High activity ethylene polymerisation catalysts based on chelating diamide ligands

Article abstract of DOI:10.1039/a706304k

Treatment of Zr(NMe₂)₄ with RNH(SiPh₂)NHR and RNH(Me₂SiCH₂CH₂SiMe₂)NHR (R = 2,6-Me₂C₆H₃) affords the four- and seven-membered chelate complexes {

Full text of DOI:10.1039/a706304k

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High activity ethylene polymerisation catalysts based on chelating diamide
ligands
Vernon C. Gibson,*a Brian S. Kimberley,a Andrew J. P. White,a David J. Williamsa and Philip Howardb
a Department of Chemistry, Imperial College, Exhibition Road, South Kensington, London, UK SW7 2AY
b BP Chemicals, Sunbury Research Centre, Chertsey Road, Sunbury on Thames, Middlesex, UK TW16 7LN
Treatment of Zr(NMe2)4 with RNH(SiPh2)NHR and
HNLi
RNH(Me2SiCH2CH2SiMe2)NHR (R = 2,6-Me2C6H3) af-
NMe2
fords the four- and seven-membered chelate complexes
i
NH
NH
ii
N
N
Ph2Si
{Zr[RN(SiPh2)NR](NMe2)2(HNMe2)} and {Zr[RN(Me2Si-
CH2CH2SiMe2)NR](NMe2)2} respectively; a dramatic effect
of chelate ring size on ethylene polymerisation activity and
kinetic profile is found.
Zr
NMe2
Ph2Si
NHMe2
iii
1
3
There is considerable interest in the development of new
generation ‘non-metallocene’ catalysts for the polymerisation
of a-olefins. Chelating diamide complexes of the Group 4
metals have recently become the focus of much attention,1–10
partly because of their close relationship to the commercially
significant half-sandwich metal amido ‘constrained geometry’
catalyst system,11,12 and more generally due to a relationship to
metallocenes that may be traced through alkoxide relatives
(Scheme 1).† A potential advantage of the bis(amido)metal
system relative to the constrained geometry half-sandwich
metal amide catalyst family is a lower formal electron count
[(R2N)2Zr is formally a 10e2 fragment, cf. 12e2 for CpZr-
(NR2)] which is likely to result in a more electrophilic and
therefore potentially more active catalyst fragment. However, it
must be recognised that the bis(amido)metal system is sterically
more open and may need steric tuning to minimise deactivation
processes.
NH
NH
Si
Si
N
Si
Si
iv
R
R
Zr
N
4 R = NMe2
5 R = Me
2
v
Scheme 2 Reagents and conditions: i, Cl2SiPh2 (0.5 equiv.), Et2O, room
temp., 12 h, 79%; ii, Zr(NMe2)4, toluene, 90 °C, 12 h, 98%; iii,
ClSi(Me)2CH2CH2Si(Me)2Cl (0.5 equiv.), Et2O, room temp., 12 h, 74%; iv,
Zr(NMe2)4, toluene, 90 °C, 12 h, 97%; AlMe3 (5.0 equiv.), toluene, room
temp., 30 min, 98%
Me2N ligands. An important effect of increasing the size of the
chelate ring in 4 (now seven-membered, cf. four-membered in
3) is for the two aryl rings to partially envelop the Zr centre and
one of the Me2N ligands [N(10)]. The geometry of the seven-
membered chelate ring appears to be somewhat strained, the
internal angles at the N (131°) and C (117°) centres being
significantly enlarged from normal trigonal and tetrahedral
geometries, respectively. The reason(s) for these distortions are
not immediately evident, although they are clearly a factor in the
envelopment of the Zr centre described above. Complex 4 is
readily converted to complex 5 upon reaction with excess
AlMe3.13
R
R
O
R
N
Zr
Zr
Zr
R
N
O
R
R
Scheme 1
We report a surprisingly active zirconium ethylene polymer-
isation catalyst system based on chelating diamide ligands. Of
particular significance is the observation of dramatically
enhanced activity and a more stable kinetic profile upon increase
in the chelate ring size. Compounds 1 and 2 are readily
The results of preliminary studies on their activities for
ethylene polymerisation are collected in Table 1. For the mono-
silyl bridged species 3, pretreatment with BunLi, to remove the
bound Me2NH, and prealkylation with excess AlMe3, followed
synthesised in high yield via reaction of LiNHR (R
=
2,6-Me2C6H3) with the appropriate dichlorosilane (Scheme 2).
Treatment of 1 and 2 with Zr(NMe2)4 in toluene at 90 °C leads to
elimination of 2 equiv. of Me2NH and formation of four- and
seven-membered chelate complexes 3 and 4 in excellent yield.‡
The structures of 3 and 4 have been determined by X-ray
crystallography.§ The structure of 3 reveals the formation of a
distorted trigonal bipyramidal Zr complex (Fig. 1), the Zr being
bonded to the bidentate chelating diamide 1, two Me2N groups
and a molecule of Me2NH. The equatorial plane is defined by
N(2), N(6) and N(9), the axial positions being occupied by N(1)
and N(3). The principal distortion in the coordination geometry
is due to the small bite [71.3(1)°] of the chelating diamide, a
consequence of which is ‘reduced’ steric congestion of the Zr
centre allowing retention of three of the original four Me2N
ligands (rather than the expected two). The N2SiZr chelate ring
is planar to within 0.01 Å.
Si
N(1)
N(2)
Zr
N(6)
N(9)
N(3)
Fig. 1 Molecular structure of 3. Selected bond lengths (Å) and angles (°):
Zr–N(1) 2.158(2), Zr–N(2) 2.159(2), Zr–N(3) 2.426(2), Zr–N(6) 2.025(3),
Zr–N(9) 2.057(3), Si–N(1) 1.709(2), Si–N(2) 1.725(2); N(6)–Zr–N(9)
108.5(1), N(6)–Zr–N(1) 106.1(1), N(9)–Zr–N(1) 105.2(1), N(6)–Zr–N(2)
128.1(1), N(9)–Zr–N(2) 122.4(1), N(1)–Zr–N(2) 71.3(1), N(6)–Zr–N(3)
91.8(1), N(9)–Zr–N(3) 89.2(1), N(1)–Zr–N(3) 151.6(1), N(2)–Zr–N(3)
80.3(1), N(1)–Si–N(2) 94.2(1), Si–N(1)–Zr 97.5(1), Si–N(2)–Zr 97.0(1).
By contrast, the structure of 4 (Fig. 2) reveals a slightly
distorted tetrahedral coordination at Zr, comprising the bi-
dentate disilyldianilide [bite angle 109.2(1)°] and just two
Chem. Commun., 1998
313

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substituents of the large ring chelate ligand. Not only do these
preventthebindingofsmallbasemoleculessuchasMe2NH,they
also undoubtedly lend protection to the active catalyst site.
BP Chemicals Ltd and the EPSRC are thanked for a CASE
studentship to B. S. K. BP Chemicals is also thanked for
assistance with catalyst evaluation.
C(3)
C(4)
N(7)
Si(5)
Si(2)
N(1)
N(6)
Zr
N(10)
Notes and References
* E-mail: v.gibson@ic.ac.uk
† The similar 1s,2p bonding characteristics of the cyclopentadienide and
alkoxide ligands affords a direct isolobal relationship. It should be noted
that, whilst closely related to the alkoxide moiety, the amide ligand is
formally a 1s,1p unit and therefore is not strictly isolobal; as a 1s,1p ligand
it also donates two fewer electrons to the metal centre.
Fig. 2 Molecular structure of 4. Selected bond lengths (Å) and angles (°):
Zr–N(10) 2.024(4), Zr–N(7) 2.032(4), Zr–N(1) 2.084(4), Zr–N(6) 2.105(4),
N(1)–Si(2) 1.735(4), Si(2)–C(3) 1.874(5), C(3)–C(4) 1.535(7), C(4)–Si(5)
1.869(5), Si(5)–N(6) 1.746(4); N(10)–Zr–N(7) 104.7(2), N(10)–Zr–N(1)
116.0(2), N(7)–Zr–N(1) 108.2(2), N(10)–Zr–N(6) 111.1(2), N(7)–Zr–N(6)
107.2(2), N(1)–Zr–N(6) 109.2(1), Si(2)–N(1)–Zr 129.0(2), N(1)–Si(2)–
C(3) 107.8(2), C(4)–C(3)–Si(2) 116.8(4), C(3)–C(4)–Si(5) 116.6(4),
N(6)–Si(5)–C(4) 110.8(2), Si(5)–N(6)–Zr 131.7(2).
‡ Satisfactory elemental analyses have been obtained. Selected data for 1:
dH(C6D6, 298 K) 2.10 (s, 12 H, PhMe2), 3.39 (br s, 2 H, NH), 6.80–6.91
(overlapping m, aryl H), 7.04–7.10 (overlapping m, aryl H), 7.66–7.84
(overlapping m, aryl H); dC(C6D6, 298 K) 20.44, 122.13, 129.05, 130.10,
130.72, 134.81, 135.02, 136.82, 142.90. For 2: dH(C6D6, 298 K) 0.76 (s, 12
H, SiMe2), 0.51 (s, 4 H, (CH2SiMe2)2, 2.18 (s, 12 H, PhMe2), 6.85 (t, 2 H,
3JHH 6.7, p-C6H3), 7.00 (d, 4 H, 3JHH 6.7, m-C6H3); dC(C6D6, 298 K) 21.10,
9.75, 19.85, 122.01, 128.70, 131.45, 143.80. For 3: dH(C6D6, 298 K) 1.42
(br s, 1 H, HNMe2), 1.68 (d, 6 H, 3JHH 5.9, HNMe2), 2.26 (br s, 6 H, PhMe),
2.42 (br s, 6 H, PhMe), 2.79 (s, 12 H, NMe2), 7.07–7.11 (overlapping m, aryl
H), 7.61–7.64 (overlapping m, aryl H); dC(C6D6, 298 K) 21.15, 39.43,
41.95, 120.99, 127.22, 128.65, 135.64, 142.83. For 4: dH(C6D6, 298 K) 0.13
(s, 12 H, SiMe2), 1.21 (s, 4 H, Me2SiCH2), 2.39 (s, 12 H, PhMe2), 2.48 (s,
12 H, NMe2), 6.83 (t, 2 H, 3JHH 7.3, aryl H), 7.06 (d, 4 H, 3JHH 7.3, aryl H);
dC(C6D6, 298 K) 1.06, 10.72, 20.61, 42.42, 123.21, 128.95, 135.36, 146.13.
For 5: dH(C6D6, 298 K) 0.12 (s, 12 H, SiMe2), 0.23 (s, 6 H, ZrMe2), 1.08 (s,
4 H, Me2SiCH2), 2.37 (s, 12 H, C6H3Me2), 6.89–6.95 (m, 2 H, p-aryl H),
7.00–7.03 (m, 4 H, m-aryl H); dC(C6D6, 298 K) 0.18 (SiMe2), 9.38
(C6H3Me2), 20.75 (C6H3Me2), 43.07 (ZrMe2), 125.48 (C6H3-Cm), 129.51
(C6H3-Cp), 137.00 (C6H3-Co), 137.94 (C6H3-Cipso).
§ Crystal data for 3: C34H47N5SiZr, M = 645.1, monoclinic, P21/n (no. 14),
a = 11.425(1), b = 19.501(1), c = 15.423(3) Å, b = 97.58(1)°, V =
3406.1(7) Å3, Z = 4, Dc = 1.26 g cm23, m(Cu-Ka) = 32.0 cm21, F(000)
= 1360. A clear prism of dimensions 0.35 3 0.23 3 0.10 mm was used. For
4: C26H46N4Si2Zr, M = 562.1, monoclinic, P21/c (no. 14), a = 9.403(2), b
= 33.301(6), c = 10.640(2) Å, b = 113.02(1)°, V = 3066(1) Å3, Z = 4,
Dc = 1.22 g cm23, m(Mo-Ka) = 4.6 cm21, F(000) = 1192. A clear prism
of dimensions 0.67 3 0.57 3 0.57 mm was used. For 3 (4), 5590 (4306)
independent reflections were measured on a Siemens P4/PC diffractometer
at 183 K (293 K) with graphite monochromated Cu-Ka—rotating anode
source—(Mo-Ka) radiation using w-scans. The structures were solved by
direct methods and all the non-hydrogen atoms were refined anisotropically
using full-matrix least-squares based on F2 to give R1 = 0.036 (0.046), wR2
by exposure to ethylene (10 atm) in the presence of MAO (750
equiv.) at 50 °C gave an active, although short-lived ( < 15 min)
catalyst; 450 mg of polyethylene was isolated, corresponding to
an activity of 3 g mmol21 h21 bar21. By contrast, under
identical conditions of temperature, pressure and cocatalyst
concentration (entry 2), complex 4 afforded a steady uptake of
ethylene over the 60 min duration of the run at an activity of 490
g mmol21 h21 bar21. Increasing the temperature (entries 2–4)
gave a corresponding increase in activity, although a noticeable
deactivation occurs over the course of the 60 min run at 50 °C,
which becomes even more enhanced at 75 °C. The effect of
MAO cocatalyst concentration can be seen from entries 3, 5 and
6, the more MAO the higher the activity and also the more stable
the kinetic profile. If the procatalyst is not pre-alkylated with
AlMe3 (entry 7) reduced activity is found, consistent with the
necessity for efficient alkylation of the Me2N complex;13 MAO
on its own is known to be a relatively poor alkylating agent. The
molecular weights of the polyethylenes generated using the
most active catalysts are in the region of 105 (Mw) with
relatively broad molecular weight distributions (PDIs 5–9).
These will be discussed in more detail in a future publication.
Treatment of dimethylzirconium procatalyst
5
with
trityltetrakis(pentafluorophenyl)borate at 50 °C initially gives a
highly active catalyst that rapidly deactivates over 10 min. The
same procatalyst in the presence of MAO gives a much more
stable kinetic profile and an activity figure of merit comparable
to prealkylated 4 (entry 3). This is consistent with the general
stabilising effect found for MAO with metallocene catalyst
systems.
The dramatically more favourable activity and kinetic profile
characteristics found for 4 relative to 3 may be attributed to the
steric protection of the zirconium centre by the bulky aryl
=
0.095 (0.099) for 5084 (3093) independent observed absorption
corrected reflections [ıFoı > 4s(ıFoı), 2q @ 128° (50°)] and 351 (299)
parameters respectively. The N–H hydrogen atom in 3 was located from a
DF map and refined isotropically subject to an N–H distance constraint
(0.90 Å). CCDC 182/700.
1 J. D. Scollard, D. H. McConville, N. C. Payne and J. J. Vittal,
Macromolecules, 1996, 29, 5241.
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5 K. Aoyagi, P. K. Gantzel, K. Kalai and T. D. Tilley, Organometallics,
1996, 15, 923.
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Table 1 Ethylene polymerisation characteristicsa for 3–5
Cocatalyst
Entry Procatalyst (equiv.)
Activity/
T/°C g mmol21 h21 bar21
1
2
3
4
5
6
7
8
9
3
4
4
4
4
4
4
5
5
MAO (750)
MAO (750)
MAO (750)
MAO (750)
MAO (100)
MAO (2000)
MAO (750)f
[Ph3C][B(C6F5)4]
MAO (750)
50
25
50
75
50
50
50
50
50
3b
250c
490d
680e
140b
990d
70
60b
400d
a
General conditions: procatalyst dissolved in toluene for runs 1–7 and 9,
11 J. C. Stevens, F. J. Timmers, D. R. Wilson, G. F. Schmidt, P. N. Nickias,
R. K. Rosen, G. W. Knight and S.-Y. Lai, Eur. Pat. Appl., 416-815-A2,
1990, Dow.
12 J. A. M. Cannich, Eur. Pat. Appl., EP-420-436-A1, 1990, Exxon.
13 I. Kim and R. F. Jordan, Macromolecules, 1996, 29, 489.
CH2Cl2 for run 8, pretreatment with excess AlMe3 (10 equiv.) for runs 1–6,
1 litre autoclave, 10 atm ethylene pressure, isobutane solvent, AlMe3
b
c
scavenger, runs carried out over 60 min. Rapid deactivation. Stable
d
ethylene uptake over 1 h duration of run. Slow deactivation over 1 h
e
f
duration of run. Deactivation more rapid than in footnote (d). No
prealkylation.
Received in Liverpool, UK, 28th August 1997; 7/06304K
314
Chem. Commun., 1998