Metal-Purine Interactions: Homo- And Heterodinuclear Platinum(II) and/or Palladium(II) Complexes of 8-Thiotheophylline. Crystal Structures of [Pt(μ-TT)(dppm)]2·2DMSO and [(dppm)Pt(μ-TT)2Pd(dppm)]·7H2O

Article abstract of DOI:10.1021/ic961288p

The reaction of cis-[MCl₂(dppm)] (M = Pt(II) and Pd(II); dppm = bis(diphenylphosphino)methane) with H₂TT and NaOH (H₂TT = 8-thiotheophylline) yields neutral mononuclear [M(HTT-S(8))₂(dppm)] complexes. Homodinuclear [M(μ-TT-N(7),S(8))(dppm)]₂ (M = Pt(II) and Pd(II)) are prepared either by the reaction of [M(HTT)₂(dppm)] with cis-[MCl₂(dppm)] and NaOH or by the direct reaction of cis-[MCl₂(dppm)] with Na₂TT, prepared in situ from H₂TT and NaOH. The crystal structure of the Pt derivative is reported: [Pt(μ-TT)(dppm)]₂·-2DMSO (3) crystallizes in the triclinic space group P1 with a = 12.949(3) A?, b = 13.009(3) A?, c = 22.980(5) A?, α = 96.89(3)°, β= 103.53(3)°, γ = 106.43(3)°, Z = 2, and R₁ = 0.045. Heterodinuclear [(dppm)Pt(μ-TT)₂-Pd(L-L)] complexes are obtained by reaction of [Pt(HTT)₂(dppm)] with [PdCl₂(L-L)] in basic medium (L-L = dppm and 2,2′-bipyridine). The crystal structure of [(dppm)Pt(μ-TT)₂Pd(dppm)]·7H₂O (5) is reported. The complex crystallizes in the orthorhombic space group P2₁2₁2₁] with a = 16.560(5) A?, b = 17.063(5) A?, c = 24.428(5) A?, Z = 4, and R₁ = 0.042. The structures of 3 and 5 are almost identical, by which 5 can be seen as an isomorphic substitution of one of the Pt(II) ions of 3 by a Pd(II) ion. The structures consist of dinuclear units having a pseudo-2-fold axis perpendicular to that defined by the metal atoms. The two metal atoms are bibridged by two μ-TT-N(7),S(8) ligands, in a head to tail arrangement. The square-planar coordination of the metal atoms is completed by a chelate dppm ligand. The steric repulsions between the bulky dppm ligands must be the main factor precluding metal-metal interaction in these compounds.

Full text of DOI:10.1021/ic961288p

1652
Inorg. Chem. 1997, 36, 1652-1656
Metal-Purine Interactions: Homo- and Heterodinuclear Platinum(II) and/or Palladium(II)
Complexes of 8-Thiotheophylline. Crystal Structures of [Pt(µ-TT)(dppm)]2‚2DMSO and
[(dppm)Pt(µ-TT)2Pd(dppm)]‚7H2O
Enrique Colacio,* Rafael Cuesta, Mustapha Ghazi, M. Angeles Huertas, Jose M. Moreno, and
Antonio Navarrete
Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad de Granada,
18071 Granada, Spain
ReceiVed October 24, 1996X
The reaction of cis-[MCl2(dppm)] (M ) Pt(II) and Pd(II); dppm ) bis(diphenylphosphino)methane) with H2TT
and NaOH (H2TT ) 8-thiotheophylline) yields neutral mononuclear [M(HTT-S(8))2(dppm)] complexes.
Homodinuclear [M(µ-TT-N(7),S(8))(dppm)]2 (M ) Pt(II) and Pd(II)) are prepared either by the reaction of
[M(HTT)2(dppm)] with cis-[MCl2(dppm)] and NaOH or by the direct reaction of cis-[MCl2(dppm)] with Na2TT,
prepared in situ from H2TT and NaOH. The crystal structure of the Pt derivative is reported: [Pt(µ-TT)(dppm)]2‚-
2DMSO (3) crystallizes in the triclinic space group P1h with a ) 12.949(3) Å, b ) 13.009(3) Å, c ) 22.980(5)
Å, R ) 96.89(3)°, â ) 103.53(3)°, γ ) 106.43(3)°, Z ) 2, and R1 ) 0.045. Heterodinuclear [(dppm)Pt(µ-TT)2-
Pd(L-L)] complexes are obtained by reaction of [Pt(HTT)2(dppm)] with [PdCl2(L-L)] in basic medium (L-L )
dppm and 2,2′-bipyridine). The crystal structure of [(dppm)Pt(µ-TT)2Pd(dppm)]‚7H2O (5) is reported. The complex
crystallizes in the orthorhombic space group P212121 with a ) 16.560(5) Å, b ) 17.063(5) Å, c ) 24.428(5) Å,
Z ) 4, and R1 ) 0.042. The structures of 3 and 5 are almost identical, by which 5 can be seen as an isomorphic
substitution of one of the Pt(II) ions of 3 by a Pd(II) ion. The structures consist of dinuclear units having a
pseudo-2-fold axis perpendicular to that defined by the metal atoms. The two metal atoms are bibridged by two
µ-TT-N(7),S(8) ligands, in a head to tail arrangement. The square-planar coordination of the metal atoms is
completed by a chelate dppm ligand. The steric repulsions between the bulky dppm ligands must be the main
factor precluding metal-metal interaction in these compounds.
Introduction
Pt(II) and Pd(II) complexes with 8-thiotheophylline (hereafter
H2TT).
Thiolated purines are of interest because some of them, such
as 6-mercaptopurine and 6-mercaptoguanine, are established
clinical agents for the therapy of human leukemias.1 In some
cases metal complexes of these bases, especially those of Pt(II)
and Pd(II), show higher anticancer activity than the free ligand.2
On the other hand, phosphines and phosphine metal containing
complexes have received much attention during the past few
years due to their potential use as antitumor agents.3 Particu-
larly, 1,2-bis(diphenylphosphino)ethane (dppe) and some of its
analogues have been shown to have antitumor activity against
a wide range of tumors, and, moreover, their activity is enhanced
upon coordination to metal ions, such as gold(I).
The possibility that thiolated purines may act in a synergetic
fashion with [M(diphosphine)]2+ moieties, giving rise to a
bifunctional antitumor agent, prompted us to prepare and
characterize purine-metal-phosphine complexes. As a con-
tinuation of our studies along this line,4 herein we report on
the preparation, characterization, and reactivity of a number of
Experimental Section
The purine derivative 1,3-methyl-8-thioxanthine (8-thiotheophylline)
was prepared according to literature procedures,5 while bis(diphe-
nylphosphino)methane (dppm) was purchased from Aldrich and used
as received. The compounds [PtCl2(dppm)] and [PdCl2(dppm)] were
prepared by standard methods.6 [PtCl2(bipy)] and [PdCl2(bipy)] were
prepared by procedures described for the related complexes with
ethylenediamine.7
Physical Measurements. Microanalyses and IR spectra were
obtained as already described.4 The 31P-NMR spectra were obtained
in dimethyl-d6 sulfoxide (DMSO-d6) at 298 K on a Bruker AM-300
operating at 121.42 MHz and using H3PO4 (85% (w/w) in D2O) as
external standard.
Preparations. [Pt(HTT)2(dppm)] (1). This complex can be
prepared by following these methods: (a) To a solution of [PtCl4(NH3)2]
(0.282 g, 0.76 mmol) in ethanol (50 mL) was added H2TT (0.424 g,
2.0 mmol). The suspension was stirred until a clear solution was
obtained. After filtration of any amount of insoluble material, the
resulting orange solution was allowed to stand at room temperature,
whereupon the dark-orange product [Pt(HTT)2(NH3)Cl] formed. This
complex (0.1 g, 0.15 mmol) and dppm (0.13 g, 0.3 mmol) were stirred
X Abstract published in AdVance ACS Abstracts, March 15, 1997.
(1) (a) Wood, H. B., Jr. Cancer Chemother. Rep., Part 3 1971, 2, 9. (b)
Williams, D. R. Chem. ReV. 1972, 72, 203. (c) Zubrod, C. G. Life
Sci. 1974, 14, 809. (d) Mautner, H. G.; Chu, S.-H.; Jaffe, J. J.;
Sartorelli, A. C. J. Med. Chem. 1963, 6, 36. (e) Van Scoik, K. G.;
Johnson, C. A.; Porter, W. R. Drug. Metab. ReV. 1985, 16, 157.
(2) (a) Kirschner, S.; Wei, Y. K.; Francis, D.; Bergman, J. G. J. Med.
Chem. 1969, 9, 369. (b) Skinner, S. M.; Swatzell, J. M.; Lewis, R.
W. Res. Commum. Chem. Pathol. Pharmacol. 1978, 19, 165. (c) Das,
M.; Livinstone, S. E. Br. J. Cancer 1978, 38, 325. (d) Maeda, M.;
Abiko, N.; Sasaki, T. J. Med. Chem. 1981, 24, 167.
(4) (a) Colacio, E.; Romerosa, A.; Ruiz, J.; Roma´n, P.; Gutie´rrez-Zorrilla,
J. M.; Mart´ınez-Ripoll, M. J. Chem. Soc., Dalton. Trans. 1989, 2323.
(b) Colacio, E.; Romerosa, A.; Ruiz, J.; Roma´n, P.; Gutie´rrez-Zorrilla,
J. M.; Vega, A.; Mart´ınez-Ripoll, M. Inorg. Chem. 1991, 30, 3743.
(c) Colacio, E.; Cuesta R.; Gutie´rrez-Zorrilla, J. M.; Luque, A.; Roma´n,
P.; Giraldi, T.; Taylor, M. R. Inorg. Chem. 1996, 35, 4232.
(5) Merz, K. W.; Stahl, P. H. Arzneim.-Forsch. 1965, 15, 10.
(6) (a) Church, M. J.; Mays, M. J. J. Inorg. Nucl. Chem. 1971, 33, 253.
(b) Booth, G.; Chatt, J. J. Chem. Soc. A 1966, 364. (c) Steffen, W. L.;
Palenik, G. J. Inorg. Chem. 1976, 15, 2432.
(3) (a) Berners-Price, S. J.; Sadler, P. J. Chem. Br. 1987, 23, 541. (b)
Berners-Price, S. J.; Sadler, P. J. Struct. Bonding 1988, 70, 27. (c)
Sadler, P. J. AdV. Inorg. Chem. Radiochem. 1991, 36, 1.
(7) Hohmann, H.; van Eldik, R. Inorg. Chim. Acta 1990, 174, 87.
S0020-1669(96)01288-8 CCC: $14.00 © 1997 American Chemical Society

Pt(II) and/or Pd(II) Complexes of H2TT
Inorganic Chemistry, Vol. 36, No. 8, 1997 1653
and heated in ethanol (50 mL) until a clear yellow solution was
obtained. This solution, kept at room temperature for several days,
gave yellow needlelike crystals of 1; yield, 70%. (b) To a solution of
H2TT (0.12 g, 0.3 mmol) in 5 mL of water containing 0.3 mmol of
NaOH was added a suspension of [PtCl2(dppm)] (0.1 g, 0.15 mmol) in
ethanol (50 mL). The reaction mixture was warmed for 15 min to
give a light yellow solution from which, after evaporation at room
temperature, yellow needlelike crystals of 1 were formed; yield, 80%.
Anal. Calcd for C39H36N8O4P2S2Pt: C, 46.75; H, 3.62; N, 11.18; S,
6.40. Found: C, 46.29; H, 3.72; N, 10.99; S, 6.50.
[Pd(HTT)2(dppm)]‚4H2O (2). The complex [PdCl2(dppm)] (0.1
g, 0.18 mmol) and H2TT (0.08 g, 0.36 mmol) were reacted by using
the preceding b procedure to yield orange crystals; yield, 75%. Anal.
Calcd for C39H44N8O8P2S2Pd: C, 47.54; H, 4.50; N, 11.37; S, 6.51.
Found: C, 47.42; H, 4.33; N, 10.91; S, 6.10.
[Pt(µ-TT)(dppm)]2‚2DMSO (3). This complex can be obtained
by following two different procedures: (a) A suspension of [PtCl2(dppm)]
(0.1 g, 0.15 mmol) in ethanol (50 mL) was added to a solution of H2-
TT (0.03 g, 0.15 mmol) in 5 mL of water containing 0.3 mmol of
NaOH. After the mixture was warmed for 15 min, a yellow light
solution was obtained, which, kept at room temperature, yielded a
yellow precipitate, which was washed with ethanol and diethyl ether.
Recrystallization from DMSO gave yellow crystals; yield, 70%. (b)
To a suspension of [PtCl2(dppm)] (0.1 g, 0.15 mmol) in 30 mL of
ethanol were added 1 (0.15 g, 0.15 mmol) and NaOH (12 mg, 0.3
mmol). The reaction mixture was heated to reflux for 15 min to give
a light yellow solution, which, kept at room temperature, provided a
yellow precipitate of 3. Anal. Calcd for C36H40N4O4P2S3Pt: C, 47.06;
H, 3.95; N, 6.46; S, 7.39. Found: C, 47.58; H, 3.88; N, 6.48; S, 7.60.
[Pd(µ-TT)(dppm)]2‚3H2O (4). This complex was prepared either
from [PdCl2(dppm)] and H2TT or from 2 and [PdCl2(dppm)], by using
the procedures described for 3, as orange crystals. Anal. Calcd for
C32H34N4O5P2SPd: C, 52.79; H, 4.29; N, 7.70; S, 4.40. Found: C,
52.16; H, 4.20; N, 7.58; S, 4.75.
Table 1. Crystal Data and Structure Refinement for 3 and 5
compd
[Pt2(µ-TT)2(dppm)2]‚
2DMSO
[PtPd(µ-TT)2(dppm)2]‚
7H2O
emp formula
fw
C68H68N8O6S4P4Pt2
1735.60
C64H70N8O11S2P4Pd Pt
1616.77
cryst syst
space group
unit cell dimens
a, Å
b, Å
c, Å
triclinic
P1h
orthorhombic
P212121
12.949(3)
13.009(3)
22.980(5)
96.89(3)
103.53(3)
106.43(3)
2
16.560(5)
17.063(5)
24.428(5)
90.000(5)
90.000(5)
90.000(5)
4
6903(3)
1.556
2.501
3256
R, deg
â, deg
γ, deg
Z
vol, Å3
3537.3(14)
dens (calcd), g cm-3 1.630
abs coeff, mm-1
F(000)
4.215
1720
cryst size, mm
θ range, deg
limiting indices
0.40 × 0.20 × 0.16
1.67-20.00
0 e h e +12
-12 e k e +12
-22 e l e +21
6976
6597 [R(int) ) 0.0227] 5848 [R(int) ) 0.0404]
full-matrix least-squares full-matrix least-squares
6566/418
0.25 × 0.18 × 0.15
1.67-22.50
-1 e h e +17
-1 e k e +18
-1 e l e +26
6117
reflcns collecd
independ reflecns
refinement method
data/params
5805/446
0.883
goodness-of-fit (F2) 1.038
R indices [I > 2σ(I)] R1 ) 0.0454,
R1 ) 0.0420,
Rw2 ) 0.1024
Rw2 ) 0.1071
R indices (all data)
R1 ) 0.0595,
Rw2 ) 0.1175
R1 ) 0.0531,
Rw2 ) 0.1557
largest peak and hole 1.463 and -0.826 e‚A-3 0.839 and -0.665 e‚A-3
isotropically, having one of them be a disordered sulfur atom; and (c)
for 5, the hydrogen atoms belonging to the water molecules were
omitted, while the positions of both metal ions are disordered with Pt
and Pd in ca. 50%. Crystal data and structure determination parameters
are given in Table 1. Selected atomic coordinates and equivalent
isotropic thermal parameters are listed in Table 2.
[PtPd(µ-TT)2(dppm)2]‚7H2O (5). Complex 1(0.15 g, 0.15 mmol)
and [PdCl2(dppm)] (0.08 g, 0.15 mmol) were reacted in ethanol using
the same procedure (b) as that for 3; yield, 70%. Anal. Calcd for
C64H70N8O11P4S2PdPt: C, 47.54; H, 4.36; N, 6.93; S, 3.97. Found:
C, 48.03; H, 4.18; N, 6.63; S, 3.75.
[Pt2(µ-TT)2(dppm)(bipy)] (6). To a stirred suspension of [Pt(HTT)2-
(dppm)] (0.15 g, 0.15 mmol) in 50 mL of MeOH/H2O (80% (w/w))
was added [PtCl2(bipy)] (0.06 g, 0.15 mmol). Then, NaOH (0.30 mmol)
was added and the reaction mixture heated to reflux for 15 min; the
color of the solution changed from yellow to orange. Evaporation of
the resulting solution at room temperature led to an orange powder,
which was washed with methanol and diethyl ether; yield, 60%. Anal.
Calcd for C49H42N10O4P2S2Pt2: C, 43.56; H, 3.13; N, 10.37; S, 4.75.
Found: C, 43.08; H, 2.96; N, 10.85; S, 4.27.
[PtPd(µ-TT)2(dppm)(bipy)] (7). The complexes [Pt(HTT)2(dppm)]
(0.15 g, 0.15 mmol) and [PdCl2(bipy)] (0.05 g, 0.15 mmol) were reacted,
in MeOH/H2O, by using the preceding procedure to give an orange
powder; yield, 59%. Anal. Calcd for C49H42N10O4P2S2PdPt: C, 46.62;
H, 3.35; N, 11.09; S, 5.08. Found: C, 46.43; H, 3.85; N, 10.94; S,
5.04.
X-ray Data Collections and Structure Determinations. Single
crystal data collections for 3 and 5 were performed at 293 K with a
Siemens R3m/V diffractometer using graphite monochromatized Mo
KR (λ ) 0.710 69 Å) radiation. The unit cell parameters were
calculated by least-squares refinement of 25 well centered reflections
in the range 15 < 2θ < 45° for 3 and 5. The data were collected by
the ω/2θ scan mode. Intensities of four check reflections measured
after every 120 min showed only statistical variation. The data were
corrected for Lorentz and polarization effects. Absorption corrections
were applied via an empirical Ψ scan. The structures were solved by
direct methods and subsequent Fourier syntheses with the SHELXTL/
PC V5.0 program.8 All non-hydrogen atoms were refined anisotropi-
cally, and the positions of the hydrogen atoms were calculated with
isotropic temperature factors, with the following exceptions: (a) the
phenyl rings were refined as a rigid group having a common isotropic
temperature factor; (b) for 3, the DMSO molecules were refined
Results and Discussion
The reaction of cis-[M(dppm)Cl2] (where M ) Pd(II) and
Pt(II) and dppm ) 1,2-bis(diphenylphosphino)methane) with
H2TT and NaOH in ethanol and a 1:2:2 molar ratio leads to
complexes 1 and 2, of empirical formula [M(dppm)(HTT)2].
Interestingly, the platinum(II) complex can also be obtained from
the reaction of [Pt(HTT)2][Pt(NH3)(HTT)Cl2] (prepared by
reduction of K2[PtCl6] with the ligand itself) with dppm in 1:2
molar ratio (see Scheme 1).
It should be pointed out that H2TT has two ionizable protons
in the imidazole ring (see Scheme 1). When these protons
dissociate in basic medium, the sulfur atom must be the most
probable binding site, since a soft polarizable metal, such as
Pt(II) and Pd(II), shows preference toward the softer S donor
over the less polarizable nitrogen donor atom. The second
position of coordination must be N(7) rather than N(9) because
of the steric hindrance from the N(3)-CH3 group.
Information about the structure of these mononuclear com-
plexes was derived from the IR and 31P-NMR results, which
confirm the S(8)-monodentate coordination of the HTT- anion
in 1 and 2. Thus, the IR spectra show no S-H bands, whereas
only one N-H band is observed in the 2800-3200 cm-1 region.
The 31P-NMR spectra exhibit a single chemical shift (with a
pair of 195Pt satellites for the platinum compound), consistent
with a square-planar geometry with two equivalent cis phosphine
moieties.9 Furthermore, the values of δ(2P) are similar to those
(9) 31P-NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G.,
(8) SHELXTL/PC V5.0; Siemens: Madison, WI, 1994.
Quin, L. D., Eds.; VCH Publishers: New York, 1986.

1654 Inorganic Chemistry, Vol. 36, No. 8, 1997
Colacio et al.
Table 2. Selected Atomic Coordinates (×104) and U(eq)
Scheme 1
Parameters (Å2 × 103) for 3 and 5
atom
x
y
z
U(eq)
[(dppm)Pt(µ-TT)2Pt(dppm)]‚2DMSO
Pt(1)
Pt(2)
P(2)
P(1)
P(3)
P(4)
S(8)
C(8)
N(7)
N(9)
C(4)
C(5)
C(6)
O(6)
N(3)
C(3)
C(2)
1716(1)
1566(1)
1053(3)
394(3)
4858(1)
3259(1)
3838(3)
5496(3)
1673(3)
2061(2)
4065(3)
4614(9)
4238(8)
5449(8)
5604(10)
4885(10)
4958(11)
4397(8)
5827(9)
5996(13)
6561(11)
7296(9)
6433(9)
7188(12)
4779(2)
5858(9)
5967(7)
6693(8)
6931(9)
7335(10)
8288(9)
8690(12)
8831(12)
9668(9)
8394(10)
9000(14)
7416(11)
7084(8)
4761(11)
1032(9)
3381(1)
1642(1)
4011(2)
3643(2)
1377(2)
1072(2)
3284(1)
2721(6)
2119(4)
2857(5)
2292(6)
1838(6)
1223(7)
774(4)
36(1)
35(1)
41(1)
46(1)
43(1)
39(1)
45(1)
37(3)
36(2)
41(3)
41(3)
38(3)
49(3)
68(3)
54(3)
83(5)
51(4)
86(3)
53(3)
81(5)
42(1)
38(3)
33(2)
40(2)
37(3)
46(3)
56(3)
75(5)
65(4)
103(4)
69(3)
109(6)
54(4)
76(3)
58(4)
48(3)
1892(3)
-77(2)
3108(3)
3676(10)
3187(7)
4668(7)
4748(10)
3889(10)
3746(11)
2985(8)
4630(9)
4543(14)
5516(12)
6216(9)
5589(8)
6499(12)
933(3)
2013(10)
2256(7)
2663(8)
3144(10)
3357(11)
4243(9)
4440(12)
4911(12)
5706(9)
4665(10)
5390(16)
3816(11)
3746(8)
326(12)
520(10)
1140(5)
515(7)
1593(7)
1480(5)
2179(6)
2677(7)
1728(1)
2239(6)
2861(4)
2053(5)
3077(6)
2587(7)
2649(6)
2110(7)
3229(9)
3279(6)
3711(6)
4313(8)
3684(7)
4161(5)
4263(6)
799(6)
O(2)
N(1)
C(1)
Table 3. Phosphorus-31 NMR Dataa
compound
δA
δX
1JA
1JX 2J
S(18)
C(18)
N(17)
N(19)
C(15)
C(14)
N(13)
C(13)
C(12)
O(12)
N(11)
C(11)
C(16)
O(16)
C(012)
C(034)
[Pt(HTT)2(dppm)] (1)
[Pd(HTT)2(dppm)] (2)
[Pt(µ-TT)(dppm)]2 (3)
[Pd(µ-TT)(dppm)]2 (4)
-42.7
-32.1
2683
-53.2 -46.0 2830 2430 68
-39.9 -31.5
97
[(dppm)Pt(µ-TT)2Pd(dppm)] (5) -40.3 -32.0 2839 2428 68
-53.1 -45.8 97
-52.9 -46.3 2820 2428 69
[(dppm)Pt(µ-TT)2Pt(bipy)] (6)
[(dppm)Pt(µ-TT)2Pd(bipy)] (7) -53.2 -45.9 2832 2428 69
a DMSO-d6 solutions, external reference 85% H3PO4.
found for other M(dppm)(dithiolates) (M ) Pd and Pt).10 In
view of all this, the compounds should be formulated as cis-
[M(dppm)(HTT-S(8))2].
On reacting cis-[M(dppm)Cl2] with Na2TT (prepared in situ
from the reaction of H2TT and NaOH) in ethanol and 1:1 molar
ratio, the dinuclear complexes 3 and 4, of empirical formula
[M(TT)(dppm)], are obtained. The IR spectra show neither
N-H nor S-H bands, suggesting the coordination of the anion
in bidentate fashion. Clear evidence for this mode of coordina-
tion can be derived from the 31P-NMR spectra (Table 3), since
[(dppm)Pt(µ-TT)2Pd(dppm)]‚7H2O
Pt(1)
Pd(2)
P(1)
P(2)
P(3)
P(4)
N(3)
C(2)
N(1)
C(6)
C(5)
C(4)
N(7)
C(8)
N(9)
C(3)
O(2)
6788(1)
8484(1)
6953(2)
5974(2)
8367(2)
9207(2)
7853(7)
8629(11)
9184(7)
9060(9)
8248(8)
7690(8)
7872(6)
7108(8)
6948(7)
7238(12)
8817(8)
10016(9)
9608(6)
6396(2)
8249(7)
7595(11)
6886(7)
6742(9)
7468(7)
8181(7)
7599(6)
8394(7)
8776(6)
8977(10)
7623(7)
6179(11)
6052(6)
8874(2)
6367(8)
9157(8)
-1202(1)
-2854(1)
-215(2)
-1467(2)
-4183(2)
-3300(2)
-2015(7)
-2130(10)
-2435(7)
-2618(7)
-2471(7)
-2210(8)
-2569(6)
-2326(7)
-2105(7)
-1684(14)
-1960(9)
-2542(10)
-2854(6)
-2282(2)
76(6)
425(9)
404(7)
-6(8)
-350(7)
-295(6)
-799(5)
-977(6)
-689(6)
25(10)
2928(1)
2655(1)
3535(1)
3636(1)
2638(1)
3354(1)
556(4)
29(1)
29(1)
39(1)
38(1)
37(1)
37(1)
52(3)
65(4)
51(3)
42(3)
37(3)
41(3)
33(2)
38(3)
47(3)
93(7)
90(4)
68(5)
57(3)
45(1)
45(3)
61(4)
48(3)
50(3)
36(3)
35(3)
34(2)
35(3)
40(3)
65(5)
75(3)
83(6)
64(3)
44(1)
44(3)
42(3)
2
363(6)
726(5)
they consists of AX doublets with JPP coupling that is
cis
appropriate to Pt(II) and Pd(II) complexes10 (Figure 1). In the
1276(5)
1443(5)
1096(5)
1952(3)
1869(5)
1341(4)
183(7)
case of the platinum complex (3), satellites due to 1JPtP couplings
1
with 195Pt are also apparent (Figure 1b). The two J values,
which are in the usual range for Pt(II), are quite different, with
the larger value being assigned to the phosphorous trans to
nitrogen on the basis of the Pt-P bond distances in [Pt(µ-TT)-
(dppm)]2, the shorter distance being associated with the larger
coupling constant. The S,N-coordinated TT2- ligand would act
in either chelate or bridging mode to form mononuclear or
oligomeric species, respectively. Nevertheless, because of
geometric requirements, the latter coordination mode is generally
favored over the former.4c The results of the X-ray structure
determination for [Pt(µ-TT)(dppm)]2‚2DMSO reveals the co-
ordination mode expected from the spectroscopic data. The
structure consists of dinuclear [Pt(µ-TT)(dppm)]2 molecules,
having a pseudo-2-fold axis perpendicular to that defined by
the platinum atoms (see Figure 2), and two DMSO crystal
solvent molecules. The two halves of the dinuclear units are
chemically but not crystallographically equivalent. Inside the
dinuclear molecule, the two platinum atoms are bibridged by
-107(4)
507(7)
C(1)
O(6)
S(8)
1568(4)
2394(1)
1107(4)
880(6)
1172(5)
1671(5)
1873(5)
1600(5)
2336(4)
2310(5)
1865(4)
782(6)
431(4)
942(8)
1852(4)
2812(1)
4082(5)
3159(5)
N(13)
C(12)
N(11)
C(16)
C(15)
C(14)
N(17)
C(18)
N(19)
C(13)
O(12)
C(11)
O(16)
S(18)
C(012)
C(034)
755(7)
822(11)
-60(6)
-1553(2)
-698(8)
-4334(7)
(10) (a) Bates, P. A.; Hursthouse, M. B.; Kelly, P. F.; Woolins, J. D. J.
Chem. Soc., Dalton Trans. 1986, 2367. (b) Verkade, J. G.; Fazlur-
Rahman, A. K. Inorg. Chem. 1992, 31, 5331.

Pt(II) and/or Pd(II) Complexes of H2TT
Inorganic Chemistry, Vol. 36, No. 8, 1997 1655
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 3 and 5
[(dppm)Pt(µ-TT)2Pt(dppm)]‚2DMSO [(dppm)Pt(µ-TT)2Pd(dppm)]‚7H2O
Pt(1)-N(17)
Pt(1)-P(2)
Pt(1)-P(1)
Pt(1)-S(8)
Pt(2)-N(7)
Pt(2)-P(4)
Pt(2)-P(3)
Pt(2)-S(18)
C(8)-N(7)
C(8)-N(9)
S(8)-C(8)
2.057(9)
2.235(3)
2.270(3)
2.356(3)
2.075(9)
2.236(3)
2.262(3)
2.349(3)
1.344(14)
1.366(14)
1.760(12)
1.741(12)
1.355(14)
1.370(14)
Pt(1)-N(17)a
Pt(1)-P(2)
Pt(1)-P(1)
Pt(1)-S(8)
Pd(2)-N(7)a
Pd(2)-P(4)
Pd(2)-P(3)
Pd(2)-S(18)
C(8)-N(7)
C(8)-N(9)
C(8)-S(8)
2.090(10)
2.238(3)
2.259(3)
2.349(3)
2.052(9)
2.221(3)
2.277(3)
2.343(3)
1.35(2)
1.37(2)
1.742(13)
1.761(12)
1.35(2)
S(18)-C(18)
C(18)-N(19)
C(18)-N(17)
C(18)-S(18)
C(18)-N(19)
C(18)-N(17)
1.35(2)
N(17)-Pt(1)-P(2)
N(17)-Pt(1)-P(1)
P(2)-Pt(1)-P(1)
N(17)-Pt(1)-S(8)
P(2)-Pt(1)-S(8)
P(1)-Pt(1)-S(8)
N(7)-Pt(2)-P(4)
N(7)-Pt(2)-P(3)
P(4)-Pt(2)-P(3)
N(7)-Pt(2)-S(18)
P(4)-Pt(2)-S(18)
P(3)-Pt(2)-S(18)
N(7)-C(8)-S(8)
171.8(3)
99.2(3)
73.35(12)
90.8(2)
N(17)-Pt(1)-P(2)
N(17)-Pt(1)-P(1)
P(2)-Pt(1)-P(1)
N(17)-Pt(1)-S(8)
P(2)-Pt(1)-S(8)
171.1(3)
97.5(3)
73.53(12)
92.9(3)
96.00(12)
169.15(12)
172.3(3)
100.3(3)
73.64(12)
92.8(3)
92.91(12)
165.97(12)
122.6(10)
96.37(11)
168.91(11) P(1)-Pd(1)-S(8)
172.5(3)
99.6(3)
73.35(12)
90.5(3)
96.28(11)
N(7)-Pd(2)-P(4)
N(7)-Pd(2)-P(3)
P(4)-Pd(2)-P(3)
N(7)-Pd(2)-S(18)
P(4)-Pd(2)-S(18)
168.26(11) P(3)-Pd(2)-S(18)
123.2(9) N(7)-C(8)-S(8)
N(17)-C(18)-S(18) 123.7(9)
N(17)-C(18)-S(18) 122.1(9)
P(1)-C(012)-P(2)
P(4)-C(034)-P(3)
P(1)-C(012)-P(2)
P(4)-C(034)-P(3)
94.8(6)
93.5(5)
94.3(6)
94.4(6)
a Positions of Pt(1) and Pd(2) are both occupied by Pt and Pd ions
at ca. 50%.
the mean coordination plane by 0.0807 and 0.0851 Å. The P-Pt
bond distances trans to nitrogen (2.235 and 2.236 Å) are shorter
than those trans to sulfur (2.262 and 2.270 Å), as expected.
Owing to the geometric requirements of the chelate dppm ligand
some of the coordination bond angles considerably differ from
the ideal value of 90°. The Pt‚‚‚Pt distance (4.212 Å) is much
longer than the sum of the van der Waals radii, so that the
metal-metal interaction can be discarded. As the N‚‚‚S bite
distance in the TT2- ligand is not much different from those
observed for other S,N-bridging ligands in dinuclear platinum-
(II) complexes with metal-metal interaction,11 the steric repul-
sions between the bulky dppm ligands must be the main factor
precluding metal-metal interaction in this compound. Owing
to these interligand steric repulsion within the molecules the
coordination planes splay apart by a dihedral angle of 69.2°.
Finally, bond distances and angles in the thiotheophyllinato
ligand do not significantly differ from those observed for other
complexes also containing this S,N-bridging ligand.4 The nine
atoms of the purine system are almost coplanar as expected.
It should be noted that the reaction of [M(µ-TT)(dppm)]2 with
H2TT in ethanol and a 1:1 molar ratio leads to the mononuclear
complexes [M(HTT)2(dppm)]. Noteworthy, the dinuclear com-
plexes can be re-formed by reacting the latter with cis-
[M(dppm)Cl2] and NaOH in 1:1:2 molar ratio (see Scheme 1).
This reaction may be monitored by 31P{1H}-NMR spectroscopy
in DMSO-d6. In the absence of base, the spectrum of the crude
reaction mixture, which does not change with time, indicates
an equilibrium between the reagents and the dinuclear compound
3. It is noticeable that no other compounds are present. The
equilibrium is pushed to the formation of 3 when NaOH is added
to the crude reaction mixture. On the other hand, when NaOH
is added to a solution of 1, no reaction was seen, which indicates
Figure 1. 31P-NMR spectra: (a) [Pd(µ-TT)(dppm)]2‚3H2O (4), (b) [Pt-
(µ-TT)(dppm)]2‚2DMSO (3), and (c) [(dppm)Pt(µ-TT)2Pd(dppm)]‚7H2O
(5).
Figure 2. View of the dinuclear unit of 3. Hydrogen atoms, solvent
molecules, and phenyl rings have been omitted for clarity.
two µ-TT ligands, in a head to tail arrangement, with Pt-N
bond distances of 2.057 and 2.075 Å and Pt-S bond lengths of
2.356 and 2.349 Å. It should be noted that cleavage of a Pt-
S(8) bond in the mononuclear precursor [Pt(HTT-S(8))2(dppm)]
is needed to give a head to tail arrangement of the purine ligands
in the dinuclear complex; however, this process should be very
rapid since it has not been detected by NMR spectroscopy. The
square-planar coordination of the Pt(II) atom is completed by a
chelate dppm ligand, the platinum atoms being deviated from
(11) Umakoshi, K.; Kinoshita, I.; Ichimura, A.; Ooi, S. Inorg. Chem. 1987,
26, 3351.

1656 Inorganic Chemistry, Vol. 36, No. 8, 1997
Colacio et al.
that, for the formation of 3, both 1 and [M(dppm)Cl2] are
needed. This fact prompted us to explore the reactions between
the mononuclear complexes and [M(L-L)Cl2] (M ) Pt(II) and
Pd(II), and L-L ) dppm and 2,2′-bipyridine) in order to obtain
homo- and heterodinuclear complexes. Following this proce-
dure we have succeeded in obtaining the complexes [(dppm)-
Pt(µ-TT)2M(L-L)] (5-7). The IR spectra of these complexes
are very similar to, almost identical with, those of 3 and 4, thus
suggesting the same S(8),N(7)-bridging mode in all of them.
This is supported by the crystal structure results for 5. The
structure of this compound consists of dinuclear [(dppm)Pt(µ-
TT)2Pd(dppm)] units and seven lattice crystal water molecules.
The dinuclear entities are almost superimposable to those of 3
(Table 4), by which the structure of the dinuclear unit of 5 can
be seen as that of 3 with an isomorphic substitution of one of
the Pt(II) ions by a Pd(II) ion, the metal ions being disordered
in both positions by ca. 50%. Nevertheless, some minor
differences are found for the relative positions of the purine
ligands which are attributed to the existence on an extended
hydrogen bond network involving the seven water molecules
and the heteroatoms of the purines. In this complex the Pt‚‚‚-
Pd distance of 4.034 Å is shorter by ca. 0.2 Å than that of 3 as
a consequence of a decrease in the dihedral angle between the
coordination planes (65.9°). Remaining bond distances and
angles fall well within their usual range and do not deserve
further comments. In good accord with the structure the
NMR spectrum of 5 exhibits two groups of AX doublets (Figure
1c), arising from the Pd(II) and the Pt(II) fragments of the
dinuclear molecule, respectively. The spectra of 6 and 7 are
very similar to that of 3, as expected.
31P-
In view of the ability of the H2TT ligand to form homo- and
heterodinuclear complexes, we have decided to extend our work
by using other M(II) pairs and/or less sterically hindered ligands
which might allow the metal-metal interaction. Work along
this line is in progress.
Acknowledgment. The authors gratefully acknowledge
financial aid from Junta de Andaluc´ıa.
Supporting Information Available: Full listings of crystal data
and structure refinement, fractional atomic coordinates, thermal pa-
rameters, and bond lengths and angles (23 pages). Ordering information
is given on any current masthead page.
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