Spacially confined M2 centers (M = Fe, Co, Ni, Zn) on a sterically bulky binucleating support: Synthesis, structures and ethylene oligomerization studies

Article abstract of DOI:10.1021/ic061286x

Two new bulky aryl-bridged pyridyl-imine compartmental (pro)ligands, 2,6-{(2,6-i-Pr₂C₆H₃)N=C(Me)C₅H ₃N}₂C₆H₃Y (Y = H L¹, OH L²-H), have been prepared in moderate to good overall yields via a Stille-type cross-coupling approach. The molecular structure of L²-H reveals a transoid configuration within the pyridyl-imine units with a hydrogen-bonding interaction maintaining the phenol coplanar with one of the adjacent pyridine rings. The interaction of 2 equiv of MX₂ with L¹ in n-BuOH at 110°C gives the binuclear complexes, [(L ¹)M₂X₄] (M = Fe, X = Cl (1a); M = Co, X = Cl (1b); M = Ni, X = Br (1c); M = Zn, X = Cl (1d)), in which the metal centers adopt distorted tetrahedral geometries and occupy the two pyridyl-imine cavities in L¹. In contrast, deprotonation of L²-H occurs upon reaction with 2 equiv of MX₂ to afford the phenolate-bridged species [(L²)M₂(μ-X)X₂] (M = Fe, X = Cl (2a); M = Co, X = Cl (2b); M = Ni, X = Br (2c); M = Zn, X = Cl (2d)). ¹H NMR studies of diamagnetic 1d and 2d reveal that the limited rotation of the N-aryl groups in 1d is further impeded in 2d by steric interactions imparted by the two closely located N-aryl groups. Partial displacement of the bridging bromide in 2c results upon its treatment with acetonitrile to afford [(L ²)Ni₂Br₃(NCMe)] [2C(MeCN)]; no such reaction occurs for 2a, 2b, or 2d. Upon activation with excess methylalumoxane (MAO), 1b, 1c, 2b, and 2c show some activity for alkene oligomerization forming low molecular-weight materials with methyl-branched products predominating for the nickel systems. Single-crystal X-ray diffraction studies have been performed on L²-H, 1c, 2b, 2c, 2c(NCMe), and 2d.

Full text of DOI:10.1021/ic061286x

Inorg. Chem. 2006, 45, 9890−9900
Spacially Confined M2 Centers (M
) Fe, Co, Ni, Zn) on a Sterically
Bulky Binucleating Support: Synthesis, Structures and Ethylene
Oligomerization Studies
Yohan D. M. Champouret, John Fawcett, William J. Nodes, Kuldip Singh, and Gregory A. Solan*
Department of Chemistry, UniVersity of Leicester, UniVersity Road, Leicester LE1 7RH, U.K.
Received July 12, 2006
Two new bulky aryl-bridged pyridyl-imine compartmental (pro)ligands, 2,6-{(2,6-i-Pr2C6H3)NdC(Me)C5H3N}2C6H3Y
(Y
)
H L1, OH L2-H), have been prepared in moderate to good overall yields via a Stille-type cross-coupling
approach. The molecular structure of L2-H reveals a transoid configuration within the pyridyl-imine units with a
hydrogen-bonding interaction maintaining the phenol coplanar with one of the adjacent pyridine rings. The interaction
of 2 equiv of MX2 with L1 in n-BuOH at 110
Co, X Cl (1b); M Ni, X
tetrahedral geometries and occupy the two pyridyl-imine cavities in L1. In contrast, deprotonation of L2-H occurs
upon reaction with 2 equiv of MX2 to afford the phenolate-bridged species [(L2)M2(
-X)X2] (M Fe, X Cl (2a);
Co, X Cl (2b); M Ni, X Br (2c); M Zn, X
Cl (2d)). 1H NMR studies of diamagnetic 1d and 2d
°
C gives the binuclear complexes, [(L1)M2X4] (M
)
Fe, X
) Cl (1a);
M
)
)
)
) Br (1c); M ) Zn, X ) Cl (1d)), in which the metal centers adopt distorted
µ
)
)
M
)
)
)
)
)
)
reveal that the limited rotation of the N-aryl groups in 1d is further impeded in 2d by steric interactions imparted
by the two closely located N-aryl groups. Partial displacement of the bridging bromide in 2c results upon its treatment
with acetonitrile to afford [(L2)Ni2Br3(NCMe)] [2c(MeCN)]; no such reaction occurs for 2a, 2b, or 2d. Upon activation
with excess methylalumoxane (MAO), 1b, 1c, 2b, and 2c show some activity for alkene oligomerization forming
low molecular-weight materials with methyl-branched products predominating for the nickel systems. Single-crystal
X-ray diffraction studies have been performed on L2-H, 1c, 2b, 2c, 2c(NCMe), and 2d.
Introduction
and alkene polymerization.4-8 Indeed, good catalytic per-
formances have been observed, and cooperative effects by
the neighboring polymerization-active metal centers have
been suggested.
Within the alkene polymerization/oligomerization arena,
the use of compartmentalized LM2 systems incorporating
early transition metals has been at the heart of many of the
key developments,4,5 while the use of late transition metal
The use of binucleating ligands as a means to impose close
spacial confinement on two metal centers has been widely
documented due, in part, because of the relevance of the
resulting bimetallic complexes to the active sites of a variety
of naturally occurring metalloenzymes.1 Moreover, the
potential for unique reactivity patterns and unusual catalytic
properties exhibited by synthetic examples of such dinuclear
species has further fueled research activity in the field.2 With
regard to polymerization applications, encapsulated two-
center systems have started to be employed as catalysts for
a range of metal-mediated processes including ring-opening3
(2) (a) Saied, O.; Simard, M.; Wuest, J. D. Organometallics 1996, 15,
2345. (b) Ooi, T.; Takahashi, M.; Yamada, M.; Tayama, E.; Omoto,
K.; Maruoka, K. J. Am. Chem. Soc. 2004, 126, 1150. (c) Kumagai,
N.; Matsunaga, S.; Kinoshita, T.; Harada, S.; Okada, S.; Sakamoto,
S.; Yamaguchi, K.; Shibasaki, M. J. Am. Chem. Soc. 2003, 125, 2169.
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2621. (f) Trost, B. M.; Ito, H.; Silcoff, E. R. J. Am. Chem. Soc. 2001,
123, 3367. (g) Trost, B. M.; Fettes, A.; Shireman, B. T. J. Am. Chem.
Soc. 2004, 126, 2660. (h) Gao, J.; Reibenspies, J. H.; Martell, A. E.
Angew. Chem., Int. Ed. 2993, 42, 6008.
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A.; Tolman, W. Dalton Trans. 2006, 928. (b) Lee, B. Y.; Kwon, H.
Y.; Lee, S. Y.; Na, S. J.; Han, S.-i; Yun, H.; Lee, H.; Park, Y.-W. J.
Am. Chem. Soc. 2005, 127, 3031. (c) Williams, C. K.; Brooks, N. R.;
Hillmyer, M. A.; Tolman, W. B. Chem. Commun. 2002, 2132.
* To whom the correspondence should be addressed. E-mail:
gas8@leicester.ac.uk.
(1) For reviews, see: (a) Gavrilova, A. L.; Bosnich, B. Chem. ReV. 2004,
104, 349. (b) van den Beuken, E. K.; Feringa, B. L. Tetrahedron 1998,
54, 12985. (c) Steinhagen, H.; Helmchen, G. Angew. Chem., Int. Ed.
Engl. 1996, 35, 2339. (d) Stra¨ter, N.; Lipscomb, W. N.; Klaubunde,
T.; Krebs, B. Angew. Chem., Int. Ed. Engl. 1996, 35, 2024. (e) Belle,
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9890 Inorganic Chemistry, Vol. 45, No. 24, 2006
10.1021/ic061286x CCC: $33.50
© 2006 American Chemical Society
Published on Web 10/24/2006

Confined M2 Centers on a Bulky Binucleating Support
combinations has only recently started to emerge in the
literature.6-8 By appreciation of the important role played
by steric bulk in late transition metal-mediated polymeriza-
tions,9 a range of sterically encumbered multidentate bi-
nucleating ligands (e.g., organo-bridged iminopyridines,
R-diimines, and iminophenolates) have been found to be
compatible supports for active dinickel,6a,7 dipalladium,8 and
diiron catalysts.6 However to date, because of the nature of
the binucleating ligand design, the late metal centers tend to
be positioned at the extremities of the ligand manifold and
thus would be expected to limit potential cooperative metal-
metal interactions.
Figure 1. Bis(iminopyridyl)benzene (L1) and bis(iminopyridyl)phenolate
[(L2)-]; Ar ) 2,6-i-Pr2C6H3.
Results and Discussion
Ligand synthesis. Treatment of 2,6-{OdC(Me)-
C5H3N}2C6H3Y (Y ) H, OH) with 2,6-diisopropylaniline,
as both reactant and solvent, at elevated temperature in the
presence of a catalytic amount of formic acid produced 2,6-
{(2,6-i-Pr2C6H3)NdC(Me)C5H3N}2C6H3Y (Y ) H (L1), OH
(L2-H)) in moderate yield (Scheme 1). The diketones, 2,6-
{OdC(Me)C5H3N}2C6H3Y (Y ) H, OH), have not been
previously reported and could be prepared in moderate to
good overall yield in two steps by treating first 1,3-
dibromobenzene or 2,6-dibromophenol with 2-(n-BuSn)-6-
{C(Me)CH2CH2O}-C5H3N10 under standard Stille cross-
coupling conditions,11 followed by acid deprotection. In the
case of 2,6-{OdC(Me)C5H3N}2C6H3OH, the formation of
the homo-coupled product, 6,6′′-diacetyl-2,2′:6′,2′′-bipyri-
dine,12 proved to be a competitive reaction pathway which
could be significantly inhibited by the addition of catalytic
amounts of cuprous bromide to the Stille reaction (see
Experimental Section).13 All the new compounds have been
characterized by 1H NMR, 13C NMR, and IR spectroscopy,
electrospray (ES) mass spectrometry, or elemental analysis.
In addition, a crystal of L2-H has been the subject of a single-
crystal X-ray diffraction study.
The molecular structure of L2-H is depicted in Figure 2;
selected bond lengths and angles are listed in Table 1.
Crystals suitable for the X-ray structure determination were
grown by slow evaporation of a chloroform solution contain-
ing the compound. The molecular structure of L2-H consists
of a central phenol group linked at its 2 and 6 positions by
two pyridyl-imine units. Within each unit, the pyridyl and
imine moieties are almost coplanar [N(1)-C(13)-C(15)-
N(2) ) 3.2° and N(3)-C(30)-C(31)-N(4) ) 2.4°] with the
respective nitrogen atoms disposed mutually trans. The
hydroxy proton of the central phenol group undergoes a
hydrogen-bonding interaction [O(1)‚‚‚N(2) ) 2.557(2) Å]
with one of the neighboring pyridine nitrogen atoms [N(2)]
resulting in one of the pyridyl-imine units being almost
coplanar with the central phenol plane [C(25)-C(20)-
C(19)-N(2) ) 3.7°], while the other is inclined at 18.6°.
The 2,6-diisopropylphenyl substituents on each imino group
With the intent of forcing the late metal centers into closer
proximity, we have targeted the novel sterically demanding
neutral bis(iminopyridyl)benzene (L1) and monoanionic bis-
(iminopyridyl)phenolate [(L2)-] ligands as potential supports
for homobimetallic iron(II), cobalt(II), nickel(II), and zinc-
(II) complexes (Figure 1). Herein, we report full details of
ligand synthesis along with the resultant coordination
chemistry. In addition, selected examples of the complexes
are screened as precatalysts for ethylene oligomerization.
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Inorganic Chemistry, Vol. 45, No. 24, 2006 9891

Champouret et al.
a
Scheme 1
a Reagents and conditions: (i) Pd(PPh3)4 (16 mol %), toluene, 90 °C, 72 h; (ii) Pd(PPh3)4 (8 mol %), CuBr (16 mol %), toluene, 100 °C, 72 h; (iii) HCl
(4 M), 60 °C, 12 h; (iv) 2,6-i-Pr2C6H3NH2, 160 °C, cat. H+.
Figure 2. Molecular structure of L2-H with atom labeling scheme and ellipsoids at 30% probability. All hydrogen atoms, apart from H1, have been omitted
for clarity.
Table 1. Selected Bond Distances (Å) and Angles (deg) for L2-H
ligand. In the IR spectra of L1 and L2-H, characteristic
absorption bands for ν(CdN) stretches are seen at ∼1639
cm-1.
N(1)-C(13)
N(4)-C(31)
C(13)-C(14)
C(31)-C(32)
1.281(4)
1.277(4)
1.491(4)
1.506(4)
O(1)-C(25)
C(24)-C(26)
C(19)-C(20)
C(13)-C(15)
1.354(4)
1.501(4)
1.492(4)
1.492(4)
Synthesis of Complexes. The reaction of L1 with 2 equiv
of MX2 [MX2 ) FeCl2, CoCl2, (DME)NiBr2, ZnCl2] in
n-butanol at elevated temperatures gave complexes [(L1)-
M2X4] (M ) Fe, X ) Cl (1a); M ) Co, X ) Cl (1b); M )
Ni, X ) Br (1c); M ) Zn, X ) Cl (1d)) in moderate yields
(Scheme 2). Similarly, complexes [(L2)M2(µ-X)X2] (M )
Fe, X ) Cl (2a); M ) Co, X ) Cl (2b); M ) Ni, X ) Br
(2c); M ) Zn, X ) Cl (2d)) were prepared in good yield by
treating 2 equiv of MX2 [MX2 ) FeCl2, CoCl2, (DME)NiBr2,
ZnCl2] with proligand L2-H in n-butanol at elevated tem-
perature (Scheme 2); no additional base was needed in any
of the transformations. All products have been characterized
by FAB mass spectrometry, IR spectroscopy, and in the cases
of 1a-1c and 2a-2c, by magnetic measurements, while
C(13)-N(1)-C(1)
C(30)-N(3)-C(26)
121.0(3)
119.1(3)
C(15)-N(2)-C(19)
C(31)-N(4)-C(33)
119.8(3)
120.6(3)
are oriented almost orthogonally to their adjacent pyridyl-
imine planes [C(13)-N(1)-C(1)-C(6) ) 87.4°, C(31)-
N(4)-C(33)-C(34) ) 84.5°]. The magnitude of the imino
C-N bond lengths [C(13)-N(1) ) 1.281(4) Å, C(31)-N(4)
) 1.277(4) Å] is consistent with the presence of double-
bond character.
In the solution state, however, the solid-state properties
of L2-H are not maintained, and the molecule possesses a
C2 plane of symmetry about the O(1)-C(25)-C(22) axis.
Similarly in L1, the 1H NMR spectrum reveals each pyridyl-
imine unit to be equivalent. In addition, characteristic signals
at ∼166 ppm are seen for the CdN carbon atoms in their
13C NMR spectra, while the MeCdN protons are seen as
1
diamagnetic 1d and 2d were characterized by H NMR
spectroscopy (see Table 2 and Experimental Section). In
addition, 1c and 2b-2d have been the subject of single-
crystal X-ray diffraction studies.
Crystals of 1c suitable for the X-ray determination were
grown by slow cooling of a hot acetonitrile solution
containing the complex. A view of 1c is depicted in Figure
3; selected bond distances and angles are listed in Table 3.
The molecular structure of 1c reveals a bimetallic complex
in which the two metal centers are supported on the same
L1 ligand frame and each bound terminally by two bromide
1
singlets at ∼2.3 ppm in their H NMR spectra. It is note-
worthy that for both L1 and L2-H some restricted rotation
of the isopropyl groups is apparent with two closely located
sets of doublets for the CHMe2 groups evident in their H
NMR spectra. The ES mass spectra of L1 and L2-H show
1
peaks corresponding to the protonated molecular ion for each
9892 Inorganic Chemistry, Vol. 45, No. 24, 2006

Confined M2 Centers on a Bulky Binucleating Support
a
Scheme 2
a Reagents and conditions: (i) 2 MX2 [MX2 ) FeCl2, CoCl2, (DME)NiBr2, ZnCl2], n-butanol, 110 °C; (ii) MeCN, heat (Ar ) 2,6-i-Pr2C6H3).
Table 2. Selected Characterization Data for the New Complexes 1 and 2
microanalysis (%)c
V(CdN)
µeff
a
complex
1a
color
brown
(cm-1
)
(µB)b
FAB mass spectrum
C
H
N
1593
7.4
5.1
4.3
d
888 [M]+,
852 [M - Cl]+
858 [M - Cl]+,
823 [M - 2Cl]+
991 [M]+,
1b
blue
1593
1594
1592
1588
1586
1589
1588
58.98
(59.07)
49.51
(49.30)
58.05
5.51
(5.63)
4.71
(4.70)
5.55
6.13
(6.26)
5.17
(5.23)
6.11
1c
red
912 [M - Br]+
871 [M - Cl]+,
836 [M - 2Cl]+
866 [M]+,
1d
yellow
brown
blue-green
red
(58.23)
53.38
(5.55)
5.24
(6.17)
5.26
2a
5.7
4.7
3.4
3.5
d
831 [M - Cl]+
837 [M - Cl]+
(53.40)e
60.52
(4.94)e
5.59
(5.51)e
6.41
2b
(60.46)
(5.65)
(6.41)
2c
927 [M - Br]+,
48.83
4.63
5.09
846 [M - 2Br]+
(49.00)e
50.65
(4.54)e
4.44
(5.11)e
5.25
2c(NCMe)
red
927 [M - Br - NCMe]+,
846 [M - 2Br - NCMe]+
851 [M - Cl]+
2300ν(C≡N)
1589
(50.85)e
59.44
(4.75)e
5.59
(5.35)e
6.25
2d
yellow
(59.58)
(5.51)
(6.17)
a Recorded on a Perkin-Elmer Spectrum One FT-IR spectrometer on solid samples. b Recorded on an Evans Balance at room temperature. c Calculated
values shown in parentheses. d Sample diamagnetic. e Calculated values include xCHCl3 [where x ) 1.25 (2a), 0.75 (2c), 0.5 [2c(NCMe)]].
ligands. The geometry at each nickel center can be best
described as distorted tetrahedral with the Nimine-Ni-Npyridine
bite angle similar in size at both pyridyl-imine cavities
[N(1)-Ni(1)-N(2) ) 81.03(17)° vs N(3)-Ni(2)-N(4) )
82.95(16)°] but with significantly different Br-Ni-Br bond
angles [Br(1)-Ni(1)-Br(2) ) 109.02(3)° vs Br(3)-Ni(2)-
Br(4) ) 125.22(4)°]. Both imino-pyridyl moieties are quasi-
planar [N(1)-C(7)-C(9)-N(2) ) 2.2°, N(3)-C(24)-C(25)-
N(4) ) 3.1°] and are oriented essentially orthogonally to
the N-aryl groups [C(2)-C(1)-N(1)-C(7) ) 94.0°, C(28)-
C(27)-N(4)-C(25) ) 90.2°]. In addition, the central aryl
group is tilted away from coplanarity with respect to both
adjacent pyridyl-imine units [N(3)-C(20)-C(18)-C(19) )
47.8°, C(19)-C(14)-C(13)-N(2) ) 42.9°]. The Ni-Br
bond lengths at each metal center are inequivalent with the
discrepancy most noticeable at Ni(1) with a difference of
0.04 Å apparent. The Ni-N distances are similar and
compare well with other crystallographically characterized
pyridyl-imine-NiBr2-containing complexes.7d,14 The imino
carbon-nitrogen bond lengths [C(7)-N(1) ) 1.290(6) Å,
C(25)-N(4) ) 1.279(6) Å] are essentially equivalent and
consistent with double-bond character. An inspection of the
intermetallic distance [5.223(4) Å] reveals that there is no
direct Ni‚‚‚Ni interaction between the two metal centers.
(14) (a) Laine, T. V.; Klinga, M.; Leskela, M. Eur. J. Inorg. Chem. 1999,
959. (b) Laine, T. V.; Piironen, U.; Lappalainen, K.; Klinga, M.; Aitola,
E.; Leskela, M. J. Organomet. Chem. 2000, 606, 112. (c) Tang, X.;
Sun, W.-H.; Gao, T.; Hou, J.; Chen, J.; Chen, W. J. Organomet. Chem.
2005, 690, 1570. (d) Britovsek, G. J. P.; Baugh, S. P. D.; Hoarau, O.;
Gibson, V. C.; Wass, D. F.; White, A. J. P.; Williams, D. J. Inorg.
Chim. Acta 2003, 345, 279. (e) Nienkemper, K.; Kotov, V. V.; Kehr,
G.; Erker, G.; Fro¨hlich, R. Eur. J. Inorg. Chem. 2006, 366.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9893

Champouret et al.
Figure 4. Molecular structure of 2b with atom labeling scheme and
ellipsoids at 30% probability. All hydrogen atoms have been omitted for
clarity.
equivalent imino-methyl signals (at 2.40 ppm) being shifted
downfield by 0.14 ppm upon coordination. Notably, the
solution behavior of 1d can be compared to [{2,6-{(2,6-i-
Pr2C6H3)NdC(Me)C5H3N}2C5H3N}Zn2Cl4] in which discon-
nection of the central pyridine group was invoked to account
for the observed C2 symmetry.16 As with the free ligand L1,
restricted rotation of the aryl groups in 1d leads to two sets
of doublets for the CH(CH3)2 groups in the 1H NMR
spectrum; the separation between signals is, however, more
pronounced for 1d.
Figure 3. Molecular structure of 1c with atom labeling scheme and
ellipsoids at 30% probability. All hydrogen atoms have been omitted for
clarity.
Table 3. Selected Bond Distances (Å) and Angles (deg) for 1c
Ni(1)-N(1)
Ni(1)-N(2)
Ni(2)-N(3)
Ni(2)-N(4)
C(7)-N(1)
Ni(1)‚‚‚Ni(2)
2.006(4)
2.023(4)
2.003(4)
2.022(4)
1.290(6)
5.223(4)
Ni(1)-Br(1)
Ni(1)-Br(2)
Ni(2)-Br(3)
Ni(2)-Br(4)
C(25)-N(4)
2.3742(9)
2.3296(9)
2.3511(10)
2.3475(9)
1.279(6)
Single crystals of 2 suitable for the X-ray determination
were grown from mixtures of acetonitrile-chloroform (2b
and 2d) and chloroform-diethyether (2c). A view of 2b is
depicted in Figure 4; selected bond distances and angles are
listed for all three species in Table 4. The structures of 2b-
2d are similar and will be discussed together. The molecular
structures comprise two metal atoms supported on the same
monoanionic (L2)- ligand frame with the phenolate oxygen
atom [O(1)] bridging the metals and the two separate pyridyl-
imine units acting as chelates. Each metal center is further
bound by one terminal halide and one bridging halide to
complete two independent five-coordinate geometries. Some
differences in the coordination sphere at each metal center
are observed with the geometry at M(1) being best described
as distorted square pyramidal [τ ) 0.51 at Co(1) (2b), 0.50
at Ni(1) (2c), and 0.38 at Zn(1) (2d)],17 while at M(2), a
more idealized square pyramidal geometry is evident [τ )
0.06 at Co(2) (2b), 0.02 Ni(2) (2c), and 0.07 at Zn(2) (2d)].
The imino-pyridyl chelating moieties in (L2)- are almost
planar [N(1)-C(13)-C(15)-N(2) ) 4.9 (2b), 14.0 (2c), and
7.1° (2d); N(3)-C(30)-C(31)-N(4) ) 7.7 (2b), 5.0 (2c),
and 10.0° (2d)] with the N-aryl groups almost orthogonal to
these planes [C(2)-C(1)-N(1)-C(13) ) 90.1 (2b), 91.3
(2c), and 93.3° (2d); C(34)-C(33)-N(4)-C(31) ) 100.4
(2b), 92.1 (2c), and 99.1° (2d)]. These inclinations of the
N(1)-Ni(1)-N(2)
Br(1)-Ni(1)-N(1)
Br(2)-Ni(1)-N(1)
Br(1)-Ni(1)-N(2)
Br(2)-Ni(1)-N(2)
81.03(17) N(3)-Ni(2)-N(4)
107.64(11) Br(3) Ni(2)-N(3)
114.27(12) Br(4)-Ni(2)-N(3)
94.79(11) Br(3) Ni(2)-N(4)
144.64(12) Br(4)-Ni(2)-N(4)
82.95(16)
115.90(12)
105.88(12)
105.10(12)
114.00(12)
Br(1)-Ni(1)-Br(2) 109.02(3)
Br(3)-Ni(2)-Br(4) 125.22(4)
The FAB mass spectra for 1a-1d show fragmentation
peaks corresponding to the loss of one or two halide groups
from the corresponding molecular ion peak of each complex.
In their IR spectra, the ν(CdN)imine bands are seen at ∼1592
cm-1 and are shifted to a lower wavenumber by ∼49 cm-1
in comparison with free L1; an observation that is in
accordance with the nitrogen atoms of the imino groups
[N(1), N(4)] being bound. Complexes 1a-1c are all para-
magnetic displaying magnetic moments of 7.2, 5.1, and 4.3
µB (Evans Balance at ambient temperature), their values
being consistent with two noninteracting high-spin Fe(II)-
Fe(II) (S ) 2 and 2, respectively), Co(II)-Co(II) (S ) 3/2
and 3/2, respectively), and Ni(II)-Ni(II) (S ) 1 and 1,
respectively) metal centers, respectively (using µ2 ) ∑µi2,
where µi is the magnetic moment of the individual metal
centers).15 In contrast, complex 1d is diamagnetic and shows
a 1H NMR spectrum (in CDCl3 at ambient temperature) that
supports molecular C2 symmetry in solution with the
(16) Champouret, Y. D. M.; Mare´chal, J.-D.; Dadhiwala, I.; Fawcett, J.;
Palmer, D.; Singh, K.; Solan, G. A. Dalton Trans. 2006, 2350.
(17) For use of τ, see: Addison A. W.; Rao, T. N.; Reedijk, J.; von Rijn
J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349.
(15) Gerli, A.; Hagen, K. S.; Marzilli, L. G. Inorg. Chem. 1991, 30, 4673.
9894 Inorganic Chemistry, Vol. 45, No. 24, 2006

Confined M2 Centers on a Bulky Binucleating Support
Table 4. Selected Bond Distances (Å) and Angles (deg) for 2b, 2c,
and 2d
reflected by the narrower M-O-M angles [Co(1)-O(1)-
Co(2) ) 103.9(2)° (2b), Ni(1)-O(1)-Ni(2) ) 102.54(16)°
(2c), Zn(1)-O(1)-Zn(2) ) 101.63(13)° (2d)]. The N(1)-
C(1) and N(4)-C(33) bond distances in 2b-2d [∼1.27 Å]
are essentially the same as the CdN bond distances in
proligand L2-H [1.281(4) and 1.277(4) Å]. Between struc-
tures, the M-N distances (and M-O) follow the order Zn-N
> Co-N > Ni-N consistent with the corresponding trend
in ionic radii [Zn(II) > Co(II)high spin > Ni(II)].
The FAB mass spectra of 2a-2d show fragmentation
peaks in each case corresponding to the loss of one or two
halide groups from their respective molecular ions. In the
IR spectra of 2a-2d, the ν(CdN)imine bands are seen at
∼1587 cm-1; this is indicative of both imino-nitrogen atoms
being coordinated to the metal centers. As with 1a-1c,
compounds 2a-2c are all paramagnetic with values of the
magnetic moments [5.7 (2a), 4.7 (2b), 3.5 (2c) µB; Evans
Balance at ambient temperature] slightly lower than the
corresponding values found for 1a-1c; this is, perhaps,
indicative of the onset of some antiferromagnetic behavior
at this temperature.21
For diamagnetic 2d, the 1H NMR spectrum (in CD2Cl2 at
ambient temperature) indicates that the asymmetry observed
for the binding sites in the solid state is not maintained in
solution as exemplified by the presence of only one type of
imino-methyl group (at 2.34 ppm). As with 1d, restricted
rotation of the N-aryl groups in 2d is apparent which is likely
further supplemented by inter-aryl steric interactions. Thus,
two broad resonances for the CHMe2 groups (1.20, 0.98 ppm;
in a ratio of 6:18), along with two broad signals both
integrating to two protons for the CHMe2 protons, are seen
at ambient temperature. When the mixture is cooled to -43
°C, however, the broad resonances sharpen to give four
separate doublets for the CHMe2 groups (0.93, 0.96, 1.00,
1.19 ppm in a ratio of 6:6:6:6) along with two apparent
septets for the CHMe2 protons; indicative of four separate
environments for the methyl groups per N-aryl substituent.
In contrast to 2b and 2d, crystallization of bromide-
containing 2c from a mixture of acetonitrile-choroform
results in the coordination of one molecule of MeCN to give
[(L2)Ni2Br3(CH3CN)] [2c(NCMe)] (Scheme 2). Complex
2c(NCMe) has been characterized by FAB mass spectrometry
along with IR spectroscopy (see Table 2 and Experimental
Section). In addition, a crystal of 2c(NCMe) has been the
subject of a single X-ray diffraction study. The molecular
structure of 2c(NCMe) is depicted in Figure 5; selected bond
lengths and angles are listed in Table 5.
M ) Co, X ) Cl M ) Ni, X ) Br M ) Zn, X ) Cl
(2b)
(2b)
(2d)
M(1)-N(2)
M(1)-O(1)
M(1)-N(1)
M(1)-X(2)
M(1)-X(1)
M(2)-O(1)
M(2)-N(4)
M(2)-N(3)
M(2)-X(3)
M(2)-X(1)
N(1)-C(13)
N(4)-C(31)
M(1)‚‚‚M(2)
2.070(6)
2.096(5)
2.149(6)
2.234(3)
2.340(3)
1.947(6)
2.072(7)
2.077(7)
2.292(2)
2.403(2)
1.258(9)
1.293(11)
3.186(5)
2.010(5)
2.012(4)
2.087(4)
2.4100(10)
2.5127(9)
1.975(4)
2.061(5)
2.000(5)
2.4378(10)
2.4779(9)
1.285(7)
1.284(7)
3.111(4)
2.077(4)
2.141(3)
2.178(4)
2.2085(14)
2.3400(14)
1.998(3)
2.129(4)
2.115(4)
2.2544(14)
2.3920(13)
1.287(6)
1.270(7)
3.209(4)
M(1)-O(1)-M(2)
N(2)-M(1)-O(1)
N(2)-M(1)-N(1)
O(1)-M(1)-N(1)
N(2)-M(1)-X(2)
O(1)-M(1)-X(2)
N(1)-M(1)-X(2)
N(2)-M(1)-X(1)
X(2)-M(1)-X(1)
O(1)-M(2)-N(4)
O(1)-M(2)-N(3)
N(4)-M(2)-N(3)
O(1)-M(2)-X(3)
N(4)-M(2)-X(3)
N(3)-M(2)-X(3)
N(4)-M(2)-X(1)
N(3)-M(2)-X(1)
X(3)-M(2)-X(1)
103.9(2)
85.9(2)
77.8(3)
102.54(16)
101.63(13)
82.55(14)
77.36(15)
149.90(14)
118.74(12)
97.70(10)
111.53(11)
127.22(12)
113.19(5)
148.00(15)
86.56(15)
77.09(16)
105.21(10)
109.37(12)
106.12(12)
93.48(12)
143.92(12)
106.70(5)
88.88(17)
80.42(18)
166.45(16)
114.97(13)
89.95(11)
102.06(12)
136.31(13)
107.78(3)
156.64(17)
90.27(17)
81.7(2)
99.20(11)
103.25(13)
94.40(13)
95.39(14)
158.36(13)
107.11(4)
157.0(2)
115.6(2)
95.56(17)
106.10(19)
126.5(2)
117.25(9)
146.9(3)
86.7(3)
79.2(3)
107.10(16)
105.1(2)
101.98(19)
94.7(2)
150.62(19)
107.34(9)
aryl groups have the effect that one isopropyl substituent
per aryl group [C(42), C(7)] lies close to the basal plane of
each square pyramid while the other points in a similar
direction as a terminal halide [C(39), C(10)]. With regard
to the central phenolate plane, one pyridyl-imine unit adopts
a pseudo-coplanar conformation [C(25)-C(24)-C(26)-N(3)
) 13.5 (2b), 16.1 (2c), 1.6° (2d)], while the other is inclined
significantly out-of-this plane [N(2)-C(19)-C(20)-C(25)
) 40.8 (2b), 28.9 (2c), and 36.2° (2d)]. As would be
expected, the M-X(bridging) distances are longer than the
M-X(terminal) distances with some asymmetry apparent
between the M-X(bridging) distances [M(1)-X(1) ) 2.340-
(3) (2b), 2.5127(9) (2c), and 2.3400(14) Å (2d) vs M(2)-
X(1) ) 2.403(2) (2b), 2.4779(9) (2c), and 2.3920(13) Å
(2d)]. A similar asymmetry is observed for the M-O(bridg-
ing) distances with the M(1)-O(1) bond [2.096(5) (2b),
2.012(4) (2c), 2.141 Å (2d)], in this case, being longer than
the M(2)-O(1) bond [1.947(6) (2b), 1.975(4) (2c), 1.998-
(3) Å (2d)]. The intermetallic M‚‚‚M distances for all three
complexes [Co(1)‚‚‚Co(2) ) 3.186(5) Å (2b), Ni(1)‚‚‚Ni-
(2) ) 3.111(4) Å (2c), Zn(1)‚‚‚Zn(2) 3.209(4) Å (2d)] are
shorter than those in previously reported complexes contain-
ing M(µ-Ophenolate)(µ-Cl)M [ranges of 3.221-3.235 (M )
Co)18 and 3.221-3.348 Å (M ) Zn)3a,19] or Ni(µ-Ophenolate)-
(µ-Br)Ni [range of 3.221-3.235 Å20] motifs which are
The molecular structure of 2c(NCMe) reveals a bimetallic
complex similar to that described for 2c, but it differs in
that one molecule of acetonitrile is additionally bound to Ni-
(2) with the result that the geometry at Ni(2) is distorted
octahedral with N(5)NCMe and N(3) disposed mutually trans
[N(3)-N(2)-N(5) ) 174.7(2)°]. At Ni(1), the square
pyramidal [τ ) 0.15] geometry is maintained. The effect of
(18) Quijano, E. R.; Stevens, Charles, E. D.; O’Connor, J. Inorg. Chim.
Acta 1990, 177, 267.
(19) You, Z.-L.; Zhu, H.-L. Z. Anorg. Allg. Chem. 2006, 632, 140.
(20) Adams, H.; Clunas, S.; Fenton, D. E. Acta Crystallogr. 2004, E60,
m338. (b) Fenton, D. E. Inorg. Chem. Commun. 2002, 5, 537.
(21) (a) Sakiyama, H.; Ito, R.; Kumagai, H, Inoue, K.; Sakamoto, M.;
Nishida, Y.; Yamasaki, M. Eur. J. Inorg. Chem. 2001, 2027. (b) Nanda,
K. K.; Das, R.; Thompson, L. K.; Venkastsubramanian, K.; Paul, P.;
Nag, K. Inorg. Chem. 1994, 33, 1188.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9895

Champouret et al.
at room temperature) of 2c(NCMe) are comparable to that
found for 2c.
The partial displacement of a bridging bromide and
reorganization of (L2)- upon conversion of 2c to 2c(NCMe)
was unexpected and notably did not occur on treatment of
chloride-bridged 2a, 2b, and 2d with acetonitrile. It might
be argued that the metal center possessing the more distorted
geometry in 2 [e.g., Co(1) τ ) 0.51 (2b), Ni(1) τ ) 0.50
(2c), Zn(1) τ ) 0.38 (2d)] is more susceptible to the approach
of a suitable monodentate ligand which is further aided by
the reduction in the inter-aryl steric interactions that would
ensue. The explanation as to why this occurs uniquely for
2c is uncertain, but it could be the result of the relative
strengths of a µ-X ligand (X ) Br vs Cl).
Screening of Complexes as Catalysts for Ethylene
Oligomerization. All the iron, cobalt, and nickel complexes
were screened as precatalysts for oligomerization or polym-
erization of ethylene. Typically, a complex in toluene was
treated with 600 equiv (300 equiv/metal center) of methyl-
alumoxane (MAO) at room temperature, and ethylene (1 bar)
gas was introduced over a period of 30 min. All the nickel
and cobalt systems displayed low activities for ethylene
oligomerization affording hydrocarbon-based materials that
were readily soluble in chloroform; both iron systems were
inactive. No evidence for higher molecular weight polymeric
materials could be detected under these experimental condi-
tions. The results of the tests are collected in Table 6 (entries
1-4).
Figure 5. Molecular structure of 2c(NCMe) with atom labeling scheme
and ellipsoids at 30% probability. All hydrogen atoms have been omitted
for clarity.
Table 5. Selected Bond Distances (Å) and Angles (deg) for 2c(NCMe)
Ni(1)-O(1)
Ni(1)-N(2)
Ni(1)-N(1)
Ni(1)-Br(1)
Ni(1)-Br(2)
N(1)-C(13)
Ni(1)‚‚‚Ni(2)
1.984(4)
2.028(4)
2.079(4)
2.4429(10)
2.4521(10)
1.283(7)
3.449(4)
Ni(2)-O(1)
Ni(2)-N(3)
Ni(2)-N(5)
Ni(2)-Br(3)
Ni(2)-Br(1)
Ni(2)-N(4)
N(4)-C(31)
2.056(4)
1.998(5)
2.019(5)
2.4888(11)
2.8182(11)
2.124(5)
1.282(7)
Ni(1)-O(1)-Ni(2)
O(1)-Ni(1)-N(2)
O(1)-Ni(1)-N(1)
N(2)-Ni(1)-Br(1)
N(1)-Ni(1)-Br(1)
O(1)-Ni(1)-Br(2)
N(1)-Ni(1)-Br(2)
117.29(18) N(3)-Ni(2)-N(5)
85.35(17) N(3)-Ni(2)-O(1)
150.14(16) N(5)-Ni(2)-N(4)
158.98(13) O(1)-Ni(2)-N(4)
99.01(13) N(5)-Ni(2)-Br(1)
101.16(11) N(4)-Ni(2)-Br(1)
174.7(2)
86.83(17)
95.08(19)
161.36(17)
86.57(15)
93.27(14)
The most active system employed 1c as the precatalyst
(entry 2) affording a film typical of the products obtained
1
with pyridyl-imine-based nickel systems.14a,14b,23 In the H
105.94(13) Br(3)-Ni(2)-Br(1) 166.53(4)
NMR spectrum, very low levels of terminal and internal
unsaturation are accompanied by higher levels of methyl
chain ends. The 13C NMR spectrum indicates that the
oligomeric product contains significant quantities of methyl
branches; no evidence for longer-chain branching is apparent.
Further inspection of the 13C NMR spectrum reveals the
separation between methyl branches to be mainly five or
more CH2 units, while separations of less than one ethylene
unit are not present.24 The activity of 1c/MAO is comparable
with the activity reported for the mononickel analogue
[{2-Ph-6-CMe)N(2,6-i-Pr2C6H3)C5H3N}NiBr2]/MAO25
(under similar conditions), although lower than for the
related nonphenyl substituted pyridyl-imine-NiBr2/MAO
Br(1)-Ni(1)-Br(2) 105.85(4)
acetonitrile coordination is 2-fold. First, the degree of
asymmetry present in the Ni-Br(bridging) distances [Ni-
(1)-Br(1) ) 2.4429(10) vs Ni(2)MeCN-Br(1) ) 2.8182(11)
Å] is significantly increased when compared to the corre-
sponding distances in 2c (Table 4) and to the related dinickel
species [(2,6-bis[2-(dimethylamino)-ethyliminomethyl]-4-
methylphenolato)Ni2(µ-Br)Br(OH2)3]Br.20a In fact, the Ni-
(2)MeCN-Br(1) distance could be considered more of an
interaction than a bond. Second, the Ni‚‚‚Ni separation
[3.445(4) Å] is considerably longer than that observed in 2c
[3.111(4) Å] and in related Ni(µ-Ophenolate)(µ-Br)Ni-containing
compounds (range of 3.221-3.235 Å)20 with the correspond-
ing Ni-O-Ni angle [117.29(18)°] more expanded. Further-
more, the flexibility of (L2)- is revealed by comparison of
2c(NCMe) with 2c, with the central phenolate group in
2c(NCMe) now tilted away from coplanarity with respect
to both adjacent pyridyl-imine planes [N(2)-C(19)-C(20)-
C(25) ) 24.7°, C(25)-C(24)-C(26)-N(3) ) 38.5°].
(22) Shin, J. H.; Savage, W.; Murphy, V. J.; Bonanno, J. B.; Churchill, D.
G.; Parkin, G. Dalton Trans. 2001, 1732.
(23) (a) Laine, T. V.; Lappalainen, K.; Liimatta, J.; Aitola, E.; Lofgren,
B.; Leskala, M. Macromol. Rapid Commun. 1999, 20, 487. (b)
Meneghetti, S. P.; Lutz, P. G.; Kress, J. Organometallics 1999, 18,
2734. (c) Koppl, A.; Alt, H. G. J. Mol. Catal. A: Chem. 2000, 154,
45. (d) Bres, P. L.; Gibson, V. C.; Mabille, C. D. F.; Reed, W.; Wass,
D.; Weatherhead R. H. (BP Chemicals Ltd., U.K.) PCT Int. Appl.
WO9849208, 1998; Chem. Abstr. 1999, 130, 4185.
(24) (a) Usami, T.; Takayama, S. Macromolecules 1984, 17, 1756. (b)
Galland, G. B.; de Souza, R. F.; Mauler, R. S.; Nunes, F. F.
Macromolecules 1999, 32, 1620. (c) Linderman, L. P.; Adams, N. O.
Anal. Chem. 1971, 43, 1245. (d) De Pooter, M.; Smith, P. B.; Dohrer,
K. K.; Bennett, K. F.; Meadows, M. D.; Smith, C. G.; Schouwenaars,
H. P.; Geerards, R. A. J. Appl. Polym. Sci. 1991, 42, 399.
The FAB mass spectrum for 2c(NCMe) shows fragmenta-
tion peaks similar to that observed for 2c. In the IR spectra
of 2c(NCMe), the ν(CdN)imine band is seen at 1590 cm-1
with an additional band at 2300 cm-1 corresponding to the
ν(CtN) absorption for the η1-bound acetonitrile molecule.22
The paramagnetic properties (µeff ) 3.5 µB; Evans balance
(25) Weinberg, W. H.; McFarland, E.; Goldwasser, I.; Boussie, T.; Turner,
H.; Van Beek, J. A. M.; Murphy, V.; Powers, T. (Symx Technologies)
International Patent WO9803521, 1998.
9896 Inorganic Chemistry, Vol. 45, No. 24, 2006

Confined M2 Centers on a Bulky Binucleating Support
Table 6. Results of the Catalytic Evaluation of the Cobalt and Nickel Systemsa
massb
(g)
activity
external
internal
vinylidenes and
av carbon
entry
precatalyst
(g mmol-1 h-1 bar-1
)
olefinc (%)
olefinc (%)
trisubstitutedc (%)
contentc (Cn)
1
2
3
4
1b
1c
2b
2c
0.010
0.200
0.050
0.070
2
40
10
14
35.9
59.4
31.7
58.4
59.5
40.6
53.5
41.6
5.1
15.7
158.8
17.5
14.8
50.5
a General conditions: 1 bar ethylene Schlenk test carried out in toluene (40 mL) at ambient temperature using 6.0 mmol MAO (Al:M ) 300:1), 0.01
mmol precatalyst, over 0.5 h. Reactions were terminated by the addition of dilute HCl. b Mass of oligomer isolated. c Oligomerization product percentages
1
and average carbon content, Cn, calculated via integration of H NMR spectra.
systems.14a,14b,23 The introduction of a bridging phenolate
group in 2c also allows for an active catalytic system (entry
4), in this case, affording a waxy material but exhibiting a
lower productivity when compared with that observed for
1c/MAO. In addition, the average carbon content (Cn) for
the oligomer obtained using 2c/MAO is reduced in com-
parison with that obtained using 1c/MAO. The microstruc-
tural properties of the oligomer furnished are, however,
similar to that produced employing 1c/MAO with methyl
branches predominating.
Both cobalt systems display only low activities (entries
1, 3) with the phenolate-bridged 2b giving the more active
system (entry 3). The 1H NMR spectra of the low molecular
weight oligomers obtained indicates in both cases the
presence of mixtures of linear R-olefins and internal olefins
along with lower degrees of vinylidenes, R1R2CdCH2 and
trisubstituted alkenes R1R2CdCHR3 (C6-C26). Unlike with
the nickel systems, no evidence for methyl branched
structures is evident from the 13C NMR spectra.
For both the nickel and cobalt systems, a coordination-
insertion mechanism seems likely, followed by â-hydride
elimination (chain transfer). Furthermore, an isomerization
process (chain walking) appears operational for both cobalt
and nickel. However, only in the case of the nickel systems
is the chain walking competitive with the chain propagation
with the effect that further insertions of ethylene into a
secondary metal-alkyl bond can occur to give the distinctive
branched microstructures.9c On the other hand, for the cobalt
systems, the isomerization process allows for a broader
distribution of unsaturated products with small quantities of
vinylidenes and trisubstituted compounds also evident.
Nevertheless, given the low molecular weight of the materi-
als, it is clear that the ligand frames L1 and (L2)- possess
insufficient steric bulk to prevent chain transfer of the
growing oligomeric chain.
mainly a mixture of linear R-olefins and internal olefins while
the Ni systems additionally promote methyl branched
structures. No pronounced effect with regard to microstruc-
tural variations of the oligomeric material is apparent between
ligand frames for a given bimetallic center, although varia-
tions in productivity are noticeable. The mechanistic role of
the two metal centers during oligomerization, however,
remains uncertain and indeed the role of cooperative effects
is unclear. Nevertheless, the capacity of these sterically bulky
compartmental ligands to act as effective scaffolds for two
oligomerization-active metal centers has been demonstrated.
The role of electronic and steric variation will be probed
elsewhere as will the ability of these systems to mediate
alternative catalytic transformations.
Experimental Section
All reactions, unless otherwise stated, were carried out under an
atmosphere of dry, oxygen-free nitrogen, using standard Schlenk
techniques or in a nitrogen purged glovebox. Solvents were distilled
under nitrogen from appropriate drying agents and degassed prior
to use.26 The infrared spectra were recorded on a Perkin-Elmer
Spectrum One FT-IR spectrometer on solid samples. The ES
(electrospray) and FAB (fast atom bombardment) mass spectra were
recorded using a micromass Quattra LC mass spectrometer and a
Kratos Concept spectrometer with dichloromethane or NBA as the
matrix, respectively. High-resolution FAB mass spectra were
recorded on Kratos Concept spectrometer (xenon gas, 7 kV) with
NBA as matrix. Oligomer products were analyzed by GC, using a
Perkin-Elmer Autosystem XL chromatograph equipped with a flame
ionization detector, a 30 m PE-5 column (0.25 mm thickness), an
injector temperature of 45 °C, and the following temperature
program: 45 °C for 7 min, 45-195 °C at 10 °C min-1, 195 °C for
5 min, 195-225 °C at 10 °C min-1, 225 °C for 5 min, 225-250
°C at 10 °C min-1, and 250 °C for 22 min. 1H and 13C NMR spectra
were recorded on a Bruker ARX spectrometer (300 MHz) at
ambient temperature unless otherwise stated; chemical shifts (ppm)
are referred to the residual protic solvent peaks, and chemical shifts
are in hertz (Hz). Magnetic susceptibility studies were performed
using an Evans balance (Johnson Matthey) at room temperature.
The magnetic moment data were calculated following standard
methods,27 and corrections for underlying diamagnetism were
applied to data.28 Elemental analyses were performed at the Science
Technical Support Unit, London Metropolitan University.
Conclusions
In this study, we have shown that two new classes of
binucleating ligands [L1, (L2)-] can be readily accessed in
which sterically bulky groups can be introduced at the termini
of the ligand manifolds. The coordination chemistry of the
resulting complexes has been investigated, and it has been
shown that L1 promotes the formation of remote bis(MX2)
bimetallic units while (L2)- favors the formation of M2(µ-
X)X2-type complexes in which the metal centers are more
closely located. Significantly, all the dicobalt and -nickel
systems display some activity for alkene oligomerization
upon activation with MAO with the cobalt systems forming
The reagents, 1,3-dibromobenzene, 2,6-dibromophenol, 2,6-
diisopropylaniline, (DME)NiBr2 (DME ) 1,2-dimethoxyethane),
(26) Armarego W. L. F.; Perrin, D. D. In Purification of Laboratory
Chemicals, 4th ed.; Butterworth Heinemann: Woburn, MA, 1996.
(27) Mabbs, F. E.; Machin, D. J. Magnetism and Transition Metal
Complexes; Chapman and Hall: London, 1973.
(28) (a) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 203. (b) Handbook
of Chemistry and Physics, 70th ed.; Weast, R. C., Ed.; CRC Press:
Boca Raton, FL, 1990; p E134.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9897

Champouret et al.
MAO (10 wt % in toluene), cuprous bromide, and the metal
dichlorides were purchased from Aldrich Chemical Co. and were
used without further purification. The compounds tetrakis(triph-
enylphosphine)palladium(0)29 and 6-tributylstannyl-2-(2-methyl-1,3-
dioxolan-2-yl)pyridine10 were prepared according to previously
reported procedures. All other chemicals were obtained com-
mercially and used without further purification.
1452 (m), 1353 (m), 1259 (m), 1138 (w), 1106 (m), 1087 (m),
1004 (m), 950 (w), 853 (w), 823 (m), 784 (s), 737 (s). FAB positive
mass spectrum (m/z): 333 [M + H]+. Acc. Mass FABMS positive
spectrum (m/z) required for (C20H16N2O3H+): 333.12394. Found:
333.12392. mp: 178-180 °C.
Synthesis of L1. 2,6-{(OdC(Me)C5H3N}2C6H4 (0.853 g, 2.70
mmol) was suspended in 2,6-diisopropylaniline (4.78 g, 27.0 mmol,
10 equiv) and stirred for 15 min at 160 °C on a heating mantle
until dissolution. A catalytic amount of formic acid was added,
and the reaction mixture was stirred for an additional 20 min at
this temperature. After the removal of the excess 2,6-diisopropyl-
aniline under reduced pressure, the resulting brown residue was
stirred in ethanol at room temperature, and the resultant precipitate
filtered and washed with ethanol. The product was recrystallized
from a dichloromethane-hexane (1:9) mixture at room temperature
to afford L1 as a yellow solid. Yield: 50% (0.857 g, 1.35 mmol).
Synthesis of 2,6-{(OdC(Me)C5H3N}2C6H4. 1,3-Dibromoben-
zene (0.472 g, 2.00 mmol), 6-tributylstannyl-2-(2-methyl-1,3-
dioxolan-2-yl)pyridine (2.00 g, 4.40 mmol, 2.2 equiv), and tetrakis-
(triphenylphosphine)palladium(0) (0.185 g, 0.16 mmol, 0.08 equiv)
were loaded in a Schlenk vessel under an atmosphere of nitrogen,
and the contents were stirred in dry toluene (25 mL) for 72 h at 90
°C. After removal of the solvent under reduced pressure, the reaction
mixture was stirred overnight at 60 °C in 4 M HCl (20 mL), cooled
to room temperature, and carefully neutralized by the addition of
4 M NaHCO3. The suspension was extracted with CHCl3 (3 × 30
mL), and the organic phase was separated, washed with water (3
× 30 mL) and brine (1 × 40 mL), and dried over magnesium
sulfate. after filtration, the solvent was removed under reduced
pressure, and the crude product was crystallized from ethanol at
-30 °C. The resulting precipitate was collected by filtration to
afford 2,6-{(OdC(Me)C5H3N}2C6H4 as a white solid. Yield: 60%
3
1H NMR (300 MHz, CDCl3): δ 1.07 (d, JHH ) 6.7, 12H, CH-
(CH3)2), 1.09 (d, 3JHH ) 6.7, 12H, CH(CH3)2), 2.26 (s, 6H, CH3Cd
3
N), 2.71 (sept, JHH ) 6.7, 4H, CH(CH3)2), 7.0-7.1 (m, 6H,
ArN-aryl-H), 7.56 (dd, 3JHH ) 7.9, 3JHH ) 7.6, 1H, Ar-H), 7.9-7.8
3
4
(m, 4H, Py-H and Ar-H), 8.19 (dd, JHH ) 7.8, JHH ) 1.8, 2H,
3
4
Py-H), 8.35 (dd, JHH ) 7.3, JHH ) 1.5, 2H, Py-H), 9.01 (s, 1H,
Ar-H). 13C {1H} NMR (75 MHz, CDCl3): δ 17.3 (CH3CdN), 22.9
(CH3), 23.2 (CH3), 28.3 (CH), 119.8 (Py), 121.2 (Ar), 123.0 (Ar),
123.6 (Py), 125.6 (Ar), 127.5 (Ar), 129.3 (Ar), 135.8 (Py), 137.3
(Ar), 139.6 (Ar), 146.5 (Ar), 155.7 (Py), 156.2 (Py), 167.3 (Cd
N). IR (cm-1): 2960 (m), 1641 (br, ν(CdN)imine), 1572 (m), 1448
(m), 1381 (m), 1360 (m), 1307 (m), 1235 (m), 1119 (m), 1092 (s),
817 (m), 786 (s), 765 (s), 689 (s). ES positive mass spectrum (m/
z): 635 [M + H]+. Acc. Mass FABMS positive (m/z) required for
(C44H50N4H+): 635.41137. Found: 635.41138. mp: 204-206 °C.
Synthesis of L2-H. A similar procedure to that outlined for L1
was employed using 2,6-{(OdC(Me)C5H3N}2C6H3(OH) (0.896 g,
2.70 mmol) in 2,6-diisopropylaniline (4.78 g, 27.0 mmol, 10 equiv).
After the removal of the excess 2,6-diisopropylaniline under reduced
pressure, the resulting brown residue was stirred in ethanol at room
temperature, and the resultant precipitate was filtered and washed
with ethanol to afford L2-H as a yellow solid. Yield: 50% (0.878
g, 1.35 mmol). Crystals suitable for the X-ray determination were
grown by slow evaporation of a chloroform solution containing
L2-H. Anal. Calcd for (C44H50N4O‚3H2O): C, 75.00; H, 7.95; N,
7.95%. Found: C, 74.83; H, 8.04; N, 8.04%. 1H NMR (300 MHz,
1
(0.379 g, 1.20 mmol). H NMR (300 MHz, CDCl3): δ 2.87 (s,
6H, CH3), 7.67 (t, 3JHH ) 7.6, 3JHH ) 7.6, 1H, Ar-H), 7.95 (app t,
3
3JHH ) 7.6, JHH ) 7.6, 2H, Py-H), 8.0-8.1 (m, 4H, Py-H and
3
4
4
Ar-H), 8.19 (dd, JHH ) 7.9, JHH ) 1.7, 2H, Py-H), 8.92 (t, JHH
) 1.7, JHH ) 1.7, 1H, Ar-H). 13C {1H} NMR (75 MHz, CDCl3):
4
δ 25.8 (CH3), 120.1 (Ar or Py), 123.6 (Ar or Py), 125.6 (Ar), 127.8
(Py), 129.5 (Ar), 137.9 (Py), 139.1 (Ar), 153.5 (Py), 156.1 (Py),
200.5 (CdO). IR (cm-1): 2960 (w), 1699 (CdO), 1580 (s), 1443
(m), 1347 (m), 1299 (m), 1235 (m), 1111 (m), 1088 (m), 993 (w),
951 (w), 818 (s), 785 (s), 731 (m). FAB positive mass spectrum
(m/z): 317 [M + H]+. Acc. Mass FAB-MS positive (m/z) required
for (C20H16N2O2H+): 317.12900. Found: 317.12894. mp: 147-
149 °C.
Synthesis of 2,6-{(OdC(Me)C5H3N}2C6H3(OH). 2,6-Dibro-
mophenol (3.00 g, 11.90 mmol), 6-tributylstannyl-2-(2-methyl-1,3-
dioxolan-2-yl)pyridine (11.84 g, 26.19 mmol, 2.2 equiv), tetrakis-
(triphenylphosphine)palladium(0) (1.10 g, 0.95 mmol, 0.08 equiv),
and cuprous bromide (0.27 g, 1.90 mmol, 0.16 equiv) were loaded
in a Schlenk vessel under an atmosphere of nitrogen, and the
contents were stirred in dry toluene (80 mL) for 72 h at 100 °C.
After removal of the solvent under reduced pressure, the resulting
oil was stirred overnight at 60 °C in 4 M HCl (50 mL), cooled to
room temperature, and carefully neutralized by addition of 4 M
NaHCO3. The suspension was extracted with CHCl3 (3 × 40 mL),
and the organic phase was separated, washed with water (3 × 40
mL), a saturated solution of the disodium salt of EDTA (2 × 30
mL), and brine (1 × 50 mL) and dried over magnesium sulfate.
Following filtration, the solvent was removed under reduced
pressure, and the crude product was crystallized from ethanol at
-30 °C. The resulting precipitate was collected by filtration to
afford 2,6-{(OdC(Me)C5H3N}2C6H3(OH) as a yellow solid.
Yield: 57% (2.24 g, 6.78 mmol). 1H NMR (300 MHz, CDCl3): δ
2.81 (s, 6H, CH3), 7.14 (t, 3JHH ) 7.9, 3JHH ) 7.9, 1H, phenol-H),
3
3
CDCl3): δ 1.16 (d, JHH ) 6.8, 12H, CH(CH3)2), 1.17 (d, JHH
)
)
3
6.8, 12H, CH(CH3)2), 2.30 (s, 6H, CH3CdN), 2.76 (sept, JHH
6.8, 4H, CH(CH3)2), 7.0-7.2 (m, 7H, Ar-H and phenol-H), 7.96
3
3
3
(app. t, JHH ) 7.9, JHH ) 7.9, 2H, Py-H), 8.05 (d, JHH ) 7.9,
3
3
2H, phenol-H), 8.22 (d, JHH ) 7.9, 2H, Py-H), 8.33 (d, JHH
)
7.9, 2H, Py-H). 13C{1H} NMR (75 MHz, CDCl3): δ 16.4 (s,
CH3CdN), 21.9 (s, CH3), 22.2 (s, CH3), 27.3 (s, CH), 118.1 (s,
Py), 118.4 (s, Py), 122.0 (s, Ar), 122.6 (s, Ar), 123.1 (s, phenol),
129.4 (s, phenol), 134.7 (s, Py), 136.4 (s, phenol), 145.3 (s, Ar),
153.4 (s, phenol), 154.6 (s, Py), 156.9 (s, Py), 165.0 (s, CdN). IR
(cm-1): 2958 (m), 1637 (m, ν(CdN)), 1590 (m), 1566 (m), 1438
(m), 1361 (m), 1263 (m), 1110 (m), 1041 (w), 796 (w), 784 (s),
760 (s) and 743 (s). ES positive mass spectrum (m/z): 651 [M +
H]+. Acc. Mass FABMS positive spectrum (m/z) required for
(C44H50N4OH+): 651.40630. Found: 651.40629. mp: 266-268
°C.
3
4
7.9-8.1 (m, 6H, Py-H and phenol-H), 8.25 (dd, JHH ) 7.3, JHH
) 2.3, 2H, Py-H). 13C {1H} NMR (75 MHz, CDCl3): δ 26.2 (s,
CH3), 119.4 (s, Py), 119.9 (s, Py), 126.1 (s, phenol), 130.9 (s,
phenol), 137.9 (s, Py), 151.5 (s, phenol), 156.0 (s, Py), 157.9 (s,
Py), 199.1 (s, CdO). IR (cm-1): 1698 (s, ν(CdO)), 1583 (m),
Synthesis of [(L1)M2X4] (1). (a) 1a (M ) Fe, X ) Cl). An oven-
dried Schlenk flask equipped with a magnetic stir bar was evacuated
and backfilled with nitrogen. The flask was charged with anhydrous
FeCl2 (0.040 g, 0.315 mmol) in n-BuOH (10 mL), and the contents
were stirred at 110 °C until the iron salt had completely dissolved.
(29) Tellier, F.; Sauvetre, R.; Normant, J.-F. J. Organomet. Chem. 1985,
292, 2.
9898 Inorganic Chemistry, Vol. 45, No. 24, 2006

Confined M2 Centers on a Bulky Binucleating Support
Table 7. Crystallographic and Data Processing Parameters for L2-H, 1c, 2b, 2c, 2c(NCMe), and 2da
L2-H
1c
2b
formula
M
C44H50N4O
650.88
C44H50Br4N4Ni2‚1.5CH3CN
1133.52
C44H49Cl3N4OCo2‚CH3CN
915.14
cryst size (mm3)
temp (k)
cryst syst
space group
a (Å)
0.23 × 0.20 × 0.12
0.28 × 0.20 × 0.10
0.38 × 0.29 × 0.08
150(2)
150(2)
150(2)
triclinic
P1h
monoclinic
C2/c
43.915(7)
8.3993(14)
26.110(4)
90
90.700(3)
90
9630(3)
triclinic
P1h
9.2269(15)
12.510(2)
16.952(3)
83.535(3)
82.322(4)
70.485(3)
1823.0(5)
2
12.549(5)
13.765(6)
14.456(6)
80.417(7)
77.167(6)
74.026(7)
2325.8(16)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
U (Å3)
Z
8
Dc (Mg m-3
F(000)
)
1.186
700
0.071
13 346
1.564
4568
4.139
36 368
1.307
952
0.924
16 645
µ(Mo KR) (mm-1
)
reflns collected
independent reflns
Rint
6357
0.0809
9476
0.0811
8111
0.2085
restraints/params
final R indices
(I > 2σ(I))
0/452
0/517
0/519
R1 ) 0.0724
wR2 ) 0.1277
R1 ) 0.1516
wR2 ) 0.1531
0.936
R1 ) 0.0508
wR2 ) 0.0854
R1 ) 0.0965
wR2 ) 0.0957
0.897
R1 ) 0.0828,
wR2 ) 0.1821
R1 ) 0.1813
wR2 ) 0.2196
0.912
all data
GOF on F2 (all data)
2c
2c(NCMe)
2d
formula
M
C44H49Br3N4ONi2‚CHCl3
1126.3
C46H52Br3N5ONi2‚3CH3CN‚0.5H2O
C44H49Cl3N4OZn2‚CH3CN
928.02
1180.25
0.33 × 0.24 × 0.18
150(2)
cryst size (mm3)
temp (k)
cryst syst
space group
a (Å)
0.22 × 0.16 × 0.07
0.38 × 0.36 × 0.15
150(2)
150(2)
monoclinic
P21/c
13.6891(19)
34.633(5)
10.2467(14)
90
107.021(3)
90
4645.1(11)
4
triclinic
P1h
triclinic
P1h
13.267(3)
14.100(3)
16.802(4)
65.587(4)
78.435(4)
66.968(4)
2631.1(11)
2
12.1071(19)
13.864(2)
14.704(2)
80.680(3)
76.300(3)
75.191(2)
2304.8(6)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
U (Å3)
Z
Dc (Mg m-3
F(000)
)
1.611
2272
3.602
33 459
1.490
1206
3.039
20 612
1.337
964
1.254
16 837
µ(Mo KR) (mm-1
)
reflns collected
independent reflns
Rint
8165
0.0858
10 213
0.0519
8062
0.0446
restraints/params
final R indices
(I > 2σ(I))
0/533
0/ 618
0/543
R1 ) 0.0525,
wR2 ) 0.0996
R1 ) 0.0913
wR2 ) 0.0996
0.943
R1 ) 0.0465
wR2 ) 0.0916
R1 ) 0.0847
wR2 ) 0.0992
0.890
R1 ) 0.0586
wR2 ) 0.1512
R1 ) 0.0824
wR2 ) 0.1636
1.048
all data
GOF on F2
a Data in common: graphite-monochromated Mo KR radiation, λ ) 0.71073 Å; R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2, w-1
2
2
2
) [σ2(Fo)2 + (aP)2 ], P ) [max(Fo ,0) + 2(Fc )]/3, where a is a constant adjusted by the program; GOF ) [∑(Fo2 - Fc )2/(n - p)]1/2, where n is the number
of reflections and p the number of parameters.
2
2
2
L1 (0.100 g, 0.158 mmol, 0.5 equiv) was added, and the reaction
mixture was stirred at 110 °C for a further 20 min. After it was
cooled to room temperature, the suspension was concentrated, and
hexane was added to induce precipitation of the product. The solid
was filtered, washed with hexane, and dried overnight under reduced
pressure to afford [(L1)Fe2Cl4] (1a) as a brown powder. Yield: 68%
(0.095 g, 0.107 mmol). IR (cm-1): 2965 (w), 1626 (w), 1593 (m,
ν(CdN)imine), 1575 (m), 1455 (m), 1443 (m), 1376 (m), 1321 (w),
1276 (w), 1251 (m), 1190 (m), 1025 (m), 933 (w), 818 (w), 800
(s), 791 (s), 775 (s), 711 (s).
(0.100 g, 0.158 mmol, 0.5 equiv), gave [(L1)Co2Cl4] (1b) as a blue
powder. Yield: 45% (0.063 g, 0.071 mmol). IR (cm-1): 2961 (w),
1622 (w), 1593 (m, ν(CdN)imine), 1565 (w), 1456 (m), 1442 (m),
1386 (w), 1370 (w), 1317 (w), 1255 (m), 1194 (w), 1014 (m), 935
(w), 827 (w), 803 (s), 794 (s), 777 (s), 710 (s).
(c) 1c (M ) Ni, X ) Br). A procedure analogous to that
described for 1a, employing NiBr2 (0.097 g, 0.315 mmol) and L1
(0.100 g, 0.158 mmol, 0.5 equiv), gave [(L1)Ni2Br4] (1c) as a red
powder. Yield: 72% (0.101 g, 0.087 mmol). Red crystals suitable
for X-ray analysis were grown by slow cooling of a hot acetonitrile
solution containing 1c. IR (cm-1): 2963 (m), 1620 (w), 1594 (m,
ν(CdN)imine), 1569 (w), 1456 (m), 1441 (m) 1386 (w), 1371 (w),
(b) 1b (M ) Co, X ) Cl). A procedure analogous to that
described for 1a, employing CoCl2 (0.041 g, 0.315 mmol) and L1
Inorganic Chemistry, Vol. 45, No. 24, 2006 9899

Champouret et al.
3
3
1321 (m), 1254 (m), 1193 (w), 1017 (m), 933 (w), 823 (w), 804
(s), 792 (s), 778 (s), 709 (s).
3.04 (app. sept, JHH ) 6.7, 2H CH(CH3)2), 7.03 (tr, JHH ) 7.8,
3JHH ) 7.8, 1H, phenolate-H), 7.2-7.3 (m, 6H, Ar-H), 7.89 (d,
3JHH ) 7.8, 2H, phenolate-H), 7.89 (d, 3JHH ) 7.4, 2H, Py-H), 8.17
(d) 1d (M ) Zn, X ) Cl). A procedure analogous to that
described for 1a, employing ZnCl2 (0.043 g, 0.315 mmol) and L1
(0.100 g, 0.158 mmol, 0.5 equiv), gave [(L1)Zn2Cl4] (1d) as a
yellow powder. Yield: 55% (0.093 g, 0.087 mmol). 1H NMR (300
3
3
(d, JHH ) 7.4, 2H, Py-H), 8.23 (d, JHH ) 7.8, 2H, Py-H). IR
(cm-1): 2964 (w), 1628 (m), 1588 (s, ν(CdN)imine), 1552 (m), 1448
(s), 1366 (m), 1321 (m), 1254 (m), 1191 (m), 1010 (m), 826 (s),
790 (s), 772 (s), 748 (s).
Synthesis of [(L2)Ni2Br3(NCMe)] [2c(NCMe)]. Complex 2c
(0.030 g, 0.030 mmol) was heated to reflux in acetonitrile (1.5 mL)
until the complex had partially dissolved. The mixture was filtered
through Celite, and the resulting solution was treated with a few
drops of CHCl3 and then left to stand at room temperature for 1
day to give [(L2)Ni2Br3(NCMe)] [2c(NCMe)] as dark red crystals.
The spectroscopic and spectrometric data were similar to those for
2c (see Table 2).
3
MHz, CDCl3): δ 1.01 (d, 12H, JHH ) 6.7, CH(CH3)2), 1.25 (d,
3
12H, JHH ) 6.7, CH(CH3)2), 2.40 (s, 6H, CH3CdN), 2.88 (sept,
4H, 3JHH ) 6.7, CH(CH3)2), 7.1-7.3 (m, 6H, Ar-H), 7.82 (dd, 1H,
3JHH ) 7.6, 3JHH ) 7.9, Ar-H), 8.0-8.1 (m, 4H, Ar-H and Py-H),
3
3
3
8.25 (dd, 2H, JHH ) 7.6, JHH ) 7.9, Py-H), 8.42 (d, 2H, JHH
)
7.9, Py-H), 8.68 (s, 1H, Ar-H). IR (cm-1): 2963 (w), 1632 (w),
1592 (m, ν(CdN)imine), 1562 (w), 1455 (m), 1442 (m) 1385 (w),
1370 (m), 1312 (w), 1254 (s), 1196 (m), 1014 (w), 933 (w), 849
(w), 823 (w), 805 (s), 795 (s), 777 (s), 712 (s).
Synthesis of [(L2)M2(µ-X)X2] (2). (a) 2a (M ) Fe, X ) Cl).
An oven-dried Schlenk flask equipped with a magnetic stir bar was
evacuated and backfilled with nitrogen. The flask was charged with
anhydrous FeCl2 (0.039 g, 0.308 mmol) in n-BuOH (10 mL), and
the contents were heated to 110 °C until the iron salt had completely
dissolved. L2-H (0.100 g, 0.154 mmol, 0.5 equiv) was added, and
the mixture was heated to 110 °C for a further 20 min. After it
was cooled to room temperature, the suspension was concentrated
and washed several times with hexane. The solid was dried
overnight under reduced pressure to afford [(L2)Fe2(µ-Cl)Cl2] (2a)
as a brown dark solid. Yield: 55% (0.093 g, 0.087 mmol). IR
(cm-1): 2964 (m), 1616 (w), 1588 (s, ν(CdN)imine), 1552 (m), 1446
(s), 1366 (m), 1322 (m), 1251 (m), 1194 (m), 1104 (w), 1006 (w),
822 (m), 791 (s), 773 (s), 753 (m).
(b) 2b (M ) Co, X ) Cl). A procedure analogous to that
described for 2a, employing CoCl2 (0.040 g, 0.308 mmol) and L2-H
(0.100 g, 0.154 mmol, 0.5 equiv), gave [(L2)Co2(µ-Cl)Cl2] 2b as a
blue-green solid. Yield: 35% (0.054 g, 0.052 mmol). Blue crystals
suitable for X-ray analysis were grown by slow cooling of a hot
acetonitrile solution containing 2b. IR (cm-1): 2964 (w), 1620 (w),
1586 (s, ν(CdN)imine), 1551 (m), 1476 (w), 1442 (s), 1408 (m),
1365 (m), 1288 (w), 1252 (m), 1191 (m), 1112 (m), 1060 (m),
1011 (m), 854 (m), 826 (m), 790 (s), 757 (s), 738 (m).
(c) 2c (M ) Ni, X ) Br). A procedure analogous to that
described in 2a, employing (DME)NiBr2 (0.094 g, 0.308 mmol)
and L2-H (0.100 g, 0.154 mmol, 0.5 equiv), gave [(L2)Ni2(µ-Br)-
Br2] (2c) as an orange solid. Yield: 55% (0.092 g, 0.085 mmol).
Red crystals suitable for X-ray analysis were grown by layering of
a chloroform solution of the complex with diethyl ether. IR (cm-1):
2963 (w), 1620 (w), 1589 (s, ν(CdN)imine), 1552 (m), 1446 (s),
1417 (m), 1387 (w), 1366 (m), 1324 (w), 1276 (m), 1241 (m), 1195
(m), 1103 (w), 1060 (w), 1021 (m), 858 (m), 823 (m), 784 (s), 774
(s), 740 (s).
Screening for Ethylene Oligomerization. An oven-dried 200
mL Schlenk vessel equipped with magnetic stir bar was evacuated
and backfilled with nitrogen. The vessel was charged with the
precatalyst (0.01 mmol) dissolved in toluene (40 mL), and MAO
was introduced (6.0 mmol, 300 equiv/metal center). After a period
of 5 min, the vessel was purged with ethylene, and the contents
were magnetically stirred under 1 bar of ethylene pressure at room
temperature for the duration of the test. After 0.5 h, the test was
terminated by the addition of dilute aqueous hydrogen chloride (5
mL). The organic phase was separated, dried over magnesium
sulfate, and analyzed by GC. For analysis of the oligomers by NMR
(1H and 13C) spectroscopy, the solvent was removed on the rotary
evaporator, and the residue was dissolved in CDCl3.
Crystallographic Studies. Data collection for L2-H, 1c, 2b, 2c,
2c(NCMe), and 2d was carried out on a Bruker APEX 2000 CCD
diffractometer using graphite-monochromated Mo KR radiation (λ
) 0.71073 Å). Details of the data collection, refinement, and crystal
data are listed in Table 7. The data were corrected for Lorentz and
polarization effects, and empirical absorption corrections were
applied. Structure solution by direct methods and structure refine-
ment on F2 were performed with SHELXTL, version 6.10.30
Hydrogen atoms were included in calculated positions (C-H )
0.96 Å) riding on the bonded atom with isotropic displacement
parameters set to 1.5 Ueq(C) for methyl H atoms and 1.2 Ueq(C)
for all other H atoms. Apart from C40 and C41 (atoms were
disordered and split) in 2b, all non-H atoms were refined with
anisotropic displacement parameters. Graphical representations of
the molecular structures were generated with the program ORTEP.31
Acknowledgment. We thank the University of Leicester
for financial assistance and Johnson Matthey PLC for the
palladium chloride.
(d) 2d (M ) Zn, X ) Cl). A procedure analogous to that
described in 2a, employing ZnCl2 (0.042 g, 0.308 mmol) and L2-H
(0.100 g, 0.154 mmol, 0.5 equiv), gave [(L2)Zn2(µ-Cl)Cl2] (2d) as
a yellow solid. Yield: 50% (0.068 g, 0.077 mmol). Yellow crystals
suitable for X-ray analysis were grown by slow cooling of a hot
acetonitrile-chloroform solution containing 2d. 1H NMR (300
MHz, CD2Cl2, 300 K): δ 0.98 (br, 18H, CH(CH3)2), 1.20 (br, 6H,
CH(CH3)2), 2.34 (s, 6H, CH3CdN), 2.87 (br, 2H, CH(CH3)2), 3.05
(br, 2H, CH(CH3)2), 6.87 (tr, 3JHH ) 8.2, 3JHH ) 8.2, 1H, phenolate-
Supporting Information Available: CIF files containing all
crystallographic data for L2-H, 1c, 2b, 2c, 2c(NCMe), and 2d. This
material is available free of charge via the Internet at http://
pubs.acs.org. The CIF files have also been deposited at the
Cambridge Crystallographic Data Centre with reference numbers
614439-614444. Copies of the data can be obtained free of charge
on application to the CCDC, 12 Union Road, Cambridge CB21EZ,
U.K. (fax +44 1223 336033; e-mail deposit@ccdc.cam.ac.uk).
3
H), 7.1-7.3 (m, 6H, Ar-H), 7.76 (d, JHH ) 7.8, 2H, phenolate-
IC061286X
H), 7.92 (dd, 3JHH ) 7.0, 4JHH ) 1.9, 2H, Py-H), 7.9-8.1 (m, 4H,
1
3
Py-H). H NMR (300 MHz, CD2Cl2, 230 K): δ 0.93 (d, JHH
)
(30) Sheldrick, G. M. SHELXTL, version 6.10; Bruker AXS, Inc.: Madison,
WI, 2000.
(31) ORTEP 3 for Windows, version 1.074; Farrugia, L. J. J. Appl.
Crystallogr. 1997, 30, 565.
6.7, 6H, CH(CH3)2), 0.96 (d, 3JHH ) 6.7, 6H, CH(CH3)2), 1.00 (d,
3JHH ) 6.7, 6H, CH(CH3)2), 1.19 (d, JHH ) 6.7, 6H, CH(CH3)2),
3
2.37 (s, 6H, CH3CdN), 2.77 (app. sept, 3JHH ) 6.7, 2H, CH(CH3)2),
9900 Inorganic Chemistry, Vol. 45, No. 24, 2006