Reactions of Boroles Formed by 1,1-Carboboration - Organometallics

Article pubs.acs.org/Organometallics

Reactions of Boroles Formed by 1,1-Carboboration Fang Ge, Gerald Kehr, Constantin G. Daniliuc,† and Gerhard Erker* Organisch-Chemisches Institut, Universität Münster, Corrensstrasse 40, D-48149 Münster, Germany S Supporting Information *

ABSTRACT: The borole 2, obtained by 1,1-carboboration of phenylbis(trimethylsilylethynyl)borane with B(C6F5)3, undergoes [4 + 2] cycloaddition reactions with 1-pentyne and with ethene to give the 7-borabicyclo[2.2.1]heptadiene and -heptene derivatives, respectively. The borole 2 reacts with pyridine at room temperature to give a pyridine-stabilized borolium ion. The reaction proceeds by phenyl migration and Me3SiF elimination. Carbon monoxide reacts rapidly with the borole 2 at room temperature to give the unusual ketene derivative 19 with Me3Si migration across the ring system.

■

INTRODUCTION

reactions (e.g., cycloadditions) and also found some rather unusual reactions of our new borole system.

1

■

Boroles are reactive formally antiaromatic compounds. They have found wide interest as components in organic materials chemistry.2 Simple boroles are mostly prepared involving borylation reactions of suitable metal-containing precursors.3,4 Sometimes even multiple transmetalation sequences may be involved.5 We recently described a new pathway for the preparation of borole derivatives by the reaction of bis(alkynyl)boranes with the B(C6F5)3 reagent.6 The sequence of subsequent 1,1-carboboration reactions7,8 led to the respective borole 2 in good yield in a convenient onepot reaction. We had shown that the new borole 2 is rather reactive and that it undergoes a [4 + 2] cycloaddition reaction with the symmetrical alkyne 3-hexyne to give the 2-borylsubstituted boranorbornadiene derivative 3 (Scheme 1).6 We have now carried out a few additional reactions of the borylsubstituted borole system 2 in order to characterize its chemical reactivity. We have found that it undergoes some typical borole

RESULTS AND DISCUSSION [4 + 2] Cycloadditions. The boryl-substituted borole 2 was prepared by treatment of the bis(alkynyl)phenylborane 1 with B(C6F5)3 under mild reaction conditions (−50 °C to room temperature) as we had previously described.6 It was isolated as a red crystalline solid in 43% yield. We have now treated the borole 2 with 1-pentyne. The reaction proceeded rapidly at room temperature, and we isolated the [4 + 2] cycloaddition product as the single regioisomer 4 from pentane at −36 °C in 34% yield (Scheme 2). A separate experiment was carried out in CD2Cl2 with direct 1H NMR monitoring. It revealed a regioselectivity of the formation of the borole/1-pentyne Diels−Alder addition product 4 of ca. 90%. The cycloaddition product 4 was characterized by X-ray diffraction (Figure 1). The X-ray crystal structure analysis Scheme 2

Scheme 1

Received: October 29, 2014 Published: December 19, 2014 © 2014 American Chemical Society

229

dx.doi.org/10.1021/om501085j | Organometallics 2015, 34, 229−235

Organometallics

Article

In solution compound 4 shows two 11B NMR resonances. The 11B NMR signal at δ 60.8 was assigned to the B(C6F5)2 substituent and the δ −9.4 resonance to the BPh moiety that features the contact to the C(5)C(6) carbon−carbon double bond. The 7-boranorbornadiene compound 4 shows 13C NMR resonances of its framework at δ 158.0 (C2−[B]), 138.1 (C5), 117.4 (C6−H), and 69.3 (C4) and 62.5 (C1). The 13C NMR signal of the carbon atom C3 was not located. The corresponding C6−H 1H NMR signal is at δ 6.71. Compound 4 shows 29Si NMR signals at δ −0.8 and −4.3, respectively. Ethylene is a rather poor dienophile. It actually is often cleaved off as the two-electron π component in synthetically useful retro-Diels−Alder reactions (Alder−Rickert cleavage).9,10 There has been one example of a [4 + 2] cycloaddition reaction of ethene with an in situ generated borole derivative,11,12 indicating that boroles may serve as components in cycloaddition reactions with inverse electron demand.13 We have exposed a pentane solution of the borole 2 to ethylene (1.5 bar). The cycloaddition reaction took place readily at room temperature (Scheme 2). After ca. 30 min crystals of the product 5 had formed and we isolated the compound eventually as a pure crystalline material in ca. 40% yield. Compound 5 was characterized by C,H elemental analysis, by spectroscopy, and by X-ray diffraction. The X-ray crystal structure analysis of compound 5 (Figure 2) has

Figure 1. Molecular structure of compound 4. Thermal ellipsoids are shown at the 50% probability level; hydrogens (except C6) and Me substituents at Si are omitted for clarity.

showed that the regioisomer was formed that featured the npropyl substituent originating from the 1-pentyne reagent at the framework carbon position C5: i.e., oriented syn to the C6F5 substituent at C3 of the borabicyclo[2.2.1]heptadiene framework. The boron atom B2 shows a trigonal-planar coordination geometry with its plane rotated markedly away from conjugation with the adjacent C2−C3 carbon−carbon double bond. The 7-boranorbornadiene framework of compound 4 is markedly distorted. The apical B1 boron atom is found significantly leaning over toward the side of the C5−C6 carbon−carbon double bond, which results in a weak coordination of the Lewis acidic B1-borane with this π system (Table 1, Scheme 2, and Figure 1). This effect had previously been observed for other Lewis acidic 7-borabicyclo[2.2.1]heptadiene systems as well (e.g., for 3).6,9 Table 1. Selected Structural Parameters of the Borole [4 + 2] Cycloaddition Products 3−5a B1−C21 B1−C1 B1−C4 B1−C2 B1−C3 B1−C5 B1−C6 B2−C2 C1−Si1 C4−Si2 C2−C3 C5−C6 C2−C1−B1 C3−C4−B1 C5−C4−B1 C6−C1−B1 ∑B1CCC ∑B2CCC θ(C3−C2−B2−C41)

3b

4

5

1.577(3) 1.645(3) 1.644(3) 2.533(3) 2.488(3) 1.782(3) 1.777(3) 1.543(3) 1.897(2) 1.897(2) 1.354(3) 1.392(3) 105.9(2) 104.2(2) 68.4(1) 68.4(1) 359.4 359.7 −55.1(3)c

1.570(3) 1.650(3) 1.650(3) 2.543(3) 2.501(3) 1.787(3) 1.755(3) 1.546(3) 1.892(2) 1.896(2) 1.355(2) 1.378(3) 106.6(1) 104.4(1) 68.6(1) 67.3(1) 359.7 360.0 −55.9(2)

1.559(3) 1.614(3) 1.619(3) 2.070(3) 2.015(3) 2.539(3) 2.490(3) 1.550(3) 1.890(2) 1.890(2) 1.379(2) 1.532(3) 82.4(1) 80.0(1) 105.7(2) 103.5(2) 359.7 359.4 −47.6(3)

Figure 2. View of the molecular structure of the borole/ethylene [4 + 2] cycloaddition product 5 . Thermal ellipsoids are shown at the 30% probability level; hydrogens (except C5 and C6) and Me substituents at Si are omitted for clarity.

confirmed the formation of the borabicyclo[2.2.1]heptene framework. It has the B(C6F5)2 and C6F5 pair of substituents attached in vicinal positions at carbon atoms C2 and C3, respectively, as it is derived from the 1,1-carboboration sequence.14 The Lewis acidic apical Ph−B1 center shows a weak bonding interaction with the C2C3 double bond similar to that previously observed for a variety of borabicyclo[2.2.1]heptadiene derivatives,9 although the interaction with the electron-poor C2C3 carbon−carbon double bond in 5 seems to be slightly weaker (Figure 2 and Table 1). In solution compound 5 shows 11B NMR features at δ 63.6 (B(C6F5)2) and δ 31.3 (PhB), respectively. The ethylene bridge

Bond lengths are given in Å and angles in deg. bFrom ref 6. cθ(C3− C2−B2−C51). a

230


Organometallics

Article

of the framework shows 13C NMR signals at δ 33.6 and 33.1 with corresponding 1H NMR resonances at δ 2.55/1.88 (2H) and 2.46/1.88 (2H). The bridgehead carbon resonances were located at δ 51.2 and 49.1, and the remaining framework carbon NMR signals occurred at δ 154.9 (C2) and δ 148.6 (C3), respectively. Reaction of the Borole 2 with Pyridine. The electrophilic boroles can add nucleophilic reagents to form stable adducts. It had been shown that pentaphenylborole (6) adds e.g. 4-methylpyridine to the boron atom to form the respective borole/pyridine adduct (7a) (Scheme 3). The borole 6 also adds the more bulky 2,6-lutidine to form the B adduct 7b, which rearranged upon photolysis to form the corresponding isomeric C adduct 8.1d,15

pyridine adduct 11 (Scheme 5), which was characterized by Xray diffraction (Figure 3). Compound 11 shows the central fiveScheme 5

Scheme 3

Figure 3. View of the molecular structure of compound 11. Thermal ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and angles (deg): B1−N51 1.617(3), B1−C1 1.641(3), B1−C4 1.622(3), C1−C2 1.368(3), C2−C3 1.517(3), C3−C4 1.349(3), B2−C2 1.651(3), B2−N61 1.645(3), C1−B1−C4 101.4(2), C1−C2−C3−C4 3.3(2), B1−C1−C2−C3 −6.6(2).

Chlorotetraphenylborole (9) was reported to also add 4methylpyridine at the electrophilic boron atom (to form the adduct 7c). Its reaction with the chloride abstractor Na[BAr4] (Ar = 3,5-(CF3)2-C6H3) in the presence of excess 4methylpyridine then gave the borolium salt 10 (11B NMR: δ 7.2 and −7.5) (Scheme 4).16 The boryl-substituted borole 2 also reacts with pyridine. Treatment with 2 molar equiv of pyridine at low temperature (ca. −30 °C) resulted in the formation of the conventional bis-

membered heterocycle. The endocyclic boron atom B1 is tetracoordinated. It contains the original phenyl substituent and a molecule of pyridine bonded to it. The carbon atoms C1 and C4 have each a SiMe3 substituent attached, C3 bears the C6F5 substituent, and the B(C6F5)2(pyridine) moiety is bonded at the ring carbon atom C2. Compound 11 is thermally sensitive in solution (see below). Therefore, we needed to measure the NMR data at sufficiently low temperature (243 K). We have monitored the 1H/13C NMR features of the attached pair of pyridines and of the single phenyl substituent at boron (for details see the Supporting Information). Compound 11 exhibits a pair of 11B NMR resonances at δ 7.8 and −2.6 and 29Si NMR signals at δ −11.7 and −12.8, respectively. The compound rearranged at room temperature (ca. 2.5 h) to give the pyridine-stabilized borolium product 14 (Scheme 6 and Figure 4).17,18 It was isolated as yellow crystals in 50% yield. The X-ray crystal structure analysis has shown that the phenyl substituent at boron has undergone a 1,2-migration from boron to carbon and that Me3SiF had been eliminated using a fluoride substituent at the single C6F5 substituent of the starting material 2 (the Me3SiF coproduct was found in an in situ NMR experiment; see the Supporting Information). The remaining tetrafluorophenylene unit is found connected to the borolium nucleus by means of the B(C6F5)2 moiety. The

Scheme 4

231


Organometallics

Article

Reaction with Carbon Monoxide. It had been described that pentaphenylborole 6 adds carbon monoxide to form the borole carbonyl 15,19,20 which subsequently rearranged to a dimeric CO insertion product (Scheme 7).

Scheme 6

Scheme 7

The borole 2 underwent a different, rather unusual reaction with carbon monoxide. Exposure of the reactive antiaromatic heterocycle 2 to CO (2 bar) at room temperature in dichloromethane led to an almost instantaneous formation of the ketene product 19 (Scheme 8 and Figure 5). We isolated Scheme 8

Figure 4. Molecular structure of the borolium system 14. Thermal ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and angles (deg): B1−N11 1.613(3), B1−N21 1.598(3), B1−C1 1.616(4), B1−C4 1.632(3), C1−C2 1.348(3), C2−C3 1.501(3), C3−C4 1.363(3), C3−C42 1.491(3), B2−C2 1.615(4), B2−C41 1.637(4), C1−B1−C4 103.7(2), N11−B1−N21 110.5(2), C2−B2−C41 97.0(2), C51−B2−C61 114.8(2), C1−C2−C3−C4 7.4(3), C1−C2−C3−C42 −166.0(2), C2−C3−C42−C41 2.0(3), B1−C1−C2−C3 −9.1(3), B1−C1−C2−B2 178.5(3).

compound 19 from the reaction mixture as yellow crystals in 62% yield. It was characterized by C,H elemental analysis, by spectroscopy, and by X-ray diffraction. In solution compound 19 features a pair of 11B NMR signals at δ 71.2 and 58.8, respectively, which indicates the presence of a pair of Lewis acidic planar-tricoordinate boron centers. It shows a single 29Si NMR resonance at δ 1.2 with a corresponding 1H NMR SiMe3 signal (δ 0.11) representing 18 hydrogen atoms. We see the 19F NMR signals of the B(C6F5)2 group and the single C6F5 substituent and the 1H/13C NMR signals of the phenyl substituent at boron. The 13C NMR resonances of the central five-membered heterocyclic core occur at δ 66.2 (CSi2), 152.6, and 148.8 and at δ 56.9 for ring carbon atom (C1) of the exocyclic ketene unit.21 The ketene carbonyl carbon atom (CC21O) shows a typical 13C NMR resonance at δ 179.2. The IR spectrum (KBr) shows a “ketene band” at ν̃ 2107 cm−1. The X-ray crystal structure analysis has confirmed the presence of the ketene moiety in a position α to boron at the five-membered heterocycle and the new structural feature of the geminal pair of SiMe3 substituents at C4.

borolium boron atom B1 has a pair of pyridine substituents bonded to it (Figure 4). In solution compound 14 features a pair of 11B NMR signals at δ 13.2 and −16.6 (cf. 11B NMR of compound 10 in Scheme 4: δ 7.2, −7.5).15 We note that the single remaining SiMe3 substituent in compound 14 features coupling with one F substituent (JFH = 4.5 Hz, JFC = 11.2 Hz, JSiF = 7.1 Hz) of the adjacent tetrafluorophenylene moiety. These findings might be rationalized by a reaction sequence initiated by intramolecular attack of the nucleophilic B−phenyl substituent at the adjacent borole carbon atom to give the borata-ethene-like intermediate 12 (Scheme 6). Transannular silyl migration would then give 13, which would form the observed product by intramolecular Me3SiF elimination and subsequent ring closure by aryl−B bond formation and stabilization of the [B+] unit by pyridine addition. 232


Organometallics

■

Article

EXPERIMENTAL SECTION

For general information and details of the characterization of the new compounds see the Supporting Information. Preparation of Compound 4. 1-Pentyne (8.2 mg, 0.12 mmol) was added to a solution of the borole 2 (79.5 mg, 0.10 mmol) in pentane (1 mL). The color of the reaction mixture changed from red to dark orange. Then the reaction mixture was stored at −36 °C. The obtained yellow crystals were collected, dried in vacuo, and characterized as compound 4 (30 mg, 0.03 mmol, 34%). Crystals suitable for the X-ray crystal structure analysis were obtained from the reaction mixture at −36 °C. Mp: 130 °C. Anal. Calcd for C39H31B2F15Si2: C, 54.31; H, 3.62. Found: C, 54.75; H, 3.71. 1H NMR (600 MHz, [D2]dichloromethane, 299 K): δ 7.21 (br, 5H, Ph), 6.71 (s, 1H, CH), 2.89, 2.54 (each m, each 1H, CH2Pr), 1.95 (m, 2H, CH2Pr), 1.16 (t, 3JHH = 7.3 Hz, 3H, MePr), −0.31 (s, 9H, SiMe3B), −0.32 (s, 9H, SiMe 3 ). 13 C{ 1 H} NMR (151 MHz, [D 2 ]dichloromethane, 299 K): δ 158.0 (br, CB), 138.1 (br, CPr), n.o. (C), 128.0, 127.8 (Ph), n.o. (i-Ph), 117.4 (CH), 69.3 (br, CSi), 62.5 (br, CSiB), 35.1 (CH2Pr), 22.5 (d, J = 2.1 Hz, CH2Pr), 14.2 (MePr), 0.3 (d, J = 1.5 Hz, SiMe3), 0.1 (SiMe3B) [C6F5 not listed; t , tentative assignment]. 11 B{ 1 H} NMR (192 MHz, [D 2 ]dichloromethane, 299 K): δ 60.8 (ν1/2 ≈ 1300 Hz, B), −9.4 (ν1/2 ≈ 400 Hz, BPh). 19F NMR (564 MHz, [D2]dichloromethane, 299 K): δ −127.4 (br, 4F, o), −148.0 (br, 2F, p), −162.0 (br, 4F, m) (BC6F5) [Δδ(19Fm,p) = 4.0]; −134.1 (br), −136.5 (m) (o), −155.5 (t, 1F, 3JFF = 20.6 Hz, p), −163.2, −164.5 (each m, m) (each 1F, C6F5) [Δδ(19Fm,p) = 7.7, 9.0]. 29Si{1H} DEPT (119 MHz, [D2]dichloromethane, 299 K): δ −0.8 (ν1/2 ≈ 2 Hz, SiMe3B), −4.3 (ν1/2 ≈ 2 Hz, SiMe3). Preparation of Compound 5. First Experiment. Borole 2 (79.0 mg, 0.1 mmol) was dissolved in pentane (1.5 mL). Ethene (1.5 bar) was introduced to the carefully degassed solution at room temperature. The color of the reaction mixture was immediately changed from red to yellow. Some pale yellow crystals formed after ca. 0.5 h at room temperature. The reaction mixture was kept at −32 °C overnight to allow the formation of more crystals, which were isolated and confirmed by NMR spectroscopy as compound 5 (30.0 mg, 0.04 mmol, 40%). Crystals suitable for the X-ray crystal structure analysis were obtained from the reaction mixture at room temperature. Mp: 112 °C. Second Experiment. Borole 2 (30 mg, 0.04 mmol) in pentane (1 mL) reacted with ethene (1.6 bar) at room temperature. The reaction mixture was kept at −35 °C to give crystals of compound 5. Anal. Calcd for C36H27B2F15Si2: C, 52.58; H, 3.31. Found: C, 52.81; H, 3.22. 1 H NMR (500 MHz, [D2]dichloromethane, 299 K): δ 7.46 (m, 2H, oPh), 7.32 (m, 3H, m,p-Ph), 2.55, 1.88 (each m, each 1H, CH2), 2.46, 1.88 (each m, each 1H, CH2B), −0.25 (s, 9H, SiMe3B), −0.28 (s, 9H, SiMe3). 13C{1H} NMR (126 MHz, [D2]dichloromethane, 299 K): δ 154.9 (br, CB), 148.6 (C), 135.4 (br, i-Ph)t, 132.5 (br, o-Ph), 128.5 (p-Ph), 127.5 (m-Ph), 51.2 (br, CSi), 49.1 (br, CSiB), 33.6 (CH2), 33.1 (CH2B), −0.4 (SiMe3B), −1.5 (SiMe3) [C6F5 not listed; t, tentative assignment]. 11 B{ 1 H} NMR (160 MHz, [D 2 ]dichloromethane, 299 K): δ 63.6 (ν1/2 ≈ 1200 Hz, B), 31.3 (ν1/2 ≈ 1400 Hz, BPh). 19F NMR (470 MHz, [D2]dichloromethane, 299 K): δ −126.9 (br, 4F, o), −146.9 (t, 3JFF = 20.3 Hz, 2F, p), −161.1 (m, 4F, m) (BC6F5) [Δδ(19Fm,p) = 14.2]; −134.8 (m, 1F, o), −135.1 (m, 1F, o′), −153.2 (t, 3JFF = 20.6 Hz, 1F, p), −162.0 (m, 1F, m), −163.0 (m, 1F, m′) (C6F5) [Δδ(19Fm,p) = 8.8, 9.8]. 29Si{1H} DEPT (99 MHz, [D2]dichloromethane, 299 K): δ −1.4 (SiMe3B, ν1/2 ≈ 2 Hz), −1.8 (SiMe3, ν1/2 ≈ 2 Hz). Preparation of Compound 11. Borole 2 (39.5 mg, 0.05 mmol) was dissolved in a solvent mixture (0.5 mL, pentane/dichloromethane 3/1) and precooled to ca. −30 °C. Then pyridine (7.9 mg, 0.10 mmol), also precooled to −30 °C, was added. The color of the reaction mixture turned from red to deep red. Then the reaction mixture was stored at −32 °C overnight. The obtained crystalline material was separated from the supernatant liquor, washed with cold dichloromethane (0.2 mL), and dried in vacuo to give a white solid (24.4 mg, 0.03 mmol, 60%) which was characterized by 1H NMR spectroscopy as a mixture of compound 14 and compound 11 (ratio

Figure 5. Molecular structure of the ketene derivative 19 obtained from the borole carbonylation reaction. Thermal ellipsoids are shown at the 30% probability level. Selected bond lengths (Å) and angles (deg): B1−C1 1.526(3), B1−C4 1.594(3), C1−C2 1.473(2), C2−C3 1.378(2), C3−C4 1.515(2), C1−C21 1.314(3), C21−O1 1.154(2), B2−C2 1.523(3), C1−C21−O1 175.5(2), B1−C1−C2−C3 −0.1(2), C21−C1−C2−C3 177.3(2), ∑C1BCC 360.0, ∑B1CCC 359.7, ∑B2CCC 360.0.

Although we have not yet experimentally observed any intermediate in the carbonylation reaction of 2, the reaction pathway of the formation of compound 19 (Scheme 8) may be remotely related to that discussed in the conversion of the borole 2 to the borolium derivative 14 (Scheme 6). A reasonable reaction sequence might be started by formation of the CO addition product 17 as a reactive intermediate, which can be considered as a stabilized zwitterionic acyl cation/ borata-ethene species.22 Subsequent transannular SiMe3 migration would then directly provide a pathway to the formation of the observed ketene product. We note that here apparently a pathway is favored which is different from that observed in the carbonylation reaction of the borole 6 (Scheme 7).

■

CONCLUSIONS Our observations indicate that the 4π system of our borylsubstituted borole 2 is rather electrophilic. It undergoes a rapid Diels−Alder reaction with ethene, which probably has to be viewed as an efficient [4 + 2] cycloaddition reaction in the inverse electron demand regime. It forms a zwitterionic borolium system upon treatment with pyridine under very mild reaction conditions. This reaction can be described as being initiated by internal nucleophilic phenyl attack at the ring α carbon atom to boron. We found the unique ketene formation upon carbonylation of the borole 2, a reaction that involves nucleophilic CO attack at the ring α carbon. Both of these cases might have profited from an enhanced electrophilic character of the central borole moiety in conjunction with the possibility to form key intermediates that contained a stabilized borata-ethene (i.e., α-boryl carbanion)21 type structural subunit. It seems that our new 1,1-carboboration entry into borole chemistry makes new derivatives of this interesting class of unsaturated cyclic π systems available which may show some uncommon reaction behavior. 233


Organometallics

■

ca. 1/15 [1H]). Crystals suitable for an X-ray crystal structure analysis were obtained by storing the supernatant liquor at −32 °C. Dec pt: 108 °C. 1H NMR (600 MHz, [D2]dichloromethane, 243 K): δ 9.10, 8.47 (each br, each 1H, o), 8.01 (tt, 3JHH = 7.7, 1.4 Hz, 1H, p), 7.53 (m, 2H, m) (Pya), 8.98 (br, 2H, o), 8.10 (tt, 3JHH = 7.7, 1.5 Hz, 1H, p), 7.69 (m, 2H, m) (Pyb), 7.47 (2H, o), 7.20 (2H, m), 7.10 (1H, p) (each m, Ph), −0.79 (s, 9H, SiMe3a), −1.15 (br s, 9H, SiMe3b). 13C{1H} NMR (151 MHz, [D2]dichloromethane, 243 K): δ 177.4, 172.0, 151.6 (CSib, CB, C)t, 175.3 (br, CSia), 150.5, 146.3 (br, o-Pya), 146.0 (br, i-Ph), 145.8 (br, o-Pyb), 142.2 (p-Pya), 141.2 (p-Pyb), 132.5 (o-Ph), 127.2 (m-Ph), 126.0 (br, m-Pyb), 125.3, 124.4 (br, m-Pya), 125.1 (p-Ph), 1.8 (br, SiMe3b), −0.4 (SiMe3a) [C6F5 not listed, t, tentative assignment]. 1 1 B{ 1 H} NMR (192 MHz, [D 2 ]dichloromethane, 243 K): δ 7.8 (ν1/2 ≈ 700 Hz), −2.6 (ν1/2 ≈ 700 Hz, BF). 19F NMR (564 MHz, [D2]dichloromethane, 243 K): δ −124.1, −124.4, −125.9, −137.5, −137.7, −139.6 (each br, each 1F, oC6F5), −157.5 (m), −159.5 (m), −159.7 (t, 3JFF = 21.0 Hz) (each 1F, p-C6F5), −164.1 (2F), −164.6 (1F), −165.4 (1F), −165.7 (1F), −166.7 (s, 1F) (each br, m-C6F5). 29Si{1H} DEPT (119 MHz, [D2]dichloromethane, 243 K): δ −11.7 (SiMe3a, ν1/2 ≈ 3 Hz), −12.8 (SiMe3b, ν1/2 ∼3 Hz). Preparation of Compound 14. After borole 2 (33 mg, 0.04 mmol) was dissolved in CD2Cl2 (0.5 mL), pyridine (14.1 mg, 0.18 mmol) was added at room temperature. The reaction mixture was monitored by NMR spectroscopy. The reaction was completed after keeping it overnight at room temperature. Yellow crystals (18.1 mg, 0.02 mmol, 50%) appeared at room temperature, which were characterized as compound 14. Crystals suitable for the X-ray crystal structure analysis were obtained from a dichloromethane/pentane solution of compound 14 at −32 °C. Decomp.:104 °C. Anal. Calcd for C41H24B2F14N2Si × CH2Cl2: C, 53.37; H, 2.77; N, 2.96. Found: C, 53.78; H, 2.53; N, 2.98. 1H NMR (600 MHz, [D2]dichloromethane, 299 K): δ 8.47 (m, 4H, o-Py), 8.28 (m, 2H, p-Py), 7.74 (m, 4H, m-Py), 6.96 (m, 1H, p-Ph), 6.86 (m, 2H, m-Ph), 5.94 (m, 2H, o-Ph), −0.04 (d, JFH = 4.5 Hz, 9H, SiMe3). 13C{1H} NMR (151 MHz, [D2]dichloromethane, 299 K): δ 179.4, 176.1 (each br, CB,  C)t, 154.6 (br, CPh), 145.1 (o-Py), 144.2 (p-Py), 142.8 (i-Ph), 137.3 (br, CSi), 128.2 (m-Ph), 127.2 (m-Py), 127.0 (o-Ph), 125.6 (p-Ph), 2.2 (d, JFC = 11.2 Hz, SiMe3) [C6F5, C6F4 not listed, t tentative assingment]. 11B{1H} NMR (192 MHz, [D2]dichloromethane, 299 K): δ 13.2 (ν1/2 ≈ 300 Hz, BPy), −16.6 (ν1/2 ≈ 30 Hz, B). 19F NMR (564 MHz, [D2] dichloromethane, 299 K): δ −131.9 (m, 4F, o), −164.9 (t, 3JFF = 20.3 Hz, 2F, p), −167.7 (m, 4F, m) (BC6F5) [Δδ19Fm,p = 2.8]; −133.7 (a), −135.4 (d), −157.0 (c), −163.5 (b) (each m, each 1F, C6F4). 29Si{1H} DEPT (119 MHz, [D2]dichloromethane, 299 K): δ −12.1 (d, JSiF = 7.1 Hz). Preparation of Compound 19. Borole 2 (360.5 mg, 0.45 mmol) and CD2Cl2 (0.5 mL) were placed in a reaction vessel, which was evacuated and then charged with CO (2 bar) at room temperature. The color of the reaction mixture changed immediately from red to deep orange. After removal of all volatiles from the reaction mixture under vacuum, compound 19 was purified by crystallization in pentane at −35 °C and isolated as yellow crystals (230.1 mg, 0.28 mmol, 62%), which were suitable for the X-ray crytal structure analysis. Mp: 84, 158 °C. Anal. Calcd for C35H23B2F15OSi2: C, 51.12; H, 2.82. Found: C, 51.18; H, 2.55. 1H NMR (600 MHz, [D2]dichloromethane, 299 K): δ 7.49 (m, 2H, o-Ph), 7.42 (m, 2H, m-Ph), 7.40 (m, 1H, p-Ph), 0.11 (s, 18H, SiMe3). 13C{1H} NMR (151 MHz, [D2]dichloromethane, 299 K): δ 179.2 (CO), 152.6 (C)t, 148.8 (br, CB)t, 140.2 (br, iPh), 131.3 (o-Ph), 129.2 (p-Ph), 128.3 (m-Ph), 66.2 (br, CSi2), 56.9 (br, CCO)t, 2.7 (SiMe3) [C6F5 not listed, t, tentative assignment]. 11 1 B{ H} NMR (192 MHz, [D2]dichloromethane, 299 K): δ 71.2 (ν1/2 ≈ 850 Hz, B), 58.8 (ν1/2 ≈ 900 Hz, BF). 19F NMR (564 MHz, [D2]dichloromethane, 299 K): δ −128.7 (m, 4F, o), −147.7 (t, 3JFF = 20.0 Hz, 2F, p), −161.0 (m, 4F, m) (BC6F5) [Δδ(19Fm,p) = 13.3]; −130.4 (m, 2F, o), −153.6 (t, 3JFF = 20.7 Hz, 1F, p), −163.2 (m, 2F, m) (C6F5) [Δδ(19Fm,p) = 9.6]. 29Si{1H} DEPT (119 MHz, [D2]dichloromethane, 299 K): δ 1.2 (ν1/2 ≈ 3 Hz).

Article

ASSOCIATED CONTENT

S Supporting Information *

Text, figures, and CIF files giving additional experimental and analytical details for compounds 4, 5, 11, 14, 19, and 20 and structural details for compounds 4, 5, 11, 14, and 19. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail for G.E.: [email protected]. Author Contributions †

X-ray crystal structure analyses.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support from the NRW Graduate School of Chemistry Münster and the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

■

REFERENCES

(1) (a) Eisch, J. J.; Galle, J. E.; Kozima, S. J. Am. Chem. Soc. 1986, 108, 379. (b) Braunschweig, H.; Fernández, I.; Frenking, G.; Kupfer, T. Angew. Chem., Int. Ed. 2008, 47, 1951. (c) Braunschweig, H.; Kupfer, T. Chem. Commun. 2011, 47, 10903. (d) Braunschweig, H.; Chiu, C.-W.; Damme, A.; Ferkinghoff, K.; Kraft, K.; Radacki, K.; Wahler, J. Organometallics 2011, 30, 3210. (e) Ansorg, K.; Braunschweig, H.; Chiu, C. W.; Engels, B.; Gamon, D.; Hügel, M.; Kupfer, T.; Radacki, K. Angew. Chem., Int. Ed. 2011, 50, 2833. (f) Braunschweig, H.; Damme, A.; Gamon, D.; Kelch, H.; Krummenacher, I.; Kupfer, T.; Radacki, K. Chem. Eur. J. 2012, 18, 8430. (g) Iida, A.; Sekioka, A.; Yamaguchi, S. Chem. Sci. 2012, 3, 1461. (2) (a) Yamaguchi, S.; Shirasaka, T.; Akiyama, S.; Tamao, K. J. Am. Chem. Soc. 2002, 124, 8816. (b) Kim, S.; Song, K. H.; Kang, S. O.; Ko, J. Chem. Commun. 2004, 68. (c) Yamaguchi, S.; Wakamiya, A. Pure Appl. Chem. 2006, 7, 1413. (d) Wakamiya, A.; Mishima, K.; Ekawa, K.; Yamaguchi, S. Chem. Commun. 2008, 579. (e) Iida, A.; Yamaguchi, S. J. Am. Chem. Soc. 2011, 133, 6952. (f) Araki, T.; Fukazawa, A.; Yamaguchi, S. Angew. Chem., Int. Ed. 2012, 51, 5484. (3) (a) Eisch, J. J.; Hota, N. K.; Kozima, S. J. Am. Chem. Soc. 1969, 91, 4575. (b) Herberich, G. E.; Buller, B.; Hessner, B.; Oschmann, W. J. Organomet. Chem. 1980, 195, 253. (c) Sperry, C. K.; Cotter, W. D.; Lee, R. A.; Lachicotte, R. J.; Bazan, G. C. J. Am. Chem. Soc. 1998, 120, 7791. (d) So, C. W.; Watanabe, W.; Wakamiya, A.; Yamaguchi, S. Organometallics 2008, 27, 3496. (e) Fukazawa, A.; Yamada, H.; Yamaguchi, S. Angew. Chem., Int. Ed. 2008, 47, 5582. (4) (a) Braunschweig, H.; Chiu, C. W.; Radacki, K.; Brenner, P. Chem. Commun. 2010, 46, 916. (b) Brauschweig, H.; Damme, A.; Jimenez-Halla, J. O. C.; Hörl, C.; Krummenacher, I.; Kupfer, T.; Mailänder, L.; Radacki, K. J. Am. Chem. Soc. 2012, 134, 20169. (c) Braunschweig, H.; Chiu, C. W.; Gamon, D.; Kaupp, M.; Krummenacher, I.; Kupfer, T.; Müller, R.; Radacki, K. Chem. Eur. J. 2012, 18, 11732. (d) Braunschweig, H.; Dyakonov, V.; Jimenez-Halla, J. O. C.; Kraft, K.; Krummenacher, I.; Radacki, K.; Sperlich, A.; Wahler, J. Angew. Chem., Int. Ed. 2012, 51, 2977. (5) (a) Chase, P. A.; Piers, W. E.; Patrick, B. O. J. Am. Chem. Soc. 2000, 122, 12911. (b) Fan, C.; Piers, W. E.; Parvez, M. Angew. Chem., Int. Ed. 2009, 48, 2955. (c) Houghton, A. Y.; Karttunen, V. A.; Piers, W. E.; Tuononen, H. M. Chem. Commun. 2014, 50, 1295. (6) Ge, F.; Kehr, G.; Daniliuc, C. G.; Erker, G. J. Am. Chem. Soc. 2014, 136, 68. (7) (a) Wrackmeyer, B.; Kehr, G.; Süß, J.; Molla, E. J. Organomet. Chem. 1998, 562, 207. (b) Wrackmeyer, B.; Tok, O. L.; Klimkina, E. V.; Milius, W. Eur. J. Inorg. Chem. 2010, 2276. See also the following

234


Organometallics

Article

C.; Bussmann, K.; Daniliuc, C. G.; Kehr, G.; Erker, G. Chem. Sci. 2015, 6, 816.

reviews: (c) Wrackmeyer, B. Coord. Chem. Rev. 1995, 145, 125. (d) Wrackmeyer, B. Heteroat. Chem. 2006, 17, 188. (8) (a) Dierker, G.; Ugolotti, J.; Kehr, G.; Fröhlich, R.; Erker, G. Adv. Synth. Catal. 2009, 351, 1080. (b) Chen, C.; Eweiner, F.; Wibbeling, B.; Fröhlich, R.; Senda, S.; Ohki, Y.; Tatsumi, K.; Grimme, S.; Kehr, G.; Erker, G. Chem. Asian J. 2010, 5, 2199. (c) Möbus, J.; Bonnin, Q.; Ueda, K.; Fröhlich, R.; Itami, K.; Kehr, G.; Erker, G. Angew. Chem., Int. Ed. 2012, 51, 1954. (d) Liedtke, R.; Harhausen, M.; Fröhlich, R.; Kehr, G.; Erker, G. Org. Lett. 2012, 14, 1448. (e) Liedtke, R.; Kehr, G.; Fröhlich, R.; Daniliuc, C. G.; Wibbeling, B.; Petersen, J. L.; Erker, G. Helv. Chim. Acta 2012, 95, 2515. See also: (f) Kehr, G.; Erker, G. Chem. Commun. 2012, 48, 1839. (9) Alder, K.; Rickert, H. F. Justus Liebigs Ann. Chem. 1936, 524, 180. (10) (a) Eller, C.; Daniliuc, C. G.; Fröhlich, R.; Kehr, G.; Erker, G. Organometallics 2013, 32, 384. (b) Eller, C.; Bussmann, K.; Kehr, G.; Wibbeling, B.; Fröhlich, R.; Daniliuc, C. G.; Erker, G. Chem. Commun. 2014, 50, 1980. (11) Fagan, P. J.; Burns, E. G.; Calabrese, J. C. J. Am. Chem. Soc. 1988, 110, 2979. (12) See also for other borole [4 + 2] cycloaddition reactions e.g.: (a) Grisdale, P. J.; Williams, J. L. R. J. Organomet. Chem. 1970, 22, C19. (b) Eisch, J. J.; Galle, J. E.; Shafii, B.; Rheingold, A. L. Organometallics 1990, 9, 2342. (c) Fan, C.; Piers, W. E.; Parvez, M.; McDonald, R. Organometallics 2010, 29, 5132. (d) Braunschweig, H.; Maier, J.; Radacki, K.; Wahler, J. Organometallics 2013, 32, 6353. (13) (a) Sauer, J.; Sustmann, R. Angew. Chem., Int. Ed. 1980, 19, 779. (b) Gleiter, R.; Böhm, M. C. Pure Appl. Chem. 1983, 55, 237. (14) (a) Chen, C.; Kehr, G.; Fröhlich, R.; Erker, G. J. Am. Chem. Soc. 2010, 132, 13594. (b) Chen, C.; Voss, T.; Fröhlich, R.; Kehr, G.; Erker, G. Org. Lett. 2011, 13, 62. (15) (a) Ansorg, K.; Braunschweig, H.; Chiu, C.-W.; Engels, B.; Gamon, D.; Hügel, M.; Kupfer, T.; Radacki, K. Angew. Chem., Int. Ed. 2011, 50, 2833. (b) Braunschweig, H.; Chiu, C.-W.; Gamon, D.; Gruß, K.; Hörl, C.; Kupfer, T.; Radacki, K.; Wahler, J. Eur. J. Inorg. Chem. 2013, 9, 1525. (16) Braunschweig, H.; Kupfer, T. Chem. Commun. 2008, 4487. (17) Piers, W. E.; Bourke, S. C.; Conroy, K. D. Angew. Chem., Int. Ed. 2005, 44, 5016. (18) (a) Agrifoglio, G. Inorg. Chim. Acta 1992, 197, 159. (b) Vedejs, E.; Nguyen, T.; Powell, D. R.; Schrimpf, M. R. Chem. Commun. 1996, 2721. (c) Hodgkins, T. G.; Powell, D. R. Inorg. Chem. 1996, 35, 2140. (d) De Biani, F. F.; Gmeinwieser, T.; Herdtweck, E.; Jäkle, F.; Laschi, F.; Wagner, M.; Zanello, P. Organometallics 1997, 16, 4776. (e) Herdtweck, E.; Jäkle, F.; Wagner, M. Organometallics 1997, 16, 4737. (f) Braunschweig, H.; Kupfer, T. Chem. Commun. 2008, 4487. (19) Fukazawa, A.; Dutton, J. L.; Fan, C.; Mercier, L. G.; Houghton, A. Y.; Wu, Q.; Piers, W. E.; Parvez, M. Chem. Sci. 2012, 3, 1814. (20) For borane carbonyl chemistry see: (a) Burg, A. B.; Schlesinger, H. I. J. Am. Chem. Soc. 1937, 59, 780. (b) Brown, H. C. Acc. Chem. Res. 1969, 2, 65. (c) Sajid, M.; Elmer, L.-M.; Rosorius, C.; Daniliuc, C. G.; Grimme, S.; Kehr, G.; Erker, G. Angew. Chem., Int. Ed. 2013, 52, 2243. (d) Sajid, M.; Kehr, G.; Daniliuc, C. G.; Erker, G. Angew. Chem., Int. Ed. 2014, 53, 1118. (21) (a) Firl, J.; Runge, W. Angew. Chem., Int. Ed. 1973, 12, 668. (b) Taskinen, E.; Pentikänen, M.-L. Tetrahedron 1978, 34, 2365. (c) Runge, W. Org. Magn. Reson. 1980, 14, 25. (d) Ponomarev, S. V.; Nikolaeva, S. N.; Molchanova, G. N.; Kostyuk, A. S.; Grishin, Yu. K. J. Gen. Chem. USSR 1984, 54, 1620. (e) Nikolaeva, S. N.; Zolotareva, A. S.; Ponomarev, S. V.; Petrosyan, V. S. Russ. Chem. Bull. 1994, 43, 857. (f) Ponomarev, S. V.; Zolotareva, A. S.; Ezhov, R. N.; Kuznetsov, Yu. V.; Petrosyan, V. S. Russ. Chem. Bull. 2001, 50, 1093. (22) (a) Pilz, M.; Allwohn, J.; Hunold, R.; Massa, W.; Berndt, A. Angew. Chem., Int. Ed. Engl. 1988, 27, 1370. (b) Pilz, M.; Allwohn, J.; Willershausen, P.; Massa, W.; Berndt, A. Angew. Chem., Int. Ed. Engl. 1990, 29, 1030. (c) Power, P. P. Chem. Rev. 1999, 99, 3463. (d) Yu, J.; Kehr, G.; Daniliuc, C. G.; Erker, G. Eur. J. Inorg. Chem. 2013, 3312. (e) Möbus, J.; Kehr, G.; Daniliuc, C. G.; Fröhlich, R.; Erker, G. Dalton Trans. 2014, 43, 632. (f) Moquist, P.; Chen, G. Q.; Mück-Lichtenfeld, 235


Reactions of Boroles Formed by 1,1-Carboboration - Organometallics

Recommend Documents