ARTICLE pubs.acs.org/Organometallics
Nonconjugated Dimesitylboryl-Functionalized Phenylpyridines and Their Cyclometalated Platinum(II) Complexes Zachary M. Hudson and Suning Wang* Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6
bS Supporting Information ABSTRACT: To investigate possible through-space charge transfer transitions between a Pt(II) ion and a triarylborane unit, the two new nonconjugated molecules 1 and 2 have been synthesized and fully characterized. Compound 1 has a V-shaped geometry, while 2 has a U-shaped geometry. In 1 a BMes2Ar group and a ppy group (Mes = mesityl, ppy = phenylpyridine) are linked together by a SiPh2 unit, while in 2 these groups are joined together by a 1,8-naphthyl linker. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analyses. Their cyclometalated compounds Pt-1 and Pt-2 with a Pt(acac) unit chelated to the ppy site have been synthesized. Computational and experimental examinations on the photophysical properties of the free ligands and the Pt(II) compounds revealed that the molecular shape and geometry of the molecule have a distinct impact on the fluorescence and phosphorescence of these molecules. Pt-1 is a bright phosphorescent emitter with λem 490 nm and Φ = 66% while Pt-2 is very weakly emissive with λem 567 nm and Φ = ∼0.05%. Anions such as fluoride were found to have no impact on the phosphorescence of these two Pt(II) compounds, thus establishing that phosphorescence of these molecules does not involve a through-space charge transfer transition between the Pt(ppy)(acac) unit and the BMes2Ar unit.
’ INTRODUCTION Optoelectronic materials containing a triarylboron group have been the subject of considerable recent research due to the electron-accepting ability of the boron center. When accompanied by appropriate electron donors such as amines, the triarylboron center promotes intense donoracceptor charge transfer luminescence in π-conjugated materials.1 The empty pπ orbital of triarylboranes stabilizes the formation of radical anions and has led to their successful use in nonlinear optical materials2 and as emissive and electron-transport materials in organic light-emitting diodes (OLEDs).3 Triarylboranes have also been extensively investigated as chemical sensors for anions. While bulky mesityl groups protect the boron center from most nucleophiles, small anions such as fluoride and cyanide are capable of binding to the boron center despite this steric protection.46 As the empty p orbital on boron typically makes a large contribution to the LUMO of the molecule, this binding event may be observed by colorimetric, luminescent, or electrochemical changes. Luminescent sensing is particularly attractive, as it allows the detection of an analyte with high sensitivity. Directly conjugated donoracceptor boranes typically act as “switch-off” luminescent sensors, as binding of an anion to the boron center blocks the empty p orbital, deactivating any charge-transfer emission. (compound A, Chart 1) We have recently shown, however, that nonconjugated donoracceptor triarylboranes can act as effective “switch-on” sensors, in which binding of an analyte may be clearly observed by a change in luminescence from one color to another.5 For r 2011 American Chemical Society
example, compounds B and C incorporate distinct donor and acceptor chromophores connected by rigid and nonrigid linkers, respectively. In the absence of fluoride, both exhibit throughspace charge transfer as broad green emission. When fluoride is added, this emission readily switches to the blue fluorescence of the arylamine chromophore. More recent research has shown that the triarylboron group is capable of greatly enhancing metal-to-ligand charge transfer (MLCT) in transition-metal compounds, leading to higher luminescent quantum yields and brighter phosphorescent emission.7 In combination with the improved electron-transporting and film-forming properties afforded by the triarylboron group, this enhanced phosphorescence has allowed for the fabrication of OLEDs with exceptional performance.7cf Furthermore, several reports have described the use of organometallic triarylboranes for phosphorescent sensing,6 in which interference from background fluorescence or scattering may be removed by time-gated detection. Despite advances in related organic systems, however, nonconjugated triarylboranes incorporating a metal center as donor have not been widely studied, and little is known about the through-space interaction between metal centers and the boron group. Only one example of such a compound, Pt(N,C-SiBNPA)(SMe2)Ph, is known to date, and this material was found to exhibit simultaneous singlet and triplet dual emission from Received: June 22, 2011 Published: August 05, 2011 4695
dx.doi.org/10.1021/om200539r | Organometallics 2011, 30, 4695–4701
Organometallics
ARTICLE
Chart 1
Scheme 1a
Reagents and conditions: (i) n-BuLi, THF, 78 °C; (ii) FBMes2, 78 °C to room temperature; (iii) 2-(SnBu3)pyridine, Pd(PPh3)4, THF, reflux; (iv) PtCl(DMSO)(acac), NaOAc, THF/MeOH, reflux; (v) ZnCl2, 0 °C, then 1,8-diiodonaphthalene, Pd(PPh3)4, 0 °C to room temperature; (vi) 4-(20 -py)phenylzinc bromide, Pd(PPh3)4, THF, room temperature. a
both chromophores.5c To further investigate these systems, we designed ligands 1 and 2 (Scheme 1) that incorporate a flexible silane and a rigid naphthyl linker for a BMes2Ar unit and a Pt(ppy)(acac) unit (ppy =2-pyridylphenyl), which may readily serve as cyclometalating ligands to a variety of transition-metal atoms. Herein we report the synthesis and photophysical properties of these compounds and their Pt(II) complexes.
’ RESULTS AND DISCUSSION Synthesis. The syntheses of compounds Pt-1 and Pt-2 are shown in Scheme 1. Pt-1 incorporates a silane linker with a high degree of rotational flexibility, while Pt-2 includes a more rigid naphthyl spacer that both decreases the metalboron separation distance and increases the steric congestion of the molecule. Intermediate 1a is prepared by introducing the boryl substituent to bis(p-bromophenyl)diphenylsilane by lithiumhalogen exchange and substitution with FBMes2. Subsequent Stille coupling with the appropriate pyridyl stannane gives 1 in good yield. It should be noted that more common Suzuki coupling reactions should be avoided once the dimesitylboron group is introduced, as the basic conditions required for this reaction can lead to unwanted side products in the presence of Pd catalyst.8 Ligand 2 is most efficiently prepared by synthesis of first the arylboron and phenylpyridine arms of the molecule, followed by their stepwise coupling to 1,8-diiodonaphthalene. This is readily achieved in
both cases by Negishi coupling via organozinc intermediates. The Pt(II) acetylacetonate (acac) complexes of these ligands were prepared under mild conditions on stirring with PtCl(DMSO)(acac) in the presence of NaOAc in refluxing methanol.7c,d,9 The use of acac as an ancillary ligand has several advantages, giving stable complexes that may be isolated in high purity by column chromatography. In addition, the rigidity and high triplet level of the acac ligand minimize its impact on the quantum yield of the phosphorescent phenylpyridine Pt(II) unit.10 Crystal Structures. Single crystals suitable for X-ray diffraction analysis were obtained for the free ligands 1 and 2 by slow evaporation from CH2Cl2/hexanes, while efforts to obtain single crystals of the Pt(II) complexes were unsuccessful. The large difference in steric congestion between ligands 1 and 2 is readily apparent on comparison of these structures (Figure 1). In the crystal structure of 1, the boron and phenylpyridine arms of the molecule show no intramolecular steric interaction, with the shortest separation distance being 9.89 Å from the boron atom to the pyridyl ring. In contrast, in ligand 2 this distance is much shorter (5.55 Å on average for the two independent molecules in the lattice), as shown in Figure 1. The crystal structure of 2 reveals considerable strain, with the naphthyl linker being out of coplanarity by approximately 14° (Figure 2). Though joined by a continuous path of sp2-hybridized atoms, the boron and phenylpyridine arms of 2 show torsion angles of 40.8 and 44.8° with 4696
dx.doi.org/10.1021/om200539r |Organometallics 2011, 30, 4695–4701
Organometallics the naphthyl ring, expected to greatly reduce electronic communication through the linker. The CC bond distances between the phenyl groups and the naphthyl ring are 1.486(4) and 1.490(4) Å, respectively, further supporting this poor conjugation. Molecules of 2 pack in such a manner in the crystal lattice that the BMes2 groups are all on the same side while the pyridylphenyl groups are parallel to each other (Figure 2). Photophysical and Electrochemical Properties. Ligands 1 and 2 both display broad absorptions centered around 325 nm, characteristic of charge transfer from the filled π orbitals of adjacent aryl groups to the empty p orbital on the boron center (Table 1). The molar extinction coefficient of this band in 2 is more than twice as intense as that in 1, owing to the additional contribution from the electron-rich naphthyl ring (Figure 3). Chelation to Pt(II) introduces a distinct low-energy absorption band in both cases, characteristic of MLCT from the Pt(II) center to the phenylpyridine chelate.7 The CV diagrams of both ligands and their Pt(II) complexes are shown in Figure 4. Ligand 2 has a poor solubility in DMF and THF, resulting in a weak reduction peak. Nonetheless, the data show that ligand 1 has a somewhat more positive reduction potential than 2 (by ∼20 mV). This may be attributed to the
ARTICLE
close proximity of the boron center to a relatively electron rich naphthyl and ppy group in 2. The Pt(acac) compounds, however, both have very similar reduction potentials. For Pt-2, two wellresolved reduction peaks are observed, which may be assigned to the reduction of the Pt(ppy) leg and the BMes2 leg, respectively. Using the CV and UVvis data, HOMO and LUMO energies for all compounds have been estimated and provided in Table 2. DFT Calculations. To understand the impact exerted by Pt(II) chelation, we performed DFT calculations at the B3LYP level of theory14 using LANL2DZ as the basis set for Pt and 6-31G* for all other atoms (Figure 5). The computational results show that while both ligands possess a distinct boron-centered LUMO, the LUMOs of the respective Pt complexes are instead centered on the ppy chelate and occur at similar energies, consistent with the CV data. Furthermore, in both cases the energy of the MO based Table 1. Photophysical Properties of All Compoundsa abs λmax (nm) compd
a
Figure 1. Diagrams showing the crystal structures of ligands 1 (left) and 2 (right) with 35% thermal ellipsoids: (red) Si; (pink) B; (blue) N. Important bond lengths (Å) and angles (deg) for 1: SiC(Ph), 1.855(4), 1.868(4); SiC(ppy), 1.871(4); SiC(ArB), 1.863(4); BC, 1.570(5), 1.571(6), 1.572(6); CSiC, 108.36(15), 108.55(18), 109.46(16), 114.20(7), 107.76(16), 108.74(18); CBC, 116.2(3), 120.4(3), 123.4(3). Important bond lengths (Å) and angles (deg) for the two independent molecules of 2: BC, 1.552(4)/1.557(4), 1.581(4)/ 1.581(4), 1.584(4)/1.582(4); CBC, 116.5(2)/117.7(2), 119.0(2)/ 117.7(2), 124.4(2)/124.7(2).
(ε (104 M1 cm1))
λem (nm)
Φb
1
271 (3.31), 285 (2.63),
401
0.21
Pt-1
304 (1.95), 325 (1.32) 262 (4.57), 285 (3.55), 325 (2.67)
494
0.66
2
286 (2.29), 331 (3.41), 400 (0.45)
406
1.0
Pt-2
287 (2.67), 333 (3.86), 413 (0.44)
473
0.005
τP (μs)
6.3 5.7
Obtained at 1.0 105 M in CH2Cl2 at 298 K. b All quantum yields (10%.
Figure 3. UVvis absorption spectra of the boryl ligands and their Pt(acac) compounds in CH2Cl2.
Figure 2. Views of 2: (left) side view showing the bending of the naphthyl ring; (right) diagram showing the orientation and packing of molecules 2 in the crystal lattice. 4697
dx.doi.org/10.1021/om200539r |Organometallics 2011, 30, 4695–4701
Organometallics
ARTICLE
on the empty p orbital on boron has been destabilized considerably. This suggests that Pt(II) chelation has a significant impact on the electronic properties of the BMes2 center, despite the lack of direct conjugation between these two portions of the
Figure 4. Cyclic voltammetry diagrams of the boryl ligands and their Pt(acac) compounds in DMF (with ∼10% THF) with NBu4PF6 as the electrolyte.
Table 2. Electrochemical Properties and Experimental HOMO and LUMO Energiesa compd
E1/2red (V)b
HOMO (eV)
LUMO (eV)
1
2.41
5.84
2.39
Pt-1
2.46
5.21
2.36
2 Pt-2
2.43
5.71
2.37
2.46, 2.67
5.17
2.34
The LUMO energy level was estimated using the first reduction potential, while the HOMO energy level was obtained by using the optical energy gap (absorption edge) and the LUMO value. b Recorded in DMF with NBu4PF6 as the electrolyte, relative to FeCp2+/0. a
molecule. This is in contrast to the effect observed in fully conjugated systems, where it has been shown that metal chelation can substantially improve the electron-accepting ability of triarylboranes by Coulombic and inductive effects.7,11 The HOMO for 1 is localized on the mesityl π orbitals, while that of 2 is localized mostly on the naphthyl ring. Introduction of the metal center is found to have the largest impact on the HOMO energies of these molecules, raising this level by 0.50.7 eV. This results in a clear change in the lowest energy electronic transition for both nonconjugated boranes, from one based on the triarylboron group itself to a transition that is largely based on the metal chelate site. It is possible that the increased electron density of the ppy chelate in the complex increases repulsive interactions between the two different arms, thus increasing the π* energy level of the triarylboron unit. Luminescence. Ligands 1 and 2 both show high-energy purple fluorescence upon irradiation with UV light, with little change in emission maximum despite considerable differences in structure (Figure 6). However, while 1 displays only a moderate fluorescence quantum yield of 0.21, that of 2 is near unity, consistent with previously reported naphthyl-functionalized triarylboranes.12 Despite the similarities in the fluorescence of the ligands, the phosphorescent properties of Pt-1 and Pt-2 are dramatically different. Both display long-lived phosphorescent emission, with decay lifetimes of 6.3 and 5.7 μs, respectively. Pt-1 shows bright blue-green emission in the solid state and solution (λem 490 nm), similar to that of Pt(ppy)(acac),10 with a remarkable quantum yield of 0.66 in degassed CH2Cl2. The vibrational features clearly visible in the emission spectrum of Pt-1 indicate that this phosphorescence may be attributed to a mixture of ligand-centered (LC) and MLCT excited states. Pt-2, however, exhibits only very weak, broad orange phosphorescence (λem 567 nm), with a quantum yield of approximately 0.005, attributable to the considerable strain in this molecule. This lowenergy emission likely has contributions from through-space intramolecular charge transfer from the Pt(ppy)(acac) unit to the
Figure 5. Molecular orbital surfaces and energies obtained from DFT calculations. 4698
dx.doi.org/10.1021/om200539r |Organometallics 2011, 30, 4695–4701
Organometallics
ARTICLE
Figure 6. Excitation spectra (dashed lines) and emission spectra (solid lines) for 1 and 2 (left) and their Pt(II) complexes (right), obtained at 105 M in CH2Cl2 at 298 K.
BMes2Ph unit, since there are considerable contributions from the BMesPh unit at the LUMO level of Pt-2 (Figure 5), while no similar contributions are present for Pt-1. The distinct phosphorescence of the two Pt(II) complexes illustrates the importance of donoracceptor geometry on modulating phosphorescent color and efficiency. The photophysical properties of all compounds are summarized in Table 1. To further explore the electronic structure of these nonconjugated molecules, we performed luminescent titration experiments using NBu4F (TBAF) in CH2Cl2. Both boryl ligands 1 and 2 display a fluorescent quenching response with the addition of fluoride (see the Supporting Information). This suggests that the fluorescence of these two molecules does not involve through-space charge transfer from the ppy group to the boron center, as such transitions are typically characterized by activation of a higher energy emission band based on the donor group once fluoride blocks the boron site.5 This is also in agreement with DFT results, which suggest that the HOMO and LUMO of both molecules are based on the boron leg. In contrast to diarylamino groups, which are excellent electron donors and promote through-space intramolecular charge transfer in nonconjugated systems,5a,b the ppy ligand cannot serve as an appropriate electron donor in molecules 1 and 2. In the case of 1, the fluorescent emission is completely quenched on saturation with F, while 2 experiences only ∼60% emission quenching. This is consistent with titrations of both molecules in absorption mode. Compound 1 displays complete quenching of the 325 nm absorption band, indicating that the boryl unit is the sole contributor to this electronic transition. Compound 2, however, only shows partial quenching of the 325 nm band, confirming that the naphthyl linker plays a role in the fluorescent emission of the molecule. When metal complexes Pt-1 and Pt-2 are titrated with fluoride, however, both show partial quenching of the broad absorption at 325 nm, while the MLCT band is in both cases totally unaffected (see the Supporting Information). This is in contrast to directly conjugated systems, suggesting that the presence of a spatially proximate but electronically separated boryl acceptor does not perturb electronic excited states at lower energy elsewhere in the molecule. Indeed, the low-energy phosphorescence displayed by Pt-1 and Pt-2 is totally unaffected by saturation of the BMes2 binding site with fluoride. These results are quite unexpected, and to our knowledge this is the first case in which the phosphorescence of BMes2-containing metal compounds could not be affected by anion binding. These results also support that the phosphorescence of both Pt-1 and Pt-2 is
mostly localized on the Pt(ppy)(acac) portion of the molecule, consistent with DFT calculations which show the HOMO and LUMO located on this arm of the complex in both cases. The phosphorescent response of Pt-1 toward fluoride ions is in sharp contrast with that of the closely related V-shaped molecule Pt(N, C-Si-BNPA)(SMe2)Ph we reported recently,5c where a BMes2Ar group and a Pt(N,C-NPA)(SMe2)Ph unit (NPA = N-(20 pyridyl)-7-azaindole) are linked together by a SiPh2 group. Pt(N,C-Si-BNPA)(SMe2)Ph displays simultaneous singlet and triplet dual emission originating from the boryl and Pt arms of the molecule, respectively, and has a distinct response to the addition of fluoride ions.5c Compounds Pt-1 and Pt-2, however, demonstrate that the dual emissive properties of a nonconjugated system are highly dependent on the nature and the energetic state of the chelate group around the metal center.
’ CONCLUSIONS A pair of nonconjugated dimesitylboron-containing Pt(II) phosphors have been achieved, with remarkably different properties based on the nature of the linker. The V-shaped Pt-1 shows bright green phosphorescence at room temperature, while the U-shaped Pt-2 is almost nonemissive under ambient conditions, indicating that the molecular geometry and shape have a significant impact on the phosphorescence of BMes2-functionalized Pt(II) compounds. With an improved understanding of their synthesis and photophysical properties, future studies will examine the impact of the spatially proximate Lewis acidic boron center on the reactivity of Pt(II) complexes. ’ EXPERIMENTAL SECTION General Considerations. All reactions were carried out under a nitrogen atmosphere. Reagents were purchased from Aldrich Chemical Co. and used without further purification. Thin-layer and flash chromatography were performed on silica gel. 1H and 13C NMR spectra were recorded on Bruker Avance 400, 500, and 600 MHz spectrometers. Deuterated solvents were purchased from Cambridge Isotopes and used without further drying. Excitation and emission spectra were recorded using a Photon Technologies International QuantaMaster Model 2 spectrometer. UVvisible absorbance spectra were recorded using a Varian Cary 50 UVvisible absorbance spectrophotometer. Cyclic voltammetry experiments were performed using a BAS CV-50W analyzer with a scan rate of 0.21.0 V/s using 1 mg of sample in 0.5 mL of dry DMF. The electrochemical cell was a standard threecompartment cell composed of a Pt working electrode, a Pt auxiliary electrode, and an Ag/AgCl reference electrode. CV measurements were 4699
dx.doi.org/10.1021/om200539r |Organometallics 2011, 30, 4695–4701
Organometallics carried out at room temperature with 0.1 M NBu4PF6 as the supporting electrolyte, with ferrocene/ferrocenium as internal standard (E° = 0.55 V). Solution quantum yields were calculated using optically dilute solutions (A ≈ 0.1), using anthracene as the standard for 1 and 2 and Ir(ppy)313 for Pt-1 and Pt-2. Elemental analyses were performed by Canadian Microanalytical Service Ltd., Delta, British Columbia, Canada. Molecular orbital and molecular geometry calculations were performed using the Gaussian 03 program suite. DFT calculations were performed at the B3LYP level of theory14 using LANL2DZ as the basis set for Pt and 6-31G* for all other atoms. The synthesis of 1a,5b 2a,5b 2-(40 -bromophenyl)pyridine,7d and PtCl(DMSO)(acac)9 have been reported previously. Synthesis of 1. In a 50 mL Schlenk flask with a stir bar and condenser were added 1a (150 mg, 0.23 mmol), Pd(PPh3)4 (13.1 mg, 0.011 mmol), and 30 mL of degassed THF. 2-(Tributylstannyl)pyridine (0.35 mL, 0.91 mmol) was then added via syringe, and the mixture was heated at reflux for 48 h. The solvent was removed under reduced pressure and the residue purified on silica (2/1 hexanes/CH2Cl2 as eluent) to give 76 mg of 1 as a white solid (51% yield). 1H NMR (400 MHz, CDCl3): δ 8.72 (d, J = 4.7 Hz, 1H, Py), 8.00 (d, J = 8.1 Hz, 2H, C6H4), 7.80 (t, J = 7.6 Hz, 1H, Py), 7.76 (d, J = 7.7 Hz, 1H, Py), 7.68 (d, J = 8.1 Hz, 2H, C6H4), 7.627.56 (m, 6H, Ph, C6H4), 7.48 (d, J = 7.8 Hz, 2H, C6H4), 7.44 (t, J = 7.3 Hz, 2H, Ph), 7.37 (t, J = 7.4 Hz, 4H, Ph), 7.28 (dd, J = 6.5 Hz, J = 4.7 Hz, 1H, Py), 6.80 (s, 4H, Mes), 2.29 (s, 6H, Mes), 2.01 (s, 12H, Mes) ppm. 13C NMR (100 MHz, CDCl3): δ 156.9, 149.2, 147.2, 141.7, 140.8, 139.7, 138.7, 138.2, 137.4, 136.9, 135.8, 135.5, 135.0, 134.0, 133.8, 129.7, 128.1, 127.9, 126.4, 122.5, 121.0, 23.4, 21.2 ppm. HRMS: m/z calcd for C47H44BNSi 661.3345, found 661.3347. Synthesis of Pt-1. In a 50 mL Schlenk flask with a stir bar and condenser were added 1 (70 mg, 0.11 mmol), PtCl(DMSO)(acac) (43 mg, 0.11 mmol), NaOAc (8.7 mg, 0.11 mmol), and 20 mL of degassed 1/1 THF/MeOH. The mixture was heated at reflux for 3 days, and then the solvent was removed under reduced pressure and the residue purified on silica (1/1 hexanes/CH2Cl2 as eluent) to give 38 mg of Pt-1 as a yellow solid (38% yield). 1H NMR (400 MHz, C6D6): δ 9.06 (d, sat, J = 5.4 Hz, 1H, Py), 8.67 Hz (s, sat, 1H, PyPh), 7.95 (d, J = 7.5 Hz, 2H, C6H4), 7.937.89 (m, 4H), 7.69 (d, J = 7.6 Hz, 2H, C6H4), 7.63 (d, J = 7.6 Hz, 1H, PyPh), 7.347.24 (m, 6H), 6.91 (d, J = 7.8 Hz, 1H, PyPh), 6.86 (s, 4H, Mes), 6.83 (t, J = 7.2 Hz, 1H, Py), 6.23 (t, J = 7.2 Hz, 1H, Py), 5.25 (s, 1H, acac), 2.27 (s, 6H, Mes), 2.21 (s, 12H, Mes), 1.79 (s, 3H, acac), 1.63 (s, 3H, acac) ppm. 13C NMR (100 MHz, C6D6): δ 185.7, 184.7, 169.0, 147.9, 147.7, 146.7, 142.7, 141.4, 140.6, 140.3, 140.2, 139.1, 138.0, 137.5, 137.1, 136.0, 135.9, 135.6, 132.1, 130.0, 129.1, 128.3, 122.9, 121.4, 118.8, 102.9, 28.5, 27.3, 24.1, 21.7 ppm. Anal. Calcd for C52H50BNO2PtSi: C, 65.40; H, 5.28; N, 1.47. Found: C, 64.30; H, 4.80; N, 1.43. The low carbon content may be caused by solvent molecules (CH2 Cl 2) trapped in the solid or incomplete combustion of boron. The purity of the sample was verified by a 1 H NMR spectrum (see the Supporting Information, Figure S2). Synthesis of 2. In a 50 mL Schlenk flask with a stir bar was added 2-(40 -bromophenyl)pyridine (181 mg, 0.77 mmol) and 30 mL of dry, degassed THF. The solution was cooled to 78 °C, and then n-BuLi (0.53 mL, 0.85 mmol, 1.6 M in hexanes) was added dropwise via syringe. After the mixture was stirred for 1 h, anhydrous ZnCl2 (137 mg, 1.01 mmol) was added. The mixture was stirred for 1 h at 78 °C and then 1 h at 0 °C, and then Pd(PPh3)4 (45 mg, 0.39 mmol) and 2a (300 mg, 0.52 mmol) were added. The mixture was stirred for 1 h at 0 °C and then slowly warmed to room temperature and stirred for 48 h. After removal of the solvent under reduced pressure, the residue was purified on silica (30/1 hexanes/EtOAc as eluent) to give 253 mg of 2 as a white solid (81% yield). 1H NMR (500 MHz, CDCl3): δ 8.66 (d, J = 4.1 Hz, 1H, Py), 7.95 (d, J = 7.9 Hz, 2H, C6H4), 7.68 (t, J = 7.6 Hz, 1H, Py), 7.64 (d, J = 8.3 Hz, 2H, C6H4), 7.59 (d, J = 6.1 Hz, 2H, naph), 7.56 (d, J = 7.2 Hz, 1H, Py), 7.45 (t, J = 7.8 Hz, 2H, naph), 7.237.14 (m, 5H, Py,
ARTICLE
naph, C6H4), 7.09 (d, J = 7.9 Hz, 2H, C6H4), 6.72 (s, 4H, Mes), 2.27 (s, 6H, Mes), 1.75 (s, 12H, Mes) ppm. 13C NMR (125 MHz, CDCl3): δ 157.0, 149.5, 147.6, 144.1, 141.5, 140.6, 140.2, 139.9, 138.1, 136.6, 136.5, 136.3, 135.6, 131.6, 131.2, 130.0, 129.2, 129.0, 128.8, 128.6, 127.9, 127.9, 125.9, 125.4, 125.2, 121.8, 23.4, 21.1 ppm. HRMS: m/z calcd for C45H40BN 605.3254, found 605.3248. Synthesis of Pt-2. In a 50 mL Schlenk flask with a stir bar and condenser was added 2 (50 mg, 0.083 mmol), PtCl(DMSO)(acac) (34 mg, 0.083 mmol), NaOAc (6.8 mg, 0.083 mmol), and 20 mL of degassed 1/1 THF/MeOH. The mixture was heated at reflux for 3 days, and then the solvent was removed under reduced pressure and the residue purified on silica (2/1 hexanes/CH2Cl2 as eluent) to give 27 mg of Pt-2 as a yellow solid (36% yield). 1H NMR (500 MHz, CDCl3): δ 9.09 (d, J = 5.4 Hz, 1H, Py), 8.04 (s, 1H, PyPh), 7.72 (d, J = 8.5 Hz, 1H, naph), 7.71 (d, J = 8.5 Hz, 1H, naph) 7.68 (d, J = 6.6 Hz, 1H, PyPh), 7.54 (d, J = 7.7 Hz, 1H, naph), 7.43 (d, J = 7.7 Hz, 1H, Naph), 7.41 (d, J = 6.6 Hz, 1H, PyPh), 7.367.28 (m, 4H), 6.87 (t, J = 7.4 Hz, 1H, Py), 6.856.79 (m, 3H), 6.73 (s, 4H), 6.26 (t, J = 6.2 Hz, 1H, Py), 5.11 (s, 1H, acac), 2.15 (s, 6H, Mes), 2.01 (s, 12H, Mes), 1.69 (s, 3H, acac), 1.53 (s, 3H, acac) ppm. 13C NMR (125 MHz, C6D6): δ 185.7, 184.7, 169.0, 147.9, 147.7, 146.7, 142.7, 141.4, 140.6, 140.2, 139.1, 138.0, 137.5, 137.1, 136.0, 135.6, 132.1, 130.0, 129.1, 122.9, 121.4, 118.8, 102.9, 28.5, 27.3, 24.1, 21.7 ppm (several quaternary carbons could not be detected due to poor solubility). Anal. Calcd for C50H46BNO2Pt: C, 66.82; H, 5.16; N, 1.56. Found: C, 66.62; H, 5.31; N, 1.46. X-ray Crystallographic Analysis. Single crystals of 1 and 2 were mounted on glass fibers and were collected on a Bruker Apex II singlecrystal X-ray diffractometer with graphite-monochromated Mo KR radiation, operating at 50 kV and 30 mA and at 180 K. Data were processed on a PC with the aid of the Bruker SHELXTL software package (version 5.10)15 and corrected for absorption effects. All nonhydrogen atoms were refined anisotropically. Complete crystal structure data can be found in the Supporting Information. The crystal data of 1 and 2 have been deposited at the Cambridge Crystallographic Data Center (CCDC No. 830933 and 830934).
’ ASSOCIATED CONTENT
bS
Supporting Information. Figures, tables, and CIF files giving electrochemical data, fluoride titration data, and complete crystal structure data. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT We thank the Natural Sciences and Engineering Research Council for financial support. ’ REFERENCES (1) For recent reviews, see: (a) Entwistle, C. D.; Marder, T. B. Angew. Chem., Int. Ed. 2002, 41, 2927. (b) J€akle, F. Coord. Chem. Rev. 2006, 250, 1107. (c) Hudson, Z. M.; Wang, S. Acc. Chem. Res. 2009, 42, 1584. (d) J€akle, F. Chem. Rev. 2010, 110, 3985. (e) Wade, C. R.; Broomsgrove, A. E. J.; Aldridge, S.; Gabbaï, F. P. Chem. Rev. 2010, 110, 3958. (2) (a) Yuan, Z.; Taylor, N. J.; Marder, T. B.; Williams, I. D.; Kurtz, S. K.; Cheng, L. T. J. Chem. Soc., Chem. Commun. 1990, 1489. (b) Lequan, M.; Lequan, R. M.; Ching, K. C. J. Mater. Chem. 1991, 1, 997. (c) Entwistle, C. D.; Marder, T. B. Chem. Mater. 2004, 16, 4574. (d) Liu, 4700
dx.doi.org/10.1021/om200539r |Organometallics 2011, 30, 4695–4701
Organometallics Z. Q.; Fang, Q.; Cao, D. X.; Wang, D.; Xu, G. B. Org. Lett. 2004, 6, 2933. (e) Yuan, Z.; Entwistle, C. D.; Collings, J. C.; Albesa-Jove, D.; Batsanov, A. S.; Howard, J. A. K.; Kaiser, H. M.; Kaufmann, D. E.; Poon, S.-Y.; Wong, W.-Y.; Jardin, C.; Fathallah, S.; Boucekkine, A.; Halet, J.-F.; Taylor, N. J.; Marder, T. B. Chem. Eur. J. 2006, 12, 2758. (f) Stahl, R.; Lambert, C.; Kaiser, C.; Wortmann, R.; Jakober, R. Chem. Eur. J. 2006, 12, 2358. (g) Tao, L. M.; Guo, Y. H.; Huang, X. M.; Wang, C. K. Chem. Phys. Lett. 2006, 425, 10. (h) Lequan, M.; Collings, J. C.; Poon, S. Y.; Le Droumaguet, C.; Charlot, M.; Katan, C.; Palsson, L. O.; Beeby, A.; Mosely, J. A.; Kaiser, H. M.; Kaufmann, D. E.; Wong, W.-Y.; BlanchardDesce, M.; Marder, T. B. Chem. Eur. J. 2009, 15, 198. and references therein. (i) Entwistle, C. D.; Collings, J. C.; Steffen, A.; Palsson, L.-O.; Beeby, A.; Albesa-Jove, D.; Burke, J. M.; Batsanov, A. S.; Howard, J. A. K.; Mosely, J. A.; Poon, S.-Y.; Wong, W.-Y.; Ibersiene, F.; Fathallah, S.; Boucekkine, A.; Halet, J.-F.; Marder, T. B. J. Mater. Chem. 2009, 19, 7532. (3) (a) Noda, T.; Shirota, Y. J. Am. Chem. Soc. 1998, 120, 9714. (b) Shirota, Y. J. Mater. Chem. 2005, 15, 75. (c) Noda, T.; Ogawa, H.; Shirota, Y. Adv. Mater. 1999, 11, 283. (d) Shirota, Y.; Kinoshita, M.; Noda, T.; Okumoto, K.; Ohara, T. J. Am. Chem. Soc. 2000, 122, 11021. (e) Jia, W. L.; Bai, D. R.; McCormick, T.; Liu, Q. D.; Motala, M.; Wang, R.; Seward, C.; Tao, Y.; Wang, S. Chem. Eur. J. 2004, 10, 994. (f) Jia, W. L.; Feng, X. D.; Bai, D. R.; Lu, Z. H.; Wang, S.; Vamvounis, G. Chem. Mater. 2005, 17, 164. (g) Li, F. H.; Jia, W. L.; Wang, S.; Zhao, Y. Q.; Lu, Z. H. J. Appl. Phys. 2008, 103, 034509/1. (4) For representative examples, see: (a) Yamaguchi, S.; Shirasaka, T.; Akiyama, S.; Tamao, K. J. Am. Chem. Soc. 2002, 124, 8816. (b) Sole, S.; Gabbaï, F. P. Chem. Commun. 2004, 1284. (c) Melaïmi, M.; Gabbaï, F. P. J. Am. Chem. Soc. 2005, 127, 9680. (d) Chiu, C. W.; Gabbaï, F. P. J. Am. Chem. Soc. 2006, 128, 14248. (e) Lee, M. H.; Gabbaï, F. P. Inorg. Chem. 2007, 46, 8132. (f) Hudnall, T. W.; Gabbaï, F. P. J. Am. Chem. Soc. 2007, 129, 11978. (g) Hudnall, T. W.; Kim, Y.-M.; Bebbington, M. W. P.; Bourissou, D.; Gabbaï, F. P. J. Am. Chem. Soc. 2008, 130, 10890. (h) Parab, K.; Venkatasubbaiah, K.; J€akle, F. J. Am. Chem. Soc. 2006, 128, 12879. (i) Zhou, G.; Baumgarten, M.; M€ullen, K. J. Am. Chem. Soc. 2008, 130, 12477. (j) Broomsgrove, A. E. J.; Addy, D. A.; Bresner, C.; Fallis, I. A.; Thompson, A. L.; Aldridge, S. Chem. Eur. J. 2008, 14, 7525. (5) (a) Liu, X. Y.; Bai, D. R.; Wang, S. Angew. Chem., Int. Ed. 2006, 45, 5475. (b) Bai, D. R.; Liu, X. Y.; Wang, S. Chem. Eur. J. 2007, 13, 5713. (c) Hudson, Z. M.; Zhao, S. B.; Wang, S. Chem. Eur. J. 2009, 15, 6081. (6) (a) Sun, Y.; Wang, S. Inorg. Chem. 2009, 48, 3755. (b) Sun, Y.; Wang, S. Inorg. Chem. 2010, 49, 4394. (c) Zhao, Q.; Li, F. Y.; Liu, S. J.; Yu, M. X.; Liu, Z. Q.; Yi, T.; Huang, C. H. Inorg. Chem. 2008, 47, 9256. (d) Lam, S. T.; Zhu, N.; Yam, V. W. W. Inorg. Chem. 2009, 48, 9664. (e) You, Y.; Park, S. Y. Dalton Trans. 2009, 1267. (f) Day, J. K.; Bresner, C.; Coombs, N. D.; Fallis, I. A.; Ooi, L. L.; Aldridge, S. Inorg. Chem. 2008, 47, 793. (g) Xu, W.-J.; Liu, S.-J.; Zhao, X.-Y.; Sun, S.; Cheng, S.; Ma, T.-C.; Sun, H.-B.; Zhao, Q.; Huang, W. Chem. Eur. J. 2010, 16, 7125. (7) (a) Sakuda, E.; Funahashi, A.; Kitamura, N. Inorg. Chem. 2006, 45, 10670. (b) Zhao, S. B.; McCormick, T.; Wang, S. Inorg. Chem. 2007, 46, 10965. (c) Zhou, G. J.; Ho, C. L.; Wong, W. Y.; Wang, Q.; Ma, D. G.; Wang, L. X.; Lin, Z. Y.; Marder, T. B.; Beeby, A. Adv. Funct. Mater. 2008, 18, 499. (d) Hudson, Z. M.; Sun, C.; Helander, M. G.; Amarne, H.; Lu, Z. H.; Wang, S. Adv. Funct. Mater. 2010, 20, 3426. (e) Hudson, Z. M.; Helander, M. G.; Lu, Z. H.; Wang, S. Chem. Commun. 2011, 47, 755. (f) Wang, Z.-B; Helander, M. G.; Hudson, Z. M.; Wang, S.; Lu, Z.-H. Appl. Phys. Lett. 2011, 98, 213301. (8) Wang, N; Hudson, Z. M.; Wang, S. Organometallics 2010, 29, 4007. (9) Crespo, M.; Anderson, C. M.; Tanski, J. M. Can. J. Chem. 2009, 87, 80. (10) Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba, I.; Bau, R.; Thompson, M. E. Inorg. Chem. 2002, 41, 3055. (11) (a) Sun, Y.; Ross, N.; Zhao, S. B.; Huszarik, K.; Jia, W. L.; Wang, R. Y.; Wang, S. J. Am. Chem. Soc. 2007, 129, 7510. (b) Wade, C. R.; Gabbaï, F. P. Inorg. Chem. 2010, 49, 714.
ARTICLE
(12) Zhao, S. B.; Wucher, P.; Hudson, Z. M.; McCormick, T. M.; Liu, X. Y.; Wang, S.; Feng, X. D.; Lu, Z. H. Organometallics 2008, 27, 6446. (13) Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.; Goddard, W. A., III; Thompson, M. E. J. Am. Chem. Soc. 2009, 131, 9813. (14) Frisch, M. J., et al. Gaussian 03, Revision C.02; Gaussian, Inc., Wallingford, CT, 2004. (15) SHELXTL Version 6.14, Bruker AXS, Madison, WI, 2000 2003.
4701
dx.doi.org/10.1021/om200539r |Organometallics 2011, 30, 4695–4701
