The reductive activation of CO2 across a Ti═Ti double bond: synthetic, structural, and mechanistic studies

[Image: see text] The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti(2)Pn(†)(2) (1) (Pn(†) = 1,4-{Si(i)Pr(3)}(2)C(8)H(4)) with CO(2) is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO(2) reaction is performed at −78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO(2) molecule bound symmetrically to the two Ti centers in a μ:η(2),η(2) binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO(2) is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a μ-O dimer in which the Ti–Ti bond has been cleaved and one pentalene ligand binds in an η(8) fashion to each of the formally Ti(III) centers. The molecular structure of 7 shows a “side-on” bound carbonyl ligand. Bonding of the double-sandwich species Ti(2)Pn(2) (Pn = C(8)H(6)) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO(2) reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-Ti(III) species to yield di-Ti(II) and di-Ti(IV) products. 1 forms a structurally characterized, thermally stable CS(2) adduct 8 that shows symmetrical binding to the Ti(2) unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(μ-S) mono(CO) species 10. Ph(3)PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(μ-S) complex 11 with a double-sandwich structure and bis(μ-S) dimer 12 in which the Ti–Ti bond has been cleaved

Temperature dependent CO2 behavior in microporous 1-D channels of a metal-organic framework with multiple interaction sites

The MOF with the encapsulated CO2 molecule shows that the CO2 molecule is ligated to the unsaturated Cu(II) sites in the cage using its Lewis basic oxygen atom via an angular eta(1)-(O-A) coordination mode and also interacts with Lewis basic nitrogen atoms of the tetrazole ligands using its Lewis acidic carbon atom. Temperature dependent structure analyses indicate the simultaneous weakening of both interactions as temperature increases. Infrared spectroscopy of the MOF confirmed that the CO2 interaction with the framework is temperature dependent. The strength of the interaction is correlated to the separation of the two bending peaks of the bound CO2 rather than the frequency shift of the asymmetric stretching peak from that of free CO2. The encapsulated CO2 in the cage is weakly interacting with the framework at around ambient temperatures and can have proper orientation for wiggling out of the cage through the narrow portals so that the reversible uptake can take place. On the other hand, the CO2 in the cage is restrained at a specific orientation at 195 K since it interacts with the framework strong enough using the multiple interaction sites so that adsorption process is slightly restricted and desorption process is almost clogged.ope

Vektorielle Katalyse mit oberflächenverankerten nano‐metallorganischen Gerüsten in mikrofluidischen Reaktoren

Vektorielle Katalyse – die Steuerung von mehrstufigen Reaktionen in einer programmierten Abfolge und durch definierte räumliche Lokalisierung in einem mikroskaligen Reaktor – ist ein grundlegendes Ziel in der bioinspirierten Katalyseforschung. Die Übertragung von Konzepten aus der natürlichen Kaskaden-Biokatalyse zu künstlichen hierarchischen chemischen Systeme bleibt jedoch eine Herausforderung. Hier zeigen wir die Integration von zwei verschiedenen oberflächenverankerten, nanometergroßen metallorganischen Gerüsten (MOFs) in einem mikrofluidischen Reaktor zur Modellierung der vektoriellen Katalyse. Die Katalysatoren wurden an definierten Abschnitten entlang des Mikrokanals immobilisiert, dies ermöglichte eine zweistufige Kaskadenreaktion mit vollständiger Umsetzung nach 30 Sekunden und hohen Umsatzfrequenzen (TOF≈105 h−1)

Organometallic Synthesis of β\beta-CoAl Nanoparticles and β\beta-CoAl/Al Nanoparticles and Their Behaviour upon Air Exposure

Nanocolloids of the intermetallic beta-CoAl phase were prepared by a soft organometallic route. They were fully characterized by (HR)TEM, EDX, WAXS, XAS and SQUID magnetometry. Their exposure to air led to an increased saturation magnetization in agreement with Co/Al segregation and the formation of Co/Al(2)O(3) nanocomposite. Furthermore, the beta-CoAl nanoparticles could be used as seeds to grow an aluminum overlayer, which passivated the alloyed core against oxidation. These nanoparticles yielded stable colloidal solutions in aromatic solvents

Ruthenium nanoparticles inside porous Zn4O(bdC)(3) by hydrogenolysis of adsorbed Ru(cod)(cot): A solid-state reference system for surfactant-stabilized ruthenium colloids

The gas-phase loading of Zn4O(bdc)(3) (MOF-5; bdc = 1,4-benzenedicarboxylate) with the volatile compound Ru(cod)(cot) (cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) was followed by solid-state C-13 magic angle spinning (MAS) NMR spectroscopy. Subsequent hydrogenolysis of the adsorbed complex inside the porous structure of MOF-5 at 3 bar and 150 degrees C was performed, yielding ruthenium nanoparticles in a typical size range of 1.5-1.7 nm, embedded in the intact MOF-5 matrix, as confirmed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and X-ray absorption spectroscopy (XAS). The adsorption of CO molecules on the obtained Ru@MOF-5 nanocomposite was followed by IR spectroscopy. Solid-state 2 H NMR measurements indicated that MOF-5 was a stabilizing support with only weak interactions with the embedded particles, as deduced from the surprisingly high mobility of the surface Ru-D species in comparison to surfactant-stabilized colloidal Ru nanoparticles of similar sizes. Surprisingly, hydrogenolysis of the Ru(cod)(cot)(3.5)@MOF-5 inclusion compound at the milder condition of 25 degrees C does not lead to the quantitative formation of Ru nanoparticles. Instead, formation of a ruthenium-cyclooctadiene complex with the arene moiety of the bdc linkers of the framework takes place, as revealed by 13C MAS NMR, PXRD, and TEM