Catalytic Access to Indole-Fused Benzosiloles by 2-Fold Electrophilic

Article pubs.acs.org/Organometallics

Catalytic Access to Indole-Fused Benzosiloles by 2‑Fold Electrophilic C−H Silylation with Dihydrosilanes Lukas Omann and Martin Oestreich* Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, 10623 Berlin, Germany S Supporting Information *

ABSTRACT: A protocol for the catalytic synthesis of indolefused benzosiloles starting from 2-aryl-substituted indoles and dihydrosilanes is reported. Compared to known procedures, this method does not require prefunctionalized starting materials and, hence, allows for a rapid access to those siloles. The net reaction is a 2-fold electrophilic C−H silylation catalyzed by cationic Ru−S complexes. Both reaction steps were separately investigated, and these results eventually led to the development of a two-step procedure. By preparing new Ru−S complexes with different weakly coordinating anions (WCAs), it is also shown that the latter can have a dramatic influence on the outcome of these reactions. Furthermore, the substrate scope of the new method is discussed.

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INTRODUCTION Organic π-conjugated molecules with incorporated silicon atoms feature interesting optoelectronic properties.1 Among this family of compounds siloles have emerged as promising molecules for the development of new materials.2 Consequently, numerous catalytic reactions for their preparation,3 in particular for benzo-4 and dibenzosiloles,5 have been reported over the last years. On the contrary, methods for the construction of indole-fused benzosiloles 1 are by far less developed despite their fascinating blue-fluorescence properties.6 In fact, only two procedures have been described in the literature:7,8 Shimizu, Hiyama, and co-worker introduced a delicate route to 1 by a palladium-catalyzed C−H/C−OTf coupling (Scheme 1, 2 → 1aa);9 this reaction involves an unusual 1,2-silyl migration.10 More recently, He and co-workers disclosed an elegant approach to these molecules by a rhodiumcatalyzed domino cyclization/Si−C bond activation reaction (3 → 1bb).11 Although both of these methods are highly efficient, we asked ourselves whether it was possible to construct these molecules from more easily accessible, i.e., not prefunctionalized, starting materials by the strategy outlined below (Scheme 2). We had reported before that cationic Ru−S complexes12 [4]+[X]− (X = BArF4) are capable of splitting the Si−H bond of hydrosilanes R3SiH into a sulfur-stabilized silicon cation and a ruthenium hydride.13 This was applied to the catalytic intermolecular SEAr of electron-rich indoles.14,15 More recently, we extended this methodology to the intramolecular SEAr of benzenes, thereby providing access to dibenzosiloles.16,17 We then anticipated that this catalytic system could also be applicable to the activation of dihydrosilanes R2SiH2 and, hence, envisioned the development of a 2-fold Friedel−Craftstype C−H silylation18,19 where 2-aryl-substituted indoles 5 and © XXXX American Chemical Society

Scheme 1. Previously Reported Methods for the Construction of Indole-Fused Benzosiloles

dihydrosilanes 6 would initially react to the C3-silylated indole 7 followed by ring closure at higher temperatures to eventually afford 1 with an overall release of two molecules of dihydrogen. The utility of this approach lies in the ready availability of 5 through directing-group-free catalytic C−H arylation methods.20 It is important to mention that the idea can be traced back to the work of Curless and Ingleson, who employed B(C6F5)3 as a catalyst in this transformation.17c The electrondeficient borane was indeed capable of forming 7, but no ring closure to 1 was observed. Instead, the catalyst was converted Received: October 18, 2016

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DOI: 10.1021/acs.organomet.6b00801 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

an electron-rich phosphine ligand (entries 1 and 2). The reaction turned out to be sensitive toward the amount of dihydrosilane, providing higher conversions with an excess of 3.0 equiv (entry 2 versus entry 3). Lowering the catalyst loading from 5 mol % to 2 mol % did not diminish the yield (entry 4), and high conversions were even obtained at a catalyst loading of 1 mol %. For screening the reaction conditions of the next reaction step, we conducted a gram-scale synthesis, which afforded 7ac in 92% isolated yield. It is noteworthy that, under these reaction conditions, we have never observed any formation of traces of indoline. Optimization of the Intramolecular C−H Bond Silylation. We next focused on the intramolecular SEAr, i.e., the ring closure of 7ac to 1ac. Our previously reported procedure for the synthesis of dibenzosiloles required microwave heating at 140 °C.16 Hence, we tested catalysts [4a]+[BArF4]− and [4b]+[BArF4]− under similar reaction conditions (Table 2, entries 1 and 2). With a catalyst loading

Scheme 2. New Approach to Indole-Fused Benzosiloles by 2Fold Electrophilic C−H Silylationa

a

ArF = 3,5-bis(trifluoromethyl)phenyl.

Table 2. Optimization of the Intramolecular Electrophilic C−H Silylation

into the catalytically inactive ion pair [indoline−H]+[H− B(C6F5)3]−, hence inhibiting the reaction at 70% conversion.21 In addition to the susceptibility of indoles to be reduced to indolines, the difficulty of such a transformation lies also in the fact that the silylated indole 7 is prone to protodesilylation in the presence of Brønsted acids.

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RESULTS AND DISCUSSION Optimization of the Intermolecular C−H Bond Silylation. We decided to begin with investigating both reaction steps separately and chose 1-methyl-2-phenylindole (5a) and MePhSiH2 (6c) as model substrates for our optimization study (Table 1). Our previously reported Table 1. Optimization of the Intermolecular Electrophilic C−H Silylation

entrya 1 2 3 4 5c

equiv of 6c 3.0 3.0 1.1 3.0 3.0

catalyst +

F

−

[4b] [BAr 4] [4a]+[BArF4]− [4a]+[BArF4]− [4a]+[BArF4]− [4a]+[BArF4]−

(5 mol %) (5 mol %) (5 mol %) (2 mol %) (1 mol %)

entrya

T (°C)

solvent

catalyst

conv (%)b

ratioc 1ac:5a:8ac

1 2 3 4 5 6d 7e 8

140 140 160 180 180 180 180 180

ClC6H5 ClC6H5 1,2-Cl2C6H4 1,2-Cl2C6H4 mesitylene mesitylene mesitylene mesitylene

[4a]+[BArF4]− [4b]+[BArF4]− [4a]+[BArF4]− [4a]+[BArF4]− [4a]+[BArF4]− [4a]+[BArF4]− [4a]+[BArF4]− [4b]+[BArF4]−

37 27 82 89 93 >99 99 91

0:29:8 5:13:9 14:50:18 25:33:31 61:10:22 13:41:45 56:11:31 54:18:19

conv (%)b 23 97 40 97 95 (92)d

a

a

All reactions were performed in an open vessel (to release H2) on a 0.05 mmol scale at a concentration of 0.5 M. bDetermined by GLC analysis with reference to 7ac. cDetermined by GLC analysis; ratio based on integration of baseline-separated peaks. dWith a higher catalyst loading (5 mol %). eWith 2,6-dichloropyridine (0.1 equiv) as an additive.

procedure for the C3 silylation of indoles with hydrosilanes R3SiH is performed without solvent.14a However, the reaction of solid 5a and volatile 6c does not allow for a solvent-free protocol. Hence, we performed all reactions in ClC6H5 as solvent at a concentration of 1 M.22 Catalyst [4a]+[BArF4]−, with an electron-poor phosphine ligand, performed significantly better than [4b]+[BArF4]−, with

of 2 mol %, desired 1ac was only formed in traces (entry 2). Instead, the major compound found was in both cases indole 5a as a result of protodesilylation of 7ac.23 In addition, another byproduct was detected and identified as fluorosilane 8ac, proving that the BArF4− counteranion is slowly decomposing under these conditions. Consequently, a gradual increase in temperature to 160 °C (entry 3) and 180 °C (entry 4) with [4a]+[BArF4]− as catalyst and higher boiling 1,2-Cl2C6H4 as solvent led to an increased formation of 8ac, but, at the same time, desired 1ac was now formed in substantial amounts. A significant improvement was obtained when apolar mesitylene was used as solvent, affording silole 1ac as the major

All reactions were performed in an open vessel (to release H2) with 0.05 mmol of 5a in ClC6H5 (1 M). Reaction times 15−18 h. b Determined by GLC analysis with reference to 5a. cReaction was performed on a 1.0 g scale (4.8 mmol of 5a); reaction time 44 h. d Isolated yield after flash chromatography and subsequent distillation in parentheses.

B


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Organometallics Table 3. Reactivity Screening of Complexes with Different Counteranions

entrya

catalyst for step 1

catalyst for step 2 or additive 9

conv (%)d

ratioe 1ac:7ac:8ac

b

[4a] [BArF4]− [4a]+[B(C6F5)4]− [4a]+[CHB11Me5Br6]− [4b]+[B(C6F5)4]− [4b]+[CHB11Me5Br6]− [4a]+[CHB11Me5Br6]− [4a]+[CHB11Me5Br6]− [4a]+[CHB11Me5Br6]− [4a]+[BArF4]−

     [4b]+[CHB11Me5Br6]− 9 9 [4b]+[CHB11Me5Br6]−

90     64 77  76

62:6:22

1 2b 3b 4b 5b 6b 7b 8b,i 9c

+

f,g f g,h h

21:43:0 73:4:0  75:1:0

a

All reactions were perfomed in an open vessel (to release H2) with 0.20 mmol of 5a and 0.60 mmol (3.0 equiv) of 6c according to GP3 (without removal of the catalyst used in step 1) or GP4 (with removal of the catalyst used in step 1; see the Experimental Section for detailed procedures). b According to GP3. cAccording to GP4. dDetermined by GLC analysis with reference to 5a. Reversion of step 1, that is, protodesilylation of 7ac to 5a, under the conditions of step 2 accounts for seemingly incomplete conversion. eDetermined by GLC analysis; ratio based on integration of baseline-separated peaks. fHigh conversion was achieved in step 1, but complete decomposition of 7ac to 5a was observed in step 2. gUnder microwave heating, additional impurities due to substituent scrambling at the silicon atom were observed by GC-MS analysis. hOnly moderate conversion was achieved in step 1. iRuthenium hydride 9 was added in step 1, resulting in complete inhibition of the reaction.

from substituent scrambling at the silicon atom.29 We next investigated the reactivity of the corresponding catalysts with an electron-rich phosphine ligand [4b] + [B(C 6 F 5 ) 4 ] − and [4b]+[CHB11Me5Br6]−. In accordance with our initial screening results, these showed only moderate conversions in the silylation of the indole core (entries 4 and 5; cf. Table 1, entry 1). Since our findings suggest that the second reaction step is less sensitive to the type of phosphine ligand in [4]+[X]− (cf. Table 2, entry 5 versus entry 8), we added [4b]+[CHB11Me5Br6]− as a catalyst after step 1 had been catalyzed by [4a]+[CHB11Me5Br6]− (entry 6). Indeed, desired 1ac was now formed in moderate amounts. The comparatively low yield of 1ac might be due to competitive reactivity of both catalysts. We next added proton-accepting ruthenium hydride 930 as an additive (entry 7), now affording 1ac as the major product in high yields. Importantly, 9 entirely shuts down the reaction if already used as an additive in step 1 (entry 8), presumably due to formation of a dimer that would not be reactive at room temperature.31 We also developed a two-step procedure, in which catalyst [4a]+[BArF4]− is removed after the first step by silica gel filtration and [4b]+[CHB11Me5Br6]− is added to perform the ring-closing reaction (entry 9). This setup seemed to be the most efficient, as it provided indole-fused benzosilole 1ac in good yield without the formation of fluorosilane 8ac. This procedure was then used to assess the substrate scope. Investigation of the Substrate Scope. Model substrate 5a afforded product 1ac in 63% isolated yield (Figure 1). Running the reaction with a single catalyst ([4a]+[BArF4]−; cf. Table 3, entry 1) allowed for isolating 1ac in still 50% yield, despite the formation of fluorosilane 8ac as an additional byproduct. Next, we probed different protective groups on the nitrogen atom. The slightly larger ethyl group in 5c already led to a decreased reactivity in the intermolecular C−H silylation step. However, with slightly higher catalyst loading (5 mol %), desired 1cc was isolated in good yield. Consequently, substrates

component (entry 5). Increasing the catalyst loading to 5 mol % was detrimental to the reaction (entry 6). Besides the expected increased formation of 8ac due to higher amounts of the BArF4− counteranion, the relative ratio between the 1ac and protodesilylated 5a also decreased. This finding can be explained by a higher concentration of Brønsted-acidic intermediates at higher catalyst loadings, demonstrating once more the lability of intermediate 7ac. Addition of Lewis bases such as 2,6-dichloropyridine had no beneficial effect on the reaction outcome (entry 7).24 Changing the catalyst to [4b]+[BArF4]− also gave 1ac predominantly in satisfactory amounts (entry 8). Given our library of Ru−S complexes with different ligands, we also applied catalysts with iPr3P25 and Ph3P26 as well as an NHC as ligands.27 Those afforded 1ac in lower yields though (not shown). It is also important to mention that conventional oil-bath heating led to complete decomposition of 7ac to 5a (not shown). Reactivity Screening of Complexes with Different Counteranions. Having identified catalyst [4a]+[BArF4]− as active in both reaction steps, we next developed a two-step procedure without the need of isolating 7ac (Table 3). Indeed, a catalyst loading of 2 mol % was sufficient to perform both bond formations, affording 1ac in good yields (entry 1). It must be mentioned here that the excess of dihydrosilane used in the first step must be removed before heating the reaction in a microwave, as otherwise no product formation is observed (see the Experimental Section for a detailed procedure). To avoid the formation of fluorosilane 8ac and to improve the yield of silole 1ac, we prepared Ru−S complexes with chemically more robust counteranions and investigated their reactivity in the two-step procedure. We succeeded in preparing [4a]+[B(C6F5)4]− and [4a]+[CHB11Me5Br6]−28 and subjected these catalysts to our protocol (entries 2 and 3). As expected, both afforded intermediate 7ac under the optimized reaction conditions, but no ring closure to 1ac was observed with [4a]+[B(C6F5)4]−, also giving additional byproducts resulting C


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Organometallics

Figure 1. Substrate scope of the 2-fold C−H silylation for the synthesis of indole-fused benzosiloles with different protective groups at the nitrogen atom (top) as well as with different dihydrosilanes (bottom). All reactions were performed with 0.20 mmol of 5 according to GP4 (Table 3, entry 9). Yields of isolated products after purification by flash chromatography. aAccording to GP3 (Table 3, entry 1). bWith 5 mol % of [4a]+[BArF4]− and 0.10 mL of ClC6H5 (2 M). cStep 1 performed at 60 °C and with 0.10 mL of ClC6H5 (2 M).

Figure 2. Substrate scope of the 2-fold C−H silylation for the synthesis of indole-fused benzosiloles with different substituents at C5 of the indole. All reactions were performed with 0.20 mmol of 5 according to GP4 (Table 3, entry 9). Yields of isolated product after purification by flash chromatography. aWith 5 mol % of [4a]+[BArF4]− and 0.10 mL of ClC6H5 (2 M). bWith 0.20 mmol (1.0 equiv) of 6c. c Obtained as a mixture containing 7% of 5i.

with larger protective groups such as benzyl (5d), phenyl (not shown), and triethylsilyl (not shown) did not react. For the latter two, electronic effects are likely to contribute to their lack of reactivity. Conversely, the newly developed protocol is applicable to different types of dihydrosilanes 6: With less reactive nBu2SiH2 (6d), a slightly higher temperature (60 °C) was necessary for the first bond formation; 1ad was eventually isolated in 53% yield. With Ph2SiH2 (6e), intermediate 7ae was readily formed under the optimized reaction setup. The Si−H bond activation in 7ae is however hampered due to steric congestion, accounting for the lower yield of 1ae (35%).32 Having identified the optimal protective group and the most reactive dihydrosilane, we further explored the scope for different precursors functionalized in the 5-position of the indole core (Figure 2). 5e and 5f decorated with either a methyl or a silyl group reacted smoothly, affording 1ec and 1 fc in 64% and 60% yield, respectively. A bromine substituent as in 5g was not tolerated, thwarting the silylation of the indole core even at a higher catalyst loading (5 mol % of [4a]+[BArF4]−). Accordingly, 5h substituted with a fluorine atom required a higher catalyst loading to achieve high conversion to intermediate 7hc. After microwave heating, 1hc was isolated in 60% yield. Substrates 5i and 5j, with an electron-donating amino group, showed significantly higher reactivity in the silylation of the indole core. In fact, no excess of dihydrosilane 6c was required for these compounds. If 3.0 equiv of dihydrosilane 6c was used, conversion of 5i to intermediate 7ic was even accompanied by the formation of an unknown byproduct. After microwave heating, 7ic had not converted into 1ic though. Strikingly, blocking the activated para-position of the aniline moiety by a methyl group (as in 5j) allowed for isolating desired 1jc. This result is impressive, given the fact that the Lewis-basic amino group is likely to provoke undesired reaction pathways in the presence of the silicon electrophile at these high temperatures. 5k decorated with a silicon-protected hydroxy group smoothly converted into corresponding 7kc. However, no ring closure to 1kc was observed (Figure 3). An ethyl group at C7 of the indole core in 5l led to a slight decrease in reactivity in the intermolecular step. Yet again, intermediate 7lc was

Figure 3. Additional substrate scope of the 2-fold C−H silylation for the synthesis of indole-fused benzosiloles. All reactions were performed with 0.20 mmol of 5 according to GP4 (Table 3, entry 9). Yields of isolated products after purification by flash chromatography. aWith 5 mol % of [4a]+[BArF4]− and 0.10 mL of ClC6H5 (2 M). b Obtained as a mixture containing 4% 5k. cObtained as a mixture containing 9% 5o.

obtained with higher catalyst loading (5 mol %), and silole 1lc was successfully prepared. The position of a chlorine substituent had a dramatic influence on the reaction outcome: 5m, with a chlorine atom at C6, was not sufficiently reactive to undergo the intermolecular SEAr step. In contrast, 5n, with a chlorinated phenyl core, underwent step 1 when using a higher catalyst loading (5 mol % of [4a]+[BArF4]−); microwave D


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Organometallics

ppm for 13C NMR; CDHCl2: δ 5.32 ppm for 1H NMR and CD2Cl2: δ 53.84 ppm for 13C NMR; CD3CD2HCO: δ 2.05 ppm for 1H NMR and (CD3)2CO: δ 29.84 ppm for 13C NMR). Data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplett, q = quartet, quin = quintet, m = multiplet, mc = centrosymmetric multiplet, br = broad signal), coupling constants (Hz), and integration. Pseudotriplets of unsymmetrical molecules were assigned as doublets of doublets. Gas−liquid chromatography (GLC) was performed on an Agilent Technologies 7820A gas chromatograph equipped with an FS-SE-54 capillary column (30 m × 0.32 mm, 0.25 μm film thickness) by CS-Chromatographie Service using the following program: N2 carrier gas, injection temperature: 240 °C, detector temperature: 300 °C, flow rate: 1.74 mL/min; temperature program: start temperature: 40 °C, heating rate 10 °C/min, end temperature: 280 °C for 10 to 30 min. Infrared (IR) spectra were recorded on an Agilent Technologies Cary 630 FT-IR spectrometer equipped with an ATR unit or a Jasco FT/IR-4100 spectrometer, and the signals are reported in wavenumbers (cm−1). Melting points (mp) were determined with a Stuart Scientific SMP20 or a Wagner & Munz Leica Galen III melting-point apparatus and are not corrected. Highresolution mass spectra (HRMS) and elemental analyses were obtained from the Analytical Facility at the Institut für Chemie, Technische Universität Berlin. General Procedure for the Preparation of N-Protected Indoles (GP1). Similar to a reported procedure,14a oil-free sodium hydride (12.0−30.1 mmol, 1.20 equiv) is placed in a Schlenk flask in a glovebox and suspended outside the glovebox in two-thirds of dry DMF (0.17 M). At 0 °C, a solution of the corresponding indole (10.0−25.5 mmol, 1.00 equiv) in the remaining third of dry DMF is added dropwise, resulting in vigorous gas evolution. After stirring for 1−2 h at 0 °C, the electrophile (13−32 mol, 1.2−1.3 equiv) is added. The mixture is kept in the ice bath for 1−2 h and then allowed to reach room temperature over 15−24 h. Saturated aqueous ammonium chloride, distilled water, and methyl tert-butyl ether are added. The aqueous phase is extracted with methyl tert-butyl ether, and the combined organic phases are dried over MgSO4. After evaporation of the solvents under reduced pressure, the residue is usually purified by silica gel filtration or flash-column chromatography using the indicated solvent mixture as eluent. Alternatively, the crude is purified by recrystallization. General Procedure for the Preparation of 2-Aryl-Substituted Indoles (GP2). Similar to a reported procedure,35 a Schlenk tube is charged with the corresponding N-protected indole (3.23−22.1 mmol, 1.00 equiv), the iodobenzene derivative (6.5−44 mmol, 1.2−2.0 equiv), palladium(II) acetate (0.33−2.2 mmol, 5.2−10 mol %), silver(I) oxide (2.4−17 mmol, 0.75−0.77 equiv), and o-nitrobenzoic acid (4.9−34 mmol, 1.5 equiv). After suspending in dry DMF (0.5 M), the mixture is stirred at room temperature for 17−71 h. Polar byproducts are removed by a silica gel filtration eluting with CH2Cl2. After removal of CH2Cl2 under reduced pressure, saturated aqueous sodium bicarbonate is added, and the aqueous phase is extracted with CH2Cl2. The combined organic phases are washed with distilled water and dried over MgSO4, and all solvents are removed under reduced pressure. The residue is prepurified by flash-column chromatography on silica gel using the indicated solvent mixture as eluent. Afterward, the residue is usually purified further by recrystallization. General Procedure for the Preparation of Indole-Fused Benzosiloles without Removal of the Catalyst Used in Step 1 (GP3). In a glovebox, the corresponding 2-aryl-substituted indole 5 (0.20 mmol, 1.00 equiv), preformed ruthenium complex [4]+[X]− (4.0 μmol, 2.0 mol %), and the corresponding dihydrosilane 6 (0.60 mmol, 3.00 equiv) are weighed into a GLC vial. Dry and degassed ClC6H5 (0.20 mL, 1.0 M) is added, the vial is closed, and a cannula is put through the septum to liberate the formed dihydrogen gas. After stirring overnight (15−18 h) at room temperature, the GLC vial is transferred into a Schlenk flask, and outside the glovebox all volatiles are removed under reduced pressure (40 °C/10−6 mbar). The reaction mixture is brought back to a glovebox, and the residue is transferred with dry and degassed mesitylene (0.40 mL, 0.5 M) into a 35 mL microwave vessel. When indicated, either [4b]+[CHB11Me5Br]− (4.0

heating afforded 1nc in an overall 38% yield. We next replaced the phenyl ring by larger naphthyl moieties. Substrate 5o could form two different ring systems. Although intermediate 7oc was formed in high yields, no ring closure was observed for this compound. We hypothesize that the rotation around the C−C bond between the indole and the sterically demanding naphth1-yl moiety is hampered in this molecule, thereby even preventing the formation of a six-membered ring. Hence, we synthesized 5p with a napth-2-yl group. Indeed, this substrate underwent both bond formations to yield 1pc in 41% yield as a single regioisomer.

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CONCLUSION In summary, we elaborated a Ru−S-catalyzed double silaFriedel−Crafts protocol that facilitates the synthesis of indolefused benzosiloles 1 from readily available 2-aryl-substituted indoles 5 and dihydrosilanes 6. As previously reported,17c this transformation is challenging due to the lability of the intermediate C3-silylated indole 7 being prone to protodesilylation. Although the substrate scope of the new method comes with limitations, it notably extends the variety of synthetically accessible silole motifs.

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EXPERIMENTAL SECTION

General Remarks. All reactions were performed in flame-dried glassware using an MBraun glovebox or conventional Schlenk techniques under a static pressure of argon (glovebox) or nitrogen unless otherwise stated. Microwave reactions were carried out in a Discover-SP microwave by CEM using 35 mL microwave flasks with silicone caps (ActiVent) by CEM. Reactions under microwave heating were performed in “open vessel mode” allowing for perforation of the cap with a cannula (0.9 mm thickness) to liberate the formed dihydrogen gas. Heating of microwave reactions was performed in “dynamic mode” at 300 W, and mixtures were stirred with “high mixing”. Liquids and solutions were transferred with syringes. Solvents for chromatography were distilled prior to use. Solvents (CH2Cl2, Et2O, 1,2-F2C6H4, THF, and toluene) were dried and purified following standard procedures. Dry DMF was purchased from Acros and degassed by bubbling nitrogen through the solvent. Dry CH2Cl2 for the catalyst syntheses was obtained from an MBraun solvent system, degassed with three freeze−pump−thaw cycles, and stored in a glovebox over thermally activated 4 Å molecular sieves. ClC6H5 for sila-Friedel−Crafts reactions was dried over CaH2, distilled, degassed with three freeze−pump−thaw cycles, and stored in a glovebox over thermally activated 4 Å molecular sieves. Mesitylene for sila-Friedel− Crafts reactions was dried over sodium/benzophenone, distilled, degassed with three freeze−pump−thaw cycles, and stored in a glovebox over thermally activated 4 Å molecular sieves. n-Butyllithium solutions were titrated using Suffert’s reagent.33 Ruthenium chloride complexes [(Et 3 P)Ru(SDmp)(Cl)] 12 and [((4-FC 6 H 4 ) 3 P)Ru(SDmp)(Cl)] 26 as well as cationic ruthenium complexes [4a]+[BArF4]−12 and [4b]+[BArF4]−26 were prepared according to reported procedures. Cs[CHB11H11] was purchased from KatChem, used as received, and further converted into Cs[CHB11Me5Br6].34 To reach pressures of 10−6 mbar, a turbomolecular pump by Edwards or a diffusion pump by Vacuubrand was used. Analytical thin-layer chromatography (TLC) was performed on silica gel 60 F254 glass plates or on basic aluminum oxide 60 F254 glass plates by Merck. Flash-column chromatography was performed on silica gel 60 (40−63 μm, 230−400 mesh, ASTM) by Grace using the indicated solvents. For purification of siloles 1, silica gel 60 (15−40 μm) by Merck was used. 1H, 11B, 13C, 19F, 29Si, and 31P NMR spectra were recorded in C6D6, CDCl3, CD2Cl2, or (CD3)2CO on a Bruker AV500 or an AV700 instrument. Chemical shifts are reported as parts per million (ppm) and are referenced to the residual solvent resonance as the internal standard (C6D5H: δ 7.16 ppm for 1H NMR and C6D6: δ 128.06 ppm for 13C NMR; CHCl3: δ 7.26 ppm for 1H NMR and CDCl3: δ 77.16 E


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Organometallics μmol, 2.0 mol %) or ruthenium hydride 9 (4.0 μmol, 2.0 mol %) is added. The vessel is capped, and the reaction mixture is heated in the microwave (300 W) outside the glovebox for 60 min at 180 °C. After ramping the temperature, the cap is perforated with a cannula. The mixture is finally diluted with cyclohexane/Et3N/CH2Cl2 (v:v:v = 93:5:2) and filtered over a small silica gel/Celite column (3 cm of silica covered with 1 cm of Celite) using the same mixture as eluent.36 After removal of all volatiles under reduced pressure, the crude is further purified by flash-column chromatography on silica gel (15−40 μm)37 using the indicated solvent mixture as eluent. General Procedure for the Preparation of Indole-Fused Benzosiloles with Removal of the Catalyst Used in Step 1 (GP4). In a glovebox, the corresponding 2-aryl-substituted indole 5 (0.20 mmol, 1.00 equiv), preformed ruthenium complex [4a]+[BArF4]− (4.0−10 μmol, 2.0−5.0 mol %), and the corresponding dihydrosilane 6 (0.20−0.60 mmol, 1.00−3.00 equiv) are weighed into a GLC vial. Dry and degassed ClC6H5 (0.10−0.20 mL, 1.0−2.0 M) is added, the vial is closed, and a cannula is put through the septum to liberate the formed dihydrogen gas. After stirring for 16 h to 18 d at room temperature or 60 °C, the reaction is stopped by diluting with cyclohexane/Et3N/CH2Cl2 (v:v:v = 93:5:2) and filtration over a small silica gel/Celite column (3 cm silica covered with 1 cm Celite) using the same mixture as eluent.36 After removal of all volatiles under reduced pressure, the crude intermediate is dried (60 °C/10−3 mbar). In a glove bo x, eithe r p re fo rm ed ru th enium com plex [4b]+[CHB11Me5Br]−] (4.0 μmol, 2.0 mol %) or ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (4.0 μmol, 2.0 mol %) together with Na[CHB11Me5Br6] (4.8 μmol, 2.4 mol %) [in situ formation of the active catalyst [4b]+[CHB11Me5Br]−] are weighed into a GLC vial. This mixture and the crude intermediate are both transferred with dry and degassed mesitylene (0.40 mL, 0.5 M) into a 35 mL microwave vessel. The vessel is capped, and the reaction mixture is heated in the microwave (300 W) outside the glovebox for 60 min at 180 °C. After ramping the temperature, the cap is perforated with a cannula. The mixture is finally diluted with cyclohexane/Et3N/CH2Cl2 (v:v:v = 93:5:2) and filtered over a small silica gel/Celite column (3 cm silica covered with 1 cm Celite) using the same mixture as eluent.36 After removal of all volatiles under reduced pressure, the crude is purified further by flash-column chromatography on silica gel (15−40 μm)37 using the indicated solvent mixture as eluent. [((4-FC6H4)3P)Ru(SDmp)]+[CHB11Me5Br6]− ([4a]+[CHB11Me5Br6]−). In a glovebox, ruthenium chloride [((4FC6H4)3P)Ru(SDmp)(Cl)]26 (10 mg, 13 μmol, 1.0 equiv) and Na[CHB11Me5Br6]34 (27 mg, 38 μmol, 3.0 equiv) were suspended in dry and degassed 1,2-F2C6H4 (1 mL). The green reaction mixture was stirred at 80 °C for 17 h. The solvent was removed under reduced pressure, and the residue was redissolved in C6H6 (ca. 2 mL). The precipitate was filtered off under an inert atmosphere. Removal of the solvent under reduced pressure afforded catalyst [4a]+[CHB11Me5Br6]− as a green powder (17 mg, 94%). 1H NMR (500 MHz, CD2Cl2): δ 0.22 (s, 15H), 1.65 (s, 3H), 1.86 (s, 6H), 1.98 (s, 6H), 2.15 (s, 1H), 2.30 (s, 3H), 4.82 (s, 2H), 6.86 (s, 2H), 7.16− 7.20 (m, 6H), 7.30−7.35 (m, 6H), 7.43 (dd, 3J(HH) = 7.5 Hz, 4J(HH) = 1.3 Hz, 1H), 7.76 (dd, 3J(HH) = 7.6 Hz, 4J(HH) = 1.0 Hz, 1H), 7.82 (dd, 3J(HH) = 7.7 Hz, J = 7.5 Hz, 1H). The signal at 7.35 ppm was attributed to the remaining C6H6. 11B NMR (161 MHz, CD2Cl2): −12.4 (s), −10.4 (s), − 3.7 (s).13C{1H} NMR (176 MHz, CD2Cl2): δ −1.7 (br m), 18.7, 19.0, 20.6, 21.1, 55.5, 75.1, 107.1, 107.6, 116.1 (d, 2 J(C,P) = 22 Hz), 117.1 (dd, 2J(C,F) = 22 Hz, 3J(C,P) = 12 Hz), 126.2 (dd, 1J(C,P) = 49 Hz, 4J(C,F) = 3 Hz), 128.3, 129.0, 132.4, 133.1, 135.6, 135.7, 136.5 (dd, 2J(C,P) = 14 Hz, 3J(C,F) = 9 Hz), 138.2, 142.7, 163.3, 164.4, 165.9. 19F NMR (471 MHz, CD2Cl2): δ −106.9 (mc). 31P{1H} NMR (203 MHz, CD2Cl2): δ 30.2. HRMS (ESI): calculated for C42H37F3PSRu [M − CHB11Me5Br6]+ 763.1349; found 763.1361. Elemental analysis results are outside the tolerance range. [(Et3P)Ru(SDmp)]+[CHB11Me5Br6]− ([4b]+[CHB11Me5Br6]−). In a glovebox, ruthenium chloride [(Et3P)Ru(SDmp)(Cl)]12 (49 mg, 82 μmol, 1.0 equiv) and Na[CHB11Me5Br6]34 (70 mg, 99 μmol, 1.2 equiv) were suspended in dry and degassed CH2Cl2 (8 mL). The

green reaction mixture was stirred at room temperature for 16 h. The solvent was removed under reduced pressure, and the residue was redissolved in C6H6 (4 mL). The precipitate was filtered off under an inert atmosphere. Removal of the solvent under reduced pressure afforded catalyst [4b]+[CHB11Me5Br6]− as a green powder (95 mg, 93%). 1H NMR (500 MHz, CD2Cl2): δ 0.19 (s, 15H), 1.01 (dt, 3 J(H,P) = 17.3 Hz, 3J(HH) = 7.4 Hz, 9H), 1.88−1.91 (m, 12H), 1.96 (s, 6H), 2.06 (br s, 1H), 2.32 (s, 3H), 2.46 (s, 3H), 4.99 (s, 2H), 6.93 (s, 2H), 7.35 (d, 3J(HH) = 6.8 Hz, 1H), 7.71−7.74 (m, 2H). 11B NMR (161 MHz, CD2Cl2): −12.7 (s), −10.2 (s), −3.5 (s). 13C{1H} NMR (176 MHz, CD2Cl2): δ −1.8 (br m), 8.6, 18.0 (d, 1J(C,P) = 28 Hz), 18.7, 20.5, 20.7, 21.3, 54.9, 72.9, 104.4, 106.5, 109.5, 128.5, 128.8, 130.0, 132.6, 133.3, 135.9, 136.4, 137.9, 142.8, 163.0. 31P{1H} NMR (203 MHz, CD2Cl2): δ 23.5. HRMS (ESI): calculated for C30H40PSRu [M − CHB11Me5Br6]+ 565.1632; found 565.1631. Elemental analysis results are outside the tolerance range. [((4-FC6H4)3P)Ru(SDmp)]+[B(C6F5)4]− ([4a]+[B(C6F5)4]−). In a glovebox, ruthenium chloride [((4-FC6H4)3P)Ru(SDmp)(Cl)]26 (50 mg, 63 μmol, 1.0 equiv) and Na+[B(C6F5)4−] (70 mg, 0.99 μmol, 1.6 equiv) were suspended in dry and degassed CH2Cl2 (5.0 mL). The green reaction mixture was stirred at 40 °C for 16 h. The precipitate was filtered off under an inert atmosphere. Removal of the solvent under reduced pressure afforded catalyst [4a]+[B(C6F5)4]− as a green powder (92 mg, 98%). 1H NMR (500 MHz, CD2Cl2): 1.60 (s, 3H), 1.85 (s, 6H), 1.94 (s, 6H), 2.30 (s, 3H), 4.71 (s, 2H), 6.85 (s, 2H), 7.13−7.17 (m, 6H), 7.29−7.34 (m, 6H), 7.44 (br d, 3J(HH) = 7.7 Hz, 1H), 7.70 (br d, 3J(HH) = 7.6 Hz, 1H), 7.80 (dd, 3J(HH) = 7.7 Hz, 3 J(HH) = 7.6 Hz, 1H). 11B NMR (161 MHz, CD2Cl2): −16.7 (s). 13 C{1H} NMR (176 MHz, CD2Cl2): δ 18.2, 18.7, 20.5, 21.1, 74.6, 107.3, 107.4, 116.1 (br d, 2J(C,P) = 20 Hz), 117.0 (dd, 2J(C,F) = 22 Hz, 3J(C,P) = 12 Hz), 124.3 (mc), 126.0 (dd, 1J(C,P) = 50 Hz, 4J(C,F) = 3 Hz), 128.3, 128.4, 131.0, 132.6, 135.5, 135.7, 136.4 (dd, 2J(C,P) = 15 Hz, 3J(C,F) = 9 Hz), 136.7 (br d, 1J(C,F) = 246 Hz), 138.4, 138.7 (br d, 1J(C,F) = 243 Hz), 142.9, 148.6 (br d, 1J(C,F) = 242 Hz), 163.6, 164.5, 166.0. 19F NMR (471 MHz, CD2Cl2): δ −167.5 (t, 3J(F,F) = 18 Hz), −163.6 (t, 3J(F,F) = 20 Hz), −133.2 (s), −106.8 (mc). 31P{1H} NMR (203 MHz, CD2Cl2): δ 30.0. HRMS (ESI): calculated for C42H37F3PRuS [M − B(C6F5)4]+ 763.1349; found 763.1354. Elemental analysis results are outside the tolerance range. [(Et3P)Ru(SDmp)]+[B(C6F5)4]− ([4b]+[B(C6F5)4]−). In a glovebox, ruthenium chloride [(Et3P)Ru(SDmp)(Cl)]12 (28 mg, 47 μmol, 1.0 equiv) and Na+[B(C6F5)4−] (39 mg, 56 μmol, 1.2 equiv) were suspended in dry and degassed CH2Cl2 (1.5 mL). The green reaction mixture was stirred at room temperature for 15 h. The precipitate was filtered off under an inert atmosphere. Removal of the solvent under reduced pressure afforded catalyst [4b]+[B(C6F5)4]− as a green powder (50 mg, 86%). 1H NMR (500 MHz, CD2Cl2): δ 0.99 (dt, 3 J(H,P) = 17.2 Hz, 3J(HH) = 7.6 Hz, 9H), 1.85−1.91 (m, 12H), 1.95 (s, 6H), 2.31 (s, 3H), 2.39 (s, 3H), 4.86 (s, 2H), 6.93 (s, 2H), 7.37 (dd, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.3 Hz, 1H), 7.69 (dd, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.3 Hz, 1H), 7.75 (dd, 3J(H,H) = 7.6 Hz, 3J(H,H) = 7.6 Hz, 1H). 11B NMR (161 MHz, CD2Cl2): −16.7 (s). 13C{1H} NMR (176 MHz, CD2Cl2): δ 8.5, 18.0 (d, 1J(C,P) = 28 Hz), 18.5, 20.3, 20.5, 21.2, 71.6, 104.7, 106.5, 109.5 (d, 2J(C,P) = 9 Hz), 124.3 (mc), 128.5, 128.7, 130.2, 132.8, 133.1, 135.9, 136.3, 136.7 (br d, 1 J(C,F) = 243 Hz), 138.1, 138.7 (br d, 1J(C,F) = 246 Hz), 142.9, 148.6 (br d, 1J(C,F) = 239 Hz), 163.2. 19F NMR (471 MHz, CD2Cl2): δ −167.5 (t, 3J(F,F) = 17 Hz), −163.5 (t, 3J(F,F) = 20 Hz), −133.2 (s). 31 1 P{ H} NMR (203 MHz, CD2Cl2): δ 23.3. HRMS (ESI): calculated for C30H40PRuS [M − B(C6F5)4]+ 565.1632; found 565.1635. Elemental analysis results are outside the tolerance range. 1-Methyl-3-(methyl(phenyl)silyl)-2-phenyl-1H-indole (7ac). In a glovebox, 1-methyl-2-phenyl-1H-indole (5a, 1.00 g, 4.84 mmol, 1.00 equiv), ruthenium complex [4a]+[BArF4]− (78 mg, 48 μmol, 1.0 mol %), and methylphenylsilane (6c, 2.00 mL, 1.78 g, 14.6 mmol, 3.01 equiv) were weighed into a flask. Dry and degassed ClC6H5 (4.8 mL, 1.0 M) was added, and the reaction mixture was stirred at room temperature for 44 h. The flask was not sealed to enable liberation of the formed dihydrogen gas. The reaction was stopped by diluting with F


Article

Organometallics cyclohexane/Et3N/CH2Cl2 (v:v:v = 93:5:2) and filtration over silica gel using the same mixture as eluent.36 The solvents were removed under reduced pressure. Remaining dihydrosilane and starting material were removed by Kugelrohr distillation (135 °C, 10−3 mbar) to give the product (1.45 g, 92%) as a brownish oil, which solidified upon cooling to −35 °C. Mp = 56 °C (CH2Cl2). Rf = 0.59 (cyclohexane/ Et3N = 95:5; basic aluminum oxide). IR (ATR): ν̃ = 3065, 2120, 2088, 1605, 1523, 1462, 1427, 1372, 1337, 1302, 1251, 1236, 1220, 1156, 1107, 1073, 1050, 1023, 987, 920, 878, 841, 824, 797, 739, 720, 698, 603 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.39 (d, 3J(H,H) = 4.1 Hz, 3H), 3.60 (s, 3H), 4.88 (q, 3J(H,H) = 4.1 Hz, 1H), 7.09 (ddd, 3J(H,H) = 7.5 Hz, 3J(H,H) = 7.4 Hz, 4J(H,H) = 1.0 Hz, 1H), 7.23−7.45 (m, 10H), 7.49−7.51 (m, 2H), 7.59 (d, 3J(H,H) = 7.9 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.4, 31.2, 102.9, 110.0, 120.3, 121.6, 122.1, 128.1, 128.4, 128.9, 129.4, 131.3, 133.4, 133.6, 134.9, 137.7, 139.0, 149.3. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −29.6. HRMS (EI): calculated for C22H21NSi [M]+ 327.1443; found 327.1448. Anal. Calcd for C22H21NSi: C, 80.68; H, 6.46; N, 4.28. Found: C, 80.20; H, 6.86; N, 4.77. 5,10-Dimethyl-10-phenyl-5,10-dihydrobenzo[4,5]silolo[3,2b]indole (1ac). This was prepared from 1-methyl-2-phenyl-1H-indole (5a, 41 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), and methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv) according to GP3. The reaction time for step 1 was 16 h. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 94:5:1)36 as eluent afforded the product (33 mg, 50%) as a brownish oil. This was also prepared from 1-methyl-2-phenyl-1H-indole (5a, 41 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature for 16 h with ClC6H5 (0.20 mL, 1.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 94:5:1)36 as eluent afforded the product (41 mg, 63%) as a brownish oil. Rf = 0.45 (cyclohexane/Et3N = 95:5; basic aluminum oxide). IR (ATR): ν̃ = 3047, 2926, 1610, 1584, 1470, 1429, 1417, 1396, 1340, 1329, 1285, 1247, 1204, 1157, 1131, 1111, 1067, 1014, 998, 979, 929, 916, 821, 792, 773, 756, 744 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.78 (s, 3H), 4.14 (s, 3H), 7.12 (br dd, 3J(H,H) = 7.8 Hz, 3J(H,H) = 7.1 Hz, 1H), 7.22−7.27 (m, 2H), 7.31−7.35 (m, 2H), 7.36−7.44 (m, 3H), 7.58 (br d, 3J(H,H) = 7.8 Hz, 1H), 7.63−7.66 (m, 3H), 7.85 (d, 3 J(H,H) = 7.8 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.9, 32.6, 109.7, 110.2, 120.9, 121.0, 121.9, 122.2, 127.2, 128.4, 130.1, 130.2, 130.5, 133.9, 134.7, 135.9, 142.1, 143.0, 143.9, 153.9. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.4 ppm. HRMS (APCI): calculated for C22H20NSi [M + H]+ 326.1360; found 326.1363. Elemental analysis results were outside the tolerance range. 5-Ethyl-10-methyl-10-phenyl-5,10-dihydrobenzo[4,5]silolo[3,2-b]indole (1cc). This was prepared from 1-ethyl-2-phenyl-1Hindole (5c, 44 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature with ClC6H5 (0.10 mL, 2.0 M) as a solvent. After stirring for 16 h, additional ruthenium complex [4a]+[BArF4]− (9.8 mg, 6.0 μmol, 3.0 mol %) was added. Step 1 was stopped after a total of 39 h. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/ methyl tert-butyl ether (v:v:v = 94:5:1)36 as eluent afforded the product (38 mg, 56%) as a brownish solid. Mp = 130 °C (CH2Cl2). Rf = 0.50 (cyclohexane/Et3N/methyl tert-butyl ether = 94:5:1; basic aluminum oxide). IR (ATR): ν̃ = 3053, 2980, 2932, 1583, 1479, 1456, 1418, 1405, 1379, 1342, 1326, 1285, 1262, 1248, 1188, 1156, 1132, 1124, 1109, 1085, 1067, 1021, 999, 988, 929, 863, 836, 798, 786, 764 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.76 (s, 3H), 1.56 (t, 3J(H,H) = 7.2 Hz, 3H), 4.59 (q, 3J(H,H) = 7.2 Hz, 2H), 7.11 (br dd, 3J(H,H) =

7.9 Hz, 3J(H,H) = 7.5 Hz, 1H), 7.20−7.26 (m, 2H), 7.31−7.34 (m, 2H), 7.36−7.39 (m, 1H), 7.41−7.44 (m, 2H), 7.58 (dd, 3J(H,H) = 7.8 Hz, 4J(H,H) = 0.8 Hz, 1H), 7.63−7.65 (m, 3H), 7.73 (d, 3J(H,H) = 7.9 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.5, 15.8, 40.0, 110.0, 110.1, 120.8, 120.9, 122.0, 122.2, 127.2, 128.4, 130.1, 130.4, 130.7, 133.9, 134.7, 135.9, 141.9, 142.1, 144.0, 152.9. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.7. HRMS (APCI): calculated for C23H22NSi [M + H]+ 340.1516; found 340.1519. Anal. Calcd for C23H21NSi: C, 81.37; H, 6.23; N, 4.13. Found: C, 80.91; H, 6.60; N, 4.12. 10,10-Dibutyl-5-methyl-5,10-dihydrobenzo[4,5]silolo[3,2-b]indole (1ad). I. Preparation of nBu2SiH2 (6d): To a solution of di-nbutyldichlorosilane (9.0 mL, 8.9 g, 42 mmol, 1.00 equiv) in dry CH2Cl2 (90 mL) at 0 °C was added a DIBAL-H solution (ca. 1.0 M in CH2Cl2, 90 mL, 90 mmol, 2.1 equiv) with a syringe pump (3 mL/ min). The reaction mixture was allowed to reach room temperature and stirred for 17 h. Freshly ground Na2SO4·10H2O was carefully added until no further gas evolution was observed. The mixture was filtrated, and the filtrate was subsequently washed with aqueous HCl (2 M), aqueous NaOH (2 M), and brine. The organic phase was dried over MgSO4, and the solvent was removed under reduced pressure. Distillation (65 °C/10 mbar) afforded the product (2.18 g, 36%) as a colorless liquid. IR (ATR): ν̃ = 2956, 2922, 2857, 2121, 1618, 1464, 1408, 1296, 1182, 1082, 1026, 941, 897, 828, 714, 632 cm−1. 1H NMR (500 MHz, C6D6): δ 0.59−0.63 (m, 4H), 0.87 (t, 3J(H,H) = 7.2 Hz, 6H), 1.26−1.38 (m, 8H), 3.93 (quin, 3J(H,H) = 3.7 Hz, 2H). 13C{1H} NMR (126 MHz, C6D6): δ 9.21, 14.0, 26.3, 28.1. 29Si DEPT NMR (99 MHz, C6D6): δ −28.6 ppm. Elemental analysis was not performed for this compound. II. Preparation of 1ad: This was prepared from 1methyl-2-phenyl-1H-indole (5a, 41 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), di-n-butylsilane (6d, 87 mg, 0.60 mmol, 3.0 equiv) ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at 60 °C for 3 d with ClC6H5 (0.10 mL, 2.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (37 mg, 53%) as a yellowish oil. This compound was found to be sensitive to air/moisture and was therefore stored in a glovebox. NMR spectra were recorded with dry CD2Cl2 in a sealed tube. Rf = 0.61 (cyclohexane/Et3N/methyl tertbutyl ether = 95:4:1; basic aluminum oxide). IR (ATR): ν̃ = 2953, 2919, 2869, 2854, 1586, 1464, 1418, 1401, 1376, 1326, 1284, 1265, 1203, 1177, 1129, 1112, 1069, 1021, 1013, 977, 919, 885, 821, 770, 738 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.83 (t, 3J(H,H) = 7.2 Hz, 6H), 0.92−1.06 (m, 4H), 1.28−1.45 (m, 8H), 4.11 (s, 3H), 7.11 (ddd, 3 J(H,H) = 7.6 Hz, 3J(H,H) = 7.3 Hz, 4J(H,H) = 1.0 Hz, 1H), 7.19− 7.24 (m, 2H), 7.36−7.41 (m, 2H), 7.57−7.60 (m, 2H), 7.82 (d, 3 J(H,H) = 7.8 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ 12.7, 13.9, 26.9, 27.0, 32.5, 110.0, 110.5, 120.5, 120.7, 121.9, 122.2, 126.7, 129.8, 130.9, 133.9, 142.3, 142.9, 144.2, 153.5 ppm. 1H,29Si-HMQC NMR (99 MHz, J = 7 Hz, CD2Cl2): δ −4.5. No signal was detected in the 29Si DEPT NMR spectrum. Another signal in the 1H,29Si HMQC NMR spectrum at −21.6 ppm was attributed to a grease impurity. HRMS (APCI): calculated for C23H30NSi [M + H]+ 348.2142; found 348.2140. Elemental analysis results were outside the tolerance range. 8-Methyl-10,10-diphenyl-5,10-dihydrobenzo[4,5]silolo[3,2b]indole (1ae). This was prepared from 1-methyl-2-phenyl-1H-indole (5a, 41 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), diphenylsilane (6e, 111 mg, 0.602 mmol, 3.01 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature for 16 h with ClC6H5 (0.20 mL, 1.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (27 mg, 35%) as a pale yellow solid. Mp = 208 °C (CH2Cl2). Rf = 0.38 (cyclohexane/Et3N = 95:5; basic aluminum oxide). IR (ATR): ν̃ = 3050, 3009, 2924, 1585, 1470, 1427, 1415, 1391, 1355, 1340, 1324, 1285, 1265, 1187, 1161, G


Article

Organometallics 1129, 1111, 1064, 1028, 1014, 997, 977, 924, 858, 819, 772, 749 cm−1. 1 H NMR (500 MHz, CD2Cl2): δ 4.15 (s, 3H), 7.15 (dd, 3J(H,H) = 7.5 Hz, 3J(H,H) = 7.4 Hz, 1H), 7.25 (br dd, 3J(H,H) = 7.8 Hz, 3J(H,H) = 7.6 Hz, 1H), 7.29 (dd, 3J(H,H) = 7.3 Hz, 3J(H,H) = 7.3 Hz, 1H), 7.35−7.38 (m, 4H), 7.40−7.47 (m, 4H), 7.66 (d, 3J(H,H) = 7.9 Hz, 1H), 7.73−7.75 (m, 4H), 7.79 (d, 3J(H,H) = 7.1 Hz, 1H), 7.89 (d, 3 J(H,H) = 7.8 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ 32.6, 108.4, 110.3, 121.2, 121.3, 122.0, 122.4, 127.5, 128.5, 130.4, 130.6, 133.9, 134.6, 135.7, 142.2, 142.4, 143.2, 154.3. The signal for one quaternary carbon atom was not detected. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −19.0. HRMS (APCI): calculated for C27H22NSi [M + H]+ 388.1516; found 388.1516. Elemental analysis results were outside the tolerance range. 5,8,10-Trimethyl-10-phenyl-5,10-dihydrobenzo[4,5]silolo[3,2-b]indole (1ec). This was prepared from 1,5-dimethyl-2-phenyl1H-indole (5e, 41 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature for 17 h with ClC6H5 (0.20 mL, 1.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/ Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (44 mg, 65%) as a white solid. Crystals suitable for X-ray diffraction were obtained by recrystallization of 1ec from cyclohexane/ n-pentane at 8 °C. Mp = 158 °C (CH2Cl2). Rf = 0.50 (cyclohexane/ Et3N/methyl tert-butyl ether = 95:4:1; basic aluminum oxide). IR (ATR): ν̃ = 3054, 3007, 2908, 1618, 1588, 1565, 1471, 1428, 1418, 1398, 1334, 1306, 1284, 1242, 1176, 1150, 1129, 1114, 1072, 1021, 997, 867, 802, 786, 765 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.76 (s, 3H), 2.42 (s, 3H), 4.10 (s, 3H), 7.06 (dd, 3J(H,H) = 8.4 Hz, 4 J(H,H) = 1.4 Hz, 1H), 7.23 (br dd, 3J(H,H) = 7.3 Hz, 3J(H,H) = 7.3 Hz, 1H), 7.28 (d, 3J(H,H) = 8.4 Hz, 1H), 7.31−7.34 (m, 2H), 7.36− 7.42 (m, 3H), 7.61−7.65 (m, 3H), 7.82 (d, 3J(H,H) = 7.8 Hz, 1H). 13 C{1H} NMR (126 MHz, CD2Cl2): δ −4.5, 21.5, 32.6, 109.1, 109.8, 120.8, 121.7, 123.8, 127.1, 128.4, 130.1, 130.2, 130.2, 130.7, 133.9, 134.7, 136.0, 141.4, 142.2, 143.9, 153.9. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.6. HRMS (APCI): calculated for C23H22NSi [M + H]+ 340.1516; found 340.1519. Anal. Calcd for C23H21NSi: C, 81.37; H, 6.23; N, 4.13. Found: C, 81.25; H, 6.37; N, 3.68. 5,10-Dimethyl-8-(dimethyl(phenyl)silyl)-10-phenyl-5,10dihydrobenzo[4,5]silolo-[3,2-b]indole (1fc). This was prepared from 5-(dimethyl(phenyl)silyl)-1-methyl-2-phenyl-1H-indole (5f, 68 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature for 18 h with ClC6H5 (0.20 mL, 1.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (55 mg, 60%) as a brownish oil. Rf = 0.45 (cyclohexane/Et3N = 95:5; basic aluminum oxide). IR (ATR): ν̃ = 3047, 2953, 1586, 1472, 1428, 1418, 1397, 1329, 1291, 1245, 1189, 1156, 1110, 1090, 1019, 987, 813, 770, 765 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.61 (s, 6H), 0.79 (s, 3H), 4.13 (s, 3H), 7.26 (br dd, 3J(H,H) = 7.5 Hz, 3J(H,H) = 7.1 Hz, 1H), 7.32−7.44 (m, 9H), 7.57−7.58 (m, 2H), 7.65−7.67 (m, 3H), 7.81 (br s, 1H), 7.85 (d, 3 J(H,H) = 7.8 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.4, −1.9, −1.8, 32.6, 109.8, 109.9, 121.0, 127.3, 127.9, 128.1, 128.4, 128.4, 128.8, 129.2, 130.1, 130.2, 130.6, 133.9, 134.6, 134.7, 135.9, 139.9, 142.0, 143.7, 143.9, 154.1. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.2, −7.9. HRMS (APCI): calculated for C30H30NSi2 [M + H]+ 460.1911; found 460.1913. Anal. Calcd for C30H29NSi2: C, 78.38; H, 6.36; N, 3.05. Found: C, 78.32; H, 6.79; N, 2.79. 8-Fluoro-5,10-dimethyl-10-phenyl-5,10-dihydrobenzo[4,5]silolo[3,2-b]indole (1hc). Prepared from 5-fluoro-1-methyl-2phenyl-1H-indole (5h, 45 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methyl-

phenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature with ClC6H5 (0.10 mL, 2.0 M) as a solvent. After stirring for 24 h, additional ruthenium complex [4a]+[BArF4]− (9.8 mg, 6.0 μmol, 3.0 mol %) was added. Step 1 was stopped after a total of 18 d. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/ Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (41 mg, 60%) as a pale violet solid. Mp = 138 °C (CH2Cl2). Rf = 0.40 (cyclohexane/Et3N/methyl tert-butyl ether = 95:4:1; basic aluminum oxide). IR (ATR): ν̃ = 3058, 2917, 2849, 1618, 1585, 1483, 1430, 1403, 1585, 1483, 1430, 1403, 1342, 1302, 1265, 1240, 1161, 1129, 1111, 1066, 1017, 989, 938, 881, 851, 818, 781, 764, 736 cm−1. 1 H NMR (500 MHz, CD2Cl2): δ 0.76 (s, 3H), 4.12 (s, 3H), 6.97 (ddd, 3 J(H,H/F) = 9.2 Hz, 3J(H,H/F) = 9.1 Hz, 4J(H,H) = 2.4 Hz, 1H), 7.22 (dd, 3J(H,F) = 9.4 Hz, 4J(H,H) = 2.4 Hz, 1H), 7.27 (dd, 3J(H,H) = 7.4 Hz, 3J(H,H) = 7.2 Hz, 1H), 7.30−7.40 (m, 4H), 7.43 (ddd, 3 J(H,H) = 7.7 Hz, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.2 Hz, 1H), 7.62− 7.65 (m, 3H), 7.84 (d, 3J(H,H) = 7.8 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.6, 32.8, 106.5 (d, 2J(C,F) = 23 Hz), 109.5 (d, 4 J(C,F) = 5 Hz), 110.1 (d, 2J(C,F) = 27 Hz), 110.8 (d, 3J(C,F) = 10 Hz), 121.1, 127.5, 128.5, 130.2, 130.2, 130.8 (d, 3J(C,F) = 10 Hz), 134.0, 134.7, 135.5, 139.6, 141.7, 143.9, 155.4, 159.0 (d, 1J(C,F) = 234 Hz). 19F NMR (471 MHz, CD2Cl2): δ −125.0 (m). 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.4. HRMS (APCI): calculated for C22H19FNSi [M + H]+ 344.1265; found 344.1268. Elemental analysis results were outside the tolerance range. 8-(N-Methyl-p-tolylamino)-5,10-dimethyl-10-phenyl-5,10dihydrobenzo[4,5]silolo[3,2-b]indole (1jc). This was prepared from 5-(N,4-dimethyl-p-tolylamino)-1-methyl-2-phenyl-1H-indole (5j, 72 mg, 0.22 mmol, 1.1 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 24 mg, 0.20 mmol, 1.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature for 16 h with ClC6H5 (0.20 mL, 1.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (33 mg, 37%) as a yellow solid. Mp = 103 °C (CH2Cl2). Rf = 0.35 (cyclohexane/Et3N/methyl tert-butyl ether = 95:4:1; basic aluminum oxide). IR (ATR): ν̃ = 3003, 2922, 2850, 2804, 1607, 1511, 1486, 1471, 1429, 1399, 1312, 1293, 1268, 1245, 1111, 1061, 1021, 987, 901, 845, 789, 759, 744 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.76 (s, 3H), 2.26 (s, 3H), 3.30 (s, 3H), 4.12 (s, 3H), 6.73−6.75 (m, 2H), 6.99−7.03 (m, 3H), 7.25 (dd, 3 J(H,H) = 7.3 Hz, 3J(H,H) = 7.2 Hz, 1H), 7.31−7.39 (m, 5H), 7.42 (ddd, 3J(H,H) = 7.7 Hz, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.2 Hz, 1H), 7.63 (m, 3H), 7.84 (d, 3J(H,H) = 7.8 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.4, 20.5, 32.7, 41.3, 109.5, 110.8, 116.5, 117.3, 120.5, 120.9, 127.2, 127.8, 128.4, 129.7, 130.1, 130.2, 131.3, 133.9, 134.7, 135.8, 140.1, 142.0, 143.7, 143.9, 148.7, 154.4. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.5. HRMS (APCI): calculated for C30H29N2Si [M + H]+ 445.2095; found 445.2090. Anal. Calcd for C30H28N2Si: C, 81.04; H, 6.35; N, 6.30. Found: C, 80.88; H, 6.96; N, 6.46. 6-Ethyl-5,10-dimethyl-10-phenyl-5,10-dihydrobenzo[4,5]silolo[3,2-b]indole (1lc). This was prepared from 7-ethyl-1-methyl2-phenyl-1H-indole (5l, 47 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature with ClC6H5 (0.10 mL, 2.0 M) as a solvent. After stirring for 15 h, additional ruthenium complex [4a]+[BArF4]− (9.8 mg, 6.0 μmol, 3.0 mol %) was added. Step 1 was stopped after a total of 5 d. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N (v:v = 97:3)36 as eluent afforded the product (33 mg, 47%) as a yellowish oil. Rf = 0.35 (cyclohexane/Et3N = 97:3; basic aluminum H


Article

Organometallics oxide). IR (ATR): ν̃ = 3050, 2955, 2929, 1587, 1464, 1428, 1406, 1324, 1251, 1111, 1064, 1013, 821, 777, 739 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.76 (s, 3H), 1.41 (t, 3J(H,H) = 7.5 Hz, 3H), 3.17 (q, 3J(H,H) = 7.5 Hz, 2H), 4.35 (s, 3H), 6.99−7.04 (m, 2H), 7.24 (dd, 3 J(H,H) = 7.3 Hz, 3J(H,H) = 7.2 Hz, 1H), 7.31−7.43 (m, 5H), 7.64− 7.65 (m, 3H), 7.83 (d, 3J(H,H) = 7.9 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.6, 16.8, 26.6, 35.7, 110.8, 120.2, 121.2, 121.3, 124.2, 127.0, 128.4, 129.0, 130.1, 130.1, 131.7, 133.9, 134.7, 135.9, 141.5, 142.3, 144.0, 155.0. 29Si DEPT NMR (99 MHz, CD2Cl2): δ − 14.4. HRMS (APCI): calculated for C24H24NSi [M + H]+ 354.1673; found 354.1674. Elemental analysis results were outside the tolerance range. 2-Chloro-5,10-dimethyl-10-phenyl-5,10-dihydrobenzo[4,5]silolo[3,2-b]indole (1nc). This was prepared from 2-(4-chlorophenyl)-1-methyl-2-phenyl-1H-indole (5n, 48 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature with ClC6H5 (0.10 mL, 2.0 M) as a solvent. After stirring for 24 h, additional ruthenium complex [4a]+[BArF4]− (9.8 mg, 6.0 μmol, 3.0 mol %) was added. Step 1 was stopped after a total of 3 d. Purification by flashcolumn chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (27 mg, 38%) as a brownish solid. Mp = 186 °C (CH2Cl2). Rf = 0.44 (cyclohexane/Et3N/methyl tert-butyl ether = 95:4:1; basic aluminum oxide). IR (ATR): ν̃ = 3064, 3022, 2926, 1583, 1558, 1459, 1428, 1400, 1381, 1330, 1249, 1204, 1147, 1109, 1097, 1014, 978, 915, 889, 817, 782, 726 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.78 (s, 3H), 4.10 (s, 3H), 7.12 (dd, 3J(H,H) = 7.5 Hz, 3 J(H,H) = 7.4 Hz, 1H), 7.24 (ddd, 3J(H,H) = 7.6 Hz, 3J(H,H) = 7.6 Hz, 4J(H,H) = 0.9 Hz, 1H), 7.32−7.41 (m, 5H), 7.56−7.57 (m, 2H), 7.62−7.64 (m, 2H), 7.75 (d, 3J(H,H) = 8.2 Hz, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ −4.7, 32.5, 109.9, 110.3, 121.1, 121.8, 122.0, 122.5, 128.5, 129.9, 130.4, 130.4, 133.1, 133.8, 134.7, 135.0, 140.4, 143.0, 146.9, 152.9. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −13.8. HRMS (APCI): calculated for C22H19ClNSi [M + H]+ 360.0970; found 360.0977. Anal. Calcd for C22H18ClNSi: C, 73.42; H, 5.04; N, 3.89. Found: C, 73.07; H, 5.31; N, 4.05. 5,12-Dimethyl-12-phenyl-5,12-dihydronaphtho[2′,3′:4,5]silolo[3,2-b]indole (1pc). This was prepared from 1-methyl-2(naphthalene-2-yl)-1H-indole (5p, 51 mg, 0.20 mmol, 1.0 equiv), ruthenium complex [4a]+[BArF4]− (6.5 mg, 4.0 μmol, 2.0 mol %), methylphenylsilane (6c, 73 mg, 0.60 mmol, 3.0 equiv), ruthenium chloride complex [(Et3P)Ru(SDmp)(Cl)] (2.4 mg, 4.0 μmol, 2.0 mol %), and Na[CHB11Me5Br6] (3.4 mg, 4.8 μmol, 2.4 mol %) according to GP4. Step 1 was performed at room temperature for 16 h with ClC6H5 (0.20 mL, 1.0 M) as a solvent. Purification by flash-column chromatography on silica gel (15−40 μm)37 using cyclohexane/Et3N/ methyl tert-butyl ether (v:v:v = 95:4:1)36 as eluent afforded the product (31 mg, 41%) as a pale yellow solid. Crystals suitable for X-ray diffraction were obtained by recrystallization of 1pc from cyclohexane/ n-pentane at 8 °C. Mp = 219 °C (CH2Cl2). Rf = 0.31 (cyclohexane/ Et3N/methyl tert-butyl ether = 95:4:1; basic aluminum oxide). IR (ATR): ν̃ = 3019, 2945, 2893, 1620, 1595, 1476, 1464, 1428, 1392, 1376, 1335, 1268, 1246, 1199, 1186, 1157, 1127, 1113, 1055, 1015, 975, 945, 894, 872, 795, 735 cm−1. 1H NMR (500 MHz, CD2Cl2): δ 0.84 (s, 3H), 4.25 (s, 3H), 7.14 (ddd, 3J(H,H) = 7.5 Hz, 3J(H,H) = 7.4 Hz, 4J(H,H) = 1.0 Hz, 1H), 7.27 (ddd, 3J(H,H) = 7.7 Hz, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.1 Hz, 1H), 7.32−7.38 (m, 3H), 7.43−7.47 (m, 2H), 7.51 (ddd, 3J(H,H) = 7.4 Hz, 3J(H,H) = 7.4 Hz, 4J(H,H) = 1.1 Hz, 1H), 7.61 (br d, 3J(H,H) = 7.7 Hz, 1H), 7.68−7.70 (m, 2H), 7.79 (br d, 3J(H,H) = 8.0 Hz, 1H), 7.88 (d, 3J(H,H) = 8.0 Hz, 1H), 8.07 (s, 1H), 8.20 (s, 1H). 13C{1H} NMR (126 MHz, CD2Cl2): δ − 4.0, 32.7, 110.2, 112.3, 119.0, 120.9, 122.2, 122.8, 126.4, 127.4, 128.3, 128.4, 128.7, 130.1, 130.5, 133.1, 134.4, 134.8, 135.0, 136.2, 138.4, 141.9, 143.5, 153.7. 29Si DEPT NMR (99 MHz, CD2Cl2): δ −14.8. HRMS (ESI): calculated for C26H22NSi [M + H]+ 376.1516; found 376.1517.

Anal. Calcd for C26H21NSi: C, 83.16; H, 5.64; N, 3.73. Found: C, 82.94; H, 5.68; N, 3.54.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00801. Synthetic procedures of weakly coordinating anions and substrates, including analytical data, NMR spectra of all compounds synthesized in this paper, and crystal structures of 1ec as well as 1pc. (PDF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lukas Omann: 0000-0002-8689-250X Martin Oestreich: 0000-0002-1487-9218 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS L.O. thanks the Fonds der Chemischen Industrie for a predoctoral fellowship (2015−2017), and M.O. is indebted to the Einstein Foundation (Berlin) for an endowed professorship. We thank Simon Karleskind (Ecole Polytechnique, Palaiseau/ France) for skillful experimental assistance during an internship, Susanne Bähr for the synthesis of the ruthenium hydride, and Dr. Elisabeth Irran for the X-ray analyses (both TU Berlin).

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REFERENCES

(1) For an overview of conjugated organosilicon materials, see: Ponomarenko, S. A.; Kirchmeyer, S. In Advances in Polymer Science; Muzafarov, A. M., Ed.; Springer: Berlin/Heidelberg, 2011; Vol. 235, pp 33−110. (2) (a) Yamaguchi, S.; Tamao, K. J. Chem. Soc., Dalton Trans. 1998, 3693−3702. (b) Yamaguchi, S.; Tamao, K. Chem. Lett. 2005, 34, 2−7. (3) For an overview of synthetic methods to access siloles, see: Kobayashi, J.; Kawashima, T. In Science of Synthesis Knowledge Updates 2014/1; Oestreich, M., Ed.; Thieme: Stuttgart, 2014; pp 351−369. (4) For a recent review of synthetic methods for the synthesis of benzo[b]heteroles, including benzosiloles, see: Wu, B.; Yoshikai, N. Org. Biomol. Chem. 2016, 14, 5402−5416. (5) For selected examples of synthetic methods to access dibenzosiloles, see: (a) Matsuda, T.; Kadowaki, S.; Goya, T.; Murakami, M. Org. Lett. 2007, 9, 133−136. (b) Yabusaki, Y.; Ohshima, N.; Kondo, H.; Kusamoto, T.; Yamanoi, Y.; Nishihara, H. Chem. - Eur. J. 2010, 16, 5581−5585. (c) Ureshino, T.; Yoshida, T.; Kuninobu, Y.; Takai, K. J. Am. Chem. Soc. 2010, 132, 14324−14326. (d) Liang, Y.; Zhang, S.; Xi, Z. J. Am. Chem. Soc. 2011, 133, 9204− 9207. (e) Kuninobu, Y.; Yamauchi, K.; Tamura, N.; Seiki, T.; Takai, K. Angew. Chem., Int. Ed. 2013, 52, 1520−1522. (f) Shintani, R.; Takagi, C.; Ito, T.; Naito, M.; Nozaki, K. Angew. Chem., Int. Ed. 2015, 54, 1616−1620. (g) Zhang, Q.-W.; An, K.; Liu, L.-C.; Yue, Y.; He, W. Angew. Chem., Int. Ed. 2015, 54, 6918−6921. (h) Leifert, D.; Studer, A. Org. Lett. 2015, 17, 386−389. (i) Xu, L.; Zhang, S.; Li, P. Org. Chem. Front. 2015, 2, 459−463. (j) Murai, M.; Matsumoto, K.; Takeuchi, Y.; Takai, K. Org. Lett. 2015, 17, 3102−3105. (k) Shibata, T.; Shizuno, T.; Sasaki, T. Chem. Commun. 2015, 51, 7802−7804. (l) Murai, M.; Okada, R.; Nishiyama, A.; Takai, K. Org. Lett. 2016, 18, 4380−4383. (m) Zhang, Q.-W.; An, K.; Liu, L.-C.; Guo, S.; Jiang, C.; Guo, H.; He, W. Angew. Chem., Int. Ed. 2016, 55, 6319−6323. I


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Organometallics

Grimme, S.; Paradies, J. Angew. Chem., Int. Ed. 2016, 55, 12219− 12223. (22) A solvent screening with CH2Cl2, toluene, mesitylene, ClC6H5, 1,2-Cl2C6H4, FC6H5, and 1,2-F2C6H4 was performed. We observed no difference in the outcome of these reactions. However, the amount of solvent used for this transformation had a significant impact on the reactivity, providing higher conversions at higher concentrations. (23) The proton source accounting for protodesilylation of 7ac is likely to be water, which cannot be entirely excluded on these smallscale reactions. Instead of forming the corresponding silanol or disiloxane as observed before,16 7ac is prone to Si−C bond cleavage in the presence of water. (24) Similar results were obtained when 2,6-di-tert-butylpyridine (0.1 equiv) was used as an additive. Upon increasing the amount of this additive (0.2 equiv), the conversion decreased significantly. (25) Hermeke, J.; Klare, H. F. T.; Oestreich, M. Chem. - Eur. J. 2014, 20, 9250−9254. (26) Stahl, T.; Klare, H. F. T.; Oestreich, M. J. Am. Chem. Soc. 2013, 135, 1248−1251. (27) Bähr, S.; Simonneau, A.; Irran, E.; Oestreich, M. Organometallics 2016, 35, 925−928. (28) We also tried to synthesize ([4a] + ) 2 [B 12 Cl 12 ] 2− and ([4b]+)2[B12Cl12]2−. These attempts were however unfruitful, most likely due to the poor solubility of Na2[B12Cl12] in common noncoordinating solvents, thus hampering the formation of cationic Ru−S complexes. (29) For substituent scrambling at the silicon atom, see: (a) Schäfer, A.; Reißmann, M.; Schäfer, A.; Saak, W.; Haase, D.; Müller, T. Angew. Chem., Int. Ed. 2011, 50, 12636−12638. (b) Schäfer, A.; Reißmann, M.; Jung, S.; Schäfer, A.; Saak, W.; Brendler, E.; Müller, T. Organometallics 2013, 32, 4713−4722. (c) Feigl, A.; Chiorescu, I.; Deller, K.; Heidsieck, S. U. H.; Buchner, M. R.; Karttunen, V.; Bockholt, A.; Genest, A.; Rösch, N.; Rieger, B. Chem. - Eur. J. 2013, 19, 12526−12536. (d) Müther, K.; Hrobárik, P.; Hrobáriková, V.; Kaupp, M.; Oestreich, M. Chem. - Eur. J. 2013, 19, 16579−16594. (e) Labbow, R.; Reiß, F.; Schulz, A.; Villinger, A. Organometallics 2014, 33, 3223− 3226. (f) Chen, J.; Chen, E. Y.-X. Angew. Chem., Int. Ed. 2015, 54, 6842−6846. (g) Khandelwal, M.; Wehmschulte, R. J. Angew. Chem., Int. Ed. 2012, 51, 7323−7326. (h) Wehmschulte, R. J.; Saleh, M.; Powell, D. R. Organometallics 2013, 32, 6812−6819. (30) Bähr, S.; Oestreich, M., unpublished results from our laboratory. Preparation and characterization of ruthenium hydrides will be reported elsewhere. (31) For studies on the reactivity of dimeric Ru−S complexes, see: (a) Ref 26. (b) Ref 27. (32) Si−H bond activation of triarylsilanes with Ru−S complexes was described to be challenging before: (a) Ref 14a. (b) Ref 16. (33) Suffert, J. J. Org. Chem. 1989, 54, 509−510. (34) For detailed procedures, see the Supporting Information and: (a) Reed, C. A. Acc. Chem. Res. 2010, 43, 121−128. (b) Stasko, D.; Reed, C. A. J. Am. Chem. Soc. 2002, 124, 1148−1149. (35) Lebrasseur, N.; Larrosa, I. J. Am. Chem. Soc. 2008, 130, 2926− 2927. (36) To avoid decomposition, the silica gel must be deactivated with the Et3N-containing eluent before loading the sample onto the column. (37) Silica gel with a larger particle size (40−63 μm) did not provide the product in satisfactory purity.

(6) For an in-depth photophysical study of indole-fused benzosiloles, see: (a) Shimizu, M.; Mochida, K.; Hiyama, T. J. Phys. Chem. C 2011, 115, 11265−11274. (b) Shimizu, M.; Mochida, K.; Asai, Y.; Yamatani, A.; Kaki, R.; Hiyama, T.; Nagai, N.; Yamagishi, H.; Furutani, H. J. Mater. Chem. 2012, 22, 4337−4342. (7) Xi and co-workers reported about similar indole-fused benzosiloles by palladium-catalyzed C−Br/Si−C coupling, where the silicon atom is attached to the C2 position of the indole: Hao, W.; Geng, W.; Zhang, W.-X.; Xi, Z. Chem. - Eur. J. 2014, 20, 2605−2612. (8) Ohmura and Suginome reported about the synthesis of indolefused dihydrosiloles that can be oxidized to the corresponding siloles: Masuda, K.; Ohmura, T.; Suginome, M. Organometallics 2011, 30, 1322−1325. (9) Mochida, K.; Shimizu, M.; Hiyama, T. J. Am. Chem. Soc. 2009, 131, 8350−8351. (10) For a synthesis of the same molecule without 1,2-silyl migration, see: Shimizu, M.; Mochida, K.; Hiyama, T. Angew. Chem., Int. Ed. 2008, 47, 9760−9764. (11) (a) Zhang, Q.-W.; An, K.; He, W. Angew. Chem., Int. Ed. 2014, 53, 5667−5671. (b) Zhang, Q.-W.; An, K.; He, W. Synlett 2015, 26, 1145−1152. (12) Ohki, Y.; Takikawa, Y.; Sadohara, H.; Kesenheimer, C.; Engendahl, B.; Kapatina, E.; Tatsumi, K. Chem. - Asian J. 2008, 3, 1625−1635. (13) For an in-depth study of the mechanism of the cooperative Si− H bond activation at Ru−S bonds, see: Stahl, T.; Hrobárik, P.; Königs, C. D. F.; Ohki, Y.; Tatsumi, K.; Kemper, S.; Kaupp, M.; Klare, H. F. T.; Oestreich, M. Chem. Sci. 2015, 6, 4324−4334. For an analysis of the related Si−H bond activation at Ir−S and Rh−S bonds, see: (b) Hesp, K. D.; McDonald, R.; Ferguson, M. J.; Stradiotto, M. J. Am. Chem. Soc. 2008, 130, 16394−16406. (14) (a) Klare, H. F. T.; Oestreich, M.; Ito, J.-i.; Nishiyama, H.; Ohki, Y.; Tatsumi, K. J. Am. Chem. Soc. 2011, 133, 3312−3315. For a related B−H bond activation and application in an SEAr reaction of indoles, see: (b) Stahl, T.; Müther, K.; Ohki, Y.; Tatsumi, K.; Oestreich, M. J. Am. Chem. Soc. 2013, 135, 10978−10981. For an iron-catalyzed C3silylation of indoles, see: (c) Sunada, Y.; Soejima, H.; Nagashima, H. Organometallics 2014, 33, 5936−5939. (15) Other intermolecular Friedel−Crafts-type C−H silylations: (a) Furukawa, S.; Kobayashi, J.; Kawashima, T. Dalton Trans. 2010, 39, 9329−9336. (b) Curless, L. D.; Clark, E. R.; Dunsford, J. J.; Ingleson, M. J. Chem. Commun. 2014, 50, 5270−5272. (c) Yin, Q.; Klare, H. F. T.; Oestreich, M. Angew. Chem., Int. Ed. 2016, 55, 3204−3207. (d) Ma, Y.; Wang, B.; Zhang, L.; Hou, Z. J. Am. Chem. Soc. 2016, 138, 3663− 3666. (e) Chen, Q.-A.; Klare, H. F. T.; Oestreich, M. J. Am. Chem. Soc. 2016, 138, 7868−7871. (16) Omann, L.; Oestreich, M. Angew. Chem., Int. Ed. 2015, 54, 10276−10279. (17) Other intramolecular Friedel−Crafts-type C−H silylations: (a) Furukawa, S.; Kobayashi, J.; Kawashima, T. J. Am. Chem. Soc. 2009, 131, 14192−14193. (b) Ref 15a. (c) Curless, L. D.; Ingleson, M. J. Organometallics 2014, 33, 7241−7246. (18) For an up-to-date review of Friedel−Crafts-type C−H silylation, see: Bähr, S.; Oestreich, M. Angew. Chem., Int. Ed. DOI: 10.1002/ anie.201608470. (19) For general reviews of C−H silylation see: (a) Cheng, C.; Hartwig, J. F. Chem. Rev. 2015, 115, 8946−8975. (b) Xu, Z.; Huang, W.-S.; Zhang, J.; Xu, L.-W. Synthesis 2015, 47, 3645−3668. (c) Sharma, R.; Kumar, R.; Kumar, I.; Singh, B.; Sharma, U. Synthesis 2015, 47, 2347−2366. (20) For recent reviews of direct C2-selective C−H arylations of indoles, see: (a) Boorman, T. C.; Larrosa, I. In Progress in Heterocyclic Chemistry; Gribble, G.; Joule, J. A., Eds.; Elsevier: Heidelberg, 2011; Vol. 22, pp 1−20. (b) Lebrasseur, N.; Larrosa, I. In Advances in Heterocyclic Chemistry; Katritzky, A., Ed.; Elsevier: Heidelberg, 2012; Vol. 105, pp 309−351. (21) Grimme, Paradies, and co-workers recently proved that such dihydrogen adducts are kinetically and thermodynamically stable: Maier, A. F. G.; Tussing, S.; Schneider, T.; Flörke, U.; Qu, Z.-W.; J


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