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Single Electron Delivery to Lewis Pairs: An Avenue to Anions by Small Molecule Activation Liu Leo Liu, Levy L. Cao, Yue Shao, and Douglas W. Stephan* Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada S Supporting Information *

ABSTRACT: Single electron transfer (SET) reactions are effected by the combination of a Lewis acid (e.g., E(C6F5)3 E = B or Al) with a small molecule substrate and decamethylferrocene (Cp*2Fe). Initially, the corresponding reactions of (PhS)2 and (PhTe)2 were shown to give the species [Cp*2Fe][PhSB(C6F5)3] 1 and [Cp*2Fe][(μ-PhS)(Al(C6F5)3)2] 2 and [Cp*2Fe][(μ-PhTe)(Al(C6F5)3)2] 3, respectively. Analogous reactions with di-tert-butyl peroxide yielded [Cp*2Fe][(μHO)(B(C6F5)3)2] 4 with isobutene while with benzoyl peroxide afforded [Cp*2Fe][PhC(O)OE(C6F5)3] (E = B 5, Al 6). Evidence for a radical pathway was provided by the reaction of Ph3SnH and p-quinone afforded [Cp*2Fe][HB(C6F5)3] 7 and [Cp*2Fe]2[(μ-O2C6H4)(E(C6F5)3)2] (E = B 8, Al 9). In addition, the reaction of TEMPO with Lewis acid and Cp*2Fe afforded [Cp*2Fe][(C5H6Me4NOE(C6F5)3] (E = B 10, Al 11). Finally, reactions with O2, Se, Te and S8 gave [Cp*2Fe]2[((C6F5)2Al(μ-O)Al(C6F5)3)2]2 12, [Cp*2Fe]2[((C6F5)2Al(μ-Se)Al(C6F5)3)2]2 13, [Cp*2Fe][(μ-Te)2(Al(C6F5)2)3] 14 and [Cp*2Fe]2[(μ-S7)B(C6F5)3)2] 15, respectively. The mechanisms of these SET reactions are discussed, and the ramifications are considered.

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INTRODUCTION In 1923, Gilbert N. Lewis classified molecules that behave as electron-pair donors and electron-pair acceptors as bases and acids, respectively.1 The combination of a Lewis base and Lewis acid leads to the formation of a Lewis acid−base adduct (Figure 1). For close to a century such adducts were viewed as thermodynamically stable species that are generally unreactive.

Initially, this reactivity was observed for a range of sterically “frustrated Lewis pairs” (FLPs). Subsequently, it has been expanded to systems where the free Lewis acid and base are accessible via dissociative equilibria, allowing the combined action of nucleophilic and electrophilic centers on small molecule substrates.3−7 This chemical behavior of FLP systems resembles that of ambiphilic transition-metal complexes and has been employed in a range of both stoichiometric and metal-free catalytic activation of small molecules.8 Other avenues to small molecule activation by main group compounds have also been developed.9−11 In 2005, Power and co-workers showed that the alkyne analogue of germanium split H2 under ambient conditions.12 Two years later, Bertrand demonstrated the facile cleavage of H2 and NH3 by a singlet carbene center. 13 Theoretical calculations revealed the activation of these substrates is analogous to the reactivity of transition metal centers,14 as the combined ability of carbenes to act as electron donors and acceptors effects the heterolytic cleavage of chemical bonds. Another strategy to reactivity involves single electron transfer (SET) processes. A variety of photocatalytic and transitionmetal-catalyzed organic transformations have been studied and shown to involve SET pathways. This has led to applications in synthetic15−17 and materials18 chemistry as well as biological sciences.19 However, SET processes are seldom encountered in

Figure 1. Reactivity of electron donor (ED) and electron acceptor (EA) combinations.

This paradigm of main group reactivity was further extended in 2006 with the report of the reversible activation of H2 by p(Mes2P)C6F4(B(C6F5)2), (Mes = mesityl).2 In this case, the Lewis acid−base adduct formation is inhibited by the sterically demanding substituents permitting concerted action of the electron donor and acceptor on the H2 molecule (Figure 1). © 2017 American Chemical Society

Received: May 17, 2017 Published: June 27, 2017 10062

DOI: 10.1021/jacs.7b05120 J. Am. Chem. Soc. 2017, 139, 10062−10071

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Journal of the American Chemical Society main group chemistry. Recently, Wang and co-workers reported the irreversible one-electron oxidation of a main group compound, namely triarylamine, by an equimolar portion of B(C6F5)3, in which the ensuing highly reactive [·B(C6F5)3]− was completely quenched by reaction with the solvent.20 The group of Agapie demonstrated the synthesis of a dianionic bis(borane) peroxide by the direct reduction of O2 by ferrocenes in the presence of B(C6F5)3.21,22 Additionally, there are a few examples of SET from transition-metal complexes to the strong Lewis acid, such as B(C6F5)3.23,24 Chen proposed the formation of the transient [·Al(C6F5)3]− followed by decomposition during heating a C6D5Br solution of Al(C6F5)3 with ferrocene at 100 °C for 3 days.25 We have previously described the generation of highly reactive radical pairs of the form [R3P·]+ and [·O(Al(C6F5)3)2]− from reaction of FLPs derived from R3P and Al(C6F5)3 with N2O.26 These species subsequently effected C−H bond activation. In the present work, we describe small molecule activation under mild conditions by delivery of a single electron from decamethylferrocene (Cp*2Fe) to a Lewis pair comprised of a small molecule donor and a Lewis acid of the form E(C6F5)3 (E = B or Al). These reactions proceed via the transient radical anions [·E(C6F5)3]− loosely associated with substrates yielding a series of decamethylferrocenium salts with novel boron- or aluminum-containing anions. The mechanistic implications are considered.

Scheme 1. Synthesis of 1−3

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RESULTS AND DISCUSSION Homolytic Cleavage of E−E Bonds (E = S, Te, O). Initial control experiments showed that the combination of Cp*2Fe with E(C6F5)3 (E = B or Al) in a molar ratio of 1:1 in toluene led to the slow formation of decamethylferrocenium [Cp*2Fe]+, with less than 20% conversion after 24 h for B(C6F5)321 and 1 h for Al(C6F5)3. This was concurrent with the formation of unidentified Lewis acid degradation byproducts as evidenced by 19F NMR spectroscopy. These results suggest SET from Cp*2Fe to strong Lewis acid E(C6F5)3 generating [· E(C6F5)3]−. These species are known to be extremely reactive and are quenched via reaction with solvent or itself at room temperature.27,28 Nonetheless, the possibility of the activation of a substrate molecule by transient [·E(C6F5)3]− or single electron delivery to loosely associated Lewis pairs was probed. Diphenyl disulfide and diphenyl ditelluride are weakly Lewis basic. Indeed, no adducts were formed on mixing of E(C6F5)3 (E = B or Al) and the substrates (PhS)2 and (PhTe)2 in toluene at room temperature as indicated by 19F NMR spectroscopy (Figures S57−S59 in the SI). Furthermore, these substrates were inert to Cp*2Fe over 3 days in toluene. However, the mixtures of E(C6F5)3 (E = B and Al), (PhS)2 and Cp*2Fe gave rise to deep green solutions in 24 h and 2 min, respectively (Scheme 1). 19F NMR spectra were consistent with newly formed tetra-coordinated boron and aluminum centers. Indeed, the products 1 and 2 were isolated and fully characterized spectroscopically and via X-ray diffraction studies (Figures 2a and b) confirming compounds 1 and 2 to be [Cp*2Fe][PhSB(C6F5)3] and [Cp*2Fe][(μ-PhS)(Al(C6F5)3)2], respectively. In the case of 1 repeated crystallization attempts yielded poor quality crystals, nonetheless preliminary X-ray studies confirmed the connectivity as the decamethylferrocenium salt of the known anion, [PhSB(C6F5)3]−.29 The Al−S bond lengths were found to be 2.358(2) Å and 2.339(2) Å. The ditelluride (PhTe)2 reacted similarly within 2 min of addition to a mixture of one equivalent of Cp*2Fe and 2 equiv of Al(C6F5)3 to give

Figure 2. POV-ray depiction of the anions of 1 (a), 2 (b) and 3 (c). C: black; F: pink; B: yellow-green; Al: turquoise; S: yellow; Te: yellowgray. All H atoms and the decamethylferrocenium cations are omitted for clarity.

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more Al(C6F5)3 to give final product P-2 and IN2 (−14.4 kcal/ mol), respectively. Finally, one electron reduction to IN2 and additional Al(C6F5)3 affords a second equivalent of P-2 (−38.6 kcal/mol). Born−Oppenheimer molecular dynamics (BOMD)30−32 simulations were performed at the UB3LYP/SVP level of theory at 300 K (Figure 3b) for this reaction. The initial complex of [(PhS)2·Al(C6F5)3]− exists in a doublet electronic state with S−S and Al−S distances of 2.065 and 2.565 Å, respectively. From 0 to 10 fs, constant lengthening of S−S distance and shortening of Al−S distance are observed. This is concurrent with a deformation of the [·Al(C6F5)3]− structure giving a tetra-coordinate Al center. This formation of the Al−S bond (2.260 Å) is facile affording a relaxed structure in approximately 10 fs at room temperature. While the O centers of carbonyl compounds33−35 or ethers36−39 are known to readily coordinate to strong Lewis acids, treatment of B(C6F5)3 with di-tert-butyl peroxide revealed no adduct formation as evidenced by the 11B and 19F NMR spectra (Figures S60 and S61 in the SI). Nonetheless, upon subsequent addition of Cp*2Fe to the mixture, a color change from yellow to green was observed after 1 h. The reaction was complete after 3 h and the product 4 was isolated as brilliant green crystals in 68% yield (Scheme 2). X-ray crystallography

[Cp*2Fe][(μ-PhTe)(Al(C6F5)3)2] 3 (Figure 2c). The Al−S−Al angle of 143.57(7)o in 2 is less acute than the Al−Te−Al angle of 123.71(5)o in 3. The electronic structures of the anions of 1 and 2, were examined via natural bond orbital (NBO) analysis at the M06/ SVP level of theory. The results demonstrated that the boron (0.43 au) and aluminum (1.63 and 1.64 au) centers are predominantly positively charged, while the negative charges are delocalized on S (−0.05 au in 1 and −0.30 au in 2), F and most C atoms. The calculated Wiberg bond indices (WBIs) suggested the weak single bond characters of B−S (0.88) and Al−S (0.48 and 0.51), respectively. For a better understanding of the mechanistic pathway leading to the homolytic cleavage of the disulfide bond, density functional theory (DFT) calculations were performed at the SMD-M06/TZVP//M06/SVP level of theory (Figure 3a) for the reaction of Al(C6F5)3, (PhS)2 and Cp*2Fe. One electron reduction of Al(C6F5)3/(PhS)2 homolytically splits disulfide bond to give IN1 (21.3 kcal/mol) generating [PhSAl(C6F5)3]− anion and neutral radical ·SPh. These species are intercepted by


confirmed the structure as [Cp*2Fe][(μ-HO)(B(C6F5)3)2] 4 (Figure 4a). This formulation inferred the loss of isobutene, and this was confirmed by NMR spectroscopy on the reaction mixture.40 The formation of the salt 4 requires the cleavage of O−O, C−O and C−H bonds. Two plausible pathways for this transformation were probed by DFT calculations (Figure 5). These data show that homolytic splitting of the O−O bond of di-tert-butyl peroxide by delivery of a single electron from Cp*2Fe to the Lewis pair affording [tBuOB(C6F5)3]− IN3 (−28.3 kcal/mol) is an exothermic reaction. However, the subsequent extrusion of an isobutene molecule via a fourmembered-ring transition state TS1 (29.4 kcal/mol) is found to be very energy-demanding (57.7 kcal/mol). An alternative pathway involves homolytic cleavage of both O−O and C−O bonds with the aid of B(C6F5)3 to afford a transient [· O(B(C6F5)3)2]−26 and tert-butyl radical40 (IN4, 18.5 kcal/mol). Subsequent abstraction of a H atom from tert-butyl radical by [· O(B(C6F5)3)2]− would yield isobutene and [(μ-HO)(B(C6F5)3)2]− (P-4 −42.3 kcal/mol). The corresponding combination of benzoyl peroxide with E(C6F5)3 (E = B or Al) led to a mixture of what are presumed to be weak adducts (Figures S62−S64 in the SI). However,

Figure 3. (a) Free energy (kcal/mol) profile for the formation of the salt 2. (b) Example BOMD (300 K) trajectories showing S−S bond cleavage and Al−S bond formation. Distances are given in Å. 10064


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boryl radical with 0.5 equiv of benzoyl peroxide reported by Yamashita, Ohkoshi and Nozaki.41 Radical Traps. Attempts to trap the transient radicals by reaction with Ph3SnH were also undertaken. While 11B and 19F NMR spectroscopy suggest weak coordination of B(C6F5)3 with the tin-hydride (Figures S65 and S66 in the SI),42 addition of Cp*2Fe with stirring at room temperature for 12 h gave a suspension containing dark gray and green powders. The dark gray powder showed sparingly solubility in common organic solvents, precluding its formulation. However, product 7 was isolated as a green powder in 60% yield (Scheme 3). The 11B Scheme 3. Synthesis of 7

NMR spectrum of 7 showed a doublet at −25.3 ppm (1JB−H = 90.0 Hz).43 The formulation of 7 as [Cp*2Fe][HB(C6F5)3] was further confirmed by X-ray diffraction studies (Figure S75 in the SI). The 119Sn NMR spectrum of the crude reaction mixture were consistent with the formation of Ph3SnSnPh3 (−138.5 ppm44). Quinones are also well-known reagents for trapping of radicals.41,45−47 As control reactions, independent solutions of E(C6F5)3 (E = B and Al) were mixed separately to an equivalent of p-benzoquinone (p-O2C6H4) and monitored by 19 F NMR spectroscopy. The formations of classical Lewis adducts were observed (Figures S67−S69 in the SI). In addition, there was no reaction observed for the mixture of Cp*2Fe and p-O2C6H4 after 48 h. Gratifyingly, the reactions of E(C6F5)3, p-O2C6H4 (E = B and Al) with Cp*2Fe proceeded cleanly within 1 min, providing the ensuing products 8 and 9, respectively (Scheme 4). The formulation of 8 and 9 as

Figure 4. POV-ray depiction of the anions of 4 (a) and 5 (b) (for 6, see Figure S75 in the SI). C: black; F: pink; B: yellow-green; O: red; All H atoms of benzoyl and the decamethylferrocenium cations are omitted for clarity.


Figure 5. Free energy (kcal/mol) profile for the formation of the salt 4.

[Cp*2Fe]2[(μ-O2C6H4)(E(C6F5)3)2] was confirmed X-ray diffraction studies (Figure 6a and S75). The B−O and Al−O bond lengths are 1.471(5) and 1.715(6) Å, respectively. While Cp*2Fe does not react with TEMPO, B(C6F5)3 is known to form an adduct (Figure S70 in the SI).48 In a similar fashion, Al(C6F5)3 also forms a neutral radical adduct within seconds as supported by 19F NMR spectroscopic data (Figure S71). DFT calculations reveal that the spin density of the radical adducts TEMPO-E(C6F5)3 (E = B and Al) is predominantly distributed over the N [62.6% and 61.6%] and O [31.5% and 31.6%] centers, respectively. The small WBIs of E−O (0.47, E = B and 0.29, E = Al) suggest weak dative bonds

slow addition of benzoyl peroxide to a mixture of E(C6F5)3 (E = B and Al) and Cp*2Fe selectively afforded products 5 and 6, respectively (Scheme 2). The formations of anions of the salts 5 and 6 were further confirmed by X-ray diffraction studies as [Cp*2Fe][PhC(O)OE(C6F5)3] (E = B 5, Al 6) (Figures 4b and S75). These reactions can be formally viewed as a homolytic cleavage of peroxide bond by a transient [·E(C6F5)3]− although the precise mechanistic picture may be more complicated. As such, these observations are analogous to the capture of a free 10065


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Scheme 5. Reactions of O2, Se, Te and S8 with E(C6F5)3 and Cp*2Fe

Figure 6. POV-ray depiction of the anions of 8 (a), 10 (b) and 11 (c). C: black; F: pink; B: yellow-green; O: red; Cl: green; Al: turquoise; N: blue. All H atoms and the decamethylferrocenium cations are omitted for clarity.

between E and O. The singly occupied molecular orbitals (SOMOs) are mainly localized at the TEMPO fragments, with minor contributions from the p orbitals of E centers (Figure S76 in the SI). This allows these species to accept one electron from Cp*2Fe prompting formation of the products 10 and 11 (Scheme 4). The nature of these products was unambiguously confirmed by X-ray crystallography to be [Cp* 2 Fe][(C5H6Me4NOE(C6F5)3] (E = B 10, Al 11, Figures 6b and c). The X-ray diffraction study of 10 revealed a drastic lengthening of the O−N bond (1.461 (4) Å) compared to that of the adduct of B(C6F5)3 with TEMPO (1.311 (2) Å). In addition, the B−O bond of 1.493 (5) Å in anion of 10 is significantly shorter than that reported for the neutral adduct (1.594 (3) Å). Reactions with Elemental O 2 , Se, Te and S 8 . Alkylaluminum(III) compounds are known to react with O2 normally gives aluminum alkoxides or alkylperoxides via insertion reaction into the Al-alkyl bond.49−51 Exposure of a chlorobenzene solution of Al(C6F5)3 to excess dry O2 at room temperature resulted in a light yellow solution. However, the 19 F NMR spectra showed no new species formed in 2 h (Figure S72 in the SI). Upon standing in O2 atmosphere at room temperature for 36 h, Al(C6F5)3 decomposed slowly affording an unidentified complex mixture. In contrast to the Agapie synthesis of a dianionic bis(borane) peroxide by the direct reduction of O2 by ferrocenes in the presence of B(C6F5)3,21 treatment of Al(C6F5)3/O2 in chlorobenzene with Cp*2Fe immediately gave a deep green solution. Although the 19F NMR spectra displayed a complex mixture, after workup salts 12 and [Cp*2Fe][Al(C6F5)4] were isolated (Scheme 5). X-ray diffraction studies revealed the formulation of 12 as [Cp*2Fe]2[((C6F5)2Al(μ-O)Al(C6F5)3)2]2 (Figure 7a). This confirms the cleavage of the O−O bond affording the unusual dianionic species 12 with an Al2O2 core (Figure 8). The geometry of Al2O2 core is planar, featuring the average Al−O bond lengths of 1.828 (5) Å, while the exocyclic O−Al(C6F5)3 distances averaged 1.813 (5) Å. The central Al− O bond lengths are longer than that (1.760 (1) and 1.763 (1) Å) observed in a neutral Al2O2 core.52 The Al−Al separation was found to be 2.656(3) Å. NBO analysis revealed that the central Al atoms (1.95 and 1.95 au) carried the most positive

charges, while the O atoms (−1.41 and −1.42 au) and F atoms are negatively charged, consistent with the ionic nature of the central Al−O core. A computational study of this reaction demonstrates the coordination of triplet O2 with Al(C6F5)3 is an endothermic process (20.4 kcal/mol), leading to the formation of IN5. The subsequent reduction of IN5 by Cp*2Fe affords a relatively stable dianionic bis(alane) peroxide IN6 (−47.9 kcal/mol). The O−O bond length is computed to be 1.515 Å. Both O atoms interact with Al centers to form a four-membered ring with Al−O bond lengths of 1.788 and 2.163 Å. IN6 could serve as a ·C6F5 radical donor. The dimerization of ·C6F5 would give decafluorobiphenyl. However, experimentally, treatment of decafluorobiphenyl with Al(C6F5)3/Cp*2Fe slowly provided a complex mixture in 48 h. Thus, trapping of ·C6F5 with Al(C6F5)3/Cp*2Fe is likely to give the observed byproduct [Cp*2Fe][Al(C6F5)4] (−57.1 kcal/mol). Finally, IN7 (−34.1 kcal/mol) is formed with the O−O distance of 2.545 Å, which then combines with Al(C6F5)3 to yield P-12 (129.3 kcal/mol). It is important to note that the release of ·C6F5 radicals results in the cleavage of O−O bond, reminiscent of the splitting of dioxygen by some transition-metal complexes.53,54 Elemental selenium was also shown to react with Al(C6F5)3 and Cp*2Fe to form a salt 13 (Scheme 5) and [Cp*2Fe][Al(C6F5)4], as well as some unidentified byproducts. The product, [Cp*2Fe]2[((C6F5)2Al(μ-Se)Al(C6F5)3)2]2 13 (Figure 7b) features a dianionic Al2Se2 core analogous to that observed in 12. The central Al2Se2 ring is nearly square (Al−Se: 2.418 (2), 2.428 (2) Å; Se−Al−Se: 92.70 (2)°; Al−Se−Al: 87.29 (8)°. The Al−Al distance was found to be 3.344 (2) Å, which is much longer than that (2.656 (3) Å) of 12. Two exocyclic Al(C6F5)3 units are located in the trans-configuration of the planar Al2Se2 ring with the average Al−Se bond length of 2.424 (2) Å. The salt 13 presented the first example of a dianionic Al2(μ-Se)2 species.55−59 10066


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Figure 8. Free energy (kcal/mol) profile for the formation of the salt 12. Bond lengths are given in Å.

ophenyl substituents exhibit π−π stacking surround the Al3Te2 core. Computations predict the average charge of Al and Te atoms of 1.14 au and −0.55 au, respectively. The corresponding reaction of S8, B(C6F5)3 and Cp*2Fe resulted in conversion to a single boron-containing product as suggested by a singlet signal at −10 ppm in 11B NMR spectrum and one set of signals in 19F NMR spectrum. Single crystals of 15 (Figure 7d) suitable for an X-ray diffraction study were grown by slow vapor diffusion of pentane into a saturated dichloromethane solution at −20 °C. These data revealed the formulation of 15 as [Cp*2Fe]2[(μ-S7)B(C6F5)3)2]. The dianion features a bent S7 chain with the average of S−S bond lengths of 2.036 (3) Å which is slightly shorter than that (2.050 (4) Å) of a free dianionic S7 chain.60 The B−S bond lengths are 1.965 (9) and 1.988 (8) Å, which is in the range of B−S single bond. The S7 chain carried negative charge of −0.47 au, whereas boron atoms (0.42 and 0.42 au) are positively charged. Repeated experiments using varying equivalents of S8 also afforded 15 suggesting that this species has both thermodynamic stability and appropriate solubility properties to permit isolation. In general, the reactions described herein provide a novel route to unique anion salts. These reactions can be viewed from two perspectives. One view involves delivery of one electron (from Cp*2Fe) to the combination of a Lewis acid (E(C6F5)3) and base (chalcogenide species). An alternatively perspective considers these reactions of a one-electron donor and Lewis acid with a chalcogenide substrate molecule. In this latter view, the present results open a new pathway to the generation of a transient frustrated radical pair (FRP) and a radical pathway for FLP chemistry. Such an avenue has recently been uncovered and substantiated.61

Figure 7. POV-ray depiction of the anions of 12 (a), 13 (b), 14 (c) and 15 (d). C: black; F: pink; Te and B: yellow-green; O: red; Cl: green; Al: turquoise. The decamethylferrocenium cations are omitted for clarity.

Treatment of elemental tellurium with Al(C6F5)3/Cp*2Fe in toluene at 0 °C afforded a green suspension within 6 h. After careful workup, 19F NMR spectrum suggested two sets of pentafluorophenyl resonances, indicating the generation of two major products. Indeed, the salt 14 with the formulation of [Cp*2Fe][(μ-Te)2(Al(C6F5)2)3] as well as [Cp*2Fe][Al(C6F5)4], were isolated by fractional recrystallization. Single crystal X-ray structure analysis shows the anion of 14 to be a bicyclo[1,1,1]pentane-like core with two tricoordinated Te atoms and three tetracoordinated Al atoms (Figure 7c). The average Te−Al bond length is 2.658 (5) Å. The pentafluor10067


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calcd. for [C24H5BF15S]− 620.9966, found 620.9973. Elemental analysis for C44H35BF15FeS: calcd.: C 55.78, H 3.72, found: C 55.70, H 3.68. Synthesis of [Cp*2Fe][(μ-PhS)(Al(C6F5)3)2] (2). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), Al(C6F5)3·tol (62.0 mg, 0.10 mmol) and diphenyl disulfide (5.5 mg, 0.025 mmol) was stirred in 2 mL toluene at room temperature. After 2 min, the green solid product starts to be precipitated. Pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 2 as a green solid (67.1 mg, 90%). Single crystals of 2 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at −15 °C. 1H NMR (400 MHz, CDCl3, 298 K) δ 7.18 (bs, 2H, o-C6H5), 7.09 (bs, 1H, m-C6H5), 6.95 (bs, 2H, p-C6H5), −36.82 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CDCl3, 298 K, Al-bonded C could not be observed) δ 149.5 (dm, 1JC−F = 237 Hz, o-C6F5), 141.0 (dm, 1JC−F = 237 Hz, p-C6F5), 136.3 (dm, 1JC−F = 250 Hz, m-C6F5), 137.4 (s, SC), 128.0 (s, o-C6H5), 127.8 (s, m-C6H5), 114.9 (s, p-C6H5). 19F NMR (377 MHz, CDCl3, 298 K) δ −120.9 (br, 12F, o-C6F5), −155.5 (br, 6F, p-C6F5), −163.8 (br, 12F, m-C6F5). 27Al NMR (104 MHz, CDCl3, 298 K) blank. Elemental analysis for C62H35Al2F30FeS: calcd.: C 49.92, H 2.36, found: C 49.97, H 2.42. Synthesis of [Cp*2Fe][(μ-PhTe)(Al(C6F5)3)2] (3). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), Al(C6F5)3·tol (62.0 mg, 0.10 mmol) and diphenyl ditelluride (10.3 mg, 0.025 mmol) was stirred in 2 mL toluene at room temperature. After 2 min, the green solid product starts to be precipitated. Pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 3 as a green solid (62.8 mg, 79%). Single crystals of 3 suitable for X-ray diffraction were obtained from layering of pentane with a saturated C6H5F solution at −15 °C. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 7.82 (d, 2H, J = 6.2 Hz, o-C6H5), 7.25 (m, 1H, m-C6H5), 7.19 (m, 2H, p-C6H5), −25.35 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K, Al-bonded C could not be observed) δ 150.2 (dm, 1JC−F = 238 Hz, o-C6F5), 141.4 (dm, 1JC−F = 257 Hz, p-C6F5), 137.0 (dm, 1JC−F = 255 Hz, m-C6F5), 138.0 (s, oC6H5), 130.0 (s, p-C6H5), 128.5 (s, m-C6H5), 125.6 (s, TeC). 19F NMR (377 MHz, CD2Cl2, 298 K) δ −120.2 (bs, 12F, o-C6F5), −150.9 (bs, 6F, p-C6F5), −160.5 (bs, 12F, m-C6F5). Elemental analysis for C62H35Al2F30FeTe: calcd.: C 46.91, H 2.22, found: C 47.17, H 2.32. Synthesis of [Cp*2Fe][(μ-HO)(B(C6F5)3)2] (4). A mixture of ditert-butyl peroxide (3.7 mg, 0.025 mmol), B(C6F5)3 (52.0 mg, 0.10 mmol) and Cp*2Fe (16.3 mg, 0.050 mmol) was stirred in 3 mL C6H5Cl for 3 h. The color of the solution changed to green. The volatiles were removed in vacuo. The resulting green solid was washed with a mixture of pentane (2 mL) and C6H5Cl (0.5 mL), and dried in vacuo to give the salt 4 as green powder (54.3 mg, 87%). Single crystals of 4 suitable for X-ray diffraction were obtained from layering of pentane with a saturated C6H5Cl solution at room temperature. 1H NMR (400 MHz, CDCl3, 298 K) δ 6.78 (bs, 1H, OH), −37.77 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ 148.1 (dm, 1 JC−F = 240 Hz, o-C6F5), 139.8 (dm, 1JC−F = 251 Hz, p-C6F5), 137.1 (dm, 1JC−F = 256 Hz, m-C6F5), 120.4 (bs, BC). 19F{1H} NMR (377 MHz, CD2Cl2, 298 K) δ −120.8 (d, J = 19.7 Hz, 12F, o-C6F5), −160.4 (bs, 6F, p-C6F5), −165.8 (bs, 12F, m-C6F5). 11B{1H} NMR (128 MHz, CD2Cl2, 298 K) δ −2.7 (bs). HRMS (ESI) calcd. for [C36HB2F30O]− 1040.9734, found 1040.9742. Synthesis of [Cp*2Fe][PhC(O)OB(C6F5)3] (5). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol) and B(C6F5)3 (26.0 mg, 0.050 mmol) was stirred in 3 mL DCM. Benzoyl peroxide (6.1 mg, 0.025 mmol) was added slowly into solution. After 1 h, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 5 as a green solid (31.7 mg, 66%). Single crystals of 5 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at −15 °C. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 8.12 (bs, 2H, o-C6H5), 7.52 (bs, 3H, p-C6H5 and m-C6H5), −33.75 (bs, Cp*2Fe+). 13C{1H} NMR (126

CONCLUSIONS The above reactivity illustrates a general and new strategy to activate small molecule substrates. Delivery of a single electron to Lewis pairs consisting of strong Lewis acids E(C6F5)3 (E = B and Al) and a variety of substrates, including small molecules or elemental chalcogenides affords access to novel anions. These reactions can be formally viewed as an avenue to access the reactivity of the elusive radical anions [·E(C6F5)3]−. The utility of this SET protocol in the production of other anions, the subsequent chemistry of these new salts and the extension of this reactivity to catalysis are the subjects of ongoing work.

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EXPERIMENTAL SECTION

General Considerations. All manipulations were performed under an atmosphere of dry, oxygen-free N2 by means of standard Schlenk or glovebox techniques (MBraun LABmaster SP drybox and Innovation Technology glovebox both equipped with a −35 °C freezer). Toluene, pentane, and dichloromethane (DCM) were collected from a Grubbs-type column system manufactured by Innovative Technology. These solvents, along with fluorobenzene (C6H5F) bromobenzene (C6H5Br) and 1,2-dichlorobenzene (1,2C6H4Cl2), were dried over 4 Å molecular sieves. Molecular sieves, type 4 Å (pellets, 3.2 mm diameter) purchased from Sigma-Aldrich were activated prior to usage by iteratively heating with 1050 W Haier microwave for 5 min and cooling under vacuo. The process was repeated until no further moisture was released upon heating. Dichloromethane-d2 (CD2Cl2), bromobenzene-d5 (C6D5Br) purchased from Cambridge Isotope Laboratories, were degassed and stored over 4 Å molecular sieves in the glovebox for at least 8 h prior to use. Chlorobenzene (C6H5Cl), benzene (C6H6) and chloroform-d (CDCl3) were degassed and dried over calcium hydride. B(C6F5)3 was purified from sublimation at 100 °C followed by stirring with chlorodimethylsilane at room temperature for 2 h, and dried under vacuo. Decamethylferrocene (Cp*2Fe), diphenyl disulfide [(PhS)2], diphenyl ditelluride [(PhTe)2], di-tert-butyl peroxide, benzoyl peroxide, triphenyltin hydride (Ph3SnH), p-benzoquinone (pO2C6H4), TEMPO, dry O2, decafluorobiphenyl, elemental Se, Te, and S8 were purchased and used directly. Al(C6F5)3·tol was prepared using literature methods. Combustion analyses were performed inhouse employing a Flash 2000 from Thermo Instruments CHN Analyzer. Spectra were recorded on a Bruker Avance III 400 MHz, an Agilent DD2 500 MHz, and an Agilent DD2 600 MHz spectrometer and spectra were referenced to residual solvents of CD2Cl2 (1H = 5.32 ppm; 13C = 53.8 ppm), CDCl3 (1H = 7.26 ppm; 13C = 77.0 ppm), or externally [11B: (Et2O)BF3 (δ 0.00), 19F: CFCl3 (δ 0.00), 27Al: Al(NO3)3 (δ 0.00)]. Chemical shifts (δ) are reported in ppm and the absolute values of the coupling constants (J) are in Hz. Highresolution mass spectra (HRMS) were obtained on a JMS-T100LC JEOL DART or AB Sciex QStarXL ESI. Synthesis of [Cp*2Fe][PhSB(C6F5)3] (1). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), B(C6F5)3 (26.0 mg, 0.050 mmol) and diphenyl disulfide (5.5 mg, 0.025 mmol) was stirred in 3 mL DCM at room temperature for 24 h to give a green solution. Pentane (5 mL) was added to the solution with rapid stirring. A green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/ solvents were removed in vacuo to afford the salt 1 as a green solid (21.8 mg, 46%). Single crystals of 1 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at −15 °C. 1H NMR (400 MHz, CD2Cl2, 298 K,) δ 7.89 (bs, 2H, oC6H5), 7.29 (bs, 3H, p-C6H5 and m-C6H5), −33.98 (bs, Cp*2Fe+). 13 C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ 147.6 (dm, 1JC−F = 241 Hz, o-C6F5), 139.4 (dm, 1JC−F = 249 Hz, p-C6F5), 136.7 (dm, 1JC−F = 251 Hz, m-C6F5), 135.7 (s, SC), 128.9 (s, o-C6H5), 128.1 (s, m-C6H5), 125.2 (s, p-C6H5) 120.9 (bs, BC). 19F NMR (377 MHz, CDCl3, 298 K) δ −120.9 (br, 12F, o-C6F5), −155.5 (br, 6F, p-C6F5), −163.8 (br, 12F, m-C6F5). 19F{1H} NMR (377 MHz, CD2Cl2, 298 K) δ −131.7 (bs, 6F, o-C6F5), −162.7 (bs, 3F, p-C6F5), −167.4 (bs, 6F, m-C6F5). 11 B NMR (128 MHz, CD2Cl2, 298 K) −9.9 (s). HRMS (DART) 10068


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Journal of the American Chemical Society MHz, CD2Cl2, 298 K, B-bonded C could not be observed) δ 167.8 (CO), 148.3 (dm, 1JC−F = 249 Hz, o-C6F5), 137.0 (dm, 1JC−F = 255 Hz, p-C6F5), 136.3 (dm, 1JC−F = 246 Hz, m-C6F5), 131.4 (s, p-C6H5), 129.9 (s, CC(O)O), 128.6 (s, o-C6H5), 128.2(s, m-C6H5). 19F{1H} NMR (377 MHz, CD2Cl2, 298 K) δ −135.0 (d, 3JC−F = 20.7 Hz, 6F, oC6F5), −163.4 (t, 3JC−F = 19.5 Hz, 3F, p-C6F5), −167.6 (m, 6F, mC6F5). 11B{1H} NMR (128 MHz, CD2Cl2, 298 K) δ −4.7 (bs). HRMS (DART) calcd. for [C25H5BF15O2]− 633.0143, found 633.0137. Elemental analysis for C45H35BF15FeO2: calcd.: C 56.34, H 3.68, found: C 56.70, H 3.80. Synthesis of [Cp*2Fe][PhC(O)OAl(C6F5)3] (6). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol) and Al(C6F5)3·tol (31.0 mg, 0.050 mmol) was stirred in 3 mL C6H5Cl. Benzoyl peroxide (6.1 mg, 0.025 mmol) was added slowly into solution. After 2 min, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/ solvents were removed in vacuo to afford the salt 6 as a green solid (37.1 mg, 76%). Single crystals of 6 suitable for X-ray diffraction were obtained from layering of pentane with a saturated C6H5Cl solution at room temperature. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 8.35 (bs, 2H, o-C6H5), 7.70 (bs, 3H, p-C6H5 and m-C6H5), −36.75 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K, Al-bonded C could not be observed) δ 169.6 (CO), 150.4 (dm, 1JC−F = 231 Hz, o-C6F5), 141.1 (dm, 1JC−F = 245 Hz, p-C6F5), 136.9 (dm, 1JC−F = 252 Hz, m-C6F5), 135.2 (s, p-C6H5), 131.9 (s, o-C6H5), 130.6 (s, CC(O)O), 128.5 (s, m-C6H5). 19F{1H} NMR (377 MHz, CD2Cl2, 298 K) δ −123.3 (bs, 6F, o-C6F5), −158.3 (bs, 3F, p-C6F5), −164.6 (bs, 6F, m-C6F5). 27Al NMR (104 MHz, CD2Cl2, 298 K) δ 108.9 (bs). Elemental analysis for C45H35AlF15FeO2: calcd.: C 55.40, H 3.62, found: C 55.51, H 3.78. Synthesis of [Cp*2Fe][HB(C6F5)3] (7). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), Ph3SnH (17.6 mg, 0.050 mmol) and B(C6F5)3 (26.0 mg, 0.050 mmol) was stirred in 3 mL DCM. After 12 h, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 7 as a green solid (25.2 mg, 60%). Single crystals of 7 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at room temperature. The generation of Ph3SnSnPh3 was confirmed by 119Sn NMR spectroscopy (−138.5 ppm in CD2Cl2). 1H NMR (400 MHz, CD2Cl2, 298 K) δ 3.72 (q, 1JB−H = 88.5 Hz, 1H, HB), −36.67 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ 148.7 (dm, 1JC−F = 226 Hz, o-C6F5), 138.6 (dm, 1JC−F = 241 Hz, p-C6F5), 131.1 (dm, 1JC−F = 249 Hz, m-C6F5), 125.8 (bs, BC). 19F{1H} NMR (377 MHz, CDCl3, 298 K) δ −134.2 (bs, 6F, o-C6F5), −164.8 (t, 3JC−F = 18.9 Hz, 3H, p-C6F5), −167.9 (m, 6F, m-C6F5). 11B NMR (128 MHz, CD2Cl2, 298 K) δ −25.3 (d, 1JB−H = 90.0 Hz). HRMS (DART) calcd. for [C18HBF15]− 512.9932, found 512.9939. Elemental analysis for C38H31BF15Fe: calcd.: C 54.38, H 3.72, found: C 54.00, H 3.68. Synthesis of [Cp*2Fe]2[(μ-O2C6H4)(B(C6F5)3)2] (8). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), p-O2C6H4 (2.7 mg, 0.025 mmol) and B(C6F5)3 (26.0 mg, 0.050 mmol) was stirred in 3 mL DCM in the dark. After 1 min, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 8 as a green solid (39.3 mg, 88%). Single crystals of 8 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at room temperature. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 6.81 (bs, 4H, C6H4), −36.48 (bs, Cp*2Fe+). 13 C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ 152.6 (s, OC), 148.6 (dm, 1JC−F = 239 Hz, o-C6F5), 139.2 (dm, 1JC−F = 250 Hz, p-C6F5), 135.5 (dm, 1JC−F = 250 Hz, m-C6F5), 125.4 (bs, BC), 118.3 (s, C6H4). 19 1 F{ H} NMR (377 MHz, CDCl3, 298 K) δ −134.0 (bs, 12F, o-C6F5), −163.6 (bs, 6F, p-C6F5), −167.9 (bs, 12F, m-C6F5). 11B NMR (128 MHz, CD2Cl2, 298 K) δ −3.2 (bs). Elemental analysis for C82H64B2F30Fe2O2: calcd.: C 55.19, H 3.61, found: C 55.61, H 3.79. Synthesis of [Cp*2Fe]2[(μ-O2C6H4)(Al(C6F5)3)2] (9). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), p-O2C6H4 (2.7 mg, 0.025 mmol) and Al(C6F5)3·tol (31.0 mg, 0.050 mmol) was stirred in 3 mL toluene in

the dark. After 1 min, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 9 as a green solid (81.7 mg, 90%). Single crystals of 9 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at −15 °C. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 7.39 (bs, 4H, C6H4), −37.21 (bs, Cp*2Fe+). 13 C{1H} NMR (126 MHz, CD2Cl2, 298 K, Al-bonded C could not be observed) δ 151.9 (s, OC), 150.5 (dm, 1JC−F = 238 Hz, o-C6F5), 141.3 (dm, 1JC−F = 249 Hz, p-C6F5), 137.2 (dm, 1JC−F = 254 Hz, m-C6F5), 128.7 (s, C6H4), 119.1 (s, C6H4). 19F{1H} NMR (377 MHz, CDCl3, 298 K) δ −122.6 (bs, 12F, o-C6F5), −158.4 (bs, 6F, p-C6F5), −164.6 (bs, 12F, m-C6F5). 27Al NMR (104 MHz, CD2Cl2, 298 K) δ 101.7. Elemental analysis for C82H64Al2F30Fe2O2: calcd.: C 54.20, H 3.55, found: C 54.41, H 3.69. Synthesis of [Cp*2Fe][(C5H6Me4NOB(C6F5)3] (10). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), TEMPO (7.8 mg, 0.050 mmol) and B(C6F5)3 (26.0 mg, 0.050 mmol) was stirred in 3 mL toluene. After 1 min, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 10 as a green solid (39.3 mg, 90%). Single crystals of 10 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at room temperature. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 1.54 (bs, 4H, CH2), 0.98 (s, 12H, CH3), −36.74 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ 147.9 (dm, 1 JC−F = 237 Hz, o-C6F5), 138.7 (dm, 1JC−F = 247 Hz, p-C6F5), 136.7 (dm, 1JC−F = 248 Hz, m-C6F5), 124.6 (bs, BC), 68.3 (s, N-C), 36.6 (s, CH2), 35.3 (s, CH2), 19.1 (bs, CH3). 19F{1H} NMR (377 MHz, CD2Cl2, 298 K) δ −136.0 (d, 1JC−F = 18.6 Hz, 6F, o-C6F5), −163.2 (t, 1 JC−F = 18.0 Hz, 3F, p-C6F5), −167.1 (bs, 12F, m-C6F5). 11B NMR (128 MHz, CD2Cl2, 298 K) δ −3.9 (s). HRMS (DART) calcd. for [C27H18BF15NO]− 668.1242, found 668.1244. Elemental analysis for C37H48BF15FeNO: calcd.: C 50.82, H 5.53, N 1.60, found: C 51.00, H 5.77, N 1.68. Synthesis of [Cp*2Fe][(C5H6Me4NOAl(C6F5)3] (11). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), TEMPO (7.8 mg, 0.050 mmol) and Al(C6F5)3·tol (31.0 mg, 0.050 mmol) was stirred in 3 mL toluene. After 1 min, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 11 as a green solid (45.5 mg, 90%). Single crystals of 11 suitable for X-ray diffraction were obtained from layering of pentane with a saturated 1,2-C6H4Cl2 solution at room temperature. 1H NMR (400 MHz, CD2Cl2, 298 K) δ 1.72 (m, 2H, CH2), 1.50 (m, 4H, CH2), 1.31 (s, 6H, CH3), 0.98 (s, 6H, CH3), −35.56 (bs). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K, Al-bonded C could not be observed) δ 150.0 (dm, 1JC−F = 230 Hz, o-C6F5), 140.2 (dm, 1JC−F = 245 Hz, pC6F5), 136.6 (dm, 1JC−F = 255 Hz, m-C6F5), 59.0 (s, N-C), 40.5 (s, CH2), 34.1 (s, CH2), 19.0 (s, CH3), 18.1 (s, CH3). 19F{1H} NMR (377 MHz, CDCl3, 298 K) δ −121.2 (bs, 12F, o-C6F5), −160.1 (m, 6F, pC6F5), −165.5 (bs, 12F, m-C6F5). 27Al NMR (104 MHz, CD2Cl2, 298 K) δ 106.8. Elemental analysis for C47H48NAlF15FeO: calcd.: C 55.85, H 4.79, N 1.39, found: C 56.30, H 4.91, N 1.40. Synthesis of [Cp*2Fe]2[((C6F5)2Al(μ-O)Al(C6F5)3)2]2 (12) and [Cp*2Fe][Al(C6F5)4]. Dry O2 (excess, 4 atm) was added into a chlorobenzene solution (1.5 mL) of Cp*2Fe (8.2 mg, 0.025 mmol) and Al(C6F5)3·tol (31.0 mg, 0.050 mmol). Immediately, the color of the solution changed to be light green. Pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford a mixture. Single crystals of 12 suitable for X-ray diffraction were obtained from slow diffusion of pentane into a saturated C6H5Cl solution at room temperature overnight (4 mg, 13%). After collection of the crystals of 12, the resulting solution was layered with pentane to give [Cp*2Fe][Al(C6F5)4] as green crystals (7.6 mg, 30%). The NMR data of the salt 12 have not been collected since the crystals of 12 grown out in some green oily byproducts that could not be completely removed. The salt [Cp*2Fe][Al(C6F5)4]: 1H NMR (400 MHz, CD2Cl2, 298 K) δ −36.43 (bs, Cp*2Fe+). 13C{1H} 10069


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mounted in Paratone-N oil on a MiTeGen cryoloop, then placed in the cold (N2) stream of the diffractometer. Unit cell parameters were determined from consecutive scans at different orientations. The data were integrated using the SAINT software package63 and a multiscan absorption correction was applied using SADABS.64 All structures were solved and refined by direct methods in the SHELXTL suite of programs using XS and refinement by full-matrix least-squares on F2 using XL.65,66 All non-hydrogen atoms were subjected to anisotropic refinement and carbon-bound hydrogen atoms were placed in calculated positions using an appropriate riding model and coupled isotropic temperature factors (Uiso(H) = 1.2Ueq(C)).

NMR (126 MHz, CD2Cl2, 298 K, Al-bonded C could not be observed) δ 150.2 (dm, 1JC−F = 232 Hz, o-C6F5), 140.8 (dm, 1JC−F = 245 Hz, p-C6F5), 136.8 (dm, 1JC−F = 252 Hz, m-C6F5. 19F{1H} NMR (377 MHz, CDCl3, 298 K) δ −122.9 (bs, 8F, o-C6F5), −158.5 (t, 3JC−F = 17.8 Hz, 4F, p-C6F5), −164.8 (bs, 8F, m-C6F5). 27Al NMR (104 MHz, CD2Cl2, 298 K) δ 114.6. HRMS (DART) calcd. for [C24AlF20]− 694.9496, found 694.9499. Elemental analysis for C34H30AlF20Fe: calcd.: C 45.30, H 3.35, found: C 45.11, H 3.60. Synthesis of [Cp*2Fe]2[((C6F5)2Al(μ-Se)Al(C6F5)3)2]2 (13) and [Cp*2Fe][Al(C6F5)4]. A mixture of Cp*2Fe (8.2 mg, 0.025 mmol), Se (2 mg, 0.025 mmol) and Al(C6F5)3·tol (31.0 mg, 0.050 mmol) was stirred in 3 mL C6H5Cl. After 12 h, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo and the resulting green solid was collected and fractional recrystallized to afford 13 (6.3 mg, 20%) and [Cp*2Fe][Al(C6F5)4] (10.7 mg, 42%). Single crystals of 13 suitable for X-ray diffraction were obtained from slow diffusion of pentane into a saturated C6H5Cl solution at room temperature. 1H NMR (400 MHz, CD5Br, 298 K) δ −33.50 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD5Br, 298 K) no signal could be observed after 10000 scans since the low solubility of the salt 13. 19F{1H} NMR (377 MHz, CD5Br, 298 K) δ −120.7 (bs, 12F, o-C6F5, Al(C6F5)3), −123.4 (d, 3JC−F = 19.9 Hz, 8F, o-C6F5, Al(C6F5)2), −154.3 (t, 3JC−F = 18.2 Hz, 4F, p-C6F5, Al(C6F5)2), −158.4 (bs, 8F, m-C6F5, Al(C6F5)2), −162.3 (bs, 6F, pC6F5, Al(C6F5)3), −165.9 (bs, 12F, m-C6F5, Al(C6F5)3). 27Al NMR (104 MHz, CD5Br, 298 K) δ blank. As shown in the 19F NMR spectrum (see SI), trace unidentified impurities exist. Efforts were made to remove the trace unidentified impurities but failed. Thus, the elemental analyses gave unsatisfying results. Synthesis of [Cp*2Fe][(μ-Te)2(Al(C6F5)2)3] (14). A mixture of Cp*2Fe (8.2 mg, 0.025 mmol), Te (3.2 mg, 0.025 mmol) and Al(C6F5)3·tol (31.0 mg, 0.050 mmol) was stirred in 3 mL toluene at 0 °C. After 6 h, cold pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with cold pentane (1 mL). All volatiles/solvents were removed in vacuo and the resulting green solid was collected and recrystallization at −15 °C to afford 14 (10.0 mg, 24%) and [Cp*2Fe][Al(C6F5)4] (12.8 mg, 50%). Single crystals of 14 suitable for X-ray diffraction were obtained from slow diffusion of pentane into a saturated 1,2-C6H4Cl2 solution at −15 °C. 1H NMR (400 MHz, CD2Cl2, 298 K) δ −33.35 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K, Al-bonded C could not be observed) δ 149.7 (dm, 1JC−F = 231 Hz, o-C6F5), 140.4 (dm, 1JC−F = 248 Hz, p-C6F5), 136.3 (dm, 1JC−F = 256 Hz, m-C6F5). 19 1 F{ H} NMR (377 MHz, CD2Cl2, 298 K) δ −120.2 (bs, 12F, oC6F5), −158.8 (t, 3JC−F = 17.7 Hz, 6F, p-C6F5), −162.1 (bs, 12F, mC6F5). 27Al NMR (104 MHz, CD2Cl2, 298 K) δ blank. The salt 14 decomposed gradually in both solution and solid state at room temperature with the formation of black powders, preventing performing elemental analysis. Synthesis of the Salt [Cp*2Fe]2[(μ-S7)B(C6F5)3)2] (15). A mixture of Cp*2Fe (16.3 mg, 0.050 mmol), S8 (12.8 mg, 0.050 mmol) and B(C6F5)3 (26.0 mg, 0.050 mmol) was stirred in 3 mL DCM. After 12 h, pentane (5 mL) was added into the solution with rapid stirring. The green solid was obtained by filtration and washed with pentane (1 mL). All volatiles/solvents were removed in vacuo to afford the salt 15 as a green solid (36.6 mg, 77%). Single crystals of 15 suitable for X-ray diffraction were obtained from layering of pentane with a saturated DCM solution at −15 °C. 1H NMR (400 MHz, CD2Cl2, 298 K) δ −35.94 (bs, Cp*2Fe+). 13C{1H} NMR (126 MHz, CD2Cl2, 298 K) δ 148.1 (dm, 1JC−F = 241 Hz, o-C6F5), 139.8 (dm, 1 JC−F = 241 Hz, p-C6F5), 137.2 (dm, 1JC−F = 246 Hz, m-C6F5), 120.3 (bs, BC). 19F{1H} NMR (377 MHz, CDCl3, 298 K) δ −131.1 (bs, 12F, o-C6F5), −162.0 (bs, 6F, p-C6F5), −166.8 (bs, 12F, m-C6F5). 11B NMR (128 MHz, CD2Cl2, 298 K) δ −10.0. Elemental analysis for C76H60B2F30Fe2S7: calcd.: C 48.02, H 3.18, found: C 47.69, H 3.10. X-ray Crystallography. X-ray crystallographic data were collected on a Bruker Apex2 X-ray diffractometer at 150 ± 2 K using a graphite monochromator with Mo Kα radiation (λ = 0.71073 Å) and the Bruker APEX-2 software62 package. Suitable crystals were selected and

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b05120. NMR spectra, crystal data and computational details (PDF) Crystallographic data for compounds 2−15 and [Cp*2Fe][Al(C6F5)4] (CIF)

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AUTHOR INFORMATION

Corresponding Author

*[email protected] ORCID

Liu Leo Liu: 0000-0003-4934-0367 Douglas W. Stephan: 0000-0001-8140-8355 Notes

The authors declare no competing financial interest. X-ray data are deposited in CCDC #1546082−1546095 and 1546544.

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ACKNOWLEDGMENTS D.W.S. gratefully acknowledges the financial support from NSERC Canada and the award of Canada Research Chair. D.W.S. is also grateful for the award of an Einstein Fellowship at TU Berlin.

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REFERENCES

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