ties of the Xantphos type diphosphine ligands possessing large
bite angles in hydrocyanation reactions. Effective nickel-
catalysed hydrocyanation of long-chain unsaturated substrates
can be achieved. The regioselectivity can be controlled by
providing a rigid ligand backbone.
We would like to thank Professor Dr Wilhelm Keim for
kindly supporting our work and Professor Dr Siegfried Warwel,
H. P. Kaufmann-Institut Mu¨nster, for the donation of the fatty
acid esters.
Table 2 Regioselectivitya towards the terminal nitriles obtained in the
hydrocyanation of oct-1-ene and methyl dec-9-enoate
Ligand
Oct-1-ene
Methyl 9-dec-1-enoate
DPEphos
Thixantphos
P(OC6H4Me-p)3
29
84
82
39
75
77
a Regioselectivity is defined as the % of linear nitrile.
Hydrocyanation of functionalised alkenes leads to interesting
chemical building blocks. Reaction of w-unsaturated fatty acid
esters with HCN gives the corresponding cyanoesters [eqn. (2),
Footnotes and References
* E-mail: dieter.vogt@post.rwth-aachen.de
† The molecular mechanics calculations were performed on a Silicon
Graphics Indigo2 workstation using SYBYL14 software version 6.3 and a
modified TRIPOS force field with a Ni–P bond length of 2.177 Å and a
P–Ni–P bending force constant of 0 kcal mol21 degree22
O
O
[Ni]
.
CN
(2)
MeO
(CH2)n
MeO
(CH2)n
§ In a typical experiment, 1 ml of a bright yellow 0.0325 mm solution of
[Ni(cod)2] in toluene was added to a Schlenk tube containing a stirring bar
and 1.05 equiv. of ligand. The mixture was stirred for 30 min to ensure
complete formation of the catalyst precursor. Then 0.65 mmol of the
substrate and 0.0325 mmol of Lewis acid (AlCl3 as a stock solution) was
added. The solution was then cooled to ca. 220 K, 30 ml of liquid HCN (0.78
mmol) was added at once and the tube was placed in a heating bath. After
16 h at 333 K, the excess of HCN was removed by a gentle stream of argon,
solid particles were removed by centrifugation and the remaining solution
was analysed by temperature-controlled gas chromatography.
HCN
n = 7–11]. The substrate acid esters are readily available from
natural resources.13 To the best of our knowledge this is the first
example of a catalytic hydrocyanation using this class of
substrates.
For methyl dec-9-enoate the obtained yields and selectivities
are similar to the unfunctionalised alkenic substrates (Table 1,
entries 1–4). The presence of the ester group does not inhibit the
catalytic reaction. However, with fatty acid esters containing a
longer chain, such as methyl undec-10-enoate or methyl
tetradec-13-enoate, the yields decrease slightly.
1 R. J. McKinney, in Homogeneous Catalysis, ed. G. W. Parshall, Wiley,
New York, 1992, p. 42.
2 C. A. Tolman, R. J. McKinney, W. C. Seidel, J. D. Druliner and W. R.
Stevens, Adv. Catal., 1985, 33, 1.
The Xantphos type diphosphines DPEphos and Thixantphos
have almost identical electronic properties but different bite
angles. Moreover, for DPEphos, the S-bridge in the backbone is
missing which makes the ligand flexible. These characteristics
influence the regioselectivity towards the nitrile products (Table
2). We suggest that the more rigid ligand backbones disfavour
conformational changes in the metal complexes formed. With
Thixantphos the observed linearity reaches 84%.
The formation of branched nitriles mainly takes place when
the double bond of the starting unsaturated substrate is
isomerised via an intermediate nickel hydride species to give an
internal alkene. Usually, isomerisation and b-elimination of a
thermodynamically favoured internal alkene (k2) is much faster
than hydrocyanation (k1) (Scheme 1). Thus another approach to
explain the difference in regioselectivity with DPEphos and
Thixantphos is a kinetic one. The more rigid a ligand is, the
more favoured is hydrocyanation (k1).
3 M. Kranenburg, P. C. J. Kamer, P. W. N. M. van Leeuwen, D. Vogt and
W. Keim, J. Chem. Soc., Chem. Commun., 1995, 2177.
4 M. Kranenburg, Y. E. M. van der Burgt, P. C. J. Kamer, P. W. N. M. van
Leeuwen, K. Goubitz and J. Fraanje, Organometallics, 1995, 14,
3081.
5 C. P. Casey and G. T. Whiteker, Isr. J. Chem., 1990, 30, 299.
6 P. Arthur, Jr., D. C. England, B. C. Pratt and G. M. Whitman, J. Am.
Chem. Soc., 1954, 76, 5364.
7 B. W. Taylor and H. E. Swift, Erdo¨l Kohle Erdgas Petrochem., 1974,
27, 93; E. S. Brown, in Aspects of Homogeneous Catalysis, ed. R. Ugo,
Reidel, Dordrecht, 1974, vol. 2, p. 57.
8 W. Keim, A. Behr, J. P. Bioul and J. Weisser, Erdo¨l Kohle Erdgas
Petrochem., 1982, 35, 436.
9 M. J. Baker, K. N. Harrison, A. G. Orpen, P. G. Pringle and G. Shaw,
J. Chem. Soc., Chem. Commun. 1991, 803.
10 T. V. RajanBabu and A. L. Casalnuovo, J. Am. Chem. Soc., 1996, 118,
6325.
11 C. A. Tolman, W. C. Seidel, J. D. Druliner and P. J. Domaille,
Organometallics, 1984, 3, 33.
12 C. A. Tolman, J. Chem. Educ., 1986, 63, 199.
13 S. Warwel, H.-G. Ja¨gers and S. Thomas, Fat Sci. Technol., 1992, 94,
323; S. Warwel, P. Bavaj, B. Ercklentz, M. Harperscheid, M. Ru¨sch gen.
Klaas and S. Thomas in Nachwachsende Rohstoffe, ed. M. Eggersdor-
fer, S. Warwel and G. Wulff, VCH, Weinheim, 1993, p. 69.
14 SYBYL version 6.3, TRIPOS Associates, St. Louis, MO 63144,
USA.
HCN
CN
k1
[Ni]
k2
Scheme 1
Received in Bloomington, IN, USA; 24th April 1997; 7/02811C
1522
Chem. Commun., 1997