Synthesis of mono- and di-potassium salts and methoxy adducts of sulfur-bridged biphenols by selective deprotonation

Article abstract of DOI:10.1039/b301015e

Mono- and di-potassium salts and methoxy adducts of sulfur-bridged biphenols by selective deprotonation were synthesized. Flame photometry analysis and a crystal x-ray structural determination were carried out to confirm the composition. Addition of an ethereal solution to a stirred suspension of stoichiometric KH in diethyl ether afforded an analytically pure pale yellow precipitate characterized as the mono-potassium salt. The non-macrocyclic ligands described show selective deprotonation chemistry, creating simple routes to tuneable, mono- or di-anionic acryloxide-based ligands.

Full text of DOI:10.1039/b301015e

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Synthesis of mono- and di-potassium salts and methoxy adducts of
sulfur-bridged biphenols by selective deprotonation†
Polly L. Arnold,* Jonathan J. Hall, Louise S. Natrajan, Alexander J. Blake and Claire Wilson
School of Chemistry, The University of Nottingham, University Park, Nottingham,
UK NG7 2RD. E-mail: Polly.Arnold@Nottingham.ac.uk
Received 24th January 2003, Accepted 14th February 2003
First published as an Advance Article on the web 21st February 2003
Treatment of the sulfur-bridged biphenol [1,1Ј-S(2-HOC6-
H2But-3-Me-5)2] with potassium hydride in diethyl ether
results in the selective deprotonation of one phenol group
to yield [1,1Ј-S(2-KO)(2Ј-HO)(C6H2But-3-Me-5)2(Et2O)],
whereas an excess of potassium hydride in thf is required
to generate the dianion [1,1Ј-S(2-KOC6H2But-3-Me-5)2-
(thf)2]; the same selective deprotonation is observed for the
binaphthol [1,1Ј-S(2-HOC10H4But2-3,6)2], suggesting that
intramolecular H-bonding stabilises the second, remaining
hydroxyl group, allowing new, simple routes to tuneable,
mono- or di-anionic aryloxide-based ligands.
tholates to be synthesised cleanly. This provides potentially tri-
dentate ligands that have a tuneable balance between electric
charge and donor functional group type and strength.
Addition of an ethereal solution of 1 to a stirred suspension
of stoichiometric KH in diethyl ether affords an analytically
pure pale yellow precipitate characterised as the mono-
potassium
salt,
[1,1Ј-S(2-KO)(2Ј-HO)(C6H2But-3-Me-5)2-
(Et2O)] 3, isolated in 82% yield,‡ Scheme 1. 1H NMR spectro-
scopic analysis of a d6-benzene solution of 3 reveals the
remaining OH resonates at 14.9 ppm (fwhm 50 Hz), compared
with 6.6 ppm in 1. This contrasts with the synthesis of the
lithiated derivatives that afford only the doubly deprotonated
material. To confirm the composition, flame photometry
(K content) analysis and a crystal X-ray structural deter-
mination, Fig. 1 have been carried out.
The d-block chemistry of sulfur bridged biphenolates based on
1 has been studied in depth in recent years. It has already been
show that lithiation of the biphenol allows easy access to
[Ti[1,1Ј-S(2-OC6H2But-3-Me-5)2](Cl)2], an excellent precatalyst
for the polymerisation and copolymerisation of alkenes in
conjunction with a cocatalyst methylalumoxane (MAO).1 In
the course of our investigations on new f-block adducts of
2,2Ј-thiobis-(2,4-di-tert-butylphenol) [1,1Ј-S(2-HOC6H2But-3-
Me-5)2], 1 and its naphthyl analogue, 2,2Ј-thiobis-(2,4-di-tert-
butylnaphthol) [1,1Ј-S(2-HOC10H4But2-3,6)2] 2, we found
that tris(aryloxide)lanthanide() complexes react cleanly with
dilithiated 1 – [S(LiOC6H2ButMe)2] to give pentane-insoluble
lithium aryloxide as a byproduct.2 However, it is now widely
accepted that the use of potassium salts gives cleaner
metathesis chemistry for the f-block elements, and reduces salt
incorporation. Since it is desirable to use metathetical routes
to access many new f- as well as new d-block systems of the
sulfur-bridged biphenolates, we have studied the Group 1
chemistry of 1 and 2. Traditionally, phenols are cleanly depro-
tonated by treatment with one equivalent of potassium hydride
in any ethereal solvent in which the phenol is soluble. A
macrocyclic analogue of 1, p-tert-butyltetrathiacalix[4]arene
has been reported; only the monopotassium salt is reported to
be accessible.3
Scheme 1
The structure of 3 is dimeric and diethyl ether solvated. The
anionic O of each ligand bridges the two potassium centres, and
in an unprecedented binding mode for this ligand, the neutral
phenol of each bridges the two potassium ions. The K–phen-
oxide distance is 2.6778(11) Å, much shorter than the mean
K–O distance measured for a range of terminal K phenoxides
(2.765 Å).4 Although the two rings are dissimilar in the solid
state, solution characterisation shows them to be equivalent at
room temperature; the molecule of diethyl ether remaining
bound to each metal. Of the few reported potassium complexes
which are stabilised by thioether interactions, structural data
show K ؒ ؒ ؒ S distances that range from 3.222 to 3.496 Å.5 In
this complex, only the closest S atom is deemed to interact. The
K–S distance of 3.3145(7) Å is only 0.112 Å longer than other
examples of K–S single bonds,6 implying a significant K–S
interaction in the solid state.7
Herein, we show that stabilisation of the monoanion of 1 or
2 allows either mono- or di-anionic biphenolate and binaph-
† Electronic supplementary information (ESI) available: full character-
isation for all complexes described and packing diagrams for 3 and 5.
See http://www.rsc.org/suppdata/dt/b3/b301015e/
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 0 5 3 – 1 0 5 5
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Fig. 2 Ellipsoid drawing (50%) of the molecular structure of 5, But
methyl groups and solvent Et groups omitted for clarity. Selected
distances (Å) and angles (Њ): K(1)–S(1) 3.436(3), K(1)–O(1) 2.776(6),
K(1)–O(2) 2.697(7), K(1)–Oether range 2.666(7)–2.80(2); O(1)–K(1)–
O(2) 52.1(2), O(1)–K(1)–O(3) 96.3(3), O1–K1–S1 55.89(11).
Fig. 1 Ellipsoid drawing (50%) of the molecular structure of 3.
Selected distances (Å) and angles (Њ): K(1)–O(1) 2.6778(11), K(1)–
O(1A) 2.7012(12), K(1)–O(6) 2.7064(12), K(1)–O(2) 2.7428(12), K(1)–
S(1) 3.3145(7), K(1)–K(1A) 3.9412(9); O(1)–K(1)–O(1A) 85.78(4),
O(1)–K(1)–O(6) 148.17(4) O(1)–K(1A)–O(2) 53.74(3).
and this interaction favours the first deprotonation over the
second in the reaction solution.
Thus a monophenolic alternative to 1, with potentially hemi-
labile O and S donor groups, is now a viable alternative ligand
with a reduced electrical requirement. Both the mono- and di-
potassium salts may be quenched with methyl iodide to afford 7
and 8 respectively in quantitative yield, Scheme 1. Compound 8
has been reported previously.8
The tetrathiacalixarene p-tert-butylthiacalix[4]arene has
recently been proposed as an alternative to non-sulfur-
containing calixarenes in the coordination of Group 1 metals,
producing different structural types for different members
of the series, with the metal ions and remaining hydroxyl
protons often disordered over the phenolic sites.3 The non-
macrocyclic ligands described above show selective deproto-
nation chemistry, creating new, simple routes to tuneable,
mono- or di-anionic aryloxide-based ligands.
Repetition of this reaction in thf, using two equivalents or an
excess of KH, affords the dipotassium [1,1Ј-S(2-KOC6H2But-3-
Me-5)2(thf )2] 4.
The binaphthol 2 can also be converted cleanly into a mono-
or a di-potassium salt, 5 and 6 in Scheme 2. The selectivity is still
quantitative (as measured spectroscopically) for the products.
We thank the EPSRC and the Royal Society for funding.
Notes and references
‡ Data for 3: 82%. δH (C6D6): 14.9 (br s, 1H, OH ), 7.65 (s, 2H, aryl H ),
2.19, (s, 6H, methyl CH3), 1.46 (s, 18H, But), 3.24, 1.13 (q, t, 4H, 3H,
(CH3CH2)2O). ν/cmϪ1: 3426.5. Calc.(found) C22H29O2SKؒEt2O: C 66.34
(66.28), H 8.35 (8.29%). Flame photometry – Calc. (found): K 8.31
Scheme 2
(8.50%). C44H58O4S2K2ؒ(C4H10O)2,
M = 941.46, monoclinic, a =
Crystals of 5 suitable for single crystal X-ray diffraction were
grown under identical conditions to 3,§ but show a mono-
nuclear structure, Fig. 2. The triangle of [OSO] donor atoms
facially caps only one K ion rather than capping a K2 fragment
of the dimeric 3. The hydroxyl H was not located, even though
K–O(2) is significantly longer than K–O(1). Here, a longer K–S
interaction of 3.436(3) Å is measured.
12.065(2), b = 17.968(3), c = 12.609(3) Å, α = 90, β = 99.857(4), γ = 90Њ,
U = 2693.1(9) Å3, T = 150(2) K, P21/c, Z = 2, Dc = 1.161 g cmϪ3, µ(Mo-
Kα) = 0.297 mmϪ1, 6310 unique reflections (Rint 0.0579). R1 [4477 F >
4σ(F)] = 0.0405, wR(all F 2) 0.0952. For 4: 63%. δH (C6D6): 7.47, 7.00
(s, 1H, aryl H ), 1.96 (s, 3H, CH3), 1.62 (s, 9H, But). Calc.(found)
C22H28O2SK2: C 60.78 (60.51), H 6.41 (6.69%). Flame photometry –
Calc.(found) [Mؒ2thf] 13.51 (13.78%). For 5: 58%. δH (C6D6): 1.31
(s, 9H, 6-But), 1. 58 (s, 9H, 3-But), 7.76 (s, 2H, 4-H, 5-H), 7.73 (s, 1H,
3
7-H), 9.40 (d, 1H, 8-H, JHH 8.73 Hz). ν/cmϪ1: 3338.39. Calc.(found)
The monopotassium salt of p-tert-butyltetrathiacalix[4]arene
forms K-sandwiched calixarene dimers with K–O distances of
2.796 Å,3 longer than all the ionic K–O bond distances in 3 and
5, with OH ؒ ؒ ؒ O and K interactions complicated by disorder,
and K–S distances 3.335(1) and 3.348(1) Å – intermediate
between the structures described above. No π-stacking inter-
actions or close K–H contacts are observed in either structure.
Interestingly, although the solid state structures of 3 and 5
are very different, in each the K–O–C angles are close to linear,
and the O(H)–K–O angle is particularly acute – 53.7 and 52.1Њ
respectively – significantly narrower than the C–S–C angle that
would normally determine this parameter (105.61(8) and
107.3(3)Њ for 3 and 5 respectively). It is possible that a sym-
metrical disposition of the remaining hydroxyl H between the
two O atoms renders the rings approximately equivalent even in
C36H45O2SK: C 74.48 (74.64), H 7.76 (7.89%). C36H45O2SKؒ(C4H10O)3.5
,
M = 840.30, monoclinic, a = 12.9794(15), b = 23.913(3), c = 17.896(2) Å,
V = 5216.5(11) Å3, T = 150(2) K, P21/c (no. 14), Z = 4, Dc = 1.070 g
cmϪ3, µ(Mo-Kα) = 0.717 mmϪ1, 12542 unique reflections (Rint 0.047). R1
[5471 F > 4σ(F)] = 0.124, wR(all F 2) 0.328. CCDC reference numbers
202297 and 202298. See http://www.rsc.org/suppdata/dt/b3/b301015e/
for crystallographic data in CIF or other electronic format. For 6:
89%. NMR/C6D6 δH: 14.2 (s, fwhm 561 Hz, 1H, OH ), 1.29 (br s, 9H,
6-But), 1. 47(br s, 9H, 3-But), 7.65 (br, 4H, 4-H, 5-H, 7-H, 8-H), 3.52
(br m, 2H, thf ), 1.39 (br m, 2H, thf ). Calc.(found) C36H44O2SK2:
C 69.85 (67.87), H 7.16 (7.69%). HRMS Calc.(found) [MH]ϩ 618.2336
(619.2345).
§ Dietherate: 10Ϫ3mbar/20 ЊC/8 h. Solvent-free: 10Ϫ3mbar/50 ЊC/16 h.
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D a l t o n T r a n s . , 2 0 0 3 , 1 0 5 3 – 1 0 5 5
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