Werner E. van Zyl

DITHIOPHOSPHONATES AND RELATED P/S-TYPE LIGANDS OF GROUP 11 METALS

Within the phosphor-1,1,-dithiolate class of compounds, the dithiophosphonato ligand [S2PAr(OR′)]− (typically Ar = aryl or ferrocenyl; R′ = alkyl) has emerged as an interesting choice for the preparation of a variety of new metal complexes. This review focuses on the dithiophosphonates and certain related thio species of the group 11 coinage metals, copper, silver and gold, with particular emphasis on structure and coordination modes. Amongst these three metals a rich coordination and structural chemistry had been developed and reported. For copper, a number of new complexes ranging from a single metal center, to di-, tetra-, and Cu14 clusters had been prepared. For silver, the number of reported complexes is not yet abundant but range in nuclearity from Ag2 to Ag28, which gives an indication of the potential scope. For gold, the majority of complexes are dinuclear gold(I) of the type [AuS2PR(OR′)]2 where the variety of R′ can be enormous. A few silver and gold complexes with the title ligand had also been subjected to theoretical studies. New coordination modes have also been observed, particularly in cases where previously isolated complexes have been subjected to further reaction with phosphines. Copper and silver complexes have not yet shown the rich luminescent properties as gold, and developments of the latter are described also.

Polyhydrido Copper Clusters: Synthetic Advances, Structural Diversity, and Nanocluster-to-Nanoparticle Conversion

Metal hydride clusters have historically been studied to unravel their aesthetically pleasing molecular structures and interesting properties, especially toward hydrogen related applications. Central to this work is the hydride ligand, H¯, the smallest closed-shell spherical anion known. Two new developments in polyhydrido nanocluster chemistry include the determination of heretofore unknown hydride coordination modes and novel structural constructs, and conversion from the molecular entities to rhombus-shaped copper nanoparticles (CuNPs). These advances, together with hydrogen evolution and catalysis, have provided both experimentalists and theorists with a rich scientific directive to further explore. The isolation of hexameric [{(Ph3P)CuH}6] (Stryker reagent) could be regarded as the springboard for the recent emergence of polyhydrido copper cluster chemistry due to its utilization in a variety of organic chemical transformations. The stability of clusters of various nuclearity was improved through phosphine, pyridine, and carbene type ligands. Our focus lies with the isolation of novel copper (poly)hydride clusters using mostly the phosphor-1,1-dithiolato type ligands. We found such chalcogen-stabilized clusters to be exceptionally air and moisture stable over a wide range of nuclearities (Cu7 to Cu32). In this Account, we (i) report on state-of-the-art copper hydride cluster chemistry, especially with regards to the diverse and novel structural types generally, and newly discovered hydride coordination modes in particular, (ii) demonstrate the indispensable power of neutron diffraction for the unambiguous assignment and location of hydride ligand(s) within a cluster, and (iii) prove unique transformations that can occur not only between well characterized high nuclearity clusters, but also how such clusters can transform to uniquely shaped nanoparticles of several nanometers in diameter through copper hydride reduction. The increase in the number of low- to high-nuclearity hydride clusters allows for different means by which they can be classified. We chose a classification based on the coordination mode of hydride ligand within the cluster. This includes copper clusters associated with bridging (μ2-H) and capping (μ3-H) hydride modes, followed by an interstitial (μ4-H) hydride mode that was introduced for the first time into octa- and hepta-nuclear copper clusters stabilized by dichalcogen-type ligands. This breakthrough provided a means to explore higher nuclearity polyhydrido nanoclusters, which contain both capping (μ3-H) and interstitial (μ(4-6)-H) hydrides. The presence of bidentate ligands having mixed S/P dative sites led to air- and moisture-stable copper hydride nanoclusters. The formation of rhombus-shaped nanoparticles (CuNPs) from copper polyhydrides in the presence of excess borohydrides suggests the presence of metal hydrides as intermediates during the formation of nanoparticles.

Phosphinogold(I) dithiocarbamate complexes : effect of the nature of phosphine ligand on anticancer properties

The reactions of potassium salts of the dithiocarbamates L {where L = pyrazolyldithiocarbamate (L1), 3,5-dimethylpyrazolyldithiocarbamate (L2), or indazolyldithiocarbamate (L3)} with the gold precursors [AuCl(PPh3)], [Au2Cl2(dppe)], [Au2Cl2(dppp)], or [Au2Cl2(dpph)] lead to the new gold(I) complexes [AuL(PPh3)] (1–3), [Au2L2(dppe)] (4–6), [(Au2L2)(dppp)] (7–9), and [Au2(L)2(dpph)] (10–12) {where dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane, and dpph = 1,6-bis(diphenylphosphino)hexane}. These gold compounds were characterized by a combination of NMR and infrared spectroscopy, microanalysis, and mass spectrometry; and in selected cases by single-crystal X-ray crystallography. Compounds 4–6, which have dppe ligands, are unstable in solution for prolonged periods, with 4 readily transforming to the Au18 cluster [Au18S8(dppe)6]Cl2 (4a) in dichloromethane. Compounds 1–3 and 7–12 are all active against human cervical epithelioid carcinoma (HeLa) cells, but the most active compounds are 10 and 11, with IC50 values of 0.51 μM and 0.14 μM, respectively. Compounds 10 and 11 are more selective toward HeLa cells than they are toward normal cells, with selectivities of 25.0 and 70.5, respectively. Further tests, utilizing the 60-cell-line Developmental Therapeutics Program at the National Cancer Institute (U.S.A.), showed 10 and 11 to be active against nine other types of cancers.

Mn doped ZrO2 as a green, efficient and reusable heterogeneous catalyst for the multicomponent synthesis of pyrano[2,3-d]-pyrimidine derivatives

A simple and an efficient method has been developed for the one-pot multicomponent synthesis of pyrano[2,3-d]-pyrimidine derivatives. This was achieved through the condensation reaction between dimethylbarbituric acid, aromatic aldehyde and malononitrile in the presence of a Mn/ZrO2 heterogeneous catalyst with ethanol/water mixture as solvent for only 1 hour. Further advantages of this synthesis methodology include excellent yields, mild reaction conditions, atom economy, environmentally friendliness, reusable catalyst and no need for chromatographic separations.

[Cu32(H)20{S2P(OiPr)2}12]: The Largest Number of Hydrides Recorded in a Molecular Nanocluster by Neutron Diffraction

An air- and moisture-stable nanoscale polyhydrido copper cluster [Cu32 (H)20 {S2 P(OiPr)2 }12 ] (1H ) was synthesized and structurally characterized. The molecular structure of 1H exhibits a hexacapped pseudo-rhombohedral core of 14 Cu atoms sandwiched between two nestlike triangular cupola fragments of (2×9) Cu atoms in an elongated triangular gyrobicupola polyhedron. The discrete Cu32 cluster is stabilized by 12 dithiophosphate ligands and a record number of 20 hydride ligands, which were found by high-resolution neutron diffraction to exhibit tri-, tetra-, and pentacoordinated hydrides in capping and interstitial modes. This result was further supported by a density functional theory investigation on the simplified model [Cu32 (H)20 (S2 PH2 )12 ].

Ceria–Vanadia/Silica‐Catalyzed Cascade for C−C and C−O Bond Activation: Green One‐Pot Synthesis of 2‐Amino‐3‐cyano‐4H‐pyrans

Abstract We designed a ceria–vanadia/silica (Ce–V/SiO2) heterogeneous catalyst and used it for the green and efficient synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives. The green reaction was a multicomponent one‐pot condensation of 5,5‐dimethylcyclohexane‐1,3‐dione, aromatic aldehyde, and malononitrile in an eco‐compatible solvent (ethanol). The catalyst was synthesized and fully characterized by powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analysis. The reported procedure offers a number of advantages including decreased reaction times, mild conditions, high yields, operational simplicity, and environmentally benign and simple work‐up procedures. Furthermore, the catalyst is economical, fully recyclable, and reusable for over five runs while preserving its high activity. The synthesized 2‐amino‐3‐cyano‐4H‐pyran products can later be used for pharmaceutical purposes.

Fluoro-, Fluoroalkyl-, and Heterofluorogold Complexes

Gold halides have been the most studied amongst all gold compounds, and provide some extremes with regards to oxidation state (especially for direct Au-F bonded cases), chemical topology, and reactivity. Gold complexes also incorporate a number of CF3 moieties in an effort to induce inter- or intramolecular hydrogen bonds in addition to aurophilic Au ··· Au interactions (of comparable strength to an H bond), leading to materials with different structures and properties when compared with non-fluorinated ligands. In the few rare cases where unsaturated ligands (such as ethylene) are coordinated to a gold center, such complexes seem to predominate amongst fluorinated gold complexes. This Comment attempts to describe all fluoro- and fluoroalkyl complexes of gold, an increasingly active area of research during the past decade. This work covers gold complexes that contain either a direct Au-F bond or a F-C(alkyl) bond, and excludes ligands of the type C6H5-nFn (n = 1–5), which have been previously reviewed. The few gold complexes that contain heterofluorinated ligands with F-X bonds (X˭P, Si, B, Sb, Sn, Ge) are also included.

Synthesis of triazolidine-3-one derivatives through the nanocellulose/hydroxyapatite-catalyzed reaction of aldehydes and semicarbazide

A novel nanocellulose/hydroxyapatite heterogeneous catalyst was used in the one-pot, two-component synthesis of triazolidine-3-one derivatives, produced from the cyclocondensation reaction between semicarbazide and an aromatic aldehyde. With the use of ethanol solvent, the products formed after a short reaction time (<30 min). The catalyst was characterized by XRD, TEM, SEM-EDS and BET analysis. The main advantages of this protocol were excellent yields (90–96%) of the products, mild and environmentally friendly reaction conditions, good atom-economy, and a simple and fast work-up with the added benefit of a recyclable catalyst, negating the need of chromatographic separations of the intermediates. The twelve triazolidine-3-one derivatives (3a–l) were characterized by 1H, 13C and 15N NMR, FT-IR, and HR-MS and represented a new family of compounds containing the 1,2,4-triazolidin-3-one moiety.

A hexanuclear gold(I) metallatriangle derived from a chiral dithiophosphate: synthesis, structure, luminescence and oxidative bromination reactivity

We report the synthesis, structure, luminescence and reactivity of a 27-membered gold(I) metallatriangle containing three separate dinuclear gold(I) units self-assembled from a chiral tetradentate dianionic dithiophosphate ligand. The hexanuclear complex luminesces in the solid-state (λmax = 488 nm) at 298 K. Additionally, the Au(I) complex forms an unexpected dinuclear Au(III) oxidative addition product upon reaction with Br2.

Nanocrystalline cellulose isolated from discarded cigarette filters

We report the isolation of nanocrystalline cellulose (NCC) produced from discarded cigarette filters (DCF). The DCF were processed into cellulose via ethanolic extraction, hypochlorite bleaching, alkaline deacetylation, and then converted into NCC by sulfuric acid hydrolysis. The morphological structures of the isolated NCC established with TEM showed that the nanocrystals were needle-like with a mean length of 143nm. FEGSEM showed the morphological transition of the micro-sized DCF to self-assembled NCC while EDX revealed the presence of Ti (as TiO2) in DCF, which was retained in the NCC. A NCC sample was freeze-dried and showed a specific surface area of 7.78m2/g. The crystallinity of the NCC film and freeze-dried samples were 96.77% and 94.47%, respectively. Crystallite sizes of the freeze-dried (8.4nm) and film (7.6nm) samples correlated with the mean width (8.3nm) of the NCC observed under TEM.