PdCl2(Xantphos) - ACS Publications - American Chemical Society

Article pubs.acs.org/Organometallics

Germa- and Stanna-closo-dodecaborate in Reaction with [PdCl2(Xantphos)]: P−C and B−H Bond Activation Jörg-Alexander Dimmer,† Martin Hornung,† Tobias Wütz,† and Lars Wesemann* Institut für Anorganische Chemie, Universität Tübingen, Auf der Morgenstelle 18, D-72076 Tübingen, Germany S Supporting Information *

ABSTRACT: The two nucleophilic heteroborates germa-closo-dodecaborate and stanna-closo-dodecaborate show different reactivity toward the electrophile [PdCl2(Xantphos)]: In the case of the germanium ligand we found straightforward substitution of one chloride ligand and formation of a Ge−Pd bond. The tin ligand also reacts to give the substitution products [PdCl(SnB11H11)(Xantphos)]− and [Pd(SnB11H11)(Xantphos)], but the complexes exhibit a subsequent reaction under activation of a B−H and P−C bond. A dinuclear Pd(I)−Pd(I) complex featuring a P−B bond was characterized, and during its formation the evolution of benzene was detected. The respective germanium derivative does not show an activation reaction even at elevated temperature.

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INTRODUCTION The family of group 14 monoheteroborates [R−EB11H11]− (E = C, R = H or alkyl; E = Si, Ge, Sn, R = Me; E = Pb, only known as the dianion without a substituent) is well known in the literature.1−3 The carbon cluster [RCB11X11]− (R = H, X = H, CH3, Cl, Br, I) and especially the halogenated derivatives are common weakly coordinating anions.4−10 After deprotonation at the carbon atom in the carbaborate [HCB11F11]− a transition metal carbon bond can be formed.9,11 In the case of silicon so far only the methyl-substituted derivative [H3C−SiB11H11]− was published.2 The germanium and tin closo-borates as dianionic clusters [EB11H11]2− (E = Ge, Sn) are versatile ligands in coordination chemistry and show reaction behavior comparable to germylene- or stannylene-type ligands.12−27 Since we have already explored the reaction of palladium complexes carrying chelating phosphines such as dppp [1,3bis(diphenylphosphinopropane)] and dppe [1,2-bis(diphenylphosphinoethane)] with the tin nuclephile [SnB11H11]2−, we wanted to study the influence of a phosphine with a larger bite angle on the heteroborate coordination.22,28 In this publication we present the reaction of the two nucleophiles [EB11H11]2− (E = Ge, Sn) with the electrophile [PdCl2(Xantphos)].

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Scheme 1. Reaction of [PdCl2(Xantphos)] with the Germanium Nucleophile [GeB11H11]2−

spectrum exhibits the typical pattern for the coordinated cluster fragment. Two signals with the ratio 1:10 are visible at −11.5 and −15.1 ppm. Due to accidental isochronism of the signals for the two B5-belts, only one signal for both B5-belts was detected, in contrast to the uncoordinated heteroborate, which shows three signals with a 1:5:5 ratio. In the 31P NMR spectrum one signal for the chelating Xantphos ligand was observed, which indicates trans coordination. In the 1H NMR spectrum only one broad signal for the CH3 groups of the Xantphos ligand was detected. Since we have observed labile coordination of the heteroborate ligands in several cases, we are of the opinion that a dissociation of the germaborate ligand allows exchange of the CH3 groups.14,24,26,29,30 Compound 1 was isolated in 65% yield after crystallization from acetonitrile/ ether as intense orange crystals. By addition of one equivalent of AgNO3 to an acetonitrile solution of 1 the color changes from orange to yellow and the neutral complex [Pd(GeB11H11)(κ3-Xantphos)] (2) was formed under precipitation of AgCl (Scheme 2). Compound 2 is a charge-compensated molecule wih a negative charge delocalized on the germa-closododecaborate unit and the positive charge localized at the

RESULTS AND DISCUSSION

The reaction of the germanium nucleophile [Et4N]2[GeB11H11] with one equivalent of the dichloride [PdCl2(Xantphos)] resulted in an orange-colored solution, from which the monosubstituted product [Et4N][PdCl(GeB11H11)(κ2-Xantphos)] (1) (Scheme 1) was isolated as orange crystals. No further substitution of the second chloride ligand was observed even with excess of the germanium nucleophile and at elevated temperature. The formation of the monoanionic compound was monitored by NMR spectroscopy. The 11B{1H} NMR © 2012 American Chemical Society

Received: May 22, 2012 Published: September 28, 2012 7044

dx.doi.org/10.1021/om300438x | Organometallics 2012, 31, 7044−7051

Organometallics

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Scheme 2. Abstraction of a Chloride Anion with Silver Nitrate and Formation of Complex 2

Scheme 4. Substitution Reaction at Palladium with Stannacloso-dodecaboratea

transition metal fragment. Molecules of this type were already published with the triphos and stanna-closo-dodecaborate ligands coordinated at Pt(II).26 In the 11B{1H} and 31P{1H} NMR spectra, the signals of complex 2 are only slightly shifted in comparison to the chloride complex 1. Again the pattern for the coordinated heteroborate is visible in the 11B{1H} NMR spectrum at −10.2 and −15.0 ppm, and the 31P{1H} NMR spectrum shows a single resonance at 30.6 ppm compared to the starting material 1 at 25.7 ppm. Compound 2 was obtained as a yellow crystalline material in 73% yield from a dichloromethane/ hexane solution. The molecule 2 is inert in solution at room temperature and also at acetonitrile reflux temperatures. The homologous tin nucleophile [Bu3NH]2[SnB11H11] was also reacted at room temperature with the [PdCl2(Xantphos)] electrophile. Immediately the solution turned red, and after two hours of stirring the solution became black. From reaction mixtures in acetonitrile or dichloromethane we were able to isolate two products by slow diffusion of diethyl ether at room temperature. The dinuclear palladium(I) complex [(C33H27P2O)(SnB11H10)Pd2(κ2-Xantphos)] (3) was obtained as black crystals in 25% yield as well as a mononuclear squareplanar-coordinated palladium(II) compound [Bu 3 NH][PdCl2(SnB11H10)(Xantphos)] (4) as yellow crystals, however, only in very small amounts (Scheme 3).

a

Conditions: (a) several minutes stirring at room temperature; (b) crystallization at −28 °C for three days; (c) experiment in a NMR tube.

signal at 28.3 ppm (in DMF, 23.9 ppm) was observed. Upon cooling to −80 °C signals exhibiting 119Sn satellites indicating a cis and a trans palladium coordination complex were detected. In our opinion these signals belong to the cis and trans isomer of the chloride complex [Bu 3 NH][PdCl(SnB 11 H 11 )(Xantphos)] (5) (further support is provided by the reaction of 6 and [Bu3NH]Cl, vide infra). Since both chloride complexes react immediately at room temperature, a salt elimination reaction with AgNO3 like in the germaborate case is not necessary in the tin case. In the 11B NMR spectrum of 6 due to accidental isochronism, the typical pattern for coordinated stanna-closo-dodecaborate was observed with signals at −11.0 (1B, B12) and −15.9 (10B, B2−B11) ppm. Furthermore in the 119Sn NMR spectrum a signal at −269 ppm is a good indicator of the formation of a Sn−Pd bond. The pure substance 6, which was isolated as orange-red crystals after crystallization at −28 °C, is soluble only in polar solvents such as dimethylformamide. The question arises whether it is possible to generate the unexpected complex 3 from the pure complex 6. Therefore a solution of crystalline complex 6 was stirred at room temperature in DMF. The color of the solution changed from orange to black over a period of 24 h, and in the 31 P NMR spectrum four new signals were observed. In the 31 1 P{ H}−31P{1H} COSY NMR spectrum cross-peaks between these signals confirm their connectivity (see Supporting Information). Furthermore in the 1H NMR spectrum the formation of benzene was detected (Scheme 5). To our surprise, the dinucelar complex 3 exhibiting a P−B bond was formed, which is the product of a redox reaction. However, the fate of the missing [SnB11H11] cluster remains unclear. Since we have found the formation of the tin-bridged complex 3 and the palladium dichloride complex 4 in the reaction mixture of [PdCl2(Xantphos)] with [Bu3NH]2[SnB11H11], we wanted to study the influence of chloride anions on the reaction of 6 in DMF. Therefore the molecule 6 was also reacted with [Bu3NH]Cl (Scheme 6). Upon addition of [Bu3NH]Cl to a solution of 6 in DMF, the color changed immediately from orange to red. On the basis of 31 P NMR spectroscopy we observe the formation of 5. The

Scheme 3. Reaction of Stanna-closo-dodecaborate at Room Temperature with [PdCl2(Xantphos)]

In order to study the formation process of the unexpected products 3 and 4, we started to investigate the reaction at low temperature. The tin nucleophile [Bu3NH]2[SnB11H11] and the transition metal electrophile [PdCl2(Xantphos)] were mixed and stirred for one minute at room temperature and afterward layered with diethyl ether and stored for several days at −28 °C. Following this procedure orange-red crystals of the complex [Pd(SnB11H11)(κ3-Xantphos)] (6) (Scheme 4) were isolated in 40% yield. The reaction mixture was also investigated by NMR spectroscopy: due to the low solubility of the chargecompensated molecule 6 in dichloromethane, the 31P NMR signal for this complex was not detected. However a broad 7045


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state II. This compound was isolated as a side product only in a very small amount as yellow crystals within the reaction mixture. Formally one tin cluster inserted in the phosphorus− palladium bond under formation of Sn−Pd and P−B bonds, and a hydride anion was separated from the respective boron atom. Structures in the Solid State. Single crystals suitable for X-ray diffraction of the monoanionic complex 1 were received by layering the filtered reaction mixture with diethyl ether. The molecular structure of the respective palladium complex is depicted in Figure 1 together with selected interatomic distances and bond angles.

Scheme 5. Reaction of the Pure Complex 6 at Room Temperature in DMF

Scheme 6. Reaction of Complex 6 in DMF in the Presence of [Bu3NH]Cla

a

Figure 1. ORTEP plot of the molecular structure of the anion of [Et4N][PdCl(GeB11H11)(κ2-Xantphos)] (1). The countercation, hydrogen atoms, and the phenyl rings except their ipso-carbon atoms have been omitted; ellipsoids at 50% probability. Interatomic distances [Å] and bond angles [deg]: Pd−P1 2.278(1), Pd−P2 2.271(1), Pd−Ge 2.338(1), Pd−Cl 2.472(1), Pd−O 2.479(3); P2− Pd−P1 158.09(4), P2−Pd−Ge 95.88(3), P1−Pd−Ge 97.96(3), P2− Pd−P1 158.09(4), P2−Pd−Cl 90.72(4), P1−Pd−Cl 87.50(4), Ge− Pd−Cl 145.36(3), P2−Pd−O 79.22(7), P1−Pd−O 79.23(7), Ge− Pd−O 139.69(7), Cl−Pd−O 74.95(7).

See Scheme 4 for the two isomers of 5.

broad signal of 5 at room temperature was studied at −60 °C, and two isomers, the cis and trans isomer, were detected (see also Scheme 4). The dynamic exchange between the cis and trans isomers was confirmed by a 31P{1H}−31P{1H} EXSY NMR experiment (Supporting Information). This mixture of 5 and 6 in DMF shows a reaction after several hours at room temperature. Besides formation of the dinuclear complex 3 the chloride complex 4 was formed and detected by NMR spectroscopy. In this chloride-driven formation of 4 we can also observe formation of a P−B bond. In the complexes [Pd2(C33H27P2O)(SnB11H10)(κ2-Xantphos)] (3) and [Bu3NH][PdCl2(SnB11H10)(Xantphos)] (4) we have found the remarkable activation of a B−H bond and formation of a B−P bond. Like in compound 3 the evolution of benzene and B−PPh2 formation was reported in the literature for the reaction of [PdCl2(PPh3)2] with sulfur- or phosphorussubstituted nido-dicarboranes.31,32 In compound 4 we have found the formation of a B−PAr3 adduct, and this type of reaction was also reported in the literature.33−35 Compound 3 is a neutral dimeric complex featuring a palladium−palladium bond bridged by one tin heteroborate. The metal atoms were reduced from Pd(II) to Pd(I). Due to the yield of 25%, another stanna-closo-dodecaborate cluster could be the reducing agent. At the upper boron ring a B−H activation and at the phosphine a P−C activation have proceeded and a B−P bond was formed together with benzene.36,37 The second species, 4, is a monomeric negatively charged complex with palladium remaining in the oxidation

The monoanionic complex of 1 crystallizes in the orthorhombic space group Pba21 containing one molecule of acetonitrile in the asymmetric unit. The interatomic palladium−germanium distance of 2.338(1) Å is significantly shorter than the one we reported earlier in the case of the homoleptic complex [Et3MeN]6[Pd(GeB11H11)4] [2.416(1) Å].18 In the range of published Pd−Ge bond lengths [2.3207(7)−2.887(1)Å]38−45 the found value belongs to the group of shorter distances. Short Pd−Ge bond length were found in the threecoordinated species [PdGe{N(SiMe3)2}2(PPh3)2] [2.3281(4) Å] and [PdGe{N(SiMe3)2}2(PEt3)2] [2.330(5) Å], in which double-bond character between metal and ligand was discussed to be responsible for the short interactions.39 Furthermore, short Pd−Ge distances [2.3207(7)−2.3344(7) Å] were also reported in the tetranuclear coordination compound [Pd{Pd(dmpe)}3(μ3-GePh2)3].40 Since we have no indications for a possible double-bond character in our germaborate complex, we believe that geometrical reasons might allow the found short interaction. The geometry of the transition metal complex can be described either as distorted square planar [Ge−Pd−Cl 145.36(3)°; P2−Pd−P1 158.09(4)°] or as trigonal bipyramidal, taking the coordination of the oxygen atom at the palladium center into account. Herein, the phosphorus atoms would be the axial ligands, with Ge, O, and Cl occupying the equatorial 7046


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positions [Ge−Pd−O = 139.69(7)°; Cl−Pd−O = 74.95(7)°]. The structure can be compared with the structure of [PdMeCl(Xantphos)], exhibiting a P−Pd−P angle of 152.61(6)° and a Pd−O distance of 2.658(4) Å.46 By slow evaporation of the solvent of an acetonitrile solution of 2, yellow crystals were received that were suited for singlecrystal X-ray analysis. The molecular structure of compound 2 is depicted in Figure 2.

Figure 3. ORTEP plot of the molecular structure of [Pd(SnB11H11)(κ3-Xantphos)] (6). The hydrogen atoms have been omitted; ellipsoids at 50% probability. Interatomic distances [Å] and bond angles [deg]: Pd−O 2.171(2), Pd−P1 2.279(1), Pd−P2 2.284(1), Pd−Sn 2.4934(2); O−Pd−P1 83.6(1), O−Pd−P2 83.7(1), P1−Pd− P2 166.4(1), O−Pd−Sn 167.4(1), P1−Pd−Sn 97.4(1), P2−Pd1−Sn 96.1(1).

Figure 2. ORTEP plot of the molecular structure of [Pd(GeB11H11)(κ3-Xantphos)] (2). The hydrogen atoms and the phenyl rings except their ipso-carbon atoms have been omitted; ellipsoids at 50% probability. Interatomic distances [Å] and bond angles [deg]: Pd−O 2.141(3), Pd−P1 2.278(1), Pd−P2 2.285(1), Pd−Ge 2.3283(6); O− Pd−P1 84.6(1), O−Pd−P2 84.1(1), P1−Pd−P2 168.56(4), O−Pd− Ge 175.9(1), P1−Pd−Ge 95.38(4), P2−Pd1−Ge 96.03(4).

The square-planar palladium complex 2 crystallizes in the monoclinic space group Pn with one molecule of acetonitrile in the asymmetric unit and exhibits a Pd−Ge distance of 2.3283(6) Å, which is slightly shorter than the one found in 1 [2.3375(5) Å] and again similar to the above-mentioned literature values.39,40 However the palladium−oxygen distance of 2.141(3) Å is much shorter compared to the starting material [2.476(2) Å]. The oxygen atom occupies the fourth coordination site at the square-planar palladium center in the neutral complex 2. The structure of the square-planarcoordinated complex [Pd(4-C6H4CN)(Xantphos)][CF3SO3] is comparable with 2 and exhibits also a short Pd−O bond of 2.1537(14) Å and a comparable P−Pd−P angle of 165.15(2)°.46 Crystals of the molecule 6 were obtained at −28 °C by slow diffusion of diethyl ether into a reaction mixture in acetone. The molecule crystallizes under inclusion of three equivalents of acetone in the monoclinic space group P21/n. An ORTEP plot of the molecule together with selected interatomic distances and angles is presented in Figure 3. In the squareplanar-coordinated complex the observed Pd−Sn interatomic distance of 2.4934(2) Å is a relatively short bond between these elements and can be compared with other complexes in the literature.47 The Xantphos ligand shows almost the same geometry and interatomic distances with the transition metal like in the germaborate derivative 2. By slow diffusion of diethyl ether into the acetonitrile reaction mixture of the tin nucleophile and the dichloride [PdCl2(Xantphos)], black crystals of the dinuclear complex 3 were obtained. Single crystals suitable for X-ray diffraction of 3 were also obtained from a solution of 6 in DMF (see Scheme 5). Compound 3 crystallizes in the monoclinic space group P21/n with 2.5 DMF molecules. One DMF molecule lies on a center of symmetry and shows a disorder. In Figure 4 compound 3 with selected bond lengths and angles is shown. The Pd−Pd distance of 2.5717(4) Å lies within the typical

Figure 4. ORTEP plot of the dinuclear complex [(C33H27P2O)(SnB11H10)Pd2d(κ2-Xantphos)] (3). The hydrogen atoms and the phenyl rings have been omitted for clarity; ellipsoids at 50% probability. Interatomic distances [Å] and angles [deg]: Sn(1)− Pd(2) 2.5487(3), Sn(1)−Pd(1) 2.9256(3), Pd(2)−Pd(1) 2.5717(4), Pd(2)−P(4) 2.3394(9), Pd(2)−P(3) 2.3770(9), Pd(1)−P(2) 2.2854(9), Pd(1)−P(1) 2.3166(8), P(1)−B(1) 1.928(4), O(1)− Pd(1) 2.234(2), P(2)−Pd(1)−Pd(2) 87.73(3), P(1)−Pd(1)−Pd(2) 105.34(2), O(1)−Pd(1)−Pd(2) 170.48(6), P(4)−Pd(2)−Pd(1) 162.95(3), P(3)−Pd(2)−Pd(1) 88.24(2), P1−Pd1−P2 160.62(3), P3−Pd2−P4 108.62(3).

range: 2.571(2) Å in [Pd(μ-t-Bu2P)(PMe3)]2, 2.691(1) Å in [{Pd(PMe3)}2[μ-SiHPh2 )2], and 2.5821(6) Å in [{Pd(PPh3)}2(μ-SeTrip)2] (Trip = 9-triptycyl) and 2.583(2) Å in Ph3PPd[Sn-(NtBu)2SiMe2]3PdPPh3.48−51 This type of metal− metal bridging by the stanna-closo-dodecaborate ligand was established in a variety of complexes with the metals silver, gold, and rhodium.12,13,15,20,23,25,27 The Sn−Pd bonds show distances of 2.9256(3) and 2.5487(3) Å. The shorter bond lies within the range of other published values of stanna-closododecaborate coordination at palladium.22 The longer interatomic distance might be due to the tension inside the four-membered ring: Sn−Pd1−P1−B. The bond between the phosphorus atom and the boron atom of 1.933(5) Å can be compared with other molecules containing phosphorus connected at a borane.31,32 The Pd−P distances show a slight variation from 2.2854(9) to 2.3770(9) Å but are within the typical range of this ligand.46 7047


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Yellow crystals of the salt 4 were obtained by slow diffusion of diethyl ether into a dichloromethane reaction mixture of the tin nucleophile and the dichloride [PdCl2(Xantphos)]. (Compound 3 was isolated from the dichloromethane solution as well.) The refinement of the X-ray diffraction data of compound 4 in the monoclinic space group P21/n results in the characterization of the salt [Bu3NH][PdCl2(SnB10H10B-Xantphos)] and three diethyl ether molecules in the asymmetric unit. The molecular structure is depicted in Figure 5 with

Article

EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out under exclusion of air and moisture in a argon atmosphere using standard Schlenk techniques. Solvents were purified by standard methods. Elemental analyses were performed by the Institut für Anorganische Chemie Universität Tübingen using a Vario EL analyzer and a Vario MICRO EL analyzer. The starting material [PdCl2(Xantphos)] was synthesized by published methods.54 [Et4N] 2[GeB11H11] and [Bu3NH]2[SnB11H11] were synthesized by a modified protocol of the work of Todd.3 All further chemicals used were purchased commercially and were not further purified. NMR. NMR spectra were recorded with a Bruker DRX-250 NMR spectrometer equipped with a 5 mm ATM probe head and operating at 250.13 (1H), 80.25 (11B), and 101.25 MHz (31P), a Bruker AVII+ 400 NMR spectrometer equipped with a 5 mm QNP (quad nucleus probe) head and operating at 400.13 (1H), and a Bruker AVII+ 500 NMR spectrometer with a 5 mm ATM probe head and operating at 500.13 (1H, Ξ = 100%), 160.5 (11B, Ξ = 32.083974%), 125.76 (13C, Ξ = 25,145020%), 202.5 (31P, Ξ = 40.480742%), and 186.5 MHz (119Sn, Ξ = 37.290632%). Chemical shifts are reported in δ values in ppm relative to external TMS (1H, 13C), BF3·Et2O (11B), 85% aqueous H3PO4 (31P), and SnMe4 (119Sn) using the chemical shift of the solvent 2H resonance frequency. For variable-temperature measurements the sample temperature was stabilized with a Bruker BVT 3200 temperature controller and equilibrated for 10 min prior to acquisition. The temperatures given are uncorrected. Crystallography. X-ray data for compounds 1, 2, and 4 were collected with a Stoe IPDS 2T diffractometer and corrected for Lorentz and polarization effects and absorption by air. The programs used in this work were Stoe’s X-Area and the WinGX suite of programs including SHELXS and SHELXL for structure solution and refinement.55−58 Numerical absorption correction based on crystalshape optimization was applied for 1, 2, and 4 with Stoe’s X-Red and X-Shape.59,60 X-ray data for compound 3 and 6 were collected with a Bruker Smart APEX II diffractometer with graphite-monochromated Mo Kα radiation. The programs used were Bruker's APEX2 v2011.8-0 including SADABS for multiscan absorption correction and SAINT for structure solution61 as well as the WinGX suite of programs v1.70.01 including SHELXL for structure refinement.56,58 Results of the crystal structure determination are presented in Table 1. [Et4N][PdCl(GeB11H11)(Xantphos)] (1). [PdCl2(Xantphos)] (163 mg, 0.22 mmol) was dissolved in MeCN (10 mL). [Et4N]2[GeB11H11] (100 mg, 0.22 mmol) in MeCN (10 mL) was added through a syringe, and the reaction mixture turned orange immediately. After stirring for one additional hour, the solution was filtered and carefully layered with ether. After several days, orange crystals of 1 (147 mg, 65% yield) were obtained. 1H NMR (400 MHz, CD3CN): δ 1.20 [t, 3J(1H−1H) = 7.3 Hz, 12H, NCH2CH3], 1.66 (s, br, 6H, C(CH3)2), 3.15 [q, 3J(1H−1H) = 7.3 Hz, 8H, NCH2], 7.2−7.3 (m, 2H, meta-HXa), 7.4−7.5 (m, 2H, ortho-HXa), 7.5−7.6 (m, 12H, para-HPh, meta-HPh), 7.7−7.8 (m, 2H, para-HXa), 7.9−8.0 (m, 8H, ortho-HPh). 11B{1H} NMR (80 MHz, CD3CN): δ −11.5 (s, 1B, B12), −15.1 (s, 10B, B2−B11). 13C{1H} NMR (126 MHz, CD3CN): δ 29.2 (s, br, (CH3)2C), 35.7 (s, (CH3)2C), 124.8 (m, meta-C-HXa), 126.0 (ipso-CXa), 128.4 (m, meta-CHPh), 128.7 (s, para-C-HXa), 129.7 (ipso-CPh), 130.9 (s, para-C-HPh), 132.1 (s, ortho-C-HXa), 134.0 (m, (CH3)2C-C-C-O), 134.0 (m, orthoC-HPh), 152.5 (s, C-O). 31P{1H} NMR (101 MHz, CD3CN): δ 25.7 (s). Anal. Calcd (%) for C47H63B11ClGeNOP2Pd (1053.37 g/mol): C 53.59, H 6.03, N, 1.33. Found: C 53.39, H 5.63, N, 1.35. [Pd(GeB11H11)(Xantphos)] (2). 1 (55 mg, 0.052 mmol) was dissolved in MeCN (5 mL), and AgNO3 (9 mg, 0.052 mmol) in MeCN (2 mL) was added through a syringe. After stirring for half an hour, all volatile components were evaporated under reduced pressure. The resulting residue was suspended in CH2Cl2 (12 mL) and filtered. By layering the solution with n-hexane, intense yellow crystals of 2 (34 mg, 73% yield) were received. 1H NMR (500 MHz, CD2Cl2): δ 1.81 (s, 6H, C(CH3)2), 7.4−7.5 (m, 4H, ortho-HXa, meta-HXa), 7.5−7.6 (m, 8H, meta-HPh), 7.6−7.7 (m, 4H, para-HPh), 7.8−7.9 (m, 10H, orthoHPh, para-HXa). 11B{1H} NMR (80 MHz, CD2Cl2): δ −10.2 (s, 1B,

Figure 5. ORTEP plot of the anion of [Bu3NH][PdCl2(SnB10H10BXantphos)] (4). The hydrogen atoms, the countercation, and the phenyl rings have been omitted for clarity; ellipsoids at 50% probability. Interatomic distances [Å] and angles [deg]: Sn(1)− Pd(1) 2.4930(8), Pd(1)−P(2) 2.238(2), Pd(1)−Cl(2) 2.364(2), Pd(1)−Cl(1) 2.384(2), B(1)−P(1) 1.924(9), P(2)−Pd(1)−Cl(1) 90.54(8), Cl(2)−Pd(1)−Cl(1) 90.20(9), P(2)−Pd(1)−Sn(1) 92.93(6), Cl(2)−Pd(1)−Sn(1) 86.52(6), Cl(1)−Pd(1)−Sn(1) 176.27(7), P(2)−Pd(1)−Cl(2) 172.91(9).

selected bond lengths and angles. Although a different type of B−P bond was found than in complex 3, the P−B bond length of 1.924(9) Å is in the same range and can be compared with B−PR3 adducts in the literature.52,53 The Pd−Sn bond length can also be compared with examples for [SnB11H 11]2− coordination at palladium.22 From the reaction between the heteroborate and the Xantphos ligand a new type of ligand is built that forms a 10-membered ring with the transition metal. Unfortunately this complex is a side product, and only a very small amount of crystals were obtained. Even after repeated reactions we were not able to improve the yield of this compound, and therefore the elemental analysis of this salt is missing.

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CONCLUSION Although the Ge−Pd bond is shorter than the Sn−Pd bond and therefore the steric crowding of the germa-closo-dodecaborate coordinated at the (Xantphos)-palladium fragment should be more substantial, we find activation of the B−H bond and P−C bond in the case of the tin ligand.18 To conclude, the stannacloso-dodecaborate cluster shows a much higher reactivity than the germanium homologue with respect to substitution at a palladium dichloride fragment, dynamics of the monosubstitution product, and reactivity of the B−H units. Obviously the stanna-closo-dodecaborate cluster provides reactivity at the tinneighbored B−H units. 7048


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Table 1. Results of the Crystal Structure Determination 1·MeCN empirical formula Mr [g mol−1] wavelength [Å] temperature [K] cryst syst space group Z a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] V [Å3] density ρcalc [g/cm3] abs coeff μ [mm−1] F(000) cryst size [mm3] θ range [deg] limiting indices reflections collected indep reflns/ Rint completeness absorp corr max./min. transmn params/ restraints R1/wR2 [I > 2σ(I)] R1/wR2 all data goodness-of-fit on F2 largest diff peak/hole [e·A−3] abs struct param CCDC

2·MeCNs

4·3Et2O

3·2.5DMF

6·3acetone

C49H66B11ClGeN2OP2Pd

C41H46B11GeNOP2Pd

C79.50H86.50B11N2.50O4.50P4Pd2Sn

C63H100B11Cl2NO4P2PdSn

C48H61B11O4P2PdSn

1094.33 0.71073

928.63 0.71073

1723.29 0.71073

1412.30 0.71073

1107.91 0.71073

173(2)

173(2)

150(2)

173(2)

120(2)

orthorhombic Pca21 4 10.8523(12) 23.421(5) 21.169(3) 90 90 90 5380.6(15) 1.351

monoclinic Pn 2 12.4283(9) 12.2637(6) 14.8561(10) 90 108.995(5) 90 2141.0(2) 1.440

monoclinic P21/n 4 15.2954(6) 23.789(1) 21.3124(9) 90 91.110(2) 90 7753.4(6) 1.476

monoclinic P21/n 4 20.273(1) 14.3171(7) 25.768(1) 90 107.057(4) 90 7150.1(7) 1.312

monoclinic P21/n 4 11.5634(4) 19.6159(6) 22.5928(7) 90 92.467(2) 90 5119.9(3) 1.437

1.040

1.232

0.913

0.764

0.944

2248 0.36 × 0.22 × 0.18

940 0.20 × 0.17 × 0.16

3496 0.19 × 0.22 × 0.28

2928 0.30 × 0.30 × 0.18

2248 0.41 × 0.32 × 0.17

1.74 to 29.19 −14 ≤ h ≤ 14, −32 ≤ k ≤ 32, −28 ≤ l ≤ 28 93 982

5.68 to 25.35 1.86 to 26.02 −14 ≤ h ≤ 14, −14 ≤ k −18 ≤ h ≤ 18, −23 ≤ k ≤ 29, ≤ 14, −17 ≤ l ≤ 17 −25 ≤ l ≤ 26 25 857 86 016

3.09 to 25.68 −24 ≤ h ≤ 24, −17 ≤ k ≤ 17, −31 ≤ l ≤ 31 59 464

2.18 to 24.36 −15 ≤ h ≤ 15, −26 ≤ k ≤ 25, −30 ≤ l ≤ 28 59 801

14 366/0.1005

7474/0.0719

15 229/0.0504

13 295/0.1379

12 824/0.0203

99.6% numerical 0.8872/0.6363

98.8% numerical 0.8818/0.8010

99.7% multiscan 0.7455/0.6828

97.9% numerical 0.9094/0.7759

98.6% multiscan 0.7457/0.6422

621/1

524/2

975/30

766/0

600/7

0.0429/0.1084

0.0385/0.0677

0.0337/0.0745

0.0900/0.1803

0.0381/0.0729

0.0534/0.1256 1.239

0.0463/0.0707 1.137

0.0597/0.0842 1.011

0.1269/0.1967 1.176

0.0297/0.0683 1.208

0.626/−1.508

0.700/−0.905

1.078/−0.830

1.732/−0.879

1.077/−1.131

0.464(10)

0.013(10)

879824

879823

879821

879822

879820

B12), −15.0 (s, 10B, B2−B11). 13C{1H} NMR (126 MHz, CD2Cl2): δ 32.7 (s, (CH3)2C), 34.9 (s, (CH3)2C), 121.8 (ipso-CXa), 126.4 (ipsoCPh), 127.3 (m, meta-C-HXa), 129.3 (m, meta-C-HPh), 132.0 (m, (CH3)2C-C−C-O), 132.0 (s, para-C-HXa), 132.5 (s, para-C-HPh), 134.4 (s, ortho-C-HXa), 134.5 (m, ortho-C-HPh), 152.1 (s, C-O). 31 1 P{ H} NMR (101 MHz, CD2Cl2): δ 30.6 (s, 2P). Anal. Calcd (%) for C39H43B11GeOP2Pd (887.67 g/mol): C 52.77, H 4.88. Found: C: 52.63, H: 4.93. [(C33H27P2O)(SnB11H10)Pd2(Xantphos)] (3). [PdCl2(Xantphos)] (15.1 mg, 0.02 mmol) and [Bu3NH]2[SnB11H11] (6.2 mg, 0.01 mmol) were dissolved in MeCN. By slow diffusion of diethyl ether into the solution, black crystals of 3 were obtained after several days (4 mg, 25% yield). (NMR spectroscopy of 3: Due to the very low solubility of crystalline 3, we recorded NMR spectra of 3 during the transformation of 6 into 3 over a period of several hours. Therefore 1H and 11B{1H} NMR data are not ambiguous since especially the signals of the aromatic protons overlay with the signal of the evolving benzene

at 7.39 ppm.) 1H NMR (500 MHz, DMF-d7, 26 °C): δ 1.62 (s, 3H, C(CH3)), 1.64 (s, 3H, C(CH3)), 1.72 (s, br, 6H, C(CH3)2), 7.0−8.0 (m, Haromatic). 11B{1H} NMR (161 MHz, DMF-d7, 26 °C): δ −2.0 to −19.0 (m, 11B). 31P{1H} NMR (202 MHz, DMF-d7, 26 °C): δ −22.0 to −18.0 (m, br, 1P, P1), 0.3 [ddd, 1P, 2J(cis-31P−31P) = 27 Hz, 3 31 J( P−31P) = 52 Hz, 3J(31P−31P) = 21 Hz, P3], 9.9 [ddd, 1P, 2 J(cis-31P−31P) = 27 Hz, 3J(31P−31P) = 27 Hz, 3J(31P−31P) = 9 Hz, P4], 15.8 [ddd, 1P, 2J(trans-31P−31P) = 335 Hz, 3J(31P−31P) = 21 Hz, 3 31 J( P−31P) = 9 Hz, P2] (in the case of P3 and P4 the assignment can also be interchanged). Anal. Calcd (%) for C72H69B11O2P4Pd2Sn·2CH2Cl2 (1710.57 g/mol): C 51.96, H 4.30. Found: C 51.69, H 4.38. [Bu3NH][PdCl2(SnB10H10B)(Xantphos)] (4). [PdCl2(Xantphos)] (7.6 mg, 0.01 mmol) and [Bu3NH]2[SnB11H11] (6.2 mg, 0.01 mmol) were dissolved in CH2Cl2. By slow diffusion of diethyl ether into the solution besides black crystals of 3 a few yellow crystals of 4 were obtained. 31P{1H} NMR (202 MHz, DMF-d7, 26 °C): δ 10.2− 7049


Organometallics

Article

11.8 (m, br, 1P, P1), 20.2 (s, 1P, 2J(cis-31P−117/119Sn) = 156 Hz, P2). Due to the very small amount of crystals of 4, an elemental analysis was not possible. [Bu3NH][PdCl(SnB11H11)(Xantphos)] (5). 1H NMR (500 MHz, DMF-d7, 26 °C): δ 1.76 (s, 6H, C(CH3)2), 7.3−7.6 (m, 16H, aromatic H), 7.8−8.0 (m, 10H, aromatic H). 11B{1H} NMR (161 MHz, DMFd7, 26 °C): δ −11.9 (s, 1B), −14.9 to −16.0 (m, 10B). 31P{1H} NMR (202 MHz, DMF-d7, 26 °C): δ 23.9 (s, br). 119Sn NMR (187 MHz, DMF-d7, 26 °C): δ −274 (s). 31P{1H} NMR (202 MHz, DMF-d7, −60 °C): cis-Xantphos isomer: δ 15.1 [d, 1P, 2J(31P−31P) = 18 Hz, 2 J(trans-31P−117Sn) = 3180 Hz, 2J(trans-31P−119Sn) = 3330 Hz], 19.6 [d, 1P, 2J(31P−31P) = 18 Hz, 2J(cis-31P−117/119Sn) = 118 Hz], transXantphos isomer: 25.8 [s, 2J(cis-31P−117/119Sn) = 121 Hz]. 119Sn NMR (187 MHz, DMF-d7, −60 °C): trans-Xantphos isomer: δ −268 (s), cisXantphos isomer: −288 ppm [d, 2J(trans-119Sn−31P) = 3330 Hz]. 5 was only detected by NMR spectroscopy as an intermediate. [Pd(SnB11H11)(Xantphos)] (6). [PdCl2(Xantphos)] (154 mg, 0.204 mmol) was dissolved in CH2Cl2 (20 mL). [Bu3NH]2[SnB11H11] (135 mg, 0.217 mmol) in CH2Cl2 (10 mL) was added via syringe. After stirring for one minute the red solution was layered with Et2O and stored at −28 °C. After several days orange-red crystals were formed. After washing with CH2Cl2 (3×) and Et2O (1×) and drying for 3 days under reduced pressure 6 (82 mg, 0.088 mmol, 40% yield) was obtained as a red, crystalline material. Single crystals of 6 suitable for crystal structure determination by X-ray diffraction were obtained by layering a reaction mixture with diethyl ether in acetone at −78 °C and stored at −28 °C for several days.. 1H NMR (500 MHz, DMF-d7, 26 °C): δ 1.89 (s, 6H, C(CH3)2), 7.5−7.6 (m, 8H, meta-HPh), 7.6 (m, 2H, meta-HXa), 7.6−7.7 (m, 6H, para-HPh, ortho-HXa), 7.9−8.0 (m, 8H, ortho-HPh), 8.1−8.2 (m, 2H, para-HXa). 11B{1H} NMR (161 MHz, DMF-d7, 26 °C): δ −11.0 (s, 1B, B12), −15.9 (s, 10B, B2−B11). 13 C{1H} NMR (126 MHz, CD3CN): δ 32.7 (s, (CH3)2C), 34.8 (s, (CH3)2C), 120.6 (ipso-CXa), 127.4 (m, meta-C-HXa), 128.0 (m, ipsoCPh), 129.2 (m, meta-C-HPh), 132.1 (m, (CH3)2C-C−C-O), 132.4 (s, para-C-HPh), 132.9 (s, para-C-HXa), 134.5 (m, ortho-C-HPh), 134.7 (s, ortho-C-HXa), 153.0 (m, C-O). 31P{1H} NMR (202 MHz, DMF-d7, 26 °C): δ 33.3 (s, 2P). 119Sn{1H} NMR (187 MHz, DMF-d7): δ −268 ppm. Anal. Calcd (%) for C39H43B11OP2PdSn (933.77 g/mol): C 50.17, H 4.64. Found: C 50.09, H 4.75.

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ASSOCIATED CONTENT

S Supporting Information *

Results of the crystal structure analysis of compounds 1−4 and 6 and cif files of all published structures. 31P{1H}−31P{1H} EXSY NMR spectrum of 5 and 31P{1H}−31P{1H} COSY of 3 and 5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Author Contributions †

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by the Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged. REFERENCES

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