Natalia M. Padial

Highly Hydrophobic Isoreticular Porous Metal-Organic Frameworks for the Capture of Harmful Volatile Organic Compounds

The release of toxic pollutants into the environment, which includes oil spills, leaks of harmful industrial products, and the deliberate emission of chemical warfare agents is a risk of growing concern. Worthy of note, oil spill cleanups amount to over 10 billion dollars annually. Remediation of these environmental problems involves the use of large amounts of adsorbents such as sand, activated carbons, or zeolites. However, the effectiveness of such adsorbents is often limited by their affinity to moisture. Consequently, the search for highly hydrophobic porous materials to be used as suitable stopgap of harmful organics spills has become of paramount importance. In the past years, porous metal–organic frameworks (MOFs) have been extensively studied to explore their possible applications in near future technologies for the safe storage of energetically and environmentally relevant gases. The tunable nature of their pores might be beneficial also in cushioning environmental problems caused by the release of harmful volatile organic compounds (VOCs). A remarkable example of the design amenability of MOFs is the well-known isoreticular [Zn4OL3] series (L= arene-dicarboxylate), wherein the size and the functionality of the pores can be modulated in a highly rational and systematic way. Nevertheless, the advantageous structural features of this family of MOFs are readily hampered by its high sensitivity to moisture, which limits its practical applications. A similar size-scaling approach has been applied by Lillerud and coworkers on the isoreticular [Zr6O4(OH)4L6] series, [9] evidencing that a significant improvement in the stability of the material can be achieved with an appropriate combination of dicarboxylate linkers and oxophylic metal fragments. Alternately, it is possible to take advantage of the enhanced stability imparted by polyazolate-containing ligands in combination with borderline metal ions. Accordingly, we designed and isolated an isoreticular series of porous MOFs, the pore size and polarity of which was modulated by coupling stiff bi-pyrazolate or mixed pyrazolate/carboxylate linkers (Scheme 1) to Ni hydroxo clusters acting as 12-connected

Ti-Catalyzed Straightforward Synthesis of Exocyclic Allenes

Exocyclic allenes constitute useful building blocks in organic synthesis and have recently been identified as key intermediates in the synthesis of natural products. Here the first general method for the most straightforward synthesis of exocyclic allenes reported to date is presented. This method is based on the Barbier-type cyclization of propargyl halides catalyzed by titanium; a safe, abundant, and ecofriendly metal. The reaction proceeds under mild conditions compatible with different functional groups and provides good yields of five-, six-, and seven-membered carbocycles and nitrogen-containing heterocycles bearing an exocyclic allene group. Experimental evidence supporting the proposed reaction mechanism is also provided. Moreover, this procedure can be carried out in an enantioselective manner by using chiral titanocene(III) catalysts. The utility of this method has been proved in the synthesis of the natural alkaloid stemoamide.

Hydrogen Atom Donors: Recent Developments

This review highlights recent developments in the field of hydrogen atom transfer (HAT) reagents that circumvent the disadvantages of classical group 14 reagents, such as Bu₃SnH. Special emphasis is laid on the lowering of bond dissociation energies (BDEs) of molecules that could, as yet, not be used as HAT reagents and on the use of organometallic HAT reagents.

Synthesis of (±)-aureol by bioinspired rearrangements.

A bioinspired and sustainable procedure for the straightforward synthesis of (±)-aureol has been achieved in eight steps (14% overall yield) from epoxyfarnesol. The key steps are the titanocene(III)-catalyzed radical cascade cyclization of an epoxyfarnesol derivative and a biosynthetically inspired sequence of 1,2-hydride and methyl shifts.

Selective reduction of aromatic ketones in aqueous medium mediated by Ti(III)/Mn: a revised mechanism.

An experimental study on the role played by each of the reagents involved in the selective reduction of aromatic ketones in aqueous medium is reported. In this reaction, the reduction of aromatic ketones is mediated by Cp2TiCl. Moreover, the presence of Mn in the reaction medium is mandatory. To account for these findings, a substantially revised mechanism is proposed.

A highly porous interpenetrated MOF-5-type network based on bipyrazolate linkers†

A novel cobalt(II) metal organic framework containing two interpenetrated nets with the cubic pcu-a topology of MOF-5 has been synthesized and characterized. In spite of being interpenetrated, this material exhibits a highly accessible porous structure.

Stereoselective Synthesis of Natural Products Promoted by Titanocene(III)

Abstract The use of radical reactions in organic synthesis is increasing every year. Bis(cyclopentadienil)titanium(III) chloride [Cp2TiCl] promotes and catalyzes several transformations under mild conditions compatible with several functional groups. Due to its power as a mild single-electron transfer reagent, Cp2TiCl has become a formidable tool in organic synthesis. Thus, this catalyst is being increasingly used in the synthesis of complex multifunctional molecules, mainly natural products and related compound useful in pharmacology. This chapter will include a comprehensive review of those works on Cp2TiCl-mediated synthesis of natural products published from 2006 onward, as there is a previous comprehensive review covering the subject until 2005. The biosynthetic origin of the natural products here reported has been chosen as the method to classify those molecules for which a synthesis is presented. Terpenoids constitute the class of natural products with more examples in this field (Rosales et al., 2015; Morcillo et al., 2014; Rosales et al., 2015; Fernandez-Mateos et al., 2011; Nugent et al., 1988; RajanBabu et al., 1989; RajanBabu et al., 1990; RajanBabu et al., 1994; Justicia et al., 2009; Jimenez et al., 2010) [2] , [3] , [4] , [5] , [6] , [7] , [8] followed by polyketides (Fernandez-Mateos et al., 2013; Lee et al., 1992; Dixit et al., 2007; Mori et al., 1997; Yadav et al., 2005; Mandal et al., 2010; Gansauer et al., 2009) [9] , [10] , [11] , [12] and phenylpropanoids (Garcia Santos et al., 2015; Barrero et al., 2001) [13] , [14] . Moreover, some nitrogen-containing substances have also been prepared by titanocene(III)-based methods, especially antibiotics and alkaloids (Bermejo et al., 2006; Perez Morales et al., 2013) [15,16]. Finally, new methodologies applying Cp2TiCl catalysis, which can potentially lead to complex natural products, are also shown (Gianino et al., 2014) [106d].