Enantiopure Ferrocenophanes with Phosphorus in Bridging Positions

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

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Enantiopure Ferrocenophanes with Phosphorus in Bridging Positions: Thermostability and Ring-Opening Polymerization My P. T. Cao,† J. Wilson Quail,‡ Jianfeng Zhu,‡ and Jens Müller*,† †

Department of Chemistry and ‡Saskatchewan Structural Sciences Centre, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada

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S Supporting Information *

ABSTRACT: The thermal stability of four related, enantiopure phospha[1]ferrocenophanes 2R, equipped with different R groups (R = Ph, iPr, CH2SiMe3, tBu) at the bridging phosphorus atom, was investigated by differential scanning calorimetry. The chirality of 2R stems from the planar chirality of the ferrocene moiety (Sp,Sp)-2,2′-diisopropylferrocenediyl. Within this group of [1]ferrocenophanes ([1]FCPs) the Phsubstituted species 2Ph resulted in the largest heat release [ΔH = −86(±2) kJ mol−1] and, therefore, was subjected to preparative thermal ring-opening polymerization (ROP). ROP of 2Ph gave a polymer fraction (44%), which was analyzed by gel permeation chromatography in its sulfurized form (Mw = 19 kDa; D̵ = 1.3). The remaining fraction of the reaction mixture was composed of cyclic oligomers that were sulfurized to facilitate their characterization. Mass spectrometric analysis revealed the presence of cyclic oligomers (n = 2−6), with the dominating dimer signal. Chromatographic separation (preparative thin-layer chromatography) gave five fractions of isomeric dimers. From these diphospha[1.1]ferrocenophanes, one could be structurally characterized by single-crystal X-ray analysis, which uncovered a 1:1 ratio between Sp- and Rpconfigured Cp rings. These results support the recent findings that ROP of phospha[1]ferrocenophanes occurs through breakage of the Fe−Cp bonds. An attempted anionic ROP of 2Ph with nBuLi revealed that the initial ring-opening reaction occurred readily, but chain growth was not happening. Quenching of the ring-opened product with Ph2PCl, followed by a sequence of sulfurization, chromatographic separation, and desulfurization, gave a new diphosphinoferrocene [(S)-3PPh2] with planar and P-central chirality. Applying a similar approach that had been used for the preparation of enantiopure phospha[1]ferrocenophanes 2R, two new diphospha[2]ferrocenophanes with either CH2SiMe3 or NiPr2 groups at phosphorus were prepared. Both compounds are enantiopure species with planar and P-central chirality.

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INTRODUCTION

ferrocenophanes before being applied to phosphorus derivatives.9,10 Since the first phospha[1]ferrocenophanes APh and AMe were published, other compounds of the same type but with different groups attached to phosphorus (R = Cl,5 iPr,11 tBu,12 CH2tBu,8a CH2SiMe3,8a p-tBuC6H4,13 2,4,6-Me3C6H2,7b,14 (−)-bornyl, 15 (−)-menthyl 15 ) as well as phospha[1]ferrocenophanes with substituents on Cp rings (B−H; Chart 1) have been described in the literature. From the chiral derivatives of the latter family, only compound H from our laboratory had been prepared as an enantiopure species;16 others were either obtained as mixtures of diastereomers or as racemates (Chart 1). Phosphines are one of the most important class of ligands in catalysis and it is not surprising that it had been shown that phosphorus in [1]FCPs as well as in derived oligomers or polymers can coordinate to transition metals.3,7a,14,15,17 In light

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After silicon, phosphorus was the second element that could be introduced as a single-atom bridge in ferrocenophanes (FCPs).2 Shortly after the first derivatives of these phospha[1]ferrocenophanes were published in 1980 (AR; Chart 1),3 their potential as monomers for polymerization was recognized; however, attempted anionic polymerizations of the phenylsubstituted [1]FCP APh (Chart 1) resulted only in oligomers.4 In 1995, it was finally shown that metallopolymers can be accessed from phospha[1]ferrocenophanes by thermal ringopening polymerization (ROP).5 One year later, it was disclosed that APh can be polymerized by living anionic ROP using nBuLi as an initiator.6 In 2000, an ROP process that requires irradiation was discovered for phospha[1]ferrocenophanes.7 Improvements of this photolytic ROP through the addition of NaCp, as a mild anionic nucleophile, led to another living polymerization of phosphorus-bridged [1]FCPs.8 The latter process, often referred to as photocontrolled living ROP, had been developed for sila[1]© XXXX American Chemical Society

Received: February 19, 2019

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DOI: 10.1021/acs.organomet.9b00114 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

methine protons of the Cp-bound iPr groups expectedly gave a septet, the second methine proton appeared as a septet of doublets with J values of 6.8 and 3.5 (2Ph), 2.8 (2iPr), and 4.2 (2tBu) Hz, respectively.22 The weaker coupling is a throughspace 1H−31P nuclear spin−spin coupling;22 only the methine proton in proximity to the lone pair on phosphorus shows the additional small coupling, indicating that this electron pair is required as a mediator (Figure 1).24 Compared to the many

Chart 1. Examples of Known Phospha[1]ferrocenophanes

Figure 1. Illustration of through-space 1H−31P nuclear spin−spin coupling in chiral phospha[1]ferrocenophanes 2R. Only the methine proton (indicated in green) adjacent to the lone pair on phosphorus couples with the phosphorus atom, whereas the proton (indicated in red) opposed to the lone pair does not.22 a

Reference 3. bReference 18. cReference 5. dOne isomer was crystallized from the mixture.19 eReference 12. fReference 20. g Reference 16.

reported examples of through-space coupling in the literature24 our phospha[1]ferrocenophanes are unique because within the same molecule one can differentiate between through-bond and through-space coupling mechanisms.21 The local C2 symmetry of the ferrocene moiety results in two equivalent bonding paths (four bonds) between one phosphorus atom and two chemically similar methine protons. The fact that only one of the two methine protons shows coupling with phosphorus proves that it cannot occur through bonds. As expected, the new [1]FCP 2CH2SiMe3 with a CH2SiMe3 group at phosphorus (Scheme 1) shows similar NMR features as those published for the [1]FCPs 2R (R = Ph, iPr, tBu).22 For example, the stronger shielded methine proton at δ of 3.10 ppm appears as a septet (JHH = 6.8 Hz), whereas the less shielded methine proton at δ of 3.43 ppm results in a septet of doublets (JHH = 6.8 Hz/JHP = 3.2 Hz). In order to evaluate if the chiral [1]FCPs might be suitable monomers for ROP, all four 2R were investigated by differential scanning calorimetry (DSC). Figure 2 shows a typical DSC thermogram from the series of measurements of

of potential applications in catalysis, we became interested in the preparation of enantiopure phospha[1]ferrocenophanes with the hope that they could be polymerized to give new chiral ligands. Within this report, the results of these explorations are discussed.

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RESULTS AND DISCUSSION Phospha[1]ferrocenophanes. Starting with the enantiopure 1,1′-dibromoferrocene derivative 1,21 lithium−bromine exchange followed by salt-metathesis reactions with dichlorophosphines RPCl 2 resulted in chiral phospha[1]ferrocenophanes 2R (Scheme 1). Scheme 1. Synthesis of Phospha[1]ferrocenophanes 2R22

In a recent short communication, we already reported on the synthesis and characterization of the three [1]FCPs 2R (R = Ph, iPr, tBu).22 The molecular structures of the phenyl and the isopropyl derivative were determined by single-crystal X-ray analysis, which revealed sets of distortion angles that are similar to those of known phospha[1]ferrocenophanes.5,8a,12,13,15−17,17f,23 For example, the angles between the two intersecting planes of Cp rings (α angles) are 26.2(1)° for 2Ph and 25.8(4) and 25.7(4)° for the two crystallographically independent molecules of 2iPr.22 These values are at the lower end of the range of 26−28° known for phospha[1]ferrocenophanes.2 The most interesting spectroscopic feature of these species was revealed by proton nuclear magnetic resonance (NMR) spectroscopy. Whereas one of the two

Figure 2. DSC thermogram of 2Ph showing a melting endotherm (Tmax = 99 °C) and an ROP exotherm (Tonset = 227 °C; Tmax = 271 °C) with an enthalpy of polymerization (ΔHROP) of −86(±2) kJ mol −1 (averaged value; see Figure S45 in the Supporting Information). B

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Organometallics species 2Ph. The exotherm above 200 °C indicates the occurrence of ROP and the average value of the associated heat exchange ΔHROP is −86(±2) kJ mol−1. The averaged polymerization enthalpies ΔHROP for the other phospha[1]ferrocenophanes were measured as −77(±2) (2iPr), −66(±2) (2CH2SiMe3), and −62(±4) kJ mol−1 (2tBu) (see Figures S45− S48 in the Supporting Information). Whereas the exothermic peaks of the thermograms of 2Ph (Figure 2) and 2iPr are symmetric, those of 2CH2SiMe3 and 2tBu are asymmetric and structured for unknown reasons. Experimentally determined ΔHROP values23a of phospha[1]ferrocenophanes are rare and, to the best of our knowledge, the only comparable values were published for the isomeric phospha[1]ferrocenophanes E (Chart 1). The cis isomer resulted in −89(±2) kJ mol−1, whereas the trans isomer gave −88(±2) kJ mol−1.20 Expectedly, the heat release of these two compounds is very similar to the related [1]FCP 2Ph with ΔHROP = −86(±2) kJ mol−1. If the phenyl group on phosphorus in 2Ph is replaced by an isopropyl group, the enthalpy changes to −77(±2) kJ mol−1 (2iPr). This significant drop in heat release does not indicate that the intrinsic strains in 2Ph and 2iPr are significantly different; both species were structurally characterized and their distortion angles are almost the same.22 The difference in ΔHROP is caused by steric effects. In the process from a monomer to oligomers or polymers, the available space for PR bridging moieties is diminished and, as a consequence, new steric repulsions between PR moieties and ferrocenediyl moieties in products can result. As iPr groups are bulkier than Ph groups, less of the intrinsic strain of 2iPr is released as residual strain remains stored in the products. One could be tempted to apply the same explanation to rationalize the further reduction of heat release for 2CH2SiMe3 and 2tBu (−66(±2) and −62(±4) kJ mol−1); however, as already mentioned, the exothermic peaks in the thermograms of these two species are asymmetric and structured. As the reasons for the peak shapes are unknown, we refrain from further interpretations. Thermal-ROP. As the phenyl-substituted species 2Ph resulted in the largest exotherm in DSC thermograms, it was selected for thermal ROP (Scheme 2).

colored supernatant. After sulfurization of this soluble part, mass spectrometric analysis revealed the presence of cyclic oligomers (2PhS)n from dimers to hexamers (n = 2−6), with the dimer signal dominating the mass diagram. From this mixture, five fractions (fractions A−E) could be separated by preparative thin-layer chromatography (PTLC). Proton NMR spectra for each of the five fractions showed different signal patterns and mass spectrometric analysis uncovered that each fraction contained a dimer with the formula [{(PhP S)(C5H3iPr)2}Fe]2, (2PhS)2. The dimer of the first published phospha[1]ferrocenophanes, PhPfc [fc = (H4C5)2Fe; APh, Chart 1],3b had been isolated by Miyoshi et al. in the course of exploring its photolytic ROP.17i After sulfurization, a syn- and an anti-isomer of the diphospha[1.1]ferrocenophane [PhP( S)fc]2 were characterized, which included single-crystal X-ray structural analysis (Figure 3).17i In both structures, the phenyl

Figure 3. Illustration of exo (R1) and endo (R2) α positions in synand anti-diphospha[1.1]ferrocenophanes. Isolated dimers (2PhS)2 will have one iPr group on each Cp ring, either in exo (R1) or in endo (R2) positions (see the text for a discussion).

groups are oriented away from ferrocene moieties, and it is fair to assume that the same holds true for the isomeric [1.1]FCPs isolated in form of the five fractions A−E. If one further assumes that on each Cp ring one of the two α positions (R1 or R2 in Figure 3) is substituted by an iPr group, 14 isomers are feasible (see Figure S1 in the Supporting Information). Six of these isomers have at least two iPr groups in endo positions (R2 in Figure 3) adjacent to each other on two different ferrocene moieties and, probably, cannot form because of steric congestion. Therefore, eight isomers result that do not exhibit these steric restrictions and, hence, are potentially accessible. We assume that five isomers from this group were isolated. It should be noted that in the 31P NMR spectrum of the crude mixture of the cyclic oligomers (Figure S20), two peaks at δ of 39.5 and 35.1 ppm of significant intensities are present that do not belong to one of the later isolated dimers. Probably, these two peaks are caused by another set of dimers. The number of signals detected for Cp-bound protons provides information about the time-averaged molecular symmetry. One of the isolated [1.1]FCPs (fraction A) resulted in 12 Cp signals (C1 point-group symmetry), three [1.1]FCPs (fractions B, C, and E) gave 6 Cp signals (C2, Cs, or Ci point-group symmetry), whereas one [1.1]FCP (fraction D) resulted in 3 Cp signals (C2v or C2h point-group symmetry; see Figure S1 for possible assignments). Crystallization attempts from the five isolated fractions resulted in a single crystal in one case only (fraction C). As it can see from the molecular structure in Figure 4, the isolated [1.1]FCP is the syn isomer with all four iPr groups in exo positions, syn-C2-(2PhS)2. Related dimers are the known syn[PhP(S)fc]217i (I in Figure 5) and species J20 with two iPr

Scheme 2. Thermal ROP of 2Ph

The monomer was heated in a flame-sealed NMR tube, resulting in a viscous melt that solidified to a red-colored glass at room temperature that completely dissolved in tetrahydrofuran (thf). Precipitation into methanol yielded a light-yellow precipitate (44%) and an orange-colored supernatant. NMR spectroscopy of the precipitate (2Ph)n revealed broad peaks indicative of polymeric materials. In order to make the polymer insensitive to oxygen, it was sulfurized applying a common procedure (Scheme 2).5 Gel permeation chromatography (GPC) analysis on the so-obtained sample (2PhS)n resulted in a mass-averaged molecular weight (Mw) of 19 kDa with a dispersity (D̵ ) of 1.3 (Figure S49 in the Supporting Information). More than half of the entire reaction mixture did not precipitate and remained dissolved in the orangeC

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enantiomers occurs at ambient temperature in CDCl3 (300 MHz; time-averaged C2v symmetry).17i In the course of the interconversion of the two enantiomers of the new [1.1]FCP syn-C2-(2PhS)2, the sulfur atoms as well as the iPr groups at the same ferrocene moiety will be forced to approach each other, causing an energy barrier through steric repulsions. Maybe the additional repulsion between iPr groups in syn-C2-(2PhS)2 slows the interconversion down so that at ambient temperature a time-averaged C2 symmetry and not a feasible C2v symmetry, like in the case of compound I (Figure 5), was observed. With respect to the performed ROP, the fact that the Sp,Sp planar chirality of monomer 2Ph gave the dimer syn-C2-(2PhS)2 with a 1:1 ratio of Sp and Rp planar chirality reveals that Fe−Cp bonds ruptured and reformed on the opposite face of the Cp ring. Even without the knowledge of the structure of syn-C2(2PhS)2 (Figure 4), the same conclusion can be drawn just from the fact that f ive isomeric [1.1]FCPs were isolated (fractions A−E), because the preservation of the Sp planar chirality of 2Ph can only lead to one syn and one anti isomer. These results match those found for thermal ROP of the racemic phospha[1]ferrocenophane trans-E (Chart 1), which also gave several isomeric [1.1]FCPs that were separated. Similar to that for 2Ph, mass spectrometry revealed that larger cyclic oligomers are formed during the thermal ROP of trans-E.20 These published results uncovered for the first time that thermal ROP of phospha[1]ferrocenophanes occurs through Fe−Cp bond rupture opposed to Cp−P bond rupture.26 Our new results obtained from the investigation of the thermal ROP of 2Ph provides additional support for this interpretation. Anionic Ring-Opening. We attempted ROP of 2Ph by applying the common initiator nBuLi. As only P−Cp bonds are expected to break and form in this process, the planar chirality of the monomer will be unaltered and preserved in a resulting polymer. In 1996, Manners et al. reported that the anionic ROP of PhPfc (APh, Chart 1) could be conducted as a living process, which allowed controlling molecular weights and molecular weight distributions.6a In addition to phospha[1]ferrocenophanes,6a,b,7,8 those bridged by silicon8b,27 or germanium28 could be polymerized by living processes. The most important method is that of anionic ROP of sila[1]ferrocenophanes that has been applied for the preparation of block copolymers to give cylindrical micelles in block-selective solvents. The properties of these unusual micelles led to the development of crystallization-driven self-assembly as a new method to prepare well-defined nanomaterial.10,29 We performed a series of experiments by varying the equivalents of nBuLi that were added to a thf solution of 2Ph at ambient temperature. Aliquots taken from the reaction mixtures were inspected by 1H and 31P NMR spectroscopy and mass spectrometry. None of the experiments showed any evidence for an oligomer of polymer formation. In all the experiments with less than one equivalent of nBuLi, NMR spectra clearly showed the presence of the remaining monomer. The use of one equivalent, as shown in Scheme 3, resulted in complete conversion toward the ring-opened product 3Li. Quenching a solution of 3Li with water and analysis of the crude product 3H gave two signals in the 31P NMR spectrum at δ of −35.8 and −36.0 ppm in a 1.0 to 3.3 ratio.30 The 1H NMR spectrum of the same sample showed two sets of signals exhibiting the presence of two asymmetric compounds. Expectedly, the addition of a butyl group gives a mixture of diastereomers with different configurations at phosphorus. From a sulfurized mixture, the main diastereomer

Figure 4. Molecular structure of syn-C2-(2PhS)2 with thermal ellipsoids at the 50% probability level. Hydrogen atoms and solvent molecules (CH2Cl2) are omitted for clarity. For bond lengths (Å) and angles (deg) (Table S2) and other crystallographic data (Table S1) see the Supporting Information.

Figure 5. Related syn isomers of diphospha[1.1]ferrocenophanes I,17i J,20 and syn-C2-(2PhS)2 (this work) with twist and tilt angles (averaged values) as determined by single-crystal X-ray analysis.

groups in α positions (Figure 5). The latter compound was isolated from a thermal ROP of the racemic phospha[1]ferrocenophane trans-E (Chart 1) using the same techniques that led to the new [1.1]FCP syn-C2-(2PhS)2 described here.20 In all three [1.1]FCPs shown in Figure 5, both ferrocene moieties are significantly twisted relative to each, resulting in approximate C2 symmetric species. Whereas the twist angle in these [1.1]FCPs is defined by the intersecting angle between the two least-squares planes of two Cp rings bridged by a PPh moiety, the tilt angle is defined by the planes of two Cp rings of one ferrocene moiety (for measured values see Figure 5).25 In the solid state, the asymmetric syn-C2-(2PhS)2 does not deviate much from the expected C2 symmetry. As the space group P21/c reveals, this [1.1]FCP is formed as a racemate. These results match those from 1H NMR spectroscopy, where a time-averaged C2 symmetric compound was detected in solution (600 MHz in CDCl3). However, the observed peaks are broadened compared to those found for all other isolated [1.1]FCPs (fractions A, B, D, and E). This line-broadening is probably the result of a fluxional behavior of syn-C2-(2PhS)2 and indicates a slow interconversion of the two C2 symmetric enantiomers of the racemate. At a higher temperature, the peaks broaden further and coalesce, but with the available spectrometers and the accessible temperature range, we could not reach conditions for a fast dynamic (500 MHz, toluene-d8, 80 °C). The proton NMR data of the known syn isomer I (Figure 5),17i which is not unsubstituted by iPr groups, reveal that a fast interconversion between both C2 symmetric D

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Organometallics Scheme 3. Anionic Ring-Opening Reaction of 2Ph

Scheme 4. Anionic Ring-Opening Reaction of 2Ph

crystallized and single-crystal X-ray analysis revealed an R configuration at phosphorus (Figure 6).

Similar to that discovered for the [1]FCPs 2R (Scheme 1 and Figure 1), the weaker interaction is a through-space 1H−31P nuclear spin−spin coupling.22,24 The fact that for (R)-3PPh2S the 1H−31P coupling is absent reveals that an electron pair is required to mediate the through-space interaction (Figure 1). In addition, the detection of a through-space coupling with similar coupling constants as those found for the ridged [1]FCPs 2R indicates that both phosphino groups, nBuPhP and Ph2P, of (S)-3PPh2 have predominant conformations where the lone pairs on phosphorus are oriented toward the methine protons. The reactions shown in Scheme 4 are not optimized and were just performed to test if the strained phospha[1]ferrocenophane 2Ph can be converted into a diphosphine with planar and central chirality. Such a sequence of reactions had been used before by ring-opening the [1]FCP APh (Chart 1) with LiPh followed by addition of electrophiles, including Ph2PCl.17a,c,19,31 However, chiral phosphines with planar and P-central chirality had not been prepared by this method before. The ring-opening reaction of 2Ph with nBuLi (Scheme 3) cannot be used for any of the other three [1]FCPs 2R (Scheme 1). Whereas 2iPr and 2tBu do not react with nBuLi at ambient temperature in thf, the new 2CH2SiMe3 reacts to give several products. The problem with the latter species is that it has two electrophilic sites, phosphorus and silicon, and both react with nBu−, leading to a mixture of species. Diphospha[2]ferrocenophanes. In contrast to the large number of known phosphorus-bridged [1]FCPs, only six diphospha[2]ferrocenophanes are known (Chart 2). We wanted to investigate if the planar-chiral ferrocene dibromide 1 (Scheme 1) can serve as a starting material to give enantiopure diphospha[2]ferrocenophanes. If successful, these chiral phosphines might be interesting bulky ligands for

Figure 6. Molecular structure of (R)-3HS with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. For bond lengths (Å) and angles (deg) (Table S3) and other crystallographic data (Table S1) see the Supporting Information.

With respect to the targeted anionic ROP, these results mean that the initiation step works well, but chain growth is not occurring. As the conduction of anionic ROP experiments can be challenging, we tested our technique with the known phospha[1]ferrocenophane APh (Chart 1), which resulted in polymers similar to those reported.6a,b These tests provided the needed certainty that the findings for monomer 2Ph are indeed a reflection of its chemical properties. Can the ring-open reaction of 2Ph be applied for the synthesis of a new chiral phosphine? A preliminary set of experiments was conducted to address this question. First, instead of quenching product 3Li with water, chlorodiphenylphosphine was used (Scheme 3). The resulting diphosphine 3PPh2 was obtained as a mixture of two diastereomers with 31P chemical shifts of −25.2 and −36.2 ppm for the minor species and −24.7 and −37.2 ppm for the major product (Figure S37). After sulfurization the main species (R)-3PPh2S could be separated by PTLC and desulfurized to give the diphosphine (S)-3PPh2 (Scheme 4). One interesting difference between the sulfurized (R)-3PPh2S and its sulfur-free version (S)-3PPh2 was revealed by 1H NMR spectroscopy. For the latter species, each methine proton of the iPr groups results in a septet of doublets at δ 3.13 and 3.21, respectively, with the larger coupling constants of 6.8 Hz (JHH) and the smaller coupling constants of 3.0 and 2.9 Hz (JHP), respectively. Through sulfurization, the smaller coupling constants disappear so that both methine protons in (R)3PPh2S occur as ordinary septets (δ = 3.95 and 4.03 ppm).

Chart 2. Known Diphospha[2]ferrocenophanes

Reference 33. bReference 34. cMnBu and MPh were isolated as Cr(CO) complexes, see refs.32,35 a

E

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Organometallics catalysis. Following the described procedure for the known [2]FCPs MR (Chart 2),32 addition of the dilithio derivative of 1 to a solution of RPCl2 followed by a reductive coupling resulted in the diphospha[2]ferrocenophanes 4R (Scheme 5). Scheme 5. Synthesis of Diphospha[2]ferrocenophanes 4R Figure 8. Definition of distortion angles in [2]FCPs.

(average) = 13.4(2) [10.8], δ = 172.16(2) [170.9], θ (average) = 97.73(7) [96.7], and τ = 36.1(2) [32.8].32 In the first step of the synthesis of the [2]FCPs 4R (Scheme 5), 1,1′-disubstituted ferrocenes are formed. NMR spectra taken from aliquots of reaction mixtures revealed that a mixture of several isomers formed for the silaneopentyl derivative, whereas predominantly one diastereomer formed for the iPr2N-substituted compound. The latter fact was evident from the 31P NMR spectrum of the reaction mixture that showed mainly one singlet at δ of 123.3 ppm. In order to characterize the isomer formed in the case of the iPr2N substitution, we isolated the product from the reaction mixture. As isolation of a pure product by chromatography or crystallization was not successful, vacuum sublimation (p ≈ 10−2 mbar, T ≈ 136 °C) was attempted and gave an almost pure product, however, in a yield of 31%. The unexpected low yield is probably due to the high temperature that is needed, which triggered unwanted chemical reactions of the targeted species. Single-crystal X-ray analysis of the isolated 1,1′bis[chloro(diisopropylamino)phosphino]ferrocene 5NiPr2 uncovered S configurations at both phosphorus atoms (Figure 9). As depicted in Chart 3, this isomer is one of three possible diastereomers. We believe that steric requirements play the main role for the selectivity in this reaction. In the isolated (S,S)-5NiPr2, the iPr2N group, as the bulkiest group, is positioned away from iron and away from the iPr group in α position. At the same time, steric interactions between chlorine, as the second largest substituent at phosphorus,

Deduced by 1H NMR spectroscopy, both compounds are C2 symmetric in solution. Single crystals for the silaneopentylsubstituted [2]FCP revealed R configurations for both phosphorus atoms (Figure 7; (R,R)-4CH2SiMe3). From the

Figure 7. Molecular structure of (R,R)-4CH2SiMe3 with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. For bond lengths (Å) and angles (deg) (Table S4) and other crystallographic data (Table S1) see the Supporting Information.

three feasible diastereomers, the isolated one has both silaneopentyl groups trans to each other and to the isopropyl groups on the adjacent Cp rings. It seems likely to assume that the preference of the (R,R)-isomer is caused by minimization of steric interactions between all alkyl groups. As the NiPr2 groups are bulkier than the CH2SiMe3 groups, we have no doubts that for 4NiPr2 the respective all trans isomer was isolated, namely the (S,S)-4NiPr2 species. The structure of (R,R)-4CH2SiMe3 can be best compared to that of the known (tBuP)2-bridged [2]FCP (Chart 2).32 The P−P bond length of 2.2402(8) Å of (R,R)-4CH2SiMe3 is slightly shorter than that of MtBu (P−P = 2.2502(8) Å).32 Both compounds exhibit a similar set of distortion angles (Figure 8) as the following comparison illustrates (values (deg) for the known compound MtBu in brackets): α = 12.2(1) [13.6], β

Figure 9. Molecular structure of (S,S)-5NiPr2 with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. For bond lengths (Å) and angles (deg) (Table S5) and other crystallographic data (Table S1) see the Supporting Information. F

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Organometallics Chart 3. Diastereomers of 5NiPr2

We discovered that the initiation occurs readily but chain growth is not happening. The failure of polymerization is most likely caused by the steric shielding of the lithiated carbon site by the adjacent isopropyl group (see 3Li in Scheme 3) so that it cannot act as a nucleophile to ring-open the monomer 2Ph. We could demonstrate that the ring-opening reaction, which gives a mixture of diastereomers that differ in the central chirality at phosphorus, can be used to prepare a diphosphine [(S)-3PPh2; Scheme 4]. This chiral compound exhibits planar as well as central chirality. Starting with the enantiopure ferrocene dibromide 1 (Scheme 1), the new diphospha[2]ferrocenophanes (R,R)4CH2SiMe3 and (S,S)-4NiPr2 were prepared (Scheme 5). It seems that the particular configuration found at phosphorus was dictated by steric requirements as in both cases all trans isomers formed. Both diphospha[2]ferrocenophanes turned out to be unsuitable for thermal ROP.

and iPr groups at Cp rings are avoided. An R configuration at phosphorus will lead to an increased steric repulsion; hence, the isolated species is the thermodynamically most stable species among the three possible diastereomers (Chart 3). A salt-metathesis reaction, like the first step of Scheme 5, should be kinetically controlled, and it is fair to assume that steric interactions as discussed for the ground-state geometries of the possible diastereomers of 5NiPr2 are reflected in the respective transition states. That means, we assume that this kinetically controlled reaction leads to the thermodynamically most stable product as the rate-determining transitions states are closely related to the ground states. In NMR samples of the sublimed product (S,S)-5NiPr2, two small signals were present in the 31P NMR spectrum (δ = 123.1 and 131.2 ppm; Figure S13). In the respective 1H NMR spectrum similarly small signals adjacent to the main signals were found (Figure S11). The signal patterns of the minor species indicates the presence of an asymmetric isomer, which must be the (S,R)-5NiPr2 isomer (Chart 3). The thermal stabilities of both [2]FCPs 4R (R = CH2SiMe3, NiPr2) were investigated by DSC measurements (< 300 °C), but exothermic peaks were not observed. In order to ensure that chemical change is indeed not occurring under these conditions, (R,R)-4CH2SiMe3 was heated for 6 h at 300 °C in a flame-sealed NMR tube. After this thermal treatment, new signals were not detected by 1H and 31P NMR spectroscopy, revealing that this [2]FCP is thermally robust under these conditions. One can assume that the same holds true for the iPr2N-substituted species.

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EXPERIMENTAL SECTION

General Methods. If not mentioned otherwise, all syntheses were carried out using standard Schlenk and glovebox techniques. Solvents were dried using an MBraun Solvent Purification System and stored under nitrogen over 3 Å molecular sieves. All solvents for NMR spectroscopy were prepared by pump−freeze−thaw cycles and stored under nitrogen over 3 Å molecular sieves. Unless otherwise noted, temperatures refer to that of the bath (e.g., dry ice/acetone bath for −78 °C). Flash chromatography was performed with neutral aluminum oxide and silica gel 60, respectively; mixed solvent eluents or other solvent mixtures are reported as vol/vol solutions. Characterization Methods. 1H, 13C, and 31P NMR spectra were recorded on a 500 MHz Bruker ADVANCE, 500 MHz Bruker ADVANCE III HD, and 600 MHz Bruker ADVANCE III HD NMR spectrometers at 25 °C in C6D6 and CDCl3, respectively. 1H chemical shifts were referenced to the residual protons of the deuterated solvent [δ = 7.15 (C6D6), 7.26 (CDCl3) ppm]. 13C chemical shifts were referenced to the C6D6 signal (δ = 128.00 ppm) and the CDCl3 signal (δ = 77.00 ppm). 31P NMR chemical shifts were reported relative to the external reference of 85% H3PO4 in D2O. The following abbreviations are used to described NMR signals: s (singlet), d (doublet), t (triplet), pst (pseudo triplet), sept (septet), m (multiplet), br (broad), and unres (unresolved). Many Cp protons appear as slightly broadened singlets, whereas others either appear as triplets or as unresolved triplets. Because of limited digital resolutions in NMR spectra, reported coupling constants obtained from 13C NMR spectra are rounded to integer values in Hz; those obtained from 1H NMR spectra are associated with an error; the digital resolution in 1H NMR spectra is either 0.2 [2CH2SiMe3, (S,S)-5NiPr2] or 0.3 Hz. Assignments for all compounds were supported by additional NMR experiments (DEPT, HMQC, COSY). High-resolution mass data were obtained with a JEOL AccuTOF GCv 4G instrument using field desorption ionization (FDI). Elemental analyses were performed on a PerkinElmer 2400 CHN Elemental Analyzer. DSC analyses were performed on a TA Instruments Q20 at a heating rate of 10 °C/min. Samples, sealed in hermetic aluminum pans, were tared using a balance with a repeatability of 0.1 mg (AB204-S Mettler Toledo). For each run, around 2−3 mg of a sample was measured. The known melting enthalpy of a sample of indium was used to check on the calibration of the DSC instrument. DSC data were analyzed with the TA Instruments Universal Analysis 2000 software (see Figures S45− S48 in the Supporting Information). For controlled addition of solutions of some phosphorus reagents, a syringe pump was used (SAGE Instruments, model 355). GPC was performed with a Viscotek 350 HT-GPC system (Malvern) that was used at low temperature (column temperature of 45 °C; thf; flow rate = 1.0 mL min−1). The instrument was equipped with the following Viscotek components: autosampler (model 430 Vortex), degasser (model 7510), two pumps (model 1122), 7° and 90° light scattering detectors, refractometer, and viscometer. GPC columns cover the

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CONCLUSIONS The thermal ROP of the enantiopure phospha[1]ferrocenophane 2Ph led to a mixture of polymers and cyclic oligomers (2Ph)n (n = 2−6). From the oligomeric fraction of the mixture, five different diphospha[1.1]ferrocenophanes were isolated and characterized by 1H NMR spectroscopy and mass spectrometry. One of the dimers could be characterized by single-crystal X-ray analysis (syn-C2-(2PhS)2; Figure 4), which uncovered a 1:1 ratio between Sp- and Rp-configured Cp rings. That means that the dimer formation involves inversion of configuration from Sp to Rp, revealing that Fe−Cp bonds ruptured and reformed on the opposite face of the Cp ring. These results support the recent findings that ROP of phospha[1]ferrocenophanes occurs through breakage of Fe− Cp bonds.20 One aim of investigating the thermal ROP of enantiopure phospha[1]ferrocenophanes was to obtain chiral polymers so that their applicability as multidentate ligands for catalysis could be explored. With respect to this aim the uncovered mechanism is bad news as the isolated linear polymer (2Ph)n (Mw = 19 kDa) must be achiral. In view of this, anionic ROP of 2Ph with the common initiator nBuLi was attempted as only P−Cp bonds will break in such a polymerization so that the planar chirality will not be altered. G

DOI: 10.1021/acs.organomet.9b00114 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics range of Mw of 500−10 000 000 g mol−1 (three main columns: Plgel 10 μM MIXED-B LS 300 × 7.5 mm; one guard column: 10 μM GUARD 50 × 7.5 mm; Agilent Technologies). The samples were dissolved in thf and filtered through 0.45 μm syringe polytetrafluoroethylene (PTFE) filters before GPC analysis. Reagents. The compounds (S p ,S p )-1,1′-dibromo-2,2′-di(isopropyl)ferrocene (1),21 (Me3SiCH2)PCl2,8a (iPr2N)PCl2,36 and 2R (R = Ph, iPr, tBu)22 were synthesized according to literature procedures. Aluminum oxide (Brockmann I, activated neutral standard grade, 58 Å pore size), nBuLi (2.5 M in hexanes), nBuLi (1.6 M in hexanes), methyl trifluoromethanesulfonate (98%), tris(dimethylamino)phosphine (97%), and 1,2-dibromoethane (99%) were purchased from Sigma-Aldrich; PhPCl2 (Alfa Aesar; 98%) and Mg turnings (99.8%) were purchased from VWR; silica gel 60 (EMD, Geduran, particle size 0.040−0.063 mm) was purchased from EMD. Synthesis of Phospha[1]ferrocenophane 2CH2SiMe3. Species 1 (1.19 g, 2.79 mmol) was dissolved in a solvent mixture (27.8 mL of hexanes/thf, 9/1) and cooled to 0 °C. A solution of nBuLi (2.5 M in hexanes, 2.4 mL, 6.0 mmol) was added dropwise and the reaction was stirred at this temperature for 30 min. After the reaction mixture was warmed to 50 °C, a solution of (Me3SiCH2)PCl2 (0.527 g, 2.79 mmol) in hexanes (15.0 mL) was added dropwise via a syringe pump within 10 min. After additional 5 min, the 50 °C warm oil bath was removed. During these 15 min of addition the color of the reaction mixture had changed from orange to red along with the formation of a white precipitate. After the reaction mixture was stirred at rt for additional 10 min, all solids were removed by flash column chromatography under N2 flow (hexanes/Et3N, 95/5; neutral Al2O3), and the dark red fraction was collected. The product was further purified by vacuum sublimation at 80 °C. Crystallization in hexanes at −80 °C gave the product 1 in form of dark red crystals (0.531 g, 50%). 1H NMR (C6D6, 500.1 MHz): δ 0.23 [s, 9H, Si(CH3)3], 1.11 [d, JHH = 6.8 Hz, 3H, CH(CH3)2], 1.16 [d, JHH = 6.9 Hz, 3H, CH(CH3)2], 1.28 [d, JHH = 6.8 Hz, 6H, CH(CH3)2], 1.36 (d/d, JHH = 13.4 Hz/JHP = 1.3 Hz, 1H, PCH2)], 1.92 (d, JHH = 13.5 Hz, 1H, PCH2), 3.10 [sept, JHH = 6.8 Hz, 1H, CH(CH3)2], 3.43 [sept/d, JHH = 6.8 Hz/JHP = 3.2 Hz, 1H, CH(CH3)2], 3.96 (pst, unres, 1H, Cp), 4.04 (s, br, 1H, Cp), 4.18 (s, br, 1H, Cp), 4.22 (s, br, 1H, Cp), 4.25 (pst, 1H, Cp), 4.41 (pst, br, 1H, Cp). 13C{1H} NMR (C6D6, 125.8 MHz): δ −0.1 [d, JPC = 6 Hz, Si(CH3)3], 10.7 [d, JPC = 33 Hz, PCH2Si(CH3)3], 19.6 [d, JPC = 49 Hz, ipso-CpP], 20.4 [d, JPC = 67 Hz, ipso-CpP], 21.3 [s, CH(CH3)2], 21.5 [s, CH(CH3)2], 27.2 [d, JPC = 11 Hz, CH(CH3)2], 27.4 [s, CH(CH3)2], 27.8 [s, CH(CH3)2], 28.6 [s, CH(CH3)2], 73.7 [d, JPC = 3 Hz, Cp], 74.1 [d, JPC = 2 Hz, Cp], 74.7 [d, JPC = 11 Hz, Cp], 76.0 (s, Cp), 81.4 [d, JPC = 8 Hz, Cp], 83.4 [d, JPC = 40 Hz, Cp], 104.7 [d, JPC = 25 Hz, ipso-CpiPr], 106.7 [d, JPC = 10 Hz, ipso-CpiPr]. 31P{1H} NMR (C6D6, 202.5 MHz): δ −4.2. HRMS (FDI; m/z): calcd for 12 C201H3156Fe31P28Si, 386.1282; found, 386.1281. Anal. Calcd for C20H31FePSi (386.128): C, 62.17; H, 8.09%. Found: C, 62.04; H, 8.03%. Thermal ROP of 2Ph. A flame-sealed NMR tube charged with 2Ph (90.3 mg, 0.240 mmol) was heated to 300 °C for 2 h. After letting the sample cool down to rt, the tube with its solidified reaction mixture was brought to a glovebox and the tube content was dissolved in thf. From this point on, the manipulation was done on the bench under N2 flow with the support of Schlenk techniques. After stirring for 15 min under N2 flow, the thf solution was filtered through a 0.2 μm syringe PTFE filter into a Schlenk flask filled with absolute MeOH (10 mL) and stirred vigorously, which resulted in a light-yellow precipitate and an orange-colored supernatant. Removal of all the volatiles from the solution resulted in an orange powder (46.1 mg, 51%), which was used to separate cyclic species (see below). The yellow solid was washed with absolute MeOH (3 × 5 mL) and dried under high vacuum. The resultant yellow solid was dissolved in thf (1.0 mL) and then precipitated again into absolute MeOH (10.0 mL). The light-yellow solid was washed with absolute MeOH several times until the MeOH solution was colorless. All the volatiles were removed under high vacuum to give polymer (2Ph)n as a light yellow powder

(40.1 mg, 44%). 1H NMR (C6D6, 600 MHz): δ 0.80−1.30 [12H, CH(CH3)2], 1.74 [1H, CH(CH3)2], 3.01 [1H, CH(CH3)2], 4.06− 4.47 (6H, Cp), 7.06 (2H, Ph), 7.67−7.54 (3H, Ph). 13C{1H} NMR (C6D6, 150.9 MHz): δ 25.9−23.1 [CH(CH3)2], 76.2−70.0 (CH of Cp and ipso-CP), 101.4 (ipso-CiPr), 128.6 (CH of Ph), 133.6 (CH of Ph), 135.9 (CH of Ph), 140.8−138.33 (CH of Ph). 31P{1H} NMR (C6D6, 243 MHz): δ −24 to −49 (several broad peaks; see Figure S16 in the Supporting Information). Sulfurization of (2Ph)n to (2PhS)n. Polymer (2Ph)n (40.1 mg) was dissolved in CH2Cl2 (3 mL) and allowed to react with an excess amount of S8 (30 mg) for 12 h. From this point on, the manipulation was done under air. The CH2Cl2 solution was then precipitated into hexanes (10 mL) to afford a light yellow solid and a pale orange supernatant. The yellow solid was washed with hexanes (3 × 5 mL) and all the volatiles were removed. The resultant product was dissolved in a minimum amount of CH2Cl2, then precipitated again into hexanes (4 mL), and washed with hexanes (3 × 4 mL) until the supernatant was colorless. The solvent was removed and the product was dried under high vacuum for 12 h, which resulted in (2PhS)n as a yellow powder (32.5 mg, 81% for the sulfurization step; 36% relative to monomer 2Ph). 1H NMR (C6D6, 500 MHz): δ 1.62−0.83 [CH(CH3)2], 2.81 [CH(CH3)2], 3.66 [CH(CH3)2], 4.70−3.96 (CH of Cp), 7.40 (Ph). 13C{1H} NMR (C6D6, 150.9 MHz): δ 26.5−24.7 [CH(CH3)2 and CH(CH3)2], 75.1−72.8 (CH of Cp and ipso-CP), 103.5−100.8 (ipso-CiPr), 127.6 (CH of Ph), 132.7−131.4 (CH of Ph), 135.6 (CH of Ph). 31P{1H} NMR (C6D6, 500.1 MHz): δ 38.2, 38.8, 40.6, 41.6, 42.0. GPC: Mw = 19 kDa, D̵ = 1.3. Isolation of Cyclic Phosphine Sulfides. The orange powder (46.1 mg, 51%) obtained from the supernatant of the thermal ROP of 2Ph was dissolved in CH2Cl2 (2 mL) and allowed to react with an excess amount of sulfur (34.5 mg) for 12 h. From this point on, the manipulation was done under air. The CH2Cl2 solution was precipitated into hexanes (5 mL) to afford a light orange solid (trace amount) and an orange supernatant. After separation, all volatiles were removed from the orange supernatant and the resultant orange solid was dried under high vacuum (62.6 mg) (Figure S20). The obtained solid was divided into two portions and PTLC was performed using two glass plates [20 × 20 cm, precoated (0.25 mm) with silica gel 60 F254]. A solvent mixture of hexanes/CH2Cl2 (1/1) was applied as an eluent, followed by a hexanes/CH2Cl2 mixture in a ratio of 2:1. Materials were detected by visualization under an ultraviolet lamp (λ = 254 nm). The corresponding strips were scraped off, extracted with CH2Cl2 (3 × 10 mL), and organic phases filtered through a fine-fritted funnel. Overall, five fractions (strips) were obtained and named as fractions A, B, C, D, and E; fraction A was closest to the solvent front and E was closest to the starting line. From each fraction approximately 3−4 mg was obtained. Only from fraction C was a suitable crystal for X-ray structural analysis obtained (from CH2Cl2 at 0 °C; see Figure 4). NMR data for the five fractions are given in the Supporting Information (see Figures S21−S30). Fraction A. 1H NMR (CDCl3, 600 MHz): δ −0.16 [d, JHH = 6.5 Hz, 3H, CH(CH3)2], −0.03 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 0.70 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 0.73 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.25 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.30 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.34 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.71 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 2.47 [sept, JHH = 6.6 Hz, 1H, CH(CH3)2], 3.46 [sept, JHH = 6.8 Hz, 1H, CH(CH3)2], 3.73 [sept, JHH = 6.8 Hz, 1H, CH(CH3)2], 4.20 [sept, JHH = 6.7 Hz, 1H, CH(CH3)2], 4.29 (br, 1H, Cp), 4.39 (br, 1H, Cp), 4.43 (br, 1H, Cp), 4.48 (br, 1H, Cp), 4.62 (br, 2H, Cp), 4.73 (br, 1H, Cp), 5.03 (br, 1H, Cp), 5.09 (br, 1H, Cp), 5.74 (br, 1H, Cp), 6.22 (br, 1H, Cp), 6.47 (br, 1H, Cp), 7.18−7.15 (m, 2H, Ph), 7.23−7.21 (m, 4H, Ph), 7.38− 7.34 (m, 2H, Ph), 7.84−7.80 (m, 2H, Ph). 31P{1H} NMR (CDCl3, 202.5 MHz): δ 36.2 (s), 41.9 (s). Fraction B. 1H NMR (CDCl3, 600 MHz): δ −0.21 [d, JHH = 7.0 Hz, 6H, CH(CH3)2], 0.79[d, JHH = 7.0 Hz, 6H, CH(CH3)2], 1.39 [d, JHH = 7.0 Hz, 6H, CH(CH3)2], 1.59 [d, JHH = 7.0 Hz, 6H, CH(CH3)2], 2.27 [sept, JHH = 6.6 Hz, 2H, CH(CH3)2], 3.61 [sept, JHH = 6.7 Hz, 2H, CH(CH3)2], 4.29 (br, 2H, Cp), 4.47 (br, 2H, Cp), 4.69 (br, 2H, Cp), 5.03 (br, 2H, Cp), 5.80 (br, 2H, Cp), 5.94 (br, 2H, H

DOI: 10.1021/acs.organomet.9b00114 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

point on, the manipulation was done under air. After addition of 0.1 mL of saturated aq. NaHCO3, all volatiles were removed under high vacuum. Hexanes (2 mL) were added and the cloudy orange solution was filtered through a PTFE syringe filter (0.45 μm) to give a clear orange solution. After removal of solvents under high vacuum, column chromatography (neutral Al2O3; hexanes/EtOAc, 20/1, plus 5% Et3N) gave 3PPh2 as the first orange fraction. Removal of all volatiles under high vacuum at rt gave 51 mg (69%) of 3PPh2 [31P{1H} NMR (C6D6, 202 MHz): δ −24.7 (s), −37.2 (s) (major); −25.2 (s), −36.2 (s) (minor)]. To a solution of 3PPh2 (50 mg, 0.081 mmol) in dry CH2Cl2 (2 mL) an excess amount of elemental sulfur (15 mg) was added, and the reaction mixture was stirred for 12 h under nitrogen. The reaction mixture was passed through a PTFE syringe filter (0.45 μm), the solvent was removed under high vacuum, which resulted in the diastereomeric mixture of 3PPh2S as an orange solid (58 mg, 70%) [31P{1H} NMR (C6D6, 202 MHz): δ 41.6 (s), 39.8 (s) (major); 39.9 (s), 39.2 (s) (minor)]. The obtained mixture was divided into two portions and PTLC was performed on glass plates [20 × 20 cm; precoated (0.25 mm) with silica gel 60 F254; hexanes/ethyl acetate (5/ 1)]. Materials were detected by visualization under an ultraviolet lamp (λ = 254 nm). The corresponding strips were scraped off, extracted with CH2Cl2 (3 × 10 mL), and the organic phases were filtered through a fine-fritted funnel. One of the strips resulted in (R)-3PPh2S as an orange solid (24 mg, 42%). 1H NMR (C6D6, 500.1): δ 0.63 (t, JHH = 7.0 Hz, 3H, nBu), 0.73 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.13− 1.05 (m, 3H, nBu), 1.19 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.34 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.44 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.90−1.81 (m, 1H, PCH2), 2.15−2.03 (m, 2H, nBu), 3.35 (s, br, 1H, Cp), 3.59 (s, br, 1H, Cp), 3.95 [sept, JHP = 6.8 Hz, 1H, CH(CH3)2], 4.03 [sept, JHH = 6.8 Hz, 1H, CH(CH3)2], 4.46 (s, br, 1H, Cp), 4.46 (s, br, 1H, Cp), 4.57 (s, br, 1H, Cp), 5.35 (s, br, 1H, Cp), 5.59 (s, br, 1H, Cp), 6.85−6.81 (m, 2H, Ph), 6.88−6.93 (m, 7H, Ph), 7.80−7.73 (m, 6H, Ph). 13C{1H} NMR (C6D6, 125.8 MHz): δ 13.6 (s, CH3-nBu), 23.5 [s, CH(CH3)2], 23.8 (s, CH2-nBu), 24.0 [s, CH(CH3)2], 25.3 [br, 2 × CH(CH3)2], 25.4 (s, CH2-nBu), 25.9 [s, CH(CH3)2], 27.2 [s, CH(CH3)2], 35.8 (d, JPC = 59.0 Hz, CH2-nBu), 72.8 (s, Cp), 72.9 (s, br, Cp), 73.0 (s, Cp), 73.1 (s, Cp), 73.2 (s, Cp), 73.6 (d, JPC = 9.6 Hz, Cp), 74.4 (s, Cp), 74.5 (s, Cp), 73.9 (d, JPC = 93.0 Hz, ipso-CpP), 75.3 (d, JPC = 85.0 Hz, ipso-CpP), 103.3 (d, JPC = 12.6 Hz, ipso-CpiPr), 103.5 (d, JPC = 12.6 Hz, ipso-CpiPr), 131.1−131.0 (m, Ph), 131.8 (d, JPC = 9.7 Hz, Ph), 131.7 (d, JPC = 10.0 Hz, Ph), 132.3−132.1 (m, Ph), 134.1 (d, JPC = 85.0 Hz, ipso-Ph), 136.2 (d, JPC = 86.0 Hz, ipso-Ph). 31P{1H} NMR (C6D6, 202.5 MHz): δ 39.6, 41.6 (s). Desulfurization of (R)-3PPh2S to (S)-3PPh2. This preparation is based on a published procedure.17i,l To a solution of (R)-3PPh2S (24 mg, 0.035 mmol) in CH2Cl2 (3 mL), F3CSO3Me (11.5 μL, 0.0992 mmol) was added; the resulting reaction mixture was stirred at rt for 1.5 h, followed by removal of all volatiles under vacuum. To a solution of the crude in CH2Cl2 (2.5 mL), P(NMe2)3 (18.5 μL, 0.0992 mmol) was added, and the reaction mixture was stirred at rt for 1.5 h. During that time, the color of the solution turned from orange to yellow. All volatiles were removed under high vacuum to leave a yellow solid (20 mg) behind. PTLC was carried out on glass plates [20 × 20 cm; precoated (0.25 mm) with silica gel 60 F254; hexanes/ethyl acetate (10/1)]. Materials were detected by visualization under an ultraviolet lamp (λ = 254 nm). The corresponding strip was scraped off, extracted with CH2Cl2 (3 × 10 mL), and the organic phase was filtered through a fine-fritted funnel. After removal of solvents in vacuum, the product (S)-3PPh2 was obtained as a yellow solid (15 mg, 69%). Note that ca. 3% of (R)-3PPh2 was present in the isolated 15 mg (see Figure S44). 1H NMR (C6D6, 500.1 MHz): δ 0.70 (t, JHH = 7.0 Hz, 3H, PCH2CH2CH2CH3), 0.92 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.22 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.27−1.19 (m, 2H, PCH2CH2CH2), 1.35−1.29 (m, 2H, PCH2CH2), 1.35 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.45 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.63− 1.70 (m, 1H, PCH2), 1.91−1.96 (m, 1H, PCH2), 2.95 (s, br, 1H, Cp), 3.13 [sept/d, JHH = 6.8 Hz/JPH = 3.0 Hz, 1H, CH(CH3)2], 3.21 [sept/d, JHH = 6.8 Hz/JPH = 2.9 Hz, 1H, CH(CH3)2], 3.33 (s, br, 1H, Cp), 4.18 (s, br, 1H, Cp), 4.23 (m, br, 1H, Cp), 4.47 (pst, unres, 1H,

Cp), 7.19−7.16 (m, 4H, Ph), 7.24−7.23 (m, 2H, Ph), 7.38−7.35 (m, 4H, Ph). 31P{1H} NMR (CDCl3, 202.5 MHz): δ 41.4 (s). Fraction C (See Figure 4). 1H NMR (CDCl3, 600 MHz): δ 0.04 [d, JHH = 6.0 Hz, 6H, CH(CH3)2], 1.12 [d, JHH = 6.0 Hz, 6H, CH(CH3)2], 1.26 [d, JHH = 6.0 Hz, 6H, CH(CH3)2], 1.45 [d, JHH = 6.0 Hz, 6H, CH(CH3)2], 3.86 [sept, JHH = 6.5 Hz, 2H, CH(CH3)2], 4.29 (br, 2H, Cp), 4.35 (br, 2H, Cp), 4.49 (br, 2H, Cp), 4.72 (br, 2H, Cp), 4.84 [sept, JHH = 6.8 Hz, 2H, CH(CH3)2], 6.05 (br, 2H, Cp), 7.20−7.18 (m, 6H, Ph), 7.71−7.67 (m, 4H, Ph). 31P{1H} NMR (CDCl3, 202.5 MHz): δ 34.0 (s). Fraction D. 1H NMR (CDCl3, 600 MHz): δ 0.29 [d, JHH = 7.0 Hz, 12H, CH(CH3)2], 1.28 [d, JHH = 7.0 Hz, 12H, CH(CH3)2], 3.93 [sept, JHH = 6.7 Hz, 4H, CH(CH3)2], 4.32 (br, 4H, Cp), 4.70 (br, 4H, Cp), 6.16 (br, 4H, Cp), 7.23−7.21 (m, 6H, Ph), 7.80−7.76 (m, 4H, Ph). 31P{1H} NMR (CDCl3, 202.5 MHz): δ 38.3 (s). Fraction E. 1H NMR (CDCl3, 600 MHz): δ 0.17 [d, JHH = 7.0 Hz, 6H, CH(CH3)2], 0.63 [d, JHH = 7.0 Hz, 6H, CH(CH3)2], 1.25−1.28 [m, 12H, CH(CH3)2], 2.77 [sept, JHH = 6.8 Hz, 2H, CH(CH3)2], 3.43 [sept, JHH = 6.7 Hz, 2H, CH(CH3)2], 4.24 (br, 2H, Cp), 4.27− 4.26 (m, 4H, Cp), 4.51 (br, 2H, Cp), 5.35 (br, 2H, Cp), 6.95 (br, 2H, Cp), 7.04 (br, 4H, Ph), 7.16 (br, 4H, Ph), 7.28 (br, 2H, Ph). 31P{1H} NMR (CDCl3, 202.5 MHz): δ 42.6 (s). Anionic Ring-Opening Reaction of 2Ph and Characterization of the Major Isomer in the Form of the Sulfurized Species (R)3HS. To a solution of 2Ph (23.7 mg, 0.0630 mmol) in thf (0.5 mL), nBuLi (1.52 M in hexanes, 41.5 μL, 0.0631 mmol) was added, and the solution was stirred for 45 min. During that time, the color of the solution turned from dark red to orange. The reaction mixture was quenched with a few drops of degassed H2O, and the crude mixture was dissolved in hexanes (8 mL). The solvent was removed under vacuum, resulting in 3H as an orange oil (24.0 mg, 88%) as a 3 to 1 mixture of two diastereomers [Figures S32−S33; 31P{1H} NMR (C6D6, 243 MHz): δ −35.8 (s; minor), −36.0 (s; major); HRMS (FDI; m/z): calcd for 12C261H3556Fe15P, 434.1826 [M+]; found, 434.1825]. To a solution of 3H (23.7 mg) in CH2Cl2 (2.0 mL), an excess amount of S8 (14 mg) was added, followed by stirring for 12 h. Removal of the solvent under high vacuum resulted in product 3HS as an orange solid (26 mg, 88%) in the form of a 3 to 1 mixture of two diastereomers [31P{1H} NMR (C6D6, 202.5 MHz): δ 42.4 (s; major), 39.9 (s; minor)]. From this point on, the manipulation was done under air. The mixture was dissolved in a minimum amount of hexanes and left for crystallization at −10 °C. After approximately 14 days, small amounts of (R)-3HS in the form of orange crystals were isolated and subjected to both NMR spectroscopy and single-crystal X-ray analysis. 1H NMR (C6D6, 500.1 MHz): δ 0.67 [t, JHH = 7.0 Hz, 3H, PCH2CH2CH2CH3], 0.88 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 0.90 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.12−1.17 (m, 1H, PCH2CH2CH2−), 1.25 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 1.30−1.24 (m, 1H, PCH2CH2−), 1.36 [d, JHH = 7.0 Hz, 3H, CH(CH3)2], 2.03− 1.94 (m, 1H, PCH2CH2), 2.10 [sept, JHH = 6.8 Hz, 1H, CH(CH3)2], 2.28−2.23 (m, 2H, PCH2), 3.82 (m, br, 1H, Cp), 3.91 (br, 1H, Cp), 3.94 (m, br, 1H, Cp), 3.99 (m, br, 1H, Cp), 4.08 [sept, JHH = 6.8 Hz, 1H, CH(CH3)2], 4.12 (br, 1H, Cp), 4.41 (m, br, 1H, Cp), 4.43 (m, br, 1H, Cp), 7.11 (m, 2H, Ph), 7.13 (d, 1H, Ph), 8.10−8.06 (m, 2H, Ph). 13C{1H} NMR (C6D6, 150.9 MHz): δ 13.7 (s, CH3-nBu), 23.4 [s, CH(CH3)2], 23.5 [s, CH(CH3)2], 23.8 [s, CH(CH3)2], 24.1 [s, CH2-nBu], 25.6 [br, CH(CH3)2], 25.7 (br, CH2-nBu), 27.3 (s, CH2nBu), 27.5 [s, CH(CH3)2], 36.3 (d, JPC = 58.0 Hz, PCH2), 67.8 (s, Cp), 69.8 (s, Cp), 69.5 (d, JPC = 10.0 Hz, Cp), 69.7 (d, JPC = 10.0 Hz, Cp), 71.0 (s, Cp), 71.2 (s, Cp), 73.1 (d, JPC = 13.0 Hz, Cp), 74.2 (d, JPC = 88.0 Hz, ipso-CpP), 97.6 (s, ipso-CpiPr), 101.67 (d, JPC = 13.0 Hz, ipso-CpiPr), 128.3−128.0 (br, Ph), 131.0 (br, Ph), 132.5 (d, JPC = 9.0 Hz, Ph), 133.0 (s, ipso-Ph). 31P{1H} NMR (C6D6, 202.5 MHz): δ 42.4 (s). Synthesis of the Chiral Diphosphine (R)-3PPh2S. To a solution of 2Ph (45.0 mg, 0.120 mmol) in Et2O (0.5 mL), nBuLi (1.52 M in hexanes, 79.0 μL, 0.120 mmol) was added, and the resulting solution was stirred for 1 h. During that time, the color of the solution turned from dark red to orange. The reaction mixture was quenched with Ph2PCl (25.0 μL, 0.135 mmol), and stirred for 30 min. From this I

DOI: 10.1021/acs.organomet.9b00114 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

After an undissolved white solid was removed by filtration, the solvents were removed under vacuum, which resulted in a reddish oil that was purified by flash column chromatography (hexanes/Et3N, 95/5; neutral Al2O3). The first orange fraction from the column was collected, and the solvents were removed under vacuum. Vacuum sublimation at 135 °C resulted in (S,S)-4NiPr2 in the form of an orange solid (0.065 g, 21%). 1H NMR (C6D6, 500 MHz): δ 1.17 [d, JHH = 6.8 Hz, 6H, CH(CH3)2], 1.23 [d, JHH = 6.6 Hz, 12H, NCH(CH3)2], 1.28 [d, JHH = 6.9 Hz, 6H, CH(CH3)2], 1.30 [d, JHH = 6.6 Hz, 12H, NCH(CH3)2], 3.51 [m, 2H, CH(CH3)2], 3.78 [s, br, 4H, NCH(CH3)2], 3.99 (m, 2H, Cp), 4.27 (pst, 2H, Cp), 4.71 (m, 2H, Cp). 13 C{1H} NMR (C6D6, 150.9 MHz): δ 22.9 [s, CH(CH3)2], 24.4 [s, NCH(CH3)2], 24.8 [s, NCH(CH3)2], 26.0 [t, JPC = 7 Hz, CH(CH3)2], 27.3 [s, CH(CH3)2], 49.3 [s, NCH(CH3)2], 67.5 (m, unres, ipso-CpP), 67.9 (pst, unres, Cp), 73.8 (s, Cp), 77.2 (s, Cp), 105.0 (t, JPC = 18 Hz, ipso-CpiPr). 31P{1H} NMR (C6D6, 202.5 MHz): δ 11.7. HRMS (FDI; m/z): calcd for 12C281H4856Fe14N231P2, 530.2642; found, 530.2657. Anal. Calcd for C 28 H 48 FeN 2 P 2 (530.499): C, 63.39; H, 9.12; N, 5.28%. Found: C, 63.11; H, 9.45; N, 5.20%. Synthesis of (Sp,Sp)-Bis-1,1′-[(S,S)-chloro(diisopropylamino)phosphanyl]-2,2′-bis(isopropyl)ferrocene (S,S)-5NiPr2. To a solution of iPr2NPCl2 (0.378 g, 1.88 mmol) in hexanes (6.00 mL) at 0 °C, the reaction mixture of the Li/Br exchange (1: 0.268 g, 0.626 mmol; hexanes/thf (9/1): 6.0 mL; nBuLi: 0.53 mL, 1.3 mmol; see the procedure for 2CH2SiMe3) was added dropwise within 10 min using a syringe pump. After 5 min, the cold bath was removed, and the color of the reaction mixture had changed to red-orange along with the formation of a white precipitate. After the reaction mixture was stirred at rt for another 15 min, the solids were removed by filtration. After the solvents were removed under vacuum, the product was obtained by vacuum sublimation at ca. 136 °C as a yellow solid (0.115 g, 31%). The resulting solid was dissolved in hexanes and crystallized at −80 °C. The so-obtained crystals were dissolved in hexanes and crystallization −20 °C yielded yellow crystals, which were suitable for single-crystal X-ray analysis. 1H NMR (C6D6, 500 MHz): δ 0.59 [d, JHH = 6.6 Hz, 6H, NCH(CH3)2], 1.05 [d, JHH = 6.6 Hz, 6H, NCH(CH3)2] 1.08 [d, JHH = 6.8 Hz, 6H, CH(CH3)2], 1.22 [d, JHH = 6.5 Hz, 6H, NCH(CH3)2], 1.35 [d, JHH = 6.8 Hz, 6H, CH(CH3)2], 1.47 [d, JHH = 6.7 Hz, 6H, NCH(CH3)2], 2.88 [sept/d, JHH = 6.8 Hz/ JHP = 2.8 Hz, 2H, CH(CH3)2], 3.06 [m, 2H, NCH(CH3)2], 4.03 [m, 2H, NCH(CH3)2], 4.27 (m, 2H, Cp), 4.69 (pst, 2H, Cp), 5.19 (m, 2H, Cp). 13C{1H} NMR (C6D6, 125.8 MHz): δ 21.2 [s, CH(CH3)2], 21.6 [s, CH(CH3)2], 23.7 [s, CH(CH3)2], 25.0 [d, JPC = 24 Hz, CH(CH3)2], 25.8 [s, CH(CH3)2], 26.6 [s, CH(CH3)2], 26.7 [d, JPC = 11 Hz, CH(CH3)2], 46.1 [d, JPC = 23 Hz, NCH(CH3)2], 49.9 [d, JPC = 10 Hz, NCH(CH3)2], 71.8 (d, JPC = 3 Hz, Cp), 72.0 (d, JPC = 6 Hz, Cp), 74.7 (s, Cp), 77.1 (d, JPC = 23 Hz, ipso-CpP), 102.8 (d, JPC = 28 Hz, ipso-CpiPr). 31P{1H} NMR (C6D6, 202.5 MHz): δ 123.3. HRMS (FDI; m/z): calcd for 12C281H4835Cl256Fe14N231P2, 600.2019; found, 600.2034. Anal. Calcd for C28H48Cl2FeN2P2 (601.399): C, 55.92; H, 8.05; N, 4.66%. Found: C, 55.54; H, 8.30; N, 4.46%. Crystal Structure Determination of syn-C2-(2PhS)2, (R)-3HS, (R,R)-4CH2SiMe3, and (S,S)-5NiPr2. Single crystals were coated with Paratone-N oil, mounted using a micromount (MiTeGen−Microtechnologies for Structural Genomics), and frozen in the cold stream of an Oxford Cryojet attached to the diffractometer. Crystal data were collected on a Bruker APEX II diffractometer at −100 °C using monochromated Mo Kα radiation (λ = 0.71073 Å). An initial orientation matrix and cell were determined by ω scans, and the X-ray data were measured using ϕ and ω scans.37 The frames were integrated with the Bruker SAINT software package38 and data reduction was performed with the APEX2 software package.37 A multiscan absorption correction (SADABS) was applied.38 The structures were solved by the intrinsic phasing method implemented with SHELXT and refined using the Bruker SHELXTL software package.39 Nonhydrogen atoms were refined with independent anisotropic displacement parameters. Hydrogen atoms were placed at geometrically idealized positions (riding model) and their displacement parameters were fixed to be 20 or 50% larger than

Cp), 6.97−6.90 (m, 3H, Ph), 7.15−7.04 (m, 6H, Ph), 7.26−7.23 (m, 2H, Ph), 7.57−7.49 (m, 4H, Ph). 13C{1H} NMR (C6D6, 125.8 MHz): δ 13.8 (s, CH3-nBu), 23.1 [s, CH(CH3)2], 23.3 [s, CH(CH3)2], 24.4 (d, JPC = 12.7 Hz, CH2-nBu), 26.5 [s, CH(CH3)2], 26.6 [s, CH(CH3)2], 26.9−27.2 [m, 2 × CH(CH3)2], 29.2 (d, JPC = 16.5 Hz, CH2-nBu), 31.0 (d, JPC = 8.4 Hz, CH2-nBu), 70.2 (d, JPC = 4.5 Hz, Cp), 70.6 (d, JPC = 4.8 Hz, Cp), 71.0 (d, JPC = 3.6 Hz, Cp), 71.2 (d, JPC = 4.6 Hz, Cp), 71.3 (m, Cp), 74.1 (d, JPC = 9.0 Hz, ipso-CpP), 77.4 (d, JPC = 18.0 Hz, ipso-CpP), 103.4 (d, JPC = 26.5 Hz, ipso-CpiPr), 103.4 (d, JPC = 26.5 Hz, ipso-CpiPr), 128.4−128.3 (m, Ph), 129.1 (d, JPC = 19.0 Hz, Ph), 132.8 (d, JPC = 18.0 Hz, Ph), 134.3 (d, JPC = 22.5 Hz, Ph), 135.8 (d, JPC = 22.0 Hz, Ph), 137.6 (d, JPC = 12.0 Hz, ipsoPh), 138.6 (d, JPC = 10.0 Hz, ipso-Ph), 141.4 (d, JPC = 10.0 Hz, ipsoPh). 31P{1H} NMR (C6D6, 202.5 MHz): δ −24.8 (s), −37.2 (s). HRMS (FDI; m/z): calcd for 12C381H4456Fe15P2, 618.2268 [M+]; found, 618.2245. Synthesis of Diphospha[2]ferrocenophane (R,R)-4CH2SiMe3. This preparation is based on a published procedure.32 To a solution of (Me3SiCH2)PCl2 (1.17 g, 6.19 mmol) in hexanes (20.0 mL) at 0 °C, the reaction mixture of the Li/Br exchange (1: 0.868 g, 2.03 mmol; hexanes/thf: 20.0 mL; nBuLi: 1.70 mL, 4.3 mmol; see the procedure for 2CH2SiMe3) was added dropwise within 10 min using a syringe pump. After 5 min, the cold bath was removed and the color of the reaction mixture started to change to red-orange along with formation of a white precipitate. After the reaction mixture was stirred at rt for another 15 min, all the solids were removed by filtration, and the solvents were removed under vacuum. The reaction mixture was dissolved in thf (15.0 mL) and the resulting solution was added dropwise via a cannula to a three-necked flask, which was charged with magnesium turnings (2.20 g, 90.5 mmol) and thf (30.0 mL). After the addition of half of the solution, 1,2-dibromoethane (0.05 mL) was added, followed by the addition of the remaining solution. After the reaction mixture was stirred overnight at rt, thf was removed under vacuum, followed by the addition of hexanes (10 mL). After an undissolved white solid was removed by filtration, the solvents were removed under vacuum, which resulted in a reddish oil that was purified by flash column chromatography (hexanes/Et3N, 95/5; neutral Al2O3). The first orange fraction from the column was collected, and solvents were removed under vacuum. Vacuum sublimation at 100 °C resulted in (R,R)-4CH2SiMe3 in the form of reddish crystals (0.306 g, 30%). These crystals were used for singlecrystal X-ray analysis. 1H NMR (C6D6, 500.1 MHz): δ 0.08 [s, 18H, Si(CH3)3], 1.16 (d/t, JHH = 13.7 Hz/JHP = 3.8 Hz, 2H, PCH2), 1.19 [d, JHH = 6.8 Hz, 6H, CH(CH3)2], 1.44 [d, JHH = 6.9 Hz, 6H, CH(CH3)2], 1.88 (d/t, JHH = 13.7 Hz/JHP = 6.1 Hz, 2H, PCH2), 3.67 (s, br, 2H, Cp), 3.79 [sept/tr (unres), JHH = 6.8 Hz, 2H, CH(CH3)2], 4.31 (pst, 2H, Cp), 4.94 (m, 2H, Cp). 13C{1H} NMR (C6D6, 125.8 MHz): δ 0.07 [m, Si(CH3)3], 18.2 [d, JPC = 2 Hz, PCH2Si(CH3)3], 22.5 [s, CH(CH3)2], 27.1 [t, JPC ≈ 5 Hz, CH(CH3)2], 27.2 [s, CH(CH3)2], 66.1 (t, JPC = 2 Hz, Cp), 72.1 (t, JPC = 14 Hz, ipso-CpP), 72.9 (s, Cp), 77.6 (s, Cp), 105.4 (t, JPC = 14 Hz, ipso-CpiPr). 31P{1H} NMR (C6D6, 202.5 MHz): δ 2.0. HRMS (FDI; m/z): calcd for 12 C241H4256Fe31P228Si2, 504.1650; found, 504.1643. Anal. Calcd for C24H42FeP2Si2 (504.563): C, 57.13; H, 8.39%. Found: C, 57.36; H, 8.58%. Synthesis of Diphospha[2]ferrocenophane (S,S)-4NiPr2. This preparation is based on a published procedure.32 To a solution of iPr2NPCl2 (0.357 g, 1.77 mmol) in hexanes (5.0 mL) at 0 °C, the reaction mixture of the Li/Br exchange (1: 0.248 g, 0.579 mmol; hexanes/thf: 5.0 mL; nBuLi: 0.49 mL, 1.2 mmol; see procedure for 2CH2SiMe3) was added dropwise within 10 min using a syringe pump. After 5 min, the cold bath was removed and the color of the reaction mixture had changed to red-orange along with the formation of a white precipitate. After all the solids were removed by filtration, the solvents were removed under vacuum. The reaction mixture was dissolved in thf (8.00 mL) and the resulting solution was added dropwise via a cannula to a three-necked flask, which was charged with magnesium turnings (1.13 g, 46.4 mmol) and thf (10.0 mL). After the reaction mixture was stirred overnight at rt, thf was removed under vacuum, followed by extraction with hexanes (8.0 × 3 mL). J

DOI: 10.1021/acs.organomet.9b00114 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics those of the attached nonhydrogen atoms. Crystallographic data are summarized in Table S1, whereas bond lengths and bond angles are shown in Table S2−S5 (Supporting Information). Crystallographic data were submitted to the Cambridge Crystallographic Data Centre [syn-C2-(2PhS)2 (CCDC 1875632), (R)-3HS (CCDC 1875633), (R,R)-4CH2SiMe3 (CCDC 1875631), (S,S)-5NiPr2 (CCDC 1875630)]. The ellipsoid plots were prepared using ORTEP-3 for Windows.40 The common set of distortion angles for (R,R)-4CH2SiMe3 was calculated using the program PLATON.41 The estimated standard deviations (esds) of all distortion angles that involve centroids of Cp rings (β, δ, and τ) might be somewhat smaller than they should be, as esds on centroids were not included in the calculation.

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(4) Withers, H. P.; Seyferth, D.; Fellmann, J. D.; Garrou, P. E.; Martin, S. Phosphorus- and Arsenic-bridged [1]Ferrocenophanes. 2. Synthesis of Poly((1,1′-ferrocenediyl)phenylphosphine) Oligomers and Polymers. Organometallics 1982, 1, 1283−1288. (5) Honeyman, C. H.; Foucher, D. A.; Dahmen, F. Y.; Rulkens, R.; Lough, A. J.; Manners, I. Thermal Ring-Opening Polymerization (ROP) of Strained, Ring-Tilted Phosphorus-Bridged [1]Ferrocenophanes: Synthesis of Poly(ferrocenylphosphines) and Poly(ferrocenylphosphine sulfides). Organometallics 1995, 14, 5503−5512. (6) (a) Honeyman, C. H.; Peckham, T. J.; Massey, J. A.; Manners, I. Living Anionic Polymerization of Phosphorus-Bridged, [1]Ferrocenophanes: Synthesis and Characterization of Poly(ferrocenylphosphine) Homopolymers and Block Copolymers. Chem. Commun. 1996, 2589−2590. (b) Peckham, T. J.; Massey, J. A.; Honeyman, C. H.; Manners, I. Living Anionic Polymerization of Phosphorus-bridged [1]Ferrocenophanes: Synthesis and Characterization of Well-Defined Poly(ferrocenylphosphine) Homopolymers and Block Copolymers. Macromolecules 1999, 32, 2830−2837. (c) Cao, L.; Manners, I.; Winnik, M. A. Synthesis and Self-Assembly of the Organic-Organometallic Diblock Copolymer Poly(isoprene-bferrocenylphenylphosphine): Shell Cross-Linking and Coordination Chemistry of Nanospheres with a Polyferrocene Core. Macromolecules 2001, 34, 3353−3360. (7) (a) Mizuta, T.; Onishi, M.; Miyoshi, K. Photolytic Ring-Opening Polymerization of Phosphorus-Bridged [1]Ferrocenophane Coordinating to an Organometallic Fragment. Organometallics 2000, 19, 5005−5009. (b) Mizuta, T.; Imamura, Y.; Miyoshi, K. Ring-Opening Reaction of Phosphorus-Bridged [1]Ferrocenophane via Ring Slippage from h5- to h1-Cp. J. Am. Chem. Soc. 2003, 125, 2068−2069. (8) (a) Patra, S. K.; Whittell, G. R.; Nagiah, S.; Ho, C.-L.; Wong, W.Y.; Manners, I. Photocontrolled Living Anionic Polymerization of Phosphorus-Bridged [1]Ferrocenophanes: A Route to Well-Defined Polyferrocenylphosphine (PFP) Homopolymers and Block Copolymers. Chem.Eur. J. 2010, 16, 3240−3250. (b) Bellas, V.; Rehahn, M. Polyferrocenylsilane-Based Polymer Systems. Angew. Chem., Int. Ed. 2007, 46, 5082−5104. (9) (a) Tanabe, M.; Manners, I. Photolytic Living Anionic RingOpening Polymerization (ROP) of Silicon-Bridged [1]Ferrocenophanes via an Iron-Cyclopentadienyl Bond Cleavage Mechanism. J. Am. Chem. Soc. 2004, 126, 11434−11435. (b) Tanabe, M.; Vandermeulen, G. W. M.; Chan, W. Y.; Cyr, P. W.; Vanderark, L.; Rider, D. A.; Manners, I. Photocontrolled living polymerizations. Nat. Mater. 2006, 5, 467−470. (10) Hailes, R. L. N.; Oliver, A. M.; Gwyther, J.; Whittell, G. R.; Manners, I. Polyferrocenylsilanes: Synthesis, Properties, and Applications. Chem. Soc. Rev. 2016, 45, 5358−5407. (11) Butler, I. R.; Cullens, W. R.; Kim, T.-J. Synthesis of Some Isopropylphosphinoferrocenes. Synth. React. Inorg. Met.-Org. Chem. 1985, 15, 109−116. (12) Butler, I. R.; Cullen, W. R.; Einstein, F. W. B.; Rettig, S. J.; Willis, A. J. Synthesis of Some Ring-Substituted [1]Ferrocenophanes and the Structure of Four Representative Examples. Organometallics 1983, 2, 128−135. (13) Cyr, P. W.; Lough, A. J.; Manners, I. (4-tert-Butylphenyl)phospha[1]ferrocenophane. Acta Crystallogr., Sect. E: Struct. Rep. Online 2005, 61, M457−M459. (14) Feyrer, A.; Armbruster, M. K.; Fink, K.; Breher, F. Metal Complexes of a Redox-Active [1]Phosphaferrocenophane: Structures, Electrochemistry and Redox-Induced Catalysis. Chem.Eur. J. 2017, 23, 7402−7408. (15) Brunner, H.; Klankermayer, J.; Zabel, M. Optically active transition-metal complexes. J. Organomet. Chem. 2000, 601, 211−219. (16) Sarbisheh, E. K.; Green, J. C.; Müller, J. Isomerization of an Enantiomerically Pure Phosphorus-Bridged [1]Ferrocenophane. Organometallics 2014, 33, 3508−3513. (17) (a) Seyferth, D.; Withers, H. P. Phosphorus- and ArsenicBridged [1]Ferrocenophanes. 1. Synthesis and Characterization. Organometallics 1982, 1, 1275−1282. (b) Fellmann, J. D.; Garrou,

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.9b00114. Crystal and structural refinement data; bond lengths and angles; overview of possible dimers of type (2PPh)2; NMR spectra; DSC thermograms (2R); GPC trace of (2PhS)n (PDF) Accession Codes

CCDC 1875630−1875633 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

Jens Müller: 0000-0002-8875-2711 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant, J.M.) for support. We thank the Canada Foundation for Innovation (CFI) and the government of Saskatchewan for funding of the X-ray and NMR facilities in the Saskatchewan Structural Sciences Centre (SSSC). We thank Dr. Wei Sun for the collection of single-crystal X-ray data of (R,R)-4CH2SiMe3. We thank Dr. Valerie MacKenzie (DSC) and K. Thoms (CHN analysis and MS) for support and measurements.

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REFERENCES

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