Analogous Palladium Research Articles

Ligand and Metal Effects in the Gas‐Phase Fragmentation of Thiomethoxymethyl Complexes

While the collision‐induced dissociation (CID) of the mass‐selected cation [(Ph3P)2Pt(CH2SCH3)]+ selectively liberates PPh3, the diphosphine complex [(dppe)Pt(CH2SCH3)]+ (dppe = 1,2‐bis(diphenylphosphino)ethane) ejects C2H4, CH2S, and (CH3)2S instead. The analogous palladium complexes [(Ph3P)2Pd(CH2SCH3)]+ and [(dppe)Pd(CH2SCH3)]+ show similar reactivity, except that C–H‐bond activation is completely lacking. For other bidentate diphosphine ligands such as dppm, dppv, dppp, dppb, dppbz, dppf, and xantphos, a correlation of the dominant reaction channels with the bite angle is observed. For bite angles > 90°, hydrogen‐atom transfer is favored, as evidenced by an increase in dimethyl‐sulfide loss. For smaller bite angles (< 90°), intramolecular activation of the thiomethoxymethyl ligand predominates, thus resulting in increased losses of thioformaldehyde and ethene. The results of the CID experiments are compared with those for [(bipy)Pt(CH2SCH3)]+, for which the loss of C2H4 is observed as the main process. DFT calculations for the complexes [(dppe)Pt(CH2SCH3)]+ and [(bipy)Pt(CH2SCH3)]+ together with the experimental findings uncover subtle differences in the underlying reaction mechanisms.

Concerted flexible and steric strategy in α-diimine nickel and palladium mediated insertion (Co-)Polymerization

To address the issues of poor thermostability of catalyst and low polymer molecular weight resulted from chain transfer at high temperature in olefin polymerization, versatile strategies have been utilized in the benchmark α-diimine nickel and palladium catalysts. In this contribution, a concerted flexible and steric strategy was highlighted in the α-diimine nickel and palladium catalysts. Compared to the seminal Brookhart catalyst, these newly generated nickel catalysts exhibited improved thermostability over a wide range of temperature from 30 °C to 130 °C, showed higher catalytic activities, and produced significantly higher (4.7–5.8 times) molecular weight polymers in ethylene polymerization, which are highly branched polyethylenes (76–110/1000C, SR = 72 %). Notably, high molecular weight polyethylene (up to 219 kg mol−1) was even afforded at 130 °C, which is extremely challenging when the flexible substituent is used in α-diimine system. The corresponding palladium analogues by using the same strategy further produced high molecular weight ethylene-methyl acrylate copolymers (up to 137 kg mol−1) at the difficult 70 °C in the copolymerization of ethylene and methyl acrylate. The incorporation of methyl acrylate could be tuned (0.6–2.9 mol%), where methyl acrylate units distribute both in the main chain and at the end of branches (15 %:85 %).

Copper(II) Complexes of 2,2'-Bisdipyrrins: Synthesis, Characterization, Cell Uptake, and Radiolabeling with Copper-64.

Complexes prepared with positron-emitting copper-64 are of interest as imaging agents for positron emission tomography (PET). This work investigates the potential of using acyclic tetrapyrrolic 2,2'-bisdipyrrins as ligands to prepare charge-neutral, lipophilic, cell-permeable, redox active complexes with positron-emitting copper-64. The synthesis and characterization of a series of tetrapyrrolic 2,2'-bisdipyrrin copper(II) complexes are reported. Four 2,2'-bisdipyrrin copper(II) complexes were prepared with different functional groups in the meso-position of the ligands. Two of the new copper(II) complexes, one palladium(II) complex, and one nickel(II) complex were characterized by X-ray crystallography, which demonstrated that the copper(II) is in a distorted square planar environment. An investigation of the electrochemical properties of the complexes by cyclic voltammetry revealed that the complexes undergo multiple quasi-reversible processes. A comparison of the cyclic voltammetry of the copper complexes with their palladium(II) analogues suggests that these redox processes are ligand-based and not metal-based. The copper(II) complexes are cell-permeable in A431 mammalian cells and are nontoxic at concentrations of 50 μM. The ligands can be radiolabeled with copper-64 at room temperature.

Palladium and Platinum Complexes of the Antimetabolite Fludarabine with Vastly Enhanced Selectivity for Tumour over Non-Malignant Cells.

The purine derivative fludarabine is part of frontline therapy for chronic lymphocytic leukaemia (CLL). It has shown positive effects on solid tumours such as melanoma, breast, and colon carcinoma in clinical phase I studies. As the treatment of CLL cells with combinations of fludarabine and metal complexes of antitumoural natural products, e.g., illudin M ferrocene, has led to synergistically enhanced apoptosis, in this research study different complexes of fludarabine itself. Four complexes bearing a trans-[Br(PPh3)2]Pt/Pd fragment attached to atom C-8 via formal η1-sigma or η2-carbene bonds were synthesised in two or three steps without protecting polar groups on the arabinose or adenine. The platinum complexes were more cytotoxic than their palladium analogues, with low single-digit micromolar IC50 values against cells of various solid tumour entities, including cisplatin-resistant ones and certain B-cell lymphoma and CLL, presumably due to the ten-fold higher cellular uptake of the platinum complexes. However, the palladium complexes interacted more readily with isolated Calf thymus DNA. Interestingly, the platinum complexes showed vastly greater selectivity for cancer over non-malignant cells when compared with fludarabine.

Dinuclear and tetranuclear group 10 metal complexes constructed from linear tetrasilane comprising both Si-H and Si-Si moieties

The activation of Si-H bonds and/or Si-Si bonds in organosilicon compounds by transition-metal species plays a crucial role for the production of functional organosilicon compounds. Although group-10-metal species are frequently used to activate Si-H and/or Si-Si bonds, so far, systematic investigation to clarify the preferences of these metal species with respect to the activation of Si-H and/or Si-Si bonds remain elusive. Here, we report that platinum(0) species that bear isocyanide or N-heterocyclic-carbene (NHC) ligands selectively activates the terminal Si-H bonds of the linear tetrasilane Ph2(H)SiSiPh2SiPh2Si(H)Ph2 in a stepwise manner, whereby the Si-Si bonds remain intact. In contrast, analogous palladium(0) species are preferably inserted into the Si-Si bonds of the same linear tetrasilane, whereby the terminal Si-H bonds remain intact. Substitution of the terminal hydride groups in Ph2(H)SiSiPh2SiPh2Si(H)Ph2 with chloride groups leads to the insertion of platinum(0) isocyanide into all Si-Si bonds to afford an unprecedented zig-zag Pt4 cluster.

Orbital Degree of Freedom in Conducting Platinum–Dithiolene Complex Salts

We report experimental evidence for the orbital degrees of freedom in anion–radical salts consisting of metal–dithiolene complexes, obtained by a simple method. We observed the NIR absorption spectra of the 2D molecular conductors Me4Q[Pt(dmit)2]2 (Q = N, P, and Sb, dmit = 1,3-dithiole-2-thione-4,5-dithiolate), which shows a phase transition from the metallic phase to the semiconducting and charge-ordered phase, and analyzed the orbital levels of dimers [Pt(dmit)2]2 near the Fermi energy. The highest-energy electrons in the charge-ordered phase occupied the bonding orbitals, whereas those in the metallic phase occupied the antibonding orbitals. The redistribution of charges and the replacement of the outermost orbitals co-occurred for all dimers in Me4Q[Pt(dmit)2]2. This phenomenon differs from that in palladium analogs, in which the replacement of the outermost orbitals does not occur or occurs only for half of all dimers. Our experimental results revealed that anion–radical salts consisting of metal–dithiolene complexes have a variety of orbital distributions.

Room-Temperature Phosphorescence from Pd(II) and Pt(II) Complexes as Supramolecular Luminophores: The Role of Self-Assembly, Metal-Metal Interactions, Spin-Orbit Coupling, and Ligand-Field Splitting.

The synthesis as well as the structural and photophysical characterization of two isoleptic bis-cyclometalated Pt(II) and Pd(II) complexes, namely [PtL] and [PdL], bearing a tailored dianionic tetradentate ligand (L2-) are reported. The isostructural character and intermolecular interactions of [PtL] and [PdL] were assessed by NMR spectroscopy and X-ray diffraction analysis. Both complexes show fully ligand-controlled aggregation, demonstrating that a judicious molecular design can tune the photophysical properties. In fact, by introduction of fluorine atoms on defined positions and methoxy groups on complementary sites, metal-metal interactions can be forced by a head-to-tail stacking. Hence, [PtL] shows luminescence from metal-perturbed ligand-centered or from metal-metal-to-ligand charge-transfer triplet states in diluted solutions, in frozen glasses and in crystals, with high photoluminescence quantum yields and long lifetimes in the microsecond range. At room temperature (RT) in concentrated fluid solutions, the palladium analogue [PdL] surprisingly emits luminescence from aggregated species involving supramolecular interactions. Time-resolved photoluminescence and transient absorption spectroscopies demonstrated that ultrafast intersystem crossing occurs for both metals, which outruns any competitive relaxation pathway from the photoexcited singlet state. Furthermore, we demonstrate that the radiationless deactivation can be suppressed in frozen glassy matrices at 77 K and by intermolecular interactions in fluid solutions at RT. In both cases and as indicated by density functional theory calculations, the lowest emissive state acts as an energy trap from which the thermal population of dissociative states with formal occupation of an antibonding Pd-centered 4dx2-y2 orbital is suppressed. This occurs as the energy gap between the emissive and the dark states surpasses kT.

Multifaceted role of silver salts as ligand scavengers and different behavior of nickel and palladium complexes: beyond halide abstraction.

The reaction of [NiArBr(PPh3)2] with AgBF4 brings about the abstraction of both the halide and phosphine from the nickel center by silver. When the reaction is carried out in CH2Cl2/toluene a mixture of the cationic aquo derivatives [NiAr(H2O)(PPh3)2]BF4 (2) and [NiAr(H2O)2(PPh3)]BF4 (3) is formed, along with AgBr and [Ag(PPh3)n]BF4. When the same reaction is carried out in acetone as the solvent, it leads to the completely different complex [NiAr(κ2-O, O-MeC(O)CH2C(OH)Me2)(PPh3)] (5), bearing a chelating ligand formed by the aldol self-condensation of acetone. Phosphine abstraction by silver is less favorable for the analogous palladium(II) complexes and only occurs if a large excess of AgBF4 is used. Thus, silver salts can be safely used as halide scavengers for palladium derivatives. However, the generation of cationic Ni complexes from neutral precursors by halide extraction with a silver salt may produce naked species, different than those expected, and highly reactive in certain media.

C(spn)−X (n=1–3) Bond Activation by Iron

AbstractThe iron‐catalyzed oxidative addition of C(spn)−X bonds (n=1–3 and X=H, CH3, Cl) in archetypal model substrates H3C−CH2−X, H2C=CH−X and HC≡C−X to Fe(CO)4was investigated using relativistic density functional theory at ZORA‐OPBE/TZ2P. The C(spn)−X bonds become substantially stronger going from C(sp3)−X to C(sp2)−X to C(sp)−X, whereas the oxidative addition reaction barrier decreases along this series. Our activation strain and energy decomposition analyses expose that the decreased reaction barrier for the oxidative addition going fromsp3tosp2tospstems from a relief of the destabilizing (steric) Pauli repulsion between the catalyst and substrate. This originates from the decreasing coordination number of the carbon atom that goes from four in C(sp3)−X to three in C(sp2)−X to two in C(sp)−X. In analogy with our previous results on palladium‐catalyzed oxidative additions, this enhances the stabilizing catalyst–substrate interaction, which is able to overcome the more destabilizing strain associated with the stronger C(spn)−X bonds. This work again demonstrates that iron‐based catalysts can resemble the behavior of their well‐known palladium analogs in the oxidative addition step of cross‐coupling reactions.

Thermal and thermo-oxidative stability of a series of palladium and platinum ferrocenylamine sulfides and selenides

Ferrocenylamine complexes have found increasing applications in the fields of catalysis in various organic reactions, industry, medical treatments and enzyme–activity determinations. Therefore, information related to the thermal and thermo-oxidative stability of these compounds is important for such applications; however, this information is currently limited. Twenty previously prepared palladium and platinum ferrocenylamine complexes with systematic structural variations are examined for their thermal (under nitrogen) and thermo-oxidation stability (under atmospheric air) using thermogravimetry (TG), differential thermal analysis (DTG), and differential scanning calorimetry (DSC) techniques. Degradation products are identified by comparing thermogravimetric analysis and theoretical calculations. Structure–stability studies are also discussed. The results show that all the compounds have high thermal and thermo-oxidative stabilities of up to 265 and 173 °C, respectively. Electron–donating substituents enhance the thermal and thermo-oxidative stabilities of the palladium complexes ( t-Bu, selenide electrophiles and dielectrophiles), while those with destabilizing effects are aromatic substituents (Ph and tolyl). Most platinum ferrocenylamine sulfides and selenides show higher thermal and thermo-oxidative stabilities than their corresponding palladium analogs. All the prepared compounds show high thermal and thermo-oxidative stability which reinforces their catalytic and industrial applications. However, their thermal stability is higher than their thermo-oxidative stability.

Rational design of iron catalysts for C-X bond activation.

We have quantum chemically studied the iron-mediated CX bond activation (X=H, Cl, CH3 ) by d8 -FeL4 complexes using relativistic density functional theory at ZORA-OPBE/TZ2P. We find that by either modulating the electronic effects of a generic iron-catalyst by a set of ligands, that is, CO, BF, PH3 , BN(CH3 )2 , or by manipulating structural effects through the introduction of bidentate ligands, that is, PH2 (CH2 )n PH2 with n=6-1, one can significantly decrease the reaction barrier for the CX bond activation. The combination of both tuning handles causes a decrease of the CH activation barrier from 10.4 to 4.6kcal mol-1 . Our activation strain and Kohn-Sham molecular orbital analyses reveal that the electronic tuning works via optimizing the catalyst-substrate interaction by introducing a strong second backdonation interaction (i.e., "ligand-assisted" interaction), while the mechanism for structural tuning is mainly caused by the reduction of the required activation strain because of the pre-distortion of the catalyst. In all, we present design principles for iron-based catalysts that mimic the favorable behavior of their well-known palladium analogs in the bond-activation step of cross-coupling reactions.

Platinum Assisted Tandem P-C Bond Cleavage and P-N Bond Formation in Amide Functionalized Bisphosphine o-Ph2PC6H4C(O)N(H)C6H4PPh2-o: Synthesis, Mechanistic, and Catalytic Studies.

The reactions of amide functionalized bisphosphine o-Ph2PC6H4C(O)N(H)C6H4PPh2-o (1) with platinum salts are described. Treatment of 1 with [Pt(COD)Cl2] yielded a chelate complex, [PtCl2{o-Ph2PC6H4C(O)N(H)C6H4PPh2-o}κ2-P,P] (2), which on subsequent treatment with LiHMDS formed a novel 1,2-azaphospholene-phosphine complex [Pt(C6H5)Cl{o-C6H4{C(O)N(o-PPh2(C6H4))P(Ph)}}κ2-P,P] (3) involving a tandem P-C bond cleavage and P-N bond formation. The same complex 3 on passing dry HCl gas afforded the dichloro complex [PtCl2{o-C6H4{C(O)N(o-PPh2(C6H4))P(Ph)}}κ2-P,P] (5). Complex 2 upon refluxing in toluene or treatment of 1 with [Pt(COD)Cl2] in the presence of a base at room temperature resulted in the pincer complex [PtCl{o-Ph2PC6H4C(O)N(C6H4PPh2-o)}κ3-P,N,P] (4). Reaction of 1 with [Pt(COD)ClMe] at room temperature also afforded the pincer complex [PtMe{o-Ph2PC6H4C(O)N(C6H4PPh2-o)}κ3-P,N,P] (6). Mechanistic studies on 1,2-azaphospholene formation showed the reductive elimination of LiCl to form a phosphonium salt that readily adds one of the P-C bonds oxidatively to the in situ generated Pt0 species to form a chelate complex 3. The analogous palladium complex [PdCl2{o-C6H4{C(O)N(o-PPh2(C6H4))P(Ph)}}κ2-P,P] (7) showed excellent catalytic activity toward N-alkylation of amines with alcohols with a very low catalyst loading (0.05 mol %), and the methodology is very efficient toward the gram-scale synthesis of many N-alkylated amines.

How to Prepare Kinetically Stable Self-assembled Pt12 L24 Nanocages while Circumventing Kinetic Traps.

Supramolecular coordination‐based self‐assembled nanostructures have been widely studied, and currently various applications are being explored. For several applications, the stability of the nanostructure is of key importance, and this strongly depends on the metal used in the self‐assembly process. Herein, design strategies and synthetic protocols to access desirable kinetically stable Pt12L24 nanospheres are reported, and it is demonstrated that these are stable under conditions under which the palladium counterparts decompose. Descriptors previously used for palladium nanospheres are insufficient for platinum analogues, as the stronger metal–ligand bond results in a mixture of kinetically trapped structures. We report that next to the dihedral angle, the rigidity of the ditopic ligand is also a key parameter for the controlled formation of Pt12L24 nanospheres. Catalytic amounts of coordinating additives to labilise the platinum‐pyridyl bond to some extent are needed to selectively form Pt12L24 assemblies. The formed Pt12L24 nanospheres were demonstrated to be stable in the presence of chloride, amines and acids, unlike the palladium analogues.

Raman spectrum of layered tilkerodeite (Pd2HgSe3) topological insulator: the palladium analogue of jacutingaite (Pt2HgSe3)

The layered mineral tilkerodeite (Pd2HgSe3), the palladium analogue of jacutingaite (Pt2HgSe3), is a promising quantum spin hall insulator for low-power nanospintronics. In this context, a fast and reliable assessment of its structure is key for exploring fundamental properties and architecture of new Pd2HgSe3-based devices. Here, we investigate the first-order Raman spectrum in high-quality, single-crystal bulk tilkerodeite, and analyze the wavenumber relation to its isostructural jacutingaite analogue. By using polarized Raman spectroscopy, symmetry analysis, and first-principles calculations, we assigned all the Raman-active phonons in tilkerodeite, unveiling their wavenumbers, atomic displacement patterns, and symmetries. Our calculations used several exchange–correlation functionals within the density functional perturbation theory framework, reproducing both structure and Raman-active phonon wavenumbers in excellent agreement with experiments. Also, it was found that the influence of the spin–orbit coupling can be neglected in the study of these properties. Finally, we compared the wavenumber and atomic displacement patterns of corresponding Raman-active modes in tilkerodeite and jacutingaite, and found that the effect of the Pd and Pt masses can be neglected on reasoning their wavenumber differences. From this analysis, tilkerodeite is found to be mechanically weaker than jacutingaite against the atomic displacement patterns of these modes. Our findings advance the understanding of the structural properties of a recently discovered layered topological insulator, fundamental to further exploring its electronic, optical, thermal, and mechanical properties, and for device fabrication.

New Neutral Nickel and Palladium Sandwich Catalysts: Synthesis of Ultra-High Molecular Weight Polyethylene (UHMWPE) via Highly Controlled Polymerization and Mechanistic Studies of Chain Propagation

New neutral nickel and palladium ethylene polymerization catalysts have been prepared that incorporate an anionic (N,O) chelating ligand. Extensive axial shielding is provided by two 3,5-dichloroaryl moieties in a "sandwich" orientation. Such shielding results in an exceptionally slow rate of chain transfer relative to migratory insertion in the nickel catalyst, and thus highly controlled polymerization of ethylene is observed, leading to lightly branched ultra-high molecular weight polyethylene with Mn values up to 4.1 × 106 g/mol. The analogous palladium catalysts provide the means for a detailed mechanistic study of chain propagation in an electronically asymmetric neutral palladium catalyst. Both isomers of the methyl ethylene complex can be generated and observed at low temperatures allowing experimental elucidation of mechanistic details of chain propagation probed in other electronically asymmetric systems only through DFT studies or by examination of model studies. The barrier to migratory insertion in these complexes is ca. 19.2 kcal/mol. Investigation of the equilibration of the methyl ethylene isomers in the presence of excess ethylene showed the isomerization rate is dependent on ethylene concentration. This is the first direct proof that isomerization in these alkyl ethylene intermediates is catalyzed by ethylene. Furthermore, isomer equilibration is much faster than migratory insertion so that the barriers for insertion of individual isomers cannot be determined.

The use of control experiments as the sole route to correct the mechanistic interpretation of mercury poisoning test results: The case of P,C-palladacycle-catalysed reactions

In the study of the metallic mercury interaction with cyclopalladated derivatives of tris-ortho-tolylphosphine [{(κ2P,C-L)Pd(μ-X)}2], the redox-transmetallation of palladacycles by metallic mercury with the formation of P,C-chelated benzylmercurials [(κ2P,C-L)HgX] was revealed at moderate temperature in the presence of excess Hg(0). In contrast, the mercury(0) testing of the Suzuki reaction with the same chloride P,C-precatalyst gave a negative result, even at a higher temperature and with a greater excess of Hg(0). The structures of these mercurials have been convincingly confirmed spectrally (1Н, 13С, 31Р and 199Hg NMR), and via X-ray diffraction study and DFT calculations for the chloride mercurial. Our results and the analysis of known data on the mercury diagnostics of catalytic systems with classical and anomalous P,C-precatalysts enable us to assume that the intact state of palladacycle is present in the key anionic intermediate [(κ2P,C-L)Pd0]– of catalytic cycles of the Suzuki and Heck reactions and a lower reactivity of Hg(0) with palladium(0) complexes in comparison with that of palladium(II) analogues.

Interaction of bis(alkylamine)dichloropalladium(II) complexes with CT-DNA and BSA; their synthesis, characterization, antitumor, and antibacterial evaluations

A series of five new and analogous palladium(II) alkylamine complexes of cisplatin derivatives such as cis-[Pd(alkyl-am)2Cl2], where alkyl-am is Ethyl-, Propyl-, Butyl-, Hexyl-, and Octyl-amine, have been prepared. They have been characterized by physicochemical methods such as FT-IR, 1H-NMR, UV-Vis, conductivity measurements and elemental analysis. These synthesized metal complexes were screened for their in-vitro antitumor activity against human MOLT-4 cells. Only [Pd(Octyl-am)2Cl2] showed moderate activity. They were also tested against some gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria by measuring the values of IZ, MIC and MBC. All Pd(II) complexes displayed comparable activity with that of cefazoline as standard antibiotics. To clarify the mode of interaction between these compounds and CT-DNA and (BSA), their interaction behavior was checked using electronic absorption spectroscopy. Results indicated that all of the above mentioned Pd(II) complexes effectively interacted with CT-DNA and BSA at low concentration and the distance between the interacted Pd(II) complexes and BSA were in the range of 3.00–3.30 nm. Fluorescence emission studies revealed that the complexes quenched CT-DNA pretreated with methylene blue (MB) and the intrinsic fluorescence of BSA through static quenching procedure. Using the binding constant (K b) obtained from fluorescence studies, thermodynamic parameters (ΔG°, ΔH° and ΔS°) suggested that hydrogen bonding and van der Waals forces, as well as hydrophobic interaction, play the major role between metal complexes with CT-DNA and BSA. In all cases the binding forces were spontaneous owing to –ΔG°. Communicated by Ramaswamy H. Sarma

Transition Metal Cooperative Lewis Pairs Using Platinum(0) Diphosphine Monocarbonyl Complexes as Lewis bases

The platinum(0)-diphosphine complex [Pt(CO)(L1)] (3, where L1 = 1,2-C6H4(CH2PtBu2)2) and its diphosphinite analogue [Pt(CO)(L2)] (11, where L2 = 1,2-C6H4(OPtBu2)2) act as Lewis bases in conjunction with the main group Lewis acid B(C6F5)3 to form frustrated or cooperative Lewis pairs. These systems activate dihydrogen, ethene/carbon monoxide, and phenylacetylene, leading to products that depend on the exact ligand used. These subtle changes to ligand structure influence reactivity, most notably in hydrogen activation where a variety of dinuclear species of the type [(diphos)Pt(μ-H)3Pt(diphos)]+ or [(diphos)Pt(μ-H)(μ-CO)Pt(diphos)]+ are observed. Activation of ethene with the Lewis pair leads to a previously reported coupling product and the mechanism is probed. The basicity of [Pt(CO)(L)] is demonstrated by deprotonation of phenylacetylene. Preliminary studies with an analogous palladium complex [Pd(CO)(L1)] 33 suggests related chemistry may be exploited for this metal. These results provide further examples of cooperative Lewis pair behavior in which one of the components is based on a transition metal complex.

Redox, transmetalation, and stacking properties of tetrathiafulvalene-2,3,6,7-tetrathiolate bridged tin, nickel, and palladium compounds.

Here we report that capping the molecule TTFtt (TTFtt = tetrathiafulvalene-2,3,6,7-tetrathiolate) with dialkyl tin groups enables the isolation of a stable series of redox congeners and facile transmetalation to Ni and Pd. TTFtt has been proposed as an attractive building block for molecular materials for two decades as it combines the redox chemistry of TTF and dithiolene units. TTFttH4, however, is inherently unstable and the incorporation of TTFtt units into complexes or materials typically proceeds through the in situ generation of the tetraanion TTFtt4−. Capping of TTFtt4− with Bu2Sn2+ units dramatically improves the stability of the TTFtt moiety and furthermore enables the isolation of a redox series where the TTF core carries the formal charges of 0, +1, and +2. All of these redox congeners show efficient and clean transmetalation to Ni and Pd resulting in an analogous series of bimetallic complexes capped by 1,2-bis(diphenylphosphino)ethane (dppe) ligands. Furthermore, by using the same transmetalation method, we synthesized analogous palladium complexes capped by 1,1′-bis(diphenylphosphino)ferrocene (dppf) which had been previously reported. All of these species have been thoroughly characterized through a systematic survey of chemical and electronic properties by techniques including cyclic voltammetry (CV), ultraviolet-visible-near infrared spectroscopy (UV-vis-NIR), electron paramagnetic resonance spectroscopy (EPR), nuclear magnetic resonance spectroscopy (NMR) and X-ray diffraction (XRD). These detailed synthetic and spectroscopic studies highlight important differences between the transmetalation strategy presented here and previously reported synthetic methods for the installation of TTFtt. In addition, the utility of this stabilization strategy can be illustrated by the observation of unusual TTF radical–radical packing in the solid state and dimerization in the solution state. Theoretical calculations based on variational 2-electron reduced density matrix methods have been used to investigate these unusual interactions and illustrate fundamentally different levels of covalency and overlap depending on the orientations of the TTF cores. Taken together, this work demonstrates that tin-capped TTFtt units are ideal reagents for the installation of redox-tunable TTFtt ligands enabling the generation of entirely new geometric and electronic structures.

Synthesis, crystal structure and intermolecular contacts in trans-bis(ethylamine) dichloro platinum(II) and palladium(II) complexes

The methods of synthesis of trans-bis(ethylamine)dichloro platinum(II) (trans-[Pt(C2H5NH2)2Cl2]) and palladium(II) (trans-[Pd(C2H5NH2)2Cl2]) complexes for obtaining monophase products were developed. For substance characterizations FTIR spectroscopy, thermogravimetric and X-ray diffraction analysis were used. The crystal structures of the synthesized compounds were determined using X-ray powder diffraction technique. The neutral complexes had specific system of intermolecular contacts in the crystals that allowed distinguishing two forms, A and B. Despite of the similar structure and sizes, trans-[Pt(C2H5NH2)2Cl2] and trans-[Pd(C2H5NH2)2Cl2] complexes created different hydrogen bond networks and crystal structures. The first had a grid topology of 36 with the cells from three and the second - 44 from four complexes. It resulted in different thermal behavior. Trans- [Pt(C2H5NH2)2Cl2]-A demonstrated irreversible solid state transition into B-form at 165 °C and got new H-bond system with the topology similar to the palladium analog (44), however, the realized complex arrangement was significantly different. The structure of B-form was stable until the decomposition at 220°С. High-temperature X-ray diffraction demonstrated high elasticity of the H-bond network in trans-[Pd(C2H5NH2)2Cl2]-A. Notwithstanding significant alterations during heating, the H-bond system returns the structure to its initial state.The interpretation of structural transformation was proposed. The H-bond network formation was influenced by the dynamic properties of the molecules. For the platinum compound, the option with more dense molecular packing occurred. For palladium, the atomic mass distribution was responsible for a larger molecular volume and for a more symmetrical packing. Thermal decomposition of both compounds occurred with simultaneous separation of the halogen and amminoalkyl particles resulting in a low-temperature reduction of the metal and the formation of nanoparticles with sizes in the range of 5–10 nm. For the palladium compound, the decay in vacuum had a noticeable rate already at 100 °C.