Chiral (diphosphonite)platinum complexes in asymmetric hydroformylation

Article abstract of DOI:10.1002/hlca.200690156

The chiral diphosphonite ligand (11bR,11‰bR)-4,4′-(9,9- dimethyl-9H-xanthene-4,5-diyl)bis[dinaphtho[2,1-d:1′,2′-f][1,3,2] dioxaphosphepin] ((R,R)-XantBino; (R)-1), based on a rigid xanthene backbone, was applied in the Pt/Sn-catalyzed hydroformylation of styrene (4a), 4-methylstyrene (4b), vinyl acetate (4c), and allyl acetate (4d), by using a Pt/Sn ratio of 1:1. High ee of up to 80% were observed, along with good regioselectivities towards the desired branched aldehydes. For styrene, an interesting inversion in the stereoselection process was observed at elevated temperatures, and a mechanism is proposed considering the temperature dependence of the regioselectivity. The complex [PtCl₂{(S,S)-XantBino}] ((S)-2) was characterized by X-ray crystal-structure analysis, revealing an unusual out-of-plane ligand coordination of the metal fragment. The complex [PtCl(SnCl₃)((R,R)-XantBino]] ((R)-3) was characterized by means of ³¹P-NMR spectroscopy.

Full text of DOI:10.1002/hlca.200690156

Helvetica Chimica Acta – Vol. 89 (2006)
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Chiral (Diphosphonite)platinum Complexes in Asymmetric
Hydroformylation
by Ruben van Durena), Leandra L. J. M. Cornelissena), Jarl Ivar van der Vlugta), Jeroen P. J. Huijbersa),
Allison M. Millsb), Anthony L. Spekb), Christian Müllera), and Dieter Vogt*a)
a) Schuit Institute of Catalysis, Laboratory for Homogeneous Catalysis, Eindhoven University of
Technology, Den Dolech 2, NL-5600 MB Eindhoven
(phone: +31402472483; fax: +31402455054; e-mail: d.vogt@tue.nl)
b) Crystal and Structural Chemistry, Utrecht University, Padualaan 8, NL-3584 CH Utrecht
Dedicated to Professor Giambattista Consiglio on the occasion of his 65th birthday
The chiral diphosphonite ligand (11bR,11’bR)-4,4’-(9,9-dimethyl-9H-xanthene-4,5-diyl)bis[dinaph-
tho[2,1-d:1’,2’-f][1,3,2]dioxaphosphepin] ((R,R)-XantBino; (R)-1), based on a rigid xanthene backbone,
was applied in the Pt/Sn-catalyzed hydroformylation of styrene (4a), 4-methylstyrene (4b), vinyl acetate
(4c), and allyl acetate (4d), by using a Pt/Sn ratio of 1:1. High ee of up to 80% were observed, along with
good regioselectivities towards the desired branched aldehydes. For styrene, an interesting inversion in
the stereoselection process was observed at elevated temperatures, and a mechanism is proposed consid-
ering the temperature dependence of the regioselectivity. The complex [PtCl2{(S,S)-XantBino}] ((S)-2)
was characterized by X-ray crystal-structure analysis, revealing an unusual out-of-plane ligand coordina-
tion of the metal fragment. The complex [PtCl(SnCl3){(R,R)-XantBino}] ((R)-3) was characterized by
means of 31P-NMR spectroscopy.
Introduction. – The asymmetric hydroformylation of alkenes is a reaction of great
potential for the production of optically active aldehydes, which are versatile building
blocks in synthetic organic chemistry [1][2]. Initial work on asymmetric hydroformyla-
tion in the presence of cobalt [3], platinum [4], and rhodium catalysts [5] resulted in
very low enantioselectivities, but the Pt/Sn-catalyst, modified with chiral diphosphine
ligands and pioneered by Consiglio and co-workers led to much better results than
any previous system [6]. However, these catalysts showed poor regioselectivities, yield-
ing the branched, chiral aldehydes in only 50–70% and in some cases of up to 80% [7].
Additionally, the formation of hydrogenated products and double-bond isomerization
as unwanted side reactions were observed.
Typically, a large excess of up to 6 equiv. of SnCl2 was necessary to form stable cat-
alysts and to avoid decomposition to Pt-black. However, this excess causes significant
product racemization, as observed problem for the early systems, leading to lower over-
all enantioselectivities [6]. To overcome these drawbacks, trapping agents, e.g., triethyl
orthoformate (HC(OEt)3) were added, to achieve in situ protection of the aldehyde and
to reach high enantioselectivities of up to 96% [8][9]. Alternatively, preformation of
the Pt/Sn bimetallic catalyst species resulted in higher enantioselectivities as well as
chemo- and regioselectivities [10][11].
© 2006 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 89 (2006)
In recent years, research on asymmetric hydroformylation has mainly focused on
Rh-systems, even though they generally displayed poor enantioselectivities but higher
activities and regioselectivities for a long time [12]. Only recently, the phosphino-phos-
phite ligand (R,S)-binaphos, introduced by Takaya and co-workers [13], and the large-
bite-angle diphosphites independently introduced by Babin and Whiteker [14] and van
Leeuwen and co-workers [15] led to real breakthroughs.
We recently became interested again in the Pt/Sn catalysts because of their isomer-
ization activity, which can be highly beneficial in the hydroformylation of internal
alkenes. In fact, large-bite-angle diphosphine ligands with a rigid xanthene backbone
give very stable and selective catalysts for the Pt-catalyzed hydroformylation of alkenes
[16]. We already successfully prepared and applied chiral xanthene-based diphosphon-
ite ligands in the nickel-catalyzed asymmetric hydrocyanation [17] and the rhodium-
catalyzed asymmetric hydroformylation [18]. Here, we report on the use of the chiral
diphosphonite ligand (R,R)-XantBino ((R)-1) [19] in the Pt/Sn-catalyzed asymmetric
hydroformylation of styrene (4a), 4-methylstyrene (4b), vinyl acetate (4c), and allyl
acetate (4d). Phosphonite ligands in general have only rarely been applied in homoge-
neous catalysis [20–27], and the use of diphosphonites in hydroformylation reactions
has been very limited so far [28–30]. Recent studies on Pt/Sn-catalyzed asymmetric
hydroformylation employed diphosphite ligands [31], but only one report has dealt
with the use of chiral diphosphonites in Pt-catalyzed asymmetric hydroformylations,
to the best of our knowledge [28].
Results and Discussion. – The chiral diphosphonite ligands (R,R)-XantBino ((R)-1)
[17][19] and (S,S)-XantBino ((S)-1) were treated with [PtCl2(MeCN)2] or [PtCl2(cod)]
(cod=cycloocta-1,5-diene), affording the corresponding Pt-complexes [PtCl2{(R,R)-
XantBino}] ((R)-2) and [PtCl2{(S,S)-XantBino}] ((S)-2), as white solids (Fig. 1) in
good yields. The 31P-NMR spectrum of complex (S)-2 showed 2 d at d 110.5 and
113.1 with 195Pt satellites, and coupling constants J(P,P)=15.9 Hz and J(Pt,P)=5000
and 5040 Hz were observed. Apparently, (S)-2 is devoid of the C2 symmetry shown
in Fig. 1, suggesting that the inequivalency of the two P-atoms is due to a distorted con-
formation around the metal center. Furthermore, the observed coupling constants
clearly indicate cis-coordination of the diphosphonite ligand towards the Pt-center
[18][28][32]. Similar ligands of the Xantphos family are known to form monomeric
Pt-complexes with both cis- and trans-coordination [16][33–35].
Fig. 1. (R,R)-XantBino ((R)-1) and [PtCl2{(R,R)-XantBino}] ((R)-2)

Helvetica Chimica Acta – Vol. 89 (2006)
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We were able to obtain single crystals of complex (S)-2, suitable for X-ray crystal-
structure analysis, by layering a CH2Cl2 solution of (S)-2 with MeCN. The molecular
structure is depicted in Fig. 2, with selected bond lengths and angles listed in Table 1.
Fig. 2. a) Molecular Structure of (S)-2. b) Detail of Backbone and Metal Fragment. Displacement
ellipsoids are drawn at the 50% probability level; H-atoms are omitted for clarity1).
Table 1. Selected Bond Lengths, Distances, and Bond Angles for (S)-2
Bond lengths [Å]
Angles [8]
PtÀP(1)
2.2229(11) PtÀP(2)
2.3504(11) PtÀCl(2)
2.2245(11) Cl(1)ÀPtÀCl(2)
2.3450(11) Cl(1)ÀPtÀP(1)
87.99(4) P(1)ÀPtÀP(2)
84.32(4) Cl(1)ÀPtÀP(2)
87.39(2) Cl(2)ÀPtÀP(1)
102.54(14) O(3)ÀPtÀO(4)
99.64(4)
172.19(4)
170.59(4)
102.61(17)
PtÀCl(1)
P(1)ÀO(1) 1.604(3)
P(2)ÀO(3) 1.603(3)
P(1)ÀP(2) 3.398
P(1)ÀO(2) 1.601(3)
Cl(2)ÀPtÀP(2)
P(2)ÀO(4) 1.616(3)
PtÀO(5) 3.335(3)
O(1)ÀPtÀO(2)
C(46)ÀO(5)ÀC(55) 112.6(3)
C(45)ÀC(47)ÀC(50) 105.7(4)
The molecular structure of (S)-2 shows a slightly distorted square-planar geometry
around the Pt-center, as is evident from the angle P(1)ÀPtÀP(2) of 99.64(4)8 [18b]. The
distance between the Pt-atom and the O-atom of the xanthene backbone is 3.335(3) Å,
which is too large to assume any bonding interaction. The PtÀP bond lengths of
2.2229(11) (PtÀP(1)) and 2.2245(11) Å (PtÀP(2)), respectively, are similar to those
observed in other (phosphonite)platinum complexes [22][28][36–38]. The arrange-
ment around the two P-atoms is depicted in Fig. 2,a. While one of the binaphthalene
moieties is oriented parallel to the xanthene backbone, the other one is orthogonal
to this backbone. This is in agreement with the observed inequivalency of the two P-
atoms observed in the 31P-NMR spectrum, establishing the existence of similar confor-
mations in solution and in the solid state. The dihedral angle between the plane Cl(1)À
PtÀCl(2) and the backbone plane P(1)ÀP(2)ÀC(41)1) is 112.28. This shows that the Pt-
atom is located outside of the plane consisting of the backbone and the P-atoms, as can
1
)
Arbitrary atom numbering; for the systematic name, see the Exper. Part.

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Helvetica Chimica Acta – Vol. 89 (2006)
be seen in Fig. 2,b (the binaphthalene units are omitted for clarity). This unusual coor-
dination behavior is in clear contrast to other known examples of xantphos-type metal
complexes, where the central atom is in the plane with the backbone (for comparison
with PtÀP bond lengths for phosphines, see [37a,b]; for (phosphite)platinum com-
plexes, see [37c]). This ‘out-of-plane’ Pt-atom gives rise to a high accessibility to the
metal center and should, therefore, increase the activity in catalytic reactions.
Reaction of the complex [PtCl2{(R,R)-XantBino}] ((R)-2) with 1 equiv. of SnCl2
in CH2Cl2 led to
a yellow solution of the corresponding Pt/Sn complex
[PtCl(SnCl3){(R,R)-XantBino}] ((R)-3). After concentrating the solution of the com-
plex, it was characterized by its 31P-NMR spectroscopy at À508 (Fig. 3). Two d with
J(P,P)=15.2 Hz were observed for the two inequivalent P-atoms as main resonances
at d 124.7 and 132.8 (Po and Px). The corresponding Pt-satellites are labeled with x
and o, respectively. Apparently, insertion of SnCl2 occurs preferentially only in one
of the two PtÀCl bonds, since two isomers are expected due to the lack of C2 symmetry
of the starting material. The presence of only one isomer indicates that insertion of
SnCl2 into the PtÀCl bond either determines the orientation of the two binaphthalene
moieties, or that an average signal of the two P-nuclei is observed even at À508. Inter-
estingly, coupling of the P-atoms, which differ substantially due to their cis- and trans-
position relative to the SnCl3 ligand, with the 119Sn and 117Sn nuclei can also be
observed. Table 2 summarizes the oberved coupling constants; the assignment is
based on a literature example with P-based ligands [39].
We applied the chiral diphosphonite ligand (R)-1 in the Pt/Sn-catalyzed asymmetric
hydroformylation of styrene (=ethenylbenzene; 4a), 4-methylstyrene (=1-ethenyl-4-
Fig. 3. 31P-NMR Spectrum of [PtCl(SnCl3){(R,R)-XantBino}] ((R)-3) in CH2Cl2 and the Correspond-
ing Assignment. sm: starting material (R)-2.
Table 2. Assignment of Signals in the 31P-NMR Spectrum of (R)-3. d in ppm, J in Hz.
d(P)
J(P,Pt)
J(P,Sn)
J(P,P)
Po
Px
124.7
132.8
4909
4108
197
5856, 5596
15.2
15.2

Helvetica Chimica Acta – Vol. 89 (2006)
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methylbenzene; 4b), vinyl acetate (=ethenyl acetate; 4c), and allyl acetate (=prop-2-
enyl acetate; 4d). For this, complex (R)-2 was pretreated with SnCl2 in CH2Cl2 and the
resulting solution containing the precatalyst (R)-3 was used in the catalysis experiments
(Scheme 1). As already mentioned, an excess of SnCl2 can lead to racemization of the
formed aldehyde 5, which results in a decrease of the enantioselectivity with increasing
conversion [9][10]. By using rigid large-bite-angle ligands, however, the amount of side
reactions can be reduced considerably, even if only 1 equiv. of SnCl2 with respect to Pt-
complex (R)-2 is used [16]. Table 3 summarizes the results of the hydroformylation of
styrene (4a) with (R)-3 at 208, showing indeed no considerable change in the ee with
conversion. The same holds for the regioselectivity, which remains high at 80% (ratio
5a/6a). These results show that the (diphosphonite)platinum/SnCl2 complex (R)-3
remains stable during the course of the catalytic reaction and does not lead to any rac-
emization of the product at room temperature.
Scheme 1. Pt/Sn-Catalyzed Hydroformylation of Prochiral Alkenes
Table 3. Enantioselective Hydroformylation of Styrene (4a) with (R)-3 as a Function of Conversiona)
t [h]
Conversion [%]
Hydrogenation [%]b)
b/lc)
ee (config.) [%]
4
6
10
10d)
4
6
15
46
39
27
18
80 :20
80 :20
79 :21
77:23
26 (R)
26 (R)
27 (R)
27 (R)
100
a) Reaction conditions: 208, 20 bar, ligand/Pt 1:1, SnCl2/Pt 1:1, substrate/Pt 1000 :1, CO/H2 1:1, CH2Cl2;
preformation 2 h at 20 bar, 608. b) Formation of 7a. c) Ratio 5a/6a, i.e., branched/linear aldehyde. d) Sub-
strate/Pt 170 :1.
An interesting observation is the fact that the amount of hydrogenation by-product
7a decreases with increasing conversion, suggesting that a different catalytic species,
only present at the beginning of the reaction, is responsible for this side reaction
(Table 3). During our studies, a short induction period of ca. 30 min was indeed recog-
nized, which could explain the observed results. Similar observations were made in ear-
lier studies of the Pt/Sn-catalyst systems [40].
To study the influence of temperature and pressure on the catalyst performance,
these parameters were varied from 0 to 1008 and from 10 to 60 bar, respectively. The
obtained data are summarized in Table 4. As expected, the productivity (TON=turn-
over number) decreases with increasing pressure, as the coordination of styrene to the
metal center requires dissociation of carbon monoxide. Compared to reaction rates
with Xantphos [34], the increased activity of this type of catalyst agrees well with the

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Helvetica Chimica Acta – Vol. 89 (2006)
Table 4. Enantioselective Hydroformylation of Styrene (4a) with (R)-3a)
p [bar] T [8] t [h]
Conversion [%] Hydrogenation [%]b) b/lc)
ee (config.) [%] TON
10
10
10
10
10
20
20
20
20
20
20
60
60
60
60
20
40
60
80
100
0
20
40
60
80
100
20
40
60
80
15
10
5
2
0.5
64
15
10
5
2
0.5
43
87
99
83
58
23
45
99
90
95
61
12
21
47
42
52
64
78
35
37
39
40
53
68
26
25
25
36
83 :17 18 (R)
430
870
999
830
580
230
450
999
900
950
610
120
210
360
350
78 :22 9 (R)
63 :37 3 (S)
45 :55 6 (S)
34 :66 4 (S)
69 :31 30 (R)
79 :21 27 (R)
79 :21 17 (R)
73 :27 10 (R)
57:43 1 (S)
45 :55 2 (S)
71:29 14 (R)
73 :27 8 (R)
74 :26 3 (S)
70 :30 2 (S)
10
4
1.75 36
0.5 35
a) Reaction conditions: ligand/Pt/SnCl2 1:1:1, substrate/Pt 1000 :1, CO/H2 1:1, CH2Cl2; preformation:
b
c
2 h at 20 bar, 608. ) Formation of 7a. ) Ratio 5a/6a, i.e., branched/linear aldehyde.
higher accessibility of the metal due to the ‘out-of-plane’ Pt-center. The lower linear-to-
branched ratio supports this even further.
Interestingly, at higher pressure, i.e., higher H2 partial pressure, the hydrogenation
reaction towards ethylbenzene (7a) is reduced (Table 4). This suggests that the transi-
tion state for hydroformylation contains at least one more CO compared to the transi-
tion state for hydrogenation (Scheme 2). Therefore, the reaction path is influenced by
the partial pressure of CO [41]. As hydrogenation increases at higher reaction temper-
atures, this process is predominantly governed by a larger temperature dependence of
the first-order reaction (alkyl formation and b-hydride elimination) compared to the
competing second-order reaction (acyl formation and acyl hydrogenolysis towards
the hydroformylation product) [41].
Scheme 2. Hydroformylation vs. Hydrogenation. Only the formation of the linear product is shown.
We further observed that the branched-to-linear ratio decreases with increasing
reaction temperature. At lower temperatures, the secondary a-methylbenzyl inter-
mediate 8 is more stable than the phenethyl intermediate 9 by 4–6 kJ/mol, as has
been shown for similar systems by Rappé and co-workers (Fig. 4) [42]. The a-methyl-
benzyl intermediate 8 will, therefore, be the preferred intermediate at lower tempera-
ture. However, at higher temperature, the sterically less demanding phenethyl inter-
mediate 9 is expected to be the predominant species due to the bigger conformational

Helvetica Chimica Acta – Vol. 89 (2006)
1553
space of the ligand framework resulting in an increased steric interaction with the sub-
strate [43]. Moreover, secondary-alkyl-coordinated Pt-complexes are more prone to b-
H elimination than primary-alkyl-coordinated ones, thus leading to the reformation of
the substrate at higher temperatures and removal of the branched-alkyl Pt-species and
slow formation of the branched aldehyde [1][41]. Whether the h3-complex 10 plays a
role as an intermediate is still a matter of debate, since p-acceptor ligands like phos-
phonites usually favor the formation of h3-complexes, rather than h1-alkyl species.
Fig. 4. Intermediates 8–10 of the Hydroformylation Reaction
Furthermore, the enantioselectivity in the hydroformylation of styrene (4a) is found
to be temperature-dependent, eventually leading to enantiomer inversion with increas-
G
ing reaction temperature (see Table 4). An inversion of the enantioselectivity is
observed for all applied pressures, but the inversion temperature is pressure-depen-
dent. The inversion of enantioselectivity has been observed before by Kollar et al.
[44] in the Pt/Sn-catalyzed asymmetric hydroformylation of styrene and has recently
been studied in more detail by Casey et al. [41]. Since the energy difference between
the enantiomeric pathways remains in the same order of magnitude with increasing
pressure, the effects of temperature and pressure are difficult to distinguish on this
scale. However, the observed conformation of the complex [PtCl2(1)] is prone to
changes under influence of solvent, temperature, and pressure, and the information
obtained from the solid-state structure cannot directly be related with the stereoselec-
tion process.
We were further interested in the hydroformylation of the substrates 4-methylstyr-
ene (4b), allyl acetate (4d), and vinyl acetate (4c) (Scheme 1). With 4b, less hydrogena-
tion was observed compared to styrene (4a) as a substrate, but no clear trend was
observed in the stereoselection process under comparable reaction conditions,
although higher branched-to-linear ratios could be observed with 4-methylstyrene
under the same conditions (Table 5).
Interestingly, the hydroformylation of allyl acetate (4d) and vinyl acetate (4c) gave
much better results in terms of enantioselectivity compared to the styrene derivatives.
Thus, 80% ee was achieved in the hydroformylation of 4d at 20 bar CO/H2 and 408.
Also when applying different reaction conditions, still high ee for the branched product
were observed. A clear drawback, however, is the fact that the chemoselectivities
(hydrogenation vs. hydroformylation) as well as the regioselectivities towards the
desired branched aldehyde are quite low and have to be improved considerably
(Table 6). Moreover, unwanted side reactions leading to unidentified products occurred

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Helvetica Chimica Acta – Vol. 89 (2006)
Table 5. Enantioselective Hydroformylation of 4-Methylstyrene (4b) with (R)-3a)
p [bar]
T [8]
t [h]
Conversion [%]
Hydrogenation [%]b)
b/lc)
ee [%]
10
20
60
60
80
80
80
40
2
2
2
2
61
100
100
85
46
40
33
21
43 :57
61:39
71:29
78 :22
12.4
3.1
4.7
4.8
a) Reaction conditions: ligand/Pt/SnCl2 1:1:1, substrate/Pt 1000 :1, CO/H2 1:1, CH2Cl2; preformation:
b
c
2 h at 20 bar, 608. ) Formation of 7b. ) Ratio 5b/6b, i.e., branched/linear aldehyde.
Table 6. Enantioselective Hydroformylation of Allyl Acetate (4d) and Vinyl Acetate (4c) with (R)-3a)
p [bar] T [8] t [h] Conversion [%] Hydroformylation [%] Hydrogenation [%]b) b/lc) ee [%]
4d 10
20
80
40
80
80
80
80
12
61
20
47
34
35
33
5
13
25
24
31
30
31
9 :91 75
13 :87 80
11:89 79
13 :87 74
12 :88 71
22 :78 58 (R)
64 100
12 100
12 100
12 100
20
40
60
10
64
36
4c 20
40
80
80
80
64
64
64 100
82
99
14
21
21
18
22
28
28 :72 67 (R)
28 :72 75 (R)
21:79 77 (R)
60
a) Reaction conditions: ligand/Pt/SnCl2 1:1:1, substrate/Pt 1000 :1, CO/H2 1:1, CH2Cl2; preformation:
2 h at 20 bar, 608. b) Formation of 7d or 7c, resp. c) Ratio 5d/6d or 5c/6c, resp., i.e., branched/linear alde-
hyde.
in some cases, accounting for the observed discrepancies in conversion and product dis-
tribution.
Also in the hydroformylation of vinyl acetate (4c), and under different reaction con-
ditions, moderate to good enantioselectivities of up to 77% were obtained. Also in this
case, low selectivities towards the desired branched aldehyde were observed (Table 6)
(for an inversion of the linear-to-branched ratio in the asymmetric hydroformylation,
see [45]).
Conclusions. – The complexes [PtCl2{(R,R)-XantBino}] ((R)-2) and [PtCl2{(S,S)-
XantBino}] ((S)-2) were prepared, and the latter one was characterized by means of
X-ray crystal-structure analysis, revealing an unusual ‘out-of-plane’ Pt-core in the
solid-state structure, which was further supported by NMR data. Reaction of (R)-2
with 1 equiv. of SnCl2 afforded the corresponding Pt/Sn complex [PtCl(SnCl3){(R,R)-
XantBino}] ((R)-3), which was characterized by 31P-NMR spectroscopy. This complex
was used as precatalyst for the asymmetric hydroformylation of styrene (4a), 4-methyl-
styrene (4b), vinyl acetate (4c), and allyl acetate (4d). In the case of 4a as substrate, che-
moselectivities of up to 75%, regioselectivities of up to 83%, and enantioselectivities of
up to 30% were reached, while high ee of 80 and 77% were reached for the substrates
allyl acetate (4d) and vinyl acetate (4c), respectively. The enantioselectivity was found
to be independent of the conversion, meaning that no racemization occurs as a conse-

Helvetica Chimica Acta – Vol. 89 (2006)
1555
quence of the stoichiometric amount of SnCl2 with respect to the Pt-complex 2. On the
basis of the reaction mechanism, the temperature and pressure dependency of the
hydroformylation is explained. For styrene (4a) as a substrate, concerning enantioselec-
tivity, an inversion of the stereoselection process was found with increasing tempera-
ture, which is attributed to conformational changes in the catalyst structure at elevated
temperature.
Umicor is kindly acknowledged for a generous loan of precious metals for our studies.
Experimental Part
General. All reactions were performed under Ar by using standard Schlenk techniques. Chemicals
were purchased from Aldrich Chemical Co., Acros or VWR. Solvents were purified by passing them
through basic alumina columns after degassing. Styrene was purified by passage through basic alumina
and distilled prior to use. PtCl2 was obtained from OMG. Synthesis gas 5.0 (CO/H2 50 :50) was purchased
from HoekLoos. GC: Shimadzu GC-17A, HP-Ultra-2 column (25 m×0.25 mm), FID detector; determi-
nation of the enantiomeric excess (ee) with Carlo Erba GC6000 Vega 2, Lipodex-E column (25 m×0.25
mm), FID detector. NMR Spectra: Varian-Mercury-400 spectrometer; d in ppm, J in Hz.
Crystal-Structure Determination of [PtCl2{(S)-1}] ((S)-2). The crystal data were collected (out to
sin(q/l)=0.65 ÅÀ1) on a Nonius-KappaCCD diffractometer with rotating anode by using graphite-mono-
chromated MoKa radiation. A face-indexed absorption correction was applied with PLATON/
ABSTOMPA (transmission range 0.508–0.844) [46]. The structure was solved by direct methods with
SHELXS97, and was refined on F2 by least-squares procedures with SHELXL97 [46]. All non-H-
atoms were refined with anisotropic displacement parameters. H-Atoms were constrained to idealized
geometries and allowed to ride on their carrier atoms with isotropic displacement parameter related
to the equivalent replacement parameter of their carrier atoms. The crystal structure contains solvent-
accessible voids with a total volume of 1339 Å3 per unit cell volume filled with disordered solvent mol-
ecules (CH2Cl2/MeCN). Their contribution to the structure factors was ascertained by using PLATON/
SQUEEZE [47]. Structure validation and molecular-graphics preparation were performed with the
PLATON package [47]. Selected bond lengths, distances, and bond angles are given in Table 1. Crystal
data (excluding disordered solvent): C55H36Cl2O5P2Pt, M 1104.76, orthorhombic, a=11.2545(1),
b=17.1813(1), c=17.4069(2) Å, V=5299.59(7) Å3, T 150 K, space group P212121 (no. 19), Z=4, m(Mo-
Ka)=2.853 mmÀ1, 60343 reflections collected, 12174 unique (Rint =0.062) which were used in all calcula-
tions. R1 =0.0302, wR2 =0.0749, s=1.05, Flack=0.012(4), 1(min)=À0.67, 1(max)=0.75 e/Å3.
CCDC-295949 contains the supplementary crystallographic data for this paper. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif from the Cambridge Crystallo-
graphic Data Centre.
(11bR,11’bR)-4,4’-(9,9-Dimethyl-9H-xanthene-4,5-diyl)bis[dinaphtho[2,1-d :1’,2’f][1,3,2]dioxaphos-
phepin] ((R,R)-XantBino); (R)-1). The synthesis of this ligand and the analogous (S,S)-isomer (S)-1 was
G
carried out as previously described [18b][20]. 1H-NMR (CDCl3): 7.94 (d, J=8.8, 2 bino H); 7.90 (d,
J=8.0, 2 bino H); 7.84 (d, J=8.0, 2 bino H); 7.63 (d, J=8.8, 2 bino H); 7.58 (d, J=8.8, 2 bino H); 7.55
(dd, J=8.0, J=0.8, 2 bino H); 7.42 (t, J=8.8, 6 xant H); 7.32 (d, J=8.4, 2 bino H); 7.28 (d quint.,
J=8.0, 1.2, 4 bino H); 7.18 (d, J=8.8, 2 bino H); 6.92 (s, J=8.8, 2 bino H); 6.90 (d, J=7.2, 4 bino H);
1.79 (s, Me
A
129.0 (d, J(P,C)=16.8); 128.5; 128.2 (d, J(P,C)=6.8); 126.9 (d, J(P,C)=3.8); 125.8 (d, J(P,C)=19.0);
124.6 (d, J(P,C)=20.6); 123.3; 121.9 (d, J(P,C)=5.3); 34.1 (Me2C); 31.9 (Me2
(CDCl3): 178.0 (s).
A
(SP-4-2)-Dichloro{(11bR,11’bR)-4,4’-(9,9-dimethyl-9H-xanthene-4,5-diyl)bis[dinaphtho[2,1-d:1’2’-f]-
ACHTREUNG

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Helvetica Chimica Acta – Vol. 89 (2006)
Alternatively, [PtCl2(cod)] (72.3 mg, 193.2 mmol) and, e.g., (S)-1 (172.3 mg, 205.3 mmol) were dis-
solved in CH2Cl2 (15 ml) and stirred for 1 h at r.t., yielding (S)-2 as a white precipitate. Colorless,
block-shaped crystals were obtained after slow diffusion of MeCN (15 ml) into a CH2Cl2/CHCl3 soln.
(5 ml/4 ml). Yield 82%. 31P{1H}-NMR (CDCl3): 110.5 (d, J(P,P)=15.9, J(Pt,P)=5000); 113.1 (d, J(P,
P)=15.9, J(Pt,P)=5040). Anal. calc. for C55H36Cl2O5P2Pt: C 59.79, H 3.28; found: C 59.84, H 3.42.
(SP-4-3)-Chloro{(11bR,11’bR)-4,4’-(9,9-dimethyl-9H-xanthene-4,5-diyl)bis[dinaphtho[2,1-d:1’,2’-f]-
A
molar amount of Pt-complex (R)-2 (15 mg, 13.7 mmol), dissolved in CH2Cl2 (10 ml), was added. After
2 h, a yellow soln. was obtained. Of this solution, 10 ml was taken, and the solvent was evaporated.
The residue was redissolved in CDCl3 (0.5 ml), and a 31P-NMR was recorded at À508. 31P{1H}-NMR
(CDCl3): 124.7 (d, J(P,P)=15.2, J(Pt,P)=4904, J(Sn,P)=197); 132.8 (d, J(P,P)=15.2, J(Pt,P)=4108,
J(Sn,P)=5856, 5596).
Hydroformylation of Styrene (4a). The soln. (10 ml) of (R)-3 in CH2Cl2 (see above) was transferred
to a 75-ml stainless steel autoclave equipped with a stirring bar. Additional CH2Cl2 (10 ml) was added.
The autoclave was pressurized to 20 bar and heated to 608. After 2 h of preformation, 4a/decane
(1.6 g/0.5 g, 15.4 mmol/3.4 mmol), dissolved in CH2Cl2 (5 ml), was added at the desired pressure and
temp. The pressure was kept constant by using a gas line with a pressure regulator. After the reaction,
the autoclave was cooled to r.t., depressurized, and the mixture was analyzed by GC to determine the
conversion and the chemo- and regioselectivities.
To a soln. of LiAlH4 (0.12 g) in Et2
ACHTREUNG
tion was quenched with H2O, the mixture extracted with Et2
AHCTREUNG
(MgSO4) and evaporated, and the residue dissolved in CH2Cl2 (5 ml) and treated with trifluoroacetic
anhydride (1,5 ml). The solvent and excess trifluoroacetic anhydride were evaporated, and the residue
was dissolved in toluene and analyzed by GC.
Hydroformylation of 4-Methylstyrene (4b), Vinyl Acetate (4c), and Allyl Acetate (4d). Catalysis
experiments were performed simultaneously in the parallel autoclave system AMTEC SPR16 [48],
equipped with pressure sensors and a mass-flow controller and suitable for monitoring and recording
gas uptakes throughout the reactions. General procedure for the catalysis experiments: Four stainless-
steel autoclaves of the AMTEC SPR16 were heated to 908 and flushed with Ar (15 bar) four times. Sub-
sequently, the reactors were cooled to r.t. and flushing with Ar was repeated again for four times. The
reactors were charged each with the soln. of the precatalyst (see below) dissolved in CH2Cl2 under Ar.
The atmosphere was further exchanged with synthesis gas (CO/H2 1:1) (gas exchange cycle 1), and
the reactors were pressurized with CO/H2 to 10 bar. After heating to 608, the pressure was increased
to 20 bar and kept constant during the preformation time. Subsequently, the substrate was injected via
syringe, and the final pressure and temperature were adjusted. In case of 4a, 4b, and 4d, decane was
used as an internal standard. In the case of 4c, ethyl propanoate was used as the internal standard. At
the end of the catalysis experiments, the reactors were cooled to r.t., and the autoclave contents were ana-
lyzed by means of GC.
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Received January 31, 2006