Pentacoordinate silicon compounds based on 2,2′-dihydroxyazobenzene ligand

Journal Pre-proof Pentacoordinate silicon compounds based on 2,2′-Dihydroxyazobenzene ligand Anastasiya S. Soldatenko, Irina V. Sterkhova, Nataliya F. Lazareva PII:

S0022-328X(19)30440-1

DOI:

https://doi.org/10.1016/j.jorganchem.2019.120997

Reference:

JOM 120997

To appear in:

Journal of Organometallic Chemistry

Received Date: 3 September 2019 Revised Date:

18 October 2019

Accepted Date: 19 October 2019

Please cite this article as: A.S. Soldatenko, I.V. Sterkhova, N.F. Lazareva, Pentacoordinate silicon compounds based on 2,2′-Dihydroxyazobenzene ligand, Journal of Organometallic Chemistry (2019), doi: https://doi.org/10.1016/j.jorganchem.2019.120997. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

PENTACOORDINATE SILICON DIHYDROXYAZOBENZENE LIGAND

COMPOUNDS

BASED

ON

2,2’-

Anastasiya S. Soldatenko, Irina V. Sterkhova, Nataliya F. Lazareva*

A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,

1,

Favorsky

st.,

664033,

Irkutsk,

Russian

Federation

E-mail:

[email protected]

Abstract The preparation and

structures of 6,6-diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines

containing the N→Si intramolecular dative bond are described. The complexes were characterized by NMR (1H, 13C, 29Si), IR and UV spectra. The crystal structures of 6-methyl-6phenyl-

and

6-(chloromethyl)-6-methylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines

were

determined by X-ray diffraction.

Introduction Hypervalent silicon compounds have attracted considerable attention due to their unique structures, physico-chemical properties and biological activity [see, for example 1-5 and ref. therein]. In order to achieve hypercoordination at the silicon atom, the different types of chelating ligands are used. The silatranes XSi(OCH2CH2)3N resulting from the interaction between silanes XSi(OAlk)3 and the tetradentate triethanolamine ligand are one of the most extensively studied neutral pentacoordinate silicon compounds with intramolecular dative bond N→Si. Unlike these, silicon complexes of O,N,O’ tridentate chelating ligand systems remain less studied, despite the fact that their first representatives were synthesized in the 70s of the last century [6 and ref. therein]. In recent years, papers dealing with pentacoordinate silicon complexes stabilized by O,N,O' tridentate Schiff base ligands have been published [7-16]. The prepared compounds were characterised by X-ray structure analysis, NMR an IR spectroscopy. The results of these investigations demonstrate the structural diversity and an interesting properties of pentacoordinate silicon compounds with O,N,O' chelating ligands. Azobenzene derivatives constitute a group of dyes which have photochromic properties and have been widely used in chemistry, medicine, biotechnology and industry [see for example rev. 17-23 and ref. therein]. 2,2'-Dihydroxyazobenzene and related compounds are excellent O,N,O’ tridentate ligands for the synthesis of different metal complexes (K, Na, Li, Ca, Mg, Zn, Co, Cr, Cu, Mo, Ni, Fe, Pd, Pt, V) [24-38]. Such complexes are promising precursors for luminescent materials, catalysts and molecular devices. There are only few complexes of group 1

14

elements

(Si,

Ge,

Sn)

with

2,2’-dihydroxyazoarenes

in

the

literature.

2,2-

Dihydroxyazobenzenato-dimethyl-tin [Me2SnL] and 2,2- dihydroxyazobenzenato-dibutyl-tin [Bu2SnL] were obtained by the reaction of 2,2-dihydroxyazobenzene (H2L) with dialkyltin oxide [39]. The structure of these compounds was confirmed by spectral data and X-ray diffraction structural analysis. 6,6-Dimethylbenzo[d,h][1,3,6,7,2]dioxadiazasilonine 1 is the first and so far the only example of the pentacoordinate silicon complex with 2,2’dihydroxyazobenzene [40]. It is interesting to note that the silicon complexes of bidentate (O,N) chelating ligand 2-hydroxy-5methylazobenzene exist as capped-tetrahedral coordination spheres

Me

Me

O Si O N

under formation of five-membered pseudo-chelates and their diazo

N 1

groups do not interaction with silicon [41]. These results show that the use of 2,2’-dihydroxyazoarenes as O,N,O tridentate ligands for synthesis of pentacoordinate siicon compounds is favoured. The study of structure and reactivity of similar compounds is of interest for development of chemistry including organic, physical, theoretical and analytical chemistry as well as materials science. Herein we report the investigation of pentacoordinated silicon

compounds

which

were

generated

from

O,N,O’-chelating

ligand

2,2’-

dihydroxyazobenzene and diorganyldichlorosilanes (MePhSiCl2, ClCH2MeSiCl2, Ph2SiCl2, (CH2=CH)MeSiCl2) or phenyltrichlorosilane (PhSiCl3). 2. Experimental section 2.1. General The 1H, 13C and 29Si NMR spectra of solutions of compounds in CDCl3 were registered on a Bruker DPX 400 spectrometer (400.1, 100.6 and 79.5 MHz respectively) with HMDS or cyclohexane as internal standard. The FTIR spectra were recorded in KBr tablets or films at room temperature on a FTIR spectrometer Varian 3100. The UV–visible spectra were recorded in acetonitrile at room temperature on a JASCO spectrometer V‐570. All reactions were performed in the flame dried glassware under an atmosphere of dry argon. The used solvents were purified according to standard procedures [42]. As a further precaution, diethyl ether was dried by filtration through column packed with neutral alumina under a positive pressure of argon. The solvents were stored under argon over molecular sieves 4A. 2.2. Synthesis 2.2.1. 6-Methyl-6-phenyl-benzo[d,h][1,3,6,7,2]dioxadiazasilonine 2. A solution of 2,2’-dihydroxyazobenzene (1.71 g, 8.00 mmol) and triethylamine (1.62 g, 16.00 mmol) in benzene (30 mL) was stirred at ambient temperature, and a solution of MePhSiCl2 (1.53 g, 8.00 mmol) in benzene was added dropwise. The resulting mixture was stirred at ambient temperature 2

for 100 h. Then the precipitate of triethylamine hydrochloride was filtered and washed with benzene (5 mL x 2) and discarded. The solvent was removed from the combined filtrate under reduced pressure. Compound 2 as red solid was isolated by the recrystallization from Et2O. Yield 1.97 g (5.93 mmol, 74%). M. p. 120 oC. 1H NMR (CDCl3, δ ppm): 0.24 (s, 3H, Me), 7.05-7.79 (m, 13H, Ph, 2C6H4). 13C NMR (CDCl3, δ ppm): 0.86 (Me), 117.2, 121.8, 127.6, 128.3, 133.9, 134.2, 134.8, 138.1, 143.8, 153.1 (Ph, 2C6H4). 29Si NMR (CDCl3, δ ppm) -67.9. Anal. Calcd. for C19H16N 2O2Si: C, 68.65; H, 4.85; N, 8.43. Found: C, 68.61; H, 4.79; N, 8.54. 2.2.2. 6-(Chloromethyl)-6-methyldibenzo[d,h][1,3,6,7,2]dioxadiazasilonine 3. The same procedure as for 2 applies. Starting materials used: (ClCH2)MeSiCl2 (1.52 g, 9.30 mmol) and triethylamine (1.88 g, 18.60 mmol) in 35 mL benzene, 2,2’-dihydroxyazobenzene (1.99 g, 9.30 mmol) in 20 mL benzene. Reaction time 80 h. Compound 3 as red solid was isolated by the recrystallization from Et2O. Yield 1.96 g (6.43 mmol, 69%). M. p. 118-119 oC. 1

H NMR (CDCl3, δ ppm): 0.09 (s, 3H, Me), 3.04 (s, 2H, ClCH2), 7.14-7.86 (m, 8H, 2C6H4). 13C

NMR (CDCl3, δ ppm): -4.1 (Me), 34.5 (ClCH2), 118.7, 122.1, 122.2, 135.4, 137.6, 135.1(2C6H4). 29Si NMR (CDCl3, δ ppm) -69.2. Anal. Calcd. For C14H13ClN2O2Si: C, 55.17; H, 4.30; N, 9.19. Found: C, 55.03; H, 4.41; N, 9.27. 2.2.3. 6,6-diphenyldibenzo[d,h][1,3,6,7,2]dioxadiazasilonine 4. The same procedure as for 2 applies. Starting materials used: Ph2SiCl2 (1.11 g, 4.40 mmol) and triethylamine (0.90 g, 8.80 mmol) in 30 mL benzene, 2,2’-dihydroxyazobenzene (0.94 g, 4.40 mmol) in 20 mL benzene. Reaction time 90 h. Compound 4 as red solid was isolated by the recrystallization from benzene-hexane (3 : 1). Yield 1.32 g (3.35 mmol, 76%). M. p. 204-206 oC. 1

H NMR (CDCl3, δ ppm): 7.06-7.78 (m, Ph, C6H4).

13

C NMR (CDCl3, δ ppm): 119.9, 122.0,

127.6, 128.8, 134.1, 134.7, 135.2., 137.9, 139.4, 153.1(Ph, C6H4). 29Si NMR (CDCl3, δ ppm): 83.7. Anal. Calcd. For C24H18N2O2Si: C, 73.07; H, 4.60; N, 7.10. Found: C, 72.95, H, 4.54; N, 7.19. 2.2.4. 6-methyl-6-vinyldibenzo[d,h][1,3,6,7,2]dioxadiazasilonine 5. The same procedure as for 2 applies. Starting materials used: (CH2=CH)MeSiCl2 (1.04 g, 7.40 mmol) and triethylamine (1.50 g, 14.80 mmol) in 30 mL benzene, 2,2’-dihydroxyazobenzene (1.59 g, 7.40 mmol) in 20 mL benzene. Reaction time 90 h. Compound 5 as dark red solid was isolated by the recrystallization from Et2O-pentane (10 : 1). Yield 1.19 g (4.21 mmol, 57%). M. p. 124-126 oC. 1H NMR (CDCl3, δ ppm): 0.16 (s, 3H, Me), 5.83-6.07 (3H, CH2=CH), 7.06-7.78 (m, 8H, 2C6H4). 13C NMR (CDCl3, δ ppm): 0.2 (Me), 120.2, 121.6, 123.4, 131.5, 134.8, 137.9, 139.6, 152.6, (CH2=CH, 2C6H4).

29

Si NMR (CDCl3, δ ppm): -68.1. Anal. Calcd. For

C15H14N2O2Si: C, 63.80; H, 5.00; N, 9.92. Found: C, 63.97; H, 5.14; N, 9.78. 2.2.4. 6-choro-6-phenyldibenzo[d,h][1,3,6,7,2]dioxadiazasilonine 6. 3

The same procedure as for 2 applies. Starting materials used: PhSiCl3 (0.70 g, 3.30 mmol) and triethylamine (1.00 g, 10.00 mmol, excess) in 30 mL benzene, 2,2’-dihydroxyazobenzene (0.71 g, 3.30 mmol) in 20 mL benzene. Reaction time 50h. Compound 6 as dark orange solid was isolated by the recrystallization from toluene. Yield o.51 g (1.45 mmol, 44%). M. p. 198 oC with the decomposition. 1H NMR (CDCl3, δ ppm): 6.95-7.97 (Ph, C6H4). 13C NMR (CDCl3, δ ppm): 117.1, 121.6, 127.1, 128.0, 131.9, 133.6, 136.5, 142.2, 153.0, 154.9. (Ph, C6H4).

29

Si NMR

(CDCl3, δ ppm): -96.6. Anal. Calcd. For C18H13ClN2O2Si: C, 61.27; H, 3.71; N, 7.94. Found: C, 61.68, H, 4.14; N, 7.01. 2.3. X-ray study and refinement Table 1. Crystal data, details of measurements, and structure refinement for compounds 2 and 3. Compound Empirical formula Formula weight / g·mol-1 Crystal system Space group a/Å b/Å c/Å α, β, γ / ˚ Volume / Å3 Z Density (calculated) / g·cm-3 Absorptions coefficient / mm-1 Radiation (λ / Å) Temperature / K 2Θ range / ° Crystal size / mm Crystal habit F(000) Index ranges

2 C19H16N2O2Si 332.43 monoclinic P 21/c 9.844(1) 9.904(1) 17.215(1) 90, 95.211(1), 90

3 C14H13ClN2O2Si 304.80 triclinic P-1 6.844(3) 8.269(4) 13.137(6) 97.377(16), 93.673(15), 106.202(15) 1671.4 (1) 704.0(6) 4 2 1.321 1.438 0.154 0.358 MoKα (0.71073) MoKα (0.71073) 293(2) 293(2) 4.62 – 60.09 5.19 – 60.08 0.230 × 0.330 × 0.380 0.030 × 0.100 × 0.250 red prism red prism 696 316 -13 ≤ h ≤ 13, -13 ≤ k ≤ 13, -24 -9 ≤ h ≤ 9, -11 ≤ k ≤ 11, -18 ≤ l ≤ 22 ≤ l ≤ 18

Reflections collected 39792 Independent reflections 4870 Max. and min. transmission 0.760 / 0.840 Number of ref. parameters 255 R1 / wR2 [I > 2σ(I)] 0.0503 / 0.1161 R1 / wR2 (all data) 0.0863 / 0.1318 2 Goodness-of-fit on F 1.024 Largest diff. peak and hole / 0.263 / -0.330 e·Å-3 Weight scheme, w = 1/[σ2(Fo2) + ( 0.0575 P)2 + 2 2 P=(Fo +2Fc )/3 0.5423 P]

18142 4104 0.687 / 0.746 182 0.0636 / 0.0934 0.1144 / 0.1749 1.003 0.258 / -0.312 w = 1/[σ2(Fo2) + ( 0.0365 P)2 + 0.2186 P]

4

The molecular structures of compounds 2 and 3 were determined by single-crystal X-ray analysis. Suitable single crystals were obtained by crystallization from Et2O. Slow cooling of the saturated solution of these compounds promotes formation of pure crystals. Crystal data were collected on a Bruker D8 Venture diffractometer with MoKa radiation (λ = 0.71073) using the φ and ω scans. The structures were solved and refined by direct methods using the SHELX programs set [43]. Data were corrected for absorption effects using the multi-scan method (SADABS). Nonhydrogen atoms were refined anisotropically using SHELX programs set [43]. Crystallographic data for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC 1916627 (2) and 1916628 (3). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Crystal data, data collection and structure refinement details are summarized in Table 1.

2.4. Quantum chemical calculations

All calculations, including NBO analysis [44, 45], were performed by the DFT B3LYP/6‐311+G(d,p) methods with full geometry optimization using the Gaussian 09 suite of programs [46]. All calculated structures are minima on the potential energy surfaces as proved by positive eigenvalues of the corresponding Hessian matrices.

3. Results and discussion

3.1. Synthesis Reaction of 2,2’-dihydroxyazobenzene with the diorganyldichlorosilanes RR’SiCl2 in a 1:1 molar

ratio

(in

the

presence

of

triethylamine

as

base)

delivered

6,6-

diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines 2-6 (Scheme 1). Dry benzene was used as solvent and the resulting mixtures were refluxed for 50-100 hrs at ambient temperature. The compounds 2-6 exhibited good solubility in benzene, chloroform and diethyl ether. Their structure was confirmed by 1H,

13

C, and 29Si NMR spectra and elemental analysis (Table 2 and

Experimental Section). In addition, structure of compounds 2 and 3 was characterized by IR, UV spectroscopy and X-ray analysis.

5

Scheme 1. Synthesis of diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines 2-6.

3.2. NMR studies The values of the 29Si NMR chemical shifts for compounds 2-6 fall in the range from -67.9 ppm to -96.6 ppm (Table 2). Notice that the value of the

29

Si NMR chemical shift for the

pentacoordinate silicon compounds 1 and 7-16 (Scheme 2) featuring the ONO’ tridentate ligands lie between -43.9 ppm and -104.3 ppm [8-12,40,47]. The degree of interaction D→Si (D = O, N) of pentacoordinate silicon compounds (the contribution of the coordination constituent of the hypervalent fragment to the shielding of the silicon atom) is determined by the difference between the values of chemical shifts for penta- and tetracoordinate silicon compounds ∆δ = δSi(V) - δSi(IV) [48]. The authors of this work noted that the correct estimation of the degree of the coordination interaction depends heavily on the correctly choose of the model tetracoordinate silicon compound with the similar chemical environment of the silicon atom. Therefore diphenoxysilanes

RR’Si(OPh)2

are

the

suitable

model

diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines 1-6. The values of

29

compounds

for

Si NMR chemical shifts

of these silanes (δ) fall range from -6.1 ppm to -37.4 ppm [49-52] and value of coordination shift (∆δ) for compounds 1-5 lies in the range 44.1 ppm to 47.3 ppm (Supp. Inf. Table 1S). Unfortunately we have failed with synthesis of pure ClPhSi(OPh)2 as model silane for compound 6. The choose of model tetracoordinate silanes for compounds 7-14 is more difficult due to the feature of structure of such ONO’ tridentate ligands. The silanes RR’Si(OAlk)2 may be used as model compounds, but in this case, the value of the coordination shift ∆δ2 is slightly higher for compounds 1-16 (Table 2).

6

Scheme 2. The pentacoordinate silicon compounds 7-16 featuring the ONO’ tridentate ligands. Table

2.

NMR

chemical

shifts

29

Si

δ

and

coordination

shifts

∆δ

for

diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines 1-6 and related compounds 7-16. Compound ∆, ppm -50.2 1 -67.9 2 -69.2 3 -83.7 4 -68.1 5 -100.7 6 -52.4 7 -84.6 8 -59.2 9 -64.9 10 -97.0 11 -95.5 12 -104.3 13 -103.3 14 -44.7 15 -43.9 16 1

Ref.

∆δ1

∆δ2

40 this work this work this work this work this work 8

44.1 46.7 50.0 46.3 47.3 46.3

47.7 53.0 57.1 54.6 53.3 82.9 49.9

8

47.2

55.5

12 9 9 11 10 10 47 47

53.1 58.8 59.6 7.3 6.5

56.7 62.4 67.9 77.7 86.5 85.5 15.6 14.8

∆δ = δSi(V) - δRR’Si(OPh)2; 2 ∆δ = δSi(V) - δRR’Si(OMe)2

7

3.3. X-Ray single crystal structure analysis The single crystals of compounds 2 and 3 were obtained by recrystallization from diethyl ether. In order to investigate their molecular structure and intermolecular interactions in the solid state, X-ray structure analysis was carried out. The molecular structures are depicted in Fig. 1. The values of the selected bond lengths and angles given in Table 3. Principal bond distances, bond angles and torsion angles are presented in Table 2S (Supporting Information). Compound 2 crystallizes in the monoclinic space group P21/c with one independent molecule in the asymmetric unit, and compound 3 – in triclinic space group P-1 also with one independent molecule in the asymmetric unit. The silicon atoms in the molecules of compounds 2 and 3 have a distorted trigonal-bipyramidal configuration, which is usually typical for the similar pentacoordinate silicon compounds with O,N,O’ tridentate ligands [8-12,40,53,54]. In compound 2 the two oxygen atoms of the bicycle (Si1–O1 and Si1–O2) and phenyl group (Si1–C3) build the equatorial plane, while the axial positions are occupied by the nitrogen atom (Si1–N1) of the bicycle and the methyl group (Si1–C17). Silicon atom of compound 3 has methyl group (Si1– C10) and two oxygen atoms of the bicycle (Si1–O1 and Si1–O2) in the equatorial positions and the nitrogen atom of the bicycle (Si1–N1) and the carbon atom of the chloromethyl group (Si1– C11) take up the axial positions. The sum of the bond angles constituent the equatorial plane around the Si atom is 354.95(2)º for compound 2 and 356.40(2)º for compound 3. The deviation of Si atom from equatorial plane in direction to carbon atom of methyl group is 0.222 Å in compound 2 and 0.165 Å in direction to carbon atom of CH2Cl group in compound 3. The C-Si-N angles equal 162.5 and 163.9 Å in compounds 2 and 3 respectively that almost on 20° off linearity. The lengths of dative bonds Si→N consist 2.171 Å and 2.079 Å in compounds 2 and 3 respectively that on 0.02÷0.22 Å less than in compound 1 (2.193 Å) [40].

2

3

Fig. 1. Molecular structures of 2 and 3 (ORTEP, 30% thermal ellipsoid plots)

8

Table 3. Selected bond lengths and angles. Compound lN→Si, Å Si-O1 Si-O2 2.193 1.714 1.701 1 1.713 1.683 2.171 2 1.711 1.684 2.079 3 2.107 1.700 1.700 8 2.068 1.713 1.737 9 1.863 1.827 1.832 10 1.834 1.803 1.815 11 1.984 1.691 1.680 12 1.980 1.656 1.662 14 2.301 1.659 1.644 15 2.680 1.621 1.642 16

Si-Xax 1.868 1.867 1.893 1.906 1.882 1.869 1.882 2.191 2.204 1.901 1.878

X-Si-N 161.23 162.5 163.9 165.6 163.4 129.0 119.9 166.0 174.2 173.9 170.5

Ref. 40 This work This work 8 12 9 9 11 10 53 54

This value of lengths of dative bonds Si→N in related compounds with O,N,O’ tridentate ligands varies in the range from 1.834 Å to 2.680 Å [8-12, 53,54]. The shortening of Si→N bond length in compound 3 in comparison with compounds 1 and 2 is due to electronegativity inductive effect of chloromethyl group CH2Cl. The pentacoordination character TBP is 84.0% and 88.6% for compounds 2 and 3 according to the Tamao equation [55]. Some azobenzenes show orientational disorder in the crystals as a result of a flipping of the orientation of the C—N=N—C unit [56-58]. It is worth noting that the conformational interconversion through pedal motion takes place [57,58]. The same behavior in the crystal of 6,6-dimethyldibenzo[d,h][1,3,6,7,2]dioxadiazasilonine 1 has been demonstrated previously by Böhme [40]. The authors of this work showed that the population of the two conformers in the single crystal depends on the temperature and cooling rate. Experimental data show that the N and O atoms in the crystal of compound 2 are disordered. The occupancy of the minor conformation is 11.3% that is approx 6% less than in compound 1 at room temperature.

3.4. DFT calculations, FTIR and UV-Vis study IR spectra of compounds 2-6 were recorded (Supp. Inf. Fig. 2S-6S). The experimental and theoretical FT-IR spectra of the molecules 2 and 3 are displayed in Figure 2. The DFT calculated wave numbers are typically higher than that of their experimental values, and thus a proper scaling factor [59, 60] (0.970) is employed to have a better agreement with the experimental wave numbers. The experimental and computed vibrational wave numbers with assignment for 2 and 3 are given in Table 4. Comparison of calculated (scaled) and experimental data shows good agreement.

9

2

3

Fig.2. Experimental and calculated IR spectra of compounds 2 and 3 in the region 400-4000 cm−1

Table 4. Vibrational analysis of compounds 2 and 3 at B3LYP/6-311+G** level Frequency, cm-1

Assignment

νs (C-H) νas (C-H) νas (C-H) δs (C-H) ν (N=N) ω (C-H) νas (C-C) νs (C-C) νas (Si-O) νs (Si-O)

2 Calculated Scaled 3187 3091 3107 3013 3033 2942 1637 1588 1536 1489 1324 1284 1138 1103 1046 1014 906 878 887 860

3 Experimental Calculated Scaled 3063 3196 3101 3026 3112 3018 2959 3096 3004 1599 1639 1590 1473 1507 1462 1290 1322 1282 1116 1166 1131 1030 1045 1013 890 911 883 873 886 859

Experimental 3064 3029 2923 1596 1477 1290 1145 1032 893 870

The electronic spectra of compounds 2 and 3 were measured in acetonitrile at room temperature. The excitation energies and oscillator strengths for the optimized geometries of compounds 2 and 3 were obtained in the framework of TD-DFT calculations with the CAMB3LYP method. TD-DFT methods are computationally more expensive in comparison with semi-empirical methods, but allow easily studies of dye molecules [61, 62]. According to literature data 6-311+G(d,p) basis set was compatible with experimental results [63-65]. For systems with proton transfer or superconjugation CAM-B3LYP method was recommended [66]. The theoretical and experimental electronic spectra of compounds 2 and 3 are displayed in Fig. 3. The maximum absorption wavelengths, HOMO, LUMO energies and HOMO-LUMO energy gaps for compounds 2 and 3 are compared in Table 5. Experimentally determined maximum absorption values for compounds 2 and 3 coincide and consist 323 and 395 nm (in CH3CN), these maximums regard to π→π* and n→π* transition respectively in conjugated 10

system of double bond N=N and benzene rings. In addition, the electron transition band at 250 nm and the long-wavelength shoulder at 435 nm was observed in the UV spectrum (Fig. 4). According to literature data [67], there are two characteristic absorption bands in the spectrum of trans-azobenzene: a strong π→π* absorption at 320 nm and a weak n→π* absorption at 440 nm. The absorption maxima due to the π→π* and n→π* electronic transitions in the UV-vis spectra of organosilicon compounds containing the 2-(phenylazo)phenyl group are near 330 nm (strong) and 440 nm (weak) respectively [68]. Compared to trans-azobenzene the blue shift of peak of n→π* transition in compounds 2 and 3 is observed, while peak of π→π* transition is very close. These spectral features are explained by the existence of the Si→N intramolecular coordination interaction in compounds 2 and 3. It should be noted that the position of the absorption bands in the UV spectra of the studied compounds in the less polar hexane (compared with acetonitrile) does not significantly change (Table 5). However, the intensity of the shoulder at 434 nm is almost equal to the intensity of the peak at 400 nm. Probably, the presence of two peaks indicates the presence in the solution of two conformers of compounds 2 and 3.

2

3 −1

Fig. 3. The experimental (blue, MeCN, c = 1 mmol L ) and theoretical (red) electronic spectra of compounds 2 and 3. Table 5. Experimental and B3LYP calculated absorption maxima for molecules 2 and 3, HOMO, LUMO energies and HOMO-LUMO energy gaps. Compound Experimental λmax (acetonitrile) Experimental λmax (hexane) Theoretical λmax (the oscillator strength) E (HOMO), eV E (LUMO), eV Energy gap, eV

2 250, 323, 395, 435 250, 326, 402, 434 297 (0.188), 327 (0.043), 395 (0.368), 406 (0.038) -6.151 -2.876 3.275

3 249, 323, 395, 431 250, 327, 400, 432 298 (0.197), 329 (0.058), 393 (0.357), 409 (0.056) -6.363 -3.080 3.283

Calculated values of λmax are 395 nm and 393 nm for compounds 2 and 3 respectively. As in the experimental spectrum, the short-wavelength band at 297 nm (298 nm for compound 3) 11

was observed in the calculated spectrum. Thus, for to π-π* transitions we can observe good agreement between experimental and theoretical data without using any scaling factors or special formulae to calculation of the values of λmax. The HOMO and LUMO of compounds 2 and 3 are presented in Fig. 4. The estimated energy gaps (∆E = ELUMO – EHOMO) for both compounds are very close and consist approximately 3.28 eV (Table 5). The HOMO is localized on whole molecule except of methyl group for compound 2 and CH2Cl-group for compound 3 and LUMO is contributed mainly by the whole of the molecule without SiMePh (2) and SiMeCH2Cl fragments (3).

HOMO

LUMO 2

3

Fig. 4. HOMO (top) and LUMO (bottom) 3D shapes for compound 2 (left) and 3 (right).

4. Conclusion The interaction between the tridentate ligand 2,2'-dihydroxyazobenzene and diorganylsilanes MePhSiCl2, ClCH2Me SiCl2, Ph2SiCl2, (CH2=CH)MeSiCl2 and PhSiCl3 lead to formation of 6,6diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines 2-6. The

29

Si chemical shifts for compounds

2-6 lie in the range from -67.9 ppm to -96.6 ppm that is typical for pentacoordinate silicon compounds. The structure of compounds was proved by NMR spectroscopy. The structure of compound 2 and 3 was proved by X-ray diffraction. The values of length of N→Si dative bond 12

are 2.171 Å and 2.079 Å for compound 2 and 3, respectively. The shortening of Si→N bond in compound 3 in comparison with compound 2 is due to electronegativity inductive effect of chloromethyl group CH2Cl. The degree of trigonal bipyramidality (TBP, %) estimated by Tamao formulae consist 84.0 and 88.6% for compounds 2 and 3 respectively. The comparative analysis of values of

29

Si NMR chemical shifts and coordination shifts for compounds 1-6 and 7-14

shows that the compounds with the identical substitutes at silicon atom and much like structure of O,N,O’ tridentatne ligand have the similar degree of N→Si coordination interaction in solution. Further investigation of physico-chemical properties of the synthesized compounds is now in progress.

Acknowledgments This work was supported by the Russian Foundation for Basic Research (Grant No. 19-0300143) using the analytical equipment of the Baikal Center for Collective Use of the SB RAS.

Appendix A. Supplementary data Supplementary data related to this article can be found at

References [1] R.R. Holmes, Chem. Rev. 90 (1990) 17-31. [2] C. Chuit, R.J.P. Corriu, C. Reye, J. C. Young, Chem. Rev. 93 (1993) 1371-1448. [3] Y. Hatanaka, J. Organometal. Chem. 685 (2003) 207-217. [4] V.A. Pestunovich, S.V. Kirpichenko, M.G. Voronkov. In: Z. Rappoport, Y. Apeloig. (Ed.), The chemistry of organic silicon compounds. Vol. 2. John Wiley & Sons Ltd., Chichester, 1998. pp. 1447-1537. [5] J.K. Puri, R. Singh, V.K. Chahal, Chem. Soc. Rev. 40 (2011) 1791-1840. [6] A.A. Selina, S.S. Karlov, G.S. Zaitseva, Chem. Heterocycl. Comp. 42 (2006) 1518-1556. [7] O. Seiler, C. Burschka, S. Metz, M. Penka, R. Tacke, Chem. Eur. J. 11 (2005) 73797386. [8] J.Wagler, E. Brendler, Z. Naturforsch. 62b (2007) 225 – 234. [9] U. Böhme, S. Fels, Inorg. Chim. Acta 406 (2013) 251–255. [10] A. Kämpfe, E. Kroke, J. Wagler, Eur. J. Inorg. Chem. (2009) 1027–1035. [11] B. Theis, S. Metz, F. Back, C. Burschka, R. Tacke, Z. Anorg. Allg. Chem. 635 (2009) 1306-1312. [12] U. Böhme, S. Fels, Acta Cryst. C66 (2010) o202–o205. 13

[13] N. Kramer, C. Jçst, A. Mackenroth, L. Greb, Chem. Eur. J. 23 (2017) 17764 – 17774. [14] J. Weiß, B. Theis, S. Metz, C. Burschka, C.F. Guerra, F.M. Bickelhaupt, R. Tacke, Eur. J. Inorg. Chem. (2012) 3216–3228. [15] J. Weiß, J.A. Baus, C. Burschka, R. Tacke, Eur. J. Inorg. Chem. (2014) 2449–2455. [16] J.Weiß, B. Theis, J.A. Baus, C. Burschka, R. Bertermann, R. Tacke, Z. Anorg. Allg. Chem. 640 (2014) 300–309. [17] F. Hamon, F. Djedaini-Pilardb, F. Barbot, C. Len, Tetrahedron 65 (2009) 10105–10123. [18] A.A. Beharry, G.A. Woolley, Chem. Soc. Rev., 40 (2011) 4422–4437. [19] E. Merino, Chem. Soc. Rev. 40 (2011) 3835–3853. [20] H.M. Dhammika Bandarab, S.C. Burdette, Chem. Soc. Rev. 41 (2012) 1809–1825. [21] V. Blanco, D.A. Leigh, V. Marcos, Chem. Soc. Rev. 44 (2015) 5341—5370. [22] Y. Wei, Q. Tang, C. Gong, M.H.-W. Lam, Analytica Chim. Acta 900 (2015) 10-20. [23] R. Dorel, B.L. Feringa, Chem. Commun. 55 (2019) 6477—6486. [24] E. Evangelio, J. Saiz-Poseu, D. Maspoch, K. Wurst, F. Busque, D. Ruiz-Molina, Eur. J. Inorg. Chem. (2008) 2278–2285. [25] G.D. Cuny, K.D. Landgrebe, T.P. Smith, M.J. Fehr, J.W. Petrich, S. Carpenter, Bioorg.&Med. Chem. Letters 9 (1999) 237-240. [26] H. Kocaokutgen, E. Erdem, Synth.&React. Inorg. and Metalorg. Chem. 34 (2004) 1843– 1853, 2004 [27] V.A. Kogan, S.N. Lyubchenko, I.N. Shcherbakov, A.M. Ionov, V.V. Tkachev, G.V. Shilov, S.M. Aldoshin, Russ. J. Coord. Chem. 31 (2005) 533–540. [28] J. Abildgaarda, P. E. Hansen, J. Josephsen, B.K.. Hansen, H.O. Shrensen, S. Larsen, Inorg. Chim. Acta 359 (2006) 4493–4502. [29] S. Baksi, R. Acharyya, S. Dutta, A.J. Blake, M.G.B. Drew, S. Bhattachary, J. Organometal. Chem. 692 (2007) 1025–1032. [30] J. Wang, C.-S. Ha, Tetrahedron 66 (2010) 1846–1851. [31] D. Sanna, K. Várnagy, N. Lihi, G. Micera, E. Garribba, Inorg. Chem. 52 (2013) 8202−8213. [32] Y. Yoshikawa, H. Sakurai, D.C. Crans, G. Micerad, E. Garribba, Dalton Trans. 43 (2014) 6965–6972. [33] H.C. Garcia, G.R. Ferreira, L.F.C. de Oliveira, J. Mol. Struct. 1061 (2014) 41–46. [34] C. Gallegos, V. Tabernero, M.E.G. Mosquera, T. Cuenca, J. Cano, Eur. J. Inorg. Chem. (2015) 5124–5132. [35] K. Takahashi, K. Kawamukai, M. Okai, T. Mochida, T. Sakurai, H. Ohta, T. Yamamoto, Y. Einaga, Y. Shiota, K. Yoshizawa, Chem. Eur. J. 22 (2016) 1253 – 1257. 14

[36] N. Lihi, A.J. Godó, G. Sciortino, E. Garribba, K. Várnagy, Polyhedron 123 (2017) 192– 205. [37] S. Murata, K. Takahashi, T. Mochida, T. Sakurai, H. Ohta, T. Yamamoto, Y. Einaga Dalton Trans. 46 (2017) 5786–5789. [38] S. Murata, K. Takahashi, T. Sakurai, H. Ohta, Polyhedron 136 (2017) 170–175. [39] K.E. Besslera, J.A. dos Santosa, V.M. Deflona, S. de Souza Lemosa, E. Niquet, Z. Anorg. Allg. Chem. 630 (2004) 742-745. [40] U. Böhme, S. Jähnigen, Acta Cryst. C64 (2008) o364–o366. [41] D. Gerlach, J. Wagler, Inorg. Chem. Comm. 10 (2007) 952–955. [42] W.L.F. Armarego, C.L.L. Chai, Purification of Laboratory Chemicals. 6th Ed., Elsevier, 2009. [43] G.M. Sheldrick, Acta Cryst. D64 (2008) 112-122. [44] F. Weinhold, C. R. Landis, Valency and Bonding: a Natural Bond Orbital Donoracceptor Perspective, University Press, Cambridge2005. [45] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1, Gaussian, Inc., Pittsburgh, PA, CT 2003. [46] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, revision B.01, Gaussian Inc, Wallingford, CT 2009. [47] E. Liepins, J. Popelis, I. Birgele, I. Urtane, G. Zelchan, E. Lukevics, J. Organometal. Chem. 201 (1980) 113-121. [48] V.V. Negrebetsky, Yu.L. Baukov, Russ. Chem. Bull. 46 (1997) 1807-1831. [49] R.H. Cragg, R.D. Lane, J. Organometal. Chem. 277 (1984) 199-201. [50] G. Engelhardt, R. Radeglia, H. Jancke, E. Lippmaa, M. Maegi, Org. Magn. Reson. 5 (1973) 561-566. [51] B. Biernat, T. Szymanґska-Buzar, J. Organometal. Chem. 690 (2005) 4656–4665. 15

[52] R. Tacke, J. Sperlich, C. Strohmann, G. Mattern, Chem. Ber. 124 (1991) 1491 – 1496. [53] J.J. Daly, F. Sanz, J. Chem. Soc. Dalton Trans. (1974), 2051-2054. [54] A. Kemme, J. Bleidelis, I. Urtane, G. Zelchan, E. Lukevics, J. Organometal. Chem. 202 (1980) 115-121. [55] K. Tamao, T. Hayashi, Y. Ito, M. Shiro, Organometallics 11 (1992) 2099-2114. [56] J.A. Bouwstra, A. Schouten, J. Kroon, Acta Cryst. C39 (1983) 1121-1123. [57] J. Harada, K. Ogawa, J. Am. Chem. Soc. 122 (2001) 10884-10888. [58] J. Harada, K. Ogawa, J. Am. Chem. Soc. 126 (2004) 3539-3544. [59] J.P. Merrick, D. Moran, L. Radom, J. Phys. Chem. A111 (2007) 11683–11700. [60] R.D. Johnson III, NIST Computational Chemistry Comparison and Benchmark Database, Precomputed vibrational scaling factors. Retrieved from web-page: http://cccbdb.nist.gov/vibscalejust.asp. [61] D. Guillaumont, S. Nakamura, Dyes Pigments 46 (2000) 85-92. [62] J. Fabian, Dyes Pigments 84 (2010) 36-53. [63] L. Briquet, D.P. Vercauteren, Phys. Lett. 435 (2007) 257-262. [64] Z. Seferoğlu, E. Aktan, N. Ertan, Color. Technol. 125 (2009) 342-351. [65] E. Aktan, B. Babür, Z. Seferoğlu, T. Hökelek, E. Şahin, J. Mol. Str. 1002 (2011) 113– 120. [66] T. Yanai, D.P. Tew, N.C. Handy, Chem. Phys. Lett. 393 (2004) 51–57. [67] H. Rau, Photochromism: Molecules and Systems; Elsevier: Amsterdam, 1990; Chapter 4. [68] N. Kano, F. Komatsu, M. Yamamura, T. Kawashima, J. Am. Chem. Soc. 128 (2006) 7097-7109.

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Highlights • 6,6-Diorganylbenzo[d,h][1,3,6,7,2]dioxadiazasilonines were obtained • NMR, IR, UV and X-Ray study • length of N→Si dative bond are 2.171 Å and 2.079 Å for compound 2 and 3 • (TBP, %) estimated by Tamao consist 84.0 and 88.6% for compounds 2 and 3