Synthesis of (1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octane and derivatives

Article abstract of DOI:10.1039/b924983d

The novel primary phosphine (1R,3S)-[1,2,2-trimethyl-3-(phosphinomethyl) cyclopentyl]methyl methanesulfonate 3a (or tosylate 3b) has been prepared in three steps from (1R,3S)-camphoric acid with a view to utilising it as a synthon for the preparation of p

Full text of DOI:10.1039/b924983d

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis of (1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octane and
derivatives†
Peter G. Edwards,* James C. Knight and Paul D. Newman*
Received 27th November 2009, Accepted 8th February 2010
First published as an Advance Article on the web 11th March 2010
DOI: 10.1039/b924983d
The novel primary phosphine (1R,3S)-[1,2,2-trimethyl-3-(phosphinomethyl)cyclopentyl]methyl
methanesulfonate 3a (or tosylate 3b) has been prepared in three steps from (1R,3S)-camphoric acid
with a view to utilising it as a synthon for the preparation of polycyclic phosphines. Efforts to prepare a
[3.2.1] bicyclic product by internal cyclisation of 3a or 3b under various conditions were unsuccessful,
but heating the neat compound at 140 ◦C for several hours gave the new asymmetric, bicyclic secondary
phosphine, (1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octane (PBO) as its methanesulfonic
acid 5a (or p-toluenesulfonic acid 5b) salt. The cyclisation involves a skeletal rearrangement and occurs
with high stereoselectivity to generate two new stereogenic carbon centres and a chiral phosphorus
atom. The secondary phosphine was obtained after base treatment of 5a/b and several derivatives of
the phosphine have been synthesised and characterised. Reaction of two mol equivalents of the borane
adduct of PBO with a,a¢-dichloro-ortho-xylene gave the bidentate derivative, o-C6H4(CH2PBO)2.2BH3,
12, and ultimately o-C6H4(CH2PBO)2, 13. Complexes of 13 with Pd(II), Pt(II), Pt(0) and Mo(0) have
been prepared and characterised by spectroscopic and analytical methods including single-crystal X-ray
structure determinations of cis-Pd{o-C6H4(CH2PBO)2}Cl2, 14, cis-Pt{o-C6H4(CH2PBO)2}Cl2, 15 and
Mo(CO)4{o-C6H4(CH2PBO)2} 17.
phosphinanes7 and phosphepanes3 have been investigated by a
Introduction
number of groups in an effort to understand how ring size
The success of phosphorus-containing ligands in homogeneous
can influence coordination behaviour and affect the catalytic
catalysis is legend.1 The reasons for this are wide-ranging but
behaviour of their metal complexes. Reported examples of bi- and
polycyclic systems8 include the well-established phobane ligands,9
the 7-phosphabicyclo[2.2.1]heptanes10 and phosphabarrelenes11
with aspects of the chemistry of these and many more heterocyclic
phosphorus compounds being the subject of a recent comprehen-
sive review.12
relate in the main to the ease with which the electronic and steric
properties of the phosphorus donor can be varied through alter-
ation of the groups attached to the P-atom. Furthermore, as the
s-donating/p-accepting properties of such ligands are determined
by the nature of the HOMO (lone pair) and LUMO (s* orbitals)
they are sensitive to the intraphosphorus angles. Thus small
heterocyclic systems can show unusual electronic and indeed steric
properties as a direct consequence of the necessarily constrained
X-P-X bond angles in these compounds.2 Cyclic derivatives such as
the C2P phosphiranes and C3P phosphetanes with typical internal
C–P–C angles of ~50◦ and ~80◦ are extraordinary while the larger
5- (phospholanes) and 6-membered (phosphinanes) homologues
with C–P–C angles of ~94◦ and 97◦ produce ligands with features
more comparable with related acyclic derivatives.
Recognition of these nuances of phosphacycles has prompted
investigation of the nature of their bonding to transition metals
especially those commonly employed in homogeneous catalysis.3
Much of the driving force for the study of the five-membered
phospholanes has come from their successful employment in
asymmetric catalysis as epitomised by the DuPHOS series
of ligands founded by Burk.4 Although less-well studied, the
smaller ring phosphiranes5 and phosphetanes6 and larger ring
We have been interested in investigating the donating ability
of phosphiranes,5a phosphetanes13 and phosphinanes,14 both as
simple monodentate donors and as part of bi- and multidentate
systems. Our early interest in phosphacycles lay in phospholane
and phobane chemistry9a and has since evolved to include
phosphacycles with rigid, inherently chiral frameworks that
may have application in asymmetric synthesis.14 As part of this
continuing study we have sought to prepare novel phosphorus
containing polycycles (preferably asymmetric) with a view to
exploring their coordination properties. The inherently chiral
secondary phosphine shown as 4 in Scheme 1 was one such
target, however efforts to obtain 4 by typical synthetic protocols
have thus far failed. That said, one of these failed routes did
furnish a related unexplored [2.2.2] bicyclic phosphacycle namely
(1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octane (PBO),
6. The present paper details the synthesis of PBO along
with the preparation and characterisation of
a number
of derivatives of the parent phosphacycle including the
potentially bidentate ligand a,a¢-bis{(1R,4S,6R)-5,5,6-trimethyl-
2-phosphabicyclo[2.2.2]octyl}-o-xylene, o-C6H4(CH2PBO)2, 13.
Some elementary coordination chemistry of a,a¢-bis{(1R,4S,6R)-
School of Chemistry, Cardiff University, Cardiff, UK CF10 3AT.
E-mail: newmanp1@cardiff.ac.uk, edwardspg@cardiff.ac.uk; Fax: +44 029
20874030; Tel: +44 029 20870464
† CCDC reference numbers 756173–756176. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b924983d
5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octyl}-o-xylene
with
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the reclamation of 3a/b after work-up. Efforts to promote a
ring closure to 4 by the addition of organolithium reagents to
3a/b were also unsuccessful with the formation of red, insoluble
precipitates occurring upon addition of the strongly basic
organolithium reagent to the phosphino-sulfonate; heating did
not lead to dissolution of the solids, which are presumably metal
phosphide species, and prolonged reflux led to decomposition.
Ring-closure was induced upon heating 3a/b to 140 ◦C for
extended periods (6–18 h) in the absence of solvent. Thus, when
either 3a or 3b was heated ina Schlenk flaskunder these conditions,
a crystalline solid sublimed in the upper reaches of the flask
in addition to some oily, unsublimed material. Spectroscopic
analysis of the sublimed solid confirmed that the compound
was not the anticipated [3.2.1] cycle shown as 4 in Scheme 1.
1
The 31P{ H} NMR spectrum of the crystalline solid recorded in
CDCl3 consists of a very broad resonance at d -65 ppm. Two
features of this spectrum are unusual. Firstly, the broad nature
of the resonance suggests the existence of an exchange process
in solution, presumably a rapid proton exchange between the
phosphonium cation and the solvent and/or mesylate(tosylate)
anion. Secondly, the position of the resonance is not in the
region expected for a protonated secondary phosphonium salt.
Indeed, the peak occurs at a chemical shift more appropriate
for a secondary phosphine and it appears that proton exchange
from the parent phosphine is rapid for the compound even in
Scheme 1 Synthesis of PBO, 6, and some derivatives. i) ROSO2Cl, Et3N,
DMAP; ii) LiP(SiMe3)2, MeOH; iii) 145◦, 18 h; iv) Na2CO3; v) 3% aq.
H2O2; vi) MeI, THF, RT; vii) xs MeI, THF, reflux.
1
fairly apolar media. The 13C{ H} DEPT NMR spectrum of the
sublimed solid revealed the presence of three CH2 groups and three
CH carbons, clearly not in accord with the distribution expected
for the [3.2.1] cycle. The forcing conditions of the cyclisation had
induced a rearrangement of the bicyclic skeleton to give the [2.2.2]
compound as the hydrophosphonium sulfonate (5a/b). A putative
mechanism for the rearrangement is shown in Scheme 2. The likely
intermediate is a tertiary carbocation (formed through loss of the
sulfonate group) that rearranges through a 1,2-hydride shift to give
the product as shown in the figure. The failure of the phosphine
to trap the initially formed carbocation is likely to be a result of
steric encumbrance although it may be that the mechanism is more
concerted with the hydride migration occurring concomitantly
with the loss of the sulfonate. One of the two original stereogenic
carbon centres (the bridgehead carbon at position 3) is unaffected
by the rearrangement and retains its S stereochemistry. The 1-
carbon atom of the phosphino-sulfonate is involved in bond
breaking and forming with the result that it is no longer a
molybdenum(0), palladium(II) and platinum(II/0) is also
reported.
Results and discussion
Synthesis of (1R,4S,6R)-5,5,6-trimethyl-2-
phosphabicyclo[2.2.2]octane (PBO) and derivatives
The synthesis of (1R,4S,6R)-5,5,6-trimethyl-2-phosphabi-
cyclo[2.2.2]octane, PBO (6), is shown in Scheme 1. The starting
point for the synthesis is the (1R,3S)-camphanediol (1) obtained
by lithium aluminium hydride reduction of (1R,3S)-camphoric
acid. The conversion of the diol to the dimesylate (2a) or
ditosylate (2b) is readily achieved through the DMAP catalysed
reaction with the relevant sulfonyl chloride in the presence of
base. Subsequent reaction of either 2a or 2b with one equivalent
of LiP(SiMe3)2 gives, after protonolysis, (1R,3S)-[1,2,2-trimethyl-
3-(phosphinomethyl)cyclopentyl]methyl methanesulfonate, 3a,
or tosylate, 3b. The regioselectivity observed in this reaction is
typical for this type of skeleton with nucleophilic substitution
occurring preferentially at the more open iso-butyl carbon rather
than the largely unreactive neo-pentyl position. Both 3a and 3b
were isolated as low-melting waxy solids with 31P resonances
around -140 ppm (1JP–H = 195 Hz) in their 31P NMR spectra as
expected for an iso-butyl-based primary phosphine.15 The most
distinctive features of the 1H NMR spectra of 3a/b are the doublet
of multiplets for the phosphine protons centered around 2.60 ppm
and the two doublets of an AB coupled system between 3.9 and
4.2 ppm for the diastereomeric protons of the methylene groups
a to the sulfonate functionality (see experimental). Attempts
to substitute both sulfonates in 2a/b by reaction with ≥2 mol
equivalents of LiP(SiMe3)2 were unsuccessful leading only to
Scheme 2 Proposed mechanism for the formation of 5a,b.
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bridgehead carbon in the product but part of one of the ethane
bridges. The transformation appears to be stereoselective with only
the 1R,4S,6R isomer of the product being observed (see below).
The unsublimed material from the reaction is a mixture of the
phosphonium salt and other, apparently oxidised, species resulting
from oxygen transfer from the sulfonate to the phosphorus. This
mixture, when treated with LiAlH4, gives the secondary phos-
phine (1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octane
(PBO), 6, as a sublimable, low-melting solid. The phosphine is
obtained as two isomers with 31P NMR chemical shifts of -60.8
(minor) and -79.6 (major) ppm, respectively. The dP values are
in the region expected for a 6-membered secondary phosphacycle
with isobutyl and isopropyl type substituents. The diastereose-
lectivity is approximately 80 : 20 as deduced from integration of
appropriate signals (most notably the CH3 resonances) in the
1H NMR spectrum (details of which, for the major isomer, are
presented in the experimental). Aside from the peaks for the methyl
groups, the 1H NMR spectrum is complex with most resonances
occurring between 2.0 and 0.5 ppm. The PH proton of the major
isomer is observed as a doublet of triplets at dP 3.04 ppm with
1JH–P of 183.8 Hz and 2JH–H of 10.1 Hz. The relatively large value
of 15.4 Hz for the 2JP–C coupling constant to the methine carbon
(C6) compared to 8.9 Hz for the methylene group (C7) in the
Fig. 1 Ortep view of the molecular structure of the cation 9.
full stereochemistry is determined as (1R,4S,6R). The P–C bond
lengths to the ring carbons and the methyl carbons are typical
˚
˚
at ~1.817(4) A and 1.789(4) A but the internal C–P–C bond
angle is compressed at 100.43(17)◦ compared to the remaining
intraphosphorus angles which average 111.3(2)◦.
1
13C{ H} NMR spectrum suggests that (SP)-6 is the major isomer.‡
This is supported by 2D NOESY NMR experiments which show
through-space contacts between the P–H proton and the two axial
hydrogens of the C3 and C7 methylene groups.
Synthesis of a,a¢-bis{(1R,4S,6R)-5,5,6-trimethyl-2-
phosphabicyclo[2.2.2]octyl}-o-xylene, o-C6H4(CH2PBO)2, 13
The secondary phosphine, 6, is unstable in CDCl3 and a solution
left standing for 48 h shows only a broad peak at -65 ppm in the
An initial premise of the work reported here was to include
compound 4 as part of a bidentate system with an ortho-xylyl
backbone. This choice of backbone reflects another long term
interest of our group stemming from early work on 1,2-bis(di-
tert-butylphosphinomethyl)benzene.16 A continued interest in this
linker has been fuelled by the flexible nature of ligands with
this backbone which show a wide range of P–M–P bite angles
dependent upon, amongst other things, the other substituents at
the P-donors.13,17 Many catalytic cycles have rate determining steps
that are strongly influenced by the ligand bite angle and it is the
impact that these flexible frameworks may have on the behaviour
of the resultant complex(es) that has maintained our interest in
these systems. Failure to isolate 4 did not diminish this desire as
the unexpected synthesis of PBO presented a similar opportunity
to study polycyclic phosphines with an o-xylyl bridge.
1
31P{ H} NMR spectrum. This resonance resembles closely that
1
for the phosphonium species 5. Inspection of the 1H and 13C{ H}
NMR spectra of the sample confirms formation of a phosphonium
salt and it is clear that the phosphine has abstracted DCl from the
CDCl3 to give the P(V) species. Compound 6 is extremely sensitive
to oxygen and decomposes very easily on exposure to air to give
the secondary phosphine oxide (1R,4S,6R)-5,5,6-trimethyl-2-oxa-
2-phosphabicyclo[2.2.2]octane, 7, which is more readily obtained
by oxidation with dilute hydrogen peroxide in a biphasic solvent.
The oxide 7 sublimes under high vacuum to give two diastereomers
in approximately 2 : 1 ratio as determined by integration of the two
1
distinct signals for the P(O)H protons in the H NMR spectrum
at dP 6.99 (dt, 1JH–P 455 Hz) for the major and dP 6.84 (dm, 1JH–P
463 Hz) ppm for the minor isomer.
The reaction of 6 with a,a¢-dichloro-ortho-xylene led to the
isolation of the heterocyclic phosphonium salt, 10 (Scheme 3).
The formation of species such as 10 has frustrated attempts to syn-
thesise a number of diphosphines of the type o-C6H4(CH2PR2)2.
The use of protecting functions, especially BH3, is generally
used to circumvent the problem of cyclic phosphonium salt
formation. PBO can be protected as the borane adduct in the
usual way giving PBO.BH3, 11, as a mixture of diastereomers
Phosphine 6 reacts cleanly with a slight molar excess of MeI
in THF to give the methylated phosphonium salt 8 as a white
precipitate which is isolated as a 70 : 30 diastereomeric mixture in
90% yield. The reaction is extremely rapid, being instantaneous at
RT as observed by the immediate precipitation of the salt when
the reaction is performed under moderate dilution (1 to 2 M).
Heating a THF solution of 6 with a large excess (10-fold) of methyl
iodide leads to double methylation of the phosphorus to give 9
as the iodide salt. The salt has been characterised in the solid-
state by a single crystal X-ray structure determination as shown
in Fig. 1. The bicyclic nature of the phosphine is immediately
evident and the chirality of the carbon centres is as expected from
the choice of (1R,3S)-camphoric acid as starting material, thus the
1
(~4 : 1 ratio) as identified from 31P{ H} NMR spectral analysis of
the solution where the major four line resonance was observed
at dP -14.4 ppm (1JP–B = 45 Hz) and the minor isomer at dP
-4.3 ppm (1JP–B = 45 Hz). The PBO.BH3 adduct was not isolated
but converted to the lithium salt in situ upon addition of one
mole equivalent of n-BuLi at low temperature. Formation of the
1
lithiated species was confirmed from the change in the 31P{ H}
NMR spectrum where a major species at -68.4 ppm (1JP–B
=
‡ This is a result of the lone pair of the phosphorus lying close to the C6
carbon atom [see ref.20].
39 Hz) ppm and a minor at -66.1 ppm (1JP–B = 40 Hz) were
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in organic solvents such as chloroform and dichloromethane
but showed higher solubility in more polar solvents such as
methanol and acetone. Cis-Pt{o-C6H4(CH2PBO)2}Cl2 shows two
AB doublets (2JP–P = 22.5 Hz) at dP = -3.5 and -4.1 ppm in
1
its 31P{ H} NMR spectrum at RT indicating asymmetry in the
bidentate ligand. Both signals have associated Pt-195 satellites
1
with JP–Pt coupling constants of 3310 and 3468 Hz, respectively.
The two phosphines are also inequivalent in the related cis-Pd{o-
C6H4(CH2PBO)2}Cl2 complex as evidenced by the presence of
1
two peaks in the room temperature 31P{ H} NMR spectrum but
in this case no observable P–P coupling was seen. As is usual
for phosphine complexes of Pd(II) and Pt(II), the chemical shift
induced upon coordination (DdP) is larger for the Pd(II) complex
(+ 54 ppm) compared to the analogous Pt(II) species (+ 34 ppm).21
The lack of C2 symmetry is a consequence of an asymmetric
backbone as shown in the crystal structures of the two complexes
(Fig. 2 and 3). The complexes are isostructural with an asymmetric
boat conformation for the 7-membered chelate ring as shown in
the figures. The sum of the angles about the metal centres are
359.94(4)◦ for Pd(II) and 359.96(8)◦ for Pt(II) emphasising the
compliance to square planar coordination. The Cl-M-Cl angle
is the smallest intrametal angle in both complexes although the
distortion from the ideal is small {88.93(4)◦ for Pd and 86.92(8)◦
for Pt}. All other metrical data accord with those expected for
such systems. The variance of the P–M–P bite angle in these o-
xylyl backbone diphosphines is of interest. Larger bite angles are
observed when the xylyl aryl ring lies flatter to the square plane
(for Pd2+, Pt2+ and Rh+ complexes) of the complex, whereas more
acute P–M–P angles are observed when the ring is orthogonal
to the coordination plane.13,17b–e,22 More specifically, the closer the
methylene carbon atoms of the xylyl group are to being coplanar
with the coordination plane, the wider the bite angle. This would
appear to be sensitive to the nature of the other substituents on
the phosphorus donors with the more obtuse P–M-–P angles being
observed with bulkier substituents. The low bite angles in 14 and
15 suggest that the [2.2.2] bicyclic framework of the P-donors in the
o-C6H4(CH2PBO)2 ligand are sterically slight, a feature associated
at least in part with the compressed internal C–P–C angles of
Scheme
3
i) 0.5 o-C6H4(CH2Cl)2; ii) BH3·THF; iii) n-BuLi, 0.5
o-C6H4(CH2Cl)2; iv) HBF4·Et2O, aq. Na2CO3.
observed in an approximate ratio of 4 : 1 for the deprotonated
secondary phosphine-borane compound (Scheme 3). Addition of
a,a¢-dichloro-ortho-xylene to the solution of the borane protected
phosphide gave the diphosphine borane, 12, as a mixture of 2
diastereomers (~8 : 1 ratio) which was deprotected with HBF4
or 1,4-bis(2-aminoethyl)piperidine as detailed by Livinghouse18
and Knochel19 respectively to give 13. The diphosphine, 13, was
acquired in 80% yield and isolated as a single diastereomer after
one recrystallisation from MeOH. The 31P{ H} NMR spectrum
1
of 13 consists of a singlet at dP -38.4 ppm. Spectroscopic analysis
by one- and two-dimensional NMR methods, especially 2D
NOESY experiments, revealed that the xylene group is orientated
axially and the P-centres have the R Chirality as shown in the
scheme. Key features of the spectroscopic data that support
2
this conclusion include a large JC–P coupling to C6 (21.1 Hz)
rather than C7 (2.5 Hz) as a consequence of the proximity
of the P lone pair to C6 and NOESY contacts between the
methylene protons H12 and the axial H3 and H6 hydrogens.20
The isolation of the diphosphine as this diastereomer suggests
that the stereogenic integrity of the P centre is largely retained
during the boronation/deprotonation/deboronation sequence as
expressed in the scheme.
Complexes of o-C6H4(CH2PBO)2 with Pd(II), Pt(II), Pt(0) and
Mo(0)
Fig. 2 Ortep view of the molecular structure of 14. Thermal ellipsoids
Reaction of the ligand 13 with Pt(1,5-COD)Cl2 or K2PdCl4
are drawn at 50% probability, hy◦drogens are omitted for clarity. Selected
in
a
1 : 1 ratio gave complexes of the type cis-M{o-
˚
bond lengths (A) and angles ( ) for 14: Pd1–P1 2.2699(12), Pd1–P2
C6H4(CH2PBO)2}Cl2 where M = Pd(II), 14, Pt(II), 15. Both com-
plexes were obtained as colourless crystals after recrystallisation
from acetonitrile. 14 and 15 were only very sparingly soluble
2.2567(11), Pd1–Cl1 2.3738(11), Pd1–Cl2 2.3405(12), P1–Pd1–P2 89.95(4),
P1–Pd1–Cl1 91.28(4), P2–Pd1–Cl2 89.78(4), Cl1–Pd1–Cl2 88.93(4),
C1–P1–C10 96.0(2), C11–P2–C20 97.0(2).
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equate to activation energies for the bridge inversion of 77 KJ
mol-1 for 14 and 71 KJ mol-1 for 15. The 1H NMR spectra
of the complexes are simplified when recorded at temperatures
above these coalescence limits as detailed in the experimental
section. Temperature-dependent NMR spectra have been reported
previously in related systems.17e
The Pt(0) complex Pt{o-C6H4(CH2PBO)2}(nb), 16, was
prepared from Pt{o-C6H4(CH2PBO)2}Cl2 by the method of
Weigand.23 The complex was obtained as a white solid which was
freely soluble in organic solvents and appeared to be stable in
the absence of added norbornene unlike most of the complexes
1
reported by Weigand.23 The 31P{ H} NMR spectrum of the
complex consists of two AB doublets with a 2JP–P coupling constant
1
of 45 Hz and Pt-195 satellites with a JP–Pt coupling constant
of 3336 Hz. The AB pattern reflects a lack of symmetry in the
complex at room temperature mimicking the pattern observed
for the Pt(II) system. Weigand has correlated the JP–Pt coupling
Fig. 3 Ortep view of the molecular structure of 15. Thermal ellipsoids
1
are drawn at 50% probability,◦hydrogens are omitted for clarity. Selected
constants of a number of Pt(R2P∧PR2)(nb) species with the bite
angle of the diphosphine observing decreasing |J| as the P–
Pt–P angle decreases.23 The value of 3336 Hz observed in the
current complex (16) is consistent with a bite angle of around
90◦ according to the correlation of Weigand. This suggests that
a conformation similar to that observed in the solid state for
cis-Pt{o-C6H4(CH2PBO)2}Cl2 is maintained in solution for the
Pt(0) complex. However, caution should be exercised in using
1JP–Pt coupling constants as indicators of chelate bite angle as
˚
bond lengths (A) and angles ( ) for 15: Pt1–P1 2.246(2), Pt1–P2 2.239(2),
Pt1–Cl1 2.374(2), Pt1–Cl2 2.346(2), P1–Pt1–P2 90.76(8), P1–Pt1–Cl1
91.65(8), P2–Pt1–Cl2 90.63(8), Cl1–Pt1–Cl2 86.92(8), C6-P1–C10 96.9(4),
C19–P2–C28 97.3(4).
around 97◦ for the phosphacycles. Small bite angles have been
observed with related cis-M{o-C6H4(CH2PR2)2}Cl2 systems where
the P-substituents are not sterically demanding.13,17b As alluded
above, when the bite angle is small (around 90◦) the xylyl aromatic
ring tends towards orthogonality to the ML4 plane; this is clearly
the case in the cis-M{o-C6H4(CH2PBO)2}Cl2 complexes shown in
Fig. 2 and 3 where the aryl ring projects almost vertically over the
ML4 plane. As a consequence, the bicyclic [2.2.2] frameworks of
the phosphacycles are forced into a position on the opposing side
of the coordination plane to the xylyl backbone such that each
potential axial coordination site is quite distinct. The chirality
at the phosphorus centres is S as deduced previously from the
NMR analysis of the free ligand (accepting that the priority of
the groups has changed with the lone pair being replaced by the
metal). The methylene groups of the xylyl backbone project axially
leading to equatorial lone pairs or, in the case of the complexes,
equatorial P–M bonds. The P–M–P bond angles are around 90◦
as anticipated for square planar complexes. These favoured bond
angles are quite different from the expanded angles of around
100◦ observed in the complexes of related ligands with tert-
butyl substituents and/or other bulky diphosphines containing
the o-xylyl backbone, but are similar to those reported for a
similar system containing phosphetane donors bound to Pd(II).13
Interestingly, this latter complex shows considerable distortion
from square planar geometry unlike the complexes reported
here.
1
the Pt{o-C6H4(CH2PtBu2)2}(nb) complex has a JP–Pt constant
of only 3331 Hz even though the majority of crystal structures
◦
1
containing this ligand show bite angles of >100 .22a The 13C{ H}
NMR spectrum of complex 16 shows a doublet of doublets for
the alkenic carbon at dC 51.3 ppm with JC–P values of 36.3 and
27.2 Hz. These carbons also show Pt-195 satellites with a JC–Pt
2
1
coupling constant of 338 Hz, a value very similar to that of
332 Hz observed for the Pt{o-C6H4(CH2PtBu2)2}(nb) complex.22a
The bridgehead methines are observed at dC 45.1 ppm with a 2JC–Pt
coupling constant of 12.8 Hz again in accord with that observed
for the tert-butyl derivative.22a A doublet at 0.11 ppm (2JH–H
=
8.2 Hz) is observed for a hydrogen of the methylene bridge CH2
group that resides near the metal suggesting that the norbornene
coordinates from the exo face of the double bond. Cooling NMR
◦
solutions of complex 16 to low temperature (< -35 C) resulted
1
in four broad peaks in the 31P{ H} NMR spectrum at dP 7.6,
5.5, -3.1, and -4.0 ppm indicating the presence of two species in
solution, both of which have asymmetry in the chelate ring. The
most likely explanation for this is the presence of two different
alkene rotamers whereby the rotation of the formal C–C double
bond about the metal-alkene axis has been slowed to the point
that both forms are observed at this low temperature.
The colourless Mo(CO)4{o-C6H4(CH2PBO)2} complex, 17, is
readily prepared from Mo(CO)4(pip)2 and one mol equivalent of
the ligand. The molybdenum complex is much more soluble in
hydrochlorocarbons than the Pd(II) or Pt(II) dichloride systems
and is readily recrystallised from toluene or 40/60 petroleum ether.
As noted above, the asymmetry observed in the crystal
structures is retained in solution with two separate reso-
1
nances being seen in the 31P{ H} NMR spectrum of cis-
Pd{o-C6H4(CH2PBO)2}Cl2 and an AB pattern for cis-Pt{o-
C6H4(CH2PBO)2}Cl2 at room temperature; the 1H and to a lesser
1
Mo(CO)4{o-C6H4(CH2PBO)2} shows only a singlet in the 31P{ H}
1
extent the 13C{ H} NMR spectra are complex at room temperature
NMR spectrum at room temperature reflecting a rapid exchange in
the xylyl bridge. Upon cooling, the singlet splits into the expected
two peaks as the chelate inversion becomes slow on the NMR
timescale. The coalescence occurs at -35 ◦C with an activation
as a result of this asymmetry in the chelate ring. Heating solutions
of the complexes in d6-dmso leads to coalescence of the two
31P{ H} resonances at temperatures of 115 ◦C for the Pd(II)
1
system and 77 ◦C for the Pt(II) complex respectively. These values
barrier to inversion of 45 KJ mol-1. The RT 1H and 13C{ H} NMR
1
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spectra are consequently much simpler than the room temperature
spectra for the Pd(II) and Pt(II) complexes allowing full assignment
of the spectra for complex 17 (see experimental).
Experimental
Methods and materials
The single-crystal X-ray structure of Mo(CO)4{o-
C6H4(CH2PBO)2} is shown in Fig. 4. Notwithstanding the
fact that 17 is an octahedral complex, many of the features
observed in the Pd(II) and Pt(II) complexes are maintained in the
structure as shown in Fig. 4. Thus, the 7-membered chelate adopts
the asymmetric boat form and the aryl ring of the backbone is
forced into an arrangement orthogonal to the (P∧P)Mo(CO)2
plane in order to accommodate a P–Mo–P bite angle of 90◦. The
orientation of the xylyl ring is such that it appears to be involved
in a p–p interaction with one of the axial carbonyls (C3) causing
the CO ligand to be bent away from the aryl group (Mo–C–O =
All synthetic procedures and manipulations were performed
under dry argon or nitrogen using standard Schlenk line tech-
niques. All solvents were freshly distilled from sodium (toluene),
sodium/benzophenone (THF) or calcium hydride (acetonitrile,
methanol and dichloromethane) under nitrogen before use. All
other chemicals were obtained commercially and used as received.
The 31P NMR spectra were recorded on a Jeol Eclipse 300 MHz
spectrometer operating at 121.7 MHz, and referenced to 85%
1
H3PO4 (d = 0 ppm). H and 13C NMR spectra were obtained
using a Bruker 500 MHz spectrometer, operating at 500.0 and
125.8 MHz, respectively, and referenced to tetramethylsilane (d =
0 ppm). Unless stated otherwise, infrared spectra were recorded
as nujol mulls on a Jasco FTIR spectrometer. Mass spectra were
obtained using a Waters LCT Premier XE mass spectrometer.
Elemental analyses were performed by Medac Ltd, UK.24
◦
˚
170 ) with the centroid of the aryl ring 3.214 A from the midpoint
of the C–O bond. The Mo–C bond lengths are shorter to the
carbonyl ligands trans to the phosphorus donors (Mo–C average
˚
1.988(9) A) as expected when compared to the mutually trans CO
˚
groups where Mo–C bond lengths of 2.044(8) A are observed.
˚
The Mo–P bond lengths average 2.541(2) A and are somewhat
Syntheses
˚
shorter than the value of 2.658(6) A observed in the analogous
Mo(CO)4{o-C6H4(CH2PtBu2)2} system13 although it should be
noted that the P–Mo–P bond angle is slightly expanded in this
latter complex {94.161(18)◦} compared to that for 17 {87.37(7)◦}.
Indeed this relatively acute bite angle appears to be a consequence
of the p–p interaction noted above. Other phosphacyclic systems
with an o-xylyl backbone have metric details very similar to those
for the complex shown here although the very acute chelate bite
and the pronounced p–p interaction are not as evident in these
related systems with smaller 4-membered phosphetanes.13
(1R,3S) - (1,2,2 - trimethylcyclopentane - 1,3 - diyl)bis(methylene)
dimethanesulfonate, 2a. To
a stirred solution of (1,2,2-
trimethylcyclopentane-1,3-diyl)dimethanol25 (3.70 g, 21.47 mmol)
and triethylamine (7.3 ml, 2.2 mol equivs) in DCM (70 ml) at
-10 ◦C was added dropwise mesyl chloride (3.66 ml, 2.2 mol
equivs) in DCM (20 ml) over 20 min. The mixture was stirred
at 0 ◦C for 1 h then at RT overnight. The mixture was washed
successively with 0.5 M HCl (100 ml) then water (2 ¥ 100 ml) and
the organic phase dried over magnesium sulfate. After filtering the
solvent was removed to give a light yellow oil that crystallised on
standing. Yield = 7.05 g (90%). 1H NMR (CDCl3, 400 MHz) d 4.20
(1H, dd, 2,3JH–H = 9.6, 6.0 Hz), 4.08 (2H, m), 3.97 (1H, d, 2JH–H
=
9.5 Hz), 2.95 (6H, s), 2.27 (1H, m), 1.94 (1H, m), 1.60 (1H, m),
1
1.49 (2H, m), 1.01 (3H, s), 0.99 (3H, s), 0.80 (3H, s) ppm. 13C{ H}
DEPT NMR (CDCl3, 100 MHz) d 75.2 (CH2), 71.5 (CH2), 47.4
(C), 46.9 (CH), 44.5 (C), 37.3 (CH3), 37.1 (CH3), 33.4 (CH2), 25.0
(CH2), 23.7 (CH3), 20.7 (CH3), 20.7 (CH3), 18.5 (CH3) ppm. Anal.:
Calc. for C12H24O6S2: C, 43.89; H, 7.38%. Found: C, 43.5; H, 7.4%.
(1R,3S) - (1,2,2 - trimethylcyclopentane - 1,3 - diyl)bis(methylene)
di-p-tolylsulfonate, 2b. This was prepared in a similar manner
to the dimesylate above. Isolated as a white solid that could be
1
recrystallised from toluene–DCM if desired. Yield = 87%. H
2
4
NMR (CDCl3, 400 MHz) d 7.70 (4H, dd, JH–H = 8.1, JH–H
=
1.8 Hz), 7.28 (4H, d, 2JH–H = 8.1 Hz), 3.95 (1H, dd, 2,3JH–H = 9.5,
6.1 Hz), 3.80 (2H, m), 3.68 (1H, d, 2JH–H = 9.3 Hz), 2.38 (6H, s),
2.10 (1H, m), 1.78 (1H, m), 1.39 (1H, m), 1.20 (2H, m), 0.84 (6H,
s), 0.54 (3H, s) ppm. 13C{ H} DEPT NMR (CDCl3, 100 MHz) d
1
144.9 (C), 144.9 (C), 132.9 (C), 132.9 (C), 129.9 (CH), 129.9 (CH),
127.9 (CH), 127.9 (CH), 75.8 (CH2), 72.0 (CH2), 47.3 (C), 46.6
(CH), 44.4 (C), 33.2 (CH2), 24.8 (CH2), 23.6 (CH3), 21.7 (CH3),
20.7 (CH3), 18.2 (CH3) ppm. Anal.: Calc. for C24H32O6S2: C, 59.98;
H, 6.73%. Found: C, 60.1; H, 6.8%.
Fig. 4 Ortep view of the molecular structure of 17. Thermal el-
lipsoids are drawn at 50% probability, hydroge◦ns are omitted for
˚
clarity. Selected bond lengths (A) and angles ( ) for 17: Mo1–P1
2.544(2), Mo1–P2 2.534(2), Mo1–C1 1.984(8), Mo1–C2 2.005(8),
Mo1–C3 2.064(7), Mo1–C4 1.977(9), C1–O1 1.151(8), C2–O2 1.168(8),
C3–O3 1.131(8), C4–O13 1.161(9), P1–Mo1–P2 85.77(7), P1–Mo1–C1
174.4(2), P1–Mo1–C2 91.3(2), P1–Mo1–C3 94.91(19), P1–Mo–C4
93.6(2), P2–Mo1–C1 88.7(2), P2–Mo1–C2 90.5(2), P2–Mo1–C3 94.2(2),
P2–Mo1–C4 179.4(2), C2–Mo1–C3 172.5(3), Mo1–C2–O2 175.8(8),
Mo1–C3–O3 170.2(7), C13–P1–C14 95.3(3), C23–P2–C32 95.8(3).
(1R,3S)-[1,2,2-trimethyl-3-(phosphinomethyl)cyclopentyl]methyl
methanesulfonate, 3a. To a stirred solution of P(SiMe3)3 (1.0 g,
3.99 mmol) in THF (20 ml) was added a solution of MeLi (2.62 ml
of a 1.6 M solution, 4.19 mmol) and the mixture stirred at RT
overnight. After removing the THF at the pump the resultant
3856 | Dalton Trans., 2010, 39, 3851–3860
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◦
cream solid LiP(TMS)2 was dissolved in diethyl ether (20 ml)
and added slowly to a stirred solution of dimesylate (1.31 g,
3.99 mmol) in a 1 : 1 mixture of diethyl ether–THF (30 ml) at
-78 ◦C. After stirring for 1 h at -78 ◦C, the solution was allowed
to reach RT and left stirring overnight. On return, ethanol (1 ml)
was added and the mixture stirred for a further 24 h. After
filtering, the solution was pumped to dryness and the desired
compound dissolved in diethyl ether and filtered off from a small
quantity of insoluble salts. The diethyl ether was removed to give
a white solid that could be recrystallised from MeOH at low
temperature. Yield = 0.82 g (77%). 1H NMR (CDCl3, 500 MHz)
d 4.10 (1H, d, 2JH–H = 9.3 Hz), 3.97 (1H, d, 2JH–H = 9.3 Hz), 2.97
0 C. After stirring overnight at RT, the mixture was hydrolysed
by the addition of water (1 ml), 15% aq. NaOH (1 ml) then water
(3 ml). The mixture was filtered and the solvent removed in vacuo
to yield a viscous oil. The desired phosphine was sublimed from
the residue upon heating between 50 and 80 ◦C under high vacuum
(0.1 mm Hg). Yield = 0.3 g (47%). 1H NMR (CDCl3, 500 MHz,
major isomer) d 3.04 (1H, d, 1JH–P = 183.8 Hz), 1.75 (1H, m), 1.58
(2H, m), 1.39 (1H, m), 1.25 (2H, m), 1.08 (2H, m), 0.68 (3H, s), 0.66
(3H, d, 3JH–H = 7.3 Hz), 0.64 (3H, s) ppm. 13C{ H} DEPT NMR
1
1
(CDCl3, 125 MHz, major isomer) d 38.2 (d, JC–P = 15.33 Hz,
CH), 36.3 (CH), 34.5 (C), 29.8 (CH3), 26.3 (CH), 24.4 (CH3), 22.5
(CH2), 22.2 (CH2), 15.6 (d, 3JC–P = 13.1 Hz, CH3), 14.7 (d, 2JC–P
=
1
1
1
(3H, s), 2.72 (1H, dm, JH–P = 195.3 Hz), 2.60 (1H, dm, JH–P
=
8.90 Hz, CH2) ppm. 31P{ H} NMR (CDCl3, 121.7 MHz): -60.8
194.8 Hz), 2.01 (1H, m), 1.83 (1H, m), 1.55 (2H, m), 1.38 (1H, m),
(minor), -79.6 (major) ppm.
1
1.22 (2H, m), 1.01 (3H, s), 0.87 (3H, s), 0.72 (3H, s) ppm. 13C{ H}
(1R,4S,6R)-5,5,6-trimethyl-2-oxa-phosphabicyclo[2.2.2]octane,
7. A solution of 6 (100 mg) in DCM was stirred with a 3%
aqueous solution of hydrogen peroxide for 30 mins. The organic
phase was isolated, dried over MgSO4, filtered and the volatiles
removed to leave a colourless oil. A pure sample of the desired
compound was obtained as a low melting solid after sublimation
under high vacuum (0.1 mm Hg). Yield = 70%. 1H NMR (CDCl3,
2
DEPT NMR (CDCl3, 125 MHz) d 76.3 (CH2), 50.7 (d, JC–P
=
3.7 Hz, CH), 46.9 (C), 45.5 (d, 3JC–P = 5.2 Hz, C), 37.0 (CH3), 32.2
(CH2), 27.5 (CH2), 22.5 (CH3), 21.2 (CH3), 17.9 (CH3), 14.2 (d,
1JC–P = 7.6 Hz, CH2) ppm. 31P{ H} NMR (CDCl3, 121.7 MHz):
1
-139.45 ppm.
(1R,3S)-[1,2,2-trimethyl-3-(phosphinomethyl)cyclopentyl]methyl
p-tolylsulfonate, 3b. Prepared as detailed above for the mesylate.
Yield of white solid = 84%. 1H NMR (CDCl3, 400 MHz) d 7.71
(2H, dd), 7.28 (2H, d), 3.87 (1H, d, J = 9.23 Hz), 3.71 (1H, d,
J = 9.23 Hz), 2.68 (1H, dm, J = 194.95 Hz), 2.55 (1H, dm,
1JH–P = 195.02 Hz), 2.09 (1H, m), 1.92 (1H, m), 1.45 (1H, m), 1.41
(1H, m), 1.25–1.05 (3H, m), 0.88 (3H, s), 0.79 (3H, s), 0.55 (3H,
400 MHz, major isomer) d 6.99 (1H, dt, 1JH–P = 454.6 Hz, 3JH–H
=
3.5 Hz), 2.3–1.0 (9H, m), 1.03 (3H, s), 0.99 (3H, d, 3JH–H = 5.80 Hz),
1
0.89 (3H, s) ppm. H NMR (CDCl3, 400 MHz, minor isomer) d
1
6.84 (1H, d, JH–P = 463.0 Hz) 2.3–1.0 (9H, m), 0.99 (3H, d,
3JH–H = 6.30 Hz), 0.92 (3H, s), 0.85 (3H, s) ppm. 13C{ H} DEPT
1
NMR (CDCl3, 125 MHz, major isomer) d 38.5 (d, 2JC–P = 4.7 Hz,
1
s) ppm. 13C{ H} DEPT NMR (CDCl3, 100 MHz) d 144.9 (C),
1
CH), 34.2 (s, C), 33.4 (d, JC–P = 61.3 Hz, CH), 31.6 (CH), 29.5
1
3
132.9 (C), 132.9 (C), 129.9 (CH), 127.8 (CH), 76.7 (CH2), 50.8 (d,
(CH3), 29.1 (d, JC–P = 53.8, CH2), 24.5 (CH3), 21.3 (d, JC–P
=
2JC–P = 3.8 Hz, CH), 46.9 (C), 45.4 (C), 33.2 (CH2), 27.5 (CH2),
3
10.9 Hz, CH2), 15.1 (d, JC–P = 12.9 Hz, CH3), 14.2 (CH2) ppm.
1
13C{ H} DEPT NMR (CDCl3, 125 MHz, minor isomer) d 38.4 (d,
1
22.5 (CH3), 21.2 (CH3), 17.8 (CH3), 14.2 (d, JC–P = 7.4, CH2)
1
ppm. 31P{ H} NMR (CDCl3, 121.7 MHz): -140.43 ppm.
2JC–P = 5.1 Hz, CH), 33.9 (C), 33.1 (d, 1JC–P = 64.0 Hz, CH), 31.6
(CH), 29.9 (CH3), 29.7 (d, 1JC–P = 54.2, CH2), 24.0 (CH3), 22.1 (d,
3JC–P = 11.4 Hz, CH2), 14.6 (d, JC–P = 17.0 Hz, CH3), 12.1 (d,
3
(1R,4S,6R)-5,5,6-trimethyl-2-phosphoniabicyclo[2.2.2]octane
methanesulfonate, 5a
2JC–P = 5.8 Hz, CH2) ppm. 31P{ H} NMR (CDCl3, 121.7 MHz):
1
34.7 (minor), 34.3 (major) ppm.
The desired compound could be prepared from either the phosphi-
nomesylate or phosphinotosylate; the following procedure is for
the methanesulfonate. A solid sample of the phosphinomethane-
sulfonate 3a (1 g, 3.76 mmol) was heated to 140◦ C under N2
overnight. During this time the desired compound sublimed as a
crystalline solid in the upper half of the Schlenk flask. The lower
residues were washed away with THF and kept. The crystalline
solid was then transferred as a THF solution to a fresh Schlenk
and pumped down to a dry solid. Yield = 40%. 1H NMR (CDCl3,
500 MHz) d 2.80 (3H, s), 2.29 (1H, d br, J = 15.5 Hz), 2.03 (2H,
(1R,4S,6R)-2,5,5,6-tetramethyl-2-phosphoniabicyclo[2.2.2]octane
iodide, 8. To a solution of PBO (200 mg, 1.17 mmol) in THF
(30 ml) was added MeI (0.5 ml) and the mixture left at 4 ◦C
overnight. On return the white precipitate was isolated by
filtration and dried at the pump. Yield = 227 mg (62%). 1H
NMR (CDCl3, 500 MHz, major isomer) d 7.70 (1H, dm, 1JH–P
=
517.67 Hz), 2.91 (1H, m), 2.46 (1H, dt, J = 11.3, 2.5 Hz), 2.22
(3H, dd, 2JC–P = 15.0 Hz, 3JH–H = 5.3 Hz), 2.10 (1H, m), 1.99 (2H,
3
m), 1.82 (2H, m), 1.65 (2H, m), 1.05 (3H, dd, JH–H = 7.2 Hz,
1
4JH–P = 1.3 Hz), 0.97 (3H, s), 0.93 (3H, s) ppm. 13C{ H} DEPT
m), 1.90 (2H, m), 1.65 (2H, m), 1.48 (1H, m), 0.97 (3H, dd, 3JH–H
=
NMR (CDCl3, 125 MHz, major isomer) d 36.3 (d, 2JC–P = 5.2 Hz,
4
1
7.1 Hz, JH–P = 1.0 Hz), 0.96 (3H, s), 0.89 (3H, s) ppm. 13C{ H}
DEPT NMR (CDCl3, 125 MHz) d 39.5 (CH3), 37.7 (CH), 35.6 (d,
2JC–P = 4.8 Hz, CH), 34.0 (C), 29.5 (CH3), 24.6 (d, 1JC–P = 25.2 Hz,
CH), 24.0 (CH3), 21.8 (d, 3JC–P = 8.2 Hz, CH2), 17.2 (CH2), 15.0
2
CH), 33.9 (C), 33.7 (d, JC–P = 2.5 Hz, CH), 29.4 (CH3), 26.2
1
1
(d, JC–P = 47.9 Hz, CH), 23.9 (d, JC–P = 43.4 Hz, CH2), 15.0
2
3
(d, JC–P = 4.4 Hz, CH2), 14.4 (d, JC–P = 14.0 Hz, CH3), 4.1 (d,
1JC–P = 52.0 Hz, CH3) ppm. 31P{ H} NMR (CDCl3, 121.7 MHz):
1
3
2
(d, JC–P = 13.1 Hz, CH3), 14.2 (d, JC–P = 21.7 Hz, CH2) ppm.
1
31P{ H} NMR (CDCl3, 121.7 MHz): -65 br ppm.
2.7 (minor), 1.4 (major) ppm. Anal.: Calc. for C11H22PI: C, 42.32;
H, 7.12%. Found: C, 42.2; H, 6.8%.
(1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]octane, PBO,
6. A solid sample of the phosphinomethanesulfonate 3a (1 g,
3.76 mmol) was heated to 140 ◦C under N2 overnight. The
resultant mixture was dissolved in THF (30 ml) and added to
a stirred suspension of LiAlH4 (1 g, excess) in THF (30 ml) at
(1R,4S,6R)-2,2,5,5,6-pentamethyl-2-phosphoniabicyclo[2.2.2]-
octane iodide monohydrate, 9. To a solution of PBO (200 mg,
1.17 mmol) in THF (30 ml) was added MeI (2 ml) and the mixture
refluxed for 2 h. After cooling the white precipitate was isolated
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©

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1
0.93 (6H, H10/11) ppm. 13C{ H} DEPT NMR (C6D6, 125 MHz)
d 137.5 (t, 2,3JC–P = 3.8 Hz, C), 130.5 (d, 3JC–P = 5.0 Hz, CH), 126.0
(s, CH), 40.1 (d, 2JC–P = 21.1 Hz, C6), 37.6 (d, 2JC–P = 1.9 Hz, C4),
33.6 (s, C5), 32.7 (dd, 1JC–P = 25.0, 5JC–P = 9.8 Hz, C12), 30.3 (s,
C10/11), 29.0 (d, 1JC–P = 12.7 Hz, C1), 24.5 (s, C10/11), 23.1 (d,
by filtration in air and dried at the pump. The compound was
recrystallised from MeCN. Yield = 388 mg (96%). 1H NMR
(CDCl3, 500 MHz) d 2.41 (3H, m), 2.33 (3H, d, 2JH–P = 3.2 Hz),
2
2.29 (3H, d, JH–P = 3.1 Hz), 2.2-1.7 (5H, m), 1.44 (1H, m), 1.09
1
(3H, d, 3JH–H = 7.0 Hz), 0.97 (3H, s), 0.93 (3H, s) ppm. 13C{ H}
DEPT NMR (CDCl3, 125 MHz) d 36.8 (d, 2JC–P = 5.1 Hz, CH),
3JC–P = 1.7 Hz, C8), 21.8 (d, 1JC–P = 17.2 Hz, C3), 15.5 (d, 3JC–P
=
34.3 (d, 2JC–P = 1.8 Hz, CH), 33.6 (C), 29.6 (CH3), 27.6 (d, 1JC–P
=
15.3 Hz, C9), 15.0 (d, JC–P = 2.5 Hz, C7) ppm. 31P{ H} NMR
2
1
1
48.8 Hz, CH), 24.1 (CH3), 23.7 (d, JC–P = 44.5 Hz, CH2), 21.0
(C6D6, 121.7 MHz): -38.4 (s) ppm.
3
3
(d, JC–P = 11.9 Hz, CH2), 14.5 (d, JC–P = 14.2 Hz, CH3), 13.3
cis-Pd{o-C6H4(CH2PBO)2}Cl2·MeCN, 14.
A mixture of
2
1
(d, JC–P = 4.7 Hz, CH2), 10.0 (d, JC–P = 49.5 Hz, CH3), 8.7 (d,
Na2PdCl4 (97 mg, 0.33 mmol) and 13 (145 mg, 0.33 mmol) in
EtOH (15 ml) was refluxed for 12 h during which time an off-white
precipitate formed. The solid was filtered off and recrystallised
from MeCN as colourless blocks. Yield = 171 mg (78%). 1H NMR
{(CD3)2SO, 500 MHz, 393 K} d 7.35 (2H, s br), 7.28 (2H, m), 3.52
(4H), 2.88 (4H, br), 2.13 (4H, m), 2.02 (6H, m), 1.67 (4H, m), 0.99
1JC–P = 52.5 Hz, CH3) ppm. 31P{ H} NMR (CDCl3, 121.7 MHz):
1
25.2 ppm. Anal.: Calc. for C12H26OPI: C, 41.86; H, 7.63%. Found:
C, 41.9; H, 7.4%.
a,a¢-bis{(1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]-
octyl}-o-xylene diborane, o-C6H4(CH2PBO)2.2BH3, 12. To a
solution of PBO (600 mg, 3.51 mmol) in THF (30 ml) at -78 ◦C
was added 1.1 mol equivalents of BH3·THF (3.9 ml of a 1 M
solution) and the mixture stirred for 20 min at this temperature
before the cold bath was removed and the solution stirred for a
further 20 min. After re-cooling to -78 ◦C, 1.1 mol equivalents of
n-BuLi (1.4 ml of a 2.5 M solution in hexanes) were added and the
solution stirred for another 20 min at this temperature and then
a further 20 min after the cold bath was removed. The solution
was again cooled to -78 ◦C before a solution of a,a¢-dichloro-o-
xylene (0.3 g, 1.75 mmol) in THF (20 ml) was added dropwise. The
solution was left to slowly reach room temperature and then left
stirring overnight. All volatiles were removed at the pump and the
residue partitioned between DCM and water. The organic phase
was isolated, dried (MgSO4), filtered and the solvent removed in
vacuo. The resultant sticky solid was stirred with Et2O (20 ml) to
give a free-flowing white solid. Yield = 370 mg (45%). A second
crop was obtained after cooling the Et2O filtrate to -35 ◦C. Yield =
140 mg (17%). 1H NMR (CDCl3, 500 MHz) d 7.10 (4H, m), 3.39
(2H, m), 3.24 (2H, dd, 2JH–H = 15.0, 2JH–P = 10.0 Hz), 2.16 (2H, m),
(6H, s), 0.96 (6H, d, 3JH–H = 7.1 Hz), 0.91 (6H, s) ppm. 13C{ H}
1
DEPT NMR {(CD3)2SO, 125.8 MHz} d 136.1 (d, 2JC–P = 4.6 Hz,
C), 133.0 (t, 2,3JC–P = 4.0 Hz, C), 131.0 (d br, 3JC–P = 5.6 Hz, CH),
3
130.2 (d br, CH), 127.6 (d, JC–P = 3.5 Hz, CH), 127.4 (s, CH),
2
2
38.4 (d, JC–P = 6.4 Hz, CH), 38.2 (d, JC–P = 6.4 Hz, CH), 36.9
(s, CH), 34.6 (s br, CH), 33.3 (s, C), 33.2 (dd, 1JC–P = 25.7, 3JC–P
=
1
4.2 Hz, CH2), 32.6 (s, C), 32.0 (d, JC–P = 23.1 Hz, CH2), 31.9
(d, 1JC–P = 19.5 Hz, CH2), 30.5 (d, 1JC–P = 31.4 Hz, CH), 29.4 (s,
CH3), 28.2 (s, CH3), 27.5 (dd, 1JC–P = 21.3, 3JC–P = 4.8 Hz, CH),
3
24.2 (s, CH3), 23.8 (s, CH3), 22.2 (d br, JC–P = 21.2 Hz, CH2),
20.8 (d, 3JC–P = 7.9 Hz, CH2), 20.6 (d, 3JC–P = 7.8 Hz, CH2), 15.0
(d, 2JC–P = 8.0 Hz, CH2), 14.9 (d, 3JC–P = 13.5 Hz, CH3), 14.1 (d,
2JC–P = 6.3 Hz, CH2), 13.6 (d, 3JC–P = 16.3 Hz, CH3) ppm. 31P{ H}
1
NMR (CD2Cl2, 121.7 MHz): 17.0 (s), 15.4 (s) ppm. MS: 618 (M+,
30%), 602 (M2L2Cl32+, 100%). IR (KBr): 2949 vs, 2871 vs, 1472 s,
1447 s, 1410 s, 1390 s, 1367 m, 1228 m, 1193 m, 1072 s, 1012 s,
911 m, 871 m, 849 s, 809 s, 784 s, 771 s, 652 m, 504 m, 460 m, 408
m cm-1. Anal.: Calc. for C30H47P2NPdCl2: C, 54.51; H, 7.18; N,
2.12%. Found: C, 54.3; H, 7.1; N, 2.3%.
2.1–1.8 (8H, m), 1.60 (4H, m), 1.42 (4H, m), 0.94 (3H, d, 3JH–H
=
cis-Pt{o-C6H4(CH2PBO)2}Cl2·MeCN, 15.
A solution of
7.27 Hz), 0.92 (3H, s), 0.89 (3H, s) ppm. 13C{ H} DEPT NMR
(CDCl3, 125 MHz) d 133.3 (d, 2JC–P = 3.8 Hz, C), 130.6 (s, CH),
127.0 (s, CH), 37.5 (d, 2JC–P = 5.2 Hz, CH), 34.5 (d, 2JC–P = 2.2 Hz,
CH), 33.9 (s, C), 29.5 (s, CH3), 29.4 (d, 1JC–P = 23.8 Hz, CH2), 28.9
(d, 1JC–P = 30.8 Hz, CH), 24.7 (s, CH3), 23.0 (d, 1JC–P = 28.8 Hz,
1
Pt(1,5-COD)Cl2 (85 mg, 0.23 mmol) and 13 (106 mg, 0.24 mmol)
in DCM (20 ml) was stirred at RT for 18 h, after which time the
volatiles were removed in vacuo and the white solid recrystallised
from hot MeCN as colourless blocks. Yield = 162 mg (94%).
1H NMR {(CD3)2SO, 500 MHz, 363 K} d 7.28 (2H, br), 7.19
(2H, m), 3.60 (5H, br), 2.15–1.50 (15H, m br), 0.99 (6H, s), 0.95
3
3
CH2), 22.1 (d, JC–P = 8.8 Hz, CH2), 15.1 (d, JC–P = 13.6 Hz,
CH3), 14.3 (d, 2JC–P = 7.5 Hz, CH2) ppm. 31P{ H} NMR (CDCl3,
1
(6H, d, 3JH–H = 7.1 Hz), 0.91 (6H, s) ppm. 13C{ H} DEPT NMR
1
121.7 MHz): 10.3 (br m) ppm. Anal.: Calc. for C28H52P2B2: C,
{(CD3)2SO, 125.8 MHz} d 137.4 (s, C), 133.8 (s, C), 131.2 (s, CH),
130.4 (s, CH), 127.6 (s, CH), 127.3 (s, CH), 38.7 (d, 2JC–P = 5.8 Hz,
CH), 38.4 (d, 2JC–P = 5.8 Hz, CH), 36.7 (s, CH), 34.6 (s, CH), 33.8
71.19; H, 11.12%. Found: C, 70.7; H, 10.9%.
a,a¢-bis{(1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo[2.2.2]-
octyl}-o-xylene, o-C6H4(CH2PBO)2, 13. To a solution of 12
(500 mg, 1.06 mmol) in DCM (100 ml) was added HBF4·Et2O
(1.7 ml) and the mixture stirred for 24 h before being added
dropwise to a degassed saturated aqueous solution of Na2CO3.
After stirring for 2 h, the organic phase was isolated and dried over
MgSO4. After filtering, the volatiles were removed in vacuo to give
a white solid that was recrytallised from MeOH at -35 ◦C. Yield =
375 mg (80%). 1H NMR (C6D6, 500 MHz) d 7.08 (2H, m, H13),
(s, C), 33.2 (s, C), 33.4 (d, 1JC–P = 27.6 Hz, CH2), 32.6 (d, 1JC–P
=
31.3 Hz, CH), 32.5 (d, 1JC–P = 27.3 Hz, CH2), 29.9 (s, CH3), 28.7 (s,
CH3), 28.7 (d, 1JC–P = 37.6 Hz, CH), 24.8 (s, CH3), 24.3 (s, CH3),
21.3 (d, 3JC–P = 8.1 Hz, CH2), 21.2 (d, 3JC–P = 9.4 Hz, CH2), 19.4
(d, 1JC–P = 31.6 Hz, CH2), 15.4 (d, 3JC–P = 13.8 Hz, CH3), 15.2 (d,
2JC–P = 4.7 Hz, CH2), 14.2 (d, 2JC–P = 4.5 Hz, CH2), 14.1 (d, 3JC–P
=
15.0 Hz, CH3) ppm. 31P{ H} NMR (CD2Cl2, 121.7 MHz): -3.5 (d,
1
2JP–P = 22.5 Hz, 1JP–Pt = 3310 Hz), -4.1 (d, 2JP–P = 22.5 Hz, 1JP–Pt
=
2
2
6.97 (2H, m, H14), 3.29 (2H, dd, JH–H = 13.4, JH–P = 1.5 Hz,
H12), 3.11 (2H, dd, 2JH–H = 13.4, 2JH–P = 1.3 Hz, H12), 2.02 (2H,
ddt, 2JH–P = 25.2, 2JH–H = 14.3, 3JH–H = 2.8 Hz, H3eq), 1.91 (4H, m,
H7), 1.80 (4H, m, H6, H8), 1.50 (2H, m, H8), 1.39 (6H, m, H3ax,
H4, H1), 0.97 (6H, s, H10/11), 0.95 (6H, d, 3JH–H = 6.7 Hz, H9),
3468 Hz) ppm. MS: 707 (M+, 85%). IR (KBr): 2952 vs, 2876 vs,
1474 s, 1458 s, 1411 m, 1388 s, 1365 m, 1263 w, 1232 w, 1192 w,
1064 s, 1011 m, 913 m, 872 m, 850 s, 810 s, 784 m, 768 s, 733 m, 653
m, 508 m, 460 m cm-1. Anal.: Calc. for C30H47P2NPtCl2: C, 48.06;
H, 6.33; N, 1.87%. Found: C, 47.7; H, 6.3; N, 1.7%.
3858 | Dalton Trans., 2010, 39, 3851–3860
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Table 1 Details of X-ray crystallographic data collection for the compounds 9, 14, 15 and 17
9
14
15
17
Empirical formula
Formula weight
Crystal system
Space group
C12H24PI
326.18
Orthorhomibic
P212121
7.1710(2)
10.4460(3)
18.5870(5)
C30H47Cl2NP2Pd
660.93
Orthorhombic
P212121
7.8766(2)
18.4788(4)
21.4062(6)
C30H47Cl2NP2Pt
749.62
Orthorhombic
P212121
7.92200(10)
21.3381(3)
18.4545(3)
C71H96O8P4Mo2
1393.24
Monoclinic
P21
17.118(3)
8.9172(18)
22.259(5)
97.60(3)
3367.9(12)
2
˚
a/A
˚
b/A
˚
c/A
b (◦)
3
˚
U/A
1392.32(7)
4
1.556
656.0
3115.67(14)
4
1.409
1376
2.91 to 27.48
3119.56(8)
4
1.596
1504
2.92 to 27.5
Z
Dc/Mg m-3
F(000)
1.374
1460
2.94 to 27.48
q range/◦
Index ranges
2.93 to 27.50
-8 ≤ h ≤ 9, -13 ≤ k ≤ 13,
-10 ≤ h ≤ 10, -23 ≤ k ≤ 23, -10 ≤ h ≤ 10, -27 ≤ k ≤ 27, -22 ≤ h ≤ 22, -11 ≤ k ≤ 11,
-24 ≤ l ≤ 24
-27 ≤ l ≤ 27
-23 ≤ l ≤ 23
-28 ≤ l ≤ 28
Reflections collected
Independent reflections
Rint
7691
20635
24594
44591
3068
0.0848
7042
0.0914
7042/0/332
1.046
0.0500, 0.0873
0.0747, 0.0968
7129
0.1288
7129/0/332
1.039
0.0560, 0.1273
0.0664, 0.1342
15091
0.1279
15091/235/806
1.031
0.0669, 0.1356
0.1204, 0.1565
Data/restraints/parameters 3068/0/132
Goodness of fit on F2
Final R1, wR2 [I > 2s(I)]
(all data)
1.042
0.0317, 0.0823
0.0348, 0.0836
Largest difference peak
-3
˚
And hole/e A
0.414 and -0.555
-0.09(3)
0.559 and -0.934
-0.02(3)
1.828, -3.370
-0.021(9)
0.755, -1.169
-0.03(4)
Flack parameter
m, H8eq), 1.72 (2H, m, H3ax), 1.56 (2H, m, H4), 1.48 (2H, m,
Pt{o-C6H4(CH2PBO)2}(nb), 16. The compound was prepared
according to the method of Weigand.23 Crystallised by vapour
diffusion of 40/60 petroleum ether into a THF solution of 16.
3
H8ax), 1.33 (2H, s br, H1), 1.00 (6H, d, JH–H = 7.1 Hz, H9),
1
0.97 (6H, s, H10/11), 0.96 (6H, H10/11) ppm. 13C{ H} DEPT
NMR (CD2Cl2, 125 MHz) d 213.9 (t, 2JC–P = 7.6 Hz, CO), 207.6
1
Yield = 52%. H NMR (C7D8, 500 MHz): d 6.98 (1H, s), 6.80
(m, CO), 136.8 (s, C13), 130.2 (s, C14), 127.3 (s, C15), 38.6 (s,
(3H, m), 3.29 (2H, m), 2.85 (2H, m), 2.64 (2H, d, J = 18.8 Hz),
1
C4), 36.6 (s, C6), 36.1 (s, C12), 34.4 (t, JC–P = 9.1 Hz, C1), 33.7
2.50 (2H, m), 2.10 (3H, m), 1.85-1.05 (20H, m), 0.90 (3H, s), 0.84
1
3
(s, C5), 30.0 (t, JC–P = 11.3 Hz, C3), 28.7 (s, C10/11), 24.4 (s,
(6H, s), 0.75 (3H, d, JH–H = 7.0 Hz), 0.68 (6H, s), 0.53 (1H,
3
1
m), 0.12 (1H, d, J = 7.5 Hz) ppm. 13C{ H} DEPT NMR (C7D8,
C10/11), 21.9 (s, C8), 15.8 (s, C7), 14.2 (d, JC–P = 7.2 Hz, C9)
1
ppm. 31P{ H} NMR (CD2Cl2, 121.7 MHz): 9.8 (s) ppm. MS: 652
125.1 MHz): d 129.5 (s, CH), 128.9 (s, CH), 128.0 (s, CH), 126.0
(s, CH), 51.3 (dd, 2JC–P = 36.3, 27.2 Hz, 1JC–Pt = 338 Hz, CH), 45.1
(M+, 25%). IR (KBr): 2962 m, 2008 s, 1906 vs, 1883 vs, 1855 vs,
1261 s, 1093 s, 1011 s, 803 s, 762 m, 617 s, 584 s, 500 w, 460 m,
413 s cm-1. Anal.: Calc. for C32H44P2O4Mo: C, 59.08; H, 6.82%.
Found: C, 58.4; H, 7.0%.
(vt, 3JC–P = 4.0 Hz, 2JC–Pt = 12.8 Hz, CH), 40.8 (s, 3JC–Pt = 58.9 Hz,
1,3
CH2), 38.9 (s, CH), 36.8 (t,
J
= 18.9 Hz, CH2), 35.6 (s br,
C–P
1
1
CH), 33.8 (d, JC–P = 8.1 Hz, C), 33.2 (m, CH), 32.2 (d, JC–P
=
19.6 Hz, CH2), 31.9 (d, 1JC–P = 19.6 Hz, CH2), 29.9 (vt, J = 9.2 Hz,
CH2), 29.4 (s, CH3), 29.2 (s, CH3), 29.2 (obs, CH2), 24.3 (d, 3JC–P
=
Crystallography
4.8 Hz, CH3), 22.5 (s, CH2), 16.0 (s, CH2), 15.0 (d, 3JC–P = 13.8 Hz,
Data collection was carried out on a Bruker-Nonius Kappa CCD
CH3), 14.7 (d, 3JC–P = 15.0 Hz, CH3) ppm. 31P{ H} NMR (C6D6,
1
diffractometer using graphite monochromoated Mo-Ka radiation
121.7 MHz, 323 K): 3.1 (d, 2JP–P = 45 Hz, 1JP–Pt = 3336 Hz), 1.6
˚
(l(Mo-Ka) = 0.71073 A). The instrument was equipped with
(d, JP–P = 45 Hz, JP–Pt = 3336 Hz) ppm. MS: 732 (M+, 100%).
Anal.: Calc. for C38H54P2Pt: C, 64.64; H, 7.72%. Found: C, 63.5;
H, 7.4%.
2
1
an Oxford Cryosystems cooling apparatus. Data collection and
cell refinement were carried out using COLLECT26 and HKL
SCALEPACK.27 Data reduction was applied using HKL DENZO
and SCALEPACK.26 The structures were solved using direct
methods (Sir92)28 and refined with SHELX-97.29 Absorption
corrections were performed using SORTAV.30 All non-hydrogen
atoms were refined anisotropically, while the hydrogen atoms were
inserted in idealised positions with Uiso set at 1.2 or 1.5 times
the Ueq of the parent atom. In the final cycles of refinement, a
weighting scheme that gave a relatively flat analysis of variance
was introduced and refinement continued until convergence was
reached. The Mo structure included a toluene molecule within
the lattice framework which was disordered over two discrete
positions. The details of the data collection and structure solution
are collected in Table 1.
Mo(CO)4{o-C6H4(CH2PBO)2},
17.
A
solution
of
Mo(CO)4(pip)2 (68 mg, 0.18 mmol) and 13 (80 mg, 0.18 mmol)
in DCM (20 ml) was stirred at RT overnight. The volatiles were
removed at the pump and the off-white solid residue dissolved
in the minimum amount of toluene. Storage at -25 ◦C over
several days gave colourless needles which were isolated by
filtration. Yield = 50 mg (43%). A second crop was obtained
upon dilution of the toluene solution with 40/60 petroleum
1
ether. Yield = 53 mg (45%). H NMR (CD2Cl2, 500 MHz) d
2
7.11 (2H, m, H15), 7.06 (2H, m, H14), 3.27 (2H, d br, JH–H
=
2
11.9, H12), 3.00 (2H, br, H12), 2.18 (2H, d br, JH–H = 14.8 Hz,
H3eq), 2.08 (4H, m, H6, H7eq), 1.93 (2H, m, H7ax), 1.86 (2H,
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Orpen, P. G. Pringle, A. Turner and R. L. Wingad, Dalton Trans., 2006,
4310.
Conclusions
8 S. G. A. van Assema, A. W. Ehlers, F. J. J. de Kanter, M. Schakel, A. L.
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Slawin, R. P. Tooze, W. J. van Rensburg, W. H. Meyer, C. Dwyer, M. M.
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11 E. Fuchs, M. Keller and B. Breit, Chem.–Eur. J., 2006, 12, 6930.
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13 D. Coleman, PhD thesis, Cardiff University, 2004.
14 (a) R. Haigh, K. M. A. Malik and P. D. Newman, Chem. Commun.,
2002, 2558; (b) K. M. A. Malik and P. D. Newman, Dalton Trans.,
2003, 3516; (c) P. G. Edwards, S. J. Paisey and R. P. Tooze, J. Chem.
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15 Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis, ed.
J. G. Verkade and L. D. Quin, VCH, Florida, 1987, p. 88.
16 P. D. Newman, R. A. Campbell, R. P. Tooze, G. R. Eastham, J. M.
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In conclusion, (1R,4S,6R)-5,5,6-trimethyl-2-phosphabicyclo-
[2.2.2]octane, PBO, has been prepared stereoselectively from
(1R,3S)-[1,2,2-trimethyl-3-(phosphinomethyl)cyclopentyl]methyl
methanesulfonate or the corresponding tosylate. The [2.2.2]
bicyclic product results from a rearrangement of the original
skeleton under the somewhat harsh reaction conditions. Several
derivatives of the phosphacycle have been prepared and
characterised including a bidentate ligand with an ortho-xylyl
backbone. This latter ligand has been coordinated to Pd(II), Pt(II),
Pt(0) and Mo(0) and the resultant complexes fully characterised.
The bite angle of the ligand conforms to the ideal 90◦ for the
divalent palladium and platinum complexes and the zerovalent
molybdenum complex as determined by single crystal X-ray
structure analysis of the respective complexes; adherence to a 90◦
P-M-P angle forces the aryl ring of the xylyl backbone into an
orientation roughly perpendicular to the ML4 coordination plane
for Pd(II) and Pt(II) and into close proximity to one of the carbonyl
ligands in the Mo(0) system. A similar arrangement is suggested
for the zerovalent platinum species, Pt{o-C6H4(CH2PBO)2}(nb)
based on the 1JP–Pt value.
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3860 | Dalton Trans., 2010, 39, 3851–3860
This journal is
The Royal Society of Chemistry 2010
©