Homochiral cyclopalladated complexes of (S)-4-tert-butyl-2-phenyl-2-oxazoline. X-ray study of (S,S)-di-μ-chlorobis-{2-[2-(4-tert-butyl)oxazolinyl]phenyl-C,N} dipalladium(II)

Article abstract of DOI:10.1016/S0022-328X(02)01376-1

Due to steric promotion of C-H bond activation, the direct ortho-palladation of (S)-4-tert-butyl-2-phenyl-2-oxazoline using Pd(OAc)₂ in AcOH provided (S,S)-di- μ-acetatobis-[2-(2-(4-tert-butyl) oxazolinyl)phenyl-C,N]dipalladium(II) (2) in an ex

Full text of DOI:10.1016/S0022-328X(02)01376-1

Journal of Organometallic Chemistry 654 (2002) 66ꢀ73
/
www.elsevier.com/locate/jorganchem
Homochiral cyclopalladated complexes of (S)-4-tert-butyl-2-phenyl-
2-oxazoline. X-ray study of (S,S)-di-m-chlorobis-{2-[2-(4-tert-
butyl)oxazolinyl]phenyl-C,N}dipalladium(II)
Darin L. Peterson a, Kristopher J. Keuseman a, Nadezhda A. Kataeva b, Lyudmila
G. Kuz’mina c, Judith A.K. Howard d, Valery V. Dunina b,*, Irina P. Smoliakova a,*
a Chemistry Department, University of North Dakota, P.O. Box 9024, Grand Forks, ND 58202-9024, USA
b Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie Gory, V-234, Moscow 119899, Russia
c N.S. Kurnakov Institute of General and Inorganic Chemistry, RAS, Leninsky Prospect, 31, Moscow 117907, Russia
d Chemistry Department, Durham University, Durham DH1 3LE, UK
Received 8 February 2002; received in revised form 7 March 2002; accepted 7 March 2002
Abstract
Due to steric promotion of CÃ
/
H bond activation, the direct ortho-palladation of (S)-4-tert-butyl-2-phenyl-2-oxazoline using
Pd(OAc)2 in AcOH provided (S,S)-di-m-acetatobis-[2-(2-(4-tert-butyl)oxazolinyl)phenyl-C,N]dipalladium(II) (2) in an excellent
yield. This complex was converted into its corresponding m-chloro analog (3) using LiCl in acetone. Dimer 3 reacted with PPh3 to
furnish the phosphane mononuclear derivative 4. The structure of the dimer complex 3 was confirmed by X-ray diffraction analysis.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Homochiral cyclopalladated complexes; Steric promotion of CÃ/H bond activation; (S)-4-tert-Butyl-2-phenyl-2-oxazoline; X-ray study
1. Introduction
metric synthesis [20]. The majority of known homochiral
CPCs are based on a-arylalkylamines [1ꢀ
/
9,18,20,21]. It
Recently, homochiral cyclopalladated complexes
(CPCs) have attracted a great deal of attention due to
the variety of their applications. In particular, they have
been used for resolution of different substrates posses-
sing ligand properties (e.g. various types of phosphines
is therefore important to develop new homochiral CPCs
(i) with high chiral recognition abilities and (ii) which
are easily obtainable from simple precursors. Homo-
chiral oxazolines have attracted our attention because a
variety of oxazoline-based metal coordination com-
plexes are known to exhibit high efficiency in stereo-
selection processes [22]. Also, these ligands can be easily
synthesized from commercially available and not very
expensive a-amino acid derivatives [23,24]. In contrast
to the numerous known coordination complexes of
oxazolines [25], the number of their cyclopalladated
derivatives remains limited [26,27]. Following our inter-
est in the use of the oxazolinyl group as a chirality
inductor in the palladacycle framework, we synthesized
and characterized homochiral CPCs of readily available
(S)-4-tert-butyl-2-phenyl-2-oxazoline. The results of
this study are reported herein.
and amines) [1ꢀ
as chiral derivatizing agents for enantiomeric purity
determination [7ꢀ10] and as reference compounds for
/6]. Palladacycles have also been utilized
/
the evaluation of absolute configuration by X-ray
crystallography [3,11], CD [12] or NMR [3,13,14]
spectroscopy. Homochiral CPCs are promising enantio-
selective catalysts [15ꢀ19] and chiral matrices in asym-
/
* Corresponding authors. Tel.: ꢁ
/
1-701-777-3942; fax: ꢁ
/
1-701-777-
2331 (I.P.S.); tel.: ꢁ7-095-939-5376; fax: ꢁ
/
/
7-095-932-8846 (V.V.D.).
E-mail addresses: dunina@org.chem.msu.ru (V.V. Dunina),
ismoliakova@chem.und.edu (I.P. Smoliakova).
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 3 7 6 - 1

D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ
/
73
67
2. Results and discussion
2.1. Preparation of cyclopalladated complexes
The ligand, (S)-4-tert-butyl-2-phenyl-2-oxazoline (1),
was synthesized in a high yield from benzonitrile and
Scheme 2.
commercially available (S)-(ꢁ)-2-amino-3,3-dimethyl-
/
1-butanol using a known procedure [28] (Scheme 1).
It has been reported that bulky substituents in a
ligand facilitate direct cyclopalladation [21,29,30]. In
accordance with these reports, the reaction of 1 with
Pd(OAc)2 took place much faster than had previously
been reported for 2-phenyl-2-oxazoline with no sub-
stituents on the heterocycle [26] (Scheme 2). The
complex formed (2) was unstable and was converted to
the corresponding Cl-bridged dimer (3) using LiCl in
acetone (Scheme 2).
We have also attempted to obtain complex 3 using the
ligand exchange reaction [31,32] of 1 with a dimeric
ortho-palladated complex of N,N-dimethylbenzyla-
mine. This method was found to be advantageous for
the preparation of the dimeric CPC of 2-phenyl-2-
oxazoline [26]. Unfortunately, in the case of 1, this
approach was unsuccessful.
Scheme 3.
The 13C-NMR spectra of dimeric complexes 2 and 3
contained only one set of signals. These data suggested
that the compounds exist in CDCl3 solutions as a single
geometrical isomer. The presence of only one signal for
OAc groups (d 2.11 ppm) in the 1H-NMR spectrum of 2
confirmed its anti configuration.
Coordination of the oxazoline ring through the imine
nitrogen atom was supported by IR spectroscopy. The
CÄ
/
N stretching bands in complexes 2, 3 and 4 appeared
at 1625, 1626 and 1637 cmꢂ1, respectively, compared to
Cyclopalladated dimer 3 was converted into its
adduct 4 by reaction with PPh3 (Scheme 3). Such
palladacycle mononuclear derivatives are more suitable
for spectral studies.
1654 cmꢂ1 for the ligand.
1
The H-NMR spectrum of complex 4 provided the
information confirming its trans(N,P)-geometry and
ortho-palladated structure. As for other known mono-
nuclear phosphane derivatives of C,N-palladacycles
with trans(N,P)-geometry [26], the signal of aromatic
H(6) at d 6.43 ppm appeared as a doublet of doublets
2.2. Spectral characterization of complexes
The presence of the PdÃ
/
C bond in all the complexes
due to spinꢀspin coupling (partially through space) with
/
the 31P nuclei of PPh3. The H(5) and especially H(6)
signals were shifted upfield due to the shielding effect of
the phosphane phenyl rings.
was supported by IR and NMR data. As expected for
disubstituted arenes, including ortho-palladated com-
pounds, the region of out-of-plane bending vibrations of
The 1H-NMR spectra have also provided valuable
data about the oxazoline ring conformations of the
aromatic CÃ/H bonds in the IR spectra of complexes 2
and 3 contained only one strong absorption band at 734
and 728 cmꢂ1, respectively, compared to two bands at
694 and 779 cmꢂ1 for the ligand. In the 1H-NMR
spectra of 2 and 3, the aromatic region had integral
intensities corresponding to disubstituted benzene moi-
eties. According to the analysis of 13C-NMR and DEPT
data, complexes 2 and 3 have two quaternary aromatic
carbons, whereas phosphane adduct 4 has three. The
signals at d 147.7, 145.3, and 151.3 in the spectra of 2, 3
and 4, respectively, were assigned to the C atom bonded
to the Pd atom based on (i) previously reported data [26]
for other oxazoline-derived CPCs and (ii) comparison
with the 13C-NMR spectrum of the ligand.
ligand as well as complexes 2ꢀ4 in CDCl3 solutions. One
/
Fig. 1. Newman projections of the (S)-oxazoline ring along the C(4)Ã
C(3) bond for two possible twisted conformations l(S) (a) and d(S)
(b) with the approximate values of dihedral angles HXÃCÃCÃHA and
HXÃCÃCÃ
HB and their corresponding coupling constants J.11
/
/
/
/
/
/
/
1
The Newman projections were drawn with regard to the flattened
conformation of the heterocycle containing a CÄN bond.
Scheme 1.
/

68
D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ73
/
can expect two principal twisted conformations of the
oxazoline ring, l(S) and d(S). Analysis of their New-
man projections (Fig. 1) and correlations to the Karplus
equation [33] predicts: (i) a significant difference in the
values of spinꢀspin coupling constants JAX and JBX for
/
the l(S) conformation and (ii) rather similar values of
these constants for the d(S) conformation. In 1H-NMR
spectra of complexes 2ꢀ/4, one constant, JAX, is con-
siderably larger (8.8ꢀ9.3 Hz) than the other, JBX (2.5ꢀ
/
/
3.5 Hz). Therefore, the heterocycle of the coordinated
ligand adopts the l(S) conformation in solutions. The
same geometry of the oxazoline ring was determined by
the X-ray structure study of complex 3 (vide infra). This
suggests that the oxazoline ring conformations of the
complexes in solutions and in solid form are practically
identical.
The values of coupling constants JAX and JBX found
in the 1H-NMR spectrum of the free ligand are not
significantly different. This suggests that the oxazoline
ring conformation of the free ligand is different from
Fig. 3. The projection of molecular structure of chloro-bridged dimer
(S,S)-3 illustrating the considerable bend of the central {Pd2Cl2} four-
membered ring and efficient screening of the space over the palladium
centers by bulky tert-butyl substituent.
Table 1
Bond lengths (A) for the chloro-bridged dimeric cyclopalladated
complex (S,S)-3 (mono-chloroform solvate)
˚
that of the complexes 2ꢀ4 and must be d(S). Therefore,
/
cyclopalladation of (S)-4-tert-butyl-2-phenyl-2-oxazo-
line results in drastic changes to the heterocycle’s
conformation.
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
Pd(2)Ã
Pd(2)Ã
Pd(2)Ã
Pd(2)Ã
Cl(11)Ã
Cl(12)Ã
Cl(13)Ã
/
C(1)
1.997(8)
2.033(6)
2.323(2)
2.455(2)
1.987(8)
2.028(7)
2.320(2)
2.470(2)
1.762(11)
1.760(11)
1.750(11)
1.295(10)
1.474(10)
1.293(10)
1.475(9)
1.351(9)
1.471(11)
1.319(9)
1.484(9)
1.380(11)
1.414(11)
1.367(11)
C(3)Ã
C(4)Ã
C(5)Ã
C(6)Ã
C(8)Ã
C(9)Ã
C(10)Ã
C(10)Ã
C(10)Ã
C(1?)Ã
C(1?)Ã
C(2?)Ã
C(3?)Ã
C(4?)Ã
C(5?)Ã
C(6?)Ã
C(8?)Ã
C(9?)Ã
C(10?)Ã
C(10?)Ã
C(10?)Ã
/
C(4)
C(5)
C(6)
C(7)
C(9)
C(10)
1.379(11)
1.396(11)
1.387(11)
1.449(10)
1.542(11)
1.559(11)
1.509(10)
1.541(11)
1.558(11)
1.392(10)
1.392(10)
1.394(10)
1.385(12)
1.375(11)
1.394(12)
1.470(11)
1.562(11)
1.540(11)
1.516(12)
1.524(11)
1.545(11)
/
N(1)
Cl(2)
Cl(1)
C(1?)
N(1?)
Cl(1)
Cl(2)
/
/
/
/
/
/
/
2.3. X-ray structure study of chloro-bridged dimer 3
/
/
/
/
C(12)
C(13)
C(11)
The most unambiguous confirmation of h2-C,N-
bonding of 4-tert-butyl-2-phenyl-2-oxazoline was ob-
tained from the X-ray study of chloro-bridged dimer 3.
Single crystals of CPC 3 suitable for the X-ray diffrac-
tion study were grown by diffusion crystallization of the
/
/
/
C(111)
C(111)
C(111)
/
/
/
C(2?)
C(6?)
C(3?)
C(4?)
C(5?)
C(6?)
C(7?)
C(9?)
C(10?)
/
/
N(1)Ã
N(1)Ã
N(1?)Ã
N(1?)Ã
O(1)Ã
O(1)Ã
O(1?)Ã
O(1?)Ã
C(1)Ã
C(1)Ã
C(2)Ã
/
C(7)
/
/
C(9)
/
/
C(7?)
C(9?)
/
compound in a dichloromethaneꢀether solvent mixture,
/
/
/
with hexane as an external solvent. The molecular
structure of compound 3 is presented in Figs. 2 and 3;
/
C(7)
/
/
C(8)
/
/
C(7?)
C(8?)
/
/
/
C(11?)
C(12?)
C(13?)
/
C(6)
C(2)
C(3)
/
/
/
/
selected bond lengths and angles are given in Tables 1
and 2, respectively.
Several chiral cyclopalladated derivatives of 2-sub-
stituted oxazolines have previously been structurally
characterized: two ferrocene-based m-iodo C,N-dimers
5a,b bearing a bulky 4-substituent [34], and two pincer
N,C,N-complexes 6a,b (Fig. 4) [35,36]. Several achiral
complexes of C,N-type have also been reported, includ-
ing the mononuclear phosphane adduct of 4-nonsub-
stituted ligand 7 [26], and the ortho-palladated m-acetato
dimers 8a,b [37] and 9a,b [38,39] derived from 2-phenyl-
2-oxazolines and two benzoxazolines, respectively (Fig.
4).
Fig. 2. Molecular structure of chloro-bridged dimer (S,S)-3. Solvent
CHCl3 molecule is omitted for clarity. Displacement ellipsoids are
shown at 40% probability level.

D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ
/
73
69
Table 2
Bond angles (8) for the chloro-bridged dimeric cyclopalladated
complex (S,S)-3 (mono-chloroform solvate)
arrangement is favorable for a weak secondary interac-
tion.
The ortho-palladated structure of this m-chloro dimer
(and, therefore, that of the starting m-acetato dimer 2) is
quite evident. In common with most structurally char-
C(1)Ã
C(1)Ã
N(1)Ã
C(1)ÃPd(1)Ã
N(1)ÃPd(1)Ã
Cl(2)ÃPd(1)Ã
C(1?)ÃPd(2)Ã
C(1?)ÃPd(2)Ã
N(1?)ÃPd(2)Ã
C(1?)ÃPd(2)Ã
N(1?)ÃPd(2)Ã
Cl(1)ÃPd(2)Ã
Pd(2)ÃCl(1)Ã
Pd(1)ÃCl(2)Ã
C(7)ÃN(1)Ã
C(7)ÃN(1)Ã
C(9)ÃN(1)Ã
C(7?)Ã
C(7?)Ã
C(9?)Ã
C(7)ÃO(1)Ã
C(7?)Ã
C(6)ÃC(1)Ã
C(6)ÃC(1)Ã
C(2)ÃC(1)Ã
C(3)ÃC(2)Ã
C(2)ÃC(3)Ã
C(3)ÃC(4)Ã
C(6)ÃC(5)Ã
C(1)ÃC(6)Ã
C(1)ÃC(6)Ã
C(5)ÃC(6)Ã
N(1)ÃC(7)Ã
N(1)ÃC(7)Ã
O(1)ÃC(7)Ã
O(1)ÃC(8)Ã
/
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
/
N(1)
80.3(3)
96.2(2)
N(1)Ã
N(1)Ã
C(8)ÃC(9)Ã
C(12)ÃC(10)Ã
C(12)ÃC(10)Ã
C(10)Ã
C(10)Ã
C(10)Ã
C(10)Ã
C(1?)Ã
C(1?)Ã
C(1?)Ã
C(2?)Ã
C(3?)Ã
C(4?)Ã
C(5?)Ã
C(6?)Ã
C(6?)Ã
C(6?)Ã
N(1?)ÃC(7?)Ã
N(1?)ÃC(7?)Ã
O(1?)ÃC(7?)Ã
O(1?)ÃC(8?)Ã
N(1?)ÃC(9?)Ã
N(1?)ÃC(9?)Ã
C(10?)Ã
C(11?)Ã
C(11?)Ã
C(12?)Ã
C(11?)Ã
C(12?)Ã
C(9?)ÃC(10?)Ã
Cl(13)ÃC(111)Ã
Cl(13)ÃC(111)Ã
Cl(12)ÃC(111)Ã
/
C(9)Ã
/
C(8)
100.7(6)
111.8(6)
116.3(7)
110.3(7)
110.2(7)
109.4(7)
110.5(6)
107.9(6)
108.5(6)
117.7(7)
128.2(6)
114.0(6)
119.9(8)
120.8(8)
120.7(8)
117.8(8)
123.2(8)
112.4(7)
124.4(7)
117.2(7)
117.9(7)
124.9(7)
103.3(6)
113.5(6)
100.4(6)
113.9(7)
109.8(7)
109.9(6)
111.4(7)
108.7(7)
109.9(7)
107.0(7)
110.8(6)
110.7(6)
110.1(6)
/
/Cl(2)
/
C(9)Ã
/C(10)
/
/
Cl(2)
176.4(2)
169.0(2)
97.0(2)
/
/
C(10)
C(13)
acterized CPCs of C,N-type [40], including ferrocenylꢀ
/
/
/Cl(1)
/
/
oxazoline derivatives 5a,b [34], dimer 3 displays an anti-
arrangement of identical donor atoms. The dimeric
molecule consists of two crystallographically indepen-
dent halves, with differences in their structural para-
meters. The main geometric peculiarity of this dimer is a
marked bend in the central four-membered cycle {Pd2(m-
/
/
Cl(1)
/
/
C(11)
C(11)
C(9)
/
/
Cl(1)
N(1?)
Cl(1)
86.56(7) C(13)Ã
81.2(3)
94.8(2)
/
/
/
/
C(12)Ã
C(13)Ã
C(11)Ã
C(2?)Ã
C(2?)Ã
/
/
/
/
/
/C(9)
/
/
Cl(1)
176.0(2)
172.4(2)
97.6(2)
/
/C(9)
/
/
Cl(2)
/
/
C(6?)
Pd(2)
Pd(2)
C(3?)
C(2?)
C(3?)
C(6?)
C(5?)
C(7?)
C(7?)
/
/
Cl(2)
Cl(2)
Pd(1)
Pd(2)
/
/
Cl)2} of 161.18 along the Cl(1)Ã
163.7ꢀ1808 for dimeric anti-configured cyclopalladated
derivatives of benzylamines [40ꢀ42]. With this bend of
/Cl(2) axis, compared to
/
/
86.29(7) C(6?)Ã
92.15(7) C(1?)Ã
91.71(7) C(4?)Ã
C(5?)Ã
C(4?)Ã
C(1?)Ã
C(1?)Ã
C(5?)Ã
/
/
/
/
/
/
/
/
/
/
/
/
/
/C(9)
109.7(6)
112.0(5)
138.1(5)
108.9(7)
113.2(5)
137.5(5)
105.5(6)
105.5(6)
117.3(7)
114.9(6)
127.6(6)
119.0(7)
122.9(8)
119.3(8)
117.4(8)
124.0(8)
111.2(7)
124.8(7)
115.5(7)
119.8(7)
124.6(7)
104.6(6)
/
/
the central four-membered cycle, the dihedral angle
between the two mean coordination planes (mcpl) is
equal to 155.28. It is of interest that m-iodo dimers 5a,b
with very bulky ferrocenyloxazoline ligands have a
/
/Pd(1)
/
/
/
/Pd(1)
/
/
/
N(1?)Ã
N(1?)Ã
N(1?)Ã
/
C(9?)
Pd(2)
Pd(2)
/
/
/
/
/
/
/
/
/
/
O(1?)
C(6?)
C(6?)
C(9?)
greater bend in the central ring {Pd2(m-I)2}, 115.5ꢀ
/
/
/
C(8)
/
/
113.38, with the dihedral angle between the mcpls equal
to 108.2 and 106.18, respectively [34].
/
O(1?)Ã
/C(8?)
/
/
/
/
C(2)
Pd(1)
Pd(1)
C(1)
C(4)
C(5)
C(4)
C(5)
C(7)
C(7)
/
/
/
/
/
/C(10?)
The PdÃ
/
C bond lengths in dimer 3, 1.997ꢀ
A, fall within the range of the values reported for other
cyclopalladated derivatives of oxazoline ligands (1.928ꢀ
/
1.987(8)
2
/
/
/
/C(8?)
˚
/
/
/
C(9?)Ã
C(10?)Ã
C(10?)Ã
C(10?)Ã
C(10?)Ã
C(10?)Ã
/
C(8?)
/
/
/
/
/C(12?)
˚
˚
2.038 A) and close to the mean value (1.981 A)
/
/
/
/C(9?)
[26,34,35,37ꢀ N bond lengths (2.033ꢀ
/
39]. The PdÃ
/
/
/
/
/
/C(9?)
˚
2.029(6) A) are also close to the mean value of 2.029
/
/
/
/C(13?)
/
/
/
/C(13?)
˚
A. However, they are shorter than those found in the m-
/
/
/
/
C(13?)
Cl(12)
˚
2.085 A).
iodo bridged ferrocenyl analogues 5a,b (2.084ꢀ
/
/
/
O(1)
C(6)
C(6)
C(9)
/
/
This is apparently due to a combination of two factors:
(i) a difference in the trans influence of m-chloro and m-
iodo ligands and (ii) the geometric differences associated
with the palladacycle being fused with the phenyl ring in
3 and the five-membered cyclopentadienyl rings in 5a,b.
/
/
/
/Cl(11)
/
/
/
/Cl(11)
/
/
The difference between the PdÃ
/
Cl bond distances in the
˚
2.470 A) and the
trans position to the carbon (2.455ꢀ
/
The unit cell of complex 3 contains four dimeric
complex molecules and four chloroform solvate mole-
cules. Two projections of the complex are shown in Figs.
2 and 3. The solvent molecule is situated near an apical
position of the Pd(2) atom (see the side projection, Fig.
˚
2.320 A) atoms of the palladacycle in
dimer 3, is in accordance with the trans influences of
nitrogen (2.323ꢀ
/
2
Here and later on, the two values cited correspond to Pd(1) and
Pd(2) containing halves of dimeric molecule, respectively.
˚
3), with the PdÁ Á ÁCl distance equaling 3.819 A. This
Fig. 4. Oxazoline-based CPCs with reported X-ray diffraction data.

70
D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ73
/
these donor atoms; their values are close to the lower
limit of the values reported previously for chloro-
bridged cyclopalladated benzylaminate dimers (2.464ꢀ
/
˚
2.493 and 2.330ꢀ
The coordination environment of the palladium atom
in dimer 3 may be described as nearly squareꢀplanar
/
2.347 A) [40ꢀ
/
42].
/
with a moderate tetrahedral distortion: the dihedral
angles between the planes {CPdN} and {Cl1PdCl2}
equal 10.8ꢀ
C(1) [C(1?)] atom equaling 0.1397ꢀ
tetrahedral distortions were also found for the sterically
crowded ferrocenyl analogues 5a,b (8.5ꢀ8.28) [34] and
/
7.58, with maximum displacement of the
˚
0.0898 A. Similar
/
/
for the 4,4-dimethyl substituted dimer 8b (7.78) [37]; this
is in contrast to the much more flattened derivatives of
4-non-substituted complexes 7 [26] and 9a,b [38,39]
Fig. 5. Twisted conformation of the oxazoline ring in the dimer 3
found by the X-ray study and projected along the CÃC bond of the
heterocycle. All atoms except those directly bonded to the oxazoline
/
(1.7ꢀ5.38).
/
ring are omitted for clarity.
The conformation of the palladacycle in dimeric
complex 3 may be described as a flattened envelope.
Its puckering is somewhat more pronounced compared
to that in the related mono- (7) [26] and binuclear
derivatives (8a) [43] of the non-substituted 2-phenyl-2-
oxazoline ligand: the averaged absolute values of
˚
sum of the van der Waals radii for these atoms (3.1 A)
[44]. As a result, the bulky tert-butyl groups can
efficiently screen the space over the metal center (as is
evident from the side projection presented in Fig. 3).
This geometry may enable the new palladacycle to
display highly effective chiral recognition properties.
intrachelate torsion angle are equal to 8.88ꢀ
3.4ꢀ4.528, respectively; their further increase was ob-
served in the case of the derivatives of bulky ferroceny-
loxazoline ligands 5a,b (10.42ꢀ11.348) [34]. Whereas
/
7.94 and
/
/
pincer complex 6a, bearing rather bulky isopropyl
groups attached to the oxazoline rings, contains two
nearly planar two fused palladacycles, with an intrache-
late torsion angle equal to 1.288 [35].
A further consequence of the bulky substituent
presence is the considerable puckering of the oxazoline
ring in 3. By contrast to the ideally planar heterocycle in
achiral C,N-complexes 7 [26], 8b [37], and chiral pincer
N,C,N-compound 6a [35] (with the displacement of the
framework atoms from the mean heterocycle plane
3. Conclusions
Due to steric promotion, readily available (S)-4-tert-
butyl-2-phenyl-2-oxazoline easily underwent direct cy-
clopalladation using Pd(OAc)2 in acetic acid in a high
yield. The structure of the obtained cyclopalladated
complex 2, as well as its two stable derivatives 3 and 4,
were confirmed by spectroscopic methods. The X-ray
crystal study of Cl-bridged dimeric CPC 3 supported the
proposed structure and revealed pronounced puckering
of the oxazoline ring and the palladacycle. The oxazo-
line ring in the CPCs adopts the l(S) conformation in
the crystal form and in CDCl3 solutions. This allows the
use of X-ray study data for predicting behavior of the
complex in stereocontrol processes. Currently, our
groups are engaged in the application of homochiral
CPCs, including oxazoline derivatives, in different
stereoselection processes.
˚
below 0.004 A), chiral dimers 3 and 5a,b [34] exhibit
marked twist-like non-planarity of the oxazoline rings
with displacement of two carbon atoms of the dicarbon
˚
0.126 and 0.121ꢀ0.131 A, respectively)
chain (at 0.111ꢀ
/
/
in opposite directions (Fig. 5). This corresponds to the
chiral l(S)-conformation of the oxazoline ring predicted
1
based on the analysis of H-NMR data (Fig. 1, vide
supra). It seems reasonable to suppose that this chiral
conformation of the heterocycle can contribute, to some
extent, to the optical activity of these complexes.
In accordance with this conformation, the bulky tert-
butyl substituents in the oxazoline rings of dimer 3
assume a position that is nearly axial: the (ox)CÃ
bonds form angles of 166.6ꢀ160.48 (adjacent angles
13.4ꢀ19.68) with the normal to the corresponding mean
/
C(But)
4. Experimental
/
/
All chemicals were purchased from Aldrich Chemical
Company, Inc., USA. Palladium acetate was purified by
refluxing in benzene for 5 min, filtering the solution, and
removing the solvent. Acetic acid was refluxed over
KMnO4 for 3 h and then distilled. Other solvents were
distilled over CaH2 prior to use.
coordination planes. It is probable that a weak second-
ary interaction between one of the methyl groups of the
tert-butyl substituent and the palladium center contri-
butes to the stability of this chiral conformation: the
H12aÁ Á ÁPd distance is 2.885 A, which is less than the
1
˚

D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ
/
73
71
4.1. Physical measurements
ppm): 0.86 s (9H, C(CH3)3), 2.11 s (3H, CH3), 2.84 dd
(1H, JAX 9.3, JBX
3.5, NCHX); 3.08 t (1H, JAB
ꢃ
/
ꢃ
/
ꢃ
/
Routine 1H- and 13C-NMR (500 and 125 MHz,
respectively), DEPT, COSY, and HETCOR spectra
were recorded in CDCl3 using TMS as an internal
8.8, OCHA), 4.13 dd (1H, OCHB), 7.04, 7.09, and 7.19
three m (2H, 1H and 1H, respectively, CH-arom.); 13C-
NMR (d, ppm): 24.2 (CH3), 25.7 (C(CH3)3), 34.4
(C(CH3)3), 70.5 (NCH), 71.3 (OCH2), 123.6, 125.4,
130.0 and 131.12 (CH-arom.), 131.10 (C(2)-arom.),
147.7 (PdC(1)), 173.8 (OCN), 180.4 (COO).
standard on an Avance 500 Bruker spectrometer. Spinꢀ
/
spin coupling constants, J, are given in Hz. IR spectra
were recorded on an ATI Mattson Genesis Series FTIR.
Optical rotations were measured on a Rudolph Autopol
III automatic polarimeter using a 1 dm tube. Analytical
TLC was performed on Merck precoated 0.2 mm plates
of silica gel 60 F254. Column chromatography was
carried out using Natland Silica Gel 60 (230ꢀ400
mesh). Melting points were measured on a Laboratory
Devices Mel-Temp apparatus and were not corrected.
4.3.2. (S,S)-Di-m-chlorobis-{2-[2-(4-tert-
butyl)oxazolinyl]phenyl-C,N}dipalladium(II) (3)
LiCl (0.0104 g, 0.245 mmol) was added to a solution
of freshly prepared crude complex 2 (0.082 g, 0.112
mmol) in abs. acetone (5 ml). The solution was stirred
for 24 h at r.t. Then the solvent was removed in vacuo
and the yellow solid was purified using column chro-
/
4.2. Ligand synthesis
matography (1:1 CHCl3ꢀ
/
hexane, hꢃ
/
8 cm, dꢃ2 cm).
/
Yield 0.0577 g (75%). M.p. 212ꢀ
/
212.5 8C (dec.); Rf 0.46
21
hexane); [a]
589
21
4.2.1. (S)-4-tert-Butyl-2-phenyl-2-oxazoline (1)
The compound was prepared from benzonitrile and
(1:1 CHCl3ꢀ
/
ꢁ
/
262.58, [a]
ꢁ336.98,
/
546
21
633
[a]
ꢁ
/
211.88 (c 0.54, CH2Cl2); IR (Nujol, n, cmꢂ1):
1
N), 728 s (CH-arom.); H-NMR (d, ppm):
(S)-(ꢁ
procedure described for other oxazolines (the reaction
time was increased from 50 to 63 h) [28]. M.p. 31ꢀ33 8C;
64.88,
197.28 (c 0.29, CH2Cl2); IR (neat,
N), 694 and 779 s (CH-arom.); 1H-
NMR (d, ppm): 0.95 s (9H, C(CH3)3); 4.05 dd (1H,
JBX 7.7, JAB 8.6,
10.1; OCHA); 4.24 dd (1H, JAX
/
)-leucinol in 84% yield using a slightly modified
1626 s (CÄ
1.05 s (9H, C(CH3)3), 3.9 dd (1H, JAX
/
ꢃ/8.9, JBX
ꢃ2.9,
/
NCHX), 3.08 t (1H, JAB
OCHB), 7.04 br. t (1H, J :
dt (1H, J1:7.1, J1:
(1H, J1:7.2, J1:1.3, CH(6)-arom.), 7.41 br. d (1H,
J1:
7.7, CH(3)-arom.); 13C-NMR (d, ppm): 26.1
ꢃ
/
9.1, OCHA), 4.13 dd (1H,
7.1, CH(5)-arom.), 7.10 br.
/
22
633
22
589
Rf 0.64 (1:3 etherꢀ
/
hexane); [a]
ꢂ
/
57.58, [a]
ꢂ
/
/
22
22
[a]
ꢂ
/
82.98, [a]
ꢂ
/
546
405
/
/
1.3, CH(4)-arom.), 7.14 br. dd
n, cmꢂ1): 1654 s (CÄ
/
/
/
/
ꢃ
/
ꢃ
/
ꢃ
/
(C(CH3)3), 35.2 (C(CH3)3), 70.7 (NCH), 72.2 (OCH2),
124.5, 126.1, 131.0 and 133.2 (CH-arom.), 130.4 (arom.
C(2)), 145.3 (PdC(1)), 175.0 (OCN). Anal. Calc. for
NCHX); 4.34 dd (1H, OCHB); 7.32, 7.46 and 7.94 three
m (2H, 1H, and 2H, respectively, H-arom.); 13C-NMR
(d, ppm): 24.8 (CH3), 33.0 (C(CH3)3), 67.7 (NCH), 75.1
(OCH2), 126.9 (C-arom.), 127.20, 127.22, 130.1 (CH-
arom.), 162.2 (OCN). Anal. Calc. for C13H17NO: C,
76.81; H, 8.43; N, 6.89. Found: C, 76.63, H 8.62, N
6.89%.
C26H32Cl2N2O2Pd2×
/
CHCl3:3 C, 40.15; H, 4.12; N, 3.47.
Found: C, 40.20; H, 4.15; N, 3.50%.
4.3.3. (S)-Chloro-{2-[2-(4-tert-
butyl)oxazolinyl]phenyl-C,N}(triphenylphosphine)-
palladium(II) (4)
4.3. Preparation of the cyclopalladated complexes
Triphenylphosphine (0.0545 g, 0.207 mmol) was
added to a suspension of complex 3 (0.0715 g, 0.103
mmol) in benzene. The mixture was stirred at r.t. for 12
h, then the solvent was removed in vacuo. A pale yellow
solid was recrystallized from CHCl3 and hexane. Yield
4.3.1. (S,S)-Di-m-acetatobis-[2-(2-(4-tert-
butyl)oxazolinyl)phenyl-C,N]dipalladium(II) (2)
A suspension of Pd(OAc)2 (0.0505 g, 0.225 mmol) in
glacial AcOH (2 ml) was added to a solution of (S)-4-
tert-butyl-2-phenyl-2-oxazoline (0.0457 g, 0.225 mmol)
in AcOH (1 ml). After stirring at room temperature (r.t.)
for 22 h, the mixture was diluted with H2O and
0.0839 g (69%). Rf 0.78 (1:9 ethyl acetateꢀ
/
CHCl3); m.p.
22
633
120 8C (dec.); IR (Nujol, n, cmꢂ1): 1637 s (CÄ
/N); [a]
22
22
546
22
435
ꢁ
[a]
/
83.28 [a]
ꢁ
/
94.68, [a]
ꢁ
/
121.68, [a]
ꢁ
/
309.68,
544.48 (c 0.17, CH2Cl2); H-NMR (d, ppm):
1.05 s (9H, C(CH3)3), 4.40 dd (1H, JAX 8.8, JBX 2.5,
8.9, OCHA), 4.75 dd (1H,
589
22
1
ꢁ
/
405
extracted with CHCl3 (3ꢄ10 ml). The organic layers
/
ꢃ
/
ꢃ
/
were combined, washed with an aqueous saturated
NaHCO3 solution, and run through a layer of Celite
NCHX), 4.54 t (1H, JAB
ꢃ
/
OCHB), 6.43 dd (1H, JHH
ꢃ
/
7.7, JHP
ꢃ
/
5.0, H(6)-
1.3, H(5)-
7.7, H(4)-arom.), 7.30 dd
1.3, H(3)-arom.), 7.35 dt (6H,
3
(hꢃ1.5 cm). After solvent removal in vacuo (r.t.), the
/
3
4
arom.), 6.59 dt (1H, JHH
ꢃ/7.7, JHH
ꢃ
/
crude product was obtained as a dark-orange oil.
1
According to the H-NMR spectrum, it contained at
3
arom.), 6.92 t (1H, JHH
ꢃ
/
3
(1H, JHH
4
7.7, JHH
ꢃ
/
ꢃ
/
least 95% product. Attempts to obtain the complex in
solid state were unsuccessful because of its rather fast
decomposition. The yield of the crude oily product was
3
The presence of one molecule of CHCl3 per one molecule of the
complex is proven by integrating signals in the 1H-NMR spectrum of
the sample in acetone-d6.
0.0820 g (99%). IR (Nujol, n, cmꢂ1): 1625 s (CÄ
/
N), 734
1
s (CH-arom.), 1585 s and 1410 s (COO); H-NMR (d,

72
D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ73
/
4
7.8, JHP
3JHH
ꢃ
/
ꢃ
/
1.8, meta-H of PPh3), 7.43 br. dt
ether solvent mixture, with hexane as an external
3
4
(3H, JHH
:/7.6, JHH
ꢃ/1.9, para-H of PPh3), 7.74 m
solvent. A colorless crystal was covered with perfluo-
rated oil and mounted on a Bruker SMART CCD
diffractometer. Crystal data, data collection and struc-
ture solution and refinement parameters are given in
Table 3.
The structure was solved by direct methods and
refined by full-matrix least-squares based on F2 for all
data using SHELX software [45,46]. Hydrogen atoms
were located objectively. All non-hydrogen atoms were
refined with anisotropic displacement parameters; H
atoms were refined with isotropic displacement para-
meters.
(6H, ortho-H of PPh3); 13C-NMR (d, ppm): 25.3
(C(CH3)3), 34.3 (C(CH3)3), 68.6 (NCH), 71.6 (OCH2),
122.6 (HC(4) of C6H4), 125.3 (HC(3) of C6H4), 127.0 d
(3JPC
HC(5) of C6H4), 129.7 d (4JPC
130.0 d (1JPC
51.6, quat. C of PPh3), 132.3 (quat. C(2)
of C6H4), 134.3 d (2JPC
13, ortho-CH of PPh3), 136.5
d (3JPC
13.8, HC(6) of C6H4), 151.3 (PdC(1)), 173.7
ꢃ
/
11.0, meta-CH of PPh3), 129.4 d (5JPC
ꢃ/4.8,
ꢃ/2, para-CH of PPh3),
ꢃ
/
ꢃ
/
ꢃ
/
(NCO). Anal. Calc. for C31H31ClNOPPd: C, 53.43; H,
4.48; N, 4.44. Found: C, 53.20; H, 4.47; N, 4.39%.
4.4. X-ray diffraction study of complex 3
5. Supplementary material
Single crystals of compound 3 were grown by diffu-
sion crystallization of the complex in a chloroformꢀ
/
Crystallographic data (excluding structure factors) for
the structural analysis have been deposited with the
Cambridge Crystallographic Data Centre, CCDC No.
176328 for compound 3. Copies of this information may
be obtained free of charge from The Director, CCDC,
Table 3
Crystal data, data collection, structure solution and refinement
parameters for the chloro-bridged dimeric cyclopalladated complex
(S,S)-3 (chloroform solvate)
12 Union Road, Cambridge CB2 1EZ, UK (Fax: ꢁ44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
/
Empirical formula
Formula weight
Color, habit
C27H33Cl5N2O2Pd2
807.60
light-yellow
Crystal size (mm)
Crystal system
Space group
0.24ꢄ
Orthorhombic
P212121
/
0.12ꢄ0.08
/
Acknowledgements
Unit cell dimensions
˚
a (A)
˚
9.2840(8)
13.5525(12)
24.448(2)
90
We would like to thank the University of North
Dakota, North Dakota EPSCoR (grant No. NSF EPS-
9874802) and the Russian Foundation for Basic Re-
search (grant No. 01-03-32474) for financial support.
Undergraduate Summer Research Assistantships for
D.P. and K.J.K. were provided by the NSF-REU
program (grant No. CHE-9619804); the Graduate
Research Assistantship for K.J.K. was provided by the
US Department of Education (GAANN grant No.
P200A000205).
b (A)
˚
c (A)
a (8)
b (8)
g (8)
90
90
3
˚
V (A )
3076.1(5)
4
1.744
Z
Dcalc (g cm3)
Absorption coefficient (mmꢂ1
F(000)
)
1.631
1608
Diffractometer
Temperature (K)
Bruker SMART
150.0(2)
˚
Radiation (l, A)
Graphite monochromatized MoꢀKa
/
(0.71073)
Scan mode
v
0.3
References
Scan step (in v) (8)
Time per step (s)
u range (8)
15
[1] J. Albert, J.M. Cadena, J. Granell, G. Muller, D. Panyella, C.
Sanudo, Eur. J. Inorg. Chem. (2000) 1283 (and references cited
˜
1.67ꢀ
125
345
28 519
7420 [Rint
/
28.00
h 5
l 531
Index ranges
ꢂ
/
/
/
12, ꢂ
/
195
/
k 516,
/
therein).
ꢂ/
/
/
[2] V.V. Dunina, L.G. Kuz’mina, A.G. Parfyonov, Y.K. Grishin,
Tetrahedron: Asymm. 9 (1998) 1917 (and references cited therein).
[3] V.V. Dunina, L.G. Kuz’mina, M.Y. Rubina, Y.K. Grishin, Y.A.
Veits, E.I. Kazakova, Tetrahedron: Asymm. 10 (1999) 1483 (and
references cited therein).
Reflections collected
Independent reflections
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
ꢃ/0.1428]
Not applied
6990/0/344
1.069
[4] A. Marinetti, P. Hubert, J.-P. Genet, Eur. J. Org. Chem. (2000)
1815 (and references cited therein).
Final R indices [I ꢀ
/
2s(I)]
R1ꢃ
R1ꢃ
0.07(5)
0.00000(14)
0.991 and ꢂ
/
0.0597, wR2ꢃ
/
0.0989
0.1121
R indices (all data)
Absolute structure parameter
Extinction coefficient
/0.0926, wR2ꢃ
/
[5] J. Kurita, F. Usuda, S. Yasuike, T. Tsuchiya, Y. Tsuda, F.
Kiuchi, S. Hosoi, J. Chem. Soc. Chem. Commun. (2000) 191 (and
references cited therein).
ꢂ/
Largest difference peak and
ꢂ3
/
0.919
[6] S.B. Wild, Coord. Chem. Rev. 166 (1997) 291.
[7] A. Bohm, D. Seebach, Helv. Chim. Acta 83 (2000) 3262.
˚
hole (e A
)
¨

D.L. Peterson et al. / Journal of Organometallic Chemistry 654 (2002) 66ꢀ
/
73
73
[8] V.V. Dunina, O.N. Gorunova, M.V. Livantsov, Y.K. Grishin,
Tetrahedron Lett. 11 (2000) 2907.
F. Speiser, J. Chem. Soc. Dalton Trans. (2000) 1067;
(d) J.M. Canal, M. Go´mez, F. Jime´nez, M. Rocamora, G. Muller,
E. Dunach, D. Franco, A. Jime´nez, F.H. Cano, Organometallics
19 (2000) 966.
[9] W. McFarlane, J.D. Swarbrick, J.L. Bookham, J. Chem. Soc.
Dalton Trans. (1998) 3233 (and references cited therein).
[10] B. Staubach, J. Buddrus, Angew. Chem. Int. Ed. Engl. 35 (1996)
1344 (and references cited therein).
[26] I.P. Smoliakova, K.J. Keuseman, D.C. Haagenson, D.M. Well-
mann, P.B. Colligan, N.A. Kataeva, A.V. Churakov, L.G.
Kuz’mina, V.V. Dunina, J. Organomet. Chem. 603 (2000) 86
(and references cited therein).
[11] S. Selvaratnam, P.-H. Leung, A.J.P. White, D.J. Williams, J.
Organomet. Chem. 552 (1998) 187.
[12] O. Cantin, C. Cativiela, M.D. Diaz-de-Villegas, R. Navarro, E.P.
Urriolabeitia, Tetrahedron: Asymm. 7 (1996) 2695.
[13] P.-H. Leung, G.H. Quek, H. Lang, A.M. Liu, K.F. Mok, A.J.P.
White, D.J. Williams, N.H. Rees, W. McFarlane, J. Chem. Soc.
Dalton Trans. (1998) 1639.
[27] M. Ohff, A. Ohff, D. Milstein, J. Chem. Soc. Chem. Commun.
(1999) 357.
[28] J.V. Allen, G.J. Dawson, C.G. Frost, M.J. Williams, S.J. Coote,
Tetrahedron 50 (1994) 799.
[29] V.V. Dunina, O.A. Zalevskaya, V.M. Potapov, Russ. Chem. Rev.
57 (1988) 434.
[14] B.-H. Aw, S. Selvaratnam, P.-H. Leung, N.H. Rees, W. McFar-
lane, Tetrahedron: Asymm. 7 (1996) 1753.
[30] V.V. Dunina, L.G. Kuz’mina, M.Y. Kazakova, O.N. Gorunova,
Y.K. Grishin, E.I. Kazakova, Eur. J. Inorg. Chem. (1999) 1029.
[31] A.D. Ryabov, A.K. Yatsimirsky, Inorg. Chem. 23 (1984) 789.
[32] A.D. Ryabov, G.M. Kazankov, J. Organomet. Chem. 268 (1984)
85.
[15] J.M. Longmire, X. Zhang, M. Shang, Organometallics 17 (1998)
4374.
[16] M.A. Stark, C.J. Richards, Tetrahedron Lett. 38 (1997) 5881.
[17] T.K. Hollis, L.E. Overman, J. Organomet. Chem. 576 (1999) 290
(and references cited therein).
[33] R.S. Macomber, A Complete Introduction to Modern NMR
Spectroscopy, Wiley, New York, 1998, p. 139.
[18] A.D. Ryabov, G.M. Kazankov, S.A. Kurzeev, P.V. Samuleev,
V.A. Polyakov, Inorg. Chim. Acta 280 (1998) 57.
[19] A.L. Seligson, W.C. Trogler, Organometallics 12 (1993) 744.
[20] P.-H. Leung, Y. Qin, G. He, K.F. Mok, J.J. Vittal, J. Chem. Soc.
Dalton Trans. (2001) 309 (and references cited therein).
[21] V.V. Dunina, M.Y. Kazakova, Y.K. Grishin, O.R. Malyshev, E.I.
Kazakova, Russ. Chem. Bull. 46 (1997) 1321 (and references cited
therein).
[34] Y. Donde, L.E. Overman, J. Am. Chem. Soc. 121 (1999) 2933.
[35] Y. Motoyama, N. Makihara, Y. Mikami, K. Aoki, H. Nishiyama,
Chem. Lett. (1997) 951.
[36] S.E. Denmark, R.A. Stavenger, A.-M. Faucher, J.P. Edwards, J.
Org. Chem. 62 (1997) 3375.
[37] G. Balavoine, J.C. Clinet, P. Zerbib, K. Boubekeur, J. Organo-
met. Chem. 389 (1990) 259.
[22] Some recent examples of the use of oxazoline-derived complexes
in asymmetric catalysis: (a) N. Østergaard, J.F. Jensen, D.
Tanner, Tetrahedron 57 (2001) 6083;
[38] M.R. Churchill, H.J. Wasserman, G.L. Young, Inorg. Chem. 19
(1980) 762.
[39] C. Navarro-Ranninger, F. Zamora, L.A. Martinez-Cruz, R. Isea,
J.R. Masaguer, J. Organomet. Chem. 518 (1996) 29.
[40] V.V. Dunina, L.G. Kuz’mina, M.Y. Kazakova, Y.K. Grishin,
Y.A. Veits, E.I. Kazakova, Tetrahedron: Asymm. 8 (1997) 2537.
[41] L.G. Kuz’mina, O.Y. Burtseva, M.A. Porai-Koshits, V.V. Du-
nina, O.A. Zalevskaya, V.M. Potapov, Zh. Obshch. Khim.
(Russ.) 59 (1989) 2525.
(b) M. Ogasawara, K. Yoshida, T. Hayashi, Heterocycles 52
(2000) 195;
(c) Y. Imai, W. Zhang, T. Kida, Y. Nakatsuji, I. Ikeda, J. Org.
Chem. 65 (2000) 3326;
(d) T. Kambara, K. Tomioka, Chem. Pharm. Bull. 48 (2000) 1577;
(e) M. Glos, O. Reiser, Org. Lett. 2 (2000) 2045.
[23] D.J. Ager, I. Prakash, D.R. Schaad, Chem. Rev. 96 (1996) 835ꢀ
875.
[24] T.G. Gant, A.I. Meyers, Tetrahedron 50 (1994) 2297ꢀ
[25] Some recent examples of oxazoline-based coordination com-
plexes: (a) P. Braunstein, F. Naud, A. Dedieu, M. Rohmer, A.
DeCian, S.J. Rettig, Organometallics 20 (2001) 2966;
/
[42] E.C. Alyea, S.A. Dias, A.J. McAlees, G. Ferguson, R. McGrin-
dle, P.J. Roberts, J. Am. Chem. Soc. 99 (1977) 4985.
[43] N.A. Kataeva, K.J. Keuseman, L.G. Kuz’mina, V.V. Dunina, I.P.
Smoliakova, unpublished data.
/2360.
[44] A. Bondi, J. Phys. Chem. 68 (1964) 441.
[45] G.M. Sheldrick, Acta Crystallogr. Sect. A 46 (1990) 467.
(b) Y. Peng, X. Feng, K. Yu, Z. Li, Y. Jiang, C. Yeung, J.
Organomet. Chem. 619 (2001) 204;
[46] G.M. Sheldrick, SHELXL-93*
/
Program for the Refinement of
Crystal Structures, University of Gottingen, Gottingen, Germany,
¨ ¨
1993.
(c) P. Braunstein, M.D. Fryzuk, M.L. Dall, F. Naud, S.J. Rettig,