Electrostatic forces that determine O,O-trans versus O,S-cis conformers in the aminated porphyrin complexes of Cd(N-NHCO-2-C4H3O-tpp)(OAc) and Cd(N-NHCO-2-C4H3S-tpp)(OAc)

Article abstract of DOI:10.1016/j.poly.2006.08.034

Two new diamagnetic, mononuclear and aminated porphyrin complexes of O,O-trans-Cd (3-trans) and O,S-cis-Cd (4-cis) have been synthesized and characterized by ¹H, ¹³C NMR spectroscopy. The crystal structures of (acetato)(N-2-furancarboxamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C₄H₃O-tpp)(OAc); 3-trans] and (acetato)(N-2-thiophenecarboxamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C₄H₃S-tpp)(OAc); 4-cis] were determined. The coordination sphere around Cd²⁺ is a distorted square-based pyramid in which the apical site is occupied by a bidentate chelating OAc^- group for 3-trans and 4-cis. The plane of three pyrrole nitrogen atoms [i.e., N(1), N(2), N(4) for 3-trans and N(1), N(2), N(3) for 4-cis] strongly bonded to Cd²⁺ is adopted as a reference plane 3N. The N(3) and N(4) pyrrole rings bearing the 2-furancarboxamido (Fr) and 2-thiophenecarboxamido groups in 3-trans and 4-cis, respectively, deviate mostly from the 3N plane, thus orienting separately with a dihedral angle of 33.4° and of 31.0°. In 3-trans, Cd²⁺ and N(5) are located on different sides at 1.06 and -1.49 A? from its 3N plane, while in 4-cis, Cd²⁺ and N(5) are also located on different sides at 1.04 and -1.53 A? from its 3N plane. An attractive electrostatic interaction between the Cd²⁺ and O(4)^- atoms in furan stabilizes the O,O-trans conformer of 3. A repulsive electrostatic interaction between Cd²⁺ and S(1)⁺ destabilizes the O,S-trans conformer of 4. Both of these repulsive and the mutually attractive interactions between S(1)⁺ and O(3)^- atoms favor the O,S-cis rotamer of 4 both in the vapor phase and in low polarity solvents. NOE difference spectroscopy, HMQC and HMBC were employed for the unambiguous assignment of the ¹H and ¹³C NMR resonances of 3-trans and 4-cis in CDCl₃ at 20 and -50 °C.

Full text of DOI:10.1016/j.poly.2006.08.034

Polyhedron 26 (2007) 589–599
www.elsevier.com/locate/poly
Electrostatic forces that determine O,O-trans versus
O,S-cis conformers in the aminated porphyrin complexes of
Cd(N-NHCO-2-C4H3O-tpp)(OAc) and
Cd(N-NHCO-2-C4H3S-tpp)(OAc)
a,
b
Jo-Yu Tung *, Jyh-Horung Chen
a
Department of Occupational Safety and Health, Chung Hwai College of Medical Technology, Tainan 713, Taiwan
b
Department of Chemistry, National Chung Hsing University, Taichung 40227, Taiwan
Received 8 June 2006; accepted 14 August 2006
Available online 19 September 2006
Abstract
Two new diamagnetic, mononuclear and aminated porphyrin complexes of O,O-trans-Cd (3-trans) and O,S-cis-Cd (4-cis) have been
1
synthesized and characterized by H, 13C NMR spectroscopy. The crystal structures of (acetato)(N-2-furancarboxamido-meso-tetra-
phenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C4H3O-tpp)(OAc); 3-trans] and (acetato)(N-2-thiophenecarboxamido-meso-tetra-
phenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C4H3S-tpp)(OAc); 4-cis] were determined. The coordination sphere around Cd2+
is a distorted square-based pyramid in which the apical site is occupied by a bidentate chelating OAcꢀ group for 3-trans and
4-cis. The plane of three pyrrole nitrogen atoms [i.e., N(1), N(2), N(4) for 3-trans and N(1), N(2), N(3) for 4-cis] strongly bonded
to Cd2+ is adopted as a reference plane 3N. The N(3) and N(4) pyrrole rings bearing the 2-furancarboxamido (Fr) and 2-thiophen-
ecarboxamido groups in 3-trans and 4-cis, respectively, deviate mostly from the 3N plane, thus orienting separately with a dihedral
angle of 33.4ꢀ and of 31.0ꢀ. In 3-trans, Cd2+ and N(5) are located on different sides at 1.06 and ꢀ1.49 A from its 3N plane, while in
˚
4-cis, Cd2+ and N(5) are also located on different sides at 1.04 and ꢀ1.53 A from its 3N plane. An attractive electrostatic interaction
˚
between the Cd2+ and O(4)ꢀ atoms in furan stabilizes the O,O-trans conformer of 3. A repulsive electrostatic interaction between
Cd2+ and S(1)+ destabilizes the O,S-trans conformer of 4. Both of these repulsive and the mutually attractive interactions between
S(1)+ and O(3)ꢀ atoms favor the O,S-cis rotamer of 4 both in the vapor phase and in low polarity solvents. NOE difference spectros-
1
copy, HMQC and HMBC were employed for the unambiguous assignment of the H and 13C NMR resonances of 3-trans and 4-cis in
CDCl3 at 20 and ꢀ50 ꢀC.
ꢁ 2006 Published by Elsevier Ltd.
Keywords: Cadmium; X-ray diffraction; Electrostatic interaction; O,O-trans; O,S-cis conformer
1. Introduction
mers of 2-acyl-furans and -thiophenes (i.e., R = H, CH3,
Et, Pri, pentan-3-yl, But, Cl, F, ButO) [1–6]
There have been numerous investigations on the rota-
tional equilibrium between the two anti and syn planar iso-
δ−
R
O
δ−
δ−
O
1
1
O
6
5
5
ð1Þ
2
7
δ−
O
2
R
4
3
4
*
3
Corresponding author. Tel.: +886
6 2674567x815; fax: +886 6
anti
syn
2894028.
(O,O-cis)
(O,O-trans)
E-mail address: joyuting@mail.hwai.edu.tw (J.-Y. Tung).
0277-5387/$ - see front matter ꢁ 2006 Published by Elsevier Ltd.
doi:10.1016/j.poly.2006.08.034

590
J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
δ−
describe the X-ray structural investigation on the metalla-
R
O
7
δ+
δ+
tion of 1 and 2 leading to mononuclear complexes of
(acetato)(N-2-furancarboxamido-meso-tetraphenylporphy-
rinato)cadmium(II) [Cd(N-NHCO-2-C4H3O-tpp)(OAc); 3]
and (acetato)(N-2-thiophenecarboxamido-meso-tetraphe-
1
1
S
S
6
5
4
5
ð2Þ
2
O
δ−
2
R
3
4
3
anti
syn
nylporphyrinato)cadmium(II)
[Cd(N-NHCO-2-C4H3S-
(O,S-cis)
tpp)(OAc); 4], respectively. This metallation introduces
the metal electrostatic interaction between the Cd(II)
atom and the heteroatom of the ring in 3 and 4 as the
diamagnetic Cd(II) is just located in the vicinity of the
furonylcarboxamido (or thiophenecarboxamido) group
in 3 (or 4). We try to figure out how the metal electro-
static effect influences the O,O-Cd and O,S-Cd conform-
ers of 3 and 4, respectively. These metal electrostatic
effects could be applied to explain the various conforma-
tions of thallium(III), bismuth(III) and tin(IV) porphyrin
complexes with O,O and O,S rotamers.
(O,S-trans)
Group charge density calculations reveal that both oxy-
gen atoms in 2-acyl-furans of the syn form, being strongly
charged, face increasing repulsive electrostatic interactions
(see Eq. (1)). However, in the thiophene carbonyl deriva-
tives, the S atom is positively charged and consequently
there is an attractive electrostatic interaction between the
S and O atoms in cis form (see Eq. (2)) [1]. The major fac-
tor determining the stability or instability of the cis-isomer
is a repulsive electrostatic interaction between the two oxy-
gen atoms for furan carbonyl and an attractive electrostatic
interaction between the sulfur and oxygen atoms for the
thiophene carbonyl. The O,O-trans form has a relatively
low dipole moment and is favored in the gas phase or in
low polar solvents with dielectric constants (e) smaller than
5. In a more polar medium, the O,O-cis isomer with a
higher dipole moment (l) is favored due to a stronger sol-
ute–solvent interaction; as a result the O,O-cis form in
2-acyl-furans can be more stable than the O,O-trans isomer
in solution when the energy difference DE (=Esyn ꢀ Eanti) is
relatively small and Dl (=lsyn ꢀ lanti) is large in the gas
phase. In the case of the thiophene-2-carbonyl derivative,
the more polar O,S-cis conformation is found to be more
stable in the vapor phase; the cis form also predominates
in solutions of different polarity; the amount of O,S-cis iso-
mer increases slightly with solvent polarity. The energy dif-
ferences (DE) between the rotamers are 4–13 kJ/mol, but
the barrier to rotation is ca. 42 kJ/mol [1].
The preparation of N-substituted-N-aminoporphyrin
has been described by three groups [7–11]. In N-substi-
tuted-N-aminoporphyrin, when the H atom of NH2 is
replaced either by the 2-furoncarboxyamino ligand or
by the 2-thiophenecarboxyamino group, two new free
aminated porphyrins are formed, namely N-2-furancarb-
oxamido-meso-tetraphenylporphyrin (N-NHCO-2-C4H3-
OHtpp; 1) and N-2-thiophenecarboxamido-meso-tetra-
phenylporphyrin (N-NHCO-2-C4H3S-Htpp; 2) [tpp =
dianion of meso-tetraphenylporphyrin], which are deriva-
tives of 2-acyl-furans and -thiophenes, respectively. A
thorough review of the literature shows that there is no
prior report on the metal complexes of 1 and 2. The lack
of previous work on metal complexes of these two ligands
prompted us to undertake the synthesis and structural
studies of the Cd(II) complexes. Metallation of these ami-
nated porphyrins could lead to mononuclear metal com-
plexes in which the metal is coordinated to four
porphyrinic N atoms. Cd(II) is a diamagnetic ion and
maintains the d10 electron configuration which minimizes
intrinsic coordination geometry preferences while favor-
ing coordination by softer ligands. In this paper, we
2. Experimental
2.1. N-NHCO-2-C4H3O-Htpp (1) [9]
A mixture of NaN3 (1.00 g, 1.54 · 10ꢀ2 mol) in distilled
water (2 cm3) and 2-furoyl chloride (2.5 mL, 2.54 ·
10ꢀ2 mol) was stirred for 30 min. After concentration, the
residue was dissolved in CH2Cl2 and filtered to remove
excess NaN3 and NaCl. The CH2Cl2 layer contained
2-furancarbonyl azide (C4H3OCON3). A solution of
Zn(tpp) (0.30 g, 1.36 · 10ꢀ3 mol) and the above
C4H3OCON3 in CH2Cl2 (100 cm3) in a stoppered 250 mL
Erlenmeyer flask was left for ca. 24 h in the sunlight. To
this solution was then added 0.5 N HCl (250 cm3) with vig-
orous shaking for 0.5 h. The organic layer, green in color,
was separated, solid ammonium carbonate was added to it,
and then dried with anhydrous Na2SO4. The excess
(NH4)2CO3 and Na2SO4 were removed by filtration. After
concentration, the residue was dissolved in a minimum of
CH2Cl2 and chromatographed on silica gel (50.00 g, 70–
230 mesh). The dimensions of the silica gel column were
1.5 · 17 in. The desired compound was eluted with ethyl
acetate (EtOAc)–CH2Cl2 [1:9 (v/v)] as a dark purple band
on silica gel. Removal of the solvent and recrystallization
from CH2Cl2–MeOH [1:2 (v/v)] gave the purple solid N-
NHCO-2-C4H3O-Htpp (1) (0.165 g, 2.28 · 10ꢀ4 mol,
46.8%), which was again dissolved in CH2Cl2 and layered
with CH3OH to get purple crystals for single crystal X-
ray analysis. 1H NMR (599.95 MHz, CDCl3, 20 ꢀC): d
3
9.12 [d, Hb(10,19), J(H–H) = 4.4 Hz], Hb(a,b) represents
two equivalent b-pyrrole protons attached to carbons a
3
and b, respectively; 8.90 [d, Hb(9,20), J(H–H) = 4.8 Hz];
8.88 [s, Hb(4,5)]; 8.35 [bs, o0-H(34,44) and o0-H(38,40)],
where o-H = ortho protons; 8.28 [d, o-H(26,28), 3J(H–
H) = 6.6 Hz]; 8.19 [d, o-H(22,32), 3J(H–H) = 6.6 Hz];
8.09 [s, Hb(14,15)]; 7.78–7.82 (m) for meta and para
protons; 5.79 [s, Fr-H5]; 4.69 [q, Fr-H4, 3J(Fr-H4, Fr-
3
H5) = 1.8 Hz and J(Fr-H4, Fr-H3) = 3.6 Hz]; 1.35 [s, Fr-
H3], where Fr = 2-furancarboxamido. MS (FAB): M+

J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
591
724 (calcd for C49H33N5O2: 724). UV/Vis spectrum, k (nm)
[e · 10ꢀ3 (Mꢀ1 cmꢀ1)] in CH2Cl2: 429 (246.6), 541 (10.2),
582 (10.2), 638 (7.8).
with toluene to afford blue crystals for single-crystal X-ray
1
analysis. H NMR (599.95 MHz, CDCl3, 20 ꢀC): d 8.89 [s,
3
Hb(2,3)]; 8.76 [d, Hb(14,35), J(H–H) = 4.5 Hz]; 8.73 [d,
Hb(13,36), 3J(H–H) = 4.5 Hz]; 8.61 [s, Hb(24,25)]; 8.62
[d, o-H(22,29), 3J(H–H) = 6.6 Hz]; 8.40 [d, o-H(18,33),
3J(H–H) = 6.6 Hz]; 7.75–7.86 (m, meta and para protons);
5.72 (s, Fr-H5); 5.20 (s, Fr-H4); 4.37 (s, Fr-H3); 0.17 (s,
2.2. Preparation of N-NHCO-2-C4H3S-Htpp (2) [9]
A mixture of NaN3 (1.00 g, 1.54 · 10ꢀ2 mol) in distilled
water (2 cm3) and 2-thiophenecarbonylchloride (2.5 mL)
was stirred for 20 min. After concentration, the residue
was dissolved in CH2Cl2 and filtered to remove excess
NaN3 and NaCl. The CH2Cl2 layer contains 2-thiophene-
carbonyl azide (C4H3SCON3). A solution of Zn(tpp)
(0.27 g, 3.04 · 10ꢀ4 mol) and the above C4H3SCON3 in
CH2Cl2 (200 cm3) in a stoppered 250 mL Erlenmeyer flask
was left for ca. 8 h in the sunlight. To this solution was then
added 0.5 N HCl (250 cm3) with vigorous shaking for
0.5 h. The organic layer was separated, solid ammonium
carbonate added to it, and then dried with anhydrous
Na2SO4. The excess (NH4)2CO3 and Na2SO4 were removed
by filtration. After concentration, the residue was dissolved
in a minimum of CH2Cl2 and chromatographed on silica
gel (100.00 g, 70–230 mesh). The dimensions of the silica
gel column were 1.5 · 17 in. The desired compound was
eluted with ethyl acetate (EtOAc)–CH2Cl2 [1:4 (v/v)] as a
dark brown band on silica gel. Removal of the solvent
and recrystallization from CH2Cl2–MeOH [1:2 (v/v)] gave
the purple solid of N-NHCO-2-C4H3S-Htpp (2) (0.17 g,
2.06 · 10ꢀ4 mol, 68%) which was again dissolved in
CH2Cl2 and layered with CH3CN to get purple crystals
1
OAc-Me), ꢀ0.99 (s, NH). H NMR (599.95 Hz, CDCl3,
ꢀ50 ꢀC): d 8.96 [s, Hb(2,3)]; 8.76 [d, Hb(14,35), 3J(H–
3
H) = 4.2 Hz]; 8.73 [d, Hb(13,36), J(H–H) = 7.8 Hz]; 8.70
[s, Hb(24,25)]; 8.64 [d, o-H(22,29), 3J(H–H) = 7.8 Hz];
3
8.48 [d, o-H(18,33), J(H–H) = 7.2 Hz]; 8.42 [d, o0-
3
H(11,40), J(H–H) = 4.8 Hz]; 8.20 [d, o0-H(7,44), 3J(H–
H) = 7.2 Hz]; 7.75–7.91 (m, meta and para protons); 5.74
3
(s, Fr-H5); 5.24 [d, Fr-H4, J(H–H) = 1.8 Hz]; 4.52 (s, Fr-
H3); 0.18 (s, OAc-Me); ꢀ1.12 (s, NH). 13C NMR
(150.87 MHz, 20 ꢀC, CDCl3): d 154.0 [s, Ca(1,4)]; 153.9
[s, Ca(15,34)]; 152.2 [s, Ca(12,37)]; 150.2 [s, Ca(23,26)];
134.11 [s, Cb(2,3)]; 134.06 [s, Cb(13,36)]; 131.5 [s,
Cb(14,35)]; 123.9 [s, Cb(24,25)]; 121.9 [s, Cm(16,17)];
152.2 [s, Fr–CO]; 141.8 [s, Fr–C2]; 108.7 [s, Fr–C3]; 110.2
[s, Fr–C4]; 143.5 [s, Fr–C5]; 176.3 [s, OAc-CO]; 18.9 [s,
OAc-Me]. MS (FAB): (MꢀOAc)+ 834 (calcd for
C49H31CdN5O2: 834). UV/Vis spectrum, k (nm) [e · 10ꢀ3
(Mꢀ1 cmꢀ1)] in CH2Cl2: 442.0 (233.1), 619.1 (17).
2.4. Preparation of Cd(N-NHCO-2-C4H3S-tpp)(OAc) (4)
Compound 4 was prepared in the same way as described
for 3 in a 52% yield using N-NHCO-2-C4H3S-Htpp (2).
Compound 4 was dissolved in CH2Cl2 and layered with tol-
uene to obtain blue crystals for single-crystal X-ray analy-
sis. 1H NMR (599.95 MHz, CDCl3, 20 ꢀC):d 8.89 [s,
Hb(4,5)]; 8.76 [d, Hb(10,19), 3J(H–H) = 4.2 Hz]; 8.72
1
for single crystal X-ray analysis. H NMR (599.95 MHz,
3
CDCl3, 20 ꢀC): d 9.10 [d, Hb(10,19), J(H–H) = 4.2 Hz];
8.87 [d, Hb(9,20), 3J(H–H) = 4.2 Hz]; 8.85 [s, Hb(4,5)];
8.36 [bs, o0-H(34,44) and o0-H(38,40)], where o-H = ortho
3
protons; 8.25 [d, o-H(22,32), J(H–H) = 7.2 Hz]; 8.16 [d,
3
3
o-H(26,28), J(H–H) = 7.2 Hz]; 8.06 [s, Hb(14,15)]; 7.75–
[d, Hb(9,20), J(H–H) = 4.2 Hz]; 8.63 [s, Hb(14,15)]; 8.60
3
7.80 (m) for meta and para protons; 5.85 [dd, S-H5, J(S-
[d, o-H(38,40), 3J(H–H) = 7.2 Hz]; 8.40 [d, o-H(34,44),
3J(H–H) = 6.6 Hz]; 7.74–7.86 (m, meta and para protons);
6.34 [d, S-H5, 3J(H–H) = 4.8 Hz]; 5.57 [t, S-H4, 3J(H–
H) = 4.2 Hz]; 2.99 [d, S-H3, 3J(H–H) = 3 Hz]; 0.15 (s,
H4, S-H5) = 5.0 Hz and 4J(S-H3, S-H5) = 1.2 Hz], where
S = 2-thiophenecarboxamido; 5.43 [dd, S-H4, 3J(S-H3,
3
S-H4) = 3.8 Hz and J(S-H4, S-H5) = 5.0 Hz]; 3.47 [dd, S-
H3, 3J(S-H3, S-H4) = 3.8 Hz and 4J(S-H3, S-H5) =
1.2 Hz]; ꢀ0.35 (s, NH). MS (FAB): M+ 740 (calcd for
C49H33N5OS: 740). UV/Vis spectrum, k (nm) [e · 10ꢀ3
(Mꢀ1 cmꢀ1)] in CH2Cl2: 430 (278), 541 (21.8), 583 (21.7),
639 (19.4).
OAc-Me), ꢀ1.23 (s, NH). H NMR (599.95 MHz, CDCl3,
1
ꢀ50 ꢀC): d 8.95 [s, Hb(4,5)]; 8.75 [d, Hb(10,19), 3J(H–
3
H) = 3.6 Hz]; 8.71 [s, Hb(14,15)]; 8.70 [d, Hb(9,20), J(H–
3
H) = 3.6 Hz]; 8.61 [d, o-H(38,40), J(H–H) = 7.0 Hz]; 8.47
3
[d, o-H(34,44), J(H–H) = 7.0 Hz]; 8.42 [s, o0-H(22,32)];
8.18 [d, o0-H(26,28), 3J(H–H) = 7.2 Hz]; 7.76–7.90 (m, meta
and para protons); 6.42 [d, S-H5, 3J(H–H) = 4.8 Hz];
5.56 [t, S-H4, 3J(H–H) = 4.2 Hz]; 2.69 [d, S-H3, 3J(H–
H) = 3 Hz]; 0.17 (s, OAc-Me), ꢀ1.42 (s, NH). 13C NMR
(150.87 MHz, 20 ꢀC, CDCl3): d 154.0 [s, Ca(3,6)]; 149.8 [s,
Ca(13,16)]; 152.2 (s) and 153.9 (s) for Ca(1,8) and
Ca(11,18); 134.2 [s, Cb(4,5)]; 134.1 [s, Cb(9,20)]; 131.7 [s,
Cb(10,19)]; 124.0 [s, Cb(14,15)]; 121.9 [s, Cm]; 155.5 [s,
S-CO]; 131.4 [s, S-C2]; 126.5 [s, S-C3]; 126.0 [s, S-C4];
130.1 [s, S-C5]; 176.6 [s, OAc-CO]; 18.9 [s, OAc-Me]. MS
(FAB): (MꢀOAc)+ 851 (calcd for C49H32CdN5OS: 851).
UV/Vis spectrum, k (nm) [e · 10ꢀ3 (Mꢀ1 cmꢀ1)] in CH2Cl2:
432.9 (235.9), 543.0 (9.79), 584.0 (11.6), 639.0 (14.3).
2.3. Preparation of Cd(N-NHCO-2-C4H3O-tpp)(OAc) (3)
A mixture of N-NHCO-2-C4H3O-Htpp (1) (76 mg,
0.1 mmol) in CH2Cl2 (5 cm3) and Cd(OAc)2 Æ 2H2O
(69 mg, 0.3 mmol) in MeOH (2 cm3) were refluxed in
CH3CN (20 cm3) for 3 h. After concentration, the residue
was dissolved in CH2Cl2 and washed with distilled water
to remove excess Cd(OAc)2 Æ 2H2O. The CH2Cl2 layer
was concentrated to dryness affording a blue precipitate,
which was recrystallized from toluene–hexane [1:3 (v/v)]
yielding a dark blue solid of 3 (51 mg, 0.0548 mmol,
55%). Compound 3 was redissolved in CH2Cl2 and layered

592
J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
Table 2
2.5. NMR spectroscopy
˚
Selected bond distances (A) and angles (ꢀ) for compound 3 Æ C6H5CH3
(trans) and 4 Æ CH2Cl2 (cis)
Proton and 13C NMR spectra were recorded at 599.95
and 150.87 MHz, respectively, on Varian Unity Inova-
600 spectrometers locked on deuterated solvent, and refer-
enced to the solvent peak. Proton NMR is relative to
CD2Cl2 or CDCl3 at d = 5.30 or 7.24 and 13C NMR to
the center line of CD2Cl2 or CDCl3 at d = 53.6 or 77.0.
The temperature of the spectrometer probe was calibrated
3 Æ C6H5CH3 (trans)
˚
Bond lengths (A)
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)ꢂ ꢂ ꢂN(3)
Cd(1)–N(4)
O(3)ꢂ ꢂ ꢂO(4)
Bond angles (ꢀ)
O(1)–Cd(1)–O(2)
O(1)–Cd(1)–N(1)
O(1)–Cd(1)–N(2)
O(1)–Cd(1)–N(4)
N(1)–Cd(1)–N(2)
N(1)–Cd(1)–N(4)
2.247(4)
2.296(4)
2.606(4)
2.318(4)
3.554(4)
Cd(1)–O(1)
Cd(1)–O(2)
Cd(1)ꢂ ꢂ ꢂO(4)
Cd(1)ꢂ ꢂ ꢂO(3)
O(4)ꢂ ꢂ ꢂH(5A)
2.302(4)
2.325(4)
5.098(4)
5.144(4)
2.369(4)
1
by the shift difference of the methanol resonance in the H
56.00(15)
100.06(15)
117.85(13)
116.25(13)
80.90(13)
80.17(13)
O(2)–Cd(1)–N(1)
O(2)–Cd(1)–N(2)
O(2)–Cd(1)–N(4)
N(2)–Cd(1)–N(4)
O(4)ꢂ ꢂ ꢂH(5A)–N(5)
156.06(16)
109.36(15)
108.66(15)
124.85(14)
104.35
NMR spectrum. HMQC (heteronuclear multiple quantum
coherence) was used to correlate protons and carbon
through one-bond coupling and HMBC (heteronuclear
multiple bond coherence) for two- and three-bond pro-
ton–carbon coupling. Nuclear Overhauser effect (NOE)
difference spectroscopy was employed to determine the
1H–1H proximity through space over a distance of up to
4 Æ CH2Cl2 (cis)
˚
Bond lengths (A)
˚
about 4 A.
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–N(3)
Cd(1)ꢂ ꢂ ꢂN(4)
O(3)ꢂ ꢂ ꢂS(1)
Bond angles (ꢀ)
O(1)–Cd(1)–O(2)
O(1)–Cd(1)–N(1)
O(1)–Cd(1)–N(2)
O(1)–Cd(1)–N(3)
N(1)–Cd(1)–N(2)
N(1)–Cd(1)–N(3)
2.277(3)
2.278(3)
2.303(3)
2.617(3)
2.991(3)
Cd(1)–O(1)
Cd(1)–O(2)
Cd(1)ꢂ ꢂ ꢂO(3)
Cd(1)ꢂ ꢂ ꢂS(1)
2.289(3)
2.291(3)
5.113(3)
6.798(3)
The positive-ion fast atom bombardment mass spectrum
(FAB-MS) was obtained in a nitrobenzyl alcohol (NBA)
matrix using a JEOL JMS-SX/SX 102A mass spectrome-
ter. UV/Vis spectra were recorded at 20 ꢀC on a HITACHI
U-3210 spectrophotometer.
56.91(11)
111.57(11)
152.02(11)
109.56(11)
80.54(11)
O(2)–Cd(1)–N(1)
O(2)–Cd(1)–N(2)
O(2)–Cd(1)–N(3)
N(1)–Cd(1)–N(3)
118.18(11)
95.12(11)
113.63(11)
74.49(10)
2.6. X-ray crystallography
Table 1 presents the crystal data for 3 Æ C6H5CH3 (trans)
and 4 Æ CH2Cl2 (cis). Measurements were taken on a
Bruker AXS SMART-1000 diffractometer using mono-
125.59(10)
˚
chromatized Mo Ka radiation (k = 0.71073 A). Empirical
absorption corrections were made for 3-trans and 4-cis.
The structures were solved by direct methods (SHELXTL-
97) [12] and refined by the full-matrix least-squares
method. The furan group within 3-trans is disordered with
an occupancy factor of 0.6 for O(4)C(51) and 0.4 for
O(40)C(510). These two atoms [i.e., O(4),C(51)] were refined
with isotropic displacement parameters for 3-trans. All
non-hydrogen atoms except the above two atoms for 3-
trans were refined with anisotropic thermal parameters,
whereas all hydrogen atoms were placed in calculated posi-
tions and refined with a riding model. Table 2 lists selected
bond distances and angles for both 3 Æ C6H5CH3 (trans)
and 4 Æ CH2Cl2 (cis).
Table 1
Crystal structure data for 3 Æ C6H5CH3 (trans) and 4 Æ CH2Cl2 (cis)
Empirical formula
C
58H43CdN5O4
C52H37CdCl2N5O3S
(4 Æ CH2Cl2 (cis))
995.23
(3 Æ C6H5CH3 (trans))
986.37
C2/c
monoclinic
26.0431(16)
11.1727(7)
31.847(2)
90
91.995(2)
90
9260.9(10)
8
Formula weight
Space group
ꢀ
P1
Crystal system
triclinic
8.6025(5)
10.2440(6)
24.8640(13)
90.616(1)
95.679(1)
97.452(1)
2161.3(2)
2
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
3
˚
V (A )
Z
F(000)
3984
1.403
0.527
1.004
1012
1.529
0.730
1.045
3. Results and discussion
Dcalc (g cmꢀ3
)
l(Mo Ka) (mmꢀ1
S
)
3.1. Molecular structures of 3 Æ C6H5CH3 and 4 Æ CH2Cl2
Crystal size (mm)
h (ꢀ)
T (K)
Number of reflections
measured
0.31 · 0.10 · 0.02
28.35
273(2)
0.30 · 0.10 · 0.10
28.31
100(2)
Using a d10 metal, namely cadmium(II), the new com-
plexes 3 Æ C6H5CH3 and 4 Æ CH2Cl2 were synthesized. The
synthetic strategy is outlined in Scheme 1. During the met-
allation of free bases 1 and 2 with Cd(OAc)2 (Scheme 1),
the soft acid Cd2+ prefers to retain one OAcꢀ ligand and
coordinate to the N–H proton [i.e., H(2A)] of 1 and 2 to
form six-coordinate complexes 3 and 4. The molecular
frameworks are depicted in Fig. 1a for 3 and in Fig. 1b
for 4.
11512
10677
Number of reflections
observed
5680
8390 [I > 2r(I)]
a
R1
wR2
0.0614
0.1634
0.0551
0.1321
b
P
P
a
R1 = [ iFoi ꢀ jFci/ jFoj].
P
P
2
2
1=2
b
wR2 ¼ f ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁg
.

J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
593
Ph
Ph
X
N
N
N
Cd(OAc)2
N
HN
N
Ph
Ph
Cd
Ph
Ph
NHY
Ph
CH2Cl2/MeOH/MeCN
N
N
NHY
Ph
X = OAc
(1)
Cd(N-NHCO-2-C4H3O-tpp)(OAc) (3-trans)
O,O-trans-Cd
O
(55 %)
Y =
O
Ph
Ph
X
N
N
N
N
HN
N
Cd(OAc)2
Ph
Ph
Ph
Ph
Cd
NHZ
CH2Cl2/MeOH/MeCN
N
N
NHZ
Ph
Ph
(2)
S
X = OAc
Cd(N-NHCO-2-C4H3S-tpp)(OAc) (4-cis)
O
O,S-cis-Cd
Z =
(52 %)
Scheme 1.
˚
The bond distance (A) of Cd(1)–O(1) is 2.302(4), Cd(1)–
amido-meso-tpp (3) and N-2-thiophenecarboxyamido-
meso-tpp (4) structures are quite similar to metal(II) N-
substituted porphyrin complexes with three strong and
one weaker metal–N bond [11,15]. Compound 3 is an
O,O-trans conformer in the solid phase with a dihedral
angle of W [O(3)–C(47)–C(48)–O(4)] = ꢀ174.17ꢀ and thus
we are able to assign it as 3-trans. Compound 4 is an O,S-
cis conformation (i.e., 4-cis) in the solid phase with W
[O(3)–C(47)–C(48)–S(1)] = 1.59ꢀ. The geometry around
Cd2+ is described as a distorted square-based pyramid in
which the apical site is occupied by a bidentate chelating
OAcꢀ group in 3-trans and 4-cis. Fig. 2 shows the actual
porphyrin skeleton of 3-trans and 4-cis.
˚
O(2) = 2.325(4), and the mean Cd(1)–N(p) = 2.287(4) A for
3; for 4, the values are Cd(1)–O(1) = 2.289(3), Cd(1)–
O(2) = 2.291(3) and the mean Cd(1)–N(p) = 2.286(3) A
(Table 2). The cadmium–nitrogen bond distances [Cd(1)–
N(1) = 2.247(3), Cd(1)–N(2) = 2.296(4) and Cd(1)–N(4) =
2.318(4) A of 3; Cd(1)–N(1) = 2.277(3), Cd(1)–N(2) =
2.278(3) and Cd(1)–N(3) = 2.303(3) A of 4] are comparable
to those of Cd(1)–N(p) = 2.301(5) A in Cd(N–NHCO-
˚
˚
˚
˚
C6H5-tpp)(OAc) [11]. The Cd(1)ꢂ ꢂ ꢂN(3) distance of
˚
2.606(4) A for 3 [or Cd(1)ꢂ ꢂ ꢂN(4) distance of 2.617(3) for
˚
4] is longer than 2.301(5) A but is significantly shorter than
˚
the sum of the van der Waals radii of Cd and N (3.15 A)
[13]. This longer Cdꢂ ꢂ ꢂN(3) contact in 3 [or Cdꢂ ꢂ ꢂN(4) in
4] may be viewed as a secondary intramolecular interaction.
This kind of secondary interaction was earlier observed for
both Cd(N-NHCOC6H5-tpp)(OAc) with Cd(1)ꢂ ꢂ ꢂN(4) =
We adopt the plane of three strongly bound pyrrole
nitrogen atoms [i.e., N(1), N(2) and N(4) for 3-trans
and N(1), N(2) and N(3) for 4-cis] as a reference plane,
3N. In 3-trans (or 4-cis), Cd2+ and N(5) are located on
˚
˚
2.612(5) A [11] and [Cd(H3daps)Cl4]CH3CN Æ 0.25H2O
different sides at 1.06 (or 1.04) and ꢀ1.49 A (or
˚
[H4dap = 2,6-bis(1-salicyloylhydrazonoethyl)pyridine] with
ꢀ1.53 A) from its 3N plane, respectively (Fig. 2). The
˚
Cdꢂ ꢂ ꢂN(6) = 2.74(1) A [14]. Most chemists seem to consider
N(3) and N(4) pyrrole rings bearing the 2-furancarboxam-
ido (Fr) and 2-thiophenecarboxamido groups in 3-trans
and 4-cis, respectively, deviate mostly from the 3N plane,
thus orienting separately with a dihedral angle of 33.4ꢀ
and of 31.0ꢀ, whereas small angles of 0.7ꢀ, 18.5ꢀ and
23.7ꢀ occur with N(1), N(4) and N(2) pyrrole for 3-trans
this secondary interaction between the metal ion and the
fourth N as a weak bond in N-substituted porphyrin metal
complexes. Furthermore, N(1), N(2) and N(4) [or N(1),
N(2) and N(3)] are bonded strongly as well as covalently
to the Cd atom in 3 [or 4]. Thus the Cd(II)–2-furancarboxy-

594
J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
-0.70
a
-0.66
C(36)
C(35)
-0.25
-0.21
0
N(4)
0
-0.07
O(2)
2.88
0.23
0.00
C(25)
0.98
C(2)
-0.01
O(1)
3.24
N(3)
-0.20
N(1)
0
Cd(1)
1.06
C(24)
0.95
N(5)
-1.49
C(3)
-0.02
0.20
-0.03
-0.07
N(2)
0
-0.19
-0.32
-0.28
C(14)
-0.88
C(13)
-0.85
Cd(N-NHCO-2-C4H3O-tspp)(OAc) (3-trans)
-0.91
-0.80
C(20)
b
C(19)
-0.38
-0.22
0
N(1)
-0.26
0.05
O(1)
2.92
0.04
0.25
O(2)
3.16
C(15)
0.75
C(4)
0.69
N(4)
-0.31
N(2)
0
Fig. 1. Molecular configuration and atom-labelling scheme for (a)
3 Æ C6H5CH3 (trans) and (b) 4 Æ CH2Cl2 (cis), with ellipsoids drawn at
30% probability. Hydrogen atoms, solvent C6H5CH3 for 3 Æ C6H5CH3
(trans) and CH2Cl2 for 4 Æ CH2Cl2 (cis) are omitted for clarity.
Cd(1)
1.04
C(14)
0.79
N(5)
-1.53
C(5)
0.67
0.10
0.24
-0.07
N(3)
0
0.08
and the corresponding angles are 18.2ꢀ, 23.5ꢀ and 17.6ꢀ
with N(2), N(1) and N(3) pyrrole for 4-cis. In 4-cis, such
a large deviation from planarity for the N(4) pyrrole is
also reflected by observing a 7.7–10.2 ppm upfield shift
of the Cb(C14, C15) at 124.0 ppm compared to
131.7 ppm for Cb(C10, C19), 134.1 ppm for Cb(C9, C20)
and 134.2 ppm for Cb(C4, C5). In 3-trans, a similar devi-
ation is also found for N(3) pyrrole by observing a 7.6–
10.2 ppm upfield shift of Cb(C24, C25) at 123.9 ppm com-
pared to 134.11 ppm for Cb(C2, C3), 134.06 ppm for
Cb(C13, C36) and 131.5 ppm for Cb(C14, C35).
-0.26
-0.16
C(10)
-0.68
C(9)
-0.61
Cd(N-NHCO-2-C4H3S-tpp)(OAc) (4-cis)
Fig. 2. Diagram of the porphyrinato core (C20N4, Cd, furan, thiophene
and OAc) of (a) 3-trans and (b) 4-cis. The values represent the
displacement (in A) of the atoms from the 3N plane [i.e., N(1), N(2),
˚
N(4) for 3-trans and N(1)–N(3) for 4-cis].
It is noted that the ionic radius for the metal ion
2+
˚
increases from 0.82 A for Zn with a coordination num-
3-trans and the corresponding angles are 44.7ꢀ, 42.9ꢀ,
34.3ꢀ and 35.7ꢀ for 4-cis.
2+
˚
ber (CN = 5) to 1.09 A for Cd (CN = 6). Because of
the larger size of Cd2+, Cd(1), O(2) and O(1) lie 1.06,
3.2. 1H and 13C NMR spectroscopy data of 3-trans and 4-cis
in CDCl3
˚
2.88 and 3.24 A, respectively, above the 3N plane in 3-
trans, compared to 1.04 A for Cd(1), 2.92 A for O(1) and
˚
˚
2+
˚
˚
3.16 A for O(2) in 4-cis [cf. 0.65 A for Zn in Zn(N-Me-
tpp)Cl] (Fig. 2) [16].
The dihedral angles between the mean plane of the skel-
eton (3N) and the planes of the phenyl groups are 57.6ꢀ
[C(9)], 32.1ꢀ [C(20)], 32ꢀ [C(31)] and 56.4ꢀ [C(42)] for
The singlet at ꢀ0.35 ppm was assigned to NH protons
[i.e., H(2A) and H(5A)] for 2 at 20 ꢀC. Moreover, the signal
arising from the NH protons [i.e., H(2A) and H(5A)] of 1
was not observed at 20 ꢀC. At ꢀ90 ꢀC, traces of water were

J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
595
frozen from solution of 1 in CD2Cl2. Thus, the frozen water
inhibits intermolecular proton exchange between water and
NH protons of 1 and allows the observation of a broad sin-
glet for the NH proton at ꢀ0.61 ppm (Dm1/2 = 23 Hz).
Upon metallation, there were no signal of NH (in pyrrole)
[i.e., H(1A) for 3 and H(2A) for 4] for metal porphyrins 3
4-cis (Fig. 1). There are four b-pyrrole protons Hb, four
b-pyrrole carbons Cb, four a-pyrrole carbons Ca, two dif-
ferent meso carbons Cmeso and two phenyl-C1 carbons for
these two complexes. In 4-cis, the doublet at 8.76 ppm is
assigned to Hb(10,19) with 3J(H–H) = 4.2 Hz, and the
3
other doublet at 8.72 ppm with J(H–H) = 4.2 Hz is due
1
and 4. The H NMR spectrum of 3 (or 4) in CDCl3 (Figs.
to Hb(9,20) (Fig. 3a). The singlet at 8.89 ppm is assigned
to Hb(4,5) and the other singlet at 8.63 ppm is due to
Hb(14,15) (Fig. 3a). In 3-trans, the doublet at 8.76 ppm is
due to Hb(14,35) with 3J(H–H) = 4.5 Hz and the other
3 and 4) showed a sharp singlet at d = ꢀ0.99 (or ꢀ1.23)
ppm (Dm1/2 = 4 Hz) for the NH proton at 20 ꢀC. These
NMR data for 3 (or 4) suggest that the NH proton [i.e.,
H(5A)] bound to N(5) undergoes rapid intermolecular pro-
ton exchange with water at 20 ꢀC.
3
doublet at 8.73 ppm is due to Hb(13,36) with J(H–H) =
4.5 Hz (Fig. 4a). The singlet at 8.89 ppm is assigned to
Hb(2,3) and the other singlet at 8.61 ppm is due to
Hb(24,25) (Fig. 4a).
1
Complexes 3-trans and 4-cis were characterized by H
(Figs. 3 and 4) and 13C NMR spectra. In solution, the mol-
ecule has effective Cs symmetry with a mirror plane running
through the N(5)–N(3)–Cd(1)–N(1)–O(1)–O(2) unit for
3-trans or the N(5)–N(4)–Cd(1)–N(2)–O(1)–O(2) unit for
1
Fig. 3 depicts the representative H spectra for 4-cis in
CDCl3 at 20 and ꢀ50 ꢀC. At 20 ꢀC, the rotation of the phe-
nyl group along C1–Cmeso [C(17)–C(39) or C(12)–C(33)]
Fig. 3. 1H NMR spectra for 4-cis at 599.95 MHz in CDCl3: (a) 20 ꢀC, (b) ꢀ50 ꢀC, where S = 2-thiophenecarboxamido.

596
J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
Fig. 4. 1H NMR spectra for 3-trans at 599.95 MHz in CDCl3: (a) 20 ꢀC, (b) ꢀ50 ꢀC, where Fr = 2-furancarboxamido.
3
bond is slow. This slow rotation is supported by the two
singlets at 8.60 and 8.40 ppm due to o-H(38,40) and o-
H(34,44), respectively (Fig. 3a). Moreover, the rotation of
the phenyl group along C(7)–C(27) [or C(2)–C(21)] bond
for 4-cis is at the intermediate exchange region. In this inter-
mediate exchange region, the signals are broadened beyond
detection. Hence, no signals of o0-H(22,32) and o0-H(26,28)
for 4-cis have been observed at 20 ꢀC (Fig. 3a). At ꢀ50 ꢀC,
this rotation is extremely slow. Hence, the rate of intramo-
lecular exchange of the ortho protons for 4-cis in CDCl3 is
also extremely slow. The doublet at 8.61 ppm is assigned
to ortho protons o-H(38,40) with 3J(H–H) = 7.0 Hz
(Fig. 3b). The other doublet at 8.47 ppm is due to ortho
protons o-H(34,44) with J(H–H) = 7.0 Hz. Likewise, the
singlet at 8.42 ppm is due to ortho proton o-H(22,32). The
corresponding doublet at 8.18 ppm is due to o-H(26,28)
with 3J(H–H) = 7.2 Hz (Fig. 3b). The interpretation of
these data were confirmed by the NOE difference spectros-
copy for 4-cis in CDCl3 at 20 and ꢀ50 ꢀC.
In a similar fashion, the rotation for the phenyl group of
3-trans in CDCl3 at 20 ꢀC along C(27)–C(28) [or C(16)–
C(17)] bond is slow and the rotation along C(38)–C(39)
[or C(5)–C(6)] is at the intermediate exchange region.
1
Hence, the H resonances for the ortho protons of 3-trans
were observed as two sets of doublets: one doublet at
8.62 ppm is assigned to ortho protons o-H(22,29) with

Table 3
Group net charges (q) for 3 and 4 by NBO calculationsa
H5
H4
O
4
5
H3
5
1
1
6
S
H4
H5
3
2
4
H3
2
3
O
O
7
7
6
1
1
H1
N
N
H1
2
2
3
3
N
N
N
N
4
N
4
N
5
5
N
N
Cd
Cd
4
3
4
3
O
O
O
O
Me
3-trans
Me
4-cis
Compound
Conformer
Metal
O1
S1
C2
C3
C4
C5
C6
O7
N1
N2
N3
N4
N5
O3
O4
O,O-Cd
O,S-Cd
a
3-trans
4-cis
1.674
1.676
ꢀ0.473
0.227
ꢀ0.310
ꢀ0.201
ꢀ0.168
ꢀ0.269
ꢀ0.202
0.188
ꢀ0.355
0.635
0.661
ꢀ0.626
ꢀ0.634
ꢀ0.399
ꢀ0.415
ꢀ0.324
ꢀ0.317
ꢀ0.739
ꢀ0.733
ꢀ0.721
ꢀ0.719
ꢀ0.727
ꢀ0.747
ꢀ0.832
ꢀ0.834
ꢀ0.799
ꢀ0.803
0.490
Group net charges including the attached hydrogen by NBO* calculations.
*E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1 in GAUSSIAN-03.

598
J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
3J(H–H) = 6.6 Hz and the other doublet at 8.40 ppm is due
to ortho protons o-H(18,33) with 3J(H–H) = 6.6 Hz
(Fig. 4a). Moreover, no signals of o0-H(11,40) and o0-
H(7,44) of 3-trans have been detected at 20 ꢀC (Fig. 4a).
However, for ortho protons, at ꢀ50 ꢀC, the rotation of phe-
nyl group along the C1–Cmeso bond in 3-trans is extremely
slow, which is evident from the appearance of the four
doublets at 8.64 [o-H(22,29)], 8.48 [o-H(18,33)], 8.42
[o0-H(11,40)], and 8.20 [o0-H(7,44)] ppm due to four differ-
ent ortho protons of the aromatic ring (Fig. 4b).
for the CO group to be characteristic of either uni- or
bidentate acetates are definitely out of the range of the
shielding effect of a porphyrin.
NBO group net charges over O(4), O(3) and Cd(1) in 3
(O,O-trans-Cd; 3-trans) are ꢀ0.473, ꢀ0.626 and 1.674,
respectively (Table 3). In 3-trans, a weakly repulsive elec-
trostatic interaction between the two oxygen atoms [i,e.,
O(3)ꢀ and O(4)ꢀ] and a strongly attractive electrostatic
force between the cadmium [Cd(1)2+] and oxygen atom
[O(4)ꢀ] are two major factors explaining the trans con-
former of 3 which dominates both in the solid phase and
in low polar solvents at low temperature. Group charges
for S(1), O(3) and Cd(1) in 4 (O,S-cis-Cd; 4-cis) are
0.490, ꢀ0.634 and 1.676, respectively (Table 3). In 4-cis,
a moderately electrostatic attraction between the sulfur
[S(1)+] and oxygen atom [O(3)ꢀ] and weakly repulsive elec-
trostatic force between the cadmium [Cd(1)2+] and sulfur
[S(1)+] are two major factors determining that the cis con-
former of 4 is favored both in the solid and in low polarity
solvents at low temperature.
1
Due to the ring current effect, upfield shifts for the H
resonances of S-H5, S-H4 and S-H3 for 4 with the O,S-cis
conformer in CDCl3 at ꢀ50 ꢀC are Dd = ꢀ1.21 [from
7.63 (obtained from 2-acetylthiophene) to 6.42 ppm],
ꢀ2.13 (from 7.69 to 5.56 ppm) and ꢀ4.44 ppm (from 7.13
to 2.69 ppm), respectively (Fig. 3b). Qualitatively, as the
distance between the geometrical center (Ct) of the 4N
plane and axial protons gets smaller, the shielding effect
becomes larger. In 4-cis, the distance for Ctꢂ ꢂ ꢂS-H3,
Ctꢂ ꢂ ꢂS-H4 and Ctꢂ ꢂ ꢂS-H5 increases from 3.235, 5.738 to
˚
7.066 A, individually. As the S-H3 proton of 4-cis is closer
to Ct, the shielding gets larger for this S-H3. A similar ring
current effect is also observed for 3-trans. The occurrence
of weak intramolecular hydrogen bonding between one
amino hydrogen [H(5A)] and the furan oxygen [O(4)] in
O,O-trans of 3 is reflected in the long N(5)–H(5A)ꢂ ꢂ ꢂO(4)
4. Conclusion
We have investigated two new, diamagnetic and mono-
nuclear cadmium(II) N-substituted-N-aminoporphyrin
complexes 3-trans and 4-cis which exist in O,O-trans and
O,S-cis conformers, respectively, and their X-ray structures
have been established. We also demonstrate how the elec-
trostatic repulsive and attractive forces influence the favor-
able conformers in the case of 3-trans and 4-cis. Both the
electrostatic attraction between Cd2+ and O(4)ꢀ and the
N–Hꢂ ꢂ ꢂO (furan) H-bond interaction stabilized the O,O-
trans form of 3-trans in CDCl3 at ꢀ50 ꢀC. Both the electro-
static repulsion between Cd2+ and S(1)+ and the attractive
interaction between S(1)+ and O(3)ꢀ stabilize the O,S-cis
conformer of 4.
˚
(furan) bond distance of 2.358 A and acute N(5)–
H(5A)ꢂ ꢂ ꢂO(4) (furan) angle of 104.35ꢀ (Fig. 1a) [6]. The
hydrogen bonding results in
a downfield shift of
0.24 ppm for the NH proton which resonances from
ꢀ1.23 ppm for 4-cis (O,S-cis-Cd) to ꢀ0.99 ppm for 3-trans
(O,O-trans-Cd) in CDCl3 at 20 ꢀC (Figs. 3 and 4). This
intramolecular H-bonding and electrostatic attraction
between Cd(1)2+ and O(4)ꢀ restricts the rotation of the
furan group along the C(48)–C(47) bond. Thus, as the tem-
perature is increased from ꢀ50 ꢀC to 20 ꢀC for 3-trans in
CDCl3, Fr-H3 rotates a degree slightly closer to Ct and a
minimum upfield shift of ꢀ0.15 ppm was observed for
the 1H resonances of Fr-H3 from 4.52 to 4.37 ppm (Fig. 4).
X-ray diffraction analysis unambiguously confirms that
3-trans and 4-cis have a chelating bidentate OAcꢀ ligand
in the solid phase. Notably, the ring current effects seldom
Acknowledgment
Financial support from the National Science Councils of
the ROC under Grant NSC 94-2113-M-005-010 is grate-
fully acknowledged.
1
exceed 10 ppm in H NMR [17] and 2 ppm in 13C NMR
[18]. Hence, the ring current contribution is relatively less
important in determining the 13C chemical shifts than
proton shifts. The 13C NMR chemical shifts were shown
to be a useful tool for diagnosing the nature of acetate
ligands, whether unidentate or bidentate in diamagnetic
complexes. Unidentate acetate ligands were located at
20.5 0.2 and 168.2 1.7 ppm and bidentate acetate
ligands at 18.0 0.7 and 175.2 1.6 ppm [17]. The
methyl and carbonyl chemical shifts of the acetate group
in 3-trans (or 4-cis) at 20 ꢀC in CDCl3 are separately
located at 18.9 (or 18.9) and 176.3 (or 176.6) ppm con-
firming that the acetate is chelating bidentately and is
coordinated to the cadmium atom in 3-trans (or 4-cis)
in the solution phase. The difference in chemical shifts
Appendix A. Supplementary material
Fig. S1 shows the molecular structure for O,O-cis of 1
at 100(2) K. Fig. S2 shows the molecular structures for
O,S-cis and O,S-trans of 2 at 100(2) K. CCDC 289590
and 289591 contains the supplementary crystallographic
data for 3 and 4. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.poly.
2006.08.034.

J.-Y. Tung, J.-H. Chen / Polyhedron 26 (2007) 589–599
599
[11] F.A. Yang, J.H. Chen, H.Y. Hsieh, S. Elango, L.P. Hwang, Inorg.
Chem. 42 (2003) 4603.
References
[12] G.M. Sheldrick, SHELXL-97: Program for the Refinement of Crystal
Structures from Diffraction Data, University of Go¨ttingen, Go¨ttin-
gen, Germany, 1997.
[1] I.S. Han, C.K. Kim, H.J. Jung, I. Lee, Theor. Chim. Acta 93 (1996) 199.
[2] R. Benassi, U. Folli, L. Schenetti, F. Taddei, J. Chem. Soc., Perkin
Trans. II (1987) 961.
[13] R.D. Shannon, Acta Crystallogr., Sect. A 32 (1976) 751.
[14] M. Fundo, A. Sousa, M.R. Bermejo, A. Gaorcia-Deibe, A. Sousa-
Pedrares, O.L. Hoyos, M. Helliawall, Eur. J. Inorg. Chem. (2002)
703.
[15] M. Ravikanth, T.K. Chandrashekar, Struct. Bond. 82 (1995) 105.
[16] D.K. Lavellee, A.B. Kopelove, O.P. Anderson, J. Am. Chem. Soc.
100 (1978) 3025.
[17] S.J. Lin, T.N. Hong, J.Y. Tung, J.H. Chen, Inorg. Chem. 36 (1997)
3886.
[18] E. Breitmaier, W. Voelter, Carbon-13 NMR Spectroscopy, 3rd ed.,
VCH, New York, 1990, pp. 110, 116, 117.
[3] S.R. Salman, Org. Magn. Reson. 20 (1982) 151.
[4] L. Lunazzi, G. Placucci, C. Chatgilialoglu, D. Macciantelli, J. Chem.
Soc., Perkin Trans. II (1984) 819.
[5] D. Casarini, L. Lunazzi, D. Macciantelli, J. Chem. Soc., Perkin
Trans. II (1985) 1839.
[6] R. Crespo-Otero, L.A. Montero, G. Rosquete, J.A. Padron-Garcia,
R.H. Gonzalez-Jonte, J. Comput. Chem. 25 (2004) 429.
[7] H.J. Callot, Tetrahedron 35 (1979) 1455.
[8] H.J. Callot, J. Fischer, R. Weiss, J. Am. Chem. Soc. 104 (1982) 1272.
[9] H.J. Callot, B. Chevrier, R. Weiss, J. Am. Chem. Soc. 100 (1978) 4733.
[10] K. Ichimura, Bull. Chem. Soc. Jpn. 51 (1978) 1444.