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Dinuclear N-Heterocyclic Dicarbene Gold Complexes in IIII and IIIIII Oxidation States: Synthesis and Structural Analysis Marco Baron,† Cristina Tubaro,*,† Marino Basato,† Andrea Biffis,† Marta M. Natile,‡ and Claudia Graiff § †
Dipartimento di Scienze Chimiche, Universita di Padova, via Marzolo 1, 35131 Padova, Italy ISTM-CNR, INSTM, Dipartimento di Scienze Chimiche, Universita di Padova, via Marzolo 1, 35131 Padova, Italy § Dipartimento di Chimica Generale e Inorganica, Chimica Analitica, Chimica Fisica, Universita di Parma, Viale delle Scienze 17/A, 43100 Parma, Italy ‡
bS Supporting Information ABSTRACT: A series of dinuclear N-heterocyclic bis-dicarbene gold(III) complexes of the general formula [Au2Br4(RIm-Y-ImR)2](PF6)2 (Im = imidazol-2-ylidene; 1b, R = Me, Y = CH2; 2b, R = Me, Y = (CH2)2; 3b, R = Me, Y = (CH2)3; 4b, R = Me, Y = (CH2)4; 5b, R = Cy, Y = CH2; 6b, R = Me, Y = m-xylylene) were successfully synthesized by oxidative addition of bromine to the corresponding dicarbene gold(I) complexes 1a6a. The stability of the digold(III) complexes depends on the length of the bridge Y between the carbene units. The complex with Y = CH2 undergoes a partial reductive elimination, giving the first example of the mixed-valence gold(I)/gold(III) dinuclear bis-dicarbene complex 1c, together with a minor quantity of the neutral digold(III) mono-dicarbene complex [Au2Br6(MeIm-CH2-ImMe)] (1d). The X-ray crystal structures of complexes 1c,d, 3b, and 6b were determined. Besides complex 3b, the addition of bromine to complex 3a gives complex 3b0 , a coordination metallopolymer, formed by an infinite chain of AuBr2 units bridged by the dicarbene ligand.
’ INTRODUCTION There is an increasing interest in gold chemistry, which spans from molecular complexes to nanoclusters and layers.1 Recent studies have revealed very interesting reactivities, so that Au complexes have been found to be, for example, good catalysts in several organic transformations (CH bond functionalization, cyclization of enynes, nucleophilic additions),2 active solar light receptors,3 and promising antitumoral agents.4 On the other hand, gold nanoclusters are very efficient catalysts: for example, in the selective aerobic oxidation of alcohols or carbon monoxide.5 As a consequence of the exploding interest in the applications of this metal, it is not surprising that the research activity on the synthesis, characterization, and application of gold compounds has been extended in recent years to gold complexes with the popularized N-heterocyclic carbene (NHC) ligands.68 Remarkably, the majority of the applications of NHCgold complexes studied until now involves organic transformations, in which mononuclear NHCgold(I) or, to a minor extent, NHC gold(III) complexes are used as catalysts;6 these processes are based on the well-known ability of gold to activate by coordination multiple CC bonds (in particular alkynes and allenes) toward the intra- or intermolecular addition of nucleophiles (hydration, hydroamination, hydroarylation).9 In this context, it is surprising that very few dicarbene gold complexes have been reported,1013 despite r 2011 American Chemical Society
their interesting characteristics. In fact, they have found useful applications in the biomedical8c,10b,14,15 and photoluminescence13 fields; in the latter case, in particular, it is known that polynuclear gold complexes with short metalmetal distances can exhibit luminescence, as a consequence of aurophilicity (aurophilic interaction).16 In the last few years, we have been interested in the coordination properties of various N-heterocyclic di- and tricarbenes toward metal centers such as Pd(II), Pt(II), Cu(I), and Ag(I). The resulting complexes, both neutral and cationic, have been shown to be very stable and tolerant to oxidative conditions and to strongly acidic environments.17 Furthermore, the steric and electronic properties of the metal centers in these complexes can be tuned by a proper choice of the bridging groups and the wingtip substituents of the dicarbene ligand. On the basis of the above and of the interesting results reported by Nocera on diphosphino gold(III) complexes,3 we set out to systematically study the synthesis of gold(III) dicarbene complexes, which differ mainly in the length and flexibility of the bridge between the two carbene units (Chart 1). It appears that stable complexes may contain not only the Au(III)Au(III) couple but also the Au(I)Au(III) couple. In this paper, we report the synthesis, X-ray structures, and preliminary studies on Received: May 20, 2011 Published: August 16, 2011 4607
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Organometallics the equilibria involved in the oxidative addition of bromine to dicarbene gold(I) complexes.
’ RESULTS AND DISCUSSION Synthesis of Gold(III) Di-NHC Complexes. Four synthetic protocols can be adopted for the synthesis of gold(III) carbene complexes: (i) reaction of a gold(III) precursor, such as KAuCl4, with the free carbene, generated by deprotonation of the imidazolium salt with a strong base (under these conditions, reduction of gold(III) mainly to gold(0) and gold(I) may occur),18 (ii) reaction of gold(III) acetate or of complexes bearing basic anions with the diimidazolium salt precursor of the dicarbene ligand (however, we found that gold(III) acetate reacts with 1,10 -dimethyl-3,30 -methylenediimidazolium diiodide in DMSO to give the corresponding gold(I) dicarbene complex as the main product), (iii) transmetalation of the carbene ligand between the corresponding Ag(I) complex and KAuCl4 , 19 and (iv) oxidative addition of halogens to the gold(I) carbene complex. The last procedure has been widely used for the synthesis of gold(III) complexes with bidentate bridging ligands, such as diylides (CH2PPh2CH2), o-metalated phosphines (2-C4F4PPh2), and diphosphines (R2PCH2PR2, R = Ph, Cy).3,20 Moreover, it is generally adopted to obtain gold(III) complexes with monocarbene ligands,18,21 and only recently it has been extended to N-heterocyclic dicarbene complexes.13a All of these evidences prompted us to consider the oxidative addition of halogen as the safest, simplest, and most easily generalizable synthetic procedure for the synthesis of gold(III) dicarbene complexes. The gold(III) complexes 1b, 2b, and 4b6b were synthesized by addition of bromine to an acetonitrile solution of the corresponding gold(I) dicarbene complexes (Scheme 1). The starting dinuclear N-heterocyclic dicarbene gold(I) complexes differ in
Chart 1. Dicarbene Ligands 16 Employed in This Study
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the bridging groups between the carbene units and the wingtip substituents at the nitrogen atoms of the heterocyclic ring.22 The products are yellow solids, soluble in common polar organic solvents (acetonitrile, dimethyl sulfoxide). The 1H and 13 C NMR spectra indicate that the highly symmetric structure is maintained upon oxidation. The oxidation of the metal center is confirmed by the shifts observed in the 1H and 13C NMR spectra in CD3CN and by XPS analysis. Specifically, the 1H signals of the two hydrogen atoms of the imidazole backbone are slightly shifted downfield in comparison with those of the corresponding gold(I) complex. The same shift is observed also in the 13C NMR spectra for the corresponding C4 and C5 carbon atoms. Nolan et al. have postulated that the higher Lewis acidity of the gold(III) vs gold(I) metal center induces a greater delocalization of the electronic density from the C4C5 double bond to the carbene carbon atom.18 This explanation also justifies the upfield shift observed for the carbene carbon resonance, from ca. 180 ppm for NHCAu(I) to ca. 150 ppm for NHCAu(III) complexes. In Figure 1a, the Au 4f XP core levels of dicarbene complexes 1a,b are shown. Concerning complex 1a, the shape and position of the peaks (85.7 and 89.3 eV for Au 4f7/2 and 4f5/2, respectively) are consistent with the values reported in the literature for Au(I).23 On the other hand, analysis of the Au 4f peak shape of complex 1b reveals the presence of two different contributions, which are also confirmed by the fitting procedure (parts a and b of Figure 1), suggesting the presence of Au in two different oxidation states. The main contributions at 87.8 and 91.5 eV are characteristic of Au(III), while the small contributions at 85.6 and 89.3 eV suggest the presence of Au(I).23 Measurements on complex 1b at increasing irradiation times reveal a progressive reduction of the Au(III) centers, as indicated by the increase of Au(I) contributions. The reduction of Au (III) by exposure to an X-ray beam has already been observed for [Au(CH2)2PPh2]2Br4, a dinuclear complex with a diylide ligand.23b In general, UVvis irradiation and also heat could favor the reductive elimination of halogen, as described for example by Nocera et al. for dinuclear diphosphino gold(III) complexes.3 The dinuclear structure of the gold(III) complexes was confirmed by ESI-MS analysis, which revealed the presence of fragments corresponding to [Au2Br4(RIm-Y-ImR)2(PF6)n](2n)+ (n = 0, 1) containing Au, dicarbene ligand, and Br in a 1:1:2 ratio. However, reduced species of general formulas [Au2Br2(RIm-YImR)2]2+ and [AuI(RIm-Y-ImR)]+ are also present. This behavior
Scheme 1. Synthesis of the Gold(III) Dicarbene Complexesa
a
Reagents and reaction conditions: (i) Br2 (Br2:Au = 1.2:1), acetonitrile, room temperature, 12 h. 4608
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Figure 1. Au 4f XP peaks: (a) 1a (gray solid line), 1b (black solid line), and 1b after exposure at X-ray source for 100 min (dotted line); (b) fitting of the 1b peak.
Figure 2. ORTEP view of complexes 1c-n (left) and 1c-p (right). PF6 anions, H atoms, and dichloromethane solvent molecules have been omitted for clarity. Selected bond distances (Å) and angles (deg) for 1c-n/1c-p: C1Au1 = 2.027(6)/2.035(9), C7Au2 = 2.019(6)/2.015(9), C10Au1 = 2.038(6)/2.054(9), C14Au2 = 2.016(6)/2.033(9), Br1Au1 = 2.4012(8)/2.407(1), Br2Au1 = 2.4229(7)/2.415(1), Au1 3 3 3 Au2 = 3.682(3)/ 3.738(3); C1Au1C10 = 172.9(2)/176.0(4), C1Au1Br1 = 86.9(2)/88.6(3), C10Au1Br1 = 87.7(2)/89.2(3), C1Au1Br2 = 91.6(2)/ 91.8(3), C10Au1Br2 = 93.5(2)/90.3(3), Br1Au1Br2 = 176.58(3)/176.39(5), C14Au2C7 = 175.0(2)/173.3(4).
has already been observed with related gold(III) dicarbene complexes, with methylene or propylene bridging groups and 2-hydroxy-2-methylpropyl as the substituent at the nitrogen atom in the 3-position of the imidazol-2-ylidene ring.13a The tendency of 1b to undergo bromine reductive elimination, observed in the XPS experiments, was confirmed also in the efforts to obtain crystals. In fact, slow diffusion of a 1/5 (v/v) CH2Cl2/n-hexane mixture into an acetonitrile solution of complex 1b yields yellow crystals suitable for X-ray analysis with two different morphologies, needlelike 1c-n and prismatic 1c-p; for both types of crystals, unexpected molecular structures were found. Compounds 1c-n and 1c-p are both derived from the starting complex 1b upon reductive elimination of bromine from one Au(III) center. The two structures are very similar (Figure 2) and differ only in the number of solvent molecules (dichloromethane).
This is the first example of a mixed-valence Au(I)/Au(III) complex with N-heterocyclic dicarbene ligands. As expected, the two gold atoms present different geometries: Au(I) is bound to two carbene units in a linear fashion, while Au(III) is tetracoordinated in a square-planar geometry. The intramolecular Br 3 3 3 Au(I) distances are 3.560(5) and 3.672(5) Å in 1c-n and 1c-p, respectively. The presence of one gold(III) atom with two coordinated bromides only slightly influences the overall structure of the complex, which is very similar to that reported for the analogous gold(I) dinuclear complex.10a The dihedral angle between the average planes, each containing the Au center and the two linearly coordinated carbene rings, is 108.01(2)° in the case of 1c-n and 111.29(2)° in the case of 1cp, only slightly higher than in the reference Au(I) dinuclear complex (106.26(1)°).10a When the crystallization of 1b is carried out from CH2Cl2/ diethyl ether mixtures, a third type of crystal is formed as the very 4609
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Organometallics minor red product 1d, which is characterized by the loss of one bridging dicarbene ligand (Figure 3). Complex 1d is a gold(III) dinuclear complex in which the dicarbene ligand 1,10 -dimethyl-3,30 -methylen-diimidazol-2,20 diylidene bridges two AuBr3 units. Overall, the geometric parameters are comparable with those of the corresponding monocarbene complexes (NHC)AuBr3 and (NHC)AuCl3.18,21a The CcarbeneAuBr and BrAuBr bond angles slightly deviate from the ideal value of 180° (C1Au1Br2 = 176.2(3)°, C5Au2Br5 = 178.4(3)°; Br1Au1Br3 = 173.87(5)°, Br6Au2Br4 = 175.68(6)°), and the CcarbeneAu bond distance is close to 2.0 Å (C1Au1 = 2.00(1) Å and C5Au2 = 2.02(1) Å). The AuBr bond length is somewhat greater for the bromide trans to the carbene ligand (Au1Br2 = 2.452(2) Å and Au2Br5 = 2.443(2) Å), in comparison with the two bromides in cis positions (between 2.418(1) and 2.431(1) Å), as a consequence of the greater trans effect of the NHC ligand.
Figure 3. ORTEP view of complex 1d. Selected bond distances (Å) and angles (deg) for 1d: Br1Au1 = 2.418(1), Br4Au2 = 2.425(2), Br2Au1 = 2.452(2), Br5Au2 = 2.443(2), Br3Au1 = 2.431(1), Br6Au2 = 2.419(2), C1N1 = 1.32(1), C5N4 = 1.34(1), C1N2 = 1.36(1), C5N3 = 1.30(1), C1Au1 = 2.00(1), C5Au2 = 2.02(1); C1Au1Br1 = 84.6(3), C5Au2Br6 = 86.1(3), C1Au1Br3 = 89.3(3), C5Au2Br4 = 89.9(3), Br1Au1Br3 = 173.87(5), Br6Au2Br4 = 175.68(6), C1Au1Br2 = 176.2(3), C5Au2 Br5 = 178.4(3), Br1Au1Br2 = 92.99(5), Br6Au2Br5 = 92.40(6), Br3Au1Br2 = 93.07(5), Br4Au2Br5 = 91.52(6).
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A more stable Au(III)/Au(III) complex was obtained upon oxidative addition of bromine to 3a (Scheme 2). Suitable crystals for X-ray analysis were obtained by slow diffusion of diethyl ether into an acetonitrile solution of the reaction mixture. This procedure yields crystals in which the two forms 3b and 3b0 are present (Figures 4 and 5). 3b is a gold(III) dinuclear complex,
Figure 4. ORTEP view of 3b. PF6 anions and H atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): C1N2 = 1.33(1), C1N1 = 1.34(1), C1Au1 = 2.03(1), C11N4 = 1.31(1), C11N3 = 1.35(1), C11Au2 = 2.04(1), C12N6 = 1.31(1), C12N5 = 1.33(1), C12Au2 = 2.05(1), C22N7 = 1.33(1), C22N8 = 1.34(1), C22Au1 = 2.02(1), Br1Au1 = 2.386(2), Br2Au1 = 2.405(2), Br3Au2 = 2.391(1), Br4Au2 = 2.407(1), Au1 3 3 3 Au2 = 6.322(4); N2C1N1 = 107.5(9), N2C1Au1 = 128.5(8), N1C1Au1 = 124.0(8), N4C11N3 = 107.0(9), N4C11Au2 = 128.5(8), N3C11Au2 = 124.6(8), N6C12N5 = 108(1), N6C12Au2 = 126.1(9), N5C12Au2 = 126.1(9), N7C22N8 = 105(1), N7C22Au1 = 129.7(8), N8C22Au1 = 125.6(8), C22Au1C1 = 177.3(4), C22Au1Br1 = 89.6(4), C1Au1Br1 = 89.9(3), C22Au1Br2 = 90.7(4), C1Au1Br2 = 89.9(3), Br1Au1Br2 = 176.85(8), C11Au2C12 = 177.9(5), C11Au2Br3 = 88.9(3), C12Au2Br3 = 90.8(3), C11Au2Br4 = 90.2(3), C12Au2Br4 = 90.2(3), Br3Au2Br4 = 178.36(7). Symmetry code: (0 ) x, y, z.
Scheme 2. Oxidative Addition of Bromine to Complex 3aa
a
Reagents and reaction conditions: (i) Br2 (Br2:Au = 1.2:1), acetonitrile, room temperature, 12 h. 4610
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Figure 5. ORTEP view of 3b0 . PF6 anions and H atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): C23N10 = 1.34(1), C23N9 = 1.33(1), C23Au3 = 2.05(1), C33N11 = 1.35(2), C33N12 = 1.39(2), C33Au4 = 2.03(1), Br5Au3 = 2.408(1), Br6Au4 = 2.404(1), Au3 3 3 3 Au4 = 6.320(3); N10C23N9 = 106.5(9), N10C23Au3 = 125.5(9), N9C23Au3 = 127.9(8), N11C33N12 = 109(1), N11C33Au4 = 127(1), N12C33Au4 = 124(1), C23Au3C230 = 179.99(2), C23Au3Br50 = 91.0(3), C23Au3Br5 = 89.0(3), Br5Au3Br50 = 180.00(7), C33Au4C330 = 179.99(2), C33Au4Br60 = 89.5(4), C33Au4Br6 = 90.5(4), Br6Au4Br60 = 179.99(1). Symmetry code: (0 ) x, y, z.
Figure 6. Crystal packing of 3b and 3b0 . View along the crystallographic b axis.
Figure 7. Crystal packing of 3b and 3b0 . View along the crystallographic a axis.
whereas 3b0 has a polymeric structure with the dicarbene ligands bridging AuBr2 centers in a staggered way (Scheme 2). 3b is a dinuclear compound of gold(III) in which the Au centers are tetracoordinated in a square-planar environment. Each gold atom is bonded to two carbene carbon atoms (the AuC bond distances span from 2.02(1) to 2.05(1) Å) and two bromine atoms (the AuBr bond distances are in the range 2.386(2)2.407(1) Å). The mean coordination planes of the
Figure 8. ORTEP view of complex 6b. PF6 anions and acetonitrile solvent molecules have been omitted for clarity. Selected bond distances (Å) and angles (deg): C1Au = 2.044(6), AuC15 = 2.042(6), Br1Au = 2.421(1), Br2Au = 2.426(1), C1N1 = 1.342(8), C1N2 = 1.358(8), C2C3 = 1.34(1), C2N1 = 1.372(8), C3 N2 = 1.370(8), C13C14 = 1.360(9), C13N3 = 1.381(7), C14N4 = 1.380(8), C15N3 = 1.327(7), C15N4 = 1.363(7); C1AuBr1 = 91.3(2), C15AuBr1 = 90.8(2), C1AuBr2 = 90.8(2), C15AuBr2 = 87.1(2), N1C1N2 = 105.2(5), N1C1Au = 129.1(5), N2C1Au = 125.5(5), C3C2N1 = 106.5(6), C2C3N2 = 107.6(6), C14C13N3 = 106.5(6), C13C14 N4 = 107.5(6), N3C15N4 = 107.3(5), N3C15Au = 127.7(4), N4C15Au = 124.9(5), C1N1C2 = 110.9(6), C1N2C3 = 109.8(6), C15N3C13 = 110.2(5), C15N4C14 = 108.5(5). Symmetry code: (0 ) x, y, z.
metal centers form a dihedral angle of 49.93(3)°. The two coordinated carbene rings to the Au2 metal center are almost parallel (dihedral angle 3.39(2)°), while those coordinated to Au1 are not, with a dihedral angle of 21.49(3)°. 3b0 is a coordination metallopolymer, formed by an infinite chain of AuBr2 units bridged by the dicarbene ligand. The polymeric structure develops along the a axes of the cell (Figures 6 and 7). To our knowledge, this is the first example of a carbene coordination metallopolymer of gold, although two examples of silver(I) carbene metallopolymers have been reported by Steed and Youngs.24 The Au(III) atoms are bonded to two carbene carbon atoms (the AuC bond distances are 2.03(1) and 2.05(1) Å) and two bromine atoms (the AuBr bond distances are 2.404(1) and 2.408(1) Å) in a square-planar arrangement. The mean coordination planes of the metal centers form a dihedral angle of 63.17(2)°, while the dihedral angle between the average planes, each containing the Au center and the two linearly coordinated carbene rings, is 110.02(2)°. In the 4611
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Organometallics crystals of 3b/3b0 , PF6 anions are also present to neutralize the positive charge and occupy the space between the chains and the dinuclear compounds. The nature of the bridge influences the stability of the dinuclear gold(III) complex, as confirmed by the X-ray analysis of complex 6b (Y = m-xylylene, Figure 8), a stable dinuclear Au(III)/Au(III) structure. The two gold(III) atoms are tetracoordinated in a squareplanar geometry, as expected for a heavy metal center in a d8 configuration. The bond angles CcarbeneAuCcarbene and BrAuBr are nearly linear (C1Au1C15 = 177.7(2)°, Br1Au1Br2 = 177.91(3)°). The complex has a centrosymmetric structure, and the two aromatic rings of the xylylene bridge are parallel. Different from compounds 3b/3b0 , the mean coordination planes of the metal centers are also parallel. The bond distances AuBr (2.421(1) and 2.426(1) Å) and AuCcarbene (2.044(6) and 2.042(6) Å) are comparable to those reported for monomeric dibromo bis-NHC gold(III) complexes.25,26 The dihedral angle between the imidazol-2-ylidene rings coordinated to the Au(III) center is 43.97(4)°, and the Au(III) 3 3 3 Au(III) distance is 8.874(5) Å, while in the corresponding Au(I) complex,10a the imidazol-2-ylidene rings are almost coplanar (9.45(2)°) and the Au(I) 3 3 3 Au(I) distance is 4.741(3) Å. To the best of our knowledge, 6b and 3b/3b0 are the first examples of crystal structures of dinuclear/polymeric gold(III) complexes with two dicarbene bridging ligands.
’ CONCLUSIONS In conclusion, we have synthesized a series of dinuclear N-heterocyclic bis-dicarbene gold(III) complexes of the general formula [Au2Br4(RIm-Y-ImR)2](PF6)2 by oxidative addition of bromine to the corresponding dicarbene gold(I) complexes. The stabilities of the various complexes in solution toward reductive elimination of Br2, as well as toward structural rearrangement triggered by ligand dissociation, are significantly different and mostly depend on the length of the bridging group connecting the two carbene units. Different molecular structures were determined by single-crystal X-ray analysis: dinuclear and polymeric bis-dicarbene Au(III)Au(III), dinuclear mono-dicarbene Au(III)Au(III), and dinuclear bis-dicarbene Au(III)Au(I) mixed-valence complexes were found. The observed reactivity opens the possibility of synthesizing mixed-valence complexes as well as complexes with different coordination sets. We are currently exploring these synthetic avenues as well as the photophysical and catalytic properties of the resulting complexes for possible applications. ’ EXPERIMENTAL SECTION General Remarks. All manipulations were carried out using standard Schlenk techniques under an atmosphere of argon or dinitrogen. The reagents were purchased by Aldrich as high-purity products and generally used as received; all solvents were technical grade and used as received. The gold(I) complexes 1a6a were prepared according to literature procedures.10a,13a,22 NMR spectra were recorded on a Bruker Avance 300 MHz (300.1 MHz for 1H and 75.5 for 13C); chemical shifts (δ) are reported in units of ppm relative to the residual solvent signals. ESI-MS were recorded on a Finnigan Thermo LCQ-Duo ESI-MS. XPS spectra were recorded using a Perkin-Elmer PHI 5600 ci spectrometer with a standard Al KR source (1486.6 eV) working at 300 W. The working pressure was less than 1 108 Pa. The spectrometer was calibrated by assuming the binding energy (BE) of the Au 4f7/2 line to lie at 84.0 eV with respect to
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the Fermi level. Extended spectra (survey) were collected in the range 01350 eV (187.85 eV pass energy, 0.5 eV step, 0.025 s step1). Detailed spectra were recorded for the following regions: Au 4f, Br 3d, N 1s, and C 1s (11.75 eV pass energy, 0.1 eV step, 0.2 s step1). The standard deviation in the BE values of the XPS line is 0.10 eV. The peak positions were corrected for charging effects by considering the C 1s peak at 285.0 eV and evaluating the BE differences. The powder for the XPS analysis was evacuated for 12 h at ca. 1 103 Pa before measurement.
General Procedure for the Oxidative Addition of Bromine to the Gold(I) Complexes. Bromine (0.48 mmol) was added to a solution of the gold(I) bis(hexafluorophosphate) complex (0.20 mmol) in acetonitrile (15 mL). The solution was stirred at room temperature overnight; then the solvent and the excess bromine were removed under vacuum. The residue was treated with diethyl ether, giving the desired product as a yellow solid, which was filtered, washed with diethyl ether (3 3 mL), and dried under vacuum. Tetrabromobis(1,10 -dimethyl-3,30 -methylenediimidazol-2,20 -diylidene)digold(III) Bis(hexafluorophosphate) (1b). Yellow solid (yield 91%). Anal. Calcd for C 18 H 24 Au 2 Br 4 F 12 N 8 P 2 : C, 15.93; H, 1.78; N, 8.26. Found: C, 16.11; H, 1.83; N, 8.24. 1H NMR (CD3CN, 25 °C, ppm): δ 3.99 (s, 12H, CH3), 6.42 (d AB system, 2JHH = 14.1 Hz, 2H, CH2), 7.02 (d AB system, 2JHH = 14.1 Hz, 2H, CH2), 7.57 (d, 3JHH = 2.0 Hz, 4H, CH), 7.79 (d, 3JHH = 2.0 Hz, 4H, CH). 13C{1H} NMR (CD3CN, 25 °C, ppm): δ 39.9 (CH3), 63.7 (CH2), 125.1 (CH), 128.6 (CH), 152.1 (NCN). ESI-MS (positive ions, CH3CN): m/z 1210.25 [AuIII2L2Br4PF6]+, 1050.85 [AuIIIAuIL2Br2PF6]+, 904.82 [AuIIAuIL2Br2]+, 824.99 [AuI2L2Br]+, 651.29 [AuI2LBr]+, 533.00 [AuIII2L2Br4]2+, 453.10 [AuIIIAuIL2Br2]2+, 373.33 [AuIL]+. Tetrabromobis(1,10 -dimethyl-3,30 -ethylenediimidazol-2,20 -diylidene)digold(III) Bis(hexafluorophosphate) (2b). Yellow solid (yield 65%). Anal. Calcd for C20H28Au2Br4F12N8P2: C, 17.34; H, 2.04; N, 8.10. Found: C, 17.66; H, 2.10; N, 7.83. 1H NMR (CD3CN, 25 °C, ppm): δ 3.97 (s, 12, CH3), 4.67 (s, 8H, CH2), 7.51 (d, 3JHH = 1.8 Hz, 4H, CH), 7.70 (d, 3JHH = 1.8 Hz, 4H, CH). 1H NMR (DMSO-d6, 25 °C, ppm): δ 4.00 (s, 12, CH3), 4.72 (s, 8H, CH2), 7.90 (d, 3JHH = 0.9 Hz, 4H, CH), 8.11 (d, 3JHH = 0.9 Hz, 4H, CH). 13C NMR (CD3CN, 25 °C, ppm): δ 38.9 (CH3), 50.2 (CH2), 126.0 (CH), 127.8 (CH), 151.7 (NCN). ESI-MS (positive ions, CH3CN): m/z 1238.58 [AuIII2L2Br4PF6]+, 1079.99 [AuIIIAuIL2Br2PF6]+, 932.89 [AuIIAuIL2Br2]+, 854.98 [AuI2L2Br]+, 665.00 [AuI2LBr]+, 546.15 [AuIII2L2Br4]2+, 467.11 [AuIIIAuIL2Br2]2+, 387.43 [AuIL]+. Tetrabromobis(1,10 -dimethyl-3,30 -propylenediimidazol-2,20 -diylidene)digold(III) Bis(hexafluorophosphate) (3b) and Metallopolymer (3b0 ). Yellow solid (yield 75%). Anal. Calcd for C22H32Au2Br4F12N8P2 3 3CH3CN: C, 20.89; H, 2.56; N, 9.37. Found: C, 21.11; H, 2.75; N, 9.04. Two sets of NMR signals are observed: the first one can be attributed to 3b by analogy with the spectra of complexes 1b, 2b, and 4b. Data for 3b are as follows. 1H NMR (CD3CN, 25 °C, ppm): δ 2.50 (m, 4H, CH2), 3.88 (s, 12H, CH3), 4.36 (m, 8H, CH2N), 7.43 (s, 4H, CH), 7.50 (s, 4H, CH). 13C NMR (CD3CN, 25 °C, ppm): δ 30.4 (CH2), 38.2 (CH3), 48.8 (CH2N), 124.3 (CH), 127.3 (CH), 151.2 (NCN). The second set of signals can possibly be attributed to the polymeric 3b0 . Data for 3b0 are as follows. 1H NMR (CD3CN, 25 °C, ppm): δ 2.50 (m, 2H, CH2), 3.43 (s, 6H, CH3), 4.15 (m, 4H, CH2N), 7.50 (s, 2H, CH), 7.55 (s, 2H, CH). 13C NMR (CD3CN, 25 °C, ppm): δ 30.4 (CH2), 38.0 (CH3), 46.9 (CH2N), 125.6 (CH), 127.6 (CH), 154.7 (NCN). ESI-MS (positive ions, CH3CN): m/z 1266.64 [AuIII2L2Br4PF6]+, 1106.94 [AuIIIAuIL2Br2PF6]+, 960.90 [AuIIAuI2L2Br2]+, 947.19 [AuI2L2PF6]+, 881.07 [AuI2L2Br]+, 679.32 [AuI2LBr]+, 561.01 [AuIII2L2Br4]2+, 481.22 [AuIIIAuIL2Br2]2+, 401.39 [AuIL]+. Tetrabromobis(1,10 -dimethyl-3,30 -butylenediimidazol-2,20 -diylidene)digold(III) Bis(hexafluorophosphate) (4b). Yellow solid (yield 58%). Anal. Calcd for C24H36Au2Br4F12N8P2: C, 20.00; H, 2.52; N, 4612
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Table 1
formula
1c-n
1c-p
1d
C18H24Au2Br2N8(PF6)2 3
C18H24Au2Br2N8(PF6)2 3
C9H12Au2Br6N4
CH2Cl2
2CH2Cl2
3b/3b0 C22H32Au2Br4N8(PF6)2/ C11H16Au1Br2N4(PF6)
6b C32H36Au2Br4N8(PF6)2 3 2CH3CN
mol wt
1281.07
1366.00
1049.62
2118.10
1618.31
cryst syst
monoclinic
monoclinic
monoclinic
triclinic
triclinic
space group a, Å
P21/n 12.1930(12)
P21/c 9.1548(8)
P21/n 8.194(3)
P1 12.6394(5)
P1 8.138(6)
b, Å
15.7836(15)
23.627(2)
13.782(4)
15.0375(6)
12.247(9)
c, Å
17.7452(17)
18.4503(16)
18.827(6)
16.4799(7)
13.659(10)
R, deg
90.00
90.00
90.00
64.6570(10)
73.870(13)
β, deg
91.785(2)
99.639(2)
82.507(6)
87.4280(10)
81.918(13)
γ, deg
90.00
90.00
90.00
89.0270(10)
74.257(13)
V, Å3
3413.4(6)
3934.5(6)
2108.1(12)
2827.9(2)
1255.7(16)
T, K Z
273 4
296 4
296 4
203 2
296 1
Dcalcd, g cm3
2.493
2.306
3.307
2.487
2.140
F(000)
2384
2552
1848
1968
764
μ(Mo KR), mm1
11.272
9.918
25.272
12.186
9.164
no. of rflns collected
40 454
61 429
32 263
45 087
20 082
no. of unique rflns
8206
11 524
6478
16 582
7384
no. of obsd rflns
5486
5203
4070
10 130 (Rint = 0.0643)
4552 (Rint = 0.0674)
(I > 2σ(I)) R (I > 2σ(I))
(Rint = 0.0508) R1 = 0.0337,
(Rint = 0.0925) R1 = 0.0520,
(Rint = 0.1089) R1 = 0.0616,
R1 = 0.0660,
R1 = 0.0506, wR2 = 0.0896
wR2 = 0.0791
wR2 = 0.1228
wR2 = 0.1321
wR2 = 0.1271
R1 = 0.0618,
R1 = 0.1404,
R1 = 0.1048,
R1 = 0.1178, wR2 = 0.1447
wR2 = 0.0864
wR2 = 0.1581
wR2 = 0.1434
R (all data)
7.78. Found: C, 20.20; H, 2.31; N, 7.76. 1H NMR (CD3CN, 25 °C, ppm): δ 2.02 (m, 8H, CH2), 3.89 (s, 12H, CH3), 4.24 (m, 8H, CH2), 7.40 (br, 8H, CH). 13C NMR (CD3CN, 25 °C, ppm): δ 28.2 (CH2), 38.6 (CH3), 51.1 (CH2), 125.2 (CH), 126.8 (CH), 150.9 (NCN). ESIMS (positive ions, CH3CN): m/z 1294.83 [AuIII2L2Br4PF6]+, 1135.06 [AuIIIAuIL2Br2PF6]+, 990.94 [AuIIAuI2L2Br2]+, 975.28 [AuI2L2PF6]+, 909.07 [AuI2L2Br]+, 691.17 [AuI2LBr]+, 575.11 [AuIII2L2Br4]2+, 495.26 [AuIIIAuIL2Br2]2+, 415.38 [AuIL]+. Tetrabromobis(1,10 -dicyclohexyl-3,30 -methylenediimidazol-2,20 diylidene)digold(III) Bis(hexafluorophosphate) (5b). Yellow solid (yield 76%). Anal. Calcd for C38H 56Au 2Br 4F 12N8P 2: C, 28.01; H, 3.47; N, 6.88. Found: C, 27.81; H, 3.45; N, 6.83. 1 H NMR (CD3 CN, 25 °C, ppm): δ 1.02.0 (m, 40H, CH2 Cy), 4.53 (br, 4H, CH Cy), 6.47 (d AB system, 2 JHH = 4.8 Hz, 2H, CH2 ), 6.89 (d AB system, 2 JHH = 4.8 Hz, 2H, CH2), 7.72 (d, 3JHH = 1.2 Hz, 4H, CH), 7.82 (d, 3 JHH = 1.2 Hz, 4H, CH). 13C NMR (CD 3CN, 25 °C, ppm): δ 25.2 (CH2 Cy), 30.9 (CH 2 Cy), 63.6 (CH Cy), 64.2 (CH 2), 126.2 (CH), 129.3 (CH), 151.0 (NCN). ESI-MS (positive ions, CH3 CN): m/z 1482.53 [AuIII2 L2Br 4PF6]+ , 1323.00 [AuIIIAuI L2Br 2PF 6]+ , 1177.07 [AuIIAuI L2Br 2]+ , 1099.27 [Au I 2L2Br]+ , 785.20 [AuI 2LBr]+ , 669.07 [AuIII 2L 2Br 4]2+ , 588.27 [Au III AuI L2Br2 ]2+ , 509.00 [AuI L]+ . Tetrabromobis(1,10 -dimethyl-3,30 -(m-xylylene)diimidazol-2,20 -diylidene)digold(III) Bis(hexafluorophosphate) (6b). Yellow solid (yield 92%). Anal. Calcd for C32H36Au2Br4F12N8P2 3 CH3CN: C, 25.88; H, 2.49; N, 7.99. Found: C, 26.02; H, 2.52; N, 8.26. 1H NMR (DMSO-d6, 25 °C, ppm): δ 2.07 (s, CH3CN), 3.96 (s, 12H, CH3), 5.08 (s, 8H, CH2), 7.01 (d, 2JHH = 7.5 Hz, 4H, xylylen), 7.39 (m, 4H, xylylen), 7.59 (d, 3JHH = 1.5 Hz, 4H, CH), 7.77 (d, 3JHH = 1.5 Hz, 4H, CH). 1H NMR (CD3CN, 25 °C, ppm): δ = 3.92 (s, 12H, CH3), 4.99 (s, 8H, CH2), 7.06 (m, 4H, xylylene), 7.23 (m, 4H, CH), 7.39 (m, 8H, CH and xylylene). 13 C NMR (CD3CN, 25 °C, ppm): δ 38.9 (CH3), 54.2 (CH2), 125.7
R1 = 0.0964, wR2 = 0.1053
(CH), 126.7 (CH), 129.1 (CH), 129.9 (CH), 131.4 (CH), 136.2 (CH), 151.1 (NCN). ESI-MS (positive ions, CH3CN): m/z 1390.73 [AuIII2L2Br4PF6]+, 1230.93 [AuIIIAuIL2Br2PF6]+, 1071.07 [AuIIAuIL2Br2]+, 1006.87 [AuI2L2Br]+, 739.07 [AuI2LBr]+, 623.13 [AuIII2L2Br4]2+, 543.00 [AuIIIAuIL2Br2]2+, 463.47 [AuIL]+.
Dibromobis(1,10 -dimethyl-3,30 -methylenediimidazol-2,2 -diylidene)digold(I,III) Bis(hexafluorophosphate) (1c). This 0
complex was obtained as the main product in attempts at obtaining crystals of 1b suitable for X-ray diffraction analysis. Crystals of 1c were grown by diffusion of CH2Cl2/n-hexane (1/5 v/v) into a solution of 1b in acetonitrile at room temperature. Crystals of two different morphologies, needles 1c-n and prisms 1c-p, were obtained; the X-ray structure determination shows the same structure. The complex was characterized using NMR spectra by dissolving the crystals 1c-n/1c-p in CD3CN. 1H NMR (CD3CN, 25 °C, ppm): δ 3.90 (s, 6H, CH3), 3.95 (s, 6H, CH3), 6.25 (d AB system, 2JHH = 14.7 Hz, 2H, CH2), 6.96 (d AB system, 2JHH = 14.7 Hz, 2H, CH2), 7.32 (s, 2H, CH), 7.49 (s, 2H, CH), 7.59 (s, 2H, CH), 7.78 (s, 2H, CH). 13C NMR (CD3CN, 25 °C, ppm): δ 39.0 (CH3), 39.5 (CH3), 63.4 (CH2), 121.9 (CH), 124.9 (CH), 126.4 (CH), 128.4 (CH), 151.8 (NCN), 186.0 (NCN).
Hexabromo(1,10 -dimethyl-3,30 -methylenediimidazolin2,20 -diylidene)digold(III) (1d). This complex was also obtained, in
very low yield, from an acetonitrile solution of 1b by slow diffusion of diethyl ether/CH2Cl2. The complex was characterized using NMR spectra by dissolving the crystals utilized for X-ray structure determination in CD3CN. 1H NMR (CD3CN, 25 °C, ppm): δ 3.89 (s, 6H, CH3), 6.64 (s, 2H, CH2), 7.46 (d, 3JHH = 1.5 Hz, 2H, CH), 7.66 (d, 3JHH = 1.5 Hz, 2H, CH).
Solid-State Structure Determination of 1c-n, 1c-p, 1d, 3b/ 3b0 , and 6b. As stated above, crystals of 1c-n, 1c-p, and 1d suitable for 4613
dx.doi.org/10.1021/om2004145 |Organometallics 2011, 30, 4607–4615
Organometallics X-ray diffraction analysis were grown in an acetonitrile solution of 1b at room temperature by diffusion of CH2Cl2/n-hexane (1/5 v/v) (1c-n and 1c-p) or of diethyl ether (1d). Crystals of 6b were grown by diffusion of diethyl ether into an acetonitrile solution of the same complex. Crystals of 3b/3b0 were grown by diffusion of diethyl ether into an acetonitrile solution of the synthesis mixture. Data for complexes 1c-p, 1d, 3b/3b0 , and 6b were collected on a Bruker APEX II single-crystal diffractometer, while data for 1c-n were obtained on a Bruker AXS SMART 1000 instrument, both working with Mo KR graphite-monochromated radiation (λ = 0.710 73 Å) and equipped with an area detector.27 Details for the X-ray data collection are reported in Table 1. The structure was solved by direct methods with SHELXS-97 and refined against F2 with SHELXL-97,28 with anisotropic thermal parameters for all non-hydrogen atoms except the carbon and chlorine atoms of the dichloromethane solvent molecule in 1c-n; this solvent molecule was found disordered in two positions. The hydrogen atoms were placed in the ideal geometrical positions. Crystallographic data for all compounds have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC 835518 for 1c-n, CCDC 835519 for 1c-p, CCDC 835520 for 1d, CCDC 835521 for 3b/3b0 , and CCDC 835522 for 6b. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, (+44) 1223 336033; e-mail,
[email protected]).
’ ASSOCIATED CONTENT
bS
Supporting Information. Figures giving NMR spectra of 1c,d and CIF files giving crystallographic data for 1c-n, 1c-p, 1d, 3b/3b0 , and 6b. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Tel: +39 049 8275655. Fax: +39 049 8275223. E-mail: cristina.
[email protected].
’ ACKNOWLEDGMENT C.T. thanks the University of Padova for financial support (CPDA085452 and HELIOS project). ’ REFERENCES (1) (a) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed. 2006, 45, 7896. (b) Dyker, G. Angew. Chem., Int. Ed. 2000, 39, 4237. (c) Hutchings, G. J.; Haruta, M. Appl. Catal. A: Gen. 2005, 291, 2. (d) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2005, 44, 6990. (e) Nolan, S. P. Nature 2007, 445, 496. (2) (a) Li, Z.; Brouwer, C.; He, C. Chem. Rev. 2008, 108, 3239. (b) Arcadi, A. Chem. Rev. 2008, 108, 3266. (c) Gorin, D. J.; Sherry, B. D.; Toste, F. D. Chem. Rev. 2008, 108, 3351. (d) Díaz-Requejo, M. M.; Perez, P. J. Chem. Rev. 2008, 108, 3379. (e) Hashmi, A. S. K.; Rudolph, M. Chem. Soc. Rev. 2008, 37, 1766. (3) Teets, T. S.; Nocera, D. G. J. Am. Chem. Soc. 2009, 131, 7411. (4) See the special issue “Bioinorganic and Biomedical Chemistry of Gold”: Coord. Chem. Rev. 2009, 253, 15971708. (5) (a) Haruta, M.; Kobayashi, T.; Sano, H.; Yamada, N. Chem. Lett. 1987, 16, 405. (b) Haruta, M.; Yamada, N.; Kobayahsi, T.; Iijima, S. J. Catal. 1989, 115, 301. (c) Hutchings, G. J. J. Catal. 1985, 96, 292. (d) Valden, M.; Lai, X.; Goodman, D. W. Science 1998, 281, 1647. (6) (a) Marion, N.; Nolan, S. P. Chem. Soc. Rev. 2008, 37, 1776. (b) Nolan, S. P. Acc. Chem. Res. 2011, 44, 91. (7) Lin, I. J. B.; Vasam, C. S. Can. J. Chem. 2005, 83, 812.
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Organometallics
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