A 13C and 1H NMR spectroscopic investigation of the structure of the iminium ion with a dipolar form in metal complexes of 2-N-substituted N-confused porphyrins

Article abstract of DOI:10.1039/c2dt31426f

The crystal structures of chloro(2-aza-2-ethoxycarbonylmethyl-5,10,15,20- tetraphenyl-21-carbaporphyrinato-N,N′N′′) zinc(ii) [Zn(2-NCH₂COOC₂H₅NCTPP)Cl; 4], (2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N, N′N′′) palladium(ii) [Pd(2-NCH₂COOC ₂H₅NCTPP); 5], bromo(2-aza-2-ethoxycarbonylmethyl-5,10,15, 20-tetraphenyl-21-carbaporphyrinato-N,N′N′′) manganese(iii) [Mn(2-NCH₂COOC₂H₅NCTPP)Br; 6], [2-aza-(3′-phenoxypropyl)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N, N′N′′] nickel(ii) [Ni(2-NCH₂CH₂CH ₂OC₆H₅NCTPP); 7] and chloro(2-aza-2- methoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N, N′N′′) zinc(ii) [Zn(2-NCH₂COOCH₃NCTPP) Cl; 8] have been established. The g value of 9.54, which was measured from the parallel polarization of the X-band EPR spectra in CHCl₃ at 4 K, is consistent with the high spin mononuclear manganese(iii) centre (S = 2) in 6. The magnitude of the axial (D) zero-field splitting (ZFS) for the mononuclear Mn(iii) centre in 6 was determined approximately to be 1.63 cm^-1 by paramagnetic susceptibility measurements. The NMR spectroscopic investigation of the iminium ion with a dipolar canonical contribution to the metal complexes 5-7, Pd(2-NCH₂C₆H₅NCTPP) (10) and Ni(2-NCH ₂C₆H₅NCTPP) (11) in CDCl₃ is reported. A resonance between the dipolar canonical form II and covalent canonical form I exists for complexes 5-7, 10 and 11 in CDCl₃. To develop the correlations between δ¹³C [C(3)], δ¹H [H(3)] and the canonical form II in 5-7, 10 and 11, this work thoroughly examines the ¹³C and ¹H NMR of N ⁺CH(Ar) fragment on seven metal complexes of 2-N substituted N-confused porphyrin. According to these results, the ¹³C [C(3)] and ¹H [H(3)] chemical shifts of the N⁺CH(Ar) fragment at 20 °C in CDCl₃ are separately located at 152.6 ± 0.5 and 8.30 ± 0.15 ppm respectively for the iminium ion. This exists as a dipolar canonical form II for complexes 5-7, 10 and 11, and the N-CH(Ar) group appears at 121.1 ± 0.1 ppm and 6.35 ± 0.01 ppm, which is in a covalent canonical form I contribution to complexes 4 and 8. X-Ray diffraction data indicate that N(2)-C(3) = 1.315 ± 0.011 A for the dipolar contribution of 5-7, 10-13, while N(2)-C(3) = 1.331 ± 0.008 A for the covalent contribution of 4 and 8.

Full text of DOI:10.1039/c2dt31426f

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PAPER
A 13C and 1H NMR spectroscopic investigation of the structure of the
iminium ion with a dipolar form in metal complexes of 2-N-substituted
N-confused porphyrins†
Wen-Pin Chang,a Wen-Chain Lin,a Jyh-Horung Chen,*a Shin-Shin Wangb and Jo-Yu Tungc
Received 2nd July 2012, Accepted 5th September 2012
DOI: 10.1039/c2dt31426f
The crystal structures of chloro(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-
carbaporphyrinato-N,N′N′′) zinc(II) [Zn(2-NCH2COOC2H5NCTPP)Cl; 4], (2-aza-2-
ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′) palladium(II)
[Pd(2-NCH2COOC2H5NCTPP); 5], bromo(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-
21-carbaporphyrinato-N,N′N′′) manganese(III) [Mn(2-NCH2COOC2H5NCTPP)Br; 6], [2-aza-
(3′-phenoxypropyl)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′] nickel(II) [Ni(2-
NCH2CH2CH2OC6H5NCTPP); 7] and chloro(2-aza-2-methoxycarbonylmethyl-5,10,15,20-tetraphenyl-
21-carbaporphyrinato-N,N′N′′) zinc(II) [Zn(2-NCH2COOCH3NCTPP)Cl; 8] have been established. The g
value of 9.54, which was measured from the parallel polarization of the X-band EPR spectra in CHCl3 at
4 K, is consistent with the high spin mononuclear manganese(III) centre (S = 2) in 6. The magnitude of
the axial (D) zero-field splitting (ZFS) for the mononuclear Mn(III) centre in 6 was determined
approximately to be 1.63 cm−1 by paramagnetic susceptibility measurements. The NMR spectroscopic
investigation of the iminium ion with a dipolar canonical contribution to the metal complexes 5–7, Pd
(2-NCH2C6H5NCTPP) (10) and Ni(2-NCH2C6H5NCTPP) (11) in CDCl3 is reported. A resonance
between the dipolar canonical form II and covalent canonical form I exists for complexes 5–7, 10 and 11
in CDCl3. To develop the correlations between δ13C [C(3)], δ1H [H(3)] and the canonical form II in 5–7,
10 and 11, this work thoroughly examines the 13C and 1H NMR of N+vCH(Ar) fragment on seven metal
complexes of 2-N substituted N-confused porphyrin. According to these results, the 13C [C(3)] and
1H [H(3)] chemical shifts of the N+vCH(Ar) fragment at 20 °C in CDCl3 are separately located at 152.6
0.5 and 8.30 0.15 ppm respectively for the iminium ion. This exists as a dipolar canonical form II for
complexes 5–7, 10 and 11, and the N–CH(Ar) group appears at 121.1 0.1 ppm and 6.35 0.01 ppm,
which is in a covalent canonical form I contribution to complexes 4 and 8. X-Ray diffraction data indicate
that N(2)–C(3) = 1.315 0.011 Å for the dipolar contribution of 5–7, 10–13, while N(2)–C(3) = 1.331
0.008 Å for the covalent contribution of 4 and 8.
Introduction
An N-confused porphyrin NCP is a porphyrin isomer with an
aDepartment of Chemistry, National Chung Hsing University,
inverted pyrrole ring. There are three main reaction sites in the
Taichung 40227, Taiwan. E-mail: JyhHChen@dragon.nchu.edu.tw;
confused pyrrole ring, i.e., 2-N, 21-C and 3-C (Scheme 1).1
Fax: +886 422862547; Tel: +886 422840412x612
Substitution of the position 3-C is catalyzed by acids.1,2 At
the external nitrogen of NCP (2-N), an electrophilic reaction can
take place resulting in the formation of alkylation products.
Ziegler and co-workers reported the synthesis of the 2-aza-2-
ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrin
2-NCH2COOEtNCTPPH (1).3 When the ethoxycarbonylmethyl
group of 1 is modified to a bulky 3′-phenoxypropyl group, the
bMaterial Chemical Laboratories ITRI, Hsin-Chu 300, Taiwan.
E-mail: ShinShinWang@ITRI.org.tw; Tel: +886 35732550
cDepartment of Occupational Safety and Health, Chung Hwai
University of Medical Technology, Taiwan.
E-mail: joyuting@mail.hwai.edu.tw; Fax: +886 62894028;
Tel: +886 62674567x815
†Electronic supplementary information (ESI) available: Fig. S1 showing
the atom number scheme for 2, 7. Fig. S2 (or Fig. S3) showing the atom
numbering scheme for 4, 8 (or 5, 6), respectively. Fig. S4 (or Fig. S5)
showing the 1H NMR spectra for 8 (or 7) in CDCl3 at 20 °C. Fig. S6
showing the UV/visible spectrum for 7 in CH2Cl2 at 20 °C. Fig. S7 (or
Fig. S8) showing the UV/visible spectra for 4, 8 (or 5, 6), respectively,
in CH2Cl2 at 20 °C. CCDC 889011–889015. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI:
10.1039/c2dt31426f
free
base
2-aza-(3′-phenoxypropyl)-5,10,15,20-tetraphenyl
N-confused porphyrin, 2-NCH2CH2CH2OC6H5NCTPPH (2), is
derived.4 In this study, we focus on the alkyl group of
2-NCH2COOEtNCTPPH (1) and 2-NCH2CH2CH2OC6H5-
NCTPPH (2).4 Unlike the NH tautomerism that exists in
13454 | Dalton Trans., 2012, 41, 13454–13464
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In this paper, we describe the X-ray structural investigation of
the metallation of 1 (or 2), leading to the zinc(II) complex chloro-
(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-car-
baporphyrinato-N,N′N′′) zinc(II) [Zn(2-NCH2COOC2H5NCTPP)-
Cl; 4], the palladium(II) complex (2-aza-2-ethoxycarbonyl-
methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′)
palladium(II) [Pd(2-NCH2COOC2H5NCTPP); 5] and the manga-
nese(III)
complex
bromo(2-aza-2-ethoxycarbonylmethyl-
manga-
5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′)
nese(III) [Mn(2-NCH2COOC2H5NCTPP)Br; 6] [or the nickel
complex 2-aza-(3′-phenoxypropyl)-5,10,15,20-tetraphenyl-21-
carbaporphyrinato-N,N′N′′) nickel(II)] [Ni(2-NCH2CH2CH2-
OC6H5NCTPP); 7] (Scheme 1).
Klein and co-workers5 reported the detection of EPR data in
S = 2 states of trivalent manganese complexes at an effective g
value of 8.7–10. The X-band perpendicular-mode EPR spectra
of manganese(III) porphyrins were detected at g ≈ 8–9 in frozen
solutions at 77 K by Talsi and Bryliakov.6 Hence, the spectrum
of the Mn(III) porphyrinoids for 6 is observable in the X-band
(only ∼9.4 GHz). The new diamagnetic compound 4 is used as a
diamagnetic correction for the paramagnetic complex 6 in the
solid-state magnetic susceptibility measurements.7 In this paper,
we also focus on the details of the electronic structure of the
manganese(III) centre of 6. Studies on the temperature depen-
dence of the magnetic susceptibility and on the effective
moment show that S = 2 is the ground state for the high-spin
mononuclear Mn3+ centre in 6 at 20 °C. Application of the
Van Vleck’s equation permits evaluation of D and an average g
value for powder samples of 6.8
The peripheral α-carbon [C(3)] is easily oxidized, and the
CvN bond [C(3), N(2)] in nickel(II) N-confused porphyrins
serves as a dienophile for the Diels–Alder reaction.9 Notably, the
high selectivity of the peripheral carbon–nitrogen bond over the
carbon–carbon bonds in metal N-confused porphyrin complexes
can be rationalized by the resonance contributions to the overall
structures of 5–7. Chart 1 shows two resonance contributors for
the two different coordination modes [the formal charge shown
for N and C(21) only].9
The dipolar canonical form II of the CvN in Chart 1(a) is
both ‘cross conjugated’ and in an iminium form which is known
to be electron deficient.10–12 NMR spectroscopy has emerged as
a powerful technique for the investigation of the dipolar reson-
ance contributors for species in Chart 1(a).13 Two groups have
shown the NMR spectroscopic studies of iminium ions derived
from secondary amines.14,15 The differentiation of the chemical
shifts has been already noticed for two major tautomers of
N-confused porphyrin.11,12 Moreover, the discrimination of the
chemical shifts data for the resonance of the dipolar and covalent
canonical forms are lacking for metal complexes of N-confused
Scheme 1 Synthesis of 4, 5, 6 and 7.‡
NCTPPH2, the free base 1 (or 2) has only one stable form. The
N-confused porphyrin 1 (or 2) can provide N3 or N3C coordi-
nated sites. Hitherto, free base 1 has been shown to coordinate
with metals in the core thereby forming a metal complex posses-
sing a carbon–metal bond for Co(II) (I = 7/2) in Co-
(2-NCH2COOEtNCTPP)py (3) [or Co(NCTPP-AcOEt)py, Co-
(NCTPP-CH2COOEt)py].3 In order to investigate the range of
metal ions that can be inserted into 1, we have extended our
studies on the insertion of zinc, palladium and manganese into 1.
1
porphyrin. Hence, we reported the H and 13C NMR spectro-
scopic evidence for the dipolar canonical form of iminium ions
in metal complexes of N-confused porphyrin 5–7 [Chart 1(a)].
The spectroscopic observations are compared with the results of
X-ray diffraction analysis. In addition, we compared this work
with the results of our recent report on the crystal structures of
Pd(2-NCH2C6H5NCTPP) (10) and Ni(2-NCH2C6H5NCTPP)
(11)16 and with the structures of Ni[2-N(CH2)8I NCTPP] (12)9
and Ni(2-NCH2CH2BrNCTPP) (13).17 For the first time, we
combine the data from the δ13C chemical shifts of C(3) and δ1H
‡The numbering scheme on the far left of Scheme 1 is used for the
nomenclature of the compounds and this numbering scheme is consist-
ent with the report in the literature. Moreover, the NMR data assignment
uses the X-ray atom labelling scheme.
This journal is © The Royal Society of Chemistry 2012
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CH2Cl2 (16 ml) and filtered. The filtrate was concentrated and
the residue was purified over a silica gel column (230–400 mesh,
50 g) using CH2Cl2–EtOAc [10 : 1 (v/v)] as the eluent to yield a
green solution of 4. Removal of the solvent gave 4 as a green
solid (0.021 g, 0.026 mmol, 61.2%). Compound 4 was dissolved
in CH2Cl2 and layered with EtOAc to afford blue crystals for
single-crystal X-ray analysis. 1H NMR (599.95 MHz, CDCl3,
3
20 °C): δ 8.30 [d, Hβ(13), J(H–H) = 4.5 Hz]; 8.18 [d, Hβ(2),
3
3J(H–H) = 5.1 Hz]; 8.13 [d, o-H(34, 38), J(H–H) = 6.6 Hz];
3
3
8.06 [d, o-H(40, 44), J(H–H) = 7.8 Hz]; 7.76 [d, Hβ(3), J(H–
H) = 5.1 Hz]; 7.75 [d, Hβ(12), 3J(H–H) = 4.5 Hz]; 7.68 [d,
Hβ(8), J(H–H) = 5.7 Hz]; 7.62 [d, Hβ(7), J(H–H) = 5.7 Hz];
7.56–7.57 [m, m-H & p-H]; 6.34 [s, Hα(19)]; 4.51 [d, H(45A) of
3
3
2
EtOAc group, J(H–H) = 18.0 Hz]; 4.03 [m, H(47) of EtOAc,
3J(H–H) = 7.2 Hz]; 4.00 [d, H(45B) of EtOAc group, 2J(H–H) =
3
18.0 Hz]; 1.17 [t, H(48) of EtOAc group, J(H–H) = 7.2 Hz];
−0.31 [s, H(17)]. MS(ESI), m/z (assignment, rel. intensity):
800.66 ([M]+, 67.44%). Anal. Calcd for C48H35ClN4ZnO2: C,
72.00; H, 4.41; N, 7.00. Found: C, 72.39; H, 4.48; N, 6.96.
UV-Vis spectrum, λ (nm) [ε × 10−3 (M−1 cm−1)] in CH2Cl2:
444 (53.3), 468 (107.2), 579 (9.1), 627 (12.7), 718 (8.7), 785
(28.2) (Fig. S7 in ESI†).
Pd(2-NCH2COOC2H5NCTPP) (5) [or 5 (Pd–Et)]
A mixture of 1 (0.03 g, 0.043 mmol) and PdCl2 (0.03 g,
0.141 mmol) was refluxed in CH3CN (16 ml) for 12 h.3 After
concentrating the reaction mixture, the residue was dissolved in
CH2Cl2 (16 ml) and filtered. The filtrate was concentrated and
the residue was purified over a silica gel column (230–400 mesh,
50 g) using CH2Cl2 as the eluent to yield a dark red solution of
5. Removal of the solvent gave 5 as a dark red solid (0.014 g,
0.017 mmol, 40.3%). Compound 5 was dissolved in CH2Cl2 and
layered with EtOAc to afford blue-black crystals for single-
Chart 1 Two resonance contributors for (a) C–M coordination mode
and (b) coordination mode of the metal N-confused porphyrin.
1
crystal X-ray analysis. H NMR (599.95 MHz, CDCl3, 20 °C):
3
δ 8.15 [s, Hα(19)]; 7.97 [d, Hβ(2), J(H–H) = 4.8 Hz]; 7.88 [d,
o-H(40, 44), 3J(H–H) = 7.8 Hz]; 7.85 [d, Hβ(13), 3J(H–H) =
6.6 Hz]; 7.81 [d, Hβ(8), 3J(H–H) = 4.8 Hz]; 7.80 [d, Hβ(3),
chemical shifts of H(3) in Scheme 1 with the X-ray diffraction
data of the N(2)–C(3) bond length in metal N-confused com-
plexes giving clear information about which one is the major
canonical form responsible for the resonance between the
dipolar canonical form II and the covalent canonical form I in
these complexes. The data will show the importance of the cano-
nical form II to the so-called resonance hybrid structure in
Chart 1(a).
3
3J(H–H) = 4.8 Hz]; 7.77 [d, Hβ(7), J(H–H) = 4.8 Hz]; 7.74 [d,
o-H(34), 3J(H–H) = 6.6 Hz]; 7.72 [d, Hβ(12), 3J(H–H) = 6.6 Hz];
7.61 [t, p-H(36), 3J(H–H) = 7.8 Hz]; 7.54–7.58 [m, m-H &
3
p-H]; 7.53 [t, m-H(35,37), J(H–H) = 7.8 Hz]; 4.56 [s, H(45) of
3
EtOAc group]; 4.05 [quintet, H(47) of EtOAc group, J(H–H) =
7.2 Hz]; 1.16 [t, H(48) of EtOAc group, 3J(H–H) = 7.2 Hz]. MS
(ESI), m/z (assignment, rel. intensity): 804.3 ([M]+, 100%).
Anal. Calcd for C48H34N4O2Pd: C, 71.60; H, 4.26; N, 6.96.
Found: C, 71.98; H, 4.18; N 7.16. UV-Vis spectrum, λ (nm)
[ε × 10−3 (M−1 cm−1)] in CH2Cl2: 449 (121.5), 534 (11.5),
576 (9.0), 700 (10.7), 766 (12.6) (Fig. S8 in ESI†).
Experimental
Preparation of 2-NCH2CH2CH2OC6H5NCTPPH (2)
The preparation of 2 is shown in the literature (Fig. S1a in
ESI†).4
Mn(2-NCH2COOC2H5NCTPP)Br (6) [or 6(Mn–Et)]
A mixture of 1 (0.03 g, 0.043 mmol) and MnBr2 (0.03 g,
0.141 mmol) was refluxed in CH3CN (16 ml) for 12 h.3 After
concentrating the reaction mixture, the residue was dissolved in
CH2Cl2 (16 ml) and filtered. The filtrate was concentrated and
the residue was purified over a silica gel column (230–400 mesh,
50 g) using CH2Cl2–EtOAc [10 : 1 (v/v)] as the eluent to yield a
Zn(2-NCH2COOC2H5NCTPP)Cl (4) [or 4 (Zn–Et)]
A mixture of 1 (0.03 g, 0.043 mmol) and ZnCl2 (0.03 g,
0.220 mmol) was refluxed in CH3CN (16 ml) for 12 h.3 After
concentrating the reaction mixture, the residue was dissolved in
13456 | Dalton Trans., 2012, 41, 13454–13464
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dark red solution of 6. Removal of the solvent gave 6 as a dark
red solid (0.018 g, 0.022 mmol, 50.3%). Compound 6 was dis-
solved in CH2Cl2 and layered with EtOAc to afford black crys-
tals for single-crystal X-ray analysis. MS(ESI), m/z (assignment,
rel. intensity): 835.2 ([M − 81Br + H]+, 30.38%); 833.2
([M − 79Br + H]+, 30.53%). Anal. Calcd for C48H34N4O2-
MnBr·CH3COOCH2CH3: C, 67.76; H, 4.59; N, 6.08. Found: C,
67.96; H, 4.51; N, 6.30. UV-Vis spectrum, λ (nm) [ε × 10−3
(M−1 cm−1)] in CH2Cl2: 457 (21.2), 474 (18.4), 508 (96.2),
582 (0.2), 753 (1.6) (Fig. S8 in ESI†).
Scheme 2 Alcoholysis of 4.
Ni(2-NCH2CH2CH2OC6H5NCTPP) (7)
3.56 [s, H(47) of MeOAc group]; −0.30 [s, H(17)]. MS (ESI),
m/z (assignment, rel. intensity): 786.634 ([M]+, 41.94%). Anal.
Calcd for C48H35ClN4ZnO2·CH3OH: C, 70.42; H, 4.56; N, 6.84.
Found: C, 70.45; H, 4.28; N, 6.85. UV-Vis spectrum, λ (nm)
[ε × 10−3 (M−1 cm−1)] in CH2Cl2: 444 (73.3), 466 (157.8), 674
(3.3), 719 (12), 787 (42.4) (Fig. S7 in ESI†).
A mixture of 2 (0.039 g, 0.04 mmol) and Ni(OAc)2 (0.05 g,
0.20 mmol) were refluxed in CH3CN (10 ml) and CH2Cl2
(10 ml) for 12 h.3,4 After concentrating the reaction mixture, the
residue was dissolved in 10 ml of CH2Cl2 and filtered. The
filtrate was concentrated and the residue was purified over a
silica gel column (230–400 mesh, 50 g) using CH2Cl2 as the
eluent to yield a dark green solution of 7. Removal of the
solvent gave 7 as a purple solid (0.021 g, 0.026 mmol, 65%).
Compound 7 was dissolved in CH2Cl2 and layered with EtOAc
to afford purple crystals for single-crystal X-ray analysis.
1H NMR (599.95 MHz, CDCl3, 20 °C): δ 8.37 [s, Hα(19)]; 7.99
[d, Hβ(2), 3J(H–H) = 4.8 Hz]; 7.93 [d, Hβ(7), 3J(H–H) =
Magnetic susceptibility measurements
The solid-state magnetic susceptibility was measured under
helium on a Quantum Design MPMS5 SQUID susceptometer
from 2 to 300 K at a field of 5 kG. The sample was held in a
Kel-F bucket. The bucket had been calibrated independently at
the same field and temperature. The raw data for 6 were cor-
rected for the molecular diamagnetism. The diamagnetic contri-
bution of the sample was measured from an analogous
diamagnetic metal complex 4. Details of the diamagnetic correc-
tions that were made can be found in ref. 7.
3
5.1 Hz]; 7.89 [d, Hβ(8), J(H–H) = 5.1 Hz]; 7.84 [d, o-H (34,
38), 3J(H–H) = 8.4 Hz]; 7.83 [d, o-H (22, 26), 3J(H–H) = 4.8 Hz];
7.80 [d, o-H (28), 3J(H–H) = 7.0 Hz]; 7.77 [d, Hβ(3), 3J(H–H) =
4.8 Hz]; 7.76 [d, m-H (23), 3J(H–H) = 4.8 Hz]; 7.62 [d, o-H (40,
3
3
44), J(H–H) = 7.8 Hz]; 7.60 [d, o-H (32), J(H–H) = 7.0 Hz];
7.56 [m, p-H (24)]; 7.56–7.55 [m, m-H & p-H]; 7.54 [d, m-H
(35, 37), 3J(H–H) = 7.8 Hz]; 7.47 [t, p-H (42), 3J(H–H) =
7.8 Hz]; 7.35 [t, m-H (41, 43), 3J(H–H) = 7.2 Hz]; 7.22 [d, m-H (50,
Spectroscopy
3
52) of phenoxypropyl group, J(H–H) = 8.4 Hz]; 6.96 [t, p-H
The EPR spectra were measured on an X-band Bruker EMX-10
spectrometer equipped with an Oxford Instruments liquid helium
cryostat. Magnetic field values were measured with a digital
counter. The X-band resonator was a dual-mode cavity (Bruker
ER 4116 DM). Proton and 13C NMR spectra were recorded at
599.95 MHz and 150.87 MHz, respectively, on a Varian Unity
Inova-600 spectrometer locked on deuterated solvent and refer-
3
(51) of phenoxypropyl group, J(H–H) = 7.2 Hz]; 6.66 [d, o-H
3
(49, 53) of phenoxypropyl group, J(H–H) = 7.8 Hz]; 4.04 [t, H
(45) of phenoxypropyl group, 3J(H–H) = 7.2 Hz]; 3.53 [t, H (47)
3
of phenoxypropyl group, J(H–H) = 5.4 Hz]; 2.00 [quintet, H
(46) of phenoxypropyl group, 3J(H–H) = 7.2 Hz]. MS (ESI), m/z
(assignment, rel. intensity): 805.4 ([M]+, 100%). Anal. Calcd for
C53H38N4O2NiO: C, 79.02; H, 4.75; N, 6.95. Found: C, 79.33;
H, 4.67; N 7.00. UV-Vis spectrum, λ (nm) [ε × 10−3 (M−1
cm−1)] in CH2Cl2: 362 (37.1), 428 (75.1), 462 (40.4), 561 (8.5),
714 (3.9) (Fig. S6 in ESI†).
1
enced to the solvent peak at 20 °C. H NMR and 13C NMR are
relative to CDCl3 at 7.24 ppm and the center line of CDCl3 at
77.0 ppm, respectively. 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 protons–carbon coupling.
The nuclear Overhauser effect (NOE) difference and 1H–1H
COSY spectra were employed to determine the 1H–1H proximity
through space over a distance of up to about 4 Å.
The mass spectra [MS(ESI)] were recorded on a Finnigan
TSQ Ultra EMR mass spectrometer with an ESI source.
UV-Vis spectra were recorded at 20 °C on a Hitachi U-3210
spectrophotometer.
Zn(2-NCH2COOCH3NCTPP)Cl (8) [or 8 (Zn–Me)]
Compound 4 was dissolved in CH2Cl2 and layered with MeOH
to afford blue crystals of compound 8 for single-crystal X-ray
analysis (Scheme 2).
1H NMR (599.95 MHz, CDCl3, 20 °C): δ 8.30 [d, Hβ(2),
3
3J(H–H) = 4.5 Hz]; 8.19 [d, Hβ(13), J(H–H) = 4.8 Hz]; 8.14
[d, o-H(40, 44), 3J(H–H) = 7.8 Hz]; 8.06 [d, o-H(34, 38),
3J(H–H) = 7.8 Hz]; 7.78 [d, Hβ(12), 3J(H–H) = 4.8 Hz]; 7.76 [d,
3
3
Hβ(3), J(H–H) = 4.5 Hz]; 7.69 [d, Hβ(7), J(H–H) = 5.7 Hz];
X-Ray crystallography
3
7.62 [d, Hβ(8), J(H–H) = 5.7 Hz]; 7.56–7.57 [m, m-H & p-H];
2
6.35 [s, Hα(19)]; 4.53 [d, H(45A) of MeOAc group, J(H–H) =
Table 1 presents the crystal data as well as other information for
4–8.
18.0 Hz]; 4.04 [d, H(45B) of MeOAc group, 2J(H–H) = 18.0 Hz];
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Table 1 Crystal data for 4–8
Empirical formula
C48H35ClN4O2Zn (4)
C48H34N4O2Pd (5)
C48H34BrN4O2Mn (6)
C53H38N4NiO (7)
C47H33ClN4O2Zn (8)
Formula weight
Space group
800.62
P21/n
805.19
P21/c
833.64
P1
805.58
P1
786.59
P21/n
ˉ
ˉ
Cryst. system
a/Å
b/Å
c/Å
α/°
β/°
Monoclinic
14.4083(5)
13.4694(5)
19.7440(6)
90
100.262(3)
90
Monoclinic
10.4698(3)
25.3342(8)
15.4465(5)
90
104.940(3)
90
Triclinic
10.4840(6)
13.3709(7)
14.5682(8)
82.570(4)
78.087(4)
88.875(4)
1981.4(2)
2
Triclinic
11.8160(5)
12.3785(5)
16.3864(7)
86.438(4)
83.692(4)
66.275(4)
2180.48(16)
2
Monoclinic
11.9685(2)
14.8500(3)
23.3388(4)
90
96.174(2)
90
γ/°
V/Å3
3770.4(2)
4
3958.6(2)
4
4124.0 (1)
4
Z
F (000)
1656
1.410
0.770
1648
1.351
0.513
852
1.397
1.387
840
1.227
0.487
1624
1.267
1.753
Dc/g cm−3
μ/mm−1
S
1.038
1.019
1.063
1.011
1.042
Cryst. size/mm3
0.40 × 0.38 × 0.10
2.87 to 29.23
105(2)
0.60 × 0.30 × 0.12
2.83 to 29.24
110(2)
0.45 × 0.20 × 0.16
2.68 to 29.29
100(2)
0.60 × 0.40 × 0.30
2.99 to 29.30
110(2)
0.60 × 0.40 × 0.20
3.53 to 71.75
110(2)
θ/°
T/K
No. of reflections measured
No. of reflections observed
8701
6270
0.0395
0.0995
9145
5743
0.0463
0.1192
9172
5747
0.0738
0.2313
10 046
6792
0.0473
0.1320
7902
6800
0.0477
0.1318
a
R1
b
wR2
a R1 = [∑||F0| − |FC||/∑|F0|]. b wR2 = [∑w(F02 − FC2)2/∑w(F02)2]1/2
.
Table 2 Selected bond distances (Å) and angles (°) for compounds
4–7
Measurements for 4–8 were taken on a Oxford Diffraction
Gemini S diffractometer using monochromatized Mo Kα radia-
tion (λ = 0.71073 Å). Semi-empirical absorption corrections
were made for all complexes. The structures were solved by
direct methods (SHELXTL-97)18 and refined by the full-matrix
least-squares method. All non-hydrogen atoms were refined with
anisotropic thermal parameters, whereas all hydrogen atoms
were placed in calculated positions and refined with a riding
model. The C(47) and C(48) atoms within 5 is disordered with
an occupancy factor of 0.71 for C(47) C (48) and 0.29 for C(47)′
C(48)′. These C(47) C(48) and C(47)′ C(48)′ were also refined
with anisotropic thermal parameters. Tables 2 and 3 list selected
bond distances and angles for the five complexes.
4
Zn–N(1)
Zn–N(2)
Zn–Cl
2.1125(18)
1.9949(18)
2.2533(6)
Zn⋯C(17)
Zn–N(3)
N(4)–C(19)
2.513(2)
2.1189(18)
1.339(3)
N(1)–Zn–N(2)
N(1)–Zn–N(3)
N(2)–Zn–N(3)
5
Pd–N(1)
Pd–N(2)
90.37(7)
146.51(7)
89.74(7)
Cl–Zn–N(1)
Cl–Zn–N(2)
Cl–Zn–N(3)
100.59(5)
118.96(5)
108.54(5)
2.030(3)
2.049(3)
1.319(5)
Pd–C(17)
Pd–N(3)
1.955(3)
2.007(3)
N(4)–C(19)
N(1)–Pd–N(2)
N(1)–Pd–N(3)
N(2)–Pd–N(3)
6
Mn–N(1)
Mn–N(2)
90.1(1)
177.7(1)
90.9(1)
N(1)–Pd–C(17)
N(2)–Pd–C(17)
N(3)–Pd–C(17)
90.11(13)
176.60(12)
89.00(14)
Results and discussion
2.050(4)
2.036(4)
2.036(4)
Mn–C(17)
Mn–Br
N(4)–C(19)
2.008(5)
2.5072(10)
1.311(6)
Structures of 4–8
Mn–N(3)
The complexes 4 and 5 were synthesized in 61.2% and 40.3%
yields, respectively, by reacting 1 with excess ZnCl2 or PdCl2 in
CH3CN under aerobic conditions (Scheme 1). Complex 6 was
produced in 50.3% yield by heating a solution of 1 in CH3CN
under aerobic conditions with an excess of MnBr2 (Scheme 1).
Complex 7 was synthesized in 65% yield by reacting 2 with
excess Ni(OAc)2 in CH3CN and CH2Cl2 under aerobic con-
ditions. When 4 was dissolved in CH2Cl2 and layered with
MeOH, a new species was formed that can be formulated as
chloro(2-aza-2-methoxycarbonylmethyl-5,10,15,20-tetraphenyl-
21-carbaporphyrinato-N,N′N′′) zinc(II) [Zn(2-NCH2COOCH3-
NCTPP)Cl; 8] (Scheme 2).
Br–Mn–N(1)
Br–Mn–N(2)
Br–Mn–N(3)
Br–Mn–C(17)
N(2)–Mn–N(3)
7
Ni–N(1)
Ni–N(2)
N(4)–C(19)
94.00(12)
97.65(12)
102.39(12)
100.49(14)
88.83(16)
C(17)–Mn–N(1)
C(17)–Mn–N(2)
C(17)–Mn–N(3)
N(1)–Mn–N(2)
N(1)–Mn–N(3)
88.27(18)
161.85(18)
87.55(18)
90.22(16)
163.56(17)
1.958(2)
1.962(2)
1.326(3)
Ni–C(17)
Ni–N(3)
1.905(2)
1.952(2)
N(1)–Ni–N(2)
N(1)–Ni–N(3)
N(2)–Ni–N(3)
90.47(8)
176.38(8)
90.64(8)
N(1)–Ni–C(17)
N(2)–Ni–C(17)
N(3)–Ni–C(17)
89.97(9)
175.81(9)
89.17(9)
The X-ray frameworks of 4–8 are depicted in Fig. 1.
The coordination sphere around the Pd2+ (or Ni) ion in 5
(or 7) is distorted square planar (DSP), and around the Zn2+ ion
in 4 and 8 is distorted tetrahedron (DT), whereas for Mn3+ in 6,
it is distorted square-based pyramid (DSBP) with a Br atom
lying in the axial site. Disregarding the axial coordination
13458 | Dalton Trans., 2012, 41, 13454–13464
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environments, the (N, N, N, C) coordination core in 5, 6 and 7 is
retained, while in 4 and 8 they become (N, N, N).
The geometry of the coordination around Mn(III) in 6 is
closely related to a square-base pyramid, giving a trigonal distor-
tion parameter (τ) value of 0.03, with Mn(III) being five coordi-
nate, consisting of a N3CBr donor set.19 The Mn–C(17), Mn–
N(1), Mn–N(2), Mn–N(3) and Mn–Br bond lengths in 6 are
2.008(5), 2.050(4), 2.036(4), 2.036(4) and 2.507(1) Å, respecti-
vely. The crystal packing of complex 6 indicates that there are no
intermolecular hydrogen bonds linking the individual monomer
of 6 into a dimer in the solid state. Complex 6 is monomeric in
the solid state.
Table 3 Selected bond distances (Å) and angles (°) for compound 8
8
Zn–N(1)
Zn–N(2)
Zn–Cl
2.123(2)
2.004(2)
2.2642(7)
Zn⋯C(17)
Zn–N(3)
N(4)–C(19)
2.566(3)
2.115(2)
1.323(4)
N(1)–Zn–N(2)
N(1)–Zn–N(3)
N(2)–Zn–N(3)
89.83(9)
143.33(9)
89.03(9)
Cl–Zn–N(1)
Cl–Zn–N(2)
Cl–Zn–N(3)
109.37(6)
119.57(7)
102.93(6)
In 4 and 8, the geometry about Zn is distorted tetrahedral
and the bond distances are as follows: Zn⋯C(17) = 2.513(2),
Zn–N(1) = 2.113(2), Zn–N(2) = 1.995(2), Zn–N(3) = 2.119(2)
Fig. 1 (a) Molecular structures of 4, (b) 8, (c) 5, (d) 6, and (e) 7, with 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity.
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and Zn–Cl = 2.2533(6) Å for 4; Zn⋯C(17) = 2.566(3), Zn–N(1) =
2.123(2), Zn–N(2) = 2.004(2), Zn–N(3) = 2.115(2) and Zn–Cl =
2.2642(7) Å for 8. The distance between the inner carbon (17)
and the Zn atom 2.513(2) [or 2.566(3) Å] in 4 (or 8) is short
enough for side-on η1-coordination. A similar distance of
2.53(1) Å was reported by Furuta et al. for the Zn(II) NCDPP
dimer complex (NCDPP = 5,20-diphenyl-NCP).20
In 5 (or 7), the geometry about Pd (or Ni) is distorted square-
planar and the bond distances are as follows: Pd–C(17) =
1.955(3) Å, Pd–N(1) = 2.030(3) Å, Pd–N(2) = 2.049(3) Å and
Pd–N(3) = 2.007(3) Å for 5; Ni–C(17) = 1.905(2) Å, Ni–N(1) =
1.958(2) Å, Ni–N(2) = 1.962(2) Å and Ni–N(3) = 1.952(2) Å
for 7. The average Pd–N and Pd–C distances are 2.029(3) and
1.955(3) Å in 5, and these are both smaller than those of Pd(II)–
N [2.031(2) Å] and Pd(II)–C [1.973(2) Å] in the square-planar
Pd(2-NCH2C6H5NCTPP) (10) complex.13 The average Ni–N
distance of 1.957(2) in 7 is comparable to the Ni–N distance of
1.955(2) Å in Ni(2-NCH2C6H5NCTPP) (11) and the Ni–C dis-
tance of 1.905(2) Å in 7 is similar to the Ni–C distance of
1.907(2) Å in complex 11.15
3J(H–H) = 5.7 Hz and the other doublet at 7.62 ppm is due to
Hβ(7) with J(H–H) = 5.7 Hz. The signal arising from the H(17)
3
proton of 4 in CDCl3 was observed as a singlet at δ =
−0.31 ppm at 20 °C. This observation confirms that there is no
coordinated bond between Zn and C(17) in 4. The geminal
protons H(45A) and H(45B) of 2-NCH2COOEtNCTPPH (1) in
CDCl3 at 20 °C are equivalent and are observed as a singlet at
δ = 4.39 ppm. Moreover, these two geminal protons become
1
nonequivalent in complex 4. Hence the H NMR revealed that
the geminal protons of H(45A) and H(45B) in 4 appear as a
2
doublet of doublets at 4.51 ppm with J ([H(45A)–H(45B)] =
18 Hz) for H(45A) and has a similar doublet of doublets at
4.00 ppm with 2J ([H(39A)–H(39B)] = 18 Hz for H(45B).
In solution, the 1H NMR spectrum for 8 exhibits seven
pyrrole resonances [Hβ(13), Hβ(12), Hβ(2), Hβ(3), Hβ(8), Hβ(7),
Hβ(17)] (Fig. 1b, Fig. S2b and S4 in ESI†). The signal arising
from the H(17) proton of 8 in CDCl3 was observed as a singlet
at δ = −0.30 ppm at 20 °C. The external methyl acetate ligand
unit in 8 gave rise to a series of 1H resonances at 4.53 [d, H(45A)
of MeOAc group, 2J(H–H) = 18.0 Hz], 4.04 [d, H(45B) of
MeOAc group, 2J(H–H) = 18.0 Hz] and 3.56 [s, H(47) of
MeOAc group].
1H NMR spectroscopy data for 4 and 8 in CDCl3
1
1H NMR spectroscopy data for 5 and 7 in CDCl3
In solution, the H NMR spectrum for 4 exhibits seven pyrrole
resonances [Hβ(13), Hβ(12), Hβ(2), Hβ(3), Hβ(8), Hβ(7), Hβ(17)]
(Fig. 1 and 2, and Fig. S2a in ESI†). The doublet at 8.30 ppm is
assigned to Hβ(13) with 3J(H–H) = 4.5 Hz and the other doublet
at 7.75 ppm is due to Hβ(12) with 3J(H–H) = 4.5 Hz. The
In solution, the 1H NMR spectrum for 5 exhibits six pyrrole
resonances [Hβ(12), Hβ(13), Hβ(7), Hβ(8), Hβ(2), Hβ(3)] (Fig. 1c
and 3, and Fig. S3a in ESI†). The doublet at 7.97 ppm is
3
3
assigned to Hβ(2) with J(H–H) = 4.8 Hz and the other doublet
doublet at 8.18 ppm is assigned to Hβ(2) with J(H–H) = 5.1 Hz
at 7.80 ppm is due to Hβ(3) with 3J(H–H) = 4.8 Hz. The doublet
and the other doublet at 7.76 ppm is due to Hβ(3) with 3J(H–H) =
5.1 Hz. The doublet at 7.68 ppm is assigned to Hβ(8) with
Fig. 2 1H NMR spectra for 4 at 599.95 MHz in CDCl3 at 20 °C: (a)
entire spectrum; (b) expansion of the region 7.50–8.30 ppm in (a)
showing seven different β-pyrrole protons Hβ and phenyl protons (o-H,
m, p-H). Chemical shifts are in ppm from CDCl3 at 7.24 ppm.
Fig. 3 1H NMR spectra for 5 at 599.95 MHz in CDCl3 at 20 °C: (a)
entire spectrum; (b) expansion of the region 7.50–8.20 ppm in (a)
showing six different β-pyrrole protons Hβ and phenyl protons (o-H, m,
p-H). Chemical shifts are in ppm from CDCl3 at 7.24 ppm.
13460 | Dalton Trans., 2012, 41, 13454–13464
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3
at 7.85 ppm is assigned to Hβ(13) with J(H–H) = 6.6 Hz and
3
the other doublet at 7.72 ppm is due to Hβ(12) with J(H–H) =
6.6 Hz. The doublet at 7.81 ppm is assigned to Hβ(8) with
3J(H–H) = 4.8 Hz and the other doublet at 7.77 ppm is due to
3
Hβ(7) with J(H–H) = 4.8 Hz. The external ethyl acetate ligand
unit in 5 gave rise to a series of 1H resonances at 4.56 [s, H(45) of
3
EtOAc group], 4.05 [quintet, H(47) of EtOAc group, J(H–H) =
7.2 Hz], and 1.16 [t, H(48) of EtOAc group, 3J(H–H) = 7.2 Hz].
1
In solution, the H NMR spectrum for 7 exhibits six pyrrole
resonances [Hβ(12), Hβ(13), Hβ(7), Hβ(8), Hβ(2), Hβ(3)] (Fig. 1e,
Fig. S1b and S5 in ESI†). However, we can only resolve four
resonances for Hβ. The external phenoxypropyl group unit in 7
1
gave rise to a series of H resonances at 7.22 [d, m-H(50, 52),
3
3J(H–H) = 8.4 Hz], 6.96 [t, p-H(51), J(H–H) = 7.2 Hz], 6.66
3
3
[d, o-H(49, 53), J(H–H) = 7.8 Hz], 4.04 [t, H(45), J(H–H) =
Fig. 4 The X-band ESR spectrum for 6 in CHCl3 at 4 K (parallel
polarization). ESR conditions: microwave frequency of 9.374 GHz,
microwave power of 15 mW, magnetic field modulation amplitude of
1.60 G, modulation frequency of 100.00 kHz for 6.
3
7.2 Hz], 3.53 [t, H(47), J(H–H) = 5.4 Hz], and 2.00 [quintet,
H(46), 3J(H–H) = 7.2 Hz].
Spin Hamiltonian
The magnetic properties of the high-spin mononuclear Mn(III)
ˆ
(S = 2) can be described by the standard spin Hamiltonian ðHSÞ
comprised of Zeeman and ZFS terms:5,21–23
ꢀ
ꢁ
1
2
ðHSÞ ¼ D SZ ꢀ SðS þ 1Þ þ EðSx2 ꢀ Sy2Þ þ βgHS ð1Þ
ˆ
3
where H is the applied magnetic field, g is the geff, S = 2 is the
electronic spin, and D and E are the parameters which describe
the effects of the axial and rhombic ligand field, respectively.
The zero-field interaction splits the levels of system with S = 2
spin into two doublets, one of them is a linear combination of
the mS = | 2> states, i.e., [|2+>, |2−>], and the other one of the
mS = | 1> states, i.e., [|1+>, |1−>], and a singlet corresponding to
the mS = |0 > state, i.e., |0′>. As a first approximation, we set
E equal to zero.
Fig. 5 Temperature variation of the molar magnetic susceptibility (χm)
and effective magnetic moment (μeff) for the powder sample of 6, in the
range 2–300 K. Points represent the experimental data; solid lines rep-
resent the least-squares fit of the data to eqn (2).
ESR studies
The X-band (9.374 GHz) ESR spectrum, using parallel polari-
zation, was recorded for a frozen solution of 6 in CHCl3 at 4 K,
and is shown in Fig. 4. As has been similarly observed in other
Mn(III) complexes, a single line centered at geff = 9.54 is found.
This signal is attributed to a formerly forbidden ΔMs = 4 tran-
sition within the |2+>, |2−> non-Kramers doublet for the high-
spin mononuclear Mn(III) (S = 2) complex of 6 (Fig. 4).5,6,24,25
spin Mn(III) complexes in which geff < 2. Low-symmetry S = 5/2
Mn(II) species, which may be present as impurities in Mn(III)
compounds, can also give rise to downfield EPR signals near g =
2. The data of χM versus T (or μeff versus T) were inserted into
the Van Vleck’s equation (eqn (2)) and the term p is the fraction
of Mn3+.8,23
Magnetic properties
Magnetic data for complex 6 are reported in Fig. 5 in the forms
of χM and μeff versus T.
As can be seen in Fig. 5, the value of μeff varies from 4.62 μB
at 300 K to 4.32 μB at 2 K. The magnetic moment clearly shows
a plateau equal to 4.67 μB at high temperature (300–25 K),
below which it decreases again. The abrupt rise in μeff in the
range 2 < T < 25 K is characteristic of compound 6 with signifi-
cant zero-field splitting (ZFS). The room-temperature effective
moment of 4.62 μB is lower than the spin-only moment of 4.9
μB for an S = 2 system, but consistent with that of other high-
ð2Þ
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ꢀ1
pffiffiffiffiffiffiffiffiffi
Þ
where y ¼ 1:44 Dðcm and μeff = 2.828 χMT. Here geff is the
the H chemical shift of H(3) downfield shift of 0.96 ppm from
7.19 ppm of 1 to 8.15 ppm of 5.15,28 A mean electronic exci-
tation energy of ΔE from π → π* transition of N+vCH(Ar) in 5
in the Karplus–Pople formulation of the 13C screen constant
causes the 13C chemical shift of C(3) downfield shift of
17.3 ppm from 135.8 ppm of 1 to 153.1 ppm of 5 (Table 4).29
The electric field effect originates from molecular dipoles of the
1
T
effective g value, TIP is the temperature independent para-
magnetism and other symbols have their standard meanings.
The best fits, as represented in Fig. 5, gave the values of geff
=
1.9, D = −1.63 cm−1, p = 0.947 and TIP = −2.8 × 10−4
(cm3 mol−1), with an agreement factor R of 1.13%.26 The R
value is defined as
dipolar form II of ⊕NvCH–CvC–C–N⊖ in 5. For H the elec-
1
(
)
1=2
P
2
½ðμeff Þobsd ꢀ ðμeff
Þ
calcdꢁ
tric field effect generally produces shifts of less than 0.5 ppm,
and for 13C the shifts produced are generally less than 4 ppm.30
The electric field effect in this work is small and can be dis-
regarded. The similar kind of deshielding were found of
15.2–16.1 ppm (or 16.2 ppm) for 13C and 0.94–1.00 ppm (or
R ¼
ꢂ100%
P
2
ðμeff Þobsd
This |D| value lies near the 1 < |D| < 4.9 cm−1 range found in
related Mn(III) porphyrin complexes.
1.1 ppm) for H of the N+vCH(Ar) group in complexes 10, 11
1
(or complex 7) (Table 4).16
The bond distance between N(2) and C(3) is 1.319(5) Å [or
1.311(6) Å] in 5 (or 6), shorter than that of compound 1
[1.334(2) Å] by 0.015 Å (or 0.023 Å), respectively (Table 4).
Similar phenomena were observed in the X-ray diffraction data
of complexes 10, 11 (or 7).16 The bond distances between N(2)
and C(3) are 1.311(4), 1.313(3) Å [or 1.326(3) Å] in 10, 11 (or
7), shorter than that of compound 9 [1.327(3) Å] [or compound
2 (1.338(2) Å)] by 0.016, 0.014 Å (or 0.012 Å) (Table 4). These
bond lengths of 1.311(4)–1.326(3) Å between N(2) and C(3) in
Table 3 clearly demonstrate the uniqueness of the N+vCH(Ar)
bond with a dipolar canonical form in 5–7, 10–13 [Chart 1(a)].
The Δℓ = ℓN(2)–C(3) (metal complex) − ℓN(2)–C(3) (free ring) for com-
plexes 4–8, and 10–11 is shown in Table 4. The metal complexes
5–7, 10, 11 with (N, N, N, C) coordination cores indicate that
1H and 13C NMR spectroscopy data for the H(3) and C(3) of
NvCH(Ar) [or N–CH(Ar)] group in complexes 4–13
Table 4 summarizes the X-ray, 1H and 13C NMR chemical
shifts of the N+vCH(Ar) [or N–CH(Ar)] group on the metal
complexes 4–13.
The resonances of the dipolar and covalent forms [Chart 1(a)]
have been suggested to explain the observation made in this
work.9,14,27 The comparison of the free ring (1) with the dipolar
form II of Pd complex (5) results in a significant deshielding of
17.3 ppm for 13C and 0.96 ppm for 1H of the N+vCH(Ar)
group [C(3) and H(3), respectively, Table 4]. The diamagnetic
anisotropy from the dipolar form II of N+vCH(Ar) in 5 causes
Table 4 Molecular structures, X-ray, 1H (599.94 MHz) and 13C (150.87 MHz) NMR chemical shifts of the N+vCH(Ar) [or N–CH(Ar)] fragment in
CDCl3 for 1, 4–14
δ (1H)a
(ppm)
δ (13C)a X-Ray dihedral angle φ(°)d,e
(ppm)
X-Ray
Coordination N(2)–C(3)
X-Ray
Major
canonical
Compound
[CH(3)]b [CH(3)]c N(22) N(23) N(24) C(21) geometryf
(Å)
Δℓg (Å) formi
13
7.19(s)
6.34 (s)
8.15 (s)
—
6.35 (s)
7.28(s)
135.8
121.2
153.1
—
121.0
136.0
152.2
136.8
152.9
152.0
—
11.0
11.9
5.4
12.8
3.4
7.0
7.4
7.0
11.4
7.6
4.9
0.9
3.4
—
15.5
10.3
8.8
25.9d
—
1.334 (2)
1.339(3)
1.319(5)
1.311(6)
1.323(4)
1.338(2)
1.326(3)
1.327(3)
1.311(4)
1.313(3)
1.311(4)
1.315(6)
0
—
Covalent
4 (Zn–Et)
5 (Pd–Et)
6(Mn–Et)
8 (Zn–Me)
44.8d DT
0.005
8.7
8.3
DSP
DSBP
−0.015 Dipolar
−0.023 Dipolar
−0.011 Covalent
5.1
4.5
13.8
11.4
7.5
4.4
4.8
7.8
—
9.0
—
11.7
16.6
5.5
12.3
3.1
2.2
—
10.3
—
45.9d DT
2-NCH2CH2CH2OC6H5NCTPPH (2)
29.9d
4.3
—
DSP
—
DSP
DSP
DSP
DSP
0
—
Ni(2-NCH2CH2CH2OC6H5NCTPP) (7) 8.38(s)
−0.012 Dipolar
0
2-NCH2C6H5NCTPPH16 (9)
Pd(2-NCH2C6H5NCTPP)16 (10)
Ni(2-NCH2C6H5NCTPP)16 (11)
Ni[2-N(CH2)8I NCTPP]9 (12)
Ni(2-NCH2CH2BrNCTPP)17 (13)
7.37(s)
8.31(s)
8.37(s)
—
—
6.74j
24.3d
5.5
—
−0.016 Dipolar
6.6
—
10.1
—
−0.014 Dipolar
h
—
—
Dipolar
Dipolar
—
h
—
117.9 j
11.3
—
Pyrrole31,32 (14)
—
1.365j
—
a The atom labelling for CH(3) and CH(3) is shown in Scheme 1. b Broad singlet. c Singlet. d The dihedral angles between the plane defined by N(22)
N(23) N(24) and the pyrrole planes [N(22), N(23), N(24), C(21)], respectively, for the free ring in 1, 2, 9 and complexes with the (N, N, N)
coordination core in 4 and 8. e The dihedral angles between the plane defined by N(22) N(23) N(24) C(21) and the pyrrole planes [N(22), N(23),
f
N(24), C(21)], respectively, for the complexes with the (N, N, N, C) coordination core in 5–7, 10–13. DT = distorted tetrahedron, DSP = distorted
square planar, DSBP = distorted square-based pyramid. g Δℓ = ℓN(2)–C(3) (metal complex) − ℓN(2)–C(3) (free ring), the bond length difference for N(2)–C(3)
between the coordination compound and its free ring. h Not reported. i Two resonances contributors for dipolar form in Chart 1(a) and covalent form in
Chart 1(b). j
H(2) in pyrrole; C(2) in pyrrole; N(1)–C(2) in pyrrole.
13462 | Dalton Trans., 2012, 41, 13454–13464
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0.012 Å < |Δℓ| < 0.023 Å (Table 4). The dihedral angle φ
between the C(21) pyrrole plane and the plane defined by N(22)
N(23) N(24) C(21) are as follows: 8.7 (5), 8.3 (6), 4.3 (7), 5.5
(10), 6.6 (11), and 10.1° (13). This small dihedral angle φ of
4.3–10.1° in complexes 5–7, 10, and 11 indicates that the
pyrrole C(21) ring is approximately coplanar with the N(22)
N(23) N(24) C(21) plane (Table 4). This coplanarity of the
pyrrole C(21) ring enhances both the delocalization of the 18
π-electron aromatic macrocyclic system of NCPs and the forma-
tion of the iminium ion for these complexes [Chart 1(a)].
Meanwhile, the peripheral carbon–nitrogen double bonds
N+vCH(Ar) of complexes 5–7, 10 and 11 are partially isolated
from the 18 π-conjugated aromatic system, and 13C and 1H
NMR provides the spectroscopic evidence for the dipolar form
II of the iminium ions in those complexes.
The change from the free ring (1) to the Zn complexes 4 and
8 is associated with a shielding of 14.6–14.8 ppm for 13C and
0.84–0.85 ppm for 1H of the N–CH(Ar) group [C(3), H(3),
respectively, Table 4]. The dihedral angle φ between the C(21)
pyrrole plane and the plane defined by N(22) N(23) N(24) in
complexes 1, 2, 4, 8 and 9, are as follows: 25.9° (1), 29.9° (2),
44.8° (4), 45.9° (8) and 24.3° (9). This large dihedral angle of
44.8–45.9° in complexes 4 and 8 indicates that the pyrrole C(21)
ring is highly tilted from the N(22) N(23) N(24) plane (Table 4).
This distortion breaks the delocalization of the two lone-pair
electrons from N(2) to the N(2)–C(3) bond and inhibits the for-
mation of the iminium ion with a dipolar form in complexes 4
and 8. Hence the covalent form should be a major canonical
form for complexes 4 and 8, as shown in Scheme 2 and Chart
1(b). Apparently the localization of two double bonds and the
large deviation (with φ = 44.8–45.9°) of the pyrrole C(21) plane
from their own N(22) N(23) N(24) planes in 4 and 8 makes the
pyrrole C(21) planes in these two complexes more like free
pyrrole (14), shown in Table 4.31 Complexes 4 and 8 show a
1H resonance of H(3) in N–CH(Ar) at δ = 6.34 and 6.35 ppm in
CDCl3, whereas free pyrrole (14) gives a similar signal at δ =
6.74 ppm in the same solvent (Table 4).32 Complexes 4 and 8
show a 13C resonance of C(3) in N–CH(Ar) at δ = 121.2 and
121.0 ppm in CDCl3, whereas free pyrrole (14) also gives a
similar signal at δ = 117.9 ppm in CDCl3 (Table 4).32
135.8 ppm of 1 to 121.2 ppm (or 121.0 ppm) of 4 (or 8), respect-
ively (Table 4).
According to Table 4, a situation in which the 13C of C(3) and
1
the H of H(3) chemical shifts for the N+vCH(Ar) fragment are
separately located at 152.6
0.5 ppm and 8.30
0.15 ppm
suggests that the dipolar form predominates in the diamagnetic
metal complexes of 2-N-substituted N-confused porphyrins with
(N, N, N, C) coordination cores [Table 4, Chart 1(a)]. In brief,
the use of resonance to describe these types of species (5–7,
10–13) has been used to explain why the cross conjugated N-
substituted NCPs retain aromatic characteristics. This is empha-
sized using 2-alkyl NCPs and the closely related azuliporphyrins
by Lash and co-workers.10 The corresponding resonances of the
covalent form for the N–CH(Ar) fragment in the diamagnetic
metal complexes with (N, N, N) coordination cores were seen at
121.1 0.1 ppm and 6.35 0.01 ppm [Table 4, Chart 1(b)].
X-Ray diffraction data unambiguously indicates that 0.012 Å
< |Δℓ| < 0.023 Å and N(2)–C(3) 1.315 0.011 Å are found for
the dipolar form of 5–7, 10–13 in Chart 1(a). Meanwhile, the
X-ray diffraction data also demonstrates that |Δℓ| < 0.011 Å and
N(2)–C(3) = 1.331 0.008 Å are observed for the covalent form
of 4 and 8 in Chart 1(b).
Conclusions
The peripheral carbon–nitrogen double bonds N+vCH(Ar) of
5–7, 10 and 11 are partially isolated from the 18 π-conjugated
aromatic system. This work applies, for the first time, the 13C
and 1H chemical shifts to diagnose the dipolar canonical form II
of the N+vCH(Ar) group in diamagnetic metal complexes of
2-N substituted N-confused porphyrins. In general, the two 13C
and 1H spectroscopic correlations proposed herein can be
applied for diamagnetic metal N-confused complexes.
Acknowledgements
The financial support from the National Science Council of the
R. O. C. under grant NSC 101-2113-M-005-013 is gratefully
acknowledged. We thank Dr S. Elango for helpful discussions.
The bond lengths of 1.339(3)–1.324(4) Å between N(2) and
C(3) in Table 4 show the existence of the N–CH(Ar) bond with
a covalent form in complexes 4 and 8 [Scheme 2 and Chart
1(b)]. Complexes 4 and 8 with (N, N, N) coordination cores
show that the absolute value of Δℓ is less than 0.011 Å. The
dihedral angle of 25.9° (or 29.9°, 24.3°) in complex 1 (or 2, 9)
indicates that the pyrrole C(21) ring is tilted from its N(22)
N(23) N(24) plane. A resonance between the dipolar form and
covalent form also exists in the free rings of 1, 2 and 9. The
covalent form predominates in 1, 2 and 9. When the pyrrole
C(21) ring in 1 is deviated from its N(22) N(23) N(24) plane and
tilted from 25.8° to 44.8° (or 45.9°), and is finally coordinated
with the Zn2+ ion, it becomes complex 4 (or 8) with a major
covalent form. During this tilt process, the minor amount of the
dipolar form of 1 is gradually depleted and causes the 1H chemi-
cal shift of H(3) to undergo an upfield shift of 0.84–0.85 ppm,
from 7.19 ppm of 1 to 6.34 ppm (or 6.35 ppm) of 4 (or 8)
(Table 4). In a similar manner, it also causes the 13C chemical
shift of C(3) to undergo an upfield shift of 14.6–14.8 ppm, from
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13464 | Dalton Trans., 2012, 41, 13454–13464
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