Large P-P distance diphosphines and their monophosphine analogues as ligands in the palladium-catalyzed telomerization of 1,3-butadiene and methanol

Article abstract of DOI:10.1021/om100980m

The potential of diphosphines based on a dibenzodioxocin or benzofurobenzofuran backbone possessing large P-P distances was studied for the selective telomerization of 1,3-butadiene with methanol under commercially relevant process conditions to obtain 1-

Full text of DOI:10.1021/om100980m

792 Organometallics 2011, 30, 792–799
DOI: 10.1021/om100980m
Large P-P Distance Diphosphines and Their Monophosphine Analogues
as Ligands in the Palladium-Catalyzed Telomerization of 1,3-Butadiene
and Methanol
†
Mathieu J.-L. Tschan, Josep-Maria Lopez-Valbuena, Zoraida Freixa, Helene Launay,
†
†
‡
ꢀ
ꢀ ꢁ
Henk Hagen,‡ Jordi Benet-Buchholz,† and Piet W. N. M. van Leeuwen*,†
†Institute of Chemical Research of Catalonia (ICIQ), Avinguda Paısos Catalans 16, 43007 Tarragona, Spain,
¨
and ‡Dow Benelux BV, Herbert H. Dowweg 5, P.O. Box 48, 4530 AA Terneuzen, The Netherlands
Received October 13, 2010
The potential of diphosphines based on a dibenzodioxocin or benzofurobenzofuran backbone
possessing large P-P distances was studied for the selective telomerization of 1,3-butadiene with
methanol under commercially relevant process conditions to obtain 1-methoxyocta-2,7-diene
(1-MOD). They were found to act as monophosphines. New bulky monophosphine analogues of
the same backbone and ferrocene were also evaluated. Several ligands showed improved selectivity
and yield compared to the benchmark ligand PPh3 and monoxantphos. Especially 1,6-bis-
(diphenylphosphino)-5a,10b-dihydro-5a,10b-dimethyl-3,8-dimethylbenzofuro[3,2-b]benzofuran (3)
and, 2,10-di-tert-butyl-4-diphenylphosphino-6,12-methano-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin (7),
a diphosphine and a monophosphine, respectively, stand out as excellent ligands in terms of yield,
selectivity, and stability.
Introduction
Currently, the catalytic system used by Dow is composed
of Pd/PPh3. The reaction leads to the formation of 1-meth-
oxy-2,7-octadiene (1-MOD) (Scheme 2). Main byproducts
of the reaction are 3-methoxy-1,7-octadiene (3-MOD) and
1,3,7-octatriene (OCT).3 The control of the selectivity in the
first step of the process is crucial, and research efforts on
catalyst design and tuning of the reaction parameters aim at
this target. Thus, the palladium-catalyzed telomerization of
1,3-butadiene with nucleophiles to give 2,7-octadienes with
100% atom efficiency from simple starting materials is a
clear target.4
Linear R-olefins, especially 1-hexene and 1-octene, are key
components for the production of highly desirable linear
low-density polyethylene (LLDPE), and as a result the demand
for 1-hexene and 1-octene has increased enormously in
recent years.1 To meet this demand, the Dow Chemical Com-
pany, which is one of the major consumers of 1-octene for the
preparation of LLDPE, developed an industrial process for
the production of 1-octene from butadiene. The process
came on stream in Tarragona (Spain) in 2007.
The commercial route to produce 1-octene based on buta-
diene as developed by Dow is presented in Scheme 1.2 The
telomerization of butadiene with methanol in the presence of
a palladium catalyst yields 1-methoxy-2,7-octadiene, which
is fully hydrogenated to 1-methoxyoctane in the next step.
Subsequent cracking of 1-methoxyoctane gives 1-octene and
methanol, which is recycled.
The telomerization process has been intensively studied by
many industrial and academic laboratories.5 The important
contribution of Jolly on mechanistic aspects has been crucial
for further development.6 Recently Beller and co-workers4h,7
reported the most selective, active, and productive catalyst,
an (NHC)Pd0 complex.7d-f This outstanding performance,
(3) Patrini, R.; Lami, M.; Marchionna.; Benvenuti, F.; Rapolli
Galletti, A. M.; Sbrana, G. J. Mol. Catal. A: Chem. 1998, 129, 179–189.
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Catalysis with Organometallic Compounds; Cornils, B., Herrmann,
W. A., Eds.; VCH: Weinheim, Germany, 2000; Vol. 1, p 361. (b) Tsuji, J.
Acc. Chem. Res. 1973, 6, 8–15. (c) Tsuji, J. Palladium Reagents and
Catalysts: Innovations in Organic Synthesis; Wiley: Chichester, U.K.,
1995; p 422. (d) Takacs, J. M. In Comprehensive Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
U.K., 1995; Vol. 12, p 785. (e) Heck, R. F. Palladium Reagents in Organic
Syntheses; Academic Press: London, 1985. (f) Behr, A. In Aspects of
Homogeneous Catalysis; Ugo, R., Ed.; Reidel: Dordrecht, The Netherlands,
1984; Vol. 5, p 3. (g) Nielsen, D. J.; Cavell, K. J. In N-Heterocyclic
Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley-VCH: Weinheim, Germany,
2006; pp 73-102. (h) Clement, N. D.; Routaboul, L.; Grotevendt, A.;
Jackstell, R.; Beller, M. Chem. Eur. J. 2008, 14, 7408–7420. (i) Behr, A.;
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*To whom correspondence should be addressed. E-mail: pvanleeuwen@
iciq.es.
(1) (a) Chauvin, Y.; Olivier, H. In Applied Homogeneous Catalysis
with Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.;
VCH: Weinheim, Germany, 1996; Vol. 1, p 258. (b) Vogt, D. In Applied
Homogeneous Catalysis with Organometallic Compounds; Cornils, B.,
Herrmann, W. A., Eds.; VCH: Weinheim, Germany, 1996; Vol. 1, p 245. (c)
Parshall, G. W.; Ittel, S. D. In Homogeneous Catalysis: The Applications
and Chemistry of Catalysis by Soluble Transition Metal Complexes;
Wiley: New York, 1992; p 68. (d) James, D. E. In Encyclopedia of Polymer
Science and Engineering; Mark, H. F., Bikales, N. M., Overberger, C. G.,;
Menges, G., Eds.; Wiley-Interscience: New York, 1985; Vol. 6, p 429. (e)
PERP report On-Purpose Octene-1; Nexant Chem Systems: White Plains,
NY, April 2007.
(2) (a) Jacobsen, G. B.; Pelt, H. L.; Schaart, B. J. WO 91/09822
(Dow), 1991. (b) Bohley, R. C.; Jacobsen, G. B.; Pelt, H. L.; Schaart, B. J.;
Schenk, M.; van Oeffelen, D. A. G. WO 92/10450 (Dow), 1992.
r
pubs.acs.org/Organometallics
Published on Web 01/21/2011
2011 American Chemical Society

Article
Organometallics, Vol. 30, No. 4, 2011 793
Scheme 1. Simplified Reaction Scheme of the Dow Process
Scheme 2. Telomerization of 1,3-Butadiene with Methanol To Produce 1-Methoxy-2,7-octadiene (1-MOD)
however, could not be achieved under the Dow production
conditions using the industrial feed.8
among the diphosphines is 2,20-bis(1,4-cyclooctylenephos-
phinomethyl)-1,10-biphenyl, which gave high selectivity to
the linear telomer (up to 94% at 70 °C).12
Diphosphines were reported as ligands for the telomeriza-
tion of dienes with amines, water,9,10 and alcohols,7f,g,11 but
often diphosphine catalysts performed worse than mono-
phosphine catalysts in terms of productivity and selectivity,
especially when an alkyl spacer was used. An exception
Recently we reported on the successful use of moderately
bulky monophosphines, for instance monoxantphos, for the
telomerization of 1,3-butadiene with methanol to selectively
produce 1-MOD under commercially relevant reaction con-
ditions; the reactions were carried out with crude C4, con-
taining ∼50% of 1,3-butadiene.13 We continued our inves-
tigations using diphosphines having a large P-P distance,
which might invoke bimetallic species or which might act as
two independent monophosphines. Large backbones con-
taining two phosphines acting independently are of interest,
because per weight they are more effective than the mono-
phosphines derived from the same backbone. Second, the
interest for such diphosphines is also related to the expected
costs of the syntheses of the ligands; obviously, using a sym-
metric backbone for the preparation of a diphosphine will be
easier than the (always tricky) monofunctionalization of the
same backbone to prepare the monophosphine.
The use of monodentate arylphosphines containing o-meth-
oxy substituents was reported recently, and these catalysts gave
a higher selectivity to 1-MOD than did PPh3,5a,14 as is also
known for allylic alkylation reactions, for which a stronger
donor trans to C3 gives more linear product.15
With regard to the potential formation of bimetallic spe-
cies, in the rhodium-catalyzed carbonylation of methanol we
found that, unexpectedly, bimetallic complexes gave much
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butadiene, impurities, ...) instead of pure 1,3-butadiene, lower reagents
and promoter (NaOMe) concentration, and lower methanol quality.
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794 Organometallics, Vol. 30, No. 4, 2011
Tschan et al.
Figure 1. Phosphines.
faster catalysts: for instance, those based on SPANphos
derivatives and related diphosphines.16,17 Diphosphines that
coordinate in a cis fashion give low selectivity to the linear
product (vide supra), and these were not considered in this
study.
A series of diphosphines, previously synthesized in our
group, which contain oxygen in the ortho position with
respect to phosphorus were tested in the telomerization reac-
tion.17,18 In addition to these diphosphines having distant
phosphine groups, their monophosphine homologues were
also investigated. The results are described in the present
publication.
tion of the corresponding new bromo compounds 9-11 at
low temperature, which are further reacted with ClPPh2 to give
the desired phosphine. These backbones were investigated for
the preparation of new ligands, first because of their
similarity to the xanthene backbone of xantphos and
the spirobischromane backbone of SPANphos and sec-
ond because of their large steric bulk compared to PPh3
(this is shown by the large P-P distances in the corre-
sponding diphosphines compared to SPANphos and
Xantphos).17 As mentioned above, the preparation of a
diphosphine will be easier than the synthesis of a mono-
phosphine via the standard procedure of bromination,
lithiation, and phosphorylation. Bromination does not
stop at the monobrominated compound, and a statistical
mixture of nonbrominated, monobrominated, and di-
brominated backbones is usually obtained, which leads
to loss of material during a cumbersome purification. For
comparison and because of the expected efficiency of the
ligands, the monophosphines were also synthesized, and
it turned out that bromination often gave somewhat
better results than might have been expected statistically.
The new monobrominated compounds (Figure 2) 4-bro-
mo-5a,10b-dihydro-2,9-dimethylbenzofuro[2,3-b]benzofuran
(9), 4-bromo-2,10-dimethyl-6,12-methano-12H-dibenz-
o[2,1-d:10,200-g][1,3]dioxocin (10), and 4-bromo-2,10-di-
tert-butyl-6,12-methano-12H-dibenzo[2,1-d:10,200-g][l,3]-
dioxocin (11) were prepared by reacting the corresponding
backbone with N-bromosuccinimide (NBS) in DMF.
Thus, backbone/monoBr/diBr mixtures were obtained
in 2/75/23, 9/76/13, and 50/50/0 ratios for 9-11, respec-
tively; washing with methanol gave monoBr/diBr mix-
tures in 75/25 and 90/10 ratios for 9 and 10, respectively.
Compound 11 can be obtained in pure form, albeit in low
yield (34%), by subsequent recrystallization from metha-
nol. The mixtures of mono- and dibrominated compounds
were used without further purification to prepare the
desired ligands 5-7.
Results and Discussion
The phosphines used are shown in Figure 1: diphosphines
1-3, SPANphos, and monophosphines 5-8. We report here
the synthesis of the new monophosphines 5-7, while 8 is a
known compound. Ligand 8 was included because the Fc
moiety also behaves as a more bulky phenyl group in a
phosphine. Unfortunately, SPANphos is insoluble in the
reaction medium and will not be considered in the following.
Ligand Syntheses and Properties. From the series of ligands
synthesized (Figure 1), diphosphines 4,7-Bis(diphenylphosp-
hino)-5a,10b-dihydro-2,9-dimethylbenzofuro[2,3-b]benzofuran
(1), 2,10-dimethyl-4,8-diphenylphosphino-6,12-methano-12H-
dibenzo[2,1-d:10,200-g][1,3]dioxocin (2), 1,6-bis(diphenylphosph-
ino)-5a,10b-dihydro-5a,10b-dimethyl-3,8-dimethylbenzo-
furo[3,2-b]benzofuran (3), and SPANphos (available from
Strem) were prepared by previously described methods.17,18
Phosphine 8 was prepared by the Friedel-Crafts reaction
reported by Sollot, between ferrocene (Fc) and chlorodi-
phenylphosphine (ClPPh2).19 The new monophosphines
5a,10b-dihydro-2,9-dimethyl-4-
diphenylphosphinobenzofuro[2,3-b]benzofuran (5), 2,10-
dimethyl-4-diphenylphosphino-6,12-methano-12H-dibe-
nzo[2,1-d:10,200-g][1,3]dioxocin (6), and 2,10-di-tert-butyl-
4-diphenylphosphino-6,12-methano-12H-dibenzo[2,1-d:
10,200-g][1,3]dioxocin (7) were prepared by direct lithia-
The crude reaction mixture contains the corresponding
hydrogenated backbones 5a,10b-dihydro-2,9-dimethylben-
zofuro[2,3-b]benzofuran,20 2,10-dimethyl-6,12-methano-12H-
dibenzo[2,1-d:10,200-g][1,3]dioxocin,21
2,10-di-tert-butyl-6,
ꢀ
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12-methano-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin,21 the
J.; Freixa, Z.; van Leeuwen, P. W. N. M. Dalton Trans. 2010, 39, 8560–
8574.
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Strijdonck, G. P. F.; Reek, J. N. H.; Kamer, P. C. J.; Goubitz, J. F. K.;
van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. 2003, 42, 1284–1287.
(19) Sollott, G. P.; Mertwoy, H. E.; Portnoy, S.; Snead, J. L. J. Org.
Chem. 1963, 28, 1090–1092.
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Article
Organometallics, Vol. 30, No. 4, 2011 795
Figure 2. Monobrominated backbones.
Figure 3. Pd-dvds complexes 12 and 13.
Figure 4. Ortep plots (thermal ellipsoids shown at the 50% probability level) of the complexes 12 (left) and 13 (right). Hydrogen atoms
have been omitted for the sake of clarity. D1, D2, D3, and D4 denote CdC bond lengths.
desired monophophines 5-7, and the corresponding dipho-
sphines, respectively. The phosphines were obtained pure in 9,
31, and 3.5% yields from the corresponding hydrocarbons,
but the synthesis has not been optimized. In the case of 5
and 6, it seems that the phosphine decomposed during the
purification by chromatography column over silica gel.
In the case of 7, an important amount of the intermediate
compound 11 was lost during its purification by recrys-
tallization.
Palladium-Diphosphine Complexes. In order to also have
structural information on the type of phosphine-Pd-
diolefin complexes that these large-backbone diphosphines
will form under catalytic conditions, we synthesized the
corresponding diphosphine-[Pd(dvds)]2 (dvds = 1,1,3,3-
tetramethyl-1,3-divinyldisiloxane) for diphosphines 1 and
2. Attempts to obtain crystals of the palladium complex
derived from 3 were unsuccessful.
ylethylenediamine) and were obtained in 60 and 75% yields,
respectively.23 Monocrystals suitable for X-ray diffraction
analysis were obtained by slow evaporation of a concentra-
ted solution of 12 and 13 in diethyl ether at -25 °C. The
molecular structures of 12 and 13 are presented in Figure 4
and selected bond lengths and angles in Table 1.
The single-crystal X-ray structure analysis of complexes
12 and 13 reveals that both diphosphines formed dinuclear
palladium complexes as expected, due to the large P-P
distance. The palladium atom has a trigonal-planar coordi-
nation environment, created by the phosphorus atom and
the two CdC bonds of the dvds ligand. As observed by
€
Porschke, the Pd(1,6-diene) moiety adopts a stable chairlike
conformation.23
As observed by us in the case of monophosphine-Pd-dvds13
and by Beller in the case of (NHC)-Pd-dvds,7d the trigonal-
planar geometry around both palladium atoms of each
complexes is highly distorted, as revealed by the value, far
from the expected 120°, of the three angles (deg) D1-
Pd1-D2 (12, 130.10(7); 13, 131.7(3)), D3-Pd2-D4 (12,
128.53(7); 13, 132.6(3)), D1-Pd1-P1 (12, 116.28(5); 13,
The two different palladium complexes 12 and 13 (Figure
3) were prepared by the straightforward method reported by
€
Porschke, reacting 1 equiv of phosphine 1 and 2 with 1 equiv
22
of (tmeda)PdMe2 in dvds (tmeda = N,N,N0,N0-tetrameth-
(22) De Graaf, W.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van
Koten, G. Organometallics 1989, 8, 2907–2917.
(23) Krause, J.; Cestaric, G.; Haack, K.-J.; Seevogel, K.; Storm, W.;
€
Porschke, K.-R. . J. Am. Chem. Soc. 1999, 121, 9807–9823.

796 Organometallics, Vol. 30, No. 4, 2011
Tschan et al.
113.9(2)), D2-Pd1-P1 (12, 113.22(5); 13, 114.2(2)), D3-
Pd2-P2 (12, 113.23(5); 13, 116.4(2)), and D3-Pd2-D4 (12,
118.20(5); 13, 111.0(2)).7 Similarly to previously reported
structures, the CdC bonds lie exactly in the coordination
plane and the CdC bond length (1.40 A) is lengthened as
˚
compared with a typical CdC bond distance (1.34 A), indi-
cating a weak back-donation by Pd.
conversion of butadiene (entry 4, Table 2) and reaction rate
(Figure 5) but did not influence significantly the selectivity to
1-MOD. Dioxocin diphosphine 2 gives results similar to those
for 1 and exhibits lower productivity with higher selectivity
than PPh3. To our surprise, diphosphine 3 gave impressive
results comparable to those for monoxantphos (entry 6,
Table 2) in a comparison of productivity and selectivity to
1-MOD; adding 2 equiv of diphosphine 3 per Pd lowered the
Pd loss from 17 to 6%. With regard to the activity, the
catalyst derived from 3 appears promising, but in this case no
increase of reaction rate was observed by adding 2 equiv of 3,
in contrast to the case for 1 (Figure 5).
The good results obtained with 3 could be explained by the
fact that the two phosphorus atoms are trans to one another,
as opposed to the case for 1 and 2. Thus, no unfavorable
steric interactions between the two phosphine-palladium-
octadienyl moieties during the catalysis can occur, as might
happen with a diphosphine possessing the two P atoms in a
cis fashion. In other words, the steric bulk of the backbone in
3 exerts the same beneficial effect as does xanthene in mono-
xantphos compared to triphenylphosphine.
With regard to the monophosphines, ligand 5 gave a more
selective but less productive catalyst for the production of
1-MOD than triphenylphosphine (entry 8, Table 2) under the
same conditions, but the Bd conversion and 1-MOD selec-
tivity are higher than those of its diphosphine analogue 1.
Unfortunately, Pd loss was very high (entry 8, Table 2). The
dioxocin-based monophosphines 6 and 7 gave very good
results in terms of conversion, selectivity in comparison to
PPh3, and also stability (entries 9 and 10, Table 2) in com-
parison to 5. The t-Bu substituents in 7 seem to increase the
catalyst performance compared to that for 6. The results
obtained for 7 are even superior to those reported for mono-
xantphos (entry 2; conversion 93%, 1-MOD 89%, Pd loss
6%).13 Ferrocenylphosphine 8 gave poor results (entry 11,
Table 2).
The activity of the catalysts derived from monopho-
sphines 5 and 8 is low (Figure 6). Phosphine 6 formed a
catalyst similar in terms of activity to the catalyst derived
from monoxantphos and is thus a more active and selective
system than the diphosphine 2 catalyst. Therefore, we can
conclude that bulky monophosphines are better ligands
than their large P-P distance diphosphine counterparts
(cf. 5 and 1 or 6 and 2; Table 2, Figures 4 and 5). As can be
observed in Figure 6, the initial reaction rate, reflected by the
larger amount of 1-MOD formed with the Pd/7 system,
surpassed that of monoxantphos at 90 °C; after 30 min the
˚
Catalytic Results. All phosphines were tested for the
telomerization of 1,3-butadiene with MeOH at 90 °C, work-
ing in crude C4 with a NaOMe/Pd ratio of 5 (NaOMe is used
as promoter), and the results are presented in Table 2 toge-
ther with the results previously reported for PPh3 and mono-
xantphos under the same conditions.13 Catalysts were formed
in situ, as no differences were obtained using a phosphi-
ne-Pd-dvds or Pd(acac)2/2L mixture for the telomeriza-
tion.13,7d Thus, precatalyst stock solutions were used for ca-
talysis prepared from palladium(II) acetylacetonate and 2
equiv of the phosphine; acetic acid was added to increase the
storage stability of the complex in solution (see the Experi-
mental Section).
Diphosphines were tested in two different ligand/Pd ra-
tios: 1 and 2; the results are presented in Table 2 and the rate
of formation of 1-MOD in the presence of these ligands is
shown in Figure 5 (ligand 2 was not tested at L/Pd = 2
because of its low solubility). Diphosphine 1 gave moderate
results: viz., a higher selectivity to 1-MOD but a lower pro-
ductivity (entry 3, Table 2) compared to triphenylphosphine.
The addition of 2 equiv of diphosphine per Pd increased the
˚
Table 1. Bond Lengths (A) and Bond Angles (deg) for 12 and 13
13
12
Pd1-P1
Pd2-P2
Pd1-D1
Pd1-D2
Pd2-D3
Pd2-D4
P1-P2
D1
2.318(2)
2.315(2)
2.054(7)
2.056(8)
2.056(7)
2.056(7)
7.310(11)
1.397(11)
1.408(11)
1.396(11)
1.416(11)
2.3026(4)
2.3154(5)
2.064(2)
2.072(2)
2.071(2)
2.069(2)
7.648(3)
1.390(3)
1.392(2)
1.398(2)
1.401(3)
D2
D3
D4
D1-Pd1-D2
D3-Pd2-D4
D1-Pd1-P1
131.7(3)
132.6(3)
113.9(2)
114.2(2)
116.4(2)
111.0(2)
130.10(7)
128.53(7)
116.28(5)
113.22(5)
113.23(5)
118.20(5)
D2-Pd1-P1
D3-Pd2-P2 (deg)
D4-Pd2-P2 (deg)
Table 2. Catalytic Results Obtained for Ligands 1-7 at 90 °C for 2.5 ha
conversn (%)
entry
ligand
L/Pd
Bd
1-MOD
3-MOD
OCT
l/b ratio (%)
chemo (%)c
Pd loss (%)b
1
2
3
4
5
6
7
8
PPh3
monoxantphos
2
2
1
2
1
1
2
2
2
2
2
85
93
63
74
79
91
91
80
92
96
76
83
89
86
87
86
88
89
88
89
90
80
5
5
4
5
5
5
5
5
5
5
5
13
6
9
8
9
7
6
7
6
94/6
94/6
95/5
94/6
94/6
95/5
95/5
95/5
95/5
95/5
94/6
87
94
91
92
91
93
94
93
94
95
85
17
6
1
1
2
3
3
5
6
7
8
12
18
7
43
22
23
9
10
11
5
15
a Reaction conditions: Pd (0.0025 mol %), NaOMe (0.0125 mol %), MeOH/Bd = 2.6. b Palladium loss was estimated by ICP-AES measurements (see
the Experimental Section); measurement error (5% absolute. c Chemoselectivity (%) = (1-MOD þ 3-MOD)/(1-MOD þ 3-MOD þ OCT) ꢀ 100.

Article
Organometallics, Vol. 30, No. 4, 2011 797
chloroform was distilled over phosphorus pentoxide under argon
prior to use. MeOH was degassed by Ar bubbling. Chlorodiphe-
nylphosphine was purchased from Fluka and distilled under an
inert atmosphere prior to use. Palladium acetylacetonate was pur-
chased from Strem and used as received. 5a,10b-Dihydro-2,9-
dimethylbenzofuro[2,3-b]benzofuran,19 2,10-dimethyl-6,12-metha-
no-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin,20 2,10-di-tert-butyl-6,
12-methano-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin20 phosphines
8,19 1,17 2,17 3,17 and 4,16 and (tmeda)PdMe2 were prepared by
previously described methods. NMR spectra were recorded on a
Bruker 400 MHz spectrometer. Chemical shifts are reported in
ppm and were calibrated using residual 1H and 13C resonances of
deuterated solvents. Coupling constants (J) are expressed in hertz.
X-ray structure analyses were done at the Research Support Unit
of the ICIQ (Tarragona, Spain). Analyses of the catalytic reactions
have been performed on a GC-FID equipped with an HP-5 (5%
phenyl methyl siloxane; 30 m ꢀ 320 m ꢀ 0.25) capillary column.
ꢀ
Elemental analyses were performed at the Unidad de Analisis
Figure 5. Rate of formation of 1-MOD (90 °C, “Pd” (0.0025
mol %), NaOMe (0.0125 mol %), MeOH/Bd = 2.6).
Elemental of the Universidad de Santiago de Compostela (Spain).
Synthesis of 5a,10b-Dihydro-2,9-dimethyl-4-diphenylphosph-
inobenzofuro[2,3-b]benzofuran (5). A solution of 4-bromo-5a,
10b-dihydro-2,9-dimethylbenzofuro[2,3-b]benzofuran (9; 1.5 g,
containing 3.55 mmol of monobromo backbone) in THF
(40 mL) was cooled to -78 °C. Then, n-BuLi (2.5 M in hexane,
2.8 mL) was added slowly. The mixture was stirred at -78 °C for
2 h, and ClPPh2 (1.065 mL) was added. The mixture was stirred
at -78 °C for 2 h and at RT overnight. Then the solvent was
evaporated and degassed water was added. The product was
extracted with dichloromethane (DCM). The organic layer was
separated and dried over MgSO4. Evaporation of the solvent gave
a crude product which was purified by a chromatography column
on silica gel (eluent gradient DCM/hexane 1/3 to 1/1). The product
was isolated impure as a white solid from the fourth fraction.
Then, the product was purified by preparative thin-layer chroma-
tography on silica (eluent hexane/DCM 1/1.5) and recovered as a
white solid from the first fraction (0.23 g, 0.544 mmol, 15%).
1H NMR (400 MHz, 25 °C, CDCl3): δ 7.37-7.26 (m, 10H,
H arom), 7.19 (br s, 2H, H arom), 6.97 (m, 1H, H arom), 6.83 (d,
J = 6.8 Hz, 1H, H arom), 6.78 (d, J = 8.1 Hz, 1H, H arom), 6.47
(m, 1H, O-CH-O), 4.95 (d, J = 6.8 Hz, 1H, CHmethynic), 2.32
(s, 3H, CH3), 2.19 (s, 3H, CH3). 13C NMR (100 MHz, 25 °C,
CDCl3): δ 158.4 (d, J = 16.0 Hz), 155.8, 135.9 (d, J = 10.1 Hz),
136.0 (d, J = 11.6 Hz), 135.9 (d, J = 10.1 Hz), 133.8 (d, J =
19.6 Hz), 133.6 (d, J = 19.6 Hz), 133.3 (d, J = 2.6 Hz), 129.3,
128.7, 128.5, 128.4, 128.3, 128.3 (d, J = 10.0 Hz), 127.1, 126.8
(d, J = 3.0 Hz), 125.3, 124.3, 118.1 (d, J = 16.0 Hz), 112.5,
109.8, 50.2, 20.9, 20.8. 31P{1H} NMR (160 MHz, 25 °C, CDCl3):
δ -15.33. Anal. Calcd for C28H23O2P: C, 79.61; H, 5.49. Found:
C, 79.85; H, 5.43.
Figure 6. Rate of formation of 1-MOD (90 °C, “Pd” (0.0025
mol %), NaOMe (0.0125 mol %), MeOH/Bd=2.6).
formation of 1-MOD is 10% higher with 7 in comparison to
monoxantphos.
Conclusion
New bulky monophosphines containing dibenzodioxocin
and benzofurobenzofuran backbones were prepared in mod-
erate to good yield. Diphosphines based on the same back-
bones possessing large P-P distances and the monophosphines
were used as ligands in the palladium-catalyzed selective
telomerization of 1,3-butadiene.
The tests of the phosphines under commercially relevant
production conditions, using a crude C4 mixture containing
∼50% of 1,3-butadiene, revealed the high potential of dipho-
sphine 3 and monophosphine 7. Both ligands emerged as very
promising alternatives for PPh3, giving a more active and
selective catalyst than PPh3 under the optimized standard
conditions. The results obtained in terms of selectivity (up to
90% in favor of 1-MOD at 90 °C), activity, and stability are
comparable or even superior to those for monoxantphos.
Synthesis of 2,10-Dimethyl-4-diphenylphosphino-6,12-metha-
no-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin (6). Asolutionof4-bro-
mo-2,10-dimethyl-6,12-methano-12H-dibenzo[2,1-d:10,200-g]-
[1,3]dioxocin (10; 1.5 g, containing 4.07 mmol of monobromo
backbone) in THF (40 mL) was cooled to -78 °C. Then, n-BuLi
(2.5 M in hexane, 2.4 mL) was added slowly. The mixture was
stirred at -78 °C for 2 h, and ClPPh2 (1.0 mL) was added. The
mixture was stirred at -78 °C for 2 h and at room temperature
overnight. Then the solvent was evaporated and degassed water was
added. The product was extracted with DCM. The organic layer
was separated and dried over MgSO4. The product was purified by a
chromatography column on silica gel (eluent gradient DCM/hexane
1/3 to 1/1) and obtained as a white solid from the third fraction
1
(0.80 g, 1.83 mmol, 45%). H NMR (400 MHz, 25 °C, CDCl3):
δ 7.38-7.20 (m, 10H, H arom), 7.04 (dd, J = 4.5, 1.9 Hz,
2H, H arom), 6.93 (ddd, J = 7.8, 2, 0.5 Hz, 1H, H arom), 6.79
(d, J = 8.2 Hz, 1H, H arom), 6.31 (ddd, J = 5, 2, 0.5 Hz, 1H,
H arom), 6.02 (q, J = 2.1 Hz, 1H, O-CH-O), 3.91 (br s, 1H,
CHmethynic), 2.30 (s, 3H, CH3), 2.20 (m, 2H, CHmethylenic), 2.13 (s,
3H, CH3). 13C NMR (100 MHz, 25 °C, CDCl3): δ 150.7 (d, J =
14.7 Hz), 148.8, 136.4 (d, J = 9.4 Hz), 136.2 (d, J = 9.4 Hz), 134.1
Experimental Section
General Procedures. All reactions were carried out under
an argon atmosphere using Schlenk techniques. Deuterated

798 Organometallics, Vol. 30, No. 4, 2011
Tschan et al.
(d, J = 19.9 Hz), 133.8 (d, J = 19.4 Hz), 132.4 (d, J = 1.9 Hz),
130.6, 130.5 (d, J = 13.1 Hz), 128.9, 128.7, 128.5, 128.3 (d, J =
7.4 Hz), 128.1 (d, J = 6.6 Hz), 127.6, 126.2 (d, J = 12.7 Hz), 126.1,
124.1 (d, J = 12.7 Hz), 116.3, 92.0, 31.9, 20.6, 20.5. 31P{1H} NMR
(160 MHz, 25 °C, CDCl3): δ -12.52. Anal. Calcd for C29H25O2P:
C, 79.80; H, 5.77. Found: C, 79.62; H, 5.86.
4-bromo-2,10-di-tert-butyl-6,12-methano-12H-dibenzo[2,1-
d:10,200-g][1,3]dioxocin was obtained as a white solid (1.07 g,
34%). H NMR (400 MHz, CDCl3): δ 1.26 (9H, s, tBu), 1.27
(9H, s, tBu), 2.24-2.29 (2H, m, CH2), 3.95 (1H, m, CH), 6.23
(1H, m, CH), 6.84 (1H, d, 3JH,H = 8.6 Hz, Ar), 7.12-7.18 (3H,
m, Ar), 7.33 (1H, d, 4JH,H = 2.2 Hz, Ar).
1
Synthesis of 2,10-Di-tert-butyl-4-diphenylphosphino-6,12-
methano-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin (7). At -78 °C
n-butyllithium (1.7 mL, 1.6 M in hexanes, 2.72 mmol) was added
dropwise to a stirred solution of 4-bromo-2,10-di-tert-butyl-6,12-
methano-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin (11; 1.07 g, 2.58
mmol) in dry THF (70 mL). The reaction mixture was stirred for
1 h and then was warmed to -40 °C. At this temperature
chlorodiphenylphosphine (0.50 mL, 2.68 mmol) was added
and the reaction mixture was warmed to room temperature
overnight. The solvent was removed in vacuo, the resulting solid
was dissolved in dry CH2Cl2, and the solution was washed with
deoxygenated water. The organic layer was removed in vacuo
and recrystallized from deoxygenated methanol to afford the
product (0.2 g, 15%) as an air-stable white solid. 1H NMR (400
MHz, 25 °C, CDCl3): δ 7.37-7.26 (m, 10H, H arom), 7.20 (dd,
J = 2.3, 6.2 Hz, 1H, H arom), 7.14 (dd, J = 2.3, 8.5 Hz, 1H, H
arom), 6.82 (d, J = 8.5 Hz, 1H, H arom), 6.49 (dd, J = 2.3, 5.4
Hz, 1H, H arom), 6.01 (br d, J = 1.7 Hz, 1H, O-CH-O), 3.96
(br s, 1H, CHmethynic), 2.20 (m, 2H, CHmethylenic), 1.31 (s, 9H,
C(CH3)3), 1.09 (s, 9H, C(CH3)3). 31P{1H} NMR (160 MHz, 25
°C, CDCl3): δ -11.63. Anal. Calcd for C35H37O2P: C, 80.74; H,
7.16. Found: C, 80.70; H, 7.12. HR-MS: (M þ Na)þ for
C35H38O2P m/z calcd 521.2609, found 521.2598.
Synthesis of 4-Bromo-5a,10b-dihydro-2,9-dimethylbenzofuro-
[2,3-b]benzofuran (9). 5a,10b-Dihydro-2,9-dimethylbenzofuro-
[2,3-b]benzofuran (1.5 g, 6.3 mmol) and N-bromosuccinimide
(NBS; 2.016 g, 11.3 mmol) were dissolved in DMF (100 mL) and
stirred at room temperature for 1 day (the flask is covered with
aluminum foil). The conversion was monitored by GC/MS. If
necessary, more NBS can be added. After 3 days, a monobromo/
dibromo/starting material mixture was formed in a 75/23/2
ratio. The solvent was evaporated to dryness, and the solid
was washed with water and extracted with DCM. The organic
layer was dried over MgSO4 and evaporated to dryness. The
solid obtained was washed with ethanol to give a white solid
(1.5 g, containing a 75/25 monobromo/dibromo mixture). The
mixture was used without further purification to prepare the
phosphine.
Synthesis of 4-Bromo-2,10-dimethyl-6,12-methano-12H-dibe-
nzo[2,1-d:10,200-g][1,3]dioxocin (10). 2,10-Dimethyl-6,12-metha-
no-12H-dibenzo[2,1-d:10,200-g][1,3]dioxocin (1.5 g, 5.95 mmol)
and NBS (1.477 g, 8.29 mmol) were dissolved in DMF (100 mL)
and stirred at room temperature for 1 day. The conversion was
monitored by GC/MS. If necessary, more NBS can be added.
After 3 days, a monobromo/dibromo/starting material mixture
was formed in a 76/9/13 ratio. The solvent was evaporated to
dryness, and the solid was washed with water and extracted with
DCM. The organic layer was dried over MgSO4 and evaporated
to dryness. The solid obtained was washed with ethanol to give a
white solid (1.5 g, containing a 90/10 monobromo/dibromo
mixture). The mixture was used without further purification to
prepare the phosphine.
Synthesis of 4-Bromo-2,10-di-tert-butyl-6,12-methano-12H-
dibenzo[2,1-d:10,200-g][1,3]dioxocin (11). To a stirred solution of
2,10-di-tert-butyl-6,12-methano-12H-dibenzo[2,1-d:10,200-g]-
[1,3]dioxocin (3.70 g, 11.0 mmol) in DMF (125 mL) was added
NBS (1.98 g, 11.0 mmol). The reaction mixture was monitored
by GC chromatography. Once a 1/1 mixture of starting material
and monobromo derivative was obtained, we decided to stop the
reaction (to avoid formation of dibromo derivative). Then
DMF was removed by evaporation. The residue was dissolved
in H2O and the solution extracted with dichloromethane. The
combined organic layers were dried over MgSO4, and the
solvent was evaporated. After recrystallization with methanol,
General Procedure for the Synthesis of the Phosphine-Palladium-
dvds Complexes. A suspension of (tmeda)Pd(CH3)2 (0.05 g, 0.20
mmol) and of the desired phosphine (0.5 equiv, 0.010 mmol, 0.060 g
for 1, 0.061 g for 2) in degassed and dried tetramethyldivinyldisilox-
ane (dvds, 2 mL) was stirred at room temperature overnight. Then,
the solvent was removed under vacuum and the white solid obtained
was washed with a small portion of pentane at -60 °C to remove
small quantities of unreacted reagents. Yield: 60 and 75% for 12 and
13, respectively. Due to their low stability at room temperature, the
phosphine-palladium-dvds complexes have been characterized
1
only by H and 31P NMR spectroscopy and should be stored as
solids under an inert atmosphere at -20 °C.
4,7-Bis(diphenylphosphino)-5a,10b-dihydro-2,9-dimethylbenzofuro-
[2,3-b]benzofuran{Pd[(η2-H2CdCHSiMe2)2O]}2 (12). 1H NMR
(400 MHz, 25 °C, CD2Cl2): δ 7.45-7.14 (m, 22H, H arom),
6.83 (br d, J = 10.8 Hz, 2H, H arom), 6.36 (d, J = 6.6 Hz,
1H, O-CH-O), 4.76 (d, J = 6.6, 1H, CHmethynic), 3.43-2.85 (m,
12H, dvds), 2.25 (s, 6H), 0.26 (s, 12H, dvds), -0.27 (s, 6H, dvds),
-0.28 (s, 6H, dvds). 31P{1H} NMR (160 MHz, 25 °C, CDCl3):
δ -25.05.
2,10-Dimethyl-4,8-diphenylphosphino-6,12-methano-12H-dibenzo-
[2,1-d:10,200-g][1,3]dioxocin{Pd[(η2-H2CdCHSiMe2)2O]}2 (13). 1H
NMR (400 MHz, 25 °C, CD2Cl2): δ 7.36-7.1 (m, 22H, H arom),
6.71 (br d, J = 9.7 Hz, 2H, H arom), 5.09 (br s, 1H, O-CH-O),
3.90 (s, 1H, CHmethynic), 3.26-2.85 (m, 12H, dvds), 2.17 (s, 2H,
CHmethylenic), 2.16 (s, 6H), 0.20 (s, 12H, dvds), -0.27 (s, 6H, dvds),
-0.28 (s, 6H, dvds). 31P{1H} NMR (160 MHz, 25 °C, CDCl3): δ
-27.19.
Precatalyst Solution. The catalyst was prepared with palla-
dium acetylacetonate (Pd(acac)2) plus 2 mol equiv of the phos-
phine. One molar equivalent of acetic acid may be added to
increase storage stability. The catalyst was prepared in methanol
by dissolving all three components such that the palladium
concentration in methanol equals about 500 ppm.
Catalytic Reaction. The reaction was carried in a 1 L (L) Parr
reactor made from electropolished stainless steel. For each
reaction, the Parr reactor’s autoclave was filled with specified
amounts of methanol, promoter (sodium methoxide, at a pro-
moter to palladium molar ratio of 5/1) and inhibitor (diethyl
hydroxyl amine, approximately 20 parts by weight per million
parts by weight (ppm) based on total weight of methanol plus
crude C4 load, ∼50% of 1,3-butadiene). The autoclave was
closed, and purged twice with low-pressure nitrogen (6 bar or
600 kilopascals (kPa)) to substantially remove oxygen contained
in the autoclave. A stainless steel sample cylinder was filled with
a crude C4 stream that contains approximately 50 wt % of 1,3-
butadiene, based upon total crude C4 stream weight and
pressure. The content was added to the autoclave with low-
pressure nitrogen (6 bar or 600 kPa). The temperature in the
autoclave was raised to the desired work temperature (90 °C or
otherwise indicated).
An amount of the catalyst solution was weighed, such that the
palladium concentration in the reactor after addition of all raw
materials was 10 ppm based upon the total weight of raw
materials, into a drybox, and then the catalyst solution was placed
into a stainless steel sample cylinder. The catalyst solution was
added to the autoclave using high-pressure nitrogen (19-20 bar, or
1900-2000 kPa). Following catalyst addition, the reaction began,
producing the final product. Samples were taken from the autoclave
at set times (5 min after catalyst addition and at 30 min intervals
thereafter), and gas and liquid phases of the samples were analyzed
via GC (internal standard m-xylene).
Palladium Precipitation Measurement. Palladium precipita-
tion in the reactor was determined by measuring the palladium

Article
Organometallics, Vol. 30, No. 4, 2011 799
concentration in the liquid phase after the reaction and compar-
ing that to a theoretical number based on the total amount of
palladium added and the total liquid volume, which includes
liquids added at the beginning of the reaction and liquids formed
due to the butadiene conversion. Palladium concentration in the
liquid was measured using inductively coupled plasma atomic
emission spectroscopy (ICP-AES).
y Ciencia for a “Ramon y Cajal” contract (Z.F.), Project
CTQ2008-00683, Consolider Ingenio 2010 (Grant No.
CSD2006_0003), and the European Union for a Marie Curie
Chair of Excellence Grant (P.W.N.M.v.L.) (MEXC-CT-
2005-0023600, http://europa.eu.int/mariecurieactions).
Supporting Information Available: Text, a table, and CIF files
giving details on data collection and crystallographic data for
the structure analyses of 12 and 13. This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by the Dow
ꢀ
Chemical Co. We thank the Spanish Ministerio de Educacion