Stepwise synthesis, structures, and reactivity of mono-, di-, and trimetallic metal complexes with a 6π + 6π quinonoid zwitterion

Article abstract of DOI:10.1021/ic049263a

The benzoquinonemonoimine N,N′-dineopentyl-2-amino-5-alcoholate-1,4- benzoquinonemonoiminium [C₆H₂(-^..NHCH ₂t-Bu)₂(-^..O)₂] 6, which is a rare example of an organic zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6π electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the π-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N-H function, and the isolated sodium salt 9, which is stable under N₂, reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh₃)] or trans-[NiCl(Ph)(PPh ₃)₂], to afford the monometallic complexes 10-15 in which the π-system is localized. A second in situ deprotonation of the remaining N-H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(μ-Cl)] ₂ (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in which the π-system of the quinonoid ligand is delocalized between the two metal centers. Deprotonation of both N-H amino functions of the square-planar complex trans-[Ni(N,O)₂] 15 with NaH and reaction with [Pd(8-mq)(μ-Cl)]₂ affords the heterotrimetallic (Pd, Ni, Pd) complex 18 in which the π-system of the two quinonoid ligands is delocalized between the three metal centers. The crystal structures of the monometallic complexes 10 and 13 and of the dipalladium complex 17 are reported and consequences of metal coordination discussed. Complex 15 was tested in catalytic ethylene oligomerization with AlEtCl₂ as cocatalyst.

Full text of DOI:10.1021/ic049263a

Inorg. Chem. 2004, 43, 6944−6953
Stepwise Synthesis, Structures, and Reactivity of Mono-, Di-, and
Trimetallic Metal Complexes with a 6π +
Quinonoid Zwitterion†
6π
Jean-philippe Taquet,‡ Olivier Siri,‡ Pierre Braunstein,*,‡ and Richard Welter§
Laboratoire de Chimie de Coordination and Laboratoire DECMET, UMR 7513 CNRS,
UniVersite´ Louis Pasteur, 4, rue Blaise Pascal, F-67070 Strasbourg Cedex, France
Received June 7, 2004
The benzoquinonemonoimine N,N
Bu)2( O)2] 6, which is a rare example of an organic zwitterion being more stable than its canonical form, is best
described as constituted of two chemically connected but electronically not conjugated 6 electron subunits. The
two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of
the -system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one
H function, and the isolated sodium salt 9, which is stable under N2, reacts with chloride-bridged Pd(II)
homodimetallic complexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2], to afford the monometallic complexes 10 15 in
which the -system is localized. A second in situ deprotonation of the remaining N H amino function of 10 with
NaH followed by reaction with [Pd(8-mq)( -Cl)]2 (8-mq orthometalated 8-methylquinoline) affords the homodimetallic
complex 17 in which the -system of the quinonoid ligand is delocalized between the two metal centers. Deprotonation
of both N H amino functions of the square-planar complex trans-[Ni(N,O)2] 15 with NaH and reaction with [Pd-
(8-mq)( -Cl)]2 affords the heterotrimetallic (Pd, Ni, Pd) complex 18 in which the -system of the two quinonoid
′-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2(-NHCH2t-
-
π
π
N
−
−
π
−
µ
)
π
−
µ
π
ligands is delocalized between the three metal centers. The crystal structures of the monometallic complexes 10
and 13 and of the dipalladium complex 17 are reported and consequences of metal coordination discussed. Complex
15 was tested in catalytic ethylene oligomerization with AlEtCl2 as cocatalyst.
Introduction
very few examples of mono- or polynuclear metal complexes
based on N,O ligands supported by a quinonoid core have
The past few years have witnessed a phenomenal growth
in research activity on chelating N,O ligands, in particular
for the preparation of highly active nickel and palladium
catalysts for olefin polymerization, copolymerization, and
oligomerization,1-14 but also for the synthesis of porphyrin
dimers and oligomers connected by metal ions.15 In contrast,
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Grubbs, R. H. Chem. Commun. 2003, 2272-2273. (b) Connor, E. F.;
Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts,
W. P.; Litzau, J. J. J. Polym. Sci., Part A: Polym. Chem. 2002, 40,
2842-2854. (c) Younkin, T. R.; Connor, E. F.; Henderson, J. I.;
Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 288,
1750-1751. (d) Younkin, T. R.; Connor, E. F.; Henderson, J. I.;
Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287,
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A. M.; Sbrana, G. Appl. Catal., A 2002, 231, 307-320.
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1576. (b) Zhang, D.; Jin, G.-X.; Hu, N. Chem. Commun. 2002, 574-
575.
* Author to whom correspondence should be addressed. E-mail: braunst@
chimie.u-strasbg.fr.
† Dedicated to Prof. J. J. Ziolkowski on the occasion of his 70th birthday,
with our warmest congratulations.
‡ Laboratoire de Chimie de Coordination.
§ Laboratoire DECMET (X-ray diffraction studies).
(1) Qian, Y.; Zhao, W.; Huang, J. Inorg. Chem. Commun. 2004, 7, 459-
461.
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X. J. Organomet. Chem. 2004, 689, 917-929. (b) Sun, W.-H.; Yang,
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6944 Inorganic Chemistry, Vol. 43, No. 22, 2004
10.1021/ic049263a CCC: $27.50
© 2004 American Chemical Society
Published on Web 10/05/2004

Metal Complexes with a 6π + 6π Quinonoid Zwitterion
Scheme 1. Synthesis of Zwitterion 6 as Reported in 200320a
Scheme 2. Reaction of 6 with [Pd(acac)2]
been reported in the literature.16-18 Furthermore, to the best
of our knowledge, only one example of N,O,N,O benzo-
quinone ligand has been reported, very recently, for the
preparation of catalytically active metal complexes.19 The
authors prepared and characterized a series of 2,5-disubsti-
tuted amino-p-benzoquinone ligands 1 and used their di-
metallic Ni(II) complexes of type 2 as single-component
catalysts in ethylene polymerization. Despite the lack of
X-ray quality crystals, the very wide molecular weight
distribution of the polyethylene formed during the reaction
was explained by electronic cooperative interactions between
their Ni(II) centers.19
in view of its potential in coordination and organometallic
chemistry. It could, for example, allow the stepwise synthesis
of mono- and dimetallic complexes, and the elaboration of
linear metallic chains.
We recently developed a versatile access to a structural
isomer of this molecule from the commercially available
diaminoresorcinol 4‚2HCl which was reacted with t-BuC-
(O)Cl in wet CH3CN and excess NEt3 to afford 5 (Scheme
1). Reduction of 5 and aerobic workup led to intermediate 3
which rearranges, by proton migration from the oxygen atom
to the more basic nitrogen site, to the zwitterionic quinone-
monoimine 6 (Scheme 1).20
The zwitterion 6 is a planar and potentially antiaromatic
12π electron system,20a constituted by two conjugated and
fully delocalized 6π electron subunits which are connected
by two C-C single bonds. We have previously shown that
it is possible to deprotonate selectively one N-H function
by reaction with [M(acac)2] (M ) Ni, Pd, Cu, or Zn) and
obtain monometallic complexes, such as 8, in which the
π-system is localized. This was confirmed by the X-ray
structure analysis of the intermediate Pd(II) complex 7 which
was obtained by reaction of 6 with [Pd(acac)2] (Scheme 2).20a
As part of our current interest in the coordination chemistry
of multifunctionnal quinonoid ligands, we describe here how
metallation by successive deprotonation of the two N-H
functions leads in the metal complexes to different electronic
distributions of the 6π + 6π system of 6. In this paper, we
describe mono-, di-, and trimetallic complexes in which the
π-system of the quinone is localized or fully delocalized
between two or three metal centers.
Sequential monodeprotonation/metallation of 1 was not
possible and its first metal complex, 2, which is a centrosym-
metric molecule, was obtained by double deprotonation in a
one-pot reaction. Therefore, a molecule such as 2-amino-5-
hydroxy-p-benzoquinonemonoimine 3, which is closely
related to 1 but with the advantage of possessing two
different N,O chelation sites, would be of particular interest
(14) Speiser, F.; Braunstein, P.; Saussine, L. Inorg. Chem. 2004, 43, 4234-
4240.
(15) (a) Richeter, S.; Jeandon, C.; Sauber, C.; Gisselbrecht, J.-P.; Ruppert,
R.; Callot, H. J. J. Porphyrins Phthalocyanines 2002, 6, 423-430.
(b) Richeter, S.; Jeandon, C.; Ruppert, R.; Callot, H. J. Chem. Commun.
2002, 266-267. (c) Richeter, S.; Jeandon, C.; Gisselbrecht, J.-P.;
Ruppert, R.; Callot, H. J. J. Am. Chem. Soc. 2002, 124, 6168-6179.
(d) Richeter, S.; Jeandon, C.; Ruppert, R.; Callot, H. J. Chem. Commun.
2001, 91-92.
(16) Moriuchi, T.; Watanabe, T.; Ikeda, I.; Ogawa, A.; Hirao, T. Eur. J.
Inorg. Chem. 2001, 277-287.
(17) Elduque, A.; Aguilera, F.; Lahoz, F. J.; Lopez, J. A.; Oro, L. A.;
Pinillos, M. T. Inorg. Chim. Acta 1998, 274, 15-23.
(18) Ku¨hlwein, F.; Polborn, K.; Beck, W. Z. Anorg. Allg. Chem. 1997,
623, 1931-1944.
(20) (a) Braunstein, P.; Siri, O.; Taquet, J.-p.; Rohmer, M.-M.; Be´nard,
M.; Welter, R. J. Am. Chem. Soc. 2003, 125, 12246-12256. (b) Siri,
O.; Braunstein, P. Chem. Commun. 2002, 208-209.
(19) Zhang, D.; Jin, G.-X. Organometallics 2003, 22, 2851-2854.
Inorganic Chemistry, Vol. 43, No. 22, 2004 6945

Taquet et al.
Scheme 3. Reaction of 6 with NaOt-Bu
Scheme 4. Reaction of 9 with Chloride-Bridged Pd(II)
Homodimetallic Complexes and with [AuCl(PPh3)]
Results and Discussion
Monometallic Complexes. Monodeprotonation of 6 with
one equiv of NaOt-Bu, in THF at room temperature, yielded
the corresponding benzoquinonemonoimine sodium enolate
9 as an orange powder which was characterized, except by
X-ray crystallography (Scheme 3). Its poor solubility in THF
or DMSO suggests a polymeric structure.21
The 1H NMR data of 9 revealed the presence of two t-Bu
groups and two CH2 signals (δ ) 2.81 and 3.11), consistent
with a lower molecular symmetry than that in 6.20b Only one
N-H signal is observed at δ ) 6.08 for the aminic proton.
Furthermore, the 13C{1H} NMR spectrum contains two
signals at δ ) 161.54 and 180.23 which are consistent with
a localized π-system (δ(C-O) and δ(CdO), respectively),
in contrast to 6 for which the negative charge is delocalized
between the two oxygen atoms (δ(C-O) ) 172.13).20b
The isolated sodium salt 9, which is stable in the solid
state under N2 for weeks, was reacted with chloride-bridged
dimetallic Pd(II) complexes and with [AuCl(PPh3)] to afford
complexes 10-14 in good yields, as a result of chloride
substitution (Scheme 4). Complex 10 could also be obtained
directly from the zwitterion 6 by reaction with 0.5 equiv of
[Pd(8-mq)(µ-OAc)]2 (8-mq ) orthometalated 8-methylquin-
oline) in refluxing THF (see Experimental Section, Procedure
B), in a manner similar to the synthesis of 7.20a For these
five complexes, formation of a σ-bond between the oxygen
and the metal center and of a dative bond between the
nitrogen and the metal center has occurred, in accordance
with the structures of related compounds.20a
N-C bond at low temperature. Furthermore, a through-space
interaction between a Pd-N-CH2 proton and the olefinic
NdC-C-H proton was detected by NOE in these com-
plexes and further shown by a H-H ROESY experiment at
-20 °C in the case of 10. In the case of 13, a 1H{31P} NMR
spectrum at 213 K allowed analysis of the Pd-N-CH2 signal
as an ABX system (X ) P) with 4JPH coupling constants of
8.8 and 3.2 Hz.
Compounds 10 and 13 were isolated as red crystalline
solids from solutions of CH2Cl2/n-hexane and analyzed by
X-ray diffraction. Their structures are shown in Figures 1
and 2, respectively. Crystallographic data, and selected bond
lengths and angles are reported in Tables 1-3. The coordi-
nation geometry around the palladium center in 10 is square-
In the case of 10, 11, and 13, only one isomer was
1
observed by H and 13C NMR spectroscopy. In all Pd(II)
1
complexes, the H NMR data revealed the presence of two
singlets for the chemically different neopentyl CH3 protons.
Only one N-H signal is observed in the range δ ) 6.34-
6.56 which is consistent with an aminic proton. A fluxional
behavior of the Pd-N-CH2 protons of 10, 11, and 13 was
observed in the 1H NMR spectrum, since their signal appears
as a very broad singlet at room temperature and becomes an
AB system below coalescence temperature (2JAB = 12 Hz).
The ∆G* values calculated for this dynamic behavior are
54.7 ( 0.5, 58.8 ( 0.5, and 50.6 ( 0.5 kJ/mol, respectively.
This phenomenon could be explained by steric interactions
between these protons and the CH2 protons of the 8-meth-
ylquinoline group in 10, the ortho C-H proton of the
aromatic cycle of the orthometalated N,N-dimethylbenzyl-
amine (dmba) group in 11, or the chloride atom in 13, which
hinder the free rotation of the neopentyl group around the
Figure 1. ORTEP view of 10. The unit cell is constituted by two
independent but very similar molecules. The aromatic and CH3 protons have
been omitted for clarity. Thermal ellipsoids enclose 50% of the electron
density.
(21) Preliminary X-ray diffraction data on 9 indicated a polymeric structure,
however the poor quality of the crystals precluded refinement of the
structure.
6946 Inorganic Chemistry, Vol. 43, No. 22, 2004

Metal Complexes with a 6π + 6π Quinonoid Zwitterion
Table 1. Crystal Data and Details of the Structure Determination for Compounds 10, 13, and 17‚2C4H8O
crystal data
10
13
17‚2C4H8O
formula
C26H33N3O2Pd
525.95
monoclinic
P21/c
18.708(5)
13.535(5)
19.687(5)
95.710(5)
4960(3)
C34H40ClN2O2PPd
681.50
orthorombic
P21 2121
12.8590(10)
10.5290(10)
24.102(2)
90
3263.2(5)
4
C36H40N4O2Pd2‚2(C4H8O)
917.73
monoclinic
C2/c
15.612(2)
12.394(2)
22.147(2)
107.84(5)
4079.0(9)
4
formula weight (g‚mol-1
)
crystal system
space group
a [Å]
b [Å]
c [Å]
â [deg]
V [Å3]
Z
8
density (calc) [g‚cm-3
]
1.409
0.775
2176
1.387
0.732
1408
1.494
0.929
1888
µ(Mo KR) [mm-1
F(000)
]
temperature (K)
θ min-max [deg]
data set [h; k; l]
173
1.1, 30.0
173
1.7, 27.0
173
1.9, 30.0
-11/26; -16/18; -27/23
27159, 14221, 0.050
9508
14221, 577
0.0640, 0.1434, 1.11
-15/16; -13/12; -22/30
23770, 7078, 0.075
5419
7078, 370
0.0476, 0.1136, 1.05
0/21; 0/17; -31/29
5936, 5936, 0.000
4274
5936, 245
0.0456, 0.1384, 1.08
tot., unique data, R(int)
observed data [I > 2σ(I)]
No. reflns, No. params
R, wR2, GOF
Table 2. Comparison of Selected Interatomic Distances (Å) in 6,20 One
of the Two Molecules of 10, 13, and 17·2C4H8O
Table 3. Selected Bond Angles (deg) in One of the Two Molecules of
10, 13, and 17·2C4H8O
6
10
13
17‚2C4H8O
10
13
17‚2C4H8O
C(1)-C(2)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(2)-O(1)
C(3)-N(1)
C(5)-N(2)
C(6)-O(2)
Pd-O(1)
Pd-N(1)
Pd-C(17)
Pd-N(3)
Pd-Cl
1.379(5)
1.399(5)
1.516(5)
1.393(5)
1.389(5)
1.523(5)
1.265(4)
1.323(5)
1.320(5)
1.254(4)
1.369(5)
1.402(5)
1.521(5)
1.415(5)
1.362(5)
1.519(5)
1.279(4)
1.307(4)
1.337(5)
1.242(4)
2.107(3)
2.028(3)
2.014(4)
2.009(3)
1.363(7)
1.413(7)
1.507(7)
1.431(7)
1.357(7)
1.517(7)
1.316(6)
1.313(6)
1.331(6)
1.247(6)
2.012(3)
2.080(4)
1.387(4)
O(1)-Pd-N(1)
O(1)-Pd-C(17)
O(1)-Pd-N(3)
N(1)-Pd-C(17)
N(1)-Pd-N(3)
C(17)-Pd-N(3)
O(1)-Pd-Cl
79.75(11)
174.61(13)
97.61(11)
99.48(14)
177.04(11)
83.03(14)
80.34(15)
79.79(11)
1.517(4)
1.396(4)
1.267(4)
1.337(4)
177.58(10)
95.12(10)
97.61(12)
174.59(12)
86.99(5)
O(1)-Pd-P
N(1)-Pd-Cl
N(1)-Pd-P
2.110(2)
2.023(3)
Cl-Pd-P
O(1)-Pd-C(10)
O(1)-Pd-N(2)
N(1)-Pd-C(10)
N(1)-Pd-N(2)
C(10)-Pd-N(2)
178.37(13)
97.70(13)
99.42(14)
177.03(13)
83.05(15)
2.2843(13)
2.2465(14)
Pd-P
Pd-C(10)
Pd-N(2)
2.018(4)
2.006(3)
reported for other complexes containing this ligand.22
Furthermore, the proximity between the Pd-N-CH2 protons
and the 8-mq CH2 protons is evidenced by a distance of 2.288
Å, and the interaction between a proton at C(12) and the
olefinic NdC-C(4)-H proton is evidenced by a distance
of 2.020 Å.
planar, with a trans arrangement of the two N atoms.
Chelation of the Pd center by the 8-methylquinoline ligand
is reflected in the Pd-N(3) and Pd-C(17) distances of
2.009(3) and 2.014(4) Å, respectively, and in the N(3)-Pd-
C(17) angle of 83.03(14)°. These values are similar to those
Complex 13 has a P trans to N arrangement, which is
consistent with the vast majority of structurally characterized
square-planar Pd(II) complexes with PR3, halide, and a N,O
chelating ligand.18,23 Like that in 10, the C(12)-C(13) bond
is almost perpendicular to the metal coordination plane. There
are short intramolecular distances between Cl or C(4)H
proton and the C(12)H2 protons of 2.724 and 2.140 Å,
respectively.
In both complexes 10 and 13, examination of the respec-
tive bond distances within the O(1)-C(2)-C(1)-C(6)-O(2)
(22) (a) Andrieu, J.; Braunstein, P.; Tiripicchio, A.; Ugozzoli, F. Inorg.
Chem. 1996, 35, 5975-5985. (b) Braunstein, P.; Fischer, J.; Matt,
D.; Pfeffer, M. J. Am. Chem. Soc. 1984, 106, 410-421. (c) Braunstein,
P.; Matt, D.; Dusausoy, Y.; Fischer, J.; Mitschler, A.; Ricard, L. J.
Am. Chem. Soc. 1981, 103, 5115-5125.
(23) (a) Koch, D.; Polborn, K.; Su¨nkel, K.; Beck, W. Inorg. Chim. Acta
2002, 334, 365-370. (b) Gomez-Simon, M.; Jansat, S.; Muller, G.;
Panyella, D.; Font-Bardia, M.; Solans, X. Dalton Trans. 1997, 3755-
3764.
Figure 2. ORTEP view of 13. The phenyl groups on the phosphorus atom,
except the ipso carbons, and the CH3 protons have been omitted for clarity.
Thermal ellipsoids enclose 50% of the electron density.
Inorganic Chemistry, Vol. 43, No. 22, 2004 6947

Taquet et al.
Scheme 5. Reaction of 9 with trans-[NiCl(Ph)(PPh3)2]
and N(1)-C(3)-C(4)-C(5)-N(2) moieties reveals an al-
ternation of single and double bonds,24 which is consistent
with two conjugated but localized π-systems (Table 2). This
result is in agreement with the localization of the π-system
found in 7, whereas 6 presents a perfect bonds equalization.20
As in all previously described related crystallographic
structures,20 the C(2)-C(3) and C(6)-C(5) distances around
1.52 Å correspond to single bonds and indicate the lack of
conjugation between the two 6π subunits. From these
observations, we can draw a more general conclusion: when
reactions with 6 result in monodeprotonation, leading to
monometallic complexes, the π-system becomes more local-
ized.
The reaction did not lead to the desired product 16 but
instead to the quantitative formation, even at low temperature
(-10 °C), of the bis(benzoquinonemonoimine) Ni(II) com-
plex 15 (Scheme 5). This complex has previously been
prepared by reaction of the zwitterion 6 with 0.5 equiv of
[Ni(acac)2].20a
Complex 15 appears to be thermodynamically favored, as
also indicated by the lack of transmetallation reaction when
15 was reacted with [PdCl2(SEt)2]. Formation of the bis-
N,O chelate results in the loss of a phenyl ligand, which is
surprising in view of the strong covalent Ni-C bond, but
this sort of reactivity has already been noted in related
systems.1,7a,25,26
Despite numerous reports on the synthesis and structural
properties of bis-N,O type complexes, relatively few studies
have been performed on their catalytic behavior; an example
is shown below.8,11 Such Ni(II) complexes can be activated
with a Lewis acid cocatalyst, which displaces one of the N,O
chelates and generates the active species.8,11
Compound 14 is the first example of a monometallic gold
complex obtained from 6. In comparison with Pd(II)
complexes, the aminic N-H signal is downfield shifted to
δ ) 7.06. We can suspect a tricoordination of the Au(I)
center, as drawn in Scheme 4, rather than binding solely
through the oxygen atom, owing to the presence of the CdN
vibration at 1580 cm-1 in the IR spectrum in CH2Cl2 which
is very similar to that of 13 at 1588 cm-1. Nevertheless,
without X-ray analysis, a linear two-coordination around Au
cannot be completely ruled out. In particular, the zwitterionic
structure drawn below, based on the isolobal analogy H+
¶ (Ph3P)Au+, is conceivable on the basis of the 13C{1H}
NMR data for the C-O resonance. We have noticed a higher
instability of 14 in solution compared to the Pd(II) com-
plexes.
As part of our interest for new ethylene oligomerization
Ni(II) catalysts,14,27 we have evaluated complex 15 for this
reaction with the aim of producing short chain oligomers in
the presence of only small quantities of alkylaluminum
cocatalyst. AlRCl2 compounds are used in the IFP Dimersol
process where in situ formation of a Ni-alkyl complex leads
to the active Ni-hydride species after â-elimination. The
Catalytic Ethylene Oligomerization with a Mono-
metallic Ni(II) Complex. By analogy with recent single-
component olefin polymerization and oligomerization cata-
lysts containing a monoanionic N,O ligand,1,2,3b,6,7,9,10,12,14,19
we have attempted the reaction of 9 with trans-[NiCl(Ph)-
(PPh3)2].
(24) van Bolhuis, F.; Kiers, C. Th. Acta Crystallogr., Sect. B: Struct. Sci.
1978, 34, 1015-1016.
(25) Klein, H.-F.; Bickelhaupt, A. Inorg. Chim. Acta 1996, 248, 111-
114.
(26) Klabunde, U.; Ittel, S. D. J. Mol. Catal. A: Chem. 1987, 41, 123-
134.
(27) (a) Speiser, F.; Braunstein, P.; Saussine, L. Dalton Trans. 2004, 10,
1539-1545. (b) Speiser, F.; Braunstein, P.; Saussine, L. Organome-
tallics 2004, 23, 2633-2640. (c) Speiser, F.; Braunstein, P.; Saussine,
L. Organometallics 2004, 23, 2625-2632. (d) Speiser, F.; Braunstein,
P.; Saussine, L.; Welter, R. Organometallics 2004, 23, 2613-2624.
(e) Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R. Inorg. Chem.
2004, 43, 1649-1658. (f) Pietsch, J.; Braunstein, P.; Chauvin, Y. New
J. Chem. 1998, 467-472. (g) Braunstein, P.; Pietsch, J.; Chauvin, Y.;
Mercier, S.; Saussine, L.; DeCian, A.; Fischer, J. J. Chem. Soc., Dalton
Trans. 1996, 3571-3574. (h) Braunstein, P.; Chauvin, Y.; Mercier,
S.; Saussine, L.; DeCian, A.; Fischer, J. J. Chem. Soc., Chem. Commun.
1994, 2203-2204.
6948 Inorganic Chemistry, Vol. 43, No. 22, 2004

Metal Complexes with a 6π + 6π Quinonoid Zwitterion
Scheme 6. In Situ Deprotonation of 10 and Reaction with
[Pd(8-mq)(µ-Cl)]2
Table 4. Oligomerization of Ethylene with 15 and AlEtCl2 as
Cocatalyst and Comparison with [NiCl2(PCy3)2]a
15
15
10
NiCl2(PCy3)2
AlEtCl2 (equiv)
6
6
selectivity C4 (mass %)
selectivity C6 (mass %)
selectivity C8 (mass %)
productivity (g C2H4/g Ni‚h)
TOF (mol C2H4/mol Ni‚h)
R-olefin (C4) (mol %)
linear C6 (mass %)
49
45
6
13 500
28 500
14
51
0.6
51
43
6
21 500
45 000
7
45
0.57
86
14
traces
13 000
27 000
9
b
kR
0.13
a Conditions: 10 bar C2H4, 35 min, T ) 30 °C, 4 × 10-2 mmol Ni
complex, solvent 15 mL of toluene. b kR ) mol C6/ mol C4.
activity and selectivity of 15 were compared to those of
[NiCl2(PCy3)2], a typical catalyst for the Ni-catalyzed dimer-
ization of R-olefins.28 All selectivities reported in the
following refer to the total amount of products formed in
each catalytic test. In all cases, ethylene pressurization
resulted in a rapid exothermic event, indicative of very short
induction periods.
In preliminary experiments, we attempted to isolate the
sodium salt resulting from deprotonation of 10 with NaH,
but only 10 was recovered owing to the high moisture
sensitivity of the metalloligand salt which undergoes repro-
tonation. This observation is consistent with related studies
on the synthesis of complexes with anilinoperinaphthenone9b
or anilinoanthraquinone ligands.18 Therefore, we favored an
in situ method for the preparation of polymetallic complexes.
Deprotonation of 10 with excess NaH in refluxing THF was
directly followed by addition of solid [Pd(8-mq)(µ-Cl)]2
(Scheme 6).
Compound 15 was completely inactive when less than 6
equiv of AlEtCl2 was added. However, turnover frequencies
of 28 500 and 45 000 mol C2H4/mol Ni‚h were obtained in
the presence of 6 or 10 equiv of cocatalyst, respectively,
compared to 27 000 mol C2H4/mol Ni‚h for [NiCl2(PCy3)2]
(Table 4). The main products were C4 and C6 oligomers in
comparable quantities, independently of the Al/Ni ratio. Only
small quantities of octenes and no long-chain oligomers were
observed, which indicates that chain transfer is much faster
than chain propagation. Favored by the relatively low-
pressure of ethylene, the branched fraction of the C6
oligomers (linear C6 includes 1,5-butadiene, hex-1-ene, hex-
2-ene, and hex-3-ene) produced by insertion of butenes in
the Ni-C bond of the active species formed after the first
ethylene insertion in the catalytic ethylene oligomerization
process (C4 + C2, consecutive reaction), was significant
(around 50%). A selectivity for 1-butene within the C4
fraction of only 14% was observed with 6 equiv of AlEtCl2
and an increase in the amount of cocatalyst resulted in its
decrease together with a slight decrease of the C6 linear
fraction.
Di- and Trimetallic Complexes. The use of metallo-
ligands for the stepwise synthesis of polymetallic compounds
is gaining increasing importance in organometallic chemistry.
Much effort has been made to find binucleating ligands, with
different reactivities of the chelating sites, suitable for
successive coordination of metal ions.29,30 The presence of
a free amino N-H function in all the monometallic
complexes suggests that it should be possible, by convergent
or divergent strategy, to obtain homo- and heteropolymetallic
complexes likely to display electronic interaction between
the two metal centers through the benzoquinonemonoimine
bridge.
The excess NaH in the reaction mixture does not react
with either the Pd precursor or the final product and can be
filtered through Celite before product isolation. The dime-
tallic complex 17 was obtained as a green powder in good
1
yield after recrystallization. Examination of its H and 13C-
{1H} NMR spectra revealed the presence of only one signal
for the two Np groups and one signal for the CH2 protons
of the two 8-methylquinoline groups, which is consistent with
a higher molecular symmetry than in 10, a symmetry axis
passing now through the two H-C-C carbon atoms. The
signals at 165.62 and 188.52 in the 13C{1H} NMR spectrum,
(δ(C-N) and δ(C-O), respectively), are consistent with a
delocalized π-system, as in 6. Surprisingly, the olefinic
N-C-C-H proton appears in the 1H NMR spectrum as a
broad singlet, and the corresponding HsC-C resonance in
the 13C{1H} NMR spectrum can only be observed when
increasing the pulse delay to 2 s at room temperature. By
analogy with the situation described above for 10, the Pd-
N-CH2 protons undergo fluxional behavior owing to
hindered rotation of the neopentyl group around the N-C
bond. The ∆G* value calculated for this dynamic behavior
is 54.3 ( 0.5 kJ/mol, which is nearly the same as that in 10
which presents a similar steric crowding. A through-space
interaction between a Pd-N-CH2 proton and the olefinic
N-C-C-H proton was detected by NOE, and further
shown by a H-H ROESY experiment at -20 °C.
Compound 17‚2THF could be isolated as a green crystal-
line solid by slow evaporation of a THF solution and
analyzed by X-ray crystallography. Its structure is shown in
Figure 3 and crystallographic data, and selected bond lengths
(28) Commereuc, D.; Chauvin, Y.; Le´ger, G.; Gaillard, J. ReV. Inst. Fr.
Pe´t. 1982, 37, 639-649.
(29) Gavrilova, A. L.; Bosnich, B. Chem. ReV. 2004, 104, 349-383.
(30) Kahn, O. AdV. Inorg. Chem. 1995, 43, 179-259.
Inorganic Chemistry, Vol. 43, No. 22, 2004 6949

Taquet et al.
Figure 3. ORTEP view of 17 in 17‚2THF. The aromatic and CH3 protons have been omitted for clarity. Thermal ellipsoids enclose 50% of the electron
density.
Scheme 7. In Situ Deprotonation of 10 and Reaction with [NiCl2(DME)]
and angles are reported in Tables 1-3. This complex appears
to be the first crystallographically characterized dimetallic
complex with a N2O2 benzoquinone type ligand set.
There is a crystallographically imposed C2 symmetry axis
passing through C(1) and C(4). The N donor atoms N(1)
and N(2) are in a mutual trans arrangement. The C(2)-C(3)
distance of 1.517(4) Å corresponds to a single bond and
indicates the lack of conjugation between the two π-systems.
In contrast, the other C-C distances within the O-C(2)-
C(1)-C(2′)-O′ and N(1)-C(3)-C(4)-C(3′)-N(1′) moi-
eties reveal a remarkable bond equalization. Therefore,
deprotonation of the N-H amino function of 10, a molecule
with a localized π-electron system, and metallation led to
a homodimetallic complex, 17, in which the π-system of the
quinonoid ligand becomes delocalized between the two Pd
centers.
complex 17 in 50% yield and the bis-chelate 15 in 25% yield.
Their formation results from a transmetallation reaction. A
related result was obtained by in situ deprotonation of 10
and reaction with [PdCl2(SEt)2], which afforded 8 and 17.
This undesired reaction was circumvented in the case of
15 by using a divergent strategy. In situ double deprotonation
of the N-H amino functions of 15 with NaH, in a large
volume of THF because of the poor solubility of the bis-
chelate complex, followed by reaction with [Pd(8-mq)(µ-
Cl)]2 led to the formation of the heterotrimetallic NiPd2
complex 18 (Scheme 8). To prepare the related homotri-
metallic Pd3 complex, we have used 8 instead of 15 under
similar conditions, but only the zwitterion 6 and Pd(0) were
obtained after workup, consistent with decomposition of the
bis sodium salt of 8 in refluxing THF. We have then
attempted to deprotonate 8 at room temperature, which was
successful with a rapid color change from black-red to green
and gaseous release, but after subsequent reaction with [Pd-
(8-mq)(µ-Cl)]2, only decomposition was observed, confirm-
ing the instability of the bis sodium salt of 8.
Following the successful synthesis of 17, based on a
convergent strategy from a monometallic complex, we have
attempted to synthesize a trimetallic complex by in situ
deprotonation of 10 with excess NaH in refluxing THF
followed by reaction with 0.5 equiv of [NiCl2(DME)]
(Scheme 7).
Complex 18 was isolated as black-violet powder in good
yield after recrystallization. It is stable in the solid state but
decomposes in solution in air to reform the monometallic
Pd complex 10 after loss of the nickel and reprotonation.
Surprisingly, this reaction did not lead to the heterotri-
metallic compound 18, but rather to the homodimetallic
6950 Inorganic Chemistry, Vol. 43, No. 22, 2004

Metal Complexes with a 6π + 6π Quinonoid Zwitterion
Scheme 8. In Situ Deprotonation and Reaction of 15 with [Pd(8-mq)(µ-Cl)]2
We could not obtain crystals suitable for X-ray diffraction,
but examination of the 1H and 13C{1H} NMR spectroscopic
data revealed a high molecular symmetry with only one
signal for the two Pd-N-Np groups and one signal for the
two Ni-N-Np groups. As in 17, the CH2 protons of the
two 8-methylquinoline groups, the two N-C-C-H and
the two O-C-C-H protons give rise to only one signal.
The four signals at δ 162.64 and 165.14 (δ(C-N)) and
187.28 and 187.85 (δ(C-O)) in the 13C NMR spectrum are
consistent with a delocalized π-system. Furthermore, as in
Experimental Section
General. 1H NMR (300, 400, or 500 MHz), 13C NMR (75, 100,
or 125 MHz) and 31P NMR (121.5 MHz) spectra were recorded on
a Bruker AC-300, AMX-400, or AMX 500 instrument. FAB mass
spectra were recorded on an autospec HF mass spectrometer and
Maldi-TOF mass spectral analyses were recorded on a Finnigan
TSQ 700. Elemental analyses were performed by the Service de
Microanalyse, Institut Charles Sadron (Strasbourg, France). Solvents
were freshly distilled under N2 prior to use. N,N′-dineopen-
tyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2-
(-NHCH2t-Bu)2(-O)2] 6,20 and the metal complexes [Pd(8-mq)-
(µ-Cl)]2,31 [Pd(8-mq)(µ-OAc)]2,32 [Pd(dmba)(µ-Cl)]2,33 [Pd(η3-
methallyl)(µ-Cl)]2,34 [PdCl(PPh3)(µ-Cl)]2,35 [AuCl(PPh3)],36 and
trans-[NiCl(Ph)(PPh3)2]37 were prepared according to the literature.
Characterization of 15 and the synthesis of 8 have been reported
in a previous paper.20a All reactions of air- or water-sensitive
compounds were performed using standard Schlenk techniques
under a dry Ar atmosphere. Gas chromatographic analyses were
performed on a thermoquest GC8000 Top Series gas chromatograph
using a HP PONA column (50 m, 0.2 mm diameter, 0.5 µm film
thickness).
‚‚‚
17, the N C-C-H proton appears also as a broad singlet
1
‚‚‚
in the H NMR spectrum, and the corresponding HsC
C
resonance in the 13C{1H} NMR spectrum can only be
observed after increasing the pulse delay to 2 s at room
temperature. All these data, together with the MALDI-TOF
mass spectrum and elemental analyses, are consistent with
a heterotrimetallic complex in which a Ni atom occupies a
center of symmetry and in which the π-system of the two
quinonoid ligands is delocalized between the three metal
centers. As in the case of 15, no transmetallation reaction
was observed between 18 and [PdCl2(SEt)2].
Synthesis of N,N′-dineopentyl-2-amino-5-sodium alcoholate-
1,4-benzoquinonemonoimine [C6H2(NHCH2t-Bu)(dNCH2t-Bu)-
(dO)(ONa)] 9. The zwitterion 6 (0.80 g, 2.88 mmol) was dissolved
in 50 mL of anhydrous THF, solid NaOt-Bu (0.28 g, 2.88 mmol)
was added to the solution, and the mixture was stirred overnight at
room temperature with progressive precipitation of an orange solid.
After evaporation of the solvent, 9 was obtained as an orange
powder and used without further purification (0.86 g, 93% yield).
1H NMR (300 MHz, DMSO-[d6], 298 K) δ: 0.92 (s, 9 H, CH3),
0.94 (s, 9 H, CH3), 2.81 (br s, 2 H, CH2), 3.11 (s, 2 H, CH2), 4.90
(s, 1 H, NdC-C-H), 5.15 (s, 1 H, OdC-C-H), 6.08 (br t, 1 H,
N-H). 13C{1H} NMR (100 MHz, DMSO-[d6], 298 K) δ: 28.36
(CMe3), 28.77 (CMe3), 32.64 (CMe3), 33.24 (CMe3), 53.36 (CH2N),
62.60 (CH2N), 84.11 (HsCdC-N), 100.78 (HsCdC-O), 147.27
(C-N), 161.54 (C-O), 176.01 (CdN), 180.23 (CdO). HRMS
(EI-, 70 eV) m/z: 277 [M - Na]-.
Conclusion
The two successive acidities of the N-H protons of the
unusual zwitterionic benzoquinonemonoimine 6 allow the
preparation of monometallic, homodimetallic, and heterot-
rimetallic complexes in which the control of the π-system
delocalization becomes possible. Ligand 6 was easily mon-
odeprotonated with NaOt-Bu, and the isolated sodium salt
9 reacted with chloride-bridged homodimetallic Pd(II) com-
plexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2] to afford
the monometallic complexes 10-15 in which the π-system
is more localized. A second in situ deprotonation of the free
N-H amino function of the metalloligand 10 followed by
metallation affords, following a convergent strategy, the
homodimetallic complex 17 in which the π-system of the
quinonoid ligand is delocalized between the metal centers.
Using a divergent strategy, the double in situ deprotonation
of the two N-H amino functions of 15 followed by
metallation affords the heterotrimetallic complex 18 in which
the π-system of the two quinonoid ligands is delocalized
between the three metal centers. These new strategies could
now be extended to a range of heterodimetallic complexes,
in particular for studies of cooperative effects in homoge-
neous catalysis and electronic communication in mixed-
valence complexes, and to the preparation of quinonoid
oligomers linked by metal ions.
Synthesis of 10: Procedure A. To a solution of [Pd(8-mq)(µ-
Cl)]2 (0.10 g, 0.17 mmol) in anhydrous THF (100 mL) was added
(31) Hartwell, G. E.; Laurence, R. V.; Smas, M. J. J. Chem. Soc. D: Chem.
Commun. 1970, 912.
(32) Deeming, A. J.; Rothwell, I. P. J. Organomet. Chem. 1981, 205, 117-
131.
(33) Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909-913.
(34) Tatsuno, Y.; Yoshida, T.; Osuka, S. Inorg. Synth. 1979, 29, 220-
223.
(35) Kla¨ui, W.; Glaum, M.; Hahn, E.; Lu¨gger, T. Eur. J. Inorg. Chem.
2000, 21-28.
(36) Braunstein, P.; Lehner, H.; Matt, D. Inorg. Synth. 1990, 27, 218-
221.
(37) Zeller, A.; Herdtweck, E.; Strassner, T. Eur. J. Inorg. Chem. 2003,
1802-1806.
Inorganic Chemistry, Vol. 43, No. 22, 2004 6951

Taquet et al.
solid 9 (0.10 g, 0.33 mmol), and the mixture was stirred overnight
at room temperature. After filtration through Celite, the solvent was
evaporated and 10 was obtained as a brown powder by recrystal-
lization from a CH2Cl2-hexane mixture (0.13 g, 75% yield). Red
crystals suitable for an X-ray analysis were isolated from a CH2-
Cl2/n-hexane solution.
(CH2-NMe2), 85.27 (HsCdC-N), 101.60 (HsCdC-O), 121.52,
123.49, 124.73, 132.59 (aryl CH), 146.82, 147.18 (aryl C), 149.24
(C-NH), 170.43 (C-O), 179.07 (CdN), 180.63 (CdO). Anal.
Calcd for C25H37N3O2Pd: C, 57.97; H, 7.20; N, 8.11. Found: C,
58.48; H, 7.41; N, 7.70. Despite numerous attempts of purification,
no better analyses were obtained. MS (Maldi-TOF) m/z: 518.564
[M + 1]+. UV-vis (CH2Cl2): λmax (log ꢀ) ) 395 (br) nm (4.31),
503 (br) nm (3.10).
Procedure B. To a solution of [Pd(8-mq)(µ-OAc)]2 (0.34 g, 0.54
mmol) in anhydrous THF (100 mL) was added solid zwitterion 6
(0.30 g, 1.08 mmol) and the mixture was refluxed for 1.5 h. After
evaporation of the solvent, 10 was obtained as a brown powder by
recrystallization from a CH2Cl2/hexane mixture (0.50 g, 82% yield).
1H NMR (300 MHz, CDCl3, 298 K) δ: 1.02 (s, 9 H, CH3), 1.14
12. (0.11 g, 75% yield). 1H NMR (300 MHz, CDCl3, 298 K) δ:
1.00 (s, 9 H, CH3), 1.05 (s, 9 H, CH3), 2.10 (s, 3 H, CH3), 2.76 (s,
3
1 H, CH allyl), 2.82 (s, 1 H, CH allyl), 2.87 (d, JHH ) 6.3 Hz, 2
2
H, NH-CH2), 3.35 (d, JHH ) 2.7 Hz, 1 H, CH allyl), 3.68 and
3.71 (d, AB system, 2JAB ) 8.6 Hz, 2 H, N-CH2), 3.82 (d, 2JHH
)
3
(s, 9 H, CH3), 2.90 (d, JHH ) 6.3 Hz, 2 H, NH-CH2), 3.38 (s, 2
2.7 Hz, 1 H, CH allyl), 5.25 (s, 1 H, NdC-C-H), 5.59 (s, 1 H,
OdC-C-H), 6.48 (br t, 1 H, N-H). 13C{1H} NMR (75 MHz,
CDCl3, 298 K) δ: 23.06 (allyl CH3), 27.63 (CMe3), 29.19 (CMe3),
32.30 (CMe3), 36.13 (CMe3), 54.05 (CH2N), 57.12, 57.31 (CH2
allyl), 66.36 (CH2N), 84.39 (HsCdC-N), 102.56 (HsCdC-O),
128.97 (allyl C-C-C), 147.27 (C-NH), 168.26 (C-O), 179.91
(CdN), 182.18 (CdO). Anal. Calcd for C20H32N2O2Pd: C, 54.73;
H, 7.35; N, 6.38. Found: C, 53.64; H, 7.26; N, 5.81. Despite
numerous attempts of purification, no better analyses were obtained.
MS (Maldi-TOF) m/z: 461.617 [M + Na]+. UV-vis (CH2Cl2):
λmax (log ꢀ) ) 365 nm (4.36), 506 (br) nm (2.88).
H, Pd-CH2), 3.50 (br s, 2 H, N-CH2), 5.36 (s, 1 H, NdC-C-
H), 5.61 (s, 1 H, OdC-C-H), 6.56 (br t, 1 H, N-H), 7.41-7.61
(m, 4 H, aryl), 8.27 (dd, 1 H, aryl), 8.96 (d, 1 H, aryl). H NMR
1
(400 MHz, CDCl3, 213 K) δ: 1.02 (s, 9 H, CH3), 1.14 (s, 9 H,
CH3), 2.84 and 2.89 (ABX system (X ) NH), 2JAB ) 13 Hz, 3JAX
) 6.4 Hz, 3JBX ) 6 Hz, 2 H, NH-CH2), 3.22 (d, B part of an AB
2
system, JAB ) 12 Hz, 1 H, N-CHH), 3.37 (s, 2 H, Pd-CH2),
2
3.62 (d, A part of an AB system, JAB ) 12 Hz, 1 H, N-CHH),
5.36 (s, 1 H, NdC-C-H), 5.61 (s, 1 H, OdC-C-H), 6.56 (br t,
1 H, N-H), 7.42-7.61 (m, 4 H, aryl), 8.28 (dd, 1 H, aryl), 8.93
(dd, 1 H, aryl). 13C{1H} NMR (75 MHz, CDCl3, 253 K) δ: 27.19
(Pd-CH2), 27.66 (CMe3), 29.47 (CMe3), 32.27 (CMe3), 36.20
(CMe3), 54.09 (CH2N), 61.43 (CH2N), 85.89 (HsCdC-N), 102.17
(HsCdC-O), 121.47, 123.35, 128.27, 128.87, 128.88, 137.56,
147.39, 149.49, 153.10 (aryl C), 148.64 (C-NH), 171.28 (C-O),
179.26 (CdN-Np), 181.32 (CdO). Anal. Calcd for C26H33N3O2-
Pd: C, 59.37; H, 6.32; N, 7.99. Found: C, 59.49; H, 6.37; N, 7.44.
UV-vis (CH2Cl2): λmax (log ꢀ) ) 313 nm (3.93), 388 (br) nm
(4.40), 513 (br) nm (2.98).
1
13‚CH2Cl2. (0.20 g, 79% yield). H NMR (300 MHz, CDCl3,
298 K) δ: 0.99 (s, 9 H, CH3), 1.13 (s, 9 H, CH3), 2.87 (d, 3JHH
)
6.3 Hz, 2 H, NH-CH2), 3.80 (br, 2 H, N-CH2), 5.24 (s, 1 H,
NdC-C-H), 5.32 (s, 1 H, OdC-C-H), 6.40 (br t, 1 H, N-H),
7.45-7.65 (m, 15 H, aryl). 1H NMR (500 MHz, CDCl3, 213 K) δ:
0.96 (s, 9 H, CH3), 1.08 (s, 9 H, CH3), 2.82 and 2.87 (ABX system
2
3
3
(X ) NH), JAB ) 13.5 Hz, JAX ) 6.2 Hz, JBX ) 6 Hz, 2 H,
2
4
NH-CH2), 3.21 (dd, JHH ) 11.5 Hz, JPH ) 8.8 Hz, 1 H,
N-CHH), 3.96 (dd, 2JHH ) 11.5 Hz, 4JPH ) 3.2 Hz, 1 H, N-CHH),
5.25 (s, 1 H, NdC-C-H), 5.26 (s, CH2Cl2), 5.33 (s, 1 H, Od
C-C-H), 6.34 (br t, 1 H, N-H), 7.43-7.63 (m, 15 H, aryl). 31P-
{1H} NMR (125 MHz, CDCl3, 268 K) δ: 25.5. 13C{1H} NMR
(100 MHz, CDCl3, 268 K) δ: 27.71 (CMe3), 29.24 (CMe3), 32.43
(CMe3), 36.47 (CMe3), 54.07 (CH2N), 58.15 (CH2N), 85.13 (Hs
CdC-N), 103.17 (HsCdC-O), 128.44, 128.56, 131.46, 134.78,
134.89, 135.13 (aryl C), 146.69 (C-N), 170.27 (C-O), 180.33
(CdN), 183.98 (CdO). Anal. Calcd for C34H40N2O2PPdCl‚CH2-
Cl2: C, 54.85; H, 5.52; N, 3.65. Found: C, 54.76; H, 5.57; N,
3.41. UV-vis (CH2Cl2): λmax (log ꢀ) ) 280 nm (4.13), 379 (br)
nm (4.43), 479 (br) nm (3.11).
Synthesis of 11, 12, and 13: General Procedure. To a solution
of the homodimetallic Pd(II) precursor (0.17 mmol) in anhydrous
THF (100 mL) was added solid 9 (0.10 g, 0.33 mmol), and the
mixture was stirred overnight at room temperature. After filtration
through Celite, the solvent was evaporated. 12 was directly obtained
as a violet powder by recrystallization from a CH2Cl2/hexane
mixture. For 11, the red-brown residue was dissolved in hexane
and placed at -30 °C, and red crystals of pure 11 were obtained
after 2 days. For 13, the red residue was dissolved in CH2Cl2 and
purified by preparative chromatography on silica gel (average
particle size of 40 µm, eluant CH2Cl2/MeOH 95:5) to afford 13‚
CH2Cl2 as a red crystalline solid. Red crystals of 13 suitable for an
X-ray analysis were obtained from a CH2Cl2/n-hexane solution.
11. (0.11 g, 65% yield). 1H NMR (300 MHz, CDCl3, 298 K) δ:
0.95 (s, 9 H, CH3), 1.00 (s, 9 H, CH3), 2.56 (s br, 3 H, N-CH3),
2.89 (d, 3JHH ) 6.2 Hz, 2 H, NH-CH2), 2.96 (br s, 3 H, N-CH3),
3.41 (br s, 1 H, H-CH-NMe2), 3.66 (br s, 2 H, N-CH2), 4.44 (br
s, 1 H, H-CH-NMe2), 5.37 (s, 1 H, NdC-C-H), 5.50 (s, 1 H,
OdC-C-H), 6.56 (br t, 1 H, N-H), 6.99-7.04 (m, 4 H, aryl).
1H NMR (500 MHz, CDCl3, 273 K) δ: 0.95 (s, 9 H, CH3), 1.00
(s, 9 H, CH3), 2.56 (s, 3 H, N-CH3), 2.89 (center of an ABX system
Synthesis of 14‚CH2Cl2. To a solution of [AuCl(PPh3)] (0.17
g, 0.33 mmol) in anhydrous THF (100 mL) was added solid 9 (0.10
g, 0.33 mmol), and the mixture was stirred overnight at room
temperature. After the mixture was filtered through Celite to retain
metallic gold, the solvent was evaporated and 14‚CH2Cl2 was
obtained as a red-orange powder by recrystallization from a CH2-
1
Cl2-hexane mixture (0.20 g, 73% yield). H NMR (300 MHz,
CDCl3, 298 K) δ: 1.02 (s, 9 H, CH3), 1.08 (s, 9 H, CH3), 2.95 (d,
3JHH ) 6.3 Hz, 2 H, NH-CH2), 3.65 (s, 2 H, N-CH2), 5.25 (s, 1
H, NdC-C-H), 5.54 (s, 1 H, OdC-C-H), 7.06 (br t, 1 H, N-H),
7.50 (m, 15 H, aryl). 31P{1H} NMR (125 MHz, CDCl3, 298 K) δ:
31.5. 13C{1H} NMR (75 MHz, CDCl3, 298 K) δ: 27.71 (CMe3),
29.36 (CMe3), 32.50 (CMe3), 35.01 (CMe3), 54.03 (CH2N), 65.08
(CH2N), 84.99 (HsCdC-N), 101.43 (HsCdC-O), 129.02,
129.17, 131.46, 134.03, 134.22, 134.64 (aryl), 151.04 (C-N),
166.29 (C-O), 175.78 (CdN), 176.74 (CdO). Anal. Calcd for
C34H40N2O2PAu‚CH2Cl2: C, 51.17; H, 5.15; N, 3.41. Found: C,
51.47; H, 4.96; N, 2.84. MS (Maldi-TOF) m/z: 737.514 [M + 1]+.
UV-vis (CH2Cl2): λmax (log ꢀ) ) 338 nm (4.41), 351 nm (4.45).
2
3
3
(X ) NH), JAB ) 13.3 Hz, JAX ) JBX ) 6.5 Hz, 2 H, NH-
CH2), 2.96 (s, 3 H, N-CH3), 3.40 (d, B part of an AB system,
2JAB ) 13 Hz, 1 H, H-CH-NMe2), 3.57 (d, B part of an AB
2
system, JAB ) 12 Hz, 1 H, N-CHH), 3.75 (d, A part of an AB
2
system, JAB ) 12 Hz, 1 H, N-CHH), 4.45 (d, A part of an AB
system, 2JAB ) 13 Hz, 1 H, H-CH-NMe2), 5.37 (s, 1 H, NdC-
C-H), 5.50 (s, 1 H, OdC-C-H), 6.56 (br t, 1 H, N-H), 6.99-
7.04 (m, 4 H, aryl). 13C{1H} NMR (75 MHz, CDCl3, 268 K) δ:
27.23 (CMe3), 28.67 (CMe3), 31.97 (CMe3), 36.07 (CMe3), 49.96
(N-CH3), 51.67 (N-CH3), 53.50 (CH2N), 59.17 (CH2N), 72.47
6952 Inorganic Chemistry, Vol. 43, No. 22, 2004

Metal Complexes with a 6π + 6π Quinonoid Zwitterion
Formation of 15. To a solution of trans-[NiCl(Ph)(PPh3)2] (0.23
g, 0.33 mmol) in anhydrous THF (100 mL) was added solid 9 (0.10
g, 0.33 mmol), and the mixture was stirred overnight at room
temperature. After the mixture was filtered through Celite, the
solvent was evaporated and 15 was obtained quantitatively as a
green powder after recrystallization from a CH2Cl2-hexane mixture.
15 was characterized by comparison of its 1H NMR data with those
of an authentic sample.20a
vis (CH2Cl2): λmax (log ꢀ) ) 309 nm (4.30), 388 nm (4.71), 495
(br) nm (3.89), 710 (br) nm (3.54), 786 (br) nm (3.68), 873 (br)
nm (3.20).
Oligomerization of Ethylene. All catalytic reactions were carried
out in a magnetically stirred (900 rpm) 100 mL stainless steel
autoclave.27 The interior of the autoclave was protected from
corrosion by a protective ceramic coating. All catalytic tests were
started at 30 °C, and no cooling of the reactor was done during the
reaction. After injection of the catalytic solution and of the
cocatalyst under a constant low flow of ethylene, the reactor was
pressurized to the desired pressure. The temperature increase that
was observed resulted solely from the exothermicity of the reaction.
The reactor was continuously fed with ethylene by a reserve bottle
placed on a balance to allow continuous monitoring of the ethylene
uptake. In all of the catalytic experiments, 4 × 10-2 mmol of Ni
complex was used. The oligomerization products and remaining
ethylene were only collected from the reactor at the end of the
catalytic experiment. At the end of each test, the reactor was cooled
to 10 °C before transferring the gaseous phase into a 10 L
polyethylene tank filled with water. An aliquot of this gaseous phase
was transferred into a Schlenk flask (previously evacuated for GC
analysis). The products in the reactor were hydrolyzed in situ by
the addition of ethanol (10 mL), transferred in a Schlenk flask,
and separated from the metal complexes by trap-to-trap distillation
(120 °C, 20 Torr). All volatiles were evaporated (120 °C, 20 Torr,
static pressure) and recovered in a second Schlenk flask previously
immersed in liquid nitrogen in order to avoid any loss of product.
For GC analyses, 1-heptene was used as an internal reference.27
The required amount of complex was dissolved in 10 mL of
chlorobenzene and injected into the reactor. Depending on the
amount of cocatalyst added, between 0 and 5 mL of cocatalyst
solution was added so that the total volume of all solutions was 15
mL.
Synthesis of 17. To a solution of 10 (0.20 g, 0.38 mmol) in
anhydrous THF (100 mL) was added excess NaH (0.29 g, 1.14
mmol). The mixture was then refluxed overnight, and solid [Pd-
(8-mq)(µ-Cl)]2 (0.11 g, 0.19 mmoL) was added under N2 at room
temperature. The solution was stirred at room temperature for 3 h.
3
After the mixture was filtered through Celite, /4 of the solvent
was evaporated under reduced pressure and 17 was obtained as a
green powder by addition of hexane and drying (0.25 g, 85% yield).
Green crystals of 17‚2THF suitable for an X-ray analysis were
1
isolated by slow evaporation of a THF solution. H NMR (300
MHz, CDCl3, 298 K) δ: 1.13 (s, 18 H, CH3), 3.33 (br, 4 H,
N-CH2), 3.36 (s br, 4 H, Pd-CH2), 5.50 (s br, 1 H, N-C-C-H),
5.64 (s, 1 H, O-C-C-H), 7.39-7.60 (m, 8 H, aryl), 8.24 (dd,
1
2 H, aryl), 8.98 (dd, 2 H, aryl). H NMR (500 MHz, CDCl3, 213
2
K) δ: 1.13 (s, 18 H, CH3), 2.91 (d, B part of an AB system, JAB
) 12.3 Hz, 2 H, N-CHH), 3.27 (d, B part of an AB system, 2JAB
) 14.5 Hz, 2 H, Pd-CHH), 3.36 (d, A part of an AB system, 2JAB
) 14.5 Hz, 2 H, Pd-CHH), 3.42 (d, A part of an AB system, 2JAB
) 12.3 Hz, 2 H, N-CHH), 5.60 (s, 1 H, NdC-C-H), 5.64 (s, 1
H, OdC-C-H), 7.42-7.64 (m, 8 H, aryl), 8.32 (dd, 2 H, aryl),
8.98 (dd, 2 H, aryl). 13C{1H} NMR (75 MHz, CDCl3, 298 K) δ:
26.63 (Pd-CH2), 29.78 (CMe3), 36.22 (CMe3), 60.59 (CH2N), 88.79
(H-C-C-N), 102.69 (H-C-C-O), 121.41, 123.13, 128.16,
128.78, 128.90, 137.08, 149.16, 149.32, 153.00 (aryl), 165.62
(C-N), 188.52 (C-O). Anal. Calcd for C36H40N4O2Pd2: C, 55.90;
H, 5.21; N, 7.24. Found: C, 55.63; H, 5.32; N, 7.02. UV-vis (CH2-
Cl2): λmax (log ꢀ) ) 289 nm (4.23), 427 nm (4.41), 444 nm (4.37),
646 (br) nm (3.67).
Crystal Structure Determinations. Diffraction data were col-
lected on a Kappa CCD diffractometer using graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å). The relevant data are
summarized in Table 1. Data were collected using phi-scans and
the structures were solved by direct methods using the SHELX 97
software,38 and the refinement was by full-matrix least squares on
F2. No absorption correction was used. All non-hydrogen atoms
were refined anisotropically with H atoms introduced as fixed
contributors (dC-H ) 0.95 Å, U11 ) 0.04). Full data collection
parameters and structural data are available as Supporting Informa-
tion.
Synthesis of 18. To a solution of 15 (0.09 g, 0.15 mmol) in
anhydrous THF (100 mL) was added excess NaH. The mixture
was then refluxed overnight and solid [Pd(8-mq)(µ-Cl)]2 (0.09 g,
0.15 mmol) was added under N2 at room temperature. The solution
was stirred at room temperature for 1 day. After the solution was
filtered through Celite and the Celite was washed with 100 mL of
THF, the solvent was evaporated under reduced pressure, and 18
was obtained as black-violet powder after recrystallization from a
CH2Cl2/heptane mixture, washing with cold heptane, and drying
(0.11 g, 67% yield).
1H NMR (300 MHz, CDCl3, 298 K) δ: 1.08 (s, 18 H, CH3),
1.12 (s, 18 H, CH3), 2.47 (s, 4 H, Ni-N-CH2), 3.32 (br, 4 H,
Pd-N-CH2), 3.38 (s, 4 H, Pd-CH2), 5.20 (s, 2 H, N-C-C-H),
5.34 (s, 2 H, O-C-C-H), 7.40-7.58 (m, 8 H, aryl), 8.24 (d, 2
H, aryl), 8.90 (d, 2 H, aryl). 13C{1H} NMR (100 MHz, CDCl3,
298 K) δ: 26.94 (Pd-CH2), 29.23 (CMe3), 29.64 (CMe3), 35.65
(CMe3), 36.23 (CMe3), 56.32 (CH2N), 61.47 (CH2N), 89.79 (H-
C-C-N), 101.66 (H-C-C-O), 121.44, 123.25, 128.32, 128.82,
128.94, 137.26, 137.59, 149.04, 149.57 (aryl), 162.64 (C-N),
165.14 (C-N), 187.28 (C-O), 187.85 (C-O). Anal. Calcd for
C52H64N6O4Pd2Ni: C, 56.34; H, 5.82; N, 7.58. Found: C, 56.63;
H, 5.74; N, 7.31. MS (Maldi-TOF) m/z: 1107.241 [M + 1]+. UV-
Acknowledgment. We are grateful to the CNRS and the
European Commission (Network Palladium HPRN-CT-2002-
00196 and COST D17) for support and to the Ministe`re de
la Recherche for a Ph.D grant to J.p.T. and to Dr. J.-D. Sauer
for NMR experiments.
Supporting Information Available: ORTEP views for 10, 13,
and 17 in 17‚2THF (PDF); X-ray data in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data for all structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
237963-237965. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax +44-1223-336033; e-mail deposit@
ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk).
(38) (a) Kappa CCD Operation Manual; Nonius B. V., Delft, The
Netherlands, 1997. (b) Sheldrick, G. M. SHELXL97, Program for the
refinement of crystal structures; University of Go¨ttingen, Germany,
1997.
IC049263A
Inorganic Chemistry, Vol. 43, No. 22, 2004 6953