Preparation of a family of hexanuclear rhenium cluster complexes containing 5-(phenyl)tetrazol-2-yl ligands and alkylation of 5-substituted tetrazolate ligands

Article abstract of DOI:10.1021/ic300877r

The preparation of two new families of hexanuclear rhenium cluster complexes containing benzonitrile and phenyl-substituted tetrazolate ligands is described. Specifically, we report the preparation of a series of cluster complexes with the formula [Re₆Se₈(PEt₃) ₅L]²⁺ where L = benzonitrile, p-aminobenzonitrile, p-methoxybenzonitrile, p-acetylbenzonitrile, or p-nitrobenzonitrile. All of these complexes undergo a [2 + 3] cycloaddition with N₃^- to generate the corresponding [Re₆Se₈(PEt ₃)₅(5-(p-X-phenyl)tetrazol-2-yl)]⁺ (or [Re ₆Se₈(PEt₃)₅(2,5-p-X- phenyltetrazolate)]⁺) cluster complexes, where X = NH₂, OMe, H, COCH₃, or NO₂. Crystal structure data are reported for three compounds: [Re₆Se₈(PEt₃) ₅(p-acetylbenzonitrile)](BF₄)₂?MeCN, [Re₆Se₈(PEt₃)₅(2,5- phenyltetrazolate)](BF₄)?CH₂Cl₂, and [Re₆Se₈(PEt₃)₅(2,5-p- aminophenyltetrazolate)](BF₄). Treatment of [Re₆Se ₈(PEt₃)₅(2,5-phenyltetrazolate)](BF ₄) with HBF₄ in CD₃CN at 100 °C leads to protonation of the tetrazolate ring and formation of [Re₆Se ₈(PEt₃)₅(CD₃CN)]²⁺. Surprisingly, alkylation of the phenyl and methyl tetrazolate complexes ([Re₆Se₈(PEt₃)₅(2,5-N ₄CPh)](BF₄) and [Re₆Se₈(PEt ₃)₅(1,5-N₄CMe)](BF₄)) with methyl iodide and benzyl bromide, leads to the formation of mixtures of 1,5- and 2,5-disubstituted tetrazoles.

Full text of DOI:10.1021/ic300877r

Article
pubs.acs.org/IC
Preparation of a Family of Hexanuclear Rhenium Cluster Complexes
Containing 5-(Phenyl)tetrazol-2-yl Ligands and Alkylation
of 5-Substituted Tetrazolate Ligands
Jessica L. Durham,† Joan N. Tirado,† Stanley A. Knott,† Meghan K. Oh,† Robert McDonald,‡
and Lisa F. Szczepura*,†
†Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States
‡Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
S
* Supporting Information
ABSTRACT: The preparation of two new families of hexanuclear
rhenium cluster complexes containing benzonitrile and phenyl-
substituted tetrazolate ligands is described. Specifically, we report
the preparation of a series of cluster complexes with the formula
[Re6Se8(PEt3)5L]2+ where L = benzonitrile, p-aminobenzonitrile,
p-methoxybenzonitrile, p-acetylbenzonitrile, or p-nitrobenzo-
nitrile. All of these complexes undergo a [2 + 3] cycloaddition
−
with N3 to generate the corresponding [Re6Se8(PEt3)5(5-(p-X-
phenyl)tetrazol-2-yl)]+ (or [Re6Se8(PEt3)5(2,5-p-X-phenyltetrazo-
late)]+) cluster complexes, where X = NH2, OMe, H, COCH3, or NO2. Crystal structure data are reported for three compounds:
[Re6Se8(PEt3)5(p-acetylbenzonitrile)](BF4)2•MeCN, [Re6Se8(PEt3)5(2,5-phenyltetrazolate)](BF4)•CH2Cl2, and
[Re6Se8(PEt3)5(2,5-p-aminophenyltetrazolate)](BF4). Treatment of [Re6Se8(PEt3)5(2,5-phenyltetrazolate)](BF4) with HBF4 in
CD3CN at 100 °C leads to protonation of the tetrazolate ring and formation of [Re6Se8(PEt3)5(CD3CN)]2+. Surprisingly,
alkylation of the phenyl and methyl tetrazolate complexes ([Re6Se8(PEt3)5(2,5-N4CPh)](BF4) and [Re6Se8(PEt3)5(1,5-N4CMe)]-
(BF4)) with methyl iodide and benzyl bromide, leads to the formation of mixtures of 1,5- and 2,5-disubstituted tetrazoles.
ligand was reported in 1998; the benzamidate ligand was formed
via the hydrolysis of a coordinated benzonitrile ligand.13a More
recently, the preparation and study of a series of Re(I) tetra-
zolate complexes was reported by Massi and co-workers.14
However, these complexes were prepared by the direct
substitution of MeCN by the 5-aryltetrazolate anion.
In 2007, two manuscripts describing how the hexarhenium
cluster core, [Re6Se8]2+, can activate coordinated acetonitrile
ligands to react with nucleophiles were published (Scheme 1).15,16
Zheng and co-workers reported the addition of alcohols to the
coordinated MeCN ligands of [Re6Se8(PEt3)6−n(MeCN)n]2+ (n =
1, 2) forming imino ester ligands.15 That same year, we reported
the formation of tetrazolate ligands via the reaction of inorganic
azides with [Re6Se8(PEt3)5(MeCN)]2+.16 Here, the cluster
activates the MeCN to undergo a cycloaddition with azide to
form a tetrazolate ring. This was the first example of a rhenium-
based complex facilitating the formation of a heterocyclic ring.
Most notable is the fact that heterocyclic formation occurs within
minutes at room temperature. Under these conditions, the N1
isomer can be generated in high yield.
INTRODUCTION
■
Tetrazoles are an important class of compounds that have
important applications in organic synthesis and medicinal
chemistry, as well as the explosives industry.1−3 In particular,
1,5-disubstituted tetrazoles are of interest because they often
serve as allosteric replacements for carboxylic acids in pharm-
aceuticals or as surrogates for the cis amide bond in peptides.4,5
In addition, transition metal complexes and coordination
polymers containing tetrazolate ligands have been shown to
display interesting physical properties.6 For example, Dunbar,
Zubietta, and co-workers prepared a microporous framework
([Co2(H0.67bdt)3]•20H2O) containing 5,5′-(1,4-phenylene)bis-
(tetrazolate) that displays single-chain magnetism.7 Because the
formation of tetrazoles via a direct reaction of nitriles and azides
often requires long reaction times, toxic substances, and harsh
conditions,8 there has been interest in examining more efficient
synthetic pathways.9 Select transition metals are capable of
facilitating the reaction between azides and nitriles to form
tetrazoles, and the advent of “click chemistry” brought these
synthetic routes to the forefront.10 A handful of metals have
been employed; however, the most common include Zn2+,
Pd2+, and Pt2+.10−12 Little is known regarding the ability of
Re to activate nitriles to undergo similar reactions with azide.
There have been reports of single metal and small cluster
rhenium(III) complexes containing nitrile ligands undergoing
hydrolysis.13 For example, a Re(III) dimer bridged by a benzamidate
Following up on our studies involving inorganic azides,
Zheng and co-workers examined the reaction of organic azides
with [Re6Se8(PEt3)5(MeCN)]2+ and other analogous acetonitrile
Received: April 29, 2012
Published: July 5, 2012
© 2012 American Chemical Society
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Scheme 1
[Re6Se8(PEt3)5(1,5-methyltetrazolate)]+ and [Re6Se8(PEt3)5(2,5-
phenyltetrazolate)]+ with alkylating agents, leading to the
formation of disubstituted tetrazoles. It is important to note that
while great strides have been made in the area of octahedral
hexanuclear clusters over the past 25 years, studies involving the
reactivity of these complexes (i.e., other than ligand substitution)
are severely lacking.19 Therefore, the studies described herein are
important in that they explore fundamental chemistry associated
with these hexarhenium cluster systems.
EXPERIMENTAL SECTION
■
Caution! Sodium azide can explode on heating, and contact of metal
azides with acids liberates the highly toxic and explosive hydrazoic acid. All
reactions involving azides and tetrazoles should be treated as potentially
explosive and handled in an appropriate manner!
cluster complexes.17 The expectation was that organic azides
would lead to the formation of functionalized tetrazole ligands.18
However, it was found that instead of forming the tetrazole ring, a
reversible ligand substitution of the organic azide for the nitrile
occurred. The cluster-azido intermediate that formed was then
found to undergo a photodecomposition reaction involving the
migration of the organic moiety and elimination of N2 leading to
the formation of an imino complex. For example, the reaction of
[Re6Se8(PEt3)5(MeCN)]2+ with (1-azidoethyl)benzene led to the
quantitative formation of the imino complex, [Re6Se8(PEt3)5-
(PhN=CHCH3)]2+. This unexpected result emphasizes the need
for further studies involving the reactivity of nitrile ligands.
We now extend our initial report16 involving the preparation
of methyltetrazolate complexes to an investigation of the reacti-
vity of coordinated benzonitrile and substituted benzonitrile
ligands. Both the preparation and reactivity of the benzonitrile
complex, [Re6Se8(PEt3)5(PhCN)]2+, and cluster complexes
containing para-substituted benzonitrile ligands (Figure 1),
General Information. [Re6Se8(PEt3)5I]I was prepared according
to a previously published procedure.20 1H NMR spectra were recorded
at either 400 or 500 MHz. Those collected using at 400 MHz were
collected on a Varian 400 Mercury or a Bruker Avance III 400 MHz
NMR spectrometer, while the spectra collected at 500 MHz were
collected on a Bruker Avance III 500 MHz NMR spectrometer. All
31P NMR spectra were proton decoupled and externally referenced to
85% H3PO4. 31P spectra were collected on the same instruments at
either 162 or 202.5 MHz, respectively. All chromatography was
performed using silica gel as the solid support. Elemental analyses
(EA) were performed by the Microanalysis Laboratory at the
University of Illinois, Urbana; mass spectral data was also obtained
at the University of Illinois. UV−visible spectra were collected on a
Varian Cary 5E UV−vis-NIR instrument. Infrared spectra (IR) were
collected on a Perkin-Elmer Spectrum One FT-IR spectrophotometer
using a KBr pellet (some of the IR spectra contain a broad peak at
approximately 3500 cm−1, which is attributed to water contamination
in the KBr). X-ray diffractometry data sets were collected and solved
by Dr. Robert McDonald at the University of Alberta, Edmonton,
Alberta, Canada T6G 2G2. Electrochemical measurements were
conducted in 0.2 M Bu4NBF4/CH2Cl2 with Pt working and auxiliary
and a Ag/AgCl reference electrode. The window scanned was 0.0−
1.50 V vs Ag/AgCl. All reported potentials were referenced to the
+
FeCp2 /FeCp2 couple, which was measured under identical
conditions. Steady state emission spectra were obtained using a
Perkin-Elmer LS55 fluorimeter at excitation wavelengths that
corresponded to the absorption wavelength.
[Re6Se8(PEt3)5(p-aminobenzonitrile)](BF4)2 (1). [Re6Se8(PEt3)5I]I
(500 mg, 0.193 mmol) and 456.8 mg of p-aminobenzonitrile (C7H6N2,
3.87 mmol) were dissolved in 12 mL of CH2Cl2. Separately, 189 mg of
AgBF4 (0.972 mmol) was dissolved in 8 mL of acetone. These solu-
tions were combined, covered with aluminum foil, and heated at reflux
for 3 h. The resulting mixture was cooled to room temperature and
filtered through Celite. The filtrate was reduced to dryness and then
precipitated using CH2Cl2 and Et2O. Purification was accomplished
via column chromatography; a 95:5 CH2Cl2:MeCN mixture was
used to elute an impurity, and then the product band was eluted
with a 85:15 CH2Cl2:MeCN mixture. The product fraction was
stripped of solvent via rotary evaporation and precipitated with
CH2Cl2 in Et2O. Crystals were obtained via vapor diffusion crystalliza-
tion using MeCN and Et2O (180.4 mg, 35% yield). 1H NMR (400 MHz,
acetone-d6, ppm): 7.48 (2H, d, −C6H4), 6.85 (2H, d, −C6H4), 6.29
(2H, s, −NH2), 2.34 (24H, m, −CH2CH3), 2.26 (6H, m, −CH2CH3),
Figure 1.
p-aminobenzonitrile, p-acetylbenzonitrile, p-methoxybenzonitrile,
and p-nitrobenzonitrile, will be discussed. These coordinated
nitriles were also found to undergo reaction with inorganic azides
to form the corresponding tetrazolate complexes (Scheme 2).
Reactivity studies involving the [Re6Se8(PEt3)5(2,5-phenyltetrazo-
late)]+ complex shows that free 2,5-phenyltetrazole can be gene-
rated via heating a solution of this complex in the presence of acid.
We also report our findings involving the reaction of both
Scheme 2
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1.16 (45H, m, −CH2CH3). 31P {1H} NMR (162 MHz, acetone-d6,
ppm): −24.71, −28.53. UV−vis (CH3CN) nm (ε in M−1 cm−1): 224
(69,000), 273 (27,000), 308 (28,000). MS (ESI(+)): m/z 1228.9
([Re6Se8(PEt3)5(C7H6N2)]2+). IR (KBr): 2227 (−C≡N) cm−1. Anal.
Calcd for C37H81N2P5B2F8Re6Se8: C, 16.89; H, 3.10; N, 1.06. Found: C,
16.50; H, 2.82; N, 1.10.
Celite; the filtrate was stripped of solvent on the Schlenk line. The
remaining residue was dissolved in 1.5 mL of CH3NO2 and dripped into
1
Et2O to afford a solid (124.8 mg, 79% yield). H NMR (400 MHz,
CDCl3, ppm): 8.43 (2H, d, −C6H4), 8.17 (2H, d, −C6H4), 2.21 (24H, m,
−CH2CH3), 2.09 (6H, m, −CH2CH3), 1.12 (45H, m, −CH2CH3).
31P {1H} NMR (162 MHz, CDCl3, ppm): −25.54, −29.55. UV−vis
(CH3CN) nm (ε in M−1 cm−1): 225 (71,000), 240, 281, 340 sh. IR
(KBr): 2265 (−C≡N), 1524 and 1344 (−NO2) cm−1. Anal. Calcd for
C37H79N2O2P5B2F8Re6Se8: C, 16.70; H, 2.99; N, 1.05. Found: C, 16.64;
H, 2.90; N, 1.12.
[Re6Se8(PEt3)5(2,5-p-aminophenyltetrazolate)](BF4) (6). A
sample of 1 (297 mg, 0.113 mmol) was dissolved in 10 mL of
acetone. Separately, 11.2 mg of NaN3 (0.172 mmol) was dissolved in
minimal DI water. These solutions were combined and stirred at room
temperature for 15 min. The solution was then filtered through Celite
and reduced to dryness. The resulting solid was precipitated using
acetone and Et2O and collected under a blanket of N2(g) (160.4 mg,
55% yield). 1H NMR (400 MHz, acetone-d6, ppm): 7.76 (2H, d,
−C6H4), 6.70 (2H, d, −C6H4), 4.77 (2H, s, −NH2), 2.27 (30H, m,
−CH2CH3), 1.15 (45H, m, −CH2CH3). 31P {1H} NMR (162 MHz,
acetone-d6, ppm) −27.10, −29.90. UV−vis (CH3CN) nm (ε in M−1 cm−1):
224 (75,000) 272 (43,000). MS (ESI(+)): m/z 2499.6 ([Re6Se8(PEt3)5-
(C7H6N5)]+). Anal. Calcd for C37H81N5P5BF4Re6Se8•2.5H2O: C, 16.88; H,
3.29; N, 2.66. Found: C, 16.53; H, 2.93; N, 2.45.
[Re6Se8(PEt3)5(p-methoxybenzonitrile)](BF4)2 (2). [Re6Se8(PEt3)5I]I
(149.4 mg, 0.058 mmol) and 69.7 mg of 4-methoxybenzonitrile
(C8H7NO, 0.523 mmol) was dissolved in 10 mL of CH2Cl2.
Separately, 30.1 mg of AgBF4 (0.155 mmol) was dissolved in 5 mL
of chlorobenzene. These solutions were combined, covered with
aluminum foil, and stirred at room temperature for 3 h. The resulting
mixture was then filtered through Celite; the filtrate was stripped of
solvent on the Schlenk line. The remaining residue was dissolved in
1.5 mL of nitromethane and dripped into Et2O to afford a crude solid
(124.9 mg, 82% yield). 1H NMR (400 MHz, CDCl3, ppm): 7.71
(2H, d, −C6H4), 7.13 (2H, d, −C6H4), 3.91 (3H, s, −OCH3), 2.21
(24H, m, −CH2CH3), 2.09 (6H, m, −CH2CH3), 1.10 (45H, m,
−CH2CH3). 31P {1H} NMR (162 MHz, CDCl3, ppm): −25.79,
−29.41. UV−vis (CH3CN) nm (ε in M−1 cm−1): 223 (71,000),
239 sh, 277 (42,000), 335 sh. MS (ESI(+)): m/z 1236.7
([Re6Se8(PEt3)5(C8H7NO)]2+). IR (KBr): 2247 (−C≡N) cm−1.
Anal. Calcd for C38H82NOP5B2F8Re6Se8: C, 17.25; H, 3.12; N, 0.53.
Found: C, 17.14; H, 2.99; N, 0.55.
[Re6Se8(PEt3)5(2,5-p-methoxyphenyltetrazolate)](BF4) (7). A
sample of 2 (136.3 mg, 0.052 mmol) was dissolved in 3 mL of acetone.
Separately, 5.2 mg of NaN3 (0.080 mmol) was dissolved in minimal DI
water. These solutions were combined and stirred at room tempera-
ture for 30 min. The resulting mixture was then filtered through Celite
into stirring Et2O to afford a crude solid (122.8 mg, 89% yield). This
solid was purified via column chromatography; the desired product
was collected as the first band, which was eluted with a 4:1 CH2Cl2/
acetone mixture. The product was dissolved in minimal CH3NO2 and
[Re6Se8(PEt3)5(NCPh)](BF4)2 (3). In a 25 mL round bottom,
60.7 mg of AgBF4 was dissolved in 0.8 mL of benzonitrile. In a
separate vial, [Re6Se8(PEt3)5I]I (306.1 mg, 0.118 mmol) was dissolved
in 8 mL of CH2Cl2 and added to the stirring AgBF4 solution. The
reaction mixture was stirred for 3 h, with exclusion of light, at room
temperature. The solution was then filtered through Celite. The filtrate
was reduced to dryness by rotary evaporation, which afforded the
product in residual benzonitrile. The crude product was further
purified by column chromatography; an initial 10:90 acetone:CH2Cl2
mixture was used to elute residual benzonitrile and then changed to
50:50 acetone:CH2Cl2 to elute the product band. The product was
reduced to dryness by rotary evaporation and precipitated with
CH2Cl2 and Et2O. Crystals were obtained via vapor diffusion using a
1
dripped into Et2O to afford a solid (79.1 mg, 57% yield). H NMR
(400 MHz, CDCl3, ppm): 7.98 (2H, d, −C6H4), 6.89 (2H, d, −C6H4),
3.81 (3H, s, −OCH3), 2.09 (30H, m, −CH2CH3), 1.10 (45H, m,
−CH2CH3). 31P {1H} NMR (162 MHz, CDCl3, ppm): −28.21,
−30.21. UV−vis (CH3CN) nm (ε in M−1 cm−1): 225 (72,000), 241,
257, 367 sh. MS (ESI(+)): m/z 2518.0 ([Re6Se8(PEt3)5(C8H7N4O)]+).
Anal. Calcd for C38H82N4OP5BF4Re6Se8: C, 17.54; H, 3.18; N, 2.15.
Found: C, 17.66; H, 2.87; N, 2.12.
1
CH2Cl2/Et2O mixture and Et2O (252.2 mg, 82% yield). H NMR
(500 MHz, CDCl3, ppm): 7.80 (2H, d, −C6H5), 7.72 (1H, t, −C6H5),
7.63 (2H, t, −C6H5), 2.22 (24H, m, −CH2CH3), 2.10 (6H, m,
−CH2CH3), 1.13 (45H, m, −CH2CH3). 31P{1H} NMR (202.5 MHz,
CDCl3 ppm): −25.61, −29.48. UV−vis (CH3CN) nm (ε in M−1
cm−1): 225 (73,000), 271, 240, 403 sh. MS (ESI(+)): m/z 1221.7
([Re6Se8(PEt3)5(NCC6H5)]2+). IR (KBr): 2253 (−C≡N) cm−1. Anal.
Calcd for C37H80NP5B2F8Re6Se8: C, 16.98; H, 3.08; N, 0.54. Found:
C, 16.78; H, 2.95; N, 0.58.
[Re6Se8(PEt3)5(p-acetylbenzonitrile)](BF4)2 (4). [Re6Se8(PEt3)5I]
I (202.1 mg, 0.078 mmol) and 113.8 mg of 4-acetylbenzonitrile
(C9H7NO, 0.784 mmol) was dissolved in 10 mL of CH2Cl2. Separately,
44.8 mg of AgBF4 (0.230 mmol) was dissolved in 5 mL of chlorobenzene.
These solutions were combined, covered with aluminum foil, and stirred
at room temperature for 2 h. The resulting mixture was then filtered
through Celite. The filtrate was stripped of solvent on the Schlenk line,
and the crude product isolated via precipitation from CH3NO2 and Et2O.
A second precipitation was required to remove residual 4-acetylbenzoni-
trile (132.2 mg, 64% yield). 1H NMR (500 MHz, CDCl3, ppm):
8.21 (2H, d, −C6H4), 7.97 (2H, d, −C6H4), 2.66 (3H, s, −CH3), 2.22
(24H, m, −CH2CH3), 2.11 (6H, m, −CH2CH3), 1.10 (45H, m,
−CH2CH3). 31P {1H} NMR (202.5 MHz, CDCl3, ppm): −25.69,
−29.31. UV−vis (CH3CN) nm (ε in M−1 cm−1): 224 (72,000), 242, 273,
340 sh. MS (ESI(+)): m/z 1241.6 ([Re6Se8(PEt3)5(C9H7NO)]2+). IR
(KBr): 2256 (−C≡N), 1687 (CO) cm−1. Anal. Calcd for
C39H82NOP5B2F8Re6Se8: C, 17.62; H, 3.11; N, 0.53. Found: C, 17.31;
H, 2.88; N, 0.51.
[Re6Se8(PEt3)5(2,5-phenyltetrazolate)](BF4) (8). A solution
containing 228 mg of (3) (0.0872 mmol) in 6.0 mL of acetone was
combined with a solution of NaN3 (16.1 mg, 0.248 mmol) in 30 drops
of DI water. The reaction mixture was stirred for 15 min at room
temperature. The solution was then filtered through Celite. The filtrate
was reduced to dryness by rotary evaporation and then precipitated
using acetone and Et2O. The product was further purified by column
chromatography; a mixture of 20:80 acetone:CH2Cl2 was used to elute
the product band. This band was reduced to dryness by rotary
evaporation and precipitated with CH2Cl2 and Et2O. Crystals were
obtained by vapor diffusion using acetone/Et2O mixture and Et2O
(120 mg, 54% yield). 1H NMR (400 MHz, CDCl3, ppm): 8.07 (2H, d,
−C6H5), 7.36 (2H, t, −C6H5), 7.26 (1H, t, −C6H5), 2.16 (30H, m,
−CH2CH3), 1.10 (45H, m, −CH2CH3). 13C NMR (100 MHz, CDCl3,
ppm): 163.7 (s, N4CC6H5), 130.2 (s, N4CC6H5), 128.5 (s, N4CC6H5),
126.7 (s, N4CC6H5), 25.8 (m, −CH2CH3), 8.9 (m, −CH2CH3).
31P{1H} NMR (162 MHz, CDCl3, ppm): −28.17, −30.15. UV−vis
(CH3CN) nm (ε in M−1 cm−1): 225 (81,000), 240, 265, 396 sh. MS
(ESI(+)): m/z 2484.2 ([Re6Se8(PEt3)5(N4CC6H5)]+). Anal. Calcd for
C37H80N4 P5BF4 Re6Se8: C, 17.28; H, 3.14; N, 2.18. Found: C, 17.37;
H, 2.91; N, 2.07.
[Re6Se8(PEt3)5(2,5-p-acetylphenyltetrazolate)](BF4) (9). A
sample of 4 (250 mg, 0.094 mmol) was dissolved in 10 mL of
CH3NO2. Separately, 9.2 mg of NaN3 (0.14 mmol) was dissolved in
minimal DI water. These solutions were combined and stirred vigo-
rously at room temperature for 15 min. The mixture was then filtered
through Celite, and the filtrate was stripped dry via rotary evaporation.
Upon dissolving in 1.5 mL of CH3NO2, a second filtration through
Celite was required before the product was precipitated by dripping
[Re6Se8(PEt3)5(p-nitrobenzonitrile)](BF4)2 (5). [Re6Se8(PEt3)5I]I
(154.8 mg, 0.060 mmol) and 89.0 mg of 4-nitrobenzonitrile (C7H4N2O2,
0.601 mmol) was dissolved in 10 mL of CH2Cl2. Separately, 33.2 mg of
AgBF4 (0.170 mmol) was dissolved in 5 mL of chlorobenzene. These
solutions were combined, covered with aluminum foil, and stirred at room
temperature for 1 h. The resulting mixture was then filtered through
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the solution into Et2O (217.4 mg, 88% yield). H NMR (400 MHz,
CDCl3, ppm): 8.17 (2H, d, −C6H4), 7.96 (2H, d, −C6H4), 2.62 (3H, s,
−CH3), 2.16 (30H, m, −CH2CH3), 1.13 (48H, m, −CH2CH3). 31P {1H}
NMR (162 MHz, CDCl3, ppm): −27.97, −29.99. UV−vis (CH3CN) nm
(ε in M−1 cm−1): 223 (75,000), 278 (35,000). MS (ESI(+)): m/z 2525.8
([Re6Se8(PEt3)5(C9H7N4O)]+). Anal. Calcd for C39H82N4OP5BF4
Re6Se8: C, 17.92; H, 3.16; N, 2.14. Found: C, 17.64; H, 3.11; N, 2.01.
[Re6Se8(PEt3)5(2,5-p-nitrophenyltetrazolate)](BF4) (10). A
169.1 mg sample of 5 (0.064 mmol) was dissolved in 7.5 mL of
CH3NO2. Separately, 6.4 mg of NaN3 (0.098 mmol) was dissolved in
minimal DI water. These solutions were combined and stirred at room
temperature for 30 min. The resulting mixture was then filtered
through Celite. The filtrate was stripped of solvent, and the remaining
residue was dissolved in 1.5 mL of CH3NO2 and dripped into Et2O to
d(C25A−C26A) = d(C25B−C26B) = 1.54(1) Å; and d(P2...C26A) =
d(P2...C26B) (within 0.01 Å). F−B distances within the disordered
−
BF4 ion (d(F5A−B2A), d(F6A−B2A), d(F7A−B2A), d(F7A−B2A),
d(F5B−B2B), d(F6B−B2B), d(F7B−B2B), and d(F8B−B2B)) were
constrained to be equal (within 0.01 Å) to a common value during
refinement. F...F distances within the minor (40%) conformer of this
−
disordered BF4 ion (d(F5B...F6B), d(F5B...F7B), d(F5B...F8B),
d(F6B...F7B), d(F6B...F8B), and d(F7B...F8B)) were constrained to
be equal (within 0.01 Å) to a common value during refinement. Dis-
tances within the disordered solvent acetonitrile molecule were fixed
during refinement: d(N1SA−C1SA) = d(N1SB−C1SB) = 1.13(1) Å;
d(C1SA−C2SA) = d(C1SB−C2SB) = 1.45(1) Å; and d(N1SA...C2SA) =
d(N1SB...C2SB) = 2.58(1) Å.
Re6S8(PEt3)5(2,5-phenyltetrazolate)]BF4•CH2Cl2. Attempts to refine
peaks of residual electron density as solvent dichloromethane carbon
or chlorine atoms were unsuccessful. The data were corrected for
disordered electron density through use of the SQUEEZE procedure
as implemented in PLATON.24−26 A total solvent-accessible void
volume of 254.5 Å3 with a total electron count of 100 (consistent with
two molecules of solvent dichloromethane or one molecule per
formula unit of the hexarhenium complex ion) was found in the unit
cell. The following distance restraints were applied to impose an
idealized geometry upon the disordered PEt3 group attached to Re2:
d(P2−C7A) = d(P2−C9A) = d(P2−C11A) = d(P2−C7B) = d(P2−
C9B) = d(P2−C11B) = 1.84 Å; d(C7A−C8A) = d(C9A−C10A) =
d(C11A−C12A) = d(C7B−C8B) = d(C9B−C10B) = d(C11B−
C12B) = 1.54 Å; d(Re2...C7A) = d(Re2...C9A) = d(Re2...C11A) =
d(Re2...C7B) = d(Re2...C9B) = d(Re2...C11B) = 3.65 Å; d(P2...C8A) =
d(P2...C10A) = d(P2...C12A) = d(P2...C8B) = d(P2...C10B) =
d(P2...C12B) = 2.85 Å; and d(C7A...C9A) = d(C7A...C11A) =
d(C9A...C11A) = d(C7B...C9B) = d(C7B...C11B) = d(C9B...C11B) =
2.84 Å. Restraints were also applied to a disordered ethyl group of the
PEt3 ligand bound to Re5: d(P5−C29) = 1.84 Å; d(C29−C30A) =
d(C29−C30B) = 1.54 Å; d(P5...C30A) = d(P5...C30B) = 2.85 Å. The
F−B distances within the disordered BF4− ion (d(F1A−B1A),
d(F2A−B1A), ... d(F4B−B1B)) were fixed at 1.35 Å during
refinement.
1
afford a solid (146.6 mg, 85% yield). H NMR (400 MHz, CDCl3,
ppm): 8.22 (4H, −C6H4), 2.14 (30H, m, −CH2CH3), 1.10 (45H, m,
−CH2CH3). 31P {1H} NMR (162 MHz, CDCl3, ppm): −27.86,
−29.90. UV−vis (CH3CN) nm (ε in M−1 cm−1): 224 (75,000), 273
(23,000), 316 sh. Anal. Calcd for C37H79N5O2P5BF4Re6Se8: C, 16.98;
H, 3.04; N, 2.68. Found: C, 16.78; H, 2.78; N, 2.34.
X-ray Crystallography. General. Single crystals of [Re6S8-
(PEt3)5(p-acetylbenzonitrile)](BF4)2·NCCH3 and [Re6S8(PEt3)5(2,5-
p-aminophenyltetrazolate)]BF4 were grown via the vapor diffusion
technique using CH3CN and Et2O at −20 °C. Crystals of [Re6S8-
(PEt3)5(2,5-phenyltetrazolate)]BF4·CH2Cl2 were grown from an
acetone−Et2O mixture at room temperature also using vapor diffusion
(the residual CH2Cl2 that was present came from the previous
reprecipitation steps). Crystals selected for diffraction experiments
were coated with Paratone-N oil then placed under a cold N2 gas
stream on the diffractometer. All three data sets were obtained using a
Bruker SMART 1000 CCD detector/PLATFORM diffractometer with
the crystals cooled to −80 °C and diffraction measurements obtained
using graphite-monochromated Mo Kα (λ = 0.71073 Å). Data were
corrected for absorption by Gaussian integration after face-indexing
and measurement of crystal dimensions. The structures were all solved
using Patterson methods and structure expansion (DIRDIF-9921
(8•CH2Cl2) or DIRDIF-200822 (4•MeCN, 6). Structures were
refined by full-matrix least-squares on F2 with SHELXL-97.23
Hydrogen atoms were included as riding atoms and were placed in
geometrically idealized positions with isotropic displacement param-
eters 120% of those of the Ueq for their parent atoms. See Table 1 for a
summary of crystallographic data.
[Re6S8(PEt3)5(2,5-p-aminophenyltetrazolate)]BF4. Distances within
the disordered PEt3 ethyl groups were fixed during refinement:
d(P1A−C11A) = d(P1A−C13A) = d(P1A−C15A) = d(P1B−C11B) =
d(P1B−C13B) = d(P1B−C15B) = 1.82(1) Å; and d(C11A−C12A) =
d(C13A−C14A) = d(C15A−C16A) = d(C11B−C12B) = d(C13B−
C14B) = d(C15B−C16B) = d(C35A−C36A) = d(C35B−C36B) =
1.54(1) Å.
Special Refinement Details. [Re6S8(PEt3)5(p-acetylbenzonitrile)]-
(BF4)2·NCCH3. Distances within a disordered PEt3 ethyl group were fixed
or restrained during refinement: d(P2−C25A) = d(P2−C25A) = 1.82(1) Å;
Table 1. Crystallographic Data for [Re6Se8(PEt3)5(p-acetylbenzonitrile)](BF4)2•MeCN (4•NCCH3), [Re6Se8(PEt3)5(2,5-
phenyltetrazolate)](BF4)•CH2Cl2, (8•CH2Cl2), and [Re6Se8(PEt3)5(2,5-p-aminophenyltetrazolate)](BF4) (6)
4•NCCH3
8•CH2Cl2
6
formula
FW (g mol−1
space group
a (Å)
C39H82B2F8NOP5Re6Se8·NCCH3
2699.46
C37H80BF4N4P5Re6Se8·CH2Cl2
2656.52
C37H81BF4N5P5Re6Se8
2586.61
)
P21/n
P1
̅
Pna21
12.2340(10)
19.9378(17)
27.756(2)
11.8298(7)
15.2084(8)
18.4824(10)
88.1099(10)
81.9099(9)
81.7607(10)
3257.9(3)
2
25.2743(27)
19.7358(14)
12.2496(8)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
91.6087(13)
6767.5(10)
6110.2(7)
4
4
T (°C)
−80
−80
−80
radiation (λ (Å))
ρcalcd (g cm−3
μ (mm−1
Mo Kα (0.71073)
Mo Kα (0.71073)
Mo Kα (0.71073)
)
2.649
2.708
2.812
)
15.16
15.81
16.78
Flack parameter
R1 [I ≥ 2σ(I)]
wR2 [all data]
−0.017(7)
0.0254
0.0366
0.0839
0.0428
0.1263
0.0518
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Protonation of (8). [Re6Se8(PEt3)5(2,5-N4CPh)](BF4) (∼5 mg)
was dissolved in ∼1.5 mL CD3CN in a stoppered NMR tube (Wilmad
Pyrex LPV). One drop of HBF4 (48% aqueous solution) was added to the
are a little higher than that reported for the acetonitrile com-
plex, [Re6Se8(PEt3)5(NCCH3)]2+, which has an E1/2 = 0.754 V
vs FeCp2 /FeCp2 under the same conditions.16 Acetonitrile is a
+
1
stronger donor (higher donor number31) than benzonitrile;
therefore, it is not surprising that the monoacetonitrile complex
is slightly easier to oxidize than the benzonitrile complexes
reported here.
solution and the tube was sealed. Within minutes of mixing the H and
31P NMR spectra were recorded (t = 0). The samples were then placed in
an oil bath at 100 °C; at various time intervals the samples were removed
from the oil bath, cooled, and subjected to NMR spectral analysis.
Alkylation Studies. The alkylation reactions that were monitored
via NMR spectroscopy involved combining 5−10 mg of
[Re6Se8(PEt3)5(2,5-N4CPh)](BF4) or [Re6Se8(PEt3)5(1,5-N4CMe)]-
(BF4) and 20 equivalents of MeI or BnBr in 1.5−2.0 mL of CDCl3 in a
stoppered NMR tube (Wilmad Pyrex LPV). These reactions were
monitored in a manner similar to the protonation studies described
above.
Even though the electronic effect of the para substituent on
the E1/2 value of this family of complexes is not measurable, the
substituent does have an effect on the donating ability of the
benzonitrile ligand as was shown in the following ligand
substitution experiments. Because MeCN is the stronger Lewis
base, we anticipated that it would substitute for the weaker
benzonitrile ligands. To test this, we prepared three separate
samples of [Re6Se8(PEt3)5(p-nitrobenzonitrile)]2+, [Re6Se8-
(PEt3)5(NCPh)]2+, and [Re6Se8(PEt3)5(p-methoxybenzo-
nitrile)]2+ each in CD3CN and monitored them via 31P NMR
spectroscopy. Within 8 h, the solution containing the p-nitro-
benzonitrile complex (resonances at −24.41 and −28.71 ppm)
already showed the presence of some [Re6Se8(PEt3)5(CD3CN)]2+
(resonances at −24.76 and −28.88 ppm). Within 2 days, about
50% of the material had been converted, and within 7 days
substitution was almost complete (Figure 2a). In contrast,
it took 7 days for 50% of [Re6Se8(PEt3)5(NCPh)]2+ to be
converted to [Re6Se8(PEt3)5(CD3CN)]2+ (Figure 2b) and a
RESULTS AND DISCUSSION
■
Synthesis. The synthesis of [Re6Se8(PEt3)5(NCPh)]2+ was
modeled after the preparation of the analogous acetonitrile
complex,20 [Re6Se8(PEt3)5(MeCN)]2+ and involves combining
a CH2Cl2 solution of [Re6Se8(PEt3)5I]I with a benzonitrile
solution of AgBF4. Because of the fact that the para-substituted
benzonitriles are solids and AgBF4 is only sparing soluble in
CH2Cl2, another solvent was needed to dissolve the silver salt
in these reactions. Chlorobenzene was found to work well in
the preparation of the p-methoxy, p-nitro, and p-acetyl
benzonitrile complexes, leading to complete conversion of the
starting material within 3 h or less. However, using the same
conditions, the substitution reaction involving p-aminobenzo-
nitrile in CH2Cl2/chlorobenzene only led to a 50% conversion
after 3 h (even after 17 h some starting material still remained).
Monitoring these substitution reactions via NMR spectroscopy
at 1 h intervals, we observed an opposite trend from what we
expected. The benzonitrile with the most electron withdrawing
substituent (nitro) was complete in the shortest amount of time
(1 h), while reaction with the most electron donating
substituent (amino) did not completely convert. We believe
this trend is due to a combination of the less polar solvent
mixture causing the AgBF4 to remain ion paired and the ability
of the more electron-donating nitriles to coordinate more
strongly to Ag(I) making it less reactive toward the cluster.27
The synthesis of [Re6Se8(PEt3)5(p-aminobenzonitrile)]2+ was
finally achieved using a more polar solvent mixture (CH2Cl2/
acetone); however, unidentified impurities were difficult to
remove, resulting in a much lower yield compared to the other
preparations. The 31P NMR spectra of the new nitrile com-
plexes show two resonances in a 4:1 ratio, which is char-
acteristic of the pentaphosphine cluster complexes.16,20,28 The
IR spectral data of compounds 1−5 all show the ν(CN) stretch
for the coordinated nitriles, which is higher than that of the free
nitriles, which was expected.29
Figure 2. 31P spectral data of samples taken at different time
intervals in the substitution reaction of (a) [Re6Se8(PEt3)5(p-nitro-
benzonitrile)](BF4)2 and (b) [Re6Se8(PEt3)5(NCPh)](BF4)2 in CD3CN.
Resonances at −24.76 and −28.88 are due to [Re6Se8(PEt3)5(CD3CN)]-
(BF4)2.
little more than 7 weeks for complete conversion (Figure S6,
Supporting Information). Monitoring the substitution of the
[Re6Se8(PEt3)5(p-methoxybenzonitrile)]2+ complex was more
difficult because the chemical shifts are so close to those of
[Re6Se8(PEt3)5(CD3CN)]2+ that the peaks overlap. However, it
is clear that at 7 weeks about two-thirds of the p-methoxy-
benzonitrile ligand had been substituted (Figure S7, Supporting
Information). Therefore, the para substituent does have an
impact on the reactivity of the coordinated nitrile ligand.
In our initial preparation of the phenyltetrazolate complex,
[Re6Se8(PEt3)5(2,5-N4CPh)]+, we combined [Re6Se8(PEt3)5-
(NCPh)]2+ and Bu4NN3 and allowed the reaction to stir for
2 h at room temperature. This led to the complete conver-
sion to the tetrazolate complex, demonstrating that benzonitrile
ligands are also activated by the [Re6Se8]2+ cluster core to
undergo [2 + 3] cycloaddition reactions with inorganic azides.
Later, we observed that sodium azide worked just as well
and that the reaction occurred more rapidly than we thought
In order to test the impact of the para substituent of the
benzonitrile ligand on the electronic nature of the cluster com-
plex, electrochemical measurements were obtained for all of the
newly prepared benzonitrile complexes. Cyclic voltammetric
data were recorded, and each of the five new complexes showed
a single oxidative redox process, assigned to the Re(IV)Re(III)5/
Re(III)6 couple, in the window scanned. Notably, all five
complexes had couples with E1/2 = 0.767 0.002 V (vs FeCp2+/
FeCp2 in CH2Cl2) indicating that the para substituent has minimal
impact on the redox properties of the cluster (Figures S1−S5,
Supporting Information). This is likely due to the fact that the effect
of the para substituent is distributed over the entire cluster and is,
therefore, reduced compared to the impact on a single metal
center.30 However, the potentials of the benzonitrile complexes
7829
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Inorganic Chemistry
Article
(i.e., the reaction involving the benzonitrile complex was complete
within minutes). Unlike the cyclization involving [Re6Se8-
wave at 0.588 V is observed (Figure 3a), which has been
assigned to the Re(IV)Re(III)5/Re(III)6 couple. We were able
to determine the ligand electronic parameter, EL, for 2,5-phenyl-
tetrazolate (−0.10) using our previously reported relationship
between E1/2 and ∑EL; this parameter is very similar to the
value determined for 1,5-methyltetrazolate (EL = −0.05).16
Scanning out to a more positive potential, an irreversible peak
at 1.239 V is evident, and on the return scan, a new cathodic
peak near 0.684 V appears. Repeat scans within this window
show a decrease in the intensity of the couple at 0.588 V and
the growth of a new quasi-reversible wave at 0.715 V (Figure 3b).
−
(PEt3)5(NCCH3)]2+ and N3 which leads to the exclusive
formation of the N1-bound tetrazolate ligand within 15 min at
room temperature, only the N2-bound tetrazolate was isolated
for the phenyltetrazolate complexes reported here. Monitoring
the reaction of [Re6Se8(PEt3)5(NCPh)]2+ with sodium azide
in acetone-d6 via 31P NMR spectroscopy, we see that all of
the benzonitrile complex is gone within the first 5 min of the
reaction (Figure S8, Supporting Information); at this time, the
major product is [Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+ at
−28.42 and −31.39 ppm. In addition, there are two smaller
peaks at −28.81 and −31.03 ppm. The peak at −28.81 ppm
disappears after 30 min; this could possibly be the N1 isomer,
but we did not attempt to isolate it as it was such a small
fraction of the overall product. The other peak appears to be an
impurity, which is removed via column chromatography. Ellis
and Purcell also report that N1 to N2 isomerization of coordi-
nated 5-phenyltetrazolate is faster than 5-methyltetrazolate.32
The 13C NMR spectral data for [Re6Se8(PEt3)5(2,5-N4CPh)]+
also supports N2 coordination. The tetrazole ring carbon in the
13C NMR spectrum was observed at 163.7 ppm and falls with
the range reported by Butler for 5-phenyl or pyridyl-substituted
tetrazolate ligands coordinated through the N2 position.33
Finally, the X-ray structure analyses of 8 and 6 also show that
the phenyltetrazolate and the p-aminophenyltetrazolate ligands
are coordinated through the N2 nitrogen. We believe this
isomer is favored because of the steric size of the phenyl
substituent. As expected, the 31P NMR spectra of all of the
tetrazolate complexes show two resonances in a 4:1 ratio, which
are indicative of the 5:1 site-differentiation. Compared to the
analogous dicationic benzonitrile complexes, there is an upfield
shift of the 31P resonances upon formation of the tetrazolate
complexes; this upfield shift of the resonances of the more
electron-rich monocationic complexes has been observed
previously.16,20 Also, there is a strong correlation between
the chemical shift of the larger peak in the 31P spectrum vs
the Hammett parameters (R2 = 0.97), demonstrating that the
electronic effect of the para substituent does impact the
1
phosphine ligands. The H NMR spectral data for all newly
prepared complexes is fairly straightforward to interpret.
However, it is interesting that the 1H NMR spectrum of
[Re6Se8(PEt3)5(2,5-p-nitrophenyltetrazolate)]+ is different from
Figure 3. Cyclic voltammograms of [Re6Se8(PEt3)5(2,5-
phenyltetrazolate)](BF4) in CH2Cl2, at a) 100 mV/s and b) 400
mV/s (multiple scans).
1
the H NMR spectra of the other para-substituted complexes.
The electrochemical study of [Re6Se8(PEt3)5(1,5-N4CMe)]+
showed similar decomposition after accessing the second
oxidative process. At the time, we proposed that the tetrazolate
ligand was decomposing back to the corresponding nitrile,
[Re6Se8(PEt3)5(NCMe)]2+, because the E1/2 values of the
decomposition product and the acetonitrile complex were so
similar (within 15 mV). For the phenyltetrazolate complex, the
redox potential of the decomposition product (E1/2 = 0.715 V)
is not the same as that of the corresponding benzonitrile
complex [Re6Se8(PEt3)5(NCPh)]2+ (E1/2 = 0.754 V). Thus, we
are no longer certain of the decomposition process.
The UV−vis spectra of the benzonitrile complexes all show
one large absorbance at 225 nm in MeCN and multiple
additional absorbances between 225 and 400 nm. The UV−vis
spectral data of the phenyltetrazolate complexes look similar in
that they also contain a large absorbance around 225 nm and
then show numerous smaller absorptions that trail off at
about 425 nm (Figures S10−S14, Supporting Information).
Compounds 1−10 all display luminescent properties. We are
Instead of the expected pattern of doublets in the aromatic
region, there is only one large peak that integrates for the same
number of protons. Evidently, the two different sets of phenyl
protons are nearly magnetically equivalent, resulting in almost
no first-order coupling. This is supported by our simulation of
1
the aromatic region of the H NMR spectrum assuming near
magnetic equivalency (Figure S9, Supporting Information). It is
difficult to identify the stretches of the tetrazolate ring itself in
the IR spectra of complexes 6 − 10. However, for all but the
[Re6Se8(PEt3)5(2,5-p-aminophenyltetrazolate)]+ complex, the
ν(C≡N) stretch of the coordinated nitrile is absent in the IR
spectra of the corresponding tetrazolate complexes. Because the
spectral and elemental analysis data for this complex do not
indicate any impurities, we believe that the complex is
decomposing under pressure applied in preparing either a
KBr pellet or collecting data via ATR.
The electrochemical properties of [Re6Se8(PEt3)5(2,5-
N4CPh)]+ were investigated via cyclic voltammetry. In scanning
+
from −0.30 to 1.00 V vs FeCp2 /FeCp2, one quasi-reversible
7830
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Inorganic Chemistry
Article
currently conducting a detailed study on the excited state
lifetimes and quantum yields of these cluster complexes.
Structure Analysis. Single crystals of 4•NCCH3,
8•CH2Cl2, and 6 were grown via vapor diffusion technique
and analyzed by X-ray diffraction. These complexes show core
bond lengths (Re−Re) and (Re−Se) and angles (Re−Re−Re,
Re−Re−Se, Se−Re−Se, and Re−Se−Re) that are not out of
the ordinary for [Re6Se8]2+-based cluster complexes.34
Table 2 shows the rhenium metal-terminal ligand bond
lengths as well as the bond lengths of the tetrazolate rings. The
Table 2. Selected Bond Lengths for [Re6Se8(PEt3)5-
(p-acetylbenzonitrile)](BF4)2•MeCN (4•NCCH3),
[Re6Se8(PEt3)5(2,5-phenyltetrazolate)](BF4)2•CH2Cl2,
(8•CH2Cl2), and [Re6Se8(PEt3)5(2,5-p-aminophenyl-
tetrazolate)](BF4)2 (6)
4•NCCH3
8•CH2Cl2
6
Re−P
2.474(2)−
2.482(2)
2.479(1)
2.4262(2)−
2.482(40)
2.467(10)
2.470(2)−
2.482(2)
2.479(3)
(mean)
Re6−N1
Re6−N2
N1−N2
N2−N3
N3−N4
2.125(7)
−
−
−
−
−
−
−
−
2.151(11)
1.335(15)
1.320(15)
1.356(16)
1.310(19)
1.349(17)
2.137(7)
1.350(10)
1.311(9)
1.322(10)
1.339(11)
1.329(10)
Figure 5. ORTEP diagrams of (a) [Re6Se8(PEt3)5(2,5-phenyltetrazo-
late)]+ and (b) [Re6Se8(PEt3)5(2,5-p-aminophenyltetrazolate)]+ showing
the atom-labeling schemes. Non-hydrogen atoms are represented by
Gaussian ellipsoids at the 30% probability level. Hydrogen atoms and the
carbon atoms of the PEt3 ligands were omitted for clarity.
N4−C31/C1
C31/C1−N1
observed Re−P bond lengths fall within the 2.414−2.512 Å
range observed for PEt3 ligands coordinated to the [Re6Se8]2+
cluster cores.20,35 The Re−N(p-acetylbenzonitrile) bond
distance in 4•NCCH3 is 2.151(11) Å; this is on the high end
of bond lengths observed for single cluster Re-NCCH3 ligands,
which range from 2.09(2)−2.146(11) Å.20,34 The ORTEP
diagram of [Re6Se8(PEt3)5(p-acetylbenzonitrile)]2+ is shown in
Figure 4. The structures of the phenyltetrazolate complexes,
ligands.36 In contrast, [Re6Se8(PEt3)5(1,5-MeN4C)]+ showed
significant differences between bond lengths within the
methyltetrazolate ring.16 The planarity of the ring is not what
is causing the difference, as all three complexes show planar
tetrazolate rings. In addition, the phenyl and tetrazolate rings
for both tetrazolate complexes nearly coplanar as indicated by
the dihedral angles between the phenyl and tetrazolate ring
for both of these structures (1.7(5)° for 6 and 7.7(10)° for
8•CH2Cl2).
Reactivity Studies. Because of the various applications of
free mono- and disubstituted tetrazoles,37 we were interested in
removing the newly formed heterocyclic rings from the
[Re6Se8]2+ cluster core. All reactivity studies were monitored
1
via H and 31P NMR spectroscopy so that product formation
could be observed over a period of time. The 31P NMR data
gave us insight into the transformation of the cluster complex,
1
while the H NMR spectral data enabled us to determine the
Figure 4. The ORTEP diagram of the [Re6Se8(PEt3)5(p-acetylbenzo-
nitrile)]2+ ion showing the atom labeling scheme. Non-hydrogen
atoms are represented by Gaussian ellipsoids at the 30% probability
level. Hydrogen atoms and the carbon atoms of the PEt3 ligands were
omitted for clarity.
outcome of the product heterocyclic rings.
Reaction of 8 with HBF4. For the reaction of
[Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+ with HBF4 (con-
ducted in CD3CN, see Experimental Section for further
details), the 31P data was more useful because it was difficult
to see the −NH hydrogen from the product in the
1H NMR spectra. Figure 6 shows the 31P spectral data for
this reaction. Initially (t = 0) only the starting rhenium cluster
(8) is present (peaks at −24.56 and −29.24 ppm). However,
within 10 min a substantial amount of the product [Re6Se8-
(PEt3)5(NCCD3)]2+ (peaks at −24.78 and −28.89 ppm) had
formed, and the reaction was complete within 30 min. Because
the reaction proceeded so quickly at 100 °C, we tested to see
if the reaction would proceed at room temperature. Even after
6 h at ∼22 °C, there was no trace of the product cluster,
[Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+ and [Re6Se8(PEt3)5-
(2,5-p-aminophenyltetrazolate)]+, favor the N2 isomer as
shown in Figure 5. The Re6−N2 bond lengths for these tetra-
zolate complexes are 2.151(11) and 2.137(7) Å for 8•CH2Cl2
and 6, respectively. This compares to a Re−N bond length of
2.143(8) Å reported earlier for the methyltetrazolate complex,
[Re6Se8(PEt3)5(1,5-MeN4C)]+.16 There is no significant differ-
ence between the bond lengths within the phenyltetrazolate
ring themselves, indicating delocalization of the π electrons.
This is what is commonly observed for nonbridging tetrazolate
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Figure 6. 31P spectral data of the a CD3CN solution containing
[Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+ with HBF4 monitored over a
30 min time period. Resonances at −24.78 and −28.89 ppm are
assigned to [Re6Se8(PEt3)5(CD3CN)]2+.
Figure 7. Reaction of [Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+ and
MeI in CDCl3 monitored via 31P NMR spectroscopy at different time
intervals. Resonances at −30.71 and −31.66 ppm are due to
[Re6Se8(PEt3)5I]+.
[Re6Se8(PEt3)5(NCCD3)]2+. Thus, heat is necessary for this
reaction to proceed. In 2007, we reported the displacement
of free 5-methyltetrazole after heating a MeCN solution of
[Re6Se8(PEt3)5(1,5-methyltetrazolate)]+ and HCl at reflux for
48 h.16 At that time, we did not monitor the reaction. Here, we
found that after monitoring the reaction of [Re6Se8(PEt3)5-
(1,5-methyltetrazolate)]+ with HBF4 in CD3CN (sealed NMR
tube at 100 °C) by 31P NMR spectroscopy, the reaction was
complete within 12 h (i.e., complete conversion to [Re6Se8-
(PEt3)5(NCCD3)]2+). Comparing the protonation of these two
tetrazolate complexes (2,5-phenyltetrazolate vs 1,5-methylte-
trazolate), we see that protonation of the phenyl-substituted
complex occurs much more quickly. This is likely caused by
differences in the substituent on the tetrazolate ring. It is re-
asonable to assume that the methyl-substituted tetrazolate ligand
would be a stronger Lewis base than the phenyl tetrazolate
ligand because of the electron-donating nature of the methyl
group, thus, making it more difficult to substitute, even when
protonated.
Scheme 3
the integration of the proton resonances. The 31P NMR spectral
data obtained from the reaction of 8 with benzylbromide (BnBr)
in CDCl3 was similar to the MeI reaction in that the resonances
of the PEt3 ligands of 8 disappear over time as the resonances
due to the [Re6Se8(PEt3)5Br]+ product grow in (Figure S16,
Supporting Information). The reaction takes about the same
1
amount of time as the MeI reaction (24 h). The H NMR
spectrum taken at 24 h also shows the presence of both isomers
of the alkylated product. Specifically, 1-benzyl-5-phenyltetrazole
was present in 91% (−CH2− protons appear at 5.52 ppm) and
the 2-benzyl-5-phenyltetrazole isomer in 9% (−CH2− protons
appear at 5.70 ppm).38,39 In both alkylation reactions, a very
small set of peaks downfield of the starting complex begins to
appear at ∼30 min to 1 h, increases in intensity at 4 h, and then
decreases again. These peaks are no longer present once the
reaction is over. We propose these are due to an intermediate,
possibly the cluster complex containing the disubstituted tetrazole
(vide infra).
We also investigated the reactivity of [Re6Se8(PEt3)5(1,5-
methyltetrazolate)]+ with both MeI and BnBr for comparison
with the reactivity of 8. Monitoring the reaction of [Re6Se8-
(PEt3)5(1,5-methyltetrazolate)]+ with MeI via 31P NMR
spectroscopy, we see that within 30 min almost all of the
starting cluster complex has been converted to what we believe
is an intermediate whose peaks are shifted downfield from
Alkylation Studies. Alkylation of the tetrazolate ring also
resulted in removal of these rings from the cluster core. The
31P NMR spectral data for the reaction of [Re6Se8(PEt3)5-
(2,5-phenyltetrazolate)](BF4) with MeI is shown in Figure 7.
Over a 17 h time period, the resonances due to 8 decrease in
intensity, while the resonances due to the formation of the
1
[Re6Se8(PEt3)5I]+ product increase in intensity. The H NMR
spectrum of the solution at 17 h shows the presence of two new
resonances in the region expected for the −NCH3 substituent,
one at 4.38 and the other at 4.17 ppm (Figure S15, Supporting
Information). Comparing our data with the previously reported
values for the 1,5- and 2,5-disubstituted products, we concluded
that a mixture of free tetrazoles, i.e., 2-methyl-5-phenyltetrazole
(N−CH3 at 4.38 ppm) and 1-methyl-5-phenyltetrazole (N−CH3
at 4.17 ppm) actually formed (see Scheme 3).38 The major
product is 1-methyl-5-phenyltetrazole (80%) as determined by
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the starting material. Over the remainder of the reaction period
(24 h), this cluster intermediate is slowly converted into
the product iodo complex, [Re6Se8(PEt3)5I]+ (Figure 8).
example, in the reaction of the [Re6Se8(PEt3)5(1,5-methyl-
tetrazolate)]+ with MeI the intermediate would be [Re6Se8-
(PEt3)5(1-methyl-5-methyltetrazole)]2+. There are examples of
metal complexes containing neutral tetrazole rings; in most
cases, these have been generated via the alkylation or
protonation of metal tetrazolate complexes with electrophilic
reagents containing weakly coordinating anions (i.e.,
CF3SO3Me instead of MeI for the alkylating agent).33,42
While intermediates are observed in all four of our alkylation
reactions, they are most prominent in reactions containing the
1,5-methyltetrazolate ligand. Thus, we propose that alkylation
of [Re6Se8(PEt3)5(1,5-methyltetrazolate)]+ is relatively fast and
subsequent substitution of the tetrazole ring by the halide
is comparatively slow, i.e., k1 > k2 (Scheme 4a). Our data
supports this theory as we see that the starting tetrazolate
complex ([Re6Se8(PEt3)5(1,5-methyltetrazolate)]+) has com-
pletely reacted within ∼1 h. (There actually appears to be a
mixture of intermediates in these reactions, which could be
assigned to the [Re6Se8(PEt3)5(1,5-dimethyltetrazole)]2+ and
[Re6Se8(PEt3)5(2,5-dimethyltetrazole)]2+ isomers.) In contrast,
it appears as though alkylation of [Re6Se8(PEt3)5(2,5-phenyl-
tetrazolate)]+ is relatively slow. Therefore, we observe only
small amounts of the intermediate. As soon as the phenyl-
tetrazolate ring is alkylated, it is replaced by the halide ion in
solution leading to the formation of the free tetrazole and the
product cluster complex (Scheme 4b, k1 < k2). This behavior is
likely a combination of both steric and electronic effects. The
methyltetrazolate ring is more electron rich and less sterically
hindered than the phenyltetrazolate ring. Therefore, we
anticipated that the tetrazolate ring in [Re6Se8(PEt3)5(1,5-
methyltetrazolate)]+ would be alkylated more quickly than that
of [Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+. Similarly, slow sub-
stitution of the neutral tetrazole ring in the intermediate shown
in Scheme 4a, compared to Scheme 4b, is also consistent with
this argument.
Even more interesting is the fact that these alkylations lead
to the formation of a mixture of isomeric tetrazoles (i.e., 1,5-
disubstituted and 2,5-disubstituted tetrazoles) as shown in
Scheme 3. Nelson and co-workers reported the exclusive forma-
tion of 1,5-disubstituted tetrazoles when reacting [Co(P(nBu)3)-
(dmgH)2(5-R-tetrazolate)] (dmgH = monoanion of dimethyl-
glyoxime, and R = CH3, C6H5, etc.) with MeI and BnBr.38 They
concluded that sole formation of the 1,5-disubstituted isomer
was indirect evidence of strictly N2 coordination of the anionic
tetrazolate ligands (alkylation of the N1 or N4 nitrogen and
subsequent removal would lead to the 1,5-disubstituted
product). Other studies have also shown that alkylation or
protonation occurs exclusively at the N4 site on both N1 and
N2 coordinated tetrazolates43 and show the formation of 1,5-
disubstituted tetrazoles from N2 coordinated tetrazolates.44
Mixtures of disubstituted tetrazoles are typically seen with
alkali metal salts or metals containing a mixture of the N1 and
N2 coordinated tetrazolate rings.45 Although the free 1,5-
disubstituted tetrazole is the major product in all of our
alkylation studies, we do see 20% or more of the 2,5-
disubstituted isomer in at least three of the reactions described
here. In the case of [Re6Se8(PEt3)5(1,5-methyltetrazolate)]+,
we are aware that the coordinated ligand will undergo isomeri-
zation to a 50:50 mixture of the N1 and N2 tetrazolates in
CDCl3, which might explain the generation of both the 1,5- and
2,5-disubstituted products. However, we are certain that
[Re6Se8(PEt3)5(2,5-phenyltetrazolate)]+ only contains the N2
coordinated tetrazolate; therefore, we were expecting to see the
Figure 8. Reaction of [Re6Se8(PEt3)5(1,5-methyltetrazolate)]+ and
MeI in CDCl3 monitored via 31P NMR spectroscopy at different time
intervals. Resonances at −30.67 and −31.63 ppm due to
[Re6Se8(PEt3)5I]+.
[Re6Se8(PEt3)5(1,5-methyltetrazolate)]+, which contains the
N1 coordinated tetrazolate, is known to isomerize to a 50:50
mixture of the N1 and N2 coordinated tetrazolate ligands.
Because we do not observe the formation of [Re6Se8-
(PEt3)5(2,5-methyltetrazolate)]+, the rapid conversion to this
intermediate species must be faster than linkage isomerization.
In terms of the alkylated products generated in this reaction, a
mixture of free tetrazole isomers (72% 1-methyl-5-methyl-
tetrazole and 28% 2-methyl-5-methyltetrazole) is shown in the
1H NMR spectrum at 24 h (Figure S17, Supporting Information).
These isomers were identified by both methyl substituents on the
free tetrazole ring, i.e., 1-methyl-5-methyltetrazole appears at
2.55 ppm (−CCH3) and 3.97 ppm (−NCH3)), while 2-methyl-
5-methyltetrazole appears at 2.50 ppm (−CCH3) and 4.26 ppm
(-NCH3)).38,40 The reaction of [Re6Se8(PEt3)5(1,5-methyltetra-
zolate)]+ with BnBr is similar to that of MeI in that within an hour
the 31P resonances of the initial tetrazolate complex have dis-
appeared and an intermediate has formed. Over the next 20 h, the
conversion of the intermediate to the product complex, [Re6Se8-
(PEt3)5Br]+, is observed (Figure S18, Supporting Information).
1
Analysis of the H NMR spectrum at 20 h shows the major
organic product to be 1-benzyl-5-methyltetrazole generated
in 74%. The resonances observed appear at 2.39 (−CH3) and
5.44 ppm (N−CH3) and match those observed by Nelson and co-
workers.38 We also observe a second set of peaks at 2.45 and
5.64 ppm, which we believe are due to the 2-benzyl-5-
methyltetrazole.41
The intermediates observed in the above reactions are
believed to be the cluster complex containing coordinated
tetrazoles (i.e., the ring after it has been alkylated). For
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Scheme 4
exclusive formation of 1,5-disubstituted tetrazoles. In the
reaction of 8 with MeI and BnBr, we observed formation of
20% of the 2-methyl-5-phenyltetrazole and 8% of 2-benzyl-5-
phenyltetrazole, respectively. This indicates an isomerization
process is taking place. There are some examples of disub-
stituted tetrazoles undergoing isomerization when one of the
nitrogen atoms contains an imino substituent but only one
known report involving the isomerization of dialkyl (or aryl)
tetrazoles.46,47 Isida et al. reported that 1-methyl-5-phenyl-
tetrazole was quantitatively converted to 2-methyl-5-phenyl-
tetrazole when heated at 130 °C in MeI for 10 h.47 However,
heating 1-methyl-5-phenyltetrazole at 70 °C for 20 h led
to a mixture of 2-methyl-5-phenyltetrazole (27%) and the 1,4-
dimethyl-5-phenyltetrazolium salt (35%).
Considering the possibility of this type of isomerization
taking place, we examined the data obtained from the reaction
of 8 with MeI more carefully. It is necessary for us to point out
that there is some discrepancy in the literature values reported
for the 2-methyl-5-phenyltetrazole (but not for 1-methyl-5-
phenyltetrazole). Therefore, while we are certain that the
resonance at 4.17 ppm is due to 1-methyl-5-phenyltetrazole, it
is difficult for us to unambiguously assign the resonance at
4.38 ppm, i.e., is it the 2,5-disubstituted product or the 1,4-
dimethyl-5-phenyltetrazolium salt? Nelson reports free 2-methyl-
5-phenyltetrazolate at 4.35 ppm, while Fraser and Haque report
it at 4.25 ppm, and the methyl resonances of the 1,4-dimethyl-
5-phenyltetrazolium salt appears at 4.30 ppm according to
Isida.38,47,48 On the basis of Isida’s isomerization study, we
would expect the 1,5-disubstituted isomer to be generated early
on in the reaction, and then the 1,5-disubstituted tetrazole
would isomerize into the 2,5-disubstituted isomer. In addition,
we would expect to see only the 2-methyl-5-phenyltetrazole
product or a mixture of the 2,5-disubstituted isomer and the
tetrazolium salt. However, the 1,5-disubstituted tetrazole is
the major product in this and all alkylation reactions. Therefore,
we propose that a different mechanism for isomerization is in play.
It seems likely that the [Re6Se8]2+ cluster core is facilitating the
isomerization process. Possibilities include π bonded tetrazole or
tetrazolate intermediates.49 However, further studies need to be
conducted to elucidate the exact mechanism.
(noncoordinated) tetrazoles. Alkylation studies revealed the
formation of 1,5- and 2,5-disbustituted tetrazoles. This unexpected
result indicates an isomerization process taking place; the data
indicate the possibility of the cluster complex facilitating this
isomerization process.
ASSOCIATED CONTENT
* Supporting Information
■
S
Cyclic voltammograms of compounds 1−5 (Figures S1−S5),
31P NMR spectra of 3 and 5 in CD3CN after 7 weeks (Figure S6),
31P NMR spectra of 2 in CD3CN at different time intervals
(Figure S7), 31P NMR spectra of 3 plus NaN3 in acetone-d6 at
different time intervals (Figure S8), simulated and experimental
1H NMR spectrum of 10 (Figure S9), UV−vis spectra of all
1
compounds (Figures S10−S14), H NMR spectrum at 17 h of
the reaction between 8 and MeI (Figure S15), 31P NMR
spectra data of the reaction between 8 and BnBr (Figure S16),
1H NMR spectrum at 24 h of the reaction between
[Re6Se8(PEt3)5(1,5-methyltetrazolate)]+ and MeI (Figure S17),
and 31P NMR spectra data of the reaction between [Re6Se8-
(PEt3)5(1,5-methyltetrazolate)]+ and BnBr (Figure S18). The
X-ray crystallographic files in CIF format for 4•NCCH3,
8•CH2Cl2, and 6. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
■
*Address: Department of Chemistry, Campus Box 4160,
Illinois State University, Normal, IL 61790-4160. Phone:
(309) 438-2359. Fax: (309) 438-5538. E-mail: lfszcze@ilstu.edu.
Funding Sources
This research was supported by the NSF (RUI-0957729).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Thanks to Steven J. Peters, Illinois State University, for helpful
discussions and for assistance on the NMR simulation program.
■
Summary. All of newly reported benzonitrile complexes
(compounds 1−5) undergo cycloaddition reactions with
inorganic azides to form 5-phenyltetrazolate rings. There is no
noticeable effect of the para substituent on the redox properties or
the cycloaddition reactivity of the benzonitrile complexes. How-
ever, the para substituent does influence the rate of substitution
of the benzonitrile ligand by MeCN. The tetrazolate complexes, 8
and [Re6Se8(PEt3)5(1,5-methyltetrazolate)]+, undergo reaction
with electrophilic reagents leading to the formation of free
REFERENCES
■
(1) (a) Butler, R. N. In Comprehensive Coordination Chemistry;
Katritzky, A. R., Rees, C. W., Eds.; Pergamon Press: New York, 1984;
pp 791−850. (B) Gilchrist, T. L. Heterocyclic Chemistry, 3rd ed.;
Longman: Essex, 1997; Chapter 1.
(2) (a) Zhan, P.; Li, Z.; Liu, X.; De Clercq, E. Mini-Rev. Med. Chem.
2009, 9, 1014−1023. (b) Yet, L. Prog. Heterocycl. Chem. 2008, 19,
208−241. (c) Park, H.; Merz, K. M., Jr. J. Med. Chem. 2005, 48, 1630−
1637. (d) Kozikowski, A. P.; Zhang, J.; Nan, F.; Petukhov, P. A.;
7834
dx.doi.org/10.1021/ic300877r | Inorg. Chem. 2012, 51, 7825−7836

Inorganic Chemistry
Article
Grajkowska, E.; Wroblewski, J. T; Yamamoto, T.; Bzdega, T.;
Wroblewska, B.; Neale, J. H. J. Med. Chem. 2004, 47, 1729−1738.
(3) Steinhauser, G.; Klapoetke, T. M. Angew. Chem., Int. Ed. 2008, 47,
3330−3347.
(4) (a) Allen, F. H.; Groom, C. R.; Liebeschuetz, J. W.; Bardwell, D.
A.; Olsson, T. S. G.; Wood, P. A. J. Chem. Inf. Model. 2012, 52, 857−
866. (b) Myznikov, L. V.; Hrabalek, A.; Koldobskii, G. I. Chem.
Heterocycl. Compd. 2007, 43, 1−9. (c) Herr, R. J. Biorg. Med. Chem.
2002, 10, 3379−3393. (d) Carini, D. J.; Duncia, J. V.; Aldrich, P. E.;
Chiu, A. T.; Johnson, A. L.; Pierce, M. E.; Price, W. A.; Santella, J. B.,
III; Wells, G. J. J. Med. Chem. 1991, 34, 2525−2547. (e) McGuire, J. J.;
Russell, C. A.; Bolanowska, W. E.; Freitag, C. M.; Jones, C. S.; Kalman,
T. I. Cancer Res. 1991, 50, 1726−1731.
N. G.; Sokolov, M. N.; Fedin, V. P. Russ. Chem. Rev. 2007, 76, 529−
552. (f) Pilet, G.; Perrin, A. C. R. Chimie 2005, 1728−1742.
(20) Zheng, Z.; Long, J. R.; Holm, R. H. J. Am. Chem. Soc. 1997, 119,
2163−2171.
(21) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garcia-Granda,
S.; Israel, R.; Gould, R. O.; Smits, J. M. M. The DIRDIF-99 Program
System; Crystallography Laboratory, University of Nijmegen: The
Netherlands, 1999.
(22) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Smits, J. M. M.;
Garcia-Granda, S.; Gould, R. O. The DIRDIF-2008 Program System;
Crystallography Laboratory, Radboud University Nijmegen: The
Netherlands, 2008.
(23) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
(24) Sluis, P.; van der; Spek, A. L. Acta Crystallogr. 1990, A46, 194−
201.
(5) (a) Yu, K.-L.; Johnson, R. L. J. Org. Chem. 1987, 52, 2051−2059.
(b) Zabrocki, J.; Marshall, G. R. Methods Mol. Med. 1999, 23, 417−
436. (c) Zabrocki, J.; Smith, G. D.; Dunbar, J. B., Jr.; Iijima, H.;
Marshall, G. R. J. Am. Chem. Soc. 1988, 110, 5875−5880.
(6) (a) Zhang, J.-P.; Zhang, Y.-B.; Lin, J.-B.; Chen, X.-M. Chem. Rev.
2012, 112, 1001−1033. (b) Aromi, G.; Barrios, L. A.; Roubeau, O.;
Gamez, P. Coord. Chem. Rev. 2011, 255, 485−546. (c) Zhao, H.; Qu,
Z.-R.; Ye, H.-Y.; Xiong, R.-G. Chem. Soc. Rev. 2008, 37, 84−100.
(7) Ouelette, W.; Prosvirin, A. V.; Whitenack, K.; Dunbar, K. R.;
Zubieta, J. Angew. Chem., Int. Ed. 2009, 48, 2140−2143.
(25) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(26) PLATON: A Multipurpose Crystallographic Tool. Utrecht
University: Utrecht, The Netherlands, 2001.
(27) (a) Engeldinger, E.; Armspach, D.; Matt, D.; Jones, P. G.
Chem.Eur. J. 2003, 9, 3901−3105. (b) Boring, W. C.; Iwamoto, R.
T. Inorg. Chim. Acta 1973, 7 (2), 264−266. (c) Shoeib, T.; El Aribi, H.;
Siu, K. W. M.; Hopkinson, A. C. J Phys. Chem. A 2001, 105, 710−719.
(28) Willer, M. W.; Long, J. R.; McLauchlan, C. C.; Holm, R. H.
Inorg. Chem. 1998, 37, 328−333.
(8) Finnegan, W. G.; Henry, R. A.; Lofquist, R. J. Am. Chem. Soc.
1958, 80, 3908−3911.
(29) Nakamoto, K. In Infrared and Raman Spectra of Inorganic and
Coordination Compounds; John Wiley and Sons, Inc.: New York, 1997;
pp 105−107.
(9) (a) Koldobskii, G. I.; Ostrovskii, V. A. Russ. Chem. Rev. 1994, 63,
797−814. (b) Das, B.; Reddy, C. R.; Kumar, D. N.; Krishnaiah, M.;
Narender, R. Synlett 2012, 3, 391−394. (c) Roh, J.; Artamonova, T. V.;
Vavrova, K.; Koldobskii, G. I.; Hrabalek, A. Synthesis 2009, 13, 2175−
2178. (d) Kantam, M. L.; Balasubrahmanyam, V.; Kumar, K. B. V.
Synth. Commun. 2006, 36, 1809−1814. (e) Su, W.-K.; Hong, Z.; Shan,
W.-G.; Zhang, X.-X. Eur. J. Org. Chem. 2006, 2723−2726.
(10) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40, 2004−2021.
(30) Garcia, M. H.; Mendes, P. J.; Dias, A. R. J. Organomet. Chem.
2005, 690, 4063−4071.
(31) Gutmann, V. The Donor−Acceptor Approach to Molecular
Interactions; Plenum Press: New York, 1978; p 20.
(32) Ellis, W. R., Jr.; Purcell, W. L. Inorg. Chem. 1982, 21, 834−837.
(33) Stagni, S.; Palazzi, A.; Zacchini, S.; Ballarin, B.; Bruno, C.;
Marcaccio, M.; Paolucci, F.; Monari, M.; Carano, M.; Bard, A. J. Inorg.
Chem. 2006, 45, 695−709.
(11) (a) Demko, Z. P; Sharpless, K. B. J. Org. Chem. 2001, 66, 7945.
(b) Demko, Z. P; Sharpless, K. B. Org. Lett. 2002, 4, 2525−2527.
(12) (a) Kukushkin, V. Y.; Pombeiro, A. J. L. Chem. Rev. 2002, 102,
1771−1802. (b) Paul, P.; Nag, K. Inorg. Chem. 1987, 26, 2969−2974.
(c) Guillard, R.; Perrot, I.; Tabard, A.; Richard, P.; Lecomte, C.; Liu, Y.
H.; Kadish, K. M. Inorg. Chem. 1991, 30, 27−37. (d) Demadis, K. D.;
Meyer, T. J.; White, P. S. Inorg. Chem. 1998, 37, 3610−3619.
(e) Mukhopadhyay, S.; Lasri, J.; Charmier, M. A. J.; Guedes da Silva,
M. F. C.; Pombiero, A. J. L. Dalton Trans. 2007, 5297−5304.
(13) (a) Bauer, C. B.; Concolino, T. E.; Eglin, J. L.; Rogers, R. D.;
Staples, R. J. J. Chem. Soc., Dalton Trans. 1998, 2813−2817.
(b) Neuman, D.; Paraskevopoulou, P.; Mertis, K.; Staples, R. J.;
Stavropoulos, P. Inorg. Chem. 2000, 39, 5530−5537. (c) Eglin, J. L.
Comments Inorg. Chem. 2002, 23, 23−43. (d) McGaff, R. W.; Dopke,
N. C.; Hayashi, R. K.; Powell, D. R.; Treichel, P. M. Polyhedron 2000,
19, 1245−1254.
(34) (a) Yoshimura, T.; Umakoshi, K.; Sasaki, Y.; Ishizaka, S.; Kim,
H.-B.; Kitamura, N. Inorg. Chem. 2000, 39, 1765−1772. (b) Long, J.
R.; McCarty, L. S.; Holm, R. H. J. Am. Chem. Soc. 1996, 118, 4603.
(c) Yoshimura, T.; Umakoshi, K.; Sasaki, Y.; Sykes, A. G. Inorg. Chem.
1999, 38, 5557−5564. (d) Brylev, K. A; Naumov, N. G.; Peris, G.;
Llusar, R.; Fedorov, V. E. Polyhedron 2003, 22, 3383. (e) Baudron, S.
A.; Deluzet, A.; Boubekeur, K.; Batail, P. Chem.Commun. 2000, 2124.
(f) Dorson, F.; Molard, Y.; Cordier, S.; Fabre, B.; Efremova, O.;
Rondeau, D.; Mironov, Y.; Circu, V.; Naumov, N.; Perrin, C. Dalton
Trans. 2009, 1297. (g) Brylev, K. A.; Mironov, Y. V.; Kozlova, S. G.;
Fedorov, V. E.; Kim, S.-J.; Pietzsch, H.-J.; Stephan, H.; Ito, A.; Ishizaka,
S.; Kitamura, N. Inorg. Chem. 2009, 48, 2309.
(35) (a) Zheng, Z.; Gray, T. G.; Holm, R. H. Inorg. Chem. 1999, 38,
4888−4895. (b) Zheng, Z.; Holm, R. H. Inorg. Chem. 1997, 36, 5173−
5178.
(36) Examined 34 structures containing N2-bound tetrazolate ligands
coordinated to a single transition metal center via a CSD search that
includes the following representative examples: (a) Liu, F.-C.; Lin, Y.-
L.; Yang, P.-S.; Lee, G.-H.; Peng, S.-M. Organometallics 2010, 29,
4282−4290. (b) Kotera, M.; Sekioka, Y.; Suzuki, T. Inorg. Chem. 2008,
47, 3498−3508. (c) Mukhopadhyay, S.; Lasri, J.; Charmier, M. A. J.;
Guedes da Silva, F. C.; Pombeiro, A. J. L. Dalton Trans. 2007, 5297−
5304. (d) Smolenski, P.; Mukhopadhyay, S.; Guedes da Silva, F. C.;
Charmier, M. A. J.; Pombeiro, A. J. L. Dalton Trans. 2008, 6546−6555.
(37) (a) Koldobskii, G. I.; Kharbash, R. B. Russ. J. Org. Chem. 2003,
39, 453−470. (b) Brigas, A. F. Sci. Synth. 2004, 13, 861−915.
(c) Katritsky, A. R.; Cai, C.; Maher, N. K. Synthesis 2007, 8, 1204−
1208. (d) Harja, S.; Sihah, D.; Bhowmick, M. J. Org. Chem. 2007, 72,
1852−1855.
(14) Werrett, M. V.; Chartrand, D.; Gale, J. D.; Hanan, G. S.;
MacLellan, J. G.; Massi, M.; Muzzioli, S.; Raiteri, P.; Skelton, B. W.;
Silberstein, M.; Stagni, S. Inorg. Chem. 2011, 50, 1229−1241.
(15) Orto, P.; Selby, H. D.; Ferris, D.; Maeyer, J. R.; Zheng, Z. Inorg.
Chem. 2007, 46, 4377−4379.
(16) Szczepura, L. F.; Oh, Meghan K.; Knott, S. A. Chem. Commun.
2007, 4617−4619.
(17) (a) Tu, X.; Boroson, E.; Truong, H.; Munoz-Castro, A.; Arratia-
̃
Perez, R.; Nichol, G. S.; Zheng, Z. Inorg. Chem. 2010, 49, 380−382.
(b) Tu, X.; Truong, H.; Alster, E.; Munoz-Castro, A.; Arratia-Perez, R.;
̃
Nichol, G. S.; Zheng, Z. Chem.Eur. J. 2011, 17, 580−587.
(18) (a) Demko, Z. P.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002,
41, 2110−2113. (b) Demko, Z. P.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2002, 41, 2113−2116.
(19) (a) Prokopuk, N.; Shriver, D. F. Adv. Inorg. Chem. 1999, 46, 1−
49. (b) Preetz, W.; Peters, G.; Bublitz, D. Chem. Rev. 1996, 96, 977−
1025. (c) Gabriel, J.-C. P.; Boubekeur, K.; Uriel, S.; Batail, P. Chem.
Rev. 2001, 101, 2037−2066. (d) Welch, E. J.; Long, J. R. Prog. Inorg.
Chem. 2005, 54, 1−45. (e) Fedorov, V. E.; Mironov, Y. V.; Naumov,
(38) Takach, N. E.; Holt, E. M.; Alcock, N. W.; Henry, R. A.; Nelson,
J. H. J. Am. Chem. Soc. 1980, 102, 2968−2979.
(39) Aridoss, G.; Laali, K. K. Eur. J. Org. Chem. 2011, 6343−6355.
(40) Markgraf, J. H.; Bachmann, W. T. J. Org. Chem. 1965, 30, 3472−
3474.
7835
dx.doi.org/10.1021/ic300877r | Inorg. Chem. 2012, 51, 7825−7836

Inorganic Chemistry
Article
(41) 1H NMR resonances for the −CH2− protons of the 2-methyl-5-
benzyltetrazole were not previously reported.
(42) (a) Palazzi, A.; Stagni, S.; Bordoni, S.; Monari, M.; Selva, S.
Organometallics 2002, 21, 3774−3781. (b) Palazzi, A.; Stagni, S. J.
Organomet. Chem. 2005, 690, 2052−2061.
(43) Jackson, W. G.; Cortez, S. Inorg. Chem. 1994, 33, 1921−1927.
(44) Chang, K.-H.; Lin, Y.-C.; Liu, Y.-H.; Wang, Y. Dalton Trans.
2001, 3154−3159.
(45) Gaponik, P. N.; Voitekhovich, S. V.; Ivanshkevich, O. A. Russ.
Chem. Rev. 2006, 75, 507−539.
(46) (a) Dabbagh, H. A.; Lwowski, W. J. Org. Chem. 2000, 65, 2784−
2790. (b) Ostrovskii, V. A.; Koren, A. O. Heterocycles 2000, 53, 1421−
1448. (c) Katritzky, A. R. J. Org. Chem. 2010, 75, 6468−6476.
(47) Isida, T.; Kozima, S.; Nabika, K.; Sisido, K. J. Org. Chem. 1971,
36, 3807−3810.
(48) Fraser, R. R.; Haque, K. E. Can. J. Chem. 1968, 46, 2855−2859.
(49) (a) Kamijo, S.; Jin, T.; Yamamoto, Y. J. Org. Chem. 2002, 67,
7413−7417. (b) John, E. O.; Willett, R. D.; Scott, B.; Kirchmeier, R.
L.; Shreeve, J. M. Inorg. Chem. 1989, 28, 893−897.
7836
dx.doi.org/10.1021/ic300877r | Inorg. Chem. 2012, 51, 7825−7836