Preparation of heterobimetallic oxide-hydroxide-hydrogensulfides [LAl(OH)(μ-O)MCp2(SH)] (M = Ti, Zr)

Article abstract of DOI:10.1002/anie.200501509

Heterobimetallic sulfides of composition [LAl(μ-S)₂MCp ₂] (M = Ti, Zr) react smoothly with two equivalents of water by ring opening and chalcogen exchange to form the heterobimetallic oxide-hydroxide- hydrogensulfides [LAl(OH) (μ-O)M

Full text of DOI:10.1002/anie.200501509

Communications
Mixed-Metal Complexes
The driving force for this intramolecular rearrangement is
the high oxophilicity of the metal centers and the higher
stability of the {Al-O-Ti} frame compared to {Al-S-Ti}.
[4]
DOI: 10.1002/anie.200501509
Compound [LAl(SH)(m-O)MCp2(SH)] reacts with a second
equivalent of water with elimination of H2S to form 3 or 4
(Scheme 1).
Preparation of Heterobimetallic
Oxide–Hydroxide–Hydrogensulfides
[LAl(OH)(m-O)MCp2(SH)] (M = Ti, Zr)**
Vojtech Jancik and Herbert W. Roesky*
Dedicated to Professor Thomas B. Rauchfuss
Recently we reported the preparation of heterobimetallic
sulfides that contained aluminum atoms [LAl(m-S)2MCp2]
(M = Ti, 1; M = Zr, 2; L = HC[C(Me)N(2,6-iPr2C6H3)]2; Cp =
C5H5).[1] The X-ray crystal structural analysis of the titanium
compound 1 confirmed the presence of a highly strained
{Al(m-S)2Ti} four-membered ring (S-Al-S 102.5(1), Al-S-Ti
84.7(1) and 83.6(1), S-Ti-S 89.3(1)8). The ring strain and the
short Al···Ti separation (3.118 Š) prompted us to examine the
reactivity of 1 and 2 with water in expectation of a
nucleophilic attack that would lead to the opening of the
ring and to the isolation of compounds containing the
{LAl(EH)(m-E)M(EH)Cp2} framework (E = O or S depend-
ing on the degree of hydrolysis). Such species could serve as
unique precursors for the preparation of trimetallic systems
comparable with the alumoxane [(m-O)[LAl(m-O)]2AlMe],
which is prepared from [(m-O)[LAl(OH)]2] and AlMe2H.[2]
Although a few dinuclear systems that contain the {M’(EH)-
(m-E)M(EH)} arrangement have been described (M’ = Al,[2]
Fe,[3a] Ge,[3b,c] In,[3d] Re,[3e] Ru,[3f] Sn,[3g] V,[3h] Zr[3i]) none has
been structurally characterized that contains two different
metal atoms stabilized by organic ligands.
The addition of two equivalents of water to a solution of 1
or 2 in THF at room temperature led, after overnight stirring,
to the precipitation of a crystalline material. H2S was
identified as a by-product. The solid product was filtered
off, dried in vacuo, and isolated as pale brown (Ti) or pale
yellow (Zr) microcrystals. The 1H NMR spectroscopic, EI
mass spectrometric, and X-ray crystal structural analysis of
these products confirmed that the ring-opening reaction had
occurred, but revealed the presence of two derivatives in the
samples. The major component (about 85%) was identified as
[LAl(OH)(m-O)MCp2(SH)] (M = Ti, 3; M = Zr, 4) whereas
the minor component (about 15%) was the intermediate of
the hydrolysis, [LAl(SH)(m-O)MCp2(SH)]. One of the first
steps of the hydrolytic ring opening is the formation of an
unobserved intermediate [LAl(OH)(m-S)MCp2(SH)], which
subsequently rearranges into [LAl(SH)(m-O)MCp2(SH)].
Scheme 1. Preparation of compounds 3 and 4.
After elucidating the course of the hydrolysis, we focused
on the optimization of the hydrolysis conditions. The presence
of the intermediates in the final product can be explained by
the low solubility of the bridged species in THF and their
crystallization from the mother liquor before the reaction was
complete. Thus, the use of THF/CH2Cl2 (1:1) in the reaction
mixture led to the formation of pure 3 or 4. It is surprising that
À
in these reactions, the Al S bond is more reactive than the
À
M S bond. [LAl(SH)2] reacts smoothly with two equivalents
of water to give [LAl(OH)2] with elimination of H2S,[5] but the
reaction is relatively slow and needs at least 20 minutes to
reach completion at room temperature. It was reported that
À
À
even traces of moisture in systems that contain Ti S or Zr S
bonds lead to fast hydrolysis of these bonds.[6] As reported
earlier, the alumoxane [{LAl(OH)}2O][2] is stable, whereas
[LAl(OH)2] decomposes even under an inert atmosphere.[7] It
seems that the presence of at least one bridging oxygen atom
is necessary for the stabilization of the species containing the
{AlO2} unit.
The isomorphous compounds 3 and 4 crystallize in the
monoclinic space group P21/n, with one molecule in the
asymmetric unit (Figure 1).[8] We were not able to crystallize
pure 4, thus data for 4 contaminated with about 15% of the
intermediate [LAl(SH)(m-O)Zr(SH)Cp2] were used. The OH
moiety on the Al atom and the SH groups on the Ti (3) and Zr
(4) atoms adopt a cis conformation and are involved in an
À
intramolecular hydrogen bond O H···S (3 2.66 Š; 4 2.80 Š).
[*] Dr. V. Jancik, Prof. Dr. H. W. Roesky
Institut für Anorganische Chemie der Universität
Tammannstrasse 4, 37077 Göttingen (Germany)
Fax: (+49)551-39-3373
À
À
The Al O(H) (3 1.726 Š; 4 1.720 Š) and Al O(M) (3
1.717 Š; 4 1.713 Š) bond lengths are similar to those in
[LAl(OH)2] (1.711 and 1.695 Š),[9] [{LAl(OH)}2O] (1.694–
1.741 Š),[2] and in the trimeric alumoxane [(m-O)[LAl(m-
O)]2(MeAl)] (1.726–1.708 Š),[2] but considerably shorter than
those in the m-OH derivatives (1.787–1.928 Š).[10] The O-Al-
O angles (3 114.08; 4 114.78) are similar to those of
E-mail: hroesky@gwdg.de
[**] L=HC[C(Me)N(Ar)]2, Ar=2,6-iPr2C6H3. This workwas supported
by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie.
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Angew. Chem. Int. Ed. 2005, 44, 6016 –6018

Angewandte
Chemie
3
1.20 (d, JH-H = 6.7 Hz, 6H, CH(CH3)2), 1.37 (d, 3JH-H = 6.9 Hz, 6H,
CH(CH3)2), 1.44 (d, 3JH-H = 6.7 Hz, 6H, CH(CH3)2), 1.77 (s, 6H, CH3),
2.08 (s, 1H, SH), 3.03 (sept, 3JH-H = 6.9 Hz, 2H, CH(CH3)2), 3.49 (sept,
3JH-H = 6.7 Hz, 2H, CH(CH3)2), 5.20 (s, 1H, g-CH), 5.36 (s, 10H, Cp
À
H), 7.04–7.20 ppm (m, 6H, m-, p-Ar H); 13C NMR (125.77 MHz,
À
CDCl3, 258C, TMS): d = 23.6, 24.2, 24.4, 24.7 (CH(CH3)2), 26.1, 27.5
(CH(CH3)2), 28.7 (CH3), 97.5 (g-CH), 113.9 (C of Cp) 124.0, 125.2,
=
127.3, 140.9, 142.9, 145.6 (i-, o-, m-, p-C of Ar), 170.6 ppm (C N); IR
(KBr pellet): n˜ = 3551 br (OH), 2574 vw (SH) cmÀ1; EI MS (70 eV):
m/z (%): 623 (10, [MÀCp]+), 605 (50, [MÀCpÀH2O]+); elemental
analysis calcd for C39H53AlN2O2STi (688.78 gmolÀ1): C 68.0, H 7.8, N
4.1; found: C 67.5, H 8.0, N 4.2%.
4: The synthesis of 4 was similar to that of 3. Compound 4 was
obtained from the reaction of H2O (25 mL, 1.37 mmol) with 2 (0.50 g,
0.69 mmol) as a pale yellow powder. Yield 0.31 g (62%); m.p.: 2358C
Figure 1. XP plots at the 50% probability level of 3 (a) and 4 (b; the
presence of the reaction intermediate that contains an SH group on
the aluminum atom, the proton of which could not be localized, is
obvious). Hydrogen atoms except those of the SH and OH groups and
the H(3A) protons are omitted for clarity. Selected bond lengths [Š]
and angles [8]: 3: Al(1)-N(1) 1.897(2), Al(1)-N(2) 1.901(2), Al(1)-O(1)
1.726(2), Al(1)-O(2) 1.719(2), O(1)-H(1) 0.85(2), Ti(1)-O(2) 1.820(2),
Ti(1)-S(1) 2.482(1), S(1)-H(2) 1.25(3), Ti(1)-XCp1 2.107(3), Ti(1)-XCp2
2.098(3); N(1)-Al(1)-N(2) 95.7(1), O(1)-Al(1)-O(2) 114.0(1), Al(1)-
O(1)-H(1) 119(3), Al(1)-O(2)-Ti(1) 148.9(1), O(2)-Ti(1)-S(1) 97.3(1),
Ti(1)-S(1)-H(2) 100(2), XCp1-Ti(1)-XCp2 128.6(2). 4: Al(1)-N(1) 1.895(2),
Al(1)-N(2) 1.898(2), Al(1)-O(1) 1.720(6), Al(1)-S(2) 2.08(1), Al(1)-O(2)
1.713(2), O(1)-H(1) 0.85(2), Zr(1)-O(1) 1.939(2), Zr(1)-S(1) 2.573(1),
S(1)-H(2) 1.19(3), Zr(1)-XCp1 2.237(3), Zr(1)-XCp2 2.240(3); N(1)-Al(1)-
N(2) 96.1(1), O(1)-Al(1)-O(2) 114.7(2), O(2)-Al(1)-S(2) 112.2(4), Al(1)-
O(1)-H(1) 122(3), Zr(1)-S(1)-H(1) 100(2), Al(1)-O(2)-Zr(1) 147.2(1),
O(2)-Zr(1)-S(1) 98.7(1), XCp1-Zr(1)-XCp2 128.0(2).
(decomp); 1H NMR (500.13 MHz, CDCl3, 258C, TMS): d = 0.36 (s,
3
1H, OH), 1.11 (d, 3JH-H = 6.8 Hz, 6H, CH(CH3)2), 1.21 (d, JH-H
=
6.8 Hz, 6H, CH(CH3)2), 1.38 (d, 3JH-H = 6.8 Hz, 6H, CH(CH3)2), 1.39
(d, 3JH-H = 6.8 Hz, 6H, CH(CH3)2), 1.65 (s, 1H, SH), 1.77 (s, 6H, CH3),
3
3
3.04 (sept, JH-H = 6.8 Hz, 2H, CH(CH3)2), 3.50 (sept, JH-H = 6.8 Hz,
2H, CH(CH3)2), 5.20 (s, 1H, g-CH), 5.46 (s, 10H, Cp-H), 7.04–
7.20 ppm (m, 6H, m-, p- Ar-H); 13C NMR (125.77 MHz, CDCl3, 258C,
TMS): d = 23.5, 24.4, 24.5, 24.6 (CH(CH3)2), 27.5, 28.6 (CH(CH3)2),
28.7 (CH3), 97.4 (g-CH), 111.8 (C of Cp) 124.0, 125.1, 127.3, 140.6,
=
143.2, 145.5 (i-, o-, m-, p- C of Ar), 170.6 ppm (C N); IR (KBr pellet):
n˜ = 3560 br (OH), 2562 vw (SH) cmÀ1; EI-MS (70 eV): m/z (%): 665
(5, [MÀCp]+), 647 (50, [MÀCpÀH2O]+); elemental analysis calcd for
C39H53AlN2O2SZr (732.12 g·molÀ1): C 64.0, H 7.3, N 3.8; found: C
63.5, H 7.4, N 3.9%.
Received: May 2, 2005
Published online: August 17, 2005
[LAl(OH)2], [{LAl(OH)}2O], and [(m-O)[LAl(m-O)]2-
(MeAl)] (108.3–115.38);[2,9] the Al-O-M angles are 148.98
Keywords: aluminum · hydroxides · sulfides · titanium ·
zirconium
.
À
À
for 3 and 147.28 for 4. The Ti O (1.820 Š) and Ti S (2.482 Š)
bond lengths and the O-Ti-S angle (97.38) are similar to those
À
reported for other [Cp2TiOS] fragments: Ti O 1.845–1.872 Š;
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Ti S 2.314–2.467 Š; O-Ti-S 87.7–97.98.[11] Furthermore, in the
À
À
À
zirconium derivative the Zr O (1.939 Š) and Zr S (2.573 Š)
bond lengths and the O-Zr-S angle (98.7 Š) are similar to
those reported previously for species that contain the
À
À
{Cp2ZrOS} moiety: Zr S 2.459–2.554 Š; Zr O 1.941–
2.199 Š; O-Zr-S 92.6–103.38.[6b,12]
In summary, the heterobimetallic sulfides [LAl(m-S)2-
MCp2] are ideal precursors for the preparation of the
heterobimetallic oxide–hydroxide–hydrogensulfides 3 and 4
by hydrolysis. The presence of two free reactive function-
alities in a cis arrangement makes them potential starting
materials for the heterotrimetallic oxide–sulfides. Such reac-
tions are the subject of our ongoing research.
Experimental Section
All manipulations were performed under a dry and oxygen-free
atmosphere (N2 or Ar) by using Schlenk-line and glovebox techni-
ques.
[4] One can argue that the unobserved intermediate could be
[LAl(SH)(m-S)MCp2(OH)],
rather
than
[LAl(OH)(m-
À
3: H2O (26 mL, 1.46 mmol) was added quickly to a solution of 1
(0.50 g, 0.73 mmol) in THF/CH2Cl2 (45 mL, 1:1) at room temperature.
The suspension was stirred for 10 h and filtered. All the volatile
species were removed under vacuum to leave a brown solid residue,
which was treated twice with cold toluene (5 mL). After filtration and
drying in vacuo, 3 was obtained as a light brown powder. Yield 0.31 g
(60%); m.p.: 2278C (decomp); 1H NMR (500.13 MHz, CDCl3, 258C,
S)MCp2(SH)]. However, the higher stability of the Ti SH
bond towards hydrolysis, the shielding of the Ti center by two Cp
À
À
rings, and the easy replacement of the Al SH group by an Al
OH moiety in the next reaction step support our conclusion.
[5] V. Jancik, H. W. Roesky, unpublished results.
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Inorg. Chem. 1986, 25, 1886 – 1891; b) D. Coucouvanis, A.
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3
TMS): d = 1.07 (s, 1H, OH), 1.10 (d, JH-H = 6.9 Hz, 6H, CH(CH3)2),
Angew. Chem. Int. Ed. 2005, 44, 6016 –6018
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Communications
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[13] SHELXS-97, Program for Structure Solution: G. M. Sheldrick,
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[8] a) Crystal data for 3: C39H53AlN2O2STi (688.77), monoclinic,
space group P21/n, a = 10.903(2), b = 20.543(4), c = 16.222(3) Š,
b = 99.02(3)8, V= 3589(1) Š3, Z = 4, 1calcd = 1.275 MgmÀ3, F-
(000) = 1472,
l = 1.54178 Š,
T= 100(2) K,
m(CuKa) =
3.075 mmÀ1. Of the 22938 measured reflections, 5087 were
independent (Rint = 0.0495). The final refinements converged at
R1 = 0.0397 for I > 2s(i), wR2 = 0.1125 for all data. The final
difference Fourier synthesis gave a min/max residual electron
density of À0.260/ + 0.477 eŠÀ3; b) crystal data for 4: C39H53Al-
N2O1.87S1.13Zr (734.14), monoclinic, space group P21/n, a =
11.064(2), b = 20.627(3), c = 16.242(3) Š, b = 97.76(3)8, V=
3673(1) Š3, Z = 4, 1calcd = 1.328 MgmÀ3
, F(000) = 1548, l =
1.54178 Š, T= 100(2) K, m(CuKa) = 3.548 mmÀ1. Of the 15708
measured reflections, 5150 were independent (Rint = 0.0351).
The final refinements converged at R1 = 0.0291 for I > 2s(i),
wR2 = 0.0764 for all data. The final difference Fourier synthe-
sis gave
a
min/max residual electron density of À0.447/
+ 0.399 eŠÀ3; c) data for the structures were collected on a
Bruker three-circle diffractometer equipped with a SMART
6000 CCD detector. Intensity measurements were performed on
a rapidly cooled crystal (0.40 ” 0.30 ” 0.30 mm3) in the range
7.00 ꢀ 2q ꢀ 117.928 (3) and in the range 6.96 ꢀ 2q ꢀ 117.948 (4;
0.10 ” 0.05 ” 0.05 mm3). The structures were solved by direct
methods (SHELXS-97)[13] and refined against all data by full-
matrix least-squares on F2.[14] All the C H hydrogen atoms
À
except H(3A) were included in geometrically idealized positions
and refined with the riding model. Localization of the H(3A)
hydrogen from the electron-density map in both structures
proved to be more accurate than its fixing in the idealized
position and led to a lowering of the R1 and wR2 values. The
hydrogen atoms of the OH and SH moieties in 3 and 4 were
localized from the difference electron-density map and refined
À
isotropically with Uij tied to the parent atom. The Al SH proton
belonging to the [LAl(SH)(m-O)ZrCp2(SH)] in the crystal of 4
could not be localized due to its low content (about 15%).
CCDC-270756 (3) and CCDC-270757 (4) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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