Cyclometallated gold(III) complexes with a trithiacrown ligand: Solventless Au(III) cyclometallation, intramolecular gold–sulfur interactions, and fluxional behavior in 1,4,7-trithiacyclononane Au(III) complexes

Journal of Organometallic Chemistry 755 (2014) 47e57

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Cyclometallated gold(III) complexes with a trithiacrown ligand: Solventless Au(III) cyclometallation, intramolecular goldesulfur interactions, and fluxional behavior in 1,4,7-trithiacyclononane Au(III) complexes Daron E. Janzen a, *, Shannon R. Doherty a, Donald G. VanDerveer b, Lindsay M. Hinkle c, Desirée A. Benefield d, Hitesh M. Vashi d, Gregory J. Grant d, ** a

Department of Chemistry and Biochemistry, #4282, St. Catherine University, St. Paul, MN 55105, USA Department of Chemistry, Clemson University, USA c Department of Chemistry, University of Minnesota, USA d Department of Chemistry, The University of Tennessee at Chattanooga, TN 37403, USA b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 December 2013 Accepted 26 December 2013

We report the synthesis and characterization for several gold(III) complexes involving a series of cyclometallating ligands. These cyclometallating ligands (C^N) are: 2-phenylpyridine (ppy), 2-(p-tolyl) pyridine (tpy), 2-(20 -benzothienyl)pyridine (btp) and 7,8-benzoquinoline (bzq). With the assistance of TGA data, we have developed solventless reactions to prepare the neutral cyclometallated Au(III) dichloro complexes. Reaction of these with the crown trithioether [9]aneS3 (1,4,7-trithiacyclononane), followed by metathesis with NH4PF6, yields the heteroleptic complexes [Au([9]aneS3)(C^N)](PF6)2. The X-ray structures of the gold(III) [9]aneS3 complexes display axial AueS interactions formed by the endodentate conformation of the thiacrown, resulting in elongated square pyramidal geometries. The AueS axial distance correlates with the electron-donating properties of the C^N ligand with the better donating btp showing the longest distance (2.855(1)  A) while the ppy shows the shortest (2.818(1)  A). The coordinated [9]aneS3 ligand shows fluxional behavior by its NMR spectroscopy, resulting in a single 13C NMR resonance despite the asymmetric coordination environment of the cyclometallating ligand. Electrochemical studies of the [9]aneS3 complexes reveal irreversible one-electron reductions which are assigned as a Au(III)/Au(II) couple. The ease of reduction correlates with the axial AueS distances with the btp being the easiest to reduce and the ppy the most difficult. In addition, we report the crystal structures for three intermediate complexes: [Au(H-tpy)Cl3], [Au(H-btp)Cl3], and [Au(btp)Cl2]. The [Au(H-btp)Cl3] complex shows an interesting AueS axial interaction at 3.139(2)  A which alters the physicochemical properties of the complex. Ó 2014 Elsevier B.V. All rights reserved.

Keywords: 1,4,7-Trithiacyclononane Gold complexes Cyclometallating ligands Crystal structures Cyclic voltammetry pep stacking

1. Introduction Gold(III) complexes involving cyclometallating ligands such as 2-phenylpyridine (ppy) (see Scheme 1) and 2-((dimethylamino) methyl)phenyl (damp) have been identified as potential alternatives to cis-platin in cancer chemotherapy [1e4]. These Au(III) complexes are similar to cis-platin, both electronically and stereochemically, and offer promise as novel anti-tumor agents. A

* Corresponding author. Tel.: þ1 651 690 6047; fax: þ1 651 690 8657. ** Corresponding author. Tel.: þ1 423 821 5675; fax: þ1 423 425 5234. E-mail addresses: [email protected] (D.E. Janzen), [email protected] (G. J. Grant). 0022-328X/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jorganchem.2013.12.048

comprehensive review of all cyclometallated complexes of gold(III) has appeared [5]. Our group has previously reported on cyclometallated complexes involving the isoelectronic metal ions Pd(II) and Pt(II) with the thiacrown ligand, 1,4,7trithiacyclononane ([9]aneS3) [6,7]. In its extensive coordination chemistry with these two d8 metal ions, the [9]aneS3 ligand shows interesting long distance metalesulfur axial interactions that are sensitive to the electronic effects of ancillary ligands present [8]. In addition, the Pd(II) complexes of ppy and the related cyclometallating ligand 7,8-benzoquinoline (bzq) demonstrated electrochemical evidence for the stabilization of the unusual Pd(III) oxidation state, the first observation of this in a heteroleptic [9]aneS3 complex [6].

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2. Results and discussion

C

N

N

C

ppy

2.1. Syntheses

tpy

The preparation of a cyclometallated gold(III) complex with [9] aneS3 involves three general steps as shown in Scheme 2. First, the direct combination of [AuCl4] in water and the potentially cyclometallating ligand in acetonitrile produces an immediate precipitate of the trichloro gold(III) complex. The initial Au(III) complex contains the protonated (neutral) form of the ligand as a monodentate ligand coordinated via the nitrogen atom. These types of complexes are subsequently referred to as the “dangler” complexes. In the second step, cyclometallation is achieved using a solid-state thermal reaction whereby loss of one HCl molecule produces the Au(III) dichloro complex now containing a bidentate anionic cyclometallating ligand. Once the Au(III) cyclometallated complex has been prepared, displacement of the remaining two chloride ligands by the [9]aneS3 results in the heteroleptic thiacrown cyclometallated complex. In general, a direct thermal reaction of this complex with [9]aneS3 in nitromethane, followed by metathesis to a hexafluorophosphate salt yields the desired gold(III) product. The original synthesis of the cyclometallated complex [Au(ppy] Cl2] was reported in 1989 [13]. Although the synthesis of the precursor “dangler” complex [Au(H-ppy)Cl3] proceeds smoothly, there are some problems in the published thermal cyclometallation reaction as noted by Eisenberg and co-workers [14]. Indeed, we have found that the original report of reflux in MeCN/water for 3 h will work only intermittently, a result of the temperature for the required CeH bond activation being too low. Employing the thermochemical data that appeared in Eisenberg’s report, we have successively employed a programmed muffle furnace to achieve consistent and controlled CeH bond activation in the solventless cyclometallation with ppy and several related gold(III) complexes. We would note, however, that the strength of the CeH bond varies from complex to complex depending upon the nature of the cyclometallating ligand involved, and this feature will necessitate widely varying heating conditions. Heating temperatures range from as low as 50 up to 200  C, and the length of heating can vary

S C

N

C

btp

N bzq

Scheme 1. Structures of cyclometallating ligands discussed in this paper.

Gold complexes with [9]aneS3 also exhibit similar unusual characteristics. Schröder and co-workers have reported the crystal structure of a rare mononuclear gold(II) complex, [Au([9] aneS3)2]2þ, a result of two AueS axial interactions [9e11]. The related Au(III) and Au(I) bis [9]aneS3 complexes were also generated and structurally characterized to complete a series of homoleptic complexes involving three Au oxidation states. One of our goals in extending gold thiacrown chemistry to cyclometallating ligands is to see if similar stabilizations of the remarkable gold(II) oxidation state might also be obtained, as was the case for our observations of Pd(III) in [9]aneS3 complexes with ppy and bzq [6]. Furthermore, as was true for Pt(II) and Pd(II) thiacrown complexes, the distance of the gold-sulfur axial interaction should serve as an excellent structural probe and provide comparisons among an assortment of cyclometallating ligands regarding their electronic affects, a useful feature in the design of potential anti-cancer drugs [8]. Lastly, our group has identified three types of intermolecular pep stacking interactions that are observed in Pt(II) and Pd(II) [9] aneS3 complexes with diimine ligands such as bipy and phen as well as cyclometallating complexes [6,12]. We were interested to see if similar stacking arrangements would occur in these related isoelectronic gold complexes. We include for our study the following four cyclometallating ligands and their gold(III) complexes: 2-phenylpyridine (ppy), 2-(p-tolyl)pyridine (tpy), 2-(20 benzothienyl)pyridine (btp), and 7,8-benzoquinoline (bzq) (see Scheme 1 for structures).

N

Cl N

Cl Cl

Au

N

H2O/ MeCN

Au

Cl

Cl

KAuCl4

Cl

Cl

heat

N

no solvent

Au Cl 2+

N

Cl

1 eq. [9]aneS3

Cl

CH3NO2 reflux

S

ex. NH4PF6

S

Au reflux

N

Au

2 PF6-

S

[Au([9]aneS3)(ppy)](PF6)2 Scheme 2. Three general synthetic steps in the preparation of Au(III) [9]aneS3 complexes with cyclometallating ligands. Gold complexes with ppy are shown.

D.E. Janzen et al. / Journal of Organometallic Chemistry 755 (2014) 47e57

49

by as much as 24 h. TGA analytical data (see S1 Experimental Supplemental information) have proven beneficial in identifying the correct thermochemical conditions employed for CeH bond activation in these gold cyclometallated complexes [15e17]. In a related work, Tilset, Heyn and co-workers have recently reported the novel use of microwave methods in the synthesis of several Au(III) cyclometallated complexes along with corresponding TGA data [18]. A successful cyclometallation is typically indicated by a distinct color change from the bright orange/yellow characteristic of the “dangler” to the dull yellow/brown of the cyclometallated gold complex. For the third and final step in the syntheses, the reaction of the [Au(C^N)Cl2] complexes with [9]aneS3 proceeds readily by thermolysis in nitromethane, followed by metathesis to the hexafluorophosphate salt. The exception is the [9]aneS3 reaction with [Au(btp)Cl2]. Due to the ease of reduction of the Au(III) center to Au(II), the btp reaction had to be carried out at room temperature. 2.2. Spectroscopy Proton NMR spectra for all gold(III) trichloro “dangler” complexes, their cyclometallated complexes, and the corresponding [9] aneS3 complexes show the correct number of peaks, peak intensities, and splitting patterns. Their 13C NMR spectra are similarly consistent, and DEPT spectra confirm proton connectivity. The synthetic products in all three steps are conveniently monitored using 1H NMR spectroscopy. Due to the asymmetry of these cyclometallating ligands, complex proton NMR spectra in the aromatic region is observed. Cyclometallation is confirmed through the loss of one of the ligand methine protons, typically the one most downfield in the “dangler” complex (See S2 in Experimental Supplemental information). DEPT 13C NMR spectroscopy also proves useful as one methine carbon resonance in the “dangler” complex will be converted to a quaternary carbon during cyclometallation. Complexation of the gold center by the [9]aneS3 ligands is confirmed using NMR spectroscopy, The coordinated [9]aneS3 ligand displays its characteristic AA0 BB0 pattern for the proton NMR spectrum and a single resonance in its 13C carbon NMR spectrum [8]. To our knowledge, this is the first demonstration of fluxional behavior of the [9]aneS3 ligand on a gold center. The fluxionality has been previously observed in complexes with the related d8 Pt(II) and Pd(II) ions. We note that the fluxional process makes all six methylene carbons of the [9]aneS3 equivalent despite the asymmetric NeC donor environment of the cyclometallating ligand. All resonances for both the [9]aneS3 and cyclometallating ligands are shifted downfield compared to the related Pt(II) and Pd(II) complexes, consistent with the higher cationic charge of the gold [6]. Representative 1H and 13C NMR spectra for the complex [Au([9]aneS3)(tpy)](PF6)2 are presented in Fig. 1. We have measured the electronic spectra for the three [9]aneS3 complexes in acetonitrile. We assign the high energy bands observed in the 215e300 nm range as ligand centered pep* transitions, and the lower energy features (300e400 nm) as metal-toligand charge transfer bands, based upon their wavelengths and reduced molar absorptivities. Consistent with the assignment as MLCT bands, we note that these bands occur at higher energy in the cyclometallated [9]aneS3 Au(III) complexes compared to related ones with Pt(II) and Pd(II) [6]. 2.3. X-ray structures A summary of data collection and refinement for seven structures, 1c, 2a, 2c and the btp ligand, 3a, 3b, and 3c, are presented in Tables 1 and 2, respectively. While comparison of free ligand

Fig. 1. Top. 1H NMR spectrum of [Au([9]aneS3)(tpy)](PF6)2 (2c) in CD3NO2. Inset shows aliphatic region. No resonances are present between 3.90 and 7.40 ppm. Bottom. 13C NMR spectrum of [Au([9]aneS3)(tpy)](PF6)2 in CD3NO2. Inset shows aliphatic region. Note AA0 BB0 splitting of [9]aneS3 in proton spectrum. No resonances are present between 35 and 120 ppm.

structural features with cyclometallated derivatives would be helpful, the free ligands 2-phenylpyridine and 2-tolylpyridine are liquids at room temperature. No efforts were made to crystallize these free ligands at low temperatures. 2.3.1. Structure of the ligand btp For comparison of ligand changes upon cyclometallation, the structure of the free ligand btp was collected. An anisotropic thermal displacement ellipsoid diagram of btp is displayed in Fig. S3 in the Experimental Supplemental information. Several features of this btp structure are notable. The pyridine and benzothiophene rings are nearly planar. This is evident from the N1eC5eC6eS1 torsion angle of 3.3(2) as well as the 7.7 angle between least squares planes formed from the pyridine ring (N1, C1eC5) and the benzothiophene moiety (S1, C6eC13). The relative orientation of the pyridine and thiophene rings is cisoid. The bond lengths C7eC8 (1.440(4)  A, slightly longer than the aromatic CeC bonds of the fused phenyl ring) and C6eC7 (1.353(4)  A, slightly shorter than aromatic CeC bonds of the fused phenyl ring) are consistent with conjugation of the thiophene carbons with the fused phenyl ring. There are several close CeH/p edge to face intermolecular interactions with close atom contacts under the van der Waals radii sum (2.720  A, C9eH9/C5 (1/2 þ x, 1/2  y, 1  z); 2.898  A, C9e

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Table 1 Crystal data, data collection, and refinement parameters for [Au([9]aneS3)(ppy)](PF6)2 (1c), Au(tpy)Cl3 (2a), [Au([9]aneS3)(tpy)](PF6)2 (2c). Compound

1c

2a

2c

Formula Habit, color Lattice type Space group a,  A b,  A c,  A a, deg b, deg g, deg V,  A3 Z Temperature (K) Fwt., g mol1 Dc, Mg m3 m, mm1 Reflections collected Unique reflections

C17H20AuF12NP2S3 Plate, yellow Triclinic P-1 10.2935(8) 10.6969(10) 10.8088(10) 84.736(6) 87.702(4) 85.893(5) 1181.41(18) 2 168(2) 821.43 2.309 6.731 10,027 4641 (Rint ¼ 0.0471) 1.0000, 0.3689

C12H11AuCl3N Needle, yellow Orthorhombic Pna21 8.0610(6) 26.803(20) 6.4157(5) 90 90 90 1386.16(18) 4 173(2) 472.53 2.264 11.167 8755 2920 (Rint ¼ 0.0232) 0.3476, 0.0715

C18H22AuF12NP2S3 Plate, orange Monoclinic P21/c 15.6921(13) 14.4210(12) 11.0760(9) 90 91.1970(10) 90 2505.9(4) 4 173(2) 835.45 2.214 6.349 23,872 5809 (Rint ¼ 0.0318) 0.7419, 0.1435

4641/0/325

2920/1/155

5809/0/335

0.0366, 0.0344 0.0863, 0.0841 1.060 1.780, 2.016

0.0216, 0.0492 0.0234, 0.0499 1.006 0.689, 1.616

0.0312, 0.0785 0.0359, 0.0811 1.044 4.285, 1.447

Max., min. transmission Data, restraints, parameters R1, wR2 (I > 2s(I)) R1, wR2 (all data) Goodness-of-fit (F2) Largest diff. peak, hole, e A3

H9/C6 (1/2 þ x, 1/2  y, 1  z); 2.887  A, C12eH12/C11 (1/ 2 þ x, 1/2  y, 1  z); 2.809  A, C12eH12/C12 (1/2 þ x, 1/2  y, 1  z); 2.886  A C12eH12/C13 (1/2 þ x, 1/2  y, 1  z). Each molecule of btp undergoes these CeH/p interactions with four other btp molecules. The overall packing of the structure can be described as edge-to-face herringbone. This structure of 2-(20 benzothienyl)pyridine (btp) is similar to the structure of 2-(20 thienyl)pyridine. The structure of 2-(20 -thienyl)pyridine crystallizes in the same space group (P212121) and has very similar unit cell parameters (a ¼ 5.769(3)  A, b ¼ 8.793(3)  A, c ¼ 15.695(6)  A) with the exception of the c-axis, which in both structures is the axis

along which the length of the molecules lie (as btp is longer than 2(20 -thienyl)pyridine) [19]. The packing is not the same, however. 2.3.2. Structures of the “dangler” complexes. [Au(H-tpy)Cl3] (2a) and [Au(H-btp)Cl3] (3a) While the structures of [Au(H-tpy)Cl3] and [Au(H-btp)Cl3] were collected as synthetic intermediates, these structures displayed their own interesting inter- and intramolecular features. Anisotropic thermal displacement ellipsoid diagrams of 2a and 3a are shown in Figs. 2 and 3, respectively. The structure of [Au(H-ppy)Cl3] has been reported previously and will be used for comparison to those structures reported here [20]. In each of these three structures, the nearly square planar coordination at the gold center is consistent with the d8 electronic configuration of Au(III). The chloride ligand trans to the nitrogen of the coordinated pyridine ring is bonded to the gold with a slightly shorter distance (Aue Cl ¼ 2.259(2)  A ([Au(H-ppy)Cl3]); 2.267(1)  A ([Au(H-tpy)Cl3]); 2.265(2)  A ([Au(H-btp)Cl3])) than the mutually trans chlorides bonded to the gold center (AueCl ¼ 2.268(2)  A, 2.280(2)  A ([Au(Hppy)Cl3]); 2.276(1)  A, 2.284(1)  A ([Au(H-tpy)Cl3]); 2.286(2)  A, 2.280(2)  A ([Au(H-btp)Cl3])). Another similarity includes the significant twist away from planarity of the aromatic group bonded to the ligated pyridine. The angles between the least-squares planes formed by the pyridine ring and aromatic substituent are 51.5 for [Au(H-ppy)Cl3], 47.1 for [Au(H-tpy)Cl3], and 42.5 for [Au(H-btp) Cl3]. The most striking difference in these structures is the presence of an additional intramolecular Au/S interaction of the benzothiophene sulfur S1 with Au1 in the structure of [Au(H-btp)Cl3] forming a pseudo-five coordinate structure. This distance Au1/S1 of 3.139(2)  A is 0.321  A less than the sum of the Au/S van der Waals radii (3.460  A) [21]. This type of intramolecular interaction with a distance that is longer than a bond but shorter than the van der Waals radii sum has been demonstrated in the structures of related Au(III) complexes. Complexes of the form [Au(H-diimine) Cl3] where a ligand lone pair not engaged in bonding to gold is located near the Au(III) center in a position to interact in a pseudofive coordinate manner have recently been described [22]. Typical short nonbonding Au/N intramolecular distances in these [Au(H-

Table 2 Crystal Data, data collection, and refinement parameters for btp (4), Au(btp)Cl3 (3a), Au(btp)Cl2 (3b), and [Au([9]aneS3)](btp)(PF6)2(3c). Compound

btp

3a

3b

3c

Formula Habit, color Lattice type Space group a,  A b,  A c,  A a, deg b, deg g, deg V,  A3 Z Temperature (K) Fwt., g mol1 Dc, Mg m3 m, mm1 Reflections collected Unique reflections Max., min. transmission Data, restraints, parameters R1, wR2 (I > 2s(I)) R1, wR2 (all data) Goodness-of-fit (F2) Largest diff. peak, hole, e  A3

C13H9NS Block, colorless Orthorhombic P212121 5.870(2) 8.630(2) 20.232(5) 90 90 90 1024.9(4) 4 173(2) 211.28 1.369 0.2757 10,633 2367 (Rint ¼ 0.0214) 0.975, 0.818 2367/0/136 0.0255, 0.0671 0.0269, 0.0680 1.081 0.20, 0.16

C13H9AuCl3NS Block, red Orthorhombic Pna21 8.1581(8) 29.046(3) 6.1993(7) 90 90 90 1469.0(3) 4 173(2) 514.61 2.327 10.7195 12,233 3337 (Rint ¼ 0.0300) 0.424, 0.253 3337/0/174 0.0290, 0.0477 0.0325, 0.0482 1.386 1.20, 1.35

C13H8AuCl2NS Block, orange Monoclinic P21/n 11.630(3) 8.268(2) 13.672(4) 90 105.992(8) 90 1263.7(6) 4 173(2) 478.15 2.513 12.2463 12,818 2905(Rint ¼ 0.0521) 0.375, 0.214 2905/0/163 0.0300, 0.0584 0.0389, 0.0612 1.057 2.56, 1.21

C22H29AuF12N4O6P2S4 Needle, red Triclinic P-1 7.8196(11) 14.291(2) 15.787(2) 89.904(2) 86.231(2) 84.339(2) 1751.7(4) 2 173(2) 1060.64 2.011 4.637 19,599 7868 (Rint ¼ 0.0448) 0.8013, 0.2052 7868/0/463 0.0518, 0.1344 0.0574, 0.1388 1.070 8.938, 2.510

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Fig. 4. Thermal ellipsoid perspective of cyclometallated complex [Au(btp)Cl2] (3b) (50% probability, H atoms omitted for clarity).

Fig. 2. Thermal ellipsoid perspective of “dangler” [Au(H-tpy)Cl3] (2a) (50% probability, H atoms omitted for clarity).

diimine)Cl3] complexes are in the range of 2.51e2.80  A (average 2.63  A, VDW radii sum minus 0.58  A). These Au/N intramolecular interactions in the [Au(H-diimine)Cl3] complexes are shorter than the Au/S interaction in [Au(H-btp)Cl3] even when accounting for

Fig. 3. Thermal ellipsoid perspective of “dangler” [Au(H-btp)Cl3] (3a) (50% probability, H atoms omitted for clarity).

the differences in van der Waals radii. However, the unligated nitrogen lone pair is oriented to interact in a sigma bonding geometry with the d2z orbital of the gold, potentially. In this [Au(H-btp)Cl3] structure, an interaction of the gold with the p system of the benzothiophene moiety is more consistent with the structure. A solution study of the “rolling” bipyridine ring twisting motion of the complex [Au(2,9-dimethyl-2,20 -bipyridine)Cl3] suggests the axial Au/N interaction present in this system is weak. Interestingly, a recent report by Eichler and co-workers suggest that fivecoordinate Au(III) complexes with diimines may be more effective that square planar complexes as anti-tumor agents [23]. Additional intermolecular features distinguish the structures of [Au(H-ppy)Cl3], [Au(H-tpy)Cl3], and [Au(H-btp)Cl3]. The unit cell and space group of the [Au(H-ppy)Cl3] structure (P1-, longest unit cell axis <10.3  A) is very different from that of the [Au(H-tpy)Cl3] and [Au(H-btp)Cl3] (both Pna21 with a b axis near 30  A). A more striking difference however is the presence of weak pep stacking in the structure of [Au(H-btp)Cl3]. The benzothiophene moieties demonstrate p overlap in an infinite stacking fashion, parallel with the unit cell a-axis. The angle between adjacent benzothiophene least-squares planes is 8.5 and alternates so every other plane in a p-stack is parallel. The distance between these alternating planes in a stack is 7.29  A, giving an average adjacent interplanar distance of 3.65  A. Only one type of nearest neighbor orientation is observed. The structure of [Au(H-tpy)Cl3] packs in the same manner as [Au(Hbtp)Cl3] except the tolyl methyl groups are located where they prevent potential p stacking of the tolyl groups. The tolyl groups pack in a similar fashion with alternating, nonparallel tolyl groups (1.6 , average interplanar distance ¼ 3.76  A). The structure of [Au(H-ppy)Cl3] does not pack in such a way as to engage any sort of p stacking. None of the structures of [Au(H-ppy)Cl3], [Au(H-tpy) Cl3], or [Au(H-btp)Cl3] show any close Au/Au intermolecular distances less than 4.21  A (VDW radii sum Au/Au ¼ 3.32  A). This axial Au/S interaction of the [Au(H-btp)Cl3] structure may be related to the significant color difference between the crystals of [Au(H-tpy)Cl3] and [Au(H-btp)Cl3] (See Fig. S4, Experimental Supplemental information). The substituted pyridine ligands in the structures of both [Au(H-tpy)Cl3] and [Au(H-btp)Cl3] are twisted significantly from planarity, and neither free ligand has any absorption features in the visible region, Therefore, the color of the crystals would be expected to be similar (related to the parent complex [Au(pyridine)Cl3]) in the absence of other unique intra- or intermolecular features. As the intermolecular p stacking distances are long and no short Au.Au intermolecular contacts are present, the short Au/S interaction present in the structure of [Au(H-btp)

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There is extensive p stacking in this herringbone packing structure. A stacking diagram of 3b is shown in Fig. S5 in the Experimental Supplemental information. There are several unique types of p overlap interactions found in the packing of [Au(btp)Cl2]. The largest p overlap is between parallel layers that are 3.41  A apart with the chlorides oriented on opposite sides of the stack axis. Another smaller p area overlap is between parallel layers that are 3.03  A apart with chlorides oriented on opposite sides of the stack axis. A third unique p overlap with a very small p overlap exists between parallel layers that are 3.34  A. Each molecule engages one of each type of these pep interactions in the structure.

Fig. 5. Thermal ellipsoid perspective of the cation in [Au([9]aneS3)(ppy)](PF6)2 (1c) (50% probability, H atoms omitted for clarity).

Cl3] is a possible explanation for the significant electronic perturbation of the Au(III) center in [Au(H-btp)Cl3] relative to [Au(H-tpy) Cl3] in the solid-state. 2.3.3. [Au(btp)Cl2] (3b) An anisotropic thermal displacement ellipsoid diagram of 3b is shown in Fig. 4. Obtaining a structure of the [Au(btp)Cl2] was unanticipated as the solubility of these cyclometallated planar neutral complexes is poor except in solvents such as DMSO which are not ideal for crystallization. Only one other simple planar cyclometallated [Au(pyridine-aryl)Cl2] structure has been reported [24]. The structure of [Au(btp)Cl2] consists of a square planar Au(III) center bonded in a bidentate fashion to the ligand 2-(2-benzothienyl)pyridinate through the pyridine nitrogen and carbanion in the 30 position of the thiophene ring, and to two cis terminal chlorides. The entire molecule is nearly planar with a mean deviation from a least-squares plane containing all non-hydrogen atoms of 0.09  A. The Au1eN1 bond (2.056(4)  A) is longer than the Au1eC7 bond (2.026(6)  A), consistent with the carbanion nature of C7 and high charge of the Au(III). Likewise, the AueCl bonds are strongly influenced by the differing donor/acceptor properties of the cyclometallated btp ligand donor atoms. The Au1eCl1 bond trans to N1 is shorter (2.277(1)  A) relative to the Au1eCl2 bond trans to C7 (2.369(2)  A).

Fig. 6. Thermal ellipsoid perspective of the cation in [Au([9]aneS3)(tpy)](PF6)2 (2c) (50% probability, H atoms omitted for clarity).

2.3.4. Structures of [Au([9]aneS3)(ppy)](PF6)2 (1c), [Au([9 [aneS3)(tpy)](PF6)2 (2c), and [Au([9]aneS3)(btp)](PF6)2 (3c) Anisotropic thermal displacement ellipsoid diagrams of 1c, 2c, and 3c are shown in Figs. 5e7, respectively. A summary of bond distances, axial Au/S interaction distances, and bond angles is found in Table 3. These three Au(III) complexes all possess a similar coordination environment and structural features. Each complex consists of a square planar Au(III) center bonded to the cyclometallating ligand in a bidentate fashion through the pyridine nitrogen and carbanion of the phenyl, tolyl, or benzothienyl moiety as well as to two sulfur atoms of the [9]aneS3 ligand. An additional Au/S axial interaction with the remaining sulfur of [9]aneS3 is present in each structure as well providing a [S2NC þ S1] coordination environment. This endodentate conformation of [9]aneS3 gives rise to a description of these structures as pseudo-five coordinate with an overall geometry that is elongated square pyramidal at Au(III). The [9]aneS3 complexes possess AueN bonds similar in length to the AueC bonds of the cyclometallating ligands, with slightly shorter values for the AueC bonds. The AueS bonds trans to nitrogen are consistently shorter than the corresponding AueS bonds trans to the carbanion carbon, a reflection of the strong trans effect of the carbanion donor. The chelate angles of the [9]aneS3 and cyclometallating ligands are very similar across this series. Close examination of the axial Au/S interactions provides insight on the effects of gold on this interaction, the role the ancillary ligand plays, and the rigidity of the coordinated [9]aneS3 ligand. The Au/S axial intermolecular interaction distances are 2.818(1)  A, 2.842(1)  A, and 2.855(1)  A for 1c, 2c, and 3c, respectively. The van der Waals radii sum of Au/S is 3.46  A. Compared with

Fig. 7. Thermal ellipsoid perspective of the cation in [Au([9]aneS3)(btp)](PF6)2 (3c) (50% probability, H atoms omitted for clarity).

D.E. Janzen et al. / Journal of Organometallic Chemistry 755 (2014) 47e57

53

Table 3 Selected bond lengths ( A) with esds in parentheses for [Au([9]aneS3)(ppy)](PF6)2 (1c), [Au([9]aneS3)(tpy)](PF6)2 (2c), [Au([9]aneS3)(btp)](PF6)2 (3c) and related complexes.

MeSeq trans to N MeSeq trans to C MeSax VDW sum MeSax dist MeC Sum of MeS dist MeN a b c

1c

2c

3c

[Au([9]aneS3)2]2þ

2.332(1) 2.387(1) 2.818(1) 0.64 2.057(5) 7.537 2.068(5)

2.301(1) 2.419(1) 2.842(1) 0.62 2.043(4) 7.562 2.063(4)

2.303(2) 2.387(2) 2.855(1) 0.60 2.071(6) 7.545 2.072(5)

2.462(5) 2.452(5) 2.839(5) 0.62 NA 7.753 NA

a

[Au([9]aneS3)2]3þ

b

2.348(4) 2.354(4) 2.9216(4) 0.54 NA 7.628 NA

[Pt([9]aneS3)(ppy)]1þ 2.264(2) 2.354(2) 2.952(2) 0.57 2.031(6) 7.570 2.050(6)

c

[Pd([9]aneS3)(ppy)]1þ

c

2.2985(9) 2.3842(9) 2.871(1) 0.56 2.029(2) 7.554 2.061(2)

Ref. [25]. Ref. [9]. Ref. [6].

the analogs [Pt([9]aneS3)(ppy)](PF6) and [Pd([9]aneS3)(ppy)](PF6), the axial Au.S interactions in 1c, 2c, and 3c are slightly shorter. The shorter metal-axial sulfur distance in the gold ppy complex (2.8181(1)  A) compared to its Pt(II) and Pd(II) analogs (2.9518(17)  A, 2.8705(10)  A, respectively) is consistent with the higher cationic charge of the gold(III) [8]. Compared with the related [Au([9] aneS3)2]2þ and [Au([9]aneS3)2]3þ complexes [9,25], (Au/S axial distances ¼ 2.839(5), 2.9216(4), respectively, the axial Au/S interactions of 1c, 2c, and 3c are much closer to the AuII than the AuIII homoleptic parent complex. The distances are consistent with the enhanced donor abilities of the cyclometallating ligands compared to the thiacrown. Perhaps a fairer comparison of M/S axial interactions is the difference between the van der Waals radii sums and the observed M/S distances. As shown in Table 3, 1c, 2c, and 3c display shorter axial M/S distances than the palladium(II) and platinum(II) analogs even when adjusted for the van der Waals radii differences in these metals. Though these axial distances are not dramatically shorter, this is consistent with the electrostatic differences in the charge at the metal (Au3þ vs. Pt2þ and Pd2þ). Comparison of the axial M/S distances for 1c, 2c, and 3c with the homoleptic [9]aneS3 gold complexes demonstrates the greater similarity to the Au(II) rather than the Au(III) complex. Within this series of Au(III) cyclometallated complexes, the ancillary ligand seems to play a role as well. The Au/S axial distance increases across the ancillary ligand series ppy < tpy < btp. The differing electron donating abilities of the cyclometallating ligands are likely the source of the change. As the btp ligand carbanion donor ring is a thiophene, the electron donating abilities of this cyclometallating ligand are expected to be better than the phenyl and tolyl rings of ppy and tpy, respectively. As the electron donating ability of the ancillary ligand increases, the distance of the Au/S axial interaction increases in response, as has been noted for the related Pt(II) and Pd(II) [9]aneS3 complexes [6,8]. Sensitive changes in the M/S axial interactions in response to the ancillary ligand for complexes of the form [Pt([9]aneS3)(L)]nþ (L ¼ diimine, diphosphine, and dihalide) have been reported by our group previously [26]. The sum of the distances of the AueS bonds and the Au/S equatorial interaction within each of these gold (III) [9]aneS3 complexes is 7.54  A, 7.56  A, and 7.55  A for 1c, 2c, and 3c, respectively. This is consistent with previous observations that the [9] aneS3 ligand is relatively rigid and maintains a narrow sum of MeS bonds and interactions in d8 complexes across a large range of structures [8,26]. Though the lengths of the AueS equatorial bonds and the Au/S axial interactions vary based on the ancillary ligand, the overall thiacrown geometry is nearly unchanged. Intermolecular pep stacking of the cyclometallating ligands is observed in the structures of each of these gold(III) [9]aneS3 complexes. A diagram showing p-interactions of the cations of 1c, 2c, and 3c is shown in Fig. 8. In the structure of [Au([9]aneS3)(ppy)](PF6)2, phenylpyrdinate ligands stack with p overlap in a

parallel fashion with two unique alternating distances within a stack. A p stacking distance of 3.60  A is observed between complexes with [9]aneS3 ligands directed at each other across the interaction. A second p stacking interaction of 3.37  A is observed between complexes with [9]aneS3 ligands directed away from each other across the interaction. We have previously identified several packing motifs common amongst complexes of the form [M([9] aneS3)(L)]nþ (M ¼ Pd2þ, Pt2þ, L ¼ diimine) [12]. The p stacking motif observed here for [Au([9]aneS3)(ppy)](PF6)2 clearly fits the defined Motif A which involves alternating inein and outeout stacks. The structure of [Au([9]aneS3)(tpy)](PF6)2 displays tolylpyrdinate ligands stacking with p overlap in a nonparallel fashion. The angle between adjacent tolylpyridinate least-squares planes is 11.1 and alternates so every other plane in a p-stack is parallel. The distance between these alternating planes in a stack is 7.17  A, giving an average adjacent interplanar distance of 3.58  A. Only one type of nearest neighbor orientation is observed. This motif is consistent with the previously described Motif B. In the structure of [Au([9] aneS3)(btp)](PF6)2, benzothienylpyridinate ligands stack with p overlap in a parallel fashion with two unique alternating distances within a stack. A p stacking distance of 3.43  A is observed between complexes with [9]aneS3 ligands directed at each other across the interaction. A second p stacking interaction of 3.42  A is observed between complexes with [9]aneS3 ligands directed away from each other across the interaction. This structure is also like that of motif A. The relationship between stacking interactions in Pt(II), Pd(II), and Au(III) complexes and their use of medicinal chemistry targets has been recently highlighted [27]. 2.4. Cyclic voltammetry The reductive electrochemistry of these cyclometallated complexes shows strong ancillary ligand effects on the reduction processes observed. We report the electrochemistry of [Au([9] aneS3)(ppy)](PF6)2 (1c), [Au([9]aneS3(tpy)(PF6)2 (2c), and [Au([9] aneS3)(btp)](PF6)2 (3c). Cyclic voltammograms of 2c and 3c are shown in Fig. 9. For all metal complexes examined in this study, no oxidations were observed < þ1.0 V (vs. Fcþ/Fc). However, irreversible reductions are observed for all three Au(III) [9]aneS3 complexes examined. In the case of (1c), an irreversible reduction is present at Epc ¼ 0.576 V (vs. Fcþ/Fc). This reduction is as assigned a metal-based reduction of the AuIII center. The very similar complex (2c) also displays a comparable irreversible reduction at Epc ¼ 0.430 V (vs. Fcþ/Fc). This is also assigned as a metal-based reduction. As the additional methyl group of the tpy ligand provides more electron density to the AuIII center than the ppy ligand, the reduction of AuIII for 2c occurs at a higher potential than 1c. To confirm the number of electrons transferred in the reduction process of 2c, a known quantity of ferrocene was added to the solution of 2c, and the cyclic voltammogram was acquired. Based on a comparison of the reductive peak currents and molar quantities for

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Fig. 8. Diagram showing pep interactions of the cations in [Au([9]aneS3)(ppy)](PF6)2 (1c, left), [Au([9]aneS3)(tpy)](PF6)2 (2c, center), and [Au([9]aneS3)(btp)](PF6)2 (3c, right). Views are perpendicular to the stacking axes.

ferrocene and 2c, a ratio of 1.2 was obtained. We accordingly assign the reduction process as a one-electron AuIII/II reduction. The complex [Au([9]aneS3)(btp)](PF6)2 (3c) shows an irreversible reduction at Epc ¼ 0.119 V (vs. Fcþ/Fc), assigned as a metal-based reduction, shifted significantly to a higher potential than 1c or 2c. This is consistent with the even more electron-rich btp ligand acting to donate more electron density to the AuIII center. We also note that the ease of metal-centered reduction among the three complexes follows the trend in AueS axial distances. The same type of experiment (described for 2c) to determine the number of electrons transferred in the reduction process observed for 3c was not carried out as the peak separation between the reductions of ferrocene and 3c were not sufficient to measure accurately the independent peak currents of each process. On a related note, during the course of acquiring cyclic voltammetry data for the compound 3c, as a final experiment, ferrocene was added to the yelloweorange solution of 3c. Immediately, the solution turned green, consistent with the spontaneous oxidation to ferrocenium and reduction of 3c expected by the proximity of these redox processes under the conditions of this experiment. Upon comparison of 3c with [Au([9]aneS3)2](PF6)3, the reduction to Au(II) is more facile for the homoleptic bis [9]aneS3 complex (E1/2 for AuIII/AuII ¼ þ0.46 V (vs. Fcþ/Fc). This is consistent with the enhanced ability of two [9]aneS3 ligands to stabilize more effectively the AuII oxidation state upon reduction from AuIII, compared to 3c which has only a single [9]aneS3 ligand. Our electrochemical data strongly suggest that two AueS axial interactions are required

to stabilize a complex involving the rare Au(II) oxidation state. When comparing the Pd(II) and Pt(II) cyclometallated analogs to the related AuIII species, the [9]aneS3 ligand stabilizes oxidation chemistry of Group 10 complexes (reversible oxidations for PdII, irreversible oxidations for PtII) while its is the reduction for gold(III) complexes that is stabilized by the presence of [9]aneS3 [6]. 3. Conclusions Gold(III) cyclometallated complexes can be prepared with a variety of ligands using a solventless, solid-state synthesis. Thermochemical data proves useful in ascertaining the heating conditions for the cyclometallating step. Heteroleptic Au(III) complexes involving the cyclometallating ligands and the thiacrown [9]aneS3 can then be prepared. These complexes form elongated square pyramidal structures containing two equatorial AueS bonds along with one longer AueS axial interaction. The distance of the axial interaction is sensitive to the identity of the cyclometallating ligand and is consistent with prior observations in related Pt(II) and Pd(II) complexes. Fluxional behavior of the coordinated [9]aneS3 is observed, resulting in a single 13C NMR methylene resonance despite the asymmetric environment of the cyclometallating ligand. Unlike the homoleptic bis [9]aneS3 complexes, the rare gold(II) oxidation state is not stabilized, showing that two AueS axial interactions must be present in order to facilitate the Au(III)/ Au(II) reduction. Among the three cyclometallating ligands fully studied in the report, both the AueS axial distances and reduction potentials correlate with the increasing donor ability as: ppy < tpy < btp. 4. Experimental 4.1. Materials and measurements

Fig. 9. Cyclic voltammograms of [Au([9]aneS3)(tpy)](PF6)2 (2c) and [Au([9] aneS3)(btp)](PF6)2 (3c) with supporting electrolyte 0.1 M (Bu)4NBF4 in CH3CN, Pt disk working electrode, and Pt wire auxiliary electrode. Bold plot is 3c, gray is 2c. Plotted current scale of 3c is 8.5 current measured.

All materials were used as received. The ligands [9]aneS3, ppy, bzq, tpy, and btp as well as NH4PF6 were purchased from Aldrich Chemical Company. The gold starting material KAuCl4 was purchased from Strem Chemicals Inc. All synthetic manipulations were carried out in air. Analyses were performed by Atlantic Microlab, Inc., of Atlanta, Georgia. Fourier transform IR spectra were obtained on crystalline solids using a Nicolet 380 FT-IR spectrometer equipped with a germanium ATR accessory (1a, 1b, 1c, 4a, 4b, 4c) or Perkin Elmer Spectrum One FTIR with PIKE Technologies ZnSe ATR accessory (btp, 2a, 2b, 2c, 3a, 3b, 3c). UVeVis spectra were obtained in acetonitrile using a Varian DMS 200 UVeVis spectrophotometer (1a, 1b, 1c, 4a, 4b, 4c) or Cary Bio UVeVisible Double Beam Spectrophotometer (btp, 2a, 2b, 2c, 3a, 3b, 3c). Proton and carbon-13 NMR spectra were obtained on a JEOL 400 MHz NMR spectrometer using residual solvent for both the deuterium lock and reference. Electrochemical measurements

D.E. Janzen et al. / Journal of Organometallic Chemistry 755 (2014) 47e57

were performed using a Bioanalytical Systems CV50W analyzer. The supporting electrolyte was 0.1 M (Bu)4NBF4 in CH3CN, and sample concentrations were between 1 and 5 mM. All voltammograms were recorded at a scan rate of 100 mV/s. The standard three-electrode configuration was as follows: Pt disk working electrode, Pt-wire auxiliary electrode, and Ag/AgCl reference electrode. All potentials are reported against the Fc/Fcþ standard couple which under these conditions was measured to have DEp ¼ 78 mV and ipc/ipa ¼ 0.98.

4.2. Crystallography Tables 1 and 2 contain crystal data, collection parameters, and refinement criteria for the crystal structures of btp, 1c, 2a, 2c, 3a, 3b, and 3c. Crystals were mounted on the tip of either a 0.1 mm diameter glass capillary (1c, 2a, 2c, 3c) or MiTiGen micromount (btp, 3a, 3b), and X-ray intensity data were measured at low temperature (173(2) K with graphite monochromated Mo Ka radiation (l ¼ 0.71073  A) on a Rigaku AFC8S Mercury CCD diffractometer (1c), Bruker APEX II Platform CCD diffractometer [28] (2a, 2c, 3c), or a Rigaku XtaLAB mini diffractometer [29] (btp, 3a, 3b). A preliminary set of cell constants was calculated from reflections harvested from several frames. The frame times for the collections were 10 s (1c), 20 s (2a), 10 s (2c), 20 s (btp), 10 s (3a), 20 s (3b), 10 s (3c). A randomly oriented region of reciprocal space was surveyed to the extent of one sphere and to a resolution of at least 0.84  A. Three or four major sections of frames were collected with either 0.30 (2a, 2c, 3a, 3c) or 1.0 (btp, 1c, 3b) steps in u at three different 4 settings. The intensity data were corrected for absorption and decay using either SADABS (2a, 2c, 3c) [30] or CrystalClear (btp, 1c, 3a, 3b) [29]. Final cell constants were calculated from the xyz centroids of strong reflections from the actual data collection after integration (2a, 2c, 3c SAINT [28]; btp, 1c, 3a, 3b CrystalClear [29]). Each structure was solved and refined using SHELXL-97 [31]. A direct-methods solution was calculated that provided most of the non-hydrogen atoms from the E-map. Full-matrix least-squares/ difference Fourier cycles were performed that located the remaining non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters. All of the hydrogen atoms in each structure were placed in ideal positions and refined as riding atoms with relative isotropic displacement parameters. Crystals of the btp ligand were grown by diffusion of diethyl ether into a solution of btp in CH2Cl2. The structure of btp consists of one entire molecule in the asymmetric unit, with all atoms on general positions. The space group is noncentrosymmetric (P212121) and the Flack parameter determined was 0.03(6) (based on 967 Friedel pairs), suggesting the structure model is the correct enantiomer structure. Crystals of 1c were grown by diffusion of diethyl ether into a solution of 1c in NO2CH3. The structure of 1c consists of one entire molecular cation and two PF-6 anions in the asymmetric unit, with all atoms on general positions. No disorder was detected in the Auligated atoms C21 and N10. Crystals of 2a were grown by diffusion of diethyl ether into a solution of 2a in CH2Cl2. The structure of 2a consists of one entire molecule in the asymmetric unit, with all atoms on general positions. An AFIX 137 restraint was used to allow the methyl group of C12 to refine freely about the C9eC12 bond to find the best position for hydrogens H12A, H12B, and H12C. Crystals of 2c were grown by diffusion of diethyl ether into a solution of 2c in NO2CH3. The structure of 2c consists of one entire molecular cation and two PF 6 anions in the asymmetric unit, with all atoms on general positions. An AFIX 137 restraint was used to

55

allow the methyl group of C7 to refine freely about the C7eC3 bond to find the best position for hydrogens H7A, H7B, and H7C. Crystals of 3a were grown by diffusion of diethyl ether into a solution of 3a in CH2Cl2. The structure of 3a consists of one entire molecule in the asymmetric unit, with all atoms on general positions. The structure was modeled in the chiral space group Pna21 as a merohedral twin. The major/minor twin components were present in a 68.6/31.4 ratio. The absolute structure was deduced based on Flack parameter, 0.00(2), refined using 1502 Friedel pairs. Crystals of 3b were grown by slow mixing of a layered solution of 3b in DMSO with a layer of diethyl ether to which was added 3 drops of NO2CH3. The structure of 3b consists of one entire molecule in the asymmetric unit, with all atoms on general positions. Crystals of 3c were grown by diffusion of diethyl ether into a solution of 3c in NO2CH3. The structure of 3c consists of one entire molecular cation, two PF 6 anions, and three solvate molecules of NO2CH3 in the asymmetric unit, with all atoms on general positions. Two large residual electron density peaks (8.94 and 5.13 e/  A3) are located very close to the Au1 center (0.891  A and 0.903  A, respectively). These are likely the result of Fourier truncation. 4.3. Syntheses of gold(III) complexes with phenylpyridine (ppy) 4.3.1. Preparation of precursors [Au(H-ppy)Cl3] (1a) and [Au(ppy) Cl2] (1b) The gold(III) complex [Au(H-ppy)Cl2] was essentially prepared by the published method [13]. We report here its 400 MHz 1H NMR proton spectrum and previously unpublished 13C NMR data. 1H NMR (acetone-d6) ppm: 9.296 (d, 1H, 6 Hz), 8.497 (td, 1H, 8 Hz, 1 Hz), 8.096 (dd, 1H, 8 Hz, 1 Hz), 8.033 (td, 1H, 7 Hz, 1 Hz), 7.917e 7.807 (m, 2H), 7.701e7.649 (m, 3H). 13C NMR (acetone-d6) ppm: 160.6 (eCe), 151.55 (eCHe), 144.14 (eCHe), 138.71 (eCe), 131.92 (eCHe), 130.97 (eCHe), 130.17 (4C, (eCHe), 128.04 (eCHe). A sample of [Au(H-ppy)Cl3] (1a) is placed in a muffle furnace, heated to 170 with a ramp rate of 2 /min, and held at that temperature for 4 h. The solid changes from bright yellow to a light brown as 1b forms. The proton NMR spectrum generally matches that previously reported for 1b [13]. 1H NMR (DMSO-d6) ppm: 9.523 (d, 1H, 6 Hz), 8.43e8.37 (m, 2H), 7.99e7.96 (m, 1H), 7.814 (d, 1H, 8 Hz), 7.768 (td, 1H, 6 Hz, 2 Hz), 7.481 (t, 1H, 8 Hz), 7.380 (t, 1H, 8 Hz). 13C NMR (DMSO-d6) ppm: 164.3 (eCHe), 152.6 (eCHe), 148.4 (eCe), 145.3(eCHe), 143.4 (eCHe), 132.2 (eCe), 130.6 (eCHe), 128.7, (eCe), 127.3 (eCHe), 125.8 (eCHe), 122.8 (eCHe). 4.3.2. Preparation of [Au([9]aneS3)(ppy)](PF6)2 (1c) A mass of [Au(ppy)Cl2] (40 mg, 0.095 mmol) and [9]aneS3 (17 mg, 0.094 mmol) heated at reflux in 20 mL of CH3NO2 for 1 h. The reaction was protected from light by covering in Al foil. After reflux, the solution was nearly colorless. Next a mass of NH4PF6 (32.0 mg, 0.196 mmol) was added, and the flask contents were heated at reflux for an additional 30 min. The solution appeared slightly yellow upon the addition of the PF6 salt, but as the reflux began, the solution turned colorless again. The mixture was cooled in an ice bath to precipitate NH4Cl as a colorless solid. The solid was removed by vacuum filtration, and the clear solution was concentrated by rotary evaporation to form an intense yellow solution. Ether diffusion of the concentrate yielded yellow crystalline plates. These were washed with 3  5 mL portions of water, EtOH, and finally ether to yield 24 mg (0.030 mmol, 30%) of [Au([9]aneS3)(ppy)](PF6)2. Anal. Calc. for C17H20AuNP2S3F12 C, 24.86; H, 2.45; N, 1.71. Found: C, 25.19; H, 2.62; N, 2.00. 1H NMR (CD3NO2) ppm: 9.008 (dd, 1H, eCHe, 6 Hz, 2 Hz), 8.461 (m, 1H, eCHe), 8.362 (m, 1H, e CHe), 8.019 (dd, 1H, eCHe, 8 Hz, 2 Hz), 7.717 (m, 1H, eCHe), 7.681e 7.613 (m, 2H, eCHe), 7.466 (m, 1H, eCHe), 3.92e3.83 (m, 6H, e CH2e, [9]aneS3), 3.79e3.70 (m, 6H, eCH2e, [9]aneS3). 1H NMR

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(CD3NO2, ppm): 165.43 (eCe), 160.55 (eCe), 151.20 (eCHe), 146.54 (eCe), 145.74 (eCHe), 135.06 (eCHe), 131.76 (eCHe), 131.29 (e CHe), 129.46 (eCHe), 128.04 (eCHe), 124.59 (eCHe), 35.52 ([9] aneS3, eCH2e). UVevis (CH3CN, l/nm (ε/M1 cm1)): shoulder at 312 (ε ¼ 5.3  104 M1 cm1), 264 nm (ε ¼ 1.1  105 M1 cm1), 235 nm (ε ¼ 1.1  105 M1 cm1). 4.4. Syntheses of gold(III) complexes with tolylpyridine (tpy) 4.4.1. Preparation of [Au(H-tpy)Cl3] (2a) This compound was prepared according to a previously reported method [32]. We report here its 400 MHz proton and 13C NMR spectra along with its electronic spectrum. 1H NMR (CD2Cl2) ppm: 8.78 (d, 1H, 6.0 Hz), 8.17 (dd, 1H, 7.8 Hz), 7.81 (d, 1H, 7.8 Hz), 7.75 (d, 2H, 7.8 Hz), 7.70 (dd, 1H, 6.9 Hz), 7.47 (d, 2H, 7.8 Hz), 2.49 (s, 3H). 13C NMR (CD2Cl2) ppm: 161.00, 150.22, 142.67, 142.60, 135.11, 130.70, 130.21, 129.44, 126.66, 21.88. UVevis (CH3CN, l/nm (ε/M1 cm1)): 292 (9.2  103), 252 (1.0  104), 224 (3.4  104), 214 (3.1  104). 4.4.2. Preparation of [Au(tpy)Cl2] (2b) A bright yellow solid sample of [Au(H-tpy)Cl3] (0.301 g, 0.637 mmol) was heated in a ceramic dish in an oven at 175  C for 6 h. The resulting cyclometallated light brown solid [Au(tpy)Cl2] was obtained in high yield (0.247 g, 0.567 mmol, 91%). The 1H NMR spectrum of [Au(tpy)Cl2] obtained by our method was consistent with the previously reported synthesis of this compound [18]. 1H NMR (DMSO-d6) ppm: 9.48 (d, 1H, 6.0 Hz), 8.40e8.31 (m, 2H), 7.85 (d, 1H, 7.8 Hz), 7.72 (dd, 1H, 6.1 Hz), 7.61 (s, 1H), 7.3 (d, 1H, 7.8 Hz), 2.40 (s, 3H). 13C NMR (DMSO-d6) ppm: 164.04, 152.20, 147.89, 143.92, 142.24, 140.06, 130.37, 129.84, 126.60, 124.82, 121.89, 21.67. 4.4.3. Preparation of [Au([9]aneS3)(tpy)](PF6)2 (2c) A solution of [Au(tpy)Cl2] (0.200 g, 0.459 mmol) and [9]aneS3 (0.080 g, 2.54 mmol) in 20 mL CH3NO2 was heated at reflux for 16 h. Solid NH4PF6 (0.150 g, 0.918 mmol) was then added to the reaction mixture, heating continued for an additional 1 h, and the mixture was allowed to cool to rt. A white precipitate (presumably NH4Cl, insoluble in CH3NO2) and a yellow precipitate ([Au([9]aneS3)(tpy)](PF6)2) were both present. Additional CH3NO2 was added (20 mL) to dissolve the yellow precipitate and the mixture was filtered to remove the NH4Cl. Solvent from the filtrate was then removed under reduced pressure to obtain a yellow residue. This residue was dissolved in the minimum amount of CH3NO2 and crystallized by vapor diffusion with diethyl ether. A moderate yield of orangeeyellow crystals of ([Au([9]aneS3)(tpy)](PF6)2 was obtained (0.249 g, 0.298 mmol, 65%). Anal. Calc. for C18H22Au1F12N1P2S3: C, 25.88; H, 2.65; N, 1.68. Found: C, 26.04; H, 2.65; N, 1.75. 1H NMR (CD3NO2) ppm: 8.95 (d, 1H, 6.0 Hz), 8.41 (dd, 1H, 7.8 Hz), 8.28 (d, 1H, 8.2 Hz), 7.88 (d, 1H, 7.8 Hz), 7.65 (dd, 1H, 7.7 Hz), 7.47 (d, 1H, 7.8 Hz), 7.43 (s, 1H), 3.81 (m, 12H, eCH2e, [9] aneS3), 2.47 (s, 3H, eCH3). 13C NMR (CD3NO2) ppm: 165.89, 161.03, 151.20, 147.43, 145.78, 141.36, 132.35, 131.76, 129.31, 127.64, 124.47, 35.69 (eCH2e, [9]aneS3), 22.05 (eCH3). UVevis (CH3CN, l/nm (ε/M1 cm1)): 338 (1.01  104), 295 (1.53  104), 272 (3.04  104), 241 (2.73  104), 219 (3.48  104). ATR-IR (cm1): 3000, 2954, 1608, 1592, 1564, 1497, 1468, 1448, 1440, 1427, 1412, 1403, 1327, 1310, 1290, 1251, 1212, 1189, 1172, 1155, 1123, 1072, 1066, 1036, 1008, 930, 878, 814, 770, 741, 728, 695, 676, 655, 624, 604, 554, 510. 4.5. Syntheses of gold(III) complexes with 2-(20 -benzothienyl) pyridine (btp) 4.5.1. Preparation of [Au(H-btp)Cl3] (3a) This compound was prepared by a method analogous to that previously reported for [Au(H-tpy)Cl3]. A solution of btp (0.115 g,

0.545 mmol) dissolved in 7 mL CH3CN was added to KAuCl4 (0.201 g, 0.532 mmol) dissolved in 10 mL water. An orange precipitate developed as the reaction was stirred for 3 h at rt. An orange solid was collected by vacuum filtration, rinsed with 10 mL water, and dried in a vacuum desiccator for 8 h. The orange solid [Au(H-btp)Cl3] was obtained in high yield (0.241 g, 0.467 mmol, 88%). Anal. Calc. for C13H9Au1Cl3N1S1: C, 30.34; H, 1.76; N, 2.72. Found: C, 30.53; H, 1.62; N, 2.75. 1 H NMR (CD2Cl2) ppm: 8.84 (d, 1H, 5.5 Hz), 8.20 (dd, 1H, 7.8 Hz), 8.11 (s, 1H), 8.07e7.95 (m, 3H), 7.73 (dd, 1H, 6.9 Hz), 7.54 (m, 2H). 13C NMR (CD2Cl2) ppm: 154.22, 150.95, 142.79, 141.68, 139.65, 138.11, 130.84, 129.27, 127.47, 127.44, 126.37, 125.85, 123.29. UVevis (CH3CN, l/nm (ε/M1 cm1)): 349 (3.5  103), 327 (8.8  103), 316 (9.7  103), 265 (6.5  103), 224 (3.03  104). ATR-IR (cm1): 3125, 3106, 3087, 3065, 3045, 3027, 1597, 1562, 1523, 1476, 1429, 1338, 1298, 1246, 1181, 1162, 1107, 1071, 1006, 954, 869, 836, 769, 741, 720, 699, 655, 579, 567, 533. 4.5.2. Preparation of [Au(btp)Cl2] (3b) The compound [Au(btp)Cl2] was prepared using a method similar to the preparation of [Au(tpy)Cl2]. An orange solid sample of [Au(H-btp)Cl3] (0.154 g, 0.300 mmol) was heated in a ceramic dish in an oven at 175  C for 13 h. The resulting cyclometallated dark orange solid [Au(btp)Cl2] was obtained in a reasonable yield (0.247 g, 0.217 mmol, 73%). Anal. Calc. for C13H8Au1Cl2N1S1: C, 32.66; H, 1.69; N, 2.93. Found: C, 33.25; H, 1.78; N, 2.99. 1H NMR (DMSO-d6) ppm: 9.46 (d, 1H, 6.0 Hz), 9.08 (d, 1H, 7.8 Hz), 8.35 (dd, 1H, 7.8 Hz), 8.14 (d, 1H, 7.3 Hz), 8.04 (d, 1H, 7.3 Hz), 7.69 (dd, 1H, 6.9 Hz), 7.50 (m, 2H). 13C NMR (DMSO-d6) ppm: 158.63, 148.31, 145.18, 144.55, 141.84, 139.71, 139.05, 126.73, 125.92, 125.56, 123.96, 123.53, 122.16. ATR-IR (cm1): 3122, 3103, 3090, 3060, 3030, 1602, 1585, 1561, 1547, 1497, 1468, 1451, 1435, 1411, 1325, 1305, 1275, 1258, 1237, 1170, 1157, 1130, 1061, 1037, 1024, 1004, 974, 943, 908, 875, 848, 769, 749, 718, 677, 661, 594, 532. 4.5.3. Preparation of [Au([9]aneS3)(btp)](PF6)2 (3c) A suspension of [Au(btp)Cl2] (0.100 g, 0.209 mmol) in 75 mL CH3NO2 was stirred vigorously with [9]aneS3 (0.038 g, 0.209 mmol) and NH4PF6 (0.068 g, 0.418 mmol) at rt for 24 h. The cloudy reaction mixture was filtered to remove unreacted [Au(btp)Cl2] and NH4Cl. The bright yellow filtrate was concentrated under reduced pressure. Crystallization was induced by vapor diffusion of this CH3NO2 solution with diethyl ether. A low yield of dark red crystals of [Au([9]aneS3)(btp)](PF6)2 was obtained (0.021 g, 0.024 mmol, 11%). Anal. Calc. for C19H20Au1F12N1P2S4: C, 26.01; H, 2.30; N, 1.60. Found: C, 25.71; H, 2.38 N, 1.68. 1H NMR (CD3NO2) ppm: 9.01 (d, 1H, 6.0 Hz), 8.45 (dd, 1H, 7.8 Hz), 8.17 (m, 2H), 8.09 (d, 1H, 7.3 Hz), 7.66 (dd, 1H, 7.8 Hz), 7.62 (m, 2H), 3.86 (m, 12H, eCH2e, [9]aneS3)). 13C NMR (CD3NO2) ppm: 160.95, 155.47, 150.79, 146.63, 144.53, 140.62, 139.77, 129.07, 128.34, 126.88, 125.64, 125.11, 124.77, 36.69 (eCH2e, [9]aneS3). UVevis (CH3CN, l/nm (ε/M1 cm1)): 374 (6.9  103), 354 (7.3  103), 292 (1.83  104), 282 (1.8  104), 228 (2.36  104), 213 (3.06  104). ATR-IR (cm1): 3088, 3003, 2959, 1605, 1540, 1506, 1472, 1447, 1411, 1309, 1295, 1280, 1261, 1238, 1168, 1137, 1036, 1000, 942, 927, 879, 862, 834, 772, 760, 740, 723, 557. 4.6. Syntheses of gold(III) complexes with benzoquinoline (bzq) 4.6.1. Preparation of [Au(H-bzq)Cl3] (4a) A dark brown solution of bzq (37.0 mg, 0.206 mmol) in 6 mL MeCN was added to a yellow solution of HAuCl3$3H2O (75.3 mg, 0.210 mmol) in 6 mL H2O with stirring, A bright yellow, crystalline solid formed rapidly, but then the mixture clears to yield a yellow solution. Gas evolution is observed, and the solution is allowed to evaporate slowly and form a yellow needles. A mass of 97.1 mg

D.E. Janzen et al. / Journal of Organometallic Chemistry 755 (2014) 47e57

(97.7%). of [Au(H-bzq)Cl3] is obtained as a crystalline, yellow solid. An elemental analysis is obtained on 4b (see below) due to the instability of the 4a during the combustion analysis. 1H NMR (acetone-d6) ppm: 9.470 (m, 1H), 9.447 (d, 1H, 5 Hz), 9.165e9.072 (m, 1H), 8.470 (dd, 1H, 14 Hz, 3 Hz), 8.41e8.38 (m, 1H), 8.36e8.34 (m, 1H), 8.38e8.27 (m, 1H), 8.116e8.049 (m, 2H). 13C NMR (acetone-d6): 148.23 (eCHe), 143.24 (eCHe), 138.59 (eCe), 135.91 (eCe), 132.67 (eCHe), 132.32 (eCHe), 130.50 (eCHe), 130.07 (eCHe), 129.83 (e Ce), 125.41 (eCHe), 124.36 (eCHe), 123.95 (eCe), 123.26 (eCHe).

57

charge from The Cambridge Crystallographic Data Centre via www. ccdc.cam.ac.uk/data_request/cif. Appendix B. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2013.12.048. References

4.6.2. Preparation of [Au(bzq)Cl2] (4b) A sample of 4a weighing 46 mg (0.096 mmol) is placed into a ceramic crucible in a programmable muffle furnace and heated up to 185 at a ramp rate of 1 /min and held at that temperature for 14 h. The color change of the solid is from a bright yellow to a dull tan color. A mass of 36 mg (84%) of 4b is recovered. Anal. Calc. for C13H8Au1N1Cl2: C, 35.00; H, 1.81; N, 3.14; Cl, 15.89. Found: C, 35.25; H, 2.00 N, 3.10; Cl, 16.00. 1H NMR (DMSO-d6) ppm: 9.694 (dd, 1H, 6 Hz, 1 Hz), 9.004 (dd, 1H, 8 Hz, 1 Hz), 8.13e8.09 (m, 2H), 8.036 (t, 2H, 8 Hz), 7.915 (d, 1H, 8 Hz), 7.738 (t, 1H, 8 Hz). 13C NMR (DMSO-d6): 152.74 (eCe), 151.14 (eCe), 147.92 (eCHe), 142.46 (eCHe), 137.57 (eCe), 135.32 (eCe), 130.37 (eCHe), 129.33 (eCHe), 128.84 (eCe), 127.83 (eCHe), 127.41 (eCHe), 125.29 (eCHe), 124.06 (eCHe). Acknowledgments Acknowledgments are made to the following for their generous support of this research: the donors of the American Chemical Society Petroleum Research Fund (GJG); the Research Corporation for Scientific Advancement (GJG), the Grote Chemistry Fund at the University of Tennessee at Chattanooga (GJG); the National Science Foundation, Research at Undergraduate Institutions Program (GJG, Award #0841655), the Endowed Chair in the Sciences, School of Humanities Arts and Sciences, St. Catherine University (DEJ), the National Science Foundation: Major Research Instrumentation award #1125975 “MRI Consortium: Acquisition of a Single Crystal X-ray Diffractometer for a Regional PUI Molecular Structure Facility” (DEJ). We thank Professor Ted Pappenfus from the Department of Chemistry at the University of Minnesota-Morris for his assistance in the TGA measurements on several compounds. Dr. Victor G. Young Jr., Director of the X-ray Crystallographic Laboratory of the Department of Chemistry, University of Minnesota where data was collected for the structures 2a, 2c, and 3c, and Dr. Lee Daniels, Director of Small-Molecule Crystallography at Rigaku Americas Corp. are thanked for sharing their crystallographic expertise. We also thank Professor Larry F. Mehne and Thomas Holcombe from the Department of Chemistry at Covenant College, Lookout Mountain, GA for their assistance in the electrochemical measurements of the [9]aneS3 ppy gold complex. Also, David Colangione from UTC is thanked for his work with the bzq complexes. Appendix A. Supplementary material CCDC 972060e972066 contain the supplementary crystallographic data for this paper. These data can be obtained free of

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