Metal string complexes: Synthesis and crystal structure of [Ni4(μ4- phdpda)4] and [Ni7(μ7-teptra)4Cl2] (H2phdpda = N- phenyldipyridyldiamine and H3teptra =

Full text of DOI:10.1021/ja982065w

250
J. Am. Chem. Soc. 1999, 121, 250-251
lene and adding tBuOK as a base. The crude product was obtained
by extraction using acetone and characterized by mass spectrom-
etry (FAB) and X-ray diffraction.15 The structure of [Ni4(µ4-
phdpda)4], obtained by X-ray single-crystal diffraction study,
shows several features as shown in Figure 1. First, the tetranickel
metal chain is helically wrapped by four syn-syn-syn type
phdpda2- ligands, with two phenyl groups positioned in cis
conformation on one side and the other two cis phenyl groups
positioned on the other side. Each of the four nickel(II) ions is
bonded by two cis Npyridine and two cis Namido atoms. This
arrangement may be the contributing factor to the stronger trans
influence by Namido than that by Npyridine. Second, the four Ni(II)
ions are collinear. The angles of Ni-Ni-Ni are nearly 180°. The
Ni-Ni distances are 2.3269(6), 2.3010(6), and 2.3280(6) Å, which
are comparable with the inner Ni-Ni distance (∼2.30 Å) in
[Ni5(µ5-tpda)4X2] complexes.8,9 Third, the average Ni-N bonds
are 1.924(4) Å for Ni(1)-N, 1.915(3) Å for Ni(2)-N, 1.913(3)
Å for Ni(3)-N, and 1.927(4) Å for Ni(4)-N, comparable to the
Ni-N distance found in the low-spin square-planar Ni(II)
configuration and consistent with the diamagnetic behavior.16
The IIb ligand was synthesized as described in the literature1,13
by the palladium-catalyzed cross-coupling of (6-bromo-2-pyridyl)-
(2′-pyridyl)amine and (6-amino-2-pyridyl)(2′-pyridyl)amine. The
nickel string complex of [Ni7(µ7-teptra)4Cl2] was synthesized in
a manner similar to the tri- and pentanuclear metal complexes.17
It was identified by mass spectrometry (FAB) and X-ray diffrac-
tion. The structure of [Ni7(µ7-teptra)4Cl2] is shown in Figure 2.
As with the [Ni3(µ3-dpa)4Cl2]5 and [Ni5(µ5-tpda)4Cl2]8,9 complexes,
the heptanickel chain is helically wrapped by four syn-syn-syn-
syn-syn-syn type teptra3- ligands. The complex exhibits ap-
proximate D4 symmetry. The seven Ni(II) ions and the two
chloride ions are collinear. Three values of Ni-Ni distances are
found in this complex. The longest ones which correspond to a
Ni ion connected with an axial ligand Cl- are 2.383(1) and
Metal String Complexes: Synthesis and Crystal
Structure of [Ni4(µ4-phdpda)4] and
[Ni7(µ7-teptra)4Cl2] (H2phdpda )
N-Phenyldipyridyldiamine and H3teptra )
Tetrapyridyltriamine)
Shie-Yang Lai, Tzu-Wei Lin, Yu-Hua Chen,
Chih-Chieh Wang, Gene-Hsiang Lee, Ming-hwa Yang,
Man-kit Leung, and Shie-Ming Peng*
Department of Chemistry, National Taiwan UniVersity
Taipei, Taiwan
ReceiVed June 15, 1998
Metal string complexes are highly interesting in the funda-
mental study of metal-metal interactions1-9 and in their potential
application as molecular metal wires. We are interested in
developing a new type of ligand, namely, oligo-R-pyridylamino
ligands, I and II, which might bind metal ions in a string.1,8,9
In previous reports, the extension of dinuclear metal com-
plexes10-12 to metal string complexes supported by oligo-R-
pyridylamino ligands was focused on the trinuclear [M3(µ3-
dpa)4X2] (M ) Cr,2 Co,3,4 Ni,5 Cu,6 Rh,7 Ru;7 dpa- ) dipyridyl-
amido anion) and pentanuclear [M5(µ5-tpda)4X2] (M ) Co, Ni)8,9
complexes. Here we report two new types of metal string
complexes; one contains an even number of the metal in a string
of ligand I [Ni4(µ4-phdpda)4], and the other is an extension of
the tri- and pentanickel(II) complexes to at this time the longest
metal string of ligand IIb [Ni7(µ7-teptra)4Cl2].
(14) The H2phdpda was synthesized by the palladium-catalyzed cross-
coupling of aryl bromide and primary amine: (6-Bromo-2-pyridyl)(2′-pyridyl)-
amine (10.0 g, 0.04 mol) and aniline (3.72 g, 0.04 mol) with catalyst Pd2(dba)3
Ligand I was synthesized by the palladium-catalyzed cross-
t
(0.84 g, 0.8 mmol), dppp (0.66 g, 0.16 mmol), BuOK (13.44 g, 0.12 mol),
coupling1,13 of (6-bromo-2-pyridyl)(2′-pyridyl)amine and aniline
and 18-crown-6 ether (28.41 g, 0.12 mol) were refluxed in 200 mL of benzene
for 48 h under argon. Water (150 mL) was added to remove the salt. Then,
the solution was extracted by 50 mL of dichloromethane three times. A 30-g
aliquot of anhydrous MgSO4 powder was added to remove the water. The
color of the solution was dark brown. The crude product, a dark brown powder,
can be obtained by filtering and removing the solvent. The powder was
recrystallized with 15 mL of dichloromethane. A pale yellow powder,
H2phdpda, was then obtained (yield 76.5%). The H2phdpda ligand is
characterized on the basis of its 1H and 13C NMR and mass spectrometry
with high yield.14 I was characterized on the basis of 1H and 13
C
NMR spectroscopy and mass spectrometry.
The nickel string complex of ligand I was synthesized by
treating equimolar amounts of NiCl2 and I in refluxing naphtha-
* Corresponding author: (e-mail) smpeng@chem35.ch.ntu.edu.tw; (tel)
886-2-23638305; (fax) 886-2-23636359.
(1) Yang, M. H.; Lin, T. W.; Chou, C. C.; Lee, H. C.; Chang, H. C.; Lee,
G. H.; Leung, M. K.; Peng, S. M. Chem. Commun. 1997, 2279.
(2) (a) Cotton, F. A.; Daniels, L. M.; Murillo, C. A.; Pascual, I. J. Am.
Chem. Soc. 1997, 119, 10223. (b) Cotton, F. A.; Daniels, L. M.; Murillo, C.
A.; Wang, X. Chem. Commun. 1998, 39.
(3) Yang, E. C.; Cheng, M. C.; Tsai, M. S.; Peng, S. M. J. Chem. Soc.,
Chem. Commun. 1994, 2377.
(4) (a) Cotton, F. A.; Daniels, L. M.; Jordan, G. T. IV Chem. Commun.
1997, 421. (b) Cotton, F. A.; Daniels, L. M.; Jordan, G. T., IV; Murillo, C.
A. J. Am. Chem. Soc. 1997, 119, 10377.
(5) (a) Wu, L. P.; Field, P.; Morrisey, T.; Murphy, C.; Nagle, P.; Hathaway,
B.; Simmons, C.; Thornton, P. J. Chem. Soc., Dalton Trans. 1990, 3835. (b)
Pyrka, G. J.; El-Mekki, M.; Pinkerton, A. A. J. Chem. Soc., Chem. Commun.
1991, 84.
1
data. The H in DMSO-d6 clearly shows two singlets (9.30, 8.81 ppm), five
doublets (8.19, 7.69, 7.63, 7.05, 6.32 ppm), and five triplets (7.56, 7.42, 7.24,
6.87, 6.82 ppm), which are consistent with the structural assignment. IR
(KBr): ν 3258, 3172 (NH), 1606, 1589 cm-1 (CdC). MS (FAB): m/z (%)
263.1 (60) [M + 1]+.
(15) NiCl2 (0.5 g, 3.8 mmol) and H2phdpda (1.0 g, 3.8 mmol) were placed
in a Erlemyer flask, to which naphthalene (15 g) was added. The mixture
was heated (∼160-180 °C) for 2 h to remove water. Then a solution of
potassium tert-butoxide (0.8 g) in tert-butyl alcohol (5 mL) was added
dropwise. Heating was continued until the volume of the naphthalene solution
was reduced to less than 10 mL. After the mixture had cooled, n-hexane was
added to wash out the naphthalene. The remaining solid was extracted by
acetone and recrystallized from acetone/n-hexane. A black crystal was then
obtained (yield 30%). IR (KBr): ν 1600, 1589, 1553 cm-1 (CdC). MS
(FAB): m/z (%) 1274.3 (5) [M]+. Crystal data for [Ni4(µ4-phdpda)4]‚C5H12:
dimensions 0.5 × 0.45 × 0.2 mm, monoclinic, space group P21/n, a )
15.2024(2) Å, b ) 24.4219(1) Å, c ) 17.1093(2) Å, â ) 96.844(1)°, V )
6306.9(1) Å3, Z ) 4; CCD SMART diffractometer with graphite monochro-
mated Mo KR radiation, and Sadabs absorption correction (Tmin ) 0.54, Tmax
) 0.72). A total of 30 356 reflections were measured and 11 134 unique
reflections (2θ < 55°, Rint ) 0.057) were used in the refinement. Full-matrix
least-squares refinement on F2 converged to RF ) 0.088 (all data), 0.046 (I >
(6) Aduldecha, S.; Hathaway, B. J. Chem. Soc., Dalton Trans. 1991, 993.
(7) Sheu, J. T.; Liu, C. C.; Chao, I.; Wang, C. C.; Peng, S. M. Chem.
Commun. 1996, 315.
(8) Shieh, S. J.; Chou, C. C.; Lee, G. H.; Wang, C. C.; Peng, S. M. Angew.
Chem., Int. Ed. Engl. 1997, 36, 56.
(9) Wang, C. C.; Lo, W. C.; Chou, C. C.; Lee, G. H.; Chen, J. M.; Peng,
S. M. Inorg. Chem. 1998, 37, 4059.
(10) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Atoms, 2nd ed.;
Clarendon Press: Oxford, 1993.
2
2σ(I)); RwF ) 0.134 (all data), 0.114 (I > 2σ(I)). The pentane molecule is
(11) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
disordered and has large thermal parameters. (U ranging from 0.352(10) to
0.483(19), Uav = 0.40.)
Wiley: New York, 1988; Chapter 23.
(12) Fackler, J. P., Ed. Metal-Metal Bonds and Clusters in Chemistry and
Catalysis; Plenum: New York, 1990.
(16) Sacconi, L.; Mani, F.; Bencini, A. In ComprehensiVe Coodination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.; Perga-
mon: Oxford, 1987; Vol. 5, Section 50.
(13) Wagaw, S.; Buchwald, S. L. J. Org. Chem. 1996, 61, 7240.
10.1021/ja982065w CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/19/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 1, 1999 251
Figure 1. (a) Crystal structure of [Ni4(µ4-phdpda)4] (ORTEP view). Pertinent bond lengths (Å) and angles (deg): Ni(1)-Ni(2) 2.3269(6), Ni(2)-Ni(3)
2.3010(6), Ni(3)-Ni(4) 2.3280(6), (Ni(1)-N)av 1.924(4), (Ni(2)-N)av 1.915(3), (Ni(3)-N)av 1.913(3), (Ni(4)-N)av 1.927(4), Ni(1)-Ni(2)-Ni(3) 178.35(3),
and Ni(2)-Ni(3)-Ni(4) 177.97(3). (b) Another illustration looking down the metal chain axis. Atoms are shown as 20% vibrational thermal ellipsoids.
Figure 2. (a) Crystal structure of [Ni7(µ7-teptra)4] (ORTEP view). Pertinent bond lengths (Å) and angles (deg): Ni(1)-Ni(2) 2.383(1), Ni(2)-Ni(3)
2.310(1), Ni(3)-Ni(4) 2.225(2), Ni(4)-Ni(5) 2.215(2), Ni(5)-Ni(6) 2.304(1), Ni(6)-Ni(7) 2.374(2), Ni(1)-Cl(1) 2.370(3), (Ni(1)-N)av 2.112(8),
(Ni(2)-N)av 1.903(7), (Ni(3)-N)av 1.917(7), (Ni(4)-N)av 1.922(7), (Ni(5)-N)av 1.910(7), (Ni(6)-N)av 1.888(7), (Ni(7)-N)av 2.104(8), Ni(7)-Cl(2)
2.357(3), Ni(1)-Ni(2)-Ni(3) 179.29(7), Ni(2)-Ni(3)-Ni(4) 179.73(7), Ni(3)-Ni(4)-Ni(5) 178.85(7), Ni(4)-Ni(5)-Ni(6) 179.75(6), Ni(5)-Ni(6)-
Ni(7) 179.15(7), Cl(1)-Ni(1)-Ni(2) 179.0(1), and Cl(2)-Ni(7)-Ni(6) 179.0(1). (b) Another illustration looking down the metal chain axis. Atoms are
shown as 20% vibrational thermal ellipsoids.
2.374(2) Å. These are shorter than the Ni-Ni distance of 2.443(1)
Å in [Ni3(µ3-dpa)4Cl2]5 but are comparable to the outer Ni-Ni
distance of 2.385(2) Å in the [Ni5(µ5-tpda)4Cl2] complex.8,9 The
intermediate ones are 2.310(1) and 2.304(1) Å, which are
comparable to the inner Ni-Ni distance of 2.306(1) Å in the
[Ni5(µ5-tpda)4Cl2] complex.8,9 The Ni-Ni distances of the in-
nermost Ni ions are 2.225(2) and 2.215(2) Å, which are the
shortest known Ni-Ni distances in any nickel complexes. The
average Niinner-N bond distances, i.e., Ni(2)-N (1.903(7) Å),
Ni(3)-N (1.917(7) Å), Ni(4)-N (1.922(7) Å), Ni(5)-N (1.910(7)
Å), and Ni(6)-N (1.888(7) Å) are short, consistent with a square-
planar, diamagnetic arrangement of nickel(II) ions.9,14 The terminal
NiII ions (Ni(1), Ni(7)) are in a square-pyramidal environment
and exhibit long Ni-Cl bonds (2.370(3), 2.357(3) Å) and long
Ni(1)-N and Ni(7)-N bonds. Their average distances, 2.112(8)
and 2.104(8) Å, are consistent with high-spin nickel(II) ions (S
) 1, µ ) 2.82 µB; µM ) 4.0 µB). A temperature-dependent
magnetic study of this complex indicates that there is a weak
antiferromagnetic interaction between the two terminal high-spin
nickel(II) ions with J ) -3.8 cm-1. This interaction is smaller
than those of similar trinuclear (J ) -99 cm-1) and pentanuclear
nickel(II) complexes (J ) -8.3 cm-1).
Attempts to isolate other metal string complexes with metal-
metal bonding and demonstration of their potential application
as molecular metal wire are underway.
Acknowledgment. We thank the National Science Council of the
Republic of China for financial support.
Supporting Information Available: Tables of crystal data, atomic
coordinates, structure solution and refinement, atomic coordinates, bond
lengths and angles, and anisotropic thermal parameters for [Ni4(µ4-
phdpda)4] and [Ni7(µ7-teptra)4Cl2] (22 pages, print/PDF). See any current
masthead page for Web access instructions.
(17) NiCl2‚6H2O (1.66 g, 7 mmol) and H3teptra (1.02 g, 4 mmol) were
placed in a Erlemyer flask, to which naphthalene (7.2 g) was added. The
mixture was heated (∼160-180 °C) for 10 min to remove water. Then
1-butanol (3 mL) was added to the heated mixtures, and heating was continued
until the 1-butanol had almost completely evaporated. A solution of potassium
tert-butoxide (1.32 g, 12 mmol) in tert-butyl alcohol (20 mL) was added
dropwise. Heating was continued until the remaining 1-butanol had evaporated
completely. After the mixture had cooled, n-hexane was added to wash out
the naphthalene. The remaining solid was extracted with CH2Cl2 and
recrystallized from CHCl3/n-hexane. A deep purple crystal was then obtained
(yield 10%). IR (KBr): ν 1596, 1579, 1545 cm-1 (CdC). MS (FAB): m/z
(%) 1890 (5) [M]+. Crystal data for [Ni7(µ7-teptra)4Cl2]‚3CHCl3: dimensions
0.35 × 0.18 × 0.15 mm, monoclinic, space group P21/n, a ) 19.7542(7) Å,
b ) 16.9432(5) Å, c ) 28.5946(9) Å, â ) 95.868(1)°, V ) 9520.4(5) Å3, Z
) 4; CCD SMART diffractometer with graphite monochromated Mo KR
radiation, and Sadabs absorption correction (Tmin ) 0.61, Tmax ) 0.80). A
total of 38 984 reflections were measured and 16 710 unique reflections (2θ
< 55°, Rint ) 0.063) were used in the refinement. Full-matrix least-squares
refinement on F2 converged to RF ) 0.153 (all data), 0.085 (I > 2σ(I)); RwF
2
) 0.309 (all data), 0.254 (I > 2σ(I)). The chloroform molecules have large
thermal parameters. (U ranging from 0.261(5) to 0.595(14), Uav = 0.41.)
JA982065W