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Oxidative addition of MeI to a rollover complex of Pt(II): isolation of the kinetic product.
No full textA pair of new Pt(II)/Pt(IV) 2,2′-bipyridine cyclometalated rollover
complexes have been synthesized and characterized. [Pt(bpy-H)(CH3)(PMe3)] (1),
where bpy-H = κ2N,C-2,2′-bipyridine, was obtained from the electron-rich precursor
cis-[Pt(CH3)2(DMSO)2] with a one-pot, two step synthesis; its reactivity has been
tested with CH3I, giving the corresponding Pt(IV) complex cis-[Pt(bpy-H)-
(CH3)2(I)(PMe3)] (2), which was fully characterized. Crystals suitable for X-ray
analysis were obtained and allowed the determination of the structure of isomer 2A
which is the product of the trans addition of CH3I, usually thought of as the kinetic
product
Voltammetric and Spectroscopic Investigation of Electrogenerated Oligo-Thiophenes: Effect of Substituents on the Energy-Gap Value
No full textOligothiophenes are especially appealing due to their promising applications in different fields, including photosensitive devices. In this context, anchoring a selected substituent on the main structure of the starting material can induce changes in redox and spectroscopic features, according to the nature of the substituent and its position on central or terminal rings. Here, an electrochemical and spectroscopic comparison between 2,2′:5′,2′′-terthiophene (2), 5-Br-terthiophene (3) and 5-ethynyl-terthiophene (5-ET) is reported, aimed at elucidating the effect of the nature of the substituent on the energy gap value of the terthiophene skeleton. Furthermore, in order to understand the influence of a selected substituent in varying its position on the terthiophene backbone, 5-ET is compared to the previously described 3′-ethynyl-terthiophene (3′-ET). Experimental results are confirmed by DFT calculations, showing a higher extension of the electron density in 5-ET compared to 2 and 3, as well as to 3′-ET. In addition, as a consequence of the presence of the unsaturated fragment on the C-5-position, the energy gap value of poly-5-ET (the electrogenerated film from 5-ET) appears significantly lower than poly-2 and poly-3. Finally, the higher conjugation effect of a terminal acetylene fragment compared to a central one is confirmed by the energy gap values of poly-5-ET and poly-3′-ET
Pt(II) derivatives with rollover-coordinated 6-substituted 2,20-bipyridines: Ligands with multiple personalities
No full textWe report here the synthesis, characterization and behavior of a series of Pt(II) cyclometalated rollover complexes with two substituted bipyridines, 6-ethyl-2,20-bipyridine (bpy6Et) and 6-methoxy-2,20-bipyridine (bpy6OMe), in comparison with previously studied 2,20-bipyridine complexes. The two ligands have similar steric hindrance but different electronic properties. As a result, the reactivity of the two series of complexes follows very different routes. In particular, the new complexes behave differently towards protonation reactions, differences given by substituents and ancillary ligands, added to the presence of several nucleophilic centers. Reaction of complex [Pt(bpy6OMe-H)(PPh3)Me)] with [H3O·18-crown-6][BF4] results in a retro-rollover reaction whose final product is the cationic adduct [Pt(bpy6OMe)(PPh3)Me)]+. Surprisingly, only the isomer with the cis-PPh3-OMe geometry is formed; in spite of an expected instability due to steric hindrance, Density-Functional theory (DFT) calculations showed that this isomer is the most stable. This result shows that the cone angle is far from being a real "solid cone" and should lead to a different interpretation of well-known concepts concerning steric bulk of ligands, such as cone angle. Proton affinity values of ligands, neutral complexes and their protonated counterparts were analyzed by means of DFT calculations, allowing a comparison of their properties
Mesoionic Complexes of Platinum(II) Derived from “Rollover” Cyclometalation: A Delicate Balance between Pt−C(sp3) and Pt−C(sp2) Bond Cleavage as a Result of Different Reaction Conditions
No full textUnexpected behaviour of organoplatinum rollover complexes: new metal-based route to C-X bond formation
No full textCyclometallated Rollover complexes: a delicate balance between M-C(sp3) and M-C(sp2) cleavage as a result of different reaction conditions.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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