands, 2-pyridonates take a special position. This review illustrates the intriguing properties of pyridonate ligands and their key roles in 3d transition metal catalysts from the natural role model [Fe]-hydrogenase to modern applications.

Crystal structure of trimeth-yl({tris-[(phenyl-sulfan-yl)meth-yl]sil-yl}meth-oxy)silane and Hirshfeld surface analysis of 3-bromo-2,2-bis-(bromo-meth-yl)propan-1-ol.

Trimeth-yl({tris-[(phenyl-sulfan-yl)meth-yl]sil-yl}meth-oxy)silane (3), C26H32OS3Si, is a new ligand for transition-metal coordination chemistry derived from 3-bromo-2,2-bis-(bromo-meth-yl)propan-1-ol (1), C5H9Br3O, through silylation and following exchange of bromine groups with NaSPh. Silylated thio-ether ligand 3 crystallizes in the centrosymmetric space group C2/c. Bromo-methyl-alcohol 1 crystallizes in the space group P in the triclinic crystal system with four mol-ecules in the asymmetric unit. Analysis of the Hirshfeld surface shows structure-defining inter-actions for bromo-methyl-alcohol 1, resulting in inter-molecular hydrogen bonds between the hydroxyl groups along the a-axis direction.

Counterintuitive Chemistry: Carbene Stabilization of Zero-Oxidation State Main Group Species

Carbenes have evolved from transient laboratory curiosities to a robust, diverse, and surprisingly impactful ligand class. A variety of different carbenes have significantly contributed to the development of low-oxidation state main group chemistry. This Perspective focuses upon advances in the chemistry of carbene complexes containing main group element cores in the formal oxidation state of zero, including their diverse synthetic strategies, unusual bonding and structural motifs, and utility in transition metal coordination chemistry and activation of small molecules.

Metal phosphine aldehyde complexes and their application in Cu-free Sonogashira and Suzuki-Miyaura cross-coupling reactions.

Transition metal coordination chemistry and catalysis are rife with phosphine ligands. One of the rather less studied members of the phosphine ligand family are phosphine aldehydes. We have synthesised 3-(diphenylphosphino)propanal (PCHO) with a slight modification of the known procedure and studied its complexation behaviour with palladium(II) and platinum(II). The catalytic activity of the palladium(II) phosphine aldehyde complexes was investigated in Cu-free Sonogashira and Suzuki-Miyaura cross-coupling reactions. Furthermore, the homogeneous nature of the catalytically active species was confirmed.

Editorial

Editorial

Alan Herbert Cowley. 29 January 1934—2 August 2020

Alan Cowley was one of the most creative main group chemists of his generation, and had a central role in what was often described as the renaissance of main group chemistry. Throughout his career Alan always had an eye for what was new. In his early years as an independent researcher, Alan made many fundamental contributions to the chemistry of phosphorus, not only in terms of the synthesis of new compounds but also in their study by employing novel analytical and computational methods. Starting in the 1980s he was at the forefront of emerging research into low-coordinate phosphorus chemistry and made seminal contributions in the areas of multiply bonded species, such as phosphenium ions and diphosphenes, as well as in the transition metal coordination chemistry of phosphinidenes. In the second half of his career, Alan also turned his attention to the study of single source precursors for important solid-state electronic materials, many of which were far superior to known examples. In all of the many areas in which Alan worked, he was a great collaborator with colleagues and researchers across the world, both in chemistry and in other disciplines. This was made all the easier by Alan's charm and easy-going nature, which was also manifest in the interactions he had with his many group members over a period of almost half a century. Alan was a gentleman in every sense and is much missed by friends, colleagues, collaborators and family.

Molecular Dynamics Simulation of 2-Benzimidazolyl-Urea with DPPC Lipid Membrane and Comparison with a Copper(II) Complex Derivative.

Benzimidazole derivatives have gained attention recently due to their wide pharmacological activity acting as anti-inflammatory, hypotensive, analgesic, and anti-aggregatory agents. They are also common ligands in transition metal coordination chemistry, forming complex compounds with enhanced biological properties, especially in targeted cancer therapy. A key issue to understand anti-tumour effects is drug permeability through cellular membranes, as poor permeability outcomes can avert further futile drug development. In this work, we conducted atomistic molecular dynamics (MD) simulations and biased MD simulations to explore the interactions of 2-benzimidazolyl-urea with a phospholipid bilayer (dipalmitoylphosphatidylcholine, DPPC) together with a previously synthesized copper(II) complex compound. The aim was to study the permeability of these compounds by assessing their free energy profile along the bilayer normal. The simulations indicated that both the ligand (2-benzimidazolyl-urea, BZIMU) and the complex show a similar behaviour, yielding high energy barriers for the permeation process. However, with increasing concentration of BZIMU, the molecules tend to aggregate and form a cluster, leading to the formation of a pore. Clustering and pore formation can possibly explain the previously observed cytotoxicity of the BZIMU molecule via membrane damage.

Synthesis of α-chiral phosphine sulfides via non-covalent organocatalysis

Despite rapid advances in phosphine-containing compound as a privileged ligand for transition metal catalysis, synthesis and coordination chemistry are underexplored for the phosphine sulfide analogs. In this article, we report the enantioselective phospha-Michael addition reaction that leads to α-chiral phosphine sulfide. An independent hydrogen-bonding co-catalyst is found essential to high enantioselectivity (up to 98% yield and 95% enantiomeric excess [ee]). Divergent derivatizations under mild conditions are also attempted for the generic phosphine and phosphine oxide compounds, further emphasizing the bridge role of phosphine sulfide. An X-ray diffraction structure of κ 3 -NNS palladium complex also authenticates the coordination ability of p = S moiety. Combination of NHC and hydrogen bonding donor catalysis α-Chiral phosphine sulfides Downstream derivatizations κ 3 -NNS palladium complex In an effort to diversify the family of phosphine ligands, Li et al. report the orchestration of NHC catalysis and an H-bond donor as a straightforward synthetic strategy to yield α-chiral phosphine sulfides. Preliminary results for downstream derivatization and metal chelation further demonstrate the applications for p = S ligands.

Fifteen Years of Scientific Investigation into Main Groups and Transition Metal Coordination Chemistry with Allan White

The outcomes of the investigations on the structures and reactivity of a massive number of main group and transition metal complexes containing different families of ligands are reviewed. All the data result from the scientific collaboration between the research groups of Claudio Pettinari and Allan White which lasted fifteen years.

(2-Pyridyloxy)silanes as Ligands in Transition Metal Coordination Chemistry

Proceeding our initial studies of compounds with formally dative TM→Si bonds (TM = Ni, Pd, Pt), which feature a paddlewheel arrangement of four (N,S) or (N,N) bridging ligands around the TM–Si axis, the current study shows that the (N,O)-bidentate ligand 2-pyridyloxy (pyO) is also capable of bridging systems with TM→Si bonds (shown for TM = Pd, Cu). Reactions of MeSi(pyO)3 with [PdCl2(NCMe)2] and CuCl afforded the compounds MeSi(µ-pyO)4PdCl (1) and MeSi(µ-pyO)3CuCl (2), respectively. In the latter case, some crystals of the Cu(II) compound MeSi(µ-pyO)4CuCl (3) were obtained as a byproduct. Analogous reactions of Si(pyO)4, in the presence of HpyO, with [PdCl2(NCMe)2] and CuCl2, afforded the compounds [(HpyO)Si(µ-pyO)4PdCl]Cl (4), (HpyO)2Si[(µ-pyO)2PdCl2]2 (5), and (HpyO)2Si[(µ-pyO)2CuCl2]2 (6), respectively. Compounds 1–6 and the starting silanes MeSi(pyO)3 and Si(pyO)4 were characterized by single-crystal X-ray diffraction analyses and, with exception of the paramagnetic compounds 3 and 6, with NMR spectroscopy. Compound 2 features a pentacoordinate Si atom, the Si atoms of the other complexes are hexacoordinate. Whereas compounds 1–4 feature a TM→Si bond each, the Si atoms of compounds 5 and 6 are situated in an O6 coordination sphere, while the TMCl2 groups are coordinated to pyridine moieties in the periphery of the molecule. The TM–Si interatomic distances in compounds 1–4 are close to the sum of the covalent radii (1 and 4) or at least significantly shorter than the sum of the van-der-Waals radii (2 and 3). The latter indicates a noticeably weaker interaction for TM = Cu. For the series 1, 2, and 3, all of which feature the Me–Si motif trans-disposed to the TM→Si bond, the dependence of the TM→Si interaction on the nature of TM (Pd(II), Cu(I), and Cu(II)) was analyzed using quantum chemical calculations, that is, the natural localized molecular orbitals (NLMO) analyses, the non-covalent interaction (NCI) descriptor, Wiberg bond order (WBO), and topological characteristics of the bond critical points using the atoms in molecules (AIM) approach.

Microwave alkylation of lithium tetrazolate

N1-substituted tetrazoles are interesting ligands in transition metal coordination chemistry, especially in the field of spin crossover. Their synthesis is performed in most cases according to the Franke-synthesis, using a primary amine as reagent introducing the substitution pattern. To enhance flexibility in means of substrate scope, we developed a new protocol based on alkylation of lithium tetrazolate with alkyl bromides. The N1–N2 isomerism of the tetrazole during the alkylation was successfully suppressed by use of highly pure lithium tetrazolate and 30 vol.% aqueous ethanol as solvent, leading to pure N1-substituted products. The feasibility of this reaction was demonstrated by a selection of different substrates.Graphical abstract

ChemInform Abstract: Phosphine Complexes of Lone Pair Bearing Lewis Acceptors

AbstractReview: 82 refs.

Synthesis and transition metal coordination chemistry of a novel hexadentate bispidine ligand.

Reported is the new bispidine-derived hexadentate ligand (L = 3-(2-methylpyridyl)-7-(bis-2-methylpyridyl)-3,7-diazabicyclo[3.3.1]nonane) with two tertiary amine and four pyridine donor groups. This ligand can form heterodinuclear and mononuclear complexes and, in the mononuclear compounds discussed here, the ligand may coordinate as a pentadentate ligand, with one of the bispyridinemethane-based pyridine groups un- or semi-coordinated, or as a hexadentate ligand, leading to a pentagonal pyramidal coordination geometry or, with an additional monodentate ligand, to a heptacoordinate pentagonal bipyramidal structure. The solution and solid state data presented here indicate that, with the relatively small Cu(II) and high-spin Fe(II) ions the fourth pyridine group is only semi-coordinated for steric reasons and, with the larger high-spin Mn(II) ion genuine heptacoordination is observed but with a relatively large distortion in the pentagonal equatorial plane.

ChemInform Abstract: Thione‐ and Selone‐containing Compounds, Their Late First Row Transition Metal Coordination Chemistry, and Their Biological Potential

ChemInform Abstract: Thione‐ and Selone‐containing Compounds, Their Late First Row Transition Metal Coordination Chemistry, and Their Biological Potential

Synthesis of pyrazole derivatives and their spectroscopic properties investigated using both experimental and theoretical approaches

Pyrazoles are unique ligands that have attracted significant research attention due to extensive use of their derivatives in transition metal coordination chemistry. Two pyrazole (pz) derivatives bpzm and bpza were synthesised and their structures are distinguished from the precursor pz using spectroscopic analysis. Many of the functional groups in these ligands are found to be Raman active, which also helps in their spectroscopic elucidation. The electronic, spectroscopic and conductivity properties of pz, bpzm, bpza and bpzpya were further studied using DFT methods. The computed values obtained from techniques such as IR, 1H-NMR, 13C-NMR and UV were found to be highly correlated with the experimental values. Many of the computed properties like the dipole, band gap, hyperpolarizability and reactivity are in the order of bpzpya > bpza > bpzm > pz. The possible application of the ligands can be predicted from the correlation of *N atomic properties with molecular properties of the ligands.

ChemInform Abstract: New Vistas in N‐Heterocyclic Silylene (NHSi) Transition‐Metal Coordination Chemistry: Syntheses, Structures and Reactivity Towards Activation of Small Molecules

AbstractReview: 77 refs.

What role has organic chemistry played in the development of molecule-based magnets?

Contributions of organic chemistry to the interdisciplinary science of molecule-based magnets are discussed in reference to transition metal coordination chemistry carried out successfully by Olivier Kahn and other scientists. Typical organic molecules have closed-shell structures and therefore organic compounds are usually diamagnetic. Organic chemists had to start with the design and construction of more-or-less stable open-shell organic molecules. Only then it became possible to study how to let their electron spins exchange-couple strongly by means of spin delocalization and polarization within a molecule and among molecules. Non-Kekulé π-systems were chosen to make the triplet carbene species to interact ferromagnetically. Approaches by means of synthetic organic chemistry proved effective. Magnetic susceptibility measurements revealed that such tetracarbene and nonacarbene have ground S=4 and S=9 states, respectively. Thus, the open-shell hydrocarbon molecules have been shown to have higher magnetic moments than those of S=5/2 Fe(III) and S=7/2 Gd(III) ions. Stable aminoxyl radicals played various roles in generating organic ferromagnets by controlling the exchange coupling between molecules in crystal, or by forming the metal/aminoxyl radical hybrid systems that were made on the basis of the supramolecular approaches and led to a number of ferro- and ferrimagnets. Metal/pyridylcarbene hybrid systems generated photochemically not only revealed the mode of the exchange coupling between the spins of metal d-orbital and those residing in organic π-orbital, but also suggested the route to novel photoresponsive magnetic materials. Most of the organic and metal/organic magnets discussed in the 80s and early 90s were trying to mimic conventional magnets by molecular materials. It is only after the advent of the single-molecule magnets when molecule-based magnets became molecular materials in their own right in the area of nano-science. Here again, novel organic molecules are used as useful, functional ligands for making single ion magnets and single chain magnets.

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