Synthesis and complexes of the new scorpionate ligand tris[3-(4- benzonitrile)-pyrazol-1-yl]borate

Article abstract of DOI:10.1071/CH06329

A new scorpionate ligand, hydro-tris[3-(4-benzonitrile)-pyrazol-1-yl]borate (Tp^4bz), was synthesized and the crystal structures of its potassium salt and its Mn^II, Co^II, Ni^II, and Cd ^II complexes were

Full text of DOI:10.1071/CH06329

Communication
CSIRO PUBLISHING
Aust. J. Chem. 2007, 60, 72–74
www.publish.csiro.au/journals/ajc
Synthesis and Complexes of the New Scorpionate Ligand
Tris[3-(4-benzonitrile)-pyrazol-1-yl]borate
Stuart R. Batten,A,B Martin B. Duriska,A Paul Jensen,A and Jinzhen LuA
ASchool of Chemistry, Monash University, Clayton VIC 3800, Australia.
BCorresponding author. Email: stuart.batten@sci.monash.edu.au
A new scorpionate ligand, hydro-tris[3-(4-benzonitrile)-pyrazol-1-yl]borate (Tp4bz), was synthesized and the crystal
structures of its potassium salt and its MnII, CoII, NiII, and CdII complexes were determined.
Manuscript received: 5 September 2006.
Final version: 6 December 2006.
The well-known tris(pyrazolyl)borates, or ‘scorpionates’ and
their derivatives have attracted wide attention across many areas
of coordination chemistry.[1] The use of pyridyl units as the
pyrazolyl C3 substituents gives rise to a variety of different
coordination modes. In the case of 2-pyridyl, a hexadentate lig-
and which can fully encapsulate a metal ion is formed.[2] When
3- or 4-pyridyl substituents are employed, polymeric networks
or dimeric moieties can result upon complexation, wherein a
pyridyl unit coordinates to an adjacent complex unit.[3,4]
porous channels within the structure due to ABC type packing
blocking the windows (Fig. 2b).
In contrast, the reaction of KTp4bz with either Co(ii) nitrate,
Ni(ii) perchlorate, Mn(ii) sulfate, or Cd(ii) perchlorate afforded
compounds with the general formula ML2·(solv). These com-
pounds are monomeric, with each octahedral metal coordinated
to two tris-chelating ligands via the pyrazolyl nitrogens only.The
nitrile groups do not coordinate.
The crystal structure of [Co(Tp4bz)2]·2MeCN is shown in
Fig. 3.Although the Ni(ii) structure contains water and methanol
molecules within the asymmetric unit all four structures are oth-
erwise isomorphous.The cobalt atom lies on an inversion centre,
and thus only one ligand is unique. The coordination geome-
try is approximately octahedral with one of the unique Co–N
sightly shorter (2.177(2) Å) than the other two (2.217(2) and
2.262(2) Å).
In this communication we report the synthesis and coordina-
tion behaviour of the new ligand hydro-tris[3-(4-benzonitrile)-
pyrazol-1-yl]borate, (Tp4bz)−, in which 4-benzonitrile units are
used as the pyrazolyl C3 substituent. This is analogous to
the (Tp4py −
ligand, except that the outer peripheral nitrogen
)
atoms, i.e. the nitriles, are further from the pyrazolyl core and
less sterically hindered.
The intermediate, 3-(4-benzonitrile)pyrazol-1-yl, required
for the formation of KTp4bz, was synthesized following
the reported two-step procedure for the synthesis of 3-(2-
pyridyl)pyrazol-1-yl,[2–6] using 4-acetylbenzonitrile as the start-
ing material. An alternative synthetic route has also been
reported.[7] Reaction of 3-(4-benzonitrile)pyrazol-1-yl with
KBH4 in a melt afforded the final desired product in high yield
(Scheme 1). The formation of the ligand was confirmed by 1H
and 13C NMR spectroscopy, electrospray mass spectrometry,
microanalysis, and crystal structure determination.
Although the nitrile groups did not coordinate in the binary
transition metal complexes, we are currently looking at other
routes to encourage coordination of the peripheral nitrile
functional groups, as seen in the K+ salt and the pyridyl
analogues,[6] in order to form larger assemblies, such as met-
allosupramolecules and coordination networks.
Experimental
The crystal structure of KTp4bz is displayed in Figs 1 and 2.
It shows the potassium ion coordinated in a distorted octahedral
fashion to three pyrazole nitrogen atoms and three nitrile nitro-
gen atoms from three independent ligand units. The symmetry
of the structure is such that there is one unique KTp4bz unit,
with 3-fold symmetry, resulting in the KTp4bz unit having only
one unique ‘arm’. The pendant benzonitrile unit coordinates to
a potassium ion of an adjacent KTp4bz moiety, and in turn a
pendant benzonitrile unit from this moiety coordinates back to
the previous moiety. This gives rise to each KTp4bz unit being
connected to three further units via double bridges. This bond-
ing mode results in the KTp4bz unit behaving as a 3-connecting
node, yielding a 2D coordination polymer in the form of a (6,3)
sheet with corrugated topology. The sheets contain truncated,
distorted triangular windows with a maximum width of 11 Å
and a minimum of 7 Å. However, these windows do not lead to
Synthesis of 3-(4-Benzonitrile)pyrazol-1-yl (4bz)
22 g (0.15 mol) of 4-acetylbenzonitrile and 30 mL (0.23 mol)
of dimethylformamide dimethylacetal was heated at 70◦C and
stirred for 3 h. During this time the pale yellow solution turned
dark orange. The solution was cooled and the volume reduced
under vacuum resulting in a dark brown precipitate. The precipi-
tate was dissolved in 100 mL of ethanol and 50 mL of hydrazine
hydrate was added. The solution was stirred and heated for 2 h
after which the volume was reduced in vacuo. An orange pre-
cipitate was obtained with the addition of water. The precipitate
was filtered and dissolved in toluene, insoluble by-products were
removed via filtration, and the filtrate was evaporated to dryness
to yield 20.3 g (79%) of the off-white product, mp 143–145◦C.
m/z (ES-MS) 169.8 (calc 170.1). νmax (KBr disk)/cm−1 3280br
(N–H), 2222s (–CN), 1609 (phenyl). δH (200 MHz, [D6]DMSO)
8.00 (dd, 2H, J 8.6, 1.8), 7.84 (dd, 2H, J 8.6, 1.8), 7.80 (d, 1H,
© CSIRO 2007
10.1071/CH06329
0004-9425/07/010072

Synthesis and Complexes of Tris[3-(4-benzonitrile)-pyrazol-1-yl]borate
73
NMe2
HN
N
O
O
(a)
(b)
N
N
N
H
B
(c)
N
N
N
N
N
N
N
N
[Tp4bz Ϫ
]
N
Scheme1. SynthesisoftheligandKTp4bz. Reagentsandconditions:(a)N,N-dimethylformamide
dimethyl acetal, 70◦C; (b) hydrazine hydrate, EtOH, reflux; (c) KBH4, 250◦C.
J 2.3), 6.87 (d, 1H, J 2.3). (Anal. Calcd for C10H7N3: C 70.9, H
4.2, N 24.8. Found: C 69.9, H 4.2, N 24.1.)
νmax (KBr disk)/cm−1 2475w, 2227s, 1609m, 1495s, 1469m,
1373s, 1336m, 1196s, 1118m, 1057s, 844s, 779s, 742s. (Anal.
Calcd for C60H38B2N18Ni: C 66.0, H 3.5, N 23.1. Found: C 65.8,
H 3.6, N 23.5.)
Synthesis of KTp4bz
6.8 g (40 mmol) of 3-(4ꢀ-benzonitrile)pyrazol-1-yl and 0.54 g
of potassium borohydride were ground together and heated at
250◦C for 3 h. The melt was cooled, crushed up and washed
with chloroform. The remaining solid was collected via filtra-
tion and dried in vacuo to yield 3.8 g (68%) of the desired borate
as the potassium salt. X-Ray quality crystals were grown from
methanol. mp 248–254◦C. m/z (ES-MS) 516.1 (calc 516.2). νmax
(KBr disk)/cm−1 2403w, 2224s, 1608s, 1490m, 1457w, 1414w,
1360sh, 1339m, 1190s, 1174sh, 1112m, 1044s, 949m, 846s. δH
(200 MHz, [D6]DMSO) 7.96 (d, 2H, J 8.6), 7.77 (d, 2H, J 8.6),
7.59 (d, 1H, J 2.2), 6.69 (d, 1H, J 2.2). δC (200 MHz, [D6]DMSO)
148.8, 141.1, 136.8, 133.2, 125.9, 120.3, 108.6, 102.6. (Anal.
Calcd for C30H19N9BK·0.5H2O: C 63.8, H 3.5, N 22.3. Found:
C 63.5, H 3.4, N 22.5.)
Synthesis of [Mn(Tp4bz)2]·2MeCN
The Mn(ii) complex was obtained using the same reaction con-
ditions as for Co(ii) using 15.1 mg (67 µmol) of Mn(SO4) · H2O.
Yield 25 mg (90%). νmax (KBr disk)/cm−1 2464w, 2225s,
1610m, 1496s, 1471m, 1373s, 1339w, 1196s, 1121m, 1056s,
834s, 782s, 741s. (Anal. Calcd for C60H38B2N18Mn: C 66.3, H
3.5, N 23.2. Found: C 66.7, H 3.8, N 22.5.)
Synthesis of [Cd(Tp4bz)2]·2MeCN
The Cd(ii) complex was obtained using the same reac-
tion conditions as for Co(ii) using 11.1 mg (36 µmol) of
Cd(NO3)2·4H2O and 3 mL of DMF. Yield 14 mg (51%). νmax
(KBr disk)/cm−1 2471w, 2222s, 1611m, 1384s, 1344w, 1117m,
1089s, 1050m, 964m, 844s, 805m, 844s, 715s, 630. (Anal. Calcd
for C60H38B2N18Cd · 1.5H2O: C 61.5, H 3.5, N 21.5. Found:
C 61.5, H 3.6, N 21.1.)
Synthesis of [Co(Tp4bz)2]·2MeCN
25 mg (45 µmol) of KTp4bz was dissolved in 5 mL of
ethanol and 19.7 mg (67 µmol) of Co(NO3)2·6H2O in 2 mL of
ethanol/acetonitrile (1/1) was added. The solution was stirred
and allowed to stand overnight yielding 20 mg (73%) of the
Co(ii) complex as large, orange-pink, X-ray quality crystals.
νmax (KBr disk)/cm−1 2469w, 2226s, 1609m, 1496s, 1470m,
1374s, 1335w, 1196s, 1119m, 1056s, 834s, 781s, 740s. (Anal.
Calcd for C60H38B2N18Co·2C2H3N: C 65.5, H 3.8, N 23.9.
Found: C 65.8, H 3.6, N 23.7.)
Structure Determination
Crystal data for K[Tp4bz]: C30H19BKN9, M 555.45, hexagonal,
¯
space group R3c, a 14.1806(3), b 14.1806(3), c 50.045(1) Å, U
8715.3(3) Å3, Z 12, Dc 1.270 Mg m−3, µ(MoKα) 0.219 mm−1
,
F(000) 3432, T 123 K, 30253 reflections, 2414 unique (Rint
0.1170), R1 0.0670 (1210 reflections, I > 2σ(I)), wR2 0.2223
(all data), S 0.967. X-ray measurements for all structures were
made using a Nonius KappaCCD diffractometer with graphite
monochromated MoKα radiation (λ 0.71073 Å). Solutions were
obtained by direct methods (SHELXS 97)[8] followed by suc-
cessive Fourier-difference methods, and refined by full matrix
least-squares on Fo2bs (SHELXL 97).[8] All non-hydrogen atoms
Synthesis of [Ni(Tp4bz)2]·0.8MeOH·1.2H2O
The Ni(ii) complex was obtained using the same reac-
tion conditions as for Co(ii) using 24.7 mg (67 µmol) of
Ni(ClO4)2·6H2O and 5 mL of methanol. Yield 19 mg (65%).

74
S. R. Batten et al.
B(1)
B(1)
N(12)
K(1)
N(12)
N(32)
N(22)
Co(1)
N(13)
Fig. 3. Crystal structure of [Co(Tp4bz)2]·2MeCN. Selected bond distances
[Å]: Co(1)–N(12) 2.262(2), Co(1)–N(22) 2.217(2), Co(1)–N(32) 2.177(2).
For Ni (Mn) the corresponding bond lengths are 2.229(7) (2.268(2)),
2.177(7) (2.218(2)), 2.117(6) (2.176(2)).
Fig. 1. Crystal structure KTp4bz. Selected bond distances [Å]: K(1)–N(12)
2.811(3), K(1)–N(13) 2.831(3).
0.350 mm−1, F(000) 2420, T 123 K, 70883 reflections, 8965
unique (Rint 0.1174), R1 0.0559 (4950 reflections, I > 2σ(I)),
wR2 0.1589 (all data), S 1.065.
[Ni(Tp4bz)2]·0.8MeOH·1.2H2O: C60.8H42B2N18O2Ni, M
1137.05, orthorhombic, space group Pccn, a 14.6742(6),
b 16.6798(7), c 24.1585(13) Å, U 5913.1(5) Å3, Z 4, D
1.277 Mg m−3, µ(MoKα) 0.387 mm−1, F(000) 2347, T 123 K,
44137 reflections, 6759 unique (Rint 0.2569), R1 0.0945 (2486
reflections, I > 2σ(I)), wR2 0.2905 (all data), S 1.012.
[Mn(Tp4bz)2]·2MeCN: C64H44B2MnN20,
M
1169.75,
orthorhombic, space group Pccn, a 14.8348(1), b 16.4475(1), c
24.2645(1) Å, U 5920.43(6) Å3, Z 4, D 1.312 Mg m−3, µ(MoKα
)
0.350 mm−1, F(000) 2412, T 123 K, 69465 reflections, 7316
unique (Rint 0.1165), R1 0.0542 (4355 reflections, I > 2σ(I)),
wR2 0.1408 (all data), S 1.021.
(a)
Unit cell data for Cd(Tp4bz)2·2MeCN showed that it was iso-
morphous with the Co, Ni, and Mn structures, and therefore
a full dataset was not collected: orthorhombic, a 14.9438(3),
b 16.3799(4), c 24.5156(5) Å, U 6000.9(2) Å3.
The crystal data has been deposited with the Cambridge Crys-
tallographic Data Centre (www.ccdc.cam.ac.uk; nos. 298261–
298264).
Acknowledgment
This work was supported by The Australian Research Council.
References
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Fig. 2. (a) Top view of a single sheet of KTp4bz showing the distorted
triangular windows. (b) Top view of three independent sheets highlighting
the ABC type stacking. (c) Side-on profile showing the corrugated nature of
a single sheet.
were made anisotropic, while all hydrogens were assigned to
calculated positions and not refined.
[Co(Tp4bz)2]·2MeCN: C64H44B2CoN20,
M
1173.74,
orthorhombic, space group Pccn, a 14.8355(1), b 16.4618(2), c
24.2553(2) Å, U 5923.6(1) Å3, Z 4, D 1.316 Mg m−3, µ(MoKα
)