Gold(I) complex of 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) as a metalloligand for encapsulation of metal ions. Crystal structures of [AuCu(dpnapy)3][ClO4]2 and [AuCd(dpnapy)3][ClO4]3

Article abstract of DOI:10.1039/a800061a

Reaction of dpnapy [dpnapy = 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine] with [Au(tht)Cl] (tht = tetrahydrothiophene) in dichloromethane afforded [Au(dpnapy)₃]⁺, which shows a strong affinity towards Cu^I and Cd^II ions; crystal structures of [AuCu(dpnapy)₃][ClO₄]₂ and [AuCd(dpnapy)₃][ClO₄]₃ revealed that [Au(dpnapy)₃]⁺ functions as a metalloligand with the three naphthyridyl groups positioned in a trigonal fashion.

Full text of DOI:10.1039/a800061a

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Gold(I) complex of 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine
(dpnapy) as a metalloligand for encapsulation of metal ions. Crystal
structures of [AuCu(dpnapy)3][ClO4]2 and [AuCd(dpnapy)3][ClO4]3
Wing-Han Chan,a Kung-Kai Cheung,a Thomas C. W. Makb and Chi-Ming Che*,†,a
a Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
b Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong
that the 2-Me resonances are comparable to those of the free
Reaction of dpnapy [dpnapy = 7-diphenylphosphino-2,4-
dimethyl-1,8-naphthyridine] with [Au(tht)Cl] (tht = tetrahydro-
thiophene) in dichloromethane afforded [Au(dpnapy)3]ϩ, which
shows a strong affinity towards CuI and CdII ions; crystal
structures of [AuCu(dpnapy)3][ClO4]2 and [AuCd(dpnapy)3]-
[ClO4]3 revealed that [Au(dpnapy)3]ϩ functions as a
metalloligand with the three naphthyridyl groups positioned
in a trigonal fashion.
ligand whereas downfield shifts are observed for those of 2 and
3.§ These downfield shifts evidence the metal–naphthyridyl
co-ordination. The 31P NMR spectra of cations 1–3 display a
single resonance revealing that the three dpnapy ligands in the
complexes are equivalent.
The structure of 1[ClO4] has been established by X-ray crys-
tal analysis. However, the high RЈ value of the structure pre-
cludes a detailed discussion. Nevertheless the structure reveals
that the Au atom adopts a trigonal-planar geometry. The
dpnapy ligands are P-monodentate with three naphthyridyl
moieties radiating from the Au atom to form a void. In this
context, the Au atom can be viewed as a template to fix the
ligating sites of the naphthyridyl rings. The crystal structures of
complexes 2[ClO4]2 and 3[ClO4]3ؒCH3CN have been determined
by X-ray analyses and perspective views of the complex cations
are depicted in Figs. 1 and 2.¶ In both complexes, the Au atom
retains a trigonal-planar geometry with P᎐Au᎐P angles and
Au᎐P distances comparable to those in 1. For 2, the [Au-
(dpnapy)3]ϩ unit binds to the Cu atom via three N1 donors to
give a face-to-face hetero-metallocycle. The Cu(1) atom adopts
a distorted trigonal-planar co-ordination and the AuP3 and
CuN3 planes are nearly parallel (dihedral angle of 3.5Њ). This
The design of macropolycyclic ligands as receptor molecules
that have binding sites positioned in a preferred geometry is an
important area in molecular recognition and in host–guest
chemistry. Examples of such ligand systems e.g. cryptands have
been reported though their preparations are usually tedious.1
In this context, we envisaged co-ordination of pyridylphos-
phine ligands to d10 metal ions via the phosphorus atoms which
could direct the spatial arrangement of the pendant pyridyl
groups. Consequently, this may lead to a new class of metal-
loligands for encapsulation of ions in a preferred geometry.2
Whereas there are many tripodal ligands, such as 1,4,7-
triazacyclononane and 1,1,1-tris(diphenylphosphinomethyl)-
ethane,3,4 which co-ordinate metal ions in a facial manner,
examples of planar tridentate chelating ligands are scarce.5
Herein is described the co-ordination of 7-diphenylphos-
phino-2,4-dimethyl-1,8-naphthyridine6 (dpnapy) to gold() to
give [Au(dpnapy)3]ϩ 1, which has the three pendant naphthyr-
idyl groups positioned in a trigonal arrangement.
Me
P
N
N
Ph2P
N
N
Me
dpnapy
Scheme 1 outlines the procedures for the preparation of cat-
ions 1–3. Complexes 2[ClO4]2 and 3[ClO4]3 were obtained by
treating 1[ClO4] with a stoichiometric amount of [Cu(CH3-
CN)4][ClO4] and Cd(ClO4)2, respectively, in acetone. Recrystal-
lisation of the crude products in acetonitrile–diethyl ether
solution afforded red crystals of 2[ClO4]2 and yellow prisms
of 3[ClO4]3ؒCH3CN.‡ The 1H and 13C NMR spectra of 1 show
Au+
+
P
N
N
P
N
N
Au
P
N
N
1
† E-Mail: CMCHE@HKUCC.HKU.HK
Cu+
Cd2+
‡ 1[ClO4]: a mixture of [Au(tht)Cl] (tht = tetrahydrothiophene) (0.32 g,
1 mmol) and dpnapy (1.0 g, 3 mmol) in dichloromethane (25 ml) was
stirred for 1 h at room temperature. Metathesis of the product with
LiClO4 (0.11 g, 1 mmol) in methanol afforded pale yellow microcrys-
tals of 1 (0.69 g, 52%) (Found: C, 58.20; H, 4.62; N, 6.22. Calc. for
1[ClO4]ؒCH3OHؒH2O: C, 58.59; H, 4.62; N, 6.12%).
2[ClO4]2: a mixture of 1[ClO4] (1.3 g, 1 mmol) and [Cu(CH3CN)4]-
[ClO4] (0.33 g, 1 mmol) in acetone (25 ml) was stirred for 1 h at room
temperature. The solvent was removed in vacuo. The crude product was
recrystallized by diffusion of diethyl ether into an acetonitrile solution
to afford red crystals (0.92 g, 62%) (Found: C, 54.02; H, 3.80; N, 5.55.
Calc. for 2[ClO4]2: C, 53.33; H, 3.86; N, 5.65%).
3+
2+
P
N
N
P
N
N
P
N
N
P
N
N
Au
Au
Cu
N
Cd
N
N
N
P
P
3
2
Scheme 1 Preparation of complexes 1–3
3[ClO4]3: a mixture of 1[ClO4] (1.3 g, 1 mmol) and Cd(ClO4)2 (0.31 g,
1 mmol) in acetone (25 ml) was stirred for 1 h at room temperature. The
solvent was removed in vacuo. The crude product was recrystallized by
diffusion of diethyl ether into an acetonitrile solution to afford yellow
crystals (0.83 g, 51%) (Found: C, 48.11; H, 3.80; N, 5.65. Calc. for
3[ClO4]3ؒCH3CN: C, 48.73; H, 3.61; N, 5.85%).
§ 1H NMR (CD3CN):δ 2-Me 1[ClO4], 2.69 (s); 2[ClO4]2, 2.79 (s);
3[ClO4]3ؒCH3CN, 2.75 (s). 13C NMR (CD3CN): δ 2-Me 1[ClO4], 25.1
(s); 2[ClO4]2, 26.1 (s); 3[ClO4]3ؒCH3CN, 25.9 (s). 31P NMR (CD3CN):
δ 1[ClO4], 39.6 (s); 2[ClO4]2, 38.5 (s); 3[ClO4]3ؒCH3CN, 41.0 (s).
J. Chem. Soc., Dalton Trans., 1998, Pages 873–874
873

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Fig. 1 A perspective view of complex cation 2. Selected bond lengths
(Å) and angles (Њ): Au(1)᎐P(1) 2.363(3), Au(1)᎐P(2) 2.367(3),
Au(1)᎐P(3) 2.367(3), Cu(1)᎐N(2) 2.025(8), Cu(1)᎐N(4) 2.029(9),
Cu(1)᎐N(6) 2.045(8); P(1)᎐Au(1)᎐P(2) 120.6(1), P(2)᎐Au(1)᎐P(3)
115.8(1), P(1)᎐Au(1)᎐P(3) 120.5(1), N(2)᎐Cu(1)᎐N(4) 126.9(4),
N(2)᎐Cu(1)᎐N(6) 119.3(4), N(4)᎐Cu(1)᎐N(6) 110.8(4)
Fig. 2 A perspective view of complex cation 3. Selected bond lengths
(Å) and angles (Њ): Au(1)᎐P(1) 2.362(3), Cd(1)᎐N(1) 2.438(9),
Cd(1)᎐N(2) 2.288(9); P(1)᎐Au(1)᎐P(1*) 118.69(3), N(1)᎐Cd(1)᎐N(1*)
100.5(2), N(1)᎐Cd(1)᎐N(2) 56.8(3), N(1)᎐Cd(1)᎐N(2*) 101.0(3),
N(1)᎐Cd(1)᎐N(2**)
N(1*)᎐Cd(1)᎐N(2**)
151.3(3),
101.0(3),
N(1*)᎐Cd(1)᎐N(2*)
N(1**)᎐Cd(1)᎐N(2**)
56.8(3),
56.8(3),
N(2)᎐Cd(1)᎐N(2*) 106.7(2)
features an interesting face-to-face d10–d10 hetero-bimetallic
complex. Complex 3 is a rare hetero-bimetallic AuI–CdII com-
plex, in which the Cd atom is captured by [Au(dpnapy)3]ϩ
through co-ordination to three naphthyridyl moieties. The co-
ordination polyhedron of the Cd atom is distorted trigonal-
prismatic, with a chelate bite [N(1)᎐Cd᎐N(2)] of 56.83(3)Њ. In
both 2 and 3, a view down the Au᎐M axis (M = Cu or Cd)
shows that the Au᎐P and M᎐N bonds are staggered with
respect to each other. The P᎐Au ؒ ؒ ؒ M᎐N torsional angles
range from 53.1 to 60.4Њ, which are near to 60Њ required for a
perfectly staggered conformation. The Au ؒ ؒ ؒ Cu and Au ؒ ؒ ؒ Cd
separations of 4.469 and 3.745 Å respectively suggest no metal–
metal interaction.
The spectroscopic data of complexes 1–3 are summarized in
Table 1. Their UV/VIS absorption spectra are characterized by
an absorption band at 320–360 nm (1: 325, 2: 320, 3: 360 nm),
which is assigned to the d(Au) → π*(dpnapy) MLCT transi-
tion. For complex 2, a low energy absorption tail from 420–450
nm has been observed, which is attributed to the d(Cu) → π*
(dpnapy) MLCT transition. The red shift in the d(Au) → π*
(dpnapy) transition from 1 to 3 is due to the lowering of the π*
energy of the naphthyridyl rings through co-ordination to CdII.
Upon excitation at 360 nm, complex 1[ClO4] displays a low
energy emission at 560 nm, which is tentatively assigned to the
Table 1 Spectroscopic data for complexes 1–3 in degassed acetonitrile
at room temperature
λem/nm (excitation
360 nm)
Complex
λabs/nm (εmax/cmϪ1 Ϫ1
)
τ/µs
1
2
268 (54 710), 325 (21 570)
264 (46 730), 320 (29 460),
435 (sh, 14 400)
560
530
0.96
—
3
268 (55 320), 318 (16 300),
360 (12 080)
606
0.71
d(Au) → π*(dpnapy) MLCT excited state. Interestingly, co-
ordination of CuI to [Au(dpnapy)3]ϩ in cation 2 results in a shift
of the MLCT emission to 530 nm, which may be attributable to
an admixture of two excited states of similar energy,
d(Au) → π*(dpnapy) and d(Cu) → π*(dpnapy). In cation
3, co-ordination of CdII to [Au(dpnapy)3]ϩ lowers the energy of
the d(Au) → π*(dpnapy) excited state and hence the MLCT
emission is red shifted to a longer wavelength, 606 nm.
Acknowledgements
We acknowledge support from the University of Hong Kong
and the Croucher Foundation of Hong Kong, and the Hong
Kong Research Grants Council.
¶ 2[ClO4]2: C66H57AuCl2CuN6O8P3, M = 1486.5, triclinic, space group
¯
P1 (no. 2), a = 15.795(1), b = 16.092(1), c = 16.491(1) Å, α = 87.75(1),
References
β = 62.93(1), γ = 65.31(1), U = 3331.7(4) Å3, Z = 2, µ(Mo-Kα) = 27.28
cmϪ1, crystal dimensions 0.20 × 0.20 × 0.18 mm, T = 293 K, F(000) =
1492, no. of unique reflections = 10 333, no. of reflections with
I у 2σ(I) = 9505, no. of variables = 829, R = 0.079, RЈ = 0.088, good-
ness of fit = 1.22.
1 J. M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995.
2 S. J. Shieh, D. Li, S. M. Peng and C. M. Che, J. Chem. Soc., Dalton
Trans., 1993, 195; R. H. Uang, C. K. Chan, S. M. Peng and C. M. Che,
J. Chem. Soc., Chem. Commun., 1994, 2561.
3 F. A. Cotton and B. Hong, Prog. Inorg. Chem., 1992, 40, 179.
4 P. Chaudhuri and K. Wieghardt, Prog. Inorg. Chem., 1987, 35, 329.
5 C. M. Hartshorn and P. J. Steel, Angew. Chem., Int. Ed. Engl., 1996,
35, 2655, and refs. therein.
3[ClO4]3ؒCH3CN: C68H60AuCdCl3N7O12P3, M = 1675.9, trigonal,
¯
space group P3 (no. 147), a = 13.873(1), c = 21.611(2) Å, U = 3602.1(3)
Å3, Z = 2, µ(Mo-Kα) = 25.78 cmϪ1
,
crystal of dimensions
0.15 × 0.10 × 0.30 mm, T = 301 K, F(000) = 1672, reflections meas-
ured = 4662, no. of unique reflections = 4258, no. of reflections with
I у 3σ(I) = 2806, no. of variables = 301, R = 0.055, RЈ = 0.075, good-
ness of fit = 2.13. Singly starred (*) atoms have coordinates at (1 Ϫ y,
1 ϩ x Ϫ y, z) and doubly starred (**) atoms have coordinates at (y Ϫ x,
1 Ϫ x, z).
6 M. Grassi, G. D. Munno, F. Nicolo and S. L. Schiavo, J. Chem. Soc.,
Dalton Trans., 1992, 2367.
Received 2nd January 1998; Communication 8/00061A
CCDC reference number 186/901.
874
J. Chem. Soc., Dalton Trans., 1998, Pages 873–874