Template synthesis of chiral vicinal diphosphinites as their PtII and PdII complexes

Article abstract of DOI:10.1002/ejic.200390121

The metal-templated synthesis of a few examples of vicinal diphenylphosphinites is accomplished when the corresponding vicinal diols react with the diphenylchlorophosphane complexes cis-[MCl₂(PPh₂Cl)₂] (M = Pt, Pd) in anhydrous THF. This process is proposed as a new synthetic route for Pt^II and Pd^II complexes of the new ligands 1,2-bis(diphenylphosphinito)butane, 2,3-bis(diphenylphosphinito)butane, and 2,3-bis(diphenylphosphinito)diisopropyl-L-tartrate, containing seven-membered chelate rings including stereogenic carbons. The new chiral phosphane-phosphinite (R)-3-(diphenylphosphanyl)-2-(diphenylphosphinito)propanol has also been obtained as a Pt^II six-membered chelate. The X-ray crystal structure of some of the described complexes and NMR evidence of the possibility of removing the ligands from the metal are reported. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200390121

FULL PAPER
Template Synthesis of Chiral Vicinal Diphosphinites as Their PtII and PdII
Complexes
Paola Bergamini,*[a] Valerio Bertolasi,[a] Michela Cattabriga,[a] Valeria Ferretti,[a]
Urania Loprieno,[a] Nicoletta Mantovani,[a] and Lorenza Marvelli[a]
Keywords: Template synthesis / Ligand design / P ligands / Platinum / Palladium
The metal-templated synthesis of a few examples of vicinal
diphenylphosphinites is accomplished when the correspond- phenylphosphanyl)-2-(diphenylphosphinito)propanol
ing vicinal diols react with the diphenylchlorophosphane
complexes cis-[MCl2(PPh2Cl)2] (M = Pt, Pd) in anhydrous
THF. This process is proposed as a new synthetic route for
PtII and PdII complexes of the new ligands 1,2-bis(diphenyl-
carbons. The new chiral phosphane-phosphinite (R)-3-(di-
has
also been obtained as a PtII six-membered chelate. The X-
ray crystal structure of some of the described complexes and
NMR evidence of the possibility of removing the ligands from
the metal are reported.
phosphinito)butane,
2,3-bis(diphenylphosphinito)butane,
and 2,3-bis(diphenylphosphinito)diisopropyl- -tartrate, con- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
L
taining seven-membered chelate rings including stereogenic
Germany, 2003)
Introduction
In fact our attempts to prepare 1,2- and 2,3-bis(diphenyl-
phosphinite)butane by the classical route (Scheme 1) Ϫ re-
Chiral diphosphinites are a well-documented alternative action of the corresponding diols with PPh2Cl Ϫ gave 1 and
to chiral diphosphanes as ligands for metal ions to give 2 as impure products in low yield.
metal complexes that can be exploited in various processes
with the double function of catalysts and asymmetry in-
ductors.[1] Particular attention has been given to vicinal di-
phosphinites whose coordination gives a seven-membered
chelate ring similar in size to the successful DIOP-Rh sys-
tem.[2]
Several examples of chiral diphosphinites obtained by the
functionalization of diols belonging to the natural chiral
pool have been reported.[3] In particular Rajan-Babu et al.
have described asymmetric diphosphinites obtained by the
Scheme 1
functionalization of sugars and have shown that it is pos-
sible to drive some enantioselective hydrogenations to one
product or to the other depending on the hydroxy groups
selected for the transformation into phosphinites.[4]
Despite the interest of diphosphinites for catalysis, the
synthesis of those deriving from low-weight vicinal diols
has not been described, with the sole exception of bis(di-
phenylphosphinite)ethane,[5] observed in 1999 in solution
but not isolated.
Nevertheless, when we succeeded in obtaining a few
square-planar PtII and PdII complexes from crude 1 and 2,
we noticed that the stability of such molecules is greatly
enhanced by the coordination. We therefore reasoned that
it should be possible to design a general alternative syn-
thetic route for diphenylphosphinites where they could be
built inside the coordination sphere of metal ions (metal
template synthesis).
The apparent lack of attention paid to the simplest vi-
cinal diphosphinites could be due to the known moisture
and oxygen sensitivity[6] reported for some members of this
group of ligands, which makes their use in catalysis not very
convenient and their synthesis quite puzzling.
In this paper we compare two synthetic pathways to plat-
inum and palladium dichloride complexes of 1 and 2: in the
first one 1 and 2 are prepared in solution as free ligands
and then coordinated to the metal by substitution of COD
in [MCl2(1,5-COD)] (M ϭ Pt, Pd); in the second, the reac-
tion of the diphenylchlorophosphane complexes cis-
[MCl2(PPh2Cl)2] (3a, M ϭ Pt; 3b, M ϭ Pd) with 1,2- or
2,3-butanediol leads to the same complexes in a shorter
time and with higher yield and purity.
[a]
`
Dipartimento di Chimica dell’Universita di Ferrara,
via L. Borsari 46, 44100 Ferrara. Italy
Fax: (internat.) ϩ39Ϫ0532/240-709
E-mail: bgp@unife.it
918
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0305Ϫ0918 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2003, 918Ϫ925

Template Synthesis of Chiral Vicinal Diphosphinites
FULL PAPER
This ‘‘metal-template’’ synthesis can be extended to more
While 1 and 2 undergo rapid decomposition in solution
functionalised ligands, and we also report NMR evidence in the presence of traces of oxygen and/or water, solutions
of the possibility of removing these ligands from the metal of 1a, 1b, 2a, or 2b in pure chloroform or in CHCl3/acetone
exploiting the sequestrating action of CNϪ on Pt and Pd.
do not show any sign of decomposition (by 31P NMR spec-
troscopy) even in the presence of oxygen and/or water after
five days: these observations indicate that coordination to
PtII or PdII dramatically reduces the susceptibility of phos-
phinites to oxidation and hydrolysis.
Results and Discussion
Generation of the Diphosphinites 1 and 2 in Solution and
Their Coordination to Pt and Pd
Template Synthesis of 1 and 2
The diphosphinites 1 and 2 can be obtained from the
reaction of 1,2- and 2,3-butanediol[7] respectively with two
equivalents of PPh2Cl in THF or pyridine (see Exp. Sect.).
The reactions were followed by 31P NMR spectroscopy and
it was observed that, in both cases, PPh2Cl (δ ϭ 82.5 ppm)
is completely consumed in about 60 min to give the re-
quired product (two singlets at δ ϭ 115.7 and 111.5 ppm
for 1 and one singlet at δ ϭ 112.2 ppm for 2) together with
a few phosphorus-containing side products.
The major drawback of this direct preparation of 1 and 2
is that impure products were obtained even under carefully
controlled conditions. The 31P NMR spectrum of the reac-
tion mixture showed the presence of side products gener-
ated both by phosphorus oxidation and by PPh2Cl decom-
position due probably to traces of water contained in the
reacting liquid diols.
All attempts to improve the purity of 1 and 2 obtained by
this route using chromatographic techniques led to further
decomposition. The instability of free phosphinites has
been observed before.[6] Nevertheless, the addition of
[MCl2(1,5-COD)] (M ϭ Pt, Pd) to a THF solution con-
taining crude 1 or 2 leads to the precipitation of their plat-
inum (1a and 2a) and palladium (1b and 2b) dichloride
complexes in pure form (Scheme 2).
In an attempt to design a more convenient route to di-
phosphinites we considered that, because the major reason
for the interest in these compounds is the use of their com-
plexes with metal ions in catalysis, it should be advantage-
ous to produce them inside the coordination sphere of
metal ions of catalytic value, thus obtaining the metal com-
plexes directly. PtII and PdII complexes appeared to be con-
venient models for this synthetic approach. The metal-tem-
plated synthesis we carried out is described in Scheme 3.
Treatment of [MCl2(1,5-COD)] (M ϭ Pt, Pd) with two
equivalents of PPh2Cl in carefully dried THF gives cis-
[MCl2(PPh2Cl)2] 3a (M ϭ Pt) and 3b (M ϭ Pd), which have
been described before.[9]
We found that the coordinated chlorophosphane in 3a
and 3b is still able to react with hydroxy groups. In fact, the
reaction of 3a or 3b with 1,2- or 2,3-butanediol gave 1a, 1b,
2a, and 2b which precipitated as pure products in high
yields, with elimination of HCl in solution.
Complexes 1a and 2b gave crystals suitable for an X-ray
crystal-structure determination.
X-ray Crystal Structures of 1a and 2b
ORTEP[10] views of the structure of 1a and 2b are shown
in Figures 1 and 2, respectively. Selected bond lengths and
angles are reported in Table 1. Both complexes present a
slightly distorted square-planar geometry, with the metal
centre bonded to two chlorides and to two phosphorus
atoms belonging to the diphosphinite ligand. The coordina-
tion of 1 or 2 to the metal leads to the formation of a seven-
membered ring with a boat conformation. The nature of
the metallic centre does not significantly affect the bond
angles and lengths in the coordination sphere.
A few examples of X-ray crystal structures of diphosphi-
nito complexes have been reported before. For example,
both fac-[ReBr(CO)3(LϪL)] and fac-[ReH(CO)3(LϪL)]
Scheme 2
[LϪL
ϭ
1,2-bis(diphenylphosphinito)ethane] contain
seven-membered ReP2O2C2 rings with a twisted chair con-
The 31P NMR spectrum of 1a shows two doublets with
satellites at δ ϭ 90.2 and 89.3 ppm indicating that each
phosphorus is coupled to platinum (1JP,Pt ϭ 4045 and
3994 Hz, typical values for phosphorus trans to chloride[8])
and to the other phosphorus (2JP,P ϭ 12 Hz). The corres-
formation.[5]
Removal of 1 from Its Pt and Pd Complexes
The sequestrating action of cyanide for platinum() is
ponding palladium complex 1b also shows a doublet of well-known.[11] When 1a was dissolved in CDCl3 and
doublets at δ ϭ 119.1 and 118.4 ppm (2JP,P ϭ 35.7 Hz).
treated with 4.5 equiv. of soluble (Bu4N)CN, the 31P NMR
Both 2a and 2b show a singlet (with satellites for 2a, spectrum showed that, in the first step, both the platinum-
1JP,Pt ϭ 4021 Hz) in the 31P NMR spectrum due to the coordinated chlorides are replaced by cyanide within 5Ϫ10
equivalence of the two phosphorus atoms in these com- minutes. Further observations show that the diphosphinite
plexes.
1 is progressively replaced by cyanide and after 30Ϫ40 mi-
Eur. J. Inorg. Chem. 2003, 918Ϫ925
919

P. Bergamini et al.
FULL PAPER
Scheme 3
˚
Table 1. Selected bond lengths [A] and angles [°] for compounds
1a and 2b
1a
2b
PtϪCl1
PtϪCl2
PtϪP1
PtϪP2
P1ϪO1
P2ϪO2
O1ϪC1
O2ϪC2
2.354(1)
2.354(1)
2.221(1)
2.224(1)
1.604(3)
1.601(2)
1.463(5)
1.446(4)
1.503(6)
88.33(3)
86.64(3)
176.09(3)
172.94(4)
91.47(3)
93.22(3)
PdϪCl1
PdϪCl2
PdϪP1
PdϪP2
P1ϪO1
P2ϪO2
O1ϪC1
O2ϪC2
2.352(1)
2.334(1)
2.235(1)
2.237(1)
1.608(2)
1.611(2)
1.451(3)
1.442(3)
1.520(3)
92.23(2)
85.74(2)
173.74(2)
175.27(3)
88.64(2)
92.92(2)
C1ϪC2
C1ϪC2
Cl1ϪPtϪCl2
Cl1ϪPtϪP1
Cl1ϪPtϪP2
Cl2ϪPtϪP1
Cl2ϪPtϪP2
P1ϪPtϪP2
Cl1ϪPdϪCl2
Cl1ϪPdϪP1
Cl1ϪPdϪP2
Cl2ϪPdϪP1
Cl2ϪPdϪP2
P1ϪPdϪP2
Figure 1. ORTEP[10] view of complex 1a showing the thermal el-
lipsoids at the 40% probability level
nutes the free ligand 1 is the only phosphorus-containing
product.
The addition of a small quantity of [PdCl2(1,5-COD)] to
this solution gives the immediate formation of 1b
(Scheme 4), indicating that the shift of 1 from platinum to
palladium can be obtained by the addition of cyanide. An
analogous experiment showed that the reverse process of
ligand transfer from palladium (1b) to platinum is also eas-
ily achievable.
Template Synthesis of the New Diphosphinite 4 on
Platinum
In an attempt to extend the applicability of our template
synthesis of phosphinites to more functionalised ligands, we
tried the addition of (ϩ)-diisopropyl -tartrate to the inter-
mediate [Pt(PPh2Cl)2Cl2] (3a) preformed in situ in THF.
After 18 hours the formation of the optically active com-
plex 4a* was complete (Scheme 5).
Figure 2. ORTEP[10] view of complex 2b showing the thermal el-
lipsoids at the 40% probability level
Scheme 4
920
Eur. J. Inorg. Chem. 2003, 918Ϫ925

Template Synthesis of Chiral Vicinal Diphosphinites
FULL PAPER
(5), whose direct synthesis would not be possible without
protection of the C(3)-hydroxy group. Not many examples
of phosphane-phosphinites have been reported,[13] and 5 is
a rare example of this class of ligand with C-chirality.
It should also be noted that the reaction of 3a with both
the OH groups of (R)-I would give a potentially tridentate
phosphane-diphosphinite ligand acting in only a bidentate
manner; no evidence of this process was observed.
Scheme 5
The deplatinization of 5a* with CNϪ in solution (CDCl3)
allowed the observation of a 31P NMR spectrum consistent
with that expected for the free ligand 5 Ϫ a doublet at δ ϭ
111 ppm, typical for a ROPPh2 group, and a second doub-
let in the phosphinic range (δ ϭ Ϫ23 ppm), each coupled
This complex was isolated and fully characterised (see
Exp. Sect.). The 31P NMR spectrum shows a singlet for the
two equivalent phosphorus atoms at δ ϭ 94.7 ppm, in the
typical downfield range of diphenylphosphinites, with satel-
lites due to the Pt coupling (1JP,Pt ϭ 4003 Hz).
The optical rotation of 4a* was measured in CHCl3
([α]2D5 ϭ Ϫ10.6 (c ϭ 0.5, CHCl3). This result confirms the
expectation that optically active complexes are obtained
when a diol bearing a stereogenic carbon is used in an op-
tically active form, due to the fact that the diol reaction
with 3a or 3b does not involve the chiral carbon.
4
to the other with a JP,P coupling constant of 7 Hz.
X-ray Crystal Structure of 5a*
The recrystallisation of 5a* from CH2Cl2 and diethyl
ether gave crystals whose X-ray structure is shown in Fig-
ure 3. Selected bond lengths and angles are given in Table 2.
Template Synthesis of the New Phosphane-phosphinite-ol 5
on Platinum
The optically active phosphane-diol (R)-I (Scheme 6) can
be obtained in two steps from the commercial precursor
(R)-2,2-dimethyl-1,3-dioxolane-4-methanol
p-toluenesul-
fonate through a known procedure.[12]
Figure 3. ORTEP[10] view of complex 5a* linked by hydrogen bonds
to a solvent molecule of diethyl ether showing the thermal ellips-
oids at the 40% probability level.
Scheme 6
˚
Table 2. Selected bond lengths [A] and angles [°] for compound 5a*
When (R)-I is added to a solution of [Pt(PPh2Cl)2Cl2]
(3a) its phosphinic group replaces the less nucleophilic
PPh2Cl and the C(2)hydroxy group reacts with the re-
maining coordinated PPh2Cl (Scheme 6). The driving force
of this process is probably the formation of a thermodyn-
amically stable six-membered chelate ring. Complex 5a* is
recovered as the only platinum-containing species.
5a*
Pt1ϪCl1
Pt1ϪCl2
Pt1ϪP1
Pt1ϪP2
P1ϪO1
2.352(4)
2.364(5)
2.209(5)
2.239(5)
1.60(1)
1.81(2)
1.44(2)
1.49(2)
1.52(2)
1.38(2)
Cl1ϪPt1ϪCl2
Cl1ϪPt1ϪP1
Cl1ϪPt1ϪP2
Cl2ϪPt1ϪP1
Cl2ϪPt1ϪP2
P1ϪPt1ϪP2
89.3(1)
87.4(2)
177.1(2)
176.6(2)
88.0(2)
95.2(1)
The identity of 5a*, determined by elemental and spec- P2ϪC2
C1ϪO1
troscopic analysis, was confirmed by X-ray crystal structure
C1ϪC2
(see below) and its optical rotation was measured (see Exp.
C1ϪC3
Sect.). The 31P NMR spectrum of 5a* shows two doublets
C3ϪO2
with satellites, one at δ ϭ 84.7 ppm, typical of a coordinate
phosphinite, while the coordinated phosphinic P resonates Hydrogen bond
at δ ϭ Ϫ0.4 ppm: each phosphorus is coupled to platinum
(1JP,Pt ϭ 3858 and 3482 Hz, respectively) and to the other
O2ϪH2
0.82
2.10
2.78(2)
140
O3···H2
O2···O3
phosphorus (2JP,P ϭ 17.7 Hz).
It is noteworthy that 5a* contains the new ligand (R)-3-
O2ϪH2···O3
(diphenylphosphanyl)-2-(diphenylphosphinito)propanol
Eur. J. Inorg. Chem. 2003, 918Ϫ925
921

P. Bergamini et al.
FULL PAPER
The complex displays a slightly distorted square-planar
geometry. The Pt1ϪP1ϪP2ϪC1ϪC2ϪO1 six-membered
ring assumes a half-chair conformation with the C1 atom in
the R configuration, as determined by the Flack parameter
[Ϫ0.02(4)] calculated after the least-square refinement. The
molecular packing forms channels which include molecules
of diethyl ether linked by means of an O2ϪH···O3 hydrogen
˚
bond [O2···O3 ϭ 2.78(2) A] to the hydroxyl group of the
complex.
Hydrolysis of 3a and 3b
The above-described synthesis of diphenylphosphinites
on Pt or Pd must be carried out in water-free conditions as
we observed that, in the presence of even small quantities
of water, competitive hydrolysis of the intermediate com-
plexes 3a and 3b prevents the formation of the diphosphin-
ite complexes.
We found that the addition of water to a THF solution
Figure 4. ORTEP[10] view of complex 7 showing the thermal ellips-
of 3a (Scheme 7) produces a mixture of complex [PtCl2-
oids at the 40% probability level
1
(PPh2OH)2] (6; δ ϭ 71.1 ppm, JP,Pt ϭ 4065 Hz) and of an-
other species, 7, whose 31P NMR spectrum shows a singlet
with satellites at δ ϭ 50.5 ppm (1JP,Pt ϭ 4090 Hz).
˚
Table 3. Selected bond lengths [A] and angles [°] for compound 7
7
Pt1ϪCl1
Pt1ϪCl2
Pt1ϪP3
Pt1ϪP4
Pt2ϪCl1
Pt2ϪCl2
Pt2ϪP1
Pt2ϪP2
P1ϪO2
P2ϪO1
P3ϪO3
P4ϪO4
2.430(1)
2.420(1)
2.237(1)
2.229(1)
2.413(1)
2.415(1)
2.227(1)
2.227(1)
1.550(4)
1.544(4)
1.544(4)
1.540(4)
Cl1ϪPt1ϪCl2
Cl1ϪPt1ϪP3
Cl1ϪPt1ϪP4
Cl2ϪPt1ϪP3
Cl2ϪPt1ϪP4
P3ϪPt1ϪP4
Cl1ϪPt2ϪCl2
Cl1ϪPt2ϪP1
Cl1ϪPt2ϪP2
Cl2ϪPt2ϪP1
Cl2ϪPt2ϪP2
P1ϪPt2ϪP2
Pt1ϪCl1ϪPt2
Pt1ϪCl2ϪPt2
81.76(4)
91.17(4)
172.25(5)
172.27(4)
93.89(4)
93.49(5)
82.21(4)
172.84(4)
93.71(4)
91.54(5)
175.28(5)
92.67(5)
97.63(4)
97.84(4)
Scheme 7
Recrystallisation of the mixture from THF and diethyl
ether gave crystals of 7, which has been identified before[9]
on the basis of its NMR spectroscopic data. The X-ray
Hydrogen bonds
crystal structure (Figure 4) showed that 7 is the dimeric O1ϪH
0.99(6)
1.44(6)
2.415(6)
165(5)
O4ϪH
O3···H
O3···O4
O4ϪH···O3
1.10(6)
1.39(6)
2.404(5)
149(5)
O2···H
neutral species [Pt(µ-Cl)(Ph2POHOPPh2)]2 with bridging
chloride ligands and terminal PPh2OH and PPh2O moieties
O1···O2
O1ϪH···O2
connected by hydrogen bonds. Although the hydrolysis of
3a has been studied in detail in the past,[9] the structure of
7 has not been reported before.
In a similar way, the presence of water converts the palla-
dium species 3b into another species whose 31P NMR spec-
trum is a singlet at δ ϭ 78.1 ppm, coincident with the signal
reported for the palladium analogue of 7 [Pd(µ-Cl)(Ph2PO-
HOPPh2)]2.[9c]
˚
O···O distances [O1···O2 ϭ 2.415(6) A and O4···O3 ϭ
Ϫ
˚
2.404(5) A]. They belong to the (OϪH···O) class of nega-
tive-charge-assisted H-bonds [(Ϫ)CAHB][14] where the
negative charge is shared between two oxygens. Accord-
ingly, all the PϪO bonds are of similar lengths [in the range
˚
1.540(4)Ϫ1.550(4) A], and are significantly longer than the
[15]
˚
PϭO distances [1.48Ϫ1.50 A]
neutral oxygen.
between phosphorus and
X-ray Crystal Structure of 7
Crystals of 7 were obtained from THF and diethyl ether
and its X-ray structure is shown in Figure 4. Selected bond
lengths and angles are given in Table 3.
The complex is essentially planar and displays a Cs sym-
metry. The molecule is characterized by two strong hydro-
Conclusions
The experiments described in this paper show that vicinal
gen bonds O1ϪH···O2 and O4ϪH···O3 with very short diphosphinites can be obtained in the metal-chelate sta-
922
Eur. J. Inorg. Chem. 2003, 918Ϫ925

Template Synthesis of Chiral Vicinal Diphosphinites
FULL PAPER
NMR spectroscopy (δ ϭ 73.4 ppm, JPPt ϭ 4069 Hz[9]). The addi-
tion of 1,2-butanediol (24 µL, 0.27 mmol) gave a colourless mix-
ture, and within 10 minutes 1a began to separate as a white micro-
crystalline precipitate. Slow addition of diethyl ether completed the
precipitation. The solid product was filtered off, washed with di-
ethyl ether, and dried under vacuum (130 mg, 67%).
C28H28Cl2O2P2Pt: calcd. C 46.4, H 3.9%; found C 46.6, H 4.0%.
1
bilised form, starting from the corresponding 1,2-diols,
whose stereochemistry is retained in the process.
We are now investigating the possibility to extend this
preparative method to asymmetric complexes of other
metals (e.g. Rh or Ru) and of other groups of ligands (e.g.
amidophosphane-phosphinites and aminophosphane-phos-
phinites[16]) relevant to asymmetric catalysis.
IR: νa(PtϪCl) 317; νs(PtϪCl) 293 cmϪ1
.
1H NMR (200 MHz,
3
CDCl3, 25 °C): δ ϭ 0.7 (t, JH,H ϭ 7 Hz, 3 H, -CH3), 1.7Ϫ1.4 (m,
2 H, -CH2Me), 3.8Ϫ4.2 (m, 2 H, -CH2OP), 4.4 (m, 1 H, -CHOP),
7.0Ϫ8.0 (m, 20 H, Ph) ppm. 31P NMR (81.01 MHz, CDCl3, 25
°C): δ ϭ Pa 90.2 (d, 1JPtP ϭ 4045 Hz,), Pb 89.3 (d, 1JPtP ϭ 3994 Hz)
Experimental Section
2
All reactions and manipulations were routinely performed under a
dry nitrogen atmosphere by using standard Schlenk-tube tech-
niques. Tetrahydrofuran was doubly distilled from over LiAlH4,
while diethyl ether was purified by distillation from over sodium/
benzophenone. Dichloromethane and methanol were purified by
distillation from calcium hydride. Pyridine was distilled and stored
over KOH. CDCl3, used as solvent for the NMR spectra, was dried
ppm, JPaPb ϭ 12 Hz.
Recrystallization of the crude product from dichloromethane/eth-
anol gave crystals suitable for an X-ray diffraction study.
Synthesis of 2a. Method a: A solution of ligand 2 was prepared
from 2,3-butanediol (117 mg, 1.3 mmol), following the method de-
scribed above for 1. The 31P NMR analysis showed the presence of
a signal consistent with 2 [31P NMR (81.01 MHz, CDCl3, 25 °C):
δ ϭ112.2 (s) ppm].
[PtCl2(1,5-COD)] (500 mg, 1.3 mmol) was added to this solution
and the procedure described above for 1a (method a) was followed.
The workup gave 2a as white crystals. (352 mg, 38%).
over molecular sieves (4 A). PPh2Cl (d ϭ 1.23 g·mLϪ1) was purified
˚
just prior to use by distillation under nitrogen. All the other solv-
ents and chemicals were reagent grade and, unless otherwise stated,
were used as received from commercial suppliers. Infrared spectra
were obtained in CsI, using a Nicolet 510 P FT-IR (4000Ϫ200
cmϪ1) spectrometer. 1H and 31P NMR spectra (always 1H de-
coupled) were recorded on Bruker AC200 spectrometers operating
at 200.13 MHz (1H) and 81.01 MHz (31P). Peak positions are given
in ppm relative to tetramethylsilane (1H) and to external 85%
H3PO4 (31P). Elemental analyses (C, H, N) were performed using
a Carlo Erba model 1106 elemental analyser. Optical rotations were
obtained on a PerkinϪElmer 241 at 25 °C.
Method b: Complex 2a was obtained as a white solid (137 mg, 70%)
following the procedure described above for 1a (method b), based
on 100 mg of [PtCl2(1,5-COD)] (0.27 mmol) and replacing 1,2-but-
anediol with 2,3-butanediol. C28H28Cl2O2P2Pt: calcd. C 46.38, H
3.89%; found C 46.43, H 3.90%. IR: νa(PtϪCl) 321; νs(PtϪCl) 295
3
cmϪ1
.
1H NMR (200 MHz, CDCl3, 25 °C): δ ϭ 1.2 (d, JH,H
ϭ
6.1 Hz, 6 H, -CH3), 4.6 (m, 2 H, -CHOP), δ ϭ 7.0Ϫ8.0 (m, 20 H,
Ph) ppm. 31P NMR (81.01 MHz, CDCl3, 25 °C): δ ϭ 90.4 ppm (s,
1JPtP ϭ 4021 Hz).
Literature methods were used for the preparation of [PtCl2(1,5-
COD)][17] and [PdCl2(1,5-COD)].[18]
Synthesis of 1b. Method a: The diphosphinite 1 was generated in
THF (20 mL) from 1,2-butanediol (153 mg, 1.7 mmol), PPh2Cl
(0.64 mL, 3.5 mmol), and pyridine (3 mL) as described above for
1a. Solid [PdCl2(1,5-COD)] (495 mg, 1.7 mmol) was then added at
room temperature with vigorous stirring. Within a few minutes, 1b
precipitated as a yellow solid. The crude product was filtered and
washed with diethyl ether (572 mg, 53%). Recrystallization from
dichloromethane/ethanol gave yellow crystals.
The diol R-I was prepared in two steps from commercial p-toluene-
sulfonate of (R)-2,2-dimethyl-1,3-dioxolane-4-methanol by the re-
ported procedure.[12]
Synthesis of Pt and Pd Complexes of Ligands 1 and 2
Synthesis of 1a. Method a: A THF (5 mL) solution of 1,2-butane-
diol (117 mg, 1.3 mmol) was prepared in a Schlenk flask equipped
with a dropping funnel and cooled to 0 °C (ice bath). The dropping
funnel was charged with THF (5 mL), PPh2Cl (0.57 mL,
3.2 mmol), pyridine (3 mL), and the mixture was added dropwise
to the diol solution whilst stirring. After the addition of a few
drops, white pyridinium chloride started to precipitate. After the
end of the addition, the reaction mixture was kept stirring at 0 °C
for an hour, then the white solid was filtered off under nitrogen on
celite, giving a colourless solution whose 31P NMR analysis showed
the presence of a main species consistent with 1 [31P NMR
(81.01 MHz, CDCl3, 25 °C): Pa 115.7(s), Pb 111.5 (s) ppm] together
with small amount of other unidentified species.
The volume of this solution was reduced to 20 mL by addition of
THF and solid [PtCl2(1,5-COD)] (500 mg, 1.3 mmol) was added at
room temperature. The reaction mixture was stirred for 1 h at room
temperature; during this period the product precipitated as a white
solid, which was then filtered and washed with diethyl ether
(390 mg, 41%).
Method b: The intermediate complex 3b was prepared in situ by
adding a solution of PPh2Cl (314 µL, 1.75 mmol) in 5 mL of THF
dropwise to a second solution of [PdCl2(1,5-COD)] (250 mg,
0.87 mmol) in THF (20 mL). When the complete formation of 3b
was confirmed by 31P NMR spectroscopy (δ ϭ 96 ppm), 1,2-but-
anediol (81 mg, 0.9 mmol) was added to give a pale yellow mixture.
Within a few minutes 1b began to precipitate as a yellow solid.
Slow addition of diethyl ether completed the precipitation. The
solid product was filtered off, washed with diethyl ether, and dried
under vacuum. (409 mg, 74%). C28H28Cl2O2P2Pd: calcd. C 52.85,
H 4.44%; found C 53.02, H 4.58%. IR: νa(PdϪCl) 315; νs(PdϪCl)
290 cmϪ1. 1H NMR (200 MHz, CDCl3, 25 °C): δ ϭ 0.7 (t, 3JH,H ϭ
6.1 Hz, 3 H, -CH3), 1.7 (m, 2 H, -CH2Me,), 4.1 (m, 2 H, -CH2OP);
4.4 (m, 1 H, -CHOP), 7.0Ϫ8.0 (m, 20 H, Ph) ppm. 31P NMR
(81.01 MHz, CDCl3, 25 °C): δ ϭ Pa 119.1 (d), Pb 118.4 (d) ppm,
2JPaPb ϭ 35.7 Hz.
Method b: A solution of PPh2Cl (100 µL, 0.56 mmol) in 5 mL of
THF was added dropwise whilst stirring to a solution of [PtCl2(1,5-
COD)] (100 mg, 0.27 mmol) in THF (10 mL) placed in a Schlenk
flask at room temperature. The immediate formation of the dichlo-
rophosphane complex 3a was unambiguously confirmed by 31P
Synthesis of 2b. Method a: Complex 2b was prepared as a yellow
crystalline solid (227 mg, 51%) from [PdCl2(1,5-COD)] (200 mg,
0.7 mmol) and a solution where ligand 2 was generated from 2,3-
butandiol (72 mg, 0.8 mmol) following the procedure described
above for 1b.
Eur. J. Inorg. Chem. 2003, 918Ϫ925
923

P. Bergamini et al.
FULL PAPER
Method b: Complex 2b was obtained also following the procedure
described above for 1b (method b), using 2,3-butanediol. Yield
74%. C28H28Cl2O2P2Pd: calcd. C 52.85, H 4.44%; found C 52.31,
NMR tube. The progress of the reaction was monitored by 31P
NMR spectroscopy: within the time necessary for NMR acquisi-
tion the substitution of both the chlorides in 1a with two cyanides
1
H 4.57%. IR: νa(PdϪCl) 311; νs(PdϪCl) 299 cmϪ1
.
1H NMR was completed (Pa δ ϭ 100.9 ppm, d, JPPt ϭ 2815 Hz and Pb δ ϭ
3
(200 MHz, CDCl3, 25 °C): δ ϭ 1.2 (d, JH,H ϭ 6.1 Hz, 6 H, -
99.5 ppm, d, 1JPPt ϭ 2834, 2JPP 19.6 Hz). The following decomposi-
CH3), 4.5 (m, 2 H, -CHOP), 7.3Ϫ8.0 (m, 20 H, Ph) ppm. 31P NMR tion of this dicyanide derivative into [Pt(CN)4]2Ϫ and free ligand 1
(81.01 MHz, CDCl3, 25 °C): δ ϭ 118.5 (s) ppm.
occurred in about 30 minutes as denoted by the observation of the
signals of 1 [δ ϭ Pa 115.7 (s), Pb 111.5 (s) ppm] exclusively.
At this point, the addition of [PdCl2(COD)] (8.5 mg, 0.03 mmol)
to the same NMR tube showed the immediate appearance of the
signals of 1b.
Template Synthesis of Other Diphosphinites on PtII
Synthesis of 4a*: The intermediate complex [PtCl2(PPh2Cl)2] (3a;
1.1 mmol) was formed in THF and checked by NMR spectroscopy
as described for the previous reactions.
An analogous multi-step transmetallation process was performed
by addition of an excess of solid (Bu4N)CN to a solution of the
palladium complex 1b (15 mg, 0.02 mmol) in 0.8 mL of CDCl3,
followed by [PtCl2(1,5-COD)] (11 mg, 0.03 mmol). The final 31P
NMR spectrum showed the phosphinito-platinum complex 1a to
be the only phosphorus-containing species.
(ϩ)-Diisopropyl -tartrate (232 µL, 1.1 mmol) dissolved in THF
(5 mL) was then added to the reaction mixture. After 18 h the com-
plete formation of 4a* was detected by 31P NMR spectroscopy.
This solution was reduced to a volume of 5 mL and the product
was precipitated with n-pentane, washed with the same solvent and
dried under vacuum (716 mg, 75%). C34H36Cl2O6P2Pt: calcd. C
47.00, H 4.15%; found C 47.30, H 4.10%. IR: ν(CO) 1745;
Removal of Ligand 5 from Platinum Complex 5a*
1
νa(PtϪCl) 302; νs(PtϪCl) 292 cmϪ1. H NMR (200 MHz, CDCl3,
A sample of complex 5a* (10 mg, 0.014 mmol) was dissolved in
CDCl3 and a 31P NMR spectrum recorded. Solid (Bu4N)CN was
progressively added to this solution. After the first addition of two
equivalents (7.5 mg), a 31P NMR spectrum consistent with the cy-
anide analogue of complex 5a* was detected (dd, δ ϭ 92 and
25 °C): δ ϭ 1.1 (dd, 3JH,H ϭ 6 Hz, 12 H, -OCH(CH3)2], 4.7 (septet,
3JH,H ϭ 6 Hz, 2H, ϪOCH(CH3)2], 5.2 (m, 2 H, -CHOP), 7.2Ϫ8.0
(m, 20 H, Ph) ppm. 31P NMR (81.01 MHz, CDCl3, 25 °C): δ ϭ
1
94.7 (s, JPtP ϭ 4003 Hz) ppm. [α]2D5 ϭ Ϫ10.6 (c ϭ 0.5, CHCl3).
1
1
2
Synthesis of Complex 5a*: The intermediate complex
[PtCl2(PPh2Cl)2] (3a; 0.77 mmol) was formed in THF and checked
by NMR spectroscopy as described for the previous reactions. A
solution of the phosphane-diol R-I (200 mg 0.77 mmol) in 5 mL of
THF was then added to the reaction mixture and within 10 minutes
a white solid began to precipitate. The addition of diethyl ether
completed the precipitation of 5a*, which was filtered off, washed
with diethyl ether and dried under vacuum. (404 mg, 74%).
C27H26Cl2O2P2Pt·C2H10O: calcd. C 47.48, H 4.59%; found C 47.55,
H 4.68%. IR: ν(OH) 3450; νa(PtϪCl) 306; νs(PtϪCl) 291 cmϪ1. 1H
NMR (200 MHz, CDCl3, 25 °C): δ ϭ 1.2 (t, 6 H,), 2.6 (m, 2 H, -
CH2P), 3.5 (m, 7 H, OH ϩ Et2O ϩ CH2OH), 3.9 (m, 1 H, -CHOP),
7.5 (m, 20 H, Ph) ppm. 31P NMR (81.01 MHz, CDCl3, 25 °C): δ ϭ
Ϫ4.4 ppm, JPPt ϭ 2716 and JPPt ϭ 2398 Hz respectively, JPP ϭ
25.6 Hz). Further addition of a large excess of (Bu4N)CN (5 equiv.,
20 mg) produced the appearance of a new pattern showing two
coupled doublets (δ ϭ 111 and Ϫ23 ppm, 4JPP ϭ 7 Hz), as expected
for the phosphane-phosphinite-ol 5.
X-ray Crystal Structure of 1a, 2b, 5a*, and 7: The crystal data were
collected using a Nonius Kappa CCD diffractometer with graphite
monochromatized Mo-Kα radiation and corrected for Lorentz, po-
larization and absorption (SORTAV)[19] effects. The structures were
solved by direct and Fourier methods (SIR92)[20] and refined on
F2 (SHELXL-97)[21] using full-matrix least-squares with all non-H
atoms anisotropic and hydrogen atoms at calculated positions, rid-
ing on their carrier atoms.
1
1
Pa 84.7 (d, JPtP ϭ 3858 Hz,), Pb Ϫ0.4 (d, JPtP ϭ 3482 Hz) ppm,
2JPaPb ϭ 17.7 Hz. [α]D25 ϭ ϩ40.0 (c ϭ 0.25, CHCl3).
1a: C28H28Cl2O2P2Pt, M ϭ 724.43, T ϭ 295 K, monoclinic, space
˚
group P21/n, a ϭ 8.9098(2), b ϭ 17.8502(4), c ϭ 18.1605(4) A, β ϭ
NMR Experiments
3
103.749(1)°, U ϭ 2805.5(1) A , Z ϭ 4, Dc ϭ 1.715 g·cmϪ3, µ ϭ
˚
Hydrolysis of 3a and 3b: A solution of PPh2Cl (300 µL, 1.67 mmol)
in dry THF (20 mL) was added dropwise in 15 min to a second
solution of [PtCl2(1,5-COD)] (308 mg, 0.82 mmol) in 30 mL of
THF containing 30 µL of water. The mixture was stirred at room
53.269 cmϪ1. Collected reflections ϭ 18446 (θ Յ 30°), unique
reflections ϭ 8130, Rint ϭ 0.031, observed reflections ϭ 6311 [I Ն
2σ(I)]. Final
R (observed reflections) ϭ 0.0335, Rw (all
reflections) ϭ 0.0659.
temperature. The 31P NMR analysis of an aliquot after two hours
2b: C28H28Cl2O2P2Pd, M ϭ 635.74, T ϭ 295 K, monoclinic, space
1
showed the formation of 3a and 6 [δ ϭ 71.1 ppm (s, JPtP
4065 Hz)] in an approximate 1:1 ratio, which increased with time.
ϭ
˚
group P21/n, a ϭ 9.2571(2), b ϭ 15.4091(3), c ϭ 19.7280(4) A, β ϭ
3
90.248(1)°, U ϭ 2814.0(1) A , Z ϭ 4, Dc ϭ 1.501 g·cmϪ3, µ ϭ 9.865
˚
After 18 h, the signal of 3a had disappeared and 6 and 7 [δ ϭ 50.5
cmϪ1. Collected reflections ϭ 18078 (θ Յ 30°), unique reflections ϭ
8135, Rint ϭ 0.036, observed reflections ϭ 6188 [I Ն 2σ(I)]. Final
R (observed reflections) ϭ 0.0347, Rw (all reflections) ϭ 0.0845.
1
ppm/s, JPtP ϭ 4090 Hz)] were observed in a 2:1 ratio.
At this point, a reduction of the solution volume and the slow
addition of diethyl ether induced the separation of a small amount
of white crystals whose X-ray structure was determined.
5a*: C27H26Cl2O2P2Pt·C4H10O, M ϭ 784.53, T ϭ 295 K, ortho-
rhombic, space group P212121, a ϭ 8.0995(1), b ϭ 18.0184(3), c ϭ
In a similar way, when water (2 equiv.) was added to the palladium
complex 3b, generated in THF from PPh2Cl (150 µL, 0.83 mmol)
and [PdCl2(1,5-COD)] (117 mg, 0.41 mmol), the 31P NMR showed
a mixture of species, the most abundant of which was represented
by a singlet at δ ϭ 78.1 ppm {[Pd(µ-Cl)(Ph2POHOPPh2)]2[9c]}.
3
21.9803(4) A, U ϭ 3207.8(1) A , Z ϭ 4, Dc ϭ 1.624 g·cmϪ3, µ ϭ
46.702 cmϪ1. Collected reflections ϭ 16288 (θ Յ 27°), unique
reflections ϭ 4850, Rint ϭ 0.049, observed reflections ϭ 4057 [I Ն
˚
˚
2σ(I)]. Flack parameter[22]
reflections) ϭ 0.0428, Rw (all reflections) ϭ 0.1102.
ϭ Ϫ0.02(4). Final R (observed
Removal and Transfer of Ligand 1
7: C48H42Cl2O4P4Pt2, M ϭ 1267.78, T ϭ 150 K, triclinic, space
˚
¯
(Bu4N)CN (4.5 equiv.; 33 mg, 0.121 mmol) was added to a CDCl3 group P1, a ϭ 11.9217(2), b ϭ 13.3152(2), c ϭ 16.1860(4) A, α ϭ
solution (0.8 mL) of 1a (15 mg, 0.027 mmol) in a 5-mm screw-cap
3
˚
94.6411(7), β ϭ 99.4177(7), γ ϭ 115.3400(7)°, U ϭ 2257.78(8) A ,
924
Eur. J. Inorg. Chem. 2003, 918Ϫ925

Template Synthesis of Chiral Vicinal Diphosphinites
FULL PAPER
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Z
ϭ
2, Dc
ϭ , µ ϭ . Collected
1.865 g·cmϪ3 64.935 cmϪ1
reflections ϭ 28569 (θ Յ 28°), unique reflections ϭ 10307, Rint
0.056, observed reflections ϭ 8727 [I Ն 2σ(I)]. Both the hydrogens
forming intramolecular hydrogen bonds O1ϪH···O2 and
O4ϪH···O3 were refined isotropically. Final
reflections) ϭ 0.0362, Rw (all reflections) ϭ 0.0928.
ϭ
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[I02340]
Eur. J. Inorg. Chem. 2003, 918Ϫ925
925