Phenylphosphatrioxa-adamantanes: Bulky, robust, electron-poor ligands that give very efficient rhodium(I) hydroformylation catalysts

Article abstract of DOI:10.1039/b418259f

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6- phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6- pnosphaadamantane (1b) have been made by the acid catalysed addition of PhPH₂ to the appropriate β-diketones; the acid used (HCl, H ₃PO₄ or H₂SO₄) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl₂(NCPh)₂] to form complexes trans-[PdCl₂(1a)₂] (2a) and trans-[PdCl ₂(1b)₂] (2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl₂(cod)], equilibrium mixtures of trans-[PtCl₂L ₂] and [Pt₂Cl₄L₂] (L = 1a or 1b) are formed in CH₂Cl₂ solution. Meso/rac mixtures of trans-[MCl(CO)(1a)₂] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl₃·nH₂O with an excess of 1a and the anionic cobalt complex [NHEt₃][CoCl₃(1a)] (9) was isolated from the product formed by CoCl₂·6H₂O and 1a. The ν_CO values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94° is observed and this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200°). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b418259f

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F U L L P A P E R
Phenylphosphatrioxa-adamantanes: bulky, robust, electron-poor
ligands that give very efficient rhodium(I) hydroformylation catalysts
R. Angharad Baber,a Matthew L. Clarke,*b Katie M. Heslop,a Andrew C. Marr,†a
A. Guy Orpen,a Paul G. Pringle,*a Andrew Warda and Damaris E. Zambrano-Williamsa
a School of Chemistry, Cantocks Close, Bristol, UK BS8 1TS.
E-mail: paul.pringle@bristol.ac.uk; Fax: +44 117 928 0509; Tel: +44 117 928 8114
b School of Chemistry, University of St Andrews, St Andrews, Fife, UK KY16 9ST
Received 3rd December 2004, Accepted 7th January 2005
First published as an Advance Article on the web 8th February 2005
The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and
1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of
PhPH2 to the appropriate b-diketones; the acid used (HCl, H3PO4 or H2SO4) and its concentration affect the rate and
selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl2(NCPh)2] to form complexes
trans-[PdCl2(1a)2] (2a) and trans-[PdCl2(1b)2] (2b) as mixtures of rac and meso diastereoisomers. The platinum(II)
chemistry is more complicated and when 1a or 1b is added to [PtCl2(cod)], equilibrium mixtures of trans-[PtCl2L2]
and [Pt2Cl4L2] (L = 1a or 1b) are formed in CH2Cl2 solution. Meso/rac mixtures of trans-[MCl(CO)(1a)2] M = Ir
(6a) or Rh (7a) are formed upon treatment of MCl3·nH2O with an excess of 1a and the anionic cobalt complex
[NHEt3][CoCl3(1a)] (9) was isolated from the product formed by CoCl2·6H2O and 1a. The mCO values from the IR
spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of
meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C–P–C angle of ca. 94◦ is observed
and this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are
similar and large (ca. 200◦). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly
high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear
selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective
hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any
previously reported catalyst.
hindrance to nucleophilic attack by phenylphosphine offered by
Introduction
the ethyl groups in the 3,5-heptadione reaction compared with
The reaction of primary phosphines with acetylacetone to give
the methyls in the 2,4-pentadione reaction. The lower solubility
phosphatrioxa-adamantanes (eqn. (1)) was first reported by
of the more lipophilic 3,5-heptadione in the aqueous reaction
medium may also contribute to its slower reaction with PhPH2.
Epstein and Buckler1 in 1961.
(1)
The coordination chemistry and potential catalytic applica-
tions of these unusual cage-phosphines have only recently been
explored.2–4 Here we report an improved synthesis of 1a and
the new cage phosphine 1b, their coordination chemistry with
(2)
Phosphines 1a and 1b are racemic mixtures of enantiomers
(labelled a and b) associated with the C1 symmetry of the cages.
palladium(II), platinum(II), cobalt(II), rhodium(I) and iridium(I),
and the remarkably high turnovers in hydroformylation catalysis
achieved with the rhodium complexes of 1a and 1b.
Results and discussion
Ligand synthesis
The ligands 1a and 1b were made by the route shown in eqn. (2)
and the products were fully characterised (see Experimental).
Under similar conditions, the reaction of PhPH2 with 3,5-
heptadione to give the new phosphine 1b was much slower
than the analogous reaction with 2,4-pentadione to give 1a.
This can be rationalised by considering the greater steric
It was found that the yields and purity of the products 1a and
1b were critically dependent on the nature and concentration of
the acid catalyst. Thus for 1a, the literature yield1 of 49% was
increased to 86% by increasing the molarity of the HCl used
in the synthesis from 6 M to 12 M HCl (see Experimental);
many by-products were observed if H2SO4 or H3PO4 were used.
For the synthesis of 1b, as expected, increasing the acid catalyst
† Current address: CenTACat, Centre for the Theory and Application of
Catalysis, The David Keir Building, The Queen’s University of Belfast,
Belfast, UK BT9 5AG.
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5
1 0 7 9
©

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Scheme 1 Proposed mechanism for cage phosphine formation.
concentration increased the rate of consumption of PhPH2 but
surprisingly, the selectivity to the product 1b, depended on
the acid: HCl (44%) < H3PO4 (62%) < H2SO4 (90%). It is
not obvious why the counterion has this effect on selectivity
since ostensibly it has no role in the suggested mechanism5
(Scheme 1). Perhaps ion-pairing is important in one or more
of the intermediates. In the light of these results, the conditions
for the synthesis of 1b were optimised to give 1b rapidly and in
high yield (see Experimental).
Both phosphines 1a and 1b are very stable to air. For example,
solid 1a has been stored in air for 2 years without any sign of
oxidation. Furthermore, a toluene solution of 1a was refluxed
in air for 4 h and no change was detected by 31P NMR.
Palladium(II) and platinum(II) complexes
Fig. 1 Crystal structure of meso-2a. All hydrogen atoms are omitted
The reaction of 2 equiv. of 1a or 1b with [PdCl2(NCPh)2] gave
mononuclear complexes of the form [PdCl2(phosphine)2] which
have been fully characterised (see Experimental for the data).
The 31P NMR spectra of the products showed, in each case, two
closely spaced singlets (ca. 1 : 1 ratio) which were assigned to
the expected meso (ab) and rac (aa/bb) diastereoisomers of 2a
and 2b shown below (only the aa enantiomer of the racemate is
depicted).
for clarity. Atoms suffixed A are related by symmetry operation (−x, −y,
−z) to those without suffix. Ellipsoids enclose 50% probability density.
Fig. 2 Crystal structure of meso-2b. All hydrogen atoms are omitted
for clarity. Atoms suffixed A are related by symmetry operation (−x,
2−y, 2−z) to those without suffix. Ellipsoids enclose 50% probability
density.
Crystals of meso-2a (as its dichloromethane solvate) and meso-
2b suitable for X-ray crystallography were obtained by slow
diffusion of hexane into their CH2Cl2 solutions. The structures
of meso-2a and meso-2b are shown in Figs. 1 and 2. The
cage phosphines are in trans postions in both cases and the
complexes both have exact Ci symmetry. The Pd–Cl and Pd–P
distances in the two complexes are essentially the same (Pd–Cl
˚
˚
2.293(1) and 2.297(1) A; Pd–P 2.340(1) and 2.338(1) A). As is
usual in these cage phosphines2,6 the intra-cage C–P–C angles
(94.0(1) and 94.6(1)◦) are small compared with C–P–C angles
in unconstrained tertiary phosphines. The cone angles for the
phosphine ligands 1a and 1b are essentially the same in 2a and
2b at 202 and 199◦ respectively, indicating that, at least in the
1 0 8 0
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5

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conformation present in the crystals of 2b, the ethyls have no
more steric influence than the methyls of 2a.
The reaction of [PdCl2(NCPh)2] with 1 equiv. of 1a gave an
orange solid, the main component of which was tentatively
assigned the binuclear structure 3a on the basis of the IR
spectrum which showed bands for terminal and bridging Pd–Cl
(see Experimental) and the 31P NMR spectrum which showed
two singlets for the predominant species (80%) assigned to
meso/rac-3a (dP 26.9, 26.8). Two 31P resonances would be
predicted for the C1-symmetric meso-3a (and the other meso-
binuclear complexes described below) but only one was observed
presumably because of accidental equivalence. Under similar
conditions 1b gave a similar mixture in solution, tentatively
assigned to the analogues meso/rac-3b on the basis of the dP
values (30.2, 30.3).
Fig. 3 Crystal structure of rac-6a. All hydrogen atoms are omitted for
clarity. Ellipsoids enclose 50% probability density.
Table 1 mCO for [MCl(CO)(PR3)2]
M
L
mCO
Reference
Ir
Ir
Ir
Ir
PPh3
1950
1962
1968
1970
1993
1965
1986
2016
10
10
PPh2(OEt)
PPh(OEt)2
1a
The reaction of 1a with [PtCl2(cod)] was monitored by 31P
NMR spectroscopy. Addition of 2 equiv. of 1a to [PtCl2(cod)]
gave a mixture of species and the following were tentatively
identified from their 31P NMR parameters: trans-mononuclear
10
a
Ir
P(OBun)3
PPh3
10
Rh
Rh
Rh
11
a
1a
P(OPh)3
1
1
4a as a meso/rac mixture (d 0.8, JPtP 2692 Hz and d 0.9, JPtP
12
1
2716 Hz) and binuclear 5a (d 11.5 JPtP 4550 Hz and d 11.9
a IR spectra from this work, recorded as Nujol mulls.
1JPtP 4524) along with free ligand at d −24.3, a broad signal,
presumably because of ligand exchange. Addition of more 1a
to the 4a/5a mixture produced more of the mononuclear 4a
and therefore the species are in equilibrium (eqn. (3)). A similar
equilibrium mixture was detected by 31P NMR spectroscopy
The electron withdrawing effect of the cage can be traced to
a combination of the electronegative O groups on the carbons a
to the P and the small C–P–C angle8 of ca. 90◦ detected in the
solid state structures discussed here.
The hydroformylation catalysts described below were gen-
erated by mixing [Rh(acac)(CO)2] with an excess of ligands
1a or 1b. The reaction of [Rh(acac)(CO)2] with one equiva-
lent of 1a produced [Rh(acac)(CO)(1a)] (8a) which was fully
characterised (see Experimental). The position of mCO in this
1
upon addition of 2 equiv. of 1b to [PtCl2(cod)]: 4b (d 4.2, JPtP
2682 Hz and d 3.9, 1JPtP 2674 Hz) and 5b (d 15.3, 1JPtP 4570 Hz
and d 14.7, 1JPtP 4531 Hz).
complex (1984 cm−1) is higher than in the PPh3 analogue (mCO
=
1975 cm−1),9 consistent with the discussion above. The reaction
of an excess of 1a with complex 8a in CH2Cl2 was monitored by
31P NMR spectroscopy. Broad peaks were observed for 1a and 8a
but there was no evidence for the formation of [Rh(acac)(1a)2].
Attempts to prepare the analogue of the well known hydro-
formylation precursors [RhH(CO)(PR3)3] by hydride reduction
of 7a failed. Similarly treatment of a mixture of 8a and two
equivalents of ligand 1a with syngas at room temperature
produces many (>8) Rh–P containing species with complete
consumption of 8a.
(3)
These equilibria reflect the binding properties of the cage
phosphines 1a and 1b. The formation of binuclear species
[Pt2Cl2(PR3)2] is typical of bulky phosphines. The similarity in
the equilibrium constants for eqn. (3) (the ratio of the intensities
of the 31P NMR signals for 4a/5a and 4b/5b was ca. 1 in each
case) and the similarity of the 1JPtP values is consistent with 1a
and 1b having very similar stereoelectronic properties.
The chemistry of the more readily available ligand 1a was
studied in further detail.
CoCl2·6H2O was treated with an excess of 1a in ethanol in the
expectation of making a bis(phosphine) complex.13 However
the blue solid product which formed upon addition of NEt3
was shown by X-ray crystallography to be the anionic cobalt(II)
complex 9.
Iridium(I), rhodium(I) and cobalt(II) complexes
The complexes trans-[MCl(CO)(1a)2] M = Ir (6a) or Rh (7a) as
meso/rac mixtures were made by methods similar to those for
their PPh3 analogues7 (see Experimental for details).
The crystal structure of rac-6a has been determined and is
shown in Fig. 3. The cage phosphines are in trans positions and
the complex has C1 symmetry in the solid state. The Ir–C, Ir–
Cl and Ir–P distances are of normal dimensions for a Vaska’s
˚
˚
compound analogue (Ir–C 1.817(4) A, Ir–Cl 2.362(1) A, Ir–P
˚
2.328 and 2.318(1) A). The intra-cage C–P–C angles are small
The crystal structure of 9 was determined and is shown in
Fig. 4. The metal anion has tetrahedral geometry at the Co(II)
centre (P–Co–Cl angles in the range 102–108◦; Cl–Co–Cl angles
in the range 107–114◦). The Co–Cl and Co–P distances are
(94.1(1) and 93.7(1)◦). Cone angles for the phosphine ligands
are again close to 200◦ (at 200 and 198◦).
The mCO for 6a, 7a and analogues with other phosphorus(III)
donors are given in Table 1 and it can be seen that the values
for the cage phosphine 1a most closely resembles the PPh(OEt)2
analogue indicating that it is relatively electron-poor and the
r/p-bonding of 1a to rhodium(I) or iridium(I) is similar to a
phosphonite.
˚
of normal dimensions for such a species (Co–Cl 2.24–2.28 A;
˚
Co–P 2.408(1) A). The intra-cage C–P–C angle is again small
(94.4(1)◦) and the cone angle for the phosphine ligand close to
earlier values (at 196◦). One chlorine ligand is hydrogen bonded
◦
˚
to the cation (Cl · · · HN 2.37 A, Co–Cl · · · H 97 ).
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5
1 0 8 1

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derived Rh catalysts, and rationalised the high activity and
low regioselectivity in terms of a mono-phosphite Rh complex,
[RhH(CO)2(L)] being the active species.12,13
(4)
The main industrial interest in hydroformylation is in the
selective synthesis of linear aldehydes which are important bulk
chemicals. However, hydroformylation reactions that deliver
branched products regioselectively are attracting increasing in-
terest due to their potential applications in organic synthesis and
fine chemical production.18–20 We therefore screened 1-hexene
and 3-hexene at higher temperatures. The normal preference for
Rh phosphine catalysts to give predominantly linear products
from terminal alkenes is reversed at high temperatures; the major
products are the branched aldehydes, 2-methylhexanal and 2-
ethylpentanal. 3-Hexene was chemoselectively hydroformylated
to predominantly 2-methylhexanal and 2-ethylpentanal.
Fig. 4 Crystal structure of the anion in 9. All hydrogen atoms are
omitted for clarity. Ellipsoids enclose 50% probability density.
The formation of the monophosphine complex anion in 9
rather than a [CoCl2(PR3)2] species is perhaps due to the first
row metal being unable to accommodate two bulky 1a ligands
in its coordination sphere.
Clarke19 has recently described the Rh/phosphite catalysed
hydroformylation of acrylate esters which, under certain con-
ditions, defies Keulemans’ rule that states ‘aldehydes are not
produced at quaternary carbon centres’.21 By variation of the
temperature and pressure, linear and branched quaternary
aldehydes were made. However, these acrylate esters were
extremely unreactive substrates requiring the use of a phosphite
based catalyst. From Table 3 the results for hydroformylation of
acrylate esters (eqn. (5)) with catalyst derived from 1a can be
compared with the bulky phosphite used in the original study.
Hydroformylation catalysis
Triphenylphosphine is an excellent ligand for hydroformylation
catalysis as shown by the megaton industrial plants that use Rh–
PPh3 catalysts.14 Bulky triarylphosphites have been shown to be
even better ligands in terms of activity and selectivity.15 However
phosphites are prone to hydrolysis and reaction with the aldehy-
des produced by the hydroformylation.14 There is considerable
interest in combining the high activity of the phosphite based
catalysts with the robust properties of the triphenylphosphine
derived catalysts.16 The cage phosphines 1a and 2a are attractive
candidates as ligands for hydroformylation catalysis because
they are inert to decomposition and stereoelectronically similar
to a bulky phosphonites vide supra. Phosphonites have also
been shown to provide highly active rhodium catalysts for
hydroformylation.17
Initially rhodium catalysed hydroformylation of 1-hexene
(eqn. (4)) under constant pressure conditions was investigated.
The syngas uptake was monitored with time to allow compar-
ison of the rates of hydroformylation using PPh3, P(OPh)3 and
the cage phosphines 1a and 1b. The results given in Table 2
show that the cage phosphines give very much more active
Rh catalysts for hydroformylation of 1-hexene than PPh3. The
turnover frequencies, which are not optimised, resemble those
observed for a phosphite-based catalyst. 1H NMR and GC
analysis of the products obtained revealed that the reactions
all gave high chemoselectivity to aldehydes. The n : i ratio of
the aldehydes produced is unusually low. Van Leeuwen and
co-workers reported similar findings using bulky phosphite
(5)
Ligand 1a formed the most selective catalyst examined so
far for this reaction, enabling extremely high regioselectiviy
and good yields in the hydroformylation of methyl atropate.
The hydroformylation of acrylate ester A2 was found to be
problematic in the original study and some improvements in
yield and selectivity were found using the Rh catalysts derived
from 1a.
Conclusion
The phospha-adamantanes 1a and 1b have been shown to be
readily made and are very stable to air and water. From a study
Table 2 Influence of ligands on rate and selectivity of rhodium catalysed hydroformylation of hexenesa
Rate / (mol prod/mol
cat) h−1
Entry Ligand 1-Hexene 2-Hexene 3-Hexene Heptanal (n : i) 2-Methyl hexanal 2-Ethyl pentanal
1b
2
3
PPh3
P(OPh)3 <1
1a
1b
1a
1a
<1
<1
8
<1
<1
1.6
<1
<1
<1
<1
<1
<1
<1
74 (3.1)
66 (2.6)
61 (1.6)
49 (1.0)
46 (0.9)
7 (0.1)
24
25
38
49
37
27
<1
<1
<1
<1
14
380
2 000
1 700
2 200
n.d.
<1
4
5c
6c,d
1.4
<1
63
n.d.
a Reactions were carried out in a 100 mL stainless steel autoclave at constant pressure (20 bar) of syngas (CO/H2 = 1 : 1) and constant temperature
(60 ◦C). 0.2 mol% of pre-catalyst [Rh(acac)(CO)2] and 0.9% of ligand were dissolved in 5 mL of toluene to form catalyst solution in each case.
Reactions were stopped after 3 h and products analysed. Rates were calculated at 50% conversion from the slope of syngas uptake versus time plots.
These plots show that the reactions are essentially complete within ≈20 minutes. Conversion (given as %), GC yield and selectivity were measured
using a GC equipped with a FID detector and are measured against biphenyl (20 mol%) added as an internal standard. Product identities and
distributions were further confirmed by 1H NMR integration and GCMS; n.d. = not determined. b Taken from ref. 16d. c These reactions were
carried out at 110 ◦C and 10 bar syngas pressure. d Hex-3-ene was used as substrate.
1 0 8 2
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5

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a
Table 3 Hydroformylation of acrylate esters A1 and A2
% Hydro-
genation
Entry
Alkene
Ligandb
Pressure/bar
Temp/◦C
Time/h
% Conv.
Q/L
1
2
3
4
5
6
7
8
9
A1
A1
A1
A1
A2
A2
A2
A2
A2
A2
tbpp
tbpp
1a
35
12
10
50
8
32
32
50
32
10
45c
100c
100
45
70
40
40
70
20
40
70
66
40
20
>98
>98
90
>98
49
15
33
61
25
62
13
13
30
15
<5
n.d.
n.d.
0
n.d.
0
13/1
1/12
1/28
49/1
1/11
4/1
2/1
7/1
4/1
1/10
1a
P(OPh)3
P(OPh)3
tbpp
1a
1a
1a
100c
40c
50
50
40
100
10
a Reactions were carried out in a 100 mL stainless steel autoclave under the conditions described in this table. Conversion, GC yield and selectivity
were measured using a GC equipped with a FID detector and are measured against biphenyl (20 mol%) added as an internal standard; n.d. =
1
not determined. Product identities and distributions were further confirmed by H NMR integration and EI or CI mass spectrometry. b tbpp =
tris(2,4-di-t-butylphenyl)phosphite. c Results taken from ref. 19.
of their coordination chemistry, it is concluded that they have
the stereoelectronic properties of a bulky phosphonite. This is
further supported by the very high hydroformylation catalytic
activity of their rhodium complexes. This high activity coupled
with their robustness makes phospha-adamantanes potentially
useful ligands for hydroformylation catalysis.
over 5 min. The reaction mixture was stirred for 5 h, after which
time yellow oil drops had formed. The solution was neutralized
with N2-saturated NaOH (80 cm3, 2.5 M) until pH = 7 and
then CHCl3 (30 cm3) was added to give two layers. The lower
organic layer was separated and the aqueous phase was washed
with CHCl3 (3 × 20 cm3), the extracts combined and the solvent
was removed in vacuo. The crude product was passed through a
(30 cm × 2 cm) silica column under N2 using CH2Cl2 as eluent
(250 cm3), and the solvent was removed in vacuo. The product
was collected to afford EtCgPPh (1.5 g, 92%) as a viscous white
oil. 1H NMR (CDCl3): dH 7.73–7.81 (m, 2H, ArH), 7.20–7.29(m,
3 H, ArH), 1.65–1.96 (m, 12 H, CH2), 0.8–1.05 (m, 12 H, CH2).
13C NMR (CDCl3): dC 134.5–135.7 (m, PC6H5), 128.1–129.4 (m,
PC6H5), 97.9 (s, OCCH2), 97.0 (m, OCCH2), 77.0 (s, PCCH2),
76.7 (s, PCCH2), 75.7 (s, PCCH2), 75.6 (s, PCCH2), 31.9–34.3 (m,
CH2CH3), 6.4–7.2 (m, CH2CH3). 31P NMR (CDCl3): dP −30.7
(s). EI mass spectrum: m/z 349 (M+ + H).
Experimental
General
Unless otherwise stated, all work was carried out under a dry ni-
trogen atmosphere, using standard Schlenk line techniques. Dry
N2-saturated solvents were collected from a Grubbs system22 in
flame and vacuum dried glassware. NMR spectra were measured
on a Jeol Eclipse 300, Jeol Eclipse 400 or Jeol GX 400. Unless
otherwise stated 1H, 13C and 31P NMR spectra were recorded at
◦
300, 100, and 121 MHz, respectively, at +23 C. Mass spectra
were recorded on a MD800. Infrared spectra were recorded
on Perkin-Elmer Spectrum 1 Spectrometer as Nujol mulls
between polythene plates. Elemental analyses were carried out
by the Microanalytical Laboratory of the School of Chemistry,
University of Bristol.
Synthesis of trans-[PdCl2(1a)2] (2a)
To a solution of [PdCl2(NCPh)2] (39.5 mg, 0.103 mmol) in
CH2Cl2 (2 cm3) was added 1a (60 mg, 0.205 mmol) in CH2Cl2
(2 cm3) and left overnight. A yellow solid formed (45 mg,
0.059 mmol, 57%) which was filtered off in air and dried in
vacuo. Elemental analysis, found (calc.): C 50.5 (50.4), H 5.8
(5.6). IR m(Pd–Cl): 357 cm−1. 31P NMR (CDCl3): dP 7.5 (s). This
compound was also characterised by X-ray crystallography.
Preparation of 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-
phosphaadamantane (1a)
A solution of 2,4-pentanedione (2.6 cm3, 25.1 mmol) in N2-
saturated aqueous HCl (10 cm3, 12 M) was stirred for ca. 1 h. To
this solution, phenylphosphine (CAUTION: highly flammable)
(1.0 cm3, 9.1 mmol) was added dropwise over 5 min. After 4 d
water (10 cm3) was added to the solution and a white precipitate
formed. The solid was filtered off under reduced pressure and
washed with water (2 × 10 cm3) to give MeCgPPh (2.314 g, 86%).
Elemental analysis, found (calc.): C 65.7 (65.7), H 7.6 (7.2). 1H
NMR (CDCl3) dH 7.78–7.86 (m, 2 H, ArH), 7.26–7.39 (m, 3 H,
ArH), 1.74–2.11 (m, 4 H, CH2), 1.42 and 1.43 (s, 3 H, CH3), 1.25
and 1.51 (d, 3 H, CH3, JPH 13 Hz). 31P NMR (CDCl3): dP −23.6
(s). 13C NMR (CDCl3): dC 133.7–135.2 (m, PC6H5), 128.2–129.4
(m, PC6H5), 96.8 (s, OCCH3), 96.1 (s, OCCH3), 73.5 (s, PCCH3),
73.3 (s, PCCH3), 73.1 (s, PCCH3), 73.0 (s, PCCH3), 45.4 (d,
2JPC = 18 Hz, PCCH2), 36.3 (s, PCCH2), 27.9 (d, 2JPC = 21 Hz,
PCCH2), 27.5 (s, PCCH3), 27.3 (s, PCCH3), 26.9 (s, OCCH3),
26.7 (s, OCCH3). EI mass spectrum: m/z 292 (M+).
Synthesis of trans-[PdCl2(1b)2] (2b)
To a solution of [PdCl2(NCPh)2] (41.0 mg, 0.11 mmol) in CH2Cl2
(2 cm3) was added 1b (75 mg, 0.216 mmol) in CH2Cl2 (2 cm3).
The pale yellow solution was stirred for 2 d, after which time
a yellow precipitate was formed. The solvent was removed in
vacuo leaving a yellow solid (65 mg, 70%). Elemental analysis,
found (calc.): C 55.9 (55.0), H 7.5 (6.7). IR m(Pd–Cl): 359 cm−1.
31P NMR (CDCl3): dP 9.7 (s). m/z (FAB) 837 (M − Cl+), 802
(M − 2Cl+). This compound was also characterised by X-ray
crystallography.
Reactions of [PdCl2(NCPh)2] with one equivalent of 1a or 1b
To a solution of [PdCl2(NCPh)2] (79 mg, 0.206 mmol) in CH2Cl2
(2 cm3) was added 1a (60 mg, 0.205 mmol) in CH2Cl2 (2 cm3)
and left overnight. An orange solid formed (38 mg) which was
filtered off in air and dried in vacuo. Elemental analysis, found
(calc. for {PdCl2(1a)}n): C 40.1 (40.9), H 4.4 (4.5). IR m(Pd–Cl):
357, 302, 290, 269 cm−1. 31P NMR (CDCl3): dP 26.9 (s), 26.8 (s),
25.6 (s), 25.2 (s). The reaction between [PdCl2(NCPh)2] and 1b
was carried out similarly but the product remained in solution
Synthesis of 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-
phosphaadamantane (1b)
A solution of 3,5-heptanedione (2.6 cm3, 1.5 g, 11.4 mmol) in
N2-saturated aqueous H2SO4 (10 cm3, 12 M) was stirred for
ca. 2 h. To this solution, phenylphosphine (CAUTION: highly
flammable) (0.5 cm3, 460 mg, 4.6 mmol) was added dropwise
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5
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Table 4 Crystal and refinement data for meso-2a·CH2Cl2, meso-2b, rac-6a and 9
Compound
meso-2a·CH2Cl2
meso-2b
rac-6a
9
Formula
C34H46Cl6O6P2Pd
931.75
C40H58Cl2O6P2Pd
874.10
C33H42ClIrO7P2
840.26
C22H37Cl3CoNO3P
559.78
Formula weight
Crystal system
Space group (no.)
Triclinic
Triclinic
Triclinic
Monoclinic
P21/c(14)
17.914(3)
11.206(2)
13.4602(19)
90.00
98.157(11)
90.00
2674.8(7)
4
¯
¯
¯
P1 (2)
P1 (2)
P1 (2)
˚
a/A
7.6097(15)
10.758(2)
12.984(3)
90.03(3)
103.56(3)
108.26(3)
978.1(4)
1
8.6852(13)
9.8884(14)
11.9403(17)
96.531(2)
98.137(2)
94.415(2)
1004.0(3)
1
8.4760(11)
13.0531(14)
16.115(2)
93.375(11)
102.595(12)
100.232(11)
1703.5(4)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
l/mm−1
1.008
0.720
4.136
1.024
Unique data
Rint
Final R1 [I > 2 r(I)]
4471
0.0308
0.0334
4576
0.0353
0.0362
7703
0.0346
0.0281
6104
0.0398
0.0297
and was characterised by 31P NMR (CH2Cl2) dP 30.2 (s), 30.3 (s)
Preparation of [Rh(acac)(CO)(1a)] (8a)
35.3 (br).
To a Schlenk tube containing [Rh(acac)(CO)2] (50 mg,
0.194 mmol) and 1a (56 mg, 0.194 mmol) was added CH2Cl2.
After stirring the mixture for 1 h, the solution was filtered
through a pipette containing cotton wool and alumina (0.3 cm ×
0.6 cm). The solvent was removed in vacuo to give analytically
pure 8a in quantitative yield. Elemental analysis, found (calc.):
C 50.4 (50.6), H 5.4 (5.2). 1H NMR (CDCl3): dH 7.80–7.95 (m,
2 H, ArH), 7.10–7.25 (m, 3 H, ArH), 1.55–1.9 (m, 12 H, CH2),
Reactions of [PtCl2(cod)] with 1a or 1b
The phosphine 1a (30 mg, 0.102 mmol) was added to a solution
of [PtCl2(cod)] (19 mg, 0.051) in CH2Cl2 (2 cm3) and the mixture
stirred. The reaction was monitored over 24 h by 31P NMR
spectroscopy (see Results and discussion for the data). The
same procedure was carried out for the reaction of 1b with
[PtCl2(cod)].
1.05–1.25 (m, 12 H, CH2). 31P NMR (CDCl3): dP = 46.3 (1JRhP
=
184 Hz). IR (Nujol) mCO: 1983 cm−1. MS (FAB) m/z 522 (M);
494 (M − CO).
Formation of [NHEt3][CoCl3(1a)] (9)
Preparation of trans-[IrCl(CO)(1a)2] (6a)
CoCl2·6H2O (34 mg, 0.14 mmol) and 1a (86 mg, 0.30 mmol)
were dissolved in ethanol (10 cm3) and the mixture heated for 4
d at 60 ◦C under N2. The volume of the resulting blue solution
was reduced to 2 cm3 at reduced pressure and then cooled in ice.
The precipitated unreacted 1a was filtered off and the filtrate
reduced to dryness to give a blue solid which analysed for
H[CoCl3(1a)]·HCl (40 mg, 50%); found (calc.): C 38.4 (38.8),
H 4.7 (4.7). The product was dissolved in Et2O and a few drops
of Et3N were added. Dark blue crystals of 9 slowly formed.
To a solution of IrCl3·nH2O (0.072g, assay 53.1% Ir) in dmf
(10 cm3) was added 1a (0.29 g, moles). The solution was heated
at reflux temperature for 20 h and then reduced to 3 cm3
under vacuum. The solution was cooled in ice to initiate the
precipitation of a yellow solid. The solid was collected and dried
under vacuum. Elemental analysis, found (calc.): C 47.5 (47.2),
H 5.0 (5.0). IR (CH2Cl2): mCO 1973 cm−1. 1H NMR (CDCl3): dH
1.37–2.04 (m, 32 H,Cg), 7.29–7.43 (m, 6 H, Ph), 7.97–8.17 (m, 4
H, Ph). 31P NMR (CDCl3): dP 23.32 (s), 23.15 (s). IR (CH2Cl2)
mCO: 1973 cm−1.
Typical procedure for hydroformylation of 1-hexene
[Rh(acac)(CO)2] (5 mg, 0.019 mmol), and biphenyl (0.468 g,
3.038 mmol) were added to a solution of 1b (30 mg, 0.086 mmol)
in dry toluene (5 cm3) and loaded into the autoclave, which was
the◦n flushed with syngas and pressurised to 10 bar. After 1 h at
60 C, the 1-hexene (1.2 cm3, 0.80 g, 9.5 mmol) was injected and
the autoclave brought up to 20 bar syngas pressure. The reaction
was monitored for 2.5 h by following the syngas uptake from
the ballast vessel. After 3 h, the autoclave was allowed to cool
and the reaction solution analysed by H NMR and GC. H
NMR (CDCl3): dH 9.7 (n, 62%), 9.6 (i, 38%). The reactions were
diluted with toluene (note that the starting materials elute from
the GC before toluene) and analysed by GC equipped with a
FID. The yields and selectivities were calculated using biphenyl
as internal standard. Authentic samples of all possible products
were calibrated against biphenyl in separate experiments. Some
reactions were also analysed by GC-MS to further authenticate
all the possible products.
Preparation of trans-[RhCl(CO)(1a)2] (7a)
Method A. The rhodium analogue of Vaska’s compound
can be prepared by warming RhCl3·3H2O and an excess of
phosphine in ethanol and formaldehyde. The solution was
cooled in ice to initiate the precipitation of a yellow solid. The
solid was collected and dried under vacuum. Elemental analysis,
found (calc.): C 53.0 (52.8), H 5.6 (5.6). 1H NMR (CDCl3): dH
1.36–1.92 (m, 32 H, Cg), 7.29–7.41 (m, 6 H, m,p-Ph), 7.94–8.05
(m, 4 H, o-Ph). 31P NMR (CDCl3): dP 26.7 (d, JRh = 133 Hz),
1
1
–P
26.8 (d, JRh P = 134 Hz). IR mCO: 1986 cm−1. MS (FAB) m/z 750
–
(M); 722 (M − CO); 715 (M − Cl).
Method B. [Rh2Cl2(CO)4] (40 mg, 0.102 mmol) dissolved
in CH2Cl2 (2 cm3) was treated with a solution of la (60 mg,
0.205 mmol) in CH2Cl2. A 31P NMR spectrum recorded at this
stage showed the formation of what is assigned as the chloride
bridged dimer formed by replacement of two CO ligands from
Typical procedure for hydroformylation of acrylate esters
[Rh2Cl2(CO)4] (dP = 46.6, 1JRh P = 184 Hz). Further addition of
–
1a (71 mg, 0.243 mmol) in CH2Cl2 (2 cm3) generates compound
7a. This compound can be isolated by concentration of the
solution and collecting the pale yellow precipitate (0.106 g, 69%).
It shows identical spectroscopic data as that described above.
These were conducted in a stainless steel autoclave sealed at the
pressures given in Table 3. The identities of the products were
established by comparison of retention times and mass spectra
with authentic samples that were prepared in the previous
1 0 8 4
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5

View Online
work.19 A solution of [Rh(acac)(CO)2] (5.0 mg, 0.019 mmol),
ligand (0.011 mmol) biphenyl (0.174 g, 1.126 mmol) and alkene
(5.63 mmol) in toluene (5 cm3), were added to the autoclave
which was then flushed with syngas. The autoclave was then
pressurised, sealed and stirred at the desired temperature for
the appropriate time (see Table 3). The reaction solutions
were then analysed by GC. The quaternary products all had
shorter retention times than the linear compounds. Conver-
sions to each product were calculated by comparing peak
integrations using the response ratios between biphenyl (internal
standard) and authentic samples of each constituent. The
products were then further characterised by 1H NMR and mass
spectrometry.
130, 1547. and; (b) G. Bekiaris and G. V. Roschenthaler, Heteroat.
Chem., 1998, 9, 173.
6 C. A. Carraz and D. W. Stephan, Organometallics, 2000, 19, 3791.
7 (a) D. Evans, J. A. Osborn and G. Wilkinson, Inorg. Synth., 1990, 28,
79; (b) J. P. Collman, C. T. Sears and M. Kubota, Inorg. Synth., 1990,
28, 92.
8 B. J. Dunne, R. B. Morris and A. G. Orpen, J. Chem. Soc., Dalton
Trans., 1991, 653.
9 A. M. Trzeciak, T. Glowiak, R. Gryzbek and J. J. Ziolkowski,
J. Chem. Soc., Dalton Trans., 1997, 1831 and references therein.
10 X. L. Luo, D. Michos, R. H. Crabtree and M. B. Hall, Inorg. Chim.
Acta, 1992, 198, 429.
11 M. L. Clarke, G. L. Halliday, A. M. Z. Slawin and J. D. Woollins,
J. Chem. Soc., Dalton Trans., 2002, 1093 and references therein.
12 K. G. Moloy and J. L. Petersen, J. Am. Chem. Soc., 1995, 117, 7696.
13 K. A. Jensen, P. H. Nielson and C. T. Pendersen, Acta Chem. Scand.,
1963, 17, 1115.
14 Rhodium Catalyzed Hydroformylation, ed. P. W. N. M. van Leeuwen,
and C. Claver, Kluwer Academic Publishers, Dordrecht, 2000.
15 (a) P. W. N. M. van Leeuwen and C. F. Roobeek, J. Organomet.
Chem., 1983, 258, 343; (b) T. Jongsma, G. Challa and P. W. N. M.
van Leeuwen, J. Organomet. Chem., 1991, 421, 121; (c) A. van Rooy,
E. N. Orji, P. C. J. Kamer, F. van der Aardweg and P. W. N. M.
van Leeuwen, J. Chem. Soc., Chem. Commun., 1991, 1096; (d) A.
van Rooy, E. N. Orji, P. C. J. Kamer and P. W. N. M. van Leeuwen,
Organometallics, 1995, 14, 34.
X-Ray crystal structure analyses of meso-2a·CH2Cl2, meso-2b,
rac-6a and 9
X-Ray diffraction experiments on meso-2a·CH2Cl2, meso-2b,
rac-6a and 9 were carried out at 173 K on Bruker CCD diffrac-
˚
tometers using Mo-Ka X-radiation (k = 0.71073 A). Crystal
and refinement data are given in Table 4 below. Absorption
corrections were based on equivalent reflections and structures
2
refined against all F0 data with hydrogen atoms riding in
16 (a) B. Breit, J. Chem. Soc., Chem. Commun., 1996, 2071; (b) B. Breit,
R. Winde, T. Mackewitz, R. Paciello and K. Harms, Chem. –Eur. J.,
2001, 7, 3106; (c) B. Breit and E. Fuchs, Chem. Commun., 2004, 694;
(d) R. A. Baber, M. L. Clarke, A. G. Orpen and D. A. Ratcliffe,
J. Organomet. Chem., 2003, 667, 112; (e) R. Jackstell, H. Klein, M.
Beller, K.-D. Wiese and D. Rottger, Eur. J. Org. Chem., 2001, 3871.
17 (a) D. Selent, K.-D. Wiese, D. Rottger and A. Borner, Angew. Chem.,
Int. Ed. Engl., 2000, 39, 1649; (b) J. I. van der Vlugt, R. Sablong,
P. C. M. M. Magusin, A. M. Mills, A. L. Spek and D. Vogt,
Organometallics, 2004, 23, 3177.
18 (a) M. M. H. Lambers-Verstappen and J. G. DeVries, Adv. Synth.
Catal., 2003, 345, 478; (b) K. Nozaki, T. Nanno and H. Takaya,
J. Organomet. Chem., 1997, 527, 103; (c) B. Breit, P. Demel and A.
Gebert, Chem. Commun., 2004, 114; (d) C. J. Cobley, J. Kloson, C.
Qin and G. T. Whiteker, Org. Lett., 2004, 6, 3277.
calculated positions. Final difference maps showed no features
of chemical significance.
CCDC reference numbers 257575–257578 for rac-6a, meso-
2a·CH2Cl2, meso-2b, and 9, respectively.
See http://www.rsc.org/suppdata/dt/b4/b418259f/ for cry-
stallographic data in CIF or other electronic format.
References
1 M. Epstein and S. A. Buckler, J. Am. Chem. Soc., 1961, 83, 3279.
2 (a) V. Gee, A. G. Orpen, H. Phetmung, P. G. Pringle and R. I. Pugh,
Chem. Commun., 1999, 901; (b) R. I. Pugh, E. Drent and P. G. Pringle,
Chem. Commun, 2001, 1476; (c) R. I. Pugh and E. Drent, Adv. Synth.
Catal., 2002, 344, 837.
3 (a) J. C. L. J. Suykerbuyk, E. Drent and P. G. Pringle, (Shell), World
Pat., 98/42717, 1998; (b) P. H. M. Buzelaar, E. Drent and P. G.
Pringle, (Shell), Eur. Pat., 97/302079, 1996; (c) W. Ahlers, (BASF),
Eur. Pat., EP 1280754, 2004.
4 G. Adjabeng, T. Brenstrum, J. Wilson, C. Frampton, A. Robertson,
J. Hillhouse, J. McNulty and A. Capretta, Org. Lett., 2003, 5, 953.
5 (a) A similar mechanism has been suggested in: G. Bekariaris, E.
Lork, W. Offermann and G. V. Roschenthaler, Chem. Ber., 1997,
19 M. L. Clarke, Tetrahedron Lett., 2004, 45, 4043.
20 B. Breit and W. Seiche, Synthesis, 2001, 1.
21 (a) H. M. Colquhoun, D. J. Thompson, and M. V. Trigg, Carbony-
lation: Direct synthesis of carbonyl compounds, Plenum Press, New
York, 1991, ch. 4; (b) A. I. M. Keulemans, A. Kwantes and T. van
Bavel, Recl. Trav. Chim. Pays-Bas, 1948, 67, 298.
22 A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen and
F. J. Timmers, Organometallics, 1996, 15, 1518.
D a l t o n T r a n s . , 2 0 0 5 , 1 0 7 9 – 1 0 8 5
1 0 8 5