Mechanistic studies of the hydroamination of norbornene with electrophilic platinum complexes: The role of proton transfer

Article abstract of DOI:10.1021/ja8030104

Hydroaminations of norbornene with arylsulfonamides and weakly basic anilines were achieved using electrophilic Pt(II) bis(triflate) complexes of the type L₂Pt(OTf)₂ (L₂ = ^tBu ₂bpy, ^tBuC₆H₄N= C(CH ₃)C(CH₃)=NC₆H₄^tBu, (C₆H₅)₂PCH₂CH₂P(C ₆H₅)₂, (C₆F₅) ₂PCH₂CH₂P(C₆F₅) ₂, S-BINAP). Pseudo-first-order kinetics reveal little to no dependence of the reaction rate on the ancillary ligand. Mechanistic studies do not favor an olefin coordination mechanism but are instead consistent with a mechanism involving sulfonamide coordination and generation of an acidic proton that is transferred to the norbornene. It is postulated that the resulting norbornyl cation is then attacked by free sulfonamide, and loss of proton from this adduct completes the hydroamination. The platinum-sulfonamide complex readily undergoes deprotonation to give μ-amido platinum-bridged dimer that was isolated from the reaction solution. These studies also involve use of Me₃SiPh and Me₃SnPh as non-nucleophilic proton traps. Cleavage of the Ph-E bonds was used to detect the acidic, catalytically active species.

Full text of DOI:10.1021/ja8030104

Published on Web 11/14/2008
Mechanistic Studies of the Hydroamination of Norbornene
with Electrophilic Platinum Complexes: The Role of Proton
Transfer
Jennifer L. McBee,†,‡ Alexis T. Bell,‡,§ and T. Don Tilley*,†,‡
Departments of Chemistry and Chemical Engineering, UniVersity of California, Berkeley,
Berkeley, California 94720, and Chemical Sciences DiVision, Lawrence Berkeley National
Laboratory, 1 Cyclotron Road, Berkeley, California 94720
Received April 23, 2008; E-mail: tdtilley@berkeley.edu
Abstract: Hydroaminations of norbornene with arylsulfonamides and weakly basic anilines were achieved
using electrophilic Pt(II) bis(triflate) complexes of the type L2Pt(OTf)2 (L2
)
tBu2bpy, tBuC6H4Nd
t
C(CH3)C(CH3)dNC6H4 Bu, (C6H5)2PCH2CH2P(C6H5)2, (C6F5)2PCH2CH2P(C6F5)2, S-BINAP). Pseudo-first-
order kinetics reveal little to no dependence of the reaction rate on the ancillary ligand. Mechanistic studies
do not favor an olefin coordination mechanism but are instead consistent with a mechanism involving
sulfonamide coordination and generation of an acidic proton that is transferred to the norbornene. It is
postulated that the resulting norbornyl cation is then attacked by free sulfonamide, and loss of proton from
this adduct completes the hydroamination. The platinum-sulfonamide complex readily undergoes
deprotonation to give a µ-amido platinum-bridged dimer that was isolated from the reaction solution. These
studies also involve use of Me3SiPh and Me3SnPh as non-nucleophilic proton traps. Cleavage of the Ph-E
bonds was used to detect the acidic, catalytically active species.
Scheme 1. Olefin Activation Mechanism for Hydroamination
Introduction
A longstanding goal of research in catalysis is the develop-
ment of general catalysts for the selective hydroamination of
unactivated alkenes.1,2 The search for such catalysts has
generated a number of plausible mechanistic strategies, and
notable progress has been made for certain substrates. Specif-
ically, hydroaminations have been observed for vinylarenes,3-5
dienes,6 alkynes,7,8 and electron-deficient alkenes.5,9-11 In
addition, several reports of hydroaminations with weakly basic
amines (such as sulfonamides, carboxamides, and electron-
deficient anilines) have appeared.12-17 Despite these important
advances, general catalysts that operate for unactivated alkenes
and more basic amines, such as aniline and ammonia, have yet
to be discovered. Only lanthanide catalysts exhibit a somewhat
wide substrate scope covering a variety of alkene and amine
substrates; however, these catalysts are highly moisture- and
oxygen-sensitive.18,19
Much of the effort directed toward development of general
hydroamination catalysts has centered on late transition metals,
since catalysts based on these metals are expected to be more
moisture- and oxygen-tolerant. Also, these metals offer a number
of potential mechanisms for activation of the amine and alkene
substrates. In particular, mechanisms based on nucleophilic
attack of amine onto a coordinated alkene (Scheme 1) and amine
activation by N-H oxidative addition (Scheme 2) have received
† Department of Chemistry, UC Berkeley.
‡ Lawrence Berkeley National Laboratory.
§ Department of Chemical Engineering, UC Berkeley.
(1) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675–704.
(2) Hartwig, J. F. Pure Appl. Chem. 2004, 507–516.
(3) Utsunomiya, M.; Kuwano, R.; Kawatsura, M.; Hartwig, J. F. J. Am.
Chem. Soc. 2003, 125, 5608–5609.
(4) Utsunomiya, M.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 2702–
2703.
(5) Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2000, 122, 9546–
9547.
(6) Lo¨ber, O.; Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2001,
123, 4366–4367.
(7) Doye, S. Synlett 2004, 10, 1653–1672.
(8) Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935–946.
(9) Fadini, L.; Togni, A. A. Chimia 2004, 58, 208–211.
(10) Fadini, L.; Togni, A. Chem. Commun. 2003, 30–31.
(11) Munro-Leighton, C.; Blue, E. D.; Gunnoe, T. B. J. Am. Chem. Soc.
2006, 128, 1446–1447.
(16) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2005, 127, 1070–
1071.
(12) Wang, X.; Widenhoefer, R. A. Organometallics 2004, 23, 1649–1651.
(13) Taylor, J. G.; Whittall, N.; Hii, K. K. Org. Lett. 2006, 8, 3561–3564.
(14) Liu, X.-Y.; Li, C.-H.; Che, C.-M. Org. Lett. 2006, 8, 2707–2720.
(15) Karshtedt, D.; Bell, A. T.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127,
12640–12646.
(17) Zhang, J.; Yang, C.-J.; He, C. J. Am. Chem. Soc. 2006, 128, 1798–
1799.
(18) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673–686.
(19) Roesky, P. W.; Mu¨ller, T. E. Angew. Chem., Int. Ed. 2003, 42, 2708–
2710.
9
16562 J. AM. CHEM. SOC. 2008, 130, 16562–16571
10.1021/ja8030104 CCC: $40.75
2008 American Chemical Society

Hydroamination by Electrophilic Platinum Complexes
A R T I C L E S
Scheme 2. Amine Activation Mechanism for Hydroamination
Chart 1
considerable attention.7,20-24 Hydroaminations via the former
mechanism would seem to require an electrophilic metal center
in the catalyst, and for this reason research has focused on
cationic complexes of the late transition metals. Several research
groups have found that cationic late metal complexes with
weakly coordinating anions catalyze a range of C-H or N-H
additions across an alkene.22,25 In our laboratories, electrophilic
platinum catalysts such as (COD)Pt(OTf)2, where COD ) 1,5-
cyclooctadiene, and [(η2-C2H4)PtCl2]2/AgBF4 have been found
to mediate hydroarylations26 and hydroaminations15 of alkenes.
The observed hydroaminations involved only weakly basic
aniline and sulfonamide derivatives, and this reaction is associ-
ated with a substrate limitation in which amines with conjugate
acid pKa values above ca. 4 are unreactive. There are several
possible mechanistic explanations for this limitation; however,
the pKa cutoff suggests the involvement of a proton transfer.
The possible role of Brønsted acidic species in observed,
metal-catalyzed hydroarylations and hydroaminations is further
suggested by the fact that strong acids are known to be catalysts
for such reactions.27-31 Thus, a detailed characterization of the
role of electrophilic metal species in catalytic element-hydrogen
additions to unsaturated substrates must include a thorough
understanding of the potential participation of protons. In
principle, this issue may be difficult to probe, since a standard
mechanistic test for involvement of a Brønsted acid involves
addition of a base (a proton trap). However, for reactions
involving Lewis acidic metal centers and relatively acidic
intermediates, an added base may inhibit the formation of
products for a variety of reasons. Thus, it is important to develop
mechanistic probes that reveal possible processes by which
protonic species might result from the interaction of a Lewis
acidic metal center with hydroamination substrates (an alkene
and an amine). One possible reaction of this type was recently
reported by Szuromi and Sharp, who described the interaction
of (COD)Pt(OTf)2 with norbornene, which results in alkene
coupling at the metal center and the elimination of triflic acid.32
Clearly, acidic species may also result from coordination of
hydrogen-substituted amines to a metal center.
This contribution describes a mechanistic investigation of
hydroaminations catalyzed by electrophilic bis(triflate) platinum
complexes. This research involves kinetic and mechanistic
studies, including the use of Me3SiPh and Me3SnPh as trapping
reagents for protons. The results point to the platinum-mediated
generation of an acidic species, which plays a crucial role in
the catalysis.
Results and Discussion
The bis(triflate) platinum complex (COD)Pt(OTf)2 has previ-
ously been reported to catalyze hydroarylations26 and hydroami-
nations15 of alkenes. For these reactions, experimental evidence
suggests that the COD ligand remains coordinated to platinum
and does not directly participate in the catalysis. Thus, to probe
the role of the platinum center in hydroaminations, it was of
interest to vary the nature of the chelating, ancillary L2 ligand
in catalysts of the type L2Pt(OTf)2.
Synthesis and Characterization of L2Pt(OTf)2 Complexes.
These complexes were obtained in high yield by reaction of
the corresponding L2PtCl2 compounds with 2 equiv of AgOTf
in dichloromethane.33-35 In this manner, a range of triflate
derivatives containing both phosphine- and nitrogen-based
ligands were prepared (Chart 1). Because these complexes are
moisture-sensitive and readily form µ-OH bridged dimeric
complexes upon exposure to water, the synthetic procedures
involved the rigorous exclusion of air.36,37 The L2Pt(OTf)2
complexes were completely characterized, and the nature of the
L2-Pt interactions was investigated by single crystal X-ray
crystallography. For each complex investigated, both triflate
ligands are coordinated to platinum through one oxygen atom.
The Pt-O distances (Å) vary depending on the ligand sets, from
2.060(4) and 2.063(4) for 1 (Figure 1) to 2.115(3) and 2.119(3)
(20) Senn, H. M.; Deubel, D. V.; Blo¨chl, P. E.; Togni, A. THEOCHEM
2000, 506, 233–242.
(21) Senn, H. M.; Blo¨chl, P. E.; Togni, A. J. Am. Chem. Soc. 2000, 122,
4098–4107.
(22) Hahn, C. Chem. Eur. J. 2004, 10, 5888–5889.
(23) Brunet, J.-J.; Chu, N. C.; Diallo, O. Organometallics 2005, 24, 3104–
3110.
(24) Brunet, J.-J.; Cadena, M.; Chu, N. C.; Diallo, O.; Jacob, K.; Mothes,
E. Organometallics 2004, 23, 1264–1268.
(25) Chianese, A. R.; Lee, S. J.; Gagne´, M. R. Angew. Chem., Int. Ed.
2007, 46, 4042–4059.
(26) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Organometallics 2004, 23,
4169–4171.
(32) Szuromi, E.; Sharp, P. R. Organometallics 2006, 25, 558–559.
(33) Oberbeckmann-Winter, N.; Morse, X.; Braunstein, P.; Welter, R. Inorg.
Chem. 2005, 44, 1391–1403.
(27) Schlummer, B.; Hartwig, J. F. Org. Lett. 2002, 4, 1471–1474.
(28) Rosenfeld, D. C.; Shekhar, S.; Takemiya, A.; Utsunomiya, M.;
Hartwig, J. F. Org. Lett. 2006, 8, 4179–4182.
(29) Anderson, L. L.; Arnold, J.; Bergman, R. G. J. Am. Chem. Soc. 2005,
127, 14542–14543.
(34) Nilsson, P.; Puxty, G.; Wendt, O. F. Organometallics 2006, 25, 1285–
1292.
(35) Liang, C.-C.; Lin, J.-M.; Lee, W.-Y. Chem. Commun. 2005, 19, 2462–
2464.
(30) Dubovyk, I.; Watson, I. D. G.; Yudin, A. K. J. Am. Chem. Soc. 2007,
129, 14172–14173.
(36) Strukul, G.; Varagnolo, A.; Pinna, F. J. Mol. Catal. A 1997, 117, 413–
423.
(31) Cochran, B. M.; Michael, F. E. J. Am. Chem. Soc. 2008, 130, 2786–
2792.
(37) Bunkan, N. M.; Gagne´, M. R. Organometallics 2002, 21, 4711–4717.
9
J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008 16563

A R T I C L E S
McBee et al.
with both electron-deficient and electron-rich functional groups
being tolerated (Table 1, entries 7-15). A similar dependence
on the conjugate acid pKa of the amine has been observed with
other late transition metal catalysts.15 Variation of the catalyst
employed did not reveal a change in the observed pKa limitation
for the hydroamination. The exclusive formation of the exo
products in these reactions indicates the intermediacy of a
norbornyl cation, since insertions of norbornene into metal-ligand
bonds result in endo products.42,43 To further evaluate involve-
ment of a norbornyl cation in the hydroamination catalysis,
norbornene and 4-tert-butylbenzenesulfonamide-d2 were sub-
jected to catalytic conditions with 5 mol % 1 as the catalyst.
By 2H NMR spectroscopy, four C-D resonances were observed
for the hydroamination product. The large number of C-D
resonances strongly implies participation of a norbornyl cation
(only one C-D product would be expected for an insertion
mechanism). Lastly, when 5 was employed as the catalyst, a
50:50 mixture of enantiomers was observed as the product (by
HPLC Chiracel OD). The complete lack of enantioselectivity
with 5 as the catalyst suggests that the reaction does not involve
the intermediacy of diastereomers and is consistent with the
involvement of a norbornyl cation. Finally, compounds 1-5
were observed to catalyze the isomerization of norbornene to
tricyclo(2.2.1.0(2,6))heptane, which is known to occur via an
intermediate norbornyl cation.42-44 For 1 as catalyst, an
equilibrium of the two isomers was established after 1 day at
25 °C (Keq ) 1.1(7), eq 1).
Figure 1. ORTEP diagram of the X-ray crystal structure of 1. Hydrogen
atoms are omitted for clarity. Bond lengths (Å): Pt-O4 ) 2.060(4), Pt-O3
) 2.063(4), Pt-N1 ) 1.967(5), Pt-N2 ) 1.980(5).
Ancillary Ligand Effects on Reaction Rate. The influence of
the ancillary ligand set on hydroamination reaction rates was
investigated with kinetic studies. Under pseudo-first-order
conditions with excess norbornene (20 equiv) and sulfonamide
(20 equiv), kobs values for each catalyst were determined at 37
°C. As shown in Table 2, there is only a small variation in rate
constants among the catalysts employed, with nitrogen-based
ancillary ligands (1, 2) giving somewhat higher rate constants
than phosphine ligands (3-5). As a reference, the kobs value for
triflic acid (5 mol %), a known catalyst for hydroaminations
with sulfonamides, is two to 3 orders of magnitude greater than
those for the platinum catalysts.
Kinetic Studies on Hydroamination. Mechanistic studies of
the hydroamination of norbornene with sulfonamide included
attempts to establish a rate law using kinetic measurements. For
this purpose, catalyst 1 was employed, and reactions were
monitored at 37 °C in chloroform-d. First-order dependence of
the reaction rate on the concentration of 1 was established under
pseudo-first-order conditions of excess norbornene and sulfona-
mide (10-100 equiv). The reaction order in sulfonamide was
determined by varying its concentration (0.01-0.1 M) in the
presence of a controlled amount of 1 (0.005 M) and excess
norbornene (0.2 M). Under these pseudo-first-order conditions,
plots of [sulfonamide] versus time were linear over 2-3 half-
lives, and a plot of ln rate versus ln[sulfonamide] provided a
reaction order of 1.1 for the sulfonamide. Variation of the
Figure 2. ORTEP diagram of the X-ray crystal structure of 5·C4H10O.
Hydrogen atoms and the C4H10O molecule are omitted for clarity. Bond
lengths (Å): Pt-O2 ) 2.115(3), Pt-O1 ) 2.119(3), Pt-P5 ) 2.2258(14),
Pt-P6 ) 2.2165(14).
for 5 (Figure 2) and 2.120(4) and 2.138(4) for 3,38 illustrating
only small variations in the Pt-triflate interactions.
Hydroamination with Weakly Basic Anilines and Sulfona-
mides. Previous studies found that the platinum bis(triflate)
complex (COD)Pt(OTf)2 is a catalyst for the hydroamination
of norbornene with sulfonamides.15 For catalysts 1-5, hy-
droaminations occurred in near quantitative yields at 60 °C
within 12 h. With catalyst 1, the amine scope for the hydroami-
nation was explored (Table 1). With 5 mol % of 1 relative to
norbornene, no hydroamination products were observed for
morpholine, aniline, or p-anisidine (conjugate acid pKa > 4) at
100 °C over 3 days (Table 1, entries 1-3). However, if the
conjugate acid pKa value for the amine substrate is lowered to
below 4, as for pentafluoroaniline, p-nitroaniline, and 3,5-(bis-
trifluoromethyl)aniline, hydroamination proceeds at 50-80 °C
in >95% yields, with high selectivity for the exo product (Table
1, entries 4-6). With more acidic amines (sulfonamides and
benzamide with pKa < 0),39-41 the hydroaminations occurred
(38) Brunkan, N. M.; White, P. S.; Gagne´, M. R. Organometallics 2002,
21, 1565–1575.
(42) Hughes, R. P.; Powell, J. J. Organomet. Chem. 1971, 30, C45–C47.
(43) Gallazzi, M. C.; Hanlon, T. L.; Vitulli, G.; Porri, L. J. Organomet.
Chem. 1971, 33, C45–C46.
(39) Virtanen, P. O.; Maikkula, M. Tetrahedron Lett. 1968, 9, 4855–4858.
(40) Laughlin, R. G. J. Am. Chem. Soc. 1967, 89, 4268–4271.
(41) Gross, K. C.; Seybold, P. G. J. Org. Chem. 2001, 66, 6919–6925.
(44) Saunders, M.; Jarret, R. M.; Pramanik, P. J. Am. Chem. Soc. 1987,
109, 3735–3739.
9
16564 J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008

Hydroamination by Electrophilic Platinum Complexes
A R T I C L E S
Table 1. Intermolecular Hydroamination of Norbornenea
b
a Reactions were conducted with 0.1 mmol of substrate and norbornene and 5 mol % of 1 in 1 mL of ClCH2CH2Cl. Yields were determined by H
NMR spectroscopy using an internal standard and confirmed by GC-MS, and only the exo product was observed. c Norbornene and starting amine were
isolated. d The long reaction time may be attributed to the low solubility of benzamide under the reaction conditions.
1
Table 2. Rate Constants for Catalytic Hydroamination of
Norbornene
Under conditions employed for the kinetic studies, the rate of
norbornene isomerization is much slower than the rate for
hydroamination (<2% isomerization at complete conversion of
norbornene in the catalysis). These experiments provide the
approximate rate law: d[product]/dt ≈ kobs[1][sulfonamide],
where kobs ) 1.4(9) × 10-3 s-1 M-1 at 37 °C (vide infra). The
results also suggest that activation of the sulfonamide by the
metal center is an important step in the catalysis and that
norbornene activation by the metal center may not play an
important role.
catalyst
kobs (s-1
)
(tBu2bpy)Pt(OTf)2 (1)
1.4(9) × 10-3
3.2(8) × 10-3
5.3(9) × 10-4
5.3(9) × 10-4
2.9(7) × 10-4
2.0(9) × 10-1
[tBuC6H4NdC(CH3)(CH3)CdNC6H4 Bu]Pt(OTf)2 (2)
[[(C6H5)2PCH2CH2P(C6H5)2]Pt(OTf)2 (3)
[[(C6F5)2PCH2CH2P(C6F5)2]Pt(OTf)2 (4)
[S-(BINAP)]Pt(OTf)2 (5)
t
To investigate the kinetic influence of triflate anion on the
catalysis, varied amounts of [NEt4][OTf] were added to solutions
of 1 (5 mol %), sulfonamide, and norbornene. As shown in
Figure 3, increasing concentrations of triflate dramatically inhibit
the catalysis. To examine the possibility of a salt effect45 on
this reactivity, hydroamination reactions with added
[NnBu4][PF6], involving a less coordinating anion, were moni-
tored. As shown by the plot of Figure 3, such reactions are faster
triflic acid
norbornene concentration (0.03-0.08 M) in the presence of 1
(0.005 M) and excess sulfonamide (0.2 M) gave only small
changes in the reaction rate, and an analogous kinetic analysis
gave a reaction order of 0.2 for norbornene, over the concentra-
tion range examined (see Supporting Information, Figure S7).
(45) Loupy, A.; Tchoubar, B. Salt Effects in Organic and Organometallic
Chemistry; VCH: Weinheim, 1992.
9
J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008 16565

A R T I C L E S
McBee et al.
Figure 3. Plot of 1/[R4NX] versus initial rate: [Et4N][OTf] (9) and
[nBu4N][PF6] (2).
in the presence of this salt, which is consistent with a typical
salt effect for reactions involving ion pairs. The observed,
opposite influence of [NEt4][OTf], in inhibiting the catalysis,
is consistent with triflate dissociation playing an important role
in activation of the sulfonamide via its coordination to platinum.
Mechanistic Investigations with Proton Trapping Reagents.
The classic test for participation of a proton transfer involves
monitoring a reaction in the presence of a sterically hindered
amine. The addition of 2,6-di-tert-butyl-4-methylpyridine (1
equiv on the basis of 1) to a catalytic mixture of 1, norbornene,
and the sulfonamide results in complete inhibition of the
catalysis, and the formation of a diplatinum species with two
Figure 4. ORTEP diagram of the X-ray crystal structure of 6·CH2Cl2.
The hydrogen atoms (excluding those bound to nitrogen) and the CH2Cl2
molecules are omitted for clarity. Bond lengths (Å): Pt1-N1 ) 2.013(5),
Pt1-N2 ) 2.009(5), Pt1-N3 ) 2.058(5), Pt1-N3(A) ) 2.082(5), O4· · ·H3
) 1.944.
(eq 2). In the absence of norbornene, these reactions proceeded
in a similar manner with cleavage of the Ph-E bond to give
benzene (5%) and Me3EOTf (5%) within 1 h. Thus, the proton
being transferred in these reactions does not originate from the
norbornene and most likely originates from the sulfonamide (in
the absence of sulfonamide, no E-Ph cleavage is observed after
1 h). To quantify the rate of platinum-mediated proton transfer
from p-tBuC6H4SO2NH2, pseudo-first-order conditions were
employed for 1 (5 mol %) with excess Me3SiPh and sulfona-
mide. At 37 °C, the rate constant (kobs) for this reaction is 1.7(9)
× 10-4 s-1. This value is consistent with results from the
competition reaction described below (eq 2), since it is similar
to the value measured for hydroamination at this temperature
(1.4(9) × 10-3 s-1). Taken together, these trapping studies
suggest that a key step for hydroamination may involve a
platinum-mediated proton transfer.
t
µ-NH(SO2C6H4 Bu) ligands (vide infra). This trapping experi-
ment suggests that an intermediate in the hydroamination
catalysis is a coordination complex of the type [(tBu2-
bpy)Pt(NH2SO2C6H4tBu)OTf]+, which may be deprotonated to
give the observed µ-amido complex. However, it seemed
possible that other deprotonations, having nothing to do with
catalysis, might be responsible for deactivation of the catalyst.
Thus, additional proton traps with different chemical properties
were sought. In particular, it is of interest to develop non-
nucleophilic proton traps that react rapidly and irreversibly with
a Brønsted acid. In this regard, main group aryl compounds of
the type RnE-Ar are attractive candidates, since they may exhibit
high rates of E-aryl bond cleavage via reaction with a Brønsted
acid. For example, Sn-Ph and Si-Ph bonds undergo rapid E-Ph
bond cleavage in the presence of an acidic proton such as TfOH,
to give benzene and the corresponding E-OTf compound.46-48
Addition of a catalytic amount of 1 (5 mol %) to a 1:1:1
mixture of Me3SiPh, sulfonamide, and norbornene in chloro-
form-d gave only a small amount of hydroamination product
(10%) after 1 h at 25 °C. In addition, benzene (5%) and
Me3SiOTf (5%) were observed as products (by 1H and 19F NMR
spectroscopy, eq 2). Thus, the transfer of protons to Me3SiPh
inhibits the hydroamination and stoichiometrically deactivates
the catalyst. Furthermore, platinum complex 1 is required to
facilitate this proton transfer, since a mixture of Me3SiPh,
sulfonamide, and norbornene in chloroform-d remained un-
changed after 1 h. Under analogous conditions, the more reactive
proton acceptor Me3SnPh completely inhibited the hydroami-
nation, while undergoing partial (5%) conversion to benzene
and Me3SnOTf with stoichiometric deactivation of the catalyst
Investigation of the Active Form of the Catalyst: Observa-
tion of Sulfonamido (µ-NHSO2Ar) and Sulfonamide (NH2-
SO2Ar) Complexes. Further experiments were designed to probe
the active form of the catalyst and to define interactions of the
substrates with the bis(triflate) platinum complexes. Particular
attention focused on interaction of the sulfonamide with 1, since
the studies described above suggested that a key process might
involve proton transfer from coordinated amine to the olefin
substrate; therefore, the possible role of this process in the
catalysis was examined.
Addition of 5 mol % of the sterically hindered amine 2,6-
di-tert-butyl-4-methylpyridine to 5 mol % of 1, norbornene, and
sulfonamide in dichloromethane-d2 resulted in inhibition of
hydroamination, such that no product was observed after 2 days
at 65 °C. To isolate a metal complex from the reaction mixture,
diethyl ether vapor was allowed to diffuse into the reaction
solution. This resulted in formation of a small amount of a
crystalline product, identified by X-ray crystallography as 6
(Figure 4). The formation of 6 upon addition of a base to the
(46) Bott, R. W.; Earborn, C.; Greasley, P. M. J. Chem. Soc. 1964, 4804–
4806.
(47) Alvanipour, A.; Eaborn, C.; Walton, D. R. M. J. Organomet. Chem.
1980, 201, 233–247.
(48) Alizadeh, M. H.; Razavi, H.; Bamoharram, F. F.; Daneshvar, K. J.
Mol. Catal. A 2003, 206, 89–93.
9
16566 J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008

Hydroamination by Electrophilic Platinum Complexes
A R T I C L E S
Scheme 3. Platinum-Generated Acid Catalysis Mechanism via
Sulfonamide Coordination
of 8 with norbornene. Addition of norbornene (1-20 equiv) to
dichloromethane-d2 solutions of 8 resulted in no reaction (by
NMR spectroscopy), even after heating to 65 °C for 2 days.
Under catalytic conditions with 5 mol % loading of 8, no
hydroamination of norbornene by sulfonamide was observed
at 65 °C after 2 days. However, the addition of two equiv of
triflic acid to 8 (in CD2Cl2) provides a mixture that is
catalytically active, as determined by the further addition of
norbornene (20 equiv) and sulfonamide (20 equiv). Complete
conversion to product was observed after 1 h (37 °C).
Scheme 4. Platinum Sulfonamide and Sulfonamido Equilibrium
The formation of µ-sulfonamido complexes 6 and 8 upon
interaction of p-tBuC6H4SO2NH2 with a platinum complex
suggests that triflic acid might be produced simply by coordina-
tion of the sulfonamide to L2Pt(OTf)2. However, sulfonamides
are known to be extremely weak nucleophiles and are rarely
observed to function as ligands in metal complexes.49,50 To
investigate this possibility, the stoichiometric interaction of
p-tBuC6H4SO2NH2 with 1 in dichloromethane-d2 was examined.
At 25 °C, a 1:1 ratio of these compounds resulted in establish-
ment of an equilibrium between 1 and a new complex, assigned
as the adduct [(tBu2bpy)Pt(NH2SO2C6H4 Bu)(OTf)]OTf (9,
t
reaction mixture suggests that the catalytic cycle for hydroami-
nation involves a sulfonamide complex of platinum. This is
described by the proposed mechanism of Scheme 3, which is
consistent with the observed kinetics if proton transfer to
norbornene is reversible (vide infra). Coordination of the
sulfonamide to an electrophilic platinum center greatly increases
the acidity of the N-H protons, and the resulting complex may
be acidic enough to protonate the olefin and affect hydroamina-
tion.27,28 In the presence of a base, deprotonation of an
intermediate sulfonamide complex of this type could lead to an
intermediate sulfonamido complex (I), which could then dimer-
ize to give 6 (Scheme 4).
Scheme 4). Note that this adduct is represented as possessing a
Pt-NH2SO2Ar bond, but the coordination mode for the sulfona-
mide ligand has not been established. The formation of 9 is
indicated by the appearance of a new set of tBu2bpy resonances,
and new resonances for the coordinated sulfonamide. For this
equilibrium mixture, only one very broad signal is observed
for the NH2 protons, at 4.92 ppm, indicating rapid exchange
between the nitrogen-bound protons of free and coordinated
t
NH2SO2C6H4 Bu. The lack of an observable platinum hydride
resonance for the reaction mixture excludes the presence of a
direct product of N-H oxidative addition (as in Scheme 2).
1
After 1 d, no further change in the H NMR spectrum was
Dimeric 6 was also observed as the exclusive product in the
stoichiometric reaction of 1 with the sulfonamide in the presence
of 2,6-di-tert-butyl-4-methylpyridine at 25 °C (by NMR spec-
troscopy). However, it proved difficult to isolate 6 in large
quantities from such reactions because of its tendency to
cocrystallize with the byproduct pyridinium triflate. Fortunately,
an analogous, bridging µ-amido complex (8) was synthesized
in 86% yield from (tBu2bpy)PtCl2 (7), by addition of 7 to a
mixture of 1 equiv of sulfonamide and 2 equiv of LiB(C6F5)4
(eq 3). The isolated product was washed multiple times with
diethyl ether, to ensure complete removal of any acidic
impurities (via proton transfer from sulfonamide), and the purity
observed, and a Keq value of 1.18(5) was established. The
addition of excess sulfonamide (2-20 equiv) did not produce
another platinum-based species (e.g., a complex with two
sulfonamide ligands); instead, a new equilibrium between 1 and
9 was reestablished. Perturbations of the equilibrium as a
function of temperature were examined in chloroform-d to
determine the enthalpy of reaction. A van’t Hoff plot gave a
∆H° value of 4.2(7) kcal/mol and a ∆S ° value of 13.9(2) eu.
Finally, this equilibrium mixture was also produced upon
addition of 2 equiv of triflic acid to the µ-NHSO2Ar dimeric
complex 6. Attempts to isolate 9 from solutions obtained by
adding sulfonamide (1 equiv or a large excess) to 1 have not
been successful.
1
of 8 was supported by elemental analysis, and by H and 19F
NMR spectroscopy. The complete removal of Brønsted acids
from samples of the dimeric µ-amido complex was essential
for evaluation of the catalytic properties of this dimer, in the
absence of any acid which could act as catalyst.27,28
The platinum-sulfonamide interaction was further examined
by 195Pt NMR spectroscopy. For 1, the 195Pt NMR resonance
was observed at -1530 ppm (in dichloromethane-d2). Addition
Because µ-sulfonamido complexes may readily form under
the conditions for catalytic hydroamination, it was important
to establish whether such species are involved in the catalytic
cycle. This was investigated by examination of the interactions
(49) Beloso, I.; Castro, J.; Garcia-Vazquez, J. A.; Perez-Lourido, P.;
Romero, J.; Sousa, A. Polyhedron 2006, 25, 2673–2682.
(50) Ishiwata, K.; Kuwata, S.; Ikariya, T. Organometallics 2006, 25, 5847–
5849.
9
J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008 16567

A R T I C L E S
McBee et al.
of 1 equiv of 4-tert-butylbenzenesulfonamide led to a new,
additional resonance attributed to complex 9 (at -2010 ppm).
This equilibrium mixture was cooled to -60 °C, and its
Mechanism of Catalytic Hydroamination. The addition of
L2Pt(OTf)2 catalysts to a mixture of substrates clearly initiates
a proton-transfer process, as indicated by several lines of
evidence including the observed pKa cutoff for hydroamination,
the lack of dramatic ancillary ligand effects on the hydroami-
1
interaction with norbornene (20 equiv) was monitored by H
NMR spectroscopy. No new platinum species were observed
at this temperature, and hydroamination products were produced
(after 10 min). Monitoring the catalysis (5 mol % 1, dichlo-
romethane-d2, 25 °C) by 195Pt NMR spectroscopy revealed the
presence of a single platinum species (δ -1980) during the
reaction. This new resonance is not attributed to the dimeric
complex 6, which exhibits a 195Pt NMR resonance of -2024
ppm. It therefore seems possible that the resonance at -1980
ppm, associated with the resting state of the catalyst, is species
I of Scheme 3. With little additional spectroscopic evidence
for I, it is difficult to assign a specific structure to this species.
However, on the basis of the observed chemistry, it appears
nation rate, and the observed chemistry for L2Pt(OTf)2
+
sulfonamide mixtures. The kinetic behavior for this reaction
(first-order dependence on L2Pt(OTf)2 and sulfonamide con-
centrations; little dependence on norbornene concentration)
implies that the first step in the catalysis involves reversible
coordination of sulfonamide to platinum, and this process has
been observed as an equilibrium involving formation of the key
intermediate [L2Pt(NH2SO2C6H4 Bu)(OTf)]+. This intermediate
t
appears to be a potent Brønsted acid, as indicated by its
relatively rapid reactions with Me3SiPh, Me3SnPh and nor-
bornene. A mechanism that is consistent with these facts is
shown in Scheme 3, and a rate law derived from this mechanism
is shown in eq 5 (where [Pt]0 is the total concentration of Pt
species).51
t
that this is a Pt-NHSO2C6H4 Bu derivative, and we tentatively
formulate it as the neutral sulfonamido complex L2Pt-
t
(NHSO2C6H4 Bu)OTf. Attempts to independently generate I by
addition of bases (2,6-di-tert-butyl-4-methylpyridine and 2,6-
K1K2[sulfonamide]2[norbornene][Pt]0
di-tert-butyl-4-methylphenol) to the equilibrium mixture involv-
d[product]
1
ing 1 and 9 gave only 6 (by H and 195Pt NMR spectroscopy,
)
dt
[I] + K1K2[sulfonamide][norbornene]
Scheme 4). It is unclear why I is stable under catalytic conditions
but is not cleanly generated from 6 or 9 under other, noncatalytic
conditions. Clearly, this question would be easier to address
with a full characterization of I.
(5)
The observed kinetic behavior is consistent with reversible
proton transfer to norbornene, followed by rate-determining
attack of sulfonamide onto the norbornyl cation to produce an
ammonium cation. The latter species then forms product by
Additional experiments were designed to investigate the
possible role of platinum norbornene complexes in the hy-
droamination catalysis. As mentioned above, complex 1 cata-
lyzes the isomerization of norbornene to tricyclo(2.2.1.0(2,6))-
heptane (eq 1), and this result implies the existence of a transient
norbornene complex that was not observed during this catalysis.
However, addition of 20 equiv of norbornene to each of the
bis(triflate) complexes 1-5, in chloroform-d at 25 °C, did not
lead to an observable Pt-norbornene complex (over 24 h). In
each case, only resonances attributed to the bis(triflate) complex,
free norbornene and tricyclo(2.2.1.0(2,6))heptane were observed
t
delivering a proton to a Pt-NH(SO2C6H4 Bu) sulfonamido
intermediate (I), which appears to correspond to the resting state
of the catalyst. Although it has not been possible to fully
t
characterize I, its formulation as a Pt-NH(SO2C6H4 Bu) deriva-
tive seems chemically reasonable as the product of proton
transfer from a cationic sulfonamide complex. The difficulty
encountered with attempts to isolate I presumably relate to its
ready conversion to 6 or 9 under appropriate conditions (see
Scheme 4). The expression of eq 5 is consistent with the
observed kinetics, if one assumes that the accessible concentra-
tion range for the experiments are near those that correspond
to saturation in norbornene. Thus, the observed reaction order
in norbornene is low (ca. 0.2), and the reaction order in
sulfonamide is somewhat above 1 (1.1). Early in the reaction,
it is likely that K1K2[sulfonamide][norbornene] . [I] and the
rate law simplifies to d[product]/dt ≈ k3[Pt]0[sulfonamide]. To
the extent that this is not true, the full rate law of eq 5 would
apply, and some dependence on [norbornene] is to be expected.
1
1
(by H and 19F NMR spectroscopy). In addition, the H NMR
spectrum of a solution of 1 and 20 equiv norbornene in
dichloromethane-d2 at -60 °C contained no evidence for an
olefin adduct. Interestingly, these studies also show that 1-5
do not mediate an olefin-olefin coupling process to generate
triflic acid, as observed for (COD)Pt(OTf)2 by Szuromi and
Sharp.32
To further explore the potential role of bound alkene in
hydroamination chemistry, a more stable, cationic alkene
complex of platinum was investigated. This complex was
obtained by addition of 10 equiv of COD to 1 in dichlo-
romethane, which quantitatively produced 10 (eq 4). Excess
COD was removed from the compound by multiple washings
with pentane followed by extended drying under vacuum.
Addition of 5 mol % of 10 to COD and the sulfonamide afforded
no hydroamination products after 3 days at 100 °C. Similarily,
1 did not behave as a catalyst for the hydroamination of COD
(for 2 days in chloroform-d at 100 °C). These conditions led to
Conclusions
The results presented here demonstrate that platinum com-
plexes of the type L2Pt(OTf)2 catalyze hydroaminations of
norbornene via a metal-mediated proton transfer to the olefin
substrate. This work has important implications for interpretation
of results from catalytic reactions involving bond activations
mediated by electrophilic metal complexes and provides evi-
dence for one type of mechanism for a metal-mediated proton-
transfer catalytic reaction. Especially with further quantitative
studies that help define this reactivity, it should be possible to
design new processes that feature control of a metal center in
delivery of a proton within a catalytic cycle. The use of main
group aryl derivatives such as Me3SiPh and Me3SnPh as non-
1
the rapid formation of 10 (by H NMR spectroscopy).
(51) This analysis is based on the assumptions of conservation of charge
and total platinum concentration (see Supporting Information).
9
16568 J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008

Hydroamination by Electrophilic Platinum Complexes
A R T I C L E S
1
to prepare 1 (77.5% yield). H NMR (CD2Cl2, 400 MHz): δ 7.46
(d, J ) 8 Hz, 4H), 7.16 (d, J ) 8 Hz, 4H), 2.05 (s, 2H), 1.28 (s,
18H). 13C{1H} NMR (CD2Cl2, 125.8 MHz): δ 184.1, 165.0, 153.4,
143.0, 126.3, 122.3, 34.8, 31.0. 19F NMR (CD2Cl2, 376.5 MHz): δ
-77.6 (s, 6F). Anal. Calcd for C26H32N2F6O6PtS2: C, 37.10; H, 3.83;
N, 3.33 Found: C, 36.79; H, 3.92; N, 3.35.
nucleophilic proton traps, as reported here, is expected to provide
key mechanistic probes in such studies.
Experimental Section
General. Unless otherwise noted, all experiments were conducted
with dry, oxygen-free solvents using standard Schlenk techniques
or in an inert atmosphere glovebox. Deuterated solvents were
purchased from Cambridge Isotopes and dried with appropriate
drying agents. The compounds AgOTf, COD, triflic acid, and
LiB(C6F5)4 were obtained from Aldrich and used without further
purification. Norbornene was obtained from Aldrich and purified
by sublimation. The compound 4-n-butoxybenzenesulfonamide was
obtained from Ryan Scientific and used without further purification.
The compound p-tBuC6H4SO2NH2 was synthesized according to
literature procedure.52 All other amines were purchased from
Aldrich and liquid amines were dried over molecular sieves. The
starting materials (S-BINAP)PtCl2,53 (tBu2bpy)PtCl2 (7),54 [tBu-
C6H4NdC(CH3)C(CH3)dNC6H4tBu]PtCl2,55 [(C6H5)2PCH2CH2P(C6-
H5)2]Pt(OTf)2 (3),56 and [(C6F5)2PCH2CH2P(C6F5)2]PtCl257 were syn-
thesized according to literature procedures.
[[(C6F5)2PCH2CH2P(C6F5)2]Pt(OTf)2 (4). To 0.155 g of
[(C6F5)2PCH2CH2P(C6F5)2]PtCl2 (0.161 mmol) was added a solution
of 0.073 g of Me3SiOTf (0.322 mmol) in 10 mL CH2Cl2. The
reaction mixture was stirred for 1 h. The solvent was removed under
reduced pressure, and the resulting solid was washed three times
with 5 mL of pentane. The white powder was dried under reduced
pressure for 4 h. The powder was then recrystallized by vapor
diffusion of ether into a methylene chloride solution (0.062 g, 31%
yield). 1H NMR (CD2Cl2, 400 MHz): δ 2.31 (m, 4H). 31P{1H} NMR
(CD2Cl2, 161.9 MHz): δ 15.7 (1JPtP ) 4552 Hz). 19F NMR (CD2Cl2,
376.5 MHz): δ -78.8 (s, 6F), -127.3 (s, 8F), -144.3 (s, 4F),
-159.1 (s, 8F). Compound 4 has previously been generated in a
solution of TfOH.57
(S-BINAP)Pt(OTf)2 (5). Compound 5 was synthesized using a
procedure analogous to that used to prepare 1 (77.5% yield). H
1
Analytical Methods. Solution NMR spectroscopy was performed
using Bruker DRX-500 MHz, AV-500 MHz, AVQ-400 MHz,
AVB-400 MHz, or AV-300 MHz spectrometers. 1H NMR spectra
were calibrated internally with the resonance for the residual proteo
solvent relative to tetramethylsilane. 13C{1H} NMR spectra were
calibrated internally with the resonance for the solvent relative to
tetramethylsilane. 19F NMR spectra were referenced relative to a
hexafluorobenzene (δ ) -163) internal standard. 31P{1H} NMR
spectra were referenced relative to an 85% H3PO4 external standard
(δ ) 0). 195Pt NMR spectra were referenced relative to a Na2PtCl6
external standard (δ ) 0). FT-IR spectra were recorded for samples
as Nujol mulls on KBr plates using a Mattson FTIR 3000
spectrometer at a resolution of 4 cm-1. Elemental analyses were
performed by the College of Chemistry Microanalytical Laboratory
at the University of California, Berkeley. GC-MS was performed
using an Agilent Technologies 6890N GC system with an HP-5MS
column. Enantiomeric compositions were determined by HPLC
using a Daicel CHIRACEL OD column (4.6 mm × 250 mm) with
UV detection at 210 and 254 nm.
NMR (CD2Cl2, 400 MHz): δ 7.87 (br m, 4H), 7.71-7.63 (m, 12H),
7.45 (m, 6H), 7.12 (vt, J ) 7.6 Hz, 2H), 6.90 (br m, 4H), 6.61 (d,
J ) 8.8 Hz, 4H). 13C{1H} NMR (CD2Cl2, 125.8 MHz): δ 140.2(br),
135.5(br), 134.6, 134.4, 133.7, 133.5, 132.5, 132.0, 131.2(br),
130.6(br), 130.0(br), 129.5(br), 129.1, 128.7, 128.3, 128.2, 127.3,
127.1. 31P{1H} NMR: δ 0.0 (1JPtP ) 4219 Hz). 19F NMR (CD2Cl2,
376.5 MHz): δ -78.2 (s, 6F). Mp 230-240 °C (decomp). IR
(cm-1): 2727 (m), 2673 (m), 1584 (w), 1342 (s), 1192 (s), 984 (s),
742 (s), 694 (m), 631 (s), 525 (w). Anal. Calcd for C46-
H32F6O6P2PtS2: C, 49.51; H, 2.89; S, 5.75. Found: C, 49.19; H,
2.84; S, 6.05. Although 5 was previously synthesized,38 its
spectroscopic data was not reported.
[(tBu2bpy)Pt(µ-NHSO2C6H4 Bu)]2(OTf)2 (6). To 0.100 g of 1
t
(0.133 mmol) was added a solution of 0.030 g of 4-tert-butylben-
zenesulfonamide (0.141 mmol) and 0.035 g of 2,6-di-tert-butyl-4-
methylpyridine (0.140 mmol) in 10 mL of CH2Cl2. The reaction
mixture was stirred for 12 h. The solvent was removed under
reduced pressure, and the resulting precipitate was washed three
times with 10 mL of ether. The yellow powder was dried under
reduced pressure for 4 h (80% yield). Complete removal of
(tBu2bpy)Pt(OTf)2 (1). Compound 1 was synthesized using a
previously reported procedure.38,58 To 0.200 g of 7 (0.375 mmol)
was added a solution of 0.200 g of AgOTf (0.781 mmol) in 10 mL
of CH2Cl2. The reaction mixture was stirred for 1 h at room
temperature. The reaction mixture was filtered, and the solvent was
removed under reduced pressure. The resulting solid was washed
three times with 5 mL of pentane. The yellow powder was dried
1
protonated pyridine was unsuccessful. H NMR (CD2Cl2 with 2
equiv of 2,6-di-tert-butyl-4-methylpyridinium triflate, 400 MHz):
δ 11.90 (br s, 2H), 8.96 (d, J ) 6.4 Hz, 4H), 8.87 (d, J ) 8.8 Hz,
4H), 7.75 (s, 4H), 7.58 (d, J ) 6.4 Hz, 4H), 7.53 (s, 4H), 7.44 (d,
J ) 8.8 Hz, 4H), 2.64 (s, 6H), 1.57 (s, 36H), 1.44 (s, 36H), 1.40
(s, 18H). 19F NMR (CD2Cl2, 376.5 MHz): δ -77.7 (s, 12F). 195Pt
NMR (CD2Cl2, 85.9 MHz): δ -2024.
1
under reduced pressure for 4 h (96% yield). H NMR (CD2Cl2,
400 MHz): δ 8.66 (d, J ) 4.9 Hz, 2H), 7.89 (s, 2H), 7.69 (d, J )
4.9 Hz, 2H), 1.45 (s, 18H). 13C NMR (CD2Cl2, 125.8 MHz): δ
167.5, 157.0, 150.5, 124.8, 120.2, 119.6, 117.1, 29.8. 19F NMR
(CD2Cl2, 376.5 MHz): δ -77.5 (s, 6F). 195Pt NMR (CD2Cl2, 85.9
MHz): δ -1530. Anal. Calcd for C20H24N2F6O6PtS2: C, 31.54; H,
3.18; N, 3.68 Found: C, 31.35; H, 2.97; N, 3.62.
[(tBu2bpy)Pt(µ-NHSO2C6H4 Bu)]2[B(C6F5)4]2 (8). To 0.100 g
t
of 7 (0.187 mmol) was added a solution of 0.050 g of 4-tert-
butylbenzenesulfonamide (0.235 mmol) and 0.256 g of LiB(C6F5)4
(0.373 mmol) in 20 mL of CH2Cl2. The reaction mixture was stirred
for 1 h and then filtered. The solvent was then removed under
reduced pressure. The resulting solid was washed three times with
10 mL of ether. The yellow powder was dried under reduced
pressure for 4 h (86% yield). 1H NMR (CD2Cl2, 400 MHz): δ 8.32
(d, J ) 6.4 Hz, 2H), 8.00 (s, 2H), 7.80 (d, J ) 8.4 Hz, 2H), 7.65
(d, J ) 6.4 Hz, 2H), 7.56 (d, J ) 8.4 Hz, 2H), 5.03 (s, 1H), 1.47
(s, 18H), 1.36 (s, 9H). 13C{1H} NMR (CD2Cl2, 125.8 MHz): δ
169.0, 166.6, 159.9, 156.5, 155.8, 149.0(br), 148.5, 148.2, 147.1(br),
139.1, 137.2(br), 135.3(br), 134.3, 127.0, 125.8, 124.9, 121.1, 120.1,
35.9, 30.2, 29.4. 19F NMR (CD2Cl2, 376.5 MHz): δ -132.26,
-162.36, -166.23. Anal. Calcd for C52H38N3BF20O2PtS: C, 46.10;
H, 2.83; N, 3.10 Found: C, 45.34; H, 2.58; N, 2.42. 195Pt NMR
(CD2Cl2, 85.9 MHz): δ -2000.
[tBuC6H4NdC(CH3)C(CH3)dNC6H4 Bu]Pt(OTf)2 (2). Com-
t
pound 2 was synthesized using a procedure analogous to that used
(52) Morimoto, H.; Shimadzu, H.; Kushiyama, E.; Kawanishi, H.; Hosaka,
T.; Kawase, Y.; Yasuda, K.; Kikkawa, K.; Yamauchi-Kohno, R.;
Yamada, K. J. Med. Chem. 2001, 44, 3355–3368.
(53) Morandini, F.; Consiglio, G.; Piccolo, O. Inorg. Chim. Acta 1982,
57, 15–19.
(54) Egan, T. J.; Koch, K. R.; Swan, P. L.; Clarkson, C.; Van Schalkwyk,
D. A.; Smith, P. J. J. Med. Chem. 2004, 47, 2926–2934.
(55) Wong-Foy, A. G.; Henling, L. M.; Day, M.; Labinger, J. A.; Bercaw,
J. E. J. Mol. Catal. A 2002, 189, 3–16.
(56) Falls, S.; erson, G.; Rath, N. P. Organometallics 1991, 10, 3180–
3184.
Equilibrium mixture of 1, 9, and 4-tert-Butylbenzenesulfona-
mide. To 0.010 g of 1 (0.0133 mmol) was added a solution of
0.0034 g of 4-tert-butylbenzenesulfonamide (0.0133 mmol) in 1
mL of chloroform-d. The reaction mixture was left for 1 day to
(57) Merwin, R. K.; Schnabel, R. C.; Koola, J. D.; Roddick, D. M.
Organometallics 1992, 11, 2972–2978.
(58) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J. J. Chem. Soc., Dalton
Trans. 1996, 1809–1813.
9
J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008 16569

A R T I C L E S
McBee et al.
Table 3. Summary of Crystallographic Data for Compounds 1, 5, and 6
1
5
6
formula
MW
C20H24F6N2O6PtS2
761.62
C50H42F6O7P2Pt2S2
1190.00
C59H78Cl2F6N6O10Pt2S4
1734.6
temperature (K)
crystal color, habit
crystal dimensions
150
153
141
colorless, block
0.04 × 0.04 ×
0.03 mm3
colorless, block
0.04 × 0.04 ×
0.03 mm3
yellow, block
0.05 × 0.04 ×
0.03 mm3
crystal system
2θ range
monoclinic
orthorhombic
triclinic
3.56 < 2θ < 52.74
a ) 19.903(3) Å
b ) 14.063(2) Å
c ) 19.279(3) Å
ꢀ ) 100.987(2)°
V ) 5297.3(14) Å3
3.08 < 2θ < 49.42
a ) 12.5853(8) Å
b ) 15.7440(10) Å
c ) 24.1309(17) Å
V ) 4781.4(5) Å3
2.58 < 2θ < 49.54
a ) 11.779(3) Å
b ) 16.296(4) Å
c ) 20.316(8) Å
R ) 100.69(3)°
ꢀ ) 100.84(3)°
γ ) 96.14(2)°
V ) 3613.7(19) Å3
lattice parameters
j
P1
2
space group
Z value
Dcalc
scan type
no. reflns measd
I2/a
8
P212121
4
1.910 g/cm3
ω (0.3° per frame)
total 14794
unique 5339
(Rint ) 0.0472)
Lorentz polarization
Abs (Tmax ) 0.846,
Tmin ) 0.801)
full-matrix least-squares
5339 [I > 2σ(I)]
334
1.650 g/cm3
ω (0.3° per frame)
total 24173
1.594 g/cm3
ω (0.3° per frame)
total 20696
unique 8109
(Rint ) 0.0486)
Lorentz polarization
Abs (Tmax ) 0.913,
Tmin ) 0.881)
full-matrix least-squares
8109 [I > 2σ(I)]
613
unique 12158
(Rint ) 0.0158)
Lorentz polarization
Abs (Tmax ) 0.886,
Tmin ) 0.820)
full-matrix least-squares
12158 [I > 2σ(I)]
811
corrections
refinement
no. reflns obsd
no. variables
R; Rw; Rall
GOF
0.037; 0.069; 0.072
0.788
0.031; 0.062; 0.063
1.018
0.039; 0.109; 0.114
1.035
max peak in final diff map
min peak in final diff map
3.026
-1.092
1.070
-0.429
2.414
-1.005
1
ensure no further changes in the concentrations. For 9: H NMR
(CDCl3, 500 MHz): δ 9.10 (d, J ) 6.4 Hz, 2H, ArH), 8.17 (d, J )
8.4 Hz, 2H, SO2ArH 9), 8.02 (s, 2H, ArH), 7.86 (overlapping with
resonance for SO2ArH, 4H, ArH), 7.76 (d, J ) 8.4 Hz, 2H,
SO2ArH), 4.92 (br s, 2H), 1.51 (s, 36H, CH3C overlapping with
resonance for the CH3C of 1), 1.40 (s, 9H, CH3C). For 1: 1H NMR
(CDCl3, 500 MHz): δ 8.53 (d, J ) 6.4 Hz, 2H, ArH), 7.98 (s, 2H,
ArH), 7.79 (d, J ) 6.4 Hz, 2H, ArH), 1.51 (s, 36H, CH3C
overlapping with resonance for the CH3C of 9). For 4-tert-
Hz, 2H), 7.55 (d, J ) 6.8 Hz, 2H), 1.35 (s, 9H). 13C{1H} NMR
(CD2Cl2, 125.8 MHz): δ 156.6, 139.0, 126.1, 126.0, 30.7. 2H NMR
(CDCl3, 76.7 MHz): δ 4.61 (s).
General Procedure for Catalytic Runs. Reactions occurred in
5 mm NMR tubes equipped with J. Young Teflon screw caps.
Temperature-controlled oil baths were utilized for heating. A
solution of 0.106 mmol of olefin and 0.106 mmol of amine was
prepared in 1 mL of 1,2-dichloroethane. To this solution was added
0.005 mmol of catalyst. The progress of the reaction was monitored
by 1H NMR spectroscopy (0.05 mL cyclohexane-d12 was added in
order to obtain a lock signal). Once no further spectral change was
observed by NMR, the solution was passed through silica to isolate
the substrate or product. Identities of the organic products were
confirmed by 1H NMR spectroscopy59,60 and GC-MS. All kinetic
data was collected on a Bruker DRX-500 MHz spectrometer and
an internal standard, 5.0 mg (0.0250 mmol) of bis(p-fluorophe-
nyl)methane, was used. For kinetic runs, the sample was placed in
an NMR probe preheated to 310.4 K and calibrated using an
external methanol standard.61 Single-scan spectra were obtained
using an automated acquisition program that was started im-
mediately after placing the sample in the probe, and the peaks were
integrated relative to the internal standard.
1
butylbenzenesulfonamide: H NMR (CDCl3, 500 MHz): δ 7.86
(overlapping m, 4H, SO2ArH and ArH, 9), 7.58 (d, J ) 8.4 Hz,
2H, SO2ArH), 4.92 (br s, 2H), 1.35 (s, 9H, CH3CArSO2). 195Pt NMR
(CD2Cl2, 85.9 MHz): δ -2010, -1530. 19F NMR (CD2Cl2, 376.5
MHz): δ -75.9, -78.0.
[(tBu2bpy)Pt(COD)](OTf)2 (10). To 0.050 g of 1 (0.066 mmol)
was added a solution of 0.010 g of COD (0.092 mmol) in 5 mL
of CH2Cl2. The reaction mixture was stirred for 2 h. The solvent
was then removed under reduced pressure and the resulting solid
was washed three times with 5 mL of pentane. The yellow pow-
1
der was dried under reduced pressure for 24 h (95% yield). H
NMR (CDCl3, 500 MHz): δ 8.25 (d, J ) 4 Hz, 2H), 8.10 (s, 2H),
7.77 (d, J ) 4 Hz, 2H), 6.33 (br t, 4H), 3.12 (d, J ) 6.8 Hz, 4H),
2.62 (d, J ) 6.8 Hz, 4H), 1.47 (s, 18H). 19F NMR (CDCl3, 376.5
MHz): δ -79.2. 13C{1H} NMR (CDCl3, 125.8 MHz): δ 167.2,
157.0, 150.9, 128.3, 124.9, 119.9, 36.3, 30.1. Anal. Calcd for
C28H36N2F6O6PtS2: C, 38.66; H, 4.17; N, 3.22 Found: C, 38.51; H,
4.11; N, 2.94.
General Considerations for X-ray Structure Determinations.
The X-ray analyses of compounds 1, 5, and 6 were carried out at
UC Berkeley CHEXRAY crystallographic facility. Measurements
were made on Bruker SMART CCD area detector with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). Data were
integrated by the program SAINT and analyzed for agreement using
XPREP. Empirical absorption corrections were made using SAD-
4-tert-butylbenzenesulfonamide-d2. To 1.00 g of 4-tert-butyl-
benzenesulfonamide in 5 mL of diethyl ether was added 3 mL of
D2O. The reaction mixture was left to stir for 24 h. The solvent
was removed under reduced pressure, and the resulting product was
treated three more times with the ether/D2O mixture. After the last
removal of solvent, the product was dissolved in diethyl ether and
1.00 g of MgSO4. After 4 h, the solution was filtered, and the solvent
was removed under reduced pressure (96% yield, 95% deuterium
(59) Ackermann, L.; Kaspar, L. T.; Gscheri, C. J. Org. Lett. 2004, 6, 2515–
2518.
(60) Fleming, I.; Frackenpohl, J.; Ila, H. J. Chem. Soc., Perkin Trans. 1
1998, 1229–1236.
(61) Ammann, C.; Meier, P.; Merbach, A. E. J. Magn. Reson. 1982, 46,
1
incorporation). H NMR (CDCl3, 500 MHz): δ 7.87 (d, J ) 6.8
319–321.
9
16570 J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008

Hydroamination by Electrophilic Platinum Complexes
A R T I C L E S
ABS. Structures were solved by direct methods and expanded using
Fourier techniques. All calculations were performed using the
SHELXTL crystallographic package. Selected crystal structure and
refinement data can be found in Table 3.
ether into the catalytic run solution of methylene chloride at -35
j
°C. The compound crystallizes in the triclinic space group P1 with
two molecules in the asymmetric unit and one molecule of
methylene chloride.
X-ray Structure Determination of 1. X-ray quality crystals of
1 formed upon slow vapor diffusion of ether into a methylene
chloride solution of 1 at -35 °C. The compound crystallizes in the
monoclinic space group I2/a with one molecule in the asymmetric
unit.
X-ray Structure Determination of 5. X-ray quality crystals of
5 formed upon slow vapor diffusion of ether into a methylene
chloride solution of 5 at -35 °C. The compound crystallizes in the
orthorhombic chiral space group P212121 with one molecule of ether
and one molecule of 5 in the asymmetric unit. The enantiomorph
of the space group and enantiomer of the molecule were determined
by inspection of Friedel pairs of reflections followed by comparison
of least-squares refinements. The results were unequivocally in favor
of the enantiomorph reported.
Acknowledgment. We thank Herman van Halbeek for NMR
assistance and Dr. Fred Hollander and Dr. Allen Oliver for
assistance with X-ray crystallography. This work was supported
by the Director, Office of Energy Research, Office of Basic Energy
Sciences, Chemical Sciences Division of U.S. Department of Energy
under Contract No. DE-AC02-05CH11231.
Supporting Information Available: Kinetic analysis, text
describing complete X-ray experimental details and X-ray
crystallographic data for 1, 5, and 6 in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.
org.
X-ray Structure Determination of 6. X-ray quality crystals of
6 were isolated from a catalytic run by slow vapor diffusion of
JA8030104
9
J. AM. CHEM. SOC. VOL. 130, NO. 49, 2008 16571