Sterically demanding diphosphonite ligands - Synthesis and application in nickel-catalyzed isomerization of 2-methyl-3-butenenitrile

Article abstract of DOI:10.1002/adsc.200303240

The synthesis of a novel class of sterically demanding diphosphonites 1-8, based on rigid backbones, is described. The starting materials are all commercially available and the methodology allows for a modular approach. All ligands have been fully characterized, including an X-ray crystal structure for compound 1, 4,5-bis{di[(2-terr-butyl)phenyl]phosphonito}-9,9-dimethylxanthene. The coordination of these diphosphonite ligands towards Ni(II) and Ni(0) precursors is investigated, both by NMR spectroscopy as well as X-ray crystallography and compared with the behaviour of diphosphine ligands such as Xantphos. The molecular structure for complex 9, trans-[NiBr₂(1)] is described in detail. The nickel-catalyzed isomerization of 2-methyl-3- butenenitrile to 3-pentenenitrile is studied, a relevant step in the industrially important hydrocyanation of butadiene (the DuPont adiponitrile process). Good activities and selectivities to the desired 3-pentenenitrile are obtained in this reversible C-C bond activation reaction.

Full text of DOI:10.1002/adsc.200303240

FULL PAPERS
Sterically Demanding Diphosphonite Ligands Synthesis and
Application in Nickel-Catalyzed Isomerization of
2-Methyl-3-Butenenitrile
Jarl Ivar van der Vlugt,a Alison C. Hewat,a Samuel Neto,a Rafael Sablong,a
Allison M. Mills,b Martin Lutz,b Anthony L. Spek,b Christian M¸ller,a
Dieter Vogta,*
a
Laboratory for Homogeneous Catalysis, Schuit Institute for Catalysis, Eindhoven University of Technology,
Den Dolech 2, 5600 MB Eindhoven, The Netherlands
Fax: (þ31)-40-245-5054, e-mail: d.vogt@tue.nl
b
Department for Crystal and Structural Chemistry, Utrecht University, Padualaan 2, 3584 CH Utrecht, The Netherlands
Received: December 23, 2003; Accepted: May 25, 2004
Dedicated to Professor Joachim Bargon (Universit‰t Bonn) on the occasion of his 65th birthday.
Abstract: The synthesis of a novel class of sterically phos. The molecular structure for complex 9, trans-
demanding diphosphonites 1 8, based on rigid back- [NiBr2(1)] is described in detail. The nickel-catalyzed
bones, is described. The starting materials are all com- isomerization of 2-methyl-3-butenenitrile to 3-pen-
mercially available and the methodology allows for a tenenitrile is studied, a relevant step in the industrial-
modular approach. All ligands have been fully charac- ly important hydrocyanation of butadiene (the Du-
terized, including an X-ray crystal structure for com- Pont adiponitrile process). Good activities and selec-
pound 1, 4,5-bis{di[(2-tert-butyl)phenyl]phosphoni- tivities to the desired 3-pentenenitrile are obtained
À
to}-9,9-dimethylxanthene. The coordination of these in this reversible C C bond activation reaction.
diphosphonite ligands towards Ni(II) and Ni(0) pre-
cursors is investigated, bothby NMR spectroscopy
as well as X-ray crystallography and compared with Keywords: hydrocyanation; isomerization; 2-methyl-
the behaviour of diphosphine ligands such as Xant- 3-butenenitrile; nickel; P ligands
Introduction
of these ligands either bear diphosphines[7 10] or diphos-
phites[11 13] as the chelating group. However, only a few
The isomerization of the unsaturated nitrile 2-methyl-3- examples of diphosphonites have been reported in the
butenenitrile is the key intermediate step in the hydro- literature to date. BothReetz et al. and Zanotti-Gerosa
cyanation of butadiene to adiponitrile, a building block et al. have published on the catalytic activity of various
for nylon-6,6 production.[1] Thorough insight into the diphosphonites[14] based on known backbones. One of
steric and electronic factors which influence this reversi- the more recent ligand systems used in homogeneous
À
ble C C bond activation reaction, however, is still lack- catalysis, suchas hydroformylation and Pd-catalyzed
ing. Recent results obtained in the hydrocyanation of C C coupling, is based on the xanthene backbone.
À
various substrates have made clear that phosphorus li- The diphosphine ligands derived from this rigid back-
gands withrigid backbone structures are needed for a se-
bone were first described by Haenel et al.[15] Independ-
lective process.[2] Strongly coordinating p-acceptor li- ently, the group of van Leeuwen focused on varioustran-
gands, however, turned out to be unsuitable because of sition metal-catalyzed reactions applying these li-
a tendency to form catalytically inactive Ni-bis-chelate gands.[16] The proposed strength of this class of ligands
complexes. On the other hand, this undesired side-reac- lies in the combination of a rigid backbone, the large nat-
tion can be suppressed using sterically demanding li- ural bite angle, a limited number of possible coordina-
gands.[3] With this in mind, we decided to explore the tion modes and possibly the favourable interaction of
synthesis of new bulky diphosphonites based on rigid the oxygen in the backbone with the metal center.
xanthene-derived backbones.
Here we report on the synthesis of a new class of steri-
In the past decades, several new classes of phospho- cally constrained diphosphonites[17] (Figure 1) based on
rus-containing ligands have been discovered.[4 Most the xanthene backbone, thereby combining all of the
6]
Adv. Synth. Catal. 2004, 346, 993 1003
DOI: 10.1002/adsc.200303240
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
993

Jarl Ivar van der Vlugt et al.
FULL PAPERS
Figure 1.
Scheme 1. Reaction scheme for the synthesis of compounds 1
and 6: i) n-BuLi, TMEDA, Et2O, À408C, 16 h; ii)
ClP(NEt2)2, pentane, À608C, 16 h; iii) 2-tert-butylphenol (4
equivs.), diglyme, tetrazole, D (45%); iv) 2,2’-dihydroxy-3,3’-
bis(tert-butyl)-5,5’-dimethoxy-1,1’-biphenyl, (4 equivs.) di-
glyme, tetrazole, D (87%).
aforementioned features. We have tested these novel li-
gands in the nickel-catalyzed isomerization of 2-methyl-
3-butenenitrile to 3-pentenenitrile. The results were
compared with those from diphosphine analogues of
the Xantphos ligand family.
Xantphos ligand is observed.[16] The P1 P2 distance is
4.1299(8) ä, slightly larger than found for a xanthene-
based diphosphine. The phosphorus-oxygen bond
lengths are 1.6496(12) 1.6570(12) ä, comparable to
bond lengths in known phosphite systems. The xanthene
backbone is only slightly twisted with an interplanar an-
Results and Discussion
Synthesis of Diphosphonite Ligands
The sterically constrained diphosphonites are obtained gle of 8.33(10)8 whichis in accordance withthe absence
in two reaction steps, starting from the commercially of any stacking of the aromatic rings due to steric con-
available compounds 9,9-dimethylxanthene, phenoxa- gestion.[19]
thiin and various phenols (Scheme 1).[17] As an inter-
mediate precursor the bis-diethylamidophosphonito-
xanthene was prepared.[18] Subsequently, reaction with X-Ray Crystallographic Study of Ni(II) Complex of
the desired phenolic compound yielded the diphosphon- Diphosphonite Ligand 1
ites 1 8 in good yields. Tetrazole was required as proto-
nation agent, in order to force the reaction to go to com- In the Ni-catalyzed hydrocyanation of styrene deriva-
pletion. Diglyme was used as a polar, high-boiling sol- tives, RajanBabu et al. have shown that both the catalyt-
vent, enabling a reaction temperature of 1508C. The re- ic resting state and the active species are Ni(II) com-
action was followed by 31P NMR spectroscopy. Com- plexes bearing only one chelating phosphorus ligand
pounds 1 8 were obtained as white or yellow solids (−monochelate×).[20] Nickel species containing two che-
1
and were fully characterized by H, 13C and 31P NMR lating ligands (−bis chelates×) have to be avoided, since
spectroscopy, mass spectrometry as well as elemental formation of the substrate complex is most likely inhib-
analysis.
ited. We believe that our new, sterically demanding di-
phosphorus ligands offer new possibilities to prevent
the formation of such undesired and catalytically inac-
tive Ni-bis-chelate complexes.
X-Ray Crystallographic Study of Compound 1
In order to study the coordination behaviour of these
We were able to obtain single crystals of compound 1 novel diphosphonites and the influence of the steric bulk
suitable for X-ray analysis by recrystallization from on the complex formation, we have prepared the nickel
hot acetonitrile. Compound 1 crystallizes as an acetoni- complex [NiBr2(1)] by reaction of Ni(dme)Br2 (dme¼
trile solvate in the space group P21/c withfour molecules
dimethoxyethane) with ligand 1 in THF at 708C for
in the unit cell. The molecular structure of 1 is depicted two days. Single crystals, suitable for X-ray analysis,
in Figure 2 and indicates that the phenol groups are bent were obtained for the paramagnetic, purple compound
in an anti-parallel fashion and due to the steric bulk of NiBr2(1), by slow diffusion of pentane into an ether sol-
the substitutents, no p-stacking as in the case of the ution of this complex. The molecular structure of com-
994
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Adv. Synth. Catal. 2004, 346, 993 1003

Sterically Demanding Diphosphonite Ligands
FULL PAPERS
Figure 3. Displacement ellipsoid plot of complex 9, trans-
[NiBr2(1)], drawn at the 50% probability level. All hydrogen
atoms are omitted for clarity. Selected bond lengths (ä), an-
Figure 2. Displacement ellipsoid plot of compound 1, drawn
at the 50% probability level. All hydrogen atoms and aceto-
nitrile solvent molecules are omitted for clarity. Selected
bond lengths (ä) angles, and torsion angles (8): P1 O1
1.6570(12); P1 O2 1.6512(12); P2 O3 1.6503(13); P2 O4
1.6496(12); P1 C1 1.8252(17); P2 C7 1.8290(17); O5 C2
1.381(2); O5 C8 1.378(2); P1 P2 4.1298(8); O1 P1 O2
99.18(6); O3 P2 O4 98.09(7); O1 P1 C1 95.89(7); O2
P1 C1 95.22(7); O3 P2 C7 97.04(7); O4 P2 C7 94.60(7);
C2 O5 C8 119.33(13); C3 C13 C9 110.34(15); C1 C2
C3 C13 173.27(17); C7 C8 C9 C13 175.03(17).
À
À
gles, and torsion angles (8): Ni P1 2.1632(7); Ni P2
À
À
2.1848(7); Ni Br1 2.2886(4); Ni Br2 2.3110(4); P1 O2
1.6020(16); P1 O3 1.6060(17); P1 C1 1.808(2); P2 O4
1.6191(16); P2 O5 1.6167(17); P2 C10 1.814(2); O1 C6
À
1.393(3); O1 C15 1.393(3); Ni O1 2.6137(16); P1 P2
4.2171(9); Br1 Ni Br2 163.073(18); P1 Ni P2 151.81(3);
Br1 Ni P1 94.69(2); Br1 Ni P2 98.56(2); Br2 Ni P1
87.68(2); Br2 Ni P2 86.78(2); O2 P1 O3 96.66(9); O4
À
À
À
À
À
À
À
À
P2 O5 106.55(9); Ni P1 O2 121.41(7); Ni P1 O3
À
À
121.38(6); Ni P2 O4 113.46(7); Ni P2 O5 121.14(7);
À
À
Ni P1 C1 109.00(8); Ni P2 C10 109.24(8); C6 O1 C15
116.87(16); C5 C7 C14 108.25(19); O2 P1 C1 100.09(9);
O3 P1 C1 105.38(10); O4 P2 C10 104.89(10); O5 P2
C10 99.62(10); C1 C6 C5 C7 179.1(2); C10 C15 C14
C7 174.4(2).
plex 9 is shown in Figure 3, together with selected bond
lengths and angles.
The geometry around the Ni-atom in complex 9 is dis-
torted square planar with the phosphonite moieties co-
ordinated in a mutual trans-fashion. This coordination
mode has been observed before for Pd and Rh com-
plexes.[21] The observed bite angle P1 Ni P2, is
151.81(3)8, while the angle Br1 Ni Br2 is
À
À
Nickel(0) Complexes with Diphosphonite Ligands
163.073(18)8. The xanthene backbone is bent, as indicat-
ed by the interplanar angle of 27.65(12)8 between the We further investigated the coordination behaviour of
two aromatic rings. This phenomenon is most likely the new diphosphonites towards Ni(0). Ni(cod)2 was
caused by the substituents on the phenolic moieties. used as a nickel(0) source and reactions withsome of
À
À
The Ni Br and the Ni P bond lengths are in their ex- these ligands were carried out. Table 1 lists the chemical
25]
pected ranges.[22
The intramolecular distance be- shifts observed in the 31P NMR spectrum for the com-
tween the two phosphorus atoms is 4.2171(9) ä, only plexes obtained by reaction of equimolar amounts of li-
slightly larger in comparison to the uncoordinated li- gand and Ni(cod)2 at room temperature. Interestingly, in
À
gand (vide supra). All P O bond lengths are between the cases of ligands 2 and 4 the Ni monochelate com-
1.6020(16) and 1.6191(16) ä. The distance between plexes were indeed formed quantitatively, showing one
the nickel and the oxygen atom in the backbone bridge singlet at approximately d¼160 ppm in the 31P NMR
is found to be 2.6137(16) ä. Together with the fact that spectrum. The more sterically demanding phosphonites
À
À
the four angles P Ni Br are in the range of 86.78(2) to 1, 5, 6 and 8 produced the desired Ni monochelate com-
98.56(2)8, the oxygen can be considered to occupy the plexes upon heating or prolonged reaction times of up to
apical position of a square pyramid. However, any inter- 48 hours.
action between the nickel and the oxygen cannot be pre-
To confirm the presence of the monochelate in the
sumed on the basis of the crystal structure alone. From case of ligand 4, PPh3 was added to Ni(cod)(4) (species
the Cambridge Crystallographic Database,[26] it appears A). PPh3 coordinated to the Ni center without displacing
that nickel complexes with coordinated ether moieties the bidentate phosphonite. However, a trigonal planar
À
show an average Ni O bond lengthof 2.15 ä.
complex containing a single PPh3 ligand and the diphos-
phonite, species B, was not observed. We attribute the
triplet in the 31P NMR spectrum at d¼139.9 ppm (phos-
Adv. Synth. Catal. 2004, 346, 993 1003
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Table 1. 31P NMR chemical shifts of Ni(cod)(PP) complexes
obtained with diphosphonite ligands.
bite angle is 123.18 witha flexibility range of 107 142 8
and the ligand has been shown to be active in the hydro-
formylation of 1-octene and trans-2- and -4-octene. The
complexation behaviour of these ligands with nickel-
precursors was investigated by 31P NMR spectroscopy.
Table 3 summarizes the chemical shifts obtained for
the nickel complexes formed in the presence of these di-
phosphines. They are comparable to reported literature
data on related systems.[3,17a,30]
Ligand
Free ligand
Ni(0) complex
1
2
4
5
6
8
147.8 (s)
148.2 (s)
144.7 (s)
169.4 (s)
168.5 (s)
167.0 (s)
148.5 (s)
158.0 (s)
157.9 (s)
163.4 (s)
164.0 (s)
163.4 (s)
Nickel-Catalyzed Isomerization of 2-Methyl-3-
phonite region) to Ni(PPh3)2(4) (species C), as depicted Butenenitrile with Diphosphonites
in Scheme 2.
Species C is highly symmetrical because the two phos- In current industrial practice, the reaction of butadiene
phorus atoms of the diphosphonite unit remain equiva- withHCN produces initially 2-methyl-3-butenenitrile
lent. While the triplet in the phosphonite region was well (2M3BN) together with the desired linear 3-penteneni-
resolved, the corresponding signal in the phosphine re- trile (3PN) in a kinetically controlled ratio of 30:70
gion appears as a broad singlet at d¼35 ppm, withan in-
[Eq. (1)].[1] This ratio, which is a kinetic rather than a
tegrated ratio of 1:1. The broadness of the singlet is most thermodynamic distribution, depends on the nature of
likely due to rapid exchange with free PPh3.[27] Upon ad- the catalyst and therefore justifies the search for systems
dition of more than 2 equivalents of PPh3, the starting that are able to isomerize the unwanted product 2M3BN
material A quantitatively disappeared. Besides C the to the more useful 3PN, which can then be further con-
formation of a new species was now observed in the verted to adiponitrile. The catalyst systems currently
31P NMR spectrum as a singlet at d¼25.8 ppm. We at- used in industry (e.g., Ni/tris-kresyl phosphite) produce
tribute this resonance to the compound Ni(PPh3)3.[27a] the isomers 3PN and 2M3BN finally after isomerization
For details on chemical shifts see Table 2.
in a ratio which is close to the thermodynamic one of
93:7 (vide infra).
Nickel Complexes with Constrained Diphosphine
Analogues
In order to make comparisons between the coordination
chemistry of the novel diphosphonites and diphosphines
we performed similar reactions withknown bidentate
phosphine systems. In the past decade, Xantphos and
ð1Þ
several of its derivatives have been extensively investi- Scheme 3 illustrates the possible isomerization reac-
gated as ligands in a number of transition metal-cata- tions that can occur. 2M3BN can undergo either un-
lyzed reactions.[28] POP-Xantphos is a derivative which wanted double bond migration-isomerization (E) to
includes a rigid phenoxaphosphine cycle (Figure 4).[29]
Based on molecular modelling calculations, the natural
Scheme 2. Addition of PPh3 to the monochelate complex of
diphosphonite ligand 4.
Figure 4. Representation of ligand POP-Xantphos (left) and
DBP-Xantphos (right).
Table 2. Complexes formed after addition of PPh3 to monochelate complex of diphosphonite ligand 4.
(cod)Ni(4)
157.9 (s)
Ni(PPh3)2(4)
Ni(PPh3)2(4)
35 ppm (br s)
Ni(PPh3)3
25.8 (s)
d
31P{1H} NMR
139.9 (t)
2JPP ¼57 (Hz)
996
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Sterically Demanding Diphosphonite Ligands
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Table 3. 31P{1H} NMR chemical shifts of diphosphine containing complexes.
Ligand
d Ligand
d Monochelate
d Bischelate
DPEphos
À16.3
À17.6
À17.3
À17.5
À69.9
33.1 (s)
26.5 (br s)
26.1 (s)
26.5
not observed
15.5 (br s)
16.0 (br), 13.5 (br)
15.0 (m), 11.7 (m)
Sixantphos
Thixantphos
Xantphos
11.1 (m, br), 9.8 (m, br)
2
POP-Xantphos
À26.7 (m, JPÀ ¼63 Hz)
P
2
À29.8 (m, JPÀ ¼63 Hz)
P
the conjugated internal alkene 2-methyl-2-butenenitrile (Ni(O) precursor. Furthermore, the effect of additional
(2M2BN) or skeletal isomerization (D) to the desired Lewis acid was studied. Selectivities to 2M2BN and 2PN
linear 3PN. The latter reaction involves a reversible were not independently determined; selectivities refer
À
C CN bond activation reaction at the metal center. Sub- to the GC area percent of 3PN as a percentage of all ob-
sequent double bond isomerization (F) of 3PN leads to served products. Table 4 summarizes the results of cata-
the likewise unwanted thermodynamically favored 2- lytic tests performed with these ligands in the absence of
pentenenitrile (2PN). Furthermore, 3PN can also under- Lewis acid and at two different preformation times, at
go kinetically controlled isomerization (G) to the termi- room temperature.
nal 4-pentenenitrile (4PN), which could lead to adiponi-
Nickel complexes containing either diphosphonite 2
trile under hydrocyanation conditions. Coordination of or 4 give close to quantitative conversion and selectivi-
a Lewis acid to the nitrile function has been proposed ties of up to 74% for 3PN. Ligands 2 and 4 are the least
to explain the observed preference.[31]
sterically hindered ligands from the newly developed di-
Isomerization reactions of unsaturated substrates phosphonite class, since the tert-butyl substituents are at
with Ni(0) complexes based on monodentate phosphites the meta positions of the phenyl moiety. The complexa-
as well as bidentate phosphines have been extensively tion withNi(cod) 2 is almost instantaneous at room tem-
investigated.[32,33] This reaction is normally facilitated perature withthe compounds 2 and 4, resulting in mono-
by the use of Lewis acids such as ZnCl2, BPh3 or AlCl3. chelate complexes. All other sterically demanding li-
The isomerization leads to a mixture of 3PN:2M3BN gands show little if any activity, probably due to insuffi-
in the thermodynamic ratio of 93:7. We are currently ex- cient preformation, yielding a low concentration of the
ploring a further account on the reversibility of substrate active nickel catalyst. The catalytic system comprising li-
coordination to such nickel-complexes and will show the gand 1 however, does yield 3PN in very good selectivity
À
implications for these C C bond activation/formation (92%). In order to promote the formation of the active
reactions in a forthcoming communication.[34]
nickel complex, more drastic preformation conditions
Given the promising X-ray crystallographic study on were applied: The preformation time was increased to
the [NiBr2(1)] complex as well as the NMR study on one hour after which the reaction temperature was set
the formation of the monochelate Ni(cod)(ligand) com- at 908C.
plexes described, we were interested in the application
of these novel diphosphonite ligands in the nickel-cata- most active nickel catalysts, withalmost quantitative
lyzed isomerization of unsaturated nitriles, with2M3BN conversion, although selectivities are slightly reduced,
as an important substrate in the Ni-catalyzed hydrocya- due to consecutive isomerization to the inactive 2PN.
nation of butadiene. The highest selectivity is obtained with the xanthene
Once again, the least bulky ligands 2 and 4 give the
The newly designed ligands were tested in the isomer- backbone (61%) versus the phenoxathiin backbone
ization of 2M3BN in toluene at 908C, using Ni(cod)2 as (51%). The catalysts formed with either ligand 5 or 6
benefit from the longer preformation time and conse-
quently, the conversion increases significantly from
about 10% (vide supra) to 35%, while selectivities of
up to 85% are observed.
We also investigated the effect of Lewis acids on the
isomerization of 2M3BN withthe same nickel-based
catalytic systems, adding AlCl3 to the reaction mixture.
The activities of the nickel catalysts derived from ligand
2 or 4 dropped only slightly, due to the presence of po-
tentially coordinating Lewis acid. The selectivity to the
linear product 3PN, however, decreased almost to
zero, while formation of 2PN was favoured and this
turned out to be the main product after one hour of re-
Scheme 3. Isomerization scheme for 2M3BN.
Adv. Synth. Catal. 2004, 346, 993 1003
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997

Jarl Ivar van der Vlugt et al.
Selectivity for 3PN [%][b]
FULL PAPERS
Table 4. Isomerization of 2M3BN in the absence of Lewis acid at different preformation times.[a]
Ligand
Preformation time [min]
Conversion [%][b]
Yield of 3PN [%][b]
1
2
2
4
4
5
5
6
6
60
60
15
60
15
15
60
15
60
15
97
97
98
98
10
36
9
14
72
59
55
50
9
29
8
29
92
74
61
57
51
82
79
89
85
34
[a]
Reaction conditions: 2 mL toluene, Ni(cod)2 (20 mg, 72.7 mmol), Ni/L/S¼1/1/40, T¼908C, t¼1 h .
[b]
Determined by GC.
action. This can be attributed to an acceleration of this phos. The difference in selectivity could be due to the
consecutive double bond isomerization reaction owing slightly more electron-withdrawing character of the
to the presence of the Lewis acid, meaning that 3PN is phosphorus heterocycle. The isomerization with DBP-
formed but subsequently isomerized to the more stable Xantphos yielded a high proportion of the thermody-
thermodynamic product.
namic product 2PN. Because of the irreversible forma-
The other more sterically hindered diphosphonite li- tion of stable alkylnickel complexes withthis internal al-
gands do not react withAlCl at room temperature, kene, the catalyst becomes inactive, most likely causing
3
but in view of the lower activity of their nickel com- the conversion to be low.[35] In experiments carried out
plexes in 2M3BN isomerization, possible Lewis acid in- with t-Bu-Xantphos and POP-Xantphos, the proportion
teraction at reaction temperature (908C) cannot be of 2PN is quite high compared to 2M2BN. Because for-
ruled out.
mation of 2PN results from 3PN double bond isomeriza-
tion, limiting the reaction time, and thus conversion,
may contribute to optimize the selectivity towards 3PN.
Comparative reactions were carried out withXant-
phos, as a good conversion (98%) and a good selectivity
(75%) were obtained at 908C after 90 minutes (Table 6).
Reducing the reaction time from 90 to 15 minutes led
Nickel-Catalyzed Isomerization of 2-Methyl-3-
Butenenitrile with Diphosphine Ligands
We explored the isomerization capabilities of several Ni
complexes with some xanthene derived diphosphine li- to lower conversion (from almost 98% to nearly 67%)
gands [POP-Xantphos, DBP-Xantphos[29] and 2,7-(di- without much effect on the selectivity. In the same
tert-butyl)Xantphos] as well, for which the results are way, reducing the reaction temperature from 908C to
listed in Table 5. As was observed in preliminary 608C lowered the conversion to 50% as expected, but
31P NMR studies, these ligands readily form bischelates. also the selectivity diminished (to 39%). To explain
The substrate was hence directly added to the catalyst.
this result, it seems plausible that the temperature effect
The most flexible ligand (t-Bu-Xantphos) affords the on the rate of double bond isomerization is different
highest conversion (98%), whereas the lowest conver- than for the isomerization of the internal alkene. The
sion (31%) is obtained withteh most rigid ligand
rate of this latter type of isomerization could greatly
(DBP-Xantphos). The best selectivity (71%) and high benefit from a set increase in temperature, whereas
conversion (89%), however, is obtained with POP-Xant- the double-bond isomerization would only slightly rise.
Table 5. Isomerization of 2M3BN using POP-Xantphos type ligands in absence of Lewis Acid.[a]
Ligand
Conversion
[%][b]
Yield of
Selectivity
Selectivity
Selectivity
3PN [%][b]
for 3PN [%][b]
for 2M2BN [%][b]
for 2PN [%][b]
DBP-Xantphos
t-Bu-Xantphos
POP-Xantphos
30.6
97.9
89.0
9.9
63.3
63.5
32.5
64.7
71.4
7.9
7.9
3.6
59.6
27.6
25.1
[a]
Reaction conditions: Ni(cod)2 (9 mg, 32.7 mmol) in 1 mL toluene, T¼908C, t¼1 h; Ni/L/S: 1/0.5/40; no catalyst preforma-
tion.
[b]
Determined by GC.
998
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 993 1003

Sterically Demanding Diphosphonite Ligands
FULL PAPERS
Table 6. Isomerization of 2M3BN using Xantphos in the absence of Lewis acid.[a]
Ligand
t [min]
T [ 8C]
Conversion
[%][b]
Yield of
Selectivity
Selectivity
Selectivity
3PN [%][b]
for 3PN [%][b]
for 2M2BN [%][b]
for 2PN [%][b]
Xantphos
Xantphos
Xantphos
15
90
90
90
90
60
66.7
97.5
50.8
48.2
73.1
19.8
72.3
75.0
39.0
7.9
7.2
10.9
19.9
17.9
50.1
{a}
Reaction conditions: Ni(cod)2 (9 mg, 32.7 mmol) in 1 mL toluene; Ni/Xantphos/S/: 1/1/40/1.05; preformation time 10 min.
Determined by GC.
[b]
2,2’-Dihydroxy-3,3’-di-tert-butyl-5,5’-dimethoxy-1,1’-
biphenyl (A)
Conclusions
In summary, we have reported on the synthesis of a nov-
el class of sterically constrained diphosphonite com-
pounds 1 8 based on rigid backbones. The coordination
behaviour of these ligands towards Ni(II) and Ni(0) has
A solution of 3-tert-butyl-4-hydroxyanisole (10 g) in methanol
(300 mL) was prepared and a solution of KOH (11.07 g) and
K3Fe(CN)6 (18.3 g) in water (300 mL) was added dropwise
over 1 hat room temperature. The mixture was stirred for
been studied by means of NMR spectroscopy and is 2 hours before the addition of 200 mL of water. The suspension
was extracted with 500 mL of ethyl acetate twice. The aqueous
solution was extracted with150 mL of ether and the organic
phases were combined and washed with 200 mL of saturated
brine. The organic phase was dried over Na2SO4. Removal of
the solvents under vacuum afforded a light brown solid. Wash-
ing with n-hexane resulted in an off-white powder; yield:
compared with that of related diphosphine ligands. We
observed sole formation of monochelate complexes in
the case of the diphosphonite ligands. The molecular
structure of the Ni(II) complex [NiBr2(1)] was elucidat-
ed by X-ray crystallography. In the nickel-catalyzed iso-
merization of 2-methyl-3-butenenitrile, these ligands
show good selectivities towards the desired linear 3-pen-
tenenitrile. A more detailed study on the influence of
the different reaction parameters is currently underway.
Recently we finished a study on the coordination behav-
iour of these diphosphonites to various transition metals
other than nickel[21] as well as on the application of the
diphosphonites in the rhodium-catalyzed hydroformy-
lation of higher alkenes.[36]
1
19.60 g (98%). H NMR (400 MHz, CD2Cl2): d¼6.96 (d, 2H,
J¼3.2 Hz), 6.62 (d, 2H, J¼3.2 Hz), 4.64 (s, 2H, OH), 3.77 (s,
6H, OMe), 1.43 (s, 18H, t-Bu); 13C NMR (100 MHz, C6D6):
d¼153.4, 146.1, 139.2, 123.5, 115.5, 112.0, 56.0, 35.4, 29.7;
anal. calcd. for C22H30O4: C 73.4, H 8.4; found: C 73.9, H 7.8.
2,2’-Dihydroxy-3,3,5,5’-tetra-tert-butyl-1,1’-diphenyl
(B)
This compound was synthesized in a similar manner as describ-
ed for compound A, starting from 11.29 g of 2,4-di-tert-butyl-
phenol; yield: 21.34 g (95%); off-white powder; 1H NMR
(400 MHz, CD2Cl2): d¼7.56 (d, 2H, J¼2.7 Hz), 7.17 (d, 2H,
J¼2.7 Hz), 5.17 (s, 2H, OH), 1.54 (s, 18H, t-Bu), 1.21 (s, 18H,
t-Bu); 13C NMR (75 MHz, C6D6): d¼150.3, 143.3, 136.7,
125.7, 124.8, 123.1, 35.3, 34.3, 31.5, 29.7; anal. calcd. for C28
H42O2: C 81.9, H 10.3; found: C 81.9, H 9.9.
Experimental Section
General
All chemicals were purchased from Aldrich Chemical Co., Ac-
ros or Merck and used as received. All preparations were car-
ried out under an argon atmosphere using standard Schlenk
techniques. Solvents were distilled from sodium/benzophe-
none (THF, ether, toluene, toluene-d8, hexanes and ethanol)
or calcium hydride (CH2Cl2 and CDCl3) prior to use. All glass-
ware was dried by heating under vacuum. The NMR spectra
were recorded on a Varian Gemini 300 MHz or Varian Mercu-
ry 400 MHz spectrometer withboththe 31P and 13C spectra be-
4,5-(Bis[bis-diethylamido]phosphonito)-9,9-
dimethylxanthene (C)
9,9-Dimethylxanthene (3.00 g, 14.3 mmol) and TMEDA
(4.14 g, 35.7 mmol) were dissolved in 50 mL of diethyl ether
and cooled to À408C. n-BuLi (14.3 mL of a 2.5 M solution in
hexanes, 35.7 mmol) was added via a syringe over a period of
10 min. The mixture was allowed to warm to up to room tem-
perature and was stirred overnight. Subsequently, ClP(NEt2)2
(6.32 g, 30.0 mmol) was dissolved in 30 mL of pentane and
cooled to À608C. The dilithioxanthene solution was slowly
added via a cannula. Subsequently, the reaction mixture was al-
lowed to warm to room temperature and stirred overnight. Sol-
vents were removed under vacuum to leave a yellow solid.
15 mL pentane were added and the suspension was filtered.
Remaining TMEDA was removed by stripping three times
with10 mL of toluene. Upon cooling to À258C colourless crys-
1
ing measured in the H decoupled mode. Chemical shifts are
given in ppm referenced to solvent (1H, 13C) or an 85% solution
of H3PO4 (31P). GC were recorded on a Shimadzu 17A Chro-
matographequipped witha Cp-wax 58 CB column. Elemental
analysis was performed on a Perkin Elmer 2400, Series II
CHNS/O Analyzer. Mass spectrometry (MALDI-TOF) was
performed on a Voyager-DETMPro (Perspective Biosystems)
and BiospectrometryTM Workstation. NiBr2(dimethoxy-
ethane)[20] and Ni(cod)2[37] were synthesized according to liter-
ature procedures.
Adv. Synth. Catal. 2004, 346, 993 1003
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Jarl Ivar van der Vlugt et al.
FULL PAPERS
1
tals were obtained; yield: 5.03 g (63%); H NMR (300 MHz,
C6D6): d¼7.60 (d, 2H, J¼7.5 Hz), 7.22 (d, 2H, J¼7.5 Hz),
7.05 (t, 2H, J¼7.5 Hz), 3.19 (m, 16H, CH2), 1.55 (s, 6H, CH3),
1.06 (t, 12H, CH3, J¼7.1 Hz); 13C NMR (75 MHz, C6D6): d¼
151.0, 130.6, 130.1, 129.5, 126.0, 122.4, 43.3 (CH2), 33.9
(CMe2), 32.7 (CMe2), 14.5 (CH3); 31P{1H} NMR (162 MHz, C6
D6): d¼92.3 (s); anal. calcd for C31H51N4OP2: C 66.6, H 9.4, N
10.0; found: C 66.3, H 9.3, N 9.9.
4,6-Bis{di[(2-tert-butyl)phenyl]phosphonito}-2,8-
dimethylphenoxathiin (3)
Starting from 2.30 g (5.20 mmol) of D and 3.12 g (20.8 mmol)
of 2-tert-butylphenol, compound 3 was obtained as a white
powder in analogy to the synthetic procedure described for li-
gand 1; yield: 1.61 g (35%); 1H NMR (400 MHz, C6D6): d¼7.87
1
2
(s, 2H), 7.26 (m, 2H, J¼2 Hz), 7.22 (dd, 1H, J¼7.6 Hz, J¼
1
2
1.6 Hz), 7.18 (dd, 2H, J¼2.8 Hz, J¼1.2 Hz), 7.18 (d, 2H,
1
2
J¼9.2 Hz), 6.93 (td, 1H, J¼7.6 Hz, J¼2 Hz), 6.81 (dd, 4H,
2
1J¼2.8 Hz, J¼1.2 Hz), 6.81 (d, 4H, J¼9.2 Hz), 6.67 (d, 1H,
4,6-(Bis[bis-diethylamido]phosphonito)-2,8-
dimethylphenoxathiin (D)
J¼1.2 Hz), 6.50 (dd, 1H, J1 ¼7.6 Hz, J2 ¼1.2 Hz), 1.47 (s, 6H,
CH3), 1.34 (s, 36H, t-Bu); 13C NMR (100 MHz, C6D6): d¼
155.5, 154.7, 139.4, 134.8, 130.2, 129.6, 128.1, 127.9, 126.9,
123.0, 120.0, 118.9, 118.9, 116.7, 34.7, 30.1, 29.7; 31P{1H} NMR
(162 MHz, C6D6): d¼145.8 (s); MS (MaldiTOF): m/z (%)¼
917.49 (100) [Mþ2O]þ; a correct microanalysis could not be
obtained.
This product was synthesized in a similar manner as described
for compound C, starting from 3.26 g (14.2 mmol) of 2,8-dime-
thylphenoxathiin. Yield: 3.55 g (43%); light yellow crystals;
1H NMR (300 MHz, C6D6): d¼7.28 (s, 2H), 6.74 (s, 2H), 3.21
(m, 16H, CH2), 2.09 (s, 6H, CH3), 1.13 (t, 12H, CH2CH3, J¼
7.0 Hz); 13C NMR (75 MHz, C6D6): d¼151.0, 132.8, 131.0,
127.7, 127.1, 118.9, 43.5 (CH2), 20.7 (CH3), 14.8 (CH2CH3);
31P{1H} NMR (162 MHz, C6D6): d¼90.4 (s).
4,6-Bis{di[(3,5-di-tert-butyl)phenyl]phosphonito}-2,8-
dimethylphenoxathiin (4)
Starting from 2.00 g (3.47 mmol) of D and 2.85 g (13.87 mmol)
of 3.5-di-tert-butylphenol, compound 4 was obtained as a white
powder in analogy to the synthetic procedure described for li-
gand 1; yield: 2.08 g (54%); 1H NMR (400 MHz, C6D6): d¼7.75
(s, br, 2H), 7.32 (d, 8H, J¼1.4 Hz), 7.16 (t, 4H, J¼1.4 Hz), 6.61
(d, 2H, J¼1.6 Hz) (16 aromatic protons), 1.22 (s, 6H, CH3),
1.16 (s, 72 H, t-Bu); 13C NMR (100 MHz, C6D6): d¼155.62,
152.30, 134.3, 129.77, 129.72, 128.40, 125.52, 119.8, 117.39,
115.41, 115.37, 115.33, 110.1, 34.82, 31.39, 20.19; 31P{1H} NMR
(162 MHz, C6D6): d 144.7 (s); anal. calcd. for C70H94O5P2S: C
75.8, H 8.5; found: C 75.8, H 8.1; MS (MaldiTOF): m/z (%)¼
1141.91 (100) [Mþ2O]þ.
4,5-Bis{di[(2-tert-butyl)phenyl]phosphonito}-9,9-
dimethylxanthene (1)
Both
A (2.11 g, 3.58 mmol), 2-tert-butylphenol (2.15 g,
14.3 mmol) and 2 mol % of tetrazole were dissolved in 20 mL
of di(2-methoxyethyl) ether. The reaction mixture was heated
to 1358C for 3 days, while the diethylamine formed during re-
action was removed under vacuum twice a day. Solvent was re-
moved under vacuum to give a light yellow solid. It was dis-
solved in 10 mL of dichloromethane and after layering of the
solution with 10 ml of ethanol a pure white powder precipitat-
1
ed; yield: 1.40 g (45%); H NMR (400 MHz, C6D6): d¼8.15
1
2
1
2
(dd, 2H, J¼7.2 Hz, J¼1.2 Hz), 7.26 (dd, 4H, J¼8 Hz, J¼
1.6 Hz), 7.17 (dd, 2H, J¼8 Hz, 2J¼1.6 Hz), 7.14 (d, 4H, 1J¼
1
4,5-Bis{dibenzo[d, f]-2,4,3’,5’-tetra-tert-butyl-
[1,3,2]dioxaphosphepino}-9,9-dimethylxanthene (5)
8 Hz, 2J¼2 Hz), 7.0 (t, 2H, 1J¼7.6 Hz), 6.86 (t, 4H, 1J¼8 Hz,
2J¼2.4 Hz), 6.81 (t, 4H, J¼7.6 Hz, J¼1.6 Hz), 1.35 (s, 6H,
CH3), 1.32 (s, 36H, t-Bu); 13C NMR (100 MHz, C6D6): d¼
155.3, 139.4, 130.5, 129.0, 128.7, 127.4, 127.1, 124.1, 122.7,
119.2, 119.1, 118.9, 34.7, 31.4, 30.1; 31P{1H} NMR (162 MHz,
C6D6): d¼147.8 (s); anal. calcd. for C55H64O5P2: C 76.2, H 7.4;
found: C 76.3, H 7.4. MS (MaldiTOF): m/z (%)¼899.45 (100)
[Mþ2O]þ.
1
2
Starting from 3.52 g (6.30 mmol) of C and 5.17 g (12.60 mmol)
of B, compound 5 was obtained as a white powder in analogy to
the synthetic procedure described for ligand 1. The reaction
1
time was increased to 4 days; yield: 5.82 g (85%); H NMR
¼
(400 MHz, C6D6): d¼7.62 (d, 2H, J 6.8 Hz), 7.50 (d, 1H,
J¼2 Hz), 7.48 (d, 3H, J¼2.4 Hz), 7.35 (d, 3H, J¼2.4 Hz),
1
2
7.23 (d, 1H, J¼2.4 Hz), 7.04 (dd, 2H, J¼2 Hz, J¼1.5 Hz),
6.62 (t, 2H, J¼7.6 Hz), 1.55 (s, 6H, CH3), 1.35 (s, 36H, t-Bu),
1.27 (s, 36H, t-Bu); 13C NMR (100 MHz, C6D6): d¼146.27,
140.74, 134.61, 129.78, 128.73, 126.84, 124.35, 123.18, 35.58 (C
t-Bu front), 35.37 (CCH3), 34.49 (C t-Bu back), 31.47 (CH3 t-
Bu front), 31.35 (CH3 t-Bu back), 29.95 (CCH3);
31P{1H} NMR (162 MHz, C6D6): d¼169.0 (s); anal. calcd. for
C71H92O5P2: C 78.4, H 8.5; found: C 78.1, H 8.2; MS (Maldi-
TOF): m/z (%)¼1119.66 (100) [Mþ2O]þ.
4,5-(Bis{di[(3,5-di-tert-butyl)phenyl]phosphonito}-9,9-
dimethylxanthene (2)
Starting from C (4.32 g, 7.73 mmol) and 3,5-bis(tert-butyl)phe-
nol (6.35 g, 30.9 mmol), compound 2 was obtained as a white
powder in analogy to the synthetic procedure described for li-
gand 1; yield: 4.57 g (54%); 1H NMR (400 MHz, C6D6): d¼8.15
(dd, 2H, J¼7.6 Hz, J¼1.2 Hz), 7.32 (d, 8H, J¼1.6 Hz), 7.15 (t,
4H, J¼1.6 Hz), 7.07 (dd, 6H, J¼7.6 Hz, J¼1.6 Hz), 6.92 (t,
2H, J¼7.6 Hz), 1.25 (s, 6H, CH3), 1.14 (s, 72H, t-Bu);
13C NMR (100 MHz, C6D6): d¼155.8, 152.2, 130.0, 129.5,
128.5, 128.3, 117.3, 115.5, 115.4, 34.8, 31.8, 31.4; 31P{1H} NMR
(162 MHz, C6D6): d¼148.4 (s); anal. calcd. for C71H96O5P2: C
78.1, H 8.9; found: C 78.0, H 8.6; MS (MaldiTOF): m/z (%)¼
1123.72 (100) [Mþ2O]þ.
4,5-Bis{dibenzo[d, f]-2,5’-di-tert-butyl-4,3’-dimethoxy-
[1,3,2]dioxaphosphepino}-9,9-dimethylxanthene (6)
Starting from 3.19 g (5.72 mmol) of C and 4.10 g (11.44 mmol)
of A, compound 6 was obtained as a white powder in analogy to
the synthetic procedure described for ligand 5; yield: 4.89 g
1000
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Adv. Synth. Catal. 2004, 346, 993 1003

Sterically Demanding Diphosphonite Ligands
FULL PAPERS
(87%); 1H NMR (400 MHz, C6D6): d¼7.6 (d, 1H, J¼7.3 Hz),
NiBr2(1), Complex 9
1
2
7.1 (dd, 1H, J¼1.5 Hz, J¼6.2 Hz), 7.04 (d, 2H, J¼2.9 Hz),
7.02 (d, 2H, J¼2.9 Hz), 7.0 (m, 1H), 6.7 (d, 2H, J¼2.9 Hz),
6.68 (t, 2H, J¼7.7 Hz), 6.65 (d, 2H, J¼2.9 Hz), 6.61 (d, 1H,
J¼2.9 Hz) (14 aromatic protons), 3.4 (s, 12H, OCH3), 1.5 (s,
18H, t-Bu), 1.22 (s, 18H, t-Bu); 13C NMR (100 MHz, C6D6):
d¼156.2, 154.0, 146.3, 143.8, 142.8, 139.8, 135.3, 129.9, 129.8,
128.7, 127.2, 123.3, 114.8, 114.6, 113.3, 112.8, 55.1 (OCH3),
55.0 (OCH3), 35.4 (C t-Bu), 35.2 (C t-Bu), 31.1 (CH3 t-Bu),
30.6 (CH3), 29.77 (CH3 t-Bu); 31P{1H} NMR (162 MHz,
C6D6): d¼168.3 (s); anal. calcd. for C47H44O13P2: C 64.2,
H 5.1; found: C 63.8, H 4.9; MS (MaldiTOF): m/z (%)¼
1015.63 (100) [Mþ2O]þ.
Ligand 1 (500 mg, 0.716 mmol) was dissolved in 40 mL of THF.
To this solution was added NiBr2(dme) (332 mg, 1.074 mmol)
in 200 mL of THF, giving a clear purple reaction mixture that
was stirred for 2 days at 708C. The mixture was then cooled
to room temperature and the solvent was removed under vac-
uum. The remaining solid was dissolved in 10 mL of CH2Cl2
and filtered by cannula to remove any residual solids. The
paramagnetic complex was obtained as crystals by layering
withpentane (1:1). Crystals of the paramagnetic complex,
suitable for X-ray analysis, were obtained by slow diffusion
of pentane into an Et2O solution of complex 9; anal. calcd.
for Br2C55H64NiO5P2: C 60.85, H 5.94; found: C 60.73, H 5.82.
X-Ray Diffraction: Crystal Structures of 1 and 9
4,6-Bis{dibenzo[d, f]-2,4,3’,5’-tetra-tert-butyl-
[1,3,2]dioxaphosphepino}-2,8-dimethylphenoxathiin
(7)
X-ray intensities were collected on a Nonius KappaCCD dif-
fractometer withrotating anode ( l¼0.71073 ä, graphite mon-
ochromator) at a temperature of 150(2) K. The structures were
[38]
Starting from 3.52 g (6.30 mmol) of D and 5.17 g (12.60 mmol)
of B, compound 7 was obtained as a white powder in analogy to
the synthetic procedure described for ligand 5; yield: 5.82 g
(83%); 1H NMR (400 MHz, C6D6): d¼7.64 (d, 1H, 1J¼
solved withdirect methods (SHELXS97,
compound 1) or
automated Patterson methods (DIRDIF99,[39] compound 9)
[40]
and refined withSHELXL97
against F2 of all reflections.
Non-hydrogen atoms were refined freely with anisotropic dis-
placement parameters; hydrogen atoms were refined as rigid
groups. Compound 1 contains an acetonitrile solvent molecule
in the asymmetric unit, which was refined with an occupancy of
1
1
6.4 Hz), 7.57 (d, 1H, J¼2.8 Hz), 7.53 (d, 2H, J¼2.4 Hz),
7.51 (d, 2H, 1J¼2.4 Hz), 7.39 (d, 2H, 1J¼2.4 Hz), 7.33 (d, 1H,
1J¼2.4 Hz), 7.17 (d, 2H, 1J¼2.4 Hz), 7.03 (dd, 1H, 1J¼
7.6 Hz, 2J¼1.6 Hz) (12 aromatic protons), 1.52 (s, 18H, t-Bu),
1.50 (s, 6H, CH3), 1.37 (s, 18H, t-Bu), 1.29 (s, 18H, t-Bu), 1.19
(s, 18H, t-Bu). 13C NMR (100 MHz, C6D6): d¼146.27, 140.74,
134.61, 129.78, 128.73, 126.84, 124.35, 123.18, 35.58 (C t-Bu
front), 35.37 (CCH3), 34.49 (C t-Bu), 31.47 (CH3 t-Bu), 31.35
(t-Bu), 29.95 (CCH3); 31P{1H} NMR (162 MHz, C6D6): d¼
169.0 (s); anal. calcd. for C70H90O5P2S: C 78.4, H 8.5; found: C
78.6, H 8.4. MS (MaldiTOF): m/z (%)¼1137.70 (100) [Mþ
2O]þ.
0.5. Illustrations, structure calculations, and structure checking
[41]
were performed withthe PLATON package.
tallographic details are given in Table 7.
Further crys-
CCDC-226738 (compound 1) and -226739 (compound 9)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge at www.ccdc.cam.
ac.uk/conts/retrieving.html [or from the Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB21EZ,
UK; fax: (internat.) þ44-1223/336-033; E-mail: deposit@ccdc.
cam.ac.uk].
Nickel-Catalyzed Isomerization of 2M3BN
4,6-Bis{dibenzo[d, f]-2,5’-di-tert-butyl-4,3’-dimethoxy-
[1,3,2]dioxaphosphepino}-2,8-dimethylphenoxathiin
(8)
Catalyst preformation: A 10 mg/mL solution of Ni(cod)2 in tol-
uene was freshly prepared and 2 mL thereof were added to 1.05
molar equivalents of the appropriate ligand in a 10 mL Schlenk
tube. The reaction mixture was stirred at room temperature for
15 min and 60 min, respectively, yielding an orange solution.
Isomerization: Under stirring 2M3BN (282 mL, 40 equivs.)
was added by Eppendorf pipette to the catalyst solution. In
those cases where an additional Lewis acid was used, a solution
of AlCl3 (280 mL of a 260 mM solution in CH3CN, 1.05 equivs.)
was added. The reaction mixture was heated to 908C for one
hour. After cooling by means of an ice-bath, an aliquot of the
solution was withdrawn for GC analysis.
Starting from 2.12 g (3.67 mmol) of D and 2.63 g (7.34 mmol)
of A, compound 8 was obtained as a white powder in analogy
to the synthetic procedure described for ligand 5; yield: 2.24 g
(61%); 1H NMR (400 MHz, C6D6): d¼7.59 (dd, 1H, 1J¼
3.2 Hz, 2J¼5.2 Hz), 7.31 (d, 1H, 1J¼1.6 Hz), 7.14 (d, 1H, 1J¼
1
1
2.8 Hz), 7.06 (d, 2H, J¼3.2 Hz) , 6.89 (d, 1H, J¼3.2 Hz),
6.74 (d, 2H, 1J¼3.2 Hz), 6.69 (d, 1H, 1J¼3.2 Hz), 6.60 (d, 1H,
1J¼3.2 Hz), 6.56 (d, 2H, 1J¼2.8 Hz), 3.31 (s, 6H, OCH3), 3.29
(s, 6H, OCH3), 1.46 (s, 18H, t-Bu), 1.42 (s, 6H, CH3), 1.35 (s,
18H, t-Bu); 13C NMR (100 MHz, C6D6): d¼167.40, 156.27,
154.81, 154.02, 146.30, 143.91, 143.01, 141.77, 140.96, 139.41,
135.20, 133.96, 133.23, 132.67, 130.64, 130.28, 129.14, 128.92,
128.28, 128.13, 127.97, 127.96, 127.88, 127.73, 127.65, 125.04,
119.26, 115.51, 115.10, 114.79, 114.68, 114.50, 113.55, 113.53,
113.47, 112.16, 67.88 (OCH3), 55.00 (OCH3), 39.04 (C t-Bu),
31.29 (C t-Bu), 30.71 (CH3), 30.66 (CH3 t-Bu), 29.65 (CH3 t-
Bu); 31P{1H} NMR (162 MHz, C6D6): d¼166.9 (s); MS (Maldi-
TOF): m/z (%)¼1033.37 (100%) [Mþ2O]þ; a correct micro-
analysis could not be obtained.
Acknowledgements
This work was financially supported by the Eindhoven Univer-
sity of Technology, the National Research School Combination
for Catalysis (NRSCC) and BASF AG and in part (A.M.M.,
M.L. and A.L.S.) by the Netherlands Organisation for Scientific
Research (NWO).
Adv. Synth. Catal. 2004, 346, 993 1003
asc.wiley-vch.de
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1001

Jarl Ivar van der Vlugt et al.
FULL PAPERS
Table 7. Selected crystallographic data for ligand 1 and complex 9.
1
9
formula
C55H64O5P2 ¥0.5C2H3N
887.53
colorless
C55H64Br2NiO5P2
1085.53
blue
formula weight
crystal colour
crystal size [mm3]
crystal system
space group
a [ä]
0.48Â0.12Â0.09
monoclinic
P21/c (no. 14)
10.9055(1)
26.3694(3)
20.0433(2)
118.306(1)
5074.68(10)
4
0.36Â0.18Â0.09
monoclinic
P21/c (no. 14)
19.2527(2)
12.7521(1)
21.5201(2)
103.2033(5)
5143.79(8)
4
b [ä]
c [ä]
b [deg.]
V [ä3]
Z
Dcalcd. [g/cm3]
1.162
0.132
1.402
2.039
m [mmÀ1
]
abs. corr.
none
PLATON (MULABS)
0.67 0.84
0.61
transmission range
(sin q/l)max [äÀ1
]
0.65
refl. collected/unique
parameters/restraints
R1/wR2 [I>2s(I)]
R1/wR2 [all refl.]
GoF
54146/11570
601/0
0.0479/0.1048
0.0858/0.1196
1.020
55037/9581
600/0
0.0320/0.0704
0.0484/0.0763
1.019
res. Density [e/ä3]
À0.34/0.34
À0.52/0.59
R1 ¼Sj jFo j jFc j j/S jFo j
2
2
wR2 ¼{S [w(Fo Fc2)2]/S [w(Fo )2]}1/2
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