From silicon(II)-based dioxygen activation to adducts of elusive … · 2010-06-23 · 2010 Macmillan Publishers Limited. All rights reserved. SUPPLEMENTARY INFORMATION doi: 10.1038/nchem.666
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From silicon(II)-based dioxygen activation to adducts of elusive dioxasilirane and cyclic sila-urea stable at room
temperature
Yun Xiong1, Shenglai Yao1, Robert Müller2, Martin Kaupp2 and Matthias Driess1*
1 Institute of Chemistry: Metalorganics and Inorganic Materials, Technische Universität Berlin,
Strasse des 17. Juni 135, Sekr. C2, D-10623 Berlin, Germany 2 Institute of Physical and Theoretical Chemistry, Universität Würzburg, Am Hubland, D-97074
Würzburg, Germany
Contents of the Supplementary Information
A. Experimental Section S2 B. Computational Details and Data S11
Figure S1. Molecular structure of compound 2a. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity. Table S1. Selected interatomic distances and angles of compound 2a
Figure S2. Molecular structure of compound 2b. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity. Table S2. Selected interatomic distances and angles of compound 2b
Figure S3. Molecular structure of compound 3. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity. Table S3. Selected interatomic distances and angles of compound 3
All structure optimizations used the gradient-corrected BP861,2 functional in conjunction with the resolution-of-identity3 (RI) approximation and TZVP4 orbital and auxiliary basis sets. All optimizations were done with the Turbomole program, version 5.10 5. Computed dissociation and reaction energies are based on molecular energies obtained by single-point calculations at B3LYP 6,7/TZVPP 8 level of theory. Figure S4 shows the model structures 2’, 3’ and 4’ which have additionally been considered for our calculations.
To get more detailed insight into the electronic structure of all compounds under consideration, additional single-point calculations with the Gaussian98 program, Revision A.9,9 were carried out. Charges from natural population analysis (NPA)10 together with Wiberg bond indices11 were obtained at the B3LYP/TZVP level. In particular, at this level we also examined 3’, 4’, 5 and 6 within the framework of natural resonance theory (NRT)10. Additional B3LYP/TZVPP single-point calculations were used to analyze the electron localization function (ELF)12 for the model structures 2’, 3’, 4’ as well as H2Si=O 6 and (H2N)2Si=O 5. NBO, NPA and NRT analyses were done with the NBO 5.0 program13. ELF analyses used the ToPMoD program package14.
Figure S4 shows the model structures 2’, 3’ and 4’ (reduced substituent sets). ELF isosurface plots (isovalue = 0.82) are given in Figure S5 for 4’, 5, 6 and in Figure S6 for 2’ and 3’. NPA and Wiberg bond indices for all models considered are listed in Table S4. Table S5 lists bond orders obtained from NRT analyses (NRT bond orders) of 3’, 4’, 5 and 6. Relevant bond lengths from optimized structures as well as related experimental data are summarized in Table S6. Figure S8 provides the leading resonance structures obtained with NRT for silanones of increasing complexity. It is clear that the number of relevant resonance structures increases dramatically from the simple silaformaldehyde 6 via the simple sila-urea 5 to the cyclic sila-urea 4’. The increase in complexity continues for 3’. In this case, the result of the NRT analyses depends appreciably on the chosen starting resonance structure. The available computational resources did not permit a completely converged NRT picture for 3’ in its entirety. Therefore, the results for 3’ (cf. Table S5) are an average over three NRT runs with different starting structures. Due to memory limitations in case of 3’, we had to restrict the basis sets in the NRT analyses to SVP (TZVP basis sets gave very small changes for the smaller model systems).
Figures S5 and S6 give ELF isosurface plots for various systems, allowing graphical bonding analyses. S7 shows how the reorganisation energy of a hypothetical free siladioxirane after removal of the NHC ligand has been obtained computationally.
Figure S7. Reaction scheme for the reorganization of a hypothetical NHC-free dioxasilirane to a square-pyramidal intermediate and subsequent coordination of the NHC ligand (B3LYP/TZVPP//RI-BP86/TZVP). All energies are in kJ/mol. R = 2,6-iPr2C6H3. R’ = iPr.
Table S4. Selected NPA atomic charges and Wiberg bond indices computed at B3LYP/TZVP level of theory.
Compound Wiberg bond indices
NPA atomic charges
H2Si=O Si-O 1.45 Si 1.53(6) O -1.07
(H2N)2Si=O Si-O 1.31 Si 2.15(5) Si-N1 0.79 O -1.15
Si-N2 0.79 N1 -1.31 N2 -1.31
4 Si-O 1.29 Si 2.23 Si-N1 0.65 O -1.16 Si-N2 0.69 N1 -0.88 N2 -0.88
4’ Si-O 1.31 Si 2.17 Si-N1 0.70 O -1.15 Si-N2 0.74 N1 -0.83 N2 -0.82
aCovalent and ionic contributions to the total bond order in percent are given in parentheses. bAveraged values over three analyses with different starting NRT resonance structures.
Figure S8. NRT resonance structures and their relative weighting for a) H2SiO 6 b) (H2N)2SiO 5 and c) model structure 4’ (B3LYP/SVP//RI-BP86/TZVP). Only resonance structures above 1% weight are shown.
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