Chromium(iii) catalysed ethylene tetramerization promoted by bis(phosphino)amines with an N-functionalized pendant

Article abstract of DOI:10.1039/b702636f

Several N-functionalized bis(phosphino)amine ligands with ether, thioether and pyridyl tethers [(R″)₂PN(R′)P(R″)₂ = PNP] (1a-1g) have been synthesized. They react with CrCl₃(THF) ₃ in CH₂Cl₂ to give dinuclear chloro bridged Cr₂(-Cl)₂Cl₄(PNP)₂ (2) which converts to the corresponding mononuclear solvento complexes fac-CrCl ₃(PNP)(NCR) (3). The structures of the ligand 1d with R′ = -(CH₂)₃SCH₃ and R″ = Ph, and the complexes with R = CH₃ (3a) and C₂H₅ (3b), R′ = -(CH₂)₃SCH₃ and R″ = Ph) have been established by single-crystal X-ray crystallography. All ligands are active towards ethylene tetramerization in the presence of Cr(iii) and excess MAO at 80 °C in toluene. The ligand with thioether pendant Et₂PN(CH ₂CH₂CH₂SCH₃)PEt₂ (1c) shows the highest selectivity (55% weight in liquid product distribution) towards 1-octene. Complexes 3a and 3b are active towards ethylene polymerization under thermal conditions. The Royal Society of Chemistry.

Full text of DOI:10.1039/b702636f

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An international journal of inorganic chemistry
www.rsc.org/dalton
Number 32 | 28 August 2007 | Pages 3461–3592
ISSN 1477-9226
PAPER
PERSPECTIVE
Zhiqiang Weng, Shihui Teo
and T. S. Andy Hor
P. Manohari Abeysinghe
and Margaret M. Harding
Antitumour bis(cyclopentadienyl)
metal complexes: titanocene
and molybdocene dichloride and
derivatives
Chromium(iii) catalysed ethylene
tetramerization promoted by
bis(phosphino)amines with
an N-functionalized pendant
1477-9226(2007)32;1-5

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PAPER
www.rsc.org/dalton | Dalton Transactions
Chromium(III) catalysed ethylene tetramerization promoted by
bis(phosphino)amines with an N-functionalized pendant†‡
Zhiqiang Weng,* Shihui Teo and T. S. Andy Hor*
Received 26th February 2007, Accepted 10th May 2007
First published as an Advance Article on the web 23rd May 2007
DOI: 10.1039/b702636f
Several N-functionalized bis(phosphino)amine ligands with ether, thioether and pyridyl tethers
[(Rꢀꢀ)2PN(Rꢀ)P(Rꢀꢀ)2 = PNP] (1a–1g) have been synthesized. They react with CrCl3(THF)3 in CH2Cl2 to
give dinuclear chloro bridged Cr2(l-Cl)2Cl4(PNP)2 (2) which converts to the corresponding
mononuclear solvento complexes fac-CrCl3(PNP)(NCR) (3). The structures of the ligand 1d with Rꢀ =
-(CH2)3SCH3 and Rꢀꢀ = Ph, and the complexes with R = CH3 (3a) and C2H5 (3b), Rꢀ = -(CH2)3SCH3
and Rꢀꢀ = Ph) have been established by single-crystal X-ray crystallography. All ligands are active
towards ethylene tetramerization in the presence of Cr(III) and excess MAO at 80 ◦C in toluene. The
ligand with thioether pendant Et2PN(CH2CH2CH2SCH3)PEt2 (1c) shows the highest selectivity (55%
weight in liquid product distribution) towards 1-octene. Complexes 3a and 3b are active towards
ethylene polymerization under thermal conditions.
such a combination could benefit ethylene oligomerization and
the thermal stability of the catalyst.
Introduction
Driven by the high technological value and economic demand for
linear a-olefins, especially the C4–C8 range, research into selective
ethylene oligomerization is gathering pace.1 Much development
has been witnessed in the trimerization technology.2–6 Selective
tetramerization, which was once thought to be improbable,7
has also been recently realized.8 The latest mechanistic studies
pointed to a metallacycloalkane pathway.9 For example, favorable
formation of 1-octene would be promoted by the stability of
metallacycloheptane and instability of the metallacyclononane.10
Although the factors behind their relative stabilities are still poorly
understood, the importance of the ligand and its electronic and
coordinative effects on the metal is unquestionable.11 The next
phase of development thus demands better ligand and catalyst
design and better understanding of the interactions among the
catalyst, co-catalyst, substrate and perhaps even the medium. It
would also be desirable to design thermally stable catalysts that can
withstand the harsh conditions used in ethylene oligomerization.
Among the catalysts known, the most effective catalysts for
ethylene tetramerization are Cr(III) supported by nitrogen linked
diphosphine ligands.8,10 In this paper, we modify the ligand
framework by introducing a functionalized and hemilabile side
chain to the N-donor of bis(phosphino)amine ligands, and
examine its effect on oligomerization activities. Notable success
has been experienced by the use of suitable side-arms in olefin
oligomerization/polymerization.12 Our earlier results suggested
that a combinative use of a hemilabile ligand and an unsaturated
metal would promote efficient catalysis.13 We herein examine if
Results and discussion
Ligand design
Bis(phosphino)amines are the ligands of choice because of their
good stability and donor characteristics to Cr(III). The addition of
a functional side-arm at the N-site would raise the denticity and
coordinative flexibility of these ligands. This potential of tethering
prompted us to prepare new N-donor-functionalized ligands (1a–
1g), in one-step (65–97% yield), from the acid condensation
reaction of stoichiometric quantities of a functionalized primary
amine and R2PCl.14 (Scheme 1) The donor functionality is
represented by ether (1e and 1f), thioether (1a–1d) and pyridyl (1g),
ranging from weak to moderate basicity. This side-arm is designed
for its potential ability to undergo reversible coordination to metal
viz. Cr during the catalytic cycle. These ligands are best represented
as [2 + 2] multidentate ligands with two strong donors (viz. P, P)
supplemented by two weak donor sites (viz. N, X). In conjunction
with a weakly coordinative solvent, such as CH3CN, they would
provide the best support for a metal that undergoes a series of
coordinative, oxidative and geometric changes during the catalytic
cycle. During the preparation of this manuscript, Bercaw et al.
published a similar approach to ethylene tri- and tetramerisation
using chromium dinuclear complexes with a similar ether tether
to support the -PPh2 donors.15 Our work focuses on both ether
and thioether “side-arms” to support mainly the -PEt2. It is also
Department of Chemistry, National University of Singapore, 3 Science
Drive 3, Kent Ridge, Singapore 117543. E-mail: chmwz@nus.edu.sg, andy-
hor@nus.edu.sg
† Dedicated to Dr Lai Yoong Goh on the occasion of her retirement
‡ Electronic supplementary information (ESI) available: ORTEP diagrams
and tables of crystallographic data for compounds 1d, 3a and 3b. See DOI:
10.1039/b702636f
Scheme 1
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notable that Bercaw’s syntheses in CH2Cl2 resulted in dinuclear
complexes whereas our preparations in CH3CN resulted in the
isolation of the solvento mononuclear complexes.
All ligands have been spectroscopically characterized. X-Ray
single-crystal crystallographic analysis was carried out on a
representative ligand viz. 1d. (Fig. 1) It shows the PNP skeleton
with a methyl propyl thioether s◦ide-chain extended from the N-
site. The P–N–P angle (110.7(3) ) reflects a higher sp3 than sp2
A related structure of {[Ph2PN(CH2CH2OCH3)PPh2]CrCl2(l2-
Cl)]}2 has been reported.15
The significance of 2 is exemplified by its ready conversion to a
potentially unsaturated Cr(III) that is catalytically active. Indeed,
in a donor-solvent such as CH3CN or CH3CH2CN, it readily un-
dergoes bridge-cleavage to yield the corresponding mononuclear
solvento complexes (represented by 3a and 3b). Single-crystal
X-ray diffraction studies of 3a and 3b revealed a mononuclear
octahedral fac-[CrIIICl3] supported by a PP-chelate and nitrile
(Fig. 2, Table 1) Not surprisingly, the metal chooses the nitrile
over the thio function, which remains a pendant side-arm. The
strained 4-membered ring forces an acute P–Cr–P chelate angle
66.37(9)◦ (3a) and 66.01(5)◦ (3b) whereas the P–N–P contracts
from 110.7(3)◦ in the ligand to 106.7(4)◦ (3a) and 105.7(2)◦ (3b) in
the complexed state. The chelate angles are smaller than those
˚
character although the short P–N bond (average 1.718(6) A)
16
˚
[compared to other typical N–P single bonds (1.70–1.95 A)]
could suggest some p character.
Fig. 1 Molecular structure of 1d (H atoms and the minor disorder
components are omitted for clarity). Thermal ellipsoids are drawn at the
40% probability level.
Complex synthesis
Complexation occurs readily at rt between the Lewis acidic
CrCl3(THF)3 and the basic ligand 1. In CH2Cl2, dinu-
clear adducts with doubly-bridging chlorides are formed
(Scheme 2). This is best represented by the formation of
{[Ph2PN(CH2CH2CH2SCH3)PPh2]CrCl2(l2-Cl)]}2 (2) from 1d.
The metal prefers to form the chloride-bridged dinuclear complex
with the stronger donors (4Cl, 2P) over the mononuclear analogue
coordinated by the much weaker thioether and amine donors.
Fig. 2 Molecular structure of 3a and 3b (H atoms and the minor disorder
components in 3a are omitted). Thermal ellipsoids are drawn at the 40%
probability level.
Scheme 2
3494 | Dalton Trans., 2007, 3493–3498
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the dinuclear complexes reported by Bercaw et al.,15 the ether-
functionalized ligands (1e and 1f) together with Cr(acac)3 appear
to be less selective towards trimerization but more so towards
tetramerization and higher oligomer formation. In all cases under
study, the selectivity of 1-octene over other octenes is excellent
(96–99%). The length of the side chain influences the selectivity.
Use of a methyl propyl thioether residue in conjunction with
an electron-donating and less hindered ethyl substituent at the
phosphine gives 1-octene in excess of 55 mass% (Entry 3).17
This is comparable to the high performance catalysts in the
Sasol process with selectivities up to 70%,8,10 both of which
exceed the conventional one-step ethylene oligomerization or
tetramerization technology that generally gives 1-octene in yields
<26 mass%.18–20 Preliminary data also suggested that the system
comprising Cr(III) with 1c can maintain its activity, without visible
loss, for 8 h at 80 ◦C under 30 bar ethylene pressure in the
presence of methylaluminoxane (MAO). This stability is higher
than those observed in many other ligands system such as those
with o-methoxyphenyl substituents.4,15 Its productivity (14659 g
g−1 Cr h−1) is also much higher than that of the PNP ligand with no
tethering donor groups, e.g. Et2PN(CH3)PEt2 (4400 g g−1 Cr h−1).8
These data, together with the differences observed for different N-
bonded tethers, provided indirect evidence that the pendant group
would affect the tetramerization outcome.
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) of 1d, 3a, and 3b
Compound
1d
3a
3b
˚
Bond lengths (A)
Cr(1)–N(2)
2.044(17)
2.244(5)
2.293(3)
2.298(3)
2.478(3)
2.482(3)
1.506(12)
1.693(8)
1.691(8)
1.767(13)
1.805(17)
2.038(4)
Cr(1)–Cl(1)
Cr(1)–Cl(2)
Cr(1)–Cl(3)
Cr(1)–P(1)
Cr(1)–P(2)
N(1)–C(1)
2.2600(15)
2.3186(16)
2.2979(16)
2.5102(15)
2.4609(15)
1.487(6)
1.483(8)
1.715(6)
1.721(5)
1.743(8)
1.779(9)
N(1)–P(1)
N(1)–P(2)
1.698(4)
1.700(4)
S(1)–C(3)
S(1)–C(4)
1.806(5)
1.780(8)
Bond angles (◦)
P(1)–Cr(1)–P(2)
Cl(1)–Cr(1)–Cl(3)
Cl(2)–Cr(1)–Cl(3)
N(2)–Cr(1)–Cl(1)
Cl(2)–Cr(1)–P(1)
Cl(3)–Cr(1)–P(2)
P(1)–N(1)–P(2)
C(3)–S(1)–C(4)
C(1)–N(1)–P(1)
C(1)–N(1)–P(2)
66.37(9)
93.27(12)
103.5(2)
171.9(5)
94.90(10)
95.3(2)
106.7(4)
102.5(7)
127.8(7)
125.5(7)
66.01(5)
92.97(6)
102.21(6)
175.93(13)
96.56(6)
94.90(5)
105.7(2)
102.3(3)
130.6(3)
123.7(3)
110.7(3)
101.5(5)
121.9(6)
124.9(6)
The higher homologues of a-C11-olefins are formed as by-
products. Current research is directed at their elimination through
other ligand and metal designs. Preliminary data suggested that
direct use of 3a or 3b as catalyst at 80 ◦C and 30 bar of ethylene
pressure in the presence of MAO gives no oligomerization product
but polymers up to TOF of 24 310 h−1 and 29 170 h−1 respectively.
It demonstrates the potential of using thermally a stable catalyst
to promote ethylene polymerization under pressured and thermal
conditions.
found in the dinuclear complexes {[Ph2PN(Rꢀ)PPh2]CrCl2(l2-
Cl)]}2 [Rꢀ = CH2CH2OCH3 (66.837(18)◦),15 Ph (66.62(7)◦)8].
The pendant thioether is located away from the metal to avoid
interference with the coordination sphere. In both complexes, the
Cr–Cl bond trans to the nitrile is distinctly shorter, and presumably
stronger, compared to the other two.
Catalytic ethylene tetramerization
A catalytic mixture containing Cr(acac)3/CrCl3(THF)3 : ligand
(1a–1g) : methylaluminoxane (MAO) (1 : 2 : 440) is mixed under
30 bar pressure of ethylene at 80 ◦C in toluene in the commercial
Endeavor Parallel Reactor. The results are summarized in Table 2.
All the mixtures are active, showing good turnovers of ∼32000–
61000 g g−1 in 3 h. The isomeric distributions however are sensitive
to the nature of the functionalized side-chain at N. The thioether
ligands show higher selectivity than their ether counterparts
with respect to octene formation (33–55% in Entries 1–4 vs.
35–38% in Entries 5–6). Both series perform significantly better
than the pyridyl derivative (19%) (Entry 7). When compared to
Conclusions
Although it is clear that the nature of the N-pendant influences
the catalytic outcome, we have no strong evidence, at least in this
system, that this is realized in the form of the expected protection
and deprotection of the metal in the course of the catalytic cycle.
Recent reports suggested possible involvement of a cationic MAO-
stabilized species and the Cr(II)/(IV) couple.9c There is also a
question of the possibility of disproportionation of Cr(II) to re-
generate the catalytically active Cr(III) [and Cr(0)], thus reviving a
Table 2 Key ethylene oligomerization data using Cr(III) and ligand 1 as catalysta
Liquid product distribution (%)
Run (ligand)
Activityb
Total product/mg
Solids (%)
Liquids (%)
C6
C8
C10
C11+
1-C8 (%)
1 (1a)
2 (1b)
3 (1c)
4 (1d)d
5 (1e)
6 (1f)
7 (1g)
41500
53600
43980
18600
61020
48870
30540
772
997
818
346
1135
909
569
11.1
24.3
4.9
62.4
26.9
26.4
23.4
88.9
75.7
95.1
37.6
73.1
73.6
77.6
25.9
18.0
26.7
9.2
17.3
17.9
11.7
49.3
36.8
55.5
33.3
35.3
37.8
19.3
1.3
1.6
1.2
1.9
1.8
1.8
2.3
24.5
43.3
16.2
54.8
45.4
42.2
66.2
97.7
98.5
98.5
97.0
97.8
97.5
96.2
a Standard reaction conditions: 0.36 lmol Cr(acac)3, 2 equiv. of ligand, 440 equiv. of MAO, 4 ml toluene, 30 bar ethylene, 3 h, 80 ◦C. (run 7; CrCl3·(THF)3).
b Activity = g prod. per g Cr. c % = weight%. d 1 h.
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catalytic process.21 Future research in our laboratory will include
the examination of the interaction of our pendant with aluminate
anion and the compatibility of our ligands with Cr(II) and Cr(IV).
1.88–1.56 (m, 8H, -PCH2-), 1.26–0.96 (m, 14H, C-CH2-C, P-C-
CH3). 13C NMR (CDCl3): d 48.00, 31.84, 22.61, 15.56, 9.77, 9.53.
31P NMR (CDCl3): d 58.55. MS (FAB+): m/z 282 [M + H]+.
Preparation of Ph2PN(CH2CH2CH2SCH3)PPh2 (1d)
Experimental
By using
a similar method as above, a mixture of 3-
General
(methylthio)propylamine (60 mg, 0.571 mmol), triethylamine
(0.6 ml) and chlorodiphenylphosphine (251 mg, 1.14 mmol) gave
Ph2PN(CH2CH2CH2SCH3)PPh2 (1d) (261 mg, 0.552 mmol, 97%
All reactions were carried out using conventional Schlenk tech-
niques under an inert atmosphere of nitrogen or argon with
an M. Braun Labmaster 130 Inert Gas System. NMR spectra
were measured on Bruker ACF300 300 MHz FT NMR spec-
trometers (1H at 300.14 MHz, 13C at 75.43 MHz and 31P at
121.49 MHz). Mass spectra were obtained on a Finnigan Mat
95XL-T spectrometer. Elemental analyses were performed by the
microanalytical laboratory in-house. All chemicals were obtained
from Sigma-Aldrich or Stem Chemicals unless stated otherwise. In
all the examples, the molar mass of methylaluminoxane (MAO)
(10 wt% in toluene solution) was taken to be 58.016 g mol−1,
corresponding to the (CH3-Al-O) unit, in order to calculate the
molar quantities of MAO used in the preparation of the catalysts
described below. Ligands (1a–1g) are prepared with modifications
on literature procedures.14
1
yield) as a white solid. H NMR (CDCl3): d 7.44–7.34 (m, 20H,
Ph), 3.47–3.35 (m, 2H, N-CH2-C), 2.15–2.10 (t, 2H, J = 7.02 Hz,
C-CH2-S), 1.86 (s, 3H, S-CH3), 1.44–1.36 (m, 2H, C-CH2-C). 31
P
NMR (CDCl3): d 63.49. MS (FAB+): m/z 474 [M + H]+. Elemental
analysis (%) calcd for C28H29NP2S: C 70.89, H 6.19, N 2.95; found:
C 70.48, H 6.28, N 2.85.
Preparation of Et2PN(CH2CH2CH2OCH2CH3)PEt2 (1e)
By using a similar method, a mixture of 3-ethoxypropylamine
(37 mg, 0.359 mmol), triethylamine (0.2 ml) and chlorodiethyl-
phosphine (90 mg, 0.722 mmol) gave Et2PN(CH2CH2CH2-
OCH2CH3)PEt2 (1e) (92 mg, 0.33 mmol, 91% yield) as a colorless
oil. 31P NMR (CDCl3): d 58.55. H NMR (CDCl3): d 3.38–3.30
1
(m, 4H, CH2–OCH2), 3.09–2.92 (m, 2H, N–CH2–), 1.70–1.04 (m,
25H, –CH2–, –CH3, PCH2CH3). 13C NMR (CDCl3): d 68.58, 67.91,
30.13, 27.32, 20.74, 19.86, 14.90. MS (FAB+): m/z 280 [M + H]+.
Preparation of Et2PN(CH2CH2SCH3)PEt2 (1a)
To a mixture of 2-(methylthio)ethylamine (101 mg, 1.11 mmol)
and triethylamine (0.6 ml) in dichloromethane (5 ml) at rt was
added a solution of chlorodiethylphosphine (277 mg, 2.22 mmol)
in CH2Cl2 (4 ml). The resulting solution was stirred for 20 h,
after which the solvent was evaporated to dryness and toluene
(5 ml) added. The suspension was filtered through a layer of
Celite to remove the triethylammonium salt formed. The product
Et2PN(CH2CH2SCH3)PEt2 (1a) (192 mg, 0.72 mmol, 65% yield)
Preparation of Et2PN(CH2CH2CH2OCH2CH2CH2CH3)PEt2 (1f)
By using a similar method, a mixture of 3-butoxypropylamine
(47 mg, 0.359 mmol), triethylamine (0.2 ml) and chlorodiethyl-
phosphine (90 mg, 0.722 mmol) gave Et2PN(CH2CH2CH2-
OCH2CH2CH2CH3)PEt2 (1f) (97 mg, 0.316 mmol, 87% yield) as
1
a colorless oil. H NMR (CDCl3): d 3.38–3.34 (m, 4H, CH2-O-
1
was isolated as a colorless oil after solvent removal. H NMR
CH2), 2.58–2.52 (m, 2H, N-CH2-), 1.86–0.87 (m, 49H, -CH2-,
-CH3, PCH2CH3). 13C NMR (CDCl3): d 70.50, 68.58, 45.88, 31.70,
22.52, 19.24, 13.79, 9.73, 9.48. 31P NMR (CDCl3): d 58.61. MS
(FAB+): m/z 308 [M + H]+, 250 [M − CH2CH2CH2CH3]+.
(CDCl3): d 3.15–3.02 (q, J = 9.18, 2H, N-CH2-C), 2.58–2.52 (m,
2H, C-CH2-S), 2.10 (s, 3H, S-CH3), 1.68–1.56 (m, 8H, -PCH2-),
1.06–0.96 (m, 12H, P-C-CH3). 13C NMR (CDCl3): d 48.49, 22.61,
15.56, 9.68, 9.44. 31P NMR (CDCl3): d 58.52. MS (FAB+): m/z
252 [M + H]+.
Preparation of Et2PN(CH2CH2(C5H4N))PEt2 (1g)
By using a similar method, a mixture of 2-(2-aminoethyl)pyridine
(141 mg, 1.157 mmol), triethylamine (0.8 ml) and chlorodiethyl-
phosphine (288 mg, 2.313 mmol) gave Et2PN(CH2CH2-
(C5H4N))PEt2 (1g) (336 mg, 1.128 mmol, 97% yield) as a colorless
Preparation of Et2PN(CH2CH2SCH2CH3)PEt2 (1b)
By using a similar method as above, a mixture of 2-(ethylthio)-
ethylamine (42 mg, 0.4 mmol) and triethylamine (0.2 ml)
with chlorodiethylphosphine (99 mg, 0.8 mmol) gave Et2PN-
(CH2CH2SCH2CH3)PEt2 (1b) (84 mg, 0.299 mmol, 75% yield) as
an colorless oil. 1H NMR (CDCl3): d 3.13–3.08 (m, 2H, N-CH2-
C), 2.60–2.52 (m, 4H, -CH2-S-CH2-), 1.88–1.62 (m, 8H, -PCH2),
1.31–1.00 (m, 15H, C-CH3, P-CH2CH3). 31P NMR (CDCl3): d
58.36. MS (FAB+): m/z 282 [M + H]+.
1
oil. H NMR (CDCl3): d 8.49–8.47 (t, 1H, J = 4.77 Hz, C-H),
7.56–7.55 (m, 1H, C-H), 7.13–7.09 (m, 2H, C-H2), 3.35–3.28 (q,
=
2H, N-CH2-), 2.99–2.95 (t, J = 6.42, 2H, C-CH-), 1.86–0.99 (m,
20H, PCH2CH3). 31P NMR (CDCl3): d 58.41.
Synthesis of {[Ph2PN(CH2CH2CH2SCH3)PPh2]CrCl2(l2-Cl)]}2
(2)
Preparation of Et2PN(CH2CH2CH2SCH3)PEt2 (1c)
To a solution of Ph2PN(CH2CH2CH2SCH3)PPh2 (1d) (141 mg,
0.298 mmol) in CH2Cl2 (5 ml) was added CrCl3(THF)3 (112 mg,
0.298 mmol) and stirred at rt for 30 min to give a green solution.
The mixture was concentrated under vacuum, after which excess
hexane was added to precipitate the dark green solid, which was
collected by filtration and washed with hexane. Yield 183 mg
(97%). IR [KBr, cm−1] 3056 (m), 2954 (m), 2917 (m), 1482 (m),
By using a similar method as adopted above, a mixture of
3-(methylthio)propylamine (29 mg, 0.276 mmol), triethylamine
(0.2 ml) and chlorodiethylphosphine (70 mg, 0.56 mmol) gave
Et2PN(CH2CH2CH2SCH3)PEt2 (1c) (64 mg, 0.228 mmol, 84%
yield) as an colorless oil. 1H NMR (CDCl3): d 3.09–2.97 (m, 2H,
N-CH2-C), 2.57–2.45. (m, 2H, C-CH2-S), 2.10 (s, 3H, S-CH3),
3496 | Dalton Trans., 2007, 3493–3498
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1434 (s), 1279 (w), 1314 (w), 1188 (w), 1095 (s), 1027 (w), 998
(w), 961 (w), 880 (m), 746 (s), 694 (s), 504 (s). MS (FAB+): m/z
632 [1/2(M)]+, 595 [1/2(M) − Cl]+, 560 [1/2(M) − 2Cl]+, 508
[1/2(M) − 2Cl − Cr]+, 474 [L]+, 185 [PPh2]+. Elemental analysis
(%) calcd for C56H61N2O1.5P4S2Cr2Cl6: (as 1.5 hydrate) C 51.04, H
4.89, N 2.13; found: C 51.16, H 5.00, N 2.08.
595 [M − Cl − CH3CH2CN]+, 560 [M − 2Cl − CH3CH2CN]+, 508
[M − 2Cl − CH3CH2CN − Cr]+, 474 [L]+, 185 [PPh2]+. Elemental
analysis (%) calcd for C31H34N2P2SCrCl3: C 54.20, H 4.99, N 4.08;
found: C 54.07, H 5.22, N 3.98.
Oligomerization of ethylene
The catalytic activities were screened by Endeavor Parallel Pres-
sure Reactor, following recommended procedures. At the end of
each experiment, the vessel was cooled to ambient temperature
and depressurized. The reaction mixture was cooled to 0 ◦C and
terminated by addition of 10% aq. HCl. A small sample of the
upper-layer solution was filtered through a layer of Celite and
analysed by GC. The individual products of oligomerization were
identified by GC-MS. The remainder of the upper-layer solution
was filtered to isolate the solid polymeric products. The solid
products were suspended in 10% aq. HCl and stirred for 24 h,
dried under reduced pressure and weighed.
Synthesis of [Ph2PN(CH2CH2CH2SCH3)PPh2]CrCl3(CH3CN)
(3a)
CH3CN (1 ml) was introduced to a test tube containing solid
2 (48 mg, 0.076 mmol), after which blue microcrystals readily
precipitated. The mixture was kept at −30 ◦C for 1 day to give
more crystals. The mother liquor was removed and the crystals
were washed with hexane, and then dried under vacuum to give of
3a. Yield 37 mg (73%). IR [KBr, cm−1] 3055 (m), 2984 (w), 2920
(w), 1482 (m), 1435 (s), 1313 (w), 1188 (w), 1094 (s), 1027 (w),
999 (w), 942 (w), 883 (m), 800 (w), 749 (s), 697 (s), 508 (m). MS
(FAB+): m/z 595 [M − Cl − CH3CN]+, 560 [M − 2Cl − CH3CN]+,
508 [M − 2Cl − CH3CN − Cr]+, 474 [L]+, 185 [PPh2]+. Elemental
analysis (%) calcd for C30H32N2P2SCrCl3: C 53.54, H 4.79, N 4.16;
found: C 53.51, H 5.04, N 4.13.
Crystal structure analyses
Diffraction-quality single crystals were obtained at −30 ◦C as
follows: 1d as light yellow diamond-like crystals after 4 days
from a toluene solution; 3a and 3b as blue needles after 2 days
from solutions in CH3CN and CH3CH2CN, respectively. These
crystals were mounted on quartz fibers and X-ray data collected
on a Bruker AXS APEX diffractometer, equipped with a CCD
Synthesis of [Ph2PN(CH2CH2CH2SCH3)PPh2]CrCl3-
(CH3CH2CN) (3b)
By following a procedure similar to that for 3a, solid 2 in
CH3CH2CN gave blue crystals of 3b. Yield 43 mg (82.70%). IR
[KBr, cm−1] 3060 (m), 2958 (w), 2920 (w), 1482 (w), 1435 (s), 1312
(w), 1187 (w), 1093 (s), 1027 (w), 999 (w), 942 (w), 888 (m), 797
(w), 749 (s), 695 (s), 541 (w), 505 (m), 489 (w). MS (FAB+): m/z
˚
detector, using Mo-Ka radiation (k 0.71073 A). The data was
corrected for Lorentz and polarisation effect with the SMART
suite of programs22 and for absorption effects with SADABS.23
Structure solution and refinement were carried out with the
Table 3 Selected crystal data, data collection and refinement parameters of compounds 1d, 3a and 3b
Compound
1d
3a
3b
Formula
C28H29NP2S
473.52
C30H32Cl3CrN2P2S
672.93
C31H34Cl3CrN2P2S
686.95
Formula weight
Crystal size/mm
Temperature/K
Crystal system
Space group
0.26 × 0.10 × 0.06
0.10 × 0.08 × 0.02
0.18 × 0.06 × 0.02
223(2)
223(2)
223(2)
Orthorhombic
P2(1)2(1)2(1)
9.2813(10)
9.8308(8)
27.659(3)
90
90
90
2523.6(4)
4
1.246
Monoclinic
P2(1)/n
11.3331(13)
16.3009(19)
17.286(2)
90
99.248(4)
90
3151.8(6)
4
1.418
Mo-Ka
0.808
1.73 to 25.00
18076
Orthorhombic
Pbca
11.213(2)
16.453(3)
34.766(7)
90
90
90
6414(2)
8
1.423
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/g cm−3
Radiation used
Mo-Ka
0.271
1.47 to 25.00
6731
Mo-Ka
0.796
2.16 to 25.00
35350
l/mm−1
h range/◦
No. of unique reflections
measured
Max., min. transmission
Final R indices [I > 2r(I)]a,b
R indices (all data)
Goodness-of-fit on F2c
0.9839 and 0.9328
R1 = 0.0838, wR2 = 0.1564
R1 = 0.1113, wR2 = 0.1758
1.077
0.9840 and 0.9235
R1 = 0.1172, wR2 = 0.1964
R1 = 0.1918, wR2 = 0.2264
1.095
0.9843 and 0.8700
R1 = 0.0713, wR2 = 0.1314
R1 = 0.1024, wR2 = 0.1432
1.112
−3
˚
Large diff. peak and hole/e A
0.447 and −0.382
0.610 and −0.498
0.401 and −0.445
a R = (R|Fo| − |Fc|)R|Fo|. b wR2 = [(Rx|Fo| − |Fc|)2/Rx|Fo|2]1/2
.
c GoF = [(Rx|Fo| − |Fc|)2/(Nobs − Nparam)]1/2
.
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3493–3498 | 3497
©

View Article Online
SHELXTL suite of programs.24 The structures were solved by
direct methods to locate the heavy atoms, followed by difference
maps for the light non-hydrogen atoms. In 1d, The C1–C2 of the
C3H6 chain is disordered into two positions with 66 : 34 ratio. The
disordered parts C1–C2 and C1x–C2x were refined with the ratio
as free-variable to give the final ratio of 65/35. The bond lengths
involving these disordered atoms were also restrained to avoid
excessive deviations of the bond lengths and thermal parameters
from normal values. There is also a disorder in 3a involving the
switching of one Cl and the acetonitrile at 61 to 39 occupancies.
The Cl/acetonitrile disordered pair occupancy ratio was refined
as a free variable. Restraints were also applied to the bond lengths
and thermal parameters of the acetonitrile to keep them in the
usual range as these did not behave well during refinement. The
data collection and processing parameters are given in Table 3.
CCDC reference numbers 637514 (1d), 637515 (3a) and 637516
(3b). For crystallographic data in CIF or other electronic format
see DOI: 10.1039/b702636f.
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Acknowledgements
Financial support from the National University of Singapore and
a scholarship to S. T. are gratefully acknowledged. The authors
are grateful to Dr L. L. Koh and Ms G. K. Tan for assistance in
the crystallographic analysis.
15 P. R. Elowe, C. McCann, P. G. Pringle, S. K. Spitzmesser and J. E.
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3498 | Dalton Trans., 2007, 3493–3498
This journal is
The Royal Society of Chemistry 2007
©