Pyridine Functionalized N-Heterocyclic Silane Complexes of Iridium

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Pyridine Functionalized N‑Heterocyclic Silane Complexes of Iridium and Rhodium−An Unexpected Change in Coordination Felix Kaiser,†,‡ Robert M. Reich,† Eric Rivard,‡ and Fritz E. Kühn*,† †

Catalysis Research Center and Department of Chemistry, Technische Universität München, Molecular Catalysis and Wacker Institute, Lichtenbergstr. 4, 85747 Garching bei München, Germany ‡ Department of Chemistry, University of Alberta, 11227 Saskatchewan Dr., Edmonton, Alberta Canada, T6G 2G2 S Supporting Information *

ABSTRACT: A new pyridine functionalized N-heterocyclic silane with ambident reactivity as a ligand has been synthesized and characterized by NMR spectroscopy (1H, 13C{1H}, 29Si), mass spectrometry, elemental analysis, and X-ray crystallography. This ligand reacts with iridium and rhodium cod precursors (cod = 1,5-cyclooctadiene) to yield two new complexes that possess divergent, and unexpected, binding properties. In particular, no oxidative addition occurs at the intraligand Si-H unit. With the iridium(I) center, the ligand acts as a tertiary amino-pyridine chelator, whereas coordination of rhodium(I) to the ligand occurs with arene πcomplexation on an opposite side. The latter interaction yields an unprecedented, electronically induced, coordination change at the silicon center over a long spatial distance. The new iridium and rhodium compounds are of high interest as they provide two potentially different reactions sites in one complex and as these sorts of complexes are known to activate small molecules like dihydrogen or silanes. Hence, the compounds are promising candidates for applications in tandem catalysis. Furthermore, the rhodium complex might be utilized for molecular switches, sensors, and comparable applications.

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some cases.14,15 Some iridium and rhodium complexes have also been shown to catalytically transform abundant CO2 into value-added building blocks such as formate or CO.22−26 The variety of catalytic applications over the decades shows that organometallic rhodium and iridium complexes are continuing to be of great value to the scientific community. Changes in reactivity profiles within these complexes can be facilitated by applying different ligands or adding a secondary functionality that promotes alternate reactivity. One possibility in this regard is the application of silanes as “additional” functionality. Due to their propensity to generate radicals via homolytic Si−H bond cleavage, organosilanes in combination with photosensitizers are widely used as initiators in radical polymerizations, for renewable and industrial relevant monomers like epoxidized soybean oil and limonene dioxide.27−30 As a result of their lower tendency to form peroxyls and their softer nature compared to carbon, silyl radicals allow polymerization to occur in the presence of oxygen.31 Combining a metal center like iridium and rhodium with a source for a soft silyl radical could provide a sustainable and economically advantageous catalyst.32−35 Herein, we report the synthesis of a new, N-heterocyclic silane with unexpectedly versatile binding properties with the

INTRODUCTION

Over the past few decades, iridium and rhodium containing metal complexes remain of high interest due to their outstanding catalytic properties. Since many Ir and Rh complexes activate small molecules like dihydrogen or silanes, they are central to many important catalytic transformations, such as hydrosilylations,1−5 isomerizations,6−9 polymerizations,10−13 and especially hydrogenations.14−21 Hydrogenation catalysts like Wilkinson’s [Rh(PPh3)3Cl] (I) and Crabtree’s [Ir(cod)(py)(PCy3)](PF6) (II) (cod = cis-1,5cyclooctadiene, Cy = cyclohexyl, py = pyridine) have been used in various syntheses, and due to their versatility and stability, they have become commercially available in the meantime (Chart 1).14,20 The substrate scope is extremely wide including even the hydrogenation of hindered, tetrasubstituted alkenes in Chart 1. Versatile and Commercially Available Hydrogenation Catalysts by Wilkinson (I) and Crabtree (II)14,20

Received: October 16, 2017

© XXXX American Chemical Society

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DOI: 10.1021/acs.organomet.7b00769 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 1. Preparation of Pyridine Diamine Intermediate Product 3a

Reagents and conditions: (i): pivaloyl chloride, 0 °C → r.t., 24 h, (pyridine/CH2Cl2); (ii): H2, [Pd/C], r.t., 2 h, (EtOH); (iii): 1. pyridine-2carboxaldehyde, r.t., 30 min, (iPrOH); 2. BH3·SMe2, r.t. → rfx. 18 h, (THF), 3. HCl, r.t. → rfx. 17 h, (MeOH).

a

Scheme 2. Preparation of Silane 5a

a

Reagents and conditions: (iv) HSiCl3, DIPEA, 30 °C, 48 h, (PhH); (v) LiN(SiMe3)2, 30 °C, 3 h, (hexane).

Figure 1. 1H NMR spectrum of 4. The signals for the methylene bridges (3.93−3.49 ppm, enlarged) appear each split into two doublets, indicating chemical inequivalence.

further workup or purification steps. Treatment of 2 with 2pyridine carboxaldehyde in isopropanol leads to the formation of the respective imine; again, nondried solvents can be used and the reaction is complete within minutes. The intermediate product is subsequently treated with BH3·SMe2, whereby both the amide and the imine moieties are reduced to the respective amines, yielding product 3 with a 99% yield over two steps. The obtained product 3, which has been characterized by NMR, MS, elemental analysis, and X-ray crystallography (see the SI, Figure S28), is therefore readily accessible in excellent yields (96% over 4 consecutive steps) on a multigram scale. Intended introduction of a silane moiety into 3 by double deprotonation with butyl lithium and subsequent treatment of the dilithiated amide with halosilanes results in ill-defined product mixtures. However, it is found that reaction of 3 with HSiCl3 in the presence of N,N-diisopropyl-N-ethylamine

late transition metals iridium and rhodium. While the coordination of the ligand to iridium leads to a pyridinetertiary amine chelate, arene π-complexation to rhodium leads to a yet unprecedented, electronically induced coordination switch at the silane.

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RESULTS AND DISCUSSION In order to develop silicon-containing chelates of Rh and Ir, a new ligand system, formally derived from o-phenylenediamine is synthesized (Scheme 1). The first step in the ligand synthesis involves the reaction of o-nitroaniline with pivaloyl chloride in a mixture of pyridine and dichloromethane, yielding amide 1 in a 98% yield after distillation. Reduction of the aromatic nitro group with hydrogen and palladium on carbon as a catalyst quantitatively gives the amide-amine 2. This reaction proceeds readily in nondry ethanol as a solvent and does not require B


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Organometallics

distinct SiMe3 moieties, due to a possible rotation barrier about the silylamine Si−N linkage. Accordingly, single-crystal X-ray crystallography confirms the above-mentioned structural assignment for the bis(trimethylsilyl)amide-functionalized product 5 (Figure 3).

(DIPEA) as a base in benzene cleanly converts 3 into the respective halosilane 4 (Scheme 2). The obtained N-heterocylic halosilane 4 is characterized by means of NMR (1H, 13C, 29Si), HRMS spectroscopy, elemental analysis, and single crystal X-ray diffraction. The 1H NMR spectrum of 4 shows two different signals for the two methylene moieties (attached to the tBu and pyridine groups), indicating chemical inequivalence. Furthermore, a singlet with characteristic satellites is observed at 6.62 ppm, indicating the presence of a Si−H bond (Figure 1). Single crystal X-ray structure analysis reveals the formation of the desired product 4 and the presence of a distorted trigonal bipyramidal geometry at silicon, including an additional coordination of the pyridine moiety (Figure 2).

Figure 3. ORTEP style X-ray structure of 5. Ellipsoids are shown at 50% probability level. The hydrogen atom is drawn with an arbitrary radius. Carbon-attached hydrogen atoms are omitted for clarity. Element colors: black − carbon, blue − nitrogen, red − silicon. Figure 2. ORTEP style X-ray structure of 4. Ellipsoids are shown at 50% probability level. The hydrogen atom is drawn with an arbitrary radius. Carbon-attached hydrogen atoms are omitted for clarity. Element colors: black − carbon, blue − nitrogen, red − silicon, green − chlorine.

Interestingly, the silicon atom Si1 in 5 is only four-coordinate and a dative interaction involving the pyridine moiety, which is observed for 4, is not present anymore. As a consequence, the bond lengths Si1−N2 and Si1−N3 are 1.7305(8) and 1.7383(8) Å and exhibit therefore almost the same length, due to a lack of a trans-influence from the pyridine moiety. Si1−N4 is slightly shorter with 1.7135(8) Å, and the N2−Si1− N3 angle is again close to rectangular (92.37(4)°). The presence of a 4-fold coordination sphere for the silicon center in 5 in contrast to 4 is most likely caused by the significantly higher steric demand of the BTSA moiety. To investigate the thermal stability of compound 5, variabletemperature NMR studies are conducted. The silane shows to be stable in boiling THF for hours; furthermore, the studies reveal that a rotational barrier for the BTSA moiety can be overcome at elevated temperatures. The coalescence point lies at 47 °C, the activation energy is calculated to be 62.9 kJ/mol (Figure 4; for calculative details, see the SI, S19−S20). In order to investigate the binding properties of its free pyridine moiety and potentially reactive silicon center and to obtain metal complexes with two potential reaction centers, 5 is reacted with several metal precursors. Reaction with many group 9 element-containing compounds yields ill-defined mixtures; however, treatment of a solution of 5 with 1 equiv of [Ir(cod)2](BArF) (BArF = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) in dichloromethane leads to an immediate color lightening from dark burgundy to light red. Crystallization at −30 °C yields orange crystals of a new product 6 (Scheme 3). Mass spectrometry of the crystals reveals a single signal at m/ z = 757.4. Mass-to-charge ratio and isotopic distribution pattern suggest the elemental composition C31H52IrN4Si3+, which fits the composition of an adduct given by [Ir5(cod)]+ (Figure 5). NMR investigations strongly support this first hypothesis, showing shifted ligand signals as well as those for the BArF

As a result, a coplanar annulated system consisting of two five-membered and two six-membered rings is formed. The bond length Si1−N1 is 2.005(1) Å, thus significantly longer than Si1−N2 [1.739(1) Å] and Si1−N3 [1.786(1) Å] and therefore suggests a polar dative interaction in contrast to the covalent bonds Si1−N2 and Si1−N3. The observed differences in Si−N bond length match well the metrical parameters within related compounds.36,37 The additional bond N1−Si1 furthermore leads to an observed trans-influence-like weakening of the opposing bond Si1−N3, which becomes apparent in the elongation of Si1−N3 in contrast to Si1−N2. Bond angles N1−Si1−N2 and N2− Si1−N3 are quite close to rectangular (80.77(5)° and 87.63(5)°), and N1−Si1−N3 is 166.61(5)°. The distance Si1−Cl1 (2.131 Å) is comparable to literature known pentacoordinated Si(IV) compounds, but longer than in donor-free, four-coordinated chlorosilanes, hence suggesting increased reactivity.38−41 As strong bases like bis-trimethylsilylamides (N(SiMe3)2)− are able to formally abstract hydrochloric acid from certain silanes, compound 4 is treated with 1 equiv of Li[N(SiMe3)2].42 High resolution mass spectrometry reveals the formation of a single product with a mass of m/z = 456.20 and a composition of C23H40N4Si3, suggesting direct nucleophilic substitution at the silicon center of Cl by N(SiMe3)2. NMR data strongly support this assertion as a Si-H 1H NMR resonance remains at 6.18 ppm. Additionally, two broad resonances at 0.00 and 0.23 ppm that each integrate to nine protons are observed, thus strongly suggesting the presence of two spectroscopically C


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Organometallics

Figure 4. 1H NMR study of 5 in THF-d8 at 0 °C (maroon, bottom) to 60 °C (purple, top). The SiMe3 (TMS) signals are highlighted in the highfield region.

Scheme 3. Preparation of the Iridium (Left, 6) and Rhodium (Right, 7) Complexes from 5 (NMR Numbers Assigned)a

a

Reagents and conditions: (vi) [Ir(cod)2](BArF), 30 °C, 10 min, (CH2Cl2); (vii) [Rh(cod)2](BF4), 30 °C, 10 min, (CH2Cl2).

counterion and a bound cod moiety in the 1H NMR spectrum. Variable-temperature NMR studies reveal that, in contrast to 5, the rotational barrier for the two SiMe3 groups in 6 cannot be overcome up to 60 °C, thus indicating a higher steric bulk near the silicon center and proving stability in solution at elevated temperatures. These results are in accord with saturation transfer experiments, in which no significant exchange can be observed. 11B and 19F spectra each show a single signal for the BArF counterion (in the 11B spectrum, the signal appears as a nonet, caused by the coupling to 8 equivalent ortho-protons). The 29Si spectrum shows three signals, two for the TMS moieties at 10.8 and 5.3 ppm, as well as one at 31.3 ppm. This corresponds to a downfield shift of about 61 ppm compared to 5, suggesting a proximity or coordination to iridium (for detailed NMR spectra, see the SI). Single crystal X-ray diffraction finally reveals the formation of an iridium(I) complex of 5 and confirms the initially assumed composition [Ir5(cod)](BArF) for product 6 (Figure 6). Besides one η4-coordinated molecule of cod, ligand 5 chelates iridium(I) with its free pyridine moiety and tertiary amino-nitrogen N2, thus breaking its former planarity and forming a distorted tetrahedral, quaternary ammonium species. As a consequence of withdrawn electron density, bond lengths N2−C6, N2−C7, and N2−Si1 are significantly elongated by up to 0.113 Å [N2−C6 (1.457(1) Å vs 1.498(8) Å); N2−C7 (1.399(1) vs 1.476(7) Å); N2−Si1 (1.730(1) Å vs 1.843(4) Å)]. The nitrogen−iridium bonds lengths (dN1−Ir1 = 2.094(5) Å, dN2−Ir1 = 2.166(4) Å) are on the bottom end of comparable, literature known compounds, hence suggesting relatively strong bonding interactions.43−47 The distances between iridium and the alkenes are around 2.00 Å and thus comparable to literature known fragments.43−45,47 Furthermore, iridium is only bound

toward two more N-donors, additionally to the two alkene submoieties, resulting in a comparatively sterically easy accessible iridium center, which might be an advantage for future applications in catalysis. Si1 is pushed out of the plane, generated by the phenylene ring C7−C12 and N2/N3 by 11.3°, most likely because of the geometry change at N2. Due to their steric demands, the tBu and −N(SiMe3)2 moieties are located on opposing sides of this plane. To the best of our knowledge, this is the first structural report of the formation of a mononuclear Ir(I) complex with a bidentate pyridine-tertiary amine chelator. Due to its similar reactivity to iridium in catalysis, the lighter rhodium homologue [Rh(cod)2](BF4) is also reacted with 5, leading to an immediate color change from red to green and finally to orange (Scheme 3). Removal of the solvent and extraction of the product into benzene afforded a yellow solution, out of which yellow crystals precipitate after several minutes. Mass spectrometry from the solid only shows one single peak for m/z = 667.3, with a mass and isotopic distribution pattern in line with an elemental composition of C31H52RhN4Si3+, correlating to a composition [Rh5(cod)](BF4) for the reaction product 7 (for complete details, see the SI). NMR spectra of the new product 7 strongly support the formation of [Rh5(cod)](BF4). In the 1H spectrum, shifted signals for the ligand, as well as those for a bound cod moiety, are observed, in 11B and 19F each only one signal for the counterion. The two signals for SiMe3 appear 0.77 ppm (308 Hz) apart and, similar to 6, no dynamic behavior can be observed up to 60 °C in variable-temperature experiments, again suggesting a higher steric bulk around Si1 compared to 5. In the 13C spectrum, the signals for C7−C11 appear as doublets D


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Organometallics

five-coordinate silane [compare: δSi,4 = −80.7 ppm (fivecoordinate silane), δSi,4 = +31.3 ppm (four-coordinate silane); for detailed NMR spectra, see the SI]. Single crystal X-ray structure analysis finally shows the formation of rhodium complex 7 (Figure 7). Unlike in 6, besides η4-coordination to

Figure 5. Mass spectroscopic results of 6 showing an isotopic distribution pattern. Comparison of the measured composition product (top) with the calculated one for C31H52IrN4Si3+ (bottom). For detailed mass spectra, see the SI.

Figure 7. ORTEP style X-ray structure of 7. Ellipsoids are shown at 50% probability level. The hydrogen atom is drawn with an arbitrary radius. Carbon-attached hydrogen atoms, counterion, and solvent molecules omitted for clarity. Element colors: black − carbon, blue − nitrogen, red − silicon, gray − rhodium.

cod, the rhodium center is η6-coordinated to the phenylene ring in 5. The averaged distance aryl−rhodium is 1.85 Å, the distances Rh1−C(7−12) in a range of 2.257(3)−2.465(2) Å, which is rather typical for η6-coordinated aryl-rhodium(I) compounds.48−50 The Rh1 center in 7 is not located symmetrically over the C7−C12 aryl unit, but is slightly displaced toward C9 and C10, reflected in shorter bond lengths C9−Rh1 and C10−Rh1 (2.272(3) Å; 2.257(3) Å) especially compared to C12−Rh1 (2.465(2) Å). This distortion is most likely caused by the steric demand and hence repulsion of the neopentyl moiety attached to N3 and in compliance with the NMR data in solution, wherein C7−C11 appear as doublets due to coupling to rhodium (J = 1.6−4.2 Hz), whereas C12 could only be detected as a singlet, most likely because of a larger distance to rhodium. What is most striking about the solid state structure of complex 7 is the pyridine coordination switch from off to on at silicon in comparison to precursor 5, even though no structural changes have been applied to the direct circumjacent chemical environment. This coordination switch at silicon is most likely a consequence of the electron withdrawing effect of Rh(I) on the aromatic system after coordination. This as well becomes apparent by contraction of the bonds N2−C7 (1.383(3) Å vs 1.399(1) Å) and N3−C12 (1.355(3) Å vs 1.408(1) Å), compared to 5, which is likely to arise from small contributions of mesomerical stabilization (Scheme 4). Due to the increased coordination number at the silicon center and hence higher steric repulsion, the Si−N bonds are

Figure 6. ORTEP style X-ray structure of 6. Ellipsoids are shown at 50% probability level. The hydrogen atom is drawn with an arbitrary radius. Carbon-attached hydrogen atoms, BArF counterion, and solvent molecules omitted for clarity. Element colors: black − carbon, blue − nitrogen, red − silicon, yellow − iridium.

with J values in between 1.6 and 4.2 Hz, suggesting a coupling to rhodium due to aryl-coordination (see also the SI). 29Si NMR shows 3 signals, two for the SiMe3 moieties at 2.5 and 1.0 ppm, as well as one at −76.8 for Si−H. This corresponds to an upfield shift of more than 55 ppm compared to 5, suggesting a E


Organometallics

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Scheme 4. Possible Mesomeric Stabilization of Complex 7a

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EXPERIMENTAL SECTION

General Remarks. Unless noted otherwise, all reactions were carried out under an argon atmosphere with standard Schlenk or glovebox techniques. All chemicals were purchased from commercial sources and unless specified otherwise used without further purification. Nondry solvents were distilled prior to use. Pentane, hexanes, acetonitrile, diethyl ether, toluene, dichloromethane, and tetrahydrofuran were dried with an MBraun MB-SPS solvent purification system. Benzene was distilled over potassium benzophenone, pyridine over CaH2, and N,N-diisopropyl-N-ethylamine (DIPEA) over Na/K alloy. HSiCl3 was distilled and afterward stored at −20 °C; LiN(SiMe3)2 was recrystallized from boiling hexanes twice. [Rh(cod)2](BF4) and [Ir(cod)2](BArF) were synthesized according to literature procedures.62,63 NMR spectra were recorded on a Bruker AV 400HD or a Bruker AV 500cryo spectrometer. Assignments are given either by functional group or as outlined in Scheme 3. Elemental analysis was performed by the microanalytical laboratory at the Department of Chemistry of the Technische Universität München. The elements C and H and N were determined with a combustion analyzer (Elementar Vario EL, Bruker Corp.). Silicon was determined photometrically as silicon molybdenum blue at 810 nm. LIFDI HRMS measurements were conducted on a Waters LCT, liquid injection field desorption ionization special ionization cell obtained from Linden CMS GmbH, Leeste, Germany, ESI MS measurements on a Thermo Scientific LCQ Fleet by Thermo Fischer Scientific using electron spray ionization and a 3D ion trap detector or on a Bruker Daltronic HCT mass spectrometer (dry gas temperature: 300 °C; injection speed 240 μL/s); the data evaluation was carried out using the Bruker Compass Data Analysis 4.0 SP 5 program (Bruker, Bremen, Germany). Synthesis and Characterization. N-(2-Nitrophenyl) Pivalamide (1). To a solution of 2-nitroaniline (60.0 g, 434 mmol, 1.00 equiv) and 4-dimethylamino pyridine (2.61 g, 21.4 mmol, 0.05 equiv) in 360 mL of pyridine and 400 mL of dichloromethane at 0 °C, pivaloyl chloride (55.8 mL, 55.0 g, 456 mmol, 1.05 equiv) is added dropwise over a period of 15 min and stirred for 35 min. The suspension is warmed to r.t. and stirred for 24 h. After addition of 200 mL of 1 M hydrochloric acid, the dark orange organic layer is separated, washed with 1 M hydrochloric acid (2 × 200 mL), saturated aqueous NaHCO3 (200 mL), and brine (200 mL), dried over sodium sulfate, and the solvent was removed in vacuo. Distillation yielded 94.5 g (425 mmol, 98%) of the desired product 1 as a yellow liquid. 1 H NMR (400 MHz, CDCl3, 297 K) δ 10.74 (s, 1H, NH), 8.83 (dd, J = 8.6, 1.4 Hz, 1H, HAr), 8.22 (dd, J = 8.5, 1.6 Hz, 1H, HAr), 7.64 (ddd, J = 8.6, 7.3, 1.6 Hz, 1H, HAr), 7.16 (ddd, J = 8.6, 7.3, 1.4 Hz, 1H, HAr), 1.36 (s, 9H, HtBu). The spectroscopic data match literature data.64 N-(2-Aminophenyl) Pivalamide (2). This reaction tolerates nonpredried solvent. To a solution of 1 (91.9 g, 414 mmol, 1.00 equiv) in 400 mL of ethanol is added Pd/C (10 wt %, 250 mg, 235 μmol, 0.06 mol %). The yellowish-black suspension is set under an atmosphere of hydrogen and a balloon, filled with approximately 1 L of hydrogen, is placed upon the flask. The suspension is stirred for 2 h at r.t., during which time the balloon is refilled with hydrogen several times. By the time the suspension loses its yellowish color, it is filtered through Celite and the solvent is removed in vacuo. 2 is obtained as a colorless solid without further purification (78.7 g, 409 mmol, 99%). 1 H NMR (400 MHz, CDCl3, 299 K): δH [ppm] = 7.38 (br, 1H, NH), 7.21−7.13 (m, 1H, H11), 7.04 (td, J = 7.6, 1.5 Hz, 1H, H9), 6.85−6.74 (m, 2H, H8,10), 3.76 (br 2H, NH2) 1.33 (s, 9H, H15). 13 C{1H} NMR (101 MHz, CDCl3, 298 K): δC [ppm] = 177.3 (C12), 141.0 (C13), 127.1 (C9), 125.3 (C11), 124.7 (C7), 119.7 (C10), 118.3 (C8), 39.5 (C14), 27.9 (C15). MS (ESI, MeCN): m/z = 193.08 [(2 + H)+] (calcd. for C11H17N2O+ 193.13). Elemental analysis: calcd. for 2 (%): C 68.72, H 8.39, N 14.57; found: C 68.49, H 8.41, N 14.58. N-Neopentyl-N’-(pyridin-2-ylmethyl) Phenylenediamine (3). The first step in the reaction sequence (preparation of the imine) tolerates noninert conditions.

[Rh] resembles the Rh(cod) fragment.

elongated in contrast to precursor 5 (dN1−Si1 = 2.134(2) Å; dN2−Si1 = 1.730(1) Å vs 1.773(2) Å; dN3−Si1 = 1.738(1) Å vs 1.846(2) Å, dN4−Si1 = 1.713(1) Å vs 1.749(2) Å). For Si1−N4, this might be attributed to a steric effect; for the others, a small contribution due to a reduced electron density is likely. In the latter case, the main share might arise from the trans-influence of the additionally coordinated pyridine moiety. This effect has already been observed for compound 4, and is as well likely to cause the stronger contraction of the N3−C12 distance in comparison to N2−C7. Thus, the coordination switch at Si1 is induced over a spatial distance of more than 4.43 Å (dSi1−Rh1) by the coordination of the Rh+-fragment to the ligand’s aryl backbone. Molecular switches are of high interest in current research, among others due to their potential application for nanocomputers, responsive drug delivery systems, or, more biologically, in the allosteric regulation of enzymes.51−53 Many molecular coordination changes have been achieved so far, but mostly after addition or removal of ligands or altering of the direct coordinating environment. More precisely, reports on coordination changes of a given system without addition of extra ligands are still scarce. Thereby, reports are largely limited to hapticity changes of arene ligands after electrochemical reduction of complexes,54,55 change of the pH and protonation or deprotonation of binding sites,56,57 interaction with proteins or DNA,58−60 or bond cleavage and reassembly due to altered geometry after photoisomerization of the ligand.61 To the best of our knowledge, there are no examples in the literature in which a distal coordination of a metal ion changes a ligand’s coordination to another reactive site.

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CONCLUSION In this work, the synthesis of a novel N-heterocyclic silane 5 and its iridium (6) and rhodium (7) complexes is presented. They have been characterized by NMR (1H, 11B, 13C, 19F, 29Si), MS, elemental analysis, and X-ray crystallography. All three compounds are stable at elevated temperatures. Variabletemperature NMR studies show that the rotational barrier of the BTSA moiety in 5 can be overcome at 47 °C, and the activation energy is calculated to be 62.9 kJ/mol. In contrast, the rotational barriers remain insuperable for 6 and 7 up to 60 °C. X-ray single crystal structures reveal that iridium(I) is chelated by the ligand’s front side, whereas arene π-complexation occurs for rhodium(I), additionally inducing a distal coordination change at silicon from 4 to 5. This behavior has, to the best of our knowledge, not been observed before. By the virtue of having two reactive sites in one complex, the new iridium and rhodium compounds are very promising candidates for future application in various catalytic processes. Future work will involve testing the ability of the coordinatively versatile complexes 6 and 7 in catalysis. F


Article

Organometallics To a solution of 2 (15.0 g, 78.0 mmol, 1.00 equiv) in 150 mL of isopropanol is added 2-pyridinecarboxaldehyde (8.36 g, 78.0 mmol, 1.00 equiv), and the solution stirred at r.t. for 30 min. The solvent is removed and the crude imine is dried in vacuo. The intermediate product is obtained as a yellow oil that crystallizes upon storage at 4 °C within several hours. It is dissolved in 150 mL of THF, cooled to 0 °C, and a 2 M solution of BH3·SMe2 in THF (100 mL, 200 mmol, 2.57 equiv) is added over a period of 1 h. The orange solution is refluxed for 17 h, cooled to r.t., and the solvent is removed in vacuo. The residue is dissolved in 200 mL of methanol, and 27 mL of 6 M HCl(aq) are added, leading to significant effervescence. The mixture is refluxed for 17 h, cooled to r.t., and poured onto 500 mL of water. To the yellow solution 10% NaOH is added until a pH of 9 is reached, whereupon copious amounts of an off-white precipitate formed. The precipitate is filtered under reduced pressure, washed with water, and dried in vacuo. 20.8 g (77.2 mmol, 99%) 3 is isolated as an off-white solid, which gradually darkens to brown upon exposure to air. 1 H NMR (400 MHz, CDCl3, 296 K): δH [ppm] = 8.60 (ddd, 3J = 6.1 Hz, 4J = 1.4 Hz, 5J = 0.9 Hz, 1H, H1), 7.64 (ddd, 3J = 7.8 Hz, 4J = 1.5 Hz, 5J = 0.9 Hz, 1H, H4), 7.33 (ddd, 3J = 7.8, 7.3 Hz, 4J = 1.4 Hz, 1H, H3), 7.18 (ddd, 3J = 7.3, 6.1 Hz, 4J = 1.5 Hz, 1H, H2), 6.80 (ddd, 3 J = 6.3 Hz, 4J = 1.5 Hz, 5J = 0.7 Hz, 1H, H8), 6.72 (ddd, 3J = 7.6, 6.3 Hz, 4J = 1.5 Hz, 1H, H9), 6.72 (ddd, 3J = 7.6, 6.9 Hz, 4J = 1.5 Hz, 1H, H10) 6.65 (ddd, 3J = 6.9 Hz, 4J = 1.5 Hz, 5J = 0.7 Hz, 1H, H11), 4.47 (s, 2H, H6), 4.24 (br, 1H, NH), 3.47 (br, 1H, NH), 2.89 (s, 2H, H13), 1.06 (s, 9H, H15). 13C{1H} NMR (101 MHz, CDCl3, 296 K): δC [ppm] = 159.1 (C5), 149.5 (C1), 138.5 (C12) 137.2 (C7) 136.7 (C4), 122.2 (C3), 121.7 (C2), 119.8 (C10), 119.0 (C9), 112.7 (C11), 112.0 (C8), 56.4 (C13), 50.3 (C6), 31.7 (C14), 28.0 (C15). MS (ESI, MeCN): m/z = 270.18 [(3 + H)+] (calcd. for C17H24N3+ 270.20). Elemental analysis: calcd for 3 (%): C 75.80, H 8.61, N 15.60; found: C 76.08, H 8.72, N 15.57. 1-Neopentyl-2,2-hydrochloro-3-((pyridin-2-yl)-methyl)-benzo[1,3,2] Diazasilol (4). To a solution of 3 (2.44 g, 9.05 mmol, 1.00 equiv) in 50 mL of benzene, N,N-diisopropyl-N-ethylamine (3.47 mL, 2.57 g, 19.9 mmol, 2.20 equiv) and HSiCl3 (0.96 mL, 1.29 g, 9.50 mmol, 1.05 equiv) are added, and the mixture is stirred at 30 °C for 48 h. The orange suspension is filtered, and the solvent is removed from the filtrate in vacuo. The remaining yellow solid is triturated with 20 mL of acetonitrile, washed with acetonitrile (2 × 5 mL), and dried in vacuo. 4 is obtained as a yellow solid (1.88 g, 5.65 mmol, 62%). The combined triturating and washing phases are reduced to a volume of 5 mL, cooled to −30 °C, and the resulting yellow precipitate is separated from the mother liquor by filtration, washed with 3 mL of acetonitrile, and dried in vacuo, yielding an additional 520 mg (1.57 mmol, 17%) of 5. The combined mother liquor and washing phases are dried in vacuo and extracted into boiling hexanes (100 mL). Removal of the solvent from the extract yielded an additional 121 mg (365 μmol, 4%) of 5. The overall yield of 5 is 2.52 g (7.59 mmol, 84%). 1 H NMR (400 MHz, C6D6, 296 K): δH [ppm] = 8.08 (ddd, 3J = 5.6 Hz, 4J = 1.4 Hz, 5J = 0.8 Hz, 1H, H1), 7.13 (dd, 3J = 7.7 Hz, 4J = 1.3 Hz, 1H, H11), 7.03−6.97 (m, 2H, H9,10), 6.68 (ddd, 3J = 8.1, 7.4 Hz, 4J = 1.4 Hz, 1H, H3), 6.62 (s, 1H, SiH), 6.60 (dd, 3J = 7.4 Hz, 4J = 1.3 Hz, 1H, H8), 6.34 (ddd, 3J = 7.4, 5.6 Hz, 4J = 1.0 Hz, 1H, H2), 6.14 (ddd, 3J = 8.1 Hz, 4J = 1.0 Hz, 5J = 0.8 Hz, 1H, H4), 3.91 (d, 2J = 18.0 Hz, 1H, H6), 3.80 (d, 2J = 14.8 Hz, 1H, H13), 3.74 (d, 2J = 18.0 Hz, 1H, H6), 3.52 (d, 2J = 14.8 Hz, 1H, H13), 1.23 (s, 9H, H15). 13C{1H} NMR (101 MHz, C6D6, 296 K): δC [ppm] = 153.5 (C5), 142.3 (C7), 141.2 (C1), 139.0 (C3), 134.7 (C12), 123.3 (C2), 121.6 (C4), 119.7 (C11), 115.5 (C10), 108.5 (C9), 108.3 (C8), 54.3 (C13), 45.2 (C6), 35.1 (C14), 29.8 (C15). 29Si{1H} NMR (99 MHz, C6D6, 296 K): δSi [ppm] = −80.7 (N3ClSiH). HRMS (LIFDI, PhMe): m/z = 331.22 [(4)+] (calcd. for C17H22N3SiCl+ 331.13). Elemental analysis: calcd. for 4 (%): C 61.52, H 6.68, N 12.66; found: C 61.66, H 6.51, N 12.90. 1-Neopentyl-2-hydro-2-(bis-trimethylsilylamido)-3-((pyridin-2yl)-methyl)-benzo[1,3,2] Diazasilol (5). 4 (472 mg, 1,42 mmol, 1.00 equiv) and LiN(SiMe3)2 are suspended in 50 mL of hexanes and stirred at 30 °C for 3 h. The orange-red suspension is filtered, and the solvent is removed in vacuo. The residue is dissolved in 3 mL of boiling hexanes, filtered, and slowly cooled to −30 °C. Large, diamond-shaped

light-yellow crystals of 5, suitable for single crystal X-ray diffraction, formed during several hours (480 mg (1.05 mmol, 74%). 1H NMR (400 MHz, C6D6, 297 K) δH [ppm] = 8.50 (ddd, J = 4.8, 1.8, 0.9 Hz, 1H, H1), 7.19 (dq, J = 7.9, 0.9 Hz, 1H, H4), 6.97 (td, J = 7.7, 1.8 Hz, 1H, H3), 6.86 (ddd, J = 7.9, 7.4, 1.4 Hz, 1H, H10), 6.78−6.71 (m, 2H, H8,9), 6.59 (dd, J = 8.0, 1.4 Hz, 1H, H11), 6.58−6.55 (m, 1H, H2), 6.18 (s, 1H, SiH), 4.90−4.63 (m, 2H, H6), 3.24−3.03 (m, 2H, H13), 1.02 (s, 9H, H15), 0.23 (br, 9H, Si(CH3)3), 0.00 (br, 9H, Si(CH3)3). 13C{1H} NMR (126 MHz, C6D6, 300 K) δC [ppm] = 160.0 (C5), 149.5 (C1), 141.1 (C12), 138.9 (C7), 136.4 (C3), 121.8 (C2), 121.0 (C4), 118.4 (C10), 118.1 (C9), 109.1 (C8), 108.6 (C11), 54.9 (C13), 48.8 (C6), 35.0 (C14), 29.1 (C15), 4.7 (Si(CH3)3), 3.5(Si(CH3)3). 29Si{1H} NMR (99 MHz, C6D6, 300 K) δSi [ppm] = 5.7 (Si(CH3)3), 3.0 (Si(CH3)3), −30.1 (N3SiH). HRMS (LIFDI, PhMe): m/z = 456.20 [(5)+] (calcd. for C23H40N4Si3·+ 456.26). Elemental analysis: calcd for 5 (%): C 60.47, H 8.83, N 12.26, Si 18.44; found: C 59.99, H 8.95, N 12.09, Si 18.01. Iridium Complex 6. Silane 5 (18.3 mg, 40.1 μmol, 1.00 equiv) is dissolved in 1 mL of dichloromethane, and a deep red solution of [Ir(cod)2](BArF) (50.9 mg, 40.1 μmol, 1.00 equiv) in 2 mL of dichloromethane is added while stirring. The color of the reaction mixture immediately becomes light orange-red; the solution is stirred for 10 min at 30 °C, and then layered with hexanes and stored at −30 °C for 3 days. Orange crystals, suitable for single crystal X-ray diffraction, are separated from the mother liqueur, washed with hexanes (2 × 1 mL), and dried in vacuo (52.0 mg, 32.1 μmol, 80%). 1 H NMR (500 MHz, CDCl3, 300 K) δH [ppm] = 8.01−7.90 (m, 2H, Hpy), 7.73−7.69 (m, 8 H, HBArF, ortho) 7.63 (d, 3J = 7.9 Hz, 1H, Hpy), 7.53−7.51 (m, 4 H, HBArF, para), 7.43 (t, 3J = 6.8 Hz, 1H, Hpy), 7.12 (d, 3J = 7.9 Hz, 1H, HPh), 7.06 (td, 3J = 7.8, 4J = 1.2 Hz, 1H, HPh), 6.94−6.84 (m, 2H, HPh), 6.54 (s, 1H, SiH), 5.14 (d, 2J = 16.1 Hz, 1H, H6), 4.68 (d, 2J = 16.1 Hz, 1H, H6), 3.76 (dtd, 3J = 10.4, 7.3, 3.4 Hz, 4H, CHcod), 3.19 (d, 2J = 14.7 Hz, 1H, H13), 2.93 (d, 2J = 14.7 Hz, 1H, H13), 2.27 (ddt, 3J = 13.7, 10.2, 6.6 Hz, 2H, CH2, cod), 2.21−2.09 (m, 2H, CH2, cod), 1.86 (ddt, 3J = 13.7, 8.0, 5.1, 2J = 3.0 Hz, 2H, CH2, cod), 1.55 (dddd, 3J = 14.8, 8.8, 6.3, 2J = 3.0 Hz, 2H, CH2, cod), 1.11 (s, 9H, H15), −0.02 (s, 9H, Si(CH3)3), −0.16 (s, 9H, Si(CH3)3). 11B NMR (128 MHz, CDCl3, 298 K) δB [ppm] = −6.6 (nonet, 3J = 2.8 Hz, BBArF). 13C{1H} NMR (126 MHz, CDCl3, 300 K) δC [ppm] = 163, 162.4, 162.0, 161.6, 161.2, 147.6, 143.5, 141.2, 134.9, 134.1, 129.2, 128.9, 127.9, 127.3, 126.1, 125.8, 123.6, 122.4, 118.8, 118.0, 117.6, 111.7, 67.6, 59.8, 54.8, 35.2, 31.0, 30.3, 28.9, 4.1, 3.6. 19F{1H} NMR (471 MHz, CDCl3, 300 K) δF [ppm] = −62.4 (BArF). 29Si{1H} NMR (99 MHz, CDCl3, 300 K) δSi [ppm] = 31.3 (N3SiH), 10.8 (Si(CH3)3), 5.3 (Si(CH3)3). MS (ESI, CH2Cl2): m/z = 757.4 [(6-BArF)+] (calcd. for C31H52IrN4Si3+ 757.3). Elemental analysis: calcd. for 6 (%): C 46.70, H 3.98, N 3.46; found: C 47.01, H 4.14, N 3.21. Rhodium Complex 7. Silane 5 (2.70 mg, 5.91 μmol, 1.00 equiv) and [Rh(cod)2](BF4) (2.40 mg, 5.91 μmol, 1.00 equiv) are dissolved in 1 mL of dichloromethane. The yellow solution turns dark green within seconds. The solution is stirred for 10 min at 30 °C, and the solvent is removed in vacuo. The residue is dissolved in 1 mL of benzene, and the orange solution is filtered via syringe filter. Within several hours, crystals of 7·2.5 C6H6, suitable for single crystal X-ray diffraction, formed. The crystals were collected and dried in vacuo, yielding 2.0 mg (5.0 μmol, 85%) of 7. 1 H NMR (400 MHz, CDCl3, 300 K) δH [ppm] = 8.53 (d, 3J = 5.5 Hz, 1H, H1), 8.07 (d, 3J = 7.4 Hz, 1H, H4), 8.02 (td, 3J = 7.4, 4J = 1.4 Hz, 1H, H3), 7.50 (ddd, 3J = 7.4, 5.5, 4J = 1.5 Hz, 1H, H2), 7.16 (d, 3J = 6.2 Hz, 1H, H11), 6.39 (d, 3J = 6.9 Hz, 1H, H8), 5.91 (t, 3J = 6.2 Hz, 1H, H9), 5.88 (s, 1H, SiH), 5.25 (ddd, 3J = 6.9, 6.2, 4J = 1.2 Hz, 1H, H10), 4.90 (d, 2J = 2.5 Hz, 2H, H6), 4.21−4.14 (m, 2H, CHcod), 3.92− 3.77 (m, 2H, CHcod), 3.31 (d, 2J = 14.7 Hz, 1H, H13), 3.06 (d, 2J = 14.7 Hz, 1H, H13), 2.45−2.26 (m, 4H, CH2cod), 2.01−1.83 (m, 4H, CH2cod), 1.32 (s, 9H, H15), 0.39 (s, 9H, Si(CH3)3), −0.38 (s, 9H, Si(CH3)3). 11B NMR (128 MHz, CDCl3, 298 K) δB [ppm] = −0.6 (pent, 1J = 1.3 Hz, BF4). 13C{1H} NMR (126 MHz, CDCl3, 300 K) δC [ppm] = 152.9 (C5), 141.6 (C1), 140.5 (C3), 136.6 (C12), 124.0 (C2), 124.0 (C4), 121.9 (d, JRh = 1.6 Hz, C7), 90.8 (d, JRh = 3.9 Hz, C11), 90.0 (d, JRh = 4.2 Hz, C8), 87.8 (d, JRh = 3.0 Hz, C9), 86.5 (d, JRh = 2.2 G


Article

Organometallics Hz, C10), 78.1 (d, JRh = 13.6 Hz, CHcod), 75.6 (d, JRh = 13.2 Hz, CHcod), 55.0 (C13), 47.5 (C6), 35.6 (C14), 32.1 (2C, CH2cod), 31.0 (2C, CH2cod), 30.6 (C15), 6.0 (Si(CH3)3), 3.4 (Si(CH3)3). 19F{1H} NMR (471 MHz, CDCl3, 300 K) δF [ppm] = −152.5 (BF4). 29Si{1H} NMR (99 MHz, CDCl3, 300 K) δSi [ppm] = 2.5 (Si(CH3)3), 1.0 (Si(CH3)3), −76.8 (N4SiH). MS (ESI, CH2Cl2): m/z = 667.4 [(7BF4)+] (calcd. for C31H52RhN4Si3+ 667.3). Elemental analysis: calcd. for 7·0.6 (C6H6) (%): C 51.84, H 6.99, N 6.99; found: C 51.88, H 7.08, N 6.67.

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(12) Wang, X.; Jin, G.-X. Chem. - Eur. J. 2005, 11, 5758−5764. (13) Hetterscheid, D. G. H.; Hendriksen, C.; Dzik, W. I.; Smits, J. M. M.; van Eck, E. R. H.; Rowan, A. E.; Busico, V.; Vacatello, M.; Van Axel Castelli, V.; Segre, A.; Jellema, E.; Bloemberg, T. G.; de Bruin, B. J. Am. Chem. Soc. 2006, 128, 9746−9752. (14) Crabtree, R. Acc. Chem. Res. 1979, 12, 331−337. (15) Crabtree, R. H.; Davis, M. W. J. Org. Chem. 1986, 51, 2655− 2661. (16) Lu, S.-M.; Bolm, C. Chem. - Eur. J. 2008, 14, 7513−7516. (17) Dobereiner, G. E.; Nova, A.; Schley, N. D.; Hazari, N.; Miller, S. J.; Eisenstein, O.; Crabtree, R. H. J. Am. Chem. Soc. 2011, 133, 7547− 7562. (18) Achiwa, K. J. Am. Chem. Soc. 1976, 98, 8265−8266. (19) Feldgus, S.; Landis, C. R. J. Am. Chem. Soc. 2000, 122, 12714− 12727. (20) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem. Soc. A 1966, 1711−1732. (21) Young, J. F.; Osborn, J. A.; Jardine, F. H.; Wilkinson, G. Chem. Commun. 1965, 131−132. (22) Schmeier, T. J.; Dobereiner, G. E.; Crabtree, R. H.; Hazari, N. J. Am. Chem. Soc. 2011, 133, 9274−9277. (23) Musashi, Y.; Sakaki, S. J. Am. Chem. Soc. 2002, 124, 7588−7603. (24) Hutschka, F.; Dedieu, A.; Eichberger, M.; Fornika, R.; Leitner, W. J. Am. Chem. Soc. 1997, 119, 4432−4443. (25) Sato, S.; Morikawa, T.; Kajino, T.; Ishitani, O. Angew. Chem., Int. Ed. 2013, 52, 988−992. (26) Kang, P.; Cheng, C.; Chen, Z.; Schauer, C. K.; Meyer, T. J.; Brookhart, M. J. Am. Chem. Soc. 2012, 134, 5500−5503. (27) Pietruszka, J. Silyl Hydrides. In Science of Synthesis; Georg Thieme Verlag KG: Stuttgart, 2017; Vol. 4, pp 159−185. (28) Lalevée, J.; El-Roz, M.; Allonas, X.; Pierre Fouassier, J. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 2008−2014. (29) Lalevée, J.; Blanchard, N.; Tehfe, M.-A.; Peter, M.; MorletSavary, F.; Fouassier, J. P. Macromol. Rapid Commun. 2011, 32, 917− 920. (30) Tehfe, M.-A.; Lalevée, J.; Gigmes, D.; Fouassier, J. P. Macromolecules 2010, 43, 1364−1370. (31) Tehfe, M.-A.; Lalevée, J.; Gigmes, D.; Fouassier, J. P. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 1830−1837. (32) Han, Q. X.; Qi, B.; Ren, W. M.; He, C.; Niu, J. Y.; Duan, C. Y. Nat. Commun. 2015, 6, 10007. (33) Li, L.; Herzon, S. B. Nat. Chem. 2013, 6, 22−27. (34) Lohr, T. L.; Marks, T. J. Nat. Chem. 2015, 7, 477−482. (35) Yamada, Y.; Tsung, C.-K.; Huang, W.; Huo, Z.; Habas, S. E.; Soejima, T.; Aliaga, C. E.; Somorjai, G. A.; Yang, P. Nat. Chem. 2011, 3, 372−376. (36) Brendler, E.; Wächtler, E.; Wagler, J. r. Organometallics 2009, 28, 5459−5465. (37) Schwarz, D.; Brendler, E.; Kroke, E.; Wagler, J. Z. Anorg. Allg. Chem. 2012, 638, 1768−1775. (38) Kobelt, C.; Burschka, C.; Bertermann, R.; Fonseca Guerra, C.; Bickelhaupt, F. M.; Tacke, R. Dalton Trans. 2012, 41, 2148−2162. (39) Frenzel, A.; Buffy, J. J.; Powell, D. R.; West, R.; Müller, T. Chem. Ber. 1997, 130, 1579−1583. (40) Karsch, H. H.; Schlüter, P. A.; Bienlein, F.; Herker, M.; Witt, E.; Sladek, A.; Heckel, M. Z. Anorg. Allg. Chem. 1998, 624, 295−309. (41) Cui, H.; Cui, C. Chem. - Asian J. 2011, 6, 1138−1141. (42) Sen, S. S.; Roesky, H. W.; Stern, D.; Henn, J.; Stalke, D. J. Am. Chem. Soc. 2010, 132, 1123−1126. (43) de Bruin, B.; Kicken, R. J. N. A. M.; Suos, N. F. A.; Donners, M. P. J.; den Reijer, C. J.; Sandee, A. J.; de Gelder, R.; Smits, J. M. M.; Gal, A. W.; Spek, A. L. Eur. J. Inorg. Chem. 1999, 1581−1592. (44) Hetterscheid, D. G. H.; Klop, M.; Kicken, R. J. N. A. M.; Smits, J. M. M.; Reijerse, E. J.; de Bruin, B. Chem. - Eur. J. 2007, 13, 3386− 3405. (45) Krom, M.; Peters, T. P. J.; Coumans, R. G. E.; Sciarone, T. J. J.; Hoogboom, J.; ter Beek, S. I.; Schlebos, P. P. J.; Smits, J. M. M.; de Gelder, R.; Gal, A. W. Eur. J. Inorg. Chem. 2003, 1072−1087.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00769. NMR spectra, ESI MS, and X-ray data for CCDC numbers 1571192−1571196 (PDF) Accession Codes

CCDC 1571192−1571196 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Eric Rivard: 0000-0002-0360-0090 Fritz E. Kühn: 0000-0002-4156-780X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Supported by Deutsche Forschungsgemeinschaft (DFG) through the TUM International Graduate School of Science and Engineering (IGSSE). F.K. is further grateful to the “Fonds der Chemischen Industrie” for his fellowship. Dr. Alexander Pöthig is acknowledged for crystallographic advice. The Wacker Institute of TUM is acknowledged for infrastructural support.

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REFERENCES

(1) Tanke, R. S.; Crabtree, R. H. J. Am. Chem. Soc. 1990, 112, 7984− 7989. (2) Iovel, I.; Popelis, J.; Gaukhman, A.; Lukevics, E. J. Organomet. Chem. 1998, 559, 123−130. (3) Gigler, P.; Bechlars, B.; Herrmann, W. A.; Kühn, F. E. J. Am. Chem. Soc. 2011, 133, 1589−1596. (4) Hill, J. E.; Nile, T. A. J. Organomet. Chem. 1977, 137, 293−300. (5) Ojima, I.; Kogure, T.; Kumagai, M.; Horiuchi, S.; Sato, T. J. Organomet. Chem. 1976, 122, 83−97. (6) Titova, E. M.; Rahaman, S. M. W.; Shubina, E. S.; Poli, R.; Belkova, N. V.; Manoury, E. J. Mol. Catal. A: Chem. 2017, 426, 376− 380. (7) Tong, X.; Li, D.; Zhang, Z.; Zhang, X. J. Am. Chem. Soc. 2004, 126, 7601−7607. (8) Shintani, R.; Okamoto, K.; Hayashi, T. J. Am. Chem. Soc. 2005, 127, 2872−2873. (9) Blum, J.; Pickholtz, Y. Isr. J. Chem. 1969, 7, 723−733. (10) Lalevée, J.; Tehfe, M.-A.; Dumur, F.; Gigmes, D.; Blanchard, N.; Morlet-Savary, F.; Fouassier, J. P. ACS Macro Lett. 2012, 1, 286−290. (11) Staubitz, A.; Presa Soto, A.; Manners, I. Angew. Chem., Int. Ed. 2008, 47, 6212−6215. H


Article

Organometallics (46) Schaub, T.; Radius, U.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J. W.; Milstein, D. Organometallics 2008, 27, 1892−1901. (47) Sciarone, T.; Hoogboom, J.; Schlebos, P. P. J.; Budzelaar, P. H. M.; de Gelder, R.; Smits, J. M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2002, 457−464. (48) Bauer, G.; Englert, C.; Nieger, M.; Gudat, D. Inorg. Chim. Acta 2011, 374, 240−246. (49) Kilian, M.; Wadepohl, H.; Gade, L. H. Organometallics 2007, 26, 3076−3078. (50) Kuo, Y. Y.; Haddow, M. F.; Perez-Redondo, A.; Owen, G. R. Dalton Trans. 2010, 39, 6239−6248. (51) Kaneda, M. M.; Messer, K. S.; Ralainirina, N.; Li, H.; Leem, C. J.; Gorjestani, S.; Woo, G.; Nguyen, A. V.; Figueiredo, C. C.; Foubert, P.; Schmid, M. C.; Pink, M.; Winkler, D. G.; Rausch, M.; Palombella, V. J.; Kutok, J.; McGovern, K.; Frazer, K. A.; Wu, X.; Karin, M.; Sasik, R.; Cohen, E. E. W.; Varner, J. A. Nature 2016, 539, 437−442. (52) Sun, J.; Wu, Y.; Wang, Y.; Liu, Z.; Cheng, C.; Hartlieb, K. J.; Wasielewski, M. R.; Stoddart, J. F. J. Am. Chem. Soc. 2015, 137, 13484−13487. (53) Klemke, R. L.; Leng, J.; Molander, R.; Brooks, P. C.; Vuori, K.; Cheresh, D. A. J. Cell Biol. 1998, 140, 961−972. (54) Bowyer, W. J.; Geiger, W. E. J. Am. Chem. Soc. 1985, 107, 5657− 5663. (55) Muratov, D. V.; Romanov, A. S.; Loginov, D. A.; Corsini, M.; Fabrizi de Biani, F.; Kudinov, A. R. Eur. J. Inorg. Chem. 2015, 804−816. (56) Semwal, S.; Choudhury, J. ACS Catal. 2016, 6, 2424−2428. (57) Cohen, S. M.; Raymond, K. N. Inorg. Chem. 2000, 39, 3624− 3631. (58) Iwasaki, Y.; Kimura, M.; Yamada, A.; Mutoh, Y.; Tateishi, M.; Arii, H.; Kitamura, Y.; Chikira, M. Inorg. Chem. Commun. 2011, 14, 1461−1464. (59) Tamanini, E.; Rigby, S. E. J.; Motevalli, M.; Todd, M. H.; Watkinson, M. Chem. - Eur. J. 2009, 15, 3720−3728. (60) De Ricco, R.; Valensin, D.; Dell’Acqua, S.; Casella, L.; Dorlet, P.; Faller, P.; Hureau, C. Inorg. Chem. 2015, 54, 4744−4751. (61) Oka, Y.; Tamaoki, N. Inorg. Chem. 2010, 49, 4765−4767. (62) Schenck, T. G.; Downes, J. M.; Milne, C. R. C.; Mackenzie, P. B.; Boucher, T. G.; Whelan, J.; Bosnich, B. Inorg. Chem. 1985, 24, 2334−2337. (63) Crisenza, G. E. M.; McCreanor, N. G.; Bower, J. F. J. Am. Chem. Soc. 2014, 136, 10258−10261. (64) Miyashita, M.; Shiina, I.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1994, 67, 210−215.

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