Synthesis and X-ray crystal structures of acenaphthenequinone-based α-diimine palladium complexes and a novel V-shape tripalladium cluster

Article abstract of DOI:10.1002/zaac.200800056

Partially fluorinated 1,4-Diazadiene (α-Diimine) ligand 3,5-CF ₃-BIAN (1) formed from 3,5-bis(trifluoromethyl)aniline and acenaphthenequinone was used in the synthesis of palladium dichlorido complex 2 and its mono methyl chlorido palladium complex 3. Both complexes as well as side products of the reaction with methyl lithium such as trans-bis(3,5- bis(trifluoromethyl)aniline complex 4 and an interesting mixed valent trinuclear V-shaped palladium cluster 5 with two bridging μ², η³-N,CN′ non-innocent BIAN ligands were structurally characterized by the single-crystal XRD method.

Full text of DOI:10.1002/zaac.200800056

DOI: 10.1002/zaac.200800056
Synthesis and X-ray Crystal Structures of Acenaphthenequinone-based
␣-Diimine Palladium Complexes and a Novel V-shape Tripalladium Cluster
Jin Zhoua, Hongjian Sun*,a,b, Klaus Harmsb, and Jörg Sundermeyerb
a Jinan / PR China, School of Chemistry and Chemical Engineering, Shandong University
b Marburg / Germany, Fachbereich Chemie der Philipps-Universität
Received January 31st, 2008.
Abstract. Partially fluorinated 1,4-Diazadiene (α-Diimine) ligand
3,5-CF3-BIAN (1) formed from 3,5-bis(trifluoromethyl)aniline and
acenaphthenequinone was used in the synthesis of palladium
dichlorido complex 2 and its mono methyl chlorido palladium
complex 3. Both complexes as well as side products of the reaction
with methyl lithium such as trans-bis(3,5-bis(trifluoromethyl)ani-
line complex 4 and an interesting mixed valent trinuclear V-shaped
palladium cluster 5 with two bridging μ2,η3-N,CNЈ non-innocent
BIAN ligands were structurally characterized by the single-crystal
XRD method.
Keywords: Palladium; 1,4-Diazadienes; Metal cluster compounds;
Crystal structures
Introduction
CF3-BIAN)] (2), and 1,2-bis(3,5-bis-trifluoromethyl-
phenylimino)acenaphthene-methylchloropalladium(II),
[Pd(Me)Cl(3,5-CF3-BIAN)] (3). The X-ray crystal struc-
tures of 2, 3, bis(3,5-di(trifluoromethyl)aniline)dichloropal-
ladium(II) (4) and bi(1,2-bis(3,5-bis-trifluoromethyl-phen-
ylimino)acenaphthene)-bis(dimethylsulfide)methylchloro-
tripalladium (5), which was obtained as an unexpected
product, were determined by single-crystal diffraction
method (Scheme 1).
α-Dimines are one of the most important ligand families,
not only in coordination chemistry but also in catalysis.
Thus the study on α-diimines and their related catalytic re-
actions is a topic of general interest [1Ϫ4]. In 1995 Brook-
hart and his coworkers reported α-diimine palladium(II)-
and nickel(II)-catalyzed olefin polymerizations and obtained
high molecular weight polymers with a branched micro-
structure [5]. The copolymerization of ethylene or propylene
with other α-olefins and acrylates could be also catalyzed
with the support of these ligands [6]. Mecking reported the
catalytic olefin polymerization with ionic diimine pal-
ladium(II) and nickel(II) complexes in aqueous solution [7].
A Pd(OAc)2/1,4-diazabutadiene (DAB-R) system was devel-
oped for the Suzuki-Miyaura cross-coupling of various aryl
bromides and activated aryl chlorides with arylboronic
acids, and it was found that the best reactivity was attained
if R is a cyclohexyl group with the stronger donating ability
of alkyl substituents, making the ligand more electron-rich
[8]. Cationic complexes [(ArNϭCR-RCϭNAr)Pt(CH3)(L)]ϩ
[BF4]Ϫ (Ar ϭ aryl; R ϭ H, CH3; L ϭ water, trifluoro-
ethanol) react smoothly with benzene at room temperature
in trifluoroethanol to activate the C-H bond of benzene [9].
Herein, we report the synthesis and characterization of
1,2-bis-(3,5-bis-trifluoromethyl-phenylimino)-acenaphthene,
3,5-CF3-BIAN (1), 1,2-bis(3,5-bis-trifluoromethyl-phen-
ylimino)acenaphthenedichloro-palladium(II), [PdCl2(3,5-
Results and Discussion
1 Synthesis
All air-sensitive and volatile materials were handled either
in vacuo or under argon by using standard Schlenk tech-
niques. The complex 2 was formed by the reaction of ligand
1 with palladium dichloride in CH3CN. The complex 4 was
obtained together with complex 2, in the same crystal cell.
It is proposed that 3,5-di(trifluoromethyl)aniline was pro-
duced from partial decomposition of ligand 1, therefore 4
was formed. The trinuclear compoud 5 was isolated as by-
product formed by reaction of ligand 1, [PdCl2(SMe2)2] and
excessive methyl lithium. The crystals were isolated from
the mother liquor at Ϫ20 °C. The yield of 5 is very low
(< 1 % estimated).
2 Spectral characteristics
The 1H NMR spectrum of compound 1 shows three signals
at 8.02, 7.48, and 6.85 ppm corresponding to positions a, b
and c, respectively (Scheme 2), of the acenaphthenequinone
backbone, and at 7.79 and 7.60 ppm for the C6H3 benzene
protons (positions d and e). On complexation to the pal-
ladium atom, a downfield shift is observed for all of the
* Dr. Hongjian Sun
School of Chemistry and Chemical Engineering
Shandong University
Shanda Nanlu 27
Jinan 250100 /P.R. China
E-mail: hjsun@sdu.edu.cn
Z. Anorg. Allg. Chem. 2008, 634, 1517Ϫ1521
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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J. Zhou, H. Sun, K. Harms, J. Sundermeyer
and Cl2-Pd1-Cl1 ϭ 91.3(2)° is 360°, which shows a square-
planar coordination of the central Pd atom. Phenyl rings
are approximately normal to the diazabutadiene moiety.
The acenaphthene moiety on the molecular structure is
practically planar. Fluoro atoms of one CF3 group are dis-
ordered in the crystal.
Scheme 1
Fig. 1 ORTEP representation of complexes 2 and 4
signals. For 13C and 19F NMR spectra similar downfield
shifts can be observed after coordination to the palladium
atom. But for the methyl palladium complex 3 those down-
field shifts are smaller than those of the dichloro palladium
complex 2. The signal of three methyl protons in complex
3 was recorded at 0.04 ppm as a singlet.
Scheme 2 Assignment of proton position
3 Crystal structures
Complex 2 (shown in Fig. 1) lies in the crystal cell with
complex 4 together. The palladium atom Pd1 in 2 is in
square-planar coordination with a cis configuration. The
sum of internal angles of the chelating ring with the value
of 539.4° indicates all of the five atoms of the chelating ring
are in one plane. The sum of four angles N2-Pd1-N1 ϭ
80.8(3)°, N2-Pd1-Cl2 ϭ 92.4(2)°, N1-Pd1-Cl1 ϭ 95.6(2)°
Fig. 2 ORTEP representation of complex 3
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Acenaphthenequinone-based α-Diimine Palladium Complexes
angle N1-Pd1-N2 is 80.8(3)°. There are no remarkable dif-
ferences of the other bond lengths apart from Pd1-N2 be-
tween complexes 2 and 3. Two sets of trifluoromethyl
groups, C20, F4, F5, F6 and C27, F7, F8, F9 are disordered
in the crystal lattice.
In the solution, from which the crystals of complex 3
were obtained, dark brown prisms were also found in very
small amount. The structure of this single crystalline species
was determined by single crystal X-ray diffraction. The
¯
compound crystallizes in space group P1. The asymmetric
unit of 5·Et2O·0.5 pentane comprises two molecules of
complex 5, two molecules of diethyl ether and one of pen-
tane. In complex 5 three palladium atoms and two 1,2-bis-
(3,5-bis-trifluoromethyl-phenylimino)-acenaphthene ligands
can be found. The latter adopts a rather unusual bridging
μ2-N,NC coordination mode. In addition, a chlorido ligand
at Pd3, a methyl group at Pd2 and two dimethyl sulfide
ligands are identified as monodentate ligands. While Pd2
and Pd3 show a coordination close to square-planar, the
coordination at the central atom Pd1 is better described as
close to tetrahedral. The coordination of the carbon atoms
C1 and C29 of both diimine units indicates, that a certain
degree of anionic charge density is located on these carbon
donor atoms. This is in accord with the assumption, that
these non-innocent ligands might be coordinated in either
their monoanion radical oxidation state or in their diamag-
netic fully reduced dianionic form. Recently we have estab-
lished that the 3,5-CF3-BIAN ligand is prone to coordinate
in its radical anionic oxidation state to nickel and cobalt
[13]. As there are only two other anionic ligands available
within the trinuclear complex, a chlorido group at Pd3 and
a methyl group at Pd2, the oxidation states in 5 could be
described within the limits of three options: A) Pd2 and
Pd3 could be considered as in formal ϩ1 oxidation state,
while Pd1 as in formal oxidation state zero, then BIAN
would be neutral [BIAN]0; B) Pd2 and Pd3 could be con-
sidered as in formal ϩ2 oxidation state, while Pd1 as in
formal oxidation state zero, then both BIAN would be a
radical anion [BIAN]Ϫ; finally C) Pd1, Pd2 and Pd3 could
be considered as in formal ϩ2 oxidation state, then both
BIAN would be a dianion [BIAN]2Ϫ. Option B) tends to be
the best description taking into account the square planar
coordination of the metal in d8 configuration and close to
tetrahedral coordination of Pd1 in d10 configuration. How-
ever as a matter of fact, it is impossible to fully assign the
metal and ligand oxidation states (and metal valence elec-
tron count) with the data in our hands. However we would
like to exclude the diamagnetic closed-shell option C), as
the dark brown-black color of 5 is in accord with a mixed
valence compound as well as with charge transfer phenom-
ena within the metal ligand core. The elongation of Pd2-
Fig. 3 Ball and Stick representation of complex 5
In the crystal cell complex 4 next to molecule 2 can be
found. The central Pd2 atom has an absolute square-planar
coordination with trans configuration. Both Pd-Cl and Pd-
N bond distances for the aniline palladium chlorido com-
plexes are in the expected range [10]. C29-N3-Pd2 ϭ
113.4(6)° indicates a nitrogen atom in sp3 hybridization
state. Angles Cl1Ј-Pd2-Cl1A and N3-Pd2-N3A are exactly
180°. The sum of four angles N3-Pd2-Cl1Ј ϭ 88.9(2), N3-
Pd2-Cl1A ϭ 91.1(2), N3a-Pd-Cl1Ј ϭ 88.9(2) and N3a-Pd2-
Cl1A ϭ 91.1(2)° with the value of 360° also implies that all
of the five atoms Pd2, N3, N3a, Cl1Ј and Cl1A are in one
coordination plane.
Bis(3,5-di(trifluoromethyl)aniline)dichloropalladium(II)
is of importance because the notable analogy between the
coordination chemistry of platinum(II) and palladium(II)
compounds has advocated studies of PdII complexes as
anti-tumor drugs [11]. Recent advances in this field have
focused on PdII compounds bearing diamino bidentate li-
gands [12].
Complex 2 can be methylated by MeLi in ether to give
complex 3 (Fig. 2). The crystal structure of 3 was deter-
mined at 193(2) K in space group P21/c. The symmetry in
complex 3 is lower than that in complex 2. In trans position
˚
˚
N4, 2.176(4) A, in comparison with Pd2-N3, 2.078(4) A, is
˚
a result from the strong trans influence of the methyl group.
to methyl group the Pd1-N2 distance of 2.227(4) A is signif-
˚
˚
For the same reason Pd1-N1, 2.189(4) A, trans to C29 of
icantly larger than Pd1-N1 ϭ 2.052(3) A being trans to the
˚
BIAN is notable longer than Pd1-N2, 2.083(4) A, Pd3-N1,
chlorido ligand indicating a stronger trans influence of the
methyl group. Therefore a relatively small bite angle N1-
Pd1-N2 ϭ 78.27(14)° is formed, while in complex 2 the bite
˚
˚
2.097(4) A, and Pd1-N3, 2.108(5) A, in complex 5 as well
˚
˚
as Pd1-N1, 2.050(7) A, Pd1-N2, 2.036(7) A, in complex 2
Z. Anorg. Allg. Chem. 2008, 1517Ϫ1521
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J. Zhou, H. Sun, K. Harms, J. Sundermeyer
˚
and Pd1-N1, 2.052(3) A, in complex 3. Comparing C29-N3,
Experimental Section
˚
˚
1.411(6) A, and C1-N1, 1.385(7) A, with all of the other
carbon-nitrogen bond lengths of imine functions in this
paper indicates elongation of these two imine (CϭN)
bonds, which fall in between a typical C-N double bond
1 General procedures and materials
All chemicals were commercially available and were used as re-
ceived. Complexes 2, 3 and 5 were prepared and handled under
nitrogen atmosphere. 1H NMR, 13C NMR and 19F NMR were
performed using a Bruker ARX 300. Mass spectra were obtained
with Varian MAT CH7 spectrometer. The elemental analyses were
carried out with a CHN-Rapid elemental analyzer (Heraeus) at the
Marburg analytical service lab.
˚
˚
(1.287 A) and a (C-N) single bond (1.471 A) [10]. Again
this is well in accord with a reduced ligand oxidation state
and the η2-coordination of two of the imine (CϭN) bonds
to the palladium atoms. C1, N1, C29, and N3 can be con-
sidered as atoms with sp3 hybridization and tetrahedral co-
ordination, while the other carbon and nitrogen atoms in
DIAN are considered as sp2 hybridized with trigonal ar-
rangement. The Pd3-C1-N1 plane is approximately orthog-
onal to the chelate plane N2-C11-C1-N1-Pd1 (dihedral an-
gle 91.7°) and the Pd1-C29-N3 plane is nearly perpendicu-
lar to the chelate plane N3-C29-C39-N4-Pd2 (dihedral an-
gle 84.3°).
2 X-ray crystallography
X-ray diffraction experiments were performed on a STOE IPDS-II
diffractometer, using graphite monochromated MoKα radiation
(λ ϭ 0.71073 A). The low temperature of the crystal was main-
tained with cryostream open-flow N2 cryostats. The collected data
have been corrected for absorption effects. The structures were
solved by direct methods and refined by the full-matrix least square
method against F2 of all unique reflections, using SHELX software
[18]. The H atoms were introduced at calculated positions and re-
fined using the riding model. The crystal of 3 was twinned. Only
data of one twin domain were used for the structure determination
of 3. Selected crystal data and experimental details are given in
Table 1.
The bridging BIAN coordination mode holds the pal-
ladium atoms in rather close proximity with distances Pd1-
Pd3 ϭ 3.172, Pd1-Pd2 ϭ 3.307, and Pd2-Pd3 ϭ 4.609 A.
˚
The angle Pd1-Pd2-Pd3 is approximately 90.7°. This ar-
rangement in complex 5 can be envisaged as a V-shape tri-
palladium cluster bridged with two nitrogen atoms of the
imine groups. Tripalladium clusters were well reviewed by
Kovala-Demertzi [14]. In most of the tripalladium clusters
with 42 valence electrons the bridging groups are halogen-
ido, carbonyl, sulfur, amines and nitriles as well as other
non-redox active ligands. If we assume option A) as realistic
valence state description, complex 5 would have a 44 val-
ence electron count, which would be responsible for the rel-
atively long Pd-Pd bond length. On the other hand it is well
documented, that the large size of the bridging ligand leads
to much larger Pd-Pd bond lengths [15, 16]. An analogous
tetraruthenium cluster with bridging μ2,η3-N,CNЈ diimine
coordination mode has been reported by Staal et al. [17].
We assume, that in our experiment, methyl lithium has
acted as reducing agent for palladium and / or the BIAN li-
gand.
Table 1 Crystal data and experimental parameters
Complex
2 ϩ 4
3
5
Formula C78H46Cl6F36N6O2Pd3(2x2· 4·2xCH3COCH3)
C29H15ClF12N2Pd(3)
C67.5H55ClF24N4OPd3S2(5·Et2O·0.5C5H12
)
Formula Weight
T/K
2311.08
193(2)
triclinic
761.28
193(2)
monoclinic
P21/c
12.3947(12)
24.388(2)
9.1324(10)
1812.92
193(2)
triclinic
¯
P1
14.3485(11)
16.5772(12)
16.7856(12)
80.744(6)
72.335(6)
69.277(6)
3551.8(5)
2
1.695
0.956
1.57Ϫ26.07
59758
13787
8681
1045
0.1051
0.0463
Crystal system
Space group
¯
P1
˚
a/A
11.843(2)
14.318(3)
15.001(3)
85.702(15)
67.475(13)
72.411(14)
2237.5(7)
1
˚
b/A
˚
c/A
Ͱ/°
β/°
γ/°
93.307(8)
3
˚
V/A
2756.0(5)
4
1.835
Z
ρcalcd /MgmϪ3
1.715
0.899
μ /mmϪ1
0.876
Conclusion
Data collection range /°
Total reflections
Unique reflections
Reflections I>2σ(I)
Parameters
1.47Ϫ25.00
21981
7463
3044
603
2.38Ϫ25.50
22907
3564
2228
434
0.0802
0.0347
0.0814
α-Diimine ligand 1 (3,5-CF3-BIAN) formed from 3,5-bi-
s(trifluoromethyl)aniline and acenaphthenequinone, its pal-
ladium dichlorido complex 2 and its mono methyl chlorido
palladium complex 3 were synthesized. Complex 2 and 3
were characterized by single-crystal XRD method. While in
both, 2 and 3, the palladium atom has a square-planar cis
coordination, bis(3,5-bis(trifluoromethyl)aniline)dichloro-
palladium(II) 4 reveals a trans square-planar arrangement.
The reaction of chlorido palladium complex 2 with methyl
lithium leads to an interesting and unexpected side
product formed via a redox reaction: The XRD structure
of the brown-black mixed valent trinuclear cluster di(1,2-
bis(3,5-bis-trifluoromethyl-phenylimino)acenaphthene)-
bis(dimethylsulfide)methylchlorotripalladium 5 reveals a
V-shape palladium core with two bridging μ2,η3-N,CNЈ
BIAN ligands.
Rint
0.1678
R(F, I>2σ(I))
0.0569
0.0919
wR(F2, all data)
0.1106
3 Synthesis
Preparation of (3,5-CF3-BIAN) (1)
3,5-Bis(trifluoromethyl)aniline (20.0 g, 87.3 mmol) and acenaph-
thenequinone (6.14 g, 33.8 mmol) were dissolved in 160 mL of tolu-
ene. To this solution 10-camphorsulfonic acid (0.26 g, 1.12 mmol)
as catalyst was added. The mixture was refluxed 10 h with a water
separator. After separating of water the solution was filtrated
through Al2O3 and Celite. The volatiles were removed in vacuo.
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Acenaphthenequinone-based α-Diimine Palladium Complexes
The resulting solid was washed with pentane or petrolether and
dried at 80 °C for 2 h in vacuo. The diimine product was obtained
as yellow crystals (16.5 g, 80 %). m.p.: 175.0-176.5 °C. Anal. Calc.
for C28H12F12N2 (604.4 g/mol): C, 55.64; H, 2.00; N, 4.63. Found:
C, 55.65; H, 2.34; N, 4.92 %.
2 and 4) and CCDC-266673 (complex 5). These data can be
obtained free of charge via http://www.ccdc.ac.uk. (or from the
Cambridge CB2 1EZ, U. K.; fax (ϩ44) 1223-336-033 and email
deposit@ccdc.cam.uk).
1H NMR (300.1 MHz, CDCl3): δ 6.85 (d, J ϭ 7.3 Hz, 2H, C10H6), 7.48 (t,
J ϭ 7.7 Hz, 2H, C10H6), 7.60 (s, 4H, C6H3), 7.79 (s, 2H, C6H3), 8.02 (d, J ϭ
8.3 Hz, 2H, C10H6) ppm. 13C NMR (50.3 MHz, CDCl3): 162.3 (s, CϭN),
153.2 (s, C-NϭC), 142.4 (s, C-CϭN), 133.1 (quartet, C-CF3, 2J (C, F) ϭ
34 Hz), 123.2 (quartet, CF3, 1J (C, F) ϭ 273 Hz), 131.6, 130.4, 128.2, 127.4,
123.9, 118.9, 118.3 (s, C and CH) ppm. 19F NMR (188.3 MHz, CDCl3):
Ϫ16.4 (s, CF3) ppm. EI-MS: m/z ϭ 604 Mϩ.
Acknowledgments. We thank the NSFC 20372042 20572062 and the
DFG for financial support.
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Preparation of [PdCl2(3,5-CF3-BIAN)] (2)
PdCl2 (0.826 g, 4.66 mmol) was dissolved in 40 mL of acetonitrile
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8.32 (d, J ϭ 8.0 Hz, 2H, C10H6) ppm. 13C NMR (75.5 MHz, d6-DMSO):
176.8 (s, CϭN), 132.6, 132.4, 131.3, 129.6, 129.3, 128.7, 125.5, 125.3, 125.1,
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To a suspension PdCl2(SMe2)2 (0.268 g, 0.886 mmol) in 30 mL of
diethyl ether methyl lithium (0.65 mL, 0.96 mmol, 1.47 mol/L in
diethyl ether) was drop wise added at Ϫ60 °C. During warm-up
time to Ϫ40 °C the reaction solution became clear. Then methanol
(0.5 mL) was added in order to remove the residual methyl lithium.
After 10 min. diimine ligand 1 (0.535 g, 0.886 mmol) was added to
the solution at Ϫ40 °C. The mixture was gradually warmed up to
the ambient temperature and then continuously stirred for 2 h. The
volatiles were removed in vacuo. The resulting dark brown solid
was extracted with diethyl ether and at Ϫ20 °C dark brown crystals
were obtained from the ether solution. Yield: 56 mg (0.073 mmol,
8.2 %). Anal. Calc. for C29H17ClF12N2Pd (763.31 g/mol): C, 45.63;
H, 2.67; N, 3.67. Found: C, 45.50; H, 2.41; N, 3.83 %.
1H NMR (300.1 MHz, CD2Cl2): δ 0.04 (s, 3H, PdCH3), 6.92 (d, J ϭ 7.3 Hz,
2H, C10H6), 7.54 (t, J ϭ 7.8 Hz, 2H, C10H6), 7.81 (s, 4H, C6H3), 8.00 (s, 2H,
C6H3), 8.18 (d, J ϭ 8.3 Hz, 2H, C10H6) ppm. 19F NMR (188.3 MHz,
CD2Cl2): Ϫ61.7 (s, CF3) ppm.
A crop of a few black-brown single crystals of compound 5 were
obtained from the pentane layered ethereal mother liquid of prep-
aration of 3.
[17] L. H. Staal, G. Van Koten, K. Vrieze, B. Van Santen, C. H.
Stam, Inorg. Chem. 1981, 20, 3598.
[18] G. M. Sheldrick, SHELXL97, SHELXS97, Program for the
Solution of Crystal Structure and Program for the Refinement
of Crystal Structures. University of Göttingen, Germany
(1997). Stoe & Cie. GmbH: STOE IPDS Software. Darmstadt,
Germany (1996).
Supplementary data: Crystallographic data for the structural analy-
sis have been deposited with the Cambridge Crystallographic Data
Centre with CCDC-266671 (complex 3), CCDC-266672 (complex
Z. Anorg. Allg. Chem. 2008, 1517Ϫ1521
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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