A trapped silicon atom: The compound (L:)2Si with low‐valent silicon was synthesized from its dichloride biradical precursor (L:)2SiCl2 by reduction with KC8. Theoretical analysis suggest that there are two donor–acceptor σ bonds L:→Si←:L. There is one σ lone‐pair orbital at Si and one π orbital which features significant π‐back‐donation L:←Si→:L giving short SiC bonds.
Silicon becomes colored: Stable biradicals were prepared from an N‐heterocyclic carbene stabilized SiCl2 and a cyclic alkyl(amino)carbene, and characterized as two polymorphs. The deep‐blue crystals of one polymorph are stable upon exposure to air for about a week, while the solution in THF decomposes rapidly when exposed to air. In a side reaction, the different carbene species react with each other under CH activation and CC bond formation in the presence of the biradical.
Nickel(0)-catalyzed cross-coupling of methoxyarenes through C-O bond activation has been the subject of considerable research because of their favorable features compared with those of the cross-coupling of aryl halides, such as atom economy and efficiency. In 2008, we have reported nickel/PCy-catalyzed cross-coupling of methoxyarenes with arylboronic esters in which the addition of a stoichiometric base such as CsF is essential for the reaction to proceed. Recently, we have also found that the scope of the substrate in the Suzuki-Miyaura-type cross-coupling of methoxyarenes can be greatly expanded by using 1,3-dicyclohexylimidazol-2-ylidene (ICy) as the ligand. Interestingly, a stoichiometric amount of external base is not required for the nickel/ICy-catalyzed cross-coupling. For the mechanism and origin of the effect of the external base to be elucidated, density functional theory calculations are conducted. In the nickel/PCy-catalyzed reactions, the activation energy for the oxidative addition of the C(aryl)-OMe bond is too high to occur under the catalytic conditions. However, the oxidative addition process becomes energetically feasible when CsF and an arylboronic ester interact with a Ni(PCy)/methoxyarene fragment to form a quaternary complex. In the nickel/ICy-catalyzed reactions, the oxidative addition of the C(aryl)-OMe bond can proceed more easily without the aid of CsF because the nickel-ligand bonds are stronger and therefore stabilize the transition state. The subsequent transmetalation from an Ar-Ni-OMe intermediate is determined to proceed through a pathway with lower energies than those required for β-hydrogen elimination. The overall driving force of the reaction is the reductive elimination to form the carbon-carbon bond.
Metal ions with radical centers in their coordination sphere are key participants in biological and catalytic processes. In the present study, we describe the synthesis of the cAAC:ZnCl2 adduct (1) using a cyclic alkylaminocarbene (cAAC) as donor ligand. Compound 1 was treated with 2 equiv of KC8 and LiB(sec-Bu)3H to yield a deep blue-colored dicarbene zinc compound (cAAC)2Zn (2) and the colorless hydrogenated zinc compound (cAACH)2Zn (3), respectively. Compounds 2 and 3 were well characterized by spectroscopic methods and single-crystal X-ray structural analysis. Density functional theory calculations were performed for 2 which indicate that this molecule possesses a singlet biradicaloid character. Moreover, we show the application of 2 in CO2 activation, which yields a zwitterionic cAAC·CO2 adduct.
The formation of H(3)(+) from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H(3)(+) formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H(3)(+) ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H(2) molecule attached to a C(2)H(4)(2+) entity but IRC calculations show that it belongs to the reaction channel yielding C(2)H(3)(+) + H(3)(+). Experimentally measured kinetic energies of the correlated H(3)(+) and C(2)H(3)(+) ions confirm the reaction path suggested by theory.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.