R
C
H
C
R
2 L
*
*
Pd
[L–Pd]
Pd
2 L Pd
C
R
C
C
3 RC CH
–30 to 20 °C
C
H
1
H
i
ii
5–14
Scheme 3 R = Bu, CMe2OH, Ph, But, SiMe3
ii
O
2 (cod)MCl2
2 L
ii
*
*
O
Pd
Pd
O
2 L Pd
O
+
2 Li2cot
Notes and References
2
iii
iii
15–20
† E-mail: poerschke@mpi-muelheim.mpg.de
‡ It is expected that donors such as pyridines, phosphoranes, carbanions and
heterocarbenes will coordinate together with 1,6-diene ligands on the Pd
and Pt centers, as has already been shown for Ni.3,8,9
iii
O
Me2Si
SiMe2
*
Pd
Me2Si
O
Me2Si
SiMe2
O
SiMe2
SiMe2
O
SiMe2
*
Pd
Pri3P Pd
§ Representative synthesis protocols: 1: a 0.2 m solution of Li2cot (150 ml,
30 mmol) in diethyl ether was slowly added to a suspension of (cod)PdCl2
(8.57 g, 30 mmol) in 40 ml of hepta-1,6-diene at 278 °C. When the
temperature was raised to 240 °C a voluminous precipitate began to form,
consisting of 1 and LiCl. At 220 °C the suspension was so dense that it
could hardly be stirred. When diethyl ether was evaporated under vacuum
at 210 °C, 1 dissolved again. LiCl was removed by filtration, and to the
light green solution 50 ml of pentane was added (230 °C), whereupon pure,
colorless 1 precipitated. The product was isolated by filtration, washed with
cold pentane, and dried under vacuum (230 °C). Yield: 4.59 mg (61%).
7: a colorless solution of 1 (501 mg, 1.00 mmol) in 1 ml of hepta-
1,6-diene was treated with a solution of PPri3 (320 mg, 2.00 mmol) in 5 ml
of pentane. When the mixture was cooled from 230 to 278 °C colorless
crystals separated. After disposal of the mother liquor the product was
washed with cold pentane and dried under vacuum (20 °C). Yield: 610 mg
(84%).
3
23
Scheme 1 Reagents and conditions: i, hepta-1,6-diene; ii, diallyl ether; iii,
tetramethyldivinyldisiloxane
SiMe2
~
<<
L
M
< L
M
O
L
M
NH
L
M
O
SiMe2
Scheme 2 Sequence of increasing stability (decreasing reactivity) of
L–M(1,6-diene) complexes (M = Ni, Pd, Pt)
and we have found that other 1,6-dienes, such as diallylsilanes,
are equally applicable. In contrast, L–M(1,6-enyne) complexes
(M = Ni, Pd, Pt) are apparently not stable.
16: a solution of 7 (363 mg, 1.00 mmol) in 5 ml of diethyl ether was
treated with diallyl ether (0.13 ml, 1.05 mmol). After 1 h the colorless
mixture was cooled to 278 °C, whereupon the crystalline product separated
(isolation as described for 7). Yield: 347 mg (95%). For identifying data see
Table 1.
The X-ray structure determination of 15 (Fig. 1)∑ reveals a
trigonal-planar (TP-3) coordination of the Pd atom by the
phosphorus atom and the CNC bonds of the diallyl ether ligand.
The geometry indicates that the 1,6-diene moiety is able to
chelate two coordination sites at a d10 TP-3 M0 center with little
strain. Thus, the angles D1–Pd–D2, P–Pd–D1, and P–Pd–D2
(D1, D2 are the mid-points of the CNC bonds) are all very close
to 120°, and the CNC carbon atoms lie exactly in the
coordination plane. Moreover, the Pd0(1,6-diene) moiety adopts
the expected chair-like conformation, and the CNC bonds [mean
1.38(1) Å] are only slightly lengthened as compared with an
uncoordinated CNC bond (1.34 Å), indicating that back-bonding
is rather weak for Pd0.
¶ Other Pd complexes with substituted diallyl ether6 and hepta-1,6-diene-
type ligands10 have been reported previously.
∑ Crystal data for 15: C9H19OPPd, Mr = 280.6, colorless prism, crystal size
0.28 3 0.42 3 0.46 mm, a = 10.050(2), b = 9.194(2), c = 13.053(1) Å,
b = 101.866(10)°, V = 1180.2(4) Å3, T 293 K, monoclinic, space group
P21/n (No. 14), Z = 4, Dc = 1.58 g cm23, m = 1.67 mm21. Enraf-Nonius
CAD4 diffractometer. Mo-Ka X-radiation, l = 0.71069 Å. 5598 measured
reflections, 2688 unique, 2315 observed [I > 2.0s(Fo2)]. The structure was
solved by direct methods (SHELXS-86) and refined by full-matrix least-
squares on F2 for all data with Chebyshev weights to R = 0.043 (obs.),
wR = 0.118 (all data), S = 1.07, H atoms isotropic, max. shift/error 0.001,
residual rmax = 1.95 e Å23, 0.8 Å from Pd. CCDC 182/845.
These complexes find application in homogeneous catalysis
in those cases where an unsaturated complex fragment [L–Pd0]
(L e.g. PPh3), rather than a coordinatively saturated complex
like Pd(PPh3)4, is expected to catalyze the reaction. For
example, we have observed that [L–Pd] complexes (e.g. 7 and
16) catalyze regio- and stereo-selectively the linear trimeriza-
tion of alk-1-ynes to 1,4,6-trisubstituted cis-hexa-1,3-dien-
5-ynes between 230 and 20 °C (Scheme 3).7
1 M. Green, J. A. K. Howard, J. L. Spencer and F. G. A. Stone, J. Chem.
Soc., Chem. Commun., 1975, 449.
2 J. Krause, Dissertation, Universita¨t Du¨sseldorf, 1993; K.-J. Haack,
Dissertation, Universita¨t Du¨sseldorf, 1994; G. Cestaric, Planned
Dissertation.
3 B. Proft, K.-R. Po¨rschke, F. Lutz and C. Kru¨ger, Chem. Ber., 1991, 124,
2667.
4 P. B. Hitchcock, M. F. Lappert and N. J. W. Warhurst, Angew. Chem.,
1991, 103, 439; Angew. Chem., Int. Ed. Engl., 1991, 30, 438;
P. B. Hitchock, M. F. Lappert, C. MacBeath, F. P. E. Scott and
N. J. W. Warhurst, J. Organomet. Chem., 1997, 528, 185.
5 M. Green, J. A. K. Howard, J. L. Spencer and F. G. A. Stone, J. Chem.
Soc., Dalton Trans., 1977, 271.
6 T. Yamamoto, M. Akimoto and A. Yamamoto, Chem. Lett., 1983, 1725;
T. Yamamoto, M. Akimoto, O. Saito and A. Yamamoto, Organome-
tallics, 1986, 5, 1559.
C(4)
C(6)
D2
C(7)
C(8)
C(5)
O
7 J. Krause, G. Cestaric and K.-R. Po¨rschke, manuscript in preparation.
8 U. Rosenthal, S. Pulst, R. Kempe, K.-R. Po¨rschke, R. Goddard and
B. Proft, Tetrahedron, 1998, 54, 1277.
C(3)
P
Pd
9 C. Pluta, K.-R. Po¨rschke, B. Gabor and R. Mynott, Chem. Ber., 1994,
127, 489.
C(2)
D1
C(1)
C(9)
10 A. Do¨ring, P. W. Jolly, R. Mynott, K.-P. Schick and G. Wilke, Z.
Naturforsch., Teil B, 1981, 36, 1198; P. W. Jolly, Angew. Chem., 1985,
97, 279; Angew. Chem., Int. Ed. Engl., 1985, 24, 283.
Fig. 1 Molecular structure of 15. Selected bond lengths (Å): Pd–P 2.303(1),
Pd–C(1) 2.151(5), Pd–C(2) 2.155(5), Pd–C(5) 2.157(5), Pd–C(6) 2.160(5),
C(1)–C(2) 1.364(8), C(5)–C(6) 1.386(9), D1···D2 3.57(1). Selected bond
angles (°): D1–Pd–D2 121.8(6), P–Pd–D1 119.4(3), P–Pd–D2 118.6(3).
Received in Cambridge, UK, 27th March 1998; 8/02381F
1292
Chem. Commun., 1998
Krause, Jochen
