Cyclometalated cluster complex with a Butterfly-Shaped Pt 2Ag2 Core

Article abstract of DOI:10.1021/ic902044g

The cyclometalated platinum complex [PtMe(bhq)(dppy)] (1), in which bhq = benzo{h}quinoline and dppy = 2-(diphenylphosphino)pyridine, was prepared by the reaction of [PtMe(SMe₂)(bhq)] with 1 equiv of dppy at room temperature. Complex 1 contains

Full text of DOI:10.1021/ic902044g

Inorg. Chem. 2010, 49, 2721–2726 2721
DOI: 10.1021/ic902044g
Cyclometalated Cluster Complex with a Butterfly-Shaped Pt2Ag2 Core
,†
†
‡
‡
,‡
ꢀ §
Sirous Jamali,* Zahra Mazloomi, S. Masoud Nabavizadeh, Dalibor Milic, Reza Kia, and Mehdi Rashidi*
†Department of Chemistry, Persian Gulf University, Bushehr 75169, Iran, ‡Department of Chemistry, College of
Sciences, Shiraz University, Shiraz 71454, Iran, and §Laboratory of General and Inorganic Chemistry,
Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia
Received October 15, 2009
The cyclometalated platinum complex [PtMe(bhq)(dppy)] (1), in which bhq = benzo{h}quinoline and dppy =
2-(diphenylphosphino)pyridine, was prepared by the reaction of [PtMe(SMe2)(bhq)] with 1 equiv of dppy at room
temperature. Complex 1 contains one free pyridyl unit and was readily characterized by multinuclear NMR
spectroscopy and elemental microanalysis. The reaction of complex 1 with 1 equiv of [Ag(CH3CN)4]BF4 gave the
cyclometalated cluster complex [Pt2Me2(bhq)2(μ-dppy)2Ag2(μ-acetone)](BF4)2 (2) in 70% yield. The crystal
structure of complex 2 was determined by X-ray crystallography, indicating a rare example of a butterfly cluster
with a Pt2Ag2 core in which the Ag atoms occupy the edge-sharing bond. In solution, the bridging acetone dissociates
from the cluster complex 2, but as shown by NMR spectroscopy, the Pt2Ag2 core is retained in solution and a dynamic
equilibrium is suggested to be established between the planar and butterfly skeletal geometries.
Introduction
of anionic (perhalophenyl)platinum(II) complexes in the
synthesis of cluster complexes containing Pt-Ag dative
bonds have been reported in the literature.5 Very recently, a
self-assembled luminescent octanuclear stellate platinacycle
has been constructed via Pt-Ag dative bonds.6 The electron-
donor ability of a PtII center containing a cyclometalating
ligand, e.g., 2-phenylpyridine (ppy) or benzo{h}quinoline
(bhq), is significantly enhanced, and this would assist in its
ability to form Pt-M dative bonds.7 In this area, a number of
cyclometalated platinum(II) complexes have been synthe-
sized in order to study the influence of the Pt-Ag dative
bonds on the their physical properties,7a,b and helical metal-
metal-bonded chains have recently been prepared from the
Metal clusters occupy a prominent position in chemistry.
In addition to the interest arising from the potential utility of
metal clusters in catalysis1 and the preparation of new
materials,2 there has also been significant interest in exploit-
ing the remarkable structural and bonding properties of these
compounds.3 Metal-metal dative bonds play an important
role in the synthesis of metal clusters,4 and electron-rich
platinum(II) complexes can expand opportunities for the
formation of metal-metal dative bonds. Examples of the use
*To whom correspondence should be addressed. E-mail: sirjamali@
pgu.ac.ir (S.J.), rashidi@chem.susc.ac.ir (M.R.).
(1) (a) Adams, R. D.; Cotton, F. A. Catalysis by Di- and Polynuclear
Metal Cluster Complexes; Wiley-VCH: New York, 1998. (b) Shimizu, K.-I.;
Sato, R.; Satsuma, A. Angew. Chem., Int. Ed. 2009, 48, 3982–3986. (c)
Bar-Nahum, I.; Gupta, A. K.; Huber, S. M.; Ertem, M. Z.; Cramer, C. J.; Tolman,
W. B. J. Am. Chem. Soc. 2009, 131, 2812–2814. (d) Adams, R. D.; Captain, B.
Angew. Chem., Int. Ed. 2008, 47, 252–257. (e) Kawashima, T.; Takao, T.;
Suzuki, H. J. Am. Chem. Soc. 2007, 129, 11006–11007. (f) Roesky, P. W.;
Melchor, G. C.; Zulys, A. Chem. Commun. 2004, 738–739.
(2) (a) Braunstein, P.; Oro, L. A.; Raithby, P. R. Metal Clusters in
Chemistry; Wiley-VCH: New York, 1999; p 1271. (b) Long, D.-L.; Burkholder,
E.; Cronin, L. Chem. Soc. Rev. 2007, 105–121. (c) Wang, J.; Loh, K. P.; Wang, Z.;
Yan, Y.; Zhong, Y.; Xu, Q.-H.; Ho, P. C. Angew. Chem., Int. Ed. 2009, 48, 6282–
6285. (d) Watzky, M. A.; Finney, E. E.; Finke, R. G. J. Am. Chem. Soc. 2008,
130, 11959–11969. (e) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke,
T. M.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319–330.
(3) (a) Adams, R. D.; Captain, B. Acc. Chem. Res. 2009, 42, 409–418. (b)
Safa, M. S.; Jennings, M. C.; Puddephatt, R. J. Chem. Commun. 2009, 1487–
1489. (c) Adams, R. D.; Captain, B.; Hall, M. B.; Trufan, E.; Yang, X. J. Am.
Chem. Soc. 2007, 129, 12328–12340. (d) Sun, Q.-F.; Lee, T. K.-M.; Li, P.-Z.;
Yao, L.-Y.; Huang, J.-J.; Huang, J.; Yu, S.-Y.; Li, Y.-Z.; Cheng, E. C.-C.; Yam,
V. W.-W. Chem. Commun. 2008, 5514–5516. (e) Lee, K.; Song, H.; Park, J. T.
Acc. Chem. Res. 2003, 36, 78–86. (f) Schuh, W.; Braunstein, P.; Benard, M.;
Rohmer, M.-M.; Welter, R. Angew. Chem., Int. Ed. 2003, 42, 2161–2164.
(4) (a) Shriver, D. F. Acc. Chem. Res. 1970, 3, 231–238. (b) Werner, H.
Angew. Chem., Int. Ed. 1983, 22, 927–929. (c) Tsutsumi, H.; Sunada, Y.; Shiota,
Y.; Yoshizawa, K.; Nagashima, H. Organometallics 2009, 28, 1988–1991. (d)
Hossain, M. M.; Lin, H.-M.; Shyu, S. G. Organometallics 2007, 26, 685–691. (e)
Adams, R. D.; Captain, B.; Fu, W.; Smith, M. D. J. Am. Chem. Soc. 2002, 124,
5628–5629. (f) Song, H.-B.; Zhang, Z.-Z.; Mak, T. C. W. Inorg. Chem. 2001, 40,
5928–5933. (g) Mashima, K.; Fukumoto, A.; Nakano, H.; Kaneda, Y.; Tani, K.;
Nakamura, A. J. Am. Chem. Soc. 1998, 120, 12151–12152. (h) Calderazzo, F.;
Poli, R.; Zanazzi, P. F. Inorg. Chem. 1991, 30, 3942–3947. (i) Einstein, F. W. B.;
Martin, L. R.; Pomeroy, R.; Rushman, P. J. Chem. Soc., Chem. Commun. 1985,
345–346.
(5) Fornies, J.; Martin, A. In Metal Clusters in Chemistry; Braunstein, P.,
Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: New York, 1999; p 417.
(6) Falvello, L. R.; Fornies, J.; Lalinde, E.; Menjon, B.; Angeles, M.;
Monforte, G.; Moreno, M. T.; Tomas, M. Chem. Commun. 2007, 3838–
3840.
(7) (a) Janzen, D. E.; Mehne, L. F.; Van Derveer, D. G.; Grant, G. J.
Inorg. Chem. 2005, 44, 8182–8184. (b) Fornies, J.; Ibanez, S.; Martín, A.; Sanz,
M. J.; Berenguer, R.; Lalinde, E.; Torroba, J. Organometallics 2006, 25, 4331–
4340. (c) Yamaguchi, T.; Yamazaki, F.; Ito, T. J. Am. Chem. Soc. 1999, 121,
7405–7406.
r
2010 American Chemical Society
Published on Web 02/09/2010
pubs.acs.org/IC

2722 Inorganic Chemistry, Vol. 49, No. 6, 2010
Jamali et al.
Scheme 1
reaction of cyclometalated platinum complexes [Pt(ppy)2]
and [Pt(thpy)2] with AgClO4.8
with AgPF6.12 These findings as well as our interest in
synthesizing binuclear cyclometalated complexes13 led us to
incorporate appropriate bridging and cyclomtalating ligands
into one PtII center and use them as precursors in the
synthesis of new bi- and multiheteronuclear complexes. We
report herein the synthesis and crystal structural analysis of
the cluster complex [Pt2Me2(bhq)2(μ-dppy)2Ag2(μ-acetone)]-
[BF4]2 (2) containing a Pt2Ag2 core with an unprecedented
butterfly skeletal geometry in which the Ag atoms occupy the
edge-sharing bond; note that two clusters with planar Pt2Ag2
cores have already been reported.14
It has been demonstrated that metal-metal-bonding inter-
actions in cooperation with bridging ligands, such as bis-
(phosphines),9 alkynyls,10 and dithiolates,11 usually favor the
formation of bi- and multinuclear complexes. In this regard,
the bridging ligands are usually designed to have a small bite
angle, e.g., 2-(diphenylphosphino)pyridine (dppy), in order
to bring the metal centers into close proximity and lock them
together, thus favoring the formation of metal-metal bonds.
For example, cluster complexes [Au3(μ3-E)Ag(dppy)3](BF4)2
(E=O, S, Se) have been prepared by the reaction of AuCl-
(dppy) with excess Ag2O and NaBF4, and cluster complex
[Pt2(dppy)4(μ3-S2)Ag3(μ3-S2)Pt2(dppy)4]PF6 has been pre-
pared by the reaction of dimeric complex [Pt2(μ-S)2(dppy)4]
Result and Discussion
As summarized in Scheme 1, the reaction of complex
[PtMe(bhq)(SMe2)], in which bhq=benzo{h}quinoline, with
1 equiv of dppy at room temperature in acetone gave the
complex [PtMe(bhq)(dppy)] (1) in good yield by replacement
of the SMe2 ligand with the P ligating atom of dppy. Complex
1 is a yellow solid that is stable in acetone or chloroform
solutions for several hours and fully characterized by multi-
nuclear NMR spectroscopy and elemental microanalysis,
and the details are described in the Experimental Section.
In the 31P NMR spectrum of complex 1, the observation of
a singlet resonance at δ 33.3 ppm, with satellites due to
coupling to the Pt atom (1JPtP=2096 Hz), was assigned to the
P atom of the dppy ligand connected to the Pt center.
Consistently, the 195Pt NMR spectrum of complex 1 showed
a doublet signal at δ 585 ppm with 1JPtP=2095 Hz. In the 1H
NMR spectrum of complex 1, the Me ligand protons
appeared at δ 0.96 ppm as a doublet due to coupling with
the P atom with 3JPH=7.8 Hz, which is further coupled to the
(8) Yamaguchi, T.; Yamazaki, F.; Ito, T. J. Am. Chem. Soc. 2001, 123,
743–744.
(9) (a) Xu, C.; Anderson, G. K.; Brammer, L.; Braddock-Wilking, J.;
Rath, N. P. Organometallics 1996, 15, 3972–3979. (b) Xia, B.-H.; Zhang,
H.-X.; Che, C.-M.; Leung, K.-H.; Phillips, D. L.; Zhu, N.; Zhou, Z.-Y. J. Am.
Chem. Soc. 2003, 125, 10362–10374. (c) Uson, R.; Uson, M. A.; Herrero, S.
Inorg. Chem. 1997, 36, 5959–5961.
(10) (a) Yin, G.-Q.; Wei, Q.-H.; Zhang, L.-Y.; Chen, Z.-N. Organo-
metallics 2006, 25, 580–587. (b) Yamazaki, S.; Deeming, A. J.; Speel, D. M.;
Hibbs, D. E.; Hursthousec, M. B.; Abdul Malikc, K. M. Chem. Commun. 1997,
177–178.
(11) (a) Chen, Y.-D.; Zhang, L.-Y.; Shi, L.-X.; Chen, Z.-N. Inorg. Chem.
2004, 43, 7493–7501. (b) Vicente, J.; Chicote, M. T.; Huertas, S. Inorg. Chem.
2003, 42, 4268–4274. (c) Vicente, J.; Chicote, M. T.; Huertas, S.; Bautista, D.;
Jones, P. G.; Fischer, A. K. Inorg. Chem. 2001, 40, 2051–2057. (d) Vicente, J.;
Chicote, M. T.; Huertas, S.; Bautista, D.; Jones, P. G.; Fischer, A. K. Inorg. Chem.
2001, 40, 6193–6200.
(12) (a) Wang, Q.-M.; Lee, Y.-A.; Crespo, O.; Deaton, J.; Tang, C.;
Gysling, H. J.; Gimeno, M. C.; Larraz, C.; Villacampa, M. D.; Laguna, A.;
Eisenberg, R. J. Am. Chem. Soc. 2004, 126, 9488–9489. (b) Yam, V. W.-W.;
Yeung, P. K.-Y.; Cheung, K.-K. Angew. Chem., Int. Ed. 1996, 35, 739–740.
(13) (a) Jamali, S.; Nabavizadeh, S. M.; Rashidi, M. Inorg. Chem. 2008,
47, 5441–5452. (b) Jamali, S.; Nabavizadeh, S. M.; Rashidi, M. Inorg. Chem.
2005, 44, 8594–8601. (c) Hoseini, S. J.; Nabavizadeh, S. M.; Jamali, S.; Rashidi,
M. J. Organomet. Chem. 2007, 692, 1990–1996. (d) Shafaatian, B.; Akbari, A.;
Nabavizadeh, S. M.; Heinemann, F. W.; Rashidi, M. Dalton Trans. 2007, 4715–
4725.
2
Pt atom with JPtH = 83.5 Hz. The proton of the CH
group adjacent to the N atom of the dppy ligand appeared
(14) (a) Moret, M.-E.; Chen, P. J. Am. Chem. Soc. 2009, 131, 5675–5690.
(b) Uson, R.; Fornies, J.; Tomas, M.; Cotton, F. A.; Falvello, L. R. J. Am. Chem.
Soc. 1984, 106, 2482–2483. (c) Uson, R.; Fornies, J.; Menjon, B.; Cotton, F. A.;
Falvello, L. R.; Tomas, M. Inorg. Chem. 1985, 24, 4651–4656.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2723
Figure 1. Molecular structure of complex 2, showing 30% probability displacement ellipsoids with selected atom numbering. The anion (BF4-), acetone
solvents of crystallization, and H atoms were omitted for clarity.
Table 1. Selected Bond Lengths (A) and Angles (deg) for Complex 2a
every Pt unit is coordinated to the Ag atoms on opposite
sides,8 the Pt-Ag dative bonds in 2 are located on the same
side of the coordination plane. Each of the [PtMe(bhq)-
(μ-dppy)] units, displaying a slightly distorted square-planar
geometry [the Pt atom displaced -0.089(1) A from the
coordination plane], is composed of C2NP donors with bond
lengths of Pt-C(bhq)=2.055(3) A, Pt-C(Me)=2.055(3) A,
Pt-P=2.3114(7) A, and Pt-N=2.158(2) A. The complex
contains two different types of Pt-Ag bonds, short and long.
Each of the short bonds, either Pt1-Ag1 or Pt1A-Ag1A, is
supported by a bridging dppy ligand [with the Ag-N bond
distance being 2.315(3) A], with both bond lengths being
2.7749(3) A; the bond length is shorter than the sum of the
metallic radii of Pt and Ag (2.83 A), indicating the formation
of a strong Pt-Ag dative bond. The bond distance for either
of the long bonds, Pt1-Ag1A or Pt1A-Ag1, amounts to
3.0311(3) A, which is shorter than the sum of the van der
Waals radii of Pt and Ag (3.45 A), demonstrating the
presence of a Pt-Ag bonding interaction; note that each
bond is also supported by a secondary weak interaction of the
Ag atom with the C atom of the bhq ligand that is coordi-
nated to the Pt atom (dashed bonds in Figure 1) with a Ag-C
distance of 2.3473(3) A. The best description for the long
bonds will probably be similar to a donor-acceptor (π
system-metal) interaction as reported previously.8,16 The
Pt-Ag vectors are tilted by 13.02(6)° and 55.15(6)° with
respect to the normal line of the platinum coordination plane.
The dihedral (“butterfly”) angle between the planes
Pt1-Ag1-Ag1A and Pt1A-Ag1-Ag1A is 148.55(1)°. The
distance between the two Ag atoms in 2 is 2.8265(5) A, which
is significantly shorter than the accepted maximum distance
for an argentophilic interaction (3.44 A, the sum of the van
Pt1-Ag1
Pt1-Ag1A
Ag1-Ag1A
Pt1-P1
2.7749(3)
3.0311(3)
2.8265(5)
2.3114(7)
2.158(2)
2.055(3)
2.055(3)
2.315(3)
2.683(3)
2.347(3)
Ag1-Pt1-Ag1A
Pt1-Ag1-Pt1A
N1-Pt1-C1
P1-Pt1-C10
N1-Pt1-C10
Ag1-Pt1-C10
58.06(1)
114.68(1)
171.81(11)
169.90(8)
80.41(10)
108.65(7)
Pt1-N1
Pt1-C10
Pt1-C1
Ag1-N2
Ag1-O1
Ag1-C10A
3
a The suffix A is for the symmetry code: -x þ 1, y, -z þ /2.
3
at δ 8.70 ppm as a doublet with JHH = 4.5 Hz with no
coupling to the Pt center, confirming that the N atom of the
pyridyl group is uncoordinated.15
As described in Scheme 1, treatment of complex 1 with a
stoichiometric amount of [Ag(CH3CN)4]BF4 in acetone at
room temperature afforded cluster complex 2 in 70% yield.
Red crystals of the complex 2 were obtained by the slow
diffusion of ether into an acetone solution of 2 in a refrige-
rator for 1 week. Cluster complex 2 crystallizes in the
monoclinic system, in the space group C2/c. The asymmetric
unit of complex 2 comprises half of the cluster cation complex
containing a Pt-Ag dative bond, a tetrafluoroborate coun-
terion, and two acetone molecules as the solvent of crystal-
lization. Each pair of these units is linked together by two
Pt-Ag bonds and one Ag-Ag bond to form a tetranuclear
cluster with a butterfly Pt2Ag2 core of alternating Pt and Ag
atoms; also, an acetone molecule bridges the two Ag atoms.
A view of the molecular structure of 2 is depicted in Figure 1,
and the selected bond lengths and angles are listed in Table 1.
In comparison with the previously reported cyclometa-
lated helical chain containing Pt-Ag dative bonds in which
(16) (a) Smith, H. G.; Rundle, R. E. J. Am. Chem. Soc. 1958, 80, 5075–
5078. (b) McMullan, R. K.; Koetzle, T. F.; Fritchie, C. J., Jr. Acta Crystallogr.,
Sect. B 1997, B53, 645–653. (c) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T.;
Maekawa, M.; Suenaga, Y.; Ning, G. L.; Kojima, T. J. Am. Chem. Soc. 1998,
120, 8610–8618. (d) Munakata, M.; Wu, L. P.; Ning, G. L.; Kuroda-Sowa, T.;
Maekawa, M.; Suenaga, Y.; Maeno, N. J. Am. Chem. Soc. 1999, 121,
4968-4976 and references cited therein.
(15) (a) Baar, C. R.; Carbray, L. P.; Jennings, M. C.; Puddephatt, R. J.
J. Am. Chem. Soc. 2000, 122, 176–177. (b) Jenkins, H. A.; Yap, G. P. A.;
Puddephatt, R. J. Organometallics 1997, 16, 1946–1955. (c) Scott, J. D.;
Puddephatt, R. J. Organometallics 1986, 5, 2522–2529. (d) Baar, C. R.; Carbray,
L. P.; Jennings, M. C.; Vittal, J. J.; Puddephatt, R. J. Organometallics 2000, 19,
4150–4158.

2724 Inorganic Chemistry, Vol. 49, No. 6, 2010
Jamali et al.
Scheme 2
sharp singlet signal (with relative intensity approximately
equal to the sum of the methyl intensities, i.e., 1 þ 1.6=2.6) at
δ 2.17 ppm was assigned to the free acetone molecule in
2
CDCl3.19 Reduction of the coupling constant JPtH of the
1
methyl ligands from the value of 83.5 Hz in the H NMR
spectrum of complex 1 to the values of 67.0 and 73.0 Hz in the
1H NMR spectrum of complex 2 confirms the persistence of
the Pt-Ag bonds in solution.20,14a
Figure 2. 195Pt NMR spectrum of complex 2 in CD2Cl2 at room
temperature.
The 1H NMR spectrum of complex 2 was monitored as a
function of the temperature in the CDCl3 solution (see the
high-field region spectra, shown in Figure 3). A change in the
relative intensities was observed upon cooling from room
temperature to -50 °C. As the temperature is lowered, the
methyl resonance at δ 0.30 ppm becomes more broadened
and its intensity decreases, while the intensity of the methyl
resonance at δ 1.26 ppm increases. We therefore suggest that
the two skeletal isomers in solution are in dynamic equilib-
rium. Considering the butterfly structure of2 inthesolid state
and previous planar structures reported for Pt2Ag2 clusters,
we propose that the equilibration involves conversion
between planar and butterfly arrangements of the metal
atoms (see Scheme 2).
It is possible that the crystal packing in conjunction with
the acetone molecule being coordinated to Ag atoms in the
solid state has strongly encouraged the butterfly arrange-
ments. Note that it has been described that for the tetra-
nuclear cluster complexes there are six possible skeletal
isomers; the butterfly geometry is the most frequently
reported metal core geometry.21 Among these six possibili-
ties, there are only four (as demonstrated in Scheme 3) in
which the metal core has a “closed” arrangement. As
mentioned before, the 195Pt NMR spectrum of complex 2
represents that each Pt atom bonds to two Ag atoms. As
such, only the four geometries described in Scheme 3, i.e.,
tetrahedral (a), butterfly (b), or planar (c or d), are possible
for complex 2 in solution. If the complex adapts a tetrahedral
geometry (a), then a Pt-Pt edge and so a P-Pt-Pt-P
arrangement, which can be characterized by the superimpo-
sition of the spectra of the three isotopomers P-Pt-Pt-P,
P-195Pt-Pt-P, and P-195Pt-I95Pt-P, are required to be
present. Analyses of these spin systems for tetrahedral and
other core geometries have been carried out previously,22 and
they are clearly not consistent with the 31P and 195Pt NMR
patterns discussed above for complex 2. Besides, it is very
unlikely that the strong argentophilic interaction between the
der Waals radii of Ag atoms).17 The Ag-Ag distance in 2 is
shorter than that observed in (NBu4)2[Pt2Ag2C14(C6F5)4]
(2.9946 A),14b,c but it is slightly longer than that found in
[(NN)PtMe2]2Ag2(OTf)2 [2.6972(2) A],14a in each of which
the Pt2Ag2 core is planar. Finally, the Ag atoms carry a
bridging acetone molecule by interacting through the O
atom, displaying Ag-O distances of 2.683(3) A, which is
longer than those found in the terminal coordination mode of
acetone molecules of [{Pt(phpy)2}2{Ag(acetone)}2]n(ClO4)2n
[2.419(9) and 2.373(9) A] and [{Pt-(thpy)2}3{Ag(acetone)}2]-
(ClO4)2 [2.532(8) and 2.471(7) A].8
In the 31P NMR spectrum of complex 2 in the CDCl3
solvent, although on the basis of its crystal structure (vide
supra) the two P atoms are equivalent, two unequal intensity
singlet signals at δ 35.9 ppm (with 1JPtP=2206 Hz) and δ 35.6
1
ppm (with JPtP = 2214 Hz) were observed. It is therefore
probable that in solution complex 2 is present as a mixture of
two skeletal isomers. The 195Pt NMR spectrum of complex 2
is particularly informative and proves that the Pt2Ag2 core,
observed in the solid state, is retained in solution. Thus, the
195Pt NMR spectrum of a CD2Cl2 solution of complex 2
(Figure 2) showed a doublet of triplets at δ -2072 ppm due to
1
coupling with the P atom with JPtP = 2203 Hz, which is
further coupled to two spin-active 107,109Ag atoms with
1J
= 580 Hz. The strength of the spin-spin
195Pt-107,109Ag
coupling depends on the magnetogyric ratios of the nuclei,
and because the difference in the magnetogyric ratios of the
silver isotopes is small [γ(107Ag)/γ(109Ag) = 1.15], it is
assumed that there is a small difference in the coupling
1
1
constants of J(Pt-107Ag) and J(Pt-109Ag). Similar cou-
pling constants of isotopes 107Ag and 109Ag have been
reported previously.18 The peaks due to the two skeletal
isomers, suggested above on the basis of the 31P NMR
spectrum, seem to have overlapped considering that the
observed signal is significantly broadened.
In the 1H NMR spectrum of a CDCl3 solution of complex
2 at 295 K (see Figure 3, spectrum on the bottom), the two
2
unequal intensity resonances at δ 0.30 ppm (with JPtH
=
(19) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62,
7512–7515.
(20) Arsenault, G. J.; Anderson, C. M.; Puddephatt, R. J. Organometal-
lics 1988, 7, 2094–2097.
67.0 Hz and 3JPH=9.4 Hz) and 1.26 ppm (with 2JPtH=73.0 Hz
and 3JPH=7.6 Hz) in a 1:1.6 ratio, respectively, were assigned
to the protons of the methyl ligands of the two isomers and a
(21) Rossell, O.; Seco, M.; Seyulis, G. In Metal Clusters in Chemistry;
Braunstein, P.; Oro, L. A.; Raithby, P. R., Eds.; Wiley-VCH: New York, 1999; p
1053.
(22) (a) Brown, C.; Heaton, B. T.; Towl, A. D. C.; Chini, P. J. Organomet.
Chem. 1979, 181, 233–254. (b) Braunstein, P.; De Meric de Bellefon, C.;
Bouaoud, S. E.; Grandjean, D.; Halet, J. F.; Saillard, J. Y. J. Am. Chem. Soc.
1991, 113, 5282–5292. (c) Moor, A.; Pregosin, P. S.; Venanzi, L. M. Inorg. Chim.
Acta 1981, 48, 153–157. (d) Farrugia, L. J.; Howard, J. A. K.; Mitroprachachon,
P.; Stone, G. A.; Woodward, P. J. Chem. Soc., Dalton Trans. 1981, 1274–1277.
(e) Pregosin, P. S. Coord. Chem. Rev. 1982, 44, 247–291.
(17) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
(18) (a) Gil, B.; Fornies, J.; Gomez, J.; Lalinde, E.; Martı
´
n, A.; Moreno,
M. T. Inorg. Chem. 2006, 45, 7788–7798. (b) Alonso, E.; Fornies, J.; Fortuno,
C.; Martín, A.; Orpen, A. G. Organometallics 2003, 22, 5011–5019. (c) Garcia,
M. P.; M. JimCnez, V.; Lahoz, F. J.; Oro, L. A. Inorg. Chem. 1995, 34, 2153–
2159. (d) Comstock, M. C.; Prussak-Wieckowska, T.; Wilson, S. R.; Shapley, J. R.
Organometallics 1997, 16, 4033–4040. (e) Wang, S.; Fackler, J. P. J.; Carlson,
T. F. Organometallics 1990, 9, 1973–1975.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2725
Figure 3. 1H NMR spectra (methyl region) of complex 2 at different temperatures.
Scheme 3
two Ag atoms of the Pt2Ag2 core in the solid state of 2 would
break up in solution, and this most probably eliminates the
possibility of an alternative geometry (d). Therefore, the
above assumption that the metal core of 2 is retained in
solution as an equilibrium mixture of the butterfly (b) and
planar(c) geometries seems to be reasonable, although there
may be alternative mechanisms that are also consistent with
the observed NMR data.
previously.13a,23 Crystal data and refinement parameters for
2 are given in Table 2.
[PtMe(bhq)(dppy)] (1). To a solution of the complex
[PtMe(bhq)(SMe2)] (100 mg, 0.22 mmol) in acetone (15 mL)
was added 1 equiv of dppy (59 mg, 0.22 mmol) at room
temperature. The mixture was stirred at this condition for 1 h,
then the solvent was removed under reduced pressure, the
residue was triturated with ether (2 ꢀ 3 mL), and the product
as a yellow solid was dried under vacuum. Yield: 65%. NMR
data in CDCl3: δ(1H) 0.96 (3H, d, 2JPtH=83.5 Hz, 3JPH=7.8 Hz,
PtMe), 6.00 (m, 1H, H atom adjacent to the coordinated C atom
of the bhq ligand), 7.0-8.0 (m, 19 H, aryl protons), 8.4 (m, 1H,
H atom adjacent to the coordinated N atom of the bhq ligand),
8.7 (d, 1H, 3JHH=4.5 Hz, H atom adjacent to the N atom of the
free pyridine ring); δ(31P) 33.3 (s, 1JPtP=2096 Hz); δ(195Pt) 585
(d, 1JPtP=2095 Hz). Anal. Calcd for C31H25N2PPt: C, 57.1; H,
3.8; N, 4.3. Found: C, 57.4; H, 3.9; N, 4.1.
Experimental Section
The 1H and 31P NMR spectra were recorded on a Bruker
Avance DRX 500-MHz spectrometer. The operating fre-
quencies and references, respectively, are shown in parenth-
eses as follows: 1H (500 MHz, tetramethylsilane, SiMe4), 31
P
(202 MHz, 85% H3PO4), and 195Pt (107 MHz, aqueous
Na2PtCl4). The chemical shifts and coupling constants are
in parts per million and hertz, respectively. Benzo-
{h}quinoline and [Ag(CH3CN)4]BF4 were purchased from
commercial sources, and a yellow solution of [PtMe(bhq)-
(SMe2)] in acetone was prepared in situ as described
[Pt2Me2(bhq)2(μ-dppy)2Ag2(μ-acetone)](BF4)2 (2). To a solu-
tion of complex 1 (200 mg, 0.31 mmol) in acetone (20 mL)
at room temperature under an argon atmosphere was added
1 equiv of [Ag(CH3CN)4]BF4 (111 mg, 0.31 mmol). The mixture
was stirred at this condition for 1.5 h in the dark, and then the
solvent was removed under reduced pressure. The residue was
washed with ether (2 ꢀ 3 mL), and the product was dried under
vacuum. Yield: 70%. NMR data in CDCl3: for the first isomer,
(23) Owen, J. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2004,
126, 8247–8255.

2726 Inorganic Chemistry, Vol. 49, No. 6, 2010
Jamali et al.
Table 2. Crystal Data and Structure Refinement Parameters of Complex 2
approximation, with Uiso(H)=1.2 or 1.5Ueq(C). All calculations
were carried out using PLATON.26 For molecular graphics, the
program SHELXTL was used.25
empirical formula
fw
[C65H56Ag2N4OP2Pt2](BF4)2 4C3H6O
3
1982.91
cryst size (mm)
cryst syst
space group
θmax (deg)
a (A)
0.25 ꢀ 0.30 ꢀ 0.60
monoclinic
C2/c
Conclusion
The complex [PtMe(bhq)(dppy)] (1), in which bhq=benzo-
{h}quinoline and dppy=2-(diphenylphosphino)pyridine, has
an electron-rich Pt center and an uncoordinated pyridyl
group, and this creates the possibility of synthesizing new
bi- and multinuclear complexes containing cyclometalated
platinum units. In the present work, complex 1 has been
coupled with 1 equiv of [Ag(CH3CN)4]BF4 to form a
Pt-Ag dative bond, which is accompanied by a bridging
dppy ligand, and the cyclometalated cluster complex
[Pt2Me2(bhq)2(μ-dppy)2Ag2(μ-acetone)](BF4)2 (2) is, in
fact, an association formed by rather strong intermolecu-
lar interactions between Pt and Ag atoms of two of the
coupled species, each supported by a secondary weak
interaction of the Ag atom with the C atom of the bhq
ligand, followed by the formation of a strong Ag-Ag
bond. Complex 2 is a tetranuclear cluster with a butterfly
Pt2Ag2 core of alternating Pt and Ag atoms [the angle
between the wings of the butterfly core is 148.55(1)°], in
which an acetone molecule has also bridged between the
two Ag atoms. Dissociation of the bridging acetone mole-
cule has probably been responsible for the establishment of
a dynamic equilibrium in solution between two possible
skeletal isomers of complex 2, shown by NMR experiments
to be planar (c) and butterfly (b), as described in Schemes 2
and 3.
32.2
23.2342(13)
18.1759(12)
17.5809(12)
96.314(10)
7379.4(8)
4
1.785
4.420
3888
-34 e h e33
-26 e k e26
-26 e l e25
44 537
b (A)
c (A)
β (deg)
V (A3)
Z
Dcalcd (Mg/m3)
M (mm-1
F(000)
index ranges
)
no. of mead reflns
no. of indep reflns/Rint
no. of obsd reflns [I > 2σ(I)] 8982
no. of param/restraints
GOF
R1 (obsd data)
wR2 (all data)a
12 091/0.027
467/52
0.95
0.0288
0.0676
a w = 1/[σ2(Fo2) þ (0.0371P)2], where P = (Fo þ 2Fc2)/3.
2
δ(1H) 0.30 (3H, d, 2JPtH=67.0 Hz and 3JPH=9.4 Hz, PtMe); for
the other isomer δ(1H) 1.26 (3H, d, 2JPtH=73.0 Hz, 3JPH=7.6
Hz, PtMe), 2.17 (s, Me groups of dissociated acetone); for one
isomer, δ(31P) 35.9 (s, JPtP =2206 Hz); for the other isomer,
1
δ(31P) 35.6 (1JPtP=2214 Hz); both isomers in CD2Cl2, δ(195Pt)
1
1
-2072 (d of t, JPtP=2203 Hz, J
Calcd for C65H56N4P2Pt2Ag2O: C, 44.5; H, 3.2; N, 3.2. Found:
C, 44.7; H, 3.1; N, 3.4.
107,109Ag=580 Hz). Anal.
195Pt-
Crystal Structure Determinations. X-ray intensity data were
collected on the Oxford Diffraction Xcalibur CCD diffract-
ometer with graphite-monochromated Mo KR radiation (λ =
0.710 73 A) at a temperature of 295(2) K. The data reduction,
including the analytical numerical absorption correction,24a was
performed using the CrysAlis software package.24b The struc-
tures were solved by direct methods (SHELXS97) and refined
by full-matrix least squares (SHELXL-97) on F2.25 The non-H
atoms were refined anisotropically. All of the H atoms were
positioned geometrically and refined with the riding model
Acknowledgment. We thank the Iran National
Science Foundation (Grant No. 8704127), Persian Gulf
University Research Council, and Shiraz University
Research Council for financial support. We thank the
Ministry of Science, Education and Sports of the Re-
ˇ
ꢀ
public of Croatia and Prof. D. Matkovic-Calogovic for
ꢀ
the X-ray diffraction facility.
Supporting Information Available: X-ray crystallographic
files in CIF format for complex 2. This material is available free
of charge via the Internet at http://pubs.acs.org.
(24) (a) Xcalibur CCD System: Emperical absorption correction; Oxford
Diffraction Ltd.: Oxfordshire, U.K., 2008. (b) CrysAlis software package, Oxford
Diffraction Ltd.: Clark, R. C.; Reid, J. S. Acta Crystallogr. 1995, A51, 887.
(25) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(26) Spek, A. L. Acta Crystallogr. 1990, A46, C34.