Synthesis of Homoleptic and Heteroleptic Bis-N-heterocylic Carbene

Jan 8, 2015 - Valerie H. L. Wong , Andrew J. P. White , T. S. Andy Hor , King Kuok (Mimi) Hii. Chemical Communications 2015 51 (100), 17752-17755 ...
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Synthesis of Homoleptic and Heteroleptic Bis-N-heterocylic Carbene Group 11 Complexes Faïma Lazreg, David B. Cordes, Alexandra M. Z. Slawin, and Catherine S. J. Cazin* EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, U.K. S Supporting Information *

ABSTRACT: A straightforward synthetic route has been developed permitting the formation of homoleptic and heteroleptic bis-N-heterocyclic carbene metal complexes. The methodology has proven efficient for all group 11 members. These complexes are easily synthesized using [M(Cl)(NHC)] with different NHC salts in the presence of inexpensive bases such as sodium hydroxide. These systems were fully characterized and displayed high stability even in the presence of light.

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INTRODUCTION Since the first stable N-heterocyclic carbene (NHC) isolated by Arduengo,1 NHCs have emerged as efficient ligands in catalysis. Their electronic and steric tunability render them ligands of choice in organometallic chemistry and homogeneous catalysis.2 NHC metal systems show high activity and stability in several transformations, giving access to essential building blocks in organic synthesis.2−4 Recently, cationic group 11 metal NHC complexes have emerged as particularly interesting systems for catalysis but also as antitumor and antimicrobial reagents.3−5 The synthetic approaches leading to such systems have mainly focused on the formation of homoleptic bis-NHC complexes.6−8 In the cases of silver and copper, homoleptic complexes are most commonly obtained by reaction of either the imidazol(idin)ium salt or the free carbene with a source of silver/copper (Scheme 1).6−8 With respect to Au systems, the most common synthetic

route is based on carbene transfer from Ag-NHC species, typically to [Au(Cl)(DMS)] (DMS = dimethyl sulfide).7 On the other hand, heteroleptic bis-NHC complexes remain scarce, due either to a lack of attention or, more likely, to a laborious synthetic access.9−13 To the best of our knowledge, only one example of a heteroleptic bis-NHC silver(I) complex has been reported to date (Scheme 2), obtained through a somewhat arduous synthetic pathway in moderate yield (48%).6a In 2010, Nolan and co-workers reported a methodology based on [Au(OH)(IPr)], allowing the formation of heteroleptic systems (Scheme 2).9,10 More recently, our group used a similar methodology to prepare copper analogues (Scheme Scheme 2. Synthetic Accesses to Heteroleptic Bis-NHC Metal Complexes9−13

Scheme 1. Synthetic Accesses to Homoleptic Bis-NHC Complexes6−8

Received: August 28, 2014

© XXXX American Chemical Society

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Organometallics 2).11−13 Both synthetic protocols require the formation and isolation of a key hydroxide synthon, [M(OH)(NHC)], which reacts in an acid−base manner with imidazol(idin)ium salts. The major drawback of this synthetic methodology is the limited number of hydroxide complexes that have been isolated thus far. In addition, to the best of our knowledge, no hydroxide silver NHC has yet been reported, probably due to the high instability of such species. Thus, a general method allowing for the formation of homoleptic and heteroleptic group 11 metal complexes without the need to isolate hydroxide intermediates remains most interesting and would give access to a large library of complexes, relevant to catalysis and other applications. Herein, we report a general protocol allowing the formation of homoleptic and heteroleptic bis-carbene silver(I), copper(I), and gold(I) complexes in short reaction times using microwave irradiation and simple starting reagents.

Scheme 3. Synthesis of Heteroleptic Bis-NHC Silver(I) Complexes

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RESULTS AND DISCUSSION As mentioned above, synthetic strategies so far developed for the formation of heteroleptic (and to some extent homoleptic) group 11 metal complexes are mainly limited to systems derived from hydroxide species (or in the silver(I) case a siloxane intermediate), hence considerably limiting the size of the library of accessible compounds. This is well exemplified by the case of silver derivatives. When attempting to isolate [Ag(OH)(IPr)], while the reaction seemed to proceed, complex isolation in high purity was not achieved and fast decomposition was observed by NMR spectroscopy.14 Similar difficulties were encountered when we attempted to increase the scope of the reaction for Cu complexes by isolating hydroxide complexes other than [Cu(OH)(IPr)].14 All data indicate that new species are formed, which might be the hydroxide derivative but that undergo rapid degradation during workup. On the basis of these initial observations, we reasoned that in situ formation of the hydroxide followed by the acid− base reaction should be possible. A reaction was first carried out using silver(I)-NHC complexes. Interestingly, when the reaction between [Ag(Cl)(IPr)] (1 equiv) and IMes·HBF4 (1 equiv) was conducted in the presence of CsOH, a new product was observed and identified by 1H NMR as [Ag(IPr)(IMes)]BF4 (3b) (Scheme 3).15 In the absence of base, only disproportion occurs and the homoleptic bis-carbene complex [Ag(IPr)2][AgCl2] is observed.6c Next, various bases were tested, and sodium hydroxide appeared as highly efficient to carry out the reaction in acetonitrile (within 2 h). Different imidazol(idin)ium salts were tested to expand the scope of this reaction, and in all cases the heteroleptic bis-NHC complexes were obtained in excellent isolated yield and purity (Scheme 3). In order to showcase the versatility of this method, [Ag(IPr)(IMes)]BF4 (3b) was prepared from either [Ag(Cl)(IMes)] or [Ag(Cl)(IPr)] and the complementary imidazolium salt. In both cases, [Ag(IPr)(IMes)]BF4 (3b) was identified as the only product formed without any detectable trace of the respective homoleptic analogues (Scheme 3). The versatility of this methodology was further shown by the synthesis of [Ag(SIPr)(IMes)]BF4 (5). Indeed 5 was obtained from either [Ag(Cl)(IMes)] or [Ag(Cl)(SIPr)]; there again, no trace of homoleptic bis-NHC complexes was detected (Scheme 4). Interestingly, in contrast to most Ag(I) complexes, these bisNHC species do not exhibit any particular sensitivity toward light in the solid state or in solution. All reactions and workups were hence carried out in the presence of light. Further tests

a

Reaction time. bIsolated yield.

Scheme 4. Synthesis of [Ag(SIPr)(IMes)]BF4 (5)

a

Isolated yield.

were performed to confirm the stability toward light (standard fluorescence fumehood lighting and sunlight) of these complexes, using 3b as a model. After several days, in the presence of light in the solid state, NMR spectra showed no decomposition of the complex and the solid appearance remained that of a microcrystalline colorless compound. The same tests were conducted in solution using chlorinated (CH2Cl2) and nonchlorinated solvents (THF). Once again, NMR experiments showed no sign of decomposition of 3b, confirming the high stability of this complex with respect to light. The viability of this one-pot protocol was next examined for the formation of copper(I) and gold(I) complexes. Following similar reaction conditions, [Cu(Cl)(IPr)] (6) was reacted with IMes·HBF4 and an excess of NaOH (Scheme 5). After 2 h at 80 °C, NMR data confirmed quantitative conversion to a single product, whose identity is supported by data reported for the heteroleptic bis-NHC copper(I) (7b) as well as elemental analysis. The product was isolated in an excellent 92% yield. The reaction was efficiently extended to a series of tetrafluoroborate imidazol(idin)ium salts (ICy·HBF4, ItBu· B

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completion. The present method allowed complete conversion to the desired compound within 2 h. The homoleptic analogues can also be obtained using this approach. Indeed, [Au(IMes)2]BF4 12 was isolated as a white solid when [Au(Cl)(IMes)] and IMes·HBF4 were used in stoichiometric amount under these simple reaction conditions (Scheme 6). The interesting feature of the latter methodology is that it is silver-f ree. The saturated analogues can also be obtained starting from the corresponding precursor. For example, [Au(SIPr)(IMes)]BF4 14a can be obtained from the reaction of [Au(Cl)(SIPr)] with IMes·HBF4 or when NHCs were interchanged (using [Au(Cl)(SIPr)] in the presence of IPr·HBF4) (Scheme 7). ICy· HBF4 and ItBu·HBF4 were also efficiently used to perform the reaction, and the desired complexes (14b and 14c) were obtained in excellent yields, 92% and 94%, respectively.

Scheme 5. Synthesis of Cationic Bis-NHC Cu Complexes

Scheme 7. Synthesis of Cationic Bis-NHC Gold(I) Complexes

a

Reaction time. bIsolated yield.

HBF4, SIMes·HBF4, and SIPr·HBF4) (Scheme 5). An unsymmetrical ligand was tested, also leading in excellent yield to the heteroleptic bis-NHC Cu complex 7f. Here again, to prove the versatility of the methodology, [Cu(IPr)(IMes)]BF4 (7b) was obtained from two routes: by reaction of [Cu(Cl)(IMes)] and IPr·HBF4 and by reaction of [Cu(Cl)(IPr)] and IMes·HBF4 (Scheme 5). In both cases, the heteroleptic complex was isolated in high yield and purity. Turning our attention to gold(I) NHC complexes, the onepot procedure also works as depicted in Scheme 6. Of note is the fact that the method reported for [Au(IPr)(IMes)]BF4 (10b) from the [Au(OH)(IPr)] requires 48 h at 70 °C to reach

a

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STRUCTURAL STUDIES Crystallographic studies were carried out to unambiguously establish the structural features of these complexes (Figures 1−4).16 No particular precaution was used to avoid the presence of light or moisture during the crystallization of the complexes (dichloromethane/pentane). All silver(I) complexes present a linear geometry with CNHC−Ag−CNHC′ angles between 176.8(3)° and 180.0(4)° (Table 1). The Ag−CNHC bond lengths lie in the range 2.055(11) to 2.137(12) Å. The steric hindrance of the NHC ligands was determined by calculation of the percent buried volume (%VBur) using the SambVca application developed by Cavallo and co-workers.17 The values obtained for the IPr moiety in complexes 3a, 3c, 3d, and 3e lie in the range 42.0 to 44.9%. For complex 3b, an unexpected high %VBur was obtained (47.1%). While NHC ligands in transition metal complexes are known to modulate their steric bulk in response to the steric requirement of coligands, in the present series, no obvious trend can be found, presumably due to the fact that both ligands “accommodate” each other.18 The %VBur found for the different ligands trans to IPr are in agreement with the literature,2e,f with the following order of bulkiness found: SIPr > ItBu > SIMes > IMes > ICy (%VBur, respectively: 43.4, 38.5, 35.8, 35.3, 27.3).

Scheme 6. Synthesis of [Au(IPr)2]BF4 10a, [Au(IPr)(IMes)]BF4 10b, and [Au(IMes)2]BF4 12

a

Reaction time. bIsolated yield.

Isolated yield. C

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Figure 4. Molecular structure of [Au(SIPr)(ICy)]BF4 (14b) and [Au(SIPr)(ItBu)]BF4 (14c). Hydrogen atoms and counteranion are omitted for clarity.16

Table 1. Selected Bond Lengths (Å) and Angles (deg) (esd) and %VBur for Complexes [Ag(NHC)(NHC′)] 3a−e and 5

a

θ = torsion angle between NHCs.

in [Ag(SIPr)(IMes)]BF4 5 (47.1 and 45.9%, respectively); this difference, through small, is striking given that saturated ligands are usually more sterically demanding than their unsaturated analogues.2 Additionally, this cannot be rationalized by the % VBur of the coligand IMes, as the smallest value is found for 5 (IMes %VBur 34.2 in 5, 35.3 in 3b). Interestingly, while the torsion angles between the NHCs do not show a correlation with the steric hindrance of the ligands, a clear difference is found depending on the nature of the N-substituents: complexes bearing only N-aryl-substituted ligands have large torsion angles (6.9−50.2°), while in contrast, complexes bearing an N-alkyl-substituted ligand have θ values close to 0°. This cannot be explained using solely steric arguments, as ItBu is bulkier than all other ligands studied here (except SIPr) and still leads to a negligible torsion angle (0.9°). The flexibility of the alkyl-substituted ligands is presumably responsible for these small θ values. The analogous copper(I) complexes 7a−f also display a nearly linear geometry, with C−Cu−C angles falling in the range 175.4(3)−180.0(2)°, which is comparable to data reported for other congeners (Table 2).11,19 The largest

Figure 1. Molecular structure of [Ag(IPr)(SIPr)]BF4 3a, [Ag(IPr)(IMes)]BF4 3b, [Ag(IPr)(SIMes)]BF4 3c, [Ag(IPr)(ICy)]BF4 3d, [Ag(IPr)(ItBu)]BF4 3e, and [Ag(SIPr)(IMes)]BF4 5. Hydrogen atoms and counter-anions are omitted for clarity.16

Figure 2. Molecular structure of [Cu(IPr){SI(Mes-Me)}]BF4, 7f. Hydrogen atoms and counteranion are omitted for clarity.16

Table 2. Selected Bond Lengths (Å) and Angles (deg) (esd) and %VBur for Complexes [Cu(NHC)(NHC′)] 7a−f

Figure 3. Molecular structure of [Au(IMes)2]BF4, 12. Hydrogen atoms and counteranion are omitted for clarity.16

A comparison between [Ag(IPr)(IMes)]BF4 3b and the saturated analogue [Ag(SIPr)(IMes)]BF4 5 leads to an unexpected observation: the IPr ligand of [Ag(IPr)(IMes)]BF4 3b is more sterically hindered than its saturated analogue SIPr

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equiv), and acetonitrile (2 mL). The reaction mixture was heated at 80 °C in a microwave for the appropriate time. The reaction mixture was concentrated in vacuo (1 mL), and diethyl ether (2 mL) was added. The product was collected by filtration. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazol-2-ylidene-N,N′-bis{2,6-(di-isopropyl)phenyl}imidazolidin-2-ylidene Silver(I) Tetrafluoroborate, [Ag(IPr)(SIPr)]BF4, 3a. [Ag(Cl)(IPr)] (100.0 mg, 0.19 mmol), NaOH (30.0 mg, 0.76 mmol), SIPr·HBF4 (90.9 mg, 0.19 mmol), 40 min. Colorless solid, 170.2 mg, 0.17 mmol, 92%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 0.75 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 0.78 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.02 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.20 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 2.22 (septet, 4H, 3 JHH = 6.9 Hz, CHCH3), 2.79 (septet, 4H, 3JHH = 6.9 Hz, CHCH3), 3.92 (s, 2H, H4 and H5 SIPr), 7.02 (d, 2H, 3JHH = 1.5 Hz, H4′ and H5′ IPr), 7.05 (d, 4H, 3JHH = 7.8 Hz, Ar), 7.12 (d, 4H, 3JHH = 7.8 Hz, Ar), 7.34 (t, 2H, 3JHH = 7.8 Hz, Ar), 7.46 (t, 2H, 3JHH = 7.8 Hz, Ar). 13 C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 23.8 (s, CHCH3), 24.1 (s, CHCH3), 24.2 (s, CHCH3), 25.6 (s, CHCH3), 28.5 (s, CHCH3), 54.4 (s, C4 and C5 SIPr), 124.4 (s, Ar), 124.7 (s, Ar), 129.8 (s, Ar), 130.7 (s, Ar IPr), 134.6 (s, CIV), 134.7 (s, C4′ and C5′ IPr), 145.2 (s, CIV), 146.3 (s, CIV).20 19F{1H} NMR (282 Hz, CDCl3, 298 K): δ = −154.6 (s, BF4), −154.7 (s, BF4). Anal. Calcd for C54H74BAgF4N4: C, 66.60; H, 7.66; N, 5.75. Found: C, 66.50; H, 7.72; N, 5.59. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazol-2-ylidene-N,N′-bis{(2,4,6-(trimethyl)phenyl)}imidazol-2-ylidene Silver(I) Tetrafluoroborate, [Ag(IPr)(IMes)]BF4, 3b. Procedure A. [Ag(Cl)(IPr)] (100.0 mg, 0.19 mmol), NaOH (30.0 mg, 0.76 mmol), IMes·HBF4 (74.5 mg, 0.19 mmol), 2 h 10 min. Colorless solid, 160.3 mg, 0.18 mmol, 95%. Procedure B. [Ag(Cl)(IMes)] (100.0 mg, 0.22 mmol), NaOH (35.7 mg, 0.88 mmol), IPr·HBF4 (104.8 mg, 0.22 mmol), 2 h 20 min. Colorless solid, 183.5 mg, 0.21 mmol, 94%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 0.80 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.13 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.67 (s, 12H, CH3 Mes), 2.26 (septet, 4H, 3JHH = 6.9 Hz, CHCH3), 2.39 (s, 6H, CH3 Mes), 6.79 (s, 4H, Ar IMes), 7.03 (s, 2H, H4 and H5 IMes), 7.16 (d, 4H, 3JHH = 7.9 Hz, Ar IPr), 7.24 (s, 2H, H4′ and H5′ IPr), 7.53 (t, 2H, 3JHH = 7.9 Hz, Ar IPr). 13 C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 17.0 (s, CH3 Mes), 21.2 (s, CH3 Mes), 23.7 (s, CHCH3), 24.3 (s, CHCH3), 28.4 (s, CHCH3), 123.5 (s, Ar IPr), 123.9 (s, C4 and C5), 129.6 (s, Ar IMes), 130.5 (s, Ar IPr), 134.2 (s, C4′ and C5′), 134.6 (s, CIV), 139.1 (s, CIV), 145.3 (s, CIV).20 19F{1H} NMR (282 Hz, CDCl3, 298 K): δ = −155.1 (s, BF4), −155.0 (s, BF4). Anal. Calcd for C48H60BAgF4N4: C, 64.95; H, 6.81; N, 6.31. Found: C, 64.83; H, 6.90; N, 6.40. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazol-2-ylidene-N,N′-bis{2,4,6-(trimethyl)phenyl}imidazolidin-2-ylidene Silver(I) Tetrafluoroborate, [Ag(IPr)(SIMes)]BF4, 3c. [Ag(Cl)(IPr)] (100.0 mg, 0.19 mmol), NaOH (30.0 mg, 0.76 mmol), SIMes·HBF4 (74.9 mg, 0.19 mmol), 2 h 20 min. Colorless solid, 160.5 mg, 0.18 mmol, 95%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 0.78 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.11 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.89 (s, 12H, CH3 Mes), 2.22 (septet, 4H, 3JHH = 6.9 Hz, CHCH3), 2.32 (s, 6H, CH3 Mes), 3.83 (s, 4H, H4 and H5 SIMes), 6.71 (s, 4H, Ar SIMes), 7.16 (d, 4H, 3JHH = 7.8 Hz, Ar IPr), 7.18 (s, 2H, H4′ and H5′ IPr), 7.53 (t, 2H, 3 JHH = 7.8 Hz, Ar IPr). 13C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 17.4 (s, CH3 Mes), 21.1 (s, CH3 Mes), 23.7 (s, CHCH3), 24.2 (s, CHCH3), 28.4 (s, CHCH3), 51.5 (s, C4 and C5 SIMes), 123.9 (s, CIV), 124.0 (s, Ar IPr), 129.9 (s, Ar SIMes), 130.5 (s, Ar IPr), 134.1 (s, C4′ and C5′ IPr), 134.7 (s, CIV), 135.1 (s, CIV), 138.0 (s, CIV), 145.2 (s, CIV).20 19F{1H} NMR (282 Hz, CDCl3, 298 K): δ = −155.1 (s, BF4), 155.0 (s, BF4). Anal. Calcd for C48H62BAgF4N4: C, 64.80; H, 7.02; N, 6.30. Found: C, 64.71; H, 6.95; N, 6.19. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazol-2-ylidene-N,N′(dicyclohexyl)imidazol-2-ylidene Silver(I) Tetrafluoroborate, [Ag(IPr)(ICy)]BF4, 3d. [Ag(Cl)(IPr)] (100.0 mg, 0.19 mmol), NaOH (30.0 mg, 0.76 mmol), ICy·HBF4 (60.8 mg, 0.19 mmol), 2 h 20 min. Colorless solid, 144.2 mg, 0.18 mmol, 93%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 0.88−1.14 (m, 6H, CH2 cyclohexyl), 1.23 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.29 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.33−1.49 (m, 4H, CH2 cyclohexyl), 1.55−1.77 (m, 10H, CH2 cyclohexyl), 2.58 (septet, 4H, 3JHH = 6.9 Hz, CHCH3), 3.26 (tt, 2H,

distortion from linearity is found in [Cu(IPr){SI(Mes-Me)]BF4 (7f) (175.4(3)° C−Cu−C), which reflects the dissymmetric Nsubstitution of one of the ligands. Here again, the flexibility of the alkyl-substituted carbenes is reflected by small torsion angles, while systems bearing solely N-aryl ligands display a substantial θ value. Complex 7f, which bears an N,N′-alkyl-arylsubstituted ligand, has a torsion angle of 18.9°, which, as expected, lies between the values obtained for the N,N′-dialkylsubstituted ligands (0−0.9°) and the values obtained for the N,N′-diaryl derivatives (43.4−59.6°). The gold(I) complexes also present a nearly linear geometry with C−Au−C angles between 176.6(9)° and 180.0(0)° (Table 3). Bond angles and distances are within the range expected for Table 3. Selected Bond Lengths (Å) and Angles (deg) (esd) and %VBur for Complexes [Au(NHC)(NHC′)] 10a, 10b, 12, 14b, and 14c

a

θ = Torsion angle between NHCs.

such complexes.10 Similarly to Cu and Ag congeners, the torsion angle between the NHCs is large for complexes bearing N,N′-diaryl derivatives (40.9−124.5°) and small for complexes bearing an N,N′-dialkyl-substituted ligand (0−10.7°). These results show again that the torsion angles do not correlate with the steric hindrance of a given ligand, but are a gauge of flexibility. The largest angle is found for the homoleptic complex 12 (124.5°), which correlates with a relatively small Au−C bond distance (1.998(5) Å). The %VBur found are in accordance with trends found in the literature for these NHCs.2e,f

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CONCLUSION A straightforward synthetic route leading to heteroleptic and homoleptic bis-NHC group 11 complexes has been developed. This methodology proceeds by an acid−base reaction possibly through in situ formation of a metal hydroxide synthon, which would react with the imidazol(idin)ium salt. The prior isolation of the hydroxo derivatives is no longer required. A library of group 11 complexes has been generated easily in short reaction times and in silver-free conditions. These complexes were found to be air, moisture, and light insensitive in solution and in the solid state. The structural studies showed a linear geometry but also the presence of torsion angles for the systems bearing N-aryl substituents. Other combinations involving other neutral copper(I), silver(I), or gold(I) complexes can be considered, thus extending the number of cationic bis-NHC systems by using this simple synthetic protocol and leading to easy access to a range of group 11 complexes. Their ease of access should facilitate their use in catalysis.

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EXPERIMENTAL SECTION

General Procedure. A vial was charged with [M(Cl)(NHC)] (1 equiv), NaOH (4 equiv), the appropriate imidazol(idin)ium salt (1 E

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JHH = 12.0 Hz, 3JHH = 4 Hz, CH cyclohexyl), 7.01 (d, 2H, 3JHH = 1.9 Hz, H4 and H5), 7.38 (d, 4H, 3JHH = 7.8 Hz, Ar), 7.41 (s, 2H, 3JHH = 1.5 Hz, H4′ and H5′), 7.58 (t, 2H, 3JHH = 7.8 Hz, Ar). 13C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 23.7 (s, CHCH3), 24.6 (s, CH2 cyclohexyl), 25.0 (s, CH2 cyclohexyl), 25.2 (s, CHCH3), 28.7 (s, CHCH3), 34.1 (s, CH2 cyclohexyl), 61.9 (s, CH cyclohexyl), 118.7 (s, C4 and C5), 124.4 (s, Ar), 124.6 (s, C4′ and C5′), 131.0 (s, Ar), 134.4 (s, CIV), 146.0 (s, CIV).20 19F-{1H} NMR (282 Hz, CDCl3, 298 K): δ = −154.7 (s, BF4). −154.6 (s, BF4). Anal. Calcd for C42H60BAgF4N4: C, 61.85; H, 7.41; N, 6.87. Found: C, 61.77; H, 7.49; N, 6.97. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazol-2-ylidene-N,N′-(ditert-butyl)imidazol-2-ylidene Silver(I) Tetrafluoroborate, [Ag(IPr)(ItBu)]BF4, 3e. [Ag(Cl)(IPr)] (100.0 mg, 0.19 mmol), NaOH (30.0 mg, 0.76 mmol), ItBu·HBF4 (50.9 mg, 0.19 mmol), 2 h 30 min. Colorless solid, 136.4 mg, 0.18 mmol, 94%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 1.20 (s, 18H, C(CH3)3), 1.22 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 0.82 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 2.62 (septet, 4H, 3 JHH = 6.9 Hz, CHCH3), 7.08 (d, 2H, 3JHH = 1.93 Hz, H4 and H5), 7.06 (s, 2H, H4 and H5), 7.35 (d, 4H, 3JHH = 7.9 Hz, CH Ar), 7.44 (d, 2H, 3JHH = 1.53 Hz, H4′ and H5′), 7.55 (t, 2H, 3JHH = 7.9 Hz, CH Ar). 13 C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 24.2 (s, CHCH3), 24.5 (s, CHCH3), 28.8 (s, CHCH3), 31.7 (s, CCH3), 57.1 (s, CCH3), 117.7 (s, C4 and C5), 124.5 (s, Ar), 124.7 (s, Ar), 130.9 (s, C4′ and C5′), 134.9 (s, CIV), 145.5 (s, CIV).20 19F{1H} NMR (282 Hz, CDCl3, 298 K): δ = −154.3 (s, BF4). −154.4(s, BF4). Anal. Calcd for C38H56BAgF4N4: C, 59.77; H, 7.39; N, 7.34. Found: C, 59.71; H, 7.45; N, 7.40. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazolidin-2-ylidene-N,N′-bis{2,4,6-(trimethyl)phenyl}imidazol-2-ylidene Silver(I) Tetrafluoroborate, [Ag(SIPr)(IMes)]BF4, 5. Procedure A. [Ag(Cl)(IMes)] (100.0 mg, 0.22 mmol), NaOH (35.7 mg, 0.88 mmol), SIPr·HBF4 (87.8 mg, 0.22 mmol), 4 h 30 min. Colorless solid, 176.2 mg, 0.20 mmol, 90%. Procedure B. [Ag(Cl)(SIPr)] (100.0 mg, 0.18 mmol), NaOH (30.0 mg, 0.72 mmol), IMes·HBF4 (73.4 mg, 0.18 mmol), 2 h 20 min. Colorless solid, 152.5 mg, 0.17 mmol, 96%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 0.93 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.22 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.61 (s, 12H, CH3 Mes), 2.37 (s, 6H, CH3 Mes), 2.80 (septet, 4H, 3JHH = 6.9 Hz, CHCH3), 4.04 (s, 2H, H4 and H5 SIPr), 6.76 (s, 4H, Ar IMes), 6.95 (s, 2H, H4′ and H5′ IMes), 7.07 (d, 4H, 3JHH = 7.7 Hz, Ar SIPr), 7.40 (t, 2H, 3JHH = 7.7 Hz, Ar SIPr). 13C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 17.1 (s, CH3 Mes), 21.3 (s, CH3 Mes), 23.9 (s, CHCH3), 25.0 (s, CHCH3), 28.5 (s, CHCH3), 54.2 (s, C4 and C5 SIPr), 123.6 (s, Ar IMes), 124.6 (s, Ar SIPr), 129.3 (s, CIV), 129.6 (s, C4 and C5 IMes), 134.2 (s, Ar SIPr), 134.6 (s, CIV), 139.2 (s, CIV), 146.3 (s, CIV).20 19F{1H} NMR (282 Hz, CDCl3, 298 K): δ = −155.2 (s, BF4), −155.1 (s, BF4). Anal. Calcd for C48H63BAgF4N4: C, 64.80; H, 7.02; N, 6.30. Found: C, 64.35; H, 7.07; N, 6.61. The CHN is slightly above the deviation; however NMR and X-ray analysis confirmed the complex identity. N,N′-Bis{2,6-(di-isopropyl)phenyl}imidazolidin-2-ylidene-N,N′-bis{2,4,6-(trimethyl)phenyl}imidazol-2-ylidene Gold(I) Tetrafluoroborate, [Au(SIPr)(IMes)]BF4, 14a. [Au(Cl)(SIPr)] (100.0 mg, 0.16 mmol), NaOH (25.6 mg, 0.64 mmol), IMes·HBF4 (62.7 mg, 0.16 mmol), 2 h 30 min. Colorless solid, 144.1 mg, 0.14 mmol, 92%. 1H NMR (400 MHz, CDCl3, 298 K): δ = 0.91 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.22 (d, 12H, 3JHH = 6.9 Hz, CHCH3), 1.62 (s, 12H, CH3 Mes), 2.39 (s, 6H, CH3 Mes), 2.81 (septet, 4H, 3JHH = 6.9 Hz, CHCH3), 4.06 (s, 2H, H4 and H5 SIPr), 6.76 (s, 4H, Ar IMes), 6.94 (s, 2H, H4′ and H5′ SIMes), 7.07 (d, 4H, 3JHH = 7.8 Hz, Ar SIPr), 7.42 (t, 2H, 3JHH = 7.9 Hz, Ar SIPr). 13C{1H} NMR (75 MHz, CDCl3, 298 K): δ = 17.06 (s, CH3 Mes), 21.2 (s, CH3 Mes), 23.9 (s, CHCH3), 24.5 (s, CHCH3), 28.4 (s, CHCH3), 54.0 (s, C4 and C5 SIPr), 123.6 (s, Ar IMes), 124.2 (s, Ar SIPr), 129.7 (s, Ar IMes), 133.7 (s, CIV), 133.8 (s, CIV), 134.2 (s, CIV), 139.2 (s, CIV), 146.3 (s, CIV), 183.4 (s, Ccarbene), 206.4 (s, Ccarbene). 19F{1H} NMR (282 Hz, CDCl3, 298 K): δ = −155.2 (s, BF4), −155.1 (s, BF4). Anal. Calcd for C48H62BAuF4N4: C, 58.90; H, 6.38; N, 5.72. Found: C, 58.79; H, 6.45; N, 5.74.

Article

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data for complexes 3a, 3b, 3c, 3d, 3e, 5, 7f, 12, 14b, and 14c, procedure for the preparation, spectroscopy data, NMR spectra, percent buried volume, and mapping for all complexes. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Fax: +44 (0) 1334 463808. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.) for funding. REFERENCES

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DOI: 10.1021/om500882t Organometallics XXXX, XXX, XXX−XXX