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SUPPLEMENTARY INFORMATIONdoi: 10.1038/nchem.666

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Supplementary Information

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


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SUPPLEMENTARY INFORMATION doi: 10.1038/nchem.666

S2

A. Experimental Section

Synthesis of Compound 2a: A solution of 1a (0.51 g, 0.82 mmol) in toluene (10 ml) was cooled to -

60 °C. The N2 atmosphere in the flask was exchanged to O2. After stirring for 5 min the resulted

solution was concentrated to about 10 ml and cooled at -20°C for 24 h to afford 2a as colorless

crystals (0.40 g, 0.61 mmol, 74 %). M.p. 104 °C (decomp.). 1H NMR (400.13 MHz, [D8] toluene, -

20ºC): δ = 0.56 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 0.83 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 0.84 (d, 3J

(H,H) = 7 Hz, 3 H; CHMe2), 0.97 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.13 (d, 3J (H,H) = 7 Hz, 3 H;

CHMe2), 1.30 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.37 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.52 (d, 3J

(H,H) = 7 Hz, 3 H; CHMe2), 1.54 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.62 (d, 3J (H,H) = 7 Hz, 3 H;

CHMe2), 1.69 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.77 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.53 (s, 3H,

CMe), 1.59 (s, 3H, CMe), 1.72 (s, 3H, CMe), 2.83 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 3.13 (sept, 3J

(H,H) = 7 Hz, 1H, CHMe2), 4.16 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 4.28 (sept, 3J (H,H) = 7 Hz, 1H,

CHMe2), 5.78 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 6.16 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 3.15 (s, 1

H; NCCH2), 3.88 (s, 1 H; NCCH2), 5.46 (s, 1 H; γ-CH), 6.98 – 7.41 ppm (m, br, 6 H; 2,6-iPr2C6H3).

13C{1H} NMR (100.61 MHz, [D8] toluene, -20ºC): δ = 10.4, 10.8 (C2Me2); 21.7 - 29.7 (NCHMe2, NCMe,

CHMe2); 50.6 , 52.0 (NCHMe2); 84.5 (NCCH2), 105.2 (γ-C), 123.4 – 151.7 (NCMe, NCCH2, 2,6-

iPr2C6H3, C2Me2), 158.6 ppm (SiC); 29Si{1H} NMR (79.49 MHz, [D8] toluene, -20ºC): δ = -131.9 ppm

(s); EI-MS: m/z (%). 656 (21 [M+]), 641 (10 [(M-Me)+]), 202(100). Elemental analysis calcd (%) for

C40H60N4SiO2 : C 73.12, H 9.20, N 8.53, found: C 72.86, H 8.94, N 8.34. IR (KBr, cm-1): 461 (w), 484

(m), 470 (w), 593 (w), 610 (w), 647 (w), 678 (w), 737 (w), 761 (m), 802 (m), 886 (w), 911 (w), 930 (w),

983 (w), 1043 (w), 1056 (m), 1080 (w), 1107 (w), 1139 (w), 1173 (w), 1193 (w), 1254 (w), 1309 (m),

1356 (s), 1381 (s), 1443 (m), 1466 (m), 1551 (w), 1576 (w), 1630 (m), 1645 (m), 1685 (w), 2866 (m),

2966 (s), 3055 (w).

Synthesis of Compound 2b: A solution of 1b (0.47 g, 0.83 mmol) in toluene (15 ml) was cooled to -

60 °C. The N2 atmosphere in the flask was exchanged to O2. After stirring for 5 min the resulted

solution was concentrated to about 8 ml and cooled at -20°C for 24 h to afford 2b as colorless crystals

(0.34 g, 0.57 mmol, 69 %). M.p. 81 °C (decomp.). 1H NMR (400.13 MHz, [D8] toluene, -20ºC): δ =

0.33 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 0.34 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 0.97 (d, 3J (H,H) = 7 Hz,

3 H; CHMe2), 1.11 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.53 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.67 (d,

3J (H,H) = 7 Hz, 3 H; CHMe2), 1.80 (d, 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.85 (d, 3J (H,H) = 7 Hz, 3 H;

CHMe2), 1.09 (s, 3H, CMe), 1.36 (s, 3H, CMe), 1.52 (s, 3H, CMe), 3.20 (s, 3H, NMe), 3.61 (s, 3H,

NMe), 2.71 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 2.88 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 4.21 (sept, 3J

(H,H) = 7 Hz, 1H, CHMe2), 4.29 (sept, 3J (H,H) = 7 Hz, 1H, CHMe2), 3.18 (s, 1 H; NCCH2), 3.91 (s, 1

H; NCCH2), 5.44 (s, 1 H; γ-CH), 6.83 – 7.40 ppm (m, br, 6 H; 2,6-iPr2C6H3). 29Si{1H} NMR (79.49 MHz,

[D8] THF, 25ºC): δ = -133.3 ppm (s). HR ESI-MS (Ion spray voltage 5kV, flow rate 5μL/min, in

THF): m/z: calcd for [M+H]+ (C36H53N4SiO2): 600.39323, found: 600.39632. Elemental

analysis calcd (%) for C36H52N4SiO2 · 0.3 C7H8) : C 72.79, H 8.74, N 8.92, found: C 72.46, H 9.13, N

8.73. IR (KBr, cm-1): 462 (w), 474 (w), 493 (w), 552 (w), 566 (w), 584 (w), 600(w), 681 (w), 695 (w),




S3

731 (w), 758 (m), 804 (m), 837 (w), 851 (w), 935 (w), 978 (w), 1022 (m), 1046 (w), 1060 (m), 1106 (w),

1135 (w), 1156 (w), 1177 (w), 1197 (w), 1254 (w), 1307 (w), 1319 (w), 1156 (m), 1380 (s), 1442 (s),

1466 (s), 1519 (w), 1544 (w), 1775 (w), 1636 (s), 1694 (w), 2866 (m), 2926 (m), 2963 (s), 3021 (w),

3055 (w), 3106 (w).

Synthesis of Compound 3: A solution of 2a (0.43 g, 0.65 mmol) in toluene (10 ml) was allowed to

stand at room temperature. After 24 h compound 3 crystallized as colorless crystals (0.31 g, 0.47

mmol, 72 %). M.p. 194 °C (decomp.). 1H NMR (400.13 MHz, [D2] dichloromethane, 25ºC): δ = 0.89 (d,

3J (H,H) = 7 Hz, 6 H; CHMe2), 1.11 – 1.18 (m, br., 15 H; CHMe2), 1.31 – 1.37 (m, br., 9 H; CHMe2),

1.48 (d, br. 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.59 (d, br., 3J (H,H) = 7 Hz, 3 H; CHMe2), 1.51 (s, 3H,

CMe), 2.18 (s, 3H, CMe), 2.24 (s, 3H, CMe), 2.84 (s, 1 H, NCCH2), 3.58 (s, 1 H, NCCH2), 3.06 – 3.15

(m, br., 1H, CHMe2), 3.16 – 3.26 (m, br., 1H, CHMe2), 3.74 (sept, 3J (H,H) = 7 Hz, 2H, CHMe2), 5.06 –

5.16 (m, br., 1H, CHMe2), 5.79 – 5.89 (m, br. 1H, CHMe2), 5.38 (s, 1 H; γ-CH), 7.06 – 7.26 ppm (m, br,

6 H; 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, [D2] dichloromethane, 25ºC): δ = 10.3 (C2Me2); 21.1 -

28.9 (NCHMe2, NCMe, CHMe2); 48.6 , 49.5 (NCHMe2); 83.8 (NCCH2), 105.9 (γ-C), 119.4 – 151.3 ppm

(NCMe, NCCH2, 2,6-iPr2C6H3, C2Me2, SiOC); 29Si{1H} NMR (79.49 MHz, [D2] dichloromethane, 25ºC):

δ = -77.1 ppm (s); EI-MS: m/z (%). 656 (1 [M+]), 460 (3 [(M-NHC=O)+]), 445 (25 [(M-NHC=O-Me)+]),

196 (49, [NHC=O+]), 112 (100). Elemental analysis calcd (%) for C40H60N4SiO2 : C 73.12, H 9.20, N

8.53, found: C 72.88, H 8.84, N 8.18. IR (KBr, cm-1): 408 (w), 433(w), 457 (w), 482 (m), 510 (w), 521

(w), 53) (w), 546 (w), 565 (w), 578 (w), 597 (w), 646 (w), 667 (w), 679 (w), 708 (w, Si-16O stretching

mode, 698 for Si-18O), 716 (w), 733 (w), 758 (m), 765 (m), 803 (m), 882 (w), 912 (w), 929 (m), 977 (w),

1102 (w), 1033 (w), 1045 (w), 1055 (w), 1108 (w), 1153 (m, Si=16O stretching mode, 1128 for Si=18O),

1179 (m), 1205 (m), 1256 (m), 1309 (m), 1330 (m), 1352 (m), 1378 (s), 1410 (w), 1441 (m), 1466 (m),

1485 (m), 1521 (w), 1553 (w), 1597 (s), 1608 (s, C=16O stretching mode, 1583 for Si=18O), 1639 (m),

1685 (w), 2865 (m), 2929 (m), 2945 (m), 2971 (s), 3057 (w), 3106 (w).




S4

Figure S0: Comparison of the IR spectra of 3: Without (red) and after 18O labelling of the “SiO2” subunit (blue)

in the range of 650cm-1 to 1650 cm-1.

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

%T

800 1000 1200 1400 1600 Wellenzahlen (cm-1)

υ�(C=16O) 1608 cm-1

υ(C=18O) 1583 cm-1

υ�(Si=16O) 1153 cm-1

υ (Si=18O) 1128 cm-1

υ(Si-18O) 698 cm-1

υ (Si-16O) 708 cm-1




S5

Crystallographic data for 2a

Empirical formula C40H60N4O2Si

Formula weight 657.01

Temperature 150(2) K

Wavelength 0.71073 Å

Crystal system Monoclinic

Space group P21/n

Unit cell dimensions a = 13.1928(3) Å α= 90°.

b = 20.6445(6) Å β= 105.754(3)°.

c = 15.0686(4) Å γ = 90°.

Volume 3949.90(18) Å3

Z 4

Density (calculated) 1.105 Mg/m3

Absorption coefficient 0.096 mm-1

F(000) 1432

Crystal size 0.24 x 0.13 x 0.11 mm3

Theta range for data collection 2.98 to 25.00°.

Index ranges -15<=h<=15, -24<=k<=24, -17<=l<=17

Reflections collected 18474

Independent reflections 6935 [R(int) = 0.0480]

Completeness to theta = 25.00° 99.7 %

Absorption correction Semi-empirical from equivalents

Max. and min. transmission 1.00000 and 0.97426

Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 6935 / 15 / 439

Goodness-of-fit on F2 1.021

Final R indices [I>2sigma(I)] R1 = 0.0675, wR2 = 0.1376

R indices (all data) R1 = 0.1211, wR2 = 0.1559

Largest diff. peak and hole 0.516 and -0.269 e.Å-3




S6

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

Interatomic distances (Å ) Angles (°)

Si1-O1 1.682(2)

Si1-O2 1.693(2)

Si1-N2 1.767(2)

Si1-N1 1.799(2)

Si1-C30 1.963(3)

O1-O2 1.547(3)

N1-C2 1.417(4)

N2-C4 1.415(3)

N3-C30 1.366(3)

N3-C32 1.381(3)

N4-C30 1.363(3)

N4-C31 1.388(3)

C2-C3 1.428(4)

C3-C4 1.341(4)

C31-C32 1.340(4)

O1-Si1-O2 54.6(1)

O1-Si1-N2 138.0(1)

O2-Si1-N2 95.9(1)

O1-Si1-N1 94.8(1)

O2-Si1-N1 144.8(1)

N2-Si1-N1 98.5(1)

O1-Si1-C30 103.9(1)

O2-Si1-C30 101.2(1)

N2-Si1-C30 111.5(1)

N1-Si1-C30 103.0(1)

O2-O1-Si1 63.1(1)

O1-O2-Si1 62.4(1)




S7

Crystallographic data for 2b

Empirical formula C36H52N4O2Si · 1/2 toluene





Space group P21/n

Unit cell dimensions a = 17.0069(5) Å α= 90°.

b = 13.0836(5) Å β= 108.997(4)°.

c = 18.0462(6) Å γ = 90°.

Volume 3796.8(2) Å3

Z 4



F(000) 1404



Index ranges -20<=h<=20, -15<=k<=14, -21<=l<=21




Absorption correction None










S8

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

Interatomic distances (Å ) Angles (°)

Si1-O1 1.667(2)

Si1-O2 1.692(2)

Si1-N1 1.777(2)

Si1-N2 1.781(2)

Si1-C30 1.933(3)

O1-O2 1.510(3)

N1-C2 1.406(3)

C1-C2 1.390(4)

N2-C4 1.413(3)

C2-C3 1.409(4)

N3-C30 1.354(3)

N3-C31 1.388(4)

C3-C4 1.372(4)

N4-C30 1.372(3)

N4-C32 1.376(4)

C31-C32 1.349(4)

O1-Si1-O2 53.4(1)

O1-Si1-N1 96.7(1)

O2-Si1-N1 145.5(1)

O1-Si1-N2 138.9(1)

O2-Si1-N2 96.1(1)

N1-Si1-N2 98.8(1)

O1-Si1-C30 104.1(1)

O2-Si1-C30 99.1(1)

N1-Si1-C30 105.5(1)

N2-Si1-C30 108.0(1)

O2-O1-Si1 64.1(1)

O1-O2-Si1 62.5(1)




S9

Crystallographic data for 3

Empirical formula C40H60N4O2Si





Space group p21/n

Unit cell dimensions a = 12.1047(3) Å �= 90°.

b = 16.4820(6) Å �= 94.666(3)°.

c = 19.5115(6) Å � = 90°.

Volume 3879.8(2) Å3

Z 4



F(000) 1432



Index ranges -14<=h<=14, -19<=k<=14, -23<=l<=23




Absorption correction Semi-empirical from equivalents

Max. and min. transmission 1.00000 and 0.96152










S10

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

Interatomic distances (Å) Angles (°)

Si1-O1 1.532(2)

Si1-O2 1.727(2)

Si1-N2 1.732(2)

Si1-N1 1.744(2)

O2-C30 1.294(3)

N1-C2 1.413(3)

N2-C4 1.410(3)

N3-C30 1.331(3)

N4-C30 1.339(3)

C2-C3 1.460(4)

C3-C4 1.341(4)

C31-C32 1.346(4)

O1-Si1-O2 112.20(9)

O1-Si1-N2 118.6(1)

O2-Si1-N2 98.5(1)

O1-Si1-N1 118.1(1)

O2-Si1-N1 104.0(1)

N2-Si1-N1 102.7(1)

C30-O2-Si1 145.4(2)

C2-N1-Si1 122.3(2)

C6-N1-Si1 119.8(2)

C4-N2-Si1 118.2(2)

N1-C2-C3 116.5(2)

C4-C3-C2 127.7(2)

C3-C4-N2 120.8(2)

O2-C30-N3 122.4(2)

O2-C30-N4 127.8(3)




S11

B. Computational Details and Data

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.




S12

Figure S4. Model systems 2’, 3’ and 4’. a) b) c) 2’ 3’ 4’

Figure S5. ELF = 0.82 isosurface plots for H2SiO 6, (H2N)2SiO 5 and 4’ (B3LYP/TZVPP//RI-BP86/TZVP).

6 5 4’

Figure S6. ELF = 0.82 isosurface plots for 2’ and 3’ (B3LYP/TZVPP//RI-BP86/TZVP).

2’ 3’




S13

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

3 Si-O1 1.06 Si 2.33 Si-O2 0.36 O1 -1.28 Si-N1 0.57 O2 -0.77 Si-N2 0.55 N1 -0.87 O2-C 1.23 N2 -0.88

3’ Si-O1 1.12 Si 2.25 Si-O2 0.40 O1 -1.27 Si-N1 0.58 O2 -0.73 Si-N2 0.60 N1 -0.51 O2-C 1.24 N2 -0.51

2 Si-O1 0.53 Si 2.13 Si-O2 0.49 O1 -0.65 Si-N1 0.56 O2 -0.65 Si-N2 0.55 N1 -0.86 N2 -0.84

2’ Si-O1 0.51 Si 2.07 Si-O2 0.54 O1 -0.65 Si-N1 0.60 O2 -0.64 Si-N2 0.62 N1 -0.78 N2 -0.81




S14

Table S5. NRT bond orders (B3LYP/SVP)a

Natural Bond Order Compound

Total Covalent Ionic

H2Si=O 2.0510 0.8437 1.2074(6) (41.14 %) (58.87 %)

(H2N)2Si=O 1.9535 0.6837 1.2699(5) (35.00 %) (65.01 %)

4’ 1.9588 0.6249 1.3339 (31.90 %) (68.10 %)

3’b 1.9945 0.5072 1.4873 (25.43 %) (74.57 %)

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.

Table S6. Selected bond lengths (RI-BP86/TZVP)a

Compound Bond r [Å]

H2Si=O Si-O 1.552

(H2N)2Si=O Si-O 1.550 Si-N1 1.710 Si-N2 1.710

4 Si-O 1.551 Si-N1 1.736 Si-N2 1.724

4’ Si-O 1.552 Si-N1 1.729 Si-N2 1.719

3 Si-O1 1.568 (1.532) Si-O2 1.858 (1.727) Si-N1 1.779 (1.732) Si-N2 1.775 (1.744) O2-C 1.287 (1.294)

2 Si-O1 1.720 (1.693) Si-O2 1.747 (1.682) Si-N1 1.819 (1.767) Si-N2 1.826 (1.799) O1-O2 1.583 (1.547)

aCrystal structure data of 3 and 2a are given in parentheses.




S15

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.

a) b) c)




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