Heterotrinuclear Complexes with Palladium, Rhodium, and Iridium

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Heterotrinuclear Complexes with Palladium, Rhodium, and Iridium Ions Assembled by Conformational Switching of a Tetraphosphine Ligand around a Palladium Center Akiko Yoshii, Hiroe Takenaka, Hiroko Nagata, Sayo Noda, Kanako Nakamae, Bunsho Kure, Takayuki Nakajima, and Tomoaki Tanase* Department of Chemistry, Faculty of Science, Nara Women’s University, Kitauoya-nishi-machi, Nara 630-8506, Japan S Supporting Information *

ABSTRACT: Reaction of [PdCl2(cod)] with a tetraphosphine, meso-bis[((diphenylphosphino)methyl)phenylphosphino]methane (dpmppm), afforded the mononuclear PdII complexes [PdCl(dpmppm-κ3)]X (X = Cl (1a), PF6 (1b)); the pincer-type dpmppm ligand coordinates to the Pd atom with two outer and one inner phosphorus atom to form fused six- and four-membered chelate rings. The remaining inner phosphine is uncoordinated and readily reacts with [Cp*MCl2]2 to give the heterodimetallic complexes [PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]X (X = Cl, M = Rh (21a), Ir (21b); X = PF6, M = Rh (23a), Ir (23b)). Attachment of the second metal fragment to the uncoordinated phosphine caused a crucial conformational change of the six-membered chelate ring from a stable chair conformation to a twist-boat structure, which concomitantly destabilizes the four-membered ring for its opening reactions. Complexes 21 (X = Cl) were converted to [PdCl2(Cp*MCl2)(dpmppmO)], in which the terminal P atom is dissociated and oxidized as Ph2P(O)CH2P(Ph)CH2P(Ph)CH2PPh2 (dpmppmO), and in the presence of another 1 equiv of [Cp*M′Cl2]2, complexes 21 were readily transformed into the heterotrinuclear complexes [PdCl2(Cp*M′Cl2)(Cp*MCl2)(μdpmppm-κ2,κ1,κ1)] (M = M′ = Rh (31a), Ir, (31b); M = Ir, M′ = Rh (31c)), where the third metal M′ is trapped by the terminal P atom with its four-membered-ring opening. Complexes 23 also reacted with another 1 equiv of [Cp*M′Cl2]2 to afford the heterotrinuclear complexes [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = M′ = Rh (32a), Ir, (32b); M = Ir, M′ = Rh (32c), M = Rh, M′ = Ir (32d)); the additional metal M′ is ligated by the terminal phosphine and is further connected to the Pd atom via a chloride bridge, resulting in a rather electron-deficient M′ center on the basis of cyclic voltammetry. These results exhibited that the addition of a bulky metal fragment to the uncoordinated phosphine of 1 brings about a conformational switch around the Pd center to promote the ring-opening reaction of the four-membered chelate ring, which leads to an incorporation of the third metal fragment to construct heterotrinuclear structures.

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INTRODUCTION Synergistic effects of heterometallic centers are of extensive interest in relation to developing multimetallic catalytic systems, electronic, optical, and magnetic devices, and biomimetic functional molecules.1 Exploring tunable assemblages of heterodinuclear and heteromultinuclear complexes would be thus an important subject and has closely been indebted to designing metal supporting ligands. Among a number of polydentate ligands used to stabilize multimetallic systems, di- and tridentate phosphines, including bis(diphenylphosphino)methane (dppm) and bis[(diphenylphosphino)methyl]phenylphosphine (dpmp), have widely been used to create metal−metal-bonded homo- and heteromultinuclear structures.1f,2−5 In general, polyphosphine ligands possess the potential ability to organize heteromultimetallic centers because their variation of denticity may generate uncoordinated dangling phosphorus atoms capable of trapping additional metals; however, polyphosphines containing more © 2011 American Chemical Society

than three P atoms have still been limited, owing to their synthetic difficulty and complicated stereoisomerism.6−11 Recently, we have prepared a methylene-bridged linear tetraphosphine ligand, meso-bis[((diphenylphosphino)methyl)phenylphosphino]methane (dpmppm), and demonstrated that it effectively stabilized versatile tetrametallic chains of group 11 metal ions.12 Two dpmppm ligands assembled four AuI ions in a syn arrangement with respect to the bent AuI4 string, and the flexible tetragold(I) chain {Au4(μ-dpmppm)2}4+ incorporated a counteranion (X) in its bent pocket to afford {[Au4(μdpmppm)2]X}3+ (X = PF6, Cl) adducts, the structures of which varied depending on the trapped anions and modulated their intriguing luminous properties.12a The flexible AuI4 chain was further converted to the cyclic hexagold(I) Received: July 23, 2011 Published: December 22, 2011 133

dx.doi.org/10.1021/om2006744 | Organometallics 2012, 31, 133−143

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Table 1. 31P{1H} NMR Spectral Data for the dpmppm Part of 1a,b, 20a,b, 23a,b, 31a−c, and 32a−da compd 1ab 1bc 20ac 20bd 23ac 23bc 31ac 31bc 31cc 32ac 32bc 32cc 32dc

δ(PA), ppm −43.4 (dd, JPP′ = 479, −44.7 (dd, JPP′ = 475, −41.4 (dd, JPP′ = 420, −41.4 (dd, JPP′ = 440, −62.4 (dd, JPP′ = 466, −62.4 (dd, JPP′ = 468, 28.4 (d, 1JRhP = 147) −1.3 (br)e −1.4 (br) 28.5 (d, 1JRhP = 144) 4.0 (d, JPP′ = 4) 4.2 (d, JPP′ = 3) 28.3 (d, 1JRhP = 145)

75) 82) 77) 78) 82) 81)

δ(PB), ppm

δ(PC), ppm

δ(PD), ppm

−30.6 (t, JPP′ = 75, 73) −33.2 (dd, JPP′ = 82, 79) −25.9 (t, JPP′ = 77, 39) −33.2 (m) −43.5 (ddd, JPP′ = 82, 30, 4) −44.2 (dd, JPP′ = 81, 23) 14.2 (br) 13.2 (br) 14.6 (br) 16.8 (br) 16.2 (d, JPP′ = 16) 16.5 (br) 16.9 (br)

−38.8 (dd, JPP′ = 73, 45) −40.3 (dd, JPP′ = 79, 52) −18.6 (br ddd, JPP′ = 39, 33, 1JAgP = 775) −19.2 (br d, 1JAgP = 780) 30.8 (ddd, JPP′ = 30, 20, 1JRhP = 149) −1.2 (dd, JPP′ = 23, 13) 31.3 (d, 1JRhP = 147) −1.3 (br)e 30.9 (dt, JPP′ = 23, 1JRhP = 148 ) 28.2 (dt, JPP′ = 27, 1JPhP = 148) −5.4 (dd, JPP′ = 20, 16) 27.2 (dt, JPP′ = 27, 1JRhP = 145) −4.6 (t, JPP′ = 21)

5.0 (dd, JPP′ = 479, 45) 5.7 (dd, JPP′ = 475, 52) −8.7 (dd, JPP′ = 420, 33) −8.7 (dd, JPP′ = 440, 32) −6.9 (ddd, JPP′ = 466, 20, 4) −7.8 (dd, JPP′ = 468, 13) 9.2 (d, JPP′ = 20) 8.3 (br) 8.9 (d, JPP′ = 23) 11.5 (d, JPP′ = 26) 12.6 (d, JPP′ = 20) 13.9 (d, JPP′ = 28) 10.3 (d, JPP′ = 21)

a

Measured at 121 MHz. J values are given in Hz. The assignments of P atoms are shown in Figures 2 and 6 and Figures S2 and S5 (Supporting Information). bIn CDCl3. cIn CD2Cl2. dIn DMF-d7. eOverlapped and not resolved. 121 MHz, respectively. 1H NMR spectra were referenced to TMS as external standard, and 31P{1H} NMR spectra were referenced to 85% H3PO4 as external standard. ESI-TOF MS spectra were recorded on Applied Biosystems Mariner and JEOL JMS-T100LC high-resolution mass spectrometers with positive ionization mode. A Hokuto-denko Model HZ-3000 electrochemical analyzer was used in all electrochemical measurements. Tetra-n-butylammonium hexafluorophosphate (0.1 M) was used as supporting electrolyte. Cyclic voltammetry was performed with a conventional electrochemical cell consisting of a glassy-carbon working electrode, a Ag/AgPF6 (0.1 M in CH3CN) reference electrode, and a platinum-wire counter electrode. The potentials were calibrated to the ferrocene/ferrocenium (Fc/Fc+) redox couple (1 mM in acetonitrile). [PdCl(dpmppm-κ3)]Cl (1a). To a solution of dpmppm (146 mg, 0.232 mmol) in dichloromethane (10 mL) was added [PdCl2(cod)] (55.5 mg, 0.194 mmol), and the reaction mixture was stirred at room temperature for 12 h. The solvent was removed under reduced pressure to dryness and the residue was washed with diethyl ether (3 mL × 3) and crystallized from a dichloromethane/diethyl ether/ n-hexane mixed solvent, allowed to stand in a refrigerator, to give pale yellow crystals of 1a·CH2Cl2, which were collected by filtration, washed with diethyl ether, and dried under vacuum (108 mg, 62%). Anal. Calcd for C40H38P4Cl4Pd: C, 53.94; H, 4.30. Found: C, 54.58; H, 4.33. IR (KBr): ν 1483 (m), 1435 (s), 1106 (m), 1095 (m), 745 (s), 712 (m), 693 (s), 509 (m), 487 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε) 338 nm (3.04). 1H NMR (CDCl3): δ 1.87 (br, CH2, 1H), 2.46 (br, 1H, CH2), 4.38 (br, 2H, CH2), 4.65 (br, 1H, CH2), 5.24 (br, 1H, CH2), 6.9−8.4 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2): m/z 769.078 (z1, [PdCl(dpmppm)]+ (769.050)), 1575.155 (z1, {[PdCl(dpmppm)]2Cl}+ (1575.069)). [PdCl(dpmppm-κ3)]PF6 (1b). The detailed synthetic procedures are described in the Supporting Information. Yield: 73%. Anal. Calcd for C39H36P5F6ClPd: C, 51.17; H, 3.96. Found: C, 50.89; H, 4.12. IR (KBr): ν 1484 (m), 1436 (s), 1017 (m), 999 (m), 836 (s), 740 (s), 689 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε) 341 nm (4.0). 1H NMR (CD2Cl2): δ 2.80 (br, 2H, CH2), 3.12 (br, 1H, CH2), 3.41 (br, 1H, CH2), 4.31 (br, 1H, CH2), 4.62 (br, 1H, CH2), 6.05−8.27 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2): m/z 769.062 (z1, [PdCl(dpmppm)]+ (769.050)). Recrystallization of 1b from an acetonitrile/diethyl ether mixed solvent yielded blockshaped crystals of 1b·CH3CN, which were suitable for X-ray crystallographic analysis. [PdX(AgX)(μ-dpmppm-κ3,κ1)]X (X = OTf (20a), OTs (20b)). Complex 20a was prepared from 1a in 49% yield (see the Supporting Information). Anal. Calcd for C42H36O9P4F9S3PdAg: C, 39.10; H, 2.81. Found: C, 38.84; H, 2.67. IR (KBr): ν 1485 (m), 1436 (s), 1252, 1102, 1027 (br, s), 819 (s), 740 (s), 688 (s), 629 (s), 573 (m), 517 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε) 337 nm (4.36). 1H NMR (CD2Cl2): δ 3.15 (br, 2H, CH2), 4.36 (br, 3H, CH2), 5.32 (m br, 1H,

complex [Au6Cl4(μ-dpmppm)2]2+ and the linear octagold(I) complex [Au8(μ-I)2(μ3-I)2(μ-dpmppm)4]4+. Silver(I) ions are also assembled by two dpmppm ligands in both syn and anti arrangements to form the bent and linear AgI4 chains, respectively, with a variety of ancillary ligands.12b In case of copper(I) ions, interconversion between ladder-type CuI8 complexes, [Cu8(μ-X)2(μ3-X)6(μ-dpmppm)2] (X = Cl, Br, I), and CuI4 chains with a bent {Cu4(μ-X)3(μ-dpmppm)2}+ core proceeded through a labile {Cu 4 (μ-X) 3 (μ-dpmppm)} + intermediate.12c These suggested potential versatility for coordination modes of the flexible dpmppm ligand which might be utilized, therefore, to construct heteromultimetallic complexes. In the present study, we have found that the dpmppm ligand surrounded a PdII mononuclear center in a pincer-type fashion to form [PdCl(dpmppm-κ3)]+ (1), in which six- and fourmembered chelate rings are fused with a uncoordinated phosphine unit involved in the six-membered ring. An attachment of the Cp*MCl2 fragment (M = Rh, Ir) to the uncoordinated phosphine, forming dinuclear species of [PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]+ (21, 23; M = Rh, Ir), interestingly brought about a conformational change of the six-membered ring from a stable chair to a twist-boat structure, which further destabilized the strained four-membered chelate ring and promoted a capture of the third metal ions via its ring opening. The conformational switch around the Pd center can be called an “allosteric effect”, was very effective to control the reactivity of Pd, and enabled us to construct the heterotrimetallic complexes [PdCl2(Cp*M′Cl2)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)] (31) and [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (32) (M, M′ = Rh, Ir), in stepwise ways. We wish to report herein the synthesis, characterization, and electrochemistry of di- and trinuclear complexes with Pd, Rh, and Ir metal ions assembled by the flexible tetraphosphine ligand.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out under a nitrogen atmosphere using standard Schlenk techniques. mesoBis[((diphenylphosphino)methyl)phenylphosphino]methane (dpmppm) was prepared by the method already reported.12a Reagent grade solvents were dried by the standard procedures and were freshly distilled prior to use. IR spectra were recorded on a Jasco FT/IR-410 spectrophotometer. 1H and 31P{1H} NMR spectra were recorded on Varian Gemini 2000 and Bruker AV-300N spectrometers at 300 and 134


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CH2), 7.11−8.21 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. By a procedure similar to that of 20a with 1a and AgOTs, 20b·0.5CH2Cl2 was isolated as colorless crystals (53%). Anal. Calcd for C60.5H58O9P4S3ClPdAg: C, 51.94; H, 4.18. Found: C, 51.61; H, 4.23. IR (KBr): ν 1485 (m), 1436 (s), 1252, 1102, 1027 (br, s), 819 (s), 740 (s), 688 (s), 629 (s), 573 (m), 517 (m) cm−1. UV−vis (DMF): λmax (log ε) 414 nm (3.81). 1H NMR (DMF-d7): δ 2.32 (s, 9H, p-CH3), 3.88 (br, 2H, CH2), 4.32−4.63 (m br, 3H, CH2), 5.34− 5.43 (m, 1H, CH2), 7.24−8.66 (m, 42H, Ph). 31P{1H} NMR data are given in Table 1. Careful crystallization of 20b for a long time afforded block-shaped crystals of 20b·H2O which were suitable for X-ray crystallography. [PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]Cl (M = Rh (21a), Ir (21b)) and [PdCl2(Cp*MCl2)(dpmppmO-κ2,κ1)] (M = Rh (22a)). A dichloromethane solution (10 mL) of 1a (28.0 mg, 0.035 mmol) and [Cp*RhCl2]2 (12.2 mg, 0.020 mmol) was stirred at room temperature for 12 h. The solvent was removed under reduced pressure to dryness, and the residue was extracted with 10 mL of CH2Cl2. The extract was passed through a filter and concentrated to ca. 3 mL, to which ca. 5 mL of diethyl ether was carefully added. The solution was allowed to stand in a refrigerator to deposit a mixture of 21a and 22a in a 1:2 ratio, which were analyzed by 31P{1H} NMR spectra and X-ray crystallography (22a·4CH2Cl2). 31P{1H} NMR (CD2Cl2) of 21a: δ −63.7 (dd, JPP = 464, 82 Hz, 1P, PA), −45.7 (dd, JPP = 82, 31 Hz, 1P, PB), −6.2 (dd, JPP = 464, 18 Hz, 1P, PD), 31.7 (ddd, 1JRhP = 148 Hz, JPP = 31, 18 Hz, 1P, PC). 31P{1H} NMR (CD2Cl2) of 22a: δ 9.8 (d, JPP = 22 Hz, 1P, PD), 12.8 (t, JPP = 27 Hz, 1P, PB), 27.5 (d, JPP = 27 Hz, 1P, PA), 29.0 (dt, 1JRhP = 148 Hz, JPP = 22 Hz, 1P, PC). Treatment of 1a (29.0 mg, 0.036 mmol) and [Cp*IrCl2]2 (14.5 mg, 0.018 mmol) similar to that described above gave 21b with uncharacterized compounds. 31P{1H} NMR (CD2Cl2) of 21b: δ −63.7 (dd, JPP = 468, 82 Hz, 1P, PA), −46.6 (dd, JPP = 82, 24 Hz, 1P, PB), −6.9 (dd, JPP = 468, 11 Hz, 1P, PD), 0.5 (dd, JPP = 24, 11 Hz, 1P, PC). [PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]PF6 (M = Rh (23a), Ir (23b)). Complex 23a was prepared from 1b in 72% yield (see the Supporting Information). Anal. Calcd for C49H51P5F6Cl3PdRh: C, 48.06; H, 4.20. Found: C, 47.55; H, 4.07. IR (KBr): ν 1483 (m), 1437 (s), 1099 (m), 1024 (m), 999 (m), 845 (s), 795, 740, 723 cm−1. UV− vis (CH2Cl2): λmax (log ε) 400 sh (3.72), 346 nm (4.18). 1H NMR (CD2Cl2): δ 1.40 (d, 4JHP = 4 Hz, 15H, Cp*), 2.8−5.3 (m, 6H, CH2), 6.8−8.3 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESIMS (CH2Cl2): m/z 1078.998 (z1, [(Cp*RhCl2)PdCl(dpmppm)]+ (1079.009)). By a procedure similar to that for 23a, using 1b and [Cp*IrCl2]2, yellow crystals of 23b·0.5CH2Cl2 were isolated (77%). Anal. Calcd for C49.5H52P5F6Cl4PdIr: C, 43.84; H, 3.86. Found: C, 44.16; H, 3.77. IR (KBr): ν 1485 (m), 1437 (s), 1163 (m), 1099 (m), 1028 (m), 849 (s), 795 (m), 690 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 346 nm (4.20). 1H NMR (CD2Cl2): δ 1.41 (d, 4JHP = 3 Hz, 15H, Cp*), 1.6 (br, 1H, CH2), 2.9 (br, 1H, CH2), 3.4 (br, 1H, CH2), 3.9 (br, 1H, CH2), 4.5 (br, 1H, CH2), 4.7 (br, 1H, CH2), 6.8−8.3 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESIMS (CH2Cl2): m/z 1169.0634 (z1, [(Cp*IrCl2)PdCl(dpmppm)]+ (1169.066)). [PdCl2(Cp*MCl2)2(μ-dpmppm-κ2,κ1,κ1)] (M = Rh (31a), Ir (31b)). Complex 31a·1.5CH2Cl2 was prepared from 1a in 91% yield (see the Supporting Information). Anal. Calcd for C60.5H69P4Cl9PdRh2: C, 46.84; H, 4.48. Found: C, 46.45; H, 4.19. IR (KBr): ν 1483 (m), 1435 (s), 1159 (m), 1097 (s), 1022 (m), 793 (m), 766 (m), 742 (s), 725 (m), 692 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 397sh (3.93), 349sh nm (4.04). 1H NMR (CD2Cl2): δ 1.37 (d, 4 JHP = 3 Hz, 15H, Cp*), 1.45 (d, 4JHP = 4 Hz, 15H, Cp*), 2.5−6.5 (m, 6H, CH2), 6.8−8.0 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2): m/z 1386.986 (z1, {(Cp*RhCl2)2PdCl(dpmppm)}+ (1386.970)). By a method similar to that of 31a, using 1a and [Cp*IrCl2]2, 31b·CH2Cl2 was obtained (83%). Anal. Calcd for C60H68P4Cl8PdIr2: C, 42.70; H, 4.06. Found: C, 42.94; H, 4.47. IR (KBr): ν 1485 (m), 1435 (s), 1159 (m), 1097 (s), 1029 (m), 793 (m), 768 (m), 742 (s), 725 (m), 694 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 340 (3.99), 461sh nm (2.88). 1H NMR (CD2Cl2): δ 1.33 (br, 15H, Cp*), 1.46 (d, 4JHP = 2 Hz, 15H, Cp*), 2.5−6.3 (m br, 6H, CH2),

6.4−8.0 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESIMS (CH2Cl2): m/z 1567.120 (z1, {(Cp*IrCl2)2PdCl(dpmppm)}+ (1567.082)), 1169.084 (z1, {(Cp*IrCl 2 )PdCl(dpmppm)} + (1169.066)). [PdCl 2 (Cp*IrCl 2 )(Cp*RhCl 2 )(μ-dpmppm-κ 2 ,κ 1 ,κ 1 )] (31c). 31c·CH2Cl2 was obtained from 1a in 80% yield (see the Supporting Information). Anal. Calcd for C60H68P4Cl8PdRhIr: C, 45.09; H, 4.29. Found: C, 44.89; H, 4.19. IR (KBr): ν 1485 (m), 1435 (s), 1159 (m), 1097 (s), 1026 (m), 791 (m), 766 (m), 742 (s), 725 (m), 692 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 346 sh (3.92), 386 sh nm (3.89). 1 H NMR (CD2Cl2): δ 1.33 (br, 15H, Cp*), 1.44 (d, 4JHP = 4 Hz, 15H, Cp*), 2.5−6.5 (m, 6H, CH2), 6.4−8.0 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2): m/z 1477.046 (z1, {(Cp*RhCl2)(Cp*IrCl2)PdCl(dpmppm)}+ (1477.026)), 1567.096 (z1, {(Cp*IrCl2)2PdCl(dpmppm)}+ (1567.082)), 1386.964 (z1, {(Cp*RhCl2)2PdCl(dpmppm)}+ (1386.970)). [PdCl(μ-Cl)(Cp*MCl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = Rh (32a), Ir (32b)). Compound 32a was obtained from 1b in 60% yield (see the Supporting Information). Anal. Calcd for C59H66P5F6Cl5PdRh2: C, 46.21; H, 4.34. Found: C, 45.94; H, 4.32. IR (KBr): ν 1485 (m), 1437 (s), 1160 (m), 1097 (m), 1022 (m), 999 (m), 845 (s), 791 (m), 768 (m), 742 (m), 694 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε) 397 nm (4.15). 1H NMR (CD2Cl2): δ 1.23 (d, 4 JHP = 4 Hz, 15H, Cp*), 1.39 (d, 4JHP = 4 Hz, 15H, Cp*), 3.0−3.7 (m, 6H, CH2), 7.0−7.8 (m, 30H, Ph). 31P{1H} NMR data are listed in Table 1. ESI-MS (CH2Cl2): m/z 1387.008 (z1, [(Cp*RhCl2)2PdCl(dpmppm)]+ (1386.970)). Recrystallization of 32a from a dichloromethane/acetone/diethyl ether mixed solvent gave orange needle crystals of 32a·(CH3)2CO suitable for X-ray crystallography. By a procedure similar to that for 32a, 32b was isolated in 76% yield. Anal. Calcd for C59H66P5F6Cl5PdIr2: C, 41.39; H, 3.89. Found: C, 40.99; H, 3.61. IR (KBr): ν 1485 (m), 1437 (s), 1161 (m), 1097 (s), 1028 (m), 843 (s), 793 (m), 768 (m), 742 (m), 727 (m), 692 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 354 sh nm (4.15). 1H NMR (CD2Cl2): δ 1.45 (d, 4JHP = 2 Hz, 15H, Cp*), 1.57 (d, 4JHP = 2 Hz, 15H, Cp*), 3.0−4.0 (m br, 6H, CH2), 7.2−8.0 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2): m/z 1567.073 (z1, [(Cp*IrCl2)2PdCl(dpmppm)] + (1567.082)), 1169.063 (z1, {(Cp*IrCl 2 )PdCl(dpmppm)}+ (1169.066)). [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = Rh, M′ = Ir (32c); M = Ir, M′ = Rh (32d)). Complex 32c·0.5CH2Cl2 was prepared from 31c in 51% yield (see the Supporting Information). Anal. Calcd for C59.5H67P5F6Cl6PdRhIr: C, 42.91; H, 4.06. Found: C, 42.95; H, 3.95. IR (KBr): ν 1485 (m), 1436 (s), 1097 (m), 842 (s), 783 (m), 743 (m), 691 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε) 393 nm (4.04). 1H NMR (CD2Cl2): δ 1.25 (d, 4JHP = 4 Hz, 15H, Cp*), 1.41 (d, 4JHP = 2 Hz, 15H, Cp*), 2.9−3.7 (m, 6H, CH2), 7.1− 7.7 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2/MeOH): m/z 1476.270 (z1, [(Cp*IrCl2)PdCl(dpmppm)(Cp*RhCl2)]+ (1477.026)). Recrystallization of 32c from a dichloromethane/acetone/diethyl ether mixed solvent gave orange needle crystals of 32c·(CH3)2CO suitable for X-ray crystallography. Complex 32d was prepared from 23b in 68% yield (see the Supporting Information). Anal. Calcd for C59H66P5F6Cl5PdRhIr: C, 43.67; H, 4.10. Found: C, 43.40; H, 3.77. IR (KBr): ν 1485 (m), 1437 (s), 1095 (s), 844 (s), 795 (m), 743 (m), 694 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 386 nm (3.92). 1H NMR (CD2Cl2): δ 1.23 (d, 4JHP = 3 Hz, 15H, Cp*), 1.40 (d, 4JHP = 3 Hz, 15H, Cp*), 2.9−4.7 (m br, 6H, CH2), 6.9−8.2 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2/MeOH): m/z 1476.248 (z1, [(Cp*RhCl2)PdCl(dpmppm)(Cp*IrCl2)]+ (1477.026)). X-ray Crystallography. The crystals of 1a·2CH2Cl2, 1b·CH3CN, 20b·H 2 O, 22a·4CH 2 Cl 2 , 23a·CH 2 Cl 2 ·Et 2 O, 23b·3CH 2 Cl 2 , 31a·2CH2Cl2, 31b·2CH2Cl2, 31c·2CH2Cl2, 32a·(CH3)2CO, and 32c·(CH3)2CO were quickly coated with Paratone N oil and mounted on top of a loop fiber at room temperature. Crystal and experimental data are summarized in Tables 2 and 3. All data were collected at −120 °C (1a,b, 20b, 22a, 23a,b, 32a,c), −105 °C (31a,b), and −100 °C (31c) on a Rigaku AFC8R/Mercury CCD diffractometer equipped with graphite-monochromated Mo Kα radiation using a rotating-anode 135


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Table 2. Crystallographic Data of the Complexes 1a·2CH2Cl2, 1b·CH3CN, 20b·H2O, 22a·4CH2Cl2, 23a·CH2Cl2·Et2O, and 23b·3CH2Cl2 1a·2CH2Cl2

1b·CH3CN

formula

C41H40Cl6P4Pd

formula wt cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z temp, °C Dcalcd, g cm−3 μ, mm−1 (Mo Kα) 2θ range, deg Rint no. of rflns coll no. of unique rflns no. of obsd rflns (I > 2σ(I)) no. of variables R1a wR2b GOF

975.78 monoclinic P21/c 11.1295(15) 29.706(3) 13.217(2)

4344.3(10) 4 −120 1.492 0.972 6−55 0.017 38 661 9565 7065

C41H39NClF6P5Pd 2780.82 triclinic P1̅ 11.9315(11) 12.4707(11) 15.8027(11) 91.876(3) 105.7458(19) 112.566(3) 2064.9(3) 2 −120 1.538 0.767 6−55 0.015 18 231 9218 7746

C60H59O10P4S3PdAg 1374.46 triclinic P1̅ 15.072(4) 15.753(4) 15.813(4) 117.773(3) 102.0868(4) 107.3202(8) 2889.5(13) 2 −120 1.580 0.927 6−55 0.019 27 218 12 756 10 109

471 0.030 0.075 1.095

497 0.045 0.115 1.071

737 0.049 0.124 1.062

a

96.1866(18)

22a·4CH2Cl2

23a·CH2Cl2·Et2O

C53H59OCl12P4RhPd 1470.69 monoclinic P21/c 12.063(5) 24.465(9) 20.922(8)

6170(4) 4 −120 1.583 1.218 6−55 0.037 55 913 13 726 7908

C54H63OF6P4Cl5RhPd 1383.52 triclinic P1̅ 12.242(4) 15.428(5) 17.398(6) 90.395(4) 108.107(4) 109.1568(15) 2928.3(16) 2 −120 1.569 1.009 6−55 0.048 27 350 12 938 7736

C52H57F6P5Cl9P5Pd 1568.58 triclinic P1̅ 12.380(2) 14.534(3) 17.841(3) 80.825(4) 75.624(5) 79.221(4) 3033.4(9) 2 −120 1.717 3.075 6−55 0.017 26 470 13 317 12 490

650 0.084 0.205 1.182

671 0.075 0.249 1.130

668 0.027 0.063 1.034

20b·H2O

92.1987(11)

23b·3CH2Cl2

R1 = ∑||Fo| − |Fc||/∑|Fo| (for observed reflections with I > 2σ(I)). bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2 (for all reflections).

Table 3. Crystallographic Data of the Complexes 31a·2CH2Cl2, 31b·2CH2Cl2, 31c·2CH2Cl2, 32a·(CH3)2CO, and 32c·(CH3)2CO formula formula wt cryst syst space group a, Å b, Å c, Å β, deg V, Å3 Z temp, °C Dcalcd, g cm−3 μ, mm−1 (Mo Kα) 2θ range, deg Rint no. of rflns coll no. of unique rflns no. of obsd rflns (I > 2σ(I)) no. of variables R1a wR2b GOF a

31a·2CH2Cl2

31b·2CH2Cl2

31c·2CH2Cl2

32a·(CH3)2CO

32c·(CH3)2CO

C61H70Cl10P4Rh2Pd 1593.86 orthorhombic Pca21 23.354(5) 15.269(3) 18.148(4)

C61H70Cl10P4PdIr2 1772.49 orthorhombic Pca21 23.3745(5) 15.3030(4) 18.1393(4)

C61H70Cl10P4RhPdIr 1683.17 orthorhombic Pca21 23.3351(7) 15.3353(4) 18.1485(6)

6471(2) 4 −105 1.636 1.328 6−55 0.033 59 170 14 561 13 412 714 0.039 0.096 1.243

6488.4(3) 4 −105 1.814 4.926 6−55 0.029 55 250 14 022 13 209 704 0.025 0.053 0.981

6494.5(3) 4 −100 1.721 3.122 6−55 0.025 55 897 13 818 13 247 713 0.030 0.075 1.013

C62H72OF6P5Cl5Rh2Pd 1591.59 monoclinic P21/n 10.848(2) 33.528(6) 19.391(4) 94.726(3) 7029(2) 4 −120 1.504 1.073 6−55 0.034 63 232 15 935 13 966 741 0.062 0.172 1.039

C62H72OF6P5Cl5RhPdIr 1680.90 monoclinic P21/n 10.964(5) 33.961(15) 19.270(9) 94.775(4) 7151(5) 4 −120 1.561 2.689 6−55 0.061 58 665 15 965 13 154 804 0.084 0.204 1.037

R1 = ∑||Fo| − |Fc||/∑|Fo| (for observed reflections with I > 2σ(I)). bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2 (for all reflections). (−70° < ω < 110° (1a), −62° < ω < 118° (1b, 20b, 22a, 23a,b, 31a−c, 32a,c)) with Δω = 0.25°. The crystal-to-detector (70 × 70 mm) distance was set at 45 or 60 mm. The data were processed using the Crystal Clear 1.3.5 program (Rigaku/MSC)13 and corrected for Lorentz−polarization and absorption effects.14 The structures of complexes were solved by

X-ray generator (50 kV, 180 mA) and a Rigaku VariMax Mo/Saturn CCD diffractometer equipped with graphite-monochromated Mo Kα radiation using an RA-Micro7 rotating-anode X-ray generator (50 kV, 24 mA). A total of 1440−2160 oscillation images, covering a whole sphere of 6° < 2θ < 55°, were corrected by the ω-scan method 136


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direct methods with DIRDIF-9415 (1b, 20b, 31b), SIR-9216a (1a, 20b, 22a, 23a,b, 31a,c, 32a), and SIR-9716b (32c) and were refined on F2 with full-matrix least-squares techniques with SHELXL-9717 using the Crystal Structure 3.7 package.18 All non-hydrogen atoms were refined with anisotropic thermal parameters, and the C−H hydrogen atoms were calculated at ideal positions and refined with riding models. All calculations were carried out on a Pentium PC with Crystal Structure 3.7 package.18 In the refinement of 20b, the water molecule of crystallization is disordered in two sites with 0.5 occupancy. In 23a, one of the phenyl groups on P4 atom is disordered and refined with a two-site rotating model with half-occupancy. In 31a,c, a Cl atom of one solvated dichloromethane is disordered and refined with two site models with 2/3 and 1/3 occupancies for 31a and 0.7 and 0.3 occupancies for 31c. In 32c, the PF6− anion is disordered in two sites, each refined anisotropically with 0.5 occupancy.

■

RESULTS AND DISCUSSION Mononuclear Pd Complexes with dpmppm, [PdCl(dpmppm-κ3)]X (X = Cl (1a), PF6 (1b)). When [PdCl2(cod)] was treated with 1 equiv of dpmppm in dichloromethane, pale yellow crystals of [PdCl(dpmppm-κ3)]Cl (1a) were obtained in 62% yield. Complex 1a was further converted by treatment with excess of NH4PF6 in acetonitrile into [PdCl(dpmppm-κ3)]PF6 (1b) in 73% yield (Scheme 1).

Figure 1. ORTEP diagram for the complex cation of [PdCl(μdpmppm-k3)]PF6 (1b). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

P3−Pd1−P4 = 71.59(2)° (1a), 71.16(2)° (1b), as in [PdCl2(dppm)] (P−Pd−P = 72.68(3)°),19 where the methylene carbon atom appreciably deviates from the [PdP2] plane. The bicyclic chelate ring system constrains three phenyl groups of P1, P3, and P4 atoms in an axial direction with respect to the Pd square plane. The other three phenyl groups are in an equatorial orientation on the other side of the plane, onto which the counteranions Cl− and PF6− are incorporated. The dpmppm-κ3 structure confirmed by the X-ray analyses is very stable in the solution state. The 31P{1H} NMR spectrum of 1b in CD2Cl2 showed four sets of resonances at δ −44.7, −40.3, −33.2, and 5.7 ppm, which are assignable to PA, PC, PB, and PD atoms in the light of PP′ coupling constants (JPP′) as indicated in Figure 2a (the labels of phosphorus atoms are

Scheme 1

Complexes 1a,b were characterized by elemental analysis, 1H and 31P{1H} NMR and ESI-MS spectra, and X-ray crystallography to have almost identical structures except for the counteranions. A perspective view for the complex cation of 1b is shown in Figure 1 (that of 1a is given in Figure S1 as Supporting Information), and the representative structural parameters are given in Table S1 (see the Supporting Information). The structures of complex cations 1a,b are essentially identical, involving a square-planar Pd(II) center coordinated by a dpmppm ligand and a chloride anion. The dpmppm ligand attaches to the Pd atom with two outer (P1, P4) and one inner (P3) phosphorus atoms to form a pincertype κ3 structure, in which six- and four-membered chelate rings are fused, and the remaining inner P atom (P2) is uncoordinated (Pd1···P2 = 4.0820(7) (1a), 4.1112(7) Å (1b)). The six-membered ring takes a stable chair conformation, and the phenyl group on the P2 atom occupies an equatorial position, similar to the six-membered ring in [PdCl2(dpmp-κ2)].4b,d The four-membered ring shows approximately planar structure with

Figure 2. The 31P{1H} NMR spectra of 1b (a), 23a (b), and 23b (c) in CD2Cl2 at room temperature with the assignments for the P atoms of dpmppm.

indicated with the spectrum); the large trans PP′ coupling (2JPAPD) of 475 Hz clearly demonstrated retainment of the κ3 pincer-type structure. The 31P{1H} spectrum of 1a in CDCl3 137


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also exhibited a similar trans coupling of 2JPAPD = 479 Hz. The ESI-MS spectra of 1a,b in CH2Cl2 showed the parent peak for [PdCl(dpmppm)]+ (m/z 769.050), which is consistent with the X-ray and NMR results. PdAg Dinuclear Complexes of [PdX(AgX)(μ-dpmppmκ3,κ1)]X (X = TfO (20a), TsO (20b)). Reaction of 1a with an excess amount of AgI salt (silver triflate or tosylate) in acetonitrile afforded PdIIAgI dinuclear complexes formulated as [PdX(AgX)(μ-dpmppm-κ3,κ1)]X (X = TfO (20a), TsO (20b)) in 49 and 53% yields, respectively (Scheme 1). In the 31P{1H} NMR spectra (Figure S2a in the Supporting Information for 20a), the peak for the PC atom, which is uncoordinated in 1a to resonate at δ −38.8 ppm, shifted to δ −18.6 (20a) and −19.2 (20b) ppm as a doublet of multiplets due to coupling to 107Ag and 109Ag (1JAgP = 775 (20a), 780 Hz (20b)), and the large trans PP′ coupling was observed with the peaks of PA and PD atoms (2JPAPD = 420 (20a), 440 Hz (20b)). The structure of 20b was determined by X-ray crystallography (Table S1 and Figure 3) to confirm that a AgOTs fragment is

Scheme 2

a long time. The 31P{1H} NMR spectrum (Figure S2b, Supporting Information) indicated that complex 21a retained the fused-ring structure of dpmppm (2JPAPD = 464 Hz) and trapped a Cp*RhCl2 fragment on the uncoordinated phosphine of 1a (δPC 31.7 ppm, 1JRhPC = 148 Hz). In contrast, the spectral patterns for 22a were entirely different, with the absence of the large trans PP′ coupling corresponding to the pincer chelate system; the four resonances were all shifted to higher frequency (δ 9.8−29.0 ppm) and coupled with small 2JPP′ values (27, 22 Hz), in addition to the 103Rh−31P coupling (1JRhPC = 148 Hz) observed for the PC peak (Figure S2c, Supporting Information). The detailed structure of 22a (Figure S3, Supporting Information) showed that the inner P2 atom is bound to the Rh atom and the remaining terminal phosphine (P4) is dissociated from the metal center and converted into a phosphine oxide. The six-membered chelate ring is remarkably deformed to take a skew or twist-boat conformation. The axial phenyl group on the P2 atom is pushed to hang over the Pd center, and on the other hand, the bulky Cp*RhCl2 fragment is directed in the equatorial position. These structural features of 22a suggested that an addition of the Cp*RhCl2 fragment on the uncoordinated P2 atom of 1a caused a crucial conformational change of the six-membered chelate ring from a stable chair to a twist-boat structure, which may further destabilize the four-membered chelate ring for its ring opening to form [PdCl2(Cp*RhCl2)(μ-dpmppm-κ2,κ1)] (21a*) with ligation of the counter chloride anion (Scheme 2), although the plausible intermediate 21a* was not detected by 31 1 P{ H} NMR spectra. The dangling phosphine groups of 21a* are likely to be oxidized when exposed to air. From the reaction of 1a with 0.5 equiv of [Cp*IrCl2]2, the analogous PdIIIrIII complex of [PdCl(Cp*IrCl2)(μ-dpmppm-κ3,κ1)]Cl (21b) was generated as a main product (Figure S2d, Supporting Information) but was not isolated as a pure form probably due to the ring-opening reaction leading to the PdIIIrIII2 trinuclear complex 31b as described later. To isolate the PdIIMIII dimetallic complexes, complex 1b with a noncoordinating PF6− counteranion was reacted with 0.5 equiv of [Cp*MCl2]2 to afford [PdCl(Cp*MCl2)(μ-dpmppmκ3,κ1)]PF6 (M = Rh (23a), Ir (23b)) in 72 and 77% yields, respectively (Scheme 1). Complexes 23a,b were quite stable in the solution state, as confirmed by spectroscopic analyses. In the 31P{1H} NMR spectra (Figure 2b,c), large trans PP′ couplings were observed for the peaks of PA and PD (2JPAPD = 466 (23a), 468 (23b) Hz). The peaks for PA, PB, and PD shifted to lower frequency compared with those of 1b, and the resonances for PC were shifted to higher energy at δ 30.8 (23a) and −1.2 ppm (23b); the former was observed as a doublet of

Figure 3. ORTEP diagram for the complex cation of [Pd(OTs)(AgOTs)(μ-dpmppm-κ3,κ1)](TsO) (20b). The thermal ellipsoids are drawn at the 40% probability level and the hydrogen atoms are omitted for clarity. One of the phenyl groups on P1 atom is disordered.

incorporated onto the uncoordinated P2 atom in 1a and the chloride ligand of 1a is replaced by a tosylate anion. The fused chelate ring structure with dpmppm-κ3,κ1 as observed in 1a is not perturbed by the addition of an AgOTs unit, and the six-membered ring adopts a chair conformation, with the AgI ion occupying the axial site of the P2 atom. The linear structure of the Ag1 atom could avoid the repulsive interactions with the phenyl groups on P1 and P3 atoms. The four-membered chelate ring of 20a,b is stable and would not undergo a ring-opening reaction even when treated with an excess amount of AgX salt. PdM Dinuclear Complexes of [PdCl(Cp*MCl2)(μdpmppm-κ3,κ1)]X (X = Cl, M = Rh (21a), Ir (21b); X = PF6, M = Rh (23a), Ir (23b)). With an aim of introducing more bulky metal species onto the free phosphine group, complex 1a was treated with 0.5 equiv of [Cp*RhCl2]2 in dichloromethane to yield a mixture of [PdCl(Cp*RhCl2)(μdpmppm-κ 3 ,κ 1 )]Cl (21a) and [PdCl 2 (Cp*RhCl 2 )(μdpmppmO-κ2,κ1)] (22a, dpmppmO = Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2(O)) (Schemes 1 and 2); the former was initially formed as a major product and the latter as a minor one, but the ratio of 22a increased with keeping the solution for 138


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multiplets with 1JRhP = 149 Hz. The ESI-MS spectra of 23a,b in dichloromethane showed the parent peaks at m/z 1078.998 and 1169.0634, which were assigned to [PdCl(Cp*MCl 2 )(dpmppm)]+ (M = Rh, m/z 1079.009; Ir, m/z 1169.066) by simulating distributions of isotopomers. The structures of 23a,b were determined by X-ray crystallography to be isomorphous with each other; an ORTEP view for the complex cation of 23a is given in Figure 4 (Figure S4 (Supporting Information) for 23b), and the structural parameters are given in Table S1 (Supporting

[PdCl2(Cp*MCl2)2(μ-dpmppm-κ2,κ1,κ1)] (M = Rh (31a), Ir (31b)) in 91 and 83% yields, respectively (Scheme 3). Scheme 3

The ESI-MS spectra in dichloromethane showed monovalent parent peaks at m/z 1386.986 (31a) and 1567.120 (31b) corresponding to {PdCl(Cp*MCl2)2(dpmppm)}+ with m/z 1386.970 (M = Rh) and 1567.082 (M = Ir). The 31P{1H} NMR spectra of 31a,b were somewhat broad with the absence of the trans PP′ coupling as observed in 23 (Figure S5, Supporting Information), indicating that ring opening of the four-membered chelate ring occurred during the reaction. In the spectrum of 31a, four peaks were observed at δ 9.2, 14.2, 28.4, and 31.3 ppm in a 1:1:1:1 integration ratio, of which the Rh−P coupled (1JRhP = 147 Hz) peaks, the doublet of broad doublets at δ 28.4 and the doublet of broad triplets at δ 31.3, were assigned to PA and PC atoms bound to the Rh ions (the labels of P atoms are shown with the spectrum in Figure S5). The doublet at δ 9.2 with 2JPP′ = 20 Hz was assignable to PD and the remaining broad peak centered at δ 14.2 to PB. In the spectrum of 31b, while the resonances for PB and PD atoms were almost identical in frequency and shape with those of 31a, the peaks for PA and PC were considerably shifted to lower frequency and accidentally overlapped at around δ −1.3 ppm. When complex 1a was treated with 0.5 equiv of [Cp*RhCl2]2 at first and then with 0.5 equiv of [Cp*IrCl2]2, the PdIIRhIIIIrIII trimetallic complex [PdCl2(Cp*IrCl2)(Cp*RhCl2)(μ-dpmppmκ2,κ1,κ1)] (31c) was isolated in 80% yield (Scheme 3). However, a similar procedure with [Cp*IrCl2]2 followed by [Cp*RhCl2]2 resulted in providing a mixture of the PdIr2 and PdRh2 trinuclear complexes 31a,b together with a small amount of the PdIrRh mixed-metal compound 31d, and eventually, failure to obtain the trinuclear complex [PdCl2(Cp*RhCl2)(Cp*IrCl2)(μ-dpmppm-κ2,κ1,κ1)] (31d) as a main product (Scheme 3). This might be attributed to the instability of complex 21b, which was likely to be transformed into the PdIIIrIII2 trinuclear complex 31b via a ring-opening reaction assisted by Cl− coordination to the PdII center. In the ESI-MS spectrum of 31c in CH2Cl2, an intense monovalent peak for [PdCl(Cp*IrCl 2 )(Cp*RhCl 2)(dpmppm)] + was found at m/z 1477.046 together with very weak peaks for [PdCl(Cp*MCl2)2(dpmppm)]+ (M = Rh, Ir). The 31P{1H} NMR spectrum of 31c consisted of four peaks at δ −1.4 (PA), 8.9 (PD), 14.6 (PB), and 30.9 (PC, 1JRhP = 148 Hz) and showed the presence of 31b in only a small amount (Figure S5c). The solid state structures of 31a−c, determined by X-ray crystallographic analyses, are isomorphous, revealing that a dpmppm ligand chelates to a square-planar cis-PdCl2 center via the outer and inner P atoms (P1, P3) to form a six-membered ring and is further bound to the first Cp*MCl2 fragment (M site) through the inner P2 atom (M = Rh (31a,c), Ir (31b)) and to

Figure 4. ORTEP diagram for the complex cation of [PdCl(Cp*RhCl2)(μ-dpmppm-κ3,κ1)]PF6 (23a). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

Information). The complex cation of 23 contains a [P3Cl] square-planar Pd(II) center with the fused bicyclic chelation rings of the dpmppm ligand, which further traps a Cp*MCl2 fragment through the uncoordinated inner phosphine unit. The [PdPCPCP] six-membered ring adopts a twist-boat conformation, as observed in 22a. The Cp*RhCl2 and Ph groups bound to the P2 atom occupy the equatorial and axial sites, respectively, and the Pd1···P2 distance (3.8916(18) Å (23a), 3.8978(7) Å (23b)) is appreciably shorter than that in 22a (3.985(2) Å) and considerably reduced from those of 1a,b (4.0820(7)− 4.1112(7) Å). The conformational switch should increase the steric repulsion between the phenyl groups on P1, P2, and P4 atoms and the strain involved in the [PdPCP] four-membered ring. Whereas the methylene carbon atom definitely deviates from the [Pd1P3P4] plane in 1a,b and 20b, in which the sixmembered ring takes a chair conformation, the carbon atom (C1) in 23a,b is constrained to be involved in the [Pd1P3P4] plane. This difference can be monitored by the dihedral angle between the Pd1P3P4 and P3P4C1 planes of 14.98 (23a) and 16.00° (23b), which are smaller than those of 30.98 (1a), 28.63 (1b), and 25.41° (20b), while the P3−Pd1−P4 bite angles (72.64(6) (23a), 72.14° (23b)) do not show a significant change. PdMM′ Trinuclear Complexes [PdCl 2(Cp*M′Cl 2 )(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)] (M = M′ = Rh (31a), Ir (31b); M = Rh, M′ = Ir (31c)). During the reaction of 1a to give 22a, ligation of the chloride counteranion of 21 was assumed to accelerate the ring-opening reaction of the fourmembered chelate ring, and this nature could be utilized for the preparation of a PdIIRhIII2 trinuclear complex assembled by the dynamically flexible dpmppm ligand. Treatment of complex 1a with 1 equiv of [Cp*MCl2]2 in CH2Cl2 readily afforded 139


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the second Cp*M′Cl2 unit (M′ site) via the outer P4 atom (M = Rh (31a), Ir (31b,c)), resulting in the trinuclear structures. A perspective view of complex 31b is shown in Figure 5 and the structural parameters are given in Table S2 (perspective views of

Scheme 4

Cp*IrCl2 counterpart is assumed to proceed rapidly and the resultant 23b would react with the Cp*IrCl2 unit to give complex 32b (Scheme 4). To isolate the trimetallic complex 32c in pure form, we used another procedure, in which complex 31c was treated with an excess of NH4PF6 in a dichloromethane/acetone mixed solvent to afford 32c in a 51% isolated yield. Notably, complexes 32a,b were also prepared by treatment of 31a,b with NH4PF6 in quantitative yields. The 31P{1H} NMR spectra of 32a−d together with the assignment of the P atoms are shown in Figure 6. In the spectrum

Figure 5. ORTEP diagram of [PdCl2(Cp*IrCl2)2(μ-dpmppmκ2,κ1,κ1)] (31b). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

31a,c are given in Figures S6 and S7 in the Supporting Information). The overall structure is similar to that of 22a, in which the oxo unit of the dangling P atom is replaced by the Cp*MCl2 fragment as expected, and in particular, the group 9 heterometal positions in 31c indicated the stepwise incorporation of the additional metals induced by the conformational change around the Pd center. The [PdPCPCP] six-membered ring takes a twist-boat conformation with P1−Pd1−P3 angles of 89.82(4) (31a), 89.95(3) (31b), and 89.89(3)° (31c), which are appreciably smaller than the corresponding values of 23a,b due to release of strain by opening of the fourmembered ring. The structures around the Pd atom are almost the same, and the M−P bond length clearly demonstrated that the Ir−P bond distances are shorter than the Rh−P distances at both M and M′ sites (Ir−P = 2.294(1)−2.298(2) Å, Rh−P = 2.306(1)−2.312(1) Å), which is interestingly reverse to the covalent radii of the metals and may suggest a stronger affinity of the IrIII center over the RhIII to the phosphine groups of dpmppm. The three metal ions PdMM′ form an equilateral triangle without any interaction between them (Table S2). PdMM′ Trinuclear Complexes [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = M′ = Rh (32a), Ir (32b); M = Rh, M′ = Ir (32c); M = Ir, M′ = Rh (32d)). When complex 1b was treated with 1 equiv of [Cp*MCl2]2 or the isolated PdIIMIII dimetallic complexes 23a (M = Rh) and 23b (M = Ir) were reacted with 0.5 equiv of the respective homometallic [Cp*MCl2]2, the PdIIMIII2 trinuclear complexes [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = M′ = Rh (32a), Ir (32b)) were obtained as crystalline forms in good yields (Scheme 4). Reaction of 23b with 0.5 equiv of [Cp*RhCl2]2 afforded a mixture of [PdCl(μCl)(Cp*Rh′Cl)(Cp*IrCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (32d) and 32b in ca. 9:1 ratio as monitored by 31P{1H} NMR spectroscopy, from which complex 32d was isolated in pure form in a yield of 68%. In contrast, reaction of 23a with 0.5 equiv of [Cp*IrCl2]2 yielded a mixture of 32c, 32a, and 32b, in a ca. 6:1:3 ratio; in this case, complex 32c was not isolated in pure form from the mixture. In the presence of [Cp*IrCl2]2, exchange reaction of the Cp*RhCl2 fragment of 23a with the

Figure 6. 31P{1H} NMR spectra of 32a (a), 32b (b), 32c (c), and 32d (d) in CD2Cl2 at room temperature with assignments for the P atoms of dpmppm.

of 32a (Figure 6a), three peaks for PB, PC, and PD were observed at δ 16.8, 28.2, and 11.5 ppm with small PP′ couplings and a 140


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characteristic coupling with 1JRhP = 148 Hz for the PC signal. The resonance for the PA atom was observed at δ 28.5 ppm as a doublet due to 1JRhP = 144 Hz without any PP′ coupling to the PB nucleus, although the reason was not clear. In the spectrum of 32b (Figure 6b), the PA and PC signals significantly shifted to lower frequency and were observed at δ 4.0 and −5.4 ppm as a doublet (JPP′ = 4 Hz) and a doublet of doublets (JPP′ = 20, 16 Hz), while the peaks for the PB and PD atoms were found at δ 16.2 and 12.6 ppm as somewhat broad doublets, as in that of 32a. The 31P{1H} NMR spectra of 32c,d were entirely different (Figure 6c,d), clearly demonstrating that no scrambling of Cp*MCl2 fragments between the M and M′ sites occurred in solution. In particular, the peaks for the PA and PC atoms were quite informative, the former being observed as a doublet (JPP′ = 3 Hz) at 4.2 ppm for 32c and a Rh−P coupled doublet (1JRhP = 145 Hz) at 28.3 ppm for 32d and, instead, the latter observed as a Rh−P coupled doublet of triplets (1JRhP = 145 Hz) at 27.2 ppm for 32c and a triplet (JPP′ = 21 Hz) at −4.6 ppm for 32d. The peaks for the PB and PD atoms of 32c,d were relatively similar in shape, as broad signals for PB at δ 16.5 (32c) and 16.9 (32d) and doublets for PD at δ 13.9 (32c) and 10.3 (32d). The ESI-MS spectra of 32a−d showed the parent peaks corresponding to [PdCl(Cp*M′Cl 2 )(Cp*MCl 2 )(dpmppm)]+, indicating that the solid-state structures were retained in the dichloromethane solutions. The structures of 32a,c were determined by X-ray crystallography. A perspective view for the complex cation of 32c is illustrated in Figure 7, and the structural parameters are

[Pd1P3C3P4Ir1Cl2] six-membered ring is constrained as a half-chair conformation tentatively due to steric repulsion between the phenyl groups of P3 and P4 atoms and the Cp* unit. The large value of 97.38(8)° for the Cl2−Pd1−P3 angle indicates some strains involved in the Pd(μ-Cl)Ir moiety. The complex cation structure of 32a is almost identical with that of 32c, in which the PdII ion and two Cp*RhCl2 units are organized in the bicyclic chelate ring system by a dpmppmκ2,κ1,κ1 ligation. The Pd1 and Rh1 atoms are bridged by the Cl2 anion (Pd1−Cl2 = 2.3822(13) Å, Rh2−Cl2 = 2.4229(14), Pd1−Cl2−Rh2 = 124.41(5)°) without a bonding interaction (Pd1···Rh2 = 4.2507(5) Å) as in 32c. In the reactions of 1b, the bulky Cp*MCl2 fragment (M = Rh, Ir) was trapped at first by the uncoordinated inner P atom of 1b on its equatorial site, which should bring about a conformational change of the [PdPCPCP] six-membered ring from the stable chair structure in 1b to the twist-boat one in 23. Induced by this structural change, the successive ring opening of the [PdPCP] four-membered ring was promoted to trap the second Cp*M′Cl2 fragment (M = Rh, Ir) by the dangling terminal P atoms, resulting in the [PdPCPM′Cl] six-membered ring completed by the chloride bridging to the Pd center, which was ensured by the absence of a Cl− counteranion. The structurally characterized complexes involving the PdII(μCl)MIII heterodimetallic moieties (M = Rh, Ir) have extremely been limited to only a few examples,4e,20 despite the fact that each metal has extensively been used in homogeneous catalytic reactions.1,21 Hence, the PdII(μ-Cl)MIII group of 32 may provide a useful platform for heterometallic reactive sites exerting their cooperative effects. Electrochemical Properties of PdIIMIIIM′III Trinuclear Complexes (32: M, M′ = Rh, Ir). Cyclic voltammograms of complexes 32a−d were measured in acetonitrile containing 0.1 M [nBu4N][PF6] with a glassy-carbon working electrode (Figure S9, Supporting Information), and the peak potentials vs Fc/Fc+ redox couple are given in Table 4 together with those for 1b and 23a,b as Table 4. Redox Potentials for Reduction of PdII, MIII, and M′III Sites of 32a−d and Reference Compounds 1b and 23a,ba

Figure 7. ORTEP diagram for the complex cation of [PdCl(μCl)(Cp*IrCl)(Cp*RhCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (32c). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

32a 32b 32c 32d 1b 23a 23b

summarized in Table S2 (the plot of 32a is shown as Figure S8 in the Supporting Information). The complex cation of 32c contains the PdII, RhIII, and IrIII metal ions assembled by a dpmppm ligand in κ2,κ1,κ1 fashion, in such a way that the [Pd1P1C1P2C2P3] and the [Pd1P3C3P4Ir1Cl2] six-membered rings are fused by sharing the Pd1−P3 bond. The Pd1 atom is coordinated by the inner (P3) and outer (P1) phosphorus atoms of dpmppm and the terminal (Cl1) and the bridging (Cl2) chloride anions in a square-planar geometry. The Cp*RhCl2 fragment is bound to the inner P2 atom of dpmppm, and the [Pd1P1C1P2C2P3] six-membered ring takes a twist-boat conformation as observed in 23a,b and 31a−c. The CpIrCl2 fragment is ligated by the outer P4 atom of dpmppm, with one of the Cl atoms (Cl2) further bridging to Pd1 (Ir1− Cl2 = 2.453(2) Å, Pd1−Cl2 = 2.418(2) Å, Ir1−Cl2−Pd1 = 123.0(1)°). The Pd1···Ir1 interatomic distance of 4.2801(8) Å indicates the absence of a direct metal−metal interaction. The

Epc1, Vb

Epc2, V

Epc3, V

−1.08 (Pd) −1.09 (Pd) −1.11 (Pd) −1.06 (Pd) −1.29 (Pd) −1.31 (Pd) −1.32 (Pd)

−1.40 (Rh′) −1.51 (Ir′) −1.47 (Ir′) −1.47 (Rh′)

−1.53 (Rh) −2.16 (Ir) −1.57 (Rh) −2.15 (Ir)

−1.47 (Rh) −2.04 (Ir)

a

Cyclic voltammograms were measured in acetonitrile (0.1 M [nBu4N][PF6]) with a glassy-carbon working electrode at a scan rate of 100 mV/s. See Scheme 4 for the labels of M and M′ atoms. bThe potentials are referenced to the redox couple of Fc/Fc+ (1 mM in acetonitrile).

reference compounds. At first, the mononuclear PdII complex 1b showed an irreversible reduction peak at −1.29 V, which was assumed to be a one-electron-reduction process by a coulometric analysis, and those of the PdIIMIII bimetallic complexes 23a (M = Rh) and 23b (M = Ir) exhibited two irreversible reduction peaks at −1.31 and −1.47 V (23a) and −1.32 and −2.04 V (23b); the more positive peak is assignable to the reduction process of the PdII center and the negative peak to that of RhIII (23a) or IrIII (23b). 141


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coordinates to the square-planar PdII center with two outer and one inner phosphorus atom to form pincer-type six- and fourmembered bicyclic rings (Figure 8). The remaining inner phosphine, involved in the [PdPCPCP] six-membered chelate ring with a stable chair conformation, is uncoordinated and readily reacted with metal fragments such as AgX (X = TfO, TsO) and Cp*MCl2 (M = Rh, Ir). Whereas the less bulky AgX unit is just attached to the uncoordinated phosphine without any structural changes (20 in Figure 8), the bulky Cp*MCl2 was trapped onto the free phosphine to bring about a crucial conformational change of the [PdPCPCP] six-membered ring from the stable chair structure in 1 to the twist-boat one in 21 and 23. This structural switch further promoted the ring opening of the four-membered chelate ring to trap the second Cp*M′Cl2 fragment to assemble the PdIIMIIIM′III trinuclear systems [PdCl2(Cp*M′Cl2)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)] (31) and [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppmκ2,κ1,κ1)]PF6 (32) (M, M′ = Rh, Ir). The flexible coordination behavior of dpmppm is able to organize a so-called “allosteric switch” around the PdII center, that is, a trap of the Cp*MCl2 species on the free phosphine involved in the six-membered ring destabilizing the fused four-membered ring, and establish the stepwise construction of the trinuclear metal ions. These results are interesting and useful to develop heterometallic systems with synergistic effects.

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ASSOCIATED CONTENT S Supporting Information * Text, tables, figures, and CIF files giving synthetic procedures, structural parameters, the structures of 1a, 22a, 23a, 31b,c, and 32a, 31P{1H} NMR spectra of 21a, 22a, and 31a−c, cyclic voltammograms of 1b, 23a, 23b, and 32a−d, and crystal data for 1a,b, 20b, 22a, 23a,b, 31a−c, and 32a,c. This material is available free of charge via the Internet at http://pubs.acs.org.

Figure 8. Structural changes of dpmppm around the PdII center during reactions of complexes 1 with AgX (X = TfO, TsO) and the Cp*MCl2 fragments (R = Rh, Ir), leading to complexes 20, 21, 23, 31, and 32. [M] = Cp*MCl2.

It should be noted that the Cp*RhCl2 center is reduced more easily than the Cp*IrCl2 center, which might be attributed to the short Ir−P bond length of 23b. In the cyclic voltammograms of 32a−d, three irreversible reduction peaks corresponding to the PdII, M′III, and MIII centers were observed. In all complexes, the peak potentials for the reduction of PdII (Epc1 = −1.06 to −1.11 V) were more positive by ca. 0.2 V than those of 1b and 23a,b (−1.29 to −1.32 V), suggesting that the electron deficiency of the PdII center increased by the Cl− bridging instead of the terminal P chelation. The irreversible reduction peaks for the M center of Rh were observed at −1.53 (32a) and −1.57 V (32c) and those of Ir at −2.16 (32b) and −2.15 V (32d), which were similar to the potentials of 23a,b as mentioned above. In contrast, the reduction potentials for the M′ site involved in the PdII(μ-Cl)M′III moiety were found at −1.40 (32a) and −1.47 V (32d) for RhIII and at −1.51 (32b) and −1.47 V (32c) for the IrIII center. Interestingly, the IrIII site in the PdII(μ-Cl)M′III unit is significantly electron deficient and is reduced at quite positive potentials in comparison with the IrIII center of the M site, whereas the two RhIII centers of the M and M′ sites showed similar redox responses. The detailed electrochemical reactions of 32 will be investigated, in particular, on the possibility of PdI−MII bond formation upon their reductions.

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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Fax: +81 742-20-3847. Tel: +81 742-20-3399.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research and that on Priority Area 2107 (no. 22108521) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. T.T. is grateful to Nara Women’s University for a research project grant.

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REFERENCES

(1) (a) Metal Clusters in Chemistry; Braunstein, P., Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, Germany, 1999; Vol. 1. (b) Catalysis by Di- and Polynuclear Metal Cluster Complexes; Adams, R. D., Cotton, F. A., Eds.; Wiley-VCH: Weinheim, Germany, 1998. (c) Comprehensive Organometallic Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier: Oxford, U.K., 2007; Vol. 12. (d) Multimetallic Catalysts in Organic Synthesis; Shibasaki, M., Yamamoto, Y., Eds.; Wiley-VCH: Weinheim, Germany, 2004. (e) Sculfort, S.; Braunstein, P. Chem. Soc. Rev. 2011, 40, 2741−2760. (f) Fernández, E. J.; Laguna, A.; López-de-Luzuriaga, J. N. Dalton Trans. 2007, 1969− 1981. (g) Lee, S. C.; Holm, R. H. Chem. Rev. 2004, 104, 1135−1157. (2) For recent examples, see: (a) Well, K. D.; McDonald, R.; Ferguson, M. J.; Cowie, M. Organometallics 2011, 30, 2654−2669. (b) Pan, Q.-J.; Zhou, X.; Guo, Y.-R.; Fu, H.-G.; Zhang, H.-X. Inorg. Chem. 2009, 48, 2844−2854. (c) Esswein, A. J.; Nocera, D. G. Chem.

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CONCLUSIONS In the present study, the tetraphosphine dpmppm (mesobis[((diphenylphosphino)methyl)phenylphosphino]methane) proved to be quite flexible and effective to assemble PdIIMIIIM′III trinuclear metal ions in a κ2,κ1,κ1 fashion (M, M′ = Rh, Ir). In the precursor complex [PdCl(dpmppm-κ3)]+ (1), the dpmppm ligand 142


Organometallics

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