Synthesis and molecular structure of vanadium(III) dithiolate complexes: A new class of alkene polymerization catalysts

Article abstract of DOI:10.1039/a900916g

The synthesis and catalytic activity in ethylene polymerization of new vanadium complexes of 2,2'-oxydiethanethiolate [O(CH₂CH₂S)₂^2-] are described; the complexes [V(μ-DIPP)₂{O(CH₂CH₂S)₂}Li(MeCN)₂] and [V(DIPP){O(CH₂CH₂S)2}(py)] [DIPP = (OC₆H₃Pr(i)₂-2,6)^-] have been structurally characterized.

Full text of DOI:10.1039/a900916g

Synthesis and molecular structure of vanadium(iii) dithiolate complexes: a new
class of alkene polymerization catalysts
Zofia Janas,a Lucjan B. Jerzykiewicz,a Raymond L. Richardsb and Piotr Sobota*a
a Faculty of Chemistry, University of Wroclaw, 14 F.Joliot-Curie, 50-383 Wroclaw, Poland.
E-mail: plas@wchuwr.uni.wroc.pl
b Nitrogen Fixation Laboratory, John Innes Centre, Norwich Research Park, Norwich, UK NR4 7UH
Received (in Basel, Switzerland) 3rd February 1999, Accepted 24th April 1999
[V(µ-DIPP)2{O(CH2CH2S)2}Li(THF)2] + py
The synthesis and catalytic activity in ethylene polymeriza-
tion of new vanadium complexes of 2,2A-oxydiethanethiolate
[O(CH2CH2S)222] are described; the complexes [V(m-
[V{O(CH2CH2S)2}(DIPP)3(py)] + Li(DIPP) + 2THF (2)
DIPP)2{O(CH2CH2S)2}Li(MeCN)2]
and
[V(DIPP)-
{O(CH2CH2S)2}(py)] [DIPP = (OC6H3Pri2-2,6)2] have been
structurally characterized.
3
The crystal structure of the heterodinuclear complex 2 is
shown in Fig. 1.† Complex 2 contains a five-coordinate Viii
center adopting a slightly distorted trigonal bipyramidal
The synthetic development of well defined single-site vanadium
catalysts for alkene polymerization is of extremely high
industrial importance1,2 because such catalysts are able to
produce high molecular weight polymers with narrow molec-
ular weight distribution as well as a-olefin copolymers with
high a-olefin incorporation.3,4 A recent trend has been the
incorporation of sulfur-containing ligands: e.g. (TBP)TiCl2/
MAO catalyst [TBP = 2,2A-thiobis(6-tert-butyl-4-methylphen-
oxide, MAO = methylaluminoxane] was ten-fold more effec-
tive in ethylene polymerization than are metallocenes
catalysts.5,6 Moreover, it is well known that vanadium-based
enzyme nitrogenase in which vanadium is thought to be bound
to sulfur-, oxygen- and nitrogen-donor ligands is able to convert
acetylene into ethylene and ethane.7 These aspects of vanadium
catalysis prompted us to prepare novel vanadium compounds
with thiolate ligands such as 2,2A-oxydiethanethiolate
[O(CH2CH2S)222] and study their reactions with alkenes,
particularly their potential as precursors of new ethylene
polymerization catalysts.
22
geometry. Two sulfur atoms from the O(CH2CH2S)2 ligand
and an aryloxide oxygen O(21) of DIPP occupy the equatorial
positions. The second aryloxide oxygen O(11) and the ether
oxygen O(1) from the O(CH2CH2S)222 group fill the axial sites.
Both aryloxide oxygen atoms are engaged in the bridging
interaction to Li, inducing distortion from the ideal trigonal
bipyramidal geometry. A similar double-bridged V(m-DIPP)2Li
unit is present in the starting material [V(m-DIPP)2(DIPP)2-
Li(THF)]. The average V–S(thiolate ) distance in 2 is 2.290(4)
Å, within the range expected for V–S single bonds and
comparable to other vanadium(iii) thiolato complexes.12–15
The X-ray analysis of 3 reveals a mononuclear complex
[V(DIPP){O(CH2CH2S)2}(py)] with slightly distorted trigonal-
bipyramidal coordination around the vanadium centre (Fig. 2).†
The V–S and V–O(aryloxide) bond distances in the equatorial
plane [V–S 2.2970(9), 2.2987(8) Å; V–O 1.8619(13) Å] do not
differ significantly from those found in complex 2. The V–N
Studies of the oxidation state of active vanadium catalysts for
ethylene polymerization by different investigators has led to the
proposal that Viii and Vii represent the important oxidation
states in the ethylene polymerization process.8,9 Herein we
report the synthesis, structural characterization and catalytic
activity of the vanadium(iii) heterodinuclear complexes [V(m-
DIPP)2{O(CH2CH2S)2}Li(L)2] 1, 2 and the mononuclear
complex [V(DIPP){O(CH2CH2S)2}(py)] 3 [DIPP = (OC6H3-
Pri2-2,6)2, py = C5H5N; L = THF 1 or MeCN 2].
Dark pink [V(m-DIPP)2{O(CH2CH2S)2}Li(THF)2] 1 was
prepared by reaction of [V(m-DIPP)2(DIPP)2Li(THF)]10 with
an excess of O(CH2CH2SH)2 in a mixture of hexane–THF [eqn.
(1)].
[V(µ-DIPP)2(DIPP)2Li(THF)] + O(CH2CH2SH)2 + L
[V(µ-DIPP)2{O(CH2CH2S)2}Li(L)2] + 2DIPPH
L = THF 1 or MeCN 2
(1)
Recrystallization of 1 from MeCN gave new X-ray quality
red crystals of [V(m-DIPP)2{O(CH2CH2S)2}Li(MeCN)2] 2
[eqn. (1)]. Addition of pyridine to toluene solutions of
compounds 1 and 2 breaks up the heterodinuclear structures
forming the monomeric species [V(DIPP){O(CH2CH2-
S)2}(py)] 3 in 85% yield (eqn. (2)].
Complex 3 can be also prepared but in lower yield (53%), by
reaction of [V(DIPP)3(py)2]11 with 1 equiv. of O(CH2CH2SH)2
in toluene. The temperature independent (80–293 K) magnetic
moments of 2.6 and 2.7 mB per vanadium atom in 2 and 3
respectively, are consistent with non-interacting d2 centres.
Fig. 1 The molecular structure of 2 (the displacement ellipsoids are drawn
at the 30% probability level; the C bonded H atoms are excluded for clarity;
the C atoms are represented by circles of arbitrary radii). Selected bond
lengths (Å): V–S(1) 2.294(1), V–S(2) 2.286(2), V–O(1) 2.154(2), V–O(11)
1.917(2), V–O(21) 1.977(2), V–Li 2.830(5), Li–O(11) 1.942(6), Li(1)–
O(21) 1.903(5), Li–N(1) 2.030(6), Li–N(2) 2.015(6).
Chem. Commun., 1999, 1105–1106
1015

monochromated Mo-Ka radiation (0.71073 Å) with w-2q scan mode. The
structures were solved by direct methods (SHELXS97)20 and refined on F2
by full-matrix least-squares (SHELXL97).21 The carbon bonded H-atoms
were included in calculated positions and refined using a riding model with
isotropic displacement parameters equal to 1.2 Ueq of the attached C atom.
Crystal structure analyses: 2: C32H48LiN2O3S2V, M = 630.72, monoclinic,
space group C2/c, a = 27.297(5), b = 18.880(4), c = 17.444(3) Å, b =
126.76(3), U = 7203(2) Å3, Z = 8, Dc = 1.163 Mg m23, m = 0.422 mm21
,
F(000) = 2688. A total of 4086 reflections with 2q @ 50° were collected,
of which 3463 had I ! 2s(I). Final residuals are R1 = 0.0357, wR2
0.1007 and GOF = 1.075 for 380 variables.
=
3: C21H30NO2S2V, M = 443.52, monoclinic, space group P21/n, a =
10.022(3), b 12.156(4), c 18.628(4) Å, b 98.44(3)°, U
=
=
=
=
2244.8(11) Å3, Z = 4, Dc = 1.312, m = 0.643 mm21, F(000) = 936. A total
of 3526 reflections with 2q @ 50° were collected, of which 3108 had I !
2s(I). Final residuals are R1 = 0.0269, wR2 = 0.0760 and GOF = 1.124 for
248 variables.
CCDC 182/1237. See http://www.rsc.org/suppdata/cc/1999/1015/ for
crystallographic files in .cif format.
1 V. J. Murphy and H. Turner, Organometallics, 1997, 16, 2495; F. J.
Feher and J. F. Walzer, Inorg. Chem., 1991, 30, 1689; F. J. Feher, J. F.
Walzer and R. L. Balnski, J. Am. Chem. Soc., 1991, 113, 3618; F. J.
Feher and R. L. Balnski, Organometallics, 1993, 12, 958; J. Am. Chem.
Soc., 1992, 114, 5886.
2 S. Scheuer, J. Fischer and J. Kress, Organometallics, 1995, 14, 2627.
3 W. L. Carrick, J. Am. Chem. Soc., 1958, 80, 6455; W. L. Carrick, R. W.
Kluiber, E. F. Bonner, L. H. Wartman, F. M. Rugg and J. J. Smith, J. Am.
Chem. Soc., 1960, 82, 3883; D. L. Christman, J. Polym. Sci., Polym.
Chem. Ed., 1972, 10, 472; M. H. Lehr and C. J. Carmen, Macromole-
cules, 1969, 2, 217; M. H. Lehr, Macromolecules, 1968, 1, 178.
4 Y. Doi, N. Tokuhiro, M. Nunomura, H. Miyake and K. Soga, in
Transition Metals and Organometallics as Catalysts for Olefin
Polymerization, ed. W. Kaminsky and H. Sinn, Springer-Verlag, Berlin,
1998; V. E. Junghanns, V. A. Gumboldt and G. Bier, Makromol. Chem.,
1962, 58, 18; V. A. Gumboldt, J. Helberg and G. Schleitzer, Makromol.
Chem., 1967, 101, 229.
Fig. 2 The molecular structure of 3 (the displacement ellipsoids are drawn
at the 30% probability level; the C bonded H atoms are excluded for clarity;
the C atoms are represented by circles of arbitrary radii). Selected bond
lengths (Å): V–S(1) 2.2970(9), V–S(2) 2.2987(8), V–O(1) 2.1195(14), V–
O(2) 1.8619(13), V–N 2.1306(17).
Table 1 Polymerizationa of ethylene with vanadium–MgCl2–AlEt2Cl
catalysts
Productivityb/
T/K kg(g V h)21
Catalyst system
Mw/Mn
d/g cm23
5 W. Kaminsky, J. Chem. Soc., Dalton Trans., 1998, 1413; M. Bochmann,
J. Chem. Soc., Dalton Trans., 1996, 255.
1/MgCl2/AlEt2Cl
3/MgCl2/AlEt2Cl
323
323
39
20
2.7
3.8
0.964
0.961
6 T. Miyatake, K. Mizunuma and M. Kakugo, Makromol. Chem.,
Macromol. Symp., 1993, 66, 203; S. Fokken, T. P. Spaniol, H-C. Kang,
W. Massa and J. Okuda, Organometallics, 1996, 15, 5069.
7 See for example R. R. Eady and G. J. Leigh, J. Chem. Soc., Dalton
Trans., 1994, 2739 and refs. therein.
a Conditions: [V]0 = 0.02 mmol dm23, [Al] = 10 mmol dm23, Mg:V =
10, Pethylene = 0.6 MPa. b Mass in kg of polymer formed per g of vanadium
atoms in 1 h.
8 F. J. Karol, K. J. Cann and B. E. Wagner, in Transition Metals and
Organometallics as Catalysts for Olefin Polymerization, ed. W.
Kaminsky and H. Sinn, Springer, New York, 1988, pp. 149–161.
9 P. D. Smith, J. L Martin, J. C. Huffman, R. L Bansemer and K. G
Caulton, Inorg. Chem., 1985, 24, 2997.
10 W. C. A. Wilisch, M. J. Scott and W. H. Armstrong, Inorg. Chem., 1988,
27, 4335.
11 S. Gambarotta, F. Van Bolhuis and M. Y. Chiang, Inorg. Chem., 1987,
26, 4303.
12 C. R. Randall and W. H. Armstrong, J. Chem. Soc., Chem. Commun.,
1988, 986.
13 S. C. Davies, D. L. Hughes, Z. Janas, L. B. Jerzykiewicz, R. L. Richards
J. R. Sanders and P. Sobota, Chem. Commun., 1997, 1261.
14 G. Henkel, B. Krebs and W. Schmidt, Angew. Chem., Int. Ed. Engl.,
1992, 31, 1366.
15 R. W. Wiggins, J. C. Huffman and G. Christou, J. Chem. Soc., Chem.
Commun., 1983, 1313; D. Szeymies, B. Krebs and G. Henkel, Angew.
Chem., Int. Ed. Engl., 1983, 22, 885; J. R. Dorfman and R. H. Holm,
Inorg. Chem., 1983, 22, 3179.
16 In a typical test of ethylene homopolymerization the catalyst was
prepared by milling a n-hexane slurry of [MgCl2(THF)2] with the
vanadium compound and AlEt2Cl as the cocatalyst. In all cases studied
an immediate exotherm indicated polymerization; reaction temperatures
were kept at 323 K and pressure at 0.6 MPa. After 1 h the reactor was
opened and the polymer was filtered off, washed with acidic methanol
and water, and dried in vacuo.
distance is also near the values observed in the other Viii–
pyridine complexes.11
Compounds 1 and 3, in combination with AlEt2Cl and
MgCl2, are highly active towards ethylene polymerization.16
Yields and polymer characterization data are listed in Table 1.
The amount of polyethylene (PE) produced by the catalysts is
comparable to the catalyst based on VCl3.17 The molecular
weight distribution Mw/Mn of the PE obtained in the first
catalytic system is < 3, and in the second one is > 3. These
findings indicate that the polymerization process in 1/MgCl2/
AlEt2Cl proceeds on a single vanadium site in a homogeneous
system, however for 3/MgCl2/AlEt2Cl a heterogeneous system
appears to operate. Hence, the catalytic activity of the 1/MgCl2/
AlEt2Cl system is almost twice that of the 3/MgCl2/AlEt2Cl
system.
To our knowledge complexes 1 and 3 represent the first
examples of vanadium-thiolate catalyst precursors for ethylene
polymerization. We suggest that the V{O(CH2CH2S)2} moiety
is maintained in the catalyst assembly and that the geometry of
such catalytic species plays an important role in determining the
reactivity. It is worth noting that vanadium catalysts are very
important in ethylene–propylene rubber production.18
The authors thank the State Committee for Scientific
Research for financial support of this work (Grant No. 3 T09A
131 15), and Dr Krzysztof Szczegot of the University of Opole
for preliminary polymerization tests.
17 K. J. Cann, D. L. Miles and F. J. Karol, US. Pat., 4 670 526, 1987; X.
Bai, US Pat., 5 410 003, 1995.
18 F. J. Karol, Macromol. Symp., 1996, 154, 83.
19 Kuma Diffraction. Kuma KM4 software. User’s Guide, version 6.1
Kuma Diffraction, Wroclaw, Poland, 1996.
20 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 467.
21 G. M. Sheldrick, SHELXL97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
Notes and references
† Crystal data for 2 and 3: The crystals were sealed in glass capillaries under
a dinitrogen stream. Preliminary examination and data collections were
carried out on a KUMA KM-4 four-circle diffractometer19 using graphite-
Communication 9/00916G
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Chem. Commun., 1999, 1105–1106