Tin(II) halide insertion or halogen exchange in the reactions of dihaloplatinum(II) complexes with tin(II) halide

Article abstract of DOI:10.1002/hlca.201100045

Reactions of SnCl₂ with the complexes cis-[PtCl ₂(P₂)] (P₂=dppf (1,1′- bis(diphenylphosphino)ferrocene), dppp (1,3-bis(diphenylphosphino)propane=1, 1′-(propane-1,3-diyl)bis[1,1-diphenylphosphine]), dppb (1,4-bis(diphenylphosphino)butane=1,1′-(butane-1,4-diyl)bis[1, 1-diphenylphosphine]), and dpppe (1,5-bis(diphenylphosphino)pentane=1,1′- (pentane-1,5-diyl)bis[1,1-diphenylphosphine])) resulted in the insertion of SnCl₂ into the Pt-Cl bond to afford the cis-[PtCl(SnCl ₃)(P₂)] complexes. However, the reaction of the complexes cis-[PtCl₂(P₂)] (P₂=dppf, dppm (bis(diphenylphosphino)methane=1,1′-methylenebis[1,1-diphenylphosphine]), dppe (1,2-bis(diphenylphosphino)ethane=1,1′-(ethane-1,2-diyl)bis[1,1- diphenylphosphine]), dppp, dppb, and dpppe; P=Ph₃P and (MeO) ₃P) with SnX₂ (X=Br or I) resulted in the halogen exchange to yield the complexes [PtX₂(P₂)]. In contrast, treatment of cis-[PtBr₂(dppm)] with SnBr₂ resulted in the insertion of SnBr₂ into the Pt-Br bond to form cis-[Pt(SnBr₃) ₂(dppm)], and this product was in equilibrium with the starting complex cis-[PtBr₂(dppm)]. Moreover, the reaction of cis-[PtCl ₂(dppb)] with a mixture SnCl₂/SnI₂ in a 2 : 1 mol ratio resulted in the formation of cis-[PtI₂(dppb)] as a consequence of the selective halogen-exchange reaction. ³¹P-NMR Data for all complexes are reported, and a correlation between the chemical shifts and the coupling constants was established for mono- and bis(trichlorostannyl) platinum complexes. The effect of the alkane chain length of the ligand and Sn^II halide is described. Copyright

Full text of DOI:10.1002/hlca.201100045

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Helvetica Chimica Acta – Vol. 94 (2011)
Tin(II) Halide Insertion or Halogen Exchange in the Reactions of
Dihaloplatinum(II) Complexes with Tin(II) Halide
by Badri Z. Momeni*, Hoori Kazmi, and Atefeh Najafi
Department of Chemistry, K. N. Toosi University of Technology, P.O. Box 16315-1618, Tehran 15418, Iran
(phone: þ 98-21-22850266; fax þ 98-21-22853650, e-mail: momeni@kntu.ac.ir)
Reactions of SnCl2 with the complexes cis-[PtCl2(P2)] (P2 ¼ dppf (1,1’-bis(diphenylphosphino)fer-
rocene),
dppp
(1,3-bis(diphenylphosphino)propane ¼ 1,1’-(propane-1,3-diyl)bis[1,1-diphenylphos-
phine]), dppb (1,4-bis(diphenylphosphino)butane ¼ 1,1’-(butane-1,4-diyl)bis[1,1-diphenylphosphine]),
and dpppe (1,5-bis(diphenylphosphino)pentane ¼ 1,1’-(pentane-1,5-diyl)bis[1,1-diphenylphosphine]))
resulted in the insertion of SnCl2 into the PtꢀCl bond to afford the cis-[PtCl(SnCl3)(P2)] complexes.
However, the reaction of the complexes cis-[PtCl2(P2)] (P2 ¼ dppf, dppm (bis(diphenylphosphino)-
methane ¼ 1,1’-methylenebis[1,1-diphenylphosphine]), dppe (1,2-bis(diphenylphosphino)ethane ¼ 1,1’-
(ethane-1,2-diyl)bis[1,1-diphenylphosphine]), dppp, dppb, and dpppe; P ¼ Ph3P and (MeO)3P) with
SnX2 (X ¼ Br or I) resulted in the halogen exchange to yield the complexes [PtX2(P2)]. In contrast,
treatment of cis-[PtBr2(dppm)] with SnBr2 resulted in the insertion of SnBr2 into the PtꢀBr bond to form
cis-[Pt(SnBr3)2(dppm)], and this product was in equilibrium with the starting complex cis-
[PtBr2(dppm)]. Moreover, the reaction of cis-[PtCl2(dppb)] with a mixture SnCl2/SnI2 in a 2 :1 mol
ratio resulted in the formation of cis-[PtI2(dppb)] as a consequence of the selective halogen-exchange
reaction. 31P-NMR Data for all complexes are reported, and a correlation between the chemical shifts
and the coupling constants was established for mono- and bis(trichlorostannyl)platinum complexes. The
effect of the alkane chain length of the ligand and SnII halide is described.
Introduction. – The interaction between chloroplatinum(II) complexes and SnCl2 is
of particular interest in light of their applications in catalytic processes [1 – 4]. These
heterobimetallic complexes are widely applied as the useful homogeneous catalysts for
the hydroformylation and hydrogenation of unsaturated hydrocarbons [5 – 7]. The
facile insertion of SnCl2 into the PtꢀCl bond and the stability of the trichlorostannyl
complexes of Pt make them attractive as the catalyst precursor, however, the co-
catalyst role of SnCl2 is not yet fully understood [1][8]. SnCl2 can act as a Lewis acid, as
the counter ion of SnClꢀ3 , and as a ligand bonded to Pt [8]. It has been reported that the
reactions of PtII complexes with SnCl2 are strongly dependent on the nature of the
solvent. Three reaction types, i.e., simple insertion of SnCl2 into the PtꢀCl bond, ligand
migration, and/or ligand rearrangement with the displacement of ligand, have been
observed in different solvents [6]. For example, the reaction of complex
[PtCl(P)(P2)]þClꢀ (P ¼ monodentate phosphine ligand, P2 ¼ bidentate tertiary phos-
phine ligand) with SnCl2 proceeds to give [PtCl(P)(P2)]þ[SnCl3]ꢀ, and no
[Pt(SnCl3)(P)(P2)]þClꢀ was observed [9]. Insertion of SnCl2 was observed into the
PtꢀPt bond but not into the PtꢀCl bond of complex [Pt2X2(CO)2(PCy3)2] (X ¼ Cl or I;
PCy3 ¼ tricyclohexylphosphine) to give [Pt2(m-SnCl2)X2(CO)2(PCy3)2][10]. By anal-
ogy with SnCl2, the catalytic systems based on SnI2, SnBr2, or SnF2 have been limited
ꢀ 2011 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 94 (2011)
1619
[11 – 13]. Accordingly, few synthetic studies have been devoted to date to the case of
the binary mixtures of Pt/Sn containing mixed halide, and their chemistry have not been
investigated in detail. Insertion of SnF2 into the PtꢀCl bond has not yet been observed
but it was found that the I/Cl exchange takes place in the reaction of cis-[PtCl2(Ph3P)2]
with SnI2 [12][14]. Recently, we reported that the reaction of cis- and trans-
[PtMe2Cl(CH2Cl)(bpy)] (bpy ¼ 2,2’-bipyridine) with SnBr2 afforded the trihalostannyl
complexes cis- and trans-[PtMe2(SnBr2Cl)(CH2Cl)(bpy)] which dissociated in CH2Cl2
solution to give [PtBr2(bpy)] [15]. Also, the reaction of cis- and trans-[PtCl2(SMe2)2]
with SnBr2 resulted in the oxidation of PtII as well as halogen exchange to produce cis-
and trans-[PtBr4(SMe2)2][2].
The coupling constant 1J(Pt,P) is one of the best tools for the characterization of the
Pt complexes containing phosphine ligands, because it is a sensitive function of the type
of phosphine ligand and of the trans effect. Therefore, the reactions of a related series
of dihaloplatinum(II) complexes containing phosphine ligands with SnX2 (X ¼ Cl, Br,
or I) are investigated in this work. The effect of the alkane chain length of the 1,1’-
(alkane-a,w-diyl)bis[1,1-diphenylphosphine] ligands and the halogen effect will also be
discussed.
Results and Discussion. – The reaction of SnCl2 with the complexes cis-[PtCl2(P2)]
1 (P2 ¼ dppf), 2 (P2 ¼ dppp), 3 (P2 ¼ dppb), and 4 (P2 ¼ dpppe) (mol ratio 5 :1)
resulted in the insertion of SnCl2 into one of the PtꢀCl bonds to afford cis-
[PtCl(SnCl3)(P2)] 5 – 8, respectively (Scheme 1)1).
Scheme 1
1
)
Ligand abbreviations: dppf ¼ 1,1’-bis(diphenylphosphino)ferrocene; dppm ¼ 1,1’-methylenebis[1,1-
diphenylphosphine]; dppe ¼ 1,1’-(ethane-1,2-diyl)bis[1,1-diphenylphosphine]; dppp ¼ 1,1’-(propane-
1,3-diyl)bis[1,1-diphenylphosphine]; dppb ¼ 1,1’-(butane-1,4-diyl)bis[1,1-diphenylphosphine];
dpppe ¼ 1,1’-(pentane-1,5-diyl)bis[1,1-diphenylphosphine]; dppa ¼ N-(diphenylphosphino)-P,P-di-
phenylphosphinous amide.

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Helvetica Chimica Acta – Vol. 94 (2011)
The 31P-NMR spectrum of complex 5 (P2 ¼ dppf) in CH2Cl2/CDCl3 displayed two
1
signals at d 12.9 and 29.2 which were flanked by Pt satellites with J(Pt,P) ¼ 3786 Hz
1
1
and J(Pt,P) ¼ 3076 Hz, respectively (Table). It has been shown that the J(Pt,P)
coupling constant is greater for the P-atom trans to the Cl ligand than for the P-atom
trans to the SnCl3 ligand [2][16]. Therefore, the magnitude of the coupling constants,
1J(Pt,P) ¼ 3786 and 3076 Hz, indicates the presence of the Cl ligand trans to P and of
2
the trichlorostannato ligand trans to P, respectively. The J(Sn,P) coupling satellites
Table. 31P-NMR Data for the Complexes [PtX2(P2)]a), cis-[PtCl(SnCl3)(P2)], and cis-[Pt(SnCl3)2(P2)]
d(P)
13.8
13.5
10.3
12.9
29.2
1J(Pt,P)
Ref.
1
cis-[PtCl2(dppf)]b)
cis-[PtBr2(dppf)]b)
cis-[PtI2(dppf)]b)
3773
3711
3565
3786
3076
this work
this work
this work
this work
15
16
5
cis-[PtCl(SnCl3)(dppf)]b)
2
cis-[PtCl2(dppp)]b)
cis-[PtBr2(dppp)]b)
cis-[PtI2(dppp)]b)
ꢀ 5.5
ꢀ 6.3
ꢀ 8.9
ꢀ 6.2
2.2
3409
3370
3217
3262
2765
this work
this work
this work
this work
12
13
6
cis-[PtCl(SnCl3)(dppp)]b)
3
cis-[PtCl2(dppb)]b)
cis-[PtBr2(dppb)]b)
cis-[PtI2(dppb)]b)
10.8
10.4
6.9
7.9
22.1
3544
3493
3345
3479
2939
this work
this work
this work
this work
14
20
7
cis-[PtCl(SnCl3)(dppb)]b)
4
8
cis-[PtCl2(dpppe)]b)
cis-[PtCl(SnCl3)(dpppe)]b)
9.4
ꢀ 6.7
15.3
3643
3127
2154
this work
this work
9
17
18
cis-[PtCl2(dppm)]c)
cis-[PtBr2(dppm)]b)
cis-[PtI2(dppm)]b)
ꢀ 63.8
ꢀ 64.1
ꢀ 70.7
ꢀ 51.7
3071
3032
2880
2368
[2]
this work
this work
[2]
cis-[Pt(SnCl3)2(dppm)]d)
10
cis-[PtCl2(dppa)]e)
cis-[Pt(SnCl3)2(dppa)]b)
ꢀ 5.2
3130
2467
[2]
[2]
6.7
11
19
24
cis-[PtCl2(dppe)]f)
cis-[PtBr2(dppe)]b)
cis-[PtI2(dppe)]b)
43.8
45.7
46.4
53.4
3600
3559
3378
2596
[2]
this work
this work
[2]
cis-[Pt(SnCl3)2(dppe)]b)
21
22
c-23
t-23
cis-[PtBr2{(MeO)3P}2]b)
cis-[PtI2{(MeO)3P}2]b)
cis-[PtBr2(Ph3P)2]b)
75.4
77.1
14.7
19.8
5655
5461
3627
2562
this work
this work
this work
this work
trans-[PtBr2(Ph3P)2]b)
a
)
31P-NMR Data for the complexes [PtX2(P2)] are obtained from the reaction of [PtCl2(P2)] with KX
(X ¼ Br, I), as mentioned in Exper. Part except in the case of [PtI2(dppe)] which is obtained from the
reaction of [PtCl2(dppe)] with SnI2. b) CH2Cl2/CDCl3. c) C2H4Cl2/CDCl3. d) C2H4Cl2/THF/CDCl3.
f
e) Solid state. ) DMSO.

Helvetica Chimica Acta – Vol. 94 (2011)
1621
could not be observed, indicating the fast PtꢀSn bond breaking on the NMR time scale.
The complex cis-[PtCl(SnCl3)(dppf)] (5) decomposed in acetone or CH2Cl2/THF
solution to yield the single crystals of cis-[PtCl2(dppf)] (1) which is consistent with the
literature [17][18]. For the other bis-phosphine analogs 6 – 8, the observation of two P-
1
signals in the 31P-NMR spectra with two J(Pt,P) around 3130 – 3480 Hz and 2150 –
2940 Hz indicates that the insertion of SnCl2 into one of the PtꢀCl bond takes place
(Table). Other Pt/Sn mol ratios than 1:5 did not give rise to new compounds. We have
recently reported that the reaction of cis-[PtCl2(P2)] 9 (P2 ¼ dppm), 10 (P2 ¼ dppa ¼
bis(diphenylphosphino)amine ¼ N-(diphenylphosphino)-P,P-diphenylphosphinous
amide), and 11 (P2 ¼ dppe) with SnCl2 results in the insertion of SnCl2 into both PtꢀCl
bonds to afford cis-[Pt(SnCl3)2(P2)] [2]. It can be seen that the preferred ring sizes for
the formation of cis-[Pt(SnCl3)2(P2)] are 4- and 5-membered chelate rings, and cis-
[PtCl(SnCl3)(P2)] is preferred for 6-, 7-, and 8-membered chelate rings. Interestingly,
the insertion of SnCl2 into the PtꢀCl bond results in an increase of d(P) and in a
1
decrease of J(Pt,P) in the trans position to the trichlorostannyl group. It appears that
the magnitude of d(P) and 1J(Pt,P) can be used as a indicator for the PtꢀP bond in the
trichlorostannyl complexes of PtII.
The order of 1J(Pt,P) for mono(trichlorostannyl) complexes of the above bis-
phosphine ligands is Jdppf > Jdppb > Jdppp > Jdpppe (see 5 > 7 > 6 > 8) and that of bis(tri-
chlorostannyl) complexes is Jdppe > Jdppa > Jdppm (Table). Notably, the relationship
between the alkane chain length of the bis-phosphine ligand and the catalytic efficiency
in a number of the reactions of bis-phosphineplatinum(II) complexes has been
observed [13][19][20]. A direct comparison of the activity of binary mixtures Pt/Sn and
the nature of the resulting Pt species has not yet been reported due to the in situ
application of the dichloroplatinum(II) complexes and SnII chloride in the catalytic
systems. It has been shown that the pent-1-ene hydroformylation catalyzed by PtCl2/
1,1’-(alkane-a,w-diyl)bis[1,1-diphenylphosphine]/SnCl2 depends on the alkane chain
length (CH2)n: The effectiveness was maximum at n ¼ 4, and it was reduced when n ¼ 5
and 6; moreover, the ligands dppm and dppe were ineffective, and the effectiveness of
dppp was the same as that of Ph3P [13][19]. Surprisingly, we established now a neat
correlation between both 1J(Pt,P) of the complexes [PtCl(SnCl3)(P2)] and their
1
catalytic activity. Thus, cis-[PtCl(SnCl3)(dppb)] (7) with the highest J(Pt,P) among
the 1,1’-(alkane-a,w-diyl)bis[1,1-diphenylphosphine] complexes displayed the maxi-
mum activity. On the other hand, the catalytic activity of cis-[PtCl(SnCl3)(dppp)] (6)
was higher than that of cis-[PtCl(SnCl3)(dpppe)] (8), consistent with the magnitude of
the 1J(Pt,P) which decreases in the order Jdppb > Jdppp > Jdpppe. In the case of complexes
[Pt(SnCl3)2(P2)] (P2 ¼ dppm and dppe), no catalytic activity has been observed [13]
[20]. Moreover, the hydrogenation and regioselectivity of the hydroformylation of
styrene and 2-phenylpropene are dependent on the alkane chain length within the
chelate ring of the catalyst. The hydrogenation reaction is markedly decreased by the
more flexible chelate rings of dppp and dppb; however, dppp proved to be the most
suitable chelating bis-phosphine for the hydroformylation reaction [20]. It has been
reported that the steric effect of the ligand and the bite angle are not the only factors
affecting the activity [21]. Our results show that the formation of mono(trichloro-
stannyl) or bis(trichlorostannyl) complexes of Pt can affect the activity of the Pt/Sn
catalysts.

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Helvetica Chimica Acta – Vol. 94 (2011)
cis-[PtBr2(dppp)] (12) and cis-[PtI2(dppp)] (13) were synthesized from the
dichloro complex 2 by metathetical replacement of the chloro ligand with KBr or KI
in acetone to compare their 31P-NMR data with the resulting products from the
reaction of 2 with SnX2 (X ¼ Br, I). Reaction of cis-[PtCl2(dppb)] (3) with KBr also
afforded cis-[PtBr2(dppb)] (14). Alternatively, complex 14 was synthesized by the
reaction of K2[PtBr4] with dppb in a higher yield. All compounds were characterized by
elemental analysis and 31P-NMR spectroscopy (Table). The NMR data showed that the
replacement with KBr or KI yielded the complexes with a cis arrangement of the bis-
phosphine ligands. It has been reported that the values of coupling constants are
dependent on the solvent to some extent [22]. Therefore, we recorded the 31P-NMR
data of the dibromo and diiodo complexes cis-[PtBr2(dppf)] (15), cis-[PtI2(dppf)] (16),
cis-[PtBr2(dppm)] (17), cis-[PtI2(dppm)] (18), cis-[PtBr2(dppe)] (19), cis-[PtI2(dppb)]
(20), cis-[PtBr2{(MeO)3P}2] (21), cis-[PtI2{(MeO)3P}2] (22), and cis-[PtBr2(Ph3P)2] (c-
23) in CH2Cl2/CDCl3 (Table).
Interestingly, the reaction of cis-[PtCl2(P2)] (P2 ¼ dppf, dppm, dppe, dppp, dppb;
P ¼ Ph3P, (MeO)3P) with SnX2 (X ¼ Br, I) resulted in the halogen exchange to afford
[PtX2(P2)] 15 (P2 ¼ dppf, X ¼ Br), 16 (P2 ¼ dppf, X ¼ I), 17 (P2 ¼ dppm, X ¼ Br), 18
(P2 ¼ dppm, X ¼ I), 19 (P2 ¼ dppe, X ¼ Br), 24 (P2 ¼ dppe, X ¼ I), 12 (P2 ¼ dppp, X ¼
Br), 13 (P2 ¼ dppp, X ¼ I), 14 (P2 ¼ dppb, X ¼ Br), 20 (P2 ¼ dppb, X ¼ I), 21 (P ¼
(MeO)3P, X ¼ Br), 22 (P ¼ (MeO)3P, X ¼ I), and 23 (P ¼ Ph3P, X ¼ Br) in good to
high yields (Scheme 2). The 31P-NMR data of cis-[PtI2(dppe)] (24) are consistent with
those given in [23]. The reactions gave products with a cis configuration of the P nuclei
around the central atom, except for the reaction of cis-[PtCl2(Ph3P)2] with SnBr2 which
yielded cis- and trans-[PtBr2(Ph3P)2] (c- and t-23). The 31P-NMR data of t-23 are
consistent with those given in [24]. Rather interestingly, c-23 was the main product in
the reaction of cis-[PtCl2(Ph3P)2] with KBr. We have already reported that the reaction
of cis-[PtCl2(Ph3P)2] with SnCl2 yields
a
mixture of cis- and trans-
[PtCl(SnCl3)(Ph3P)2], but cis-[Pt(SnCl3)2{P(OMe)3}2] was the only product in the
reaction of cis-[PtCl2{P(OMe3)2}] with SnCl2 [2].
Scheme 2
The Br/Cl or I/Cl halogen exchange can be explained by an elusive SnX2 (X ¼ Br, I)
insertion which is followed by the dissociation of SnClX. Due to the simultaneous
presence of several tin compounds in the mixed-halide systems and low natural
abundance of 119Sn in NMR (I ¼ 1/2, 8.85%), satisfactory 119Sn-NMR spectra were not

Helvetica Chimica Acta – Vol. 94 (2011)
1623
obtained. PtII is a soft acid and has a tendency to bind to soft bases according to the
HSAB (hard and soft acids and bases) principle. The preference of the halides toward
PtII is I > Br> Cl > F [25]. Therefore, due to the greater tendency of PtII to bind the soft
iodide, the insertion of SnCl2 into the PtꢀI bond would be difficult. Conversely, the
reaction of dichloroplatinum(II) complexes with SnBr2 or SnI2 results in the formation
of corresponding dibromo or diiodoplatinum(II) complexes due to the softꢀsoft
1
interaction. There is a decrease of the chemical shift and of J(Pt,P) as halogen X
changes from Cl to Br to I in the complexes cis-[PtX2(P2)] (P2 ¼ dppf, dppm, dppp,
dppb) (Table). An increase of the chemical shift and a decrease of 1J(Pt,P) is observed
for the complexes cis-[PtX2(dppe)], as a consequence of ring strain by a five-
membered chelate ring [26] (Table); the decrease in the coupling constant from Cl to
Br to I is in accord with the increasing order of trans influence of I > Br> Cl [27].
On the basis of the 31P-NMR study, the treatment of cis-[PtBr2(dppm)] (17) with
SnBr2 in a mol ratio Pt/Sn 0.05 :0.27 resulted in the insertion of SnBr2 into the PtꢀBr
bond to form a red solution of the product cis-[Pt(SnBr3)2(dppm)] (25) which is in
equilibrium with the starting complex 17 as shown in Scheme 3. In the related 31P-NMR
spectrum (CH2Cl2/THF), apart from the signal for the starting complex 17 at d ꢀ 64.2
(1J(P,Pt) ¼ 3026 Hz) [28], another signal with Pt satellites was observed at d ꢀ 4.1 with
1J(P,Pt) ¼ 2427 Hz, that is due to the inserted product cis-[Pt(SnBr3)2(dppm)] (25).
Consistently, in the 119Sn-NMR spectrum of the mixture a broad signal at d ꢀ 657 was
observed which was assigned to 25. Notice that the free SnBr2 was observed at d ꢀ 61,
consistent with the literature [29].
Scheme 3
We also investigated the reaction of cis-[PtI2(P2)] with SnCl2. The insertion of SnCl2
into the PtꢀI bond of the complexes cis-[PtI2(P2)] (P2 ¼ dppf, dppm, dppe, dppp, and
dppb) could not be observed in different solvents and with different mol ratios of the
reactants. Moreover, the growth of single crystals from the reaction of cis-[PtI2(P2)]
(P2 ¼ dppm, dppe) with SnCl2 in CH2Cl2/THF indicated the presence of the starting
material cis-[PtI2(P2)], consistent with the literature [23][30]. When the reactions of
cis-[PtI2(P2)] (P2 ¼ dppf, dppm, dppe, dppp, dppb) with SnI2 were investigated, no
traces of the SnI2 insertion products like [PtI(SnI3)(P2)] or [Pt(SnI3)2(P2)] were
observed.
The comparative insertion of SnII halide and halogen exchange has also been tested.
Surprisingly, the selective formation of cis-[PtI2(dppb)] (20) was observed in the
reaction of cis-[PtCl2(dppb)] (3) with a 2 :1 mixture SnCl2/SnI2 (Scheme 4). No traces
of SnCl2 or SnI2 insertion products like cis-[PtCl(SnI2Cl)(dppb)] or cis-
[PtCl(SnCl3)(dppb)] (7) were observed. It has been reported that the Cl/I exchange
in phosphineplatinum compounds is influenced by the size of the chelating bis-
phosphine ligand [14]. It was found that the halogen exchange takes place in the Pt
complex with a five-membered chelate ring, but both the SnCl2 insertion and halogen
exchange have been observed in the reaction of [PtCl2(2,4-bis(diphenylphosphino)-

1624
Helvetica Chimica Acta – Vol. 94 (2011)
pentane] containing a six-membered chelate ring with 0.5 equiv. of SnCl2 and 0.5 equiv.
of SnI2 [14]. Our results show that exclusive Cl/I halogen exchange takes place in the Pt
complex with a seven-membered chelate ring (3 ! 20).
Scheme 4
In conclusion, the simple insertion reaction of SnCl2 into the PtꢀCl bond of bis-
phosphineplatinum(II) complexes takes place. However, in the case of dichloropla-
tinum(II) complexes containing labile ligands such as Me2S or Et2S, insertion of SnCl2
as well as ligand rearrangement takes place to form the anionic complex [Pt(SnCl3)5]3ꢀ
[2 – 4]. Moreover, the treatment of SnBr2 with dihaloplatinum(II) complexes contain-
ing phosphine ligands can be influenced by the formation of cis/trans geometrical
isomers. It has been reported that the effectiveness of SnII halides as the co-catalyst for
cis-[PtCl2(Ph3P)] is given by the order SnCl2 > SnBr2 > SnI2 [13]. This order
corresponds to their preference to form trihalostannyl complexes of Pt which has
been considered as the main reason for their catalytic effectiveness.
There are a number of published procedures for the preparation of complexes
[PtBr2(P2)] and [PtI2(P2)], but our reaction of [PtCl2(P2)] with SnBr2 or SnI2 is a simple
and selective synthesis which requires a shorter reaction time than the corresponding
reactions with KBr or KI.
We would like to thank the Iran National Science Foundation (INSF) for financial support (Grant
No. 85073/24). We also thank the Science Research Council of K. N. Toosi University of Technology for
financial support. Furthermore, we are grateful to Frank Rominger and Andrzej Wojtczak for the X-ray
crystal-structure analyses of cis-[PtI2(P2)] (P2 ¼ dppm, dppe) and cis-[PtCl2(dppf)]. The generous loan of
Pt metal salt by Johnson Matthey is gratefully appreciated.
Experimental Part
1. General. CH2Cl2 was distilled from P2O5 and Et2O from Na/benzophenone ketyl. Acetone and the
other reagents were used without further purification. The following reagents were used as supplied: dppf
(Aldrich), dppm (Merck), dppe (Merck), dppp (Merck), dppb (Acros), and dpppe (Alfa Aesar). 31P-
and 119Sn-NMR Spectra: Bruker-Avance-DRX 500 MHz spectrometer; at 202 (31P; rel. to 85% H3PO4)
and 186 MHz (119Sn; rel. to Me4Sn); d in ppm and J in Hz. Elemental analyses: Perkin-Elmer-2400-II
elemental analyzer.
2. Known Complexes. cis- and trans-[PtCl2(Me2S)2] and cis-[PtCl2(P2)] (P ¼ Ph3P and (MeO)3P;
P2 ¼ dppm (see 9), dppe (see 11), and dpppe (see 4)) were prepared as described in [2][4][31][32]. cis-
[PtCl2(dppf)] (1) [33], cis-[PtCl2(dppp)] (2) [32], and cis-[PtCl2(dppb)] (3) [32] were prepared in good
yield by the reaction of cis- and trans-[PtCl2(Me2S)2] with 1 equiv. of bis-phosphine in CH2Cl2.
Complexes cis-[PtBr2(dppf)] (15) [33], cis-[PtI2(dppf)] (16) [33], cis-[PtBr2(dppm)] (17) [28], cis-
[PtI2(dppm)] (18) [28], cis-[PtBr2(dppe)] (19) [34], cis-[PtI2(dppb)] (20) [14], cis-[PtBr2{(MeO)3P}2]
(21) [35], cis-[PtI2{(MeO)3P}2] (22) [35], and cis-[PtBr2(Ph3P)2] (c-23) [24] were prepared in good yield
by metathesis of cis-[PtCl2(P2)] with two equiv. of KX (X ¼ Br, I) in acetone. All compounds were
characterized by their 31P-NMR spectra in CH2Cl2/CDCl3 (Table).
3. Reaction of cis-[PtCl2(dppp)] (2) with KX (X ¼ Br, I): Formation of [PtX2(dppp)].
cis-Dibromo[1,1’-(propane-1,3-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtBr2(dppp)];
12). To a soln. of cis-[PtCl2(dppp)] (2; 68 mg, 0.10 mmol) in acetone (50 ml) was added KBr (24 mg,

Helvetica Chimica Acta – Vol. 94 (2011)
1625
0.20 mmol). The resulting soln. was stirred for 24 h. After filtration, the solvent was evaporated and the
resulting residue crystallized from CH2Cl2/hexane: 12 (76%). White solid. M.p. 2808 (dec). 31P-NMR
(CH2Cl2/CDCl3): ꢀ 6.3 (s, 1J(P,Pt) ¼ 3370). Anal. calc. for C27H26Br2P2Pt: C 42.24, H 3.42; found: C
41.55, H 3.01.
cis-Diiodo[1,1’-(propane-1,3-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtI2(dppp)]; 13).
As described for 12, with cis-[PtCl2(dppp)] (2; 84 mg, 0.12 mmol) and KI (100 mg, 0.60 mmol): 13
(89%). Yellow solid. M.p. 1198. 31P-NMR (CH2Cl2/CDCl3): ꢀ 8.9 (s, 1J(P,Pt) ¼ 3217). Anal. calc. for
C27H26I2P2Pt: C 37.63, H 3.04; found: C 37.13, H 2.98.
4. cis-Dibromo[1,1’-(butane-1,4-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtBr2(dppb)];
14). A soln. of dppb (72 mg, 0.17 mmol) in CH2Cl2 (2 ml) was added to a soln. of K2[PtBr4] (100 mg,
0.17 mmol) in H2O (10 ml). The mixture was then stirred at r.t. for 24 h. The org. phase was dried
(MgSO4) and concentrated and the white solid washed with Et2O: 14 (74%). M.p. 1788. 31P-NMR
(CH2Cl2/CDCl3): 10.4 (s, 1J(P,Pt) ¼ 3493). Anal. calc. for C28H28Br2P2Pt: C 43.02, H 3.61; found: C 42.88,
H 3.37.
Alternatively, complex 14 was prepared in the same manner as cis-[PtBr2(dppp)] (12) from cis-
[PtCl2(dppb)] (3) and KBr: Yield 63%.
5. cis-[1,1’-Bis(diphenylphosphino-kP)ferrocene]chloro(trichlorostannyl)platinum (cis-[PtCl-
(SnCl3)(dppf)]; 5). A soln. of SnCl2 (114 mg, 0.60 mmol) in THF (2 ml) was added to a stirred soln.
of cis-[PtCl2(dppf)] (1; 100 mg, 0.12 mmol) in CH2Cl2 (6 ml) under Ar (rapidly yellow ! orange soln.).
The solvent was evaporated and the yellow oily residue crystallized from CH2Cl2/hexane. The product
was purified by recrystallization from CH2Cl2: 5 (80%). M.p. 273 – 2758. 31P-NMR (CH2Cl2/CDCl3): 12.9
1
1
(d, J(P,Pt) ¼ 3786, 2J(P,P) ¼ 9.7, P trans to Cl); 29.2 (d, J(P,Pt) ¼ 3076, 2J(P,P) ¼ 9.6, P trans to SnCl3).
Anal. calc. for C34H28Cl4FeP2PtSn: C 40.41, H 2.79; found: C 39.65, H 2.16.
cis-Chloro[1,1’-(propane-1,3-diyl)bis[1,1-diphenylphosphine-kP]](trichlorostannyl)platinum (cis-
[PtCl(SnCl3)(dppp)]; 6). As described for 5, with cis-[PtCl2(dppp)] (2; 100 mg, 0.15 mmol) and SnCl2
(142 mg, 0.75 mmol). The soln. was refluxed for 4 h under Ar: 6 (70%). Orange solid. M.p. 218 – 2208.
31P-NMR (CH2Cl2/CDCl3): ꢀ 6.2 (d, 1J(P,Pt) ¼ 3262, 2J(P,P) ¼ 25, P trans to Cl); 2.2 (d, 1J(P,Pt) ¼ 2765,
2J(P,P) ¼ 24, P trans to SnCl3). Anal. calc. for C27H26Cl4P2PtSn: C 37.34, H 3.02; found: C 37.61, H 3.21.
cis-[1,1’-(Butane-1,4-diyl)bis[1,1-diphenylphosphine-kP]]chloro(trichlorostannyl)platinum (cis-
[PtCl(SnCl3)(dppb)]; 7). As described for 6, with cis-[PtCl2(dppb)] (3; 84 mg, 0.12 mmol) and SnCl2
(114 mg, 0.60 mmol): 7 (67%). Orange solid. M.p. 2378. 31P-NMR (CH2Cl2/CDCl3): 7.9 (s, 1J(P,Pt) ¼ 3479,
2J(P,P) not resolved, P trans to Cl); 22.1 (s, 1J(P,Pt) ¼ 2939, 2J(P,P) not resolved, P trans to SnCl3). Anal.
calc. for C28H28Cl4P2PtSn: C 38.10, H 3.20; found: C 37.72, H 2.92.
cis-Chloro[1,1’-(pentane-1,5-diyl)bis[1,1-diphenylphosphine-kP]](trichlorostannyl)platinum (cis-
[PtCl(SnCl3)(dpppe)]; 8). As described for 6, with cis-[PtCl2(dpppe)] (4; 71 mg, 0.10 mmol) and SnCl2
1
(95 mg, 0.50 mmol): 8 (74%). Orange solid. M.p. 2878. 31P-NMR (CH2Cl2/CDCl3): ꢀ 6.7 (s, J(P,Pt) ¼
2
1
2
3127, J(P,P) not resolved, P trans to Cl); 15.3 (d, J(P,Pt) ¼ 2154, J(P,P) ¼ 18, P trans to SnCl3). Anal.
calc. for C29H30Cl4P2PtSn: C 38.84, H 3.37; found: C 38.00, H 3.02.
6. Reaction of cis-[PtCl2(P2)] with SnX2: Formation of [PtX2(P2)] (X ¼ Br, I). cis-[1,1’-Bis(diphe-
nylphosphino-kP)ferrocene]dibromoplatinum (cis-[PtBr2(dppf)]; 15). To a soln. of cis-[PtCl2(dppf)] (1;
100 mg, 0.12 mmol) in CH2Cl2 (3 ml) was added a suspension of SnBr2 (167 mg, 0.60 mmol) in THF
(2 ml) (!dark yellow soln.). The mixture was stirred for 2 h until all the solid had dissolved. The mixture
was concentrated to ca. 1 ml and then filtered into an NMR tube. 31P-NMR (CH2Cl2/THF/CDCl3): 12.5
1
(s, J(P,Pt) ¼ 3730). 31P-NMR (CH2Cl2/CDCl3): 13.5 (s, 1J(P,Pt) ¼ 3711).
cis-[1,1’-Bis(diphenylphosphino-kP)ferrocene]diiodoplatinum (cis-[PtI2(dppf)]; 16). To a soln. of
cis-[PtCl2(dppf)] (1; 100 mg, 0.12 mmol) in CH2Cl2 (30 ml) was added a soln. of SnI2 (224 mg, 0.60 mmol)
in THF (3 ml) (! red soln.), and the mixture was stirred for 4 h. The solvent was evaporated and the
brown oily residue crystallized from CH2Cl2/hexane: 16 (85%). 31P-NMR (CH2Cl2/CDCl3): 10.3 (s,
1J(P,Pt) ¼ 3570).
cis-Dibromo[1,1’-methylenebis[1,1-diphenylphosphine-kP]]platinum (cis-[PtBr2(dppm)]; 17). To a
soln. of cis-[PtCl2(dppm)] (9; 100 mg, 0.15 mmol) in CH2Cl2 (5 ml) was added SnBr2 (209 mg,
0.75 mmol) in THF (3 ml). The soln. was stirred for 2 h and then concentrated. The creamy oily residue
1
was crystallized from Et2O: 17 (92%). 31P-NMR (CH2Cl2/CDCl3): ꢀ 64.1 (s, J(P,Pt) ¼ 3035).

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Helvetica Chimica Acta – Vol. 94 (2011)
The following complexes were prepared in the same manner as cis-[PtI2(dppf)] (16) from the
appropriate starting materials.
cis-[1,1’-Methylenebis[1,1-diphenylphosphine-kP]]diiodoplatinum (cis-[PtI2(dppm)]; 18): Yield
1
83%. 31P-NMR (CH2Cl2/CDCl3): ꢀ 70.7 (s, J(P,Pt) ¼ 2879).
cis-Dibromo[1,1’-(ethane-1,2-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtBr2(dppe)]; 19):
Yield 75%. 31P-NMR (CH2Cl2/CDCl3): 44.8 (s, 1J(P,Pt) ¼ 3560).
cis-[1,1’-(Ethane-1,2-diyl)bis[1,1-diphenylphosphine-kP]]diiodoplatinum (cis-[PtI2(dppe)]; 24):
Yield 74%. 31P-NMR (CH2Cl2/CDCl3): 46.4 (s, 1J(P,Pt) ¼ 3378).
cis-Dibromo[1,1’-(propane-1,3-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtBr2(dppp)];
12): Yield 60%. 31P-NMR (C2H4Cl2/CDCl3): ꢀ 6.3 (s, 1J(P,Pt) ¼ 3361).
cis-Diiodo[1,1’-(propane-1,3-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtI2(dppp)]; 13).
Yield 72%. 31P-NMR (CH2Cl2/CDCl3): ꢀ 9.0 (s, 1J(P,Pt) ¼ 3217).
cis-Dibromo[1,1’-(butane-1,4-diyl)bis[1,1-diphenylphosphine-kP]]platinum (cis-[PtBr2(dppb)]; 14):
Yield 63%. 31P-NMR (CH2Cl2/CDCl3): 10.4 (s, 1J(P,Pt) ¼ 3494).
cis-[1,1’-(Butane-1,4-diyl)bis[1,1-diphenylphosphine-kP]]diiodoplatinum (cis-[PtI2(dppb)]; 20):
Yield 70%. 31P-NMR (CH2Cl2/CDCl3): 7.4 (s, 1J(P,Pt) ¼ 3342).
cis-Dibromobis(trimethyl phosphite-kP)platinum (cis-[PtBr2{(MeO)3P}2]; 21): Yield 52%. 31P-NMR
(CH2Cl2/CDCl3): 74.6 (s, 1J(P,Pt) ¼ 5659).
cis-Diiodobis(trimethyl phosphite-kP)platinum (cis-[PtI2{(MeO)3P}2]; 22): Yield 63%. 31P-NMR
(CH2Cl2/CDCl3): 76.7 (s, 1J(P,Pt) ¼ 5468).
cis- and trans-Dibromobis(triphenylphosphine)platinum (cis- and trans-[PtBr2(Ph3P)2]; c- and t-23):
Yield 76%. 31P-NMR (CH2Cl2/CDCl3): 14.7 (s, 1J(P,Pt) ¼ 3627, c-23 (major); 19.8 (s, 1J(P,Pt) ¼ 2562, t-23
(minor).
7. Reaction of cis-[PtBr2(dppm)] (17) with SnBr2. To a soln. of cis-[PtBr2(dppm)] (17; 40 mg,
0.05 mmol) in CH2Cl2 (30 ml) was added a soln. of SnBr2 (75 mg, 0.27 mmol) in THF (3 ml) under Ar
(yellow ! dark red soln.). The soln. was stirred for 2 h and then concentrated to ca. 1 ml. This soln.
containing cis-[Pt(SnBr3)2(dppm)] (25) was transferred into an NMR tube and examined spectroscopi-
cally. 31P-NMR (CH2Cl2/THF/CDCl3): ꢀ 64.2 (s, 1J(P,Pt) ¼ 3026, 17); ꢀ 4.1 (s, 1J(P,Pt) ¼ 2427, 25). 119Sn-
NMR: ꢀ 61 (SnBr2); ꢀ 657 (25).
8. Reaction of cis-[PtCl2(dppb)] (3) with SnI2/SnCl2 1:2. As described for the reaction of 3 with
SnCl2 (see 7), with cis-[PtCl2(dppb)] (3; 62 mg, 0.09 mmol), SnCl2 (34 mg, 0.18 mmol), and SnI2 (34 mg,
0.09 mmol): cis-[PtI2(dppb)] (20) as yellow solid. 31P-NMR (CH2Cl2/CDCl3): 7.4 (s, 1J(P,Pt) ¼ 3345).
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Received January 31, 2011