Synthesis and structure of a cationic diplatinum μ-alkylidene μ-hydride complex

Article abstract of DOI:10.1021/om9708034

The dinuclear μ-alkylidene μ-hydride cation [Pt₂(dppf)₂(μ-CHCH₂Ar)(μ-H)][Br] (2, dppf = Ph₂PC₅H₄FeC₅H₄PPh ₂, Ar = p-MeOC₆H₄) was obtained unexpectedly from reaction of p-methoxybromostyrene (3) with Pt(dppf)Cl₂/NABH₄/norbornene and crystallographically characterized. Solutions of the hydride [Pt(dppf)H]₂ (7), prepared by deprotonation of the known cation [Pt₂(dppf)₂H₃]⁺ (6) or by treatment of Pt(dppf)Cl₂ with two equiv of LiBEt₃H, deposit an insoluble precipitate formulated as [Pt(dppf)H]_n (11), which also gives 2 on treatment with 3.

Full text of DOI:10.1021/om9708034

574
Organometallics 1998, 17, 574-578
Syn th esis a n d Str u ctu r e of a Ca tion ic Dip la tin u m
µ-Alk ylid en e µ-Hyd r id e Com p lex
Michael A. Zhuravel and David S. Glueck*
6128 Burke Laboratory, Department of Chemistry, Dartmouth College,
Hanover, New Hampshire 03755
Louise M. Liable-Sands and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received September 11, 1997
The dinuclear µ-alkylidene µ-hydride cation [Pt2(dppf)2(µ-CHCH2Ar)(µ-H)][Br] (2, dppf )
Ph2PC5H4FeC5H4PPh2, Ar ) p-MeOC6H4) was obtained unexpectedly from reaction of
p-methoxybromostyrene (3) with Pt(dppf)Cl2/NaBH4/norbornene and crystallographically
characterized. Solutions of the hydride [Pt(dppf)H]2 (7), prepared by deprotonation of the
known cation [Pt2(dppf)2H3]+ (6) or by treatment of Pt(dppf)Cl2 with two equiv of LiBEt3H,
deposit an insoluble precipitate formulated as [Pt(dppf)H]n (11), which also gives 2 on
treatment with 3.
Sch em e 1a
Although many dinuclear platinum complexes are
known, a particularly rare class of these compounds
contains bridging alkylidene and hydride ligands.1
Minghetti and co-workers reported the unusual reaction
shown in Scheme 1 to give what, so far, is the unique
example [Pt2(dppe)2(µ-CHCH2Ph)(µ-H)]+ (1, dppe ) Ph2-
PCH2CH2PPh2).2 We report here a new synthetic route
to the closely related complex [Pt2(dppf)2(µ-CHCH2Ar)-
(µ-H)]+ (2, dppf ) Ph2PC5H4FeC5H4PPh2, Ar ) p-
MeOC6H4) and its spectroscopic and crystallographic
characterization.
a
dppe ) Ph2PCH2CH2PPh2. Reference 2.
Sch em e 2a
Complex 2 was initially obtained in poor yield (Scheme
2) as an unexpected product from the reaction of
p-methoxybromostyrene (3) with a material generated
in situ from Pt(dppf)Cl2, NaBH4, and norbornene in
CH2Cl2/EtOH, according to a procedure for the prepara-
tion of Pt(dppf)(CHdCHAr)Br (4) reported by Brown
and Cooley.3 Complex 2 was prepared reproducibly
several times (see Experimental section). The original
preparation of 4 reported the use of dry solvents, and
we used absolute ethanol without further purification,
but this does not explain our results since the expected
Pt(II) oxidative addition product 4 could also be made
under very similar conditions (see Experimental Sec-
tion). Although we do not understand the reason for
these observations, we have developed an alternative
reproducible synthesis of 2 (see below).
a
Ar ) p-MeOC6H4. Reagents: (i) 2 equiv of NaBH4, nor-
bornene, CH2Cl2/EtOH; (ii) p-methoxybromostyrene (3).
fine structure in the spectrum could be reproduced by
simulation (Figure 1a,b, see Figure 2 for atom labeling)
using the coupling constants above in addition to J 14
)
3, J 15 ) 230, J 34 ) 2, J 35 ) 16, J 56 ) 43.5 These results
are similar to those for 1 (for P trans to H, 1J Pt-P ) 4350,
3J Pt-P ) 173; for P trans to C, J Pt-P ) 2082) and for 5
1
at low temperature (1J Pt-P ) 4927, 3J Pt-P ) 600 (P trans
1
to H); J Pt-P ) 2892 (P trans to C)). In all three
Complex 2 was identified spectroscopically in com-
parison to 1 and the µ-carbonyl complex4 [Pt2(dppf)2(µ-
CO)(µ-H)]+ (5). The 31P{1H} NMR spectrum (CD2Cl2,
Figure 1) shows two multiplets at δ 22.2 (1J Pt-P ) 4690,
trans to H), and 11.9 (1J Pt-P ) 2403, trans to C). The
1
3
compounds, both J Pt-P and J Pt-P values for P trans to
the µ-hydride are much larger than those for P trans to
the µ-alkylidene or µ-carbonyl, reflecting the relative
trans influences of these ligands.
In the 1H NMR spectrum (CD2Cl2) the hydride
resonance appears at δ -3.31 (tt, 2J P-H ) 13, 79, 1J Pt-H
) 566), which is very similar to the results for 1 (2J P-H
) 7.8, 76, 1J Pt-H ) 578) and 5 at low temperature (2J P-H
(1) For a review, see: Anderson, G. K. Adv. Organomet. Chem. 1993,
35, 1-39.
(2) Minghetti, G.; Albinati, A.; Bandini, A. L.; Banditelli, G. Angew.
Chem., Int. Ed. Engl. 1985, 24, 120-121.
(3) Brown, J . M.; Cooley, N. A. Organometallics 1990, 9, 353-359.
(4) Bandini, A. L.; Banditelli, G.; Cinellu, M. A.; Sanna, G.; Ming-
hetti, G.; Demartin, F.; Manassero, M. Inorg. Chem. 1989, 28, 404-
410.
(5) Simulation with gNMR (Cherwell Scientific). J 12 ) 200 was used
in the simulation, but the spectrum was not sensitive to this coupling
constant.
S0276-7333(97)00803-0 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/24/1998

A Cationic Pt2 µ-Alkylidene µ-Hydride Complex
Organometallics, Vol. 17, No. 4, 1998 575
F igu r e 3. ORTEP diagram of 2‚0.5CH2Cl2‚0.5H2O. For
clarity, the bromide counterion and cocrystallized solvents
are not shown. Selected bond lengths (Å) and angles (deg):
Pt(1)-C(101) 2.065(7), Pt(1)-P(1) 2.246(2), Pt(1)-P(2)
2.337(2), Pt(1)-Pt(2) 2.7314(4), Pt(2)-C(101) 2.076(8),
Pt(2)-P(3) 2.259(2), Pt(2)-P(4) 2.311(2), C(101)-C(102)
1.522(11); Pt(1)-C(101)-Pt(2) 82.5(3), C(101)-Pt(1)-P(1)
90.1(2), C(101)-Pt(1)-P(2) 169.0(2), P(1)-Pt(1)-P(2)
100.60(7), C(101)-Pt(1)-Pt(2) 48.9(2), P(1)-Pt(1)-Pt(2)
134.93(5), P(2)-Pt(1)-Pt(2) 121.61(6), C(101)-Pt(2)-P(3)
86.5(2), C(101)-Pt(2)-P(4) 170.3(2), P(3)-Pt(2)-P(4)
102.20(7), C(101)-Pt(2)-Pt(1) 48.6(2), P(3)-Pt(2)-Pt(1)
126.28(6), P(4)-Pt(2)-Pt(1) 125.91(5).
F igu r e 1. Experimental (top) and simulated (bottom)
31P{1H} NMR spectrum of 2 in CD2Cl2. (a) full spectrum,
(b) expansion.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
empirical formula
fw
C77.5H69BrClFe2O1.5P4Pt2
1765.58
temp
223(2) K
wavelength
cryst syst
0.71073 Å
monoclinic
space group
unit cell dimensions
C2/c
a ) 23.69760(10) Å, R ) 90°
b ) 13.8429(2) Å, â ) 91.4520(10)°
c ) 41.73820(10) Å, γ ) 90°
13687.5(2) Å3, 8
1.711 mg/m3
F igu r e 2. Atom labeling for complex 2.
) 16, 82, 1J Pt-H ) 453).2,4 The protons of the alkylidene
ligand give rise to broad (even at -60 °C) peaks at δ
1.33 (CH2) and 4.87 (CH); these are coupled to each
volume, Z
density (calcd)
abs coeff
5.253 mm-1
F(000)
cryst color, size
θ range for data collection 0.98-28.49°
limiting indices
6912
1
other in the H-1H COSY spectrum, and C-H correla-
yellow block, 0.50 × 0.50 × 0.40 mm
tion spectra obtained with the HMQC sequence show
they are attached to carbons with 13C NMR signals at
44.5 and 135.8 ppm, respectively. For comparison, the
µ-CH 13C NMR signal in 1 appears at δ 124.5; the rest
-31 e h e 31, 0 e k e 16, 0 e
l e 55
26 044
14 352 (Rint ) 0.0427)
empirical from DIFABS
no. of reflns collected
no. of indep reflns
abs corr
max and min transmission 1.000 and 0.798
refinement method
1
of the H and 13C NMR spectra were not reported.2
The crystal structure of 2 as the bromide salt, with
cocrystallized CH2Cl2 and water, is shown in Figure 3.
Figure S1 in the Supporting Information shows the
structure from a different angle. Data collection and
structure refinement are summarized in Table 1, se-
lected bond lengths and angles appear in the figure
caption, and additional details are given in the Experi-
mental Section and the Supporting Information. The
metal hydride was not observed. The C-C bond length
in the alkylidene ligand (1.522(11) Å) confirms reduction
of the CdC double bond and is similar to that in 1
(1.52(2) Å).2 The geometry of the Pt2C triangle compares
well with those in the related complexes 1 and 5: Pt-
Pt distances for these three compounds are 2.7314(4),
2.735(1), and 2.790(1) Å, while the Pt-C-Pt angles are
82.5(3)°, 84.1(6)°, and 87.3(3)°. The Pt-C bond lengths
full-matrix least-squares on F2
data/restraints/parameters 14343/0/813
goodness-of-fit on F2
1.348
final R indices [I > 2σ > (I)] R1 ) 0.0591, wR2 ) 0.1161
R indices (all data)
largest diff peak and hole
R1 ) 0.0844, wR2 ) 0.1305
3.710 and -4.126 e Å-3
are also very similar: 2.065(7) and 2.076(8), 2.02(2) and
2.07(2), and 2.039(8) and 2.004(7) Å. The Pt-P(dppf)
distances in 2 and 5 (for P trans to H, 2.246(2) and
2.259(2) Å in 2, 2.300(2) and 2.293(2) Å in 5; for P trans
to C, 2.337(2) and 2.311(2) Å in 2, 2.358(2) and 2.359(2)Å
in 5) are also similar. This indicates, consistent with
the 31P NMR results, that the trans influence of the
bridging carbonyl and alkylidene ligands is similar and
larger than that of the µ-H ligand.6 Finally, the bite

576 Organometallics, Vol. 17, No. 4, 1998
Zhuravel et al.
Sch em e 3a
known compounds were identified by 31P NMR.8 Thus,
as previously reported for the analogous [Pt(dppe)H]2,9
complex 7 is a convenient source of Pt(0).
When hydride 7 was generated by either of these
methods, a yellow solid (11) rapidly precipitated from
solution (Scheme 3). Unfortunately, the formation of
this solid prevented us from acquiring low-temperature
NMR spectra of 7. The precipitate was insoluble in the
common solvents and could not be recrystallized. Pre-
sumably, it is oligomeric with bridging dppf ligands;10
elemental analysis and IR (νPt-H ) 2018 cm-1, KBr) are
consistent with the composition [Pt(dppf)H]n. The deu-
teride [Pt(dppf)D]n was prepared similarly from LiBEt3D
(νPt-D ) 1494 cm-1, KBr). Addition of HBF4‚Me2O to a
CH2Cl2 slurry of 11 gave a yellow-orange solution of
trihydride cation 6 (Scheme 3). Similarly, treatment of
THF slurries of 11 with trans-stilbene or dppf slowly
led to the formation of the zero-valent complexes 8 and
10.
a
[Pt] ) Pt(dppf), Ar ) p-MeOC6H4. Reagents: (i) 2 equiv of
LiBEt3H (ii) 1 equiv of L per Pt, L ) trans-stilbene (for 8),
bromostyrene 3 (for 9), or dppf (for 10); (iii) 1 equiv of L per
Pt, L ) trans-stilbene or dppf; (iv) THF, room temperature,
ca. 1 h (v) KOt-Bu or LiN(SiMe3)2; (vi) HBF4‚Me2O; (vii)
bromostyrene 3; (viii) bromostyrene 3 in CH2Cl2, then KOt-
Bu or LiN(SiMe3)2
angle of the dppf ligands in 2 (100.60(7)° and 102.20(7)°)
is similar to that in carbonyl complex 5 (103.68(6) and
103.64(6)°).
Reaction of a THF slurry of 11 with bromostyrene 3
reproducibly led to the formation of dinuclear cation 2;
in one case (see Experimental Section), it was isolated
after recrystallization in 42% yield. However, this
reaction sometimes gave, in addition to 2, the bromosty-
rene π-complex 9 and the oxidative addition product
Pt(dppf)(CH)CHAr)Br (4). In CH2Cl2, 2 and 4 were
observed (Scheme 3). Despite the occasional formation
of these byproducts, this procedure is the best and most
reproducible way to make 2. These results and the
physical properties of 7 and 11 are consistent with the
idea that these compounds have different structures and
hence different reactivity.
The unexpected formation of 2 suggested the inter-
mediacy of a platinum hydride. Therefore, treatment
of Pt(dppf)Cl2 with NaBH4 in CH2Cl2/EtOH without
norbornene was investigated. The IR (KBr) spectrum
of the insoluble yellow solid formed showed an absorp-
tion at 2019 cm-1 assigned to a Pt-H stretch. When
this material was treated with AgBF4 in CH2Cl2, it
dissolved and 31P NMR showed that an ∼1:1 mixture
2+
of the known cations [Pt(dppf)(µ-OH)]2
and [Pt2-
(dppf)2H3]+ (6) was present.4 The insoluble material on
treatment with bromostyrene 3 gave dinuclear 2 plus
several other products after heating in CH2Cl2 at 60 °C
for 3 days, according to 31P NMR.
These observations suggest that a Pt hydride is
involved in the formation of 2, presumably via bro-
mostyrene insertion into a Pt-H bond followed by Pt-C
bond formation with the loss of bromide ion. However,
the details of the mechanism and the factors responsible
for the varied yields of the products in either of the
syntheses of 2 remain unclear. It is possible that the
insoluble material formed in the initial Pt(dppf)Cl2/
NaBH4 mixture contains 11, as suggested by the
similarity of their IR spectra. However, since neither
of these materials could be purified, further mechanistic
speculation seems imprudent.
To investigate the role of trihydride cation 6 further,
it was prepared independently and treated with bro-
mostyrene 3 in CH2Cl2 (Scheme 3). No reaction oc-
curred even on heating to 55 °C for 3 days. However,
when this reaction mixture was treated with NaBH4 in
EtOH, KOt-Bu, or LiN(SiMe3)2, dinuclear 2 was formed.
These observations suggested the intermediacy of the
neutral hydride [Pt(dppf)H]2 (7), generated by deproto-
nation of cation 6. Indeed, treatment of 6 with KOt-
Bu or LiN(SiMe3)2 in THF gave 7 as a red solution
whose 31P NMR spectrum (δ 37.3, 1J Pt-P ) 4184, 3J Pt-P
2
) 218, J P-P ) 40) is similar to that of related hydride
dimers (Scheme 3).7 When the deprotonation was
In conclusion, the unusual µ-alkylidene µ-hydride
cation 2 has been prepared and spectroscopically and
crystallographically characterized. The new hydrides
[Pt(dppf)H]2 (7) and [Pt(dppf)H]n (11) were prepared;
although 11 reacts with bromostyrene 3 to give 2, the
mechanism of this reaction remains unclear. Finally,
the synthesis of 2 by reaction of a bromostyrene deriva-
carried out in THF-d8, the hydride resonance for 7 was
1
observed by H NMR as a broad signal at -3.4 ppm.
Complex 7 could also be prepared conveniently by
reaction of Pt(dppf)Cl2 with 2 equiv of LiBEt3H in THF
(Scheme 3), which gave a dark solution whose 31P NMR
spectrum was the same as that described above. THF
solutions of 7 generated by deprotonation of cation 6
reacted immediately (Scheme 3) with trans-stilbene,
bromostyrene 3, and dppf to give Pt(dppf)(trans-stilbene)
(8), Pt(dppf)(3) (9), and Pt(dppf)2 (10), respectively; these
(8) Pt(dppf)(trans-stilbene) (8) has been prepared independently by
treatment of a mixture of Pt(dppf)Cl2 and trans-stilbene with 2 equiv
of LiBEt3H in THF. 31P{1H} NMR (C6D6): δ 24.5 (1J Pt-P ) 3763). Full
details of the synthesis and characterization will be reported sepa-
rately. For the bromostyrene π-complex (9), see ref 3. For Pt(dppf)2
(10), see: Fang, Z.-G.; Low, P. M. N.; Ng, S.-C.; Hor, T. S. A. J .
Organomet. Chem. 1994, 483, 17-20. Treatment of a mixture of 6 and
3 in THF with KOt-Bu also gave the π-complex 9, but a similar
experiment in CH2Cl2 gave cation 2 plus vinyl bromide complex 4.
(9) Carmichael, D.; Hitchcock, P. B.; Nixon, J . F.; Pidcock, A. J .
Chem. Soc., Chem. Commun. 1988, 1554-1556.
(6) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335-422.
(7) 31P NMR data for a series of [Pt(diphos)H]2 dimers (diphos )
dippe ((i-Pr)2PCH2CH2P(i-Pr)2), dcpe (Cy2PCH2CH2PCy2; Cy ) cyclo-
C6H11), dtbpe ((t-Bu)2PCH2CH2P(t-Bu)2), dppe) is given in Schwartz,
D. J .; Andersen, R. A. J . Am. Chem. Soc. 1995, 117, 4014-4025 and
references therein. A referee pointed out that the Pt-P coupling
constants in 7 compare better with those of the dfepe analog (dfepe )
(C2F5)2PCH2CH2P(C2F5)2), see Bennett, B. L.; Roddick, D. M. Inorg.
Chem. 1996, 35, 4703-4707) than with these examples.
(10) For a review of dppf coordination chemistry with examples of
µ-dppf coordination, see: Gan, K.-S.; Hor, T. S. A. In Ferrocenes.
Homogeneous Catalysis, Organic Synthesis, Materials Science; Togni,
A., Hayashi, T.; Eds.; VCH: Weinheim, Germany, 1995; pp 3-104.

A Cationic Pt2 µ-Alkylidene µ-Hydride Complex
Organometallics, Vol. 17, No. 4, 1998 577
centrosymmetric space group, which was verified by the
chemically reasonable and computationally stable results of
refinement. The structure was solved using direct methods,
completed by subsequent difference Fourier syntheses, and
refined by full-matrix least-squares procedures. An empirical
absorption correction was applied, based on a Fourier series
in the polar angles of the incident and diffracted beam paths
and was used to model an absorption surface for the difference
between the observed and calculated structure factors.12 The
asymmetric unit contains one cation, a bromide anion on a
2-fold axis, a bromide anion disordered over an inversion
center, one-half of a molecule of dichloromethane, and one-
half of a molecule of water. All non-hydrogen atoms were
refined with anisotropic displacement coefficients, and hydro-
gen atoms, except those on the water molecule, which were
omitted, were treated as idealized contributions. One signifi-
cant peak remained on the difference map (3.71 e/Å3) but was
in a chemically unreasonable position (<0.5 Å from Pt) and
was considered noise.
tive with a metal hydride is novel and may provide a
general route to µ-alkylidene complexes.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Unless otherwise noted, all
reactions and manipulations were performed in dry glassware
under a nitrogen atmosphere at 20 °C in a drybox or using
standard Schlenk techniques. Petroleum ether (bp 38-53 °C),
ether, THF, and toluene were dried and distilled before use
by employing Na/benzophenone. CH2Cl2 was distilled from
CaH2. Absolute ethanol was used as purchased without
further purification.
Unless otherwise noted, all NMR spectra were recorded on
a Varian 300 MHz spectrometer. 1H and 13C NMR chemical
shifts are reported relative to Me4Si and were determined by
reference to the residual 1H or 13C solvent peaks. 31P NMR
chemical shifts are reported relative to H3PO4 (85%), used as
an external reference. Unless otherwise noted, peaks in the
NMR spectra are singlets. Coupling constants are reported
in hertz. Infrared spectra were recorded on a Perkin-Elmer
All software and sources of the scattering factors are
contained in the SHELXTL (5.03) program library (G. Sheld-
rick, Siemens XRD, Madison, WI).
1600 series FTIR instrument and are reported in cm-1
.
Rea ction of P t(d p p f)Cl2 w ith Na BH4. To a stirred
solution of Pt(dppf)Cl2 (50 mg, 0.06 mmol) in CH2Cl2 (15 mL)
was added an excess of NaBH4 (8 mg, 0.21 mmol) in ethanol
(10 mL). The color of the solution changed from yellow to dark
orange, and after 1 h of stirring a yellow solid formed. The
solution was decanted, and the solid residue was washed with
petroleum ether (2 × 7 mL) and dried under vacuum to give
an insoluble yellow solid. IR (KBr): 3049, 2970, 2295, 2019
(νPt-H), 1479, 1434, 1166, 1095, 1028, 744. This solid is
probably a mixture of compounds, as indicated by the following
experiments.
(a) A sample of this material (50 mg) was suspended in
CH2Cl2, and an excess of AgBF4 (20 mg, 0.1 mmol) was added.
After 15 min of stirring, the dark green solution was filtered.
The 31P NMR spectrum of the solution showed a mixture of
the known4 hydroxide [Pt2(dppf)2(µ-OH)2][BF4]2 and trihydride
cation 6 in approximately equal amounts.
(b) A sample of this material (20 mg) was placed into an
NMR tube with excess of bromostyrene 3 (9 mg, 0.05 mmol)
in CH2Cl2, and the solution was heated at 60 °C. After 3 days,
the solid dissolved to give a dark yellow solution; 31P NMR
showed 2 was the major product.
Com plex 2 via [P t2(dppf)2H3][BF4] (6). [Pt2(dppf)2H3][BF4]
(144 mg, 0.09 mmol) was dissolved in CH2Cl2. Bromostyrene
3 (20 mg, 0.15 mmol) was added as a CH2Cl2 solution, and
the reaction was monitored by 31P NMR. After 6 days of
stirring, no reaction occurred. LiN(SiMe3)2 was added to the
solution in excess, and the solution was stirred for 5 days. The
major product, 2, was identified by 31P NMR.
[P t(d p p f)H]2 (7) a n d [P t(d p p f)H]n (11). To a stirred
solution of Pt(dppf)Cl2 (113 mg, 0.13 mmol) in THF (5 mL)
was added Super-Hydride (LiBEt3H, 0.27 mL of 1M THF
solution, 0.27 mmol) to afford a dark red solution. At this
point, the 31P{1H} NMR spectrum showed a peak at δ 37.3
(1J Pt-P ) 4184, 3J Pt-P ) 218, 2J P-P ) 40), plus minor impurities.
After 1 h of stirring, a yellow solid precipitated out of the
solution. The solution was decanted, and the solid was washed
with THF and dried in vacuum to give 89 mg (78% yield) of
11 as insoluble yellow powder. IR (KBr): 3050, 2925, 2018
(Pt-H), 1479, 1434, 1166, 1096, 1067, 1029, 822, 745, 695. Anal.
Calcd. for C68H58P4Fe2Pt2: C, 54.41; H, 3.89%. Found: C,
54.13; H, 4.39%.
Elemental analyses were provided by Schwarzkopf Microana-
lytical Laboratory. Unless otherwise noted, reagents were
from commercial suppliers. The following compounds were
4
made by the literature procedures: Pt(dppf)Cl2, p-MeOC6H4-
CH)CHBr,11 [Pt2(dppf)2H3][BF4].4
[P t2(d p p f)2(µ-CHCH2Ar )(µ-H)][Br ] (2, Ar ) pMeOC6H4).
To a solution of Pt(dppf)Cl2 (prepared from Pt(COD)Cl2 and
dppf and recrystallized from CH2Cl2/ether, 189 mg, 0.23 mmol,
COD ) 1,5-cyclooctadiene) in CH2Cl2 (5 mL) was added a
solution of norbornene (113 mg, 1.20 mmol) in absolute ethanol
(5 mL), which was purged with nitrogen for 60 min. When
solid NaBH4 (39 mg, 1.0 mmol) was added, the solution
bubbled, then changed color from yellow to dark orange and
then to olive/khaki. After 3 h of stirring, the solution was
filtered. The solid was washed with ether (2 × 5 mL) and dried
in vacuum. The solid was suspended in CH2Cl2 (5 mL) and
p-MeOC6H4CH)CHBr (3, 60 mg, 0.28 mmol) was added to
afford, after 2 days of stirring, a dark yellow solution. The
solution was filtered, and the solvent was removed. The solid
residue was redissolved in CH2Cl2 and recrystallized with
ether at -20 °C to give the product as a dark yellow solid in
∼30% yield. Subsequent additional recrystallizations afforded
dark orange crystals of X-ray quality. This preparation could
be reproduced several times, but a separate batch of Pt(dppf)-
Cl2, which was not recrystallized, gave the reported Pt(dppf)-
(CH)CHAr)Br (4).3 We have not been able to discover the
reason(s) for the success or failure of these syntheses.
1H NMR (CD2Cl2, 500 MHz): δ 7.71 (4H, m, Ar), 7.53 (2H,
m, Ar), 7.4-7.1 (24H, m, Ar), 7.0-6.8 (12H, m, Ar), 6.61 (2H,
m, Ar), 4.87 (br, 1H, CH), 4.63 (2H, CH), 4.46 (2H, CH), 4.41
(2H, CH), 4.39 (2H, CH), 4.34 (2H, CH), 4.20 (2H, CH), 3.81
(3H, Me), 3.77 (2H, CH), 3.60 (2H, CH), 1.33 (2H, br, CH2),
-3.31 (1H, tt, 2J P-H ) 13, 2J P-H ) 79, 1J Pt-H ) 566, Pt-H). 13C
NMR (CD2Cl2): δ 157.8 (Ar), 135.8 (CH), 135.2 (m, Ar), 134.1
(m, Ar), 133.3 (m, Ar), 131.8 (Ar), 130.7 (m, Ar), 128.5 (m, Ar),
113.0 (Ar), 76.0 (m, Cp), 75.1 (m, Cp), 73.8 (m, Cp), 72.9 (m,
Cp), 55.4 (OMe), 44.5 (CH2). 31P{1H} NMR (CD2Cl2): δ 22.2
1
1
(m, J Pt-P ) 4690), 11.9 (m, J Pt-P ) 2403). IR (KBr): 3050,
1508, 1480, 1435, 1385, 1306, 1243, 1166, 1097, 1030, 748, 696.
Anal. Calcd for C77H67BrFe2OP4Pt2: C, 53.96; H, 3.94.
Found: C, 53.57; H, 4.55.
Cr yst a llogr a p h ic St r u ct u r a l Det er m in a t ion for
2‚0.5CH2Cl2‚0.5H2O. Crystal, data collection, and refinement
parameters are given in Table 1. The systematic absences in
the diffraction data are consistent with the space groups Cc
or C2/c. The E-statistics and the value of Z indicated the
[P t(d p p f)D]n (11-D) was prepared following a similar
procedure as that for the hydride, using Super-Deuteride, and
was isolated as a brown solid, which did not give satisfactory
elemental analyses. IR (KBr): 3051, 2923, 1494, 1480, 1435,
1097, 1067, 823, 747, 696.
(11) Trumbull, E. R.; Finn, R. T.; Ibne-Rasa, K. M.; Sauers, C. K. J .
Org. Chem. 1962, 27, 2339-2344.
(12) Walker, N.; Stuart, D. Acta. Crystallogr. 1983, A39, 158-166.

578 Organometallics, Vol. 17, No. 4, 1998
Zhuravel et al.
Dep r oton a tion of 6: F or m a tion of 7 a n d its Rea ction s
w ith tr a n s-Stilben e, d p p f, a n d Br om ostyr en e 3. To an
orange slurry of trihydride cation 6 (30 mg, 0.019 mmol) in
THF-d8 (0.5 mL) was added a solution of KOt-Bu (5 mg, 0.05
mmol) in 0.3 mL of THF-d8. On mixing, a red solution formed;
some suspended solid remained. The 31P{1H} NMR spectrum
was the same as that described above in the synthesis from
Pt(dppf)Cl2 and LiBEt3H. 1H NMR (THF-d8): δ 7.66 (br, 14H),
7.30 (4H), 7.11 (apparent t, “J ” ) 7, 8H), 6.93 (apparent t, “J ”
) 7, 14H), 4.21 (8H), 4.15 (8H), -3.4 (br, 2H). After 1 h, most
of the material had precipitated out as an orange-brown solid,
which turned yellow over several hours.
In related experiments, hydride 7 was generated as a red
THF solution by addition of KOt-Bu (2 mg, 0.02 mmol) to 10
mg (0.006 mmol) of cation 6. Addition of trans-stilbene (5 mg,
0.03 mmol) to one such mixture caused an immediate color
change to yellow-orange; 31P NMR confirmed the formation of
Pt(dppf)(trans-stilbene) (8). Similarly, addition of dppf (10 mg,
0.02 mmol) in a separate experiment gave a yellow solution;
31P NMR showed the presence of Pt(dppf)2 (10) and excess dppf.
In another experiment, 20 mg (0.012 mmol) of 6 was treated
with 2 mg (0.02 mmol) of KOt-Bu. To the resulting orange-
red slurry was added bromostyrene 3 (5 mg, 0.02 mmol). The
color of the solution changed to yellow, and 31P NMR showed
that the π-complex Pt(dppf)(p-MeOC6H4CH)CHBr) (9) had
formed.
P r oton a tion of [P t(d p p f)H]n (11). Hydride complex 11
(40 mg, 0.03 mmol) was suspended in THF (2 mL). Upon
addition of HBF4‚Me2O (5 mg, 0.04 mmol) the solution acquired
a yellow color. After 3 h of stirring, the color of the solution
became orange and the solid dissolved completely. The solvent
was removed, and the solid residue was redissolved in CH2-
Cl2 and filtered. The product [Pt2(dppf)2H3][BF4] (6) was
identified by 31P NMR. This reaction can also be carried out
on a larger scale in CH2Cl2.
Rea ction s of [P t(d p p f)(H)]n (11) w ith d p p f a n d tr a n s-
Stilben e. A slurry of [Pt(dppf)(H)]n (20 mg, 0.01 mmol) and
dppf (10 mg, 0.02 mmol) in 1 mL of THF was placed in an
NMR tube. No visible reaction occurred. After 15 h, 31P NMR
showed that Pt(dppf)2 (10) had formed; some dppf was also
observed, as well as some remaining insoluble solid. In a
similar experiment with trans-stilbene (6 mg, 0.03 mmol), Pt-
(dppf)(trans-stilbene) (8) was observed by 31P NMR after 15
h; again, some insoluble solid remained.
Com p lex 2 via [P t(d p p f)H]n (11). Pt(dppf)Cl2 (108 mg,
0.13 mmol) was suspended in THF (5 mL). Upon addition of
Super-Hydride (0.27 mL of 1M solution in THF, 0.27 mmol),
the yellow solid rapidly dissolved with bubbling to form a dark
orange solution. After 1 h at room temperature a yellow
precipitate formed. The solution was decanted, and the solid
residue was washed with ether (3 × 5 mL) and dried.
p-MeOC6H4CHdCHBr (15 mg, 0.07 mmol) was added to the
solid as a solution in THF (10 mL). After 2 days of stirring,
the solution was filtered, the solvent was removed, and the
solid residue was redissolved in CD2Cl2. The 31P NMR
spectrum showed mostly 2 with minor impurities of other
unidentified compounds. Addition of ether and cooling to -20
°C gave 48 mg (42% yield) of 2.
Ack n ow led gm en t. We thank the donors of the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society, the Exxon Education Foundation,
DuPont, the NSF CAREER program, and Dartmouth
College for partial support, and the Department of
Education for a fellowship for M.A.Z. We also thank
J ohnson-Matthey/Alfa/Aesar for loans of Pt salts. The
University of Delaware acknowledges the NSF for their
support of the purchase of the CCD-based diffractometer
(Grant No. CHE-9628768).
Su p p or tin g In for m a tion Ava ila ble: Tables of the crystal
data and structure refinement, atomic coordinates, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates and ORTEP diagram of 2‚0.5H2O‚0.5CH2-
Cl2 (12 pages). Ordering information is given on any current
masthead page.
OM9708034