Functionalized Carborane Complexes of the [M(CO)2(NO)]2+ Core (M = 99mTc, Re): A New Class of Organometallic Probes for Correlated in Vitro and in Vivo Imaging

The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology

Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.

Synthesis and Reactivity of Cyclic Oxonium Derivatives of nido-Carborane: A Review

Nucleophilic ring-opening reactions of cyclic oxonium derivatives of anionic boron hydrides are a convenient method of their modification which opens practically unlimited prospects for their incorporation into various macro- and biomolecules. This contribution provides an overview of the synthesis and reactivity of cyclic oxonium derivatives of nido-carborane as well as half-sandwich complexes based on it.

Microwave-Assisted Synthesis of Organometallic Rhenium (I) Pentylcarbonato Complexes: New Synthon for Carboxylato, Sulfonato and Chlorido Complexes

Tricarbonylrhenium(I)(α-diimine) complexes are of importance because of their strong cytotoxic and fluorescence properties. Syntheses of such complexes were achieved through a two-step process. First, the pentylcarbonato complexes, fac-(CO)₃(α-diimine)ReOC(O)OC₅H₁₁ were synthesized through a microwave-assisted reaction of Re₂(CO)₁₀, α-diimine, 1-pentanol and CO₂ in a few hours. Second, the pentylcarbonato complexes are treated with carboxylic, sulfonic and halo acids to obtain the corresponding carboxylato, sulfonato and halido complexes. This is the first example of conversion of Re₂(CO)₁₀ into a rhenium carbonyl complex through microwave-assisted reaction.

Expanding the Scope of Palladium-Catalyzed B - N Cross-Coupling Chemistry in Carboranes

Over the past several years, a number of strategies for the functionalization of dicarba-closo-dodecaboranes (carboranes) have emerged. Despite these developments, B - N bond formation on the carborane scaffold remains a challenge due to the propensity of strong nucleophiles to partially deboronate the parent closo-carborane cluster into the corresponding nido form. Here we show that azide, sulfonamide, cyanate, and phosphoramidate nucleophiles can be straightforwardly cross-coupled onto the B(9) vertices of the o- and m-carborane core from readily accessible precursors without significant deboronation by-products, laying the groundwork for further study into the utility and properties of these new B-aminated carborane species. We further showcase select reactivity of the installed functional groups highlighting some unique features stemming from the combination of the electron-donating B(9) position and the large steric profile of the B-connected carborane substituent.

Neutral Rhenadicarbaboranes with Re(CO)2(NO) Vertices: A Theoretical Study of Building Blocks for Rhenacarborane-Based Drug Delivery Agents

The rhenadicarbaborane carbonyl nitrosyls (C₂B_n−3H_n−1)Re(CO)₂(NO), (n = 8 to 12), of interest in drug delivery agents based on the experimentally known C₂B₉H₁₁Re(CO)₂(NO) and related species, have been investigated by density functional theory. The lowest energy structures of these rhenadicarbaboranes are all found to have central ReC₂B_n−3 most spherical closo deltahedra in accord with their 2n + 2 Wadean skeletal electrons. Carbon atoms are found to be located preferentially at degree 4 vertices in such structures. Furthermore, rhenium atoms are preferentially located at a highest degree vertex, typically a vertex of degree 5. Only for the 9-vertex C₂B₆H₈Re(CO)₂(NO) system are alternative isocloso deltahedral isomers found within ~8 kcal/mol of the lowest energy closo isomer. Such 9-vertex isocloso structures provide a degree 6 vertex for the rhenium atom flanked by degree 4 vertices for each carbon atom.

Metal complexes containing natural and and artificial radioactive elements and their applications

Recent advances (during the 2007–2014 period) in the coordination and organometallic chemistry of compounds containing natural and artificially prepared radionuclides (actinides and technetium), are reviewed. Radioactive isotopes of naturally stable elements are not included for discussion in this work. Actinide and technetium complexes with O-, N-, N,O, N,S-, P-containing ligands, as well π-organometallics are discussed from the view point of their synthesis, properties, and main applications. On the basis of their properties, several mono-, bi-, tri-, tetra- or polydentate ligands have been designed for specific recognition of some particular radionuclides, and can be used in the processes of nuclear waste remediation, i.e., recycling of nuclear fuel and the separation of actinides and fission products from waste solutions or for analytical determination of actinides in solutions; actinide metal complexes are also usefulas catalysts forcoupling gaseous carbon monoxide, as well as antimicrobial and anti-fungi agents due to their biological activity. Radioactive labeling based on the short-lived metastable nuclide technetium-99m (^99mTc) for biomedical use as heart, lung, kidney, bone, brain, liver or cancer imaging agents is also discussed. Finally, the promising applications of technetium labeling of nanomaterials, with potential applications as drug transport and delivery vehicles, radiotherapeutic agents or radiotracers for monitoring metabolic pathways, are also described.

Multimodal radio- (PET/SPECT) and fluorescence imaging agents based on metallo-radioisotopes: current applications and prospects for development of new agents

This perspective focuses on complexes of radioactive metal ions applied in multimodal radio- and optical imaging. The application of metal ions in radioimaging techniques such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) has advantages over lighter nuclei in terms of half-life, but there are particular issues related to their speciation (particularly leaching from complexes) and with the combination of certain ions with fluorescent systems. The basic coordination chemistry of the ions involved and issues relating to biological conditions and their compatibility with optical imaging techniques are reviewed, the current literature presented in context, and the prospect of exploiting the intrinsic luminescence of certain metal-ligand complexes is discussed.