Ligand electronic effect on reductive elimination of biphenyl from ci s-[Pt(Ph)2(diphosphine)] complexes bearing electron-poor diphosphine: Correlation study between experimental and theoretical results

Article abstract of DOI:10.1021/om100073j

The reductive elimination of biphenyl from cis-[Pt(Ph) ₂(diphosphine)] (3) was studied to clarify the electronic effects of diphosphine ligands on the reaction. Reaction kinetic data were evaluated in d₈-toluene within 80-110 °C usin

Full text of DOI:10.1021/om100073j

Organometallics 2010, 29, 4025–4035 4025
DOI: 10.1021/om100073j
Ligand Electronic Effect on Reductive Elimination of Biphenyl from
cis-[Pt(Ph)2(diphosphine)] Complexes Bearing Electron-Poor Diphosphine:
Correlation Study between Experimental and Theoretical Results
Toshinobu Korenaga,* Kayoko Abe, Aram Ko, Ryota Maenishi, and Takashi Sakai*
Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology,
Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
Received January 28, 2010
The reductive elimination of biphenyl from cis-[Pt(Ph)2(diphosphine)] (3) was studied to clarify the
electronic effects of diphosphine ligands on the reaction. Reaction kinetic data were evaluated in d8-toluene
within 80-110 °C using 1,2-bis(diphenylphosphino)ethane (dppe) and seven of its fluoroaromatic
analogues as ancillary diphosphine ligands. The fastest reaction rate corresponded to 3, bearing the
electron-poor 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (dfppe) ligand, and was 1240 times faster
than that for dppe-bearing 3, which has the slowest. The estimated rate constants k were highly correlated
with Taft’s σ* values for phosphorus-bound aromatics in 3. However, their correlation was split between
2,6-fluorine aromatic and 2,6-hydrogen aromatic-bearing diphosphines, suggesting steric effects from the
2,6-fluorine atoms. The observed ΔHq values were correlated with theoretical values, which were calculated
by the DFT method. The correlations revealed that electron-poor diphosphine ligands decrease the energy
gaps between the HOMO-1of3and the HOMO of transition state 3-TS, including the platinum d orbital,
and reduce the destabilization of the platinum d orbital upon binding with the diphosphine in 3-TS as
compared to the cases of an electron-donating ligand. This last mentioned effect is the true nature of
electronic influence of the electron-poor diphosphine ligands in the reductive elimination from 3.
Introduction
ancillary phosphine ligands on reductive elimination has been
widely studied and shown to mostly be steric. In particular, a
large bite angle greatly accelerates reductive elimination for
bidentate ligands.1 For example, the rate constant of cis-Pd-
(CH2TMS)(CN)(diphosphine) is accelerated 4760 times by the
P-Pd-P bite angle.5 On the other hand, the electronic effects
of ancillary phosphine ligands on the reductive elimination
rates have also been reported experimentally.6 In [Pd(2,5-
dichlorophenyl)(η3-2-propenyl){P(C6H4-R)3}], for example,
the weakest σ-donor phosphine (R = Cl) led to a reductive
elimination that was 5.6 times faster than for the strongest
σ-donor phosphine (R=OMe).6a Hartwig et al. reported simi-
lar accelerations, which were influenced by electronic effects of
the ancillary diphosphine ligand in R-1,10-bis(diphenylphos-
phino)ferrocene (R-dppf )-ligated palladium complexes.1c,7
The [Pd(CF3-dppf )(C6H4-4-CN)(OC6H4-4-OMe)] complex
underwent reductive elimination 2 times faster than its analo-
gous dppf complex.7e Similarly, reductive elimination was 6.5
times faster for [Pd(CF3-dppf )(C6H4-4-CF3){N(Me)-p-tolyl}]
than for the MeO-dppf-ligated analogue.7d Although less
σ-donating phosphines accelerated the reductive elimination
in those results, electronic effects were not as significant as bite
Reductive elimination is an essential step in many transition
metal catalyzed reactions.1 In particular, carbon-carbon2 and
carbon-heteroatom3 bond-forming cross-coupling reactions
undergo reductive elimination in their catalytic cycles, and this
step is occasionally rate-determining in catalysis.4 The rate of
reductive elimination greatly depends on the nature of the cen-
tral metal (e.g., Ni > Pd > Pt) and on the steric and electronic
properties of reactive and ancillary ligands.1b The influence of
*To whom correspondence should be addressed. E-mail: korenaga@
cc.okayama-u.ac.jp.
(1) Reviews: (a) Brown, J. M.; Cooley, N. A. Chem. Rev. 1988, 88,
1031. (b) Ozawa, F. In Fundamentals of Molecular Catalysis; Kurosawa,
H., Yamamoto, A., Eds.; Elsevier: New York, 2003; Vol. 3, p 479.
(c) Hartwig, J. F. Inorg. Chem. 2007, 46, 1936.
(2) Recent reviews: (a) Chen, X.; Engle, K. M.; Wang, D.-H.; Yu
J.-Q. Angew. Chem., Int. Ed. 2009, 48, 5094. (b) Phapale, V. B.; Cardenas,
D. J. Chem. Soc. Rev. 2009, 38, 1598. (c) Terao, J.; Kambe, N. Acc. Chem.
Res. 2008, 41, 1545. (d) Martin, R.; Buchwald, S. L. Acc. Chem. Res. 2008,
41, 1461.
(3) Reviews: (a) Surry, D. S.; Buchwald, S. L. Angew. Chem., Int. Ed.
2008, 47, 6338. (b) Hartwig, J. F. Acc. Chem. Res. 2008, 41, 1534. (c) Janey,
J. M. Name Reactions for Functional Group Transformations; Wiley: New
York, 2007; p 564. (d) Buchwald, S. L.; Mauger, C.; Mignani, G.; Scholz, U.
Adv. Synth. Catal. 2006, 348, 23. (e) Hartwig, J. F. Comprehensive
Coordination Chemistry II; Elsevier: Amsterdam, 2004; Vol. 9, p 369.
(f ) Stuermer, R. Organic Synthesis Highlights V; Wiley-VCH: Weinheim,
2003; p 22. (g) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2002, 219,
131. (h) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046.
(4) Recent examples: (a) Lanni, E. L.; McNeil, A. J. J. Am. Chem.
Soc. 2009, 131, 16573. (b) Jin, L.; Zhang, H.; Li, P.; Sowa, J. R.; Lei, A.
J. Am. Chem. Soc. 2009, 131, 9892. (c) Boren, B. C.; Narayan, S.;
Rasmussen, L. K.; Zhang, L.; Zhao, H.; Lin, Z.; Jia, G.; Fokin, V. V.
J. Am. Chem. Soc. 2008, 130, 8923.
(5) Marcone, J. E.; Moloy, K. G. J. Am. Chem. Soc. 1998, 120, 8527.
(6) (a) Kurosawa, H.; Emoto, M. Chem. Lett. 1985, 1161. (b) Komiya,
S.; Shibue, A. Organometallics 1985, 4, 684. (c) Negishi, E.; Takahashi, T.;
Akiyoshi, K. J. Organomet. Chem. 1987, 334, 181.
(7) (a) Shekhar, S.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 13016. (b)
Culkin, D. A.; Hartwig, J. F. Organometallics 2004, 23, 3398. (c) Yamashita, M.;
Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 5344. (d) Yamashita, M.; Vicario,
J. V. C.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 16347. (e) Mann, G.; Shelby,
Q.; Roy, A. H.; Hartwig, J. F. Organometallics 2003, 22, 2775.
r
2010 American Chemical Society
Published on Web 08/24/2010
pubs.acs.org/Organometallics

4026 Organometallics, Vol. 29, No. 18, 2010
Korenaga et al.
angle effects. This may be due to the small difference in electro-
nic properties between the compared phosphines. Therefore, a
more electron-poor ancillary phosphine ligand would result in
a greater acceleration of the reaction rate. Although a highly
electron-poor phosphine slows down metal coordination in
some cases,8 the use of a bidentate electron-poor diphosphine
analogue reduces the lability of the metal complex.9 Roddick
et al. reported the reductive elimination of biaryl from [Pt(Ar)2-
(dfppe)] (dfppe: 1,2-bis[bis(pentafluorophenyl)phosphino]-
ethane).10 Their report was summarized as follows. (a)
Reductive elimination from [Pt(Ph)2(dfppe)] proceeds
through a direct path to give biphenyl and [Pt(dfppe)2]. (b)
Intermolecular exchange does not occur between reactive
phenyl groups. (c) An approximately 10-fold elimination
rate enhancement was observed in nonpolar solvents such as
benzene over polar solvents such as DMSO. (d) The elimination
rates from [Pt(Ar)2(dfppe)] are of advantage to electron-rich
reactive aryl groups. This report showed significant results but
does not compare the elimination rates of the dfppe-containing
complexes with complexes bearing a more σ-donating dipho-
sphine such as dppe. Therefore, we conducted a kinetic study on
reductive elimination from [Pt(Ph)2(diphosphine)] complexes
formed with several dppe analogues, including fluoroaromatic
diphosphines, to compare their reaction rates and evaluate the
diphosphine electronic effects. Studies using electronically
tuned ligand analogues promise a better understanding of the
electronic nature of ancillary diphosphine ligands in reductive
elimination. In general, the electronic influence of phosphine
ligands has been proposed to contribute to the decrease in
electron density at the metal center, thus accelerating reductive
elimination.1 In response, the electronic effects of phosphine
ligands have been analyzed using MO or DFT calculations.11
Although previous reports have described many significant
findings regarding the electronic effects of some phosphines,
their major focus was to clarify whether the mechanism of
reductive elimination followed a direct or a dissociative path1
using monodentate phosphines. Therefore, the electronic effects
of ancillary phosphine ligands in reductive elimination may not
have been clarified sufficiently. Hence, we also performed DFT
calculations for our system and correlated the computational
results with experimental values to understand the electronic
effects of diphosphines in reductive elimination.
Figure 1. Diphosphine-bearing fluoroaromatics.
Table 1. νCdO Values of Complex 2
Ar of diphosphine 1
ν
CdO of 2 (cm-1 a
)
Taft’s σ* of Ar
Et
Ph (1a)
2012b
-0.10
0.60
0.63
1.01
1.02
1.04
1.08
1.36
1.50
1.75
2.83
3.19
2021.4 [2a]
2023.4 [2b]
2029.6 [2c]
2030.1 [2d]
2031.3 [2e]
2032.1 [2f]
2038.8 [2g]
2040.7 [2h]
2044.8 [2i]
2064b
4-F-C6H4 (1b)
3,5-F2-C6H3 (1c)
2,6-F2-C6H3 (1d)
3,4,5-F3-C6H2 (1e)
2,4,6-F3-C6H2 (1f)
2,3,5,6-F4-C6H (1g)
C6F5 (1h)
4-CF3-C6F4 (1i)
C2F5
F
2074b
a The highest A1 stretching mode in CH2Cl2. b From ref 15.
diphosphines 1 (Figure 1) were prepared by reacting 1,2-bis-
(dichlorophosphino)ethane with ArFMgBr or ArFLi in Et2O
or THF.12 Before investigating the reductive elimination, we
studied the electronic effects induced by 1 with fluorinated
phenyl groups on the central metal, because electronic effects
are affected by steric influences for some bidentate ligands.13 In
particular, it is known that fluorine atoms at the 2,6-positions of
aryl groups on phosphorus significantly increase the steric
effects of phosphine ligands on the metal complex.14,15 The
electronic effects of diphosphine ligands on the central metal
were evaluated by comparing the highest infrared CO stretching
frequencies (νCO) for cis-Mo[diphosphine](CO)4 complexes
(2, Table 1),15,16 which were synthesized from Mo(norborna-
diene)(CO)4. As expected, the σ-donating ability of 1 tended to
decrease with increasing number of fluorine atoms on the
diphosphine aromatic rings. Interestingly, the σ-donating ability
of diphosphines bearing 2,6-fluorinated aryl groups was slightly
lower than those bearing the same number of fluorine atoms
at different positions. This can be explained by the inductive
effect of the ArF group on the diphosphine. The νCO values
of 2including nonaromatic diphosphine-ligated complexes were
highly correlated with Taft’s σ* values (Figure 2, r2 > 0.99),17,18
which closely correlate with the basicity of the corresponding
phosphines,19 suggesting that the νCO values are mainly induced
by not steric but electronic effects of diphosphine. In other
Results and Discussion
Preparation and Electronic Property of Diphosphine Ligand 1.
Except for commercially available dppe (1a) and dfppe (1h),
(8) (a) Tiburcio, J.; Bernes, S.; Torrens, H. Polyhedron 2006, 25, 1549.
(b) Clarke, M. L.; Ellis, D.; Mason, K. L.; Orpen, A. G.; Pringle, P. G.;
Wingad, R. L.; Zaher, D. A.; Baker, R. T. Dalton Trans. 2005, 1294.
(9) Pollock, C. L.; Saunders, G. C.; Smyth, E. C. M. S.; Sorokin, V. I.
J. Fluorine Chem. 2008, 129, 142.
(10) Merwin, R. K.; Schnabel, R. C.; Koola, J. D.; Roddick, D. M.
Organometallics 1992, 11, 2972.
€
(11) (a) Tatsumi, K.; Hoffmann, R.; Yamamoto, A.; Stille, J. K. Bull.
Chem. Soc. Jpn. 1981, 54, 1857. (b) Ananikov, V. P.; Musaev, D. G.;
Morokuma, K. Eur. J. Inorg. Chem. 2007, 5390. (c) Ariafard, A.; Yates, B. F.
J. Organomet. Chem. 2009, 694, 2075. (d) Ananikov, V. P.; Musaev, D. G.;
Morokuma, K. J. Am. Chem. Soc. 2002, 124, 2839. (e) Hofmann, P.
Organosilicon Chem. 1994, 231.
(12) Synthesis of dppe analogues bearing fluoroaryls: (a) Mirabelli,
C. K.; Hill, D. T.; Faucette, L. F.; McCabe, F. L.; Girard, G. R.; Bryan,
D. B.; Sutton, B. M.; Barus, J. O. L.; Crooke, S. T.; Johnson, R. K.
J. Med. Chem. 1987, 30, 2181. (b) Corcoran, C.; Fawcett, J.; Friedrichs, S.;
Holloway, J. H.; Hope, E. G.; Russell, D. R.; Saunders, G. C.; Stuart, A. M.
J. Chem. Soc., Dalton Trans. 2000, 161. (c) Fischer, R.; Langer, J.; Malassa,
A.; Walther, D.; Goerls, H.; Vaughan, G. Chem. Commun. 2006, 2510.
(13) Kuendig, E. P.; Dupre, C.; Bourdin, B.; Cunningham, A., Jr.;
Pons, D. Helv. Chim. Acta 1994, 772, 421.
(14) Cone angle of PAr3 bearing 2,6-fluorinated aryl (C6F5 = 184° or
172°; 2,6-F2C6H3 = 176° or 171°) is greatly larger than that bearing 2,6-
nonfluorinated aryl (3,4,5-F3C6H2 = 4-FC6H4 = Ph = 145°) (ref 12b).
(15) Cone angle of dfppe (151°) vs dppe (125°): Ernst, M. F.;
Roddick, D. M. Inorg. Chem. 1989, 28, 1624.
(16) Hoge, B.; Panne, P. Chem.;Eur. J. 2006, 12, 9025.
(17) The νCO values of monophosphine ligands are highly correlated with
its Taft’s σ* values: Bigorgne, M. J. Inorg. Nucl. Chem. 1964, 26, 107.
(18) Korenaga, T.; Kadowaki, K.; Ema, T.; Sakai, T. J. Org. Chem.
2004, 69, 7340.
€
(19) Babij, C.; Poe, A. J. J. Phys. Org. Chem. 2004, 17, 162.

Article
Organometallics, Vol. 29, No. 18, 2010 4027
Scheme 1. Reductive Elimination from 3
Figure 3. Results of reductive elimination from 3 in d8-toluene
at 100 °C.
Figure 2. Correlation between Taft’s σ* of Ar in 1 and νCdO of 2.
Scheme 2. Capture of Reactive Species 5h by the Addition of 6
words, the electronic nature of the diphosphine ligands is
reflected directly in the molybdenum d orbitals.
Synthesis of cis-[Pt(Ph)2(diphosphine)] (3). cis-[Pt(Ph)2-
(diphosphine)] complexes (3) were prepared using (COD)-
PtCl2 as a starting material. The diphosphines (1) reacted
with(COD)PtCl2 to give the corresponding cis-[Pt(Cl)2(1)] com-
plexes, which were treated with PhMgBr to produce platinum
complexes 3a-h. Complex 3i, which bears heptafluorotolyl
groups, could not be isolated because the reductive elimination
proceeded at ambient temperature. A similar result had been
observed by Roddick et al. in the case of cis-[Pt(Ph)2(dfepe)]
[dfepe=(C2F5)2PCH2CH2P(C2F5)2], whose complex was more
unstable thermally than 3i.10 31P NMR spectra for all synthe-
sized complexes 3 showed a single resonance peak with 195Pt
satellites, whose coupling constants 1JPt-P were within ca. 1500
to 1700 Hz. These results indicate that all complexes 3 were cis-
isomers20 with C2 symmetry.
Experimental Study of Reductive Elimination of Biphenyl
from 3. The reductive elimination of biphenyl from complex
3 is shown in Scheme 1. The recrystallized complexes 3 and
degassed d8-toluene were placed in an NMR tube under an
argon atmosphere. The sealed NMR tube was immersed in
an oil bath, which was maintained constant at 100 ( 0.1 °C,
and the reaction was monitored by 1H NMR.
The reaction rate of the reductive elimination (k) was mea-
sured by comparing the integral values of phenyl protons in
complex 3 and biphenyl (4). The kinetic data are summarized in
Figure 3. The decomposition of complex 3 was adequately
described by a pseudo-first-order rate law (r2 >0.99). This is
consistent with results obtained for 3h by Roddick et al., who
reported that the reductive elimination gave Pt(dfppe)2 through
a coordinatively unsaturated 14e Pt(dfppe) complex (5h) in an
aromatic solvent.10 However, the existence of a reverse reaction
between highly reactive 5 and 4 could not be completely denied.
Therefore, the reductive elimination of 3h was performed in the
presence of diphenylacetylene (6), which traps the 14e Pt com-
plex to give a stable platinum alkyne complex (7h) (Scheme 2).21
1H NMR analysis for an equimolar mixture of 3h and 6 in
d8-toluene clearly showed four-proton signals for 3h (δ=6.79
ppm) and 6 (δ=7.46 ppm) initially. After heating for several
minutes at 100 °C, equal amounts of 4 (δ = 7.40 ppm) and
complex 7h (δ=7.74 ppm)22 were generated, while the amounts
of 3h and 6 decreased. This suggests that 6 captures 5h imme-
diately without significant side reaction. The reaction of 3h in
thepresenceof6also followed a pseudo-first-order rate law, and
the rate constant was evaluated to be 2.25 ꢀ 10-4 s-1, similar
to the reaction without 6 (k=2.23 ꢀ 10-4 s-1) (Figure 3). Fur-
thermore, the rate constant of 3h in the presence of 1.0 equiv of
additional 4 also showed a similar value (k=2.30 ꢀ 10-4 s-1).
These results suggest that the reverse reaction between 5h and 4
does not occur; in other words, the reaction rate of 3h shows the
rate of reductive elimination itself.
The reductive elimination of dfppe complex 3h was found
to be the fastest, with a rate constant that is 1240 times
greater than that for dppe complex 3a (Figure 3). This 3 order
(21) (a) Ozawa, F.; Hikida, T.; Hayashi, T. J. Am. Chem. Soc. 1994,
116, 2844. (b) Ozawa, F.; Hikida, T.; Hasebe, K.; Mori, T. Organometallics
1998, 17, 1018. (c) Hasebe, K.; Kamite, J.; Mori, T.; Katayama, H.; Ozawa, F.
Organometallics 2000, 19, 2022.
1
(20) JPtP of cis-[PtPh2(PPh3)2] = 1762 Hz, cis-[PtPh2(PMe2Ph)2] =
(22) Complex 7h was confirmed by alternative synthesis according to
€
1754 Hz, trans-[PtPh2(PMe2Ph)2] = 2916 Hz in CD2Cl2: Nilsson, P.;
Plamper, F.; Wendt, O. F. Organometallics 2003, 22, 5235.
the procedure of the synthesis of [Pt(dppe)(6)]: Muller, C.; Iverson,
C. N.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc. 2001, 123, 9718.

4028 Organometallics, Vol. 29, No. 18, 2010
Korenaga et al.
Figure 4. Correlation between Taft’s σ* of Ar in 1 and ln k of 3.
Figure 5. Correlation between 1JPtP of 3 and ln k of 3.
Table 2. Activation Parameters of Reductive Elimination from 3a
of magnitude difference is rare for ligand electronic effects,
though large bite angles in bidentate ligands are known to
increase rate constants by more than a factor of 103, as men-
tioned above. The reaction rate constants increased with in-
creasing number of fluorine atoms in the diphosphine ligands,
indicating that the reaction rates depend on the electron-
withdrawing strength of the diphosphine ligands. However,
when the phosphines contained the same number of fluorine
atoms, reaction rates observed for complexes with 2,6-fluori-
nated phenyl-bound diphosphines such as 3d and 3f were
smaller than for complexes that did not contain 2,6-fluorinated
phenyl-bound diphosphines such as 3c and 3e. This result does
not agree with the trends shown by the νCO values for Mo-
(diphosphine)(CO)4 and Taft’s σ* values (Table 1). Strong corre-
lations were actually obtained between ln k and Taft’s σ* values
for diphosphine aryl groups (Figure 4) when the diphosphines
were split into two systems (r2 = 0.97 and 0.99). The 2,6-H
system consisted of complexes 3a, 3b, 3c, and 3e, which did not
contain fluorine atoms at the 2- and 6-positions of the dipho-
sphine aryl groups. The 2,6-F system consisted of complexes 3d,
3f, 3g, and 3h, with diphosphines containing 2,6-fluorinated
phenyl groups. This result indicates that differences in dipho-
sphine steric and electronic effects on platinum exist between
2,6-H and 2,6-F system complexes, despite an acceleration of the
reaction induced by an increase in fluorine atom numbers in the
100
complex
[2,6-]
ΔHq
ΔSq
ΔGq
obs
obs
(kcal mol-1
obs
(cal mol-1 K-1
)
)
(kcal mol-1
)
3a [H]
3b [H]
3c [H]
3d [F]
3e [H]
3f [F]
3g [F]
3h [F]
37.8 ( 1.4b
37.2 ( 1.2b
35.0 ( 0.2b
31.7 ( 1.1b
34.7 ( 0.2c
30.9 ( 0.7c
29.1 ( 0.1c
28.7 ( 0.2d
11.5 ( 1.6b
11.8 ( 1.3b
11.0 ( 0.6b
1.1 ( 0.9b
11.6 ( 0.6c
0.1 ( 0.5c
1.0 ( 0.5c
1.4 ( 0.5d
33.5
32.8
30.9
31.3
30.3
30.8
28.7
28.2
a Activation enthalpies (ΔHqobs) and entropies (ΔSqobs) were de-
termined by Arrhenius plots for the thermolysis of complex 3 within.
b 100-110 °C. c 90-110 °C. d 80-105 °C.
mol-1 K-1) and 2,6-F systems (ca. 1 cal mol-1 K-1) may
suggest similar differences in both systems. The experimental
values were interpreted using DFT calculations. In particular,
we focused on clarifying (1) the nature of diphosphine electronic
effects and (2) the effect of diphosphine 2,6-fluorine atoms on
reductive elimination.
Computational Analysis of Reductive Elimination. A.
Conformational Discussion of Complexes 3 and TS-3. We
performed a computational analysis of the reductive elimination
of 3 (details are described in the Experimental Section). All
optimized structures are shown in the Supporting Information.
In the cases of complexes 3a, 3b, 3c, and 3e in the 2,6-H system,
we found three conformers (Figure 6, A-C), depending on the
conformation of the diphosphine aryl groups. Among them,
conformer B was the most stable conformation by ca. 1 kcal
mol-1 as compared to the other conformers. Therefore, we de-
cided that the starting materials from the 2,6-H system would be
conformer B for reductive elimination.23 On the other hand, the
optimization of complexes 3d, 3f, 3g, and 3h from the 2,6-F sys-
tem produces only conformer A. The structures were validated
by comparison with the crystal structure of 3d (Supporting
Information, Figure S25).23
The reductive elimination of 3 proceeds through either direct
or dissociative reaction paths.1b The optimizations of transition
states 3a-3h-TS from a direct path and 3a-3h-TS0 from a
dissociative path gave the single conformers, respectively. The
activation energies (ΔEa) were calculated by subtracting the
energy of the starting material (3) from the energy of the transi-
tion state (3-TS or 3-TS0), which corresponded to a direct path
or dissociative path, respectively (Table 3). In all cases the
1
diphosphines. The correlation between ln k and the JPt-P
coupling constant of complex 3 also showed variations in the
ligand effects on reaction rates (Figure 5). The correlations were
determined by dividing the diphosphines into 2,6-H and 2,6-F
systems, whose correlation coefficients were over 0.99. The
strong correlations between ln k and 1JPt-P suggested that the
electronic nature of the diphosphines played a dominant role in
reductive elimination rates for each system. The kinetic para-
meters of the reductive eliminations were estimated within
90-110 °C (80-105 °C for 3h) to obtain further information
(Table 2). The calculated parameters gave significant informa-
tion regarding differences between 2,6-H and 2,6-F system
trends. Higher ΔHqobs values were obtained for the 2,6-H system
compared to the 2,6-F system, consistent with the trend ob-
tained from Taft’s σ* values for diphosphine aryl groups and
with the νCO values of a molybdenum complex (Table 1).
However, unlike the trend of electron-donating ability of dipho-
sphines, the ΔHq value was greater for 3e, which contains
obs
3,4,5-trifluorophenyl, than for 3d, which contains 2,6-difluor-
ophenyl. This result suggests the existence of conformational
differences between 2,6-H and 2,6-F systems. Furthermore, a
small discrepancy in ΔSq values between 2,6-H (ca. 11 cal
(23) A detailed discussion is described in the Supporting Information.
obs

Article
Organometallics, Vol. 29, No. 18, 2010 4029
Figure 6. Possible conformations of complexes 3.
Table 3. Calculated Activation Energies from 3 to 3-TS
Figure 7. Correlation between calculated ΔEa and experimen-
tal ΔHq
.
obs
ΔEa (kcal mol-1 a,b
)
ligand
3 to 3-TS
3 to 3-TS0
2,6-H system
2,6-F system
1a
1b
1c
1e
1d
1f
30.35
30.09
28.01
27.66
27.18
26.61
25.50
25.06
36.37
36.01
33.08
32.44
32.24
31.82
29.95
29.79
1g
1h
a All structures were optimized at the B3LYP/6-31G* (LANL2DZ
for Pt) level. The energies were calculated at the same level with ZPE
correction. b ΔEa = (energy of 3-TS) - (energy of 3).
Figure 8. Definition of angles for 3 and 3-TS.
previous report,11c the structural changes were very small. The
P1-Pt bond lengths shortened with an increasing number of
fluorine atoms in 3 and 3-TS.25 However, no meaningful
differences were observed for C1-Pt bond lengths, suggesting
that the trans influence of the diphosphine on the reactive phenyl
groups made no difference. The values of θ (Figure 8) were
smaller for 2,6-F-type complexes 3 than for the 2,6-H system
and tended to decrease with increasing number of fluorine
atoms. A greater difference between 2,6-F and 2,6-H systems
was attributed to the twist of the diphosphine aryl groups in
conformers A and B. A similar trend was found in 3-TS, but the
difference was smaller compared to 3. The values of θ in 2,6-H
(90.5-90.8°) and in 2,6-F systems (88.8-88.3°) wereclosetothe
ideal angle (90°), indicating that the conformations facilitate the
overlap of the reactive phenyl sp2 orbitals at the C1-position
regardless of the diphosphine. A larger difference in the tilt angle
(Figure 8) was found in the 2,6-H system in 3-TS compared to
3.26 Relatively large changes in tilt angles from 3 to 3-TS in the
2,6-H system would result in significantly different activation
parameters compared to the 2,6-F system.
dissociative path required a larger ΔEa by ca. 5-6kcalmol-1 as
compared with those of the direct path. Therefore, we con-
cluded that the reductive elimination of 3 proceeded through
the direct path.24 The values of ΔEa in 3 to 3-TS were highly
correlated with experimentally observed ΔHq
values in
Table 2 (Figure 7), indicating that our calculated models are
obs
reliable for evaluating reductive elimination.
B. Steric Effects: Bond Lengths and Angles of Complexes 3
and 3-TS. The calculated bond lengths and angles are
summarized in Table S1 in the Supporting Information for com-
plexes 3 and 3-TS. The bite angles (β, Figure 8) of 2,6-H type
complexes 3 were slightly wider (ca. 0.1-0.3°) than for 2,6-F
type complexes, in concert with the C1-Pt-C2 angles being
narrower, and the C1 C2 distances were shortened with larger
3 3 3
bite angles. However, small differences in β, C1-Pt-C2, and
C1 C2 do not significantly impact the reductive elimination.
3 3 3
In transition states 3-TS, C1-Pt-C2 was broadened within ca.
1.3° and C1 C2 was lengthened within ca. 0.04 A with
˚
3 3 3
increasing number of fluorine atoms. This suggests that the
transition states in the cases of electron-poor diphosphines
lie slightly toward the starting material because of electron-
withdrawing effects. Although this trend is identical to a
Overall, the electronic effect of diphosphines on the structures
of complexes 3 and 3-TS was found to be small. Although steric
effects of diphosphines also had little effect on β and C1-Pt-C2
bond angles and P1-Pt and C1-Pt bond lengths, they were
shown to influence the conformation of the diphosphine aryl
groups (Figure 6, Conformer-A vs. B) and the twist of the reac-
tive phenyl rings (see Supporting Information, Figures S19-
S21). These results would impact the differences in ΔHq and ΔSq
between 2,6-H and 2,6-F systems and can be used to compare
(24) The bite angle of dppe is the geometry where dissociation from
palladium(II) is not easy: Moiseev, D. V.; Malysheva, Y. B.; Shavyrin,
A. S.; Kurskii, Y. A.; Gushchin, A. V. J. Organomet. Chem. 2005, 690,
3652.
(25) This trend has been sometimes observed in the crystal
structure bearing a fluoroaromatic phosphine: (a) Wursche, R.;
Debaerdemaeker, T.; Klinga, M.; Rieger, B. Eur. J. Inorg. Chem.
2000, 9, 2063. (b) Atherton, M. J.; Coleman, K. S.; Fawcett, J.; Holloway,
J. H.; Hope, E. G.; Karacar, A.; Peck, L. A.; Saunders, G. C. J. Chem. Soc.,
Dalton Trans. 1995, 4029.
(26) Ananikov, V. P.; Musaev, D. G.; Morokuma, K. Organometal-
lics 2005, 24, 715.

4030 Organometallics, Vol. 29, No. 18, 2010
Korenaga et al.
Figure 9. Schematic correlation diagram between 3 and 3-TS.
Table 4. Orbital Energies of HOMO-1 in 3 and HOMO in 3-TS
differences in reactivity between both systems. However, they do
not provide explanations for diphosphine electronic effects on
the acceleration of reductive elimination.
orbital energy (eV)a
ligand 3 (HOMO-1) 3-TS (HOMO) ΔEgap (eV)b
C. Electronic Effect of Diphosphine. To obtain information
regarding diphosphine electronic effects on reductive elimina-
tion, we first focused on the platinum electron density in com-
plex 3, because the electron density of the central metal is gene-
rally supposed to influence reductive elimination.1 Platinum
atomic charges in complex 3 were calculated to give Mulliken
and NPA charges.27 However, no good correlation was ob-
2,6-H system
2,6-F system
1a
1b
1c
1e
1d
1f
-5.290
-5.503
-5.647
-5.833
-5.139
-5.336
-5.507
-5.682
-3.639
-3.866
-4.069
-4.268
-3.588
-3.814
-4.038
-4.236
1.650
1.637
1.577
1.566
1.552
1.522
1.469
1.446
1g
1h
served between ΔHq and the platinum atomic charge in
obs
complex 3 (Supporting Information, Table S2, Figure S26).
In the reductive elimination of cis d8 L2MR2 (M=Ni, Pd, Pt)
through a direct path, two electrons are transferred into the d
orbital of M, and then two M-R bond cleavages and R-R
bond formations occur to give d10 L2M and R2. Therefore, the d
orbital of the transition-state HOMO plays a significant role in
the reductive elimination at this stage. The dx2-y2 orbitals of
platinum in the transition state were located in the HOMO
of 3-TS (Figure 9).11c,28 The same d orbitals were found in
HOMO-1 and HOMO-16 of complex 3 (Figure 9), in which
theorbitalsymmetrywasthesameasfortheHOMOof3-TS. In
an early study of the reductive elimination from [PdMe2(PH3)2]
using EHMO calculations, the bonding b2 orbital of [PdMe2-
(PH3)2], whichhadtwoPd-Cσ-bonding orbitals, was shown to
be highly correlated to the activation energy of the reductive
elimination.11a This result suggested that the b2 orbital, which
was the lowest d orbital, was linked to the transition-state
HOMO. The orbital of complex 3corresponding to its b2 orbital
was HOMO-16, which had two Pt-C σ-bonding orbitals
(Figure 9). However, HOMO-16 of 3 did not appear to be
linked to the HOMO of 3-TS, because the HOMO of 3-TS had
π orbitals at the reactive phenyl instead of Pt-C σ-bonding
orbitals. Therefore, the HOMO of 3-TS was connected to the
HOMO-1 of 3, which also had π orbitals at the reactive
phenyl. On the other hand, the HOMO-16 of 3 was linked to
a Orbital energies were calculated at the B3LYP/6-31G* (LANL2DZ for
Pt) level. b ΔEgap=(energy of HOMO in 3-TS) - (energyofHOMO-1in3).
Figure 10. Correlation between ΔEgap and ΔHq
.
obs
the HOMO-16 or HOMO-15 of 3-TS, which had Pt-C
σ-bonding orbitals (Figure 9). The higher energy of HOMO-1
of 3 relative to HOMO-16 of 3 narrows the energy difference
with the HOMO of 3-TS. This is consistent with the fact that the
reductive elimination of two phenyl groups bearing π orbitals is
significantly faster than for two methyl groups bearing only σ
orbitals.11c,26 The energy gap between the HOMO-1 of 3 and
the HOMO of 3-TS (ΔEgap) showed a linear correlation with
ΔHq for the 2,6-H and 2,6-F systems (Table 4, Figure 10). This
result suggests that these d orbitals play a significant role in
the reductive elimination and that electron-poor diphosphines
(27) ESP charges (CHelpG) on platinum showed negative values. See
also the following report: Zimmermann, T.; Zeizinger, M.; Burda, J. V.
J. Inorg. Biochem. 2005, 99, 2184.
(28) Perez-Rodriguez, M.; Braga, A. A. C.; Garcia-Melchor, M.;
Perez-Temprano, M. H.; Casares, J. A.; Ujaque, G.; de Lera, A. R.;
Alvarez, R.; Maseras, F.; Espinet, P. J. Am. Chem. Soc. 2009, 131, 3650.

Article
Table 5. Energies of 3, 3-TS, and Fragment Structuresa
Organometallics, Vol. 29, No. 18, 2010 4031
q
ΔEint
ligand (kcal mol-1 b
ΔEint
(kcal mol-1 c
ΔΔEint
)
)
(kcal mol-1 d
)
2,6-H system
2,6-F system
1a
1b
1c
1e
1d
1f
-51.04
-49.07
-43.86
-42.23
-41.52
-39.27
-35.15
-33.48
-49.65
-47.93
-44.47
-43.07
-40.77
-39.05
-36.78
-35.13
1.39
1.14
-0.61
-0.84
0.75
0.22
-1.63
-1.65
1g
1h
a Energies were calculated at the B3LYP/6-31G* (LANL2DZ for Pt)
level without ZPE correction. b ΔEint = (energy of 3) - (energy of [Pt-
Ph2] þ [L2]). c ΔEintq = (energy of 3-TS) - (energy of [Pt-Ph2]q þ [L2]q).
d ΔΔEint = ΔEintq - ΔEint.
decrease ΔEgap to lower the reaction energy barrier. Although
ΔEgap values decreased with increasing number of fluorine
atoms in each system, the values were not proportional to the
overall electron-withdrawing ability of 1.
Figure 11. Correlation between ΔΔEint and ΔHq
.
obs
ΔΔEMO, whose positive values mean that the destabilization of
the platinum d orbital upon binding to diphosphine is larger in 3-
TS than in 3, identified the nature of diphosphine electronic
effects in the reductive elimination. A good correlation was
obtained between ΔΔEMO and ΔHqobs regardless of the presence
of 2,6-difluorine atoms (Figure 12), suggesting that highly
electron-poor diphosphines may reduce the destabilization in
3-TS relative to the cases of less electron-poor diphosphines to
decrease the activation enthalpy.
To obtain information on the electronic effects of diphosphine,
the energies of fragment structures were calculated by the DFT
method. The structures of 3 and 3-TS were divided into dipho-
sphine fragments ([L2] or [L2]q) and PtPh2 fragments ([Pt-Ph2] or
[Pt-Ph2]q) with the same geometry as the original optimized struc-
tures.11c The calculated energies are summarized in Table 5. The
energy difference (ΔEint) between 3 and [L2] þ [Pt-Ph2] was con-
sidered as the interaction energy between the diphosphine and
platinum complex, and ΔEintq represents the interaction energy in
the transition states in the same way. Both ΔEint and ΔEintq values
were negative and tended to increase with increasing number of
fluorine atoms. This indicates that the diphosphine significantly
stabilizes the nonligated 12eplatinum-diphenyl complex and that
stronger σ-donating diphosphines stabilize this 12e complex to a
greater extent. The results show that the diphosphines stabilized
platinum through σ-donation rather than π-back-donation.29
The ΔΔEint values were calculated from the difference between
ΔEintq and ΔEint. Negative ΔΔEint values thus suggest that the
stabilization by diphosphine is greater in 3-TS than in 3. The
calculated ΔΔEint values were highly correlated to ΔHqobs in each
system (Figure 11), indicating that the electron-poor diphosphine
stabilizes transition state 3-TS rather than reactant 3 to lower the
reaction energy barrier.11c However, the existence of the two
correlations showed that the stabilization did not originate from
diphosphine electronic effects only.
Conclusion
Through the study of the reductive elimination of biphenyl
from 3, we obtained the following conclusions.
(1) The reductive elimination of biphenyl from cis-[Pt-
(Ph)2(diphosphine)] was found to be highly accelerated by
the electronic effects of electron-poor diphosphines. The
fastest reaction, which was observed for 3h, is over 1000
times faster than the slowest reaction.
(2) The nature of the diphosphine ligand effects on re-
ductive elimination was separated into steric 2,6-fluorine
effects and genuine electronic effects. The existence of 2,6-
fluorine or 2,6-hydrogen atoms in the aryl rings on phos-
phorus strongly influenced the conformations of starting
complex 3 and transition state 3-TS to give two correlations
between k (or ΔHqobs) and several parameters.
(3) Strong correlations showed that diphosphine electronic
effects were the main factor in the reductive elimination rates,
although the results were also influenced by steric effects. The
correlation between ΔHqobs and platinum electron density in 3
was not satisfactory, but the d orbital energy gap between
HOMO-1 in 3 and the HOMO in 3-TS was highly correlated
with ΔHqobs. The electron-poor diphosphines decrease the
energy gap to decrease the reaction energy barrier. Reasons
for this decrease in energy gap are that (a) the stabilization of 3-
TS by electron-poor diphosphines exceeds that of 3 and (b) the
destabilization of the platinum d orbital upon binding to dipho-
sphines in 3-TS is reduced by electron-poor diphosphines, which
is the nature of diphosphine electronic effects on reductive
elimination from 3. These results show the electronic effects of
diphosphines on the reductive elimination of biphenyl from
platinum complexes.
Next, we focused on the orbital energies of the fragment struc-
tures (Table 6). The HOMO-2 of [Pt-Ph2] fragments displayed
the same orbital symmetry as the HOMO-1 in complex3. Simi-
larly, the HOMO in [Pt-Ph2]q fragments corresponded to the
HOMO in TS-3. The energy differences between the correspon-
ding orbitals, ΔEMO = (energy of HOMO-1 in 3) - (energy of
q
HOMO-2 in [Pt-Ph2]) and ΔEMO = (energy of HOMO in
3-TS) - (energy of HOMO in [Pt-Ph2]q), were considered as the
stabilization energy of the platinum d orbital upon binding with
q
diphosphine. All ΔEMO and ΔEMO were positive, indicating
that the platinum d orbitals were destabilized upon binding
with diphosphines. This destabilization results from the P-
Pt σ*-antibonding character (see Supporting Information,
Figure S27), which disfavors the strong σ-donating character
q
of diphosphines.11c The decrease in ΔEMO and ΔEMO values
with increasing number of fluorine atoms suggests that electron-
poor diphosphines tend to ease the destabilization. The values of
Although only one aspect of ligand effects could be shown,
the conclusions are not always applicable to other reductive
elimination systems. For example, differences in the central
metals will cause changes in the d orbital energy order, and
(29) (a) Yamanaka, M.; Shiga, A. J. Theor. Comput. Chem. 2005, 4,
345. (b) Yamanaka, M.; Mikami, K. Organometallics 2005, 24, 4579.

4032 Organometallics, Vol. 29, No. 18, 2010
Table 6. Orbital Energies of 3, 3-TS, and Fragment Structures
Korenaga et al.
orbital energy (eV)a
orbital energy (eV)a
ligand 3, HOMO-1 [Pt-Ph2], HOMO-2 ΔEMO (eV)b 3-TS, HOMO [Pt-Ph2]q, HOMO ΔEMOq (eV)c ΔΔEMO (eV)d
2,6-H system
2,6-F system
1a
1b
1c
1e
1d
1f
-5.290
-5.503
-5.647
-5.833
-5.139
-5.336
-5.507
-5.682
-6.496
-6.499
-6.463
-6.475
-6.540
-6.566
-6.571
-6.585
1.206
0.996
0.816
0.642
1.401
1.230
1.064
0.903
-3.639
-3.866
-4.069
-4.268
-3.588
-3.814
-4.038
-4.236
-5.150
-5.159
-5.173
-5.179
-5.163
-5.174
-5.208
-5.217
1.511
1.293
1.104
0.911
1.575
1.360
1.170
0.981
0.305
0.297
0.288
0.269
0.174
0.130
0.106
0.078
1g
1h
a Orbital energies were calculated at the B3LYP/6-31G* (LANL2DZ for Pt) level. b ΔEMO = (energy of HOMO-1 in 3) - (energy of HOMO-2 in
[Pt-Ph2]). c ΔEMOq = (energy of HOMO in 3-TS) - (energy of HOMO in [Pt-Ph2]q). d ΔΔEMO = ΔEMOq - ΔEMO.
was purchased from Kanto Chemical Co., Inc. Other reagents were
purchased at the highest commercial quality and used without further
purification, unless otherwise noted. Preparative column chromatog-
raphy was carried out by using silica gel (Fuji Silysia BW-127 ZH,
100-270 mesh). 1H NMR and 13C NMR spectra were measured at
300 or 500 MHz and 75 or 125 MHz or 150 MHz, respectively, and
chemical shifts are given relative to tetramethylsilane (TMS). 19F
NMR spectra were measured at 282 MHz, and chemical shifts are
given relative to CCl3F using C6F6 as a secondary reference (-162.9
ppm). 31P NMR spectra were measured at 121 MHz, and chemical
shifts are given relative to 85% H3PO4 as an external standard.
Thermolysis samples were heated in an oil bath (Mini-heater MH-
5E, Riko).
[1,2-Bis{diphenylphophino}ethane]tetracarbonylmolybdenum
[2a].30 Dppe (51.5 mg, 129 μmol) and [Mo(CO)4(nbd)] (46.2 mg,
154 μmol) were dissolved in 4 mL of dichloroethane, and then the
solution was stirred for 3 h at 60 °C under argon atmosphere. The
filtered solution was concentrated under reduced pressure. The
Figure 12. Correlation between ΔΔEMO and ΔHq
.
obs
desired product was purified by recrystallization from CH2Cl2-
hexane. The white crystalline product was obtained in a yield of
74% (58.3 mg). Mp: 190-191 °C (dec). 1H NMR (acetone-d6, 300
MHz): δ 2.71-2.87 (m, 4H), 7.38-7.47 (m, 12H), 7.67-7.74 (m,
8H). 31P NMR (acetone-d6, 121 MHz): δ 59.5 (s). IR (CH2Cl2):
the reaction following the dissociative path will result in
different orbital states in the transition state compared to the
reaction following the direct path. These cases might lead to
different results and conclusions. However, the correlation
method between experimental and theoretical values that we
performed in this study will play an important role in clarifying
other mechanisms for the reductive elimination reaction.
2021.4, 1912, 1884, 1099, 895, and 587 cm-1
.
[1,2-Bis{bis(4-fluorophenyl)phophino}ethane]tetracarbonyl-
molybdenum [2b]. Complex 2b was prepared similarly to the syn-
thesis of 2a from [Mo(CO)4(nbd)] (58.9 mg, 196 μmol) and 1,2-
bis[bis(4-fluorophenyl)phophino]ethane (80.3 mg, 171 μmol). The
white crystalline product was obtained in a yield of 65% (75.2 mg).
Mp: 178-179 °C (dec). 1H NMR (acetone-d6, 300 MHz): δ 2.75-
2.89 (m, 4H), 7.22-7.29 (m, 8H), 7.71-7.80 (m, 8H). 19F NMR
(acetone-d6, 282 MHz): δ -107.8 (s, 4F ). 31P NMR (acetone-d6,
121 MHz): δ 59.1 (s). IR (CH2Cl2): 2023.4, 1912, 1889, 1592, 1496,
1235, 1162, 1096, and 828 cm-1. Anal. Calcd for C30H20F4MoO4P2:
C, 53.12; H, 2.97. Found: C, 53.03; H, 3.14.
Experimental Section
General Experimental Methods. All reactions were carried out
under an argon atmosphere with dry solvents under anhydrous
conditions, unless otherwise noted. Dehydrated benzene, dichloro-
methane, hexane, tetrahydrofuran (THF ), diethyl ether, and
toluene were purchased from Kanto Chemical Co., Inc. and then
were stored in Schlenk tubes under an argon atmosphere. 1,2-Bis-
[bis(pentafluorophenyl)phosphino]ethane (DFPPE) was purchased
from Sigma-Aldrich. 1,2-Bis(diphenylphosphino)ethane (DPPE)
(30) Grim, O. G.; Briggs, W. L.; Barth, R. C.; Tolman, C. A.; Jesson,
J. P. Inorg. Chem. 1974, 13, 1095.

Article
[1,2-Bis{bis(3,5-difluorophenyl)phophino}ethane]tetracarbonyl-
Organometallics, Vol. 29, No. 18, 2010 4033
synthesis of 2a from [Mo(CO)4(nbd)] (34.4 mg, 115 μmol) and
1,2-bis[bis(4-heptafluorotolyl)phophino]ethane (93.6 mg, 97.7
μmol). The yellow crystalline product was obtained in a yield of
molybdenum [2c]. Complex 2c was prepared similarly to the
synthesis of 2a from [Mo(CO)4(nbd)] (45.9 mg, 153 μmol) and
1,2-bis[bis(3,5-difluorophenyl)phophino]ethane (73.3 mg, 135
μmol). The white crystalline product was obtained in a yield of
60% (61.0 mg). Mp: 175-176 °C (decompose). 1H NMR
(acetone-d6, 300 MHz): δ 3.04-3.13 (m, 4H), 7.13-7.24 (m,
4H), 7.34-7.44 (m, 8H). 19F NMR (acetone-d6, 282 MHz): δ
-104.6 (s, 8F ). 31P NMR (acetone-d6, 121 MHz): δ 67.4 (s). IR
(CH2Cl2): 2029.6, 1921, 1608, 1590, 1421, 1288, 1125, 988, and
860 cm-1. Anal. Calcd for C30H16F8MoO4P2: C, 48.02; H, 2.15.
Found: C, 48.20; H, 2.07.
1
46% (53.7 mg). Mp: 234-235 °C (dec). H NMR (acetone-d6,
300 MHz): δ 3.38-3.45 (m, 4H). 19F NMR (acetone-d6, 282
MHz): δ -136.3 to -136.2 (m, 8F ), -124.9 (m, 8F ), -53.6 to
-53.5 (m, 12F ). 31P NMR (acetone-d6, 121 MHz): δ 43.6 (s). IR
(CH2Cl2): 2044.8, 1967, 1942, 1472, 1326, 1187, 1160, and 980
cm-1. Anal. Calcd for C34H4F28MoO4P2: C, 35.02; H, 0.35.
Found: C, 34.84; H, 0.63.
[1,2-Bis{bis(4-fluorophenyl)phosphino}ethane]dichloroplati-
num(II). A solution of [PtCl2(cod)] (56.1 mg, 150 μmol) and 1b
(70.6 mg, 150 μmol) in toluene (3 mL) was stirred at reflux for 12 h
under argon atmosphere. The reaction mixture was cooled to room
temperature, and the insoluble white crystalline product was
filtered and washed several times with diethyl ether in air.
The white crystals were obtained in a yield of 93% (102 mg). Mp
> 300 °C. 1H NMR (acetone-d6, 300 MHz): δ 2.63-2.76 (m, 4H),
7.31-7.35 (m, 8H), 7.99-8.05 (m, 8H). 13C NMR (CD2Cl2, 75
MHz): δ 27.6-29.3 (m), 115.9-116.3 (m), 121.5-122.8 (m),
135.3-135.9 (m), 163.1-166.5 (m). 19F NMR (acetone-d6, 282
MHz): δ -105.2 (s, 4F ). 31P NMR (acetone-d6, 121 MHz): δ 45.5
(s w/Pt-satellites, 1JPt-P = 3598 Hz). IR (KBr): 1589, 1497, 1240,
1163, 1103, 829, and 530 cm-1. Anal. Calcd for C26H20Cl2F4P2Pt:
C, 42.41; H, 2.74. Found: C, 42.10; H, 2.74.
[1,2-Bis{bis(3,5-difluorophenyl)phosphino}ethane]dichloroplati-
num(II). The title complex was prepared from [PtCl2(cod)]
(56.1 mg, 150 μmol) and 1c (81.4 mg, 150 μmol) in a similar
manner to the synthesis of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II). The white crystalline pro-
duct was obtained in a yield of 97% (118 mg). Mp > 300 °C. 1H
NMR (acetone-d6, 300 MHz): δ 2.90-3.20 (m, 4H), 7.30-7.38
(m, 4H), 7.67-7.74 (m, 8H). 19F NMR (acetone-d6, 282 MHz): δ
-104.6 to -104.5 (m, 8F ). 31P NMR (acetone-d6, 121 MHz): δ
49.0 (s w/Pt-satellites, 1JPt-P = 3594 Hz). IR (KBr): 1653, 1589,
1425, 1294, 1124, 860, and 675 cm-1. Anal. Calcd for C26H16Cl2-
F8P2Pt: C, 38.63; H, 2.00. Found: C, 38.33; H, 1.98.
[1,2-Bis{bis(2,6-difluorophenyl)phosphino}ethane]dichloroplati-
num(II). The title complex was prepared from [PtCl2(cod)]
(56.1 mg, 150 μmol) and 1d (81.4 mg, 150 μmol) in a similar
manner to the synthesis of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II). The white crystalline pro-
duct was obtained in a yield of 84% (102 mg). Mp > 300 °C. 1H
NMR (DMSO-d6, 300 MHz): δ 2.73-2.87 (m, 4H), 7.26-
7.29 (m, 8H), 7.74-7.79 (m, 4H). 19F NMR (acetone-d6, 282
MHz): δ -93.6 (s, 8F ). 31P NMR (DMSO-d6, 121 MHz): δ 15.4
(s w/Pt-satellites, 1JPt-P = 3733 Hz). IR (KBr): 1612, 1558, 1456,
1225, 1111, 986, and 791 cm-1. Anal. Calcd for C26H16Cl2F8P2Pt:
C, 38.63; H, 2.00. Found: C, 38.34; H, 2.20.
[1,2-Bis{bis(2,6-difluorophenyl)phophino}ethane]tetracarbonyl-
molybdenum [2d]. 12b Complex 2d was prepared similarly to
the synthesis of 2a from [Mo(CO)4(nbd)] (58.1 mg, 194 μmol)
and 1,2-bis[bis(2,6-difluorophenyl)phophino]ethane (92.3
mg, 170 μmol). The white crystalline product was obtained
in a yield of 70% (89.7 mg). Mp: 195-196 °C (dec). 1H NMR
(300 MHz, acetone-d6): δ 3.04-3.11 (m, 4H), 7.04-7.11 (m,
8H), 7.53-7.63 (m, 4H). 19F NMR (acetone-d6, 282 MHz): δ
-97.1 (s, 8F ). 31P NMR (acetone-d6, 121 MHz): δ 32.2 (s). IR
(CH2Cl2): 2030.1, 1939, 1916, 1611, 1458, 1232, 1104, 987,
and 791 cm-1
.
[1,2-Bis{bis(3,4,5-trifluorophenyl)phophino}ethane]tetracarbonyl-
molybdenum [2e]. Complex 2e was prepared similarly to the
synthesis of 2a from [Mo(CO)4(nbd)] (59.0 mg, 197 μmol) and
1,2-bis[bis(3,4,5-trifluorophenyl)phophino]ethane (106 mg, 173
μmol). The white crystalline product was obtained in a yield of
1
79% (112 mg). Mp: 221-222 °C (dec). H NMR (acetone-d6,
300 MHz): δ 3.05-3.15 (m, 4H), 7.52-7.60 (m, 8H). 19F NMR
(acetone-d6, 282 MHz): δ -154.8 to -154.6 (m, 4F ), -129.8 to
-129.7 (m, 8F ). 31P NMR (acetone-d6, 121 MHz): δ 68.7 (s). IR
(CH2Cl2): 2031.3, 1941, 1922, 1616, 1522, 1419, 1320, 1081,
1051, and 897 cm-1. Anal. Calcd for C30H12F12MoO4P2: C,
43.82; H, 1.47. Found: C, 43.61; H, 1.78.
[1,2-Bis{bis(2,4,6-trifluorophenyl)phophino}ethane]tetracarbonyl-
molybdenum [2f]. Complex 2f was prepared similarly to the
synthesis of 2a from [Mo(CO)4(nbd)] (52.5 mg, 175 μmol) and
1,2-bis[bis(2,4,6-trifluorophenyl)phophino]ethane (80.9 mg,
132 μmol). The white crystalline product was obtained in a yield
of 48% (52.4 mg). Mp: 181-182 °C (dec). 1H NMR (acetone-d6,
300 MHz): δ 3.03-3.10 (m, 4H), 7.03-7.10 (m, 8H). 19F NMR
(acetone-d6, 282 MHz): δ -100.9 to -100.8 (m, 4F ), -94.0 to
-93.9 (m, 8F ). 31P NMR (acetone-d6, 121 MHz): δ 32.1 (s). IR
(CH2Cl2): 2032.1, 1942, 1920, 1630, 1605, 1586, 1429, 1171,
1126, 1084, 1006, 897, and 847 cm-1. Anal. Calcd for C30H12-
F12MoO4P2: C, 43.82; H, 1.47. Found: C, 44.07; H, 1.63.
[1,2-Bis{bis(2,3,5,6-tetrafluorophenyl)phophino}ethane]tetra-
carbonylmolybdenum [2g]. Complex 2g was prepared similarly to
the synthesis of 2a from [Mo(CO)4(nbd)] (31.9 mg, 106 μmol) and
1,2-bis[bis(2,3,5,6-tetrafluorophenyl)phophino]ethane (67.1 mg,
97.8 μmol). The white crystalline product was obtained in a yield
of 45% (39.4 mg). Mp: 237-238 °C (dec). 1H NMR (acetone-d6,
300 MHz): δ 3.26-3.33 (m, 4H), 7.74-7.83 (m, 4H). 19F NMR
(acetone-d6, 282 MHz): δ -134.5 to -134.5 (m, 8F ), -127.9 (m,
8F ). 31P NMR (acetone-d6, 121 MHz): δ 40.3 (s). IR (CH2Cl2):
2038.8, 1958, 1931, 1483, 1231, 1176, and 917 cm-1. Anal. Calcd for
C30H8F16MoO4P2: C, 40.29; H, 0.90. Found: C, 40.12; H, 0.57.
[1,2-Bis{bis(pentafluorophenyl)phophino}ethane]tetracarbonyl-
molybdenum [2h].15. Complex 2h was prepared similarly to the
synthesis of 2a from [Mo(CO)4(nbd)] (42.0 mg, 140 μmol) and
dfppe (100 mg, 132 μmol). The white crystalline product was
obtained in a yield of 24% (30.1 mg). Mp: 237-238 °C (dec). 1H
NMR (acetone-d6, 300 MHz): δ 3.25-3.32 (m, 4H). 19F NMR
(acetone-d6, 282 MHz): δ -161.8 to -161.6 (m, 8F ), -151.0 to
-150.8 (m, 4F ), -131.3 to -131.2 (m, 8F ). 31P NMR (acetone-
d6, 121 MHz): δ 35.8 (s). IR (CH2Cl2): 2040.7, 1961, 1933, 1093,
[1,2-Bis{bis(3,4,5-trifluorophenyl)phosphino}ethane]dichloro-
platinum(II). The title complex was prepared from [PtCl2(cod)]
(56.1 mg, 150 μmol) and 1e (92.2 mg, 150 μmol) in a similar
manner to the synthesis of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II). The white crystalline pro-
duct was obtained in a yield of 94% (124 mg). Mp > 300 °C. 1H
NMR (acetone-d6, 300 MHz): δ 2.99-3.10 (m, 4H), 7.87-7.93
(m, 8H). 13C NMR (acetone-d6,125 MHz): δ 28.2-28.8 (m),
119.5-119.8 (m), 123.8-124.4 (m), 141.9-144.1 (m), 150.6-
152.9 (m). 19F NMR (acetone-d6, 282 MHz): δ -151.4 to -151.2
(m, 4F), -129.6 to -129.4 (m, 8F ). 31P NMR (acetone-d6,
1
121 MHz): δ 48.2 (s w/Pt-satellites, JPt-P = 3606 Hz). IR
(KBr): 1618, 1526, 1421, 1325, 1090, 1051, and 625 cm-1. Anal.
Calcd for C26H12Cl2F12P2Pt: C, 35.47; H, 1.37. Found: C, 35.56;
H, 1.08.
[1,2-Bis{bis(2,4,6-trifluorophenyl)phosphino}ethane]dichloro-
platinum(II). The title complex was prepared from [PtCl2(cod)]
(56.1 mg, 150 μmol) and 1f (92.2 mg, 150 μmol) in a similar
manner to the synthesis of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II). The white crystalline pro-
duct was obtained in a yield of 94% (124 mg). Mp > 300 °C.
981, and 894 cm-1
.
[1,2-Bis{bis(4-heptafluorotolyl)phophino}ethane]tetracarbonyl-
molybdenum [2i]. Complex 2i was prepared similarly to the

4034 Organometallics, Vol. 29, No. 18, 2010
Korenaga et al.
1H NMR (acetone-d6, 300 MHz): δ 2.90-3.09 (m, 4H), 7.12-7.19
(m, 8H). 19F NMR (acetone-d6, 282 MHz): δ -97.7 to -97.6 (m,
4F ), -90.4 (s, 8F ). 31P NMR (acetone-d6, 121 MHz): δ 15.4 (s w/
Pt-satellites, 1JPt-P = 3698 Hz). IR (KBr): 1684, 1636, 1609, 1585,
1558, 1435, 1130, 1099, 1024, 1003, and 841 cm-1. Anal. Calcd for
C26H12Cl2F12P2Pt: C, 35.47; H, 1.37. Found: C, 35.47; H, 1.53.
[1,2-Bis{bis(2,3,5,6-tetrafluorophenyl)phosphino}ethane]dichlo-
roplatinum(II). The title complex was prepared from [PtCl2(cod)]
(56.1 mg, 150 μmol) and 1g (103 mg, 150 μmol) in a similar
manner to the synthesis of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II). The white crystalline product
was obtained in a yield of 95% (136 mg). Mp > 300 °C. 1H NMR
(DMSO-d6, 300 MHz): δ 3.14-3.18 (m, 4H), 8.34-8.41 (m, 4H).
19F NMR (DMSO-d6, 282 MHz): δ -133.6 to -133.4 (m, 8F ),
-124.2 to -124.1 (m, 8F ). 31P NMR (DMSO-d6, 121 MHz): δ
21.9 (s w/Pt-satellites, 1JPt-P = 3681 Hz). IR (KBr): 1522, 1477,
1240, and 1238 cm-1. Anal. Calcd for C26H8Cl2F16P2Pt: C, 35.47;
H, 1.37. Found: C, 32.79; H, 0.85.
136.2-136.7(m), 160.4-162.0 (m). 31P NMR (CDCl3, 121 MHz):
δ 41.0 (s w/Pt-satellites, 1JPt-P = 1689 Hz). IR (KBr): 3058, 1569,
1474, 1434, 1104, 1025, 876, 817, 748, 733, 727, 691, 680, and
528 cm-1
.
[1,2-Bis{bis(4-fluorophenyl)phosphino}ethane]diphenylplati-
num(II) (3b).32 A slurry of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II) (102 mg, 139 μmol) in di-
ethyl ether (7 mL) was cooled to -78 °C, and PhMgBr in
diethyl ether (3 M, 280 μL, 0.84 mmol) was added dropwise
under argon atmosphere. The reaction mixture was stirred for
14 h at room temperature. The solvent was removed under
reduced pressure, and the residue was dissolved in dichloro-
methane. The solution was washed with degassed water. The
organic layer was dried over MgSO4, and was filtered by glass
wool. After concentration of the solution, hexane was added
to the reaction mixture slowly. After standing at -20 °C for
16 h, the white crystals were obtained in a yield of 88% (101 mg).
1
Mp > 250 °C (dec). H NMR (CDCl3, 300 MHz): δ 2.14-
[1,2-Bis{bis(pentafluorophenyl)phosphino}ethane]dichloro-
platinum(II).10 The title complex was prepared from [PtCl2-
(cod)] (50.0 mg, 134 μmol) and DFPPE (1h) (101 mg,
133 μmol) in a similar manner to the synthesis of [1,2-bis{bis-
(4-fluorophenyl)phosphino}ethane]dichloroplatinum(II). The
white crystalline product was obtained in a yield of 98% (133
mg). Mp > 300 °C. 1H NMR (acetone-d6, 300 MHz,): δ 3.20-
3.38 (m, 4H). 13C NMR (acetone-d6, 150 MHz): δ 30.5-31.4
(m), 101.3-102.0 (m), 138.0-139.9 (m), 144.6-146.5 (m),
147.4-149.3 (m). 19F NMR (acetone-d6, 282 MHz): δ -157.2
to -157.1 (m, 8F ), -142.6 to -142.4 (m, 4F ), -123.5 to -123.4
(m, 8F ). 31P NMR (acetone-d6, 121 MHz,): δ 20.9 (s w/Pt-
satellites, 1JPt-P = 3644 Hz). IR (KBr): 1520, 1479, 1094, and
2.27 (m, 4H), 6.63-6.67 (m, 2H), 6.76-6.80 (m, 4H), 7.00-
7.26 (m, 12H), 7.37-7.45 (m, 8H). 13C NMR (CDCl3, 125
MHz): δ 28.0-28.5 (m), 116.3-116.7 (m), 122.0, 127.4-127.9
(m), 128.0-128.4 (m), 136.5-136.6 (m), 137.5-137.8 (m),
161.5-162.5 (m), 164.0-166.0 (m). 19F NMR (CDCl3, 282
MHz): δ -110.2 to -110.3 (m, 4F ). 31P NMR (CDCl3, 121
1
MHz): δ 39.3 (s w/Pt-satellites, JPt-P = 1679 Hz). IR (KBr):
1589, 1558, 1495, 1232, 1159, 1099, 827, 814, 729, 704, 527, and
517 cm-1
.
[1,2-Bis{bis(3,5-difluorophenyl)phosphino}ethane]diphenylplati-
num(II) (3c). The complex 3c was prepared from [1,2-bis{bis-
(3,5-difluorophenyl)phosphino}ethane]dichloroplatinum(II)
(93.0 mg, 115 μmol) and PhMgBr in diethyl ether (3 M, 240 μL,
0.72 mmol) in a similar manner to the synthesis of 3b. The white
crystals were obtained in a yield of 76% (78 mg). Mp> 200 °C
(dec). 1H NMR (CDCl3, 300 MHz): δ 2.26-2.31 (m, 4H),
6.70-6.75 (m, 2H), 6.85-6.95 (m, 16H), 7.02-7.26 (m, 4H).
980 cm-1
.
[1,2-Bis{bis(4-heptafluorotolyl)phosphino}ethane]dichloroplati-
num(II). The title complex was prepared from [PtCl2(cod)]
(56.1 mg, 150 μmol) and 1i (144 mg, 150 μmol) in a similar
manner to the synthesis of [1,2-bis{bis(4-fluorophenyl)phos-
phino}ethane]dichloroplatinum(II). The white crystalline pro-
duct was obtained in a yield of 96% (177 mg). Mp > 300 °C. 1H
NMR (acetone-d6, 300 MHz,): δ 3.39-3.58 (m, 4H). 19F NMR
(acetone-d6, 282 MHz): δ -135.7 to -135.8 (m, 8F ), -121.1 to
-121.2 (m, 8F ), -54.0 to -53.8 (m, 12F ). 31P NMR (acetone-d6,
121 MHz): δ 24.6 (s w/Pt-satellites, 1JPt-P = 3604 Hz). IR (KBr):
1479, 1329, 1190, 1159, 982, 947, and 716 cm-1. Anal. Calcd for
C30H4Cl2F28P2Pt: C, 35.47; H, 1.37. Found: C, 35.56; H, 1.08.
[1,2-Bis(diphenylphosphino)ethane]diphenylplatinum(II)
(3a).31 To a slurry of [PtCl2(cod)] (206 mg, 550 μmol) in diethyl
ether (29 mL) was added dropwise PhMgBr in diethyl ether
(2.5 M, 490 μL, 1.2 mmol), and the mixture was stirred for 13 h
at room temperature under argon atmosphere. The reaction mix-
ture was washed with saturated aqueous NH4Cl in air. Then,
the organic layer was dried over MgSO4, filtered, and concen-
trated. The residue was recrystallized from CH2Cl2-pentane to
13C NMR, (acetone-d6, 125 MHz):
δ 27.6-28.1 (m),
107.1-107.5 (m), 116.9-117.2 (m), 122.7, 127.8-128.4 (m),
135.4-135.9 (m), 137.1-137.4 (m), 160.0-161.0 (m), 162.4-
164.7 (m). 19F NMR (CDCl3, 282 MHz): δ -108.0 to -107.9 (m,
8F ). 31P NMR (CDCl3, 121 MHz): δ 42.0 (s w/Pt-satellites,
1JPt-P = 1641 Hz). IR (KBr): 1609, 1587, 1420, 1292, 1123, 986,
854, 743, and 669 cm-1. Anal. Calcd for C38H26F8P2Pt: C, 51.19;
H, 2.94. Found: C, 50.90; H, 3.13.
[1,2-Bis{bis(2,6-difluorophenyl)phosphino}ethane]diphenylplati-
num(II) (3d). The complex 3d was prepared from [1,2-bis{bis-
(2,6-difluorophenyl)phosphino}ethane]dichloroplatinum(II)
(119 mg, 147 μmol) and PhMgBr in diethyl ether (3 M, 300 μL,
0.90 mmol) in a similar manner to the synthesis of 3b. The white
crystals were obtained in a yield of 58% (76 mg). Mp>300 °C
(dec). 1H NMR (CDCl3, 300 MHz): δ 2.71-2.81 (m, 4H),
6.48-6.53 (m, 2H), 6.60-6.64 (m, 4H), 6.76-6.80 (m, 8H),
6.90-7.20 (m, 4H), 7.29-7.35 (m, 4H). 13C NMR (CD2Cl2, 125
MHz): δ 28.3-29.0 (m), 106.4-107.9 (m), 111.4-111.7 (m),
1
give 177 mg of brown crystals (70%). Mp > 300 °C. H NMR
(CDCl3, 500 MHz): δ 2.51-2.55 (m, 8H), 5.15 (s w/Pt-satellites,
1JPt-H = 36.6 Hz, 4H), 6.85-6.89 (m, 2H), 7.03-7.06 (m, 4H),
7.30 (m w/Pt-satellites, 3JPt-H = 69.3 Hz, 4H). 13C NMR (CDCl3,
125 MHz): δ 28.8, 104.3-104.7 (m), 122.8, 127.3-127.9 (m),
134.5-134.9 (m), 155.6.
(33) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision D.02 and E.01; Gaussian,
Inc.: Wallingford, CT, 2004.
[Pt(Ph)2(cod)] (62.0 mg, 136 μmol) and DPPE (1a) (54.0 mg,
136 μmol) in benzene (5.4 mL) were stirred for 1.5 h. The solvent
was removed under reduced pressure, and the residue was recrys-
tallized from CH2Cl2-hexane to give 71.4 mg of brown crystals
1
(70%). Mp > 300 °C (dec). H NMR (CDCl3, 300 MHz): δ
2.19-2.34 (m, 4H), 6.59-6.64 (m, 2H), 6.72-6.76 (m, 4H),
7.04-7.28 (m, 4H), 7.31-7.50 (m, 20H). 13C NMR (CD2Cl2, 75
MHz): δ 27.3-28.2 (m), 120.8-120.9 (m), 126.0-127.0 (m),
128.0-128.1 (m), 130.1, 130.6-131.5 (m), 132.8-133.1 (m),
(31) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738.
(32) Clarke, M. L.; Heydt, M. Organometallics 2005, 24, 6475.

Article
Organometallics, Vol. 29, No. 18, 2010 4035
120.6, 125.6-126.6 (m), 132.6-132.9 (m), 134.7-135.2 (m),
158.7-160.5 (m), 161.2-164.7 (m). 19F NMR (CDCl3, 282
MHz): δ -99.6 (s, 8F ). 31P NMR (CDCl3, 121 MHz): δ 11.3
(s w/Pt-satellites, 1JPt-P= 1634 Hz). IR (KBr): 1684, 1612, 1570,
1456, 1231, 986, and 785 cm-1. Anal. Calcd for C38H26F8P2Pt:
C, 51.19; H, 2.94. Found: C, 50.89; H, 3.15.
Crystals of 3d for X-ray analysis were obtained from
CH2Cl2-hexane at room temperature. Crystal data and anal-
ysis results are given in the Supporting Information.
-158.3 (m, 8F ), -146.4 to -146.2 (m, 4F ), -125.7 to -125.6
(m, 8F ). 31P NMR (CDCl3, 121 MHz): δ 14.3 (s w/Pt-satellites,
1JPt-P = 1537 Hz).
[1,2-Bis{bis(pentafluorophenyl)phosphino}ethane]diiodoplati-
num(II). To a solution of [(dfppe)PtCl2] (121 mg, 118 μmol) in
CH2Cl2 (15 mL) was added KI (102 mg, 614 μmol) under argon
atmosphere. The reaction mixture was stirred overnight and was
filtered through neutral alumina. The solvent was removed
under reduced pressure. The residue was recrystallized from
CH2Cl2-hexane to give 118 mg of light yellow crystals (83%).
Mp > 300 °C (dec). 1H NMR (acetone-d6, 300 MHz): δ
2.95-3.12 (m, 4H). 19F NMR (acetone-d6, 282 MHz): δ
-157.3 to -157.2 (m, 8F ), -142.6 to -142.5 (m, 4F ), -123.6
to -123.4 (m, 8F ). 31P NMR (acetone-d6, 121 MHz): δ 46.6 (s
w/Pt-satellites, 1JPt-P = 3368 Hz). IR (KBr): 1618, 1526, 1421,
1325, 1090, 1051, and 625 cm-1. Anal. Calcd for C26H4I2F20-
P2Pt: C, 25.87; H, 0.33. Found: C, 25.79; H, 0.64.
[1,2-Bis{bis(3,4,5-trifluorophenyl)phosphino}ethane]diphenyl-
platinum(II) (3e). The complex 3e was prepared from [1,2-bis-
{bis(3,4,5-trifluorophenyl)phosphino}ethane]dichloroplati-
num(II) (132 mg, 150 μmol) and PhMgBr in diethyl ether (3 M,
300 μL, 0.90 mmol) in a similar manner to the synthesis of 3b. The
white crystals were obtained in a yield of 67% (98 mg). Mp> 200
1
°C (dec). H NMR (CDCl3, 300 MHz): δ 2.19-2.29 (m, 4H),
6.74-6.79 (m, 2H), 6.89-6.98 (m, 12H), 6.90-7.20 (m, 4H). 13
C
NMR (acetone-d6, 75 MHz): δ 27.2-28.0 (m), 118.6-119.3 (m),
122.8, 127.5-127.7 (m), 127.7-128.7 (m), 137.0-137.4 (m),
140.2-144.0 (m), 149.8-153.5 (m), 159.4-161.1 (m). 19F NMR
(CDCl3, 282 MHz):δ-131.5 to -131.7 (m, 8F ), -154.7 to -154.9
(m, 4F). 31P NMR (CDCl3, 121 MHz): δ 41.2 (s w/Pt-satellites,
1JPt-P = 1626 Hz). IR (KBr): 1684, 1558, 1522, 1418, 1323, and
1049 cm-1. Anal. Calcd for C38H22F12P2Pt: C, 47.37; H, 2.30.
Found: C, 47.56; H, 2.68.
[1,2-Bis{bis(2,4,6-trifluorophenyl)phosphino}ethane]diphenyl-
platinum(II) (3f). The complex 3f was prepared from [1,2-bis-
{bis(2,4,6-trifluorophenyl)phosphino}ethane]dichloroplati-
num(II) (124 mg, 141 μmol) and PhMgBr in diethyl ether (3 M,
280 μL, 0.84 mmol) in a similar manner to the synthesis of 3b.
The white crystals were obtained in a yield of 76% (103 mg).
Mp>250 °C (dec). 1H NMR (CDCl3, 300 MHz): δ 2.66-2.78
(m, 4H), 6.55-6.60 (m, 10H), 6.65-6.70 (m, 4H), 6.90-7.15 (m,
4H). 13C NMR (CD2Cl2, 75 MHz): δ 28.2-29.1 (m), 100.4-
101.1 (m), 102.4-103.3 (m), 120.9-121.1 (m), 125.9-126.9 (m),
134.5-135.0 (m), 158.2-160.1 (m), 161.5-165.3 (m), 162.6-
166.4 (m). 19F NMR (CDCl3, 282 MHz): δ -104.3 to -104.1 (m,
4F ), -96.8 (s, 8F ). 31P NMR (CDCl3, 121 MHz): δ 11.0 (s w/Pt-
satellites, 1JPt-P = 1621 Hz). IR (KBr): 1632, 1605, 1585, 1429,
1171, 1128, 1092, 1024, 1003, 851, 841, 737, 729, 716, 702, and
515 cm-1. Anal. Calcd for C38H22F12P2Pt: C, 47.37; H, 2.30.
Found: C, 47.10; H, 2.50.
[1,2-Bis{bis(pentafluorophenyl)phosphino}ethane]diphenyl-
acetyleneplatinum(II) (7h). To a solution of [(dfppe)PtI2] (118 mg,
97.8 μmol) in degassed 1,2-dichloroethane (25 mL) was added
diphenylacetylene (17.5 mg, 98.2 μmol) under argon atmosphere.
The reaction mixture was stirred at 80 °C for 1.5 h, and then the
solvent was concentrated under reduced pressure. The resulting light
yellow solid was dissolved in 25 mL of degassed ethanol, NaBH4
(8.6 mg, 0.23 mmol) in H2O (4 mL) was added, and the mixture was
then was stirred for 3 h under argon atmosphere. The yellow
precipitate was filtered quickly and was dried in vacuo. The solid
was recrystallized from CH2Cl2-hexane to give 68.0 mg of light
yellow crystals (61%). 1H NMR (acetone-d6, 300MH):δ2.95-3.10
(m, 4H), 7.15-7.22 (m, 2H), 7.23-7.32 (m, 4H), 7.40-7.47 (m,
4H). 13C NMR (acetone-d6, 75 MHz): δ 31.3-32.2 (m),
109.0-110.0 (m), 127.8, 129.0, 130.3-130.9 (m), 134.2-134.5
(m), 136.8-140.9 (m), 141.8-145.9 (m), 146.0-149.5 (m). 19F
NMR (toluene-d8, 282 MHz): δ -160.7 to -160.5 (m, 8F ),
-149.0 to -148.8 (m, 4F ), -132.3 to -132.2 (m, 8F ). 31P NMR
(toluene-d8, 121 MHz): δ 14.8 (s w/Pt-satellites, 1JPt-P = 3312 Hz).
IR (KBr): 1643, 1520, 1474, 1387, 1294, 1094, 976, 760, 692, and 527
cm-1. Anal. Calcd for C40H14F20P2Pt: C, 42.46; H, 1.25. Found: C,
42.09; H, 1.41.
Theoretical Calculations. Complexes 3 and the transition
states, which were assumed to be 3-TS from direct path or
T-shaped structures (3-TS0, from dissociative path), were opti-
mized by DFT calculations. All calculations were performed
using the B3LYP functional as implemented in Gaussian 03.33
The 6-31G(d) basis set was applied to all elements except Pt,
which was described with the LANL2DZ effective core poten-
tial and the LANL2DZ basis set. Harmonic vibrational fre-
quencies were computed for all stationary points in order to
characterize them as local minima for 3 and saddle points for 3-
TS and 3-TS0. The energies of optimized 3, 3-TS, and 3-TS0 were
corrected using the zero-point energy. IRC calculations were
performed to confirm biphenyl bond formation. Mulliken and
NPA charges of optimized structure of 3 were calculated at the
LANL2DZ level. The energies of the fragment structures of 3
and 3-TS were calculated at the B3LYP/6-31G* level for all
atoms, except for Pt, which was computed using LANL2DZ.
[1,2-Bis{bis(2,3,5,6-tetrafluorophenyl)phosphino}ethane]di-
phenylplatinum(II) (3g). The complex 3g was prepared from [1,2-
bis{bis(2,3,5,6-tetrafluorophenyl)phosphino}ethane]dichloroplati-
num(II) (124 mg, 130 μmol) and PhMgBr in diethyl ether (3 M, 240
μL, 0.72 mmol) in a similar manner to the synthesis of 3b. The white
crystals were obtained in a yield of 83% (112 mg). Mp:> 200 °C
1
(dec). H NMR (acetone-d6, 500 MHz): δ 3.12-3.19 (m, 4H),
6.49-6.52 (m, 2H), 6.64-6.68 (m, 4H), 6.90-7.17 (m, 4H),
7.67-7.74 (m, 4H). 13C NMR (CD2Cl2, 75 MHz): δ 28.2-
28.9 (m), 109.0-109.6 (m), 121.7-121.8 (m), 126.3-127.3 (m),
133.9-134.4 (m), 143.9-147.9 (m), 156.7-158.6 (m), 162.7-164.7
(m). 19F NMR (CDCl3, 282 MHz): δ -137.9 to -138.0 (m, 8F ),
-130.4 (s, 8F ). 31P NMR (CDCl3, 121 MHz): δ 14.6 (s w/Pt-sate-
llites, 1JPt-P = 1551 Hz). IR (KBr, cm-1): 1653, 1558, 1481, 1373,
1234, 918, 735, and 712 cm-1. Anal. Calcd for C38H18F16P2Pt: C,
44.07; H, 1.75. Found: C, 44.37; H, 1.94.
Acknowledgment. This work was supported by JSPS
KAKENHI (20550099). We thank Professor Fumiyuki
Ozawa and Professor Kazuhiko Takai for helpful discus-
sions, and Dr. Toshiyuki Oshiki for assistance with X-ray
crystallography. We thank the SC-NMR Laboratory of
[1,2-Bis{bis(pentafluorophenyl)phosphino}ethane]diphenylplati-
num(II) (3h).10 The complex 3h was prepared from [1,2-bis{bis-
(pentafluorophenyl)phosphino}ethane]dichloroplatinum(II)
(77.0 mg, 75.2 μmol) and PhMgBr in diethyl ether (2 M, 140 μL,
0.28 mmol) in a similar manner to the synthesis of 3b. The white
crystals were obtained in a yield of 64% (53 mg). Mp> 230 °C
(dec). 1H NMR (CDCl3, 500 MHz): δ 2.81-2.85 (m, 4H),
6.62-6.65 (m, 2H), 6.75-6.78 (m, 4H), 6.90-7.20 (m, 4H).
13C NMR (CD2Cl2, 75 MHz): δ 28.2-29.3 (m), 102.4-
103.6 (m), 122.0-122.2 (m), 126.6-127.6 (m), 133.6-134.2
(m), 135.5-139.5 (m), 141.2-144.9 (m), 145.0-148.6 (m),
156.2-158.2 (m). 19F NMR (CDCl3, 282 MHz): δ -158.4 to
1
Okayama University for H, 13C, 19F, and 31P NMR
measurements.
Supporting Information Available: Experimental details of
synthesis of ligands 1, kinetic analyses, NMR data, crystal-
lographic data, CIF file of 3d, and computational details of 3, 3-
TS, and 3-TS0. This material is available free of charge via the
Internet at http://pubs.acs.org.