Reduction of imines by hydroxycyclopentadienyl ruthenium hydride: intramolecular trapping evidence for hydride and proton transfer outside the coordination sphere of the metal

Reduction of imines by [2,5-Ph2-3,4-Tol2(eta(5)-C4COH)]Ru(CO)2H (2) produces kinetically stable ruthenium amine complexes. Reduction of an imine by 2 in the presence of an external amine trap gives only the complex of the newly generated amine. Reaction of 2 with H2N-p-C6H4N=CHPh (11), which contains an intramolecular amine trap, gave a 1:1 mixture of [2,5-Ph2-3,4-Tol2(eta(4)-C4CO)](CO)2RuNH(CH2Ph)(C6H4-p-NH2) (8), formed by coordination of the newly generated amine to the ruthenium center, and [2,5-Ph2-3,4-Tol2(eta(4)-C4CO)](CO)2RuNH2C6H4-p-NHCH2Ph (9), formed by coordination of the amine already present in the substrate. These results require transfer of hydrogen to the imine outside the coordination sphere of the metal to give a coordinatively unsaturated intermediate that can be trapped inside the initial solvent cage. Amine diffusion from the solvent cage must be much slower than coordination to the metal center. Mechanisms requiring prior coordination of the substrate to ruthenium would have led only to 8 and can be eliminated.     

Simulation of metal ion coordination sphere in crystals with fluorite structure

Using quantum-chemical methods, it has been found that the structure of fluorite coincides with the symmetry and coordination number of central calcium atom in the (O_h)-Ca₇F₁₄ cluster. The Ca–F and F–F interatomic distances in the cluster are 3–4% shorter than in the crystal. The symmetry of the (O_h)–(ScCa₆F₁₄)⁺ cluster mimicking the cationic defect after the β-decay of ⁴⁵Ca does not correspond to the energy minimum. The increase in the cation charge from 1.79 to 2.80 a. u. reduces the radius of the first coordination sphere by 0.14 Å. For ytterbium dihalides, the bond lengths Yb–F 2.344, Yb–Cl 2.897 Å and the cation charges 1.81, 1.64 a. u., respectively, have been found.

     

C-H bond activation by hyperconjugation with Al-C bonds and by chelating coordination of the hydride ion

On treating di(tert-butyl)butadiyne with dimethylaluminum hydride under different reaction conditions two unprecedented organoelement compounds, containing cationic carbon atoms stable in solution at room temperature, were obtained. A vinyl cation (2) in which the cationic carbon atom is part of a C=C double bond was produced from 3 equiv of the hydride, whereas a large excess of the hydride yielded an aliphatic carbocation (3) by complete hydroalumination of all C-C multiple bonds. Each compound is zwitterionic with the hydride counterion effectively coordinated in a chelating manner by two strongly Lewis acidic aluminum atoms. In agreement with quantum-chemical calculations the C-H bond activation and the stabilization of the cationic species are further supported by a strong hyperconjugation with Al-C single bonds. This considerably diminishes the effective positive charge at the respective cationic carbon atoms.     

Carboxymethylation of cage amines: control of alkylation by metal ion coordination

Reactions between chloroacetate and both "free" and coordinated forms of the cage amine diaminosarcophagine (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) result in the introduction of between one and four pendent carboxymethyl substituents on the nitrogen atoms of the cage. While at least the first two steps in the reaction of the free ligand have been found to involve only the secondary nitrogen centers, in both the Cu(II) and Co(III) complexes alkylation occurs only at the primary (1,8) centers, the greater ease of achieving a higher degree of alkylation of the Cu(II) complex being attributed to the lower charge of this species causing a lesser reduction of the nucleophilicity of the uncoordinated primary nitrogen atoms. All the new ligands have been characterized by X-ray structure determinations of their Cu(II) or Co(III) complexes. In some cases, this has shown that the methods used to isolate the crystalline complexes result in lactamization of the ligand.     

Using the outer coordination sphere to tune the strength of metal extractants

A series of 3-substituted salicylaldoximes has been used to demonstrate the importance of outer-sphere interactions on the efficacy of solvent extractants that are used to produce approximately one-quarter of the world's copper. The distribution coefficient for extraction of copper by 5-tert-butyl-3-X-salicylaldoximes (X = H, Me, (t)Bu, NO(2), Cl, Br, OMe) varies by more than two orders of magnitude. X-ray structure determinations of preorganized free ligand dimers (10 new structures are reported) indicate that substituents with a hydrogen-bond acceptor atom attached to the 3-carbon atom, ortho to the phenolic oxygen, buttress the intermolecular hydrogen bond from the oximic proton. Density functional theory calculations demonstrate that this hydrogen-bond buttressing is maintained in copper(II) complexes and contributes significantly to their relative stabilities in energy-minimized gas-phase structures. A remarkable correlation between the order of the calculated enthalpies of formation of the copper complexes in the gas phase and the observed strength of the ligands as copper solvent extractants is ascribed to the low solvation energies of species in the water-immiscible phase and/or the similarities of the solvation enthalpies of the preorganized ligand dimers and their copper(II) complexes.     

Functionalization of white phosphorus in the coordination sphere of transition metal complexes

This review highlights the stoichiometric functionalization of both white phosphorus and naked P_n fragments derived from the metal-mediated demolition of the P₄ tetrahedron. In a first section, the alkylation of P_n ligands is discussed giving specific examples such as: (i) the electrophilic alkylation of η³-P₃ or, μ,η³-P₃ ligands: (ii) the transfer of a methyl group from molybdenum to η⁵-P₅ ligands to yield a norbornadiene-like μ₃,η⁴:η¹:η¹-MeP₇ ligand; (iii) the formation of P-C or P-H bonds mediated by rhodium and iron complexes; (iv) the use of ammonium salts to transfer an alkyl to polyphosphido clusters. Different methods to functionalise white phosphorus or other P_n ligands, including the cyclization of acrolein with diphosphenes and the insertion of CO or carbenes across P-P, P-M bonds, and P-E bonds (E = S, Se), are illustrated in appropriate sections. Finally, the last part of the article, reports on the astounding coupling of alkynes and phosphalkynes with P_n ligands which is a versatile, not yet completely explored, method to form an unprecedented variety of carbon-phosphorus heterocycles.     

Improving thermal stability of biodegradable aliphatic polycarbonate by metal ion coordination

Poly(propylene carbonate) (PPC), a typical aliphatic polycarbonate, has attracted much attention during the last two decades due to its biodegradability and commercializing perspective. However, the application of this material as thermoplastics has been limited by its poor thermal stability. Metal soaps, such as calcium stearate (CaSt₂), are important processing additives in plastics industry. In the present work, PPC-CaSt₂ complexes were prepared, the thermal stability of which was investigated by thermogravimetric analysis (TGA). The results show that the complexes are more thermal stable than pure PPC material. Supramolecular lamellar mesomorphous structures of the complexes were corroborated by the combination of small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and polarizing optical microscopy (POM). Metal ion coordination of CaSt₂ to flexible PPC chains was determined by Fourier transform infrared spectroscopy (FT-IR). This coordination interaction plays the key role in improving the thermal property of PPC and constructing the self-organized structure of the complexes.     

Microscopic environment of metal ion controlled by the balance between preferential solvation and coordination

The preferential solvation and the coordination characterizing metal ions (Mg2+ and Zn2+) in solution, which control the microscopic environments around the metal ions, were directly observed through the mass spectrometric analysis of clusters isolated from liquid droplets.     

Porphyrin acidity and metal ion coordination revisited: electronic substitution effects

Macrocycle acidity and Zn²⁺ ion coordination are reported for three porphyrin derivatives which differ in both steric and electronic substitution effects on the macrocycle π-conjugated system. The role of the electronic substitution effects in the macrocycle deprotonation and metal ion chelating was found to be dominating whereas the macrocycle nonplanar distortions contribute to the acidity and metal chelation rate of the studied porphyrins in less extent. The contributions of both resonance and inductive electronic substitution effects have been distinguished based on the relationship between the weighted sum of resonance and inductive Hammett constants and the acidity and metal ion chelation rate.     

Magnetic properties and EPR spectroscopy of molecular metal clusters

The magnetic properties of molecular metal cluster compounds resemble those of small metal particles in the metametallic size regime. Even-electron metal carbonyl clusters with 10 or more metal atoms are paramagnetic, because their frontier orbital separations of less than 1 eV lead to high-spin electronic configurations. The rhodium cluster [Rh₁₇S₂(CO)₃₂]^3? gives EPR below 200 K withg=2.04, the first example of this type of paramagnetism in an even-electron carbonyl cluster of this 4d metal. Its spectral parameters are compared with those of osmium carbonyl clusters and some significant differences highlighted. Attempts have also been made to generate radical cations from lower-nuclearity, diamagnetic molecular clusters such as Rh₆(CO)₁₆ by chemical oxidation in sulphuric acid. An EPR active species (g=2.09) believed to be [Rh₆(CO)₁₆]⁺ has been obtained.     

N-乙酰基-N-苯酰基二茂铁基腙的IIB族和主族金属螯合物

本文报道了N-乙酰基-N-苯酰基二茂铁基腙[Fe-C(CH3)=NNH-COC6H5,Fc=C5H5FeC5H4]的IIB族和某些主族金属螯合物.     

Factors governing the metal coordination number in isolated group IA and IIA metal hydrates

Many of the group IA and IIA metal ions, such as Na+, K+, Mg2+, and Ca2+, play crucial roles in biological functions. Previous theoretical studies generally focus on the number of water molecules bound to a particular (as opposed to all) alkali or alkaline earth cations and could not establish a single preferred CN for the heavier alkali and alkaline earth ion-water complexes. Crystal structures of hydrated Na+, K+, and Rb+ also cannot establish the preferred number of inner-shell water molecules bound to these cations. Consequently, it is unclear if the gas-phase CNs of group IA metal hydrates increase with increasing ion size, as observed for the group IIA series from the Cambridge Structural Database, and if the same factors govern the gas-phase CNs of both group IA and IIA ion-water complexes. Thus, in this work, we determine the number of water molecules directly bound to the series of alkali (Li+, Na+, K+, and Rb+) and alkaline earth (Be2+, Mg2+, Ca2+, Sr2+, and Ba2+) metal ions in the gas phase by computing the free energy for forming an isolated metal-aqua complex as a function of the number of water molecules at 298 K. The preferred gas-phase CNs of group IA hydrates appear insensitive to the ion size; they are all 4, except for Rb+, where a CN of 6 seems as likely. In contrast, the preferred gas-phase CNs of the group IIA dications increase with increasing ion size; they are 4 for Be2+, 6 for Mg2+ and Ca2+, and 7 for Sr2+ and Ba2+. An entropic penalty disfavors a gas-phase CN greater than 4 for group IA hydrates, but it does not dictate the gas-phase CNs of group IIA hydrates. Instead, interactions between the metal ion and first-shell water molecules and between first-shell and second-shell water molecules govern the preferred gas-phase CNs of the group IIA metal hydrates.     

Three main group metal coordination polymers bearing imidazole-based dicarboxylates: Hydro(solvo)thermal syntheses, crystal structures and properties

Three coordination polymers [Pb(HMIDC)]_n (1), [Ba(H₂MIDC)₂]_n (2) and {[Mg(HMIDC)(H₂O)₂]·H₂O}_n (3) (H₃MIDC = 2-methyl-1H-imidazole-4,5-dicarboxylic acid) have been yielded under different hydro(solvo)thermal conditions. X-ray diffraction analysis reveals that compound 1 exhibits a 3-D framework constructed by 2-D networks joined by μ₄-HMIDC²⁻ bridges. Compound 2 also presents a 3-D structure, which is generated from 2-D layers pillared by 1-D chains along the c-axis. Compound 3 is a 1-D infinite chain and forms supramolecular layers through hydrogen bonds. The thermal and solid-state photoluminescence properties of polymers 1-3 have been determined as well. The theoretical predication of the methyl substituent effect of the ligand H₃MIDC has been investigated.     

Compatibility of nitrilotriacetate andN-methylisatin-β-amidinohydrazone in the coordination sphere of transition metal ions

Summary A study of the competition of nitrilotriacetate (NTA) andN-methylisatin--amidinohydrazone (-MIAG) in the coordination sphere of transition metal ions has been carried out by calculating the reproportionation constant which relates the stability of the mixed-ligand complex to those of the complexes formed by each ligand independently. NTA and -MIAG are incompatible ligands, and the mixed-ligand complexes formed are less stable than either of the parent complexes. This is also supported by the change in free energy occurring during mixed-ligand complex formation. All these studies have been carried out at 30±0.5°C and =0.1 M NaClO₄ in 50% v/v aqueous dioxan medium.     

Functionalization of SWNTs to facilitate the coordination of metal ions, compounds and clusters

The carboxylate residues of the open ends of aryl-tert-butyl and arylsulfonic acid side-walled functionalized single walled carbon nanotubes (SWNTs) have been investigated for the complexation conditions of the iron-molybdenum cluster [H(x)PMo(12)O(40)CH(4)Mo(72)Fe(30)(O(2)CMe)(15)O(254)(H(2)O)(98)] ("FeMoC"). A range of alternative donor groups for the attachment of FeMoC have been investigated for piranha etched SWNTs, dodecyl side-walled functionalized SWNTs (DD-SWNTs) and ultra-short SWNTs (US-SWNTs), including include pyridines, thiols and phosphines, using coupling reactions to either the carboxylate or hydroxide residues of the SWNTs' open ends. The functionalized SWNTs have been characterized by XPS, uptake of Fe(3+) and, where appropriate, MAS (31)P NMR. The efficacy of binding is dependent on the presence and identity of the ligand moiety. TEM and AFM of the SWNT-FeMoC conjugates show the presence of a 2-3 nm spherical feature on the tip of individual SWNTs.     

Distinguishing metal halide molecular clusters from perovskite magic sized clusters in the synthesis of metal halide perovskite nanostructures

Background

Research into perovskite nanocrystals (PNCs) has uncovered interesting properties compared to their bulk counterparts, including tunable optical properties due to size-dependent quantum confinement effect (QCE). More recently, smaller PNCs with even stronger QCE have been discovered, such as perovskite magic sized clusters (PMSCs) and ligand passivated PbX₂ metal halide molecular clusters (MHMCs) analogous to perovskites.

Objective

This review aims to present recent data comparing and contrasting the optical and structural properties of PQDs, PMSCs, and MHMCs, where CsPbBr₃ PQDs have first excitonic absorption around 520 nm, the corresponding PMSCS have absorption around 420 nm, and ligand passivated MHMCs absorb around 400 nm.

Results

Compared to normal perovskite quantum dots (PQDs), these clusters exhibit both a much bluer optical absorption and emission and larger surface-to-volume (S/V) ratio. Due to their larger S/V ratio, the clusters tend to have more surface defects that require more effective passivation for stability.

Conclusion

Recent study of novel clusters has led to better understanding of their properties. The sharper optical bands of clusters indicate relatively narrow or single size distribution, which, in conjunction with their blue absorption and emission, makes them potentially attractive for applications in fields such as blue single photon emission.     

Ionic and coordination diene polymerization and organic derivatives of main group metals

The effects of the nature of an organic derivative of a main group metal (cocatalyst), its composition, the cocatalyst : transition metal compound ratio, and the way of introducing the cocatalyst on the formation and operation of the active sites in the Ziegler—Natta catalytic systems in the polymerization of conjugated dienes are discussed. A correlation between the cocatalyst nature and the number and kinetic heterogeneity of the active sites is shown.     

A modular approach toward regulating the secondary coordination sphere of metal ions: differential dioxygen activation assisted by intramolecular hydrogen bonds

Metal ion function depends on the regulation of properties within the primary and second coordination spheres. An approach toward studying the structure-function relationships within the secondary coordination sphere is to construct a series of synthetic complexes having constant primary spheres but structurally tunable secondary spheres. This was accomplished through the development of hybrid urea-carboxamide ligands that provide varying intramolecular hydrogen bond (H-bond) networks proximal to a metal center. Convergent syntheses prepared ligands [(N'-tert-butylureayl)-N-ethyl]-bis(N' '-R-carbamoylmethyl)amine (H(4)1R) and bis[(N'-tert-butylureayl)-N-ethyl]-(N' '-R-carbamoylmethyl)amine (H(5)2R), where R=isopropyl, cyclopentyl, and (S)-(-)-alpha-methylbenzyl. The ligands with isopropyl groups H(4)1iPr and H(5)2iPr were combined with tris[(N'-tert-butylureayl)-N-ethyl]amine (H6buea) and bis(N-isopropylcarbamoylmethyl)amine (H(3)0iPr) to prepare a series of Co(II) complexes with varying H-bond donors. [CoIIH(2)2iPr]- (two H-bond donors), [CoIIH1iPr]- (one H-bond donor), and [CoII0iPr]- (no H-bond donors) have trigonal monopyramidal primary coordination spheres as determined by X-ray diffraction methods. In addition, these complexes have nearly identical optical and EPR properties that are consistent with S=3/2 ground states. Electrochemical studies show a linear spread of 0.23 V in anodic potentials (Epa) with [CoIIH(2)2iPr]- being the most negative at -0.385 V vs [Cp2Fe]+/[Cp2Fe]. The properties of [CoIIH3buea]- (H3buea, tris[(N'-tert-butylureaylato)-N-ethyl]aminato that has three H-bond donors) appears to be similar to that of the other complexes based on spectroscopic data. [CoIIH3buea]- and [CoIIH(2)2iPr]- react with 0.5 equiv of dioxygen to afford [CoIIIH3buea(OH)]- and [CoIIIH(2)2iPr(OH)]-. Isotopic labeling studies confirm that dioxygen is the source of the oxygen atom in the hydroxo ligands: [CoIIIH3buea(16OH)]- has a -(O-H) band at 3589 cm-1 that shifts to 3579 cm-1 in [CoIIIH3buea(18OH)]-; [CoIIIH(2)2iPr(OH)]- has -(16O-H)=3661 and -(18O-H)=3650 cm-1. [CoIIH1iPr]- does not react with 0.5 equiv of O2; however, treating [CoIIH1iPr]- with excess dioxygen initially produces a species with an X-band EPR signal at g=2.0 that is assigned to a Co-O2 adduct, which is not stable and converts to a species having properties similar to those of the CoIII-OH complexes. Isolation of this hydroxo complex in pure form was complicated by its instability in solution (kint=2.5x10-7 M min-1). Moreover, the stability of the CoIII-OH complexes is correlated with the number of H-bond donors within the secondary coordination sphere; [CoIIIH3buea(OH)]- is stable in solution for days, whereas [CoIIIH(2)2iPr(OH)]- decays with a kint=5.9x10-8 M min-1. The system without any intramolecular H-bond donors [CoII0iPr]- does not react with dioxygen, even when O2 is in excess. These findings indicate a correlation between dioxygen binding/activation and the number of H-bond donors within the secondary coordination sphere of the cobalt complexes. Moreover, the properties of the secondary coordination sphere affect the stability of the CoIII-OH complexes with [CoIIIH3buea(OH)]- being the most stable. We suggest that the greater number of intramolecular H-bonds involving the hydroxo ligand reduces the nucleophilicity of the CoIII-OH unit and reinforces the cavity structure, producing a more constrained microenvironment around the cobalt ion.     

An adamantane-based coordination framework with the first observation of discrete metal sulfonate clusters

By employing a rigid adamantane-based unit as a spacer, a coordination solid with an open channel layered structure results showing the first observation of metal sulfonate clusters. The design approach employed enforces a structural mismatch of metal and ligand coordinative preferences.