Platinum(II) complexes containing quaternized nitrogen ligands: Synthesis, stability, and evaluation as catalysts for methane and benzene H/D exchange

Article abstract of DOI:10.1021/om900889k

This paper describes an efficient synthesis of the cationic platinum complex [(N-CH₃-bpym)PtCl₂]⁺ (N-CH ₃-bpym = N-methylbipyrimidinium) and evaluation of its catalytic activity in H/D exchange reactions of CH

Full text of DOI:10.1021/om900889k

Organometallics 2010, 29, 257–262 257
DOI: 10.1021/om900889k
Platinum(II) Complexes Containing Quaternized Nitrogen Ligands:
Synthesis, Stability, and Evaluation as Catalysts for Methane and
Benzene H/D Exchange
Janette M. Villalobos, Amanda J. Hickman, and Melanie S. Sanford*
Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor,
Michigan 48109
Received October 12, 2009
This paper describes an efficient synthesis of the cationic platinum complex [(N-CH3-bpym)PtCl2]þ
(N-CH3-bpym=N-methylbipyrimidinium) and evaluation of its catalytic activity in H/D exchange
reactions of CH4 (with D2SO4) and benzene (with CF3CO2D). With both substrates [(N-CH3-bpym)
PtCl2]þ shows C-H activation reactivity comparable to that of its neutral analogue (bpym)PtCl2
(bpym=bipyrimidine). The origin of this similar reactivity is proposed to be the in situ formation of
the same active catalyst in both cases.
The development of direct, efficient, and selective catalysts
for the oxygenation of hydrocarbons continues to be a great
challenge in organometallic chemistry.1 Advances in this
field could significantly impact the synthesis of fuels, com-
modity chemicals, and pharmaceuticals. In 1972, Shilov
demonstrated the use of Pt salts to catalyze the oxidation
of CH4 to CH3OH in water under mild conditions,2 and this
seminal discovery sparked tremendous research effort in the
area of Pt-catalyzed C-H bond oxidation.3
Scheme 1. Oxidation of CH4 to CH3OSO2H Catalyzed by 1
The best Pt-based CH4 oxidation process to date involves the
conversion of methane to methyl bisulfate in fuming H2SO4
with (bpym)PtCl2 (1; bpym=2,2-bipyrimidine) as a precatalyst
(Scheme 1).4,5 The cationic complex [(N-H-bpym)Pt(X)2]þ (2;
X=Cl, OSO3H)6 is believed to form in situ under the highly
acidic reaction conditions and has been proposed as the active
catalyst (Scheme 1). Computational studies6,7 suggest that this
protonation is critical for limiting oxidative catalyst degrada-
tion and increasing the electrophilicity of the Pt center (and
thereby its reactivity with CH4). However, these effects have
proven difficult to study experimentally, due to the challenges
of working in fuming H2SO4 and the multiple accessible
protonation states and X-type ligands in this medium. As such,
the exact nature of the active catalyst remains the subject of
some debate.8 Additionally, the limited experimental under-
standing of the effects of protonation on reactivity has hindered
further catalyst development, which is required to render this
methane oxidation process commercially viable.
*To whom correspondence should be addressed. E-mail: mssanfor@
umich.edu.
(1) For select pertinent reviews, see: (a) Shilov, A. E.; Shul’pin, G. B.
Chem. Rev. 1997, 97, 2879. (b) Labinger, J. A.; Bercaw, J. E. Nature 2002,
417, 507. (c) Dick, A. R.; Sanford, M. S. Tetrahedron 2006, 62, 2439.
(d) Godula, K.; Sames, D. Science 2006, 312, 67. (e) Bergman, R. G. Nature
2007, 446, 391. (f) Hermans, I.; Spier, E. S.; Neuenschwander, U.; Turra, N.;
Baiker, A. Top. Catal. 2009, 52, 1162.
In an effort to address these challenges, we aimed to replace
bpym with the cationic quaternized nitrogen-coþntaining ligand
N-methyl-2,20-bipyrimidininum (N-CH3-bpym ). Quaternary
(2) Gol’dshleger, N. F.; Eskova, V. V.; Shilov, A. E.; Shteinman,
A. A. Zh. Fiz. Khim. 1972, 46, 1353.
(3) For select pertinent reviews, see: (a) Stahl, S. S.; Labinger, J. A.;
Bercaw, J. E. Angew. Chem., Int. Ed. 1998, 37, 2181. (b) Lersch, M.; Tilset,
M. Chem. Rev. 2005, 105, 2471. (c) Fekl, U.; Goldberg, K. I. Adv. Inorg.
Chem. 2003, 54, 259. (d) Conley, B. L.; Tenn, W. J.; Young, K. J. H.; Ganesh,
S. K.; Meier, S. K.; Ziatdinov, V. R.; Mironov, O.; Oxgaard, J.; Gonzales, J.;
Goddard, W. A.; Periana, R. A. J. Mol. Catal. A 2006, 251, 8.
(4) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.;
Fujii, H. Science 1998, 280, 560.
(5) For second-generation versions of analogous catalyst systems,
see: (a) Cheng, J.; Li, Z.; Haught, M.; Tang, Y. Chem. Commun. 2006,
4617. (b) Palkovits, R.; Antonietti, M.; Kuhn, P.; Thomas, A.; Sch€uth, F.
Angew. Chem., Int. Ed. 2009, 48, 6909.
(8) (a) Gilbert, T. M.; Hristov, I.; Ziegler, T. Organometallics 2001,
20, 1183. (b) Hristov, I. H.; Ziegler, T. Organometallics 2003, 22, 1668.
(9) Black, M. L. J. Phys. Chem. 1955, 59, 670.
(10) For examples of other metal complexes containing ligands with
quaternized nitrogen substituents, see: (a) Johnson, C. R.; Shepherd,
R. E. Inorg. Chem. 1983, 22, 2439. (b) Wishart, J. F.; Bino, A.; Taube, H.
Inorg. Chem. 1986, 25, 3318. (c) Kaim, W.; Matheis, W. Chem. Ber. 1990,
123, 1323. (d) Matheis, W.; Kaim, W. J. Chem. Soc., Faraday Trans. 1990,
86, 3337. (e) Matheis, W.; Poppe, J.; Kaim, W.; Zaliz, S. J. Chem. Soc.,
€
(6) (a) Kua, J.; Xu, X.; Periana, R. A.; Goddard, W. A. Organome-
tallics 2002, 21, 511. (b) Xu, X.; Kua, J.; Periana, R. A.; Goddard, W. A.
Organometallics 2003, 22, 2057. (c) Ahlquist, M.; Periana, R. A.; Goddard,
W. A. Chem. Commun. 2009, 2373.
Perkin Trans. 2 1994, 1923. (f) Waldhor, E.; Kaim, W.; Olabe, J. A.; Slep,
L. D.; Fiedler, J. Inorg. Chem. 1997, 36, 2969. (g) Coe, B. J.; Chamberlain,
M. C.; Essex-Lopresti, J. P.; Gaines, S.; Jeffery, J. C.; Houbrechts, S.;
Persoons, A. Inorg. Chem. 1997, 36, 3284. (h) Fujihara, T.; Wada, T.;
Tanaka, K. Inorg. Chim. Acta 2004, 357, 1205.
(7) Paul, A.; Musgrave, C. B. Organometallics 2007, 26, 793.
r
2009 American Chemical Society
Published on Web 12/15/2009
pubs.acs.org/Organometallics

258 Organometallics, Vol. 29, No. 1, 2010
Scheme 2. Methane Oxidation with Proposed Catalyst A12
Villalobos et al.
Figure 1. pKa of N-methylisonicotinic acid.
Figure 3. X-ray structure of the complex 4-PF6 (PF6 counterion
omitted for clarity).
of additional experiments implicated [(bpym)Pt-
(DMSO)Cl][CH3OSO3] (4-CH3OSO3) as the structure of
this product. First, elemental analysis was consistent with
4-CH3OSO3, but not with 3. Second, electrospray mass
spectrometry showed an [Mþ] peak at m/z 466, consistent
with [(bpym)Pt(DMSO)Cl]þ and not [(N-CH3-bpym)-
PtCl2]þ ([Mþ] at m/z 438). Third, no NOE enhancement of
any of the bpym protons was observed upon irradiation of
the CH3 resonance at 3.36 ppm (originally assigned as the
N-methyl group of 3).12 In structure 3, this group should be
in close proximity to H4. Finally, reaction of the product with
Figure 2. PtII complexes compared in this study.
nitrogen substituents are highly electron withdrawing; for
example, the pKa of N-methylisonicotinic acid (Figure 1) is
1.72, which corresponds to a Hammett σpara value of 2.47 for
the N-CH3 group.9,10 We anticipated that the cationic PtII N-
CH3-bpymþ complex 3 (Figure 2) would possess electronic
properties similar to those of 2 but would be accessible in the
4,6
absence of strong acids such as fuming H2SO4 or HF/
1
SbF6.11 This paper describes studies on the synthesis, char-
acterization, stability, and C-H activation reactivity of com-
plex 3 and its analogues.
NaPF6 led to disappearance of the H NMR signal at 3.36
ppm, consistent with ion exchange to form the hexafluor-
ophosphate salt [(bpym)Pt(DMSO)Cl]PF6 (4-PF6) (eq 2).
The structure of 4-PF6 was confirmed by elemental analysis
and X-ray crystallography (Figure 3).
Results and Discussion
Our initial investigations focused on reproducing the
literature synthesis of [(N-CH3-bpym)PtCl2][HSO4] (3),12
a reported intermediate in the preparation of [(N-CH3-
bpym)PtCl2][H4PV2Mo10O40] (A) (Scheme 2). Complex A
exhibits modest activity for the aerobic oxidation of
CH4 to a mixture of CH3OH, HCHO, and CH3CHO
under mild conditions (50 °C, 30 bar of CH4, and 2 bar
of O2 in acidic H2O) (Scheme 2). The reaction conditions
and the product distribution differ substantially from CH4
oxidation reactions with precatalyst 1, and this unusual re-
activity was originally attributed to the presence of the poly-
oxometalate counterion. Surprisingly, possible contributions
from the alkylation of the bipyrimidine ring were not dis-
cussed; furthermore, the catalytic activity of the proposed
precursor 3 was not evaluated.
The literature procedure for the synthesis of 3 involved
methylation of (bpym)PtCl2 (1) with (CH3)2SO4 in dimethyl
sulfoxide (DMSO) (eq 1).12 In our hands, this reaction
provided a compound with identical 1H and 13C NMR
spectra to those in the literature report. However, a variety
An alternate route to 3 was next explored via metalation of
N-methylbipyrimidinium [(N-CH3-bpym)]BF4. However,
13
treatment of (DMSO)2PtCl2 with [(N-CH3-bpym)]BF4 in
(11) Seidel, S.; Seppelt, K. Inorg. Chem. 2003, 42, 3846.
(12) Bar-Nahum, I.; Khenkin, A. M.; Neumann, R. J. Am. Chem.
Soc. 2004, 126, 10236.
(13) Price, J. H.; Williamson, A. N; Schramm, R. F.; Wayland, B. B.
Inorg. Chem. 1972, 11, 1280.

Article
Organometallics, Vol. 29, No. 1, 2010 259
Figure 4. X-ray structure of complex 6.
methanol at 60 °C did not afford the desired complex.
Instead, metalation proceeded with concomitant addition
of CH3OH into the ligand to provide the neutral complex
(2-(4-methoxy-3-methyl-4,5-dihydropyrimidin-2-yl)pyrimi-
1
dine)PtCl2 (5) in 86% yield (eq 3). The H and 13C NMR
spectra of 5 show signals consistent with loss of aromaticity in
1
one ring of the bpym; for example, upfield H NMR reso-
nances at 5.49 and 5.69 ppm are observed for H4 and H5,
respectively. Crystals of 5 were obtained by diffusion of Et2O
into a solution of 5 in wet CH3CN. This led to substitution of
the OCH3 for an OH group to form complex 6 (eq 4), which
was characterized by X-ray crystallography (Figure 4).
Figure 5. Turnover numbers (TON’s) for H/D exchange be-
tween C6H6 and TFA-d catalyzed by 1 and 3. Conditions: PtII
catalyst (2 mol %, 5 μmol), benzene (23.2 μL, 0.26 mmol),
AgOAc (1 equiv, 0.85 mg, 5 μmol; 2 equiv, 1.7 mg, 10 μmol) in
TFA-d (0.5 mL, 6.5 mmol, 25 equiv relative to benzene) at 75 or
150 °C for 2 or 24 h. Reported TON’s are the average of at least
two trials.
protonation of 1 to afford cationic complex 2 should be
significantly less favorable than in more strongly acidic
media typically employed in methane oxidation.14-16 Our
group has recently developed a procedure to directly com-
pare Pt catalysts for H/D exchange between C6H6 and
TFA-d.17,18 Thus, precatalysts 1 and 3 were evaluated under our
standard conditions (2 mol % [Pt], 4 mol % AgOAc, 0.5 M
C6H6 in TFA-d at 75 and 150 °C) after 2 and 24 h. The extent
of H/D exchange was assayed by GCMS,18 and the data are
summarized in Figure 5. Interestingly, 1 and 3 provided very
similar TON’s under all conditions examined. In both cases,
very little H/D exchange activity was observed at 75 °C, even
after 24 h (TON values after 24 h are 19 and 15, respectively,
for 1 and 3). Both showed higher activity at 150 °C, with
similar TON values (202 and 187 after 24 h) and turnover
frequencies (TOF = 0.8 and 0.3 min-1 after 2 h) at this
temperature.
We hypothesized that 3 could be accessed from 5 via
protonation of the CH3O group followed by loss of CH3OH.
Gratifyingly, dissolving complex 5 in trifluoroacetic acid-d
(TFA-d) led to instantaneous formation of a new inorganic
species with concomitant release of 1 equiv of CH3OD
(which was converted in situ to CF3CO2CH3) (eq 5). The
1H and 13C NMR resonances associated with the new
complex (3) are shifted significantly downfield relative to
those of 5. For example, while the ligand proton resonances
for 5 appear between 9.84 and 5.49 ppm, those in the product
appear between 10.6 and 8.0 ppm. Similarly, in the 13C NMR
spectrum of 3, six aromatic resonances are observed between
162.7 and 158.6 ppm, while the starting material 5 shows
six peaks between 161.9 and 123.9 ppm. These data are all
fully consistent with aromatization of the N-CH3-bpymþ
ligand to form 3.
To gain insights into the similar reactivities of 1 and 3 in
C6H6/TFA-d H/D exchange, we probed the structure of the
active Pt catalyst in both systems. We have previously
demonstrated that complex 1 reacts rapidly with AgOAc in
TFA-d to form (bpym)Pt(TFA)2 (8; TFA = O2CCF3).18
(15) Ernst, S.; Kaim, W. J. Am. Chem. Soc. 1986, 108, 3578.
(16) Negligible H/D exchange was observed between CH4 and TFA-d
with precatalyst 1 or 3.
(17) (a) Hodges, R. J.; Webster, D. E.; Wells, P. B. J. Chem. Soc.,
Chem. Commun. 1971, 462. (b) Hodges, R. J.; Webster, D. E.; Wells, P. B.
J. Chem. Soc. A 1971, 3230. (c) Hodges, R. J.; Webster, D. E.; Wells, P. B.
J. Chem. Soc., Dalton Trans. 1972, 2571. (d) Gerdes, G.; Chen, P.
Organometallics 2004, 23, 3031. (e) Ziatdinov, V. R.; Oxgaard, J.; Mironov,
O. A.; Young, K. J. H.; Goddard, W. A.; Periana, R. A. J. Am. Chem. Soc.
2006, 128, 7404. (f) Kloek, S. M.; Goldberg, K. I. J. Am. Chem. Soc. 2007,
129, 3460.
Having generated the desired complex in trifluoroacetic
acid, we next examined the C-H activation reactivity of 1
and 3 (generated in situ from 5) in TFA-d. In this solvent, the
(14) Keq for protonation of coordinated bpym in TFA should be
greater than 2 orders of magnitude lower than in H2SO4. The pKa of
H2SO4 is -3, while the pKa of trifluoroacetic acid is -0.3 in H2O.
(18) Hickman, A. J.; Villalobos, J. M.; Sanford, M. S. Organometal-
lics 2009, 28, 5316.

260 Organometallics, Vol. 29, No. 1, 2010
Villalobos et al.
Similarly, dissolving 5 in TFA-d at room temperature in the
presence of 2 equiv of AgOAc led to the formation of a single
detectable organometallic product, along with release of 1
equiv of CF3CO2CH3 and 2 equiv of AcOD. On the basis of
the stoichiometry of organic byproducts as well as the
observed 1H and 13C NMR resonances (which show an un-
symmetrical species in which the N-methyl group is intact),18
this new complex is proposed to be [(N-CH3-bpym)Pt-
(TFA)2](TFA) (7) (eq 6).
Heating 7 at 150 °C for 15 min in TFA-d in a flame-sealed
NMR tube resulted in complete disappearance of its dia-
gnostic 1H NMR resonances and concomitant formation of
symmetrical (bpym)Pt(TFA)2 (8) along with 1 equiv of
CF3CO2CH3 (eq 7).18 This result indicates that nucleophilic
demethylation of the N-CH3-bpymþ ligand is very fast under
the H/D exchange conditions. Although demethylation was
slower at 75 °C, significant (∼30%) decomposition of 7 to 8
was observed after 24 h even at this temperature.19 In sum,
these data indicate that 7 readily decomposes to 8 at elevated
temperatures in TFA-d. On this basis, we hypothesize that
the similar H/D exchange reactivity of 1 and 3 is likely due to
the generation of the same active catalyst, 8, under the
reaction conditions.
Figure 6. Turnover numbers for H/D exchange between CH4
and D2SO4 catalyzed by 1, 3, and 4. Conditions: PtII catalyst
(1 mol %, 20 μmol), CH4 (∼13 bar, 2.0 mmol, 1 equiv), D2SO4
(1 mL, 20 mmol, 10 equiv) at 200 °C for 24 h. Reported TON’s
are the average of two trials.
bpym under these conditions. Investigation of the active
1
catalyst in D2SO4 by H NMR spectroscopy is consistent
with rapid demethylation of 1 (see the Supporting In-
formation). Therefore, it is likely that both 1 and 3 are
converted to the N-protonated species 2 in situ; however, we
were unable to definitively characterize the active species in
sulfuric acid.4,6,7
We next examined the catalytic activity of 1, 3 (generated
in situ from 5),20 and 4 in the H/D exchange between CH4
and D2SO4, which serves as a direct assay for methane C-H
activation. The three catalysts were compared under a
standard set of conditions (1 mol % of [Pt], 2 mmol of
CH4, 1 mL of D2SO4, 200 °C, 24 h).4,21 The headspace gases
were analyzed by GCMS, and the distribution of CDnH4-n
isotopologues was determined using a published worksheet
(see the Supporting Information).22 As summarized in
Figure 6, turnover numbers (TON’s)23 of 193, 208, and 151
were obtained with 1, 3, and 4, respectively.24 The similarity
between the TON’s for 1 and 3 suggests that the N-methylated
ligand does not offer a significant advantage over simple
Conclusions
In conclusion, we have developed a new, efficient synthetic
route to [(N-CH3-bpym)PtCl2]þ (3). Complex 3 catalyzes H/D
exchange between D2SO4 and CH4 as well as between
CF3CO2D and C6H6 with turnover numbers similar to those
for (bpym)Pt(Cl)2 (1). In both cases, the similar reactivities are
proposed to result from in situ demethylation of the
N-CH3-bpymþ precatalyst. These results indicate that more
stable ligands are needed to definitively study the influence of
quaternized nitrogen substituents on Pt C-H activation
catalysts. The preparation of such ligands and their applica-
tion in arene and alkane H/D exchange and oxidation reac-
tions is currently underway in our laboratory and will be
reported in due course.
(19) Complex 8 was also the sole inorganic product observed when 1
was heated to 150 °C for 15 min in TFA-d in the presence of 2 equiv of
AgOAc.
(20) Complex 3 is expected to be generated in situ by protonation of
the OCH3 group by D2SO4 followed by an SN1 reaction to aromatize the
N-CH3-bpymþ ligand.
(21) Young, K. J. H.; Meier, S. K.; Gonzales, J. M.; Oxgaard, J.;
Goddard, W. A.; Periana, R. A. Organometallics 2006, 25, 4734.
(22) Notably, under these conditions, all three of the catalytic reac-
tion solutions remained homogeneous, and no Pt black or other
precipitate was observed after 24 h.
(23) Turnover numbers were calculated as mol of D incorporated per
mol of catalyst minus the background D incorporation in the absence of
catalyst.
(24) The moderately lower reactivity of 4 versus that of 1 suggests that
the DMSO may inhibit H/D exchange.
Experimental Section
General Procedures. 1H and 13C NMR spectra were recorded
on Varian Inova 500 or 400 MHz NMR spectrometers with the
residual solvent peak (CDCl3: 1H 7.27 ppm, 13C 77.23 ppm) as
the internal reference unless otherwise noted. Chemical shifts
are reported in parts per million (ppm) (δ). Multiplicities are
reported as follows: br (broad resonance), s (singlet), t (triplet),
q (quartet), d (doublet), m (multiplet), app (apparent). Coupling
constants (J) are reported in Hz. Infrared (IR) spectroscopy was
performed on a Perkin-Elmer FTIR. Peaks are reported in

Article
Organometallics, Vol. 29, No. 1, 2010 261
cm-1. Elemental analyses were performed by Atlantic Microlab,
Inc., Norcross, GA.
[N-Me(bpym)]BF4. Under N2, bipyrimidine (bpym) (100 mg,
0.63 mmol, 1.0 equiv) was dissolved in CH2Cl2 (13 mL, dried
over 4 A molecular sieves). The mixture was cooled to -5 °C in
˚
Materials and Methods. Dichloromethane (CH2Cl2), dime-
thyl sulfoxide (DMSO), and methanol (CH3OH) were pur-
chased from Aldrich and used as received unless otherwise
noted. Diethyl ether (Et2O), ethyl acetate (EtOAc), and aceto-
nitrile (MeCN) were obtained from EM Science and used as
purchased. Ethanol (EtOH), 200 proof, was obtained from
Deacon Laboratories, Inc., and used as received. Celite was
purchased from EM Science. Silver acetate (AgOAc), Me2SO4,
NaPF6, bipyrimidine (bpym), and [Me3O]BF4 were purchased
from Aldrich. (DMSO)2PtCl2 was prepared according to a litera-
ture procedure.25 D2SO4 and CF3CO2D (TFA-d) were purchased
from Cambridge Isotopes Lab in 10 g ampules and were stored in
Schlenk tubes under N2. Ultrahigh-purity methane gas was obtain
from Airgas, Inc. Stock solutions of AgOAc were prepared using
volumetric glassware, and all liquid reagents were dispensed by
difference using gastight Hamilton syringes. Benzene H/D ex-
change was carried out using a literature procedure.18
(bpym)PtCl2 (1). Complex 1 was prepared according to a
literature procedure.12 The spectroscopic data for this com-
plex matched those reported in the literature. Anal. Calcd for
C8H6Cl2N4Pt: C, 22.65; H, 1.43; N, 13.21. Found: C, 22.83; H,
1.32; N, 13.16.
[(bpym)Pt(DMSO)Cl][CH3OSO3] (4-CH3OSO3). Under N2,
(bpym)PtCl2 (1; 344 mg, 0.81 mmol, 1.0 equiv) was dissolved in
˚
dry DMSO (60 mL, dried over 4 A molecular sieves). Me2SO4
an ice bath. [Me3O]BF4 (103 mg, 0.69 mmol, 1.1 equiv) was then
added as a solid, and the resulting mixture was stirred for 2 h at
-5 °C. A white precipitate slowly formed that was subsequen-
tly filtered. The crude product was washed with CH2Cl2 (2 ꢀ
5 mL) and Et2O (3 ꢀ 5 mL) to remove unreacted bipyrimidine.
The resulting mixture of mono- and dimethylated bipyrimidine
was purified by recrystallization from MeOH/Et2O at -35 °C to
give the product as a white powder (78 mg, 48% yield). This
product was unstable; therefore, it was stored at -15 °C and
used for subsequent reactions within 12 h. 1H NMR (500 MHz,
CD3CN): δ 9.54 (d, J=4.9 Hz, 1H), 9.13 (d, J=4.9 Hz, 2H), 9.09
(d, J=6.6 Hz, 1H), 8.26 (app t, J=5.6 Hz, 1H), 7.78 (app t,
J=4.9 Hz, 1H), 4.39 (s, 3H). HRMS (EI): m/z calcd for C9H9N4
173.0827, found 173.0819.
(2-(4-methoxy-3-methyl-4,5-dihydropyrimidin-2-yl)pyrimi-
dine)PtCl2 (5). Under an inert atmosphere, (DMSO)2PtCl2
(74.2 mg, 0.22 mmol, 1.0 equiv) was dissolved in CH3OH (27 mL).
This mixture was heated to 60 °C, and then [N-Me(bpym)]BF4
(58 mg, 0.22 mmol, 1.0 equiv) was added. The reaction was
refluxed overnight and then cooled to room temperature, re-
sulting in the precipitation of a pale yellow solid. The precipitate
was collected, washed with Et2O (3 ꢀ 5 mL), and dried under
vacuum to afford the product as a yellow solid (77 mg, 75%
yield). 1H NMR (500 MHz, CD3CN): δ 9.84 (dd, J=5.7, 1.9 Hz,
1H), 9.09 (dd, J=4.5, 1.9 Hz, 1H), 7.79 (d, J=7.6 Hz, 1H), 7.68
(app t, J=4.5 Hz, 1H), 5.69 (dd, J=7.3, 5.0 Hz, 1H), 5.49 (d, J=
5.0 Hz, 1H), 3.89 (s, 3H), 3.22 (s, 3H). 13C NMR (100 MHz,
CD3CN): δ 161.9, 157.2, 155.3, 155.2, 133.4, 123.9, 106.7, 85.8,
51.6, 42.0. IR (KBr pellet, cm-1): 1562 (s). Anal. Calcd for
C10H12Cl2N4OPt: C, 25.54; H, 2.57; N, 11.92. Found: C, 25.69;
H, 2.51; N, 11.82.
Procedure for CH4 H/D Exchange. All glassware and stir bars
were treated with aqua regia, washed with copious amounts of
water and acetone, and dried before each use. Figure S9
(Supporting Information) shows the glassware and setup used
for these reactions. A 7 mL glass Schlenk tube with 1.6 mm
walls capable of sustaining pressures up to 200 psi equipped
with a resealable Teflon stopcock and side arm 14/20 female
adaptor was attached to a 50 mL bulb equipped with a screw-
cap septum, a 14/20 male adaptor, and a gas/vacuum inlet.
The Schlenk tube was charged with catalyst (0.02 mmol, 0.01
equiv, 1 mol %) in D2SO4 (1 mL, 20 mmol, 10 equiv). The
entire system was then degassed by three freeze-pump-thaw
cycles. The 50 mL bulb was backfilled with ultrapure methane
(2.0 mmol, 1.0 equiv) three times to 1 atm at room tempera-
ture. The Schlenk tube was submerged in liquid N2 and then
opened to the methane-filled bulb. The methane condensed
into the reaction vessel for 10 min. After the Schlenk tube was
resealed and warmed to room temperature, it was submerged
up to the stopcock channel in a 200 °C oil bath for 18 h.
At the end of the reaction, the reaction vessel was cooled
to room temperature. The gas was re-expanded in the same
(0.65 mL, 7.1 mmol, 8.75 equiv) was added dropwise at room
temperature over 5 min. The resulting mixture was heated at
60 °C for 15 h. The solvent volume was reduced to 10 mL by
vacuum distillation. Ethanol (15 mL) was then added to pre-
cipitate the product. The resulting light yellow solid was col-
lected, washed with ethanol (2 ꢀ 10 mL) and Et2O (1 ꢀ 10 mL),
and then dried under vacuum. The product was obtained as a
1
pale yellow solid (361 mg, 77% yield). H NMR (500 MHz,
DMSO-d6): δ 9.88 (dd, J=5.8, 1.4 Hz, 1H), 9.59 (dd, J=5.8, 1.7
Hz, 1H), 9.47 (m, 2H), 8.20 (app t, J=5.1 Hz, 1H), 8.16 (app t,
J=5.3 Hz, 1H), 3.36 (s, 3H), 2.54 (s, 6H). 13C NMR (125 MHz,
DMSO-d6): δ 162.5, 161.3, 160.8, 160.6, 156.3, 155.3, 124.6,
124.5, 52.8, 40.4. IR (KBr pellet, cm-1) 1584 (m), 1410 (m), 1246
(s), 1226 (s), 1128 (m). HRMS (EI): m/z calcd for
[C10H12ClN4OPtS]þ 466.0068, found 466.0073. Anal. Calcd
for C11H15ClN4O5PtS2: C, 22.86; H, 2.62; N, 9.69. Found: C,
22.64; H, 2.52; N, 9.49.
[(bpym)Pt(DMSO)Cl][PF6] (4-PF6). [(bpym)Pt(DMSO)Cl]-
[CH3OSO3] (4; 361 mg, 0.62 mmol, 1.0 equiv) was dissolved in
deionized water (10 mL) to give a homogeneous solution.
NaPF6 (341 mg, 2.0 mmol, 3.0 equiv) in deionized water
(5 mL) was added. A white precipitate formed and was imme-
diately collected via filtration and dried under vacuum. The
product was obtained as a white solid (309 mg, 81% yield). 1H
NMR (500 MHz, DMSO-d6): δ 9.89 (dd, J=5.8, 1.4 Hz, 1H),
9.59 (dd, J=5.8, 1.7 Hz, 1H), 9.49-9.46 (multiple peaks, 2H),
1
8.22-8.14 (multiple peaks, 2H), 2.54 (s, 6H). H NMR (400
MHz, acetone-d6): δ 10.15 (dd w/Pt satellites, 3JPt-H=39.7 Hz,
J=6.1, 2.3 Hz, 1H), 9.79 (dd, w/Pt satellites, 3JPt-H=39.0 Hz,
J=6.1, 1.5 Hz, 1H), 9.55 (m, 2H), 8.29 (dd, J=5.8, 4.8 Hz, 1H),
8.26 (dd, J=6.1, 4.6 Hz, 1H), 3.87 (s w/Pt satellites, 3JPt-H=20.6
50 mL bulb and analyzed by GC-MS using
a GS-
CarbonPLOT column obtained from Agilent Technologies.
The percent deuterium incorporation was defined as the
percent of C-H bonds converted to C-D bonds. Turnover
numbers (TON’s) are calculated as mol of D incorporated
per mol of catalyst. Reported values have been corrected
for the background reaction. The reported TON is the average
of at least two trials. The error associated with deconvolu-
tion is 5%.
Hz, 6H). 19F NMR (282 MHz, DMSO-d6): δ -70.17 (d, 1JP-F
=
711.4 Hz). 19F NMR (377 MHz, acetone-d6): δ -72.53 (d,
1JP-F=707.0 Hz). 13C NMR (100 MHz, acetone-d6): δ 162.8,
161.7, 161.1, 161.0, 156.9, 155.7, 124.8, 124.7, 45.0. IR (KBr
pellet, cm-1): 1585 (m), 1416 (m), 1133 (m), 839 (s). HRMS (EI):
m/z calcd for [C10H12ClN4OPtS]þ 466.0068, found 466.0063.
Anal. Calcd for C10H12ClF6N4OPPtS: C, 19.63; H, 1.98; N,
9.16. Found: C, 19.67; H, 1.89; N, 9.13.
Acknowledgment. We thank the National Science
Foundation for support through the Center for Enabling
New Technologies through Catalysis (CENTC). In addi-
tion, A.J.H. thanks the NSF for a graduate fellowship. We
(25) Price, J. H.; Williamson, A. N.; Schramm, R. F.; Wayland, B. B.
Inorg. Chem. 1972, 11, 1280.

262 Organometallics, Vol. 29, No. 1, 2010
Villalobos et al.
also thank Dr. Jeff Kampf for crystallography support,
Brannon Gary for repeating several CH4 H/D ex-
change experiments, and Professors Karen Goldberg,
Bill Jones, Mike Heinekey, and Elon Ison for valuable
discussions.
Supporting Information Available: Text and figures giving
additional experimental details and characterization data
and CIF files giving crystal data for 4-PF6 and 6. This mate-
rial is available free of charge via the Internet at http://pubs.
acs.org.