Bis(alkyl)thioethers on a biphenyl scaffold: A spectroscopic and structural insight

Article abstract of DOI:10.1016/j.molstruc.2017.04.108

A series of bis(alkyl)thioether compounds utilising biphenyl as the backbone of the type 2,2′-bis(alkylthio)-1,1′-biphenyl have been prepared with yields of 32–70%. The six benzyl derivatives all displayed an AB quartet for the CH₂ hydrogens within their ¹H NMR spectra due to restricted rotation within the molecule. Where the alkyl group was changed to neopentyl the CH₂ protons became equivalent giving rise to a singlet within the ¹H NMR spectrum. The compounds have been characterised principally using multinuclear NMR spectroscopy and single crystal X-ray diffraction.

Full text of DOI:10.1016/j.molstruc.2017.04.108

Accepted Manuscript
Bis(alkyl)thioethers on a biphenyl scaffold: A spectroscopic and structural insight
Rhiann Ferguson, Phillip S. Nejman, Alexandra M.Z. Slawin, J. Derek Woollins
PII:
S0022-2860(17)30560-4
10.1016/j.molstruc.2017.04.108
MOLSTR 23731
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 15 March 2017
Revised Date: 25 April 2017
Accepted Date: 26 April 2017
Please cite this article as: R. Ferguson, P.S. Nejman, A.M.Z. Slawin, J.D. Woollins, Bis(alkyl)thioethers
on a biphenyl scaffold: A spectroscopic and structural insight, Journal of Molecular Structure (2017), doi:
10.1016/j.molstruc.2017.04.108.
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ACCEPTED MANUSCRIPT
Graphical Abstract

ACCEPTED MANUSCRIPT
Bis(alkyl)thioethers on a biphenyl scaffold: A
spectroscopic and structural insight
Rhiann Fergusona, Phillip S. Nejmana, Alexandra M. Z. Slawina and J. Derek
Woollinsa,*
a
EaStCHEM School of Chemistry, University of St Andrews, St Andrews, Fife,
KY16 9ST, Scotland
* Corresponding author: E-mail: jdw3@st-and.ac.uk
Abstract
A series of bis(alkyl)thioether compounds utilising biphenyl as the backbone of the type 2,2′-
bis(alkylthio)-1,1′-biphenyl have been prepared with yields of 32-70%. The six benzyl derivatives all
1
displayed an AB quartet for the CH2 hydrogens within their H NMR spectra due to restricted
rotation within the molecule. Where the alkyl group was changed to neopentyl the CH2 protons
1
became equivalent giving rise to a singlet within the H NMR spectrum. The compounds have been
characterised principally using multinuclear NMR spectroscopy and single crystal X-ray diffraction.
Keywords
Thioether, sulfur; biphenyl; NMR spectroscopy; X-Ray structure
1

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1. Introduction
Organosulfur compounds have a long and rich history in organic synthesis acting as valuable
intermediates.[1, 2] Compounds containing C‒S bonds are highly desirable, in particular alkyl aryl
and dialkyl sulfides, resulting in a large number of reported methods for their synthesis.[3]
Thioethers have a wide and varied use within chemistry with compounds containing this sulfur
linkage studied in medicinal chemistry (A),[4] as ligands in organometallic chemistry (B)[5] and in
catalysis (C) (Figure 1).[6] Additionally, compounds of this type have been shown to be useful
precursors for the formation of other highly interesting species.[7]
Figure 1: Compounds demonstrating the various uses of thioethers.
Of particular relevance to the work presented here are bis(alkyl)thioethers, and their derivatives,
attached to polyaromatic backbones such as acenaphthene, naphthalene, biphenyl and
binaphthalene. The chemistry of these systems has seen fair less investigation than those based
upon the 1,2-benzene scaffold. A number of reports have been published describing the synthesis of
simple thioether compounds (D),[8-11] (E)[12, 13] and (F)[14] (Figure 2). However, to date there has
been no report of the acenaphthene derivative. The work conducted by Barbero, which describes
the synthesis of E, was examining synthetic routes to arene mono- and disulfonyl chlorides which are
key intermediates for the synthesis of strong Brønsted acids which are useful organocatalysts.[13]
Longer chain alkyl groups have also been utilised including ethyl derivatives of naphthalene (G)[15]
and biphenyl (H)[12] as well as a butyl analogue on naphthalene (I)[16] (Figure 2).
2

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Figure 2: Simple thioether compounds based upon polyaromatic backbones.
Thioethers bound to polyaromatic backbones are not limited to only alkyl derivatives. A variety of
bis(aryl)thioethers and their derivatives attached to naphthalene, acenaphthene, biphenyl and
binaphthalene are also known. Figure 3 (J-M) shows the phenyl analogues that have been prepared
based upon these backbones.[15, 17-19] As part of a wider investigation into using peri-substitution
in the formation of novel bonding motifs Aschenbach and Knight prepared compounds K and J
respectively alongside other chalcogen derivatives including selenium and tellurium analogues. In
both cases the onset of an attractive interaction, in the form of a 3c-4e bond, across the peri-gap
was proposed based upon single crystal X-ray diffraction data and computational analysis (B3LYP
level of DFT).[15, 17] A one-pot synthesis of 2,2′-bis-substituted biphenyls, of which L is an example,
was developed by Studer in 2015. This involved the addition of Mg-thiolates to benzyne followed by
homocoupling of the resulting ortho-substituted arylmagnesium species. They found a number of
the 2,2′-bis-substituted biphenyls readily crystallised revealing interesting interactions within the
solid state as determined by single crystal X-ray diffraction.[18]
3

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Figure 3: bis(aryl)thioether compounds on polyaromatic backbones.
The Woollins group has recently been investigating the use of rigid organic backbones such as
naphthalene and acenaphthene in the formation of novel bonding interactions (3c-4e bonds)
between chalcogens.[15, 17, 20-22] Building on this work we proposed to introduce a more
rotationally free backbone to investigate the importance of the rigidity on the potential formation of
a 3c-4e bond. Biphenyl was selected as the backbone as a number of potential synthetic routes to
the desired chalcogenoether compounds could be designed based upon the known literature
compounds 2,2′-dibromo-1,1′-biphenyl (1) and dibenzo[c,e][1,2]dithiine (2). Additionally, the
introduction of axially chirality from the biphenyl backbone makes these compounds of interest as
potential ligands for asymmetric catalysis[23] as they represent a simpler alternative to, for example,
binaphthalene. The work presented here represents the first step in designing synthetic routes
towards the related selenium and tellurium chalcogenoethers. In this work we describe the synthesis
and crystal structures of six 2,2′-bis(benzylthio)-1,1′-biphenyl compounds with varying para
substituents on the benzyl group. Additionally 2,2′-bis(neopentylthio)-1,1′-biphenyl has been
1
prepared and spectroscopically characterised. The features of their H NMR spectra and solid state
structures are examined and compared.
2. Synthetic Methods
2.1 General
All synthetic manipulations were performed under an atmosphere of dry nitrogen using standard
Schlenk-line techniques. Dry solvents were either collected from an MBraun Solvent Purification
System, or were dried and stored according to common procedures.[24] Chemicals were purchased
from Sigma Aldrich, Acros Organics, Alfa Aesar or were taken from the laboratory inventory and
used without further purification. 2,2′-dibromo-1,1′-biphenyl was prepared according to the
literature procedure.[25] Dibenzo[c,e][1,2]dithiine and 1,1′-biphenyl-2,2′-dithiol were synthesised
according to modified literature procedures.[26, 27] The synthetic protocols for 1-3 are included
within the supplementary information for completeness. All NMR spectra were recorded using a
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Bruker Avance II 400 or Bruker Avance III 500 spectrometer at 25 °C. Assignments of 1H and 13C NMR
spectra were made with the use of H‒H DQF-COSY, H‒C HSQC, H‒C HMBC two-dimensional
1
13
19
experiments. For H and C NMR tetramethylsilane was used as an external standard, for F{1H}
NMR CCl3F was used as an external standard. Residual solvent peaks were also used for calibration
(CDCl3 δH 7.26, δC 77.2 ppm). Chemical shifts (δ) are given in parts per million (ppm). Coupling
constants (J) are given in Hertz (Hz). Mass Spectrometry spectra were acquired at the EPSRC UK
National Mass Spectrometry Facility in Swansea using a Waters Xevo G2-S (ASAP). Infrared spectra
were recorded as KBr discs in the range of 4000-400 cm−1 using a Perkin-Elmer System 2000 NIR
Fourier Transform spectrometer. Elemental analyses were performed by Stephen Boyer at the
London Metropolitan University.
2.2 Experimental
General Method A
To a solution of 3 (1 eq.) dissolved in ethanol (15 mL), sodium hydroxide (2.2 eq.) was added and the
solution stirred for 30 minutes. The benzyl bromide (2.2 eq.) was added to the reaction flask, and the
resulting mixture stirred for 24 hours at room temperature. The solvent was removed and the crude
product dissolved in diethyl ether (20 mL). The suspension was filtered under vacuum to remove the
salt by-product. The filtrate was concentrated under reduced pressure yielding the crude product.
Recrystallisation from ethanol afforded the product.
2,2’-bis(benzylthio)-1,1’-biphenyl (4)
NMR atom numbering for 4.
Prepared following method A using 3 (100 mg, 0.46 mmol), sodium hydroxide (39 mg, 1.01 mmol)
and benzyl bromide (0.12 mL, 1.01 mmol). Compound 4 was obtained as a white crystalline solid (96
mg, 0.24 mmol, 53%), m.p 110-113 °C (lit. 116 °C).[12] Crystals suitable for X-ray work were obtained
by recrystallisation from ethanol. Anal. calcd. for C26H22S2 (398.58 g mol−1): C, 78.34; H, 5.56. Found
5

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1
3
4
C, 78.27; H, 5.66. H NMR: δH (400.1 MHz, CDCl3) 7.37 (2H, dd, JHH 7.9, JHH 1.3 Hz, H-5), 7.29 (2H,
3
4
3
pseudo-td, JHH 7.6, JHH 1.6 Hz, H-4), 7.24-7.16 (12H, m, H-3, 9,10,11), 7.07 (2H, dd, JHH 7.5, 1.6 Hz,
2
13
H-2), 3.99 (4H, ABq, ΔδAB 0.02, JHH 12.9 Hz, H-7). C NMR: δc (100.6 MHz, CDCl3) 141.1 (ArCq, C-6),
137.3 (ArCq, C-8), 136.3 (ArCq, C-1), 130.5 (ArCH, C-5), 129.1 (ArCH, C-9), 128.9 (ArCH,C-2), 128.5
(ArCH, C-10), 128.3 (ArCH, C-3), 127.2 (ArCH, C-11), 125.9 (ArCH, C-4), 38.6 (CH2, C-7). HRMS (APCI+):
m/z (%) 399.1236 (20) [M+H]+, 321.0767 (5) [M−C6H5]+, 307.0610 (10) [M−C7H7]+, 287.0889 (15)
[M−C7H8S]+, 229.0140 (25) [M−C13H13]+, 181.1011 (100). IR (KBr): νmax/cm−1 3126w (νAr-H), 2922m (νC-
H), 1578m, 1510m, 1424m, 1041m, 1069s, 717s (νC-S). Raman (glass capillary): νmax/cm−1 3053s (νAr-H),
2924m (νC-H), 1588s, 1237m, 1040m, 1003s, 723s (νC-S), 466m.
2,2’-bis((4-methylbenzyl)thio)-1,1’-biphenyl (5)
NMR atom numbering for 5.
Prepared following method A using 3 (118 mg, 0.54 mmol), sodium hydroxide (46 mg, 1.18 mmol)
and 4-methylbenzyl bromide (220 mg, 1.18 mmol). Compound 5 was obtained as a white crystalline
solid (103 mg, 0.24 mmol, 45%), m.p 128-130 °C. Crystals suitable for X-ray work were obtained by
recrystallisation from ethanol. Anal. calcd. for C28H26S2 (426.63 g mol−1): C, 78.83; H, 6.14. Found C,
1
3
4
78.69; H, 6.24. H NMR: δH (500.1 MHz, CDCl3) 7.38 (2H, dd, JHH 7.9, JHH 1.3 Hz, H-2) 7.30 (2H,
pseudo-td, 3JHH 7.6, 4JHH 1.6 Hz, H-3), 7.21 (2H, pseudo-td, 3JHH 7.4, 4JHH 1.3 Hz, H-4), 7.14-7.08 (6H, m,
H-5, 9), 7.04 (4H, d, 3JHH 7.9 Hz, H-10), 3.98 (4H, ABq, ΔδAB 0.02, 2JHH 12.8 Hz, H-7), 2.31 (6H, s, H-12).
13C NMR: δc (125.8 MHz, CDCl3) 140.9 (ArCq, C-6), 136.8 (ArCq, C-11), 136.6 (ArCq, C-1), 134.1 (ArCq, C-
8), 130.5 (ArCH, C-5), 129.2 (ArCH C-10,) 128.9 (ArCH, C-9), 128.7 (ArCH, C-2), 128.3 (ArCH, C-3),
125.7 (ArCH, C-4), 38.1 (CH2, C-7), 21.2 (CH3, C-12). HRMS (APCI+): m/z (%) 427.1539 (3) [M+H]+,
105.0693 (100) [M−C20H17S2]+. IR (KBr): νmax/cm−1 3052w (νAr-H), 2919m (νC-H), 1579s, 1452s, 1087m,
1040s, 741m (νC-S). Raman (glass capillary): νmax/cm−1 3060s (νAr-H), 2922m (νC-H), 1587m, 1237m,
1042m, 744s (νC-S).
6

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2,2’-bis((4-bromobenzyl)thio)-1,1’-biphenyl (6)
NMR atom numbering for 6.
Prepared following method A using 3 (104 mg, 0.48 mmol), sodium hydroxide (40 mg, 1.05 mmol)
and 4-bromobenzyl bromide (260 mg, 1.05 mmol). Compound 6 was obtained as white needle like
crystals (132 mg, 0.24 mmol, 51%), m.p 125-127 °C. Crystals suitable for X-ray work were obtained
by recrystallisation from ethanol. Anal. calcd. for C26H20Br2S2 (556.37 g mol−1): C, 56.12; H, 3.62.
1
Found C, 55.98; H, 3.60. H NMR: δH (500.1 MHz, CDCl3) 7.38-7.30 (8H, m, H-2, 3, 10), 7.25 (2H,
pseudo-td, 3JHH 7.4, 4JHH 1.2 Hz, H-4), 7.06 (2H, dd, 3JHH 7.5, 4JHH 1.4 Hz, H-5), 7.04 (4H, d, 3JHH 8.3, H-9),
2
13
3.87 (4H, ABq, ΔδAB 0.02, JHH 12.9 Hz, H-7). C NMR: δc (125.8 MHz, CDCl3) 141.3 (ArCq, C-6), 136.3
(ArCq, C-8), 135.4 (ArCq, C-1), 131.4 (ArCH, C-10), 130.5 (ArCH, C-9), 130.4 (ArCH, C-5), 129.4 (ArCH,
C-2), 128.3 (ArCH, C-3), 126.2 (ArCH, C-4), 120.9 (ArCq, C-11), 37.9 (CH2, C-7). HRMS (APCI+): m/z (%)
184.0334 (15) [M−C14H12Br2S]+, 170.9620 (81Br) & 168.9640 (79Br) (100) [M−C19H14BrS2]+. IR (KBr):
νmax/cm−1 3054w (νAr-H), 1560m, 1454s, 1423s, 1214s, 1025m, 760s (νC-Br), 723m (νC-S). Raman (glass
capillary): νmax/cm−1 3047s (νAr-H), 2923w (νC-H), 1588s, 1485s, 1069m, 750 (νC-Br).
7

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2,2’-bis((4-fluorobenzyl)thio)-1,1’-biphenyl (7)
NMR atom numbering for 7.
Prepared following method A using 3 (108 mg, 0.50 mmol), sodium hydroxide (39 mg, 1.0 mmol) and
4-fluorobenzyl bromide (0.12 mL, 1.0 mmol). Compound 7 was obtained as white needle crystals
(148 mg, 0.34 mmol, 69%), m.p 108-110 °C. Crystals suitable for X-ray work were obtained by
recrystallisation from ethanol. Anal. calcd. for C26H20F2S2 (434.56 g mol−1): C, 71.85; H, 4.64. Found C,
1
3
4
71.77; H, 4.61. H NMR: δH (500.1 MHz, CDCl3) 7.35 (2H, dd, JHH 7.8, JHH 1.0 Hz, H-2), 7.29 (2H,
pseudo-td, 3JHH 7.6, 4JHH 1.5 Hz, H-3), 7.22 (2H, pseudo-td, 3JHH 7.4, 4JHH 1.3 Hz, H-4), 7.14-7.11 (4H, m,
3
4
2
H-9), 7.06 (4H, dd, JHH 7.9, JHH 1.4 Hz, H-5), 6.91-6.86 (4H, m, H-10), 3.93 (4H, ABq, ΔδAB 0.02, JHH
13
1
12.9 Hz, H-7). C NMR: δc (125.8 MHz, CDCl3) 161.9 (ArCq, d, JCF 245.6 Hz, C-6), 141.2 (ArCq, C-6),
4
135.7 (ArCq, C-1), 132.9 (ArCq, d, JCF 3.2 Hz, C-8), 130.5 (ArCH, C-5), 130.4 (ArCH, C-9), 129.3 (ArCH,
2
19
C-2), 128.5 (ArCH C-3), 126.1 (ArCH, C-4), 115.3 (ArCH, d, JCF 21.7 Hz, C-10), 37.8 (CH2, C-7). F{1H}
NMR: δF (376.5 MHz, CDCl3) −115.55 (s). HRMS (APCI+): m/z (%) 184.0338 (45) [M−C14H12F2S]+,
109.0444 (100) [M−C19H14FS2]+. IR (KBr): νmax/cm−1 3060w (νAr-H), 1597m, 1504s, 1214s, 1087m, 839s
(νC-F), 741m (νC-S). Raman (glass capillary): νmax/cm−1 3075s (νAr-H), 1591s, 1236m, 1040m, 851s, 749s
(νC-F), 665s (νC-S).
8

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2,2'-bis((4-trifluoromethyl)thio)-1,1'-biphenyl (8)
NMR atom numbering for 8.
Prepared following method A using 3 (106 mg, 0.49 mmol), sodium hydroxide (42 mg, 1.08 mmol)
and 1-(bromomethyl)-4-(trifluoromethyl)benzene (255 mg, 1.07 mmol). Compound 8 was obtained
as a crystalline solid (98 mg, 0.18 mmol, 38%), m.p 100-102 °C. Crystals suitable for X-ray work were
obtained by recrystallisation from ethanol. Anal. calcd. for C28H20F6S2 (534.58 g mol−1): C, 62.90; H,
3.77. Found C, 62.94; H, 3.72. 1H NMR: δH (400.1 MHz, CDCl3) 7.44 (4H, d, 3JHH 8.1 Hz, H-10), 7.37 (2H,
dd, 3JHH 7.8, 4JHH 1.0 Hz, H-2), 7.33 (2H, pseudo-td, 3JHH 7.6, 4JHH 1.5 Hz, H-3), 7.23-7.20 (6H, m, H-4, 9),
6.98 (2H, dd, 3JHH 7.5, 4JHH 1.4 Hz, H-5), 3.95 (4H, ABq, ΔδAB 0.01, 2JHH 13.4 Hz, H-7). 13C NMR: δc (100.6
MHz, CDCl3) 141.6 (ArCq, C-8), 141.5 (ArCq, C-6), 135.1 (ArCq, C-1), 130.4 (ArCq, C-5), 129.7 (ArCH, C-
2
2), 129.3 (ArCq, q, JCF 32.0 Hz, C-11), 129.1 (ArCH, C-9), 128.4 (ArCH, C-3), 126.4 (ArCH, C-4), 125.3
3
1
19
(ArCH, q, JCF 3.7 Hz, C-10), 124.1 (ArCq, q, JCF 273 Hz, C-12), 38.3 (CH2, C-7). F{1H} NMR: δF (376.5
MHz, CDCl3) −62.52 (s). HRMS (APCI+): m/z (%) 535.0970 (5) [M+H]+, 159.0410 (100) [M−C20H14F3S2]+.
IR (KBr): νmax/cm−1 3056w (νAr-H), 1616m, 1455m, 1420m, 1323s, 1121m, 854m (νC-F), 754m (νC-S).
Raman (glass capillary): νmax/cm−1 3063w (νAr-H), 2917m (νC-H), 1618m, 1590s, 1242s, 1324m (νC-F),
1044m, 831m, 713m (νC-S).
9

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2,2'-bis((4-nitrobenzyl)thio)-1,1'-biphenyl (9)
NMR atom numbering for 9.
To a solution of 3 (106 mg, 0.49 mmol) dissolved in ethanol (15 mL), sodium hydroxide (42 mg, 1.08
mmol) was added and the solution was stirred for 30 minutes. 4-nitrobenzyl bromide (232 mg, 1.08
mmol) was added to the reaction flask, and the mixture was stirred for 24 hours at room
temperature. The solvent was removed and the crude product dissolved in dichloromethane (20
mL). The reaction mixture was filtered under vacuum to remove the salt. The filtrate was
concentrated under reduced pressure, yielding the crude product. Recrystallisation via a diffusion of
diethyl ether into a saturated DCM solution containing the product resulted in colourless crystals (76
mg, 0.15 mmol, 32%), m.p 185-188 °C. Crystal suitable for X-ray work were obtained by diffusion of
diethyl ether into a saturated DCM solution of 9. Anal. calcd. for C26H20N2O4S2 (512.60 g mol−1): C,
63.91; H, 4.12; N, 5.73. Found C, 63.88; H, 3.96; N, 5.81. 1H NMR: δH (500.1 MHz, CDCl3) 8.06 (4H, d,
3
3
3JHH 8.7 Hz, H-10), 7.38 (2H, d, JHH 7.8 Hz, H-2), 7.33 (2H, pseudo-td, JHH 7.6, 4JHH 1.4 Hz, H-3), 7.29-
7.23 (6H, m, H-4, 9), 7.02 (2H, dd, 3JHH 7.5, 4JHH 1.2 Hz, H-5), 3.97 (4H, ABq, ΔδAB 0.02, 2JHH 13.6 Hz, H-
13
7). C NMR: δc (125.8 MHz, CDCl3) 146.9 (ArCq, C-8), 145.2 (ArCq, C-11), 141.9 (ArCq, C-6), 134.4
(ArCq, C-1), 130.4 (ArCH, C-5), 130.3 (ArCH, C-2), 129.6 (ArCH, C-4), 128.6 (ArCH, C-3), 126.9 (ArCH, C-
9), 123.6 (ArCH, C-10), 38.3 (CH2, C-7). HRMS (APCI+): m/z (%) 216.0063 (100) [M−C14H12N2O4]+,
184.0341 (45) [M−C14H12N2O4S]+. IR (KBr): νmax/cm−1 3072w (νAr-H), 1601m, 1517s (νN-O), 1341s (νN-O),
1087m, 860s, 754m (νC-S). Raman (glass capillary): νmax/cm−1 3070w (νAr-H), 1601m, 1520m (νN-O),
1345s (νN-O), 1110m, 863m, 754m (νC-S).
10

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2,2’-bis(neopentylthio)-1,1’-biphenyl (10)
NMR atom numbering for 10.
To a solution of 3 (101 mg, 0.46 mmol) dissolved in ethanol (15 mL), sodium hydroxide (49 mg, 1.22
mmol) was added and the solution was stirred for 30 minutes. Neopentyl bromide (0.13 mL, 1.03
mmol) was added to the reaction flask and the mixture was stirred for 10 minutes at room
temperature before being heated under reflux for 66 hours. The solvent was removed and the crude
product dissolved in diethyl ether (20 mL). The reaction mixture was filtered under vacuum to
remove the salt. The filtrate was concentrated under reduced pressure, yielding a white/pale yellow
1
oil which slowly solidified over several days (114 mg, 0.32 mmol, 70%). H NMR: δH (500.1 MHz,
3
4
CDCl3) 7.45 (2H, dd, J 8.0, 1.2 Hz, H-2), 7.31 (2H, pseudo-td, JHH 7.6, JHH 1.7 Hz, H-3), 7.21 (2H,
3
4
3
4
pseudo-td, JHH 7.4, JHH 1.2 Hz, H-4), 7.16 (2H, dd, JHH 7.6, JHH 1.7 Hz, H-5), 2.75 (4H, s, H-7), 0.92
13
(18H, s, H-9). C NMR: δc (125.8 MHz, CDCl3) 141.1 (ArCq, C-6), 137.7 (ArCq, C-1), 130.3 (ArCH, C-5),
128.3 (ArCH, C-2), 127.9 (ArCH, C-3), 124.9 (ArCH, C-4), 48.1 (CH2, C-7), 32.18 (Cq, C-8) 28.9 (CH3, C-
9). HRMS (APCI+): m/z (%) 359.1864 (100) [M+H]+, 233.0100 (25). IR (KBr): νmax/cm−1 3052w (νAr-H),
2956s (νC-H), 2865m (νC-H), 1580m, 1364m, 1452s, 1086s, 751s, 475w.
2.3 X-ray Crystallography
Table 1 lists the details of data collections and refinements for 4-9. Data for 4-7 and 9 were collected
using a Rigaku FRX (Mo-Kα, confocal optic) equipped with a Dectris P200 detector at −100 °C; for 8
using a Rigaku Saturn724 (Mo-Kα) at −148 °C. The data for all compounds were collected and
processed using CrystalClear (Rigaku). The crystal structures were solved using direct methods and
refined by full-matrix least-squares against F2 (SHELXL) or heavy-atom Patterson methods and
expanded using Fourier techniques.[28] The non-hydrogen atoms were refined anisotropically,
hydrogen atoms were assigned riding isotropic displacement parameters and constrained to
idealised geometries. Searches of the Cambridge Structure Database were performed using the
WebCSD.[29].
These
data
can
be
obtained
free
of
charge
via
11

ACCEPTED MANUSCRIPT
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax (+44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk. CCDC
Numbers XXXXX-XXXXX.
Table 1: Details of the X-ray data collections and refinements for compounds 4-9.
Compound
4
C26H22S2
398.58
Triclinic
P-1
5
C28H26S2
426.63
Monoclinic
I2/a
6
7
8
9
C26H20N2O4S2
488.57
Monoclinic
P21/n
Formula
C26H20Br2S2
536.37
Monoclinic
P21/n
C26H20F2S2
434.56
C28H20F6S2
534.58
Monoclinic
P21/n
M
Crystal system
Triclinic
P-1
Space group
a/Å
9.663(4)
9.882(5)
11.617(6)
111.388(10)
93.614(6)
91.962(11)
1028.9(9)
2
19.162(8)
6.116(3)
20.836(4)
90
10.942(3)
7.7060(19)
26.893(7)
90
7.9777(18)
11.591(2)
12.626(2)
68.091(14)
75.561(15)
81.733(17)
1047.3(4)
2
11.318(8)
7.664(5)
27.051(19)
90
8.0281(10)
36.034(5)
15.957(2)
90
b/Å
c/Å
α
β
112.12(2)
90
91.039(5)
90
93.152(17)
90
102.219(3)
90
γ
U/A3
2265.6(15)
4
2267.2(10)
4
2343(3)
4
4511.5(10)
8
Z
µ/mm-1
0.267
0.247
3.782
0.282
0.291
0.274
Reflections collected
Independent reflections
Rint
13941
9504
19488
15119
30073
44187
3703
2041
4157
3810
4300
8266
0.0541
0.0639
0.1439
0.0478
0.0649
0.1255
0.0299
0.0390
0.0637
0.0500
0.0606
0.1039
0.1797
0.0447
0.0528
0.1251
Rall
0.0634
wR2 [I > 2σ(I)]
0.1210
3. Results and Discussion
3.1 Synthesis
The previous method of synthesising chalcogenoether compounds on naphthalene and
acenaphthene used within the Woollins group started from 1,8-dibromonaphthalene and 5,6-
dibromoacenaphthene respectively. A low temperature lithium halogen exchange using n-butyl
lithium followed by addition of RE‒ER (where R = alkyl or aryl; E = S, Se, Te) resulted in the desired
compounds. 2,2′-dibromo-1,1′-biphenyl is easily prepared in good yields (74%) as shown in Scheme
1,[25] the addition of 2 molar equivalents of n-butyl lithium to 1 followed by PhE‒EPh (E = S, Te)
resulted in inseparable mixtures. Some evidence for the successful formation of the tellurium
analogue was found within the mass spectrum with a signal at m/z 562.9575 with the isotope
pattern matching that predicted for this [M+H]+ peak (Figures S1 and S2 in ESI). In the case of the
12

ACCEPTED MANUSCRIPT
tellurium derivative the main compound isolated after a purification attempt using column
chromatography was dibenzo[b,d]tellurophene (43%).
Scheme 1: Initial synthetic route towards bis(chalcogen) biphenyls.
Since adding the aryl-chalcogen species directly onto the biphenyl backbone was unsuccessful a new
synthetic route starting from 2 was devised for the sulfur derivatives (Scheme 2). The equivalent
tellurium compound is unknown in the literature with attempts to prepare it resulting in the
formation of dibenzo[b,d]tellurophene.[30] For this reason the sulfur compounds became the focus
for the rest of this investigation. By forming a reactive dithiolate species a simple SN2 reaction with a
compound such as R‒Br was expected to occur. The reduction of 2 to 1,1′-biphenyl-2,2′-dithiol (3)
using sodium borohydride was achieved almost quantitatively (yield >99%).[26] The deprotonation
of 3 to form the dithiolate is easily achieved using a base such as sodium hydroxide. We chose a
series of benzyl bromides with varying substituents in the para position of the phenyl ring in addition
to neopentyl bromide to react with the biphenyl dithiolate (Scheme 2).
13

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S
S
SH
NaBH4
EtOH/THF, 0 °C
HS
2
3
NaOH, EtOH
RCH2-Br
R
S
4, R = Ph;
5, R = (p-Me)Ph
6, R = (p-Br)Ph; 7, R = (p-F)Ph
8, R = (p-CF3)Ph; 9, R = (p-NO2)Ph
10, R = t-Bu
S
R
Scheme 2: Synthetic route to 2,2′-bis(alkylthio)-1,1′-biphenyls 4-10.
Compound 3 was stirred in ethanol with 2 equivalents of sodium hydroxide for 0.5 h prior to
addition of the alkyl bromide. Compounds 4-9 were obtained in 32-69% yields as white/off-white
solids after purification. Purification of 4-8 was achieved via recrystallisation from boiling ethanol
resulting in crystals which were suitable for single crystal X-ray diffraction. Compound 9 was purified
by recrystallisation from a mixture of CH2Cl2/diethyl ether. During the attempt to recrystallise 10 the
compound decomposed, attempts to purify via column chromatography also proved unsuccessful.
1
The impurity present within 10 was identified as 2 via examination of its H NMR spectrum; this
showed that 10 made up 82% of the mixture allowing the yield to be calculated as 70%. The bulk
purity of 4-9 was determined by elemental analysis. Compound 9 has been previously reported by
Millar in 1971 as part of a study synthesising macrocyclic compounds with sulfur and oxygen within
1
the ring.[12] Modern spectroscopic techniques allow for a more detailed analysis of its H NMR
spectrum with additional 13C and infrared spectroscopic data reported alongside its mass spectrum.
3.2 Crystallographic Analysis
Crystal structures of 4, 5, 7 and 9 are shown Figure 4 with 6 and 8 in Figure 5. Selected structural
parameters listed in Table 2. All the C‒S bond lengths are comparable to the average CAlk‒S and CAr‒S
bond lengths (CAlk‒S, 1.762 Å and CAr‒S, 1.790 Å) determined from similar structures within the
Cambridge Structural Database.[31] The C‒S‒C angles all confirm the expected non-linear geometry
around the sulfur atom with little deviation across the series (C‒S‒C, 99.3(1)-104.6(1)°). The torsion
14

ACCEPTED MANUSCRIPT
angle between the two phenyl rings within the biphenyl backbone shows more variation.
Compounds 5 (72.1(3)°), 6 (−84.7(3)°), 7 (−76.7(3)°) and 8 (−83.9(6)°) all have values below 90° as the
two phenyl rings close up slightly. Compounds 4 (−112.3(3)°) and 9 (110.0(2)°) both display torsion
angles greater than 90° as the phenyl rings move further apart.
Table 2: Selected bond lengths [Å], angles [°] and torsions [°] for 4-9.
4
5
6
S‒C†
1.765(3)-1.822(3)
1.768(2)-1.822(3)
1.775(3)-1.827(2)
C1‒S1‒C13
C1‒S1‒ C7
104.4(1)
−
101.2(1)
−
103.4(5)
−
C8‒S8‒C20
C1‒C2‒C7‒C8
C1‒C2‒C2′‒C1′
103.4(1)
−
104.6(1)
−112.3(3)
−
72.1(3)
8
−84.7(3)
−
−
7
1.773(2)-1.824(3)
102.5(1)
99.3(1)
9
S‒C†
1.753(5)-1.815(5)
100.9(2)
−
1.779(2)-1.826(2)
101.71(9) [102.32(8)]
102.40(9) [101.92(9)]
−
C1‒S1‒C13
C8‒S8‒C20
C8‒S8‒C21
C1‒C2‒C7‒C8
−
104.8(2)
−83.9(6)
−76.7(3)
110.0(2) [−110.4(2)]
[] denotes from second molecule within the asymmetric unit.
† ranges quoted for S‒C bond lengths of molecules within the asymmetric unit.
15

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Figure 4: Crystal structures of 4 (top left), 5 (top right), 7 (bottom left) and 9 (bottom right). Only one
molecule within the asymmetric unit is shown for 9. Hydrogen atoms omitted for clarity, ellipsoids
plotted at the 40% probability level.
16

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Two different conformers are present within the crystal structures of compounds 4-9. For 4, 5, 7 and
9 the compound attains an “open” structure, i.e. the two benzyl substituents point away from each
other (anti-parallel). This is expected as it results in minimal steric repulsion between the two benzyl
groups. Interestingly in 6 and 8 the structures adopt a “closed” structure with the two benzyl
substituents pointing roughly in the same direction (parallel). This is likely due to packing effects
with long range Br‒H (3.044 Å) and F‒H (2.594 Å) interactions present within 6 and 8 respectively.
Figure 5: Crystal structures of 6 (left) and 8 (right). Hydrogen atoms omitted for clarity, ellipsoids
plotted at the 40% probability level.
3.3 Spectroscopic Analysis
1
The benzyl and neopentyl bromide starting materials all display singlets in their H NMR spectra
corresponding to the CH2 fragment (δH 4.43-4.53 (benzyls) and 3.27 (neopentyl) ppm). Compounds
4-10 all display an upfield shift in this signal with the benzyl derivatives at δH 3.93-3.99 ppm and the
neopentyl at δH 2.75 ppm. This upfield shift is as a result of exchanging the bromine atom with a
1
more donating sulfur atom. Interestingly in the case of 4-9 this signal within the H NMR spectra
appears as four lines in an AB system. The signal appears this way as the difference in chemical shift
between the two CH2 protons determined in hertz is very close in magnitude to the coupling
between them. This second order coupling suggests restricted rotation around the aryl‒aryl bond in
the biphenyl backbone. This restricted rotation arises owing to the bulky nature of the benzyl groups
17

ACCEPTED MANUSCRIPT
in the ortho positions preventing free rotation around the biphenyl aryl‒aryl bond. Such restriction
results in axial chirality[32] within the molecule which causes the nearby hydrogen atoms (CH2
group) to become diastereotopic. Similar observations were made by Mazzanti during their
investigation into hindered biphenyl carbinols.[33] They used enantioselective HPLC to resolve the
enantiomers and determined the absolute configuration on the basis of the obtained CD (circular
dichroism) spectra. The true centres for each of the doublets within the AB systems for 4-9 were
determined with the calculations included within the supplementary information. The true centres
1
determined differed only slightly from those seen using the H NMR spectra directly (ΔδAB ≈ 0.02
ppm). Figure 6 shows the AB system present within 4 with the true centres of each doublet
highlighted. For 10 this signal appears as a singlet indicating the aryl‒aryl bond can now freely
rotate. Within the aromatic region of 4-9 the signals corresponding to the phenyl ring of the benzyl
group display shifts downfield compared to those in the respective starting materials. For the
fluorine containing compound 7 these signals appeared as multiplets due to coupling to the NMR
active fluorine atom.
Figure 6: AB system present within the 1H NMR spectrum of 4 with the calculated true centres
shown.
18

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The biphenyl backbone was expected to result in four signals, two doublet of doublets (Ha and Hd,
1
Figure 7) and two doublet of doublet of doublets (Hb and Hc, Figure 7) in the H NMR spectra.
However, the signals corresponding to Hb and Hc actually appear as pseudo triplet of doublets.
3
Taking Hb as an example this occurs due to the almost identical magnitude of the JHH coupling
between Hb and Ha as well as Hb and Hc as shown in Figure 7. These observations mirror those made
in other compounds where we have used the biphenyl dithiolate backbone.[34, 35] The aromatic
signals arising from the benzyl substituents in 4-9 are present as expected with some appearing as
multiplets due to overlapping with the biphenyl signals.
Figure 7: The section of the 1H NMR spectrum of 5 showing the two pseudo triplet of doublets with a
splitting diagram showing how these signals are formed.
19

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13C NMR spectra were obtained for 4-10 and in all cases the number of signal corresponding to
quaternary, CH and CH3 carbon atoms matched what was expected. No indication of any other
13
species being present was observed for 4-9. The expected signals for the impurity (2) within the C
NMR spectrum of 10 were observed. The fluorine containing compounds 7 and 8 resulted in the
phenyl ring carbon atoms of the benzyl group being split into doublets as expected. The CF3 group in
8 gave rise to a quartet in the 13C NMR spectrum (δC 124.1 ppm) with a large 1JCF coupling constant of
273 Hz which was similar to other compounds incorporating the S‒CH2‒(Ph(p-CF3)) moiety.[36] The
19F{1H} NMR spectra of 7 and 8 showed only one signal at δF −115.6 (7) and −62.5 (8) ppm providing
further evidence that only one species is present. High resolution mass spectroscopy of 4-10 showed
[M+H]+ ions for 4, 5, 8 and 10 each displaying the expected isotopic distribution pattern. For 6, 7 and
9 signals corresponding to [XPhCH2]+ (X = Br (6), F (7), NO2 (9)) and [BiphenS]+ were observed
however no [M+H]+ peaks were present.
4. Conclusions
A series of bis(alkyl)thioethers based upon a biphenyl backbone were successfully synthesised. The
benzyl containing compounds all displayed an AB quartet for the benzyl CH2 signal owing to axially
chirality introduced by restricted rotation around the aryl‒aryl bond of the biphenyl backbone.
When the benzyl group was changed to neopentyl this signal appeared as a singlet as the biphenyl
backbone can now freely rotate. Analysis of the solid state structures of the benzyl derivatives
showed two conformers, anti-parallel where the benzyl groups point away from each other and
parallel where they are pointing in the same direction. The potential of these compounds to act as
ligands will be investigated next.
20

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Bis(alkyl)thioethers on a biphenyl scaffold: A
spectroscopic and structural insight
Rhiann Ferguson, Phillip S. Nejman, Alexandra M. Z. Slawin and J. Derek
Woollins*
EaStCHEM School of Chemistry,
University of St Andrews,
St Andrews, Fife, KY16 9ST
jdw3@st-and.ac.uk
Highlights
•
•
Robust synthetic procedure towards bis(alkyl)thioethers on a polyaromatic backbone.
Restricted rotation of the biphenyl backbone induces axial chirality and results in
diastereotopic benzyl CH2 hydrogens.
•
X-ray structures show two conformers present within the benzyl series.