Ferrocenophanes with Nitrogen in Bridging Positions - ACS Publications

Jun 3, 2015 - and Jens Müller*. ,†. †. Department of Chemistry and. ‡. Saskatchewan Structural Sciences Centre, University of Saskatchewan, 110 Scienc...
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[2]Ferrocenophanes with Nitrogen in Bridging Positions Subhayan Dey,† J. Wilson Quail,‡ and Jens Müller*,† †

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

ABSTRACT: Three [2]ferrocenophanes ([2]FCPs) bridged by nitrogen and silicon (7SiMe2) and nitrogen and tin (7SnMe2, 7SntBu2) were synthesized by salt metathesis between a dilithioferrocene derivative, prepared in situ from 1-bromo1′-(trimethylsilylamino)ferrocene (6), and Me 2 SiCl 2 , Me2SnCl2, and tBu2SnCl2, respectively. A multistep synthesis of precursor 6 is described. Only 7SiMe2 and 7SntBu2 could be prepared as analytically pure compounds. The molecular structures of all three [2]FCPs were determined by single-crystal X-ray analysis. Expectedly, the tilting of the Cp ligands in the silicon species 7SiMe2 is larger [α = 15.73(13)°] than in the tin compounds 7SnMe2 [α = 9.36(17) and 9.45(18)°] and 7SntBu2 [α = 10.13(11)°]. Ring-opening polymerizations of 7SiMe2 and 7SntBu2 were attempted using the common methods of thermal, transition-metal-catalyzed, anionic, and photocontrolled ring-opening polymerization, but none of the experiments gave polymeric materials.

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INTRODUCTION During the last two decades or so many strained sandwich compounds had been prepared and their ring-opening polymerizations (ROPs) were investigated.1 This method of polymerization is attractive for the incorporation of metals into polymers because it allows the synthesis of high-molecularweight polymers. This had been shown for the first time in 1992 by employing the Me2Si-bridged [1]ferrocenophane ([1]FCP) (A; Chart 1).2 The largest class of strained sandwich

[2]FCPs with two different bridging elements are comparably rare. The first compound of that type was equipped with sulfur and nitrogen in bridging positions (C; Chart 1).14 In 1983, Wrighton et al. used a metathesis between the dilithio derivative of (Me 5 C 5 )FeCp and SiCl 4 to obtain the carbasila[2]ferrocenophane D (ERx = SiCl2; Chart 1).15 This species was used to functionalize electrode surfaces.15 On the basis of this synthetic method, Manners et al. prepared new unsymmetrically bridged [2]FCPs of type D with a variety of bridging elements (ERx = S,5g,16 SiMe2,16 GeR2,17 SnR2,17 PbPh2,18 PAr,16 ZrCp218). In order to expand the family of accessible monomers for polymerization, we intended to prepare unsymmetrically bridged [2]FCPs. However, the radii of bridging elements should be rather small so that significant amounts of strain can be present. Furthermore, we thought that a diatomic bridging unit with a high polarity should facilitate the initiation of ROP by polar reagents. Finally, the high abundance of nitrogen in the backbone of natural as well as in synthetic polymers led us to prepare [2]FCPs with nitrogen in bridging position. Within this paper, the first results of these investigations are described.

Chart 1. Strained Ferrocenophanes

compounds is that of [n]ferrocenophanes, with silicon-bridged [1]FCPs being the most developed subclass, in particular, with respect to ROP.1a,b,f−h,3 The first dicarba[2]ferrocenophane was described in 1960 (B; Chart 1), which is the first reported strained sandwich compound.4 Since these early investigations of metallocenophanes, many reports on carbon-bridged [2]FCPs were published.5 In addition to these symmetrically carbon-bridged sandwich compounds, heteroatom-bridged [2]FCPs are known for a variety of elements (B,6 Si,7 Ge,7a−c,8 Sn,6g,9 P10). Compared to these ferrocene derivatives, significantly fewer examples are known for ruthenium; that is, [2]ruthenocenophanes are known with carbon,5h,i,k,11 silicon,11a,12 and tin13 in bridging positions. The only [2]osmocenophanes known to date were equipped with either a Si2Me4 or a Sn2tBu4 linkage.13 © XXXX American Chemical Society

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RESULTS AND DISCUSSION We intended to develop a flexible synthetic approach to aza[2]ferrocenophanes (Scheme 1). A key compound for this strategy is the known 1-amino-1′-bromoferrocene, which was prepared before by using O-benzylhydroxylamine as an amination reagent (Scheme 1).19 In the next step, we wanted to first replace one of the two acidic H atoms on nitrogen so that the intended dilithiation could proceed cleanly. Finally, Received: April 22, 2015

A

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Using the literature method for diaminoferrocene,23 1amino-1′-bromoferrocene (5) was converted to the silylated derivative 6 (Scheme 3). Applying 2 equiv of nBuLi, followed by addition of R2ECl2, gave the targeted strained sandwich compounds 7 (Scheme 3). While the silicon species 7SiMe2 was isolated as an analytically pure compound by vacuum sublimation in a yield of 53%, its tin counterpart 7SnMe2 formed with a significantly lower conversion and was obtained by vacuum sublimation as an impure species in an approximate yield of 14%. Increasing the steric bulk around the tin atom through the usage of tBu2SnCl2 for the salt-metathesis reaction improved the yield, and 7SntBu2 could be isolated in 62% yield. Whereas 7SiMe2 and 7SntBu2 were obtained as analytically pure species, compound 7SnMe2 could not be completely separated from impurities. Mass spectrometry for all three species showed the expected mass for the molecular ion supporting the expectation that indeed the targeted molecules were obtained. NMR spectra of the three [2]FCPs exhibited a signal pattern as expected for Cs symmetrical molecules. For example, for all three compounds the Cp range in the 1H NMR spectra exhibit four peaks of equal intensity. Suitable crystals for single-crystal X-ray analysis were obtained for the three [2]FCPs. While Figures 1 and 2 show

Scheme 1. Synthetic Strategy

addition of a variety of element dichlorides should provide access to the targeted nitrogen-bridged [2]FCPs (Scheme 1). However, the synthesis of 1-amino-1′-bromoferrocene, which has been described in the literature with isolated yields of 45− 55%, did not work acceptably well in our laboratory.19 Repeated attempts gave only small amounts of the targeted compound that we could not separate from the obtained reaction mixture. Therefore, we used a common synthetic methodology to add an NH2 group to a ferrocene moiety and prepared 1-amino-1′-bromoferrocene (5) through a multistep synthesis (Scheme 2). As illustrated in Scheme 2, monoScheme 2. Synthesis of 1-Amino-1′-bromoferrocene (5)a

a (a) nBuLi, thf, −78 °C, 30 min; (b) 20 equiv of ClC(O)OEt, −78 °C; (c) 40 equiv of KOH in EtOH:H2O (1:8), reflux, 40 h; (d) 3 equiv of (COCl)2, CH2Cl2, DMF (cat.); (e) 1.5 equiv of NaN3, CH2Cl2, Bu4NBr (cat.); (f) excess of PhCH2OH, 90 °C, 2 h; (g) H2, Pd−C, iPrOH, 2.5 h.

Figure 1. Molecular structure of 7SiMe2 with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and bond angles [deg]: N1−C1 = 1.442(2); N1−Si1 = 1.7484(17); N1−Si2 = 1.7529(17); Si2−C6 = 1.877(2); Si2−C14 = 1.861(2); Si2−C15 = 1.860(2); Si1−N1−C1 = 115.33(13); Si1−N1− Si2 = 129.86(9); C1−N1−Si2 = 114.57(13); N1−Si2−C6 = 105.73(8); N1−Si2−C14 = 111.35(10); N1−Si2−C15 = 111.95(10); C6−Si2−C14 = 108.91(10); C6−Si2−C15 = 109.44(10); C14−Si2−C15 = 109.35(11).

lithiation of 1,1′-dibromoferrocene followed by reaction with ethyl chloroformate gave the ester 1, which was hydrolyzed to give the carboxylic acid 2.20 Following a procedure that was described for the preparation of (Ph5C5)Fe[C5H4(CON3)],21 azide 3 was prepared and thermolyzed in benzyl alcohol. The resulting carbamate 4 finally gave the targeted 1-amino-1′bromoferrocene (5) with 6% of aminoferrocene as an impurity in an overall yield of 32% (Scheme 2).22 It should be noted that each product of the reaction sequence 1 to 5 was isolated with a respective impurity where hydrogen instead of bromine was present. We could not remove these nonbrominated compounds from the targeted species and, therefore, used species 5 contaminated with 6% of aminoferrocene for the next chemical transformations (Scheme 3).

the molecular structures of 7SiMe2 and 7SntBu2, Table S1 lists crystal and structural refinement data. As the molecular structures of the two tin species are very similar, the structure of 7SnMe2 is depicted only in the Supporting Information (Figure S1); however, selected bond lengths and angles are shown in the caption of Figure 2. All three [2]FCPs show nitrogen being trigonal planar coordinated with sums of the surrounding angles between 359° and 360° (see Figures 1 and 2), while the second bridging element is in the center of a distorted tetrahedron [range of tetrahedral angles: 105.73(8)−111.95(10)° (7SiMe2), 98.86(8)− 114.79(12)° (7SnMe2), and 98.24(6)−117.59(8)° (7SntBu2)]. Figure 3 illustrates the common distortion angles in [2]FCPs, whereas in Table 1 the values for these angles for all three species are compiled. As expected, the Cp rings of the siliconbridged species are tilted more strongly (α angle of ca. 16°) than those of the tin-bridged species (α angle of ca. 9−10°; Table 1).

Scheme 3. Synthesis of Aza[2]ferrocenophanesa

(a) CH2Cl2, Me3SiCl, 19 h; (b) thf, −78 °C, 2 equiv of nBuLi; (c) R2ECl2. a

B

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of the three [2]FCPs 7SiMe2, 7SnMe2, and 7SntBu2 are significantly different, with a small β angle for nitrogen between 2.31(16)° and 6.53(18)° and large β angles for silicon or tin between 17.38(15)° and 19.18(17)° (Table 1). From a simple mechanical model these differences make sense as the level arm for nitrogen [N1−C1 between 1.426(3) and 1.442(2) Å] will be significantly shorter than that for silicon [Si2−C6 = 1.877(2) Å] or tin [Sn1−C6 between 2.129(3) and 2.1526(17) Å]. The angle between the bridging bond vector and the plane defined as Cpcentriod−Fe−Cpcentroid is small, with values of τ between 1.9(2)° and 8.09(4)° (Table 1). One would expect that the SiMe3 group at nitrogen prefers a staggered conformation with the two alkyl groups at silicon or tin, hence causing the measured small τ angles. Ring-opening polymerizations of 7SiMe2 and 7SntBu2 were attempted using the common methods of thermal, transitionmetal-catalyzed, anionic, and photocontrolled ROP.1g In short, none of the experiments gave polymeric materials. Heating of 7SiMe2 at 300 °C in a sealed NMR tube for 21 h left the compound unchanged. Species 7SntBu2 did withstand 200 °C, but further heating to 260 °C resulted in a decomposition into elemental tin, (trimethsilylamino)ferrocene, and other unidentified species (Figure S29). Attempts of photocontrolled ROP with 0.10, 0.25 or even 1.0 equiv of NaCp as an initiator did not give any reactions. A similar negative result was obtained for both monomers when transition-metal-catalyzed ROP with Karstedt’s catalyst in C6D6 at 50 °C was attempted. After 65 h respective 1H NMR spectra revealed that chemical reactions did not occur. In order to evaluate if anionic ROP would be possible, ringopening reactions of 7SiMe2 and 7SntBu2 were attempted with 1 equiv of nBuLi. A solution of 7SntBu2 in thf and 1 equiv of nBuLi was quenched with Me3SiCl after 0.5 h at ambient temperature. 1 H NMR spectroscopy on the reaction mixture revealed the presence of compound 8 (Chart 2) as the only product

Figure 2. Molecular structure of 7SntBu2 with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. The tBu group (C18) is disordered; only the main species is shown. Selected bond lengths [Å] and bond angles [deg] (respective values for the two independent molecules of 7SnMe2 are shown in braces): N1−C1 = 1.435(2) {1.432(3)/1.426(3)}; N1−Si1 = 1.7309(15) {1.721(2)/ 1.723(2)}; N1−Sn1 = 2.0775(14) {2.067(2)/2.060(2)}; Sn1−C6 = 2.1526(17) {2.133(2)/2.129(3)}; Sn1−C14 = 2.1937(19) {2.124(3)/ 2.122(3)}; Sn1−C18 = 2.1984(18) {2.129(3)/2.130(3)}; Si1−N1− C1 = 115.56(11) {118.72(16)/117.95(16)}; Si1−N1−Sn1 = 131.94(8) {127.74(11)/128.29(11)}; C1−N1−Sn1 = 112.44(10) {113.23(15)/113.23(15)}; N1−Sn1−C6 = 98.24(6) {98.86(8)/ 99.14(9)}; N1−Sn1−C14 = 109.92(7) {108.91(10)/108.62(10)}; N1−Sn1−C18 = 111.91(7) {108.80(10)/108.78(11)}; C6−Sn1−C14 = 108.81(7) {115.20(11)/112.92(11)}; C6−Sn1−C18 = 108.58(7) {111.71(12)/111.34(12)}; C14−Sn1−C18 = 117.59(8) {112.34(11)/ 114.79(12)}.

Chart 2 Figure 3. Common angles to characterize distortions in [2]FCPs.1b

Table 1. Common Angles [deg] to Characterize [2]FCPs (Figure 3) angle

7SiMe2

7SnMe2 a

7SntBu2

α βb β′c δ τd

15.73(13) 6.53(18) 17.38(15) 168.62(2) 3.31(13)

9.36(17) {9.45(18)} 3.4(2) {3.5(2)} 19.18(17) {19.12(19)} 172.75(2) {172.73(3)} 4.2(2) {1.9(2)}

10.13(11) 2.31(16) 18.52(12) 172.50(2) 8.08(4)

(Figures S30−32). The same result was obtained when the reaction time was extended from 0.5 h to 6 h, revealing that the in situ formed lithio species does not react with thf. The 1H NMR spectrum of species 8 shows four equally intense signals in the Cp region (δ = 3.71, 3.90, 3.98, 4.27 ppm in DCCl3), two singlets (δ = 0.02, 1.23 ppm) with a relative intensity of 18 hydrogen atoms each, and a set of signals assigned to one nBu group (Figure S30). These values compare well with those of the related known species 1,1′-bis(tributylstannyl)ferrocene (E; Chart 2) and the 1,1′-diaminoferrocene derivative F (Chart 2). The Cp signals in the 1H NMR spectra of species E (δ = 3.96, 4.23 ppm in CDCl3)24 and F (δ = 3.66, 3.75, 3.81, 3.83 ppm in CD2Cl2)25 are very similar to the four Cp signals of species 8, so that peaks at δ = 3.98 and 4.27 ppm can be assigned to the stannyl-substituted Cp ring, whereas those at δ = 3.71 and 3.90 ppm can be assigned to the amino-substituted Cp ring. A

a

Values for the second independent molecule of the asymmetric unit are shown in braces. bβ for E = N. cβ′ for E = Si or Sn. dτ is defined as the angle between the least-squares plane Cpcentriod−Fe−Cpcentroid and the bridging bond vector (N−Sn or N−Si).1f

Overall, this is a moderate (7SiMe2) to small (7SnMe2, 7SntBu2) degree of tilting, as a comparison with known [2]FCPs with the following bridging moieties reveals: α = 28.8° [1,1′,2,2′(C2H4)2],5b 23° (NSO2; C in Chart 1),14c 22.6° (CH CH),5c,d 21.6(5)° (C2H4),5e 18.51(14)° (CH2S),5g 18.3(2)° (CH2PMes),16 15.0(4)° and 14.8(3)° (CH2PPh),16 12.82(16)° [B 2 (NMe 2 ) 2 ], 6 c 11.8(1)° (CH 2 SiMe 2 ), 1 6 11.4(7)° (CH 2 PMePh + ), 16 10.99(2)° (CH 2 GeMe 2 ), 17 7.5(1)° (CH2SnMe2),17 4.19(2)° (Si2Me4),7g 3.9° (Ge2Me4),8a 0.7° (Sn2Me4),9a −5.5(2)° (CH2ZrCp2).18 The two β angles in each C

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Organometallics similar reaction was performed with 7SiMe2 when a solution of 7SiMe2 in thf and 1 equiv of nBuLi was quenched with Me3SiCl after 1 h at ambient temperature. 1H NMR spectroscopy on the reaction mixture revealed the presence of the expected compound 9 along with the starting material (Figures S33− 34). The Cp signals in the 1H NMR spectra of species 9 (δ = 3.71, 3.90, 4.04, 4.24 ppm in CDCl3) are so similar to those of 8 (δ = 3.71, 3.90, 3.98, 4.27 ppm in CDCl3) that the peaks at δ = 3.71 and 3.90 can be assigned to the amino-substituted Cp ring, whereas δ = 4.04 and 4.24 ppm can be assigned to the silyl-substituted Cp ring. First attempts to polymerize compounds 7SiMe2 and 7SntBu2 by addition of approximately 0.25 equiv of nBuLi in thf solution at ambient temperature and subsequent quenching with Me3SiCl did not give polymeric material. While the 1H NMR spectrum for the reaction with 7SiMe2 showed only leftover starting compound and the expected ring-opened product 9 (Figure S38), that for the reaction with 7SntBu2 showed starting compound, species 8, and the protonated compound 10 (Figures S35−S37). As the reaction with the silicon species 7SiMe2 using a 1:1 or 1:0.25 ratio did not show a protonated species similar to 10, we wanted to make sure that its formation was not caused by an error in performing the reaction. Therefore, the two reactions with 1.0 and 0.25 equiv of nBuLi with 7SntBu2 were performed simultaneously using the same reagents. Both mixtures were quenched with Me3SiCl after 6 h, and the reaction mixtures analyzed by 1H NMR spectroscopy. Again, while the batch with the 1:1 ratio showed only the ringopened product 8, the substoichiometric amounts of nBuLi resulted in the mixture of 7SntBu2, 8, and 10. In addition to NMR spectroscopy, mass spectrometry was used and confirmed the presence of products 8, 9, and 10 in respective reaction mixtures.

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. 1H and 13C NMR spectra were recorded on a 500 MHz Bruker Avance NMR spectrometer at 25 °C in C6D6 and CDCl3, respectively. 1H chemical shifts were referenced to the residual protons of the deuterated solvents (δ = 7.15 ppm for C6D6 and 7.26 ppm for CDCl3); 13C chemical shifts were referenced to the C6D6 signal at δ = 128.00 ppm and CDCl3 signal at δ = 77.00 ppm. Assignments for 1−6 and 7 were supported by additional NMR experiments (HMQC, COSY) and by applying the published increment method to assign 1H NMR chemical shifts in 1,1′-disubstituted ferrocenes.26 Except for species 8, 9, and 10, mass spectra were measured on a VG 70SE and were reported in the form m/z (rel intens) [M+], where “m/z” is the observed mass. The intensities are reported relative to the most intense peak, and [M+] is the molecular-ion peak or a fragment; only characteristic mass peaks are listed. For the isotopic pattern, only the mass peak of the isotopologue or isotope with the highest natural abundance is listed. Mass data for 8, 9, and 10 were obtained with a JEOL AccuTOF GCv 4G using field desorption (FD) as ionization method. Elemental analyses were performed on a PerkinElmer 2400 CHN elemental analyzer using V2O5 to promote complete combustion. For calculations of molar amounts and yields of compounds 1−6, the amounts of known impurities as determined by 1H NMR spectroscopy (4% impurity for 1−4; 6% impurity for 5 and 6; see SI file) were taken into account, resulting in the following average formula weights: 333.84 (1), 305.78 (2), 330.80 (3), 410.92 (4), 275.21 (5), and 347.39 g/mol (6). Safety Note: As the preparation of species 3 involves the use of NaN3 in CH2Cl2, there is slight risk of the formation of hazardous organic azides. We performed the described preparation of 3 multiple times without any difficulties. Reagents. The compounds (LiC 5 H 4 ) 2 Fe·2/3tmeda 27 and (BrC5H4)2Fe28 were synthesized according to literature procedures. Ferrocene (98%), nBuLi (2.5 M in hexanes), C2Br4H2 (98%), Me2SiCl2 (≥99.5%), and Karstedt’s catalyst (2% Pt, in xylene) were purchased from Sigma-Aldrich; ClCOOEt (97%, Alfa Aesar), (COCl)2 (98%, Alfa Aesar), PhCH2OH (99%, Alfa Aesar), Me3SiCl (≥98%, Alfa Aesar), tBu2SnCl2 (98%, Alfa Aesar), and Me2SnCl2 (99%, Alfa Aesar) were purchased from VWR; N,N,N′,N′-tetramethylethylenediamine (tmeda; 99%, Acros Organics), KOH (pellets), NaN3 (reagent grade), and NEt3 (99%) were purchased from Fisher Scientific; Pd−C (10% on activated carbon, reduced) was purchased from Strem Chemicals. Silica gel 60 (EMD, Geduran, particle size 0.040−0.063 mm) was used for column chromatography. Synthesis of 1-Bromo-1′-(ethoxycarbonyl)ferrocene (1). Employing a known lithiation procedure,19 nBuLi (2.5 M in hexane, 14.6 mL, 36.5 mmol) was added dropwise to a cold (−78 °C) solution of (BrC5H4)2Fe (12.28 g, 35.72 mmol) in thf (100 mL) followed by stirring for 25 min at this temperature. The cold reaction mixture (−78 °C) containing a red precipitate was added dropwise by a cannula to a stirred solution (−78 °C) of ethyl chloroformate (68.0 mL, 711 mmol) in thf (100 mL). The reaction mixture was warmed to rt and stirred for 20 h, followed by the addition of deionized water (100 mL) and Et2O (100 mL). Using a separatory funnel, the aqueous phase was removed and the organic phase was washed with brine (4 × 200 mL) and dried over anhydrous Na2SO4. All the volatiles were removed by a rotary evaporator, resulting in a red oil (11.96 g). The red oil was subjected to column chromatography on silica gel using a mixture of hexanes and CH2Cl2 (1:1 by volume) as eluent. The second red band was collected, and all the volatiles were removed by high vacuum, resulting in 1 as a red oil (8.56 g, 72%), which was used for the next step without further purification. Product 1 contained ca. 4% of [(EtOCO)H4C5](C5H5)Fe as an impurity. 1H NMR (CDCl3): δ 1.35 (t, 3H, Me), 4.12 (s, 2H, CH-β of CpBr), 4.29 (q, 2H, CH2), 4.41 (s, 4H, CH-α of CpBr, CH-β of CpCOOEt), 4.82 (s, 2H, CH-α of CpCOOEt). 13 C NMR (CDCl3): δ 14.51 (Me), 60.26 (CH2), 68.75 (C-β of CpBr), 69.64 (ipso-C-COOEt), 71.59 (C-α of CpBr), 72.23 (C-α of CpCOOEt), 73.63 (CH-β of CpCOOEt), 78.10 (ipso-C-Br), 170.33 (−COO−). MS (70 eV): m/z (%) 336 (100) [M+], 308 (38) [M+ − 2CH2]. HRMS

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SUMMARY AND CONCLUSIONS A new aminobromoferrocene (6) was prepared through a multiple-step synthesis and used for the preparation of the three unsymmetrically bridged [2]FCPs 7SiMe2, 7SnMe2, and 7SntBu2 (Schemes 2 and 3). The strain in these species is expected to be moderate to small, as indicated by measured α angles around 16° for the silicon compound and around 9−10° for the tin species (Table 1). Unfortunately, all attempts to polymerize species 7SiMe2 and 7SntBu2 applying common ROP methodologies did not yield polymers. While the silicon species 7SiMe2 is thermally robust (300 °C), the tin compound 7SntBu2 decomposes at 260 °C. Both strained [1]FCPs react with nBuLi in thf. Using a 1:1 ratio of reagents showed that the tin species 7SntBu2 reacts cleanly by a substitution of the amino by a nBu group at tin. The similar ring-opening reaction for the silicon species 7SiMe2 is sluggish, and after quenching with ClSiMe3, leftover 7SiMe2 was found alongside the ring-opened product 9. The propensity of these [2]FCPs toward ROP was tested with substoichiometric amounts of nBuLi, but no evidence of formation of oligomers or polymers was found. This is not very surprising, as the nucleophilic nBu− group was transformed by the initiation to a sterically encumbered Cp(Me3Si)N− group. Consequently, we are currently replacing the SiMe3 group on nitrogen with less bulky groups in the hopes that this might result in strained aza[2]ferrocenophanes that are polymerizable.

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EXPERIMENTAL SECTION

Syntheses. All silylations, lithiations, and salt-metathesis reactions were carried out using standard Schlenk and glovebox techniques. D

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Article

Organometallics

52.21; H, 3.89; N, 3.38. Anal. Calcd for a mixture of C18H16BrFeNO2 (414.08; 96%) and C18H17FeNO2 (335.18; 4%): C, 52.70; H, 3.94; N, 3.41. Found: C, 52.87; H, 3.61; N, 3.38. Synthesis of 1-Amino-1′-bromoferrocene (5). Employing a known procedure,22 Pd−C (0.99 g) was added to a solution of compound 4 (4.32 g, 10.5 mmol) in dry and deoxygenated iPrOH (160 mL) taken in a Schlenk flask. After the reaction flask was purged with hydrogen by six consecutive cycles of evacuation and refilling, a balloon, filled with hydrogen gas, was placed on the well-stirred reaction mixture for 2.5 h. All the volatiles were removed under high vacuum, and the resulting black solid was suspended in dry Et2O (100 mL). All insoluble materials were filtered off by Schlenk filtration, resulting in a bright yellow solution, which, after removal of all the volatiles, resulted in a yellow crystalline solid. This yellow solid was dissolved in CH2Cl2 (75 mL), and the organic phase was washed by an aqueous NaOH solution (6 M, 5 × 20 mL) and deionized water (20 mL). After drying the organic phase over anhydrous Na2SO4, all volatiles were removed under high vacuum to give a yellow solid, which according to 1H NMR spectroscopy was composed of compound 5 (85%) and aminoferrocene (15%). Some of the aminoferrocene was removed by sublimation (96 h; 38 °C oil bath temperature; p ≈ 10−2 mbar). Further sublimation (24 h; 60 °C oil bath temperature; p ≈ 10−2 mbar) gave product 5 as a yellow, amorphous solid contaminated with ca. 6% of aminoferrocene (2.03 g, 70%). 1H NMR (C6D6): δ 2.08 (bs, 2H, NH2), 3.57 (pst, 2H, CpBr), 3.68 (pst, 2H, CpNH2), 3.71 (pst, 2H, CpNH2), 4.12 (pst, 2H, CpBr). 13C NMR (C6D6): δ 60.02 (C of CpNH2), 65.68 (C of CpNH2), 67.54 (C of CpBr), 71.06 (C of CpBr), 79.86 (ipso-C-Br), 107.89 (ipso-C-NH2). MS (70 eV): m/z (%) 279 (100) [M+], 199 (10) [M+ − HBr]. HRMS (70 eV): calcd for C 10 H 10 BrFeN, 278.9346; found, 278.9357. Anal. Calcd for C10H10BrFeN: C, 42.90; H, 3.60; N, 5.00. Anal. Calcd for a mixture of C10H10BrFeN (279.94; 94%) and C10H11FeN (201.05; 6%): C, 43.91; H, 3.72; N, 5.12. Found: C, 43.74; H, 3.74; N, 5.07. Synthesis of 1-Bromo-1′-(trimethylsilylamino)ferrocene (6). Employing a known procedure,23 compound 5 (0.28 g, 1.0 mmol) was suspended in hexanes (20.0 mL), and NEt3 (1.2 mL, 8.6 mmol) was added, followed by addition of a solution of chlorotrimethylsilane (0.20 mL, 1.6 mmol) in hexanes (4.0 mL). After stirring the solution for 20 h at rt, all the insoluble materials were removed by Schlenk filtration, resulting in a red solution. After removal of all the volatiles under high vacuum, compound 6 was left behind as a red oil (0.32 g, 92%). Product 6 contained ca. 6% of [(Me3SiNH)H4C5](C5H5)Fe as an impurity. 1H NMR (CDCl3): δ 0.23 (s, 9H, SiMe3), 2.42 (bs, 1H, NH), 3.85 (pst, 2H, CH of CpNHSiMe3), 3.88 (pst, 2H, CH of CpNHSiMe3), 3.99 (pst, 2H, CH of CpBr), 4.25 (pst, 2H, CH of CpBr). 13 C NMR (CDCl3): δ 0.18 (SiMe3), 59.64 (C of CpNHSiMe3), 65.24 (C of CpNHSiMe3), 67.62 (C-β of CpBr), 70.87 (C-α of CpBr), 79.07 (ipsoC-Br), 109.34 (ipso-C-NHSiMe3). MS (70 eV): m/z (%) 353 (76) [M+], 273 (16) [M+ − Br]. HRMS (70 eV): calcd for C13H18BrFeNSi, 350.9741; found, 350.9745. Note: Due to technical difficulties in analyzing liquids, an elemental analysis could not be performed for species 6. Synthesis of 2,2-Dimethyl-1-trimethylsilyl-1,2-azasila[2]ferrocenophane, 7SiMe2. nBuLi (0.40 mL, 1.0 mmol) was added dropwise to a −78 °C cooled solution of 6 (0.17 g, 0.49 mmol) in thf (24.0 mL), resulting in a color change from pale yellow to bright orange. After the reaction mixture was stirred for 40 min at −78 °C, the cold bath was replaced by an ice bath, followed by stirring of the reaction mixture at 0 °C for 1 h. The resulting deep red solution was cooled to −78 °C, and a solution of Me2SiCl2 (0.064 g, 0.50 mmol) in thf (5.0 mL) was added dropwise over 5 min. The reaction mixture was warmed to ambient temperature and stirred for 4 h. After all volatiles were removed under high vacuum, the product was dissolved in hexanes (15.0 mL) and LiCl was removed by Schlenk filtration. From this red solution, solvents were removed under high vacuum, resulting in a red, sticky solid. Product 7SiMe2 was obtained by vacuum sublimation (45 °C oil bath temperature; p ≈ 10−2 mbar) in the form of red crystals (0.085 g, 53%). 1H NMR (C6D6): δ 0.07 (s, 9H, Me3Si), 0.43 (s, 6H, Me2Si), 3.80 (pst, 2H, CH of CpNSiMe3), 4.23 (pst, 2H, CH of CpNSiMe3), 4.27 (pst, 2H, CH of CpSiMe2), 4.63 (pst, 2H,

(70 eV): calcd for C13H13BrFeO2, 335.9448; found, 335.9449. Anal. Calcd for C13H13BrFeO2: C, 46.33; H, 3.89. Anal. Calcd for a mixture of C13H13BrFeO2 (336.99; 96%) and C13H14FeO2 (258.10; 4%): C, 46.90; H, 3.95. Found: C, 46.59; H, 3.87. Synthesis of 1-Bromo-1′-carboxyferrocene (2). Employing a known procedure,29 compound 1 (8.56 g, 25.6 mmol) and KOH (55.42 g, 987.8 mmol) were dissolved in a mixture of EtOH (780 mL) and deionized water (80 mL). After the solution was heated under reflux for 40 h, deionized water (100 mL) was added to the reaction mixture at rt. The aqueous phase was washed with CH2Cl2 (4 × 200 mL; discarded) and acidified by concentrated HCl(aq) (60 mL) to give a yellow precipitate, which was extracted by CH2Cl2 (3 × 100 mL). After the CH2Cl2 phase was dried over anhydrous Na2SO4, all volatiles were removed in a rotary evaporator, resulting in product 2 as an orange powder (6.05 g, 77%). Compound 2 contained ca. 4% of [(HO2C)H4C5](C5H5)Fe as an impurity. 1H NMR (CDCl3): δ 4.20 (pst, 2H, CH-β of CpBr), 4.49 (pst, 2H, CH-α of CpBr), 4.51 (pst, 2H, CH-β of CpCOOH), 4.91 (pst, 2H, CH-α of CpCOOH), 11.95 (bs, 1H, COOH). 13C NMR (CDCl3): δ 69.29 (C-β of CpBr), 70.13 (ipso-CCOOH), 71.88 (C-α of CpBr), 72.67 (C-α of CpCOOH), 74.62 (CH-β of CpCOOH), 78.06 (ipso-C-Br), 176.12 (COOH). MS (70 eV): m/z (%) 308 (100) [M+], 165 (57) [M+ − CpBr]. HRMS (70 eV): calcd for C11H9BrFeO2, 307.9135; found, 307.9127. Anal. Calcd for C11H9BrFeO2: C, 42.77; H, 2.94. Anal. Calcd for a mixture of C11H9BrFeO2 (308.94; 96%) and C11H10FeO2 (230.04; 4%): C, 43.36; H, 3.00. Found: C, 43.50; H, 2.89. Synthesis of 1-Azidocarbonyl-1′-bromoferrocene (3). Employing a known procedure,21 (COCl)2 (1.6 mL, 19 mmol) was added dropwise to a solution of 2 (1.82 g, 5.95 mmol) in CH2Cl2 (35 mL), followed by the addition of DMF (four drops). After stirring the solution for 3 h, all the volatiles were removed under high vacuum. To a solution of the so-obtained red solid in CH2Cl2 (35 mL), nBu4NBr (0.015 g, 0.046 mmol) and an aqueous solution of NaN3 (0.575 g, 8.84 mmol in 7.0 mL of deionized water) were added. The biphasic solution was stirred for 16 h at rt, followed by the addition of deionized water (100 mL). The aqueous phase was removed by a separatory funnel, and the organic phase was washed with deionized water (4 × 200 mL) and dried over anhydrous Na2SO4. All volatiles were removed by a rotary evaporator, resulting in compound 3 as a brown powder (1.83 g, 93%). Compound 3 contained ca. 4% of [(N3OC)H4C5](C5H5)Fe as an impurity. 1H NMR (CDCl3): δ 4.19 (pst, 2H, CH-β of CpBr), 4.49 (pst, 2H, CH-α of CpBr), 4.54 (pst, 2H, CH-β of CpCON3), 4.87 (pst, 2H, CH-α of CpCON3). 13C NMR (CDCl3): δ 69.28 (C-β of CpBr), 70.25 (ipso-C-COON3), 72.01 (C-α of CpBr), 72.33 (C-α of CpCON3), 75.07 (CH-β of CpCON3), 78.37 (ipso-C-Br), 175.92 (COON3). MS (70 eV): m/z (%) 333 (13) [M+], 305 (29) [M+ − N2]. HRMS (70 eV): calcd for C11H8BrFeN3O, 332.9200; found, 332.9198. Anal. Calcd for C11H8BrFeN3O: C, 39.56; H, 2.41; N, 12.58. Anal. Calcd for a mixture of C11H8BrFeN3O (333.95; 96%) and C11H9FeN3O (255.06; 4%): C, 40.05; H, 2.46; N, 12.74. Found: C, 39.94; H, 2.20; N, 12.64. Synthesis of Benzyl N-(1′-Bromoferrocen-1-yl)carbamate (4). Employing a known procedure,22 a solution of 3 (3.05 g, 9.22 mmol) in PhCH2OH (15.0 mL) was heated at 90 °C for 2 h, resulting in a color change from burgundy red to yellow. The yellow solution was cooled to rt, and all volatiles were removed under high vacuum. The mixture was further purified by column chromatography on silica gel (hexanes/CH2Cl2/NEt3; 15:83:2 by volume). The product was obtained as a golden yellow crystalline solid (3.35 g, 88%). Compound 4 contained ca. 4% of [{PhCH2O(O)CNH}H4C5](C5H5)Fe as an impurity. 1H NMR (CDCl3): δ 4.04 (s, 2H, CH-β of CpNHCOOBz), 4.09 (s, 2H, CH-β of CpBr), 4.38 (s, 2H, CH-α of CpBr), 4.52 (s, 2H, CH-α of CpNHCOOBz), 5.18 (s, 2H, CH2), 6.00 (bs, 1H), 7.25−7.42 (m, 5H, Ph). 13C NMR (CDCl3): δ 62.77 (CH2), 66.69 (C-β of CpNHCOOBz), 67.02 (ipso-C-NH), 67.93 (C-β of CBr), 69.11 (C-α of CpNHCOOBz), 71.09 (C-α of CpBr), 78.93 (ipso-C-Br), 128.23 (C of Ph), 128.30 (ipso-C of Ph), 128.59 (C of Ph), 136.16 (CO). MS (70 eV): m/z (%) 413 (37) [M+], 335 (2) [M+ − HPh], 278 (26) [M+ − NHCOOCH2Ph]. HRMS (70 eV): calcd for C18H16BrFeNO2, 412.9714; found, 412.9700. Anal. Calcd for C18H16BrFeNO2: C, E

DOI: 10.1021/acs.organomet.5b00340 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics CH of CpSiMe2). 13C NMR (C6D6): δ 0.68 (SiMe3), 2.99 (SiMe2), 67.15 (C of CpNSiMe3), 69.97 (ipso-C-SiMe2), 70.93 (C of CpSiMe2), 72.11 (C of CpNSiMe3), 75.90 (C of CpSiMe2), 101.99 (ipso-C-NSiMe3). MS (70 eV): m/z (%) 329 (100) [M+], 314 (16) [M+ − Me]. HRMS (70 eV; m/z): calcd for C15H23FeNSi2, 329.0718; found, 329.0724. Anal. Calcd for C15H23FeNSi2: C, 54.70; H, 7.04; N, 4.25. Found: C, 55.01; H, 6.73; N, 4.29. Synthesis of 2,2-Dimethyl-1-trimethylsilyl-1,2-azastanna[2]ferrocenophane, 7SnMe2. nBuLi (0.57 mL, 1.4 mmol) was added dropwise to a −78 °C cooled solution of 6 (0.25 g, 0.72 mmol) in thf (36.0 mL), resulting in a color change from pale yellow to bright orange. After the reaction mixture was stirred for 40 min at −78 °C, the cold bath was replaced by an ice bath, followed by stirring of the reaction mixture at 0 °C for 1 h. The resulting deep red solution was cooled to −78 °C, and a solution of Me2SnCl2 (0.15 g, 0.68 mmol) in thf (5.0 mL) was added dropwise over 5 min. The reaction mixture was warmed to ambient temperature and stirred for 4 h. After all volatiles were removed under high vacuum, the product was dissolved in hexanes (15.0 mL) and LiCl was removed by Schlenk filtration. From this red solution, solvents were removed under high vacuum, resulting in a red, sticky solid. Product 7SnMe2 was obtained by vacuum sublimation (120 °C oil bath temperature; p ≈ 10−2 mbar) in the form of red crystals, which sublimed together with a red, sticky oil (0.043 g, approximately 14%). According to 1H NMR data, the isolated mixture was composed of 7SnMe2 (ca. 90%) and 1-trimethylsilylamino-1′(chlorodimethylstannyl)ferrocene (ca. 10%). 1H NMR (C6D6): δ 0.06 (s, 9H, Me3Si), 0.40 (s, 6H, Me2Sn), 3.78 (pst, 2H, CH of CpNSiMe3), 4.23 (pst, 2H, CH of CpNSiMe3), 4.45 (pst, 2H, CH of CpSnMe2), 4.69 (pst, 2H, CH of CpSnMe2). 13C NMR (C6D6): δ −2.04 (SiMe3), 1.32 (SnMe2), 65.38 (C of CpNSiMe3), 70.41 (ipso-C-SnMe2), 70.61 (C of CpSnMe2), 72.85 (C of CpSnMe2), 76.68 (C of CpNSiMe3), 114.21 (ipsoC-NSiMe3). 119Sn NMR (C6D6): δ 83.22. MS (70 eV): m/z (%) 421 (100) [M+], 391 (17) [M+ − 2Me]. HRMS (70 eV; m/z): calcd for C15H23FeNSiSn, 420.9971; found, 420.9973. Synthesis of 2,2-Di-tert-butyl-1-trimethylsilyl-1,2-azastanna[2]ferrocenophane, 7SntBu2. nBuLi (0.48 mL, 1.2 mmol) was added dropwise to a −78 °C cooled solution of 6 (0.20 g, 0.57 mmol) in thf (29.0 mL), resulting in a color change from pale yellow to bright orange. After the reaction mixture was stirred for 40 min at −78 °C, the cold bath was replaced by an ice bath, followed by stirring of the reaction mixture at 0 °C for 1 h. The resulting deep red solution was cooled to −78 °C, and a solution of tBu2SnCl2 (0.17 g, 0.56 mmol) in thf (6.0 mL) was added dropwise over 5 min. The reaction mixture was warmed to ambient temperature and stirred for 4 h. After all volatiles were removed under high vacuum, the product was dissolved in hexanes (20.0 mL) and LiCl was removed by Schlenk filtration. From this red solution, solvents were removed under high vacuum, resulting in a red, sticky solid. Product 7SntBu2 was obtained by vacuum sublimation (95 °C oil bath temperature; p ≈ 10−2 mbar) in the form of red crystals (0.18 g, 62%). 1H NMR (C6D6): δ 0.13 (s, 9H, SiMe3), 1.40 (s, 18H, SntBu2), 3.80 (pst, 2H, CH of CpNHSiMe3), 4.26 (pst, 2H, CH of CpNHSiMe3), 4.36 (pst, 2H, CH of CpSntBu2), 4.69 (pst, 2H, CH of CpSntBu2). 13C NMR (C6D6): δ 1.78 (SiMe3), 31.30 (SntBu2), 34.19 (SntBu2), 65.70 (C of CpNSiMe3), 70.86 (C of CpSntBu2), 70.89 (C of CpNSiMe3), 74.52 (ipso-C-SntBu2), 77.65 (C of CpSntBu2), 113.74 (ipsoC-NSiMe3). 119Sn NMR: δ 44.06 (C6D6); 44.75 (CDCl3). MS (70 eV): m/z (%) 505 (22) [M+], 391 (100) [M+ − 2tBu]. HRMS (70 eV; m/z): calcd for C21H35FeNSiSn, 505.0910; found, 505.0907. Anal. Calcd for C21H35FeNSiSn: C, 50.03; H, 7.00; N, 2.78. Found: C, 49.97; H, 7.22; N, 2.81. Attempted Thermal ROP of Compounds 7SiMe2 and 7SntBu2. In an evacuated and sealed NMR tube, compound 7SntBu2 (0.020 g, 0.040 mmol) was heated at temperatures of 200 °C (for 40 min), while no significant change of viscosity was observed. When the sample was further heated at 260 °C for another 40 min, a black solid resulted. The sealed tube was removed from the oven and cooled to ambient temperature. Inside a glovebox, the sealed tube was opened and C6D6 (0.5 mL) was added. The orange supernant was then decanted from a solid black residue. The 1H NMR spectrum of the supernant showed signals of the starting material (7SntBu2), of (trimethylsilylamino)-

ferrocene, and of unidentified species. Mass spectrometry confirmed the presence of 7SntBu2 and (trimethylsilylamino)ferrocene. The black residue was then dissolved in concentrated HCl, which resulted in evolution of gas. Neutralization by 6 M NaOH(aq) gave a white precipitate, which disolved in an excess amount of NaOH(aq). The precipitate did not change its color after long exposure to air, showing that the black residue did not contain any iron.30 Compound 7SiMe2 (0.020 g, 0.061 mmol) was taken in an evacuated and sealed NMR tube and heated at 200 °C for 40 min, while the compound melted and the vapor started to condense on the inner wall of the NMR tube. No significant change of viscosity was observed even when the compound was further heated at 260 °C (40 min) and 300 °C (21 h). The sealed tube was then cooled to ambient temperature and opened inside a glovebox. The sample completely dissolved in C6D6 (0.5 mL). The NMR spectrum of the resulting solution indicated only the presence of 7SiMe2. Attempted Catalytic ROP of Compounds 7SiMe2 and 7SntBu2. Karstedt’s catalyst (7.0 μL, 0.016 mmol) was added to a solution of 7SntBu2 (0.015 g, 0.030 mmol) in C6D6 (0.5 mL). After 24 h of storage at rt, 1H NMR spectroscopy revealed the presence of only starting reagents. After 65 h at 50 °C, again, only starting materials were detected by 1H NMR spectroscopy. A similar experiment was performed with compound 7SiMe2 when Karstedt’s catalyst (8.0 μL, 0.018 mmol) was added to a solution of 7SiMe2 (0.012 g, 0.036 mmol) in C6D6 (0.5 mL) and the solution was heated to 50 °C for 65 h. The 1 H NMR spectrum of the resulting reaction mixture showed only the peaks of 7SiMe2 and Karstedt’s catalyst. Anionic Ring Opening of Compounds 7SiMe2 and 7SntBu2. nBuLi (1.6 M, 19 μL, 0.030 mmol) was added to a solution of 7SntBu2 (0.014 g, 0.028 mmol) in thf (0.5 mL). After 0.5 h at rt, with shaking of the NMR sample every 5 to 10 min, Me3SiCl (30 μL, 0.24 mmol) was added to the reaction mixture. All volatiles were removed, and the resulting red, sticky oil was dissolved in CDCl3 (0.5 mL). The 1H NMR spectrum of the resulting solution showed [{(Me3Si)2N}H4C5][(nButBu2Sn)H4C5]Fe (8; Chart 2) as the main product (Figures S30−32). 1H NMR (CDCl3): δ 0.22 (s, 9H, SiMe3), 1.23 (s, 18H, SntBu2), 0.96 (t, 3H, CH3), 1.06 (m, 2H, CH2-Sn), 1.44 (m, 2H, CH2), 1.70 (m, 2H, CH2), 3.71 (pst, 2H, CH of CpNHSiMe3), 3.89 (pst, 2H, CH of CpNHSiMe3), 3.98 (pst, 2H, CH of CpSntBu2), 4.27 (pst, 2H, CH of CpSntBu2). 13C NMR (CDCl3): δ 3.47 (SiMe3), 9.58 (CH3), 13.69 (CH2), 27.58 (CH2), 28.19 (CH2), 29.69 (SntBu), 31.54 (SntBu2), 63.65 (C of Cp), 65.34 (C of Cp), 68.75 (ipso-C-SntBu2), 73.17 (C of Cp), 74.83 (C of Cp), 107.90 (ipso-C-N[SiMe3]2). 119Sn NMR (CDCl3): δ −32.16. HRMS (FDI): calcd for C28H53FeNSi2Sn, 635.2088; found, 635.2079. A similar experiment was performed with compound 7SiMe2 when nBuLi (1.6 M, 19 μL, 0.030 mmol) was added to a solution of 7SiMe2 (0.010 g, 0.030 mmol) in thf (0.5 mL). After the solution was left at rt for 1 h, Me3SiCl (30 μL, 0.24 mmol) was added. All the volatiles were removed, and the resulting sticky, red oil was dissolved in CDCl3 (0.5 mL). The 1H NMR and 13C NMR spectra revealed the presence of 7SiMe2 along with [{(Me3Si)2N}H4C5][(nBuMe2Si)H4C5]Fe (9) (Figures S33, S34). A similar reaction mixture was left for 6 h as reaction time and subsequently quenched with an excess amount of Me3SiCl. After removing all the volatiles, 0.5 mL of CDCl3 was added. The 1H and 13C NMR spectra indicated a similar reaction mixture to that found after 1 h. The presence of compound 9 was confirmed by the observed [M+] using mass spectrometry. The complete assignments of 1H and 13C NMR spectra of the reaction mixture are shown in the Supporting Information. HRMS (FDI): calcd for C22H41FeNSi3, 459.1896; found, 459.1884. Attempted Anionic Ring-Opening Polymerization of Compounds 7SiMe2 and 7SntBu2. nBuLi (1.6 M, 7 μL, 0.011 mmol) was added to a solution of 7SntBu2 (0.024 g, 0.048 mmol) in thf (0.85 mL). After 6 h at rt, with occasionally shaking of the NMR sample, Me3SiCl (30 μL, 0.24 mmol) was added to the reaction mixture. All volatiles were removed, and the resulting red, sticky oil was dissolved in CDCl3 (0.5 mL). The 1H NMR spectrum of the resulting solution showed the peaks of 7SntBu2, [{(Me3Si)2N}H4C5][(nButBu2Sn)H4C5]Fe (8), and [{(Me3Si)HN}H4C5][(nButBu2Sn)H4C5]Fe (10) (Figures S35−S37). F

DOI: 10.1021/acs.organomet.5b00340 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

7SiMe2 and 7SntBu2. We thank K. Thoms (CHN analysis and MS) for support and measurements.

The presence of compound 10 was further confirmed by mass spectrometry (MS (FDI): m/z 563 [M+]). A similar experiment was performed with compound 7SiMe2 when nBuLi (1.6 M, 9 μL, 0.014 mmol) was added to a solution of 7SiMe2 (0.020 g, 0.061 mmol) in thf (1.00 mL). After the solution was stored at rt for 6 h, Me3SiCl (30 μL, 0.24 mmol) was added. All the volatiles were removed, and the resulting red, sticky oil was dissolved in CDCl3 (0.5 mL). The 1H NMR spectrum revealed the presence of 7SiMe2 along with [{(Me3Si)2N}H4C5][(nBuMe2Si)H4C5]Fe (9) (Figure S38). Attempted Photocontrolled ROP of Compounds 7SiMe2 and 7SntBu2. A solution of 7SiMe2 (0.025 g, 0.076 mmol) in thf in an NMR tube was treated with (i) 0.10 equiv, (ii) 0.25 equiv, and (iii) 1.0 equiv of Na(C5H5). The three solutions were placed in a 5 °C bath and irradiated for 5 h. All volatiles were removed, and the resulting red, sticky solid was dissolved in C6D6 (0.5 mL). In each case, the 1H NMR spectrum of the resulting solution showed only the peaks of starting reagents. Similar experiments were performed with compound 7SntBu2, which also resulted only in unreacted starting reagents (1H NMR spectroscopy). Crystal Structure Determinations. Single crystals were coated with Paratone-N oil, mounted using a Micromount (MiTeGen, Microtechnologies for Structural Genomics), and frozen in the cold stream of the 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 = 0.710 73 Å). An initial orientation matrix and cell was determined by ω scans, and the X-ray data were measured using ϕ and ω scans.31 The frames were integrated with the Bruker SAINT software package.32 Data reduction was performed with the APEX2 software package.31 A multiscan absorption correction (SADABS) was applied.32 The structures were solved by direct methods (SHELXS-2014) and refined using the Bruker SHELXL-2014 software package.33 For all three compounds non-hydrogen atoms were refined anisotropically; hydrogen atoms were included at geometrically idealized positions but not refined. The isotropic thermal parameters of the hydrogen atoms were fixed at 1.5 or 1.2 times that of the preceding carbon atom. Crystallographic data are summarized in Table S1. Ellipsoid plots were prepared using ORTEP-3 for Windows.34 Special angles for the [2]FCPs shown in Table 1 were calculated using the program PLATON.35

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(1) (a) Russell, A. D.; Musgrave, R. A.; Stoll, L. K.; Choi, P.; Qiu, H.; Manners, I. J. Organomet. Chem. 2015, 784, 24−30. (b) Musgrave, R. A.; Russell, A. D.; Manners, I. Organometallics 2013, 32, 5654−5667. (c) Braunschweig, H.; Kupfer, T. Eur. J. Inorg. Chem. 2012, 1319− 1332. (d) Braunschweig, H.; Kupfer, T. Acc. Chem. Res. 2010, 43, 455−465. (e) Tamm, M. Chem. Commun. 2008, 3089−3100. (f) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew. Chem., Int. Ed. 2007, 46, 5060−5081. (g) Bellas, V.; Rehahn, M. Angew. Chem., Int. Ed. 2007, 46, 5082−5104. (h) Manners, I. Synthetic MetalContaining Polymers; Wiley-VCH: Weinheim, 2004. (i) Braunschweig, H.; Breitling, F. M.; Gullo, E.; Kraft, M. J. Organomet. Chem. 2003, 680, 31−42. (2) Foucher, D. A.; Tang, B.-Z.; Manners, I. J. Am. Chem. Soc. 1992, 114, 6246−6248. (3) Selected recent applications of poly(ferrocenylsilane)s: (a) Zhang, K. H.; Feng, X. L.; Sui, X. F.; Hempenius, M. A.; Vancso, G. J. Angew. Chem., Int. Ed. 2014, 53, 13789−13793. (b) Finnegan, J. R.; Lunn, D. J.; Gould, O. E. C.; Hudson, Z. M.; Whittell, G. R.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2014, 136, 13835−13844. (c) Cumurcu, A.; Feng, X. L.; Dos Ramos, L.; Hempenius, M. A.; Schon, P.; Vancso, G. J. Nanoscale 2014, 6, 12089− 12095. (d) Hudson, Z. M.; Boott, C. E.; Robinson, M. E.; Rupar, P. A.; Winnik, M. A.; Manners, I. Nat. Chem. 2014, 6, 893−898. (e) Cai, C. H.; Lin, J. P. Nat. Chem. 2014, 6, 857−858. (f) Choi, H. K.; Aimon, N. M.; Kim, D. H.; Sun, X. Y.; Gwyther, J.; Manners, I.; Ross, C. A. ACS Nano 2014, 8, 9248−9254. (g) Jia, L.; Zhao, G. Y.; Shi, W. Q.; Coombs, N.; Gourevich, I.; Walker, G. C.; Guerin, G.; Manners, I.; Winnik, M. A. Nat. Commun. 2014, 5, 3882. (h) Feng, X. L.; Sui, X. F.; Hempenius, M. A.; Vancso, G. J. J. Am. Chem. Soc. 2014, 136, 7865− 7868. (i) Sui, X. F.; Shui, L. L.; Cui, J.; Xie, Y. B.; Song, J.; van den Berg, A.; Hempenius, M. A.; Vancso, G. J. Chem. Commun. 2014, 50, 3058−3060. (j) Qiu, H. B.; Du, V.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2013, 135, 17739−17742. (k) Qiu, H.; Cambridge, G.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2013, 135, 12180−12183. (4) Rinehart, K. L.; Frerichs, A. K.; Kittle, P. A.; Westman, L. F.; Gustafson, D. H.; Pruett, R. L.; McMahon, J. E. J. Am. Chem. Soc. 1960, 82, 4111−4112. (5) Selected publications: (a) Nelson, J. M.; Rengel, H.; Manners, I. J. Am. Chem. Soc. 1993, 115, 7035−7036. (b) Hafner, K.; Mink, C.; Lindner, H. J. Angew. Chem., Int. Ed. 1994, 33, 1479−1480. (c) Aggarwal, V. K.; Jones, D.; Turner, M. L.; Adams, H. J. Organomet. Chem. 1996, 524, 263−266. (d) Buretea, M. A.; Tilley, T. D. Organometallics 1997, 16, 1507−1510. (e) Nelson, J. M.; Nguyen, P.; Petersen, R.; Rengel, H.; Macdonald, P. M.; Lough, A. J.; Manners, I.; Raju, N. P.; Greedan, J. E.; Barlow, S.; O’Hare, D. Chem.Eur. J. 1997, 3, 573−584. (f) Brandt, P. F.; Compton, D. L.; Rauchfuss, T. B. Organometallics 1998, 17, 2702−2706. (g) Resendes, R.; Nguyen, P.; Lough, A. J.; Manners, I. Chem. Commun. 1998, 1001−1002. (h) Tanabe, M.; Bourke, S. C.; Herbert, D. E.; Lough, A. L.; Manners, I. Angew. Chem., Int. Ed. 2005, 44, 5886−5890. (i) Herbert, D. E.; Tanabe, M.; Bourke, S. C.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2008, 130, 4166−4176. (j) Herbert, D. E.; Mayer, U. F. J.; Gilroy, J. B.; Lopez-Gómez, M. J.; Lough, A. J.; Charmant, J. P. H.; Manners, I. Chem.Eur. J. 2009, 15, 12234−12246. (k) Herbert, D. E.; Gilroy, J. B.; Staubitz, A.; Haddow, M. F.; Harvey, J. N.; Manners, I. J. Am. Chem. Soc. 2010, 132, 1988−1998. (l) Gilroy, J. B.; Russell, A. D.; Stonor, A. J.; Chabanne, L.; Baljak, S.; Haddow, M. F.; Manners, I. Chem. Sci. 2012, 3, 830−841. (m) Russell, A. D.; Gilroy, J. B.; Manners, I. Chem.Eur. J. 2014, 20, 4077−4085. (6) (a) Herberhold, M.; Dörfler, U.; Wrackmeyer, B. J. Organomet. Chem. 1997, 530, 117−120. (b) Braunschweig, H.; Kupfer, T.; Lutz, M.; Radacki, K.; Seeler, F.; Sigritz, R. Angew. Chem., Int. Ed. 2006, 45, 8048−8051. (c) Braunschweig, H.; Seeler, F.; Sigritz, R. J. Organomet. Chem. 2007, 692, 2354−2356. (d) Braunschweig, H.; Kupfer, T. J. Am. Chem. Soc. 2008, 130, 4242−4243. (e) Braunschweig, H.; Grunewald,

ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data for 7SiMe2, 7SnMe2, and 7SntBu2 in CIF file format; crystallographic data (Table S1); ORTEP plot of 7SnMe2 (Figure S1); NMR spectra (Figures S2−S38). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00340.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

ACKNOWLEDGMENTS

Dedicated to Prof. Peter Paetzold (RWTH Aachen) on the occasion of his 80th birthday. 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. G. Schatte for the initial crystallographic data of species G

DOI: 10.1021/acs.organomet.5b00340 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics B.; Schwab, K.; Sigritz, R. Eur. J. Inorg. Chem. 2009, 4860−4863. (f) Bauer, F.; Braunschweig, H.; Schwab, K. Organometallics 2010, 29, 934−938. (g) Bera, H.; Braunschweig, H.; Oechsner, A.; Seeler, F.; Sigritz, R. J. Organomet. Chem. 2010, 695, 2609−2613. (h) Braunschweig, H.; Damme, A.; Kupfer, T. Eur. J. Inorg. Chem. 2010, 2010, 4423−4426. (i) Bauer, F.; Braunschweig, H.; Gruss, K.; Kupfer, T. Organometallics 2011, 30, 2869−2884. (j) Bauer, F.; Braunschweig, H.; Gruß, K.; Lambert, C.; Pandey, K. K.; Radacki, K.; Reitzenstein, D. Chem.Eur. J. 2011, 17, 5230−5233. (7) (a) Kondo, T.; Yamamoto, K.; Kumada, M. J. Organomet. Chem. 1972, 43, 315−321. (b) Kumada, M.; Kondo, T.; Mimura, K.; Ishikawa, M.; Yamamoto, K.; Ikeda, S.; Kondo, M. J. Organomet. Chem. 1972, 43, 293−305. (c) Kumada, M.; Kondo, T.; Mimura, K.; Yamamoto, K.; Ishikawa, M. J. Organomet. Chem. 1972, 43, 307−314. (d) Jutzi, P.; Krallmann, R.; Wolf, G.; Neumann, B.; Stammler, H. G. Chem. Ber. 1991, 124, 2391−2399. (e) Finckh, W.; Tang, B.-Z.; Lough, A. J.; Manners, I. Organometallics 1992, 11, 2904−2911. (f) Dementev, V. V.; Cervanteslee, F.; Parkanyi, L.; Sharma, H.; Pannell, K. H.; Nguyen, M. T.; Diaz, A. Organometallics 1993, 12, 1983−1987. (g) Finckh, W.; Tang, B.-Z.; Foucher, D. A.; Zamble, D. B.; Ziembinski, R.; Lough, A.; Manners, I. Organometallics 1993, 12, 823−829. (h) Peckham, T. J.; Foucher, D. A.; Lough, A. J.; Manners, I. Can. J. Chem. 1995, 73, 2069−2078. (i) Wrackmeyer, B.; Ayazi, A.; Maisel, H. E.; Herberhold, M. J. Organomet. Chem. 2001, 630, 263− 265. (j) Wang, B.; Mu, B.; Chen, D.; Xu, S.; Zhou, X. Organometallics 2004, 23, 6225−6230. (k) Wagner, H.; Baumgartner, J.; Marschner, C. Organometallics 2007, 26, 1762−1770. (8) (a) Mochida, K.; Shibayama, N.; Goto, M. Chem. Lett. 1998, 339−340. (b) Zürcher, S.; Gramlich, V.; Togni, A. Inorg. Chim. Acta 1999, 291, 355−364. (9) (a) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Angew. Chem., Int. Ed. 1996, 35, 1803−1804. (b) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Angew. Chem., Int. Ed. 1997, 36, 1508− 1510. (c) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. J. Organomet. Chem. 1997, 533, 109−115. (d) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Chem.−Eur. J. 1998, 4, 1027−1032. (e) Herberhold, M.; Steffl, U.; Wrackmeyer, B. J. Organomet. Chem. 1999, 577, 76−81. (f) Ward, J.; Al-Alul, S.; Forbes, M. W.; Burrow, T. E.; Foucher, D. A. Organometallics 2013, 32, 2893−2901. (g) Ward, J.; Al-Alul, S.; Harrypersad, S.; Foucher, D. A. Can. J. Chem. 2014, 92, 525−532. (10) (a) Allcock, H. R.; Lavin, K. D.; Riding, G. H.; Suszko, P. R.; Whittle, R. R. J. Am. Chem. Soc. 1984, 106, 2337−2347. (b) Moser, C.; Belaj, F.; Pietschnig, R. Chem.Eur. J. 2009, 15, 12589−12591. (c) Tanimoto, Y.; Ishizu, Y.; Kubo, K.; Miyoshi, K.; Mizuta, T. J. Organomet. Chem. 2012, 713, 80−88. (11) (a) Herberhold, M.; Bärtl, T. Z. Naturforsch. B 1995, 50, 1692− 1698. (b) Russell, A. D.; Gilroy, J. B.; Lam, K.; Haddow, M. F.; Harvey, J. N.; Geiger, W. E.; Manners, I. Chem.Eur. J. 2012, 18, 8000−8003. (c) Russell, A. D.; Gilroy, J. B.; Lam, K.; Haddow, M. F.; Harvey, J. N.; Geiger, W. E.; Manners, I. Chem.Eur. J. 2014, 20, 16216−16227. (12) Nelson, J. M.; Lough, A. J.; Manners, I. Organometallics 1994, 13, 3703−3710. (13) Braunschweig, H.; Hupp, F.; Kramer, T.; Mager, J. Inorg. Chem. 2013, 52, 9060−9065. (14) (a) Abramovitch, R. A.; Azogu, C. I.; Sutherland, R. G. J. Chem. Soc., Chem. Commun. 1969, 1439−1440. (b) Abramovitch, R. A.; Azogu, C. I.; Sutherland, R. G. Tetrahedron Lett. 1971, 1637−1640. (c) Abramovitch, R. A.; Atwood, J. L.; Good, M. L.; Lampert, B. A. Inorg. Chem. 1975, 14, 3085−3089. (15) Chao, S.; Robbins, J. L.; Wrighton, M. S. J. Am. Chem. Soc. 1983, 105, 181−188. (16) Resendes, R.; Nelson, J. M.; Fischer, A.; Jäkle, F.; Bartole, A.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2001, 123, 2116−2126. (17) Bartole-Scott, A.; Resendes, R.; Jäkle, F.; Lough, A. J.; Manners, I. Organometallics 2004, 23, 6116−6126. (18) Bartole-Scott, A.; Lough, A. J.; Manners, I. Polyhedron 2006, 25, 429−436.

(19) While the authors stated yields of 45−55% in the Results and Discussion section of the publication, a yield of 71% was stated in the Experimental section; see: Butler, I. R.; Quayle, S. C. J. Organomet. Chem. 1998, 552, 63−68. (20) Species 1 and 2 were described before, but were characterized only by 1H NMR spectroscopy and mass spectrometry; see: Lai, L.-L.; Dong, T.-Y. J. Chem. Soc., Chem. Commun. 1994, 2347−2348. (21) Butler, D. C. D.; Richards, C. J. Organometallics 2002, 21, 5433−5436. (22) Bertogg, A.; Camponovo, F.; Togni, A. Eur. J. Inorg. Chem. 2005, 2005, 347−356. (23) Wrackmeyer, B.; Maisel, H. E.; Herberhold, M. J. Organomet. Chem. 2001, 637, 727−732. (24) Guillaneux, D.; Kagan, H. B. J. Org. Chem. 1995, 60, 2502− 2505. (25) Wrackmeyer, B.; Klimkina, E. V.; Milius, W. Inorg. Chem. Commun. 2004, 7, 412−416. (26) Pickett, T. E.; Richards, C. J. Tetrahedron Lett. 1999, 40, 5251− 5254. (27) Butler, I. R.; Cullen, W. R.; Ni, J.; Rettig, S. J. Organometallics 1985, 4, 2196−2201. (28) Shafir, A.; Power, M. P.; Whitener, G. D.; Arnold, J. Organometallics 2000, 19, 3978−3982. (29) Jana, R.; Kumar, M. S.; Singh, N.; Elias, A. J. J. Organomet. Chem. 2008, 693, 3780−3786. (30) Svehla, G. Vogel’s Qualitative Inorganic Analysis, 5th ed.; Longman: New York, 1979; pp 237−241. (31) Bruker. APEX2, 2014.3-0 ed.; Bruker AXS Inc.: Madison, WI, USA, 2014. (32) Bruker. SAINT and SADABS, v8.34a ed.; Bruker AXS Inc.: Madison, WI, USA, 2013. (33) (a) Sheldrick, G. M. SHELXL-2014; University of Göttingen, Germany. (b) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112− 122. (34) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (35) Spek, A. L. PLATON; University of Utrecht: The Netherlands, 2011.

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DOI: 10.1021/acs.organomet.5b00340 Organometallics XXXX, XXX, XXX−XXX