Hydrogen bonding in transition metal complexes: Synthesis, dynamics, and reactivity of platinum hydride bifluoride complexes

Article abstract of DOI:10.1021/ja0010913

Platinum hydride bifluoride (FHF) complexes trans-[Pt(PR₃)₂H(FHF)] (R = Cy, ⁱPr) were prepared from the reaction of the corresponding trans-dihydride complexes with NEt₃?3(HF) in THF. They were also formed in C-F activation reactions of the same precursors with C₆F₆ in the presence of [Me₄N]F. The low-temperature NMR spectra exhibit a complete network of coupling between the spin 1/2 nuclei, ¹H, ³¹P, ¹⁹F, and ¹⁹⁵Pt. At higher temperatures, fluxional behavior is observed which is principally associated with intermolecular exchange of HF between platinum centers. However, satisfactory simulation of the spectra also requires inclusion of intermolecular exchange of the distal fluoride. Addition of [Bu₄N]FHF results in coalescence of the bifluoride proton resonance of the complex and the added bifluoride, demonstrating that the bifluoride ligand can exchange with free bifluoride, FHF^-. The IR spectrum of trans-[Pt(PCy₃)₂H(FHF)] shows two broad bands at 2604 and 1832 cm^-1 assigned to the H-F stretching modes and a sharp band at 2272 cm^-1 for the Pt-H stretching mode. Bifluoride is a weakly coordinated ligand which can be replaced to give trans-[Pt(PCy₃)₂(H)X] complexes where X = N₃, OTf. Hydrogen fluoride may be removed from trans-[Pt(PCy₃)₂H-(FHF)] by treatment with CsOH in the presence of [NMe₄]F, yielding trans-[Pt(PCy₃)₂(H)F]. In addition, these bifluoride complexes fluorinate organic compounds, such as CH₃I, CH₃COCl, and C₆H₅COCl, to give CH₃F, CH₃COF, and C₆H₅COF together with trans-[Pt(PCy₃)₂(H)X] (X = Cl, I). Reactions with PPh₃ and pyridine yield trans-[Pt(PCy₃)₂(PPh₃)H]FHF and trans-[Pt(PCy₃)₂(C₅H₅N)H]FHF.

Full text of DOI:10.1021/ja0010913

J. Am. Chem. Soc. 2000, 122, 8685-8693
8685
Hydrogen Bonding in Transition Metal Complexes: Synthesis,
Dynamics, and Reactivity of Platinum Hydride Bifluoride Complexes
Naseralla A. Jasim and Robin N. Perutz*
Contribution from the Department of Chemistry, UniVersity of York, York YO10 5DD, U.K.
ReceiVed March 28, 2000
Abstract: Platinum hydride bifluoride (FHF) complexes trans-[Pt(PR3)2H(FHF)] (R ) Cy, iPr) were prepared
from the reaction of the corresponding trans-dihydride complexes with NEt3‚3(HF) in THF. They were also
formed in C-F activation reactions of the same precursors with C6F6 in the presence of [Me4N]F. The low-
1
1
temperature NMR spectra exhibit a complete network of coupling between the spin /2 nuclei, H, 31P, 19F,
and 195Pt. At higher temperatures, fluxional behavior is observed which is principally associated with
intermolecular exchange of HF between platinum centers. However, satisfactory simulation of the spectra also
requires inclusion of intermolecular exchange of the distal fluoride. Addition of [Bu4N]FHF results in coalescence
of the bifluoride proton resonance of the complex and the added bifluoride, demonstrating that the bifluoride
ligand can exchange with free bifluoride, FHF-. The IR spectrum of trans-[Pt(PCy3)2H(FHF)] shows two
broad bands at 2604 and 1832 cm-1 assigned to the H-F stretching modes and a sharp band at 2272 cm-1 for
the Pt-H stretching mode. Bifluoride is a weakly coordinated ligand which can be replaced to give trans-
[Pt(PCy3)2(H)X] complexes where X ) N3, OTf. Hydrogen fluoride may be removed from trans-[Pt(PCy3)2H-
(FHF)] by treatment with CsOH in the presence of [NMe4]F, yielding trans-[Pt(PCy3)2(H)F]. In addition,
these bifluoride complexes fluorinate organic compounds, such as CH3I, CH3COCl, and C6H5COCl, to give
CH3F, CH3COF, and C6H5COF together with trans-[Pt(PCy3)2(H)X] (X ) Cl, I). Reactions with PPh3 and
pyridine yield trans-[Pt(PCy3)2(PPh3)H]FHF and trans-[Pt(PCy3)2(C5H5N)H]FHF.
Introduction
The strongest known hydrogen bond is found in bifluoride,
FHF-.4 This ion has only recently been recognized as a ligand
in transition metal complexes. There is extensive documentation
of the hydrogen bonding of HF to nonmetal bases, for instance
via matrix isolation,5 but the bonding of HF to a metal fluoride
has the scope for altering the strength of the M-F interaction
substantially. Parkin et al. reported the bifluoride complexes,
[Mo(PMe3)4H2F(FHF)] and [W(PMe3)4H2F(FHF)], synthesized
with aqueous HF.6 The best evidence of structure in the solid
state comes from X-ray and neutron diffraction of [W(PMe3)4H2F-
(FHF)].6 The structure is based on a trigonal dodecahedron, with
a distorted tetrahedral array of PMe3 ligands. The hydrogen
bonding is far from symmetric, with the hydrogen atom located
much closer to the distal fluorine (0.961 Å) than to the proximal
fluorine (1.43 Å) (the distal fluorine is furthest from the metal,
while the proximal fluorine is directly bound to the metal). The
FHF unit approaches linearity with a bond angle of 170.6°. The
observation that J(HF) exceeds 400 Hz suggests that the HF in
these complexes is nearly dissociated in solution.
The role of hydrogen bonding in the chemistry of transition
metal complexes is now recognized both in solution and the
solid state, and new types of hydrogen bonds have been
discovered. Crabtree and Morris have shown that metal hydride
complexes can hydrogen bond to conventional H-bond donors
forming M-H‚‚‚HX interactions where H-X is an H-bond
donor.1 Richmond has reviewed the role of hydrogen bonding
in transition metal fluoride complexes.2 For instance, the crystal
structure of a tungsten-fluoride complex reveals head-to-tail
dimerization via N-H‚‚‚F-W hydrogen bonds.2 Brammer et
al. have shown that hydrogen bonding at metal fluoride
complexes is stronger than that for other halides, and that
H‚‚‚F-M angles are more obtuse than angles to other H‚‚‚X-M
bonds.3 Crabtree et al. reported a complex exhibiting intra-
molecular hydrogen bonding between Ir-F and a pendant NH2
group attached to another ligand.1 This interaction is revealed
in solution by the coupling J(HF) of 52 Hz in one of the amino
Perutz et al. were the first to characterize an η1-FHF complex
in solution and solid state. They prepared trans-[Ru(dmpe)2-
H(FHF)] by the reaction of cis-[Ru(dmpe)2H2] either with
fluoroarenes (C6F6, C5F5H, or others) or with NEt3‚3(HF).7 The
NMR and IR parameters suggest the presence of an asymmetric
bifluoride ligand with predominant M-F‚‚‚H-F character (note
proton resonances. Upon protonation at low temperature, a
+
complex is formed with coordinated F-H as Ir-F-H‚‚‚NH2
,
with a much larger value of J(HF) (440 Hz).1
(1) Lee, D.-H.; Kown, H. J.; Patel, B. P.; Liable-Sands, L. M.; Rheingold
A. L.; Crabtree, R. H. Organometallics 1999, 18, 1615. Crabtree, R. H. J.
Organomet. Chem. 1998, 577, 111. Crabtree, R. H.; Eisenstein, O.; Sini,
G.; Peris, E. J. Organomet. Chem. 1998, 567, 7. Patel, B. P.; Kavallieratos,
K.; Crabtree, R. H. J. Organomet. Chem. 1997, 528, 205. Patel, B. P.;
Crabtree, R. H. J. Am. Chem. Soc. 1996, 118, 13105. Crabtree, R. H.;
Siegbahn, P. E. M.; Eisenstein, O.; Rheingold, A. L.; Koetzle, T. F. Acc.
Chem. Res. 1996, 29, 348. Park, S.; Ramachandran, R.; Lough, A. J.; Morris,
R. H. J. Chem. Soc., Chem. Commun. 1994, 2201.
(4) Emsley, J. Chem. Soc. ReV. 1980, 9, 91.
(5) Hunt, R. D.; Andrews, L. J. Chem. Phys. 1987, 87, 6219.
(6) Murphy, V. J.; Hascall, T.; Chen, J. Y.; Parkin, G. J. Am. Chem.
Soc. 1996, 118, 7428. Murphy, V. J.; Rabinovich, D.; Hascall, T.; Klooster,
W. T.; Koetzle, T. F.; Parkin, G. J. Am. Chem. Soc. 1998, 120, 4372.
(7) Whittlesey, M. K.; Perutz, R. N.; Greener, B.; Moore, M. H. J. Chem.
Soc., Chem. Commun. 1997, 187. Whittlesey, M. K.; Perutz, R. N.; Moore,
M. H. J. Chem. Soc., Chem. Commun. 1996, 787.
(2) Richmond, T. G. Coord. Chem. ReV. 1990, 105, 221.
(3) Brammer, L.; Bruton, E. A.; Sherwood, P. New J. Chem. 1999, 23,
965.
10.1021/ja0010913 CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/24/2000

8686 J. Am. Chem. Soc., Vol. 122, No. 36, 2000
Jasim and Perutz
Table 1. NMR Data for Complexes trans-[Pt(PR3)2H(FHF)] (R )
J(HFdistal) ) 274 Hz and J(HFproximal) < 30 Hz). It was proposed
that the reaction of the transition metal dihydride with C6F6
yields trans-[Ru(dmpe)2(C6F5)H] with release of HF which
reacts with cis-[Ru(dmpe)2H2] to form the bifluoride complex.7
Perutz and Parkin6,7 both found that the bifluoride ligand is
not coordinated linearly to the metal center but exhibits an
M-F‚‚‚F angle of ∼130°. The F‚‚‚F separation in each of these
complexes is considerably less than twice the van der Waals
radius of fluorine (1.4 Å).8 The metal-fluorine bond lengths
are extremely long, probably as a result of weakening through
the hydrogen bond to the distal fluorine.
Cy, PiPr3) in [2H8]-THF at 193 Ka
δ(1H)
δ(1H)
complex
temp (K) acidic hydride
δ(19F)
δ(31P)
Pt(PCy3)2H(FHF)
290
190
290
190
11.3
11.9
11.3
11.6
-27.2 -283.3
-185
42.5
Pt(PCy3)2H(FHF)
Pt(PiPr3)2H(FHF)
Pt(PiPr3)2H(FHF)
-27.2 -283.6
-182.5
42.4
55.9
54.6
-26.8 -281.5
-179.5
-27.0 -280
-179
Recently, we have described the crystal structure and solution
NMR spectra of a nickel bifluoride complex, trans-[Ni(PEt3)2-
(difluoropyrimidinyl)(FHF)].9 Of the remaining reports of
bifluoride complexes, the one for [RhdCCHPh(PiPr3)2(FHF)]
is the most complete.10 The NMR spectrum shows low-
temperature fluorine resonances at δ -228 and δ -179 (J(HF)
) 418 Hz and J(FF) ) 101 Hz). The coupling constants indicate
that the M-F‚‚‚H-F interaction is weaker than the trans-[Ru-
(dmpe)2H(FHF)] system and similar to [MoH2F(FHF)(PMe3)4].
There are a few other incomplete reports of bifluoride com-
plexes. Coulson reported the elemental analysis of trans-[Pt-
(PEt3)2(C6H5)(FHF)] without further evidence.11 Hintermann et
al. detected trans-[Pt(PCy3)2H(FHF)] in solution by NMR
spectroscopy following the electron-transfer reaction of trans-
[Pt(PCy3)2H2] with fluorinated benzonitrile, but the complex
was not isolated.12 Grushin et al. identified trans-[Pd(PPh3)2-
(FHF)R] (R ) Me, Ph) from the reaction of [Pd2(PPh3)2R2(µ-
OH)2] with NEt3‚3(HF) on the basis of microanalysis and a
broad proton NMR resonance.13 One report describes FHF as a
bridging ligand in the structure of a niobium dimer, but no
evidence is given for this species in solution.14
a Coupling constants are shown in Figure 5.
Figure 1. 1H NMR spectra (300 MHz) of hydride region of trans-
[Pt(PiPr3)2H(FHF)] in [2H8]-THF at 273 K.
Table 2. IR Data (ν/cm-1) for trans-[Pt(PR3)2H(X)] (X ) H, FHF,
or F; R ) Cy or PiPr3)
We have now isolated the complex originally detected by
Hintermann et al.,12 trans-[Pt(PCy3)2H(FHF)], by using NEt3‚
3(HF) as a mild source of HF. We report its characterization,
solution dynamics, and reactivity and also investigate its tri-
isopropylphosphine analogue. We show that the connectivity
of these complexes can be established completely by low-
temperature NMR spectroscopy. We find that they are also
generated in C-F bond activation reactions.
X
Pt(PCy3)2H(X)
Pt(PiPr3)2H(X)
assignment
H
F
FHF
1707
2206, 2235
2272
1832
2604, 2630
426, 442
1736
ν
asym(Pt-H)
ν(Pt-H)
ν(Pt-H)
ν(H-F)
2273
1903
2528
424-432
ν(H-F)
ν(Pt-F)
The complexes, trans-[Pt(PR3)2H(FHF)], were also identified
among the products of reaction of trans-[Pt(PR3)2H2] with
pentafluoropyridine.
Results
Synthesis of Bifluoride Complexes. The dihydride com-
plexes trans-[Pt(PR3)2H2] (R ) Cy, iPr) react immediately with
NEt3‚3(HF) in THF solution to give hydrogen and trans-
[Pt(PR3)2H(FHF)], respectively. Hydrogen bubbled off for the
first few minutes of the reaction. All products were characterized
by 1H, 19F, and 31P NMR spectroscopy (Table 1), IR (Table 2),
mass spectrometry, and elemental analysis (C, H). Twinning
of crystals prevented us from obtaining useful crystallographic
data.
Identification of Bifluoride Complexes by NMR Spectros-
copy. The 19F NMR spectra for each of the platinum bifluoride
complexes show two resonances, a doublet at ∼δ -280 and a
broad resonance at δ -180, which appears as a doublet of
doublets at low temperature (more details are given below). The
1H NMR spectrum for each of the platinum bifluoride complexes
exhibits a hydride resonance at ∼δ -27 which appears as a
doublet with platinum satellites. Upon cooling, this resonance
resolves into a doublet of triplets with platinum satellites (Figure
1), consistent with coupling to one fluorine nucleus and two
equivalent phosphine nuclei. The values of J(PtH) of ∼1340
Hz are close to those assigned by Hintermann for trans-
[Pt(PCy3)2H(FHF)].12 With selective 19F decoupling at ∼δ
-283, the hydride doublet of trans-[Pt(PCy3)2H(FHF)] collapses
to a singlet with platinum satellites.
The acidic proton of each complex appears as a broad
resonance at room temperature at ∼δ 11.5. At low temperature
(193 K), this resonance resolves into a doublet of doublets at δ
11.9 for trans-[Pt(PCy3)2H(FHF)] with coupling constants of
412 and 48 Hz. For trans-[Pt(PiPr3)2H(FHF)], the resonance is
observed at δ 11.3 and has couplings of 393 and 43 Hz. In
i
The complexes trans-[Pt(PR3)2H2] (R ) Cy, Pr) react with
C6F6 in the presence of [NMe4]F in THF at 50 °C for 48 h to
yield trans-[Pt(PCy3)2H(FHF)] and trans-[Pt(PCy3)2H(C6F5)].
(8) Bondi, A. J. J. Phys. Chem. 1964, 68, 441.
(9) Braun, T.; Foxon, S. P.; Perutz, R. N.; Walton, P. H. Angew. Chem.,
Int. Ed. Engl. 1999, 38, 3326.
(10) Gil-Rubio, J.; Weberdo¨rfer, B.; Werner, H. J. Chem. Soc., Dalton
Trans. 1999, 1437.
(11) Coulson, D. R. J. Am. Chem. Soc. 1976, 98, 3111.
(12) Hintermann, S.; Pregosin, P. S.; Ru¨egger, H.; Clark, H. C. J.
Organomet. Chem. 1992, 435, 225.
(13) Fraser, S. L.; Antipin, M. Y.; Khroustalyov, V. N.; Grushin, V. V.
J. Am. Chem. Soc. 1997, 119, 4769.
(14) Roesky, H. W.; Sotoodeh, M.; Xu, Y.; Schrumpf, F.; Noltemeyer,
M. Z. Anorg. Chem. 1990, 580, 131.

Platinum Hydride Bifluoride Complexes
J. Am. Chem. Soc., Vol. 122, No. 36, 2000 8687
Figure 2. 1H NMR spectrum (300 MHz) of acidic proton region of
trans-[Pt(PiPr3)2H(FHF)] in [2H8]-THF (a) at room temperature, (b) at
193 K.
both cases, the small coupling arises from interaction with the
proximal fluorine and the large coupling from the distal fluorine
1
of the bifluoride ligand (Figure 2). The H NMR spectrum of
trans-[Pt(PCy3)2H(FHF)] recorded with selective 19F decoupling
at ∼δ -283 at low temperature collapses to a doublet which
retains the large coupling. The corresponding spectrum with
19F decoupling at ∼δ -182 at low temperature shows an
unresolved singlet, providing evidence that the distal fluorine
is most strongly coupled to the acidic proton.
Figure 3. 19F NMR spectra (376 MHz) of trans-[Pt(PiPr3)2H(FHF)]
The 31P{1H} NMR spectrum of trans-[Pt(PCy3)2H(FHF)]
shows a singlet with platinum satellites at δ 42.5 at room
temperature. At low temperature, the resonance resolves into a
doublet with satellites (J(PtP) ) 2860 Hz and J(PF) ) 8 Hz).
NMR data for the PiPr3 analogue are given in Table 1. The
solution geometry of Pt(PR3)2X2 complexes can be deduced
from the magnitude of J(PtP): for cis complexes, typically
greater than 3000 Hz, for trans complexes J(PtP), usually less
than 3000 Hz.15
in [2H8]-THF in the region of the proximal fluorine (a) at room
1
temperature, (b) with H decoupling at ∼δ -27 at room temperature,
(c) without decoupling at 193 K.
The second 19F resonance observed is at ∼δ -180 and appears
as a doublet of doublets at low temperature with coupling
constants J(HF) ≈ 400 and J(FF) ) 103 Hz (Figure 4a). This
resonance is assigned to the distal fluorine of the bifluoride
ligand. The 19F NMR spectrum, recorded with proton decoupling
at δ 12-13, shows a doublet with the small coupling retained
(Figure 4b). With the full set of couplings, it becomes apparent
why the 19F resonance of the proximal fluorine is poorly
resolved, even at low temperature: the coupling to the distal
fluorine is close to twice the coupling to the acidic hydrogen.
Additional small couplings to 31P will reduce the apparent
resolution.
The NMR coupling patterns at low temperature provide a
complete and unambiguous demonstration of the presence of
the complexes trans-[Pt(PR3)2H(FHF)] (Figure 5). However, the
room-temperature data make it evident that dynamic processes
are occurring (see below).
In the 19F NMR spectra, two resonances are observed at room
temperature for the trans-[Pt(PR3)2H(FHF)] complexes. One
resonance is a doublet with platinum satellites at δ -283 (J(HF)
) 112 Hz and J(PtF) ) 572 Hz) for trans-[Pt(PCy3)2H(FHF)]
and δ -281 (J(HF) ) 116 Hz and J(PtF) ) 588 Hz) for trans-
[Pt(PiPr3)2H(FHF)] (Figure 3a). This resonance is assigned to
the proximal fluorine, which is coupled to the Pt and hydride
nuclei. When the hydride resonance at δ -27 is decoupled, the
fluorine spectrum collapses to a singlet with platinum satellites
(Figure 3b). At room temperature, coupling is not observed from
the proximal fluorine to either the acidic hydrogen or the distal
fluorine. The fully coupled 19F resonance turns into a broad
triplet upon cooling to 193 K for trans-[Pt(PCy3)2H(FHF)] and
a triplet of doublets for trans-[Pt(PiPr3)2H(FHF)] (Figure 3c).
IR Spectroscopy of the Bifluoride Complexes. The IR
spectra of the dihydride and the bifluoride complexes were
recorded from 4000 to 200 cm-1 in Nujol mulls. The ν(M-H)
bands for the dihydride starting materials at 1700-1750 cm-1
were replaced by new bands on formation of the bifluoride
complex (Table 2 and Figure 6). Each product complex shows
(15) Haggerty, B. S.; Housecroft, C. E.; Rheingold, A. L.; Shaykh, B.
A. M. J. Chem. Soc., Dalton., Trans. 1991, 2175. Miyashita, A.; Hotta,
M.; Saida, Y. J. Organomet. Chem. 1994, 473, 353. Alibrandi, G.; Scolaro,
L. M.; Minniti, D.; Romeo, R. Inorg. Chem. 1990, 29, 3467.

8688 J. Am. Chem. Soc., Vol. 122, No. 36, 2000
Jasim and Perutz
Figure 6. IR spectra (Nujol mull) of trans-[Pt(PiPr3)2H(FHF)] and
trans-[Pt(PiPr3)2H2].
Figure 4. 19F NMR spectra (376 MHz) of trans-[Pt(PiPr3)2H(FHF)]
in [2H8]-THF at 193 K in the region of distal fluorine (a) fully coupled,
1
(b) with H decoupling at ∼δ 11.
Figure 7. IR spectra (Nujol mull) of trans-[Pt(PCy3)2H(FHF)] and
Pt(PCy3)2(H)N3.
ligand trans to H with low trans influence, such as trans-[Pt-
(PR3)2HCl], the value of (PtH) is very high (∼2270 cm-1),
whereas, in the parent trans-[Pt(PR3)2H2], the IR active modes
ν
asym(PtH2) have very low frequencies (∼1700 cm-1) because
of the strong trans influence of hydride.
Two broad bands found at 420-445 cm-1 for trans-[Pt-
(PR3)2H(FHF)] are assigned to the metal-fluoride stretching
mode. Our assignments are supported by the observation that
the bifluoride and the metal fluoride stretching bands dis-
appeared when the bifluoride ligand was exchanged with any
other ligands (H-, OTf-, N3-, PPh3, and pyridine, Figure 7).
Andrews and associates have studied complexes formed
between HF and a variety of organic bases by IR spectroscopy
in matrixes. For the majority of bases the H-F stretching mode
Figure 5. Coupling constants (Hz) in the low-temperature NMR spectra
of (a) trans-[Pt(PCy3)2H(FHF)], (b) trans-[Pt(PiPr3)2H(FHF)].
a broad peak around 2500-2650 cm-1, a sharp peak at ∼2270
cm-1, and a broad peak at 1800-1900 cm-1. In this region,
three modes are expected: two H-F modes and one M-H
stretching mode. The two broad bands are assigned to the H-F
stretching modes. The higher frequency band is very close to
that of the molybdenum bifluoride complex at 2682 cm-1.6 The
value of ν(H-F) is higher than that of the bifluoride anion in
its salts (1225-1740 cm-1),16 demonstrating that the hydrogen
bonding interaction in the bifluoride ligand is asymmetric. The
sharp band at ∼2270 cm-1 is assigned to the ν(M-H) stretching
mode, since it lies close to those found for trans-[Pt(PR3)2HCl]17
and trans-[Pt(PPh3)2HF] (2240 cm-1).18 In a complex with a
lies above 3000 cm-1 19
; even with strong bases such as NMe2H,
it lies no lower than 2670 cm-1. In contrast, νasym of FHF- has
been found at 1377 cm-1 in an argon matrix.20 Our observations
of H-F stretching modes of coordinated bifluoride complexes
lie in an intermediate region.
Dynamic NMR. To explain the temperature dependence of
the NMR spectra, we considered five intermolecular dynamic
processes (loss of HF, loss of FHF-, exchange with free FHF-,
(18) Doyle, G. J. Organomet. Chem. 1982, 224, 355. Kiplinger, J. L.;
Richmond, T. G.; Osterberg, C. E. Chem. ReV. 1994, 94, 373.
(19) Davis, S. R.; Andrews, L. J. Am. Chem. Soc. 1987, 109, 4768.
Johnson, G. L.; Andrews, L. J. Phys. Chem. 1983, 87, 1852. Patten, K. O.;
Andrews, L. J. Phys. Chem. 1986, 90, 1073.
(20) Andrews, L.; Davis, S. R.; Johnson, G. L. J. Phys. Chem. 1986,
90, 4273. Hunt, R. D.; Andrews, L. J. Chem. Phys. 1987, 87, 6819.
(16) Ault, B. S. Acc. Chem. Res. 1982, 15, 103. Hibbert, F.; Emsley, J.
AdV. Phys. Org. Chem. 1990, 26, 255.
(17) Michelin, R. A.; Ros, R. J. Chem. Soc., Dalton Trans. 1989, 1149.

Platinum Hydride Bifluoride Complexes
J. Am. Chem. Soc., Vol. 122, No. 36, 2000 8689
Table 3. Apparent Rate Constants and Second Order Rate
Constants Simulated for Intermolecular Exchange for
trans-[Pt(PCy3)2H(FHF)] in THF Solution
exchange of HF between platinum complexes, and exchange
of F- between platinum complexes (eqs 1-5)) and intra-
molecular exchange of the fluorine within the bifluoride ligand
(eq 6). Asterisks distinguish equivalent atoms.
app
app
temp
k4
k4
k5
(s-1
k5
(K) (×102 s-1
)
(dm3 mol-1 s-1
)
)
(dm3 mol-1 s-1
)
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
2.00 × 104
1.25 × 104
6.25 × 103
3.75 × 103
3.75 × 103
4.69 × 103
3.79 × 103
2.85 × 103
2.04 × 103
1.62 × 103
1.1 × 103
9.8 × 102
7.28 × 102
6.3 × 102
4.38 × 102
3.33 × 102
2.47 × 102
1.81 × 102
1.9 × 102
1.17 × 105
9.48 × 104
7.13 × 104
5.10 × 104
4.05 × 104
2.75 × 104
2.45 × 104
1.82 × 104
1.58 × 104
1.10 × 104
8.33 × 103
6.18 × 103
4.53 × 103
4.75 × 103
M-F-H-F h MF + H-F
(1)
(2)
290
285
275
270
265
260
255
250
245
240
235
230
225
215
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
5.0
2.5
1.5
1.5
M-F-H-F h M+ + F-H-F-
M-F-H-F + F*-H*-F*-
M-F*-H*-F* + F-H-F- (3)
h
M-F-H-F + M*-F*-H*-F* h
M-F-H*-F* + M*-F*-H-F (4)
M-F-H-F + M*-F*-H*-F* h
M-F-H-F* + M*-F*-H*-F (5)
broad at room temperature and resolves into a doublet of
doublets upon cooling. By 213 K, the dd pattern is clear and
well resolved.
M-F-H-F* h M-F*-H-F
(6)
Free bifluoride anion is expected to exchange with coordi-
nated bifluoride if eq 3 applies. In addition to measurements
on the complexes on their own, we therefore carried out
experiments in which a solution of bifluoride as dry [Bu4N]-
FHF was mixed with the complex trans-[Pt(PCy3)2H(FHF)] in
[2H8]-THF. Variable-temperature NMR spectra were recorded
at 300 MHz for the following solutions: (a) a solution of each
bifluoride complex alone both in [2H8]-THF and in [2H8]-THF/
[2H8]-toluene mixtures; (b) a solution of [Bu4N]FHF in [2H8]-
THF; (c) a solution of a 1:1 mixture of [Bu4N]FHF and
bifluoride complex; (d) a solution of a 2:1 mixture of [Bu4N]-
FHF and bifluoride complex.
It is instructive to consider first the high-temperature spectra
of the pure complexes together with the chemical evidence. The
solutions of these complexes in THF are stable for months, and
there is no sign of etching of the glass. Moreover, we have been
unable to abstract HF by adding bases such as triethylamine or
pyridine. We therefore exclude loss of HF (eq 1). The room-
At this stage, only eqs 4 and 5 remain in play for the solutions
of the pure complexes. These equations describe intermolecular
exchange processes, implying that the rates of exchange should
be dependent on the concentration of complex. To test this
1
hypothesis, we recorded 400 MHz H NMR spectra at low
temperatures for a concentrated sample and then diluted the
sample by a factor of ∼10 and recorded the spectrum again at
the same temperature. The concentrated sample showed two
peaks in the region of the acidic proton, with full width at half
maximum (fwhm) of 185 Hz separated by 210 Hz. They were
not resolved to the baseline. The peaks in the dilute sample
were narrower (fwhm 92 Hz), much better resolved, and further
apart (390 Hz separation). These experiments give strong support
for intermolecular exchange processes.
Simulation of the NMR spectra of the acidic resonance for
trans-[Pt(PCy3)2H(FHF)] in THF for these processes was carried
out by using the program g-NMR.21 Fitting of the spectra gives
the average rate of exchange (Table 3, Figure 8) for a particular
exchange process. The exchange is simulated under the as-
sumption of a pseudo-first-order process, yet eqs 4 and 5 require
second-order kinetics. We refer to the first-order rate constant
from the simulation as kapp, and the resulting first-order lifetime
1
temperature H NMR spectrum shows the hydride resonance
as a doublet with platinum satellites; the splitting arises from
coupling to the proximal fluoride and is essentially temperature
independent. This evidence demonstrates that the Pt-F bond
remains intact and that loss of FHF- (eq 2) is insignificant under
these conditions, as is exchange of proximal with distal fluorine
(eq 6). These conclusions are confirmed by the room-temper-
ature 19F NMR spectra showing the proximal fluorine as a
doublet with platinum satellites (Figure 3).
We now turn to the effect of cooling on the NMR spectra of
solutions of the pure complexes. The acidic proton resonance
appears as a broad singlet at δ 11.6 at room temperature. Upon
cooling, this resonance separates and sharpens into a doublet
(Tc ∼ 265 K) and at lower temperatures into a distorted doublet
of doublets (Tc ∼ 220 K). The spectrum is sharpest at 210 K;
even then, this spectrum shows sharp outer peaks with broader
inner peaks (Figure 2b). Upon cooling further (with THF/toluene
mixtures, we have measured down to 165 K), the inner
resonances broaden again. Over the complete temperature range,
the chemical shift of the acidic proton changes by only ∼0.3
ppm, suggesting that exchange with species of different chemical
shift is insignificant. The resonance of the hydride proton shows
little temperature dependence. In the 19F NMR spectrum, the
resonance of the proximal fluorine is a doublet with platinum
satellites at room temperature but resolves into a complex
multiplet upon cooling. The resonance of the distal fluorine is
τapp ) (kapp -1
) . By noting the expressions for the half-life of a
first-order reaction as (ln 2)/k, and that for a second-order
reaction (of type A + A f products) as 1/k[A]0, we derive an
approximate expression for the second-order rate constant as
kapp/([Pt] × ln 2), where [Pt] is the concentration of the complex
(∼0.06 mol dm-3).22
The first process which we simulate is exchange of distal
fluoride between Pt centers (eq 5). Such an exchange removes
the large coupling on the acidic proton and the distal fluorine,
while maintaining the smaller coupling (Figure 8, column 2).
This process also maintains the distinction between the two types
of fluorine nuclei and maintains the coupling of the hydride to
proximal fluorine. Coalescence of the large doublet on the acidic
proton occurs when k5 ) 2 × 103 s-1
.
app
Equation 5 does not account for the loss of the smaller
coupling between the acidic proton and the proximal fluorine
and the corresponding sharpening of the resonances (cf. columns
2 and 3 in Figure 8). We therefore postulate that a second
(21) Budzelaar, P. H. M. g-NMR; version 4; Cherwell Scientific
Publishing Limited: Oxford, 1995-97.
(22) Atkins, P. W. Physical Chemistry; 4th ed.; Oxford University
Press: Oxford, 1990; p 788.

8690 J. Am. Chem. Soc., Vol. 122, No. 36, 2000
Jasim and Perutz
Figure 8. Variable-temperature NMR spectra (300 MHz) in [2H8]-THF for the acidic proton of trans-[Pt(PCy3)2H(FHF)]. Left-hand column:
simulated spectra for exchange as in eq 4. Central column: simulated spectra for exchange as in eq 5. Right column: experimental spectra overlaid
with simulated spectra for exchange as in eqs 4 and 5 combined.
process contributes to the exchange, namely the intermolecular
exchange of H-F between platinum complexes (eq 4). If this
process operated alone, the integrity of the H-F unit and the
larger couplings would be maintained, but the couplings of these
nuclei to the proximal fluorine would be lost (Figure 8, column
1). Coalescence of the smaller coupling of the acidic proton is
215-220 K. However, when eqs 4 and 5 operate together,
collapse of the smaller doublet of the acidic proton is predicted,
followed by collapse of the large doublet splitting, as observed.
The simulated spectra for both processes operating together are
overlaid with the observed spectra in the third column of Figure
8. The resulting kinetic data are listed in Table 3, and the Eyring
predicted when k4 ) 1.9 × 102 s-1 and is observed around
plot for k5 is shown in Figure 9, yielding ∆H5 ) 25.2 ( 1.0
app
q

Platinum Hydride Bifluoride Complexes
J. Am. Chem. Soc., Vol. 122, No. 36, 2000 8691
1
Figure 10. Variable-temperature H NMR spectra (300 MHz) of Pt-
(PCy3)2H(FHF) + [Bu4N]FHF in [2H8]-THF.
Figure 9. Eyring plot for the simulated rate constant, k5.
Scheme 1. Ligand Replacement Reactions of
trans-[Pt(PCy3)2H(FHF)]
kJ mol-1 and ∆S5q ) -61 ( 4 J K-1 mol-1. Values of k4 were
not sufficiently well determined to deduce reliable enthalpies
and entropies of activation, since the simulation is only sensitive
to k4 over a narrow temperature range. The value of ∆G4q is 39
kJ mol-1 at 235 K; for comparison, ∆G5 is 39.5 kJ mol-1 at
q
235 K. The changes in the spectra with the concentration
described above support the postulated bimolecular exchange.
Additionally, the low value of ∆H5q and the very negative value
q
of ∆S5 are fully consistent with a bimolecular process.
The 1H NMR spectra measured at very low temperature show
broadening of the inner resonances of the doublet of doublets.
This broadening increases upon lowering the temperature, the
opposite of expectations for a dynamic exchange process close
to the low-temperature limit. Although there could be dynamic
processes with very low activation energies which we do not
freeze out, this broadening could arise from differences in the
relaxation rates of the different spin combinations.23
Further dynamic behavior was observed upon addition of
[Bu4N]FHF (see the Experimental Section for synthesis of
anhydrous [Bu4N]FHF). We first describe the behavior of
solutions of [Bu4N]FHF alone. At room temperature in [2H8]-
THF, the bifluoride proton is observed as the expected triplet
at δ 16.57 (J(HF) ) 120 Hz), but on cooling, the outer
resonances of the triplet broaden and weaken without change
in frequency. This effect probably originates in ion-pair forma-
tion. A spectrum of a mixture of [Bu4N]FHF and trans-[Pt-
(PCy3)2H(FHF)] at 193 K corresponds fairly closely to the
spectra for the components alone. Upon warming, the resonances
of the bifluoride complex and the free bifluoride coalesce into
one resonance at δ 13.1 (Figure 10). This can be understood in
terms of associative exchange of bifluoride (eq 3).
(see below). However, reaction with anhydrous CsOH in THF
yielded evidence for trans-[Pt(PCy3)2(H)F] together with traces
of PF6-. Reasoning that the latter arose from HF, we repeated
the reaction with CsOH in the presence of [NMe4]F. Under these
conditions, we obtained clean conversion to trans-[Pt(PCy3)2-
(H)F] (see Table 4).
Reaction of trans-[Pt(PCy3)2H(FHF)] with NaH in dry THF
regenerates trans-[Pt(PCy3)2H2]. The same complex reacts with
Me3SiX (X ) N3 or OTf) in THF to give the products trans-
[Pt(PR3)2HX], which have been fully characterized (Scheme 1).
1
The H NMR spectrum of the triflate complex shows a triplet
resonance with platinum satellites at δ -27.1 (J(PH) ) 14 Hz
and J(PtH) ) 1548 Hz), which is assigned to the hydride ligand.
The corresponding resonance of the azide complex is found at
δ -18.9 (J(PH) ) 13 Hz and J(PtH) ) 1132 Hz). Further NMR
data are listed in Table 4.
The IR spectrum of the platinum hydride triflate complex
showed a band at 2359 cm-1 for the Pt-H stretching mode
and two bands at 1311 and 1204 cm-1 which were assigned to
ν(SO3) and ν(CF3) of the OTf ligand. A further band at 623
cm-1 was assigned to the δa(SO3) vibrational mode. These
values agree well with reported values.24 The IR spectrum of
the platinum hydride azide complex shows a sharp band at 2185
cm-1 and a strong band at 2030 cm-1, which were assigned to
ν(Pt-H) and the azide stretching mode, respectively (Figure
7).25
Ligand Replacement and Reactivity. The bifluoride com-
plexes, trans-[Pt(PR3)2H(FHF)], might be expected to lose HF
on reaction with base. We did not succeed in removing HF with
pyridine, Et3N, NaH, or [NMe4]F. Nevertheless, other products
were identified in the reactions with pyridine and sodium hydride
(23) The effect of relaxation on the low-temperature 1H NMR spectrum
of the acidic proton may be considered as follows. With the usual
conventions for labeling the spins and the same signs for the coupling
constants, the outer transitions are labeled RRR f âRR and Rââ f âââ
(written in the order proton, fluorine, fluorine). The inner lines arise from
the transitions RRâ f âRâ and RâR f ââR. The spin states of the inner
lines are subject to zero quantum relaxation processes of the fluorine nuclei,
usually labeled W0 (e.g., RâR f RRâ), in addition to single-quantum
processes (W1). When the temperature is very low, the W0 processes may
contribute significantly to the spectral density function, resulting in broad
inner lines and sharp outer lines, especially when the spectral density profile
varies rapidly with ω. Harris, R. K. In Nuclear Magnetic Resonance
Spectroscopy; Pitman: London, 1983.
(24) Lawrance, G. A. Chem. ReV. 1986, 86, 17. Blake, D. M. J. Chem.
Soc., Chem. Commun. 1974, 815. Brown, S. D.; Gard, G. L. Inorg. Chem.
1975, 14, 2273. Batchelor, R. J.; Ruddick, J. N. R.; Sams, J. R.; Aubke, F.
Inorg. Chem. 1977, 16, 1414.
(25) Wang, Y.; Frausto Da Silva, J. R.; Pombeiro, A. J. L.; Pellinghelli,
M. A.; Tiripicchio, A. J. Organomet. Chem. 1993, 454, 211.

8692 J. Am. Chem. Soc., Vol. 122, No. 36, 2000
Jasim and Perutz
Table 4. NMR Data (δ/ppm, J/Hz C6D6) for Complexes of the Type trans-[Pt(PCy3)2HX] and trans-[Pt(PCy3)2H(L)](FHF)
complex
δ(1H) hydride
δ(19F)
δ(31P)
J(PtP) J(PtH) J(PH)
Pt(PCy3)2(H)F
Pt(PCy3)2(H)Cl
Pt(PCy3)2(H)Br
Pt(PCy3)2(H)I
Pt(PCy3)2(H)N3
Pt(PCy3)2(H)(OTf)
[Pt(PCy3)2(H)(PPh3)]FHF
-24.4 dt
-17.9 t
-293.0, J(HF) ) 88, J(PF) ) 11, J(PtF) ) 402 42.1
2938
2813
2792
2747
2776
2838
2530
2280
2706
1115
1250
1302
1330
1132
1548
778
13
13
12
12
13
14
15
160
13
39.1
38.6
37.6
40.9
45.8
34.5 d
-16.7 t
-14.05 t
-18.9 t
-27.1 t
-75.5 (CF3)
-171
-6.1 dt
14.1 (acidic)
20.5 t, J(PP) ) 19
36.5
[Pt(PCy3)2(H) (C5H5N)]FHF -19.3 t
-175
1050
12.8
Chart 1. Transition States for Bimolecular Exchange of (a)
Distal Fluoride as in Eq 5 and (b) HF as in Eq 4
Reaction of trans-[Pt(PCy3)2H(FHF)] with triphenylphosphine
or pyridine resulted in displacement of the bifluoride ligand to
form the complexes trans-[Pt(PCy3)2(H)L](FHF) (L ) PPh3,
pyridine) which were identified by NMR spectroscopy (Table
4, Scheme 1). The triphenylphosphine complex exhibits a
hydride resonance at δ -6.1 (dt, J ) 160, 15 Hz) with a large
coupling to the trans phosphine ligand and smaller couplings
to the cis-PCy3 ligands. The bifluoride is characterized by a
broad resonance in the 1H NMR at δ 14.1 and in the 19F NMR
spectrum at δ -171. The absence of a high-field resonance in
the 19F NMR spectrum supports our assignment of the bifluoride
as a counterion and not a ligand. However, it is likely that there
is association between the platinum cation and the bifluoride
anion. The identification of the pyridine analogue was made
similarly.
The complex, trans-[Pt(PCy3)2H(FHF)], undergoes exchange
of halide in the reaction with various halo-organic compounds
in THF. In the cases of CH3I, CH3COCl, and C6H5COCl, we
have established the formation of CH3F, CH3COF, and C6H5-
COF (Scheme 1, NMR data in Table 4), together with the
corresponding halo complex [Pt(PCy3)2(H)X] (X ) Cl, I).
Reactions with CH2Cl2, CHBr3, CHCl3, C6H5X (X ) Cl, Br,
I), and 2-bromopyridine also result in the formation of platinum
halo complexes [Pt(PCy3)2(H)X] (X ) Cl, Br, I) (Scheme 1).
The organic products of this group of reactions have not been
investigated.
The analysis of the dynamic NMR spectra shows exchange of
hydrogen fluoride or of the distal fluoride between platinum
centers (eqs 4 and 5). The intermediates and transition states
for these exchange processes must contain at least two platinum
centers linked by hydrogen bonds. Such networks would
facilitate the exchange process (Chart 1).
This investigation demonstrates the importance of hydrogen
bonding to metal fluoride complexes. Such possibilities need
to be considered3 as awareness grows that the metal-fluorine
bond coexists with traditional soft ligands9,27 and that transition
metal-fluoride complexes have significant applications in
catalysis.28,29 There has also been considerable recent interest
in the determination of coupling constants between nuclei linked
by a hydrogen bond.30,31 The bifluoride unit offers opportunities
for such couplings, but J(FF) is only accessible by calculation
in free FHF-. Our work provides experimental values of 103
Hz for this coupling in both platinum bifluoride complexes,
compared to a calculated value of 225 Hz in the free bifluoride
ion.
C-F Activation. The bifluoride complexes can also be
synthesized by a C-F activation route. Reaction of trans-[Pt-
(PCy3)2H2] with hexafluorobenzene in the presence of [NMe4]F
yields the bifluoride complex trans-[Pt(PCy3)2H(FHF)] and
trans-[Pt(PCy3)2H(C6F5)] in a ratio of 1:13 (eq 7). The latter
C6F6, NMe4F
Conclusions
trans-Pt(PCy3)2H2
8
THF/50 °C
Two platinum bifluoride complexes, trans-[Pt(PCy3)2H(FHF)]
and trans-[Pt(PiPr3)2H(FHF)], have been synthesized by reaction
of the corresponding dihydride complexes with NEt3‚3(HF) or
via C-F activation of C6F6. The NMR and IR spectra show
that the bifluoride ligand involves a hydrogen bond Pt-
F‚‚‚H-F. The distal fluoride of the bifluoride ligand undergoes
exchange between two platinum centers, and exchange of HF
between platinum centers occurs similarly. The bifluoride ligand
can be replaced easily by anionic ligands (e.g. OTf -) or neutral
ligands, such as PPh3 or pyridine. The bifluoride complex, trans-
trans-Pt(PCy3)2H(C6F5) + trans-Pt(PCy3)2H(FHF) (7)
was characterized by Stone et al. following C-H activation of
C6F5H with Pt(PCy3)2.26 A control experiment showed no
reaction between trans-[Pt(PCy3)2H2] and [NMe4]F.
Discussion
Detailed spectroscopic analysis has enabled us to characterize
two platinum bifluoride complexes. Their IR and NMR spectra
make it evident that the hydrogen bond is far from symmetric
and that they should be described as containing the Pt-F‚‚‚
H-F moiety. Nevertheless, the vibrational frequency of the HF
unit is lower than that for typical HF adducts with organic bases.
It is also a surprise that simple removal of HF is so difficult,
occurring only with CsOH. Instead of removal of HF, we find
that the entire FHF unit may be replaced by a variety of reagents.
(27) Tilset, M.; Hamon, J. R.; Hamon, P. Chem. Comm. 1998, 765.
Cronin, L.; Higgitt, C. L.; Karch, R.; Perutz, R. N. Organometallics. 1997,
16, 4920.
(28) Pagenkopf, B. L.; Carreiro, E. M. Chem.-Eur. J. 1999, 5, 3437.
(29) Murphy, E. F.; Murugavel, R.; Roesky, H. W. Chem. ReV. 1997,
97, 3425.
(30) Cordier, F.; Grzesiek, S. J. Am. Chem. Soc. 1999, 121, 1601.
Cornilescu, G.; Hu, J.-S.; Bax, A. J. Am. Chem. Soc. 1999, 121, 2949.
Golubev, N. S.; Shenderovich, I. G.; Smirnov, S. N.; Denisov, G. S.;
Limbach, H. H. Chem.-Eur. J. 1999, 5, 492.
(26) Fornies, J.; Green, M.; Spencer, J. L.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 1977, 1006.
(31) Perera, S. A.; Bartlett, R. J. J. Am. Chem. Soc. 2000, 122, 1231.

Platinum Hydride Bifluoride Complexes
J. Am. Chem. Soc., Vol. 122, No. 36, 2000 8693
Synthesis of trans-[Pt(PiPr3)2H(FHF)]. This complex was prepared
in identical fashion to trans-[Pt(PCy3)2H(FHF)]. The product was
recrystallized from hexane at -30 °C to give white crystals (yield 65%).
Anal. Found: C, 38.9; H, 8.19. Calcd for C18F2H44P2Pt: C, 38.8; H,
7.96. MS (FAB): m/z ) 555 (M+), 515 (M+ - 2HF).
The 1H NMR spectrum shows a multiplet at δ 1.4 which is assigned
to the CH3 protons of the isopropyl groups and a complicated multiplet
at δ 2.52 assigned to the C-H protons of the isopropyl group. Other
NMR data are listed in Table 1. IR (Nujol ν/cm-1): 2532 (b), 2273
(m), 1903 (s), 1242 (sh), 1230 (m), 1159 (w), 1094 (w), 1061 (w),
1032 (m), 928 (w), 885 (w), 849 (w), 670 (m), 581 (w), 528 (w), 424
(m, br).
[Pt(PCy3)2H(FHF)], may be converted to trans-[Pt(PCy3)2(H)F]
by reaction with CsOH in the presence of [NMe4]F.
Experimental Section
All syntheses and manipulations were carried out under argon using
standard Schlenk (10-2 mbar) and high-vacuum techniques (10-4 mbar)
or in a glovebox. Ether, toluene, benzene, hexane, and tetrahydrofuran
(Fison AR or HPLC grade) were dried over sodium/benzophenone and
distilled under argon. Ethanol (Fison AR grade) was dried over
magnesium turnings and iodine and distilled under argon. The dried
solvents were stored under argon in ampules fitted with a Young’s
ptfe cap. All deuterated solvents, [2H6]-benzene, [2H8]-toluene, and
[2H8]-tetrahydrofuran (Goss Scientific) were dried over potassium and
vacuum distilled prior to use. All NMR tubes (Wilmad 528-PP) either
were fitted with a Young’s tap to allow sealing under argon atmosphere
or were flame sealed under vacuum.
Most NMR spectra were recorded on a Bruker MSL300 (1H recorded
at 300.13 MHz, 19F at 282.35 MHz, 31P at 121.49 MHz) or Bruker
AMX500 spectrometer (1H recorded at 500.13 MHz, 19F at 470.4 MHz,
31P at 202.46 MHz). The temperature of the spectrometer was calibrated
with an internal capillary containing 4% MeOD in MeOH.32 19F NMR
spectra with 1H decoupling were recorded on a Bruker DRX400
spectrometer, as were 1H spectra with 19F decoupling. Simulations were
carried out with g-NMR.21 Mass spectra were recorded on a VG
Autospec instrument and are quoted for 195Pt.
Chemicals were obtained from the following sources: potassium
tetrachloroplatinate was supplied by Aldrich (or recovered from
platinum residues by a standard procedure); PCy3, PiPr3, [NMe4]F,
[NBu4]F‚3H2O, and NEt3‚3HF were supplied by Aldrich, Me3SiOTf
was obtained from Gelest, and Me3SiN3 was synthesized by standard
methods.
[NMe4]F was dried by heating at 50-55 °C under high vacuum (1-2
× 10-4 mbar) for several days.33 It was dissolved in dry 2-propanol
and the volume of the solvent reduced to precipitate most of the material
as [NMe4]F‚(iPrOH)x. The mother liquor was decanted off. The
2-propanol was removed from the crystallized material under dynamic
vacuum and then under high vacuum for a few days. The NMR
spectrum of the product showed no signs of bifluoride or water. [NBu4]-
FHF was synthesized by heating [NBu4]F‚3H2O at 90 °C under high
vacuum for 48 h.34 Under these conditions the only involatile product
should be anhydrous [NBu4]FHF. A room-temperature 1H NMR
spectrum of our product in dry [2H8]-THF showed a 1:2:1 triplet at δ
16.57 (J(HF) ) 120 Hz) and fwhm 24 Hz. The 19F NMR spectrum
showed a doublet at δ -150.2 (J(HF) ) 118 Hz, fwhm ) 25 Hz);
both are consistent with [NBu4]FHF.
Synthesis of trans-[Pt(PCy3)2(H)N3]. trans-[Pt(PCy3)2H(FHF)] (0.1
g, 0.125 mmol) was dissolved in THF (20 cm3) in a Schlenk tube, and
(CH3)3SiN3 (0.0144 g, 0.125 mmol) was added to the solution. The
mixture was stirred at room temperature for 1 h, and the solvent was
then removed under vacuum. The product was extracted with benzene
and then dried under vacuum. The product was recrystallized from THF/
hexane at -30 °C to give white crystals (yield 80%). Anal. Found: C,
54.15; H, 8.51; N, 5.05. Calcd for C36H67N3P2Pt: C, 54.12; H, 8.45;
N, 5.26. MS (FAB): m/z 798 (M+), 755 (M+ - HN3).
The 1H NMR spectrum shows a complicated multiplet at δ 1.0-2.4
for the cyclohexyl groups. Other data are listed in Table 4. IR (Nujol
ν/cm-1): 2180 (s), 2036 (vs), 1340 (vw), 1392 (vw), 1294 (m), 1264
(w), 1171 (m), 1128 (w), 1108 (w), 915 (vw), 896 (w), 888 (w), 865
(s), 816 (vw), 741 (s), 542 (w), 512 (m), 490 (m), 453 (vw), 427 (vw),
409 (vw), 402 (vw), 396 (vw), 336 (vw).
Synthesis of trans-[Pt(PCy3)2H(OTf)]. trans-[Pt(PCy3)2H(FHF)]
(0.1 g, 0.125 mmol) was dissolved in THF (20 cm3) in a Schlenk tube,
and (CH3)3SiOTf (0.027 g, 0.125 mmol) was added to the solution.
The mixture was stirred at room temperature for 2 h, and the solvent
was then removed under vacuum. The product was extracted with
hexane (50 cm3). The solution volume was then reduced to ∼10 cm3,
and white crystals formed at -30 °C (yield 80%). Anal. Found: C,
49.57; H, 7.26. Calcd for C37F3H67O3P2PtS: C, 49.05; H, 7.45. MS
(FAB): m/z 905 (M+), 755 (M+ - OTf).
1
The H NMR spectrum shows a complicated multiplet at δ (1.2-
2.4) for the cyclohexyl protons. Other data are listed in Table 4. IR
(Nujol ν/cm-1): 1311 (m), 1232 (w), 1204 (m), 1159 (w), 1114 (vw),
1073 (vw), 1014 (s), 888 (w), 851 (w, sh), 842 (w), 818 (vw), 806
(vw), 721 (m), 632 (m), 523 (m), 471 (vw), 404 (vw), 380 (vw).
Platinum Dihydride [Pt(PCy3)2H2] with Hexafluorobenzene.
[trans-Pt(PCy3)2H2] (0.5 g, 0.66 mmol) was dissolved in THF (60 cm3)
in a Schlenk tube, and a 2-fold excess of dried C6F6 (0.24 g, 1.3 mmol)
and an excess of dried tetramethylammonium fluoride were added. The
Schlenk tube was heated at 50 °C for 48 h, yielding a mixture of 5%
trans-[Pt(PCy3)2H(FHF)] and 65% of trans-[Pt(PCy3)2H(C6F5)], ac-
cording to NMR spectroscopy. The bifluoride complex trans-[Pt-
(PCy3)2H(FHF)] was extracted with hexane. The reaction products were
Synthesis of Platinum Dihydride Complexes. The complexes trans-
i
[Pt(PR3)2H2] (R ) Cy, Pr) were prepared according to the literature
procedures.26,35
Synthesis of trans-[Pt(PCy3)2H(FHF)]. trans-[Pt(PCy3)2H2] (0.5 g,
0.66 mmol) was dissolved in THF (50 cm3) in a Schlenk tube, and a
3-fold excess of NEt3‚3(HF) (0.32 g, 1.98 mmol) was added to the
solution. The mixture was stirred at room temperature for 1 h. The
solvent was removed under vacuum, and the product was dissolved in
benzene and filtered through a cannula and dried under vacuum. The
product was recrystallized from THF/hexane at -30 °C to give white
crystals (yield 76%). Anal. Found: C, 53.87; H, 8.73. Calcd for
C36F2H68P2Pt: C, 54.38; H, 8.60. Mass spectra (FAB-MS): m/z ) 795
(M+), 755 for (M+ - 2HF).
1
1
characterized by H, H{31P}, 31P{1H }, and 19F NMR spectroscopy.
Reaction of trans-[Pt(PCy3)2H(FHF)] with CsOH. trans-[Pt-
(PCy3)2H(FHF)] (0.1 g, 0.125 mmol) was dissolved in THF (20 cm3)
in a Schlenk tube. The solution was added to a mixture of excess solid
[NMe4]F (∼20 mg) and CsOH (∼20 mg) under argon. The resulting
suspension was stirred at room temperature for 1 h, and the solvent
was then removed under vacuum. The product was extracted with
hexane (30 cm3) and then dried under vacuum to yield a white product.
IR (Nujol ν/cm-1): 2235 (w), 2236 (m), 1296 (vw), 1294 (m), 1267
(w), 1173 (m), 1128 (w), 1109 (w), 1070 (m), 1003 (m), 916 (vw),
898 (w), 887 (w), 865 (s), 848 (s), 819 (vw), 739 (s), 721 (s).
The 1H NMR spectrum shows a complicated multiplet at δ 1.2-2.4
which is assigned to the cyclohexyl protons. Other NMR data are listed
in Table 1. IR (Nujol ν/cm-1): 2630 (m, br), 2604 (m, br), 1832 (s),
1342 (w), 1302 (w), 1262 (w), 1110 (w), 1003 (m), 970 (w), 848 (m),
745 (w), 717 (w), 514 (w), 490 (w), 442 (w), 426 (w).
Acknowledgment. We acknowledge financial support from
the EPSRC and the University of York for a studentship. We
wish to thank Professor B. Mann, Dr. S. B. Duckett, and C.
Aspley for help and advice.
(32) Ammann, C.; Meier, P.; Merbach A. E. J. Magn. Reson. 1982, 46,
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