Preparation, structures, and electrochemical properties of silaplatinacyclohexadienes with ferrocenyl pendant groups

Article abstract of DOI:10.1021/om020733n

Preparation, structures and electrochemical properties of silaplatinacyclohexadienes with ferrocenyl pendant groups were discussed. Electrochemical measurements and spectroscopic analysis were performed. Results showed that the oxidation of these compounds indicate a mixed valence of two ferrocene units.

Full text of DOI:10.1021/om020733n

Organometallics 2003, 22, 373-376
373
P r ep a r a tion , Str u ctu r es, a n d Electr och em ica l P r op er ties
of Sila p la tin a cycloh exa d ien es w ith F er r ocen yl P en d a n t
Gr ou p s
Makoto Tanabe, Masaki Horie, and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, J apan
Received September 6, 2002
Summary: The reactions of ethynylferrocene with
with the silaplatinacyclobutene that was recently iso-
lated by our group9 are applied to introduce ferrocenyl
groups to the silaplatinacycles. Structural and electro-
chemical properties of the obtained complexes are
discussed.
Pt(CZdCZ-SiPh2)(PMe3)2 (Z ) COOMe) and with
Pt(SiHPh2)2(PMe3)2 form the six-membered silaplati-
nacycles, Pt(CZdCZ-SiPh2-CHdCFc)(PMe3)2 (1) and
Pt(CFcdCH-SiPh2-CHdCFc)(PMe3)2 (2, Fc ) ferroce-
nyl), respectively. Electrochemical measurement and
spectroscopic analyses of the oxidation product of 2
indicate a mixed valence of two ferrocene units.
Resu lts a n d Discu ssion . Pt(CZ)CZ-SiPh2)(PMe3)2
(Z ) COOMe)9b reacts with equimolar ethynylferrocene
at 60 °C in toluene to produce the six-membered
metallacycle containing a ferrocenyl pendant group,
In t r od u ct ion . Many synthetic organic reactions
promoted by transition metal complexes involve inter-
mediate metallacycles with four- to six-membered rings.1,2
Kinetic stability of the metal-carbon bond of these
compounds is mainly attributed to the restricted con-
formation of the ring system, which prevents free
rotation of the M-C and C-C bonds and retards the
decomposition of the complexes via reductive elimina-
tion or â-hydrogen elimination. The five-membered
cobaltacycles having two ferrocenyl groups, prepared
from 2:1 addition of ethynylferrocene to a Co(I) complex,
exhibit the electrochemical interaction between the
ferrocenyl centers.3 Four-membered silametallacyclobu-
tenes4-7 have been proposed to react with unsaturated
molecules, such as alkynes, leading to the formation of
a C-Si bond. The reaction of phenylacetylene with
Pt(SiHMe2)2(PEt3)2 produces the silaplatinacyclohexa-
diene, which has been considered to involve the inter-
mediate silaplatinacyclobutene and its ring expansion
by an alkyne.8 In this study, the reactions of an alkyne
Pt(CZdCZ-SiPh2-CHdCFc)(PMe3)2 (1, Fc ) ferrocenyl)
(eq 1), which is isolated by recrystallization from THF-
hexane in 63% yield. The reaction of excess ethynylfer-
rocene with Pt(SiHPh2)2(PMe3)2 in toluene affords the
six-membered Pt complex with two ferrocenyl groups
at the R-carbon of the metal center, Pt(CFcdCH-SiPh2-
CHdCFc)(PMe3)2 (2), as shown in eq 2. Complex 2,
which is precipitated during the reaction, is isolated in
62% yield as an orange powder by filtration of the
solvent. Equation 2 probably involves the initial forma-
tion of the 4-sila-3-platinacyclobutene via equimolar
reaction of the bis(diphenylsilyl)platinum complex with
ethynylferrocene followed by ring expansion triggered
by insertion of another ethynylferrocene molecule into
the Pt-Si bond, similarly to eq 1. Evidence of the
intermediate four-membered metallacycle was not found
in the NMR spectra of the reaction mixture.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry, 2nd
ed.; University Science: Sausalito, CA, 1987; p 459.
(2) (a) Ca´mpora, J .; Palma, P.; Carmona, E. Coord. Chem. Rev. 1999,
193-195, 207. (b) J ennings, P. W.; J ohnson, L. L. Chem. Rev. 1994,
94, 2241.
(3) (a) Ohkubo, A.; Fujita, S.; Ohba, K.; Aramaki, K.; Nishihara, H.
J . Chem. Soc., Chem. Commun. 1992, 1553. (b) Murata, Y.; Hoshi, T.;
Matsuoka, I.; Nankawa, T.; Kurihara, M.; Nishihara, H. J . Inorg.
Organomet. Polym. 2000, 10, 209. (c) Nishihara, H. Bull. Chem. Soc.
J pn. 2001, 74, 19. See also: Yamada, Y.; Mizutani, J .; Kurihara, M.;
Nishihara, H. J . Organomet. Chem. 2001, 637, 80.
(4) (a) Okinoshima, H.; Yamamoto, K.; Kumada, M. J . Am. Chem.
Soc. 1972, 94, 9263. (b) Yamamoto, K.; Okinoshima, H.; Kumada, M.
J . Organomet. Chem. 1971, 27, C31.
(5) (a) Seyferth, D.; Vick, S. C.; Shannon, M. L.; Lim, T. F. O.;
Duncan, D. P. J . Organomet. Chem. 1977, 135, C37. (b) Seyferth, D.;
Duncan, D. P.; Vick, S. C. J . Organomet. Chem. 1977, 125, C5. (c)
Seyferth, D.; Shannon, M. L.; Vick, S. C.; Lim, T. F. O. Organometallics
1985, 4, 57.
(6) Sakurai, H.; Kamiyama, Y.; Nakadaira, Y. J . Am. Chem. Soc.
1977, 99, 3879.
(8) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1992, 11,
3227. See also: Eaborn, C.; Metham, T. N.; Pidcock, A. J . Organomet.
Chem. 1977, 131, 377.
(7) (a) Ishikawa, M.; Ohshita, J .; Ito, Y.; Iyoda, J . J . Am. Chem. Soc.
1986, 108, 7417. (b) Ohshita, J .; Isomura, Y.; Ishikawa, M. Organo-
metallics 1989, 8, 2050.
(9) (a) Tanabe, M.; Yamazawa, H.; Osakada, K. Organometallics
2001, 20, 4451. (b) Tanabe, M.; Osakada, K. J . Am. Chem. Soc. 2002,
124, 4550.
10.1021/om020733n CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/20/2002

374 Organometallics, Vol. 22, No. 2, 2003
Notes
F igu r e 1. OTREP drawing of (a) 1 and (b) 2 with 30% thermal ellipsoidal plots. Hydrogen atoms were omitted for simplicity.
Selected bond distances (Å) and angles (deg) for 1: Pt-P1 2.315(3), Pt-P2 2.314(3), Pt-C1 2.067(7), Pt-C4 2.055(7),
C1-C2 1.33(1), C1-C5 1.48(1), C2-Si 1.840(8), Si-C3 1.880(7), C3-C4 1.33(1), P1-Pt-P2 95.3(1), P1-Pt-C1 87.5(2),
P1-Pt-C4 171.9(2), P2-Pt-C1 173.9(2), P2-Pt-C4 91.8(2), C1-Pt-C4 85.1(3), Pt-C1-C5 118.1(6), Pt-C1-C2 118.7-
(6), C2-C1-C5 123.2(7), C1-C2-Si 119.0(6), C2-Si-C3 102.4(3), Si-C3-C4 117.0(6), C3-C4-Pt 121.6(6). Selected bond
distances (Å) and angles (deg) for 2: Pt-P1 2.329(4), Pt-P2 2.331(4), Pt-C1 2.08(1), Pt-C4 2.04(1), C1-C2 1.32(2),
C1-C5 1.48(2), C2-Si 1.82(1), Si-C3 1.86(1), C3-C4 1.34(2), P1-Pt-P2 94.7(1), P1-Pt-C1 177.4(3), P1-Pt-C4 91.5(4),
P2-Pt-C1 87.8(3), P2-Pt-C4 168.0(4), C1-Pt-C4 86.2(5), Pt-C1-C5 116.9(9), Pt-C1-C2 119.4(9), C2-C1-C5 124(1),
C1-C2-Si 120(1), C2-Si-C3 103.4(6), Si-C3-C4 119(1), C3-C4-Pt 119(1).
Figure 1 depicts the molecular structures of 1 and 2.
The boat conformation of the six-membered rings,
formed by cis addition of the Pt-Si bond to the alkyne,
makes the Si and Pt centers closer; the Pt‚‚‚Si distances
of 1 and 2 are 3.28 and 3.27 Å, respectively. The
ferrocenyl groups of the complexes are situated at a site
opposite to the silyl group on the coordination plane of
the Pt center. The conformation of the six-membered
metallacyclic ring and the orientation of the ferrocenyl
pendants are quite similar between 1 and 2. The
distance between the two Fe centers of 2 is approxi-
mately 6.0 Å. The NMR spectra of the complexes are
also consistent with the structure confirmed by X-ray
crystallography.
The cyclic voltammogram of 1 in Figure 2a shows a
single reversible ferrocene-ferrocenium redox at E1/2
)
-0.06 V (vs Ag+/Ag), which is lower than that of
ferrocene (E1/2 ) 0.15 V vs Ag+/Ag). Complex 2 exhibits
two redox waves as shown in parts b and c in Figure 2;
two reversible oxidation and reduction peaks are ob-
served at E1/2 ) -0.08 and 0.07 V (∆E ) 0.15 V) (vs
Ag+/Ag) at -40 °C. The electrochemical reactions (Eox
) -0.03 and 0.08 V vs Ag+/Ag) lack reversibility at 15
°C due to concomitant chemical oxidation of the product
at that temperature. The two reversible peaks at the
low temperature indicate the presence of two mixed
valence ferrocene units.10 The absorption spectra of 2
under electrochemical oxidation conditions, measured
by a flow electrolysis technique,11 indicate a stepwise
increase of the absorption of ferrocenium (380 nm) upon
electrolysis at -0.20 and 0.15 V. This is in accordance
with the mixed valence state of the Fe(II)-Fe(III)
species. The difference between the two potentials
F igu r e 2. Cyclic voltammograms of (a) 0.22 mM of 1 at
15 °C, (b) 0.52 mM of 2 at 15 °C, and (c) 0.52 mM of 2 at
-40 °C in CH2Cl2 solutions containing Et4NBF4 (0.10 M)
(scan rate ) 0.1 V s-1). 1: E1/2 ) -0.06 V. 2 at -40 °C:
E1/2 ) -0.08 and 0.07 V (∆E ) 0.15 V).
reflects the magnitude of the interaction. Recently,
Ribou et al. reported electrochemical communication
between two ferrocenyl units through a π-conjugated
organic bridge.12 The difference of the redox potential
of 2 (∆E ) 0.15 V) is between those of 1,2-diferrocenyl-
(10) (a) Cowan, D. O.; Levanda, C.; Park, J .; Kaufman, F. Acc. Chem.
Res. 1973, 6, 1. (b) Levanda, C.; Bechgaard, K.; Cowan, D. O. J . Org.
Chem. 1976, 41, 2700.
(11) (a) Nakao, H.; Hayashi, H.; Okita, K. Anal. Sci. 2001, 17, 545.
(b) Sakano, T.; Horie, M.; Osakada, K.; Nakao, H. Bull. Chem. Soc.
J pn. 2001, 74, 2059.

Notes
Organometallics, Vol. 22, No. 2, 2003 375
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Deta ils of
Refin em en t for 1 a n d 2
ethylene (0.17 V) and 1,4-diferrocenylbutadiene (0.13 V).
Thus, the ferrocenyl groups of 2 communicate with each
other through the nonconjugated metallacyclic part of
the complex.
1
2
chemical formula
formula wt
cryst syst
space group
a, Å
C
36H44O4FeP2PtSi
C42H48Fe2P2PtSi
949.66
Exp er im en ta l Section : (a ) Gen er a l Meth od s. All
manipulations of the complexes were carried out using
standard Schlenk techniques under an argon or a
nitrogen atmosphere. Hexane, toluene, and THF were
distilled from sodium/benzophenone and stored under
nitrogen. NMR spectra (1H, 13C{1H}, and 31P{1H}) were
recorded on a J EOL EX-400 spectrometer. Peak posi-
tions of the 31P{1H} NMR spectra were referenced to
an external 85% H3PO4. Elemental analyses were
carried out with a Yanaco MT-5 CHN autocorder. Cyclic
voltammetry was measured in CH2Cl2 solution contain-
ing 0.10 M Et4NBF4 with ALS Electrochemical Analyzer
Model-600A. The measurement was carried out in a
standard one-compartment cell under inert gas equipped
with an Ag+/Ag reference electrode, a platinum-wire
counter electrode, and a platinum disk working elec-
881.71
triclinic
P1h (no. 2)
11.983(6)
15.284(4)
10.600(2)
100.60(2)
97.21(3)
75.38(3)
1839.9
2
triclinic
P1h (no. 2)
12.496(4)
14.876(2)
11.432(3)
102.56(2)
108.54(8)
87.958(2)
1965.3
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
2
µ, mm-1
F(000)
4.331
880
1.591
4.404
948
1.605
D
calcd, g cm-3
cryst size, mm
0.32 × 0.40 × 0. 56 0.16 × 0.28 × 0.58
2θ range, deg
5.0-55.0
5.0-55.0
16
scan rate, deg min-1 16
no. of unique reflns
no. of used reflns
(I > 3σ(I))
no. of variables
R
8842
6999
9029
6507
trode. Pt(SiHPh2)2(PMe3)2,13 Pt(CZdCZ-SiPh2)(PMe3)2,9b
and ethynylferrocene14 were prepared according to the
literature method. Et4NBF4 for the electrochemical
measurement was recrystallized from methanol before
use.
406
0.052
0.051
433
0.070
0.074
Rw
2
Hz), 183.7 (dd, PtCd, J (CP) ) 11.0, 106.5 Hz), 193.6
(dd, PtCd, 2J (CP) ) 11.0, 101.0 Hz). 31P{1H} NMR (162
2
MHz, CDCl3): δ -28.8 (d, J (PP) ) 15.5 Hz, J (PPt) )
(b) P r ep a r a tion of P t(F cCdCH-SiP h 2-CZdCZ)-
(P Me3)2 (F c ) fer r ocen yl, Z ) COOMe) (1). A
2
1681 Hz), -27.8 (d, J (PP) ) 15.5 Hz, J (PPt) ) 2185
Hz).
solution of Pt(CZdCZ-SiPh2)(PMe3)2 (124 mg, 0.18
mmol) and ethynylferrocene (43 mg, 0.21 mmol) in
toluene (5 mL) was stirred at 60 °C for 48 h. The solvent
was removed under reduced pressure. Hexane was
added to the residue, which caused separation of an
orange solid. The product was collected by filtration,
washed with hexane two times (3 mL), and dried in
vacuo. Recrystallization from THF-hexane gave 1 as
(c) P r ep a r a tion of P t(F cCdCH-SiP h 2-CHdCF c)-
(P Me3)2 (2). To a toluene (7 mL) solution of ethynyl-
ferrocene (542 mg, 2.5 mmol) was added Pt(SiHPh2)2-
(PMe3)2 (737 mg, 1.0 mmol) at room temperature. After
the mixture was stirred for 12 h at 60 °C, an orange
solid was gradually generated. The product was col-
lected by filtration, washed with toluene two times (2
mL) and hexane (3 mL), and dried in vacuo. Yield 607
mg (62%). Recrystallization from THF-hexane gave red
crystals for X-ray crystallography. Anal. Calcd for
C42H48Fe2P2PtSi: C, 53.12; H, 5.09. Found: C, 53.30;
H, 5.04. 1H NMR (400 MHz, CDCl3): δ 0.87 (d, P(CH3),
18H, 2J (HP) ) 7.9 Hz, 3J (HPt) ) 16.8 Hz), 4.07 (m, 2H,
C5H4), 4.13 (m, 2H, C5H4), 4.19 (s, 10H, Cp), 4.43 (m,
2H, C5H4), 4.47 (m, 2H, C5H4), 7.15 (d, 2H, dCH, 4J (HP)
orange crystals (102 mg, 63%). Anal. Calcd for C36H44
-
FeO4P2PtSi: C, 49.04; H, 5.03. Found: C, 48.87; H, 5.15.
1H NMR (400 MHz, CDCl3): δ 1.00 (d, P(CH3), 9H,
3
2J (HP) ) 8.4 Hz, J (HPt) ) 19.6 Hz), 1.20 (d, P(CH3),
2
3
9H, J (HP) ) 8.4 Hz, J (HPt) ) 17.2 Hz), 3.26 (s, 3H,
OCH3), 3.78 (s, 3H, OCH3), 4.09 (m, 1H, C5H4), 4.13 (s,
6H, Cp and one proton signal of C5H4 group), 4.43 (m,
1H, C5H4), 4.64 (m, 1H, C5H4), 7.08 (dd, 1H, dCH,
3
4J (HP) ) 2.4, 19.2 Hz, J (HPt) ) 116.7 Hz), 7.27-7.31
3
) 15.6 Hz, J (HPt) ) 123.9 Hz), 7.23 (m, 3H, C6H5-m
(m, 6H, C6H5-m and -p), 7.45 (m, 2H, C6H5-o), 7.76 (m,
2H, C6H5-o). 13C{1H} NMR (100 MHz, CDCl3): δ 16.6
(d, P(CH3)3, J (CP) ) 11.0 Hz), 17.0 (d, P(CH3)3, J (CP)
) 12.9 Hz), 50.5 (OCH3), 51.2 (OCH3), 66.1 (d, C5H4-2,
4J (CP) ) 5.5 Hz, 3J (CPt) ) 29.5 Hz), 67.0 (C5H4-3), 67.8
and -p), 7.35 (m, 3H, C6H5-m and -p), 7.66 (m, 4H, C6H5-
o). 13C{1H} NMR (100 MHz, CDCl3): δ 17.1 (m, P(CH3)3),
66.2 (C5H4-3), 66.8 (C5H4-3), 68.7 (C5H4-2, 3J (CPt) )
3
29.4 Hz), 69.7 (Cp), 70.5 (C5H4-2, J (CPt) ) 46.0 Hz),
101.8 (apparent triplet, C5H4-1, 3J (CP) ) 7.4 Hz, 2J (CPt)
) 55.0 Hz), 125.6 (SiC), 2J (CPt) ) 22.0 Hz), 126.9
(C6H5-m), 127.5 (C6H5-p), 127.6 (C6H5-m), 128.1 (C6H5-
p), 135.0 (C6H5-o), 135.8 (C6H5-o), 141.1 (C6H5-i), 142.8
(C6H5-i), 189.0 (dd, PtCd, 2J (CP) ) 11.0, 110.1 Hz).
31P{1H} NMR (162 MHz, CDCl3): δ -28.7 (J (PPt) )
1782 Hz).
(d ) Cr ysta l Str u ctu r e Deter m in a tion . Crystals of
1 and 2 were mounted in glass capillary tubes under
Ar. Intensities were collected for Lorentz and polariza-
tion effects on a Rigaku AFC-5R automated four-cycle
diffractometer by using Mo KR radiation (λ ) 0.71069
Å) and the ω-2θ scan method, and an empirical
absorption correction (Ψ scan) was applied. Calculations
were carried out by using the program package teXsan
3
(C5H4-3), 70.1 (Cp), 71.2 (C5H4-2, J (CPt) ) 49.6 Hz),
97.1 (apparent triplet, C5H4-1, 3J (CP) ) 7.3 Hz, 2J (CPt)
) 40.4 Hz), 120.7 (d, SiC(H)d, 3J (CP) ) 3.6 Hz, 2J (CPt)
) 16.6 Hz), 127.2 (C6H5-m), 127.3 (C6H5-m), 128.3
(C6H5-p), 128.4 (C6H5-p), 135.0 (C6H5-o), 135.8 (C6H5-
o), 137.9 (C6H5-i), 140.1 (C6H5-i), 141.8 (br, SiC(Z)d),
3
2
171.5 (d, PtCCdO, J (CP) ) 10.9 Hz, J (CPt) ) 107.4
Hz), 176.1 (d, SiCCdO, 4J (CP) ) 5.5 Hz, 3J (CPt) ) 20.2
(12) Ribou, A.-C.; Launay, J .-P.; Sachtleben, M. L.; Li, H.; Spangler,
C. W. Inorg. Chem. 1996, 35, 3735.
(13) Kim, Y.-J .; Park, J .-I.; Lee, S.-C.; Osakada, K.; Tanabe, M.; Choi,
J .-C.; Koizumi, T.; Yamamoto, T. Organometallics 1999, 18, 1349-
1352.
(14) Doisneau, G.; Balavoine, G.; Fillebeen-Khan, T. J . Organomet.
Chem. 1992, 425, 113.

376 Organometallics, Vol. 22, No. 2, 2003
Notes
for Windows. Atomic scattering factors were obtained
from the literature.15 A full-matrix least-squares refine-
ment was used for non-hydrogen atoms with anisotor-
opic thermal parameters. Hydrogen atoms were located
by assuming the ideal geometry and included in the
structure calculation without further refinement of the
parameters. Crystallographic data and details of refine-
ment of 1 and 2 were summarized in Table 1.
Ack n ow led gm en t. This work was supported by
Grants-in-Aid for Scientific Research from the Ministry
of Education, Science, Sports, Culture, and Technology,
J apan and from the J apan Society for the Promotion of
Science (J SPS). M.T. is grateful to the fellowship from
J SPS.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for 1 and 2. This material is available free of charge via
the Internet at http://pubs.acs.org.
(15) International Tables for X-ray Crystallography; Kynoch: Bir-
mingham, England, 1974; Vol. 4.
OM020733N