A unique functional group transformation of planar chiral diolefinic organonitrogen cycles utilizing PtCl2(2,4,6-trimethylpyridine) Complexes

Article abstract of DOI:10.1021/om1009704

The planar chiral diolefinic organonitrogen cycles 1 underwent stereospecific and group-selective olefin exchange with 3 to give 4, whose molecular structure was characterized on the basis of NMR and X-ray diffraction. The bonded (E)-olefin moieties in 4

Full text of DOI:10.1021/om1009704

6632 Organometallics 2010, 29, 6632–6635
DOI: 10.1021/om1009704
A Unique Functional Group Transformation of Planar Chiral Diolefinic
Organonitrogen Cycles Utilizing PtCl2(2,4,6-trimethylpyridine)
Complexes
Katsuhiko Tomooka,*,† Maki Shimada,‡ Kazuhiro Uehara,† and Masato Ito†
†Institute of Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka 816-8580, Japan,
and ‡Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of
Technology, Meguro, Tokyo 152-8552, Japan
Received October 7, 2010
Summary: The planar chiral diolefinic organonitrogen cycles 1
underwent stereospecific and group-selective olefin exchange
with 3 to give 4, whose molecular structure was characterized
on the basis of NMR and X-ray diffraction. The bonded (E)-
olefin moieties in 4 were robust enough to allow untouched (Z)-
olefin to undergo epoxidation and hydrogenation to give the
corresponding PtCl2(η2-olefin) complexes, whose treatment
with PPh3 smoothly liberated their olefinic parts, which would
be otherwise difficult to synthesize.
Recently, we have found a novel class of planar chiral nine-
membered organonitrogen compounds 1a-d, in which two
distinct (E)- and (Z)-olefins are suitably embedded in the
C3-C4 and C7-C8 positions, respectively.1 Their stereo-
genic planes are easily constructed by the cyclization of
readily available acyclic precursors, in which sugar-derived
chiral lithium alkoxides determine whether the mode of
cyclization is sinistral or dextral.1d Also noteworthy is their
adequate reactivity to allow further synthetic elaborations,
in which multiple stereogenic centers are developed with
perfect stereospecificity.1a-c The molecular structures of
1a-d are characterized by their restricted orientation of
olefinic parts, whose π orbitals should be effectively bisected
to be located either inside or outside of the loop. More
For example, the reaction of (S)-(þ)-1b with 9-BBN
followed by oxidative workup provided (3S,4R)-2bx
exclusively,1a and a similar reaction with m-CPBA predomi-
nantly afforded (3R,4R)-2by.1e These selectivities can be
interpreted as a result of the preferential electrophilic attack
of reagents on the outer π orbital at the (E)-olefin. This result
has led us to anticipate that a stereoselective coordination of
an appropriate transition-metal fragment2 would provide a
new complex with a unique π-bonding property, whose effect
on the molecular chirality of the original skeleton would also
be of great interest. In fact, we have found that trans-PtCl2-
(2,4,6-trimethylpyridine)(η2-ethylene) (3)3 undergoes an ole-
fin exchange4,5 with (()-1a or (()-1b at their (E)-olefin to
give the corresponding platinum(II) complexes (()-4a and
(()-4b, whose structures have been unequivocally deter-
mined by X-ray diffraction studies. Notably, the trans-PtCl2-
(2,4,6-trimethylpyridine) fragment has proved to serve as a
protecting group to enable selective functionalization at the
specifically, the (E)-olefins in 1a-d may bear a distorted
structure while the (Z)-olefins may not, as exemplified by the
solid-state structure of 1b with the dihedral angles of C-
(2)-C(3)-C(4)-C(5) (29.5°) and C(6)-C(7)-C(8)-C(9)
(2.8°).1a These two unique structural features should be the
underlying basis of the high selectivity observed in their
transformation.
*ktomooka@cm.kyushu-u.ac.jp.
(1) (a) Tomooka, K.; Suzuki, M.; Shimada, M.; Yanagitsuru, S.;
Uehara, K. Org. Lett. 2006, 8, 963–965. (b) Tomooka, K.; Suzuki, M.;
Uehara, K.; Shimada, M.; Akiyama, T. Synlett 2008, 2518–2522. (c)
Tomooka, K.; Akiyama, T.; Man, P.; Suzuki, M. Tetrahedron Lett. 2008,
49, 6327–6329. (d) Tomooka, K.; Uehara, K.; Nishikawa, R.; Suzuki, M.;
Igawa, K. J. Am. Chem. Soc. 2010, 132, 9232–9233. (e) Details will be
reported separately.
(2) (a) Crabtree, R. H. The Organometallic Chemistry of the Transi-
tion Metals; Wiley: New York, 1994; Chapter 5. (b) Gladysz, J. A.; Boone,
B. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 550–583.
(3) (a) Orchin, M.; Schmidt, P. J. Inorg. Chim. Acta Rev. 1968, 123–
135. (b) Chottard, J. C.; Mansuy, D.; Bartoli, J. F. J. Organomet. Chem.
1974, 65, C19–C22. (c) Mansuy, D.; Bartoli, J. F.; Chottard, J. C. J.
Organomet. Chem. 1974, 73, C39–C42. (d) Caruso, F.; Spagna, R.;
Zambonelli, L. J. Cryst. Mol. Struct. 1978, 8, 47–57. (e) Natile, G.;
Maresca, L.; Cattalini, L. J. Chem. Soc., Dalton Trans. 1977, 651–655.
(f) Canovese, L.; Tobe, M. L.; Cattalini, L. J. Chem. Soc., Dalton Trans.
1985, 27–30.
(4) (a) Joy, J. R.; Orchin, M. J. Am. Chem. Soc. 1959, 81, 305–309. (b)
Joy, J. R.; Orchin, M. J. Am. Chem. Soc. 1959, 81, 310–311. (c) Cramer, R.
Inorg. Chem. 1965, 4, 445–447. (d) Olsson, A.; Kofod, P. Inorg. Chem.
1992, 31, 183–186. (e) Plutino, M. R.; Otto, S.; Roodt, A.; Elding, L. I. Inorg.
Chem. 1999, 38, 1233–1238.
(5) (a) Meester, M. A. M.; Stufkens, D. J.; Vrieze, K. Inorg. Chim.
Acta 1977, 21, 251–258. (b) Kurosawa, H.; Urabe, A.; Emoto, M. J. Chem.
Soc., Dalton Trans. 1986, 891–893.
r
pubs.acs.org/Organometallics
Published on Web 11/23/2010
2010 American Chemical Society

Communication
Organometallics, Vol. 29, No. 24, 2010 6633
Figure 1. Molecular structure of (()-4a. Thermal ellipsoids are
drawn at the 40% probability level. The H atoms are omitted for
clarity.
Figure 2. Molecular structure of (()-4b. Thermal ellipsoids are
drawn at the 40% probability level. The H atoms are omitted for
clarity.
remaining (Z)-olefin to give the new platinum(II) complexes
(()-4ax, (()-4ay, and (()-4bx selectively. Furthermore, the
treatment with PPh3 of these complexes has caused the
smooth liberation of their olefinic moieties. We will disclose
these results herein.
pyridine, 2-picoline, and quinoline, gave less satisfactory
results. For example, the reaction of (()-1b with an equimo-
lar amount of trans-PtCl2(pyridine)(η2-ethylene) at 0 °C for
20 min gave a complicated mixture containing a considerable
amount of (()-6b, from which the isolation of the desired
platinum complex was difficult in our hands. Therefore, the
2,4,6-trimethylpyridine ligand in 3 should also contribute
significantly to minimize the possible formation of (()-6a or
(()-6b, which is explainable by a Cope-type rearrangement
that is similar to the previously reported catalytic variant
using PdCl2(PhCN)2.1a,6
Our initial experiments focused on the discrimination of
two olefinic groups in (()-1a by the complexation using 3.
The reaction of (()-1a with an equimolar amount of 3 in
CH2Cl2 at 30 °C for 21 h followed by chromatographic
purification using silica gel allowed isolation of an air-stable
yellow solid as a major product ((()-4a). Recrystallization
by diffusing n-hexane into the solution of this solid in a mixed
solvent system of CH2Cl2 and diethyl ether gave single
crystals that were subjected to an X-ray diffraction study,
which determined the selective coordination of the trans-
PtCl2(2,4,6-trimethylpyridine) fragment at the (E)-olefin of
(()-1a (Figure 1). As the isolated yield of (()-4a was
moderate (60% yield), the fate of (()-1a not being incorpo-
rated in (()-4a merits specific mention. In addition to (()-4a,
the aforementioned chromatographic separation gave two
minor fractions, whose 1H NMR analysis indicated that one
is a 44:56 mixture of (()-1a and (()-6a (25% yield; vide
infra) and the other is the dinuclear complex (()-5a (4%
yield), whose identity was further established by 13C{1H}
NMR and IR spectroscopy as well as elemental analysis (see
the Supporting Information). It should be noted that (()-5a
was obtainable in 31% yield by a separate reaction of
isolated (()-4a with an equimolar amount of 3 in CH2Cl2
at 30 °C for 21 h. These results clearly demonstrated that the
remaining (Z)-olefin in (()-4a is also susceptible to coordi-
nation by the trans-PtCl2(2,4,6-trimethylpyridine) fragment.
A similar reaction of (()-1b with 3 proceeded rather
sluggishly, but the corresponding mononuclear complex
(()-4b was obtained as the sole product after the chromato-
graphic workup, albeit in modest yield (23%). Unlike the
case of (()-1a, no other product other than (()-1b was
isolable from the reaction mixture. The molecular structure
of (()-4b determined by an X-ray diffraction study is
depicted in Figure 2.
While the stabilizing effect of complexation with the Pt-
(PPh3)2 fragment on torsionally strained olefins7 such as
bicyclo[2.2.0]hexene,8a bicyclo[4.2.1]non-1-ene,8b and bi-
cyclo[3.3.1]non-1-ene8c has been well-documented in several
reports,8 similar studies using a PtCl2 fragment have been
rather limited. The most notable among them is a report by
Godleski and co-workers in 1983, demonstrating that ther-
mally unstable bicyclo[3.3.1]non-1-ene can be effectively
trapped upon treatment with trans-PtCl2(pyridine)(η2-
ethylene) to afford trans-PtCl2(pyridine)(η2-bicyclo[3.3.1]non-
1-ene) (7), whose structure was characterized on the basis of 1H
(6) For a review on the electrophilic activation of alkenes by Pt(II),
ꢀ
see: Chianese, A. R.; Lee, S. J.; Gagne, M. R. Angew. Chem., Int. Ed.
2007, 46, 4042–4059.
(7) (a) Luef, W.; Keese, R. Top. Stereochem. 1991, 20, 231–318. (b)
Warner, P. M. Chem. Rev. 1989, 89, 1067–1093. (c) Shea, K. J. Tetrahedron
1980, 36, 1683–1715.
(8) (a) Jason, M. E.; McGinnety, J. A.; Wiberg, K. B. J. Am. Chem.
Soc. 1974, 96, 6531–6532. (b) Stamm, E.; Becker, K. B.; Engel, P.; Ermer,
O.; Keese, R. Angew. Chem., Int. Ed. Engl. 1979, 18, 685–686. (c)
Godleski, S. A.; Gundlach, K. B.; Valpey, R. S. Organometallics 1985, 4,
296–302. (d) Nicolaides, A.; Smith, J. M.; Kumar, A.; Barnhart, D. M.;
Borden, W. T. Organometallics 1995, 14, 3475–3485. (e) The pyramidalized
alkenes are predicted to be much more strongly bonded to the Pt(PPh3)2
fragment than is ethylene. Morokuma, K.; Borden, W. T. J. Am. Chem. Soc.
1991, 113, 1912–1914.
The 2,4,6-trimethylpyridine ligand in 3 has turned out to
be the ligand of choice, since it provides (()-4a and (()-4b as
air-stable, easy-to-handle, crystalline compounds. In con-
trast, similar reactions with other PtCl2(η2-ethylene) com-
plexes with less substituted pyridinic ligands, including

6634 Organometallics, Vol. 29, No. 24, 2010
Tomooka et al.
and 13C{1H} NMR spectroscopic analysis.9 Since this bridge-
head alkene with a unique nonplanar π system can be regarded
as a bicyclic analogue of (E)-cyclooctene, which has been the
legendary prototypical example of planar chiral cyclic com-
pounds, it is of interest to compare the NMR data of (()-4b
with the reported data of 7.
Table 1. 13C{1H} Chemical Shifts and 1JPt-C Coupling
Constantsa
δ
C(1), ΔδC(1), 1JPt-C(1), δC(2), ΔδC(2), 1JPt-C(2)
,
ppm ppm
Hz
ppm ppm
Hz
ref
PtCl2
(()-4a
83.2b 41.0c
193.1d 95.7e 41.3f 170.0g this
work
175.7 92.7e 40.9f 162.6 this
work
(()-4b
105.1b 29.4c
7
8a
120.4 27.8
92.5 29.0
116.0 14.7
211.6 84.3 41.5
155
143.6 84.7 34.0
202.9
9
10
9
8b
Pt(PPh3)2
147.2
A
B
C
D
61.4 86.6
66.9h
320
407h
343h
296i
194
52.5 73.5
220
8c
8d
8d
8d
8c
74.9h
78.8i
Pt(C2H4)(PPh3)2 39.6 88
d 1
a In CDCl3 unless otherwise noted. b δC(3)
.
c ΔδC(3)
.
J
.
e δC(4)
.
Pt-C(3)
g 1
f ΔδC(4)
.
J
.
h C6D6, 298 K. i In toluene-d8, 338 K.
Pt-C(4)
Table 1 gives select 13C{1H} NMR data for (()-4a and (()-
4b along with those for related platinum complexes. Note-
worthy are the large upfield shifts on coordination (Δδ) for
disubstituted carbons C(3) and C(4) in (()-4a (41.0 and 41.3
ppm, respectively) as well as C(4) in (()-4b (40.9 ppm), which
are very similar to that for C(2) in 7 (41.5 ppm). Also, the
upfield shift for trisubstituted carbon C(3) in (()-4b (29.4
ppm) is also similar to that for C(1) in 7 (27.8 ppm). More-
over, the 1JPt-C coupling constants ((()-4a, 193.1 and 170.0
Hz; (()-4b, 175.7 and 162.6 Hz) far exceeding those for 8a or
8b around 150 Hz are indicative of a stronger interaction of
the (E)-olefin in (()-1a and (()-1b, with the platinum center
arising from more pronounced rehybridization relative to
ordinary unstrained olefins, while the degree of contribution
of a platinacyclopropane structure in (()-4a or (()-4b may
surrounding the platinum in the solid state, as shown in
Figures 1 and 2.12 Their pyridine nuclei also adopt an almost
perpendicular arrangement with respect to the coordination
plane.3d,13 These features are interpreted as a result of a steric
repulsion between the two o-methyl groups and the two
chloro ligands, which should provide an opportunity for
the 5d orbitals of platinum to overlap with the two π*
molecular orbitals at the pyridine nucleus and olefin (i.e.,
back-donation). The overlap should be positioned trans but
orthogonal to each other. We believe that the two o-methyl
groups should contribute to the reduction of the lability of
ligands around the central platinum in (()-4a and (()-4b
(vide infra).14
The selected bond lengths for the coordinated C(3)-C(4)
unit in the solid-state structure of (()-4a and (()-4b are
summarized in Table 2. However, distinctive features for our
complexes cannot be fully extracted, due to the paucity of
data for the solid-state structures of PtCl2 complexes having
a multisubstituted olefin or an originally distorted olefinic
ligand, except for the well-known trans-PtCl2((E)-cyclo-
octene)[(R)-(þ)-PhCH(NH2)CH3] (9).15 It has been claimed
that the magnitude of back-donation in Pt(η2-olefin) com-
plexes may be more appreciably manifested in the solid-state
structures at the C-C bond length rather than at the Pt-C
bond length, which can greatly hinge on steric require-
ments.8c,16 However, we note that the C(3)-C(4) bond
1
be less prominent than that in 7 with JPt-C values over
200 Hz or in a series of Pt(PPh3)2 complexes A-D with much
larger 1JPt-C values.11
Not surprisingly, the C(3)-C(4) units of (()-4a and (()-4b
adopt an upright geometry with respect to the square plane
(9) Godleski, S. A.; Valpey, R. S.; Gundlach, K. B. Organometallics
1983, 2, 1254–1257.
(10) (a) van der Poel, H.; van Koten, G.; Kokkes, M.; Stam, C. H.
Inorg. Chem. 1981, 20, 2941–2950. (b) Erdogan, G.; Grotjahn, D. B. J. Am.
Chem. Soc. 2009, 131, 10354–10355.
(11) A slight decrease in the olefinic 1JC-H value upon complexation
was commonly observed in the case of torsionally strained olefin
complexes such as 7 (from 160.6 to 159.8 Hz)9 or RuCl2(pybox-ip)-
[(-)-(E)-cyclooctene] (from 150.6 to 148.7 Hz); see: Nishiyama, H.;
Naitoh, T.; Motoyama, Y.; Aoki, K. Chem. Eur. J. 1999, 3509–3513.
Similar changes for (()-4a, (()-4b, and their congeners will be measured and
reported separately.
(14) As early as 1969, Orchin and co-workers reported14a that
pyridinic ligands undergo more rapid ligand exchange with solvent
molecules than olefinic ligands in this class of compounds, but the
anomalous feature of 3 arising from 2,6-disubstitution at the pyridine
nuclei has been documented later by a number of research groups3b-f
including themselves.14b (a) Kaplan, P. D.; Schmidt, P.; Brause, A.;
Orchin, M. J. Am. Chem. Soc. 1969, 91, 85–88. (b) Pesa, F.; Spaulding, L.;
Orchin, M. J. Coord. Chem. 1975, 4, 225–230.
(12) (a) Hartley, F. R. Chem. Rev. 1969, 69, 799–844. (b) Hartley, F. R.
Angew. Chem., Int. Ed. Engl. 1972, 11, 596–606. (c) Albright, T. A.;
Hoffmann, R.; Thibeault, J. C.; Thorn, D. L. J. Am. Chem. Soc. 1979, 101,
3801–3812. (d) Tsipis, A. C. Organometallics 2008, 27, 3701–3713 and
references therein.
(13) Either the (E)-olefin or 2,4,6-trimethylpyridine ligand of (()-4a
and (()-4b should rotate freely in solution, at least at ambient tempera-
ture, since the two methyl groups at the 2,6-position of the pyridine ring
were observed as equivalent signals in NMR spectra of their CDCl3
solution, despite the unsymmetrical structure of their olefinic units (see
the Supporting Information).
(15) (a) Cope, A. C.; Ganellin, C. R.; Johnson, H. W., Jr.; van Auken,
T. V.; Winkler, H. J. S. J. Am. Chem. Soc. 1963, 85, 3276–3279. (b) Monor,
P. C.; Shoemaker, D. P.; Parkes, A. S. J. Am. Chem. Soc. 1970, 92, 5260–5262.
(16) (a) Evans, A.; Mortimer, C. T.; Puddephatt, R. J. J. Organomet.
Chem. 1974, 72, 295–297. (b) Tsuchiya, K.; Kondo, H.; Nagashima, H.
Organometallics 2007, 26, 1044–1051 and references therein.

Communication
Table 2. Selected Bond Lengths (A)
Organometallics, Vol. 29, No. 24, 2010 6635
˚
reactions, since these products are otherwise difficult to
obtain.19
a
˚
˚
˚
˚
Pt-C(1), A Pt-C(2), A C(1)-C(2), A Δ(C-C), A
ref
PtCl2
(()-4a 2.172(11)b 2.166(15)c
(()-4b 2.266(10)b 2.137(10)c
1.364(19)d
1.400(16)d
1.35
this work
this work
15b
Moreover, the aforementioned attachment and detach-
ment of olefins onto the trans-PtCl2(2,4,6-trimethylpyridine)
fragment was characterized by high stereospecificity, which
was confirmed by separate experiments starting from opti-
cally active 1a or 1b. For example, the reaction of (R)-(-)-1a
or (R)-(-)-1b with >98% ee with 3 gave the optically active
complexes (þ)-4a and (þ)-4b, displaying a specific rotation
of þ150.3° (c = 1.20, CHCl3) or þ119.3° (c = 0.46, CHCl3),
both of which were proven to be >98% ee, as evidenced by
HPLC analysis using a Daicel Chiralcel OD-H column.
On the other hand, the PPh3-induced liberation of (-)-4b
with 34% ee afforded (S)-(þ)-1b without any loss of enan-
tiopurity. We have also confirmed that the hydrogenation of
(þ)-4a with >98% ee afforded (þ)-4ay, displaying a specific
rotation of þ112.2° (c = 1.10, CHCl3), which was confirmed
to be >98% ee by HPLC analysis using a Daicel Chiralpak
AS-H column. It is worth noting that the recovered 1ay from
an optically pure (þ)-4ay turned out to be completely
racemic, possibly due to the insufficient stability of the
planar chirality of 1ay at ambient temperature.
0.07
9
2.11
Pt(PPh3)2
B
C
D
E
F
2.068(8)
2.105(9)e
2.129(4)
2.07
2.056(8)
2.115(8)e
2.113(4)
2.14
1.475(11)
1.441(9)e
1.421(7)
1.55
8d
8d
8d
8a
8b
2.16
2.11
1.41
a Difference between the coordinated and noncoordinated forms of
the alkene ligand. b Pt-C(3). c Pt-C(4). d C(3)-C(4). e Data for the
other independent molecule of the two are 2.086(8), 2.095(8), and
˚
1.467(9) A, respectively.
˚
length in (()-4b was elongated by 0.07 A from that of (()-
1b1a and that the dihedral angle C(2)-C(3)-C(4)-C(5) in
(()-4b (38.8°) was remarkably increased from that in (()-1b
(29.5°). These results indicated that the inherent olefinic
strain17 of 1 can be effectively released by the complexation,
which should be a critical beneficial factor in the formation
and the stability of 4.
In summary, we have found that the (E)-olefin moiety in a
series of planar chiral diolefinic organonitrogen cycles un-
dergoes selective complexation with the trans-PtCl2(2,4,6-
trimethylpyridine) fragment to give novel chiral platinum
complexes, whose structural feature and reactivities have
been clarified.20 Of particular note was the robustness of
their coordinated moiety, which allowed further functiona-
lizations at the untouched olefin to furnish new platinum
complexes. Several unique synthetic fabrications could be
attained with a combination of these results and the PPh3-
induced liberation of their coordinated olefin. These results
should open up a deeper understanding of the molecular
topological constraints, which should allow us to manipulate
tailor-made planar chiral molecules. Further studies toward
this final goal are actively underway in our laboratory.
The stability of (()-4a and (()-4b caused their (Z)-olefin
moiety to undergo further functionalization, as long as it
proceeds under conditions milder than those for a Cope-type
rearrangement.18 For example, the reactions of (()-4a and
(()-4b with an excess amount of m-CPBA in CH2Cl2 at
0-30 °C followed by an extractive workup with aqueous
Na2S2O3 selectively furnished corresponding complexes
having an epoxide moiety, (()-4ax and (()-4bx, in 32 and
86% yields, respectively. Also, the hydrogenation of (()-4a
in toluene containing Pd/C as a catalyst (P(H2) = 1 atm,
30 °C) for a very short period provided (()-4ay in 80%
yield, although the fully saturated N-tosylcycloazanonane
(10) was detectable in the crude reaction mixture. Notwith-
standing the masked reactivity of the (E)-olefin moiety in a
series of platinum complexes, all of the platinum complexes
obtained in this study were susceptible to smooth liberation
of the corresponding olefinic ligands upon treatment with
an excess amount of PPh3. The high efficiency in the
recovery of (()-1ax, (()-1bx, and (()-1ay from (()-4ax,
(()-4bx, and (()-4ay (85%, 85%, and 78% yields, re-
spectively) has strengthened the synthetic utility of these
Acknowledgment. This research was supported by the
MEXT (Nos. 22350019 and 21550096) and the Global
COE Program (Kyushu University). We are grateful to
Professor Hiroharu Suzuki (Tokyo Institute of Tech-
nology) for valuable discussions.
Supporting Information Available: Text, tables, figures, and
CIF files giving experimental procedures and X-ray crystal-
lographic data for (()-4a, (()-4b, (()-4bx, and (()-5a. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(17) Maier, W. F.; Schleyer, P. v. R. J. Am. Chem. Soc. 1981, 103,
1891–1900.
(18) The thermolysis of (()-4b in toluene at 80 °C for 1.5 h resulted in
its complete consumption to give a mixture, from which (()-6b was
isolated in 54% yield.
(19) The newly obtained (()-1ay is not obtainable by a Mitsunobu-
type reaction of HO(CH2)5CHdCHCH2NHTs in refluxing THF con-
taining PPh3 and C2H5O2CNdNCO2C2H5, although similar reaction
conditions have been very effective for the preparation of the series (()-
1a-d.
(20) (a) 13C{1H} NMR data for the coordinated olefinic parts of (()-
4ax, (()-4bx, (()-4ay, and (()-5a are compiled in the Supporting
Information. (b) The solid-state structures of (()-4bx and (()-5a were
also determined by X-ray diffraction. See the Supporting Information.