Frustrated Lewis Pair Oxidation Permits Synthesis of a

5 days ago - By employing a Frustrated Lewis Pair (FLP) strategy, XeF2 was able ... However, oxidation of a proazaphosphatrane/BPh3 frustrated Lewis p...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Frustrated Lewis Pair Oxidation Permits Synthesis of a Fluoroazaphosphatrane, [FP(MeNCH2CH2)3N]+ Timothy C. Johnstone, Alvaro I. Briceno-Strocchia, and Douglas W. Stephan* Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF WINNIPEG on 11/30/18. For personal use only.

S Supporting Information *

ABSTRACT: Proazaphosphatranes, also known as Verkade’s superbases, are among the strongest nonionic bases available. Their extreme basicity derives in part from their ability to form a P−N transannulation upon interaction of the P atom with an electrophile. Although haloazaphosphatrane cations of the form [XP(RNCH2CH2)3N]+ have previously been reported for X = Cl, Br, and I, no fluoroazaphosphatranes (X = F) have been prepared. Unlike treatment with Cl2, Br2, I2, and surrogates thereof, reaction of proazaphosphatranes with XeF2 results in decomposition. Analysis of the decomposition products suggested that fluoride ions may be the destructive agent. However, oxidation of a proazaphosphatrane/BPh3 frustrated Lewis pair affords [FP(RNCH2CH2)3N][FBPh3]. Systematic trends in the experimental and computed NMR and structural data are considered. A computational analysis suggests that the transannular P−N distance varies as a result of the flexibility of the molecules and their capacity to deform in the solid state.

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INTRODUCTION The proazaphosphatranes P(RNCH2CH2)3N comprise a class of cagelike bicyclic molecules featuring bridgehead P and N atoms spanned by three amidoethylene linkers. These molecules were first reported by the Verkade group, who demonstrated that they could function as Brønsted bases, undergoing protonation at the P atom.1−3 In fact, the proton affinities of these molecules are among the highest known for nonionic species and have garnered the proazaphosphatranes a place in the superbase category alongside molecules such as phosphazenes, amidines, and guanidines.4 The ability to tune the steric bulk at the site of basicity by varying the R groups has allowed for the generation of bases that are highly potent and non-nucleophilic. These characteristics allow proazaphosphatranes to function effectively as organocatalysts for a range of chemical transformations including, among others, alkylation, acylation, dehydrohalogenation, synthesis of α,β-unsaturated nitriles, and the cyclotrimerization of isocyanates.5 The function of these molecules as ligands in transition metal based catalytic systems has also been explored in Stille cross-coupling reactions.6 The utility of this class of molecules arises from their unique reactivity, which in turn derives from their molecular and electronic structures. The cage-like geometry places a trivalent N atom directly below the P atom. Upon interaction of the P atom with an electrophile X, the lone pair on the transannular N atom (Nta) donates into the P−X antibonding orbital (Scheme 1).7 This transannular donation requires a contraction of the cage, which is facilitated by the flexibility of the amidoethylene linkers. Although population of the P−X antibonding orbital by the lone pair on Nta effectively weakens © XXXX American Chemical Society

Scheme 1. Transannulation Induced by Interaction of Proazaphosphatrane P(RNCH2CH2)3N with Electrophile X

the P−X bond, the final result is an overall stabilization of the proazaphosphatrane-electrophile Lewis acid−base adduct. The formation of the transannular interaction divides the formally bicyclic proazaphosphatrane into a tricyclic azaphosphatrane, although it should be noted that the extent of transannulation can vary, as reflected in the P···Nta distance (dPN).3,7 Molecules exhibiting an intermediate level of interaction have been dubbed quasiazaphosphatranes.3,7 This transannulation has been identified as one of the main contributors to the strength of this class of bases and factors influencing this intramolecular interaction have been explored both computationally and experimentally. pKa determinations revealed that variation of the R group bound to the equatorial N atoms (Neq) among H, Me, iso-Pr, and sec-Bu has a minor influence on basicity.8−10 Characterization of tricarbonylproazaphosphatranenickel(0) complexes revealed, however, that such substitutions have a large impact on the cone angle of these ligands.11 For a given R group, variation of the electrophile X, to which the P atom binds, has a very significant impact on the extent of transannulation; more Received: September 13, 2018

A

DOI: 10.1021/acs.inorgchem.8b02605 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry electrophilic X groups generally favor a greater degree of transannulation.3,12 The haloazaphosphatranes provide a convenient series with which to study the influence of the apical X substituent. A variety of haloazaphosphatranes have been prepared generally via the action of the corresponding halogen on the free base.3 Indeed, many physically observable properties of these compounds qualitatively follow an expected systematic variation. For example, 31P NMR resonances shift upfield for the lighter halogens, and the transannular distance concomitantly decreases. Interestingly, although the fluoroazaphosphatranes have been included in computational studies,7 no report of their synthesis has appeared in the literature to our knowledge. The lack of experimental evidence regarding the influence of an F substituent is particularly noticeable because computational studies provide predictions that are at odds with the trends established by the other members of the series. For example, on the basis of wave function and density functional theory (DFT) calculations, it has been proposed that a chloroazaphosphatrane will be the more strongly transannulated than the corresponding fluoroazaphosphatrane,7 whereas the trend experimentally established by iodo-, bromo-, and chloroazaphosphatranes suggests that the fluoroazaphosphatrane should be more strongly transannulated.3 Herein, we investigate the conspicuous absence of the fluoroazaphosphatranes to shed light on the nature of their electronic and molecular structure. In the course of this investigation, we observed that the action of F2 surrogates on free-base proazaphosphatranes leads to decomposition. Analysis of the decomposition products suggested that free fluoride ions released during the reaction may be the cause of the decomposition. A synthetic strategy involving a frustrated Lewis pair (FLP) was used to successfully prepare and characterize a fluoroazaphosphatrane salt, allowing a detailed comparison with its heavier congeners.

Figure 1. Displacement ellipsoid plots (50% probability level) of minor decomposition products crystallized from the reaction of XeF2 with (a) P(iPrNCH2CH2)3N or (b) P(MeNCH2CH2)3N. Color code: C gray, N blue, P orange, F pink, H white spheres.

released fluoride ions on the fluoroazaphosphatrane cation is thought to extrude the P atom from the ligand framework, generating PF6−. FLP Strategy. We reasoned that if the reaction of XeF2 with P(RNCH2CH2)3N was performed in the presence of a Lewis acid then the fluoride ions could be captured precluding the above undesired reactivity. We have previously reported on the ability of the Lewis adduct (C6F5)3B−P(MeNCH2CH2)3N to effect FLP addition reactions, and Krempner et al. have described the FLP hydrogenation chemistry of the fully frustrated BPh3/P(iPrNCH2CH2)3N pair.21,22 A 1:1 combination of P(MeNCH2CH2)3N and BPh3 affords 11B and 31P NMR spectra with broadened signals, indicative of an equilibrium between the Lewis adduct and the dissociated acid and base. Oxidation Reactions. The presence of the Lewis acid does not interfere with the oxidation of the proazaphosphatrane, as addition of 1 equiv of I2 to a DCM solution of BPh3/ P(MeNCH2CH2)3N afforded a colorless solution with spectroscopic properties consistent with formation of the iodoazaphosphatrane cation [IP(MeNCH2CH2)3N]+ (1) (Scheme 2). The 1H and 13C NMR spectra revealed the

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RESULTS AND DISCUSSION Reaction of XeF2 with Proazaphosphatranes. Given that many haloazaphosphatranes can be prepared by the action of a halogen on the free base,3 we surmised that this approach could provide access to the fluoroazaphosphatranes. To avoid the use of corrosive and hazardous F2 gas, a fluorine surrogate, namely, XeF2, was employed as this reagent has been used to oxidize a range of phosphines.13−18 Unfortunately, even if performed as a dropwise combination of cold solutions of the reagents, reaction of XeF2 with P(RNCH2CH2)3N (R = iPr or Me) resulted in a mixture of products as evidenced by 19F and 31 P NMR spectroscopy. From each of these reaction mixtures, minor products were obtained as colorless crystals. X-ray diffraction analysis revealed that the crystals were the salts of the fluoroazaphosphatrane cations with the PF6− counterion (Figure 1). Degradation pathways are evidently operative that result in removal of a portion of the P atoms from the azaphosphatrane scaffold preventing an efficient synthetic route from being established. The Verkade group previously proposed that a small nucleophilic ion might be able to attack the P center of a five-coordinate azaphosphatrane and generate a six-coordinate intermediate or transition state.19,20 The fluoroazaphosphatrane cations formed in the reaction with XeF2 result from the formal addition of F+ to the P center with release of Xe gas and an equivalent of F−. Repeated nucleophilic attack of these

Scheme 2. Synthesis of Haloazaphosphatranes

B

DOI: 10.1021/acs.inorgchem.8b02605 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry product is 3-fold symmetric, and the 31P NMR resonance (0.68 ppm) was shifted significantly upfield from that of the free base (118 ppm). The 11B NMR spectrum was effectively silent, suggesting that the BPh3 is in rapid equilibrium with the [IBPh3]− adduct. The product was isolated as a colorless crystalline material and washed thoroughly with pentane. A crystallographic structure determination revealed the compound to be the iodide salt of 1 (Figure 2). The lack of

Table 1. Select NMR Spectroscopic Parameters for 1−4 1

H(CH3)δ; 3JPH (ppm; Hz)

1 2 3 4 a

2.89; 2.98; 2.91; 2.66;

16 16 15 11

13

C(CH3)δ; 3JPH (ppm; Hz) 39.62; 40.54; 39.90; 36.69;

7 6 6 13

31

Pδ (ppm) exp. 0.68 −12.02 −24.40 −42.93

31

Pδ (ppm) calc.a 0.68 −19.29 −33.74 −55.46

Referenced to value calculated for 1

notion that a smaller dPN arises from increased donation of the Nta lone pair into the P−X antibonding orbital, which shields the P atom. Computational NMR Data. 31P chemical shifts and Jcoupling constants were computed (PBE0-D3/def2-TZVPP) for optimized geometries of 1−4. The trend in the computed shifts agrees well with the experimental trend (Table 1). A bidirectional relaxed surface scan was then carried out along the P−Nta vector and the 31P chemical shift was evaluated at each constrained minimum. For each cation, the 31P chemical shift increases (moves upfield) as the transannular distance decreases (Figure 3). The data from all four species are not collinear, however, highlighting that transannular separation is not the sole determinant of the 31P chemical shift.

Figure 2. Displacement ellipsoid plots (50% probability level) of the cations 1 (a), 2 (b), 3 (c), and 4 (d). Color code: C gray, N blue, P orange, halogens (F, Cl, Br, and I) pink, H white spheres.

significant interaction between the iodide anion and BPh3 is consistent with the hard−soft mismatch between the acid and base. The reaction with Br2 proceeded similarly, yielding the bromide salt of [BrP(MeNCH2CH2)3N]+ (2) (Figure 2, Scheme 2). Targeting the analogous chloride reaction, iodobenzene dichloride, a crystalline, air-stable compound, proved to be a convenient surrogate for Cl2. Reaction with BPh3/P(MeNCH2CH2)3N proceeded smoothly, and the NMR spectra indicated that the cation [ClP(MeNCH2CH2)3N]+ (3) was formed (Scheme 2). Moreover, the 11B NMR resonance at 44.8 ppm indicates that the borane binds the halide to give the anion [ClBPh3]−, a fact that was confirmed by X-ray crystal structure determination (Figure 2). Finally, the reaction of BPh3/P(MeNCH2CH2)3N with XeF2 provided clean formation of the fluoroborate salt of [FP(MeNCH2CH2)3N]+ (4) (Scheme 2), as evidenced by the doublets at −70.4 ppm in the 19 F NMR spectrum and −42.9 ppm in the 31P NMR spectrum, with corresponding coupling constants of 735 Hz. The broad 19 F NMR resonance at −196.1 ppm and sharp 11B NMR doublet at 3.86 ppm confirm the formation of the [FBPh3]− anion. The composition of the compound was further corroborated by a single-crystal X-ray diffraction study (Figure 2). In 1−4, the 31P NMR resonance is drastically shifted upfield from that of the free base (118 ppm). The upfield shift increases from 1 to 4 with the latter having the most upfield chemical shift (Table 1). In early work, Verkade and coworkers observed a correlation between the chemical shift and the transannular P−N distance, with more upfield shifts corresponding to smaller dPN.23 This is consistent with the

Figure 3. Computed variation in 31P NMR chemical shift as a function of transannular distance (dPN).

X-ray Crystallography. The anions do not engage in any noteworthy secondary interactions. The cations 1−4 are pseudotrigonal bipyramidal at P and pseudopyramidal at Nta, with P−Nta distances ranging from 1.921(2)−2.310(3) Å (Table 2). Although the dPN values of 2 and 4 do not Table 2. Select Crystallographic Parameters for 1−4 1 2 3 4

ΣNeq−P−Neq

ΣC−Nta−C

dPN (Å) exp.

dPN (Å) calc.a

354.7 358.8 358.4 359.3

345.4 338.5 339.2 336.0

2.310(3) 1.921(2) 1.939(2) 1.932(3)

2.010 1.987 1.978 1.962

a

Obtained from the structure optimized at the PBE0-D3/def2TZVPP level of theory.

statistically differ at the 95% confidence level in the presently described salts, 2 does have a significantly shorter dPN than that of 3.These differing extents of transannulation are also reflected in the metrics describing pyramidalization at P and Nta (Table 2). Previously reported crystallographic data for haloazaphosphatranes provide further evidence for an erratic C

DOI: 10.1021/acs.inorgchem.8b02605 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

donation occurring in 2. Redetermination of the NBOs of 3 and 4 with the restriction that no NBO be allowed to form between P and Nta, reveals a donor−acceptor interaction between Nta and P, similar to that in 1 and 2. The strength of this interaction increases monotonically from 1 to 4 (Table 3).

variation in transannulation. The two crystallographically independent molecules of 3 in a structure of 3[PCl6] featured dPN values of 1.932(9) and 1.937(9) Å,24 whereas [IP(iBuNCH2CH2N)3N]I, which is related to 1[I], has a dPN value of 2.219(3) Å.25 In contrast, the computed transannular distances decrease steadily from 1 to 4. We observed a steady contraction of the transannular distance as the basis set was increased from double-ζ (def2-SVP) to triple-ζ (def2-TZVPP) and as the level of theory was increased from pure DFT (BP86), to hybrid DFT (PBE0), to dispersion-corrected hybrid DFT (PBE0-D3). In all cases, however, the trend in dPN (1 > 2 > 3 > 4) persisted. We hypothesize that the discrepancy between the smooth variation of dPN in the computational data and the erratic variation in the crystallographic data stems from the overall flexibility of these molecules. Frequency calculations (PBE0-D3/def2-TZVPP) show a normal vibrational mode that predominantly features elongation and compression of the P− Nta vector for each of these haloazaphosphatrane cations. The stretching frequencies of these normal modes were 379 cm−1 (1), 415 cm−1 (2), 462 cm−1 (3), and 518 cm−1 (4), suggesting that deformation along this internal coordinate is facile, particularly for the ions bearing the heavier halogens. An analysis of the energy profiles from the relaxed surface scans along the P−Nta vector confirms the ease with which the molecules can be deformed along this coordinate (Figure S18). Notably, the ease of deformation varies from 1 > 2 > 3 > 4, consistent with the discrepancy between the calculated and experimental transannular distances being greatest for 1 and 2. Moreover, the smooth variation in both the computed and experimental 31P NMR chemical shifts (Table 1) and the steep slope of the curves in Figure 3 suggest that in solution the molecules are free of the distorting forces present in the solid state and decrease in transannular distance from 1 to 4. Computational Electronic Structure. The electronic structures (PBE0-D3/def2-TZVPP) of these cations were examined in greater detail at the geometries optimized for the free molecules to remove the influence of potentially distorting crystal packing forces. A natural bond orbital (NBO) analysis showed no formal bonding NBO between P and Nta for 1 and 2. In contrast, both 3 and 4 exhibit a two-electron P−Nta bonding orbital. In the case of 1 and 2, the interaction between Nta and P is best described as a donation from the lone pair on Nta into the P−X antibonding orbital (Figure 4), with greater

Table 3. Selected Computational Parameters for 1−4 1 2 3 4

NBO E2 (kcal mol−1)a

ρ (e a0−3)b

P···CP(Å)c

40.2 44.8 46.4 48.0

0.105 0.109 0.110 0.113

0.800 0.779 0.772 0.758

a

Strength of donor−acceptor interaction estimated from secondorder perturbation theory. bElectron density at the (3, −1) critical point between P and Nta. cDistance between the P atom and the (3, −1) critical point

Finally, as an orthogonal means of assessing the magnitude of the P−Nta interaction, we analyzed the topology of the electron density within the Atoms in Molecules (AIM) framework. In all four cations, a (3, −1) bond critical point was identified between P and Nta (Figure 4). The critical point moved progressively closer to the P atom, and the values of the electron density at the critical point increased in the direction 1 < 2 < 3 < 4. We note that although the increase in electron density at the critical point is systematic it is very small and is likely within the error of these calculations. Collectively, the computational data are consistent with the gradual increase in the strength of the transannular interaction for the I, Br, Cl, and F derivatives and provide an explanation for why the compounds of the heavier halides deform more readily.

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CONCLUSION Herein, we have synthesized a series of haloazaphosphatrane cations. Although direct oxidation of proazaphosphatranes using XeF2 results in decomposition, oxidation in the presence of a Lewis acid proceeds cleanly. Spectroscopic characterization of this series of haloazaphosphatrane cations revealed systematic trends in 31P chemical shift. Although this parameter has been previously used as a spectroscopic reporter for azaphosphatrane transannulation, the crystallographic data are not consistent with the trend inferred by the NMR data. DFT calculations suggest that the discrepancy could arise because the molecules are flexible to deformation along the P− Nta axis, indicating that caution in using such correlations should be exercised.

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EXPERIMENTAL SECTION

General Considerations. Reactions were performed in a Vacuum Atmospheres glovebox under an atmosphere of dry nitrogen. All glassware was oven-dried and cooled under vacuum prior to use. Pentane and dichloromethane were dried on a Grubbs-style solvent purification system and stored under N2 over activated 4 Å molecular sieves. CD2Cl2 was purchased from Cambridge Isotopes Laboratories and dried over activated 4 Å molecular sieves, degassed, and subsequently stored under N2. Commercial reagents were purchased from Sigma-Aldrich and used as received. PhICl2 was prepared as previously described.26 BPh3 was prepared as previous described from (NHMe3)(BPh4),27 which was recrystallized from a mixture of dichloromethane and hexane. Diffraction quality crystals were obtained and the crystal structure is provided in the Supporting Information. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre: 1[I]: 1867533, 2[Br]:

Figure 4. Electronic structure of 1. (a) Isosurface overlap plot of the Nta lone pair and P−I antibonding NBOs Color code: I purple, P orange, N blue, C gray, H white. (b) Contour plot of the electron density (black) and gradient of the electron density (gray) with van der Waals distance shown as a heavy blue line and critical points as discs: (3, −3) brown, (3, −1) blue, (3, +1) yellow. D

DOI: 10.1021/acs.inorgchem.8b02605 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

(dd, JPH = 11 Hz, JFH = 2 Hz, 9H, CH3), 2.88 (dtd, JPH = 8 Hz, JHH = 6 Hz, JFH = 2 Hz, 6H, CH2), 6.96 (t, JHH = 7 Hz, 3H, CHAr), 7.10 (t, JHH = 7 Hz, 6H, CHAr), 7.46 (d, JHH = 7 Hz, 6H, CHAr). 13C{1H} NMR (100 MHz, CD2Cl2) δ 36.69 (dd, JPC = 13 Hz, JFC = 5 Hz, CH3), 44.59 (dd, JPC = 12 Hz, JFC = 2 Hz, CH2), 47.13 (dd, JPC = 9 Hz, JFC = 1 Hz, CH2), 123.82 (s, CHAr), 126.79 (s, CHAr), 133.08 (s, CHAr). 31P (162 MHz, CD2Cl2) δ −42.93 (d, JPF = 735 Hz). 11B NMR (128 MHz, CD2Cl2) δ 3.86 (d, JFB = 60 Hz). 19F NMR (376 MHz, CD2Cl2) δ −70.43 (d, JPF = 735 Hz), −196.11 (br s). Anal. Calcd (found) for C27H36BF2N4P C 65.33 (65.73), H 7.31 (7.01), N 11.29 (11.49). X-ray Crystallography. The crystallization conditions described above, excepting the pentane wash and vacuum drying, afforded diffraction-quality single crystals of (NHMe3)(BPh4), 1[I], 2[Br]· CH2Cl2, 3[ClBPh3], and 4[FBPh3]. The crystals were submerged in Paratone oil and analyzed microscopically. Suitable single crystals were placed in a MiTeGen polyimide cryoloop, mounted on the goniometer of a Bruker Apex II X-ray diffractometer, and cooled to 150(2) K under a stream of cold N2 controlled by an Oxford Cryosystems cryostat. Diffraction was performed with Mo Kα radiation (0.71073 Å) passed through a graphite monochromator. The data were processed using SAINT,28 and a multiscan absorption correction was applied with SADABS.29 All structures were solved via intrinsic phasing with SHELXT,30 and refined with SHELXL using established strategies.31,32 Crystallographic parameters are collected in Tables S1 and S2. Computational Chemistry. Electronic structure calculations, including geometry optimizations and frequency calculations, were performed with Gaussian 09.33 For geometry optimization, frequency calculation, NBO analyses, and AIM analyses, the PBE0-D3/def2TZVPP model chemistry was employed.34,35 Optimized Cartesian coordinates are provided in Tables S3−S6. For NMR chemical shift calculations using the gauge-independent atomic orbital method, implicit DCM solvation was also included. Orbital interactions were analyzed using NBO 6.0,36 and electron density topology was evaluated using MULTIWFN 4.3.37

1867534, 3[ClBPh3]: 1867535, 4[FBPh3]: 1867536, 4[PF6]: 1867537, [FP(iPrNCH2CH2)3N][PF6]: 1867538, [HNMe3][BPh4]· CH2Cl2: 1867539 1H, 19F, 31P, 11B, and 13C NMR spectra were acquired on a Bruker Avance III 400 MHz spectrometer. NMR chemical shifts are reported in ppm and referenced to SiMe4 (1H and 13 C), CFCl3 (19F), 85% H3PO4 (aqueous) (31P), and BF3·OEt2 (11B). NMR spectra are reproduced in Figures S1−S17. Elemental analyses were performed at the University of Toronto on a PerkinElmer 2400 Series II CHNS Analyzer. Synthesis of [IP(MeNCH2CH2)3N]I ([1]I). A solution of I2 (24 mg, 0.09 mmol) in DCM (1.5 mL) was added in a dropwise manner to a solution of P(MeNCH2CH2)3N (20 mg, 0.09 mmol) and BPh3 (22 mg, 0.09 mmol) in DCM (1.5 mL). As each drop was added, the purple color of the I2 was immediately discharged. The colorless reaction mixture was stirred at room temperature for 10 min and then layered under 7 mL of pentane and allowed to stand at room temperature for 3 days. Colorless crystals deposited during this time. The supernatant was removed, and the crystals were washed with pentane and dried under vacuum. Yield: 33 mg (75%). 1H NMR (400 MHz, CD2Cl2) δ 2.89 (d, JPH = 16 Hz, 9H, CH3), 3.11 (t, JHH = 5.7 Hz, 6H, CH2), 3.23 (dt, JPH = 17 Hz, JHH = 6 Hz, 6H, CH2). 13C{1H} NMR (100 MHz, CD2Cl2) δ 39.62 (d, JPC = 7 Hz, CH3), 49.66 (d, JPC = 2 Hz, CH2), 51.84 (d, JPC = 5 Hz). 31P (162 MHz, CD2Cl2) δ 0.68 (m, JPH = 17 Hz). Anal. Calcd (found) for C9H21I2N4P: C 23.00 (22.83), H 4.50 (4.45), N 11.92 (12.21). Synthesis of [BrP(MeNCH2CH2)3N]Br ([2]Br). A solution of Br2 (14 mg, 0.09 mmol) in DCM (1.5 mL) was added in a dropwise manner to a solution of P(MeNCH2CH2)3N (20 mg, 0.09 mmol) and BPh3 (22 mg, 0.09 mmol) in DCM (1.5 mL). As each drop was added, the orange color of the Br2 was immediately discharged. The colorless reaction mixture was stirred at room temperature for 10 min and then layered under 7 mL of pentane and allowed to stand at room temperature for 3 days. Colorless crystals deposited during this time. The supernatant was removed, and the crystals were washed with pentane and dried under vacuum. Yield: 27 mg (80%). 1H NMR (400 MHz, CD2Cl2) δ 2.98 (d, JPH = 16 Hz, 9H, CH3), 3.42 (dt, JPH = 13 Hz, JHH = 6 Hz, 6H, CH2), 3.52 (td, JHH = 6 Hz, JPH = 3 Hz, 6H, CH2). 13C{1H} NMR (100 MHz, CD2Cl2) δ 40.54 (d, JPC = 6 Hz, CH3), 47.52 (d, JPC = 2 Hz, CH2), 47.58 (d, JPC = 3 Hz). 31P (162 MHz, CD2Cl2) δ −12.02. Anal. Calcd (found) for C9H21Br2N4P C 28.74 (28.54), H 5.63 (5.25), N 14.90 (15.32). Synthesis of [ClP(MeNCH2CH2)3N]ClBPh3 ([3]ClBPh3). A solution of PhICl2 (14 mg, 0.09 mmol) in DCM (1.5 mL) was added in a dropwise manner to a solution of P(MeNCH2CH2)3N (20 mg, 0.09 mmol) and BPh3 (22 mg, 0.09 mmol) in DCM (1.5 mL). As each drop was added, the pale yellow color of the PhICl2 was immediately discharged. The colorless reaction mixture was stirred at room temperature for 10 min and then layered under 7 mL of pentane and allowed to stand at room temperature for 3 days. Colorless crystals deposited during this time. The supernatant was removed, and the crystals were washed with pentane and dried under vacuum. Yield: 37 mg (79%). 1H NMR (400 MHz, CD2Cl2) δ 2.91 (d, JPH = 15 Hz, 9H, CH3), 3.29 (dt, JPH = 13 Hz, JHH = 6 Hz, 6H, CH2), 3.38 (dt, JPH = 4 Hz, JHH = 6 Hz, 6H, CH2), 7.34 (m, 9H, CHAr), 7.54 (m, 6H, CHAr). 13C{1H} NMR (100 MHz, CD2Cl2) δ 39.90 (d, JPC = 6 Hz, CH3), 45.65 (d, JPC = 9 Hz, CH2), 46.69 (d, JPC = 9 Hz, CH2), 127.45 (s, CHAr), 129.00 (s, CHAr), 137.48 (s, CHAr), ipso-C not observed. 31P (162 MHz, CD2Cl2) δ −24.40. 11B NMR (128 MHz, CD2Cl2) δ 44.79. Anal. Calcd (found) for C27H36BCl2N4P C 61.27 (61.34), H 6.86 (6.81), N 10.59 (10.11). Synthesis of [FP(MeNCH2CH2)3N]FBPh3 ([4]FBPh3). A solution of XeF2 (16 mg, 0.09 mmol) in DCM (1.5 mL) was added in a dropwise manner to a solution of P(MeNCH2CH2)3N (20 mg, 0.09 mmol) and BPh3 (22 mg, 0.09 mmol) in DCM (1.5 mL). The colorless reaction mixture was stirred at room temperature for 10 min and then layered under 7 mL of pentane and allowed to stand at room temperature for 3 days. Colorless crystals deposited during this time. The supernatant was removed, and the crystals were washed with pentane and dried under vacuum. Yield: 33 mg (74%). 1H NMR (400 MHz, CD2Cl2) δ 2.61 (td, JPH = 4 Hz, JHH = 6 Hz, 6H, CH2), 2.66

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02605. NMR spectra, crystallographic data, and computationally optimized atomic coordinates (PDF) Accession Codes

CCDC 1867533−1867539 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Timothy C. Johnstone: 0000-0003-3615-4530 Douglas W. Stephan: 0000-0001-8140-8355 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS D.W.S. gratefully acknowledges the financial support from NSERC Canada, the award of Canada Research Chair, and the E

DOI: 10.1021/acs.inorgchem.8b02605 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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award of an Einstein Fellowship at TU Berlin. T.C.J. gratefully acknowledges NSERC Canada for a postdoctoral fellowship.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.8b02605 Inorg. Chem. XXXX, XXX, XXX−XXX