Synthetic, 119Sn NMR spectroscopic, electrochemical, and reactivity study of organotin A3 corrolates including chiral and ferrocenyl derivatives

Article abstract of DOI:10.1021/ic302335c

Various R/Ar-functionalized tin 5,10,15-tris(pentafluorophenyl)corrolate derivatives are reported herein including the first ferrocenyltin corrolate species. The isopropyl, sec-butyl-, 2-methyl-n-butyl-, phenyl-, 2-thienyl-, and ferrocenyltin species have

Full text of DOI:10.1021/ic302335c

Article
pubs.acs.org/IC
119
Synthetic, Sn NMR Spectroscopic, Electrochemical, and Reactivity
Study of Organotin A3 Corrolates Including Chiral and Ferrocenyl
Derivatives
Olga G. Tsay, Byung-Kwon Kim, Tuong Loan Luu, Juhyoun Kwak,* and David G. Churchill*
Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Yuseong-gu,
Daejeon, 305-701, Republic of Korea
S
* Supporting Information
ABSTRACT: Various R/Ar-functionalized tin 5,10,15-tris-
(pentafluorophenyl)corrolate derivatives are reported herein
including the first ferrocenyltin corrolate species. The
isopropyl, sec-butyl-, 2-methyl-n-butyl-, phenyl-, 2-thienyl-,
and ferrocenyltin species have been prepared and characterized
1
through H, 13C, and 119Sn HMQC NMR spectroscopy, mass
spectrometry, UV−vis and photoluminescent spectroscopy,
and cyclic voltammetry studies. JC/H−Sn NMR spectroscopic
couplings and ring-current effects (upfield shifting) were
determined for the R−Sn axial hydrogen and carbon atoms.
This report adds to older conceptually similar reports, by, i.e.,
Janson et al. (J. Am. Chem. Soc. 1969, 91, 5210) and Walker et al. (J. Am. Chem. Soc. 1983, 105, 6923−6929), as discussed herein.
Such NMR spectroscopic aspects are discussed for these model systems. Compound Sn−Ph bond cleavage was achieved by
treatment with I2.
previously reported by Kadish and others (Figure 1).12b,15,16
Tin corroles are interesting to investigate because the static
I. INTRODUCTION
Natural cyclic polypyrroles and their metal complexes
axial group involves atoms proximal to the metal that are under
constitute a major compound class that serves as a vital basis
the influence of both (i) the macrocyclic ring current and (ii)
for, e.g., essential iron and cobalt chemistry in biology.
Synthetic systems also abound and have found important use
in catalysis and model studies. The offerings in the literature on
porphyrin and metalloporphyrin frameworks were described
inherent NMR-coupling characteristics imposed by NMR
spectroscopically active tin nuclei. Thus, the axial position can
impose a dual signature onto potentially all atoms of the axial
group in a kind of “double stamping” that would be interesting
more than 35 years ago to have “mushroomed outwards and
blossomed in a quite remarkable manner”.1a−d Therefore, lesser
to pursue in molecular recognition. Conceptually, however,
reports of porphyrinoid systems with both metal axial−ligand
explored and newer cyclic polypyrrole skeleton types allow
researchers to recapitulate important metalation and catalysis
studies freely with an appreciation for the large changes that
and macrocyclic ring−ligand interactions originate from efforts
decades ago.17 A chapter by Scheer and Katz encompasses
various kinds of transition-metal- and main-group-based
may occur in metal-centered reactivity, valence, and complex
systems (Figure 1).17b Additionally, certain subsequent reports
geometry upon seemingly relatively subtle formal changes in
stand out as well including interesting reports by Walker et al.
the macrocyclic ligand design. In recent years, one growing
on the NMR properties of iron porphyrins (Figure 2).17a This
class of synthetic (contracted) porphyrin is the corroles and
metal corrolates.1e−h Their interesting properties have been
concept can now be extended to tin corroles here, in which the
underscored by the research efforts of Gross et al.,2−4 Kadish et
tin axial site can host a variety of aliphatic and aromatic groups;
al.,5−7 Gryko et al.,7,8 Paolesse et al.5,9,10 and others and to a
these strongly bound groups can serve as basic model systems
lesser extent by our research group.11 There has been a
for would-be analytes. Related porpyrinoid systems such as the
octaethylporphyrin and phthalocyanine versions involving the
relatively thorough treatment of transition-metal systems, with
lighter group 14 elements contain dual axial O−R groups
main-group derivatives being less thoroughly examined. Main-
ligands, as described in earlier reports (Figure 1).1b−d
group corrolates are interesting because of the adaptation of the
Additionally, aryl groups can extend to the cyclopentadienyl
otherwise transition-metal-based [N4] core system to various
moiety; this ligand can be bound further to other metals. Here,
central elements that attenuate properties enabled by the
the common, versatile, and robust ferrocenyl (Fc) system was
contracted ligand. Group 14 corrolates of silicon, germanium,
and lead have been reported.10b,12 Furthermore, tin(4+)
porphyrinoids have been previously reported by Hosseini et
Received: October 25, 2012
Published: February 1, 2013
al. and Nemykin et al.13,14 Tin(4+) corroles have been
© 2013 American Chemical Society
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Figure 1. Notable previous species: (top left) diferrocenyltin porphycene and (center and right) tin corroles.25,15 (right) Various R and Ar groups,
including chiral and ferrocenyl groups, discussed herein. (bottom) Earlier porphyrinoid systems involving dual axial ligation at group 14 centers.1b−d
bromide, isopropylmagnesium bromide, sec-butylmagnesium bromide,
2-thienyllithium, CH2Cl2, hexane, and toluene) were of analytical
grade and were used as received from commercial chemical suppliers
(Aldrich, TCI, and Junsei companies) except for pyrrole. Pyrrole was
distilled over CaH2 under vacuum prior to use. Analytical and
preparative thin-layer chromatography (PTLC) was performed on the
original plates (20 × 20 cm, 60 F silica gel, Merck). A Vilber Lourmat
4LC UV lamp (4 W, 365 nm, 50/60 Hz) was used to assay the colored
and fluorescent TLC components of the reaction mixture. The silica
gel used in column chromatography was of diameter 0.04−0.063 mm.
The silica gel used for dry-column vacuum chromatography was of
diameter 0.015−0.040 mm (Merck). All solvents used in NMR
spectral analyses were purchased commercially and were of
1
spectroscopic grade. One-dimensional H and 13C NMR spectra and
two-dimensional heteronuclear multiple-quantum coherence
(HMQC) spectra were measured on a Bruker Avance 400 MHz
spectrometer; tetramethylsilane was used as an internal standard. 119Sn
NMR spectra were acquired on a Bruker Avance spectrometer (149.21
MHz) and quoted in ppm relative to tetramethyltin (SnMe4; 119Sn = 0
ppm) as an external standard and are reported as fully decoupled
spectra. UV−vis spectra were recorded with a JASCO V-503 UV−vis
spectrophotometer (1000 nm/min). Emission spectra were obtained
using a Shimadzu RF-5310pc spectrofluorophotometer. High-
resolution matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectrometry was performed on a Bruker
Autoflex III [ionization method, laser source Nd YAG (355 nm);
analyzer, 2.0 m linear mode; 3.0 reflector mode], and α-cyano-4-
hydroxycinnamic acid was used as the matrix. High-resolution mass
spectrometry (HRMS) spectra were recorded on Bruker micrOTOF-
Q II mass spectrometer [electrospray ionization (ESI-TOF), positive
mode]. Time-correlated single-photon-counting spectra were collected
using a FL920 spectrofluorimeter (Edinburgh Instruments) utilizing
Figure 2. Elegant earlier example of the “double-stamping” concept
reported by Walker et al. involving the bulk of the meso groups able to
“dial” the axial group to different metal-based orbital interactions. In
this way, the nuclei of the axial ligands are under the influence of both
(i) the macrocyclic ring current and (ii) electronic interactions from
the metal center, and the nuclei of the atoms in the axial group can
therefore be said to be “double-stamped”. Red dotted lines indicate the
alignment of the top N-methylimidazole group (bottom one omitted
for clarity) and that for the imposition of the proximal top pivalamido
groups (spheres).17a
the pulses from an EPL 470-ps-pulsed diode laser and a H5773-04
detector (Hamamatsu). Cyclic voltammetry (CV) was carried out with
a CHI 900B electrochemical analyzer (CH instruments) using a
solution of 0.1 M TBAP in acetonitrile. A three-electrode system was
incorporated. There are only a few reports to date regarding
Cor−Fc conjugates, but these examples do not contain Fc
groups that are bound to the metal.18,19 Previous reports relate
used and consisted of a platinum disk working electrode, a platinum
wire counter electrode, and an Ag/Ag+ reference electrode containing
0.01 M AgNO3. All solutions for electrochemical measurements were
deoxygenated by sparging with argon prior to experimentation. All
potentials are referenced against the Ag/Ag+ redox couple. Values of
E1/2 of the ferrocene/ferrocenium ion couple were −0.01 V under our
experimental conditions.
mainly to catalysis, not to sensing. Ferrocenyl conjugation may
be desired for chemosensing in its own right. It has been
established for related systems for control of the redox
activity,20 robustness, optics,21 and photoluminescence,14,22
electron-transfer properties,23 and charge-transfer capabil-
ities.24,25 Chirality has also been addressed with corrole
complexes but sparingly; previous reports involve ligand N
substitution and metal centers.26,27,3,11d
General Procedure for the Preparation of Tin(IV) Corrolate
Complexes with Alkyl and Aryl Axial Ligands. Details for the
synthesis of 5,10,15-tris(pentafluorophenyl)corrole4,28 and [5,10,15-
tris(pentafluorophenyl)corrolato]tin(IV) chloride [Sn(tpfc)Cl; 1]
have been previously reported.12b To a stirred solution of 1 in dry
tetrahydrofuran (THF; 5 mL) was added 4.0 equiv of alkyl- or
arylmagnesium bromide or aryllithium under an inert atmosphere; the
II. EXPERIMENTAL SECTION
Materials and Physical Measurements. All chemicals used
herein (e.g., pentafluorobenzaldehyde, SnCl2, phenylmagnesium
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reaction mixture was stirred for 5 min at room temperature. Aqueous
ammonium chloride was added, after which dichloromethane was
added. The organic layer was separated and washed with water two
times and then evaporated to dryness. Residue was subjected to dry-
column vacuum chromatography; the title compound was the purified
again by PTLC. Detailed purification systems for individual
compounds are given below.
procedure15 starting from 219 mg (0.22 mmol) of 1 and phenyl-
magnesium bromide (308 μL of a 3.0 M solution in diethyl ether).
Dry-column vacuum chromatography (silica, CH2Cl2/hexane, 0.2:1)
and preparative TLC (silica, CH2Cl2/hexane, 0.5:2) afforded the pure
1
expected compound (120 mg, 0.12 mmol, 55% yield). H NMR (300
3
MHz, CDCl3, 7.24 ppm): δ 9.25 (d, J(H,H) = 4.18 Hz, 2Hβ‑pyrrole),
3
9.06 (d, J(H,H) = 4.75 Hz, 2Hβ‑pyrrole, 8.86 (m, 4Hβ‑pyrrole), 6.20 (t,
3
Isopropyl [5,10,15-Tris(pentafluorophenyl)corrolato]tin(IV)
[Sn(tpfc)iPr; 2). This reaction was performed by the following
literature procedure,15 starting from 242 mg (0.26 mmol) of 1 and 520
μL (1.04 mmol) of isopropylmagnesium chloride (2.0 M in THF).
Dry-column vacuum chromatography (silica, CH2Cl2/hexane, 0.2:1)
and PTLC (silica, CH2Cl2/hexane, 0.5:2) afforded the pure compound
(67 mg, 0.07 mmol, 27%). 1H NMR (400 MHz, CDCl3, 7.24 ppm): δ
3J(H,H) = 7.49 Hz, 1H, Hd), 5.96 (t, J(H,H) = 7.6 Hz; satellites
3
J(1H,119Sn) = 31.6 and 46.7 Hz, Hc and He), 3.63 (d, J(H,H) = 7.0
Hz, satellites J(1H,119Sn) = 88.5 Hz, 2H, Hb and Hf), 13C NMR (100
MHz, CDCl3, 77 ppm): δ 148.3 (br), 147.1 (br), 145.9 (br), 144.5
(br), 143.7 (s), 140.7 (s), 139.5, 137.5, 133.6, 131.2 (satellites
J(13C,119Sn) = 59.1 Hz, Cb and Cf), 129.5 (Cd), 128.1, 127.4 (satellites
J(13C,119Sn) = 48.7 Hz, Cc and Ce), 125.8, 124.6, 118.4, 115.5, 114.8,
100, 93.45. 119Sn NMR (149.21 MHz, CDCl3): δ −404.60. HRMS:
989.9878 (M+, obsd), 989.9923 (calcd for C43H13F15N4Sn). MALDI-
TOF [(M + H)+]: 990.463 (100%), 913.404 (8%) (obsd). λmax
(toluene), nm (ε × 10−4, L·mol−1·cm−1): 426 (39.3), 536 (1.06),
575 (2.29), 604 (3.07).
3
3
9.21 (d, J(H,H) = 4.2 Hz, 2Hβ‑pyrrole), 8.96 (d, J(H,H) = 3.4 Hz,
2Hβ‑pyrrole), 8.75 (m, 4Hβ‑pyrrole), −1.85 (d, 3J(H,H) = 7.24 Hz,
satellites J(1H,119Sn) = 66.8 and 74.3 Hz, 6H, Hb and Hc), −2.06 (m,
1H, Ha). 13C NMR (100 MHz, CDCl3, 77 ppm): δ 148.3 (br), 146.9
(br), 145.8 (br), 144.5 (br), 143.9 (C6,14 or 9,11), 140.9 (C9,11 or 6,14),
139.5 (C1,19 or 4,16), 137.6 (C4,16 or 1,19), 127.9 (C7,13), 125.4
(C3,17 or 8,12), 124.3 (C3,17 or 8,12), 118.6 (C2,18), 115.8, 114.8, 99.9
(C5,15), 93.1 (C10), 19.5 (Ca), 15.6 (Cb and Cc). 119Sn NMR (149.21
MHz, CDCl3): δ −371. HRMS: 956.0034 (M+, obsd), 956.0079 (calcd
for C40H15F15N4Sn). MALDI-TOF [(M + H)+]: 956.583 (44%),
913.509 (100%) (obsd). λmax (toluene), nm (ε × 10−4, L·mol−1·cm−1):
428 (36.1), 536 (1.3), 577 (2.2), 608 (3.0).
2-Thienyl [5,10,15-Tris(pentafluorophenyl)corrolato]tin(IV)
[Sn(tpfc)-2-thienyl, 6]. The reaction was performed following a
general procedure15 starting from 184 mg (0.19 mmol) of 1 and 760
μL of 2-thienyllithium (1.0 M in THF). Dry-column vacuum
chromatography (silica, CH2Cl2/hexane, 0.2:1) and PTLC (silica,
CH2Cl2/hexane, 0.4:1.5) afforded compound 6 in pure form (63 mg,
1
0.063 mmol, 33% yield). H NMR (300 MHz, CDCl3, 7.24 ppm): δ
3
3
2-Butyl [5,10,15-Tris(pentafluorophenyl)corrolato]tin(IV)
[Sn(tpfc)secBu, 3]. This reaction was performed following a general
procedure15 starting from 100 mg (0.10 mmol) of 1 and 440 μL of sec-
butylmagnesium bromide (1.0 M in THF). Dry-column vacuum
chromatography (silica, CH2Cl2/hexane, 0.2:1.0) and PTLC (silica,
CH2Cl2/hexane, 0.5:2.0) afforded the pure product compound (14
9.27 (d, J(H,H) = 4.22 Hz, 2Hβ‑pyrrole), 8.99 (d, J(H,H) = 4.65 Hz,
3
2Hβ‑pyrrole), 8.81 (m, 4Hβ‑pyrrole), 6.48 (d, J(H,H) = 4.76 Hz, satellites
J(1H,119Sn) = 34 Hz, Hd), 5.94 (t, 3J(H,H) = 4.5 Hz, satellites
J(1H,119Sn) = 18.3 Hz, Hc), 3.92 (d, J(H,H) = 3.47 Hz, satellites
3
J(1H,119Sn) = 45 Hz, Hb). 13C NMR (100 MHz, CDCl3, 77 ppm): δ
148.3 (br s), 146.9 (br s), 145.7 (br s), 144.5 (br), 143.5 (C6,14 or 9,12),
140.6 (C6,14 or 9,11), 139.3 (C1,19 or 4,16), 137.3 (C4,16 or 1,19), 133.6
(satellites J(13C,119Sn) = 69 Hz, Cb), 131.3 (satellites J(13C,119Sn) =
49.4 Hz, Cd), 128.2 (C7,13), 126 (Cc), 125.9 (C3,17 or 8,12), 124.7
(C3,17 or 8,12), 122.0 (Ca), 118.6 (C2,18), 115.1, 114.5, 100 (C5,15), 93.5
(C10). 119Sn NMR (149.21 MHz, CDCl3): δ −394.11. HRMS:
995.9448 (M+, obsd), 995.9487 (calcd for C41H11F15N4SSn). MALDI-
TOF [(M + H)+]: 996.554 (100%) (obsd). λmax (toluene), nm (ε ×
10−4, L·mol−1·cm−1): 425 (39.2), 535 (1.07), 574 (2.37), 601 (2.93).
Ferrocenyl [5,10,15-Tris(pentafluorophenyl)corrolato]tin(IV)
[Sn(tpfc)Fc, 7]. Diethyl ether (1.5 mL) was added to magnesium
(turnings, 103 mg, 4.24 mmol) under an inert atmosphere. A solution
of bromoferrocene (280 mg, 1.06 mmol) and 1,2-dibromoethane (182
μL, 2.12 mmol) in diethyl ether (3 mL) was added dropwise. When
heating and boiling are stopped, the freshly prepared Grignard reagent
solution was added to the solution of 1 (100 mg, 0.106 mmol) in dry
THF (2.5 mL). After 10 min, the reaction was quenched with water.
Methylene chloride was added, and the organic layer was separated
and washed with water two times and then evaporated to dryness. Dry-
column vacuum chromatography (silica, CH2Cl2/hexane, 0.2:1) and
PTLC (silica, CH2Cl2/hexane, 0.5:1 and then 2:0.5) afforded
1
mg, 0.014 mmol, 14%). H NMR (300 MHz, CDCl3, 7.24 ppm): δ
3
3
9.20 (d, J(H,H) = 4.32 Hz, 2Hβ‑pyrrole), 8.89 (d, J(H,H) = 4.45 Hz,
3
2Hβ‑pyrrole), 8.71 (m, 4Hβ‑pyrrole), −1.13 (m, Hc), −1.45 (t, J(H,H) =
7.2 Hz, Hd), −1.71 (m, Hc), −1.94 (d, J(H,H) = 7.56 Hz, Hb), −2.17
(m, Ha). 13C NMR (100 MHz, CDCl3, 77 ppm): δ 148.3 (br), 147.0
(br), 145.8 (br), 144.5 (br), 143.9 (C6,14 or 9,11), 140.9 (C6,14 or 9,11),
139.4 (C1,19 or 4,16), 137.6 (C1,19 or 4,16), 127.8 (C7,13), 125.3
(C3,17 or 8,12), 124.3 (C3,17 or 8,12), 118.1 (C2,18), 115.6, 114.8, 99.9
(C5,15), 93.1(C10), 29.4 (Ca), 24.2 (Cc), 13.0 (Cb), 10.6 (Cd). 119Sn
NMR (149.21 MHz, CDCl3): δ −376.64. HRMS: 970.0185 (M+,
obsd), 970.0236 (calcd for C41H17F15N4Sn):). MALDI-TOF [(M +
H)+]: 970.674 (19%), 913.562 (100%) (obsd). λmax (toluene), nm (ε
× 10−4, L·mol−1·cm−1): 428 (30.68), 536 (0.92), 577 (1.78), 606
(2.46).
2-Methyl-n-butyl [5,10,15-Tris(pentafluorophenyl)-
corrolato]tin(IV) [Sn(tpfc)(2-Me-n-Bu), 4]. The reaction was
performed following a general procedure15 starting from 190 mg
(0.2 mmol) of 1 and 1.0 mL of 2-methyl-n-butylmagnesium bromide
(1.2 M in diethyl ether) prepared in situ from 0.408 mL of (S)-(+)-1-
bromo-2-methylbutane. Dry-column vacuum chromatography (silica,
CH2Cl2/hexane, 0.2:1) and PTLC (silica, CH2Cl2/hexane, 0.5:2)
afforded a pure compound (27 mg, 0.027 mmol, 14%). 1H NMR (300
1
compound 7 in pure form (33 mg, 0.30 mmol, 28.5%). H NMR
(300 MHz, CDCl3, 7.24 ppm): δ 9.26 (d, 3J(H,H) = 4.26 Hz,
2Hβ‑pyrrole), 8.93 (dd, 3J(H,H) = 4.7 and 1.17 Hz, 2Hβ‑pyrrole), 8.75 (m,
3
MHz, CDCl3, 7.24 ppm): δ 9.21 (d, J(H,H) = 4.14 Hz, 2Hβ‑pyrrole),
3
4Hβ‑pyrrole), 3.1 (t, J(H,H) = 1.79 Hz, 119Sn satellites J(H,Sn) = 16.8
3
8.94 (d, J(H,H) = 4.6 Hz, 2Hβ‑pyrrole), 8.74 (m, 4Hβ‑pyrrole), −0.54 (t,
3
Hz, 2H, Hc), 2.65 (s, 10H, Hd), 0.94 (t, J(H,H) = 1.73 Hz, 119Sn
3J(H,H) = 9.69 Hz, 3H, satellites J(1H,119Sn) = 49.5 Hz, He), −1.04
satellites J(H,Sn) = 15.9 Hz, 2H, Hb). 13C NMR (100 MHz, CD2Cl2,
53.8 ppm): δ 148.7, 147.5, 145.2, 145, 144.1 (C6,14 or 9,11), 143.7
(C6,14 or 9,11), 141.1(C1,19 or 4,16), 139.8 (C1,19 or 4,16), 137.7, 137.0, 128.5
(C7,13), 126.1 (C3,17 or 8,12), 124.9 (C3,17 or 8,12), 118.9 (C2,18), 115.9,
115.1, 100.3 (C5,15), 93.6 (C10), 69.8 (satellites J(13C,119Sn) = 90.8 Hz,
Cc), 69.5 (satellites J(13C,119Sn) = 106.9 Hz, Cb), 67.7 (Cd), 60.2 (Ca).
119Sn NMR (149.21 MHz, CD2Cl2): δ −352.7. HRMS: 1097.9552
(M+, obsd), 1097.9585 (calcd for C47H17F15FeN4Sn). MALDI-TOF
[(M + H)+]: 1098.647 (100%) (obsd). λmax (toluene), nm (ε × 10−4,
L·mol−1·cm−1): 425 (31.4), 535 (1.09), 576 (2.19), 606 (2.87).
Reactivity of Sn−C Bond Cleavage with I2. A small amount of
compound 5 was taken into a sealable NMR tube for reaction with 10
equiv of I2 (0.018 mmol). The reaction was monitored conveniently
(m, 2H, Hd), −1.53 (d, 3J(H,H) = 6.21 Hz, 3H, satellites J(1H,119Sn) =
49.4 Hz, Hc), −1.78 (m, 1H, Hb), −2.66 (dd, J(H,H) = 7.56 Hz, 2H,
Ha). 13C NMR (100 MHz, CDCl3, 77 ppm): δ 148.3 (br), 147.0 (br),
145.8 (br), 144.5 (br), 143.6 (C6,14 or 9,11), 140.6 (C6,14 or 9,11), 139.3
(C1,19 or 4,16), 137.4 (C1,19 or 4,16), 128.0 (C7,13), 125.4 (C3,17 or 8,12),
124.4 (C3,17 or 8,12), 118.2 (C2,18), 115.8, 114.8, 100.0 (C5,15), 93.2
(C10), 29.9 (Cb), 28.3 (Cd), 22.5 (Ca), 19.6 (Cc), 9.9 (Ce). 119Sn NMR
(149.21 MHz, CDCl3): δ −362.52. HRMS: 984.0339 (M+, obsd),
984.0392 (calcd for C42H19F15N4Sn). MALDI-TOF [(M + H)+]:
984.664 (65%), 913.562 (100%) (obsd). λmax (toluene), nm (ε × 10−4,
L·mol−1·cm−1): 428 (36.6), 535 (1.1), 576 (2.17), 606 (2.98).
Phenyl [5,10,15-Tris(pentafluorophenyl)corrolato]tin(IV)]
[Sn(tpfc)Ph, 5]. The reaction was performed following a general
1993
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by 1H NMR spectroscopy, whereupon after 2 days quantitative
conversion of the starting materials to a new product was observed,
devoid of the original phenyl group and with H NMR spectroscopic
signals consistent with tin−iodine corrole and PhI (see Figure S2 in
the Supporting Information).
Testing for Halide Sensing. A solution of compound 6 (1.0 μM
in MeCN) was taken and treated with a small excess (10 equiv) of
iodide (KI) to effect the exposure of the corrolate−tin alkyl with I−
ions. This was performed in a cuvette, where a control sample allowed
for gauging possible optical fluorescent changes. There was no spectral
change upon treatment with I−, signifying no chemical change, in
contrast with that found for I2. Also, analogous trials were done for Br−
and Cl− and shown to give no optical responses.
macrocyclic β-proton signals are present (δ ∼8−9.5)29
(Supporting Information). Upfield shifting was clearly
observed: 0.12 ppm differences for aryl groups and 0.20 ppm
for alkyl groups, relative to 1.12b 119Sn NMR spectral signals of
δ −350 to −400 were obtained, supporting pentacoordination
of the tin atom and comparable to values previously published
for closely related compounds.30 These tin values are the first
values obtained for corroles. HRMS spectra revealed M+ signals
within acceptable limits of error (≤5 ppm); MALDI-TOF mass
spectral data featured prominent signals in accordance with the
calculated values (see reproductions of these spectra in the
Supporting Information). The ferrocenyl derivative is the first
such ferrocenyl−metal corrolate conjugate. Unfortunately,
attempts to obtain solid-state structural data led to a tentative
crystal structure of compound 7 only (Supporting Informa-
tion).
1
III. RESULTS AND DISCUSSION
Three main steps were taken to prepare model systems 2−7:
(i) corrole free-base synthesis, (ii) stannylation, and (iii)
arylation/alkylation. First, the well-known tris-
(pentafluorophenyl)corrole species tpfc(H)3 was prepared.28
Next, the derivative 1 was then synthesized by treatment of
tpfc(H)3 with SnCl2 in N,N-dimethylformamide.9,12b,15 Finally,
target compounds 2−7 (Figure 4) were synthesized according
NMR spectroscopic details were further analyzed, especially
with respect to the axial moieties. These values are both
connected covalently to tin, which is NMR-active30 and which
n
reveals J(1H,119Sn) coupling values that allow for a handle for
determining the Sn···H through-bond distance. Additionally,
these hydrocarbon atoms also fall under the influence of the
macrocyclic ring current, seeing as they are proximal enough to
the mean macrocyclic plane. As shown before for related
systems, the ring-current axial group ligand proton signals are
found far upfield:1 aromatic signals, 6 to 3 ppm; aliphatic
signals, −1 to −4 ppm (Figure 4 and figures in the Supporting
Information). This is typified by compound 7: Fc-based
protons are also shifted to higher field because of the effects
of the ring current (ferrocene: δ 4.1, CDCl3, Supporting
Information).31 In Figure 4, Δδ (δcomplex−δferrocene) values are
more pronounced for the ferrocenyl atoms proximal to the tin
atom in 7 (Table S2 in the Supporting Information). The other
substituents (isopropyl, sec-butyl, 2-methyl-n-butyl, phenyl, and
2-thienyl) have also been spectroscopically characterized. These
1
values in the H NMR spectrum are also all found upfield;
reproductions of these spectra and those for 13C NMR
spectroscopic data are provided in the Supporting Information.
Larger Δδ values are found in related porphyrin complexes (i.e.,
trans-SnFc2TPP; Figure S39 and Table S2 in the Supporting
Information).14 In addition to the ring current, 119Sn nuclei (I =
1/2) impose a secondary identifier on these axially positioned
n
n
nuclei in the form of J(1H,119Sn) and J(13C,119Sn) coupling
constant values (Figure 4 and the Supporting Information).32,33
These through-bond coupling constants show a clear trend of
decreasing intensity as a function of the internuclear distance,
as expected; they are gauged for the first time with a variety of
sp2- and sp3-hybridized carbon groups. The interest in C/H-
based ligands that bear these hallmarks could be in future
molecular detection modalities, whereby analyte binding occurs
at the single axial position in tin corrolates and the atoms are
both upfield-shifted and tin-coupled.
Figure 3. 1H NMR spectral shifts for related phthalocyanine and
octaethyl porpyrin group 14 systems. Here, there are two axial ligands;
the nuclei here do not afford secondary coupling such as that found for
tin.
to the procedure provided by the Kadish report.15 Hydrocarbon
axial groups (R/Ar) were incorporated onto 1 in the form of
Grignard reagents, except for 2-thienyl and ferrocenyl groups,
which were prepared as lithium salts (see the Experimental
Section). These reagents afforded the respective isopropyl (2),
sec-butyl (3), 2-methyl-n-butyl (4), phenyl (5), 2-thienyl (6),
and ferrocenyl (7) derivatives (Figure 4). For the synthesis of 4,
(S)-(+)-1-bromo-2-methylbutane was first converted to 2-
methyl-n-butylmagnesium bromide, which was then able to be
used directly in the preparation of 4 (observation of a very
weak Cotton effect; see the Supporting Information). The
In the context of this present scrutiny with these tin corrolate
systems, related details of previously reported systems of group
1
14 porphyrinoid systems are depicted here (Figure 3). H
NMR spectral chemical shifts of axial ligand atoms are provided
for comparison. With these early examples, we can plainly see
the ring-current effects for related group 14 systems, albeit for
porphyrin species. In one report, the silicon(IV) thiocyanine
species were characterized (Figure 1); specifically, three silicon
versions and one germanium version bearing alkyl and siloxyl
groups were obtained.1b For the reported silicon ( and
germanium) octaethylporphyrins, the methoxide and phen-
1
compounds were characterized in solution by H, 13C, and
119Sn NMR spectroscopy. The various axial ligands in 2−7 were
1
further assigned through the use of H−13C HMQC NMR
spectroscopy. In 1H NMR spectra, the eight expected
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Figure 4. Alkyl and aryl moieties for compounds 2−7 and their ring-current-shifted δ and their J(H/C,Sn) values obtained herein.
oxide derivatives were also obtained (Figure 3).1c,d The
differences in the proton chemical shift in the axial ligand are
very small upon comparison of the silicon and germanium
analogues.
Cyclic voltammograms were obtained for compounds 2−7
and allow for a solution analysis of the electronic capacity of the
different derivatives (Figure 6 and the Supporting Information).
Single, reversible one-electron reductions were observed at E1/2
= −1.50
0.03 V. The values for the alkyl derivative
Optically, the absorption spectra of corroles 2−7 in toluene
at room temperature revealed characteristic Q and Soret bands.
The Q bands are found at 535−536, 574−577, and 601−608
nm, and the Soret bands are found at values of 425−428 nm;
additional bands that appear as shoulders to the principal Soret
signal at 404−407 nm are also found but are less pronounced
for compound 7 (Figure 5). In general, the bathochromic
shifting of bands was observed for compounds 2−4 with alkyl
axial groups in comparison with that for compounds 5−7.
Emission spectra (λex = ∼530 nm) of 2−6 in toluene are also
shown in Figure 5. No emission was detected for the ferrocenyl
derivative (7) under our experimental conditions. For
comparison, in porphyrin species, the incorporation ferrocenyl
moiety leads to a 2.7-fold drop in the fluorescence quantum
yield.14 The emission peaks, Stokes shifts, and calculated
fluorescence quantum yields of all compounds are provided in
Table 1. Time-correlated single photon counting was also
undertaken, and these spectra are displayed in the Supporting
Information. The data reveal short fluorescence lifetimes of
∼0.307−0.353 ns. The longest lifetime was that obtained for 6,
which showed a higher fluorescence quantum yield (6.71
0.12) × 10−3 than the other samples. Both ΦF and τ values
obtained (Table 1) are of the same order of magnitude as that
for the tin−chlorine corrolate [ΦF = (9.4 0.9) × 10−3, τ =
140 50 ps, toluene, 77 K], reported by the research groups of
Guilard and Harvey.16d
(compounds 2−4) were found clustered at a value of ca. −1.5
V with subtle differences between them. Values for the aryl
derivative compounds 5−7 varied and were found shifted
slightly positive. By comparison, tin porphyrins bear two one-
electron reductions.14,15 Compounds 2−7 undergo three quasi-
reversible oxidations. In general, the second oxidation peak is 2-
or 3-fold larger than the first, pointing to an unstable doubly
oxidized species that partially reverts to being singly oxidized
before being reoxidized (Figure 6). Compound 7 has an
additional oxidation peak at Ep = 0.23 V, ascribed to the
presence of the ferrocenyl group, oxidized at higher potential
than that for the free ferrocene (Ep = −0.01 V). Taken together
and in the context of all corrole compounds, these measure-
ments underscore the electron-withdrawing nature of the
supporting tpfc ligand. This macrocyclic ligand is also
electrochemically different from the porphyrin analogue
found at lower potential.14 Also, the first corrole ring oxidation
in compound 7 is shifted positively (Ep = 0.70 V) relative to the
other compounds. The absolute potential difference ΔE1/2
between the first reversible oxidation/reduction in 2−6 is
∼2.04
0.02 V, indicative of exclusive corrole-based redox
activity (see the Supporting Information). Sn4+ is effectively
inactive toward reduction. For compound 7, the ferrocenyl
moiety is oxidized at 0.20 V before oxidation of the macrocycle
occurs. The value of the highest occupied molecular orbital
(HOMO)−lowest unoccupied molecular orbital (LUMO) gap
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Figure 5. Absorption (black lines) and emission spectra (blue lines) of compounds 2−7 (toluene, 1.0 × 10−6 M). Excitation at Q bands.
Table 1. Photophysical Properties for Compounds 2−7 (Toluene, 290 K)
a
b
compound
Soret bands (nm)
Q bands (nm)
λemis (nm)
Stokes shift, (cm−1
)
ΦF × 103
τ1 (ns)
τ2 (ns)
2
3
4
5
6
7
428
428
428
426
425
536, 577, 608
536, 577, 606
535, 576, 606
536, 575, 604
535, 574, 601
535, 576, 606
616
614
614
612
608
c
217
213
213
216
192
c
5.0 0.31
4.57 0.08
4.23 0.22
5.04 0.14
6.71 0.12
c
0.310
0.310
0.307
0.312
0.353
c
1.784
2.371
2.005
1.25
425
c
a
b
c
Excited at Q band. Relative to the fluorescence of ZnTPP (Φ = 0.033).38 Too weak to be measured.
of 2.04 0.02 V, obtained experimentally by electrochemical
methods, is in good agreement with previously reported values
for metallocorroles15,12b and metalloporphyrins.34 However,
this value is smaller than that for compound 1 (ΔE1/2 = 2.14
V).12b This electronic gap is consistent with other acquired
data; the observed red-shifted Soret and Q bands also define a
shift toward lower energy for the S0−S2 and S0−S1 transitions.
This bathochromic shift is a desirable feature for potential near-
IR emission sensing purposes based on this design (Figure 5).
Organotin transformations were also studied, as monitored
by 1H NMR spectroscopic and UV−vis/photoluminescent
cuvette studies. In these reactions, the axial ligand generally
undergoes a facile reaction to cleanly afford a new axial group.
Treatment of compound 5 with I2 gives clean Sn−C6H5 bond
cleavage and corrole−Sn−I bond formation (Figure 7).30,35
The proton signals assigned to the phenyl group in 5
completely disappear after 2 days at 25 °C. New signals that
appear in the aromatic region can be confidently assigned to the
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Figure 6. Compilation of cyclic voltammogram data for compounds 2−7. The CH3CN solvent was used with 0.1 M TBAP at a scan rate of 0.1 V·s−1,
with E1/2 in volts.
Figure 7. Scheme of, and spectroscopic data supporting, the cleavage of the Sn−C bond in compound 5 upon treatment with I2. 1H NMR spectra
are of compound 5 before (a) and after (b) the addition of I2.
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protons of phenyl iodide.36 Also, signals of β-pyrrolic protons
are shifted downfield by 0.1 ppm; chemical shift values are close
to those of the chloride derivative 1 but not to the metal-free
corrole.12b This NMR spectroscopic observation helps for the
easy assignment of tin−iodide derivative formation. Further, it
was noticed that, under the same conditions, the aryl−Sn bond
is more reactive to halogens than the alkyl−Sn bond.30,37 When
the same reaction was carried out for compound 2, no product
formation was detected by 1H NMR spectroscopy, even after 1
week (25 °C). Anions such as iodide were also tested for
completeness to determine whether oxidation is possible with
closely related species. Unlike I2, I− gave no optical/
photoluminescent change; Br− and Cl− (as K+ salts) also
gave no responses (see the Supporting Information).
ACKNOWLEDGMENTS
■
The Molecular Logic Gate laboratory, operated by D.G.C.,
acknowledges support from the Korea Science and Engineering
Foundation (KOSEF; Grant R01-2008-000-12388-0) and the
National Research Foundation of Korea (Grant N01090203).
J.K. acknowledges support from the Nano/Bio Science &
Technology Program (Grant 2010-0008213) of the Ministry of
Education, Science and Technology.
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IV. CONCLUSIONS
In conclusion, alkyl and aryl derivatives of tin 5,10,15-
tris(pentafluorophenyl)corrolate have been prepared and
studied by different characterization techniques. The derivatives
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1
Among other data, H and 13C NMR spectroscopic signals of
the axial group were assigned and closely inspected to help
quantify various positional effects imposed on one these atoms
by the ring-current and tin-proton (119Sn−1H and 119Sn−13C)
through-bond coupling. The influence of the ring current and
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This so-called “double stamping” has now been expanded here
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ASSOCIATED CONTENT
■
S
* Supporting Information
(7) Ou, Z.; Shen, J.; Shao, J.; E, W.; Galezowski, M.; Gryko, D. T.;
Kadish, K. M. Inorg. Chem. 2007, 46, 2775−2786.
Multinuclear NMR, full reproductions of NMR spectra,
compiled UV−vis spectra, mass spectra, tables, textual passages
of discussion and experimental protocol, X-ray diffraction
structures, and packing diagrams. This material is available free
of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: Juhyoun_Kwak@kaist.ac.kr (J.K.), dchurchill@kaist.
ac.kr (D.G.C.).
Notes
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The authors declare no competing financial interest.
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