Cobalt, Rhodium, Iridium, and Ruthenium Carbonyl Complexes with

May 18, 2011 - Herein we report the coordination chemistry of stanna-closo- dodecaborate with carbonyl complexes of cobalt, rhodium, iridium, and ruth...
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Cobalt, Rhodium, Iridium, and Ruthenium Carbonyl Complexes € ssbauer with Stanna-closo-dodecaborate: 103Rh NMR, 119Sn Mo 119 Spectroscopy, and Solid-State Sn NMR Sebastian Fleischhauer,† Klaus Eichele,† Inga Schellenberg,‡ Rainer P€ottgen,‡ and Lars Wesemann*,† † ‡

Institut f€ur Anorganische Chemie, Universit€at T€ubingen, Auf der Morgenstelle 18, D-72076 T€ubingen, Germany Institut f€ur Anorganische und Analytische Chemie, Universit€at M€unster, Corrensstrasse 30, D-48149 M€unster, Germany

bS Supporting Information ABSTRACT: Depending on the stoichiometry stanna-closododecaborate [SnB11H11]2 reacts with the dimeric carbonyl complex [Rh(CO)2Cl]2 to give a dinuclear rhodium coordination compound with bridging tin ligands, [Et3MeN]6[Rh2(CO)4(SnB11H11)4] (1), or a pentagonal-bipyramidal complex, [Et4N]5[Rh(CO)2(SnB11H11)3] (2), with the carbonyl ligands in axial position. The analogous iridium and cobalt complexes [Et4N]5[Ir(CO)2(SnB11H11)3] (3) and [Me4N]5[Co(CO)2(SnB11H11)3] (4) exhibit a pentacoordinated structure with the tin ligands in axial positions. The dimeric ruthenium chlorocarbonyl complex [Ru(CO)3Cl2]2 reacts with four equivalents of the tin nucleophile to give the octahedrally coordinated ruthenium complex [Et3MeN]4[Ru-cis-(CO)2-cis-Cl2-trans-(SnB11H11)2] (5). The synthesized coordination compounds were characterized by X-ray crystal structure analysis, by 103Rh, 119Sn, and 11B NMR spectroscopy in solution, and in the case of the rhodium complexes 1 and 2 by 119Sn solid-state NMR and 119Sn M€ossbauer spectroscopy.

’ INTRODUCTION The coordination chemistry of tin is an attractive field of research.1 Many research goups have synthesized new tin ligands and studied the reactivity and structures of the transition metal tin complexes.115 Stannylenes such as bis(dialkylamino)tin2 or dialkyltin3,5 derivatives are prominent ligands. Novel chelating ligands with two tin donor sites were designed in recent years.4 Furthermore, cluster-type tin coordination was developed in reaction with Zintl anions.6 Recently we have prepared a novel tripodal tin ligand and the first copper complex with this facialcoordinating ligand.16 Three years ago we investigated the chemistry of Vaska’s complex with the tin nucleophile [SnB 11 H 11 ]2, resulting in a trigonal-bipyramidal iridium(I) complex, [Me 4 N]3 [Ir(SnB11H11)2(CO)-trans-(PPh3)2].11 This complex was protonated even by weak acids and undergoes oxidative addition with hydrogen. Rhodium coordination chemistry with this type of tin ligands was documented in two cases: [Cp*Rh(SnB 11 H 11 )(bipy 0 )] (bipy 0 = 4,4 0 -di-tert-butyl-2,2 0 bipyridine) and [Bu4N]2[Rh(SnCB10H11)3-trans-(PPh3)2].12,13 Further examples of coordination compounds with group(IV)heteroborate ligands show these ligands in a variety of coordination modes.1316 So far the coordination chemistry between carbonyl complexes and the nucleophilic heteroborate ligands is almost unexplored. Herein we report the coordination chemistry of stanna-closododecaborate with carbonyl complexes of cobalt, rhodium, iridium, and ruthenium. r 2011 American Chemical Society

’ RESULTS AND DISCUSSION Syntheses. The rhodium carbonyl chloride complex [Rh(CO)2Cl]2 was reacted with the nucleophile stanna-closododecaborate in various stoichiometries to give the dimeric complex [Et3MeN]6[Rh2(CO)4(SnB11H11)4] (1) and the monomeric pentacoordinated complex [Et4N]5[Rh(CO)2(SnB11H11)3] (2) (Scheme 1, 2) {stoichiometry [Rh(CO)2Cl]2/[SnB11H11]2 (a) 1/2: [Rh(CO)2Cl]2 and product 1; (b) 1/4: product 1; (c) 1/6: product 2}. Both coordination compounds 1 and 2 show a remarkable stability toward air and water. A comparable pentacoordinated complex with the trichlorostannate ligand, [PPN]2[Rh(CO)2 (SnCl3)3], was synthesized by Pregosin et al. starting with [(nbdRhCl)2] (nbd = norbornadiene).17 119Sn NMR and IR spectroscopy in solution indicate that the monomeric complex 2 is also the product of the reaction of the dimer 1 with a further equivalent of tin nucleophile. In contrast to the complex [Rh2Cl2(SnC13)4]4, which shows substitution with carbon monoxide, the rhodium complex 1 shows no reaction with further CO molecules.18 Alternatively, the dinuclear rhodium compound 1 was synthesized from the reaction between rhodium cluster [Rh4(CO)12] and eight equivalents of the salt [Et3NH]2[SnB11H11]. The reaction of the polymer [Ir(CO)2Cl]n with three equivalents of the tin nucleophile leads directly to the pentacoordinated iridium complex 3 in good yields (Scheme 3). So far no further Received: April 11, 2011 Published: May 18, 2011 3200

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Scheme 1. Reaction of [Rh(CO)2Cl]2 with Four Equivalents of [SnB11H11]2

Scheme 2. Reaction of [Rh(CO)2Cl]2 with Six Equivalents of [SnB11H11]2

Scheme 5. Reaction of [Ru(CO)3Cl2]2 with Four Equivalents of [Et3MeN]2[SnB11H11] Forming [Et3MeN]4[Ru(CO)2Cl2(SnB11H11)2]

Scheme 3. Reaction of Polymeric [Ir(CO)2Cl]n with Three Equivalents of [SnB11H11]2

Scheme 4. Reaction of Co2(CO)8 with Two Equivalents of [Me4N]2[SnB11H11] and Oxidation Forming [Me4N]5[Co(CO)2(SnB11H11)3] (4)

products of this iridium carbonyl complex in reaction with other stoichiometries of [SnB11H11]2 were characterized. Trans

coordination in pentagonal iridium complexes with tin and carbonyl ligands was characterized in complex [Et4N][transIr(CO)3(SnPh3)2], which was synthesized by reaction of the reduction product Na3[Ir(CO)3] with Ph3SnCl.19 In the case of cobalt we used Co2(CO)8 as the starting material. Reaction of the cobaltcarbonyl with two equivalents of nucleophile [SnB11H11]2 led to an air-sensitive green solution, which was stirred under air to give a yellow solution. From this reaction mixture we isolated by crystallization the Co(I) complex [Me4N]5[Co(CO)2(SnB11H11)3] (4) (Scheme 4). Unfortunately we could not isolate and characterize the green intermediate. Pentagonal-coordinated cobalt complexes containing tin and carbonyl ligands are known for a variety of derivatives such as [{Co(CO)4}4xSnRx] (R = halides, phenyl, or alkyl) (x = 13).1923 Finally, the reaction of the ruthenium carbonyl chloride [Ru(CO)3Cl2]2 with four equivalents of tin nucleophile in acetonitrile results in almost quantitative isolation of the ruthenium complex [Et 3 MeN]4 [Ru(CO)2 Cl2 (SnB 11 H 11 )2 ] (5) (Scheme 5). In this case no formation of a dimeric complex was observed. Comparable coordination compounds such as [Me4N]2[Ru(CO)2Cl2(SnCl3)2] were published by Wilkinson et al., but results of crystal structure analyses were not presented.24,25 Solid-State Structures. The solid-state structures of compounds 15 have been determined by single-crystal X-ray structure analysis. Single crystals of the dimeric rhodium complex 1 were obtained with the cations Et3MeNþ, Et3NHþ, and Et4Nþ in almost quantitative yield. The rhodium carbonyl complex 1 crystallizes in the triclinic space group P1 with an inversion center 3201

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Figure 1. ORTEP plot of the anion [Et 3 MeN]6 [Rh 2 (CO)2 (SnB11H11)4] (1). The cations and hydrogen atoms have been omitted for clarity; ellipsoids are at 50% probability. Interatomic distances [Å] and angles [deg]: Sn1Rh10 2.7149(6), Sn1Rh1 2.7189(6), Rh1C1 1.896(6), Rh1C2 1.894(6), Rh1Sn2 2.5451(5), Rh1Rh10 2.7343(7), O1C1 1.137(6), O2C2 1.140(6), Rh10 Sn1Rh1 60.43(2), C1Rh1C2 169.7(2), C1Rh1Sn2 85.2(2), C2Rh1Sn2 85.4(2), C1Rh1Sn10 91.5(2), C2Rh1Sn10 91.0(2), Sn2Rh1Sn10 127.86(2), C1Rh1Sn1 94.7(2), C2Rh1Sn1 92.9(2), Sn2Rh1Sn1 112.55(2), Sn10 Rh1 Sn1 119.57(2), C1Rh1Rh10 96.1(2), C2Rh1Rh10 93.8(2), Sn2Rh1Rh1 0 172.21(2), Sn1 0 Rh1Rh1 0 59.86(2), Sn1 Rh1Rh1 0 59.72(2), O2C2Rh1 178.2(5), O1C1Rh1 177.6(5).

Figure 2. ORTEP plot of the anion of [Et4N]9[Na][Rh(CO)2(SnB11H11)3]2 (2). The cations and the hydrogen atoms have been omitted for clarity; ellipsoids are at 50% probability. Interatomic distances [Å] and angles [deg]: Sn1Rh1 2.568(1), Sn2Rh1 2.567(1), Sn3Rh1 2.565(1), O1C1 1.16(1), C1Rh1 1.87(1), O2C2 1.14(1), C2Rh1 1.87(1), O1C1Rh1 178(1), O2C2Rh1 178(1), C1Rh1C2 179.2(6), C1Rh1Sn3 88.0(3), C2Rh1Sn3 91.3(4), C1Rh1Sn2 88.1(3), C2Rh1Sn2 92.3(5), Sn3Rh1Sn2 119.70(3), C1Rh1Sn1 87.8(3), C2Rh1Sn1 92.6(4), Sn3Rh1Sn1 120.96(4), Sn2Rh1Sn1 118.96(4).

between the rhodium atoms. Compared to the chloride-bridged starting material [Rh(CO)2Cl]2 (3.324 Å) the distance between the rhodium atoms in the tin-bridged complex 1 is shorter (2.7343 Å) and in the range of a typical rhodiumrhodium bond.2630 Like in the coinage metal chemistry of the stannacloso-dodecaborate ligand the terminal bonded cluster shows a

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Figure 3. ORTEP plot of the anion of [Et4N]5[Ir(CO)2(SnB11H11)3] (3). The cations and the hydrogen atoms have been omitted for clarity; ellipsoids are at 50% probability. Selected interatomic distances [Å] and angles [deg]: IrC2 1.90(1), IrC1 1.90(1), IrSn1 2.5707(5), IrSn2 2.5757(5), IrSn3 2.6226(5), O1C1 1.14(1), O2C2 1.15(1), C2IrC1 144.6(5), C2IrSn1 89.0(3), C1IrSn1 89.9(3), C2IrSn2 87.4(3), C1IrSn2 87.5(3), Sn1IrSn2 169.80(2), C2IrSn3, 105.0(4), C1IrSn3 110.3(4), Sn1IrSn3 97.51(2), Sn2IrSn3 92.64(2).

significantly shorter RhSn bond length (2.54 Å) than the edgebridging ligand (2.72 Å).15 Interestingly, in complex [Rh3(CO)6(μ-SnPh2)3(SnPh3)3] the bridging Ph2Sn ligand (RhSn on average 2.655 Å) shows a slightly shorter RhSn interatomic distance in comparsion to the terminal Ph3Sn ligand (RhSn on average: 2.675 Å).5a The rhodiumtin distances in complex 1 can be compared with RhSn bond lengths in the literature.2d,5a,e,8,12,13,3133 Furthermore the heteroborate bridging ligand in compound 1 exhibits a smaller RhSnRh bond angle of 60.43° in comparison to the edge-bridging Ph2Sn ligand (average 66.95°) in the cluster [Rh3(CO)6(μ-SnPh2)3(SnPh3)3].5a Therefore the RhRh bond lengths in this trinuclear cluster (2.912.95 Å) are also longer in comparison to the dimer 1. So far tin-bridging stanna-closo-dodecaborate coordination was only published in the case of the coinage metals.15 The monomeric rhodium complex 2 crystallizes in the monoclinic space group C2/c. The rhodium atom shows a trigonalbipyramidal coordination mode with the carbonyl ligands in trans position. Single crystals could be obtained only by accident after addition of the sodium salt Na2[SnB11H11]. The complex crystallizes as the dimeric sodium salt [Et4N]9[Na][Rh(CO)2 (SnB11H11)3]2 with the sodium cation coordinated by two clusters of two complexes. Three BH units of each heteroborate show interactions with the sodium cation, which lies on a center of symmetry. In Figure 2 the structure of the anion is presented. The tinrhodium distances of Sn(1)Rh(1), 2.568 Å, Sn(2)Rh(1), 2.567 Å, and Sn(3)Rh(1), 2.565 Å, are comparable with the terminal-coordinated cluster in dimer 1. The bonding angles in complex 2 exhibit an almost ideal trigonalbipyramidal coordination mode at rhodium. This complex follows the 18-electron count. The iridium salt [Et4N]5[Ir(CO)2(SnB11H11)3] (3) crystallizes in the orthorhombic space group P212121 with one equivalent 3202

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Figure 4. ORTEP plot of the anion of [Me4N]5[Co(CO)2(SnB11H11)3] (4). The cations and the hydrogen atoms have been omitted for clarity; ellipsoids are at 50% probability. Selected interatomic distances [Å] and angles [deg]: Sn1Co 2.437(3), Sn2Co 2.433(3), Sn3Co 2.4937(6), CoC2 1.734(5), CoC1 1.767(6), O2C2 1.171(7), O1C1 1.132(7), C2CoC1 128.8(2), C2CoSn2 86.6(5), C1CoSn2 90.0(6), C2CoSn1 90.5(5), C1CoSn1 89.1(6), Sn2CoSn1 175.52(3), C2CoSn3 116.0(2), C1CoSn3 115.1(2), Sn2CoSn3 92.26(7), Sn1CoSn3 92.09(7), O2C2Co 174(1), O1C1Co 174(1).

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Figure 6. Experimental and simulated 119Sn M€ossbauer spectrum of [Et3MeN]6[Rh2(CO)4(SnB11H11)4] (1) at 77 K.

Figure 7. Experimental and simulated 119Sn M€ossbauer spectrum of [Et4N]5[Rh(CO)2(SnB11H11)3] (2) at 77 K.

Figure 5. ORTEP plot of the anion of [Et3MeN]4[Ru(CO)2Cl2(SnB11H11)2] (5). The cations and the hydrogen atoms have been omitted for clarity; ellipsoids are at 50% probability. Interatomic distances [Å] and angles [deg]: RuSn1 2.6171(4), Cl1Ru 2.479(5), C1O1 1.10(2), C1Ru 1.79(2), Cl2Ru 2.500(5), C2O2 1.11(2), C2Ru 1.80(2), O1C1Ru 175(2), O(2)C(2) Ru 176(2), Cl(1)RuCl(2) 87.3(2), C1Ru1C2 91(1).

of the salt in the asymmetric unit. The pentacoordination at the transition metal can also be described as a trigonal bipyramid (Figure 3). However, in this complex two tin ligands are in trans position (169.8°) and the carbonyl ligands show an angle of 145° with the transition metal. The tin ligand in the equatorial coordination shows a longer bond to iridium than the two apical located heteroborates. Compared with the complex [Ir(SnB11H11)2CO(PPh3)2]3 [IrSn: 2.646, 2.662 Å] the equatorial iridium tin bond is not significantly different11 and the shorter distances lie in the range of published IrSn complexes.2,32,34 In the solid state the cobalt complex 4 shows the same geometry as the trigonal bipyramid of the iridium compound 3. Two tin ligands are in trans position, and carbonyl ligands exhibit an angle of 129.4° with the cobalt atom (Figure 4). The CoSn bond lengths of 2.437, 2.433, and 2.494 Å can be compared with the following complexes published

in the literature: [Et 4 N][Co(SnCl 3 )2 (CO)3 ]35 2.444 Å, [Li(THF)4][Cp*Co(SnCl3)3]36 2.471 Å, and Co(SnCl3)(CO)3 2.477 Å.22 The octahedrally coordinated ruthenium compound crystallizes in the monoclinic space group C2/c and lies on a center of symmetry. The two halide ligands and the CO groups show a disorder of 50%. The complex exhibits trans arrangement of the tin ligands and cis coordination of the carbonyl and chloride ligands (Figure 5). With respect to the tin and carbonyl coordination at ruthenium the complex [Ru(SnPh3)2(CO)2(N, N0 -diisopropyl-1,4-diaza-1,3-butadiene)] shows the same geometry.37 The RuSn bond lengths in this complex of 2.686(2) and 2.691(2) Å and in the tetracarbonyl [Ru(SnPh3)2(CO)4] (2.712 Å) are comparable with the distances in coordination compound 4 of 2.617 Å.38 We have already characterized several stanna-closo-dodecaborate ruthenium complexes showing a range of RuSn bonds: 2.5742.685 Å.10 The shorter interactions belong to dimeric ruthenium complexes with the cluster coordinating two metals via a RuSn bond and three BHSn interactions. The longer interactions show the cluster in a typical terminal tin coordination at ruthenium.10 €ssbauer Spectroscopy of [Et3MeN]6[Rh2(CO)4 Tin-119 Mo (SnB11H11)4] (1) and [Et 4N]5[Rh(CO)2 (SnB 11 H11 )3 ] (2). Figure 6 shows the 119Sn M€ossbauer spectrum of compound 1 recorded at 77 K together with a transmission integral fit. The spectrum was well reproduced with a single tin signal at an isomer 3203

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Figure 8. 15.80 MHz 103Rh{1H} NMR spectrum of a 0.4 M solution of [Rh2(CO)4(SnB11H11)4]6 in dichloromethane measured at 298 K. The asterisk indicates an impurity.

Figure 10. Experimental (top) and calculated (bottom) 119Sn CP/ MAS NMR spectrum of a powder sample of 1 spinning at 12 kHz, 118 000 scans. The isotropic peaks are indicated by arrows.

Table 1. Principal Componentsa of the 119Sn Chemical Shift Tensors of Compounds 1 and 2 no.

δiso (ppm)

1

262

125

202

695

820

0.2

393

253

253

673

420

1.0

294

63

204

743

806

0.3

2

δ11 (ppm)

δ22 (ppm)

δ33 (ppm)

Ω (ppm)

k

δ11 g δ22 g δ33, isotropic chemical shift δiso = (δ11 þ δ22 þ δ33)/3, span Ω ≈ δ11δ33, skew k = 3(δ22  δiso)/Ω; 1 e k e 1. a

Figure 9. 15.80 MHz 103Rh{1H} NMR spectrum of a 0.4 M solution of [Rh(CO)2(SnB11H11)3]5 in dichloromethane measured at 298 K.

shift of δ = 1.63(1) mm/s, which is subjected to significant quadrupole splitting of ΔEQ = 1.30(1) mm/s. The experimental line width has a value Γ = 0.92(1) mm/s. Although the solid-state structure shows two tin sites, only one signal in the M€ossbauer spectrum was detected (superposition of the two subspectra). Obviously the tin in the terminal and bridging coordination mode is similar with respect to the isomer shift, which is a direct measure of the s electron density at the tin nuclei. This situation can be compared with Mingos' M€ossbauer investigations of the dinuclear rhodium complex mer-[{Rh(CNC8H9)3(SnCl3)(μ-SnCl2)}2], exhibiting two different tin ligands in bridging and terminal position with one isomer shift of 1.82 mms1.8 The 119 Sn M€ ossbauer spectrum of the pentacoordinated rhodium complex [Et4N]5[Rh(CO)2(SnB11H11)3] (2) is presented in Figure 7. The spectrum shows a single signal at δ = 1.78(1) mm/s, Γ = 0.88(4) mm/s, and ΔEQ = 1.53(2) mm/s. The higher isomer shift (as compared to [Et 3 NMe]6 [Rh 2 (CO)4 (SnB11H11)4]) is indicative of slightly higher electron density at the tin nuclei. Furthermore we observe higher electric quadrupole splitting for the compound with the RhSn3 core as compared to the Rh2Sn4 one, indicating stronger structural distortion. The isomer shift values are close to the ones observed for [Pt(SnB11H11)4]6 (δ = 1.66 mms1) and [Bu3NH]8

[Ni(SnB11H11)6] (δ = 1.60 mms1), and thus strongly support the strong electron-donating effect of the [SnB11H11]2 ligand.14 In the intermetallic compounds LaRhSn (δ = 1.98 mms1), LaRhSn2 (δ = 1.93 mms1), and CaRhSn2 (δ = 1.96 mms1) with different rhodiumtin substructures, the isomer shift values are significantly higher, in agreement with higher electron density at these tin nuclei.39 NMR Spectroscopy in Solution. In order to elucidate the structures of compounds 15 in solution, multinuclear NMR studies have been carried out. The 11B{1H} NMR spectra of compounds 15 provide strong evidence for the coordination of the tin ligand at the transition metal [11B{1H} NMR spectrum of the uncoordinated cluster [SnB11H11]2: 5.1(1B), 10.6(5B), 11.9(5B); because of isochronism the signal at 15 ppm is the signal for the two B5 belts of the cluster; the signal of B12 is covered by the broad base of the signal]. In the cases of the carbonyl complexes 1 and 35, we were able to detect the 13C NMR signals of the carbonyl groups. For the dimeric rhodium complex 1, a 13C NMR shift of 183.8 ppm was found, with a rhodium carbon coupling of 1 103 J( Rh,13C) = 72 Hz. Compound 3 reveals a singlet at 171.2 ppm with a tin carbon coupling of 2J(117/119Sn,13C) = 43.4 Hz, whereas the cobalt homologue 4 has a carbonyl shift of 199 ppm with a tin carbon coupling of 2J(117/119Sn,13C) = 99.5 Hz. 3204

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Organometallics The octahedral ruthenium complex 5 shows a shift for the CO group of 198 ppm, but no coupling with the tin ligands was found. As expected, compound 1 shows in the 119Sn{1H} NMR spectrum in dichloromethane solution two signals for the terminal and bridging coordinated tin ligands at 291 and 411 ppm. The signal at 291 ppm exhibits a coupling with the rhodium nucleus of 1J(119Sn103Rh) = 604 Hz and can be assigned to the terminal coordinating tin ligands. The coupling

Figure 11. Schematic 119Sn chemical shift tensors as a function of the coordination mode of the stannaborate ligand. Data presented in the current study are indicated as bold solid lines; results from previous studies are drawn as dashed lines.10,14c,43

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between the bridging ligands and the rhodium atoms is not resolved in the signal at 411 ppm. In solution, the pentacoordinated complex 2 shows in the 119 Sn{1H} NMR spectrum a doublet for three equivalent tin ligands in equatorial positions. The 119Sn103Rh coupling constant of 500 Hz is slightly smaller than the coupling constant of the terminal-coordinated ligand in the dimer 1. The iridium complex 3 shows in the crystal structure two tin ligands in axial and one in equatorial position. Therefore, the 119Sn{1H} NMR spectrum in solution exhibiting two signals with an intensity ratio of 2:1 and chemical shifts of 473 and 505 ppm can be regarded as a confirmation of the solid-state structure. Because of the coupling with the 59Co nucleus, the isostructural cobalt complex 4 shows one broad resonance in the 119Sn NMR spectrum at 205 ppm. The 119Sn{1H} NMR resonance for the ruthenium compound 5 could be found at 352 ppm, comparable to other stannacloso-dodecaborate ruthenium compounds: [Ru(SnB11H11)2 (dppb)]2, 366, 374 ppm, and [Ru(SnB11H11)2(PPh3)2]2, 398 ppm.10a The 103Rh{1H} NMR of the dinuclear complex 1 (Figure 8) shows a singlet at 9327 ppm. Due to coupling of the 117Sn and 119 Sn isotopes with the 103Rh nucleus, the terminal and bridging tin ligands give rise to tin satellites. However the different 117Sn and 119Sn coupling constants are not resolved. Two doublets result from the coupling with the terminal-coordinated tin ligand (1J 103Rh119/117Sn = 622 Hz) and the bridging tin ligand (1J 103Rh119/117Sn = 338 Hz). The probabilities for the different isotopomers result in different intensities of the doublets (calculated 0.1/0.2/1/0.2/0.1; the quality of the spectrum does not allow an accurate measurement of the satellite intensities). However, the comparison of the calculated and recorded tin satellites results in the confirmation of the Rh2Sn4 composition in solution. In the case of the mononuclear complex 2 (Figure 9),

Figure 12. Representation of the LUMO (top left), HOMO (top right), HOMO2 (left), and HOMO3 (right) orbitals of complex 1. 3205

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Table 2. Crystal Data and Structure Refinement Parameters for 15 1 3 2CH3CN formula

2 3 4CH3CN

3 3 4CH3CN

4 3 4CH3CN

5 3 2CH3CN

C54H164B44N10-

C46H135B33N8.5-

C50H145B33Ir1-

C30H105B33-

C32H97B22Cl2-

O4Rh2Sn4

Na0.5O2RhSn3

N9Sn3O2

CoN9O2Sn3

N5O2RuSn2

fw [g/mol]

2174.17

1666.83

1809.75

1395.96

1231.32

wavelength [Å]

0.71073

0.71073

0.71073

0.71073

0.71073

T [K]

173

173

173

173

173

θ range [deg]

5.6725.35

5.6825.03

5.6925.35

5.6725.68

6.0825.03

crystal system

triclinic

monoclinic

orthorhombic

orthorhombic

monoclinic

space group Z

P1 h 1

C2/c 8

P212121 4

Pc21n 4

C2/c 4

a [Å]

11.0038(12)

17.0539(15)

13.7901(5)

12.4299(6)

26.758(2)

b [Å]

16.5840(16)

29.5348(18)

19.9695(10)

17.8892(8)

17.9420(8)

c [Å]

16.4540(16)

36.649(3)

32.4045(14)

31.7370(16)

14.4783(11)

R [deg]

64.620(7)

β [deg]

79.697(8)

γ [deg]

76.556(8)

V [Å3] Fcalc [g/cm3]

2627.8(5) 1.37

96.259(7)

120.897(5)

18349(3) 1.21

8923.6(7) 1.35

7057.1(6) 1.31

5964.5(7) 1.37

μ [mm1]

1.3

1.0

2.4

1.3

1.2

no. of reflections

34 156

55 200

60 567

73 755

36 831

no. of indep reflns/Rint

9510/0.0606

15 913/0.1113

16 149/0.1046

13 100/0.0638

5197/0.0950

parameters/restraints

515/44

842/74

817/5

581/185

312/2

absorbtion/correction

numerical

numerical

numerical

numerical

numerical

min./max. transmission

0.8416, 0.6995

0.9064, 0.7436

0.7782, 0.4790

0.8676, 0.7799

0.8891, 0.5701

R1/wR2 indices [I > 2σ(I)] R1/wR2 for all reflections

0.0444/0.0992 0.0581/0.1054

0.0861/0.1866 0.1315/0.2041

0.0488/0.1086 0.0568/0.1123

0.0449/0.1077 0.0574/0.1142

0.0596/0.1530 0.0708/0.1614

GooF on F2

1.020

1.084

1.001

1.028

1.083

largest diff peak/hole [e Å3]

0.988/0.567

0.721/1.119

1.462/1.324

1.620/0.613

2.731/0.903

0.518(6)/0.482(6)

0.47(4)/0.53(4)

twin ratio

the 103Rh NMR spectrum exhibits a singlet at 9626 ppm with satellites representing three tin ligands (calculated ratio 0.3/1/0.3; measured 0.23/1/0.20). The different coupling constants (1J 119Sn103Rh = 588 Hz, 1J 117Sn103Rh = 564 Hz) can be assigned. In comparison to the educt [Rh(CO)2Cl]2 with δ(103Rh) = 8219 ppm, the stannaborate complexes 1 and 2 are shifted by more than 1000 ppm.40 The 1J 103Rh119/117Sn coupling constants of 1 and 2 are smaller in comparison to coupling constants found in the literature: [Rh(CO)2(LSnCl)Cl] with L = {2,6-(Me2NCH2)2C6H3} 880 Hz,9c [Bu4N]2[Rh(PPh3)2(SnCB10H11)3] 760 Hz,13 [MeSi{SiMe2N(4-tol)}3SnRh(PEt3)(COD)] 846 Hz,2k [MeSi{SiMe2N(4tol)}3SnRh(PiPr3)(COD)] 829 Hz.2k The difference between the 1J 119Sn103Rh coupling constants determined in the 119Sn and 103Rh NMR spectra must be attributed to the 119Sn NMR spectra, which exhibit broad signals (half-width: 1, 1070 Hz; 2, 1100 Hz) and therefore imprecise coupling constants. Tin-119 NMR Spectroscopy in the Solid State. The 119Sn cross-polarization magic-angle-spinning (CP/MAS) NMR spectrum of a powder sample of 1 (Figure 10) consists of two signal groups with isotropic chemical shifts of 262 and 393 ppm and associated spinning sidebands, spaced about the isotropic peaks at integer multiples of the spinning frequency. The isotropic peak at 262 ppm is split into a doublet, with 1J(119Sn,103Rh) = 580 ( 10 Hz, and is assigned to the terminal tin ligand with Sn2 (Figure 1), whereas the isotropic peak at 393 ppm reveals its triplet structure only after resolution enhancement, with

J( Sn,103Rh) = 360 ( 20 Hz, hence is assigned to the bridging tin ligands with Sn1. Due to the presence of three crystallographically nonequivalent tin ligands in the crystal structure of 2, the 119Sn CP/MAS spectrum of 2 shows one broad signal group with an isotropic chemical shift of 294 ppm. Because magnetic shielding is a three-dimensional property by nature, characterization of the chemical shift tensor can provide a more detailed picture of the relationship between structure and chemical shift. Solid-state NMR of powder samples provides the unique chance to determine directly the magnitudes of the principal components of the chemical shift tensors by analysis of the spinning sideband intensities (Table 1).41,42 A synopsis of 119 Sn chemical shift tensors reported so far for stannaborate ligands in different coordination modes is presented in Figure 11. While the isotropic chemical shifts are not very conclusive, the shape of the 119Sn chemical shift tensor is more indicative of the coordination mode. At present, the database is relatively small; hence the apparent trends may change in the future as more data become available. Tin in the uncoordinated stannaborate features a small span Ω. This changes upon coordination, with values of Ω between 480 and 1205 ppm. In particular, η1(Sn) coordination results in Ω = 480820 ppm, with k ≈ 1 in most cases, except for M = Rh in the present study. Despite all variations, the direction corresponding to highest shielding is basically invariant, δ33 = 695 to 743 ppm. The only example of bridging η1-μ2(Sn) coordination, obtained in the present study of dinuclear 1, shows a chemical shift anisotropy that is, on 1 119

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Organometallics first sight, similar to terminal η1(Sn) coordination to Fe, Ru, or Ni, but differs clearly from the terminal η1(Sn) coordination involving Rh in 1. While the spans of the η3(BH)-coordinated ligands, 735 to 761 ppm, are comparable to those of the η1(Sn) ligands, the skews, 0.28 to 0.39, change sign, indicating a change in symmetry. The greatest spans, 894 to 1205 ppm, have been observed for η3(BH)η1(Sn) coordination. IR Spectroscopy. Due to the strong electron-donating properties of the stanna-closo-dodecaborate ligand, the CO stretching frequency of compounds 15 appears at smaller wave numbers in comparison to the starting materials and comparable complexes with the trichlorostannate ligand: [Rh(SnCl3)3(CO)2]2, 2060, 2010 cm1;17 [RuCl2(SnCl3)2(CO)2]2, 2058, 2000 cm1.25 Molecular Orbital Calculations. To develop an understanding of the metal bonding in the dimer 1, DFT calculations with the basis set LAC3VP and the functional B3LYP were carried out.4449 The dimer shows for the first time stanna-closo-dodecaborate in a nondynamic bridging coordination mode. The structure of 2 obtained from geometry optimization fits well with the structural parameters determined by single-crystal structure analysis. In Figure 12 the HOMO, which is a RhSnRh bonding orbital, and two lower lying HOMO2 and HOMO3 orbitals exhibiting RhRh bonding character are shown. The LUMO of the dimer 1 shows with respect to the RhRh bond antibonding character. In this complex the rhodium atoms follow a 16-electron count with the bridging clusters donating one electron to each rhodium atom and not counting a metalmetal bond. However, regarding the RhRh interaction as a double bond, each transition metal follows an 18-electron count. The pentagonal-coordinated complexes of rhodium, iridium, and cobalt show different structures in the solid state. In the rhodium complex the carbonyl ligands are in trans position, whereas in the iridium and cobalt derivative the tin ligands are in the axial positions. Both isomers A (trans CO) and B (trans SnB 11 H 11 ) were calculated for the complexes [M(CO)2(SnB11H11)3]5 (M = Co, Rh, Ir). In the gas phase and with a solvent water model the trans CO isomer shows for all metals a slight stabilization in comparison to geometry B. However the rhodium complex exhibits the strongest stabilization of isomer A in this series, which is in accordance with the structure in the solid state. Obviously due to packing forces the cobalt and iridium complex crystallize with a trans tin ligand arrangement.

’ CONCLUSION Carbonyl halides of rhodium, iridium, and ruthenium react with the tin ligand stanna-closo-dodecaborate under formation of metal tin bonds. In the case of rhodium besides a pentacoordinated complex a dimer exhibiting a bridging tin ligand was characterized. The homologous pentacoordinated cobalt complex was isolated from the reaction of the nucleophile with dicobaltoctacarbonyl under air. The donor properties of the dianionic stannylene-type ligand [SnB11H11]2 were determined by IR spectroscopy and 119Sn M€ossbauer spectroscopy. ’ EXPERIMENTAL SECTION General Procedures. All manipulations were carried out under argon in Schlenk glassware. Solvents were dried and purified by standard methods and stored under argon. NMR spectra were recorded with a Bruker DRX-250 NMR spectrometer using a 5 mm ATM probehead operating at 250.13 (1H), 80.25 (11B), 62.9 (13C), and 93.25 MHz

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(119Sn), and a Bruker AVIIþ500 NMR spectrometer using a 10 mm low-γ probehead operating at 500.13 (1H) and 15.80 MHz (103Rh). Chemical shifts are reported in δ values in ppm relative to external TMS (1H, 13C), BF3 3 Et2O (11B), or SnMe4 (119Sn) using the chemical shift of the solvent 2H resonance frequency. For 103Rh NMR the IUPAC reference standard with Ξ = 3.186447% has been used.50 Solid-state 119 Sn ramped-amplitude cross-polarization magic-angle spinning NMR spectra were recorded on a Bruker DSX-200 widebore NMR spectrometer using a 4 mm double-bearing MAS probehead and are referenced to SnMe4 using external Sn(C6H12)4 as secondary standard. The analysis of spinning sideband intensities has been carried out using WSolids1.51 Elemental analyses were performed at the Institut f€ur Anorganische Chemie University of T€ubingen using a Vario EL analyzer. A Ca 119 mSnO3 source was used for the 119Sn M€ossbauer spectroscopic investigation. The samples were placed within thin-walled glass containers at a thickness of about 10 mg Sn/cm2. A palladium foil of 0.05 mm thickness was used to reduce the tin K X-rays concurrently emitted by this source. The measurements were conducted in the usual transmission geometry at 77 K. Stanna-closo-dodecaborate salts with the cations [Et4N], [Me4N], [Et3MeN], and [Et3HN] were synthesized by using a modified protocol of the original work of the Todd group.52 [Rh(CO)2Cl]2 and [Ir(CO)2Cl]n were synthesized according to literature procedures.53,54 [Ru(CO)3Cl2]2, Co2(CO)8, and Rh4(CO)12 were purchased from STREM chemical. Crystallography. X-ray data for compounds 15 were collected on a Stoe IPDS 2T diffractometer and were corrected for Lorentz and polarization effects and absorption by air. The crystallographic data and refinement parameters of compound 15 are listed in Table 2. The programs used in this work are Stoe’s X-Area and the WinGX suite of programs including SHELXS and SHELXL for structure solution and refinement. Numerical absorption correction based on crystal shape optimization was applied for compound 15 with Stoe’s X-Red and X-Shape. In the case of compounds 3 and 4, due to racemic twinning, the appropriate racemic twin matrix was applied.5559 Synthesis of [Et3MeN]6[Rh2(CO)4(SnB11H11)4] (1). A 194 mg (0.5 mmol) amount of [Rh(CO)2Cl]2 and 964 mg (2 mmol) of [Et3MeN]2[SnB11H11] were dissolved in 20 mL of acetonitrile. Stirring of this mixture for two hours resulted in a dark red solution. Diffusion of ether into the reaction mixture gave single crystals suitable for X-ray analysis. The orange-red compound is air stable in the solid state but somewhat labile toward air in solution. (Yield: 79%.) 1 H NMR (CD3CN): 1.25 (m, 9H, CH2-CH3), 2.92 (s, 3H, N-CH3), 3.30 (m, 6H, N-CH2). 11B{1H} NMR (CD3CN): 10.8 (s, 1B, B12), 14.9 (s, 10B, B211). 13C{1H} NMR (CD3CN): 8.1 (s, CH2-CH3), 47.3 (s, N-CH3), 56.4 (s, N-CH2), 183.8 [d, CO, 1J(103Rh13C) = 72 Hz]. 103Rh{1H} NMR (CD2Cl2): 9327 [s, 1J(119/117Sn103Rh) = 622 Hz, 1J(119/117Sn103Rh) = 338 Hz]. 119Sn{1H} NMR (CD3CN): 291 [d, 1J(119Sn103Rh) = 604 Hz], 411. 119Sn{1H} NMR (RAMP): 260 [1J(119Sn103Rh) = 580 Hz], 392 [1J(119Sn103Rh) = 360 Hz]. IR (KBr, cm1): 2484 (s, BH), 1986 (s, CdO). IR (DCM, cm1): 2486 (s, BH), 1995 (s, CdO). Anal. Calcd (%) for C46H152B44N6O4Rh2Sn4 (2010.09): C, 27.49; H, 7.62; N, 4.18. Found: C, 27.38; H, 7.78 N, 4.06. Synthesis of [Et4N]5[Rh(CO)2(SnB11H11)3] (2). A 97 mg (0.25 mmol) amount of [RhCl(CO)2]2 was dissolved in 25 mL of acetonitrile, and 764 mg (1,5 mmol) of [Et4N]2[SnB11H11] was added. The orange solution was stirred for 12 h, resulting in a yellow solution. Slow diffusion of ether into the reaction mixture gave crystals of 2 not suitable for X-ray analysis in high yield. (Yield: 75%.) Single crystals were obtained by addition of one equivalent of Na2SnB11H11, resulting in the formation of small amounts of crystals of [Et4N]4.5Na0.5[Rh(SnB11H11)3(CO)2]. 1H NMR (CD3CN): 1.2 (m, 12H, CH3) 3.2 (m, 8H, N-CH2). 11B{1H} NMR (CD3CN): 11.0 (s, 1B, B12), 14.9 (s, 10B, B211). 13C{1H} NMR (CD3CN): 6.0 (s, CH3), 51.3 (s, N-CH2). 103Rh{1H} NMR 3207

dx.doi.org/10.1021/om200301v |Organometallics 2011, 30, 3200–3209

Organometallics (CD2Cl2): 9626 [1J(119Sn103Rh) = 588 Hz, 1J(117Sn103Rh) = 564 Hz]. 119Sn{1H} NMR (CD3CN): 290 [d, br, 1J(119Sn103Rh) ≈ 500 Hz]. IR (KBr, cm1): 2477 (s, BH), 1955 (s, CO). Anal. Calcd (%) for C42H133B33N5O2RhSn3 (1318.93): C, 32.41; H, 8.61; N, 4.50. Found: C, 32.12; H, 8.30; N, 4.40. Synthesis of [Et 4N]5 [Ir(CO)2 (SnB 11 H11 )3 ] (3). A 28 mg (0.1 mmol) amount of dark green [Ir(CO)2Cl]n polymer was suspended in 10 mL of acetonitrile. A 153 mg (0.3 mmol) portion of [Et4N]2[SnB11H11] was added while stirring. Within minutes the color of the solution changed to yellow. Slow diffusion of ether into a solution of 3 in acetonitrile gave yellow crystals suitable for X-ray analysis. (Yield: 78%.) 11B{1H} NMR (CD3CN): 11.4 (1B, B12), 15.9 (10B, B2-B11). 13C{1H} NMR (CD3CN): 171.2 [s, CO, 2J(119Sn13C) = 43.4 Hz]. 119Sn{1H} NMR (CD3CN): 473 (2 Sn), 505 (1 Sn). IR (KBr, cm1): 2478 (s, BH), 1954 (m, CO), 1904 (s, CO). Anal. Calcd (%) for C42H133B33N5O2IrSn3 (1645.66): C, 30.65; H, 7.81; N, 4.26. Found: C, 30.26; H, 7.81; N, 4.29. Synthesis of [Me4N]5[Co(CO)2(SnB11H11)3] (4). A 79 mg (0.2 mmol) amount of [Me4N]2[SnB11H11] and 34.2 mg (0.1 mmol) of Co2(CO)8 were stirred for 2 h in 10 mL of acetonitrile to give a green solution. The argon vessel was removed, and the solution was stirred for 24 h under air, resulting in a yellow solution and a gray precipitate. Diffusion of ether into a filtered reaction mixture gave single crystals suitable for single-crystal structure analysis. Additional single crystals were obtained using the countercations Et4N and Me3NH. Compound 4 is stable to air and light. (Yield: 32%.) 1H NMR (CD3CN): 3.1 (s, N-CH3). 11B{1H} NMR (CD3CN): 15.3. 13C{1H} NMR (CD3CN): 56 (s, N-CH3), 199 [s, CO 2J(119Sn13C) = 99.5 Hz]. 119 Sn{1H} NMR (CD3CN): 205 [s, 2J(119Sn119/117Sn) = 3122 Hz]. IR (KBr, cm1): 2473 (s, BH), 1944 (m, CO), 1890 (s, CO). Anal. Calcd (%) for C42H133B33CoN5O2Sn3 3 CH3CN (1553.43): C, 34.02; H, 8.82; N, 5.41. Found: C, 33.77; H, 9.11; N, 5.95. Synthesis of [Et3MeN]4[Ru(CO)2Cl2(SnB11H11)2] (5). A 51 mg (0.1 mmol) amount of [RuCl2(CO)3]2 and 193 mg (0.4 mmol) of [Et3MeN]2SnB11H11 were dissolved in 10 mL of acetonitrile. After stirring for four hours, while changing its color to pale yellow crystals were grown by slow diffusion of ether. Compound 5 is stable to air but sensitive to light. (Yield: 80%.) 1H NMR (CD3CN): 1.26 (m, 9H, CH2CH3), 2.90 (s, 3H, N-CH3), 3.31 (m, 6H, N-CH2). 13C{1H} NMR (CD3CN): 8.3 (s, CH3), 48.1 (s, N-CH3), 55.9 (s, N-CH2), 198 (1C, CO). 11B{1H} NMR (CD3CN): 15 (s, 11B, B2-B12). 119Sn{1H} NMR (CD3CN): 352. IR (KBr, cm1): 2483 (BH, s), 2008, 1940 (CdO, s). Anal. Calcd (%) for C30H94B22Cl2N4O2RuSn2 3 CH3CN (1231.39): C, 31.21; H, 7.94; N, 5.69. Found: C, 31.11; H, 8.25; N, 5.48. Molecular Orbital Calculations. Quantum chemical calculations were performed on a Linux-based, dual-core computer with the program package JAGUAR from Schr€odinger.44 The orbital diagrams were plotted with Maestro from Schr€odinger. All structures were optimized at the DFT level with the B3LYP functional. The used basis sets were LACVP or LACV3P, including effective core potentials and outermost core orbitals. All calculations were performed in C1 symmetry. The solvent was described by a PBF solvent model (PoissonBoltzmann solvation model). Water as solvent was used with a probe radius of 1.40 and dielectric constant of 80.37.4549

’ ASSOCIATED CONTENT Supporting Information. Cif files of all published structures are available free of charge via the Internet at http://pubs.acs.org.

bS

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; [email protected].

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’ ACKNOWLEDGMENT This work was supported by the Deutsche Forschungsgemeinschaft. ’ REFERENCES (1) (a) Cardin, D. J. In Metal Clusters in Chemistry; Braunstein, P., Oro, A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, Germany, 1999; Vol. 1, p 48. (b) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. Rev. 1989, 89, 11. (2) (a) Lappert, M. F.; Power, P. P. J. Chem. Soc., Dalton Trans. 1985, 51. (b) Campbell, G. K.; Hitchcock, P. B.; Lappert, M. F.; Misra, M. C. J. Organomet. Chem. 1985, 289, C1. (c) Hitchcock, P. B.; Lappert, M. F.; Misra, C. M. J. Chem. Soc., Chem. Commun. 1985, 863. (d) Hawkins, S. M.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1985, 1592. (e) Al-Allaf, T. A. K.; Eaborn, C.; Hitchcock, P. B.; Lappert, M. F.; Pidcock, A. J. Chem. Soc., Chem. Commun. 1985, 548. (f) Veith, M.; M€uller, A.; Stahl, L.; N€otzel, M.; Jarczyck, M.; Huch, V. Inorg. Chem. 1996, 35, 3848. (g) Knorr, M.; Hallauer, E.; Huch, V.; Veith, M.; Braunstein, P. Organometallics 1996, 15, 3868. (h) Grassi, M.; Meille, S. V.; Musco, A.; Pontellini, R.; Sironi, A. J. Chem. Soc., Dalton Trans. 1990, 251. (i) Veith, M.; Stahl, L.; Huch, V. Inorg. Chem. 1989, 28, 3278. (j) Veith, M.; Stahl, L.; Huch, V. J. Chem. Soc., Chem. Commun. 1990, 359. (k) Kilian, M.; Wadepohl, H.; Gade, L. H. Eur. J. Inorg. Chem. 2008, 1892. (l) Kilian, M.; Wadepohl, H.; Gade, L. H. Organometallics 2008, 27, 524. (m) Kilian, M.; Wadepohl, H.; Gade, L. H. Dalton Trans. 2008, 5, 582. (3) (a) Krause, J.; Pluta, C.; P€orschke, K. R.; Goddard, R. J. Chem. Soc., Chem. Commun. 1993, 1254. (b) Krause, J.; Haack, K. J.; P€orschke, K. R.; Gabor, B.; Goddard, R.; Pluta, C.; Seevogel, K. J. Am. Chem. Soc. 1996, 118, 804. (c) Schneider, J. J.; Hagen, J.; Bl€aser, D.; Boese, R.; Kr€uger, C. Angew. Chem. Int. Ed. 1997, 36, 739. (4) (a) Zabula, A. V.; Pape, T.; Hepp, A.; Schappacher, F. M.; Rodewald, U. C.; P€ottgen, R.; Hahn, F. E. J. Am. Chem. Soc. 2008, 130, 5648. (b) Zabula, A. V.; Pape, T.; Hepp, A.; Hahn, F. E. Organometallics 2008, 27, 2756. (c) Hahn, F. E.; Zabula, A. V.; Pape, T.; Hepp, A.; Tonner, R.; Haunschild, R.; Frenking, G. Chem.—Eur. J. 2008, 14, 10716. (5) (a) Adams, R. D.; Captain, B.; Smith, J. L., Jr.; Hall, M. B.; Beddie, C. L.; Webster, C. E. Inorg. Chem. 2004, 43, 7576. (b) Adams, R. D.; Trufan, E. Organometallics 2008, 27, 4108. (c) Adams, R. D.; Boswell, E. M.; Captain, B.; Hungria, A. B.; Midgley, P. A.; Raja, R.; Thomas, J. M. Angew. Chem., Int. Ed. 2007, 46, 8182. (d) Adams, R. D.; Captain, B.; Hall, M. B.; Trufan, E.; Yang, X. J. Am. Chem. Soc. 2007, 129, 12328. (e) Adams, R. D.; Captain, B.; Smith, J. L., Jr.; Hall, M. B.; Beddie, C. L.; Webster, C. E. Inorg. Chem. 2004, 43, 7576. (6) (a) Kesanli, B.; Fettinger, J.; Gardner, D. R.; Eichhorn, B. J. Am. Chem. Soc. 2002, 124, 4779. (b) Goicoechea, J. M.; Sevov, S. C. Organometallics 2006, 25, 4530. (c) Wang, J.-Q.; Wahl, B.; F€assler, T. F. Angew. Chem., Int. Ed. 2010, 49, 6592. (d) Wang, J.-Q.; Stegmeier, S.; Wahl, B.; F€assler, T. F. Chem.—Eur. J. 2010, 16, 1793. (7) (a) Garlaschelli, L.; Greco, F.; Peli, G.; Manassero, M.; Sansoni, M.; Della Pergola, R. Dalton Trans. 2003, 4700. (b) Downing, D., O.; Zavalij, P.; Eichhorn, B. W. Eur. J. Inorg. Chem. 2010, 890. (8) Bott, S. G.; Machell, J. C.; Mingos, D. M. P.; Watson, M. J. Dalton Trans. 1991, 859. (9) (a) Moriyama, H.; Pregosin, P. S.; Sito, Y.; Yamakawa, T. Dalton Trans. 1984, 2329. (b) Deaky, V.; Sch€urmann, M.; Jurkschat, K. Z. Anorg. Allg. Chem. 2009, 635, 1380. (c) Martincova, J.; Dostalova, R.; Dostal, L.;  Ru zicka, A.; Jambor, R. Organometallics 2009, 28, 4823. (10) (a) G€adt, T.; Grau, B.; Eichele, K.; Pantenburg, I.; Wesemann, L. Chem.—Eur. J. 2006, 12, 1036. (b) G€adt, T.; Wesemann, L. Dalton Trans. 2006, 328. (c) G€adt, T.; Eichele, K.; Wesemann, L. Dalton Trans. 2006, 2706. (11) Kirchmann, M.; Fleischhauer, S.; Wesemann, L. Organometallics 2008, 27, 2803. (12) Marx, T.; Wesemann, L.; Dehnen, S. Z. Anorg. Allg. Chem. 2001, 627, 1146. (13) Joosten, D.; Weissinger, I.; Kirchmann, M.; Maichle-M€ossmer, C.; Schappacher, F. M.; P€ottgen, R.; Wesemann., L. Organometallics 2007, 26, 5696. 3208

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