Fine tuning RhII complexes with tethered, axial coordination: structural studies and application to diazo-mediated cyclopropanation reactions

The cyclopropane moiety is an attractive synthetic target due to its application in pharmaceuticals and medicinal research. One effective strategy involves the formation of metal carbenoid species from diazo reagents. The carbenoid then reacts with an olefin substrate to generate the cyclopropane ring. Of the metal complexes that can facilitate this reaction, dirhodium(II) paddlewheel complexes are arguably the most prevalent catalysts. This is because modification of the bridging ligands enables control to be exerted over the catalyst’s chemoselectivity and enantioselectivity. Exploiting the axial site as a control element is often overlooked as strongly coordinated Lewis bases inhibit catalysis. Despite this, Lewis base additives have been observed to increase enantioinduction in cyclopropanation reactions and axial coordination has been suggested as a possible explanation. However, leveraging axial coordination as a control element remains a problem due to the difficulty of controlling the coordination of exogenous ligand. The goal of my research is the development of heteroleptic dirhodium(II) paddlewheel complexes with tethered thioether ligands that are capable of axial coordination. Tethering of the Lewis base anchors the thioether proximal to the axial site to provide control over axial coordination. Solid and solution-state characterization indicated that axial coordination was present as part of a rapid equilibrium. The electrochemical analysis demonstrated the ability of different thioethers to modulate the electrophilicity of the complex. These complexes were then tested as catalysts in the cyclopropanation of olefins and diazo reagents. It was shown that the novel complexes were better suited for more reactive diazo reagents and afforded higher yields than control catalysts

A water soluble Ni-Schiff base complex for homogeneous green catalytic C S cross-coupling reactions

Since the embarkation of C – S cross-coupling from aryl halides with thiols a handful of works have been contemplated in aqueous medium. Herein, we report an example of a water soluble Ni-Schiff base complex as the green catalyst for the synthesis of thioethers. We have synthesized a Ni-Schiff base complex [NiL(H2O)2 ](ClO4)2 using N 4 -donor Schiff base ligand (1,3-bis(((E)-pyridin-2-ylmethylene)amino)propan-2-ol) and characterized by single crystal X-ray diffraction (SC-XRD) study along with different spectral analyses. The complex is mono-nuclear and cationic in nature having two perchlorate anions. Two water molecules remain coordinated with the Ni(II)-centre. The hydrogen bonding interaction through coordinated water and perchlorate anions connect the monomeric units to form 2D supramolecular structure. Based on its aqueous solubility, the complex has been used for the catalytic C – S cross-coupling reaction between aryl iodide and aryl or alkyl thiols using TBAB at 60 ◦ C in aqueous media (yield 92%). At room temperature, an isolated yield of 57% can be achieved. This environmentally benign protocol is paramount in view of the environmental sustainability

Competitor analysis of functional group H-bond donor and acceptor properties using the Cambridge Structural Database.

Intermolecular interactions found in the Cambridge Structural Database (CSD) are analysed as the outcomes of competitions between the different functional groups that are present in each structure: the most energetically favourable interactions are expected to win more often than weaker interactions. Tracking winners and losers through each crystal structure in the CSD provides data that can be analysed using paired comparison algorithms to rank functional group H-bonding properties based on how frequently they outcompete other functional groups in the crystal. This treatment is superior to simple statistical analyses of whether functional groups H-bond or not, because the distribution of H-bond donors and acceptors in the structures of the molecules found in the CSD is non-random. Most organic molecules contain more acceptors than donors, so that all H-bond donors are almost always H-bonded in all crystal structures, and most acceptors are not. The rankings of H-bond acceptors obtained by applying the TrueSkill paired comparison algorithm to the CSD agree well with the corresponding experimentally determined solution phase H-bond acceptor parameters β, but there is insufficient data to corroborate H-bond donor rankings calculated in the same way. The method is used to make predictions of the H-bond acceptor properties of functional groups for which solution phase measurements are not available.Engineering and Physical Sciences Research Council, Cambridge Crystallographic Data Centr

Komplexchemie perhalogenierter Cyclopentadiene und Alkine

(1,2,3,4,5)Pentachlorferrocen reagiert mit Butyllithium und anschließend mit MeSSMe zu [C5Cl4(SMe)]FeCP (Cp = η5-C5H5) (1). Durch Wiederholung dieser Prozedur lassen sich [C5Cl3(SMe)2]FeCp (2) und [C5Cl2(SMe)3]FeCp (3) erhalten. Eine Kristallstrukturanalyse von 2 zeigt eine 1,3-Anordnung der beiden SMe-Gruppen. Eine Anzahl unsymmetrischer Cymantrenbis- und tristhioether (4–6) wurde auf ähnliche Weise aus [C5Cl4(SR)]Mn(CO)3 bzw. [C5Cl3(SR)2]Mn(CO)3 (R = Me, Ph) dargestellt. Auch Cymantrenyl-Selenoether [C5Cl5−n(SeR)n]Mn(CO)3 (7–10) (R = Me, n = 1, 2, 3; R = Ph, n = 2) konnten erhalten werden

Investigating the Effects of Tethered, Axial Lewis Base Coordination on Rhodium(II) Paddlewheel Complexes

Dirhodium(II) paddlewheel complexes are highly renowned for their use in diazo decomposition to form a metallic-carbenoid species. This species has been used for a diverse range of chemical transformations including cyclopropanation, cycloproprenation, C-H functionalization, and X-H (Si, S, O, N) insertion reactions. Modulation of these catalysts traditionally involve the exchange of bridging ligands which have profound effects on the catalyst’s reactivity, chemo, and enantioselectivity. Recent interest has turned towards to modifying the axial sites present in the complex as an additional means of modulating catalytic activity. These sites normally serve as the active site of the catalyst, but coordination of Lewis Bases one of the sites are known to be beneficial to chemo and enantioselectivity. However, a main problem encountered in this field is the lack of control of coordination to axial site. This work aims to examine the development of novel ligands containing a pendant chain containing a Lewis base, and their incorporation into the rhodium(II) paddlewheel scaffold. Incorporation of these tether containing ligands allows for more direct control of the location of the Lewis base and effectively increasing the local concentration of the Lewis base near the active site. Ligands derived from amino acids that contained either a phosphite or a thioether moiety were synthesized and attempts to exchange onto the rhodium complex were investigated. Exchange of the phosphite containing ligands was unsuccessful due to problems with oxidation. The thioether ligands proved to be more robust in comparison with successful exchange on to the catalyst scaffold with a variety of thioether derivatives. Evaluation of these complexes in Si-H insertion and cyclopropanation reactions revealed that the presence of the tethered thioether does indeed provide a positive benefit, with increase yields as compared to a control with no tethered thioether additive

Platinum(0)-η2-1,2-(E)ditosylethene Complexes Bearing Phosphine, Isocyanide and N-Heterocyclic Carbene Ligands: Synthesis and Cytotoxicity towards Ovarian and Breast Cancer Cells

A wide range of platinum(0)-η2-(E)-1,2-ditosylethene complexes bearing isocyanide, phosphine and N-heterocyclic carbene ancillary ligands have been prepared with high yields and selectivity. All the novel products underwent thorough characterization using spectroscopic techniques, including NMR and FT-IR analyses. Additionally, for some compounds, the solid-state structures were elucidated through X-ray diffractometry. The synthesized complexes were successively evaluated for their potential as anticancer agents against two ovarian cancer cell lines (A2780 and A2780cis) and one breast cancer cell line (MDA-MB-231). The majority of the compounds displayed promising cytotoxicity within the micromolar range against A2780 and MDA-MB-231 cells, with IC50 values comparable to or even surpassing those of cisplatin. However, only a subset of compounds was cytotoxic against cisplatin-resistant cancer cells (A2780cis). Furthermore, the assessment of antiproliferative activity on MRC-5 normal cells revealed certain compounds to exhibit in vitro selectivity. Notably, complexes 3d, 6a and 6b showed low cytotoxicity towards normal cells (IC50 > 100 μM) while concurrently displaying potent cytotoxicity against cancer cells

A fused poly(truncated rhombic dodecahedron)-containing 3D-coordination polymer : a multifunctional material with exceptional properties

Abstract : The design of new and inexpensive metal-containing functional materials is of great interest. Herein is reported a unique thermochromic near-IR emitting coordination polymer, 3D- [Cu8I8(L1)2]n, CP2, which isformed when ArS(CH2)4SAr (L1, Ar = 4-C6H4OMe) reacts with 2 eq. of CuI in EtCN. In MeCN, CP1 ([Cu4I4(L1)(MeCN)2]n, consisting of an alternating [-Cu4I4-L1- Cu4I4-L1-]n chain where the Cu4I4 cubane units bears two metal-bound MeCN molecules, is formed. Heat-driven elimination of these MeCN’s in solid CP1 also leads to CP2 through a predisposed organisation of the Cu4I4 units prone to fusion after MeCN eliminations (i.e. a rare case of template effect). The CP2 structure exhibits parallel 1D-(Cu8I8)n chains, (z-axis; designated 1D-[CuI]n) as secondary building units (SBU) held together by parallel thioether ligands (x,y-axes) forming a non-porous 3D-network. The structure of this1D-[CuI]n SBU is unprecedented and consists of a series of fused and twisted open Cu4I4 cubanes forming a fused poly(truncated rhombic dodecahedron). Unexpectedly, the compact 3D CP2 exhibits a solid-tosolid phase transition at 100°C and a hysteresis of ~20 °C. CP1 emits intensively (298K: emi = 564 nm; e = 0.35) while CP2 presents a strongly red-shifted weaker emission (298K: emi ~ 740 nm, e < 0.0001). Moreover, CP2, which is stable over long periods of time, exhibits thermochromism where the emission intensity of the near-IR band decreases significantly at the benefit of a ligand-centred phosphorescence at 415 nm. Altogether these properties listed above makes CP2 exceptional. The low-energy singlet and triplet excited states have been assigned to ligand/metal-to-ligand charge transfer based on DFT and TD-DFT computations

Properties and applications of copper halide-chalcogenoether and -chalcogenone networks and functional materials

Abstract : When copper(I) halide salts react with various mono- and poly-chalcogenoether and -chalcogenone ligands, two general shapes of neutral polynuclear CuxXxEy species (E = S, Se, Te; X = Cl, Br, I; x = 2-8) are formed within the resulting 0-3D coordination materials. These polymetallic forms exhibit either globular and quasi-planar motifs, mainly closed cubane Cu4I4S4 and rhomboid Cu2X2S4, respectively, but not exclusively. Depending on the shape of these polynuclear species and the dimensionality of the network, their properties and applications are profoundly different. These materials include luminescent and electroactive materials, small molecules sensing, thermo-, electro- and photocatalysts, therapeutic and antibacterial species, electrically conducting solids, solar cells and light emitting diodes, and functional and stimuli-responsive materials (such as self-healing). Specific properties such as occurrence of solid-to-solid phase transition and thermo- and mechano-chromism have also been observed. This work summarizes these properties and applications and presents their current research directions