Synthesis, molecular structures, and fluxional behavior of dppm-bridged complexes of platinum(II) with linear gold(I), trigonal silver(I), or tetrahedral mercury(II) centers

Article abstract of DOI:10.1021/om960355k

The complexes [PtR(dppm-P,P)(dppm-P)]PF₆ (R = Me, Et, Ph) react with [AuCl(SMe₂)] to generate the dppm-bridged platinum-gold complexes trans-[PtClR(μ-dppm)₂Au]PF₆ (1). Addition of [PtR(dppm-P,P)(dppm-P)]Cl to a solution of silver(I) acetate, followed by acetyl chloride, yields the neutral platinum-silver species trans-[PtClR(μ-dppm)₂AgCl] (2). Similarly, addition of [PtR(dppm-P,P)(dppm-P)]Cl to a solution of mercury(II) acetate, followed by acetyl chloride, yields the neutral platinum-mercury species trarns-[PtClR(μ-dppm)₂HgCl₂] (3). Each of the complexes has been characterized by ¹H and ³¹P{¹H}l NMR spectroscopy and by elemental analysis. The crystal structure of 1 as its methyl derivative 1a (CHCl₃ solvate) has been determined by X-ray diffraction. The compound exhibits approximate square-planar geometry at platinum and linear geometry at gold. The platinum-gold internuclear distance is 3.008(1) A?. The methyl complex 2a crystallizes as its CHCl₃ solvate. The geometry at platinum is distorted square planar, and the Pt?Ag distance is 3.049(1) A?. The geometry at silver is approximately trigonal planar. The pyramidal distortion taken together with a long Ag-Cl bond (2.610(4) A?) is discussed in the context of C-H?Cl hydrogen bonding and a possible incipient Pt?Ag interaction. The structure of 3a was also determined by X-ray diffraction. The geometry at platinum is distorted square planar, and the Pt?Hg distance is 3.302(1) A?. The geometry at mercury can be described as pyramidally distorted tetrahedral. However, taken together with an unusually long axial Hg-Cl distance (2.715-(4) A?), this distortion may be viewed in terms of an incipient S_N2 reaction at the Hg center that invokes a weak Pt?Hg interaction. The complexes have static structures at ambient temperature, as evidenced by the nonequivalence of the methylene hydrogens of the dppm ligands, but they exhibit fluxional behavior at higher temperatures. Free energies of activation in the range 13-19 kcal/mol have been determined, being higher for the Pt-Au species, and a mechanism involving reversible dissociation of chloride is proposed to account for the observed behavior.

Full text of DOI:10.1021/om960355k

3972
Organometallics 1996, 15, 3972-3979
Syn th esis, Molecu la r Str u ctu r es, a n d F lu xion a l Beh a vior
of d p p m -Br id ged Com p lexes of P la tin u m (II) w ith Lin ea r
Gold (I), Tr igon a l Silver (I), or Tetr a h ed r a l Mer cu r y(II)
Cen ter s
Chongfu Xu, Gordon K. Anderson,* Lee Brammer, J anet Braddock-Wilking, and
Nigam P. Rath
Department of Chemistry, University of MissourisSt. Louis,
8001 Natural Bridge Road, St. Louis, Missouri 63121
Received May 13, 1996X
The complexes [PtR(dppm-P,P)(dppm-P)]PF6 (R ) Me, Et, Ph) react with [AuCl(SMe2)] to
generate the dppm-bridged platinum-gold complexes trans-[PtClR(µ-dppm)2Au]PF6 (1).
Addition of [PtR(dppm-P,P)(dppm-P)]Cl to a solution of silver(I) acetate, followed by acetyl
chloride, yields the neutral platinum-silver species trans-[PtClR(µ-dppm)2AgCl] (2). Simi-
larly, addition of [PtR(dppm-P,P)(dppm-P)]Cl to a solution of mercury(II) acetate, followed
by acetyl chloride, yields the neutral platinum-mercury species trans-[PtClR(µ-dppm)2HgCl2]
1
(3). Each of the complexes has been characterized by H and 31P{1H} NMR spectroscopy
and by elemental analysis. The crystal structure of 1 as its methyl derivative 1a (CHCl3
solvate) has been determined by X-ray diffraction. The compound exhibits approximate
square-planar geometry at platinum and linear geometry at gold. The platinum-gold
internuclear distance is 3.008(1) Å. The methyl complex 2a crystallizes as its CHCl3 solvate.
The geometry at platinum is distorted square planar, and the Pt‚‚‚Ag distance is 3.049(1)
Å. The geometry at silver is approximately trigonal planar. The pyramidal distortion taken
together with a long Ag-Cl bond (2.610(4) Å) is discussed in the context of C-H‚‚‚Cl hydrogen
bonding and a possible incipient Pt‚‚‚Ag interaction. The structure of 3a was also determined
by X-ray diffraction. The geometry at platinum is distorted square planar, and the Pt‚‚‚Hg
distance is 3.302(1) Å. The geometry at mercury can be described as pyramidally distorted
tetrahedral. However, taken together with an unusually long axial Hg-Cl distance (2.715-
(4) Å), this distortion may be viewed in terms of an incipient SN2 reaction at the Hg center
that invokes a weak Pt‚‚‚Hg interaction. The complexes have static structures at ambient
temperature, as evidenced by the nonequivalence of the methylene hydrogens of the dppm
ligands, but they exhibit fluxional behavior at higher temperatures. Free energies of
activation in the range 13-19 kcal/mol have been determined, being higher for the Pt-Au
species, and a mechanism involving reversible dissociation of chloride is proposed to account
for the observed behavior.
In tr od u ction
most, if not all, cases the synthetic methods have been
limited to the preparation of symmetrical complexes. We
have reported recently the use of organoplatinum spe-
cies of the type [PtR(dppm-P,P)(dppm-P)]PF6 in the
synthesis of unsymmetrical chloride- and hydride-
bridged diplatinum or platinum-palladium complexes.7,8
In this paper we describe an extension of the use of
these organoplatinum cations to the preparation of
heterobimetallic complexes of platinum with gold, silver,
and mercury.
The use of bis(diphenylphosphino)methane (dppm)
or related ligands in the construction of bimetallic
and trimetallic complexes has developed tremendously
over the last 20 years, and a number of reviews of this
area have appeared.1-6 In particular, dppm-bridged
complexes of platinum or palladium have received
considerable attention, including A-frame species that
contain a bridging group such as a halide, hydride, CH2,
CO, S, SO2, or another metal. Several methods have
been utilized in the preparation of such species, but in
A number of complexes of platinum and one of these
metals have been reported previously, notably by Shaw
and co-workers, in most cases prepared from platinum
complexes containing two monodentate dppm ligands,
although in certain instances the bis(chelate) complex
[Pt(dppm-P,P)2]Cl2 was employed.9-13
X Abstract published in Advance ACS Abstracts, August 15, 1996.
(1) Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99.
(2) Balch, A. L. In Homogeneous Catalysis with Metal Phosphine
Complexes; Pignolet, L. H., Ed., Plenum: New York, 1983; pp 167-
213.
(3) Balch, A. L. Comments Inorg. Chem. 1984, 3, 51.
(4) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev.
1988, 86, 191.
(5) Puddephatt, R. J .; Manojlovic-Muir, L.; Muir, K. W. Polyhedron
1990, 9, 2767.
(7) Fallis, K. A.; Xu, C.; Anderson, G. K. Organometallics 1993, 12,
2243.
(8) Xu, C.; Anderson, G. K. Organometallics 1994, 13, 3981.
(9) Hassan, F. S. M.; Markham, D. P.; Pringle, P. G.; Shaw, B. L. J .
Chem. Soc., Dalton Trans. 1985, 279.
(6) Anderson, G. K. Adv. Organomet. Chem. 1993, 35, 1.
S0276-7333(96)00355-X CCC: $12.00 © 1996 American Chemical Society

dppm-Bridged Complexes of Platinum(II)
Organometallics, Vol. 15, No. 19, 1996 3973
Resu lts a n d Discu ssion
clear, yellow solution formed initially, whose 31P NMR
spectrum contained two sets of similar signals (δ(P) 23.5
dd, 1J (Pt,P) ) 3030 Hz, δ(P) -8.6 d of multiplets,
Syn th esis a n d Ch a r a cter iza tion . When [AuCl-
(SMe2)] was treated with 1 mol equiv of [PtMe(dppm-
P,P)(dppm-P)]PF6 in dichloromethane solution, followed
by addition of excess NH4PF6, the heterobimetallic
complex trans-[PtClMe(µ-dppm)2Au]PF6 (1a) was formed.
It was isolated in excellent yield as a pale yellow solid
following purification. The ethyl- and phenylplatinum
analogues (1b,c) were prepared similarly (eq 1). Each
1
1J (Ag,P) ) ca. 460 Hz; δ(P) 25.7 dd, J (Pt,P) ) 3075
1
Hz, δ(P) -2.4 d of multiplets, J (Ag,P) ) ca. 445 Hz),
indicating the presence of two related species. These
have been tentatively identified as trans-[PtClR(µ-
dppm)2Ag(OAc)] and trans-[Pt(OAc)R(µ-dppm)2AgCl].
Further addition of a CH2Cl2 solution of acetyl chloride
produced a colorless solution from which the product
was isolated in high yield as a white powder (eq 2). A
compound was characterized by elemental analysis and
by NMR spectroscopy, and 1a has been the subject of
an X-ray diffraction study. The 31P{1H} NMR spectrum
of 1a consists of two apparent triplets, the separation
large excess of acetyl chloride resulted in destruction
of the bimetallic complex and formation of [PtCl2-
(dppm)]. Use of [PtMe(dppm-P,P)(dppm-P)]PF6 instead
of its chloride salt did not produce 2a , indicating that
the chloride ion is incorporated into the final product.
Treatment of a solution of 2a with NH4PF6 caused
decomposition of the complex, which suggests that
in solution the complex is neutral rather than con-
sists of an organometallic cation and a free chloride
counterion.
2
of the outer lines of which is given by | J (Pa,Pb) +
10,11
4J (Pa,Pd)|
Each resonance is flanked by 195Pt satel-
lites, one with a coupling constant of 3049 Hz, due to
the P atom attached to platinum, and one with a long-
range coupling of 126 Hz, due to the P atom bonded to
gold. The 31P{1H} NMR spectra of 1b,c are qualitatively
similar, although the ethyl complex exhibits a larger
1J (Pt,P) value, as we have observed previously in
diplatinum and platinum-palladium dppm-bridged com-
plexes.7 The 1J (Pt,P) values are typical of trans-
The compounds 2a -c were characterized by mi-
croanalysis, 1H and 31P{1H} NMR spectroscopy, and, in
the case of 2a , X-ray crystallography. The 1H NMR
spectra of 2a -c are unremarkable, with two broad CH2
resonances, separated in each case by 1.1 ppm, due to
the dppm ligands. The 31P{1H} NMR spectra each
consist of a doublet of doublets for the P atoms coordi-
nated to platinum (see Experimental Section), and a
complex multiplet for the P atoms attached to silver.
3
PtClRP2 moieties. The J (Pt,P) values of 126-142 Hz
are slightly smaller than that found in [Pt(CH2CH2CH2-
CH2)(µ-dppm)2Au]+ (where the dppm ligands adopt a
cis configuration at platinum),11 slightly larger than that
in trans-[Pt(CtCPh)(CNBut)(µ-dppm)2AuCl]+,10 and con-
siderably larger than those in trans-[Pt(CN)2(µ-dppm)2-
Au]+ and trans-[PtCl(CNBut)(µ-dppm)2AuCl]+.9,10 Thus,
there is no clear dependence of 3J (Pt,P) on the geometry
at platinum or on whether the gold center is two- or
1
The J (Pt,P) couplings are around 3030 Hz for 2a and
2c and are over 200 Hz larger for 2b, an observation
analogous to that made for the Pt-Au species. The
1J (Ag,P) couplings can also be determined, couplings to
109Ag and 107Ag being 460 and 400 Hz, respectively, in
1
three-coordinate. The H NMR spectrum of 1a consists
of a triplet at 0.47 ppm, with a 78 Hz coupling to 195Pt,
due to the methyl group, two broad signals due to the
dppm CH2 hydrogens, and resonances due to the phenyl
1
each case. The J (Ag,P) coupling constants are similar
to those observed for trans-[PtX(CtCPh)(µ-dppm)2-
AgCl] (X ) Cl, C≡CPh)12 but smaller than those in
trans-[Pt(CtCPh)2(µ-dppm)2Ag]PF612 and [Pt(CH2CH2-
CH2CH2)(µ-dppm)2Ag]PF6,11 again consistent with a
three-coordinate silver center. The 3J (Pt,P) coupling
constants could not be determined in the present
Pt-Ag complexes.
The platinum-mercury complexes trans-[PtClR(µ-
dppm)2HgCl2] (3a -c; R ) Me, Et, Ph) were prepared
similarly by treating a suspension of mercury(II) acetate
with [PtR(dppm-P,P)(dppm-P)]Cl, followed by addition
of acetyl chloride. In this case several species were
detected by NMR spectroscopy initially, but following
addition of CH3COCl the desired products were obtained
in good yield (eq 3). Compounds 3a -c were character-
1
hydrogens. The H NMR spectra of 1b,c also exhibit
two broad resonances for the methylene groups of the
dppm ligands.
The platinum-silver complexes trans-[PtClR(µ-dppm)2-
AgCl] (2a -c) were prepared by addition of [PtR(dppm-
P,P)(dppm-P)]Cl (R ) Me, Et, Ph) to a suspension of
silver(I) acetate in dichloromethane. In each case, a
(10) Langrick, C. R.; Pringle, P. G.; Shaw, B. L. J . Chem. Soc., Dalton
Trans. 1984, 1233.
(11) Pringle, P. G.; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1984,
849.
(12) Cooper, G. R.; Hutton, A. T.; Langrick, C. R.; McEwan, D. M.;
Pringle, P. G.; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1984, 855.
(13) Langrick, C. R.; McEwan, D. M.; Pringle, P. G.; Shaw, B. L. J .
Chem. Soc., Dalton Trans. 1983, 2487.

3974 Organometallics, Vol. 15, No. 19, 1996
Xu et al.
ized by elemental analysis and NMR spectroscopy. The
structure of 3a was determined by X-ray crystal-
lography. The 1H NMR spectra of 3a ,b show the
expected signals for the alkyl groups, and all three
complexes exhibit two broad resonances, separated by
about 1 ppm, for the ligand CH2 groups. The 31P{1H}
NMR spectra of 3a -c each consist of two apparent
triplets. The high-frequency resonance exhibits a short-
range coupling to 195Pt of over 3000 Hz, indicating that
it is due to the P atoms bonded directly to platinum,
and a long-range coupling to 199Hg of around 50 Hz.
The low-frequency signal due to the P atoms coordi-
1
nated to mercury shows a J (Hg,P) value of 5600-5700
Hz and a 3J (Pt,P) coupling of around 200 Hz. The
chemical shifts and coupling constants are consistent
with those found for P atoms coordinated to a HgCl2
moiety in related dppm-bridged platinum-mercury com-
pounds.9,13
X-r a y Str u ctu r e Deter m in a tion s. The crystal
structures of [PtClMe(µ-dppm)2Au]PF6‚CHCl3 (1a ‚
CHCl3), [PtClMe(µ-dppm)2AgCl]‚CHCl3 (2a ‚CHCl3), and
[PtClMe(µ-dppm)2HgCl2] (3a ) have been determined by
X-ray diffraction. Pertinent interatomic distances and
angles are presented in Table 1. The molecular struc-
tures of [PtClMe(µ-dppm)2Au]+, [PtClMe(µ-dppm)2AgCl],
and [PtClMe(µ-dppm)2HgCl2] are shown in Figure 1.
In each structure the square-planar platinum center
is linked via two dppm bridges to a second metal center,
which has an approximately linear (Au), trigonal (Ag),
or tetrahedral (Hg) coordination environment. The
diphosphine ligands are disposed in a trans configura-
tion at Pt but show sufficient flexibility to accommodate
the different coordination geometries presented by the
second metal center (Table 1). Each of the PtClMe(P-
C-P)2MCln cores shows approximate mirror symmetry
through the mean plane of the two metals, the Cl and
Me substituents of Pt, and the Cl ligands of M. Thus,
the orientation of the methylene groups of the dppm
ligands gives rise to a boat conformation of the Pt(P-
C-P)2M ring in each case.
This boat conformation may result from any, or in
part from all, of a number of factors. The positions of
the phenyl groups must in part be dictated by packing
forces and are inevitably related to the Pt(P-C-P)2M
ring conformation, such that the former may exert
constraints on the latter. Further, it is interesting to
note that in each structure the square plane of the
ligands at Pt is tilted such that Cl(1) is moved toward
the other metal center; i.e., the angle M‚‚‚Pt-Cl(1) is
less than 90°. While it is tempting to then invoke Pt-
Cl(1)‚‚‚M bridging interactions, the long Cl(1)‚‚‚M sepa-
rations (3.113 Å for 1a and >3.5 Å for 2a , 3a ) suggest
F igu r e 1. (Top to bottom) Molecular structures of [Pt-
ClMe(µ-dppm)2Au]+ (1, cation), [PtClMe(µ-dppm)2AgCl] (2),
and [PtClMe(µ-dppm)2HgCl2] (3) shown with 50% prob-
ability ellipsoids for non-hydrogen atoms.
that this is not the case. The tilting may simply result
from a minimization of repulsive interactions between

dppm-Bridged Complexes of Platinum(II)
Organometallics, Vol. 15, No. 19, 1996 3975
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d An gles (d eg) for 1-3
1
2
3
Pt‚‚‚M
3.008(1)
3.049(1)
2.302(3)
2.294(3)
2.420(3)
2.045(10)
2.488(3)
2.513(3)
3.570(3)
2.610(4)
3.302(1)
2.269(4)
2.286(4)
2.416(4)
2.190(12)
2.506(4)
2.487(4)
3.524(5)
2.531(5)
2.715(4)
1.835(14)
1.814(14)
1.84(2)
1.84(2)
1.811(8)-1.839(9)
Pt-P(1)
Pt-P(2)
Pt-Cl(1)
Pt-C(3)
M-P(3)
2.294(5)
2.297(5)
2.425(5)
2.10(2)
2.317(5)
2.304(6)
3.113(5)
M-P(4)
M‚‚‚Cl(1)
M-Cl(2)
M-Cl(3)
P(1)-C(1)
P(3)-C(1)
P(2)-C(2)
P(4)-C(2)
P-C(Ph)
1.85(2)
1.81(2)
1.83(2)
1.86(2)
1.840(10)
1.849(11)
1.834(10)
1.849(10)
1.78(2)-1.83(2)
1.797(10)-1.836(11)
P(1)-Pt-P(2)
Cl(1)-Pt-C(3)
Cl(1)-Pt-P(1)
Cl(1)-Pt-P(2)
C(3)-Pt-P(1)
C(3)-Pt-P(2)
P(3)-M-P(4)
Cl(2)-M-P(3)
Cl(2)-M-P(4)
Cl(2)-M-Cl(3)
Cl(3)-M-P(3)
Cl(3)-M-P(4)
M‚‚‚Pt-Cl(1)
Pt-Cl(1)‚‚‚M
175.2(2)
172.1(5)
87.8(2)
87.7(2)
92.6(5)
91.8(5)
170.8(2)
176.9(1)
170.4(4)
90.8(1)
89.0(1)
91.0(4)
89.8(4)
134.3(1)
115.1(1)
108.4(1)
176.2(2)
173.2(4)
89.0(2)
87.4(2)
89.9(4)
93.4(4)
135.9(1)
111.1(1)
111.1(1)
90.9(2)
95.5(1)
96.1(1)
74.3(1)
64.4(1)
68.9(1)
64.4(1)
80.6(1)
57.4(1)
the methyl ligand and the two phenyl groups of the
dppm ligands (Figure 1). However, in each structure
the Cl ligand on platinum is well-positioned to maximize
any stabilization that may be gained from weak in-
tramolecular hydrogen bonding (Table 2) involving the
methylene hydrogens of the dppm ligands, and such
interactions may contribute to stabilization of the boat
conformer. Details of all intra- and other intermolecular
C-H‚‚‚X (X ) F, Cl) hydrogen bonds are given in Table
2 and are depicted in Figure 2.
sumably moderately strong) C-H‚‚‚Cl hydrogen bond
that links the chloroform solvate to the Cl ligand bound
to Ag in 2a . This reflects the enhanced polarity of the
chloroform C-H bond relative to typical hydrocarbon
C-H groups. At 2.47 Å, the H‚‚‚Cl separation is some
0.48 Å less than the anticipated van der Waals contact
for these atoms. A survey of the CSD19 reveals some
40 observations of C-H‚‚‚Cl hydrogen bonding involving
chloroform solvate as the (hydrogen bond) donor group
in which the H‚‚‚Cl separation is less than 2.6 Å. In
each case20 the acceptor group chlorine is bound to a
transition metal, which would be expected to give rise
to greater charge accumulation on the Cl group than
for organic chlorine. For comparison, the shortest
H‚‚‚Cl separation recorded is 2.29 Å in the chlorofrom
solvate of a pentagonal-bipyramidal dichloro(10-crown-
5)copper(II) compound.21
The Ag-Cl bond length in 2a ‚CHCl3, at 2.610(4) Å,
is the longest reported in a three-coordinate organosilver
compound, to our knowledge,22 and warrants more
detailed investigation. The CSD contains 24 structures
with terminal Ag-Cl bonds, which range in length from
2.261 to 3.034 Å. Examination of these structures
reveals two general trends: (i) increasing coordination
number at Ag is associated with increasing Ag-Cl
separation, and (ii) increasing Ag-Cl separation is
associated with increased X-H‚‚‚Cl-Ag hydrogen bond-
ing (both in strength and in number of interactions).
The widespread presence of “soft” C-H‚‚‚X hydrogen
bonds (particularly X ) O14 and also X ) F,15 Cl16) in
the crystal structures of organometallic complexes has
begun to receive attention in recent years, especially
with reference to efforts in supramolecular design17 and
crystal engineering.18 The presence of such interactions
in the crystal structures presented here also warrants
further discussion. The compound 1a ‚CHCl3 exhibits
intermolecular C-H‚‚‚F hydrogen bonding linking both
the chloroform solvate and one of the methylene groups
-
of the cation to the PF6 anion. A longer (weaker)
C-H‚‚‚Cl interaction (not shown in Figure 2) links
molecules of 3a via a methylene C-H group and the
axial chloride, Cl(2), associated with the Hg center. The
participation of the methylene C-H groups in hydrogen
bonding suggests that the polarity (acidity) of the groups
is greater than that of the phenyl C-H groups. How-
ever, perhaps most remarkable is the short (and pre-
(19) (a) See: Allen, F. H.; Kennard, O.; Taylor, R. Acc. Chem. Res.
1983, 16, 146. (b) The October 1995 version of CSD was used.
(20) Chloride ions were excluded as possible acceptor groups so as
to focus only on bound chlorine substituents and ligands.
(21) Sakurai, T.; Kobayashi, K.; Tsuboyama, S.; Kohno, Y.; Azuma,
N.; Ishizu, K. Acta Crystallogr. 1983, C39, 206.
(22) (a) The mean terminal Ag-Cl bond length from the 18
structures [17, excluding the anomalously long Ag-Cl separations in
structure AGSURE1019a] which meet the criteria for structure quality
used by Orpen et al.22b is 2.506 [2.465], with the sample standard
deviation σ22b ) 0.182 [0.121]. (b) Orpen, A. G.; Brammer, L.; Allen,
F. H.; Kennard, O.; Watson, D. G.; Taylor, R. J . Chem. Soc., Dalton
Trans. 1989, S1-S83.
(14) Braga, D.; Grepioni, F.; Sabatino, P.; Desiraju, G. R. J . Am.
Chem. Soc. 1995, 117, 3156.
(15) Brammer, L.; Klooster, W. T.; Lemke, F. R. Organometallics
1996, 15, 1721.
(16) Brammer, L.; Charnock, J . M.; Goggin, P. L.; Goodfellow, R.
J .; Orpen, A. G.; Koetzle, T. F. J . Chem. Soc., Dalton Trans., 1991,
1789.
(17) Braga, D.; Grepioni, F. J . Chem. Soc., Chem. Commun. 1996,
571.
(18) (a) Desiraju, G. R. Crystal Engineering: The Design of Organic
Solids; Elsevier: Amsterdam, 1989. (b) Desiraju, G. R. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2311.

3976 Organometallics, Vol. 15, No. 19, 1996
Xu et al.
taken into account. However, the trends suggest that
the short Cl3C-H‚‚‚Cl-Ag hydrogen bond in 2a ‚CHCl3
may be an important factor in determining the Ag-Cl
bond length.
Related to the above argument concerning the Ag-
Cl bond length is the extent to which an attractive
interaction between the metal centers is present. Na-
scent Pt-Ag bond formation could be regarded as an
incipient SN2 reaction at Ag in which the Pt center
serves as the nucleophile and the chloride ligand, Cl-
(2), would serve as the leaving group. This is not to
suggest that such a reaction could progress to comple-
tion, but merely that a weak attractive Pt‚‚‚Ag inter-
action could contribute to elongation of the Ag-Cl
bond. Consideration of the relative geometries of the
two metal centers supports such an assertion. Both
metals are displaced from the mean plane of their
ligands23 toward each other (Ag by 0.21 Å and Pt by
0.06 Å). The Pt-Ag vector makes an angle of 13.9°
with the normal to the Pt ligand plane,23 indicating that
2
this direction is close to the orientation of the Pt 5dz
(and 6pz) orbitals. The Pt-Ag-P(3) and Pt-Ag-P(4)
angles are 90.5(7) and 86.9(7)°, whereas the Pt-Ag-
Cl(2) angle is 110.4(9)°. This can be interpreted to
suggest that the chloride ligand is bent back away
from the “approaching” Pt nucleophile, consistent with
the suggested incipient SN2 reaction at Ag. However,
unlike the geometrically similar SN2 reaction at a
trigonal organic carbonyl carbon, in 2a the sp2-hybrid-
2
ized trigonal center (Ag) possess a donor (5dz ) in
addition to its acceptor (6pz) orbital. Thus incipient
Pt-Ag bond formation could equally involve AgfPt
electron donation. At 3.049(1) Å, the Pt‚‚‚Ag separa-
tion is longer than a typical Pt-Ag single bond (mean
2.743 Å, range 2.637-2.893 Å),19 and further analysis,
including consideration of a repulsive interaction be-
2
tween the filled 5dz orbitals of the two metal centers,
would be necessary in order to provide definitive expla-
nations for the questions posed by the observed geom-
etry of 2a .
The geometry about the Hg center in 3a also war-
rants similar examination. The two phosphines and Cl-
(2) lie in an approximate trigonal plane with the axial
chloride, Cl(3), oriented in a perpendicular direction,
resulting in a trigonal-pyramidal arrangement. The
Hg-Cl(2) bond length, at 2.531(5) Å, lies within the
wide range of values typical of four-coordinate mer-
cury species (2.28-2.68 Å,19 mean22b 2.430 Å), while the
axial Hg-Cl(3) bond, at 2.715(4) Å, is the longest
terminal Hg-Cl bond yet observed in an organomer-
cury compound.19 Indeed, we were able to find only
one compound with a longer terminal Hg-Cl bond
(2.968 Å), involving the five-coordinate mercury center
in the anion of [Co(en)2(NH3)(py)][Hg2Cl7].24,25 The
elongated Hg-Cl(3) bond in 3a may perhaps best be
explained in terms of the hybridization at Hg, in which
one can view the three equatorial ligands as interacting
with a set of 6sp2 hybrid orbitals on Hg and the axial
chloride interacts with the more radially diffuse 6pz
orbital. Auxiliary contributions to the lengthening of
the axial Hg-Cl(3) bond might be considered to arise
from intermolecular short C-H‚‚‚Cl hydrogen bonding
F igu r e 2. (Top to bottom) Molecular structures of 1-3,
depicting hydrogen-bonding interactions. Intermolecular
interactions are indicated by bold dashed lines and in-
tramolecular interactions by fine dashed lines. The C(2)-
H(2b)‚‚‚Cl(2) hydrogen bond linking molecules of 3 is not
shown.
The latter can perhaps be rationalized in terms of
greater Agδ+-Clδ- charge separation upon lengthening
the Ag-Cl bond. A summary is provided in the Sup-
porting Information. There are some exceptions to these
trends where other factors, such as coordination geom-
etry in addition to coordination number, must also be
(23) Mean planes of P(3)-P(4)-Cl(2) for Ag and P(1)-P(2)-Cl(1)-
C(3) for Pt.
(24) House, D. A.; McKee, V.; Robinson, W. T. Inorg. Chim. Acta
1989, 160, 71.

dppm-Bridged Complexes of Platinum(II)
Organometallics, Vol. 15, No. 19, 1996 3977
Ta ble 2. In ter a tom ic Dista n cesa (Å) a n d An glesa (d eg) for Hyd r ogen Bon d sb in 1-3
Intramolecular H Bonds
1
2
3
Cl(1)‚‚‚H(1a)
2.81
2.90
89
109
88
2.65
2.78
88
116
88
2.69
2.82
89
109
90
Cl(1)‚‚‚H(2a)
Pt-Cl(1)‚‚‚H(1a)
C(1)-H(1a)‚‚‚Cl(1)
Pt-Cl(1)‚‚‚H(2a)
C(2)-H(2a)‚‚‚Cl(1)
H(1a)‚‚‚Cl(1)‚‚‚H(2a)
106
151
107.5
156
102.5
162
Intermolecular H Bonds
1
2
3
H(52)‚‚‚F(2)
2.34
156
123
2.29
151
155
H(52)‚‚‚Cl(2)
C(52)-H(52)‚‚‚Cl(2)
Ag-Cl(2)‚‚‚H(52)
2.47
163
139
H(2b)‚‚‚Cl(2)
C(2)-H(2b)‚‚‚Cl(2)
Hg-Cl(2)‚‚‚H(2b)
2.73
135
159
C(52)-H(52)‚‚‚F(2)
P(3)-F(2)‚‚‚H(52)
H(1a) ‚‚‚F(5)
C(1)-H(1a)‚‚‚F(5)
P(3)-F(5)‚‚‚H(1a)
a
b
Calculated on the basis of C-H bonds extended to 1.09 Å. Sum of van der Waals radii for H + F is 2.67 Å, and for H + Cl is
2.95 Å.
(albeit weak), and as in 2a from invoking nascent Pt-
Hg bond formation26 and therefore an incipient SN2
reaction27 at Hg in which Cl(3) would serve as the
leaving group.
energy of activation being nearly 2 kcal/mol higher in
the methylplatinum complexes. Whereas the H NMR
1
spectra of the Pt-Au complexes also revealed a higher
∆Gq value for the methyl complex, albeit by only 1 kcal/
mol in this case (1a , Tc ) 415 K, ∆Gq ) 19.3 ( 0.2 kcal/
mol; 1c, Tc ) 389 K, ∆Gq ) 18.2 ( 0.1 kcal/mol), the
∆Gq values were 4-5 kcal/mol higher than in the Pt-
Ag and Pt-Hg species.
Va r ia b le-Tem p er a t u r e NMR St u d ies. Each of
the complexes under study exhibited two well-sepa-
rated, but poorly resolved, multiplets due to the CH2
hydrogens of the bridging dppm ligands in its 1H
NMR spectrum at ambient temperature. This is to
be expected, irrespective of the conformation of the
eight-membered Pt(P-C-P)2M ring in solution, be-
cause one hydrogen will lie on the same side of the
ring as the Pt-Cl bond and the other hydrogen will
lie on the opposite side. Qualitatively similar observa-
tions have been made for a number of dppm-bridged
species.10,11,28-31
When 1,1,2,2-tetrachloroethane-d2 solutions of the
methyl- and phenylplatinum complexes were heated
above ambient temperature, the dppm CH2 resonances
broadened further and eventually coalesced into one
broad, featureless signal. In each case the coalescence
temperature was obtained and ∆Gq for the exchange
process was calculated.32 (The ethyl complexes decom-
posed extensively on heating, and coalescence temper-
atures could not be determined.) The Pt-Ag and Pt-
Hg complexes exhibited similar behavior (2a , Tc ) 343
K, ∆Gq ) 15.3 ( 0.1 kcal/mol; 2c, Tc ) 303 K, ∆Gq )
13.4 ( 0.1 kcal/mol; 3a , Tc ) 341K, ∆Gq ) 15.3 ( 0.1
kcal/mol; 3c, Tc ) 305 K, 13.7 ( 0.1 kcal/mol), the free
We interpret this NMR behavior to indicate that the
complexes are static at ambient temperature, at least
in terms of inversion about the Pt(P-C-P)2M ring, but
at higher temperatures the molecules are fluxional. This
fluxional behavior renders the two dppm CH2 hydrogens
equivalent on the NMR time scale. It has been shown
that dppm-bridged A-frame complexes of platinum of
the type [Pt2R2(µ-X)(µ-dppm)2]+ undergo inversion of the
A-frame structure at ambient temperature, presumably
via a linear R-Pt-X-Pt-R intermediate, when X ) H,
but not when X ) Cl.33 The bridging hydrogen can pass
through the center of the Pt(P-C-P)2Pt ring, but the
bridging chloride is too large to do so. In fact, we have
heated solutions of the [Pt2Me2(µ-Cl)(µ-dppm)2]+ cation
to 343 K and the two CH2 signals remained sharp,
indicating that no fluxional motion occurs even at this
temperature. In the present complexes 1-3, rotation
about the P-Pt-P axis would render the CH2 hydrogens
equivalent. Such a mechanism is ruled out, however,
because it would require the Cl or CH3 (or Ph) to pass
through the eight-membered Pt(P-C-P)2M ring. Al-
ternative mechanisms could involve (1) Pt-P bond
cleavage, followed by rotation of the resulting three-
coordinate PtPClR unit and reattachment of the phos-
phino group, or (2) dissociation of chloride, followed by
rotation about the P-Pt-P axis and coordination of Cl-
to the opposite face of the molecule. We cannot distin-
guish unambiguously between these mechanisms, but
the higher ∆Gq values observed for the cationic Pt-Au
complexes support the latter, since we would expect that
Cl- dissociation from an already positively charged
species would represent a higher energy process. The
proposed mechanism is illustrated in eq 4. A mecha-
(25) Consistent with arguments on hydrogen bonding presented
earlier, the chloride ligand in this salt participates in a number of short
N-H‚‚‚Cl interactions and might even be thought of as a Cl- anion
that is weakly coordinated to the Hg center.
(26) Typical Pt-Hg single-bond lengths lie in the range19 2.510-
2.835 Å (mean 2.658 Å).
(27) (a) Such a reaction has been described by Bu¨rgi27b for Cd(II)
centers in an application of the Structure Correlation Method.27c (b)
Bu¨rgi, H.-B. Inorg. Chem. 1973, 12, 2321. (c) Bu¨rgi, H.-B.; Dunitz, J .
D. Acc. Chem. Res. 1983, 16, 153.
(28) Brown, M. P.; Fisher, J . R.; Puddephatt, R. J .; Seddon, K. R.
Inorg. Chem. 1979, 18, 2808.
(29) Langrick, C. R.; Pringle, P. R.; Shaw, B. L. J . Chem. Soc., Dalton
Trans. 1985, 1015.
(30) Hutton, A. T.; Langrick, C. R.; McEwan, D. M.; Pringle, P. R.;
Shaw, B. L. J . Chem. Soc., Dalton Trans. 1985, 2121.
(31) Neve, F.; Ghedini, M.; De Munno, G.; Crispini, A. Inorg. Chem.
1992, 31, 2979.
(32) Martin, M. L.; Delpuech, J .-J .; Martin, G. J . Practical NMR
Spectroscopy; Heydon: London, 1980; p 340.
(33) 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.

3978 Organometallics, Vol. 15, No. 19, 1996
Xu et al.
residue was washed several times with pentane and then
extracted into CH2Cl2 (10 mL). The resulting solution was
passed through a column of Hyflo Supercel, and the column
was washed with further CH2Cl2 (15 mL). The resulting
solution was evaporated to dryness, washed with small por-
tions of pentane and ether, and dried in vacuo, leaving the
product as a pale yellow powder (0.120 g, 88%). Anal.
Found: C, 44.72; H, 3.57. Calcd for C51H47AuClF6P5Pt: C,
45.16; H, 3.49. 1H NMR (CDCl3): δ(H) 0.47 t, 3J (P,H) ) 6 Hz,
2J (Pt,H) ) 78 Hz (CH3); 4.0 br, 4.4 br (PCH2P); 7.0-7.9 m
(4)
2
(C6H5). 31P{1H} NMR: δ(P) 19.8 t, 1J (Pt,P) ) 3049 Hz, | J (P,P)
4
3
+ J (P,P)| ) 49 Hz; δ(P) 29.8 t, J (Pt,P) ) 126 Hz. Crystals
suitable for X-ray diffraction were grown from CHCl3 solution.
trans-[PtClEt(µ-dppm)2Au]PF6 (1b) was prepared similarly
and isolated as a pale yellow powder in 87% yield. Anal.
Found: C, 45.54; H, 3.62. Calcd for C52H49AuClF6P5Pt: C,
45.58; H, 3.60. 1H NMR (CDCl3): δ(H) 0.38 t, 3J (H,H) ) 7
Hz (CH3); 1.08 q (CH2); 4.1 br, 3J (Pt,H) ) 38 Hz, 4.4 br
(PCH2P); 7.1-8.0 m (C6H5). 31P{1H} NMR: δ(P) 21.1 t,
nism involving halide dissociation has been proposed
previously to account for the fluxional behavior observed
in the face-to-face palladium dimers [Pd2X2R2(µ-dppm)2]
(X ) Br, R ) Me; X ) I, R ) Me, COMe).34
2
4
1J (Pt,P) ) 3292 Hz, | J (P,P) + J (P,P)| ) 48 Hz; δ(P) 29.9 t,
3J (Pt,P) ) 142 Hz.
Su m m a r y
trans-[PtClPh(µ-dppm)2Au]PF6 (1c) was prepared similarly
and isolated as a pale yellow powder in 87% yield. Anal.
Found: C, 47.51; H, 3.45. Calcd for C56H49AuClF6P5Pt: C,
47.42; H, 3.48. 1H NMR (CDCl3): δ(H) 3.7 br, 4.3 br (PCH2P);
6.7-8.0 m (C6H5). 31P{1H} NMR (CDCl3, -50 °C): δ(P) 16.3
The [PtR(dppm-P,P)(dppm-P)]+ cations (R ) Me, Et,
Ph) have been employed in the synthesis of the series
of dppm-bridged heterobimetallic complexes trans-[Pt-
ClR(µ-dppm)2MCln] (MCln ) Au+, AgCl, HgCl2), which
were isolated in good yield. The Pt-Au species were
prepared by reaction of [AuCl(SMe2)] with the cations
as their hexafluorophosphate salts, whereas the Pt-Ag
and Pt-Hg derivatives required initial reaction of [PtR-
(dppm-P,P)(dppm-P)]Cl with AgOAc or Hg(OAc)2, fol-
lowed by addition of acetyl chloride. Each of the
methylplatinum complexes has been characterized by
X-ray crystallography, and the molecular structures
reveal linear, trigonal, and tetrahedral geometries at
the gold, silver, and mercury centers, respectively. The
last two exhibit unusually long Ag-Cl (2.610(4) Å) and
Hg-Cl (2.716(4) Å) bonds. These appear to be associ-
ated with a moderately strong Cl3C-H‚‚‚Cl-Ag hydro-
gen bond in one case and hybridization of the mercury
valence orbitals in the other. However, both might be
viewed in terms of an incipient metal-centered SN2
reaction resulting in nascent Pt‚‚‚M bond formation and
M-Cl bond weakening. The complexes are static in
solution at ambient temperature, but they exhibit
fluxional behavior at higher temperatures which ren-
ders the dppm CH2 hydrogens equivalent on the NMR
time scale. A mechanism involving reversible chloride
dissociation is proposed to account for this behavior.
2
t, 1J (Pt,P) ) 3026 Hz, | J (P,P) + 4J (P,P)| ) 55 Hz; δ(P) 30.5 t,
3J (Pt,P) ) 139 Hz.
P r ep a r a tion of tr a n s-[P tClMe(µ-d p p m )2AgCl] (2a ). Sil-
ver(I) acetate (0.017 g, 0.10 mmol) was suspended in CH2Cl2
(5 mL), and a CH2Cl2 solution (5 mL) of [PtMe(dppm-P,P)-
(dppm-P)]Cl (0.101 g, 0.10 mmol) was added dropwise. The
solid gradually dissolved to give a clear, colorless solution.
After 1 h, a CH2Cl2 solution (5 mL) of acetyl chloride (2 drops)
was added dropwise, and the reaction was allowed to continue
for a further 15 min. The solvent was evaporated, and the
solid residue was washed with pentane. The solid was
redissolved in CH2Cl2 (10 mL), and the resulting solution was
passed through a column of Hyflo Supercel. The column was
rinsed with further CH2Cl2 (15 mL). The solutions were
combined and evaporated to dryness. The resulting solid was
washed with pentane and dried in vacuo, leaving the product
as a white powder (0.110 g, 96%). Anal. Found: C, 53.02; H,
4.14. Calcd for C51H47AgCl2P4Pt: C, 52.91; H, 4.09. 1H NMR
(CDCl3): δ(H) 0.84 t, 3J (P,H) ) 6 Hz, 2J (Pt,H) ) 84 Hz (CH3);
3.4 br, 4.5 br (PCH2P); 7.0-8.0 m (C6H5). 31P{1H} NMR: δ(P)
1
2
24.0 dd, J (Pt,P) ) 3034 Hz, | J (P,P) + 4J (P,P)| ) 96 Hz; δ(P)
10.0 dddd, 1J (109Ag,P) ) 458 Hz, 1J (107Ag,P) ) 397 Hz.
Crystals suitable for X-ray diffraction were grown from CHCl3
solution.
trans-[PtClEt(µ-dppm)2AgCl] (2b) was prepared similarly
and isolated as a white powder in 90% yield. Anal. Found:
C, 53.41; H, 4.28. Calcd for C52H49AgCl2P4Pt: C, 53.30; H,
4.22. 1H NMR (CDCl3): δ(H) 0.64 t, 3J (H,H) ) 8 Hz, 3J (Pt,H)
Exp er im en ta l Section
2
) 63 Hz (CH3); 1.67 q, J (Pt,H) ) 78 Hz (CH2); 3.4 br, 4.5 br
All reactions were carried out under an atmosphere of argon.
Complexes of the type [PtR(dppm-P,P)(dppm-P)]PF6 (R ) Me,
Et, Ph) were prepared as described previously. Routine 1H
and 31P{1H} NMR spectra were recorded on a Varian XL-300
spectrometer. Variable-temperature NMR spectra were re-
corded on a Bruker ARX-500 spectrometer. Microanalyses
were performed by Atlantic Microlab, Inc., Norcross, GA.
P r ep a r a tion of tr a n s-[P tClMe(µ-d p p m )2Au ]P F 6 (1a ).
[AuCl(SMe2)] (0.030 g, 0.10 mmol) was dissolved in CH2Cl2 (5
mL), and a CH2Cl2 solution (5 mL) of [PtMe(dppm-P,P)(dppm-
P)]PF6 (0.112 g, 0.10 mmol) was added dropwise. NH4PF6
(0.033 g, 0.20 mmol) was added as a solid, followed by
methanol (2.5 mL), and the mixture was stirred at ambient
temperature for 1 h. The solvents were removed, and the
(PCH2P); 7.0-8.0 m (C6H5). 31P{1H} NMR: δ(P) 24.7 dd,
2
1J (Pt,P) ) 3261 Hz, | J (P,P) + 4J (P,P)| ) 94 Hz; δ(P) 10.1 dddd,
1
1J (109Ag,P) ) 456 Hz, J (107Ag,P) ) 396 Hz.
trans-[PtClPh(µ-dppm)2AgCl] (2c) was prepared similarly
and isolated as a white powder in 83% yield. Anal. Found:
C, 54.84; H, 4.10. Calcd for C56H49AgCl2P4Pt: C, 55.14; H,
4.05. 1H NMR (CDCl3, -40 °C): δ(H) 3.3 br, 4.4 br (PCH2P);
6.7-8.0 m (C6H5). 31P{1H} NMR (CDCl3, -50 °C): δ(P) 21.6
1
2
4
dd, J (Pt,P) ) 3033 Hz, | J (P,P) + J (P,P)| ) 94 Hz; δ(P) 8.9
dddd, J (109Ag,P) ) 461 Hz, J (107Ag,P) ) 399 Hz.
1
1
P r ep a r a tion of tr a n s-[P tClMe(µ-d p p m )2HgCl2] (3a ). A
CH2Cl2 solution (5 mL) of [PtMe(dppm-P,P)(dppm-P)]Cl (0.101
g, 0.10 mmol) was added dropwise to a suspension of mercury-
(II) acetate in CH2Cl2 (5 mL). The solid dissolved gradually
to give a clear yellow solution. After 1 h, a solution of acetyl
chloride (2 drops) in CH2Cl2 (5 mL) was introduced dropwise,
and the solution changed from yellow to colorless. After a
(34) Balch, A. L.; Hunt, C. T.; Lee, C.-L.; Olmstead, M. M.; Farr, J .
P. J . Am. Chem. Soc. 1981, 103, 3764. Lee, C.-L.; Hunt, C. T.; Balch,
A. L. Organometallics 1982, 1, 824.

dppm-Bridged Complexes of Platinum(II)
Organometallics, Vol. 15, No. 19, 1996 3979
Ta ble 3. Da ta Collection , Str u ctu r e Solu tion , a n d Refin em en t P a r a m eter s for 1-3
1
2
3
cryst system
space group, Z
a (Å)
b (Å)
c (Å)
orthorhombic
P212121, 4
10.685(2)
18.817(6)
27.366(4)
monoclinic
C2/c, 8
orthorhombic
P212121, 4
10.011(1)
16.572(1)
28.243(1)
39.749(11)
13.027(4)
21.928(7)
115.50(2)
10 248(5)
1.655
â (deg)
V (Å3)
5502(2)
1.781
295(2)
5.598
Siemens R3m/V
1.84-25.06
5841
5668 (0.020)
604
-0.01(1)
0.055, 0.093
0.098, 0.108
1.03
4685.3(1)
1.823
143(5)
density (g/cm3)
temp (K)
295(2)
3.530
µ(Mo KR)a (mm-1
diffractometer
θ range (deg)
)
6.598
Siemens R3m/V
1.66-27.56
12 540
11 845 (0.050)
568
Siemens SMART CCD
1.42-26.50
43 815
9715 (0.078)
320
no. of rflns collected
no. of indep rflns (Rint
ls params
)
abs structure param,b x
R(F), Rw(F2) (F2 > 2.0σ(F2))c
R(F), Rw(F2) (all data)c
S(F2) (all data)c
n.a.
0.01(1)
0.075, 0.113
0.171, 0.145
1.00
0.077, 0.206
0.085, 0.214
1.84
a
b
Graphite-monochromated X-rays, wavelength 0.710 73 Å. Flack parameter (Flack, H. Acta Crystallogr. 1983, A39, 876). c R(F) )
Σ|Fo - Fc|/ΣFo; Rw(F2) ) [Σw(Fo - Fc2)2/ΣwFo
]
1/2; S(F2) ) [Σw(Fo - Fc2)2/(n - p)]1/2
.
2
4
2
further 15 min the solvent was removed, and the solid residue
was washed with several small portions of pentane. The solid
was redissolved in CH2Cl2 (10 mL), and the resulting solution
was passed through a Hyflo Supercel column. The column was
washed with further CH2Cl2 (15 mL), and the combined
solution was evaporated to dryness. The resulting solid was
washed with pentane and then dried in vacuo, leaving the
product as a white powder (0.105 g, 82%). Anal. Found: C,
47.37; H, 3.70. Calcd for C51H47Cl3HgP4Pt: C, 47.64; H, 3.68.
contribution, which necessarily rendered the absorption cor-
rection less effective. For 1a ‚CHCl3 and 2a ‚CHCl3, all non-
hydrogen atoms were refined anisotropically; hydrogens were
included in calculated positions and treated using a riding
model constraint with fixed isotropic displacement parameters.
For 3a , an unconstrained model for the non-hydrogen atoms
led to chemically unreasonable geometries within the phenyl
groups. Thus, the final model included constraints on these
groups: the ring geometry was constrained to be a regular
hexagon, and ortho and meta carbons were constrained to have
anisotropic displacement parameters identical with those of
the carbon opposite in the ring. No systematic changes in ge-
ometry or displacement parameters of the PtClMe(P-C-P)2-
HgCl2 core were observed in changing from the (unreasonable)
unconstrained model to the final (constrained) model. Hydro-
gen atoms were treated in the same manner as for 1a ‚CHCl3
and 2a ‚CHCl3. Experimental data pertinent to these structure
determinations are given in Table 3.
3
2
1H NMR (CDCl3): δ(H) 0.77 t, J (P,H) ) 5 Hz, J (Pt,H) ) 82
Hz (CH3); 3.75 br, 4.7 br (PCH2P); 7.0-8.2 m (C6H5). 31P{1H}
NMR: δ(P) 22.3 t, 1J (Pt,P) ) 3135 Hz, 3J (Hg,P) ) 45 Hz,
2
4
1
| J (P,P) + J (P,P)| ) 64 Hz; δ(P) 15.6 t, J (Hg,P) ) 5657 Hz,
3J (Pt,P) ) 227 Hz. Crystals suitable for X-ray diffraction were
grown from CHCl3 solution.
trans-[PtClEt(µ-dppm)2HgCl2] (3b) was prepared similarly
and isolated as a white powder in 73% yield. Found: C, 47.98;
H, 3.91. Anal. Calcd for C52H49Cl3HgP4Pt: C, 48.05; H, 3.80.
Va r ia ble-Tem p er a tu r e NMR Exp er im en ts. 1H NMR
spectra were recorded in 1,1,2,2-tetrachloroethane-d2 solution,
and the CH2 resonance of the dppm ligand was monitored. In
the slow exchange regime two signals were observed, and the
frequency difference (∆ν) for the two hydrogens at the coales-
cence temperature (Tc) was obtained by extrapolation from the
low-temperature data. Exchange rate constants, kc, at the
coalescence temperature were calculated using the equation
kc ) π(∆ν)/21/2. The exchange constants were used to deter-
mine ∆Gq at the coalescence temperature from the Eyring
equation kc ) (k′/h)Tc exp(-∆Gq/RTc), where k′ ) Boltzmann’s
constant, h ) Planck’s constant, and R ) the ideal gas
constant.32
3
3
1H NMR (CDCl3): δ(H) 0.60 t, J (H,H) ) 8 Hz, J (Pt,H) ) 66
Hz (CH3); 1.63 q (CH2); 3.7 br, 4.7 br (PCH2P); 7.1-8.2 m
(C6H5). 31P{1H} NMR: δ(P) 23.1 dd, 1J (Pt,P) 3371 Hz, 3J (Hg,P)
) 46 Hz, | J (P,P) + 4J (P,P)| ) 63 Hz; δ(P) 15.2 dd, 1J (Hg,P) )
2
3
5614 Hz, J (Pt,P) ) 253 Hz.
trans-[PtClPh(µ-dppm)2HgCl2] (3c) was prepared similarly
and isolated as a white powder in 84% yield. Anal. Found:
C, 49.63; H, 3.77. Calcd for C56H49Cl3HgP4Pt: C, 49.90; H,
3.66. 1H NMR (CDCl3, -40 °C): δ(H) 3.6 br, 4.5 br (PCH2P);
6.8-8.1 m (C6H5). 31P{1H} NMR (CDCl3): δ(P) 18.1 br t,
2
4
1J (Pt,P) ) 3140 Hz, 3J (Hg,P) ) 56 Hz, | J (P,P) + J (P,P)| )
1
3
54 Hz; δ(P) 15.8 br t, J (Hg,P) ) 5701 Hz, J (Pt,P) ) 185 Hz.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s of [P tClMe-
(µ-d p p m )2Au ]P F 6‚CHCl3 (1a ‚CHCl3), [P tClMe(µ-d p p m )2-
AgCl]‚CH Cl3 (2a ‚CH Cl3), a n d [P t ClMe(µ-d p p m )2H gCl2]
(3a ). The crystal structures were solved by Patterson methods
and subsequently refined to convergence by full-matrix least
squares using the SHELXTL suites of programs.35 In each
case a semiempirical correction for the effects of absorption
was applied on the basis of ψ-scan (1a ‚CHCl3 and 2a ‚CHCl3)
or symmetry-equivalent (3a ) data. In the latter case the
calculated correction was minor, despite the clear suggestion
of absorption effects manifested in large residual density peaks
ca. 1 Å from the metal atoms. The presence of low-angle
reflections with Fo2 > Fc2 suggested an additional contribution
to these reflections from a twin component. However, despite
measurement of a number of data sets from different crystals
and at different temperatures, we were unable to model this
Ack n ow led gm en t. Thanks are expressed to the
National Science Foundation (Grant Nos. CHE-9101834
and CHE-9508228), the donors of the Petroleum Re-
search Fund, administered by the American Chemical
Society, and the University of MissourisSt. Louis for
support of this work and to J ohnson Matthey Aesar/
Alfa for generous loans of platinum salts. C.X. acknowl-
edges the receipt of a Dissertation Fellowship from the
University of MissourisSt. Louis.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
crystallographic data, positional parameters, anisotropic dis-
placement parameters, and interatomic distances and angles
for 1a ‚CHCl3, 3a ‚CHCl3, and 3a (24 pages). Ordering infor-
mation is given on any current masthead page.
(35) SHELXTL 5.0; Siemens Analytical X-ray Instruments Inc.,
Madison, WI, 1995.
OM960355K