Subscriber access provided by READING UNIV
Communication
A Stable Push-Pull Disilene: Substantial DonorAcceptor Interactions through the Si=Si Double Bond Tomoyuki Kosai, and Takeaki Iwamoto J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b09989 • Publication Date (Web): 01 Dec 2017 Downloaded from http://pubs.acs.org on December 2, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Journal of the American Chemical Society
A Stable Push-Pull Disilene: Substantial Donor-Acceptor Interactions through the Si=Si Double Bond Tomoyuki Kosai and Takeaki Iwamoto* Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
Supporting Information Placeholder ABSTRACT: The push-pull effect has been widely used to effectively tune π-electron systems. Herein, we report the synthesis and properties of 1-amino-2-boryldisilene 1 as the first push-pull disilene. Its spectroscopic and structural features show substantial interactions between the Si=Si double bond and the amino and boryl substituents. The π→π* absorption band of 1 is remarkably red-shifted compared to that of the corresponding alkylsubstituted disilene 2. Treatment of 1 with H2 resulted in the cleavage of two molecules of H2 under concomitant formation of the corresponding trihydridodisilane and hydroborane.
Mes
N(SiMe3)2 Dsi2(i-Pr)Si
Si Si (Me3Si)2N
B Si Si
Mes H
A
Si(i-Pr)Dsi2 B
R R t-Bu Si Si
Tip
Tip Si Si
Tip
R R
ZrClCp2 D
C R R
The simultaneous introduction of donors and acceptors to πelectron systems has been widely used to tune their electronic and optical properties.1 These so-called push-pull compounds have often been applied to functional organic dyes, as their orbital energy levels can be effectively controlled by judiciously choosing the donors and acceptors. Over the past decades, π-electron systems involving Si=Si double bonds, i.e., disilenes, which exhibit an intrinsically narrow π–π* gap, have been considered as novel prospective functional π-electron systems.2 Disilenes with organic π-electron systems,3 transition-metal-based d-electron systems,4 and silicon-based σ-electron systems5 have been reported. Nevertheless, compared to conventional organic π-electron systems, the diversity of such functionalized disilenes remains limited, as bulky protecting groups are inevitable to stabilize the disilenes sufficiently to be isolated. Although stable disilenes containing either a π-donor such as an amino group (A),6 or a π-acceptor such as a boryl group (B),7 anthryl group (C),8 or transition metal (D)4a have been reported (Chart 1), examples of disilenes that contain both a π-donor and a π-acceptor (push-pull disilenes) remain elusive. Herein, we report 1-amino-2-boryldisilene 1 as the first push-pull disilene, which shows, due to the push-pull effect, a substantial bathochromic shift of its absorption band compared to that of the corresponding alkyl-substituted disilene 2 (Chart 1). Interestingly, treatment of 1 with H2 at room temperature resulted in the cleavage of two molecules of H2 under concomitant formation of an aminotrihydridodisilane and a hydroborane.
Me 3Si
SiMe3
B
Si Si N Tip Ad 1
Si Si Tip Me 3Si
SiMe3 2
Chart 1. Examples of disilenes that contain either a donor or an acceptor group, as well as disilenes 1 and 2 [Mes = mesityl; Dsi = CH(SiMe3)2; Tip = 2,4,6-triisopropylphenyl; R = SiMe3; Ad = 1-adamantyl]. Air-sensitive dark red crystals of push-pull disilene 1 were obtained in 59% yield from the reaction of 2-aminodisilenide 3, which was prepared by the reduction of an adduct of the cyclic (alkyl)(amino)silylene (CAASi) E9 and TipSiCl3 (5) with KC8 (for details, see SI), and B-chloro-9-borabicyclo[3.3.1]nonane in benzene (Scheme 1). Although 1 is stable at room temperature, it decomposes after 12 h at 70 °C in C6D6. To reveal the effects of the amino and boryl groups on the Si=Si double bond in 1, we synthesized disilene 2, which contains alkyl groups instead of amino and boryl groups in a similar structural motif (Scheme 2). The molecular structures of 1 and 2 were determined by a combination of multinuclear NMR spectroscopy and single-crystal Xray diffraction (XRD) analyses.
ACS Paragon Plus Environment
Journal of the American Chemical Society 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Scheme 1. Synthesis of 1 (Ad = 1-adamantyl; Tip = 2,4,6triisopropylphenyl). Me3Si SiMe3 Si N Ad E
1) TipSiCl3, THF, rt
Me3Si SiMe3
Cl B
K(thf)
Si Si
2) 5 KC8, THF, –30 °C
N Ad 3
benzene, rt
Tip
1 (59%)
Scheme 2. Synthesis of 2. Me 3Si
SiMe3 Si
Me 3Si
SiMe3
TipSiCl3, 5 KC8 THF, rt
Me3Si SiMe3
K
Si Si Tip
Br THF, rt, 3 h
2 (40%)
Me3Si SiMe3 4
The molecular structures of 1 and 2 are shown in Figure 1.10 In 1, the boryl group is arranged trans to the amino group (Z-isomer according to the CIP nomenclature). The Si1–Si2 bond in 1 [2.2146(6) Å] is longer than that in 2 [2.1828(6) Å]. The N1–Si1 bond in 1 [1.7215(15) Å] is much longer than typical Si=N double bonds (1.55-1.59 Å),11 but relatively short compared to those in reported aminodisilenes (1.703-1.775 Å)6 and comparable to that in E [1.7143(15) Å], which exhibits a moderate but nevertheless significant N=Si double bond character.9 The Si2–B1 bond in 1 [1.945(2) Å] is longer than conventional Si=B double bonds [1.8379(17) and 1.859(2) Å],12 but substantially shorter than that in reported boryldisilenes [1.996-2.022 Å].7 The geometry around the N1, Si1, Si2, and B1 atoms is almost planar, i.e., the angle sum around each atom is ~360° (N1: 358.2°; Si1: 358.1°; Si2: 358.3°; B1: 359.7°). The π-orbital axis vectors (POAVs)13 suggest that the p orbitals on the N1, Si1, Si2, and B1 atoms are almost parallel to each other, albeit that they include small twist angles (N1–Si1: 4.5°; Si1–Si2: 15.9°; Si1–B1: 8.7°), which allows efficient interactions between the p orbitals. Although steric effects of the bulky substituents on the Si=Si double bond cannot be ruled out at this point,14 these structural features are consistent with a significant contribution of canonical structures that contain N+=Si and Si=B− double bonds, which have previously been proposed for (Dsi2i-PrSi)HSi=Si(SiDsi2i-Pr)(ER2) [E = N or B].7b The Tip groups adopt an almost perpendicular arrangement relative to the Si=Si double bond, i.e., the p orbitals on Si2 and Cipso(Tip) are twisted (1: 77.2°; 2: 84.5°).
Figure 1. ORTEP drawings of (a) 1 and (b) 2 (only one of the two crystallographically independent molecules in the unit cell of 2 is shown) with thermal ellipsoids set at 50% probability and hydrogen atoms omitted for clarity.
ally optimized at the B3PW91-D3/6-31G(d) level of theory (1opt). The 13C NMR spectrum showed only two signals for secondary and one signal for tertiary carbon atoms in the 9-BBN moiety, which indicates fast rotation around the Si–B bond in solution on the NMR time scale. The 29Si NMR spectrum of 1 showed three signals at 142.4 [(alkyl)(amino)Si=], 2.5 (SiMe3), and –33.0 ppm [=Si(boryl)Tip]. The difference in chemical shift for the doublebonded silicon nuclei in 1 (∆δSi = 175.4 ppm) is much larger than that in 2 [117.9 ((alkyl)2Si=) and 77.2 ppm (=SiTip(i-Pr)); ∆δSi = 40.7 ppm], indicative of a substantially polar Si=Si double bond in 1.15 The UV-vis absorption spectrum of 1 revealed push-pull effects for the amino and boryl groups on the Si=Si double bond. A hexane solution of 1 exhibited its longest-wavelength absorption band at 482 nm, which is considerably red-shifted relative to that of 2 [~407 (shoulder) and 357 nm] (Figure 2).
Figure 2. UV-vis absorption spectra of 1 (red) and 2 (black) in hexane. The electronic structure of 1 was also examined by theoretical calculations (cf. SI). The structures of 1 and 2 were optimized at the B3PW91-D3/6-31G(d) level of theory (1opt and 2opt), and are in good agreement with those obtained from the XRD analyses (Table S1). The band positions and their oscillator strengths determined by TDDFT calculations on the optimized structures at the TD-B3LYP/6-31+G(d) level of theory were also consistent with those obtained from the experimental spectra (Figure S66), suggesting that the structures of 1 and 2 in solution are close to those observed in the crystalline state (Table S1). The HOMO of 1opt is the π(Si=Si) orbital, while the LUMO is the π*(Si=Si) orbital (Figure 3a). Both the HOMO and the LUMO involve a substantial contribution from the 2p orbital of the N atom and the 2p orbital of the B atom, which reflects the π-donor effect of the amino group and the π-acceptor effect of the boryl group on the Si=Si double bond. These orbital features are similar to those observed in 1-amino-2-borylacetylene.16 The TDDFT calculations support the assignment of the absorption band of 1 at 482 nm to the HOMO→LUMO transition. Although the HOMOs of 1 (–4.45 eV) and 2 (–4.42 eV) are virtually identical in energy, the LUMO of 1 (–1.53 eV) is substantially stabilized relative to that of 2 (– 0.74 eV). These orbital features suggest that the electronwithdrawing effect of the boryl group on the Si=Si double bond dominates the electron-donating effect of the amino group. This notion is also consistent with the bond lengths determined by the XRD analysis and the results of the following calculations.17
The multinuclear NMR spectra of 1 in C7D8 from –80 °C to 80 °C indicated the presence of one isomer, which is probably the Z-isomer, i.e., the isomer observed in the solid state. This notion was also supported by DFT calculations, as the geometric isomer of 1 (E-1opt) is 16.2 kJ/mol higher in energy than 1, when structur-
ACS Paragon Plus Environment
Page 2 of 5
Page 3 of 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Journal of the American Chemical Society
(a)
isomerize to acyclic silylene 8opt (activation energy: +53.5 kJ mol–1) via a 1,2-hydrogen migration.23 Subsequently, a second molecule of H2 should be inserted at the silylene center of 8opt (activation energy: +62.0 kJ mol–1)24,25 to give 6opt. Although the direct anti-addition of H2 across the Si=Si double bond of 7opt in a manner similar to the reaction of 1,2-diiminodisilene with H2, which has very recently been reported by Inoue and Rieger,21e,26 was also examined, the activation energy (143.9 kJ mol–1) of this process was estimated to be substantially higher than that in the pathway proceeding via 8opt.
(b)
Scheme 3. Reaction of 1 with H2 (R = SiMe3). R R
B
Si Si N R2
B
Si Si 3
R 1a
R R
N R2
B
Si Si 3
R 1b
R R
N R2
R R
B
Si Si 3
R 1c
R R
N R2
H2 (1 atm)
1
C6D6, rt
3
R
A natural resonance theory (NRT)18 analysis of model compound 1', which bears methyl and 2,6-dimethylphenyl (Dip) groups instead of the bulky adamantyl and Tip groups (R2 = Me; R3 = Dip; Figure 3b) and was optimized at the B3PW91-D3/631G(d) level of theory,19 also showed a dominant contribution of canonical structures with an Si=B− moiety and a significant contribution of structures with an N+=Si moiety (1'a: 54.8%; 1'b: 7.0%; 1'c: 31.4%; 1'd: 4.1%) (Figure 3b). A second-order perturbation analysis afforded the stabilization energies for the π(Si=Si) →2p(B) donation (165.0 kJ mol–l) and the n(N)→π*(Si=Si) donation (93.2 kJ mol–1). The Wiberg bond indices (WBI) of the Si=Si double bond in 1' (1.44) are lower compared to that in 2opt (1.78), while the WBI of the N–Si bond in 1' (0.73) is slightly larger than that in cyclic (alkyl)(amino)dihydridosilane F (a dihydrogenated derivative of E) (0.67).9 The WBI of the Si–B bond in 1' (1.25) suggests a slight double bond character for the Si–B bond. Natural population analysis (NPA) charges in 1' [(alkyl)(amino)Si: +1.34; boryl(Tip)Si: +0.28] indicated the presence of a polar Si=Si double bond, which is consistent with the large ∆δSi observed in the 29 Si NMR spectra. Based on these results, the remarkable bathochromically shifted absorption band observed for 1 should be attributed to the pronounced push-pull effect of the amino and boryl groups. When a C6D6 solution of 1 was exposed to an atmosphere of H2 (1 atm) at room temperature, the red color of the solution disappeared gradually.20,21 Multinuclear NMR spectra indicated the formation of trihydridodisilane 6 and the dimer of 9borabicyclo[3.3.1]nonane [(9-BBN)2] (Scheme 3). When D2 was used instead of H2, the corresponding deuterated products 6-d3 and (9-BBN-d1)2 were obtained. The formation of these products indicates that the hydrogenation of the Si=Si double bond occurs under concomitant cleavage of the Si–B bond. Disilene 2 did not react with H2 at temperatures up to 70 °C. The mechanism for the reaction of 1 with H2 was investigated theoretically at the B3PW91-D3/6-31G(d) level of theory (Figure 4). The results of these calculations suggest that initially, a molecule of H2 should coordinate to the empty 2p orbital on the B atom (activation energy: +115.0 kJ mol–1)22 to cleave the Si–B bond of 1opt and provide the corresponding hydridodisilene 7opt and 9-BBN, whereupon the latter should dimerize to afford (9-BBN)2. Then, 7opt should
H H
Si
+
1/2
H B
B H
N Ad Tip 6 (82%)
1d
Figure 3. (a) The HOMO and LUMO of 1opt (isosurface value = 0.05); hydrogen atoms are omitted for clarity. (b) Major canonical resonance structures for 1 (R = SiMe3; R2 = 1-adamantyl; R3 = Tip).
H
Si
(a) Cleavage of the first molecule of H2. H B
C
115.0 (67.5)
Si Si N
Tip 1opt + H2 0.0 (0.0)
7opt9-BBN
H C
H
B
17.3 (–25.1)
Si Si N
R R
B
C
H Si Si N Tip
Si =
C
Tip TS1
N –3.5 (30.6) H Si Si N Tip 7opt + 9-BBN
Si N Ad
7opt + 1/2 (9-BBN)2
C
–43.9 (–49.0)
(b) Cleavage of the second molecule of H2.
H Si Si N Tip 53.5 (50.0) 7opt + H2 C H 0.0 Si Si (0.0) N Tip TS2 + H2 C
C HH C H H Si Si Si Si N N Tip Tip 111.1 9opt TS4 (61.0) 8opt + H2 114.6 109.7 C H H H (56.8) (60.9) 52.6 Si (47.5) Si N Tip TS3
C H H Si H Si N Tip 6 opt –128.0 (–193.1)
Figure 4. Reaction pathways and energy levels for the reaction of 1opt with two molecules of H2, calculated at the B3PW91-D3/631G(d) level of theory. Free energy and electron energy values shown in parentheses are given in kJ/mol (R = SiMe3, Ad = 1adamantyl, Tip = 2,4,6-triisopropylphenyl). In summary, we have synthesized push-pull 1-amino-2boryldisilene 1. The observed large difference in the 29Si NMR chemical shifts of the Si nuclei in the Si=Si double bond suggests substantial polarization. The structural features determined by single-crystal XRD analysis indicate a significant double bond character with contributions from N+=Si and Si=B− moieties. The push-pull effect on the Si=Si double bond is also reflected in a bathochromic shift of the longest-wavelength absorption band of 1. Moreover, 1 cleaves two molecules of H2 at room temperature. It seems feasible to anticipate that the push-pull effect could become a key interaction in functional compounds based on Si=Si double bonds, as well as in carbon-based π-bonds.
ASSOCIATED CONTENT Supporting Information
ACS Paragon Plus Environment
Journal of the American Chemical Society 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
The Supporting Information for this article is available free of charge on the ACS Publications website at DOI: Experimental and theoretical details (PDF) Crystallographic data for 1-3 and 5 (CIF)
AUTHOR INFORMATION Corresponding Author *
[email protected] ORCID Tomoyuki Kosai: 0000-0003-3435-1354 Takeaki Iwamoto: 0000-0002-8556-5785
Notes The authors declare no competing financial interests.
ACKNOWLEDGMENT This work was supported by MEXT KAKENHI grant JP24109004 (T.I.) (Grant-in-Aid for Scientific Research on Innovative Areas "Stimuli-responsive Chemical Species") and the JSPS KAKENHI grant JPK1513634 (T.I.). The authors thank Prof. Satoshi Maeda (Hokkaido University) for helpful discussions on theoretical calculations.
REFERENCES (1) For a recent review on the push-pull effect, see: Meier, H. Angew. Chem., Int. Ed. 2005, 44, 2482-2506. (2) For recent comprehensive reviews on species that contain multiply bonded silicon, see: (a) Lee, V. Ya.; Sekiguchi, A. Organometallic Compounds of Low-Coordinate Si, Ge, Sn, and Pb: From Phantom Species to Stable Compounds, John Wiley & Sons Ltd: Chichester, UK, 2010. (b) Fischer, R. C.; Power, P. P. Chem. Rev. 2010, 110, 3877-3923. (c) Iwamoto, T.; Ishida, S. Struct. Bonding 2014, 156, 125-202. (d) Präsang, C.; Scheschkewitz, D. Chem. Soc. Rev. 2016, 45, 900–921. (3) (a) Bejan, I.; Scheschkewitz, D. Angew. Chem., Int. Ed. 2007, 46, 5783-5786. (b) Fukazawa, A.; Li, Y.; Yamaguchi, S.; Tsuji, H.; Tamao, K. J. Am. Chem. Soc. 2007, 129, 14164-14165. (c) Jeck, J.; Bejan, I.; White, A. J. P.; Nied, D.; Breher, F.; Scheschkewitz, D. J. Am. Chem. Soc. 2010, 132, 17306-17315. (d) Li, L.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. J. Am. Chem. Soc. 2015, 137, 15026-15035. (4) (a) Nguyen, T.-l.; Scheschkewitz, D. J. Am. Chem. Soc. 2005, 127, 10174-10175. (b) Sasamori, T.; Yuasa, A.; Hosoi, Y.; Furukawa, Y.; Tokitoh, N. Organometallics 2008, 27, 3325-3327. (c) Yuasa, A.; Sasamori, T.; Hosoi, Y.; Furukawa, Y.; Tokitoh, N. Bull. Chem. Soc. Jpn. 2009, 82, 793-805. (d) Cowley, M. J.; Abersfelder, K.; White, A. J. P.; Majumdar, M.; Scheschkewitz, D. Chem. Commun. 2012, 48, 6595-6597. (5) Kosai, T.; Ishida, S.; Iwamoto, T. J. Am. Chem. Soc. 2017, 139, 99102. (6) (a) Michalczyk, M. J.; West, R.; Michl, J. Organometallics 1985, 4, 826-829. (b) Schmedake, T. A.; Haaf, M.; Apeloig, Y.; Müller, T.; Bukalov, S.; West, R. J. Am. Chem. Soc. 1999, 121, 9479-9480. (c) Jutzi, P.; Mix, A.; Rummel, B.; Schoeller, W. W.; Neumann, B.; Stammler, H.-G. Science 2004, 305, 849-851. (d) Takeuchi, K.; Ikoshi, M.; Ichinohe, M.; Sekiguchi, A. J. Organomet. Chem. 2011, 696, 1156-1162. (e) Willmes, P.; Junk, L.; Huch, V.; Yildiz, C. B.; Scheschkewitz, D. Angew. Chem. Int. Ed. 2016, 55, 10913-10917. (7) (a) Inoue, S.; Ichinohe, M.; Sekiguchi, A. Chem. Lett. 2008, 37, 1044-1045. (b) Takeuchi, K.; Ikoshi, M.; Ichinohe, M.; Sekiguchi, A. J. Am. Chem. Soc. 2010, 132, 930-931. (c) Takeuchi, K.; Ichinohe, M.; Sekiguchi, A. Organometallics 2011, 30, 2044-2050.
Page 4 of 5
(8) (a) Iwamoto, T.; Kobayashi, M.; Uchiyama, K.; Sasaki, S.; Nagendran, S.; Isobe, H.; Kira, M. J. Am. Chem. Soc. 2009, 131, 3156-3157. (b) Takeuchi, K.; Ichinohe, M.; Sekiguchi, A. J. Am. Chem. Soc. 2012, 134, 2954-2957. (c) Kobayashi, M.; Hayakawa, N.; Matsuo, T.; Li, B.; Fukunaga, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. J. Am. Chem. Soc. 2016, 138, 758-761. (d) Obeid, N. M.; Klemmer, L.; Maus, D.; Zimmer, M.; Jeck, J.; Bejan, L.; White, A. J. P.; Huch, V.; Jung, G.; Scheschkewitz, D. Dalton. Trans. 2017, 46, 8839-8848. (e) Kosai, T.; Ishida, S.; Iwamoto, T. Dalton Trans. 2017, 46, 11271-11281. (9) Kosai, T.; Ishida, S.; Iwamoto, T. Angew. Chem. Int. Ed. 2016, 55, 15554-15558. (10) Disilene 2 contains two crystallographically independent molecules per asymmetric unit. As the double-bonded silicon atoms of one molecule were disordered, we used the other molecule for the discussion. (11) (a) Wiberg, N.; Schurz, K.; Reber, G.; Müller, G. J. Chem. Soc. Chem. Commun. 1986, 591-592. (b) Niesmann, J.; Klingebiel, U.; Schäfer, M.; Boese, R. Organometallics 1998, 17, 947-953. (c) Iwamoto, T.; Ohnishi, N.; Gui, Z.; Ishida, S.; Isobe, H.; Maeda, S.; Ohno, K.; Kira, M. New. J. Chem. 2010, 34, 1637-1645. (12) (a) Nakata, N.; Sekiguchi, A. J. Am. Chem. Soc. 2006, 128, 422423. (b) Suzuki, Y.; Ishida, S.; Sato, S.; Isobe, H.; Iwamoto, T. Angew. Chem. Int. Ed. 2017, 56, 4593-4597. (13) Haddon, R. C. J. Am. Chem. Soc. 1990, 112, 3385-3389. (14) The structural parameters were reproduced by the permethylated model compounds (for details, see SI). (15) We failed to observe a 11B NMR signal for 1, which is probably due to the large chemical shift anisotropy of the 11B nucleus. (16) Onuma, K.; Suzuki, K.; Yamashita, M. Chem. Lett. 2014, 44, 405407. (17) Although cyclic voltammetry (CV) measurements should afford further information on the electronic structures, such measurements were unfortunately unsuccessful. (18) For a detailed citation of the NRT analysis, see ref S14 in the SI. (19) NRT analyses on the real molecule 1opt were unsuccessful as its molecular size was too large. Therefore, we used a model compound, whose structural parameters around the Si=Si double bond were constrained during the geometry optimization to those of 1opt. (20) For a recent review on the activation of small molecules using main-group element, see: Power, P. P. Nature 2010, 463, 171-177. (21) For examples on the activation of H2 using heavier double- and triple-bonded compounds, see: (a) Spikes, G. H.; Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 12232-12233. (b) Peng, Y.; Brynda, M.; Ellis, B. D.; Fettinger, J. C.; Power, P. P. Chem. Commun. 2008, 60426044. (c) Li, J.; Schenk, C.; Goedecke, C.; Frenking, C.; Jones, C. J. Am. Chem. Soc. 2011, 133, 18622-18625. (d) Nagata, K.; Murosaki, T.; Agou, T.; Sasamori, T.; Matsuo, T.; Tokitoh, N. Angew. Chem. Int. Ed. 2016, 55, 12877-12880. (e) Wendel, D.; Szilvást, T.; Jandl, C.; Inoue, S.; Rieger, B. J. Am. Chem. Soc. 2017, 139, 9156-9159. (22) A similar transition state has been proposed for the reaction between diborane(4) and H2; see: Tsukahara, N.; Asakawa, H.; Lee, K.-H.; Lin, Z.; Yamashita, M. J. Am. Chem. Soc. 2017, 139, 2593-2596. (23) Agou, T.; Sugiyama, Y.; Sasamori, T.; Sakai, H.; Furukawa, Y.; Takagi, N.; Guo, J.-D.; Nagase, S.; Hashizume, D.; Tokitoh, N. J. Am. Chem. Soc. 2012, 134, 4120-4123. (24) Protchenko, A. V.; Birjkumar, K. H.; Dange, D.; Schwarz, A. D.; Vidovic, D.; Jones, C.; Kaltsoyannis, N.; Mountford, P.; Aldridge, S. J. Am. Chem. Soc. 2012, 134, 6500-6503. (25) For recent theoretical studies on the addition of H2 to silylenes, see: (a) Wang, Y.; Ma, J. J. Organomet. Chem. 2009, 694, 2567-2575. (b) Devarajan, D.; Doubleday, C. E.; Ess, D. H. Inorg. Chem. 2013, 52, 88208833. (c) Kuriakose, N.; Vanka, K. Dalton Trans. 2014, 43, 2194-2201. (26) Similar anti-addition of σ(Si–Si) bonds across the Si=Si double bond have been reported for a tricyclic disilene; see: Tanaka, R.; Iwamoto, T.; Kira, M. Angew. Chem. Int. Ed. 2006, 45, 6371-6373.
ACS Paragon Plus Environment
Page 5 of 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Journal of the American Chemical Society
ACS Paragon Plus Environment
5
