Synthesis of Donor–Acceptor-Type Benzo [b] phosphole and Naphtho

May 3, 2017 - Naohiko Yoshikai,* Mithun Santra, and Bin Wu. Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Scienc...
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Synthesis of Donor−Acceptor-Type Benzo[b]phosphole and Naphtho[2,3‑b]phosphole Oxides and Their Solvatochromic Properties Naohiko Yoshikai,* Mithun Santra, and Bin Wu Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore S Supporting Information *

ABSTRACT: A series of donor−acceptor-type benzo[b]phosphole and naphtho[2,3-b]phosphole oxides have been synthesized through metal-catalyzed reactions as key steps: that is, (1) cobalt- and copper-catalyzed multicomponent coupling of an arylzinc reagent, an alkyne, and dichlorophenylphosphine to assemble the electrondeficient benzophosphole or naphthophosphole oxide core and (2) palladium-catalyzed cross-coupling to introduce an electrondonating substituent to the “benzo” or “naphtho” moiety. These donor−acceptor molecules are strongly fluorescent, showing weak to strong solvatochromism depending on the electron-donating substituent.

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INTRODUCTION

approaches, however, have a few crucial drawbacks. The intramolecular cyclization requires multistep preparation of the cyclization precursors, which make variation of the substituent on the “benzo” moiety particularly cumbersome. On the other hand, the intermolecular annulation suffers formation of a mixture of regioisomers from a substituted arylphosphine oxide, which is inevitable due to the mechanism involving radical processes.6 As such, this approach also has difficulty with regiocontrolled preparation of benzophospholes substituted on the benzo moiety. Recently, we developed a method for the synthesis of benzophospholes from arylzinc reagents, alkynes, and chlorophosphines, capitalizing on the cobalt-catalyzed migratory arylzincation reaction of alkynes (Scheme 1c).8a,13 Due to the modular and regioselective nature, this multicomponent method allows expedient preparation of functionalized benzophospholes, those bearing different substituents on the “benzo” moiety in particular. Many of the above and other synthetic studies have highlighted the strong fluorescence of benzophosphole derivatives, especially benzophosphole oxides.4,5,7−9 Focusing on the strongly fluorescent and electron-accepting nature of the benzophosphole oxide skeleton, Yamaguchi and co-workers recently developed a 2,3-diarylbenzophosphole oxide bearing an electron-donating diphenylamino group at the 2-position as a solvatochromic fluorescent dye and demonstrated its utility as an environment-sensitive biological probe (Figure 1a).4b This probe exhibits high fluorescence quantum yields in various solvents of different polarity, large Stokes shifts, and significant

Benzo[b]phosphole (benzophosphole), the phosphorus congener of indole, has recently gained significant attention as a structural element for novel π-conjugated materials with lightemitting and electron-transporting properties, along with the development of new methods for their synthesis.1−11 The majority of reported syntheses of this class of compounds employ either of two common approaches.12 One is the intramolecular cyclization of an alkynylarene bearing a phosphorus substituent on the ortho position (Scheme 1a).2−5 The other is the intermolecular dehydrogenative annulation of a secondary arylphosphine oxide and an internal alkyne under oxidative conditions (Scheme 1b).6 These Scheme 1. Synthetic Approaches to Benzo[b]phospholes

Special Issue: Tailoring the Optoelectronic Properties of Organometallic Compounds with Main Group Elements Received: April 5, 2017

© XXXX American Chemical Society

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DOI: 10.1021/acs.organomet.7b00244 Organometallics XXXX, XXX, XXX−XXX

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RESULTS AND DISCUSSION Synthesis of Donor-Substituted Benzo[b]phosphole and Naphtho[2,3-b]phosphole Oxides. We decided to synthesize benzophosphole and naphthophosphole oxides bearing 2,3-dialkyl groups in order to focus on the effect of conjugation between the benzophosphole (naphthophosphole) core and an electron-donating group at the 6-position while eliminating any other π conjugation. The present synthesis started with a multicomponent assembly of 2,3-dibutyl-6trimethylsilylbenzophosphole oxide 2a (Scheme 2). Thus, Scheme 2. Synthesis of Benzophosphole Oxide Precursors

Figure 1. Donor−acceptor-type benzophosphole oxides exhibiting solvatochromic fluorescence: (a) reported examples; (b) present design. Definitions: λabs, longest wavelength absorption maxima; λem, emission maxima; ΦF, fluorescence quantum yield.

changes in the emission color depending on the solvent polarity, which represent common attributes of existing environment-sensitive fluorescent probes such as Prodan, Dapoxyl, and Nile Red.14 The benzophosphole probe also features near-constant absorption around 405 nm and excellent photostability. The Yamaguchi group further studied the solvatochromic fluorescence of 2,3-diarylbenzophosphole oxides bearing an electron-donating group on the 3-position,4c while Matano and co-workers also independently reported on the solvatochromic properties of 2-arylbenzophosphole and 2arylnaphtho[2,3-b]phosphole oxides bearing a diphenylamino group.7c Inspired by the aforementioned studies on donor−acceptortype benzophosphole oxides, we wondered if it is possible to develop new benzophosphole-based solvatochromic fluorophores by the introduction of electron-donating groups to the “benzo” moiety rather than the 2- or 3-position of the benzophosphole core (Figure 1b). The multicomponent benzophosphole synthesis developed by our group (Scheme 1c)8a appeared ideally suited to pursue this idea because of its flexibility with respect to the arylzinc reagent as well as its predictable regioselectivity. Herein we report on the synthesis of a series of benzo[b]phosphole oxides bearing an amino group, with or without a π spacer (i.e., phenylene, phenylenevinylene, phenyleneethynylene), at the 6-position. We also synthesized analogous naphtho[2,3-b]phosphole oxides. These donor−acceptor-type benzophosphole and naphthophosphole oxides were found to exhibit highly environment sensitive fluorescent properties in response to the solvent polarity, particularly when the amino group and the phosphole core were separated by a π spacer.

cobalt−Xantphos-catalyzed zinc insertion into (4trimethylsilyl)bromobenzene (1a)15 was followed by the addition of the resulting arylzinc reagent to 5-decyne, coppercatalyzed condensation with dichlorophenylphosphine, and oxidation with hydrogen peroxide to furnish the desired product 2a in a respectable yield of 65%. Iododesilylation of 2a with ICl took place cleanly to afford 6-iodobenzophosphole oxide 3a, which served as a key intermediate for the divergent synthesis of donor-substituted benzophosphole oxides. The analogous naphthophosphole derivative 3b was also synthesized in the same manner starting from 2-bromo-6trimethylsilylnaphthalene (1b), in a moderate overall yield. With the key intermediates 3a,b in hand, we performed their transformations into donor-substituted benzophosphole and naphthophosphole oxides via Pd-catalyzed cross-coupling (Scheme 3). Buchwald−Hartwig coupling of 3a with diethylamine using a Pd−Xantphos catalyst afforded the corresponding 6-amino-substituted benzophosphole oxide 4a in a high yield. While the diphenylamino- and carbozolyl-substituted derivatives 5a and 6a were synthesized by different methods in our previous work,8a the Buchwald−Hartwig coupling could be used to synthesize all of the amino-substituted naphthophosphole analogues 4b−6b. Suzuki−Miyaura coupling using (4dimethylamino)phenylboronic acid in the presence of Pd(PPh3)4 allowed preparation of the aminoaryl-substituted benzophosphole oxide 7a and naphthophosphole oxide 7b. A P d ( P- t- B u 3 ) 2 -c a t a l y z e d H e c k r e ac t i o n u s i n g (4 dimethylamino)styrene furnished the aminoarylethenyl-substituted derivatives 8a,b. Finally, Sonogashira couplings were B

DOI: 10.1021/acs.organomet.7b00244 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 3. Transformation of 3a,b into Donor-Substituted Benzophosphole and Naphthophosphole Oxides

Table 1. UV/Vis Absorption and Fluorescence of Compounds 4a−10a and 4b−10b in CH2Cl2 compd

λabs/nma

ε/104 M−1 cm−1

λemb/nm

ΦFc

Δν/cm−1d

4a 5a 6a 7a 8a 9a 10a 4b 5b 6b 7b 8b 9b 10b

396 394 341 375 396 388 382 364 366 341 355 378 380 381

0.47 0.75 0.84 1.37 1.48 2.68 4.06 1.80 2.26 2.40 2.74 2.44 3.31 4.41

489 484 447 504 529 522 537 473 471 430 494 513 498 511

0.41 0.63 0.94 0.67 0.49 0.60 0.40 0.04 0.08 0.14 0.39 0.33 0.70 0.64

4802 4720 6954 6825 6349 6616 7556 6331 6091 6070 7926 6962 6235 6677

a Longest wavelength absorption maxima. bExcited at λabs. cFluorescence quantum yields determined using quinine sulfate as standard (54% in 0.1 M H2SO4). dStokes shift (1/λabs − 1/λem).

a

Prepared directly from (4-diphenylamino)phenylzinc reagent and 5decyne (ref 8a). bPrepared by Cu-catalyzed Ullmann coupling between 3a and carbazole (ref 8a).

performed to synthesize the aryleneethynylene-tethered derivatives 9a,b and their elongated analogues 10a,b in good yields. Absorption and Fluorescence of Benzo[b]phosphole and Naphtho[2,3-b]phosphole Oxides in CH2Cl2. With the donor−acceptor-type benzophosphole oxides 4a−10a and naphthophosphole oxides 4b−10b in hand, we initially evaluated their optical properties in CH2Cl2 solution. The absorption and emission properties of these compounds are summarized in Table 1, and the spectra of selected compounds are displayed in Figure 2. The longest wavelength absorption maxima (λabs) of the benzophosphole derivatives 4a−10a fell in a relatively narrow range of 375−396 nm, except for the distinctly shorter λabs of the carbazole-substituted derivative 6a. Not unexpectedly, the molar extinction coefficients (ε) were larger for the compounds with π spacers (7a−10a) than for those without π spacers (4a−6a). The compounds 4a−10a showed strong fluorescence with the emission maxima (λem) ranging from 445 to 537 nm and moderate to high quantum

Figure 2. UV/vis absorption (solid lines) and fluorescence spectra (dashed lines; excited at the absorption maxima) of selected (a) benzo[b]phosphole oxides and (b) naphtho[2,3-b]phosphole oxides.

yields (0.40−0.94). While there was no clear dependence of λabs on the presence of the π spacer, the compounds with π spacers (7a−10a) showed apparently longer λem. In general, the absorption and emission spectra had a relatively small overlap with moderate to large Stokes shifts (4720−7556 cm−1). The spectral data of the naphthophosphole derivatives 4b− 10b also featured large Stokes shifts (6070−7926 cm−1) and longer emission maxima with the presence of a π spacer. In comparison with 4a−10a, 4b−10b exhibited somewhat shorter C

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Organometallics absorption and emission maxima and distinctly larger molar extinction coefficients, which were also observed for the benzophosphole/naphthophosphole series of compounds studied by Matano and co-workers.7c Note also that some of them, i.e., 4b−6b, showed substantially lower quantum yields in comparison with their benzophosphole counterparts, while the rest showed moderate to high quantum yields. Solvatochromic Properties of Benzo[b]phosphole and Naphtho[2,3-b]phosphole Oxides. We next examined the effect of solvent polarity on the optical properties of the benzophosphole and naphthophosphole derivatives. Table 2

Table 3. Fluorescence Properties of Compounds 5a, 7a, 9b, and 10b

Table 2. UV/Vis Absorption and Fluorescence of Compounds 4a−10a and 4b−10b in Cyclohexane (λabs1/ λem1) and DMSO (λabs2/λem2)

a Excited at longest wavelength absorption maxima. bFluorescence quantum yields determined using quinine sulfate as standard (54% in 0.1 M H2SO4).

compd

λabs1/nma

λem1/nmb

λabs2/nmc

λem2/nmd

νem1 − νem2/cm−1 e

4a 5a 6a 7a 8a 9a 10a 4b 5b 6b 7b 8b 9b 10b

388 390 339 368 390 382 375 359 364 341 352 379 370 372

479 465 429 483 503 486 462 458 453 420 460 478 459 451

399 394 341 380 403 393 387 367 365 342 362 390 384 386

498 494 456 554 584 580 539 490 480 437 548 569 556 591

753 1079 1006 2870 2757 3506 2724 1005 1001 757 3257 3129 3848 4724

λem/nma

ΦFb

solvent

5a

7a

9b

10b

5a

7a

9b

10b

c-C6H12 toluene dioxane CH2Cl2 EtOH MeCN DMSO

465 469 475 484 505 496 494

483 478 493 504 549 537 554

459 458 469 498 548 546 556

451 462 475 511 545 577 591

0.64 0.73 0.62 0.58 0.44 0.58 0.45

0.69 0.72 0.67 0.60 0.33 0.38 0.32

0.74 0.79 0.70 0.67 0.18 0.16 0.15

0.58 0.91 0.64 0.69 0.02 0.01 0.03

a

Longest wavelength absorption maxima in cyclohexane. bExcited at λabs1. cLongest wavelength absorption maxima in DMSO. dExcited at λabs2. eShift of emission maxima (1/λem1 − 1/λem2).

summarizes the absorption and fluorescence maxima of 4a−10a and 4b−10b in nonpolar cyclohexane solution and in polar DMSO solution. For all of the compounds, the absorption maxima increased only to a small extent (less than 15 nm) by a change in the solvent from cyclohexane to DMSO. On the other hand, the emission maxima showed more characteristic responses to the solvent polarity. For the compounds without π spacers (4a−6a and 4b−6b), the bathochromic shift by the solvent change was moderate (ca. 20−30 nm). In contrast, the compounds with π spacers (7a−10a and 7b−10b) underwent a much more drastic bathochromic shift (>70 nm). In fact, the shifts in the emission maxima (νem1 − νem2) of these compounds (ca. 3000 cm−1 or larger) were of magnitude comparable to that of typical environment-sensitive fluorophores (e.g., νhexane − νDMSO = 4062 cm−1 for Prodan).14,16 Table 3 summarizes fluorescence properties of selected compounds, that is, weakly solvatochromic 5a, moderately solvatochromic 7a, and strongly solvatochromic 9b and 10b, in different solvents. Figure 3 shows the absorption (in toluene) and fluorescence spectra of 5a, 7a, and 9b. The strong solvatochromism of 9b is also illustrated by the pictures of its fluorescence in toluene (blue) and EtOH (yellowish) (Figure 3c). The weakly solvatochromic 5a maintained moderate quantum yields even in polar (ΦF = 0.45 in DMSO) and protic (ΦF = 0.44 in EtOH) solvents, as was the case with the moderately solvatochromic 7a (ΦF = 0.32 in DMSO, 0.33 in EtOH). The quantum yield in these solvents decreased substantially for the highly solvatochromic 9b (ΦF = 0.15 in

Figure 3. Absorption (solid lines) and fluorescence (dashed lines) spectra of (a) 5a, (b) 7a, and (c) 9b in various solvents. On the upper right of spectrum (c) are shown fluorescence images of 9b under a UV lamp (365 nm).

DMSO, 0.18 in EtOH). Furthermore, compound 10b featuring a bis(phenyleneethynylene) spacer showed distinctly low D

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Organometallics quantum yields in polar and protic solvents (ΦF ≤ 0.03). These observations appear reasonable, assuming larger degrees of charge separation of 9b and 10b in their excited states, which would facilitate nonradiative decay processes. The Lippert−Mataga plots17 for compounds 5a, 7a, and 9b in different solvents including EtOH showed moderate to good linearity (Figure 4), as was also observed for the Yamaguchi

electron-donating triarylamine moiety and the electron-withdrawing benzophosphole moiety, respectively (Figure 5a). However, because the benzophosphole ring is a part of the triarylamine moiety, both the HOMO and LUMO share substantial orbital coefficients on the benzophosphole moiety. In contrast, the placement of a π spacer between the benzo- or naphthophosphole moiety and the amino group causes more apparent HOMO/LUMO separation, as can be seen for 7a and 9b′ (Figure 5b,c). Thus, for 9b′, the HOMO and LUMO are mostly localized on the dimethylaminophenylethynyl moiety and the naphthophosphole ring, respectively. These MO profiles would imply a greater degree of intramolecular charge transfer character of the HOMO−LUMO transition of 7a and 9b in comparison to 5a and are consistent with the large change in the dipole moment of 9b from the ground state to the excited state.

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CONCLUSION In summary, we have synthesized a series of donor−acceptortype benzo[b]phosphole and naphtho[2,3-b]phosphole oxides as fluorophores that feature the connection of an electrondonating amino group, with or without a π spacer, to the “benzo” or “naphtho” moiety of the electron-withdrawing phosphacycle. For both the benzophosphole and naphthophosphole series, the compounds without a π spacer showed relatively weak solvatochromism, while those with a phenylene, phenyleneethylene, or phenyleneethynylene spacer displayed moderate to large solvatochromism. At the same time, the installation of a longer π spacer was found to cause an apparent drop in the quantum yield of these fluorophores in polar and protic solvents. It is important to note that the synthetic method used in this study not only allows installation of different substituents at the benzo and naphtho moieties but also offers an opportunity to modify the substituents on the 2-, 3-, and even 1 (phosphorus)-positions. As such, the present study could serve as a basis for the further design and development of benzophosphole- and naphthophosphole-based fluorophores and their use for imaging and sensing applications.

Figure 4. Lippert−Mataga plots for compounds 5a, 7a, and 9b. Definitions: Δν (Stokes shift) = νabs − νem; Δf (orientation polarizability) = (ε − 1)/(2ε + 1) − (n2 − 1)/(2n2 + 1) (ε = dielectric constant, n = refractive index).

donor−acceptor benzophosphole (Figure 1a).4b Thus, this linearity would suggest that hydrogen bonding in protic solvents does not play a significant role in the fluorescence properties of the present donor-substituted benzophosphole and naphthophosphole oxides. The distinctly different slopes (Δν/Δf) observed for these compounds support that 9b undergoes the largest change in the dipole moment from the ground state to the excited state. To gain additional insight into the electronic nature of the present benzophosphole and naphthophosphole oxides, we performed density functional theory (DFT) calculations for 5a, 7a, and the N,N-dimethylamino analogue of 9b (9b′) at the B3LYP/6-31G(d) level. Figure 5 displays the Kohn−Sham frontier orbitals of the optimized structures of these compounds. The HOMO and LUMO of 5a reside on the

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EXPERIMENTAL SECTION

General Information. All air- or moisture-sensitive reactions were performed by standard Schlenk techniques in oven-dried reaction vessels under a nitrogen atmosphere. 1H NMR (400 MHz) and 13C NMR (100 or 75 MHz) chemical shifts are reported in ppm with reference to tetramethylsilane (0 ppm) and CHCl3 (77.0 ppm), respectively. 31P NMR (162 MHz) chemical shifts are externally referenced to 85% H3PO4. Melting points were determined using a capillary melting point apparatus and are uncorrected. All of the UV/ vis absorption and fluorescence spectra were measured using sample solutions at a concentration of 30 μM. For 5a and 6a, the UV/vis measurements in the previous report8a were performed with 100 μM samples, and we noted some deviation in the molar extinction coefficient. The purity of the newly synthesized compounds was established by 1H, 13C, and 31P NMR spectra, while compounds 7a, 8a,b, and 9b were accompanied by persistent aromatic impurities as indicated by their 1H NMR spectra (see the Supporting Information). The synthesis of benzophosphole derivatives 2a, 3a, 5a, and 6a were reported previously.8a 2,3-Dibutyl-1-phenyl-7-(trimethylsilyl)benzo[f ]phosphindole 1-Oxide (2b). Anhydrous LiCl (42.4 mg, 1.0 mmol) was placed in a 10 mL Schlenk tube equipped with a stirrer bar, dried under vacuum (1 mbar) at 150 °C for 20 min, and cooled to room temperature under N2. To the Schlenk tube was added zinc powder (98 mg, 1.5 mmol). The resulting heterogeneous mixture was dried again under vacuum (1 mbar) at 150 °C for 15 min and cooled to

Figure 5. Kohn−Sham frontier orbitals of (a) 5a, (b) 7a, and (c) 9b′ (N,N-dimethylamino analogue of 9b) at the B3LYP/6-31G(d) level. E

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Organometallics

diluted with ethyl acetate (5 mL) and filtered through a pad of silica gel. The filtrate was washed with water, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (eluent hexane/EtOAc (2/1)) to afford the desired coupling product (4a,b, 5b, or 6b). 2,3-Dibutyl-6-(diethylamino)-1-phenylphosphindole 1-oxide (4a): yellow solid (90%); mp 110−112 °C; 1H NMR (400 MHz, CDCl3) δ 7.68−7.63 (m, 2H), 7.47−7.43 (m, 1H), 7.39−7.35 (m, 2H), 7.16 (dd, J = 8.4, 3.6 Hz, 1H), 6.90 (dd, J = 11.6, 2.4 Hz, 1H), 6.64 (dd, J = 8.4, 1.6 Hz, 1H), 3.30 (q, J = 7.2 Hz, 4H), 2.52 (t, J = 7.6 Hz, 2H), 2.48−2.36 (m, 1H), 2.27−2.14 (m, 1H), 1.60−1.53 (m, 2H), 1.49−1.39 (m, 2H), 1.37−1.16 (m, 4H), 1.08 (t, J = 7.2 Hz, 6H), 0.96 (t, J = 7.2 Hz, 3H), 0.76 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.1 (d, JPC = 21 Hz), 148.0 (d, JPC = 12 Hz), 134.1 (d, JPC = 104 Hz), 131.8 (d, JPC = 95 Hz), 131.4, 131.0 (d, JPC = 13 Hz), 130.6, 129.9 (d, JPC = 98 Hz), 128.5 (d, JPC = 12 Hz), 122.3 (d, JPC = 13 Hz), 113.7 (d, JPC = 1.4 Hz), 112.4 (d, JPC = 11 Hz), 44.4, 31.5 (d, JPC = 2 Hz), 30.8 (d, JPC = 2 Hz), 26.4 (d, JPC = 13 Hz), 25.6 (d, JPC = 11 Hz), 23.1, 22.8, 13.9, 13.7, 12.5; 31P{1H} NMR (162 MHz, CDCl3) δ 40.6; HRMS (ESI) calcd for C26H37NOP [M + H]+ 410.2613, found 410.2610. 2,3-Dibutyl-7-(diethylamino)-1-phenylbenzo[f ]phosphindole 1oxide (4b): yellow solid (72%); mp 112−114 °C; 1H NMR (400 MHz, CDCl3) δ 7.79 (d, J = 11.5 Hz, 1H), 7.70−7.65 (m, 3H), 7.52− 7.51 (m, 1H), 7.47−7.43 (m, 1H), 7.38−7.34 (m, 2H), 7.08 (dd, J = 9.1, 2.5 Hz, 1H), 6.78 (d, J = 2.3 Hz, 1H), 3.41 (q, J = 7.5 Hz, 4H), 2.66 (t, J = 7.7 Hz, 2H), 2.57−2.45 (m, 1H), 2.34−2.23 (m, 1H), 1.67−1.60 (m, 2H), 1.55−1.46 (m, 2H), 1.44−1.31 (m, 2H), 1.30− 1.23 (m, 2H), 1.18 (t, J = 7.0 Hz, 6H), 1.00 (t, J = 7.2 Hz, 3H), 0.78 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 152.0 (d, JPC = 19 Hz), 146.5, 135.3 (d, JPC = 29 Hz), 134.9 (d, JPC = 12 Hz), 132.9 (d, JPC = 96 Hz), 131.9 (JPC = 97 Hz), 131.54 (d, JPC = 3 Hz), 131.1 (d, JPC = 11 Hz), 130.9 (d, JPC = 105 Hz) 129.5, 128.6, 128.5 (d, JPC = 12 Hz), 127.2, 119.8 (d, JPC = 11 Hz), 116.9, 106.9, 44.5, 31.3, 31.0, 26.5 (d, JPC = 13 Hz), 26.0 (d, JPC = 10 Hz), 23.2, 22.9, 14.0, 13.7, 12.6; 31P{1H} NMR (162 MHz, CDCl3) δ 38.6; HRMS (ESI) calcd for C30H39NOP [M + H]+ 460.2769, found 460.2765. 2,3-Dibutyl-7-(diphenylamino)-1-phenylbenzo[f ]phosphindole 1-oxide (5b): yellow solid (92% yield); mp 165−167 °C; 1H NMR (400 MHz, CDCl3) δ 7.76−7.67 (m, 4H), 7.63 (d, J = 2.7 Hz, 1H), 7.50−7.47 (m, 1H), 7.42−7.37 (m, 2H), 7.36−7.31 (m, 2H), 7.29− 7.25 (m, 4H), 7.13−7.0 (m, 6H), 2.73 (t, J = 7.7 Hz, 2H), 2.62−2.51 (m, 1H), 2.39−2.28 (m, 1H), 1.71−1.65 (m, 2H), 1.60−1.51 (m, 2H), 1.48−1.37 (m, 2H), 1.35−1.24 (m, 2H), 1.04 (t, J = 7.2 Hz, 3H), 0.82 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.7 (d, JPC = 18 Hz), 147.3, 146.5, 138.1 (d, JPC = 30 Hz), 134.8 (d, JPC = 96 Hz), 134.0 (d, JPC = 11 Hz), 131.7, 131.4, 131.26 (JPC = 102 Hz), 131.21 (JPC = 105 Hz), 131.1 (d, JPC = 11 Hz), 129.4, 129.3, 129.2 (d, JPC = 10 Hz), 128.6 (d, JPC = 12 Hz), 125.4, 124.8, 123.5, 120.3, 119.8 (d, JPC = 10 Hz), 31.2, 30.9, 26.5 (d, JPC = 13 Hz), 26.1 (d, JPC = 10 Hz), 23.2, 22.9, 14.0, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 38.2; HRMS (ESI) calcd for C38H39NOP [M + H]+ 556.2769, found 556.2768. 2,3-Dibutyl-7-(9H-carbazol-9-yl)-1-phenylbenzo[f ]phosphindole 1-oxide (6b): off-white solid (86%); mp 220−222 °C; 1H NMR (400 MHz, CDCl3) δ 8.13 (d, J = 7.7 Hz, 2H), 8.04−8.02 (m, 2H), 7.96 (d, J = 1.7 Hz, 1H), 7.81 (d, J = 2.7 Hz, 1H), 7.75−7.70 (m, 3H), 7.52− 7.48 (m, 1H), 7.44−7.35 (m, 6H), 7.29−7.25 (m, 2H), 2.77 (t, J = 7.7 Hz, 2H), 2.65−2.53 (m, 1H), 2.42−2.30 (m, 1H), 1.74−1.67 (m, 2H), 1.61−1.54 (m, 2H), 1.49−1.39 (m, 2H), 1.34−1.23 (m, 2H), 1.05 (t, J = 7.2 Hz, 3H), 0.81 (t, J = 7.3 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.4 (d, JPC = 18 Hz), 140.8, 140.3 (d, JPC = 30 Hz), 136.7 (d, JPC = 96 Hz), 136.1, 134.5 (JPC = 1 Hz), 133.6 (d, JPC = 12 Hz), 132.1 (d, JPC = 104 Hz), 132.1 (d, JPC = 2 Hz), 131.2 (d, JPC = 11 Hz), 130.7 (JPC = 96 Hz), 130.4, 129.9 (d, JPC = 10 Hz), 128.8 (d, JPC = 12 Hz), 127.4, 126.3, 126.1, 123.6, 120.4 (d, JPC = 13 Hz), 120.0 (d, JPC = 10 Hz), 109.7, 31.1, 30.9, 26.6 (d, JPC = 13 Hz), 26.3 (d, JPC = 10 Hz), 23.2, 23.0, 14.1, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 38.0; HRMS (ESI) calcd for C38H37NOP [M + H]+ 554.2613, found 554.2618.

room temperature under N2. The mixture was suspended with THF (1 mL), followed by the addition of 1,2-dibromoethane (5 μL, 0.05 mmol) and Me3SiCl (1.5 μL, 0.01 mmol). After the mixture was stirred for 5 min, Xantphos (28.9 mg, 0.05 mmol) and CoCl2 (6.5 mg, 0.05 mmol) were added. After additional stirring for 5 min, (6bromonaphthalen-2-yl)trimethylsilane (1b; 279 mg, 1.0 mmol) was added in one portion. The mixture was stirred at room temperature for 12 h. To the resulting arylzinc reagent was added 5-decyne (138 mg, 1.0 mmol). The resulting mixture was stirred at 60 °C for 8 h and then cooled to room temperature. To the mixture of the organozinc intermediate was added a THF solution of CuCN·2LiCl (0.30 mmol) and PhPCl2 (662 mg, 3.0 mmol) at 0 °C. The resulting mixture was stirred at 60 °C for 12 h and then cooled to room temperature. To this was added an aqueous solution of H2O2 (ca. 30%, a few drops) at 0 °C, and the resulting mixture was stirred at room temperature for 0.5 h. After completion of the oxidation, the reaction mixture was diluted with ethyl acetate (5 mL) and filtered through a pad of silica gel with additional ethyl acetate (15 mL) as the eluent. The filtrate was washed with brine (10 mL), dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (eluent hexane/EtOAc (2/1)) to afford the title compound as a pale yellow solid (240 mg, 52%): mp 142−146 °C; 1 H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 11.2 Hz, 1H), 7.91 (s, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.69−7.64 (m, 4H), 7.50−7.45 (m, 1H), 7.40−7.37 (m, 2H), 2.72 (t, J = 7.6 Hz, 2H), 2.61−2.54 (m, 1H), 2.37−2.27 (m, 1H), 1.68−1.62 (m, 2H), 1.55−1.50 (m, 2H), 1.46− 1.37 (m, 2H), 1.32−1.23 (m, 2H), 1.01 (t, J = 7.2 Hz, 3H), 0.79 (t, J = 7.2 Hz, 3H), 0.31 (s, 9H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.5 (d, JPC = 18.4 Hz), 139.9 (d, JPC = 29.5 Hz), 139.5, 136.2 (d, JPC = 96.2 Hz), 135.8, 134.8, 132.4, 132.3, 131.8 (d, JPC = 2.3 Hz), 131.1 (d, JPC = 99.2 Hz), 131.0 (d, JPC = 10.7 Hz), 130.4 (d, JPC = 9.0 Hz), 129.6 (d, JPC = 99.6 Hz), 128.6 (d, JPC = 12.1 Hz), 127.7, 120.0 (d, JPC = 10.6 Hz), 31.1 (d, JPC = 1.3 Hz), 30.9 (d, JPC = 1.0 Hz), 26.5 (d, JPC = 12.7 Hz), 26.2 (d, JPC = 10.2 Hz), 23.2, 23.0, 14.0, 13.7, −1.2; 31P{1H} NMR (162 MHz, CDCl3) δ 38.1; HRMS (ESI) calcd for C29H38OPSi [M + H]+ 461.2430, found 461.2436. 2,3-Dibutyl-7-iodo-1-phenylbenzo[f ]phosphindole 1-Oxide (3b). A Schlenk tube equipped with a stirrer bar was charged with 2b (189 mg, 0.41 mmol), K2CO3 (228 mg, 1.6 mmol), and dry CH2Cl2 (3 mL) under a nitrogen atmosphere. The resulting suspension was cooled to 0 °C, followed by the addition of ICl (270 mg, 1.6 mmol) in CH2Cl2 (1 mL) via syringe. The resulting mixture was stirred at 0 °C for 1 h and then poured into a solution of NaHSO3 (0.30 g) in water (5 mL). The mixture was stirred at room temperature for 1 h and then diluted with 5 mL of CH2Cl2. The organic phase was washed successively with saturated aqueous NaHCO3 and brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure. The residue was subjected to flash chromatography on silica gel (eluent hexane/EtOAc (2/1)) to afford the title compound as an off-white solid (188 mg, 89%): mp 125−127 °C; 1H NMR (400 MHz, CDCl3) δ 8.09 (d, J = 0.8 Hz, 1H), 7.86 (d, J = 10.8 Hz, 1H), 7.73 (dd, J = 8.8, 2.0 Hz, 1H), 7.67−7.62 (m, 3H), 7.55 (d, J = 8.4 Hz, 1H), 7.49−7.45 (m, 1H), 7.40−7.35 (m, 2H), 2.69 (t, J = 7.6 Hz, 2H), 2.60−2.48 (m, 1H), 2.37−2.25 (m, 1H), 1.68−1.59 (m, 2H), 1.55−1.50 (m, 2H), 1.44−1.32 (m, 2H), 1.31−1.20 (m, 2H), 0.99 (t, J = 7.2 Hz, 3H), 0.77 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.2 (d, JPC = 18.2 Hz), 140.2 (d, JPC = 29.4 Hz), 137.2 (d, JPC = 95.6 Hz), 136.9 (d, JPC = 95.4 Hz), 134.4 (d, JPC = 1.4 Hz), 134.3 (d, JPC = 11.8 Hz), 132.0 (d, JPC = 2.6 Hz), 131.9 (d, JPC = 104.0 Hz), 131.1, 131.0 (d, JPC = 10.6 Hz), 130.2, 130.0, 128.9 (d, JPC = 9.5 Hz), 128.7 (d, JPC = 12.1 Hz), 119.9 (d, JPC = 10.5 Hz), 92.2, 31.0 (d, JPC = 1.8 Hz), 30.8 (d, JPC = 1.7 Hz), 26.4 (d, JPC = 12.8 Hz), 26.2 (d, JPC = 10.4 Hz), 23.2, 22.9, 14.0, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 37.8; HRMS (ESI) calcd for C26H29IOP [M + H]+ 515.1001, found 515.1005. Buchwald−Hartwig Coupling. A mixture of benzophosphole oxide 3a or naphthophosphole oxide 3b (0.20 mmol), Pd2(dba)3 (4.6 mg, 5 μmol), Xantphos (5.8 mg, 10 μmol), and KO-t-Bu (45 mg, 0.40 mmol) in toluene (1 mL) was stirred at room temperature for 5 min. Secondary amine (0.40 mmol) was added, and the resulting mixture was stirred at 110 °C for 12 h. Upon cooling, the reaction mixture was F

DOI: 10.1021/acs.organomet.7b00244 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Suzuki−Miyaura Coupling. A mixture of benzophosphole oxide 3a or naphthophosphole oxide 3b (0.10 mmol), N,N-dimethyl-4(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline18 (40 mg, 0.16 mmol), Pd(PPh3)4 (12 mg, 10 μmol), and K2CO3 (30 mg, 0.20 mmol) in THF (2 mL) and water (1 mL) was stirred at 80 °C for 12 h. Upon cooling, the reaction mixture was diluted with ethyl acetate (5 mL). The organic phase was washed with water, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (eluent hexane/EtOAc (2/1)) to afford the desired coupling product (7a,b). 2,3-Dibutyl-6-(4-(dimethylamino)phenyl)-1-phenylphosphindole 1-oxide (7a): brown oil (81%); 1H NMR (400 MHz, CDCl3) δ 7.77− 7.74 (m, 1H), 7.70−7.64 (m, 3H), 7.45 (d, J = 8.8 Hz, 3H), 7.40−7.34 (m, 3H), 6.73 (d, J = 8.8 Hz, 2H), 2.95 (s, 6H), 2.61 (t, J = 7.5 Hz, 2H), 2.56−2.45 (m, 1H), 2.33−2.20 (m, 1H), 1.62−1.58 (m, 2H), 1.53−1.44 (m, 2H), 1.41−1.33 (m, 2H), 1.31−1.22 (m, 2H), 0.99 (t, J = 7.3 Hz, 3H), 0.78 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 150.5 (d, JPC = 20 Hz), 150.3, 141.23 (d, JPC = 10 Hz), 141.17 (d, JPC = 29 Hz), 133.8 (d, JPC = 96 Hz), 133.0 (JPC = 97 Hz), 131.8 (d, JPC = 2 Hz), 131.2, 131.0 (d, JPC = 11 Hz), 130.7 (d, JPC = 96 Hz), 129.8, 128.6 (d, JPC = 12 Hz), 127.5, 126.4 (d, JPC = 10 Hz), 121.7 (d, JPC = 12 Hz), 112.7, 40.4, 31.1, 30.7, 26.5 (d, JPC = 14 Hz), 25.9 (d, JPC = 11 Hz), 23.1, 22.9, 14.0, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 39.7; HRMS (ESI) calcd for C30H37NOP [M + H]+ 458.2613, found 458.2619. 2,3-Dibutyl-7-(4-(dimethylamino)phenyl)-1-phenylbenzo[f ]phosphindole 1-oxide (7b): brown solid (61%); mp 126−128 °C; 1H NMR (400 MHz, CDCl3) δ 8.01 (d, J = 11.2 Hz, 1H), 7.85−7.82 (m, 2H), 7.76−7.74 (m, 1H), 7.68−7.61 (m, 3H), 7.54 (d, J = 8.8 Hz, 2H), 7.46−7.42 (m, 1H), 7.37−7.33 (m, 2H), 6.77 (d, J = 8.8 Hz, 2H), 2.95 (s, 6H), 2.68 (t, J = 7.7 Hz, 2H), 2.58−2.46 (m, 1H), 2.35− 2.24 (m, 1H), 1.66−1.62 (m, 2H), 1.54−1.47 (m, 2H), 1.43−1.32 (m, 2H), 1.30−1.22 (m, 2H), 0.98 (t, J = 7.3 Hz, 3H), 0.76 (t, J = 7.3 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.6 (d, JPC = 19 Hz), 150.2, 139.7, 139.0 (d, JPC = 30 Hz), 135.6 (d, JPC = 96 Hz), 134.0, 133.4 (d, JPC = 12 Hz), 131.8, 131.2 (d, JPC = 10 Hz), 131.2 (JPC = 99 Hz), 130.8 (JPC = 105 Hz), 130.3 (d, JPC = 9 Hz), 128.8, 128.7 (JPC = 12 Hz), 128.0, 127.8, 127.4, 125.3, 119.9 (d, JPC = 10 Hz), 112.8, 40.5, 31.2, 30.9, 26.5 (d, JPC = 12 Hz), 26.2 (d, JPC = 10 Hz), 23.2, 23.0, 14.0, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 38.3; HRMS (ESI) calcd for C34H39NOP [M + H]+ 508.2769, found 508.2767. Heck Reaction. A solution of benzophosphole oxide 3a or naphthophosphole oxide 3b (0.21 mmol) and N,N-dimethyl-4vinylaniline (35 mg, 0.23 mmol) in toluene (2 mL) was degassed with N2. Pd(P-t-Bu3)2 (10 mg, 20 μmol) and diisopropylamine (32 mg, 0.31 mmol) were added, and the resulting mixture was stirred at 80 °C for 24 h. Upon cooling, the reaction mixture was diluted with ethyl acetate (10 mL). The organic phase was washed with brine, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (eluent hexane/ EtOAc (2/1)) to afford the desired coupling product (8a,b). (E)-2,3-Dibutyl-6-(4-(dimethylamino)styryl)-1-phenylphosphindole 1-oxide (8a): brown oil (57%); 1H NMR (400 MHz, CDCl3) δ 7.72−7.65 (m, 3H), 7.50−7.46 (m, 2H), 7.41−7.37 (m, 2H), 7.33 (d, J = 8.4 Hz, 2H), 7.29 (dd, J = 8.0, 3.2 Hz, 1H), 7.00 (d, J = 16.4 Hz, 1H), 6.82 (d, J = 16.4 Hz, 1H), 6.66 (d, J = 8.8 Hz, 2H), 2.95 (s, 6H), 2.59 (t, J = 7.6 Hz, 2H), 2.47−2.44 (m, 1H), 2.32−2.21 (m, 1H), 1.62−1.44 (m, 4H), 1.43−1.33 (m, 4H), 0.98 (t, J = 7.2 Hz, 3H), 0.77 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 150.6 (d, JPC = 20 Hz), 150.3, 141.7 (d, JPC = 29 Hz), 138.6 (d, JPC = 11 Hz), 134.1 (d, JPC = 96 Hz), 133.0 (d, JPC = 103 Hz), 131.8, 131.0 (JPC = 10 Hz), 130.7 (JPC = 96 Hz), 130.4, 130.0, 128.7 (d, JPC = 12 Hz), 127.8, 125.7 (d, JPC = 10 Hz), 125.2, 122.8, 121.5 (d, JPC = 12 Hz), 112.3, 40.4, 31.1, 30.7, 26.4 (d, JPC = 14 Hz), 25.9 (d, JPC = 11 Hz), 23.1, 22.9, 14.0, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 39.4; HRMS (ESI) calcd for C32H39NOP [M + H]+ 484.2769, found 484.2766. (E)-2,3-Dibutyl-7-(4-(dimethylamino)styryl)-1-phenylbenzo[f ]phosphindole 1-oxide (8b): dark red solid (58%); mp 96−98 °C; 1H NMR (400 MHz, CDCl3) δ 7.98 (d, J = 11.2 Hz, 1H), 7.81−7.75 (m, 2H), 7.72−7.65 (m, 4H), 7.49−7.38 (m, 5H), 7.19−7.12 (m, 1H),

7.02−6.97 (m, 1H), 6.72 (d, J = 8.8 Hz, 2H), 2.99 (s, 6H), 2.71 (t, J = 7.2 Hz, 2H), 2.60−2.51 (m, 1H), 2.38−2.31 (m, 1H), 1.70−1.64 (m, 2H), 1.56−1.51 (m, 2H), 1.45−1.36 (m, 2H), 1.31−1.23 (m, 2H), 1.02 (t, J = 7.2 Hz, 3H), 0.80 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (75 MHz, CDCl3) δ 151.6 (d, JPC = 20 Hz), 150.3, 139.1 (JPC = 30 Hz), 136.9, 135.6 (JPC = 96 Hz), 134.6, 133.3 (JPC = 12 Hz), 131.8, 131.1 (JPC = 99 Hz), 131.1 (JPC = 11 Hz), 130.9 (JPC = 105 Hz), 130.1 (d, JPC = 13 Hz), 128.7, 128.6 (JPC = 12 Hz), 127.8, 126.4, 125.8, 125.4, 123.6, 122.4 (JPC = 26 Hz), 119.9 (d, JPC = 14 Hz), 112.4, 40.4, 31.2, 30.9, 26.5 (d, JPC = 14 Hz), 26.2 (d, JPC = 14 Hz), 23.2, 22.9, 14.0, 13.7; 31P{1H} NMR (162 MHz, CDCl3) δ 38.2; HRMS (ESI) calcd for C36H41NOP [M + H]+ 534.2926, found 534.2925. Sonogashira Coupling. A mixture of benzophosphole oxide 3a or naphthophosphole oxide 3b (0.10 mmol), N,N-diethyl-4-ethynylaniline19 or N,N-diethyl-4-((4-ethynylphenyl)ethynyl)aniline20 (0.12 mmol), PdCl2(PPh3)2 (4 mg, 5 μmol), CuI (1 mg, 5 μmol), and diisopropylamine (20 μL, 0.12 mmol) in THF (2 mL) was stirred at 80 °C for 12 h. Upon cooling, the reaction mixture was diluted with ethyl acetate (5 mL). The organic phase was washed with brine, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (eluent hexane/ EtOAc (2/1)) to afford the desired coupling product (9a,b, 10a,b). 2,3-Dibutyl-6-((4-(diethylamino)phenyl)ethynyl)-1-phenylphosphindole 1-oxide (9a): dark brown oil (79%); 1H NMR (400 MHz, CDCl3) δ 7.68−7.63 (m, 3H), 7.56 (d, J = 8.0 Hz, 1H), 7.51−7.47 (m, 1H), 7.42−7.38 (m, 2H), 7.31−7.26 (m, 3H), 6.57 (d, J = 8.7 Hz, 2H), 3.35 (q, J = 7.1 Hz, 4H), 2.59 (t, J = 7.5 Hz, 2H), 2.54−2.45 (m, 1H), 2.33−2.22 (m, 1H), 1.60−1.52 (m, 2H), 1.52−1.45 (m, 2H), 1.43−1.36 (m, 2H), 1.31−1.23 (m, 2H), 1.16 (t, J = 7.0 Hz, 6H), 0.98 (t, J = 7.3 Hz, 3H), 0.78 (t, J = 7.3 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 150.4 (d, JPC = 20 Hz), 147.7, 142.1 (d, JPC = 29 Hz), 135.2, 135.2 (d, JPC = 96 Hz), 133.0, 132.7 (d, JPC = 103 Hz), 131.9 (d, JPC = 3 Hz), 131.3 (d, JPC = 10 Hz), 131.0 (d, JPC = 11 Hz), 130.0 (d, JPC = 97 Hz), 128.7 (d, JPC = 12 Hz), 124.5 (d, JPC = 12 Hz), 121.2 (d, JPC = 12 Hz), 111.2, 108.4, 93.2, 86.6 (d, JPC = 1 Hz), 44.3, 31.0 (d, JPC = 2 Hz), 30.6 (d, JPC = 1 Hz), 26.4 (d, JPC = 13 Hz), 26.0 (d, JPC = 11 Hz), 23.1, 22.9, 14.0, 13.7, 12.6; 31P{1H} NMR (162 MHz, CDCl3) δ 39.2; HRMS (ESI) calcd for C34H41NOP [M + H]+ 510.2926, found 510.2931. 2,3-Dibutyl-6-((4-((4-(diethylamino)phenyl)ethynyl)phenyl)ethynyl)-1-phenylphosphindole 1-oxide (10a): yellow solid (77%); mp 156−158 °C; 1H NMR (400 MHz, CDCl3) δ 7.72−7.63 (m, 4H), 7.52 (t, J = 6.3 Hz, 1H), 7.46−7.34 (m, 9H), 6.61 (d, J = 8.9 Hz, 2H), 3.37 (q, J = 7.0 Hz, 4H), 2.62 (t, J = 7.4 Hz, 2H), 2.58−2.48 (m, 1H), 2.36−2.25 (m, 1H), 1.62−1.56 (m, 2H), 1.52−1.45 (m, 2H), 1.42− 1.33 (m, 2H), 1.31−1.22 (m, 2H), 1.18 (t, J = 7.0 Hz, 6H), 1.00 (t, J = 7.2 Hz, 3H), 0.81 (t, J = 7.3 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 150.3 (d, JPC = 20 Hz), 147.7, 143.1 (d, JPC = 29 Hz), 135.88, 135.86 (d, JPC = 96 Hz), 133.1, 132.9 (d, JPC = 104 Hz), 132.1 (d, JPC = 3 Hz), 131.6 (JPC = 10 Hz), 131.5, 131.1, 130.9 (d, JPC = 10 Hz), 129.8 (d, JPC = 97 Hz), 128.8 (d, JPC = 12 Hz), 124.6, 123.3 (d, JPC = 8 Hz), 121.4, 121.3 (d, JPC = 11 Hz), 111.2, 108.5, 93.4, 91.5, 90.0 (d, JPC = 1 Hz), 87.0, 44.4, 30.9 (d, JPC = 1 Hz), 30.6, 26.4 (d, JPC = 13 Hz), 26.1 (d, JPC = 11 Hz), 23.1, 22.9, 14.0, 13.7, 12.6; 31P{1H} NMR (162 MHz, CDCl3) δ 39.2; HRMS (ESI) calcd for C42H45NOP [M + H]+ 610.3239, found 610.3246. 2,3-Dibutyl-7-((4-(diethylamino)phenyl)ethynyl)-1-phenylbenzo[f ]phosphindole 1-oxide (9b): brown solid (77%); mp 146−148 °C; 1 H NMR (300 MHz, CDCl3) δ 7.98 (d, J = 8.2 Hz, 1H), 7.90 (s, 1H), 7.80−7.61 (m, 5H), 7.54−7.42 (m, 5H), 6.62 (d, J = 6.1 Hz, 2H), 3.38 (q, J = 7.1 Hz, 4H), 2.73 (t, J = 7.5 Hz, 2H), 2.65−2.50 (m, 1H), 2.42−2.23 (m, 1H), 1.70−1.65 (m, 2H), 1.58−1.51 (m, 2H), 1.45− 1.39 (m, 2H), 1.33−1.25 (m, 2H), 1.18 (t, J = 7.0 Hz, 6H), 1.04 (t, J = 7.2 Hz, 3H), 0.82 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.4 (d, JPC = 18 Hz), 147.7, 139.9 (d, JPC = 29 Hz), 136.3 (d, JPC = 95 Hz), 134.5, 133.1, 132.7 (d, JPC = 13 Hz), 131.9, 131.4, 131.3 (JPC = 105 Hz), 131.1 (d, JPC = 11 Hz), 130.9 (JPC = 98 Hz), 130.7, 129.8 (d, JPC = 10 Hz), 128.7 (d, JPC = 12 Hz), 128.4, 122.8, 119.9 (d, JPC = 11 Hz), 111.2, 108.5, 92.6, 87.1, 44.3, 31.1, 30.9, 26.5 (d, JPC = 13 Hz), 26.2 (d, JPC = 10 Hz), 23.2, 22.9, 14.0, 13.7, 12.6; G

DOI: 10.1021/acs.organomet.7b00244 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics P{1H} NMR (162 MHz, CDCl3) δ 38.0; HRMS (ESI) calcd for C38H43NOP [M + H]+ 560.3082, found 560.3088. 2,3-Dibutyl-7-((4-((4-(diethylamino)phenyl)ethynyl)phenyl)ethynyl)-1-phenylbenzo[f ]phosphindole 1-oxide (10b): brown solid (70%); mp 215−217 °C; 1H NMR (400 MHz, CDCl3) δ 7.97 (d, J = 11.1 Hz, 1H), 7.91 (s, 1H), 7.79 (d, J = 8.5 Hz, 1H), 7.71−7.64 (m, 3H), 7.59 (d, J = 8.4 Hz, 1H), 7.47−7.34 (m, 9H), 6.56 (d, J = 8.9 Hz, 2H), 3.31 (q, J = 7.0 Hz, 4H), 2.68 (t, J = 7. Six Hz, 2H), 2.60−2.49 (m, 1H), 2.37−2.25 (m, 1H), 1.66−1.63 (m, 2H), 1.55−1.35 (m, 4H), 1.31−1.22 (m, 2H), 1.12 (t, J = 7.0 Hz, 6H), 0.99 (t, J = 7.2 Hz, 3H), 0.78 (t, J = 7.3 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 151.4 (d, JPC = 18 Hz), 147.7, 140.4 (d, JPC = 29 Hz), 136.7 (d, JPC = 95 Hz), 135.1, 133.0, 132.6 (d, JPC = 12 Hz), 132.3, 132.0 (d, JPC = 3 Hz), 131.5, 131.5 (JPC = 102 Hz), 131.0, 130.8, 130.8 (JPC = 98 Hz), 129.9 (d, JPC = 10 Hz), 128.8, 128.7, 124.6, 121.6, 120.0 (d, JPC = 11 Hz), 111.2, 108.5, 93.5, 90.9, 90.7, 87.0, 44.4, 31.1, 30.9, 26.5 (d, JPC = 13 Hz), 26.3 (d, JPC = 10 Hz), 23.2, 23.0, 14.0, 13.7, 12.6; 31P{1H} NMR (162 MHz, CDCl3) δ 38.0; HRMS (ESI) calcd for C46H47NOP [M + H]+ 660.3395, found 660.3391. DFT Calculations. All calculations were performed with the Gaussian 09 program package.21 The geometry optimization was performed employing the B3LYP functional and the 6-31G(d) basis sets for all atoms. 31

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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.7b00244. Absorption and fluorescence spectra for 4a−10a and 4b−10b in various solvents and NMR spectra of new compounds (PDF) Cartesian coordinates of the DFT-optimized structures (XYZ) Cartesian coordinates of the DFT-optimized structures (XYZ) Cartesian coordinates of the DFT-optimized structures (XYZ)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for N.Y.: [email protected]. ORCID

Naohiko Yoshikai: 0000-0002-8997-3268 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Singapore Ministry of Education (RG 114/15), Nanyang Technological University, and JST, CREST.

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REFERENCES

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DOI: 10.1021/acs.organomet.7b00244 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.02; Gaussian, Inc., Wallingford, CT, 2009.

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DOI: 10.1021/acs.organomet.7b00244 Organometallics XXXX, XXX, XXX−XXX