η2-coordination and C-H activation of electron-poor arenes

Article abstract of DOI:10.1021/om020459x

The reductive elimination of neopentane from (dtbpm)Pt(Np)H (dtbpm = bis(di-tertbutylphosphino)methane, Np = neopentyl) results in the formation of the highly reactive intermediate [(dtbpm)Pt⁰]. This species reacts with a variety of electron-de

Full text of DOI:10.1021/om020459x

5320
Organometallics 2002, 21, 5320-5333
η2-Coor d in a tion a n d C-H Activa tion of Electr on -P oor
Ar en es
Carl N. Iverson, Rene J . Lachicotte, Christian Mu¨ller, and William D. J ones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received J une 10, 2002
The reductive elimination of neopentane from (dtbpm)Pt(Np)H (dtbpm ) bis(di-tert-
butylphosphino)methane, Np ) neopentyl) results in the formation of the highly reactive
intermediate [(dtbpm)Pt0]. This species reacts with a variety of electron-deficient benzenes
(1,4-bis(trifluoromethyl)benzene and 1,3,5-tris(trifluoromethyl)benzene) and biphenyls (3,5,4′-
tris(trifluoromethyl)biphenyl and 3,5,3′,5′-tetrakis(trifluoromethyl)biphenyl) to form η2-arene
complexes. X-ray crystallography confirms the η2-bonding motif. The arene complexes all
1
display broad H NMR spectroscopic features at room temperature that sharpen considerably
at lower temperatures. Thermolysis or photolysis of the arene complexes results in C-H
activation and the formation of platinum(II) aryl hydride complexes. The products observed
depend on whether the reaction is thermal or photolytic. Reaction with 4,4′-bis(trifluoro-
methyl)biphenyl yields two C-H activated products directly. Oxidative addition occurs at
the 2 and 3 positions of the biphenyl in a 5:1 ratio, respectively. Continued heating of the
mixture results in a second C-H activation to form a platinacyclopentane.
In tr od u ction
ligand would prove useful in our studies of C-X bond
activation processes (eq 1, X ) H, C, F, S).
Bis(phosphino)methanes have long been used in
platinum transition metal chemistry.1 The versions
primarily used in the synthesis of most complexes have
simple alkyl (methyl, ethyl, or isopropyl) or phenyl
substituents on the phosphorus atoms. A notable va-
cancy in this series is the tert-butyl analogue, bis(di-
tert-butylphosphino)methane (dtbpm). Presumably due
to the arduous and unreliable nature of its synthesis,
the use of this ligand in inorganic and organometallic
syntheses and reactivity has been reported relatively
infrequently. Notably, Hofmann and co-workers have
made significant contributions to the literature in
regards to the use of this ligand in various transition
metal systems.2 On the basis of the theoretical and
experimental work published over the past decade we
believed that certain systems containing the dtbpm
One report in particular described a platinum com-
pound that appeared to be ideal for our investigations.
Reductive elimination of neopentane from (dtbpm)Pt-
(Np)H (1, Np ) neopentyl) yields an unsaturated L2Pt0
intermediate species.2c Theoretical studies predict that
the small chelation angle due to a single methylene
bridge between two phosphorus atoms will result in a
significant increase in the energy of the HOMO and a
decrease in the energy of the LUMO of the fragment.2a
This perturbation of the frontier orbitals leads to the
highly reactive nature of the intermediate. The tert-
butyl substituents on the phosphorus atoms of the
dtbpm ligand also provide key benefits: a sterically
protected reactive pocket, stronger P-Pt bonds due to
the increased basicity at phosphorus (in contrast to
(1) (a) Puddephatt, R. J . Coord. Chem. Rev. 1980, 33, 149-194. (b)
Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99-127. (c) Anderson, G.
K. Adv. Organomet. Chem. 1993, 35, 1-39. (d) Chraudet B.; Delavaux,
B.; Poilblanc, R. Coord. Chem. Rev. 1988, 86, 191-243.
(2) (a) Hofmann, P.; Heiss, H.; Mueller, G. Z. Naturforsch. 1987,
42b, 395-409. (b) Hofmann, P.; Perez-Moya, L. A.; Krause, M. E.;
Kumberger, O.; Mueller, G. Z. Naturforsch. 1990, 45b, 897-908. (c)
Hofmann, P.; Heiss, H.; Neiteler, P.; Mueller, G.; Lachmann, J . Angew.
Chem., Int. Ed. Engl. 1990, 29, 880-882. (d) Hofmann, P.; Meier, C.;
Englert, U.; Schmidt, M. U. Chem. Ber. 1992, 125, 353-365. (e)
Hofmann, P.; Unfried, G. Chem. Ber. 1992, 125, 659-661. (f) Hofmann,
P.; Meier, C.; Hiller, W.; Heckel, M.; Riede, J .; Schmidt, M. U. J .
Organomet. Chem. 1995, 490, 51-70. (g) Straub, B. F.; Hofmann, P.
Inorg. Chem. Commun. 1998, 1, 350-353. (h) Hansen, S. M.; Rominger,
F.; Metz, M.; Hofmann, P. Chem. Eur. J . 1999, 5, 557-566. (i) Hansen,
S. M.; Volland, M. A. O.; Rominger, F.; Eisentra¨ger, F.; Hofmann, P.
Angew. Chem., Int. Ed. 1999, 38, 1273-1276. (j) Straub, B. F.;
Rominger, F.; Hofmann P. Inorg. Chem. Commun. 2000, 3, 214-217.
(k) Straub, B. F.; Rominger, F.; Hofmann P. Inorg. Chem. 2000, 39,
2113-2119. (l) Straub, B. F.; Rominger, F.; Hofmann P. Inorg. Chem.
Commun. 2000, 3, 358-360. (m) Grotjahn, D. B.; Bikzhanova, G. A.;
Collins, L. S. B.; Concolino, T.; Lam, K.-C.; Rheingold, A. L. J . Am.
Chem. Soc. 2000, 122, 5222-5223. (n) Urtel, H.; Meier, C.; Eisentrae-
ger, F.; Rominger, F.; J oschek, J . P.; Hofmann, P. Angew. Chem., Int.
Ed. 2001, 40, 781-784. (o) Urtel, H.; Bikzhanova, G. A.; Grotjahn, D.
B.; Hofmann, P. Organometallics 2001, 20, 3938-3949.
i
other R2PCH2PR2 ligands, R ) Me, Pr, and Ph, which
are frequently observed to form A-frame type dimeric
compounds1), and substituents on phosphorus that
disfavor intramolecular C-H activation. Although a
definitive example of C-H activation by this intermedi-
ate has not yet been realized, insertion of the (dtbpm)-
Pt fragment into C-Si, C-F, and C-C bonded sub-
strates has been reported.2
Platinum complexes, among many other transition
metal compounds, have long been studied in C-H
activation processes3 and C-H and C-C reductive
elimination reactions.4 More recent work has focused
10.1021/om020459x CCC: $22.00 © 2002 American Chemical Society
Publication on Web 10/30/2002

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5321
on electrophilic Pt(II) oxidation chemistry;5-11 however,
Pt0 compounds have been known to activate a variety
of hydrocarbons. In seminal work by Whitesides and co-
workers in the late 1980s, C-H activation of aromatic
and aliphatic alkanes by (dcpe)Pt(Np)H (dcpe ) 1,2-bis-
(dicyclohexylphosphino)ethane) was reported.12 In the
case of aromatic substrates, although not observed,
there was clear experimental evidence for η2-arene
intermediates in the formation of aryl hydrides.
We have recently published accounts utilizing the
dtbpm ligand in activating C-C bonds by compound
113a,b and the functionalization of C-C bonds by [(dtbpm)-
RhCl]2.13c We now wish to report a more convenient
synthesis of dtbpm and its application toward C-H
bond activation in the L2Pt0 system. In particular, we
have isolated and characterized an η2-arene intermedi-
ate involved in the stepwise activation of an aryl C-H
bond.
Sch em e 1
1), as has been reported in the patent literature.16
Standard methodologies for the synthesis of (dtbpm)-
Pt(Np)H were used and have been previously re-
ported.2c,17
R ea ct ion w it h Ar en es. While the fragment
[(dtbpm)Pt] does not react with benzene, trifluoro-
methyl-substituted benzenes react with (dtbpm)Pt(Np)H
to yield η2-arene or aryl hydride complexes, depending
on the reaction conditions.18 For instance, when com-
pound 1 is heated at 55 °C in the presence of 20 equiv
of 1,4-C6H4(CF3)2 or 1,3,5-C6H3(CF3)3 for 90 min, η2-
arene complexes 2 and 3, respectively, are produced (eq
2). The 1H NMR spectra of both products featured broad
Resu lts a n d Discu ssion
The reported synthesis of dtbpm requires the addition
t
of excess BuLi to a solution of bis(dichlorophosphino)-
methane.14 The reaction is not clean, as a mixture of
bis, tris, and tetrakis substituted diphosphinomethanes
is formed. A less direct but more selective route employs
the combination of tBu2PCH2Li15 and PCltBu2 (Scheme
(3) For general reviews on C-H activation, see: (a) Shilov, A. E.,
Shul’pin, G. B. Activation and Catalytic Reactions of Saturated
Hydrocarbons in the Presence of Metal Complexes; Kluwer Academic
Publishers: Dordrecht, 2000. (b) J ones, W. D. In Activation of Unre-
active Bonds and Organic Synthesis; Murai, S., Ed.; Topics in Orga-
nometallic Chemistry; Springer: New York, 1999; pp 9-46. (c) Kaki-
uchi, F.; Murai, S. In Activation of Unreactive Bonds and Organic
Synthesis; Murai, S., Ed.; Topics in Organometallic Chemistry; Springer:
New York, 1999; pp 47-80. (d) Shilov, A. E.; Shul’pin, G. B. Acc. Chem.
Rev. 1997, 97, 2879-2932. (e) Arndtsen, B. A.; Bergman, R. G.; Mobley,
T. A.; Peterson, T. H. Chem. Res. 1995, 28, 154-162.
(4) For examples discussing the mechanism, see: Abis, L.; Sen, A.;
Halpern, J . J . Am. Chem. Soc. 1979, 100, 2915-2916. Gille, A.; Stille,
J . K. J . Am. Chem. Soc. 1980, 102, 4933-4941. Bartlett, K. L.;
Goldberg, K. I.; Borden, W. T. J . Am. Chem. Soc. 2000, 122, 1456-
1465.
(5) (a) Zhong, H. A.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 2002, 124, 1378-1399. (b) J ohansson, L.; Tilset, M.; Labinger, J .
A.; Bercaw, J . E. J . Am. Chem. Soc. 2000, 122, 10846-10855. (c) Stahl,
S. S.; Labinger, J . A.; Bercaw, J . E. Angew. Chem., Int. Ed. 1998, 37,
2181-2192.
signals at room temperature. Cooling a THF-d8 solution
of compound 2 to -60 °C resolves the aromatic protons
into four resonances at δ 7.10 (br s), 6.31 (d), 5.69 (br d
with 195Pt shoulders), and 3.72 (br t). The signal at 3.72
ppm has 195Pt satellites that are partially buried by one
of the residual solvent peaks and the signal due to the
bridging methylene protons. This set of resonances is
consistent with the arene being bound to the metal
center in an unsymmetrical fashion. 19F NMR and 31P
NMR spectroscopy also support this structural assign-
ment. The 19F NMR spectrum has two resonances at δ
-61.3 and -65.2. The former has 195Pt satellites (4J Pt-F
(6) (a) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J . L. J .
Am. Chem. Soc. 2001, 123, 6425-6426. (b) Reinartz, S.; White, P. S.;
Brookhart, M.; Templeton, J . L. Organometallics 2001, 20, 1709-1712.
(c) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J . L. Orga-
nometallics 2000, 19, 3854-3866.
(7) (a) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J . Am. Chem. Soc.
2001, 123, 6423-6424. (b) Wick, D. D.; Goldberg, K. I. J . Am. Chem.
Soc. 1997, 119, 10235-10236.
(8) Periana, R. A.; Taube, D. J .; Gamble, S.; Taube, H.; Satoh, T.;
Fujii, H. Science 1998, 280, 560-564.
(9) Thomas, J . C.; Peters, J . C. J . Am. Chem. Soc. 2001, 123, 5100-
5101.
(10) Sen, A. Acc. Chem. Res. 1998, 31, 550-557.
(11) (a) J ohansson, L.; Ryan, O. B.; Romming, C.; Tilset, M. J . Am.
Chem. Soc. 2001, 123, 6579-6590. (b) J ohansson, L.; Tilset, M. J . Am.
Chem. Soc. 2001, 123, 739-740. (c) Heiberg, H.; J ohansson, L.; Gropen,
O.; Ryan, O. B.; Swang, O.; Tilset, M. J . Am. Chem. Soc. 2000, 122,
10831-10845.
(12) (a) Hackett, M.; Whitesides, G. M. Organometallics 1987, 6,
403-410. (b) Hackett, M.; Ibers, J . A.; Whitesides, G. M. J . Am. Chem.
Soc. 1988, 110, 1436-1448. (c) Hackett, M.; Whitesides, G. M. J . Am.
Chem. Soc. 1988, 110, 1449-1462. (d) Brainard, R. L.; Miller, T. M.;
Whitesides, G. M. Organometallics 1987, 5, 1481-1490.
(13) (a) Simhai, N.; Iverson C. N.; Edelbach, B. L.; J ones, W. D.
Organometallics 2001, 20, 2759-2766. (b) Mueller, C.; Iverson, C. N.;
Lachicotte, R. J .; J ones, W. D. J . Am. Chem. Soc. 2001, 123, 9718-
9719. (c) Iverson, C. N.; J ones, W. D. Organometallics 2001, 20, 5745-
5750.
(15) Karsch, H. H.; Schmidbaur, H. Z. Naturforsch. 1977, 32b, 762-
767.
(16) Feldman, J .; Hauptman, E.; McCord, E. F.; Brookhart, M. S.
Polymerization of olefins in the presence of cationic nickel complexes,
phosphines, and Lewis acids. World Patent, WO 9847934, October 29,
1998. Hofmann, P.; Heiss, H. Preparation of bis(di-tert-butylphosphi-
no)methane. German Patent, DE 4134772, May 7, 1992.
(17) Hackett, M.; Ibers, J . A.; Whitesides, G. M. J . Am. Chem. Soc.
1988, 110, 1436-1448.
(18) We also examined the reactivity of C6H5CF3 and 1,3-C6H4(CF3)2
with (dtbpm)Pt(Np)H. The resulting 1H and 31P NMR spectra displayed
a complex product mixture of Pt-H and Pt-Pt dimeric and monomeric
compounds. We have been unable to determine the identity of the
products thus far, although it is clear that a small amount of the
“simple” C-H activated products, (dtbpm)Pt(aryl)H, have been formed.
(14) Karsch, H. H., Z. Naturforsch. 1983, 38b, 1027-1030.

5322 Organometallics, Vol. 21, No. 24, 2002
Iverson et al.
) 88 Hz), whereas the latter is a simple singlet. Two
signals are also expected in the 31P NMR spectrum, but
only a single resonance is observed at 50.4 ppm.
Presumably the two phosphorus nuclei are coincidental,
as higher order coupling is observed for the 195Pt
satellites. The downfield satellite appears as a quartet,
and the upfield satellite appears as a singlet.
The aromatic protons in the 1H NMR spectrum of
compound 3 resolve into three distinct signals at -20
°C: δ 7.01 (br s), 6.02 (d with 195Pt shoulders), and 3.72
(br d). Again, the 195Pt satellites for the signal at 3.72
ppm are partially obscured. The 31P NMR spectrum
yields the expected two doublets at δ 47.9 and 46.7. The
2
value J P-P of 91 Hz is unusually large for a cis L2Pt
complex. However, larger J values are often observed
when the signals are very close together as in this case.
The appearance of the 195Pt satellites is similar to that
of compound 2. Three resonances are observed for the
three unique trifluoromethyl groups at δ -59.9, -64.0,
and -64.4. Only the signal at -59.9 ppm is coupled to
the platinum metal center (3J Pt-F ) 81 Hz).
F igu r e 1. ORTEP diagram for 3. Ellipsoids are shown at
the 30% probability level. Selected distances (Å) and angles
(deg): C(18)-C(19), 1.472 (7); C(19)-C(20), 1.451 (7);
C(20)-C(21), 1.355 (8); C(21)-C(22), 1.433 (9); C(22)-
C(23), 1.385 (8); C(23)-C(18), 1.461 (7); Pt(1)-C(18), 2.105
(5); Pt(1)-C(19), 2.119 (4); P(1)-Pt(1)-P(2), 75.45 (5).
A comparison can be made to the reaction of C6(CF3)6
with (PMe3)3Pt and (PEt3)3Pt reported by Stone and co-
workers nearly three decades ago.19 An η2-C6(CF3)6
complex was formed and crystallographically character-
ized in the triethylphosphine complex. On the other
hand, C-C activation of the ring structure occurred in
the trimethylphosphine complex, resulting in the forma-
tion of a platinacycloheptatriene.20 The authors sug-
gested that a probable intermediate in the second
reaction was an η2-arene complex. Reaction of 1 with
C6(CF3)6 appears to give a similar fluxional η2-species.
The proposed η2 bonding of the arene ring to the metal
center in compound 3 was confirmed by X-ray crystal-
lography (Figure 1). The complex adopts a distorted
trigonal planar configuration with the bound double
bond from the ring (C18 and C19) taking up the third
ligand position in addition to the two phosphorus atoms.
The plane consisting of the arene double bond and the
platinum metal center is distorted from the P1-Pt-P2
plane by 10.8°. Carbon atoms C18 and C19 have bond
lengths nearly identical to the metal center at 2.105(5)
and 2.119(4) Å, respectively. The P1-Pt-P2 angle of
75.45(5)° is typical for platinum complexes with the
dtbpm ligand as a chelate.2a,c,12a,b Isolated and structur-
ally characterized complexes featuring an independent
arene ring bound in an η2 fashion are somewhat
rare.19b,21 For platinum in particular, there are an
additional five complexes that display intramolecular
η2-arene binding with ligands that contain an ancillary
phenyl substituent.22 Both 3 and the other η2-arene
complexes described here (vide infra) all show similar
structural features with regard to the aromatic C-C
bond distances. A localized diene structure is seen for
the nonbound portion of the ring (short-long-short
bonds, ∆d ≈ 0.08 Å), and the η2-bound CdC is length-
ened to the distance observed for the sp2-sp2 C-C bonds
(∼1.47 Å). In contrast, the other known platinum-η2-
arene complexes in the literature show little or no bond
alternation.22
The reactivities of compounds 2 and 3 differ when the
solutions are heated for longer periods of time. Com-
pound 3 is thermally stable toward C-H activation,
whereas compound 2 readily produces an aryl hydride
in the presence of excess arene (eq 3). The dimer
(dtbpm)2Pt2 (4) is the major product formed when a
solution of only compound 2 is heated.23 Clear evidence
(21) (a) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J . L.
J . Am. Chem. Soc. 2001, 123, 12724-12725. (b) Meiere, S. H.; Brooks,
B. C.; Gunnoe, T. C.; Sabat, M.; Harman, W. D. Organometallics 2001,
20, 1038-1040. (c) Batsonov, A. S.; Crabtree, S. P.; Howard, J . A. K.;
Lehmann, C. W.; Kilner, M. J . Organomet. Chem. 1998, 550, 59. (d)
Higgitt, C. L.; Klahn, A. H.; Moore, M. H.; Oelckers, B.; Partridge, M.
G.; Perutz, R. N. J . Chem. Soc., Dalton Trans. 1997, 1269. (e) Tagge,
C. D.; Bergman, R. G. J . Am. Chem. Soc. 1996, 118, 6908. (f) Casas, J .
M.; Fornies, J .; Martin, A.; Menjon, B.; Tomas, M. J . Chem. Soc., Dalton
Trans. 1995, 2949. (g) Belt, S. T.; Helliwell, M.; J ones, W. D.; Partridge,
M. G.; Perutz, R. N. J . Am. Chem. Soc. 1993, 115, 1429. (l) Belt, S. T.;
Duckett, S. B.; Helliwell, M.; Perutz, R. N. J . Chem. Soc., Chem.
Commun. 1989, 928. (j) van der Heijden, H.; Orpen, A. G.; Pasaman,
P. J . Chem. Soc., Chem. Commun. 1985, 1576.
(22) (a) Wright, L. L.; Moore, S. J .; McIntyre, J . A.; Dowling, S. M.;
Overcast, J . D.; Grisel, G. R.; Nelson, K. K.; Rupert, P. R.; Pennington,
W. T. Organometallics 1999, 18, 4558-4562. (b) Ara, I.; Falvello, L.
R.; Fornies, J .; Lalinde, E.; Martin, A.; Martinez, F.; Moreno, M. T.
Organometallics 1997 16, 5392-5405. (c) Casas, J . M.; Fornies, J .;
Martin, A.; Menjon, B. Organometallics 1993, 12, 4376-4380. (d)
Fornies, J .; Menjon, B.; Gomez, N.; Tomas, M. Organometallics 1992,
11, 1187-1193. (e) Li, C. S.; Cheng, C. H.; Liao, F. L.; Wang, S. L. J .
Chem. Soc., Chem. Commun. 1991, 710-712.
(19) (a) Browning, J .; Green, M.; Penfold, B. R.; Spencer, J . L.; Stone,
F. G. A. J . Chem. Soc., Chem. Commun. 1973, 31-32. (b) Browning,
J .; Green, M.; Laguna, A.; Smart, L. E.; Spencer, J . L.; Stone, F. G. A.
J . Chem. Soc., Chem. Commun. 1975, 723-724.
(20) When a THF-d8 solution of C6(CF3)6 and (dtbpm)Pt(Np)H was
heated, 31P NMR spectroscopy indicated that an η2-arene complex had
been formed. The compound was stable toward extended heating, as
evidenced by the lack of change in the spectrum. Unfortunately, we
were unable to cleanly isolate this compound. For details, see the
Experimental Section. It should be noted that C-C cleavage by
(dtbpm)Pt(Np)H is not observed for any of the electron-deficient arenes
described here.

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5323
1
Sch em e 2
for the formation of the hydride is presented in the H
NMR spectrum. A doublet of multiplets appears at δ
-6.06 (1J Pt-H ) 1297 Hz, 2J P(trans)-H ) 211 Hz). Coupling
of the hydride to the cis phosphorus is normally easily
observed in L2Pt(R)H complexes, but the resonance is
complicated by coupling to the three 19F nuclei of the
nearest trifluoromethyl group. Therefore, the combined
5
2J P(cis)-H and J F-H values make the peaks appear as
sextets with an average value of 3.0 Hz (J P-H ≈ 2J F-H).
Sharp resonances are also observed in the aromatic
region for the remaining three protons of the arene ring
3
at δ 8.69 (d with 195Pt satellites, J Pt-H ) 68 Hz), 7.64
(d with 195Pt shoulders), and 7.07 (d). The tert-butyl
groups emerge as two sharp doublets (4J P-H ) 13 Hz)
with an integration of 18 each. In contrast, the tert-butyl
groups of compounds 2 and 3 both appear as a range of
three broad resonances at room temperature. The 19F
NMR spectrum displays two resonances at δ -59.7 (s
with 195Pt satellites, 4J Pt-F ) 53 Hz) and -61.5 (s). The
former is on a carbon ortho to the Pt-C bond, whereas
the latter is meta to the Pt-C bond. The 31P NMR
spectrum displays two resonances as well, both with
195Pt satellites, at δ 7.5 (1J Pt-P ) 1549 Hz) and -2.5
(1J Pt-P ) 1199 Hz). The NMR data are all consistent
with characterization of the product as (dtbpm)Pt[2-
(1,4-bis(trifluoromethyl)phenyl)](H) (5).
The need for electron-withdrawing substituents on
the arene is demonstrated by the reaction of compound
1 with benzene. Thermolysis of (dtbpm)Pt(Np)H in the
presence of 40 equiv of C6H6 in THF-d8 results in the
production of only (dtbpm)2Pt2. In accordance with
Hofmann’s results, C-H activation was not observed
even in pure benzene solutions.2c There appears to be a
synergistic effect between the electron-rich [(dtbpm)Pt]
moiety and the electron-poor benzenes. Electron-with-
drawing groups have been shown to favor the formation
of η2-arene complexes, which should help prevent the
[(dtbpm)Pt] moiety from dimerizing to (dtbpm)2Pt2.24
Additionally, the oxidative addition of C-H bonds in
electron-poor arenes is a favorable exothermic reaction
(where sterically feasible) due to the production of a
strong metal-aryl bond.25
resonance for the major product 6 appears as a doublet
of doublets with 195Pt satellites also with J values
consistent with an (dtbpm)Pt(R)H formulation (1J Pt-H
) 1311 Hz, 2J P(trans)-H ) 207 Hz, 2J P(cis)-H ) 7.6 Hz). 1H
and 31P NMR spectroscopy indicate a 5:1 mixture of
compounds 6 and 7. The 31P NMR spectrum supports
the (dtbpm)Pt(Ar)H formulations as well. The major
product displays two singlets (with Pt satellites) at δ
12.6 (1J Pt-P ) 1648 Hz) and 2.4 (1J Pt-P ) 1296 Hz), and
the minor product also shows two singlets at δ 13.1
(1J Pt-P ) 1759 Hz) and 2.7 (1J Pt-P ) 1253 Hz). Dimer 4
is formed in the reaction as well in approximately 30%
yield relative to the combined C-H activated products,
as judged by 31P NMR spectroscopy. Compound 6 is
identified as the product due to activation of the C-H
bond meta to the CF3 group (2 position of the biphenyl
ligand), as the corresponding resonances in the 19F NMR
are simple singlets in a 1:1 ratio. Compound 7 is
therefore characterized as the product due to activation
of the C-H bond ortho to the CF3 group (3 or 3′ position
of the biphenyl ligand). Confirmation of the minor
product’s structure, via analysis of the 19F NMR spec-
trum and/or the aromatic resonances in the 1H NMR
spectrum, unfortunately could not be made, as there
was too much interference from the excess biphenyl
present in solution. Also, we were unable to isolate the
minor isomer from the reaction mixture. No evidence
characteristic of an η2-arene complex was observed in
Rea ction w ith Bip h en yls. We also examined the
reactivity of compound 1 with trifluoromethyl-substi-
tuted biphenyls. The reaction of 10 equiv of 4,4′-bis-
(trifluoromethyl)biphenyl with (dtbpm)Pt(Np)H in THF-
d8 results in the formation of two hydride complexes
(Scheme 2). The formation of (dtbpm)Pt(biphenyl)H
complexes via C-H activation in this reaction is evident
given the observation of two unique platinum hydride
1
resonances in the H NMR spectrum at δ -6.21 (major
product, 6) and -6.58 (minor product, 7). The hydride
resonance for the minor product 7 appears as a doublet
of sextets with 195Pt satellites and J values consistent
with an (dtbpm)Pt(Ar)H formulation (1J Pt-H ) 1373 Hz,
2J P(trans)-H ) 204 Hz). Similar to compound 5, J P(cis)-H
≈ 2 J C-F, giving rise to a sextet pattern. The hydride
1
either the H or 31P NMR spectra during the course of
this reaction.
The major isomer 6 was isolated in 43% yield from a
larger scale reaction via fractional crystallization. Re-
versible C-H activation was observed in this system
when a THF-d8 solution of compound 6 was heated in
the presence of 10 equiv of 4,4′-bis(trifluoromethyl)-
biphenyl, and the reaction was followed by 1H, 19F, and
31P NMR spectroscopies. The reaction was initially
heated at 55 °C, but no change was observed after 18
(23) (dtbpm)2Pt2 has been reported before as
a decomposition
product in reactions involving the [(dtbpm)Pt] intermediate by us and
Hofmann. See refs 12a and 2c.
(24) (a) Belt, S. T.; Dong, L.; Duckett, S. B.; J ones, W. D.; Partridge,
M. G.; Perutz, R. N. J . Chem. Soc., Chem. Commun. 1991, 266-269.
(b) Chin, R. M.; Dong, L.; Duckett, S. B.; Partridge, M. G.; J ones, W.
D.; Perutz, R. N. J . Am. Chem. Soc. 1993, 115, 7685-7695.
(25) Selmeczy, A. D.; J ones, W. D.; Osman, R.; Perutz, R. Organo-
metallics 1995, 14, 5677-5685.

5324 Organometallics, Vol. 21, No. 24, 2002
Iverson et al.
h. Increasing the temperature to 85 °C resulted in some
reactivity as formation of compound 7 was observed. An
equilibrium between the two isomers exists, as the 5:1
ratio seen in the initial experiment is reached after
approximately 65 h. This ratio stays constant during
the course of the reaction. A commonly invoked inter-
mediate in arene isomerizations is an η2-arene com-
plex.26 In this case, the biphenyl and hydride ligands
reductively eliminate to form an unstable (dtbpm)Pt-
[η2-(4,4′-bis(trifluoromethyl)biphenyl] complex, which
then follows one of the subsequent three steps: (1)
oxidative addition of biphenyl at the 3 position of the
biphenyl to form product 7, (2) oxidative addition of
biphenyl at the 2 position to re-form product 6, or (3)
biphenyl dissociation to form [(dtbpm)Pt].
at room temperature that sharpen upon cooling (-20
°C). Two doublets due to an AB spin system are
observed for the 4′-CF3-substituted ring in addition to
three resonances for the 3,5-(CF3)2-substituted ring. One
of the latter three signals is relatively far upfield from
the others at 4.03 ppm and is coupled to the platinum
metal center (J Pt-H ) 74 Hz). This points to the biphenyl
being bound to the metal through the bis substituted
ring and the other ring freely rotating about the C-C
bridging bond. Confirming the structural assignment
are the three unique resonances in the 19F NMR at δ
-61.2, -63.0, and -65.7. The signal at -63.0 is a sharp
singlet, whereas the other two are broad resonances
with 195Pt shoulders.
C-H activation occurs when a THF solution of
compound 9 is heated at 85 °C. 1H and 31P NMR
spectroscopy indicated that the η2 complex had been
converted into an aryl hydride complex (10). The reac-
tion was complete after 55 h. A small amount (ap-
proximately 10%) of dimer 4 was formed during the
course of the reaction. On the basis of NMR spectro-
scopic data, C-H activation occurs at the 2′ position of
the 4′-CF3-substituted phenyl ring. A new set of reso-
nances for the aromatic protons included two singlets
at δ 8.39 and 7.82 in a 2:1 ratio and three signals, with
an integration of one each, at δ 8.06, 7.24, and 7.09. The
signal at 8.06 ppm is assigned as ortho to the Pt-C
bond. Coupling to the platinum metal center can be
seen, although the exact J value could not be calculated,
as the 195Pt satellites are partially obscured by other
resonances. The other two aromatic resonances are
doublets and are coupled to each other. The hydride
resonance is a doublet of doublets at δ -6.12 with 195Pt
satellites (1J Pt-H ) 1293 Hz). Coupling to any of the CF3
groups is not observed. The 19F NMR spectrum reveals
only two resonances at δ -62.84 and -62.98 in a 1:2
ratio. Neither peak displays coupling to the 195Pt
nucleus. Two doublets with 195Pt satellites are observed
in the 31P NMR spectrum for the bisphosphine ligand
at δ 6.2 (1J Pt-P ) 1680 Hz) and -3.2 (1J Pt-P ) 1291 Hz).
It is interesting to note that indirect C-H bond activa-
tion occurs in this case; that is, the ortho C-H bond on
the ring not bound initially to the platinum metal center
undergoes oxidative addition. We assume that steric
factors discourage insertion into the ortho C-H bond
of the 3,5-substituted ring.
A new product, most easily seen in the 31P NMR
spectrum, started to grow in as well. A sharp singlet at
5 ppm with 195Pt satellites (1J Pt-P ) 1523 Hz) suggested
the formation of a symmetric bisphosphine complex with
1
two Pt-Caryl bonds. A simple doublet in the H NMR
spectrum for the tert-butyl groups of the bisphosphine
ligand also reveals the symmetric nature of the product.
The aromatic region of the 1H NMR spectrum of the
mixture contains three unique resonances for the prod-
uct, whereas a C-C bond cleavage product would be
expected to have only two resonances.27 The lack of new
resonances in the hydride region therefore suggested a
second C-H activation. Insertion of the platinum metal
center into a C-H bond of the nonbonded ring ortho to
the C-C bridge would result in formation of a 4,4′-bis-
(trifluoromethyl) platinacyclopentane complex (8) analo-
gous to that of (dtbpm)Pt(2,2′-biphenyl).12a Concomitant
loss of H2 would be expected, but gas evolution was not
detected during the course of the reaction. Neither was
1
a resonance for H2 observed in the H NMR spectrum.
This is perhaps not surprising, as the overall amount
of compound 8 formed was relatively small (18% isolated
yield in a larger scale reaction). We were able to obtain
crystals of the complex, and a single-crystal X-ray
analysis confirmed the connectivity of the platinacyclo-
pentane.28 The overall reaction is shown in Scheme 2.
When 5 equiv of 3,5,4′-tris(trifluoromethyl)biphenyl
is reacted with compound 1 in THF for 2 h at 55 °C,
the η2 complex (dtbpm)Pt[η2-(3,5,4′-bis(trifluoromethyl)-
biphenyl)] (9) is formed exclusively and isolated in 76%
(eq 4). As seen in the 1H NMR spectrum for the
The reaction of 5 equiv of 3,5,3′,5′-tetrakis(trifluo-
romethyl)biphenyl with (dtbpm)Pt(Np)H in THF at 55
°C also resulted in the formation of an η2-biphenyl
complex, which was isolated in 57% yield (eq 5). The
previously described arene complexes, broad signals are
observed for the aromatic protons of the biphenyl ligand
1H NMR spectrum of (dtbpm)Pt[η2-3,5,3′,5′-tetrakis-
(trifluoromethyl)biphenyl] (11) at -20 °C is similar to
that observed for compound 9. Three signals are seen
(26) (a) Perthuisot, C.; J ones, W. D. J . Am. Chem. Soc. 1994, 116,
3647-3648. (b) Gozin, M.; Weisman, A.; Bendavid, Y.; Milstein, D.
Nature 1993, 364, 699-701. (c) Feher, F. H.; J ones, W. D. J . Am. Chem.
Soc. 1986, 108, 4814-4819.
(27) The C-C activated product was independently synthesized. The
1H, 19F, and 31P NMR data of (dtbpm)Pt(4-C6H4CF3)2 does not match
that of the product formed. See Experimental Section for the synthesis
and NMR spectroscopic data.
(28) Although the platinacyclopentane motif of the compound was
verified, there was disorder of the trifluoromethyl groups that we were
unable to satisfactorily model during refinement of the structure.

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5325
F igu r e 3. ORTEP diagram for 11. Ellipsoids are shown
at the 30% probability level. Selected distances (Å) and
angles (deg): C(18)-C(19), 1.452 (13); C(19)-C(20), 1.468
(13); C(20)-C(21), 1.365 (14); C(21)-C(22), 1.421 (14);
C(22)-C(23), 1.356 (14); C(23)-C(18), 1.477 (13); Pt(1)-
C(18), 2.121 (9); Pt(1)-C(19), 2.117 (9); P(1)-Pt(1)-P(2),
75.42 (9).
F igu r e 2. ORTEP diagram for 9. Ellipsoids are shown at
the 30% probability level. Selected distances (Å) and angles
(deg): C(18)-C(19), 1.472 (6); C(19)-C(20), 1.437 (6);
C(20)-C(21), 1.349 (6); C(21)-C(22), 1.428 (6); C(22)-
C(23), 1.358 (6); C(23)-C(18), 1.465 (6); Pt(1)-C(18), 2.109
(4); Pt(1)-C(19), 2.121 (4); P(1)-Pt(1)-P(2), 75.53 (4).
1
products (approximately 5%) can be observed in the H
NMR hydride region when the mixed 4-methoxy-4′-
(trifluoromethyl)biphenyl is used. The primary product,
however, is again (dtbpm)2Pt2.
for the protons of the bound ring, including the typical
upfield resonance for the proton attached to the bound
carbon at δ 4.06 (2J Pt-H ) 63 Hz). The resonances for
the tert-butyl groups of compound 11 are significantly
broadened at room temperature, as is seen in all the
η-bound arene complexes reported in this study. Three
signals are observed in the 19F NMR spectrum at δ
-63.10, -65.24, and -67.46 in a 1:2:1 ratio, again
indicating free rotation about the C-C bridging bond.
The resonances at -63.1 and -67.46 ppm are broad due
to 195Pt shoulders. Compound 11 is more robust than
its tris(trifluoromethyl) analogue. Thermolysis of this
compound did not yield clean C-H activation even after
5 days at 85 °C. Increasing the temperature to 125 °C
eventually leads to complete decomposition to (dtbpm)2Pt2
and the free biphenyl.
Compounds 9 and 11 were both characterized by
single-crystal X-ray analysis (Figures 2 and 3, respec-
tively). The structural characteristics of both compounds
are relatively similar, and the core bonds and angles
are nearly identical to those of compound 3. In both
cases the biphenyl ligand is bound to the platinum metal
center in an η2 fashion along the Cortho-Cmeta bond
(positions labeled with respect to the C-C bridge) of one
ring. For compound 9, the ligand is bound through the
3,5-bis(trifluoromethyl)-substituted ring, confirming the
structural characterization from NMR spectroscopic
analysis. The P1-Pt-P2 and Cortho-Pt-Cmeta planes are
not quite parallel, being offset by 7.5° and 5.6°, respec-
tively, for compounds 9 and 11. The rings of the
biphenyl ligands also maintain a nearly coplanar ori-
entation with dihedral angles of 5.2° and 6.6°. The CF3
group attached to the carbon atom bound to platinum
is bent back from the aromatic ring by 27.5° for
compound 9 and 27.9° for compound 11. Finally, the
P1-Pt-P2 angles for 9 and 11 are 75.5° and 75.4°.
Electron-withdrawing substituents are also necessary
for the η2 coordination and C-H activation of biphenyls.
The reaction of 4,4′-dimethoxybiphenyl or 3,5,3′,5′-
tetramethylbiphenyl with compound 1 leads only to the
formation of dimer 4. Small amounts of C-H activated
The aryl hydrides of [(dtbpm)Pt] react cleanly with
halogenated solvents (CDCl3 or CH2Cl2) to effect a
halide/hydride exchange. Four distinct doublets with an
integration of nine each are observed for the tert-butyl
1
groups in the H NMR of (dtbpm)Pt[2-(1,4-bis(trifluo-
romethyl)phenyl)]Cl (12), (dtbpm)Pt[2-(4,4′-bis(trifluo-
romethyl)biphenyl)]Cl (13), and (dtbpm)Pt[2′-(3,5,4′-
tris(trifluoromethyl)biphenyl)]Cl (14). (dtbpm)Pt(2-
biphenyl)Cl (15), synthesized via reaction of (dtbpm)-
Pt(2,2′-biphenyl) with HCl(conc), displays the same char-
1
acteristic pattern in its H NMR spectrum. This indi-
cates steric interference caused by the chloride ligand
with respect to the rotation of the aryl ligand about the
Pt-C bond, as only two doublets with an integration of
18 each are observed in each hydride analogue.29 The
structure of compound 12 was determined by single-
crystal X-ray analysis and is displayed in Figure 4. The
complex adopts a distorted square planar geometry. The
aryl ligand is oriented perpendicular to the square
plane, and the main distortion is a result of the P1-
Pt-P2 angle of 73.95(3)°.
The chloride-substituted compounds can be labeled
via a Cl/D exchange reaction with deuteride reagents.

5326 Organometallics, Vol. 21, No. 24, 2002
Iverson et al.
1
Ta ble 1. Su m m a r y of H a n d 31P NMR Sp ectr oscop ic Da ta for Hyd r id e Com p lexes
Pt(dtbpm) compound
δ P
1J Pt-P, Hz
δ H
1J Pt-H
2J P-H
Pt(neopentyl)H
(1), C6D6
Pt((CF3)2phenyl)H
(5), C6D6
Pt(2-(CF3)2biphenyl)H
(6), C6D6
Pt(3-(CF3)2biphenyl)H
(7), C6D6
Pt(2′-(CF3)3biphenyl)H
(10), THF-d8
Pt((CF3)3phenyl)H
(16), C6D6
Pt(2-(CF3)3biphenyl)H
(17), C6D6
Pt(2-(CF3)4biphenyl)H
(18), C6D6
9.7
-5.4
7.5
-2.5
7.4
-2.8
13.1
2.7
6.2
-3.2
12.7
4.13
9.2
1.6
8.9
1.8
1345 (trans Np)
1338 (trans H)
1549 (trans Ar)
1199 (trans H)
1648 (trans Ar)
1287 (trans H)
1759 (trans Ar)
1253 (trans H)
1680 (trans Ar)
1291 (trans H)
2041 (trans Ar)
1339 (trans H)
1872 (trans Ar)
1237 (trans H)
1875 (trans Ar)
1242 (trans H)
1549 (trans Ar)
1381 (trans H)
-4.88
1350
214, 11
-6.06
-5.78
-6.58
-6.12
-8.78
-7.66
-7.57
-5.37
1297
1311
1373
1293
1257
1266
1267
1339
211
207, 7.6
204
204, 7.1
207
206
203
Pt(2-biphenyl)H
(19), C6D6
8.0
-3.2
210, 8.8
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Da ta for 3, 9, 11, a n d 12
crystal parameter
3
9
11
12
emp formula
fw
C
26H41F9P2Rh
C32H45F9P2Pt
857.71
C33H44F12P2Pt
925.72
C25H41ClF6P2Pt
748.06
781.62
temperature (°C)
cryst syst
space group
a (Å)
b (Å)
c (Å)
-80
-80
-80
-80
orthorhombic
Pna21
triclinic
triclinic
orthorhombic
Pna21
P1h
P1h
16.0468(8)
10.5316(5)
17.5815(9)
90
90
90
2971.2(3), 4
1.747
4.901
9.2656(4)
9.7282(4)
20.1575(9)
91.4580(10)
99.3640(10)
107.7850(10)
1701.6(1), 2
1.674
9.1979(8)
9.8021(9)
21.6730(19)
102.451(2)
90.077(2)
107.434(2)
1815.8, 2
1.693
25.2091(10)
12.4820(5)
9.4183(4)
90
90
90
2963.6(2), 4
1.677
4.983
R (deg)
â (deg)
γ (deg)
volume (Å3), Z
density (calc, Mg/m3)
abs coeff (mm-1
)
4.288
4.036
F(000)
1544
852
916
1480
cryst size (mm3)
θ range (deg)
.15 x 0.12 x 0.10
2.25 to 23.25
12755
3633, 0.0318
SADABS
3633/1/343
1.003
.18 x 0.02 x 0.24
2.05 to 23.27
7648
4815, 0.0206
SADABS
4815/0/409
1.027
.16 x 0.08 x 0.08
2.23 to 23.25
8302
5164, 0.0313
SADABS
5164/0/433
1.320
.04 x 0.22 x 0.40
1.62 to 23.26
12622
4020, 0.0316
SADABS
4020/1/328
0.986
no. of reflns collected
no. of ind reflns, Rint
abs corr
no. of data/restraints/params
GOF on F2
R1, wR2 (all data)
R1, wR2 [I > 2σ(I)]
largest diff peak
0.0209, 0.0480
0.0195, 0.0474
1.045 and -0.537
0.0290, 0.0511
0.0237, 0.0498
0.931 and -0.716
0.0699, 0.1091
0.0623, 0.1070
1.215 and -3.610
0.0229, 0.0423
0.0195, 0.0415
0.597 and -0.627
and hole (e/Å-3
)
1
A suspension of compound 13 and dicyclopentadienezir-
conium dideuteride (Cp2ZrD2) was mixed at room tem-
perature for 4 h, and conversion to the deuterium-
labeled compound was judged complete by H and 31P
NMR spectroscopy. The spectra were identical to com-
pound 6 except for the missing hydride resonance at δ
1
-5.78 in the H NMR spectrum. Also, the resonance at
δ -2.2 in the 31P NMR spectrum appeared as a 1:1:1
triplet, indicating coupling to the H nucleus (2J P(trans)-D
2
) 36 Hz). The mixture was allowed to stand at room
temperature for 18 h, and no discernible change in the
1H NMR spectrum was observed. The mixture was then
1
heated at 85 °C for 30 min and again checked by H
NMR spectroscopy to reveal no discernible H/D ex-
change. Continued heating at 85 °C resulted in nearly
complete reductive elimination of 4,4′-bis(trifluoro-
methyl)biphenyl-d1 with concomitant formation of dimer
4 after 16 h. This again is an indication of the instability
of the η2-(4,4′-bis(trifluoromethyl)biphenyl) complex. It
appears that without a significant excess of biphenyl
in solution the major reaction pathway is dimerization
of [(dtbpm)Pt] to (dtbpm)2Pt2.
F igu r e 4. ORTEP diagram for 12. Ellipsoids are shown
at the 30% probability level. Selected distances (Å) and
angles (deg): Pt(1)-C(1), 2.087 (4); Pt(1)-Cl(1), 2.3631 (12);
P(1)-Pt(1)-P(2), 75.25 (5); C(1)-Pt(1)-Cl(1), 87.42 (12).
(29) For other examples of hindered metal-aryl rotation see: J ones,
W. D.; Feher, F. J . Inorg. Chem. 1984, 23, 2376.

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5327
F igu r e 5. 1H VT NMR spectrum of 3 in THF-d8. The
aromatic resonances are denoted with arrows, and the
P-CH2-P resonance by a *. Residual THF protons appear
at δ 3.58.
F igu r e 6. 1H VT NMR spectrum of 2 in THF-d8. The
aromatic resonances are denoted with arrows, and the
P-CH2-P resonance by a *. Residual THF protons appear
at δ 3.58.
Va r ia ble-Tem p er a tu r e NMR Sp ectr a . The ap-
pearance at room temperature of several broad reso-
nances in the 1H NMR spectra of the η2-arene complexes
prompted the examination of these compounds for
dynamic NMR behavior. Of particular interest are the
aromatic resonances for compounds 2, 3, 9, and 11,
although the bridging methylene and tert-butyl groups
also sharpen and broaden with changes in temperature.
At room temperature, (dtbpm)Pt[η2-1,3,5-C6H3(CF3)3] (3)
shows a broad signal at δ 3.99 for the hydrogen that is
on the C-C double bond of the ring that is bound to
the metal center. Two other resonances at δ 6.99 (br s)
and 6.02 (br d with 195Pt shoulders) are also observed
for the arene ring (Figure 5). Cooling the THF-d8
solution to -20 °C sharpened the singlet at δ 6.99
considerably. The resonance at δ 3.99 shifted upfield by
0.28 ppm and sharpened into a doublet. The expected
coupling to 195Pt was obscured by the bridging methyl-
ene protons on one side and the residual THF protons
on the other. The resonance at δ 6.02 was not signifi-
cantly altered. All three signals begin to coalesce toward
a single resonance at 40 °C, but the fast-limit structure
was not observed below 75 °C.
(dtbpm)Pt[η2-3,5,4′-tris(trifluoromethyl)biphenyl] (9) and
(dtbpm)Pt[η2-3,5,3′,5′-tetrakis(trifluoromethyl)biphen-
yl] (11) display behavior similar to that of compound 3.
The resonances are relatively broad at room tempera-
ture and resolve nicely at -20 °C (see Supporting
Information). An obvious difference between the com-
pounds is that only the two ortho hydrogens of the
nonbound ring begin to coalescence at higher temper-
atures for compound 9 and 11 as opposed to all three
in compound 3. However, an interesting observation is
made regarding the nonbound ring in compound 9. In
a 1,4-substituted phenyl ring, two doublets would be
expected, and this is observed at both the fast- and slow-
limit structures. Near room temperature though, the
doublet due to the protons at δ 7.99 (ortho to the bound
ring) undergoes some line broadening. One explanation
could be that the ring is not rotating as fast; therefore,
the two ortho protons are beginning to experience
different electronic environments. If this were the case,
the doublet due to the meta protons should behave
similarly, but the appearance of this signal does not
change at all. Another explanation may be that the
ortho protons are experiencing coupling to the platinum
metal center. Similar broadening of the ortho protons
to a 195Pt nucleus are observed in η2-styrene platinum
complexes, yet the crystal structure of compound 9
clearly does not place these hydrogens in an appropriate
position for coupling to platinum.30 Scheme 3 shows a
mechanism that allows for an η2-styrene-like configu-
ration to occur for this compound. The dynamic behavior
observed for the protons of the bound ring is consistent
with ring-walking, and so access to an η2-styrene-like
compound (structures B and C) is possible.
The room-temperature 1H NMR spectrum of (dtbpm)-
Pt[η2-1,4-C6H4(CF3)2] (2) has two broad peaks at δ 6.37
and 5.07 that decoalesce into four broad signals at -20
°C (Figure 6). The slow-limit structure is finally achieved
at -60 °C with four resonances at δ 7.10 (br s), 6.31
(d), 5.69 (br d with 195Pt shoulders), and 3.72 (br t).
Again, the expected coupling to 195Pt was obscured for
the resonance at δ 3.72. Increasing the temperature of
the solution caused the pairwise coalescence of the
resonances at δ 7.10/5.69 and 6.31/3.72 into two broad
singlets, which then coalesced into the baseline at 75
°C. The above data are consistent with migration of the
metal around the arene ring, with a slightly higher
barrier for migration past a trifluoromethyl group.
The aromatic protons of the η-bound arene rings in
P h otolysis of Com p ou n d s. Alternative reactivity
patterns are observed when solutions of (dtbpm)Pt(η2-
(30) Crascall, L. E.; Spencer, J . L. J . Chem. Soc., Dalton Trans. 1992,
3445-3452.

5328 Organometallics, Vol. 21, No. 24, 2002
Iverson et al.
Sch em e 3
contrast to the thermolytic reaction, where the platinum
metal center inserts into the 2′ C-H bond of the mono-
(trifluoromethyl)-substituted phenyl ring, photolysis
induces insertion into the C-H bond of the η2-C-C
double bond of the bis(trifluoromethyl)-substituted phen-
yl ring. A photostabilized state (2.2:1 preferring com-
pound 9) is achieved in several hours. Extended pho-
tolysis (1 week) did not result in significant decomposi-
tion.
(dtbpm)Pt(η2-3,5,3′,5′-tetrakis(trifluoromethyl)bi-
phenyl), also inert toward C-H activation under ther-
molytic conditions, undergoes a similar photochemical
transformation, as insertion takes place at the ortho-H
of the η2-C-C double bond (eq 8). A hydride resonance
arene) and (dtbpm)Pt(biphenyl)H are irradiated as
opposed to thermolysis. The apparent kinetic products
of C-H activation are achieved via photolysis. For
instance, compound 3, thermally inert toward C-H
activation, is converted to a Pt(II) aryl hydride complex
under photolytic conditions in C6D6 (eq 6). The sterically
at δ -7.57 (d of mult. with 195Pt satellites, 1J Pt-H ) 1267
Hz, 2J P(trans)-H ) 203 Hz) and two resonances in the 31P
hindered product, (dtbpm)Pt[2-(1,3,5-tris(trifluorometh-
1
1
yl)phenyl)](H) (16), is formed as judged by H, 19F, and
NMR spectrum at δ 8.9 (s, J Pt-P ) 1875 Hz) and 1.8
31P NMR spectra. Presumably, the photolytic conditions
allows the complex to reach an activated state where
C-H bond cleavage is accessible in such a bulky
environment. A sharp singlet at δ 8.14 is observed for
the two aryl hydrogens as well as a hydride resonance
at δ -8.78. The hydride resonance appears as a doublet
with 195Pt satellites (1J Pt-H ) 1257 Hz, 2J P(trans)-H ) 207
(second-order multiplet, 1J Pt-P ) 1242 Hz) are observed.
1H and 31P NMR data are consistent with the formula-
tion as (dtbpm)Pt[2-(3,5,3′,5′-tetrakis(trifluoromethyl)-
biphenyl](H) (18). The same product could be formed
by activation at the 2′ C-H bond of the nonbound ring;
however, given the structural similarities between
compounds 9 and 11 it seems reasonable that both
reactions occur in an identical fashion. A photostabilized
state is once again reached in several hours, where the
η2-biphenyl complex is favored 2.3:1 over the C-H
activated complex.
Compound 4 was the major platinum-containing
species formed along with the reductive elimination of
4,4′-bis(trifluoromethyl)biphenyl when a C6D6 solution
of (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphenyl)]H was
photolyzed. The reaction is approximately 38% complete
after 4 h of irradiation and completely finished after 16
h. The other platinum(II) isomer, (dtbpm)Pt[3-(4,4′-bis-
(trifluoromethyl)biphenyl)]H, is formed in a very small
amount during the course of the reaction but is eventu-
ally converted to (dtbpm)2Pt2 as well. Photolysis of
compound 2 for 90 min in C6D6 results in C-H activa-
tion similar to that observed in the thermal reaction.
Continued exposure for 24 h leads to reductive elimina-
tion of the arene and complete decomposition of the
platinum-containing species.
2
Hz). J P(cis)-H, normally observable in these systems, is
obscured due to coupling to the six 19F nuclei of the
adjacent CF3 groups. 31P NMR spectroscopy reveals two
new resonances with 195Pt satellites at δ 12.7 and 4.13
(1J Pt-P ) 2041 and 1339 Hz, respectively). Two new
signals are also observed in the 19F NMR spectrum in
a 2:1 ratio at δ -57.8 and -61.5. The former resonance
is coupled to platinum (3J Pt-F ) 80 Hz), whereas the
latter is a simple singlet. The reaction does not go to
completion, as a photostabilized state is reached after
5.5 h, with the η2-arene the predominant species (1.5:
1).
Photolysis of (dtbpm)Pt(η2-3,5,4′-tris(trifluoromethyl)-
biphenyl) (9) results in C-H activation as well, albeit
with alternate regioselectivity with respect to the
thermal activation. The product (17) displays a new
1
hydride resonance in the H NMR spectrum at δ -7.66
(eq 7). The signal is a doublet of multiplets with 195Pt
Con clu sion s
We have prepared a number of (dtbpm)Pt(η2-arene)
complexes which are intermediates in the stepwise
activation of aromatic C-H bonds. Several direct and
nondirect C-H activated products derived from the
arene complexes have also been synthesized and char-
acterized. The electronic character of the aromatic
ligands has a significant effect on the stability of the
arene complexes. Only electron-poor arenes react with
the [(dtbpm)Pt0] intermediate to form new complexes,
as electron-rich or neutral arenes result in the formation
2
satellites (1J Pt-H ) 1266 Hz, J P(trans)-H ) 206 Hz).
2J P(cis)-H is obscured due to coupling to a CF3 group. Two
new resonances with 195Pt satellites at δ 9.2 (s, J Pt-P
1
1
) 1872 Hz) and 1.6 (second-order multiplet, J Pt-P
)
1237 Hz) are observed in the 31P NMR spectrum. In

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5329
3
s, 2 H, C6H4(CF3)2), 3.85 (t with 195Pt satellites, J Pt-H ) 27
of the dimer 4. Additionally, the arene complexes that
contain extremely electron-poor benzenes or biphenyls
are more stable toward thermal reaction, e.g., compound
3 versus compound 2. The reactivity of the arene
complexes also differs when subjected to thermal versus
photolytic conditions. The more accessible C-H bonds
are preferentially cleaved when solutions of the arene
complexes are heated. In contrast, photolysis yielded
complexes that activate C-H bonds in sterically en-
cumbered positions, indicating that the reaction pro-
ceeds through a different activated complex under either
reaction condition.
Hz, J P-H ) 7.4 Hz, 2 H), 1.34 (br m, 36 H, Bu). 19F NMR
2
t
4
(THF-d8, rt): δ -61.3 (br s with 195Pt satellites, J Pt-F ) 88
Hz, 3 F, ipso CF3 on Pt-Caryl bond), -65.2 (br s, 3 F). 31P NMR
(THF-d8, rt): δ 50.4 (resonances for the phosphorus atoms are
coincidental for this compound, approximate 1J Pt-P ) 3196 Hz).
1H NMR (THF-d8, -60 °C): δ 7.10 (br s, 1H, C6H4(CF3)2), 6.31
(br d, 3J H-H ) 9.2 Hz, 1 H, C6H4(CF3)2), 5.69 (br d, 3J H-H ) 8.7
Hz, 1 H, C6H4(CF3)2), 3.72 (br m, J Pt-H obscured due to other
resonances, 1 H, ipso H on Pt-Caryl bond), 4.02 (m, 1 H,
PCH2P), 3.89 (m, 1 H, PCH2P), 1.42 (br m, 18 H, tBu), 1.31 (br
d, 9 H, Bu), 1.25 (br d, 9 H, Bu). For (dtbpm)Pt[η2-(1,4-bis-
(trifluoromethyl)benzene)] Anal. Calcd (found): C, 42.07 (42.84);
H, 5.93 (6.26).
t
t
(d tbp m )P t[η2-(1,3,5-tr is(tr iflu or om eth yl)ben zen e)] (3).
(dtbpm)Pt(Np)H (80 mg, 0.14 mmol) was dissolved in 25 mL
of THF in a 100 mL air-free flask, and 1,3,5-tris(trifluoro-
methyl)benzene (790 mg, 2.4 mmol) was added to the solution
by pipet. The mixture was stirred at 55 °C for 1.5 h. The
volatile material was removed in vacuo and the residue
extracted with 2 × 2 mL of hexanes. The remaining solids were
redissolved in THF, layered with hexanes, and cooled to -25
°C. Orange-yellow crystals (22 mg, 20%) deposited after several
days. 1H NMR (THF-d8, rt): δ 6.99 (br s, 1 H), 6.02 (d with
195Pt shoulders, J ) 4.3 Hz, 1 H), 3.99 (br s, 1 H, ipso H on
Pt-Caryl bond), 3.84 (br s, 2 H, PCH2P), 1.2-1.5 (br resonance,
36 H, tBu). 19F NMR (THF-d8, rt): δ -59.9 (m with 195Pt
satellites, 3J Pt-F ) 81 Hz, 3 F, CF3 ipso to Pt-Caryl bond), -64.0
(br s, 3 F), -64.4 (br s, 3 F). 31P NMR (THF-d8, rt): δ 47.9 (d
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed using glovebox, Schlenk, or vacuum-line techniques.
Diethyl ether, hexanes, toluene, pentane, and benzene were
predried over sodium and distilled from sodium/benzophenone
ketyl. CH2Cl2 was dried over CaH2 and distilled prior to use.
C6D6 and THF-d8 were purchased from Cambridge Isotope
Laboratories and dried and distilled from sodium/benzophe-
none ketyl. CDCl3 was purchased from Cambridge Isotope
Laboratories and dried over 3 Å sieves. CD2Cl2 was dried over
P2O5 and vacuum distilled prior to use. (dtbpm)Pt(Np)H,2c
(COD)Pt(4-C6H4CF3)2, tBu2PCl,31 tBu2PMe,32 and Bu2PCH2Li15
t
were prepared according to literature methods. dtbpm was
prepared as described in the Supporting Information. Biphen-
yls were purchased from Aldrich or Alfa Aesar or prepared
via Suzuki coupling methods.33
with 195Pt satellites, J Pt-P ) 3338 Hz, J P-P ) 91 Hz), 46.7 (d
with 195Pt satellites, 1J Pt-P ) 2967 Hz, 2J P-P ) 91 Hz). 1H NMR
(THF-d8, -20 °C): δ 7.01 (s, 1 H), 6.02 (d with 195Pt shoulders,
J ) 4.1 Hz, 1 H), 4.08 (br m, 1 H, PCH2P), 3.86 (br m, 1 H,
PCH2P), 3.72 (d, 195Pt satellites are obscured by other reso-
nances, 1 H, ipso H on Pt-Caryl bond), 1.53 (m, 9 H, tBu), 1.46-
1.24 (m, 27 H, tBu). For (dtbpm)Pt[η2-(1,3,5-tris(trifluoromethyl)-
benzene)] Anal. Calcd (found): C, 39.95 (40.05); H, 5.29 (5.53).
(d t b p m )P t [2-(1,4-b is(t r iflu or om et h yl)p h en yl)]H (5).
(dtbpm)Pt(Np)H (160 mg, 0.28 mmol) was dissolved in 50 mL
of THF in a 250 mL round bottom Schlenk flask, and 1,4-bis-
(trifluoromethyl)benzene (2.2 g, 5.6 mmol) was added to the
solution by pipet. The flask was fitted with a reflux condensor
and stirred at 55 °C for 2 h and then at 85 °C for 4 h. The
volatile material was removed in vacuo. The residue was
redissolved in THF, layered with hexanes, and cooled to -25
°C to yield light orange crystals (112 mg, 56%). 1H NMR
1
2
1H NMR spectra were recorded at ambient temperature
(except as noted) on Bruker AMX400 or Avance400 spectrom-
eters and referenced to residual proton solvent signals. 31P
NMR spectra were recorded on Bruker AMX400 or Avance400
spectrometers operating at 162 MHz and were referenced to
an 85% phosphoric acid external standard set to 0 ppm. 19F
NMR spectra were recorded on a Bruker Avance400 spectrom-
eter operating at 376 MHz, and chemical shifts were refer-
enced to a CFCl3 external standard set to 0 ppm. GC/MS was
conducted on a 5890 Series II gas chromatograph fitted with
an HP 5970 series mass selective detector. Elemental analyses
were performed by Desert Analytics. A Siemens SMART
system with a CCD area detector was used for X-ray structure
determinations.
(d tbp m )P t(n eop en tyl)H (1).2c 1H NMR (C6D6): δ 3.05 (t,
2J P-H ) 6.9 Hz, 2 H, PCH2P), 2.64 (dd with 195Pt satellites,
3
(C6D6): δ 8.69 (d with 195Pt satellites, 1 H, J ) 6.3 Hz, J Pt-H
) 68 Hz), 7.64 (d with 195Pt shoulders, 1 H, J H-H ) 8.3 Hz),
3
2
2J Pt-H ) 86 Hz, J P-H ) 7.1 Hz, J P-H ) 8.8 Hz, 2 H, CH2C-
(CH3)3), 1.62 (s, 9 H, CH2C(CH3)3), 1.22 (d, 18 H, (CH3)3CP,
3J P-H ) 12 Hz), 1.18 (d, 18 H, (CH3)3CP, 3J P-H ) 13 Hz), -4.88
2
7.07 (d, 1 H, J H-H ) 8.3 Hz), 3.06 (t, J P-H ) 8.0 Hz, 2 H,
3
3
PCH2P), 1.13 (d, 18 H, (CH3)3P, J P-H ) 14 Hz), 1.07 (d, J P-H
) 13 Hz, 18 H, (CH3)3P), -6.06 (d of sextets with 195Pt
(dd with 195Pt satellites, J P(trans)-H ) 214 Hz, J P(cis)-H ) 11
2
2
1
2
Hz, J Pt-H ) 1350 Hz, Pt-H). 31P NMR (C6D6): δ 9.7 (d with
1
satellites, J Pt-H ) 1297 Hz, J P(trans)-H ) 211 Hz, J ) 3 Hz, 1
H, Pt-H). 31P NMR (C6D6): δ 7.5 (s with 195Pt satellites, 1J Pt-P
) 1549 Hz, trans aryl), -2.5 (second-order multiplet with 195Pt
1
2
195Pt satellites, J Pt-P ) 1345 Hz, J P-P ) 11 Hz, trans
neopentyl), -5.4 (d with 195Pt satellites, 1J Pt-P ) 1338 Hz, 2J P-P
) 9 Hz, trans hydride).
satellites, J Pt-P ) 1199 Hz, trans hydride). 19F NMR (THF-
1
d8): δ -59.7 (s with 195Pt satellites, J Pt-F ) 53 Hz, 3 F, CF3
4
(d t b p m )P t [η2-(1,4-b is(t r iflu or om et h yl)b en zen e)] (2).
(dtbpm)Pt(Np)H (115 mg, 0.20 mmol) and 1,4-bis(trifluoro-
methyl)benzene (861 mg, 4.02 mmol) were dissolved in 40 mL
of THF and transferred to a 100 mL Schlenk flask fitted with
a reflux condensor. The mixture was stirred at 50 °C for 1.5
h. The volatile material was removed in vacuo and the residue
extracted with 5 × 2 mL of hexanes. The remaining material
was redissolved in THF, layered with hexanes, and cooled to
-25 °C. Orange crystals (20 mg, 14%) deposited after a week.
1H NMR (THF-d8, rt): δ 6.37 (br s, 2 H, C6H4(CF3)2), 5.07 (br
ortho to Pt-Caryl), -61.5 (s, 3 F, CF3 meta to Pt-Caryl). For
(dtbpm)Pt[2-(1,4-bis(trifluoromethyl)phenyl)]H Anal. Calcd
(found): C, 42.07 (41.74); H, 5.93 (6.32).
(d tbp m )P t[2-(4,4′-bis(tr iflu or om eth yl)bip h en yl)]H (6).
(dtbpm)Pt(Np)H (125 mg) and 4,4′-bis(trifluoromethyl)biphenyl
(2.03 g, 7.0 mmol) were placed in a 250 mL round bottom flask
fitted with a Schlenk adaptor and dissolved in 50 mL of THF.
The mixture was stirred at 40 °C for 3 h, at which time a
second amount of (dtbpm)Pt(Np)H (75 mg, 0.35 mmol total)
in 5 mL of THF was added to the solution via syringe. The
solution was stirred at 40 °C for an additional 16 h. The
volatile material was removed in vacuo and the residue
extracted with 6 × 5 mL of hexanes. Recrystallization from
THF/hexanes at -25 °C yielded white crystals (118 mg, 43%).
(31) Hoffmann, H.; Schellenbeck, P. Chem. Ber. 1967, 100, 692-
693.
(32) Kolodyazhnyi, O. I. J . Gen. Chem., U.S.S.R. 1981, 51, 2125-
2137.
(33) Cullen, K. E.; Sharp, J . T. J . Chem. Soc., Perkin Trans. 1 1995,
2565-2579.
4
1H NMR (C6D6): δ 8.57 (d with 195Pt satellites, J P-H ) 6.0

5330 Organometallics, Vol. 21, No. 24, 2002
Iverson et al.
3
Hz, J Pt-H ) 67 Hz, 1 H, H ortho to Pt-Caryl bond), 8.11 (d,
2 H), 7.69 (d, J ) 8.4 Hz, 2 H), 6.96 (s, 1 H), 6.31 (br s with
3J H-H ) 7.9 Hz, 2 H, -C6H4CF3), 7.50 (d, 3J H-H ) 8.0 Hz, 2 H,
-C6H4CF3), 7.30 (m, 2 H, H meta and para to Pt-Caryl bond),
2.91 (t, J P-H ) 7.5 Hz, 2 H, PCH2P), 1.04 (d, J P-H ) 14 Hz,
195Pt shoulders, 1 H), 4.03 (d with 195Pt satellites, J Pt-H ) 74
2
Hz, J ) 5.6 Hz, 1 H), 3.88 (m, 2 H, PCH2P), 1.41 (m, 18 H,
2
3
tBu), 1.31 (d, 3J P-H ) 13 Hz, 9 H, tBu), 0.93 (d, 3J P-H ) 13 Hz,
t
3
t
t
18 H, Bu), 0.80 (d, J P-H ) 14 Hz, 18 H, Bu), -5.78 (dd with
195Pt satellites, 1J Pt-H ) 1311 Hz, 2J P(trans)-H ) 207 Hz, 2J P(cis)-H
) 7.6 Hz, 1 H, Pt-H). 31P NMR (C6D6): δ 7.4 (d with 195Pt
9 H, Bu). For (dtbpm)Pt[η2-(3,5,4′-tetrakis(trifluoromethyl)-
biphenyl)] Anal. Calcd (found): C, 44.97 (44.81); H, 4.95 (5.35).
Gen er a tion of (d tbp m )P t[2′-(3,5,4′-tr is(tr iflu or om eth -
yl)bip h en yl)]H (10). A solution of (dtbpm)Pt[η2-(3,5,4′-tris-
(trifluoromethyl)biphenyl)], generated in situ from (dtbpm)-
Pt(Np)H (8.0 mg, 0.014 mmol) and 3,5,4′-tris(trifluoro-
methyl)biphenyl (50 mg, 0.14 mmol) in 600 µL of THF-d8 in a
resealable NMR tube, was heated at 85 °C for 37 h. 1H and
31P NMR spectroscopy indicated that the η2 complex had been
converted into an aryl hydride complex. The reaction was
nearly complete (∼10% η2 complex remained) and with a small
amount of (dtbpm)2Pt2 present. Continued heating at 85 °C
1
2
satellites, J Pt-P ) 1648 Hz, J P-P ) 7.0 Hz, trans biphenyl),
-2.8 (second-order d with 195Pt satellites, J Pt-P ) 1287 Hz,
1
2J P-P ) 7.9 Hz, trans hydride). 31P NMR (THF-d8): δ 12.6 (d),
2.4 (d). For (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphenyl)]H
Anal. Calcd (found): C, 47.14 (47.31); H, 5.87 (6.05).
(d tbp m )P t[3-(4,4′-bis(tr iflu or om eth yl)bip h en yl)]H (7).
Compound 7 was formed in a limited amount in the reaction
above and could not be isolated in larger scale reactions. The
available H and 31P NMR spectroscopic data are given below.
1
1H NMR (THF-d8): δ 1.48 (d, J P-H ) 13 Hz, 18 H, Bu), 1.38
3
t
1
completed the conversion. H NMR (THF-d8): δ 8.39 (s, 2 H,
(d, J P-H ) 13 Hz, 18 H, Bu), -6.58 (d of sextets with 195Pt
3
t
4
C6H3(CF3)2), 8.06 (d, J P-H ) 6.0 Hz, 195Pt satellites obscured
satellites (1J Pt-H ) 1373 Hz, J P(trans)-H ) 204 Hz, J ) 3 Hz, 1
2
by other resonances, 1 H, H ortho to Pt-Caryl bond), 7.82 (s, 1
H, Pt-H). 31P NMR (THF-d8): δ 13.1 (1J Pt-P ) 1759 Hz) and
2.7 (1J Pt-P ) 1253 Hz).
3
3
H), 7.24 (d, J H-H ) 7.7 Hz, 1 H), 7.09 (d, J H-H ) 8.0 Hz, 1
H), 3.69 (t with 195Pt shoulders, J P-H ) 7.6 Hz, 2 H, PCH2P),
2
3
t
3
Th er m olysis of (d tbp m )P t[η2-(1,4-bis(tr iflu or om eth yl)-
ben zen e)]. (dtbpm)Pt[η2-(1,4-bis(trifluoromethyl)benzene)] (8.3
mg, 0.012 mmol) was placed in a resealable NMR tube and
dissolved in 600 µL of THF-d8. The solution was heated at 55
1.38 (d, J P-H ) 14 Hz, 18 H, Bu), 1.09 (d, J P-H ) 13 Hz, 18
H, tBu), -6.12 (dd with 195Pt satellites, J Pt-H ) 1293 Hz,
1
2J P(trans)-H ) 204 Hz,2J P(cis)-H ) 7.1 Hz). 19F NMR (THF-d8): δ
-62.84 (s, 3 F), -62.98 (s, 6 F). 31P NMR (THF-d8): δ 6.2 (d
with 195Pt satellites, J Pt-P ) 1680 Hz, J P-P ) 5 Hz), -3.2 (d
1
2
°C and monitored by H and 31P NMR spectroscopy. After 1.5
1
with 195Pt satellites, J Pt-P ) 1291 Hz, J P-P ) 5 Hz).
1
2
h 59% of the starting arene remained, 11% had been converted
to the C-H activated product 6, and the balance (30%) had
been converted to (dtbpm)2Pt2 (31P NMR, THF-d8: δ 84.3, 1J Pt-P
) 4572 Hz, with higher order couplings. See Supporting
Information). After 15.5 h, 13% of the starting arene remained,
35% had been converted to the C-H activated product, and
the balance (52%) had been converted to (dtbpm)2Pt2.
(d t b p m )P t [η2-(3,5,3′,5′-t e t r a k is(t r iflu or om e t h yl)b i-
p h en yl)] (11). (dtbpm)Pt(Np)H (85 mg, 0.15 mmol) and
3,5,3′,5′-tetrakis(trifluoromethyl)biphenyl (633 mg, 1.49 mmol)
were dissolved in 30 mL of THF and transferred to a 100 mL
air-free Teflon-stoppered flask. The mixture was stirred at 55
°C for 2 h. The volatile material was removed in vacuo and
the residue extracted with 3 × 3 mL of hexanes. Recrystalli-
zation of the insoluble portion from CH2Cl2/Et2O at -25 °C
yielded red crystals (55 mg, 40%). An additional crop of crystals
(23 mg) was recovered from the mother liquor for a total yield
(d tbp m )P t(2,2′-bis(4,4′-tr iflu or om eth yl)bip h en yl) (8).
(dtbpm)Pt(Np)H (80 mg, 0.14 mmol) and bis-(4,4′-trifluoro-
methyl)biphenyl were dissolved in 25 mL of THF in a 100 mL
Teflon-stoppered air-free flask. The solution was stirred at 55
°C for 2 h and then at 85 °C for 15 days. The volatile material
was removed in vacuo and the residue extracted with 3 × 4
mL of hexanes. The remaining solids were redissolved in CH2-
Cl2 and layered with Et2O by slow diffusion. Feathery yellow
crystals (20 mg, 18%) deposited after several days. 1H NMR
(CD2Cl2): δ 7.96 (m with 195Pt satellites, 3J Pt-H ) 67 Hz, 2 H),
1
of 57%. H NMR (THF-d8, rt): δ 8.23 (br s, 2 H), 7.90 (s, 1 H),
7.01 (br s, 1 H), 6.39 (br d, J ) 4.2 Hz, 1 H), 4.08 (br s, 1 H),
3
t
3.85 (br m, 2 H, PCH2P), 1.42 (br d, J P-H ) 13 Hz, 9 H, Bu),
1.34 (br m, 18 H, Bu), 0.98 (br s, 9 H, Bu). 19F NMR (THF-
d8): δ -63.10 (br s with 195Pt shoulders, 3 F), -65.24 (s, 6 F),
-67.46 (d with 195Pt shoulders, J ) 4.5 Hz, 3 F). 31P NMR
t
t
(THF-d8, rt): δ 43.2 (d with 195Pt satellites, J Pt-P ) 3318 Hz,
1
3
3
7.40 (d, J H-H ) 7.6 Hz, 2 H), 7.21 (d, J H-H ) 7.7 Hz, 2 H),
2J P-P ) 96 Hz), 41.1 (d with 195Pt satellites, J Pt-P ) 2967 Hz,
1
3.66 (t, 3J P-H ) 7.9 Hz, 2 H, PCH2P), 1.51 (d, 4J P-H ) 13.1 Hz,
2J P-P ) 96 Hz). 1H NMR (THF-d8, -20 °C): δ 8.37 (s, 2 H),
8.00 (s, 1 H), 7.02 (br s, 1 H), 6.44 (br d with 195Pt shoulders,
J ) 4.8 Hz, 1 H), 4.06 (dd with 195Pt satellites, 2J Pt-H ) 63 Hz,
36 H, Bu). 19F NMR (CD2Cl2): δ -62.6 (s). 31P NMR (CD2-
t
Cl2): δ 4.95 (s with 195Pt satellites, J Pt-P ) 1523 Hz). For
1
(dtbpm)Pt(2,2′-bis(4,4′-trifluoromethyl)biphenyl) Anal. Calcd
(found): C, 47.27 (47.35); H, 5.63 (5.91).
2J P-H ) 10 Hz, J H-H ) 4.4 Hz, 1 H), 3.90 (m, 2 H, PCH2P),
4
3
t
3
(dtbpm )P t[η2-(3,5,4′-tr is(tr iflu or om eth yl)biph en yl)] (9).
(dtbpm)Pt(Np)H (71 mg, 0.12 mmol) and 3,5,4′-tris(trifluo-
romethyl)biphenyl (222 mg, 0.62 mmol) were dissolved in 17.5
mL of THF and transferred to a 100 mL air-free Teflon-
stoppered flask. The mixture was stirred at 55 °C for 2 h. The
volatile material was removed in vacuo and the residue
extracted with 5 × 2 mL of hexanes. The remaining solids were
a relatively pure sample of (dtbpm)Pt[η2-(3,5,4′-bis(trifluoro-
methyl)biphenyl)]. Recrystallization from THF/hexanes at -25
°C yielded orange-red crystals (73 mg, 68%). An additional crop
1.42 (d, J P-H ) 13 Hz, 9 H, Bu), 1.37 (d, J P-H ) 13 Hz, 9 H,
tBu), 1.32 (d, 3J P-H ) 13 Hz, 9 H, tBu), 0.93 (d, 3J P-H ) 13 Hz,
9 H, tBu). For (dtbpm)Pt[η2-(3,5,3′,5′-tetrakis(trifluoromethyl)-
biphenyl)] Anal. Calcd (found): C, 42.81 (43.01); H, 4.79 (4.86).
(d tbp m )P t[2-(1,4-bis(tr iflu or om eth yl)p h en yl)]Cl (12).
(dtbpm)Pt[2-(1,4-bis(trifluoromethyl)phenyl)]H (94 mg, 0.13
mmol) was dissolved in 21 mL of THF in a scintillation vial.
Then 1 mL CH2Cl2 was added and the mixture was stirred at
room temperature for 2 h. The volatile material was removed
in vacuo and the residue washed with 5 × 2 mL of hexanes.
The remaining solids were redissolved in THF, layered with
hexanes, and cooled at -25 °C. White crystals (64 mg, 65%)
deposited after 3 days. 1H NMR (C6D6): δ 8.47 (d with 195Pt
of crystals was recovered from the mother liquor for
a
combined yield of 76%. This compound has a complicated 31P
NMR spectrum which appears to be typical for the η2 arene
complexes in this system. 1H NMR (THF-d8, 20 °C): δ 7.99
(br d, J ) 7.9 Hz, 2 H), 7.64 (d, J ) 8.3 Hz, 2 H), 6.95 (br s, 1
H), 6.31 (br s, 1 H), 4.08 (br s, 1 H), 3.84 (br m, 2 H, PCH2P),
1.37 (br m, 27 H, tBu), 0.98 (br s, 9 H, tBu). 19F NMR (THF-d8,
20 °C): δ -61.21 (br s with 195Pt shoulders, 3 F), -63.04 (s, 3
F), -65.67 (s with 195Pt shoulders, 3 F). 31P NMR (THF-d8, 20
3
satellites, 1 H, J ) 6.8 Hz, J Pt-H ) 45 Hz), 7.52 (d, 1 H, J H-H
) 6.0 Hz), 7.07 (d, 1 H, J H-H ) 8.0 Hz), 2.69 (t with 195Pt
shoulders, 2J P-H ) 8.2 Hz, 2 H, PCH2P), 1.31 (d, 9 H, (CH3)3P,
3
3J P-H ) 14 Hz), 1.20 (d, 9 H, (CH3)3P, J P-H ) 14 Hz), 1.10 (d,
3
3
9 H, (CH3)3P, J P-H ) 14 Hz), 0.87 (d, 9 H, (CH3)3P, J P-H
)
14 Hz). 31P NMR (C6D6): δ -10.3 (d with 195Pt satellites, 1J Pt-P
1
2
2
°C): δ 44.8 (d with 195Pt satellites, J Pt-P ) 3307 Hz, J P-P
)
) 3518 Hz, J P-P ) 20 Hz, trans Cl), -16.2 (d with 195Pt
101 Hz), 43.9 (d with 195Pt satellites, J Pt-P ) 2991 Hz, J P-P
) 101 Hz). H NMR (THF-d8, -20 °C): δ 8.07 (d, J ) 8.2 Hz,
satellites, J Pt-P ) 1519 Hz, J P-P ) 19 Hz, trans aryl). 19F
1
2
1
2
1
NMR (C6D6): δ -54.7 (br s, 3 F, CF3 ortho to Pt-Caryl), -62.0

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5331
(s, 3 F, CF3 meta to Pt-Caryl). For (dtbpm)Pt[2-(1,4-bis-
(trifluoromethyl)phenyl)]Cl Anal. Calcd (found): C, 40.14
(40.21); H, 5.53 (5.64).
Conversion to the deuterium-labeled compound was judged
1
complete by H and 31P NMR spectroscopy. The spectra were
identical to compound (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)-
biphenyl)]H except for the missing hydride resonance at δ
-5.78 in the 1H spectrum, and the resonance at δ -2.24
(dtbpm )P t[2-(4,4′-bis(tr iflu or om eth yl)biph en yl)]Cl (13).
(dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphenyl)]H (60 mg, 0.076
mmol) was dissolved in 6 mL of toluene in a scintillation vial.
Then 50 µL of CCl4 was added and the mixture was stirred at
room temperature for 30 min. The volatile material was
removed in vacuo. The remaining solids were dissolved in THF,
layered with hexanes, and cooled at -25 °C. White crystals
2
revealed coupling to the H nucleus in the 31P NMR spectrum.
4
1H NMR (C6D6): δ 8.57 (d with 195Pt satellites, J P-H ) 6.0
3
Hz, J Pt-H ) 67 Hz, 1 H, H ortho to Pt-Caryl bond), 8.10 (d,
3J H-H ) 7.9 Hz, 2 H, -C6H4CF3), 7.50 (d, 3J H-H ) 8.0 Hz, 2 H,
-C6H4CF3), 7.31 (m, 2 H, H meta and para to Pt-Caryl bond),
2
3
1
2.90 (t, J P-H ) 7.5 Hz, 2 H, PCH2P), 1.04 (d, J P-H ) 14 Hz,
(36 mg, 58%) deposited after 3 days. H NMR (C6D6): δ 8.42
18 H, tBu), 0.80 (d, J P-H ) 14 Hz, 18 H, tBu). 31P NMR
3
3
(d with 195Pt shoulders, 1 H, J ) 8.1 Hz, J Pt-H ) 45 Hz), 8.39
(C6D6): δ 7.8 (s with 195Pt satellites, 1J Pt-P ) 1649 Hz, P trans
biphenyl), -2.24 (t with 195Pt satellites, 1J Pt-P ) 1274 Hz, 2J D-P
) 36 Hz, P trans D).
(d, 2 H, J H-H ) 8.0 Hz), 7.49 (d, 2 H, J H-H ) 8.0 Hz), 7.26 (d,
1 H, J H-H ) 7.9 Hz), 7.14 (d partially obscured by residual
solvent peak, 1 H), 2.62 (m, 1 H, PCH2P), 2.48 (m, 1 H, PCH2P),
3
1.22 (d, 9 H, (CH3)3P, J P-H ) 14 Hz), 1.14 (d, 9 H, (CH3)3P,
Th er m olysis of (d tbp m )P t[2-(4,4′-bis(tr iflu or om eth yl)-
b ip h en yl)]H . (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphen-
yl)]H (7 mg, 0.0089 mmol) was dissolved in 600 µL of THF-d8
in a sealable NMR tube and capped. The tube was frozen in
liquid N2 and quickly flame-sealed. The solution was heated
at 125 °C for 6 h. Reductive elimination of biphenyl was
complete along with concomitant formation of (dtbpm)2Pt2.
Continued heating (14 days) at 125 °C resulted in the eventual
decomposition of the platinum dimer.
Th er m olysis of (d tbp m )P t[2-(4,4′-bis(tr iflu or om eth yl)-
b ip h en yl)]D. (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphen-
yl)]D was prepared as above in 600 µL of C6D6 in a resealable
NMR tube. The mixture was allowed to stand at room
temperature for 18 h, and no discernible change in the 1H
NMR spectrum was observed. The mixture was then heated
at 85 °C for 30 min and again checked by 1H NMR spectroscopy
to reveal no significant H/D exchange. Continued heating at
85 °C resulted in nearly complete reductive elimination of 4,4′-
bis(trifluoromethyl)biphenyl-d1 with concomitant formation of
(dtbpm)2Pt2 after 16 h, as confirmed in the 1H and 31P NMR
spectra.
Gen er a tion of (d tbp m )P t[2-(1,3,5-tr is(tr iflu or om eth -
yl)p h en yl)]H (16). (dtbpm)Pt[η2-(1,3,5-tris(trifluoromethyl)-
benzene)] (9.8 mg, 0.13 mmol) was dissolved in 0.6 mL of C6D6
and transferred to a resealable NMR tube. The tube was
photolyzed (λ > 300 nm) and the reaction monitored by 1H,
19F, and 31P NMR spectroscopy. The starting complex was
converted to an aryl hydride and reached a photostabilized
state after 5.5 h (ratio of η2 arene to aryl hydride is 3:2).
Photolysis for 2 days did not result in any significant decom-
position. 1H NMR (C6D6): δ 8.14 (s, 2 H), 3.07 (t with 195Pt
3
3J P-H ) 14 Hz), 0.96 (d, 9 H, (CH3)3P, J P-H ) 14 Hz), 0.38 (d,
9 H, (CH3)3P, 3J P-H ) 15 Hz). 31P NMR (C6D6); δ -10.1 (d with
195Pt satellites, 1J Pt-P ) 3645 Hz, 2J P-P ) 2 Hz, trans Cl), -13.4
1
2
(d with 195Pt satellites, J Pt-P ) 1426 Hz, J P-P ) 2 Hz, trans
aryl). For (dtbpm)Pt[2-(1,4-bis(trifluoromethyl)phenyl)]Cl Anal.
Calcd (found): C, 45.17 (45.16); H, 5.50 (5.48).
(d t b p m )P t [2′-(3,5,4′-t r is (t r iflu o r o m e t h y l)b ip h e n -
yl)]Cl (14). (dtbpm)Pt(Np)H (66 mg, 0.16 mmol) and 3,5,4′-
tris(trifluoromethyl)biphenyl (207 mg, 0.58 mmol) were dis-
solved in 22 mL of THF and transferred to a 100 mL air-free
Teflon-stoppered flask. The mixture was stirred at 55 °C for 2
h and then at 85 °C for 40 h. The volatile material was
removed in vacuo and the residue washed once with 3 mL of
hexanes. The residue was then redissolved in 6 mL of THF.
Then 0.5 mL of CH2Cl2 was added, and the mixture was stirred
at room temperature for 2 h. The solvent was removed under
vacuum and the residue washed with 4 × 3 mL of pentane.
The remaining solids were dissolved in THF, layered with
pentane, and allowed to stand at room temperature. Pale
1
yellow crystals (32 mg, 31%) deposited after several days. H
NMR (CDCl3): δ 8.57 (s, 2 H, C6H3(CF3)2), 7.98 (d with 195Pt
shoulders, 4J P-H ) 7.4 Hz, 1 H, H ortho to Pt-Caryl bond), 7.76
(s, 1 H, C6H3(CF3)2), 7.19 (s, 2 H), 3.33 (m, 1 H, PCH2P), 3.15
3
t
(m, 1 H, PCH2P), 1.58 (d, J P-H ) 14 Hz, 9 H, Bu), 1.37 (d,
3J P-H ) 14 Hz, 9 H, Bu), 1.29 (d, J P-H ) 15 Hz, 9 H, Bu),
t
3
t
0.79 (d, 3J P-H ) 15 Hz, 9 H, tBu). 31P NMR (CDCl3): δ -9.3 (d
with 195Pt satellites, J Pt-P ) 3689 Hz, J P-P ) 16 Hz), -12.7
1
2
(d with 195Pt satellites, J Pt-P ) 1424 Hz, J P-P ) 16 Hz). For
(dtbpm)Pt[2′-(3,5,4′-tris(trifluoromethyl)biphenyl)]Cl Anal. Cal-
cd (found): C, 43.08 (43.30); H, 4.97 (5.00).
1
2
2
3
(d tbp m )P t(2-bip h en yl)Cl (15). (dtbpm)Pt(2,2′-biphenyl)
(70 mg, 0.11 mmol) was suspended in 8 mL of THF, and 18
µL of concentrated HCl was added via microsyringe. The
suspension was stirred for 15 min at room temperature, during
which time the yellow crystals dissolved and the solution
became colorless. The volatile material was removed in vacuo.
The residue was taken up in CH2Cl2 and layered with Et2O.
Colorless crystals deposit after several days at -20 °C. 1H
shoulders, J P-H ) 7.9 Hz, 2 H, PCH2P), 1.16 (d, J P-H ) 14
t 3 t
Hz, 9 H, Bu), 1.05 (br d, J P-H ) 13 Hz, 27 H, Bu), -8.78 (d
with 195Pt satellites, J Pt-H ) 1257 Hz, J P(trans)-H ) 207 Hz, 1
1
2
H, Pt-H). 19F NMR (C6D6): δ -57.8 (t with 195Pt satellites,
3J Pt-F ) 80 Hz, 6 F, CF3 ipso to Pt-Caryl bond), -61.5 (br s, 3
F). 31P NMR (C6D6): δ 12.7 (s with 195Pt satellites, J Pt-P
)
1
2041 Hz, trans aryl), 4.13 (s with 195Pt satellites, 1J Pt-P ) 1339
Hz, trans H).
3
NMR (CDCl3): δ 8.13 (d, 2 H, J H-H ) 7.4 Hz), 7.67 (t, 1 H,
Gen er a tion of (d tbp m )P t[2-(3,5,4′-tr is(tr iflu or om eth -
yl)bip h en yl)]H (17). (dtbpm)Pt[η2-(3,5,4′-tris(trifluorometh-
yl)biphenyl)] (7.5 mg, 0.0087 mmol) was placed in a sealable
NMR tube and dissolved in 600 µL of C6D6. The tube was
capped, frozen in liquid N2, and quickly flame-sealed. The tube
was photolyzed and the reaction monitored by 1H and 31P NMR
spectroscopy. The starting complex was converted to an aryl
hydride and reached a photostabilized state after 11 h.
Extended photolysis (1 week) did not significantly alter the
ratio of η2 arene to aryl hydride (2.2:1) nor did the reaction
mixture decompose. 1H NMR (C6D6): δ 8.23 (s with 195Pt
3
J H-H ) 7.3 Hz, J Pt-H ) 39 Hz), 7.27 (t, 2 H, J H-H ) 7.5 Hz),
7.16 (m, 2 H), 7.04 (t, 1 H, J H-H ) 7.2 Hz), 6.91 (t, 1 H, J H-H
3
) 7.4 Hz), 3.18 (m, 2 H, PCH2P), 1.54 (d, J P-H ) 13 Hz, 9 H,
3
3
(CH3)3P), 1.46 (d, J P-H ) 14 Hz, 9 H, (CH3)3P), 1.34 (d, J P-H
3
) 14 Hz, 9 H, (CH3)3P), 0.76 (d, J P-H ) 15 Hz, 9 H, (CH3)3P).
31P NMR (CDCl3): δ -8.6 (d with 195Pt satellites, 1J Pt-P ) 3904
Hz, J P-P ) 15 Hz, trans Cl), δ -9.2 (d with 195Pt satellites,
2
1J Pt-P ) 1328 Hz, 2J P-P ) 15 Hz, trans biphenyl). For (dtbpm)-
Pt(2-biphenyl)Cl Anal. Calcd (found): C, 50.61 (50.45); H, 6.88
(6.87).
3
Gen er a tion of (d tbp m )P t[2-(4,4′-bis(tr iflu or om eth yl)-
bip h en yl)]D (6-d 1). (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)-
biphenyl)]Cl (6 mg, 0.0073 mmol) was placed in a resealable
NMR tube and dissolved in 600 µL of C6D6. Dicyclopentadi-
enylzirconium dideuteride (3.4 mg, 0.015 mmol) was added,
and the suspension was mixed at room temperature for 4 h.
shoulders, 1 H, Pt-C6H2(CF3)2), 7.90 (br d, J H-H ) 7.8 Hz, 2
H, C6H4(CF3)), 7.61 (s with 195Pt shoulders, 1 H, Pt-C6H2-
3
(CF3)2), 7.40 (br d, J H-H ) 7.8 Hz, 2 H, C6H4(CF3)), 2.97 (dt,
2J H-H ) 17 Hz, 2J P-H ) 7.6 Hz, 1 H, PCH2P), 2.72 (dt, 2J H-H
)
2
3
17 Hz, J P-H ) 7.6 Hz, 1 H, PCH2P), 1.17 (d, J P-H ) 14 Hz, 9
t
3
t
3
H, Bu), 0.94 (d, J P-H ) 14 Hz, 9 H, Bu), 0.92 (d, J P-H ) 13

5332 Organometallics, Vol. 21, No. 24, 2002
Iverson et al.
t
3
t
Hz, 9 H, Bu), 0.45 (d, J P-H ) 13 Hz, 9 H, Bu), -7.66 (d of
reaction was complete, the solvent was removed and the
residue washed with hexanes to remove (dtbpm)2Pt2 and free
biphenyl. The remaining solid was redissolved in CD2Cl2 and
1H, 19F, and 31P NMR were taken. The spectral features
indicated a symmetric Pt(II) species. Three aromatic signals,
mult. with 195Pt satellites, J Pt-H ) 1266 Hz, J P(trans)-H ) 206
1
2
Hz, J P(cis)-H is obscured due to coupling to CF3). 31P NMR
2
(C6D6): δ 9.2 (s with 195Pt satellites, J Pt-P ) 1872 Hz), 1.6
1
(second-order multiplet with 195Pt satellites, 1J Pt-P ) 1237 Hz).
Gen er a t ion of (d t b p m )P t [2-(3,5,3′,5′-t r is(t r iflu or o-
m eth yl)bip h en yl)]H (18). (dtbpm)Pt[η2-(3,5,3′,5′-tetrakis-
(trifluoromethyl)biphenyl)] (7.0 mg, 0.0081 mmol) was placed
in a resealable NMR tube and dissolved in 600 µL of C6D6.
The mixture was photolyzed and the reaction monitored by
1H and 31P NMR spectroscopy. The starting complex was
converted to an aryl hydride and reached a photostabilized
state after several hours. An additional 2 days of photolysis
did not significantly alter the ratio of η2-arene to aryl hydride
a singlet and two doublets, were observed in a 2:2:2 ratio. The
195
singlet was further downfield than the others and displays
-
Pt satellites. The bridging methylene of the diphosphine ligand
appeared as a triplet and integrated as two protons, and the
t
doublet for the Bu groups integrated as 36 protons. Only one
resonance was observed in the 19F NMR. The 31P NMR
spectrum showed the same resonance as previously observed.
All the NMR evidence indicated that a second C-H activation
process had occurred resulting in the formation of a 4,4′-bis-
(trifluoromethyl)-substituted analogue of (dtbpm)Pt(2,2′-bi-
phenyl). The structure of this complex was confirmed by X-ray
crystallography.
(2.3:1). H NMR (C6D6): δ 8.24 (s with 195Pt shoulders, 1 H),
1
7.76 (s, 1 H), 7.41 (s with 195Pt shoulders, 1 H), (two aromatic
2
H’s are obscured by residual C6D6), 2.99 (dt, J H-H ) 17 Hz,
2J P-H ) 8.5 Hz, 1 H, PCH2P), 2.69 (dt, 2J H-H ) 17 Hz, 2J P-H
)
Th er m olysis of (d tbp m )P t[η2-(3,5,3′,5′-tetr a k is(tr iflu o-
r om eth yl)bip h en yl)]. (dtbpm)Pt[η2-(3,5,3′,5′-tetrakis(trifluo-
romethyl)biphenyl)] (10.5 mg, 0.011 mmol) was placed in a
resealable NMR tube and dissolved in 600 µL of C6D6. The
mixture was heated at 85 °C for 5 days and the reaction
monitored by 1H and 31P NMR spectroscopy. Although a
biphenyl hydride was formed in the reaction, the transforma-
tion was not clean and other products were formed, including
the free biphenyl and (dtbpm)2Pt2. Continued heating at 125
°C resulted in nearly quantitative formation of the dimer after
16 h.
3
t
8.5 Hz, 1 H, PCH2P), 1.14 (d, J P-H ) 14 Hz, 9 H, Bu), 0.95
(d, 3J P-H ) 14 Hz, 9 H, tBu), 0.87 (d, 3J P-H ) 13 Hz, 9 H, tBu),
0.51 (d, J P-H ) 13 Hz, 9 H, Bu), -7.57 (d of mult. with 195Pt
3
t
1
2
2
satellites, J Pt-H ) 1267 Hz, J P(trans)-H ) 203 Hz, J P(cis)-H is
obscured due to coupling to CF3). 31P NMR (C6D6): δ 8.9 (s
with 195Pt satellites, J Pt-P ) 1875 Hz), 1.8 (second-order
1
multiplet with 195Pt satellites, J Pt-P ) 1242 Hz).
1
Gen er a tion of (d tbp m )P t(2-bip h en yl)H. (19) (dtbpm)-
Pt(2-biphenyl)Cl (7.8 mg, 0.011 mmol) and [Cp2ZrH2]2 (3.8 mg,
0.0085 mmol) were placed in a resealable NMR tube, and 600
µL of C6D6 was added. The mixture was allowed to react at
room temperature for 3 h. Conversion to the hydride was
judged to be quantitative by 1H and 31P NMR spectroscopy.
Rea ction of (d tbp m )P t(n eop en tyl)H w ith C6H6 in THF -
d 8. (dtbpm)Pt(neopentyl)H (8 mg, 0.014 mmol) was placed in
a resealable NMR tube and dissolved in 1 mL of THF-d8. Then
40 equiv of C6H6 (50 µL, 0.56 mmol) was then added to the
solution via microsyringe, and the mixture was heated at 55
°C for 90 min. The 1H and 31P NMR spectra of the mixture
revealed that (dtbpm)2Pt2 was the primary product (>95%) and
C-H activation of benzene had not occurred.
1H NMR (C6D6): δ 8.34 (d, 2 H, J H-H ) 7.0 Hz), 8.24 (t with
3
195Pt satellites, 1 H, J H-H ) 7.0 Hz, J Pt-H ) 68 Hz), 7.61 (d
3
with 195Pt satellites, 1 H, J H-H ) 7.7 Hz, 4J Pt-H ) 6.9 Hz), 7.32
(m, 3 H), 7.20 (t, 1 H, J H-H ) 7.3 Hz), 7.13 (t obscured by C6D5H
resonance, 1 H), 3.01 (t, 2J P-H ) 7.3 Hz, 2 H, PCH2P), 1.16 (d,
18 H, (CH3)3P, 3J P-H ) 13 Hz), 0.92 (d, 18 H, (CH3)3P, 3J P-H
)
(d t b p m )P t [η2-h e x a k is (t r iflu o r o m e t h y l)b e n ze n e )].
(dtbpm)Pt(Np)H (8.0 mg, 0.014 mmol) and hexakis(tri-
fluoromethyl)benzene (34 mg, 0.070 mmol) were placed in a
resealable NMR tube and dissolved in 0.6 µL of THF-d8. The
mixture was heated at 55 °C and monitored by 1H, 19F, and
31P NMR spectroscopy. After 1 h, the starting platinum
complex had been consumed. Two broad resonances were
13 Hz), -5.37 (dd with 195Pt satellites, J P(trans)-H ) 210 Hz,
2
2J P(cis)-H ) 8.8 Hz, J Pt-H ) 1339 Hz). 31P NMR (C6D6): δ 8.0
1
(d with 195Pt satellites, 1J Pt-P ) 1549 Hz, 2J P-P ) 11 Hz, trans
biphenyl), -3.2 (d with 195Pt satellites, 1J Pt-P ) 1381 Hz, 2J P-P
) 9 Hz, trans hydride).
Th er m olysis of (d tbp m )P t[2-(4,4′-bis(tr iflu or om eth yl)-
bip h en yl)]H in th e P r esen ce of 4,4′-bis(tr iflu or om eth yl)-
bip h en yl. (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphenyl)]H (5
mg, 0.0063 mmol) and 4,4′-bis(trifluoromethyl)biphenyl (18 mg,
0.063 mmol) were placed in a resealable NMR tube and
dissolved in 600 µL of THF-d8. The solution was heated at 55
°C and monitored by 1H and 31P NMR spectroscopy. After 3 h,
no change was observed. The solution was then heated at 85
°C. After 3 h, 5% of the starting material had been converted
to (dtbpm)Pt[3-(4,4′-bis(trifluoromethyl)biphenyl)]H. After 15
h at 85 °C 12% of the starting complex had converted to
(dtbpm)Pt[3-(4,4′-bis(trifluoromethyl)biphenyl)]H, 12% had
been converted to (dtbpm)Pt[2,2′-(4,4′-bis(trifluoromethyl)-
biphenyl)], and 2% had been converted to (dtbpm)2Pt2. After
65 h at 85 °C the reaction mixture consisted of 51.6% of the
starting complex, 7.9% of (dtbpm)Pt[3-(4,4′-bis(trifluorometh-
yl)biphenyl)]H, 27.2% of (dtbpm)Pt[2,2′-(4,4′-bis(trifluorom-
ethyl)biphenyl)], and 13.3% of (dtbpm)2Pt2. After 7.5 days at
85 °C the reaction mixture consisted of 24% of the starting
complex, 4.5% of (dtbpm)Pt[3-(4,4′-bis(trifluoromethyl)biphen-
yl)]H, 58% of (dtbpm)Pt[2,2′-(4,4′-bis(trifluoromethyl)biphen-
yl)], and 13.5% of (dtbpm)2Pt2. The two doublets due to the
tBu groups of (dtbpm)Pt[2-(4,4′-bis(trifluoromethyl)biphenyl)]H
slowly decreased in intensity and gave rise to a single doublet
in the same region of the 1H NMR spectrum. A single
1
observed in the H NMR spectrum at δ 2.45 and 1.52 for the
methylene and tBu hydrogens, respectively. The 31P NMR
spectrum revealed an asymmetric bisphosphine complex with
multiplet resonances at δ 75.3 and 69.6 with accompanying
195Pt satellites. The 19F NMR spectrum was a single, very broad
resonance at -54.55. The solution was then heated at 125 °C
for 48 h. Neither the 31P nor 19F NMR spectra changed, but
significant sharpening of the resonances was observed in the
1H NMR spectrum. 1H NMR (THF-d8): δ 2.44 (t with 195Pt
2
shoulders, J P-H ) 7.6 Hz, 2 H, PCH2P), 1.52 (quartet, J )
t
6.9 Hz, 36 H, Bu). 19F NMR (THF-d8): δ -54.55 (br singlet).
1
31P NMR (THF-d8): δ 75.3 (m with 195Pt satellites, J Pt-P
)
3279 Hz), 69.6 (m with 195Pt satellites, J Pt-P ) 2741 Hz).
1
(d tbp m )P t(4-C6H4CF 3)2. A solution of bis(di-tert-butylphos-
phino)methane (47 mg, 0.15 mmol) in 2 mL of THF was added
to a solution of (COD)Pt(4-C6H4CF3)2 (83 mg, 0.14 mmol) in 8
mL of THF in a Schlenk round-bottom flask. The flask was
fitted with a reflux condensor and heated at 85 °C for 4 days.
The volatile material was removed in vacuo and the residue
recrystallized from CH2Cl2/Et2O at -25 °C. Two crops of a
white crystalline material (70 mg, 64% total) were collected.
1H NMR (C6D6): δ 7.75 (t with 195Pt satellites, J ) 7.0 Hz,
3
3J Pt-H ) 60 Hz, 4 H, H ortho to Pt-Caryl bond), 7.39 (d, J H-H
2
resonance with 195Pt satellites (δ 4.5, J Pt-P ) 1523 Hz) was
also observed to appear in place of the two resonances for the
starting complex in the 31P NMR spectra. H2 gas evolution was
not observed during the course of the reaction. Once the
1
) 7.6 Hz, 4 H, H meta to Pt-Caryl bond), 2.85 (t, J P-H ) 7.5
Hz, 2 H, PCH2P), 1.00 (d, 3J P-H ) 13 Hz, 36 H, tBu). 31P NMR
(C6D6): δ -6.1 (s with 195Pt satellites, 1J Pt-P ) 1426 Hz. Anal.
Calcd (found): C, 47.15 (47.11); H, 5.87 (6.19).

η2-Coordination of Electron-Poor Arenes
Organometallics, Vol. 21, No. 24, 2002 5333
3, 9, 11, and 12. Data for the preparation of dtbpm, and the
reaction of 1 with 1,4-bistrifluoro-methylbenzene are also
included. Figures for the higher order 31P NMR spectrum of 4
and the VT NMR of 9 and 11 are also included. This material
is available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. This work was supported by the
U.S. Department of Energy (Grant FG02-86ER13569.
Su p p or tin g In for m a tion Ava ila ble: Summary of crys-
tallographic procedures, data, intramolecular distances and
angles, and positional and thermal parameters for compounds
OM020459X