IR Spectra of n-Bu4M (M = Si, Ge, Sn, Pb), n ... - ACS Publications

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IR Spectra of n‑Bu4M (M = Si, Ge, Sn, Pb), n‑BuAuPPh3‑d15, and “n‑Bu” on a Gold Surface Jiří Kaleta,†,‡ Lucie Bednárová,† Martina Č ížková,† Jin Wen,† Eva Kaletová,† and Josef Michl*,†,‡ †

Institute of Organic Chemistry and Biochemistry AS CR, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States

‡

S Supporting Information *

ABSTRACT: Observed and DFT-calculated IR spectra of n-Bu4M (M = Si, Ge, Sn, Pb), (CH3CH2CH213CD2)4Sn, and n-BuAuPPh3-d15 are reported and assigned. The asymmetric CH stretching vibration of the CH2 group adjacent to the metal atom appears as a distinct shoulder at ∼2934 cm−1, whereas for other CH2 groups it is located at ∼2922 cm−1. The characteristic peak at ∼2899 cm−1 is attributed to an overtone of a symmetric CH2 bend at ∼1445 cm−1. In nBuAuPPh3-d15, the CH stretching vibrations of the butyl group are shifted to lower frequencies by ∼10 cm−1, and two possible rationalizations are offered.

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INTRODUCTION In studies of monolayers produced by direct alkylation of gold surfaces with organostannanes1,2 and organomercurials3,4 and of single-molecule electrical conductivity of alkane5 and other6−9 chains attached directly to gold surfaces by treatment with organostannanes, the exact structure and mode of attachment of the organic residue transferred to the gold surface from the organometallic compound under ambient conditions have so far remained unclear, as has the alkylation mechanism. Vibrational spectroscopy is one of the most useful means of characterization of surface-bound species and in conjunction with isotopic labeling with deuterium not only removes ambiguities associated with (undeuteriated) ambient impurities2 but also promises to elucidate the structural details of the attachment. The first carbon of the attached alkyl could indeed be a methylene group attached to one or more surface gold atoms, as is often assumed, ...CH2Aun..., but a loss of one or more hydrogen atoms could also have remained undetected and the structure could be ...CHAun..., ... CAun..., or even ...−(CH)2Aun..., and so on. With suitable deuterium and/or 13C labeling, these possibilities could be distinguished. As a first step in our investigation we decided to take a closer look at the IR spectra of alkyl groups attached to heavier metal atoms in general. Surprisingly little information on the assignment of IR spectra of this type of organometallics is available in the literature.10−12 An example of a question that we are attempting to answer is whether the vibrations of the CH2 group that is adjacent to the metal atom can be distinguished from those of more distant CH2 groups, as has been claimed for alkylsilanes.13,14 We chose n-butyl as a typical alkyl for which many gold surface IR spectra are now available2 © 2017 American Chemical Society

and which is small enough for a detailed analysis. We prepared the organometallics 1−5 (Chart 1) and (CH3CH2CH213CD2)4Sn, [3(13CD2)] (Chart 1), measured their mid-IR spectra, used density functional theory (DFT) to help with band assignments in terms of group vibrations in the 1350−3500 cm−1 region that is most accessible in surface spectroscopy, and compared them with the polarization modulated IR reflection/absorption spectra (PM IRRAS) of butylated gold surfaces.

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RESULTS Synthesis. Compounds 1−4 were prepared from n-BuLi or n-BuMgBr and SiCl4, GeCl4, SnCl4, or Pb(OAc)4 in THF (Scheme 1) and purified by vacuum distillation as colorless liquids. The butylgold derivative 5 was prepared from HAuCl4 Chart 1. Structures of Molecules 1−5

Received: April 10, 2017 Published: May 12, 2017 4619

DOI: 10.1021/acs.jpca.7b03404 J. Phys. Chem. A 2017, 121, 4619−4625

Article

The Journal of Physical Chemistry A Scheme 1. Synthesis of Tetra-n-butyl Derivatives 1−4

by quantitative reduction with PPh3-d15 to white crystalline ClAuPPh3-d15 (6),15 which was then treated with n-BuLi at −40 °C (Scheme 2).16 It is a colorless oil, stable at room temperature for less than an hour in solution and for a few hours neat. It can be stored neat at −30 °C for a few days. Scheme 2. Preparation of the Butylgold Derivative 5 Figure 1. IR spectra of 1−4 and the assignments of CH stretching and bending peaks.

Isotopically labeled compound 3(13CD2) was synthesized from SnCl4 and a Grignard reagent derived from 7 according to Scheme 1 and purified by column chromatography. The iodide 7 was prepared in three steps from nPrBr. Reaction of n-PrBr with magnesium, followed by the addition of 13CD2-labeled paraformaldehyde, gave the butanol 8, which was almost quantitatively converted to 9. Subsequent solvent-free Finkelstein reaction gave 7 in nearly quantitative yield (Scheme 3). Scheme 3. Synthesis of Isotopically Labeled Iodide 7

Figure 2. Comparison of the CH stretching regions in IR spectra of 4 and 5 with PM IRRAS of n-butyls attached to gold surface.2

Spectra and Assignments. The IR spectra of 1−4 and the assignments of their CH stretching and bending peaks are shown in Figure 1. In Figure 2, we compare the CH stretching region in the IR spectra of 4 and 5 with the PM IRRAS of butylated gold surface.2 Figure 3 compares the CH stretching regions in 3 and 3(13CD2). The observed vibrational frequencies and their assignments are collected in Table 1. The DFT computations needed for the assignment were performed with the B3LYP functional, and the results are collected in the Supporting Information (Table S1). The attribution of observed vibrational peaks to calculated frequencies or overtones in the stretching region was straightforward. At lower frequencies in the bending region it became increasingly questionable, and we did not attempt to make assignments below ∼1350 cm−1. In the case of 5, the situation in the lower frequency region was complicated by the presence of vibrations due to the aromatic rings.

Figure 3. Comparison of the CH stretching regions in IR spectra of 3 with 3(13CD2).

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2922 2896

2873 2856

2847 2816 2730 1465 1458 1445 1420 1376

νas(CH2): all CH2 groups 2 × βs(CH2) or βs(CH2) + δas(CH3) νs(CH3) νs(CH2): all CH2 groups

2 × βs(CH2) 2 × δs(CH3) βs(CH2): all CH2 groups δas(CH3) βs(CH2): C2, C3, and C4 βs(CH2): only C1 δs(CH3)

2922 2898

2800 2730 1465 1458 1445 1413 1377

ν (cm−1)b νas(CH3) νas(CH2): C1(s), C2(w), νas(CD2) νas(CH2): all CH2 groups 2 × βs(CH2) or βs(CH2) + δas(CH3) νs(CH3) νs(CH2): all CH2 groups νs(CD2) νs(CH2): C2 2 × βs(CH2) 2 × δs(CH3) βs(CH2): all CH2 groups δas(CH3) βs(CH2): C2, C3, and C4 βs(CH2): only C1 δs(CH3)

assignment

n-Bu4Sn (3 and [3(13CD2)])

2956 [2956] 2934 [absent]c [2174] νas(CH2): all CH2 groups 2922 [2918]c 2 × βs(CH2) or βs(CH2) + 2898 [2897] δas(CH3) νs(CH3) 2872 [2872] νs(CH2): all CH2 groups 2855 [2855] [2092] νs(CH2): C1 and C2 2844 [2845] 2 × βs(CH2) 2813 [absent]c 2 × δs(CH3) 2730 [2730] βs(CH2): all CH2 groups 1465 [1464] δas(CH3) 1457 [1456] βs(CH2): C2, C3, and C4 1443 [1444] βs(CH2): only C1 1418 [absent]c δs(CH3) 1376 [1377]

νas(CH3) νas(CH2): C1 and C3

assignment

n-Bu4Ge (2)

2835 2818 2730 1465 1457 1442 1420 1377

2872 2853

2917 2901

2957 2934

ν (cm−1)

νs(CH2): C2 2 × βs(CH2) 2 × δs(CH3) βs(CH2): all CH2 groups δas(CH3) βs(CH2): C2, C3, and C4 βs(CH2): only C1 δs(CH3)


νas(CH3) νas(CH2): C1

assignment

n-Bu4Pb (4)

2817 2796

2866 2844

2911 2892

2948 2926

ν (cm−1)

νs(CH2): C2 2 × βs(CH2)


νas(CH3)

assignment

n-BuAuPPh3-d15 (5)

2878 2862

2929

2964

ν (cm−1)

νs(CH3) νs(CH2)

νas(CH2)

νas(CH3)

assignment

n-Bu on Au surface2

a C atoms in the butyl group are numbered 1−4 starting at the terminal CH2 group. bValues in brackets refer to 3(13CD2). cIn 3(13CD2) the fundamental at 1418 cm−1 [βs(CH2)] and its overtone at 2813 cm−1 are missing, as is the shoulder at 2934 cm−1 [νas(CH2)], and the νas(CH2) vibration of all CH2 groups is shifted to 2918 cm−1.

2872 2857

2957 2933

ν (cm−1)

νas(CH3) νas(CH2): C1 and C3

assignment

2958 2933

ν (cm−1)

n-Bu4Si (1)

Table 1. IR Spectra of 1−5, 3(13CD2), and Butyl Chains Attached to Au(111) Surfacea

The Journal of Physical Chemistry A Article

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The Journal of Physical Chemistry A

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transitions in excitonic interactions.19 To our knowledge, the latter possibility has not been considered before in vibrational spectroscopy but appears plausible to us. A decision between the two possibilities will require the synthesis and measurements on a large number of suitably designed compounds and lies outside the framework of the present study. In the surface-bound n-butyl group the shift to higher frequencies might simply reflect an increase in the occurrence of gauche defects, but in 1−5 there is no reason to expect the conformations of the butyl groups to be different. Also, the results of calculations shown in Table S1 reproduce the observed shifts, yet all have been performed exclusively for the all-anti geometry.

DISCUSSION Fundamental Vibrations and Spectral Regularities in 1−4. Compounds 1−4 have almost the same vibrational frequencies for both the CH3 and the CH2 groups: νas(CH3) at ∼2960 cm−1, νs(CH3) at ∼2870 cm−1, δas(CH3) at ∼1460 cm−1, and δs(CH3) at ∼1380 cm−1. Except for the νas(CH2) vibration of the methylene group adjacent to the heavy atom, seen as a shoulder at 2934 cm−1, the νas(CH2) stretching vibrations of all CH2 groups in 1−3 appear at the same frequency (2922 cm−1). In compound 4, these vibrations shift to a lower frequency, 2917 cm−1. The symmetric stretching vibrations of all CH2 groups in 1−4 occur at ∼2855 cm−1, and the symmetric bends βs(CH2) occur at 1465 cm−1. Overtone Assignment in 1−4. Three overtone vibrations have been identified in the CH stretching region.13 The most intense one at ∼2900 cm−1 is assigned as 2βs (CH2), but it could also be βs (CH2) + δas (CH3). Its intensity drops as the central atom M becomes heavier and it is not observed in 4. Replacement of one CH2 group by 13CD2 reduces the intensity of this peak in 3(13CD2). The other two overtones, 2βs (CH2) at ∼2800 cm−1 and 2δs (CH3) at 2730 cm−1, are considerably weaker. The former is missing in 3(13CD2), which has no C(1)H2 groups. In our prior work on the butylation of the gold surface,2 we noted the presence of a diagnostic peak at 2900 cm−1 in the spectra of tetraalkylstannanes and its absence in the spectra of the alkylated surfaces but were unsure whether the peak is due to a fundamental vibration of the C(1)H2 group located next to the tin atom or to an overtone. This question has now been settled in favor of the overtone, since we have identified the former as a shoulder at 2934 cm−1 by comparison with calculations and by isotopic labeling. The frequency of the overtone corresponds well to twice the fundamental, but as noted above, an assignment to βs (CH2) + δas (CH3) cannot be excluded. The absence of this shoulder in the spectrum of 3(13CD2) and the shift of the νas(CH2) peak attributed to all CH2 groups from 2922 cm−1 in 3 to 2918 cm−1 in 3(13CD2) support the assignment of the peak at 2900 cm−1 as an overtone. Spectra of 5 and of a Gold Surface-Bound Butyl Group. The CH stretching peaks observed in the spectrum of the n-butylgold derivative 5 (Figure 2) are in a one-to-one correspondence with the peaks of 1−4 (Table 1), but their frequencies are 5−8 cm−1 lower. These shifts are reproduced by the DFT calculations for the anti conformers (Table S1). The relative intensities of the peaks located below about 2800 cm−1 are considerably increased. A much weaker tendency toward similar shifts can also be detected in 4. The intensity distribution in the PM IRRAS reported for gold surface-bound butyl groups (Figure 2)2 resembles the pattern in the IR spectra of 2 or 3 more than that in 5. All clearly observed peaks of the surface-attached butyl groups are shifted by 5−7 cm−1 to higher frequencies relative to 1−4. The origin of the shifts observed for 5 and for surface-bound n-butyl groups is not certain. It occurs even for the vibrations of the relatively remote terminal methyl group and might be due to the electric field of the static dipole associated with the substituent (intramolecular variant17 of the vibrational Stark effect18) or to a through-space coupling of the vibrational transition dipole moments with electronic transition moments on the heavy atom (“vibronic excitonic effect”), analogous to the transition dipole−transition dipole coupling of electronic

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CONCLUSIONS

We believe that the reported IR spectral assignments of n-butyl vibrations will be useful generally and especially for studies of gold surface alkylation with alkylstannanes. Specifically, (i) it has been established that the asymmetric CH stretching vibration of the CH2 group adjacent to the metal atom appears as a distinct shoulder at ∼2934 cm−1, whereas for other CH2 groups it is located at ∼2922 cm−1, and (ii) the characteristic peak at ∼2899 cm−1 present in the stannanes and absent in surface-mounted butyl groups has been attributed to an overtone of a symmetric CH2 bend at ∼1445 cm−1. The observation of frequency shifts in 5 relative to 1−4 suggests that a major study of their origin is called for.

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EXPERIMENTAL SECTION IR Spectroscopy. Room-temperature infrared (IR) spectra were recorded in pellets made with dried KBr (Merck) using a Nicolet 6700FT-IR spectrometer (Thermo Scientific, Waltham, MA) with a standard MIR source, KBr beam splitter, DTGS detector, and dry nitrogen purge, collecting 256 scans in spectral region 3800−400 cm−1 at a spectral resolution 2 cm−1 and using a Happ-Genzel apodization function. Data were processed using OMNIC software. Computations. Calculations used the Gaussian 09 package.20 Geometry and vibrational frequency were computed in the gas phase using DFT with B3LYP functional. Light atoms (C, H, Si, Ge) were described with the 6-31+g(d,p) basis set. Effective core potential (ECP) with LANL2DZ basis set was used for Sn, Pb, and Au. Materials. All reactions were carried out under an argon atmosphere with dry solvents freshly distilled under anhydrous conditions, unless otherwise noted. Standard Schlenk and vacuum line techniques were employed for all manipulations of air- or moisture-sensitive compounds. Yields refer to isolated and chromatographically and spectroscopically homogeneous materials. THF and ether were dried over sodium with benzophenone and distilled under argon prior to use. Benzene was dried over sodium and freshly distilled under argon prior to use. All other reagents were used as supplied unless otherwise stated. NaI was dried for 3 h at 600 mTorr and 120 °C. Procedures. Analytical thin-layer chromatography (TLC) was performed using precoated TLC aluminum sheets (Silica gel 60 F254). TLC spots were visualized using either UV light (254 nm) or a 5% solution of phosphomolybdic acid in ethanol and heat (200 °C) as a developing agent. Melting points are reported uncorrected. IR spectra were recorded in KBr pellets. Chemical shifts in 1H, 2H, 13C, and 31P NMR spectra are reported in ppm on the δ scale relative to CHCl3 (δ = 7.26 4622


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The Journal of Physical Chemistry A ppm for 1H NMR) and CHCl3 (δ = 77.0 ppm for 13C NMR) as internal references. Splitting patterns are assigned s = singlet, d = doublet, t = triplet, m = multiplet, br = broad signal. High-resolution mass spectra (HRMS) using electrospray ionization (ESI) were obtained with a mass analyzer combining linear ion trap and the Orbitrap, and those using chemical ionization (CI) mode were taken with a time-of-flight mass spectrometer. The content of 2H was determined by elemental analysis as 1 H because this method is not able to recognize the difference between 2H and 1H (both are converted to water during the analysis, and its amount is finally determined by the thermal conductometry; 1H2O and 2H2O have the same thermal conductivity). Tetrabutylsilane (1).21 To a solution of n-BuLi in hexane (2.5 M, 24.0 mL, 60 mmol, 4.0 equiv) in THF (30 mL) cooled to −78 °C was added SiCl4 (1.72 mL, 15 mmol, 1.0 equiv) over a period of 20 min. A dense white solid precipitated. Cooling was stopped and the white suspension was stirred at room temperature for an additional 16 h. The reaction mixture was diluted with ether (150 mL) and washed with saturated aqueous NH4Cl (2 × 40 mL), and the clear organic phase was dried over MgSO4. Kugelrohr distillation (130 °C, 600 mTorr) gave 1 as a colorless oil (3.751 g, 14.622 mmol, 97%). 1 H NMR (400 MHz, CDCl3): δ 0.49 (m, 8H), 0.88 (t, J = 7.08 Hz, 12H), 1.25 (m, 8H), 1.31 (m, 8H). 13C NMR (100 MHz, CDCl3): δ 12.2, 13.8, 26.2, 26.9. IR (KBr): 2958, 2922, 2873, 2858, 1465, 1413, 1377, 1341, 1296, 1273, 1196, 1177, 1082, 1051, 1030, 1001, 964, 888, 788, 760, 731, 444 cm−1. MS, m/z (%): 256.3 (3, M), 199.2 (100, M−C4H9), 143.1 (94), 101.1 (20), 87.1 (12), 73.0 (5), 59.0 (9). HRMS, (EI) for (C16H36Si+): calcd 256.2586, found 256.2590. Anal. Calcd for C16H36Si: C, 74.91; H, 14.14. Found: C, 74.94; H, 14.05. Tetrabutylgermane (2).22 A 50 mL two-necked flask equipped with a stir-bar and a gas condenser was charged with magnesium (741 mg, 30.5 mmol), and evacuated and filled with argon three times. Afterward, a grain of iodine and THF (20 mL) were added. The brownish suspension was stirred for 10 min. Then, n-BuBr (3.22 mL, 30.0 mmol) was added dropwise. The grayish reaction mixture was stirred at room temperature for an additional 30 min and then was cooled to 0 °C. Subsequently, GeCl4 (581 μL, 5.00 mmol) was added slowly from a syringe. An exothermic reaction occurred and was followed by the formation of a dense white precipitate. Cooling was stopped and the suspension was stirred at room temperature for an additional 4 h. Subsequently, saturated aqueous NH4Cl (10 mL) was added dropwise, and the reaction mixture was diluted with ether (80 mL), washed with saturated aqueous NH4Cl (2 × 30 mL), and dried over MgSO4. Solvents were removed under reduced pressure, and Kugelrohr distillation (120 °C, 600 mTorr) provided 2 as colorless oil (1.250 g, 4.151 mmol, 83%). 1 H NMR (400 MHz, CDCl3): δ 0.69 (m, 8H), 0.89 (t, J = 7.08 Hz, 12H), 1.32 (m, 16H). 13C NMR (100 MHz, CDCl3): δ 12.5, 13.8, 26.7, 27.5. IR (KBr): 2957, 2924, 2872, 2856, 1465, 1421, 1377, 1341, 1294, 1269, 1173, 1083, 1028, 1002, 964, 884, 717, 696, 644, 556 cm−1. MS, m/z (%): 245.1 (65, center of isotope cluster, M−C4H9), 189.1 (100, center of isotope cluster), 133.0 (42), 103.0 (12), 91.0 (14), 72.9 (5). HRMS, (EI) for (C12H2774Ge+): calcd 245.1324, found 245.1327. Anal. Calcd for C16H36Ge: C, 63.82; H, 12.05. Found: C, 63.83; H, 11.95.

Tetrabutylstannane (3). A previously published procedure23 was adapted as follows: A 150 mL two-necked flask equipped with a stir-bar and a gas condenser was charged with magnesium (1.580 g, 65.00 mmol) and evacuated and filled with argon three times. Afterward, a grain of iodine and ether (40 mL) were added. The brownish suspension was stirred for 10 min. Then, n-BuBr (5.71 mL, 60.0 mmol) was added dropwise. The grayish reaction mixture was stirred at room temperature for an additional 3 h. Solvents were then distilled off under atmospheric pressure at an oil bath temperature of 70 °C. The gray solid was suspended in benzene (20 mL), and a solution of SnCl4 (1.17 mL, 10.000 mmol) in benzene (2 mL) was added slowly from a syringe during a course of 20 min at room temperature. An exothermic reaction was followed by the formation of a dense white precipitate. The suspension was stirred at room temperature for an additional 16 h and then was diluted with ether (150 mL) and washed with water (2 × 40 mL), and clear organic phase was dried over MgSO4. Solvents were removed under reduced pressure, and the distillation under reduced pressure (124 °C, 600 mTorr) provided 3 as colorless oil (3.011 g, 8.673 mmol, 87%). 1 H NMR (400 MHz, CDCl3): δ 0.80 (m, 8H), 0.89 (t, J = 7.28 Hz, 12H), 1.29 (m, 8H), 1.45 (m, 8H). 13C NMR (100 MHz, CDCl3): δ 8.7, 13.7, 27.4, 29.3. IR (KBr): 2957, 2925, 2872, 2854, 1465, 1418, 1376, 1357, 1340, 1292, 1249, 1182, 1150, 1072, 1044, 1021, 1002, 960, 874, 768, 745, 690, 667, 593, 505 cm−1. MS, m/z (%): 291.1 (96, center of isotope cluster, M−C4H9), 235.0 (100, center of isotope cluster), 179.0 (88, center of isotope cluster), 120.9 (38, center of isotope cluster). HRMS, (EI) for (C12H27120Sn+): calcd 291.1135, found 291.1129. Anal. Calcd for C16H36Sn: C, 55.35; H, 10.45. Found: C, 55.40; H, 10.55. Tetra-[1-13C-1,1-2H2]-butylstannane 3(13CD2). 3(13CD2) was synthesized according to conditions described for 3 using iodobutane 7 (300 mg, 1.604 mmol), Mg turnings (44 mg, 1.800 mmol) in THF (5 mL), and then SnCl4 (41 μL, 0.350 mmol) in benzene (5 mL). Column chromatography on silica gel (hexane) gave 3(13CD2) as clear colorless oil (71 mg, 0.198 mmol, 57%). 1 H NMR (400 MHz, CDCl3): δ 0.89 (t, J = 7.31 Hz, 12H), 1.29 (m, 8H), 1.45 (m, 8H). 2H NMR (77 MHz, CDCl3): δ 0.79 (d, J = 19.32 Hz, 2D). 13C NMR (100 MHz, CDCl3): δ 7.9 (q, J = 18.8 Hz), 13.7 (d, J = 3.8 Hz), 27.3, 29.1 (d, J = 33.1 Hz). IR (KBr): 2957, 2920, 2872, 2854, 2174, 2092, 1464, 1457, 1377, 1353, 1333, 1281, 1236, 1125, 1107, 1070, 1040, 972, 952, 914, 861, 795, 767, 734, 714, 657, 576 cm−1. MS, m/z (%): 300.2 (78, center of isotope cluster, M−Bu), 241.1 (86, center of isotope cluster), 182.0 (100, center of isotope cluster), 120.9 (54, center of isotope cluster). HRMS, (EI) for (12C913C31H212H6Sn+): calcd 300.1612, found 300.1617. Anal. Calcd for 12C1213C41H282H8Sn: C, 54.61; H, 10.45. Found: C, 54.33; H, 10.25. Tetrabutylplumbane (4).24 A 50 mL two-necked flask equipped with a stir-bar and a gas condenser was charged with magnesium (741 mg, 30.500 mmol), and apparatus was evacuated and filled with argon three times. A grain of iodine and THF (20 mL) were added. The brownish suspension was stirred for 10 min. Then, n-BuBr (3.22 mL, 30.000 mmol) was added dropwise. The grayish reaction mixture was stirred at room temperature for an additional 30 min and then was cooled to 0 °C. Pb(OAc)4 (2.217 g, 5.000 mmol) was slowly added in portions over next 40 min, while the reaction temperature was kept below 5 °C. The reaction mixture turned 4623


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Complex 6 was obtained as a white crystalline solid (178 mg, 0.349 mmol, 99%). Mp 244.1−245.8 °C (dec.). 2H NMR (77 MHz, CHCl3): δ 7.53−7.57 (m, 15D). 13C NMR (125 MHz, CDCl3): δ 128.5 (d, JC,P = 62.6 Hz), 131.5 (t, JC,D = 24.8 Hz), 128.7 (dt, JC,P = 11.4 Hz, JC,D = 24.8 Hz), 133.7 (dt, JC,P = 14.3 Hz, JC,D = 24.8 Hz). 31P NMR (202 MHz, CDCl3): δ 33.14. IR (KBr): 2287, 2275, 2255, 1622, 1592, 1549, 1533, 1454, 1424, 1346, 1309, 1277, 1209, 1178, 1072, 1055, 1028, 956, 869, 849, 834, 824, 763, 755, 680, 664, 634, 591, 553, 549, 544, 517, 474, 415 cm−1. MS, m/z (%): 532.1 (100, M + Na). HRMS, (ESI) for (C182H15AuClP + Na+): calcd 532.10991, found 532.11004. Anal. Calcd for C182H15AuClP: C, 42.41; H, 3.06. Found: C, 42.68; H, 2.88. 1-Iodo-[1-13C-1,1-2H2]-butane (7). An argon-filled apparatus consisting of a 10 mL reaction flask connected to a gas condenser equipped with a 5 mL receiving flask cooled in acetone/dry ice bath at −78 °C was charged with 9 (750 mg, 3.242 mmol, 1.0 equiv) and anhydrous NaI (583 mg, 3.890 mmol, 1.2 equiv). The white suspension in the distillation flask was stirred for 2.5 h at 100 °C, while the receiving flask was cooled to −78 °C. A dense white precipitate was formed. Subsequent careful distillation under reduced pressure (water aspirator) gave 7 as colorless liquid (571 mg, 3.053 mmol, 94%). 1 H NMR (400 MHz, CDCl3): δ 0.92 (t, J = 7.38 Hz, 3H), 1.42 (m, 2H), 1.79 (m, 2H). 2H NMR (77 MHz, CDCl3): δ 3.20 (d, J = 22.45 Hz, 2D). 13C NMR (100 MHz, CDCl3): δ 6.8 (q, J = 22.9 Hz), 13.0 (d, J = 5.0 Hz), 23.6, 35.2 (d, J = 35.2 Hz). MS, m/z (%): 187.0 (100, M), 158.0 (14), 126.9 (8, I), 60.1 (47, M−I). HRMS, (EI) for (12C313C1H72H2I+): calcd 186.9908, found 186.9909. Anal. Calcd for 12C313C1H72H2I: C, 26.22; H, 5.93. Found: C, 25.91; H, 5.79. [1-13C-1,1-2H2]-Butan-1-ol (8). An argon-filled apparatus consisting of a two-necked flask equipped with a gas condenser was charged with Mg turnings (231 mg, 9.500 mmol), grain of iodine, and ether (15 mL). Then, n-PrBr (818 μL, 9.000 mmol) was added dropwise at room temperature, and the grayish reaction mixture was stirred for 60 min. Subsequently, dry (13CD2O)n (250 mg, 7.569 mmol) was added directly to the reaction mixture, which was stirred for an additional 16 h at room temperature. A saturated aqueous NH4Cl (4 mL) was carefully added to the reaction mixture, organic phase was separated, and water phase was extracted with ether (4 × 10 mL). Combined ethereal phases were dried over MgSO4, and solvent was carefully distilled off at 50 °C and atmospheric pressure. The temperature of the oil bath was then increased to 150 °C, causing distillation of clean butanol 8 as colorless liquid (370 mg, 4.792 mmol, 63%) with a boiling point of 115−118 °C. 1 H NMR (400 MHz, CDCl3): δ 0.92 (t, J = 7.34 Hz, 3H), 1.37 (m, 2H), 1.51 (m, 2H), 1.92 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 13.9 (d, J = 4.5 Hz), 18.8, 34.6 (d, J = 36.9 Hz), 62.0 (q, J = 21.3 Hz). MS, m/z (%): 77.1 (100, M). HRMS, (EI) for (12C313C1H82H2O+): calcd 77.0891, found 77.0883. Anal. Calcd for 12C313C1H82H2O: C, 63.58; H, 13.60. Found: C, 63.20; H, 13.45. [1-13C-1,1-2H2]-Butyl 4-methylbenzenesulfonate (9). A solution of butanol 8 (300 mg, 3.890 mmol) in THF (10 mL) was added dropwise to a suspension of NaH (98 mg, 4.100 mmol) in THF (5 mL) at 0 °C. The white suspension was stirred for 20 min at room temperature. Subsequently, p-TsCl (782 mg, 4.100 mmol) was added and the reaction mixture was

yellow, and a dense gray suspension formed. Cooling was stopped, and the suspension was stirred for 15 min at room temperature. Subsequent careful addition of 1% aqueous HCl (5 mL) resulted in the formation of a dark dense aqueous phase, which was carefully removed by syringe. The clear yellow organic phase was then transferred to a different argonfilled flask containing MgSO4. Solvents were then carefully removed, and Kugelrohr distillation (140 °C, 600 mTorr) yielded 4 as colorless oil (1.881 g, 4.318 mmol, 86%). 1 H NMR (400 MHz, CDCl3): δ 0.90 (t, J = 7.33 Hz, 12H), 1.28 (m, 8H), 1.46 (m, 8H), 1.70 (m, 8H). 13C NMR (100 MHz, CDCl3): δ 13.7, 18.1, 27.7, 31.4. IR (KBr): 2956, 2917, 2871, 2854, 2836, 1464, 1420, 1376, 1356, 1339, 1291, 1269, 1241, 1181, 1155, 1129, 1065, 1040, 1015, 1003, 963, 872, 862, 840, 766, 746, 692, 562, 467, 444 cm−1. MS, m/z (%): 379.1 (79, center of isotope cluster, M−C4H9), 323.0 (25, center of isotope cluster), 265.0 (100, center of isotope cluster), 208.9 (48, center of isotope cluster). HRMS, (EI) for (C12H27208Pb+): calcd 379.1879, found 379.1875. Anal. Calcd for C16H36Pb: C, 44.11; H, 8.33. Found: C, 44.23; H, 8.30. Butyl(triphenylphosphine-d15)gold (5). A previously published procedure16 was adapted as follows: To a colorless solution of ClAuPPh3-d15 (6) (110 mg, 0.216 mmol, 1.0 equiv) in THF (3 mL) was dropwise added a solution of n-BuLi in hexane (1.6 M, 148 μL, 0.237 mmol, 1.1 equiv) at −40 °C. The yellowish reaction mixture was stirred at −40 °C for 10 min. The cooling was stopped, and the reaction mixture was allowed to reach room temperature and was stirred for additional 90 min. The color of the reaction mixture disappeared. Solvents were removed under reduced pressure, and the white oily suspension was dissolved in benzene (5 mL). The solid fraction was removed using a syringe filter, and the solvent was removed under reduced pressure. The oily product was triturated with pentane (3 mL) and thoroughly dried under reduced pressure (30 min, 600 mTorr). Compound 5 was obtained as unstable colorless oil (91 mg, 0.171 mmol, 79%), which slowly decomposes to undefined gold clusters. 1 H NMR (500 MHz, CDCl3): δ 0.94 (t, J = 7.34 Hz, 3H), 1.45 (m, 4H), 1.83 (m, 2H). 2H NMR (77 MHz, CHCl3): δ 7.49−7.57 (m, 15D). 13C NMR (125 MHz, CDCl3): δ 14.2, 29.5 (d, JC,P = 5.3 Hz), 30.7 (d, JC,P = 95.0 Hz), 34.1 (d, JC,P = 3.9 Hz), 128.3 (dt, JC,P = 10.3 Hz, JC,D = 24.8 Hz), 130.2 (dt, JC,P = 1.9 Hz, JC,D = 24.8 Hz), 131.6 (d, JC,P = 44.8 Hz), 133.8 (dt, JC,P = 13.4 Hz, JC,D = 24.8 Hz). 31P NMR (202 MHz, CDCl3): δ 33.14. IR (KBr): 2948, 2911, 2890, 2865, 2845, 2817, 2286, 2275, 1615, 1580, 1549, 1533, 1462, 1452, 1414, 1370, 1346, 1332, 1309, 1277, 1242, 1182, 1162, 1142, 1069, 1051, 1029, 1005, 955, 868, 834, 826, 793, 755, 676, 659, 633, 592, 543, 517, 502, 470 cm−1. MS, m/z (%): 554.2 (100, M + Na), 474.2 (65, M−C4H9). HRMS, (ESI) for (C221H92H15AuP + Na+): calcd 554.21149, found 554.21158. Anal. Calcd for C221H92H15AuP: C, 49.72; H, 4.68. Found: C, 50.04; H, 4.55. (Triphenylphosphine-d15)gold Chloride (6). A previously published procedure15 was adapted as follows: A warm solution of PPh3-d15 (196 mg, 0.706 mmol, 2.0 equiv) in dry ethanol (5 mL) was slowly added to the clear yellow solution of HAuCl4·nH2O (120 mg, 0.353 mmol, 1.0 equiv) in dry ethanol (3 mL). The color of the reaction mixture immediately disappeared, and a dense white solid precipitated. The white suspension was stirred at the room temperature for an additional 60 min. The white solid was filtered on frit and subsequently washed with ethanol (3 × 2 mL) and ether (3 × 2 mL) and finally thoroughly dried under reduced pressure. 4624


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Alkyl Monolayers by Organomercury Deposition on Gold. J. Phys. Chem. Lett. 2013, 4, 2624−2629. (5) Cheng, Z. L.; Skouta, R.; Vázquez, H.; Widawsky, J. R.; Schneebeli, S.; Chen, W.; Hybertsen, M. S.; Breslow, R.; Venkataraman, L. In situ formation of highly conducting covalent Au−C contacts for single-molecule junctions. Nat. Nanotechnol. 2011, 6, 353−357. (6) Chen, W.; Widawsky, J. R.; Vázquez, H.; Schneebeli, S. T.; Hybertsen, M. S.; Breslow, R.; Venkataraman, L. Highly conducting πconjugated molecular junctions covalently bonded to gold electrodes. J. Am. Chem. Soc. 2011, 133, 17160−17163. (7) Aradhya, S. V.; Venkataraman, L. Single-molecule junctions beyond electronic transport. Nat. Nanotechnol. 2013, 8, 399−410. (8) Widawsky, J. R.; Chen, W.; Vázquez, H.; Kim, T.; Breslow, R.; Hybertsen, M. S.; Venkataraman, L. Length-Dependent Thermopower of Highly Conducting Au-C Bonded Single Molecule Junctions. Nano Lett. 2013, 13, 2889−2894. (9) Batra, A.; Kladnik, G.; Gorjizadeh, N.; Meisner, J.; Steigerwald, M.; Nuckolls, C.; Quek, S. Y.; Cvetko, D.; Morgante, A.; Venkataraman, L. Trimethyltin-Mediated Covalent Gold-Carbon Bond Formation. J. Am. Chem. Soc. 2014, 136, 12556−12559. (10) Sourisseau, C.; Pasquier, B. Spectres de vibration et structures de composés allyliques du sodium, du lithium et du magnésium. Application a l’étude de l’allyllithium et du chlorure d’allylmagnésium en solution. Spectrochim. Acta, Part A 1975, 31, 287−302. (11) Nagel, B.; Brüser, W. Schwingungsspektren und Normalkoordinatenanalyse von Dimethylzink, Dimethylzink-d6 und Diäthylzink. Z. Anorg. Allg. Chem. 1980, 468, 148−152. (12) Kvisle, S.; Rytter, E. Infrared matrix isolation spectroscopy of trimethylgallium, trimethylaluminium and triethylaluminium. Spectrochim. Acta, Part A: Molecular Spectroscopy 1984, 40, 939−951. (13) Marchand, A.; Forel, M. T.; Metras, F.; Valade, J. Infrared spectroscopy of organosilicon compounds. II. Siloxanes, silazanes, amino- and diaminosilanes. J. Chim. Phys. Phys.-Chim. Biol. 1964, 3, 343−362. (14) Durig, J. R.; Pan, C.; Guirgis, G. A. Spectra and structure of silicon containing compounds. XXXII. Raman and infrared spectra, conformational stability, vibrational assignment and ab initio calculations of n-propylsilane-d0 and Si-d3. Spectrochim. Acta, Part A 2003, 59, 979−1002. (15) Braunstein, P.; Lehner, H.; Matt, D.; Burgess, K.; Ohlmeyer, M. J. A Platinum-Gold Cluster: Chloro-1KCl-Bis(Triethylphosphine1KP)Bis(Triphenyl-Phosphine)-2KP, 3KP-Triangulo- Digold-Platinum(1+) Trifluoromethanesulfonate. Inorg. Synth. 2007, 27, 218−221. (16) Peña-López, M.; Ayán-Varela, M.; Sarandeses, L. A.; Pérez Sestelo, J. Palladium-Catalyzed Cross-Coupling Reactions of Organogold(I) Reagents with Organic Electrophiles. Chem.−Eur. J. 2010, 16, 9905−9909. (17) Fafarman, A. T.; Webb, L. J.; Chuang, J. I.; Boxer, S. G. SiteSpecific Conversion of Cystein Thiols into Thiocyanate Creates an IR Probe for Electric Fields in Proteins. J. Am. Chem. Soc. 2006, 128, 13356−13357. (18) Andrews, S. S.; Boxer, S. G. Vibrational Stark Effects of Nitriles. I. Methods and Experimental Results. J. Phys. Chem. A 2000, 104, 11853−11863. (19) Kasha, M.; Rawls, H. R.; Ashraf El-Bayoumi, M. The exciton model in molecular spectroscopy. Pure Appl. Chem. 1965, 11, 371− 392. (20) Frisch, M. J.; et al. Gaussian 09, revision A.02; Gaussian, Inc.: Wallingford, CT, 2009. (21) Gilman, H.; Clark, R. N. Ethyl ß-Triethylsiloxycrotonate and Tetra-n-butylsilane. J. Am. Chem. Soc. 1947, 69, 967−968. (22) Colacot, T. J. Cp2TiCl2 catalyzed one-pot synthesis of nBu3GeH from GeCl4. J. Organomet. Chem. 1999, 580, 378−381. (23) Carlisle Chemical Works. Alkyl Tin, U.S. Patent: US3059012 A1962. (24) Danzer, R. Ü ber organische Bleiverbindungen. Monatsh. Chem. 1925, 46, 241−244.

vigorously stirred for 16 h at room temperature. A dense white solid precipitated. All volatiles were distilled off under reduced pressure. The white solid residue was suspended in ether (100 mL) and washed with water (2 × 20 mL). Combined water phases were washed with ether (2 × 10 mL), and combined ethereal phases were dried over MgSO4. The solvent was removed under reduced pressure, and column chromatography on silica gel (hexane/CH2Cl2 3:1) gave 9 as a clear colorless oil (791 mg, 3.418 mmol, 88%). 1 H NMR (400 MHz, CDCl3): δ 0.86 (t, J = 7.39 Hz, 3H), 1.34 (m, 2H), 1.61 (m, 2H), 2.45 (s, 3H), 7.33−7.35 (m, 2H), 7.78−7.80 (m, 2H). 2H NMR (77 MHz, CDCl3): δ 4.02 (d, J = 22.74 Hz, 2D). 13C NMR (100 MHz, CDCl3): δ 13.4 (d, J = 4.6 Hz), 18.5, 21.6, 30.5 (d, J = 37.8 Hz), 69.7 (q, J = 22.7 Hz), 127.9, 129.8, 133.2, 144.6. IR (KBr): 3069, 3034, 2963, 2936, 2876, 2222, 2137, 1599, 1496, 1465, 1459, 1431, 1400, 1361, 1307, 1292, 1210, 1191, 1179, 1132, 1121, 1096, 1058, 1042, 1020, 953, 929, 860, 816, 782, 748, 713, 688, 662, 573, 554 cm−1. MS, m/z (%): 231.1 (12, M), 173.0 (100), 155.0 (94), 107.1 (17), 91.0 (96), 65.0 (33), 59.1 (57). HRMS, (EI) for (12C1013C1H142H2O3S+): calcd 231.0979, found 231.0981. Anal. Calcd for 12C1013C1H142H2O3S: C, 57.55; H, 7.06. Found: C, 57.44; H, 6.79.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.7b03404. Copies of 1H and 13C NMR spectra of compounds 1−6. Results of calculations and the full text of ref 20. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Josef Michl: 0000-0002-4707-8230 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Grant Agency of the Czech Republic (14-02337S) and the Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic (RVO: 61388963). We are grateful to Dr. Miloš Buděsı̌ ́nsky,́ Dr. Radek Pohl, and Dr. Martin Dračı ́nsky ́ for help with NMR spectra and Dr. Pavel Fiedler for help with IR spectra.

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REFERENCES

(1) Khobragade, D.; Stensrud, E. S.; Mucha, M.; Smith, J. R.; Pohl, R.; Stibor, I.; Michl, J. Preparation of Covalent Long-Chain Trialkylstannyl and Trialkylsilyl Salts and an Examination of their Adsorption on Gold. Langmuir 2010, 26, 8483−8490. (2) Kaletová, E.; Kohutová, A.; Hajduch, J.; Kaleta, J.; Bastl, Z.; Pospíšil, L.; Stibor, I.; Magnera, T. F.; Michl, J. The Scope of Direct Alkylation of Gold Surface with Solutions of C1-C4 n-Alkylstannanes. J. Am. Chem. Soc. 2015, 137, 12086−12099. (3) Mucha, M.; Kaletová, E.; Kohutová, A.; Scholz, F.; Stensrud, E. S.; Stibor, I.; Pospíšil, L.; von Wrochem, F.; Michl, J. Alkylation of Gold Surface by Treatment with C18H37HgOTs and Anodic Hg Stripping. J. Am. Chem. Soc. 2013, 135, 5669−5677. (4) Scholz, F.; Kaletová, E.; Stensrud, E. S.; Ford, W. E.; Kohutová, A.; Mucha, M.; Stibor, I.; Michl, J.; von Wrochem, F. Formation of n4625


IR Spectra of n-Bu4M (M = Si, Ge, Sn, Pb), n ... - ACS Publications

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