Angewandte
Chemie
À
tions generally result in the insertion of sulfur into one Zn R
therefore indicates that sulfide ions are not suited to bind to
bond and afford alkylzinc thiolate clusters of the type
[Zn(SR)R]n. Interestingly, the reaction of Et2Zn with two
equivalents of sulfur in toluene at room temperature,
followed by addition of an excess of 3,5-lutidine (Lut),
produced the mixed sulfidozinc thiolates [Zn10S4(SEt)12-
(Lut)4]and [Zn 2S(SEt)(Et)(Lut)4].[15b] To our knowledge,
the interaction of sulfur with monoalkyl RZn(L) complexes
(L is a monoanionic ligand) has not been studied before. The
reaction of S8 with 1 in THF solution proceeds with a color
change from yellow to colorless after several hours at ambient
temperature accompanied by the slow deposition of colorless
crystals of the novel zinc sulfidocarboxylate [Zn6(m3-S)2-
(O2Ph)8(thf)2] (3; Scheme 2). Thus, the introduction of
sulfur results in the formation of an unusual hexanuclear
species instead of giving a tetranuclear analogue of 2 or mixed
sulfidozinc thiolate complexes supported by carboxylate
ligands.
four zinc ions simultaneously in polynuclear zinc carboxylate
complexes. The metal centers within each SZn3 unit are
connected by m-1,2-carboxylate bridges, and two such units
are also linked by similar m-1,2-carboxylate bridges through
one of their Zn atoms. Thus, compound 3 may formally be
viewed as a dimer of Zn3(m3-S)(O2CPh)4(thf) moieties where
the metal–sulfur framework of these moieties is based on a
metal-deficient {M}4 tetrahedron lacking one vertex.
All the zinc centers are four-coordinate with an
SZn(Ocarboxylate
) or SZn(Ocarboxylate)2(Othf) environment. The
3
À
Zn S bond lengths fall within a narrow range of 2.252–
2.275 (the shortest Zn···S distance in the vicinity of a m3-S
À
center is 3.700 ). A similar situation is found for the Zn
À
O
carboxylate interactions (av.: 1.967 ) and the Zn Othf distances
(2.031(5) ). Both the composition and structure of 3 seem to
be without precedent in zinc coordination chemistry. The
presence of the peripheral thf ligand coordinated to two zinc
centers in 3 holds considerable promise for the development
of this unique sulfidocarboxylate zinc cluster as an SBU in the
construction of extended inorganic–organic structures.
In conclusion, we have reported a new efficient route to
zinc oxo- and sulfidocarboxylate complexes. In addition, the
isolation and characterization of 1–3 has afforded new
insights into the unexplored field of oxygenation and
sulfuration of alkylzinc carboxylates.
Scheme 2.
Experimental Section
1: ZnEt2 (0.494 g, 4.00 mmol) was added to a suspension of benzoic
acid (0.488 g, 4.00 mmol) in hexane (7 mL) at À788C. The reaction
mixture was allowed to warm to room temperature and the resulting
white slurry was stirred vigorously for a further 6 h. Colorless crystals
were obtained from CH2Cl2/hexane at À208C (0.655 g, 76%);
elemental analysis (%) calcd for C9H10O2Zn: C 50.15, H 4.68;
Compound 3 crystallizes as a molecular hexanuclear
cluster with Ci symmetry with one uncoordinated THF
molecule in the unit cell. The structure consists of a zinc
carboxylate cluster in which each central sulfide ion is
surrounded by three Zn atoms positioned at the corners of
a tetrahedron (Figure 3). The presence of Zn3(m3-S) units is
striking as the central S atom in most reported structures of
mixed sulfidozinc thiolate complexes is found in an Zn4(m4-S)-
type environment and the former coordination mode has
hitherto only been observed very rarely.[5] This observation
1
found: C 50.21, H 4.83; H NMR (400 MHz, CDCl3): d = À0.23 (q,
2H; ZnCH2CH3), 1.07 (t, 3H; ZnCH2CH3), 7.42 (m, 2H; Ar), 7.57 (m,
1H; Ar), 8.09 ppm (m, 2H; Ar); IR (Nujol): n˜ = 1622(w), 1599(s),
1562(s), 1493(m), 1448(m), 1418(s), 1377(s), 1309(w), 1179(w),
1147(w), 1026(w), 719(s), 681(m), 614(w) cmÀ1. Our attempts to
perform molecular-weight measurements failed owing to the low
solubility of this complex in aromatic solvents.
2: A stirred solution of 1 (0.216 g, 1 mmol) in THF (5 mL) was
cooled to À208C in a Schlenk tube then an excess of dry dioxygen
(1 atm) was introduced. After 5 min the excess of O2 was removed on
a vacuum/nitrogen line. Colorless crystals deposited from a THF/
hexane mixture after several hours at À208C (0.107 g, 64%);
elemental analysis (%) calcd for C42H30O13Zn4: C 50.23, H 3.01;
found: C 50.31, H 3.08; 1H NMR (400 MHz, CDCl3): d = 7.42 (m, 2H;
CH2), 7.53 (m, 1H; Ar), 8.22 ppm (m 2H; Ar); IR (Nujol): n˜ =
1622(w), 1608(s), 1571(s), 1493(m), 1461(m), 1418(s), 1378(m),
1178(w), 1072(w), 1027(w), 716(s), 686(m), 679(m), 605(w) cmÀ1
.
3: A solution of 1/8S8 (0.064 g, 2 mmol) in THF was added to a
stirred solution of 1 (0.216 g, 1 mmol) in THF (5 mL). The color of the
reaction mixture changed immediately to yellow and after two days
the solution became colorless. The mixture was concentrated to about
2 mL and stored at 08C. Colorless, block-shaped crystals deposited
after one day (0.108 g, 55%). Compound 3 is slightly soluble in THF
and poorly soluble in CH2Cl2 and aromatic solvents; elemental
analysis (%) calcd for C32H28O9SZn3 (sample dried in vacuo for 10 h):
C 48.97, H 3.60, S 4.09; found: C 49.06, H 3.69, S 4.06; 1H NMR
(400 MHz, [D8]THF): d = 1.78 (m, 6H; CH2), 3.62 (m, 6H; CH2), 7.36
(m 16H; Ar), 7.47 (m 8H; Ar), 8.11 ppm (m 16H; Ar); IR (nujol): n˜ =
Figure 3. Molecular structure of 3 with thermal ellipsoids set at 40%
probability. Hydrogen atoms have been omitted for clarity.
Angew. Chem. Int. Ed. 2008, 47, 573 –576
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
575