Protonation of (PCP)PtH to give a dihydrogen complex

Article abstract of DOI:10.1021/om0108651

The protonation of (PCP)PtH (PCP=η³-2,6-(^tBu₂PCH₂) ₂C₆H₃) to give a (PCP)Pt^II dihydrogen complex was reported. The reaction was accomplished in CD₂Cl₂ with [H(OEt₂)₂]⁺BAr′₄^- [Ar′ = 3,5-bis(trifluoromethyl)phenyl]. The analysis showed that the H₂ ligand was expelled when the solution was warmed to room temperature, but the dihydrogen complex was reformed when H₂ was added.

Full text of DOI:10.1021/om0108651

1504
Organometallics 2002, 21, 1504-1507
P r oton a tion of (P CP )P tH To Give a Dih yd r ogen Com p lex
Barbara F. M. Kimmich and R. Morris Bullock*
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
Received October 3, 2001
Summary: Protonation of (PCP)PtH (PCP ) η3-2,6-(tBu2-
Sch em e 1
-
PCH2)2C6H3) in CD2Cl2 at -78 °C with [H(OEt2)2]+BAr′4
[Ar′ ) 3,5-bis(trifluoromethyl)phenyl] gives the PtII di-
hydrogen complex [(PCP)Pt(H2)]+. The H2 ligand is
expelled when the solution is warmed to room temper-
ature, but the dihydrogen complex is re-formed when H2
is added.
Since dihydrogen complexes were first discovered by
Kubas and co-workers in 1984,1 the large number of
studies of such complexes has led to an increased
understanding of their reactivity, structures, and bond-
ing.2 While dihydrogen complexes are now known for
many different metals, the majority of them involve a
d6 electron configuration. It was not until 10 years after
the first dihydrogen complex that the first example of
a d8 PtII dihydrogen complex was reported,3 when
Caulton and co-workers published their results on trans-
[(PtBu3)2Pt(H)(H2)]+OTf -. Additional examples of Pt
dihydrogen complexes were subsequently reported by
Kubas4 and by Bercaw,5 but dihydrogen complexes with
a d8 electron configuration (including RhI dihydrogen
complexes6 along with PtII dihydrogen complexes) re-
main rare in comparison to d6 dihydrogen complexes.
Moulton and Shaw reported the first examples of a
new class of tridentate ligands in 1976.7 These ligands,
shown in generalized form in Scheme 1, have two trans
phosphines and an aryl ligand and are commonly called
pincer8 or PCP ligands. Complexes with PCP ligands
have been prepared for numerous combinations of metal
(M), alkyl group (R), and ligands X trans to the carbon
ligand (X ) H, halide, alkyl, etc.). Metal complexes with
PCP ligands have been successfully used in reactions
that are difficult to achieve, including cleavage of
carbon-carbon bonds9 and reduction of CO2.10 van
Koten and others have developed an extensive chemis-
try using related pincer ligands with nitrogens (“NCN”
ligands) in place of the phosphorus.8,11 A particularly
appealing attribute of some metal complexes with PCP
ligands is their remarkable thermal stability. Kaska,
J ensen, Goldman, and co-workers have developed Ir
complexes with PCP ligands as catalysts for the dehy-
drogenation of alkanes,12 some of which can be used for
hours at 200 °C! Even more thermally stable catalysts
were recently reported by Kaska and co-workers, who
synthesized Ir complexes with PCP-type ligands con-
taining an anthracene backbone, thus providing an
aromatic instead of benzylic bond to the phosphine.
Their complexes catalyzed the dehydrogenation of al-
kanes at 250 °C.13 Milstein and co-workers found that
{[η3-2,6-(iPr2PCH2)2C6H3)]Pd(OCOCF3) was a highly
active catalyst for the Heck reaction and that it showed
no noticeable degradation even after 300 h at 140 °C.14
(9) (a) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature
1993, 364, 699-701. (b) Liou, S.-Y.; Gozin, M.; Milstein, D. J . Chem.
Soc., Chem. Commun. 1995, 1965-1966. (c) Liou, S.-Y.; Gozin, M.;
Milstein, D. J . Am. Chem. Soc. 1995, 117, 9774-9775. (d) Rybtchinski,
B.; Vigalok, A.; Ben-David, Y.; Milstein, D. J . Am. Chem. Soc. 1996,
118, 12406-12415. (e) van der Boom, M. E.; Kraatz, H.-B.; Ben-David,
Y.; Milstein, D. J . Chem. Soc., Chem. Commun. 1996, 2167-2168. (f)
van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Gozin, M.; Milstein,
D. J . Am. Chem. Soc. 1998, 120, 13415-13421. (g) van der Boom, M.
E.; Ben-David, Y.; Milstein, D. J . Chem. Soc., Chem. Commun. 1998,
917-918. (h) Rybtchinski, B.; Milstein, D. J . Am. Chem. Soc. 1999,
121, 4528-4529. (i) van der Boom, M. E.; Kraatz, H.-B.; Hassner, L.;
Ben-David, Y.; Milstein, D. Organometallics 1999, 18, 3873-3884. (j)
Gandelman, M.; Vigalok, A.; Konstantinovski, L.; Milstein, D. J . Am.
Chem. Soc. 2000, 122, 9848-9849. (k) Gauvin, R. M.; Rozenberg, H.;
Shimon, L. J . W.; Milstein, D. Organometallics 2001, 20, 1719-1724.
(10) Kaska, W. C.; Nemeh, S.; Shirazi, A.; Potuznik, S. Organome-
tallics 1988, 7, 13-15.
(1) Kubas, G. J .; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J .;
Wasserman, H. J . J . Am. Chem. Soc. 1984, 106, 451-451.
(2) (a) Kubas, G. J . Metal Dihydrogen and σ-Bond Complexes:
Structure, Theory, and Reactivity; Kluwer Academic/Plenum Publish-
ers: New York, 2001. (b) Heinekey, D. M.; Oldham, W. J ., J r. Chem.
Rev. 1993, 93, 913-926. (c) J essop, P. G.; Morris, R. H. Coord. Chem.
Rev. 1992, 121, 155-284. (d) Esteruelas, M. A.; Oro, L. A. Chem. Rev.
1998, 98, 577-588.
(3) Gusev, D. G.; Notheis, J . U.; Rambo, J . R.; Hauger, B. E.;
Eisenstein, O.; Caulton, K. G. J . Am. Chem. Soc. 1994, 116, 7409-
7410.
(4) Butts, M. D.; Scott, B. L.; Kubas, G. J . J . Am. Chem. Soc. 1996,
118, 11831-11843.
(5) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. Inorg. Chem. 1998,
37, 2422-2431.
(6) (a) Nemeh, S.; J ensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442-1447. (b) Vigalok, A.; Ben-David, Y.;
Milstein, D. Organometallics 1996, 15, 1839-1844.
(7) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020-1026.
(8) (a) van Koten, G. Pure Appl. Chem. 1989, 61, 1681-1694. (b)
Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750-
3781.
(11) (a) Gossage, R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem.
Res. 1998, 31, 423-431. (b) Gossage, R. A.; Ryabov, A. D.; Spek, A. L.;
Stufkens, D. J .; van Beek, J . A. M.; Rudi, v. E.; van Koten, G. J . Am.
Chem. Soc. 1999, 121, 2488-2497.
(12) (a) Gupta, M.; Hagen, C.; Flesher, R. J .; Kaska, W. C.; J ensen,
C. M. J . Chem. Soc., Chem. Commun. 1996, 2083-2084. (b) Gupta,
M.; Kaska, W. C.; J ensen, C. M. J . Chem. Soc., Chem. Commun. 1997,
461-462. (c) Gupta, M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.;
J ensen, C. M. J . Am. Chem. Soc. 1997, 119, 840-841. (d) Xu, W.-W.;
Rosini, G. P.; Gupta, M.; J ensen, C. M.; Kaska, W. C.; Krogh-J espersen,
K.; Goldman, A. S. J . Chem. Soc., Chem. Commun. 1997, 2273-2274.
(e) Liu, F.; Pak, E. B.; Singh, B.; J ensen, C. M.; Goldman, A. S. J . Am.
Chem. Soc. 1999, 121, 4086-4087. (f) Kanzelberger, M.; Singh, B.;
Czerw, M.; Krogh-J espersen, K.; Goldman, A. S. J . Am. Chem. Soc.
2000, 122, 11017-11018. (g) J ensen, C. M. J . Chem. Soc., Chem.
Commun. 1999, 2443-2449.
(13) Haenel, M. W.; Oevers, S.; Angermund, K.; Kaska, W. C.; Fan,
H.-J .; Hall, M. B. Angew. Chem., Int. Ed. 2001, 40, 3596-3600.
10.1021/om0108651 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/22/2002

Notes
Organometallics, Vol. 21, No. 7, 2002 1505
We report here the protonation of (PCP)PtH to give
paratively little activated (compared to free HD) and is
suggestive of a short H-D distance.
a (PCP)PtII dihydrogen complex. In the remainder of
this paper we use the abbreviation PCP to indicate [η3-
Warming of the solution of [(PCP)Pt(H2)]+OTf- to 22
°C, followed by recording an NMR spectrum at low
temperature, gave evidence for the formation of (PCP)-
t
2,6-(tBu2PCH2)2C6H3)], with R ) Bu.)
-
PtOTf. As was observed with the BAr′4 counterion,
Resu lts a n d Discu ssion
addition of H2 to (PCP)PtOTf resulted in conversion
back to the dihydrogen complex [(PCP)Pt(H2)]+OTf-.
The dihydrogen complex [(PCP)Pt(H2)]+OTf- is stable
for at least 3 days at -80 °C, but decomposes over a
period of days at room temperature.
P r oton a tion of (P CP )P tH To Give [(P CP )P t-
(H2)]+. Protonation of (PCP)PtH in CD2Cl2 at -78 °C
with [H(OEt2)2]+BAr′4- [Ar′ ) 3,5-bis(trifluoromethyl)-
phenyl] leads to clean formation of the dihydrogen
complex [(PCP)Pt(η2-H2)]+BAr′4- (eq 1). The dihydrogen
Protonation of (PCP)PtH with HBF4‚Et2O produces
[(PCP)Pt(H2)]+BF4-, which has spectroscopic charac-
teristics similar to those found with the BAr′4- and OTf-
counterions. When this complex is warmed, several
1
products were observed by H and 31P NMR. Plausible
products include [(PCP)Pt(ClCD2Cl)]+BF4-, [(PCP)Pt-
(OEt2)]+BF4-, and (PCP)PtFBF3.
Stahl, Labinger, and Bercaw characterized [(PCy3)2Pt-
(Ph)(H2)]+BAr′4- by low-temperature NMR.5 This com-
plex eliminates benzene at -50 °C (eq 2). Aside from
resonance of this complex appears as a broad singlet at
δ 0.18 (J Pt-H ) 306 Hz). The T1 of the dihydrogen
resonance of [(PCP)Pt(H2)]+BAr′4 was 14 ms at -86
-
°C and increased to 23 ms at -38 °C. When the solution
-
of [(PCP)Pt(H2)]+BAr′4 was warmed to 22 °C, gas
evolution (H2) was observed. The solution was cooled
back to -80 °C, and the NMR spectrum showed a
mixture of 30% [(PCP)Pt(H2)]+BAr′4- and 70% of a new
complex assigned as [(PCP)Pt(ClCD2Cl)]+. When this
solution was placed under 4 atm H2, the dihydrogen
complex was replenished, indicating that the H2 ligand
can displace the very weakly bound methylene chloride
ligand. Precedent for the displacement of a CH2Cl2
ligand on Pt by H2 comes from the work of Kubas and
co-workers,4 who prepared trans-[(PiPr3)2Pt(H)(H2)]+-
-
BAr′4 from the reaction of H2 with trans-[(PiPr3)2Pt-
their use of cyclohexyl groups on the phosphines com-
pared to tert-butyls in our PCP complexes, the main
difference in their dihydrogen complex and [(PCP)Pt-
-
(H)(ClCH2Cl)]+BAr′4
.
When a solution of [(PCP)Pt(H2)]+BAr′4 was kept
under H2 at 22 °C for about 2 weeks, some irreversible
decomposition was observed. Although [(PCP)Pt(H2)]+
and [(PCP)Pt(ClCD2Cl)]+ were the two major complexes
(∼40% each) observed in the NMR spectrum, some
decomposition to (PCP)PtCl occurs through reaction
with the CD2Cl2 solvent. Along with (PCP)PtCl, a small
amount (<5%) of free PCP-H ligand is observed, as well
as some precipitate presumed to be Pt(0). In a separate
experiment, about 63% conversion to (PCP)PtCl was
observed when a solution of (PCP)PtH was heated in
CD2Cl2 at 70 °C for 12 h.
-
(H2)]+BAr′4 is the chelating ligand of the PCP, which
-
connects both phosphines to the arene ring. The chela-
tion of the PCP ligand affords a substantial stabilizing
influence on the dihydrogen complex, since [(PCy3)2Pt-
(Ph)(H2)]+BAr′4- decomposes at -50 °C, whereas [(PCP)-
Pt(H2)]+BAr′4- slowly decomposes over a period of days
at room temperature. The small amounts of free PCP-H
ligand observed after several days from decomposition
of [(PCP)Pt(H2)]+BAr′4- may form through an elimina-
tion of the arene, analogous to that shown in eq 2,
followed by dissociation of the phosphine ligand. In-
tramolecular reductive elimination of an alkane nor-
mally requires a cis configuration, but the rigidity of
the chelated PCP backbone locks the aryl and dihydro-
gen ligands into a trans configuration, thereby disfavor-
ing elimination. A dihydride might be more readily able
than the dihydrogen complex to obtain a geometry that
would be favorable for the elimination of arene, though
we have no data indicating that our dihydrogen complex
is actually in equilibrium with a dihydride. Proton
transfer from the dihydrogen ligand of [(PCP)Pt(H2)]+
to the arene ring could be a step in the elimination of
the arene ligand. Pertinent to this possibility are studies
by van Koten and co-workers, who carried out extensive
studies on η1-arenium complexes of platinum with NCN-
The dihydrogen complex with a triflate counterion is
readily observed by low-temperature NMR upon proto-
nation of (PCP)PtH with triflic acid (CF3SO3H, abbrevi-
ated as HOTf). The T1 of the dihydrogen ligand of
[(PCP)Pt(H2)]+OTf- was 14 ms at -80 °C. Further
evidence for the assignment as a dihydrogen ligand
comes from the protonation of (PCP)PtH by DOTf to give
[(PCP)Pt(HD)]+OTf-. The 1:1:1 triplet (1J H-D ) 33.4 Hz)
observed for the HD ligand is characteristic of bound
HD ligands, and the magnitude of the coupling constant
is similar to those observed in other Pt(H2) complexes.3-5
1
The large J H-D indicates that the H-D bond is com-
(14) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J . Am.
Chem. Soc. 1997, 119, 11687-11688.

1506 Organometallics, Vol. 21, No. 7, 2002
Notes
pincer ligands.15 Their studies provide information
relevant to the formation of C-C bonds between arenes
and alkyl groups in Pt complexes, which is of interest
in connection with electrophilic aromatic substitutions.
Their results may provide some insight into the reactiv-
ity of our Pt system.
Exp er im en ta l Section
Gen er a l Meth od s. All manipulations were carried out
under argon using standard Schlenk or vacuum line tech-
niques, or in a drybox. THF was distilled from Na/benzophe-
none and CH2Cl2 was distilled from P2O5; deuterated NMR
solvents were purified similarly. (PCP)PtCl7 and [H(OEt2)2]+-
- 20
BAr′4
[Ar′ ) 3,5-bis(trifluoromethyl)phenyl] was prepared
Attem p ted Ca ta lytic Rea ction s. One reason for our
interest in these Pt complexes was to explore their
possible utility in homogeneous hydrogenation catalysis.
Along with the previously mentioned uses of PCP
complexes as catalysts for dehydrogenation and the
Heck reaction, metal complexes with PCP ligands have
also been used in hydrogenation catalysis. Ruthenium
complexes with pincer ligands were reported to catalyze
the transfer hydrogenation of ketones.16 We recently
developed a series of Mo and W complexes that serve
as catalysts for the homogeneous hydrogenation of
ketones.17 These reactions were proposed to proceed by
an ionic hydrogenation mechanism, involving proton
transfer from a cationic dihydride as the first step. Many
cationic dihydrogen complexes are acidic,18 and hydride
transfer capabilities of neutral metal hydrides are well-
established.19 Compared to Pt complexes not containing
the tridentate PCP-type ligands, the enhanced stability
we observed for [(PCP)Pt(H2)]+BAr′4- appeared to be a
promising attribute for our intents to use either [(PCP)-
Pt(H2)]+ or [(PCP)Pt(ClCH2Cl)]+ as possible hydrogena-
tion catalysts. Unfortunately, attempts to use [(PCP)-
Pt(H2)]+ as a catalyst for hydrogenation of Et2CdO
showed no significant catalytic activity. A variety of
solvents (chlorobenzene, THF, and toluene) were em-
ployed in these scouting studies, with temperatures as
high as 80 °C and pressures of H2 up to 800 psi.
Decomposition of the catalyst precursors was observed,
with precipitates thought to be Pt(0) being observed in
many cases.
as previously described. DOTf and HBF4‚Et2O (85% in Et2O)
were purchased from Aldrich and used without further puri-
fication. HOTf was purified by distillation. NMR spectra were
recorded on a Bruker AM-300 instrument (300 MHz for 1H).
1H NMR spectra were referenced to the residual proton peaks
of the deuterated solvents, and 31P NMR spectra were refer-
enced to 85% phosphoric acid. NMR probe temperatures were
calibrated using methanol.21 The T1 measurements were
carried out at 300 MHz using the standard inversion-recovery
pulse sequence. For experiments indicated as carried out under
4 atm H2, a 5 mm NMR tube equipped with a J . Young valve
was attached to a vacuum line and cooled in liquid nitrogen
(77 K). The tube was then filled with 1 atm H2. Using this
procedure, the pressure of H2 after the tube was warmed to
room temperature will be about 4 atm (298/77 ) 3.9).
P r ep a r a tion of (P CP )P tH. (PCP)PtH was previously
prepared from the reaction of (PCP)PtCl with NaBH4.7 In our
hands, higher yields were obtained from a modified prepara-
tion using LiAlH4, as used in the synthesis of a related Pd
complex.22 (PCP)PtCl (619 mg, 9.91 × 10-4 mol) and LiAlH4
(50.0 mg, 1.31 × 10-3 mol) were stirred at room temperature
in THF (20 mL) for 6 h. The reaction was quenched with H2O
(50 µL), and the solvent was evaporated. The product was
extracted with pentane (150 mL), which was evaporated to give
(PCP)PtH as a white solid (440 mg, 75%). 1H NMR (22 °C,
CD2Cl2): δ -2.32 (t, J P-H ) 16 Hz, J Pt-H ) 741 Hz, 1H, PtH);
t
1.32 (t, J ) 6.8 Hz, 36H, Bu); 3.45 (m, 4H, CH2); 6.91-7.10
(m 3H, C6H3). 31P{1H} NMR (22 °C, CD2Cl2): δ 87.9 (J P-Pt
2895 Hz).
)
P r ep a r a t ion of [(P CP )P t (H 2)]+BAr ′4-. A solution of
[H(OEt2)2]+BAr′4- (9.9 mg, 9.9 × 10-6 mol) in CD2Cl2 (500 µL)
at -78 °C was added to a solution of (PCP)PtH (5.8 mg, 9.8 ×
10-6 mol, 1 equiv) in 500 µL of CD2Cl2 in an NMR tube at -78
°C. The tube was inverted to mix the contents and was then
placed in an NMR probe precooled to -80 °C. The dihydrogen
complex [(PCP)Pt(H2)]+BAr′4- was present in g90% purity. 1H
NMR (-90 °C, CD2Cl2): δ 0.18 (br s, J Pt-H ) 306 Hz, 2H, Pt-
We suspect that the reason for failure of these Pt
complexes to function as ionic hydrogenation catalysts
is that [(PCP)Pt(H2)]+ is not sufficiently acidic to ef-
fectively protonate the ketone. No hydrogenation of
acetone to 2-propanol was observed when HOTf was
added to a CD2Cl2 solution of (PCP)PtH and acetone.
We did find evidence for the expected hydridic reactivity
of (PCP)PtH. Hydride transfer from Pt to carbon occurs
t
H2); 1.23 (t, J ) 7.4 Hz, 36H, Bu); 3.47 (m, 4H, CH2); 6.82-
7.18 (m 3H, C6H3); 7.53 (br, 4H, p-H of BAr′4-); 7.72 (br, 8H,
o-H of BAr′4-). 31P{1H} NMR (-90 °C, CD2Cl2): δ 88.4 (J P-Pt
) 2510 Hz).
Wa r m in g of [(P CP )P t(H2)]+BAr ′4- a n d Ad d ition of H2.
When the solution of [(PCP)Pt(H2)]+BAr′4- prepared above was
warmed to 22 °C for 2 min, gas evolution was observed. The
solution was recooled to -80 °C, and the 31P{1H} NMR
spectrum indicated a 7:3 ratio of [(PCP)Pt(ClCD2Cl)]+:[(PCP)-
Pt(H2)]+. Hydrogen (4 atm) was then added to the tube, and
the NMR spectrum indicated that the dihydrogen complex was
re-formed, with a 10:1 ratio of [(PCP)Pt(H2)]+ to [(PCP)Pt-
(ClCD2Cl)]+ being determined by NMR. After the tube was left
-
rapidly when (PCP)PtH is reacted with Ph3C+BF4 at
room temperature, with Ph3CH being formed in high
yield.
(15) (a) Grove, D. M.; van Koten, G.; Louwen, J . N.; Noltes, J . G.;
Spek, A. L.; Ubbels, H. J . C. J . Am. Chem. Soc. 1982, 104, 6609-6616.
(b) Terheijden, J .; van Koten, G.; Vinke, I. C.; Spek, A. L. J . Am. Chem.
Soc. 1985, 107, 2891-2898. (c) Albrecht, M.; Spek, A. L.; van Koten,
G. J . Am. Chem. Soc. 2001, 123, 7233-7246.
(16) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten, G.
Angew. Chem., Int. Ed. 2000, 39, 743-745.
(17) (a) Bullock, R. M.; Voges, M. H. J . Am. Chem. Soc. 2000, 122,
12594-12595. (b) Voges, M. H.; Bullock, R. M. J . Chem. Soc., Dalton
Trans. 2002, in press.
(18) (a) Chinn, M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D.
Organometallics 1989, 8, 1824-1826. (b) J ia, G.; Morris, R. H. J . Am.
Chem. Soc. 1991, 113, 875-883. (c) Abdur-Rashid, K.; Fong, T. P.;
Greaves, B.; Gusev, D. G.; Hinman, J . G.; Landau, S. E.; Lough, A. J .;
Morris, R. H. J . Am. Chem. Soc. 2000, 122, 9155-9171.
(19) (a) For a review of nucleophilic reactivity of metal hydrides,
see: Labinger, J . A. In Transition Metal Hydrides; Dedieu, A., Ed.;
VCH: New York, 1992; Chapter 10, pp 361-379. (b) Cheng, T.-Y.;
Brunschwig, B. S.; Bullock, R. M. J . Am. Chem. Soc. 1998, 120, 13121-
13137. (c) Cheng, T.-Y.; Bullock, R. M. J . Am. Chem. Soc. 1999, 121,
3150-3155.
1
under H2 (4 atm) at 22 °C for 12 days, H and 31P{1H} NMR
spectra recorded at 22 °C indicated the following complexes:
[(PCP)Pt(H2)]+ (42%), [(PCP)Pt(ClCD2Cl)]+ (39%), (PCP)PtCl
(16%), and PCP-H (3%). Some dark precipitate had also
formed, presumably Pt(0). 1H NMR of [(PCP)Pt(ClCD2Cl)]+-
-
t
BAr′4 (-80 °C, CD2Cl2): δ 1.26 (m, 36H, Bu); 3.12 (m, 4H,
CH2); 6.90-7.17 (m, 3H, C6H3); 7.53 (br, 4H, p-H of BAr′4 -);
7.72 (br, 8H, o-H of BAr′4-). 31P{1H} NMR (-80 °C, CD2Cl2):
δ 73.4 (J P-Pt ) 2845 Hz).
(20) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
(21) Van Geet, A. L. Anal. Chem. 1970, 42, 679-680.
(22) Seligson, A. L.; Trogler, W. C. Organometallics 1993, 12, 738-
743.

Notes
T1 Mea su r em en ts of [(P CP )P t(H2)]+BAr ′4-. The follow-
ing T1 values were determined for the dihydrogen peak of
[(PCP)Pt(H2)]+BAr′4- in CD2Cl2 at 300 MHz: 14 ms (-86 °C),
14 ms (-74 °C), 16 ms (-62 °C), 19 ms (-50 °C), and 23 ms
(-38 °C).
Organometallics, Vol. 21, No. 7, 2002 1507
(1:1:1 t, J Pt-H ) 312 Hz, J H-D ) 33.4 Hz, 1H, Pt-HD); 1.27 (t,
t
J ) 7.4 Hz, 36H, Bu); 3.48 (m, 4 H, CH2) 7.16 (m, 3H, C6H3).
31P{1H} NMR of [(PCP)Pt(HD)]+OTf- (-80 °C in CD2Cl2): δ
87.9 (d, J P-Pt ) 2510 Hz).
P r ep a r a tion of [(P CP )P t(H2)]+BF 4-. Tetrafluoroboric acid
(3.1 µL of 85% HBF4‚Et2O in Et2O) was added to a solution of
(PCP)PtH (10.7 mg, 1.81 × 10-5 mol) in CD2Cl2 (0.70 mL) at
-80 °C. The tube was inverted to mix the contents, and the
P r ep a r a tion of [(P CP )P t(H2)]+OTf-. (PCP)PtH (9.6 mg,
1.6 × 10-5 mol) was dissolved in 0.70 mL of CD2Cl2, and the
solution was cooled to -80 °C. Triflic acid (HOTf, 1.4 µL, 1.6
× 10-5 mol) was added by syringe, and the tube was inverted
to mix the contents. [(PCP)Pt(H2)]+OTf- was formed in about
93% yield by NMR. About 7% (PCP)PtOTf was observed,
apparently due to unintentional warming of part of the
solution, since the ratio of these two complexes did not change
significantly after 3 days at -80 °C. 1H NMR of [(PCP)Pt(H2)]+-
OTf- (-80 °C, CD2Cl2): δ 0.23 (br s, J Pt-H ) 304 Hz, 2H, Pt-
H2); 1.26 (m, 36H, tBu); 3.49 (m, 4H, CH2) 7.19 (m, 3H, C6H3).
31P{1H} NMR of [(PCP)Pt(H2)]+OTf- (-80 °C, CD2Cl2): δ 88.3
NMR spectrum indicated that [(PCP)Pt(H2)]+ was formed in
1
>90% yield. H NMR (-90 °C, CD2Cl2): δ 0.29 (br s, J Pt-H
)
t
310 Hz, 2H, Pt-H2); 1.26 (m, 36H, Bu); 3.48 (m, 4H, CH2);
7.16-7.21 (m 3H, C6H3). 31P{1H} NMR (-90 °C, CD2Cl2): δ
88.2 (d, J P-Pt ) 2509 Hz).
Wa r m in g of [(P CP )P t(H2)]+BF 4-. When the solution of
[(PCP)Pt(H2)]+BF4 prepared above was warmed to 22 °C for
-
1 min, gas evolution was observed. The solution was recooled
to -80 °C, and the 31P{1H} NMR spectrum indicated that the
relative amount of [(PCP)Pt(H2)]+BF4- had decreased to about
29%. Several other decomposition products were also formed,
as indicated by 31P{1H} resonances at δ 75.6 (21%), δ 76.7
(19%), and δ 72.9 (17%).
1
(J P-Pt ) 2509 Hz). H NMR of (PCP)PtOTf (-80 °C, CD2Cl2):
t
δ 1.27 (m, 36H, Bu); 3.08 (m, 4H, CH2) 6.87-7.18 (m, 3H,
C6H3). 31P{1H} NMR of (PCP)PtOTf (-80 °C, CD2Cl2): δ 75.6
(J P-Pt ) 2901 Hz).
Wa r m in g of [(P CP )P t(H2)]+OTf- a n d Ad d ition of H2.
When the solution of [(PCP)Pt(H2)]+OTf- prepared above was
warmed to 22 °C for 2 min, gas evolution was observed. The
solution was recooled to -80 °C, and the 31P{1H} NMR
spectrum indicated a 4:1 ratio of (PCP)PtOTf to [(PCP)Pt(H2)]+-
OTf-. Hydrogen (4 atm) was added to the tube, and the NMR
spectrum (-80 °C) indicated that the dihydrogen complex was
re-formed (87%). After the tube was left under H2 (4 atm) at
22 °C for 3 days, a 31P{1H} NMR spectrum recorded at 22 °C
indicated the following complexes: [(PCP)Pt(H2)]+ (44%),
(PCP)PtOTf (31%), (PCP)PtCl (δ 67.6, 13%), and PCP-H (δ
40.4, 5%).
Ack n ow led gm en t. We thank the U.S. Department
of Energy, Office of Science, Laboratory Technology
Research Program, and the Division of Chemical Sci-
ences, Office of Basic Energy Sciences, for support. This
research was carried out at Brookhaven National Labo-
ratory under contract DE-AC02-98CH10886 with the
U.S. Department of Energy. We thank DuPont Central
Research for additional support of this work through a
CRADA grant. We gratefully acknowledge Dr. Paul
Fagan and Dr. Elisabeth Hauptman (DuPont) for many
helpful discussions, and the reviewers for several helpful
suggestions.
P r ep a r a tion of [(P CP )P t(HD)]+OTf-. Using a procedure
analogous to that described above, protonation of (PCP)PtH
by DOTf at -80 °C gave [(PCP)Pt(HD)]+OTf- in 94% yield.
1H NMR of [(PCP)Pt(HD)]+OTf- (-80 °C in CD2Cl2): δ 0.33
OM0108651