Easy making and breaking of metal-metal donor-acceptor bonds in the chemistry of binuclear methylplatinum(II) complexes

Article abstract of DOI:10.1021/om030116e

Reaction of [Pt₂Me₄ (μ-SMe₂)₂] with PN = 2-Ph₂PC₅H₄N gave cis,cis-[Pt₂Me₄(μ-SMe₂)-(μ-PN)], which reacts regioselectively with CF₃CO

Full text of DOI:10.1021/om030116e

2612
Organometallics 2003, 22, 2612-2618
Ea sy Ma k in g a n d Br ea k in g of Meta l-Meta l
Don or -Accep tor Bon d s in th e Ch em istr y of Bin u clea r
Meth ylp la tin u m (II) Com p lexes
Mehdi Rashidi,1 Michael C. J ennings, and Richard J . Puddephatt*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
Received February 20, 2003
Reaction of [Pt2Me4(µ-SMe2)2] with PN ) 2-Ph2PC5H4N gave cis,cis-[Pt2Me4(µ-SMe2)-
(µ-PN)], which reacts regioselectively with CF3CO2H at low temperature to give [Me2Pt-
(µ-SMe2)(µ-PN)PtMe(O2CCF3)], which then isomerizes to give [Me(CF3CO2)Pt(µ-PN)PtMe2-
(SMe2)], which contains a PtPt donor-acceptor bond. This bond is broken on addition at
low temperature of more ligand PN to give [Me(NP)Pt(µ-SMe2)(µ-PN)PtMe2](CF3CO2), which
loses dimethyl sulfide easily to form the unusual head-to-head bis(PN)-bridged complex
[MePt(µ-PN)2PtMe2](CF3CO2), and this complex then isomerizes to the head-to-tail isomer
[MePt(µ-PN)(µ-NP)PtMe2](CF3CO2). These isomers both contain donor-acceptor PtPt bonds.
The complexes are characterized by multinulear NMR methods, and the structures of cis,-
cis-[Pt2Me4(µ-SMe2)(µ-PN)] and [MePt(µ-PN)2PtMe2](CF3CO2) have been determined crys-
1
tallographically. The complexes with PtPt bonds give couplings J (PtPt) in the range 2721-
2
3812 Hz, while those without such bonds give couplings J (PtPt) in the range 0-275 Hz in
the 195Pt NMR spectra.
In tr od u ction
tends to favor short metal-metal separations in its
bridged complexes.8 It was of interest to study methyl-
platinum complexes with the ligand PN, and this article
describes how the reversible formation of PtPt donor-
acceptor bonds can play a key role in the reactions. An
unusual example of characterization of both head-to-
head and head-to-tail isomers in doubly PN-bridged
complexes is also established.6,8
The complex [Pt2Me3(µ-dppm)2]+, dppm ) Ph2PCH2-
PPh2, was one of the first organometallic compounds to
be formulated with a donor-acceptor metal-metal
bond, A, with both platinum atoms present as Pt(II),
rather than the alternate structure B, containing both
Pt(I) and Pt(III).2 Since that time, such donor-acceptor
Resu lts
Syn th esis of th e Bis(d im eth ylp la tin u m ) Com -
p lex cis,cis-[P t2Me4(µ-SMe2)(µ-P N)] Dimethylplati-
num(II) complexes with PN ligands were prepared
(6) (a) Newkome, G. R. Chem. Rev. 1993, 93, 2067. (b) Zhang, Z.-Z.;
Cheng, H. Coord. Chem. Rev. 1996, 147, 1. (c) Espinet, P.; Soulantica,
K. Coord. Chem. Rev. 1999, 193, 499.
bonds have been proposed in several other dppm-
bridged binuclear complexes,3 and even unbridged
donor-acceptor bonds have been established.4 There
has also been much interest in the use of other binucle-
ating ligands to extend the early dppm chemistry,5 and
P,N donors such as 2-diphenylphosphinopyridine, PN,
have proved to be especially useful in forming reactive
binuclear complexes.6-9 In particular, the ligand PN
(7) (a) Xie, Y.; Lee, C. L.; Yang, Y. P.; Rettig, S. J .; J ames, B. R.
Can. J . Chem. 1992, 70, 751. (b) Drent, E.; Arnoldy, P.; Budzelaar, P.
H. M. J . Organomet. Chem. 1993, 455I, 247. (c) Don, M. J .; Yang, K.
Y.; Bott, S. G.; Richmond, M. G. J . Coord. Chem. 1996, 40, 273. (d)
Dervisi, A.; Edwards, P. G.; Newman, P. D.; Tooze, R. P.; Coles, S. J .;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1998, 3771. (e) Chan,
W. H.; Zhang, Z. Z.; Mak, T. C. W.; Che, C.-M. J . Chem. Soc., Dalton
Trans.1998, 803. (f) Kiankarimi, M.; Lowe, R.; McCarthy, J . R.;
Whitten, J . P. Tetrahedron Lett. 1999, 40, 4497. (g) Ishii, H.; Goyal,
M.; Ueda, M.; Takeuchi, K.; Asai, M. J . Mol. Catal. A 1999, 148, 289.
(h) Dervisi, A.; Edwards, P. G.; Newman, P. D.; Tooze, R. P. J . Chem.
Soc., Dalton Trans. 2000, 523. (i) Ishii, H.; Goyal, M.; Ueda, M.;
Takeuchi, K.; Asai, M. Macromol. Rapid Commun. 2001, 22, 376. (j)
Catalano, V. J .; Bennett, B. L.; Muratidis, S.; Noll, B. C. J . Am. Chem.
Soc. 2001, 123, 173.
(1) On leave from Shiraz University, Iran.
(2) (a) Brown, M. P.; Cooper, S. J .; Frew, A. A.; Manojlovic-Muir,
Lj.; Muir, K. W.; Puddephatt, R. J .; Seddon, K. R.; Thomson, M. A.
Inorg. Chem. 1981, 20, 1500. (b) Bancroft, G. M.; Chan, T.; Puddephatt,
R. J . Inorg. Chim. Acta 1981, 53, L119.
(3) Sterenberg, B. T.; McDonald, R.; Cowie, M. Organometallics
1997, 16, 2297.
(8) Farr, J . P.; Wood, F. E.; Balch, A. L. Inorg. Chem. 1983, 22, 3387.
(b) Farr, J . P.; Olmstead, M. M.; Balch, A. L. J . Am. Chem. Soc. 1980,
102, 6654. (c) Maisonnat, A.; Farr, J . P.; Balch, A. L. Inorg. Chim. Acta
1981, 53, L217.
(9) (a) Arena, C. G.; Bruno, G.; De Munno, G.; Rotondo, E.; Drommi,
D.; Faraone, F. Inorg. Chem. 1993, 32, 1601. (b) Arena, C. G.; Ciani,
G.; Drommi, D.; Faraone, F.; Proserpio, D. M.; Rotondo, E. J . Orga-
nomet. Chem. 1994, 484, 71.
(4) J iang, F.; J enkins, H. A.; Biradha, K.; Davis, H. B.; Pomeroy, R.
K.; Zaworotko, M. J . Organometallics 2000, 19, 5049.
(5) (a) Puddephatt, R. J . Chem. Soc. Rev. 1983, 99. (b) Balch, A. L.
In Homogeneous Catalysis with Metal Phosphine Complexes; Pignolet,
L. H., Ed.; Plenum: New York, 1983. (c) Anderson, G. K. Adv.
Organomet. Chem. 1993, 35, 1.
10.1021/om030116e CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/31/2003

Binuclear Methylplatinum(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2613
Sch em e 1a
F igu r e 1. View of the structure of [Me2Pt(µ-SMe2)(µ-PN)-
PtMe2], 2, showing 25% probability ellipsoids.
a
PN ) 2-Ph2PC5H4N.
Ta ble 1. Selected NMR Da ta for th e Com p lexes
Ta ble 2. Bon d Len gth s [Å] a n d An gles [d eg] for
[P t2Me4(µ-SMe2)(µ-2-P h 2P C5H4N)], 2
complex δ(P) 1J (PtP) transa δ(Pt) 1J (PtPt) M-M bond
Pt(1)-C(12)
Pt(1)-P(1)
Pt(2)-C(22)
Pt(2)-N(2)
2.059(6)
2.302(1)
2.038(6)
2.125(4)
Pt(1)-C(11)
Pt(1)-S(31)
Pt(2)-C(21)
Pt(2)-S(31)
2.079(5)
2.345(1)
2.036(6)
2.319(1)
2
26.9
35.2
25.0
1855
1840
5040
C
C
O
-940
-300
-917
-160
-896
-48
-1397
-241
-1270
510
130
no
5
275
no
6
3200
b
yes
no
C(12)-Pt(1)-C(11)
C(11)-Pt(1)-S(31)
C(22)-Pt(2)-C(21)
C(21)-Pt(2)-S(31)
84.2(3)
92.7(2)
87.6(3)
93.1(2)
C(12)-Pt(1)-P(1)
P(1)-Pt(1)-S(31)
C(22)-Pt(2)-N(2)
C(22)-Pt(2)-S(31)
91.7(2)
91.57(5)
91.1(2)
88.2(1)
9
24.8
25.2
42.5
3160
3060
3200
P
P
P
10
11
3810
2720
yes
yes
Sch em e 2a
23.8
21.5
4260
1085
N
C
-747
-61
a
Atom trans to phosphorus; where there are two nonequivalent
P or Pt atoms in a complex, the atom labeled a in Chart 1 is given
b
first. Not resolved, so presumed to be less than 100 Hz.
according to Scheme 1. Thus reaction of [Pt2Me4(µ-
SMe2)2], 1,10 with 1 equiv of PN led to displacement of
SMe2 and formation of cis,cis-[Pt2Me4(µ-SMe2)(µ-PN)],
2. Reaction of 1 with 2 equiv of PN did not give the
expected complex cis,cis-[Pt2Me4(µ-PN)2], analogous to
[Pt2Me4(µ-dppm)2],11 but instead gave a mixture of 2 and
the known complex cis-[PtMe2(PN-κ1P)2], 3.12 Complex
3 could be prepared in pure form by reaction of 1 with
4 equiv of PN or by reaction of 2 with 3 equiv of PN.
Similarly complex 3 reacted with 1 to give 2, but did
not form cis,cis-[Pt2Me4(µ-PN)2], 4. The failure to form
4 is presumed to be associated with strain when two
PN ligands span a long metal‚‚‚metal distance.6,8
Complex 2 is unsymmetrical, and this is reflected in
the 1H NMR spectrum, which contains four methyl-
platinum resonances and two methylsulfur resonances,
and in the 195Pt NMR spectrum, which contains two
platinum resonances at δ(Pt) ) -940 [1J (PtP) ) 1860
Hz] and -300 [3J (PtP) ) 90 Hz] and with 2J (PtPt) )
130 Hz (Table 1). The structure of 2 was confirmed
crystallographically, with the structure illustrated in
a
PN ) 2Ph2PC5H4N, X ) CF3CO2.
Figure 1 and with selected bond parameters in Table
2. There are two square-planar platinum(II) centers
with PtC2SN and Pt2C2SP coordination, respectively,
with platinum atoms separated by 3.85 Å. The two
square planes are mutually twisted to accommodate the
one- and three-atom bridging groups SMe2 and PN,
respectively.
Rea ction s w ith Acid s. The reaction of complex 2
with trifluoroacetic acid occurred according to Scheme
2, yielding methane and complex 6. Complex 6 contains
a donor-acceptor PtPt bond, and the selectivity of its
formation suggests that cleavage of a methylplatinum
bond occurs at the PtMe2PS rather than the PtMe2NS
center, but this is not actually the case. Thus, reaction
of complex 2 with trifluoroacetic acid at -75 °C gave
the complex 5 (Scheme 2), which is formed by selective
cleavage of the PtMe bond trans to sulfur at the PtMe2-
(10) (a) Hill, G. S.; Irwin, M. J .; Rendina, L. M.; Puddephatt, R. J .
Inorg. Synth. 1998, 32, 149. (b) Scott, J . D.; Puddephatt, R. J .
Organometallics 1983, 16, 1947. (c) Song, D.; Wang, S. J . Organomet.
Chem. 2001, 648, 302.
(11) Manojlovic-Muir, Lj.; Muir, K. W.; Frew, A. A.; Ling, S. S. M.;
Thomson, M. A.; Puddephatt, R. J . Organometallics 1984, 3, 1637.
(12) J ain, V.; J akkal, V. S.; Bohra, R. J . Organomet. Chem. 1990,
389, 417.

2614 Organometallics, Vol. 22, No. 13, 2003
Rashidi et al.
Sch em e 3a
NS center. The conversion of complex 5 to 6 involves
formation of a PtPt donor-acceptor bond, rearrange-
ment of the dimethyl sulfide ligand from a bridging to
a terminal position, and one more step that is less well
defined. It could involve reorientation of the PN ligand,6-8
or it could involve methyl for trifluoroacetate exchange
between platinum centers;13 the cited references show
that either mechanism can occur easily. The conversion
of 5 to 6 was complete at -10 °C.
The 195Pt NMR spectrum of complex 6 contained two
1
resonances at δ(Pt) ) -896 [d, J (PtP) ) 5040 Hz] and
-48 [s, 3J (PtP) not resolved], and the presence of a PtPt
bond is indicated by the observation of a large coupling
1J (PtPt) ) 3200 Hz (Table 1). Complex 5, with phos-
phorus trans to methyl, has a much smaller coupling,
1J (PtP) ) 1840 Hz, compared to 6, in which phosphorus
is trans to oxygen. The absence of a PtPt bond in 5 is
indicated by the much smaller platinum-platinum
2
coupling J (PtPt) ) 275 Hz. The magnitude of J (PtPt)
is thus a good criterion of the presence or absence of a
PtPt bond in these closely related compounds (Table 1).
Complex 5 gives two methylsulfur resonances in either
1
the H or 13C NMR spectra for the bridging dimethyl
sulfide ligand, but complex 6 gives only one resonance
for the terminal dimethyl sulfide. The structure of 6 is,
at first glance, surprising since it appears that a
bridging dimethyl sulfide could be formed by displace-
ment of trifluoroacetate (Scheme 2). However formation
of a µ-SMe2 group would require twisting about the PtPt
axis that is rather rigidly oriented as a result of the five-
membered PtPtPCN ring formed by the PN ligand and
PtPt bond, and the resulting ring strain does not allow
closure. The stereochemistry of 5, in which the PtMeX
center has the methyl group trans to nitrogen rather
than sulfur, is indicated by the low value of the coupling
constant 3J (PtNCH) trans to methyl and also by the
a
PN ) 2-Ph2PC5H4.
Br ea k in g a n d Ma k in g Meta l-Meta l Don or -Ac-
cep tor Bon d s by Liga n d Ad d ition a n d Loss. Com-
plex 6 reacted easily with a second equivalent of the
ligand PN at -78 °C to give [Pt2Me3(µ-SMe2)(µ-PN)(PN-
κ1P)](CF3CO2), complex 9. This reaction involves dis-
placement of the weakly bound trifluoroacetate ligand
by the phosphorus donor of the PN ligand and cleavage
of the PtPt bond by re-forming the dimethyl sulfide
bridge. On warming to -10 °C, the free nitrogen center
in complex 9 displaces the bridging dimethyl sulfide
ligand to form [Pt2Me3(µ-PN)2](CF3CO2), complex 10,
and the PtPt donor-acceptor bond is formed again.
Complex 10 is a rare example of a compound with the
head-to-head arrangement of two bridging PN ligands.6-8
This complex could be isolated in pure form, but in
solution, it rearranged over a period of 10 days at room
temperature to form the head-to-tail isomer 11. This
represents a rare case in which both the head-to-head
and head-to-tail isomers of complexes containing the M2-
(µ-PN)2 unit can be isolated.6-8 The isomerization was
readily monitored by NMR spectroscopy, as illustrated
by the 31P NMR spectra in Figure 2.
2
higher value of J (PtPt) in 5 compared to 2.
In the reaction of complex 2 with CF3CO2D in a mixed
CD3OD/CD2Cl2 solvent mixture, the methane was formed
as CH3D with CH2D2 as minor product. The formation
of CH2D2 indicates that the mechanism of methylplati-
num bond protonolysis involves reversible formation of
a methane complex and also reversible protonation of
the platinum(II) center, as indicated in Scheme 3.
According to Scheme 3, the proposed CH3D complex
intermediate can either lose CH3D to give 5 or go back
to the deuteride/hydride 7a */7a **. Deprotonation of
7a ** gives 2*, and this can then react with more CF3-
CO2D to give CH2D2.14 It was not possible to observe
either proposed intermediate 7a or 8a in this reaction,
but the reaction of 2 with HCl did give a transient
intermediate identified by the 1H NMR spectrum at -75
°C as a hydride with δ(PtH) ) -17.8 [1J (PtH) ) 1506
Hz]. The coupling constant is consistent with a plati-
num(IV) hydride with the hydride trans to chloride, and
the absence of coupling to phosphorus shows that the
hydride is present at the pyridylplatinum center, con-
sistent with structure 7b.14
Complex 9 contains two nonequivalent PN ligands,
and the phosphorus atoms are bound trans to each other
at the same platinum atom, so that the two 31P
1
resonances appear with similar couplings J (PtP) (Table
1). This platinum atom with PtP2SC coordination thus
appears as an apparent triplet in the 195Pt NMR
(13) Puddephatt, R. J .; Thompson, P. J . J . Chem. Soc., Dalton Trans.
1977, 1219.
1
spectrum due to J (PtP) coupling, whereas the other
platinum atom with PtSNC2 coordination gives a singlet
resonance. The presence of a bridging dimethyl sulfide
ligand in 9 was shown by the presence of two methyl-
sulfur resonances in the 1H NMR spectrum, and the lack
(14) (a) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1995, 117, 9371. (b) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J .
Organometallics 1995, 14, 4966. (c) Stahl, S. S.; Labinger, J . A.;
Bercaw, J . E. Angew. Chem. Int. Ed. 1998, 37, 2181. (d) Puddephatt,
R. J . Coord. Chem. Rev. 2001, 219, 157.

Binuclear Methylplatinum(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2615
F igu r e 2. 31P NMR spectra for the head-to-head and head-
to-tail isomers of [Pt2Me3(µ-PN)2]+: (a) the head-to-head
isomer 10; (b) about midway through the isomerization;
(c) the head-to-tail isomer 11. The center peak and satel-
1
lites due to J (PtP) coupling are labeled in (a) and (c).
of PtPt coupling indicates the absence of a PtPt bond.
The head-to-head isomer of [Pt2Me3(µ-PN)2](CF3CO2),
10, gave two methylplatinum resonances in a 1:2 ratio,
and only a single 31P resonance (Figure 2). There were
two 195Pt resonances, with the PtCP2Pt center appearing
as a triplet as a result of 1J (PtP) coupling and the
PtC2N2Pt center appearing as a singlet. The magnitude
of 1J (PtPt) ) 3812 Hz is a clear indication of the
presence of a PtPt bond. In contrast, the less sym-
metrical head-to-tail isomer of [Pt2Me3(µ-PN)2](CF3CO2),
11, gave three methylplatinum resonances in a 1:1:1
ratio and two 31P resonances (Figure 3). There were two
195Pt resonances, and each appeared as a doublet of
F igu r e 3. Selected NMR spectra for complex 11: (a and
b) the 195Pt resonances, showing the doublet of doublet
pattern arising from 1J (PtP) and 2J (PtP) couplings, with
satellite spectra arising from 1J (PtPt) in the 195Pt2 isoto-
pomer; and (c) the 13C NMR spectrum in the methylplati-
num region, showing resonances of the three inequivalent
methylplatinum groups (see Chart 1 for the NMR labeling
scheme).
1
doublets as a result of J (PtP) and 2J (PtP) couplings
(Figure 3). The magnitude of 1J (PtPt) ) 2720 Hz is
again a clear indication of the presence of a PtPt bond.
The differences in the 31P NMR spectra between com-
plexes 10 and 11 are clearly illustrated in Figure 2.
The structure of the head-to-head isomer of [Pt2Me3-
(µ-PN)2](CF3CO2), 10, was determined crystallographi-
cally. The structure of the diplatinum cation is shown
in Figure 4, and selected bond distances and angles are
in Table 3. The atom Pt(1) has distorted square-planar
stereochemistry with trans-PtP2CPt coordination, while
Pt(2) is square-pyramidal with cis-PtN2C2Pt coordina-
tion. The Pt-Pt bond distance of 2.6491(4) Å is in the
normal range for a single bond. It is shorter than the
PtPt distance in the dppm analogue [Pt2Me3(µ-dppm)2]+,
which has PtPt ) 2.769(1) Å.2 A comparison can also
be made with the similar head-to-tail complex [MeCOPt-
(µ-Ph2PC5H4N)2PtClMe]+, which has Pt-Pt ) 2.728(3)
Å and J (PtPt) ) 2440 Hz.9 All of these complexes have
1
been formulated as containing a donor-acceptor PtPt
bond, but the PtPt distance for 10 is significantly shorter
than for the other two examples.
F igu r e 4. View of the structure of the head-to-head isomer
of the cationic complex [Pt2Me3(µ-PN)2]+, showing 25%
probability ellipsoids.
5 and to make a Pt-Pt bond in 6. There are other,
presumably favorable, changes in the rearrangement
from 5 to 6, but the result suggests that the Pt-Pt and
Pt-S bonds are comparable in energy. A similar argu-
ment can be based on the rearrangement of complex 9
to 10 (Scheme 4). The strong PtPt bond in complex 10
is confirmed by the structure determination that shows
the shortest PtPt donor-acceptor bond yet estab-
lished.2,9 Complex 10 also has the highest value of the
Discu ssion
This work has illustrated very distinctive properties
of binuclear methylplatinum complexes with PN ligands.
Most noteworthy is the demonstration that donor-
acceptor platinum-platinum bonds can play an impor-
tant role in the reaction chemistry. In the isomerization
of complex 5 to 6 (Scheme 2), the net effect is to break
a Pt-S bond to the bridging dimethyl sulfide ligand of

2616 Organometallics, Vol. 22, No. 13, 2003
Rashidi et al.
Ch a r t 1. NMR La belin g Sch em e
Ta ble 3. Selected Bon d Len gth s [Å] a n d An gles
a
[d eg] for Com p lex 10[CF 3CO2]‚2CH2Cl2
Pt(1)-C(8)
Pt(1)-P(1)
Pt(1)-Pt(2)
2.046(7)
2.259(1)
2.6491(4)
Pt(2)-C(7)
Pt(2)-N(2)
2.049(5)
2.163(4)
C(8)-Pt(1)-P(1)
92.24(5) C(7A)-Pt(2)-C(7)
87.1(3)
P(1)-Pt(1)-P(1A) 161.29(7) C(7A)-Pt(2)-N(2)
172.5(2)
88.0(2)
96.4(2)
85.7(1)
C(8)-Pt(1)-Pt(2)
P(1)-Pt(1)-Pt(2)
C(7)-Pt(2)-Pt(1)
N(2)-C(1)-P(1)
176.8(2)
88.27(3) N(2)-Pt(2)-N(2A)
C(7)-Pt(2)-N(2)
100.7(2)
116.5(4)
N(2)-Pt(2)-Pt(1)
a
Symmetry for equivalent atoms: A, x, -y+1/2, z.
Sch em e 4a
Exp er im en ta l Section
1H, 13C, and 31P NMR spectra were recorded as solutions in
CD2Cl2 by using Varian Mercury 400 or Inova 400 spectrom-
eters, while 195Pt NMR spectra were recorded using Varian
Inova 400 or 600 MHz spectrometers. The spectra are refer-
enced with respect to TMS (1H, 13C), H3PO4 (31P), or [PtCl2-
(SMe2)2] (195Pt). In the aryl region of the 1H and 13C NMR
spectra, many resonances overlapped and data are given only
for the ortho-pyridyl proton (H6) and carbon atoms (C2 and C6),
which were resolved in all cases. The atom labeling used in
describing the NMR data is defined in Chart 1. The complex
[Pt2Me4(µ-SMe2)2] was prepared by the literature method.10
cis,cis-[P t2Me4(µ-SMe2)(µ-P N)], 2. To a solution of [Pt2-
Me4(µ-SMe2)2] (1.72 g, 3.0 mmol) in C6H6 (100 mL) was added
2-Ph2PC5H4N (0.789 g, 3.0 mmol). After 5 min, the solvent was
removed and the product was washed with ether and dried
under vacuum. It was recrystallized from CH2Cl2/hexane.
a
PN ) 2-Ph2PC5H4N, X ) CF3CO2.
coupling constant 1J (PtPt) for any of the complexes
studied here. It is interesting to note that the rear-
rangement of the head-to-head complex 10 to its head-
to-tail isomer 11 (Scheme 4) occurs with a reduction of
1
the value of J (PtPt) from 3812 to 2721 Hz. Although
there is no general correlation of values of 1J (PtPt) and
PtPt bond distance,15 within these closely related com-
pounds it is likely that this significant change does
reflect a decrease in PtPt bond energy. The difference
is readily explained in terms of electronic effects. Thus
in 10 the donor center has PtMe2N2 coordination and
so will be more electron rich, and hence a better donor,
than the PtMe2NP center in 11.16 In addition, the
acceptor center in 10 has PtMeP2+ coordination and so
will be more electron poor, and so a stronger acceptor,
than the PtMeNP+ center in 11. Why then does the
rearrangement occur? We suggest that there is a reduc-
tion in steric effects in 11 along with minor electronic
stabilization of other bonds and that this combination
outweighs the effect of weakening the PtPt bond. The
slow rearrangement of 10 to 11 allows both isomers to
be obtained in pure form and to be fully characterized
by multinuclear NMR spectroscopy. This is unusual
despite the popularity of the PN ligand in coordination
chemistry and catalysis, as is the structure determina-
tion of the relatively scarce head-to-head bis(PN)-
bridged complex 10.6-8
Yield: 2.15 g (93%), mp135-138 °C. Anal. Calcd for C23H32
-
NPPt2S: C, 35.6; H, 4.1; N, 1.8. Found: C, 35.2; H, 4.2; N,
1.5. NMR in CD2Cl2: δ(1H) 0.36 [d, 3H, 2J (PtH) ) 84 Hz,
2
3
3J (PH) ) 9 Hz, Mea]; 0.66 [d, 3H, J (PtH) ) 71 Hz, J (PH) )
7 Hz, Meb]; -0.19 [s, 3H, J (PtH) ) 86 Hz, Mec]; 0.31 [s, 3H,
2
2J (PtH) ) 86 Hz, Med]; 2.23, 2.76 [s, each 3H, SMe2]; 9.05 [m,
1H, 3J (HH) ) 5 Hz, 3J (PtH) ) 25 Hz, H6]; δ(13C) -17.5 [s,
1J (PtC) ) 788 Hz, Med]; -1.2 [s, J (PtC) ) 833 Hz, Mec]; 0.0
1
[d, J (PtC) ) 738 Hz, J (PC) ) 5 Hz, Mea]; 9.5 [d, J (PtC) )
1
2
1
670 Hz, J (PC) ) 103 Hz, Meb]; 22.6, 31.6 [ s, MeS]; 158.9 [d,
2
3J (PC) ) 10 Hz, J (PtC) ) 25 Hz, C6]; 162.6 [d, J (PC) ) 48
2
1
Hz, C2]; δ(31P) 26.9 [s, J (PtP) ) 1860 Hz, J (PtP) ) 90 Hz];
1
3
δ(195Pt) -940 [d, J (PtP) ) 1860 Hz, J (PtPt) ) 130 Hz, Pta];
1
2
-300 [d, J (PtP) ) 90 Hz, J (PtPt) ) 130 Hz, Ptb].
3
2
cis-[P t Me2(P N-κ1P )2], 3. A solution of [Pt2Me4(µ-SMe2)2]
(300 mg, 0.52 mmol) and 2-Ph2PC5H4N (549 mg, 2.09 mmol)
in C6H6 (30 mL) was stirred for 1 h. The solvent was removed
under vacuum, and the product was washed with hexane
(2 × 4 mL) and dried under vacuum. Yield: 675 mg, 86%. The
NMR data were identical to the literature values.12
[P t2Me3(O2CCF 3)(µ-SMe2)(µ-P N)], 5. To a solution of CF3-
CO2H (6.2 µL, 0.08 mmol) in CD2Cl2 (0.2 mL) at -78 °C in an
NMR tube was added a solution of cis,cis-[Pt2Me4(µ-SMe2)(µ-
PN)] (62 mg, 0.08 mmol) in CD2Cl2 (0.2 mL). Reaction occurred
cleanly to give 5 and CH4 in equimolar amounts at -75 °C, as
(15) Pregosin, P. S. Coord. Chem. Rev. 1982, 44, 1601.
(16) There is considerable independent evidence that nitrogen is a
stronger net donor than phosphorus in platinum(II) complexes.14
Independent confirmation comes from the observation that complex 2
undergoes protonation at the PtMe2NS rather than the PtMe2PS
center.

Binuclear Methylplatinum(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2617
Ta ble 4. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for th e Com p lexes
confirmed by integration of the NMR spectrum, but 5 rear-
ranged to 6 above -30 °C, so it was characterized spectro-
scopically at low temperature. NMR in CD2Cl2 at -75 °C: δ(1H)
0.46 [d, 3H, 2J (PtH) obscured, 3J (PH) ) 9 Hz, Mea]; 0.55
[d, 3H, 2J (PtH) ) 71 Hz, 3J (PH) ) 7 Hz, Meb]; 0.33 [s, 3H,
2J (PtH) ) 82 Hz, Mec]; 2.22, 2.81 [s, each 3H, SMe2]; 9.23
[m, 1H, 3J (HH) ) 4 Hz, H6]; δ(31P) 35.2 [s, 1J (PtP) ) 1840
Hz, 3J (PtP) ) 120 Hz]; δ(195Pt) -917 [d, 1J (PtP) ) 1840 Hz,
2J (PtPt) ) 275 Hz, Pta]; -160 [d, 3J (PtP) ) 120 Hz,
2J (PtPt) ) 275 Hz, Ptb].
[P t2Me3(O2CCF 3)(SMe2)(µ-P N)], 6. To a solution of cis,-
cis-[Pt2Me4(µ-SMe2)(µ-PN)] (372 mg, 0.49 mmol) in CH2Cl2 (10
mL) was added a solution of CF3CO2H (37.2 µL, 0.49 mmol)
in CH2Cl2 (10 mL). The solvent was evaporated immediately
under vacuum, and the product was washed with hexane
(2 × 4 mL) and dried under vacuum. Yield: 370 mg (91%),
mp110-114 °C. Anal. Calcd for C24H29F3NO2PPt2S: C, 33.0;
H, 3.3; N, 1.6. Found: C, 32.6; H, 3.0; N, 1.5. NMR in CD2Cl2:
2
10‚CF3CO2.2CH2Cl2
formula
fw
C
23H32NPPt2S
C41H41Cl4F3N2O2P2Pt2
1244.68
200(2)
0.71073
orthorhombic
Pnma
31.6474(3)
14.9179(1)
9.4778(1)
90
4474.59(7)
4
775.71
200(2)
temperature/K
wavelength/Å
cryst syst
space group
a/Å
0.71073
monoclinic
P21/n
9.7900(1)
15.2304(3)
15.8954(3)
94.018(1)
2364.27(7)
4
b/Å
c/Å
â/deg
vol/Å3
Z
d(calc)/Mg m-3
abs coeff /mm-1
F(000)
2.179
11.986
1456
1.848
6.605
2392
no. of reflns
no. of ind reflns
abs corr
29 746
52 009
6934 [R(int) ) 0.059] 5980 [R(int) ) 0.066]
integration
0.981
2
3
3
δ(1H) 0.79 [d, 3H, J (PtH) ) 84 Hz, J (PtH) ) 6 Hz, J (PH) )
integration
1.029
2 Hz, Mea]; 0.86 [s, 3H, 2J (PtH) ) 80 Hz, Meb]; 0.54 [s, 3H,
Goof (F2)
2J (PtH) ) 80 Hz, Mec]; 2.26 [s, 6H, J (PtH) ) 18 Hz, SMe2];
3
R1, wR2 [I>2σ(I)] 0.0354, 0.0777
R1, wR2 (all data) 0.0568, 0.0849
0.0376, 0.0874
0.0677, 0.0970
8.90 [m, 1H, 3J (HH) ) 4 Hz, 3J (PtH) ) 20 Hz, H6]; δ(13C) -13.6
[s, 1J (PtC) ) 742 Hz, Meb]; -10.0 [d, 2J (PC) ) 4 Hz, Mea]; -1.5
[s, J (PtC) ) 723 Hz, Mec]; 20.2 [s, Me2S]; 152.3 [d, J (PC) )
12 Hz, C2]; 154.9 [d, 1J (PC) ) 80 Hz, C2]; δ(31P) 25.0 [s,
1J (PtP) ) 5040 Hz, 2J (PtP) ) 53 Hz]; δ(195Pt) -896 [d,
1J (PtP) ) 5040 Hz, 1J (PtPt) ) 3200 Hz, Pta]; -48 [d,
1
3
1
2
1
[d, J (PtC) ) 693 Hz, J (PC) ) 3 Hz, Meb]; -6.4 [t, J (PtC) )
713 Hz, 2J (PtC) ) 98 Hz, 2J (PC) ) 4 Hz, Mea]; 21.5 [d,
1J (PtC) ) 650 Hz, J (PC) ) 103 Hz, Mec]; 150.2 [d, J (PtC) )
2
2
36 Hz, 3J (PC) ) 13 Hz, C6 of pyPta]; 152.9 [d, 2J (PtC) ) 26
Hz, J (PC) ) 12 Hz, C6 of pyPtb]; 156.6 [d, J (PtC) ) 44 Hz,
1J (PC) ) 83 Hz, C2 of pyPta]; 159.8 [d, 2J (PtC) ) 39 Hz,
1J (PC) ) 70 Hz, C2 of pyPtb]; δ(31P) 23.8 [d, 1J (PtP) ) 4260
Hz, 2J (PtP) ) 60 Hz, 3J (PP) ) 2 Hz, Pa]; 21.5 [d, 1J (PtP) )
1085 Hz, 2J (PtP) ) 123 Hz, 3J (PP) ) 2 Hz, Pb]; δ(195Pt)
3
2
1
2J (PtP) ) 53 Hz, J (PtPt) ) 3200 Hz, Ptb].
[P t2Me3(µ-SMe2)(µ-P N)(P N-κ1P )](CF 3CO2), 9. To a solu-
tion of [Pt2Me3(O2CCF3)(SMe2)(µ-PN)], 6 (66 mg, 0.08 mmol),
in CD2Cl2 (0.4 mL) at -78 °C in an NMR tube was added a
solution of PN (20 mg, 0.08 mmol) in CD2Cl2 (0.3 mL). Reaction
occurred cleanly to give 9 at -70 °C, but 9 reacted further to
give 10 above -20 °C, so 9 was characterized spectroscopically
at low temperature. NMR in CD2Cl2 at -70 °C: δ(1H) -0.05
[d, 3H, 2J (PtH) ) 80 Hz, 3J (PH) ) 9 Hz, Mea]; 0.33 [s, 3H,
2J (PtH) ) 80 Hz, Meb]; 0.32 [s, 3H, 2J (PtH) obscured, Mec];
1.88, 2.06 [s, each 3H, SMe2]; 8.84 [m, 1H, free py H6]; 8.97
[m, 1H, 3J (PtH) ) 30 Hz, coord py H6]; δ(31P) 24.8 [d,
1J (PtP) ) 3160 Hz, 2J (PP) ) 400 Hz, Pa]; 25.2 [d, 1J (PtP) )
1
2
1
-747 [dd, J (PtP) ) 4260 Hz, J (PtPt) ) 123 Hz, J (PtPt) )
2720 Hz Pta]; -61 [dd, J (PtP) ) 1085 Hz, J (PtP) ) 60 Hz,
1
2
1J (PtPt) ) 2720 Hz, Ptb].
h t-[P t2Me3(µ-P N)2]Cl, 11a . To a solution of [Pt2Me4(µ-
SMe2)(µ-PN)], 2 (62 mg, 0.08 mmol), in CD2Cl2 (0.5 mL) at -78
°C in an NMR tube was added HCl (0.08 mmol, generated by
reaction of Me3SiCl with H2O). The NMR recorded immediately
at -78 °C showed the presence of a hydride resonance at
1
δ(1H) ) -17.8 [s, J (PtH) ) 1506 Hz, PtH], but this complex
2
1
3058 Hz, J (PP) ) 400 Hz, Pb]; δ(195Pt) -1397 [t, J (PtP) ca..
was short-lived even at -78 °C giving methane, identified by
its 1H NMR spectrum. On warming the solution, a complex
series of reactions occurred, finally giving ht-[Pt2Me3(µ-PN)2]-
3120 Hz, Pta]; -241 [s, Ptb].
h h -[P t2Me3(µ-P N)2](CF 3CO2), 10. To a solution of [Pt2-
Me3(O2CCF3)(SMe2)(µ-PN)], 6 (210 mg, 0.24 mmol), in CH2Cl2
(10 mL) was added a solution of PN (63 mg, 0.24 mmol) in
CH2Cl2 (10 mL). The mixture was stirred for 1 min, then the
solvent was evaporated under vacuum and the product was
washed with hexane (2 × 3 mL) and dried under vacuum.
Yield: 228 mg (88%), mp165-168 °C. Anal. Calcd for
1
Cl, 11a , as major product. The H, 31P, and 195Pt NMR spectra
were as reported above for the trifluoroacetate salt.
The same product was formed, along with [(PtMe3Cl)4] and
minor unidentified compounds,17,18 by the slow decomposition
(over 10 days at room temperature) of complex 2 in CHCl3.
Xr a y Str u ctu r e Deter m in a tion s. Crystals were mounted
on glass fibers. Data were collected at 200 K using a Nonius
Kappa-CCD diffractometer with COLLECT software (Nonius
B.V., 1998). The unit cell parameters were calculated and
refined from the full data set. Crystal cell refinement and data
reduction were carried out using DENZO (Nonius B.V., 1998).
The data were scaled using SCALEPACK (Nonius B.V., 1998).
The SHELXTL-NT V5.1 (Sheldrick, G. M.) suite of programs
was used to solve the structure by direct methods and to refine
by using difference Fouriers. All of the non-hydrogen atoms
were refined with anisotropic thermal parameters. The hy-
drogen atom positions were calculated geometrically and were
included as riding on their respective carbon atoms. Crystal
data are listed in Table 4.
C
39H37F3N2O2P2Pt2: C, 43.6; H, 3.4; N, 2.6. Found: C, 43.1;
H, 3.3; N, 2.5. NMR in CD2Cl2: δ(1H) 0.95 [t, 3H, J (PtH) )
75 Hz, 3J (PH) ) 6 Hz, Mea]; 0.41 [s, 6H, 2J (PtH) ) 73 Hz,
Meb]; 9.80 [m, 1H, 3J (HH) ) 5 Hz, 3J (PtH) ) 12 Hz, H6]; δ(31P)
42.5 [s, 1J (PtP) ) 3200 Hz, 2J (PtP) ) 89 Hz, Pa]; δ(195Pt)
-1270 [t, 1J (PtP) ) 3200 Hz, 1J (PtPt) ) 3812 Hz, Pta]; 510
2
[d, J (PtP) ) 96 Hz, J (PtPt) ) 3812 Hz, Ptb].
2
1
h t-[P t2Me3(µ-P N)2](CF 3CO2), 11. A solution of hh-[Pt2-
Me3(µ-PN)2](CF3CO2), 10 (228 mg), in CH2Cl2 (20 mL) was
allowed to stand for10 days at room temperature. The solvent
was evaporated, and the product was crystallized from CH2-
Cl2/hexane. Yield: 198 mg (89%), mp 155-160 °C. Anal. Calcd
for C39H37F3N2O2P2Pt2‚0.5CH2Cl2: C, 42.5; H, 3.4; N, 2.5.
Found: C, 42.7; H, 3.4; N, 2.4 (presence of dichloromethane
solvate confirmed by NMR). NMR in CD2Cl2: δ(1H) 0.99 [d,
For complex 2 all of the non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atom
3H, J (PtH) ) 79 Hz, J (PtH) ) 12 Hz J (PH) ) 3 Hz, Mea];
2
3
3
2
3
3
0.63 [d, 3H, J (PtH) ) 79 Hz, J (PtH) ) 8 Hz J (PH) ) 8 Hz,
(17) Kite, K.; Smith, J . A. S.; Wilkins, E. J . J . Chem. Soc. A 1966,
1744.
(18) Rashidi, M.; Fakhroeian, Z.; Puddephatt, R. J . J . Organomet.
Chem. 1991, 406, 261.
Meb]; 0.41 [d, 3H, J (PtH) ) 66 Hz, J (PtH) ) 8 Hz J (PH) )
8 Hz, Mec]; 9.04 [m, 1H, 3J (HH) ) 4 Hz, 3J (PtH) ) 37 Hz, H6];
9.06 [m, 1H, 3J (HH) ) 5 Hz, 3J (PtH) ) 17 Hz, H6]; δ(13C) -11.2
2
3
3

2618 Organometallics, Vol. 22, No. 13, 2003
Rashidi et al.
positions were calculated geometrically and were included as
riding on their respective carbon atoms.
Ack n ow led gm en t. We thank the NSERC (Canada)
for financial support and Shiraz University for granting
sabbatical leave to M.R.
For complex 10‚CF3CO2‚2CH2Cl2 the cation was located on
a mirror plane. The anion was also located on a mirror plane,
but the fluorine atoms were disordered. They were modeled
as a 60/40 mixture. The C-F bond lengths were constrained
to be equal (SADI). The two methylene chlorides of solvation
were located on mirror planes and so were modeled at half-
occupancy.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray data
for the complexes are available free of charge via the Internet
at http://pubs.acs.org.
OM030116E