Bimetallic nickel complexes of trimethyl phenyl linked salicylaldimine ligands: Synthesis, structure and their ethylene polymerization behaviors

Article abstract of DOI:10.1016/j.inoche.2006.08.017

Bimetallic salicylaldimine-nickel complexes, 2,4,6-Me₃-1,3-{[N{double bond, long}CH-(3′-R-5′-Y-2′-O-C₆H₃)-κ²-N,O]Ni(Ph) (PPh₃)}₂ [R = tert-Bu, Y = Me, 1b; R = Ph, Y = H, 2b] were prepared a

Full text of DOI:10.1016/j.inoche.2006.08.017

Inorganic Chemistry Communications 9 (2006) 1322–1325
www.elsevier.com/locate/inoche
Bimetallic nickel complexes of trimethyl phenyl linked
salicylaldimine ligands: Synthesis, structure and
their ethylene polymerization behaviors
*
Dao Zhang, Guo-Xin Jin
Shanghai Key Laboratory of Molecular Catalysis and Innovative Material, Department of Chemistry, Fudan University, Shanghai 200433, China
Received 31 July 2006; accepted 25 August 2006
Available online 3 September 2006
Abstract
Bimetallic salicylaldimine-nickel complexes, 2,4,6-Me3-1,3-{[N@CH–(30-R-50-Y-20-O–C6H3)-j2-N,O]Ni(Ph) (PPh3)}2 [R = tert-Bu,
Y = Me, 1b; R = Ph, Y = H, 2b] were prepared and their catalytic behaviors of ethylene polymerization were investigated. The bimetallic
complex 2b shows higher activities (2.9 · 105 g PE molꢀ1 Ni hꢀ1) for ethylene polymerization and affords polymer with high molecular
weight (Mw = 1.41 · 105) and broad molecular weight distribution (Mw/Mn = 6.1) than its mononuclear matrix, {[(2,6-Me2C6H3)–
N@CH–(30-Ph-20-O–C6H3)-j2-N,O]Ni(Ph)(PPh3)} (3) (Activity = 5.5 · 104 g PE molꢀ1 Ni hꢀ1; Mw = 1.86 · 104; Mw/Mn = 2.8).
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Nickel; Dinuclear; Catalyst; Ethylene polymerization; Molecular structure
During the past decades, the homogenous single-site ole-
fin polymerization catalysis including metallocene and non-
metallocene catalysts has been intensively investigated
[1,2]. Since Grubbs et al. [3] pioneered that the neutral sal-
icylaldiminato nickel complexes could be used as catalysts
for ethylene/(functionalized norbornene) co-polymeriza-
tions and ethylene homo-polymerizations even in the pres-
ence of polar compounds without any cocatalysts, various
neutral nickel catalysts have been prepared [3–8]. And eth-
ylene polymerizations even in water phase have been suc-
cessfully achieved with the neutral nickel catalysts to
produce polyethylene latex [9].
1b and 2b (Scheme 1) and their ethylene polymerization
behaviors.
The free salicyldimine ligands 1a–2a were conveniently
prepared from a 2, 4, 6-trimethyl-1, 3-phenylenediamine
and 2.0 equiv. of substituted salicylaldehyde derivatives
by Schiff base condensation in methanol with formic acid
as a catalyst in good yields. The corresponding bimetallic
nickel complexes 1b–2b were obtained by the reaction of
trans- [Ni(Ph)Cl(PPh3)2] with 0.5 equiv. of the sodium salts
of ligands 1a–2a using a similar procedure we previously
reported (Scheme 1). All complexes were characterized by
1
EA, IR, and H NMR; 13C NMR [14].
We and other groups have designed and synthesized
several different binuclear nickel catalysts for olefin poly-
merization [10–12]. On the basis of our previous research
work on nickel catalysts [13], herein we wish to report the
synthesis of bimetallic salicylaldiminato nickel complexes
The characteristic feature of this ligand system is that the
two coordination sites lie in the meta-positions and are
linked by a trimethylphenyl unit. In solution such confor-
mational variations can be modulated by rotational move-
ment around C–N or C–C bonds, which makes it possible
for the two metal centers become more close to show good
cooperative effects during the polymerization process. And
the two nickel atoms were separated and almost fixed on a
certain distance, which made us believe that they have some
*
Corresponding author. Tel.: +86 21 65643776; fax: +86 21 65641740.
E-mail address: gxjin@fudan.edu.cn (G.-X. Jin).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.08.017

D. Zhang, G.-X. Jin / Inorganic Chemistry Communications 9 (2006) 1322–1325
1323
Y
Y
Y
2
R
R
PPh3
Ph
N
OH
R
O
OH
i) 7 equiv. of NaH
THF, RT, 2h
R
O
Ni
CH3OH/HCO2H
+
O
N
N
ii) 2trans-[Ni(PPh
3)2PhCl]
N
Ni
Y
toluene, RT, 12h
NH2
PPh3
Ph
HO
R
1a: R = tert-Bu, Y = Me
2a: R = Ph, Y = H
1b: R = tert-Bu, Y = Me
2b: R = Ph, Y = H
Y
NH2
2
Scheme 1. Synthesis of bimetallic complex 1b–2b.
unique catalytic behaviors compared with their mononu-
clear analogous [(2,6-Me2C6H3)–N@CH–(30-Ph-20-O–
C6H3)-j2-N,O]Ni(Ph) (PPh3) (3) that was synthesized
according to the reported method [15].
Orange-red single crystals of 2b were grown in THF/
hexane (1:1) at room temperature and the corresponding
X-ray crystallographic structure analysis was carried out
[16]. As depicted in Fig. 1, complex 2b contains two nickel
centers which bind to a chelating salicylaldiminato ligand,
a triphenyl phosphine group and a phenyl group. The Ni
atom with four atoms of ligands (P(1), O(1), N(1), C(20))
are arranged almost exactly planar and the nickel atom is
˚
Fig. 1. Crystal structure of 2b. Selected bond lengths (A) and angles (deg): Ni(1)–O(1), 1.903(3); Ni(1)–C(20), 1.905(3); Ni(1)–N(1), 1.911(4); Ni(1)–P(1),
2.1784(15); N(1)–C(14), 1.455(5); O(1)–C(7), 1.307(5); O(1)–Ni(1)–C(20), 165.3(2); O(1)–Ni(1)–N(1), 93.12(15); C(20)–Ni(1)–N(1), 93.16(16); O(1)–Ni(1)–
P(1), 89.98(10); C(20)–Ni(1)–P(1), 85.79(11); N(1)–Ni(1)–P(1), 171.14(14). (a) Top view (b) Side view.

1324
D. Zhang, G.-X. Jin / Inorganic Chemistry Communications 9 (2006) 1322–1325
˚
0.049 A out of the plane [least-squares plane equation:
ꢀ1.183x + 13.019y ꢀ 10.993z = 2.0963]. The most nota-
ble feature of the structure lies in that the dihedral angle
defined by coordination plane Ni(1) and Ni(1A) is 37.3ꢁ
and the distance between the two nickel centres is
at higher temperature. And we ever isolated binuclear
nickel bearing two bridged salicylaldiminato ligand 1a at
high temperature (100 ꢁC). This different catalytic behavior
clearly suggested that high temperature have a negative
influence on polymerization activity.
˚
7.654 A (Fig. 1, top view). The plane of the C(20) and
GPC analysis of polyethylene obtained employing binu-
clear 2b and mononuclear 3 revealed molecular weights of
typically Mw = 1.41 · 105 and Mw = 1.86 · 104 respec-
tively. The relatively wide molecular weight distribution
(Mw/Mn) of 6.1 for binuclear 2b was quite different from
mononuclear 3 (Mw/Mn = 2.8) and other well-behaved sin-
gle-site catalysts that afforded polyethylene with narrower
molecular weight distribution of 1.68–2.81 [3,17,18]. The
observed effect on very wide molecule weight distribution
can be explained on the basis of electronic effects and coop-
erative interactions of the two adjacent nickel centers in
binuclear complexes. These two metal centers possibly
are electronically coupled through the ligand bridge. When
one of the centers was active by removing of phosphine at a
given time it has an electronic withdrawing effect on
another center. The interaction between two metals made
it possible to create more than one kind of active species
during the polymerization.
For binuclear catalyst 2b, polymer crystallinity amounts
to ca. 38% and the melt peaks occur at ca 128 ꢁC. From the
DSC curves of polymer produced by mononuclear catalyst
3 at same temperature lower crystallinity amounts (ca.
23%) and melt point (ca. 115 ꢁC) were found. High-temper-
ature 13C NMR showed that the polymers produced by 2b
are moderately branched. Methyl branching predominate
with ca. 20 methyl branched per 1000 carbon atoms. No
other additional signals suggested that higher branches,
such as butyl, are present. The polymer microstructure is
similar to that obtained with mononuclear nickel complex
3 that afforded polyethylene with ca. 6 methyl branch per
1000 carbon atoms.
C(14) phenyl rings are oriented almost orthogonally
(81.7ꢁ and 85.8ꢁ, respectively) to this plane, which is a little
different from analogous mononuclear nickel complex we
previously reported (82.6ꢁ and 86.1ꢁ, respectively) [14].
There is no interaction between C(14) phenyl ring and
C(20) phenyl ring because their dihedral angle is 34.2ꢁ
and the distance between the two ring centers is ca.
˚
4.0 A. Moreover, the cis angles at nickel are in the range
of 85.79ꢁ–93.16ꢁ. The Ni–O, Ni–C, and Ni–P bond dis-
tances are similar to those in known nickel complexes
[3,10–13,17,18].
The tests of ethylene polymerization with complexes 1b–
2b and 3 were carried out in toluene solution at 10 atm of
ethylene pressure. The results of polymerizations are listed
in Table 1. Complexes 1b was catalytically less active
toward ethylene polymerization with ca. 2–3 equiv. of
Ni(COD)2 as phosphine scavenging agent, while complex
2b comprising a phenyl group was demonstrated to have
high potential for ethylene polymerization without any
cocatalyst. Although tert-butyl groups are generally con-
sidered to be bulkier than unsubstituted phenyl group, phe-
nyl is more electron-withdrawing than tert-butyl. Complex
2b (R = Ph), therefore, revealed a marked increase from
3.7 · 104 g PE molꢀ1 Ni hꢀ1 for 1b (R = tert-butyl) to
1.1 · 105 g PE molꢀ1 Ni hꢀ1. This electron-deficient effect
is consistent with the electronic effect of mononuclear
Grubbs catalysts [3,17,18].
It is notable that the polymerization temperature greatly
influences the activity of the binuclear nickel catalyst. For
2b, lower temperature (30 ꢁC) represents the optimum
and at an increased temperature of 50 ꢁC or 70 ꢁC, catalytic
performance quickly decreased to be 6.4 and 2.1 · 104
g PE molꢀ1 Ni hꢀ1respectively. It has been reported that
mononuclear Grubbs catalysts usually work more active
at ca. 45 ꢁC and the deactivation of this kind of catalysts
was due to the formation of bisligand nickel compound
In conclusion, binuclear salicylaldimine nickel catalyst
2b represent a new type of single-component catalysts con-
taining two catalytically active or dormant sites in a nickel
catalyst. Catalytic activities, molecular weights and molec-
ular weight distribution of polyethylene have been investi-
gated under the various reaction conditions.
Acknowledgements
Table 1
Results of Ethylene Polymerizationa
Financial support by the National Science Foundation
of China for Distinguished Young Scholars (20421303,
20531020), by the National Basic Research Program of
China (2005CB623800) and by Shanghai Science and Tech-
nology Committee (05JC14003, 05DZ22313) is gratefully
acknowledged.
Entry
Catalyst (lmol Ni)
T (ꢁC)
PE (g)
Activityb
1
2
3
4
5
6
a
1b (22)c
2b (22)
2b (41)
2b (15)
2b (31)d
3 (22)
30
30
45
70
30
30
0.81
2.66
1.41
0.46
4.45
1.21
3.7
12.1
6.4
2.1
28.7
5.5
Appendix A. Supplementary data
Conditions: ethylene pressure: 10 atm; polymerization time: 1 h; total
volume of toluene: 50 mL; 600 rpm; PE = polyethylene.
Details on experimental section are deposited. Supple-
mentary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2006.08.017.
b
104 g PE molꢀ1 Ni hꢀ1
.
c
with ca. 2–3 equiv. of Ni(COD)2 as phosphine scavenging agent.
d
polymerization time is 30 min.

D. Zhang, G.-X. Jin / Inorganic Chemistry Communications 9 (2006) 1322–1325
1325
75.17; H, 6.31; N, 2.34%. IR (KBr): 1592 cmꢀ1 (vs, C@N). H NMR
(CDCl3): d = 7.82 ꢀ 5.77(m, 47H, H–Ar + CH@N), 2.52 (s, 6H,
CH3), 2.20 (s, 6H, CH3), 1.59 (s, 3H, CH3), 0.59 ppm (s, 18H,
C(CH3)3). 2a: Yield 88%. Anal. Calcd for C35H30N2O2: C, 82.33; H,
5.92; N, 5.49. Found: C, 82.02; H, 5.81; N, 5.11. IR (KBr): 1618 cmꢀ1
(vs, C@N). 1H NMR (CDCl3): d 13.59 (s, 2H, OH), 8.39 (s, 2H,
N@CH), 7.67 (d, J = 7.4 Hz, 4H, phenyl-oH), 7.44–7.51 (m, 6H,
phenyl-mH + phenyl-pH), 7.35 (m, 4H, phenol-mH), 6.99–7.25 (m,
3H, phenol-pH + mestyl-H), 2.19 (s, 6H, CH3-mestyl), 2.05 ppm (s,
3H, CH3-mestyl). 2b: Yield 91%. Anal. Calcd for C83H68N2Ni2O2P2:
C, 76.40; H, 5.25; N, 2.15. Found: C, 76.51; H, 5.31; N, 2.14. IR
(KBr): 1593 cmꢀ1 (vs, C@N). 1H NMR (CDCl3): d = 7.67 ꢀ 5.85 (m,
59H, H–Ar + CH@N), 2.49 (s, 6H, CH3–Ar), 1.59 ppm (s, 3H, CH3–
Ar).
1
References
[1] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 83.
[2] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169.
[3] (a) T.R. Younkin, E.F. Connor, J.I. Henderson, S.K. Friedrich, R.H.
Grubbs, D.A. Banselben, Science 287 (2000) 460;
(b) C. Wang, S. Friedrich, T.R. Younkin, R.T. Li, R.H. Grubbs,
D.A. Bansleben, M.W. Day, Organometallics 17 (1998) 3149.
[4] J.C. Jenkins, M. Brookhart, Organometallics 22 (2003) 250.
[5] F.A. Hicks, J.C. Jenkins, M. Brookhart, Organometallics 22 (2003)
3533.
[6] L.-C. Liang, W.-Y. Lee, C.-C. Yin, Organometallics 23 (2004) 3538.
[7] J.C. Jenkins, M. Brookhart, J. Am. Chem. Soc. 126 (2004) 5827.
[8] C. Mueller, L.J. Ackerman, J.N.H. Reek, P.C.J. Kamer, P.W.N.M.
van Leeuwen, J. Am. Chem. Soc. 126 (2004) 14960.
[9] (a) M.A. Zuideveld, P. Wehrmann, C. Roehr, S. Mecking, Angew.
Chem. Int. Edit. 43 (2004) 869;
[15] X.F. Li, Y.-S. Li, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 2680.
[16] Crystal data for 2b: C83H68N2Ni2O2P2, Mr = 1304.75, Monoclinic,
˚
˚
Space group, C2/c, a = 13.491(5) A
,
b = 13.742(5) A
,
c =
3
˚
˚
36.379(13) A , b = 93.307(7)ꢁ, V = 3728(3) (A ), Z = 4, Dc = 1.287
(mg/m3), F(000) = 2728, reflections measured (1.12–25.01), R(wR) =
0.0437(0.0452) for 13,987 reflections with I > 2r(I). The diffraction
data were collected on a Siemens SMART CCD diffractometer. The
structures are solved using direct methods and refined on F2 by full-
matrix least-squares methods using the SHELX 97 program package.
Crystallographic data for the structure of 2b reported in this paper
has been deposited in the Cambridge Crystallographic Data Centre
No. CCDC-612132. Copies of the data can be obtained free of charge
on application to CCDC, 12, Union Road, Cambridge CB2 1EZ,
UK, fax: (internat.) +44 1233 336 033; e-mail: deposit@ccdc.
cam.ac.uk.
(b) F.M. Bauers, R. Thomann, S. Mecking, J. Am. Chem. Soc. 125
(2003) 8838;
(c) F.M. Bauers, M.M. Chowdhry, S. Mecking, Macromolecules 36
(2003) 6711.
[10] D. Zhang, G.-X. Jin, Organometallics 22 (2003) 2851.
[11] S. Sujith, Dae J. Joe, S.J. Na, Y.-W. Park, C.H. Choi, B.Y. Lee,
Macromolecules 38 (2005) 10027.
[12] T. Hu, L.-M. Tang, X.-F. Li, Y.-S. Li, N.-H. Hu, Organometallics 24
(2005) 2628.
[13] J. Zhang, X. Wang, G.X. Jin, Coordin. Chem. Rev. 250 (2006) 95.
[14] 1a: Yield 77%. Anal. Calcd for C33H42N2O2: C, 79.48; H, 8.49; N,
5.62. Found: C, 79.45; H, 8.52; N, 5.84. IR (KBr): 1619 cmꢀ1 (vs,
1
[17] J. Feldman, S.J. McLain, A. Parthasarathy, W.J. Marshall, J.C.
Calabrese, S.D. Arthur, Organometallics 16 (1997) 1514.
[18] S.Y. Desjardins, K.J. Cavell, J.L. Hoare, B.W. Skelton, A.N.
Sobolev, W.A. White, W. Keim, J. Organomet. Chem. 554 (1997)
163.
C@N). H NMR (CDCl3): d13.37 (s, 2H, OH), 8.28 (s, 2H, N@CH),
7.22 (s, 2H, phenol-mH), 7.00 (s, 1H, H-mestyl), 6.98 (s, 2H, phenol-
mH), 2.32 (s, 6H, pCH3-phenol), 2.18 (s, 6H, CH3-mestyl), 2.05 (s,
3H, CH3-mestyl), 1.47 ppm (s, 18H, tert-Bu). 1b: Yield 84%. Anal.
Calcd for C81H80N2Ni2O2P2: C, 75.25; H, 6.24; N, 2.17. Found: C,