[pi]-acidity of thioethers and selenoethers: Truth or fiction A comparative density functional study
- Univ. of Calgary, Alberta (Canada)
The relevance of thioether-transition metal complexes as possible intermediates in the hydrodesulfurization of fossil fuels has prompted numerous investigations into the structure and reactivity of transition metal-thioether complexes, as well as its heavier congener selenoether. Using density functional theory (DFT) within the local density approximation (LDA), the electronic and geometrical structure of octahedral (OC)[sub 5]Cr-L with L = CO, NR[sub 3], PR[sub 3], AsR[sub 3], SR[sub 2], SeR[sub 2] (N, P, As, R = F, H; S, Se, R = F, H, Me), and OR[sub 2] (R = H, Me) were studied. All structures have been optimized in C[sub s] symmetry. The resulting geometries are rationalized in terms of orbital interactions. The metal-ligand bond energy has been determined for all systems in calculations where nonlocal corrections were added to the LDA energy expression. It was possible to break down the total metal-ligand bond energy into contributions stemming from [sigma]-donation and [pi]-back-bonding; hence, it is possible to rank thioethers and selenoethers in terms of [sigma]-donor and [pi]-acceptor ability. In general, thio- and selenoethers are rather poor [pi]-acceptors and weak [sigma]-donors. The methyl-substituted chalcogenoethers are better [sigma]-donors than the chalcogenhydrides. It is found that the fluoro-substituted chalcogen systems exhibit good [pi]-acceptor abilities, comparable to those found for PF[sub 3]. Surprisingly, the fluorine substitution does not significantly decrease the [sigma]donor ability. The Cr-E bond energies increase in the order Cr-EH[sub 2] < Cr-EMe[sub 2] < Cr-EF[sub 2] (E = O, S, Se). 21 refs., 3 figs., 4 tabs.
- OSTI ID:
- 6539047
- Journal Information:
- Organometallics; (United States), Journal Name: Organometallics; (United States) Vol. 12:1; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
BONDING
CALCULATION METHODS
CHROMIUM COMPOUNDS
ELECTRONIC STRUCTURE
FABRICATION
HYDROGEN COMPOUNDS
INORGANIC ACIDS
JOINING
LEWIS ACIDS
MATHEMATICAL MODELS
MOLECULAR ORBITAL METHOD
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
REACTIVITY
SELENIUM COMPOUNDS
SULFUR COMPOUNDS
SYMMETRY
TRANSITION ELEMENT COMPOUNDS