Theoretical study of O - > X (S, Se, Te) coordination in organic compounds

1998 ◽  
Vol 76 (6) ◽  
pp. 776-788 ◽  
Author(s):  
Ruslan M Minyaev ◽  
Vladimir I Minkin
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Organic Compounds ◽  
Theoretical Study ◽  
Intramolecular Coordination ◽  
Chalcogen Atom ◽  
Structural Peculiarities

Ab initio (RHF/LanL2DZ, MP2(fc)/LanL2DZ, MP2(fc)/6-31G**, and MP2(fc)/6-311++G**) calculations were performed for a series of β -chalcogenovinylaldehydes, 1,6-dioxa-6a-chalcogenopentalenes, and bimolecular complexes of formaldehyde with chalcogen hydrides and chlorides. The calculations reproduce well the existence and experimentally observed structural peculiarities of the intra- and intermolecular Ο - > chalcogen attractive interactions that stabilize the hypervalent T-shaped bond configuration at a chalcogen atom. These interactions increase in the order S, Se, Te and with the increasing electronegativity of a substituent attached to the chalcogen center. The ab initio calculations performed predict the existence of sufficiently stable bimolecular complexes H2CO . . .XR1R2 (X = S, Se, Te; R1, R2 = H, Cl) with a complexation energy comparable to the energy of a strong hydrogen bond.Key words: ab initio calculations, chalcogen-containing compounds, intramolecular coordination.

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

2000 ◽  
Vol 78 (11) ◽  
pp. 1496-1510 ◽  
Author(s):  
Yitzhak Apeloig ◽  
Stepan Sklenak
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Gas Phase ◽  
Theoretical Study ◽  
Single Step ◽  
Membered Ring ◽  
Basis Set ◽  
Double Bonds ◽  
Ring Compounds ◽  
Encounter Complex

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.

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