Antimony-Carbon bond activation in a Pt(II) complex: The crystal structure of [Pt(9S3)(SbPh3)(Ph)](PF6)·CH3NO2

Article abstract of DOI:10.1016/j.jorganchem.2009.11.010

The complex [Pt(9S3)(SbPh₃)(Ph)](PF₆) forms directly from [Pt(9S3)(SbPh₃)₂](PF₆)₂ during the room temperature crystallization of the latter in nitromethane. The crystal structure shows a five-coordinate Pt(II) center containing the tridentate thiacrown ligand, a Sb donor from the triphenylstibine ligand, and a σ-coordinating phenyl group. The phenyl group forms via Sb-C bond cleavage from one of the SbPh₃ ligands in the bis complex.

Full text of DOI:10.1016/j.jorganchem.2009.11.010

Journal of Organometallic Chemistry 695 (2010) 634–636
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Journal of Organometallic Chemistry
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Note
Antimony–Carbon bond activation in a Pt(II) complex: The crystal structure
of [Pt(9S3)(SbPh3)(Ph)](PF6)ÁCH3NO2
a
b
Gregory J. Grant a, , Desirée A. Benefield , Donald G. VanDerveer
*
a Department of Chemistry, The University of Tennessee at Chattanooga, Chattanooga, TN 37403, United States
b School of Chemistry, Clemson University, Clemson, SC 29634, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 October 2009
Received in revised form 10 November 2009
Accepted 11 November 2009
Available online 14 November 2009
The complex [Pt(9S3)(SbPh3)(Ph)](PF6) forms directly from [Pt(9S3)(SbPh3)2](PF6)2 during the room tem-
perature crystallization of the latter in nitromethane. The crystal structure shows a five-coordinate Pt(II)
center containing the tridentate thiacrown ligand, a Sb donor from the triphenylstibine ligand, and a
r-
coordinating phenyl group. The phenyl group forms via Sb–C bond cleavage from one of the SbPh3 ligands
in the bis complex.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
1,4,7-trithiacyclononane
Platinum complexes
Triphenylstibine
Phenyl group cleavage
1. Introduction
determination and was found to contain a r-coordinated phenyl
ring to the Pt(II) center. The current report describes that com-
The cleavage of a phenyl group via Sb–C bond activation has
been reported in several transition metal complexes containing tri-
phenylstibine as a ligand [1–8]. Adams and co-workers have re-
pound and some of its properties.
2. Results and discussion
cently noted the formation of dirhenium complexes with
r-
coordinated phenyl rings formed from a coordinated SbPh3 ligand
[1]. Other examples of Sb–C bond cleavage of triphenylstibene in
metal complexes include a triruthenium cluster [2], a triosmium
cluster [3], a rhodium(II) dimer [4], hexaruthenium and osmium
clusters [5], a stibine–gallium mononuclear complex [6], the for-
mation of a nonanuclear organostiboxane cage via Sb–C bond
cleavage [7], and carbon–antimony bond cleavage in a mononu-
clear Pd(II) complex [8]. Reid and co-workers have similarly re-
ported carbon–antimony bond activation in bidentate Sb donor
ligands which were coordinated to Rh(I) [9] while the Levason
group reported photoactivation of a Sb–C bond in a binuclear Pd(II)
complex [10]. Our group has been interested in probing periodic
effects in heteroleptic Pt(II) and Pd(II) complexes involving the
thiacrown ligand, 1,4,7-trithiacyclononane (9S3) and a variety of
Group 15 donor ligands. In that regard, we have recently published
two papers describing these complexes [11,12], and the second pa-
per includes two complexes containing the ligand triphenylstibine,
[Pt(9S3)(SbPh3)2](PF6)2 (1) and [Pt(9S3)(SbPh3)(Cl)](PF6). During
the crystallization of Compound 1, we simultaneously isolated a
second crystalline product was suitable for a crystal structure
2.1. Syntheses and spectroscopy
Slow crystallization (multiday) of an analytically pure sample of
[Pt(9S3)(SbPh3)2](PF6)2 (1) via ether diffusion into nitromethane
yields two distinctive crystalline habits, red chips and yellow nee-
dles. The partial conversion occurs over a period of several days
during which the solution is exposed to normal laboratory lighting.
Single crystal X-ray diffraction confirms the former to be the bis
SbPh3 complex (1) while the latter proved to be [Pt(9S3)-
(SbPh3)(Ph)](PF6) (2), which is isolated as a mono nitromethane
solvate. The proton and carbon-13 NMR spectra of complex 2 show
the correct number of peaks, splittings, and intensities associated
with the three organic components; the 9S3 macrocyclic ligand,
the triphenylstibine, and the
r-bound phenyl ring. In mixtures of
the two, the phenyl-coordinated Pt complex (2) is readily differen-
tiated from complex 1 via the chemical shift difference in the 13C
NMR spectra for their fluxional 9S3 ligands (37.54 vs. 34.98 ppm
for 1 and 2, respectively). The formation of complex 2 is further
supported by a combustion analysis. Although it is fairly stable
in the solid state, complex 2 does degrade in solution making pro-
tracted NMR data acquisitions problematic. The electronic spec-
trum of complex 2 shows one well-defined transition at 373 nm
along with three shoulders in the ultraviolet of higher intensity.
* Corresponding author. Fax: +1 4234255234.
E-mail address: Greg-Grant@utc.edu (G.J. Grant).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.11.010

G.J. Grant et al. / Journal of Organometallic Chemistry 695 (2010) 634–636
635
The replacement of the weaker field SbPh3 ligand with a strong
field phenyl ligand causes the low energy transition in complex 2
to become blue-shifted by approximately 80 nm, compared to
the same transition in complex 1. This blue-shift is also consistent
with the relative colors of both compounds.
The conversion of 1 into complex 2 correlates with the loss of
one of SbPh3 ligands and the rupture of a Sb–C bond of a phenyl
ring in the triphenylstibine. The remaining reaction products have
not been identified. Our working hypothesis for the formation of
the complex is that there is an initial loss of one of the two SbPh3
ligands which are weakly bound to the platinum center. Next, Sb–C
bond activation occurs via the {Pt 9S3 SbPh3} moiety since the
Pt(II) requires a replacement ligand for that vacant coordination
site. Both the poor coordinating ability of the SbPh3 ligands and
the weak Sb–C bond strength play important roles in the process.
We would note that this Sb–C bond cleavage in SbPh3 is somewhat
unusual in that it readily occurs in a simple, mononuclear complex
at room temperature, without heating or the assistance of metal–
metal bonds [1–8]. Neither of the two related complexes,
[Pt(9S3)(SbPh3)(Cl)](PF6) nor [Pt(9S3)(AsPh3)2](PF6)2 displays this
reactivity [12]. We have attempted to convert complex 1 to com-
plex 2 using both controlled thermal and photochemical reactions.
However, no reaction occurs when 1 is refluxed in a nitromethane/
chloroform mixture for 5 h. We were able to get a partial conver-
sion to complex 2 (monitored via NMR) by a two-hour exposure
to ultraviolet light, but a complete conversion to 2 still did not oc-
cur. Furthermore, NMR samples of [Pt(9S3)(SbPh3)2](PF6)2 which
are not exposed to light (covered in aluminum foil) for a seven-
day period show no conversion to the phenyl-coordinated com-
plex. These experiments suggest that the reaction is photochemi-
cally induced. Our complex does not display the robustness of
similar systems reported previously [11], as we see degradation
in solution of the phenyl complex. In a related paper, Sharma, Carb-
rera, and co-workers have reported Sb–C bond cleavage in a Pt(II)
Fig. 1. Thermal ellipsoid perspective (50% probability) of cation in [Pt(9S3)(SbPh3)-
(Ph)]PF6ÁCH3NO2.
Table 1
Crystallographic data for [Pt(9S3)(SbPh3)(Ph)](PF6)ÁCH3NO2 (2).
Empirical formula
Formula weight (amu)
Lattice
Space group
C31H35F6NO2PPtS3Sb
1011.59
monoclinic
P21/c
a (Å)
b (Å)
c (Å)
20.428(4)
10.949(2)
16.610(3)
108.16(3)
3530(1)
4
b (°)
V (Å3)
complex to form a
r-coordinated phenyl ligand along with two
Z
Radiation (k) (Å)
0.71073
1.903
5.008
SbPh3 ligands, trans-[Pt(SbPh3)2(Ph)Br] [13]. However, the starting
source of the Sb ligand is the salt [Me4N][Ph2SbBr2], which con-
tains an anionic phenyl group in equilibrium with the neutral Sb
species, and the phenyl-coordinated complex forms concurrently
during the preparation of cis-[Pt(SbPh3)2Br2].
Dcalc (g cmÀ3
)
l
(mmÀ1
T (K)
)
153(2)
Reflections collected
28939
Independent reflections (Rint)
7205
0.0401
0.0951
a
R1
b
wR2
2.2. Crystal structure of [Pt(9S3)(SbPh3)(Ph)](PF6)ÁCH3NO2 (2)
Goodness-of-fit (GOF)
1.116
a
R1
wR2 = [
=
R
||Fo| À |Fc||/
R|Fo|.
A thermal ellipsoid perspective of the complex cation is shown
in Fig. 1, and crystallographic along with structural data are pre-
sented in Tables 1 and 2. The structure includes the Pt complex cat-
ion, a hexafluorophosphate counter ion, and one nitromethane
solvent molecule. The Pt(II) center is five-coordinate with a
[S3SbC] environment and is surrounded by three sulfur donors
from the facially coordinating trithiacrown ligand, the Sb donor
R
[w(F2o À F2c )2]/
R .
[w(F2o )2]]1/2
b
Table 2
Selected bond lengths (Å) and angles (°)a for [Pt(9S3)(SbPh3)(Ph)](PF6)ÁCH3NO2 (2).
Lengths
Pt–S1
Pt–S4
Pt–S7
Pt–Sb1
Pt–C10
Angles
2.549(2)
2.350(2)
2.391(2)
2.4939(6)
2.039(6)
from the triphenylstibine, and a single
r-coordinated carbon do-
nor from the anionic phenyl ring. Although there are approxi-
mately fifty Pt(II) 9S3 crystal structures reported in the literature
[14], there is only a single prior example involving a
r-coordinated
phenyl ring, that one being reported by Bennett and co-workers for
[Pt(9S3)(Ph)2] [15]. In our structure, the three Pt–S bond lengths
are 2.350(2), 2.391(2), and 2.549(2) Å. The pattern contrasts the
elongated square pyramidal structures commonly seen in other
Pt 9S3 complexes in which the axial and longer Pt–S distance can
be as much as 0.7 Å greater than the two equatorial Pt–S bonds. In-
deed, our group has highlighted the ability of the 9S3 to adjust its
coordination mode to compensate for poorer donor qualities in
Group 15 ligands such as Sb donors [12]. In addition, we have
noted that bis complexes with the formula [Pt(9S3)(EPh3)2](PF6)2
(E = Ph, As, Sb) all show distortions toward a trigonal bipyramidal
structure (and away from a square pyramidal structure) and the
S4–Pt–S7
S4–Pt–S1
S7–Pt–S1
C10–Pt–S4
Sb1–Pt–S7
88.26(6)
86.57(6)
87.37(6)
177.8(2)
147.16(4)
a
Estimated standard deviations are given in parentheses.
degree of distortion is surprisingly independent of the Group 15
donor. The distortion is most conveniently defined by the param-
eter developed by Reedijk and co-workers where a value of 0 rep-
resents an ideal square pyramid and a trigonal bipyramid has a
value of 1 [16]. Complex 2 has a
s
s value of 0.51 intermediate be-

636
G.J. Grant et al. / Journal of Organometallic Chemistry 695 (2010) 634–636
tween the two extremes indicating some distortion towards trigo-
nal bipyramid, but not to the same degree as the three bis pnicto-
gen 9S3 complexes (s = 0.58) [12]. We have argued that p–p
intermolecular interactions between phenyl rings are responsible
for the distortion, but these cannot occur here due to the relative
orientation of the phenyl and SbPh3 ligands. However, we would
note a hydrogen atom (H32) from one of the phenyl rings in the tri-
found to be in an approximate 1/4 ratio (complex 1/complex 2)
by mass. Anal. Calc. for C31H35F6NO2PPtS3Sb: C, 36.81; H, 3.49; S,
9.51. Found: C, 36.80; H, 3.29; S, 9.51%. 2: 1H NMR (CD3NO2) d
(ppm): complex multiplets at 7.46–7.34 (15 H, Sb(C6H5)3), 7.54–
7.49 (2 H, Ph, o-H), 6.84–6.75 (3 H Ph, m, p-H), symmetrical multi-
plet at 3.10–2.97 (12 H, 9S3). 13C {1H} NMR (CD3NO2): d (ppm):
141.85, 136.79, 132.16, 130.78 (Sb(C6H5)3); 136.36, 130.01,
126.52, 125.00 (Ph); 34.98 (9S3). We have not been able to observe
phenylstibine is directed to the
p system of the coordinated phenyl
ring and lays only 2.17 Å from its mean-least-squares plane. This is
considerably less than the sum of the van Der Waals radii (2.8 Å)
and could be the source of the distortion. For over eighty 9S3 com-
plexes with Pt(II) or Pd(II) centers, only the three bis EPh3 Pt(II)
complexes of 9S3 mentioned above show a greater distortion to-
wards a trigonal bipyramidal geometry than does complex 2.
a
195Pt-{1H} NMR resonance for the compound, possibly due to line
broadening by the quadrupolar Sb nuclei and/or sample degrada-
tion in solution. The electronic absorption spectrum measured in
acetonitrile showed one peak with kmax at 373 nm
(e = 468
M
À1 cmÀ1) and shoulders at 292 nm (
e
= 12,000 MÀ1 cmÀ1) and 235 nm (
e
e
= 7000 MÀ1 cmÀ1), 253 nm
= 35,000 MÀ1 cmÀ1). Solu-
(
The
r
-coordinated phenyl ring lays trans to S4 (C10–Pt–
tions of [Pt(9S3)(SbPh3)2](PF6)2 in CD3NO2, which were kept in
the dark by covering the NMR tube in aluminum foil, were un-
changed after a seven-day period as measured using NMR.
S4 = 177.8(2) Å) while the Sb donor is nearly trans to the centroid
between S1 and S7 (Sb–Pt–centroid (S1–S7) = 167.23(6) Å). Due
to its strong trans directing strength, the shortest Pt–S bond (Pt–
S4 = 2.350(2) Å) is also the one that is trans to the phenyl group.
When the complex is viewed as a distorted trigonal bipyramid,
the phenyl group is in an axial position (along with S4). The longest
Pt–S bond is Pt–S1 at 2.549(2) Å. Alternatively, if viewed as an
elongated square pyramidal shape, the Pt–S1 bond then would cor-
respond to the axial position. The Pt–S distances as well as the Pt–
C(phenyl) in 2 are comparable to those reported in the structure of
[Pt(9S3)Ph2] [15]. The Pt–C distances in either of these two 9S3/Ph
complexes are considerably longer (2.039(6) Å in our case) than
those seen in trans-[PtBr(Ph)(SbPh3)2] (1.990(2) Å), due to the
4.3. Data collection and processing
The intensity data for these were measured at low temperature
with graphite-monochromated Mo Ka radiation (k = 0.71073 Å) on
a Rigaku AFC8S diffractometer equipped with a 1 K mercury CCD
detector [17,18]. Structure solution, refinement and the calculation
of derived results were performed with the SHELXTL package of com-
puter programs [19].
Acknowledgments
p
-acceptor electronic effects of the 9S3 ligand. The influence of
the strongly -donating phenyl group on the Pt(II) center is clearly
seen in the Pt–Sb bond distance. Here the Pt–Sb bond length
(2.4939(6) Å) is 0.05 Å shorter than in the bis Complex
(Pt–Sbavg = 2.5467(8) Å or [Pt(9S3)(SbPh3)(Cl)](PF6) (Pt–Sb =
2.5304(7) Å) which contains a -donating chloro group. [12]. The
r
This research was generously supported by grants from the Re-
search Corporation, the Petroleum Research Fund of the American
Chemical Society, and the Grote Chemistry Fund at UTC.
1
p
Appendix A. Supplementary material
phenyl ring is oriented nearly perpendicular to the mean-least-
squares equatorial plane (Sb–S1–S7–Pt) at an angle of 88.7°.
CCDC 744844 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.jorganchem.
2009.11.010.
3. Conclusions
Cleavage of an antimony–carbon bond in the complex
[Pt(9S3)(SbPh3)2](PF6)2 results in the formation of [Pt(9S3)(SbPh3)-
(Ph)](PF6) which contains a
r-coordinating phenyl ligand. The
References
structure of the phenyl bound complex shows a high degree of dis-
tortion towards a trigonal bipyramidal geometry with a S3SbC(phe-
nyl ring) environment around the Pt(II) center.
[1] R.D. Adams, B. Captain, W.C. Pearl Jr., J. Organomet. Chem. 693 (2008) 1636.
[2] Obin Shawkataly, K. Rmalingam, H.K. Fun, A. Abdul Rhamna, I.A. Razak, J.
Cluster Sci. 15 (2004) 387.
[3] W.K. Leong, G. Chen, Organometallics 20 (2001) 2280.
[4] S.P. Best, A.J. Nightingale, D.A. Tocher, Inorg. Chim. Acta 181 (1991) 7.
[5] G. Chen, W.K. Leong, J. Cluster Sci. 17 (2006) 111.
4. Experimental
[6] V. Chandrasekhar, R. Thiurmoorthi, Organometallics 28 (2009) 2637.
[7] C. Jones, C. Schulten, A. Stasch, Main Group Chem. 28 (2005) 89.
[8] A. Mentes, R.D.W. Kemmitt, J. Fawcett, D.R. Russell, J. Organomet. Chem. 528
(1997) 59.
[9] M.D. Brown, W. Levason, G. Reid, M. Webster, Dalton Trans. (2006) 4039.
[10] A.D. Chiffey, J. Evans, W. Levason, M. Webster, Organometallics 14 (1995)
1522.
[11] G.J. Grant, D.A. Benefield, D.G. VanDeerveer, Main Group Chem. 6 (2007) 249.
[12] G.J. Grant, D.A. Benefield, D.G. VanDeerveer, Dalton Trans. (2009) 1872.
[13] P. Sharma, A. Cabreera, M. Sharma, C. Alvarez, R.M. Gomez, S. Hernandez, Z.
Anorg. Allg. Chem. 626 (2000) 2330.
[14] Cambridge Structural Database v 5.30, May, 2009, Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK.
4.1. Materials and measurements
Complex 1, [Pt(9S3)(SbPh3)2](PF6)2, was prepared by the litera-
ture method [12]. All solvents and other reagents were used as re-
ceived. Analyses were performed by Atlantic Microlab, Atlanta, GA.
All 13C{1H} and 1H NMR spectra were recorded on a JEOL ECX-400
NMR spectrometer using CD3NO2 for both the deuterium lock and
internal reference. UV–Vis. spectra were obtained in acetonitrile
using a Varian Cary 100-Bio UV–Vis. spectrophotometer. A Rayo-
met MGR-100 circular UV lamp operating at 50 watts was used
for photochemical reactions.
[15] M.A. Bennett, A.J. Canty, J.K. Felixberger, L.M. Rendina, C. Sunderland, A.C.
Willis, Inorg. Chem. 32 (1993) 1951 (Interestingly, the structure shows a rare
exodentate conformation of the 9S3 ligand.).
[16] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc.,
Dalton Trans. (1984) 1349.
[17] CrystalClear, Rigaku/MSC, The Woodlands, TX, USA, 1999.
[18] Jacobson, R.A., REQAB, Subroutine of CrystalClear, Rigaku/MSC, The
Woodlands, TX, USA, 1999.
4.2. Isolation of [Pt(9S3)(SbPh3)(Ph)](PF6)ÁCH3NO2 (2)
Slow diffusion (1 wk) of diethyl ether into a nitromethane con-
centrate of Complex 1 produced two sets of crystals – red chips of 1
and yellow needles of 2. These are mechanically separated and
[19] SHELXTL 5.1, 1998–1999, Bruker AXS, Madison, WI, USA.