Search

Alkane elimination reactions between the diamino- and dianilino-bridged tetrakis(phenolate) proligands 1a,b-H and precursors M(CH 4 and precursors M(CH 2 SiMe 3 ) 3 , M(CH 2 , M(CH 2 C 6 H 4 - o -NMe 2 (M = Sc and Y), and Hf(CH 3 (M = Sc and Y), and Hf(CH 2 Ph) 4 were investigated. The diamino-bridged 1a-H 4 afforded nonsymmetric complex 2a-Y 2 incorporating two metal centers in different coordination environments. This one and other dinuclear compounds 2b-Sc 2 , 2a-Hf 2 , and 2b-Hf 2 were characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study (for 2a-Y 2 and 2b-Sc 2 ) and turned out to be symmetric in solution. Compound 2a-Y 2 , upon treatment with 2 equiv of 2-phenylpyridine, afforded symmetric bis(aryl) product 3a-Y 2 , which was authenticated by NMR spectroscopy and X-ray crystallography. The mechanism of its formation was studied by DFT computations and presumably involves a cooperative reorganization process within the nonsymmetric parent 2a-Y 2 to afford a symmetric isomer prior to its reaction with 2-phenylpyridine.

We provide a comprehensive study of the coordination of oxocyclam with palladium(II), including presentation of a novel bifunctional analogue, p -H 2 N-Bn-oxocyclam, bearing an aniline pendant. The complexation of palladium(II) with oxocyclam was examined by various techniques, including NMR analysis and potentiometric titrations which revealed that the Pd(II) complex can adopt different configurations such as trans -I and trans -III. In addition, oxocyclam forms a thermodynamically stable palladium(II) complex, the stabilization being attributed to the deprotonation of the amide function. The crystal structures of [Pd(H -1 oxocyclam )] + and [Pd( oxocyclam )] 2+ were obtained, revealing the structural details previously anticipated, including, in the second case, the presence of the proton on the carbonyl oxygen atom. Additionally, the study explored the redox behavior of the Pd(II)- oxocyclam complex through reduction and oxidation voltammograms at different pH values. Successful 109 Pd-labeling of oxocyclam and p -H 2 N-Bn-oxocyclam at pH 3.5 demonstrated high labeling efficiencies, whatever the species formed. The stability of the radiocomplexes was assessed and moderate transchelation toward EDTA was observed. Overall, oxocyclam displayed favorable properties for Pd(II) coordination and radiolabeling, suggesting its potential as a chelating agent for this metal in palladium-based applications.

We synthesized, thanks to the regiospecific N -functionalization using an orthoamide intermediate, two 1,4,7-triazacyclononane derivatives containing an acetate arm and either a methylpyridine or a picolinic acid group, respectively, H noapy and H 2 noapa , as new Ga 3+ chelators for potential use in nuclear medicine. The corresponding Ga 3+ complexes were synthesized and structurally characterized in solution by 1 H and 13 C NMR. The [Ga( noapy )] 2+ complex appears to exist in solution as two diasteroisomeric pairs of enantiomers, as confirmed by density functional theory (DFT) calculations, while for [Ga( noapa )] + , a single species is present in solution. Solid-state investigations were possible for the [Ga( noapa )] + complex, which crystallized from water as a pair of enantiomers. The average length of the N-Ga bonds of 2.090 Å is identical with that found for the [Ga( nota )] complex, showing that the presence of the picolinate arm does not hinder the coordination of the ligand to the metal ion. Protonation constants of noapy - and noapa 2- were determined by potentiometric titrations, providing an overall basicity ∑log K i H ( i = 1-4) that increases in the order noapy - < noapa 2- < nota 3- with increases in the negative charge of the ligand. Stability constants determined by pH-potentiometric titrations supplemented with 71 Ga NMR data show that the stabilities of [Ga( noapy )] 2+ and [Ga( noapa )] + are lower compared to that of [Ga( nota )] but higher than those of other standards such as [Ga( aazta )] - . 67 Ga radiolabeling studies were performed in order to demonstrate the potential of these chelators for 67/68 Ga-based radiopharmaceuticals. The labelings of H noapy and H 2 noapa were nearly identical, outperforming H 3 nota . Stability studies were conducted in phosphate-buffered saline and in the presence of human serum transferrin, revealing no significant decomplexation of [ 67 Ga][Ga( noapy )] 2+ and [ 67 Ga][Ga( noapa )] + compared to [ 67 Ga][Ga( nota )]. Finally, all complexes were found to be highly hydrophilic, with calculated log D 7.4 values of -3.42 ± 0.05, -3.34 ± 0.04, and -3.00 ± 0.23 for H noapy , H 2 noapa , and H 3 nota , respectively, correlating with the charge of each complex and the electrostatic potentials obtained with DFT.

Copper(I) halides are well-known for their structural diversity and rich photoluminescence properties, showing great potential for the development of solid-state lighting technology. A series of four molecular copper iodide clusters based on the [Cu 4 I 4 ] cubane geometry is reported. Among them, [Cu 8 I 8 ] octanuclear clusters of rare geometry resulting from dimerization of the tetranuclear counterparts were also synthesized. Two different phosphine ligands were studied, bearing either a styrene or an ethyl group. Therefore, the effect of the dimerization and of the ligand nature on the photophysical properties of the resulting clusters is investigated. The structural differences were analyzed by single-crystal X-ray diffraction (SCXRD), solid-state nuclear magnetic resonance (NMR), infrared, and Raman analyses. Compared to the ethyl group, the styrene function appears to greatly impact the photophysical properties of the clusters. The luminescence thermochromic properties of the ethyl derivatives and the intriguing photophysical properties of the clusters with styrene function were rationalized by density functional theory (DFT) calculations. Thus, the styrene group significantly lowers in energy the vacant orbitals and consequently affects the global energetic layout of the clusters. From this study, it was found that the nuclearity of copper iodide clusters eventually has less influence on the photophysical properties than the nature of the ligand. The design of proper ligands should therefore be considered when developing materials for specific lighting applications.

The palladium-catalyzed annulation reaction of alkynes enables an attractive approach to siloles. Their access from silirenes and terminal alkynes proved rather general, involving reactive intermediates that have remained elusive to date. Starting from 1,2-bis(3-thienyl)silirene as a source of photochromic siloles, the mechanism of the annulation reaction has been revisited, and palladasilacyclobutenes resulting from the activation of the silirene could be isolated and thoroughly characterized (NMR, X-ray, and DFT). Their role as reactive intermediates and their fate in the course of the reaction were also studied in situ. In combination with in-depth DFT calculations, a clearer picture of the mechanism and the reactive key species is disclosed.

In an effort to synthesize cobalt-rich metallaheteroboranes from decaborane(14) analogues, we have studied the reaction of 10-vertex nido -[(Cp*Co) 2 B 6 H 6 E 2 ] (Cp* = η 5 -C 5 Me 5 , 1 : E = Se and 2 : E = Te) with [Co 2 (CO) 8 ] under thermolytic conditions. All of these reactions yielded face-fused clusters, [(Cp*Co) 2 B 6 H 6 E 2 {Co(CO)}(μ-CO){Co 3 (CO) 6 }] ( 3 : E = Se and 4 : E = Te). Further, when clusters 3 and 4 were treated with [Co 2 (CO) 8 ], they underwent further cluster buildup reactions leading to the formation of 16-vertex doubly face-fused clusters [(Cp*Co) 2 B 6 H 6 E 2 {Co 2 (CO) 2 }(μ-CO) 2 {Co 4 (CO) 8 }] ( 5 : E = Se and 6 : E = Te). Cobaltaheteroboranes 3 and 4 comprise one icosahedron {Co 4 B 6 E 2 } and one square pyramidal {Co 3 B 2 } moiety, whereas 5 and 6 are made with one icosahedron {Co 4 B 6 E 2 } and two square pyramidal {Co 3 B 2 } cores. In an attempt to generate heterometallic metal-rich clusters, we have explored the reactivity of decaborane(14) analogue nido -[(Cp*Co) 2 B 7 TeH 9 ] ( 7 ) with [Ru 3 (CO) 12 ] at 80 °C, which afforded face-fused 13-vertex cluster [(Cp*Co) 2 B 7 H 7 Te{Ru 3 (CO) 8 }] ( 8 ). Cluster 8 is a rare example of a metal-rich metallaheteroborane in which one icosahedron {Co 2 Ru 2 B 7 Te} and a tetrahedron {Ru 2 B 2 } units are fused through a common {RuB 2 } triangular face. Further, the treatment of nido -[(Cp*Co) 2 B 6 S 2 H 4 (CH 2 S 2 )] ( 9 ) with [Fe 2 (CO) 9 ] afforded 11-vertex nido -[(Cp*Co) 2 B 6 S 2 H 4 (CH 2 S 2 ){Fe(CO) 3 }] ( 10 ). The core structure of 10 is similar to that of [C 2 B 9 H 11 ] 2- with a five-membered pentahapto coordinating face. All of the synthesized metal-rich metallaheteroboranes have been characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy, ESI-MS, and structurally solved by single-crystal X-ray diffraction analysis. Furthermore, theoretical investigations gave insight into the bonding of such higher-nuclearity clusters containing heavier chalcogen atoms.

The synthesis and photophysical and chiroptical properties of novel aza[ n ]helicenes ( 6a - d , 10a , b , n = 4-7) substituted with one or two 2-pyridyl groups are described. The preparation was performed via an adapted Mallory reaction using aromatic imines as precursors. The obtained novel class of helical 2,2'-bipyridine ligands was then coordinated to Ru(bipy) 2 2+ units, thus affording the first diastereomerically and enantiomerically pure [RuL(bipy) 2 ] 2+ ( 11a , c , L = 6a , c ) or [Ru 2 L'(bipy) 4 ] 4+ ( 12 , L' = 10b ) complexes. The topology and stereochemistry of these novel metal-based helical architectures were studied in detail, notably using X-ray crystallography. Interestingly, the coordination to ruthenium(II) enabled the preparation of fused multihelical systems incorporating aza- and ruthena-helicenes within the same scaffold. The photophysical, chiroptical, and redox properties of these complexes were examined in detail, and efficient redox-triggered chiroptical switching activity was evidenced.

Herein, we report a comprehensive coordination study of the previously reported ligands cyclam , CB-cyclam , TMC , DMC , and CB-DMC and of their C -functional analogues, cyclam-E , CB-cyclam-E , TMC-E , DMC-E , and CB-DMC-E . This group of ligands includes cyclam , cross-bridged cyclams , their di- or tetramethylated derivatives, and the analogues bearing an additional hydroxyethyl group on one β-N position of the ring. The Cu(II) and Zn(II) complexes of these macrocycles have been highlighted previously for the biological interest, but the details of their structures in the solid state and in solution remained largely unexplored. In particular, we analyzed the impact that adding noncoordinating N -methyl and C -hydroxyethyl functionalities has in the structures of the complexes. All the Cu(II) and Zn(II) complexes were synthesized and investigated using single crystal X-ray diffraction and NMR, electronic absorption, and EPR spectroscopies, along with DFT studies. Dissociation kinetics experiments in acidic conditions and electrochemical studies were also performed. Special attention was paid to analyze the different configurations present in solution and in the solid state, as well as the impact of the C -appended hydroxyethyl group on the coordination behavior. Various ratios of the trans -I, trans -III, and cis -V configurations have been observed depending on the degree of N -methylation and the presence of the ethylene cross-bridge.

Mono- and dinuclear group 3 metal complexes incorporating polydentate bis(imino)phenoxy {N 2 O} - and bis(amido)phenoxy {N 2 O} 3- ligands were synthesized by alkane elimination reactions from the tris(alkyl) M(CH 2 SiMe 3 ) 3 (THF) 2 and M(CH 2 C 6 H 4 - o -NMe 2 ) 3 (M = Sc, Y) precursors. Complex 1a-Y was used for the selective C-H activation of 2-phenylpyridine at the 2'-phenyl position affording the corresponding bis(aryl) product 3a-Y , which was found to be reacted reluctantly with weak electrophiles (styrene, imines, hydrosilanes). The mechanism of formation of 3a-Y was established by DFT calculations, which also corroborated high stability of the complex toward insertion of styrene, apparently stemming from the inability to form the corresponding adduct. Copolymerization of cyclohexene oxide and CO 2 promoted by 1a-Y (0.1-0.5 mol %) was demonstrated to proceed under mild conditions (toluene, 70 °C, P CO2 = 12 bar) giving polycarbonates with high efficiency (maximal TON of 460) and selectivity (97-99% of carbonate units).

In the field of stimuli-responsive luminescent materials, mechanochromic compounds exhibiting reversible emission color changes activated by mechanical stimulation present appealing perspectives in sensor applications. The mechanochromic luminescence properties of the molecular cubane copper iodide cluster [Cu 4 I 4 [PPh 2 (C 6 H 4 -CH 2 OH)] 4 ] ( 1 ) are reported in this study. This compound can form upon melting an amorphous phase, giving an unprecedented opportunity to investigate the mechanochromism phenomenon. Because the mechanically induced crystalline-to-amorphous transition is only partial, the completely amorphous phase represents the ultimate state of the mechanically altered phase. Furthermore, the studied compound could form two different crystalline polymorphs, namely, [Cu 4 I 4 [PPh 2 (C 6 H 4 -CH 2 OH)] 4 ]·C 2 H 3 N ( 1·CH 3 CN ) and [Cu 4 I 4 [PPh 2 (C 6 H 4 -CH 2 OH)] 4 ]·3C 4 H 8 O ( 1·THF ), allowing the establishment of straightforward structure-property relationships. Photophysical and structural characterizations of 1 in different states were performed, and the experimental data were supported by theoretical investigations. Solid-state NMR analysis permitted quantification of the amorphous part in the mechanically altered phase. IR and Raman analysis enabled identification of the spectroscopic signatures of each state. Density functional theory calculations led to assignment of both the NMR characteristics and the vibrational bands. Rationalization of the photoluminescence properties was also conducted, with simulation of the phosphorescence spectra allowing an accurate interpretation of the thermochromic luminescence properties of this family of compounds. The combined study of crystalline polymorphism and the amorphous state allowed us to get deeper into the mechanochromism mechanism that implies changes of the [Cu 4 I 4 ] cluster core geometry. Through the combination of multistimuli-responsive properties, copper iodide clusters constitute an appealing class of compounds toward original functional materials.

The photoluminescent stimuli-responsive properties of two crystalline polymorphs with the formula (PPh 4 ) 2 [Cu 2 I 4 ] are reported. Distinct luminescence properties are exhibited by these ionic copper iodide compounds with blue or yellow emission, and original luminescence thermochromism and mechanochromism are demonstrated. While one polymorph displays contrasted temperature-dependent emission properties, the other shows great modification of its emission upon mechanical solicitation. The establishment of structure-properties relationships, supported by a theoretical approach, permits us to get insights into the origin of the photoluminescence properties and the mechanisms at play. According to DFT calculations, the different emission bands originate either from the (PPh 4 ) + organic cation or from the [Cu 2 I 4 ] 2- anion. Activation of these two emissive centers appears to be dependent on the crystalline packing of the polymorph. The thermochromism displayed by one polymorph can be attributed to a variation in temperature of the relative intensities of two emission bands of two different excited states. The origin is different for the other polymorph, with emission bands coming from two independent emissive centers: namely, (PPh 4 ) + and [Cu 2 I 4 ] 2- . The luminescence mechanochromism is attributed to a polymorphic transition. The mechanical solicitation induces a partial transformation of one polymorph into the other within a disordered phase. The mechanochromic mechanism can be related to mechanical modifications of intermolecular interactions between the (PPh 4 ) + cations. By displaying luminescence properties that depend on crystalline structure, excitation wavelength, temperature, and mechanical solicitation, the studied copper iodides offer a great possibility of emissive color control and switching, a clear demonstration of the great potentialities of this family of compounds for the development of photoactive materials.

Irradiation of [Re 2 (CO) 10 ] in the presence of BH 3 ·thf resulted in the formation of several rhenium diborane(6) species, for example, [{(OC) 4 Re}{Re(CO) 3 } 2 (μ 3 -η 2 :η 2 :η 2 -B 2 H 6 )(μ-H)], 1 ; [{(OC) 4 Re} 2 {Re(CO) 3 }(μ 3 -η 2 :η 2 :η 1 -B 2 H 6 )(μ-H)], 2 ; and [{(OC) 4 Re} 2 (μ-η 2 :η 2 -B 2 H 6 )], 3 , comprising diverse coordination modes of the [B 2 H 6 ] 2- ligand. Compound 1 contains a tris(bidentate) [B 2 H 6 ] 2- unit, whereas 2 consists of an unsymmetrically bound [μ 3 -η 2 :η 2 :η 1 -B 2 H 6 ] 2- ligand. In contrast, the irradiation of [Mn 2 (CO) 10 ] with BH 3 ·thf yielded only the Mn analogue of 1 , [{(OC) 4 Mn}{Mn(CO) 3 } 2 (μ 3 -η 2 :η 2 :η 2 -B 2 H 6 )(μ-H)], 1' . In an attempt to generate the bimetallic Mn-diborane(6), we have carried out the reaction of 1' with PCy 3 under photolytic conditions. The reaction led to the formation of two single base stabilized unsymmetrical diborane(5) species, [{Mn(CO) 3 }{Mn(CO) 2 PCy 3 }(μ-η 2 :η 2 -B 2 H 5 ·PCy 3 )(μ-H)], 4 , and [{Mn(CO) 2 PCy 3 }(η 3 -B 2 H 5 ·PCy 3 )], 5 . As [B 2 H 6 ] 2- and [B 2 H 5 ·PCy 3 ] - are isoelectronic, the bondings in 4 and 5 are analogous to that of diborane(6) species 1 - 3 . All the new species have been characterized spectroscopically, and their structures were further confirmed by single-crystal X-ray diffraction studies. DFT-type quantum chemical calculations were carried out that provided insight into the bonding interaction of [B 2 H 6 ] 2- and [B 2 H 5 ·PCy 3 ] - with the M(CO) n fragments.

The tailoring of the coordination chemistry around f-element centers is a crucial step for the development of compounds with slow magnetic relaxation, including single-molecule magnets (SMMs), which have great potential in molecular spintronics and for future quantum computing devices. Lanthanide ions are particularly interesting because the predominant electrostatic model of their bonding allows rationalizing their coordination symmetry. However, to the best of our knowledge, the redox properties of the lanthanides are not taken into account for the design of SMMs, and therefore all SMMs reported to date contain lanthanide ions in their trivalent oxidation state. In this Article, divalent lanthanide compounds presenting field-induced slow magnetic relaxation are reported. The rational design and synthesis of two Tm II complexes with the 18-crown-6 ligand are presented along with their emission and EPR properties, which help to probe the desired nature of the ground state, that is, maximizing the anisotropy. The observed magnetic properties demonstrate their slow magnetic relaxation behavior in a moderate external magnetic field.

Nanoscale molecular clusters are attractive for the design of materials exhibiting original functions and properties. In particular, copper iodide clusters of high nuclearity are well-known for their stimuli-responsive luminescence properties. The synthesis and characterization of an unprecedented copper(I) iodide molecular cluster based on an original heptanuclear inorganic core are reported. This nanometer-size cluster is formulated as [Cu 7 I 7 (P(C 6 H 4 CF 3 ) 3 ) 6 (CH 3 CN)] and its novel structure has been characterized by X-ray diffraction and multinuclear solid-state 63 Cu, 31 P, 13 C, 19 F, and 1 H NMR spectroscopy. The photoluminescence properties of this cluster have been studied at variable temperature. Density functional theory calculations have been performed on this large molecular structure and allow one to rationalize the observed luminescence properties. This study highlights the crucial role of cuprophilic interactions in molecular copper iodide clusters for exhibiting photoactive properties.

Luminescent materials based on copper complexes are currently receiving increasing attention because of their rich photophysical properties, opening a wide field of applications. The copper iodide clusters formulated [Cu 4 I 4 L 4 ] (L = ligand), are particularly relevant for the development of multifunctional materials based on their luminescence stimuli-responsive properties. In this context, controlling and modulating their photophysical properties is crucial and this can only be achieved by thorough understanding of the origin of the optical properties. We thus report here, the comparative study of a series of cubane copper iodide clusters coordinated by different phosphine ligands, with the goal of analyzing the effect of the ligands nature on the photoluminescence properties. The synthesis, structural, and photophysical characterizations along with theoretical investigations of copper iodide clusters with ligands presenting different electronic properties, are described. A method to simplify the analysis of the 31 P solid-state NMR spectra is also reported. While clusters with electron-donating groups present classical luminescence properties, the cluster bearing strong electron-withdrawing substituents exhibits original behavior demonstrating a clear influence of the ligands properties. In particular, the electron-withdrawing character induces a decrease in energy of the unoccupied molecular orbitals, that consequently impacts the emission properties. The modification of the luminescence thermochromic properties of the clusters are supported by density functional theory (DFT) calculations. This study demonstrates that the control of the luminescence properties of these compounds can be achieved through modification of the coordinated ligands, nevertheless the role of the crystal packing should not be underestimated.

Luminescent mechanochromic materials exhibiting reversible changes of their emissive properties in response to external mechanical forces are currently emerging as an important class of stimuli-responsive materials because of promising technological applications. Here, we report on the luminescence mechanochromic properties of a [Cu 4 I 4 (PPh 3 ) 4 ] copper iodide cluster presenting a chair geometry, being an isomer of the most common cubane form. This molecular cluster formulated [Cu 4 I 4 (PPh 3 ) 4 ]·2CHCl 3 (1) exhibits a highly contrasted emission response to manual grinding, and, interestingly, the optical properties of the ground phase present striking similarities with those of the cubane isomer. In order to understand the underlying mechanism, a comparison with two related compounds has been conducted. The first one is a pseudopolymorph of 1 formulated as [Cu 4 I 4 (PPh 3 ) 4 ]·CH 2 Cl 2 (2), which exhibits luminescent mechanochromic properties as well. The other one is also a chair compound but with a slightly different phosphine ligand, namely, [Cu 4 I 4 (PPh 2 C 6 H 4 CO 2 H) 4 ] (3), lacking mechanochromic properties. Structural and optical characterizations of the clusters have been analyzed in light of previous electronic structure calculations. The results suggest an unpreceded mechanochromism phenomenon based on a solid-state chair → cubane isomer conversion. This study shows that polynuclear copper iodide compounds are particularly relevant for the development of luminescent mechanochromic materials.