Generation of trans-spanning diphosphine ligands via alkene metathesis: Synthesis, structure, and dynamic behavior of a missing link in a series of square-planar platinum complexes

Article abstract of DOI:10.1016/j.molcata.2005.12.047

Reaction of KPPh₂ and Br(CH₂)₅CH{double bond, long}CH₂ gives the phosphine PPh₂(CH₂)₅CH{double bond, long}CH₂ (89%), which is treated with the platinum tetrahydrothiophene complex [Pt(μ-Cl)(C₆F₅)(S(CH₂CH₂-)₂)]₂ to yield trans-(Cl)(C₆F₅)Pt(PPh₂(CH₂)₅CH{double bond, long}CH₂)₂ (4b, 80%). Ring-closing alkene metathesis (Grubbs' catalyst) gives {A figure is presented} (5b, 84%), which features a trans-spanning diphosphine ligand. The Z/E C{double bond, long}C mixture is hydrogenated (1 atm, 10% Pd/C) to give {A figure is presented} (6b, 99%). The crystal structures of 4b and (Z)-5b are determined. In the former, both (CH₂)₅CH{double bond, long}CH₂ moieties are directed on the same side of the platinum square plane. Low temperature ¹³C NMR spectra of 6b show two sets of signals for the diastereotopic PPh₂ groups. These coalesce upon warming, which requires the passage of the chloride ligand through the macrocycle. Analysis by the complete bandwidth method gives ΔH^? and ΔS^? values of 6.0 ± 0.4 kcal mol^-1 and -13.9 ± 2.6 eu. The ³¹P, ¹³C, and ²H CP/MAS NMR spectra of polycrystalline 6b and 6b-d₂ are studied, and indicate appreciable conformational mobility of the methylene chain in the solid state.

Full text of DOI:10.1016/j.molcata.2005.12.047

Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
Generation of trans-spanning diphosphine ligands via alkene metathesis:
Synthesis, structure, and dynamic behavior of a missing link
in a series of square-planar platinum complexes
a
a
Natascha Lewanzik , Thomas Oeser , Janet Blumela,∗, John A. Gladyszb,∗
¨
a Department of Organic Chemistry, University of Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
b Institut fu¨r Organische Chemie, Friedrich-Alexander-Universita¨t Erlangen-Nu¨rnberg, Henkestraße 42, 91054 Erlangen, Germany
Available online 8 May 2006
Abstract
Reaction of KPPh2 and Br(CH2)5CH CH2 gives the phosphine PPh2(CH2)5CH CH2 (89%), which is treated with the platinum tetrahydrothio-
phene complex [Pt(␮-Cl)(C6F5)(S(CH2CH2–)2)]2 to yield trans-(Cl)(C6F5)Pt(PPh2(CH2)5CH CH2)2 (4b, 80%). Ring-closing alkene metathesis
(Grubbs’ catalyst) gives
(5b, 84%), which features a trans-spanning diphosphine ligand. The Z/E
(6b, 99%). The crystal structures of 4b and (Z)-5b
C C mixture is hydrogenated (1 atm, 10% Pd/C) to give
are determined. In the former, both (CH2)5CH CH2 moieties are directed on the same side of the platinum square plane. Low temperature 13C
NMR spectra of 6b show two sets of signals for the diastereotopic PPh2 groups. These coalesce upon warming, which requires the passage of
the chloride ligand through the macrocycle. Analysis by the complete bandwidth method gives ꢀH‡ and ꢀS‡ values of 6.0 0.4 kcal mol−1 and
−13.9 2.6 eu. The 31P, 13C, and 2H CP/MAS NMR spectra of polycrystalline 6b and 6b-d2 are studied, and indicate appreciable conformational
mobility of the methylene chain in the solid state.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Alkene/olefin metathesis; Hydrogenation; Platinum; Macrocycle; Rotational barrier; Dynamic NMR; Solid-state NMR; Molecular rotor
1. Introduction
When the bridges connecting the phosphorus atoms are long
enough, and the central LnM fragments are small enough, such
compounds can be viewed as molecular rotors [7]. The symme-
tries of the iron complexes 2 are too high for Fe(CO)3 rotation to
be probed by conventional solution NMR techniques. However,
the corresponding Fe(CO)2(NO)+ complexes 3 [5] are ideal.
The 13C NMR spectrum of 3b, which features 12 methylene
groups in each bridge, showed two sets of methylene signals
(2:1) at room temperature. These coalesced at elevated tem-
perature. The 13C NMR spectrum of 3c, which features 14
methylene groups in each bridge, showed only one set of methy-
lene signals at room temperature. This decoalesced to two sets at
low temperature. Complete bandwidth analysis gave ꢀH‡ and
ꢀS‡ values of 9.5 kcal mol−1 and −6.5 eu for Fe(CO)2(NO)+
rotation. Pathways involving ligand dissociation could be
excluded.
This paper is part of a collection of articles describing devel-
opments reported at the 16th International Symposium on Olefin
Metathesis and Related Chemistry, which was held August 7–12
´
in Poznan, Poland. One prominent theme was the emergence of
alkene metathesis, particularly with the Grubbs’ catalyst family,
for the synthesis of architecturally sophisticated organometallic
compounds [1,2]. In this context, we have shown that a vari-
ety of complexes that contain trans-phosphine ligands with one
or more substituents of the formula (CH2)nCH CH2 (n ≥ 4)
undergo efficient ring-closing metathesis [3–5]. The macro-
cyclic products feature trans-spanning diphosphine ligands [6].
In nearly all cases, the C C linkages can be cleanly hydro-
genated. Schemes 1 and 2 illustrate sequences leading to the
triply bridged iron tricarbonyl complexes 2a–c [5] and the singly
bridged platinum complexes 6a,c,e–f [3].
Unfortunately, inthecaseofthesinglybridgedplatinumcom-
plexes 6a,c,e–f, no rotational barriers could be determined [3].
As illustrated in Scheme 3, the PPh2 groups and PCH2 protons
of 6 are diastereotopic. When the bridge is sufficiently long,
the smaller chloride ligand can pass underneath, and the groups
∗
Corresponding authors.
E-mail addresses: gladysz@organik.uni-erlangen.de (J.A. Gladysz),
j.bluemel@urz.uni-heidelberg.de (J. Blu¨mel).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.12.047

N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
21
Scheme 1. Iron carbonyl complexes with trans-spanning diphosphine ligands.
report the successful realization of these objectives, as well as (a)
crystal structures of two precursor complexes that exhibit several
surprising features, and (b) multinuclear solid-state CP/MAS
NMR data for polycrystalline 6b and a dideutero derivative 6b-
d2 that provide further information on dynamic properties.
2. Results
2.1. Syntheses
As expected from similar procedures described earlier [3],
reaction of KPPh2 and the ␣,␻-bromoalkene Br(CH2)5CH CH2
gavePPh2(CH2)5CH CH2 in89%yield. Asshownin Scheme4,
this phosphine was combined with the platinum tetrahydroth-
iophene complex [Pt(␮-Cl)(C6F5)(S(CH2CH2–)2)]2 [9] under
Scheme 2. Previously synthesized platinum complexes with trans-spanning
diphosphine ligands.
are rendered equivalent [8]. When this process is rapid enough,
the corresponding signals will coalesce. For 6a, which features
10 methylene groups in the bridge, two sets of PPh2 13C NMR
signals were observed at room temperature. These did not coa-
lesce at 95 ◦C in toluene-d8. Application of the coalescence
formula allowed a lower limit of 17.4 kcal/mol (ꢀG‡, 95 ◦C)
to be placed upon the barrier. With 6c, which features 14 methy-
lene groups in the bridge, only one set of signals was observed
at room temperature. No decoalescence occurred at −90 ◦C in
THF-d8. From these data, an upper limit of 8.4 kcal/mol could
be estimated for the barrier.
In order to better design related platinum-based molecular
rotors, it was desirable to obtain an exact barrier for a member
of this series of molecules. Hence, we set out to synthesize and
study the variable temperature NMR spectra of the missing link
6b, with 12 methylene groups in each bridge. In this paper, we
Scheme 4. Syntheses of new platinum complexes with trans-spanning diphos-
Scheme 3. Exchange of diastereotopic groups in platinum complexes 6.
phine ligands.

22
N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
conditions analogous to those previously used for the synthesis
of 4a,c,e–f. Workup gave the bis(phosphine) complex trans-
(Cl)(C6F5)Pt(PPh2(CH2)5CH CH2)2 (4b) as a white solid in
80% yield, which was characterized by NMR (1H, 13C, 31P, 19F)
and IR spectroscopy and mass spectrometry as summarized in
Section 4. All properties were similar to those of 4a,c,e–f. As
Table 1
Summary of crystallographic data
Compound
4b
(Z)-5b
C42 42ClF5P2Pt
934.24
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C
44H46ClF5P2Pt
H
962.29
200(2)
0.71073
Monoclinic
P21/n
200(2)
˚
expected, the enantiotopic PPh2 groups gave a single set of 13
C
0.71073
Monoclinic
C2/c
NMR signals, most of which were triplets due to virtual coupling
to both phosphorus nuclei [10]. The original NMR spectra for
all new compounds in this paper have been depicted elsewhere
[11].
Alkene metathesis was conducted under conditions analo-
gous to those used in Scheme 2. As shown in Scheme 4, CH2Cl2
solutions of 4b (ca. 0.0021 M) and Grubbs’ catalyst (8 mol%,
added in three portions) were refluxed for 5 h. Workup gave the
Unit cell dimensions
˚
a (A)
11.033(2)
14.841(2)
25.864(4)
98.817(3)
4185(1)
4
39.173(6)
11.071(2)
20.367(3)
117.454(4)
7838(2)
8
˚
b (A)
˚
c (A)
β (◦)
3
˚
Volume (A )
Z
ρcalc (g/cm3)
1.53
3.54
1.58
3.78
µ (mm−1
)
crude macrocycle
(5b) in 84% yield. The 31P NMR spectrum indicated a 74:26
mixture of C C isomers. Based upon the calculated values of
the chemical shifts of the CH 1H NMR signals, and the crystal
structure below, the major isomer is tentatively proposed to be
Z (cis). Subsequent hydrogenation (1 atm, 10% Pd/C catalyst)
Max. and min.
transmission
Crystal size
(mm3)
0.68 and 0.50
0.86 and 0.64
0.23 × 0.20 × 0.12
0.13 × 0.09 × 0.04
θ limit (◦)
Index ranges (h; k;
l)
2.4–24.7
2.4–22.0
−12, 12; −17, 17;
−41, 41; −11, 11;
−30, 30
−21, 21
gave the title complex
(6b) in
Reflections
collected
Independent
reflections
Observed
reflections
[I > 2σ(I)]
Data/restraints/parameters7053/48/473
Goodness-of-fit
on F2
Final R indices
[I > 2σ(I)]
32011
23153
99% yield. This material was characterized analogously to 4b.
The diastereotopic PPh2 groups gave a single set of 13C NMR
signals.
7053 [R(int) = 0.039]
4762 [R(int) = 0.073]
5592
4063
In order to prepare a substrate for a solid-state NMR exper-
iment below, the preceding reaction was repeated with D2. The
1
13C{ H, 31P} NMR spectrum of the resulting 6b-d2 showed
4762/0/480
1.10
that deuterium had also been incorporated into what would
correspond to the allylic position of 5b. This suggested a com-
peting C C isomerization. Accordingly, an analogous reaction
was conducted with Wilkinson’s catalyst. The resulting 6b-d2
showed only a single 13C NMR signal with a directly bound
deuterium atom, and a single 2H NMR signal.
1.04
R1 = 0.046,
R1 = 0.040,
ωR2 = 0.104
2.88 and −2.02
ωR2 = 0.080
0.57 and −1.57
Largest diff. peak
−3
˚
and hole (eA
)
2.2. Crystal structures
The crystal structures of 6a,c,e–f have been reported previ-
ously. However, no data on the precursors 4a,c–e or 5a,c,e–f
have heretofore been available. Interestingly, single crystals of
4b could be obtained from CH2Cl2/ethanol. X-ray data were
collected as summarized in Table 1 and Section 4. Refinement
revealed considerable disorder, involving both (CH2)4CH CH2
moieties, one PPh2 moiety, and certain C6F5 fluorine atoms.
Nonetheless, the structure could be solved, and a representa-
tive conformation is depicted in Fig. 1. The other conformations
were similar, and the structure is further analyzed below.
A crystal of 5b was also obtained from CH2Cl2/ethanol. X-
ray data were collected, and refinement gave the cis or Z structure
shown in Fig. 2. However, NMR spectra showed the presence of
both C C isomers in the sample (74:26). Key metrical parame-
ters for 4b and (Z)-5b are summarized in Table 2. In each case,
stacking interactions involving the pentafluorophenyl ligand and
a phenyl group on each phosphorus are evident. The averages of
˚
˚
the two centroid–centroid distances are 3.76 A (4b) and 4.05 A
((Z)-5b). In (Z)-5b, the distances from the platinum atom to
the most remote carbon atoms of the macrocycle, C(54), C(55),
Fig. 1. Molecular structure of 4b (one of several disordered conformations; see
text).

N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
23
Table 2
Key bond lengths, bond angles, and torsion angles
Complex
4ba
(Z)-5b
˚
Bond lengths (A)
Pt(1) P(1)
Pt(1) P(2)
Pt(1) Cl(1)
Pt(1) C(1)
2.302(2)
2.300(2)
2.365(2)
2.014(7)
1.818(7)
1.819(8)
1.53(1)
–
–
–
–
–
–
–
–
–
2.307(2)
2.314(2)
2.364(2)
2.004(7)
1.820(7)
1.812(7)
1.53(1)
1.52(1)
1.52(1)
1.54(1)
1.50(1)
1.30(1)
1.47(2)
1.58(1)
1.49(1)
1.54(1)
1.52(1)
P(1) C(51)
P(2) C(61)/C(62)
C(51) C(52)
C(52) C(53)
C(53) C(54)
C(54) C(55)
C(55) C(56)
C(56) C(57)
C(57) C(58)
C(58) C(59)
C(59) C(60)
C(60) C(61)
C(61) C(62)
1.50(1)
Fig. 2. Molecular structure of (Z)-5b.
Bond angles (◦)
C(1) Pt(1) P(1)
C(1) Pt(1) P(2)
P(1) Pt(1) P(2)
C(1) Pt(1) Cl(1)
P(1) Pt(1) Cl(1)
P(2) Pt(1) Cl(1)
C(55) C(56) C(57)
C(56) C(57) C(58)
91.6(2)
90.2(2)
175.12(7)
177.7(2)
89.70(6)
88.57(6)
–
90.6(2)
94.7(2)
174.69(7)
178.7(2)
89.19(7)
85.55(7)
132(1)
C(56), C(57), C(58), and C(59), were 5.61, 5.38, 6.21, 6.17,
5.15, and 5.55 A, respectively.
˚
2.3. Solution NMR studies
–
126(1)
As noted in the introduction, the 13C NMR spectra of the
17–23-membered macrocycles 6c–e (Scheme 2) gave only a
single set of PPh2 signals, whereas that of the 13-membered
macrocycle 6a gave two sets. This indicates that the chloride
ligands rapidly pass underneath the methylene chains of the
trans-spanning diphosphine ligands in 6c–e on the NMR time
scale (Scheme 3). Complex 6b similarly gave a single set of
13C NMR signals for the PPh2 groups at room temperature. At
−95 ◦C in THF-d8, the signals broadened, but did not decoa-
Torsion angles (◦)
P(2) Pt(1) P(1) C(51)
Pt(1) P(1) C(51) C(52)
P(1) C(51) C(52) C(53)
C(51) C(52) C(53) C(54)
C(52) C(53) C(54) C(55)
C(53) C(54) C(55) C(56)
C(54) C(55) C(56) C(57)
C(55) C(56) C(57) C(58)
C(56) C(57) C(58) C(59)
C(57) C(58) C(59) C(60)
C(58) C(59) C(60) C(61)
C(59) C(60) C(61) C(62)
C(60) C(61) C(62) P(2)
C(61) C(62) P(2) Pt(1)
C(62) P(2) Pt(1) P(1)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
57.4(8)
46.3(6)
175.2(6)
61(1)
63(1)
70(1)
−114(1)
4(2)
−117(1)
−165(1)
−53(1)
−75(1)
−178.9(6)
66.7(6)
65.3(8)
1
lesce. No decoalescence phenomena were observed when H
NMR spectra were recorded at −95 ◦C.
13C NMR spectra were therefore recorded in CDFCl2 [12],
which has a lower melting point than THF-d8 (−135 ◦C ver-
sus −108 ◦C), between room temperature and −110 ◦C (163 K).
Two limiting spectra are shown in Fig. 3. The signals for the
ortho, para, and meta carbon atoms in the higher temperature
spectrum (bottom; ca. 132.8, 130.4, and 128.1 ppm) decoalesced
into two sets (top). This process is traced by the spectra in
Fig. 4, which furthermore illustrate a moderate temperature
dependence of the chemical shifts. The evolution of the weaker
and more strongly coupled signal for the ipso carbon atoms is
obscured by the noise and other signals. At the low tempera-
ture limit, the splittings of the para and meta signals (1.9 and
1.2 ppm or 191 and 121 Hz) are less than that of the ortho signals
(4.3 ppm or 433 Hz).
a
Several disordered conformations are present in the crystal; see text.
ues of 6.0 0.4 kcal mol−1 and −13.9 2.6 eu for the process
that renders the PPh2 groups equivalent. The virtual coupling
of the ipso, ortho, and meta signals to both phosphorus nuclei
at the high-temperature limit excludes mechanisms involving
phosphine dissociation. The 31P NMR signal also remains
1
coupled to platinum at the high-temperature limit JPPt
2683 Hz).
=
The spectra in Fig. 4 (left) were simulated using the Com-
plete Bandshape Simulation (CBS) routine of the program
gNMR 4.1 (right) [13]. The simulation of the spectrum in
Fig. 3 is shown elsewhere [11]. The overall agreement was
reasonably satisfying, and rate constants could be calculated
at each temperature. An Eyring plot gave ꢀH‡ and ꢀS‡ val-
2.4. Solid-state NMR studies
The wideline 31P CP NMR spectrum of 6b was measured first
(depicted elsewhere [11]). The chemical shift anisotropy (CSA)
[14] was typical for polycrystalline metal complexes with two
phosphine ligands. The span (δ11–δ33) of the signal amounted

24
N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
Fig. 5. 31P CP/MAS spectrum of 6b (161.9 MHz) at a rotational frequency of
11 kHz. The two peaks close to the isotropic line are 195Pt satellites, the outer
lines are rotational sidebands.
spectrum of polycrystalline 6b, rotated at 11 kHz. Interestingly,
195Pt satellites are visible close to the isotropic line, and the 1JPPt
value (2685 Hz) is in good agreement with the solution data.
Two 13C CP/MAS spectra of polycrystalline 6b are illustrated
in Fig. 6. The signals of the aliphatic carbons overlap (26 ppm),
but they have rather small CSA values, such that even at the low
spinning speed of 4 kHz there are no rotational sidebands. This
indicates that the aliphatic chain is rather flexible and mobile
even in the solid state. The 13C signals of the phenyl carbon
atoms at about 132 ppm (ortho, meta, and para) and 146 ppm
(ipso) show however characteristically large CSA values with
multiple sets of rotational sidebands.
Fig. 3. 13C NMR spectra of 6b in CDFCl2 (100.6 MHz, aromatic region only).
Top, 163 K; bottom, 273 K.
to 125 ppm, with δ11 = 85.1, δ22 = 13.2, and δ33 = −31.0 ppm.
From these data, an isotropic chemical shift of 13.6 ppm
could be calculated (δiso = 1/3(δ11 + δ22 + δ33)), which in turn
allowed the asymmetry parameter η of 0.25 to be calculated
(η = (δ22 − δ33)/(δ11 − δiso)) [14]. Fig. 5 shows the 31P CP/MAS
Fig. 4. 13C NMR spectra of 6b in CDFCl2 (100.6 MHz, aromatic region only) at various temperatures. Left, experimental data; right, corresponding simulations.

N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
25
3. Discussion
The syntheses of the new complexes 4b–6b in Scheme 4
proceed analogously to those of the lower and higher homologs
described earlier (Scheme 2). However, several types of comple-
mentary data could be acquired. For example, the first crystal
structure of a complex of the type 4 has been determined. As
shown in Fig. 1, the substituents on the two phosphorus atoms
in 4b are eclipsed along the P–Pt–P axis (torsion angles 3◦).
The two (CH2)5CH CH2 groups are syn, and extend on the
same side of the platinum square plane. This conformation is
ideal for ring-closing metathesis! Since we have been unable to
provide rationales for the high yields obtained in these macrocy-
clizations, this prompts scrutiny for a previously unrecognized
pre-organizational effect. However, we are presently unable
to identify any molecule-based driving force for the observed
conformation, and provisionally attribute it to a packing
effect.
The first crystal structure of a complex of the type 5 has
also been determined (Fig. 2). In the cases of 13-membered
macrocycles such as (a) 5a [3], (b) the analogous platinum com-
plex with two (CH2)4CH CH(CH2)4 bridges [4], and (c) the
tris(alkene) precursor to the iron complex 2a (Scheme 1) [5,18],
alkene metathesis is highly selective for E C C isomers. We sug-
gest that (CH2)4CH CH(CH2)4 bridges with E C C linkages
are better able to span trans-coordination sites. With longer and
presumably less strained bridges, E/Z mixtures are obtained;
there is often good evidence that Z isomers predominate [3]. In
the case of 5b, a 74:26 mixture of isomers is obtained. Although
a definitive assignment is not possible from the NMR data, we
suggest that the Z isomer dominates in accord with the crystal
structure.
Fig. 6. 13C CP/MAS spectra of polycrystalline 6b (100.6 MHz) at rotational
frequencies of 9 kHz (top trace) and 4 kHz (bottom trace). The asterisks denote
rotational sidebands.
When 6b was brought as a monolayer on a silica surface,
the CSA values in the 31P and 13C CP/MAS spectra were not
reduced, and identical signal patterns resulted. This is a clear
indication that no adsorption on (or reaction with) the silica
surface occurs, important information for the later use of such
compounds as immobilized catalysts [15].
The 2H CP/MAS spectrum of polycrystalline 6b-d2 is
depicted in Fig. 7, together with a simulated lineshape [16]. In
contrast to spectra of crystalline compounds with non-mobile 2H
nuclei, no “classical” Pake pattern is observed. The quadrupo-
lar coupling constant can only be roughly estimated as between
6 and 15 kHz. Nonetheless, this indicates that the methylene
chain in 6b-d2 is conformationally mobile, although the com-
pound is crystalline with a high melting point near 200 ◦C. In
view of the large size of the pentafluorophenyl ligand in Fig. 2,
it is clear that the methylene chain cannot completely rotate
about the metal center. Otherwise, the phenyl carbon signals
(Fig. 7) would have displayed reduced CSA values. However,
ca. 60◦ and 180◦ torsional motions about CH2–CH2–CH2–CH2
segments are feasible [17]. Comparing the lineshape in Fig. 7
with those obtained for hexane-d14 and decane-d22 [17], it
can be concluded that the frequency of such conformational
changes involving the CHD carbons of 6b-d2 is between 100 and
1000 kHz.
The conformation of the macrocycle in (Z)-5b shares
certain features with those of 6a,c,e–f. In all cases, the
Pt–PPh2–CH2–CH2 segments adopt gauche conformations, and
the PPh2–CH2–CH2–CH2 segments anti conformations (as
reflected by the torsion angles for (Z)-5b in Table 2). A rationale
for the former, which is also believed to be favored in solu-
tion, has been proposed [3]. The PPh2–CH2–CH2–CH2–CH2
segments in (Z)-5b exhibit gauche conformations, in contrast to
those of 6c–e and one of the two linkages in 6a.
Attempts have been made to qualitatively correlate the crys-
tal structures of 6a and c to the rates of the exchange process in
Scheme 3 [3]. The distances from the platinum atoms to the most
˚
remote macrocyclic carbon atoms are 5.62 and 7.83 A, respec-
tively. When the van der Waals radius of an sp3 carbon atom
˚
is subtracted (1.70 A), values that might be viewed as “bridge
˚
heights”, 3.92 and 6.13 A, are obtained. The platinum-chloride
˚
distances are ca. 2.36 A, and when the van der Waals radius of
˚
˚
the chlorine atom is added (1.78 A), a “vehicle height” of 4.14 A
is obtained. With 6a, the clearance is obviously not sufficient for
the chloride ligand to pass under the macrocycle, whereas with
6c it is ample.
Althoughacrystalstructureof6bisnotavailable, thedistance
from the platinum atom to the most remote macrocyclic carbon
˚
Fig. 7. 2H CP/MAS spectrumof polycrystalline 6b-d2 (61.2 MHz) ata rotational
frequency of 4 kHz. Smooth curve: simulated lineshape [16].
atom in (Z)-5b (6.21 A) can be taken as an approximation. This
˚
translates to a “bridge height” of 4.51 A for a “vehicle height”

26
N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
4.2. PPh2(CH2)5CH CH2
˚
of 4.14 A. Empirically, the transit of the chlorine ligand through
the macrocycle remains fast on the NMR time scale at room
temperature. However, the clearance becomes low enough such
that decoalescence can be observed at very low temperatures
(Figs. 3 and 4) and activation parameters determined. Although
this model is intuitive, it is vastly oversimplified, and it is impor-
tant to emphasize that correlated conformational changes of the
macrocycle are to be expected along the reaction coordinate.
In this regard, the solid-state NMR data verify the confor-
mational mobility of the CH2–CH2–CH2–CH2 segments of the
macrocycle. These facile solid-state torsional equilibria have
major implications for the use of such complexes as molecu-
lar “compasses” [19] and related devices. Although the goal of
this initial effort was to establish the feasibility of certain types
of solid-state NMR measurements, it can be expected that the
frequencies of torsional conformational changes will increase
upongoingfromthesmallestandpresumablysomewhatstrained
macrocycle 6a–6b and then to 6c and higher homologs. This will
be tested with related complexes in future work.
A Schlenk flask was charged with Br(CH2)5CH CH2
(0.92 mL, 1.80 g, 10.2 mmol) and THF (14 mL), and cooled to
−18 ◦C. Then KPPh2 (0.5 M in THF, 20.3 mL, 10.2 mmol) was
added dropwise with stirring. The mixture was stirred for 1 h,
and then allowed to warm to room temperature. The solvent was
removed by oil pump vacuum, and CH2Cl2 (3–6 mL) was added.
The sample was chromatographed on silica gel (15 cm × 2.5 cm
column; eluted with 1:2, v/v, CH2Cl2/hexanes). The solvent was
removed from the product fraction by rotary evaporation and
oil pump vacuum to give PPh2(CH2)5CH CH2 as a clear oil
(2.559 g, 9.06 mmol, 89%). Calc. for C19H23P:C, 80.82; H, 8.21.
Found: C, 80.40; H, 8.35%.
NMR (␦, C6D6): 1H (500.1 MHz) [22] 7.43 (t, 3JHH = 7 Hz,
4H of 2C6H5), 7.08 (m, 6H of 2C6H5), 5.70 (m, CH CH2),
4.96 (m, CH2), 1.93 (m, PCH2), 1.88 (m, CH2CH ), 1.41 (m,
3
PCH2CH2), 1.28 (quintet, JHH = 8 Hz, PCH2CH2CH2), 1.20
3
1
(quintet, JHH = 8 Hz, CH2CH2CH ); 13C{ H} (125.8 MHz)
1
[22] 139.9 (d, JCP = 15.0 Hz, i-Ph), 139.0 (s, CH ), 133.1
Inconclusion, thisstudyhasfilledinimportantgapsregarding
(1) syntheses of square-planar platinum complexes 6 with trans-
spanning diphosphine ligands, (2) their dynamic properties, and
(3) solid-state structures of cyclic and acyclic alkene-containing
precursors to 6. Future reports will describe new families of
square-planar platinum and palladium complexes with trans-
spanning ligands analogous to those in 2 [20].
2
3
(d, JCP = 18.8 Hz, o-Ph), 128.64 (d, JCP = 6.5 Hz, m-Ph),
128.59 (s, p-Ph), 114.6 (s, CH2), 34.0 (s, CH2CH ), 31.0
(d, 3JCP = 12.5 Hz, PCH2CH2CH2), 28.8 (s, CH2CH2C ), 28.5
(d, 1JCP = 12.8 Hz, PCH2), 26.2 (d, 2JCP = 16.2 Hz, PCH2CH2);
1
31P{ H} (202.5 MHz) −16.8 (s).
IR (cm−1, oil film) 3071 (m), 3054 (m), 2928 (s), 2854 (m),
2451 (w), 1884 (w), 1812 (w), 1640 (m), 1585 (w), 1481 (m),
1462 (w), 1431 (m), 1027 (m), 999 (m), 909 (s), 739 (s), 696
(s). MS23 283 (M+ + H, 100%), 282 (M+, 57%).
4. Experimental
4.3. trans-(Cl)(C6F5)Pt(PPh2(CH2)5CH CH2)2 (4b)
4.1. General data
A
Schlenk
flask
was
charged
with
[Pt(␮-
All reactions were conducted in the absence of oxy-
gen. Chemicals were treated as follows: THF, distilled from
Na/benzophenone; CH2Cl2, distilled from CaH2 (reactions)
or simple distillation (chromatography); ClCH2CH2Cl (99%,
Fluka) and ethanol, used as received; CDFCl2, prepared by a
literature procedure [12]; CDCl3, C6D6, THF-d8 (3× Deutero
GmbH or Eurisotop), Br(CH2)5CH CH2, KPPh2 (2× Aldrich),
Grubbs’ catalyst, Wilkinson’s catalyst (2× Strem), Pd/C (10%,
Lancaster or Acros), and D2 gas (Linde), used as received.
Solid-state NMR spectra were recorded on a digital Bruker
Avance 400 NMR spectrometer equipped with a 4 mm MAS
probehead. For the 31P (13C) CP/MAS measurements a con-
tact time of 1 ms (5 ms), and a pulse delay of 10 s were
applied. Polycrystalline (NH4)H2PO4 (adamantane) was used
as the Hartmann-Hahn and external chemical shift standard.
The Hartmann-Hahn matching condition was established as
previously described [21]. For 2H CP/MAS spectra, a con-
tact time of 5 ms with a 4 s pulse delay was applied. The
90◦ pulse length was 8.6 ␮s, as determined with perdeuterated
poly(methylmethacrylate) (Deutero GmbH). The Hartmann-
Hahn match was optimized using P(p-C6H4D)3. Other spectra
were recorded on standard modern instruments as described in
previous papers [3,4]. Additional details are supplied elsewhere
[11].
Cl)(C6F5)(S(CH2CH2–)2)]2 (0.491 g, 0.505 mmol) [9],
PPh2(CH2)5CH CH2 (0.570 g, 2.02 mmol), and CH2C12
(30 mL). The mixture was stirred (16 h) and the solvent was
removed by oil pump vacuum. Then CH2Cl2 (1 mL) was added,
followed by ethanol (6 mL). The sample was shaken, and a
white solid precipitated. The sample was stored for several days
at −30 ◦C. The supernatant was removed by pipette and the
residue dried by oil pump vacuum to give 4b as a white solid
(0.780 g, 0.811 mmol, 80%), mp 110–116 ◦C.
1
NMR (δ, C6D6) [22]: H (500.1 MHz) 7.55 (br s, 8H of
4C6H5), 7.37–7.27 (br s, 12H of 4C6H5), 5.73 (m, 2CH ),
5.01 (m, 2 CH2), 2.60 (m, 2PCH2), 1.95 (m, 2PCH2CH2
and 2CH2CH ), 1.25 (m, 2CH2CH2CH2CH ); 13C{ H}
1
(125.8 MHz) [22,24,25] 138.9 (s, CH ), 133.5 (virtual t [10],
2JCP = 5.7 Hz, o-Ph), 131.5 (virtual t [10], 1JCP = 28.4 Hz, i-Ph),
130.4 (s, p-Ph), 128.4 (partially obscured by solvent signal,
m-Ph), 114.7 (s, CH2), 33.9 (s, CH2CH ), 31.0 (virtual t
3
[10], JCP = 7.6 Hz, PCH2CH2CH2), 28.7 (s, CH2CH2CH ),
26.4 (virtual t [10], 1JCP = 17.2 Hz, PCH2), 25.7 (s, PCH2CH2);
1
1
31P{ H} (202.5 MHz) 16.1 (s, JPPt = 2656 Hz) [26]; 19F
3
3
(282.4 MHz) −118.8 (d, JFF = 23 Hz, JFPt = 402 Hz [26], o-
C6F5), −165.5 (m, m- and p-C6F5).
IR (cm−1, oil film) 3077 (m), 3050 (m), 2930 (s), 2855 (m),
1639 (m), 1501 (s), 1484 (m), 1463 (m), 1436 (s), 1103 (s), 1059

N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
27
(s), 977 (m), 957 (s), 909 (m), 805 (s), 739 (s), 693 (s), 513 (s),
492 (s). MS [23] 961 (4b+, 5%), 926 ([4b-Cl]+, 100%), 759
([4b-Cl-C6F5]+, 18%), 477 ([4b-Cl-C6F5-Ph2PR]+, 37%), 282
(Ph2PR+, 67%).
to give 6b as a white powder (0.079 g, 0.084 mmol, 99%), mp
195–202 ◦C.
NMR (δ, C6D6): 1H (500.1 MHz) [27] 7.55 (m, 8H of
4C6H5), 6.92 (m, 12H of 4C6H5), 2.57 (m, 2PCH2) [28], 2.43
(m, 2PCH2CH2) [28], 1.58 (m, 2PCH2CH2CH2CH2CH2),
1
1.52 (m, 2PCH2CH2CH2CH2CH2CH2); 13C{ H} [24,25,27]
4.4.
(5b)
2
(125.8 MHz) 133.2 (virtual t [10], JCP = 5.5 Hz, o-Ph),
1
132.5 (virtual t [10], JCP = 27.0 Hz, i-Ph), 130.3 (s, p-
A two-necked flask was charged with 4b (0.165 g,
0.171 mmol), Grubbs’ catalyst (0.004 g, 0.005 mmol), and
CH2Cl2 (80 mL; the resulting solution is 0.0021 M in 4b),
and fitted with a condenser. The solution was refluxed. After
2 h, a second charge of Grubbs’ catalyst was added (0.004 g,
0.005 mmol). After another 2 h, a third charge of Grubbs’ cata-
lyst was added (0.003 g, 0.004 mmol; 8 mol% total). After 1 h,
the mixture was cooled to room temperature. The solvent was
removed by rotary evaporation and oil pump vacuum. Then
CH2Cl2 (1 mL) was added, followed by ethanol (4 mL). The
mixture was swirled, and a white solid precipitated. The sample
was concentrated to 2 mL and stored overnight at −30 ◦C. The
supernatant was removed by pipette. The residue was washed
with ethanol (4 mL) and dried by oil pump vacuum (1 day) to
give 5b as a white powder (0.135 g, 0.144 mmol, 84%) that was
a 74:26 mixture of C C isomers (tentatively assigned as Z/E;
see text), mp 190–206 ◦C.
Ph), 127.9 (partially obscured by solvent signal, m-Ph),
3
30.2 (virtual t [10], JCP = 8.1 Hz, PCH2CH2CH2), 27.7 (s,
1
PCH2CH2CH2CH2), 27.5 (virtual t [10], JCP = 17.4 Hz,
PCH2), 27.2 (s, PCH2CH2CH2CH2CH2CH2), 26.7 (s,
1
PCH2CH2CH2CH2CH2), 25.9 (s, PCH2CH2); 31P{ H}
2
(202.5 MHz) 16.1 (s, JPPt = 2683 Hz) [26]; 19F (282.4 MHz)
−118.9 (d, 3JFF = 23 Hz, 3JFPt = 410 Hz [10], o-C6F5), −165.7
(m, m- and p-C6F5).
1H NMR (δ, THF-d8, 500.1 MHz): at 25 ◦C, 7.53 (dd,
3
JHH = 5.5, 12.3 Hz, 8H of 4C6H5), 7.31 (t, JHH = 7.3 Hz,
3
4H of 4C6H5), 7.24 (t, JHH = 7.4 Hz, 8H of 4C6H5),
2.69 (m, w1/2 = 23.1 Hz, 2PCH2), 2.33 (m, w1/2 = 23.3 Hz,
2PCH2CH2), 1.61 (br s, w1/2 = 19.1 Hz, 2PCH2CH2CH2-
CH2CH2), 1.50 and 1.43 (2 s (2:1), w1/2 = 10.5 and
10.5 Hz,
2PCH2CH2CH2CH2CH2CH2);
at
−95 ◦C,
7.55 (br m, w1/2 = 91.0 Hz, 8H of 4C6H5), 7.37 (br m,
w1/2 = 24.7 Hz, 4H of 4C6H5), 7.31 (br m, w1/2 = 27.1 Hz,
8H of 4C6H5), 2.70 (m, w1/2 = 26.0 Hz, 2PCH2), 2.32
(m, w1/2 = 39.5 Hz, 2PCH2CH2), 1.61 (m, w1/2 = 25.9 Hz,
2PCH2CH2CH2CH2CH2), 1.46 and 1.40 (2 s (2:1), w1/2 = 18.5
and 18.5 Hz, 2PCH2CH2CH2CH2CH2CH2).
1
NMR (δ, C6D6): H (500.1 MHz, major/minor) 7.46 (br d,
3
3JHH = 5.2 Hz, 8H of 4C6H5), 7.31 (t, JHH = 7.3 Hz, 4H of
3
4C6H5), 7.24 (t, JHH = 7.3 Hz, 8H of 4C6H5), 5.45/5.62 (t,
3JHH = 4.9/3.8 Hz, CH CH), 2.63 (br s, 2PCH2), 2.41 (br s,
2PCH2CH2), 2.17/2.22 (m, 2CH2CH ), 1.60/1.60, 1.54/1.56
IR (cm−1, KBr pellet) 2929 (m), 2856 (w), 1630 (br), 1502
(s), 1461 (s), 1436 (m), 1261 (m), 1246 (m), 1103 (m), 1060 (m),
1000 (w), 957 (s), 805 (m), 740 (m), 693 (m), 512 (m). MS [23]
935 (6b+, 23%), 900 ([6b-Cl]+, 100%), 733 ([6b-Cl-C6F5]+,
85%).
(2 m, 2CH2CH2CH2CH ); 13C{ H} (125.8 MHz, major iso-
1
2
mer unless noted) [24,25] 132.6 (virtual t [10], JCP = 5.6 Hz,
1
o-Ph), 132.2 (virtual t [10], JCP = 27.3 Hz, i-Ph), 130.4 (s, p-
Ph), 130.18/130.14 (2 s, minor/major CH CH), 128.0 (virtual
3
t [10], JCP = 5.2 Hz, m-Ph), 30.9 (s, CH2CH ), 29.5 (virtual
3
t [10], JCP = 8.3 Hz, PCH2CH2CH2), 28.3 (s, CH2CH2CH ),
26.9 (virtual t [10], 1JCP = 19.1 Hz, PCH2), 25.4 (s, PCH2CH2);
4.6.
(6b-d2)
31P{ H} (202.5 MHz) 16.4 (s, 74%), 15.6 (s, 26%); 19F
1
(282.4 MHz) −119.3 (m, o-C6F5), −165.3 (m, m- and p-C6F5).
IR (cm−1, oil film) 2928 (m), 2853 (w), 1634 (br), 1502 (s),
1461 (s), 1447 (m), 1104 (s), 1061 (s), 957 (s), 805 (m), 740
(m), 694 (m). MS [23] 933 (5b+, 17%), 898 ([5b-Cl]+, 100%),
731 ([5b-Cl-C6F5]+, 70%).
This complex was prepared analogously to 6b using either
10% Pd/C (some label scrambling, see text) or Wilkinson’s cat-
alyst.
2H NMR (δ, C6D6, 61.4 MHz) 1.39 (m). MS [23] 938 (6b-
d2+, 14%), 902 ([6b-d2-Cl]+, 91%), 735 ([6b-d2-Cl-C6F5]+,
40%).
4.5.
(6b)
4.7. Crystallography
A Schlenk flask was charged with 5b (0.080 g, 0.086 mmol),
10% Pd/C (0.0089 g, 0.0089 mmol Pd), ClCH2CH2Cl (4.5 mL),
and ethanol (4.5 mL), flushed with H2, and fitted with a balloon
of H2. The mixture was stirred for 96 h, during which time the
balloon was periodically recharged with H2. The mixture was
filtered through Celite, and the solvent was removed by oil pump
vacuum. Then CH2Cl2 (0.5 mL) was added, followed by ethanol
(3 mL). The mixture was concentrated under vacuum until a
precipitate began to form. The sample was stored overnight at
−30 ◦C. The supernatant was removed by pipette. The residue
was washed with ethanol and dried by oil pump vacuum (1 day)
Colorless irregular crystals of 4b and (Z)-5b were obtained
from ethanol/CH2Cl2. Data were collected as outlined in
Table 1. Lorentz, polarization, and absorption (empirical, using
SABABS (2.03) [29] and based upon the Laue symmetry of
reciprocal space) corrections were applied. The structures
were solved by direct methods (4b, Sir-97 [30]; (Z)-5b, XS
[29]). The parameters were refined with all data by full-
matrix-least-squares on F2 using XL of the SHELXL (6.12)
software package [29]. Non-hydrogen atoms were refined
with anisotropic thermal parameters unless disordered. The

28
N. Lewanzik et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 20–28
hydrogen atoms were fixed in idealized positions using a riding
model. In 4b, one set of PPh2 rings and the meta and para
C6F5 fluorine atoms were disordered between two sites that
refined to 50:50 occupancy. The five terminal carbon atoms
of the (CH2)5CH CH2 segments were disordered between
two or more sites, the occupancies of which could not be
refined.
CCDC-283900 (4b) and CCDC-283901 ((Z)-5b) contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving/html (or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e mail: deposit@ccdc.cam.
ac.uk).
diastereotopic with Hb and Hc. Ha in I exchanges with Hc in II, which is
in turn chemical shift equivalent with enantiotopic Hb. Similarly, Hb in I
exchanges with Hd in II, which is in turn chemical shift equivalent with
enantiotopic Ha. The diastereotopic PPh2 groups (Pha, Phb) exchange
analogously.
[9] R. Uso´n, J. Fornie´s, P. Espinet, G. Alfranca, Synth. React. Inorg. Met.-
Org. Chem. 10 (1980) 579.
[10] W.H. Hersh, J. Chem. Educ. 74 (1997) 1485 (in the experimental section,
the apparent couplings between adjacent peaks of the triplets are given).
[11] N. Lewanzik, Diplom Thesis, Ruprecht-Karls-Universita¨t Heidelberg,
2004.
[12] J.S. Siegel, F.A.L. Anet, J. Org. Chem. 53 (1988) 2629.
[13] Available from Cherwell Scientific (http://www.cherwell.com) and other
suppliers.
[14] T.M. Duncan, A Compilation of Chemical Shift Anisotropies, Farragut
Press, Chicago, 1990.
[15] (a) C. Merckle, J. Blu¨mel, Adv. Synth. Catal. 345 (2003) 584;
(b) C. Merckle, J. Blu¨mel, Topics Catal. 34 (2005) 5;
ˇ
(c) S. Reinhard, P. Soba, F. Rominger, J. Blu¨mel, Adv. Synth. Catal.
Acknowledgments
345 (2003) 589;
(d) S. Reinhard, K.D. Behringer, J. Blu¨mel, New J. Chem. 27 (2003)
776;
(e) T. Posset, F. Rominger, J. Blu¨mel, Chem. Mater. 17 (2005) 586;
(f) Y. Yang, J. Blu¨mel, in preparation;
We thank the Deutsche Forschungsgemeinschaft (DFG; SFB
623 (Heidelberg) and GL 300/1-3 (Erlangen) and Johnson
Matthey PMC (platinum and ruthenium loans) for support, and
Dr. Kai Hultzsch (Erlangen) for technical assistance.
(g) A. Seifert, R. Fetouaki, J. Blu¨mel, in preparation.
[16] D.J. McAdoo, C.E. Hudson, J. Am. Chem. Soc. 103 (1981) 7710.
[17] N. Nakaoka, T. Ueda, N. Nakamura, Z. Naturforsch. A 57 (2002)
435.
References
[18] The formation of the E,E,E Isomer has been confirmed crystallograph-
ically: L. Wang, F. Hampel, unpublished results, Universita¨t Erlangen-
Nu¨rnberg, 2005.
[19] M.A. Garcia-Garibay, Proc. Natl. Acad. Sci. 102 (2005) 10771.
[20] A. Nawara, T. Shima, F. Hampel, J.A. Gladysz, J. Am. Chem. Soc. 128
(2006) 4962.
[21] S. Reinhard, J. Blu¨mel, Magn. Reson. Chem. 41 (2003) 406.
[22] Definitive 1H and 13C NMR assignments for this compound were made
using 1H,1H-COSY and 1H,13C-COSY spectra, as detailed elsewhere
[11].
[1] E.B. Bauer, J.A. Gladysz, in: R.H. Grubbs (Ed.), Handbook of Metathe-
sis, vol. 2, Wiley–VCH, Weinheim, Germany, 2003, pp. 403–431.
[2] Lead references to contributions from other research groups:
(a) A.V. Chuchuryukin, H.P. Dijkstra, B.M.J.M. Suijkerbuijk, R.J.M.
Klein Gebbink, G.P.M. van Klink, A.M. Mills, A.L. Spek, G. van Koten,
Angew. Chem., Int. Ed. 42 (2003) 228;
A.V. Chuchuryukin, H.P. Dijkstra, B.M.J.M. Suijkerbuijk, R.J.M. Klein
Gebbink, G.P.M. van Klink, A.M. Mills, A.L. Spek, G. van Koten,
Angew. Chem. 115 (2003) 238;
(b) V. Martinez, J.-C. Blais, D. Astruc, Angew. Chem., Int. Ed. 42 (2003)
4366;
[23] m/z (FAB) for most intense peak of isotope envelope (relative intensity,
%).
V. Martinez, J.-C. Blais, D. Astruc, Angew. Chem. 115 (2003) 4502;
(c) L.-E. Perret-Aebi, A. von Zelewski, C. Dietrich-Buchecker, J.-P.
Sauvage, Angew. Chem., Int. Ed. 43 (2004) 4482;
L.-E. Perret-Aebi, A. von Zelewski, C. Dietrich-Buchecker, J.-P.
Sauvage, Angew. Chem. 116 (2004) 4582.
[24] The C6F5 carbon resonances were not observed. These require larger
numbers of transients due to the fluorine and platinum couplings.
[25] The PtPC6H5 13C NMR assignments have abundant precedent. See for
example:
P.W. Jolly, R. Mynott, Adv. Organomet. Chem. 19 (1981) 2571.
[26] This coupling represents a satellite (d; 195Pt = 33.8%), and is not reflected
in the peak multiplicity given.
[3] E.B. Bauer, F. Hampel, J.A. Gladysz, Organometallics 22 (2003) 5567.
[4] T. Shima, E.B. Bauer, F. Hampel, J.A. Gladysz, Dalton Trans. (2004)
1012.
[5] T. Shima, F. Hampel, J.A. Gladysz, Angew. Chem., Int. Ed. 43 (2004)
5537;
T. Shima, F. Hampel, J.A. Gladysz, Angew. Chem. 116 (2004) 5653.
[6] C.A. Bessel, P. Aggarwal, A.C. Marschilok, K.J. Takeuchi, Chem. Rev.
101 (2001) 1031.
[7] G.S. Kottas, L.I. Clarke, D. Horinek, J. Michl, Chem. Rev. 105 (2005)
1281.
[27] Definitive 1H and 13C NMR assignments for this compound were made
using 1H,1H-COSY, 1H,13C-COSY, and HMBC spectra, as detailed else-
where [11].
[28] The aliphatic 1H NMR and 13C NMR signals were assigned from a 1H,
13C COSY spectrum.
[29] G.M. Sheldrick, Bruker Analytical X-ray-Division, Madison, Wisconsin,
2001.
[30] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giacovazzo,
A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst.
32 (1999) 115.
[8] The exchange of Ha and Hb in Scheme 3 can be analyzed as follows.
In both I and II, Ha and Hd are enantiotopic, as are Hb and Hc. Ha is