IR Spectra of n-Bu4M (M = Si, Ge, Sn, Pb), n-BuAuPPh3-d15, and "n-Bu" on a Gold Surface

Article abstract of DOI:10.1021/acs.jpca.7b03404

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 n-BuAuPPh₃-d₁₅, the CH stretching vibrations of the butyl group are shifted to lower frequencies by ～10 cm^-1, and two possible rationalizations are offered.

Full text of DOI:10.1021/acs.jpca.7b03404

Article
pubs.acs.org/JPCA
IR Spectra of n‑Bu M (M = Si, Ge, Sn, Pb), n‑BuAuPPh ‑d , and “n‑Bu”
4
3
15
on a Gold Surface
†
,‡
†
†
†
†
and Josef Michl*,†,‡
̌
Jirí
†
̌
Kaleta, Lucie Bednar
́
ova,
́
Martina Cízk
̌
ova,
́
Jin Wen, Eva Kaletova,
́
Institute of Organic Chemistry and Biochemistry AS CR, Flemingovo nam
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
S Supporting Information
́
. 2, 166 10 Praha 6, Czech Republic
‡
*
ABSTRACT: Observed and DFT-calculated IR spectra of n-Bu M (M = Si, Ge,
4
1
3
Sn, Pb), (CH CH CH CD ) Sn, and n-BuAuPPh -d are reported and
3
2
2
2 4
3
15
assigned. The asymmetric CH stretching vibration of the CH group adjacent to
2
−
1
the metal atom appears as a distinct shoulder at ∼2934 cm , whereas for other
−
1
−1
CH groups it is located at ∼2922 cm . The characteristic peak at ∼2899 cm
2
−1
is attributed to an overtone of a symmetric CH bend at ∼1445 cm . In n-
BuAuPPh -d , the CH stretching vibrations of the butyl group are shifted to
lower frequencies by ∼10 cm , and two possible rationalizations are offered.
2
3
15
−1
INTRODUCTION
and which is small enough for a detailed analysis. We prepared
t h e o r g a n o m e t a l l i c s 1 − 5 ( C h a r t 1 ) a n d
3 2 2 2 4 2
their mid-IR spectra, used density functional theory (DFT) to
■
In studies of monolayers produced by direct alkylation of gold
13
13
1
,2
3,4
(CH CH CH CD ) Sn, [3( CD )] (Chart 1), measured
surfaces with organostannanes and organomercurials 5 and
of single-molecule electrical conductivity of alkane and
6
−9
help with band assignments in terms of group vibrations in the
other
chains attached directly to gold surfaces by treatment
1
1
350−3500 cm− region that is most accessible in surface
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
spectroscopy, and compared them with the polarization
modulated IR reflection/absorption spectra (PM IRRAS) of
butylated gold surfaces.
RESULTS
■
Synthesis. Compounds 1−4 were prepared from n-BuLi or
n-BuMgBr and SiCl , GeCl , SnCl , or Pb(OAc) in THF
2
4 4 4 4
impurities but also promises to elucidate the structural details
(
Scheme 1) and purified by vacuum distillation as colorless
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, ...CH Au ..., but a loss of
liquids. The butylgold derivative 5 was prepared from HAuCl4
2
n
Chart 1. Structures of Molecules 1−5
one or more hydrogen atoms could also have remained
undetected and the structure could be ...CHAu ..., ...
n
CAu ..., or even ...−(CH) Au ..., and so on. With suitable
n
2
n
1
3
deuterium and/or C 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
10−12
available in the literature.
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 CH groups, as has
2
13,14
been claimed for alkylsilanes.
We chose n-butyl as a typica2l
Received: April 10, 2017
Published: May 12, 2017
alkyl for which many gold surface IR spectra are now available
©
2017 American Chemical Society
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Article
Scheme 1. Synthesis of Tetra-n-butyl Derivatives 1−4
by quantitative reduction with PPh -d to white crystalline
3
15
1
5
ClAuPPh -d (6), which was then treated with n-BuLi at −40
C (Scheme 2). It is a colorless oil, stable at room
temperature for less than an hour in solution and for a few
3
15
16
°
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.
1
3
Isotopically labeled compound 3( CD ) was synthesized
2
from SnCl and a Grignard reagent derived from 7 according to
4
Scheme 1 and purified by column chromatography. The iodide
7
was prepared in three steps from nPrBr. Reaction of n-PrBr
1
3
with magnesium, followed by the addition of CD -labeled
2
paraformaldehyde, gave the butanol 8, which was almost
quantitatively converted to 9. Subsequent solvent-free Finkel-
stein 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
2
and 5 with PM IRRAS of n-butyls attached to gold surface.
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
2
butylated gold surface. Figure 3 compares the CH stretching
1
3
regions in 3 and 3( CD ). The observed vibrational
2
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
Figure 3. Comparison of the CH stretching regions in IR spectra of 3
13
with 3( CD ).
2
−1
make assignments below ∼1350 cm . In the case of 5, the
situation in the lower frequency region was complicated by the
presence of vibrations due to the aromatic rings.
4
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DOI: 10.1021/acs.jpca.7b03404
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DOI: 10.1021/acs.jpca.7b03404
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1
9
DISCUSSION
transitions in excitonic interactions. 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 measure-
ments on a large number of suitably designed compounds and
lies outside the framework of the present study.
■
Fundamental Vibrations and Spectral Regularities in
1
−4. Compounds 1−4 have almost the same vibrational
frequencies for both the CH and the CH groups: ν (CH ) at
3
2
as
3
−
1
−1
∼
2960 cm , ν (CH ) at ∼2870 cm , δ (CH ) at ∼1460
s
3
as
3
−1 −1
cm , and δ (CH ) at ∼1380 cm . Except for the ν (CH )
s
3
as
2
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.
vibration of the methylene group adjacent to the heavy atom,
−
1
seen as a shoulder at 2934 cm , the ν (CH ) stretching
vibrations of all CH groups in 1−3 appear at the same
frequency (2922 cm ). In compound 4, these vibrations shift
to a lower frequency, 2917 cm . The symmetric stretching
vibrations of all CH groups in 1−4 occur at ∼2855 cm , and
the symmetric bends β (CH ) occur at 1465 cm .
as
2
2
−
1
−
1
−
1
2
−1
s
2
Overtone Assignment in 1−4. Three overtone vibrations
13
CONCLUSIONS
have been identified in the CH stretching region. The most
■
−
1
intense one at ∼2900 cm is assigned as 2β (CH ), but it
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
s
2
could also be β (CH ) + δ (CH ). Its intensity drops as the
s
2
as
3
central atom M becomes heavier and it is not observed in 4.
1
3
Replacement of one CH group by CD reduces the intensity
2
2
1
3
of this peak in 3( CD ). The other two overtones, 2β (CH )
at ∼2800 cm and 2δ (CH ) at 2730 cm , are considerably
weaker. The former is missing in 3( CD ), which has no
vibration of the CH
2
group adjacent to the metal atom appears
2
s
2
−1
−1
−1
as a distinct shoulder at ∼2934 cm , whereas for other CH
s
3
2
1
3
−1
groups it is located at ∼2922 cm , and (ii) the characteristic
−1
2
C(1)H groups.
peak at ∼2899 cm present in the stannanes and absent in
2
2
In our prior work on the butylation of the gold surface, we
surface-mounted butyl groups has been attributed to an
−1
noted the presence of a diagnostic peak at 2900 cm− in the
spectra of tetraalkylstannanes and its absence in the spectra of
the alkylated surfaces but were unsure whether the peak is due
1
overtone of a symmetric CH bend at ∼1445 cm . The
2
observation of frequency shifts in 5 relative to 1−4 suggests
that a major study of their origin is called for.
to a fundamental vibration of the C(1)H group located next to
2
the tin atom or to an overtone. This question has now been
EXPERIMENTAL SECTION
■
settled in favor of the overtone, since we have identified the
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
−1
former as a shoulder at 2934 cm 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 β (CH ) + δ (CH ) cannot be
s
2
as
3
excluded. The absence of this shoulder in the spectrum of
−1
−1
spectral region 3800−400 cm at a spectral resolution 2 cm
1
3
3
( CD ) and the shift of the ν (CH ) peak attributed to all
2 as 2
and using a Happ-Genzel apodization function. Data were
processed using OMNIC software.
−1
−1
13
CH groups from 2922 cm in 3 to 2918 cm in 3( CD )
support the assignment of the peak at 2900 cm as an
2
2
−1
Computations. Calculations used the Gaussian 09 pack-
overtone.
20
age. Geometry and vibrational frequency were computed in
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
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.
(
−1
frequencies are 5−8 cm 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−
are considerably increased. A much weaker tendency toward
similar shifts can also be detected in 4.
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.
1
The intensity distribution in the PM IRRAS reported for
2
gold surface-bound butyl groups (Figure 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
−1
shifted by 5−7 cm 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
17
substituent (intramolecular variant of the vibrational Stark
1
8
effect ) 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
1
2
13
31
Chemical shifts in H, H, C, and P NMR spectra are
reported in ppm on the δ scale relative to CHCl (δ = 7.26
3
4
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Article
1
13
ppm for H NMR) and CHCl (δ = 77.0 ppm for C NMR) as
Tetrabutylstannane (3). A previously published proce-
3
23
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.
dure 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
=
2
The content of H was determined by elemental analysis as
1
H because this method is not able to recognize the difference
2
1
between H and H (both are converted to water during the
solution of SnCl (1.17 mL, 10.000 mmol) in benzene (2 mL)
analysis, and its amount is finally determined by the thermal
conductometry; H O and H O have the same thermal
conductivity).
Tetrabutylsilane (1). 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 SiCl (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 NH Cl (2 × 40 mL), and the clear organic phase was
dried over MgSO . Kugelrohr distillation (130 °C, 600 mTorr)
gave 1 as a colorless oil (3.751 g, 14.622 mmol, 97%).
H NMR (400 MHz, CDCl ): δ 0.49 (m, 8H), 0.88 (t, J =
.08 Hz, 12H), 1.25 (m, 8H), 1.31 (m, 8H). C NMR (100
MHz, CDCl ): δ 12.2, 13.8, 26.2, 26.9. IR (KBr): 2958, 2922,
873, 2858, 1465, 1413, 1377, 1341, 1296, 1273, 1196, 1177,
082, 1051, 1030, 1001, 964, 888, 788, 760, 731, 444 cm . MS,
m/z (%): 256.3 (3, M), 199.2 (100, M−C H ), 143.1 (94),
01.1 (20), 87.1 (12), 73.0 (5), 59.0 (9). HRMS, (EI) for
C H Si ): calcd 256.2586, found 256.2590. Anal. Calcd for
C H Si: C, 74.91; H, 14.14. Found: C, 74.94; H, 14.05.
4
1
2
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
2
2
2
1
(
4
mL), and clear organic phase was dried over MgSO . Solvents
4
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, CDCl ): δ 0.80 (m, 8H), 0.89 (t, J =
3
4
13
7
.28 Hz, 12H), 1.29 (m, 8H), 1.45 (m, 8H). C NMR (100
4
MHz, CDCl ): δ 8.7, 13.7, 27.4, 29.3. IR (KBr): 2957, 2925,
3
1
2872, 2854, 1465, 1418, 1376, 1357, 1340, 1292, 1249, 1182,
1150, 1072, 1044, 1021, 1002, 960, 874, 768, 745, 690, 667,
3
1
3
7
−1
5
93, 505 cm . MS, m/z (%): 291.1 (96, center of isotope
3
cluster, M−C H ), 235.0 (100, center of isotope cluster), 179.0
4
9
2
1
(
88, center of isotope cluster), 120.9 (38, center of isotope
−1
120
+
cluster). HRMS, (EI) for (C H
Sn ): calcd 291.1135,
12
27
4
9
found 291.1129. Anal. Calcd for C H Sn: C, 55.35; H, 10.45.
16
36
1
(
Found: C, 55.40; H, 10.55.
+
16
36
13
2
13
13
Tetra-[1- C-1,1- H ]-butylstannane 3( CD ). 3( CD )
2
2
2
16
36
was synthesized according to conditions described for 3 using
iodobutane 7 (300 mg, 1.604 mmol), Mg turnings (44 mg,
2
2
Tetrabutylgermane (2). 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.
1
.800 mmol) in THF (5 mL), and then SnCl (41 μL, 0.350
4
mmol) in benzene (5 mL). Column chromatography on silica
13
gel (hexane) gave 3( CD ) as clear colorless oil (71 mg, 0.198
2
mmol, 57%).
1
H NMR (400 MHz, CDCl ): δ 0.89 (t, J = 7.31 Hz, 12H),
3
2
1
0
.29 (m, 8H), 1.45 (m, 8H). H NMR (77 MHz, CDCl ): δ
.79 (d, J = 19.32 Hz, 2D). C NMR (100 MHz, CDCl ): δ
3
13
3
Subsequently, GeCl (581 μL, 5.00 mmol) was added slowly
4
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,
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 NH Cl (10 mL) was added dropwise, and the reaction
mixture was diluted with ether (80 mL), washed with saturated
aqueous NH Cl (2 × 30 mL), and dried over MgSO . 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%).
H NMR (400 MHz, CDCl ): δ 0.69 (m, 8H), 0.89 (t, J =
.08 Hz, 12H), 1.32 (m, 16H). C NMR (100 MHz, CDCl ):
δ 12.5, 13.8, 26.7, 27.5. IR (KBr): 2957, 2924, 2872, 2856,
465, 1421, 1377, 1341, 1294, 1269, 1173, 1083, 1028, 1002,
64, 884, 717, 696, 644, 556 cm . MS, m/z (%): 245.1 (65,
center of isotope cluster, M−C H ), 189.1 (100, center of
isotope cluster), 133.0 (42), 103.0 (12), 91.0 (14), 72.9 (5).
1
9
(
457, 1377, 1353, 1333, 1281, 1236, 1125, 1107, 1070, 1040,
−1
72, 952, 914, 861, 795, 767, 734, 714, 657, 576 cm . MS, m/z
%): 300.2 (78, center of isotope cluster, M−Bu), 241.1 (86,
4
center of isotope cluster), 182.0 (100, center of isotope
cluster), 120.9 (54, center of isotope cluster). HRMS, (EI) for
1
2
13
1
2
+
4
4
( C C H H Sn ): calcd 300.1612, found 300.1617. Anal.
9 3 21 6
Calcd for 2C C H H Sn: C, 54.61; H, 10.45. Found: C,
1
13
1
2
12
4
28
8
5
4.33; H, 10.25.
2
4
(
Tetrabutylplumbane (4). A 50 mL two-necked flask
1
3
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
1
3
7
3
1
9
−1
4
9
7
4
+
HRMS, (EI) for (C H Ge ): calcd 245.1324, found
45.1327. Anal. Calcd for C H Ge: C, 63.82; H, 12.05.
cooled to 0 °C. Pb(OAc) (2.217 g, 5.000 mmol) was slowly
1
2
27
4
2
added in portions over next 40 min, while the reaction
1
6
36
Found: C, 63.83; H, 11.95.
temperature was kept below 5 °C. The reaction mixture turned
4
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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
Complex 6 was obtained as a white crystalline solid (178 mg,
0.349 mmol, 99%).
2
M 244.1−245.8 °C (dec.). H NMR (77 MHz, CHCl ): δ
p
3
13
(5 mL) resulted in the formation of a dark dense aqueous
7.53−7.57 (m, 15D). C NMR (125 MHz, CDCl ): δ 128.5
3
phase, which was carefully removed by syringe. The clear
(d, J = 62.6 Hz), 131.5 (t, JC,D = 24.8 Hz), 128.7 (dt, JC,P =
C,P
yellow organic phase was then transferred to a different argon-
11.4 Hz, J = 24.8 Hz), 133.7 (dt, JC,P = 14.3 Hz, JC,D = 24.8
C,D
filled flask containing MgSO . Solvents were then carefully
Hz). 31P NMR (202 MHz, CDCl ): δ 33.14. IR (KBr): 2287,
4
3
removed, and Kugelrohr distillation (140 °C, 600 mTorr)
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 .
yielded 4 as colorless oil (1.881 g, 4.318 mmol, 86%).
1
−1
H NMR (400 MHz, CDCl ): δ 0.90 (t, J = 7.33 Hz, 12H),
3
1
3
1
.28 (m, 8H), 1.46 (m, 8H), 1.70 (m, 8H). C NMR (100
MS, m/z (%): 532.1 (100, M + Na). HRMS, (ESI) for
(C182H AuClP + Na ): calcd 532.10991, found 532.11004.
+
MHz, CDCl ): δ 13.7, 18.1, 27.7, 31.4. IR (KBr): 2956, 2917,
3
15
2
2
1
8
871, 2854, 2836, 1464, 1420, 1376, 1356, 1339, 1291, 1269,
241, 1181, 1155, 1129, 1065, 1040, 1015, 1003, 963, 872, 862,
40, 766, 746, 692, 562, 467, 444 cm . MS, m/z (%): 379.1
Anal. Calcd for C18 H AuClP: C, 42.41; H, 3.06. Found: C,
15
42.68; H, 2.88.
−1
13
2
1-Iodo-[1- C-1,1- H ]-butane (7). An argon-filled appa-
2
(
79, center of isotope cluster, M−C H ), 323.0 (25, center of
ratus 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,
4
9
isotope cluster), 265.0 (100, center of isotope cluster), 208.9
208
+
(
48, center of isotope cluster). HRMS, (EI) for (C H
Pb ):
1
2
27
calcd 379.1879, found 379.1875. Anal. Calcd for C H Pb: C,
4
1
6
36
4.11; H, 8.33. Found: C, 44.23; H, 8.30.
Butyl(triphenylphosphine-d )gold (5). A previously
1
5
16
published procedure was adapted as follows: To a colorless
solution of ClAuPPh -d (6) (110 mg, 0.216 mmol, 1.0 equiv)
3
15
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
94%).
1
H NMR (400 MHz, CDCl ): δ 0.92 (t, J = 7.38 Hz, 3H),
3
2
1.42 (m, 2H), 1.79 (m, 2H). H NMR (77 MHz, CDCl ): δ
3
3.20 (d, J = 22.45 Hz, 2D). 13C NMR (100 MHz, CDCl ): δ
3
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),
1
2
13
1
2
+
60.1 (47, M−I). HRMS, (EI) for ( C C H H I ): calcd
3
7
2
1
2
13
1
2
7
186.9908, found 186.9909. Anal. Calcd for C3 C H H I: C,
2
26.22; H, 5.93. Found: C, 25.91; H, 5.79.
1
3
2
[1- C-1,1- H ]-Butan-1-ol (8). An argon-filled apparatus
2
(
30 min, 600 mTorr). Compound 5 was obtained as unstable
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
colorless oil (91 mg, 0.171 mmol, 79%), which slowly
decomposes to undefined gold clusters.
1
H NMR (500 MHz, CDCl ): δ 0.94 (t, J = 7.34 Hz, 3H),
3
2
1
7
2
3
.45 (m, 4H), 1.83 (m, 2H). H NMR (77 MHz, CHCl ): δ
.49−7.57 (m, 15D). C NMR (125 MHz, CDCl ): δ 14.2,
9.5 (d, J = 5.3 Hz), 30.7 (d, JC,P = 95.0 Hz), 34.1 (d, JC,P
3
1
3
13
( CD O) (250 mg, 7.569 mmol) was added directly to the
3
2
n
=
reaction mixture, which was stirred for an additional 16 h at
C,P
.9 Hz), 128.3 (dt, JC,P = 10.3 Hz, JC,D = 24.8 Hz), 130.2 (dt,
room temperature. A saturated aqueous NH Cl (4 mL) was
4
JC,P = 1.9 Hz, JC,D = 24.8 Hz), 131.6 (d, J = 44.8 Hz), 133.8
carefully added to the reaction mixture, organic phase was
C,P
3
1
(
dt, JC,P = 13.4 Hz, JC,D = 24.8 Hz). P NMR (202 MHz,
separated, and water phase was extracted with ether (4 × 10
CDCl ): δ 33.14. IR (KBr): 2948, 2911, 2890, 2865, 2845,
mL). Combined ethereal phases were dried over MgSO , and
3
4
2
1
1
5
817, 2286, 2275, 1615, 1580, 1549, 1533, 1462, 1452, 1414,
370, 1346, 1332, 1309, 1277, 1242, 1182, 1162, 1142, 1069,
051, 1029, 1005, 955, 868, 834, 826, 793, 755, 676, 659, 633,
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
−1
92, 543, 517, 502, 470 cm . MS, m/z (%): 554.2 (100, M +
1
2
Na), 474.2 (65, M−C H ). HRMS, (ESI) for (C H H AuP
°C.
4
9
22
9
15
+
1
+
Na ): calcd 554.21149, found 554.21158. Anal. Calcd for
H NMR (400 MHz, CDCl ): δ 0.92 (t, J = 7.34 Hz, 3H),
3
C221H H AuP: C, 49.72; H, 4.68. Found: C, 50.04; H, 4.55.
2
9
1.37 (m, 2H), 1.51 (m, 2H), 1.92 (s, 1H). C NMR (100
13
15
(
Triphenylphosphine-d )gold Chloride (6). A previ-
MHz, CDCl ): δ 13.9 (d, J = 4.5 Hz), 18.8, 34.6 (d, J = 36.9
1
5
3
1
5
ously published procedure was adapted as follows: A warm
solution of PPh -d (196 mg, 0.706 mmol, 2.0 equiv) in dry
ethanol (5 mL) was slowly added to the clear yellow solution of
Hz), 62.0 (q, J = 21.3 Hz). MS, m/z (%): 77.1 (100, M).
1
2
13
1
2
+
HRMS, (EI) for ( C C H H O ): calcd 77.0891, found
3
15
3 8 2
1
2
13
1
2
77.0883. Anal. Calcd for C3 C H H O: C, 63.58; H, 13.60.
8 2
HAuCl ·nH O (120 mg, 0.353 mmol, 1.0 equiv) in dry ethanol
Found: C, 63.20; H, 13.45.
4
2
1
3
2
(
3 mL). The color of the reaction mixture immediately
[1- C-1,1- H ]-Butyl 4-methylbenzenesulfonate (9). A
2
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.
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
4
624
DOI: 10.1021/acs.jpca.7b03404
J. Phys. Chem. A 2017, 121, 4619−4625

The Journal of Physical Chemistry A
Article
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
Alkyl Monolayers by Organomercury Deposition on Gold. J. Phys.
Chem. Lett. 2013, 4, 2624−2629.
́
(5) Cheng, Z. L.; Skouta, R.; Vazquez, 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,
ethereal phases were dried over MgSO . The solvent was
4
6
(
, 353−357.
́
6) Chen, W.; Widawsky, J. R.; Vazquez, H.; Schneebeli, S. T.;
removed under reduced pressure, and column chromatography
on silica gel (hexane/CH Cl 3:1) gave 9 as a clear colorless oil
2
2
Hybertsen, M. S.; Breslow, R.; Venkataraman, L. Highly conducting π-
conjugated molecular junctions covalently bonded to gold electrodes.
J. Am. Chem. Soc. 2011, 133, 17160−17163.
(
791 mg, 3.418 mmol, 88%).
H NMR (400 MHz, CDCl ): δ 0.86 (t, J = 7.39 Hz, 3H),
1
3
1
7
2
4
1
2
1
1
.34 (m, 2H), 1.61 (m, 2H), 2.45 (s, 3H), 7.33−7.35 (m, 2H),
(7) Aradhya, S. V.; Venkataraman, L. Single-molecule junctions
beyond electronic transport. Nat. Nanotechnol. 2013, 8, 399−410.
2
.78−7.80 (m, 2H). H NMR (77 MHz, CDCl ): δ 4.02 (d, J =
3
2.74 Hz, 2D). 13C NMR (100 MHz, CDCl ): δ 13.4 (d, J =
́
(8) Widawsky, J. R.; Chen, W.; Vazquez, H.; Kim, T.; Breslow, R.;
3
Hybertsen, M. S.; Venkataraman, L. Length-Dependent Thermopower
of Highly Conducting Au-C Bonded Single Molecule Junctions. Nano
Lett. 2013, 13, 2889−2894.
.6 Hz), 18.5, 21.6, 30.5 (d, J = 37.8 Hz), 69.7 (q, J = 22.7 Hz),
27.9, 129.8, 133.2, 144.6. IR (KBr): 3069, 3034, 2963, 2936,
876, 2222, 2137, 1599, 1496, 1465, 1459, 1431, 1400, 1361,
307, 1292, 1210, 1191, 1179, 1132, 1121, 1096, 1058, 1042,
020, 953, 929, 860, 816, 782, 748, 713, 688, 662, 573, 554
(
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
−1
cm . MS, m/z (%): 231.1 (12, M), 173.0 (100), 155.0 (94),
07.1 (17), 91.0 (96), 65.0 (33), 59.1 (57). HRMS, (EI) for
1
1
2
13
1
2
+
(
C10 C H H O S ): calcd 231.0979, found 231.0981. Anal.
de composes
Application a l’et
en solution. Spectrochim. Acta, Part A 1975, 31, 287−302.
11) Nagel, B.; Bruser, W. Schwingungsspektren und Normal-
koordinatenanalyse von Dimethylzink, Dimethylzink-d6 und Diathyl-
zink. Z. Anorg. Allg. Chem. 1980, 468, 148−152.
́
allyliques du sodium, du lithium et du magnes
́
ium.
ium
14
2
3
12
13
1
2
́
ude de l’allyllithium et du chlorure d’allylmagnes
́
Calcd for C10 C H H O S: C, 57.55; H, 7.06. Found: C,
14
2
3
57.44; H, 6.79.
(
̈
̈
ASSOCIATED CONTENT
Supporting Information
■
*
S
(12) Kvisle, S.; Rytter, E. Infrared matrix isolation spectroscopy of
trimethylgallium, trimethylaluminium and triethylaluminium. Spectro-
chim. Acta, Part A: Molecular Spectroscopy 1984, 40, 939−951.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpca.7b03404.
(13) Marchand, A.; Forel, M. T.; Metras, F.; Valade, J. Infrared
1
13
Copies of H and C NMR spectra of compounds 1−6.
spectroscopy of organosilicon compounds. II. Siloxanes, silazanes,
amino- and diaminosilanes. J. Chim. Phys. Phys.-Chim. Biol. 1964, 3,
Results of calculations and the full text of ref 20. (PDF)
3
(
43−362.
14) Durig, J. R.; Pan, C.; Guirgis, G. A. Spectra and structure of
AUTHOR INFORMATION
Corresponding Author
E-mail: josef.michl@colorado.edu.
■
silicon containing compounds. XXXII. Raman and infrared spectra,
conformational stability, vibrational assignment and ab initio
calculations of n-propylsilane-d and Si-d . Spectrochim. Acta, Part A
*
0
3
2
(
003, 59, 979−1002.
ORCID
15) Braunstein, P.; Lehner, H.; Matt, D.; Burgess, K.; Ohlmeyer, M.
Josef Michl: 0000-0002-4707-8230
Notes
The authors declare no competing financial interest.
J. A Platinum-Gold Cluster: Chloro-1 Cl-Bis(Triethylphosphine-
1KP)Bis(Triphenyl-Phosphine)-2 P, 3 P-Triangulo- Digold-Platinum-
(1+) Trifluoromethanesulfonate. Inorg. Synth. 2007, 27, 218−221.
(
K
K
K
16) Pena-Lopez, M.; Ayan-Varela, M.; Sarandeses, L. A.; Perez
̃
́
́
́
ACKNOWLEDGMENTS
Sestelo, J. Palladium-Catalyzed Cross-Coupling Reactions of
■
Organogold(I) Reagents with Organic Electrophiles. Chem.−Eur. J.
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
2
(
010, 16, 9905−9909.
17) Fafarman, A. T.; Webb, L. J.; Chuang, J. I.; Boxer, S. G. Site-
Specific Conversion of Cystein Thiols into Thiocyanate Creates an IR
Probe for Electric Fields in Proteins. J. Am. Chem. Soc. 2006, 128,
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(18) Andrews, S. S.; Boxer, S. G. Vibrational Stark Effects of Nitriles.
I. Methods and Experimental Results. J. Phys. Chem. A 2000, 104,
(
RVO: 61388963). We are grateful to Dr. Milos
̌ ̌ ̌
Budesınsky,
́
́
Dr. Radek Pohl, and Dr. Martin Dracı
spectra and Dr. Pavel Fiedler for help with IR spectra.
̌
n
́
sky for help with NMR
́
1
(
1853−11863.
19) Kasha, M.; Rawls, H. R.; Ashraf El-Bayoumi, M. The exciton
model in molecular spectroscopy. Pure Appl. Chem. 1965, 11, 371−
92.
20) Frisch, M. J.; et al. Gaussian 09, revision A.02; Gaussian, Inc.:
Wallingford, CT, 2009.
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Tetra-n-butylsilane. J. Am. Chem. Soc. 1947, 69, 967−968.
22) Colacot, T. J. Cp TiCl catalyzed one-pot synthesis of n-
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