Synthesis and structures of platinum A-frame complexes

Article abstract of DOI:10.1021/om000337+

Reactions of [PtCl₂(cod)] with the appropriate Grignard reagents produce [PtR₂(cod)] (R = C₆H₅, C₆H₄CH₃-4, C₆H₄CH₃-2, CH₂C₆H₅), which, on treatment with 1 mol equiv of HCl, yield the corresponding chloroplatinum complexes [PtClR(cod)]. The 2-tolyl compounds exhibit hindered rotation about the Pt-C bonds at ambient temperature, the barrier to rotation being greater in [PtCl(C₆H₄CH₃-2)(cod)] than in the ditolyl derivative. The chloroplatinum compounds react with 1 mol equiv of dppm to give [PtClR(dppm)], which are in equilibrium with the A-frame complexes [Pt₂R₂(μ-Cl)(μ-dppm)₂]Cl. The extent of dimerization depends on the nature of R, but in each case the A-frame complex could be obtained quantitatively by treatment of the solution with NH₄PF₆ or TlPF₆. The structures of [Pt₂R₂(μ-Cl)(μ-dppm)₂]PF₆ (R = CH₂C₆H₅, C₆H₄CH₃-4) were determined by X-ray crystallography. In the benzyl derivative, one of the ortho hydrogens on each phenyl (benzyl) ring points towards the centroid of a dppm phenyl ring, and this may account for the low-frequency signal associated with the ortho hydrogens in solution. The chloride-bridged A-frames could be converted to the corresponding hydride-bridged derivatives, [Pt₂R₂(μ-H) (μ-dppm)₂]PF₆ (R = C₆H₅, C₆H₄-CH₃-4, CH₂C₆H₅), by treatment with NaBH₄.

Full text of DOI:10.1021/om000337+

Organometallics 2000, 19, 5071-5076
5071
Syn th esis a n d Str u ctu r es of P la tin u m A-F r a m e
Com p lexes
Mesfin J anka, Gordon K. Anderson,* and Nigam P. Rath
Department of Chemistry, University of MissourisSt. Louis, 8001 Natural Bridge Road,
St. Louis, Missouri 63121
Received April 20, 2000
Reactions of [PtCl2(cod)] with the appropriate Grignard reagents produce [PtR2(cod)] (R
) C6H5, C6H4CH3-4, C6H4CH3-2, CH2C6H5), which, on treatment with 1 mol equiv of HCl,
yield the corresponding chloroplatinum complexes [PtClR(cod)]. The 2-tolyl compounds exhibit
hindered rotation about the Pt-C bonds at ambient temperature, the barrier to rotation
being greater in [PtCl(C6H4CH3-2)(cod)] than in the ditolyl derivative. The chloroplatinum
compounds react with 1 mol equiv of dppm to give [PtClR(dppm)], which are in equilibrium
with the A-frame complexes [Pt2R2(µ-Cl)(µ-dppm)2]Cl. The extent of dimerization depends
on the nature of R, but in each case the A-frame complex could be obtained quantitatively
by treatment of the solution with NH4PF6 or TlPF6. The structures of [Pt2R2(µ-Cl)(µ-dppm)2]-
PF6 (R ) CH2C6H5, C6H4CH3-4) were determined by X-ray crystallography. In the benzyl
derivative, one of the ortho hydrogens on each phenyl (benzyl) ring points towards the
centroid of a dppm phenyl ring, and this may account for the low-frequncy signal associated
with the ortho hydrogens in solution. The chloride-bridged A-frames could be converted to
the corresponding hydride-bridged derivatives, [Pt2R2(µ-H)(µ-dppm)2]PF6 (R ) C6H5, C6H4-
CH3-4, CH2C6H5), by treatment with NaBH4.
In tr od u ction
bridged A-frames of the form [Pt2R2(µ-X)(µ-dppm)2]+
have been generated by cleavage of a Pt-C bond in
[PtMe2(dppm)] by HCl17 or by displacement of cyclo-
octadiene from [PtClR(cod)] by dppm.18 In either case,
the reaction proceeds via the monomeric species [PtClR-
(dppm)]. Although these types of complexes have been
known for some time, no structures of halide-bridged
platinum(II) A-frames have been determined by X-ray
crystallography.
In this paper we describe the preparation and solution
behavior of a series of cyclooctadieneplatinum(II) com-
plexes of the types [PtR2(cod)] and [PtClR(cod)] (R )
C6H5, C6H4CH3-4, C6H4CH3-2, CH2C6H5), their reactions
with dppm to form the chloride-bridged compounds
[Pt2R2(µ-Cl)(µ-dppm)2]PF6, the molecular structures of
the 4-tolyl and benzyl derivatives, and conversion of the
phenyl, 4-tolyl, and benzyl A-frames to the correspond-
ing hydride-bridged species.
The bis(diphenylphosphino)methane (dppm) ligand
has been used extensively in the construction of bi-
metallic complexes. For platinum(II), these structures
include cis,cis, cis,trans, and trans,trans dimers, as well
as A-frame derivatives where, in addition to the two
bridging dppm ligands, the metals are connected through
another bridging atom or group.1 A-frame complexes of
platinum(II) have been known for over 20 years, and
compounds with a number of different bridging groups
have been structurally characterized.2-16 Cationic halide-
* To whom correspondence should be addressed. E-mail:
ganderson@umsl.edu. Fax: 314-516-5342.
(1) Anderson, G. K. Adv. Organomet. Chem. 1993, 35, 1.
(2) Azam, K. A.; Frew, A. A.; Lloyd, B. R.; Manojlovic-Muir, L.; Muir,
K. W.; Puddephatt, R. J . Organometallics 1985, 4, 1400.
(3) Hutton, A. T.; Shebanzadeh, B.; Shaw, B. L. J . Chem. Soc., Chem.
Commun. 1984, 549.
(4) Manojlovic-Muir, L.; Muir, K. W. Acta Crystallogr. A 1984, 40,
C292.
(5) Cameron, T. S.; Gardner, P. A.; Grundy, K. R. J . Organomet.
Chem. 1981, 212, 19.
Resu lts a n d Discu ssion
(6) Sharp, P. R. Inorg. Chem. 1986, 25, 4185.
Cycloocta d ien ep la tin u m P r ecu r sor s. Treatment
of [PtCl2(cod)] with at least 2 mol equiv of the appropri-
ate Grignard reagent RMgBr produced the diorgano-
platinum complexes [PtR2(cod)] (R ) C6H5, C6H4CH3-
4, C6H4CH3-2, CH2C6H5). Further reaction with 1 mol
equiv of HCl, generated in situ from acetyl chloride and
methanol, resulted in cleavage of one of the Pt-C bonds
(7) Arsenault, G. J .; Manojlovic-Muir, L.; Muir, K. W.; Puddephatt,
R. J .; Treurnicht, I. Angew. Chem., Int. Ed. Engl. 1987, 26, 86.
(8) Alcock, N. W.; Kemp, T. J .; Pringle, P. G.; Bergamini, P.;
Traverso, O. J . Chem. Soc., Dalton Trans. 1987, 1659.
(9) Brown, M. P.; Cooper, S. J .; Frew, A. A.; Manojlovic-Muir, L.;
Muir, K. W.; Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1982,
299.
(10) Hadj-Bagheri, N.; Puddephatt, R. J .; Manojlovic-Muir, L.;
Stefanovic, A. J . Chem. Soc., Dalton Trans. 1990, 535.
(11) Neve, F.; Ghedini, M.; Tiripicchio, A.; Ugozzoli, F. Organo-
metallics 1992, 11, 795.
(15) Yam, V. W.; Chan, L.-P.; Lai, T.-F. Organometallics 1993, 12,
2197.
(16) Toronto, D. V.; Balch, A. L. Inorg. Chem. 1994, 33, 6132.
(17) Cooper, S. J .; Brown, M. P.; Puddephatt, R. J . Inorg. Chem.
1981, 20, 1374.
(12) Irwin, M. J .; J ia, G.; Vittal, J . J .; Puddephatt, R. J . Organo-
metallics 1996, 15, 5321.
(13) Ghedini, M.; Neve, F.; Mealli, C.; Tiripicchio, A.; Ugozzoli, F.
Inorg. Chim. Acta 1990, 178, 5.
(14) Neve, F.; Ghedini, M.; De Munno, G.; Crispini, A. Inorg. Chem.
1992, 31, 2979.
(18) Anderson, G. K.; Clark, H. C.; Davies, J . A. J . Organomet.
Chem. 1981, 210, 135.
10.1021/om000337+ CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/27/2000

5072 Organometallics, Vol. 19, No. 24, 2000
J anka et al.
to give the [PtClR(cod)] derivatives. The complexes were
isolated as white or off-white solids that were stable to
air and moisture, and they were characterized by
is that in which the aryl ring lies perpendicular to the
platinum square plane. In dmso-d6 solution, the signals
appear at 4.32, 4.49, and 5.62 (1:1:2). As the tempera-
ture is raised, the lower frequency signals broaden, and
coalescence is reached at 370 K, leading to a ∆Gq value
of 18.1 kcal/mol. Although coalescence of the signals
could be clearly observed, dissociation of cyclooctadiene
1
elemental analysis and H NMR spectroscopy.
The NMR spectra of the phenyl, 4-tolyl, and benzyl
complexes are unremarkable. The diorganoplatinum
species exhibit a broad multiplet for the methylene
hydrogens of the cyclooctadiene, a single resonance for
the coordinated olefinic hydrogens (with a coupling to
195Pt of 37-39 Hz), and the expected signals for the R
groups. In [Pt(CH2C6H5)2(cod)], the benzylic CH2 reso-
nance exhibits a 2J (Pt,H) value of 114 Hz. The two
olefinic groups lie trans to different ligands in the
[PtClR(cod)] compounds, so two resonances are observed
for the olefinic hydrogens, in addition to the signals for
the R group and the four CH2 groups. The olefinic
hydrogens that lie trans to the R group are shifted to
higher frequency compared with their diorganoplatinum
precursors, and they exhibit a smaller coupling to
platinum (24-32 Hz). In contrast, the olefinic hydrogens
trans to chloride appear at lower frequency and have
1
begins to occur at 350 K, as evidenced by H signals at
2.50 and 5.71 ppm, although the solution remains clear.
Complete displacement of cyclooctadiene occurs after 20
min at 405 K. Presumably, displacement of cycloocta-
diene by dmso-d6 takes place to yield a species of the
type [PtCl(C6H4CH3-2)(dmso-d6)2]. The higher barrier
to rotation about the Pt-C bond in [PtCl(C6H4CH3-2)-
(cod)], compared with its di-2-tolylplatinum analogue,
may indicate that the Pt-C bond is stronger in the
chloroplatinum complex.
Rea ction s of [P tClR(cod )] w ith d p p m . When a
solution of [PtCl(C6H5)(cod)] was treated with 1 mol
equiv of dppm, conversion to the dimeric A-frame
complex [Pt2(C6H5)2(µ-Cl)(µ-dppm)2]+ was complete within
1 h. Addition of NH4PF6 to the reaction mixture allowed
2
greater J (Pt,H) values (75-77 Hz). The J (Pt,H) value
in [PtCl(CH2C6H5)(cod)] is 102 Hz, slightly smaller than
that in its dibenzylplatinum analogue.
-
isolation of the A-frame as its PF6 salt. When the
reaction was monitored by 31P{1H} NMR spectroscopy,
the intermediate monomer [PtCl(C6H5)(dppm)] (δP -40.5
The bulky 2-tolylplatinum derivatives give rise to
broad NMR spectra, suggesting that in these cases
rotation about the Pt-C bonds is relatively slow on the
NMR time scale. At ambient temperature, a CDCl3
solution of [Pt(C6H4CH3-2)2(cod)] exhibits a singlet for
the two methyl groups, but two very broad signals for
the olefinic hydrogens. The latter signals coalesce at 305
K, and they sharpen as the temperature is lowered. At
250 K, two resonances are observed at 4.89 and 5.02
ppm, each with a J (Pt,H) value of 39 Hz. These data
lead to a ∆Gq value of 14.7 kcal/mol for the bond rotation
process. The detection of only two olefinic CH signals
at low temperatures indicates that only one rotamer is
present in appreciable concentration, unless the signals
for both species are coincident. If a single isomer is
present, it could be the syn or anti form, but the latter,
in which the two methyl groups are directed away from
each other, is the more likely. The di-2-tolylplatinum
complex [Pt(C6H4CH3-2)2(dppm)] exhibited a single
resonance in its 31P NMR spectrum at ambient temper-
ature, but both syn and anti isomers were observed at
203 K.19
2
1
d, J (P,P) ) 41 Hz, J (Pt,P) ) 1239 Hz; δP -42.0 d,
1J (Pt,P) ) 3913 Hz) could be detected. When the 4-tolyl
complex was treated with dppm, a mixture of monomer
2
1
(δP -40.4 d, J (P,P) ) 41 Hz, J (Pt,P) ) 1213 Hz; δP
1
-42.3 d, J (Pt,P) ) 3944 Hz) and dimer was obtained,
even after 24 h, but addition of excess NH4PF6 led to
isolation of [Pt2(C6H4CH3-4)2(µ-Cl)(µ-dppm)2]PF6. The
reaction of [PtCl(CH2C6H5)(cod)] with dppm produced
2
[PtCl(CH2C6H5)(dppm)] (δP -34.5 d, J (P,P) ) 48 Hz,
1
1J (Pt,P) ) 1235 Hz; δP -38.2 d, J (Pt,P) ) 4049 Hz)
only, and addition of NH4PF6 produced a mixture of the
monomer and [Pt2(CH2C6H5)2(µ-Cl)(µ-dppm)2]+, which
persisted even after 48 h. It proved necessary to use
TlPF6, which would generate a very insoluble precipitate
of TlCl, to drive the reaction to completion. In the bulky
2-tolyl case, conversion of [PtCl(C6H4CH3-2)(dppm)] (δP
-39.6 d, 2J (P,P) ) 41 Hz, 1J (Pt,P) ) 1214 Hz; δP -42.9
1
d, J (Pt,P) ) 3885 Hz) to the A-frame required 24 h,
even when TlPF6 was used. In the sequence shown in
eq 1, substitution of the diene by dppm occurs rapidly
in each case, but the rate and degree of dimerization is
strongly dependent on the nature of the R group. In the
benzyl and 2-tolyl cases only [PtClR(dppm)] can be
observed by 31P NMR spectroscopy, and rearrangement
to the A-frame is slow even after addition of NH4PF6 or
TlPF6. The dimerization probably proceeds by dissocia-
tion of one end of a dppm ligand, which then attacks a
second molecule of [PtClR(dppm)], displacing a chloride
ligand. The larger R groups most likely inhibit attack
of the free phosphino group on the second platinum
center.
The chloroplatinum derivative, [PtCl(C6H4CH3-2)(cod)],
gives rise to a single methyl resonance, but three signals
due to the olefinic hydrogens in a 1:1:2 ratio at 298 K.
The two resonances at 4.45 and 4.59 ppm each exhibit
a large coupling to platinum, indicating that they lie
trans to the chloride. The most intense signal, which is
presumably due to two overlapping resonances, has a
J (Pt,H) value of only 32 Hz and therefore may be
assigned to the olefinic hydrogens trans to the tolyl
1
group. A H-1H TOCSY spectrum recorded at 298 K
reveals that all four CH signals are coupled to each
other and also to the methylene hydrogens of the
cyclooctadiene. This confirms that all of the signals are
due to a single compound. The nonequivalence of the
four olefinic hydrogens indicates that there is hindered
rotation about the Pt-C bond, and the favored rotamer
The chloride-bridged A-frame complexes were isolated
as their PF6- salts, which were characterized by 1H and
31P{1H} NMR spectroscopy. They are white or yellow
solids, which are stable to air and moisture. Crystals of
the 4-tolyl and benzyl derivatives were grown from
CH2Cl2/Et2O solution, and their structures were deter-
mined by single-crystal X-ray diffraction. With the
exception of the 2-tolyl complex, the 31P{1H} NMR
(19) Hassan, F. S. M.; McEwan, D. M.; Pringle, P. G.; Shaw, B. L.
J . Chem. Soc., Dalton Trans. 1985, 1501.

Synthesis of Platinum A-Frame Complexes
Organometallics, Vol. 19, No. 24, 2000 5073
spectrum consists of a single central resonance, flanked
1
by two sets of satellites due to J (Pt,P) and 3J (Pt,P)
couplings. The coupling patterns have been analyzed in
1
detail previously.20 The J (Pt,P) values are consistently
in the range 3000-3100 Hz, which is typical for species
of the form trans-[PtClAr(PR3)2].21 In the 2-tolyl case
two central resonances at 9.2 and 9.5 ppm, in an
approximate 2:1 ratio, are observed. This may be due
to hindered rotation about the Pt-C bonds at ambient
temperature. Since all four P atoms are equivalent in
each species, the two 2-tolyl groups must lie perpen-
dicular to the Pt2P4 plane, as found previously for the
mesitylpalladium complex [Pd2{C6H2(CH3)3-2,4,6}2(µ-
Br)(µ-dppm)2]PF6.22 One can imagine three such rota-
mers for [Pt2(C6H4CH3-2)2(µ-Cl)(µ-dppm)2]+, with the
methyl groups both directed into the pocket of the
A-frame, both on the outside face, or one on the inside
and one on the outside face of the A-frame. Only two
are observed, however. Consideration of space-filling
models of the three rotamers reveals that no serious
steric interactions should be present in any of them
provided the tolyl rings remain nearly perpendicular to
the Pt2P4 plane, but rotation of the methyl substituents
past the dppm phenyls may be restricted. In dmso-d6
solution, the two signals are found at 12.9 and 13.2 ppm.
As the solution is heated, the signals move closer
together, but they appear to coalesce at 415 K. By ex-
trapolating the chemical shift difference to the coales-
cence temperature, a minimum value of ∆Gq of 21.3
kcal/mol is obtained. If the signals are indeed due to
two rotamers, it is unclear which two are observed.
The 1H NMR spectra of the four chloride-bridged
A-frames exhibit the expected numbers of resonances
for the organic groups attached to platinum and the
phenyl groups on phosphorus. Two signals are observed
for the two pairs of methylene hydrogens of the dppm
ligands that lie syn and anti to the bridging chloride.
In the benzyl derivative the CH2 group resonates at 2.67
ppm, and it exhibits a coupling to 195Pt of 97 Hz. The
ortho hydrogens of the benzyl fragment give rise to an
unusually low-frequency resonance at 5.17 ppm (vide
infra).
F igu r e 1. Molecular structure of the [Pt2(CH2C6H5)2(µ-
Cl)(µ-dppm)2]+ cation, showing the atom-labeling scheme.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [P t2(CH2C6H5)2(µ-Cl)(µ-d p p m )2]P F 6
Pt1-C3
Pt1-Cl
Pt1-P1
Pt1-P2
Pt1-Pt2
2.079(5)
Pt2-C10
Pt2-Cl
Pt2-P3
Pt2-P4
2.087(5)
2.4810(11)
2.2897(13)
2.3078(13)
2.4602(11)
2.2892(13)
2.3022(13)
P1-Pt1-P2
P1-Pt1-C3
P1-Pt1-Cl
C3-Pt1-Cl
C3-Pt1-P2
P2-Pt1-Cl
Pt1-C3-C4
C3-Pt1-Pt2
Pt1-Cl-Pt2
175.09(4)
89.30(14)
91.91(4)
174.25(14)
94.66(15)
84.43(4)
P3-Pt2-P4
P3-Pt2-C10
P3-Pt2-Cl
C10-Pt2-Cl
C10-Pt2-P4
P4-Pt2-Cl
173.82(4)
89.56(15)
91.63(4)
171.75(14)
94.74(15)
84.75(4)
113.2(3)
Pt2-C10-C11
C10-Pt2-Pt1
111.9(4)
83.45(4)
membered chair conformation such that one CH2 group
is oriented towards the bridging chloride, and the other
lies on the opposite face of the Pt2P4 plane. The bridging
chloride is nearly equidistant from the two Pt atoms,
the Pt-Cl distances differing by only 0.021 Å, and the
Pt-Cl-Pt angle is 83.45(4)°. The Pt-Pt separation is
3.289 Å. The Pt-P distances lie within the range
2.289(1)-2.308(1) Å, and the Pt-C distances are 2.079(5)
and 2.087(5) Å. These are typical for platinum(II) units
of the form trans-[PtXR(PR3)2].23 The benzyl groups
exhibit the expected bend at C3 and C10, and the phenyl
rings are tilted such that the ortho hydrogens attached
to C9 and C16 point directly toward the centroids of the
C23-C28 and C47-C52 rings, respectively. These
hydrogens will experience significant shielding due to
the ring current of the aromatic ring. Although rotation
about the Pt-C and C-C bonds in solution will average
the environments of H5 and H9 (and H12 and H16),
this feature must account for the low-frequency signal
X-r a y Str u ctu r e Deter m in a tion s. [Pt2(CH2C6H5)2-
(µ-Cl)(µ-dppm)2]PF6 crystallizes in the space group P1h.
The molecular structure of the cation is shown in Figure
1, and selected bond distances and angles are presented
in Table 1. The Pt2P4 unit is almost planar. The eight-
membered Pt2P4C2 ring adopts an elongated, eight-
1
associated with the ortho hydrogens observed in the H
NMR spectrum.
The 4-tolyl analogue crystallizes in the P21/c space
group. The molecular structure of the [Pt2(C6H4CH3-4)2-
(µ-Cl)(µ-dppm)2]+ cation is shown in Figure 2, and
selected bond distances and angles are given in Table
2. As in the first structure, the Pt2P4 unit is nearly
planar, and the Pt2P4C2 ring adopts an elongated chair
(20) Brown, M. P.; Puddephatt, R. J .; Rashidi, M.; Seddon, K. R. J .
Chem. Soc., Dalton Trans. 1977, 951.
(21) Anderson, G. K.; Cross, R. J . J . Chem. Soc., Dalton Trans. 1980,
l434.
(22) Stockland, R. A., J r.; Anderson, G. K.; Rath, N. P. Organo-
metallics 1997, 16, 5096.
(23) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.

5074 Organometallics, Vol. 19, No. 24, 2000
J anka et al.
clear correlation between the M-M distance and the
M-Cl-M angle, the smallest angle being found in
[Hg2Cl2(µ-Cl)(µ-dppm)2]+, which also exhibits the great-
est metal-metal distance.26
The Pt-Pt distances found here lie at the high end
of the range of previously reported values for platinum
A-frame complexes, which vary from 2.71 Å in [Pt2Cl2-
(µ-HgCl2)(µ-dppm)2],30 where there is a significant Pt-
Pt interaction, to over 3.2 Å in [Pt2Cl2(µ-L)(µ-dppm)2]+
(L ) NO, N2C6H4OCH3-4)31,32 and [Pt2(CtCPh)2(µ-Ct
CPh)(µ-dppm)2]+.33 A survey of the previously reported
platinum(II) A-frame complexes reveals that they all
adopt an elongated boat conformation, in which the
bridging moiety lies on the same face of the Pt2P4 plane
as the dppm methylene groups. The present structures
are unusual, therefore, in that they exist in the solid
state as elongated chairs. The reasons for this are
unclear.
F igu r e 2. Molecular structure of the [Pt2(C6H4CH3-4)2(µ-
Cl)(µ-dppm)2]+ cation, showing the atom-labeling scheme.
Ta ble 2. Selected Bon d Dista n ces a n d An gles for
Syn th esis of Hyd r id e-Br id ged A-F r a m es. The
chloride-bridged complexes [Pt2R2(µ-Cl)(µ-dppm)2]PF6 (R
) C6H5, C6H4CH3-4, CH2C6H5) could be converted to the
corresponding hydride-bridged derivatives by treatment
of a CH2Cl2 solution of the A-frame (generated in situ)
with 1 mol equiv of NaBH4 at low temperature. After
purification, the complexes [Pt2R2(µ-H)(µ-dppm)2]PF6
were isolated as yellow solids. The hydride-bridged
2-tolyl complex could not be isolated because, although
it could be detected in solution, it formed only slowly
and it decomposed almost as rapidly as it was formed.
The three isolable hydride-bridged derivatives were
characterized by microanalysis and by NMR spectros-
copy. In each case, the complex gives rise to a single
resonance with 195Pt satellites in its 31P{1H} NMR
spectrum. The resonance is shifted slightly to higher
frequency, compared with the chloride-bridged precur-
[P t2(C6H4CH3-4)2(µ-Cl)(µ-d p p m )2]P F 6
Pt1-C1
Pt1-Cl
Pt1-P1
Pt1-P2
Pt1-Pt2
2.015(4)
Pt2-C8
Pt2-Cl
Pt2-P3
Pt2-P4
2.024(3)
2.4368(8)
2.3020(10)
2.3049(9)
3.2337(2)
2.4519(8)
2.3074(9)
2.3125(10)
P1-Pt1-P2
P1-Pt1-C1
P1-Pt1-Cl
C1-Pt1-Cl
C1-Pt1-P2
P2-Pt1-Cl
C1-Pt1-Pt2
Pt1-Cl-Pt2
172.88(3)
92.97(11)
86.03(3)
162.10(11)
89.43(11)
93.72(3)
P3-Pt2-P4
P3-Pt2-C8
P3-Pt2-Cl
C8-Pt2-Cl
C8-Pt2-P4
P4-Pt2-Cl
C8-Pt2-Pt1
173.35(3)
94.10(10)
82.80(3)
170.37(10)
91.69(10)
90.96(3)
149.09(11)
82.82(3)
141.10(10)
conformation. The bridging chloride is again nearly
equidistant from the two Pt atoms, the Pt-Cl distances
being 2.4368(8) and 2.4519(8) Å, and the Pt-Cl-Pt
angle is 82.82(3)°. The Pt-Pt separation is 3.2337(2) Å.
The Pt-P distances fall between 2.302(1) and 2.313(1)
Å, and the Pt-C distances are 2.015(5) and 2.024(5) Å.
The Pt-C(aryl) distances are slightly shorter than the
Pt-C(alkyl) distances in the previous structure. The
4-tolyl groups lie almost perpendicular to the Pt2P4
plane, the C1-C6 and C8-C13 rings being tilted with
respect to the Pt2P4 plane by 88.6° and 60.7°, respec-
tively.
In contrast to these two structures, the [Pt2(COCH3)2-
(µ-Cl)(µ-dppm)2]+ cation adopts a twisted boat confor-
mation, with a Pt-Pt separation of 3.1130(5) Å.24 In
that case, the Pt-Cl-Pt bridge is slightly asymmetric
and the Pt-Cl distances are greater (2.556(2) and
2.519(2) Å) than those found in the present complexes.
The Pt-Cl-Pt angle of 75.67(6)° is considerably more
acute than those observed here. The M-Cl-M angles
are also close to 75° in [Pd2H(CH3)(µ-Cl)(µ-dppm)2]+ and
[Hg2Cl2(µ-Cl)(µ-dppm)2]+,25,26 whereas in [Rh2(CO)2(µ-
Cl)(µ-dppm)2]+, [PtRhPh(CO) (µ-Cl)(µ-dppm)2]+, and
[Cu2Cl(NCNMe2)(µ-Cl)(µ-dppm)2]+ the M-Cl-M angles
are more similar to those found here.27-29 There is no
1
sors. The value of J (Pt,P) in [Pt2Ph2(µ-H)(µ-dppm)2]+
is 130 Hz smaller than that in [Pt2Ph2(µ-Cl)(µ-dppm)2]+,
but the couplings are nearly identical in the hydride-
and chloride-bridged derivatives where R ) C6H4CH3-4
or CH2C6H5. In the 1H NMR spectrum, a quintet is
observed in the range -9.0 to -9.5 ppm due to the
1
bridging hydride, with J (Pt,H) values of 486-496 Hz.9,34
A broad resonance is observed around 4.5 ppm, due to
the methylene hydrogens of the dppm ligands, and the
expected signals for the organic substituents attached
to platinum and the dppm phenyls are also present. A
single, broad resonance is observed for the dppm meth-
ylene hydrogens at all accessible temperatures, indicat-
ing that they are equivalent on the NMR time scale.
This is due to the fluxional nature of the complexes,
resulting from rapid migration of the bridging hydride
between the two metal centers.35
(28) Xu, C.; Anderson, G. K.; Rath, N. P. Inorg. Chim. Acta 1997,
265, 241.
(29) Bera, J . K.; Nethaji, M.; Samuelson, A. G. Inorg. Chem. 1999,
38, 218.
(30) Sharp, P. R. Inorg. Chem. 1986, 25, 4185
(31) Neve, F.; Ghedini, M.; Tiripicchio, A.; Ugozzoli, F. Organo-
metallics 1992, 11, 795.
(24) Gerisch, M.; Heinemann, F. W.; Bruhn, C.; Scholz, J .; Steinborn,
D. Organometallics 1999, 18, 564.
(25) Young, S. J .; Kellenberger, B.; Reibenspies, J . H.; Himmel, S.
E.; Manning, M.; Anderson, O. P.; Stille, J . K. J . Am. Chem. Soc. 1988,
110, 5744.
(32) Neve, F.; Ghedini, M.; De Munno, G.; Crispini, A. Inorg. Chem.
1992, 31, 2979.
(33) Yam, V. W.; Chan, L.; Lai, T. Organometallics 1993, 12, 2197.
(34) Brown, M. P.; Puddephatt, R. J .; Rashidi, M.; Seddon, K. R. J .
Chem. Soc., Dalton Trans. 1978, 516.
(26) Harvey, P. D.; Aye, K. T.; Hierso, K.; Isabel, E.; Lognot, I.;
Mugnier, Y.; Rochon, F. D. Inorg. Chem. 1994, 33, 5981.
(27) Cowie, M.; Dwight, S. K. Inorg. Chem. 1979, 18, 2700.
(35) Puddephatt, R. J .; Azam, K. A.; Hill, R. H.; Brown, M. P.;
Nelson, C. D.; Moulding, R. P.; Seddon, K. R.; Grossel, M. C. J . Am.
Chem. Soc. 1983, 105, 5642.

Synthesis of Platinum A-Frame Complexes
Organometallics, Vol. 19, No. 24, 2000 5075
4.59 (br s, J (Pt,H) ) 75 Hz, 2H CH), 5.79 (br s, J (Pt,H) ) 24
Hz, 2H, CH), 6.91-7.31 (m, 4H, C6H4).
Su m m a r y
We have prepared the platinum(II) complexes [PtR2-
(cod)] and [PtClR(cod)] (R ) C6H5, C6H4CH3-4, C6H4CH3-
2, CH2C6H5). The 2-tolyl derivatives exhibit restricted
rotation about the Pt-C bonds. Reactions of the chloro-
platinum species with dppm generate first [PtClR-
(dppm)], which is in equilibrium with the A-frame
complex [Pt2R2(µ-Cl)(µ-dppm)2]Cl. The position of equi-
librium favors the dimer when R ) C6H5, but with the
bulkier R groups only the monomer is observed. Addi-
tion of NH4PF6 or TlPF6 results in quantitative conver-
sion to [Pt2R2(µ-Cl)(µ-dppm)2]PF6. The solid state struc-
tures of the benzyl and 4-tolyl derivatives have been
determined. These represent the first structures of
halide-bridged platinum(II) A-frames, and the first
examples that adopt an elongated chair conformation.
With the exception of the 2-tolyl complex, the chloride-
bridged A-frames could be converted to their hydride-
bridged analogues.
P r ep a r a tion of [P tCl(C6H4CH3-2)(cod )]. This compound
was prepared analogously from [Pt(C6H4CH3-2)2(cod)] (0.14 g,
0.29 mmol) and CH3COCl (2.1 mL of a 0.5 M solution in CCl4)
and isolated as an off-white powder (0.093 g, 75%). Anal. Calcd
for C15H19ClPt: C, 41.91; H, 4.46. Found: C, 41.87; H, 4.60.
1H NMR (CDCl3): δ 2.56 (s, 3H, CH3), 2.52 (m, 8H, CH2), 4.45
(br, J (Pt,H) ) 79 Hz, 1H, CH), 4.59 (br, J (Pt,H) ) 73 Hz, 1H,
CH), 5.81 (br, J (Pt,H) ) 32 Hz, 2H, CH), 6.91-7.31 (m, 4H,
C6H4).
P r ep a r a tion of [P tCl(CH2C6H5)(cod )]. This compound
was prepared similarly from [Pt(CH2C6H5)2(cod)] (0.23 g, 0.47
mmol) and CH3COCl (3.4 mL of a 0.5 M solution in CCl4) and
isolated as an off-white powder (0.18 g, 86%). Anal. Calcd for
C
15H19ClPt: C, 41.91; H, 4.46. Found: C, 41.42; H, 4.51. 1H
NMR (CDCl3): δ 2.38 (m, 8H, CH2), 3.16 (s, 2J (Pt,H) ) 102
Hz, 2H, PtCH2), 4.33 (br s, J (Pt,H) ) 76 Hz, 2H, CH), 5.59 (br
s, J (Pt,H) ) 32 Hz, 2H, CH), 7.01-7.31 (m, 5H, C6H5).
P r ep a r a tion of [P t2P h 2(µ-Cl)(µ-d p p m )2]P F 6. [PtClPh-
(cod)] (0.21 g. 0.50 mmol) and dppm (0.19 g, 0.50 mmol) were
dissolved in CH2Cl2 (30 mL). To this stirred solution was added
NH4PF6 (0.24 g, 1.5 mmol) and methanol (3 mL). After 1 h
the solvents were removed and the resulting solid was washed
twice with pentane. The solid was extracted with CH2Cl2 (15
mL) and passed down a short alumina column, then the
column was washed with CH2Cl2 (15 mL) in small portions.
The total effluent was collected, and the solvent was removed.
The residue was washed twice with pentane, leaving the
Exp er im en ta l Section
All reactions were carried out under an atmosphere of argon.
1H and 31P{1H} NMR spectra were recorded on a Bruker ARX-
500 or a Varian Unity plus 300 or XL-300 spectrometer.
Microanalyses were performed by Atlantic Microlab, Inc.,
Norcross, GA.
1
product as a white powder (0.53 g, 70%). H NMR (CDCl3): δ
[Pt(C6H5)2(cod)] and [PtCl(C6H5)(cod)] were prepared as
reported previously.36 [Pt(C6H5)2(cod)], 1H NMR (CDCl3): δ
2.52 (br, 8H, CH2), 5.11 (br s, J (Pt,H) ) 39 Hz, 4H, CH), 6.65-
7.31 (m, 10H, C6H5). [PtCl(C6H5)(cod)]. 1H NMR (CDCl3): δ
2.65 (m, 8H, CH2), 4.67 (br s, J (Pt,H) ) 77 Hz, 2H, CH), 5.80
(Br s, J (Pt,H) ) 30 Hz, 2H, CH), 6.81-7.29 (m, 5H, C6H5).
P r ep a r a tion of [P t(C6H4CH3-4)2(cod )]. [PtCl2(cod)] (0.44
g, 1.2 mmol) was suspended in ether (60 mL), and 4-CH3C6H4-
MgBr (5.9 mL of a 1.0 M solution in ether) was added. The
solution was allowed to stir overnight, then the mixture was
quenched with methanol and water. The ether layer was
separated, and the aqueous layer was washed with three 10
mL portions of ether. The solvent was removed from the
combined ether solution under reduced pressure to leave the
product as a white powder (0.45 g, 78%). H NMR (CDCl3): δ
2.18 (s, 6H, CH3), 2.53 (m, 8H, CH2), 5.12 (br s, J (Pt,H) ) 37
Hz, 4H, CH), 6.84-7.31 (m, 8H, C6H4).
P r ep a r a tion of [P t(C6H4CH3-2)2(cod )]. This complex was
prepared similarly from [PtCl2(cod)] (0.50 g, 1.3 mmol) and
2-CH3C6H4MgBr (3.3 mL of a 2.0 M solution in ether) and
isolated as a white powder (0.41 g, 63%). H NMR (CDCl3): δ
2.56 (s, 6H, CH3), 2.61 (m, 8H, CH2), 4.94 and 5.05 (v br, 4H,
2
2
3.94 (dq, J (H,H) ) 13.7 Hz, J (P,H) ) 3.4 Hz, 2H, CH2), 4.29
2
2
(dq, J (H,H) ) 13.7 Hz, J (P,H) ) 4.9 Hz, 2H, CH2), 6.37 (d,
3J (H,H) ) 6.3 Hz, 4H, CH-2,6), 6.50 (t, J (H,H) ) 6.3 Hz, 4H,
3
3
CH-3,5), 6.81 (t, J (H,H) ) 6.3 Hz, 2H, CH-4), 6.98-7.60 (m,
40H, PPh2). 31P{1H} NMR: δ 9.1, J (Pt,P) ) 3027 Hz.
1
P r ep a r a t ion of [P t2(C6H4CH3-4)2(µ-Cl)(µ-d p p m )2]P F 6.
This complex was prepared in the same manner from [PtCl-
(C6H4CH3-4)(cod)] (0.21 g. 0.50 mmol), dppm (0.19 g, 0.50
mmol), and NH4PF6 (0.32 g, 2.0 mmol), but the mixture was
allowed to stir for 24 h. The product was obtained as a yellow
powder (0.55 g, 72%). Anal. Calcd for C64H58ClF6P5Pt2: C,
1
50.52; H, 3.84. Found: C, 50.78; H, 3.88. H NMR (CDCl3): δ
2
2
1.94 (s, 6H, CH3), 3.90 (dq, J (H,H) ) 14.0 Hz, J (P,H) ) 3.0
2
2
Hz, 2H, CH2), 4.28 (dq, J (H,H) ) 14.0 Hz, J (P,H) ) 4.0 Hz,
2H, CH2), 6.20 (d, 3J (H,H) ) 7.6 Hz, 4H, CH-2,6), 6.76 (d,
3J (H,H) ) 7.6 Hz, 4H, CH-3,5), 6.98-7.60 (m, 40H, PPh2).
1
31P{1H} NMR: δ 8.5, J (Pt,P) ) 3055 Hz.
1
P r ep a r a t ion of [P t2(C6H4CH3-2)2(µ-Cl)(µ-d p p m )2]P F 6.
[PtCl(C6H4CH3-2)(cod)] (0.21 g. 0.50 mmol) and dppm (0.19 g,
0.50 mmol) were dissolved in CH2Cl2 (30 mL). To this stirred
solution was added TlPF6 (0.17 g, 0.50 mmol) and methanol
(3 mL). The reaction was allowed to proceed overnight, then
the solvents were removed and the resulting solid was washed
twice with pentane. The solid was extracted with CH2Cl2 (10
mL) and passed down a short alumina column, then the
column was washed with CH2Cl2 (15 mL) in small portions.
The total effluent was collected, and the solvent was removed.
The residue was washed with small portions of pentane,
leaving the product as a yellow powder (0.50 g, 66%). Anal.
Calcd for C64H58ClF6P5Pt2: C, 50.52; H, 3.84. Found: C, 50.60;
1
CH), 6.77-7.37 (m, 8H, C6H4).
P r ep a r a tion of [P t(CH2C6H5)2(cod )]. This complex was
prepared similarly from [PtCl2(cod)] (0.52 g, 1.4 mmol) and
C6H5CH2MgBr (14 mL of a solution prepared from 1.2 g of Mg
and 3.0 mL of C6H5CH2Br in 50 mL of dry ether) and isolated
1
as a white powder (0.46 g, 68%). H NMR (CDCl3): δ 2.25 (s,
2
8H, CH2), 2.91 (s, J (Pt,H) ) 114 Hz, 4H, PtCH2), 4.61 (br s,
J (Pt,H) ) 39 Hz, 4H, CH), 6.65-7.31 (m, 10H, C6H5).
1
H, 4.20. 31P{1H} NMR (CDCl3): δ 9.2, J (Pt,P) ) 3101 Hz; δ
P r ep a r a tion of [P tCl(C6H4CH3-4)(cod )]. [Pt(C6H4CH3-4)2-
(cod)] (0.21 g, 0.43 mmol) was dissolved in ether (30 mL), and
CH3COCl (3.2 mL of a 0.5 M solution in CCl4) and methanol
(5 drops) were added. The mixture was allowed to stir
overnight, then the solvents were removed under reduced
pressure. The resulting solid was washed twice with pentane
to leave the product as an off-white powder (0.16 g, 70%). Anal.
Calcd for C15H19ClPt: C, 41.91; H, 4.46. Found: C, 41.90; H,
4.62. 1H NMR (CDCl3): δ 2.24 (s, 3H, CH3), 2.52 (m, 8H, CH2),
1
9.5, J (Pt,P) ) 3101 Hz.
P r ep a r a tion of [P t2(CH2C6H5)2(µ-Cl)(µ-d p p m )2]P F 6. This
complex was prepared in
a similar manner from [PtCl-
(CH2C6H5)(cod)] (0.21 g, 0.50 mmol), dppm (0.19 g, 0.50 mmol),
and TlPF6 (0.17 g, 0.50 mmol), but the reaction was allowed
to proceed for only 3 h. The product was obtained as a yellow
powder (0.47 g, 62%). Anal. Calcd for C64H58ClF6P5Pt2: C,
1
50.52; H, 3.84. Found: C, 50.47; H, 4.23. H NMR (CDCl3): δ
2
2
2.67 (s, J (Pt,H) ) 97 Hz, 4H, CH2), 3.76 (dq, J (H,H) ) 14.0
2
2
(36) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411.
Hz, J (P,H) ) 3.7 Hz, 2H, CH2), 4.42 (dq, J (H,H) ) 14.0 Hz,

5076 Organometallics, Vol. 19, No. 24, 2000
J anka et al.
Ta ble 3. Cr ysta llogr a p h ic Da ta for
2J (P,H) ) 5.8 Hz, 2H, CH2), 5.17 (d, 3J (H,H) ) 7.5 Hz, 4H,
CH-2,6), 6.31 (t, 3J (H,H) ) 7.5 Hz, 4H, CH-3,5), 6.54 (t, 3J (H,H)
) 7.5 Hz, 2H, CH-4), 6.95-7.80 (m, 40H, PPh2). 31P{1H}
[P t2R2(µ-Cl)(µ-d p p m )2]P F 6 (R ) C6H4CH3-4,
CH2C6H5)
1
NMR: δ 8.6, J (Pt,P) ) 3044 Hz.
R ) C6H4CH3-4
R ) CH2C6H5
P r ep a r a tion of [P t2P h 2(µ-H)(µ-d p p m )2]P F 6. [PtClPh-
(cod)] (0.21 g, 0.51 mmol) and dppm (0.19 g, 0.51 mmol) were
dissolved in CH2Cl2 (30 mL) and stirred magnetically. NH4PF6
(0.24 g, 1.5 mmol) was then added to form a suspension, and
MeOH (3.0 mL) was added to assist the dissolution of NH4PF6.
The reaction was allowed to proceed for 1 h, then cooled to 0
°C. NaBH4 (1.0 mL of a 0.50 M solution in dimethoxyethane)
was added, and the reaction was allowed to proceed for a
further 1 h. The solvent was removed under reduced pressure,
and the solid was washed twice with pentane. The solid was
extracted with CH2Cl2 (10 mL), and the resulting solution was
carefully decanted and passed through a short column of
neutral alumina. The column was washed with CH2Cl2 (15 mL)
in small portions. The effluent was collected, and the solvent
was removed under reduced pressure. The solid was washed
with small portions of pentane to give the product as a yellow
powder (0.29 g, 78%). 1H NMR (CDCl3): δ -9.29, (quintet,
2J (P,H) ) 9 Hz, 1J (Pt,H) ) 486 Hz, 1H, PtH), 4.59 (br, 4H,
CH2), 6.19-7.80 (m, 50H, C6H5). 31P{1H} NMR: δ 12.6 (s,
1J (Pt,P) ) 2898 Hz).
cryst syst
space group, Z
a, Å
b, Å
c, Å
monoclinic
P21/c, 4
16.1901(5)
21.3483(7)
17.0454(6)
90
97.147(2)
90
5845.6(3)
1.729
218(2)
5.023
1.27-26.42
88 341
11 999
empirical
705
0.0235, 0.0528
0.0360, 0.0578
1.016
triclinic
P1h, 2
11.7628(12)
14.2670(8)
20.3564(14)
78.712(5)
85.531(8)
85.851(5)
3334.2(5)
1.674
R, deg
â, deg
γ, deg
cell vol, Å3
D(calcd), Mg/m3
temp, K
218(2)
4.491
1.02-27.57
64 918
14 928
empirical
793
0.0417, 0.0761
0.0494, 0.0784
1.259
abs coeff, mm-1
θ range, deg
no. of reflns collected
no. of ind reflns
abs corr
no. of params refined
R(F), Rw(F2) (F2>2.0σ(F2))
R(F), Rw(F2) (all data)
goodness of fit
largest difference peak
and hole, e Å-3
0.966, -0.609
1.203, -1.356
P r ep a r a tion of [P t2(C6H4CH3-4)2(µ-H)(µ-d p p m )2]P F 6.
This complex was prepared similarly from [PtCl(4-tolyl)(cod)]
(0.21 g, 0.51 mmol) and dppm (0.19 g, 0.51 mmol) and isolated
as a yellow powder (0.27 g, 73%). Anal. Calcd for C64H59F6P5-
Pt2: C, 51.68; H, 3.97. Found: C, 51.89; H, 4.11. 1H NMR
(CDCl3): δ -9.54 (quintet, 2J (P,H) ) 12 Hz, 1J (Pt,H) ) 496
Hz, 1H, PtH), 1.85 (s, 6H, CH3), 4.62 (br, 4H, CH2), 6.15 (d,
3J (H,H) ) 6.4 Hz, 4H, CH-2,6), 6.25 (d, 3J (H,H) ) 6.4 Hz, 4H,
CH-3,5), 7.10-7.70 (m, 40H, PPh2). 31P{1H} NMR: δ 12.8 (s,
1J (Pt,P) ) 3036 Hz).
mined by a global refinement of xyz centroids of 8192 reflec-
tions. An empirical absorption correction was applied using
SADABS.38 Structure solution and refinement were carried out
using the SHELXTL-PLUS (5.03) software package.39 Crystal-
lographic data are collected in Table 3.
Ack n ow led gm en t. Thanks are expressed to the
National Science Foundation (grant no. CHE-9530085)
and the University of Missouri Research Board for
support of this work. Acknowledgment is made to the
National Science Foundation (grant nos. CHE-9318696
and 9309690), the U.S. Department of Energy (grant
no. DE-FG02-92CH10499), and the University of Mis-
souri Research Board for instrumentation grants.
P r ep a r a tion of [P t2(CH2C6H5)2(µ-H)(µ-d p p m )2]P F 6. This
complex was prepared similarly from [PtCl(CH2C6H5)(cod)]
(0.21 g, 0.51 mmol) and dppm (0.19 g, 0.51 mmol) and isolated
1
as a yellow powder (0.24 g, 65%). H NMR (CDCl3): δ -9.03
2
1
(quintet, J (P,H) ) 10 Hz, J (Pt,H) ) 493 Hz, 1H, PtH), 2.39
2
(s, J (Pt,H) ) 96 Hz, 4H, PtCH2), 4.37 (br, 4H, CH2), 6.02 (d,
3J (H,H) ) 6.9 Hz, 4H, CH-2,6), 6.50 (t, J (H,H) ) 6.9 Hz, 4H,
3
Su p p or tin g In for m a tion Ava ila ble: A listing of crystal
data and structure refinement parameters, atomic coordinates
and equivalent isotropic displacement parameters, bond lengths
and angles, anisotropic displacement parameters, and hydro-
gen coordinates and isotropic displacement parameters for
[Pt2R2(µ-Cl)(µ-dppm)2]PF6 (R ) CH2C6H5, C6H4CH3-4). This
material is available free of charge via the Internet at
http://pubs.acs.org.
3
CH-3,5), 6.60 (t, J (H,H) ) 6.9 Hz, 2H, CH-4), 7.27-7.65 (m,
40H, PPh2). 31P{1H} NMR: δ 14.2, J (Pt,P) ) 3059 Hz.
1
X-r a y Str u ctu r e Deter m in a tion s. Preliminary examina-
tion and data collection were performed using a Siemens
SMART CCD detector system single-crystal X-ray diffractom-
eter equipped with a sealed tube X-ray source (50 kV × 40
mA) using graphite-monochromated Mo KR radiation (λ )
0.71073 Å). Preliminary unit cell constants were determined
with a set of 45 narrow frame (0.3° in ω) scans. The double
pass method of scanning was used to exclude any noise. The
collected frames were integrated using an orientation matrix
determined from the narrow frame scans. The SMART soft-
ware package37 was used for data collection, and SAINT37 was
used for frame integration. Final cell constants were deter-
OM000337+
(37) SMART and SAINT; Siemens Analytical X-Ray Division: Madi-
son, WI.
(38) SADABS. Blessing, R. H. Acta Crystallogr. A 1995, 51, 33.
(39) Sheldrick, G. M. SHELXTL-PLUS (5.03) software package;
Siemens Analytical X-ray Division: Madison, WI, 1995.