Nickel(II) Complexes Bearing N,O-Chelate Ligands: Synthesis, Solid-Structure Characterization, and Reactivity toward the Polymerization of Polar Monomer

Article abstract of DOI:10.1021/om030292n

Two new moisture- and air-stable bis(β-ketoamino)nickel(II) complexes Ni[R1C(O)CHC-(NAr)R2]₂ (Ar ≡ 2,6-ⁱPr ₂C₆H₃; R1 = R2 = CH₃, 1; R1 = C ₆H₅, R2 = CH₃, 2), together with the moderately stable complex Ni₂[CH₃C(O)CHC(O)CH ₃]₄[H₂N^tBu]₂ (3), which bears a monoanionic O,O-chelate bidentate β-diketone and an sp ³-N atom of ^tBuNH₂ mixed ligands, were synthesized and characterized. The solid-state structures of the complexes have been determined by single-crystal X-ray diffractions. Additionally, these new complexes act as catalyst precursors for methyl methacrylate polymerization after activation with methyla-luminoxane (MAO). The polymers obtained by 1 and 2 show broader polydispersity than that obtained by 3. ¹³C NMR analyses indicate that these catalytic systems initiate MMA polymerization to yield PMMA with rich syndiotacticity microstructure.

Full text of DOI:10.1021/om030292n

4952
Organometallics 2003, 22, 4952-4957
Nick el(II) Com p lexes Bea r in g N,O-Ch ela te Liga n d s:
Syn th esis, Solid -Str u ctu r e Ch a r a cter iza tion , a n d
Rea ctivity tow a r d th e P olym er iza tion of P ola r Mon om er
Xiaohui He,†,‡ Yingzheng Yao,† Xiang Luo,† J unkai Zhang,† Yunhai Liu,†
Ling Zhang,† and Qing Wu*,†
Institute of Polymer Science, Key Laboratory for Polymeric Composite and Functional
Materials of the Ministry of Education, Zhongshan University, Guangzhou 510275, China,
and The School of Environment and Chemical Engineering, Nanchang University,
Nanchang 330029, China
Received April 22, 2003
Two new moisture- and air-stable bis(â-ketoamino)nickel(II) complexes Ni[R1C(O)CHC-
(NAr)R2]2 (Ar ≡ 2,6-iPr2C6H3; R1 ) R2 ) CH3, 1; R1 ) C6H5, R2 ) CH3, 2), together with
the moderately stable complex Ni2[CH3C(O)CHC(O)CH3]4[H2NtBu]2 (3), which bears a
monoanionic O,O-chelate bidentate â-diketone and an sp3-N atom of tBuNH2 mixed ligands,
were synthesized and characterized. The solid-state structures of the complexes have been
determined by single-crystal X-ray diffractions. Additionally, these new complexes act as
catalyst precursors for methyl methacrylate polymerization after activation with methyla-
luminoxane (MAO). The polymers obtained by 1 and 2 show broader polydispersity than
that obtained by 3. 13C NMR analyses indicate that these catalytic systems initiate MMA
polymerization to yield PMMA with rich syndiotacticity microstructure.
In tr od u ction
subsequently interesting to mixed-ligand-complex cata-
lytic systems, which are shown to be very effective
catalysts in R-olefin and polar olefin polymerization, for
example, nickel-based systems.15,16 The late transition
metals can be stabilized by various heterodonor ligands
and give mono- or dinuclear complexes with several
coordination modes. In particular, complexes with two
metal centers can catalyze the polar olefins more
efficiently than analogous monometallic species. There-
fore, bimetallic systems are of considerable interest.
Although the late transition metals bearing â-ketoam-
ines N,O mixed ligands and members of the general
family have been extensively studied,17-19 only a few
Ni(II) complexes containing analogous tetradentate
â-ketoamines have been reported.20-24 The development
The early transition metal complexes are difficult to
handle and incompatible with polar monomers due to
the high oxophilicity and the tendency for functionalities
to coordinate to active species. Examples of vinyl po-
lymerization of polar vinyl monomer are few.1,2 Some
early transition metals have been shown to polymerize
olefins with distant polar groups, but possibilities are
limited.3-6 Late transition metal catalysts are less
oxophilic than their early transition metals and poten-
tially not poisoned by O-containing polar functional-
ities.7,8 In recent years there has been increasing
interest in the development of late transition metal
based complexes as catalysts for the polymerization of
R-olefins and polar olefins.9-14 Ligands of the type O-Y
(where Y is N or S) are particularly interesting and
(11) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267.
* Corresponding author. Fax: (086)-(20)-84112245. E-mail:
ceswuq@zsu.edu.cn.
(12) Brookhart, M.; Wagner, M. I. J . Am. Chem. Soc. 1996, 118,
7219.
† Zhongshan University.
(13) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R.
H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
(14) Elia, C. N.; Sen, A.; Albeniz, A. C.; Espinet, P. Proceedings of
the ACS National Meeting; Washington, August 20-24, 2000.
(15) Peukert, M.; Keim, W. Organometallics 1983, 2, 594.
(16) Reuben, B.; Wittcoff, H. J . Chem. Educ. 1988, 65, 605.
(17) Robards, K.; Patsalides, E.; Dilli, S. J . Chromatogr. 1987, 411,
1.
(18) (a) Everett, G. W., J r.; Holm, R. H. J . Am. Chem. Soc. 1965,
87, 2117. (b) Everett, G. W., J r.; Holm, R. H. J . Am. Chem. Soc. 1966,
88, 2442. (c) Everett, G. W., J r.; Holm, R. H. Inorg. Chem. 1968, 7,
776. (d) Ernst, G. R. E.; O’Connor, M. J .; Holm, R. H. J . Am. Chem.
Soc. 1967, 89, 6104.
(19) Veya, R.; Floriani, C.; Chiest-Villa, A.; Rizzoh, C. Organome-
tallics 1993, 12, 4892.
(20) Corazza, F.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Guastini,
C. J . Chem. Soc., Dalton Trans. 1990, 1335.
(21) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F.; Petersen, J . L.
Organometallics 1995, 14, 371.
(22) Floriani, C. Polyhedron 1989, 8, 1717.
‡ Nanchang University.
(1) Stehling, U. M.; Stein, K. M.; Kesti, M. R., Waymouth, R. M.
Macromolecules 1998, 31, 9679.
(2) Hennis, A. D.; Sen, A. Polym. Prepr. 2000, 41 (2), 1383.
(3) Deng, H.; Soga, K. Macromolecules 1996, 29, 1847.
(4) Chung, T. C.; Rhubright, D. Macromolecules 1993, 26, 3019.
(5) Aaltonen, P.; Lofgren, B. Macromolecules 1995, 28, 5353.
(6) Yasuda, H.; Ihara, E. Macromol. Chem. Phys. 1995, 196, 2417.
(7) Recent reviews: (a) Brltovsek, G. J . P.; Gibson, V. C.; Wass, D.
M. Angew. Chem., Int. Ed. 1999, 38, 428. (b) Itself, S. D.; J hnson, L.
K.; Brookhart, M. Chem. Rev. 2000, 100, 1169. (c) Meking, S. Coord.
Chem. Rev. 2000, 203, 325. (d) Meking, S. Angew. Chem., Int. Ed. 2001,
40, 534.
(8) New nickel(II) catalysts were recently developed by Bazan and
co-workers and Brookhart, and co-workers: (a) Lee, B. Y.; Bazan, G.
C.; Vela, J .; Komon, Z. J . A.; Bu, X. J . Am. Chem. Soc. 2001, 123, 5352.
(b) Hicks, F. A.; Brookhart, M. Organometallics 2001, 201, 3217.
(9) Rix, F. C.; Brookhart, M. B.; White, P. S. J . Am. Chem. Soc. 1996,
118, 4746.
(10) Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 888.
(23) Mazzanti, M.; Rosset, J . M.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. J . Chem. Soc., Dalton Trans. 1989, 953.
10.1021/om030292n CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/23/2003

Ni(II) Complexes Bearing N,O-Chelate Ligands
Organometallics, Vol. 22, No. 24, 2003 4953
Sch em e 1
of new mixed-ligand Ni(II) complexes is important for
the discovery of new late transition metal catalysts for
R-olefin and polar olefin polymerization.
F igu r e 1. ORTEP plots of complex 1 showing the atom-
labeling scheme. Hydrogen atoms are omitted for clarity.
The fact that a little variation of the ligand structure
may lead to profound changes in the catalytic reactivity
prompted us to synthesize nickel catalysts chelated by
various ligand frameworks containing N,O-chelate at-
oms. In this contribution, we report the syntheses and
solid-structure characterizations of three new Ni(II)
complexes with N,O-chelate mixed ligands. This is the
first report on their syntheses and solid-structure
characterizations and their application as catalyst
precursors for methyl methacrylate polymerization after
activation with methylaluminoxane (MAO).
Resu lts a n d Discu ssion
â-Ketoa m in e Liga n d s a n d Bis(â-k etoa m in o)n -
ick el(II) Com p lex Syn th eses. Two N-aryl-substituted
â-ketoamine ligands, 2-(2,6-diisopropylphenyl)amino-
pent-2-en-4-one (L1) and 3-(2,6-diisopropylphenyl)amino-
1-phenyl-but-2-en-4-one (L2), were synthesized by con-
densationofthecorrespondingacetylacetone(orbenzoylacetone)
and 2,6-diisopropylaniline by refluxing in toluene while
removing water by a water separator. The further
reaction of L1 and L2 with [Et4N]2[NiBr4] in the
presence of a strong base, BuOK and BuOH, afforded
the corresponding bis(â-ketoamino)nickel(II) complexes
1 and 2 in moderate yields (as shown in Scheme 1).
The molecular structures were determined by single-
crystal X-ray diffraction. The ORTEP plots are shown
in Figures 1 and 2, respectively. Table 1 lists the
selected bond lengths and angles. Crystallographic data
are summarized in Table 2. The coordination geometries
of both 1 and 2 were demonstrated to be very similar
in the solid state and are mononuclear and nearly
ideally four-coordinate, square-planar configurations.
Interestingly, the anticipated formation of tetrahedral
complexes, although sterically possible, was not ob-
served either. The nickel atoms in both 1 and 2 are
arranged in a nearly perfect square-planar coordination
environment where the metal ion via â-ketoamine acts
as a monoanionic bidentate N,O-chelator with N,O-
donor atom sets and lies in the trans-configuration to
create two stable six-membered metallacyclic chelate
rings (NiOCCCN). The mean deviation of the metal
center from the least-squares plane (CCCNONiONCCC)
F igu r e 2. ORTEP plots of complex 2 showing the atom-
labeling scheme. Hydrogen atoms are omitted for clarity.
is 0.0103 Å for 1 and 0.0567 Å for 2. The bulky 2,6-
diisopropylbenzene rings substituted on the imine moi-
eties are satisfactorily planar with the mean deviation
of 0.0048 Å for 1 and 0.0072 Å for 2, respectively. They
occupy the position trans and essentially perpendicular
to the metallacycle plane. The phenyl ring unit attached
to C instead of methyl in 2 is also quite planar (the mean
deviation is 0.0025 Å); however, it swings slightly out
of the previous metallacycle plane, forming an ap-
proximately 23.9° dihedral angle. The angles of O-Ni-O
and N-Ni-N are all equal at 180.0° for both 1 and 2.
The N-Ni-O angles are slightly more than 90° (92.74-
(6)° in 1, whereas 93.23(5)° in 2). The O#1-Ni-N is
slightly less than 90° (87.26(6)° for 1 and 86.77(5)° for
2). An average metal-ligand bond length of Ni-O is
1.8177(13) Å for 1 and 1.8384(11) Å for 2, and Ni-N is
1.9188(14) Å for 1 and 1.9300(13) Å for 2, respectively.
Ni2[CH3C(O)CHC(O)CH3]4[H2NtBu ]2 (3) Syn th e-
sis. The attempt to prepare the â-ketoamine MeC(O)-
CHC(NtBu)Me ligand like L1 and L2 was unsuccessful
t
t
t
using BuNH2 instead of 2,6-diisopropylaniline. This is
t
because the boiling point of BuNH2 is very low, and
the amine only reacts with acetylacetone directly rather
than reacting by refluxing in toluene while removing
water by a water separator, as in the preparation of L1
and L2. Interestingly, a white solid product was ob-
tained. Unfortunately, satisfactory elemental analysis,
FAB-MS, and melting point cannot be obtained since
(24) Rosset, J . M.; Floriani, C.; Mazzanti, M. Chiesi-Villa, A.;
Guastini, C. Inorg. Chem. 1990, 29, 3991.

4954 Organometallics, Vol. 22, No. 24, 2003
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles (d eg) for Com p lexes 1, 2, a n d 3
He et al.
1
2
3
bond
length
bond
length
bond
length
Ni(1)-O(1)1
Ni(1)-O(1)#1
Ni(1)-N(1)
Ni(1)-N(1)#1
C(2)-O(1)
1.8177(13)
1.8177(13)
1.9188(14)
1.9188(14)
1.285(2)
1.320(2)
1.444(2)
1.506(2)
1.362(3)
1.411(2)
1.513(2)
1.398(3)
1.516(3)
1.530(4)
1.504(5)
Ni(1)-O(1)
Ni(1)-N(1)
N(1)-O(1)#1
Ni(1)-N(1)#1
O(1)-C(7)
1.8384(11)
1.9300(13)
1.8384(11)
1.9300(13)
1.2893(19)
1.323(2)
1.446(2)
1.511(2)
1.489(2)
1.368(2)
1.401(2)
1.515(3)
1.505(4)
1.523(4)
1.531(4)
Ni(1)-O(1)
Ni(1)-N(1)
Ni(1)-O(2)
Ni(1)-O(4)
Ni(1)-O(3)
O(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-O(2)
N(1)-C(11)
O(4)-C(9)
C(9)-C(8)
C(8)-C(7)
C(7)-O(3)
Ni(1)-O(1)#1
2.075(2)
2.116(5)
2.011(3)
1.999(2)
2.027(2)
1.280(4)
1.380(5)
1.397(5)
1.250(4)
1.423(11)
1.269(4)
1.384(5)
1.390(5)
1.262(4)
2.156(2
C(4)-N(1)
C(9)-N(1)
C(6)-N(1)
C(11)-N(1)
C(9)-C(23)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(16)-C(17)
C(12)-C(21)
C(17)-C(18)
C(21)-C(22)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(11)
C(11)-C(12)
C(12)-C(13)
C(12)-C(14)
bond
angle
bond
angle
bond
angle
O(1)1-Ni(1)-N(1)1
O(1)#1-Ni(1)-N(1)#1
O(1)-Ni(1)-O(1)#1
N(1)#1-Ni(1)-N(1)
O(1)-Ni(1)-N(1)#1
O(1)#1-Ni(1)-N(1)
C(2)-O(1)-Ni(1)
C(6)-N(1)-Ni(1)
C(4)-N(1)-Ni(1)
C(4)-N(1)-C(6)
92.74(6)
92.74(6)
180.0
180.0
87.26(6)
O(1)-Ni(1)-N(1)
93.23(5)
93.23(5)
180.00(8)
180.00(8)
86.77(5)
O(1)-Ni(1)-O(1)#1
O(1)-Ni(1)-O(2)
O(2)-Ni(1)-O(4)
O(4)-Ni(1)-O(3)
O(3)-Ni(1)-O(1)#1
O(1)-Ni(1)-O(4)
O(1)-Ni(1)-N(1)
N(1)-Ni(1)-O(4)
O(4)-Ni(1)-O(1)#1
O(1)-Ni(1)-O(3)
C(11)-N(1)-Ni(1)
Ni(1)-O(1)-Ni(1)#1
C(9)-O(4)-Ni(1)
C(7)-O(3)-Ni(1)
O(3)-Ni(1)-N(1)
Ni(1)-O(1)-C(2)
Ni(1)-O(2)-C(4)
O(2)-Ni(1)-O(3)
N(1)-Ni(1)-O(1)#
O(2)-Ni(1)-N(1)
79.65(9)
91.17(10)
87.97(10)
90.65(10)
88.88(10)
178.93(8)
81.07(17)
98.28(17)
101.22(10)
89.99(9)
134.2(7)
100.35(9)
124.5(2)
123.7(2)
164.6(3)
O(1)#1-Ni(1)-N(1)#1
O(1)#1-Ni(1)-O(1)
N(1)#1-Ni(1)-N(1)
O(1)#1-Ni(1)-N(1)
O(1)-Ni(1)-N(1)#1
C(7)-O(1)-Ni(1)
87.26(6)
86.77(5)
130.14(12)
117.25(11)
125.63(12)
117.12(14)
120.41(16)
123.40(16)
118.62(16)
118.96(16)
123.64(17)
121.90(17)
111.6(3)
128.63(11)
120.55(10)
124.41(11)
115.01(13)
119.43(17)
118.63(16)
123.74(15)
121.06(16)
121.90(17)
121.17(17)
116.9(2)
C(11)-N(1)-Ni(1)
C(9)-N(1)-Ni(1)
C(9)-N(1)-C(11)
C(12)-C(11)-N(1)
C(16)-C(11)-N(1)
N(1)-C(9)-C(8)
N(1)-C(9)-C(23)
C(12)-C(11)-C(16)
C(11)-C(16)-C(17)
C(11)-C(12)-C(13)
C(11)-C(12)-C(21)
N(1)-C(4)-C(5)
N(1)-C(4)-C(3)
C(11)-C(6)-N(1)
C(7)-C(6)-N(1)
C(2)-C(3)-C(4)
C(6)-C(11)-C(12)
C(14)-C(12)-C(11)
C(14)-C(12)-C(13)
123.0(2)
125.3(2)
90.12(11)
89.91(18)
89.66(19)
110.4(3)
122.21(18)
Ta ble 2. Cr ysta llogr a p h ic Da ta for Com p lexes 1, 2, a n d 3a
1
2
3
empirical formula
fw
C
34H48N2NiO2
C44H52N2NiO2
699.59
C28H50N2Ni2O8
660.12
575.45
cryst color and form
cryst syst
space group
a (Å)
b (Å)
c (Å)
dark brown
triclinic
P1h
8.5642(15)
9.5979(17)
11.260(2)
67.718(3)
83.281(3)
73.108(3)
819.5(3)
dark green
monoclinic
P2(1)/c
11.2309(19)
8.8805(15)
20.487(4)
90
107.707(3)
90
1946.5(6)
2
green
triclinic
P1h
9.073(5)
9.141(5)
11.513(6)
110.555(9)
99.252(9)
100.637(9)
851.9(8)
1
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
1
Dc (Mg/m3)
1.166
0.622
310
1.194
0.536
748
1.287
1.149
352
abs coeff µ (mm-1
F(000)
)
cryst size (mm)
θmax (deg)
0.49 × 0.42 × 0.26
0.50 × 0.21 × 0.18
0.41 × 0.31 × 0.15
27.02
27.04
27.22
index ranges
-10 e h e 9
-12 e k e 12
-13 e I e 14
178
-14 e h e 13
-11 e k e 11
-15 e I e 26
223
-11 e h e 11
-11 e k e 10
-14 e I e 14
191
no. of params
goodness-of-fit on S (F2)a
final R indices [I > 2σ(I)]
R indices (all data)
1.112
1.108
1.091
0.0358; 0.1065
0.0375; 0.1082
0.381, -0.311
0.0359; 0.0987
0.0466; 0.1070
0.373, -0.309
0.0439; 0.1165
0.0597; 0.1288
0.340, -0.488
largest diff peak and hole (e/Å-3
)
R ) ∑||Fo| - |Fc||∑|Fo|; Rw ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2
.
a
2
the solid is less stable at higher temperature and readily
evaporates or decomposes by the external analytical
conditions. However, the solid-state 13C NMR spectrum
of the product in CDCl3 solvent (see Figure 4 and Figure
5, respectively) could be obtained. The solid-state 13C
NMR spectrum is excellent, consistent with a simple
acetylacetone ammonium salt, [tBuNH3][acac] (A). The
1
(see Figure 3) and the solution 13C and H NMR spectra

Ni(II) Complexes Bearing N,O-Chelate Ligands
Organometallics, Vol. 22, No. 24, 2003 4955
F igu r e 3. Spectrum of 13C NMR of [tBuNH3][acac] (A)
carried out on a Bruker AVANCE 400 Hz at room temper-
ature in the solid state.
1
F igu r e 5. Spectrum of H NMR of [tBuNH3][acac] (A +
B) carried out on an INOVA 500 Hz at room temperature
in CDCl3 solution and using TMS as internal standard.
Sch em e 2
BuNH3][acac] can stably exist in the presence of tBuOH
solvent and can coordinate directly to the Ni ion, and
the remaining acac and [tBuNH3]+ were further depro-
F igu r e 4. Spectrum of 13C NMR of [tBuNH3][acac] (A +
B) carried out on an INOVA 500 Hz at room temperature
in CDCl3 solution.
t
toned by the strong base BuOK to form the correspond-
t
ing [acac]- and BuNH2 and then further coordinated
to the Ni ion to give the resulting nickel(II) complex with
t
â-diketone monoanions and the sp3-N atom of BuNH2
mixed ligands.
splitting carbonyl carbon resonance peaks (labeled e)
apparently reflect that A has the cation H bonded to
one oxygen of the acac anion and the charge of the acac
anion is mainly concentrated on the oxygen within the
solid lattice. Unlike the solid-state 13C NMR spectrum,
both solution 13C and 1H NMR spectra exhibit extra
resonance peaks for another structure, B, besides the
peaks for A,implying that [tBuNH3][acac] exists in
equilibrium between the ionic form A and the H-bonded
form B in polar solvent (as shown in Scheme 2, the ratio
of A:B is about 6:1 calculated from both 13C and 1H
NMR spectra). The unsplitting carbonyl carbon (labeled
e) resonance peak of A in the solution 13C spectrum
reflects that the charge of the acac anion is more
dispersed among the OCCCO field in solution. There-
fore, [tBuNH3][acac] reacts with [Et4N]2[NiBr4] in the
Crystallographic analysis of 3 (as shown in Figure 6)
reveals the molecular structure is a binuclear and six-
coordinate, pseudo-octahedral geometric coordination
sphere around the nickel center, in which one â-dike-
tonato is a monoanionic bidentate O,O-chelator with
O,O-donor atoms sets, while another O,O-ligand, besides
acting as a terminal oxygen coordination, also acts as a
bridging oxygen coordinator between two metal centers,
forming a binuclear structure. In each nickel(II) center,
five positions were occupied by one â-diketonato anion
bidentate ligand, a bridging oxygen, and the terminal
oxygen atoms of another â-diketonato anion, respec-
tively. The sixth coordination position is occupied by a
sp3-N atom of tBuNH2, which is located at the position
trans to the terminal oxygen atom of the O,O-donor
t
presence of BuOK and tBuOH solvent to form the
complex Ni2[CH3C(O)CHC(O)CH3]4[H2NtBu]2 (3), al-
though following procedures similar to the preparation
of complexes 1 and 2. This is because the [acac]- of [t-
atom sets with a nearly linear N-Ni-O angle
(164.6(3)°), to complete a slight distorted octahedral
geometry around the metal center. The entire Ni2O6

4956 Organometallics, Vol. 22, No. 24, 2003
Ta ble 3. Meth yl Meth a cr yla te P olym er iza tion w ith Ca ta lysts 1-3/MAOa
He et al.
d
entry
catalyst
Tp (°C)b
act.c
1.20
3.59
18.6
9.54
0.75
1.33
7.65
4.89
Mw (×10-5
)
Mw/Mn
mm (%)e
mr (%)e
rr (%)e
1
2
3
4
5
6
7
8
1
1
1
1
2
2
2
2
3
3
3
3
0
25
50
70
0
25
50
70
0
0.38
0.65
0.83
1.45
0.42
0.60
0.74
1.54
0.94
1.07
1.16
1.09
2.33
2.64
4.34
6.01
2.46
2.93
5.64
6.07
1.56
1.44
1.41
1.47
n.d.
n.d.
7.6
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.5
n.d.
n.d.
33.4
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
17.2
n.d.
n.d.
n.d.
n.d.
59.0
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
82.3
n.d.
n.d.
9
12.0
10
11
12
25
50
70
279.4
327.4
125.1
n.d.
n.d.
a
b
Ni ) 5 × 10-3 mmol; MMA ) 0.05 mol; tp ) 7 h (for 1 and 2); Ni ) 5.56 × 10-3 mmol; MMA ) 0.05mol; tp ) 1 h (for 3). Polymerization
temperature. c Activity in kg polymer (mol catalyst h)-1
.
Solvent: chloroform; temperature: 40 °C; Mw are the relative weight-average
d
molecular weights; calibration with polystyrene standards. e Tacticity determined by 13C NMR. n.d. ) not determined.
cantly as the temperature is increased to 70 °C. The
polymers obtained by 1 and 2 show broader polydisper-
sity than that obtained by 3. The results of PMMA
stereotriad distributions with [rr] ) 59.0%, [mr] )
33.4%, [mm] ) 7.6% (entry 3), and [rr] ) 82.3%, [mr] )
17.20%, [mm] ) 0.5% (entry 10) indicated that these
catalytic systems initiate MMA polymerization to yield
PMMA with rich syndiotacticity microstructure.
Exp er im en ta l Section
Gen er a l P r oced u r es a n d Ma ter ia ls. All manipulations
involving air- and moisture-sensitive compounds were carried
out under an atmosphere of dried and purified nitrogen using
standard Schlenk techniques. Solvents were purified using
standard procedures. Benzoylacetone (98%) and 2,6-diisoprop-
ylphenylamine (90%) were obtained from Aldrich and used
without further purification. L1 and L2 were synthesized by
condensation of the corresponding acetylacetone (or benzoyl-
acetone) and 2,6-diisopropylaniline following published pro-
cedures with minor modifications.25-27 [tBuNH3][acac] (A) was
synthesized by the direct reaction of acetylacetone with
tBuNH2. [Et4N]2[NiBr4] was prepared according to the litera-
ture.28 The Ni(II) complexes were synthesized according to the
modified procedure of analogous Ni(II) complexes reported by
Holm and co-workers.18 MMA was purified by drying from
CaH2 and distilling under vacuum (42 °C/70 mmHg) and
dissolved in toluene to make a 5.0 mol/L solution. Elemental
analyses were performed on a Vario EL microanalyzer. Mass
spectra were measured on a VG ZAB-HS instrument using fast
atom bombardment (FAB). NMR spectra were carried out on
an INOVA 500 Hz at room temperature in CDCl3 solution
F igu r e 6. ORTEP plot of complex 3 showing the atom-
labeling scheme. Hydrogen atoms are omitted for clarity.
portion of the molecule has a small deviation of 0.010
Å, and both nickel ions are essentially in the Ni2O6
plane with Ni(1) displaced by +0.0023 Å and Ni(1)# by
-0.0023 Å from the plane of its ligands. The mean
deviation of the NiOCCCO plane is 0.0584 Å, and that
of another NiOCCCO plane is 0.0788 Å, with a 91.6°
swing angle. The O-Ni-O angles average 87.664°, in
the range from 79.65(9)° to 91.17(10)°. The O-Ni-N
t
angles of the nitrogen atom of the BuNH2 ligand also
average 89.675°, although the range is greater, from
81.07(17)° to 98.28(17)°. Four C-O bond lengths are
almost the same (av 1.2605(4) Å), and the five Ni-O
bond lengths are roughly equivalent (av 2.0536(2) Å).
The Ni(1)-N(1) bond length is equal to 2.116(5) Å and
N(1)-C(11) is 1.423(11) Å. A longer Ni(1)‚‚‚Ni(1)#
separation (the Ni-Ni distance is 3.250 Å) suggests that
there is no Ni-Ni interaction between the metal ions.
This is also reflected in the fairly large Ni-Ob-Ni
angles (Ob and Ot ) bridging and terminal oxygen
atoms, respectively) of 100.35(9)°.
1
(using TMS as internal standard for H NMR) and on a Bruker
AVANCE 400 Hz at room temperature in the solid state (using
a glycine standard sample spectrum to calibrate). Gel perme-
ation chromatography (GPC) analyses of the molecular weight
and molecular weight distribution of the polymers were
performed on a Waters 150C instrument using standard
polystyrene as the reference and with chloroform as the eluent
at 40 °C. Melting points were recorded on a Tormas model 40
micro hot stage and are uncorrected.
P olym er iza tion of MMA. All of the complexes can
be activated with MAO to catalyze MMA polymeriza-
tion. The polymers were isolated as white solids and
characterized by GPC in chloroform using standard
polystyrene as the reference. The triad microstructure
of the PMMA was analyzed using 13C NMR spectros-
copy. The results of polymerizations are summarized in
Table 3. The activity of 3 is higher, while those of 1 and
2 are only moderate, and all increase in activity with
increasing reaction temperature. The highest catalytic
activities are obtained at 50 °C, but decrease signifi-
[CH3C(O)CHC(HNAr )CH3] (L1, Ar ) 2,6-iP r 2C6H3). Acet-
ylacetone (15 mL, 0.143 mol), 2,6-diisopropylphenylamine (30
mL, 0.143 mol), and a catalytic amount of p-toluenesulfonic
acid in toluene (150 mL) were combined and heated to reflux
(25) Martin, D. F.; J anusonis, G. A.; Martin, B. B. J . Am. Chem.
Soc. 1961, 83, 73.
(26) Martin, D. F. In Reactions of Coordinated Ligands and Homo-
geneous Catalysis; Advances in Chemistry Series, No. 37; American
Chemical Society: Washington, DC, 1963; p 192-200.
(27) Clegg, W.; Cope, E. K.; Edwards, A. J .; Mair, F. S. Inorg. Chem.
1998, 37, 2317.
(28) Giil, N. S.; Nyholm, R. S. J . Chem. Soc. 1959, 3997.

Ni(II) Complexes Bearing N,O-Chelate Ligands
Organometallics, Vol. 22, No. 24, 2003 4957
for 2-3 h, while H2O was removed as a toluene azeotrope at
125-130 °C using a water separator. Vacuum distillation and
recrystallization from hexane yielded 2-(2,6-diisopropylphe-
nyl)aminopent-2-en-4-one (21.4 g, 56.5%, based on initial
amount of acetylacetone (lit. 22.23 g, 58.7%)). Mp: 46.05 °C
(lit. 44-46 °C). Anal. Calcd for C17H25NO: C, 78.72; H, 9.72;
N, 5.40. Found: C, 79.05; H, 9.60; N, 5.26. Positive FAB-MS
(m/z): 260 (M + 1); 244 (M - CH3); 202 (M - CH3C(O)CH).
1H NMR (CDCl3), δ (ppm): 12.1 (s, 1H, -NH); 7.2-7.3 (3H,
-C6H3(iPr)2); 5.2 (s, 1H, CH3C(O)CHd); 3.0 (2H, 2 -CH(CH3)2);
2.1 (s, 3H,CH3C(O)-); 1.6 (s, 3H, -CH3); 1.1-1.2 (d, 12H, 2
-CH(CH3)2). 13C NMR (CDCl3), δ (ppm): 195.8, 163.3, 146.2,
133.5, 128.2, 123.5, 95.5, 29.0, 28.4, 24.5, 22.6, 19.1.
g, 45.6%. Mp: 236 °C (dec). Anal. Calcd for C34H48N2NiO2: C,
75.54; H, 7.49; N, 4.00. Found: C, 75.34; H, 7.64; N, 3.95. H
1
NMR (CDCl3), δ (ppm): 7.0-7.1 (3H, -C6H3(CH(CH3)2)); 4.8
(s, 1H, CH3C(O)CHd); 3.8 (2H, 2 -CH(CH3)2); 1.6 (d.6H, -CH-
(CH3)2); 1.4 (s, 3H, CH3C(O)-); 1.2 (d.6H, -CH(CH3)2); 0.9 (s,
3H, -CH3). 13C NMR (CDCl3), δ (ppm): 174.5, 165.3, 144.4,
142.0, 124.6, 122.6, 97.7, 28.3, 24.2, 24.1, 23.7, 22.2.
Ni[C6H5C(O)CHC(NAr )CH3]2 (2). Ni(II) complex 2 (as
dark green block crystals) was obtained analogously to the
preparation of 1: 0.260 g (0.0065 mol) of potassium, 22 mL of
t
dried BuOH, 2.02 g (0.0063 mol) of L2, and 2.271 g (0.0037
mol) of [Et4N]2[NiBr4]. Yield: 1.140 g, 46.1%. Mp: 262 °C (dec).
Anal. Calcd for C44H52N2NiO2: C, 70.96; H, 8.41; N, 4.87.
1
[C6H 5C(O)CH C(H NAr )CH3] (L2). 3-(2,6-Diisopropyl-
phenyl)imino-1-phenylbut-2-en-1-one (L2) was obtained as
white crystals by using a procedure similar to that described
for the synthesis of L1, using 2,6-diisopropylphenylamine (13
mL, 0.062 mol), benzoylacetone (10 g, 0.060 mol), and a
catalytic amount of p-toluenesulfonic acid in toluene (80 mL).
Yield: 8.654 g, 44.61%, based on initial amount of benzoylac-
etone. Mp: 109.6 °C. Anal. Calcd for C22H27NO: C, 82.20; H,
8.47; N, 4.36. Found: C, 82.24; H, 8.28; N, 4.14. FAB-MS (m/
z): 322 (M + 1); 306 (M - CH3); 202 (M - C6H5C(O)CH); 105
(M - CH3(HNAr)CCH). 1H NMR (CDCl3), δ (ppm): 12.8 (s,
1H, -NH); 8.0 (2H, C6H5C(O)-); 7.2-7.3 (2H, -HNC6H3(iPr)2);
7.3-7.5 (4H, C6H5C(O)CHC(HNC6H3(iPr)2)CH3); 6.4 (s, 1H,
C6H5C(O)CHd); 3.1 (2H, -(CHCH3)2); 1.8 (s, 3H, CH3); 1.2 (d,
12H, 2 -CH(CH3)2). 13C NMR (CDCl3), δ (ppm): 188.4, 165.2,
146.2, 140.0, 133.5, 132.2, 130.7, 128.6, 128.4, 128.2, 127.1,
127.0 124.2, 123.6, 92.1, 28.5, 28.3, 24.6, 22.7, 19.7.
Found: C, 69.86; H, 8.48; N, 4.75. H NMR (CDCl3), δ (ppm):
7.0-7.3 (6H, C6H5C(O)CH(NC6H3(CH(CH3)2)2)CH3); 6.3 (2H,
C6H5C(O)-); 5.5 (s, 1H, C6H5C(O)CHd); 4.3 (2H, -CH(CH3)2);
1.5 (s, 3H, -CH3); 1.3 (d, 12H, 2 -CH(CH3)2). 13C NMR
(CDCl3), δ (ppm): 170.0, 166.6, 144.9, 142.5, 136.8, 128.7,
127.1, 126.5, 125.1, 97.3, 28.6, 25.2, 24.0, 23.7.
Ni2[CH3C(O)CHC(O)CH3]4[H2NtBu ]2 (3). Ni(II) complex
3 (as green block crystals) was obtained by following proce-
dures similar to those for the preparation of 1 and 2: 0.294 g
t
(0.007 mol) of potassium, 25 mL of dried BuOH, 1.998 g (0.011
mol) of A, and 3.056 g (0.005 mol) of [Et4N]2[NiBr4]. Yield:
0.672 g, 40.7%. Anal. Calcd For C28H50N2Ni2O8: C, 50.95; H,
7.64; N, 4.22. Found: C, 50.88; H, 7.59; N, 4.14. The melting
point was not obtained above 310 °C.
P olym er iza tion Exp er im en t. The appropriate MAO solid
was introduced into the round-bottom glass flask, then toluene
(15 mL), an appropriate amount of Ni(II) complex solution,
and 10 mL of MMA (0.05 mol) were syringed into the well-
stirred solution in order, and the reaction was continuously
stirred for an appropriate period at polymerization tempera-
ture. Polymerizations were stopped by addition of the acidic
EtOH. The resulting precipitated PMMA was collected and
treated by filtering, washing with EtOH several times, and
drying in vacuum at 60 °C to a constant weight.
Cr ysta l Str u ctu r e Deter m in a tion . The crystals were
mounted on a glass fiber using the oil drop scan method.29 Data
obtained with the ω-2θ scan mode were collected on a Bruker
SMART 1000 CCD diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å) at 293 K. The
structures were solved using direct methods, while further
refinement with full-matrix least squares on F2 was obtained
with the SHELXTL program package.30,31 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
introduced in calculated positions with the displacement
factors of the host carbon atoms.
[tBu NH3][a ca c] (A). A white needle crystal formed im-
t
mediately when 20 mL (0.20 mol) of BuNH2 was introduced
slowly into 21 mL (0.2002 mol) of acetylacetone without a large
amount of heating. Filtering isolated the crude product. The
purified product was obtained with a yield of 84% by further
washing with approximately 20 mL of hexane several times
and drying at 0 °C. 13C NMR (solid state), δ (ppm): 27.7 (CH3C-
(O)CHC(O)CH3(a)); 30.6 ((CH3)3CNH3(b)); 50.8 ((CH3)3CNH3-
(c)); 98.5 (CH3C(O)CHC(O)CH3(g)); 185.9, 188.6 (CH3C(O)-
CHC(O)CH3(e)). 1H NMR (CDCl3), δ (ppm): 1.0 ((CH3)3CNH2(j));
1.1 ((CH3)3CNH3(b)); 2.0 (CH3C(O)CHC(O)CH3(a)); 2.2 (CH3C-
(O)CH2C(O)CH3(f)); 3.6 (CH3C(O)CH2C(O)CH3(g)); 5.0 ((CH3)3-
CNH3(i)); 5.5 (CH3C(O)CHC(O)CH3(d)). 13C NMR (CDCl3), δ
(ppm): 24.6 (CH3C(O)CHC(O)CH3(a)); 30.6 (CH3C(O)CH2C(O)-
CH3(f)); 32.3 ((CH3)3CNH3(b)); 47.1 ((CH3)3CNH3(c)); 58.4
(CH3C(O)CH2C(O)CH3(f)); 100.2 (CH3C(O)CHC(O)CH3(g)); 190.9
(CH3C(O)CHC(O)CH3(e)); 201.7 (CH3C(O)CH2C(O)CH3(h)).
Ni[CH3C(O)CHC(NAr )CH3]2 (1). A 0.293 g (0.007 mol)
sample of potassium was added to 25 mL of dried tBuOH. After
the potassium had dissolved completely, the solution was
heated to 50 °C and 1.950 g (0.0075 mol) of L1 added. The
solution changed to yellow-orange as L1 completely reacted
with tBuOK and was kept stirring for 20 min. The solution
was cooled slowly to room temperature, and 2.320 g (0.0038
mol) of [Et4N]2[NiBr4] was introduced in; the reacting mixture
immediately formed a gray-green precipitate. After it was
stirred vigorously at room temperature for several hours, the
Ack n ow led gm en t. This work was financially sup-
ported by the National Natural Science Foundation of
China and the Science Foundation of Guangdong Prov-
ince. The authors thank Mr. Feng for single-crystal
X-ray technical assistance.
Su p p or tin g In for m a tion Ava ila ble: Tables and figures
giving X-ray crystallographic details for1, 2, and 3 in CIF
format. This material is available free of charge via the
Internet at http://pubs.acs.org.
t
residual BuOH was removed by evaporating in vacuum. The
residue slurry was then extracted successively with enough
hot n-heptane/toluene, the filtrate was collected by fast hot
filtering, and the resulting hot filtrate was induced to crystal-
lize by cooling slowly overnight. Then the product was isolated
by filtering and drying under reduced pressure. One or two
further recrystallizations from n-heptane/toluene mixture
solution can result in dark brown block crystals. Yield: 0.997
OM030292N
(29) Kottke, T.; Stalke, D. J . Appl. Crystallogr. 1993, 26, 615.
(30) SHELXTL, Version 5.1; Bruker AXS: Madison, WI, 1998.
(31) Sheldrick, G. M. SHELXL-97, program for X-ray Crystal
Structure Solution and Refinement; Go¨ttingen University: Germany,
1998.