4 research outputs found

    Mesoionic complexes of platinum(II) derived from “Rollover” cyclometalation: a delicate balance between Pt–C(sp<sup>3</sup>) and Pt–C(sp<sup>2</sup>) bond cleavage as a result of different reaction conditions

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    “Rollover” cyclometalation is a particular case of metal-mediated C−H bond activation, and the resulting complexes constitute an emerging class of cyclometalated compounds. In the case of 2,2′-bipyridine “rollover cyclometalation” has been used to synthesize the complexes [Pt(bipy-H)(Me)(L)] (L = PPh3, PCy3, P(OPh)3, P(p-tolyl)3), whose protonation produces a series of stable corresponding pyridylenes [Pt(bipy*)(Me)(L)]+. The unusual bipy* ligand may be described as an abnormalremote heterocyclic chelated carbene or simply as a mesoionic cyclometalated ligand. These cationic species spontaneously convert in solution, through a retro-rollover reaction, to the corresponding isomers [Pt(bipy)(Me)(L)]+, where the 2,2′-bipyridine is coordinated in the classical N,N bidentate mode. Isomerization is achieved at different rates (ranging over three orders of magnitude), depending on the nature of the phosphane ligand, the most basic (PCy3) providing the fastest reaction. The mesoionic species [Pt(bipy*)(Me)(L)]+ contain two Pt−C bonds: the balance between the Pt−C(sp2) and Pt−C(sp3) bond rupture is subtle, and competition is observed according to the reaction conditions. In the presence of an external neutral ligand L′ methane is released to give the cationic derivatives [Pt(bipy-H)(L)(L′)]+, whereas reaction of the neutral [Pt(bipy-H)(Me)(L)] with HCl may follow different routes depending on the nature of the neutral ligand L. Assuming all reactions take place through the formation of a hydride intermediate, quantum chemical calculations show that computed energy barriers are qualitatively consistent with observed reaction rates

    The lithosphere in Italy: structure and seismicity

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    We propose a structural model for the lithosphere-asthenosphere system for the Italic region by means of the S-wave velocity (VS) distribution with depth. To obtain the velocity structure the following methods are used in the sequence: frequency-time analysis (FTAN); 2D tomography (plotted on a grid 1°×1°); non-linear inversion; smoothing optimization method. The 3D VS structure (and its uncertainties) of the study region is assembled as a juxtaposition of the selected representative cellular models. The distribution of seismicity and heat flow is used as an independent constraint for the definition of the crustal and lithospheric thickness. The moment tensor inversion of recent damaging earthquakes which occurred in the Italic region is performed through a powerful non-linear technique and it is related to the different rheologic-mechanic properties of the crust and uppermost mantle. The obtained picture of the lithosphere-asthenosphere system for the Italic region confirms a mantle extremely vertically stratified and laterally strongly heterogeneous. The lateral variability in the mantle is interpreted in terms of subduction zones, slab dehydration, inherited mantle chemical anisotropies, asthenospheric upwellings, and so on. The western Alps and the Dinarides have slabs with low dip, whereas the Apennines show a steeper subduction. No evidence for any type of mantle plume is observed. The asymmetric expansion of the Tyrrhenian Sea, which may be interpreted as related to a relative eastward mantle flow with respect to the overlying lithosphere, is confirmed

    Mesoionic Complexes of Platinum(II) Derived from “Rollover” Cyclometalation: A Delicate Balance between Pt–C(sp<sup>3</sup>) and Pt–C(sp<sup>2</sup>) Bond Cleavage as a Result of Different Reaction Conditions

    No full text
    “Rollover” cyclometalation is a particular case of metal-mediated C–H bond activation, and the resulting complexes constitute an emerging class of cyclometalated compounds. In the case of 2,2′-bipyridine “rollover cyclometalation” has been used to synthesize the complexes [Pt­(bipy-H)­(Me)­(L)] (L = PPh<sub>3</sub>, PCy<sub>3</sub>, P­(OPh)<sub>3</sub>, P­(<i>p</i>-tolyl)<sub>3</sub>), whose protonation produces a series of stable corresponding pyridylenes [Pt­(bipy*)­(Me)­(L)]<sup>+</sup>. The unusual bipy* ligand may be described as an abnormal-remote heterocyclic chelated carbene or simply as a mesoionic cyclometalated ligand. These cationic species spontaneously convert in solution, through a retro-rollover reaction, to the corresponding isomers [Pt­(bipy)­(Me)­(L)]<sup>+</sup>, where the 2,2′-bipyridine is coordinated in the classical N,N bidentate mode. Isomerization is achieved at different rates (ranging over three orders of magnitude), depending on the nature of the phosphane ligand, the most basic (PCy<sub>3</sub>) providing the fastest reaction. The mesoionic species [Pt­(bipy*)­(Me)­(L)]<sup>+</sup> contain two Pt–C bonds: the balance between the Pt–C­(sp<sup>2</sup>) and Pt–C­(sp<sup>3</sup>) bond rupture is subtle, and competition is observed according to the reaction conditions. In the presence of an external neutral ligand L′ methane is released to give the cationic derivatives [Pt­(bipy-H)­(L)­(L′)]<sup>+</sup>, whereas reaction of the neutral [Pt­(bipy-H)­(Me)­(L)] with HCl may follow different routes depending on the nature of the neutral ligand L. Assuming all reactions take place through the formation of a hydride intermediate, quantum chemical calculations show that computed energy barriers are qualitatively consistent with observed reaction rates

    The Second International Asteroid Warning Network Timing Campaign: 2005 LW3

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    The Earth close approach of near-Earth asteroid 2005 LW3 on 2022 November 23 represented a good opportunity for a second observing campaign to test the timing accuracy of astrometric observation. With 82 participating stations, the International Asteroid Warning Network collected 1046 observations of 2005 LW3 around the time of the close approach. Compared to the previous timing campaign targeting 2019 XS, some individual observers were able to significantly improve the accuracy of their reported observation times. In particular, U.S. surveys achieved good timing performance. However, no broad, systematic improvement was achieved compared to the previous campaign, with an overall negative bias persisting among the different observers. The calibration of observing times and the mitigation of timing errors should be important future considerations for observers and orbit computers, respectively.Funder: Institute of Cosmos SciencesUniversity of Barcelona (CEX2019-000918-M); European Union (PID2021-122842OB-C21);Full text license: CC BY</p
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