Katharine R.
Sampford
a,
Jamie L.
Carden
a,
Edward B.
Kidner
a,
Abigail
Berry
a,
Kingsley J.
Cavell
a,
Damien M.
Murphy
a,
Benson M.
Kariuki
a and
Paul D.
Newman
*ab
aSchool of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK
bCardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK. E-mail: newmanp1@cardiff.ac.uk; Fax: +44 (0) 2920 874030; Tel: +44 (0) 2920 870464
First published on 17th January 2019
A series of diaryl, mono-aryl/alkyl and dialkyl mono- and bicyclic expanded-ring N-heterocyclic carbenes (ER-NHCs) have been prepared and their complexation to Au(I) investigated through the structural analysis of fifteen Au(NHC)X and/or [Au(NHC)2]X complexes. The substituted diaryl 7-NHCs are the most sterically encumbered with large buried volume (%VB) values of 40–50% with the less flexible six-membered analogues having %VB values at least 5% smaller. Although the bicyclic systems containing fused 6- and 7-membered rings (6,7-NHCs) are constrained with relatively acute NCN bond angles, they have the largest %VB values of the dialkyl derivatives reported here, a feature related to the fixed conformation of the heterocyclic rings and the compressional effect of a pre-set methyl substituent.
The examples noted above serve to emphasise a need to understand and appreciate the stereoelectronic features associated with ER-NHCs to provide a holistic appreciation of stereoelectronic character and potential catalytic facility. Although the extent to which the wingtips impose upon a metal depends significantly on the NCN bond angle there are other, more subtle, factors that play a part. Six-membered monocyclic derivatives have little conformational freedom precluding structural promiscuity, whereas the larger 7-membered analogues show greater flexibility in the ring leading to less predictable features. Bicyclic NHCs derived from camphor contain fused 6,7-membered rings and are relatively rigid.6 They contain spatially-set methyl groups that can dictate the adoption of specific orientations of the exo-substituents on the N-atoms. However, to date, there is insufficient structural data to illuminate the distinctions between these bicyclic derivatives and their monocyclic counterparts.
A comprehensive database of crystallographically characterised NHC complexes is invaluable to understanding these differences. Although metal complexes of ER-NHCs do appear in the Cambridge Crystallographic Database (CCD), their number is still small compared to 5-NHCs. Of the ER-NHCs, bicyclic examples where the ligand is comprised of fused 6- and 7-membered rings (6,7-NHCs) are particularly rare. These ligands are anticipated to be structurally rigid as a consequence of the dimethylmethylene bridge that connects the 4 and 7 positions of the 7-membered ring (and hence creates the 6-membered ring) and previous studies have shown that they share some properties more akin to 5-NHCs than ER-NHCs.5 However these preliminary conclusions were based on a relatively small number of observations and further study is necessary in order to provide a satisfactory comparison. This current paper aims to go some way toward doing this through a structural examination of Au(I) complexes of dialkyl and alkyl/aryl substituted bicyclic 6,7-NHC ligands and appropriate comparison with related monocyclic 6- and 7-membered derivatives.
The [Au(NHC)Cl] complexes were prepared by procedures similar to those reported by Dunsford et al.7g The NHC precursor is deprotonated using KHMDS in THF forming the free carbene in solution, which is then added dropwise to a stirred solution of either [Au(SMe2)Cl] or [Au(THT)Cl] (THT = tetrahydrothiophene) in THF at ambient temperature. The crude solids were purified by vapour diffusion techniques to give crystalline samples in isolated yields of 20 to 70%. Intriguingly, although several attempts were made to isolate mono-ligated (L)AuCl derivatives of the ligand shown in complex 13, this compound was all that could be isolated from reactions of 1:1 stoichiometry. It is unclear why this proved to be the case as no issues were encountered with the related pyridine derivative shown in 12. 14 and 15 which were deliberately targeted as attempts to isolate the mono-ligated (L)AuX compounds were frustrated by the formation of inseparable mixtures (14) and/or competing dimer formation (15).
The successful complexation of the NHC ligands is confirmed on inspection of the 1H and 13C{1H} NMR spectra of the isolated solids. Diagnostic features include the loss of the NCHN signal in the 1H NMR spectra and, when observable, a shift of the signal for the carbene carbon in the 13C{1H} NMR spectra. These are accompanied by chemical shift changes for the ring hydrogens in the monocyclic NHCs which move upfield by approximately 0.8 ppm upon coordination and similar, although generally smaller shifts, for the heterocyclic methine hydrogen in the bicyclic systems. These latter shifts are in line with those anticipated for the change from a cationic heterocycle to a neutral form. Although the NCN carbon was not seen in all cases in the 13C{1H} NMR spectra, where observed, the chemical shifts for this carbon in the monocyclic 7-membered systems were at least 10 ppm downfield (∼200 ppm) of the 6-membered analogues (∼190 ppm). These shifts mimic those observed previously with 6- and 7-membered NHCs.7g,8 Those complexes of the type Au(L)Cl where L is a bicyclic ER-NHC for which the NCN carbon signal could be assigned showed this resonance at 190.0 (11) and 188.8 (12) ppm respectively. Thus it would appear, based on this evidence alone, that these constrained NHCs resemble the 6-membered monocyclics more than the larger 7-NHCs. The NCN shifts in the 13C{1H} NMR spectra compare to like complexes of saturated 5-membered analogues such as 1,3-diethyl-4,5-dihydroimidazol-2-ylidene, 1,3-dibenzyl-4,5-dihydroimidazol-2-ylidene and 1,3-dipicolyl-4,5-dihydroimidazol-2-ylidene.9 The larger downfield shifts for complexes 13 and 15 are commensurate with those expected for cationic complexes compared to neutral species (Scheme 1).10
Complex 11 was not isolated in a pure form as it always crystallised as a mixture of the complex and the amidinium salt, (1R,5S)-2,4-dibenzyl-1,8,8-trimethyl-4-aza-2-azoniabicyclo[3.2.1]oct-2-ene tetrafluoroborate, [Bz2-6,7-NHCH][BF4]. It was not certain whether this was the result of carry though of unreacted precursor salt or the result of partial in situ hydrolysis of the gold(I) complex. The NMR spectra clearly showed both species, one of which was readily identified as the amidinium salt.
The 31P{1H} NMR spectrum of 15 contained a very broad peak at a chemical shift little changed from the free ligand (−17.8 ppm). The fact that the resonance is broad does suggest some fluxional process in solution which may indicate a transient interaction of the phosphine groups with the Au(I) centre; this is not borne out in the solid state (see below). Exclusion of O2 was critical for the isolation of 15 as failure to do so resulted in rapid oxidation of the phosphine groups. This observation reinforces the suggestion that the P-donors remain unbound in the complex (Scheme 2).
Fig. 2 Ortep view of the molecular structure of 4. Hydrogen atoms, lattice solvent and disordered atoms have been omitted for clarity. Ellipsoids drawn at 50% probability. |
Fig. 3 Ortep view of the molecular structure of 8. Hydrogen atoms, lattice solvent and disordered atoms have been omitted for clarity. Ellipsoids drawn at 50% probability. |
Fig. 4 Ortep views of the molecular structures of 10–12 (top to bottom). Hydrogen atoms, lattice solvent and disordered atoms have been omitted for clarity. Ellipsoids drawn at 50% probability. |
Complex | Au–C, Å | N–C–N, ° | C–N–Cexo, ° | %Vbur |
---|---|---|---|---|
1 | 1.984(9) | 117.8(8) | 121.2(7) | 41.1 |
119.3(8) | ||||
2 | 2.001(4) | 117.9(3) | 120.1(3) | 41.5 |
120.0(3) | ||||
3 | 2.072(11) | 116.8(13) | 119.3(12) | 32.7 |
123.3(9) | ||||
4 | 1.993(11) | 117.8(10) | 117.4(9) | 40.8 |
115.4(10) | ||||
5 | 2.001(7) | 119.9(7) | 119.9(6) | 42.9 |
117.9(6) | ||||
6 | 2.006(3) | 120.3(3) | 119.5(2) | 43.3 |
118.9(2) | ||||
7 | 2.026(4) | 120.7(4) | 118.2(4) | 34.4 |
120.8(4) | ||||
8 | 2.016(3) | 117.3(3) | 120.0(3) | 33.6 |
118.4(3) | ||||
9 | 2.024(5) | 117.7(5) | 120.4(5) | 29.4 |
122.5(5) | ||||
10 | 2.012(8) | 116.6(8) | 120.0(8) | 36.6 |
121.4(8) | ||||
11 | 2.102(9) | 121.6(8) | 119.2(7) | 36.9 |
123.4(7) | ||||
12 | 1.997(6) | 117.1(6) | 118.9(5) | 38.2 |
121.9(5) | ||||
13 | 2.037(10) | 118.1(7) | 118.1(7) | 37.9 |
2.045(9) | 117.4(8) | 118.8(7) | ||
118.2(7) | ||||
120.1(7) | ||||
14 | 2.051(8) | 118.8(7) | 120.0(6) | 35.3 |
2.063(7) | 117.8(7) | 122.1(6) | ||
119.1(7) | ||||
120.9(6) | ||||
15 | 2.064(10) | 117.2(9) | 117.0(8) | 43.1 |
2.065(11) | 117.7(9) | 122.7(9) | ||
119.1(9) | ||||
121.7(10) |
The molecular structures of two monocyclic 6-NHC compounds are shown in Fig. 1. All 6-NHC complexes share a common envelope conformation for the diazacycle with a close to co-planar CNCNC unit (most notably for 1 and 2) and the remaining CH2 group out of plane. The aromatic exo-substituents are orthogonal to the NCN plane in 1 and 2 with dihedral angles averaging 91.7° and 92.3° respectively. These structural features compare closely with those for complexes of similar ligands.11 The NCN angle is 117.3 ± 0.6° in all three complexes with the Au–C bond length showing some variation being at its longest in 3 (Table 1). This is also true for the Au–Cl bond length which is substantially longer in 3, an observation that might be attributable to the relatively acute C–Au–Cl bond angle of 166.9° (this angle is 179.1° in 1 and 176.3° in 2). Inspection of the unit cell contents shows no obvious reason for this distortion. The 6-membered ring in 3 is more distorted than in complexes 1 and 2, with intra-cycle CNCN dihedral angles of 32° and 13° respectively (cf. averages of 1° and 5° for 1 and 2). The 2-propyl groups on the nitrogens are arranged with their methyl groups directed away from the metal centre which leads to a reduced steric profile for this ligand (see later). The primary features observed here accord with other Au(I) complexes of 6-NHCs.2b,3a,b,12 Related complexes with 5-NHCs tend to show shorter Au–C bond lengths as a consequence of a reduced steric profile associated with more acute NCN bond angles (<110°).3a,13
A representative molecular structure of the complexes bearing diarylated 7-NHC ligands is shown in Fig. 2. Although there is very little variation in the ligand metrics in 4–6 the conformation of the 7-membered ring is not consistent across the three. This ring has an exaggerated envelope conformation in 6 with an essentially coplanar CNCN unit and the three other CH2 groups orientated on one side of this plane to form the flap of the envelope. A similar conformation is observed in 4, but the CH2CH2CH2 chain is skewed in 5 with one terminal carbon above the CNCN plane and the other below with the central carbon almost coplanar with the CNCN unit. In a like manner to the diarylated 6-NHC complexes the arene rings tend to orthogonal with regard to the central diazacycle although this is less pronounced than in 1 and 2 with relevant dihedral angles ranging from 73° to 105° in 4–6. Both the Au–C bond length and NCN bond angle increase along the series 4 < 5 < 6 as expected based on increasing steric profiles.
The molecular structure of complex 8 reveals a 7-membered ring conformation that is quite distinct to those observed in the other 7-NHC complexes reported here (Fig. 4). This ring adopts a chair conformation in 8 with the NCN atoms and the two carbon atoms β to the nitrogens being coplanar and the two α methylene groups being arranged on opposite sides of this plane. The driving force for the adoption of this conformation would appear to be, at least in part, the desire for the two out-of-plane CH2 groups to lie away from the neo-pentyl substituents on their neighbouring nitrogens. This necessarily leads to a mutually trans arrangement of the (CH3)3CCH2– groups. Although it is clear from the structures of the five 7-NHC complexes reported herein that the conformation of the diazacycle is conformationally flexible and sensitive to the nature of the exo-substituent, the effect of these differing geometries on the other metrics, notably the NCN angle and the Au–C bond length, would appear to be small (see below).
The structures in Fig. 4 exemplify the geometry observed in the bicyclic NHC ligand. The rigid conformation is defined by a five-atom (CNCNC) plane with the terminal carbon atoms supporting the dimethylmethine and dimethylene bridges which lie on opposing sides of the plane. All previously reported molecular structures of complexes containing this central NHC core with various wingtip functions conform to this general structure with NCN bond angles ranging from 115.4° to 120.2°.6e,f However, the majority of these contain secondary donors in one or more of the exo-groups which will have influenced these values. Part of the current remit was to extend the number of structurally characterised complexes containing simple alkyl or alkyl/aryl groups to try and understand inherent limitations on geometry, NCN bond angle etc. Expansion of the 6,7-NHC series was also critical for comparison with appropriate 6- and 7-NHCs.
The structure of the dimethyl-6,7-NHC Au(I) complex (see ESI†) shows very little distortion of the coordination sphere with an C–Au–Cl bond angle of 177.4° and Au–C and Au–Cl bond lengths of 2.024(5) and 2.2937(15) Å respectively. Although this ligand is the least sterically encumbered of those reported here, this does not lead to a particularly short Au–C bond which is presumably largely dictated by electronic factors. The molecular structure of the gold complex of the di-2-propyl derivative is shown in the upper part of Fig. 4. There is little distinction between the metrics seen with this complex and 9. However, one point of note is the relative orientation of the two 2-propyl groups with the methyls being presented towards the metal for the 1-amino substituent and away from the metal for those at the 3-amino position. This reflects the impact of the 6-methyl group of the bicyclic framework which forces the neighbouring 2-propyl group to orientate as shown to limit steric impedance. This has a significant effect on the steric profile of the ligand (see below).
The structural data recorded for 11 are distorted by the presence of the amidinium precursor salt [Bz2-6,7-NHCH][BF4] which co-crystallises with the complex. The metrics reported for 11 (Table 1) are thus an average of those for the two species and gives an inflated value for the NCN angle of 121.6(8)°; this is not a true representation of this metric in 11 and is more typical of amidinium salts of this molecular framework.
A noteworthy structural feature in all the complexes is the presence of disparate C–N–Cexo angles with one appreciably larger than the other. As might be expected, the larger angle is for the substituent at the 3-amino position as those off the 1-amino nitrogen experience a steric compression from the neighbouring methyl leading to more acute C–N–Cexo. This creates an asymmetric steric space by emboldening the substituent at the 1-position relative to that at the 3-amino. The greatest disparity in these bond angles are seen in 12 and 13.
The structures of the bis(ligand) complexes are not discussed explicitly here but details are available in the ESI.† Even though they are constitutionally distinct from the Au(L)Cl complexes and carry a formal positive charge, there appears to be little difference in the pertinent metrics (Table 1). The Au–C bond lengths are similar to but longer than those reported for [(5-NHC)2Au]+ (ref. 14) and [(6-NHC)2Au]+ complexes.2b,15 Compound 13 has a trans configuration in the solid-state which is largely dictated by the need for the bulky mesityl groups to reside away from one another. There is clear pi-stacking between pyridyl groups from two separate ligands in the structure of 14 with a distance of 3.682 Å between the centroids of each ring. The large wingtips evident in 15 lead to a distortion of the C–Au–C bond angle to 166.33° at the extreme and contribute to the disparate CNC angles mentioned above and shown in Table 1.
As much of the current study is to inform future ligand design, we are keen to identify structural characteristics that can be exploited to enhance the stereoelectronic profile of (especially) the bicyclic NHCs. While the electronic character is difficult to assess in the current series of complexes, the steric nature is easier to qualify through analysis of the buried volumes (%Vbur) of the ligands.16 The %Vbur values reported in Table 1 reveal, as noted previously, a controlling influence of the exo-substituents on the nitrogen atoms with conformational variations in the diazacyclic ring of the 7-NHCs having little obvious effect. Those ligands with common or closely related wingtips, e.g.1, 2, 4, 5 and 6, have very similar %Vbur values irrespective of the size and nature of the monocyclic ring. This analogy extends to the di-alkylated derivatives with 10 being an exception. As noted above, the steric impact of the methyl group at the position α- to one of the nitrogens forces the methyls on the 2-propyl group towards the metal. This has the effect of increasing the steric profile of the ligand relative to derivatives without this feature. This framework-induced enhancement of apparent bulk is useful as 3-(2-propyl)-3-mesityl-6,7-NHC should prove as space-hungry as monocyclic bis(mesityl)-6-NHC and bis(mesityl)-7-NHC derivatives; we are currently investigating the preparation of such a ligand and its metal complexes.
1: Yield = 33%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 7.20–7.10 (8H, ArH, m) 3.50 (4H, CH2, m), 2.30 (2H, CH2, m), 2.25 (6H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 191.1 (NCH), 145.9 (C), 134.6 (C), 131.5 (CH), 128.8 (CH), 128.1 (CH), 127.3 (CH), 47.0 (CH2), 21.0 (CH2), 17.8 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 502.1567 (C20H23N3Au requires 502.1558). Analysis calculated for C18H20N2AuCl: C, 43.52; H, 4.06; N, 5.64. Found: C, 43.43; H, 3.98; N, 5.69.
2: Yield = 36%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 7.15 (2H, ArH, m) 7.05 (4H, ArH, d, 7.5 Hz), 3.40 (4H, CH2, t, 5.9 Hz), 2.30 (2H, CH2, m), 2.25 (12H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 144.3 (C), 134.8 (C), 129.2 (CH), 128.7 (CH), 45.3 (CH2), 20.7 (CH2), 18.0 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 530.1877 (C22H27N3Au requires 530.1871). Analysis calculated for C20H24N2AuCl: C, 45.77; H, 4.61; N, 5.34. Found: C, 45.86; H, 4.59; N, 5.46.
3: Yield = 42%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 5.25 (2H, CH2, m), 3.05 (4H, CH2, m), 1.85 (2H, CH2, m), 1.10 (12H, CH3, d, 6.8 Hz) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 187.0 (NCN), 60.1 (CH), 38.3 (CH2), 20.5 (CH2), 20.0 (CH3). MS(ES) m/z: [M+ − Cl + 2MeCN] 447.1926 (C14H26N4Au requires 447.1823). Analysis calculated for C10H20N2AuCl: C, 29.98; H, 5.03; N, 6.99. Found: C, 29.89; H, 4.97; N, 6.98.
4: Yield = 24%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 7.20–7.10 (8H, ArH, m), 4.10–3.65 (4H, CH2, m), 2.25 (6H, CH3, s), 2.15 (4H, CH2, m) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 146.9 (C), 131.7 (C), 128.6 (CH), 128.2 (CH), 127.6 (CH), 127.3 (CH), 54.3 (CH2), 24.6 (CH2), 18.1 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 516.1732 (C21H25N3Au requires 516.1714). Satisfactory elemental analysis could not be obtained for this compound.
5: Yield = 42%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 7.15 (2H, ArH, m) 7.05 (4H, ArH, d, 7.3 Hz), 3.85 (4H, CH2, m), 2.30 (12H, CH3, s), 2.25 (4H, CH2, m) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 201.1 (NCN), 146.6 (C), 134.5 (C), 129.3 (CH), 128.4 (CH), 53.1 (CH2), 25.1 (CH2), 18.6 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 544.2005 (C23H29N3Au requires 544.2027). Analysis calculated for C21H26N2AuCl: C, 46.81; H, 4.86; N, 5.20. Found: C, 46.78; H, 4.76; N, 5.17.
6: Yield = 38%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 7.20 (2H, ArH, t, 7.9 Hz) 7.10 (4H, ArH, d, 7.9 Hz), 3.85 (4H, CH2, m), 2.85 (4H, CH2, m), 2.60 (4H, CH2, m), 2.20 (4H, CH2, m), 1.30 (12H, CH3, t, 7.5 Hz) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 201.7 (NCN), 145.7 (C), 139.9 (C), 128.6 (CH), 126.7 (CH), 54.3 (CH2), 24.9 (CH2), 24.0 (CH2), 14.4 (CH3). MS(ES) m/z: [M + MeCN] 635.1718 (C23H29N3Au requires 635.1823). Analysis calculated for C25H34N2AuCl: C, 50.47; H, 5.76; N, 4.71. Found: C, 50.53; H, 5.79; N, 4.88.
7: Yield = 42%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 5.10 (2H, CH, m), 3.25 (4H, CH2, m), 1.75 (2H, CH2, m), 1.20 (12H, CH3, d, 6.8 Hz) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 199.0 (NCN), 60.2 (CH), 44.1 (CH2), 25.0 (CH2), 20.2 (CH3). MS(ES) m/z: [M + K+] 453.0777 (C11H22N2AuClK requires 453.0774). Analysis calculated for C11H22N2AuCl: C, 31.86; H, 5.35; N, 6.75. Found: C, 31.97; H, 5.46; N, 6.72.
8: Yield = 33%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 3.90 (4H, CH2, s), 3.45 (4H, CH2, t, 5.0 Hz), 1.75 (4H, CH2, m), 0.85 (18H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 204.5 (NCN), 74.7 (CH2), 56.0 (CH2), 33.3 (C), 28.8 (CH3), 24.7 (CH2). MS(ES) m/z: [M+ − Cl + 2MeCN] 517.37 (C19H36N4Au requires 517.26). Analysis calculated for C15H30N2AuCl: C, 38.27; H, 6.42; N, 5.95. Found: C, 38.41; H, 6.42; N, 6.05.
9: Yield = 38%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 3.40 (3H, CH3, s), 2.95 (1H, CH, d, 4.0 Hz), 2.20 (1H, CH2, m) 1.95 (2H, CH2, m), 1.75 (1H, CH2, m), 1.15 (3H, CH3, s), 0.95 (3H, CH3, s), 0.90 (3H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 69.1 (CH), 68.6 (C), 46.2 (CH3), 41.6 (CH3), 37.9 (C), 34.1 (CH2), 30.3 (CH2), 22.1 (CH3), 17.6 (CH3), 16.2 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 418.20 (C13H23N3Au requires 418.16). Analysis calculated for C11H20N2AuCl: C, 32.01; H, 4.88; N, 6.79. Found: C, 31.88; H, 4.73; N, 6.83.
10: Yield = 58%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 4.63 (1H, CH, m), 3.47 (1H, CH, m), 2.90 (1H, CH, d, 5.2 Hz), 2.02 (2H, CH2, m), 1.66 (2H, CH2, m), 1.35 (3H, CH3, d, 6.3 Hz), 1.28 (3H, CH3, d, 6.8 Hz), 1.13 (3H, CH3, s), 0.99 (3H, CH3, d, 6.8 Hz), 0.93 (3H, CH3, d, 6.7 Hz), 0.91 (3H, CH3, s), 0.86 (3H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 207.1 (NCN), 67.7 (CH), 57.6 (C), 45.5 (CH), 42.3 (C), 36.8 (CH2), 31.4 (CH2), 22.6 (CH3), 22.3 (CH3), 20.7 (CH3), 20.1 (CH3), 19.7 (CH3), 17.7 (CH3), 15.9 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 474.2161 (C17H31N3Au requires 474.2184). Analysis calculated for C15H28N2AuCl: C, 38.43; H, 6.02; N, 5.98. Found: C, 38.66; H, 6.16; N, 5.82.
11: Yield = 61%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 7.45 (2H, ArH, d, 7.0 Hz), 7.40 (2H, ArH, d, 7.2 Hz), 7.25 (4H, ArH, m), 7.20 (2H, ArH, m), 5.10 (1H, CH2, d, 14.1 Hz), 5.05 (1H, CH2, d, 16.3 Hz), 4.42 (1H, CH2, d, 16.3 Hz), 4.24 (1H, CH2, d, 14.1 Hz), 2.80 (1H, CH, d, 4.7 Hz), 1.98 (1H, CH2, m), 1.72 (1H, CH2, m), 1.59 (1H, CH2, m), 1.40 (1H, CH2, m), 0.96 (3H, CH3, s), 0.87 (3H, CH3, s), 0.52 (3H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 190.0 (NCN), 138.4 (C), 135.4 (C), 128.9 (CH), 128.7 (CH), 127.8 (CH), 126.9 (CH), 70.6 (CH), 66.3 (C), 62.3 (CH2), 58.5 (CH2), 40.5 (CH), 39.1 (C), 30.9 (CH2), 21.9 (CH3), 17.8 (CH3), 16.9 (CH3). MS(ES) m/z: [M + Na+] 587.2426 (C23H28N2AuClNa requires 587.2429). Satisfactory elemental analysis could not be obtained for this complex.
12: Yield = 61%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 8.41 (1H, ArH, d, 5.0 Hz), 7.80 (1H, ArH, d, 7.5 Hz), 7.73 (1H, ArH, t, 7.5 Hz), 7.46 (2H, ArH, d, 7.2 Hz), 7.33–7.17 (4H, ArH, m), 5.49 (1H, CH2, d, 16.0 Hz), 5.18 (1H, CH2, d, 16.0 Hz), 3.98 (1H, CH, d, 5.0 Hz), 2.25 (2H, CH2, m), 1.73 (2H, CH2, m), 1.22 (3H, CH3, s), 1.14 (3H, CH3, s), 0.99 (3H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 188.8 (NCN), 156.5 (C), 147.4 (CH), 136.6 (C), 127.4 (CH), 126.5 (CH), 125.5 (CH), 121.5 (CH), 120.0 (CH), 70.6 (CH), 67.8 (C), 57.9 (CH2), 39.5 (C), 38.4 (CH2), 30.1 (CH2), 20.6 (CH3), 16.8 (CH3), 15.6 (CH3). MS(ES) m/z: [M+ − Cl + MeCN] 557.1988 (C23H28N4Au requires 557.1980). Analysis calculated for C21H25N3AuCl: C, 45.70; H, 4.57; N, 7.61. Found: C, 45.41; H, 4.40; N, 7.61.
13: Yield = 27%. 1H NMR (400 MHz, CDCl3, 298 K) δ = 6.91 (1H, ArH, s), 6.82 (1H, ArH, s), 3.05 (1H, CH, d, 3.6 Hz), 2.33–1.72 (4H, CH2, m), 2.22 (3H, CH3, s), 2.14 (3H, CH3, s), 2.08 (3H, CH3, s), 1.23 (3H, CH3, s), 1.06 (3H, CH3, s), 0.95 (3H, CH3, s) ppm. 13C{1H} NMR (CDCl3, 125 MHz, 298 K), δ 200.6 (NCN), 139.3 (C), 137.0 (C), 135.6 (C), 133.7 (C), 129.2 (CH), 129.0 (CH), 69.2 (CH), 67.8 (C), 40.6 (C), 38.6 (CH2), 38.0 (CH2), 29.4 (CH3), 21.3 (CH3), 19.9 (CH3), 18.6 (CH3), 18.5 (CH3), 17.9 (CH3), 15.5 (CH3). MS(ES) m/z: [M+] 765.4152 (C38H56N4Au requires 765.4170). Analysis calculated for C38H56N4Au2I2: C, 37.51; H, 4.64; N, 4.61. Found: C, 37.22; H, 4.44; N, 4.60.
14: Yield = 70%. 1H NMR (400 MHz, d6-DMSO, 298 K) δ = 8.34 (2H, ArH, d, 1.8 Hz), 8.27 (2H, ArH, d, 1.8 Hz), 7.88 (2H, ArH, t, 7.5 Hz), 7.69 (2H, ArH, t, 7.6 Hz), 7.52–7.25 (8H, ArH, m), 5.22 (4H, CH2, dd, 15.8, 14.8 Hz), 4.70 (4H, CH2, dd, 15.8, 14.8 Hz), 3.36 (2H, CH, d, 3.2 Hz), 1.90–1.70 (8H, CH2, m), 1.52 (6H, CH3, s), 1.40 (6H, CH3, s), 1.31 (6H, CH3, s) ppm. 13C{1H} NMR (d6-acetone, 125 MHz, 298 K), δ 203.5 (NCN), 158.9 (C), 156.7(C), 150.1 (CH), 137.5 (CH), 124.0 (CH), 123.8 (CH), 123.5 (CH), 122.2 (CH), 71.4 (CH), 68.7 (C), 62.8 (CH2), 59.0 (CH2), 41.2 (C), 39.7 (CH2), 31.0 (CH2), 22.0 (CH3), 18.4 (CH3), 16.6 (CH3). MS(ES) m/z: [M+] 865.3974 (C42H52N8Au requires 865.3980). Analysis calculated for C42H52N8AuBF4: C, 52.95; H, 5.50; N, 11.76. Found: C, 52.90; H, 5.39; N, 11.54.
15: Yield = 21%. 1H NMR (400 MHz, d6-DMSO, 298 K) δ = 7.53–6.85 (56H, ArH, m), 4.72 (2H, CH2, d, 14.5 Hz), 4.66 (2H, CH2, d, 14.5 Hz), 4.48 (2H, CH2, d, 14.9 Hz), 4.40 (2H, CH2, d, 14.9 Hz), 3.10 (2H, CH, br), 2.42 (2H, CH2, m), 1.82 (4H, CH2, m), 1.23 (6H, CH3, s), 1.15 (2H, m), 0.87 (6H, CH3, s), 0.83 (6H, CH3, s) ppm. 13C{1H} NMR (d6-acetone, 125 MHz, 298 K), δ 207.0 (NCN), 140–125 (16 × C, 36 × CH), 71.7 (CH), 65.3 (C), 53.5 (CH2), 41.2 (C), 37.9 (CH2), 29.4 (CH2), 21.0 (CH3), 17.9 (CH3), 14.7 (CH3). 31P{1H} NMR (162 MHz, CDCl3, 298 K) δ −17.8 (br) ppm. MS(ES) m/z: [M+] 1597.5940 (C94H92N4P4Au requires 1597.5938). Satisfactory elemental analysis could not be obtained for this complex.
Footnote |
† Electronic supplementary information (ESI) available: NMR spectra for all the complexes together with crystallographic details for those compounds characterized by single crystal X-ray techniques. CCDC 1877805–1877819. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt04462g. Information on the data underpinning the results presented here, including how to access them, can be found in the Cardiff University data catalogue at DOI: 10.17035/d.2018.0065259122 |
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