Unexpected formation of [(Me2-Xyl-DAB)Pd(η3-6- methyloct-2-en-1- id)][SbF6] (Me2-Xyl-DAB = 2,3-dimethyl-1,4-bis(2,6-dimethylphenyl)- diazabuta-1,3-diene)

Article abstract of DOI:10.1016/j.jorganchem.2013.07.071

Reaction of [(COD)Pd(Me)Cl] with Ag[SbF⁶] and 1.5 eq of the N N Me₂-Xyl-DAB (2,3-dimethyl-N,N0- bis(2,6-dimethylphenyl)-diazabuta-1, 3-dien) afforded the title complex [(Me₂-Xyl-DAB) Pd(η³-6-methylcyclooct- 2-en-1-id)][SbF₆]. From a single crystal XRD study, ¹H NMR and MS it is clear, that the compound contains a cationic Pd(II) complex with a neutral diaza-butadiene chelate ligand and an anionic, thus allylic, η³-6-methyl- cyclooct-2-en-1-id coligand. Presumably, the cationic complex has been formed by methylation of one of the olefin groups of the coordinated COD ligand. Details of this very interesting reaction were discussed in view of much related observations.

Full text of DOI:10.1016/j.jorganchem.2013.07.071

Journal of Organometallic Chemistry 751 (2014) 821e825
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Unexpected formation of [(Me2-Xyl-DAB)Pd(h
3-6-methyloct-2-en-1-
id)][SbF6] (Me2-Xyl-DAB ¼ 2,3-dimethyl-1,4-bis(2,6-dimethylphenyl)-
diazabuta-1,3-diene)
,
Robert Lepski a, Anna Lüning a, Kathrin Stirnat a, Axel Klein a
*
a Institut für Anorganische Chemie, Universität zu Köln, Department für Chemie, Greinstraße 6, D-50939 Köln, Germany
a r t i c l e i n f o
a b s t r a c t
Reaction of [(COD)Pd(Me)Cl] with Ag[SbF6] and 1.5 eq of the N^N Me2-Xyl-DAB (2,3-dimethyl-N,N0-
Article history:
bis(2,6-dimethylphenyl)-diazabuta-1,3-dien) afforded the title complex [(Me2-Xyl-DAB)Pd(h
3-6-methyl-
Received 27 May 2013
Received in revised form
25 July 2013
cyclooct-2-en-1-id)][SbF6]. From a single crystal XRD study, 1H NMR and MS it is clear, that the com-
pound contains a cationic Pd(II) complex with a neutral diaza-butadiene chelate ligand and an anionic,
Accepted 26 July 2013
thus allylic, h
3-6-methyl-cyclooct-2-en-1-id coligand. Presumably, the cationic complex has been formed
by methylation of one of the olefin groups of the coordinated COD ligand. Details of this very interesting
reaction were discussed in view of much related observations.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Palladium
Olefin complexes
Migratory olefin insertion
NMR spectroscopy
XRD
1. Introduction
dimethylphenyl)-2,3-dimethyldiazabuta-1,3-dien (Me2-Xyl-DAB)
(Scheme 2), we unexpectedly obtained the orange title
compound
In our efforts to synthesise new binuclear organometallic
palladium(II) complexes of the composition [(
-N^N0){(N^N)
Pd(Me)}2]2þ, containing diimines (diazenes) as chelate N^N and
bridging N^N0 ligands we recently reported the two compounds [(
h1 1-N^N){Pd(Me)(N^N)}2][SbF6]2 in which both ligands were 2,20-
bipyridine (bpy) or 4,40-Dimethyl-2,20-bipyridine (dmbpy). The
crystal structure of the bpy derivative clearly shows the
h1 h1
[(Me2-Xyl-DAB)Pd(h
3-6-methyl-cyclooct-2-en-1-id)]
m
[SbF6] on which we want to report in this note.
m
-
2. Experimental
,h
2.1. General
m
- ,
binding mode of the bridging ligand, which is also retained in
solution (1H NMR) [1]. The two complexes were synthesised by two
different routes (Scheme 1), one using the isolated mononuclear
complexes [(N^N)Pd(Me)Cl] as intermediates and reacting them with
Ag[SbF6] and 0.5 eq. of the bridging N^N ligand, and the other trying
to obtain the products in a one-pot reaction using [(COD)Pd(Me)Cl]
(COD ¼ cycloocta-1,5-diene) Ag[SbF6] and 1.5 eq. of the N^N ligand.
Both routes gave moderate yields (40e60%). Attempts to use N^N
All preparations were carried out in a dry argon atmosphere
using Schlenk techniques. Solvents (CH2Cl2, THF, toluene, diethyl
ether and MeCN) were dried using an MBRAUN MB SPS-800 solvent
purification system.
2.2. Instruments
NMR spectra were recorded using a Bruker Avance II 300 MHz
spectrometer (1H: 300.13 MHz, 13C: 75.47 MHz) using a triple
resonance 1H, 19F, BB inverse probehead. The unambiguous
assignment of the 1H and 13C resonances was obtained from 1H
TOCSY, 1H COSY, 1H NOESY, gradient selected 1H, 13C HSQC and
HMBC experiments. All 2D NMR experiments were performed us-
ing standard pulse sequences from the Bruker pulse program li-
brary. Chemical shifts were relative to TMS for 1H and 13C. The
spectra analyses were performed by the Bruker TopSpin 2 software.
Elemental analyses were carried out using a Hekatech CHNS
with superior
p-accepting abilities such as the so-called 1,4-
diazabutadienes [2e8], failed largely. In most cases we observed
the rapid formation of elemental Pd and oily product mixtures. In
one case, using the bulky diimine (diazene) ligand N,N0-bis(2,6-
* Corresponding author.
E-mail address: axel.klein@uni-koeln.de (A. Klein).
URL: http://www.klein.uni-koeln.de/
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.07.071

822
R. Lepski et al. / Journal of Organometallic Chemistry 751 (2014) 821e825
Route A
–
–
COD, AgCl
+ AgSbF6
+ 1.5 eq N^N
2+
N
N
Me
N
Pd
Pd
Cl
N
Me
Pd
N
N
Me
+ 1 eq. N^N
–
1) + AgSbF6, AgCl
N
Cl
–
COD
Pd
2) + 0.5 eq. N^N or N^N'
N
Route B
Route B
Me
Scheme 1.
EuroEA 3000 Analyzer. EI-MS spectra were measured with a Fin-
nigan MAT 900 S. Simulations were performed using ISOPRO 3.0.
UV/Vis absorption spectra were recorded with a Varian Cary50 Scan
spectrophotometer.
(s, 3H, CH3imine trans to CH3), 0.43 (s, 3H, PdeCH3). EI-MS: m/
z ¼ 450 [M]þ. UV/Vis (MeCN):
l
¼ 406 sh (ε ¼ 1200 Mꢀ1 cmꢀ1),
346 sh, 315 (3600), 250 sh, 227 (32000), 206 sh nm.
2.6. Synthesis of [(Me2-Xyl-DAB)Pd(
id)][SbF6]
h
3-6-methyl-cyclooct-2-en-1-
2.3. Crystal structure determination
The data collection was performed at T ¼ 293(2) K on a STOE IPDS
To a solution of [(COD)Pd(Me)Cl] (200 mg, 0.75mmol) dissolved in
THF (50 mL), an amount of 259.2 mg (0.75 mmol) Ag[SbF6] was added
in the dark. After stirring for 15 min, the precipitated AgCl wasfiltered
off using Celite. The filtrate was added to a solution of 380 mg
(1.3mmol)ofMe2-Xyl-DABdissolvedinTHF(10 mL). After6 hstirring,
all solvents were distilled off and the resulting material was recrys-
tallised three times using acetone and n-heptane and finally dried
under vacuum (10ꢀ3 mbar). Yield: 150 mg (0.2 mmol, 26%) of an or-
ange solid. Anal. C29H39F6N2Pd1Sb1 (MW ¼ 757.8 g/mol): C, 45.96; H,
5.19;N, 3.70%. Found:C,46.02;H, 5.16;N,3.69%.1HNMR(acetone-d6):
ꢀ
I diffractometer with Mo-K
u
a
radiation (
l
¼ 0.71073 A) employing
ꢀ 2
q scan technique. The structure was solved by direct methods
using the SHELXTL package [9] or SHELX-97 and WinGX [10] and
refinement was carried out with SHELXL97 employing full-matrix
least-squares methods on F2 [11] with F02 ꢁ 2
a
(F20) with the results
shown in Table 1 (and Supporting information). All non-hydrogen
atoms were treated anisotropically; hydrogen atoms were
included by using appropriate riding models.
d
¼ 7.32e7.19 (m, 6H, HXyl), 5.77 (t, 3J ¼ 8.2 Hz, 1H, H2coed), 4.07 (q,
2.4. Reagents
3J ¼ 7.9 Hz, 2H, H1H3coed), 2.42 (s, 6H, CH3imine), 2.36 (s, 6H, CH3-
Xyl), 2.24 (s, 6H, CH3-Xyl), 1.90 (m, 2H, CH2coed), 1.69 (m, 3H,
CH2coed þ C6Hcoed-CH3), 1.36 (m, 2H, CH2coed), 1.09 (d, 2H,
CH2coed), 0.74 (d, 3J ¼ 6.6 Hz, 3H, CH3coed). 13C NMR (acetone-d6):
The complex [(COD)Pd(Me)Cl] [12] and the ligand Me2-Xyl-DAB
[6] were synthesised according to literature procedures. All other
chemicals were purchased by commercial suppliers and were used
without further purification.
d
¼ 178 (2C, C2,3-imine), 148 (2C, C1Xyl), 129 (4C C3,5Xyl), 128 (4C,
C2,6Xyl), 128 (2C, C4Xyl), 113 (1C, C2coed), 80 (2C, C1,3coed), 35 (2C,
C5,7coed), 30 (1C, C6coed), 29 (2C, C4,8coed) 22 (1C, CH3coed),19 (2C,
CH3imine),18(4C,CH32,6Xyl). EI-MS:m/z¼ 523[M]þ. UV/Vis(MeCN):
2.5. Synthesis of [(Me2-Xyl-DAB)Pd(Me)Cl]
l
¼ 386sh(ε ¼ 650Mꢀ1 cmꢀ1), 267(9870), 226sh(22000), 207shnm.
To a solution of 200 mg (0.75 mmol) [(COD)Pd(Me)Cl] 25 mL of
toluene, an amount of 240 mg (0.82 mmol) of Me2-Xyl-DAB were
added stirred for 60 min. The volume was reduced to 10 mL and the
precipitated product was collected by filtration, washed with
diethyl ether and dried. Yield: 302 mg (0.671 mmol, 89%) yellowe
orange solid. Anal. C21H27Cl1N2Pd1 (Mw ¼ 449.33 g/mol): C, 56.13; H
6.06; N, 6.23%. Found: C, 56.10; H, 6.03; N, 6.21%. 1H NMR (CDCl3):
3. Results and discussion
3.1. Preparations and analytical characterisation
Upon reaction of [(COD)Pd(Me)Cl] with Ag[SbF6] in THF solu-
tion, removal of the immediately precipitated AgCl and addition of
1.5 equivalents of the rather bulky N^N Me2-Xyl-DAB to the filtrate
d
¼ 7.20e7.06 (m, 6H, HXyl), 2.25 (s, 6H, CH3Xyl trans to Cl), 2.22 (s
(br), 6H, CH3Xyl trans to CH3), 2.03 (s, 3H, CH3imine trans to Cl), 1.98
CH3
CH3
H3C
CH3
N
CH3
N
H3C
N
CH3
H3C
H3C
N
Pd
L
L
H3C
H3C
CH3
Scheme 2.

R. Lepski et al. / Journal of Organometallic Chemistry 751 (2014) 821e825
823
Table 1
Details of the crystal structure determination and selected structural data of [(Me2-
Xyl-DAB)Pd(
3-6-methyl-cyclooct-2-en-1-id)][SbF6].
The molecular structure of the complex [Pd(
h
3-6-methyl-cyclooct-
2-en-1-id)(Me2-Xyl-DAB)] shows the Me2-Xyl-DAB ligand in a
h
chelate coordination and a
h
3-coordinated 6-Me-cyclooct-2-en-1-
Formula/weight [g/mol]
C29H39F6N2Pd1Sb1/757.77
Tetragonal/P4cc
17.856(2)/20.167(2)
6430.1(12)/8
id (coed), representing an allyl ligand.
Crystal system/space group
The bonding parameters of the complex show unequivocally a
ꢀ
Cell a ¼ b/c [A]
ꢀ
C11eC12 distance of 1.488(9) A in line with a single bond and C11e
3
ꢀ
V [A] /Z
ꢀ
rcalc [g/cm3]/
m
[mmꢀ1
]
1.565/1.454
N1 and C12eN2 distances of 1.284(7) and 1.282(8) A, respectively,
Limiting indices
Refl. coll./uniq./Rint
ꢀ23 < h < 23; ꢀ23 < k < 23; ꢀ26 < l < 26
57764/7842/0.0987
7842/1/368
0.871
0.0438/0.0899
0.0894/0.1036
ꢀ0.964/0.786
clearly showing the double bond character, thus representing the
Me2-Xyl-DAB ligand in its neutral state. Consequently, the anionic
h
Data/restraints/param.
3-6-Me-cyclooct-2-en-1-id represents a cyclic allyl coligand, as
Goof. on F2
has been recently found also in the neutral Pd(II) complex [(Xyl-
Final R1, wR2 [I > 2
R1, wR2 (all data)
a(I)]
Ket)Pd(
h
3-6-methyl-cyclooct-2-en-1-id)] (Xyl-Ketꢀ ¼ N,N-di(2,6-
Drmin/max [10ꢀ6 e/pm3]
xylyl)-1,3-dimethyl-b-ketiminato) [13]. A closer look on the
ꢀ
Distances [A]
bonding properties of the allyl coligand in our complex reveals high
similarity with related [(diimine)Pd(allyl)]þ complexes [14e20].
Subtle differences can be observed in the bonding details of the
[Pd(allyl)] fragment. In our complex the central PdeC2 bond is
shortest, while PdeC1 and PdeC3 are similar (sequence: longe
shortelong), as in the related complex [(Me2-(iPr-C6H4)-DAB)
PdeN1,N2
PdeC1,C2,C3
PdeXa
C1eC2, C2eC3
Angles [ꢂ]
NePdeN
NePdeC1,C3
C1ePdeC3
2.084(5), 2.088(4)
2.126(6), 2.067(6), 2.145(5)
1.988(5), 1.978(5)
1.393(9), 1.387(10)
76.7(2)
105.8(3), 107.7(3)
69.1(3)
Pd(allyl)]þ [14] and the ketiminato complex [(Xyl-Ket)Pd( 3-6-
h
methyl-cyclooct-2-en-1-id)] [13]. A different modus, in which the
central PdeC2 bond is longer than the peripheral PdeC bonds
(shortelongeshort) is observed in [(4-Tol-DAB)Pd(2-Me-allyl)]þ
[15] and [(iPreC6H4eDAB)Pd(allyl)]þ [16], while the complex
[(Me2-Xyl-DAB)Pd(2-Me-allyl)]þ reveals a short PdeC1 bond and
two longer PdeC2 z PdeC3 bonds (shortelongelong) [17]. Sub-
stitution on C1 or C3 as in [Me2-(iPr-C6H4)-DAB)Pd(1-MeO-allyl)]þ
[18] or [(Me2-Xyl-DAB)Pd(MeC(O)CH2eCH(Ө)ꢀC6H4CH3-4)]þ [19],
the latter containing an arene-yl ligand derived from p-methyl-
styrene, leads to three marked different PdeC bonds for the
[Pd(allyl)] fragment. All these modi reflect the high binding flexi-
bility of the allyl coligand, which seems to be largely influenced by
the steric bulk of the other ligands [16], and crystal packing forces.
A very nice example for this flexibility is provided by the compound
[(allyl)Pd(AH2)]þ.[Cl2(Pd(allyl)]ꢀ, in which the oxalamidine ligand
AH2 ((R)N]C(NH(R)ꢀC(]NHR)]NR with R ¼ p-tolyl) forms
strong hydrogen bonds to the Cl atoms of the complex anion. For
the two very different Pd(allyl) moieties shortelongelong se-
quences for the PdeC distances were observed, with the absolute
bond lengths shorter for the anionic complex [Cl2Pd(allyl)]ꢀ [20].
Replacement of the complex anion by trifilate leaves two strong
hydrogen bonds AH.2 O2CCF3, however, slight modification of the
ligand scaffold lead to a shortelongeshort PdeC sequence for the
Pd(allyl) group of the cation [(allyl)Pd(AH2)]þ (the two compounds
were isostructural P-1).
a
Centroids of the C1eC2 and C2eC3 bonds.
we obtained an orange oil (details in the Experimental Section).
Careful recrystallisation from acetone-n-heptane mixtures gave an
orange solid, which turned out to be the novel complex [(Me2-Xyl-
DAB)Pd(
pected complex [(m- ,h
h
3-6-methyl-cyclooct-2-en-1-id)][SbF6]. The initially ex-
h1 1-Me2-Xyl-DAB){Pd(Me)(Me2-Xyl-DAB)}2]
[SbF6]2 (compare Scheme 1) was not obtained.
When trying the route B (Scheme 1) using the ligand Me2-Xyl-
DAB (Scheme 2) we obtained the orange complex [(Me2-Xyl-DAB)
Pt(Me)Cl] in good yield and purity (see Experimental section).
However, carrying out the second part of the reaction under various
conditions always led to decomposition reactions, yielding
elemental Pd, methane and further unidentifiable material. Both
new complexes were analysed and characterised by elemental
analyses, MS, NMR and UV/Vis absorption spectroscopy.
3.2. Crystal and molecular structures
The crystal structure of [(Me2-Xyl-DAB)Pd(h
3-6-methyl-cyclo-
oct-2-en-1-id)][SbF6] was solved and refined in the tetragonal
space group P4cc with results listed in Table 1. The crystal structure
did not reveal any pronounced intermolecular interactions (Fig. 1).
Fig. 1. Crystal structure of [(Me2-Xyl-DAB)Pd(
(right; at 50% probability level (with numbering); protons were omitted for clarity).
h
3-6-methyl-cyclooct-2-en-1-id)][SbF6] (left; viewed along the crystallographic c axis) and molecular structure of the complex cation

824
R. Lepski et al. / Journal of Organometallic Chemistry 751 (2014) 821e825
3.3. NMR spectroscopy
monodentate COD in intermediate (I). Alternatively, the penta-
coordinated intermediate (II) can be formed, which might be in
equilibrium with (I). A number of such pentacoordinated olefin
Pd(II) or Pt(II) complexes with diimines have been reported [21e
27]. Amongst them, the very similar complexes [(N^N)
The complex [(Me2-Xyl-DAB)Pd(h
3-6-methyl-cyclooct-2-en-1-
id)]þ is stable in solution and was studied by 1H and 13C NMR
spectroscopy and mass spectrometry (full data in the Experimental
Section). The 1H NMR spectrum reveals a triplet signal for the HeC2
proton with a 3J coupling constant of 8.2 Hz, which was also
Pd(Me)(COD)]þ with N^N
¼
2,9-dimethyl-1,10-phenanthroline
(dmphen) [24] and 2,9-diaryl-1,10-phenanthroline [25] or [(N^N0)
Pt(Me)(COD)]þ with N^N0
unsymmetrical pyridine-2-
reported for the ketiminato complex [(Xyl-Ket)Pd(
h
3-6-methyl-
¼
cyclooct-2-en-1-id)] [13], while for the cation [(allyl)Pd(AH2)]þ
6.8 Hz were reported [20]. Importantly, for the allyl HC1 or
HC3 protons only one signal of approximate quartet character
carbaldimines 6-R2-Py-2-CH]NR1 with various alkyl groups R1
and R2 [26], exhibit distorted trigonal bipyramidal coordination
with the Me group in one of the two axial (apical) positions,
together with one of the olefin groups, while the other olefin donor
function and the diimine chelate ligand form the equatorial plane
in both the solid state (XRD) and in solution (NMR).
is observed for [(Me2-Xyl-DAB)Pd(h
3-6-methyl-cyclooct-2-en-1-
id)]þ. Also the following H2C(4,8) and H2C(5,7) (for numbering,
see Fig. 1) moieties are magnetically equivalent and obviously the
3
3JHC3-HC4 coupling constant lies in the same range as the JHC3eHC2
The following series of reactions starting from II to the end
coupling (w8 Hz). However, for these four CH2 moieties four
multiplets were detected, thus the two protons of an individual CH2
group are diastereotopic. Detailed 1H1H, 1H13C COSY, long-range
1H13C and 1H1H NOESY experiments allowed the complete assign-
ment of all groups (for details and spectra see Supplementary
material).
product VI are migratory insertions and b-hydride eliminations.
Some of the individual steps in this sequence have been observed in
very related systems [28e30]. Milani et al. recently reported the
reaction of [(bpy)Pd(h1 2-C8H12OMe)], which is the product of
,h
addition of ꢀOMe to the COD complex [27], (compare intermediate
III in Scheme 3) with dppp leading to the allyl complex [(dppp)
Pd(
posed
h
3-1-OMe-cyclooct-2-en-1-id)] [28]. An example of the pro-
s,p insertionseeliminations sequence (III to V) with a final
3.4. Formation of the complex e proposed reaction mechanism
formation of an allyl complex (V to VI) has been reported for the
dimeric complex [Pd(
m
-Cl)(
h
2-2,3-
h
1-7-C8H12R-6)]2 (R ¼
a-chlor-
The unique formation of the 6-Me-cyclooct-2-en-1-id coligand
from the precursor complex [(COD)Pd(Me)Cl] during the formation
oethyl), which forms the allyl complex [Pd(m-Cl)(h
3-1,2,3-C8H12R-
of the ketiminato complex [(Xyl-Ket)Pd(h
3-6-methyl-cyclooct-2-
6)]2 upon moderate heating, as has been shown in detail by NMR
spectroscopy and single crystal XRD [29]. Reactions, very much
related to the very last step in the sequence, the formation of the
anionic allyl ligand from an alkene through palladium-assisted
deprotonation (Hüttel conditions), have been explored for various
cyclic unsaturated systems including cyclooctene and the crystal
en-1-id)] was briefly discussed by Labinger and Bercaw on the
basis of fundamental organometallic reactions [13]. Based on their
assumptions and our observations, we propose the following
mechanism (Scheme 3): After the Cl coligand is cleaved from the
precursor [(COD)Pd(Me)Cl] the resulting solvent complex [(COD)
Pd(Me)(THF)]þ coordinates the N^N. As assumed by Labinger and
Bercaw, the fourth coordination site of the Pd atom is occupied by
structure of the dimeric cyclooct-2-en-1-id complex [(h
3-C8H9)
Pd(
m
-Cl)2Pd(
h
3-C8H9)] has been reported [30].
H3C
CH3
CH3
H3C
+
[(COD)Pd(Me)Cl]
Me
+
N
N
Xyl
5
CH3
N
H3C
CH3
Me
6
Pd
Pd
CH3
–
+ AgSbF6 / AgCl
N
4
2
+ 1.5 eq Me -Xyl-DAB
2
3
7
Xyl
(I)
(II)
8
1
migratory insertion
H
H
+
Me
Me
+
6
7
6
7
β
-hydride
elimination
Xyl
Xyl
5
CH3
CH3
5
8
N
N
8
H
1
Pd
1
Pd
4
CH3
CH3
4
N
N
2
Xyl
Xyl
3
3
2
(IV)
(III)
β
migratory insertion / -hydride elimination
H
Me
5
+
6
+
7
migratory
Xyl
2
Xyl
CH3
CH3
insertion
N
H
N
8
Pd
Pd
1
5
3
CH3
CH3
4
4
N
N
Me
6
1
7
Xyl
2
Xyl
3
8
H
(VI)
(V)
Scheme 3.

R. Lepski et al. / Journal of Organometallic Chemistry 751 (2014) 821e825
825
Interestingly, the formation of pentacoordinated species II seem
Appendix A. Supplementary data
to be largely favoured for N^N with bulky substituents close to the
coordinating site (e.g. dmphen) [21e24]. This might explain, why the
ligands bpy and dmbpy fail to show these reaction sequences and
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.07.071.
form the binuclear complexes [(m- ,h
h1 1-N^N){Pd(Me)(N^N)}2] instead,
following route A in Scheme 1 [1]. The same type of binuclear
complexes were formed, using chelate phosphine ligands, such as
dppe and also here, no methyl transfer has been observed [31].
Presumably, these strong ligands react rapidly with the intermediate
(I) resulting in the binuclear complexes and no intermediate II
having an axial “activated” methyl group [21] is formed. For the
markedly weaker diazabuta-1,3-dien ligands such as Me2-Xyl-DAB,
Xyl-DAB (N,N0-bis(2,6-dimethylphenyl)-diazabuta-1,3-dien) or iPr-
DAB (N,N0-bis(isopropyl)-diazabuta-1,3-dien) the reorganisation to
the pentacoordinated state (I to II) seems to be favoured over the
formation of the binuclear complexes and the axial positioned
methyl group is activated to undergo the proposed migratory
insertion. However, under which condition this axial methyl group is
activated or not (see the above stable complexes) and why the very
related ligands Xyl-DAB and iPr-DAB fail to give the corresponding
allyl complex (although allyl Pd complexes of these ligands were
reported) [17,19,32] remains unclear and will be subject of further
investigations.
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diazabuta-1,3-dien) afforded the title complex [(Me2-Xyl-DAB)
Pd(h
3-6-methyl-cyclooct-2-en-1-id)][SbF6], which has been char-
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The cationic Pd(II) complex contains an anionic 6-Me-cyclooct-2-
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and the Me coligand, presumably in the coordination sphere of Pd.
Bringing together our results with other recent reports on similar
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methyl-cyclooct-2-en-1-id (allyl) Pd(II) complex.
h
3-6-
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We are indebted to Dr. Ingo Pantenburg and Miss Ingrid Müller
(University of Cologne) for single crystal XRD measurements. We
are also grateful for a loan of K2PdCl4 by Johnson Matthey (JM) and
for financial support by Deutsche Forschungsgemeinschaft (project
KL 1194/11-1 (A. L. and A. K).
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Appendix A. Supplementary material
[31] Binuclear complexes [(m- ,h
h1 1-P^P){Pd(Me)(P^P)}2][SbF6]2 have been success-
fully prepared by us following route A for P^P ¼ dppm, dppe, dppp (A. Klein, R.
Lepski, unpublished results). For P^P ¼ dppe, the reaction and product have
been reported: M.A. Zhuravel, D.S. Glueck, C.D. Incarvito, A.L. Rheingold Or-
ganometallics 18 (1999) 4673e4676.
CCDC 939758 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[32] C. Carfagna, G. Gatti, L. Mosca, P. Paoli, A. Guerri, Organometallics 22 (2003)
3967e3970.