Niobium-silica catalysts for the selective epoxidation of cyclic alkenes: the generation of the active site by grafting niobocene dichloride.

Niobium-containing silica materials obtained by deposition via liquid-phase grafting or dry impregnation of niobocene(iv) dichloride are active and selective catalysts in the epoxidation of alkenes in the presence of aqueous hydrogen peroxide. The generation of the catalytically-active Nb species was followed step-by-step, and investigated using a combined DR-UV-Vis, NIR, Raman, XRD, XANES and EXAFS analyses. At the end of the grafting procedure, the nature of the surface active species can be described as an oxo-Nb(v) site, tripodally grafted onto the silica surface in close proximity to other Nb(v) centres.

New high-nuclearity carbonyl and carbonyl-substituted rhodium clusters and their relationships with polyicosahedral carbonyl-substituted palladium- and gold-thiolates.

A reinvestigation of the synthesis of [H(5-n)Rh(13)(CO)(24)](n-) (n = 2, 3) led to isolation of a series of Rh(19), Rh(26), and Rh(33) high-nuclearity carbonyl and carbonyl-substituted rhodium clusters. The [Rh(19)(CO)(31)](5-) (1) is electronically equivalent with [Pt(19)(CO)(22)](4-), but poor crystal diffraction data of all salts obtained to date have prevented its geometrical analysis. The structures of Rh(26)(CO)(29)(CH(3)CN)(11) (2) as 2·2CH(3)CN and [Rh(33)(CO)(47)](5-) (3) as [NEt(4)](5)[3]·Me(2)CO were determined from complete X-ray diffraction determinations.

Synthesis, structure, and spectroscopic characterization of [H(8-n)Rh22(CO)35](n-) (n = 4, 5) and [H2Rh13(CO)24{Cu(MeCN)}2](-) clusters: assessment of CV and DPV as techniques to circumstantiate the presence of elusive hydride atoms.

The previously ill-characterized [H(x)Rh(22)(CO)(35)](4-/5-) carbonyl cluster has been obtained as a byproduct of the synthesis of [H(3)Rh(13)(CO)(24)](2-) and effectively separated by metathesis of their sodium salts with [NEt(4)]Cl. Although the yields are modest and never exceed 10-15% (based on Rh), this procedure affords spectroscopically pure [H(3)Rh(22)(CO)(35)](5-) anion. Formation of the latter in mixture with other Rh clusters was also observed by electrospray ionization-mass spectrometry (ESI-MS) in the oxidation of [H(2)Rh(13)(CO)(24)](3-) with Cu(2+) salts.

Characterization of iron-carbonyl-protected gold clusters.

Ligand-stabilized nanometer-sized gold particles are interesting building blocks for molecular electronics, precursors for catalysts, optical labels for biomolecules and diagnosis, and potential nontoxic carriers for therapeutics. In this work we characterize for the first time, by means of near-infrared and Raman spectroscopy and time-dependent density functional calculations, gold clusters protected with iron-carbonyl ligands, such as {Au(22)[Fe(CO)(4)](12)}(6-) shown in the figure. Surprisingly, our results show that these novel compounds bear many analogues to another, well-studied, class of gold clusters, namely those of thiolate-monolayer-protected gold clusters.

The loss of CO from [Rh12(mu12-Sn)(CO)27]4-: synthesis, spectroscopic and structural characterization of the electron-deficient, icosahedral [Rh12(mu12-Sn)(CO)25]4- and [Rh12(mu12-Sn)(CO)26]4- tetra-anions.

Heating (80 degrees C) the electron-precise, Sn-centred, icosahedral cluster [Rh(12)Sn(CO)(27)](4-) under a nitrogen atmosphere affords in sequence the electron-deficient icosahedral [Rh(12)Sn(CO)(26)](4-) and [Rh(12)Sn(CO)(25)](4-) derivatives. The reaction is reversible in solution and the parent compound is quantitatively regenerated upon exposure to carbon monoxide. The reaction course has been unravelled via a combination of Band-target Entropy Minimization (BTEM) IR analysis and X-ray studies.

Sn-centred icosahedral Rh carbonyl clusters: synthesis and structural characterization and 13C-{103Rh} HMQC NMR studies.

The reaction of [Rh7(CO)16]3- with SnCl(2).2H2O in a 1 : 1 molar ratio under N2 results in the formation of the new heterometallic cluster, [Rh12Sn(CO)27]4-, in very high yield (ca. 86%).

Synthesis and electrochemistry of new Rh-centered and conjuncto rhodium carbonyl clusters. X-ray structure of [NEt(4)](3)[Rh(15)(CO)(27)], [NEt(4)](3)[Rh(15)(CO)(25)(MeCN)(2)] x 2MeCN, and [NEt(4)](3)[Rh(17)(CO)(37)].

A reinvestigation of the redox chemistry of [Rh7(CO)16]3- resulted in the finding of new alternative syntheses for a series of previously reported Rh-centered carbonyl clusters, i.e., [H4-nRh14(CO)25]n- (n = 3 and 4) and [Rh17(CO)30]3-, as well as new species such as a different isomer of [Rh15(CO)27]3-, the carbonyl-substituted [Rh15(CO)25(MeCN)2]3-, and the conjuncto [Rh17(CO)37]3- clusters.

New hybrid semiconductor materials based on viologen salts of bimetallic Fe-Pt and Fe-Au carbonyl clusters: first structural characterization of the diradical pi-dimer of the diethylviologen monocation and EPR evidence of its triplet state.

The synthesis, structure, spectroscopic characterization and electrical resistivity of the [EtV](2)[Fe(4)Pt(CO)(16)], [EtV][Fe(3)Pt(3)(CO)(15)].THF, [EtV][Fe(4)Au(CO)(16)](2)2.THF (EtV=1,1'-diethyl-4,4'-bipyridilium cation) and [NEt(4)](2)[Fe(4)Au(CO)(16)] is reported.

A novel family of minimal PMRI cyclic peptides as versatile scaffolds for generating new molecular topology.

The surface loops of proteins and active peptides are implicated in the activation of biological responses upon recognition by enzymes and receptors. Obviously, it is of interest to investigate these loops as potential leads for drug discovery. Currently, there is an urgent need for novel, general, and conformationally definite cyclic peptidomimetic scaffolds capable to mimic small portions of the protein surface.