Binuclear cyclometalated organoplatinum complexes containing 1,1′-bis(diphenylphosphino)ferrocene as spacer ligand: Kinetics and mechanism of Mel oxidative addition

Article abstract of DOI:10.1021/ic701910d

The binuclear complex [Pt₂Me₂(ppy) ₂(μ-dppf)], 1, in which ppy = deprotonated 2-phenylpyridyl and dppf = 1,1′-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe₂)(ppy)] with 0.5 equiv of dppf at room temperature. In this reaction when 1 equiv of dppf was used, the dppf chelating complex 2, [PtMe(dppf)(ppy-κ¹C)], was obtained. The reaction of Pt(II)-Pt(II) complex 1 with excess MeI gave the Pt(IV)-Pt(IV) complex [Pt ₂l₂Me₄(ppy)₂(μ-dppf)], 3. When the reaction was performed with 1 equiv of MeI, a mixture containing unreacted complex 1, a mixed-valence Pt(II)-Pt(IV) complex [PtMe(ppy)(μ-dppf)PtlMe ₂(ppy)], 4, and complex 3 was obtained. In a comparative study, the reaction of [PtMe(SMe₂)(ppy)] with 1 equiv of monodentate phosphine PPh₃ gave [PtMe(ppy)(PPh₃)], A. MeI was reacted with A to give the platinum(IV) complex [PtMe₂I(ppy)(PPh₃)], C. All the complexes were fully characterized using multinuclear (¹H, ³¹P, ¹³C, and ¹⁹⁵Pt) NMR spectroscopy, and complex 2 was further identified by single crystal X-ray structure determination. The reaction of binuclear Pt(II)-Pt(II) complex 1 with excess MeI was monitored by low temperature ³¹P NMR spectroscopy and further by ¹H NMR spectroscopy, and the kinetics of the reaction was studied by UV-vis spectroscopy. On the basis of the data, a mechanism has been suggested for the reaction which overall involved stepwise oxidative addition of MeI to the two Pt(II) centers. In this suggested mechanism, the reaction proceeded through a number of Pt(II)-Pt(IV) and Pt(IV)-Pt(IV) intermediates. Although MeI in each step was trans oxidatively added to one of the Pt(II) centers, further trans to cis isomerizations of Me and I groups were also identified. A comparative kinetic study of the reaction of monomeric platinum(II) complex A with MeI was also performed. The rate of reaction of MeI with complex 1 was some 3.5 times faster than that with complex A, indicating that dppf in the complex 1, as compared with PPh₃ in the complex A, has significantly enhanced the electron richness of the platinum centers.

Full text of DOI:10.1021/ic701910d

Inorg. Chem. 2008, 47, 5441-5452
Binuclear Cyclometalated Organoplatinum Complexes Containing
1,1′-Bis(diphenylphosphino)ferrocene as Spacer Ligand: Kinetics and
Mechanism of MeI Oxidative Addition
Sirous Jamali,*,† S. Masoud Nabavizadeh,‡ and Mehdi Rashidi‡
Chemistry Department, Persian Gulf UniVersity, Bushehr 75169, Iran, and Chemistry Department,
College of Sciences, Shiraz UniVersity, Shiraz 71454, Iran
Received September 27, 2007
The binuclear complex [Pt2Me2(ppy)2(µ-dppf)], 1, in which ppy ) deprotonated 2-phenylpyridyl and dppf ) 1,1′-
bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(ppy)] with 0.5 equiv of dppf at
room temperature. In this reaction when 1 equiv of dppf was used, the dppf chelating complex 2, [PtMe(dppf)(ppy-
κ1C)], was obtained. The reaction of Pt(II)-Pt(II) complex 1 with excess MeI gave the Pt(IV)-Pt(IV) complex
[Pt2I2Me4(ppy)2(µ-dppf)], 3. When the reaction was performed with 1 equiv of MeI, a mixture containing unreacted
complex 1, a mixed-valence Pt(II)-Pt(IV) complex [PtMe(ppy)(µ-dppf)PtIMe2(ppy)], 4, and complex 3 was obtained.
In a comparative study, the reaction of [PtMe(SMe2)(ppy)] with 1 equiv of monodentate phosphine PPh3 gave
[PtMe(ppy)(PPh3)], A. MeI was reacted with A to give the platinum(IV) complex [PtMe2I(ppy)(PPh3)], C. All the
complexes were fully characterized using multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy, and complex 2
was further identified by single crystal X-ray structure determination. The reaction of binuclear Pt(II)-Pt(II) complex
1 with excess MeI was monitored by low temperature 31P NMR spectroscopy and further by 1H NMR spectroscopy,
and the kinetics of the reaction was studied by UV-vis spectroscopy. On the basis of the data, a mechanism has
been suggested for the reaction which overall involved stepwise oxidative addition of MeI to the two Pt(II) centers.
In this suggested mechanism, the reaction proceeded through a number of Pt(II)-Pt(IV) and Pt(IV)-Pt(IV)
intermediates. Although MeI in each step was trans oxidatively added to one of the Pt(II) centers, further trans to
cis isomerizations of Me and I groups were also identified. A comparative kinetic study of the reaction of monomeric
platinum(II) complex A with MeI was also performed. The rate of reaction of MeI with complex 1 was some 3.5
times faster than that with complex A, indicating that dppf in the complex 1, as compared with PPh3 in the complex
A, has significantly enhanced the electron richness of the platinum centers.
1. Introduction
applications in many fields, such as photocatalysts,1e–g
metallomesogens,2 and optoelectronic devices.3 Square planar
cyclometalated platinum complex species were also used as
“building blocks” for complex systems such as self-assembly
and supramolecular entities.4
Cyclometalated platinum complexes have recently at-
tracted1–4 a great deal of attention because of their potential
* To whom correspondence should be addressed. E-mail: sirjamali@
pgu.ac.ir.
†
Persian Gulf University.
Shiraz University.
(2) (a) Slater, J. W.; Lydon, D. P.; Rourke, J. P. J. Organomet. Chem.
2002, 645, 246. (b) Lydon, D. P.; Rourke, J. P. J. Chem. Soc., Chem.
Commun. 1997, 1741. (c) Ghedini, M.; Pucci, D.; Crispini, A.;
Barberio, G. Organometallics 1999, 18, 2116.
‡
(1) (a) Gallego, C.; Martinez, M.; Safont, V. S. Organometallics 2007,
26, 527. (b) Bernhardt, P. V.; Gallego, C.; Martinez, M.; Parella, T.
Inorg. Chem. 2002, 41, 1747. (c) Crespo, M.; Font-Bardia, M.; Solans,
X. Organometallics 2004, 23, 1708. (d) Thomas, S. W., III; Venkate-
san, K.; Muller, P.; Swager, T. M. J. Am. Chem. Soc. 2006, 128, 16641.
(e) Zhang, D.; Wu, L.-Z.; Zhou, L.; Han, X.; Yang, Q.-Z.; Zhang,
L.-P.; Tung, C.-H. J. Am. Chem. Soc. 2004, 126, 3440. (f) Connick,
W. B.; Gray, H. B. J. Am. Chem. Soc. 1997, 119, 11620. (g) Hissler,
M.; McGarrah, J. E.; Connick, W. B.; Geiger, D. K.; Cummings, S. D.;
Eisenberg, R. Coord. Chem. ReV. 2000, 208, 115.
(3) (a) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem. ReV.
2006, 250 (15-16), 2093. (b) Lu, W.; Mi, B.-X.; Chan, M. C. W.;
Hui, Z.; Che, C.-M.; Zhu, N.; Lee, S.-T. J. Am. Chem. Soc. 2004,
126, 4958. (c) Wong, W.-Y.; He, Z.; So, S.-K.; Tong, K.-L.; Lin, Z.
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Juiz, S.; Vila, J. M.; Pereira, M. T. Organometallics 2001, 20, 1350.
10.1021/ic701910d CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 12, 2008 5441
Published on Web 05/17/2008

Jamali et al.
1,1′-bis(diphenylphosphino)ferrocene, dppf, has exten-
sively been used as a very useful bidentate ligand in many
chelating, binuclear, and cluster complexes of transition
metals.5 In the present work, a new binuclear complex was
synthesized by connecting two cyclometalated organoplati-
num(II) species, containing a deprotonated 2-phenylpyridyl
(ppy) ligand, with dppf as a spacer ligand, combining the
individual properties of these two ligands in one molecular
system. The platinum(II) centers in this complex underwent
oxidative addition of MeI to give the corresponding binuclear
Pt(IV)-Pt(IV) complex. On the basis of low temperature
31P NMR studies, we have shown that this reaction would
occur via different steps involving binuclear Pt(II)-Pt(IV)
and Pt(IV)-Pt(IV) intermediates in which the Pt(IV) centers
performed some interesting facile trans-cis isomerizations.
Although cis-trans isomerization of square-planar platinu-
m(II) complexes is an interesting subject and has extensively
been studied,6 the isomerization involving Pt(IV) centers,
which is expected to occur via a dissociative pathway, is
not common.7
Oxidative addition is a fundamental reaction in many
catalytically important processes.8,9 The reactions involving
addition of a variety of reagents to mononuclear square-
planar organoplatinum(II) complexes have been extensively
studied.10,11 However, the reactions involving binuclear
platinum(II) complexes which help in understanding the
neighborhood effects of the metallic centers have not been
studied much. We have recently studied the oxidative
addition of MeI to a binuclear organoplatinum(II) complex
and found that the bridging diphosphine ligand conveys
electronic influences among the metals.12 It is well-known
that in ferrocene complexes, when a reaction is taking place
in one of the cyclopentadienyl rings, the electronic informa-
tion is transferred to the second ring via the iron atom. In
the present work, we have studied the kinetics of reaction
of MeI with the above binuclear cyclometalated organo-
platinum complex in an attempt to test the cooperative effect
of the platinum(II) centers connected to each other by 1,1′-
bis(diphenylphosphino)ferrocene ligand. Such studies may
be useful in the quantitative assessment of electronic
transformations among the cyclopentadienyl rings.
2. Experimental Section
1
The H, 13C, 31P and 195Pt NMR spectra were recorded on a
Bruker Avance DRX 500-MHz spectrometer. The operating
frequencies and references, respectively, are shown in parentheses
1
as follows: H (500 MHz, TMS), 13C (125 MHz, TMS), 31P (202
MHz, 85% H3PO4), and 195Pt (107 MHz, aqueous Na2PtCl4).
Monitoring the 1H NMR spectra were recorded on a Bruker Avance
DPX 250 MHz spectrometer. The chemical shifts and coupling
constants are in ppm and Hz, respectively. Kinetic studies were
carried out by using a Perkin-Elmer Lambda 25 spectrophotometer
with temperature control using an EYELA NCB-3100 constant-
temperature bath. 2-Phenylpyridine and 1,1′-bis(diphenylphosphi-
no)ferrocene were purchased from commercial sources, and [PtMe2(µ-
SMe2)]2 was prepared as described previously.13 The in situ yellow
solution of [PtMe(ppy)(SMe2)] in acetone was prepared as reported:14
2-phenylpyridine (100 µL, 0.7 mmol) was added dropwise via
syringe to a solution of [PtMe2(µ-SMe2)]2 (200 mg, 0.35 mmol) in
20 mL of acetone at room temperature in air. The solution
immediately turned yellow, and small bubbles formed. This was
stirred for 1.5 h and used freshly.
[Pt2Me2(ppy)2(µ-dppf)], 1. To the above in situ solution of
[PtMe(ppy)(SMe2)] was added 0.5 equiv of dppf (193 mg, 0.35
mmol), and the solution was further stirred for 1 h. A bright yellow
solid was precipitated which was separated and dried under vacuum.
Yield: 268 mg, 68%. Anal. Calcd for C58H50FeN2P2Pt2: C, 54.2;
H, 3.9; N, 2.1; Found: C, 54.2; H, 4.0; N, 2.3. NMR data in CDCl3:
(5) (a) Bandoli, G.; Dolmella, A. Coord. Chem. ReV. 2000, 209, 161. (b)
Canales, F.; Gimeno, M. C.; Laguna, A.; Jones, P. G. Organometallics
1996, 15, 3412. (c) Diez, J.; Gamasa, M. P.; Gimeno, J.; Aguirre, A.;
Garcia-Granda, S.; Holubova, J.; Falvello, L. R. Organometallics 1999,
18, 662. (d) Low, P. M. N.; Tan, A. L.; Hor, T. S. A.; Wen, Y.-S.;
Liu, L.-K. Organometallics 1996, 15, 2595.
(6) (a) Tobe, M. L.; Burgess, J. Inorganic Reaction Mechanism; Longman:
Essex, U.K., 1999. (b) Vicente, J.; Arcas, A.; Galvez-Lopez, M.-D.;
Jones, P. G. Organometallics 2006, 25, 4247.
δ(1H) 0.97(d, 6H, JPtH ) 83.4 Hz, JPH ) 7.7 Hz, 2 Me), 4.36(br
s, 4H, ꢀ, ꢀ′ Cp protons), 4.39(br s, 4H, R, R′ Cp protons), (aromatic
protons): 6.45(m, 2H, 3JPtH ) 12.9 Hz, 3JHH ) 1.4 Hz, CH groups
adjacent to coordinated C atoms), 7.1-7.8(m, 32H, overlapping
2
3
(7) (a) von Zelewsky, A.; Suckling, A. P.; Stoeckli-Evans, H. Inorg. Chem.
1993, 32, 4585. (b) Hughes, R. P.; Meyer, M. A.; Tawa, M. D.; Ward,
A. J.; Williams, A.; Rheingold, A. L.; Zakharov, L. N. Inorg. Chem.
2004, 43, 747.
3
multiplets), 7.95(m, 2H, JPtH ) 45.9, 2 CH groups adjacent to
1
2
coordinated N atoms); δ(13C) -13.5 (d, 2C, JPtC ) 732 Hz, JPC
) 6 Hz, 2 Me), 73.9(d, 4C, 3JPC ) 8 Hz, ꢀ, ꢀ′ Cp Cs), 75.7(d, 4C,
2JPC ) 11 Hz, R, R′ Cp Cs), 76.7 (d, 2C, 1JPC ) 47 Hz, 2JPtC ) 33
(8) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Fink, R. J. Principles
and Application of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1987. (b) Crabtree, R. H. Organo-
metallic Chemistry of the Transition Metals; 3rd ed.; John Wiley &
Sons: New York, 2001. (c) Atwood, J. D. Inorganic and Organome-
tallic Reaction Mechanism; 2nd ed.; Wiley-VCH: New York, 1997.
(9) (a) Manna, J.; Kuehl, C. J.; Whiteford, J. A.; Stang, P. J. Organo-
metallics 1997, 16, 1897. (b) Fraser, C. S. A.; Eigler, D. J.; Jennings,
M. C.; Puddephatt, R. J. J. Chem. Soc., Chem. Commun. 2002, 1224.
(c) Fraser, C. S. A.; Jennings, M. C.; Puddephatt, R. J. J. Chem. Soc.,
Chem. Commun. 2001, 1310. (d) Achar, S.; Puddephatt, R. J. J. Chem.
Soc., Chem. Commun. 1994, 1895. (e) Barrios-Landeros, F.; Hartwig,
J. F. J. Am. Chem. Soc. 2005, 127, 6944. (f) Alcazar-Roman, L. M.;
Hartwig, J. F. Organometallics 2002, 21, 491.
Hz, ipso Cp Cs), 118.7(s, JPC ≈ 12 Hz), 121.6(s), 123.6(d, JPC
)
5 Hz, JPtC ≈ 38 Hz), 124.2(s), 128.1(d, JPC ) 9.5 Hz), 129.7(d, JPC
) 7 Hz, JPtC ) 63 Hz), 130(d, JPC ) 1 Hz), 132.2 (s, JPtC ) 90
Hz), 134(s), 134.3 (d, JPC ) 12 Hz), 136.9(s), 147.7(s, JPtC
≈
1
6 Hz), 150.6 (d, JPtC ≈ 12 Hz, JPC ) 5 Hz), 164.5(d, 2C, JPtC
)
2
942 Hz, JPC ) 123 Hz, C atoms of the ppy ligands connected to
Pt atoms), 167.0(d, JPtC ) 70 Hz, JPC ) 6 Hz; δ(31P) 24.1 (1JPtP
)
1
2092 Hz, 2P of dppf); δ(195Pt) -537 (d, JPtP ) 2090 Hz, 2Pt).
[PtMe(dppf)(ppy-K1C)], 2. To the above in situ solution of
[PtMe(ppy)(SMe2)] was added 1 equiv of dppf (386 mg, 0.7 mmol),
(10) Rendina, L. M.; Puddephatt, R. J. Chem. ReV. 1997, 97, 1735.
(11) (a) Rashidi, M.; Esmaeilbeig, A. R.; Shahabadi, N.; Tangestaninejad,
S.; Puddephatt, R. J. J. Organomet. Chem. 1998, 568, 53. (b) Rashidi,
M.; Momeni, B. Z. J. Organomet. Chem. 1999, 574, 286. (c) Rashidi,
M.; Nabavizadeh, S. M.; Hakimelahi, R.; Jamali, S. J. Chem. Soc.,
Dalton Trans. 2001, 3430. (d) Rashidi, M.; Shahabadi, N.; Nabaviza-
deh, S. M. Dalton Trans. 2004, 619. (e) Rashidi, M.; Nabavizadeh,
S. M.; Akbari, A.; Habibzadeh, S. Organometallics 2005, 24, 2528.
(f) De Felice, V.; Giovannitti, B.; De Renzi, A.; Tesauro, D.; Panunzi,
A. J. Organomet. Chem. 2000, 593-594, 445.
(12) Jamali, S.; Nabavizadeh, S. M.; Rashidi, M. Inorg. Chem. 2005, 44,
8594.
(13) Hill, G. S.; Irwin, M. J.; Levy, C. J.; Rendina, L. M.; Puddephatt,
R. J. Inorg. Synth. 1998, 32, 149.
(14) Owen, J. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2004,
126, 8247.
5442 Inorganic Chemistry, Vol. 47, No. 12, 2008

Binuclear Cyclometalated Organoplatinum Complexes
and the solution was further stirred for 1 h. A bright yellow solution
was formed, then the solvent was removed under reduced pressure
and the residue was triturated with ether (2 × 3 mL). The product
as a yellow solid was dried under vacuum. Yield: 508 mg, 79%.
Anal. Calcd for C46H39FeNP2Pt: C, 60.1; H, 4.3; N, 1.5; Found: C,
60.3; H, 4.5; N, 1.7. NMR data in CDCl3: δ(1H) 0.27(dd, 3H, 2JPtH
[PtMe(ppy)(µ-dppf)PtIMe2(ppy)], 4. In the above procedure,
used to prepare complex 3, when complex 1 (100 mg in 20 mL of
chloroform) was reacted with 1 equiv of MeI (4.8 µL, 0.078 mmol),
then complex 4 was obtained as a mixture with 3 and the starting
complex 1, in approximately 1:1:1 mol ratio, and the components
of the mixture were not isolable. NMR data for complex 4 in CDCl3:
2
3
δ(1H) 0.84[d, 3H, JPtH ) 88.5 Hz, JPH ) 7.7 Hz, Me ligand on
3
) 66.5 Hz, JPH ) 6.7 Hz, Me), 3.54, 3.68, 4.04(each a br s, 1H,
Pt(II) center], 1.09[d, 3H, 2JPtH ) 61.0 Hz, 3JPH ) 7.6 Hz, Me ligand
1H, 2H, respectively, ꢀ, ꢀ′ Cp protons), 4.35, 4.38, 4.42, 4.65(each
a br s, 4H, R, R′ Cp protons), (aromatic protons): 6.72 (m, 2H,
3JPtH ) 14.1 Hz, different CH groups adjacent to coordinated C
atoms), 6.9-7.9(overlapping multiplets), 8.5(m, 2H, CH groups
2
3
trans to P on Pt(IV) center], 1.53[d, 3H, JPtH ) 71.1 Hz, JPH
)
7.8 Hz, Me ligand trans to N on Pt(IV) center], 3.35, 3.52[each a
br s, 2H, ꢀ, ꢀ′ Cp protons in the Pt(IV) site], 3.74, 3.86(each a br
s, 2H, R, R′ Cp protons in the Pt(IV) site), 3.90, 4.04[each a br s,
2H, ꢀ, ꢀ′ Cp protons in the Pt(II) site], 4.08, 4.14[each a br s, 2H,
R, R′ Cp protons in the Pt(II) site], (aromatic protons): mostly
overlapped with the aromatic protons of complexes 1 and 3, 7.8[m,
1H, CH group adjacent to coordinated N atom, on Pt(II) site],
1
adjacent to coordinated N atoms); δ(13C) 5.4(dd, 1C, JPtC ) 610
Hz, 2JPC ) 7 and 92 Hz, Me ligand), 70.9, 71.1, 72.4, 72.7(each a
3
2
doublet, 4C, with JPC ) 5 Hz, ꢀ, ꢀ′ Cp Cs), [74.0(d, 1C, JPC
)
)
8 Hz), 74.2(d, 1C, 2JPC ) 8 Hz), 75.2(d, 1C, 2JPC ) 10 Hz, 3JPtC
2
3
12 Hz), 75.8(d, 1C, JPC ) 11 Hz, JPtC ) 18 Hz), R, R′ Cp Cs],
3
9.35[d, 1H, JHH ) 5.3 Hz, JPtH ≈ 12 Hz, CH group adjacent to
[78.1(dd, 1C, 1JPC ) 48 Hz, 3JPC ) 4 Hz, 2JPtC ) 45 Hz), 80.0 (dd,
coordinated N atom, on Pt(IV) site]; 6.43(m, 1H, 3JPtH ) 12.0 Hz,
CH group adjacent to coordinated C atom on Pt(II) site), 6.69[m,
1H, CH group adjacent to coordinated C atom on Pt(IV) site]; δ(31P)
1
3
2
1C, JPC ) 47 Hz, JPC ) 4 Hz, JPtC ) 50 Hz), ipso Cp Cs],
166.9(dd, 1C, JPC ) 11 Hz, JPC ) 120 Hz, JPtC ) 892 Hz, C
2
2
1
atom of the ppy ligand connected to Pt atom), other aromatic Cs
-13.2[s, 1JPtP ) 990 Hz, 1P of dppf on Pt(IV) site], 23.9[s, 1JPtP
)
2
1
were not assigned; δ(31P) 20.5(d, JPP ) 15 Hz, JPtP ) 1888 Hz,
2090 Hz, 1P of dppf on Pt(II) site]; δ(195Pt) -538 [d, 1JPtP ) 2088
2
1
1P trans to Me), 23.9(d, JPP ) 15 Hz, JPtP ) 1995 Hz, 1P trans
1
Hz, Pt(II)], 315[d, JPtP ) 985 Hz, Pt(IV)].
to ppy); δ(195Pt) -2890(dd, JPtP ) 1883 Hz and 1990, Pt).
1
[PtMe(ppy)(PPh3)], A. To the above in situ solution of [PtMe-
(ppy)(SMe2)] was added 1 equiv of PPh3 (183.5 mg, 0.7 mmol)
and the solution was further stirred for 1 h. A yellow solution was
formed, and 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: 352 mg, 80%.
Anal. Calcd for C30H26NPPt: C, 57.5; H, 4.2; N, 2.2; Found: C,
57.2; H, 4.1; N, 2.5. NMR data in CDCl3: δ(1H) 0.78 (d, 3H, 2JPtH
[Pt2I2Me4(ppy)2(µ-dppf)], 3. An excess of MeI (50 µL) was
added to a solution of complex 1 (100 mg in 20 mL of chloroform)
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
an orange solid was dried under vacuum. Yield: 73 mg, 60%. Anal.
Calcd for C60H56I2FeN2P2Pt2: C, 45.8; H, 3.6; N, 1.8; Found: C,
2
45.3; H, 3.7; N, 1.8. NMR data in CDCl3: δ(1H) 1.07(d, 6H, JPtH
3
) 83.0 Hz, JPH ) 8.0 Hz, Me ligand), (aromatic protons): 6.49
3
) 61.0 Hz, JPH ) 7.6 Hz, 2 Me groups trans to P), 1.44(d, 3H,
3
4
(m, 1H, JPtH ) 11.3 Hz, JPH ) 1.5 Hz CH group adjacent to
coordinated C atom), 7.1-7.8 (overlapping multiplets), 8.1 (m, 1H,
3
2JPtH ) 70.8 Hz, JPH ) 7.8 Hz, 1 Me group trans to N), 1.46 (d,
3H, 2JPtH ) 70.9 Hz, 3JPH ) 7.9 Hz, 1 Me group trans to N), 3.01,
3.10, 3.18, 3.25(each a br s, 4H, ꢀ, ꢀ′ Cp protons), 3.58, 3.62,
3.63(each a br s, 1H, 2H, 1H, respectively, R, R′ Cp protons),
CH group adjacent to coordinated N atom); δ(31P) 33.2 [s, 1JPtP
)
2105 Hz, 1P of PPh3].
[PtMe2I(ppy)(PPh3)], C. An excess of MeI (100 µL) was added
to a solution of complex [PtMe(ppy)(PPh3)], A, (100 mg, 0.16 mmol
in 20 mL of acetone) at room temperature. The mixture was allowed
to stand at this condition for 1 h, and then the solvent was removed
under reduced pressure. The residue was washed twice with ether,
and the product was dried under vacuum. Yield: 103 mg, 84%.
Anal. Calcd for C31H29INPPt: C, 48.4; H, 3.8; N, 1.8; Found: C,
3
3
(aromatic protons): 6.66(d, 1H, JPtH ) 42.8 Hz, JHH ) 7.8, CH
3
group adjacent to coordinated C atom), 6.71(d, 1H, JPtH ) 43.0
Hz, JHH ) 7.8, CH group adjacent to coordinated C atom),
6.8-7.7(overlapping multiplets), 9.39 (d, 1H, JHH ) 5.1 Hz, JPtH
3
3
≈ 7 Hz, CH group adjacent to coordinated N atom), 9.43(d, 1H,
3
JHH ) 5.2 Hz, JPtH ≈ 7 Hz, CH group adjacent to coordinated N
atom); δ(13C) -6.3(d, 1C, 1JPtC ) 637 Hz, 2JPC ) 3 Hz, Me trans
2
48.6; H, 3.7; N, 1.9. NMR data in CDCl3: δ(1H) 1.28(d, 3H, JPtH
1
2
to N), -6.2(d, 1C, JPtC ) 637 Hz, JPC ) 3 Hz, Me trans to N),
3
) 60.7 Hz, JPH ) 7.5 Hz, Me ligand trans to P), 1.65 (d, 3H,
1
2
6.1(d, 1C, JPtC ) 491 Hz, JPC ) 112 Hz, Me trans to P), 6.2(d,
3
2JPtH ) 70.8 Hz, JPH ) 7.7 Hz, Me ligand trans to N), (aromatic
1JPtC ) 492 Hz, JPC ) 112 Hz, Me trans to P), 71.8, 72.1, 72.6,
2
protons): 6.7-7.7 (overlapping multiplets), 9.7 (d, 1H, JHH ) 5.3
73.0(each a doublet, 4C, with 3JPC ) 8 Hz, ꢀ, ꢀ′ Cp Cs) 74.0, 74.1,
74.8(each a doublet, 1C, 1C, 2C, respectively, with 2JPC ) 11 Hz,
3JPtC ≈ 6 Hz, R, R′ Cp Cs), 75.6, 75.9(each a doublet, 2C, with
3
Hz, JPtH ≈ 10 Hz, CH group adjacent to coordinated N atom);
1
δ(31P) -9.2 [s, JPtP) 961 Hz, 1P of PPh3].
Kinetic Study. In a typical experiment, a solution of complex 1
in CHCl3 (3 mL, 1.5 × 10-4 M) in a cuvette was thermostatted at
25 °C, and a known excess of MeI was added using a microsyringe.
After rapid stirring, the absorbance at λ ) 360 nm was monitored
with time.
X-ray Structure Determination. Single crystals of [PtMe(dp-
pf)(ppy-κ1C)], 2, were grown from a concentrated chloroform
solution by slow diffusion of hexane. A yellow needle of ap-
proximate 0.15 × 0.08 × 0.05 mm in size was mounted on a glass
fiber. All measurements were made on a STOE IPDSII diffracto-
meter with graphite monochromator using Mo KR radiation. The
data were collected and integrated using the Stoe X-AREA15
software package. Crystal data, data collection, and structure
refinement details are listed in Table 1. A numerical absorption
1JPC ) 18 Hz, JPtC ) 27 Hz, ipso Cp Cs), 147.7, 147.8(each a
2
doublet, 2C, with 2JPC ) 5 Hz, 1JPtC ) 880 Hz, C atoms of the ppy
ligands connected to Pt atoms), other aromatic Cs were not assigned;
δ(31P) -13.3(s, 1JPtP ) 990 Hz, 1P), -13.4(s, 1JPtP ) 990 Hz, 1P);
δ(195Pt) 316 and 317(2 overlapping d, each with 1JPtP ) 990 Hz, 2
Pt).
This reaction was also monitored by 31P and 1H NMR spectros-
copy at low and room temperature, respectively, in an NMR tube
as follows: a small sample (10 mg) of 1 was dissolved in CDCl3
(0.75 mL) in a sealed NMR tube, and while the tube was cooled
by liquid N2 (when necessary), an excess of MeI was added. The
NMR spectra were recorded several times over about 4 h until the
mixture was gradually converted to complex 3 in solution.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5443

Jamali et al.
Table 1. Crystal Data, Data Collection and Structure Refinement
Details for Complex 2
When the above solution of [PtMe(SMe2)(ppy)] was
reacted with 1 equiv of dppf, the monomeric complex
[PtMe(dppf)(ppy-κ1C)], 2, was obtained. The strong chelating
ability of dppf has forced the Pt-N bonding of the cyclo-
metalated part to break up and form the unusual monodentate
Pt(ppy-κ1C) complex 2. This complex did not react with MeI
probably because the bulky ortho substitution on the aryl
ligand, which is an aromatic group, prevented the reaction
to occur.
When 1 equiv of PPh3 was reacted with the in situ solution
of [PtMe(SMe2)(ppy)] in acetone, a yellow solid product was
obtained which was identified as [PtMe(ppy)(PPh3)], A.
Reaction of the Pt(II)-Pt(II) binuclear complex 1 with
excess methyl iodide at room temperature led to formation
of the binuclear Pt(IV)-Pt(IV) complex 3 as the only
product. The reported platinum complexes containing dppf
ligand are usually square-planar Pt(II) complexes,5a and
therefore the binuclear Pt(IV)-Pt(IV) complex 3 is an
interesting example of dppf complexes. When complex 1
was reacted with 1 equiv of MeI, the mixed-valence
Pt(II)-Pt(IV) complex 4 was formed as a mixture with the
Pt(IV)-Pt(IV) complex 3 along with some unreacted starting
complex 1. This indicates that MeI has been oxidatively
added to one of the Pt(II) centers of the Pt(II)-Pt(II) starting
complex 1 to give the Pt(II)-Pt(IV) complex 4 and in parallel
has been added to the Pt(II) center of complex 4 to give the
final product Pt(IV)-Pt(IV) complex 3. Because the amount
of MeI has not been enough for completing the process, some
starting complex 1 has remained unreacted. As mentioned
above, when excess MeI was used, only the final product
complex 3 was obtained.
formula
C46H39FeNP2Pt
918.65
293(2)
formula weight
temperature/K
wavelength/Å
crystal system
space group
a/Å
0.71073
orthorhombic
P212121 (No. 19)
10.6124(9)
11.7917(13)
30.138(3)
3771.5(6)
4
1.618
4.209
numerical
0.674/0.810
1824
b/Å
c/Å
vol/Å3
Z
D(calc)/Mg m-3
Abs coeff/mm-1
abs. correction
Tmin/Tmax
F(000)
no. of reflns
no. of independent reflns
no. of observed reflns [I > 2σ(I)]
GooF (F2)
20966
8835[R(int) ) 0.0292]
8371
1.114
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.0231, 0.0442
0.0265, 0.0452
correction was applied using the X-RED16 and X-SHAPE17
software programs. The data were corrected for Lorentz and
polarization effects. No decay correction was applied. The structure
was solved by direct methods.18 All of the non-hydrogen atoms
were refined anisotropically. All of the hydrogen atoms were located
in ideal positions except C37-C46 hydrogens that placed in the
different Fourier map. Molecular graphics were performed using
the ORTEP319 and WinGX20 crystallographic software programs.
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
no. 687007. Copies of this information may be obtained free of
charge from the Director, CCDC, 12 Union Road, CB2 1EZ, U.K.
(http://www.ccdc.cam.ac.uk).
MeI oxidatively added to the mononuclear Pt(II) complex
A and the expected Pt(IV) product B with the Me and I
ligands in trans position to each other was most probably
formed first and very quickly isomerized to the final Pt(IV)
product C with Me and I ligands in cis position to each other.
3.2. Characterization of the Complexes. The complexes
were fully characterized by multinuclear (1H, 31P, 13C, and
195Pt) NMR spectroscopy. The data are collected in the
Experimental Section, and the structures are shown in
Schemes 1 and 2.
3. Results and Discussion
3.1. Synthesis of the Complexes. The routes to prepare
the cyclometalated organoplatinum complexes are described
in Scheme 1. The reaction of a yellow solution of [PtMe-
(SMe2)(ppy)], prepared in situ by reaction of [PtMe2(µ-
SMe2)]2 with 2 equiv of 2-phenylpyridine in acetone,14 with
0.5 equiv of dppf at room temperature gave in good yield
the binuclear complex [Pt2Me2(ppy)2(µ-dppf)], 1, in which
ppy ) deprotonated 2-phenylpyridyl and dppf ) 1,1′-
bis(diphenylphosphino)ferrocene, by replacement of SMe2
ligands with the P ligating atoms of dppf. Complex 1 is an
air-stable yellow solid that has green luminescence both in
solution and solid state. The observations suggest that the
Pt-ppy subunits are “separated” at these conditions and so
no Pt-Pt or π-π interaction of any kind between ppy
ligands is expected in this complex.3b Complex 1 is stable
in acetone or chloroform solutions for several hours.
In the 31P NMR spectrum of complex 1, the two equivalent
P atoms appeared as a singlet signal at δ 24.1 which were
coupled to Pt atoms to give satellites with 1JPtP ) 2092 Hz.
Consistent with this, in the 195Pt NMR spectrum of 1, a
doublet at δ -537 with 1JPtP ) 2090 Hz was observed. The
equivalency of the P atoms suggests that dppf is acting as a
spacer ligand between the two PtMe(ppy) moieties, and each
P atom is coordinated to a Pt atom in a trans disposition to
the coordinating C atom of the phenyl ring of the ppy ligand.
Each Me ligand is thus located trans to the coordinated N
atom of the ppy ligand. In the1H NMR spectrum of complex
1, the two equivalent methyl ligands resonated at δ 0.74 with
(15) X-AREA Program for the acquisition and analysis of data, version
1.30. Stoe & Cie GmbH: Darmstadt, Germany, 2005.
(16) X-RED Program for data reduction and absorption correction, version
1.28b. Stoe & Cie GmbH. Darmstadt, Germany, 2005.
(17) X-SHAPE Program for crystal optimization for numerical absorption
correction, version 2.05. Stoe & Cie GmbH: Darmstadt, Germany,
2004.
(18) G. M. Sheldrick,. SHELX97 Program for crystal structure solution
and refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(19) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(20) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
2
a rather large value of JPtH ) 84.5 Hz, confirming that the
methyl ligands are located trans to imine N atoms than to P
atoms. The four equivalent R and four equivalent ꢀ protons
of the cyclopentadienyl rings appeared as two broad singlets
at δ 4.2 and 4.1, respectively.
5444 Inorganic Chemistry, Vol. 47, No. 12, 2008

Binuclear Cyclometalated Organoplatinum Complexes
Scheme 1
In the 13C NMR spectrum of 1, the methyl ligands
that Ph and p-MeC6H4 ligands exert higher trans influence
than the Me ligand.22 The considerably lower value of 1JPtP
) 1995 Hz for the P atom trans to the C atom of ppy, as
1
appeared as a doublet at δ -13.5 with JPtC ) 732 Hz and
2JPC ) 6 Hz. The low value of the latter coupling confirms
that the methyl groups are in cis position to the P atoms.
The parameters of the doublet at δ 164.5 with1JPtC ) 942
1
compared with the value of JPtP ) 2092 Hz observed for
the similar P atom in complex 1, described above, is probably
due to the dppf ligand being more strained in chelating form
in complex 2 than in complex 1, acting as a spacer ligand.
2
Hz and JPC ) 123 Hz observed for C atoms of the ppy
ligands connected to Pt atoms are comparable with previously
reported data for N,C(sp2) cyclometalated Pt(II) complexes,21
Consistently, a doublet of doublets at δ -2890 with 1JPtP
)
2
and the relatively large value of JPC is consistent with the
1883 and 1990 Hz was observed in the 195Pt NMR spectrum
of 2. In the1H NMR spectrum of complex 2, the methyl
ligand, which is trans to the P atom, was resonated at δ 0.27
C atom being trans to the P atom.
In the 31P NMR spectrum of the dppf chelating complex
2, two signals appeared at δ 23.9 (1JPtP ) 1995 Hz) and δ
20.5(1JPtP ) 1888 Hz). As will be discussed later, the Pt-P
bond trans to the Me ligand is rather longer than that of the
Pt-P bond trans to C atom of ppy-κ1C ligand. We therefore
assume that the trans influence of the Me ligand is higher
than that of the ppy-κ1C ligand and therefore assign the first
signal to the P atom trans to the ppy-κ1C ligand and the
second one to the P atom trans to the Me ligand. In fact,
one might have expected the reverse, as it has been shown
2
and as expected its JPtH value of 66.5 Hz was significantly
2
lower than the value of JPtH ) 84.5 Hz, observed for the
methyl ligands located trans to imine N atoms in complex
1. The observation of eight different peaks at δ 3.54-4.65
indicated that all eight R and ꢀ protons of the cyclopenta-
dienyl rings are different, showing that the staggered
conformation of the dppf ring is rigid. In line with this, in
(22) (a) Rashidi, M.; Jamali, S.; Hashemi, M. J. Organomet. Chem. 2001,
633, 105. (b) Hashemi, M.; Rashidi, M. J. Organomet. Chem. 2005,
690, 982. (c) Nilsson, P.; Plamper, F.; Windt, O. F. Organometallics
2003, 22, 5235. (d) Appleton, T. G.; Bennett, M. A.; Tomkines, B.
J. Chem. Soc., Dalton Trans. 1976, 439. (e) Appleton, T. G.; Clark,
H. C.; Manzer, L. E. Coord. Chem. ReV. 1973, 10, 335.
(21) (a) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B.; Zucca, A.
Organometallics 2003, 22, 4770. (b) Chassot, L.; von Zelewsky, A.
Inorg. Chem. 1987, 26, 2814.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5445

Jamali et al.
Scheme 2
the 13C NMR spectrum of complex 2, eight different doublet
signals at δ 70.9-75.8 have been observed for the R and ꢀ
C atoms of the Cp ligands. The corresponding ipso Cs of
to platinum to give a 1JPtC value close to 490 Hz. Two other
doublets appeared further high field at δ -6.3 and -6.2 each
with a JPC value of 3 Hz, indicating that they are located
2
3
Cp ligands appeared at δ 78.1 (with JPtC ) 45 Hz) for the
cis to the P atom and thus must be trans to the N atom; the
1JPtC value of 637 Hz for each of the signals is also
significantly higher than the value of 490 Hz found for Me
CPPt trans to the Me ligand and at δ 80.0 (with a higher
value of 3JPtC ) 50 Hz) for the CPPt trans to the ppy ligand,
having a lower trans influence that the Me ligand.
1
groups trans to P atoms. Consistently, in the H NMR
1
In the H NMR spectrum of complex 3, the relative
spectrum of complex 3, the Me groups trans to P were
observed at δ 1.07 as overlapping doublets with, 2JPtH ) 61.0
Hz, while Me groups locating trans to N ligating atoms
appeared at δ 1.44 and 1.46, with a considerably higher 2JPtH
values close to 71 Hz because of the lower trans influence
of a N atom as compared with that of a P atom22d,e (see
Figure 1A). In the 31P NMR spectrum of the Pt(IV)-Pt(IV)
complex 3, two different P signals at δ -13.3 and -13.4
intensity of Me ligand protons to dppf protons is exactly
12:8, confirming that the complex is a dimer. However, on
the basis of both 1H and 13C NMR spectra, which are shown
in Figure 1, two different Me groups being trans to P and
two different Me groups locating trans to N ligating atoms
were assigned. Thus, in the 13C NMR spectrum of 3, in the
Me region (see Figure 1B), two closely located doublets
2
1
appeared at δ 6.1 and 6.2 each with a JPC value of 112 Hz
(each with JPtP ) 990 Hz, a value much smaller than the
for the Me groups trans to P; each doublet further coupled
values of around 2000 Hz observed in the spectra of the Pt(II)
5446 Inorganic Chemistry, Vol. 47, No. 12, 2008

Binuclear Cyclometalated Organoplatinum Complexes
ligands trans to P and C-H groups adjacent to the
coordinated N atoms of the ppy ligands, while no effect was
observed for Me groups that are located trans to N atoms of
the ppy ligands. Also, Me ligands trans to P indicated NOE
effect with R, R′ Cp protons (and not with ꢀ, ꢀ′ Cp protons),
while the Me groups trans to N atom indicated NOE effects
with both R and ꢀ Cp protons.
As mentioned above, the Pt(II)-Pt(IV) complex 4, was
obtained as a mixture with complexes 1 and 3. By subtracting
the peaks due to complexes 1 and 3 from the spectra obtained
for the mixture, we determined the structure of complex 4.
Thus, in the 31P NMR spectrum, a singlet at δ -13.2 with
1JPtP ) 990 Hz, the values very close to those obtained for
the Pt(IV)-Pt(IV) complex 3, and another singlet at δ 23.9
with 1JPtP ) 2090 Hz, the values very close to those obtained
for the Pt(II)-Pt(II) complex 1, were assigned to the Pt(IV)
and Pt(II) centers of complex 4, respectively. In line with
this, two doublets at δ -538 (1JPtP ) 2088 Hz) and 315 (1JPtP
) 985 Hz) in the 195Pt NMR spectrum of complex 4 were
observed in the Pt(IV) and Pt(II) regions, respectively. The
1H NMR spectrum was very useful in the structure deter-
2
mination of complex 4. A doublet at δ 0.84 (with JPtH
)
88.5 Hz and 3JPH ) 7.7 Hz) was clearly assigned to the Me
ligand on the Pt(II) center which is trans to the N ligating
atom. For the Me ligands on the Pt(IV) center, two doublets
at δ 1.09 (for the Me ligand trans to P with 2JPtH ) 61.0 Hz
3
and JPH ) 7.6 Hz) and 1.53 (for the Me ligand trans to N
2
3
with JPtH ) 71.1 Hz and JPH ) 7.8 Hz) were observed.
In the 31P NMR spectrum of the mononuclear complex
A, as expected, a singlet signal at δ 33.2 was observed with
1JPtP ) 2105 Hz. In the H NMR spectrum of the complex,
1
the Me ligand that is trans to N atom was observed at δ
0.78 with a typical value of 2JPtH ) 83.0 Hz and 3JPH ) 8.0
Hz. In the 31P NMR spectrum of the corresponding Pt(IV)
complex C, the phosphorus signal, as is expected when
compared to the same signal in the Pt(II) complex A,
appeared at a higher field of δ -9.2 with a much lower value
1
1
1
Figure 1. NMR spectra of complex 3 in the Me region. (A) H and (B)
13C, with the expansion of the central peaks due to Me ligands observed at
higher field (shown in inset).
of JPtP ) 961 Hz. The H NMR spectrum of complex C
was useful in determining its stereochemistry. Observation
2
of a doublet at δ 1.28(3JPH ) 7.5 Hz) with JPtH ) 60.7 Hz
confirmed that the Me ligand is located trans to P;22d,e the
value is similar to the value of 2JPtH ) 61.0 Hz observed for
the Me ligand trans to the P in the Pt(IV) complex 3. The
second doublet signal at 1.65(3JPH ) 7.7 Hz) was assigned
to the Me ligand trans to N; this has a value of 2JPtH ) 70.8
Hz, the same value obtained for the Me ligand trans to N in
complex 3. This confirms that MeI is oxidatively added to
complex A to give the expected Pt(IV) complex intermediate
B with Me and I ligands trans to each other, and a further
trans to cis isomerization occurs to yield the final Pt(IV)
complex C with Me and I ligands cis to each other.
complexes 1 and 2) were observed, and these are consistent
with the observation of two signals in the 195Pt NMR
spectrum of complex 3 at δ 316 and 317 (two almost
1
overlapping doublets each with JPtP ) 990 Hz). Although
the data would well establish the relative disposition of the
different ligands on each Pt center as indicated in Scheme 2
(with chirality at each Pt center), it is impossible to use the
present data to actually propose any “frozen” conformer(s)
for complex 3 resulting from rotation around one or two of
the Pt-P bonds. As twice the “expected” number of signals
was observed in the NMR spectra of complex 3, the
formation of a statistical 1:1:2 mixture of three stereoisomers
(the first two being enantiomers that are not distinguishable
by NMR spectroscopy) may be a reasonable explanation. A
NOE experiment was also carried out for complex 3 to
further investigate the geometry around the platinum centers.
As would be expected for the suggested arrangement around
each Pt center, the NOE effect was observed between Me
The structure of complex [PtMe(dppf)(ppy-κ1C)], 2, was
determined by X-ray crystallography and is shown in Figure
2; selected bond parameters are listed in Table 2. H atoms
were treated by a mixture of independent and constrained
refinement. The complex contains a square planar platinu-
m(II) center with the Me group, the ortho C of the ppy ligand,
and two P atoms of the dppf. The angles around the Pt center
Inorganic Chemistry, Vol. 47, No. 12, 2008 5447

Jamali et al.
Figure 2. Molecular structure of complex [PtMe(dppf)(ppy-κ1C)], 2, (50%
probability ellipsoids, H atoms omitted for clarity).
Table 2. Selected Bond Distances (Å) and Angles (°) for Complex 2
Pt(1)-C(1)
Pt(1)-C(12)
Pt(1)-P(1)
Pt(1)-P(2)
P(1)-C(37)
P(2)-C(42)
2.075(4)
2.117(4)
2.3024(9)
2.3186(9)
1.824(4)
1.801(3)
P(2)-Pt(1)-P(1)
C(1)-Pt(1)-C(12)
C(1)-Pt(1)-P(2)
C(12)-Pt(1)-P(1)
C(1)-Pt(1)-P(1)
C(12)-Pt(1)-P(2)
97.61(3)
84.39(15)
89.96(10)
88.03(10)
172.24(10)
174.35(12)
are rather close to the ideal angle of 90°, and this could be
contrasted with the strain observed in, for example, orga-
noplatinum complexes containing bis(diphenylphosphino)am-
ine, dppa, as chelating ligand. Thus, in complex [PtMe3I(η2-
dppa)], dppa ) bis(diphenylphosphino)amine, the angle
P(1)-Pt(1)-P(2) ) 68.93(5)° is much less than the ideal
angle of 90°.23 The imine N is not coordinated and is
positioned opposite to the platinum center, and this is in
contrast to the usual preference of the ppy ligand to form
cyclometalated complexes. The dppf is arranged in the
usually preferred ”synclinal-staggered” conformation.5a The
Pt-P(2) distance of 2.3186(9) Å is rather significantly longer
than the Pt(1)-P(1) distance of 2.3024(9) Å, indicating that
the Me ligand probably exerts a higher trans influence than
the ppy-κ1C ligand.
Figure 3. 1H NMR spectra of reaction of complex 1 with a 25 fold excess
of MeI at 27 °C; (a) 8 min after addition, (b) 13 min after addition (c), 20
min after addition, and (d) 2 h after addition.
Pt(IV) center, largely appeared along with a significant
amount of both the monomeric complex 2 and the final
Pt(IV)-Pt(IV) complex 3. Five minutes later, the Pt(II)-Pt(IV)
complex 4 was largely diminished while complexes 2 and 3
were appearing and the starting complex 1 had almost
completely disappeared. The conversion of complex 2 to the
final complex 3 was rather slow (see spectrum c obtained
after 20 min). Two hours after the addition of MeI at this
condition, as shown in Figure 3d, all complexes 1, 2, and 4,
disappeared, and the final Pt(IV)-Pt(IV) complex 3 was
almost the only species present. Attempts to follow the
3.3. Kinetic and Mechanism of the Reaction of
Complex 1 with MeI. On the basis of the NMR and UV-vis
spectroscopic studies, described below, a mechanism for
reaction of complex 1 with MeI is suggested as shown in
Scheme 2.
1
(i) Monitoring the Reaction by H NMR Spectros-
copy. The reaction of complex 1 with a 25 fold excess MeI
was monitored by using 1H NMR spectroscopy in CDCl3 in
an NMR tube at 27 °C, and the resulting spectra are shown
in Figure 3. As can be seen, 8 min after the addition of MeI,
complex 4, which is supposed to be the result of SN2 addition
of MeI to one of the Pt(II) centers of the starting complex 1
followed by a rapid trans-cis isomerization of the resulting
1
reaction at low temperatures by H NMR spectroscopy to
gain insight about the other intermediates in the reaction
sequence were not successful as extensive overlapping of
the peaks prevented any useful conclusions. As can be seen,
after addition of MeI to the first Pt(II) center, complex 2 is
rapidly formed, and its disappearance to give complex 3 was
very slow. We measured the rate constant, k1, for this “very
slow intermediate step” in CDCl3 at 27 °C using the above
(23) Hoseini, S. J.; Mohamadikish, M.; Kamali, K.; Heinemann, F. W.;
Rashidi, M. Dalton Trans. 2007, 1697.
5448 Inorganic Chemistry, Vol. 47, No. 12, 2008

Binuclear Cyclometalated Organoplatinum Complexes
Figure 4. Concentration-time curve for the disappearance of the intermedi-
ate complex 2, in reaction of complex 1 with MeI in CDCl3 at 27 °C, using
1H NMR spectroscopy.
1
mentioned H NMR technique. The peaks for complex 2
appeared rather quickly, and the disappearance of the signal
at δ ) 4.64 (due to one of the CH groups of dppf in complex
2) was used to monitor the reaction. The process followed
good first-order kinetics (Figure 4) and by fitting of [2]/time
data with a first order equation (eq 1), the k1 value for the
disappearance of complex 2 was found to be 1.04((0.04)
× 10-3 s-1 . By using eq 2, it was also possible to calculate
k1 by an alternative method.24 Thus, substituting the value
of k2 (in CHCl3 at 27 °C), the rate constant for the first
addition of MeI to complex 1 to form complex 4 as obtained
easily by UV-vis spectroscopy (calculated from the data in
Table 2, see below), in eq 2, k1 ) 1.03((0.09) × 10-3 s-1
is obtained. As can be seen, the values resulted by the two
methods are almost identical.
Figure 5. Reaction of complex 1 with excess methyl iodide as monitored
by 31P NMR spectroscopy at low temperatures. Top view: Pt(II) region.
Down view: Pt(IV) region. (a) Pure 1 (253 K), (b) immediately after addition
of excess MeI (253 K), (c) 10 min after addition of excess MeI (253 K),
(d-k) successive runs each after 10 min and 2-3 K temperature raise, (l)
after 100 min and temperature of 278 K, (m) 1 h after the temperature was
raised up to room temperature. Peak assignments are shown; platinum
satellites are observed for all involved species but are shown only for
intermediates 5 and 6.
A ) A - A exp -k t + A
∞
(1)
(
)
[
(
)]
t
0
∞
obs
[
]
k MeI A
[
]
0
2
[ ]
2 t )
[
]
exp -k MeI t - exp -k t
( ) ( )]
2 1
(2)
[
]
[
k1 - k2 MeI
(ii) Monitoring the Reaction By 31P NMR Spectros-
copy. To investigate the details of mechanism, the reaction
of complex 1 with excess methyl iodide was monitored by
31P NMR spectroscopy at low temperatures, as shown in
Figure 5. On the basis of the results, the complexes and
intermediates suggested for the reaction sequence described
in Scheme 2 were assigned. Note that complexes 1, 2, 3,
and 4 appeared in the suggested sequence, all characterized
as described in the Characterization of the Complexes
section, and so their characteristic 31P NMR data were used
to indicate the complexes. Also, by using 31P NMR param-
eters of these complexes, good support for the structures of
the suggested intermediates 5 and 6 (see below) was
obtained. Thus, immediately after the addition of MeI at -20
°C, apart from complex 1, a Pt(II)-Pt(IV) species assigned
as intermediate 5 was detected. Two singlet signals, one at
δ 25.0 (with 1JPtP ) 2072 Hz), which is located in the Pt(II)
region and its 1JPtP value is close to that of the Pt(II)-Pt(II)
starting complex 1, and another one at δ -9.8, located in
the Pt(IV) region with 1JPtP ) 1205 Hz, were observed. The
latter value is typical for Pt(IV)-P coupling but is signifi-
cantly higher than the corresponding value found for
Pt(IV)-Pt(IV) complex 3; as we indicated above, this is
probably due to higher trans influence of Me as compared
to that of the ppy-κ1C ligand. Although the data provide a
reasonable support for the relative disposition of the different
ligands on both Pt(II) and Pt(IV) centers as indicated in
Scheme 2 for 5, because of the limited available data it is
not possible to suggest any specific conformation for the
intermediate 5. As the time was passing and the tempera-
ture was rising, the signals due to the starting material 1
were disappearing while those due to the intermediate 5 were
growing and then later started fading away. Meanwhile,
comparatively weak signals due to complex 4 were also
(24) Espenson, J. H. Chemical Kinetics and Reaction Mechanisms, 2nd
ed.; McGraw-Hill: New York, 1995.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5449

Jamali et al.
was quickly disappearing while the concentration of complex
2 was rather rapidly increasing and the final Pt(IV)-Pt(IV)
complex 3 started to appear. Around this time on, complex
2 was slowly disappearing while the signals due to the final
product 3 were being slowly increased. Although the slow
conversion of 2 to 3 is suggested as occurring via intermedi-
ates 4 and 6, the latter intermediate could not be seen at
these stages as its conversion to 3 was relatively fast. Note
that for the suggested intermediate 6, a set of two singlets
are predicted, one for Pt(IV)-P trans to the Me ligand, which
is expected to be located close to the corresponding signal
for complex 4 (or close to the signals for complex 3), and
another one for Pt(IV)-P trans to the ppy-κ1C ligand, which
is expected to be located close to the corresponding signal
for intermediate 5. In fact, we observed two sets of such
1
signals in the expected regions with expected JPtP values
Figure 6. Changes in the UV-vis spectrum during the reaction of complex
1 (1.5 × 10-4 M) with MeI (0.533 M) in CHCl3 at T ) 25 °C: (a) initial
spectrum (before adding MeI); (b) spectrum at t ) 0 s. Successive spectra
were recorded at intervals of 30 s.
(one set at δ -11.7, with 1JPtP ) 1012 Hz, and δ -9.7, with
1JPtP ) 1214 Hz, and another set at δ -11.8, with JPtP
)
1
1
1012 Hz, and δ -9.8, with JPtP ) 1214 Hz). We therefore
suggest that the intermediate 6, as was pointed out above
regarding the structure of complex 3, is also obtained as a
statistical 1:1:2 mixture of three stereoisomers and although,
because of the possibility of rotation around one or two of
the Pt-P bonds, it is impossible to actually propose any
particular configuration for any of the conformers because
of the limited data, the suggested relative disposition of the
different ligands on each Pt center, as indicated in Scheme
2, seems to be reasonable. After 100 min (temperature 278
K) all the signals, except a small amount of the complex 2,
disappeared. It is to be noted that when the temperature was
raised up to room temperature, signals due to the remaining
small amount of complex 2 completely disappeared after 1 h,
and the final Pt(IV)-Pt(IV) product 3 was purely obtained.
Figure 7. Absorbance-time curves for the reaction of complex 1 with MeI
(0.16-0.8 M; [MeI] increases reading downward) in CHCl3 at 25 °C.
(iii) Kinetic Studies Using UV-vis Spectroscopy. The
binuclear complex 1 contains a MLCT band in the visible
region that could be used to monitor its reaction with MeI
and study the kinetics of the reaction by using UV-vis
spectroscopy. Thus, an excess of MeI was used at 25 °C
and the disappearance of the metal-to-ligand charge-transfer
(MLCT) band at λ ) 360 nm in a CHCl3 solution was used
to monitor the reaction. The change in the spectrum during
a typical run is shown in Figure 6.
The time-dependence curves of the spectra of the reaction
in CHCl3 at this condition are shown in Figure 7. Thus, the
pseudo-first-order rate constants kobs were evaluated by
nonlinear least-squares fitting of the absorbance-time profiles
to the monophasic first-order equation (eq 1). Plots of the
first-order rate constants, kobs, versus [MeI] was linear with
no intercepts (Figure 8), showing a first-order dependence
of the rate on the concentration of MeI. The slope in each
case gave the second-order rate constant, and the results are
collected in Table 3. Therefore, the reaction obeys a simple
second-order rate law, first order in both the corresponding
dimer and MeI. The reproducibility of the data was remark-
able (4%). The same method was used at other temperatures,
and activation parameters were obtained from the Eyring
Figure 8. Plots of first-order rate constants for the reaction of complex 1
with MeI at different temperatures (a, 10 °C; b, 15 °C; c, 20 °C; d, 25 °C;
d, 30 °C) versus the concentration of MeI in CHCl3.
observed in the first stages. In the meantime, the suggested
intermediate 6 along with complex 2 started to show up. As
the reaction progressed, the Pt(IV)-Pt(IV) intermediate 6
5450 Inorganic Chemistry, Vol. 47, No. 12, 2008

Binuclear Cyclometalated Organoplatinum Complexes
Table 3. Rate Constants (L mol-1 s-1) for the Reaction of the Complexes with MeI in CHCl3
T ) 10 °C
T ) 15 °C
T ) 20 °C
T ) 25 °C
T ) 30 °C
a
complex 1, 102k2
complex A, 102k2
1.11 ( 0.02
1.57 ( 0.02
2.17 ( 0.03
3.00 ( 0.05
0.85 ( 0.02
3.79 ( 0.06
1.10 ( 0.04
a Activation parameters for the reaction of complex 1 with MeI were calculated as ∆H‡ ) 41.8 ( 1.2 (kJ mol-1) and ∆S‡ ) -134 ( 4 (J K-1 mol-1).
lead to 3 by reaction with MeI through the intermediate 6.
The disappearance of 2, as monitored by 1H NMR spectros-
copy, was slow, and the rate constant k1 ) 1.04((0.04) ×
10-3 s-1 (at 27 °C) was some 30 times slower than the initial
SN2 attack of complex 1 to MeI (see Table 3). The
intermediate 6 would then quickly perform a facile trans to
cis isomerization of the Pt(IV) center having Me and I in
trans disposition to form the final product 3.
4. Conclusions
The Pt(II)-Pt(II) dimer [Pt2Me2(ppy)2(µ-dppf)], 1, is an
interesting case of the less common diplatinum complexes
containing an “open bridge” dppf. On the basis of the NMR
spectra, the two PtMe(ppy) species are shown to be identical
and the four R protons (or the four ꢀ protons) of the Cp
rings of the dppf spacer ligand are also equivalent. This
shows that the conformation of dppf5a has most probably
an ideal “antiperiplanar staggered” conformation with a
Cp(centroid)· · ·Fe · · ·Cp(centroid) twist angle τ ) 180°. This
is preferred to an “anticlinal eclipsed” conformation with τ
) 108°, as the latter would require an extra conformational
flipping of “open bridge” dppf to make the above mentioned
equivalency of the R and ꢀ protons of the Cp rings.
Figure 9. Eyring plot for the reaction of complex 1 with MeI in CHCl3.
equation (see eq 3 and Figure 9). The data are collected in
Table 3.
∆S‡ ∆H‡
k2
kB
ln
) ln
+
-
(3)
( )
( )
T
h
R
RT
In a comparative study, we studied the kinetics of reaction
[PtMe(ppy)(PPh3)], A, with MeI as a “calibration reaction”
to evaluate the effect of dppf ligand on the rate of the reaction
of MeI with complex 1. The monomeric Pt(II) complex A
also contains a MLCT band in the visible region and was
used similarly to study the kinetics of its reaction by using
UV-vis spectroscopy in CHCl3 at λ ) 358 nm. The data
are collected in Table 3.
The [PtMe(dppf)(ppy-κ1C)] complex, 2, is a common
example of complexes with the preferred chelating confor-
mation of dppf. This complex is formed when the starting
complex [PtMe(SMe2)(ppy)], containing a chelating cyclo-
metalated ligand, is reacted with 1 equiv of dppf. It thus
appears that the chelating ability of dppf is actually domi-
nated and has caused the rather strong cyclometalated chelate
to open up from the N donor atom. The NMR spectra
indicated that the staggered conformation of the dppf ring,
as determined by X-ray crystallography, is rigid in solution.
The Pt-P distance for P atom trans to Me is rather longer
than that of the P atom trans to the C atom of ppy ligand.
The difference, although modest, indicates that the Me ligand
probably exerts a higher trans influence than the ppy-κ1C
ligand. This is in contrast to the reports that Ph or p-MeC6H4
ligands exert a higher trans influence than the Me ligand,22
and this has been attributed to the higher s character of
Pt-C(sp2) for aryl ligands as compared to Pt-C(sp3) for Me.
When the dimer 1, with two square-planar Pt(II) centers,
was reacted with excess MeI, based on the observations, the
normal Me and I trans oxidative addition occurred. However,
the structure of the final product Pt(IV)-Pt(IV) dimer
complex 3, as determined by multinuclear NMR studies,
indicated that further trans to cis isomerization would have
happened to place the added ligands, Me and I, in a cis
position to each other. We believe that a steric effect has
probably been responsible for the isomerization to occur. An
“antiperiplanar staggered” conformation has been suggested
(iv) Mechanistic Interpretation of the Data. A mecha-
nism, as shown in Scheme 2, therefore has been suggested
for the reaction of complex 1 with MeI. As described above,
the suggested mechanism has been supported by low
temperature 31P NMR study, 1H NMR spectroscopy and also
by kinetic studies using UV-vis spectrophotometry. Thus,
MeI is first trans oxidatively added to one of the platinum(II)
centers of complex 1 by a classical SN2 reaction with a rate
constant k2, yielding intermediate 5. The latter has undergone
a relatively fast conversion of the trans arrangement of the
Me and I ligands on the platinum(IV) center to the cis
arrangement to form complex 4. Then, the latter would either
react with MeI to form intermediate 6 by a classical SN2
reaction or disintegrate to form a pair of species M and N,
with the suggested structures shown in Scheme 2. Formation
of the Pt(II) species M by such a dissociative process could
probably be the best explanation for the formation of complex
2 during the reaction, and the unusual penta-coordinated
Pt(IV) species that should subsequently be released is best
suggested to dimerize to form N. We believe that 2 and N
could then slowly reassociate back to 4 which would then
Inorganic Chemistry, Vol. 47, No. 12, 2008 5451

Jamali et al.
for the dppf spacer ligand. Although the relative disposition
of the different ligands on each Pt center as indicated in
Scheme 2 was well established, it was impossible to propose
any “frozen” conformer for complex 3 resulting from rotation
around one or two of the Pt-P bonds. As twice the
“expected” number of signals was observed in the NMR
spectra of complex 3, the formation of a statistical 1:1:2
mixture of three stereoisomers (the first two being enanti-
omers that are not distinguishable by NMR spectroscopy)
may be a reasonable explanation. To the best of our
knowledge, no Pt(IV)-Pt(IV) dimer with a dppf spacer
ligand has already been reported.
The kinetic studies in the present work indicated that MeI
was initially reacted with one of the Pt(II) centers of
[Pt2Me2(ppy)2(µ-dppf)], 1, with a rate significantly higher
by a factor of 3.5 than that of the corresponding reaction
involving the mononuclear complex [PtMe(ppy)(PPh3)], A,
which was studied as a “calibration reaction”. This has been
attributed to more electron donating ability of the P ligands
in complex 1 as compared to the P ligands of PPh3 in
complex A because of the presence of ferrocenyl moieties
in the dppf containing complex 1. After the addition of MeI
to the first Pt(II) center of complex 1, measurement of the
rate of the addition of MeI to the second Pt(II) center was
not possible. This was indicated to be due to the occurrence
of a slow side reaction in between the two steps involving
stepwise addition of MeI to the two Pt(II) centers.
Acknowledgment. We thank the Persian Gulf University
Research Council, the Iran National Science Foundation
(Grant No. 86033/13), and the Shiraz University Research
Council for financial support. We also thank Professor James
H. Espenson for many good suggestions and helpful discus-
sions. The very constructive comments of the reviewers are
also appreciated. M.R. thanks Johnson Matthey PLC for a
generous loan of platinum metal salts.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC701910D
5452 Inorganic Chemistry, Vol. 47, No. 12, 2008