Syntheses of Arylphosphonium Salts from Cyclotrimerization of

Oct 30, 2014 - ABSTRACT: The synthesis of polyaryl phosphonium salts by cyclotrimerization of aryl alkynes is induced by a stoichio- metric amount of ...
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Syntheses of Arylphosphonium Salts from Cyclotrimerization of Terminal Aryl Alknyes by a Ruthenium Pentadienyl Complex and Revisiting the Catalytic Dimerization Chi-Ren Chen and Ying-Chih Lin* Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China S Supporting Information *

ABSTRACT: The synthesis of polyaryl phosphonium salts by cyclotrimerization of aryl alkynes is induced by a stoichiometric amount of the ruthenium η5-pentadienyl complex (η5C5H7)(PPh3)2RuCl (1). With only 1 mol % quantity, complex 1 efficiently catalyzed the dimerization of aryl alkynes at room temperature to afford the corresponding (Z)-1,4-diarylbut-1en-3-yne derivatives as the major products.

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which displayed a singlet resonance at δ 25.5 in the 31P NMR spectrum in low yield and was not fully characterized. Our product formed in the presence of KPF6 shows a slightly different resonance at δ 23.0 and displays a set of peaks at δ −150 attributed to PF6−. The previously reported complex is believed to have a chloride counterion, instead of PF6−, thus showing slightly different 31P NMR data.5 The structure of our brown powder has been fully characterized by a single-crystal X-ray diffraction analysis as the polyaryl phosphonium salt 6a, resulting from addition of PPh3 to the trimerization product of 2a (see Figure S1 in the Supporting Information). Several aryl phosphonium salts (APSs) were reported recently to display the ability to associate with DNA.6 Since small molecules that can interact with DNA have been intensely investigated as potential therapeutics for ailments as diverse as cancer, psychosis, and malaria,7 the biological activity of APSs has also been extensively studied.8−11 Conventionally, APS compounds have been synthesized by the reaction of phenyl halides with PPh3 and 50 mol % of anhydrous NiCl2 at 200 °C after aqueous acidic workup and recrystallization from THF.12 Our strategy provides an alternative method under much milder conditions. To extend the scope of the reaction, different arylalkynes were then tested (eq 1), and the results are

INTRODUCTION Research over several decades on transition-metal pentadienyl compounds has revealed significant differences in the steric and electronic properties between the η5-pentadienyl (C5H7) and η5-cyclopentadienyl (C5H5 or Cp) ligands in transition-metal compounds.1 The two ligands are isoelectronic; however, the C5H7 ligand (cone angle 180°),2 which is both a better δ backbonding acceptor and a better σ donor than the Cp ligand,1 is also sterically more demanding than the Cp ligand (cone angle 145°).3 Calculations predict that η5 to η3 conversions in the C5H7 ligand should be easier than that in a C5H5 ligand.1 These differences among C5H7, Cp, and indenyl (C9H7) ligands are expected to influence various properties of their compounds. The potential ring slippage from η5 to η3 in the C5H7 ligand that may possibly create novel catalytic reactivity in ruthenium metal complexes has been investigated.4 Dimerization of a terminal aryl alkyne catalyzed by [Ru]-Cl (1, [Ru] = (η5C5H7)(PPh3)2Ru) concomitantly giving an unidentified brown powder was disclosed in 2007.5 Aiming at understanding the chemistry of ruthenium pentadienyl species derived from alkyne, we explore the reactions of arylacetylene with 1. In this paper, we report a practical and switchable reaction system using either a stoichiometric or a catalytic quantity of 1, leading either to the synthesis of polyaryl phosphonium salts via cyclotrimerization or to dimerization of aryl alkynes under mild condition, respectively.

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RESULTS AND DISCUSSION Trimerization. Treatment of phenylacetylene (2a) with a stoichiometric quantity of 1 affords no ruthenium acetylide or vinylidene complexes which are generally formed from the reaction of the corresponding (η5-C5H5)(PPh3)2RuCl complex. Instead, the reaction of 2a with 1 and KPF6, both in stoichiometric quantities, gives a brown powder as the major product. The previously reported catalytic dimerization of 2a by 1 without any additive5 revealed a similar brown powder © 2014 American Chemical Society

given in Table 1. For aryl alkynes 2c,d, with methyl substituents (entries 2 and 3), the same relatively high loadings of the metal complex were employed for the synthesis of APSs, affording products 6c,d in 65−67% yields. Similar procedures were used Received: July 21, 2014 Published: October 30, 2014 6408

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Table 1. Arylphosphonium Saltsa entry 1 2 3 4 5 6

R C6H5 (2a) 3-MeC6H4 (2c) 4-MeC6H4 (2d) 4-MeOC6H4 (2e) 4-BrC6H4 (2i) 4-ClC6H4 (2h)

Table 2. Optimization of Dimerization of 2a product 6a 6c 6d 6e 6i 6h

yield (%) entry

b

63 67b 65b 59c 66c 68c

a c

Conditions: 2:1 = 3:1, THF, 24 h, room temperature. bIsolated yield. NMR yield in the mixture.

for aryl alkynes 2i,h, with halide substituents (entries 5 and 6), and the 31P NMR data as well as mass spectrum of the mixture clearly indicate the formation of APSs 6i,h in moderate yield with phosphine oxide as a minor side product. Unfortunately, it is difficult to purify 6i,h from the crude mixtures. Dimerization. Following the previously reported dimerization5 in C6H6, we carries out the dimerization reaction of 2a using a catalytic amount of 1 in THF. The reaction at room temperature for 24 h resulted in formation of the head-to-head dimer (Z)-1,4-diphenyl-1-buten-3-yne (4a) as the major product, with a small amount of the E isomer 3a (eq 2). The total yield was improved significantly by the use of THF.5 APS in approximately 1−3% yield was again found after each catalytic reaction.

cat. loading (mol %)

1 2 3 4c 5 6d 7e 8f 9 10 11 12 13

10 5 1 1

14 15 16 17 18

1 1 1 1 1

1 1 1 1 1 1 1 1

solvent THF THF THF THF THF THF THF THF toluene CH2Cl2 MeOH acetone diethyl ether 1,4-dioxane hexane NEt3 MeCN pyridine

product ratioa (3a:4a)

isolated yield (%)b

20:80 18:82 14:86 25:75 n.d. n.d. 20:80 14:86 14:86 20:80 21:79 9:91 10:90

70 73 78 20 n.d. n.d. 30 54 36 36 36 61 63

40:52 29:71 52:48

trace trace trace n.d. n.d.

a Determined by 1H NMR analysis. bIsolated yield. cWith 2 mol % of PPh3. dCpRu(PPh3)2Cl was used instead of 1. eRu(PPh3)3Cl2 was used instead of 1. fReaction at 50 °C.

the phosphine-rich complex Ru(PPh3)3Cl2 (entry 7) did not effectively promote the dimerization of aryl alkynes. Upon heating, formation of the enyne product diminished significantly (entry 8). Dimerization reactions in different solvents (entries 3 and 9−18) showed that oxygen-containing solvents such as THF, diethyl ether, and acetone are better solvents than nitrogen-containing solvents. O-containing solvents are known to have relatively weaker coordinating power than the Ncontaining solvents.27 These results possibly indicate that the process could be assisted by the weak coordination between a solvent molecule and the metal center to stabilize the active intermediate. On comparison to previously reported reactions using other metal complexes,24c,g,28 it is quite significant that our reaction gave the Z isomer as the major product. Studies on the scope of the catalytic system with the optimized conditions have been performed on various substituted aryl alkynes employing 1 (eq 3). Because each substrate displays a different activity, catalyst loadings were tuned to afford the optimal results shown in Table 3.

This catalytic dimerization process of terminal alkynes is an attractive route for the preparation of 1,4-disubstituted enynes, which are important and versatile building blocks in organic synthesis.14 These enynes, easily derived from aryl alkynes, are key units in naturally occurring compounds15 and in organic materials.16 Mild dimerization conditions are highly desirable for extending the application profile of this atom-economical reaction. In past decades a number of metal complexes of Pd,17 Ni,17i Al,18 Fe,19 Ir,20 Au,21 Re,22 Rh,23 Ru,24 and lanthanide25 have also been demonstrated to catalyze alkyne dimerization efficiently. However, a mixture of different regio- and stereoisomeric enynes was obtained in common cases. A selective Pd-catalyzed head-to-tail dimerization of terminal alkynes toward 1,3-enynes has been developed by Trost.17a,b Previously we reported the dimerization of alkynes catalyzed by a rhodium complex in the presence of MeI, resulting in the formation of (E)-1,3-enynes with excellent stereoselectivity.23c Results to optimize the reaction condition are given in Table 2. A catalyst loading as low as 1 mol % gave better yields and selectivities (entries 1−3) of the desired product. Free PPh3 in a 2 mol % amount in the reaction (entry 4) inhibited the dimerization of alkyne. This result is consistent with a previous study on a comparable ruthenium pentadienyl complex that described facile exchange between free and coordinated phosphine and relatively difficult conversion of the C5H7 ligand from η5 to η3 at room temperature.26 Therefore, this catalytic cycle is likely initiated by loss of a PPh3 ligand, giving a coordinatively unsaturated species. The dimerization did not proceed without Ru catalyst (entry 5). The analogous Cp complex CpRu(PPh3)2Cl (entry 6) and

The results in entries 3 and 4 of Table 3 show that aryl alkynes 2c,d, containing methyl substituents on the aromatic ring, dimerized effectively to produce 4c,d, respectively. For 2b, the lower yield (entry 2) is probably caused by the steric effect. It is worth noting that the assistance of K2CO3 is necessary for the dimerization of 2e to furnish the desired product in 50% yield (entry 5). In contrast, dimerization of 2f, containing an electron-withdrawing trifluoromethyl substituent, gave a poor yield of the dimer and was accompanied by formation of the cyclotrimerization product 1,2,4-(4-CF3C6H4)3C6H3 (5f) in good yield (entry 6). A halide substituent such as 4-bromo or 4-chloro on the aryl ring of the alkynes (entries 8 and 9) could also be tolerated 6409

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Table 3. Product Distributions of Different Alkynes entry

R

cat. loading (mol %)

product ratio (3:4)

1 2 3 4 5c 6 7 8 9

C6H5 (2a) 2-MeC6H4 (2b) 3-MeC6H4 (2c) 4-MeC6H4 (2d) 4-MeOC6H4 (2e) 4-CF3C6H4 (2f) 2-CF3C6H4 (2g) 4-ClC6H4 (2h) 4-BrC6H4 (2i)

1 2 1 1 1 1 2 1 1

14:86 18:82 17:83 17:83 18:76 50:50 20:80 25:75 33:66

Scheme 1. Possible Mechanism for Dimerization and Cyclotrimerization

a

yield (%)b 78 50 62 65 50 35 (63)d 49 60 65

a

Determined by 1H NMR analysis. bIsolated yield. c5 mol % of K2CO3 was added. dThe isolated yield of the 1,2,4-trisubstituted arene 5f (Scheme 1) is given in parentheses.

without greatly affecting the yield. The results in entries 2 and 7 seem to indicate that the steric effect affects the yields of the desired product more than the electronic effect. Thus, for substrates with bulkier groups, such as the cyclohexyl ring, 4biphenyl, or tert-butyl substituents, no dimerization reaction takes place. With regard to the mechanism of dimerization, it is generally agreed that generation of a free vacant site is followed by coordination of the alkyne.4 Studies on a Ru indenyl complex revealed that access of alkyne to the metal center is not at the expense of a coordinated phosphine. One possibility is that this may occur through the classical η5 to η3 shift of the indenyl ligand.4 However, other studies5 indicate that dissociation of PPh3 from the metal center creates the free coordination site. In our study with the η5-C5H7 ligand, it is useful to know whether it occurs through the classical η5 to η3 shift to generate a vacant site or via the dissociation of a PPh3 ligand. The fact that free PPh3 in 2 mol % amount in the reaction (entry 4 in Table 2) inhibits the dimerization of alkyne seems to reveal that dimerization may proceed via dissociation of a coordinated phosphine ligand. Mechanism. The previously recognized mechanistic pathway4 for the dimerization of acetylene involves formation of a complex with both acetylide and vinylidene ligands followed by an intramolecular acetylide migration to the vinylidene αcarbon to form a labile butenynyl complex. In order to properly explain both dimerization and trimerization for the formation of enynes and APSs using 1, a slightly different mechanism is proposed, as shown in Scheme 1. On the basis of the results described above, a plausible reaction pathway is believed to start with metal activation of the terminal alkynyl C−H bond, leading to formation of the acetylide complex A possibly with liberation of HCl.5 Then dissociation of a phosphine ligand generates a vacant site for coordination and subsequent insertion of the alkyne into the Ru−C bond of A, giving the butenynyl complexes B and B′, which contain alkynyl-substituted alkenyl groups.29 Then a formal σ-bond metathesis of the Ru−alkenyl bonds of B and B′ with a free alkyne forms the (Z)- and (E)-enyne products, respectively, and regenerates A. For trimerization, in the presence of KPF6 in a stoichiometric quantity, a second insertion of an alkyne into the Ru−C bond of B′ generates C. Coordination of the CC bond to the Ru metal center induced by dissociation of PPh3, as shown in C, can occur only for B′. Similar coordination is not possible for B after insertion of an alkyne. Therefore, B is not a suitable precursor to

trimerization. The possible coordination of the CC bond to the Ru metal center in C also reduces the basicity of the chelating ligand, thus preventing protonation of the ligand to give the linear dienyne product. Moreover, coordination of the CC bond to the ruthenium also enhances the electrophilic reactivity and promotes the cyclization reaction. Subsequent intramolecular insertion of the coordinated alkyne in C is favored to produce the new Ru−C bond, and this would lead to the formation of the arylruthenium species D after phosphine coordination.29 Finally, reductive elimination30 of the polyaryl organic moiety with the coordinated PPh3 ligand from the metal center of D generates the APS and causes decomposition of the metal complex. In the formation of 5f, protonation of D affords the cyclotrimerization product and regenerates A in the presence of aryl alkyne.29 Under the catalytic conditions in which the aryl alkyne is in great excess, σbond metathesis of B and B′ with protonation rather than insertion of the second aryl alkyne takes place to give the observed enyne products 3 and 4.

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CONCLUSION In summary, a new method has been found for the preparation of polyaryl phosphonium salts (APSs) from terminal aryl alkynes and (η5-C5H7)(PPh3)2RuCl (1). Treatment of an aryl alkyne with 1 and KPF6, both in stoichiometric quantities, gives an APS, whose structure has been confirmed. Complex 1 is also an efficient catalyst for the synthesis of 1,4-disubstituted butenynes in THF from the dimerization of aryl alkynes with a catalyst loading as low as 1−2 mol % under mild conditions, furnishing the (Z)-butenyne as the major product along with a small amount of the E isomer. The steric effect affects the yields of the desired enyne products more than the electronic effect of the substituents. A mechanism consisting of continuous insertion reactions of aryl alkynes into Ru−C bonds is proposed for the formations of enynes and APSs. 6410

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133.2, 134.1, 134.2, 134.8, 134.9, 135.8, 141.3, 141.5, 145.0, 146.1, 146.8, 158.9, 159.0, 160.5; 31P NMR (162.0 MHz, CDCl3) δ 22.8, −144.2 (PF6−); HRMS (ESI) calcd for C48H38O3P (M+) 657.2559, found 657.2543. Compound 6h (68% NMR yield): brown powder; 1H NMR (400 MHz, CDCl3) δ 6.43−6.45 (2H, m), 6.52−6.54 (2H, m), 6.98−7.00 (2H, m), 7.06−7.08 (2H, m), 7.34 (6H, m), 7.58−7.66 (9H, m), 7.72−7.75 (3H, m), 7.91 (1H, m), 8.06 (1H, m); 13C NMR (100 MHz, CDCl3) δ 20.7, 21.1, 21.3, 117.4, 118.3, 118.7, 119.6, 124.0, 126.4, 127.3, 127.5, 127.7, 127.8, 127.9, 128.4, 128.5, 128.7, 129.2, 129.4, 130.0, 130.2, 131.6, 131.9, 132.0, 132.1, 133.9, 134.0, 134.6, 135.8, 137.0, 137.3, 137.9, 138.9, 139.0, 141.5, 141.6, 145.6, 146.6, 146.7; 31P NMR (162.0 MHz, CDCl3) δ 23.2, −144.0 (PF6−); HRMS (ESI) calcd for C42H29Cl3P (M+) 669.1072, found 669.1078. Compound 6i (66% NMR yield): brown powder; 1H NMR (400 MHz, CDCl3) δ 6.37−6.40 (2H, m), 6.66−6.68 (2H, m), 6.92−6.97 (3H, m), 7.27−7.29 (3H, m), 7.41−7.44 (2H, m), 7.48−7.52 (4H, m), 7.59−7.62 (9H, m), 7.73 (3H, m), 7.90 (1H, m); 13C NMR (100 MHz, CDCl3) δ 117.7, 118.5, 119.4, 121.9, 122.6, 123.2, 128.0, 128.4, 128.5, 128.9, 130.3, 130.4, 130.6, 131.1, 131.2, 132.0, 132.2, 132.3, 134.1, 134.2, 134.4, 134.8, 135.9, 137.0, 137.7, 141.2, 141.3, 144.3, 145.4. 31P NMR (162.0 MHz, CDCl3) δ 23.3, −144.0 (PF6−); HRMS (ESI) calcd for C42H29Br3P (M+) 802.9537, found 802.9569. General Procedure for Dimerization of Phenylacetylene by (η5-C5H7)(PPh3)2RuCl. Under a dry nitrogen atmosphere, 1 (7.3 mg, 0.01 mmol) was placed in a reaction vessel. Phenylacetylene (2a; 102.2 mg, 1.0 mmol) in 6 mL of dry THF was transferred to the reaction vessel under nitrogen, and the resulting solution was stirred under a dry nitrogen atmosphere at room temperature for 24 h. The solvent was removed under vacuum, the solid residue was extracted with a small amount of hexane, and the mixture was filtered through a short aluminum oxide pad (1−2 cm), which was washed with hexane until the eluent was colorless. The filtrate was evaporated to dryness and the crude product purified by column chromatography eluted with hexane to give a mixture of 3a and 4a (80.1 mg, 14:86 in 78% total yield). (Z)-1,4-Diphenylbut-1-en-3-yne (4a): 13 yellow liquid; 1H NMR (400 MHz, CDCl3) δ 5.93 (1H, d, J = 11.8 Hz), 6.70 (1H, d, J = 11.8 Hz), 7.30−7.42 (6H, m), 7.48−7.51 (2H, m), 7.93 (2H, d, J = 7.5 Hz); 13C NMR (100 MHz, CDCl3) δ 88.2, 95.8, 107.4, 123.5, 128.3, 128.4, 128.5, 128.6, 128.8, 131.5, 136.6, 138.7. The spectroscopic data of 4b−e are consistent with those in previous literature.13 (Z)-1,4-Bis(p-trifluoromethylphenyl)but-1-en-3-yne (4f): 25a yellow liquid; 1H NMR (400 MHz, CDCl3) δ 6.05 (1 H, d, J = 12.0 Hz), 6.77 (1 H, d, J = 12.0 Hz), 7.55−7.67 (6 H, m), 7.98 (d, J = 8.2 Hz, 2 H); 13 C NMR (100 MHz, CDCl3) δ 89.6, 95.2, 109.4, 123.8, 124.0, 125.2, 125.3, 126.7, 128.8, 130.2, 130.3, 131.6, 138.0, 139.4. The spectroscopic data of 4h,i are consistent with those in previous literature.25a 1,2,4-Tris(p-trifluoromethylphenyl)benzene (5f): 31 1H NMR (400 MHz, CDCl3) δ 7.22−7.28 (4H, m) 7.49−7.53 (5H, m) 7.64 (1H, s), 7.71−7.78 (5H, m); 13C NMR (100 MHz, CDCl3): δ 122.7, 125.2, 125.3, 125.4, 125.9, 127.1, 127.4, 12.9, 130.0, 130.1, 131.0, 131.4, 139.0, 139.9, 143.5, 144.0, 144.3; 19F NMR (470.6 MHz, CDCl3) δ −62.47, −62.48. (Z)-1,4-Bis(o-trifluoromethylphenyl)but-1-en-3-yne (4g): 32 yellow liquid; 1H NMR (400 MHz, CDCl3) δ 6.03 (1H, d, J = 11.8 Hz), 6.91 (1H, d, J = 11.8 Hz), 7.12−7.22 (6H, m), 7.39 (1H, d, J = 7.3 Hz), 8.25−8.27 (1H, m); 13C NMR (100 MHz, CDCl3) δ 91.1, 92.2, 110.4, 121.3, 122.1, 122.8, 124.8, 125.6, 125.7, 125.9, 125.9, 127.5, 127.8, 128.2, 128.2, 130.2, 131.0, 131.3, 131.4, 131.5, 134.3, 135.7.

EXPERIMENTAL SECTION

General Considerations. The manipulations were performed under an atmosphere of dry nitrogen using vacuum line and standard Schlenk techniques. Solvents were dried by standard methods and distilled under nitrogen before use. Hexane and CH2Cl2 were distilled from CaH2, diethyl ether and THF were distilled from sodium benzophenone ketyl, and methanol was distilled from Mg/I2. All reagents were obtained from commercial suppliers and used without further purification. The ruthenium complex (η5-C5H7)(PPh3)2RuCl was prepared by following the method reported in the literature.26 NMR spectra were recorded at room temperature and are reported in units of δ with residual protons in the solvents as a standard. Proton and carbon chemical shifts are referenced to δ 7.26 and 77.1, respectively, in CDCl3. The 31P NMR spectra were measured relative to external 85% phosphoric acid. Both 13C and 31P spectra were proton-decoupled spectra. Electrospray ionization mass spectrometry, elemental analysis, and X-ray diffraction studies were carried out at the Regional Center of Analytical Instrument located at the National Taiwan University. General Procedure for Synthesis of Arylphosphonium Salts by (η5-C5H7)Ru(PPh3)2Cl. Under a dry nitrogen atmosphere, 1 (72.8 mg, 0.1 mmol) and KPF6 (18.4 mg, 0.1 mmol) were placed in a reaction vessel. Phenylacetylene (2a; 31.1 mg, 0.3 mmol) in 6 mL of dry THF was transferred to the reaction vessel under nitrogen, and the resulting solution was stirred at room temperature for 24 h. Then the solvent was removed under vacuum and CH2Cl2 (3 × 5 mL) was used to extract the product. The extract was concentrated to ca. 5 mL and was added to a 100 mL stirred mixture of diethyl ether and hexane (1/ 1) to produce precipitates. This brown powder was collected and dried under vacuum. The powder was further purified by passing through a neutral Al2O3 column with acetone/ether as eluent to give 6a (44.9 mg, 63% yield). Compound 6a: brown powder; 1H NMR (400 MHz, CDCl3) δ 6.46−6.48 (1H, m), 6.58−6.62 (1H, m), 6.82−6.86 (2H, m), 7.02− 7.03 (2H, m), 7.10−7.11 (3H, m), 7.40−7.47 (8H, m), 7.58−7.70 (14H, m), 8.05 (1H, m); 13C NMR (100 MHz, CDCl3) δ 117.5, 118.4, 118.7, 119.6, 127.1, 127.3, 127.6, 127.8, 127.9, 128.8, 129.3, 129.5, 130.3, 130.4, 130.8, 133.7, 133.8, 134.0, 134.1, 134.8, 135.5, 136.0, 138.0, 139.1, 141.7, 141.8, 145.5, 145.6, 146.8, 146.9; 31P NMR (162.0 MHz, CDCl3) δ 23.2, −144.0 (PF6−); HRMS (ESI) calcd for C42H32P (M+) 567.2242, found 567.2332. Anal. Calcd for C42H32F6P2: C, 70.79; H, 4.53. Found: C, 70.42; H, 4.46. Compound 6c (67% yield): brown powder; 1H NMR (400 MHz, CDCl3) δ 1.74 (3H, s), 2.17 (3H, s), 2.37 (3H, s), 6.52−6.56 (1H, m), 6.96−7.00 (2H, m), 7.21−7.23 (2H, m), 7.30−7.32 (2H, m), 7.46− 7.77 (21H, m), 8.03 (1H, m); 13C NMR (100 MHz, CDCl3) δ 20.7, 21.1, 21.3, 117.4, 118.3, 118.7, 119.6, 124.0, 126.4, 127.3, 127.5, 127.7, 127.8, 127.9, 128.4, 128.5, 128.7, 129.2, 129.4, 130.0, 130.2, 131.6, 131.9, 132.0, 132.1, 133.9, 134.0, 134.6, 135.8, 137.0, 137.3, 137.9, 138.9, 139.0, 141.5, 141.6, 145.6, 146.6, 146.7; 31P NMR (162.0 MHz, CDCl3) δ 23.1, −144.0 (PF6−); HRMS (ESI) calcd for C45H38P (M+) 609.2177, found 609.2703. Anal. Calcd for C45H38F6P2: C, 71.61; H, 5.07. Found: C, 71.38; H, 4.92. Compound 6d (65% yield): brown powder; 1H NMR (400 MHz, CDCl3) δ 2.03 (3H, s), 2.19 (3H, s), 2.34 (3H, s), 6.30−6.36 (4H, m), 6.89 (3H, m), 7.19−7.31 (4H, m), 7.52−7.63 (14H, m), 7.71−7.72 (3H, m), 7.98 (1H, m); 13C NMR (100 MHz, CDCl3) δ 20.9, 21.0, 21.1, 117.8, 118.7, 118.9, 119.8, 126.8, 128.3, 128.5, 129.3, 130.0, 130.1, 130.2, 130.6, 131.9, 132.6, 133.3, 133.4, 134.0, 134.1, 134.7, 135.1, 135.9, 136.3, 137.0, 137.7, 138.9, 141.4, 141.5, 145.4, 146.6, 146.7; 31P NMR (162.0 MHz, CDCl3) δ 23.2, −144.0 (PF6−); HRMS (ESI) calcd for C45H38P (M+) 609.2177, found 609.2746. Anal. Calcd for C45H38F6P2: C, 71.61; H, 5.07. Found: C, 71.43; H, 4.98. Compound 6e (59% yield): brown powder; 1H NMR (400 MHz, CDCl3) δ 3.94 (3H, s), 3.73 (3H, s), 3.85 (3H, s), 6.14−6.16 (1H, m), 6.37−6.39 (2H, m), 6.67−6.69 (2H, m), 6.95−6.98 (2H, m), 7.40− 7.71 (17H, m), 7.75−7.80 (3H, m), 8.00 (1H, m); 13C NMR (100 MHz, CDCl3) δ 54.0, 55.3, 55.6, 113.3, 113.5, 115.0, 119.2, 120.1, 128.4, 128.6, 128.7, 130.4, 130.6, 130.9, 131.8, 132.1, 132.2, 132.3,

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ASSOCIATED CONTENT

S Supporting Information *

Figures, a table, and a CIF file giving the solid-state structure and crystallographic data for 6a and NMR and mass spectra. This material is available free of charge via the Internet at http://pubs.acs.org. 6411

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AUTHOR INFORMATION

Corresponding Author

*Y.C.L.: e-mail, [email protected]; fax, (+886) 233668670. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Ministry of Science and Technology of Taiwan, ROC, under grant no. NSC 100-2113-M-002-003MY3 is appreciated.

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dx.doi.org/10.1021/om500745y | Organometallics 2014, 33, 6408−6412