Isolation of cationic and neutral (allenylidene)(carbene) and bis(allenylidene)gold complexes.

The one-electron reduction of a cationic (allenylidene)[cyclic(alkyl) (amino)carbene]gold(i) complex leads to the corresponding neutral, paramagnetic, formally gold(0) complex. DFT calculations reveal that the spin density of this highly robust coinage metal complex is mainly located on the allenylidene fragment, with only 1.8 and 3.1% on the gold center and the CAAC ligand, respectively. In addition, the first homoleptic bis(allenylidene)gold(i) complex has been prepared and fully characterized

A Convenient Preparation of Organofluorosilanes. A Possible Involvement of Tetracoordinated Siliconium Ion Pairs

Organofluorosilanes and their complexes with weakly coordinating fluorine con- taining salts are frequently used in mechanistic studies of organosilicon compounds.1 Examples include studies of nucleophilic attack at silicon2 and attempts to generate silicenium ions of type R3Si+.3’4 Silyl fluorides are also used in key steps in the synthesis of sterically hindered tetraalkylsilanes5’6 or of highly congested trialkylsilyl halides (chlorides, bromides and iodides).6’7 In view of these important applications, it is surprising that until very recently the available synthetic methods for preparing silyl fluorides were limited and used quite inconvenient chemicals, procedures and reaction conditions. Thus, organofluorosilanes were prepared by the treatment of the corresponding silyl halides with anhydrous hydrofluoric acid,8 antimony trifluoride,9 or zinc fluoride.7,10 Only one report in the older literature indicated that triphenylfluorosilane can be prepared under much milder conditions, i.e., by the reaction of the corresponding chloride with sodium fluoroborate in acetone at room temperature.11 The lack of simple straightforward methods for preparing silyl fluorides is especially intriguing in view of the fact that the Si-F bond is the strongest known bond to silicon, and consequently fluorosilanes are expected to exhibit high thermodynamic stability.12 Progress towards a more simple synthesis of fluorosilanes was made in recent years. Bassindale and Stout noted that the reaction of Me3SiCl with silver tetrafluoroborate yields trimethylfluorosilane138 (not trimethylsilyl tetrafluoroborate as previously suggested).136 Della and Tsanaktidis reported in 1988 that silyl triflates react at 25-70 °C with potassium fluoride in DMF in the presence of 18-crown-6 to produce the corresponding silyl fluorides.1

The Diamond Within a Silicon Analog of Cyclobutadiene

The distinctive rhombic structure of the central ring of a stable silicon analog of cyclobutadiene provides new insights into antiaromaticity.</jats:p

On the possible formation of Si=O, Si=S, and Si=Se double bonds via the reaction of silylenes with oxirane, thiirane, and selenirane, respectively. An ab initio theoretical study

The reactions between silylene, H2Si, and the three-membered ring compounds, oxirane (9), thiirane (10), and selenirane (11), which provide possible routes to Si=X (X = O, S, Se) double bonds were studied by ab initio calculations at the MP2 and QCISD correlated levels of theory employing the polarized 6-31G** basis set. The calculations show that the three reactions are all highly exothermic, (–61.8, –45.2, –52.9 kcal/mol at MP2/6-31G**//MP2/6-31G** for X = O, S, Se, respectively). In the gas phase, at 0 K, these reactions are predicted to be also spontaneous (i.e., the calculated transition states are lower in energy than the reactants). At 298 K, entropy contributions result in small barriers on the ΔG surface for X = O, S (7.4 kcal/mol for both reactions at QCISD (full)/6-31G**), but for X = Se the reaction remains spontaneous. Thus, the calculations suggest that these reactions are viable routes for the preparation of compounds with Si=X (X = O, S, Se) double bonds. The first step in all the reactions is the barrier-less formation of an encounter-complex between the silylene and the X atom of the precursor. For X = O, S, these complexes are predicted to be sufficiently stable to be observed in a matrix. The reaction steps which follow depend on X; for X = O fragmentation of the silylene-XC2H4 complex proceeds in two steps via a biradical intermediate, while for X = S and X = Se the fragmentation occurs in a single step. The first ab initio calculations for H2Si=Se are reported.Key words: silylene, silanone, silanethione, silaneselone. </jats:p