Meso-substituent effects on redox properties of the 5,10-porphodimethene- type P,S,N2-hybrid calixphyrins and their metal complexes

Article abstract of DOI:10.1021/om900745t

The 5,10-porphodimethene-type P,S,N₂-hybrid calixphyrins bearing p-methoxyphenyl or p-(trifluoromethyl)phenyl groups at the sp ²-hybridized meso carbons and their palladium(II) and rhodium(I) complexes were prepared and characterized

Full text of DOI:10.1021/om900745t

Organometallics 2009, 28, 6213–6217 6213
DOI: 10.1021/om900745t
Meso-Substituent Effects on Redox Properties of the 5,10-Porphodimethene-
Type P,S,N2-Hybrid Calixphyrins and Their Metal Complexes
Yoshihiro Matano,*,† Masato Fujita,† Tooru Miyajima,† and Hiroshi Imahori†,‡,§
†Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku,
Kyoto 615-8510, Japan, ‡Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University,
Nishikyo-ku, Kyoto 615-8510, Japan, and Fukui Institute for Fundamental Chemistry, Kyoto University,
§
Sakyo-ku, Kyoto 606-8103, Japan
Received August 26, 2009
The 5,10-porphodimethene-type P,S,N2-hybrid calixphyrins bearing p-methoxyphenyl or
p-(trifluoromethyl)phenyl groups at the sp2-hybridized meso carbons and their palladium(II) and
rhodium(I) complexes were prepared and characterized. The electronic effects of the meso-aryl
substituents on the redox properties of the π-conjugated subunits were evaluated for both the free
bases and the palladium complexes, and the hemilabile nature of the P,S,N2-calixphyrin platforms in
the rhodium complexes was revealed.
Calixphyrins1 are a class of macrocyclic ligands that contain
multiple pyrrole rings bridged by sp2- and sp3-hybridized meso
carbons. It is well-known that the structural, redox, and
coordinating properties of calixphyrins vary widely, depending
on the number of sp3-hybridized meso carbons as well as the
character of peripheral substituents.2 Core modification is also a
versatile methodology to drastically change the fundamental
properties of the calixphyrin platform.3,4 Recently, we reported
the first examples of phosphole-containing P,S,N2-hybrid calix-
phyrins 1 and 2, in which the phosphorus atom incorporated in
the rim plays a crucial role in tightly binding various late
transition metals.4a,b Notably, 1 and 2 are interconvertible by
redox reactions, and 1 behaves as a redox-active mixed-donor
(hybrid) macrocyclic ligand toward palladium.5 However, for a
fine tuning of the electronic structure of the P,S,N2-hybrid
calixphyrin platform, it is necessary to evaluate the electronic
effects of peripheral substituents on the redox properties of
the π-conjugated subunits. In this context, we prepared new
P,S,N2-hybrid calixphyrins bearing para-substituted phenyl
groups on the sp2-hybridized meso carbons. Herein, we report
electronic effects of the meso substituents on redox properties of
the 5,10-porphodimethene-type P,S,N2-hybrid calixphyrins
and their metal complexes. In addition, the unique coordina-
tion structures of the Rh(I)-P,S,N2 complexes are described
in detail.
*To whom correspondence should be addressed. E-mail: matano@
scl.kyoto-u.ac.jp.
ꢀ
(1) (a) Kral, V.; Sessler, J. L.; Zimmerman, R. S.; Seidel, D.; Lynch,
V.; Andrioletti, B. Angew. Chem., Int. Ed. 2000, 39, 1055–1058.
(b) Sessler, J. L. J. Porphyrins Phthalocyanines 2000, 4, 331–336.
ꢀ
(c) Sessler, J. L.; Zimmerman, R. S.; Bucher, C.; Kral, V.; Andrioletti, B.
Pure Appl. Chem. 2001, 73, 1041–1057.
(2) For example, see: (a) Krattinger, B.; Callot, H. J. Tetrahedron
Lett. 1998, 39, 1165–1168. (b) Benech, J.-M.; Bonomo, L.; Solari, E.;
Scopelliti, R.; Floriani, C. Angew. Chem., Int. Ed. 1999, 38, 1957–1959.
(c) Bonomo, L.; Toraman, G.; Solari, E.; Scopelliti, R.; Floriani, C. Orga-
ꢀ
nometallics 1999, 18, 5198–5200. (d) Bucher, C.; Seidel, D.; Lynch, V.; Kral,
V.; Sessler, J. L. Org. Lett. 2000, 2, 3103–3106. (e) Senge, M. O.; Kalisch,
W. W.; Bischoff, I. Chem. Eur. J. 2000, 6, 2721–2738. (f) Harmjanz, M.;
Gill, H. S.; Scott, M. J. J. Org. Chem. 2001, 66, 5374–5383. (g) Furuta, H.;
Ishizuka, T.; Osuka, A.; Uwatoko, Y.; Ishikawa, Y. Angew. Chem., Int. Ed.
ꢀ
2001, 40, 2323–2325. (h) Dolensky, B.; Kroulík, J.; Kral, V.; Sessler, J. L.;
ꢁꢀ
ꢀ
ꢁ
ꢀ
ꢀ
Dvorakova, H.; Bour, P.; Bernatkova, M.; Bucher, C.; Lynch, V. J. Am.
Chem. Soc. 2004, 126, 13714–13722. (i) Senge, M. O. Acc. Chem. Res.
ꢀ
ꢀ
ꢁꢀ
ꢀ
ꢀ
2005, 38, 733–743. (j) Bernatkova, M.; Dvorakova, H.; Andrioletti, B.; Kral,
V.; Bour, P. J. Phys. Chem. A 2005, 109, 5518–5526. (k) Bucher, C.;
Devillers, C. H.; Moutet, J.-C.; Pecaut, J.; Royal, G.; Saint-Aman, E.;
ꢁ
ꢀ
Thomas, F. Dalton Trans. 2005, 3620–3631. (l) O'Brien, A. Y.; McGann,
J. P.; Geier, G. R., III J. Org. Chem. 2007, 72, 4084–4092.
ꢀ
_ ꢀ
(3) (a) Stepien, M.; Latos-Grazynski, L.; Szterenberg, L.; Panek, J.;
Latajka, Z. J. Am. Chem. Soc. 2004, 126, 4566–4580. (b) Gupta, I.;
€
Frohlich, R.; Ravikanth, M. Chem. Commun. 2006, 3726–3728. (c) Hung,
C.-H.; Chang, G.-F.; Kumar, A.; Lin, G.-F.; Luo, L.-Y.; Ching, W.-M.; Diau,
E. W.-G. Chem. Commun. 2008, 978–980. (d) Chang, G.-F.; Kumar, A.;
Ching, W.-M.; Chu, H.-W.; Hung, C.-H. Chem. Asian J. 2009, 4, 164–173.
ꢀ
(e) Skonieczny, J.; Latos-Graz_ynski, L.; Szterenberg, L. Chem. Eur. J. 2008,
14, 4861–4874.
(4) (a) Matano, Y.; Miyajima, T.; Nakabuchi, T.; Imahori, H.; Ochi,
N.; Sakaki, S. J. Am. Chem. Soc. 2006, 128, 11760–11761. (b) Matano, Y.;
Miyajima, T.; Ochi, N.; Nakabuchi, T.; Shiro, M.; Nakao, Y.; Sakaki, S.;
Imahori, H. J. Am. Chem. Soc. 2008, 130, 990-1002; 2009, 131, 14123
(Additions and Corrections) . (c) Matano, Y.; Miyajima, T.; Ochi, N.; Nakao,
Y.; Sakaki, S.; Imahori, H. J. Org. Chem. 2008, 73, 5139–5142. (d) Matano,
Y.; Fujita, M.; Miyajima, T.; Imahori, H. Phosphorus, Sulfur Silicon Relat.
Elem., in press. (e) Ochi, N.; Nakao, Y.; Sato, H.; Matano, Y.; Imahori, H.;
Sakaki, S. J. Am. Chem. Soc. 2009, 131, 10955–10963. (f) Matano, Y.;
Imahori, H. Acc. Chem. Res. 2009, 42, 1193–1204.
(5) Metal complexes coordinated by phosphole-containing macro-
cyclic ligands have been reported by Mathey and co-workers:
(a) Mathey, F.; Mercier, F.; Nief, F.; Fischer, J.; Mitschler, A. J. Am.
Chem. Soc. 1982, 104, 2077–2079. (b) Bevierre, M.-O.; Mercier, F.; Ricard,
L.; Mathey, F. Angew. Chem., Int. Ed. Engl. 1990, 29, 655–657. (c) Laporte,
F.; Mercier, F.; Ricard, L.; Mathey, F. J. Am. Chem. Soc. 1994, 116, 3306–
3311. (d) Deschamps, E.; Ricard, L.; Mathey, F. J. Chem. Soc., Chem.
Commun. 1995, 1561. (e) Mercier, F.; Laporte, F.; Ricard, L.; Mathey, F.;
€
Schroder, M.; Regitz, M. Angew. Chem., Int. Ed. Engl. 1997, 36, 2364–
2366.
r
2009 American Chemical Society
Published on Web 10/14/2009
pubs.acs.org/Organometallics

6214 Organometallics, Vol. 28, No. 21, 2009
Matano et al.
Scheme 1. Synthesis of σ3-P,S,N2-Hybrid Calixphyrins 9 and 10
Scheme 2. Synthesis of Hybrid Calixphyrin-Palladium
Complexes
parts of 6 and 10 were not obtained at all. Apparently, the
p-methoxyphenyl groups stabilize the 4e-oxidized form of the
pyrrole-thiophene-pyrrole (N-S-N) subunit, whereas the
p-(trifluoromethyl)phenyl groups stabilize the 2e-oxidized form.
Newly prepared calixphyrins were characterized by 1H
and 31P NMR spectroscopy and high-resolution mass
(HRMS) spectrometry. The 31P chemical shifts of 9
(δ 26.7) and 10 (δ 31.3) are almost identical with those of 1
(δ 26.7) and 2 (δ 31.0), respectively, indicating that the meso-
aryl groups at the N-S-N subunits do not affect the
1
electronic character of the phosphorus nucleus. In the H
Results and Discussion
NMR spectra, 9 shows the pyrrole-β and thiophene-β pro-
tons at δ 6.60-6.68 and 6.67 ppm (in CDCl3), respectively,
whereas 10 displays the corresponding protons at
δ 5.74-5.99 and 6.39 ppm. The difference in chemical shifts
of the heterole-β protons between 9 and 10 clearly supports
the different oxidation states of their N-S-N subunits. The
2e-oxidized P,S,N2-calixphyrin 10 shows reversible two-step
oxidation processes at Eox,1=þ0.46 V and Eox,2=þ0.64 V (vs
FeCp*2/FeCp*2þ; Cp* = C5Me5). These values are more
positive than the corresponding values of 2 (Eox,1 =þ0.34
V and Eox,2=þ0.54 V), indicating that the introduction of
two p-(trifluoromethyl)phenyl groups makes the π-conju-
gated N-S-N subunit less oxidizable by ca. 0.1 V.9
The new σ3-P,S,N2-calixphyrins 9 and 10 were pre-
pared from σ4-phosphatripyrrane 36 and the corresponding
2,5-bis[hydroxy(aryl)methyl]thiophenes 4b,c7 (Scheme 1)
according to the reported procedure for the synthesis of 1
and 2.4a,b Addition of BF3 OEt2 to a CH2Cl2 solution contain-
3
ing 3 and 4b, followed by treatment with 2.2 equiv of 2,3-
dichloro-5,6-dicyanobenzoquinone (DDQ), afforded the
4e-oxidized σ4-P,S,N2-calixphyrin 5 as a major product. When
4c was used in place of 4b, the 2e-oxidized σ4-P,S,N2-calixphyr-
in 6 was obtained as the sole isolable product in low yield.
Compound 6 was produced in better yield via BF3-promoted
condensation of phosphole 78 with thiatripyrrane 8 (eq 1).
With the new P,S,N2-hybrid ligands 9 and 10 in hand, we
investigated their coordination behavior toward palladium
and rhodium. As previously reported, the hybrid ligands 1
and 2 reacted with Pd(dba)2 (dba=dibenzylideneacetone)
and Pd(OAc)2, respectively, yielding the same palladium
complex 11a (Scheme 2).4a,b Both the experimental and
theoretical results revealed that the formal oxidation state
of the palladium center in 11a is þ2. Thus, the redox-
coupled complexation occurs between 1 and Pd(dba)2,
whereas the metathesis takes place between 2 and Pd-
(OAc)2. Similar reactivities were observed for 9 and 10.
The p-methoxyphenyl derivative 9 underwent redox-
coupled complexation with Pd(dba)2 to give palladium(II)
complex 11b, whereas the p-(trifluoromethyl)phenyl deri-
vative 10 underwent metathesis with Pd(OAc)2 to afford
Treatment of 5 and 6 with excess P(NMe2)3 in refluxing
toluene yielded the 4e-oxidized σ3-P,S,N2-calixphyrin 9 and the
2e-oxidized σ3-P,S,N2-calixphyrin 10, respectively. Probably
due to the electronic effects of the para substituents (vide infra),
2e-oxidized counterparts of 5 and 9 and 4e-oxidized counter-
(9) Provided that the electronic effect is quantitatively evaluated on
the basis of ΔEox value per one meso-aryl substituent, the electronic
effect observed for 10 vs 2 (ca. 0.05-0.06 V) is comparable to that
reported for TPP derivatives (TPP=5,10,15,20-tetraphenylporphyrin)
bearing the same para substituents (ca. 0.04 V). For Eox values of the
TPP derivatives under the same CV measurement conditions, see:
(a) Wolberg, A. Isr. J. Chem. 1974, 12, 1031–1035. (b) Hariprasad, G.;
Dahal, S.; Maiya, B. G. J. Chem. Soc., Dalton Trans. 1996, 3429–3436.
(c) Richter-Addo, G. B.; Hodge, S. J.; Yi, G.-B.; Khan, M. A.; Ma, T.;
Van Caemelbecke, E.; Guo, N.; Kadish, K. M. Inorg. Chem. 1996, 35,
6530–6538.
(6) (a) Matano, Y.; Nakabuchi, T.; Miyajima, T.; Imahori, H.
Organometallics 2006, 25, 3105–3107. (b) Nakabuchi, T.; Matano, Y.;
Imahori, H. Organometallics 2008, 27, 3142–3152.
(7) Hilmey, D. G.; Abe, M.; Nelen, M. I.; Stilts, C. E.; Baker, G. A.;
Baker, S. N.; Bright, F. V.; Davies, S. R.; Gollnick, S. O.; Oseroff, A. R.;
Gibson, S. L.; Hilf, R.; Detty, M. R. J. Med. Chem. 2002, 45, 449–461.
(8) Matano, Y.; Miyajima, T.; Nakabuchi, T.; Matsutani, Y.; Im-
ahori, H. J. Org. Chem. 2006, 71, 5792–5795.

Article
Organometallics, Vol. 28, No. 21, 2009 6215
11c (Scheme 2). The spectral features of 11b,c are essentially
the same as those of 11a, suggesting that the palladium
center in 11b,c takes a þ2 oxidation state. The UV-vis
absorption spectra of 11b,c (Figure S2 in the Supporting
Information) also show the similarity of their electronic
structures. Evidently, the hybrid calixphyrin platforms
in 11b,c behave as dianionic P,S,N2-tetradentate ligands.
The 31P chemical shifts of 11b (δ 45.9) and 11c (δ 47.3) are
close to the 31P chemical shift of 11a (δ 47.0), indicating that
the para substituents have little impact on the electronic
character of the phosphorus nucleus, even in the palladium-
(II) complexes.
Scheme 3. Synthesis of Hybrid Calixphyrin-Rhodium(I) Com-
plexes
To examine the electronic effects of meso-aryl substitu-
ents on the N-S-N π-conjugated subunits of the palla-
dium complexes, the first and second oxidation potentials
(Eox,1 and Eox,2) of 11b,c were compared with those of 11a.
Both Eox,1 and Eox,2 of 11b (þ0.17 and þ0.28 V vs FeCp*2/
FeCp*2þ) are shifted to the negative side, while Eox,1 and
Eox,2 of 11c (þ0.32 and þ0.42 V) are shifted to the positive
side, as compared to the corresponding potentials of the
phenyl derivative 11a (þ0.23 and þ0.34 V). These data
simply reflect the electron-donating (for 11b) and electron-
withdrawing (for 11c) abilities of the para substituents on
the meso phenyl groups.9 The differences in the oxidation
potentials between 11c and 11a (þ0.08 to þ0.09 V) are
comparable to those observed for the free bases 2 and 10
(þ0.10 to 0.12 V). It seems likely that the electronic effects
of the para substituents on the N-S-N subunit are little
affected by the complexation with palladium. Addition-
ally, it is evident that the palladation at the core raises the
HOMO level of the P,S,N2-hybrid calixphyrin platform by
ca. 0.1 V.
carbonyl complexes.12 In the mass spectra, intense peaks
due to the fragment ions ([M - (CO, Cl)]þ) are detected at
m/z 774 (for 12a), 833 (12b), and 909 (12c), together with
1
weak fragment [M - (CO)]þ ion peaks. In the H NMR
spectra of 12b,c in CDCl3 at room temperature, the
pyrrole-β protons are observed as significantly broadened
peaks, which suggests the occurrence of dynamic exchange
processes between two conformers. This spectroscopic fea-
ture will be discussed later.
The rhodium(I) complexes 12a,b show irreversible oxida-
tion processes at þ0.56 and þ0.52 V (vs FeCp*2/FeCp*2þ),
respectively. The electrochemical oxidation behavior of 12a,b is
close to that of 13 and 14, which is reported to involve a Rh(I)-
to-Rh(II) transition followed by a chemical reaction.13 The
difference in the oxidation potentials between 12a and 12b
is very small, suggesting that the electronic effect of the meso-
aryl substituents on the P,N-chelated rhodium(I) center is
small.
Similar to 1, free base 9 reacted with [RhCl(CO)2]2 in
CH2Cl2 to give rhodium complex 12b in high yield
(Scheme 3).10 As described below, 12b was found to possess
the neutral 4e-oxidized N-S-N subunit. To our surprise,
10 also reacted with [RhCl(CO)2]2 to produce a similar type
of rhodium complex 12c, albeit in low yield. Presumably,
the 2e-oxidized N-S-N subunit was converted to the 4e-
oxidized form under the reaction conditions employed. The
structures of 12a-c were characterized by NMR and IR
spectroscopy, MS spectrometry, and X-ray crystallography
(for 12a,b). The diagnostic spectral features of 12a-c are as
follows. In the 31P NMR spectra, the characteristic doublet
peaks are observed at δ 69.6 (for 12a), δ 69.4 (for 12b), and
δ 69.6 (for 12c) with 31P-103Rh coupling constants of 171
Hz (for 12a), 177 Hz (for 12b), and 171 Hz (for 12c),
indicating that the oxidation state of the rhodium center
in 12a-c is þ1.11 The IR spectra display sharp CO stretch-
ing bands at ν 1977 cm-1 (for 12a), 1978 cm-1 (for 12b), and
1981 cm-1 (for 12c), which are at the shorter end of the
reported values (ca. 1980-2000 cm-1) of typical Rh(I)
The structures of 12a,b were unambiguously elucidated
by X-ray crystallographic analyses.10,14 As shown in
Figure 1 and Figure S3 (Supporting Information), the P,
S,N2-hybrid ligands in these complexes provide essentially
the same coordination environments. In each complex, the
rhodium center adopts
L-Rh-L0
a
square-planar geometry
P
(
= ca. 360°) supported by the phosphorus,
nitrogen, chlorine, and carbonyl carbon atoms. The Cl
and CO ligands occupy positions trans to the P and N(1)
atoms, respectively. The CO stretching frequencies of
12a-c (see above) reflect the trans influence of the azaful-
vene-type N ligand. One of the nitrogen atoms, N(1),
coordinates to the rhodium center, while the other, N(2),
does not. Accordingly, the N-S-N π-conjugated subunit
is highly twisted, and the phosphole ring is almost perpen-
dicular to a mean plane formed by the four meso car-
bons. All the structural features observed for 12a,b are
completely different from those reported for octahedral
(12) Conradie, M. M.; Conradie, J. Inorg. Chim. Acta 2008, 361,
2285–2295.
(10) In our previous paper,4b we assigned 12a (complex 9 in ref 4b)
as a cationic rhodium(I) complex coordinated by the four core elements
(P, S, and two N) on the basis of only spectral data (1H NMR, 31P NMR,
and MS). However, this assignment has proven to be incorrect. New
data (IR and X-ray) unambiguously elucidated that 12a is a neutral,
square-planar rhodium(I) complex coordinated by two core elements
(P and N), a chlorine atom, and a CO group, as mentioned in the text.
Reinvestigation of the reported spectral data also supports this assign-
ment. Accordingly, the spectral features of 12a are described again in the
present paper. The correction of the structure of 12a (compound 9 in ref
4b) has been published in J. Am. Chem. Soc. as an Addition and
Correction.4b
(13) Yao, C.-L.; Anderson, J. E.; Kadish, K. M. Inorg. Chem. 1987,
26, 2725–2727.
(14) Crystal data for 12a: C46H39ClN2OPRhS, MW=837.18, mono-
˚
˚
˚
clinic, P21/c, a=13.669(6) A,b=14.829(7) A,c=18.824(8) A, β=91.964(8)°,
3
V=3814(3) A , Z=4, Dc=1.458 g cm-3, 10 161 reflections collected, 8467
˚
independent reflections, 479 variables, Rw = 0.2285, R = 0.1127
(I > 2.00σ(I)), GOF = 1.264. The CIF file of 12a was submitted
as an Addition/Correction of ref 4b. Crystal data for 12b:
C48H43ClN2O3PRhS 0.5CH2Cl2, MW = 939.70, monoclinic, P21/c, a=
3
˚
˚
˚
16.168(5) A, b=14.487(4) A, c=18.921(6) A, β=100.612(6)°, V=4356(2)
3
A , Z=4, Dc=1.433 g cm-3, 33 314 collected reflections, 9943 independent
˚
(11) Brown, T. H.; Green, P. J. J. Am. Chem. Soc. 1970, 92, 2359–
2362.
reflections, 542 variables, Rw=0.1576, R=0.1001 (I > 2.00σ(I)), GOF=
1.233.

6216 Organometallics, Vol. 28, No. 21, 2009
Matano et al.
˚
Table 1. Selected Bond Lengths and Distances (A) of 12a,b and
11aa
12ab
12b
11ac
a, a0
b, b0
c, c0
d, d0
e, e0
f, f0
g
1.42, 1.45
1.36, 1.34
1.45, 1.46
1.37, 1.36
1.45, 1.47
1.42, 1.38
1.38
1.42, 1.44
1.34, 1.34
1.44, 1.45
1.38, 1.36
1.44, 1.45
1.38, 1.39
1.38
1.38, 1.39
1.39, 1.39
1.40, 1.39
1.45, 1.46
1.36, 1.36
1.45, 1.45
1.35
N
N
S
4.93
3.97
4.88
3.98
4.15
4.45
3 3 3
P
3 3 3
a The values are rounded off to the second decimal place. b Data from
Figure 1. Top and side views of 12b (30% probability ellipsoids).
Hydrogen atoms are omitted for clarity. Selected bond lengths
ref 4b (Addition/Correction) . c Data from ref 4b.
˚
(A) and bond angles (deg): Rh-P, 2.2348(16); Rh-N(1), 2.177(5);
˚
lengths of 12a,b (1.783(9) and 1.792(6) A) are appreciably
Rh-Cl, 2.4116(16); Rh-C(46), 1.792(6); C(46)-O(1), 1.152(7);
Rh-C(46)-O(1), 176.3(7); P-Rh-N(1), 91.15(13); P-Rh-
C(46), 92.5(2); Cl-Rh-N(1), 89.59(13); Cl-Rh-C(46), 86.4(2).
shorter than those of 13-15, implying that the back-dona-
tion from Rh to CO in 12a,b is more prominent than that
in 13-15. The structural features observed for 12a,b repre-
sent the characteristic role of the phosphole ligand incor-
porated in the calixphyrin platform.
P,N3-calixphyrin-rhodium(III) complexes,4b in which all
of the core elements occupy the basal positions coordinat-
ing to the rhodium center.
Table 1 summarizes carbon-carbon bond lengths at the
N-S-N subunits and selected interatomic distances of
12a,b together with those of the previously reported Pd(II)
complex 11a.4b The pattern of carbon-carbon bond
length alternation at the N-S-N subunit of 12a,b well
explains the 4e-oxidation state depicted as the canonical
structure in Scheme 3 and is in sharp contrast to that
observed for 11a containing a dianionic N-S-Nsubunit with
the 2e-oxidation state. The difference in coordination structures
between 12a and 11a is also reflected in their N N and P
S
3 3 3
3 3 3
To get an insight into the dynamic behavior of the P,S,
N2-calixphyrin-Rh(I) complexes, we measured variable-
temperature (VT) 1H NMR spectra of 12b in 1,1,2,2-tetra-
chloroethane-d2 from -40 to 100 °C (Figure S4 in the
Supporting Information). As mentioned above, at room
temperature, the pyrrole-β protons were observed as broad
peaks. At -40 °C, however, the pyrrole-β protons became
sharpened and split into four separate peaks (δ 6.50, 6.56,
6.64, and 6.83) with the same intensity (each d, 1H, J =
3.9 Hz) implying that the two pyrrole rings are placed in
nonequivalent magnetic environments. With an increase in
the temperature, the peak pattern gradually changed, and the
pyrrole-β protons coalesced at ca. 50 °C and appeared as two
peaks (δ 6.61 and 6.76, each br s, 2H) at 100 °C. It should be
noted that the 31P chemical shift is little affected by tempera-
ture. These observations can be interpreted by considering an
interconversion between two coordination structures, 121 and
122 (eq 2). At low temperatures, the exchange rate between 121
and 122 is slow on the NMR time scale, whereas at high
temperatures it is fast. The dynamic behavior observed by
distances. The Rh-N (core nitrogen atom) and Rh-C (trans
to the nitrogen atom) bond lengths of dinuclear rhodium(I)
porphyrins 1315 and 1416 and rhodium(I) N-confused porphyrin
1516c were reported to be 2.069(3)-2.098(3) and 1.837(10)-
˚
1.860(4) A, respectively. The Rh-N bond lengths of the present
˚
Rh(I) complexes 12a,b(2.185(6) and 2.177(5) A) are considerably
longer than those of 13-15, which may reflect differences
in chelating structures (P,N versus N,N) and Lewis acidity
at the rhodium center. The Rh-N bond lengths of 12a,b
are also longer than the Rh-N bond lengths observed
for the octahedral P,N3-calixphyrin-Rh(III) complexes
4b
˚
(2.062(4)-2.082(4) A). On the other hand, the Rh-C bond
(15) (a) Yoshida, Z.; Ogoshi, H.; Omura, T.; Watanabe, E.; Kurosaki,
T. Tetrahedron Lett. 1972, 13, 1077–1080. (b) Takenaka, A.; Sasada, Y.;
Omura, T.; Ogoshi, H.; Yoshida, Z. Chem. Commun. 1973, 792–793.
(c) Takenaka, A.; Sasada, Y.; Omura, T.; Ogoshi, H.; Yoshida, Z. Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1975, B31, 1–6.
(16) (a) Fleischer, E. B.; Dixon, F. Bioinorg. Chem. 1977, 7, 129–139.
(b) Srinivasan, A.; Furuta, H.; Osuka, A. Chem. Commun. 2001, 1666–1667.
(c) Srinivasan, A.; Toganoh, M.; Niino, T.; Osuka, A.; Furuta, H. Inorg.
Chem. 2008, 47, 11305–11313.

Article
Organometallics, Vol. 28, No. 21, 2009 6217
VT-NMR measurements exemplifies the hemilabile nature
of the P,S,N2-calixphyrin platform.
effects on the electrochemical oxidation processes of the
π-conjugated subunits are clearly observed for a series of
palladium(II)-P,S,N2-calixphyrin complexes. In addi-
tion, we have unambiguously characterized the struc-
tures of the rhodium(I)-P,S,N2-calixphyrin complexes
by X-ray crystallography and disclosed the hemilabile
nature of their macrocyclic platforms by NMR spectros-
copy.
Acknowledgment. This work was supported by a
Grant-in-Aid for Science Research on Priority Areas
(No. 20036028, Synergy of Elements) from the Ministry
of Education, Culture, Sports, Science and Technology of
Japan and the Sumitomo Foundation.
In summary, we have revealed electronic effects of the
meso substituent on the redox properties of the 5,10-
porphodimethene-type P,S,N2-hybrid calixphyrins and
their metal complexes for the first time. The electron-
donating p-methoxyphenyl groups stabilize the 4e-oxidation
state of the π-conjugated N-S-N subunit, whereas the
electron-withdrawing p-(trifluoromethyl)phenyl groups
stabilize the 2e-oxidation state. The meso-substituent
Supporting Information Available: Text and figures giving
experimental details, characterization data, and 1H NMR charts
for new compounds and a CIF file giving crystallographic data
for 12b. This material is available free of charge via the Internet
at http://pubs.acs.org.