Syntheses and structures of W2(μ-Cl)3Cl6- and W2(μ-Cl)2Cl82-, new d2-d2 confacial and edge-sharing bioctahedral ditungsten compounds, and a convenient synthesis of W2(μ-Cl)3Cl62-

Article abstract of DOI:10.1039/a803903h

(NR₄)W₂Cl₉ and (NR₄)₂W₂Cl₁₀, prepared by addition of NR₄Cl (R = alkyl) to (WCl₄)_x powder in CH₂Cl₂, have confacial [W=W, 2.689(1) A] and edge-sharing bioctahedral [W=W, 2.792(1) A] structures, respectively, as NBnEt₃⁺ salts, and convert with added NR₄Cl to (NR₄)₂W₂Cl₉ and (NR₄)WCl₆ and eventually (NR₄)₂WCl₆; (NR₄)W₂Cl₉ can be converted to (NR₄)₂W₂Cl₁₀ by NR₄Cl at -30 °C.

Full text of DOI:10.1039/a803903h

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Syntheses and structures of W2(m-Cl)3Cl62 and W2(m-Cl)2Cl822, new d2–d2
confacial and edge-sharing bioctahedral ditungsten compounds, and a
22
convenient synthesis of W2(m-Cl)3Cl6
Vladimir Kolesnichenko, Dale C. Swenson and Louis Messerle*
Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA. E-mail: lou-messerle@uiowa.edu
3 (NR4)2[W2(µ-Cl)2Cl8]
2 (NR4)2[W2(µ-Cl)3Cl6] + 2 (NR4)WCl6
(NR4)W2Cl9 and (NR4)2W2Cl10, prepared by addition of
NR4Cl (R = alkyl) to (WCl4)x powder in CH2Cl2, have
confacial [W§W, 2.689(1) Å] and edge-sharing bioctahedral
3
1
6 WCl4
+
[W§W, 2.792(1) Å] structures, respectively, as NBnEt3
6 (NR4)[W2(µ-Cl)3Cl6] (2)
salts, and convert with added NR4Cl to (NR4)2W2Cl9 and
(NR4)WCl6 and eventually (NR4)2WCl6; (NR4)W2Cl9 can
be converted to (NR4)2W2Cl10 by NR4Cl at 230 °C.
2
isolated yield) at 230 °C by NBnEt3Cl in CH2Cl2; isolation is
possible because of the low solubility of the NBnEt3+ salt. We
believe that 1 and 2 have not been observed in previous
studies5,6,14 because they disproportionate in solution (1) or in
the presence of Cl2 (2). Compound 2 is reduced to 3 by either
(NBnEt3)2WCl6 or Cp2Fe in CH2Cl2. Scheme 1 summarizes the
principal transformations.
High symmetry confacial [M2(m-L)3L6, D3h; L = ligand] and
edge-sharing [M2(m-L)2L8, D2h] bioctahedral complexes are
known for many transition metals and are of considerable
importance for understanding metal–metal single and multiple
bonding.1 The effect of orbital population on M–M distance can
be understood by studying isostructural compounds with
various d-electron counts. Confacial bioctahedral congeners
with differing d-electron counts are known for few metals (e.g.
Re,2 W). For tungsten, W2(m-Cl)3Cl632 (d3–d3; one of the first3
metal–metal bonded compounds to be recognized4 as such) and
22
d2–d3 W2(m-Cl)3Cl6
have been reported.5,6 The W–W
distance in the former, which has been studied theoretically,7 is
a short 2.409(7)–2.4329(6) Å,6,8,9 (depending on cation), and
increases6 by 0.12 Å upon oxidation to W2(m-Cl)3Cl622. While
there are many preparations10 of W2(m-Cl)3Cl632, few are
known for the dianion;5,6,11 W2(m-Br)3Br622 is also known.12
We recently developed new syntheses of powdered and
crystalline (WCl4)x and showed that its structure was a linear
polymer of edge-sharing bioctahedra with alternating short
(double bond) and long (no bond) W···W separations.13 The
unusually reactive powder form, prepared from Sn reduction of
WCl6 in ClCH2CH2Cl, reacts with NR4Cl to give the new
Scheme 1
The syntheses of 1, 2, and 3 are facilitated by the use of
(WCl4)x powder.13 Reactions of (WCl4)x, as prepared by
reduction of WCl6 with red phosphorus, W(CO)6, or Sb,13 with
NR4Cl proceed more slowly and lead to lower purity materials
because the lower solubility of these (WCl4)x materials results
in an excess of NR4Cl in the early stages of the reactions.
Single crystals of (NBnEt3)2[W2(m-Cl)2Cl8]·3CH2Cl2 1 were
obtained from 235 °C CH2Cl2 solution. The solid-state struc-
ture¶ of the centrosymmetric ditungstate portion of 1 (Fig. 1)
consists of an edge-sharing bioctahedron with a W(1)–W(1A)
distance of 2.792(1) Å, a W(1)–Cl(1)–W(1A) angle of
71.88(6)°, and a Cl(1)–W(1)–Cl(1A) angle of 108.12(6)°. The
crystallographically independent axial Cl(2) and Cl(3) in each
bioctahedral hemisphere are bent away from Cl(3A) and Cl(2A)
with Cl(2)–W(1)–W(1A) and Cl(3)–W(1)–W(1A) angles of
22
2
chloroditungstates W2(m-Cl)2Cl8 1 and W2(m-Cl)3Cl6 2 as
22
well as W2(m-Cl)3Cl6 3. We report synthetic and structural
details.
The reaction of NR4Cl (R4 = BnEt3, BnBu3, Bu4) with
(WCl4)x leads to scission of dinuclear fragments, disproportio-
nation, and then comproportionation depending on stoichio-
metry and temperature. At 25 °C, reaction of (WCl4)x with one
equiv. of NBnEt3Cl (a cation which facilitates product separa-
tion) in CH2Cl2 leads to (NBnEt3)2(W2Cl9) [3; 96% isolated
yield, eqn. (1)]† and (NBnEt3)WCl6. The mixture is compro-
portionated by NBnEt3Cl to (NBnEt3)2WCl6 [94% yield, eqn.
(1)]. UV–VIS spectra of products matched literature data.11,14
3 NR4Cl
3 NR4Cl
3 WCl4
(NR4)2[W2(µ-Cl)3Cl6]
3 (NR4)2WCl6 (1)
–(NR4)WCl6
3
The reaction between (WCl4)x and NBnEt3Cl in CH2Cl2 at
230 °C yields (NBnEt3)2[W2(m-Cl)2Cl8] 1 which crystallizes
along with undissolved (WCl4)x. Upon warming to 25 °C, 1
redissolves and disproportionates to 3 and (NBnEt3)WCl6 [eqn.
(2)], thus establishing that 1 is an intermediate in eqn. (1). With
additional (WCl4)x, 3 and (NR4)WCl6 comproportionate to
emerald green (NBnEt3)[W2(m-Cl)3Cl6] [2; eqn. (2)]. Com-
pound 2 can be prepared conveniently‡ in one step (90%
isolated yield) by combining (WCl4)x with 0.5 equiv. NBnEt3Cl
in CH2Cl2 at 25 °C, and can be converted§ back to 1 (95%
Fig. 1 Thermal ellipsoid plot of the molecular structure of the ditungsten
anion portion of 1
Chem. Commun., 1998
2137

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wash became light blue-purple, and dried in vacuo. Weight = 0.525 g (96%
22
yield). The UV–VIS spectrum (CH2Cl2) matched those of known W2Cl9
salts. Anal: W, 33.7; Cl, 29.01. Calc. for (NBnEt3)2W2Cl9: W, 34.32; Cl,
29.78%. The supernatant was cooled to 230 °C for one day and a first crop
of the brown crystalline product was isolated by filtration for analysis and
dried in vacuo; weight 0.110 g (37% yield) (NBnEt3)WCl6. Anal: W, 31.2;
Cl, 36.43. Calc. for (NBnEt3)WCl6: W, 31.22; Cl, 36.12%.
‡ Synthesis of 2: a stirred mixture of WCl4 (1.00 g, 3.07 mmol), NBnEt3Cl
(0.350 g, 1.54 mmol), and CH2Cl2 (15 mL) gave a deep blue-green solution
after 10–30 min. After one day, the deep blue-green solution was filtered
and rotary-evaporated to a viscous oil, which crystallized to 1.218 g dark
emerald-green product (90% yield). Anal: W, 41.1; Cl, 35.58. Calc. for
(NBnEt3)W2Cl9: W, 41.83; Cl, 36.29%. UV–VIS, l/nm (e/dm3 mol21
cm21): 650 (825), 530 (370), 360 (shoulder), and 305 (22600). MS (FAB,
Fig. 2 Thermal ellipsoid plot of the molecular structure of the ditungsten
anion portion of 2
negative ion mode, m/z): 687 (M+, base peak for W2Cl9 isotope
2
pattern).
§ Synthesis of 1 via Cl2 addition to W2Cl92: pre-cooled (230 °C) solutions
of 0.052 g (0.228 mmol) NBnEt3Cl in 2 mL of CH2Cl2 and 0.200 g (0.228
mmol) (NBnEt3)(W2Cl9) in 4 mL of CH2Cl2 were mixed. Deep purple-
brown microcrystals formed immediately. After aging at 230 °C for 1 day,
the crystals were filtered off cold, washed with cold CH2Cl2 (ca. 5 mL) and
dried in vacuo. Weight = 0.257 g (95% yield). Anal: W, 30.8. Calc. for
(NBnEt3)2W2Cl10.CH2Cl2: W, 30.85%.
94.38(6)° and 93.98(6)°, respectively, and a Cl(2)···Cl(3A) non-
bonded distance which is appreciably closer [3.131(3) Å] than
twice the Cl van der Waals (VDW) radius of 1.70–1.90 Å.15
The anion in 1 is similar to that of the W§W bonded portion
of (WCl4)x, and can be formally viewed as the scission of that
edge-sharing bioctahedral portion of the polymeric structure13
and addition of two Cl2 endcaps. The W§W distance in
crystalline (WCl4)x is 2.688(2) Å, with W–Cl–W bridge angles
of 69.4(2)° and bent-back axial Cl [W–W–Cl(axial),
94.99(12)°]. The axial Cl in each bioctahedral hemisphere of
(WCl4)x are also closer [3.085(10) Å] than twice the Cl VDW
radius. There is no similarity between the structures of 1 and
W2Cl10 [i.e. W2(m-Cl)2Cl8] which has a long W···W separation
of 3.814(2) Å and a Clm–W–Clm angle of 81.5(1)°.16
¶ Crystallographic data for 1: C29H50Cl16N2W2, [(NBnEt3)2(W2Cl10)-
(CH2Cl2)3], M = 680.81, monoclinic, a = 14.620(3), b = 15.430(3), c =
10.860(2) Å, b = 108.38(3)°, V = 2324.9(8) Å3, T = 213 K, space group
P21/n, Z
= 2, m =
5.889 mm21, 5553 reflections measured, 4053
independent reflections, R1 = 0.0451, wR2 = 0.0918.
∑ Crystallographic data for 2: C13H22Cl9NW2, M = 879.07, monoclinic, a
= 8.910(2), b = 15.350(3), c = 17.920(4) Å, b = 94.80(3)°, V =
2442.3(9) Å3, T = 213 K, space group P21/c, Z = 4, m = 10.398 mm21
,
4672 reflections measured, 3819 independent reflections, R1 = 0.0500,
wR2 = 0.0987. CCDC 182/968.
The only other Group 6 M2(m-Cl)2Cl822 compound is edge-
sharing bioctahedral (PPh4)2[Mo2Cl10],17 with no Mo–Mo bond
(Mo···Mo, 3.80 Å). The reason(s) for the substantial differences
between Mo2(m-Cl)2Cl822 and W2(m-Cl)2Cl822 1 are presently
1 (a) F. A. Cotton and R. A. Walton, Multiple Bonds Between Metal
Atoms, 2nd edn. Clarendon Press, Oxford, 1993, p. 3; (b) F. A. Cotton
and D. A. Ucko, Inorg. Chim. Acta, 1972, 6, 161; (c) R. H. Summerville
and R. Hoffmann, J. Am. Chem. Soc., 1979, 101, 3821;
(d) S. Shaik, R. Hoffmann, C. R. Fisel and R. H. Summerville, J. Am.
Chem. Soc., 1980, 102, 4555; (e) W. C. Trogler, Inorg. Chem., 1980, 19,
697; (f) F. A. Cotton and X. Feng, Int. J. Quantum Chem., 1996, 58,
671.
2 G. A. Heath, J. E. McGrady, R. G. Raptis and A. C. Willis, Inorg.
Chem., 1996, 35, 6838.
3 (a) O. Olsson, Ber. Dtsch. Chem. Ges., 1913, 46, 566; (b) O. Olsson,
Z. Anorg. Allg. Chem., 1914, 88, 1914.
4 (a) C. Brosset, Ark. Chem., Miner. Geol. A, 1935, 12, no. 4; (b) C.
Brosset, Nature, 1935, 135, 874.
5 R. Saillant and R. A. D. Wentworth, J. Am. Chem. Soc., 1969, 91,
2174.
6 F. A. Cotton, L. R. Falvello, G. N. Mott, R. R. Schrock and L. G.
Sturgeoff, Inorg. Chem., 1983, 22, 2621.
7 (a) R. Stranger, S. A. Macgregor, T. Lovell, J. E. McGrady and G. A.
Heath, J. Chem. Soc., Dalton Trans., 1996, 4485; (b) J. E. McGrady, T.
Lovell and R. Stranger, Inorg. Chem., 1997, 36, 3242.
8 W. H. Watson, Jr. and J. Waser, Acta Crystallogr., 1958, 11, 689.
9 K. R. Dunbar and L. E. Pence, Acta Crystallogr., Sect. C, 1991, 47,
23.
10 (a) H. B. Jonassen, A. R. Tarsey, S. Cantor and G. F. Helfrich, Inorg.
Synth., 1957, 5, 139; (b) R. A. Laudise and R. C. Young, Inorg. Synth.,
1960, 6, 149; (c) E. A. Heintz, Inorg. Synth., 1963, 7, 142; (d) R. C.
Young, J. Am. Chem. Soc., 1932, 54, 4515; (e) R. Uzel and R. Pribil,
Coll. Czech. Chem. Commun., 1938, 10, 330; (f) O. Collenberg and J.
Backer, Z. Electrochem., 1924, 30, 230; (g) R. Saillant, J. L. Hayden and
R. A. D. Wentworth, Inorg. Chem., 1967, 6, 1497.
11 W. H. Delphin and R. A. D. Wentworth, Inorg. Chem., 1973, 12,
1914.
unknown, though the difference in degree of metal–metal
32
bonding parallels that for Mo2(m-Cl)3Cl6
and W2(m-
32
Cl)3Cl6
.
Single crystals of (NBnEt3)[W2(m-Cl)3Cl6] 2 were obtained
from cooled (235 °C) CH2Cl2/CHCl3 solutions. Single-crystal
X-ray diffractometry∑ confirmed that the anion portion of 2
possesses a confacial bioctahedral structure (Fig. 2) with a
W(1)–W(2) distance of 2.696(3) Å and an acute W(1)–Cl(m)–
W(2) average angle of 66.6(1)° which is smaller than the bridge
angle of 70.53° for an idealized confacial bioctahedron. The
W–W distance and W–Clm–W angles are consistent with a
2
2
formal W(1)–W(2) double-bonding (a1A eA ) interaction.
n2
The W–W distance in W2(m-Cl)3Cl6 (n = 3, 2, 1) thus
increases from 2.409(7) to 2.4329(6) Å for n = 3, to 2.540(1) Å
for n = 2, and to 2.696(3) Å for n = 1 (compound 2), as would
be expected from s-bond weakening with increasing nuclear
charge and/or the decrease in formal bond order from 3 to 2.5 to
2.6 The UV–VIS data for 2 correspond to those reported11 for
(Bu4N)2(W4Cl17), whose structure was not determined. The
analytical accuracy, as the authors noted, did not rule out an
alternative formulation such as NBu4(W2Cl9). It is interesting
that W4Cl1722 was reported11 to react with excess Cl2 to give
products including W2Cl922, as does 2.
The mechanism of formation of 1, 2, and 3 from chloride
attack on (WCl4)x, the solid-state and solution magnetochem-
istry of 1 and 2 (which exhibits a surprisingly low moment of @
1.3 mB in solution by the Evans method), theoretical studies
using the GAMESS program,18 and the reactivity of the new
ditungsten(IV) perchloroanions are under investigation.
The support of Nycomed, Inc. and the University of Iowa
Biosciences Initiative Research Program is gratefully acknowl-
edged, as are the useful comments of a reviewer.
12 J. L. Templeton, R. A. Jacobsen and R. E. McCarley, Inorg. Chem.,
1977, 16, 3320.
13 V. Kolesnichenko, D. C. Swenson and L. Messerle, Inorg. Chem., 1998,
37, 3257.
14 T. B. Scheffler and C. L. Hussey, Inorg. Chem., 1984, 23, 1926.
15 A. Bondi, J. Phys. Chem., 1964, 68, 441.
16 F. A. Cotton and C. E. Rice, Acta Crystallogr., Sect. B, 1978, 34,
2833.
17 E. Hey, F. Weller and K. Dehnicke, Z. Anorg. Allg. Chem., 1984, 508,
86.
Notes and References
† Synthesis of 3: a stirred mixture of 0.500 g (1.535 mmol) WCl4 and 0.350
g (1.537 mmol) NBnEt3Cl in 10 mL CH2Cl2 converted in 10 min from a
gray suspension to a deep purple-brown suspension with microcrystals, and
eventually to a deep blue-purple precipitate in a green-brown solution. After
several days, the precipitate was filtered off, washed with CH2Cl2 until the
18 J. Jensen and L. Messerle, unpublished results.
Received in Bloomington, IN, USA, 26th May 1998; 8/03903H
2138
Chem. Commun., 1998