Chiral phosphorus(III) triflates. On the nature of the phosphorus-oxygen interaction

Article abstract of DOI:10.1016/S0022-328X(98)00683-4

Reaction of chiral phosphorodiamidites with trimethylsilyltriflate affords chiral phophorus(III) triflate species, such as 1-trifluoromethylsulfonato-2,9-(dibenzyl)diaza-1-phospha[4.0.3]bicyclononane 4, which has been examined by a combination of solution and solid state analytical techniques. Arguably the most important feature of this molecule is the nature of the interaction between phosphorus and triflate oxygen atoms. Single crystal X-ray diffraction analysis reveals that the phosphorus atom interacts principally with two oxygen atoms from two different triflate groups in the solid state, implying overall four-coordination at phosphorus. At distances of 2.841 and 2.755 A, these interactions are well within the van der Waals distance for a phosphorus-oxygen [P-O] interaction (ca. 3.35 A) but are nevertheless over 1 A longer than expected for a single [P-O] covalent bond. Investigations in solution via a combination of ³¹P, ¹⁹F, ¹³C, variable concentration, variable temperature NMR spectroscopy and solution conductivity provide support for a phosphorus-oxygen interaction which is intermediate between 'ionic' (two-coordinate phosphorus) and 'covalent' (three-coordinate phosphorus) and which possesses dynamic character in solution. Indeed, it has proved possible to calculate a relative equilibrium constant between 'ionic' and 'covalent' forms of 4 using empirical NMR data (¹³C and ¹⁹F; CH₂Cl₂ solvent; 300 K). These calculations return an equilibrium constant of ca. 3 (2.8 using ¹³C-NMR data and 3.3 using ¹⁹F-NMR data) in favour of the ionic form, a result commensurate with those suggested from variable temperature ¹⁹F-NMR and solution conductivity studies. Indeed, that the triflate group in 4 is capable of being displaced readily has been demonstrated by reaction with two-electron nitrogen, oxygen and phosphorus donor molecules. We have found ¹³C{¹H}-NMR spectroscopy to be an extremely valuable probe of the ionic character of the triflate group in such systems providing a quantitative measure of the relative strength of interaction (relative basicity B_r) between donor molecule and phosphorus atom of 4; the stronger the interaction, the more ionic the character of the triflate group and the lower the value of B_r. Indeed, B_r values for various ligands correlate well with steric and electronic properties of the latter and ³¹P-NMR resonances of the adducts themselves. As expected, the relative basicity of a given ligand correlates to the equilibrium constants K for adduct formation, which range from 39 M^-1 for the weakest binding ligand studied (1,4-dioxane) to 5.4×10⁴ M^-1 for the strongest binding ligand (4-Me₂N-NC₅H₄).

Full text of DOI:10.1016/S0022-328X(98)00683-4

Journal of Organometallic Chemistry 567 (1998) 199–218
Chiral phosphorus(III) triflates. On the nature of the
1
phosphorus–oxygen interaction
Victoria A. Jones, Sarin Sriprang, Mark Thornton-Pett, Terence P. Kee *
School of Chemistry, Woodhouse Lane, Uni6ersity of Leeds, Leeds LS2 9JT, UK
Received 30 October 1997; received in revised form 14 April 1998
Abstract
Reaction of chiral phosphorodiamidites with trimethylsilyltriflate affords chiral phophorus(III) triflate species, such as
1
-trifluoromethylsulfonato-2,9-(dibenzyl)diaza-1-phospha[4.0.3]bicyclononane 4, which has been examined by a combination of
solution and solid state analytical techniques. Arguably the most important feature of this molecule is the nature of the interaction
between phosphorus and triflate oxygen atoms. Single crystal X-ray diffraction analysis reveals that the phosphorus atom interacts
principally with two oxygen atoms from two different triflate groups in the solid state, implying overall four-coordination at
˚
phosphorus. At distances of 2.841 and 2.755 A, these interactions are well within the van der Waals distance for a
˚
˚
phosphorus–oxygen [P–O] interaction (ca. 3.35 A) but are nevertheless over 1 A longer than expected for a single [P–O] covalent
31
19
13
bond. Investigations in solution via a combination of P, F, C, variable concentration, variable temperature NMR
spectroscopy and solution conductivity provide support for a phosphorus–oxygen interaction which is intermediate between
‘ionic’ (two-coordinate phosphorus) and ‘covalent’ (three-coordinate phosphorus) and which possesses dynamic character in
solution. Indeed, it has proved possible to calculate a relative equilibrium constant between ‘ionic’ and ‘covalent’ forms of 4 using
1
3
19
empirical NMR data ( C and F; CH Cl solvent; 300 K). These calculations return an equilibrium constant of ca. 3 (2.8 using
2
2
13
19
C-NMR data and 3.3 using F-NMR data) in favour of the ionic form, a result commensurate with those suggested from
1
9
variable temperature F-NMR and solution conductivity studies. Indeed, that the triflate group in 4 is capable of being displaced
readily has been demonstrated by reaction with two-electron nitrogen, oxygen and phosphorus donor molecules. We have found
13
1
C{ H}-NMR spectroscopy to be an extremely valuable probe of the ionic character of the triflate group in such systems
providing a quantitative measure of the relative strength of interaction (relative basicity B ) between donor molecule and
r
phosphorus atom of 4; the stronger the interaction, the more ionic the character of the triflate group and the lower the value of
31
B . Indeed, B values for various ligands correlate well with steric and electronic properties of the latter and P-NMR resonances
r
r
of the adducts themselves. As expected, the relative basicity of a given ligand correlates to the equilibrium constants K for adduct
−
1
4
−1
formation, which range from 39 M
for the weakest binding ligand studied (1,4-dioxane) to 5.4×10 M
for the strongest
binding ligand (4-Me N–NC H ). © 1998 Elsevier Science S.A. All rights reserved.
2
5
4
Keywords: Chiral phophorus(III) triflates; Phosphorus–oxygen interaction; NMR spectroscopy
1
. Introduction
Phosphorus possesses a voracious appetite for bond-
*
Corresponding author. Tel.: +44 113 2336421; fax: +44 113
ing other elements; metallic, metalloid and non-metallic
elements are all known to form bonds with phosphorus
2
336565; e-mail: T.P.Kee@chem.leeds.ac.uk
1
‘
‘The nature of art is to be not a part, nor yet a copy of the real
world (as we commonly understand that phrase), but a world in itself,
independent, complete, autonomous; and to possess it fully you must
enter that world, conform to its laws, and ignore for the time the
beliefs, aims and particular conditions which belong to you in the
other world of reality.’’ Oxford letters on poetry: Professor Bradley,
[
1]. Nevertheless, despite the wide range of element–
phosphorus bonds known, relatively few combinations
form the bedrock of modern phosphorus chemistry
(
Fig. 1); interconversions involving these moieties ac-
1901.
count for the majority of transformations involving
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00683-4

200
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
Fig. 1. Most commonly encountered bonds to phosphorus.
phosphorus. Consequently, using and rationalising any
synthetic transformation involving phosphorus re-
quires, at some point, an investigation of the nature of
the [P–X] interactions involved.
main-group element triflates, especially the isoelec-
tronic and isolobal relationship between trimethylsilyl-
triflate, one of the most widely exploited main-group
Lewis acids in organic synthesis [11] and phosphorus
triflates [12] (shown schematically in the covalent
forms; Fig. 4). We envisage this isolobal relationship
to reflect similar reactivities for the phosphorus variant
with the added advantages of activity associated with
the lone-pair of electrons on phosphorus and the pres-
ence of chirality in the phosphorus coordination
sphere.
Phosphorus is one of the most versatile elements in
terms of the combination of coordination spheres avail-
4
5
2
able (Fig. 2). Of these, members of the | u species [2],
such as the family of phosphate esters (X=Y=O),
form the basis of biological phosphorus chemistry [3]
3
3
whilst three-coordinate, trivalent (| u , Fig. 2) com-
pounds of phosphorus have myriad applications in
chemistry [4–7] and biochemistry [1].
2
3
Among the less well developed classes are | u spe-
cies such as, phosphenium cations, represented in
Scheme 1 [8]. Phosphenium cations are intriguing
moecules, being valence isoelectronic with singlet carbe-
2.2. Choice of chiral ligand framework and synthesis of
chiral phophorus(III) triflates
We selected the chelating auxiliary trans-1,2-di-
aminocyclohexane, an organonitrogen based frame-
work with proven stereodifferentiating ability in
asymmetric synthesis involving phosphorus [13]. This
species appeared suitable since nitrogen-rich coordina-
tion spheres have been shown to stabilise phosphe-
nium centres most effectively and modification of the
nitrogen substituents is straight-forward using estab-
lished chemistry as outlined in Scheme 2 (vide infra).
3
3
nes (Fig. 3) and formally related to their | u tautomer
via the dynamic equilibrium of Scheme 1, the position
of which depends intimately upon the nature of the
counter anion and the groups coordinated to phospho-
rus [9]. Despite being studied for over 20 years, pho-
sphenium chemistry has not yet progressed to the same
3
3
stage as their | u tautomers in part because of the
rapid development of chiral variants of the latter in
asymmetic catalysis. This paper provides a full account
of (i) the syntheses and characterisation of enantiomer-
ically pure phophorus(III) triflates; (ii) detailed investi-
gations into the dynamic interaction between
phosphorus and triflate under in both solid state and
solution culminating in; (iii) determination of a relative
equilibrium constant between ionic and covalent forms
of triflate; and (iv) a quantitative scale of relative
basicity (B ) of various nitrogen, oxygen and phospho-
r
rus donors towards phosphenium centres. Parts of this
work have formed the basis of a preliminary communi-
cation [10].
2. Results and discussion
2.1. Strategy to chiral phosphenium compounds
Our strategy recognises the relationship between
2
|num notation refers to phosphorus coordination number (|) and
valance state (u).
Fig. 2. Connectivity profiles for common phosphorus species.

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
201
and H resonating to higher frequency than H and H ,
E
C
D
3
as expected .
2
.3. On the nature of the phosphorus–triflate
interaction
Our original perception of the phophorus(III) triflate
unit was based on previous work by Sanchez et al. [12].
31
These scientists concluded, on the basis of P-NMR
chemical shifts alone that phophorus(III) triflates exist in
Scheme 1. Dynamic relationship between |2u3 and |3u3 phosphorus.
3
3
2 3
a dynamic equilibrium between | u covalent and | u
ionic forms (Scheme 1; X=OSO CF ). Since there is
2
3
undoubtedly a close connection between phosphenium
reactivity and the nature of the counterion employed [8],
we have undertaken to investigate the nature of the
interaction between phophorus(III) and triflate moieties
in both solid and solution phases via a combination of
spectroscopic, dynamic and conductimetric techniques;
our objective being to develop a method of quantifying
this interaction under different conditions and more
importantly, in the presence of other molecules.
We have examined solid and solution phase structural
features of representative examples of both diimines (1a,
d) and diamine (2a) via single crystal X-ray diffraction
1
and NMR spectroscopy, respectively. The solid phase
structures of 1a, 1d and 2a are comparable to previously
published derivatives [14] and serve here to identify the
amino functions as occupying mutually trans di-equato-
rial positions within a cyclohexane chair backbone (full
structural details are available as supplementary material
accompanying this paper). A combination of selective
2
.3.1. Physical and mass spectrometric properties of 4
Compound 4 possesses strikingly different physical
1
1
1
homonuclear decoupling H (Fig. 5), H– H COSY and
properties to both its precursor 3 and close relatives
-phenyl-2,9-(dibenzyl)diaza-1-phospha[4.0.3]bicyclono-
nane 5 and 1-methoxy-2,9-(dibenzyl)diaza-1-phospha
4.0.3]bicyclononane 6. Compound 4 is far less soluble in
1
13
H– C COSY NMR spectroscopy allows complete
1
assignment of the proton connectivity profile for the
chiral framework molecule 2a. Even though the spin
system of the cyclohexyl protons is complex
[
aromatic and aliphatic solvents than 3, 5 and 6, although
[
AA%BB%CC%DD%EE%], it is still possible to rationalise
4
highly soluble in both THF and dichloromethane, from
connectivity on the basis of the relative magnitude of
coupling lost upon selective irradiation of the individual
resonances (Fig. 5) [15].
which analytically pure samples may be obtained upon
crystallisation. Moreover, 4 displays significantly differ-
ent mass spectrometric (EI mode) signatures to 3, 5 and
Irradiation of H (methine proton on carbon adjacent
A
6 the latter compounds revealing parent ions at m/z 358
1
3
1
to nitrogen, assigned via C– H COSY) causes the loss
35
(
Cl), 400 and 354, respectively, whereas the highest
of a large coupling to proton resonance H which must
C
mass peak for 4 may be assigned to the cation {N,N%-
therefore correspond to the axial proton on C . Irradia-
+
2
[trans-1,2C H (NCH Ph) ]P} (see Section 3).
6 10 2 2
tion of H then should result in large coupling being lost
C
to the two anti-periplanar hydrogens H and H and to
2.3.2. Molecular and crystal structure of 4
A
D
the geminal hydrogen H . Indeed, this is observed in
A single crystal X-ray diffraction study of racemic 4
(selected bond distances and angles are reproduced in
Table 1 and a ball-and-stick model in Fig. 6) reveals what
appears to be a formally two-coordinate, trivalent phos-
phorus centre in which both nitrogen atoms possess
B
practise, signals at l ca. 2.1 and 1.18 ppm being
assignable as either H and H . Differentiation between
B
D
these two is possible since irradiation of H should show
B
loss of only one large coupling (to H ) whereas irradia-
C
tion of HD should show large coupling lost to two
resonances, HE and H . The decoupling experiments
C
3
(
Fig. 5) reveal that the l 2.1 and 1.18 ppm resonances
The only significant difference being that the relative shift posi-
tions of HC and HD have been reversed. These observations are
corroborated by the 1H– C COSY spectrum which reveal the same
relative ordering of carbon atoms C and C as in compound 2a, but
be assigned as H and H , respectively. H is then readily
B
D
E
13
assigned by inference. These assignments of axial and
equatorial protons of the cyclohexyl ring are supported
1
2
carbon atom C3 is shifted to low frequency by ca. 8 ppm and its
associated hydrogen atom displaced by ca. 1 ppm to high frequency
with respect to the corresponding nuclei in 2a, significant differences
despite the change in solvent from CDCl3 (2a) to CD Cl (4).
1
3
1
1
1
by C– H and H– H correlations.
1
Examination of the H-NMR spectrum of 4 reveals the
cyclohexyl region to be equally complex to that of the
parent diamine 2a as expected, but without the NH
resonance, and homonuclear decoupling experiments
reveal a similar overall connectivity and chemical shift
profile to that of 2a with the equatorial hydrogens HB
2
2
Presumably, these perturbations are associated with the formation of
the diazaphospholidine heterocycle in 4.
4
Although stable in THF solution for over an hour under dinitro-
gen at ambient temperature, prolonged exposure results in polymeri-
sation of the solvent to an intractable resin-like material.

202
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
Fig. 3. Isoelectronic and isolobal relationship between main-group species.
2
significant sp character as evidenced by their trigonal
planar environments; the deviations of N(1) and N(2)
from the best fit planes connecting atoms P(1)–C(1)–
chemistry of chiral phophorus(III) triflates in solution, it
is vitally important to be able to build a picture of the
interaction between phosphorus and trifluoromethylsul-
fonate (triflate) of compound 4 in this phase. One
analytical tool which has proved highly useful in identi-
fying formally two-coordinate phosphenium cations is
˚
C(7) and P(1)–C(2)–C(14) are −0.05 and +0.19 A,
respectively (sum of angles around N(1) and N(2); 359.6
and 355.2°; Fig. 7). Such trigonal planarity is expected
to facilitate effective delocalisation of formal positive
charge on phosphorus through [P–N] y-bonding. Un-
doubtedly the most interesting features are connected
with the phosphorus–triflate interaction. P(1) has close
contacts to one oxygen atom of each of two triflate groups
31
31
P-NMR spectroscopy [17]. Indeed, P chemical shifts
have been correlated with coordination number, coordi-
nation geometry, oxidation state and the electronegative
character of the groups bonded to phosphorus and indeed
empirical relationships have been developed and tabu-
lated [18].
˚
in the crystal (Fig. 8); at distances of 2.841 and 2.755 A
these interactions are well within the van der Waals
distance for a phosphorus–oxygen interaction (ca. 3.35
Phosphorus chemical shifts (l ) of phosphenium com-
p
pounds are normally located within the range +220 to
+380 ppm (wrt 85% aqueous phosphoric acid as zero)
[17] although values have been recorded as low as +77.4
ppm and as high as +513 ppm [17]. It has been generally
supposed that the better able a phosphorus-bound sub-
stitutent is at delocalising the positive charge formally
associated with the phosphenium centre, then the lower
will be the phosphorus chemical shift. Conversely, the
more localised the positive charge on phosphorus, the
˚
˚
A) but are nevertheless over 1 A longer than expected for
˚
a single [P–O] covalent bond (ca. 1.63 A) [16]. Further-
more, the two [O–P] ‘bond’ vectors are directed along
the axes expected for interaction with opposite lobes of
2
3
a vacant phosphorus 3p-orbital of a formally | u
phosphenium cation; the angles between the P–O vectors
and normals to the plane N(1)–(1)–N(2) are 11.5 and
1
0.2°. Furthermore, given an OPO angle of 164°, it seems
higher the frequency of l will be.
p
clear that the phosphorus atom occupies a rather unusual
four-coordinate geometry. The conclusion from these
solid state data is that phosphorus–triflate interactions
are present although likely to be significantly weaker than
for a formal [P–O] single covalent bond.
31
A single P-NMR resonance is observed for com-
pound 4 at +271.1 ppm (0.54 M , 300 K, CH Cl ),
−
1
2
2
well within the range expected for two-coordinate pho-
sphenium cations however, 4 also appears to display
some intriguing, non-linear concentration dependent
31
5
3
1
P-NMR behaviour at room temperature (Fig. 9) ; a
2
.3.3. P-NMR properties of 4
Since we are ultimately interested to explore the
5
Thecurveofl versus4appearstofollowasecond-orderpolynomial
p
relationship very closely. Although we do not wish to over-emphasise
a relationship which we have not examined in more detail, it may suggest
a mathematical relationship between chemical shift and the relative
2
3
3 3
proportions of | u and | u species in the equilibrium depicted in
Scheme 1. One further feature which we have yet to investigate in any
detail is the question of a [monomer] X [dimer] equilibrium in solutions
of 4, wherein it is quite possible for triflate to act as a bridging ligand.
The different ways in which the various equilibria change upon altering
both dilution and temperature may explain linearity in one scenario
(temperature) and a non-linearity in the other (dilution).
Fig. 4. Isoelectronic triflates.

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
203
Fig. 5. Partial 1H-NMR spectrum (cyclohexyl region; 400 MHz; CDCl ) of 2a.
3

204
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
+
Scheme 2. (i) Two equivalents. ArCHO, EtOH, H ; (ii) three equivalents. LiAlH , THF; (iii) (R=H); PCl , N-methylmorpholine, toluene or
4
3
CH Cl ; (iv) (R=H); Me SiOTf (Y=OTf=OSO CF ), CH C1 ; (v) (R=H); PhMgBr, THF; (vi) (R=H); MeOH; N-methylmorpholine,
2
2
3
2
3
2
2
toluene.
2
4-fold increase in concentration from 0.025 to 0.6 M
in the solid state (Fig. 8) where each phosphorus atom
would then be effectively four-coordinate. This would
only be a reasonable proposal if there were some evi-
3
1
results in a change to the P-chemical shift value (DP)
of +5.98 ppm. We interpret such behaviour as evi-
dence of a dynamic interaction between phosphorus
and triflate oxygen(s) at room temperature leading to a
more ‘naked’ phosphenium cation with slightly lower
dence for l \ca. 270 ppm in such a four-coordinate
p
compound. Whilst we recognise that four-coordinate
phosphorus usually resonate below ca. 100 ppm, solid
31
frequency l at higher dilution. We envisage that the
state P-NMR spectroscopy of 4 reveals a chemical
p
greater the degree of delocalisation of the positive
charge from phosphorus onto the nitrogen atoms will
shift of l 290 ppm, we presumably reflecting the most
p
unusual oxidation state and coordination geometry of
the phosphorus atom in 4 and consistent also with the
above hypothesis ([10]b).
3
1
lead to a slightly lower frequency P-chemical shift, as
found in other phosphenium systems ([17]b). Such a
scenario is consistent with the equilibrium depicted in
Scheme 1 lying more to the left hand side at higher
dilution, as expected for any weak electrolyte. However,
Should the above scenario be correct, then increasing
temperature should favour increased dissociation in
accordance with Le Chateliers’ Principle [19]. Consis-
3
1
31
−3
given that the P-chemical shifts of 5 and 6 are far
lower than that of 4, we expected that increased interac-
tion between phosphorus and triflate oxygen should
lead to lower not higher frequency shifts. One explana-
tion recognises the possibility for intermolecular inter-
actions in solution leading to each phosphorus atom
binding to two triflate groups by analogy to that found
tently, P-NMR chemical shifts of 4 (0.3 mol dm
,
CH Cl ), reveal a linear dependence upon temperature
2
2
between 295 K (l 269.2 ppm) and 203 K (l 274.2
p
p
−
2
−1
ppm) with a slope of −5.4×10
ppm K ; higher
temperatures presumably favouring uncoordinated
phosphenium cation as suggested by the low frequency
perturbation of l (Fig. 10a). This behaviour contrasts
p

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
205
3
3
with the configurationally stable l u phosphorus
derivatives 5 and 6 which, although displaying linear
behaviour, have gradients in the opposite direction to
that of 4 with DP of +4.2 ppm between 203 and 298 K
where the balance of behaviour is closer to the ionic
than the covalent.
2.3.5. Infrared properties of 4
−
2
−1
19
and slope +4.6×10
ppm K
(5; Fig. 10b) and DP
of +4.2 ppm between 203 and 298 K and slope
In addition to F-NMR, infrared spectroscopy is
known to be a useful analytical technique for distin-
guishing between bound and unbound triflate groups in
metal complexes [20]. In particular, one of the asym-
−
2
−1
+
4.6×10 ppm K (6; Fig. 10c). We interpret such
a difference in behaviour in terms of molecules 5 and 6
being less able to engage in intermolecular interactions
such as those in Fig. 8 than for 4.
metric [SO ] stretching modes is especially sensitive to
3
the ionic or covalent nature of the moiety as a whole.
−
1
n
+
We find this vibration at 1270 cm for ionic [ Bu N]
4
1
9
−
−1
2
.3.4. F-NMR Properties of 4
[OTf] , 1255 cm
for covalent Me SiOTf and 1260
for 4 (all in THF solution at 1 mol dm ), again
3
1
9
−1
−3
F-NMR spectroscopy is an excellent technique for
cm
characterising triflate groups, in particular for distin-
guishing ‘ionic’ triflates from ‘covalent’ triflates [20].
We have taken as our ionic and covalent triflate refer-
consistent with intermediate character in solution.
1
13
1
2.3.6. H and C{ H}-NMR beha6iour of compounds
3–6
n
+
−
ence points, the compounds [ Bu N] [OTf]
and
4
19
Me SiOTf, respectively, which return F-NMR reso-
Further evidence for a dynamic interaction between
3
nances of lF −80.0 and −78.7 ppm, respectively
phosphorus and triflate in 4 is revealed upon examina-
tion of the H-NMR spectrum. Should 4 possess a
1
(
CD Cl ; 293 K; referenced to C F at −162.9 ppm).
2
2
6 6
1
9
Variable temperature F-NMR studies on 4 (CD Cl ;
static covalent structure or be engaged in a dynamic
process involving slow exchange of configuration at
phosphorus, then the methylene hydrogens on each
benzyl substituent (H , H ) should express themselves
2
2
2
03–293 K; referenced to C F at −162.9 ppm) reveal
6 6
temperature behaviour which parallels both ionic
n
+ −
4 3
[
Bu N] [OTf] and covalent Me SiOTf (Fig. 11) al-
a
b
though it seems clear that behaviour is intermediate
between the two extremes, again supportive of a dy-
namic equilibrium of the type indicated in Scheme 1,
as two distinct [ABX] patterns (Scheme 3; X, phospho-
rus; Y, triflate). Indeed, in the configurationally fixed
derivatives 5 (Y, Ph 5; OMe 6; Scheme 3), two [ABX]
patterns are observed (Section 3). However, between
300 and 200 K only a single [ABX] pattern is observ-
able for the methylene hydrogens of 4 centred at 4.55
Table 1
˚
Selected bond lengths (A) and angles (°) for compound 4
2
3
ppm ( J
14.5 Hz and J
11.3 Hz; Fig. 12), be-
˚
HH
PH
Bond length (A)
haviour consistent with local C -symmetry at the phos-
P(1)–N(1)
N(1)–C(l)
N(2)–C(2)
C(1)–C(6)
C(2)–C(3)
C(4)–C(5)
C(7)–C(8)
S(1)–O(2)
S(1)–O(1)
C(21)–F(3)
C(21)–F(1)
1.616(3) P(1)–N(2)
1.465(5) N(l)–C(7)
1.470(5) N(2)–C(14)
1.447(6) C(1)–C(2)
1.441(7) C(3)–C(4)
1.506(7) C(5)–C(6)
1.511(6) C(8)–C(9)
1.435(3) S(1)–O(3)
1.452(3) S(1)–C(21)
1.320(6) C(21)–F(2)
1.336(6)
1.625(3)
1.468(5)
1.469(5)
1.459(6)
1.480(7)
1.493(7)
1.380(6)
1.447(3)
1.785(5)
1.331(6)
2
phorus atom of 4 caused presumably by rapid exchange
of coordinated (Scheme 3A) and un-coordinated triflate
(
Scheme 3B) [21]. Indeed, as expected, it is possible to
monitor the interaction between phosphorus and trifl-
31
ate in solution via P-NMR titration experiments.
n
+
Thus, the addition of ten equivalents of [ Bu N]
4
−
−3
[O SCF ] to a CH Cl solution of 4 (0.02 mol dm
;
3
3
2
2
3
00 K) results in a small perturbation to l , of +4.4
p
ppm. Presumably, this perturbation reflects a dynamic
process such that higher concentrations of triflate fa-
vour increased interactions with phosphorus, and con-
Bond angle (°)
N(1)–P(1)–N(2)
C(1)–N(1)–P(1)
C(2)–N(2)–C(l4)
C(14)–N(2)–P(1)
C(6)–C(l)–N(1)
C(3)–C(2)–C(1)
C(1)–C(2)–N(2)
C(3)–C(4)–C(5)
C(1)–C(6)–C(5)
N(2)–C(14)–C(l5)
O(2)–S(1)–O(1)
O(2)–S(1)–C(21)
O(1)–S(1)–C(2l)
F(3)–C(21)–F(l)
F(3)–C(21)–S(l)
F(1)–C(21)–S(l)
94.9(2)
113.5(3)
121.0(3)
121.4(3)
123.4(4)
115.8(4)
107.1(3)
116.7(4)
112.0(5)
113.8(3)
116.1(2)
103.0(2)
103.6(2)
107.5(4)
112.1(3)
111.5(4)
C(1)–N(1)–C(7)
119.6(3)
C(7)–N(1)–P(1)
C(2)–N(2)–P(1)
C(6)–C(1)–C(2)
C(2)–C(l)–N(1)
C(3)–C(2)–N(2)
C(2)–C(3)–C(4)
C(6)–C(5)–C(4)
N(1)–C(7)–C(8)
O(2)–S(1)–O(3)
O(3)–S(1)–O(1)
126.5(3)
112.8(3)
117.5(4)
107.6(3)
125.5(4)
113.5(5)
117.1 (5)
112.3(4)
114.6(2)
114.2(2)
sequently, a shift in l to high frequency.
p
What possibilities exist for the dynamic mechanism
leading to equivalence of the two benzyl functions?
Two scenarios suggest themselves as likely contenders;
dissociative and associative models. In the former
mechanism, an ionic phosphenium intermediate is en-
visaged which possesses local C -symmetry. Triflate an-
2
ion is then in a position to attack phosphorus on either
face, leading to interconversion of the two benzyl
groups. In the latter transformation, the phosphorus–
triflate interaction is considered as purely covalent; two
such molecules may come together to form a triflate
O(3)–S(1)–C(21) 102.9(2)
F(3)–C(21)–F(2) 106.6(5)
F(2)–C(21)–F(1) 106.5(4)
F(2)–C(21)–S(l)
112.3(3)
bridged dimer, also possessing local C -symmetry at
2

206
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
Fig. 6. Molecular structure of compound 4.
3
3
2 3
phosphorus. Alternatively, associative exchange
may take place between a covalent oligomeric species
for which X-ray diffraction analysis already pro-
2.3.8. The [l u X l u ] equilibrium—An empirical
measure using NMR spectroscopy
If we consider the dynamic equilibrium between co-
valent and ionic extremes of compound 4, as shown in
Scheme 3, as being rapid on the NMR time-scale then
we can readily see that chemical shift measurments in
NMR experiments will be time-averaged over both
ionic and covalent forms. Thus, we may deduce for
1
vides some support. Although H-NMR experiments
do not differentiate between these two mechanistic
31
possibilities, single-crystal X-ray diffraction, P- and
1
9
F-NMR studies on 4 suggest partial ionic, phosphe-
nium character to 4, possibly supporting a dissociative
mechanism for triflate exchange. Solution conductivity
experiments (vide supra), also support such a conclu-
sion.
31
19
13
example that the P- , F- and C(CF )-NMR chemi-
3
cal shifts of 4 be represented as averages of those for
the covalent (A) and ionic (B) extremes, weighted ac-
cording to their respective mole fractions in solution.
This may be represented as in Eq. (1):
2
.3.7. Solution conducti6ity studies on 4
n
+
−
Me SiOTf and [ Bu N] [OTf] possess solution mo-
3
4
l =F l +F l
(1)
where l is the chemical shift of the system; l is the
S
c
C
I I
lar conductivities L in THF solvent (296 K; 0.11 mol
−
3
−1
2
−1
dm ) of 0.03 and 3.14 V
cm mol , respectively
S
c
whilst corresponding measurements under the same
chemical shift of pure covalent 4; l is the chemical shift
I
conditions for 4 reveal a molar conductivity L of 0.43
of pure ionic 4; F is the mole fractions of the covalent
c
−
1
2
−1
V
cm mol . From these values, although very
and ionic forms of 4, respectively. F =[A]/[A ] and
c
o
much lower than for ionic species in aqueous solu-
F =[B]/[A ] where [A ] is the total concentration of 4
I
o
o
tion as expected, it is clear that 4 is a stronger
and [A] and [B] represent concentrations of covalent
and ionic forms, respectively. We can see immediately
that F +F =1 so that F =1−F . Therefore, Eq. (1)
electrolyte than Me SiOTf by a factor of ca. 14. Obvi-
3
ously, compound 4 is, formally speaking, a weak
c
I
c
I
electrolyte and is less conducting than the ionic tri-
can be rearranged to Eq. (2) upon eliminating terms in
F .
c
n
+
−
flate [ Bu N] [OTf]
by a factor of ca. 7; yet
4
these data are consistent with significant yet dyna-
mic solution interaction between phosphorus and
triflate in 4 of a type that would involve ionic
species.
[
l −l ]/[l −l ]=F
(2)
Now, the equilibrium between covalent (A) and ionic
(B) forms of 4 maybe represented by the equilibrium
S
C
I
C
I

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
207
Fig. 7. Molecular structure of 4 emphasising the planarity of the cyclohexyl nitrogen atoms.
constant K=x/([A ]−x), where x represents the de-
able to assign values to l and l . This is not a trivial
C I
o
gree of dissociation at equilibrium. Since we know that
matter since bona fide examples of pure ionic or pure
covalent phophorus(III) triflates are not known [12];
however, it might yet prove possible to provide refer-
x=F ·[A ] this latter expression for x in terms of K
I.
O
may be rearranged to express K in terms of F as in Eq.
I
n
+
(
3);
ence points by recalling our earlier use of [ Bu N]
4
−
[
OTf] as a representative ionic triflate and Me SiOTf
3
K=F /(1−F )
(3)
I
I
as representative of a covalent triflate. We envisage that
the ionic triflate will pose little problem in terms of
Since F , is a measureable parameter, in order to
I
13
19
quantify the position of equilibrium between ionic and
comparing C- and F-NMR data to ionic 4 but there
covalent forms in phosphenium 4, we need only to be
may be discrepancies in equating covalent Me SiOTf to
3
a covalent form of 4. Despite the fact that they are
isoelectronic and isolobal, there are still likely to be
differences in chemical shifts due to the different elec-
tronegativities and coordination spheres of silicon and
phosphorus. Nevertheless, in CD Cl solvent, 0.3 mol
2
2
−
3
−3
19
dm
(0.1 mol dm
for F) and 300 K, l for
I
n
+
−
13
[
Bu N] [OTf] are 121.10 ppm ( C) and −80.0 ppm
4
19
(
F) whilst the corresponding values for Me SiOTf (l )
3 C
are 118.53 ppm ( C) and −78.7 ppm ( F). Under the
13
19
same conditions of solvent, concentration and tempera-
13
19
ture, the C- and F-chemical shifts for 4 were found
to be 120.44 and −79.6 ppm, respectively which, upon
solution of Eq. (2) and Eq. (3) above reveals an equi-
librium constant K between covalent and ionic forms of
13
19
4
of 2.8 (from C-NMR data) and 3.3 (from F-NMR
data); results in broad agreement with the trend ob-
served from solution conductivities and variable tem-
19
perature F-NMR studies that the equilibrium lies
more to the side of ionic than covalent 4 (vide infra).
19
Furthermore, we have measured F-NMR chemical
shifts of compound 4 at various temperatures which,
along with commensurate shift values for our ionic and
covalent calibrants under identical conditions, allows us
to calculate K as a function of temperature (Table 2).
Obviously, the results would appear to suggest very
little difference in the position of equilibrium between
Fig. 8. Expanded molecular structure revealing interactions between
phosphorus and the oxygen atoms of two triflate anions.

208
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
−
3
Fig. 9. Relationship between lp (ppm) and concentration (mol dm ) for compound 4 (CH Cl ; 300 K).
2
2
2
93 and 203 K. Since we are not certain to what extent
In effect, the donor molecule acts as a competitive
inhibitor of triflate for the phosphorus centre such that
the stronger the interaction of a given donor molecule
with phosphorus, then the more ionic in character will
be the triflate moiety (monitored here by C-NMR
spectroscopy; Scheme 3). The NMR-based method out-
lined in Section 2.3.8 allows us to compute values of
these values reflect the non-ideal nature of the cali-
brants that we are using or the complexity of the
equilibria present in solution, the best we can say at
present is that the equilibrium constant between cova-
lent and ionic forms of 4 is ca. 3 with respect to
13
n
+
−
TMSOTf and [ Bu N] [OTf] as standards of cova-
4
lent and ionic character respectively; suggesting more
ionic, phosphenium-like character for 4, closer in char-
acter to the latter calibrant than the former.
relative basicity (B ) for each donor molecule and to
r
correlate such values with electronic and possible steric
properties (Table 3). This technique works particularly
well since we find the interaction between phosphenium
and donor compounds to be a dynamic one and one
which is rapid on the NMR time-scale (vide infra).
Consequently, only a single set of NMR resonances
2.3.9. Quantitati6e assay of the strength of interaction
between phosphorus and donor phophorus(III) triflates
For any potential application of phosphenium
cations as chiral Lewis acids it will be necessary to
examine the binding abilities of different donor
molecules and, where feasible, correlate the strength of
binding to both electronic and steric properties of the
donor.
31
13
1
( P, C and H) are observed for each system at 300 K.
We define an empirical scale of relative basicity Br
according to the equation; B ={[l −l ]/l }×1000
r
I
S
I
where definitions are the same as those in Section 2.3.8.
We can see immediately that as l approaches l , more
S
I
Using the same NMR-based method described
above, it should prove possible to quantify the strength
of interaction between a given donor molecule and
phosphenium centre, under certain conditions, by mon-
itoring the effect of a known concentration of donor on
the equilibrium between covalent and ionic forms of 4.
closely so the donor must be a better competitive
inhibitor of triflate and consequently interact better
with the phosphorus centre. Therefore, according to
this scale, the smaller the value of B , the stronger the
r
interaction between donor and phosphorus. Analysis of
the B values in Table 3 reveals a relative order of base
r

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
209
Fig. 10. Relationship between lp (ppm) and temperature (K) for (a) compound 4; (b) compound 5; (c) compound 6 (CH Cl ; 0.3 mol dm−3).
2
2
3
1
strength as indicated in Scheme 4, electron-donating
pyridines being the strongest binders, correlating
crudely with combined field and resonance Hammett
parameters | (Table 3). A number of further points
may be made on these empirical relative basicities;
basicity appears to decrease as the steric environment at
P-chemical shift as expected ([17]b). Consequently, it
is now possible, within reasonable boundary conditions
of ca. 910%, to predict the relative basicity of a given
donor molecule towards this phosphenium centre from
a knowledge of the P-chemical shift of the system.
In addition to an empirical measure of relative basic-
ity, it is possible, as outlined in Section 2.3.8, to calcu-
late equilibrium constants K for each donor. We
recognise again that the C-NMR chemical shift of the
triflate moeity will be determined by the relative mole
fractions of ionic and covalent forms in solution
(Scheme 3, Eqs. (1) and (2); definitions as in Section
2.3.8). Now, the equilibrium between 4 and the donor
31
the donor atom increases (B values for 2-Br and 3-Br-
r
pyridines), a not unreasonable result. A similar expla-
13
nation may be used to rationalise the smaller B for
r
PPh than that for NPh (although electronic effects are
3
3
less easy to neglect here) and possibly also the smaller
B of N-methylmorpholine over that of NPh , although
r
3
the latter is also likely to have a lower pK Ethereal
a
oxygen donors such as 1,4-dioxane clearly bind only
very weakly to the phosphorus centre.
adducts depicted in Scheme 4 may be represented by
2
the equilibrium constant K=x/([A ]−x) in which
o
Since there is a clear relationship between the
strength of interaction between phosphenium and
x=F ·[A ] ([A ] being the initial concentration of 4
I
o
o
and donor molecule added). Rearrangement leads to
Eq. (4) which can be solved readily upon knowing [Ao]
and FI.
1
3
donor and C-NMR chemical shifts, it is perhaps not
surprising that a relationship exists between strength of
3
1
interaction and P-NMR shifts. This is revealed in
Table 3 and represented graphically in Fig. 13 as an
agreeably linear relationship where the better the donor
2
K=F /{[A ]·(1−F ) }
(4)
I
o
I
Values of K are collected in Table 3 where it can be
towards phosphorus (lower B ), the lower also the
seen that, as expected, B values shadow K values; the
r
r

210
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
Fig. 10. (Continued)
stronger binding donors (low B ) have the larger equi-
3. Experimental
r
librium constants (high K), especially so for the elec-
tron-donating pyridines. Indeed, re-examination of the
3
.1. General
1
9
variable temperature F-NMR experiments on Fig. 11
reveals that the presence of one equivalent of pyridine
in a dichloromethane solution of 4 results in a signifi-
cant increase in ionic character of the triflate group as
expected with an ca. 8000 times perturbation in equi-
librium constant towards the ionic.
All reactions and manipulations were performed as
reported previously [23]. Optical rotations were
recorded on an optical activity AA 10 polarimeter
operating at 589.44 nm. All other compounds were
purchased from commercial sources and were either
recrystallised, chromatographed on a short column of
Brockmann grade I basic alumina or distilled under
nitrogen prior to use. Conductance measurements were
performed in tetrahydrofuran solvent at ambient tem-
perature using a custom-built Weatstone bridge circuit
using a probe with cell constant=1.36. Enantiopure
trans-1,2-diaminocyclohexaxe was prepared according
to the published procedures [24], as the tartrate salts
2.4. The future—chiral phophorus(III) triflates in
asymmetric chemistry
We believe that we have laid the foundations here,
through qualitative and quantitative examination of the
nature of the interaction between phophorus(III) and
triflate oxygen, for a detailed examination of reactivity
studies. Our experiments suggest the phophorus(III)
triflate interaction to have significant ionic character
which, in turn, augers well for phosphenium-like reac-
tivity with the added advantage of, for the first time in
this class of molecule, chirality.
{
(R,R)-diamine}{(+)-tartrate}; [h]D20: +10.8° (c=1,
H O), Lit., +12.5° (c=4, H O) or {(S,S)-di-
2
2
amine}{(+)-tartrate}; [h]
20: +25.2° (c=1, H O),
D
2
Lit., +25° (c=1, H O) [23].
2

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
211
1
9
n
+
−
Fig. 11. Relationship between F-NMR chemical shifts of 4 (ꢀ); 4-Py (2); [ Bu ] [OTf] (ꢁ) and TMSOTf (") as a function of temperature
4
−
3
(
CH Cl ; 0.1 mol dm ).
2 2
3
.2. Syntheses of
synthesised via the above route from enatiopure di-
amine. [h] 20 +248.4° (c=1, CH CO H).
b: (9)-Trans-1,2 diaminocyclohexane (5.0 cm , 4.76
N,N%-dibenzylidine-trans-1,2-diaminocyclohexanes 1a–d
D
3
2
3
1
3
g, 0.042 mol) and 4-methoxybenzaldehyde (10.1 cm ,
1
1.34 g, 0.083 mol) were combined in methanol solvent
3
˚
(
60 cm ), with 4 A molecular sieves and a few drops of
acetic acid. After refluxing for 15 min a yellow precipi-
tate was evident. Recrystallisation of this material from
hot methanol afforded 1b as a pale yellow solid. Yield:
1
3.96 g, (95%). l (CDCl ): 8.11 (s, 2H, C H), 7.52 (m,
H 3 4
4
H, C H), 6.81 (m, 4H, C H), 3.77 (s, 6H, OMe), 3.33
6
7
(
m, 2H, C H), 1.87–1.84 (m, 6H, C H and C H ), 1.48
3 2 1 eq
(
m, 2H, C H ) l (CDC1 ): 161 24 (s, C ), 160.26 (s,
3
1
ax
C
3
8
1
a: (9)-Trans-1,2-diaminocyclohexane (10.0 cm ,
C ), 129.44 (s, C ), 129.41 (s, C ), 137.74 (s, C ), 73.77
3
4
5
6
7
9
0
.51 g, 0.083 mol) and benzaldehyde (18.0 cm , 17.62 g,
(
s, C ), 55.24 (s, OMe), 33.11 (s, C ), 24.58 (s, C ) m/z:
3
3 2 1
+
.166 mol) were combined in ethanol solvent (100 cm ).
3
50 (M) . Found C, 75.3; H, 7.4; N, 8.0, C H N O
22 26 2 2
After stirring at ambient temperature for 0.5 h, a
precipitate was evident, which was collected and dried
in air. Washing with cold ethanol (30 cm ) afforded 1a
as a white, analytically pure crystalline solid. Yield:
0.2 g, (85%). l (CDC1 ): 8.33 (s, 2H, C H), 7.73–7.69
m, 4H, C H), 7.46–7.38 (m, 6H, C H and C H),
.59–3.48 (m, 2H, C H), 2.01–1.80 (m, 6H, C H and
C H ), 1.71–1.54 (m, 2H, C H ) l (CDCl ): 161 02
requires C, 75.4; H, 7.5; N, 8.0.
1
c: Using the procedure outlined above for 1b, but
3
stirring for 16 h, reaction of (9)-trans-1,2-diaminocy-
clohexane (0.7 cm , 0.67 g, 0.006 mol) with 4-bro-
mobenzaldehyde (2.20 g, 0.012 mol) afforded 1c as
white crystals. Yield: 1.9 g, (74%). l (CDCl ): 8.10 (s,
2H, C H), 7.43 (br.s, 8H, C H and C H), 3.37 (m, 2H,
3
2
(
3
H 3 4
6 7 8
H
3
3
2
4 6 7
1
eq
1
ax
C
3
C H), 1.87–1.82 (m, 6H, C H C H and C H or
3 1 eq 2 eq 1 eq
C H ), 1.47 (m, 2H, C H or C H ) l (CDCl ): 159
(
s, C ), 136.43 (s, C ), 130.2 (s, C ), 128.30 (s, C ),
4
5
6
7
2 eq 1 eq 2 ax C 3
1
27.93 (s, C ), 73.82 (s, C ), 32.99 (s, C ), 24.52 (s, C )
70 (s, C ), 135 15 (s, C ), 131.65 (s, C ), 129.30 (s, C ),
4 5 7 6
8
3
2
1
+
m/z:290 (M) . Found C, 82.5; H, 7.7; N, 9.7;
C H N requires C, 82.7; H, 7.7; N, 9.7. (S,S)-1a was
124.66 (s, C ), 73.74 (s, C ). 32.79 (s, C ), 24.40 (s, C )
8 3 2 1
+
m/z: 449 (M–H) . Found C, 53.4; H, 4.7; N, 6.1; Br,
2
0
22
2

212
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
−
Scheme 3. Relationship between coordinated (A) and uncoordinated (B) in 4-[Y]; Y=[OTf] , [C H N] etc.
5
5
3
3
5.8; C H N Br requires C, 53.6; H, 4.5; N, 6.3; Br,
2b: Compound 1b (5.24 g, 0.015 mol) in THF sol-
2
0
20
2
2
3
5.7.
d: (9)-Trans-1,2 diaminocyclohexane (8.0 cm ,
.61 g, 0.067 mol) and 4-dimethylaminobenzaldehyde
vent (20 cm ) was added slowly to LiAlH (1.70 g,
4
3
3
1
0.045 mmol) in THF solvent (80 cm ) at ambient
7
temperature under dinitrogen. After refluxing for 16 h,
3
3
(
19.9 g, 0.133 mol) were combined in toluene solvent
water (3.5 cm ), sodium hydroxide (15% w/v, 10 cm )
and refluxed for 15 min using a Dean-Stark trap. On
cooling to room temperature a yellow precipitate
which was collected and air dried. Recrystallisation of
the crude product from hot chloroform/ether (4:1 v/v)
afforded 1d as a bright yellow crystalline solid. Yield:
1
2
2
1
1
3
and water (3.5 cm ) were added and the resulting
mixture stirred for 3 h. The mixture was filtered and
the volatiles removed under reduced pressure yielding
the crude product as a white solid. Recrystallisation
from pentane afforded 2b as white crystals. Yield: 4.5
g, (85%). l (CDCl ): 7.21 (m, 4H, C H), 6.82 (m, 4H,
8.7 g, (75%). l (CDCl ): 8.08 (s, 2H, C H), 7.46 (m,
H 3 4
H
3
6
H, C H), 6.58 (m, 2H, C H), 3.30 (m, 2H, C H),
6
7
3
2
C H), 3.82 (d, 2H, J =12.9 Hz, C H), 3.77 (s, 6H,
OMe), 3.56 (d, 2H, J =12.9 Hz, C H), 2.23 (m,
7
HH
2
HH
4
.92 (s, 6H, NMe ), 1.83 (m, 6H, C H and C H ),
2
2
1
eq
4
.71–1.54 (m, 2H, C H ). l (CDCl ): 160.71 (s, C ),
1
ax
C
3
4
2
1
H, C H), 2.14 (m, 2H, C H ), 1.81 (br. s, 2H, NH),
3 2 eq
51.73 (s, C ), 129.29 (s, C ), 125.00 (s, C ), 111.56 (s,
8
6
5
.71 (m, 2H, C H ), 1.22 (m, 2H, H H ), 1.01 (m,
1 eq 1 ax
C ), 73.93 (s, C ), 40.22 (s, NMe ), 30.44 (s, C ), 24.52
6
3
2
2
+
2H, C
2
Hax). l
C
(CDCl
3
): 158.47 (s, C
8
), 133.32 (s, C ),
5
(
s, 20 C ). m/z:376 (M) . Found C, 79.6; H, 9.0; N,
1
1
29.16 (s, C ), 113.73 (s, C ), 60.83 (s, C ), 55.24 (s,
6
7
3
12.0, C H N requires C, 79.5; H, 8.6; N, 12.0;
31 40 4
OMe), 50.31 (s, C ), 31.61 (s, C ), 25.13 (s, C ) m/z:
C H N -title compound with one mole equivalent of
toluene.
4
2
1
3
1
40
4
+
3
54 [M] . Found C, 74.5; H, 8.6; N, 8.0, C H N O
22 30 2 2
requires C, 74.6; H, 8.6; N, 7.9.
2
d: Compound 1d (5.0 g, 0.013 mol) was added
3
.3. Syntheses of
N,N%-dibenzyl-trans-1,2-diaminocyclohexanes 2
slowly to LiAlH
80 cm ) at ambient temperature under dinitrogen. Af-
ter refluxing for 64 h, water (2.5 cm ), sodium hydrox-
4
(1.27 g, 0.034 mmol) in THF solvent
3
(
3
2
a: A solution of la (1.27 g, 4.38 mmol) in THF
3
3
3
solvent (10 cm ) was added dropwise to LiAlH (0.66
g, 17.5 mmol) in THF solvent (20 cm ) at ambient
temperature under dinitrogen. After refluxing for 40 h;
water (1 cm ), sodium hydroxide (15% w/v, 2.5 cm )
ide (15% w/v, 7.5 cm ) and water (2.5 cm ) were added
and the resulting mixture stirred at room temperature
for a further 2.5 h. The mixture was filtered and the
volatiles removed under reduced pressure to afford the
crude product as a pale yellow oil, which was dried in
pentane solution over magnesium sulphate (10 g). Re-
moval of volatiles in vacuo with recrystallized from
pentane/ether afforded 2d as a bright yellow solid.
Yield: 3.8 g, (75.1%). l (CDCl ): 7.17 (m, 4H, C H),
4
3
3
3
3
and water (1 cm ) were added and the resulting mix-
ture stirred for a further 2 h. The mixture was then
filtered and the volatiles removed under reduced pres-
sure to afford the crude product. Recrystallisation
from dry pentane afforded the title compound as a
white crystalline solid. Yield: 0.9 g, (67%). l (CDCl ;
compound numbering as in 1a: 7.32–7.23 (m, 10H,
C H, C H and C H), 3.83 (d, 2H, JHH=13.2 Hz,
C H,), 3.77 (d, 2H, J =13.2 Hz, C H), 2.26 (m,
2
1
2
1
H
3
6
H
3
2
6
.70 (m, 4H, C H), 3.79 (d, 2H, JHH=12.7 Hz,
7
2
C H), 3.34 (d, 2H, JHH=12.7 Hz, C H), 2.91 (s,
2
4
4
6
7
8
1
1
2
(
6
2H, NMe ), 2.24 (m, 2H, C H), 2.1 (m, 2H, C H ),
.88 (br. s, 2H, NH), 1.70 (m, 2H, C H ), 1.43 (m,
H, C H ), 1.21 (m, 2H, C H ). l (CDCl ): 149.70
s, C ), 129.36 (s, C ), 128.93 (s, C ), 112.82 (s, C ),
2
2 3 2 eq
4
HH
4
1
eq
H, C H), 2.21 (m, 2H, C H ), 1.91 (s, 2H, NH),
3 2 eq
1
ax
2
ax
C
3
.75 (m, 2H, C H ), 1.27 (m, 2H, C H ), 1.05 (m,
1
eq
1
ax
5 8 6 7
H, C H ). l (CDCl ): 141.24 (s, C ), 128.53 (s, C ),
2
ax
C
3
5
6
0.74 (s, C ), 50.35 (s, C ), 40.85 (s, NMe ), 31.60 (s,
3 4 2
28.43 (s, C ), 126.78 (s, C ), 61.02 (s, C ), 51.26 (s,
7
8
3
+
+
C ), 25.13 (s, C ) m/z: 380 [M] . Found C, 75.8; H,
2 1
C ), 31.68 (s, C ), 25.15 (s, C ) m/z: 294 [M] . Found
C, 81.6; H, 8.9; N, 9.5, C H N requires C, 81.6; H,
8
4
2
1
9
1
.7; N, 14.8, C H N requires C, 75.8; H, 9.5; N,
24 36 4
4.7.
2
0
26
2
.9; N, 9.5.

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
213
Fig. 12. 1H-NMR spectrum of compound 4 (400 MHz, CD Cl ).
2
2
3
3.4. Synthesis of 1-chloro-2,9-(dibenzyl)diaza-1-
solvent (20 cm ) was added at −78°C under dinitrogen
over a period of 15 min. The reaction mixture was then
allowed to warm to room temperature and stirred for 4
h. After this time the volatiles were removed under
reduced pressure to afford a crude solid. Extraction
into pentane, filtration and removal of the volatiles
under reduced pressure afforded pure 3 as a white
crystalline solid. Yield: 1.07 g, (60%). l (CDCl ): 181.6
phospha[4.0.3]bicyclononane 3
3
To a mixture of PCl (0.44 cm , 0.7 g, 5.1 mmol) and
3
3
NEt (2.13 cm , 0.73 g, 15.3 mmol) in toluene solvent
3
3
(
20 cm ), a solution of 2a (1.5 g, 5.1 mmol) in toluene
Table 2
P
3
Equilibrium constant (K) between covalent and ionic forms of 4 as a
function of temperature (K)
(
s). l (CDCl ): 7.4–7.2 (m, 10H, PhH), 4.36 (dd, 2H,
H 3
2
2
JHH=15 Hz, CH Ph), 4.20 (dd, 2H, JHH=15 Hz,
2
a,b
C
a,c
I
CH Ph), 3.00 (d, 2H, NCH), 1.94 (m, 2H, CH ), 1.72
Temperature (K)
l
l
lS(4)
FI
K
2
2
(
1
1
m, 2H, CH ), 1.51–0.95 (m, 4H, CH ). l (CDCl )
2 2 C 3
2
2
2
2
2
2
93
73
53
33
03
−78.71
−78.77
−78.77
−78.77
−78.83
−79.99
−80.10
−80.16
−80.22
−80.33
−79.64
−79.69
−79.81
−79.87
−79.93
0.73
0.69
0.75
0.76
0.73
2.7
2.2
3.0
3.2
2.7
38.31 (d, JPC=7 Hz, Ph–Cipso), 128.52 (s, Ph–C),
2
28.26 (s, Ph–C), 127.66 (s, Ph–C), 67.69 (d, JPC=9
2
Hz, NCH), 49.05 (d, J =21 Hz, NCH ), 29.70 (s,
CH2), 24.28 (s, CH2). m/z: 358.1355 [M] ;
C H N PCl requires 358.1366. Found: C, 66.8; H,
6
PC
2
+
35
20
24
2
a
b
c
CH Cl2 solvent, 0.1 M, in ppm.
2
.8; N, 7.6; Cl, 10.0; C H N PCl requires: C, 66.9; H,
20 24 2
Me SiOTf.
3
n
+
−
6.8; N, 7.8; Cl, 9.9. Chlorophosphoridite 3 has also
[
Bu N] [OTf] .
4

214
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
Table 3
Relative basicities (B ) and equilibrium constants for the interaction of various donor molecules with 4
r
a
C
a
P
K (mol−1 dm3)
|b
Donor
l
l
Br
Me SiOTf
118.53
121.10
121.07
120.53
120.88
121.07
121.08
120.97
120.76
120.43
120.61
120.51
—
—
—
—
—
—
24 066
53
—
—
0.0
—
3
n
+
−
[
Bu N] [OTf]
4
NC H5
168.3
266.1
212.4
161.1
140.7
170.8
211.0
268.5
259.5
269.0
0.25
4.7
1.8
0.25
0.17
1.1
2.8
5.5
4.0
4.9
5
2
3
4
4
4
-Br–NC H4
5
-Br–NC H
416
—
5
4
t
- Bu–NC H
24 066
54 361
1236
165
−0.15
−0.63
0.05
—
—
—
5
4
-Me N–NC H
2
5
4
-Ph–NC H4
5
MeN(CH ) O
2
4
O(CH ) O
39
74
49
2
4
PPh3
NPh3
—
a
CH C12 solvent, 0.3 M, 300 K in ppm.
Combined field and resonance Hammett parameter.
2
b
been prepared in enantiomerically enriched form using
resolved (S,S)-trans-1,2-diaminocyclohexane. Enan-
tiopurity of such enriched-3 has been determined by
derivatisation with commercially available enantioen-
riched R (Aldrich; 97% e.e. by GLC) and S (Aldrich;
l (CD Cl ; 300 K; 0.54 M) 271.1 (s). l (CD Cl ; 300
P 2 2 P 2 2
K; 0.54 M) −79.5 (s; referenced to C F at −162.9
6
6
+
ppm). m/z 323.1687 [M–OTf] ; C H N P requires
2
0
24
−
2
1
2
−1
323.1677. L (thf; 296 K; 0.11 M) 0.43 V cm mol
.
0
Found: C, 53.1; H, 5.2; N, 5.8. C H F N O PS re-
2
1
24
3
2
3
9
8% e.e. by GLC) methylmandelate in CDCl solution
quires C, 53.4; H, 5.1; N, 5.9.
3
in the presence of NEt as HCl acceptor following a
3
3
1
1
chiral derivatisation procedure based on P{ H}-NMR
spectroscopy that we have developed recently ([25]a).
The two possible diastereoisomers {(S,S)-3} {R-
methylmandelate} and {(S,S)-3} {S-methylmandelate}
are observed to resonate at 140.2 and 135.6 ppm and,
from integration of the resonances, the enatiopurity of
3.6. Synthesis of 1-phenyl-2,9-(dibenzyl)diaza-1-
phospha[4.0.3]bicyclononane 5
{(S,S)-3} was found to be 96(1)% ([25]b).
3.5. Synthesis of 1-trifluoromethylsulfonato-2,9-
(dibenzyl)diaza-1-phospha[4.0.3]bicyclononane 4
3
Trimethylsilyltriflate (0.37 cm , 0.424 g, 1.90 mmol)
was added to a solution of 3 (0.68 g, 1.90 mmol) in
3
CH Cl solvent (20 cm ) and the reaction mixture
2
2
stirred for 30 min under dinitrogen. All volatiles were
removed under reduced pressure and the resulting solid
3
washed with pentane (2×5 cm ), filtered and recrys-
A solution of 2a (2.16 g, 7 mmol) in dichloromethane
3
tallisation with cooling to −35°C from a mixture of
CH Cl :toluene (10:1 v/v) afforded the title compound
as colourless crystals. Yield: 0.62 g, (69%), lH
CD Cl , 300 K) 7.42–7.30 (m, 10H, Ph–H), 4.57 (dd,
H, J =11.3 Hz, J =14.5 Hz, PhCH ), 4.53 (dd,
H, J =11.3 Hz, J =14.5 Hz, PhCH ), 3.41 (dt,
H, J =1.5 Hz, JHH=6.0 Hz, NCH), 2.13 (m, 2H,
CH ), 1.81 (m, 2H, CH ), 1.36 (m, 2H, CH ), 1.24 (m,
H, CH ). l (CD Cl , 300 K) 134.94 (d, JPC=6.2 Hz,
Ph–Cipso), 129.38 (s, Ph–C), 129.15 (s, Ph–C), 128.76
s, Ph–C), 122.26 (q, JCF=320 Hz, CF ), 69.12 (d,
JPC=7.5 Hz, NCH), 49.32 (d, JPC=18.2 Hz,
solvent (20 cm ) was added dropwise to a solution of
3
PPhCl (1.0 cm , 1.31 g, 0.007 mol) and N-methylmor-
2
2
2
3
4
pholine (2.40 cm , 2.20 g, 0.022 mol) also in
dichloromethane solvent (30 cm ) at −78°C (cardice
3
(
2
2
3
2
2
2
2
bath) under an atmosphere of dinitrogen. The mixture
was allowed to warm to room temperature with stirring
over the course of 4 h. Subsequent filtration and re-
moval of the volatiles under reduced pressure afforded
a pale yellow oil which upon extraction into and recrys-
PH
HH
2
3
2
PH
HH
2
3
3
PH
2
2
2
3
2
2 C 2 2
3
tallisation from pentane (3×50 cm ) afforded the title
1
(
compound as a white crystalline solid. Yield: 2.12 g,
3
2
3
(73%). lH–{P} (CDCl ) 7.53 (m, 2H, H ), 7.37–7.21 (m,
3
10
2
PhCH N), 28.67 (s, NHCH ), 23.99 (s, NHCH CH ).
13H, H6–9 and H11–12), 4.41 (d, 1H, JHH=14.7 Hz,
2
2
2
2

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
215
Scheme 4. Relative donor strengths with respect to the phosphorus centre in 4. Strength of competitive inhibition of triflate.
2
H ), 4.29 (d, 1H, J =14.7 Hz, H ), 3.76 (d, 1H,
3.7. Synthesis of 1-methoxy-2,9-(dibenzyl)diaza-1-
phospha[4.0.3]bicyclononane 6
4
a
HH
4a%
2
2
JHH=14.8 Hz, H ), 3.56 (d, 1H, JHH=14.8 Hz,
4b
H ), 2.62 (m, 2H, H ), 2.05 (m, 1H, H or 2%eq), 1 66
4
b
3
2
(
m, 3H, H or
and H1/1%eq) 1.21 (m, 1H, H or
2%eq 2
2
%eq), 1.04 (m, 3H, H or 1%eq and H1/1%ax) l (CDCl )
2
1
C
3
1
1
41.5–140.7 (various resonances, C , C and C9),
5 5%
2
10 PC
33.00 (d, C , J =9.6 Hz), 128.99–126.78 (several
2
resonances C6–8 and C
), 69.10 (d, JPC=4.5 Hz,
11–12
2
C or ), 66.13 (d, J =7.1 Hz, C or 3%), 55.21 (d,
3
3%
PC
3
2
2
JPC=33 Hz, C or ),49.27 (d, J =20 Hz, C or
4
4%
PC
4
%)
, 31 39 (s, C or ), 30.30 (s, C or ), 24 72 (s, C1
2 2% 2 2%
4
+
and ). l (CDCl ) 109.6 (s). m/z 400 [M] . Found C,
1
%
P
3
7
7
8.0; H, 7.3; N, 7.1; C H N P requires C, 78.0; H,
.3; N, 7.0.
26 29 2
3
Methanol (0.066 cm , 0.05 g, 1.5 mol) was added to
a solution of 3 (0.53 g, 1.5 mmol) and N-methylmor-
3
pholine (0.24 cm , 0.22 g, 2 mmol) in dichloromethane
3
solvent (30 cm ) at −78°C (cardice bath) under an
atmosphere of dinitrogen. The mixture was allowed to
warm to room temperature with stirring over the course
of 3 h whereupon the volatiles were removed under
reduced pressure to afford a white solid. Recrystallisa-
tion from pentane:toluene (5:1 v/v) afforded the title
compound as whist crystals. Yield: 0.34g, (65.1%), lH–
{
P} (CDCl ) 7.37–7.25 (m, 10H, H ), 4.34 (d, 1H,
3 6–8
2
2
JHH=15.4 Hz, H ), 4.19 (d, 1H, JHH=15.4 Hz,
4a%
2
HH
H ), 4.26 (d, 1H, J =14.9 Hz, H ), 3.95 (d, 1H,
4a%
4b%
2
JHH=14.9 Hz, H ,), 3.33 (s, 6H, H ), 3.00 (m,
4b%
9
1
H, H or ), 2 55 (m, 1H, H or ), 1 86 (m, 2H, H2eq),
3 3% 3 3%
1
.63 (m, 2H, H1eq), 1.21–0.86 (m, 4H, H1ax and H2ax
)
lC (CDCl ) 141.5–140.7 (various resonances, C ,
3
5
2
C5% and C ), 133.00 (d, J =9.6 Hz, C ,), 128.99–
9
PC
10
1
26.78 (several resonances C6 and C11–12), 67 65 (d,
–8
2
2
C or , J =6.5 Hz), 66.35 (d, J =8.2 Hz, C or
3
3%
PC
PC
3
2
%)
, 50.99 (d, C4 or
JPC=33.2 Hz), 48.21 (d,
3
2
4%
JPC=14.3 Hz, C or ), 31.37 (s, C or 2%), 30.28 (s,
4
4%
2
C or ), 24.54 (s, C or ), 24.26 (s, C or 1%). lP
2
2%
1
1%
1
+
(
CDCl ) 138.5 (s). m/z 354 [M] . Found C, 70.9; H,
3
7
7
.8; N, 7.9; C H N OP requires C, 71.2; H, 7.7; N,
21 27 2
.9.
3
.8. Reactions of phosphenium 4 with donor molecules
To a solution of compound 4 (0.07 g, 0.148 mmol) in
3
CD Cl (0.5 cm ) solvent contained in a 5 mm NMR
2
2
tube under an atmosphere of dinitrogen, the appropri-
ate Lewis base (0.148 mmol; one equivalent) was intro-
Fig. 13. Relationship between lp (ppm) and relative basicity (Br).
Y-axis deviation bars are set at 910%.

216
V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
Table 4
Crystal data for compounds 1a, 1d, 2a and 4
1a
1d
2a
4
Formula
C20H22N2
290.40
0.61×0.48×0.38 0.70×0.39×0.08
Orthorhombic
Pbna
C31H40N C H
468.67
C20H26N2
294.43
0.35×0.10×0.10
Orthorhombic
Pbca
C21H24F N O PS
472.45
4
7
8
3
2
3
a
Formula weight
Crystal dimensions (mm)
Crystal system
Monoclinic
P2 /c
1
Monoclinic
P2 /a
1
Space group
Unit cell dimensions
˚
a (A)
9.2631(9)
9.3088(8)
19.9157(11)
—
1717.3(2)
4
1.123
0.066
624
11.9562(11)
13.903(2)
16.396(2)
91.474(12)
2724.6(5)
4
1.143
0.515
1016
18.323(2)
8.2949(9)
22.951(2)
—
3488.4(5)
8
1.121
0.496
1280
13.961(2)
11.292(2)
15.742(2)
114.846(12)
2251.9(6)
4
1.394
2.399
984
˚
b (A)
˚
c (A)
i (°)
˚
3
V (A )
Z
Dcalc. (g cm−3)
m (mm
F(000)
−
1
)
Absorption correction
Max/min transmission factors
q range (°)
None
—
3.275q526.34
„-scans
0.913, 0.758
3.705q 564.42
None
—
3.8550564.43
„-scans
0.546, 0.207
3.095q564.45
Index ranges
05h511, 05k5 −125h513,−125k516,
−215h521, −25k59, − −165h516, 05k513, −
1
5666
1, 05/524
−175l519
4333
265l526
3908
135l517
3978
Reflections collected
Unique reflections (n)
1746
0.044
1205
4333
—
4050
2689
0.024
2111
3532
0.040
3320
b
int
R
2
2
c
Reflections with F \2.0|(F )
c
Temperature (K)
No. parameters (p)
290
101
1.052
0.0404
0.1253
0.0752, 0.0176
0.034(7)
0.106, −0.106
100
382
1.099
0.0517
0.1754
0.0755, 1.696
0.0037(4)
0.240, −0.212
160
208
1.037
0.0488
190
276
1.574
0.0759
2
c
Goodness-of-fit on F , s
d
R1
wR
e
2
0.1360
0.1474
f
Weighting parameters a,b
0.0544, 2.3143
0.00092(11)
0.208, −0.207
0.0156, 3.5567
0.00154(14)
0.903, −0.653
Extinction parameterg
Largest difference peak and
˚
−3
hole (e A
)
a
b
c
d
e
f
Includes toluene solvate.
2
2
2
Rint=SꢀF −F (mean)ꢀ/S[F ].
o
o
2 2
o
2
1/2
s=[ꢁ[w(F −F ) ]/(n−p)]
.
o
c
SꢂF ꢀ−ꢀF ꢂ/SꢀF ꢀ.
o
c
o
wR =[ꢁ[w(F −F ) ]/ꢁ[w(F ) ]]1/2.
2
o
2 2
c
2 2
o
2
2
2
2
−1
2
o
2
c
w=[| (F )+(aP) +bP] , where P=(F +2F )/3.
o
g
2
c
3
−1/4
F =kF {1+0.001*F u /sin (2q)]
.
c
c
˚
duced at ambient temperature. After addition, the sam-
ple tube was sealed with a press-top plastic cap and
cling flim before being shaken briskly to ensure com-
plete dissolution and the reaction products analysed via
multinuclear NMR spectroscopy. In no case was a
discrete adduct observed, only a single set of NMR
resonances indicative of a dynamic system exchanging
rapidly on the NMR time-scale (see Table 3 for repre-
sentative NMR data).
1.54184 A). Data for 1a were collected on an Enraf-No-
nius KappaCCD area-detector diffractometer using
graphite monochromated Mo-Kh radiation (u=
˚
0.71073 A) using 1.0° ƒ-rotation frames. Full details of
crystal data, data collection and structure refinement
are given in Table 4 whilst ball-and-stick representa-
tions of 1a, 1d and 2a along with selected bond dis-
tances and angles are available as part of the
supplementary package with this paper.
The structures of all four compounds were solved by
direct methods using SHELXS 86 [26]. The asymmetric
unit of 1d was found to contain a molecule of toluene
disordered over two positions. Refinement, by full-ma-
trix least-squares on F: using SHELXL 93 [27], was
essentially the same for all four compounds. Non-hy-
3
.9. Single-crystal X-ray diffraction analyses
Data for 1d, 2a and 4 were collected on a Stoe
STADI4 diffractometer operating in the ꢀ-q scan mode
using graphite monochromated Cu–K radiation (u=
h

V.A. Jones et al. / Journal of Organometallic Chemistry 567 (1998) 199–218
217
[
[
[
5] F.G. Mann, The Heterocyclic Derivatives of Phosphorus, Ar-
senic, Antimony and Bismuth, 2nd ed, Wiley Interscience, Lon-
don, 1970.
6] D.S. Payne, The Chemistry of Phosphorus Halides, in: M.
Grayson, E.J. Griffith (Eds.), Topics in Phosphorus Chemistry,
Wiley Interscience, New York, 1967.
7] R.S. Edmondson, in: I.O. Sutherland (Ed.), Comprehensive Or-
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8] A.H. Cowley, R.A. Kemp, Chem. Rev. 85 (1985) 367.
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R.W. Parry, M.G. Thomas, C.W. Shultz, Inorg. Chem. 16 (1977)
drogen atoms (including those of the toluene solvate
molecule of 1d) were refined with anisotropic displace-
ment parameters. Hydrogen atoms were constrained to
idealised positions using a riding model (with free rota-
tion for methyl groups) with the exception of the
hydrogen atoms attached to the nitrogen atoms of 2a
which were all located on Fourier difference syntheses
and freely refined with isotropic displacement
parameters.
[
[
4. Supplementary material
9
94. (e) N. Burford, P. Losier, C. MacDonald, V. Kyrimis, P.K.
Crystal structure data on compounds 1a, 1d and 2a is
available as e-mail attachment upon request from Dr
Kee at T.P.Kee@chem.leeds.ac.uk.
Bakshi, T.S. Cameron, Inorg. Chem. 33 (1994) 1434. (f) M.R.
Marre, M. Sanchez, R. Wolf, J. Chem. Soc. Chem. Commun.
(
1984) 566. (g) A.H. Cowley, M.C. Cushner, J.S. Szobata, J. Am.
Chem. Soc. 100 (1978) 7784. (h) N. Burford, P. Losier, P.K.
Bakshi, T.S. Cameron, J. Chem. Soc. Dalton Trans. (1993) 201.
(
i) C.W. Schultz, R.W. Parry, Inorg. Chem. 15 (1976) 3046. (j)
R.W. Parry, M.G. Thomas, C.W. Schultz, Inorg. Chem. 16
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Acknowledgements
(
The authors extend their grateful thanks to the EP-
SRC for an Earmarked Studentship to V.A.Jones, the
Government of Thailand for a Visiting Fellowship to
S.Sriprang and to Albright and Wilson for most valu-
able gifts of chemicals. We are indebted also to Frederic
Vetel (The Open University, UK) for kindly performing
solid state NMR analysis of 4 and Dr M. Adam
(
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