Synthesis and structure of penta-platinum σ-bonded derivatives of corannulene

Article abstract of DOI:10.1016/j.jorganchem.2009.07.015

The synthesis of a new class of Pt(II) complexes with corannulene by way of either oxidative addition or reductive coupling is reported and their crystal structures are investigated. The crystal structure for {trans-Pt(PEt₃)₂Cl}

Full text of DOI:10.1016/j.jorganchem.2009.07.015

Journal of Organometallic Chemistry 694 (2009) 3529–3532
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Synthesis and structure of penta-platinum
r
-bonded derivatives of corannulene
a,
Hyunbong Choi a, Chulwoo Kim a, Ki-Min Park b, Jinho Kim c, Youngjin Kang c, , Jaejung Ko
*
*
a Department of New Material Chemistry, Korea University, Jochiwon, Chungnam 339-700, Republic of Korea
b Research Institute of Natural Science Gyeongsang National University, Jinju 660-701, Republic of Korea
c Division of Science Education, Kangwon National University, Chuncheon 200-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 May 2009
Received in revised form 1 July 2009
Accepted 6 July 2009
Available online 5 August 2009
The synthesis of a new class of Pt(II) complexes with corannulene by way of either oxidative addition or
reductive coupling is reported and their crystal structures are investigated. The crystal structure for
{trans-Pt(PEt3)2Cl}4{cis-Pt(PEt3)2Cl}C20H5 (1) consists of two enantiomers in a unit cell and shows cis-
and trans-configuration around Pt(II) due to bulky PEt3 ligands. The pentanuclear Pt(II) complex, 1, read-
ily reacts with 1-ethynyl-4-nitrobenzene to afford the penta-alkynyl substituted Pt(II) complex (2).
Although there are still bulky PEt3 ligands around the Pt atoms in 2, all five Pt(II) have trans-configura-
tions. The bowl of corannulene in 2 is shallower than that of 1. Therefore, the bowl depth of corannulene
Keywords:
Corannulene
Oxidative addition
X-ray structure
plays a key role in the determination of molecular geometry of
ing corannulene.
r-bonded pentanuclear complexes bear-
Ó 2009 Elsevier B.V. All rights reserved.
Recently, transition metal complexes with non-planar polycy-
clic aromatic hydrocarbons, such as fullerene, corannulene, have
been attention due to their reactivity, bonding modes and struc-
tural diversity [1]. Among polycyclic aromatic hydrocarbons, cor-
This compound is sterically crowed due to the bulky substituents
at the rim positions, leading to a shallow corannulene bowl (bowl
depth: 0.72 Å). However, further study on the reactivity of metals
using the penta-substituted corannulene and structural character-
istics of metal complexes in the solid state have not been reported
until now. We are interested in the structural features and reactiv-
ity of sterically crowded pentanuclear metal complexes bearing
sigma-bonds between the metal and the carbon of corannulene.
Herein, we report an X-ray crystal structure of metal-corannulene
complex that shows two enantiomers in a unit cell and its reactiv-
ity to alkyne functionality.
annulene (C20H10
) is the minimum fragment of a fullerene
retaining the characteristic curvature. Substantial efforts have
been directed toward the synthesis of transition metal complexes
of corannulene [2], in order to understand the participation of cor-
annulene in the bowl to bowl inversion process [3], and to reveal
the reactivity of corannulene [4]. Bowl-to-bowl inversion is a dy-
namic process in which the convex and concave faces interconvert
through a planar transition state [5]. Previous studies [6] indicate
that peri substituents make the bowl shape of corannulene flatten,
leading to decrease the inversion barrier, however bridging the peri
positions serve to increase the bowl inversion barrier.
Although a number of studies on the structural features and
reactivity of sandwiched metal complexes bearing corannulene
and corannulene derivatives have been reported, the preparation
of metal complexes through a direct sigma-bond between the me-
tal and the corannulene core still remains rare. Sharp group has re-
cently reported Ni(II) and Pt (II) complexes by the reaction of low-
valent Ni(0) and Pt(0) metals with corannulene [7]. The relation-
ship between the bowl depth of corannulene derivatives and the
substituents at the rim position of corannulene is considered major
issue in accordance with reactivity and selectivity of corannulene
to the metal [8,9]. Meanwhile, the X-ray structure of 1,3,5,7,9-pen-
ta-tert-butylcoranulene was reported by the Petrukhina group [9].
To synthesize
r-bonded platinum derivatives of corannulene,
we adopted a synthetic route involving an oxidative addition reac-
tion between bromocorannulenes and Pt(PEt3)4, which was re-
cently reported by the Sharp group [7]. Addition of 10.5 equiv of
Pt(PEt3)4 to 1,3,5,7,9-pentachlorocorannulene in toluene at 130 °C
gave yellow solution. Standard work-up and crystallization from
methanol gave [Pt5(PEt3)10Cl5-(corannulenyl)] (1) as a spectroscop-
ically pure yellow crystalline solid (Scheme 1) [10]. Yellow crystals
of [Pt5(PEt3)10Cl5(C20H5)](1) suitable for an X-ray structure were
grown in methanol at À10 °C.
The X-ray study revealed 1 to be an unusual oxidative addition
product of a platinum complex containing two types of phosphine
ligands, {trans-Pt(PEt3)2Cl}4{cis-Pt(PEt3)2Cl}C20H5 (Fig. 1), instead
of the expected structure of {trans-Pt5(PEt3)10Cl5}C20H5 [11]. Inter-
estingly, the asymmetric unit of 1 consists of a racemic mixture of
the two enantiomers (A:B = 1:1). Similarly, a sumanene ligand has
recently been used to form a trimethyl substituted compound [12]
or transition metal Fe(II) complex that displays the enantiomeric
isomer of buckybowls [13].
* Corresponding author.
E-mail addresses: kangy@kangwon.ac.kr (Y. Kang), jko@korea.ac.kr (J. Ko).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.07.015

3530
H. Choi et al. / Journal of Organometallic Chemistry 694 (2009) 3529–3532
Cl
Pt
The bowl depths for A and B in Fig. 1, which is defined as the
separation distances between a centroid of the interior hub plane
and the mean plane of the ten atoms on the rim, are 0.77 and
0.80 Å, respectively. While the bowl depths for non-substituted
and penta-alkyl substituted corannulene are 0.87 and 0.72 Å,
respectively. This fact suggests that there is no room to locate
the triethylphosphine ligand of the fifth platinum atom in the trans
conformation because the bowl depth of 1 is deeper than that of
penta- t-butyl substituted corannulene. Henceforth, a Cl atom in-
stead of a PEt3 ligand is located at the endo-position (concave),
as shown in Fig. 1.
Et3 P
PEt3
Cl
PEt3
Cl
Pt
Cl
Cl
PEt3
Pt
Et3
P
Pt(PEt3
)
4
Cl
Cl
PEt3
tol,3days,130 °C
Et
3P
Pt
Cl
PEt3
Cl
Pt
P
Cl
Et3
PEt3
1
Scheme 1.
Fig. 1. (a) Ortep drawing of 1 with atom numbering scheme. Hydrogen atoms are omitted for clarity. (b) Perspective view of 1 showing two enantiomeric bowl forms in a unit
cell. (c) POAV pyramidalization angles and averaged bond lengths of bowl A form; C–Chub = 1.40 (2), C–Crim = 1.43(2), C–Cflank = 1.44(2), C–Cspoke = 1.39(2). (d) Space filling
models of 1 showing steric congestion. Left: A, right: B.

H. Choi et al. / Journal of Organometallic Chemistry 694 (2009) 3529–3532
NO2
3531
O2N
PEt3
Pt
Et3P
PEt3
Et3P
PEt3
Pt
Pt
Cl
PEt3
Cl
Pt
Pt
Et3P
Et3P
PEt3
Pt
PEt3
Pt
Et3P
a
Cl
PEt3
Et3P
Cl
Et3P
Pt
PEt
NO2
Pt
PEt3
Et3P
PEt3
3Et3P
PEt3
Pt
Cl
O2N
NO2
2
Scheme 2. Reagents and conditions: (a) 1-ethynyl-4-nitrobenzene, Et2NH, then toluene, CuI.
Such cis and trans-formation of platinum phosphine complexes
has been observed in the oxidative addition product, cis-
Pt(PEt3)2(Br)(1,5,6-tribromo-corannulen-2-yl). This observation
for 1 is attributed to both steric hinderance caused by PEt3 ligands
and bowl depth of corannulene.
Complex 1 was found to be an efficient reactant for the reduc-
tive coupling reaction with an alkyne under mild condition [17].
The reaction of 1 with 1-ethynyl-4-nitrobenzene in the presence
of CuI and Et2NH afforded the penta-alkynyl substituted corannu-
lene 2 (Scheme 2). All of the spectral data of 2 were consistent with
the expected product. A key feature in the 1H NMR spectrum indi-
cates a singlet at d 7.73 assigned to the corannulene proton, indi-
cating that five protons on corannulene are now chemically
equivalent. One high-field resonance at d 6.4 (1JPtP = 2660 Hz) in
the 31P NMR spectrum provides evidence that all platinum planes
are orthogonal to the corannulene bowl.
The red single crystals, crystallized from a solution of toluene
and hexane slowly decomposed under air. The crystal structure re-
veals that the corannulene with a regular pentagon conformation
is coordinated to a platinum moiety at five carbon sites and five
peripheral substituents on the corannulene have a flat configura-
tion. The bond lengths (2.07(3)–2.29(4) Å) of Pt–C(corannulene)
observed in 2 are slightly longer than those (1.98(17)–2.08(16) Å)
of 1. These observed elongations imply a stronger trans influence
of carbon atom attached on triple bond. In order to compare the
difference of bowl depth between 1 and 2, the separation distance,
which is defined as the distance of the centroid between two adja-
cent Pt atoms and Pt atom located in opposite side in the Pt penta-
gon, was estimated (Fig. 2) [18].
Curvature is one of the characteristic features in strained aro-
matic hydrocarbons. The diminution of curvature in 1 is clearly
demonstrated using the
p-orbital axis vector (POAV) analysis
[14]. The pyramidalization angles of the hub carbon atoms and
those that are attached to them are on average 7.31° and 2.92°,
respectively. The analogous values for corannulene are 8.4° and
3.8°, respectively. Thus, the curvature of the corannulene bowl in
the hub carbons of 1 is reduced to 87% of that of corannulene; how-
ever, curvature for the outer spoke carbons is reduced to 77%. A
significant difference in bond lengths is observed in the rim bonds
which are elongated to an average of 1.43(2) from 1.402(5) Å in
corannulene itself [15]. An elongation of the rim bonds represents
an addition of strain to the corannulene unit of 1. This stretching
partially accommodates the steric congestion of the substituents
[16]. The 1H and 31P NMR spectra of 1 in solution were consistent
with the structure determined by X-ray crystallography. Four sing-
lets (d 8.00, 7.88, 7.82, and 7.78) and one doublet at d 7.92
(JPH = 8.4 Hz) in the 1H NMR spectrum of 1 indicates that the five
corannulene protons are not equivalent. The 31P NMR spectrum
of 1 exhibits four resonances at d 9.50, 9.19, 8.37, and 7.86 with
As being anticipated, the average separation distance of 2
(9.68 Å) was measured to be longer than that of 1 (9.48 Å). More-
over, the average separation distance (6.18 Å) between two adja-
cent Pt atoms in 1 is shorter than that (6.29 Å) of 2. Both
observations imply that the bowl of 2 is shallower than that of 1,
as shown in Fig. 2. Therefore, all of the Pt atoms have a trans-con-
1
a rather large coupling constant of JPtP (2728–2748 Hz), and two
doublets at d 4.98 and À0.78 with a small coupling constant of 1JPtP
(1678 Hz) due to the presence of phosphines with different
arrangements around the Pt atom. These results are consistent
with the crystal structure, as shown in Fig. 1.
Fig. 2. Separation distances (Å) of 1(a) and 2(b) in the Pt pentagon. Symmetry code: (i) 2Àx, y, 1.5Àz.

3532
H. Choi et al. / Journal of Organometallic Chemistry 694 (2009) 3529–3532
[6] (a) T.J. Seiders, K.K. Baldridge, J.M. O’Connor, J.S. Siegel, Chem. Commun.
(2004) 950;
figuration despite the presence of steric crowding at the endo-po-
sition. The structure of 2 in the solid state is consistent with the
data of 1H and 31P NMR. Based on our observation and illustration,
we believe that the bowl depth of corannulene plays a key role in
(b) M.A. Petrukhina, K.W. Andreini, V.M. Tsefrikas, L.T. Scott, Organometallics
24 (2005) 1394;
(c) S. Samdal, L. Hedberg, K. Hedberg, A.D. Richardson, M. Bancu, L.T. Scott, J.
Phys. Chem. A 107 (2003) 411.
the determination of molecular geometry in
ar complexes bearing corannulene.
r-bonded pentanucle-
[7] H.B. Lee, P.R. Sharp, Organometallics 24 (2005) 4875.
[8] B. Zhu, A. Ellern, A. Sygula, R. Sygula, R.J. Angelici, Organometallics 26 (2007)
1721.
[9] Y. Sevryugina, A.Y. Rogachev, E.A. Jackson, L.T. Scott, M.A. Petrukhina, J. Org.
Chem. 71 (2006) 6615.
In summary, an oxidative addition reaction of 1,3,5,7,9-penta-
chlorocorannulene with Pt(PEt3)4 afforded an interesting platinum
r
-bonded derivative of corannulene. The crystal structure for 1
[10] General considerations: All experiments were performed under dry N2
atmosphere using standard Schlenk technique. All solvents were freshly
distilled over appropriate drying reagents prior to use. All starting materials
were purchased from either Aldrich or Strem and used without further
purification. 1H NMR were recorded on a Varian 300 MHz spectrometer and
phosphorus resonance was referenced with respect to external 85% H3PO4.
Preparation of 1: To a stirred solution of Pt(PEt3)4 (0.63 g, 0.94 mmol) in
freshly distilled toluene (60 mL) under nitrogen was added, in portions,
1,3,5,7,9-pentachlorocorannulene (40 mg, 0.09 mmol). The resulting bright red
solution was then maintained for 3 days in an oil bath at 130 °C. The solvent
was removed in vacuo at 40 °C, and the residue was suspended in methanol
(15 mL) and gently refluxed for 45 min. The suspension was allowed to cool.
The product was collected on a frit and washed with cold methanol (5 mL Â 2)
to give 1 as a yellow solid. Yield: 0.12 g (52%); mp 283 °C; 1H NMR (CDCl3): d
8.00 (s, 1H), 7.92 (d, JPH = 8.4 Hz, 1H), 7.88 (s, 1H), 7.82 (s, 1H), 7.78 (s, 1H),
2.02-1.52 (m, 54H), 1.27–0.99 (m, 81H), 0.80 (m, 6H), 0.56 (t, J = 8.0 Hz, 9H);
consists of two enantiomers in a unit cell and shows both cis-
and trans-configurations around Pt ions due to the steric conges-
tion of bulky ligands. Compound 1 readily reacts with 1-ethynyl-
4-nitrobenzene to afford the penta-alkynyl substituted corannu-
lene with trans-configuration around platinum. The bulky periphe-
ral substituents cause a flattening of the bowl.
Acknowledgment
This work was supported by the Korea Science and Engineering
Foundation (KOSEF) through the National Research Lab. Program
funded by the Ministry of Science and Technology (No. ROA-
2005-000-10034-0), WCU (the Ministry of Education and Science)
Program (No. R31-2008-000-10035-0), and BK-21 (2006).
1
31P{1H}NMR (CDCl3): d 9.50 (s with satellites, JPtP = 2742 Hz), 9.19 (s with
1
1
satellites, JPtP = 2728 Hz), 8.37 (s with satellites, JPtP = 2736 Hz), 7.86 (s with
1
1
1
satellites, JPtP = 2748 Hz), 4.98 (d with satellites, JPtP = 1678, JPP = 11.8 Hz),
1
1
À0.78 (d with satellites, JPtP = 1678 Hz, JPP = 11.8 Hz), À0.76 (d with
1
1
satellites, JPtP = 1678 Hz, JPP = 11.8 Hz); Elemental analysis Calc. for C80H155
-
Appendix A. Supplementary material
Cl5P10Pt5: C, 37.25; H, 6.06. Found: C, 36.98; H, 5.96.
[11] Crystal data for 1: C80H155Cl5P10Pt5, Mr = 5158.88, crystal dimensions
0.18 Â 0.07 Â 0.04 mm3, monoclinic, space group P21/n, a = 38.946(8),
CCDC 609288 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via http://www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2009.07.015.
b = 14.601(3),
calcd = 1.634 g cmÀ3
index range: À47 6 h 6 47, À17 6 k 6 17, À47 6 l 6 47,
39820 measured reflection, 1772 independent reflection, R1 = 0.0692,
wR2 = 0.1584 (I > 2 (I)), GOF = 1.007.
c = 39.197(8) Å,
b = 109.85(3)°,
) = 0.71073 Å, T = 233(2) K, 2hmax = 51.36°,
V = 20965(7) Å3,
Z = 4,
q
,
k
(Mo
K
a
l
= 6.964 mmÀ1
,
r
[12] S. Higashibayashi, H. Sakurai, J. Am. Chem. Soc. 130 (2008) 8592.
[13] H. Sakane, T. Amaya, T. Moriuchi, T. Hirao, Angew. Chem., Int. Ed. 48 (2009)
1640.
[14] (a) R.C. Haddon, L.T. Scott, Pure Appl. Chem. 58 (1986) 137;
(b) R.C. Haddon, Acc. Chem. Res. 21 (1988) 243;
References
(c) R.C. Haddon, Science 261 (1993) 1545.
[1] M.A. Petrukhina, Angew. Chem., Int. Ed. 47 (2008) 1550 (and references cited
therein).
[2] (a) T.J. Seiders, K.K. Baldridge, J.M. O’Connor, J.S. Siegel, J. Am. Chem. Soc. 119
(1997) 4781;
[15] (a) J.C. Hanson, C.E. Nordman, Acta Crystallogr., Sect. B (1976) 1147;
(b) L. Hedberg, K. Hedberg, P.-C. Cheng, L.T. Scott, J. Phys. Chem. A 104 (2000)
7689.
[16] T.J. Seiders, K.K. Baldridge, G.H. Grube, J.S. Siegel, J. Am. Chem. Soc. 123 (2001)
517.
(b) C.M. Alvarez, R.J. Angelici, A. Sygula, R. Sygula, P.W. Rabideau, Organo-
metallics 22 (2003) 624;
(c) M.V. Frash, A.C. Hopkinson, D.K. Böhme, J. Am. Chem. Soc. 123 (2001) 6687;
(d) M.A. Petrukhina, K.W. Andreini, J. Mack, L.T. Scott, Angew. Chem., Int. Ed.
42 (2003) 3375;
[17] Preparation of 2: To a stirred solution of 1 (0.10 g, 0.038 mmol) and 1-ethynyl-
4-nitrobenzene (57 mg, 0.387 mmol) in diethylamine (15 mL) was added CuI
(1.8 mg) in toluene (15 mL). The reaction was stirred in the dark for 24 h. A
white precipitate of diethylammonium iodide was appeared. The solvent was
removed on a rotatory evaporator, and the product was purified by column
chromatography on silica gel (eluent: ethylacetate/hexane, 1:2). The pure
product was obtained by recrystallization from a toluene/hexane solution.
Yield: 0.072 g (60%); mp 175 °C; 1H NMR (CDCl3): d 8.10 (d, J = 9.0 Hz, 10H),
7.73 (s, 5H), 7.34 (d, J = 9.0 Hz, 10H), 1.79 (br, 60H), 1.06 (m, 90H);
13C{1H}NMR (CDCl3): d 148.6, 148.1, 144.3 (d), 138.8, 137.1, 136.4, 131.7,
130.8, 128.4, 123.8, 110.1, 108.4, 16.2 (d), 8.3; 31P{1H}NMR (CDCl3): d 6.4 (s
(e) P.A. Vecchi, C.M. Alvarez, A. Ellern, R.J. Angelici, A. Sygula, R. Sygula, P.W.
Rabideau, Angew. Chem., Int. Ed. 43 (2004) 4497.
[3] (a) L.T. Scott, M.M. Hashemi, M.S. Bratcher, J. Am. Chem. Soc. 114 (1992) 1920;
(b) T.J. Seiders, K.K. Baldridge, J.S. Siegel, J. Am. Chem. Soc. 118 (1996) 2754;
(c) A. Sygula, A.H. Abdourazak, P.W. Rabideau, J. Am. Chem. Soc. 118 (1996)
339.
[4] (a) L.T. Scott, Pure Appl. Chem. 68 2 (1996) 291;
(b) A. Sygula, P.W. Rabideau, J. Am. Chem. Soc. 122 (2000) 6323;
(c) R. Benshafrut, E. Shabtai, M. Rabinovitz, L.T. Scott, Eur. J. Org. Chem. (2000)
1091;
with satellites, 1JPtP = 2660 Hz); Elemental analysis calc. for C120H175N5O10P10
Pt5: C, 46.01; H, 5.63. Found: C, 45.87; H, 5.48.
[18] In the case of 2, the bowl depth is hardly obtained by the way of the same
method for measuring the depth in 1, because the carbon atoms of
corannulene are disordered.
-
(d) A. Sygula, G. Xu, Z. Marcinow, P.W. Rabideau, Tetrahedron 57 (2001) 3637;
(e) P.E. Georghiou, A.H. Tran, S. Mizyed, M. Bancu, L.T. Scott, J. Org. Chem. 70
(2005) 6158.
[5] P.U. Biedermann, S. Pogodin, I. Agranat, J. Org. Chem. 64 (1999) 3655.