Synthesis and reactivity of palladium and nickel β-diimine complexes: Application as catalysts for Heck, Suzuki, and Hiyama coupling reactions

Article abstract of DOI:10.1021/om050201h

The synthesis of a range of sterically hindered β-diimine ligands and their complexes with palladium(II) and nickel(II) of the formula Pd(κ²N,N-RN=CHC(CH₂)_n-CH=NR)(Cl ₂) (R = 2,6-i-Pr₂Ph, 2,6-Me₂Ph, Cy, t-Bu, n = 4, 5) and Ni(κ²N,N-RN=CHC(CH₂)₄-CH=NR) (Br₂) (R = 2,6-i-Pr₂Ph, 2,6-Me₂Ph) has been investigated. Representative X-ray structures of both ligands and complexes have been determined. The use of the palladium complexes as catalysts for Suzuki coupling of aryl halides and arylboronic acids has been examined. In addition, it has been shown that the palladium complexes are also active in the Heck reaction of aryl bromides and methyl acrylate as well as in the Hiyama coupling of aryl halides and phenyltrimethoxysilane.

Full text of DOI:10.1021/om050201h

Organometallics 2005, 24, 3957-3965
3957
Synthesis and Reactivity of Palladium and Nickel
â-Diimine Complexes: Application as Catalysts for Heck,
Suzuki, and Hiyama Coupling Reactions†
Doris Domin,‡ David Benito-Garagorri,‡ Kurt Mereiter,§
Johannes Fro¨hlich,*,‡ and Karl Kirchner*,‡
Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics,
Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
Received March 17, 2005
The synthesis of a range of sterically hindered â-diimine ligands and their complexes with
palladium(II) and nickel(II) of the formula Pd(κ2N,N-RNdCHC(CH2)n-CHdNR)(Cl2) (R )
2,6-i-Pr2Ph, 2,6-Me2Ph, Cy, t-Bu, n ) 4, 5) and Ni(κ2N,N-RNdCHC(CH2)4-CHdNR)(Br2)
(R ) 2,6-i-Pr2Ph, 2,6-Me2Ph) has been investigated. Representative X-ray structures of both
ligands and complexes have been determined. The use of the palladium complexes as catalysts
for Suzuki coupling of aryl halides and arylboronic acids has been examined. In addition, it
has been shown that the palladium complexes are also active in the Heck reaction of aryl
bromides and methyl acrylate as well as in the Hiyama coupling of aryl halides and
phenyltrimethoxysilane.
Introduction
lytic activity of these compounds as polymerization
catalysts may be attributed to such reactions. Recently,
Woods and co-workers synthesized several â-diimine
ligands in which the problematic CH acidity has been
removed by diimine dialkylation.9 In a subsequent
paper, these authors described the synthesis of some
palladium â-diimine complexes and provided structural
comparisons with the corresponding R-diimine ana-
logues.10 The catalytic activity of these complexes has
not been studied so far.
Here we wish to report on the synthesis and charac-
terization of a series of palladium and nickel complexes
containing sterically demanding new â-diimine ligands.
To ascertain that the ligands maintain their diimine
form even under basic conditions, the central carbon
atoms of these ligands are part of five- and six-
membered-ring systems. In addition, we describe the
use of these palladium complexes in the catalytic cross-
coupling of various aryl halides with arylboronic acids
(Suzuki reaction),11 methyl acrylate (Heck reaction),12
and phenyltrimethoxysilane (Hiyama reaction).13
Nickel and palladium complexes containing sterically
demanding R-diimine (diazabutadiene) ligands are highly
efficient catalysts for olefin polymerizations,1-3 for
alkyne cyclotrimerizations,4 and as shown recently also
for Suzuki cross-coupling reactions.5 On the other hand,
few investigations have focused on the chemistry of
analogous nickel and palladium â-diimine complexes.
Feldman et al. reported the synthesis of a sterically
hindered â-diimine ligand bearing no substitutents at
the Câ atom and examined its reactions with Pd(II) and
Ni(II) catalyst precursors.6 However, â-diimines lacking
substituents at the central carbon atom typically form
hydrogen-bridged â-iminoamine tautomers. Accordingly,
in the presence of base, e.g., under catalytic conditions,
facile deprotonation occurs giving rise to the formation
of â-diketiminate complexes7 and other products8 rather
than â-diimine complexes. Consequently, the poor cata-
† Dedicated to Prof. Fritz Sauter on the occasion of his 75th birthday.
* To whom correspondence should be addressed. E-mail: (K.K.)
kkirch@mail.zserv.tuwien.ac.at; (J.F.) jfroehli@ioc.tuwien.ac.at.
‡ Institute of Applied Synthetic Chemistry.
§ Institute of Chemical Technologies and Analytics.
(1) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem.
Soc. 1995, 117, 6414. (b) Svejda, S. A.; Onate, E.; Killian, C. M.;
Johnson, L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33,
2320. (c) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169 (and references therein).
(9) Carey, D. T.; Cope-Eatough, E. K.; Vilaplana-Mafe´, E.; Mair, F.
S.; Pritchard, R. G.; Warren, J. E.; Woods, R. J. J. Chem. Soc., Dalton
Trans. 2003, 1083.
(10) Cope-Eatough, E. K.; Mair, F. S.; Pritchard, R. G.; Warren, J.
E.; Woods, R. J. Polyhedron 2003, 22, 1447.
(11) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (b)
Suzuki, A. In Metal-catalyzed Cross-coupling Reactions; Diederich, F.,
Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998; pp 49-97, and
references therein.
(12) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009.
(13) Mowery, M. E.; DeShong, P. J. Org. Chem. 1999, 64, 1684. (b)
Mowery, M. E.; DeShong, P. J. Org. Chem. 1999, 64, 3266. (c) Brescia,
M.-R.; DeShong, P. J. Org. Chem. 1998, 63, 3156. (d) Pilcher, A. S.;
DeShong, P. J. Org. Chem. 1996, 61, 6901. (e) Denmark, S. E.; Wu, Z.
Org. Lett. 1999, 1, 1495. (f) Denmark, S. E.; Choi, J. Y. J. Am. Chem.
Soc. 1999, 121, 5821. (g) Horn, K. A. Chem. Rev. 1995, 95, 1317. (h)
Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. Rev. 1993, 93,
1317. (i) Gouda, K.; Hagiwara, E.; Hatanaka, Y.; Hiyama, T. J. Org.
Chem. 1996, 61, 7232. (j) Hagiwara, E.; Gouda, K.; Hatanaka, Y.;
Hiyama, T. Tetrahedron Lett. 1997, 38, 439.
(2) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskela¨, M.; Rieger, B.
Organometallics 2001, 20, 2321.
(3) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151.
(4) van der Poel, H.; van Koten, G.; Kokkes, M.; Stam, C. H. Inorg.
Chem. 1981, 20, 2941.
(5) Grasa, G. A.; Hillier, A. C.; Nolan, S. P. Org. Lett. 2001, 3, 1077.
(6) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(7) Parks, J. P.; Holm, R. H. Inorg. Chem. 1968, 7, 1408. (b) Clegg,
W.; Cope, E. K.; Edwards, A. J.; Mair, F. S. Inorg. Chem. 1998, 37,
2317. (b) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev.
2002, 102, 3031.
(8) Radzewich, C. E.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc.
1999, 121, 8673.
10.1021/om050201h CCC: $30.25 © 2005 American Chemical Society
Publication on Web 05/28/2005

3958 Organometallics, Vol. 24, No. 16, 2005
Domin et al.
Scheme 1
Table 1. Details for the Crystal Structure Determinations of Complexes 4a, 4b, 8a, 8b‚3CHCl3, 11a‚CHCl3,
12, and 13
4a
4b
8a
8b‚3CHCl3
11a‚CHCl3
12
13
formula
C
31H44N2
C
32H46N2
C
31H44Cl2N2-
Pd
C
35H49Cl11N2-
Pd
C
16H29Cl5N2-
Pd
C
31H44Cl4N2-
Pd2
C
31H44Br2N2-
Ni
fw
444.68
0.70 × 0.30 × 0.72 × 0.39 × 0.25 × 0.08 × 0.42 × 0.30 ×
0.25 0.32 0.05 0.24
P21/c (no. 14) P1h (no. 2) Pna21 (no. 33) P212121 (no. 19) P21/n (no. 14) C2/c (no. 15)
14.513(1)
27.241(2)
14.662(1)
90
92.308(1)
90
5791.6(6)
8
1.020
458.71
621.98
994.11
533.06
799.28
663.21
cryst size, mm
0.35 × 0.26 × 0.18 × 0.06 × 0.41 × 0.31 ×
0.21
0.06
0.25
P21/n (no. 14)
15.1188(7)
13.3814(6)
17.6356(8)
90
space group
a, Å
b, Å
c, Å
11.6301(5)
11.6674(5)
11.9371(5)
77.150(1)
71.050(1)
69.572(1)
1424.7(1)
2
21.2936(11)
12.1438(6)
12.0665(7)
90
90
90
3120.2(3)
4
1.324
296(2)
0.787
12.1042(5)
17.2671(7)
21.1808(8)
90
90
90
4426.9(3)
4
1.492
173(2)
1.111
10.8303(7)
18.3935(11)
11.8584(7)
90
91.664(1)
90
2361.3(3)
4
1.499
26.0226(10)
19.7160(7)
16.4642(6)
90
126.375(1)
90
6769.6(4)
8
1.568
R, deg
â, deg
γ, deg
V, Å3
Z
115.189(1)
90
3228.6(3)
4
F
calc, g cm-3
1.069
1.364
T, K
297(2)
0.058
173(2)
297(2)
1.354
297(2)
1.401
297(2)
µ, mm-1
0.061
3.096
(Mo KR)
F(000)
θmax, deg
1952
25
59 867
504
27
17 396
1296
30
45 629
2024
30
59 221
1080
30
34 950
3232
25
35 120
1368
30
25 095
no. of rflns
measd
no. of unique
rflns
no. of rflns
I>2σ(I)
10 152
6768
6196
5119
9046
7602
12 865
11 413
6883
5556
5964
4320
9368
6882
no. of params
R1 (I > 2σ(I))a
R1 (all data)
wR2 (all data)
diff Fourier
peaks
611
307
325
446
217
352
325
0.0578
0.0858
0.1922
-0.18/0.30
0.0423
0.0516
0.1193
-0.21/0.26
0.0274
0.0377
0.0655
-0.27/0.30
0.0391
0.0480
0.1031
-0.73/1.05
0.0408
0.0549
0.1032
-0.46/1.04
0.0395
0.0647
0.0931
-0.58/1.00
0.0334
0.0537
0.0924
-0.42/0.62
min./max., e Å-3
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑(w(Fo - Fc )2)/∑(w(Fo2)2)]1/2
.
Results and Discussion
good yields. Characterization of the diimines was ac-
complished by a combination of elemental analysis and
1H and 13C{1H} NMR spectroscopy. In addition, the solid
state structures of 4a and 4b were determined by single-
crystal X-ray diffraction. Crystal data are presented in
Table 1. ORTEP diagrams are depicted in Figures 1 and
2. Despite their chemical similarity, the two compounds
crystallize in entirely different crystal lattices, namely,
4a in a monoclinic lattice with two independent mol-
ecules and 4b in a triclinic lattice with only one
independent molecule (Table 1). However, all the mol-
ecules do exhibit similar key bond lengths and angles
(Table 2 and Supporting Information). They are also
related in conformations including the property that the
electron lone pairs of nitrogens N1 and N2 point in
diverging directions and do not participate in any
significant interaction with surrounding H atoms. The
â-diimine ligand studied by Woods and co-workers10
Ligand Synthesis. The â-diimines 4-7 were syn-
thesized according to the four-step procedure sum-
marized in Scheme 1. The diesters 1a,b were obtained
in good yields using an improved and simplified method14
by alkylation of diethyl malonate with terminal dibro-
moalkanes and sodium ethoxylate as base. Reduction
with LiAlH415 in THF as the solvent led to the formation
of the dialcohols 2a,b. In contrast to the procedure
described in the literature,16 the dialdehydes 3a,b were
generated by a Swern oxidation under standard condi-
tions17 in reasonable isolated yields. Condensation with
different amines in the presence of p-toluenesulfonic
acid afforded finally the desired new â-diimines 4-7 in
(14) Cason, J.; Allen, C. F. J. Org. Chem. 1949, 14, 1036.
(15) Schubert, W. M.; Leahy, S. M. J. Am. Chem. Soc. 1957, 79, 1.
(16) Appelhans, D.; Reichardt, C. Liebigs Ann./Recl. 1997, 2385.
(17) Omura, K.; Swern, D. Tetrahedron 1978, 34, 1651. (b) Ziegler,
F. E.; Sobolov, S. B. J. Am. Chem. Soc. 1990, 112, 2749.

Palladium and Nickel â-Diimine Complexes
Organometallics, Vol. 24, No. 16, 2005 3959
Table 2. Selected Distances and Angles (Å, deg) of Complexes 4a, 4b, 8a, 8b‚3CHCl3, 11a‚CHCl3, 12, and 13
4a
4b
8a
8b‚3CHCl3
11a‚CHCl3
12
13
Pd-Cl1/Ni-Br1
Pd-Cl2/Ni-Br2
Pd-N1
2.276(1)
2.279(1)
2.054(2)
2.041(2)
1.272(3)
1.270(3)
1.488(3)
1.487(3)
1.468(3)
1.461(3)
89.52(3)
91.22(5)
89.44(6)
90.38(7)
0.097
2.292(1)
2.292(1)
2.050(2)
2.046(2)
1.271(4)
1.268(4)
1.502(3)
1.507(3)
1.456(4)
1.463(3)
88.89(3)
91.62(7)
90.15(7)
90.06(9)
0.111
2.305(1)
2.305(1)
2.016(2)
2.023(2)
1.260(3)
1.269(4)
1.508(4)
1.510(4)
1.517(4)
1.514(4)
89.05(3)
92.80(7)
93.78(7)
83.95(9)
0.075
2.323(1)
2.324(1)
2.013(3)
2.008(4)
1.277(5)
1.278(5)
1.493(6)
1.482(6)
1.459(5)
1.459(6)
84.00(5)
93.43(11)
92.92(11)
89.85(15)
0.057
2.3295(3)
2.3581(3)
2.006(2)
1.998(2)
1.270(2)
1.267(2)
1.496(2)
1.498(3)
1.455(2)
1.453(2)
120.34(1)
Pd-N2
N1-C1
1.244(2)
1.245(2)
1.511(3)
1.500(3)
1.431(2)
1.434(2)
1.258(1)
1.258(1)
1.511(1)
1.510(1)
1.435(1)
1.427(1)
N2-C3
C1-C2
C2-C3
N1-C11
N2-C21
Cl1-Pd-Cl2/Br1-Ni-Br2
Cl1-Pd-N1
Cl2-Pd-N2
N1-Pd-N2
rms aplanaritya
boat angle 1b
boat angle 2c
91.24(6)
48.3(2)
41.3(2)
88.0(2)
47.6(3)
41.4(2)
30.4(1)
35.1(1)
31.1(2)
65.5(2)
35.4(2)
a rms aplanarity: root-mean-square deviation (Å) of the atoms Pd, Cl1, Cl2, N1, and N2 from a common least-squares plane. b Boat
angle 1: angle between the planes N1-Pd-N2 and C1-C2-C3. c Boat angle 2: angle between the least-squares planes Pd-N1-C1-C2
and Pd-N2-C3-C2.
Scheme 2
boiling CH3CN for 2 h afforded complexes 8-11 cleanly
in good isolated yields (Scheme 2). All complexes are
thermally robust yellow or brown solids that are stable
to air both in the solid state and in solution.
Figure 1. Structural view of 4a showing 20% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Only
one of the two independent molecules in this structure is
shown.
The identity of the compounds was established by 1H
and 13C{1H} NMR spectroscopy and by elemental analy-
sis. The NMR spectra of 8-11 bear no unusual features,
and it is sufficient to point out that the proton of the
imine CHdN moiety of the â-diimine ligands gives a
characteristic singlet resonance in the range 7.26-7.77
ppm. Likewise, in the 13C{1H} NMR spectra the imine
carbon atom exhibits a singlet resonance at about 174
ppm. Structural views of 4a, 4b, and 11a, as determined
by X-ray crystallography (Table 1), are depicted in
Figures 3-5. Selected geometric data are reported in
Table 2. The expected bidentate coordination of the
diimine nitrogen atoms to the Pd(II) center, forming
distorted square-planar coordination environments, is
found for all three complexes (Figures 3-5, Table
2).1-3,6,10 As in related Pd(II) â-diimine complexes,10 the
six-membered chelate ring adopts a boat conformation.
This boat conformation is the result of the presence of
two planar Pd-N(sp2)dCH(sp2)-C systems and two
comparatively low bond angles N1-Pd-N2 ≈ 90° and
C1-C2-C3 ≈ 108° in the chelate ring. It can be noted
that the degree of the boat conformation is strongly
dependent on the space requirement of the N substitu-
ent R (e.g., t-Bu vs 2,6-i-P2Ph): In case of the less
demanding t-Bu substituent (complex 11a) the boat
conformation of the six-membered chelate ring is most
Figure 2. Structural view of 4b showing 40% thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
adopts in free state a conformation of the approximate
symmetry C2 and differs in this respect from 4a and
4b.
Synthesis of Pd and Ni â-Diimine Complexes.
Treatment of PdCl2(CH3CN)2 with the ligands 4-7 in

3960 Organometallics, Vol. 24, No. 16, 2005
Domin et al.
Scheme 3
at one side of the complex with consequent short
separations between C(110) and C(210) and their hy-
drogen atoms (cf. Figures 3 and 4). Quantities showing
this feature have been included in Table 2. The protrud-
ing character of the two chloride ions in these complexes
makes them prone to further interactions or reactions
(vide infra). In the case of 8b and 11a this leads to the
formation of the well-crystallized solvates 8b‚3CHCl3
and 11a‚CHCl3, which are both stabilized by C-H‚‚‚Cl
hydrogen bonds from chloroform to chloride. In particu-
lar 11a‚CHCl3 stands out in having an almost perfectly
symmetrically bifurcated C-H‚‚‚Cl interaction (H(16)‚
‚‚Cl(1) ) 2.64 Å, H(16)‚‚‚Cl(1) ) 2.67 Å) (Figure 5).
It has to be noted that if PdCl2 is reacted overnight
with 4a in CH2Cl2 at room temperature, the dinuclear
complex 12 is obtained in 36% isolated yield (Scheme
3). For comparison, an analogous complex with the same
structural motif has been reported recently by Woods
and co-workers.10 Spectroscopic features are very similar
to those of 8a and are not discussed here. An ORTEP
diagram is depicted in Figure 6. Selected bond distances
of this complex, not given in Table 2, are reported in
the caption.
Figure 3. Structural view of 8a showing 20% thermal
ellipsoids.
The corresponding â-diimine complexes of Ni(II) (13,
14) were readily prepared by reaction of NiBr2(DME)
with the ligands 4a and 4b in 86 and 65% isolated yields
(Scheme 4). The purple complexes are paramagnetic and
Figure 4. Structural view of 8b‚3CHCl3 showing 40%
thermal ellipsoids. Hydrogen atoms and CHCl3 molecules
are omitted for clarity.
Figure 5. Structural view of 11a‚CHCl3 showing 20%
thermal ellipsoids. Most hydrogen atoms are omitted. The
broken lines from Cl(1) and Cl(2) to H(1s)-C(1s) represent
a symmetrically branched C-H‚‚‚Cl hydrogen bond.
pronounced (Figure 5). On replacement of the t-Bu by
the much bulkier 2,6-i-Pr2Ph substituent (complexes 8a,
8b, 12, and 13), the boat conformation is forced to be
distinctly flatter because of mutual i-Pr interferences
Figure 6. Structural view of 12 showing 20% thermal
ellipsoids. Selected distances (Å; for further data see
Table 2): Pd2-Cl1 2.334(1), Pd2-Cl3 2.270(1), Pd2-Cl2
2.327(1), Pd2-Cl4 2.266(2).

Palladium and Nickel â-Diimine Complexes
Organometallics, Vol. 24, No. 16, 2005 3961
Table 3. Suzuki Cross-Coupling of Aryl Halides
with Arylboronic Acidsa
Scheme 4
entry
X
R
R′
catalyst
isolated yield (%)
1
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 4-Me
Br 2-Me
Br 4-COMe
Br 4-OMe
Br 2-OMe
Br 2,6-Me
Br 2,6-Me
Br 4-Me
Br 4-Me
Cl 4-Me
Cl 4-Me
Cl 4-COMe
Cl 4-COMe
Cl 4-COMe
Cl 4-OMe
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
PdCl2
PdCl2, 4a
PdCl2, 4b
PdCl2, 5a
PdCl2, 5b
PdCl2, 6a
PdCl2, 6b
PdCl2, 7a
PdCl2, 7b
8a
18b
65 (82b)
80b
74b
73b
97b
96b
93b
76b
89
2
3
4
5
display contact-shifted 1H NMR spectra with relatively
narrow line widths at room temperature. The X-ray
crystal structure of 13 is shown in Figure 7. The Ni(II)
atom adopts a pseudo-tetrahedral coordination geom-
etry. In analogy with the above-described Pd complexes,
the six-membered chelate ring adopts a boat conforma-
tion of flat shape similar to the Pd complexes.
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
8b
98b
83
9a
9b
95b
74 (97b)
93b
73 (89b)
90b
56
10a
10b
11a
11b
8a
8a
96
8a
82c
57
8a
8a
7
8a
41c
6
2,6-Me 8a
3-OMe 8a
53
H
H
H
H
H
H
8a
8a
8a
8a
9a
8a
9d
18c
25e
51c
35e
0c
a Reaction conditions: aryl halide (1.0 mmol), boronic acid (1.5
mmol), Cs2CO3 (2.0 mmol) and catalyst (3 mol %). b Determined
by GC. c The reaction was stirred for 18 h. d The reaction was
stirred for 4.5 h. e The reaction was stirred for 4 h.
Figure 7. Structural view of 13 showing 20% thermal
ellipsoids.
Suzuki Coupling. Palladium complexes containing
R-diimine ligands are excellent catalysts for the Suzuki
coupling.5 On the basis of these findings we were
interested in whether palladium complexes containing
â-diimine ligands exhibit similar reactivities in C-C
bond coupling reactions. Accordingly, we investigated
the activity of PdCl2 in the presence of â-diimine ligands
4-7 as well as the activity of complexes 8-11 as
catalysts for the coupling of various aryl halides with
aryl boronic acids. The results of this study are sum-
marized in Table 3. In all cases the reactions were
performed with 3 mol % of catalysts in dioxane at 80
°C with Cs2CO3 acting as base. These conditions have
not been optimized.
In general, the coupling reaction is more efficient if
complexes 8-11 are used (entries 10-17) instead of
PdCl2 in the presence of 1 equiv of ligands 4-7 (entries
2-9). While it is difficult to establish any clear trends
in the catalytic activity of complexes 8-11 on these
preliminary data, on average complexes 8 and 9 show
higher activity than complexes 10 and 11 (entries 10-
17). This reactivity trend suggests that the stronger
donating ability of alkyl substituents, making the ligand
more electron-rich, renders the catalyst less active.
We observed that the coupling of 4-bromoacetophe-
none and 4-bromotoluene with phenylboronic acid pro-
ceeded smoothly to give 4-acetylbiphenyl and 4-meth-
ylbiphenyl in high yields (entries 10-17, 19). Moreover,
with the electronically deactivated and thus more chal-
lenging substrate 4-bromoanisole, good conversions
could be achieved (entry 20). Even the sterically de-
manding 2-bromotoluene and 2-bromoanisole gave ac-
ceptable yields (entries 18 and 21). On the other hand,
little or no activity was observed for 2,6-disubstituted
substrates (entries 22-24). Attempts to couple 4-bro-
motoluene with the meta-substituted 3-methoxyphenyl-
boronic acid resulted in reasonable yields (entry 25). In
contrast, with meta-substituted substrates low yields
were observed in the case of palladium R-diimine
complexes.5 Finally, the catalytic effect was confirmed
by running the standard reaction on 4-bromotoluene
without ligand (entry 1). The reaction proceeds, but led
to only low yields.
Finally, it has to be mentioned that attempts to couple
arylbromides with phenylboronic acid in the presence
of nickel â-diimine complexes proved to be little effec-
tive, resulting in yields < 10%. Accordingly, the nickel-
catalyzed Suzuki coupling has not been further inves-
tigated.
Heck and Hiyama Coupling. Catalytic reactions
other than the Suzuki cross-coupling were also probed.
The Heck reaction between various aryl bromides and

3962 Organometallics, Vol. 24, No. 16, 2005
Domin et al.
Table 4. Heck Cross-Coupling of Aryl Halides with
Olefinsa
Table 5. Hiyama Cross-Coupling of Aryl Halides
with Phenyltrimethoxysilanea
entry
X
R
catalyst
isolated yield (%)
1
I
H
H
H
H
H
PdCl2
PdCl2, 4a
PdCl2, 5a
8a
66c
99c
96c
93c
98c
53b
39b
74b
27b
74b
73b
62b
86b
87b
87
entry
X
R
catalyst
isolated yield (%)
2
I
1
2
3
4
5
6
Br
Br
Br
Br
Br
Cl
4-COMe
4-COMe
4-OMe
2-OMe
2,6-Me
4-COMe
PdCl2, 4a
64
3
I
8a
8a
8a
8a
8a
87
4
I
33b
0b
5
I
9a
6
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-COMe
4-Me
PdCl2
PdCl2, 4a
PdCl2, 4b
PdCl2, 5a
PdCl2, 5b
PdCl2, 6a
PdCl2, 6b
PdCl2, 7a
PdCl2, 7b
8a
29b
62b
7
8
a Reaction conditions: aryl halide (1.0 mmol), phenyltrimeth-
oxysilane (2 mmol), Bu4NF (2.0 mmol), and catalyst (3 mol %).
b The reaction was stirred for 18 h.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Conclusion
We report the efficient synthesis of new sterically
hindered N,N′-diaryl and dialkyl â-diimines with the
central carbon atom being part of both five- and six-
membered-ring systems to avoid the formation of
â-diketiminates. These compounds are excellent ligands
for the preparation of Pd(II) and Ni(II) complexes. The
use of the palladium complexes in the catalytic cross-
coupling of various aryl halides with arylboronic acids,
methyl acrylate, and phenyltrimethoxysilane is de-
scribed. These complexes proved to be active as catalysts
for Suzuki coupling reactions and are comparable to
related R-dimine systems, thus representing an inter-
esting alternative to existing catalytic systems. In
preliminary results the investigated palladium â-di-
imine complexes turned out to be less efficient for Heck
and Hiyama coupling reactions under the reaction
conditions chosen. Attempts to optimize these processes
are currently in progress.
8b
82b
85
9a
9b
93b
100b
66b
99b
100b
15
10a
10b
11a
11b
8a
4-Me
8a
16d
0
2-OMe
8a
2,6-Me
8a
5d
a Reaction conditions: aryl halide (1.0 mmol), methyl acrylate
(1.2 mmol), NEt3 (1.4 mmol), and catalyst (3.5 mol %). b Deter-
mined by GC. c The reaction was stirred for 2 h. d The reaction
was stirred for 18 h.
methyl acrylate has been studied utilizing both PdCl2
in the presence of â-diimine ligands 4-7 and complexes
8-11 as catalyst precursors. The results are sum-
marized in Table 4. In all cases the reactions were
performed with 3.5 mol % of catalysts in NMP as the
solvent at 140 °C with NEt3 (1.4 equiv) acting as base.
Again, the conditions have not been optimized.
Experimental Section
General Information. All manipulations were performed
under an inert atmosphere of argon by using Schlenk tech-
niques. All chemicals were standard reagent grade and used
without further purification. The solvents were purified ac-
cording to standard procedures.18 The deuterated solvents were
purchased from Aldrich and dried over 4 Å molecular sieves.
PdCl2(CH3CN)2 and NiBr2(DME) were prepared according to
the literature.19,20 1H and 13C{1H} NMR spectra were recorded
on Bruker AVANCE-200 and -250 spectrometers and were
referenced to SiMe4. 1H and 13C{1H} NMR signal assignments
were confirmed by 1H-COSY, DEPT-135, and HMQC(1H-13C)
experiments.
1,1-Cyclopentanedicarboxylicacid Diethyl Ester (1a).
Malonic acid ethyl ester (40.8 g, 255 mmol) was added
dropwise to a solution of sodium ethoxide and dry ethanol
freshly prepared from sodium (11.7 g, 508 mmol) and dry
ethanol (250 mL). The mixture was refluxed for 30 min. After
dilution with dry ethanol (165 mL) 1,4-dibromobutane (50.0
g, 232 mmol) was added dropwise, and the mixture was kept
boiling for 3 h and was stirred then at room temperature for
18 h. After evaporation of the solvent the residue was dissolved
In the case of aryl iodides, coupling products are
formed in essentially quantitative yield independent of
whether complexes 8-11 are used directly (entries 2-5)
or whether PdCl2 is used with 1 equiv of ligands 4-7
(entries 7-14). In the case of 4-bromoacetophenone,
however, the Heck reaction is clearly more efficient if
complexes 8-11 are used directly (entries 15-22). There
is no clear trend in the catalytic activity of complexes
8-11. With the electronically deactivated and/or steri-
cally demanding aryl bromides little or no activity was
observed (entries 23-26). This may be attributed to
catalyst deactivation due to the observed formation of
palladium black.
The Hiyama coupling was evaluated with PdCl2/4a
and 8a as catalyst precursors. The results of this study
are summarized in Table 5. Both 4-bromo- and 4-chloro-
acetophenone can be coupled with phenyltrimethoxy-
silane in dioxane at 80 °C in reasonable yields (entries
1, 2, and 6). The catalyst/ligand system was not suitable
for electronically deactivated and/or sterically demand-
ing substrates. The reaction with 4-bromoanisole and
1-bromo-2,6-dimethylbenzene gave only 33 and 29%
yield, respectively, while with 2-bromoanisole no con-
version could be achieved (entries 3-5).
(18) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: New York, 1988.
(19) Hartley, F. R.; Murray, S. G.; McAuliffe, C. A. Inorg. Chem.
1979, 18, 1394.
(20) Casalnuovo, A. L.; RajanBabu, T. V.; Ayers, T. A.; Warren, T.
H. J. Am. Chem. Soc. 1994, 116, 9869.

Palladium and Nickel â-Diimine Complexes
Organometallics, Vol. 24, No. 16, 2005 3963
in water (270 mL) and extracted with Et2O (5 × 100 mL). The
combined organic layers were washed with saturated NaCl
solution (2 × 100 mL), dried over Na2SO4, and filtered. The
solvent was evaporated and the crude product was purified
by vacuum distillation to give a colorless liquid. Yield: 46.8 g
1,1-Cyclohexanedicarbaldehyde (3b). 1,1-Cyclohex-
anedimethanol (4.4 g, 30.7 mmol) gave analogously to the
procedure described for 3a a colorless liquid. Yield: 2.1 g (49%).
1H NMR (CDCl3): δ 9.46 (s, 2H, CHO), 1.92-1.77 (m, 4H,
C(CH2CH2)2CH2), 1.55-1.29 (m, 4H, C(CH2CH2)2CH2). 13C{1H}
NMR (CDCl3): δ 200.40 (CHO), 63.51 (C(CH2CH2)2CH2), 26.43
(C(CH2CH2)2CH2), 24.70 (C(CH2CH2)2CH2), 21.61 (C(CH2CH2)2-
CH2). Bp: 40-45 °C/0.05 mbar.
3
(94%). 1H NMR (CDCl3): δ 4.11 (q, 4H, JHH ) 7.1 Hz,
COOCH2CH3), 2.18-2.03 (m, 4H, C(CH2CH2)2), 1.67-1.55 (m,
3
4H, C(CH2CH2)2), 1.17 (t, 6H, JHH ) 7.1 Hz, COOCH2CH3).
13C{1H} NMR (CDCl3): δ 172.44 (COOCH2CH3), 60.96 (CO-
OCH2CH3), 60.18 (C(CH2CH2)2), 34.26 (C(CH2CH2)2), 25.27
(C(CH2CH2)2), 13.84 (COOCH2CH3). Bp: 110-114 °C/15 mbar.
1,1-Cyclohexanedicarboxylic Acid Diethyl Ester (1b).
Malonic acid ethyl ester (30.0 g, 187 mmol) and 1,5-dibro-
mopentane (39.1 g, 170 mmol) gave analogously to the
procedure described for 1a a colorless liquid. Yield: 21.3 g
N,N′-(1,1-Cyclopentylidenedimethylidyne)bis(2,6-bis-
(1-methylethyl)benzenamine) (4a). 1,1-Cyclopentanedicar-
baldehyde (0.30 g, 2.38 mmol), 2,6-diisopropylaniline (0.84 g,
4.76 mmol), p-toluenesulfonic acid monohydrate (0.09 g, 0.48
mmol), and toluene (10 mL) was heated under reflux over a
Dean-Stark trap for 6 h. After cooling to room temperature
the solvent was evaporated and saturated Na2CO3 solution (10
mL) and Et2O (10 mL) were added to the residue. The mixture
was stirred for 10 min, the layers were separated, and the
water layer was extracted with Et2O (3 × 10 mL). The
combined organic layers were washed with water (1 × 10 mL)
and saturated NaCl solution (1 × 10 mL). The solution was
dried over Na2SO4 and filtered, and the solvent was evapo-
rated. The oily residue was purified by bulb-to-bulb distillation
to give colorless crystals. Yield: 8.90 g (84%). 1H NMR
(CDCl3): δ 7.84 (s, 2H, CHN), 7.18-7.03 (m, 6H, Haromat), 3.01
3
(59%). 1H NMR (CDCl3): δ 4.12 (q, 4H, JHH ) 7.0 Hz,
COOCH2CH3), 1.98-1.83 (m, 4H, C(CH2CH2)2CH2), 1.56-1.27
3
(m, 6H, C(CH2CH2)2CH2), 1.18 (t, 6H, JHH ) 7.0 Hz,
COOCH2CH3). 13C{1H} NMR (CDCl3): δ 171.75 (COOCH2-
CH3), 60.85 (COOCH2CH3), 54.74 (C(CH2CH2)2CH2), 31.17
(C(CH2CH2)2CH2), 25.06 (C(CH2CH2)2CH2), 22.56 (C(CH2CH2)2-
CH2), 13.88 (COOCH2CH3). Bp: 116-122 °C/11 mbar.
1,1-Cyclopentanedimethanol (2a). A solution of 1,1-
cyclopentanedicarboxylic acid diethyl ester (10.2 g, 47 mmol)
in dry THF (50 mL) was added dropwise over a period of 30
min to a suspension of LiAlH4 (4.0 g, 104 mmol) in dry THF
(100 mL) at 5 °C. The reaction mixture was stirred at room
temperature for 90 min. After cooling to 5 °C EtOAc (50 mL)
was added, and the resulting solution was poured into 2 M
HCl (125 mL). After separation of the layers, the water layer
was extracted with EtOAc (5 × 80 mL). The combined organic
layers were washed with saturated NaCl solution (2 × 80 mL),
dried over Na2SO4, and filtered. The solvent was removed, and
the crude solid was recrystallized from a mixture of EtOAc
and petroleum ether to give colorless crystals. Yield: 5.1 g
3
(septet, 4H, JHH ) 6.9 Hz, CH(CH3)2), 2.32-2.18 (m, 4H,
C(CH2CH2)2), 1.98-1.86 (m, 4H, C(CH2CH2)2), 1.17 (d, 24H,
3JHH ) 7.0 Hz, CH(CH3)2). 13C{1H} NMR (CDCl3): δ 168.76
(CHN), 148.82 (Caromat), 137.40 (Cortho), 123.86 (Cpara), 122.78
(Cmeta), 58.39 (C(CH2CH2)2), 33.32 (C(CH2CH2)2), 27.66 (CH-
(CH3)2), 25.54 (C(CH2CH2)2), 23.38 (CH(CH3)2). Bp: 110-120
°C/0.02 mbar. Mp: 56-58 °C. Anal. Calcd for C31H44N2
(444.71): C, 83.73; H, 9.97; N, 6.30. Found: C, 83.78; H, 10.10;
N, 6.28.
N,N′-(1,1-Cyclohexylidenedimethylidyne)bis(2,6-bis(1-
methylethyl)benzenamine) (4b). 1,1-Cyclohexanedicarbal-
dehyde (1.00 g, 7.93 mmol) and 2,6-diisopropylaniline (3.10 g,
15.86 mmol) gave analogously to the procedure described for
4a colorless crystals. Yield: 2.08 g (57%). 1H NMR (CDCl3): δ
7.66 (s, 2H, CHN), 7.09-6.93 (m, 6H, Haromat), 2.94 (septet, 4H,
3JHH ) 6.9 Hz, CH(CH3)2), 2.04-1.89 (m, 4H, CH(CH2CH2)2-
CH2), 1.75-1.61 (m, 4H, CH(CH2CH2)2CH2), 1.60-1.43 (m, 2H,
1
(82%). H NMR (CDCl3): δ 3.60 (s, 4H, CH2OH), 2.73 (s, 2H,
OH), 1.68-1.56 (m, 4H, C(CH2CH2)2), 1.49-1.35 (m, 4H,
C(CH2CH2)2). 13C{1H} NMR (CDCl3): δ 70.11 (CH2OH), 48.30
(C(CH2CH2)2), 31.77 (C(CH2CH2)2), 25.12 (C(CH2CH2)2). Mp:
94-95 °C.
1,1-Cyclohexanedimethanol (2b). Cyclohexane-1,1-di-
carboxylic acid diethyl ester (28.4 g, 124 mmol) gave analo-
gously to the procedure described for 2a colorless crystals.
Yield: 12.7 g (71%). 1H NMR (CDCl3): δ 3.76 (s, 2H, OH), 3.45
(s, 4H, CH2OH), 1.44-1.13 (m, 10H, C(CH2CH2)2CH2). 13C{1H}
NMR (CDCl3): δ 68.94 (CH2OH), 38.01 (C(CH2CH2)2CH2),
29.45 (C(CH2CH2)2CH2), 26.24 (C(CH2CH2)2CH2), 21.16
(C(CH2CH2)2CH2). Mp: 96-97 °C.
3
CH(CH2CH2)2CH2), 1.07 (d, 24H, JHH ) 7.0 Hz, CH(CH3)2).
13C{1H} NMR (CDCl3): δ 169.59 (CHN), 148.85 (Caromat), 137.38
(Cortho), 123.90 (Cpara), 122.81 (Cmeta), 50.41 (C(CH2CH2)2CH2),
21.12 (C(CH2CH2)2CH2), 27.61 (CH(CH3)2), 25.59 (C(CH2-
CH2)2CH2), 23.48 (CH(CH3)2), 22.07 (C(CH2CH2)2CH2). Bp:
110-120 °C/0.05 mbar. Mp: 81-82 °C. Anal. Calcd for
C32H46N2 (458.74): C, 83.79; H, 10.11; N, 6.11. Found: C,
83.75; H, 10.29; N, 6.04.
1,1-Cyclopentanedicarbaldehyde (3a). A solution of dry
dimethyl sulfoxide (9.6 mL, 135.2 mmol) in dry CH2Cl2 (20
mL) was added dropwise at -78 °C to oxalyl chloride (5.8 mL,
67.6 mmol) in dry CH2Cl2 (40 mL). After stirring for 30 min
at this temperature, 1,1-cyclopentanedimethanol (4.0 g, 30.7
mmol) in dry CH2Cl2 (40 mL) was added dropwise at a
temperature of -78 to -70 °C. After stirring for 90 min at
-70 °C the mixture was cooled to -78 °C, NEt3 (30.6 mL, 215
mmol) was added slowly, and the mixture was stirred for 30
min at this temperature. The reaction mixture was allowed
to warm to room temperature over the course of 1 h. The
reaction was terminated by addition of saturated NH4Cl
solution (75 mL), and the two layers were separated. The
aqueous layer was extracted with CH2Cl2 (4 × 50 mL), and
the combined organic layers were washed with 2 M HCl (5 ×
70 mL) and saturated NaCl solution (2 × 70 mL). The solution
was dried over Na2SO4, and after filtration the solvent was
evaporated. The crude liquid was purified by bulb-to-bulb
distillation to give a colorless liquid. Yield: 2.0 g (52%). 1H
NMR (CDCl3): δ 9.67 (s, 2H, CHO), 2.14-1.99 (m, 4H, C(CH2-
CH2)2), 1.77-1.60 (m, 4H, C(CH2CH2)2). 13C{1H} NMR (CD-
Cl3): δ 199.62 (CHO), 69.81 (C(CH2CH2)2), 29.15 (C(CH2CH2)2),
25.90 (C(CH2CH2)2). Bp: 20-22 °C/0.01 mbar.
N,N′-(1,1-Cyclopentylidenedimethylidyne)bis(2,6-di-
methylbenzenamine) (5a). 1,1-Cyclopentanedicarbaldehyde
(0.30 g, 2.38 mmol) and 2,6-dimethylaniline (0.58 g, 4.76 mmol)
gave analogously to the procedure described for 4a a colorless
oil. Yield: 0.61 g (77%). 1H NMR (CDCl3): δ 7.73 (s, 2H, CHN),
6,97-6.88 (m, 4H, Hmeta), 6.87-6.77 (m, 2H, Hpara), 2.18-2.05
(m, 4H, C(CH2CH2)2), 2.01 (s, 12H, CH3), 1.85-1.74 (m, 4H,
C(CH2CH2)2). 13C{1H} NMR (CDCl3): δ 169.48 (CHN), 150.90
(Caromat), 127.93 (Cmeta), 126.73 (Cortho), 123.42 (Cpara), 58.45
(C(CH2CH2)2), 33.26 (C(CH2CH2)2), 25.26 (C(CH2CH2)2), 18.26
(CH3). Bp: 80-100 °C/0.02 mbar.
N,N′-(1,1-Cyclohexylidenedimethylidyne)bis(2,6-di-
methylbenzenamine) (5b). 1,1-Cyclohexanedicarbaldehyde
(0.50 g, 3.56 mmol) and 2,6-dimethylaniline (1.06 g, 8.72 mmol)
gave analogously to the procedure described for 4a a colorless
oil. Yield: 0.96 g (70%). 1H NMR (CDCl3): δ 7.73 (s, 2H, CHN),
7.11-7.02 (m, 4H, Hmeta), 7.01-6.89 (m, 2H, Hpara), 2.16 (s,
12H, CH3), 1.89-1.72 (m, 4H, CH(CH2CH2)2CH2), 1.71-1.55
(m, 4H, CH(CH2CH2)2CH2), 1.54-1.35 (m, 2H, CH(CH2-
CH2)2CH2). 13C{1H} NMR (CDCl3): δ 170.13 (CHN), 150.95
(Caromat), 127.93 (Cmeta), 126.55 (Cortho), 123.43 (Cpara), 50.59
(C(CH2CH2)2CH2), 31.17 (C(CH2CH2)2CH2), 25.64 (C(CH2-

3964 Organometallics, Vol. 24, No. 16, 2005
Domin et al.
CH2)2CH2), 22.21 (C(CH2CH2)2CH2), 18.45 (CH3). Bp: 110-
115 °C/0.05 mbar.
CH2 and CH(CH2CH2)2CH2), 1.46-1.44 (d, JHH ) 6.70 Hz, 12H,
CH(CH3)2), 1.21-1.18 (d, JHH ) 7.31 Hz, 12H, CH(CH3)2). 13C-
{1H} NMR (CDCl3): δ 173.50 (HCdN), 145.91 (Caromat), 140.44
(Cortho), 128.17 (Cpara), 123.64 (Cmeta), 51.15 (C(CH2CH2)2CH2),
34.70 (C(CH2CH2)2CH2), 28.65 (CH(CH3)2), 24.06 (C(CH2-
CH2)2CH2), 23.56 (CH(CH3)2), 21.22 (C(CH2CH2)2CH2).
N,N′-(1,1-Cyclopentylidenedimethylidyne)bis(cyclo-
hexaneamine) (6a). 1,1-Cyclopentanedicarbaldehyde (0.42 g,
3.32 mmol) and cyclohexanamine (0.72 g, 7.32 mmol) gave
analogous to the procedure described for 4a a colorless oil.
1
Yield: 0.67 g (70%). H NMR (CDCl3): δ 7.60 (s, 2H, CHN),
Pd{N,N′-(1,1-Cyclopentylidenemethylidyne)bis(2,6-di-
methylbenzenamine)}Cl2 (9a). This complex has been pre-
pared analogously to 8a with PdCl2 (267 mg, 1.50 mmol) and
5a (500 mg, 1.50 mmol) as the starting materials. Yield: 690
mg (90%). Anal. Calcd for C23H28Cl2N2Pd (509.80): C, 54.19;
3.01-2.76 (m, 2H, CH(CH2CH2)2CH2), 1.90-1.01 (m, 28H, Cy
+ Cp). 13C{1H} NMR (CDCl3): δ 165.10 (CHN), 69.36 (CH-
(CH2CH2)2CH2), 56.23 (C(CH2CH2)2), 34.26 (CH(CH2CH2)2-
CH2), 33.86 (C(CH2CH2)2), 25.59 (C(CH2CH2)2), 24.72 (CH-
(CH2CH2)2CH2), 24.65 (CH(CH2CH2)2CH2). Bp: 60-70 °C/0.05
mbar.
1
H, 5.54; N, 5.50. Found: C, 54.22, H, 5.48; N, 5.60. H NMR
(CDCl3): δ 7.52 (s, 2H, HCdN), 7.18-7.11 (m, 6H, Ph), 2.66
(s, 12H, CH3), 2.40-1.79 (m, 8H, CH(CH2CH2)2 and CH-
(CH2CH2)2. 13C{1H} NMR (CDCl3): δ 165.54 (HCdN), 146.32
(Caromat), 139.70 (Cortho), 129.14 (Cpara), 122.34 (Cmeta), 51.26
(C(CH2CH2)2), 34.85 (C(CH2CH2)2), 25.72 (C(CH2CH2)2), 18.42
(CH3).
N,N′-(1,1-Cyclohexylidenedimethylidyne)bis(cyclo-
hexaneamine) (6b). 1,1-Cyclohexanedicarbaldehyde (0.60 g,
4.28 mmol) and cyclohexanamine (1.05 g, 10.47 mmol) gave
analogously to the procedure described for 4a a colorless oil.
1
Yield: 0.61 g (47%). H NMR (CDCl3): δ 7.40 (s, 2H, CHN),
3.00-2.75 (m, 2H, CH(CH2CH2)2CH2), 1.83-0.99 (m, 30H, Cy
+ Cp). 13C{1H} NMR (CDCl3): δ 165.60 (CHN), 69.80 (CH-
(CH2CH2)2CH2), 47.58 (C(CH2CH2)2CH2), 34.28 (CH(CH2CH2)2-
CH2), 32.02 (C(CH2CH2)2CH2), 25.85 (C(CH2CH2)2CH2),
25.54 (CH(CH2CH2)2CH2), 24.69 (CH(CH2CH2)2CH2), 22.06
(C(CH2CH2)2CH2). Bp: 60-70 °C/0.05 mbar.
Pd{N,N′-(1,1-Cyclohexylidenemethylidyne)bis(2,6-di-
methylbenzeneamine)}Cl2 (9b). This complex has been
prepared analogously to 8a with PdCl2 (307 mg, 1.73 mmol)
and 5b (600 mg, 1.73 mmol) as the starting materials. Yield:
750 mg (84%). Anal. Calcd for C24H30Cl2N2Pd (523.82): C,
1
55.03; H, 5.77; N, 5.35. Found: C, 54.87, H, 5.79; N, 5.41. H
NMR (CDCl3): δ 7.61 (s, 2H, HCdN), 7.13-7.04 (m, 6H, Ph),
2.44 (s, 12H, CH3), 1.40-1.70 (m, 10H, CH(CH2CH2)2CH2, CH-
(CH2CH2)2CH2 and CH(CH2CH2)2CH2). 13C{1H} NMR (CD-
Cl3): δ 174.76 (HCdN), 148.53 (Caromat), 129.96 (Cmeta), 128.48
(Cortho), 127.64 (Cpara), 51.19 (C(CH2CH2)2CH2), 31.54 (C(CH2-
CH2)2CH2), 27.97 (C(CH2CH2)2CH2), 21.86 (C(CH2CH2)2CH2),
19.93 (CH3).
N,N′-(1,1-Cyclopentylidenedimethylidyne)bis(1,1-di-
methylethaneamine) (7a). 1,1-Cyclopentanedicarbaldehyde
(0.50 g, 3.96 mmol) and tert-butylamine (0.65 g, 8.71 mmol)
gave analogously to the procedure described for 4a a colorless
oil. Yield: 0.52 g (55%). 1H NMR (CDCl3): δ 7.51 (s, 2H, CHN),
1.90-1.77 (m, 4H, C(CH2CH2)2), 1.58-1.47 (m, 4H, C(CH2-
CH2)2), 1.06 (s, 18H, C(CH3)3). 13C{1H} NMR (CDCl3):
δ
161.70 (CHN), 56.39 (C(CH2CH2)2), 33.45 (C(CH2CH2)2), 29.64
(C(CH3)3), 24.68 (C(CH2CH2)2). Bp: 40-50 °C/0.05 mbar.
N,N′-(1,1-Cyclohexylidenedimethylidyne)bis(1,1-di-
methylethaneamine) (7b). 1,1-Cyclohexanedicarbaldehyde
(0.60 g, 4.27 mmol) and tert-butylamine (0.78 g, 10.47 mmol)
gave analogously to the procedure described for 4a a colorless
oil. Yield: 0.68 g (57%). 1H NMR (CDCl3): δ 7.31 (s, 2H, CHN),
1.79-1.58 (m, 4H, C(CH2CH2)2CH2), 1.49-1.24 (m, 6H,
C(CH2CH2)2CH2), 1.07 (s, 18H, C(CH3)3). 13C{1H} NMR
(CDCl3): δ 162.28 (CHN), 56.67 (C(CH2CH2)2CH2), 31.92
(CH(CH2CH2)2CH2), 29.62 (C(CH3)3), 25.33 (CH(CH2CH2)2CH2),
22.18 (C(CH2CH2)2CH2). Bp: 40-50 °C/0.05 mbar.
Pd{N,N′-(1,1-Cyclopentylidenemethylidyne)bis(cyclo-
hexaneamine)}Cl2 (10a). This complex has been prepared
analogously to 8a with PdCl2 (247 mg, 1.40 mmol) and 6a (400
mg, 1.40 mmol) as the starting materials. Yield: 350 mg (55%).
Anal. Calcd for C19H32Cl2N2Pd (465.78): C, 48.99; H, 6.92; N,
1
6.01. Found: C, 48.86, H, 6.81; N, 6.10. H NMR (CDCl3): δ
7.26 (s, 2H, HCdN), 4.28-4.33 (t, JHH ) 10.39 Hz, 2H,
CH(CH2CH2)2CH2), 1.90-1.11 (m, 28H, Cy + Cp). 13C{1H}
NMR (CDCl3): δ 168.96 (HCdN), 66.15 (CH(CH2CH2)2CH2),
60.42 (C(CH2CH2)2), 35.12 (CH(CH2CH2)2CH2), 33.25 (C(CH2-
CH2)2), 31.55 (C(CH2CH2)2), 27.84 (CH(CH2CH2)2CH2), 26.41
(CH(CH2CH2)2CH2).
Pd{N,N′-(1,1-Cyclohexylidenemethylidyne)bis(cyclo-
hexaneamine)}Cl2 (10b). This complex has been prepared
analogously to 8a with PdCl2 (130 mg, 0.73 mmol) and 6b (220
mg, 0.73 mmol) as the starting materials. Yield: 290 mg (83%).
Anal. Calcd for C20H34Cl2N2Pd (479.81): C, 50.07; H, 7.14; N,
Pd{N,N′-(1,1-Cyclopentylidenedimethylidyne)bis(2,6-
bis(1-methylethyl)benzenamine)}Cl2 (8a). A suspension of
PdCl2 (200 mg, 1.13 mmol) in CH3CN (10 mL) was refluxed
until a clear orange solution of Pd(CH3CN)2Cl2 was formed.
4a (500 mg, 1.13 mmol) was then added, whereupon the color
of the solution changed from orange to yellow. After the
mixture was refluxed for 2 h, the solvent was removed under
vacuum, and the resulting yellow solid was collected on a glass
frit and washed twice with Et2O (10 mL). Yield: 698 mg (99%).
Anal. Calcd for C31H44Cl2N2Pd (622.01): C, 59.86; H, 7.13; N,
1
5.84. Found: C, 50.12, H, 7.02; N, 5.73. H NMR (CDCl3): δ
7.26 (s, 2H, HCdN), 4.42-4.34 (t, JHH ) 9.82 Hz, 2H, CH(CH2-
CH2)2CH2), 2.00-1.12 (m, 30H, Cy + Cp). 13C{1H} NMR
(CDCl3): δ 168.10 (HCdN), 66.61 (CH(CH2CH2)2CH2), 52.99
(C(CH2CH2)2CH2), 35.11 (CH(CH2CH2)2CH2), 33.26 (C(CH2-
CH2)2CH2), 25.49 (C(CH2CH2)2CH2), 25.21 (CH(CH2CH2)2CH2),
24.71 (CH(CH2CH2)2CH2), 22.59 (C(CH2CH2)2CH2).
1
4.50. Found: C, 58.59, H, 7.24; N, 4.30. H NMR (CDCl3): δ
7.47 (s, 2H, HCdN), 7.26-7.14 (m, 6H, Haromat), 3.42-3.37 (m,
JHH ) 6.62 Hz, 2H, CH(CH3)2), 2.44 (bs, 4H, C(CH2CH2)2), 1.98
(bs, 4H, C(CH2CH2)2), 1.48-1.46 (d, JHH ) 6.55 Hz, 12H, CH-
(CH3)2), 1.17-1.14 (d, JHH ) 6.85 Hz, 12H, CH(CH3)2). 13C-
{1H} NMR (CDCl3): δ 172.95 (HCdN), 145.84 (Caromat), 140.38
(Cortho), 128.15 (Cpara), 123.55 (Cmeta), 58.18 (C(CH2CH2)2), 38.93
(C(CH2CH2)2), 28.80 (CH(CH3)2), 25.60 (C(CH2CH2)2), 24.79
(CH(CH3)2).
Pd{N,N′-(1,1-Cyclohexylidenemethylidyne)bis(2,6-bis-
(1-methylethyl)benzenamine)}Cl2 (8b). This complex has
been prepared analogously to 8a with PdCl2 (194 mg, 1.10
mmol) and 4b (500 mg, 1.10 mmol) as the starting materials.
Yield: 500 mg (72%). Anal. Calcd for C32H46Cl2N2Pd (636.03):
C, 60.43; H, 7.29; N, 4.40. Found: C, 60.29, H, 7.34; N, 4.25.
1H NMR (CDCl3): δ 7.77 (s, 2H, HCdN), 7.29-7.20 (m, 6H,
Haromat), 3.40-3.29 (m, JHH ) 6.85 Hz, 2H, CH(CH3)2), 1.97-
1.93 (m, 4H, C(CH2CH2)2CH2), 1.77-1.62 (m, 6H, CH(CH2CH2)2-
Pd{N,N′-(1,1-Cyclopentylidenemethylidyne)bis(1,1-di-
methylethaneamine)}Cl2 (11a). This complex has been
prepared analogously to 8a with PdCl2 (247 mg, 1.40 mmol)
and 7a (330 mg, 1.40 mmol) as the starting materials. Yield:
450 mg (78%). Anal. Calcd for C15H28Cl2N2Pd (413.71): C,
1
43.55; H, 6.82; N, 6.77. Found: C, 43.45, H, 6.76; N, 6.81. H
NMR (CDCl3): δ 7.47 (s, 2H, HCdN), 2.40 (bs, 4H, C(CH2-
CH2)2), 1.98 (bs, 4H, C(CH2CH2)2), 1,58 (s, 18H, C(CH3)3). 13C-
{1H} NMR (CDCl3): δ 174.12 (HCdN), 65.37 (C(CH3)3), 62.49
(C(CH2CH2)2), 37.76 (C(CH2CH2)2), 32.14 (C(CH3)3), 26.61
(C(CH2CH2)2).
Pd{N,N′-(1,1-Cyclohexylidenemethylidyne)bis(1,1-di-
methylethaneamine)}Cl2 (11b). This complex has been
prepared analogously to 8a with PdCl2 (297 mg, 1.70 mmol)
and 7b (420 mg, 1.70 mmol) as the starting materials. Yield:
600 mg (82%). Anal. Calcd for C16H30Cl2N2Pd (427.73): C,

Palladium and Nickel â-Diimine Complexes
Organometallics, Vol. 24, No. 16, 2005 3965
1
44.93; H, 7.07; N, 6.55. Found: C, 44.72, H, 6.98; N, 6.59. H
NMR (CDCl3): δ 7.31 (s, 2H, HCdN), 1.75-1.31 (m, 28H, Cy
and tBu CH3). 13C{1H} NMR (CDCl3): δ 160.97 (HCdN), 47.00
(C(CH2CH2)2CH2), 31.58 (CH(CH2CH2)2CH2), 29.64 (C(CH3)3),
25.66 (CH(CH2CH2)2CH2), 21.75 (C(CH2CH2)2CH2).
in dry 1-methyl-2-pyrrolidinone (3 mL) was stirred at 140 °C
for 30 min. Arylbromide (1 mmol), methyl acrylate (1.2 mmol),
and NEt3 (1.4 mmol) were added, and the mixture was stirred
at 140 °C. A saturated NH4Cl solution (10 mL) was added,
and the mixture was extracted with CH2Cl2 (3 × 10 mL). The
combined organic layers were washed with 2 M HCl (5 × 10
mL), water (1 × 10 mL), and saturated NaCl solution (2 × 10
mL), dried over Na2SO4, and filtered. The solvent was evapo-
rated, and the crude product was purified by flash chroma-
tography.
Pd{N,N′-(1,1-Cyclopentylidenemethylidyne)bis(2,6-bis-
(1-methylethyl)benzeneamine)}(µ-Cl2)PdCl2 (12). A solu-
tion of 4a (300 mg, 0.68 mmol) in CH2Cl2 (10 mL) was treated
with PdCl2 (121 mg, 0.68 mmol) and stirred overnight. After
removal of the solvent under reduced pressure, a dark yellow
solid was obtained, which was collected on a glass frit, washed
twice with n-hexane, and dried under vacuum. Yield: 193 mg
(36%). Anal. Calcd for C31H44Cl4N2Pd2 (799.31): C, 46.58; H,
5.55; N, 3.50. Found: C, 46.66, H, 5.34; N, 3.52. 1H NMR
(CDCl3): δ 7.26-7.09 (m, 8H, HCdN and Haromat), 3.21-3.10
(m, JHH ) 6.74 Hz, 2H, CH(CH3)2), 2.90-2.47 (m, 4H, C(CH2-
CH2)2), 2.11-1.84 (m, 4H, C(CH2CH2)2), 1.26-1.15 (m, 24H,
CH(CH3)2).
Ni{N,N′-(1,1-Cyclopentylidenedimethylidyne)bis(2,6-
bis(1-methylethyl)benzenamine)}Br2 (13). To a solution of
NiBr2(DME) (150 mg, 0.49 mmol) in CH2Cl2 (10 mL) was added
4a (216 mg, 0.49 mmol), and the mixture was stirred overnight
at room temperature. Insoluble materials were removed by
filtration, and the solution was evaporated to dryness. The
remaining purple solid was collected on a glass frit, washed
twice with Et2O, and dried under vacuum. Yield: 300 mg
(86%). Anal. Calcd for C31H44Br2N2Ni (663.22): C, 56.14; H,
6.69; N, 4.22. Found: C, 56.12, H, 6.58; N, 4.18. 1H NMR (CD2-
Cl2): δ 22.82 (s, 4H, Hmeta), 7.30 (s, 2H, HCdN), 5.33 (s, 4H,
CH(CH3)2), 4.21 (s, 12H, CH(CH3)2), 3.10 (s, 12H, CH(CH3)2),
-0.04 (s, 4H, C(CH2CH2)2), -2.63 (s, 4H, C(CH2CH2)2), -10.68
(s, 2H, Hpara).
Ni{N,N′-(1,1-Cyclopentylidenemethylidyne)bis-
(2,6-dimethylbenzenamine)}Br2 (14). This complex has
been prepared analogously to 13 with NiBr2DME (278 mg, 0.90
mmol) and 5a (300 mg, 0.9 mmol) as the starting materials.
Yield: 320 mg (65%). Anal. Calcd for C23H28Br2N2Ni (551.00):
C, 50.14; H, 5.12; N, 5.08. Found: C, 50.19, H, 5.14; N, 5.00.
1H NMR (CD2Cl2): δ 26.36 (s,12H, CH3), 23.56 (s, 4H, Hmeta),
5.35 (s, 2H, HCdN), -0.08 (s, 4H, C(CH2CH2)2), -2.52 (s, 4H,
C(CH2CH2)2), -11.61 (s, 2H, Hpara).
General Suzuki Procedure. Under an atmosphere of
argon a solution of catalyst (0.03 mmol) and ligand (0.03 mmol)
in dry dioxane (3 mL) was stirred at 80 °C for 30 min.
Arylhalide (1 mmol), phenylboronic acid (1.5 mmol), and Cs2-
CO3 (2 mmol) were added, and the mixture was stirred at 80
°C for an additional 3 h. After addition of 1 M NaOH solution
(10 mL), the mixture was stirred for 15 min at room temper-
ature. The layers were separated, and the water layer was
extracted with Et2O (5 × 5 mL). The combined organic layers
were washed with water (2 × 10 mL) and a saturated NaCl
solution (1 × 10 mL), dried over Na2SO4, and filtered. After
evaporation of the solvent, the crude product was purified by
flash chromatography.
General Hiyama Procedure. Under an atmosphere of
argon a solution of catalyst (0.03 mmol) and ligand (0.03 mmol)
in dry dioxane (3 mL) was stirred at 80 °C for 30 min.
Arylhalide (1.0 mmol), phenyltrimethoxysilane (2.0 mmol), and
Bu4NF (2.0 mmol, from 1 M solution in THF) were added, and
the mixture was stirred at 80 °C. After addition of water (30
mL), the mixture was extracted with Et2O (4 × 30 mL). The
combined organic layers were washed with saturated NaCl
solution (2 × 30 mL), dried over Na2SO4, and filtered. The
solvent was evaporated, and the crude product was purified
by flash chromatography.
X-ray Structure Determination for 4a, 4b, 8a, 8b‚
3CHCl3, 11a‚CHCl3, 12, and 13. Crystals were obtained at
room temperature by solvent evaporation (4a and 4b from
ethanol; 8b and 11a from CHCl3) or by diffusion of diethyl
ether into CH2Cl2 solutions (8a, 12, and 13). X-ray data were
collected on a Bruker Smart APEX CCD area detector diffrac-
tometer (graphite-monochromated Mo KR radiation, λ )
0.71073 Å, 0.3° ω-scan frames covering usually complete
spheres of the reciprocal space up to 2θmax). The frame data
were integrated with the program SAINT.21 Corrections for
detector effects, crystal decay, and absorption were applied
using the multiscan method and the program SADABS.19 The
structures were solved by direct methods using the program
SHELXS97.22 Structure refinement on F2 was carried out with
the program SHELXL97.22 All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were inserted in
idealized positions and were refined riding with the atoms to
which they were bonded.
Acknowledgment. Financial support by the “Fonds
zur Fo¨rderung der wissenschaftlichen Forschung” (Project
No. P16600-N11) is gratefully acknowledged. D.B.-G.
thanks the Basque Government (Eusko Jaurlaritza/
Gobierno Vasco) for a doctoral fellowship.
Supporting Information Available: Complete crystal-
lographic and structural data of 4a, 4b, 8a, 8b‚3CHCl3, 11a‚
CHCl3, 12, and 13 in CIF form. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM050201H
(21) Bruker, Programs SMART, version 5.054; SAINT, version 6.2.9;
SADABS version 2.03; XPREP, version 5.1; SHELXTL, version 5.1;
Bruker AXS Inc.: Madison, WI, 2001.
(22) Sheldrick, G. M. SHELX97: Program System for Crystal
Structure Determination; University of Go¨ttingen: Germany, 1997.
General Heck Procedure. Under an atmosphere of argon
a solution of catalyst (0.035 mmol) and ligand (0.035 mmol)