An unusual 30-membered copper(i) cluster derived from the C-S bond cleavage and its use in heterogeneous catalysis

Article abstract of DOI:10.1039/c2cc36736j

The Cu(i)-mediated C-S bond cleavage of 5-methyl-4-(p-tolyl)pyrimidine-2- thiol (mtpmtH) gave one 30-nuclear cluster [Cu₃₀I₁₆(mtpmt) ₁₂(μ₁₀-S₄)], one polymeric complex [(bmtpms)Cu-(μ-I)]_n and one tetranuclear complex [(bmptmds){Cu(μ-I)}₂]₂; the 30-nuclear cluster displayed excellent catalytic performances in the coupling reactions of N-heterocycles and arylboronic acids and could be recycled and reused.

Full text of DOI:10.1039/c2cc36736j

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[Cu30I16(mtpmt)12(l10-S4)]: an unusual 30-membered
copper(I) cluster derived from the C–S bond cleavage
and its use in heterogeneous catalysis†‡
Hong-Xi Li,*a Wei Zhao,a Hai-Yan Li,a Zhong-Lin Xu,a Wen-Xia Wanga and
Jian-Ping Lang*ab
Cite this: Chem. Commun., 2013,
49, 4259
Received 12th August 2012,
Accepted 11th October 2012
DOI: 10.1039/c2cc36736j
www.rsc.org/chemcomm
The Cu(I)-mediated C–S bond cleavage of 5-methyl-4-(p-tolyl)pyrimi- motifs be employed to capture the possible S-containing species
dine-2-thiol (mtpmtH) gave one 30-nuclear cluster [Cu30 16(mtpmt)12 derived from the copper(I)-mediated C–S bond cleavage of a thiol?
I
-
(l10-S4)], one polymeric complex [(bmtpms)Cu-(l-I)]n and one tetra- With these in mind, we employed 5-methyl-4-(p-tolyl)pyrimidine-2-
nuclear complex [(bmptmds){Cu(l-I)}2]2; the 30-nuclear cluster displayed thiol (mtpmtH) as a substrate to react with CuI under solvothermal
excellent catalytic performances in the coupling reactions of N-hetero- conditions. This system did proceed with an intriguing Cu(I)-
cycles and arylboronic acids and could be recycled and reused.
assisted C–S bond cleavage and several cleaved species such as a
unique S42ꢀ ion, organic thioethers and disulfides were trapped by
High nuclear copper coordination complexes are of great different [CuxIy] motifs to form a set of [CuxIy]-based coordination
interest because of their synthetic challenges1 and their complexes, one 30-nuclear cluster [Cu30I16(mtpmt)12(m10-S4)] (1),
potential applications in advanced materials2 and catalysis.3 one polymeric complex [(bmtpms)Cu(m-I)]n (bmtpms = bis(5-
The inorganic4 and/or organic sulfur5 ligands are frequently methyl-4-(p-tolyl)pyrimidin-2-yl)sulfide) (2) and one tetranuclear
used to prepare these high nuclear Cu(I) complexes. Among the complex [(bmptmds){Cu(m-I)}2]2 (bmtpmds = 1,2-bis(5-methyl-4-
organosulfur ligands, nitrogen-donor-containing thiolates such (p-tolyl)pyrimidin-2-yl)disulfide) (3). In addition, some Cu(I) thio-
as pyridine-2-thiolate or pyrimidine-2-thiolate ligands could be lates are known to exhibit high reactivity in many organic
employed in the assembly of mono-, di-, tri-, tetra-, hexa- transformations, including C–X (X = O, N, C, S, B) bond for-
nuclear and polymeric complexes,6 which may largely depend mation.11 They mainly work as homogeneous catalysts and can
on their coordination modes (Scheme S1, ESI‡).7 These ligands be used only once. Thus the development of heterogeneous and
have also shown a rich redox chemistry based on both oxidative recyclable catalysts for such coupling reactions would be of great
formation and reduction cleavage of the C–S bond.8 However, importance. In this work, the insoluble cluster 1 displayed excel-
the inorganic sulfur ligands generated in situ from the C–S lent catalytic performances in the coupling reactions of N-hetero-
bond rupture of pyrimidine-2-thiol ligands have been less cycles with arylboronic acids and could be used for several cycles.
explored for synthesizing high nuclear Cu(I) clusters.9
The solvothermal reaction of CuI with equimolar mtpmtH in
On the other hand, when bulk CuI was reacted with various MeCN at 120 1C for one day followed by cooling to 65 1C
organic nitrogen and/or sulfur donor ligands, its 3D framework afforded red prisms of a large Cu–S–I cluster 1ꢁ3MeCN
could be cleaved into various [CuxIy]xꢀy motifs. These motifs may (ca. 1% yield) coupled with a small amount of black solid
interact with those coexisting in these systems like organic ligands Cu2S. The filtrate was subsequently cooled to 25 1C to form a
and counter ions to form the corresponding [CuxIy]-based coordi- yellow crystalline solid of bmtpms (42% yield). Further cooling
nation complexes.10 Then could these in situ-generated [CuxIy]xꢀy the filtrate to 0 1C gave several red needles of a Cu–I–bmtpms
polymeric complex 2ꢁ0.5MeCN coupled with some yellow
powder of bmtpms. An X-ray analysis revealed that 1ꢁ3MeCN
a College of Chemistry, Chemical Engineering and Materials Science, Soochow
University, 199 RenAi Road, Suzhou 215123, Jiangsu, P. R. China.
E-mail: jplang@suda.edu.cn, lihx@suda.edu.cn; Fax: +86 512 65880089
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 210032, P. R. China
† This article is part of the ChemComm ‘Emerging Investigators 2013’ themed
issue.
2ꢀ
contains one disordered m10-S4
ion with a rare zigzag
conformation that connects eight rhomboid [Cu3I] fragments
2ꢀ
(Fig. S1, ESI‡). On each of the two sides of this S4 ion, four
[Cu3I] fragments are bridged by two pairs of mtpmt ligands.
The resulting two [(Cu3I)4(mtpmt)4] units are further linked by
four mtpmt ligands, four iodides and two [Cu3I2] fragments,
forming an oval-shaped structure with a two-fold axis running
‡ Electronic supplementary information (ESI) available: Synthesis of 1–4, and the
coupling reactions catalysed by 1. CCDC 890819–890822 (1–4). For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c2cc36736j
2ꢀ
through the I(6)ꢁ ꢁ ꢁI(6A) contact (Fig. 1). The m10-S4 ion binds
to ten Cu atoms, which is different from the chelating or
c
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It is noteworthy that in such a reductive C–S bond-cleaving
reaction, O2 acted as an oxidant, which is different from the
Cu2+ ion as an oxidant in the hydro(solvo)thermal reactions.7 In
our system, O2 existed since the reactants and solvents were
loaded in the Pyrex glass tubes and sealed in open air. While
the solvothermal reactions of CuI and two equiv. of mtpmtH in
MeCN–DMF were carried out under an argon atmosphere, they
did not form 1 but gave rise to one hexanuclear complex
[Cu6(mtpmt)6] (4) in 67% yield. When the solution of 3 in
MeCN–DMF or the solution containing CuI/bmptmds was
heated under solvothermal conditions, 1 could be isolated in
medium yields. However, 1 could not be isolated from the
similar solvothermal reactions of 2 or 4. Compounds 2 and 3
could be readily prepared in high yields from the corres-
ponding reactions of CuI with equimolar bmtpms or bmptmds
in MeCN–CHCl3. Because of the formation of S42ꢀ, bmtpms
and bmptmds, mtpmtH must partially undergo the desulfur-
ization reaction with the aid of CuI, which activated us to
propose the following mechanism for the formation of these
species along with 1–3. In the presence of CuI, the homolytic
rupture of the C–S bond of mtpmtH or bmptmds may lead to
the formation of three free radical intermediates [Sꢂ], [S2ꢂ] and
[mꢂptpmꢂ].9 With the assistance of O2, the self-recombination of
[S2 ] or [Sꢂ] radicals may entail the S42ꢀ ion while recombination
Fig. 1 View of the oval-shaped structure of 1. All H atoms are omitted for clarity.
Atom color codes: Cu green, I pink, S yellow, N blue, C black.
chelating/bridging coordination modes found in (Et4N)2[Ni(S4)2]
12
and [NH4(CuS4)]n Interestingly, each mtpmt acts as a m-(k1-N,k1-
N,k3-S) tridentate ligand to bridge five Cu atoms (mode J in Scheme
S1, ESI‡), which is different from other modes. In 1, some Cu
centers are three-coordinated by one I and two N atoms [Cu(1),
Cu(1A), Cu(5), Cu(5A), Cu(8), Cu(8A), Cu(11), Cu(11A), Cu(15),
Cu(15A)] or by one S and two I atoms [Cu(7), Cu(7A), Cu(10),
Cu(10A), Cu(13), Cu(13A)]. Other Cu atoms are tetrahedrally coordi-
nated by one I and three S atoms [Cu(9), Cu(9A), Cu(12), Cu(12A)] or
by two S and two I atoms [Cu(14), Cu(14A)]. The CuꢁꢁꢁCu contacts
range from 2.545(2) Å to 2.918(2) Å. The strong absorption at
475 cmꢀ1 in the Raman spectrum of 1 (Fig. S11, ESI‡) could be
assigned to the v(S–S) vibration of S42ꢀ ions, which is similar to the
stretching vibration of elemental S8 (473 cmꢀ1).13
Intriguingly, analogous reactions of CuI with half an equiva-
lent of mtpmtH in MeCN–DMF (v/v = 4 : 1) followed by cooling
the solution to ambient temperature produced red prisms of 1ꢁ
3MeCN (53% yield). Subsequent diffusion of Et2O into the
filtrate afforded red plates of 3ꢁMeCN (9% yield). The liquid
chromatography–mass spectrometry (LC-MS) was employed
to monitor the possible species of the above-mentioned
Cu(I)-mediated C–S cleavage reaction. There were several main
peaks in the mass spectra. Two peaks at m/z = 431.1 and 453.1
may be ascribed to bmptmds ([M + H+] = 431.1 and [M + Na+] =
453.1). Another peak at m/z = 399.1 could be assignable to
bmtpms ([M + H+] = 399.1). Column chromatography on silica
was further used to separate bmtpms (ca. 5%) and bmptmds
(ca. 5%) ligands from the filtrate. Changing the molar ratios of
CuI/mtpmtH or reaction temperatures or other solvent systems
did not increase the yield of 1. The structure of 2 consists of a
1D chain of [(bmtpms)CuI] units, which extends along the c axis
(Fig. S2, ESI‡). The zigzag [CuI]n chain is not in one plane. Each
Cu(I) atom is tetrahedrally coordinated by two m-I atoms and
two N atoms from one bmtpms ligand. In 3ꢁMeCN, there is a
crystallographic center of inversion located at the mid-point of
Cu(2)ꢁ ꢁ ꢁCu(2A) contact. Two Cu atoms on each side in the
chairlike [Cu2(m-I)(m3-I)]2 unit is coordinated by one bmptmds
ligand via the N,S,N-tridentate coordination mode (Fig. S3,
ESI‡). All Cu atoms are tetrahedrally coordinated by one m-I,
one m3-I, one N and one S.
ꢂ
of the [mptpmꢂ] radical with mtpmtH or [S2 ] may produce
bmtpms or bmptmds. Compound 4 has a cage-like structure
in which six trigonally-coordinated Cu(I) atoms are connected by
six mptpmt ligands. Each mptpmt ligand binds to three Cu(I)
atoms in the N,S-bidentate mode (Fig. S4, ESI‡).
N-Arylazoles are ubiquitous in biochemical, biological, and
medicinal structures and functions and copper thiolates have
been shown to be excellent catalysts for these cross-coupling
reactions.11a Complex 1 is insoluble in common organic
solvents and may work as a heterogeneous catalyst. We found
that 1 could display excellent catalytic performances in
the coupling reactions of arylboronic acids with N-containing
heterocycles in the absence of additional bases. As shown in
Table 1, the initial reaction was conducted between imidazole
and an excess of phenylboronic acid with a loading of 0.17
mol% 1, in refluxing MeOH for 5 h, affording the N-phenyl-
imidazole product in 99% yield. The reaction temperature
exerted great impact on this reaction. At lower temperature
(25 1C to 45 1C), the reactions gave the product in lower yields
(23% and 67%). When the catalyst loading for this reaction was
increased from 0.17 to 1 mol%, it did not affect the yields of the
products. When the optimized reaction conditions were fixed,
we chose a family of arylboronic acids as the substrates in this
cross-coupling reaction. When the m-, p-tolylboronic acids or
3,5-dimethylphenylboronic acid were used, the corresponding
N-arylation products were obtained in almost quantitative
yields. However, this reaction was sensitive to the o-substituent
of the phenyl group, and the moderate yield was obtained for
o-tolylboronic acids (35% yield; entry 4), which may be ascribed
to the large steric hindrance during the cross-coupling reaction.
As shown in entries 6 and 7, electron-donating p-substituted
arylboronic acids were found to proceed in higher yields than
those with electron-deficient substituent groups. The 1- or
c
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Table 1 Reaction of nitrogen-containing heterocycle compounds with various
for the fresh cross-coupling reaction. The resulting product was
formed in 88% yield after reusing 1 five times. Complexes 2–4
could also catalyze such cross-coupling reactions, producing
N-phenyl-imidazole in 87–94% yields. The catalytic activity of 1
is higher than those of 2–4, simple copper salts in MeOH,14a and
[Cu(OH)(TMEDA)]2Cl2 (TMEDA = N,N,N0,N0-tetramethyl-ethane-
1,2-diamine) in CH2Cl2.14b
boronic acidsa
Entry
Amine
Boronic acid
Product
Yieldb (%)
1
99
23
67
99
99
99
2c
3d
4e
5f
6
In summary, we have demonstrated that a unique copper(I)-
mediated C–S bond cleavage reaction of mtpmtH under
2ꢀ
solvothermal conditions resulted in the formation of S4 and
bmtpms and bmptmds, which were captured by different
in situ-generated [CuxIy] motifs, producing the corresponding
coordination complexes 1–3. The methodology using [CuxIy]
motifs to trap the cleaved species might be applicable to other
biorelevant systems. Compound 1 showed excellent catalytic
performances in the coupling reactions of N-heterocycles and
arylboronic acids, and is anticipated to be used for catalyzing
other C–X (X = C, O, S) bond formation.
7
8
99
35
We thank financial support from the National Natural
Science Foundation of China (90922018, 20871038, 21171124
and 21171125). We are grateful to the comments of the
reviewers and the editor.
9
98
10
11
99
90
Notes and references
12
13
60
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´
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c
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Chem. Commun., 2013, 49, 4259--4261 4261