(M = Rh, Pt, Pd, Ni) Supported by meso-1,3-Bis ... - ACS Publications

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Cyclic Trinuclear Rh2M Complexes (M = Rh, Pt, Pd, Ni) Supported by meso-1,3-Bis[(diphenylphosphinomethyl)phenylphosphino]propane Takayuki Nakajima,* Sachi Kurai, Sayo Noda, Maki Zouda, Bunsho Kure, 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 [MCl2(cod)] (M = Pd, Pt) with a tetraphosphine, meso-1,3-bis[(diphenylphosphinomethyl)phenylphosphino]propane (dpmppp), afforded the mononuclear complexes [MCl2(dpmppp)] (M = Pd (3a), Pt (3b)), in which the dpmppp ligand coordinated to the M ion by two inner phosphorus atoms to form a six-membered chelate ring with two outer phosphines uncoordinated. The pendant outer phosphines readily reacted with [RhCl(CO)2]2 to give the cationic heterotrinuclear complexes [MRh2(μ-Cl)3(μdpmppp)(CO)2]X (X = [RhCl2(CO)2], M = Pd (4a), Pt (4b); X = PF6, M = Pd (5a), Pt (5b)). The nickel analogue [NiRh2(μ-Cl)3(μ-dpmppp)(CO)2]PF6 (5c) was also prepared. A neutral homotrinuclear Rh3 complex, [Rh3(μ-Cl)3(μdpmppp)(CO)2] (6), was synthesized by the reaction of [RhCl(CO)2]2 with dpmppp and was further reacted with HgX2 (X = Cl, Br, I) to afford the Rh3Hg tetranuclear complexes [Rh3(HgX)(μ-Cl)2(μX)(μ-dpmppp)(CO)2]PF6 (X = Cl (7a), Br (7b), I (7c)), where the Rh3(μ-Cl)2(μ-X) cores act as tridentate ligands to form three donor−acceptor Rh→Hg interactions. The two CO ligands of 7a−c were replaced by XylNC to yield [Rh3(HgX)(μCl)2(μ-X)(μ-dpmppp)(XylNC)2]PF6 (X = Cl (8a), Br (8b), I (8c)). The isocyanides had an appreciable influence on the three Rh→Hg interactions, which was monitored by the 2JHgP values observed in the 31P{1H} NMR spectra and discussed on the basis of DFT calculations. Complex 6 also reacted with CuCl and HBF4 to give [Rh3(CuCl)(μ-Cl)3(μ-dpmppp)(CO)2] (9) and [Rh3(μ3-H)(μ-Cl)3(μ-dpmppp)(CO)2]BF4 (10), respectively. These results suggested that the new tetraphosphine dpmppm proved quite useful in constructing fine-tunable heterometallic frameworks.

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INTRODUCTION Transition-metal clusters are of potential interest due to their diverse properties as molecular-based functional materials such as catalysts and electronic and magnetic devices induced by synergistic effects between adjacent metal centers.1 Designing metal supporting ligands is crucial to tuning metal−metal interactions in various structures of multinuclear complexes. Among a number of polydentate ligands stabilizing multimetallic systems, polyphosphine ligands such as bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphinomethyl)phenylphosphine (dpmp) have been widely used to create metal−metal-bonded homo- and heteromultinuclear structures.2 However, tetraphosphine ligands, in contrast to di- and triphosphines, have still been limited due to their synthetic difficulty and complicated stereoisomerism. The linearly ordered tetraphosphines bis[((2-diphenylphosphino)ethyl)phenylphosphino]methane (tetraphos-2,1,2), 1,2-bis[((2-diphenylphosphino)ethyl)phenylphosphino]ethane (tetraphos-2,2,2), and 1,3-bis[((2diphenylphosphino)ethyl)phenylphosphino]propane (tetraphos-2,3,2) and their derivatives have been known to form mono- and dinuclear systems;3 however, multinuclear structures containing more than three metal ions supported by these linear tetraphosphines are limited to a few examples with Au4, Re4, Pt2Pd, and PdRu2 centers.4 Recently, we have synthesized a methylene-bridged linear tetraphosphine ligand, meso-bis© 2012 American Chemical Society

[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm, tetraphos-1,1,1), which has proven very effective in assembling linearly ordered tetrametallic chains of group 11 metal ions. Two dpmppm ligands support a flexible tetragold(I) chain with a bent {Au4(μ-dpmppm)2}4+ motif which captured a counteranion (X = PF6, Cl) having intriguing switching luminous properties.5a Ag(I) and Cu(I) ions have also been assembled by two dpmppm ligands to form the bent and linear chains {Ag4(μ-dpmppm)2}4+ and {Cu4(μ-X)3(μ-dpmppm)2}+ with a variety of ancillary ligands,5b,c and the latter CuI4 chains could further be transformed to the ladder-type CuI8 complexes [Cu8(μ-X)2(μ3-X)6(μ-dpmppm)2] (X = Cl, Br, I). The heterometallic octanuclear rings {[Au 2 MCuCl 2 (μdpmppm)2]2}4+ (M = Au, Ag, Cu) were also synthesized and elucidated to incorporate a BF4− anion into the ring in the solid and solution states.5d The flexible coordination behavior of dpmppm further organized the stepwise assembly of the heterotrinuclear metal ions [PdCl2(Cp*M′Cl2)(Cp*MCl2)(μdpmppm-κ2,κ1,κ1)] and [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μdpmppm-κ2,κ1,κ1)]+ (M, M′ = Rh, Ir, Cp* = pentamethylcyclopentadienyl).5e These studies demonstrated the potential versatility of multimetallic structures constructed by utilizing methylene-bridged tetraphosphine ligands. Received: April 6, 2012 Published: May 22, 2012 4283

dx.doi.org/10.1021/om300278k | Organometallics 2012, 31, 4283−4294

Organometallics

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(KBr): ν 1433 (s), 735 (s), 691 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 331 nm (4.95). ESI-MS (CH2Cl2): m/z 796.860 (z1, [PdCl(dpmppp)]+ (797.082)). [PtCl2(dpmppp)]·0.5CH2Cl2 (3b·0.5CH2Cl2). By a procedure similar to that for 3a, treating 2 (37 mg, 0.056 mmol) with [PtCl2(cod)] (21 mg, 0.056 mmol), colorless crystals of 3b·0.5CH2Cl2 were isolated in 42% yield (22 mg). Anal. Calcd for C41.5H41Cl3P4Pt: C, 51.65; H, 4.28. Found: C, 51.72; H, 4.02. IR (KBr): ν 1434 (s), 736 (s), 691 (s) 490 (m) cm−1. ESI-MS (CH2Cl2): m/z 886.945 (z1, [PtCl(dpmppp)]+ (887.142)). [PdRh2(μ-Cl)3(μ-dpmppp)(CO)2][RhCl2(CO)2] (4a). A dichloromethane solution (10 mL) of 3a (18 mg, 0.020 mmol) and [RhCl(CO)2]2 (8.5 mg, 0.020 mmol) was stirred at room temperature for 1 h. The solvent was concentrated to ca. 3 mL. After addition of diethyl ether, the solution was allowed to stand in the refrigerator to afford orange crystals of 4a. Yield: 12 mg, 44%. Anal. Calcd for C45H40Cl5O4P4PdRh3: C, 39.71; H, 2.96. Found: C, 39.36; H, 3.00. IR (KBr): ν 2067 (s), 2008 (s), 1996 (s), 1984 (s), 1434 (m) cm−1. UV− vis (CH2Cl2): λmax (log ε) 332 nm (3.94). 1H NMR (CD2Cl2): δ 0.88 (br, 2H, CH2), 1.36 (br, 2H, CH2), 2.41 (br, 2H, CH2), 3.08 (br, 2H, CH2), 3.99 (br, 2H, CH2), 7.3−8.3 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2): δ 13.0 (d, JPP = 20 Hz, Pin), 38.2 (dd, JPRh = 167 Hz, JPP = 20 Hz, 2P, Pout). [PtRh 2 (μ-Cl) 3 (μ-dpmppp)(CO) 2 ][RhCl 2 (CO) 2 ]·0.5CH 2 Cl 2 (4b·0.5CH2Cl2). By a method similar to that for 4a, using 3b (19 mg, 0.020 mmol) and [RhCl(CO)2]2 (8.2 mg, 0.021 mmol), orange crystals of 4b·0.5CH2Cl2 were isolated. Yield: 12 mg, 40%. Anal. Calcd for C45.5H41Cl6O4P4PdRh3: C, 36.72; H, 2.77. Found: C, 36.79; H, 2.55. IR (KBr): ν 2067 (s), 2009 (s), 1996 (s), 1985 (s), 1434 (m), 1098(m) cm−1. UV−vis: λmax (log ε) 358 (4.02), 430 nm (3.99). 1H NMR (CD2Cl2): δ 1.15 (br, 3H, CH2), 2.15 (br, 1H, CH2), 2.55 (br, 2H, CH2), 3.03 (br, 2H, CH2), 3.84 (br, 2H, CH2), 7.2−8.2 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2): δ −8.1 (dd, JPP = 10, 5 Hz, JPPt = 3479 Hz, 2P, Pin), 38.4 (ddd, JPRh = 166 Hz, JPP = 10, 5 Hz, 2P, Pout). [PdRh2(μ-Cl)3(μ-dpmppp)(CO)2](PF6) (5a). To a solution of 3a (20.5 mg, 0.025 mmol) and [RhCl(CO)2]2 (9.7 mg, 0.025 mmol) in dichloromethane (5 mL) were added NH4PF6 (21 mg, 0.13 mmol) and methanol (5 mL), and the reaction mixture was refluxed for 1 h. Concentration of the solvent gave orange crystals of 5a. Yield: 16 mg, 46%. Anal. Calcd for C43H40Cl3F6O2P5PdRh2: C, 40.47; H, 3.16. Found: C, 40.36; H, 3.41. IR (KBr): ν 2010 (s), 1435 (m), 836 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 348 nm (3.22). ESI-MS (CH 2 Cl 2 ): m/z 1130.552 (z1, [PdRh 2 Cl 3 (dpmppp)(CO) 2 ] + (1130.818)). 1H NMR (CD2Cl2): δ 0.88 (br, 2H, CH2), 1.26 (br, 2H, CH2), 2.18 (br, 2H, CH2), 2.87 (br, 2H, CH2), 4.05 (br, 2H, CH2), 7.3−8.4 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2): δ 12.2 (d, JPP = 20 Hz, Pin), 38.2 (dd, JPRh = 167 Hz, JPP = 20 Hz, 2P, Pout), −144.5 (sep, JPF = 712 Hz, 1P). [PtRh2(μ-Cl)3(μ-dpmppp)(CO)2](PF6)·CH2Cl2 (5b·CH2Cl2). By a procedure similar to that for 5a, using 3b (20 mg, 0.021 mmol), [RhCl(CO)2]2 (8.5 mg, 0.022 mmol), and NH4PF6 (18 mg, 0.11 mmol), orange crystals of 5b·CH2Cl2 were isolated. Yield: 16 mg, 55%. Anal. Calcd for C44H42Cl5F6O2P5PdRh2: C, 36.45; H, 2.92. Found: C, 36.22; H, 2.89. IR (KBr): ν 2010 (s), 1436 (m), 1098 (m), 840 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 364 nm (4.02), 432 (3.99). ESIMS (CH2Cl2): m/z 1218.974 (z1, [PtRh2Cl3(dpmppp)(CO)2]+ (1218.879)). 1H NMR (CD2Cl2): δ 1.15 (br, 3H, CH2), 2.08 (br, 1H, CH2), 2.26 (br, 2H, CH2), 2.76 (br, 2H, CH2), 3.87 (br, 2H, CH2), 7.2−8.2 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2): −8.8 (dd, JPP = 10, 5 Hz, JPPt = 3478 Hz, 2P, Pin), 38.5 (ddd, JPRh = 165 Hz, JPP = 10, 5 Hz, 2P, Pout), −144.6 (sep, JPF = 711 Hz, 1P). [NiRh2(μ-Cl)3(μ-dpmppp)(CO)2](PF6) (5c). To a solution of dpmppp (52 mg, 0.078 mmol) in dichloromethane (10 mL) and methanol (7.5 mL) was added NiCl2·6H2O (18 mg, 0.077 mmol), and the reaction mixture was stirred at room temperature for 1 h. The solvent was removed under reduced pressure to dryness, and the residue was washed with Et2O (5 mL × 3) and extracted with 10 mL of dichloromethane. To the extract were added [RhCl(CO)2]2 (30 mg, 0.076 mmol) and NH4PF6 (66 mg, 0.40 mmol), and the reaction mixture was stirred at room temperature for 12 h. The mixture was

In this study, we have extended our study with dpmppm to that with a new tetraphosphine, meso-1,3-bis[(diphenylphosphinomethyl)phenylphosphino]propane (dpmppp, tetraphos-1,3,1), aiming to construct various homoand heteromultinuclear structures by tuning the length of the central methylene chain to a 1,3-propylene unit. The dpmppp ligand has been shown to stabilize cyclic trinuclear Rh2M complexes, [Rh3(μ-Cl)3(μ-dpmppp)(CO)2] and [MRh2(μCl)3(μ-dpmppp)(CO)2]+ (M = Pt, Pd, Ni). In addition, the homotrinuclear Rh3 complex was revealed to further react with HgII and CuI salts to form tetranuclear Rh3Hg complexes, [Rh3(HgX)(μ-Cl)2(μ-X)(μ-dpmppp)(CO)2]+ (X = Cl, Br, I), and [Rh3(CuCl)(μ-Cl)3(μ-dpmppp)(CO)2]. We wish to report herein the synthesis, characterization, and electronic structures of the tri- and tetranuclear complexes assembled by the new tetraphosphine ligand dpmppp.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out under a nitrogen atmosphere using standard Schlenk techniques. 1,3-Bis(phenylphosphino)propane was prepared by the reported procedure.6 Reagent grade solvents were dried by 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 a Bruker AV-300N spectrometer at 300 and 121 MHz, respectively. 1H NMR spectra were referenced to TMS as an external standard, and 31P{1H} NMR spectra were referenced to 85% H3PO4 as an external standard. ESI-TOF MS spectra were recorded on a JEOL JMS-T100LC high-resolution mass spectrometer with positive ionization mode. meso-/rac-Bis[(trimethylsilylmethyl)phenylphosphino]propane (1; tmsppp). To a solution of 1,3-bis(phenylphosphino)propane (4.98 g, 17.8 mmol) in THF (140 mL) was added dropwise n-BuLi (25 mL, 39.3 mmol, 1.57 M in hexane) at −78 °C. At the same temperature, N,N,N′,N′-tetramethyl-1,2-diaminoethane (TMEDA; 0.55 mL, 3.67 mmol) was added. Then, the cooling bath was removed and the mixture was stirred at room temperature for 1.5 h. To the mixture was added (chloromethyl)trimethylsilane (10 mL, 71.6 mmol) at −78 °C. The resultant solution was stirred overnight at room temperature before degassed H2O (140 mL) was added. The organic phase was separated, and the aqueous phase was extracted with Et2O (20 mL × 3). The combined organic extract was dried over Na2SO4, filtered, and concentrated under reduced pressure to give 1 (7.2 g, 93%). 1H NMR (CDCl3): δ −0.10 (s, 18H, CH3), −0.09 (s, 18H, CH3), 0.88 (m, 8H, CH2), 1.25 (m, 4H, CH2), 1.66 (m, 8H, CH2), 7.3−7.5 (m, 20H, Ph). 31 1 P{ H} NMR (CDCl3): δ −31.1 (s, 2P), −31.0 (s, 2P). meso-1,3-Bis[(diphenylphosphinomethyl)phenylphosphino]propane (2; dpmppp). To 7.20 g (16.6 mmol) of 1 was added PPh2Cl (7.35 g, 33.3 mmol) at room temperature, and the mixture was refluxed at 120 °C for 1 h. By addition of dry EtOH (140 mL) white precipitates were formed, which were filtered off, washed with Et2O (20 mL × 3), and dried under vacuum to give dpmppp as a mixture of meso and rac isomers (2; meso:rac = 3:1; 2.13 g, 20%). 1H NMR (CDCl3): δ 1.39 (m, 2H, CH2), 1.78 (m, 4H, CH2), 2.37 (m, 4H, CH2), 7.3−7.4 (m, 30H, Ph). 31P{1H} NMR (CDCl3): δ −30.8 (d, JPP = 116 Hz, rac), −30.6 (d, JPP = 115 Hz, meso), −22.7 (d, JPP = 115 Hz, meso), −22.6 (d, JPP = 116 Hz, rac). [PdCl2(dpmppp)]·0.75CH2Cl2 (3a·0.75CH2Cl2). To a solution of 2 (46 mg, 0.071 mmol) in dichloromethane (10 mL) was added [PdCl2(cod)] (20 mg, 0.071 mmol), and the reaction mixture was stirred at room temperature for 1 h. The solvent was removed under reduced pressure to dryness, and the residue was washed with Et2O (5 mL × 3) and extracted with 5 mL of dichloromethane. The extract was concentrated to ca. 3 mL. After addition of diethyl ether, the solution was allowed to stand in the refrigerator to afford pale yellow crystals of 3a, which were collected by filtration, washed with Et2O, and dried under reduced pressure. Yield: 44 mg, 75%. Anal. Calcd for C41.75H40.5Cl3.5P4Pd: C, 55.86; H, 4.66. Found: C, 55.92; H, 4.55. IR 4284


Organometallics

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Table 1. Crystallographic Data of Complexes 3a, 3b·H2O, and 4a,b formula 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(Mo Kα), mm−1 2θ range, deg Rint no. of rflns collected no. of unique rflns no. of obsd rflns (I > 2σ(I)) no. of variables R1a wR2b GOF a

3a

3b·H2O

4a

4b

C41H40Cl2P4Pd 833.97 triclinic P1̅ 12.9431(6) 12.9473(1) 14.0177(4) 79.240(15) 70.22(1) 60.12(1) 1916.2(1) 2 −120 1.445 0.820 6−55 0.015 17 246 8281 7613 435 0.028 0.073 0.948

C41H42Cl2OP4Pt 940.67 triclinic P1̅ 12.9466(2) 12.9941(2) 14.0856(1) 81.45(2) 70.32(2) 60.17(2) 1935.0(4) 2 −120 1.614 3.947 6−55 0.033 17 661 8441 7838 443 0.038 0.100 1.023

C45H40Cl5O4P4PdRh3 1361.09 monoclinic P21/n 14.751(1) 22.467(1) 15.888(1)

C45H40Cl5O4P4PtRh3 1449.78 monoclinic P21/n 14.806(5) 22.404(7) 15.943(5)

113.480(3)

113.955(4)

4829.4(6) 4 −120 1.872 1.822 6−55 0.070 43 730 10 774 7065 565 0.038 0.077 0.880

4833(3) 4 −120 1.992 4.329 6−55 0.048 44 130 10 879 8726 561 0.033 0.075 0.935

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

passed through a filter and concentrated to ca. 3 mL. After addition of diethyl ether, the solution was allowed to stand in the refrigerator to afford dark brown crystals of 5c. Yield: 39 mg, 40%. Anal. Calcd for C43H40Cl3F6O2P5NiRh2: C, 42.04; H, 3.28. Found: C, 41.84; H, 3.68. IR (KBr): ν 2009 (s), 1436, 1098 (s), 837 (m). ESI-MS (CH2Cl2): m/ z 1082.900 (z1, [NiRh2Cl3(dpmppp)(CO)2]+ (1082.848)). 1H NMR (CD2Cl2): δ 0.93 (br, 2H, CH2), 1.19 (br, 1H, CH2), 1.78 (br, 2H, CH2), 2.00 (br, 1H, CH2), 2.50 (br, 2H, CH2), 3.71 (br, 2H, CH2), 7.3−8.3 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2): δ 3.3 (t, JPP = 11 Hz, 2P, Pin), 38.3 (dt, JPRh = 164 Hz, JPP = 11 Hz, 2P, Pout), −144.6 (sep, JPF = 711 Hz, 1P). [Rh3(μ-Cl)3(μ-dpmppp)(CO)2]·0.25CH2Cl2 (6·0.25CH2Cl2). To a solution of 2 (28 mg, 0.042 mmol) in dichloromethane (10 mL) was added [RhCl(CO)2]2 (25 mg, 0.063 mmol), and the reaction mixture was stirred at room temperature for 1 h. The solvent was removed under reduced pressure to dryness, and the residue was washed with Et2O (5 mL × 3) and extracted with 5 mL of dichloromethane. The extract was concentrated to ca. 3 mL, and diethyl ether was carefully added; this mixture was allowed to stand in the refrigerator to afford red crystals of 6·0.25CH2Cl2. Yield: 17 mg, 37%. Anal. Calcd for C43.25H40.5Cl3.5O2P4Rh3: C, 45.21; H, 3.55. Found: C, 45.19; H, 3.86. IR (KBr): ν 1980 (s), 1433 (m), 735 (s), 691 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 300 nm (3.52), 434 (3.53). 1H NMR (CD2Cl2): δ 0.96 (br, 3H, CH2), 1.24 (br, 1H, CH2), 1.75 (br, 2H, CH2), 2.48 (br, 2H, CH2), 3.80 (br, 2H, CH2), 7.2−8.3 (m, 30H, Ph). 31 1 P{ H} NMR (CD2Cl2): δ 22.5 (ddd, JPRh = 175 Hz, JPP = 20, 12 Hz, 2P, Pin), 38.7 (ddd, JPRh = 173 Hz, JPP = 20, 20 Hz, 2P, Pout). [Rh3(HgCl)(μ-Cl)3(μ-dpmppp)(CO)2]PF6 (7a). To a solution of 6 (50 mg, 0.044 mmol) in dichloromethane (13 mL) were added HgCl2 (12 mg, 0.045 mmol) and NH4PF6 (52 mg, 0.32 mmol), and the reaction mixture was stirred at room temperature overnight. The solvent was concentrated to ca. 3 mL. After addition of diethyl ether, the solution was allowed to stand in the refrigerator to afford dark purple crystals of 7a. Yield: 47 mg, 71%. Anal. Calcd for C43H40Cl4F6HgO2P5Rh3: C, 34.23; H, 2.67. Found: C, 34.47; H, 2.77. IR (KBr): ν 2043 (s), 1436 (m), 1097 (m), 839 (s) cm−1. UV− vis (CH2Cl2): λmax (log ε) 544 nm (4.35). ESI-MS (CH2Cl2): m/z 1362.837 (z1, [Rh3(HgCl)Cl3(dpmppp)(CO)2]+ (1362.758)). 1H

NMR (CD3CN): δ 2.11 (m, 1H, CH2), 2.50 (m, 2H, CH2), 2.81 (m, 1H, CH2), 2.98 (m, 2H, CH2), 3.24 (m, 2H, CH2), 3.47 (m, 2H, CH2), 7.17−7.91 (br, 30H, Ph). 31P{1H} NMR (CD3CN): δ 30.7 (dt, 1 JRhP = 131 Hz, JPP = 6 Hz, 2JHgP = 335 Hz), 39.5 (dt, 1JRhP = 151, Hz JPP = 7 Hz, 2JHgP = 66 Hz), −144.2 (sep, JPF = 706 Hz, 1P). [Rh 3 (HgBr)(μ-Cl) 2 (μ-Br)(μ-dpmppp)(CO) 2 ]PF 6 ·0.5CH 2 Cl 2 (7b·0.5CH2Cl2). By a procedure similar to that for 7a, 6 (24.6 mg, 0.021 mmol) was reacted with HgBr2 (8.1 mg, 0.023 mmol) and NH4PF6 (27.3 mg, 0.17 mmol) to afford purple crystals of 7b·0.5CH2Cl2 (13.6 mg, 39%). Anal. Calcd for C43.5H41Br2Cl3F6HgO2P5Rh3: C, 31.86; H, 2.52. Found: C, 31.63; H, 2.56. IR (KBr): ν 2042 (s), 2019 (s) 1435 (m), 1097 (m), 836 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 546 nm (4.36). ESI-MS (CH2Cl2): m/z 1451.766 (z1, [Rh3(HgBr)Cl2Br(dpmppp)(CO)2]+ (1451.648)). 1H NMR (CD3CN): δ 2.04 (m, 1H, CH2), 2.50 (m, 2H, CH2), 2.82 (m, 1H, CH2), 3.00 (m, 2H, CH2), 3.25 (m, 2H, CH2), 3.48 (m, 2H, CH2), 7.18−7.86 (br, 30H, Ph). 31P{1H} NMR (CD3CN): δ 29.3 (dt, 1JRhP = 135 Hz, JPP = 6 Hz, 2JHgP = 302 Hz), 38.7 (dt, 1JRhP = 150 Hz, JPP = 7 Hz, 2JHgP = 69 Hz), −144.3 (sep, JPF = 706 Hz, 1P). [ R h 3 ( H g I) ( μ - C l ) 2 (μ - I ) ( μ - d p m p p p ) ( C O ) 2 ] P F 6 · 3 C H 2 C l 2 (7c·3CH2Cl2). By a procedure similar to that for 7a, using 6 (52 mg, 0.045 mmol), HgI2 (21 mg, 0.047 mmol), and NH4PF6 (54 mg, 0.33 mmol), complex 7c·3CH2Cl2 was isolated as dark purple crystals (52 mg, 59%). Anal. Calcd for C46H46Cl8F6Hg I2O2P5Rh3: C, 28.29; H, 2.38. Found: C, 28.26; H, 2.48. IR (KBr): ν 2036 (s), 2013 (s) 1436 (m), 1098 (m), 836 (s) cm−1. UV−vis (CH2Cl2): λmax (log ε) 382 (4.36), 548 nm (4.18). ESI-MS (CH3CN): m/z 1545.711 (z1, [Rh3(HgI)Cl2I(dpmppp)(CO)2]+ (1546.631)). 1H NMR (CD3CN): δ 1.60 (m, 1H, CH2), 2.35 (m, 2H, CH2), 2.62 (m, 1H, CH2), 2.84 (m, 2H, CH2), 3.19 (m, 2H, CH2), 3.38 (m, 2H, CH2), 7.17−7.91 (m, 30H, Ph). 31P{1H} NMR (CD3CN): δ 26.4 (br d, 1JRhP = 139 Hz, 2 JHgP = 253 Hz), 35.1 (br d, 1JRhP = 148 Hz), −144.2 (sep, JPF = 706 Hz, 1P). [Rh3(HgCl)(μ-Cl)3(μ-dpmppp)(XylNC)2]PF6 (8a). To a solution of 7a (13 mg, 8.3 μmol) in acetonitrile (10 mL) was added 2,6-xylyl isocyanide (XylNC) (2.5 mg, 0.019 mmol), and the reaction mixture was stirred at room temperature overnight. The solvent was 4285


Organometallics

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Table 2. Crystallographic Data of Complexes 5a·1.5CH2Cl2, 5b·2CH2Cl2, 5c·2CH2Cl2, 6, and 7a·2CH2Cl2 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(Mo Kα), mm−1 2θ range, deg Rint no. of rflns collected no. of unique rflns no. of obsd rflns (I > 2σ(I)) no. of variables R1a wR2b GOF a

5a·1.5CH2Cl2

5b·2CH2Cl2

5c·2CH2Cl2

6

7a·2CH2Cl2

C44.5H43Cl6F6O2P5PdRh 1403.62 monoclinic P21/c 9.3394(3) 17.9855(6) 32.255(1) 90.333(2) 5417.9(3) 4 −120 1.721 1.429 6−55 0.033 50 574 12 321 10 851 608 0.057 0.162 1.086

C45H44Cl7F6O2P5RhPd 1534.77 monoclinic P21/c 9.3739(8) 18.0130(2) 32.212(3) 90.7900(9) 5438.5(8) 4 −120 1.874 3.702 6−55 0.034 44 089 12 180 10 726 623 0.047 0.126 1.083

C45H44Cl7F6NiO2P5Rh2 1398.38 monoclinic P21/c 9.4603(9) 18.403(1) 31.204(2) 98.529(4) 5372.6(7) 4 −120 1.729 1.507 6−55 0.055 48 286 12 156 9466 613 0.066 0.194 1.099

C43H40Cl3O2P4Rh3 1127.76 trigonal P3̅ 28.966(6)

C45H44Cl8F6HgO2P5Rh3 1678.63 monoclinic P21/n 12.881(6) 19.929(8) 21.468(9) 100.104(5) 5425(4) 4 −120 2.055 4.323 6−55 0.032 50 583 12 307 10 851 621 0.037 0.100 1.092

9.561(2) 6948(3) 6 −120 1.617 1.399 6−55 0.081 64 804 10 634 7539 498 0.068 0.208 0.987

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 Complexes 7b·2CH2Cl2, 7c·2CH2Cl2, 8a·4CH2Cl2, 8b·3.5CH2Cl2, and 8c·3.5CH2Cl2 7b·2CH2Cl2

7c·2CH2Cl2

8a·4CH2Cl2

8b·3.5CH2Cl2

8c·3.5CH2Cl2

formula

C45H44Br2Cl6F6HgO2P5Rh3

C63H66Cl10F6HgN2P5Rh3

C62.5H65Br2Cl9F6HgN2P5Rh3

C62.5H65Cl9F6HgI2N2P5Rh3

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

1767.53 monoclinic P21/n 12.894(10) 20.027(14) 21.505(16) 99.159(12) 5482(7) 4 −120 2.141 5.643 6−55 0.059 65 420

C45H44Cl6 F6HgI2O2P5Rh3 1861.53 monoclinic P21/c 12.896(4) 20.279(6) 21.529(7) 99.757(4) 5549(3) 4 −120 2.228 5.244 6−55 0.039 51 907

2019.38 monoclinic P21/c 10.069(5) 40.21(2) 17.987(8) 90.570(4) 7282(6) 4 −120 1.842 3.343 6−55 0.066 52 478

2101.27 monoclinic P21/c 10.164(7) 40.57(3) 18.108(13) 90.263(7) 7466(9) 4 −120 1.864 4.262 6−55 0.054 54 178

2195.27 monoclinic P21/c 10.095(7) 40.30(3) 18.002(12) 90.680(12) 323(9) 4 −120 1.991 4.095 6−55 0.064 41 958

12 519 11 033

12 625 10 713

15 947 11 900

15 196 11 408

14 925 10 520

631 0.041 0.119 1.117

659 0.042 0.106 1.104

824 0.068 0.190 1.063

824 0.063 0.192 1.088

814 0.065 0.188 1.011

a

R1 = ∑||Fo| − |Fc||/∑|Fo| (for observed reflections with I > 2σ(I)). bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2 (for all reflections). 2H, CH2), 2.73 (m, 2H, CH2), 3.36 (m, 2H, CH2), 6.54 (d, 4H, Xyl), 6.74 (t, 2H, Xyl), 7.2−7.8 (m, 30H, Ph). 31P{1H} NMR (CD3CN): δ 29.1 (ddd, JPRh = 150 Hz, JPP = 13, 8 Hz, JPHg = 189 Hz, 2P, Pin), 40.0 (ddd, JPRh = 150 Hz, JPP = 13, 7 Hz, JPHg = 111 Hz, 2P, Pout) −144.5 (sep, JPF = 707 Hz, 1P). [Rh 3 (HgBr)(μ-Cl) 2 (μ-Br)(μ-dpmppp)(XylNC) 2 ]PF 6 ·Et 2 O (8b·Et2O). By a procedure similar to that for 8a, using 7b (8.9 mg, 5.4 μmol) and XylNC (1.5 mg, 11.4 μmol), dark purple crystals of

concentrated to ca. 3 mL. After addition of diethyl ether, the solution was allowed to stand in the refrigerator to afford dark purple crystals of 8a. Yield: 8.0 mg, 61%. Anal. Calcd for C59H58N2Cl4F6P5HgRh3: C, 41.32; H, 3.41; N, 1.63. Found: C, 41.58; H, 3.31; N, 1.63. IR (KBr): ν 2130 (s), 1435 (m), 1097 (m), 840 (s) cm−1. UV−vis (CH3CN): λmax (log ε) 570 nm (3.97). ESI-MS (CH2Cl2): m/z 1568.969 (z1, [Rh 3 (HgCl)Cl 3 (dpmppp)(XylNC) 2 ] + (1568.916)). 1 H NMR (CD3CN): δ 1.19 (m, 2H, CH2), 1.71 (s, 12H, o-CH3), 2.58 (m, 4286


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8b·Et2O were isolated. Yield: 5.2 mg, 53%. Anal. Calcd for C63H68N2OCl2Br2F6P5HgRh3: C, 40.29; H, 3.65; N, 1.49. Found: C, 39.97; H, 3.54; N, 1.47. IR (KBr): ν 2128 (s), 1435 (m), 1096 (m), 840 (s) cm−1. ESI-MS (CH3CN): m/z 1614.920 (z1, [Rh3HgCl3Br(dpmppp)(XylNC)2]+ (1614.865)), 1658.902 (z1, [Rh3(HgBr)Cl2Br(dpmppp)(XylNC)2]+ (1658.814)). 1H NMR (CD3CN): δ 1.19 (m, CH2), 1.82 (s, o-CH3), 1.25 (m, CH2), 2.44 (m, CH2), 2.59 (m, CH2), 2.79 (m, CH2), 3.29 (m, CH2), 3.55 (m, CH2), 6.62−6.90 (m, Xyl), 7.2−7.9 (m, Ph). 31P{1H} NMR (CD3CN): δ 29.9 (d, JPRh = 150 Hz), 38.2 (d, JPRh = 150 Hz, main), 38.9 (d, JPRh = 149 Hz, minor), −144.5 (sep, JPF = 707 Hz). [Rh 3 (HgI)(μ-Cl) 2 (μ-I)(μ-dpmppp)(XylNC) 2 ]PF 6 ·(CH 3 ) 2 CO (8c·(CH3)2CO). By a procedure similar to that for 8a, using 7c (13.8 mg, 7.1 μmol) and XylNC (2.1 mg, 16 μmol), from acetone/diethyl ether solution, dark purple crystals of 8c·(CH3)2CO were isolated. Yield: 8.7 mg, 65%. Anal. Calcd for C62H64N2OCl2I2F6P5HgRh3: C, 38.07; H, 3.30; N, 1.43. Found: C, 38.46; H, 3.07; N, 1.45. IR (KBr): ν 2125 (s), 1436 (m), 1096 (m), 842 (s) cm−1. ESI-MS (CD3CN): m/z 1660.963 (z1, [Rh 3 HgCl 3 I(dpmppp)(XylNC) 2 ] + (1660.852)), 1752.923 (z1, [Rh3(HgI)Cl2I(dpmppp)(XylNC)2]+ (1752.788)). 1H NMR (CD3CN): δ 1.20 (m, CH2), 1.82 (s, o-CH3), 1.88 (s, o-CH3), 1.25 (m, CH2), 2.46 (m, CH2), 2.61 (m, CH2), 2.72 (m, CH2), 3.26 (m, CH2), 3.65 (m, CH2), 6.62−7.00 (m, Xyl), 7.2−8.0 (m, Ph). 31 1 P{ H} NMR (CD3CN): δ 27.4 (JPRh = 153 Hz, main), 27.9 (ddd, JPRh = 152 Hz, minor), 35.7 (d, JPRh = 160 Hz), −144.5 (sep, JPF = 707 Hz). [Rh 3 (CuCl)( μ-Cl) 3 (μ-dpmppp)(CO) 2 ]·Et 2 O·0.5CH 2 Cl 2 (9·Et2O·0.5CH2Cl2). To a solution of 6 (16 mg, 0.014 mmol) in dichloromethane (10 mL) was added CuCl (1.4 mg, 0.014 mmol), and the reaction mixture was stirred at room temperature overnight. From a dichloromethane/diethyl ether solution at 2 °C, dark violet microcrystals of 9·Et2O·0.5CH2Cl2 were obtained in 68% yield (12 mg). Anal. Calcd for C47.5H51Cl5Cu3P4Rh3: C, 42.47; H, 3.83. Found: C, 42.35; H, 4.01. IR (KBr): ν 2024 (s), 1434 (m), 1095 (m), 840 (s), 705 (s) cm−1. 1H NMR (CD2Cl2): δ 1.23 (m, 2H, CH2), 2.38 (m, 2H, CH2), 3.00 (m, 2H, CH2), 3.44 (m, 2H, CH2), 3.62 (m, 2H, CH2), 7.21−8.01 (br, 30H, Ph). 31P{1H} NMR (CD2Cl2): δ 26.4 (ddd, 1JRhP = 164 Hz, JPP′ = 14, 8 Hz), 37.6 (ddd, 1JRhP = 158 Hz, JPP′ = 14, 8 Hz). X-ray Crystallography. Crystals of 3a, 3b·H 2 O, 4a,b, 5a·1.5CH 2 Cl 2 , 5b·2CH 2 Cl 2 , 5c·2CH 2 Cl 2 , 6, 7a·2CH 2 Cl 2 , 7b·2CH 2 Cl 2 , 7c·2CH 2 Cl 2 , 8a·4CH 2 Cl 2 , 8b·3.5CH 2 Cl 2 , and 8c·3.5CH 2Cl 2 suitable for X-ray analyses were obtained by recrystallization from dichloromethane/diethyl ether solutions and 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 1−3. All data were collected at −120 °C on a Rigaku AFC8R/Mercury CCD diffractometer equipped with graphitemonochromated Mo Kα radiation using a rotating-anode 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. 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)7 and corrected for Lorentz−polarization and absorption effects.8 The structures of complexes were solved by direct methods with SHELX-979 (4a,b, 6, 7b,c, 8c), SIR-9210a (5c, 7a, 8a,b), and SIR-9710b (3a, 3b, 5a, 5b), and were refined on F2 with full-matrix least-squares techniques with SHELXL-979 using the CrystaStructure 4.0 package.11 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 Windows PC with the Crystal Structure 4.0 package.11

of 1,3-bis(phenylphosphino)propane with n-BuLi and subsequent addition of Me3SiCH2Cl in the presence of TMEDA afforded 1 (tmsmppp) in 93% yield. Addition of Ph2PCl to 1, followed by precipitation from EtOH and washing with Et2O, afforded dpmppp (2) in 20% yield as a mixture of meso and rac isomers, the ratio of which was determined as ca. 3:1 by NMR spectroscopic methods (Scheme 1). The meso isomer rich mixture of dpmppp was used in the preparation of the following metal complexes. Scheme 1

When [MCl2(cod)] (M = Pd, Pt) was treated with 1 equiv of dpmppp in dichloromethane, the mononuclear complexes [MCl2(dpmppp-κ2)] (M = Pd (3a), Pt (3b)) were obtained in 75 and 42% yields, respectively. Complexes 3a,b were characterized by elemental analysis, ESI-MS spectra, and X-ray crystallography (Figure 1 and Figure S5 (see the Supporting

Figure 1. ORTEP diagram for the complex [PdCl2(dpmppp)] (3a). Thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

Information)). The solid-state structures of 3a,b are isomorphous with each other, having a square-planar MII center coordinated by a dpmppp ligand and two chloride anions. The dpmppp ligand attaches to the M ion by two inner phosphorus atoms (P2−Pd−P3 = 88.67(2)° (3a), P2−Pt−P3 = 91.18(3)° (3b)) to form a six-membered chelate ring with the two outer P atoms being uncoordinated. The square-planar structures around MII centers for 3a,b are similar to those found in [MCl2(dppp)].12 The structures of 3a,b are entirely different from the case for 1,2-bis[((2-diphenylphosphino)ethyl)phenylphosphino]ethane (tetraphos-2,2,2), where the mononuclear complexes [M(tetraphos-2,2,2)]2+ (M = Ni, Pd, Pt)3a−e were formed with four coordinating phosphorus atoms. The difference could be attributed to methylene-bridged diphosphine units in dpmppp, since the four-membered chelate ring is known to be less stable than five- and six-membered rings. Due to the presence of uncoordinated outer phosphines, complexes 3a,b could be good precursors to assemble other metal ions. The ESI-MS spectra of 3a,b in CH2Cl2 exhibited the parent peaks for [PdCl(dpmppp)]+ (m/z 796.860) and [PtCl-

■

RESULTS AND DISCUSSION Mononuclear PdII and PtII Complexes with dpmppp. The dpmppp ligand was synthesized by a modification of the procedure used for the synthesis of dpmppm.5a Deprotonation 4287


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(dpmppp)] + (m/z 886.945), showing the presence of mononuclear species in the solution state. However, the 31 1 P{ H} NMR spectra of 3a,b in CD2Cl2 showed only broad or complicated signals in the range of −10 to −50 ppm, which indicated fluxional behavior of th dpmppp ligand and/or the presence of asymmetric structures generated by the coordination of outer phosphorus atoms to the metal center and simultaneous dissociation of chloride anions from the metal and vice versa. Cyclic Heterotrinuclear Complexes of [MRh2(μ-Cl)3(μdpmppp)(CO)2]X (X = [RhCl2(CO)2], M = Pd (4a), Pt (4b); X = PF6, M = Pd (5a), Pt (5b), Ni (5c)). Treatment of 3a and 3b with 1 equiv of [RhCl(CO)2]2 in dichloromethane yielded cyclic Rh 2M heterotrinuclear complexes formulated as [MRh2(μ-Cl)3(μ-dpmppp)(CO)2][RhCl2(CO)2] (M = Pd (4a), Pt (4b)) in 44 and 40% yields, respectively (Scheme 2). The 31P{1H} NMR spectrum of 4a showed two sets of Scheme 2

Figure 2. ORTEP diagrams for the complex cations of (a) [PdRh 2 Cl 3 (dpmppp)(CO) 2 ][RhCl 2 (CO) 2 ] (4a) and (b) [PdRh2Cl3(dpmppp)(CO)2]PF6 (5a). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

resonances at δ 13.0 (d, JPP = 20 Hz) and 38.2 ppm (dd, 1JPRh = 167, 2JPP = 20 Hz), which are assigned to two inner P atoms bound to Pd atom and two outer P atoms bound to Rh atoms, in light of the characteristically large P−Rh coupling constant. In the spectrum of 4b, the signal for the inner P atoms significantly shifted to lower frequency in comparison to that of 4a and was observed at δ −8.1 ppm as a doublet of doublets (JPP = 10, 5 Hz) accompanied by one-bond 195Pt satellite peaks (1JPPt = 3479 Hz), and the signal for the outer atoms appeared at δ 38.4 ppm as a doublet of doublets (JPP = 10, 5 Hz) with 31 P−103Rh coupling (1JPRh = 166 Hz). The structures of 4a,b were determined by X-ray crystallography to be isomorphous with each other; ORTEP views for the complex cations of 4a,b are given in Figure 2a and Figure S6 (Supporting Information), respectively, and the structural parameters are given in Table S1 (Supporting Information). The complex cation of 4 involves a cyclic sixmembered {MRh2(μ-Cl)3} core, in which the MII ion is chelated by the inner phosphine units of dpmppp and the two Rh(I) metals are coordinated by the outer P atoms. The interatomic distances between three metal ions (2.9917(3)− 3.3748(4) Å (4a) and 3.0163(3)−3.3883(4) Å (4b)) indicate the absence of metal−metal bonding interactions. The squareplanar structure around the M atom is retained as found in 3, and each RhI metal adopts a square-planar geometry with a terminal CO ligand and the outer P and two μ-Cl atoms. An agnostic or weak interaction between Rh2 and the o-H atom (H1) of the phenyl ring bound to the P4 atom is observed (Rh2−H1 = 2.85 (4a), 2.90 Å (4b)), which brings about a slight distortion of the square-planar geometry around the Rh2 center with the CO ligand tilted away from the square plane (Cl2−Rh2−C2 = 166.9(1) (4a), 166.7(1)° (4b)). Such an interaction and distortion was not observed around the Rh1 atom (Cl1−Rh1−C1 = 174.1(1) (4a), 173.8(1)° (4b)), leading

to asymmetrical structures in the solid state, which should be contrasted with the symmetrical features in the solution state. Analogous complexes with a PF6− counteranion, [MRh2(μCl)3(μ-dpmppp)(CO)2]PF6 (M = Pd (5a), Pt (5b)), were synthesized by reacting 3a,b with 1 equiv of [RhCl(CO)2]2 in the presence of an excess amount of NH4PF6 in 46 and 55% yields, respectively (Scheme 2). The Rh2Ni analogue [NiRh2(μCl)3(μ-dpmppp)(CO)2]PF6 (5c) was prepared in 40% yield by successive reactions of NiCl2·6H2O, first treated with 1 equiv of dpmppp in methanol and followed by 1 equiv of [RhCl(CO)2]2 in the presence of NH4PF6. The crystal structures of 5a−c are isomorphous and essentially identical. A perspective plot for the complex cation of 5a is illustrated in Figure 2b (those of 5b,c are shown in Figures S7 and S8, Supporting Information), and the representative structural parameters are given in Table 4. The complex cations of 5a−c possess pseudo-Cs symmetry and are similar to those of 4a,b except for the absence of the weak Rh−H interaction. For the six-membered {MRh2(μ-Cl)3} cores in 5a−c, the metal−metal distances in 5c (3.0558(7)− 3.1961(6) Å) are shorter by ca. 0.1−0.2 Å than the corresponding distances in 5a,b (3.1884(4)−3.2975(4) (5a), 3.2565(4)−3.3112(5) Å (5b)), which is ascribed mainly to the Ni−Cl bond lengths being shorter than those for Pd and Pt ions. The ν(CO) frequency of 5a−c appeared around 2010 cm−1, consistent with the presence of terminal CO. In the 31 1 P{ H} NMR spectrum of 5a−c, two sets of resonances were observed (Figure S13, Supporting Information); the peaks for the outer P atoms appeared at δ 38.2 (5a), 38.5 (5b), and 38.3 ppm (5c) with characteristic Rh−P couplings of 1JRhP = 167 4288


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Table 4. Structural Parameters of 5a−c

M M···Rh1, Å M···Rh2, Å Rh1···Rh2, Å M−P2, Å M−P3, Å Rh1−P1, Å Rh2−P4, Å M−Cl1, Å M−Cl2, Å Rh1−Cl1, Å Rh1−Cl3, Å Rh2−Cl2, Å Rh2−Cl3, Å Rh1−C1, Å Rh2−C2, Å Cl1−M−Cl2, deg Cl1−Rh1−Cl3, deg Cl2−Rh2−Cl3, deg M−Cl1−Rh1, deg M−Cl2−Rh2, deg Rh1−Cl3−Rh2, deg Cl1−Rh1−C1, deg Cl2−Rh2−C2, deg

Scheme 3

5a

5b

5c

Pd 3.2584(4) 3.1884(4) 3.2975(4) 2.2467(9) 2.2570(9) 2.225(1) 2.230(1) 2.3952(9) 2.3920(9) 2.396(1) 2.4170(9) 2.398(1) 2.4349(9) 1.811(5) 1.811(5) 88.91(3) 88.79(3) 88.90(3) 85.69(3) 83.46(3) 85.63(3) 175.0(2) 175.5(2)

Pt 3.2702(4) 3.2565(4) 3.3112(5) 2.236(1) 2.246(1) 2.231(1) 2.229(1) 2.402(1) 2.390(1) 2.413(1) 2.424(1) 2.411(1) 2.449(1) 1.811(7) 1.811(6) 87.06(4) 88.54(4) 89.23(4) 85.57(3) 85.43(4) 85.60(3) 176.6(2) 173.0(2)

Ni 3.1026(8) 3.0558(7) 3.1961(6) 2.169(2) 2.179(2) 2.228(1) 2.248(2) 2.247(2) 2.206(3) 2.391(2) 2.434(2) 2.353(3) 2.452(1) 1.803(7) 1.812(8) 89.03(8) 87.75(6) 87.35(7) 83.91(7) 84.10(8) 81.70(5) 175.3(3) 175.9(3)

31

P{1H} NMR spectrum of 6 showed two sets of resonances at δ 22.5 (JPRh = 175 Hz) and 38.7 ppm (JPRh = 173 Hz) (Figure S14a, Supporting Information), which are assignable to two inner and two outer P atoms, respectively, by 2D 1H−31P HMBC NMR techniques (Figure S15, Supporting Information).

(5a), 165 (5b), and 164 Hz (5c), while the peaks for the inner P atoms significantly shifted depending on the M ion at δ 12.2 (5a), −8.8 (5b), and 3.3 ppm (5c). The ESI−MS spectra in dichloromethane showed monovalent parent peaks at m/z 1130.552 (5a), 1218.974 (5b), and 1082.900 (5c) corresponding to {MRh2Cl3(dpmppp)(CO)2}+ with m/z 1130.818 (M = Pd), 1218.879 (M = Pt), and 1082.848 (M = Ni), indicating that the solid-state structures were retained in solution. A few related complexes with cyclic M3(μ-Cl)3 (M = Rh, Pd, Pt) structures have been reported so far; however, all of these were homotrimetallic compounds.13 The complexes 4a,b and 5a−c are the first examples of such heteronuclear complexes, demonstrating that the dpmppm ligand is effective in assembling heterometal ions into the cyclic MRh2(μ-Cl)3 motif in two steps. In the first step, the inner phosphines bind to MII ions to form a stable six-membered chelate ring, and in the second step, the uncoordinated outer phosphines trap the Rh2 fragment to complete the unusual cyclic {MRh2(μCl)3} core in good yields. Homotrinuclear Complex [Rh3(μ-Cl)3(μ-dpmppp)(CO)2] (6). Reaction of dpmppp with 1.5 equiv of [RhCl(CO)2]2 in dichloromethane afforded a neutral Rh3 homotrinuclear complex, [Rh3(μ-Cl)3(μ-dpmppp)(CO)2] (6), in 37% yield (Scheme 3). Unlike the stepwise formation of the Rh2M complexes (M = Pd, Pt, Ni), any mononuclear complex formulated as {RhCl(CO)(dpmppm)} were not obtained even when 2 was treated with 0.5 equiv of [RhCl(CO)2]2. The

Figure 3. ORTEP diagram of [Rh3Cl3(dpmppp)(CO)2] (6). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

The solid-state structure of 6 (Figure 3, Table 5) is closely similar to those of 4 and 5, in which the divalent MII ion (M = Pd, Pt, Ni) is replaced by a monovalent RhI ion, resulting in a neutral complex with a Rh3(μ-Cl)3 cyclic structure. Three RhI ions form an equilateral triangle without any bonding interaction between them (Rh−Rh = 3.1461(7)−3.2293(7) Å), the values of which are comparable to those found in the related trinuclear rhodium complexes [Rh3(μ-Cl)3(MeN(PF2)2)3] (Rh−Rh = 3.0964(1) Å (average))13a and [Rh3(μCl)3(CH2(P(OPh)2)2)3] (Rh−Rh = 3.2023(3)−3.4627(4) Å).13b Whereas the Rh−CO distances (average 1.809 Å) are not appreciably reduced from those of complexes 5a−c, the ν(CO) frequency of 6 (1980 cm−1) shifted remarkably to lower energy from the corresponding values of complexes 5a−c (2009−2010 cm−1), suggesting stronger π back-donation from 4289


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Table 5. Structural Parameters of 6, 7a, and 8a

6 Rh1−Hg, Å Rh2−Hg, Å Rh3−Hg, Å Rh1···Rh2, Å Rh1···Rh3, Å Rh2···Rh3, Å Rh1−P1, Å Rh2−P2, Å Rh2−P3, Å Rh3−P4, Å Rh1−Cl1, Å Rh1−Cl3, Å Rh2−Cl1, Å Rh2−Cl2, Å Rh3−Cl2, Å Rh3−Cl3, Å Rh1−C1, Å Rh3−C2, Å Rh1−Hg−Rh2, deg Rh1−Hg−Rh3, deg Rh2−Hg−Rh3, deg Cl1−Rh1−Cl3, deg Cl1−Rh2−Cl2, deg Cl2−Rh3−Cl3, deg Rh1−Cl1−Rh2, deg Rh2−Cl2−Rh3, deg Rh1−Cl3−Rh2, deg

3.1813(9) 3.2293(7) 3.1461(7) 2.225(2) 2.180(2) 2.191(2) 2.216(2) 2.393(2) 2.416(2) 2.441(2) 2.416(2) 2.402(2) 2.429(2) 1.80(1) 1.817(8)

87.98(6) 89.46(5) 87.86(6) 82.33(4) 81.53(5) 83.61(4)

7a

8a

2.7414(9) 2.6408(8) 2.7295(9) 3.194(1) 3.617(1) 3.265(1) 2.254(1) 2.228(1) 2.222(1) 2.280(1) 2.383(1) 2.447(1) 2.432(1) 2.426(1) 2.374(1) 2.436(1) 1.830(4) 1.825(4) 72.76(3) 82.77(2) 74.88(2) 91.46(4) 87.20(4) 87.67(5) 83.08(4) 85.73(4) 95.59(5)

2.733(1) 2.685(1) 2.707(1) 3.282(2) 3.533(2) 3.271(2) 2.235(3) 2.226(3) 2.226(3) 2.237(3) 2.378(3) 2.419(3) 2.408(3) 2.412(3) 2.384(3) 2.426(3) 1.880(9) 1.876(9) 74.56(3) 81.01(3) 74.71(3) 89.80(8) 87.44(7) 92.10(8) 86.56(8) 86.00(7) 93.65(8)

with 1 equiv of HgX2 (X = Cl, Br, I) in the presence of an excess amount of NH4PF6 to afford Rh3Hg tetranuclear complexes formulated as [Rh3(HgX)(μ-Cl)2(μ-X)(μ-dpmppp)(CO)2]PF6 (X = Cl (7a), Br (7b), I (7c)) in 71, 39, and 59% yields, respectively (Scheme 3). An ORTEP diagram for the complex cation of 7a is given in Figure 4a (those of 7b,c are shown in Figures S9 and S10 in the Supporting Information), and the structural parameters are summarized in Table 5 and Table S2 (Supporting Information). The complex cations of 7a−c have an incomplete cubane framework comprised of a {Rh3(HgX)(μ-Cl)2(μ-X)} core, where the d10 HgIIX fragment occupies three apical positions of the square-pyramidal coordination geometry of each rhodium ion in a Rh3(μ3HgX) fashion. The chloride ion bridging Rh1 and Rh3 in 6 is selectively replaced by an X− ion (X = Br, I) in 7b,c; the other bridging chloride ions were not replaced by X− even on treatment with an excess amount of HgX2, monitored by 31 1 P{ H} NMR spectra. Although there have been many examples of M3(μ3-Hg) clusters reported so far,14 the Rh3Hg(μ-Cl)2(μ-X) cores found in 7 are the first example of complexes containing three Rh→Hg dative bonds with a Rh3(μ3-HgX) mode and are similar to those found in the complexes (NBu4)[Pt3PbCl3(C6F5)6],15 (NBu4)[Pt3SnCl3(C6F5)6],16 and (NBu4)2[Pt3(HgCl)-

the Rh1 and Rh3 atoms occurring due to the presence of the Rh2 atom. Reactions of 6 Leading to Tetranuclear Rh3Hg and Rh3Cu Complexes. The cluster cores of the Rh2M and Rh3 complexes can be recognized as two-apex-truncated cubanes (Chart 1), possessing two vacant sites surrounded by three Chart 1

metal ions (site A) and by three chloride anions (site B); hence, we have tried to examine their reactions with d10 HgII and CuI salts to build up the cubane framework. At first, the heterotrinuclear Rh2M complexes 5a−c were examined and no longer reacted with HgCl2 as well as with CuCl and HBF4. In contrast, the Rh3 homotrinuclear complex 6 readily reacted 4290


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and Hg[RhCl2(PPh3)2]2 (2.5494(8) Å).24 The three Rh−Rh distances (3.194(1)−3.265(1) (7a), 3.210(2)−3.660(2) (7b), and 3.2335(5)−3.7560(5) Å (7c)) are elongated systematically from those of 6 (3.1461(7)−3.2293(7) Å) by introduction of μ3-HgX and μ-X bridging units. In particular, the halide anions (X = Cl, Br, I) bridging the Rh1 and Rh3 atoms bring about structural changes in the Rh3(μ-Cl)2(μ-X) cores depending on their ionic radii, where the Rh1−Rh3 distances become longer and the Rh1−X−Rh3 angles smaller in the order I− > Br− > Cl−. The Rh1−Hg−Rh3 angles (82.77(2) (7a), 83.99(4) (7b), 86.47(1)° (7c)) are slightly larger than the other Rh1−Hg− Rh2 and Rh2−Hg−Rh3 angles (average 73.82 (7a), 73.97 (7b), 74.71° (7c)) and become larger in the order I− > Br− > Cl−. These values are comparable to those found in (NBu4)2[Pt3(HgCl)(OH)3(C6F5)6] but larger than those found in well-known face-capped M3(μ3-Hg) clusters.14a,b The ν(CO) vibrational bands in 7a−c appeared at 2043 (7a), 2042 (7b), and 2036 cm−1 (7c), respectively, which were considerably shifted to higher energy as compared with that of the parent complex 6 (1980 cm−1), suggesting that the electron density of Rh1 and Rh3 was reduced by the Rh→Hg donor− acceptor interactions. The 31P{1H} NMR spectra of 7a,b exhibited two sets of resonances (39.5, 30.7 (7a); 38.7, 29.3 ppm (7b)) (Figures S14b and S16a, Supporting Information), which are assigned to two inner and outer P atoms, respectively, by 1H−31P HMBC NMR techniques and are accompanied by one-bond 103Rh−31P coupling and two-bond 199 Hg−31P satellites. In the case of 7c (Figure S16b, Supporting Information), two sets of resonances at δ 35.1 and 26.4 ppm are broad and the two-bond 199Hg−31Pout satellite peaks are not well resolved. The 2JHgPin values of 334 (7a) and 302 Hz (7b) are fairly larger than the 2JHgPout values (66 (7a) and 69 Hz (7b)), clearly demonstrating that the Rh2−Hg interaction is stronger than the other two Rh1/Rh3−Hg interactions in the solution state. These results are in agreement with the differences of Rh−Hg distances observed in the crystal structures. The ESI-MS spectra of 7a−c in acetonitrile showed parent peaks corresponding to [Rh3(HgX)Cl2X(dpmppp)(CO)2]+, consistent with the X-ray and NMR results. With an aim of tuning the electronic properties of the Rh3Hg tetranuclear complexes, an attempt was made to introduce terminal isocyanide ligands which have stronger σ-donating and weaker π-accepting abilities in comparison to those of CO ligands. Complexes 7a−c were treated with 2 equiv of 2,6-xylyl isocyanide (XylNC) to afford [Rh3(HgX)(μ-Cl)2(μ-X)(μdpmppp)(XylNC)2]PF6 (X = Cl (8a), Br (8b), I (8c)) in 61, 53, and 65% yields, respectively (Scheme 3). The structures of 8a−c were determined by X-ray crystallographic analyses; an ORTEP diagram for the complex cation of 8a is shown in Figure 4b (those for 8b,c are shown in Figures S11 and S12 in the Supporting Information), and the structural parameters are given in Table 5 and Table S2 (Supporting Information). The structures of 8a−c are isomorphous and similar to those of 7a− c, where two CO ligands are replaced by two XylNC ligands. Importantly, these replacements lead to a remarkable change in the three Rh−Hg interactions as follows. The Rh2−Hg distances (2.685(1) (8a), 2.709(2) (8b), 2.679(2) Å (8c)) in 8a−c are still the shortest among the three Rh−Hg interactions and, however, are appreciably longer than those of the corresponding bonds in 7a−c (2.6408(8) (7a), 2.666(2) (7b), 2.6483(3) Å (7c)). On the other hand, the Rh1−Hg and Rh3−Hg bond distances (average 2.7199 (8a), 2.7310

Figure 4. ORTEP diagrams for the complex cations of (a) [Rh3(HgCl)Cl3(dpmppp)(CO)2]PF6 (7a) and (b) [Rh3(HgCl)Cl3(dpmppp)(XylNC)2]PF6 (8a). The thermal ellipsoids are drawn at the 40% probability level, and the hydrogen atoms are omitted for clarity.

(OH)3(C6F5)6],17 which involve three Pt→M dative interactions with Pt3(μ3-M) structures. In other words, the cyclic Rh3(μ-Cl)2(μ-X) core act as a tridentate ligand with three Rh centers serving as donors to the Lewis acidic HgII ion. Among the three Rh−Hg interactions, Rh2−Hg distances (2.6408(8) (7a), 2.6660(15) (7b), 2.6483(3) Å (7c)) are significantly shorter than the other two distances (Rh1−Hg and Rh3−Hg; average 2.7355 (7a), 2.7350 (7b), and 2.7414 Å (7c)), indicating that Rh2→Hg dative interactions are stronger than the other two Rh1→Hg and Rh3→Hg interactions because the Rh2 ion attached by the two inner P atoms is more electronrich than the Rh1 and Rh3 ions, which are each coordinated by one outer phosphine and an electron-withdrawing CO ligand. The Rh−Hg bond lengths are comparable to those found for donor−acceptor bonds in [Rh2(HgCl)(PPh3)2(CO)2Cl2(pz)2] (pz = pyrazole; 2.804(3) Å),18 [Rh2(HgCl)(H)(CO)2(EtN(P(OPh)2)2)] (2.711(1), 2.778(1) Å),19 [Cp2Rh2(HgCl2)(CO)(dppm)] (2.692(1), 2.774(2) Å),20 and Hg[CpFe2Rh(COMe)(CO)7]2 (2.737(2) Å)21 but slightly longer than the covalent bonds in [Rh(HgCl)(CO)Cl2(PPh2Py)2] (2.572(1) Å),22 [Rh(HgPh)Cl(CCCH2OMe)(PiPr3)2] (2.5008(4) Å),23 4291


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(8b), 2.7158 Å (8c)) are shorter than those in 7a−c (average 2.7355 (7a), 2.7350 (7b), 2.7417 Å (7c)). These results indicate that the Rh2−Hg interaction becomes weaker and the Rh1/Rh3−Hg interactions become stronger upon replacement of CO ligands by XylNC. The 31P{1H} NMR spectrum of 8a (Figure S14c, Supporting Information) is consistent with these structural changes, showing that the 2JHgP value for the inner P atoms (189 Hz) is smaller and that for the outer P atoms (111 Hz) is larger than the respective corresponding values in 7a (2JHgPin = 334 Hz, 2JHgPout = 66 Hz). The interesting structural switch could be recognized as the introduction of the σdonating isocyanides increasing the electron density on the Rh1 and Rh3 centers and, consequently, increasing the strength of the Rh1/Rh3→Hg donor−acceptor interactions.25 When complex 6 was treated with 1 equiv of CuCl, dark violet microcrystals of [Rh3(CuCl)(μ-Cl)3(μ-dpmppp)(CO)2] (9) were obtained in good yield. The IR spectrum showed the presence of terminal CO ligands at 2023 cm−1, and the 31P{1H} NMR spectrum (Figure S14d, Supporting Information) exhibited two sets of resonances (doublet of doublets) at δ 37.6 (1JRhP = 158 Hz, JPP′ = 14, 8 Hz) and 26.8 ppm (1JRhP = 164 Hz, JPP′ = 14, 8 Hz). By analogy to the spectral data of 7a and 8a, complex 9 is assumed to have a Rh3Cu tetranuclear structure as depicted in Chart 2, where the d10 CuCl unit caps

Figure 5. (a) 1H{31P} NMR and (b) 1H NMR spectra for the hydride peak of 10 in CD2Cl2 at room temperature.

with their crystal structures, apart from a systematic elongation of distances between heavy atoms usually observed in DFT methods. For 6, higher-lying MOs (HOMO, HOMO-1, HOMO-4, and HOMO-5) are depicted in Figure S18 (Supporting Information) and are mainly derived from combinations of dσ orbitals of Rh atoms with respect to the square coordination planes. The energy level of the most symmetrical MO (HOMO-4), composed of an in-phase interaction between the three dσ orbitals, is −5.664 eV, which is remarkably higher in comparison with the corresponding MO of 5a (HOMO-21 −10.202 eV) due to the lower energy of Pd d orbitals (Figure S19, Supporting Information). An energy mismatch between the occupied Pd d orbitals and empty Hg sp-hybridized orbital might be responsible for the robust nature of 5a against the d10 HgIX unit. For 7a, the symmetrical MO (HOMO-4) of 6 interacts well with an empty sp-hybridized orbital of the HgX fragment to generate the LUMO with an antibonding interaction at −5.674 eV and HOMO-25 with a bonding interaction at −10.224 eV (Figure 6). The latter MO is quite stabilized and is thus responsible for the Rh3(μ-Hg) bonding interaction in an Rh→ Hg dative fashion. The natural charge population (Rh1, −0.54; Rh2, −0.61; Rh, −0.51; Hg, +0.88) and Wiberg bond indices (Hg−Rh1, 0.234; Hg−Rh2, 0.303; Hg−Rh3, 0.233)25 suggest a stronger dative interaction for Hg−Rh2 than for Hg−Rh1 and Hg−Rh3 (Figure S20, Supporting Information). In the case of 8a with terminal XylNC ligands instead of COs, the symmetrical MO (HOMO-4) of 6 interacts more intensely with the empty sp-hybridized orbital of HgX fragment to generate an antibonding MO as the LUMO at −4.944 eV and a bonding MO of HOMO-38 at −10.935 eV (Figure 6), and as a result, the bonding MO is more stabilized by 0.711 eV on replacing CO with XylNC. The natural charge population (Rh1, −0.46; Rh2, −0.61; Rh, −0.45; Hg, +0.86) and Wiberg bond indices (Hg−Rh1, 0.267; Hg−Rh2, 0.278; Hg−Rh3, 0.266)26 definitively demonstrate that degree of the Hg−Rh2 dative interaction decreases and, instead, those of Hg−Rh1 and Hg−Rh3 increase (Figure S20, Supporting Information), which is in good agreement with the results of X-ray crystallographic and 31P NMR spectroscopic analyses of 7a and 8a as described above.

Chart 2

the apex surrounded by the three RhI ions with Rh→Cu dative interactions. Complex 6 readily reacted with 1 equiv of HBF4 to give the adduct [Rh3(μ-H)(μ-Cl)3(μ-dpmppp)(CO)2]BF4 (10) in solution quantitatively, which was analyzed by 1H and 31 1 P{ H} NMR spectroscopy. The 31P{1H} NMR spectrum (Figure S14e, Supporting Information) showed two resonances at δ 42.7 (1JRhP = 156 Hz, JPP′ = 17, 9 Hz) and 27.9 ppm (1JRhP = 143 Hz, JPP′ = 17, 9 Hz), the spectral patterns of which were close to those of 9 except for a further downfield shift of the Pout signals. In the 1H{31P} NMR spectrum (Figure 5), a hydride peak was clearly observed at δ −12.32 as a doublet of triplets with 1JRhH = 29 and 12 Hz. These spectral features are in good agreement with a hydride-bridged Rh3 structure as shown in Chart 2, in which the hydride is assumed to interact more strongly with Rh2 and more weakly with Rh1 and Rh3 centers. DFT Calculations on 5a, 6, 7a, and 8a. In order to understand the electronic structures of the Rh3Hg complexes, especially the Rh→Hg dative interactions, DFT calculations were performed on complexes 5a, 6, 7a, and 8a with the Gaussian 03 software package. The initial structures from the X-ray data were optimized with B3LYP methods using the lanl2dz basis set; the Los Alamos ECP plus DZ basis set was used for heavy atoms. The fully optimized structures (Figure S17a−d, Supporting Information) are essentially consistent

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CONCLUSION In the present study, the tetraphosphine dpmppp (meso-1,3bis[(diphenylphosphinomethyl)phenylphosphino]propane) was prepared and proved to be effective in assembling unusual cyclic MRh2(μ-Cl)3 complexes, [MRh2(μ-Cl)3(μ-dpmppp)4292


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Figure 6. Representative MO diagrams for the optimized structures of 7a (left) and 8a (right) by DFT calculations with B3LYP methods.

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(CO)2]+ (4, 5: M = Ni, Pd, Pt), in a stepwise fashion through the mononuclear intermediate complexes [MCl2(dpmppp)] (3), in which the outer phosphine units of dpmppp are uncoordinated. The cyclic homotrinuclear complex [Rh3(μCl)3(μ-dpmppp)(CO)2] (6) was also stabilized by dpmppp and showed interesting reactivity toward Lewis acidic d10 HgIIX and CuICl units as well as HBF4, yielding the donor−acceptor adducts [Rh3(HgX)(μ-Cl)2(μ-X)(μ-dpmppp)(CO)2]PF6 (7), [Rh3(CuCl)(μ-Cl)3(μ-dpmppp)(CO)2] (9), and [Rh3(μ-H)(μCl)3(μ-dpmppp)(CO)2]BF4 (10), whereas the analogous Rh2M complexes would not react with such species. Further, the π-acidic carbonyl ligands of 7 were readily replaced by σdonating XylNC ligands to afford [Rh3(HgX)(μ-Cl)2(μ-X)(μdpmppp)(XylNC)2]PF6 (8). In light of the X-ray crystal structures, 31P{1H} NMR spectral data with 2JHgP values, and DFT calculations for 7 and 8, replacement of the auxiliary terminal ligands (L) from CO to XylNC brought about an interesting structural change with respect to the Rh→Hg dative interactions in the Rh3(μ3-Hg) bonding system. These results suggested that heterometallic multinuclear complexes were effectively built up by utilizing dpmppm and their electronic properties could be tuned by varying the auxiliary ligands.

ASSOCIATED CONTENT

S Supporting Information *

Tables, figures, and CIF files giving the structural parameters of 4a,b, 7b,c, and 8b,c, ESI-MS of 3a,b, 5a−c, 7a−c, and 8a−c, crystal structures of 3b, 4b, 5b,c, 7b,c, and 8b,c, 31P−1H HMBC spectrum of 6, 31P{1H} NMR spectra of 5a−c, 6, 7a−c, 8a, 9, and 10, results of DFT calculations on 5a, 6, 7a, and 8a, and crystallographic data for 3a,b, 4a,b, 5a−c, 6, 7a−c, and 8a− c. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (T.T.); [email protected] (T.N.). Fax: +81 742-20-3847. Tel: +81 742-20-3399. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research 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. T.N. is grateful to Tokuyama Science 4293


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Foundation, Kurata Memorial Hitachi Science and Tecnology Foundation, and Nara Women’s University for a research project grant.

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