Ditopic N-Heterocyclic Pincer Carbene Complexes Containing a

Article pubs.acs.org/Organometallics

Ditopic N‑Heterocyclic Pincer Carbene Complexes Containing a Perylene Backbone Susanne Langbein, Hubert Wadepohl, and Lutz H. Gade* Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: A new class of ditopic perylene-based N-heterocyclic pincer ligands, tetrakis(phosphinomethyl)-1,2,3,8,9,10hexahydrobenzo[1,2,3-gh:4,5,6-g′h′]diperimidine derivatives (TPHDP), were synthesized via a one-pot reaction from 3,4,9,10-tetraaminoperylene either directly with the corresponding phosphine and paraformaldehyde or with the phosphonium salt and triethylamine as base. In this way the diphenyl-, dicyclohexyl-, and isopropylphosphinomethyl-functionalized protioligands were obtained (1a−1c). Reaction of 1a−1c with [RhCl(PPh3)3] led to a double geminal C−H activation and coordination of the ditopic PCP pincer to the rhodium centers, yielding the rhodium(I)chloro complexes (2a−2c) of all three ligands. These were found to be suitable starting materials for further ligand exchange of the chloride. Reaction with lithium phenylacetylide or the abstraction of the chloride ligand with thallium(I) hexafluorophosphate in the presence of neutral donors gave the corresponding alkynyl complexes 3a and 3b or the ionic complexes [Rh(Ph3P)]2-PhTPHDP (4a) and [Rh(C5H5N)]2-iPr-TPHDP (4b). The most characteristic feature in the absorption spectra of all compounds is the intense band of the π* ← π transition of the aromatic (perylene) core with its partially resolved vibrational progression. The fluorescence quantum yields (ϕ) of compounds 1a−1c were found to be between 72% and 86%. Upon coordination to rhodium, the intraligand transition in the absorption spectra is only slightly shifted, whereas the fluorescence is almost completely quenched.

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with different transition metals.48 These ligands not only proved to give rise to robust late transition metal complexes and to display a certain degree of flexibility in their detailed coordination modes but allowed an in-depth study of the metalinduced C−H activation leading to the PCP ligation.49,50

INTRODUCTION N-Heterocyclic carbenes (NHCs)1−5 have been primarily employed as mono- or polydentate ancillary ligands with a concave arrangement of the donor functions.5−9 This is the case, for example, in their use as ligating units in meridinally coordinating tridentate ligands, frequently referred to as “pincers”.10−14 The latter, in particular, have given rise to highly robust coordination compounds, which have found widespread applications in molecular catalysis.15−20 On the other hand, di- or polytopic NHC−ligand systems, in which the ligating units are exoligating (possessing a convex arrangement) may act as building blocks for larger molecular units.21−26 In the same way, pincer-binding sites may be combined in such a way as to give rise to di- or polytopic ligands.27−35 Although five-membered NHCs remain the most widely studied systems, a significant number of contributions to the field concern NHCs derived from six-membered heterocycles, which frequently display an even greater σ basicity than their five-membered analogues.36−44 A special case of the latter is dihydroperimidine-based NHC ligands, introduced by Richeson et al., which are derived from 1,8-diaminonaphthaline or related species.37,40,43,45−47 Hill and co-workers recently developed an elegant synthetic route to dihydoperimidinebased PCP pincer systems containing phosphino groups in the wingtip positions and investigated their complexation behavior © XXXX American Chemical Society

The facile accessibility of the dihydroperimidine-derived PCP pincers reported by Hill et al. led us to consider the development of ditopic pincers based on the same strategy in which the 1,8-diaminonaphthalene backbone would be replaced by a 3,4,9,10-tetraaminoperylene unit, thus essentially “douReceived: January 20, 2016

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DOI: 10.1021/acs.organomet.6b00049 Organometallics XXXX, XXX, XXX−XXX

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Organometallics bling” the structure. This would not only provide access to the corresponding dinuclear complexes but introduce a chromophore/fluorophore into the connecting backbone. We note that NHCs have recently been included in poly-N-heterocyclic aromatics.25,51−55 3,4,9,10-Tetraaminoperylene (TAP), which was first reported in 1919 by Zinke and Unterkreuter,56,57 consists of two diaminonaphthalene units linked to each other through the peri position. In recent years, we developed an efficient synthetic route to TAP derivatives,58,59 which were shown to bind inter alia to boron and aluminum via the nitrogen atoms, forming highly fluorescent derivatives.60 Herein, we report the synthesis of ditopic PCP pincer ligands in which the metal-binding sites are connected via a central 3,4,9,10-tetraaminoperylene-derived fluorophore, their coordination chemistry with rhodium, and the influence of the metal coordination on their photophysical properties.

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RESULTS AND DISCUSSION Synthesis of the Ditopic Pincer Ligand Precursors. The tetrakis(phosphinomethyl)-1,2,3,8,9,10-hexahydrobenzo[1,2,3-gh:4,5,6-g′h′]diperimidine derivatives (TPHDP) were synthesized via a one-pot reaction following the protocol for the dihydoperimidine-based PCP pincer systems reported by Hill et al.48 The starting material 3,4,9,10-tetraaminoperylene was directly reacted either with the corresponding phosphine and paraformaldehyde or with the phosphonium salt and triethylamine as base in N,N-dimethylformamide as solvent. In this way the diphenyl-, dicyclohexyl-, and diisopropylphosphinomethyl-functionalized protioligands were synthesized (1a− 1c). Whereas compounds 1b and 1c were obtained in adequate yields via the direct synthetic route displayed in Scheme 1, the

Figure 1. View of the molecular structure of 1a along an axis orthogonal to the plane of the aromatic core (top) and of 1b viewed along the short molecular axis, illustrating the twist between the perimidine halves (bottom); displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms were omitted for clarity. Selected bond lengths (Å) and angles (deg) for 1a: C21−N1 = 1.451(2), C21−N2 = 1.455(2), C1−N1 = 1.399(2), C7−N2 = 1.407(2); N1−C21−N2 = 110.06(15), C1−N1−C23 = 117.99(15). Selected bond lengths (Å) and angles (deg) for 1b: C21−N1 = 1.475(7), C21−N2 = 1.449(8), C1−N1 = 1.408(4), C7−N2 = 1.416(6); N1−C21−N2 = 111.9(6), C1−N1−C23 = 118.2(3).

Scheme 1. Synthesis of TPHDP Ligandsa

dicyclohexylphosphine derivatives 1a and 1b are depicted along with selected bond lengths and angles. The structure of 1c is displayed in the Supporting Information. The molecular structures of the three ligand precursors are very similar. Minor structural differences are mainly due to the different steric bulk of the phosphine units, the dicyclohexylphosphine derivative 1b being the sterically most encumbered. A notable parameter is the varying twist between the perimidine halves of the central perylene unit, represented by the torsion angle α (Figure 2), which was found to be the highest for compound 1b (Figure 1, bottom), resulting in the greatest twist of the perylene core (7.4° and 14.1°). This is greater than in any of the previously characterized TAP derivatives. In contrast, 1a is nearly planar, with α = 1.6°.

a

The synthesis of 1a was achieved by conversion of paraformaldehyde and diphenylphosphine with hydrochloric acid to diphenylphosphonium chloride and subsequent addition together with triethylamine to the reaction mixture.

diphenylphosphino derivative 1a was isolated only in low yields. However, 1a was accessed in good yields following the route via diphenylbis(hydroxymethyl)phosphonium chloride and triethylamine. Single crystals of all three ligand precursors were grown from saturated solutions of tetrahydrofuran (1a) or benzene (1b, 1c) and were analyzed by X-ray diffraction in order to establish the structural details of these new perylene derivatives. In Figure 1 the molecular structures of the diphenylphosphine and

Figure 2. Schematic illustration of torsion angles α and α′. B


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Organometallics Table 1. Torsion Angles Measured in the Molecular Structures of 1a−1c compound

torsion angle α (deg)

torsion angle α′ (deg)

1a 1b 1c

1.6(3) 7.4(5) 3.2(3)

1.6(3) 14.1(5) 11.3(3)

Coordination Chemistry of the Tetrakis(phosphinomethyl)hexahydrobenzodiperimidines. Reaction of compounds 1a−1c with [RhCl(PPh3)3], following the strategy by Hill et al. for the dihydroperimidene-PCP ligands,48 led to a double geminal C−H activation61,62 and coordination of the ditopic PCP pincer to the rhodium centers (Scheme 2). In this way the rhodium(I)chloro complexes of all three ligands were isolated and characterized. Scheme 2. Synthesis of TPHDP Complexes with a Rhodium(I) Precursor Figure 3. Two views of the molecular structure of 2c with displacement ellipsoids drawn at the 50% probability level. Hydrogen atoms were omitted for clarity. Selected bond lengths (Å) and angles (deg): Rh(1)−Rh(2) 15.3397(7), Rh(1)−P(1) 2.2410(14), Rh(1)− P(2) 2.2442(14), Rh(1)−C(21) 1.932(5), Rh(2)−P(3) 2.2361(15), Rh(2)−P(4) 2.2336(15), Rh(2)−C(22) 1.928(5), N(1)−C(1) 1.407(6), N(1)−C(21) 1.394(6), N(1)−C(23) 1.464(7), N(2)− C(7) 1.400(6), N(2)−C(21) 1.387(6), N(2)−C(24) 1.467(6), N(3)−C(14) 1.403(6), N(3)−C(22) 1.384(7), N(3)−C(25) 1.461(7), N(4)−C(20) 1.405(6), N(4)−C(22) 1.396(7), N(4)− C(26) 1.465(7), P(1)−Rh(1)−Cl(1) 96.88(5), P(1)−Rh(1)−P(2) 168.81(5), P(2)−Rh(1)−Cl(1) 93.69(5), C(21)−Rh(1)−Cl(1) 177.04(16), P(3)−Rh(2)−Cl(2) 95.58(5), P(4)−Rh(2)−Cl(2) 94.77(5), P(4)−Rh(2)−P(3) 169.47(5).

Scheme 3. Synthesis of Acetylide and Dicationic Rhodium(I) Complexes

The isolated dark red rhodium complexes 2a−2c were found to be only sparingly soluble in organic solvents, and in particular the Ph2P-substituted derivative 2a was difficult to fully characterize in solution. Therefore, 13C labeling experiments were carried out for 2a to prove the formation of a carbene species by 13C NMR spectroscopy. The metalcoordinated carbene C atom was found at δ = 206.1 ppm and thus resonating at a similar chemical shift to those in 2b and 2c (δ = 205.3 and 205.8 ppm, respectively). The higher solubility of 2c in organic solvents allowed the growth of single crystals suitable for X-ray crystallography by diffusion of hexane into a solution of 2c in THF, giving a THF solvate of compound 2c. The molecular structure of 2c determined by X-ray diffraction (Figure 3) confirms the pincer-type geometry of the ligand that is coordinated to two square planar rhodium complex fragments with a Rh−carbene−C bond length of 1.93 Å, which is within the range reported in the literature for NHC−Rh complexes.48,63 Compared to the corresponding ligand precursor 1c, the nitrogen−C(carbene) bonds are shortened (2c: 1.38−1.39 Å, 1c: 1.45−1.46 Å), reflecting the π-donation of the nitrogen lone pairs into the orthogonal porbital at the carbene−carbon atom.64 The rhodium complexes 2a−2c were found to be suitable starting materials for further ligand exchange of the chloride. Reaction with lithium phenylacetylide or the abstraction of the chloride ligand with thallium(I) hexafluorophosphate in the presence of neutral donors gave the corresponding products shown in Scheme 3. The alkynyl complexes 3a and 3b, which

were isolated as purple-red solids, were only sparingly soluble in organic solvents. On the other hand, the ionic complexes 4a and 4b (Scheme 3) displayed better solubility as well as stability in chlorinated solvents. Absorption and Emission Properties of the TPHDPs and Their Rh Complexes. The ditopic ligand precursors as well as their rhodium PCP pincer complexes were characterized by UV−vis and emission spectroscopy. The most characteristic feature in the absorption spectra of all compounds is the intense band of the π* ← π transition of the aromatic C


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Organometallics

low solubility of complex 2c initially suggested that this behavior was due to aggregation in solution. However, even upon high dilution, the absence of emission pertained. Notably, the species 3a and 4a displayed emission, with the band maximum Stokes shifted by 11 and 12 nm, respectively, albeit with a low fluorescence quantum yield of 7% (which did not vary upon dilution). The partial or complete quenching of the emission in the RhI complexes is attributed to the availability of (metal-centered) nonradiative relaxation pathways.66

(perylene) core with its partially resolved vibrational progression (Figure 4).59 As expected, no significant influence of

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CONCLUSION In summary, we synthesized three new ligand precursors to ditopic PCP pincers containing central six-membered NHC units as ligating “anchors” and a characteristic chromophore in their backbone structure. These species display high fluorescence quantum yields of up to 86%. Reacting 1a−1c with [RhCl(PPh3)3] gave rise to the corresponding chloro complexes 2a−2c, which in turn were further derivatized. A hypsochromic coordination shift of the absorption maxima of the intraligand π* ← π band of about 7−15 nm was observed upon metalation as well as quenching of the fluorescence.

Figure 4. Normalized absorption spectra (red) and emission spectra (black) exemplarily of 1a in THF.

the phosphinoalkyl substituents on the position of this absorption band in the range 535−539 nm was observed for the TPHDP derivatives 1a−1c (Table 2). However, compared

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Table 2. Absorption and Emission Data of 1a−1c, 2c, 3a, and 4a in THF

a

compound

λmax (nm)

log ε

Δν (cm−1)a

λem.(nm)

ϕ (%)

1a 1b 1c 2c 3a 4a

539 537 535 520 524 522

4.73 4.45 4.55 4.39 4.20 4.36

1249 1298 1308 1345 1366 1251

575 564 562

0.72 0.86 0.81

534 534

0.07 0.07

EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out using standard Schlenk and glovebox techniques under an argon atmosphere. Solvents such as toluene, THF, pentanes, hexanes, and diethyl ether were purified by passing over activated alumina columns (MBraun Solvent Purification System). THF-d8 and benzene-d6 were refluxed over sodium and purified by distillation. CD2Cl2 was dried over CaH2 and purified by distillation. H2O was purged with argon. NMR spectra were recorded on a Bruker Avance II 400 MHz or a Bruker Avance III 600 MHz spectrometer at room temperature. 1H and 13C NMR chemical shifts are given in ppm and referenced to residual proton solvent resonances. The more detailed attribution of the signals occurred by DEPT, HSQC, and HMBC spectra. 31P NMR spectra were referenced to external H3PO4. Mass spectra were recorded on a JEOL JMS-700, Bruker Biflex (HR-FAB+), Bruker apexQe FT-ICR, or Bruker FlexAnalysis V mass spectrometer (HRMALDI/HR-ESI) at the mass spectrometry facility of the Organic Department of the University of Heidelberg. IR spectroscopy was carried out on a Varian 3100 FT-IR with KBr pellets. The UV−vis spectra were measured on a Cary 5000 UV/vis/NIR spectrometer and were baseline- and solvent-corrected. The emission and fluorescence spectra as well as fluorescence quantum yields were carried out on a Varian Cary Eclipse spectrometer. The fluorescence quantum yields were determined in optically dilute solutions (OD < 0.1 at the excitation wavelength) and compared to fluorescein as reference by using the following equation.

Frequency of the vibrational progression.

to the parent compound TAP (524 nm)59 the absorption maxima of the TPHDPs are shifted bathochromically by about 15 nm, thus mirroring the previously studied absorption spectra of the diborylene TAP derivatives, which absorb in a range 535−341 nm.59,60,65 The emission spectra of compounds 1a−1c show the characteristic mirror image to the absorption spectra, as shown exemplarily for compound 1a in Figure 4. The fluorescence quantum yields (ϕ) of the compounds 1a−1c were found to be between 72% (1a) and 86% (1b). Upon coordination to rhodium, the intraligand transition in the absorption spectra is only slightly shifted, whereas the fluorescence is almost completely quenched (Figure 5). The

⎡ A (λ ) ⎤⎡ I (λ ) ⎤⎡ n 2 ⎤⎡ D ⎤ ϕx = ϕr⎢ r r ⎥⎢ r r ⎥⎢ x2 ⎥⎢ x ⎥ ⎣ A x (λ x ) ⎦⎣ Ix(λ x ) ⎦⎣ nr ⎦⎣ Dr ⎦ A is the absorbance at the excitation wavelength (λ), I the intensity of the excitation light at the excitation wavelength (λ), n the refractive index of the solvent, and D the integrated scripts. The indices r and x refer to the reference sample and sample, respectively. All quantum yields were measured at an identical excitation wavelength for the sample and reference, therefore canceling out the term I(λr)/I(λx). Standard corrections were utilized for all spectra. Microanalysis (C, H, N) was carried out at the Department of Chemistry at the University of Heidelberg. 3,4,9,10-Tetraaminoperylene59,60 and diphenylbis(hydroxymethyl)phosphonium chloride67 were prepared according literature procedures. All other materials were purchased commercially and used without further purification. Synthesis of 1,3,8,10-Tetrakis((diphenylphosphino)methyl)1,2,3,8,9,10-hexahydrobenzo[1,2,3-gh:4,5,6-g′h′]diperimidine (1a). A dried Schlenk flask was charged with 400 mg (1.28 mmol, 1

Figure 5. Decreasing emission intensity from compound 1a, via 4a to 2c. D


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Organometallics

the product (81% yield). 1H NMR (600.13 MHz, CD2Cl2): δ 7.93 (m, 16H, HAr), 7.52 (d, 3J = 8.67 Hz, 4H, H(perylene)), 7.44 (m, 24H, HAr), 6.48 (d, 3J = 8.23, 4H, H(perylene)), 4.49 (bs, 8H, NCH2P). 13C NMR/HMBC (150.90 MHz,CD2Cl2): δ 206.1 (C(carbene)), 134.4 (C(perylene)), 133.6 (CAr), 133.8 (vt, CAr), 130.5 (CAr) 130.1 (C(perylene)), 128.8 (vt, CAr), 125.2 (C(perylene)), 120.7 (C(perylene)), 119.4 (C(perylene)), 108.0 (C(perylene)), 58.1 (m, NCH2P). 31P NMR (242.94 MHz,CD2Cl2): δ 22.98 (d, 1JPRh = 151.43 Hz). HR-MS (HR-MALDI): m/z calcd. for C74H56Cl2N4P4Rh2: 1400.0943; found: 1400.1124. Anal. Calcd for C74H56Cl2N4P4Rh2: C 63.40; H 4.03; N 4.00. Found: C 62.57; H 4.15; N 4.13. Although these results for microanalytical data are outside the established range for analytical purity, they are provided to show the best values obtained to date. Synthesis of [RhCl]2-Cy-TPHDP (2b). A synthetic route similar to the protocol for 2a was used, affording 65 mg of the desired product as a red solid (53% yield). 1H NMR (600.13 MHz, CD2Cl2): δ 7.62 (d, 3J = 9.16 Hz, 4H, H(perylene)), 6.57 (d, 3J = 9.16 Hz, 4H, H(perylene)), 3.77 (bs, 8H, NCH2P), 2.21−1.57 (m, 84H, HCy). 13C NMR/HMBC (150.90 MHz, CD2Cl2): δ 205.3 (C(carbene)), 135.2 (C(perylene)), 130.4 (C(perylene)), 125.0 (C(perylene)), 120.7 (C(perylene)), 119.0 (C(perylene)), 107.7 (C(perylene)), 51.0 (vt, NCH2P), 33.8 (vt, CCy′), 29.1 (CCy), 28.9 (CCy), 27.3 (m, CCy), 26.7 (CCy). 31P NMR (242.94 MHz, CD2Cl2): δ 37.67 (d, 1JPRh = 148.60 Hz). HR-MS (HRMALDI): m/z calcd for C74H104Cl2N4P4Rh2 1448.4699; found 1448.4785. Anal. Calcd for C74H104Cl2N4P4Rh2: C 61.29; H 7.23; N 3.86. Found: C 61.59; H 7.57; N 3.87. Synthesis of [RhCl]2-IPr-TPHDP (2c). A procedure similar to the protocol for 2a was used, affording 120 mg of the desired product as a red solid (91% yield). 1H NMR (600.13 MHz, CD2Cl2): δ 7.62 (d, 3J = 8.37 Hz, 4H, H(perylene)), 6.57 (d, 3J = 8.37 Hz, 4H, H(perylene)), 3.74 (bs, 8H, NCH2P), 2.37 (m, 8H, HiPr), 1.39−1.22 (m, 48H, HiPr). 13 C NMR/HMBC (150.90 MHz, CD2Cl2): δ 205.8 (C(carbene)), 135.6 (C(perylene)), 130.5 (C(perylene)), 124.0 (C(perylene)), 121.1 (C(perylene)), 118.8 (C(perylene)), 108.2 (C(perylene)), 51.1 (NCH2P), 23.1 (CiPr), 19.2 (CiPr), 18.4 (CiPr). 31P NMR (242.94 MHz, CD2Cl2): δ 46.20 (d, 1JPRh = 148.68 Hz). HR-MS (HRFAB+): m/z calcd for C50H72Cl2N4P4Rh2 1128.2195; found 1128.2451. Anal. Calcd for C50H72Cl2N4P4Rh2·THF: C 54.15; H 6.40; N 4.68. Found: C 54.26; H 6.10; N 5.20. The obtained crystals with THF as solvate molecule were used for microanalysis. Synthesis of [Rh(C8H5)]2-Ph-TPHDP (3a). A 100 mg (0.07 mmol, 1 equiv) amount of compound 2a was dissolved in 50 mL of THF, and 0.15 mL of 1 M PhC2Li in THF was added. The mixture was stirred overnight at 70 °C, and subsequently another 0.15 mL of 1 M PhC2Li in THF was added. The mixture was stirred again overnight at 70 °C. The solvent was reduced to about 10 mL, and the precipitate filtered. The resultant red solid was washed twice with 20 mL of water and 20 mL of n-pentane, respectively. The residue was dried under vacuum to yield 51 mg of the product (47% yield). 1H NMR (600.13 MHz, CD2Cl2): δ 8.04 (m, 16H, HAr), 7.62 (d, 3J = 8.25 Hz, 4H, H(perylene)), 7.44 (m, 24H, HAr), 7.22 (d, 3J = 6.19 Hz, 4H, HAr), 7.16 (t, 3J = 6.19 Hz, 4H, HAr), 7.01 (t, 3J = 6.99 Hz, 2H, HAr), 6.65 (d, 3 J = 8.25 Hz, 4H, H(perylene)), 4.73 (bs, 8H, NCH2P). Due to poor solubility, no useful 13C NMR data were obtained. 31P NMR (242.94 MHz, CD2Cl2): δ 28.75 (d, 1JPRh = 151.55 Hz, PPh2). IR (KBr cm−1): 3051 νarom(C−H); 2064 νalkin; 1960 νalkyl; 1578 νarom. HR-MS (HR-ESI): m/z calcd for C90H66N4P4Rh2·2H+ 767.1247; found 767.1277. Anal. Calcd for C90H66N4P4Rh2·2H2O: C 68.88; H 4.50; N 3.57. Found: C 68.51; H 4.55; N 3.48. Synthesis of [Rh(C8H5)]2-iPr-TPHDP (3b). A procedure similar to the protocol for 3a was used, giving 66 mg of the red product (59% yield). 1H NMR (600.13 MHz, CD2Cl2): δ 7.63 (d, 3J = 7.77 Hz, 4H, H(perylene)), 7.15 (m, 8H, HAr), 6.98 (m, 2H, HAr), 6.61 (d, 3J = 7.81 Hz, H(perylene)), 3.91 (bs, 8H, NCH2P), 2.40 (m, 8H, HiPr), 1.41 (m, 24H, HiPr), 1.26 (m, 24H, HiPr). Due to poor solubility, no useful 13C NMR data were obtained. 31P NMR (242.94 MHz, CD2Cl2): δ 51.23 (d, 1JPRh = 148.59, PiPr2). IR (KBr cm−1): 3052 νarom(C−H); 2956 νalkyl;; 2869 νalkyl; 2058 νalkin; 1578 νarom. HR-MS (HR-MALDI): m/z calcd for C66H82N4P4Rh2 1260.3600; found 1260.3595. Anal. Calcd for

equiv) of tetraaminoperylene and suspended in 100 mL of N,Ndimethylformamide, and 1.47 g (5.12 mmol, 4 equiv) of freshly made bis(hydroxymethyl)diphenylphosphonium chloride was added to the mixture in an argon counterflow. Further, 0.72 mL (5.12 mmo, 4 equiv) of dried triethylamine was added, and the mixture stirred at 50 °C for 24 h. The solvent was reduced to about 30 mL, and diethyl ether was added to afford the product as a precipitate, which was separated by filtration and washed three times with 20 mL of vented water, methanol, and n-pentane, respectively. The resulting magenta solid was dried under vacuum to yield 0.94 g of the product (65% yield). 1H NMR (600.13 MHz, d8-THF): δ 7.71 (d, 3J = 8.6 Hz, 4H, H(perylene)), 7.47−7.28 (m, 40H, HPh), 6.58 (d, 3J = 7.9 Hz, 4H, H(perylene)), 4.18 (s, 4H, NCH2N), 4.00 (d, 3J = 4.6 Hz, 8H, NCH2P). 13C NMR (150.90 MHz, d8-THF): δ 142.3 (C(perylene)), 138.9 (d, 1JCP = 15.8 Hz, CPh), 133.8 (d, 3JCP = 19.0 Hz, CPh), 130.2 (C(perylene)), 129.3 (CPh), 129.1 (d, 2JCP = 7.9 Hz, CPh), 124.2 (C(perylene)), 119.5 (C(perylene)), 114.5 (C(perylene)), 108.0 (C(perylene)), 64.7 (NCH2N), 53.4 (d, 1JCP = 10.3 Hz, NCH2P). 31 P NMR (242.94 MHz, d8-THF): δ −27.74. HR-MS (HR-FAB+): m/ z calcd for C74H60N4P4 1128.3768; found 1128.3767. Anal. Calcd for C74H60N4P4: C 78.71; H 5.36; N 4.96. Found: C 78.59; H 5.95; N 4.95. Synthesis of 1,3,8,10-Tetrakis((dicyclohexylphosphino)methyl)-1,2,3,8,9,10-hexahydrobenzo[1,2,3-gh:4,5,6-g′h′]diperimidine (1b). In a dried Schlenk flask 288 mg (9.6 mmol, 6 equiv) of paraformaldehyde was stirred with 1.3 mL (6.4 mmol, 4 equiv) of dicyclohexylphosphine for approximately 10 min at room temperature. Subsequently, 500 mg (1.6 mmol, 1 equiv) of tetraaminoperylene was added, and the mixture was dissolved in 50 mL of N,N-dimethylformamide and stirred for 24 h at 130 °C. The solvent was removed, and the resulting magenta solid washed three times with 20 mL of hexane and diethyl ether, respectively. The solid was dried under vacuum to yield 883 mg of the product (47% yield). 1 H NMR (600.13 MHz, C6D6): δ 8.04 (d, 3J = 8.12 Hz, 4H, H(perylene)), 6.96 (d, 3J = 8.12 Hz, 4H, H(perylene)), 4.63 (s, 4H, NCH2N), 3.45 (d, 2JHP = 2.42 Hz, 8H, NCH2P), 1.92−1.23 (m, 80H, HCy). 13C NMR (150.90 MHz, C6D6): δ 143.7 (C(perylene)), 130.7 (C(perylene)), 124.3 (C(perylene)), 119.8 (C(perylene)), 117.8 (C(perylene)), 107.9 (C(perylene)), 66.8 (NCH2N), 46.4 (d, 1JCP = 11.57 Hz, NCH2P), 33.7 (d, 1JCP = 15.76 Hz, CCy), 30.4 (2JCP = 11.85 Hz, CCy), 29.9 (d, 2JCP = 11.17, CCy), 27.8 (m, CCy), 26.9 (CCy). 31P NMR (242.94 MHz, C6D6): δ −16.76. HR-MS (HR-FAB+): m/z calcd for C74H108N4P4 1176.7524; found 1176.7550. Anal. Calcd for C74H108N4P4: C 75.48; H 9.24; N 4.76. Found: C 74.84; H 8.70; N 5.18. Synthesis of 1,3,8,10-Tetrakis((diisopropylphosphino)methyl)-1,2,3,8,9,10-hexahydrobenzo[1,2,3-gh:4,5,6-g′h′]diperimidine (1c). An analogous procedure to that for 1b was used, utilizing 700.0 mg (2.24 mmol, 1 equiv) of the tetraaminoperylene and therefore 403.2 mg (13.44 mmol, 6 equiv) of paraformaldehyde and 1.26 mL (8.96 mmol, 4 equiv) of diisopropylphosphine. The product was obtained as a magenta solid to yield 1.38 g (72% yield). 1H NMR (600.13 MHz,C6D6): δ 8.01 (d, 3J = 8.23 Hz, 4H, H(perylene)), 6.91 (d, 3J = 8.23 Hz, 4H, H(perylene)), 4.51 (s, 4H NCH2N), 3.32 (d, 2 JHP = 3.30, 8H, NCH2P), 1.70 (m, 8H, HiPr), 1.09 (m, 48H, HiPr). 13C NMR (150.90 MHz,C6D6): δ 143.3 (C(perylene)), 130.4 (C(perylene)), 124.0 (C(perylene)), 119.5 (C(perylene)), 117.6 (C(perylene)), 107.1 (C(perylene)), 66.8 (NCH2N), 46.4 (d, 1JCP = 13.03 Hz, NCH2P), 23.2 (s, 1JCP = 12.96 Hz, CiPr), 19.7 (d, 2JCP = 14.66, CiPr), 19.5 (d, 2JCP = 12.75 Hz, CiPr). 31P NMR (242.94 MHz, C6D6): δ −8.81. HR-MS (HR-FAB+): m/z calcd for C50H76N4P4 856.5020; found 856.5047. Anal. Calcd for C50H76N4P4: C 70.07; H 8.94; N 6.54. Found: C 69.84; H 8.97; N 6.34. Synthesis of [RhCl]2-Ph-TPHDP (2a). A 100 mg (0.088 mmol, 1 equiv) amount of compound 1a was suspended in 40 mL of toluene, and 162.8 mg (0.176 mmol, 2 equiv) of [RhCl(PPh3)3] added. The mixture was stirred at 80 °C overnight and cooled to room temperature afterward. The solvent was reduced to 10 mL, and the resulting precipitate filtered of. The red solid was washed three times with 30 mL of n-pentane and dried under vacuum to yield 100 mg of E


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Organometallics C66H82N4P4Rh2·2thf: C 63.61; H 6.49; N 4.01. Found: C 63.28; H 6.43; N 3.52. Synthesis of [Rh(Ph3P)]2-Ph-TPHDP (4a). A solution of 100 mg (0.07 mmol, 1 equiv) of 2a, 49 mg (0.14 mmol, 2 equiv) of TlPF6, and 37 mg (0.14 mmol, 2 equiv) of PPh3 in 30 mL of CH2Cl2 was stirred for 2 h at room temperature. The solvent was removed, and the residue washed three times with 10 mL of diethyl ether, respectively. The red solid was dissolved again in CH2Cl2 and filtered over Celite, and the solvent removed afterward. The product was dried under vacuum to give 87 mg (57% yield). 1H NMR (600.13 MHz, CD2Cl2): δ 7.37 (m, 25H, HAr), 7.26 (m, 16H, HAr), 7.15 (m, 20H, HAr), 7.03 (m, 4H, H(perylene)), 6.98 (m, 10H, HAr), 6.23 (d, 3J = 5.43 Hz, 4H, H(perylene)), 4.52 (bs, 8H, NCH2P). 13C NMR/HMBC (150.90 MHz, CD2Cl2): δ 210.9 (m, C(carbene)), 134.4 (C(perylene)), 134.3 (d, 3JCP = 12.50 Hz, CAr), 134.1 (CAr), 133.9 (CAr), 133.8 (CAr), 131.4 (CAr), 130.6 (C(perylene)) 130.3 (CAr), 129.3 (vt, CAr), 128.4 (d, 2JCP = 9.73 Hz, CAr), 125.9 (C(perylene)), 121.3 (C(perylene)), 121.7 (C(perylene)), 109.3 (C(perylene)), 62.0 (vt, NCH2P). 31P NMR (242.94 MHz, CD2Cl2): δ 36.92 (dd, 1JPRh = 145.84 Hz, 2JPP = 35.43 Hz, 4P, PPh2), 30.89 (dt, 1JPRh = 118.73 Hz, 2JPP = 35.43 Hz, 2P, PPh3), −144.29 (m, 2P, PF6). HR-MS (HR-FAB+): m/z calcd for [C110H86N4P6Rh2]2+ 927.6705; found 927.6715. Anal. Calcd for [C110H86N4P6Rh2][PF6]: C 61.58; H 4.04; N 2.61. Found: C 61.42; H 4.22; N 2.57. Synthesis of [Rh(C5H5N)]2-iPr-TPHDP (4b). A 100 mg (0.089 mmol, 1 equiv) amount of 2c was stirred together with 62.2 mg (0.176 mmol, 2 equiv) of TlPF6 in an excess of 5 mL of pyridine at room temperature for 1 h. The solution was then filtered over Celite, and the solvent removed to give a dark red solid, which was washed three times with 10 mL of diethyl ether and then dried under vacuum. An 80 mg amount of the product was obtained (60% yield). 1H NMR (600.13 MHz,CD2Cl2): δ 8.65 (d, 3J = 4.92 Hz, 4H, H(perylene)), 7.85 (t, 3J = 7.38 Hz, 2H, HPy), 7.77 (d, 3J = 8.47, 4H, HPy), 7.48 (m, 4H, HPy), 6.75 (d, 3J = 8.74, 4H, H(perylene)), 3.97 (vt, 8H, NCH2P), 2.27 (m, 8H HiPr), 1.33−1.12 (m, 48H, HiPr). 13C NMR/HMBC (150.90 MHz, CD2Cl2): δ 210.8 (C(carbene)) 152.5 (C(perylene)), 137.9 (Cpy), 134.2 (C(perylene)), 130.5 (C(perylene)), 126.2 (C(perylene)), 126.0 (CPy), 121.4 (Cpy), 120.3 (C(perylene)), 108.8 (C(perylene)), 50.7 (vt, NCH2P), 24.6 (vt, CiPr), 18.9 (vt, CiPr), 18.3 (CiPr). The carbene carbon atom could not be unambiguously identified due to poor signal-to-noise. 31P NMR (242.94 MHz, CD2Cl2): δ 45.05 (d, 1JPRh = 144.27 PiPr2), −144.43 (m, PF6). HR-MS (HR-FAB+): m/z calcd for [C60H82N6P4Rh2]2+ 608.1825; found 608.1843. Anal. Calcd for [C60H82N6P4Rh2][PF6]: C 47.82; H 5.48; N 5.58. Found: C 47.35; H 5.16; N 5.38.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00049. NMR spectra, IR, UV−vis, and emission spectra (PDF) Additional Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the University of Heidelberg for support of this work. REFERENCES

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