Reactions of indene and indoles with platinum methyl cations: Indene C-H activation, indole π versus nitrogen lone-pair coordination

Article abstract of DOI:10.1021/om0606643

Reactions of indene and various substituted indoles with [(diimine)Pt ^II(Me)(TFE)]⁺ cations have been studied (diimine = ArN=C(Me)-C(Me)=NAr; TFE = 2,2,2-trifluoroethanol). Indene displaces the TFE ligand from platinum to form a stable π coordination complex that, upon heating, undergoes C-H activation with first-order kinetics, ΔH?= 29 kcal/mol, ΔS? = 10 eu, and a kinetic isotope effect of 1.1 at 60°C. Indoles also initially form coordination complexes through the C2=C3 olefin, but these undergo rearrangement to the corresponding N-bound complexes. The relative rates of initial coordination and rearrangement are affected by excess acid or methyl substitution on indole.

Full text of DOI:10.1021/om0606643

Organometallics 2007, 26, 281-287
281
Reactions of Indene and Indoles with Platinum Methyl Cations:
Indene C-H Activation, Indole π versus Nitrogen Lone-Pair
Coordination
Travis J. Williams, Jay A. Labinger,* and John E. Bercaw*
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology,
Pasadena, California 91125
ReceiVed July 25, 2006
Reactions of indene and various substituted indoles with [(diimine)PtII(Me)(TFE)]+ cations have been
studied (diimine ) ArNdC(Me)-C(Me)dNAr; TFE ) 2,2,2-trifluoroethanol). Indene displaces the TFE
ligand from platinum to form a stable π coordination complex that, upon heating, undergoes C-H
activation with first-order kinetics, ∆Hq) 29 kcal/mol, ∆Sq ) 10 eu, and a kinetic isotope effect of 1.1
at 60 °C. Indoles also initially form coordination complexes through the C2dC3 olefin, but these undergo
rearrangement to the corresponding N-bound complexes. The relative rates of initial coordination and
rearrangement are affected by excess acid or methyl substitution on indole.
Scheme 1
Introduction
Selective C-H bond activation is a potentially valuable
approach to synthetic problems in areas ranging from fuels and
bulk chemicals to fine chemicals and pharmaceutical synthesis.1
Studies of C-H activation in our laboratory have focused on
models of the Shilov system,2 particularly [(diimine)PtII(Me)-
(solv)]+ (2, diimine ) ArNdC(Me)-C(Me)dNAr; solv )
2,2,2-trifluoroethanol (TFE), H2O).3 These cations are capable
of activating a variety of carbon-hydrogen bonds.4 Cations 2
can be generated by protonolysis of (diimine)PtIIMe2 species 1
in TFE with aqueous HBF43,4a,b or BX3 (X ) C6F5,4c,d F5), the
latter producing H+ by boron coordination to TFE.4c In
deuterated solvent 2 is formed as a mixture of two isotopologues.
Reaction of 2 with a C-H group then results in liberation of
methane as a mixture of CH4 and CH3D along with the
formation of a new alkyl or aryl platinum(II) complex [(di-
imine)PtII(R)(solv)]+ (Scheme 1).6
ether,4e stable complexes of the organic substrate with platinum
are observed, but kinetics studies indicate that substrate-
platinum binding is rapid and reversible and that rebinding (or
rearrangement) of the substrate to a C-H bond-coordinated
intermediate is rate-determining. Heteroatom binding can be
used to advantage, however, in coordinatively directed cyclo-
metalation reactions,7 the basis of many synthetic methods.
Several recent examples of these involving nitrogen-containing
heterocycles have appeared.8 Specifically regarding indole, a
functionality found frequently in natural products and pharma-
ceutical agents, several groups have identified conditions for
cyclization of indoles with pendent olefins,9 and both Sames10
and Sanford11
The presence of donor heteroatoms (N, O, S, etc.) in the
substrate might inhibit C-H activation because these heteroa-
toms tend to bind tightly to electrophilic metal centers and block
C-H bond coordination. In the cases of methanol and dimethyl
* Corresponding authors. E-mail: bercaw@caltech.edu.
(1) For recent reviews on C-H activation and functionalization, see:
(a) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc.
Chem. Res. 1995, 28, 154-162. (b) Erker, G. Angew. Chem. Int. Ed. 1999,
38, 1699-1712. (c) Davies, H. M. L.; Antoulinakis, E. G. J. Organomet.
Chem. 2001, 617-618, 47-55. (d) Crabtree, R. H. J. Chem. Soc., Dalton
Trans. 2001, 17, 2437-2450. (e) Labinger, J. A.; Bercaw, J. E. Nature
2002, 417, 507-514. (f) Fekl, U.; Goldberg, K. I. AdV. Inorg. Chem. 2003,
54, 259-320.
(2) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879-2932.
(3) Johansson, L.; Ryan, O. B.; Tilset, M. J. Am. Chem. Soc. 1999, 121,
1974-1975. Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 739-
740.
(4) (a) Johansson, L.; Tilset, M.; Labinger, J. A.; Bercaw, J. E. J. Am.
Chem. Soc. 2000, 122, 10846-10855. (b) Zhong, A. H.; Labinger, J. A.;
Bercaw, J. E. J. Am. Chem. Soc. 2002, 124, 1378-1399. (c) Heyduk, A.
F.; Driver, T. G.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2004,
126, 15034-15035. (d) Driver, T. G.; Day, M. W.; Labinger, J. A.; Bercaw,
J. E. Organometallics 2005, 24, 3644-3654. (e) Owen, J. S., Labinger, J.
A.; Bercaw, J. E. J. Am. Chem. Soc. 2006, 128, 2005-2016.
(5) Driver, T. G.; Williams, T. J.; Labinger, L. A.; Bercaw, J. E.
Organometallics, in press.
(7) (a) Dunina, V. V.; Zalevskaya, O. A.; Potapov, V. M. Russ. Chem.
ReV. 1988, 57, 250-269. (b) Ryabov, A. D. Chem. ReV. 1990, 90, 403-
424.
(8) Some examples include: (a) Dick, A. R.; Hull, K. L.; Sanford, M.
S. J. Am. Chem. Soc. 2004, 126, 2300-2301. (b) Desai, L. V.; Hull, K. L.;
Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 9542-9543. (c) Tan, K. L.;
Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2001, 123, 2685-2686.
(d) Tan, K. L.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc, 2002,
124, 13964-13965. (e) Dangel, B. D.; Godula, K.; Youn, S. W.; Sezen,
B.; Sames, D. J. Am. Chem. Soc. 2002, 124,11856-11857.
(9) Recent examples include Pd: (a) Ferreira, E. M.; Stoltz, B. M. J.
Am. Chem. Soc. 2003, 125, 9578-9579. (b) Abbiati, G.; Beccalli, E. M.;
Broggini, G.; Zoni, C. J. Org. Chem. 2003, 68, 7625-7628. Pt: (c) Liu,
C.; Han, X.; Wang, X.; Widenhoefer, R. A. J. Am. Chem. Soc. 2004, 126,
3700-3701.
(6) Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 739-740.
10.1021/om0606643 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/10/2006

282 Organometallics, Vol. 26, No. 2, 2007
Williams et al.
Scheme 2
Scheme 3
have reported selective arylation of simple indoles via palladium-
catalyzed C-H activation.
Prior literature reports of stable group 10 metal-indole
complexes are few in number. Platinum-coordinated tryptophan
and tryptamine derivatives have been studied,12 but only a single
platinum complex, cis-Pt(indole)2Cl2, having a neutral, simple
L-type donor indole ligand13 has been reported. Unfortunately,
it was characterized only by elemental analysis and infrared,
and neither offers insight into the binding of the indole ligand.14
Moreover, although (1-indolyl)metal amides (functioning as
X-type ligands) are common,15 and indole-metal arene com-
plexes have been described for several transition metals,16 we
are aware of no examples of transition metal complexes having
indole C2dC3 olefin ligation.
Table 1. First-Order Rate Constants for the Conversion of
Indene π Complex 3a to η3-Indenyl Complex 4a
entry
T (°C)
k (s-1
)
t(1/2) (min)
1
2
3
4
5
50
60
70
80
90
3.38 (11) × 10-5
1.31 (9) × 10-4
4.60 (18) × 10-4
1.84 (10) × 10-3
5.10 (10) × 10-3
342(11)
88.5(58)
25.1(10)
6.28(32)
2.28(38)
The present work examines the reactions of indoles with
cations 2. Toward this end, we describe the reaction of these
cations with indene, indole’s hydrocarbon analogue, as well as
with various methyl-substituted indoles. We find that indene
forms a stable olefin coordination complex that undergoes C-H
activation upon heating. Analogously, indoles initially form
olefin coordination complexes, but rather than undergoing C-H
activation, these complexes rearrange to stable N-bound 3H-
indole species. We expect that C-H activation of nitrogen-
containing unsaturated heterocycles is more likely to proceed
from a metal-heterocycle π complex than an N-complex, so
strategies to extend the lifetime of platinum(II)-indole π
complexes have been pursued. We find that the rate of
rearrangement of indole π complexes to N-complexes can be
diminished by introducing steric bulk on the indole or by
increasing [H+].
stable olefin complexes, 3 (Scheme 2). In each case, complex-
ation is efficient and rapid. Exchange of coordinated indene with
1 equiv (15 mM) of added indene-d3 under the same conditions
is slower, with kobs ≈ 5 × 10-3 s-1, t1/2 ≈ 1 min (from McKay
analysis).17 The resulting products 3 can be characterized by
1
NMR and electrospray MS methods. The H NMR spectrum
for 3a is sharp at ambient temperature, and 195Pt-H coupling
constants of 74 and 79 Hz are observed for the C2 and C3
protons of indene. The C1 methylene protons appear as a pair
of doublets (2JH-H ) 23 Hz) with weak 195Pt satellites (JPt-H
1
) 41 Hz). By contrast, ambient-temperature H NMR spectra
of 3b, 3c, and 3d give broad signals for the C1, C2, and C3
indenyl C-H protons near 3.2, 6.5, and 5.6 ppm, respectively.
In all cases, Pt-CH3 signals are shifted significantly upfield
from the parent cation 2: whereas 2 typically displays δ(Pt-
CH3) in the range 0.6-1.3 ppm, indene complexes 3 have δ-
(Pt-CH3) between -0.8 and -0.3 ppm. This shift is similar to
that for a previously reported η2-benzene adduct, which has δ-
(Pt-CH3) ) -1.3 ppm at -33 °C.4a Upon gentle heating,
complexes 3 react to form η3-indenyl complex 4 and methane
(Scheme 2). In the case of 3a, the reaction is clean (>95% yield)
as determined by 1H NMR. By contrast, heating complexes 3b
and 3c results in formation of a complex mixture of products,
including 4.
Results and Discussion
Reactions of Indene with Cations 2. Treatment of platinum
cations 2 with 1 equiv of indene results in the formation of
(10) Lane, B. S.; Brown, M. A.; Sames, D. J. Am. Chem. Soc. 2005,
127, 8050-8057.
(11) Deprez, N. R.; Kalyni, D.; Krause, A.; Sanford, M. S. J. Am. Chem.
Soc. 2006, 128, 4972-4973.
(12) Kaminskaia, N. V.; Ullmann, G. M.; Fulton, D. B.; Kostic´, N. M.
Inorg. Chem. 2000, 39, 5004-5013.
Mechanism of Indene Activation. First-order rate constants
were measured for the conversion of indene complex 3a to
indenyl complex 4a (Table 1). Importantly, two trials at 60 °C
with 1 and 5 equiv of indene gave the same rate constants (1.24-
(9) × 10-4 and 1.37(9) × 10-4 s-1) within error, indicating a
zero-order rate dependence on [indene]. Activation parameters
for the conversion of 3a to 4a, measured by Eyring analysis
for kinetic runs conducted at temperatures ranging from 50 to
90 °C (Figure 1), are ∆Hq ) 28.7 ( 0.7 kcal·mol-1 and ∆Sq )
9.7 ( 2.2 eu.18 A kinetic isotope effect was determined for the
conversion of indene-d3 to deuterated indenyl complex 4a-d2
(Scheme 3). 1,1,3-Trideuteroindene was prepared according to
(13) Osa, T.; Hino, H.; Fujieda, S.; Shiio, T.; Kono, T. Chem. Pharm.
Bull. 1986, 34, 3563-3572.
(14) We believe that indole is bound through N1 as suggested by the
authors, but is in the 3H-tautomer. 1H NMR (300 MHz, dichloromethane-
d2) δ: 8.37 (s, JPt-H ) 30 Hz, 2H, C2H), 8.58 (d, JPt-H ) 8.2 Hz, 2H),
7.62-7.08 (m, 6H), 4.03 (s, 4H, C3-H2).
(15) For example: indole + Pt0(PEt3)4 f trans-[(PEt3)2PtII(H)(1-
indolyl)] + 2 PEt3. Chantson, J. T.; Lotz, S. J. Organomet. Chem. 2004,
689, 1315-1324.
(16) [(η6-C8H7N)MLn] complexes are known for several metals. Common
examples include MLn ) Cr(CO)3; see: Fischer, E. O.; Goodwin, H. A.;
Kreiter, C. G.; Simmons, H. D.; Sonogashira, K.; Wild, S. B. J. Organomet.
Chem. 1968, 14, 359-374. Nesmeyanov, A. N.; Ustynyuk, N. A.; Thoma,
T.; Prostakov, N. S.; Soldatenkov, A. T.; Pleshakov, V. G.; Urga, K.;
Ustynyuk, Y. A.; Trifonova, O. I.; Oprunenko, Y. F. J. Organomet. Chem.
1982, 231, 5-24. MLn ) CpRu+, see: Moriarty, R. M.; Ku, Y. Y.; Gill,
U. S. Organometallics 1988, 7, 660-665. Other examples include M )
MnI, CoIII, RhI, RhIII, IrI, and IrIII. [(η5-C8H6N)MLn] complexes are known
for MLn ) Mn(CO)3+; see: Ji, L. N.; Kershner, D. L.; Rerek, M. E.; Basolo,
F. J. Organomet. Chem. 1985, 296, 83-94. MLn ) Cp*Ir2+, see: White,
C.; Thompson, S. J.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1977,
1654-1661. Other examples include M ) TiIV, MoII, and FeII.
(17) Analyzed as in: Romeo, R.; Monsu, Scolaro, L.; Nastasi, N.; Arena,
G. Inorg. Chem. 1996, 35, 5087-5096.
(18) Error determined by established methods. See: Morse, P. M.;
Spencer, M. D.; Wilson, S. R.; Girolami, G. S. Organometallics 1994, 13,
1646-1655.

Reactions of Indene and Indoles with Pt Methyl Cations
Organometallics, Vol. 26, No. 2, 2007 283
Scheme 5
NMR), which converts to 8a in minutes. H/D exchange of
N1-H with solvent is rapid relative to complexation, but
exchange of C3-H may occur before or after π complexation.21
Although the participation of platinum in the H/D exchange
cannot be excluded, this exchange is rapid in the presence of
0.2 mol % BF3-TFE solution (not containing 1a) and is
complete in minutes at room temperature. NMR spectra are
consistent with assignment of the 3D tautomer 8: in all three
complexes (8a, 8b, 8c) the 13C signal for the C3 methylene
Figure 1. Eyring plot for the conversion of 3a to 4a.
Scheme 4
1
carbon appears as a multiplet at ∼44 ppm, and the H signal
for the C2 hydrogen appears as a singlet with 195Pt satellites
(JPt-H ≈ 40 Hz) at ∼8 ppm.
Reactions of methyl-substituted indoles were studied with
cation 2a. Reactions of 2a with 1-methylindole and 2-meth-
ylindole proceed through the intermediacy of observable and
more stable π complexes (9, 11; Scheme 6).22 1H NMR spectra
for 9 and 11 share important features with indene complex 3a:
each shows a significantly upfield Pt-CH3 chemical shift
relative to cation 2a. Upon rearrangement to the corresponding
N-bound complexes 10 and 12, the Pt-CH3 signal returns
downfield (Table 2). Other heterocycles (pyrrole, carbazole,
benzofuran) did not afford clean results under these conditions;
most notably, N-protected indoles gave rise to complex mixtures
of products.23
a previously reported procedure19 and was complexed to 2a as
above. Conversion of 3a-d3 to 4a-d2 proceeded smoothly to
afford a selectively deuterated product. Comparisons of mea-
sured rate constants for parallel runs gave a kinetic isotope effect
of kH/kD ) 1.1.
The small, positive value for ∆Sq and the small KIE are
suggestive of an intramolecular 3a-to-4a process not involving
rate-determining C-H oxidative addition. A mechanistic sce-
nario that is in accord with these features involves rate-
determining rearrangement of π complex 3a to C-H σ complex
5, followed by more rapid C-H oxidative cleavage and
reductive elimination of methane (Scheme 4). Analogous
reaction of 2e (solv ) CF3CD2OD) with p-xylene was found
to afford a mixture of products resulting from competitive aryl
(kH/kD ≈ 4) and benzylic (kH/kD ≈ 1) C-H activation processes,
the latter affording an η3-benzylic product.4c Rearrangement of
3a to 4a thus resembles the benzylic activation process and
suggests that benzylic C-H bond activation by 2e also proceeds
via an initially formed arene π complex that undergoes rate-
determining rearrangement to a C-H σ complex, followed by
C-H oxidative cleavage.
(21) C3-H in 6a can be observed at early stages of kinetic runs (δ )
5.95 ppm, JPt-H ) 87 Hz (500 MHz)), but N1-H was never found for
coordinated indole.
(22) A reviewer proposed an alternative C3 σ-bound structure for 6a, 9,
and 11, but we favor the π complexes as shown. The σ-bound structure is
1
inconsistent with H and 13C chemical shifts for C3-H: δ C3-H ) 5.4
and 6.0 for compounds 6a and 11, respectively, as identified by JPt-H and
H/D exchange. This is more consistent with an sp2 carbon center. Moreover,
no 13C signal is present in the 175-180 region of the spectrum of 11, as
would be needed for C2 in the σ-bound structure. It is likely, however, that
the platinum center is more tightly associated with the more electron rich
C3 side of the olefin. This is a possible explanation for the low JPt-H for
C2 in 11.
Reactions of Cations 2 with Indoles. Indole reacts rapidly
with platinum cations 2, ultimately to give N-complexation
products 8 (Scheme 5). Analogously to reaction with indene,
the initially formed adduct is a C2dC3 π complex 6; however,
N-ligation, likely via transient 7, inhibits C-H activation, and
tautomer 8 is the stable adduct that is generated.20 Reaction of
2a with indole at 40 °C begins with a buildup of 6a-d2 (1H
(23) Reactions of N-protected indoles (Ac, Tf, Ts) and benzofuran
afforded complex mixtures of C-H activation products. Pyrrole, carbazole,
and 3-methylindole afforded complex mixtures of coordination complexes
of the general form [(diimine)Pt(Me)(CnHnN-dn)]+. Hydrogenated homo-
logues of indene and indole also react with 2a. Indane forms a mixture of
C-H activation products, which includes an η3-benzyl complex analogous
to that obtained from ethylbenzene; see notes 4c,d. 2,3-Dihydroindole forms
a stable N-bound coordination complex, which has 1H NMR (300 MHz,
TFE-d3) δ: 7.21-7.14 (m, 3H), 7.07-7.06 (m, 4H), 6.89 (s, 1H), 3.47-
3.30 (m, 2H), 2.87-2.75 (m, 1H), 2.58-2.47 (m, 1H), 2.33 (s, 3H), 2.30
(s, 6H), 2.17 (s, 3H), 2.17 (s, 3H), 1.93 (s, 3H), 1.80 (s, 3H), 1.75 (s, 3H),
0.53 (s, JPt-H ) 76 Hz, 3H).
(19) Yasuda, M.; Pak, C.; Sakurai, H. Bull. Chem. Soc. Jpn. 1980, 53,
502-507.
(20) Some [(3H-indole)MLn] complexes are known for other metals. For
examples of [Re] complexes, see: Johnson, T. J.; Arif, A. M.; Gladysz, J.
A. Organometallics 1994, 13, 3182-3193. For [Ir] see: Chen, S.; Noll, B.
C.; Peslherbe, L.; Rakowski DuBois, M. Organometallics 1997, 16, 1089-
1092.

284 Organometallics, Vol. 26, No. 2, 2007
Williams et al.
Scheme 6
Table 2. NMR Data for Pt-Me Groups of TFE Adduct 2a,
Indene π Complex 3a, and the π and N-Indole Adducts
Table 3. First-Order Rate Constants for Rearrangement of
π Complexes at 40 °C
complex
1H δa (ppm)
13C δ (ppm)
JPt-Hb (Hz)
entry π complex product
k (s-1
)
t1/2 (min)
2a (TFE)c
3a (indene)
6a (indole π)
8a (indole N)
+0.66
-0.74
-1.02
0.74
-0.75
0.53
21.5
4.7
-
72
72
62a
78
73
78
73
78
1
2
3
4
6a
9
11
3a
8a 1.24(16) × 10-2
0.94(12) π f N
37.9(86) π f N
10
12
3.05(7) × 10-4
7.87(37) × 10-5 147(71)
π f N
d
-12.1
-3.6
4a 8.4(6) × 10-6 a 1380(98)
C-H activation
9
a Extrapolated from Eyring plot.
10
11
12
-13.7
-3.0
-1.16
0.26
Table 4. Acid Dependence of Rate Constant for
Rearrangement of 6aa
-16.8
a Data recorded at 500 or 600 MHz. b Recorded at 300 MHz. c Notes
4b,c. d The lifetime of this species is too short to record 13C NMR.
entry
BF3 (equiv)
k (s-1
)
t1/2 (min)
1
2
1.1
2.5
4.0
5.0
1.24(16) × 10-2
1.09(21) × 10-2
3.51(12) × 10-3
1.48(5) × 10-4
0.94(12)
1.09(19)
3.29(11)
78.3(27)
3
4b
a Conditions: BF3 is added to 1a in TFE; 5 equiv of indole in TFE is
then injected. b Indole binding and tautomerization are slow relative to kRAR
.
indole). For the conversion of 2a to 10 at 30 °C, the rate of
rearrangement of 9 to 10 is close to the rate for the binding of
2-methylindole to cation 2a, thus enabling NMR observation
of all three species simultaneously in a single experiment (Figure
2). First-order rate constants for the rearrangements of π
complexes 9 and 11 were measured at 40 °C in the presence of
excess indole (Table 3). Strikingly, rearrangement of these π
complexes requires hours at 40 °C, whereas N-ligated complexes
8 are fully formed at room temperature in only minutes,
indicating that methylation of the indole in the 1 or 2 position
substantially retards the rate of rearrangement of indole π
complexes.
The rate of rearrangement of indole π complex 6a to N-ligated
complex 8a is significantly diminished by added acid. When
2a is mixed with 1 equiv of indole in the presence of a small
amount (15 mol %) of excess acid at room temperature, 6a is
completely converted to 8a in minutes at room temperature,
but conversion takes hours in the presence of 50 mol % excess
acid. In a more systematic set of experiments, 2a is prepared
from 1a with a variable excess of acid, then 5 equiv of indole
is added, and reaction progress is monitored by NMR at 40 °C;
apparent rate constants for rearrangement of 6a are shown in
Table 4. Only modest reductions of rate are observed up to about
3-fold excess acid, but when the excess acid becomes compa-
rable to the amount of excess indole, the rate slows dramatically
(entry 4). Under these conditions indole complexation to form
6a is also slowed, to only approximately 3 times the rate of
rearrangement (compared to at least 2 orders of magnitude faster
in the absence of acid). Furthermore, the initial product of π to
N1 rearrangement is not 8a but a different N-adduct (presumably
7a); the rate of tautomerization of the first-formed N-adduct to
Figure 2. Formation of complex 9 from 2a and its conversion to
10. Cation 2a (red O) is treated with 1 equiv of 2-methylindole at
30 °C to form 9 (blue 0), which rearranges to 10 (green ]), kRAR
) 6.72(2) × 10-5 s-1 (9 f 10).
The mechanism of conversion of π-bound indole complexes
to final N-bound complexes 8, 10, and 12 likely involves direct
(intramolecular) slippage of platinum from the C2dC3 π bond
to N1 because the rate of π to N1 conversion is independent of
[indole]. Moreover, in a simple crossover experiment, a solution
of the 2-methylindole adduct 9 (∼90% conversion from 2a)
was treated with 1 equiv of 1-methylindole. Upon further
reaction, a distribution of 81(1)% 9, 10(1)% 10, and 9(1)% 11
was observed, and finally a mixture containing 91(1)% 10 and
9(1)% 12 was observed. Thus little crossover is observed,
excluding a mechanism involving indole displacement from the
metal center.
Rearrangements of complexes 9 and 11 to complexes 10 and
12 are spontaneous at room temperature (also zero-order in

Reactions of Indene and Indoles with Pt Methyl Cations
Organometallics, Vol. 26, No. 2, 2007 285
the ultimate product 8a is slow under these acidic conditions.24
Thus protonation of the nitrogen lone pair slows both coordina-
tion of platinum to the CdC double bond and subsequent
migration of platinum to nitrogen; the inhibition of [1D] to [3D]
indole tautomerization suggests that it is mediated by free
(unprotonated) indole.
38 µL) were then added, and the suspension was stirred until it
became a homogeneous orange solution. Indene (19.2 µmol, 2.24
mg, 2.25 µL) was added, and the solution was transferred to an
oven-dried J-Young NMR tube. After incubation at room temper-
ature (24 h in this case) the solution was analyzed by NMR and
found to contain 3a in >95% yield.
1H NMR (600 MHz, TFE-d3) δ: 7.51 (dt, JH-H ) 6.8 Hz
(doublet), 1.5 Hz (triplet), 1H), 7.26-7.23 (m, 3H), 7.15 (s, 1H),
7.10 (s, 1H), 6.99 (s, 1H), 6.96 (s, 1H), 6.16 (d, JH-H ) 4 Hz,
JPt-H ) 79 Hz, 1H), 5.24 (apparent t, JH-H ≈ 6.4 Hz, JPt-H ) 74
Hz, 1H), 3.30 (d, JH-H ) 23 Hz, JPt-H ) 41 Hz, 1H), 3.07 (d,
JH-H ) 23 Hz, JPt-H ) 38 Hz, 1H), 2.32 (s, 6H), 2.25 (s, 3H),
2.20 (s, 3H), 2.13 (s, 3H), 2.12 (s, 3H), 2.07 (s, 3H), 1.97 (s, 3H),
-0.74 (s, JPt-H ) 53 Hz, 3H). 13C NMR (150 MHz, TFE-d3) δ:
185.6, 178.7, 148.4, 142.7, 141.5, 141.0, 140.9, 139.7, 131.8, 131.6,
131.0, 131.0, 130.8, 130.5, 130.4, 129.5, 129.2, 128.9, 126.2, 125.5,
103.1, 92.4, 40.7, 21.1, 21.1, 20.4, 20.2, 17.9, 17.9, 17.9, 17.8, 4.7.
FTIR (neat): 2920 (w), 1476 (w), 1384 (w), 1237 (w), 1180 (m),
1160 (m), 1051 (s), 847 (w), 766 (w), 718 (w) cm-1. FAB+ MS,
calcd for C32H40N2Pt ([M + H]+): 647.2840, found 647.2822. Calcd
for C31H36N2Pt ([M - Me]+): 631.2526, found 631.2302.
Conclusions
The new indole complexes generated by addition of indole,
1-methylindole, and 2-methylindole to [(diimine)Pt(Me)(solv)]+
cations are very rare examples of stable complexes of this class
of heterocycle with late transition metals. The initial interaction
is not with the nitrogen lone pair, but rather indole C2dC3 olefin
ligation, the first examples of such complexation. Indene forms
a more stable π complex with cation 2a that undergoes
subsequent activation of the indenyl C-H group in hours at 60
°C to afford methane and an η3-indenyl adduct. By contrast,
indole π complexes of cation 2a rearrange to N-ligated species.
The rate of rearrangement can be controlled by substitution of
the indole or by added H+. Presumably, productive C-H
activation chemistry on the indole nucleus is more likely to
proceed from a complex of the indole C2dC3 olefin rather than
N1; therefore strategies to prevent the formation of apparently
inert N complexes from the corresponding π complexes are of
interest to the continued development of synthetic strategies for
functionalization of indoles by metal-mediated C-H activation,
although we have not yet achieved the latter. Progress toward
these objectives is ongoing in our laboratories.
1
Indene complex 3a-d3 was prepared as above. H NMR (500
MHz, TFE-d3) matches the data above, except that signals at δ )
6.16, 3.30, and 3.07 ppm are absent.
Indene Complexes 3b, 3c, and 3d. Complexes 3b, 3c, and 3d
were prepared by direct analogy to complex 3a above, starting from
platinum dimethyl species 1b, 1d,4a and 1c.3 3b: 1H NMR (300
MHz, TFE-d3) δ: 7.51 (d, 7.23 Hz, 1H), 7.29-7.19 (m, 3H), 7.02
(br s, 2H), 6.57 (br s, 4H), 6.46 (br s, 1H), 5.64 (br s, 1H), 3.20 (br
s, 2H), 2.32 (br s, 12H), 2.07 (br s, 6H), -0.59 (s, JPtH-H ) 71 Hz,
3H). 3c: 1H NMR (300 MHz, TFE-d3) δ: 7.96 (s, 2H), 7.56-7.52
(m, 1H), 7.53 (s, 4H), 7.29-7.11 (m, 3H), 6.53 (s, 1H), 5.68 (s,
1H), 3.22 (s, 2H), 2.12 (s, 6H), -0.34 (s, JPt-H ) 69 Hz, 3H). 3d:
1H NMR (300 MHz, TFE-d3) δ: 7.52-7.47 (m, 3H), 7.31-7.20
(m, 3H), 6.84 (br s, 4H), 6.33 (br s, 1H), 5.54 (br s, 1H), 3.13 (br
s, 2H), 2.11 (br s, 6H), 1.33 (br s, 36H), -0.66 (s, JPt-H ) 69 Hz,
3H).
Eyring Analysis for the Conversion of 3a to 4a. 3a was
prepared as a solution in TFE-d3 as described above, with the
exception that 2.50 equiv of B(C6F5)3 was used as the acid source.
Conversion and rate were then recorded as described in the main
text.
Indenyl Complex 4a. The solution of 3a prepared above was
heated in its J-Young tube to the temperature and time described
in the main text.
Experimental Section
General Considerations. 1H NMR and 13C NMR spectra were
recorded at ambient temperature using a Varian Inova 500 or 600
or Mercury 300 spectrometer. The data are reported by chemical
shift (ppm) from tetramethylsilane, multiplicity (s, singlet; d,
doublet; t, triplet; m, multiplet; dd, double doublet; dt, double triplet;
br, broad), coupling constants (Hz), and integration. All 13C NMR
data were collected proton-decoupled (13C{1H}), except for those
for 4a, as specified. Mass spectra were acquired on a Finnigan LCQ
ion trap or Agilent 5973 Network mass selective detector and were
obtained by peak matching. All reactions were carried out under
an atmosphere of nitrogen in glassware that had been oven-dried.
Unless otherwise noted, all reagents were commercially obtained
and, where appropriate, purified prior to use. Tris(pentafluorophe-
nyl)borane [B(C6F5)3] was purified by sublimation (90 °C, 0.5 Torr).
2,2,2-Trifluoroethanol-d3 (TFE-d3) was dried over 3 Å molecular
sieves for at least 5 days and then vacuum distilled onto B(C6F5)3.
After 6 h, the trifluoroethanol-d3 was vacuum distilled and stored
in a Teflon needle-valved vessel. Boron trifluoride was purified
according to Brown’s procedure25 and stored as a solution in TFE-
d3. The platinum dimethyl complexes were synthesized following
earlier reported procedures, as noted. 2,2,2-Trifluoroethanol-d3,
B(C6F5)3, and platinum dimethyl complexes were stored in a
Vacuum Atmospheres dinitrogen atmosphere drybox.
1H NMR (500 MHz, TFE-d3) δ: 7.12-7.10 (m, 6H), 6.79 (dd
JH-H ) 5.7, 3.1 Hz, ∼3H), 5.01 (s,26 2H), 2.40 (s, 6H), 2.12 (s,
6H), 1.97 (s, 12H). 13C NMR (150 MHz, TFE-d3) δ: 172.6 (2C),
147.6 (2C), 140.8 (2C), 134.6, 131.2 (4C), 129.9 (4C), 129.3 (4C),
120.0 (2C), 71.6 (JPt-C ) 130 Hz, 2C), 21.2 (2C), 18.0 (2C), 17.6
(4C). 13C NMR (125 MHz, not {1H}, TFE-d3) δ: 172.5 (s, 2C),
147.6 (s, 2C), 140.8 (d, JC-H ) 6 Hz, 2C), 134.6, 132-130 (m,
J1,C-H ≈ 150 Hz, 2C), 131.2 (d, JC-H ) 152 Hz, 2C), 129.9 (d,
JC-H ) 154 Hz, 4C), 129.3 (s, 4C), 120.0 (d, JC-H ) 163 Hz, 2C),
71.6 (d, JC-H ) 181 Hz, 2C), 21.2 (q, JC-H ) 126 Hz, 2C), 18.0
(q, JC-H ) 132 Hz, 2C), 17.6 (q, JC-H ) 126 Hz, 4C). FTIR
(neat): 2919 (w), 1476 (w), 1331 (w), 1385, 1244 (w), 1182 (m),
1157 (m), 1054 (s), 851, 754 (w) cm-1. FAB+ MS, calcd for
Indene Complex 3a. Platinum dimethyl complex 1a4a (19.2
µmol, 10.5 mg) was weighed out in an oven-dried 4 mL vial in the
drybox. TFE-d3 (700 µL) and BF3 (0.477 M in TFE-d3, 18 µmol,
2
C31H36N2Pt ([M + H]+): 631.2526, found 631.2530 l. H NMR
(76.7 MHz, TFE-h3) for this compound is shown in the Supporting
(24) Rate constants for this experiment were determined by modeling
[6a] as an intermediate in a scheme of consecutive reactions. For the reaction
scheme
Information.
1
Indenyl complex 4a-d2 was prepared as above. H NMR (500
MHz, TFE-d3) matches the data above, except that the signal at δ
) 5.01 ppm is absent. FAB+ MS, calcd for C31H342H2N2Pt ([M-d2
+ H]+): 633.2652, and for C31H322H3N2Pt ([M-d3]+): 633.2637,
kbinding
kRAR
2a + indole (excess)
8 6a
8 products
RARt
[6a]/[6a]o ) (kbinding/(kbinding + kRAR))(e-k
t - e-k ). See: Laidler, K.
binding
J. Chemical Kinetics, 3rd ed.; Harper & Row: New York, 1987.
(25) Brown, H. C.; Johannesen, R. B. J. Am. Chem. Soc. 1953, 75, 16-
20.
(26) Observed JPt-H ) 22 Hz for this signal in a spectrum acquired at
300 MHz.

286 Organometallics, Vol. 26, No. 2, 2007
Williams et al.
found 633.2631. 2H NMR (76.7 MHz, TFE-h3) for this compound
is shown in the Supporting Information.
2C), 124-122 (m, apparent 4C), 122.3 (q, JC-F ) 227 Hz), 122.0,
∼44 (m, 1C), 21.9, 20.5, -9.4. Three CF3 quartets cannot be
identified because of coincidences with the solvent CF3; each has
δ ≈ 126 ppm, JC-F ≈ 280 Hz. FTIR (neat): 3065 (w), 2932 (w),
2882 (w), 1622 (w), 1460 (m), 1373 (s), 1281 (s), 1182 (s), 1141
Indole π-Complex 6a. Complex 6a is observed as an intermedi-
ate in kinetic runs (Table 4, entry 4). 1H NMR (500 MHz, TFE-d3)
δ: 7.62 (s, 1H), 7.60 (d, JH-H ) 7.8 Hz, 1H), 7.25-7.22 (m, 2H),
7.17 (t, JH-H ) 8.0 Hz, 1H), 7.14 (s, 1H), 7.01 (s, 1H), 6.97 (s,
1H), 6.94 (s, 1H), 5.40 (s, JH-H ) 94 Hz, ∼0H),27 2.39 (s, 3H),
2.31 (s, 3H), 2.25 (s, 3H), 2.18 (s, 3H), 2.13 (s, 3H), 2.03 (s, 3H),
1.83 (s, 3H), 1.81 (s, 3H), -1.02 (s, JPt-H ) 62 Hz, 3H).
(s), 1067 (m), 903 (m), 848 (w), 771 (w), 705 (w), 684 (m) cm-1
.
FAB+ MS, calcd for C29H19F12N3Pt2H2 ([M - H]+): 836.1317,
found 836.1333.
2-Methylindole-π-complex 9. Platinum dimethyl complex 1a4a
(33.4 µmol, 18.2 mg) was weighed out in an oven-dried 4 mL vial
in the drybox. TFE-d3 (700 µL) and BF3 (0.455 M in TFE-d3, 38.4
µmol, 84.3 µL) were then added, and the suspension was stirred
until it became a homogeneous orange solution. 2-Methylindole
(33 µmol, 4.4 mg) was added, and the solution was transferred to
an oven-dried screw-capped NMR tube. The solution was analyzed
by NMR and found to contain 9 in >95% yield.
1H NMR (500 MHz, TFE-d3) δ: 7.35 (d, JH-H ) 7.5 Hz, 1H),
7.29 (d, JH-H ) 7.5 Hz, 1H), 7.25 (s, 1H), 7.20-7.14 (m, 3H),
6.97 (s, 1H), 6.90 (s, 1H), 2.53 (s, 3H), 2.43 (s, 3H), 2.35 (s, 3H),
2.29 (s, 3H), 2.25 (s, 3H), 2.10 (s, 3H), 1.90 (s, 3H), 1.83 (s, 3H),
1.63 (s, 3H), -0.75 (s, JPt-H ) 67, 3H). 13C NMR (125 MHz, TFE-
d3) δ: 178.0, 176.8, 143.3, 142.7, 141.9, 141.5, 140.2, 139.7, 131.5,
131.4, 130.7, 130.6, 130.5, 130.4, 130.1, 129.4, 126.7, 126.1, 123.9,
114.1, 21.1, 21.0, 20.2, 19.9, 18.1, 18.0, 17.5 (2C), -3.6. (3 C
cannot be uniquely identified because of dispersity in the aryl region
and the transitory nature of 9.) FTIR (neat): 2918 (w), 1612 (w),
1505 (w), 1479 (w), 1458 (w), 1383 (w), 1329 (w), 1238 (m), 1157
(m), 1059 (s), 848 (w), 742 (m), 571 (w), 534 (w) cm-1. 9 is not
sufficiently long-lived for HRMS.
Indole N-Complex 8a. Platinum dimethyl complex 1a4a (46.6
µmol, 25.4 mg) was weighed out in an oven-dried 4 mL vial in the
drybox. TFE-d3 (350 µL) and BF3 (0.455 M in TFE-d3, 53.5 µmol,
118 µL) were then added, and the suspension was stirred until it
became a homogeneous orange solution. Indole (47 µmol, 5.5 mg)
was added, and the solution was transferred, rinsing with TFE-d3
(350 µL), to an oven-dried J-Young NMR tube. The solution was
analyzed by NMR and found to contain 8a in >95% yield.
1H NMR (500 MHz, TFE-d3) δ: 7.89 (s, JPt-H ) 34 Hz, 1H),
7.73 (d, JH-H ) 7.3 Hz, 1H), 7.40-7.35 (m, 3H), 7.12 (s, 1H),
7.09 (s, 1H), 6.97 (s, 1H), 6.50 (s, 1H), 2.35 (s, 3H), 2.34 (s, 3H),
2.27 (s, 3H), 2.20 (s, 3H), 2.16 (s, 3H), 1.88 (s, 3H), 1.87 (s, 3H),
1.80 (s, 3H), 0.61 (s, JPt-H ) 73 Hz, 3H). 13C NMR (125 MHz,
TFE-d3) δ: 182.1, 175.6, 175.1, 153.9, 142.7, 140.9, 140.4, 139.8,
134.5, 130.9, 130.9, 130.8, 130.7, 130.6, 130.5, 130.1, 130.0, 129.3,
128.9, 125.8, 122.3, ∼44 (m, 1C), 21.1, 20.8, 20.0, 19.5, 17.9, 17.8
(2C), 17.7, -12.1. FTIR (neat): 2921 (m), 2094 (w), 1474 (m),
1449 (m), 1382 (m), 1313 (m), 1240 (m), 1184 (s), 1128 (s), 1069
(s), 1018 (s), 852 (m), 818 (m), 769 (m), 644 (m), 534 (m) cm-1
.
FAB+ MS, calcd for C31H35N3Pt2H2 ([M - H]+): 649.2839, found
649.2847.
2-Methylindole-N-complex 10. The crude solution of 9 prepared
above was incubated at room temperature for 50 h to give 10 in
>95% yield.
Indole Complex 8b. Platinum dimethyl complex 1b4a (32.5
µmol, 16.8 mg) was weighed out in an oven-dried 4 mL vial in the
drybox. TFE-d3 (700 µL) and BF3 (0.478 M in TFE-d3, 37.3 µmol,
78.1 µL) were then added, and the suspension was stirred until it
became a homogeneous orange solution. Indole (33 µmol, 3.8 mg)
was added, and the solution was transferred to an oven-dried screw-
capped NMR tube. The solution was analyzed by NMR and found
to contain 8b in >95% yield.
1H NMR (500 MHz, TFE-d3) δ: 7.74 (d, JH-H ) 7.8 Hz, 1H),
7.32 (d, JH-H ) 7.9 Hz, 1H), 7.29-7.27 (m, 2H), 7.11 (s, 1H),
7.10 (s, 1H), 6.87 (s, 1H), 6.44 (s, 1H), 2.41 (s, 3H), 2.35 (s, 3H),
2.33 (s, 3H), 2.24 (s, 3H), 2.19 (s, 3H), 2.12 (s, 3H), 1.86 (s, 3H),
1.85 (s, 3H), 1.83 (s, 3H), 0.53 (s, JPt-H ) 74, 3H). 13C NMR (125
MHz, TFE-d3) δ: 186.0, 181.7, 175.8, 154.9, 142.8, 142.0, 140.3,
139.6, 135.0, 130.9, 130.7, 130.4, 129.9, 128.9, 128.8, 128.7, 122.5,
121.6, 121.1, 121.0, 112.4, ∼45 (m, 1C), 22.1, 21.1, 20.8, 20.1,
19.5, 18.4, 17.9, 17.8, 13.5, -13.7. FTIR (neat): 3512 (br, w),
3399 (br, w), 2921 (br, w), 1613 (w), 1573 (w), 1476 (m), 1456
(m), 1384 (m), 1316 (m), 1240 (m), 1187 (s), 1130 (s), 1069 (s),
852 (w), 756 (w), 646 (w), 535 (w) cm-1. FAB+ MS, calcd for
C32H38N3Pt2H2 ([M]+): 663.2996, found 663.2980.
1H NMR (500 MHz, TFE-d3) δ: 8.01 (s, JPt-H ) 36 Hz, 1H),
7.87 (d, JH-H ) 7.9 Hz, 1H), 7.46-7.41 (m, 2H), 7.38-7.35 (m,
1H), 7.06 (s, 1H), 6.75 (s, 1H), 6.71 (s, 1H), 6.66 (s, 1H), 6.49 (s,
br, 1H), 6.06 (s, br, 1H), 2.39 (s, 3H), 2.37 (s, 3H), 2.25 (s, br,
3H), 1.96 (s, 3H), 1.95 (s, 3H), 1.69 (s, 3H), 0.74 (s, JPt-H ) 73
Hz, 3H). 13C NMR (125 MHz, TFE-d3) δ: 182.3, 174.6, 175.1,
153.9, 147.8, 145.7, 141.9, 141.8, 141.9-141.5 (m, br, 2C), 134.5,
131.2, 130.5, 130.2, 129.4, 125.9, 122.7, 121.0, 121.0, 120.7 (br,
1C), 119.5 (br, 1C), ∼44 (m, 1C), 21.6, 21.5, 21.2, 21.9-21.8 (m,
2C), -11.3. FTIR (neat): 3014 (w), 2921 (w), 2875 (w), 1609 (w),
1593 (w), 1468 (w), 1453 (w), 1384 (w), 1308 (w), 1185 (m), 1130
(m), 1060 (s), 863 (w), 771 (w), 685 (w) cm-1. FAB+ MS, calcd
for C29H31N3Pt2H2 ([M - H]+): 620.2448, found 620.2459.
Indole Complex 8c. Platinum dimethyl complex 1c3 (36.0 µmol,
26.4 mg) was weighed out in an oven-dried 4 mL vial in the drybox.
TFE-d3 (700 µL) and BF3 (0.478 M in TFE-d3, 41.4 µmol, 86.6
µL) were then added, and the suspension was stirred until it became
a homogeneous orange solution. Indole (36 µmol, 9.2 mg) was
added, and the solution was transferred to an oven-dried screw-
capped NMR tube. The solution was analyzed by NMR and found
to contain 8c in >95% yield.
1-Methylindole-π-complex 11. Platinum dimethyl complex 1a4a
(46.9 µmol, 25.6 mg) was weighed out in an oven-dried 4 mL vial
in the drybox. TFE-d3 (700 µL) and BF3 (0.455 M in TFE-d3, 54
µmol, 119 µL) were then added, and the suspension was stirred
until it became a homogeneous orange solution. 1-Methylindole
(46.9 µmol, 6.16 mg, 6.00 µL) was added, and the solution was
transferred to an oven-dried screw-capped NMR tube. The solution
was analyzed by NMR and found to contain 11 in >95% yield.
1H NMR (500 MHz, TFE-d3) δ: 7.57 (d, JH-H ) 8.7 Hz, 1H),
7.50 (s, JPt-H ) 49 Hz, 1H), 7.28 (t, JH-H ) 7.8 Hz, 1H), 7.22-
7.17 (m, 2H), 7.16 (s, 1H), 7.07 (s, 1H), 6.97 (s, 1H), 6.91 (s, 1H),
5.95 (s, JH-H ) 88 Hz, ∼0H),27 3.65 (s, 3H), 2.41 (s, 3H), 2.32 (s,
3H), 2.24 (s, 6H), 2.14 (s, 3H), 2.00 (s, 3H), 1.86 (s, 3H), 1.80 (s,
3H), -1.16 (s, JPt-H ) 70 Hz, 3H). 13C NMR (125 MHz, TFE-d3)
δ: 179.4, 177.1, 144.9, 142.6, 141.5, 140.4, 140.1, 137.3, 131.7,
131.5, 130.8, 130.7, 130.6, 130.2, 130.1, 129.8, 125.2, 125.0, 128.9,
128.3, 111.9, 34.2, 21.1, 21.0, 20.0, 19.8, 18.0, 17.7 (2C), 17.6,
-3.0. Because of dispersion in the 130 ppm region, 1C cannot be
located. FTIR (neat): 2919 (w), 1477 (w), 1454 (w), 1383 (w),
1327 (w), 1238 (w), 1184 (m), 1128 (m), 1054 (s), 847 (w), 753
(w), 679 (w) cm-1. FAB+ MS, calcd for C32H39N3Pt2H1 ([M]+):
662.2933, found 662.2932.
1H NMR (500 MHz, TFE-d3) δ: 8.27 (s, JPt-H ≈ 40 Hz, 1H),
8.02 (s, 1H), 7.78 (d, JH-H ) 8.5 Hz, 1H), 7.73 (s, 1H), 7.68 (s,
1H), 7.55 (S, 1H), 7.45-7.27 (m, 5H), 2.04 (s, 3H), 2.03 (s, 3H),
0.76 (s, JPt-H ≈ 60 Hz, 3H). 13C NMR (125 MHz, TFE-d3) δ:
184.5, 177.7, 175.6 (m, 1C), 152.9 (m, 1C), 148.5, 147.0, 136.1-
134.1 (m, apparent 4C), 134.1, 130.7, 129.4, 126.2, 124.6 (apparent
(27) This signal (C3-H) is rapidly deuterated under the reaction
conditions, but can be observed at the beginning of a kinetics run.

Reactions of Indene and Indoles with Pt Methyl Cations
Organometallics, Vol. 26, No. 2, 2007 287
1-Methylindole-N-complex 12. The crude solution of 11
and the content of 1 syringe was added to the NMR tube (to make
10.9 µmol of Pt, 5 equiv of BF3, 5 equiv of indole, and 700 µL of
TFE-d3). The tube was shaken and reinserted. After rapid re-
shimming, kinetic data were recorded for 7.5 h. A second trial was
then conducted with the other NMR tube and syringe. Reaction
progress was monitored by NMR. Rate constants for this experiment
are kbinding ) 5.35 × 10-4 s-1 and kRAR ) 1.44 × 10-4 s-1, where
prepared above was incubated at room temperature for 2 days, then
1
heated to 40 °C for 4 h to give 12 in ∼78% yield by NMR. H
NMR (500 MHz, TFE-d3) δ: 7.32 (t, JH-H ) 7.6 Hz, 1H), 7.28 (d,
JH-H ) 7.4 Hz, 1H), 7.22 (t, JH-H ) 7.4 Hz, 1H), 7.19 (d, JH-H
)
8.4 Hz, 1H), 7.08 (s, 1H), 7.07 (s, 1H), 6.91 (s, 1H), 6.69 (s, 1H),
3.83 (s, 3H), 2.33 (s, 3H), 2.30 (s, 3H), 2.24 (s, 3H), 2.18 (s, 3H),
2.13 (s, 3H), 2.01 (s, 3H), 1.98 (s, 3H), 1.85 (s, 3H), 0.26 (s, JPt-H
) 77 Hz, 3H). 13C NMR (125 MHz, TFE-d3) δ: 180.1, 176.3,
148.4, 144.6, 142.0, 139.9, 139.7, 137.0, 136.9, 130.9, 130.7, 130.7,
130.4, 130.2, 129.3, 128.8, 128.8, 128.6, 127.6, 125.6, 125.5, 112.7,
39.9 (JPt-C ) 81 Hz), 21.1, 20.7, 20.0, 19.8, 17.9, 17.9, 17.9, 17.8,
-16.8. FTIR (neat): 2923 (m, br), 2100 (w), 1609 (w), 1515 (m),
1463 (s), 1384 (m), 1312 (m), 1238 (m), 1186 (s), 1130 (s), 1069
(s, br), 860 (w), 818 (w), 759 (m), 646 (w), 535 (w) cm-1. FAB+
MS, calcd for C32H39N3Pt2H ([M]+): 662.2933, found 663.2939.
Crossover Experiment between 9 and 1-Methylindole. Plati-
num dimethyl complex 1a (22.4 µmol, 12.2 mg) was weighed out
in an oven-dried screw-capped NMR tube in the drybox. TFE-d3
(511 µL) and BF3 (0.477 M in TFE-d3, 24.6 µmol, 51.6 µL) were
then added. The suspension was removed from the drybox and
sonicated until it became a homogeneous orange solution. The
reaction was then thermally equilibrated to 30 °C in a Varian
mercury 300 MHz NMR, and 2-methylindole (0.183 M in TFE-d3,
22.4 µmol, 122 µL) was then injected. [9] was monitored and
reached a maximum in ca. 2 min, at which time conversion of 2a
to 9 was ∼90% complete. The tube was then removed from the
instrument, 1-methylindole (2.93 mg, 22.4 µmol, 2.86 µL) was
injected, and the sample was reinserted (∼30 s.) An initial ratio of
81(1)% 9, 10(1)% 10, 9(1)% 11 was observed with 0(1)% 2a.
Kinetic data were recorded for 9.7 h. After an additional 2 days at
RT, 9 was completely converted to 10 (kRAR ) 9.1(3) × 10-5 s-1),
and 11 was completely converted to 12. A ratio of 91(1)% 10 to
9(1)% 12 was observed.
kbinding is the pseudo-first-order rate constant for the binding of indole
to 2a.24
Comment Regarding H/D Exchange and Methane Isotopo-
logues Formed in the Conversion of 3 to 4. In the conversion of
3a to 4a the methane that is formed is 65% CH4, 35% CH3D due
to D+ incorporation in the formation of 2a from 1a. A distribution
of 53% CH4, 47% CH3D is observed in the conversion of 3a-d3 to
4a-d2. 2H NMR spectra of 4a and 4a-d2 were recorded to track 2H
incorporation in these compounds (see Supporting Information).
2H incorporation is observed in C2-H (6.8 ppm) in both 4a and
4a-d2. Little 2H incorporation is observed in C1,3-H (5.0 ppm) in
2
4a. As expected, H is observed in this signal in 4a-d2. A small
amount of H/D exchange with solvent is observed in the diimine
backbone (2.4 ppm), but none is observed in the mesityl methyl
groups. Accordingly, the high level of CH4 relative to CH3D
observed in the formation of 4a-d2 is attributed to some H/D
exchange with C2-H in the indenyl fragment prior to methane
liberation and a low level of decomposition of the diimine ligand.
Acknowledgment. This work was supported by the BP MC2
program and by the NIH (NRSA fellowship GM075691 to
T.J.W.). These sponsors are gratefully acknowledged. We thank
Dr. Tom G. Driver for helpful discussions, especially regarding
the preparation and use of BF3-TFE-d3.
Note Added in Proof. A preliminary X-ray structure for 8a
has recently been obtained. This is a preliminary, low-resolution
structure from a poorly diffracting crystal. Connectivity is
unambiguous although distance and angle measurements have
large errors. These data, CCDC 628218, can be obtained free
of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Conversion of 6a to 8a at High [H+]. Platinum dimethyl
complex 1a (22.7 µmol, 12.4 mg) was weighed out in a 1 mL
graduated cylinder in the drybox. BF3 (0.477 M in TFE-d3, 56.8
µmol, 119 µL) and TFE-d3 (to make 1.00 mL) were then added. A
480 µL portion of this solution (10.9 µmol Pt, 2.5 equiv of BF3)
was then distributed into each of two screw-capped NMR tubes.
Separately, indole (14.5 mg, 124 µmol), BF3 (0.477 M in TFE-d3,
62.0 µmol, 130 µL), and TFE-d3 (356 µL) were mixed in a 10 mL
culture tube. Then 220 µL of this solution (5 equiv of indole to Pt,
2.5 equiv of BF3 to Pt) was then distributed into each of two 1 mL
syringes. The NMR tubes and syringes were removed from the
drybox. One NMR tube was then thermally equilibrated to 40 °C
in a Varian Inova 500 MHz NMR spectrometer. It was then ejected,
Supporting Information Available: Spectral data for the
crossover experiment between 9 and 1-methylindole, spectral and
kinetic data for the conversion of 6a to 8a in the presence of excess
2
1
acid, H NMR spectra for 4a and 4a-d2, and graphical H NMR
spectra for 3a, 3a-d3, 4a, 4a-d2, 8a, 8b, 8c, 9, 10, 11, and 12 are
available free of charge via the Internet at http://pubs.acs.org.
OM0606643