New water-soluble azido- and derived tetrazolato-platinum(ii) complexes with PTA. Easy metal-mediated synthesis and isolation of 5-substituted tetrazoles

Article abstract of DOI:10.1039/b808156e

The water-soluble four- and five-coordinate diazido-platinum(ii) complexes cis-[Pt(N₃)₂(PTA)₂] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), cis-[Pt(N₃)₂(Me-PTA) ₂]I₂ (2) (Me-PTA = N-methyl-1,3,5-triaza-7- phosphaadamantane cation) and [Pt(N₃)₂(PTA)₃] (3) were obtained by reactions of cis-[Pt(N₃)₂(PPh ₃)₂] with PTA or [Me-PTA]I in dichloromethane. [2 + 3] cycloadditions of 1 with organonitriles NCR gave the bis(tetrazolato) complexes trans-[Pt(N₄CR)₂(PTA)₂] (R = Ph (4), 4-ClC ₆H₄ (5) or 3-NC₅H₄ (6)), the reactions being greatly accelerated by microwave irradiation. 5-R-1H-Tetrazoles N₄CR (R = Ph, 4-ClC₆H₄ and 3-NC ₅H₄) were easily liberated from the tetrazolato complexes 4-6 and isolated in high yields, in a single-pot process, upon reaction with aqueous diluted HCl, with concomitant formation of the water soluble cis-[Pt(Cl)₂(PTA-H)₂] complex 7. Alternatively, in a less convenient method, the tetrazoles could be liberated on reaction of 4-6 with propionitrile which also leads to the dicyano trans-[Pt(CN)₂(PTA) ₂] complex 8. The compounds were characterized by IR, ¹H, ¹³C and ³¹P{¹H} NMR spectroscopies, FAB ⁺-MS or ESI-MS, elemental analyses and (for 1 and 4) also by X-ray diffraction.

Full text of DOI:10.1039/b808156e

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www.rsc.org/dalton | Dalton Transactions
New water-soluble azido- and derived tetrazolato-platinum(II) complexes with
PTA. Easy metal-mediated synthesis and isolation of 5-substituted tetrazoles†
Piotr Smolen´ski,a Suman Mukhopadhyay,a M. Fa´tima C. Guedes da Silva,a,b M. Ad´ılia Janua´rio Charmiera,b
and Armando J. L. Pombeiro*a
Received 14th May 2008, Accepted 7th August 2008
First published as an Advance Article on the web 9th October 2008
DOI: 10.1039/b808156e
The water-soluble four- and five-coordinate diazido-platinum(II) complexes cis-[Pt(N3)2(PTA)2] (1)
(PTA = 1,3,5-triaza-7-phosphaadamantane), cis-[Pt(N3)2(Me-PTA)2]I2 (2) (Me-PTA =
N-methyl-1,3,5-triaza-7-phosphaadamantane cation) and [Pt(N3)2(PTA)3] (3) were obtained by
reactions of cis-[Pt(N3)2(PPh3)2] with PTA or [Me-PTA]I in dichloromethane. [2 + 3] cycloadditions of 1
with organonitriles NCR gave the bis(tetrazolato) complexes trans-[Pt(N4CR)2(PTA)2] (R = Ph (4),
4-ClC6H4 (5) or 3-NC5H4 (6)), the reactions being greatly accelerated by microwave irradiation.
5-R-1H-Tetrazoles N4CR (R = Ph, 4-ClC6H4 and 3-NC5H4) were easily liberated from the tetrazolato
complexes 4–6 and isolated in high yields, in a single-pot process, upon reaction with aqueous diluted
HCl, with concomitant formation of the water soluble cis-[Pt(Cl)2(PTA-H)2] complex 7. Alternatively,
in a less convenient method, the tetrazoles could be liberated on reaction of 4–6 with propionitrile
which also leads to the dicyano trans-[Pt(CN)2(PTA)2] complex 8. The compounds were characterized
1
by IR, 1H, 13C and 31P{ H} NMR spectroscopies, FAB+-MS or ESI-MS, elemental analyses and (for 1
and 4) also by X-ray diffraction.
resulting in a shortening of the reaction time relatively to the
Introduction
conventional heating and eventually in a higher selectivity. To
In view of the wide applications and pharmacological interest
explore further our previous studies in this arena towards the syn-
of N-containing heterocycles, the chemistry of tetrazoles and
thesis and isolation of 5-substituted-1H-tetrazoles in environment-
their complexes, in particular, has received a good attention.1 A
friendly conditions, the use of the hydrophilic 1,3,5-triaza-7-
variety of tetrazole compounds was obtained by cycloaddition
phosphaadamantane (PTA, Fig. 1) instead of the hydrophobic
reactions of organonitriles or isocyanides with azido ligands at
PPh3 has been taken into account as a promising alternative.
Group 10 metals.2 Namely, the reactions of various nitriles with
The coordination chemistry of this aqua-soluble phosphine and
derived species has received an increased interest in recent years,8
in view of the good solubility of transition metal PTA complexes in
water, thus making possible their efficient application in aqueous
phase catalysis,8–10 as water-soluble antitumor agents8,11–13 and
photoluminescent materials.8,14–15 In the last years a few new
complexes of platinum(II) and PTA have been tested as catalysts,
e.g. cis-[PtX2(PTA)2] (X = Cl, Br, I),16 and in biological activity
studies, e.g. (SP-4,2)-[PtCl(8-MTT)(PPh3)(PTA)] and cis-[Pt(8-
MTT)2(PPh3)(PTA)] [8-MTT = 8-(methylthio)theophylline].17
Equilibrium constants for the formation of [PtX(PTA)3]+ were
also investigated by reacting [PtCl(PTA)3]Cl with various halides
the diazidoplatinum(II) complex cis-[Pt(N3)2(PPh3)2], investigated
by Fehlhammer et al.,3 gave the corresponding bis(tetrazolato)
complexes trans-[Pt(N4CR)2(PPh3)2]. However, among the several
synthetic methods reported so far, most of them have some
drawbacks like drastic reaction conditions, water sensitivity and
presence of highly toxic, explosive and volatile hydrazoic acids.4
Sharpless et al.5 improved the method by using a zinc salt
as a Lewis acid promoter and performing the reactions in
aqueous media. Amantini et al.6 efficiently synthesized tetrazoles
by the addition of trimethylsilyl azide to organic nitriles using
tetrabutylammonium fluoride as catalyst. Nevertheless, reduction
of the reaction time and temperature and isolation of the final
product by an easy and convenient way usually remain challenging
issues.
and pseudohalides (X = Br-, N3 , NCS-, and I-),18 and the
-
structural characterization of the unusual five-coordinate dis-
torted square pyramidal Pt(II) complex [PtI2(PTA)3] was also
presented.19
Some of us recently showed7 that microwave irradiation pro-
motes the [2 + 3] cycloaddition of organonitriles with azide,
aCentro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico,
TU Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal. E-mail:
pombeiro@ist.utl.pt; Fax: +351 21 8464455; Tel: +351 21 8419237
bUniversidade Luso´fona de Humanidades e Tecnologias, ULHT Lisbon, Av.
do Campo Grande, 376, 1749-024, Lisbon, Portugal
† CCDC reference numbers 688071 & 688072. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b808156e
Fig. 1 Structures of PTA and the derived alkylated (Me-PTA) and
protonated (PTA-H) species.
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We now report the synthesis of the new water-soluble
four- and five-coordinate diazido-platinum(II) complexes cis-
[Pt(N3)2(PTA)2] (1), cis-[Pt(N3)2(Me-PTA)2]I2 (2) (Me-PTA =
N-methylated-PTA, Fig 1) and [Pt(N3)2(PTA)3] (3), as well as of
the bis(tetrazolato) compounds trans-[Pt(N4CR)2(PTA)2] [R =
Ph (4), 4-ClC6H4 (5) and 3-NC5H4 (6)], derived from [2 + 3]
cycloaddition of NCR with 1, the reaction being accelerated by
microwave irradiation. We have also found an easy and convenient
way to liberate the ligated 5-R-1H-tetrazoles upon treatment of the
complexes with an aqueous 0.1 M HCl solution, which provides
a particularly promising method in view of the good solubility
of the complex product cis-[Pt(Cl)2(PTA-H)2]Cl2 in water, in
contrast with tetrazoles, what greatly facilitates their separation.
microwave CEM Discover reactor (10 mL, 13 mm diameter, 300 W,
2450 50 MHz) which is fitted with a rotational system and an IR
detector of temperature.
Preparation of compounds
cis-[Pt(N3)2(PTA)2]·0.5CH2Cl2, 1·0.5CH2Cl2. To a solution
(15.0 mL) of [Pt(N3)2(PPh3)2] (141 mg, 0.175 mmol) in dichlo-
romethane (15.0 mL), PTA (55.0 mg, 0.350 mmol) was added.
The mixture was stirred for ca. 1 h under dinitrogen at room
temperature. The white precipitate 1 was separated from the
colourless solution by filtration, washed with dichloromethane
(3 ¥ 10 mL) and dried in vacuo to afford complex 1·0.5CH2Cl2 as
a white microcrystalline solid. Yield of 1·0.5CH2Cl2 83% (93 mg).
All complexes were characterized by IR, H, 13C and 31P{ H}
NMR spectroscopies, FAB+-MS (positive fast atom bombardment
mass spectrometry, elemental analyses and (for 1 and 4) also by
X-ray structural analysis.
1
1
Complex 1 is soluble in H2O (S25 C ª 2 mg mL-1), DMSO, MeOH,
◦
slightly soluble in EtOH, CHCl3, CH2Cl2 and THF and insoluble
in C6H6. [Pt(N3)2(PTA)2]·0.5CH2Cl2, C12.5H25N12ClP2Pt (635.89):
calcd C 23.61, N 26.43 H 3.96; found C 23.60, N 26.29, H 3.98.
FAB+-MS: m/z = 593 [M]+, 551 [M-(N3)]+, 509 [M-(N3)2]+, 352
-3
[Pt(PTA)]+. Molar conductivity (CH3NO2, conc. = 10
M):
Experimental
KM 0.3 X-1 cm2 mol-1. IR (KBr): 2924 (s br) n(CH), 2033 (s br)
n(N3), 1448 (m), 1410 (m), 1283 (m), 1242 (s), 1101 (m), 1014 (s),
978 (s), 947 (s), 901 (m), 806 (m), 740 (m), 580 (m) (PTA) cm-1. 1H
Warning!
Much care should be taken when working with azides, especially
when heating, as they are potentially explosive compounds.
NMR (300 MHz, DMSO-d6): d = 4.66 HA and 4.40 HB (JAB
=
13.0 Hz, NCHAHBN, 12H), 4.23 (s, PCH2N, 12H). 31P{ H} NMR
(121.4 MHz, D2O): d = -59.1 (s, J(Pt-P) = 3139 Hz). X-Ray
quality single crystals were grown by slow evaporation in air at
room temperature of a water solution of 1.†
1
General materials and experimental procedures
All manipulations were done under an inert atmosphere of dry
oxygen-free dinitrogen, using standard Schlenk techniques. All
solvents were dried, degassed and distilled prior to use. K2[PtCl4]
(Aldrich), was used as received. 1,3,5-Triaza-7-phosphaada-
mantane (PTA)20, N-methyl-1,3,5-triaza-7-phosphaadamantane
iodide [PTA-Me]I20 and [Pt(N3)2(PPh3)2]21 were synthesized in
accordance with literature methods. C, H and N elemental analyses
were carried out by the Microanalytical Service of the Instituto
Superior Te´cnico in Lisbon. The electrical conductance of the
solutions was measured with a SCHOTT CG 855 conductimeter
at room temperature. The FAB+-MS spectra were obtained on
a Trio 2000 instrument by bombarding 3-nitrobenzyl alcohol
(NBA) matrices of the samples with 8 keV (ca. 1.18 1015 J)
Xe atoms. Mass calibration for data system acquisition was
achieved using CsI. Electrospray mass spectra of 5-substituted-
1H-tetrazoles were carried out with an ion-trap instrument (Varian
500-MS LC Ion Trap Mass Spectrometer) equipped with an
electrospray ion (ESI) source. The solutions in dichloromethane
were continuously introduced into the mass spectrometer source
with a syringe pump at a flow rate of◦10 mL min-1. The drying gas
temperature was maintained at 350 C and dinitrogen was used
as nebulizer gas at a pressure of 35 psi. Scanning was performed
from m/z = 50 to 1500. The compounds were observed in the
negative mode (capillary voltage = -4000 V). Infrared spectra
(4000–400 cm-1) were recorded on a BIO-RAD FTS 3000MX
cis-[Pt(N3)2(Me-PTA)2]I2·CH2Cl2, 2·CH2Cl2. To a solution of
[Pt(N3)2(PPh3)2] (192 mg, 0.239 mmol) in CH2Cl2 (30.0 mL), 20 mL
of a MeOH solution of [Me-PTA]I (143 mg, 0.478 mmol) was
added. The mixture was stirred for ca. 12 h under dinitrogen. The
precipitate 2 was separated from the slightly yellow solution by
filtration, washed with dichloromethane (3 ¥ 20 mL) and dried
in vacuo to afford complex 2 as a pale-yellow microcrystalline
solid. Yield of 2·CH2Cl2 80% (184 mg). Complex 2 is soluble in
H2O, DMSO, MeOH, slightly soluble in EtOH and insoluble in
CHCl3, CH2Cl2, THF and C6H6. [Pt(N3)2(Me-PTA)2]I2·CH2Cl2,
C15H32N12I2Cl2P2Pt (962.24): calcd C 18.72, N 17.42, H 3.35; found
C 18.45, N 17.39, H 3.42. FAB+-MS: m/z = 835 [M-(N3)]+, 793
[M-(N3)2]+, 666 [Pt(Me-PTA)2I]+. Molar conductivity (CH3NO2,
-3
conc. = 10 M): KM 172 X-1 cm2 mol-1. IR (KBr): 2960 (s br)
n(CH), 2060 (s br) n(N3), 1452 (m), 1310 (m), 1279 (m), 1121 (m),
1091 (s), 1026 (m), 968 (m), 932 (m), 901 (m), 815 (m), 751 (m),
1
571 (m) (M-PTA) cm-1. H NMR (300 MHz, DMSO-d6): d =
5.15 HA and 5.05 HB (JAB = 11.2 Hz, NCHAHBN+, 8H), 4.89 (s,
PCH2N+, 4H), 4.56 HA and 4.36 HB (JAB = 11.9 Hz, NCHAHBN,
4H), 4.53 HA and 4.31 HB (JAB = 12.9 Hz, PCHAHBN, 8H), 2.84
1
(s, CH3, 6H). 31P{ H} NMR (121.4 MHz, DMSO-d6): d = -47.2
(s, J(Pt-P) = 3153 Hz).
[Pt(N3)2(PTA)3]·CH2Cl2, 3·CH2Cl2. To a solution (35.0 mL)
of [Pt(N3)2(PPh3)2] (111 mg, 0.138 mmol) in dichloromethane,
PTA (65.0 mg, 0.414 mmol) was added. The cloudy solution was
stirred for ca. 1 h under dinitrogen at room temperature and the
formed colourless solution was taken to dryness in vacuo. The
residue was washed with diethyl ether (3 ¥ 10 mL) to remove PPh3
and crystallized from CH2Cl2 in a fridge (+4 ◦C) to afford complex
3 as a white microcrystalline solid. Yield of 3·CH2Cl2 58% (67 mg).
1
instrument in KBr pellets. H, 13C and 31P NMR spectra were
measured on a Bruker 300 and 400 UltraShieldTM spectrometers
at ambient and low temperatures. 1H and 13C chemical shifts d are
expressed in ppm relative to Si(Me)4 and d(31P) relative to 85%
H3PO4. Coupling constants are in Hz; abbreviations: s, singlet; d,
doublet; m, complex multiplet; vt, virtual triplet; br, broad. The
microwave irradiation experiments were undertaken in a focused
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Complex 3 is soluble in H2O, DMSO, MeOH, EtOH, CHCl3 and
CH2Cl2, sparingly soluble in toluene and insoluble in C6H6 and
diethyl ether. [Pt(N3)2(PTA)3]·CH2Cl2, C19H38N15Cl2P3Pt (835.51):
calcd C 27.31, N 25.15, H 4.58; found C 27.80, N 24.81, H 4.88.
FAB+-MS: m/z = 708 [M]+, 606 [M-(N3)]+. Molar conductivity
d = 8.10, 7.48 (2 dd, C6H4, 3J(HH) = 8.7 Hz, 4J(HH) = 1.32 Hz,
1
8H), 4.43 (s, NCH2N, 12H), 4.13 (s, PCH2N, 12H). 31P{ H} NMR
1
(121.4 MHz, CDCl3): d = -56.3 (s, J(Pt-P) = 2491 Hz). 13C{ H}
NMR (100.6 MHz, CDCl3,): d = 164.3 (s, N4C), 135.6 (s, 4-C,
C6H4), 129.2 (s, 2,6-C, C6H4), 127.7 (s, 3,5-C, C6H4), 127.4 (s, 1-
-3
-1
3
(CH3NO2, conc. = 10 M): KM 0.4 X cm2 mol-1. IR (KBr):
2926 (s br) n(CH), 2052 (s br) n(N3), 1441 (m), 1419 (m), 1289 (m),
1243 (m), 1015 (s), 975 (s), 945 (s), 903 (m), 809 (m), 741 (m),
C, C6H4), 73.2 (vt, J(CP) = 3.5 Hz, N-CH2-N, PTA), 50.3 (vt,
1J(CP) = 9.6 Hz, P-CH2-N, PTA).
trans-[Pt{N4C(3-NC5H4)}2(PTA)2]·0.5CH2Cl2, 6·0.5CH2Cl2.
A mixture of [Pt(N3)2(PTA)2]·0.5CH2Cl2 (1·0.5CH2Cl2) (65.0 mg,
0.10 mmol), 3-NC5H4CN (104 mg, 1.00 mmol) and DMF
(5.0 mL) was added to a cylindrical Pyrex tube which was
then placed in the focused microwave reactor. The system was
left under irradiation for 1 h at 125 ◦C. The solvent was then
removed in vacuo and the resulting residue was washed repeatedly
with 5 mL portions of diethyl ether. Recrystallization from a
dichloromethane–diethyl ether mixture gave off-white crystals
of 6·0.5CH2Cl2. Yield 58% (50 mg). Complex 6 is soluble in
DMSO, MeOH, EtOH, CHCl3, CH2Cl2, sparingly soluble in
H2O and insoluble in diethyl ether and C6H6. trans-[Pt{(3-
NC5H4)}2(PTA)2]·0.5CH2Cl2, C24.5H33N16ClP2Pt (844.11): calcd
C 34.86, N 26.55, H 3.94; found C 35.05, N 26.04, H 3.96.
FAB+-MS: m/z = 802 [M]+, 656 [M–N4C(3-NC5H4)]+. IR (KBr):
2924 (s br), 1621 (m), 1584 (s), 1467 (m), 1413 (m), 1280 (s),
1243 (m), 1096 (m), 1032 (s), 1012 (s), 973 (s), 943 (s), 897 (m),
1
583 (m) (PTA) cm-1. H NMR (400 MHz, CDCl3, 298 K): d =
4.24 (s, PCH2N, 18H,), 4.33 HA and 4.24 HB (JAB = 13.0 Hz,
NCHAHBN, 18H,). 1H NMR (400 MHz, CDCl3, 213 K): d = 4.63
(s, PCH2N, 18H), 4.59 HA and 4.51 HB (JAB = 13.0 Hz, NCHAHBN,
1
18H,). 31P{ H} NMR (162.0 MHz, CDCl3, 298 K): unresolved
1
very broad spectrum. 31P{ H} NMR (162 MHz, CDCl3, 213 K):
2
d = -51.6 (t, J(Pt-P) = 3304 Hz, J(P-P) = 23.5 Hz), -57.6 (d,
J(Pt-P) = 2187 Hz, 2J(P-P) = 23.5 Hz).
trans-[Pt(N4CPh)2(PTA)2]·0.5PhCN, 4·0.5PhCN. A mixture
of [Pt(N3)2(PTA)2]·0.5CH2Cl2 (1·0.5CH2Cl2) (65.0 mg, 0.10 mmol)
and PhCN (5.0 mL, 48.5 mmol) was added to a cylindrical Pyrex
tube which was then placed in the focused microwave reactor.
The system was left under irradiation for 1 h at 100 ◦C. The
excess of PhCN was then removed in vacuo and the resulting
residue was washed repeatedly with 5 mL portions of diethyl ether.
Recrystallization from a dichloromethane/diethyl ether mixture
gave off-white crystals of trans-[Pt(N4CPh)2(PTA)2]·0.5PhCN
(4·0.5PhCN) Yield 65% (57 mg). Complex 4 is soluble in DMSO,
EtOH, CHCl3, CH2Cl2, and insoluble in H2O, diethyl ether
and C6H6. trans-[Pt(N4CPh)2(PTA)2]·0.5PhCN, C29.5H36.5N14.5P2Pt
(851.2): calcd C 41.62, N 23.86, H 4.32; found C 41.38, N 23.16,
H 4.36. FAB+-MS: m/z = 800 [M]+, 654 [M–N4CPh]+. IR (KBr):
2931 (s br), 2230 (m), 1615 (m), 1445 (m), 1384 (m), 1280 (m),
1242 (m), 1100 (m), 1014 (s), 973 (s), 803 (m), 735 (m), 583 (m) cm-1.
1H NMR (300 MHz, CDCl3): d = 8.18-7.45 (m, 2Ph + 0.5 PhCN,
1
798 (m), 762 (m), 737 (m) 582 (m) cm-1. H NMR (300 MHz,
CDCl3): d = 9.42 (dd, H2, 4J(H2H6) = 2.0 Hz, 5J(H2H5) = 0.9 Hz,
3
4
2H), 8.70 (dd, H6, J(H6H5) = 8.0 Hz, J(H6H2) = 2.0 Hz, 2H),
8.45 (ddd, H5, 3J(H5H6) = 8.0 Hz, 3J(H5H4) = 4.9 Hz, 5J(H5H2) =
0.9 Hz, 2H), 7.46 (d, H4, 3J(H4H5) = 4.9 Hz, 2H), 4.44 (s, NCH2N,
1
12H), 4.16 (s, PCH2N, 12H). 31P{ H} NMR (121.4 MHz, CDCl3):
1
d = -56.2 (s, J(Pt-P) = 2479 Hz). 13C{ H} NMR (100.6 MHz,
CDCl3,): d = 162.8 (s, N4C), 150.7 (s, 4-C, py), 149.8 (s, 2-C, py),
3
134.7 (s, 6-C, py), 124.0 (s, 5-C, py), 73.2 (vt, J(CP) = 3.5 Hz,
1
12.5H), 4.45 (s, NCH2N, 12H), 4.23 (s, PCH2N, 12H). 31P{ H}
N-CH2-N, PTA), 50.4 (vt, 1J(CP) = 9.6 Hz, P-CH2-N, PTA).
NMR (121.4 MHz, CDCl3): d = -56.2 (s, J(Pt-P) = 2497 Hz).
1
13C{ H} NMR (100.6 MHz, CDCl3,): d = 164.3 (s, N4C), 135.6
Method (a) for 5-R-1H-tetrazoles (R = Ph, 4-ClC6H4 or 3-
NC5H4) and cis-[Pt(Cl)2(PTA-H)2]Cl2 (7). A suspension of trans-
[Pt(N4CR)2(PTA)2] [4 (170 mg, 0.20 mmol) or 5 (174 mg,
0.20 mmol) or 6 (169 mg, 0.20 mmol)] in aqueous 0.1 M HCl
(15 mL) was refluxed for 0.5 h. The white precipitate formed
during the reaction, after separation by filtration, analyzed as
the corresponding 5-R-1H-tetrazole (R = Ph, 4-ClC6H4 or 3-
NC5H4) (yields ca. 80%). Evaporation to dryness of the filtered
reaction solution led to 7 as a off-white solid. [Pt(Cl)2(PTAH)2]Cl2,
C12H26Cl4N6P2Pt (653.22): calcd C 22.06, N 12.86, H 4.01; found
C 22.54, N 12.67, H 4.63. IR (KBr): 2971 (s br) n(CH), 1447 (m),
1419 (m), 1303 (m), 1242 (w), 1024 (s), 977 (s), 951 (s), 813 (m),
(s, 4-C, C6H5), 133.6 (s, 4-C, C6H5, PhCN), 132.7 (s, 2,6-C, C6H5,
PhCN), 129.2 (s, 2,6-C, C6H5), 128.7 (s, 3,5-C, C6H5 PhCN), 127.7
(s, 3,5-C, C6H5), 127.4 (s, 1-C, C6H5), 113.4 (s, 1-C, C6H5, PhCN),
3
1
73.2 (vt, J(CP) = 6.0 Hz, N-CH2-N, PTA), 50.3 (vt, J(CP) =
15.7 Hz, P-CH2-N, PTA). X-Ray quality single crystals were grown
from CHCl3–toluene solution of 4 in air at room temperature.†
trans-[Pt{N4C(4-ClC6H4)}2(PTA)2], 5. A mixture of [Pt(N3)2-
(PTA)2]·0.5CH2Cl2 (1·0.5CH2Cl2) (65.0 mg, 0.10 mmol), 4-
ClC6H4CN (138 mg, 1.00 mmol) and DMF (5.0 mL) was added
to a cylindrical Pyrex tube which was then placed in the focused
microwave reactor. The system was left under irradiation for 1 h at
125 ◦C. The solvent was then removed in vacuo and the resulting
residue was washed repeatedly with 5 mL portions of diethyl ether.
Recrystallization from a dichloromethane–diethyl ether mixture
gave off-white crystals of 5. Yield 60% (53 mg). Complex 5 is
soluble in DMSO, MeOH, EtOH, CHCl3, CH2Cl2, sparingly
soluble in H2O and insoluble in diethyl ether and C6H6. trans-
[Pt{N4C(4-ClC6H4)}2(PTA)2], C26H32N14Cl2P2Pt (868.6): calcd C
35.95, N 22.58, H 3.71; found C 36.10, N 22.51, H 3.66. FAB+-MS:
m/z = 869 [M]+, 689 [M–N4C(4-ClC6H4)]+. IR (KBr): 2933 (s br),
1630 (m), 1440 (m), 1273 (m), 1239 (m), 1096 (m), 1010 (s), 975 (s),
1
770 (m), 572 (m) (PTA) cm-1. H NMR (400 MHz, D2O): d =
1
4.47 (br s, PCH2N, NCH2N and NCH2N+, 24 H). 31P{ H} NMR
(162.0 MHz, D2O): d = -47.9 (s, J(Pt-P) = 3480 Hz).
Method (b) for 5-R-1H-tetrazoles (R = Ph, 4-ClC6H4 or 3-
NC5H4) and trans-[Pt(CN)2(PTA)2] (8). A solution of trans-
[Pt(N4CR)2(PTA)2] [4 (170 mg, 0.20 mmol) or 5 (174 mg,
0.20 mmol) or 6 (169 mg, 0.20 mmol)] in NCEt (15 mL) was
refluxed for 36 h whereupon the solvent was removed to half
of its volume in vacuo. The reaction mixture was left to cool to
room temperature and then treated with diethyl ether (15 mL).
The white solid of trans-[Pt(CN)2(PTA)2] 8 was isolated by
1
802 (m), 736 (m), 582 (m) cm-1. H NMR (300 MHz, CDCl3,):
6548 | Dalton Trans., 2008, 6546–6555
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filtration, washed with dichloromethane (2 ¥ 5 mL) and dried
in vacuo. The mother liquor (diethyl ether fraction) was evaporated
to dryness and the resulting compound was identified as the
corresponding 5-R-1H-tetrazole (R = Ph, 4-ClC6H4 or 3-NC5H4).
The above dichloromethane fractions from washing 8 contained
some decomposition products of the platinum complexes, such
as PTA oxide and traces of unknown compounds, which were
R1 = 0. 0533 (all data)] for 1, and the maximum and minimum
peaks in the final difference electron density map are of 1.324 and
-3
˚
-1.294 e A , close to the platinum atom. For 4 there is disordered
solvent in the structure. Attempts were made to model them, but
were unsuccessful. PLATON/SQUEEZE25 was used to correct
3
˚
the data. A potential solvent volume of 273.9 A was found. 17
electrons per unit cell worth of scattering were located in the void.
The stoichiometry was tentatively calculated as 1 water molecule
which results in 20 electrons per unit cell. The modified dataset
improved the R1 value by ca. 7%; final R1 = 0.0787. In both struc-
tures, the maximum and minimum peaks in the final difference
electron density map are located close to the platinum atom.
The selected bonding parameters for 1 and 4 are given in Table 1,
and the crystallographic data summarized in Table 2. CCDC
reference numbers 688071 & 688072.†
1
observed by 31P{ H} NMR. 8 was crystallized from hot methanol.
Yield of 8 ca. 60% (70 mg). 8 is soluble in H2O, DMSO, MeOH,
slightly soluble in EtOH, CHCl3, CH2Cl2 and insoluble in C6H6.
trans-[Pt(CN)2(PTA)2]. IR (KBr): 2927 (s br) n(CH),
2127 (m) n(CN), 1442 (m), 1279 (m), 1242 (s), 1013 (s), 1014 (s),
971 (s), 944 (s), 901 (m), 804 (m), 737 (m), 696 (m) (PTA) cm-1. 1H
NMR (400 MHz, CD3OD): d = 4.62 (s, NCH2N, 12H), 4.43 (s,
1
PCH2N, 12H). 31P{ H} NMR (162.0 MHz, CD3OD): d = -64.5
1
(s, J(Pt-P) = 2060 Hz). 13C{ H} NMR (100.6 MHz, DMSO-d6):
◦
˚
d = 126.9 (s, CN), 72.1 (s, br, N-CH2-N, PTA), 51.2 (vt, 1J(CP) =
Table 1 Selected bond lengths (A) and angles ( ) for 1 and 4
16.0 Hz, P-CH2-N, PTA).
1
4
5-(Ph)-1H-Tetrazole, IR (KBr). 2980 (s br), 2974 (s br), 2955 (s
br), 2932 (s br), 1611 (s), 1570 (m), 1450 (m), 1415 (m), 730 (s) cm-1.
1H NMR (400 MHz, DMSO-d6): d = 8.12 (m, H2, H6, 2H), 7.50
Pt1–P1
Pt1–P2
Pt1–N1
Pt1–N4
Pt1–N5
N1–N2
N1–N4
N2–N3
N4–N5
N5–N6
N5–N6
N5–N8
2.2305(15)
2.2231(16)
2.074(5)
2.076(5)
—
1.208(7)
—
1.159(8)
1.211(7)
1.153(8)
—
—
—
95.56(5)
—
87.8(2)
121.7(4)
122.1(4)
174.2(6)
174.6(6)
2.306(4)
2.311(5)
1.999(12)
1
(m, H3, H5, 2H), 7.45 (m, H4, 1H). 13C{ H} NMR (100.6 MHz,
—
2.019(14)
1.315(17)
1.367(17)
1.363(18)
—
—
1.382(18)
1.286(17)
1.315(19)
177.99(13)
177.9(5)
—
124.9(10)
—
DMSO-d6): d = 154.0 (s, N4C), 131.6 (s, 4-C, C6H5), 129.2 (s, 2,6-
C, C6H5), 127.0 (s, 3,5-C, C6H5), 125.3 (s, 1-C, C6H5). ESI-MS:
m/z 145.1 [M-H]-.
5-(4-ClC6H4)-1H-Tetrazole, IR (KBr). 3096 (m), 3070 (m),
2977 (s br), 2910 (s br), 2850 (s br), 2867 (m), 2832 (m), 1610 (s),
1
1564 (m), 1436 (s), 1384 (s), 1095 (s), 745 (s), 509 (s) cm-1. H
N6–N7
NMR (400 MHz, CDCl3): d = 7.70, 7.50 (2 m, 4-ClC6H4C, 4H).
P1–Pt1–P2
N1–Pt1–N5
N1–Pt1–N4
Pt1–N1–N2
Pt1–N4–N5
N1–N2–N3
N4–N5–N6
1
13C{ H} NMR (100.6 MHz, CDCl3): d = 148.2 (s, N4C), 132.5 (s,
4-C, C6H5), 130.9 (s, 2,6-C, C6H5), 128.8 (s, 3,5-C, C6H5), 123.8 (s,
1-C, C6H5). ESI-MS: m/z 179.0 [M-H]-.
107.7(11)
—
5-(3-NC5H4)-1H-Tetrazole, IR (KBr). 3011 (s br), 2983 (s br),
2959 (s br), 1670 (m), 1620 (s), 1561 (s), 1025 (m), 830 (m),
1415 (m), 830 (m), 723 (m) cm-1. 1H NMR (400 MHz, DMSO-d6):
d = 8.1-8.0 (m, H2 and H6, 2H), 7.6–7.5 (m, H4 and H5, 2H).
◦
Table 2 Hydrogen bonds (A, ) in 1a
˚
1
13C{ H} NMR (100.6 MHz, DMSO-d6): d = 153.2 (s, 4-C, py),
D–H ◊ ◊ ◊ A
d(H ◊ ◊ ◊ A)
d(D ◊ ◊ ◊ A)
∠(D–H ◊ ◊ ◊ A)
152.6 (s, 2-C, py), 148.2 (s, N4C), 132.5 (s, 6-C, py), 128.0 (s, 5-C,
py). ES-MS: m/z 146.1 [M-H]-.
Between water network
O1–H1A ◊ ◊ ◊ O2
O2–H2A ◊ ◊ ◊ O3i
O3–H3B ◊ ◊ ◊ O4
O4–H4B ◊ ◊ ◊ O3
O5–H5B ◊ ◊ ◊ O4ii
O6–H6A ◊ ◊ ◊ O5
1.92
2.03
2.32
2.47
2.06
1.76
2.758(7)
2.842(6)
2.868(5)
2.868(5)
2.809(6)
2.759(5)
147.0
168.0
122.0
108.0
164.0
175.0
Refinement details for the X-ray crystal structure analysis
of 1 and 4†
Intensity data were collected using a Bruker AXS-KAPPA APEX
II diffractometer with graphite monochromated Mo Ka radiation.
Data were collected at 150 K using omega scans of 0.5◦ per frame
and a full sphere of data was obtained. Cell parameters were
retrieved using Bruker SMART software and refined using Bruker
SAINT on all the observed reflections. Absorption corrections
were applied using SADABS. Structures were solved by direct
methods by using the SHELXS-97 package22 and refined with
SHELXL-9723 with the WinGX graphical user interface.24 All
hydrogens were inserted in calculated positions except those of
crystallization water molecules in 1, which were located in the
difference Fourier map. Least-square refinement with anisotropic
thermal motion parameters for all the non-hydrogen atoms and
isotropic for the remaining atoms gave R1 = 0. 0311 [I > 2s(I);
Between water network and N-azide or N-PTA
O1–H1B ◊ ◊ ◊ N3iii
O2–H2B ◊ ◊ ◊ N22
O3–H3A ◊ ◊ ◊ N11iv
O4–H4A ◊ ◊ ◊ N21v
Other H-contacts
C12–H12B ◊ ◊ ◊ N6vi
C14–H14A ◊ ◊ ◊ O5vii
C15–H15B ◊ ◊ ◊ N6viii
C16–H16B ◊ ◊ ◊ N4iii
C16–H16B ◊ ◊ ◊ N5iii
2.07(4)
2.21
2.914(7)
2.991(6)
2.873(6)
2.871(5)
173(6)
165.0
170.0
173.0
2.02
2.04
2.51
2.59
2.61
2.57
2.45
3.305(7)
3.394(7)
3.586(8)
3.521(8)
3.398(7)
138.00
138.00
168.00
161.00
161.00
1
1
2
a Symmetry codes: (i) -x, y, - z; (ii) x, 1+ y, z; (iii) - x, 3/2 - y, -z;
(iv) - x, -1 + y, - z; (v) x2, -1 + y, z; (vi) - x, 5/2 - y, -z; (vii) 12 - x,
1
1
2
1
2
2
1/2 + y, -2z; (viii) x, 2 - y, + z.
1
2
1
2
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Scheme 1 Syntheses of platinum(II) complexes with PTA and Me-PTA.
PTA)2]I2 2 displays in the 1H NMR spectrum the expected10b four
types of methylene protons: NCH2N+, NCH2N, PCH2N (as AB
spin systems centred at 5.10, 4.36 and 4.42 ppm respectively) and
PCH2N+ (singlet at 4.89 ppm).
Results and discussion
Syntheses and characterization of the azide-PTA complexes 1–3
The reaction of stoichiometric quantities of PTA and cis-
[Pt(N3)2(PPh3)2] (Pt : PTA = 1 : 2) in CH2Cl2 at room temperature
leads to the precipitation of cis-[Pt(N3)2(PTA)2] (1) as an off-white
microcrystalline solid in 83% yield (Scheme 1). The analogous
compound with N-methylated PTA cis-[Pt(N3)2(Me-PTA)2]I2 (2)
was obtained as a pale-yellow solid (80% yield) from the reaction
with [Me-PTA]I, under similar conditions (Scheme 1). However,
treatment of cis-[Pt(N3)2(PPh3)2] with an excess of PTA (Pt : PTA=
1 : 3), in the same solvent, affords the penta-coordinate tris(PTA)
complex [Pt(N3)2(PTA)3] (3) in 58% isolated yield, which is soluble
in CH2Cl2.
Complexes 1–3 are air-stable as solids and in water solution.
Although they are readily soluble in H2O and in other polar
solvents, such as Me2SO, NCMe and Me2C(O)NH2, they are less
soluble in MeOH and insoluble in Et2O and in apolar solvents
such as C6H14 and CCl4. Complex 3, in contrast to 1 and 2, is also
soluble in solvents like CHCl3, CH2Cl2 and EtOH with medium
polarity.
1
The 31P{ H} NMR spectra of 1 and 2 show singlets with
platinum satellites, at -59.1 and -47.2 ppm. The values of the
JPt-P coupling (3139 or 3153 Hz respectively) clearly show the
cis phosphine configuration.16b,27 The penta-coordinate complex
[Pt(N3)2(PTA)3] (3) exhibits a fluxional behaviour in solution
1
as shown by variable temperature 31P{ H} NMR (in CDCl3).
Although at 298 K no resonances could be identified, cooling the
solution until 213 K (Fig. 2) results in the appearance of a clear
pattern consisting of one doublet and one triplet (2JPP = 23.5 Hz,
intensities of 2 : 1) at -57.6 and -51.6 ppm, respectively, with
the corresponding platinum satellite (JPt-P = 2187 and 3304 Hz,
respectively). They are assigned to the two PTA ligands in
The complexes have been characterized by elemental analysis,
FAB-MS, IR, 1H and 31P NMR spectroscopies. The FAB-MS
spectra of 1 and 3 show the expected isotopic pattern for the
respective molecular ion [M]+, and for all the compounds the
peaks corresponding to the stepwise fragmentation by loss of the
azide ligands, [M-(N3)]+ and [M-2(N3)]+, are also detected. The IR
spectra of 1–3 exhibit the typical azide band in the range 2060–
1
2033 cm-1. The H NMR spectra of the PTA complexes 1 and
3 at 298 K show two types of methylene protons. One of them,
P–CH2-N, occurs as a broad singlet at 4.23 and 4.24 ppm for 1 and
3 respectively. The second type, N–CH2-N, displays an AB spin
system centred at 4.53 and 4.28 ppm for 1 and 3respectively (JAB
13 Hz for both compounds), assigned to the N–CHax-N and the
N–CHeq-N protons.26 The Me-PTA compound cis-[Pt(N3)2(Me-
=
1
Fig. 2 Variable temperature 31P{ H} NMR spectra of 3 in CDCl3
(d, doublet; t, triplet). 195Pt satellites are denoted by S and S¢.
6550 | Dalton Trans., 2008, 6546–6555
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mutually trans position and to the unique PTA, either in a square
pyramidal or trigonal bipyramidal geometry, or a distorted form.
The tris(PTA) complexes [Pt(N3)(PTA)3]+18 and [PtI2(PTA)3]19 (the
latter also penta-coordinate as 3), in D2O and at room temperature,
also exhibit broad overlapping 31P NMR peaks, but a coupling
system similar to that of the low-temperature limit spectrum of 3
is observed18 at room temperature for [Pt(Br)(PTA)3]+ in D2O.
Solution (in nitromethane) conductivity measurements of 1–
3 (see experimental) confirm the expected non-electrolyte nature
of 1 and 3 and the 1 : 2 electrolyte behaviour of 2 (the molar
conductivity falls in the typical range for such an electrolyte28).
Moreover, treatment of an aqueous solution of 2 with AgNO3 in
water readily leads to the formation of a AgI precipitate in the
amount corresponding to the presence of the two iodide counter-
ions.
Fig. 4 Hydrogen bonding network (dashed lines) and atom labeling
scheme (hydrogen atoms are omitted for clarity) showing the interactions
involving all water molecules (O6 is in a special position with 1/2 of site
occupation), the terminal N-azide and some PTA-N atoms, which provides
the formation of a 3D assembly.
X-Ray crystal structure of 1†
Compound 1 crystallizes in the monoclinic space group C2/c
(Fig. 3), the moiety formula including 2 molecules of the metal–
organic moiety and 11 molecules of water. Crystal and refinement
data, selected interatomic distances and angles are given in Tables 1
and 2. The platinum atom is coordinated in a slightly distorted
square planar geometry with the phosphines and the end-on azide
ligands in the cis orientation. The azide ligands are almost linear
[N1–N2–N3 and N4–N5–N6 angles of 174.2(6) and 174.6(6)◦
respectively], with corresponding Pt1–N1–N2 and Pt1–N4–N5
angles of 121.7(4) and 122.1(4)◦. The azide N–N bonds adjacent
and N6 atoms of one of the azides as well as O5 water oxygen
with PTA methylene hydrogens, help to stabilize the structure.
Moreover, the intercalated crystallization water molecules are
associated to form symmetry-generated infinite water clusters
composed of alternatively linked cyclic decamers and pentamers
˚
(Fig. 5). The average O ◊ ◊ ◊ O contact of ca. 2.79 A is similar to
that found in the structure of ice,30,31 and to those reported32–41 for
˚
to the azide Pt–N bond (N1–N2 and N4–N5, av. 1.209 A) are
significantly longer than the terminal azide N–N bond (N2–N3
other hosted water clusters.
˚
and N5–N6, av. 1.156 A), which is common for coordinated
azides.29 The Pt–P bond lengths (av. 2.227 A) are similar to those
˚
in cis-[PtX2(PTA)2] (X = Cl, Br and I).16b
Fig. 5 Perspective representation (arbitrary view) of the extended cyclic
crystallization water clusters hosted in the matrix of 1, showing alternate
cyclic decamers and pentamers. Hydrogens were omitted for clarity.
The crystal packing diagrams in Fig. 6 show layers of water
clusters trapped by two metal–organic chains. In Fig. 6b, the
vertical separation between neighbouring [Pt(N3)2(PTA)2] layers,
˚
Fig. 3 Thermal ellipsoid (50% probability) plot of compound 1 with
atomic numbering scheme. Hydrogens atoms and water molecules were
omitted for clarity.
i.e. between the planes (010) and (020), is of 4.642 A (half the
b axis) and the horizontal separation between water layers, i.e.,
˚
between the planes (100) and (200), is of 13.251 A (half the a axis).
The single-crystal X-ray examination of compound 1 shows that
it forms, in the solid state, 3D hydrogen bonded metal–organic
frameworks with intercalated crystallization water molecules,
which outline extensive hydrogen bonding with the terminal N3
azide atom and the N11, N21 and N22 of the PTA ligands (Table 2
and Fig. 4). Additional contact interactions involving the N4, N5
Syntheses and characterization of the tetrazolato-PTA
complexes 4–6
The bis(tetrazolato) complexes trans-[Pt(N4CR)2(PTA)2] [R = Ph
(4), 4-ClC6H4 (5) or 3-NC5H4 (6)] were obtained by reaction of cis-
[Pt(N3)2(PTA)2] 1 with the appropriate organonitrile NCR, which
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in solution under air. They are readily soluble in middle polar
solvents, such as CHCl3, CH2Cl2, sparingly soluble in polar ones
such as MeOH, MeCN, Me2SO and Me2C(O)NH2, and insoluble
in low polar and apolar solvents like Et2O, C6H6 and CCl4. 5
and 6 are also sparingly soluble in H2O. Complexes 4–6 have
1
been characterized by elemental analysis, FAB-MS, IR, H and
1
31P{ H} NMR spectroscopies. Their IR spectra in KBr display a
strong band within the 1615–1630 cm-1 range due to the tetrazole
ring, in agreement with the literature42 The FAB-MS spectra show
the isotopic pattern for the corresponding complex molecular ion
[M]+ and peaks resulting from the fragmentations by loss of one
1
tetrazole, i.e. due to [M-(N4CR)]+. Their H NMR spectra, in
CDCl3 at ambient temperature, show two patterns of methylene
protons for the coordinated PTA, similarly to complexes 1–3, and
the phenyl ring pattern for 4 and 5, and that of the pyridyl group
for 6. In contrast to the PPh3 complex trans-[Pt(N4CR)2(PPh3)2]7,
1
the 31P{ H} NMR spectra of 4–6 exhibit singlets with platinum
satellites at d -56.2, -56.3 and -56.2, with JPt-P of 2497, 2491
and 2479 Hz, respectively. These coupling values clearly show
the trans configuration of the phosphines27, and the singlet
resonance indicates the existence of only one type of N-coor-
dination of the tetrazoles (the sterically favourable N2 mode, as
established in the solid state by X-ray diffraction, see below).
The cis-to-trans conversion of cis-[Pt(N3)2(PTA)2] (1) into trans-
[Pt(N4CR)2(PTA)2] (4–6) is similar to that of cis-[Pt(N3)2(PPh3)2]7
into trans-[Pt(N4CR)2(PPh3)2]. Thermal isomerizations of cis-
[Pt(Cl)2(RCN)2] into trans-[Pt(Cl)2(RCN)2] have been reported
previously43,44 and indicate that the trans isomer is thermodynam-
ically more favoured.
Fig. 6 Fragment of the crystal packing diagram of 1 showing two parallel
metal–organic frameworks of [Pt(N3)2(PTA)2] with three intercalated
layers of water water clusters represented by a space-filling model viewed
along the crystallographic (a) b and (b) c axes.
◦
is accelerated by microwave irradiation (typically at 120–135 C,
for 1 h). They were isolated in moderate yields (ca. 60–65%) as
off-white powders (Scheme 2) and are stable in the solid state and
Scheme 2 Syntheses of the bis(tetrazolato) complexes trans-[Pt(N4CR)2(PTA)2] (4–6) and the corresponding 5-substitued-1H-tetrazoles HN4CR.
6552 | Dalton Trans., 2008, 6546–6555 This journal is The Royal Society of Chemistry 2008
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X-Ray crystal structure of 4†
methylene groups of PTA in neighbouring molecules (Fig. 8) with
the C12 ◊ ◊ ◊ Pt and C22 ◊ ◊ ◊ Pt bond distances being 3.532(14) and
3.519(13) A. These distances are short, as compared with the sum
Crystals of compound 4 suitable for X-ray analysis were obtained
from slow evaporation of a CHCl3–toluene solution at room
temperature. A view of the complex is shown in Fig. 7, crystal
data and selected bond lengths and angles are given in Tables 1
and 3 respectively. The platinum center is tetracoordinated in a
slightly distorted planar geometry with both the phosphine and
the tetrazolate ligands in mutually trans positions. The tetrazolates
are coordinated to the metal centre by the N2-nitrogen atom of
the ring. Each pyridyltetrazolato ligand is roughly planar but
their planes are twisted as indicated by the non-equivalence of
the torsion angles P1–Pt1–N5–N8 [27.1(12)◦] and P1–Pt1–N1–
N4 [95.0(11)◦]. The structure of 4 is similar to that previously
described for the related platinum complex with PPh3, i.e. trans-
[Pt(N4CPh)2(PPh3)2].7 While the Pt–N distances in 4 are compara-
ble to those in 1, the Pt–P bond distances in the former are longer
than those in the latter (Table 1) as a result of the stronger trans
influence of the phosphorus moiety (in 4) as compared to azide
(in 1).
˚
˚
of the van der Waals radii, 4.0 A, of carbon and platinum. Such
intermolecular pseudo-agostic (IPA)45 interactions appear to play
a role in the packing of the structure.
Fig. 8 Fragment of the crystal packing diagram (arbitrary view) of
˚
4 showing the short CH2 ◊ ◊ ◊ Pt contacts: Pt1 ◊ ◊ ◊ H12A 2.850 A and
˚
Pt1 ◊ ◊ ◊ H22A 2.920 A. The tetrazol ligands and hydrogen atoms were
omitted for clarity.
Liberation and characterization of the 5-R-1H-tetrazoles
HNN3CR (R = Ph, 4-ClC6H4 or 3-NC5H4)
Liberation of the ligated tetrazoles from the coordination sphere
of the complexes 4–6 was an important aim of the current study,
and this was achieved by two different methods, one by treatment
with aqueous HCl and the other by reaction with propionitrile. The
former method is more effective, simpler and also advantageous in
terms of providing an easier separation of the tetrazole products. It
involves simple refluxing, for 0.5 h, a suspension of the appropriate
tetrazolato trans-[Pt(N4CR)2(PTA)2] complex in aqueous 0.1 M
HCl, leading to spontaneous precipitation in high yield (ca. 80%)
of the corresponding 5-R-1H-tetrazole. This product is not water
soluble, in contrast with the chloro-complex cis-[Pt(Cl)2(PTA-
H)2]Cl2 7 that is also formed (Scheme 2) which bears protonated
Fig. 7 Molecular structure of trans-[Pt(N4CPh)2(PTA)2] 4 with atomic
numbering scheme (hydrogens were omitted for clarity). Displacement
ellipsoids are drawn at the 50% probability level.
Interestingly, the exposed sides of the platinum ion (perpendic-
ular to the plane defined by the coordinated P and N atoms)
form two short contacts to H atoms (H12A and H22A) of
Table 3 Crystal data and structure refinement details for 1 and 4
Empirical formula
C24H70N24O11P4Pt2 C26H34N14P2Pt
1
PTA and remains in aqueous medium. Its 31P{ H} NMR spectrum
Formula weight
1385.08
799.69
shows one singlet (d -47.9) with platinum satellites (JPt-P 3480 Hz)
indicative16b,27 of the cis phosphines configuration. These data are
comparable to those reported46 for cis-[Pt(Cl)2(PTA)2], although
the 31P resonance of 7 is at a lower field than that (d -50.4) of the
¯
Crystal system, space group
Monoclinic, C2/c Triclinic, P1
˚
a/A
27.079(7)
9.284(3)
18.982(5)
90
101.845(16)
90
6.176(2)
˚
b/A
16.211(6)
17.019(6)
95.176(19)
92.28(2)
94.15(2)
1690.8(10)
2, 1.571
˚
c/A
a/◦
b/◦
g /◦
latter complex in view of the effect of the PTA protonation, as
n+
has been previously reported26a for [ReCl(N2)(PTA-H)n(PTA)4-n
]
(n = 1–4).
3
˚
Volume/A
4670(2)
The second method for liberating the tetrazolato ligands from
complexes 4–6 involves refluxing a solution of any of these
complexes in propionitrile for 36 h. Further working up (con-
centration and addition of diethyl ether) leads to the precipitation
of the dicyano complex trans-[Pt(CN)2(PTA)2] 8 (Scheme 2), the
5-R-1H-tetrazoles being isolated only after evaporation of the
mother liquor to dryness. The reaction is believed to proceed
via oxidative addition of propionitrile with NC–C bond cleavage
followed by reductive elimination and evolution of ethylene, as
Z, calculated density rcalc/Mg m-3 4, 1.970
F(000)
2744
792
Reflections collected/unique
14 147/4761
[R(int) = 0.0477]
4761/1/297
0.982
14 928/6209
[R(int) = 0.1264]
6209/0/388
0.976
Data/restraints/parameters
Goodness-of-fit on F2
Final R1,a wR2b (I ≥ 2s)
R1 = 0.0311,
R1 = 0.0787,
wR2 = 0.0629
wR2 = 0.1723
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ/ |Fo|. b wR2 = [ [w(Fo - Fc2)2]/ [w(Fo2)2]]1/2
.
2
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we have previously observed7 for the related reactions of trans-
References
∫
[Pt(N4CR)2(PPh3)2] with N CC2H5.
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1
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1
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Conclusions
We have found a simple route for new water-soluble azido-
platinum(II) complexes based on reaction of cis-[Pt(N3)2(PPh3)2]
with hydrosoluble PTA or [PTA-Me]I at room temperature.
As shown for one of the complexes, cis-[Pt(N3)2(PTA)2], these
azido-compounds can be applied as starting materials for the
platinum mediated synthesis of 5-substituted tetrazoles upon [2 +
3] cycloadditions with organonitriles NCR to give bis(tetrazolato)
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This type of approach for metal- mediated synthesis and easy
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reactions is under way in our laboratory.
Acknowledgements
This work has been partially supported by the Foundation
for Science and Technology (FCT), grants and BPD/20869/04
and SFRH/BPD/14690/2003, and its POCI 2010 programme
(FEDER funded).
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