The first rare earth organometallic complex of 1,4,7-trithiacyclononane: A precursor to unique cationic ethylene and α-olefin polymerisation catalysts supported by an all-sulfur donor ligand

Article abstract of DOI:10.1039/b503967c

[Sc([9]aneS₃)(CH₂SiMe₃)₃], the first rare earth organometallic complex of 1,4,7-trithiacyclonane, is a precursor to ethylene and α-olefin polymerisation catalysts upon activation with BArF₃ or [CPh₃][BAr^F ₄] (Ar^F = C₆F₅); these are the first cationic rare earth organometallic catalysts supported by an all-sulfur donor ligand. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b503967c

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COMMUNICATION
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The first rare earth organometallic complex of 1,4,7-
trithiacyclononane: a precursor to unique cationic ethylene and a-olefin
polymerisation catalysts supported by an all-sulfur donor ligand{
Cara S. Tredget, Fanny Bonnet, Andrew R. Cowley and Philip Mountford*
Received (in Cambridge, UK) 18th March 2005, Accepted 9th May 2005
First published as an Advance Article on the web 1st June 2005
DOI: 10.1039/b503967c
[
Sc([9]aneS )(CH SiMe ) ], the first rare earth organometallic
structurally authenticated (but catalytically inactive) rare earth
6
alkyl cations (e.g. V) with crown ethers, and also showed that
3
2
3 3
complex of 1,4,7-trithiacyclonane, is a precursor to ethylene and
F
2+
mono-alkyl di-cations of the type [Ln(CH SiMe )(solvent) ]
2
a-olefin polymerisation catalysts upon activation with BAr
F
3
or
3
x
7
F
CPh ][BAr ] (Ar 5 C F ); these are the first cationic rare
(modelled by VI) were active ethylene polymerisaton catalysts.
Hessen et al. and Piers et al. have reported recently on catalytically
[
3
4
6 5
earth organometallic catalysts supported by an all-sulfur donor
ligand.
active cationic alkyl complexes with monoanionic N -donor
2
8
ligands (e.g. VII). Very recently, Gade et al. reported that the
i
C
3
-symmetric [Sc( Pr-trisox)(CH
podand-like ligand akin to III) catalysed the isoselective poly-
merisation of 1-hexene on activation with equivs. of
2
SiMe
3
)
3
]
VIII (featuring a
Non-cyclopentadienyl Group 3 and lanthanide organometallic
1
chemistry is a topic of considerable current activity, especially
2
2
with regard to the development of olefin polymerisation catalysts.
F
9
[CPh
3 4
][BAr ] and a di-cationic active species was postulated.
Over the last 5 years in particular the focus in these regards has
3
almost exclusively been on cationic alkyl systems.
Concurrent with these rapid advances for cationic rare earth
alkyl catalysts (all with hard N- or O-donor co-ligands) have been
reports that the presence of neutral S-donor groups may be
beneficial to the performance of cationic Group 4 alkyl
Bercaw et al. showed that when the trimethyl complex I-Sc
F
F
(Chart 1) was treated with BAr
3 6 5 8
(Ar 5 C F ) in THF-d a
F
3
species formulated as Sc(Me [9]aneN )Me (m-Me)BAr ‘‘proved
3
3
2
10a
polymerisation catalysts. Such an effect has yet to be tested
for cationic Group 3 alkyl catalysts and indeed no such complexes
competent’’ for ethylene polymerization (no activity data were
4a
4b
given). Subsequently, we found that the tris(trimethylsilyl-
methyl) homologue II-Sc and the podand ligand system III-Sc
were the most active ethylene polymerisation catalysts reported to
date for Sc (a re-evaluation of I-Sc found it to be only ca 15% as
10b
with S-donor ligands have been described. Stimulated by the
capacity of the Sc compounds I-Sc, II-Sc and III-Sc for
ethylene polymerisation and the recent demonstration of
4
c
1-hexene polymerisation by VIII (all with neutral fac-N
ligands) we set out to explore the use of the all-sulfur donor
macrocycle 1,4,7-trithiacyclononane ([9]aneS ). Although [9]aneS
3
donor
active as II-Sc ). The yttrium analogues I-Y, II-Y or III-Y showed
no activity. However, Hessen and co-workers’ amide-functiona-
lised yttrium systems IV do polymerise ethylene upon activation
3
3
F
4
5
has an extensive coordination chemistry of the mid to late
with [PhNMe H][BAr
2
]. Okuda et al. were the first to report
transition and p-block metals (nearly 250 organometallic com-
1
1
pounds alone have been described), no organometallic rare earth
or transition metal compound before Group 6 has ever been
reported. Indeed the first rare earth coordination complexes at all
12
of [9]aneS (La and U triiodides) have only recently appeared.
3
Reaction of [Sc(CH SiMe
2
3
)
3
(THF)
2
] with one equivalent of
)(CH SiMe ] 1 as a
[
9]aneS in cold toluene afforded [Sc([9]aneS
3
3
2
3 3
)
white solid in 75% isolated yield (Scheme 1). Compound 1 was
characterised by NMR and IR spectroscopy and elemental
1
analysis.{ The H NMR spectrum of 1 indicates a product of C
3v
symmetry. The ring methylene protons appear as two sets of sharp,
mutually-coupled second order multiplets consistent with the
3
macrocycle being k bound to the Sc(CH SiMe ) fragment, the
2
3 3
resonances for which are as expected. Diffraction-quality crystals
of 1 were grown from a toluene–pentane mixture and the
molecular structure is shown in Fig. 1 together with selected bond
distances.{
As expected the [9]aneS ligand adopts a fac-coordination mode
3
Chart 1
and the geometry at Sc is approximately octahedral. The average
˚
Sc–S bond length of 2.793 A in 1 is comparable to the
{
Electronic supplementary information (ESI) available: characterising
F
limited literature data for S–Sc dative bonds (av. 5 2.833;
data for 1 and 2-BAr
available. See http://www.rsc.org/suppdata/cc/b5/b503967c/
philip.mountford@chem.ox.ac.uk
4
and details of the polymerisation experiments are
1
0b
˚
range 5 2.744–2.872 A for one report). The average Sc–CH
2
4c
˚
distance of 2.249 A in 1 is somewhat less than in II-Sc (2.279 A).
˚
*
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3
in toluene (250 cm ) in the presence of Al Bu
i
3
(250 equivs.)
under 5 bar ethylene pressure afforded 11.4 g of free-
flowing polyethylene after 1 h and acidic work-up. The
2
1
21
21
bar ) is
polymerisation activity of 1 (110 kg mol
21
h
21
21
superior to that of I-Sc (30 kg(PE) mol
h
bar ) and indeed
most scandium based ethylene polymerisation catalysts
3
described to date. However, 1 is significantly less active
2
1
21
21
than either II-Sc (220–240 kg(PE) mol
h
bar ) or III-Sc
bar ). As a control experiment we found
(THF) ] afforded no polyethylene when
activated in the same way, demonstrating the ability of the
9]aneS macrocycle to stabilise the presumed cationic alkyl
21
21
21
(290 kg(PE) mol
h
that [Sc(CH SiMe
2
3
)
3
2
[
3
initiating and propagating species.
There has been only one very recent report of 1-hexene
9
polymerisation by a cationic rare earth alkyl catalyst, and none at
F
all for styrene. Activation of 1 with [CPh ][BAr ] (1 equiv.) at
3
4
room temperature{ in C H Cl followed by addition of 1-hexene
6
5
led to the slow formation of poly(1-hexene) (ca. 30% conversion
21
h ) Mindful of Okuda
21
after 15 min, activity 200 kg(PH) mol
F
4
Scheme 1 Synthesis of 1 and in situ synthesis of 2-BAr .
and co-workers’ report that di-cationic alkyls can also be effective
polymerisation catalysts we examined the polymerisation of
F
1-hexene by 1 when activated with 2 equivs. of [CPh ][BAr
3
4
].
At room temperature the reaction was extremely vigorous, almost
immediately boiling the 1-hexene monomer. Even at 230 uC the
polymerisation was very rapid and exothermic with 90% conver-
21
21
sion (activity 3660 kg(PH) mol
h ) of 1-hexene to essentially
atactic poly-1-hexene (32% mmmm pentads (isotactic component)
1
3
as judged by C NMR) within 2.5 mins but with very
poor control of molecular weight (Mw 5 769,500, M 5 33,400,
n
M /M 5 23.0§). Repeating the room temperature reaction at a
w
n
higher dilution and lower [monomer] : [catalyst] ratio{ predictably
gave lower reaction rates (50% conversion after 10 mins; activity
2
1
21
1
44 kg(PH) mol
weight (M 5 77,390, M
otherwise identical control experiment with [Sc(CH
THF) ] showed negligible conversion, confirming once more the
strong beneficial role of the S -donor macrocycle.
h
) but much better control of molecular
5 13,280, M /M 5 5.8§). Again an
SiMe
w
n
w
n
2
3 3
) -
(
2
3
Finally we report our preliminary observation that styrene is
also very rapidly polymerised in the presence of 1 when
F
3 2 3 3
Fig. 1 Molecular structure of [Sc([9]aneS )(CH SiMe ) ] 1. Selected
activated with 2 equivs. of [CPh ][BAr
3
4
] at 230 uC (100%
distances and angles: Sc(1)–S(1) 2.7947(7), Sc(1)–S(2) 2.7799(6), Sc(1)–
S(3) 2.8039(6), Sc(1)–C(7) 2.250(2), Sc(1)–C(11) 2.265(2), Sc(1)–C(15)
˚
2.231(2) A; S(1)–Sc(1)–S(2) 74.439(18), S(1)–Sc(1)–S(3) 74.240(17), S(2)–
21 21
conversion after 1 min, activity 13 600 kg(PS) mol
h ). Full
characterisation of the polymer and mechanistic investigations
are underway.
Sc(1)–S(3) 74.380(18)u.
In conclusion, we have demonstrated for the first time that
neutral S-donor ligands may be used as supporting groups for
catalytically active, rare earth organometallic cations and have
shown that a-olefins can also be polymerised with them.
Remarkably, although sulfur donors are often viewed as ‘‘poisons’’
for late transition metal catalysts, such ligands do indeed give rise
to activity comparable to complexes of their N-donor analogues
F
4
Reaction of 1 with [CPh ][BAr ] in CD Cl gave a fluxional
3
2
2
compound assigned as the five-coordinate cation [Sc([9]aneS )-
3
+
(
CH
Ph CCH
produced a fine white precipitate of polyethylene. Addition of
2
SiMe
3
)
2
]
along with the expected side-product
3
2
SiMe
3
. Addition of ethylene gas (1 atm) to the sample
+
13
THF (1 equiv.) to samples of [Sc([9]aneS
the Lewis base adduct [Sc([9]aneS )(CH
Scheme 1) which showed resonances for a firmly bound THF
3
)(CH
2
SiMe
3
)
2
] afforded
for the systems reported here. However, additional ligand
+
+
3
2
SiMe
3
)
2
(THF)]
2
substitution may be necessary to control the stereochemistry of
insertion for a-olefins and molecular weight distributions. We are
actively developing the stoichiometric and catalytic chemistry
(including other monomers, other functionalisation reactions of
unsaturated substrates and the optimisation of catalytic conditions
(
and fac-coordinated [9]aneS ligands.{ While relatively stable over
several days when made on the NMR tube scale, 2-BAr could
3
F
4
not be isolated cleanly on a preparative scale. Analogous
4
b
14
observations were made for II-Sc.
Under identical conditions to those described for I-Sc, II-
in general) of rare earth alkyl complexes with different families of
fac-N3 and fac-S3 donor ligands and their mixed-donor atom
4b,c
Sc and III-Sc
F
3
reaction of 1 (20 mmol) with BAr
(1 equiv.)
homologues.
3
302 | Chem. Commun., 2005, 3301–3303
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C. M. Kozak and P. Mountford, Chem. Commun., 2003, 2880; (c)
C. S. Tredget and P. Mountford, unpublished results.
S. Bambirra, D. van Leusen, A. Meetsma, B. Hessen and J. H. Teuben,
Chem. Commun., 2001, 637.
We thank the EPSRC and Leverhulme Trust for support, DSM
F
3 4
Elastomers for gifts of [CPh ][BAr ] and Dr P L Burn for use of
5
his GPC apparatus. CST thanks St. Edmund Hall, Oxford, for a
Graduate Scholarship.
6 S. Arndt, T. P. Spaniol and J. Okuda, Chem. Commun., 2002, 896.
7
S. Arndt, T. P. Spaniol and J. Okuda, Angew. Chem., Int. Ed., 2003, 42,
075.
P. G. Hayes, W. E. Piers and R. McDonald, J. Am. Chem. Soc., 2002,
24, 2132; S. Bambirra, M. W. Bouwkamp, A. Meetsma and B. Hessen,
5
Cara S. Tredget, Fanny Bonnet, Andrew R. Cowley and
Philip Mountford*
8
1
Chemistry Research Laboratory, University of Oxford, Mansfield Road,
Oxford, UK OX1 3TA. E-mail: philip.mountford@chem.ox.ac.uk
J. Am. Chem. Soc., 2004, 126, 9182.
B. D. Ward, S. Bellemin-Laponnaz and L. H. Gade, Angew. Chem., Int.
Ed., 2005, 44, 1668.
9
Notes and references
10 (a) D. C. H. Oakes, B. S. Kimberley, V. C. Gibson, D. J. Jones, A. J.
P. White and D. J. Williams, Chem. Commun., 2004, 2174;
C. Capacchione, A. Proto, H. Ebeling, R. M u¨ lhaupt, K. M o¨ ller,
T. P. Spaniol and J. Okuda, J. Am. Chem. Soc., 2003, 125, 4964; (b) A
handful of rare earth compounds with dianionic ligands possessing
additional thioether S-donors have been reported. For example: H. Ma,
T. P. Spaniol and J. Okuda, Dalton Trans., 2003, 4770 and references
therein.
{
C
Crystal data for [Sc([9]aneS
18 45
H
3 2 3 3 7 8 7 8
)(CH SiMe ) ]?0.5(C H ) (1?0.5(C H )):
S
3
ScSi , M 5 533.04, monoclinic, C2/c, a 5 20.0776(4),
w
3
?C3.5
H
4
˚
b 5 15.6656(3), c 5 20.0619(4) A, a 5 90.00, b 5 100.0286(9), c 5 90.00u,
3
U 5 6213.6(2) A , Z 5 8, F(000) 5 2312, T 5 150 K, Nonius Kappa CCD,
˚
Mo-Ka radiation, 5.13 ¡ 2h ¡ 27.48u, 7044 independent reflections, 5027
w
reflections I . 3s(I), R 5 0.0350, R 5 0.0436. CCDC 267474. See http://
www.rsc.org/suppdata/cc/b5/b503967c/ for crystallographic data in CIF or
other electronic format.
1
1 A. J. Blake and M. Schr o¨ der, Adv. Inorg. Chem., 1990, 35, 1; S. C. Rawle
and S. R. Cooper, Struct. Bonding (Berlin), 1990, 1; W. Levason and
G. Reid, J. Chem. Soc., Dalton Trans., 2001, 2963.
§
GPC data recorded at 30 uC in THF referenced to polystyrene standards.
1
2 L. Karmazin, M. Mazzanti and J. P e´ caut, Chem. Commun., 2002, 654.
13 For an exception to this general rule in the area of late metal olefin
polymerisation catalysis see: S. D. Ittel, L. K. Johnson and
M. Brookhart, Chem. Rev., 2000, 100, 1169; O. Daugulis,
M. Brookhart and P. S. White, Organometallics, 2002, 21, 5935.
1
W. E. Piers and D. J. H. Emslie, Coord. Chem. Rev., 2002, 233, 131;
P. Mountford and B. D. Ward, Chem. Commun, 2003, 1797 (review).
J. Gromada, J.-F. Carpentier and A. Mortreux, Coord. Chem. Rev.,
2
2004, 248, 397; V. C. Gibson and S. K. Spitzmesser, Chem. Rev., 2003,
103, 283.
S. Arndt and J. Okuda, Adv. Synth. Catal., 2005, 347, 339.
(a) S. Hajela, W. P. Schaefer and J. E. Bercaw, J. Organomet. Chem.,
1997, 532, 45; (b) S. C. Lawrence, B. D. Ward, S. R. Dubberley,
14 For an account of the synthesis and structures of a number of rare earth
3
4
3 3
complexes of the type M(fac-N ligand)X (X 5 Cl, alkyl) see:
C. S. Tredget, S. C. Lawrence, B. D. Ward, R. G. Howe, A. R. Cowley
and P. Mountford, Organometallics, 2005, 24, DOI: 10.1021/om050209r.
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Chem. Commun., 2005, 3301–3303 | 3303