Synthesis and characterization of fluorescent pyrrolyldipyrrinato Sn(IV) complexes

Article abstract of DOI:10.1021/ic200731t

A series of neutral, 5-coordinate pyrrolyldipyrrinato Sn(IV) complexes have been synthesized via reaction of a pyrrolyldipyrrin, or its corresponding hydrochloride salt, with dibutyltin or diphenyltin oxide. The complexes are structurally unique in that a

Full text of DOI:10.1021/ic200731t

ARTICLE
pubs.acs.org/IC
Synthesis and Characterization of Fluorescent Pyrrolyldipyrrinato
Sn(IV) Complexes
Sarah M. Crawford, Adeeb Al-Sheikh Ali,† T. Stanley Cameron, and Alison Thompson*
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada
S Supporting Information
b
ABSTRACT: A series of neutral, 5-coordinate pyrrolyldipyrri-
nato Sn(IV) complexes have been synthesized via reaction of a
pyrrolyldipyrrin, or its corresponding hydrochloride salt, with
dibutyltin or diphenyltin oxide. The complexes are structurally
unique in that all three nitrogen atoms of the pyrrolyldipyrri-
nato ligand bind to the tin center, making these complexes the
first examples of pyrrolyldipyrrins behaving as LX2 ligands. The
complexes are highly fluorescent, exhibiting fluorescence quan-
tum yields between 0.28 and 0.61, and display interesting
preliminary biological activity.
’ INTRODUCTION
coordinating to copper(II) through all three atoms of the tripyr-
rolic core;12 however, in this case, the prodigiosin C-ring is
oxidized, and so the tripyrrolic core is no longer a pyrrolyldipyrrin.
Despite these few examples, pyrrolyldipyrrins are potentially
interesting ligands as they can coordinate in the same fashion as a
dipyrrinato ligand and have a pyrrolic substituent in the 9-posi-
tion. The pyrrole, or pyrrolide, could also coordinate to a metal
center, either in an η1 interaction through the nitrogen atom or
in an η5 interaction to give a π complex. Herein, we report
the synthesis and properties of fluorescent pyrrolyldipyrrinato
Sn(IV) complexes that exhibit moderate to high fluorescence
quantum yields.
Dipyrrinato boron complexes (BODIPYs) are the largest and
most well-studied class of dipyrrinato complexes due to their
high thermal, photochemical, and physiological stability, chemi-
cal robustness, and high fluorescence efficiency.1 There has been
an increasing number of reports of dipyrrinato complexes of
other metals, which also exhibit fluorescence. Indeed, homoleptic
dipyrrinato complexes (ML2 and ML3) of Zn(II),2,3 In(III), and
Ga(III)4 where the meso-aryl groups of the corresponding
dipyrrinato ligand are rotationally restricted exhibit small to
moderate fluorescence quantumyields. Furthermore, a homoleptic
Rh(III) complex (ML3) with rotationally unrestricted meso-aryl
groups has also been reported to be weakly fluorescent.5 Hetero-
leptic dipyrrinato complexes (MLXn) of Zn(II),6 Sn(II),7 and
Pt(II)8 where the meso-aryl groups of the corresponding dipyrri-
nato ligand are rotationally restricted also exhibit small to large
fluorescence quantum yields. Recently, several strongly fluorescent
π-extended dipyrrinato zinc(II) and calcium(II)9 complexes
(MLX) have been reported along with some highly fluorescent
aluminum(III)10 dipyrrinato complexes (MLX2). With these ex-
amples, the development of fluorescent dipyrrinato metal com-
plexes is underexplored.
Pyrrolyldipyrrins are a subclass of dipyrrins extended through
the presence of a pyrrole in the 9-position. Many pyrrolyldipyr-
rins, including the natural product prodigiosin, have been
isolated and synthesized, in part due to interest in the biological
activity of members of the prodigiosene family.11 In contrast,
pyrrolyldipyrrinato complexes are rare (Figure 1). Homoleptic
zinc(II) complexes, where two dipyrrinato units of two identical
pyrrolyldipyrrins bind to the zinc metal center, are known for
prodigiosin12 and several synthetic pyrrolyldipyrrins.13ꢀ15 Fluo-
rescent boron difluoride complexes (F-BODIPYs) of synthetic
pyrrolyldipyrrins are also known.16,17 There is also an example of
a tripyrrolic analogue, with an oxidized C-ring, cf. prodigiosin,
A small amount of a highly fluorescent material (2a) was
isolated from an attempted transesterification reaction of 1a,18
which employed catalytic amounts of dibutyltin oxide.19 We
postulated that 2a was a 5-coordinate, pyrrolyldipyrrinato Sn(IV)
complex in which the tin center was coordinated to all three
nitrogen atoms of the pyrrolyldipyrrinato core. To our knowl-
edge, there are no examples of dipyrrinato Sn(IV) complexes;
however, there are a number of Sn(IV) dipyrromethane com-
plexes. Such complexes are formed by adding dibutyltin dichlor-
ide to a solution of the dipyrromethane and were developed as
part of a purification strategy for dipyrromethanes.20 There are a
number of restrictions on the scope of the Sn(IV) complexation:
only tin complexes of dipyrromethanes with diketo,20 diformyl,20
and diester21 substituents in the 1- and 9-positions are known,
and these flanking carbonyl moieties play a coordinative role.
There is only one example of a diester dipyrromethane tin
complex, and it was synthesized using hexabutylditin as the tin
reagent.21
Received: April 8, 2011
Published: July 25, 2011
r
2011 American Chemical Society
8207
dx.doi.org/10.1021/ic200731t Inorg. Chem. 2011, 50, 8207–8213
|

Inorganic Chemistry
ARTICLE
Figure 1. Complexes of pyrrolyldipyrrins.
To further investigate the scope, structure, and optical proper-
ties of pyrrolydipyrrinato Sn(IV) complexes, a series of pyrrolyl-
dipyrrinato tin complexes were synthesized by varying the
substituents about the pyrrolyldipyrrin skeleton and the substit-
uents on the tin center. Pyrrolyldipyrrins 1aꢀ1f (or their
corresponding hydrochloride salts) (Figure 2) were selected as
pyrrolyldipyrrins for further investigation.
The selected pyrrolyldipyrrins contain a variety of substituents
about the pyrrolyldipyrrin skeleton. Compounds 1aꢀ1c contain
a methoxy group at the R2 position, making them members of the
prodigiosene family, which is characterized by the 7-methoxy-
pyrrolyldipyrrin unit. Compounds 1d and 1e maintain the ester
functionality at R1 but contain alkyl substituents at the R2 and R3
positions. Compound 1f also contains an alkyl group at the R1
position. To our knowledge, there are no dipyrrinato complexes,
other than the pyrrolyldipyrrinato complexes previously dis-
cussed, that contain a methoxy group in the 7-position. For that
reason, we chose compounds 1dꢀ1f, containing the alkyl- and
carbonyl-based substituents, to mirror typical dipyrrinato
complexes.22 Utilizing a ligand (1f) that was free of carbonyl
functionality was also of interest because the carbonyl function-
ality could potentially play a role in stabilizing the tin center in an
intermolecular interaction, as such an interaction had been
observed to be key to the stability of the Sn(IV) dipyrromethane
complexes.20
Figure 2. Pyrrolyldipyrrins (1).
1
reference for H and 13C, BF3 OEt2 as an external reference for 11B,
3
C6H5CF3 as an external reference for 19F, and Sn(CH3)4 as an external
reference for 119Sn. Splitting patterns are indicated as follows: br, broad;
s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. All coupling
constants (J) are reported in Hertz (Hz). Mass spectra were obtained
using ion trap (ESI) instruments operating in positive mode. Melting
points are reported uncorrected. Column chromatography was per-
formed using 230ꢀ400 mesh ultra pure silica or 150 mesh Brockmann
III activated, basic alumina oxide, as indicated.
General Procedure for the Synthesis of Dibutyl Tin Com-
plexes (GP1). To a solution of prodigiosene 1 (free base or HCl salt)
(0.05 mmol) in methanol (3 mL) was added dibutyltin oxide (0.07
mmol). The resulting solution was stirred at 65 °C for 18 h and then
dried in vacuo. The residue was dissolved in ethyl acetate and poured
onto a saturated aqueous solution of sodium bicarbonate (20 mL) and
extracted with ethyl acetate (3 ꢁ 20 mL). The organic fractions were
combined, dried with sodium sulfate, and the solvent was removed in
vacuo to give the crude product.
General Procedure for the Synthesis of Diphenyl Tin
Complexes (GP2). To a solution of prodigiosene 1 (free base or
HCl salt) (0.05 mmol) in methanol (3 mL) was added diphenyltin oxide
(0.10 mmol). The resulting solution was stirred at 65 °C for 18 h and
then dried in vacuo. The residue was dissolved in ethyl acetate and
poured onto a saturated aqueous solution of sodium bicarbonate
(20 mL) and extracted with ethyl acetate (3 ꢁ 20 mL). The organic
fractions were combined, dried with sodium sulfate, and the solvent was
removed in vacuo to give the crude product.
Pyrrolyldipyrrins 1a18 and 1c23 are known compounds and
were synthesized according to literature procedures. Pyrrolyldi-
pyrrin 1b was synthesized via the acylation of pyrrolyldipyrrin 1a
using a known procedure.24 Compounds 1d and 1e were
synthesized in four steps using a modification of D’Alessio’s
methodology,24,25 and 1f was synthesized via a Suzuki coupling
between an unsymmetrical bromodipyrrin26 and N-Boc-pyrrole-
2-boronic acid. Details of the syntheses of 1b, 1d, 1e, and 1f
including synthetic schemes and characterization of intermedi-
ates can be found in the Supporting Information.
General Procedure for Absorbance and Emission Mea-
surements. The absorbance measurements were performed using a
CARY 100 Bio UV/visible spectrophotometer. The fluorescence mea-
surements were performed using a Shimadzu RF-5301PC spectro-
fluorimeter. A 10 mm quartz cuvette was used in all measurements.
For the fluorescence experiments, the slit width was 3 nm for both
excitation and emission. Relative quantum efficiencies of derivatives
were obtained by comparing the areas under the emission spectra of the
’ EXPERIMENTAL SECTION
General Experimental. All 1H NMR (500 MHz), 13C NMR (125
MHz), 11B NMR (160 MHz), 19F NMR (285.2 MHz), and 119Sn NMR
(186 MHz) spectra were recorded on a Bruker Avance AV-500 spectro-
meter. Chemical shifts are expressed in parts per million (ppm) using the
solvent signal [CDCl3 (1H 7.26 ppm; 13C 71.16 ppm)] as an internal
8208
dx.doi.org/10.1021/ic200731t |Inorg. Chem. 2011, 50, 8207–8213

Inorganic Chemistry
ARTICLE
test with that of a solution of rhodamine 101 in ethanol (ΦF = 0.96) or
rhodamine 6G in ethanol (ΦF = 0.94).27 The excitation wavelength was
520 nm for rhodamine 6G, 2a, 2b, 2c, 3c, and 4a. The excitation
wavelength was 546 nm for rhodamine 101, 2d, 3d, 2e, and 3d.
Quantum yields were determined using eq 1.28
hexanes as an eluent and removal of the solvent in vacuo gave 2d as
a dark purple solid (36 mg, 0.056 mmol, 86%). mp = 91ꢀ93 °C; δH
(500 MHz, CDCl3) 7.47ꢀ7.45 (2H, m), 7.40ꢀ7.38 (2H, m), 7.35ꢀ7.32
(1H, m), 6.99 (1H, m), 6.93 (1H, dd, J = 2,3), 6.83 (1H, s), 6.47 (1H, dd,
J = 2,3), 5.32 (2H, s), 2.74 (2H, q, J = 7), 2.65 (3H, s), 2.48 (3H, s), 2.27
(3H, s), 1.49ꢀ1.41 (8H, m), 1.26ꢀ1.18 (7H, m), 0.75 (6H, t, J = 8);
δC (125 MHz, CDCl3) 165.8, 157.2, 152.7, 144.6, 138.2, 137.8, 137.1,
134.2, 132.0, 131.8, 131.3, 128.6, 128.2, 128.0, 115.6, 115.5, 114.2, 113.0,
65.4, 27.0, 26.5, 23.9, 18.5, 17.4, 14.2, 13.6, 12.4, 9.9; δSn (186 MHz,
!
ꢀ
ꢁꢀ
ꢁ
IX
Ist
Ast
AX
ηX2
η2st
ϕX ¼ ϕst
ð1Þ
CDCl3) ꢀ214.2; UV/vis (DCM) λmax (nm): 585, ε 87 000 mol Lꢀ1 cmꢀ1
.
where ϕst is the reported quantum yield of the standard, I is the area from
the integrated emission spectra, A is the absorbance at the excitation
wavelength, and η is the refractive index of the solvent used. The X
subscript denotes the unknown, and “st” denotes the standard.
Fluorescence (DCM) λexci (nm), 546; λmax (nm), 607. ΦF: 0.52. m/z ESI+
found 645.2473 [M + H]+, calculated for C34H44N3O2Sn 645.2450.
[(Bu)2(1f)Sn(IV)] 2f Was Synthesized Using GP1. Purification over
basic alumina using an eluent gradient of hexanes to 1:10 ethyl acetate:
hexanes and removal of the solvent in vacuo gave 2f as a blue film (17 mg,
0.049 mmol, 22%). mp = 99ꢀ101 °C; δH (500 MHz, CDCl3)
6.91ꢀ6.90 (1H, m), 6.79 (1H, dd, J = 1,3) 6.75 (1H, s), 6.43 (1H, dd,
J = 2,3), 2.65 (2H, q, J = 7), 2.41 (2H, q, J = 7), 2.37 (3H, s), 2.26 (3H, s),
2.02 (3H, s), 1.49ꢀ1.38 (9H, m), 1.26ꢀ1.18 (9H, m), 1.07 (3H, t, J = 7),
0.78 (3H, t, J = 7); δC (125 MHz, CDCl3) 153.9, 150.3, 149.0, 135.1,
134.52, 134.50, 132.4, 129.7, 129.3, 121.2, 115.8, 112.7, 109.8, 27.1, 26.7,
23.3, 18.2, 17.9, 16.4, 15.2, 14.7, 13.6, 10.4, 10.0; δSn (186 MHz, CDCl3)
Synthesis. [(Bu)2(1a)Sn(IV)] 2a Was Synthesized Using GP1.
Purification over basic alumina using dichloromethane as an eluent
and removal of the solvent in vacuo gave 2a as a purple film (26 mg,
0.046 mmol, 93%). mp = 115ꢀ117 °C; δH (500 MHz, CDCl3)
6.97ꢀ6.95 (2H, m), 6.82 (1H, d, J = 3), 6.43 (1H, dd, J = 2,3), 6.06
(1H, s), 4.29 (2H, q, J = 7), 4.00 (3H, s), 2.64 (3H, s), 2.45 (3H, s), 1.65ꢀ
1.18 (15H, m), 0.75 (6H, t, J = 7); δC (125 MHz, CDCl3) 168.5, 166.1,
157.2, 152.1, 137.3, 133.4, 132.1, 132.0, 129.5, 115.7, 114.1, 113.8, 112.3,
92.7, 59.4, 58.6, 27.0, 26.4, 24.0, 17.3, 14.7, 13.6, 12.2; δSn (186 MHz,
CDCl3) ꢀ245.9; δN (50.7 MHz, CDCl3) ꢀ229.9, ꢀ165.5; UV/vis
(EtOH) λmax (nm): 568, ε 85 000 mol Lꢀ1 cmꢀ1. Fluorescence (EtOH)
λexci (nm), 520; λmax (nm), 579. ΦF: 0.57. m/z ESI+ found 594.1749
[M + Na]+, calculated for C27H37N3NaO3Sn 594.1755.
[(Bu)2(1b)Sn(IV)] 2b Was Synthesized Using GP1. Purification over
neutral alumina using 5% ethyl acetate in hexanes as an eluent and
removal of the solvent in vacuo gave 2b as a purple film (29 mg, 0.047
mmol, 95%). mp = 162ꢀ164 °C; δH (500 MHz, CDCl3) 7.18 (1H, s),
6.99 (1H, d, J = 3.5), 6.64 (1H, d, J = 3.5), 6.13 (1H, s), 4.30 (2H, q, J =
7.5), 4.00 (3H, s), 2.66 (3H, s), 2.50 (3H, s), 2.56 (3H, s), 1.66ꢀ1.49
(4H, m), 1.38 (3H, t, J = 7.5), 1.12ꢀ0.97 (8H, m), 0.59 (6H, t, J = 7); δC
(125 MHz, CDCl3) 189.6, 167.6, 165.8, 156.0, 153.9, 142.5, 139.6,
137.6, 135.3, 128.3, 120.0, 118.3, 117.5, 110.5, 93.0, 59.6, 58.6, 27.1, 25.8,
25.6, 23.9, 17.3, 14.7, 13.5, 12.3; δSn (186 MHz, CDCl3) ꢀ221.9; UV/
vis (DCM) λmax (nm): 568, ε 85 000 mol Lꢀ1 cmꢀ1. Fluorescence
(DCM) λexci (nm), 520; λmax (nm), 579. ΦF: 0.57. m/z ESI+ found
614.1993 [M + H]+, calculated for C29H39N3O4Sn 614.2035. A crystal
suitable for X-ray crystallography was obtained from a slow evaporation
of a solution of compound 2b in dichloromethane in the presence of few
drops of methanol. Data for 2b: C29H38N3O4Sn, M = 611.34 g, dark-red
needle, 0.42 ꢁ 0.23 ꢁ 0.12 mm3, primitive triclinic, space group P-1
(No. 2), a = 12.1339 Å, b = 13.04640(10) Å, c = 19.65300(10) Å, V =
2903.79(3) Å3, Z = 4, T = 200(1) K, F = 1.398 g cmꢀ3, μ(Mo KR) =
9.167 cmꢀ1, 106 009 reflections (22 429 unique, Rint = 0.065), R =
0.0358, Rw = 0.0439, GOF = 1.082.
ꢀ253.3; UV/vis (DCM) λmax (nm): 599, ε 120 000 mol Lꢀ1 cmꢀ1
.
Fluorescence (DCM) λmax (nm): 617. ΦF: 0.28. m/z ESI+ found
540.2354 [M + H]+, calculated for C28H42N3Sn 540.2395.
[(Ph)2(1c)Sn(IV)] 3c Was Synthesized Using GP2. Purification over
basic alumina using dichloromethane as an eluent and removal of the
solvent in vacuo gave 3c as a purple film (40 mg, 0.059 mmol, 82%). mp
= 262 ꢀ264 °C; δH (500 MHz, CDCl3) 7.61ꢀ7.59 (4H, m, tin satellites
3
1
at tin satellites at 7.69ꢀ7.67 and 7.52ꢀ7.51, J (119Snꢀ H) = 40),
7.44ꢀ7.31 (12H, m), 7.12 (1H, s), 6.82 (1H, dd, J = 1,3), 6.49 (1H, dd,
J = 2,3), 6.04 (1H, s), 5.29 (2H, s), 3.98 (3H, s), 2.58 (3H, s), 2.14 (3H,
s); δC (125 MHz, CDCl3) 168.9, 165.8, 157.1, 154.3, 141.0, 138.1,
137.4, 136.9, 135.4, 134.2, 133.5, 131.6, 130.1, 129.9, 129.2, 128.9, 128.8,
128.6, 128.3, 128.0, 127.4, 127.3, 115.9, 114.8, 113.7, 93.0, 65.5, 58.7,
18.1, 12.6. δSn (186 MHz, CDCl3) 367.1; UV/vis (DCM) λmax (nm):
561, ε 74 000 mol Lꢀ1 cmꢀ1. Fluorescence (DCM) λmax (nm), 520;
λmax (nm), 583. ΦF: 0.55. m/z ESI+ found 674.1465 [M + H]+,
calculated for C36H32N3O3Sn 674.1460.
[(Ph)2(1e)Sn(IV)] 3e Was Synthesized Using GP2. The crude ma-
terial was dissolved in dichloromethane, the resulting solution was
filtered through basic alumina eluting with dichloromethane, and the
solvent was removed in vacuo. Purification over basic alumina using 1:1
dichloromethane:hexanes as an eluent and removal of the solvent in
vacuo gave the methyl ester 3e as a dark purple film (41 mg, 0.06 mmol,
75%). mp = 254ꢀ256 °C; δH (500 MHz, CDCl3) 7.60ꢀ7.59 (4H, m,
1
tin satellites at 7.69ꢀ7.67 and 7.52ꢀ7.51, 3J (119Snꢀ H) = 40),
[(Bu)2(1c)Sn(IV)] 2c Was Synthesized Using GP1. Purification over
basic alumina using dichloromethane as an eluent and removal of the
solvent in vacuo gave 2c as a purple film (57 mg, 0.09 mmol, 90%). mp =
120ꢀ122 °C; δH (500 MHz, CDCl3) 7.46ꢀ7.44 (2H, m), 7.40ꢀ7.37
(2H, m), 7.34ꢀ7.31 (1H, m), 6.95ꢀ6.94 (1H, m), 6.94 (1H, s), 6.83
(1H, dd, J = 1,3), 6.43 (1H, dd, J = 2,3), 6.13 (1H, s) 5.30 (2H, s), 4.00
(3H, s), 2.63 (3H, s), 2.45 (3H, s), 1.52ꢀ1.39 (8H, m), 1.22ꢀ1.18 (4H,
m), 0.75 (6H, t, J = 8); δC (125 MHz, CDCl3) 168.6, 165.8, 157.4, 152.2,
137.3, 137.1, 133.4, 132.2, 132.2, 132.0, 129.6, 128.6, 128.2, 128.0, 115.3,
114.2, 113.7, 112.5, 65.4, 58.6, 27.0, 26.4, 24.0, 17.4, 13.6, 12.3; δSn (186MHz,
7.52ꢀ7.51 (1H, m), 7.36ꢀ7.31 (6H, m), 6.99 (1H, s), 6.92ꢀ6.91
(1H, m), 6.52 (1H, dd, J = 2,3), 3.81 (3H, s), 2.68 (2H, q, J = 8), 2.60
(3H, s), 2.27 (3H, s), 2.12 (3H, s), 1.19 (3H, t, J = 8); δC (125 MHz,
CDCl3) 166.5, 156.9, 154.7, 145.0, 141.1, 138.7, 138.3, 135.4, 135.0,
133.3, 132.1, 131.0, 130.0, 129.2, 116.5, 115.6, 114.9, 113.9, 50.8, 18.5,
18.0, 14.1, 12.4, 9.9; 15N HMBC δN (CDCl3) ꢀ178.2, ꢀ217.9; δSn (186
MHz, CDCl3) 363.5; UV/vis (DCM) λmax (nm): 587, ε 86 000 mol
L
ꢀ1 cmꢀ1. Fluorescence (DCM) λexci (nm), 546; λmax (nm), 609. ΦF:
0.51. m/z ESI+ found 610.1524 [M + H]+, calculated for C32H32N3O2Sn
610.1511.
CDCl3) ꢀ209.5; UV/vis (DCM) λmax (nm): 561, ε 88 000 mol Lꢀ1 cmꢀ1
.
[(Ph)2(1f)Sn(IV)] 3f Was Synthesized Using GP2. The crude material
was dissolved in dichloromethane, the resulting solution was filtered
through basic alumina eluting with dichloromethane, and the solvent
was removed in vacuo. Purification over basic alumina using 1:5
dichloromethane:hexanes as an eluent and removal of the solvent in
vacuo gave 3f as a blue film (13 mg, 0.022 mmol, 33%). mp =
225ꢀ227 °C; δH (500 MHz, CDCl3) 7.64ꢀ7.62 (4H, m, with tin
Fluorescence (DCM) λexci (nm), 520; λmax (nm), 584, ΦF: 0.53. m/z ESI+
found 634.2082 [M + H]+, calculated for C32H40N3O3Sn 634.2086.
[(Bu)2(1d)Sn(IV)] 2d Was Synthesized Using GP1. The crude
material was dissolved in dichloromethane and filtered through basic
alumina eluting with dichloromethane, and the solvent was removed
in vacuo. Purification over basic alumina using 1:1 dichloromethane:
8209
dx.doi.org/10.1021/ic200731t |Inorg. Chem. 2011, 50, 8207–8213

Inorganic Chemistry
ARTICLE
Scheme 1. General Synthetic Scheme for the Synthesis of
Pyrrolyldipyrrinato Sn(IV) Complexes
Scheme 2. Synthesis of Pyrrolyldipyrrinato F-BOIDPY
Complex 4a
Table 1. Yields of Pyrrolyldipyrrinato Sn(IV) Complexes
R1
R2
R3
R4
isolated yield/%
Figure 3. Thermal ellipsoid diagram (50%) of a twinned crystal of 2b.
Sn(1) butyl groups and all hydrogen atoms are removed for clarity.
Selected bond distances (Å): Sn(1)ꢀN(1), 2.309(2); Sn(1)ꢀN(2),
2.128(2); Sn(1)ꢀN(3), 2.239(2). Selected bond angles (deg):
N(1)ꢀSn(1)ꢀ(N2), 81.46(9); N(1)ꢀSn(1)ꢀN(3), 155.25(10);
N(2)ꢀSn(1)ꢀN(3), 73.85(10); C(43)ꢀSn(1)ꢀC(47), 137.84(14)
(C(43) and C(47) are the carbon atoms of each attached butyl group,
respectively).
2a
2b
2c
3c
2d
3e
2f
CO2Et
CO2Et
CO2Bn
CO2Bn
CO2Bn
CO2Me
Et
OMe
OMe
OMe
OMe
Et
H
H
93
95
90
82
86
84
22
33
H
C(O)Me
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Et
Et
3f
Et
Et
(DCM) λmax (nm): 536, ε 184 000 mol Lꢀ1 cmꢀ1. Fluorescence
(DCM) λexci (nm), 520; λmax (nm), 551. ΦF: 0.92. m/z ESI+ found
410.1458 [M + Na]+, calculated for C19H20BF2N3O3Na 410.1463. A
crystal suitable for X-ray crystallography was obtained from a slow
evaporation of a solution of compound 4a in dichloromethane. Data for
4a: C19H20N3O3BF2, M = 387.19 g, dark-red, needle, 0.39 ꢁ 0.13 ꢁ 0.08
mm, primitive monoclinic, P21/c (No. 14), a = 7.3029(4) Å, b =
25.1293(11) Å, c = 9.7763(5) Å, V = 1779.52(15) Å3, Z = 4, T = 123(1)
K, F = 1.445 g cmꢀ3, μ(Mo KR) = 1.116 cmꢀ1, 52 752 reflections
(19 174 unique, Rint = 0.074), R = 0.0441, Rw = 0.0557, GOF = 1.022.
satellites at 7.72ꢀ7.70 and 7.56ꢀ7.54, 3J (119Snꢀ H) = 40), 7.40ꢀ7.31
(7H, m), 6.90 (1H, s), 6.77 (1H, dd, J = 1,3), 6.47 (1H, dd, J = 2,3), 2.66
(2H, q, J = 7), 2.39 (2H, q, J = 7), 2.32 (3H, s), 2.20 (3H, s), 1.79 (3H, s),
1.21 (3H, t, J = 7), 1.05 (3H, t, J = 7); δC (125 MHz, CDCl3) 153.5,
152.7, 149.4, 141.8, 136.1, 135.8, 135.6, 134.8, 132.0, 131.0, 130.0, 129.7,
128.9, 121.7, 115.8, 113.4, 110.8, 18.3, 17.9, 16.3, 15.3, 15.2, 10.3 (1 C
missing, alkyl region); δSn (186 MHz, CDCl3) 363.0; UV/vis (DCM)
λmax (nm): 603, ε 87 000 mol Lꢀ1 cmꢀ1. Fluorescence (DCM) λexci
(nm), 546; λmax (nm), 622. ΦF: 0.32. m/z ESI+ found 579.1694 [M]+,
calculated for C32H33N3Sn 579.1691.
1
[(1a)BF2] (4a). To a solution of 1aHCl (25 mg, 0.07 mmol) in dry
dichloromethane under a nitrogen atmosphere was added triethylamine
(0.2 mL, 1.4 mmol, 21 equiv). The resulting reaction mixture was stirred
’ RESULTS AND DISCUSSION
Pyrrolyldipyrrins 1a, 1b, 1c, 1e, and 1f were converted to their
corresponding dibutyltin complexes (2a, 2b, 2c, 2e, and 2f) by
heating a methanolic solution of each pyrrolyldipyrrin with an
excess of dibutyltinxide at reflux temperature for a period of 18 h.
Similarly, pyrrolyldipyrrins 1c, 1e, and 1f were converted into
their corresponding diphenyltin complexes (3c, 3e, and 3f) by
heating a methanolic solution of pyrrolyldipyrrin with an excess
of diphenyltin oxide at reflux temperature (Scheme 1, Table 1).
The conversion of pyrrolyldipyrrin to the corresponding
Sn(IV) complex was quantitative according to analysis using
TLC, and the isolated yields of the pyrrolyldipyrrinato dibutyl
and diphenyl Sn(IV) complexes were high with the exception of
the fully alkyl substituted derivatives 2f and 3f (Table 1). The
diphenyltin complexes (3c, 3d, and 3f) exhibited some decom-
position to return the pyrrolyldipyrrin starting material upon
purification over neutral or basic alumina, a procedure that was
for 10 min, then BF3 OEt2 (0.2 mL, 1.1 mmol, 17 equiv) was added
3
slowly, and the resulting mixture was stirred at room temperature for 2 h.
The reaction mixture was poured into a 5% aqueous solution of citric
acid (20 mL) and extracted with ether (20 mL). The organic layer was
washed with 5% aqueous citric acid (3 ꢁ 20 mL), dried over Na2SO4,
and concentrated in vacuo. Filtration over a pad of silica eluting with
dichloromethane followed by concentration in vacuo gave 4a as a purple,
crystalline solid (28 mg, 0.07 mmol, 100%). mp = 210ꢀ211 °C; δH (500
MHz, CDCl3) 10.5 (1H, s), 7.15ꢀ7.13 (1H, m), 7.13 (1H, s),
6.94ꢀ6.92 (1H, m), 6.39ꢀ6.37 (1H, m), 6.14 (1H, s), 4.31 (2H, q,
J = 7), 3.99 (3H, s), 2.80 (3H, s), 2.43 (3H, s), 1.37 (3H, t, J = 7); δC
(125 MHz, CDCl3) 165.4, 164.3, 152.9, 151.4, 136.5, 129.4, 129.3,
126.4, 123.5, 118.6, 117.8, 115.0, 111.7, 97.2, 59.7, 58.7, 14.6, 14.4, 11.8;
δB (80.25 MHz, CDCl3) 1.06 (t, JBF = 36); δF (235.2 MHz, CDCl3)
ꢀ139 (q, JFB = 31); 15N HMBC δN (CDCl3) ꢀ198.3, ꢀ221.6. UV/vis
8210
dx.doi.org/10.1021/ic200731t |Inorg. Chem. 2011, 50, 8207–8213

Inorganic Chemistry
ARTICLE
Figure 5. Complexes 2, 3, and 4 in dichloromethane solution (∼7.0 ꢁ
10ꢀ5 M) visualized under ambient light (top) and long wave UV
irradiation (bottom).
Figure 4. Thermal ellipsoid diagram (50%) of 4a. Hydrogens removed
for clarity. Selected bond distances (Å): B(1)ꢀN(1), 2.309(2);
B(1)ꢀN(2), 2.128(2). Selected bond angles (deg): N(1)ꢀB(1)ꢀ(N2),
81.46(9). Selected torsional angles (deg): N(1)ꢀC(1)ꢀC(10)ꢀ(N3),
structure first with twinned data led to the possible location of
the composite plane, which allowed for dissection of a fragment
of untwinned crystal (Figure 3). The disorder still present in the
crystal is likely dynamic as the crystal survives cooling to ꢀ73 °C,
but shatters, after some time, when cooled to ꢀ93 °C. The
structure shows a pentacoordinate tin atom with distorted
trigonal bypyramidal geometry. All three nitrogen atoms of the
pyrrolyldipyrrin are coordinated to the tin center, making this
structure, to the best of our knowledge, the first of its kind.
The complex has distorted trigonal bipyramidal geometry.
The N(3)ꢀSn(1)ꢀN(1) bond angle of 155.25(10)° is the
largest of the angles involving the tin center, suggesting that
N(1) and N(3) are occupying the pseudoaxial positions in the
complex. However, the C(43)ꢀSn(1)ꢀC(47) bond angle is
larger than the 120° normally separating equatorial substituents
in a trigonal bipyramidal complex with a value of 137.84(14)°.
The bond angles between N(1)ꢀSn(1) or N(3)ꢀSn(1) and the
equatorial atoms (N(2), C(43), C(47)) range from 73° to 95° ,
while the bond angles between C(43)ꢀSn(1) or C(47)ꢀSn(1)
and N(1), N(2), or N(3) range from 93° to 112°. The trigonal
pyramidal geometry is significantly distorted in the complex,
likely due to the restrictions imposed by the rigid pyrrolyldipyr-
rinato ligand framework. The tinꢀnitrogen bond lengths in
complex 2b range from 2.128 to 2.309 Å. These bond lengths
are within the reported ranges of other nitrogen tin bonds in
neutral, pentacoordinate Sn(IV) complexes.29ꢀ31
The coordinated pyrrolyldipyrrinato unit is essentially planar
in complex 2b. In the X-ray crystal structure of the hydrochloride
salt of 1a, which contains a pyrrolyldipyrrinato unit similar to 2b
(differing only in an acyl group on the pyrrole ring), the
pyrrolydipyrrin is also planar (see Supporting Information,
Figure S1). This planarity has also been observed in other crystal
structures of pyrrolyldipyrrin hydrochloride salts and is enforced
by hydrogen bonds between the chloride counteranion and the
pyrrolyldipyrrin,32 but not all hydrochloride salts exhibit this
planarity.33 Interestingly, in the F-BODIPY 4a, the uncoordi-
nated pyrrole unit is 16° out of the plane of the coordinated
dipyrrinato unit (Figure 4). This twist may accommodate a
hydrogen bond between the hydrogen attached to the pyrrolic
nitrogen atom and the fluorine atom below the dipyrrinato plane
with a contact distance of 1.860 nm.
ꢀ16.09. Contact distance (Å): N(3)ꢀH F(1), 1.860.
3 3 3
Table 2. Optical Properties of Tin Pyrrolyldipyrrinato
Complexes and BODIPY Complex 4a in DCM at 22 °C
complex abs λmax (nm) ε (ꢁ104 mol Lꢀ1 cmꢀ1
) em λmax (nm) ΦF
2a
2b
2c
2d
2f
561
570
561
585
599
561
587
603
543
8.78
11.6
584
582
584
607
617
583
609
622
559
0.53a
0.61a
0.53a
0.52b
0.28b
0.55a
0.51b
0.32b
0.92a
8.82
8.69
11.6
3c
3e
3f
7.40
8.63
8.70
4a
10.5
a Relative to rhodamine 6G in EtOH (ΦF = 0.94). b Relative to
rhodamine 101 in EtOH (ΦF = 0.96).
utilized to remove the excess diphenyltin oxide. Attempts to
optimize the reaction and purification were conducted using
pyrrolyldipyrrin 1c. Unfortunately, if only 1 equiv of diphenyltin
oxide was used in the reaction of 1c, the reaction was sluggish, and
small amounts of unreacted 1c remained in the reaction mixture
after 4 days at reflux temperature. Attempts to use crystallization as
a purification strategy were similarly unsuccessful.
Notably, the diphenyltin complexes (3) are less stable in
solution than their corresponding dibutyltin complexes (2) and
decompose to free ligand (1) slowly over the period of a week.
The diphenyltin and dibutyltin complexes are sensitive to acid,
and the corresponding pyrrolyldipyrrin HCl salts are generated
rapidly and quantitatively after adding aqueous hydrochloric acid
to a solution of the corresponding tin complex in a 1:1 solution of
dichloromethane and methanol.
For purposes of comparison in structure and fluorescence
properties, the boron difluoride (F-BODIPY) complex (4a) of
pyrrolydipyrrin 1a was synthesized in quantitative yield (Scheme 2).
A crystal of the dibutyltin complex 2b was obtained from a
slow evaporation of a dichloromethane solution in the presence
of a few drops of methanol. All crystals in the sample were found
to be nonmerohedral twins, and solving the X-ray crystal
Although the pyrrolyldipyrrin ligands do not display percep-
tible fluorescence, all of the synthesized tin complexes exhibit
appreciable fluorescence quantum yields (ΦF = 0.28ꢀ0.61) in
dichloromethane with maximum wavelengths of emission in the
8211
dx.doi.org/10.1021/ic200731t |Inorg. Chem. 2011, 50, 8207–8213

Inorganic Chemistry
ARTICLE
with an alkyl group (2f), the wavelength of maximum absorption
was bathochromically shifted 14 nm. The same trend is obser-
vable for the diphenyltin complexes (3). When the pyrrolyldi-
pyrrinato ligand was not modified, but the groups on the tin
center were changed from butyl to phenyl, there was little to no
effect on the wavelength of maximum emission or the quantum
yields of fluorescence for the related complexes (compare 2c and
2f with butyl substituents to 3c and 3f with aryl substituents).
All of the absorption spectra have a similar band structure in
the visible region: a large peak with a shoulder. This band
structure is commonly observed for dipyrrinato complexes.2,34
For each complex, the emission spectra are approximately the
mirror image of the absorption profile; however, the vibronic
features are less prominent in the emission spectra. The normal-
ized absorption and emission spectrum of tin complex 2b is
shown in Figure 6 as a representative example. The absorption
and emission spectra of the tin complexes 2 and 3 and BODIPY
4a can be found in the Supporting Information.
This high yielding route to dibutyltin complexation and
decomplexation allows for a potential new pyrrolyldipyrrin
purification strategy, similar to that for 1,9-carbonyl substituted
dipyrromethanes.20 Many pyrrolyldipyrrins of the prodigiosene
family are generated via a Suzuki coupling reaction with a boronic
acid containing pyrrole. If the reaction is not clean, the resulting
mixture is often difficult to purify, and so tin complexation has
promise as a useful purification strategy.
Figure 6. Normalized absorption (ꢀ ꢀ ꢀ) and emission (ꢀ) spectra of
2b obtained using 520 nm excitation in DCM at 21 °C.
orange region (584 and 622 nm). The complexes also exhibit
broad absorption bands between 550 and 625 nm (ε (7ꢀ11) ꢁ
104 Mꢀ1 cmꢀ1) (Table 2, Figure 5).
The F-BODIPY pyrrolyldipyrrinato complex (4a) has the
highest fluorescence quantum yield of the compounds (ΦF =
0.92), and this value is comparable to the fluorescence quantum
yields of other strongly emitting F-BODIPYs.1 The pyrrolyldi-
pyrrinato tin complexes show an interesting pattern in their
quantum yields based on the substitution pattern about the
ligand. When the ligand contains a conjugated ester substituent
(2a, 2b, 2c, 3c, 2d, and 3e), the fluorescence quantum yield was
high (ΦF > 0.50). However, when the ligand contained only alkyl
substituents (2f and 3f), the fluorescence quantum yields were
much lower (ΦF < 0.32). The Stokes shifts of the complexes are
small and range from 334 to 702 cmꢀ1 (11ꢀ23 nm).
Many organotin(IV) complexes with nitrogen-containing
ligands exhibit antimicrobial activity.35 Compound 2a was tested
for antimicrobial activity against several S. aureus, S. epidermidis,
P. aeruginosa, E. faecalis, and B. subtilis strains. However, the erythro-
mycin control had activity comparable to or better than that against
all of the strains with the exception of S. aureus 623 (a clinical
methicillin resistant Staphylococcus aureus isolate);36 compound 2a
was found to have a MIC of 2 μg mLꢀ1 against S. aureus 623, while
Dipyrrinato complexes with rotationally unrestricted meso
substituents generally exhibit little or no detectable fluorescence.
However, there are two examples of complexes that do exhibit
fluorescence: π-extended dipyrrinato complexes of Ca(II) and
Zn(II) (ΦF = 0.58ꢀ0.70)9 and a tetradentate N2O2-type dipyr-
rinato Al(III) complex (ΦF = 0.23).10 In the case of the
aluminum complex, the ligand is held in a rigid position by the
additional coordination of phenolic oxygens. In the case of the π-
extended dipyrrinato complexes, the ligands contain esters in the
1- and 9-positions, and the proximate carbonyl oxygen atoms
likely play a role in ligandꢀmetal bond stabilization. Our series of
pyrrolyldipyrrinato Sn(IV) complexes is a further example of
dipyrrinato-type complexes without rotationally restricted meso
groups that exhibit high fluorescence quantum yields. The added
rigidity induced through coordination of the flanking pyrrolide
binding unit reduces the number of pathways for nonradiative
decay, thereby allowing for higher observed fluorescence quantum
yields than those of traditional dipyrrinato complexes with only
two coordination sites. F-BODIPY 4a has the highest fluorescence
quantum yield of the synthesized complexes. In this case, the
pyrrolyldipyrrin rigidity is due to the presence of the hydrogen
bond between the unbound pyrrole and the neighboring fluorine.
The effects of changing the substituents around the pyrroly-
dipyrrinato core of the complexes are evident after analysis of the
wavelengths of maximum absorption. When the pyrrolyldipyrri-
nato ligand contained both ester and methoxy groups (2a and
2c), the wavelength of maximum absorption was 561 nm (2a and
2c). When the methoxy group was replaced with an alkyl group
(2d), the wavelength of maximum absorption shifted 24 nm
bathochromically, and when the ester group was also replaced
the erythromycin control had a MIC of >128 μg mLꢀ1
.
Pyrrolyldipyrrins of the prodigiosin family are known to
exhibit anticancer activity through several different mechanisms,
some of which require complexation of the tripyrrolic core to a
metal or anion.11 In addition, there are also several examples of
neutral, 5-coordinate tin complexes, which exhibit in vitro anti-
cancer activity.31,37 Preliminary tests against the NCI 60 cancer
cell lines indicate that compound 2c shows activity in all 60
cancer cell lines, and further evaluation of compounds 2c and 3c
is ongoing.
These biological results are preliminary as further studies are
necessary to address the stability of the tinꢀnitrogen bonds
under the test conditions. Although the observed biological
activities may be specific, they could alternatively be due to the
nonspecific action of hydrolyzed R2Sn+ moieties that are known
for their undesirable neurotoxicity and immune suppression.37
’ CONCLUSION
A methodology to access both dibutyl and pyrrolyldipyrrinato
complexes has been developed. Pyrrolyldipyrrins or their corre-
sponding HCl salts can be converted to there pyrrolyldipyrrinato
Sn(IV) complexes in high yields, with the exception of two
cases, by treatment with a diphenyl or dibutyl tin oxide. These
complexes exhibit a previously unknown binding mode in
which the pyrrolyldipyrrin is a tridentate dianionic ligand. These
complexes are strongly fluorescent (ΦF = 0.28ꢀ0.61), and sub-
stitution about the pyrrolyldipyrrin skeleton has been shown to
8212
dx.doi.org/10.1021/ic200731t |Inorg. Chem. 2011, 50, 8207–8213

Inorganic Chemistry
ARTICLE
influence the fluorescence quantum yields. Further studies into
their biological properties are ongoing.
(20) Tamaru, S.; Yu, L. H.; Youngblood, W. J.; Muthukumaran, K.;
Taniguchi, M.; Lindsey, J. S. J. Org. Chem. 2004, 69, 765–777.
(21) Kitamura, C.; Yamashita, Y. J. Chem. Soc., Perkin Trans. 1 1997,
1443–1448.
(22) Wood, T. E.; Thompson, A. Chem. Rev. 2007, 107, 1831–1861.
(23) Uddin, M. I.; Thirumalairajan, S.; Crawford, S. M.; Cameron,
T. S.; Thompson, A. Synlett 2010, 2010, 2561–2564.
(24) D’Alessio, R.; Bargiotti, A.; Carlini, O.; Colotta, F.; Ferrari, M.;
Gnocchi, P.; Isetta, A.; Mongelli, N.; Motta, P.; Rossi, A.; Rossi, M.;
Tibolla, M.; Vanotti, E. J. Med. Chem. 2000, 43, 2557–2565.
(25) D’Alessio, R.; Rossi, A. Synlett 1996, 513–514.
(26) Paine, J. B.; Hiom, J.; Dolphin, D. J. Org. Chem. 1988, 53, 2796–
2802.
’ ASSOCIATED CONTENT
S
Supporting Information. Synthetic schemes, experimen-
b
tal procedures, and characterization data for prodigiosene ligands
(free bases or HCl salts) (1b, 1d, 1e, and 1f); 13C NMR spectra
for all new compounds; and X-ray crystallographic data for
compounds 1aHCl, 2b, and 4a (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
(27) Rurack, K. Fluorescence Quantum Yields: Methods of Deter-
mination and Standards. In Standardization and Quality Assurance in
Fluorescence Measurements I; Resch-Genger, U., Ed.; Springer: Berlin,
Heidelberg, 2008; Vol. 5, pp 101ꢀ145.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: alison.thompson@dal.ca.
(28) Williams, A. T. R.; Winfield, S. A.; Miller, J. N. Analyst 1983,
108, 1067–1071.
Present Addresses
†Chemistry Department, Taibah University, Almadinah
Almunawarah, P.O. Box 30002, Saudi Arabia.
(29) Basu, S.; Gupta, G.; Das, B.; Rao, K. M. J. Organomet. Chem.
2010, 695, 2098–2104.
(30) Ramírez, A.; Gꢀomez, E.; Hernꢀandez, S. N. J. Organomet. Chem.
2009, 694, 2965–2975.
(31) Wiecek, J.; Dokorou, V.; Ciunik, Z.; Kovala-Demertzi, D.
Polyhedron 2009, 28, 3298–3304.
’ ACKNOWLEDGMENT
This work was supported by the Canadian Institutes of Health
Research (CIHR). We thank Dr. Srinivasulu Bandi, Dr. David L.
Jakeman, and Dr. Susan E. Douglas for the antimicrobial screen-
ing of compound 2a, and Dr. Md. Imam Uddin for assistance
with the preparation of 1a and 1c.
(32) Jenkins, S.; Incarvito, C. D.; Parr, J.; Wasserman, H. H.
CrystEngComm 2009, 11, 242–245.
(33) Sessler, J. L.; Eller, L. R.; Cho, W.-S.; Nicolaou, S.; Aguilar, A.;
Lee, J. T.; Lynch, V. M.; Magda, D. J. Angew. Chem., Int. Ed. 2005,
44, 5989–5992.
(34) Kee, H. L.; Kirmaier, C.; Yu, L.; Thamyongkit, P.; Youngblood,
W. J.; Calder, M. E.; Ramos, L.; Noll, B. C.; Bocian, D. F.; Scheidt, W. R.;
Birge, R. R.; Lindsey, J. S.; Holten, D. J. Phys. Chem. B 2005, 109,
20433–20443.
(35) Basu Baul, T. S. Appl. Organomet. Chem. 2008, 22, 195–204.
(36) Jakeman, D. L.; Bandi, S.; Graham, C. L.; Reid, T. R.; Wentzell,
J. R.; Douglas, S. E. Antimicrob. Agents Chemother. 2009, 53, 1245–1247.
(37) Nath, M.; Eng, G.; Song, X.; Beraldo, H.; de Lima, G. M.;
Pettinari, C.; Marchetti, F.; Whalen, M. M.; Beltrꢀan, H. I.; Santillan, R.;
Farfꢀan, N. Medicinal/Biocidal Applications of Tin Compounds and
Environmental Aspects; John Wiley & Sons, Ltd.: New York, 2008;
pp 413ꢀ496.
’ REFERENCES
(1) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891–4932.
(2) Sazanovich, I. V.; Kirmaier, C.; Hindin, E.; Yu, L.; Bocian, D. F.;
Lindsey, J. S.; Holten, D. J. Am. Chem. Soc. 2004, 126, 2664–2665.
(3) Maeda, H. J. Inclusion Phenom. Macrocyclic Chem. 2009,
64, 193–214.
(4) Thoi, V. S.; Stork, J. R.; Magde, D.; Cohen, S. M. Inorg. Chem.
2006, 45, 10688–10697.
(5) Hall, J. D.; McLean, T. M.; Smalley, S. J.; Waterland, M. R.;
Telfer, S. G. Dalton Trans. 2010, 39, 437–445.
(6) Sutton, J. M.; Rogerson, E.; Wilson, C. J.; Sparke, A. E.;
Archibald, S. J.; Boyle, R. W. Chem. Commun. 2004, 1328–1329.
(7) Kobayashi, J.; Kushida, T.; Kawashima, T. J. Am. Chem. Soc.
2009, 131, 10836–10837.
(8) Bronner, C.; Baudron, S. A.; Hosseini, M. W.; Strassert, C. A.;
Guenet, A.; Cola, L. D. Dalton Trans. 2010, 39, 180–184.
(9) Filatov, M. A.; Lebedev, A. Y.; Mukhin, S. N.; Vinogradov, S. A.;
Cheprakov, A. V. J. Am. Chem. Soc. 2010, 132, 9552–9554.
(10) Ikeda, C.; Ueda, S.; Nabeshima, T. Chem. Commun.
2009, 2544–2546.
(11) Furstner, A. Angew. Chem., Int. Ed. 2003, 42, 3582–3603.
(12) Park, G.; Tomlinson, J. T.; Melvin, M. S.; Wright, M. W.; Day,
C. S.; Manderville, R. A. Org. Lett. 2003, 5, 113–116.
(13) Gerber, N. N. J. Heterocycl. Chem. 1973, 10, 925–929.
(14) Sꢀaez Díaz, R. I.; Bennett, S. M.; Thompson, A. ChemMedChem
2009, 4, 742–745.
(15) Wasserman, H. H.; Rodgers, G. C.; Keith, D. D. Tetrahedron
1976, 32, 1851–1854.
(16) Invitrogen. BODIPY 650/665-X, SE, http://products.invitrogen.
com/ivgn/product/D10001.
(17) Gee, K. R.; Archer, E. A.; Kang, H. C. Tetrahedron Lett. 1999,
40, 1471–1474.
(18) Regourd, J.; Al-SheikhAli, A.; Thompson, A. J. Med. Chem.
2007, 50, 1528–1536.
(19) Baumhof, P.; Mazitschek, R.; Giannis, A. Angew. Chem., Int. Ed.
2001, 40, 3672–3674.
8213
dx.doi.org/10.1021/ic200731t |Inorg. Chem. 2011, 50, 8207–8213