A study of the reaction of PtMe(2)(bipy) with IPh(C[triple bond]CSiMe(3))(OTf) at low temperature in acetone, leading to detection of the Pt-Pt-bonded cation [Pt(2)Me(4)(C[triple bond]CSiMe(3))(bipy)(2)](+), an intermediate in the oxidation of Pt(II) to Pt(IV), is reported. The cation is assessed as Pt(III)-Pt(III) <--> Pt(IV)-Pt(II), and at the other extreme may be regarded as a cationic alkynylplatinum(IV) center, "[Pt(IV)Me(2)(C[triple bond]CSiMe(3))(bipy)](+)", stabilized by "Pt(II)Me(2)(bipy)" as a donor ligand. The detection and isolation of the [Pt(2)Me(4)(C[triple bond]CSiMe(3))(bipy)(2)](+) cation provides a number of insights into the mechanisms of oxidation reactions.
Surprising catalytic activities have been found for the actinide complexes Cp*(2)ThMe(2) (1), Th(NEtMe)(4) (2), and Me(2)SiCp''(2)Th(C(4)H(9))(2) (3) toward oxygenated substrates. During the catalytic dimerization of benzaldehydes to their corresponding esters, complexes 1 and 2 gave 65 and 85% yield in 48 h, respectively, while the geometry-constrained complex 3 gave 96% yield in 24 h. Exploring the effect of substituents on benzaldehyde, it has been found that, in general, electron-withdrawing groups facilitate the reaction. Kinetic study with complexes 1 and 3 reveals that the rate of the reaction is first order in catalyst and substrate, which suggests the rate equation "rate = k[catalyst](1)[aldehyde](1)". The activation energy of the reaction was found to be 7.16 ± 0.40 and 3.47 ± 0.40 kcal/mol for complexes 1 and 3 respectively, which clearly indicates the advantage of the geometry-constrained complex. Astonishing are the reactivity of the organoactinide complexes with oxygen-containing substrates, and especially the reactivity of complex 3, toward the dimerization of substrates like p-methoxybenzaldehyde, m/p-nitrobenzaldehyde, and furanaldehyde and the reactivity toward the polymerization of terephthalaldehyde. Density functional theory mechanistic study reveals that the catalytic cycle proceeds via an initially four-centered transition state (+6 kcal/mol), followed by the rate-determining six-centered transition state (+13.5 kcal/mol), to yield thermodynamically stable products.
is strongly dependent on the structural shape and size of the nanoparticle, the polarization of incoming light, and the surrounding dielectric medium. This was shown to provide a promising way to generate, as well as modulate, color in the visible region with high efficiency. [4,8,[11][12][13][14][15] Therefore, plasmonic metasurfaces are attractive for use in high-resolution color displays, counterfeiting elements, and various imaging applications. However, the functionality of the metasurfaces is usually limited, due to their physical design properties, which are fixed once device is fabricated. In order to overcome this limitation, and to realize dynamically controlled devices, a mechanism for strong and tunable light-matter interaction needs to be introduced within a thin layer of active material. This has led to an extensive search for new active materials that offer highly dynamic and tunable responses. [1,[5][6][7][8][9][10][11][12][13] For this goal, liquid crystals (LCs) are promising active materials that exhibit large optical birefringence, ability to control the polarization of incoming light, and most importantly the LC molecules can be efficiently controlled by external electric or magnetic fields, light, and temperature. [16,17] It was shown that LCs possess the highest birefringence compared to any other natural materials over the entire visible-IR-THz-microwave spectrum, together with low power consumption and low operating voltage. Therefore, the LC based active control mechanisms have a significant advantage over other suggested mechanism to develop active metasurface platforms. [4][5][6][7][8][18][19][20][21] Recently, some studies [22][23][24][25][26][27][28][29][30][31][32] have reported on nematic LC enabled metasurfaces that were activated by two different methods. One method was based on the ability to control the LC dielectric constants by external stimuli, which in turn can significantly influence the resonant response of the metasurface. The other approach was based on the ability to rotate the polarization of incoming light by a twisted nematic LC (TN-LC) configuration, and utilize the polarization selectivity of the metasurfaces. Specifically, for color manipulation applications, Olson et al. [22] have employed a TN-LC layer over plasmonic nanorod arrays and demonstrated that the intensity of the plasmonic color pixels can be modulated with an applied voltage. This approach can be used in order to replace the color filters in conventional Bayer pattern, where the combination of three different color pixels is required. Lee et al. [27] proposed an asymmetric lattice nanohole array based electrically tunable Recent demonstrations of metasurfaces show their great potential to realize flat and multifunctional optical elements, viable for many new device applications. Yet, a major frontier in this field is to develop active, tunable, and reconfigurable metasurface platforms. These are highly desirable in modern technologies that require dynamic modulation of light. To achieve this goal, i...
Ligand effects in bimetallic high oxidation state systems containing a X-Pd-Pd-Y framework have been explored with density functional theory (DFT). The ligand X has a strong effect on the dissociation reaction of Y to form [X-Pd-Pd](+) + Y(-). In the model system examined where Y is a weak σ-donor ligand and a good leaving group, we find that dissociation of Y is facilitated by greater σ-donor character of X relative to Y. We find that there is a linear correlation of the Pd-Y and Pd-Pd bond lengths with Pd-Y bond dissociation energy, and with the σ-donating ability of X. These results can be explained by the observation that the Pd d(z(2)) population in the PdY fragment increases as the donor ability of X increases. In these systems, the Pd(III)-Pd(III) arrangement is favored when X is a weak σ-donor ligand, while the Pd(IV)-Pd(II) arrangement is favored when X is a strong σ-donor ligand. Finally, we demonstrate that ligand exchange to form a bimetallic cationic species in which each Pd is six-coordinate should be feasible in a high polarity solvent.
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