Synthesis of Heterobimetallic Complexes by Coordination of Rhodium

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

Synthesis of Heterobimetallic Complexes by Coordination of Rhodium(III) and Iridium(III) Poly-N,O-NHC Complexes to Silver(I), Copper(II), and Zinc(II) Michael Tegethoff,† Florian Roelfes,† Christian Schulte to Brinke,† Tristan Tsai Yuan Tan,† Florian Kampert,† Guo-Xin Jin,‡ and F. Ekkehardt Hahn*,† †

Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 28-30, 48149 Münster, Germany ‡ Department of Chemistry, Fudan University, Shanghai 200433, People’s Republic of China S Supporting Information *

ABSTRACT: The reaction of [RhCl2(Cp*)]2 with 2-trimethylsiloxyphenyl isocyanide (1) led to the mononuclear diisocyanide complex [RhCl(Cp*)(1)2]. Cleavage of the Si− O bonds of the coordinated isocyanide ligands with a catalytic amount of KF and H2O gave the neutral rhodium(III) complex [RhCl(Cp*)(NH,O-NHC)(N,O-NHC)] ([2]) bearing a C2metalated N,O-benzoxazolinato ligand and an NH,O-benzoxazolin-2-ylidene ligand. In the presence of AgBF4 the same reaction sequence with [MCl2(Cp*)]2 (M = Rh, Ir) and 1 led to the removal of all halogeno ligands and formation of the complexes [M(Cp*)(NH,O-NHC)(N,O-NHC)2] (M = Rh, [3]; M = Ir, [4]) bearing one C-metalated NH,O-NHC benzoxazolin-2-ylidene and two C-metalated N,O-benzoxazolinato ligands. Deprotonation of the remaining N−H function in complexes [3] and [4] generated complexes with three amido donor functions which act as tripodal metalloligands for the coordination to additional transition metals such as AgI, CuII, and ZnII, thus allowing the preparation of the polynuclear heterobimetallic complexes [5]−[10] bearing C/N-metalated benzoxazolinato ligands.

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INTRODUCTION Over the last few decades, N-heterocyclic carbenes (NHCs) have developed into a well-studied class of ligands in organometallic chemistry.1 On the basis of their useful electronic properties, NHCs have been employed for various applications in coordination chemistry,1,2 for the construction of metallosupramolecular assemblies,3 and as organocatalysts4 and their transition-metal complexes are used today as efficient catalysts for various transformations.5 The vast majority of NHC transition-metal complexes have been synthesized by the coordination of previously isolated free NHCs6a to an appropriate transition-metal center or by the in situ C2deprotonation of azolium cations in the presence of suitable transition-metal complexes.1 These methods lead to complexes bearing NHC ligands, which feature N,N′-alkyl or -aryl substituents at both ring nitrogen atoms, making a subsequent functionalization of these nitrogen atoms difficult and normally only possible at the N substituents by postmodification strategies.6b−f The situation is different in complexes bearing protic NHC (pNHC) ligands with NH,NR- or NH,NHsubstituted ring nitrogen atoms. Such complexes are obtained by the oxidative addition of the C2−H bond of N-donorfunctionalized azoles7a−d or of the C2−X (X = Cl, Br, I) bond of azoles7e−h to low-valent transition metals.7i Alternatively, © XXXX American Chemical Society

complexes with pNHC ligands can be obtained by the template-controlled transformation of coordinated isocyanides.8 This template synthesis uses isocyanides which are βfunctionalized with nucleophiles such as amine and hydroxyl groups. The intramolecular attack of these nucleophiles at the metal-coordinated isocyanide carbon atom via an intramolecular 1,2-addition across the CNR triple bond results in the formation of complexes with NH,NH- or NH,O-NHC ligands (Scheme 1). Due to the instability of free β-amine- or βhydroxyl-functionalized isocyanides, which would spontaneously cyclize to the corresponding imidazoles or oxazoles, the built-in nucleophiles have to be protected: for example, as trimethylsilyl ethers or as an azido or nitro function. After coordination of the isocyanide to a suitable transition-metal center, the amine or hydroxyl function is liberated by cleavage of the silicon−oxygen bond or by reduction of the nitrogen protecting group followed by the intramolecular nucleophilic attack of the liberated protonated nucleophile at the isocyanide carbon atom and shift of one hydrogen atom to the ring nitrogen atom (Scheme 1). Received: April 23, 2018

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DOI: 10.1021/acs.organomet.8b00252 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

indicate the formation of an N−H···N hydrogen bond between the two NHC ligands, allowing the formation of a neutral complex with two chemically equivalent NHC ligands on the NMR time scale. Similar behavior has been observed previously for the analogous iridium(III) complex,3e an iron(II) complex,8f and a platinum(II) complex.12 The resonance for the carbene carbon atoms was detected in the 13C{1H} NMR spectrum at δ 196.0 ppm as a doublet with a coupling constant of 1JRhC = 55 Hz. Due to a rapid exchange of the proton between the two ring nitrogen atoms, only one resonance for the carbene carbon atoms was detected. The high-resolution mass spectrum (ESI, positive ions) exhibited the most intense peaks at m/z 511.06386 (calcd for [[2] + H]+ 511.06596) and 475.08736 (calcd for [[2] − Cl]+ 475.08928). Formation of complex [2] was also confirmed by an X-ray diffraction analysis of single crystals obtained by slow evaporation of the solvent from a dichloromethane solution of [2] at ambient temperature. The molecular structure is depicted in Figure 1. The Rh−CNHC bond length falls in the

Scheme 1. Template Synthesis of Complexes Bearing Protic NHC Ligands

The metal template controlled transformation of coordinated β-functionalized isocyanides has led to complexes of various metals, some with multiple pNHC ligands. Such complexes are interesting precursors for several other applications, such as the preparation of complexes with macrocyclic poly-NHC ligands which are obtained by deprotonation of the pNHC ligands followed by bridging alkylation of the NHC ring nitrogen atoms.9 After deprotonation of pNHC ligands, not only Nalkylation but also coordination of the ring nitrogen atom to other metal centers is possible, leading to doubly C/N metalated heterocycles with the option to generate heterobimetallic derivatives.10 Herein we describe the template synthesis of rhodium(III) and iridium(III) poly-pNHC complexes bearing benzoxazolin2-ylidene ligands using the known 2-trimethylsiloxyphenyl isocyanide11 (1) as starting material for the pNHC ligands. The N deprotonation of the pNHC ligands in these complexes generates polydentate metalloligands which can react with various transition-metal complexes, leading to heterobimetallic complexes bearing C/N-metalated heterocycles.

Figure 1. Molecular structure (50% displacement ellipsoids) of [2]. Hydrogen atoms (except for NH) have been omitted for clarity. The asymmetric unit of [2] contains half of the molecule, related to the other half by a mirror plane passing through atoms Rh, Cl, C10, and C13. Selected bond lengths (Å), angles (deg), and dihedral angle (deg): Rh−Cl 2.4069(8), Rh−C2 2.000(2); Cl−Rh−C2 87.47(6), C2−Rh−C2* 88.80(11); torsion angle C2−N3*−C2*−O1* 22.13(9).

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RESULTS AND DISCUSSION 2-Trimethylsiloxyphenyl isocyanide (1) is, apart from its unpleasant odor, an easy to handle substance. It can be prepared according to a published procedure11 by treatment of benzoxazole with n-butyllithium followed by reaction with trimethylsilyl chloride. Reaction of 4 equiv of 1 with [RhCl2(Cp*)]2 followed by cleavage of the O−SiMe3 bonds with KF/H2O without isolation of the initially formed diisocyanide complex results in the formation of complex [2] in 94% yield (Scheme 2). We have previously reported the synthesis of the homologous iridium(III) complex.3e Complex [2] has been characterized by 1H NMR spectroscopy, showing the resonance for the single N−H proton at δ 9.96 ppm. This chemical shift and the observation of only one set of resonances

range found for previously described [RhIIICl(Cp*)NHC]0/+ complexes.13 The bond angles C2−Rh−C2* (88.80(11)°) and Cl−Rh−C2 (87.47(6)°) confirm the formation of a pseudooctahedral complex with piano-stool geometry. The positional parameters of atom H3 were identified from a difference Fourier map and were refined with SOF = 0.5. Due to the N3− H···N3* hydrogen bond, the two heterocycles are oriented in an almost coplanar arrangement with the torsion angle between the planes measuring 22.13(9)°. The metric parameters of [2] closely match those previously reported for the homologous iridium(III) complex.3e The remaining chloro ligand in [2] could not be substituted even in the presence of an excess of isocyanide ligand 1. Similar behavior was reported for the analogous iridium complex.3e In order to obtain rhodium and iridium complexes bearing three C-metalated heterocycles, we reacted the metal precursors [MCl2(Cp*)]2 (M = Rh, Ir) in acetonitrile solution with 4 equiv of AgBF4. Subsequently, 6 equiv of 1 were added and all O−SiMe3 bonds were cleaved by addition of KF/MeOH to give complexes [3] and [4] in 87% and 77% yields, respectively (Scheme 3). The intermediate tris-isocyanide complexes were

Scheme 2. Template Synthesis of Rhodium(III) Complex [2]

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of only one broad singlet with an integrated intensity of 1 for the single NH proton at δ 14.61 ppm for complex [3] and at δ 13.14 ppm for complex [4]. The resonances for the carbene carbon atoms in the 13C{1H} NMR spectra are detected at δ 194.1 ppm as a doublet with a coupling constant of 1JRhC = 54 Hz for complex [3] and at δ 167.6 ppm as a singlet for complex [4]. High-resolution mass spectrometry (ESI, positive ions) shows the peaks for the cationic complex ions [[3] + H]+ and [[4] + H]+ as the signals of highest intensity. Slow diffusion of diethyl ether into a solution of [3] in dichloromethane and slow evaporation of the solvents from a dichloromethane/acetonitrile solution of [4] afforded single crystals of [3] and [4], respectively, suitable for X-ray diffraction analyses. The molecular structures of [3] and [4] are depicted in Figure 2. The molecular structure determinations confirmed the formation of neutral complexes [3] and [4], each only bearing one protonated benzoxazolin-2-ylidene ligand and two benzoxazolinato ligands (Figure 2, top). While NMR spectroscopy of [3] and [4] indicated the presence of three identical NHC ligands on the NMR time scale, three different NHC ligands can be distinguished in the solid state. Two of these (the protonated benzoxazolidin-2-ylidene and one deprotonated anionic benzoxazolinato-2-ylidene) are linked by N3−H3···N12 hydrogen bonds, leading to an almost coplanar arrangement of these ligands (dihedral angles 4.94(3)° for [3] and 6.14(3)° for [4]) as was observed in [2] (Figure 2,

Scheme 3. Template Synthesis of Tris(N,O-NHC) Complexes [3] and [4]

not isolated. Only one of the three C-metalated heterocycles is N-protonated, which leads to the formation of neutral complexes bearing one neutral benzoxazolin-2-ylidene ligand and two anionic benzoxazolinato-2-ylidene ligands. This behavior resembles the observations made with complex [2]. Complexes [3] and [4] were fully characterized by NMR spectroscopy, high-resolution mass spectrometry, elemental analysis, and X-ray diffraction studies. Comparable spectroscopic parameters for complexes [3] and [4] do not differ significantly. In the NMR spectra (1H and 13C{1H}) of the complexes only one set of signals is observed for all three Cmetalated heterocycles, indicating their chemical equivalence on the NMR time scale. In addition, formation of N−H···N hydrogen bonds involving all three NHC ligands simultaneously is indicated in the 1H NMR spectra by the observation

Figure 2. Molecular structures (50% displacement ellipsoids) of complexes [3] (left) and [4] (right). Hydrogen atoms (except for NH) have been omitted for clarity. Selected bond lengths (Å) and bond angles (deg) for [3]: Rh−C2 1.988(2), Rh−C11 2.013(2), Rh−C20 2.000(2); C2−Rh− C11 89.58(6), C2−Rh−C20 88.83(6), C11−Rh−C20 83.17(6), O1−C2−N3 107.83(13), O10−C11−N12 111.81(13), O19−C20−N21 112.70(13). Selected bond lengths (Å) and bond angles (deg) for [4]: Ir−C2 1.9886(13), Ir−C11 2.0216(13), Ir−C20 2.0144(13); C2−Ir−C11 89.26(5), C2−Ir−C20 88.38(6), C11−Ir−C20 83.52(5), O1−C2−N3 108.26(11), O10−C11−N12 111.75(11); disorder in the third heterocycle prevented recording of reliable data. C


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Crystals suitable for X-ray diffraction analyses of complexes [5] and [6]·0.5CH2Cl2·H2O were obtained by slow diffusion of diethyl ether into a solution of [5] in dichloromethane or by slow evaporation of the solvents from a dichloromethane/npentane solution of [6], respectively. The molecular structures of complexes [5] and [6] are depicted in Figure 3. Both complexes reside on a crystallographic inversion center located at the midpoint of the Ag···Ag* connection line. The molecular structure determinations of complexes [5] and [6]·0.5CH2Cl2·H2O confirm the coordination of two deprotonated tris(N,O-NHC) metalloligands to two silver(I) ions via the nitrogen donors and to two additional metal ions (M = RhIII, IrIII) via the carbene carbon atoms. The coordination environment around silver is strongly distorted trigonal planar with two nitrogen donors belonging to one metalloligand and the third donor to the second metalloligand. Three-coordinated silver ions are rare, and only a few examples have been described in the literature.15 The Rh−CNHC and Ir− CNHC bond lengths are identical within experimental error for each complex and fall in the range previously observed for complexes [2]−[4] and other related NHC complexes.3e,13,16 The Ag−N bond lengths in complexes [5] and [6] compare well to those found for silver(I) complexes bearing three nitrogen donors.15 The separation between the two AgI ions (3.0077(4) Å in [5] and 2.9665(5) Å in [6]) is significantly shorter than the sum of the van der Waals radii of two silver atoms (ca. 3.44 Å) and thus indicates the presence of an argentophilic interaction in both complexes.17 The two RhIII ions in complex [5] are separated by 8.000 Å and the two IrIII ions in complex [6] by 7.929 Å. After the preparation of complexes [5] and [6], we became interested in the complexation of other group 11 transition metals by the tridentate metalloligands obtained by deprotonation of [3] and [4]. The reaction of complex [3] with [Cu(NCMe)4](BF4) in the presence of a stoichiometric amount of potassium acetate as base results in the formation of the heterobimetallic, trinuclear complex [7] in 40% yield (Scheme 5). During the reaction disproportionation of copper(I) was observed and elemental copper precipitated. As a result, the octahedral complex [7] bearing two metalloligands facially coordinating to copper(II) was obtained. Due to the presence of the paramagnetic copper(II) ion, complex [7] was only characterized by high-resolution mass spectrometry and an X-ray diffraction study. The mass spectrum (HR-ESI, positive ions) shows the molecular mass of the cationic complex ion [[7] + H]+ as the peak of highest intensity and an additional signal for a fragment obtained from [7] by loss of two NHC ligands. Slow diffusion of diethyl ether into a solution of [7] in dichloromethane yielded crystals of [7], which were suitable for an X-ray diffraction study. The molecular structure of complex [7] is depicted in Figure 4. The molecular structure determination confirms the facial coordination of two deprotonated metalloligands derived from [3] to the copper(II) ion in [7]. The coordination geometry around the rhodium(III) ions is slightly different in the related complexes [5] and [7]. While the CNHC−Rh−CNHC angles in [5] vary between 83.46(10) and 94.39(10)°, apparently caused by the unsymmetrical coordination mode of the metalloligand, statistically identical CNHC−Rh−CNHC angles are observed in [7]. The Rh−CNHC bond distances are identical within experimental error for [5] and [7]. The copper(II) ion in [7] is coordinated in a distorted-octahedral fashion with N−Cu−N angles within one facially coordinated metalloligand deviating

bottom). The remaining anionic benzoxazolinato ligand does not interact with the other ligands and is oriented almost perpendicular to the plane made up from the hydrogen-linked ligands. This arrangement is also reflected in the metric parameters. The M−CNHC bond distances show an identical trend, with the M−C(NH,O-NHC) distance involving the protonated benzoxazolin-2-ylidene being the shortest. The O− C−N bond angles are also clearly dependent on the protonation state of the ring nitrogen atom. In [3], for example, the protonated benzoxazolin-2-ylidene features an O1−C2−N3 angle of 107.83(13)° while the O10−C11−N12 and O19−C20−N21 angles of the deprotonated ligands are much larger (111.81(13) and 112.70(13)°). The same situation was found in iridium complex [4], which is in accord with the observations made for complexes bearing protonated and deprotonated benzimidazolin-2-ylidenes.7i,14 As described above, only one signal for the NH proton in [3] and [4] was observed in the 1H NMR spectra, confirming the chemical equivalence of the three NHC ligands on the NMR time scale. This observation requires a simultaneous interaction of all three NHC ring nitrogen atoms with the single NH proton in solution. In addition, the nitrogen atoms of the heterocycles must also point in the same direction to allow for such a fluctuating interaction. From the point of view of coordination chemistry, complexes [3] and [4] can be described as tripodal metalloligand precursors with three nitrogen donor functions. After removal of the single N−H proton, complex formation of the resulting anion with a transition metal should be possible and was studied next. The heterobimetallic tetranuclear complexes [5] and [6] were obtained by treatment of complexes [3] and [4] with silver acetate in the presence of potassium acetate as an additional base in yields of 65% and 55%, respectively (Scheme 4). The formation of the complexes was confirmed by NMR Scheme 4. Synthesis of Heterobimetallic, Tetranuclear Complexes [5] and [6]

spectroscopy, high-resolution mass spectrometry, and X-ray diffraction analysis. High-resolution mass spectrometry showed the molecular mass of cationic complex ions [[5] + H]+ and [[6] + H]+ and several additional signals caused by loss of one or more NHC donors or silver ions. The backbone protons of the NHC ligands of both complexes were detected by 1H NMR spectroscopy at chemical shifts between δ 7.44 and 6.46 ppm. The signal for an N−H proton was no longer observed. The 13 C{1H} NMR spectra exhibited only one set of signals for all NHC ligands. The resonance for the carbene carbon atoms of complex [5] was not observed, while the carbene carbon atoms of complex [6] were detected at δ 169.7 ppm. D


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Figure 3. Molecular structures (50% displacement ellipsoids) of complexes [5] (left) and [6] in [6]·0.5CH2Cl2·H2O (right). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and bond angles (deg) for [5]: Rh−C2 2.004(3), Rh−C11 2.006(3), Rh−C20 2.010(3), Ag−N3 2.200(2), Ag−N12* 2.353(2), Ag−N21* 2.231(2); C2−Rh−C11 91.09(10), C2−Rh−C20 83.46(10), C11−Rh−C20 94.39(10), N3−Ag−N12* 115.38(8), N3−Ag−N21* 152.43(8), N12*−Ag−N21* 88.04(8); Ag···Ag* 3.0077(4). The asymmetric unit of [6]·0.5CH2Cl2·H2O contains two essentially identical independent halves of the complex related to the other halves by crystallographic inversion centers. Only one of the two independent molecules is shown in the figure. Selected bond lengths (Å) and bond angles (deg) for [6]·0.5CH2Cl2·H2O: Ir−C2 2.017(3), Ir−C11 2.017(3), Ir−C20 2.006(3), Ag−N3 2.338(3), Ag−N12 2.217(3), Ag−N21* 2.184(3); C2−Ir−C11 94.52(12), C2−Ir−C20 89.42(12), C11−Ir− C20 87.31(12), N3−Ag−N12 89.96(9), N3−Ag−N21* 114.23(9), N12−Ag−N21* 151.17(10); Ag···Ag* 2.9665(5).

Scheme 5. Synthesis of the Heterobimetallic, Trinuclear Complex [7]

by a maximum of 3.5° from 90°. The axial Cu−N3/N3* bond lengths (2.317(3) Å) are significantly longer than the equatorial bond lengths (Cu−N12/N12* 2.046(3) Å and Cu−N21/N21* 2.032(3) Å), which indicates a strong Jahn−Teller distortion.18 The Cu−Nax and Cu−Neq bond lengths in the axially stretched CuN6 octahedron of complex [7] are comparable to those observed in previously described complexes containing an octahedral Jahn−Teller distorted copper(II) ion.19 Further studies of the synthesis of heterobimetallic complexes from N-deprotonated [3] or [4] and [Cu(NCMe)4](BF4) revealed that the reaction products obtained depend on the amount of potassium acetate added. The reaction of complexes [3] and [4] with [Cu(NCMe)4](BF4) in the presence of an excess of potassium acetate results in the formation of the dinuclear, heterobimetallic complexes [8] (in 40% yield) and [9] (in 48% yield) instead of complexes of type [7]. In the dinuclear complexes [8] and [9], a {CuOAc} complex fragment is coordinated by only one tripodal metalloligand obtained by deprotonation of [3] or [4] (Scheme 6). The excess of acetate ligand prevents the coordination of a second metalloligand by occupying two coordination sites at the copper(II) ion which is formed by disproportionation of [Cu(NCMe)4](BF4) in analogy to the observations made in the synthesis of [7].

Figure 4. Molecular structure (50% displacement ellipsoids) of complex [7]. Hydrogen atoms have been omitted for clarity. The complex resides on a crystallographic inversion center. Selected bond lengths (Å) and bond angles (deg) for [7]: Rh−C2 2.013(3), Rh−C11 2.007(3), Rh−C20 2.006(3), Cu−N3 2.317(3), Cu−N12 2.046(3), Cu−N21 2.032(3); C2−Rh−C11 86.64(12), C2−Rh−C20 86.51(13), C11−Rh−C20 86.92(13), N3−Cu−N12 86.43(10), N3−Cu−N12* 93.57(10), N3−Cu−N21 86.95(10), N3−Cu−N21* 93.05(10), N12−Cu−N21 87.69(10), N12−Cu−N21* 92.31(10).

Formation of the new complexes was confirmed by highresolution mass spectrometry and X-ray diffraction studies. The presence of the paramagnetic copper(II) ion did not allow the recording of NMR spectra. The high-resolution mass spectra (ESI, positive ions) show peaks of high intensity corresponding to the molecular mass of the cationic complex ions [[8] + H]+ and [[9] + H]+. Crystals of complexes [8] and [9] suitable for X-ray diffraction experiments were obtained by slow diffusion of diethyl ether into a solution of [8] in dichloromethane or by E


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2.106(2) Å) are significantly longer than the Cu−N bond distances involving the basal nitrogen donors ([8], Cu−N3 1.967(2) Å and Cu−N21 1.976(2) Å; [9], Cu−N3 1.965(2) Å and Cu−N12 1.967(2) Å). These values fall within the range observed for related square-pyramidal copper(II) complexes featuring a CuN3OAc donor set with an identical arrangement of the donors.20 The coordination geometry of pentacoordinated metal centers such as the copper(II) ion in [8] and [9] can be described using the τ value.21 For complexes [8] and [9] τ values of 0.201 and 0.171, respectively, were calculated, which indicates that the coordination geometry at the copper centers is indeed best described as square pyramidal rather than trigonal bipyramidal, which would lead to τ values closer to 1.0 (see also Figure 5, bottom). Finally, we have studied the coordination chemistry of the metalloligand obtained from [3] with d10 metals that do not prefer a specific coordination geometry. Complex [3] was reacted with zinc(II) acetate and an excess of potassium acetate as additional base. From this reaction the dinuclear, heterobimetallic complex [10] was obtained in 61% yield (Scheme 7). As already seen during the synthesis of complexes [8] and [9], the excess of acetate as base leads to the coordination of only one tridentate metalloligand obtained from [3] to the zinc(II) ion, which completes its coordination environment by coordination of one acetate as a monodentate ligand. Complex [10] was characterized by NMR spectroscopy, high-resolution mass spectrometry, elemental analysis, and an X-ray diffraction study. The high-resolution mass spectrum (ESI, positive ions) shows a peak with high intensity for the cationic complex ion [[10] + H]+ and a peak for an additional

Scheme 6. Synthesis of Heterobimetallic, Dinuclear Complexes [8] and [9]

the slow evaporation of the solvents from a dichloromethane/npentane solution of [9], respectively. The molecular structure determinations of complexes [8] and [9] (Figure 5) confirm the coordination of the three ring nitrogen atoms of one octahedral metalloligand obtained from [3] or [4] to a copper(II) ion, which in turn is coordinated by one acetate ligand. The Rh−CNHC and Ir−CNHC bond lengths and the CNHC−M−CNHC bond angles ([8], M = Rh; [9], M = Ir) exhibit no remarkable features and fall in the range of values previously recorded for the related complexes [2]−[7]. In both complexes, the copper(II) ion is coordinated by three ring nitrogen atoms of the metalloligand and two oxygen atoms of the acetate ligand, forming a distorted-squarepyramidal polyhedron. The acetate oxygen atoms and two nitrogen donors form the basal plane of the square pyramid, and one nitrogen atoms occupies the apical position. Although three identical nitrogen donors are coordinated to copper(II), two types of Cu−N bond lengths are observed. The apical Cu− N bond lengths ([8], Cu−N12 2.102(2) Å; [9], Cu−N21

Figure 5. Molecular structures (50% displacement ellipsoids) of complexes [8] (top left) and [9] (top right) and coordination geometry of the metal ions in the complexes (bottom). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and bond angles (deg) for [8]: Rh−C2 2.016(2), Rh−C11 2.016(2), Rh−C20 1.995(2), Cu−O38 2.043(2), Cu−O40 2.021(2), Cu−N3 1.967(2), Cu−N12 2.102(2), Cu−N21 1.976(2); C2−Rh−C11 87.51(8), C2−Rh−C20 82.48(8), C11−Rh−C20 90.45(8), O38−Cu−O40 63.98(6), O38−Cu−N3 103.21(7), O38−Cu−N12 110.20(7), O38−Cu−N21 151.42(8), O40−Cu−N3 163.50(7), O40−Cu−N12 101.94(7), O40−Cu−N21 97.24(7), N3−Cu−N12 92.15(7), N3− Cu−N21 90.19(7), N12−Cu−N21 94.13(7). Selected bond lengths (Å) and bond angles (deg) for [9]: Ir−C2 2.001(2), Ir−C11 2.012(3), Ir−C20 2.018(2), Cu−O38 2.043(2), Cu−O40 2.027(2), Cu−N3 1.965(2), Cu−N12 1.967(2), Cu−N21 2.106(2); C2−Ir−C11 82.89(10), C2−Ir−C20 90.16(9), C11−Ir−C20 87.04(10), O38−Cu−O40 64.39(8), O38−Cu−N3 153.09(8), O38−Cu−N12 103.02(9), O38−Cu−N21 108.90(9), O40−Cu−N3 97.33(8), O40−Cu−N12 163.35(8), O40−Cu−N21 102.15(8), N3−Cu−N12 90.19(9), N3−Cu−N21 93.69(9), N12−Cu−N21 92.10(9). F


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111.07(5)°), while the N−Zn−N bond angles are significantly smaller (range 97.13(5)−91.04(5)°). This type of distortion is typical of ZnII complexes bearing a tripodal N3 ligand (mostly tris-pyrazolyl borates) and a monodentate coordinated acetate ligand.22 The Rh−CNHC bond lengths and CNHC−Rh−CNHC bond angles are not affected by the N3O coordination to ZnII, and the recorded values for these parameters do not differ significantly from equivalent parameters found in complexes [3], [5], [7], and [8].

Scheme 7. Synthesis of the Heterobimetallic, Dinuclear Complex [10]

cation resulting from loss of the acetate anion. In the 1H NMR spectrum of complex [10] the resonances of the backbone protons of the NHC ligands were observed at δ 7.75−7.10 ppm and the methyl protons of the acetate anion were detected at δ 2.41 ppm. A signal for an NH proton is no longer observed, suggesting coordination of all three NHC ring nitrogen atoms to the zinc(II) ion. The 13C{1H} NMR spectrum features a resonance for the carbene carbon atoms at δ 192.4 ppm as a doublet with a coupling constant of 1JRhC = 54 Hz. The resonances of the acetate anion are observed at δ 179.6 and 22.3 ppm. Slow evaporation of the solvents from a dichloromethane/npentane solution of [10] afforded single crystals of [10] which were suitable for an X-ray diffraction study. The molecular structure of [10] is depicted in Figure 6. The molecular

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CONCLUSIONS

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EXPERIMENTAL SECTION

We have demonstrated the preparation of complexes bearing two or three N,O-NHC ligands by the template-controlled cyclization of the β-functionalized 2-trimethylsiloxyphenyl isocyanide (1). For electroneutrality reasons, the complexes with both two ([2]) and three C-metalated N,O-heterocycles ([3] and [4]) each bear only one N-protonated NHC ligand. Removal of this proton from the latter complexes leads to tripodal metalloligands which have been used for the preparation of various heterobimetallic complexes. Complexes [3] and [4] react with AgOAc in the presence of KOAc to give tetranuclear heterobimetallic complexes [5] and [6], where two metalloligands coordinate to two silver(I) ions, leading to a rare trigonal coordination environment for silver(I). The reaction of copper(I) with [3] in the presence of KOAc yields the trinuclear complex [7], featuring coordination of two metalloligands to copper(II), obtained by disproportionation of the initially employed copper(I). A strong Jahn−Teller distortion was observed for the CuN6 polyhedron in [7]. Only one tripodal metalloligand coordinates to copper(II) in complexes [8] and [9], when metalloligand precursors [3] or [4] are reacted with [Cu(NCMe)4](BF4) in the presence of an excess of KOAc. Complexes [8] and [9] each bear one bidentate acetate ligand, and the tetragonal-pyramidal-coordinated copper(II) centers are obtained by disproportionation of the copper(I) starting material. Finally, complex [10] was obtained from the metalloligand precursor [3] and zinc acetate in the presence of an excess of KOAc. Complex [10] features a zinc(II) ion coordinated in a distorted-tetrahedral fashion by three nitrogen donors of the metalloligand and a monodentate acetate donor. Our studies demonstrate that tris-NHC complexes [3] and [4] are useful starting materials for the generation of tripodal N3-metalloligands and for the preparation of heterobimetallic complexes bearing C/N-metalated benzoxazolinato heterocycles.

Figure 6. Molecular structure (50% displacement ellipsoids) of complex [10] (top) and coordination geometry around the zinc(II) cation (bottom). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and bond angles (deg): Rh−C2 2.0178(14), Rh−C11 2.0051(14), Rh−C20 2.0222(15), Zn−N3 1.9884(12), Zn−N12 2.0104(12), Zn−N21 2.0378(12), Zn−O38 1.9505(11); C2−Rh−C11 90.17(6), C2−Rh−C20 89.31(6), C11− Rh−C20 83.25(6), O38−Zn−N3 124.94(5), O38−Zn−N12 128.15(5), O38−Zn−N21 111.07(5), N3−Zn−N12 97.13(5), N3− Zn−N21 95.37(5), N12−Zn−N21 91.04(5).

All preparations were carried out under an argon atmosphere using standard Schlenk techniques or in a glovebox. Solvents were dried by standard methods and distilled prior to use. Commercially available chemicals were used without further purification. [RhCl2(Cp*)]2, [IrCl2(Cp*)]2,23 [Cu(NCMe)4](BF4),24 and 2-trimethylsiloxyphenyl isocyanide (1)11 were prepared by published procedures. NMR spectra were recorded at 298 K on Bruker AVANCE I 400 and Bruker AVANCE III 400 spectrometers. Chemical shifts (δ) are expressed in ppm using the residual protonated solvent signal as internal standard. Coupling constants are expressed in Hz. HRMS spectra were obtained with an Orbitrap LTQ XL (Thermo Scientific) spectrometer. For the assignment of the NMR resonances see the numbering in the molecular plots. 1H and 13C{1H} NMR spectra are provided in the Supporting Information.

structure analysis confirms the coordination of one metalloligand obtained from [3] as a tridentate ligand to the zinc(II) ion in addition to one monodentate acetate ligand. This leads to a distorted-tetrahedral coordination environment for the zinc(II) ion. The distortion is mostly caused by the expansion of the O38−Zn−N bond angles (range 128.15(5)− G


Article

Organometallics Synthesis of Complex [4].

Synthesis of Complex [2].

A sample of [RhCl2(Cp*)]2 (111 mg, 0.18 mmol) was dissolved in dichloromethane (20 mL), and the solution was cooled to −78 °C. To this solution was added 2-trimethylsiloxyphenyl isocyanide (1; 136 mg, 0.71 mmol). While it was stirred for 12 h, the reaction mixture was warmed to ambient temperature. Then a catalytic amount of potassium fluoride (2 mg) and distilled water (10 mL) were added and the mixture was stirred at ambient temperature for another 12 h. Subsequently, the solvent and all volatiles were removed in vacuo. The crude reaction product was suspended in dichloromethane (25 mL), and insolubles were separated by filtration. After removal of the solvent from the filtrate in vacuo, complex [2] was obtained as an orange powder. Yield: 172 mg (0.34 mmol, 94%). 1H NMR (400 MHz, CDCl3): δ 9.96 (s, 1H, NH), 7.57 (t, 3JHH = 6.5 Hz, 4H, H6, H9), 7.27−7.19 (m, 4H, H7, H8), 1.86 (s, 15H, Cp*-CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 196.0 (d, 1JRhC = 55 Hz, C2), 154.2 (C5), 135.9 (C4), 123.7 (C7), 122.9 (C8), 114.6 (C6), 110.1 (C9), 101.2 (d, 1JRhC = 5 Hz, Cp*-C), 9.6 (Cp*-CH3). HRMS (ESI, positive ions): m/z 511.06386 (calcd for [[2] + H]+ 511.06596), 475.08736 (calcd for [[2] − Cl]+ 475.08928). Anal. Calcd for C24H24N2ClO2Rh: C, 56.43; H, 4.74; N, 5.48. Found: C, 55.46; H, 4.90; N, 5.16. Synthesis of Complex [3].

To a solution of [IrCl2(Cp*)]2 (150 mg, 0.19 mmol) in dichloromethane (20 mL) was added a solution of AgBF4 (148 mg, 0.77 mmol) in acetonitrile (10 mL). The mixture was stirred at ambient temperature for 12 h. After removal of the solvent in vacuo, the residue was suspended in dichloromethane (20 mL) and insolubles were removed by filtration. The filtrate was then cooled to −78 °C and 2trimethylsiloxyphenyl isocyanide (1; 217 mg, 1.13 mmol) was added. The mixture was stirred for another 12 h while it was warmed to ambient temperature. After addition of a catalytic amount of potassium fluoride (2 mg) in methanol (10 mL), the mixture was stirred at ambient temperature for another 12 h. Subsequently, all volatiles were removed in vacuo. The solid mixture was suspended in dichloromethane (20 mL), and the suspension was filtered through Celite. The filtrate was mixed with n-hexane (20 mL) and concentrated in vacuo until a solid precipitated. The solid was isolated by filtration and washed with n-hexane (3 × 10 mL). Drying of the solid in vacuo gave complex [4] as a reddish powder. Yield: 197 mg (0.29 mmol, 77%). 1 H NMR (400 MHz, CDCl3): δ 13.14 (br s, 1H, NH), 7.70 (d, 3JHH = 7.7 Hz, 3H, H9), 7.43 (d, 3JHH = 7.7 Hz, 3H, H6), 7.20−7.11 (m, 6H, H7, H8), 2.14 (s, 15H, Cp*-CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 167.6 (C2), 153.7 (C5), 139.4 (C4), 122.8 (C7), 121.8 (C8), 115.2 (C6), 109.1 (C9), 98.2 (Cp*-C), 9.7 (Cp*-CH3). HRMS (ESI, positive ions): m/z 684.18261 (calcd for [[4] + H]+ 684.18397), 565.14550 (calcd for [[4] − (C7H5NO) + H]+ 565.14996). Anal. Calcd for C31H28N3IrO3: C, 54.53; H, 3.96; N, 5.89. Found: C, 54.28; H, 4.35; N, 5.31. Synthesis of Complex [5].

To a solution of [RhCl2(Cp*)]2 (150 mg, 0.24 mmol) in dichloromethane (25 mL) was added a solution of AgBF4 (189 mg, 0.97 mmol) in acetonitrile (10 mL). The mixture was stirred at ambient temperature for 12 h. After removal of the solvent in vacuo, the residue was suspended in dichloromethane (20 mL) and precipitated solid AgCl was separated by filtration. The remaining solution was cooled to −78 °C, and 2-trimethylsiloxyphenyl isocyanide (1; 279 mg, 1.46 mmol) was added. Over 12 h with stirring, the mixture was warmed to ambient temperature. After addition of a catalytic amount of potassium fluoride (2 mg) in methanol (10 mL), the mixture was stirred at ambient temperature for an additional 12 h. The solvent was then removed in vacuo. The obtained solid was suspended in dichloromethane (25 mL), and the resulting suspension was filtered through Celite. The filtrate was mixed with n-hexane (20 mL) and concentrated in vacuo until a solid precipitated. The solid was isolated by filtration and was washed with n-hexane (3 × 10 mL). After it was dried in vacuo, complex [3] was obtained as a yellow powder. Yield: 250 mg (0.42 mmol, 87%). 1H NMR (400 MHz, CDCl3): δ 14.61 (br s, 1H, NH), 7.84−7.82 (m, 3H, H9), 7.61−7.59 (m, 3H, H6), 7.25−7.23 (m, 6H, H7, H8), 2.01 (s, 15H, Cp*-CH3). 13 C{1H} NMR (100 MHz, CDCl3): δ 194.1 (d, 1JRhC = 54 Hz, C2), 153.5 (C5), 133.6 (C4), 124.9 (C7), 124.3 (C8), 115.3 (C6), 110.1 (C9), 103.9 (d, 1JRhC = 4 Hz, Cp*-C), 9.7 (Cp*-CH3). HRMS (ESI, positive ions): m/z 594.12518 (calcd for [[3] + H]+ 594.12640), 475.08825 (calcd for [[3] − (C7H5NO) + H]+ 475.08928). Anal. Calcd for C31H28N3O3Rh: C, 62.74; H, 4.76; N, 7.08. Found: C, 62.49; H, 4.57; N, 6.86.

Samples of complex [3] (30 mg, 0.05 mmol), silver(I) acetate (17 mg, 0.10 mmol), and potassium acetate (10 mg, 0.10 mmol) were suspended in dichloromethane (10 mL), and the mixture was stirred at ambient temperature for 5 days under exclusion of light. After removal of the solvent in vacuo, the solid residue was suspended in dichloromethane (20 mL) and the suspension was filtered. The filtrate was filtered again through a plug of alumina (4% H2O), and the solvent was then removed in vacuo to give [5] as an off-white powder. Yield: 23 mg (0.016 mmol, 65%). 1H NMR (400 MHz, CD2Cl2): δ 7.21 (d, 3JHH = 8.0 Hz, 6H, H6), 6.77−6.73 (m, 6H, H9), 6.50−6.46 (m, 12H, H7, H8), 1.83 (s, 30H, Cp*-CH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ 153.9 (C4), 143.0 (C5), 122.7 (C8), 121.9 (C7), 115.8 (C9), 108.1 (C6), 103.5 (d, 1JRhC = 4 Hz, Cp*-C), 10.4 (Cp*CH3). The resonance for the carbene carbon atom (C2) was not observed. HRMS (ESI, positive ions): m/z 1401.04140 (calcd for [[5] + H]+ 1401.04001), 1295.14160 (calcd for [[5] − Ag + 2H]+ 1295.14340), 1055.06750 (calcd for [[5] − Ag−2(C7H4NO)]+ 1055.06801). H


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Organometallics

ions): m/z 715.06190 (calcd for [[8] + H]+ 715.06148), 655.04065 (calcd for [[8] − (C2H3O2)]+ 655.04035). Anal. Calcd for C33H30N3CuO5Rh: C, 55.43; H, 4.23; N, 5.88. Found: C, 53.21; H, 4.28; N, 5.37. Synthesis of Complex [9].

Synthesis of Complex [6].

Samples of complex [4] (30 mg, 0.04 mmol), silver(I) acetate (15 mg, 0.09 mmol), and potassium acetate (9 mg, 0.09 mmol) were suspended in dichloromethane (10 mL), and the mixture was stirred am ambient temperature for 5 days under exclusion of light. After removal of the solvent in vacuo, the residue was suspended in dichloromethane (20 mL) and the suspension was filtered. The filtrate was filtered again through a plug of alumina (4% H2O), and the solvent was removed in vacuo to give [6] as an off-white powder. Yield: 19 mg (0.012 mmol, 55%). 1H NMR (400 MHz, CD3OD): δ 7.44−7.39 (m, 12H, H6, H9), 7.14−7.07 (m, 12H, H7, H8), 2.03 (s, 30H, Cp*-CH3). 13C{1H} NMR (100 MHz, CD3OD): δ 169.7 (C2), 155.0 (C4), 140.6 (C5), 124.3 (C8), 123.6 (C7), 115.8 (C9), 110.1 (C6), 99.6 (Cp*-C), 9.7 (Cp*-CH3). HRMS (ESI, positive ions): m/z 1579.15569 (calcd for [[6] + H]+ 1579.15286), 1473.26022 (calcd for [[6] − Ag + 2H]+ 1473.25648), 1354.22306 (calcd for [[6] − Ag − (C7H4NO) + H]+ 1354.21921). Synthesis of Complex [7].

Samples of complex [4] (30 mg, 0.04 mmol), [Cu(NCMe)4](BF4) (13 mg, 0.04 mmol), and potassium acetate (17 mg, 0.17 mmol) were suspended in dichloromethane (10 mL), and the mixture was stirred at ambient temperature for 5 days. After removal of the solvent in vacuo, the solid residue was suspended in dichloromethane (20 mL) and the suspension was filtered. The filtrate was filtered again through a plug of alumina (4% H2O), and the solvent was removed in vacuo to give [8] as a green powder. Yield: 15 mg (0.019 mmol, 48%, relative to [4]). Due to the presence of the paramagnetic copper(II) ion, no meaningful NMR data could be obtained. HRMS (ESI, positive ions): m/z 805.11608 (calcd for [[9] + H]+ 805.11820), 745.09450 (calcd for [[9] − (C2H3O2)]+ 745.09705). Synthesis of Complex [10].

Samples of complex [3] (30 mg, 0.05 mmol), zinc(II) acetate dihydrate (11 mg, 0.05 mmol), and potassium acetate (10 mg, 0.10 mmol) were suspended in dichloromethane (10 mL), and the mixture was stirred at ambient temperature for 5 days. After removal of the solvent in vacuo, the solid residue was suspended in dichloromethane (20 mL) and the suspension was filtered. The filtrate was brought to dryness in vacuo to give [10] as a brown powder. Yield: 22 mg (0.03 mmol, 61%). 1H NMR (400 MHz, CDCl3): δ 7.75 (d, 3JHH = 7.8 Hz, 3H, H9), 7.39 (d, 3JHH = 7.9 Hz, 3H, H6), 7.19 (pseudo-t, 3JHH = 7.6 Hz, 3H, H7), 7.10 (pseudo-t, 3JHH = 7.7 Hz, 3H, H8), 2.41 (s, 3H, H41), 2.16 (s, 15H, Cp*-CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 192.4 (d, 1JRhC = 54 Hz, C2), 179.6 (C39), 153.5 (C5), 139.0 (C4), 123.5 (C8), 122.3 (C7), 116.4 (C9), 108.5 (C6), 104.7 (d, 1JRhC = 4 Hz, Cp*-C), 22.3 (C41), 10.6 (Cp*-CH3). HRMS (ESI, positive ions): m/z 716.06170 (calcd for [[10] + H]+ 716.06102), 656.04016 (calcd for [[10] − (C2H3O2)]+ 656.03989). Anal. Calcd for C33H30N3O5RhZn: C, 55.29; H, 4.22; N, 5.86. Found: C, 54.85; H, 4.46; N, 5.38. X-ray Diffraction Studies. X-ray diffraction data were collected at low temperature (for specific temperatures see the crystallographic details for the individual complexes) with a Bruker AXS APEXII CCD diffractometer equipped with a microsource using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Diffraction data were collected over the full sphere and were corrected for absorption. Structure solutions were found with the SHELXS25 package using direct methods and were refined with SHELXL-201425 against |F2| using first isotropic and later anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen atoms were added to the structure models on calculated positions. Crystal Data for Complex [2]. Suitable crystals for an X-ray diffraction analysis were obtained by slow evaporation of the solvent from a dichloromethane solution of [2]. Crystal data: C24H24N2ClO2Rh, M = 510.81, orange prism, 0.15 × 0.07 × 0.05 mm3, orthorhombic, space group Ima2, T = 153(2) K, a = 16.8440(3) Å, b = 17.3130(3) Å, c = 7.5172(2) Å, V = 2192.17(8) Å3, Z = 4, ρcalcd = 1.548 g cm−3, μ = 0.924 mm−1, ω and φ scans, 19959 measured

Samples of complex [3] (30 mg, 0.05 mmol), [Cu(NCMe)4](BF4) (16 mg, 0.05 mmol), and potassium acetate (5 mg, 0.05 mmol) were suspended in dichloromethane (10 mL), and the mixture was stirred at ambient temperature for 5 days. After removal of the solvent in vacuo, the solid residue was suspended in dichloromethane (20 mL) and all insolubles were separated by filtration. The filtrate was filtered again through a plug of alumina (4% H2O), and the solvent was removed in vacuo to give [7] as a green powder. Yield: 13 mg (0.01 mmol, 40%, relative to [3]). Due to the presence of the paramagnetic copper(II) ion, no meaningful NMR data could be obtained. HRMS (ESI, positive ions): m/z 1248.16028 (calcd for [[7] + H]+ 1248.15892), 1011.09357 (calcd for [[7] − 2(C7H4NO)]+ 1011.09252). Synthesis of Complex [8].

Samples of complex [3] (30 mg, 0.05 mmol), [Cu(NCMe)4](BF4) (16 mg, 0.05 mmol), and potassium acetate (20 mg, 0.20 mmol) were suspended in dichloromethane (10 mL), and the mixture was stirred at ambient temperature for 5 days. After removal of the solvent in vacuo, the residue was suspended in dichloromethane (20 mL) and the suspension was filtered. The filtrate was filtered again through a plug of alumina (4% H2O), and the solvent was removed in vacuo to give [8] as a green powder. Yield: 17 mg (0.02 mmol, 40%, relative to [3]). Due to the presence of the paramagnetic copper(II) ion, no meaningful NMR data could be obtained. HRMS (ESI, positive I


Article

Organometallics intensities (4.7° ≤ 2θ ≤ 62.1°), semiempirical absorption correction (0.877 ≤ T ≤ 0.953), 3579 independent (Rint = 0.0246) and 3485 observed intensities (I ≥ 2σ(I)), refinement of 146 parameters against |F2| of all unique intensities. R = 0.0178, Rw = 0.0446, Rall = 0.0187, Rw,all = 0.0451. The asymmetric unit contains a half-molecule of [2] related to the other half by a mirror plane passing through atoms Cl, Rh, C10, and C13. Only one NH proton, disordered between the two nitrogen atoms of the NHC heterocycles, is present, and the positional parameters of these two hydrogen positions have been added to the structure model with SOF = 1/2. Crystal Data for Complex [3]. Suitable crystals for an X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into a dichloromethane solution of [3]. Crystal data: C31H28N3O3Rh, M = 593.47, yellow blocks, 0.28 × 0.27 × 0.16 mm3, monoclinic, space group P21/c, T = 120(2) K, a = 12.2310(2) Å, b = 10.33200(10) Å, c = 22.7398(3) Å, β = 116.7790(10)°, V = 2565.45(6) Å3, Z = 4, ρcalcd = 1.537 g cm−3, μ = 0.705 mm−1, ω and φ scans, 43349 measured intensities (5.7° ≤ 2θ ≤ 59.2°), semiempirical absorption correction (0.640 ≤ T ≤ 0.746), 7200 independent (Rint = 0.0360) and 6420 observed intensities (I ≥ 2σ(I)), refinement of 348 parameters against |F2| of all unique intensities. R = 0.0246, Rw = 0.0590, Rall = 0.0289, Rw,all = 0.0611. Crystal Data for Complex [4]. Suitable crystals for an X-ray diffraction analysis were obtained by slow evaporation of the solvent from a dichloromethane/acetonitrile solution of [4]. Crystal data: C31H28N3IrO3, M = 682.76, orange blocks, 0.24 × 0.22 × 0.16 mm3, monoclinic, space group P21/n, T = 153(3) K, a = 12.2481(7) Å, b = 10.3924(6) Å, c = 20.3944(12) Å, β = 94.4960(10)°, V = 2588.0(3) Å3, Z = 4, ρcalcd = 1.752 g cm−3, μ = 5.198 mm−1, ω and φ scans, 55584 measured intensities (4.0° ≤ 2θ ≤ 76.8°), semiempirical absorption correction (0.375 ≤ T ≤ 0.496), 13907 independent (Rint = 0.0272) and 12475 observed intensities (I ≥ 2σ(I)), refinement of 366 parameters against |F2| of all unique intensities. R = 0.0206, Rw = 0.0452, Rall = 0.0256, Rw,all = 0.0468. The N and O atoms of one of the NHC ligands are disordered over two positions (SOF 0.685 and 0.315). Crystal Data for Complex [5]. Suitable crystals for an X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into a dichloromethane solution of [5]. Crystal data: C62H54N6Ag2O6Rh2, M = 1400.67, colorless needles, 0.22 × 0.03 × 0.03 mm3, monoclinic, space group P21/n, T = 153(2) K, a = 10.6778(4) Å, b = 10.0161(4) Å, c = 24.6116(10) Å, β = 95.989(2)°, V = 2617.8(2) Å3, Z = 2, ρcalcd = 1.777 g cm−3, μ = 1.418 mm−1, ω and φ scans, 36290 measured intensities (5.6° ≤ 2θ ≤ 59.5°), semiempirical absorption correction (0.807 ≤ T ≤ 0.914), 7412 independent (Rint = 0.0550) and 5823 observed intensities (I ≥ 2σ(I)), refinement of 357 parameters against |F2| of all unique intensities. R = 0.0323, Rw = 0.0654, Rall = 0.0496, Rw,all = 0.0703. The complex resides on a crystallographic inversion center located at the midpoint between the two silver atoms and each asymmetric unit contains 1/2 molecule of [5]. Crystal Data for Complex [6]·0.5CH2Cl2·H2O. Suitable crystals of compound [6]·0.5CH2Cl2·H2O for an X-ray diffraction analysis were obtained by slow evaporation of the solvents from a dichloromethane/ n-pentane solution of [6]. Crystal data: C62.5H57N6Ag2Cl1Ir2O7, M = 1639.77, colorless blocks, 0.22 × 0.10 × 0.10 mm3, monoclinic, space group P21/c, a = 21.4642(4) Å, b = 13.1086(3) Å, c = 26.3808(5) Å, β = 127.8390(10)°, V = 5861.9(2) Å3, Z = 4, ρcalcd. = 1.859 g cm−3, μ = 5.298 mm−1, ω and φ scans, 161728 measured intensities (6.5° ≤ 2θ ≤ 60.1°), semiempirical absorption correction (0.564 ≤ T ≤ 0.746), 17133 independent (Rint = 0.0639) and 14186 observed intensities (I ≥ 2σ(I)), refinement of 737 parameters against |F2| of all unique intensities. R = 0.0258, Rw = 0.0525, Rall = 0.0379, Rw,all = 0.0562. The asymmetric unit contains one molecule of [6] residing on a crystallographic inversion center, half of a disordered molecule of CH2Cl2, and one molecule of H2O disordered over two positions. Crystal Data for Complex [7]. Suitable crystals for an X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into a dichloromethane solution of [7]. Crystal data: C62H54N6CuO6Rh2, M = 1248.47, light green plates, 0.11 × 0.10 ×

0.07 mm3, monoclinic, space group P21/n, T = 153(2) K, a = 12.5810(2) Å, b = 14.0637(3) Å, c = 15.7028(4) Å, β = 108.5570(10)°, V = 2633.93(10) Å3, Z = 2, ρcalcd = 1.574 g cm−3, μ = 1.080 mm−1, ω and φ scans, 44646 measured intensities (6.4° ≤ 2θ ≤ 59.2°), semiempirical absorption correction (0.686 ≤ T ≤ 0.746), 7392 independent (Rint = 0.1232) and 4983 observed intensities (I ≥ 2σ(I)), refinement of 354 parameters against |F2| of all unique intensities. R = 0.0461, Rw = 0.0775, Rall = 0.0881, Rw,all = 0.0890. The copper atom of complex [7] resides on a crystallographic inversion center, and each asymmetric unit thus contains a half-molecule of [7]. Crystal data for Complex [8]. Suitable crystals for an X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into a dichloromethane solution of [8]. Crystal data: C33H30N3CuO5Rh, M = 715.05, green blocks, 0.33 × 0.32 × 0.20 mm3, monoclinic, space group P21/c, T = 153(2) K, a = 9.88030(10) Å, b = 16.8473(3) Å, c = 17.9950(3) Å, β = 97.0910(10)°, V = 2972.47(8) Å3, Z = 4, ρcalcd = 1.598 g cm−3, μ = 1.317 mm−1, ω and φ scans, 46877 measured intensities (4.8° ≤ 2θ ≤ 59.1°), semiempirical absorption correction (0.603 ≤ T ≤ 0.746), 8295 independent (Rint = 0.0454) and 6893 observed intensities (I ≥ 2σ(I)), refinement of 394 parameters against |F2| of all unique intensities. R = 0.0296, Rw = 0.0695, Rall = 0.0395, Rw,all = 0.0748. The asymmetric unit contains one formula unit of [8]. Crystal Data for Complex [9]. Suitable crystals for an X-ray diffraction analysis were obtained by slow evaporation of the solvents from a dichloromethane/n-pentane solution of [9]. Crystal data: C33H30N3CuIrO5, M = 804.34, green blocks, 0.63 × 0.51 × 0.46 mm3, monoclinic, space group P21/c, Z = 4, a = 9.9167(3) Å, b = 16.7159(5) Å, c = 17.9075(5) Å, β = 97.2970(10)°, V = 2944.4(2) Å3, Z = 4, ρcalcd = 1.814 g cm−3, μ = 5.285 mm−1, ω and φ scans, 52912 measured intensities (4.8° ≤ 2θ ≤ 62.0°), semiempirical absorption correction (0.062 ≤ T ≤ 0.190), 9236 independent (Rint = 0.0629) and 8472 observed intensities (I ≥ 2σ(I)), refinement of 394 parameters against |F2| of all unique intensities. R = 0.0271, Rw = 0.0616, Rall = 0.0304, Rw,all = 0.0630. The asymmetric unit contains one formula unit of [9]. Crystal Data for Complex [10]. Suitable crystals for an X-ray diffraction analysis were obtained by slow evaporation of the solvents from a dichloromethane/n-pentane solution of [10]. Crystal data: C33H30N3IrO5Zn, M = 716.88, yellow prisms, 0.39 × 0.26 × 0.25 mm3, monoclinic, space group P21/c, T = 100(2) K, a = 9.60230(10) Å, b = 16.9914(2) Å, c = 18.3119(2) Å, β = 97.0040(10)°, V = 2965.41(6) Å3, Z = 4, ρcalcd = 1.606 g cm−3, μ = 1.412 mm−1, ω and φ scans, 53222 measured intensities (5.1° ≤ 2θ ≤ 61.0°), semiempirical absorption correction (0.845 ≤ T ≤ 1.000), 9029 independent (Rint = 0.0344) and 7996 observed intensities (I ≥ 2σ(I)), refinement of 394 parameters against |F2| of all unique intensities. R = 0.0235, Rw = 0.0585, Rall = 0.0285, Rw,all = 0.0613. The asymmetric unit contains one formula unit of [10].

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00252. NMR spectra for all compounds (PDF) Accession Codes

CCDC 1838866−1838874 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 for F.E.H.: [email protected]. J


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Organometallics ORCID

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Guo-Xin Jin: 0000-0002-7149-5413 F. Ekkehardt Hahn: 0000-0002-2807-7232 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft (SFB 858 and IRTG 2027).

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