Tunable hydrophobicity: Efficient air filters for the protection against chemical warfare agents might be achieved by surface functionalization of the pores in robust metal–organic frameworks (MOFs) ...with fluoroalkyl residues and the precise control of their pore size (see picture). These MOFs capture harmful volatile organic compounds even under extremely moist conditions (80 % relative humidity).
The development of protective self-detoxifying materials is an important societal challenge to counteract risk of attacks employing highly toxic chemical warfare agents (CWAs). In this work, we have ...developed bifunctional zirconium metal–organic frameworks (MOFs) incorporating variable amounts of nucleophilic amino residues by means of formation of the mixed ligand Zr6O4(OH)4(bdc)6(1–x)(bdc-NH2)6x (UiO-66-xNH 2 ) and Zr6O4(OH)4(bpdc)6(1–x)(bpdc-(NH2)2)6x (UiO-67-x(NH 2 ) 2 ) systems where bdc = benzene-1,4-dicarboxylate; bdc-NH2= benzene-2-amino-1,4-dicarboxylate; bpdc = 4,4′-biphenyldicarboxylate; bpdc-(NH2)2 = 2,2′-diamino-4,4′-biphenyldicarboxylate and x = 0, 0.25, 0.5, 0.75, 1. In a second step, the UiO-66-xNH 2 and UiO-67-x(NH 2 ) 2 systems have been postsynthetically modified by introduction of highly basic lithium tert-butoxide (LiO t Bu) on the oxohydroxometallic clusters of the mixed ligand MOFs to yield UiO-66-xNH 2 @LiO t Bu and UiO-67-x(NH 2 ) 2 @LiO t Bu materials. The results show that the combination of pre and postsynthetic modifications on these MOF series gives rise to fine-tuning of the catalytic activity toward the hydrolytic degradation of both simulants and real CWAs in unbuffered aqueous solutions. Indeed, UiO-66-0.25NH 2 @LiO t Bu is able to hydrolyze both CWAs simulants (diisopropylfluorophosphate (DIFP), 2-chloroethylethylsulfide (CEES), and real CWAs (soman (GD), sulfur mustard (HD)) quickly in aqueous solution. These results are related to a suitable combination of robustness, nucleophilicity, basicity, and accessibility to the porous framework.
The vast range of reactions mediated by titanocene monochloride (Cp2TiCl, the Nugent reagent) in organic synthetic chemistry is reviewed. The power of the Nugent reagent in organic chemistry is ...demonstrated by its ability to promote and/or catalyse several efficient transformations under mild reaction conditions in the presence of several functional groups, in an environmentally friendly manner and with use of simple experimental procedures.
The different reactions promoted and/or catalysed by the Nugent reagent, a contemporary single‐electron transfer agent, are reported. The combination of radical intermediates and transition‐metal catalysis is an excellent tool for the development of new and efficient synthetic procedures.
Preparation, EPR analysis, and advantages in green organic chemistry of CpTiCl2, an improved single‐electron transfer catalyst, are reported. Under mild conditions, this organometallic complex ...provides excellent yields of homoallylic and homopropargylic alcohols in Barbier‐type allylation and propargylation reactions. Moreover, in the presence of a bidentate BOX ligand, Barbier‐type cyclization reactions catalyzed by CpTiCl2 can be carried out in an enantioselective manner.
CpTiCl2, an improved titanocene(III) single‐electron transfer catalyst, under mild conditions provides excellent yields of homoallylic and homopropargylic alcohols in Barbier‐type allylation and propargylation reactions. Moreover, in the presence of a BOX ligand, it was capable of catalyzing enantioselective intramolecular allylations and propargylations (cyclizations) of ketones.
The alkyne functional group is found in many bioactive natural products and is the key to many important chemical transformations developed over recent years. Moreover, allenes have recently gained ...relevance as versatile reagents in organic synthesis. Mild, catalytic methods to enable the selective introduction of either alkyne or allene motifs into organic molecules are very valuable but, as yet, quite scarce. We describe an extremely mild and selective method for either the propargylation or allenylation of carbonyl compounds catalyzed by the abundant, safe, and inexpensive metal titanium. These reactions can selectively provide homopropargylic alcohols from aldehydes and ketones or α‐hydroxy‐allenes from aldehydes. The mechanisms involved were also investigated.
Effectiveness, selectivity, and sustainability are key properties of this novel method for Ti‐catalyzed Barbier‐type propargylation/allenylation. The reaction proceeds at RT under mild conditions compatible with numerous functional groups and affords homopropargylic alcohols from aldehydes and ketones and α‐hydroxy‐allenes from aldehydes (see scheme).
C2H2/CO2 separation is a highly challenging process as a consequence of their similar physicochemical properties. In this work we have explored, by static and dynamic gas sorption techniques and ...computational modelling, the suitability of a series of two isoreticular robust Ni(II)pyrazolate‐based MOFs, bearing alkyne moieties on the ligand backbones, for C2H2/CO2 separation. The results are consistent with high adsorption capacity and selectivity of the essayed systems towards C2H2 molecules. Furthermore, a post‐synthetic treatment with KOH ethanolic solution gives rise to linker vacancy defects and incorporation of extraframework potassium ions. Creation of defects is responsible for increased adsorption capacity for both gases, however, strong interactions of the cluster basic sites and extraframework potassium cations with CO2 molecules are responsible for a lowering of C2H2 over CO2 selectivity.
Robust defective nickel(II) pyrazolate‐based MOFs, bearing alkyne moieties on the organic spacers have been explored for C2H2/CO2 separation. As proven by static and dynamic gas adsorption and computational modelling the non‐defective34 systems give rise to selective interactions with C2H2 over CO2 as a result of a mixture of pore confinement and H‐bonding and alkyne‐alkyne interactions. Creation of defects is responsible for strong interactions of cluster basic sites and extraframework potassium cations with CO2 with a concomitant lowering of C2H2 over CO2 selectivity.
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.
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.
Mild allene synthesis: Ti, an abundant, safe and ecofriendly metal, is capable of catalyzing the one‐step synthesis of exocyclic allenes from propargyl halides. This method affords a new retrosynthetic disconnection in the α position of an exocyclic allene (see scheme).
The highly porous and robust Ni(8)(OH)(4)(OH(2))(2)(4,4'-(buta-1,3-diyne-1,4-diyl)bispyrazolato)(6)(n) MOF can be used as a proof of concept for the incorporation and release of the non-conventional ...Ru(p-cymene)Cl(2)(pta) RAPTA-C metallodrug.
A novel concept for the synthesis of halogenated, conjugated dienes is disclosed: the CpTiCl2‐catalyzed coupling of keto‐alkynes, in the presence of Me3SiBr/Et3N⋅HBr. This reaction provided five‐, ...six‐, and seven‐membered carbocycles, nitrogenated heterocycles, as well as six‐membered oxygenated heterocycles leading to a brominated conjugate diene. These products showed high reactivity in the Diels–Alder, Suzuki, and Sonogashira reactions, giving complex chemical structures in only three steps from the corresponding acyclic keto‐alkyne. Hopefully, this strategy will pave the way towards the synthesis of bioactive natural products and new materials.
Synthesis of bicyclic product III, from acyclic keto‐alkyne I, catalyzed by CpTiIIICl2, followed by a Diels–Alder cycloaddition provided III in an acceptable overall yield. Ten CpTiIIICl2‐catalyzed cyclizations and seven Diels–Alder reactions are reported. Moreover, seven and five examples of the Suzuki and Sonogashira cross‐couplings with halogenated dienes obtained from the above cyclizations are also described.
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