Synthesis, solution and solid-state structure of Pd(II), Pt(II), Ir(III) and Zn(II) complexes with 5-pyridyl substituted N-methyl isoxazolidines

Article abstract of DOI:10.1016/S0277-5387(01)00711-2

Pd(II), Pt(II), Zn(II) and Ir(III) complexes with 5-pyridine substituted N-methyl isoxazolidines (4-(2-methyl-3-phenylisoxazolidin-5-yl)-pyridine (L¹), 2-(2-methyl-3- phenylisoxazolidin-5-yl)-pyridine (L²), 2-(2-methyl-3 -ferrocenylisoxazolidin-5-yl)-pyridine (L³) have been prepared and characterized by ¹H, ¹³C, and ³¹P NMR. The configurations of coordinated isoxazolidines have been assigned by the analysis of NMR coupling constants and by nuclear Overhauser measurements through 2D-ROESY experiments. The molecular structures of [Cp*Ir(L²)Cl][BPh₄] (6) (Cp*-pentamethylcyclopentadienyl) and trans-[PdCl₂(L³)PEt₃] (8) have been established by means of X-ray crystallography. The crystal structure of 6 consists of piano stool geometry with respect to the Ir(III) center with N,N-bidentate coordinated ligands. The six-membered chelate ring formed by Ir(1), N(1), C(5), C(6), O(1), N(2) possesses a 'twist-tub' conformation. The crystal structure of 8 consists of neutral square planar Pd(II) complexes. L³ is coordinated in a monodentate manner via the pyridine nitrogen atom. The isoxazolidine fragment of both compounds has an envelope conformation. NMR data are consistent with an O,N-bidentate coordination of L² for [Zn(L²)Cl₂] (5), while L¹ act as a monodentate ligand through the nitrogen atom of the pyridine in Zn(L¹)₂Cl₂ (4).

Full text of DOI:10.1016/S0277-5387(01)00711-2

Polyhedron 20 (2001) 957–967
www.elsevier.nl/locate/poly
Synthesis, solution and solid-state structure of Pd(II), Pt(II), Ir(III)
and Zn(II) complexes with 5-pyridyl substituted N-methyl
isoxazolidines
Andrey B. Lysenko a, Svetlana V. Shishkina b, Oleg V. Shishkin b,
Emma Peralta-Pe´rez c, Fernando Lo´pez-Ortiz c, Rostislav D. Lampeka a,*
a Department of Inorganic Chemistry, Kie6 National Uni6ersity, Vladimirskaja st. 64, 01033 Kie6, Ukraine
b Scientific Research Department of Alkali Halide Crystals, STC ‘Institute for Single Crystals’, Lenina st. 60, 310001 Khar’ko6, Ukraine
c
´
Area de Qu´ımica Orga´nica, Uni6ersidad de Almer´ıa, Carretera Sacramento s/n 04120 Almeria, Spain
Received 2 November 2000; accepted 29 January 2001
Abstract
Pd(II), Pt(II), Zn(II) and Ir(III) complexes with 5-pyridine substituted N-methyl isoxazolidines (4-(2-methyl-3-phenylisoxazo-
lidin-5-yl)-pyridine (L1), 2-(2-methyl-3-phenylisoxazolidin-5-yl)-pyridine (L2), 2-(2-methyl-3-ferrocenylisoxazolidin-5-yl)-pyridine
(L3)) have been prepared and characterized by 1H, 13C, and 31P NMR. The configurations of coordinated isoxazolidines have been
assigned by the analysis of NMR coupling constants and by nuclear Overhauser measurements through 2D-ROESY experiments.
The molecular structures of [Cp*Ir(L2)Cl][BPh4] (6) (Cp*-pentamethylcyclopentadienyl) and trans-[PdCl2(L3)PEt3] (8) have been
established by means of X-ray crystallography. The crystal structure of 6 consists of piano stool geometry with respect to the
Ir(III) center with N,N-bidentate coordinated ligands. The six-membered chelate ring formed by Ir(1), N(1), C(5), C(6), O(1), N(2)
possesses a ‘twist-tub’ conformation. The crystal structure of 8 consists of neutral square planar Pd(II) complexes. L3 is
coordinated in a monodentate manner via the pyridine nitrogen atom. The isoxazolidine fragment of both compounds has an
envelope conformation. NMR data are consistent with an O,N-bidentate coordination of L2 for [Zn(L2)Cl2] (5), while L1 act as
a monodentate ligand through the nitrogen atom of the pyridine in [Zn(L1)2Cl2] (4). © 2001 Elsevier Science Ltd. All rights
reserved.
Keywords: Isoxazolidines; Complexes; X-ray data; NMR data
contrast, the coordination chemistry of these five-mem-
bered heterocycles remains practically unexplored. A
literature search revealed that previous to our work the
molecular structure of only three complexes 1–3 of
transition metals with isoxazolidine-containing ligands
had been described [5–7]. Furthermore, in these com-
pounds the heterocycle is not directly coordinated to
the metal, except for the tungsten carbene 3 where the
metal is bonded to the carbon adjacent to the nitrogen
of the isoxazolidine ring. Recently, it has been shown
that isoxazolidine derivatives can be used as mecha-
nism-based inactivators of carboxypeptidase A, a zinc-
containing protease [8].
1. Introduction
Isoxazolidines have attracted a great deal of attention
over recent years due to their applications in organic
synthesis [1,2], the industrial uses they have [3] and the
role they play as biologically active substances [4]. In
* Corresponding author. Fax: +380-44-4907185.
E-mail addresses: shishkin@xray.isc.kharkov.com (O.V. Shishkin),
flortiz@ualm.es (F. Lo´pez-Ortiz), r.lampeka@clariant.com.ua (R.D.
Lampeka).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00711-2

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A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
The highly flexible isoxazolidine ring [9] is an inter-
of palladium complexes were characterized based on
their elemental analysis, UV–VIS and H NMR spec-
1
esting ligand whose coordination properties may be
tuned by introducing suitable substituents in the hetero-
cycle. The substitution on the carbon skeleton renders
the ligand chiral and the complexation to a metal could
contribute to fix the conformation of the ring and
therefore to define specific stereoelectronic interactions
of relevance in asymmetric synthesis reactions [10].
In order to enhance the coordination ability of the
isoxazolidine heterocycle we decided to introduce a
pyridine substituent on carbon 5. The isoxazolidine
contains two neighboring s-donor heteroatoms (N,O)
and depending on the way of linking the pyridine
moiety to the five-membered ring we have different
coordination possibilities. We selected the 5-pyridine
substituted N-methylisoxazolidines L1–L3 as ligands
for complexation with d8 and d10 transition metals.
troscopic data. The molecular structure of [PdL2Cl2]
was determined by X-ray diffraction showing for the
first time the link of an isoxazolidine ring to a metal
[12]. In this particular case, L2 was coordinated to
palladium through the two nitrogen atoms.
Here we report the full details of the synthesis and
characterization of a new complex of Pd(II), Pt(II),
Zn(II) and Ir(III) with 5-pyridine substituted N-
methylisoxazolidines L1, L2, L3. The coordination pat-
tern observed for these ligands was dependent of the
metal used. According to the NMR spectra, the nitro-
gen atom of the pyridine is the preferred coordination
site for L1 in the zinc complex [Zn(L1)2Cl2] (4). L2
showed in all cases a bidentate complexing behavior.
The presence in L1 of a 4%-pyridine group implies that
the compound may act as a monodentate ligand
through any one of the three heteroatoms of the
molecule. On the other hand, the 2%-pyridine substituent
of L2 and L3 would allow the use of these reagents
either as monodentate or as N,O versus N,N bidentate
donor ligands affording five- or six-membered chelate
rings through coordination to a metal.
Thus, L2 is acting as an N,N-bidentate ligand in
[Cp*Ir(L2)Cl][BPh4] (6) and [Pt(L2)Cl2] (7). For the
iridium complex the assignment has been confirmed
through its X-ray structure. However, the NMR spec-
tra of [Zn(L2)Cl2] (5) allows us to conclude that in this
case L2 is chelating the metal by N,O coordination.
Interestingly, the crystal structure of trans-
[PdCl2(L3)PEt3] (8) shows a coordination for L3 exclu-
sively through the nitrogen of the pyridine.
We have recently described the syntheses of the
above-mentioned organic ligands including a prelimi-
nary study of their coordinating behavior [11]. A series

A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
959
Fig. 1. View of the structure of the complex cation [Cp*Ir(L2)Cl]+ with the numbering scheme adopted. Some hydrogen atoms are omitted for
clarity and ellipsoids are drawn at 40% probability.
2. Results and discussion
Compounds 4–8 were isolated in moderate to excel-
lent yields through recrystallization of the reaction mix-
ture. All the new complexes are air stable both as solids
and in solution, except for compound 6 that decom-
poses in solution. They are readily soluble in chloro-
form, dichloromethane, acetonitrile, N,N-dimethyl-
formamide, dimethyl sulfoxide and almost insoluble in
hexane.
2.1. Synthesis
The organic ligands L1–L3 were obtained as racemic
mixtures of cis- and trans-isomers by [3+2] dipolar
cycloaddition of N-methyl-C-phenylnitrone and N-
methyl-C-ferrocenylnitrone with 2-vinylpyridine and 4-
vinylpyridine [11,12]. For L1 and L2 the two
stereisomers could not be separated and the crude
mixtures (trans:cis ratio of 38:62 for L1and 75:25 for
L2) were used directly in the complexation step. In the
case of L3, the trans-isomer could be isolated through
column chromatography [11]. The reaction of com-
pounds L1–L3 with the selected metal halides was
carried out by mixing hot solutions of both components
in suitable solvents (see Section 4) in accordance with
the scheme:
2.2. Crystal structures of [Cp*Ir(L2)Cl][B(Ph)4] (6) and
trans-[PdCl2(trans-L3)PEt3] (8)
The yellow single crystals suitable for X-ray analysis
were prepared by the slow liquid diffusion of a hexane–
2-propanol solution into an acetone solution of 6. The
molecular structure of 6 is a salt formed by a cationic
Ir(III) complex and a tetraphenylborate anion. The
iridium ion adopts a nearly tetrahedral coordination
with one chlorine atom, h5-coordinated pentamethylcy-
clopentadienyl anion and the isoxazolidine ligand L2.
The latter is bound to the metal center in a bidentate
chelate manner via two nitrogen atoms. The six-mem-
bered chelate ring formed by Ir(1), N(1), C(5), C(6),
O(1), N(2) has a twist-tub conformation. A view of the
complex cation [Cp*Ir(L2)Cl]+ is shown in Fig. 1.
Selected bond distances and angles are given in Table 1.
The crystal lattice consists of a racemate of {(3R,5R)-2-
ZnCl2+nLm“[Zn(Lm)nCl2]
m=1; n=2; 4
m=2; n=1; 5
[Cp*IrCl2]2+2L2+2NaBPh4−ꢀꢀ2NꢀaꢀCꢁl2Cp*Ir(L2)Cl]BPh4:6
K2[PtCl4]+L2 ꢀꢀꢀꢁ cis-[Pt(L2)Cl2]:7
−2KCl
[PdPEt3Cl2]2+2L3“2 trans-[Pd(L3)PEt3Cl2]:8
(2-methyl-3-phenyl-isoxazolidin-5-(yl)-pyridine}
and

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A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
{(3S,5S) - 2 - (2 - methyl - 3 - phenylisoxazolidin - 5 - yl)-
pyridine}. The crystal structure of 6 consists of the
three-legged piano stool geometry polyhedrons of irid-
ium ions. The plane of the pentamethylcyclopentadienyl
fragment is slightly inclined to the Ir(1)ꢀX vector
(where X is a center of the pentamethylcyclopentadi-
enyl cycle) with a corresponding angle of approximately
has an equatorial orientation to the isoxazolidine ring
(torsion angle C(6)ꢀO(1)ꢀN(2)ꢀC(9) 165.2(6)°), while
the phenyl group has an axial location (torsion angle
C(6)ꢀC(7)ꢀC(8)ꢀC(10) 95.7(8)°).
Yellow single crystals of compound 8 suitable for
X-ray analysis were grown by the slow diffusion of
hexane into a chloroform solution containing this com-
plex. The structure of 8 (Fig. 2, Table 2) consists of
neutral square planar complexes of Pd(II) in which two
chlorine atoms and two neutral ligands (L3 and PPh3)
are trans-coordinated. The crystal lattice consists of
{(3S,5S)-2-(2-methyl-3-ferrocenylisoxazolidin-5-yl)-
pyridine}. The ligand L3 is coordinated to the metal
center in a monodentate manner via the pyridine nitro-
gen atom. The bond angles at the palladium atom are
in the range of 88.1(1)–93.68(6) and their sum is close
to 360°. The distances N(1)ꢀC(5), N(1)ꢀC(1) (1.362(7)
,
101.9° and a Ir(1)ꢀX distance of 1.834 A. Distances and
angles of the iridium polyhedron of complex 6 are
comparable with the corresponding related complexes
with bidentate N,N-donors [13]. The distances
O(1)ꢀC(6), N(1)ꢀC(5), N(2)ꢀC(8), Ir(1)ꢀCl(1) (1.47(1),
,
1.39(1), 1.54(1), 2.433(2) A) are elongated compared to
,
their average values (1.43, 1.34, 1.47, 2.390 A) [14] as a
result of the coordination of the nitrogen atoms to the
metal atom. The geometry parameters of the isoxazo-
lidine ring in 6 are similar to those found for cis-
[Pd(L2)Cl2] [12] with deviations of O(1) and N(2) from
the mean plane of others atoms of the isoxazolidine
,
,
and 1.376(8) A; averaged values 1.337 A) are elongated,
while the bonds Pd(1)ꢀN(1), Pd(1)ꢀCl(1), Pd(1)ꢀP(1)
,
ring by 1.10 and 0.45 A, respectively. The isoxazolidine
,
(2.173(5), 2.346(2), 2.271(1) A) are shorter than their
average values (2.089, 2.326 and 2.315 A) as a result of
heterocycle has an envelope conformation. The devia-
tion of N(2) from the mean plane of atoms
,
the coordination of the pyridine nitrogen atom and the
phosphorus atom to the palladium ion. The isoxazo-
lidine ring has an envelope conformation. The devia-
tion of N(2) from the mean plane of atoms
,
C(8)C(7)C(6)O(1) is 0.70 A. The pyridine ring is located
almost coplanar to C(6)ꢀH(6) with a torsion angle for
C(4)ꢀC(5)ꢀC(6)ꢀH(6) equal to 14.2°. The methyl group
,
C(8)C(7)C(6)O(1) is 0.72 A. The pyridine ring is copla-
Table 1
nar to O(1)ꢀC(6) (torsion angle N(1)ꢀC(5)ꢀC(6)ꢀO(1)
179.0(5)°) and located anticlinal to C(7)ꢀC(8) (torsion
angle C(5)ꢀC(6)ꢀC(7)ꢀC(8) 127.7(5)°). The methyl
group has an equatorial orientation on the isoxazo-
lidine ring (torsion angle C(19)ꢀN(2)ꢀO(1)ꢀC(6)
169.9(5)°). The ferrocenyl fragment is also found in an
anticlinal arrangement with the C(6)ꢀC(7) bond (torsion
angle C(6)ꢀC(7)ꢀC(8)ꢀC(9) 143.6(5)°).
,
Selected bond lengths (A) and angles (°) for structure of the complex
cation [Cp*Ir(L1)Cl]+
Bond lengths
Ir(1)ꢀC(18)
Ir(1)ꢀC(16)
Ir(1)ꢀC(19)
Ir(1)ꢀC(17)
O(1)ꢀC(6)
N(2)ꢀC(9)
C(6)ꢀC(7)
2.190(8)
2.210(8)
2.218(7)
2.226(8)
1.47(1)
1.49(1)
1.56(1)
Ir(1)ꢀN(1)
Ir(1)ꢀN(2)
Ir(1)ꢀC(20)
Ir(1)ꢀCl(1)
O(1)ꢀN(2)
N(2)ꢀC(8)
C(7)ꢀC(8)
2.191(6)
2.218(7)
2.224(8)
2.433(2)
1.477(8)
1.54(1)
1.55(1)
2.3. NMR studies
Bond angles
C(18)ꢀIr(1)ꢀN(1)
N(1)ꢀIr(1)ꢀC(16)
N(1)ꢀIr(1)ꢀN(2)
C(18)ꢀIr(1)ꢀC(19)
C(16)ꢀIr(1)ꢀC(19)
C(18)ꢀIr(1)ꢀC(20)
C(16)ꢀIr(1)ꢀC(20)
C(19)ꢀIr(1)ꢀC(20)
N(1)ꢀIr(1)ꢀC(17)
N(2)ꢀIr(1)ꢀC(17)
C(20)ꢀIr(1)ꢀC(17)
N(1)ꢀIr(1)ꢀCl(1)
N(2)ꢀIr(1)ꢀCl(1)
C(20)ꢀIr(1)ꢀCl(1)
C(6)ꢀO(1)ꢀN(2)
O(1)ꢀN(2)ꢀC(9)
C(9)ꢀN(2)ꢀC(8)
C(9)ꢀN(2)ꢀIr(1)
O(1)ꢀC(6)ꢀC(5)
C(5)ꢀC(6)ꢀC(7)
N(2)ꢀC(8)ꢀC(10)
C(10)ꢀC(8)ꢀC(7)
109.5(3)
114.0(3)
89.0(2)
38.5(3)
64.7(3)
64.4(3)
38.3(3)
38.3(3)
94.2(3)
141.1(3)
63.7(3)
83.9(2)
88.2(2)
122.9(3)
104.4(5)
103.6(6)
114.4(6)
113.1(5)
109.5(6)
113.6(7)
116.1(7)
112.9(7)
C(18)ꢀIr(1)ꢀC(16)
C(18)ꢀIr(1)ꢀN(2)
C(16)ꢀIr(1)ꢀN(2)
N(1)ꢀIr(1)ꢀC(19)
N(2)ꢀIr(1)ꢀC(19)
N(1)ꢀIr(1)ꢀC(20)
N(2)ꢀIr(1)ꢀC(20)
C(18)ꢀIr(1)ꢀC(17)
C(16)ꢀIr(1)ꢀC(17)
C(19)ꢀIr(1)ꢀC(17)
C(18)ꢀIr(1)ꢀCl(1)
C(16)ꢀIr(1)ꢀCl(1)
C(19)ꢀIr(1)ꢀCl(1)
C(17)ꢀIr(1)ꢀCl(1)
C(1)ꢀN(1)ꢀIr(1)
O(1)ꢀN(2)ꢀC(8)
O(1)ꢀN(2)ꢀIr(1)
C(8)ꢀN(2)ꢀIr(1)
O(1)ꢀC(6)ꢀC(7)
C(8)ꢀC(7)ꢀC(6)
N(2)ꢀC(8)ꢀC(7)
65.3(3)
161.4(3)
105.6(3)
147.4(3)
123.4(3)
152.2(4)
98.1(3)
38.5(3)
38.6(3)
63.9(3)
95.9(2)
1H and 13C NMR data of the complexes 4–6 are
collected in Table 3. We will focus on complexes 4 and
5 because both contain the same metal and therefore
the electronic effects induced on the respective organic
ligands will be similar and could be used as a tool of
diagnostic value in the identification of the coordina-
tion mode of the same ligands to different metals.
1
The H NMR spectrum of 4 shows the presence of
two diastereomeric complexes formed by coordination
of the zinc to the trans-(trans-L1) and cis-isoxazolidines
(cis-L1) in an approximate ratio of 40:60, respectively.
The complexation of both ligands is easily deduced
from the variations of the proton chemical shifts com-
pared with the free isoxazolidines. Thus, hydrogens
ortho to the pyridine nitrogen appear as a multiplet
centered at 8.8 and 8.77 ppm for the minor [Zn(trans-
L1)Cl2] (4a) and major [Zn(cis-L1)Cl2] (4b) stereoiso-
mers, respectively. These values represent a low field
shift of 0.2–0.17 ppm relative to L1 [l(Hp0y) 8.60 ppm,
157.0(2)
92.5(2)
130.7(2)
123.5(5)
100.9(5)
109.7(4)
113.8(5)
106.6(6)
102.9(7)
101.3(6)

A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
961
Fig. 2. View of the structure of complex 8 with the numbering scheme adopted. Some hydrogen atoms are omitted for clarity and ellipsoids are
drawn at 40% probability.
the intense cross peak observed between H-3 and H-5.1
overlapped for the two isomers at 300 MHz]. The meta
protons of the pyridine are also significantly deshielded
Consequently, compound 4a is the trans-L1 isomer.
This assignment is corroborated by the small NOE
correlation between H3 and the meta protons of the
pyridine ring at l 7.64. Additionally, in the cis isomer
4b the methylene proton at l 2.30 shows the expected
(Dl 0.2 and 0.28 for the trans and cis isomer, respec-
tively). In contrast, the aliphatic protons of the isoxazo-
lidine ring and the methyl group are not affected by the
complexation and are found practically at the same
field as the corresponding non-coordinated L1 isomers.
Therefore, we can conclude that L1 behaves as a
monodentate ligand and is coordinated only via the
pyridine nitrogen atom.
Table 2
,
Selected bond lengths (A) and angles (°) for structure of complex 8
Bond lengths
It has been shown in a series of 3,5-disubstituted
isoxazolidines, that the relative stereochemistry of the
stereogenic centers can be assigned based on the analy-
sis of the coupling constants and NOEs observed for
the proton at C-5 [15]. For the compounds referred to
in that study this proton appeared systematically as a
double doublet (3JHH 3ꢀ6 Hz) for the cis isomer, and
a doublet for the trans (3JHHꢀ5 Hz) one. Unfortu-
nately, both isomers 4a,b produced the same multiplic-
ity pattern for H-5, a double doublet, with vicinal
couplings of the same magnitude (3JHH 6 and 9 Hz) (see
Table 3), precluding the assignment of the configura-
tion of the isoxazolidine moiety. To our delight the
2D-NOESY spectrum of the mixture 4a and 4b allowed
us to assign the stereochemistry of the two isomers. The
cis arrangement of the substituents on C-3 and C-5 of
the heterocycle in the major isomer 4b is deduced from
Pd(1)ꢀN(1)
Pd(1)ꢀCl(2)
N(2)ꢀC(19)
N(2)ꢀC(8)
C(6)ꢀC(7)
2.173(5)
2.331(2)
1.469(8)
1.513(8)
1.57(1)
Pd(1)ꢀP(1)
Pd(1)ꢀCl(1)
N(2)ꢀO(1)
O(1)ꢀC(6)
C(7)ꢀC(8)
2.271(1)
2.346(2)
1.491(7)
1.462(7)
1.559(8)
Bond angles
N(1)ꢀPd(1)ꢀP(1)
P(1)ꢀPd(1)ꢀCl(2)
P(1)ꢀPd(1)ꢀCl(1)
C(24)ꢀP(1)ꢀPd(1) 117.1(2)
C(20)ꢀP(1)ꢀPd(1) 113.0(2)
Cl(1)ꢀN(1)ꢀPd(1) 116.6(4)
C(19)ꢀN(2)ꢀC(8) 113.2(5)
C(6)ꢀO(1)ꢀN(2)
O(1)ꢀC(6)ꢀC(7)
C(8)ꢀC(7)ꢀC(6)
175.3(1)
87.24(6)
93.68(6)
N(1)ꢀPd(1)ꢀCl(2)
N(1)ꢀPd(1)ꢀCl(1)
Cl(2)ꢀPd(1)ꢀCl(1)
C(22)ꢀP(1)ꢀPd(1)
C(5)ꢀN(1)ꢀPd(1)
C(19)ꢀN(2)ꢀO(1)
O(1)ꢀN(2)ꢀC(8)
O(1)ꢀC(6)ꢀC(5)
C(5)ꢀC(6)ꢀC(7)
C(9)ꢀC(8)ꢀN(2)
88.1(1)
90.9(1)
174.13(7)
108.4(2)
124.3(3)
104.5(5)
100.9(4)
109.0(4)
115.0(5)
111.2(4)
102.5(4)
104.8(4)
103.6(5)
1 The signal for H3 in both isomers is practically overlapped. Only
H-3 of the cis isomer can give a NOE enhancement on H-5.

962
A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
Table 3
1H and 13C NMR data of complexes 4–8
Compound
1H NMR (l)
Assignment
Hb
13C NMR (l) Assignment
[Zn(trans-L1)2Cl2] 4a, minor isomer, (CDCl3, 20°C)
2.52 (ddd, 12.3,
8.3, 6.3 Hz, 1H)
2.74 (s, 3H)
43.03
NCH3
NCH3
Hc
Hd
47.79
72.80
76.49
122.71
C4
C3
C5
Cb
2.96 (bm a, 1H)
3.72 (bm a, 1H)
5.37 (dd, 9.2, 6.3
Hz, 1H)
Ha
7.20–7.50 (m, 5H) Ph
127.61
128.84
p-Ph
m-Ph
7.64 (m, 2H)
8.8 (m, 2H)
b-py
a-py
137.46
148.66
158.69
ipso-Ph
Ca
ipso-Py
[Zn(cis-L1)2Cl2] 4b, major isomer, (CDCl3, 20°C)
2.30 (ddd, 12.3,
9.5, 6.0 Hz, 1H)
2.68 (s, 3H)
3.29 (ddd, 12.3,
9.0, 7.3 Hz, 1H)
3.72 (bm a, 1H)
5.30 (dd, 9.0, 6.0
Hz, 1H)
Hb
43.03
NCH3
NCH3
Hc
47.79
73.85
C4
C3
Hd
Ha
75.67
122.45
C5
Cb
7.20–7.50 (m, 5H) Ph
127.61
128.29
128.80
137.41
148.57
155.50
p-Ph
o-Ph
7.69 (m, 2H)
8.77 (m, 2H)
b-py
a-py
ipso-Ph
Ca
ipso-Py
[Zn(trans-L2)Cl2] 5a, major isomer (CDCl3, 20°C)
2.70 (s, 3H)
3.13 (dd, 13.6, 9.5 Hc
Hz, 1H)
NCH3
41.76
43.86
NCH3
C4
3.34 (ddd, 13.6,
7.9, 5.8 Hz, 1H)
5.18 (d, 7.9 Hz,
1H)
5.58 (dd, 9.5, 5.8
Hz, 1H)
Hb
Hd
Ha
69.38
77.95
123.15
C3
C5
Cd
7.30–7.5 (m, 5H)
7.5 (m,
Ph
d-Py
125.51
129.11
Cb
m-Ph
overlapped, 1H)
7.63 (m,
b-Py
129.32
o-Ph
overlapped, 2H)
8.03 (m, 1H)
8.78 (m, 1H)
g-Py
a-Py
129.42
134.66
140.84
150.80
159.84
p-Ph
ipso-Ph
Cg
Ca
ipso-Py
[Pt(trans-L2)Cl2] 7a, (CDCl3, 20°C)
3.13 (s, 3H)
NCH3
Hc
Hb
48.22
41.04
78.80
NCH3
C4
3.15 (m, 1H)
4.31 (ddd, 13.6,
9.7, 4.5, 1H)
5.45 (dd, 9.7, 4.5, Ha
1H)
6.05 (d, 8.0, 1H)
7.2–7.6 (m, 8H)
9.78 (d, 5.2 Hz,
1H)
C3
80.0
C5
Hd
Ph+3HPy
a-Py
124.76–138.86
154.28
155.72
Cb,g,d+Ph
Ca
ipso-Py

A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
963
Table 3 (Continued)
Compound
1H NMR (l)
Assignment
13C NMR (l) Assignment
[Pt(cis-L2)Cl2] 7b, (CDCl3, 20°C)
3.57 (s, 3H)
3.11 (m, 1H)
3.73 (ddd, 13.6, 9.7,Hb
4.5, 1H)
4.0 (dd, 9.7, 4.5, 1H)Hd
5.29 (dd, 9.7, 4.5,Ha
1H)
NCH3
Hc
51.15
38.46
78.65
NCH3
C4
C5
83.43
124.76–138.86
C3
Cb,g,d+Ph
7.2–8.1 (m, 8H)
10.13 (d, 5.2 Hz, 1H)a-Py
Ph+3HPy
154.49
155.11
Ca
ipso-Py
Trans-[PdCl2(trans-L3)PEt3] 8, (CDCl3, 20°C)
1.34 (m, 9H)
1.99 (m, 6H)
2.69 (s, 3H)
ꢀCH3, (PEt3)
ꢀCH2ꢀ, (PEt3)
NCH3
Hc
Hb
Ha
Fc
Hd
8.35
ꢀCH3, (PEt3)
ꢀCH2ꢀ, (PEt3)
NCH3
16.26
43.23
46.02
66.33
68.04
68.83
69.53
77.92
83.49
122.59
123.33
138.30
150.10
3.05 (m a, 1H)
3.53 (m a, 1H)
4.33 (m a, 1H)
4.13 (s, 9H)
C-4
ipso-Cp
a-Cp
unsubstituted-Cp
6.30 (m a, 1H)
b-Cp
C-3
C-5
Cd
7.28 (q, 4.5 Hz, 1H) g-Py
7.78 (d, 3.8 Hz, 2H) b-Py
8.80 (m a, 1H)
a-Py
Cb
Cg
Ca
a Broad multiplet.
and the proton at C-5 (Dl 0.2 ppm). On the contrary,
the methyl protons remain practically unaffected (Dl
0.03 ppm). These shift effects are consistent with a
coordination of L2 in a bidentate manner via the nitro-
gen of the pyridine and the oxygen of the isoxazolidine.
It is worth noting the large downfield shift of the
proton at C-3 (l 5.19 for 5a vs 3.72 for L2) which
suggests the proximity of this proton to the positively
charged metal ion. This type of interaction would be
possible assuming a trans arrangement of the sub-
stituents on the isoxazolidine ring, as is proved to be
the case (see below).
cross peaks with both the pyridine and the phenyl
substituents corresponding to their syn orientation (l
H4anti 3.29). For the trans isomer 4a the highest
shielded methylene proton is the one syn to the pyridine
ring (cf. l H4syn(py) 2.52 vs H4anti(py) 2.96).
The stereochemistry of the stereogenic carbons C-3
and C-5 could not be determined from the multiplicity
pattern or the magnitude of the coupling constants of
the respective protons. H-5 appeared at l 5.58 again as
a double doublet with vicinal couplings of 6.2 and 9.2
Hz. Interestingly, zinc coordination of L1 in 4 and of L2
in 5 produce similar effects on the couplings of H-5
with its neighbor protons. The proton H-3 exhibit only
one vicinal coupling 3JH3H4=7.5 Hz (Table 3). This is a
common property of isoxazolidine systems, where the
dihedral angle between H-3 and Hb-4 is close to 90°
and therefore the corresponding coupling vanishes [15].
The 2D-NOESY spectra of 5ba do not allow us to
identify the stereochemistry. All signals show negative
cross peaks with all other protons, which is a typical
spin diffusion problem [16]. The relative trans arrange-
ment of the substituents at C-3/C-5 of the isoxazolidine
The proton spectrum of complex 5 also shows a
mixture of two compounds in a ratio 88:12. Due to the
low concentration of the minor component and the
overlap of some signals with those of the major one, we
could achieve the structural assignment of only the
major species labeled as 5a. We have followed a similar
analysis to that carried out with complex 4. First, we
have identified the coordination mode of the ligand L2
1
by comparing the H chemical shifts of the complex
and the free ligand. The complexation produces a low
field shift of the pyridine protons (Dl ꢀ0.1–0.3 ppm)

964
A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
Fig. 3. The 2D-ROESY spectrum of [Zn(L2) Cl2] complex (300 MHz, CDCl3).
1
ring could be established by acquiring the 2D-ROESY
[17] spectrum (Fig. 3). Thus, H-3 shows a cross peak
with pyridine protons at l 8.03 (H-4%) and 7.5 (H-3%),
while H-5 exhibits a ROE cross peak with the ortho
protons of the phenyl ring on carbon C-3. Moreover,
the cross peaks of H-3 and H-5 with the methylene
protons of C-4 allow us to assign H4syn(py) and H4anti(py)
as the multiplets centered, respectively at l 3.19 and
3.30 ppm.
The H NMR spectra of complexes 6 and 7 show a
low-field shift of almost all resonances of L2 compared
to those of the ‘free’ ligand. Relatively large shifts are
observed for the protons of the N-methyl group, the
pyridine substituent and the proton at C-5. The
deshielding observed for the protons close to the nitro-
gen atoms of the isoxazolidine allows us to conclude
that in these complexes the organic ligand is coordi-
nated to the metal in a bidentate manner via the
two nitrogen atoms. Analogous shift effects have
been previously observed for complex [PdL2Cl2],
whose molecular structure, determined by X-ray dif-
fraction, showed that the ligand acts as a N,N-biden-
tate donor.
Complex 6 has four stereocenters (C*-3, C*-5, Ir*
1
and N*) and the H NMR spectrum indicates that a
complex mixture of compounds is present. A group of
peaks in the range l 1.25–2.05 can be assigned to the
methyl protons of Cp* and the tetraphenylboron anion
shows several multiplets in the aromatic region l 6.8–
7.1. Unfortunately, the signals of the isoxazolidine ring
are broadened and partially overlapped. Furthermore,
the relative intensity of ortho protons of the pyridine

A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
965
Table 4
and/or in a bidentate manner involving the pyridine
nitrogen and the oxygen atom of the isoxazolidine ring.
On standing in solution the thermodynamically favored
N,N-complex is formed.
Crystal data and structure refinement for compounds 6 and 8
Compound
6
8
Chemical formula
C
47H50ClN2OBIr
C25H35Cl2N2OFe
PPd
643.67
Complex [PdCl2(trans-L3)PEt3] 8 is isolated as a sin-
gle species as deduced from the only signal observed in
the 31P spectrum at l 36.5 corresponding to the coordi-
M
T (K)
897.35
293(2)
0.71073
triclinic
P1
293(2)
1
nated PEt3. The H NMR spectrum differs significantly
,
u (A)
0.71073
monoclinic
P21
from that of the ligand. Upon complexation the pro-
tons of the pyridine substituent of isoxazolidine trans-
L3 shift to low field (l: a-Py 8.55, 7.67 b-Py, 7.15 g-Py
for trans-L3; a-Py 8.80, 7.78 b-Py, 7.28 g-Py for 8). This
shift is a clear indication of the coordination of palla-
dium to the nitrogen atom of the pyridine group. The
signal of the methyl group in complex and in ‘free’
ligand appears at the same shift at l 2.69 ppm. These
results suggests that trans-L3 is acting as a monodentate
ligand through the nitrogen of the pyridine, in agree-
ment with the X-ray structure discussed above. Interest-
ingly, the signals of all the protons of the isoxazolidine
ring are also found at lower field (cf. Table 3, l 3.52
(H-3), 5.28 (H-5), 3.27 and 2.75 (H-4) for trans-L3).
The h1 coordination of the ligand and the deshielding
effects observed can be explained by considering that
the large size of the ferrocenyl substituents sterically
hinders the approach of palladium to the nitrogen of
the isoxazolidine, though its proximity to the five-mem-
bered heterocycle promotes a deshielding of the protons
of the ring.
Crystal system
Space group
(
Unit cell dimensions
,
a (A)
12.697(5)
13.632(5)
14.564(6)
96.36(1)
113.84(0)
89.73(1)
2289.3(16)
2
8.405(2)
16.394(4)
10.433(3)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
96.94(2)
3
,
U (A )
Z
1427.0(6)
2
1.498
1.401
3780, 3563
Dcalc (Mg m−3
)
1.302
3.008
8262, 7878
v (mm−1
)
Reflections collected,
unique
Rint
R1
wR2
0.0788
0.0707
0.1757
0.0494
0.0418
0.1077
rings is very low, indicating that in solution the sample
decomposes to a large extent.
The H NMR spectrum of 7 consists of a mixture of
1
four compounds in a relative ratio 14:18:50:18 deter-
mined through the integrals of the ortho pyridine pro-
tons appearing at l 10.1, 9.74, 9.39, 9.18 ppm,
respectively. On standing in the CDCl3 solution, the
two signals at l 9.39, 9.18 ppm disappear and the
intensity of the lowest field multiplet increases to afford
a new mixture of two components in a ratio 1:1. The
chemical shifts and multiplicity patterns of the signals
are very similar to the corresponding signals of complex
[PdL2Cl2] previously characterized. The strong low field
3. Conclusions
We have demonstrated that pyridyl-substituted N-
methyl isoxazolidines are suitable ligands to form com-
plexes with halides of metals of the Groups IIB and
VIIIB. In the case of 5-(4-pyridyl)-substituted N-methyl
isoxazolidines the coordination takes place exclusively
through the nitrogen of the pyridine. On the other
hand, 5-(2-pyridyl)-substituted N-methyl isoxazolidines
are more versatile ligands and all heteroatoms may be
used for coordination to a metal. We have shown they
may act either as monodentate ligands through the
nitrogen of the pyridine or bidentate ligands (N,N;
N,O), where the metal coordinates to the pyridine and
one of the heteroatoms of the isoxazolidine ring. The
different coordination modes observed may be ex-
plained in terms of the hardness of the metal and the
constraints derived by the steric hindrance in its sur-
roundings. Current work is aimed to validate this hy-
pothesis by studying a larger set of complexes of the
same metals with a large variety of isoxazolidine lig-
ands. The configuration and conformation of the isoxa-
zolidine ring have been determined by NOE NMR
experiments and confirmed by means of the corre-
sponding X-ray structure for complexes 6 and 8.
shift of the ortho protons of the pyridine ring (Dl H°
1.6, Dl H° 1.2 ppm) and the N-methyl protons (Dl
cis
trans
Mecis 0.88, Dl Metrans 0.41 ppm) compared to the free
ligands are strong indications that in both cases the two
nitrogen atoms are involved in the coordination to the
platinum. The NOESY spectrum showed that the two
compounds correspond to the expected cis–trans iso-
mers derived from the orientation of the substituents in
the isoxazolidine ring (see assignment in Table 3). In
order to understand the evolution of the original four
components in solution to a new mixture of two species
we can assume that no epimerization occurs by allow-
ing the sample to stand in chloroform. A reasonable
explanation would be to consider that the compounds
with the H° protons absorbing at l 9.39, 9.18 ppm are
py
complexes where the metal is coordinated to cis-L2
either through only one nitrogen atom of the ligand

966
A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
58.12; H, 5.02; N, 8.92. Calc. for C30H32Cl2N4O2Zn: C,
4. Experimental
58.41; H, 5.23; N, 9.08%).
[Zn(L2)Cl2] (5). A warm 2-propanol solution (5 ml)
of L2 (0.129 g, 0.54 mmol) was added to a warm
mixture of 2-propanol (5 ml) and acetone (2 ml) con-
taining ZnCl2 (0.074 g, 0.54 mmol). The reaction mix-
ture was stirred at ꢀ50°C for 0.5 h. After cooling to
room temperature, the white precipitate of 5 was
filtered off, washed with cold 2-propanol and recrystal-
lized from chloroform to afford a white solid 5 0.119 g
(0.32 mmol, 59%) (Anal. Found: C, 48.00; H, 4.53; N,
7.34. Calc. for C15H16Cl2N2OZn: C, 47.84; H, 4.28; N,
7.44%).
All solvents were used as supplied or distilled using
standard methods. The compounds ZnCl2, K2[PtCl4],
[Cp*IrCl2]2, trans-[PdCl2PEt3]2 were obtained from
Fluka Chemical Company and Aldrich Chemical Com-
pany Ltd. The organic ligands L1, L2 L3 have been
prepared according to previously described procedures
[11,12].
1H (300 MHz), 13C (75.5 MHz), 31P (121.49 MHz)
NMR spectra were recorded at room temperature on a
Bruker Avance DPX300 spectrometer equipped with a
5 mm QNP-Z probe (1H, 13C, 15N, 31P). Deuterochloro-
form was used as the solvent. Chemical shifts are given
relative to internal tetramethylsilane for 1H and 13C
spectra, and to external 85% phosphoric acid for 31P
spectra. Standard Bruker software and microprograms
were applied for all NMR experiments. The sweep
[Cp*Ir(L2)Cl][BPh4] (6). A chloroform–acetonitrile
solution (1:1 v/v, 5 ml) of NaBPh4 (0.078 g, 0.23 mmol)
was added to a mixture of chloroform (5 ml) and
acetonitrile (5 ml) containing L2 (0.055 g, 0.23 mmol)
and [Cp*IrCl2]2 (0.091 g, 0.114 mmol). The color
changed immediately from orange to yellow. The solu-
tion was stirred at room temperature for 1 h. The white
precipitate of NaCl was filtered off and the filtrate was
evaporated under reduced pressure. The yellow solid
residue was recrystallized from chloroform to afford
crystalline 6 0.177 g (0.20 mmol, 87%) (Anal. Found: C,
63.14; H, 5.93; N, 2.99. Calc. for C47H50ClN2OBIr: C,
62.91; H, 5.62; N, 3.12%).
1
width covered was 3000 Hz for H, digitalized in 16 K,
and 15,000 Hz for 13C, digitalized in 64 K.
Phase sensitive 2D ROESY spectra were recorded
with a spin-lock field of 2.5 kHz, a mixing time of 200
ms and 256 increments. The 2048×1024 final matrix
was apodized by a sine squared of factor 2 in both
dimensions prior to Fourier transformation.
cis-[Pt(L2)Cl2] (7). A warm aqueous methanolic solu-
tion (1:1 v/v, 10 ml) of L2 (0.095 g, 0.40 mmol) was
added to a mixture of warm methanol (5 ml) and water
(5 ml) containing K2[PtCl4] (0.164 g, 0.40 mmol). The
reaction mixture was stirred at ꢀ50°C for 0.5 h. After
evaporating of the methanol, the solution was cooled to
room temperature. The brown precipitate of 7 was
filtered, washed with cold aqueous methanol and re-
crystallized from dichloromethane to afford a yellow
solid. Yield: 0.127 g (0.25 mmol, 63%) (Anal. Found: C,
35.80; H, 3.33; N, 5.50. Calc. for C15H16Cl2N2OPt: C,
35.59; H, 3.19; N, 5.53%).
5. Crystal structure determination
For compounds 6 and 8 a four circle Siemens P3/PC
automated diffractometer with graphite monochroma-
tized Mo Ka radiation (u=0.7173 A) was employed.
,
Crystallographic data are presented in Table 4. The
structures for 6 and 8 were solved by direct methods
using the SHELXTL PLUS set of programs [18], and
refined by full-matrix least-squares methods. For both
structures all H atoms were placed in geometrically
calculated positions and included in the refinement
using the riding model with Uiso(H)=1.2Ueq(C) with
the exception of H atoms of methyl groups (Uiso(H)=
1.5Ueq(C)). For 6 the final wR(F2) was 0.176 (on F2 for
7978 reflections), with conventional R1=0.071 (on F
for 6980 reflections with I\2|(I)), for 503 parameters,
goodness of fit=1.045. For 8 the final wR(F2) was
0.108 (on F2 for 3563 reflections), with conventional
R1=0.042 (on F for 3144 reflections with I\2|(I)),
for 303 parameters, goodness of fit=1.017.
trans-[PdCl2(L3)PEt3] (8). trans-Bis(triethylphos-
phine)palladium(II) chloride (0.044 g, 0.80 mmol) in
dichloromethane (5 ml) was added to
a
dichloromethane solution (2 ml) of L3 (0.052 g, 0.40
mmol); the yellow mixture was stirred at room temper-
ature for 12 h. Addition of 15 ml hexane to the reaction
mixture produced the precipitation of 8, that was
filtered and dried in vacuo to afford a yellow solid
0.085 g (0.32 mmol, 88%) (Anal. Found: C, 46.65; H,
5.48; N, 4.35. Calc. for C25H35Cl2N2OFePPd: C, 46.10;
H, 5.59; N, 4.35%).
[Zn(L1)2Cl2] (4). ZnCl2 (0.034 g, 0.25 mmol) dis-
solved in a mixture of warm 2-propanol (5 ml) and
acetone (2 ml) was added to a warm 2-propanol solu-
tion (5 ml) of L1 (0.12 g, 0.50 mmol) The reaction
mixture was stirred at room temperature for 12 h.
Solvent evaporation under vacuum afforded a white
solid residue, that was recrystallized from chloroform
6. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 139277 (for complex 6) and
to yield 4 0.142 g (0.23 mmol, 92%) (Anal. Found: C,
.

A.B. Lysenko et al. / Polyhedron 20 (2001) 957–967
967
[5] C. Mukai, I.J. Kim, W.J. Cho, M. Kido, M. Hanaoka, J. Chem.
Soc., Perkin Trans. 1 (1993) 2495.
[6] C. Baldoli, P.D. Buttero, E. Licandro, S. Maiorana, A. Papagni,
A. Aibinati, Tetrahedron: Asymmetry 6 (1995) 1711.
[7] G. Roth, H. Fisher, J. Organomet. Chem. 507 (1996) 125.
CCDC No. 139278 (for complex 8). Copies of this
information may be obtained free of charge from The
Director, CCDC, 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).
[8] K.J. Lee, H.D. Kim, Bioorg. Med. Chem. Lett.
2431.
6 (1996)
[9] I.M. Mohammed, S.M.A. Hashmi, Sk.A. Ali, J. Anal. Sci.
Spectrosc. 42 (1997) 190.
[10] P. DeShong, C.M. Dicken, J.M. Leginus, R.R. Whittle, J. Am.
Chem. Soc. 106 (1984) 5598.
References
[1] (a) K.B.G. Torssell, Nitrile Oxides, Nitrones, and Nitronates in
Organic Synthesis Novel Strategies in Synthesis, VCH, New
York, 1988. (b) P. DeShong, W. Li, J.W. Kennington, J.L.
Ammon, H.L. Ammon, J. Org. Chem. 56 (1991) 1364. (c) R.J.
Ferrier, R.H. Furneaux, P. Prasit, P.C. Tyler, J. Chem. Soc.,
Perkin Trans. 1 (1983) 2495.
[11] R.D. Lampeka, A.B. Lysenko, Zh. Obshchei Khim. 70 (2000)
1900.
[12] A.B. Lysenko, O.V. Shishkin, R.D. Lampeka, Z. Naturforsch.,
Teil B 55 (2000) 373.
[13] R.D. Lampeka, PhD thesis, University of Kiev, 1996.
[14] H.-B. Burgi, J.D. Dunitz, Structure Correlations, vol. 2, VCH,
Weinheim, 1994.
[15] P. DeShong, C.M. Dicken, R.R. Staib, A.J. Freyer, S.M. Wein-
reb, J. Org. Chem. 47 (1982) 4397.
[16] D. Neuhaus, M. Williamson, The Nuclear Overhauser Effect in
Structural and Conformational Analysis, VCH, New York,
1989.
[17] (a) A.A. Bothner-By, R. L. Stephens, J. Lee, C.D. Warren, R.W.
Jeanloz, J. Am. Chem. Soc. 106 (1984) 811. (b) A. Bax, D.G.
Davis, J. Magn. Reson. 63 (1985) 207.
[18] G.M. Sheldrick, SHELXTL PLUS. PC Version. A system of com-
puter programs for the determination of crystal structure from
X-ray diffraction data. Rev. 5. 02.1994.
[2] (a) M. Frederickson, Tetrahedron 53 (1997) 403. (b) A. Abiko,
Rev. Heteroat. Chem. 17 (1997) 51.
[3] (a) W. Schwab, H. Anagnostopulos, E. Porsche-Wiebking, J.
Grome, Eur. Pat. Appl. EP 451, 790; C. A. 116 (1992) 9, N
P83658h. (b). D. Babin, M. Benoit, J. P. Demoute, PCT Int.
Appl. WO 93, 16, 054; Chem. Abstr. 120 (1994) 9, N P107405j.
[4] (a) M. Ito, Ch. Kibayashi, Tetrahedron 47 (1991) 9329. (b) M.
Maeda, F. Okazaki, M. Murayama, Y. Tachibana, Y. Aoyagi,
A. Ohta, Chem. Pharm. Bull. 45 (1997) 962. (c) P. Marino, S.
Franco, N. Garces, F.L. Merchan, T. Tejero, Chem. Commun.
(1998) 493. (d) E. Colacino, A. Converso, A. De Nino, A.
Leggio, A. Liguori, L. Maiulo, A. Napoli, A. Procopio, C.
Siciliano, G. Sindona, Nucleosides Nucleotides 18 (1990) 581.
.