Metal Complexes with a Hexadentate Macrocyclic ... - ACS Publications

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Metal Complexes with a Hexadentate Macrocyclic DiamineTetracarbene Ligand Taotao Lu,† Chu-Fan Yang,† Li-Yi Zhang,# Fan Fei,† Xue-Tai Chen,*,† and Zi-Ling Xue§ †

State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China # State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Fuzhou 350002, P. R. China § Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States S Supporting Information *

ABSTRACT: A hexadentate macrocyclic N-heterocyclic carbene (NHC) ligand precursor (H4L)(PF6)4 containing four benzimidazolium and two secondary amine groups, has been synthesized and characterized. Coordination chemistry of this new macrocyclic diamine-tetracarbene ligand has been studied by the synthesis of its Ag(I), Au(I), Ni(II), and Pd(II) complexes. Reactions of (H4L)(PF6)4 with different equiv of Ag2O result in Ag(I) complexes [Ag(H2L)](PF6)3 (1) and [Ag2(H2L)](PF6)4 (2). A mononuclear Au(I) complex [Au(H2L)](PF6)3 (3) and a trinuclear Au(I) complex [Au3(H2L)(Cl)2](PF6) (4) are obtained by transmetalation of 1 and 2 with AuCl(SMe2), respectively. Reactions of (H4L)(PF6)4 with Ni(OAc)2 and Pd(OAc)2 in the presence of NaOAc yield [Ni(L)](PF6)2 (5) and [Pd(L)](PF6)2 (6), respectively, containing one Ni(II) and Pd(II) ion with distorted square-planar geometry. Using more NaOAc results in the formation of unusual dinuclear complexes [Ni2(L− 2H)](PF6)2 (7) and [Pd2(L−2H)](PF6)2 (8) (L−2H = deprotonated ligand after removing two H+ ions from two secondary amine groups in L), respectively, featuring a rare M2N2 core formed by two bridging amides. 7 is also formed by the reaction of 5 with 1.0 equiv of Ni(OAc)2·4H2O in the presence of NaOAc. Transmetalation of 2 with 2.0 equiv of Ni(PPh3)2Cl2 gives [Ni2(L)(μ-O)](PF6)2 (9), the first example of a dinuclear Ni(II) complex with a singly bridging oxo group. 9 is converted to 7 in good yield through the treatment with NaOAc.

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include tetraNHC macrocyclic ligands with various linkers5 and hybrid di-NHC/dipyridine6 or di-NHC/2P macrocyclic ligands.7 Relatively few examples have been known for macrocyclic NHC ligands with more than four donor groups.4c,8−11 Two macrocyclic imidazolium salts (H4A)(X)4 and (H4B)(X)4 (Chart 1)4c,8 were constructed by the combination of imidazolium units and pyridine, from which mononuclear, dinuclear, and tetranuclear Ag(I)/Au(I) complexes were prepared. A macrocyclic imidazolium salt (H4C)(X)4, formed from imidazolium and pyrazole units, was employed to access the dinuclear Ni(II) complexes.9 Besides, macrocyclic salen-bisNHC ligands,10 a large (32 ring-atom) macrocyclic NHC-containing ligand, 11 and their metal

INTRODUCTION Over the past two decades, the chemistry of N-heterocyclic carbenes (NHCs) has developed rapidly.1 Although various NHC-containing ligands have been designed and synthesized, most efforts have been focused on monodentate, bidentate, and acyclic polydentate NHC ligands.1 Recently, polydentate macrocyclic NHC ligands,2 in which the donors could be just the NHC groups3,4a,5 or NHC mixed with other donors,4b−d,5,8−11 have also attracted considerable interest due to their diverse coordination chemistry. To date, an increasing number of metal complexes bearing bidentate,3 tridentate,4 and tetradentate5−7 macrocyclic NHC ligands have been reported, some of which have found potential applications in homogeneous catalysts,5c,j medicine,4b guest recognition,9b and luminescence.3 The most important subclass is the tetradentate macrocyclic NHC-containing ligands, which © XXXX American Chemical Society

Received: July 26, 2017

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DOI: 10.1021/acs.inorgchem.7b01896 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

amine such as R2Htacn can also act as anionic macrocyclic ligands for early transition metals and main group elements.14 Considering the rich coordination chemistry of saturated polyamine macrocyclic ligands and polydentate NHC ligands, we have postulated that the combination of NHC and secondary amine donors would give high-dentate macrocyclic NHC ligands with versatile coordination modes. Herein, we present a novel macrocyclic diamine-tetrabenzimidazolium salt (H4L)(PF6)4 (Chart 1), from which nine new complexes, [Ag(H2L)](PF6)3 (1), [Ag2(H2L)](PF6)4 (2), [Au(H2L)](PF6)3 (3), [Au3(H2L)](PF6) (4), [Ni(L)](PF6)2 (5), [Pd(L)](PF6)2 (6), [Ni2(L-2H)](PF6)2 (7), [Pd2(L-2H)](PF6)2 (8), and [Ni2(L)(μ-O)](PF6)2 (9), have been prepared. 7 and 8 are the rare examples of dinuclear Ni(II)- and Pd(II)-NHC complexes with doubly bridged amido donors. 9 is unprecedented with the two Ni(II) ions bridged by an oxo group. Their synthesis and structural characterization are described here.

Chart 1. Examples of Polydentate Macrocyclic Imidazolium Salts

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RESULTS AND DISCUSSION Macrocyclic Benzimidazolium Salt. The macrocyclic diamine-tetrabenzimidazolium salt (H4L)(PF6)4 or (H4L)(OTf)4 (OTf− = SO3CF3−) has been synthesized via the cyclization reaction between N-bis[(benzimidazol-1-yl)ethyl]4-methylbenzenesulfonamide (a)15 and ethane-1,2-ditosylate (b)16 (Scheme 1). This procedure affords a large macrocyclic benzimidazolium salt c, in which the two amine units are protected with the tosyl groups. It is worth noting that the procedure does not yield a smaller macrocyclic benzimidazolium salt d. No dilution is required for this cyclization reaction. The detosylation of c by HBr in the presence of PhOH gives e, which is then converted to the desired diamine-tetrabenzuoimidazolium salts (H4L)(PF6)4 or (H4L)(OTf)4 by anion exchange.

complexes have appeared. These limited examples show the interesting coordination chemistry of high-dentate macrocyclic NHC ligands with more than four donor groups. Saturated polyamine macrocyclic compounds are among the most important macrocyclic ligands in coordination chemistry.12 The secondary amine usually coordinates to the metal ion as a neutral donor in the macrocyclic secondary amine ligands. However, in some cases, the secondary amine donor could be deprotonated and bonded to the metal ion as an amide donor. For example, the N2P2 macrocycle PhP(CH2SiMe2NSiMe2CH2)2PPh developed by the Fruzuk group coordinates to many metal ions as a tetradentate diphoshinediamide ligand.13 The triazacyclononanes with a secondary

Scheme 1. Synthesis of Macrocyclic Benzoimidazolium Salts (H4L)(PF6)4 and (H4L)(OTf)4

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Inorganic Chemistry (H4L)(PF6)4 has been characterized by NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Only one 1H NMR singlet at 9.63 ppm and one 13C NMR signal at 142.61 ppm are observed for the four NCHN protons and carbon atoms, indicating a symmetric structure in solution. The MS peaks at m/z 478.25, 955.33, and 1101.25 correspond to [M−2PF6]2+, [M−2PF6]+, and [M−PF6]+, respectively. X-ray diffraction study shows that (H4L)(OTf)4 crystallizes in the triclinic space group P21/c (Table S1, Supporting Information). Single crystals of (H4L)(OTf)4 were grown by slow diffusion of diethyl ether into an acetonitrile solution. The asymmetric unit cell contains two symmetrically independent half molecules. The structural parameters of these two molecules are almost the same, with only small differences in bond distances and angles. Therefore, only the structure of one molecule in the unit cell is discussed here. The structure of cationic portion of (H4L)(OTf)4 is shown in Figure 1, and

Scheme 2. Synthesis of Ag(I) and Au(I) Complexes 1−4 from (H4L)(PF6)4

signals at 134.51 and 133.46 ppm for the two backbone carbon atoms of the benzimidazole rings are split as well (JAg−C = 5 and 6 Hz, respectively). In 2, only a broad and complicated set of 1 H resonances and overlapping 13C NMR signals for the benzoimidazolium carbons have been observed, suggesting the existence of several species or ligand fluxionality in solution. Similar observations were reported for other Ag-NHC species.4,17a ESI-MS spectra of 1 exhibit the peaks at m/z 459.25 and 1063.25, corresponding to [M−2PF6]2+ and [M− PF6]+, respectively. The peaks at m/z 439.25 and 1023.08 are due to [M−4PF6]2+ and [M−3PF6]+ in 2, respectively. Au(I) complexes [Au(H2L)](PF6)3 (3) and [Au3(H2L)](PF6) (4) have been obtained from 1 and 2 as the transmetalating agent, respectively (Scheme 2). Reacting 1 and 2 with AuCl(SMe2) yields 3 and 4, respectively, in moderate yield. The NMR and ESI-MS data for 3 are similar to 1 and are listed in Experimental Section and not discussed further here. 4 shows two 13C NMR signals at 189.27 and 177.30 ppm for the carbene carbons. The signal at the lower field corresponds to two carbene carbons coordinated to the central Au atom,5e,h while the other one at high field can be ascribed to the carbene carbon coordinated to the Au atom along with the terminal Cl atom. ESI-MS analyses of 4 exhibit the peaks at m/z 1323.50, corresponding to [M−PF6]+. The molecular structures of 1−4 have been studied by singlecrystal X-ray diffraction (Tables S1 and S3). Suitable crystals of 1−4 were grown by slow vapor diffusion of ether into a concentrated acetonitrile solution. 1·CH3CN and 2·6CH3CN crystallize in the triclinic space group P-1, while 3·2CH3CN and 4·2CH3CN crystallize in the monoclinic space groups P21/c and P2/n, respectively. The structures of the cationic portions of 1 (top) and 2 (bottom) are shown in Figure 2. Selected structural parameters are listed in Table 1. In 1, two benzimidazolium and two secondary amine groups are

Figure 1. Molecular structure of (H4L)(OTf)4. Anions, solvent molecules, and hydrogen atoms including N−H are omitted for clarity. Ellipsoids are drawn at 30% probability.

selected bond lengths and angles are listed in Table S2. Each of two pairs of benzimidazolium rings are parallel to each other due to the presence of an inversion center. The benzimidazolium ring containing C1 or C1A forms a dihedral angle of about 11° with the plane containing C10 or C10A. Benzimidazolium rings containing C1 and C10A (or C1A and C10) point down and up with respect to the macrocyclic ring. In addition, the OTf− anions sit on the two sides of the macrocyclic through strong C−H1···O10 and C−H10···O8 hydrogen bonds with distances of 2.394 and 2.229 Å, respectively. Furthermore, intermolecular π−π stacking interaction is found between the benzimidazolium rings of adjacent cation moieties with distances of 3.375 Å (Figure S1). Ag(I) and Au(I) Complexes. Here (H4L)(PF6)4 has been used as the NHC precursor for the preparation of metal complexes due to its relatively higher solubility than (H4L)(OTf)4. Treatment of (H4L)(PF6)4 with 1.0 and 2.5 equiv of Ag2O yields a mononuclear [Ag(H2L)](PF6)3 (1) and dinuclear Ag(I) complex [Ag2(H2L)](PF6)4 (2) (Scheme 2), respectively. Both complexes have been characterized by ESI/ MS, elemental analysis, and NMR spectroscopy. In 1, the 1H NMR signal at 8.35 ppm is found for the two remaining benzimidazolium protons, showing a significant upfield shift relative to those in (H4L)(PF6)4 (9.63 ppm). The 13C NMR signal at 187.88 ppm with the Ag−C coupling (JAg−C = 196 Hz) is assigned to the coordinated carbene carbon. In addition, the C


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Inorganic Chemistry

Each Ag(I) ion is coordinated by one carbene carbon and one amine atom in the linear fashion with the C1−Ag1−N5 bond angle of 173.66(17)o. Even though the linear coordination mode as in CNHC−Ag−CNHC is normal,17 the CNHC−Ag−N mode remains rare for Ag(I)−NHC complexes.18 The Ag1−C1 bond distance of 2.100(5) Å is similar to those in 1. The Ag1− N5 bond distance of 2.211(4) Å is comparable to those reported for the complexes with the linear NHC−Ag−amine moiety.18 The Ag−Ag distance of 3.0969(11) Å is shorter than the sum of the van der Waals radii of Ag (3.44 Å), indicating an argentophilic interaction between the two Ag(I) centers.19 In the crystal structures of 1·CH3CN and 2·6CH3CN, intermolecular π−π stacking is found between benzimidazolium rings of adjacent cation moieties with the distance of 3.198, 3.279 (Figure S2) and 3.325 Å (Figure S3), respectively. Molecular structures of the cationic portions in 3 and 4 are shown in Figure 3, and selected structural parameters are listed

Figure 2. Molecular structures of 1 (top) and 2 (bottom). Anions, solvent molecules, and hydrogens including N−H are omitted for clarity. Thermal ellipsoids are drawn at 30% probability.

Table 1. Selected Bond Lengths (Å) and Angles (o) of 1−4 1 Ag1−C1 C1−Ag1−C21

2.098(2) 175.38(8)

Ag1−C21

2.100(2)

2 Ag1−C1 Ag1−Ag1A C1−Ag1−Ag1A

2.100(5) 3.0969(11) 92.92(14)

Ag1−N5 C1−Ag1−N5 N5−Ag1−Ag1

2.211(4) 173.66(17) 93.41 (11)

3 Au1−C1 C1−Au1−C21

2.042(4) 178.44(16) 4

Au1−C1 Au2−Cl1 C10−Au2−Cl1

2.029(9) 2.261(2) 176.4(3)

Au1−C21

Au2−C10 C1−Au1−C1A

2.044(4)

1.972(8) 177.7(4)

Figure 3. Molecular structures of 3 (top) and 4 (bottom). Solvent molecules and hydrogens including N−H are omitted for clarity. Thermal ellipsoids are drawn at 30% probability.

uncoordinated. The Ag(I) ion is coordinated by the two carbene carbon atoms in an almost linear fashion with the C1− Ag1−C21 angle of 175.38(8)o. Similar macrocyclic Ag(I)- and Au(I)-NHC complexes with uncoordinated benzimidazolium were reported by Hahn et al.5h,k,8 The Ag−C1 and Ag−C21 bond lengths are 2.098(2) and 2.100(2) Å, respectively, which are within the range reported for similar two-coordinate Ag(I)NHC complexes.5d,e,g,h Two Ag(I) ions in 2 are bound inside the cavity of one macrocyclic ligand. Two benzimidazolium units are deprotonated and coordinated to two Ag(I) ions, while the other two remain as protonated and uncoordinated.

in Table 1. Similar to the structure of 1, Au(I) is located in the cavity of the macrocyclic ligand and coordinated by two carbene carbons with a C1−Au1−C21 bond angle of 178.44(16)o. The Au1−C1 and Au1−C21 bond distances are 2.042(4) and 2.044(4) Å, which are typical for two coordinate Au-NHC complexes.5d,e,h 4 is a trinuclear Au(I) complex, in which the central Au(I) ion is coordinated by two carbene carbons with a slight distorted bond angle of 177.7(4)o, while D


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Inorganic Chemistry Scheme 3. Synthesis of the Ni(II) and Pd(II) Complexes 5−9 from (H4L)(PF6)4

Pd, 8) have been obtained (Scheme 3). Interestingly, the two secondary amines are deprotonated, and the resulting dinegative ligand L-2H is coordinated to two Ni(II) or two Pd(II) ions in the doubly bridging mode. The coordination of both NHC and amide to Ni(II) or Pd(II) is consistent with the absence of both the resonances for NCHN and NH protons previously detected in (H4L)(PF6)4. 13C NMR resonances for carbene carbons of 7 and 8 are observed at 174.26 and 179.33 ppm, respectively, comparable to those of 5 (183.20 ppm) and 6 (180.23 ppm). ESI-MS spectra show the peaks at m/z 388.33 and 921.25 for 7 and 437.25 and 1019.17 for 8 associated with [M−2PF6]2+ and [M−PF6]+ for both complexes. It is noted that few examples of dinuclear Ni(II) complexes with bridging amides are reported,20a−g while more Pd(II) analogues are known.20h−m,o−s Both 7 and 8 are stable toward air and moisture. This stability of 7 is unusual in contrast with the airsensitivity of other reported Ni(II) complexes with bridging amides.20a−g Encouraged by the novel structure of the dinuclear Ni(II) complex 7, we have proposed to prepare Ni(II) complexes featuring different structures via other metalation strategies. The transmetalation reaction using a silver NHC complex was proved to be a particularly useful route toward metal-NHC complexes,17 but has been rarely used for the synthesis of macrocyclic NHC metal complexes.5d Here, we have employed

the other two outer Au(I) ions are bound with one carbene carbon and one Cl ligand. The coordination mode of 4 is similar to the trinuclear Ag(I) complex with a macrocyclic tetracarbene ligand that was reported by Jenkins et al.5d,k Ni(II) and Pd(II) Complexes. As shown in Scheme 3, mononuclear metal complexes [M(L)](PF6)2 (M = Ni, 5; M = Pd, 6) have been prepared via the reaction of (H4L)(PF6)4 with 1.0 equiv of Ni(OAc)2 or Pd(OAc)2 in the presence of 4.0 equiv of NaOAc in DMSO at 85 °C for 12 h. 1H and 13C NMR data are consistent with their formulas. The 1H NMR resonance at 9.63 ppm for NCHN protons of (H4L)(PF6)4 is not observed in the spectra of 5 or 6. Only one 13C resonance at 183.20 and 180.23 ppm is observed for all four carbene carbon atoms in 5 and 6, respectively, and is low-field shift compared to the NCHN resonance at 142.61 ppm for (H4L)(PF6)4. The ESI-MS spectra exhibit the peaks at m/z 360.42 and 865.33 for 5 and 384.33 and 913.33 for 6, which are ascribed to [M−2PF6]2+ and [M−PF6]+. Considering that the two secondary amine groups remain uncoordinated in 5 and 6, we have envisioned that L could act as a binucleating ligand to coordinate to two Ni(II) or Pd(II) ions. In order to test this assumption, we have attempted to employ more Ni(II) or Pd(II) precursor in the reaction. With 2.1 equiv of Ni(OAc)2 or Pd(OAc)2 and 6.0 equiv of NaOAc, dinuclear metal complexes [M2(L-2H)](PF6)2 (M = Ni, 7; M = E


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Inorganic Chemistry this route to prepare the Ni(II) complex with L. Transmetalation of 2 with 2.0 equiv of Ni(PPh3)2Cl2 in acetonitrile gives a new dinuclear Ni(II) complex [Ni2(L)(μ-O)](PF6)2 (9) as a golden yellow solid in 50% yield (Scheme 3). 1H and 13C NMR spectra of 9 show that the signals for both the benzimidazole rings and the CH2 groups exhibit a significant upfield shift compared to those of 5 and 7 (SI). Moreover, the carbene carbon resonance at 173.53 ppm in 9 is similar to that in 7 (174.26 ppm). The cationic species [M−2PF6]2+ and [M− PF6]+ are detected at m/z 397.33 and 939.33, respectively, in the ESI-MS spectrum. Interestingly, 9 could be transformed into 7 in the presence of NaOAc in DMSO at 85 °C in 10 h. It is assumed that the loss of one water molecule from 9 is promoted by NaOAc in this conversion. Furthermore, the mononuclear complex 5 could also be transformed into 7 via the reaction of 5 with Ni(OAc)2. However, many attempts to obtain a dinuclear Pd complex by the reaction of 6 with Pd(OAc)2 were unsuccessful. Molecular structures of the Ni(II) and Pd(II) complexes have been determined by single crystal X-ray diffraction (Tables S3 and S4). 5 crystallizes in the tetragonal space group P43212, while 6 crystallizes in the orthorhombic space group Cmca. Structures of the cationic portions of 5 and 6 are shown in Figure 4. Selected structural parameters are listed in Table 2. The central Ni or Pd atom is coordinated to four carbene carbons and wrapped by the macrocyclic ligand L. The two secondary amine groups remain uncoordinated. The macrocyclic NHC ligand is twisted to meet the square-planar configuration. Similar macrocyclic tetraNHC−Ni and tetraNHC−Pd complexes with square-planar geometry are wellknown.5d−g The Ni−C1 and Ni−C10 bond lengths are 1.902(5) and 1.905(5) Å, respectively, which are in agreement with those found for analogous Ni-NHC complexes.5d−g,6a,9 The C1−Ni1−C1A and C10−Ni1−C10A bond angles are 176.4(3)° and 171.8(3)°, respectively. For 6, the C−Pd−C bond angle is 171.23(18) Å. The Pd−C bond lengths in the range of 2.047(4)∼2.055(4) Å are similar to the values reported in the literature.5d,e,g,i 7·2CH3CN crystallizes in the monoclinic space group P21/c (Table S4). The structure of the cationic portions of 7 is shown in Figure 5. Selected structural parameters are listed in Table 3. Two Ni(II) ions are found inside the macrocyclic ring. Each Ni(II) ion is coordinated to two carbene carbons and two bridged amides to adopt a slightly distorted square-planar geometry. Few dinuclear Ni(II) complexes with bridging amides are known.20a−g The structural parameters of these reported complexes are summarized in Table S5 and Chart S1. The central Ni(II)2N2 core exhibits either a planar or puckered conformation. The Ni−Ni distance seems to be dependent on the coordination number of the Ni(II) ion, the configuration of the Ni2N2 core, and the substituent of the amide group. Shorter Ni−Ni distances of 2.512(4) ∼ 2.751(1) Å are found for three reported examples with a puckered Ni2N2 core,20b,e,f while relatively long Ni−Ni distances are observed in the range of 2.803−3.182(8) Å for those with a planar Ni(II)2N2 core.20b−d An exception is the Ni(II)−Ni(II) distance of 2.327(2) Å in (Ph2N)Ni(μ-NPh2)2Ni(NPh2),20a which is probably due to the coordination number of three in the complex. 7 is the first example of a dinuclear Ni(II) complex with two bridging amides incorporated in a macrocyclic ligand. The Ni−Ni distance (2.8549(6) Å) in 7 is significantly longer than those in (Ph2N)Ni(μ-NPh2)2Ni(NPh2) (2.327(6) Å)20a and the complexes containing a puckered Ni(II)2N2 core,20b,e,f but is in the

Figure 4. Molecular structures of 5 (top) and 6 (bottom). Anions and hydrogens including N−H have been omitted for clarity. Ellipsoids are drawn at 30% probability.

Table 2. Selected Bond Lengths (Å) and Angles (deg) of 5 and 6 M−C1 M−C10 C1−M−C1A C10−M−C10A C1−M−C10 C1−M−C10A

5

6

1.902(5) 1.905(5) 176.4(3) 171.8(3) 81.9(2) 97.8(2)

2.049(3) 2.055(4) 96.4(3) 95.7(3) 83.27(19) 171.35(18)

range (2.803(15) ∼ 3.1818(8) Å) reported for the complexes with a planar Ni2N2 core.20b−d The average Ni−N bond length of 1.95 Å is within the range of 1.898(9) ∼ 2.277(3) Å reported for the dinuclear Ni(II) complexes with bridging amides.20 The Ni−C bond lengths of 1.844(2) and 1.885(18) Å in 7 are consitent with those reported for Ni(II)-NHC complexes.5d−g,6a,9 Unfortunately, only poor quality data was obtained for the X-ray crystal structure of 8, but the atom connectivity was definitely determined, showing that the structure of 8 is similar to that of 7 (Figure S4). Complex 9 crystallizes in the monoclinic space group C2/m (Table S4). In 9, two Ni(II) ions are singly bridged by one oxo group. Each Ni(II) ion is further coordinated by two carbene F


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es,21a−e but longer than those (1.76(3)∼1.870(8) Å) in dinuclear bridged-oxo Ni(III)-complexes,21c−f except one Ni(III)−O bond (1.888(6) Å) in [Ni2(O)2(Me3-tpa)2](BF4)2· 6MeOH.21d The Ni−O−Ni linkage is bent in 9, exhibiting an angle of 125.2(3)o. The Ni−Ni distance of 3.329(6) Å is significantly longer than that observed in 7 (2.855(6) Å). C1− Ni−N5 and C10−Ni−O1 bond angles are 173.1(2)o and 170.6(2)o, respectively. The Ni−C bond length in 9 is 1.864(6), comparable to those in 7 (Table 3). The ESI-MS and X-ray diffraction studies have confirmed the assignment of the bridging atom as oxygen. However, the origin of the oxygen atom remains unclear. To investigate the source of the oxygen atom in 9, we have repeated this synthetic reaction under high-purity N2 (≥99.999%) atmosphere after careful drying and purification of all solvents, reagents, and glassware. 9 is still obtained. The possible source of oxygen could be the residual water in the starting materials, solvent or the surface of the glassware, which is not completely removed. If the bridging oxygen is from water, the amount of water necessary to make 15 mg (0.014 mmol) of 9 is calculated to be only 0.24 mg (0.24 μL). We have performed the synthesis of 9 by addition of excess 18O-enriched water (20 equiv or 50 equiv in 5 mL of dry acetonitrile). In this case, both 16O- and 18Oenriched water molecules are present in the reaction mixture. The analysis by ESI-MS of the as-obtained product shows that the intensities of 397.33 and 939.33 peaks for 16O-enriched [M−2PF6]2+ and [M−PF6]+ decreased, while those of 398.33 and 941.25 peaks for 18O-enriched [M−2PF6]2+ and [M−PF6]+ species increased (Figure S5). These results demonstrate that the bridging oxo ligand in 9 is indeed from the residual water.22 The redox properties of Ni(II) and Pd(II) complexes have been studied by cyclic voltammetry in acetonitrile solution and referenced to the ferrocenium/ferrocene redox couple (Fc+/0). The results demonstrate that 5, 6, and 8 are redox inactive. As shown in Figure 7, 7 exhibits a reverse wave with E1/2 = 0.236 V

Figure 5. Molecular structure of 7. Anions, solvent molecules, and hydrogens have been omitted for clarity. Ellipsoids are drawn at 30% probability.

Table 3. Selected Bond Lengths (Å) and Angles (o) of 7 and 9 7 Ni1−C1 Ni1−C10 Ni1−N5 Ni1−N5A Ni1−NiA C1−Ni1−N5 C10−Ni1−N5A N5−Ni1−N5A Ni1−N5−Ni1 C10−Ni1−C1 C10−Ni1−N5 C1−Ni1−N5A

1.8847(18) 1.844(2) 1.9451(16) 1.9590(16) 2.8549(6) 165.78(8) 175.05(7) 86.02(7) 93.98(7) 90.90(8) 89.33(7) 93.20(7)

9 Ni1−C1 Ni1−C10 Ni1−N5 Ni1−O1 Ni1−Ni1A C1−Ni1−N5 C10−Ni1−O1 Ni1−O1−Ni1A C1−Ni1−O1 C10−Ni1−C1 C10−Ni1−N5 N5−Ni1−O1

1.864(6) 1.864(6) 1.973(5) 1.875(2) 3.329(6) 173.1(2) 170.6(2) 125.2(3) 89.01(19) 92.0(2) 92.7(2) 87.21(16)

carbon atoms and one amine nitrogen atom to adopt the slightly distorted square-planar configuration (Figure 6). This

Figure 7. Cyclic voltammograms of 7 in acetonitrile containing 0.1 M NBu4ClO4. Scan rate = 0.1 V·s−1. Figure 6. Molecular structure of 9. Anions and hydrogens including N−H are omitted for clarity. Ellipsoids are drawn at 30% probability.

versus Fc+/0. It is fully reversible for at least 16 cycles with the scan rate increasing from 0.025 to 0.5 V/s (Figure S6). Moreover, the E1/2 value does not change with the scan rate. The peak separation ΔEp is 72 mV for 7, and very close to 68 mV for Fc+/0, which is also independent of the scan rate. These results show that 7 undergoes a reversible one-electron redox process which is associated with the Ni(III)Ni(II)/Ni(II)Ni(II) redox couple. 9 undergoes an irreversible reduction at −1.79 V, followed by an irreversible oxidation at −0.50 V vs Fc+/0 in the reverse scan (Figure S7).

Ni(II)(μ-O)Ni(II) core is highly unusual. To the best of our knowledge, no example of a dinuclear Ni(II) complex with a bridging oxo group has been reported. The assignment of the bridging atom as oxo, rather than hydroxo, is based on the following two points. First, it is based on the charge balance with two Ni(II) ions and two PF6− anions. Second, the Ni−O1 bond length of 1.875(3) Å in 9 is much shorter than those (1.964(3)∼2.128(2) Å) in Ni(II)-bridging hydroxo complexG


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Inorganic Chemistry

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(H4L)(PF6)4: 4.11 g (3.30 mmol, 94% yield). 1H NMR (DMSO-d6, 400 MHz): δ 9.63 (s, 4 H, NCHN), 8.10 (d, J = 8 Hz, 4 H, bzim), 7.97 (d, J = 8 Hz, 4 H, bzim), 7.64−7.77 (m, 8 Hz, bzim), 5.06 (br, 8 H, bzimCH2CH2bzim), 4.45 (br, 8 H, bzimCH2CH2NH), 2.96 (br, 8 H, bzimCH2CH2NH), 2.24 (br, 2 H, NH). 13C NMR (DMSO-d6, 100 MHz): δ 142.61 (NCN), 131.14 (bzim), 130.96 (bzim), 126.96 (126.96) (bzim), 113.88 (bzim), 113.30 (bzim), 46.86 (bzimCH2CH2bzim), 46.23 (bzimCH2CH2NH), 45.56 (bzimCH2CH2NH). Anal. Calcd for C40H46N10F24P4: C, 38.54; H, 3.72; N, 11.23. Found: C, 38.27; H, 3.98; N, 11.15%. ESI-MS: m/z 478.25 [M−2PF6]2+, 955.33 [M−2PF6]+, 1101.25 [M−PF6]+. (H4L)(OTf)4: 3.86 g (3.05 mmol, 87% yield). 1H NMR (DMSO-d6, 400 MHz): δ 9.48 (s, 4 H, NCHN), 8.11 (d, J = 8 Hz, 4 H, bzim), 7.99 (d, J = 8 Hz, 4 H, bzim), 7.62−7.79 (m, 8 Hz, bzim), 5.05 (br, 8 H, bzimCH2CH2bzim), 4.48 (br, 8 H, bzimCH2CH2NH), 2.99 (br, 8 H, bzimCH2CH2NH), 2.23 (br, 2 H, NH). 13C NMR (DMSO-d6, 100 MHz): δ 142.52 (NCN), 131.13 (bzim), 130.92 (bzim), 126.92 (126.92) (bzim), 121.1 (q, JF−C = 320 Hz, CF3), 113.89 (bzim), 113.28 (bzim), 46.82 (bzimCH2CH2bzim), 46.30 (bzimCH2CH2NH), 45.56 (bzimCH2CH2NH). Anal. Calcd for C44H46N10F12O12S4: C, 41.84; H, 3.67; N, 11.09. Found: C, 41.79; H, 3.88; N, 10.86%. Synthesis of 1·CH3CN and 2·6CH3CN. A mixture of (H4L)(PF6)4 (100 mg, 0.08 mmol) and Ag2O (0.08 or 0.20 mmol) in acetonitrile (5 mL) was stirred in the absence of light for 24 h. Then, the mixture was filtered. Vapor diffusion of ether into the filtrate gave colorless crystals. 1·CH3CN: 64 mg (0.053 mmol, 66% yield). 1H NMR (CD3CN, 400 MHz): δ 8.35 (s, 2 H, NCHN), 7.87 (d, J = 8 Hz, 2 H, bzim), 7.56−7.80 (m, 10 H, bzim), 7.38 (d, J = 8 Hz, 2 H, bzim), 7.21 (t, J = 8 Hz, 2 H, bzim), 4.72 (br, 4 H, CH2), 3.90−4.45 (br+br, 12 H, CH2), 2.85−3.15 (br+br, 8 H, CH2), 1.39 (br, 2 H, NH). 13C NMR (CD3CN, 100 MHz): δ 187.88 (d, JAg−C = 196 Hz, NCN), 141.98 (NCHN), 134.51 (d, JAg−C = 5 Hz, bzim), 133.46 (d, JAg−C = 6 Hz, bzim), 132.69 (bzim), 131.15 (bzim), 128.34 (bzim), 127.46 (bzim), 125.69 (bzim), 125.51 (bzim), 115.20 (bzim), 113.00 (bzim), 112.79 (bzim), 112.51 (bzim), 50.28 (CH2), 48.56 (CH2), 48.32 (CH2), 47.60 (CH2), 47.08 (CH2), 47.04 (CH2). Anal. Calcd for C40H44N10AgP3F18 (1): C, 39.78; H, 3.67; N, 11.60. Found: C, 40.01; H, 3.75; N, 11.39%. ESI-MS: m/z 459.25 [M−2PF6]2+, 1063.25 [M−PF6]+ 2·6CH3CN: 90 mg (0.062 mmol, 77% yield). Anal. Calcd for C40H44N10Ag2P4F24 (2): C, 32.90; H, 3.04; N, 9.59. Found: C, 33.17; H, 3.15; N, 9.76. ESI-MS: m/z 439.25 [M−4PF6]2+, 1023.08 [M− 3PF6]+. Synthesis of 3·2CH3CN and 4·2CH3CN. Compound 1 or 2 (0.066 mmol), AuCl(SMe2) (0.066 or 0.198 mmol) and CH3CN (5 mL) were added to a flask. The mixture was stirred at room temperature for 12 h and was filtered. Vapor diffusion of ether into the filtrate gave colorless crystals. 3·2CH3CN. 42 mg (0.033 mmol, 49.6% yield). 1H NMR (CD3CNd6, 400 MHz): δ 8.16 (s, 2 H, NCHN), 7.74−7.96 (m, 8 H, bzim), 7.60−7.72 (m, 4 H, bzim), 7.41 (d, J = 8 H, 2 H, bzim), 7.21 (t, J = 8 H, 2 H, bzim), 4.71 (br, 4H, CH2), 3.75−4.48 (m, 12 H, CH2), 3.12 (br, 4 H, CH2), 2.98 (br, 4 H, CH2), 1.49 (br, 2 H, NH). 13C NMR (CD3CN-d3, 100 MHz): δ 189.42 (NCN), 141.98 (NCHN), 133.85 (bzim), 133.27 (bzim), 132.99 (bzim), 131.27 (bzim), 128.47 (bzim), 126.96 (bzim), 126.17 (bzim), 125.98 (bzim), 116.31 (bzim), 113.28 (bzim), 112.87 (bzim), 112.64 (bzim), 49.26 (CH2), 48.86 (CH2), 48.82 (CH2), 47.80 (CH2), 46.78 (CH2), 46.60 (CH2). Anal. Calcd for C40H44N10AuP3F18 (3): C, 37.05; H, 3.42; N, 10.80. Found: C, 37.24; H, 3.18; N, 10.69%. ESI-MS: m/z 503.33 [M−2PF6]2+, 1151.42 [M− PF6]+. 4·2CH3CN. 31 mg (0.021 mmol, 32% yield). 1H NMR (DMSO-d6, 400 MHz): δ 8.04 (d, J = 8 Hz, 2 H, bzim), 7.93 (d, J = 8 Hz, 2H, bzim), 7.83 (d, J = 8 Hz, 2 H, bzim), 7.44−7.62 (m, 6 H, bzim), 7.29 (d, J = 8 Hz, 2 H, bzim), 6.90 (t, J = 8 Hz, 2 H, bzim), 4.78 (d, J = 16 Hz, 2 H, CH2), 4.37−4.54 (m, 8 H, CH2), 4.23 (d, J = 16 Hz, 2 H, CH2), 4.00−4.11 (m, 2 H, CH2), 3.62 (t, J = 16 Hz, 2 H, CH2), 2.72− 3.14 (m, 8 H, CH2), 2.23 (br, 2 H, NH). 13C NMR (DMSO-d6, 100 MHz): δ 189.27 (NCN), 177.30 (NCNAuCl), 134.53 (bzim), 132.73 (bzim), 132.19 (bzim), 131.64 (bzim), 124.70 (bzim), 124.56 (bzim), 124.54 (bzim), 123.00 (bzim), 114.06 (bzim), 113.27 (bzim), 111.41

CONCLUSIONS Nine new metal complexes 1−9 have been prepared with a macrocyclic diamine-tetracarbene ligand precursor. The metal ions adopt a linear configuration in the Ag(I) and Au(I) complexes, while the metal ions take a square-planar configuration in the Ni(II) and Pd(II) complexes. The two metal(II) ions in 7 and 8 are bridged by two amides. 9 is the first example of a dinuclear Ni(II) complex with a bridging oxo group. The oxygen in 9 is from residual water as revealed by the experiments with 18O-enriched water. The various structures of these metal complexes show rich coordination chemistry of this hexadentate macrocyclic diamine-tetraNHC ligand.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were performed under dry nitrogen, using standard Schlenk techniques unless otherwise stated. Acetonitrile was dried over CaH2 and distilled under nitrogen before use. All other solvents and chemicals are commercially available and were used as received without further purification. The starting materials N-bis[(benzimidazol-1-yl)ethyl]-4-methylbenzenesulfonamide (a)15 and ethane-1,2-ditosylate (b)16 (Scheme 1) were prepared according to the literature procedures. NMR spectra were recorded on a Bruker Avance 400 MHz (1H, 400 MHz; 13C, 100 MHz) spectrometer at 298 K. Elemental analyses (C, H, and N) were carried out on a PerkinElmer 240C analytic instrument. Mass spectra were measured with ESI-MS (LCQ Fleet, Thermo Fisher Scientific). The cyclic voltammograms (CV) were recorded on a potentiostat/ galvanostat Model 263A in acetonitrile solutions containing 0.1 M NBu4ClO4 as supporting electrolyte. Platinum and glassy graphite were used as counter and working electrodes, respectively, and the potential measured against the Ag/AgCl reference electrode. The potential measured was always referenced to the half-wave potentials of the ferrocenium/ferrocene couple (E1/2 = 0). Synthesis of c. Ethane-1,2-ditosylate (b) (4.01 g, 10.83 mmol) in acetonitrile (60 mL) was added dropwise to a stirred solution of a (5.0 g, 10.83 mmol) in acetonitrile (60 mL). The mixture was refluxed for 3 days to give a white precipitate. After the precipitate was cooled to room temperature, it was collected and washed with acetone to give c as a white solid (2.2 g, 1.33 mmol, 24.5% yield). 1H NMR (DMSO-d6, 400 MHz): δ 9.80 (s, 4 H, NCHN), 8.05 (d, 4 Hz, bzim), 7.96 (d, 4 Hz, bzim), 7.68 (m, 8 H, bzim), 7.22−7.38 (m, 12 H, OTS and NTs), 7.05 (d, 12 H, OTS and NTs), 5.16 (br, 8 H, bzimCH2CH2bzim), 4.81 (br, 8 H, bzimCH2CH2NTs), 3.82 (br, 8 H, bzimCH2CH2NTs), 2.31 (s, 6 H, CH3), 2.27 (s, 12 H, CH3). 13C NMR (DMSO-d6, 100 MHz): δ 144.62 (Ts), 143.84 (Ts), 142.68 (NCN), 138.15 (Ts), 134.84, 130.86, 129.44, 128.16, 127.08, 126.84, 126.40, 125.32 (125.32) (bzim), 113.45 (bzim), 113.41 (bzim), 45.39 (bzimCH2CH2bzim), 45.36 (bzimCH2CH2NTs), 44.84 (bzimCH2CH2NTs), 21.06 (CH3), 20.79 (CH3). Anal. Calcd for C82H86N10O16S6: C, 59.33; H, 5.22; N, 8.44. Found: C, 59.15; H, 4.98; N, 8.48%. Synthesis of e. Compound c (5.0 g, 3.01 mmol), PhOH (1.42 g, 15.02 mmol), and 48% HBr (50 mL) were added to a flask. The mixture was stirred at 128 °C for 24 h and was then cooled to room temperature. Acetone (500 mL) was added into the mixture to precipitate a solid, which was filtered and washed with acetone to afford e as a white solid (3.1 g, 2.70 mmol, 89.7% yield). 1H NMR (DMSO-d6 and D2O (1:1), 400 MHz): δ 9.69 (s, 4 H, NCHN), 7.95 (d, J = 8 Hz, 4 H, bzim), 7.73 (t, J = 8 Hz, 4 H, bzim), 7.51−768 (m, 8 H, bzim), 5.13 (br, 8 H, bzimCH2CH2bzim), 4.75 (br, 8 H, bzimCH2CH2NH2), 3.42 (br, 8 H, bzimCH2CH2NH2). Anal. Calcd for C40H48N10Br6: C, 41.84; H, 4.21; N, 12.20. Found: C, 41.65; H, 4.39; N, 12.08%. Synthesis of (H4L)(PF6)4 and (H4L)(OTf)4. Compound e (3.5 g, 3.51 mmol), H2O (100 mL), and Et3N (1.06 g, 10.53 mmol) were added to a flask. The mixture was stirred at room temperature for 30 min. Then, NH4PF6 (2.28 g, 14.04 mmol) or NaSO3CF3 (2.42 g, 14.04 mmol) was add slowly to precipitate a white solid, which was filtered and washed with H2O to afford the product as a white solid. H


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Inorganic Chemistry

as a golden yellow solid (15 mg, 0.014 mmol, yield 50%). 1H NMR (CD3CN, 400 MHz): δ 7.96 (d, J = 8 Hz, 2 H, bzim), 7.72 (d, J = 8 Hz, 2 H, bzim), 7.67 (t, J = 8 Hz, 2 H, bzim), 7.55 (t, J = 8 Hz, 4 H, bzim), 7.25−7.42 (m, 6 H, bzim), 5.42 (dd, J = 8 and 4 Hz, 2 H, CH2), 4.91 (t, J = 12 Hz, 2 H, CH2), 4.52−4.82 (m, 6 H, CH2), 4.08−4.38 (m, 6 H, CH2), 3.94 (d, J = 12 Hz, 2 H, CH2), 3.46−3.62 (m, 2 H, CH2), 3.22−3.36 (br, 4 H, CH2), 1.80 (br, 2 H, NH). 13C NMR (CD3CN, 100 MHz): δ 173.53 (NCN), 161.92 (NCN), 136.21 (bzim), 136.09 (bzim), 134.31 (bzim), 134.19 (bzim), 125.84 (bzim), 125.40 (bzim), 125.08 (bzim), 124.64 (bzim), 113.08 (bzim), 111.56 (bzim), 111.20 (bzim), 111.00 (bzim), 53.42 (CH2), 49.06 (CH2), 47.26 (CH2), 46.79 (CH2), 46.64 (CH2), 42.64 (CH2). Anal. Calcd for C40H42N10ONi2P2F12: C, 44.23; H, 3.90; N, 12.90. Found: C, 44.11; H, 4.07; N, 13.15%. ESI-MS: m/z 397.33 [M−2PF6]2+, 939.33 [M− PF6]+. Conversion of 5 into 7. Complex 5 (50 mg, 0.049 mg), Ni(OAc)2·4H2O (14 mg, 0.049 mmol) and NaOAc (8 mg, 0.099 mmol) and DMSO (2 mL) were added to a flask. The light yellow mixture was stirred at 85 °C for 12 h. After the mixture was cooled to room temperature, it was filtered. The filtrate was poured into water (30 mL) to precipitate a crude solid, which was collected and washed with ethanol. The product was further purified by recrystallization from CH3CN/ether to afford a yellowish brown solid (48 mg, 0.045 mmol, 92% yield). Examination by 1H NMR spectra, ESI-MS, and Xray diffraction analyses confirmed the formation of 7. Conversion of 9 into 7. Complex 9 (20 mg, 0.018 mg), NaOAc (15 mg, 0.18 mmol), and DMSO (2 mL) were added to a flask. The light yellow mixture was stirred at 85 °C for 10 h to give a yellowish brown solution. After the mixture was cooled to room temperature, it was poured into water (15 mL) to precipitate a crude solid, which was filtered and washed with H2O. The product was further purified by recrystallization from CH3CN/ether to afford a yellowish brown solid. Examination by 1H NMR spectra, ESI-MS, and X-ray diffraction analyses confirmed the formation of 7. X-ray Structure Determination. X-ray diffraction data were collected on a Bruker APEX DUO diffractometer with a CCD area detector (Mo Kα radiation, λ = 0.71073 Å). Data were integrated through the SAINT.23 Absorption corrections were performed using SADABS.24 The structures were solved using SHELXS-97 and subsequently completed by Fourier recycling using SHELXL 97 program.25 All structures were solved using the direct method. Nonhydrogen atoms were refined by anisotropic displacement parameters. Crystallographic data, data collection, and refinement parameters for (H4L)(OTf)4, 1−7 and 9 are listed in Tables S1−S3 in the SI.

(bzim), 110.87 (bzim), 49.82 (CH2), 49.06 (CH2), 47.10 (CH2), 46.98 (C H 2 ), 46. 77 ( CH 2 ) , 4 5 . 5 9 ( CH 2 ) . A n a l . C al cd f o r C40H42N10Au3Cl2PF6 (4): C, 32.69; H, 2.88; N, 9.53. Found: C, 32.47; H, 3.01; N, 9.62%. ESI-MS: m/z 1323.50 [M−PF6]+. Synthesis of 5 and 6. Compound (H4L)(PF6)4 (100 mg, 0.08 mmol), Ni(OAc)2 or Pd(OAc)2 (0.08 mmol), NaOAc (26 mg,0.32 mmol), and DMSO (3 mL) were added to a flask. The mixture was stirred at 85 °C under nitrogen for 12 h. After the mixture was cooled to room temperature, it was filtered. The filtrate was poured into water (30 mL) to precipitate a solid, which was filtered and washed with H2O. The residue was dissolved in acetone (1 mL) and then passed through a short alumina plug (pipet, 8 cm, washed with acetone) to give a solid. 5. 43 mg light yellow solid (0.042 mmol, 53% yield). 1H NMR (CD3CN, 400 MHz): δ 7.55−7.64 (m, 4 H, bzim), 7.41−7.48 (m, 4 H, bzim), 7.21−7.33 (m, 8 H, bzim), 5.77−5.95 (m, 4 H, CH2), 5.43− 5.60 (m, 4 H, CH2), 5.25−5.40 (m, 4 H, CH2), 5.56 (d, J = 12 Hz, 4 H, CH2), 3.72 (t, J = 13.2 Hz, 4 H, CH2), 3.14 (d, J = 16 Hz, 4 H, CH2), 1.49 (s, 2 H, NH). 13C NMR (CD3CN, 100 MHz): δ 183.20 (NCN), 136.15 (bzim), 134.61 (bzim), 124.45 (bzim), 124.32 (bzim), 112.18 (bzim), 110.93 (bzim), 52.91 (bzimCH2CH2bzim), 50.37 (bzimCH 2 CH 2 N), 43.98 (bzimCH 2 CH 2 N). Anal. Calcd for C40H42N10NiP2F12: C, 47.50; H, 4.19; N, 13.85. Found: C, 47.26; H, 4.01; N, 13.98%. ESI-MS: m/z 360.42 [M−2PF6]2+, 865.33 [M− PF6]+. 6. 38 mg white solid (0.036 mmol, 45% yield). 1H NMR (DMSOd6, 400 MHz): δ 7.78 (d, J = 8 Hz, 4 H, bzim), 7.67 (d, J = 8 Hz, 4 H, bzim), 7.22−7.40 (m, 8 H, bzim), 5.48−5.65 (m, 4 H, CH2), 5.26− 5.43 (m, 8 H, CH2), 4.48 (d, J = 12 Hz, 4 H, CH2), 3.59 (br, 4 H, CH2), 2.98 (d, J = 12 Hz, 4 H, CH2), 2.17 (br, 2 H, NH). 13C NMR (CD3CN, 100 MHz): δ 180.23 (NCN), 135.74 (bzim), 134.13 (bzim), 124.72 (bzim), 124.60 (bzim), 112.48 (bzim), 112.31 (bzim), 52.88(CH 2 ), 50.85 (CH 2 ), 43.98 (CH 2 ). Anal. Calcd for C40H42N10P2F12Pd: C, 45.36; H, 4.00; N, 13.22. Found: C, 45.48; H, 4.13; N, 13.43%. ESI-MS: m/z 384.33 [M-2PF6]2+, 913.33 [MPF6]+. Synthesis of 7 and 8. Compound (H4L)(PF6)4 (100 mg, 0.08 mmol), Ni(OAc)2·4H2O or Pd(OAc)2 (0.17 mmol), NaOAc (40 mg, 0.48 mmol), and DMSO (3 mL) were added to a flask. The mixture was stirred at 85 °C under nitrogen for 12 h. After the mixture was cooled to room temperature, it was filtered. The filtrate was poured into water (30 mL) to precipitate a solid, which was filtered and washed with H2O. The crude product was further purified by recrystallization from CH3CN/ether to afford a solid. 7. 74.3 mg yellowish brown solid (0.069 mmol, 86.6% yield). 1H NMR (CD3CN, 400 MHz): δ 7.54−7.62 (d, J = 8 Hz, 4 H, bzim), 7.48−7.54 (d, J = 8 Hz, 4 H, bzim), 7.34−7.46 (m, 8 H, bzim), 5.30− 5.46 (m, 4 H, CH2), 4.71−4.84 (m, 4 H, CH2), 4.48−4.63 (m, 8 H, CH2), 4.18−4.34 (m, 4 H, CH2), 2.42−2.56 (m, 4 H, CH2). 13C NMR (CD3CN, 100 MHz): δ 174.26 (NCN), 134.98 (bzim), 134.60 (bzim), 124.70 (bzim), 124.50 (bzim), 111.29 (bzim), 110.90 (bzim), 48.11 (bzimCH2CH2bzim), 45.28 (bzimCH2CH2N), 44.20 (bzimCH2CH2N). Anal. Calcd for C40H40N10Ni2P2F12: C, 44.98; H, 3.77; N, 13.11. Found: C, 45.21; H, 4.04; N, 13.17%. ESI-MS: m/z 388.33 [M−2PF6]2+, 921.25 [M−PF6]+. 8. 30 mg white solid (0.026 mmol, 32% yield). 1H NMR (CD3CN, 400 MHz): δ 7.64−7.70 (m, 4 H, bzim), 7.55−7.61 (m, 4 H, bzim), 7.43−7.54 (m, 8 H, bzim), 5.19−5.31 (m, 4 H, CH2), 4.76−5.88 (m, 4 H, CH2), 4.35−4.55 (m, 12 H, CH2), 3.08−3.22 (m, 4 H, CH2). 13C NMR (DMSO-d6, 100 MHz): δ 179.33 (NCN), 133.85 (bzim), 133.68 (bzim), 124.36 (bzim), 124.12 (bzim), 111.28 (bzim), 111.19 (bzim), 49.47 (CH2), 45.51 (CH2), 43.43 (CH2). Anal. Calcd for C40H40N10P2F12Pd2: C, 41.29; H, 3.47; N, 12.04. Found: C, 41.16; H, 3.25; N, 12.17%. ESI-MS: m/z 437.25 [M-2PF6]2+, 1019.17 [M-PF6]+. Synthesis of 9. Complex 2 (40 mg, 0.027 mmol), NiCl2(PPh3)2 (35 mg, 0.053 mmol), and CH3CN (5 mL) were added to a flask. The mixture was stirred at room temperature under nitrogen for 5 h and then filtered. The filtrate was poured into ether (30 mL) to precipitate a solid. The solid was dissolved in acetonitrile and then passed through a short alumina plug (pipet, 8 cm, washed with acetonitrile) to give 9

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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.inorgchem.7b01896. Table for the summary of crystal data and refinement; bond parameters; table for structural parameters for dinuclear Ni(II)-amide complexes; NMR spectra; additional structural data (PDF) Accession Codes

CCDC 1547653−1547657, 1561206, 1561208−1561209, and 1561215 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 data_ [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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Corresponding Author

*E-mail: [email protected]. I


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Xue-Tai Chen: 0000-0001-5518-5557 Zi-Ling Xue: 0000-0001-7401-9933 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support from the Natural Science Grant of China (No. 21471078 to XTC), the National Basic Research Program of China (No. 2013CB922102 to XTC), and the US National Science Foundation (CHE1633870 to ZLX).

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