Synthesis and Ligand Substitution Reactions of a Mesitylphosphido-Bridged Platmum(II) Dimer

Article abstract of DOI:10.1021/ic951020i

The stable primary phosphine complexes trans-M(PH₂Mes*)₂Cl₂ (1, M = Pd; 2, M = Pt; Mes* = 2,4,6-(t-Bu)₃C₆H₂) were prepared from Pd(PhCN)₂Cl₂ and K₂PtCl₄, respectively. Reaction of Pt(COD)Cl₂ (COD = 1,5-cyclooctadiene) with less bulky arylphosphines gives the unstable cis-Pt(PH₂Ar)₂Cl₂ (3, Ar = Is = 2,4,6-(i- Pr)₃C₆H₂; 4, Ar = Mes = 2,4,6-Me₃C₆H₂). Spontaneous dehydrochlorination of 4 or direct reaction of K₂PtCl₄ with 2 equiv of PH₂Mes gives the insoluble primary phosphido-bridged dimer [Pt(PH₂Mes)(μ-PHMes)Cl₂ (5), which was characterized spectroscopically, including solid-state ³¹P NMR studies. The reversible reaction of 5 with PH₂Mes gives [Pt(PH₂Mes)₂(μ-PHMes)]₂[Cl]₂ (6), while PEt₃ yields [Pt(PEt₃)₂(μ-PHMes)MCl]₂ (7), which on recrystallization forms [Pt(PEt₃)(μ-PHMes)Cl]₂ (8). Complex 5 and PPh₃ afford [Pt(PPh₃)(μ-PHMes)Cl]₂ (9). Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to 5 gives the dicationic [Pt(dppe)(μ-PHMes)]₂[Cl]₂2 (10-Cl), which was also obtained as the tetrafluoroborate salt 10-BF₄ by deprotonation of [Pt(dppe)(PH₂Mes)Cl]-[BF₄] (11) with Et₃N or by reaction of [Pt(dppe)(μ-OH)]₂[BF₄]₂ with 2 equiv of PH₂Mes. Complexes 8, 9, and 10-C1·2CH₂Cl₂·2H₂O were characterized crystallographically.

Full text of DOI:10.1021/ic951020i

1478
Inorg. Chem. 1996, 35, 1478-1485
Synthesis and Ligand Substitution Reactions of a Mesitylphosphido-Bridged Platinum(II)
Dimer
Igor V. Kourkine, Michael B. Chapman, and David S. Glueck*
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755
Klaus Eichele and Roderick E. Wasylishen
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3
Glenn P. A. Yap, Louise M. Liable-Sands, and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
ReceiVed August 4, 1995X
The stable primary phosphine complexes trans-M(PH2Mes*)2Cl2 (1, M ) Pd; 2, M ) Pt; Mes* ) 2,4,6-(t-
Bu)3C6H2) were prepared from Pd(PhCN)2Cl2 and K2PtCl4, respectively. Reaction of Pt(COD)Cl2 (COD ) 1,5-
cyclooctadiene) with less bulky arylphosphines gives the unstable cis-Pt(PH2Ar)2Cl2 (3, Ar ) Is ) 2,4,6-(i-
Pr)3C6H2; 4, Ar ) Mes ) 2,4,6-Me3C6H2). Spontaneous dehydrochlorination of 4 or direct reaction of K2PtCl4
with 2 equiv of PH2Mes gives the insoluble primary phosphido-bridged dimer [Pt(PH2Mes)(µ-PHMes)Cl]2 (5),
which was characterized spectroscopically, including solid-state 31P NMR studies. The reversible reaction of 5
with PH2Mes gives [Pt(PH2Mes)2(µ-PHMes)]2[Cl]2 (6), while PEt3 yields [Pt(PEt3)2(µ-PHMes)]2[Cl]2 (7), which
on recrystallization forms [Pt(PEt3)(µ-PHMes)Cl]2 (8). Complex 5 and PPh3 afford [Pt(PPh3)(µ-PHMes)Cl]2 (9).
Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to 5 gives the dicationic [Pt(dppe)(µ-PHMes)]2[Cl]2 (10-
Cl), which was also obtained as the tetrafluoroborate salt 10-BF4 by deprotonation of [Pt(dppe)(PH2Mes)Cl]-
[BF4] (11) with Et3N or by reaction of [Pt(dppe)(µ-OH)]2[BF4]2 with 2 equiv of PH2Mes. Complexes 8, 9, and
10-Cl‚2CH2Cl2‚2H2O were characterized crystallographically.
Introduction
Scheme 1
Many dinuclear metal complexes with bridging secondary
phosphido (µ-PR2) ligands are known,1 but the corresponding
µ-PHR primary derivatives are less common.2 Such complexes
are of interest, since the P-H bond is reactive. For example,
M-PHR groups are precursors to phosphinidene (PR) ligands,
formed by further proton transfer from phosphorus,3 and are
proposed intermediates in metal-catalyzed olefin hydrophos-
phination, in which alkenes undergo formal insertion into the
P-H bond.4
Primary phosphido complexes have been prepared by dehy-
drohalogenation of primary phosphine halide complexes.5 For
example, cis-Pd(PH2Cy)2Cl2 (Cy ) cyclo-C6H11) loses HCl to
form [Pd(PH2Cy)(µ-PHCy)Cl]2,6 while related chemistry with
PH2Ph was claimed to result in [Pd(PH2Ph)2Cl]2(µ-PPh) as a
result of further loss of HCl.7 We report here the synthesis of
related Pd(II) and Pt(II) chloride complexes of sterically
demanding primary arylphosphines. The dehydrochlorination
of one such compound leads to formation of the primary
phosphido-bridged Pt(II) dimer [Pt(PH2Mes)(µ-PHMes)Cl]2 (5;
Mes ) 2,4,6-Me3C6H2). Ligand substitution reactions of 5 give
a series of other phosphido-bridged dimers.
Results and Discussion
The complexes trans-M(PH2Mes*)2Cl2 (Mes* ) 2,4,6-(t-
Bu)3C6H2; M ) Pd (1), Pt (2)) were prepared by addition of 2
equiv of the phosphine to Pd(PhCN)2Cl2 or to K2PtCl4 (Scheme
1). The palladium complex could also be made directly from
PdCl2 in hot toluene, or from PdCl2 in acidic ethanol. These
air- and water-stable yellow solids are characterized by their
X Abstract published in AdVance ACS Abstracts, February 15, 1996.
(1) Carty, A. J.; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus-31
NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin,
L. D., Eds.; VCH: Deerfield Beach, FL, 1987; pp 559-619.
(2) For some recent examples and leading references, see: (a) Bleeke, J.
R.; Rohde, A. M.; Robinson, K. D. Organometallics 1995, 14, 1674-
1680. (b) Haupt, H.-J.; Schwefer, M.; Florke, U. Inorg. Chem. 1995,
34, 292-297. (c) Hey-Hawkins, E.; Kurz, S.; Sieler, J.; Baum, G. J.
Organomet. Chem. 1995, 486, 229-235.
1
distinctive 31P and H NMR spectra (AA′X2X′2 spin systems).
2
2
The P-P coupling constants (for 1, JPP ) 668 Hz; for 2, JPP
) 596 Hz) and the Pt-P coupling constant of 2707 Hz for 2
indicate that 1 and 2 are the trans isomers, as expected for the
(3) (a) Bonanno, J. B.; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem.
Soc. 1994, 116, 11159-11160. (b) Ho, J.; Hou, Z.; Drake, R. J.;
Stephan, D. W. Organometallics 1993, 12, 3145-3157.
(4) (a) Hoye, P. A. T.; Pringle, P. G.; Smith, M. B.; Worboys, K. J. Chem.
Soc., Dalton Trans. 1993, 74, 269-274. (b) Pringle, P. G.; Smith, M.
B. J. Chem. Soc., Chem. Commun. 1990, 1701-1702.
(5) (a) Bianco, V. D.; Doronzo, S. J. Organomet. Chem. 1971, 30, 431-
433. (b) Anand, S. P.; Goldwhite, H.; Spielman, J. R. Transition Met.
Chem. 1977, 2, 158-160.
(6) (a) Goldwhite, H.; Hirschon, A. S. Transition Met. Chem. 1977, 2,
144-149. (b) Issleib, K.; Roloff, H.-R. Z. Anorg. Allg. Chem. 1963,
324, 250-258.
(7) Issleib, K.; Wilde, G. Z. Anorg. Allg. Chem. 1961, 312, 287-298.
0020-1669/96/1335-1478$12.00/0 © 1996 American Chemical Society

A Mesitylphosphido-Bridged Pt(II) Dimer
Inorganic Chemistry, Vol. 35, No. 6, 1996 1479
Scheme 2
Scheme 3
bulky PH2Mes* ligand.8 One large and one small P-H coupling
1
3
1
Figure 1. 31P CP/MAS NMR spectrum of a powder sample of 5
obtained at 81.0 MHz. The isotropic regions are indicated by asterisks.
Conditions: spinning rate, 5.2 kHz; 1H π/2 pulse width, 3.4 µs; contact
time, 5 ms; recycle delay, 8 s; 422 scans.
are also observed (for 1, JPH ) 374, JPH ) 4 Hz; for 2, JPH
3
) 389, JPH ) 1 Hz). IR spectroscopy confirms the presence
of P-H bonds (for 1, νPH 2410 cm-1; for 2, νPH 2409 cm-1).
These complexes are stable with respect to dehydrochlorination
and remain unchanged in solution for weeks.
the alternative synthesis from K2PtCl4. Loss of HCl was greatly
accelerated by addition of Et3N to a CH2Cl2 solution of 4, which
resulted in the immediate precipitation of 5. GC-MS analysis
of the volatile materials formed in the reaction of Pt(COD)Cl2
with PH2Mes in CH2Cl2 indicated that COD was released.
The structure proposed for 5 is consistent with these data
and with literature reports of the formation of closely related
µ-phosphido dimers from primary and secondary phosphines.
In particular, similar Pt(II) chemistry with diphenylphosphine
gives [Pt(PHPh2)(µ-PPh2)Cl)]2,11 and the synthesis6 of [Pd(PH2-
Cy)(µ-PHCy)Cl]2, mentioned above, is directly related. How-
ever, the insolubility of 5 (in contrast, the above dimers are
soluble in organic solvents) was puzzling and prevented further
characterization by solution NMR. A solid-state 31P NMR study
provided more evidence for the proposed structure.
Reactions of Pt(COD)Cl2 (COD ) 1,5-cyclooctadiene) with
the less sterically demanding phosphines (L) PH2Is (Is ) 2,4,6-
(i-Pr)3C6H2) and PH2Mes gave the complexes cis-PtL2Cl2 (3
and 4; Scheme 2), as determined from 31P NMR spectroscopy.
In these cases, spectral simulation affords characteristically
2
1
smaller cis JPP values of 15 Hz in each case, while the JPtP
couplings of 3317 and 3340 Hz are also consistent with the cis
1
geometry. The P-H coupling constants (for 3, JPH ) 420,
1
3
3JPH ) 5 Hz; for 4, JPH ) 423, JPH ) 5 Hz) and IR spectra
(for 3, νPH 2399, 2367 cm-1) are similar to those observed for
1 and 2.9
Complexes 3 and 4 could not be isolated in analytically pure
form because they decompose in solution, producing white
solids that are insoluble in common solvents.10 For example,
complex 4 in CH2Cl2 deposited a precipitate, identified as the
phosphido-bridged Pt(II) complex [Pt(PH2Mes)(µ-PHMes)Cl]2
(5; Scheme 3). Moreover, the reaction of K2PtCl4 in water with
2 equiv of PH2Mes led directly to solid 5. This material is
thermally stable and does not melt up to 250 °C. Powder X-ray
diffraction studies show that when it is formed rapidly, as in
the decomposition of 4 in CH3NO2 or from K2PtCl4 in water,
it is amorphous. Slower precipitation from CH2Cl2 solutions
of 4, however, gives crystalline material. In some cases, we
observed by elemental analysis and/or CP/MAS 31P NMR (see
below) that isolated 5 was contaminated by complex 4, which
could be removed by extraction with CH2Cl2.
Elemental analysis and the FAB mass spectrum of complex
5, which shows a peak at m/z 1052.0 ((M - Me)+) and several
fragments corresponding to loss of Me, Mes, or PH2Mes groups,
are consistent with the formulation of 5. The IR (KBr) spectrum
of 5 shows a P-H stretch at 2366 cm-1; when deuterium-labeled
5 was prepared from PD2Mes, this band was significantly
reduced in intensity, but no νPD band could be confidently
assigned.
The 31P CP/MAS NMR spectrum of 5 (Figure 1) shows two
apparent doublet signals, each flanked by Pt satellites, in an
approximately 1:1 ratio. The isotropic chemical shifts of these
peaks are -67 and -247 ppm. The solution 31P NMR spectra
of related complexes, e.g. [Pt(PEt3)(µ-PPh2)Cl]2, have been
analyzed in detail by Brandon and Dixon12 and are analogous
to the one observed here, except for the much greater natural
line width of the solid-state 31P NMR spectrum. The peak at
-67 ppm can be assigned to the terminal PH2Mes group of 5,
while the chemical shift of the peak at much lower frequencies,
-247 ppm, is consistent with the literature on phosphido-bridged
dimers without metal-metal interactions.1 Each phosphorus
site of 5 consists of two chemically equivalent but magnetically
nonequivalent 31P nuclei, giving rise to an AA′XX′ spin system.
For such spin systems, the apparent doublet splitting in the AA′
and XX′ regions of the spectrum (here 360 Hz) is known to
correspond approximately to the sum of JAX and JAX′. This
observation is similar to the results for [Pt(PEt3)(µ-PPh2)Cl]2
(JAX + JAX′ ) 378.8 Hz) and [Pt(PHPh2)(µ-PPh2)Cl]2 (JAX
+
JAX′ ) 394.4 Hz).12
Titration of the CH2Cl2 solution remaining after 5 precipitates
showed that approximately 2 equiv of acid (presumably HCl)
was formed; this was also observed for the aqueous filtrate in
For the terminal phosphine, 1JPtP is 1960 ( 20 Hz, consistent
with the results for [Pt(PEt3)(µ-PPh2)Cl]2 (1JPtP ) 2171.8 Hz)
and [Pt(PHPh2)(µ-PPh2)Cl]2 (1JPtP ) 2184.0 Hz). For the
bridging phosphido ligand, the 1JPtP couplings (1954 ( 50 (trans
to PH2Mes) and 2503(50 Hz (trans to Cl)) reflect the trans
influence. These results are also similar to those observed for
[Pt(PEt3)(µ-PPh2)Cl]2 (1690.5 and 2634.7 Hz) and [Pt(PHPh2)-
(µ-PPh2)Cl]2 (1991.1 and 2364.2 Hz).12
(8) Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition Metal
Phosphine Complexes; Springer-Verlag: New York, 1979; Vol. 16,
pp 94-95. The Tolman cone angle (measured by the procedure of:
Tolman, C. A. Chem. ReV. 1977, 77, 313-348) of PH2Mes* is 132°.
(9) Related cis complexes of 1-adamantylphosphine have been reported
recently: Goerlich, J. R.; Schmutzler, R. Z. Anorg. Allg. Chem. 1994,
620, 898-907.
(10) Complex 5 does not dissolve in petroleum ether, diethyl ether, benzene,
toluene, THF, CH2Cl2, CHCl3, CH3NO2, dioxane, CS2, DMSO, DMF,
or chlorobenzene.
(11) Carty, A. J.; Hartstock, F.; Taylor, N. J. Inorg. Chem. 1982, 21, 1349-
1354.
(12) Brandon, J. B.; Dixon, K. R. Can. J. Chem. 1981, 59, 1188-1200.

1480 Inorganic Chemistry, Vol. 35, No. 6, 1996
Kourkine et al.
Figure 1 demonstrates that the peak due to the phosphido
group exhibits many spinning sidebands at multiples of the
spinning frequency, in contrast to the peak due to the terminal
PH2Mes ligand, which has only first-order spinning sidebands.
This indicates drastic differences in the chemical shift anisotro-
pies (CSA) of these two species.13 Analysis of the 31P CP NMR
spectrum of a static powder sample of 5 yields the principal
components of the chemical shift tensors: for the PH2Mes
ligand, δ11 -27, δ22 -62, δ33 -112 ppm; for the µ-PHMes
ligand, δ11 28, δ22 -85, δ33 -684 ppm. The CSA of the
terminal ligand is typical of phosphines coordinated to plati-
num.14 Obviously, the high shielding observed for the 31P of
the phosphido group as compared to the terminal ligand arises
mainly from the direction corresponding to δ33. So far, there
are only very few phosphorus compounds known with such high
shielding of the phosphorus nucleus along a particular direction
(note that the chemical shift of the free 31P atom15 is -632 ppm).
Such molecules are linear, where for reasons of symmetry16
there is no paramagnetic contribution to the direction along the
molecular axis (e.g. PN,17 HCP18 ), or are highly strained cyclic
molecules such as 1,2,3-triphenylphosphirene19 and P4.20 Un-
fortunately, there are no reasonable interpretations of these
effects available at this time. Note, however, that the phos-
phorus nuclei of phosphido groups bridging formal metal-metal
bonds are usually much less shielded than in corresponding
terminal phosphines.21
Scheme 4
Although 5 is insoluble, it reacts with donor ligands (Scheme
4). A slurry of 5 in a polar solvent (CH3NO2 or CH2Cl2) rapidly
reacted with an excess of PH2Mes or PEt3 at room temperature
to give a homogeneous yellow solution; 31P{1H} NMR monitor-
ing suggested that the ionic compounds [PtL2(µ-PHMes)]2[Cl]2
(6, L ) PH2Mes; 7, L ) PEt3) were formed. The 31P{1H} NMR
spectrum of a mixture of PH2Mes and 6 in CD2Cl2 at room
temperature shows broad peaks at δ -76 (coordinated PH2-
Mes), -147 (free PH2Mes), and -215 ppm (µ-PHMes),
consistent with rapid exchange of the terminal PH2Mes groups.22
However, at -60 °C this exchange is slowed and the peak
assigned to free PH2Mes is sharp, while that at δ -76 is resolved
as a complex multiplet. The peak assigned to coordinated
PHMes, however, remains broad. From these observations, we
cannot determine if the compound exists as a mixture of syn
and anti isomers differing in the relative stereochemistry of the
phosphido ligands. Similarly, the 31P{1H} NMR spectrum of
a mixture of PEt3 and 7 in CH3NO2 shows a multiplet at δ 17.6
(coordinated PEt3), resonances at δ -12.4 (free PEt3) and
-152.0 (free PH2Mes), and a broad signal at δ -252.2
(µ-PHMes). The ionic formulation of complexes 6 and 7 is
consistent with solution conductivity measurements in CH3NO2,
which show that these compounds are 2:1 electro-
lytes.23
The reaction of 5 with PH2Mes is reversible; attempted
recrystallization of 6 gave the insoluble starting material 5.
Similarly, attempts to recrystallize the PEt3 complex 7 produced
another insoluble compound, which was identified as [Pt(PEt3)-
(µ-PHMes)Cl]2 (8) by elemental analysis, IR spectroscopy, FAB
mass spectroscopy, and X-ray crystallography (see below). The
IR spectrum of 8 shows νPH at 2374 cm-1; the FAB mass
spectrum shows a peak at m/z 927.2 ((M - 2Cl - H)+) and
several fragments corresponding to loss of PEt3, Cl, and Me
groups.
The related reaction of 5 with the larger and less nucleophilic
PPh3 required elevated temperature and led to the formation of
the insoluble yellow [Pt(PPh3)(µ-PHMes)Cl]2 (9) (Scheme 4).
In this case, no soluble intermediate was observed. Heating of
the reaction mixture (THF, 55 °C, 8 days) gave X-ray-quality
crystals. Complex 9 was characterized by elemental analysis,
IR spectroscopy, FAB mass spectroscopy, and X-ray crystal-
lography (see below). In the IR (KBr) spectrum of 9 νPH 2380
cm-1 is observed; the FAB mass spectrum of 9 shows peaks at
m/z 1252.1 ((M - Cl)+) and 1216.2 ((M - 2Cl)+).
Addition of 2 equiv of 1,2-bis(diphenylphosphino)ethane
(dppe) to a CH2Cl2 slurry of 5 rapidly gave a solution containing
a mixture of [Pt(dppe)(µ-PHMes)]2[Cl]2 (10-Cl) and [Pt(dppe)2]-
[Cl]2 (13) (Scheme 4), as shown by 31P NMR. The 31P{1H}
NMR spectrum of 13 has been reported elsewhere24 and shows
a peak at δ 47.2 (1JPtP ) 2374 Hz). Separation of 10-Cl from
13 by recrystallization or by chromatography was difficult;
therefore, 10 was prepared independently as the BF4 salt 10-
BF4 (Scheme 4).
(13) Maricq, M. M.; Waugh, J. S. J. Chem. Phys. 1979, 70, 3300.
(14) (a) Harris, R. K.; McNaught, I. J.; Reams, P.; Packer, K. J. Magn.
Reson. Chem. 1991, 29, S60. (b) Lindner, E.; Fawzi, R.; Mayer, H.
A.; Eichele, K.; Hiller, W. Organometallics 1992, 11, 1033. (c) Power,
W. P.; Wasylishen, R. E. Inorg. Chem. 1992, 31, 2176.
(15) Jameson, C. J.; de Dios, A.; Jameson, A. K. Chem. Phys. Lett. 1990,
167, 575.
(16) Ramsey, N. F. Phys. ReV. 1950, 78, 699.
(17) Raymonda, J.; Klemperer, W. J. Chem. Phys. 1971, 55, 232.
(18) Kutzelnigg, W.; Fleischer, U.; Schindler, M. In NMR Basic Principles
and Progress; Diehl, P., Fluck, E., Gu¨nther, H., Kosfeld, R., Seelig,
J., Eds.; Springer-Verlag: Heidelberg, Germany, 1990; Vol. 23, pp
165-262.
Addition of AgBF4 to Pt(dppe)Cl2 followed by treatment with
PH2Mes gave the intermediate complex [Pt(dppe)(PH2Mes)Cl]-
[BF4] (11), which was characterized spectroscopically. The 31P-
(19) Barra, A. L.; Robert, J. B. Chem. Phys. Lett. 1987, 136, 224.
(20) Spiess, H. W.; Grosescu, R.; Haeberlen, U. Chem. Phys. 1974, 6, 226.
(21) Carty, A. J.; Fyfe, C. A.; Lettinga, M.; Johnson, S.; Randall, L. H.
Inorg. Chem. 1989, 28, 4120.
(22) A related exchange process was observed between neutral [Ni(PMe3)2-
{µ-PH(t-Bu)}]2 and PMe3: Jones, R. A.; Norman, N. C.; Seeberger,
M. H.; Atwood, J. L.; Hunter, W. E. Organometallics 1983, 2, 1629-
1634.
(23) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81-122.
(24) Anderson, G. K.; Davies, J. A.; Schoeck, D. J. Inorg. Chim. Acta 1983,
76, L251-L252.

A Mesitylphosphido-Bridged Pt(II) Dimer
Inorganic Chemistry, Vol. 35, No. 6, 1996 1481
Figure 2. Atom labeling for complex 10.
{1H} NMR spectrum of 11 shows three signals due to the
inequivalent phosphorus nuclei; the coordinated primary phos-
2
2
phine resonates at δ -70.5 (dd, JPP ) 398 Hz, JPP ) 18 Hz,
1JPtP ) 2180 Hz). Treatment of 11 with Et3N gave pure 10-
BF4. We assume that this reaction proceeds by initial depro-
tonation of the complexed primary phosphine, followed by
formation of the phosphido bridges with displacement of
chloride as an anion. Alternatively, 10-BF4 can be prepared
from the known25 hydroxo complex [Pt(dppe)(µ-OH)]2[BF4]2
by addition of PH2Mes (Scheme 4), as evident from 31P{1H}
NMR spectroscopy.
31P{1H} NMR spectroscopy shows that dication 10 exists in
solution as two isomers 10a (complex multiplets at δ 55.2 (dppe)
and -273.9 (µ-PHMes)) and 10b (complex multiplets at δ 51.6
(dppe) and -243.3 (µ-PHMes)). From the available data, we
cannot tell which of these is the syn and which is the anti isomer.
When 10-Cl is prepared from 5, the initial ratio of isomers 10a:
10b is approximately 2:1; after several days in CH2Cl2 the ratio
changes to about 1:1. However, when 10-BF4 is prepared by
either of the two methods described above, the initial ratio of
the isomers 10a:10b is 1:2 and further changes in the ratio were
not observed. Note that the 31P chemical shifts for the
phosphido ligands differ for 10-Cl and 10-BF4; we have not
investigated the reasons for this observation.
Figure 3. ORTEP diagram for [Pt(PEt3)(µ-PHMes)Cl]2 (8). Thermal
ellipsoids are shown at 30% probability. Hydrogen atoms are omitted
for clarity, except for the P-H atoms, which were treated as idealized
contributions.
Although complex 8 is insoluble in organic solvents, crystals
of it were obtained on attempted recrystallization of dication 7
from CH2Cl2/Et2O. Similarly, the heterogeneous reaction of
insoluble 5 with PPh3 in hot THF gave crystals of insoluble 9
directly from the reaction mixture. Suitable crystals of 10-Cl
as a methylene chloride/water solvate were grown by diffusion
of Et2O into a CH2Cl2 solution.
Crystal, data collection, and refinement parameters for
complexes 8, 9, and 10-Cl‚2CH2Cl2‚2H2O are given in Table
1. Atomic coordinates and equivalent isotropic displacement
coefficients are included as Supporting Information. ORTEP
diagrams are shown in Figures 3-5. Selected bond lengths and
angles appear in Tables 2 and 3, with data for analogous
platinum µ-phosphido dimers for comparison. Further details
of the structure determinations are given in the Experimental
Section and the Supporting Information.
All three complexes crystallize as the more symmetrical anti
isomer, as observed previously for other µ-phosphido dimers.26
The central Pt2P2 rings are planar, and the ideal square-planar
geometry at Pt(II) is distorted since the core P-Pt-P angle is
76-77°, as previously described by Carty11 for [Pt(PHPh2)(µ-
PPh2)Cl]2 and [Pt(dppe)(µ-PPh2)]2[Cl]2. The data in Tables 2
and 3 show that bond lengths and angles in these rings are
relatively insensitive to substitution. For both 8 and 9, the
difference between the Pt-PHMes (trans to PR3, R ) Et or
Ph) bond length (2.323(2) and 2.318(2) Å, respectively) and
the Pt-PHMes (trans to Cl) bond length (2.265(2) and
2.268(2) Å) may be rationalized by the greater trans influence
of a tertiary phosphine in comparison to chloride.27
The 31P{1H} NMR spectra of cations 10a,b are similar to
those of the closely related12 secondary phosphido complex [Pt-
(dppe)(µ-PPh2)]2[Cl]2, whose 31P NMR spectrum has been
analyzed in detail by Brandon and Dixon and which displays
similar coupling constants. For 10a-Cl, 31P NMR spectral
simulation gives the following coupling constants (the labeling
in Figure 2 and the sign convention follow Brandon and
4
Dixon): J1,2 ) 7.0, 2J1,3 ) 292.5, 2J1,4 ) 0, 1J1,5 ) 2180, 2J1,6
4
3
2
1
) 0, J1,7 ) 0, J2,5 ) 58, J3,4 ) -182, and J3,5 ) 1636 Hz.
4
2
2
1
For 10b-Cl, J1,2 ) 5.0, J1,3 ) 286.5, J1,4 ) 0, J1,5 ) 2236,
2J1,6 ) 0, 4J1,7 ) 0, 3J2,5 ) 50, 2J3,4 ) -165, and 1J3,5 ) 1632
Hz. The JPtP (J1,5) value for the dppe 31P nuclei (2180 and
1
2236 Hz) is larger for 10a,b than for [Pt(dppe)(µ-PPh2)]2[Cl]2
(2112.6 Hz), indicating that the µ-PPh2 ligand has a larger trans
influence than the µ-PHMes ligand.
1
The mixture of isomers 10a,b was also characterized by H
NMR spectroscopy. The Ar and Me groups of the two isomers
give rise to well-resolved signals, although peaks due to the
1
P-H protons could not be observed. The H NMR spectrum
of 10-BF4 shows peaks due to three inequivalent Me groups
and two inequivalent Mes ring protons for each of the isomers
10a and 10b. Similarly, the 13C NMR spectrum exhibits two
sets of three signals assigned to the mesityl methyl carbons of
10a,b. These results are consistent with restricted rotation
around the P-Mes bonds, which probably arises as a result of
The Pt-Cl bond length in 8 (2.376(2) Å) is significantly
longer than that in 9 (2.355(2) Å), perhaps because of the relative
cis influences of PEt3 and PPh3.28 However, these bond lengths
may also be affected by the different PR3-Pt-Cl (δ) and PR3-
Pt-PHMes (γ) angles observed in these compounds.
1
interaction between the Mes and the dppe Ph groups. The H
NMR spectrum also shows signals due to six different types of
dppe aryl protons per isomer. This confirms that the two phenyl
groups bound to a dppe phosphorus are inequivalent, as required
by symmetry.
(26) For examples, see: (a) Reference 2 a. (b) Brown, M. P.; Buckett, J.;
Harding, M. M.; Lynden-Bell, R. M.; Mays, M. J.; Woulfe, K. W. J.
Chem. Soc., Dalton Trans. 1991, 3097-3102. (c) Clegg, W.; Morton,
S. Inorg. Chem. 1979, 18, 1189-1192.
(27) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV. 1973,
10, 335-422.
(28) Hartley, F. R. Chem. Soc. ReV. 1973, 2, 163-179.
(25) Scarcia, V.; Furlani, A.; Longato, B.; Corain, B.; Pilloni, G. Inorg.
Chim. Acta 1988, 153, 67-70.

1482 Inorganic Chemistry, Vol. 35, No. 6, 1996
Kourkine et al.
Table 1. Crystallographic Data for 8, 9, and 10-Cl‚2CH2Cl2‚2H2O
8
9
10-Cl‚2CH2Cl2‚2H2O
formula
fw
space group
a, Å
b, Å
c, Å
C30H54Cl2P4Pt2
999.69
P21/c
7.804(4)
12.724(6)
18.618(15)
C54H52Cl2P4Pt2
1285.92
P21/n
10.210(3)
16.226(8)
15.066(5)
C72H78Cl4O2P6Pt2
1693.14
P1h
12.449(7)
12.510(7)
12.926(7)
77.52(4)
65.80(4)
81.87(5)
1790(2)
1
R, deg
â, deg
92.53(5)
90.21(4)
γ, deg
V, Å3
1847(2)
2
2496(2)
2
Z
D(calc), g cm-3
µ(Mo KR), cm-1
temp, K
radiation
R(F), %a
R(wF 2), %
1.798
79.02
296
1.711
58.69
296
1.571
42.30
296
Mo KR (λ ) 0.710 73 Å)
3.54 (6.25)b
6.95 (7.47)b
3.02 (4.24)b
6.89 (7.42)b
2.84 (3.73)b
6.16 (6.31)b
a Quantity minimized ∑[w(Fo - Fc2)2]/∑[(wFo )2]1/2; R ) ∑∆/∑(Fo); R(w) ) ∑∆w1/2/∑(Fow1/2), ∆ ) |(Fo - Fc)|. b Residual based on all data.
2
2
Figure 4. ORTEP diagram for [Pt(PPh3)(µ-PHMes)Cl]2 (9). Thermal
ellipsoids are shown at 30% probability. Hydrogen atoms are omitted
for clarity.
Figure 5. ORTEP diagram for [Pt(dppe)(µ-PHMes)]2[Cl]2‚2CH2-
Cl2‚2H2O (10-Cl‚2CH2Cl2‚2H2O). Only the cation is shown. Thermal
Comparison of the Pt-P(dppe) bond lengths in 10 (average
ellipsoids are shown at 30% probability. Hydrogen atoms are omitted
2.310(2) Å) and [Pt(dppe)(µ-PPh2)]2[Cl]2 (2.331(3) Å)11 indi-
for clarity.
cates that the µ-PPh2 ligand has a greater trans influence than
ligand in this series of compounds. Comparison of precursors
3 and 4 with the stable PH2Mes* complexes 1 and 2 suggests
µ-PHMes, consistent with the results from the 31P NMR analysis
above.
that a cis geometry (probably related to the steric bulk of the
No close intermolecular contacts or unusual packing was
phosphine ligands) is required for dehydrochlorination and the
observed in the structures of 8 or 9, so their lack of solubility,
formation of bridging phosphido complexes. We are continuing
and that of 5, remains mysterious. The µ-PHR group is present
to explore the reactivity of 5 and the related phosphido
in these compounds and in Woollins’ insoluble29 [Pt(PPh2Me)2-
complexes 6-10, both as precursors to phosphinidene ligands
(µ-PHPh)]24+, but [Pt(PHPh2)(µ-PPh2)Cl)]2 and [Pd(PH2Cy)-
by further proton transfer from phosphorus and as model
(µ-PHCy)Cl]2, mentioned above,6,11 as well as 10, are soluble
intermediates for olefin hydrophosphination.
in common solvents. However, Leoni et al. recently reported
that {Pt[PH(t-Bu)2][µ-P(t-Bu)2]H}2 is only sparingly soluble,30
and an understanding of the effect of ligand substituents on the
solubility of such dimers is evidently not yet available.
In conclusion, the primary phosphine complex cis-Pt(PH2-
Experimental Section
General Considerations. Unless noted otherwise, all reactions and
manipulations were performed in dry glassware under a nitrogen
atmosphere at 20 °C in a drybox or using standard Schlenk techniques.
All solvents were dried and distilled prior to use from Na/benzophenone
Mes)2Cl2 (4) decomposes under mild conditions to form the
phosphido-bridged Pt(II) dimer [Pt(PH2Mes)(µ-PHMes)Cl]2 (5),
which, although insoluble, reacts with other phosphine ligands
to give complexes 6-10. NMR and X-ray structural data have
been used to characterize the properties of the µ-phosphido
(petroleum ether (bp 38-53 °C), ether, THF, toluene) or CaH2 (CH2-
Cl2).
NMR spectra of all solutions examined in this study were recorded
by using a Varian Unity Plus 300 spectrometer. 1H or 13C NMR
chemical shifts are reported vs Me4Si and were determined by reference
1
to the residual H or 13C solvent peaks. 31P NMR chemical shifts are
(29) Parkin, I. P.; Slawin, A. M. Z.; Williams, D. J.; Woollins, J. D. Inorg.
Chim. Acta 1990, 172, 159-163.
(30) Leoni, P.; Manetti, S.; Pasquali, M. Inorg. Chem. 1995, 34, 749-
752.
reported vs H3PO4 (85%) used as an external reference. Coupling
constants are reported in Hz. Unless noted otherwise, peaks in NMR
spectra are singlets.

A Mesitylphosphido-Bridged Pt(II) Dimer
Inorganic Chemistry, Vol. 35, No. 6, 1996 1483
Table 2. Selected Bond Lengths (Å) for Phosphido-Bridged Platinum Dimers
a
b
complex
Pt---Pt
Pt-PR3
Pt-PR2
Pt-PR2
Pt-Cl
[Pt(PEt3)(µ-PHMes)Cl]2 (8)
[Pt(PPh3)(µ-PHMes)Cl]2 (9)
3.60
3.60
3.585(1)
3.699(1)
2.311(2)
2.311(2)
2.313(3)
2.331(3)
2.331(3)
2.302(2)
2.318(2)
2.341(3)
2.338(3)
2.336(1)
2.339(2)
2.323(2)
2.318(2)
2.329(3)
2.362(3)
2.335(3)
2.356(2)
2.348(2)
2.319(3)
2.330(3)
2.334(1)
2.326(2)
2.265(2)
2.268(2)
2.260(3)
2.376(2)
2.355(2)
2.379(4)
[Pt(PHPh2)(µ-PPh2)Cl]2‚C3H6Oc
c
[Pt(dppe)(µ-PPh2)]2[Cl]2‚2.5C2H4Cl2
[Pt(dppe)(µ-PHMes)]2[Cl]2‚2CH2Cl2‚2H2O (10-Cl‚2CH2Cl2‚2H2O)
3.70
3.7
d
[Pt(PPh2Me)2(µ-PHPh)]2[Cl]4‚1.5CH2Cl2
[Pt(PPh2Me)2(µ-PHPh)]2[Cl]2‚[PhPO2OH]2‚[PhPO(OH)2]d
3.7
a Trans to PR3. b Trans to Cl. c Carty, A. J.; Hartstock, F.; Taylor, N. J. Inorg. Chem. 1982, 21, 1349-1354. d Parkin, I. P.; Slawin, A. M. Z.;
Williams, D. J.; Woollins, J. D. Inorg. Chim. Acta 1990, 172, 159-163.
Table 3. Selected Bond Angles (deg) for Phosphido-Bridged Platinum Dimers
complex
R
â
γ
δ
ꢀ
[Pt(PEt3)(µ-PHMes)Cl]2 (8)
[Pt(PPh3)(µ-PHMes)Cl]2 (9)
103.58(9)
103.32(6)
102.8(0)
103.9(0)
76.42(9)
76.68(6)
77.2(0)
76.1(0)
101.38(9)
97.28(5)
94.8(1)
88.73(9)
94.33(6)
93.2(1)
93.47(9)
91.57(6)
94.8(1)
[Pt(PHPh2)(µ-PPh2)Cl]2‚C3H6Oa
a
[Pt(dppe)(µ-PPh2)]2[Cl]2‚2.5C2H4Cl2
99.6(1)
101.9(1)
99.34(6)
101.24(6)
95.5(1)
93.5(1)
95.9(1)
[Pt(dppe)(µ-PHMes)]2[Cl]2‚2CH2Cl2‚2H2O (10-Cl‚2CH2Cl2‚2H2O)
103.81(6)
104.9(1)
105.4(1)
76.19(6)
75.1(1)
74.6(1)
b
[Pt(PPh2Me)2(µ-PHPh)]2[Cl]4‚1.5CH2Cl2
[Pt(PPh2Me)2(µ-PHPh)]2[Cl]2‚[PhPO2OH]2‚[PhPO(OH)2]b
93.3(1)
a Carty, A. J.; Hartstock, F.; Taylor, N. J. Inorg. Chem. 1982, 21, 1349-1354. b Parkin, I. P.; Slawin, A. M. Z.; Williams, D. J.; Woollins, J. D.
Inorg. Chim. Acta 1990, 172, 159-163.
Solid-state 31P CP/MAS spectra were obtained using Bruker MSL-
200 (B0 ) 4.7 T) and AMX-400 (B0 ) 9.4 T) spectrometers. Powdered
samples were packed into 7 mm o.d. (4.7 T) or 4 mm o.d. (9.4 T)
zirconia rotors. Spectra were acquired after cross-polarization and under
high-power proton decoupling and are referenced with respect to
external H3PO4 (85%) via external NH4H2PO4 at 0.8 ppm. The isotropic
positions were determined as the peaks invariant to changes in MAS
rates or the strength of the applied magnetic field.
IR spectra were recorded on a Perkin-Elmer 1600 series FTIR
machine. Only the νPH values (when observed) are reported; full IR
spectra are given in the Supporting Information. GC-MS spectra were
obtained on a Hewlett-Packard 5890 Series II instrument. Conductivity
measurements were done by using a Fisher Digital Conductivity Meter.
Elemental analyses were provided by Schwarzkopf Microanalytical
Laboratory, Oneida Research Services, Inc. (complex 5), or Quantitative
Technologies, Inc. (complex 10). Low-resolution FAB mass spectros-
copy was performed by S. L. Mullen on a VG ZAB-SE instrument at
the University of Illinois. MS results are reported in m/z units and
percent intensity, and assignments are made using the most intense
peak in an envelope, calculated31 for the isotopomer containing the
most abundant isotopes 194Pt and 35Cl.
[trans-Pd(PH2Mes*)2Cl2] (1). In the air, a solution of PH2Mes*
(152 mg, 0.55 mmol) in 5 mL of toluene was added, with stirring, to
a suspension of Pd(PhCN)2Cl2 (100 mg, 0.26 mmol) in 15 mL of
toluene. The orange solution instantly lightened, and on complete
addition it was lemon yellow with some orange solid remaining. After
3.5 h the reaction mixture was filtered through Celite, which was
washed with 2 × 5 mL of toluene. The solvent was removed from the
orange filtrate with a rotary evaporator. Crystallization of the light
orange residue from hot toluene/petroleum ether at -80 °C gave 114
mg (60% yield) of yellow solid in three crops. The compound may
also be recrystallized from chloroform/petroleum ether or dichlo-
romethane/petroleum ether. It may also be prepared directly from PdCl2
and PH2Mes* in hot toluene or in acidic aqueous ethanol. 1H NMR
(C6D6): δ 7.51 (4H, Ar), 6.4-5.1 (m, 4H, PH2), 1.66 (36H, o-t-Bu),
1.19 (18H, p-t-Bu). In the 13C{1H} NMR spectra of both 1 and 2 (see
below), the multiplicities reported for the Mes* aryl resonances refer
to apparent splitting patterns. Accordingly, the values reported for J
do not reflect true coupling constants. For a more detailed discussion
of these AXX′ spin systems, see ref 8. 13C{1H} NMR (CDCl3): δ
156.7 (t, J ) 3.6, o Ar), 152.8 (p Ar), 123.8 (t, J ) 4.4, Ar), 114.3
(broad, Ar), 38.7 (CMe3), 35.4 (CMe3), 33.9 (CMe3), 31.3 (CMe3). 31
P
Unless noted otherwise, reagents were from commercial suppliers.
The following compounds were made by the literature procedures: PH2-
Mes*,32 PH2Mes,33 PH2Is,34 Pt(COD)Cl2,35 Pt(dppe)Cl2,24 [Pt(dppe)(µ-
OH)]2[BF4]2.25
NMR (CDCl3): δ -66.2 (m). 31P{1H} NMR (CDCl3): δ -66.2. IR
(KBr): 2410 cm-1. Anal. Calcd for C36H62Cl2P2Pd: C, 58.89; H, 8.53.
Found: C, 58.94; H, 8.59.
[trans-Pt(PH2Mes*)2Cl2] (2). A slurry of PH2Mes* (1000 mg, 3.59
mmol) in 40 mL of EtOH was added to a red solution of K2PtCl4 (745
mg, 1.79 mmol) in 15 mL of degassed water. The resulting pink slurry
was stirred for 4 days, after which most of the red color had disappeared.
In the air, the mixture was filtered on a fine frit and washed with water.
The solid was dissolved in CH2Cl2, and the resulting solution was dried
over MgSO4. The solvent was removed in vacuo to give 1138 mg of
pale yellow powder (77%). An analytical sample was recrystallized
from CH2Cl2/petroleum ether to give light yellow feathery crystals. 1H
NMR (CDCl3): δ 7.52 (4H, Ar), 6.34-5.05 (m, 4H, PH2), 1.69 (36H,
(31) Isotope Version 1.6, by Les Arnold, University of Waikato, New
Zealand, 1991.
(32) Cowley, A. H.; Norman, N. C.; Pakulski, M. Inorg. Synth. 1990, 27,
235-240.
(33) (a) Oshikawa, T.; Yamashita, M. Chem. Ind. 1985, 126-127. (b)
Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Sigel, G. A. Inorg.
Chem. 1987, 26, 1941-1946.
(34) Smit, C. N.; Bickelhaupt, F. Organometallics 1987, 6, 1156-1163.
(35) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc.
1976, 98, 6521-6528.

1484 Inorganic Chemistry, Vol. 35, No. 6, 1996
Kourkine et al.
o t-Bu), 1.31 (18H, p t-Bu). 13C{1H} NMR (CDCl3): δ 155.9 (t, J )
3.3, o Ar), 152.8 (p Ar), 123.7 (t, J ) 4.7, Ar), 113.1 (t, J ) 23.1, Ar),
38.8 (CMe3), 35.3 (CMe3), 33.8 (CMe3), 31.3 (CMe3). 31P NMR
(CDCl3): δ -64.8 (m, 1JPtP ) 2707). 31P{1H} NMR (CDCl3): δ -64.8
(1JPtP ) 2707). IR (KBr): 2409 cm-1. Anal. Calcd for C36H62Cl2P2-
Pt: C, 52.54; H, 7.61. Found: C, 52.23; H, 7.72.
frequency observed between this and other samples of 5 prepared in
different ways.
PD2Mes. MesBr (10 g, 50.2 mmol) was dissolved in THF (150
mL) and cooled to -78 °C. Cold (-78 °C) n-BuLi (34.0 mL of 1.6
M hexane solution, 54 mmol) was added, and the resulting mixture
was stirred for 2 h at -78 °C. This cold mixture was added slowly to
a solution of PCl3 (7.55 g, 55.0 mmol) in THF (15 mL) at -78 °C.
The mixture was warmed to room temperature; the volatile materials
were pumped off, and the residue was extracted with diethyl ether (2
× 50 mL). The diethyl ether solution was added to a slurry of LiAlD4
(4.2 g, 10.0 mmol) in diethyl ether (100 mL) at -78 °C and stirred for
30 min. During this time it was warmed to room temperature and then
quenched with a saturated aqueous solution of NH4Cl (40 mL). The
organic phase was separated and dried over MgSO4. The solvent was
removed, and the yellow viscous residue was distilled under vacuum
to give 3.4 g (43% yield) of PD2Mes. Analysis of the 31P{1H} NMR
spectrum suggested that the product was a mixture of PD2Mes (δ
-157.8 (five-line multiplet, 1JPD ) 32), 80%), PHDMes (-156.7 (three-
cis-Pt(PH2Is)2Cl2 (3). A solution of PH2Is (316 mg, 1.34 mmol) in
CH2Cl2 (1 mL) was added to a slurry of Pt(COD)Cl2 (200 mg, 0.53
mmol) in CH2Cl2 (5 mL) to give a white suspension. The reaction
mixture was stirred for 2 h. The solvent was removed in vacuo, and
the residue was washed with petroleum ether to give 230 mg (60%
yield) of a white solid. Complex 3 was not obtained in analytically
pure form; attempted recrystallization or chromatography on silica was
unsuccessful. 1H NMR (CD2Cl2): δ 7.20 (d, J ) 4, 4H, Ar), 4.95 (m,
4H, PH2), 3.14 (septet, J ) 6.5, 4H, o-CH(CH3)2), 2.90 (septet, J ) 7,
2H, p-CH(CH3)2), 1.30 (d, J ) 6.5, 24H, o-CH(CH3)2), 1.22 (d, J )
6.9, 12H, p-CH(CH3)2). 13C{1H} NMR (CD2Cl2): δ 154.6 (Ar), 153.0
(Ar), 122.7 (Ar), 35.0 (CHMe2), 33.4 (CHMe2), 24.4 (Me), 24.0 (Me).
The ipso Ar C peak was not observed. 31P{1H} NMR (CD2Cl2): δ
-80.6 (1JPtP ) 3317). 31P NMR (CD2Cl2): δ -80.6 (m, 1JPtP ) 3317).
1
line multiplet, JPD ) 32), 15%), and PH2Mes (-155.7, 5%).
[Pt(PD2Mes)(µ-PDMes)Cl]2 (5-D). A slurry of Pt(COD)Cl2 (370
mg, 0.99 mmol) in CH2Cl2 (3 mL) and PD2Mes (318 mg, 2.1 mmol)
were mixed together and stirred for 10 min, during which time a white
solid precipitated. The solvent was decanted, and the solid was washed
with CH2Cl2 (10 mL) and petroleum ether (5 mL) to give 340 mg (69%
yield) of the title complex. Anal. Calcd for C36H44D6Cl2P4Pt2: C,
40.26; H, 5.26; Cl, 6.6. Found: C, 39.30; H, 4.77; Cl, 9.19. IR
(KBr): 2384 cm-1 (weak). 31P{1H} CP/MAS NMR: δ -67 (m), -85
(complex 4-D present as an impurity), -247 (m).
[Pt(PH2Mes)2(µ-PHMes)]2[Cl]2 (6). Complex 5 (80 mg, 0.08
mmol) was slurried in CH2Cl2 (1.5 mL). Addition of PH2Mes (68 mg,
0.45 mmol) resulted in a yellow solution. 31P{1H} NMR (CH2Cl2) (20
°C): δ -76.0 (br), -147.0 (br), -215.0 (br). 31P{1H} NMR (CH2-
Cl2) (-60 °C): δ -76.0 (m), -147.0, -215.0 (br).
IR (KBr): 2399, 2367 cm-1
.
cis-Pt(PH2Mes)2Cl2 (4). A solution of PH2Mes (24 mg, 0.16 mmol)
in CH2Cl2 (1 mL) was added to Pt(COD)Cl2 (30 mg, 0.08 mmol)
slurried in CH2Cl2 (1 mL), and the resulting mixture was stirred for 2
min to give a yellow solution. The solvent was removed to afford 38
mg of an off-white residue, which was washed with diethyl ether (15
mL). 1H NMR (CD2Cl2): δ 6.89 (m, 4H, Ar), 5.04 (m, 4H, PH2),
2.36 (m, 12H, o-CH3), 2.23 (6H, p-CH3). 31P{1H} NMR (CD2Cl2): δ
-82.7 (1JPtP ) 3340). 31P NMR (CD2Cl2): δ -82.7 (m, 1JPtP ) 3340).
Attempted recrystallization of the complex from a CH2Cl2/Et2O mixture
gave insoluble 5. Attempts at purifying complex 4 by chromatography
on silica were unsuccessful.
[Pt(PH2Mes)(µ-PHMes)Cl]2 (5). A slurry of Pt(COD)Cl2 (50 mg,
0.13 mmol) in CH2Cl2 (4 mL) was mixed with PH2Mes (56 mg, 0.37
mmol) and stirred for 3 h, during which time an insoluble solid
precipitated. The solid was collected, washed with diethyl ether (2 ×
10 mL), and dried in vacuo to afford 98 mg (80% yield) of the off-
white product. Anal. Calcd for C36H50Cl2P4Pt2: C, 40.49; H, 4.73;
[Pt(PEt3)2(µ-PHMes)]2[Cl]2 (7). Complex 5 (40 mg, 0.04 mmol)
was slurried in CH2Cl2 (1.5 mL). Addition of PEt3 (30 mg, 0.25 mmol)
resulted in a yellow solution. 31P{1H} NMR (CH2Cl2): δ 14.6 (m),
-12.4, -152.0, -252.2 (m).
Solution Conductivity Measurements on 6 and 7. Complex 5
(32 mg, 0.03 mmol) was slurried in CH3NO2 (30 mL). Addition of
PH2Mes (15 mg, 0.1 mmol) led to a yellow solution, whose specific
conductivity was 0.146 Ω-1. In a similar experiment PEt3 (10 mg,
0.13 mmol) was added to a slurry of 5 (32 mg, 0.03 mmol) in CH3-
NO2 (30 mL) to give a yellow solution, whose specific conductivity
Cl, 6.64. Found: C, 39.78; H, 4.64; Cl, 6.78. IR (KBr): 2366 cm-1
.
31P CP/MAS NMR: δ -67 (m, 1JPtP ) 1960), -247 (m, 1JPtP ) 1954,
2503). Low-resolution FAB MS (3-NBA): 1052.0 [20, (M - Me)+],
991.0 [18, (M - 5Me -H)+], 961.0 [15, (M - 7Me)+], 903.9 [28, (M
- Mes - 3Me)+], 856.9 [18, (M - Mes - 6Me)+], 841.9 [20, (M -
Mes - 7Me)+], 763.0 [20, (M - 2PH2Mes - H)+]. Melting point:
>250 °C.
was 0.156 Ω-1
. With the concentrations and apparatus used, these
values correspond to molar conductivities of 146 and 156 Ω-1 cm2
mol-1, respectively.
The GC-MS spectrum of the mother liquor, separated from 5 by
distillation at room temperature, showed one peak with m/z 108, 93,
80, 67, 54, 39, 32 (COD). The mother liquor was titrated with a 0.0999
M methanol solution of KOH with thymol blue used as an indicator.36
In two separate experiments, 1.9 and 1.6 equiv of an acid were formed
per equivalent of complex 5.
Synthesis of 5 from K2PtCl4. A solution of K2PtCl4 (500 mg, 1.2
mmol) in H2O (30 mL) was treated with PH2Mes (385 mg, 2.5 mmol)
to give a yellow solid, which was collected and washed with water
(40 mL) and petroleum ether (20 mL) to give 500 mg (47% yield) of
complex 5. The 31P{1H} CP/MAS NMR spectrum showed that 5 was
contaminated by complex 4: δ -67 (m), -85 (complex 4), -247 (m).
Elemental analysis also showed that this sample was impure: Anal.
Calcd for C36H50Cl2P4Pt2: C, 40.49; H, 4.73. Found: C, 45.83; H,
5.67. IR (KBr): 2367 cm-1. X-ray powder diffraction showed that
the complex was amorphous. Titration of the mother liquor in two
separate experiments showed that 1.7 and 1.9 equiv of an acid were
formed per equivalent of dimer 5.
[Pt(PEt3)(µ-PHMes)Cl]2 (8). Addition of PEt3 (40 mg, 0.34 mmol)
to a slurry of 5 (100 mg, 0.094 mmol) in CH2Cl2 (10 mL) resulted in
a yellow solution, from which 50 mg (54% yield) of X-ray-quality
crystals were obtained by addition of diethyl ether (5 mL) at room
temperature over a period of a few days. Anal. Calcd for C30H54-
Cl2P4Pt2: C, 36.03; H, 5.46. Found: C, 35.93; H, 5.13. IR (KBr):
2374 cm-1. Low-resolution FAB MS (3-NBA): 1081.3 [30, (M -
2Cl + PH2Mes + H)+], 927.2 [49, (M - 2Cl - H)+], 720.0 [15, (M
- 2Cl - PEt3 - 6Me)+], 632.0 [15, (M - 2Cl -2PEt3 - 4Me)+],
603.0 [26, (M - 2Cl - 2PEt3 - 6Me + H)+].
[Pt(PPh3)(µ-PHMes)Cl]2 (9). PPh3 (210 mg, 0.8 mmol) was added
to a slurry of 5 (200 mg, 0.19 mmol) in THF (10 mL), and the resulting
mixture was heated at 55 °C for 8 days. During this time an insoluble
yellow solid, some of which was X-ray-quality crystals, formed. It
was collected, washed with THF (2 × 10 mL), and dried under vacuum
to give 120 mg (53% yield) of complex 9. Anal. Calcd for C54H54-
Cl2P4Pt2: C, 50.35; H, 4.23. Found: C, 50.42; H, 4.25. IR (KBr):
2380 cm-1. Low-resolution FAB MS (3-NBA): m/z 1369.0 [10, (M
- 2Cl + PH2Mes + H)+], 1252.1 [61, (M - Cl)+], 1216.2 [44, (M -
2Cl)+].
Synthesis of 5 in the Presence of Et3N. A solution of Et3N (27
mg, 0.27 mmol) in THF (2 mL) was added to the solution obtained by
mixing a slurry of Pt(COD)Cl2 (50 mg, 0.13 mmol) and PH2Mes (40
mg, 0.27 mmol). A yellow solid precipitated immediately. It was
[Pt(dppe)(µ-PHMes)]2[Cl]2 (10-Cl). A solution of dppe (62 mg,
0.15 mmol) in CH2Cl2 (3 mL) was added to complex 5 (70 mg, 0.07
mmol) to afford a yellow solution. Addition of diethyl ether (1 mL)
precipitated a white solid, which was collected and dried to give 105
mg (76% yield) of 10-Cl. The 31P{1H} NMR spectrum showed that a
mixture of isomers 10a,b and [Pt(dppe)2]Cl2 (13) was formed. Attempts
collected and dried in vacuo. IR (KBr): 2348 cm-1
. We do not
understand the origin of the small differences in the P-H stretching
(36) Kucharsky, J.; Safarik, L. Titrations in Non-Aqueous Solutions;
Elsevier: New York, 1965; pp 97-98.

A Mesitylphosphido-Bridged Pt(II) Dimer
Inorganic Chemistry, Vol. 35, No. 6, 1996 1485
at separating 10-Cl from 13 by recrystallization or by chromatography
were unsuccessful, but on one occasion X-ray-quality crystals of 10-
Cl were grown by diffusion of diethyl ether into a CH2Cl2 solution at
room temperature. 31P{1H} NMR (CD2Cl2) for the mixture of 10-Cl
and 13: δ 55.2 (m), 51.6 (m), 47.2 (1JPtP ) 2374, 13), -243.3 (m),
-273.9 (m).
multiplicities reported refer to apparent splitting patterns, and the values
reported for J do not reflect true coupling constants. Data from the
1H{31P} NMR spectrum were used to assign the JPH couplings reported.
1H NMR (CD2Cl2): δ 8.02 (dm, J ) 2.3, JPH ) 10.0, 8H, m or o Ar,
isomer a), 7.91 (dd, J ) 8.1, JPH ) 12.3, 8H, m or o Ar, isomer b),
7.83 (m, 12H, m or o Ar + p Ar, a), 7.64 (m, 12H, m or o Ar + p Ar,
b), 7.36 (t, J ) 8, 4H, p Ar, b), 7.19 (t, J ) 7.2, 4H, p Ar, a), 7.11 (dt,
J ) 7.5, JPH ) 2.7, 8H, m or o Ar, b), 6.93 (dt, J ) 7.8, JPH ) 2.7, 8H,
m or o Ar, a), 6.83 (dd, J ) 7.8, JPH ) 12.3, 8H, m or o Ar, b), 6.63
(dd, J ) 7.8, JPH ) 12.3, 8H, m or o Ar, a), 6.21 (2H, Mes, b), 5.91
[4H, Mes, a; in CDCl3 this signal is resolved as two peaks, δ 6.03
(2H) and 5.79 (2H)], 5.66 (2H, Mes, b), 2.95 (6H, Me, a), 2.50 (br m,
4H, CH2, a), 2.36 (6H, Me, b), 2.25 (br m, 4H, CH2, b), 2.12 (6H, Me,
b), 2.08 (6H, Me, a), 1.9 (br m, 4H, CH2, b), 1.7 (br, 4H, CH2, a),
1.40 (6H, Me, b), 1.28 (6H, Me, a). 13C{1H} NMR (CD2Cl2): δ 141.0
(Ar), 140.2 (Ar), 140.0 (Ar), 139.5 (Ar), 134.9 (d, J ) 11.6, Ar), 134.2
(Ar), 133.2 (Ar), 132.6 (Ar), 132.1 (Ar), 131.6 (d, J ) 11, Ar), 131.2
(Ar), 131.0 (Ar), 130.4 (d, J ) 25.0), 129.3 (m, Ar), 128.6 (Ar), 127.1
(Ar), 126.9 (Ar), 126.2 (m, Ar), 125.5 (d, J ) 11, Ar), 124.7 (Ar),
32.5 (m, CH2), 32.0 (m, CH2), 30.5 (m, CH2), 30.0 (m, CH2), 26.4 (m,
Me), 25.8 (m, Me), 23.7 (Me), 22.8 (Me), 21.8 (Me), 20.8 (d, J ) 4,
Me). 31P{1H} NMR (CD2Cl2): δ 55.3 (m), 51.6 (m), -251.1 (m),
-275.1 (m).
X-ray Crystallographic Studies on Complexes 8, 9, and 10-Cl‚-
2CH2Cl2‚2H2O. Crystal, data collection, and refinement parameters
are given in Table 1. The systematic absences were uniquely consistent
with the reported space groups for 8 and 9. No evidence of symmetry
higher than triclinic was observed in either the photographic or
diffraction data for 10. The structure was solved and refined in the
centrosymmetric space group, which yielded chemically reasonable and
computationally stable results. The structures were solved by direct
methods, completed by subsequent difference Fourier syntheses, and
refined by full-matrix least-squares procedures. Semiempirical absorp-
tion corrections were applied to the data sets. In each case, the
compound molecule was centered on an inversion point. A methylene
chloride solvent molecule and an adventitious water molecule were
located in the asymmetric unit of 10. The remaining peaks in the
difference map of 9 (maximum 1.72 e Å-3) occur at positions <1 Å
from the platinum atom and were considered as noise. All other non-
hydrogen atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were treated as idealized contributions except on the
solvent molecules of 10, which were ignored. All software and sources
of the scattering factors are contained in the SHELXTL (5.1) program
library (G. Sheldrick, Siemens XRD, Madison, WI).
Synthesis of 10-BF4 from [Pt(dppe)(µ-OH)]2[BF4]2. To a solution
of [Pt(dppe)(µ-OH)]2[BF4]2 (30 mg, 0.022 mmol) in CH2Cl2 (1.5 mL)
was added PH2Mes (7 mg, 0.046 mmol) to afford a pale yellow solution.
31P{1H} NMR (CH2Cl2): δ 55.3 (m), 51.6 (m), -251.1 (m), -275.1
(m).
[Pt(dppe)(PH2Mes)Cl][BF4] (11). To a slurry of Pt(dppe)Cl2 (480
mg, 0.72 mmol) in CH2Cl2 (15 mL) was added a solution of AgBF4
(140 mg, 0.72 mmol) in CH3CN (4 mL). AgCl precipitated im-
mediately and was filtered off. Then, PH2Mes (25 mg, 0.16 mmol)
was added to the filtrate to give a pale yellow solution. The solution
was concentrated to ca. 5 mL, and diethyl ether (3 mL) was added. A
white solid precipitated over a period of a few hours and was filtered
and dried under vacuum to give 450 mg of complex 11 (72% yield).
31P{1H} NMR (CH2Cl2/CH3CN): δ 51.3 (d, 2JPP ) 398, 1JPtP ) 2612),
Acknowledgment. We thank Dartmouth College and the
Petroleum Research Fund, administered by the American
Chemical Society, for partial support. We also thank Johnson
Matthey/Aesar/Alfa for loans of Pd and Pt salts. K.E. and
R.E.W. acknowledge the NSERC of Canada for financial
support.
2
1
2
2
41.5 (d, JPP ) 18, JPtP ) 3288), -70.5 (dd, JPP ) 398, JPP ) 18,
Supporting Information Available: Tables of crystallographic
data, atomic coordinates and equivalent isotropic displacement coef-
ficients, anisotropic displacement coefficients, H-atom coordinates, and
all bond distances and angles for 8, 9, and 10-Cl‚2CH2Cl2‚2H2O and
text giving additional IR, mass spectral, and X-ray powder diffraction
data (20 pages). This material is contained in many libraries on
microfiche, immediately follows this article in the microfilm version
of the journal, can be ordered from the ACS, and can be downloaded
from the Internet; see any current masthead page for ordering
information and Internet access instructions.
1JPtP ) 2180).
[Pt(dppe)(µ-PHMes)]2[BF4]2 (10-BF4). Complex 11 (40 mg, 0.04
mmol) was slurried in THF (2 mL), and Et3N (0.006 mL, 0.04 mmol)
was added to give a yellow solution. Addition of petroleum ether
precipitated a white solid. The solution was decanted, and the solid
was washed with H2O (10 mL), washed with ether (50 mL), and dried
under vacuum to give 65 mg (68% yield) of 10-BF4 as a mixture of
isomers. Anal. Calcd for C70H72B2F8P6Pt2: C, 50.55; H, 4.37.
Found: C, 50.20; H, 4.53.
1
Because of the large 31P-31P coupling, the resonances in the H
and 13C NMR spectra are not first-order multiplets. Therefore, the
IC951020I