Selective Derivatization of a Hexaphosphane from Functionalization of

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Cite This: J. Am. Chem. Soc. 2017, 139, 14592-14604

Selective Derivatization of a Hexaphosphane from Functionalization of White Phosphorus Felix Hennersdorf, Julia Frötschel, and Jan J. Weigand* Chair of Inorganic Molecular Chemistry, Technische Universität Dresden, D-01062 Dresden, Germany S Supporting Information *

ABSTRACT: The reaction of LGa (L = Dipp(4-(Dipp-imino)pent-2-en-2-yl)amide; Dipp: 2,6-diisopropylphenyl) and white phosphorus was revisited. A plethora of unprecedented polyphosphanes in addition to the known monoinserted product LGaP4 (1) are observed. An optimized synthesis of the hitherto unknown hexaphosphane (LGa)2P6 (3) is presented, and its subsequent selective derivatization with Brønsted acids, MeOTf, Ph2ECl (E = P, As), and NaOCP provides access to a wealth of functionalized hexa- and heptaphosphanes.

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INTRODUCTION The functionalization of white phosphorus by low valent main group and transition metal compounds is being studied extensively, granting access to both degradation and aggregation of polyphosphorus compounds.1−4 Although subsequent selective derivatization of polyphosphanes has only rarely been studied, a successful implementation provides access to an adapted constitution of target molecules in order to tune their properties for potential applications. Herein, we present the synthesis of a prodigious and hitherto unknown hexaphosphane by functionalization of white phosphorus and its subsequent derivatization. The conveniently accessible nacnac ligand L (Dipp(4-(Dippimino)pent-2-en-2-yl)amide; Dipp: 2,6-diisopropylphenyl) has been used as the preferred backbone for stabilizing both low valent main group and transition metals. The former are isoelectronic to carbenes and show a comparable reactivity toward P4. Comparing the neutral compounds [(L′Si)(η2-P4)] (A),5 [(L′Si)2(μ-η2:η2-P4)] (B),5 [(LGa)(η2-P4)] (1),6 and [(LAl)2(μ-η2:η2-P4)] (C),7 mono- and di-inserted tetraphosphanes have been observed (Chart 1). Whereas L′SiII, bearing the doubly deprotonated form of the diketimine ligand, gives both insertion modes A and B, its group 13 congeners LGaI and LAlI were reported to give only either form 1 or C, selectively. The late transition metal complexes FeIL, CoIL, NiIL, and CuIL were shown to give different coordination modes in 2:1 complexes in which the P4 moiety is planarized as observed in D8 and E.9,10 However, D exhibits equidistant P−P bonds and is described as complex with [P4]0 ligand,8 whereas E possesses two elongated and two shortened P−P bonds which are assigned to a [P4]2− ligand.9 Three bonds are elongated to give a prismane-like Ni2P4 core as in [(LNi)2{μ-[1(1,2,4-η):2(1,3,4-η)]-P4}] (F),11 or the P4 tetrahedron is still intact (G).12 A has been used to synthesize the unique mixed main group−transition metal compound H © 2017 American Chemical Society

Chart 1. Compounds Obtained from the Functionalization of P4 by Low Valent Main Group and Transition Metal Compounds Bearing the Nacnac Ligands L or L′ and the Related Antimony Compound [(LGa)2(μ-η2:η2-Sb4)] (I)

containing both L′Si and LNi. The amido-vanadium complex [(LV)(N(p-Tol)2)] reacts with P4 to give a cyclo-P3 complex [(LV)(N(p-Tol)2)(P3)], which is hardly related to compounds A−H.13

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RESULTS AND DISCUSSION As part of our general interest in P4 functionalization to build up larger polyphosphorus scaffolds,14 we recently presented the unprecedented synthesis of the tetracyclic octaphosphane Received: July 23, 2017 Published: September 8, 2017 14592

DOI: 10.1021/jacs.7b07704 J. Am. Chem. Soc. 2017, 139, 14592−14604

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Journal of the American Chemical Society Chart 2. Formulae of Compounds 1−7 Obtained from the Reaction of LGa and White Phosphorusa

a

For compounds 3-7 the nuclei are assigned according to their 31P NMR spin system.

(LGaBr)2P8.15 In the course of this study, we encountered that the synthesis of the starting material 1 is not as simple as described before.6 While aiming for 1 at varying conditions, we discovered the formation of the hitherto unknown di-inserted product [(LGa)2(μ-η2:η2-P4)] (2) in addition to the larger polyphosphorus compounds (LGa)2P6 (3), (LGa)2P8 (4), (LGa)2P12 (5), (LGa)2P14 (6), and (LGa)2P16 (7) (Chart 2). 2−7 are characterized by X-ray diffraction, 31P−31P COSY NMR spectroscopy, NMR simulation as well as vibration spectroscopy, melting point, and elemental analysis in selected cases. An optimized synthesis to give 3 and its reactivity toward Brønsted acids, MeOTf, Ph2ECl (E = P, As; Tf = trifluoromethylsulfonyl), and NaOCP are presented. The reaction of P4 and LGaI in a 1:1 ratio in toluene at room temperature gives only very slow conversion to 1 and small amounts of 3. To favor the reaction outcome to 3, we adapted the ratio to 3:4, increased the concentration, and performed the reaction at 180 °C in a pressure flask for 3 days. After filtration, the removal of all volatiles, and extraction of impurities, 3 is obtained in 50% yield. The reaction solution contains small amounts of 1, 2, and 4. Eighty milligrams of 2 were isolated from a different batch after eight fractional crystallization steps and another recrystallization in less than 1% yield.16 Attempts to selectively synthesize 2 failed, but highest concentrations in the product mixture were obtained by a solvent-free melt reaction in the ratio of 1:2. 1 does not react with LGa in a 1:1 mixture when heated to reflux in toluene overnight. 4 could be enriched by fractional crystallization up to 68% in addition to 3. The precipitate of the reaction mixture contains the sparingly soluble polyphosphanes 5, 6, and 7.13 NMR Spectroscopic Investigation. The 31P NMR spectrum of 2 exhibits a singlet at δ = 201.8 ppm. The lowfield shift compared to that with B (δ = 158.0 and 153.4 ppm) and C (δ = 78.6 ppm) might be explained by the higher electronegativity of Ga in comparison to that of Al and Si. The 1H and 13C NMR spectra show the expected 7 and 10 signals, respectively, indicating molecular D2d symmetry of compound 2 in solution. Compound 3 has apparent Cs symmetry in solution and exhibits an AEMM′XX′ spin system in the 31P NMR spectrum. The bicyclic [3.1.0]hexaphosphane core is known from the hexaphosphanes R4P6 (R = tBu,17 Cp*18), which adopt an alltrans-configuration. Signal A at δ = −434.7 ppm is part of the three-membered ring and is connected to gallium atom Ga1, which bridges the nuclei A and E. Including Ga1, the P6Ga scaffold resembles the nortricyclane motif that is typical for polyphosphorus compounds.19 Compared to those and tBu4P6,17 the value of δ(PA) is extraordinarily high-field-shifted. The other basal nuclei represent the M part of the spectrum at δ = −145.2 ppm, which is in agreement with other known nortricyclane type compounds.19 The apical nucleus E resonates at δ = −290.6 ppm, which is also strongly highfield-shifted. The X part of the 31P NMR spectrum of 3

represents the equatorial phosphorus nuclei bonded to Ga2 and is observed most as low-field-shifted at δ = 97.2 ppm. The extreme values in opposite directions can be explained by both electronic and geometrical aspects. Strongly high-fieldshifted values have also been observed for the structurally related [(SiMe3)3CGa]3P4 with gallium atoms in all equatorial positions (δbasal = −202.8 ppm, δapical = −521.9 ppm)20 and for the P−Sn cage compounds (SnPR)n (R = iPr3Si,21,22 tBu3Si,23 tBu;24 n = 4, 6, 7). This shift is partially caused by the more electropositive bridging gallium atom compared to phosphorus bridging P7 cages. Additionally, for [SnP(iPr3Si)]6, spin−orbit effects are discussed as a reason for an additional shielding of the nucleus.22 The X part of the 31P NMR spectrum is comparable to that of tBu4P6 (δ = 115.6 ppm) and the cations [(Ph3As)3P7]3+ (δ = 69.6 ppm)19 and [Ph6P7]3+ (δ = 112.6 ppm).25 Silyl-substituted cages (R3Si)3P7 (R = Ph,26 Me,27 tBu,27 SiMe328) exhibit chemical shifts ranging from δequat. = 4 to −31.2 ppm, whereas the phosphorus bridged equatorial P atoms in (LGaBr)2P8 resonate at δ = 161.6 ppm and δ = 234.5 ppm. The chemical shift of X compared to these examples could be related to the electronegativity of gallium, which is between that of phosphorus and silicon. Iterative fitting of the 31 P NMR spectrum allows the determination of the coupling constants. The coupling constants within the three-membered ring (1J(PAPM) = −266 Hz, 1J(PMPM′) = −234 Hz) are slightly higher but comparable to that in (Me3Si)3P7 (1J = −216 Hz).27 In contrast, 1J(PMPX) of −269 Hz is significantly smaller in 3 than in the P7 compounds ([(Ph3As)3P7]3+: −355 Hz;19 (Me3Si)3P7: −354 Hz27). The same applies for 1J(PEPX) with a value of −236 Hz ([(Ph3As)3P7]3+: −324 Hz;19 (Me3Si)3P7: −323 Hz27). The coupling constant 2J(PAPE) across gallium with a value of 70 Hz is larger than that in [(SiMe3)3CGa]3P4 (2J = 31 Hz),20 whereas 2J(PEPM) of 45 Hz perfectly matches the P7 tricycles ([(Ph3As)3P7]3+: 45 Hz;19 (Me3Si)3P7: 47 Hz27). Octaphosphane 4 comprises a C2v symmetric realgar-type scaffold with two bridging gallium substituents similar to the dinuclear nickel complex [(NiCp‴)2P8]2− (Cp‴ = 1,2,4tBu3C5H2) published recently.29 Three different phosphorus environments can be differentiated in accordance with the observed AA′BB′XX′X″X‴ spin system in the 31P NMR spectrum. The X part resonating at δ = 235.4 ppm represents the nuclei bonded to gallium. Assigning A and B part is difficult due their similar connectivity. We do not believe that simply swapping the A and B part of the simulation as done for [(NiCp‴)2P8]2− can answer this question.29 We investigated the angle sums of the corresponding atoms obtained from X-ray diffraction data and the coupling constants 1J(PAPX) and 1 J(PBPX) as indicators (Figure 1 and Table 1). Whereas one atom is part of three five-membered rings, the other one also participates in one four-membered ring. In the nickel complex, the values differentiate by 4.1°, with the more acute environment being assigned to the more low-field-shifted atom 14593


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Figure 1. Molecular structures of compounds 1−7. Hydrogen atoms and solvent molecules omitted for clarity; ellipsoids are set at 50% probability. In case of disorder, only the major component is depicted. Fold angles α and β are exemplarily indicated in 5.

Table 1. Selected Bond Lengths (in Å) and Angles (in deg) of Compounds 1−7a P1−P2/P3 P2−P3 P2−P4/P3−P5 P4−P6/P5−P6 P4−P7/P5−P8 Ga1−P1/P6 Ga2−P4/P5 P1−Ga1−P6 P4−Ga2−P5 fold angle α fold angle β a

1

2

2.237(3)

2.267(4)

2.200(5) 2.227(14) 2.241(3) 2.202(5)

3

2.350(6)

2.376(7) 2.405(8)

2.349(5)

84.87(12)

78.3(4)

4

5 2.214(2) 2.194(4) 2.227(2) 2.184(2)

2.401(7) 102.3(8) 85.4(5) −127.83(11) 105.6(5)

6

7

2.368(6)

2.365(10)

2.195(6) 2.199(2) 2.237(3) 2.176(5) 2.261(1) 2.370(4)

2.201(1) 2.206(5) 2.227(4) 2.173(2) 2.265(3) 2.347(9) 2.377(4)

87.65(6)

103.0(2)

103.3(2)

103.2(7)

−143.2(3) 99.57(6)

−136.8(3) 102.47(16)

−137.9(5) 101.84(19)

Values are averaged from all structures of the same compound and from all equivalent bonds related by symmetry within a molecule.

(ψ(P555): 297.3°, δ = 10.1 ppm; ψ(P455): 293.2°, δ = 30.6 ppm), which is against the general trend predicting a high-field shift.30 The difference of only 0.6° in 4 leaves some uncertainty remaining (ψ(P555): 297.4°, ψ(P455): 296.8; δ(PA) = 38.4 ppm, δ(PB) = 56.0 ppm). The coupling constants indicate the opposite assignment considering that the smaller dihedral angle of the lone pairs (LP) is supposed to cause an increased value of 1JPP30 (4: LP-X-P555-LP: ≈54°, LP-X-P455-LP: ≈37°; 1JAX = −281 Hz; 1 JBX = −187 Hz). From this, we conclude not without wariness that nucleus A is part of the four-membered ring. The 31P NMR spectra of compounds 5−7 exhibit less resolved resonances, preventing the determination of the coupling constants. To prove the connectivity, we recorded 31 P− 31 P COSY NMR spectra. 13 Compound 5 has C 2h symmetry in solution and therefore exhibits four signals. The most high-field-shifted nuclei A and E are bonded to gallium and resonate at δ = −246.7 ppm and δ = −230.4 ppm (Chart 2). Nuclei M are part of the three-membered ring with a rather low-field chemical shift of δ = −89.4 ppm. The nuclei X directly link the two nortricyclane cages and resonate at δ = −8.3 ppm. Compounds 6 and 7 have C2v and C2h symmetry

in solution, respectively, and exhibit both a spin system of seven independent phosphorus nuclei. The order of nuclei being part of the nortricyclane scaffold is the same for both 6 and 7 as assigned in 3 and 5. The bridging phosphorus nuclei are the most low-field-shifted in 6 (δ(PY) = 64.8 ppm) but have only the second highest shift in 7 (δ(PX) = 24.4 ppm). The chemical shift of the bridgehead nuclei correlates with the angle sum obtained from X-ray diffraction data (5: av. ψ = 309.4°, δ(PX) = −8.3 ppm; 6: av. ψ = 297.6°, δ(PX) = 46.4 ppm; 7: av. ψ = 298.1°, δ(PY) = 32.5 ppm) but does not obey the general trend of more acute phosphorus atoms being found at higher field.30 The bridgehead phosphorus atoms in the related triorganyl nonaphosphane tBu3P9 show much higher chemical shifts at δ = 85.5 ppm (ψ = 300.0°) and δ = 122.7 ppm (ψ = 303.2°).31 Crystallographic Investigation. From a toluene solution containing 2 and an excess of 3, they crystallized as a solid solution with both molecules on the same position in the crystal structure in the ratio 88:12. This material can be recrystallized from CH2Cl2 at −30 °C to give two different solvates of pure 2 (Figure 1). At room temperature, decomposition takes place in CH2Cl2 solution. Each gallium atom forms two slightly different bonds to the P4 ring (av. Ga−P(short): 2.376(7) Å, av. 14594


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regular single bonds (Table 1; Σrcov = 2.22 Å).33 The bonds within the four-membered P3Ga rings are slightly longer (av. P−P: 2.237(14) Å) than their counterparts in the fivemembered rings (av. P−P: 2.193(3) Å). The trans-annular P1−P2 bond bridging the five-membered rings is the longest at 2.2743(15) Å. All Ga−P bonds are almost equally long at 2.368(3) Å on average. The P8 scaffold (tricyclo[3.3.0.03,7]octaphosphane) is the only one in the series that contains only five-membered rings. The fragment is also part of the structure of Hittorf’s phosphorus.36 Crystals of 5 were obtained from dichloromethane by slow evaporation in space group P21/c or from hot benzene or methylnaphthalene in the space group P1.̅ In all cases, it cocrystallized with the solvent and only half of the molecule in the asymmetric unit. The second half is generated by inversion. The bond lengths within the nortricyclane fragment are similar to those in 3. The fold angles α and β of the annulated threeand five-membered rings are slightly different compared to 3. P6 is less kinked (av. −143.2(3)°), and β is more acute (av. 99.57(6)°). This can be related to less steric congestion above the apical phosphorus atom caused by the close proximity of three Dipp groups in 3. Two different crystal structures were determined of compound 6. From the reaction mixture in toluene, 6 crystallized in the space group P21/n with 1 equiv of both toluene and white phosphorus (Figure 2). Only very few crystal structures37−39 with cocrystallized P4 have been reported to the best of our knowledge. The molecule has an unrestrained average bond length of 2.176(5) Å, which is in agreement with the value reported by Scheer et al. (2.162(2) Å).37 Crystals in the space group Pnma were obtained from dichloromethane by slow evaporation. The asymmetric unit contains one molecule of dichloromethane and a half molecule of 6. The second half is generated by a mirror plane. The bond lengths are similar to 3 and 5. The longest P−P bond is found between the two atoms P7 and P8 of the bridging P2 unit (av. P−P: 2.261(3) Å). The fold angles α and β are between those of 3 and 5 (av. α = −136.8(3)°; av. β = 102.47(16)°). In 6, the two nortricyclane cages are tilted by 63.9(6)°, whereas they are antiparallel in 5 and 7 (180°). Two different crystal structures were determined of compound 7. From the reaction mixture, 7 crystallized in the space group I2/a with 1 equiv of both toluene and white phosphorus.

Ga−P(long): 2.405(8) Å) related to the two Dipp groups being slightly bent out of the GaN2C3 plane toward the side with the shorter Ga−P bond. The same observation was made for B and C, as well. All P−P bond lengths are very similar (av. P−P: 2.267(4) Å) within the three crystal structures of 2 but marginally shorter than in B (av. P−P: 2.288(8) Å) and C (av. P−P: 2.289(4) Å). 2 is also structurally related to the heavier antimony congener (LGa)2Sb4 (Chart 1, I). The E−X−E angle (E: P, Sb; X: Al, Si, Ga; 88.7° (I), 82.2° (B), 80.3° (C), 78.3° (2)) decreases in the series I ≫ B > C > 2, which can be related to the X−P bond lengths and therefore to the smaller radii of Si and Al compared to that in Ga (rcov: Si, 1.11 Å; Al, 1.21 Å; Ga, 1.22 Å)32 and the larger radius of Sb compared to P (rcov: P, 1.07 Å; Sb, 1.39 Å).32 Single crystals of 3 suitable for diffraction analysis were obtained from a concentrated toluene solution after being cooled to −30 °C. The asymmetric unit contains two independent molecules of both 3 and toluene. The gallium and phosphorus atoms together form a [3.3.0.0.2,704,6] tetracyclic scaffold, which we recently described in octaphosphane (LGaBr)2P8.15 The P−P bond lengths are all in the range of regular single bonds (Table 1; Σrcov = 2.22 Å).33 Those between the basal and equatorial phosphorus atoms are slightly longer (av. P−P: 2.241(3) Å) than all others (av. P−P: 2.201(5) Å). The Ga−P bonds at Ga1 are slightly shorter than that at Ga2 (av. Ga1−P: 2.349(5) Å; av. Ga2−P: 2.401(7) Å). The former are part of two five-membered rings, whereas the latter are in a four- and a five- membered ring. This strongly affects the P−Ga−P angle, which is much more acute at Ga2 (av. P−Ga1−P: 102.3(8)°; av. P−Ga2−P: 85.4(5)°) but wider than in 2 with two four-membered rings (av. P−Ga1−P: 78.3(4)°). Compared to R4P6 in which the five-membered ring is almost planar with a fold angle α of 163.07° (for α, see Figure 1; R = tBu;34 Cp*4P6: 142.8°18) in 3, it is much stronger and inversely kinked (av. −127.81(13)°), resulting in a boat conformation of the P6 corpus. In contrast, the fold angle β between the three- and five-membered ring is less acute in 3 (for β, see Figure 1; 3: av. 105.6(5)°; tBu4P6: 89.65°;34 Cp*4P6: 88.83°18). Crystals of 4 were obtained by diffusion of n-pentane into a mixture of 3 and 4 in toluene. It crystallizes in the space group R3̅ with enormous cavities. As the disordered content could not be modeled, the Squeeze routine of PLATON needed to be applied.35 All P−P bonds are in the range of

Figure 2. Packing diagrams of the crystal structures of 7·C7H8·P4, 37·2C7H8·C6H14·2P4, and 6·C7H8·P4 containing white phosphorus in the crystal lattice. Hydrogen atoms and disordered parts are omitted for clarity. Carbon and nitrogen atoms are depicted as a stick model, P4 molecules as ellipsoids at 50% probability level, and all other P and Ga atoms as space-filling model. 14595


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than that of its aluminum congener (C3H5N2Ga: 52.6 kcal mol−1; C3H5N2Al: 34.8 kcal mol−1),47,48 making a radical mechanism in the formation of 1 and 2 less likely. It should be noted that the syntheses of A and C were described at room temperature, whereas the reaction of LGa and P4 gives only poor conversion rates under these conditions. Therefore, we performed the reaction at very high temperature such as 180 °C. The synthesis of B was also not selective but gave a mixture of L′Si, A, and B in the ratio 1:1.9:0.7.5 To propose a credible mechanism, computational studies need to be conducted and are objectives for future investigations. Selective Derivatization of 3. A corresponding reactivity15 of 1 compared to 3 was assumed, and thus, we performed the reaction with 1 equiv of Ph2PCl in THF solution (Scheme 2). The reaction proceeds very fast, even at −30 °C, giving a mixture of two compounds, exo,endo-8 and endo,endo-8,49 which were isolated with 71% yield. The ratio of 65:35 is independent of the temperature or reaction time in solution. Both components contain a similar P7 scaffold as determined from a detailed investigation of the 31P NMR data. The reaction proceeds in such a way that one Ga−P bond of the fourmembered ring is cleaved via the nucleophilic attack of the chlorophosphane. In both cases, the phosphanyl moiety is bonded to the equatorial phosphorus atoms, whereas the chlorine atom binds to the cleaved gallium moiety. This is comparable to the outcome of the reaction of 1 and Ph2PCl. Crystal structure analysis revealed exo,endo-8 to be the dominant species in a significantly different ratio (95:5) as derived from the NMR investigation. A minor disordered component with both phosphorus atoms of the newly formed bond being inverted (endo,endo-8) can be refined. Dissolving the isolated crystals in THF at −30 °C shows the same ratio of diastereomers as the reaction solution described above. The reaction of 3 with Ph2AsCl proceeds accordingly and gives the mixed polypnictogen compounds exo,endo-9 and endo,endo-9 in a product mixture similar to that of the reaction with Ph2PCl in 80% yield. To gain a deeper understanding of this behavior, we also employed HCl in diethyl ether to investigate the addition reaction. The reaction proceeds much slower, and more importantly, only one product, exo,endo-10, is formed initially. However, the solution of exo,endo-10 slowly equilibrates over time to a mixture of exo,endo-10 and endo,endo-10 in a 13:87 ratio. The NMR chemical shifts and coupling constants of the phosphorus nuclei are related to those in exo,endo-8 and endo,endo-8 and are summarized in Table 2. In order to shed light on the formation of this equilibrium, we performed the same reaction with independent H+ and Cl− sources by employing HNTf2 and [nBu4N]Cl, respectively. 3 shows no reaction even at elevated temperature if only Cl− is present. The addition of HNTf2 to the Cl−-containing mixture results in the clean formation of only exo,endo-10, which could be isolated in 64% yield. With only HNTf2 being added, 3 rapidly converts to the new species 11, which upon addition of [nBu4N]Cl again yields the exo,endo-10 and endo,endo-10 isomers in the 13:87 ratio. To our surprise, endo,endo-10 is the only reaction product if [Et3NH]Cl is used as a source of hydrochloric acid (79% yield). The solution of pure endo,endo-10 also slowly equilibrates to the mixture of exo,endo-10 and endo,endo-10 in the ratio of 13:87. This reaction behavior was found to be the same in THF and benzene. The addition of a strong base such as KHMDS to this mixture in benzene gives 3 in one step. Thus, it seems that the deprotonation does not form the phosphanide species

The P4 molecule (av. P−P: 2.146(9) Å) is disordered with two slightly displaced moieties. In a second structure obtained from a diffusion crystallization batch containing 6, 7, and P4, 7 cocrystallized with P4, toluene, and n-hexane in the ratio 3:2:2:1 with three independent half molecules of 7 in the asymmetric unit. The second halves are generated by inversion. The P4 molecule has an average bond length of 2.15(2) Å. The bond lengths and fold angles of 7 are very similar to those of compound 6 (Table 1). The molecule features a planar fourmembered ring linking the two nortricyclane-type units. Such fragments are very rare in polyphosphorus chemistry but have been described before (e.g., (2,4,6-tBu3C6H2)2P6 and (CuI)8P12).40,41 The P−P bond between the two atoms P7 and P8 is again the longest (av. P7−P8: 2.265(3) Å) but only slightly longer than those across the inversion center (av. P7−P8′: 2.223(6) Å). The values are in agreement with previously reported ones (av. P−P: 2.237(5) Å in (2,4,6tBu3C6H2)2P6).40 It should be mentioned that the structural motifs of 5 and 6 are known from the polyphosphides P142− and P162− if each LGa unit is replaced by a phosphanide unit.42,43 To the best of our knowledge, a polyphosphide P182− related to 7 is unknown. Mechanism. The mechanism of the formation of this plethora of new polyphosphorus motifs remains unknown so far. The fact that only even numbered polyphosphanes are identified in this work supports the assumption that a transfer of a P2 unit is part of the mechanism. The pathways of the formation of compounds A and C have been studied in detail by computation (Scheme 1). The low singlet−triplet gap of LAl Scheme 1. Proposed Mechanisms for the Formation of C (Top)44 and A (Bottom),45 Respectively

favors a biradical mechanism in the formation of C.44 This was also interpreted as the reason why only the di-inserted product was observed but not [(LAl)(η2-P4)] related to 1.7 In contrast, a nucleophilic attack of the silylene L′Si at P4 forming a triphosphirene intermediate was found the most likely access to A.45 Such an intermediate has also been observed by Bertrand et al. in the reaction of P4 with N-heterocyclic carbenes by trapping with dimethylbutadiene. They also proposed that it is able to transfer P4 units, which results in the formation of a dodecaphosphane.46 The reaction mixture of LGa and P4 in the presence of an excess of dimethylbutadiene resulted in four very broad signals in the 31P{1H} NMR,13 which did not sharpen upon cooling to −35 °C. So far, no reaction product could be identified. However, for a fully hydrogen-substituted model compound of LGa, the singlet−triplet gap was calculated to be much higher 14596


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Scheme 2. Reactivity of 3 toward Brønsted Acids HCl, HNTf2, HOTf, and Water as Well as MeOTf, Ph2AsCl, and Ph2PCl

[3Cl]− with chlorine attached to gallium (Scheme 3) as an isolable intermediate. Employing HOTf in a toluene solution instead of HNTf2 gives exo,endo-12 with 31P NMR shifts similar to those of 11 in benzene solution, which slowly equilibrates to a mixture of exo,endo-12 and endo,endo-12. The mixture of 3 and HNTf2 gives very different spectra depending on the solvent this reaction is performed in. In benzene, the 31P NMR spectrum is comparable to exo,endo-12, whereas in THF nuclei X and S resonate at almost the same frequency. The different behavior might be related to the low nucleophilicity of NTf2− compared to any other nucleophile employed in this study as a result of the leveling effect of the respective solvent.50 Thus, THF acts as a Lewis base and coordinates toward the gallium atom in a dynamic fashion. Crystals grown from a mixture of toluene and n-pentane contain the NTf2− anion in addition to the intact P6Ga corpus as found in 3. Due to severe disorder and lacking close contacts to the anion, the hydrogen atom could not be located. However, 31P NMR spectroscopy of the crystalline material dissolved in THF at −30 °C clearly indicates a phosphorusbonded hydrogen atom due to a significant 1J(PH) coupling constant (Table 2). Assuming a mechanism according to Scheme 3, in which 3 is protonated first to yield the electrophilic cationic species [3H]+ which is prone to a nucleophilic attack at the gallium atom, we considered the isomerism to be of different nature. The observation of two independent species in the 31P NMR spectra could on one hand be related to the equilibrium of rotamers 10′ and exo,endo-10 (Scheme 3), which is caused by a hindered rotation of the LGaCl moiety around the Ga−P bond after an SN2-type attack of chloride. Subsequently, the rotated orientation allows a stabilizing P−H···Cl hydrogen bond by the simple inversion of the P−H group, giving endo,endo-10. On the other hand, the observed species could also be diastereomers exo,endo-10 and endo,endo-10 if the rotation was only a pre-equilibrium with a low energy barrier. Which process possesses the lower activation energy is difficult to estimate, and particularly for this type of rotation, no reference values are available in literature. Comparing the barriers by computational calculations requires the full molecular model without any simplifications of the ligands which would require extensive computational time for this type of compound, which is not feasible. We succeeded in crystallizing both species exo,endo-10 and endo,endo-10 and determined their crystal structures. Whereas the LGaCl moiety adopts the same orientation for both

isomers, electron density of the hydrogen atom can be found from the difference Fourier map, indicating two diastereomers with different orientation of the P−H group. Furthermore, the adjacent phosphorus atom is slightly displaced, and together with the pronounced different 31P NMR shifts (vide infra), this assumption is nicely supported. The P−H stretching frequency observed in the Raman spectrum is slightly red-shifted upon formation of the hydrogen bond (exo,endo-10: 2310 cm−1; endo,endo-10: 2301 cm−1). Surprisingly, the addition of water to 3 gives the endo,endo product in first place, which then isomerizes to a mixture of exo,endo-13 and endo,endo-13 in the ratio 68:32. A concerted addition of water could explain the reverse reaction sequence compared to the protonation reactions. The exo,endo-isomer is likely to be more stable due to the stronger H−P···H−O hydrogen bond compared to P−H···O−H in endo,endo-13. It should be mentioned that exo,endo-10 exhibits a P−H···π interaction to one of the Dipp groups, which is proposed to apply for and exo,endo-13 accordingly. To substantiate our hypothesis, we reacted 3 with MeOTf, which gives only one product, exo,endo-14, in 92% yield. The spin system in 31P{1H} NMR is similar to that of exo,endo-12 (vide infra). The addition of [nBu4N]Cl to a solution of exo,endo-14 replaces the triflate anion by a chloride substituent to give exo,endo-15 in 96% yield. The crystal structures prove the same configuration of the P−Me and the P−H group in exo,endo-14, exo,endo-15, and exo,endo-10. Finally, we tested the reactivity of 3 toward the ambiphilic reagent NaOCP.51 Phosphaethynolate has been shown to act as a [P−] transfer reagent, for example, in the reaction with imidazolium salts.52 Reacting NaOCP with 3 in THF solution gives a species 16− with four partially unresolved signals in the 31P NMR spectrum.13 Upon protonation, it gives solely heptaphosphane 17 in 93% yield with a deltacyclane-type structure of the P7Ga2 corpus. It can be considered as the formal insertion product of a P−H moiety into the P4−Ga2 bond in the four-membered ring of 3. NMR Spectroscopy. Upon addition of a QZ species (Q = H, Me, PPh2, AsPh2; Z = Cl, OTf, NTf2, OH) to 3, the spin system in the 31 P{ 1 H} NMR changes from the symmetrical AEMM′XX′ to an unsymmetrical AEMNSX system (Table 2; for numbering, see Figure 3) in which the general order of the abbreviation remains the same. The most dominant shift toward higher field is observed for the nuclei X and S (P4 and P5), which were part of the opened four-membered ring in 3. 14597


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Spin system in compound 3 according to Chart 2. bIn compound endo,endo-12, nucleus M is represented by P3 and nucleus N by P2. cSpin system AEGMNOX according to Scheme 2, in THF-d8.

Scheme 3. Proposed Mechanism for the Addition of Brønsted Acids to 3a

Anion [3Cl]− is not accessible but could be an intermediate in the deprotonation of exo,endo-10 and endo,endo-10.

a

In compound exo,endo-10, the nuclei X and S are found to be shifted more than 160 ppm further upfield than in 3 (exo,endo-10: Δδ(PX) = −161.6 ppm, Δδ(PS) = −187.2 ppm). Nucleus S does not even change its chemical environment in the first coordination sphere. The reaction is associated with an increase of the angle around nucleus S (3: av. ψ(P5) = 273.1(5)°, exo,endo-10: 305.3(2)°, exo,endo-8: 310.45(2)°) but again violates the trend of a low-field shift with increasing angle.30 An even larger shift is observed for the addition of Ph2PCl to 1 (Δδ = −318.7 and −302.8 ppm).15 The other nuclei A, E, M, and N are only moderately shifted in either direction. Upon inversion of P4, all nuclei shift significantly toward lower field. The corresponding X part of compound endo,endo-10 resonates at −9.2 ppm, which is Δδ = 55.3 ppm further downfield compared to exo,endo-10. This difference is predominantly caused by a change of the direction of a hydrogen atom of a secondary phosphane and the lone pair thereof. Comparable shifts are also observed for compounds exo,endo8, endo,endo-8, exo,endo-9, and endo,endo-9. The inversion at P4 goes along with a significant deformation of the P6Ga notricyclane cage. The effect is most precisely observed in the crystal structure of the two cocrystallized isomers exo,endo-9 and endo,endo-9 (Figure 3). In the secondary phosphane species endo,endo-10 and endo,endo-12, the 1J(PXH) coupling constant is increased by an intramolecular hydrogen bond to the chlorine atom and the triflate group, respectively. The nonstabilized P−H bonds show 1J(PH) values of about 170 Hz, which have been observed for the anion [HP7]2− and its molybdenum, tungsten, and iron complexes (cf. [HP7]2−: 1 J(PH) = 160 Hz;53 [η2-HP7M(CO)4]2−: 1J(PH) = 172 Hz (M = Mo, W);54 [Fe(P7H)2]2−: 1J(PH) = 169 Hz55). The established hydrogen bond leads to an increase of this value to about 200 Hz (Table 1). Compound exo,endo-13 shows a second J(PH) coupling of 15 Hz across the hydrogen bond to the OH group attached to the gallium atom. This hydrogen bond decreases electron density at nucleus X and thus leads to an increase of the 1J(PXH) to 188 Hz. Another indication for the configuration at P4 is the large 2J(PSPX) coupling constant of more than 120 Hz in the endo,endo compounds. These are derivatives in which Ga2 and the substituent point in the same direction (Table 1, endo,endo-isomers). The exo,endo-isomers and the methylated compounds exo,endo-14 and exo,endo-15 (Table 2) exhibit a very small magnitude of 2J(PSPX). The same trend has been observed for the

a

173 79 −288 18 −355 165 −324 −1 −389

−2 −389

168 −331

2.66 206 120 −266 2.03 171 5 −309

4.43 226 30 −311

2.19 172 5 −311

0.57 199 122 −263

188 3 −316

206 113 −264

24 −344

−349.8 −131.7 −119.7 35.4 −138.9 −212.8 −247.0 −432.9 −199.4 −169.7 15.4 −92.2 −303.3 −385.4 −111.6 −105.2 −5.3 −54.2 −249.8 −380.1 −111.0 −107.5 −9.2 −42.9 −249.5 −350.7 −62.4 −51.6 65.8 −31.4 −202.1 −24.6

δ(P1) δ(P2) δ(P3) δ(P4) δ(P5) δ(P6) δ(P7) δ(H-P4) 1 J(PXH) 2 J(PSPX) 1 J(PEPX)

A M N X S E

−434.5 −145.2 −145.2 97.1 97.1 −290.5

−395.9 −165.8 −162.2 −2.4 −77.2 −282.8 −11.6

−397.2 −167.8 −158.8 −7.3 −75.7 −286.9

−349.9 −59.1 −48.8 62.1 −33.3 −203.9

−409.2 −156.0 −129.8 −64.6 −81.0 −291.6

−444.1 −220.7 −175.1 −31.8 −47.8 −332.2

−423.7 −162.7 −143.3 −66.5 −79.2 −305.1

−385.9 −108.2 −111.1 14.5 −22.6 −255.6

−409.1 −157.6 −129.0 −64.1 −102.8 −294.0

−448.5 −209.3 −183.6 33.0 −80.2 −316.6

17c exo,endo-15 exo,endo-14 endo,endo-13 exo,endo-13 endo,endo-12b exo,endo-12 11 endo,endo-10 exo,endo-10 endo,endo-9 exo,endo-9 endo,endo-8 exo,endo- 8 3a

Table 2. NMR Chemical Shifts of the 31P and the P-Bonded 1H Nuclei (in ppm) and Selected Coupling Constants (in Hz) of Compounds exo,endo-8, endo,endo-8, exo,endo-9, endo,endo-9, exo,endo-10, endo,endo-10, 11, exo,endo-12, endo,endo-12, exo,endo-13, exo,endo-14, and exo,endo-15 in Benzene Solution and of 17


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Figure 3. 31P{1H} NMR spectrum of compounds exo,endo-9 and endo,endo-9 with nuclei assigned to the AEMNSX spin system. Molecular structures of exo,endo-9 (red) and endo,endo-9 (black) as two disordered parts in the same crystal structure representing the deformation of the P6Ga notricyclane cage by inversion at P4 (nucleus X). All carbon, nitrogen, and hydrogen atoms and solvent molecules are omitted for clarity; ellipsoids are set at 50% probability. Signal marked with an asterisk belongs to traces of compound 3.

asymmetrical and symmetrical isomers of Me3P7.56 On the contrary, the 1J(PEPX) coupling constant increases by approximately 50 Hz from the endo,endo- to the exo,endo-isomers. 16− shows four partially resolved signals in the 31P NMR spectrum in a THF solution. Upon addition of crown ether, the signals sharpen and exhibit an AA′MM′QXX′ spin system which can be attributed to a rapidly fluctuating structure, as suggested in Scheme 4. The orientation of the hydrogen atom

8.5 and 5%; endo,endo-9, 20%). Upon dissolution of a large single crystal, which was found to be predominantly exo,endo-8, at −30 °C in THF, the low-temperature 31P{1H} NMR spectrum showed the same composition as the mother liquor, indicating a fast equilibration in solution. In contrast, singlecrystal measurements at five temperatures in the range between 100 and 300 K revealed no significant change in the occupancy of the disordered component.13 The methylated compounds exo,endo-14 and exo,endo-15 as well as endo,endo-13 were crystallized by vapor diffusion from benzene/n-pentane. Compound endo,endo-13 was also crystallized from toluene/ n-pentane at −30 °C in order to prevent any isomerization. Single crystals of exo,endo-10 were obtained from the reaction mixture of 3, [nBuN4]Cl, and HNTf2 in toluene by vapor diffusion with n-pentane at −30 °C. Compound endo,endo-10 crystallized from fluorobenzene by vapor diffusion with n-pentane. 17 crystallized by vapor diffusion from benzene/n-pentane together with remaining traces of solvent free NaOCP (for details see the Supporting Information). Crystals of exo,endo-10, endo,endo-8, endo,endo-13, and 17 show disorder in a way that in both parts the gallium atoms Ga1 and Ga2 are swapped and the cage is inverted and rotated by 90° accordingly. Crystals of 11 were obtained by vapor diffusion of n-pentane into a 1:1 mixture of 3 and HNTf2 in toluene at −30 °C. Crystals of [Na(16)(thf)3]·THF and 17·THF were obtained from THF solution by slow evaporation or vapor diffusion with n-pentane, respectively. Both compounds crystallize together with THF in the lattice. All P−P bonds in the compounds investigated are in the range of regular single bonds (Table 3; Σrcov = 2.22 Å).33 Compared to those of 3, the Ga1−P bond lengths are longer and less similar, reaching a maximum for the P−H compounds exo,endo-10, endo,endo-8, and endo,endo-13. The angle P1−Ga1−P6 remains the same as that in 3. In contrast, the angle Z−Ga2−P5, with Z being the nucleophile in the addition to 3, is largely increased upon cleavage of the four-membered ring (Table 3; 3: 85.4(5)°, products: 107.2(3)−123.9(3)°). The gallium atom Ga2 stays in the pseudo-tetrahedral environment. The angle at Ga2 within the GaN2C3 heterocycle is smaller than the ideal tetrahedral angle, allowing Z−Ga2−P5 angle to increase up to 123.7° in endo,endo-13. Compound exo,endo-14 steps out of the line as the weakly coordinating triflate anion sits almost perpendicular on the close to trigonal planar surrounded atom Ga2 (angle sum ψ(Ga2) = 356.87(5)°). Accordingly, the Ga2−O1 bond is significantly longer by 0.12 Å in exo,endo-14 compared to that in endo,endo-13.

Scheme 4. Reaction of 3 and NaOCP Gives the Sodium Salt of Anion 16−a

a

It is in equilibrium between two valence isomers, giving rise to an AA′MM′QXX′ spin system in the 31P NMR spectrum, which becomes sharp upon addition of crown ether 18c6.

in 17 is not trivially determined; however, the X-ray diffraction data reveals a significant electron density in the difference Fourier map above P7 (Figure 4). Furthermore, two significant coupling constants are considered. A 3J(PH) coupling of 43 Hz is observed toward P2 and 2J(PP) to the same nucleus, which is comparatively large at 146 Hz. The latter coupling constant is compared to the triorganyl nonaphosphanes R3P9 (R = Et, tBu) which have the same skeleton as the P7Ga2 core in 17 but with two tBu groups pointing upward and downward from the P2 linker.57 The adjacent phosphorus atoms have significantly different 2J(PP) coupling constants to the basal three-membered ring. The larger one is found for the upward orientation (Et3P9: 81.6 Hz; tBu3P9: 93.2 Hz), which strongly supports our assumption. The 3J(PH) cannot be used for indication as both orientations are expected to have high values.58 Crystallographic Investigation. Crystals of exo,endo-8 and exo,endo-9 were obtained by vapor diffusion of n-pentane into a dichloromethane or benzene solution of a mixture of exo,endo-8 and endo,endo-8 or exo,endo-9 and endo,endo-9, respectively. The structures contain both solvents. Two different structures of exo,endo-8 containing different solvents and one of exo,endo-9 were determined with small amounts of the other isomer as disorder in the same position (endo,endo-8, 14599


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Figure 4. Molecular structures of compounds exo,endo-8, exo,endo-9, endo,endo-10, exo,endo-10, endo,endo-13, exo,endo-14, exo,endo-15, [Na(16)(thf)3] and 17. Carbon-bonded hydrogen atoms and solvent molecules omitted for clarity; ellipsoids are set at 50% probability. In case of disorder, only the major component is depicted. Labeling scheme shown for 17 applies to all other structures.

The isomerization from endo,exo to endo,endo causes a deformation of the nortricyclane scaffold by a displacement of P4. This effect is best observed in the torsion angles Ga1− P1−P2−P4, which have opposite signs for either configuration (Table 3). In the solid state, the LGaZ moiety (Z = Cl, OTf, OH) seems to have a preferred orientation, indicated by the torsion angle P3−P5−Ga2−Z, with Z roughly pointing toward P4 (θtheo ≈ 70 ± 30°). This is obvious for those compounds including a hydrogen bond (endo,endo-10, endo,endo-13; θ ≈ 50°) but is also observed for others. Exceptions of these findings are the methylated compounds exo,endo-14 and exo,endo-15, which bear Z on top or below the equatorial plane. This may give a hint to an SN2-type substitution at Ga2 from exo,endo-14 to exo,endo-15. A result of the latter orientations is that the coordination sphere of Ga2 is highly distorted with very different P5−Ga−N angles (exo,endo-14 = 105.40(5)° vs 135.49(5)°; exo,endo-15 = 113.90(4)° vs 144.31(5)°). The crystal structure of 11 contains two disordered independent half triflimide anions and half of a toluene molecule on special positions and an ordered toluene molecule and the disordered P6Ga2 cage. The hydrogen atom cannot undoubtedly be localized in the structure due to the overall severe disorder. Some electron density is found in a reasonable distance to atom P4A, but we abstain from refining this as the missing hydrogen atom. The S−N bond lengths (av. 1.567(18) Å) clearly indicate the presence of the anion (cf. KNTf2: av. 1.569(4) Å)59 instead of the free acid HNTf2 (1.6465(8) Å).59 The P−P bond lengths within the P6Ga2 moiety are similar to those in 3. The distance between P4A and P5A and the P4− Ga2−P5 angle, however, decrease significantly (11: d(P4A− P5A) = 2.9767(19) Å, 76.20(5)°; 3: av. d(P4−P5) = 3.257(8) Å,

85.4(5)°). The separation of cation and anion is related to the increased steric demand of the triflimide moiety compared to triflate or chloride and its lower nucleophilicity.50 16− acts as a ligand in the solid state, coordinating the sodium ion via phosphorus atoms P2 and P7. The pseudooctahedral coordination sphere is furthermore filled by three THF ligands and a close contact to a methyl group of one Dipp substituent. In compound 17, the P7 scaffold is disordered in a way that each part is represented by one of the resonance structures of 16− in Scheme 4, with an additional proton at the phosphanide site. Upon protonation, the geometry of the P7Ga2 cage hardly changes. The most dominant difference is found in the Ga2−P bond lengths. The anion exhibits a shorter Ga2−P7 bond but a longer Ga2−P5 bond, which is converse in 17 (Table 3). The position of the sodium cation in 16− between P2 and P7 allows preferred access of a protonation agent from above P7. This supports the hydrogen position in 17 as discussed before, if the coordination persists in solution.

■

SUMMARY AND CONCLUSION We have shown that, in contrast to the first report on the reaction of LGa and white phosphorus, not only 1 is formed but also a plethora of larger polyphosphanes and also the di-inserted product 2. The hexaphosphane 3 was shown to be accessible in reasonable yield, and its selective reactivity toward the Brønsted acids HCl, HOTf, HNTf2, and water, the methylating agent MeOTf, and the chloropnictanes Ph2ECl (E = P, As) is presented. The reactant is added to 3 in a way that the nucleophile (i.e., Cl−, [OTf]−, OH−) is bonded to gallium, whereas the electrophile (i.e., H+, Me+, [Ph2E]+) forms a bond to the P6 scaffold. Two different stereoisomeric 14600


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−

The second value is determined in the disordered part of the structure representing endo,endo-8 and endo,endo-9. Z: Cl1 or P4 (11), O1 (endo,endo-13, exo,endo-14), P7 (16 , 17).

63.8(4) −17.81(3) 50.3(2)

■

46.29(10) 46.35(15) P3−P5−Ga2−Zb

EXPERIMENTAL SECTION

All manipulations were performed in a glovebox MB Unilab or using Schlenk techniques under an atmosphere of purified argon or nitrogen. Dry oxygen-free solvents (CH2Cl2, C6H5F, MeCN (distilled from CaH2), THF, toluene, benzene (distilled from potassium/benzophenone), n-hexane, n-pentane (distilled from potassium)) were employed. Deuterated benzene and tetrahydrofuran were purchased from Sigma-Aldrich and distilled from potassium/benzophenone. Anhydrous deuterated dichloromethane was purchased from SigmaAldrich. All distilled and deuterated solvents were stored over molecular sieves (4 Å: CH2Cl2, C6H5F, C6D6, CD2Cl2, THF, benzene, toluene, n-hexane, n-pentane; 3 Å: MeCN). All glassware was ovendried at 160 °C prior to use. Suitable single crystals were coated with Paratone-N oil, mounted using either a glass fiber or a nylon loop, and frozen in the cold nitrogen stream. Crystals were measured at 100 K on a Rigaku Oxford Diffraction SuperNova system using Cu Kα radiation (λ = 1.54184 Å) generated by a Nova microfocus X-ray source. NaOCP was measured using Mo Kα radiation (λ = 0.71073 Å) generated by a Mova microfocus X-ray source. Reflections were collected with an Atlas S2 detector. Data reduction and absorption correction was performed with CrysAlisPro60 software. Using Olex2,61 the structures were solved with SHELXS/T62 by direct methods and refined with SHELXL63 by least-squares minimization against F2. Hydrogen atoms bonded to carbon were added to the structure models on calculated positions using the riding model. All other hydrogen atoms were located in the difference Fourier map. Synthesis of 3. LGa (5.12 g, 10.5 mmol) and white phosphorus (989 mg, 7.89 mmol, 0.76 equiv) were suspended in 20 mL of toluene in a screw-cap Schlenk flask. The mixture was heated to 180 °C for 70 h in an oil bath. The dark red suspension was filtered at room temperature, and the filtrate was dried in vacuo. The remaining oil was suspended in 4 mL of toluene to give a thick orange-red suspension, which was filtered through a G3 glass frit. The solid was washed with 1 mL of toluene and subsequently dried in vacuo (2.035 g). The filtrate was dried and suspended in 1.5 mL of toluene and filtered through a G3 glass frit. The solid was washed with 2 mL of n-pentane and subsequently dried in vacuo (0.810 g; combined yield: 2.845 g, 2.451 mmol; 47%). Synthesis of 2. LGa (5.000 g, 10.26 mmol) and white phosphorus (950 mg, 7.67 mmol, 0.75 equiv) were suspended in 17 mL of toluene in a screw-cap Schlenk flask. The mixture was heated to 180 °C for 19 h in an oil bath. The dark red suspension was filtered at room temperature, and the solid was washed two times with 4 mL of toluene. The combined filtrates were dried in vacuo, and the remaining oil was suspended in a mixture of 40 mL of n-hexane and 5 mL of toluene. The suspension was filtered again. Both filtration residues

a

102.43(5) 76.20(5) 101.80(5) 121.58(5) -3.63(7) 101.58(10) 122.08(11) 4.70(8) 102.3(8) 85.4(5) −1(2)

2.202(5)

2.227(14) 2.241(3)

2.401(7) 2.200(5)

products are formed in most reactions of which the HCl adducts exo,endo-10 and endo,endo-10 could be synthesized and isolated selectively but equilibrate in solution. The extraordinary influence of the secondary phosphane’s configuration on spectroscopic and crystallographic characteristics is highlighted. The hydrogen atom’s position and a small displacement of the adjacent phosphorus atom cause a chemical shift difference of 55 ppm and even more for other derivatives in the 31P NMR spectrum. Single crystals of the Ph2PCl adduct, consisting of predominantly exo,endo-10, were shown to be stable with respect to isomerization at 300 K, but the compound rapidly isomerizes to equilibrium in solution even at 243 K. Furthermore, NaOCP was employed in the transfer of a [P−] to give anion 16−, which is subsequently protonated, yielding the unique heptaphosphane 17. Those reactions extend the scope of our recently presented, unprecedented approach to selectively synthesize novel polyphosphanes from functionalized white phosphorus. The novel strategy provides access to polyphosphanes of adapted constitution and configuration in order to tune its properties for potential future applications.

b

100.62(17) 123.9(3) 3.20(11)

−152.62(4)

64.75(5)

2.351(3) 2.365(5) 2.345(5) 2.319(10) 2.218(4) 2.216(5) 2.195(2) 2.225(3) 2.209(11) 2.223(7) 2.179(12) 2.189(7) 104.52(15) 107.2(3) 0.97(19) 2.3648(5) 2.3748(5) 2.2277(5) 2.3686(5) 2.2003(7) 2.2069(6) 2.1859(7) 2.2344(7) 2.2615(6) 2.1606(6) 2.1862(6) 1.856(2) 102.633(17) 111.344(18) −9.67(3) Ga1−P1 Ga1−P6 Ga2−Zb Ga2−P5 P1−P2 P1−P3 P2−P3 P2−P4 P3−P5 P4−P6 P5−P6 P4−R P1−Ga1−P6 Z−Ga2−P5b Ga1−P1−P2−P4

2.353(6) 2.346(2)

2.3679(5) 2.3906(5) 2.2156(5) 2.3568(5) 2.2054(7) 2.2018(6) 2.1945(7) 2.2303(7) 2.2534(6) 2.1659(6) 2.1961(6) 2.2249(7) 101.617(17) 122.217(18) −14.47(3) 9.59(12)a 97.33(4)

2.3679(10) 2.3928(9) 2.2168(8) 2.3486(8) 2.2034(12) 2.2058(11) 2.1952(12) 2.2463(14) 2.2398(11) 2.1669(13) 2.1928(11) 2.3554(11) 101.35(3) 119.58(3) −14.64(5) 12.11(14) 103.58(4)

2.3526(11) 2.425(4) 2.2669(11) 2.270(4) 2.2036(15) 2.204(2) 2.183(3) 2.211(2) 2.233(5) 2.202(5) 2.180(5)

2.3522(7) 2.417(2) 2.2467(7) 2.283(2) 2.2008(10) 2.210(3) 2.184(3) 2.233(2) 2.234(4) 2.185(4) 2.179(2)

2.3550(17) 2.3690(15) 2.4123(14) 2.4117(12) 2.1880(18) 2.1739(19) 2.191(3) 2.2400(19) 2.250(2) 2.162(2) 2.1728(18)

2.3656(14) 2.432(6) 1.915(4) 2.252(4) 2.204(2) 2.203(3) 2.196(3) 2.217(4) 2.229(6) 2.186(8) 2.179(7)

2.3602(4) 2.3628(4) 2.0334(10) 2.3242(4) 2.1995(5) 2.2056(5) 2.1888(6) 2.2311(5) 2.2710(5) 2.1560(5) 2.1774(5) 1.8470(16) 102.702(14) 94.36(3) −10.99(3)

2.3548(10) 2.3425(9) 2.3068(9) 2.3709(9) 2.2222(13) 2.2210(12) 2.1833(13) 2.2155(13) 2.2361(13) 2.2172(12) 2.1724(12) 2.1829(12) 104.95(3) 109.93(3) 1.26(6)

17 16− exo,endo- 15 exo,endo- 14 endo,endo- 13 11 exo,endo- 10 endo,endo- 10 exo,endo-9 exo,endo- 8 3

Table 3. Selected Bond Lengths (in Å) and Angles (in deg) of 3, exo,endo-8, exo,endo-9, exo,endo-10, endo,endo-10, 11, endo,endo-13, exo,endo-14, exo,endo-15, 16−, and 17


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allow crystallization of endo,endo-13 by vapor diffusion of n-pentane into the reaction mixture. Synthesis of exo,endo-14. 3 (31.5 mg, 0.0271 mmol) was dissolved in a stock solution of MeOTf in benzene (0.0341 M, 795 μL, 0.0271 mmol). After 5 min, the solution was layered with 3 mL of n-pentane. After 3 days, crystals of pure exo,endo-14 were separated from the mother liquor and dried in vacuo (33.1 mg, 0.0250 mmol, 92%). Synthesis of exo,endo-15. 3 (31.5 mg, 0.0271 mmol) was dissolved in a stock solution of MeOTf in benzene (0.0341 M, 795 μL, 0.0271 mmol). After 30 min, [nBu4N]Cl (7.4 mg, 0.027 mmol) was added to the solution. After another 30 min, the solution was layered with 3 mL of n-pentane. After 5 days, a colorless solid was separated from the mother liquor, washed two times with 0.5 mL of MeCN, and dried in vacuo to yield pure exo,endo-15 (31,6 mg, 0.0261 mmol, 96%). Synthesis of [Na(16)(thf) 3]. A mixture of 3 (80.0 mg, 0.0689 mmol) and [NaOCP(dioxane)2.33] (19.7 mg, 0.0685 mmol) were dissolved in 2 mL of THF and heated in a microwave to 80 °C for 2 h under stirring, giving a dark red solution. The volume was reduced to half, and 5 mL of n-pentane was added to precipitate the crude product. The red solid was isolated by filtration, washed with 1 mL of n-pentane, and dried in vacuo to yield pure [Na(16)(thf)3].... [Na(16)(thf)3] (25 mg, 0.0175 mmol, 25%). Further product could be isolated from the mother liquor. Synthesis of 17. A mixture of 3 (79.9 mg, 0.069 mmol) and [NaOCP(dioxane)2.33] (19.6 mg, 0.068 mmol) was dissolved in 2 mL of THF and heated in a microwave to 66 °C for 2 h under stirring. [Et3NH]Cl (9.5 mg, 0.069 mmol) was added to the deep red reaction mixture, giving a color change to yellow. The volume was reduced to half in vacuo, and 4 mL of MeCN was added to precipitate 17 (51 mg). The volume of the filtrate was again reduced to half in vacuo, and a second batch of precipitated 17 (26 mg) was collected by filtration. Both fractions were washed with 1 mL of MeCN and dried in vacuo to yield pure pale yellow product (combined 77 mg, 0.65 mmol, 93%).

contain a mixture of 5 and 6, which eventually crystallized from a DCM solution. The filtrate was cooled to −30 °C to induce crystallization of 1. The mother liquor was concentrated to 5 mL, and another 20 mL of n-hexane was added. The mixture was cooled to −30 °C. Crystals obtained after 3 days were isolated and appeared to be a mixture of 2, 1, and 3. Washing the solid twice with 5 mL of n-hexane extracted predominantly 2 and 1 but did not yield any pure compound. The primary mother liquor was stored again at −30 °C. After 2 weeks ,a minor amount of LGa was isolated, and the solution was concentrated to 10 mL. The next compound to crystallize was pure 3, but some 3 remained in solution in the mother liquor. From this solution, a tiny amount of pure 7·P4 crystallized sufficient for X-ray diffraction and NMR characterization. The seventh crystalline fraction separated from the mother liquor consisted of small amounts of pure 2. The eighth isolated fraction (200 mg) contained 2 and 3 in the ratio 80:20. This mixture was dissolved in DCM and immediately cooled to −30 °C to prevent decomposition. Vapor diffusion of n-pentane into the solution induced the crystallization of DCM containing crystalline 2. The compound was isolated by filtration and dried in vacuo to yield pure 2 (80 mg, 0.073 mmol, 0.7% yield). The last isolated crystalline fraction contained 2 and 3 in the ratio 1:9. Synthesis of exo,endo-8 and endo,endo-8. 3 (102.6 mg, 0.0884 mmol) was dissolved in 1 mL of THF. Ph2PCl (23.4 mg, 0.106 mmol) in 1 mL of THF was added to the solution and stirred for 2.5 h at room temperature. Twelve milliliters of MeCN was added to the solution to precipitate the crude product. The precipitate was isolated by filtration, washed with 1 mL of MeCN, and dried in vacuo to give a pure mixture of the isomers as a pale yellow solid (87.1 mg, 0.0631 mmol, 71%). Synthesis of exo,endo-9 and endo,endo-9. 3 (99.1 mg, 0.0854 mmol) was dissolved in a mixture of 1.5 mL of THF and 8 mL of MeCN. Ph2AsCl (33.2 mg, 0.125 mmol, 1.5 equiv) in 0.5 mL MeCN was added to the solution and stirred for 1 day at room temperature. The precipitate was isolated by filtration (68.4 mg). The filtrate was dried in vacuo. The residue was suspended in 0.5 mL of THF and 4 mL of MeCN to yield another crop of product (29 mg). The combined solids were dried in vacuo to give a pure mixture of the isomers as a pale yellow solid (97.4 mg, 0.0683 mmol, 80%). Synthesis of exo,endo-10. To a mixture of 3 (38.0 mg, 0.0327 mmol) and [nBu4N]Cl (9.1 mg, 0.033 mmol) were added 1 mL of toluene and 335 μL of a stock solution of HNTf2 in toluene (0.0975 M, 0.0327 mmol). The solution was allowed to stir for 5 min and was then cooled to −30 °C. The colorless crystalline product was isolated after 1 week of vapor diffusion into the reaction mixture. The crude product was washed with 1 mL of MeCN and subsequently dried in vacuo (25.0 mg, 0.0327 mmol, 64%). Synthesis of endo,endo-10. A mixture of 3 (167.7 mg, 0.145 mmol) and [Et3NH]Cl (19.9 mg, 0.145 mmol) was dissolved in 1.5 mL of THF and stirred for 3 h at room temperature. The solution was concentrated to 0.5, and 4 mL of MeCN was added to precipitate the product. Compound endo,endo-10 was isolated by filtration, washed with 1 mL of MeCN, and dried in vacuo to yield pure product (137 mg, 0.114 mmol, 79%). Procedure to Form 11. To a precooled solution of 3 (40.1 mg, 0.0346 mmol) dissolved in 0.5 mL toluene was added 355 μL of a precooled stock solution of HNTf2 in toluene (0.097 M, 0.0346 mmol) at −30 °C. The mixture was shaken and set for crystallization by vapor diffusion of n-pentane at −30 °C. After 3 days, crystals were grown, which were separated from the mother liquor and used for single-crystal analysis and NMR spectroscopic studies. Procedure to Form exo,endo-12. In a J.-Young NMR tube, a solution of 3 (44.5 mg, 0.0383 mmol) in 200 μL of toluene and 380 μL of a stock solution of HOTf in toluene (0.102 M, 0.0388 mmol) were mixed and subsequently studied by NMR spectroscopy. Procedure to Form endo,endo-13. In a Schlenk flask, 3 (45.1 mg, 0.0389 mmol) was dissolved in 1 mL of toluene. To the yellow solution was added a capillary soaked with water (1.40 mg, 0.0777, 2 equiv), sonicated for 30 s, and subsequently cooled to −30 °C to

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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.7b07704. Details on X-ray crystal structure analyses, spectroscopic data (NMR, IR, Raman), NMR simulation, melting points, and elemental analysis results (PDF) X-ray data for 1 (CIF) X-ray data for 2_1 (CIF) X-ray data for 2_2 (CIF) X-ray data for 2_3 (CIF) X-ray data for 3 (CIF) X-ray data for 4 (CIF) X-ray data for 5_1 (CIF) X-ray data for 5_2 (CIF) X-ray data for 5_3 (CIF) X-ray data for 6_1 (CIF) X-ray data for 6_2 (CIF) X-ray data for 7_1 (CIF) X-ray data for 7_2 (CIF) X-ray data for 8_1 (CIF) X-ray data for 8_2_100 (CIF) X-ray data for 8_2_150 (CIF) X-ray data for 8_2_200 (CIF) X-ray data for 8_2_250 (CIF) X-ray data for 8_2_300 (CIF) X-ray data for 9 (CIF) X-ray data for 10_1 (CIF) X-ray data for 10_2 (CIF) 14602


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11 (CIF) 13_1 (CIF) 13_2 (CIF) 14 (CIF) 15 (CIF) 16 (CIF) 17 (CIF) NaOCP_1 (CIF) NaOCP_2 (CIF)

AUTHOR INFORMATION

Corresponding Author

*[email protected] ORCID

Felix Hennersdorf: 0000-0002-3729-030X Jan J. Weigand: 0000-0001-7323-7816 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Deutsche Forschungsgemeinschaft for funding (DFG WE 4621/3-1). F.H. thanks the Fonds der Chemischen Industrie, the Studienstiftung des Deutschen Volkes, and the Graduate Academy at TU Dresden for doctoral fellowships. The article is dedicated to Professor Neil Burford on the occasion of his 60th birthday.

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Selective Derivatization of a Hexaphosphane from Functionalization of

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