Article pubs.acs.org/Organometallics
The Sulfur−Fluorine Gauche Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation Nico Santschi,*,†,‡ Christian Thiehoff,† Mareike C. Holland,†,§ Constantin G. Daniliuc,†,∥ K. N. Houk,*,§ and Ryan Gilmour*,†,‡ †
Institute for Organic Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany Excellence Cluster EXC 1003, Cells in Motion, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany § Department of Chemistry and Biochemistry, University of California Los Angeles, 607 Charles E. Young Drive East, Los Angeles 90095-1569, United States ‡
S Supporting Information *
ABSTRACT: Controlling the rotation about unhindered C(sp3)− C(sp3) bonds by simple structural changes has obvious benefits in molecular design. While the avoidance of nonbonding interactions remains one of the cornerstones of acyclic conformational control, stabilizing stereoelectronic effects have the added benefit that conformer populations can be fine-tuned by augmenting or diminishing the central interaction. Strategies may include adjusting the oxidation state of a substituent or reversible formation of a complex to modulate MO levels. In the case of the sulfur−fluorine gauche effect, the propensity of the S−C−C−F motif to adopt a synclinal arrangement (ΦFCCS = 60°), the conformer population distribution of the three dominant rotamers partitioned by 120° can be biased by oxidation of the S atom. Motivated by the importance of sulfur-based ligands in main structural chemistry, the sulfur−fluorine gauche effect was translated to an organometallic paradigm as a potential tool to achieve structural preorganization. This would allow the influence of coinage-metal complexation on conformer population to be initially assessed. The synthesis and characterization of a model gold(I) and silver(I) metal complex featuring a ligand system containing a freely rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic effect manifests itself in the expected conformation, with the synclinal-endo conformer being preferred. This was corroborated by X-ray crystallography and DFT analysis, and the molar fraction of rotamers was extrapolated from a detailed solution-phase NMR spectroscopic analysis. Complexation was found to reinforce the sulfur−fluorine gauche effect.
■
INTRODUCTION
It was therefore envisaged that, in addition to direct oxidation or electronic perturbation of sulfur, the gauche/anti equilibrium might also be influenced by coordination of sulfur to a suitable metal center. Coinage metals are appropriate platforms from which to explore this notion on account of their known chalcogenophilic behavior5 and the prominence of group 16 elements in various ligand designs.6 In particular, the sulfur−gold bond is easily formed and remarkably stable5,7 and has, not surprisingly, advanced to the center point of surface modification strategies.8 Consequently, the suitability of structure 1a as a potential ligand in gold(I) and also silver(I) complexes was considered: these two metals were of specific interest on account of their oxidation state stability. Herein, the sulfur−fluorine gauche effect is studied in the framework of two coinage-metal complexes (Figure 1c, bottom) by a combined experimental and computational approach. In addition to studying the title interaction, this offers the possibility to search for remote metal−fluorine interactions with an aliphatic C(sp3)−F bond and interrogate the structure in a broader sense. The ability of simple Ag and Au complexation to
The heteroatom−fluorine gauche effect describes the propensity of a common X−Cα−Cβ−F system to adopt an overall conformation in which the C−X and C−F bonds are oriented in a synclinal arrangement (±gauche).1 Coulombic interactions (Xδ+···Fδ‑), as well as stabilizing hyperconjugative electron donation (i.e., σCH → σ*CF), account for this phenomenon, thereby superseding the expected conformation in which dipole cancellation is achieved (Figure 1, top). Since embedding the X−Cα−Cβ−F motif (X = electron-withdrawing group) leads to a predictable conformation, this effect has become an expansive approach to predictably control molecular (pre)organization in organic systems.1c,2 Dominated for several decades by oxygenand nitrogen-based systems, the heteroatom-gauche effect was only recently extended to include sulfur (Figure 1, middle).3 This extension to a period 3 element offers the possibility to tune the conformational equilibrium by stepwise adjustments of the sulfur oxidation state. Interestingly, the degree to which gauche conformers ((+gauche) + (−gauche)) predominate over the anti conformer is heavily dependent on the sulfur oxidation state (sulfoxide > sulfone > sulfide), in both acyclic and cyclic systems,3 and sulfur’s electronic environment.4 © 2016 American Chemical Society
Received: July 14, 2016 Published: August 25, 2016 3040
DOI: 10.1021/acs.organomet.6b00564 Organometallics 2016, 35, 3040−3044
Article
Organometallics
In the solid state, complex 2 was found to form discrete aggregates consisting of three metal centers linked by aurophilic contacts of 3.0872(7) and 3.2082(8) Å and an Au−Au−Au angle of 124.08(2)° (Figure 2). In contrast, the parent complex
Figure 1. Heteroatom−fluorine gauche effect and its extension to sulfur-based systems.
Figure 2. ORTEP representation of the trimeric molecular structure of 2 (CCDC 1487378). Thermal ellipsoids are displayed at the 50% probability level. Aurophilic contacts are highlighted with dashed lines.
augment the gauche/anti conformational equilibrium about an unhindered C(sp3)−C(sp3) bond is evaluated with NMR spectroscopy and constitutes preliminary validation of this approach to acyclic conformational control.
[Au(THT)Cl] is reported to form an infinite polymeric structure with slightly longer Au−Au distances of 3.353(1) Å and wider Au−Au−Au angles of 159.30(6)°.11 In structure 2, the Au−S and Au−Cl bonds measure 2.271(4)−2.278(3) and 2.280(4)−2.297(4) Å, respectively, and the S−Au−Cl angle was determined to lie between 170.07(13) and 174.14(12)° these values compare well to those of the parent compound (Au−S, 2.279(9)−2.259(11) Å; Au−Cl, 2.274(8)−2.292(13) Å; S−Au−Cl, 176.5(4)−177.1(4)°). The metal coordinates trans to the pendant side chain (C5), thereby minimizing unfavorable nonbonding interactions and or dipoles. This latter notion is pertinent, since the oxidation of structure 1a to the corresponding sulfoxide 1b is highly diastereoselective.3 Complex 3 formed a zigzag-shaped, infinite polymer with every sulfur ligand being coordinated to two Ag(I) centers (Ag−S−Ag angle 127.33(7)−135.44(8)°); in sulfone 1c the corresponding OSO angle measures 117.68(10)° and in the related zigzag-shaped [Ag(THT)BF4] system a value of 126.6° is reported for the linking Ag−S−Ag fragments.3,12 The Ag−S bond lengths in 3 (2.4568(18)−2.5748(18) Å) also lie within the range of those for the prototypical Ag(THT) complex (2.520−2.554 Å). The most intriguing feature in the molecular structure of 3, however, is a short Ag−F contact (2.387(5)−2.527(6) Å): ligand system 1a is coordinating in a chelating manner. This in turn heavily affects the solution-phase population (vide inf ra). However, due to the absence of a measurable Ag−F NMR coupling, this interaction is likely ephemeral in solution. Nevertheless, this Ag−F bond presents a convincing argument as to why cis coordination is preferred in 3 over the intuitively more stable trans mode (Figure 3).10 This was further substantiated by computational means (vide inf ra). In both complexes (2 and 3) the sulfur−fluorine gauche effect can be observed, with the C5−F bond being oriented in a synclinal-endo fashion relative to the C4−S bond. In keeping with our previous studies on the free ligand 1a, the C1−S bond was also significantly longer than the C4−S bond (Table 1). On average, bond lengths and the difference Δd in 2 are best reflected by structure 1b; however, the C1−S−C4 angle proved
■
RESULTS AND DISCUSSION Investigations began with the preparation of the desired gold(I) complex 2 starting from chloroauric acid (1 equiv) and an excess of ligand 1a (2.3 equiv) in a H2O/EtOH mixture, following the reported preparation of the parent [Au(THT)Cl] complex.9 The product was obtained as a white solid in 68% yield, and single crystals suitable for X-ray diffraction were successfully grown by slow vapor diffusion of pentane into a solution in CH2Cl2 at −20 °C. The corresponding silver(I) complex 3 was obtained in 88% yield by mixing equimolar amounts of ligand 1a and AgSbF6 in CH2Cl2, followed by crystallization at −20 °C by vapor diffusion of pentane. Single crystals suitable for X-ray diffraction were successfully grown by slowly evaporating a solution in CD2Cl2 at ambient temperature. With both complexes in hand, solution-phase characterizations and population analyses were performed. Effective coordination of ligand 1a to each metal center was confirmed by a marked downfield shift of the C4H proton (Au, 5.43 ppm; Ag, 4.97 ppm) relative to the free ligand (4.60 ppm). However, at 299 K only broad signals were observed for complex 2. Whereas the 3JHF coupling (31.5 Hz) of the C4H signal was observed, any discernible coupling to the C3 methylene unit was not observed (see the Supporting Information). At 253 K the signal became fully resolved (dt, 3JHF = 32.0 Hz, 3JHH = 8.3 Hz) and further cooling to 193 K led only to an increased downfield shift (dt, 3JHF = 32.1 Hz, 3JHH = 8.3 Hz). Intriguingly, over this broad temperature range the 3JHF coupling remained relatively unaffected (31.5−32.1 Hz), which may indicate that the overall solution-phase population does not shift significantly. In the case of complex 3, the C4H signal (dt, 3JHF = 29.6 Hz, 3JHH = 7.1 Hz) was already fully resolved at 299 K. Also noteworthy is the observation that no Ag−F coupling could be discerned in the 19F NMR spectrum: this in turn would have indicated a direct metal−fluorine contact (i.e., chelating coordination).10 3041
DOI: 10.1021/acs.organomet.6b00564 Organometallics 2016, 35, 3040−3044
Article
Organometallics
Figure 3. ORTEP representation of the monomeric (A) and polymeric (B) molecular structures of 3 (CCDC 1487379). Thermal ellipsoids are displayed at the 50% probability level. Protons and counteranion are omitted for clarity in (B). Ag−F contacts are highlighted with dashed lines.
Table 1. Selected Angles and Bond Lengths in the Ligand Scaffold compound
ΦFCCS (deg)
dS−C4 (Å)
dS−C1 (Å)
Δd (Å)
ΦC1−S−C4 (deg)
1a3 1b3 1c3 2a
−62.07 −60.89 −62.37 −55.6(11) −59.8(12) −68.2(12) −63.8(6) −57.7(6)
1.8379(16) 1.853(2) 1.832(2) 1.845(13) 1.861(14) 1.879(13) 1.852(7) 1.862(7)
1.8107(19) 1.814(2) 1.799(2) 1.817(15) 1.813(13) 1.835(16) 1.828(8) 1.832(8)
0.027 0.039 0.054 0.028 0.048 0.044 0.024 0.030
94.39(8) 90.83(10) 96.37(10) 93.1(6) 94.3(6) 94.4(6) 93.1(3) 91.6(3)
3b a
Asymmetric unit contains three molecules of 2 (CCDC 1487378). bAsymmetric unit contains two molecules of 3 (CCDC 1487379).
populations predicted for compound 2 closely match those reported for the trans sulfoxide 1b, the anti conformer seems to be even less populated in the silver complex 3. In the latter case this may be a consequence of the stabilizing Ag−F interaction described previously. Finally, the conformational behavior of complexes 2 and 3 was interrogated by computational methods. Geometry optimizations of minima were carried out in the gas phase with the B3LYP functional and the LANL2DZ pseudopotential for Au and Ag and the 6-311+G(d,p) basis set for all other atoms (Table 3).15 In the free ligand system 1a the synclinalendo conformer was found to be the most stable, closely followed by the anti orientation (0.29 kcal/mol) and the synclinal-exo arrangement, predicted to be significantly less stable (2.94 kcal/mol). The experimental analysis reported before also pointed toward the endo conformer being preferred (Table 2); however, the +gauche and anti conformers should be roughly equal in energy. In keeping with the molecular structure of complex 2 (Figure 2), the trans coordination mode of Au(I) afforded the energetically lowest lying conformers with endo predominating. Notably, however, cis coordination with concomitant endo orientation of the C5−F bond (3.40 kcal/mol) is energetically very comparable to the trans, anti and trans, exo arrangements, which are predicted to lie 2.74 and 3.81 kcal/mol above the lowest energy structure, respectively. This conformational flexibility could therefore constitute the reason for the relatively broad NMR spectra obtained at room temperature (vide supra) and increasing resolution at lower temperature. While the prediction of the stability of an endo orientation is again in agreement with the
to be slightly wider. For system 3, average bond lengths also match those of sulfoxide 1b in contrast to the Δd value. Next, a solution-phase population analysis was carried out, as previously described,3,4b,13 on the basis of the experimental 3JHF and 3JCF coupling constants determined at 299 K (Table 2). Table 2. Solution-Phase Population Analysis Reported for 1a,b and Performed on 2 and 3a compound 1a 1b 2b 3c
3
JHF (Hz) 29.2 37.8 31.5 29.6
JCF (Hz)
−gauche
+gauche
anti
3.2 3.2 2.7 3.6
61.3 74.7 70.7 74.0
20.0 20.0 20.0 24.0
18.7 5.3 9.3 2.0
3
a
Group electronegativities used: 0.45 (Ph), 0.69 (SO2Cl), 0.76 (CH2CH2R).14 bBased on averaged angles ΦFCC and ΦCCH in the FCCH motif of 107.24 and 108.68°, respectively. cBased on averaged angles ΦFCC and ΦCCH in the FCCH motif of 109.57 and 108.14°, respectively.
Specifically, it was assumed that only staggered conformers (−gauche, +gauche, anti) contribute significantly to these values and consequently, an observable coupling constant ⟨J⟩ can be decomposed according to ⟨J⟩ = χ−gJ−g+ χ+gJ+g + χaJa. In this weighted sum, χZ corresponds to the molar fraction of a specific rotamer Z. JZ is the respective coupling constant and can be estimated on the basis of reported substituent group electronegativities and angles derived from the solid-state structure. This analysis further confirmed that coordination to a suitable metal center can perturb the electronic nature of the system and by extension bias the population equilibrium. Whereas the 3042
DOI: 10.1021/acs.organomet.6b00564 Organometallics 2016, 35, 3040−3044
Organometallics Table 3. Computed Relative Gibbs Free Energies of Ligand 1a, Complex 2, and Models for Complex 3a
−gauche (kcal/mol)
+gauche (kcal/mol)
anti (kcal/mol)
1a
0.00
2.94
0.29
trans-2 cis-2
0.00 3.40
3.81 7.42
2.74 7.14
trans-[AgI1a]+ cis-[AgI1a]+ [AgI21a]2+
5.26 0.00 1.18
12.25 6.30 5.41
7.45 6.77 0.00
compound
a
Article
■
CONCLUSION
■
EXPERIMENTAL SECTION
A combined spectroscopic, crystallographic, and computational investigation of the sulfur−fluorine gauche effect in two welldefined coinage-metal complexes bearing ligand 1a confirmed that complexation can be employed to augment conformational behavior. The sulfur−Au(I) and sulfur−Ag(I) interactions afforded structural features (bond lengths and angles) reminiscent of trans sulfoxide 1b, in the solid state such that oxidation and complexation can be exploited as complementary strategies to shift the conformational equilibrium of these systems (by up to 20%). A computational analysis at the DFT level of theory indicates a marked energetic restructuring of the conformational space. This preliminary validation of controlling rotation about unhindered C(sp3)−C(sp3) bonds by simple structural changes will be the subject of future studies in this laboratory.
(S)-(2-(Fluorodiphenylmethyl)tetrahydrothiophene)gold(I) Chloride. (S)-2-(Fluorodiphenylmethyl)tetrahydrothiophene (20.0 mg, 0.07 mmol, 2.3 equiv) was suspended in EtOH (0.5 mL), and then HAuCl4·3H2O (12.5 mg, 0.03 mmol, 1 equiv) in water (0.2 mL) and EtOH (0.5 mL) was added, leading to the precipitation of a yellow-colored solid. The suspension was stirred at ambient temperature for 14 h and then filtered. The residue was washed with copious amounts of EtOH and dried at HV to provide the title product (10.9 mg, 0.02 mmol, 68%) as a white solid. Single crystals for X-ray diffraction were obtained by slow evaporation of a solution in DCM under a pentane atmosphere at −20 °C. Mp: 140.6 °C dec. 1H NMR (600 MHz, CD2Cl2): δ 7.56 (d, J = 8.2 Hz, 2H, oPh), 7.45−7.35 (m, 6H, oPh and mPh), 7.35 (t, J = 7.3 Hz, 1H, pPh), 7.31 (t, J = 7.3 Hz, 1H, pPh), 5.43 (d, J = 31.5 Hz, 1H, C4H), 3.50−3.38 (m, 1H, C1H), 3.38−3.23 (m, 1H, C1H), 2.49−2.26 (m, 2H, C2H), 2.20−2.08 (m, 1H, C3H), 2.04−1.88 (m, 1H, C3H). 13 C NMR (151 MHz, CD2Cl2): δ 142.9 (iPh, HMBC), 141.6 (iPh, HMBC), 129.5 (mPh), 129.4 (d, J = 1.4 Hz, mPh), 129.2 (pPh), 128.8 (pPh), 125.2 (d, J = 9.0 Hz, oPh), 124.9 (d, J = 9.5 Hz, oPh), 100.0 (d, J = 190.3 Hz, C5, HMBC), 67.0 (C4, HMBC), 42.3 (C1), 33.5 (C2, HSQC), 31.3 (d, J = 2.7 Hz, C3). 19F NMR (564 MHz, CD2Cl2) δ −167.75 (bs). IR (ATR): ν 3063 w, 2963 w, 1600 w, 1494 m, 1450 s, 1290 w, 1262 w, 1233 w, 1190 m, 1115 w, 1067 m, 1054 m, 1035 m, 1020 m, 979 s, 917 w, 890 m, 784 m, 737 s, 701 s cm−1. HRMS (ESI): [M + C17H17SF]+ calcd for C34H34AuF2S2, 741.1730; found, 741.1732. Anal. Calcd for C17H17AuClFS: C, 40.45; H, 3.39. Found: C, 40.00; H, 3.85. These values represent the best microanalytical data obtained to date (deviations C −0.45, H +0.46). (S)-(2-(Fluorodiphenylmethyl)tetrahydrothiophene)silver(I) Hexafluoroantimonate. To (S)-2-(fluorodiphenylmethyl)tetrahydrothiophene (4.8 mg, 0.02 mmol, 1 equiv) was added 0.2 mL of a 90 mM AgSbF6 stock solution (0.02 mmol, 1 equiv) in dry DCM. The title product (9.5 mg, 0.02 mmol, 88%) was obtained as colorless crystals by vapor diffusion of pentane at −20 °C, followed by washing with copious amounts of pentane and drying at HV. NMR data were obtained by using an AgSbF6 stock solution prepared with dry DCM-d2. Single crystals for X-ray diffraction were obtained by slow evaporation of a solution in dry DCM-d2 at ambient temperature. Mp: 106.7−109.1 °C dec. 1H NMR (600 MHz, CD2Cl2): δ 7.54−7.52 (m, 2H, oPh′), 7.52−7.47 (m, 2H, mPh′), 7.46−7.42 (m, 3H, oPh and pPh′), 7.41−7.37 (m, 2H, mPh), 7.34−7.30 (m, 1H, pPh), 4.97 (dt, J = 29.6, 7.1 Hz, 1H, C4H), 3.22−3.13 (m, 2H, C1H), 2.41−2.34 (m, 1H, C2H), 2.17−2.01 (m, 3H, C2H and C3H). 13C NMR (151 MHz, CD2Cl2): δ 143.7 (d, J = 22.8 Hz, iPh′), 140.9 (d, J = 24.9 Hz, iPh), 130.5 (d, J = 1.4 Hz, mPh′), 129.8 (pPh′), 129.5 (d, J = 1.7 Hz, mPh), 129.0 (pPh), 124.8 (d, J = 9.8 Hz, oPh), 124.4 (d, J = 8.8 Hz, oPh′), 100.0 (d, J = 184.6 Hz, C5), 61.0 (d, J = 22.0 Hz, C4), 38.5 (C1), 32.2 (C2), 31.5 (d, J = 3.6 Hz, C3). 19F NMR (564 MHz, CD2Cl2): δ −167.18 (d, J = 29.7 Hz). IR (ATR): ν 3617 w, 2963 w, 1610 m, 1492
Trans/cis nomenclature and calculated lowest energy conformers.
experimental solution-phase population analysis (Table 2), the +gauche orientation was slightly favored over the anti. Additionally, the Au−S bond lengths were also slightly overestimated at 2.37 Å in comparison to the solid-state structure. For complex 3 several scenarios were considered, since direct treatment of the oligomeric system was not feasible. Unsurprisingly, when only one Ag(I) center was present, the cis, endo conformer was determined to be the energetic minimum, in good agreement with the molecular structure (Figure 3B). Furthermore, a short Ag−F contact (2.95 Å) was also predicted to occur and the calculated Ag−S bond lengths (2.57 Å) nicely reflected the experimental findings. All other conformers, including the trans coordination mode, lie significantly higher in energy (6.30−12.25 kcal/mol). This fits the experimental data well (although the +gauche conformer is populated in solution), and these high energetic barriers may be the reason for nicely resolved NMR spectra at room temperature. Interestingly, when a second Ag(I) center was introduced to mimic sulfur’s environment in the crystal, the anti arrangement was favored slightly over the endo conformer (1.18 kcal/mol); the exo conformer was predicted to be the least stable (5.41 kcal/mol), although it would allow for a short Ag− F interaction of 2.69 Å. However, it should be kept in mind that these last considerations suffer from the charge imbalance artificially introduced. Overall, the computational investigations also unraveled that electronic perturbation is achieved by coordination to a metal center. While the ligand system 1a features a relatively flat energetic profile, coordination of Au(I) and, even more so, introduction of Ag(I) led to a clear endo preference. 3043
DOI: 10.1021/acs.organomet.6b00564 Organometallics 2016, 35, 3040−3044
Article
Organometallics
(10) (a) Plenio, H.; Diodone, R. Chem. Ber. 1996, 129, 1211−1217. (b) Plenio, H. Chem. Rev. 1997, 97, 3363−3384. (c) Plenio, H. ChemBioChem 2004, 5, 650−655. (11) Ahrland, S.; Dreisch, K.; Norén, B.; Oskarsson, Å. Mater. Chem. Phys. 1993, 35, 281−289. (12) Norén, B.; Oskarsson, Å. Acta Chem. Scand. 1984, 38a, 479− 484. (13) (a) Dahbi, A.; Hamman, S.; Beguin, C. G. Magn. Reson. Chem. 1986, 24, 337−342. (b) Thibaudeau, C.; Plavec, J.; Chattopadhyaya, J. J. Org. Chem. 1998, 63, 4967−4984. (c) Dolbier, W. B., Jr. Guide to Fluorine NMR for Organic Chemists; Wiley, Hoboken, NJ, 2009. (14) Altona, C.; Ippel, J. H.; Westra Hoekzema, A. J. A.; Erkelens, C.; Groesbeek, M.; Donders, L. A. Magn. Reson. Chem. 1989, 27, 564− 576. (15) Full computational details are given in the Supporting Information.
m, 1447 s, 1293 w, 1269 w, 1242 m, 1189 m, 1161 w, 1138 w, 1065 m, 1050 m, 1022 m, 1000 m, 982 m, 971 m, 926 m, 913 m, 885 m, 784 s, 754 s, 704 s cm−1. MS (EI): [M]+ calcd for C17H17AgFS, 379.0080; found, 379.0081. Anal. Calcd for C17H17SAgF7Sb: C, 33.15; H, 2.78. Found: C, 33.46; H, 3.37. These values represent the best microanalytical data obtained to date (deviations C +0.31, H +0.59).
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00564. Experimental details and computational data (PDF) Computational data (XYZ) Crystallographic data (CIF)
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail for N.S.:
[email protected]. *E-mail for K.N.H.:
[email protected]. *E-mail for R.G.:
[email protected] Author Contributions ∥
X-ray crystallographer.
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We acknowledge generous financial support from the Swiss National Science Foundation (N.S., P300P2_161070), the German Academic Exchange Service (M.C.H., P.R.I.M.E. fellowship) the Deutsche Forschungsgemeinschaft (SFB 858 and Excellence Cluster EXC 1003 “Cells in Motion − Cluster of Excellence”), the European Research Council (ERC-2013-StG Starter Grant. Project number 336376-ChMiFluorS), and the WWU Münster.
■
REFERENCES
(1) (a) Wolfe, S. Acc. Chem. Res. 1972, 5, 102−111. (b) O’Hagan, D. Chem. Soc. Rev. 2008, 37, 308−319. (c) Hunter, L. Beilstein J. Org. Chem. 2010, 6, 38. (d) Zimmer, L. E.; Sparr, C.; Gilmour, R. Angew. Chem., Int. Ed. 2011, 50, 11860−11871. (2) Sparr, C.; Schweizer, W. B.; Senn, H. M.; Gilmour, R. Angew. Chem., Int. Ed. 2009, 48, 3065−3068. (3) Thiehoff, C.; Holland, M. C.; Daniliuc, C.; Houk, K. N.; Gilmour, R. Chem. Sci. 2015, 6, 3565−3571. (4) (a) Aleksić, J.; Stojanović, M.; Baranac-Stojanović, M. J. J. Org. Chem. 2015, 80, 10197−10207. (b) Thiehoff, C.; Schifferer, L.; Daniliuc, C. G.; Santschi, N.; Gilmour, R. J. Fluorine Chem. 2016, 182, 121−126. (5) Pakiari, A. H.; Jamshidi, Z. J. Phys. Chem. A 2010, 114, 9212− 9221. (6) (a) Murray, S. G.; Hartley, F. R. Chem. Rev. 1981, 81, 365−414. (b) Mellah, M.; Voituriez, A.; Schulz, E. Chem. Rev. 2007, 107, 5133− 5209. (7) Xue, Y.; Li, X.; Li, H.; Zhang, W. Nat. Commun. 2014, 5, 4348. (8) (a) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides, G. M. Chem. Rev. 2005, 105, 1103−1170. (b) Vericat, C.; Vela, M. E.; Benitez, G.; Carro, P.; Salvarezza, R. C. Chem. Soc. Rev. 2010, 39, 1805−1834. (c) Häkkinen, H. Nat. Chem. 2012, 4, 443−455. (9) Uson, R.; Laguna, A.; Laguna, M.; Briggs, D. A.; Murray, H. H.; Fackler, J. P. (Tetrahydrothiophene)Gold(I) or Gold(III) Complexes. In Inorganic Syntheses; Kaesz, H. D., Ed.; Wiley, Hoboken, NJ, 1989; Vol. 26, pp 85−91. 3044
DOI: 10.1021/acs.organomet.6b00564 Organometallics 2016, 35, 3040−3044
