N-Phosphino-amidines and -guanidines: Synthesis, structure and P,N-chelate chemistry

Article abstract of DOI:10.1039/b715736c

The syntheses of the cyclic N-phosphino-amidines and -guanidines Ph ₂PN(Prⁱ)C(NPrⁱ₂)N(Prⁱ) (1) and Ph₂PN(c-Hex)C(R)N(c-Hex) [R = piperazino (2), morpholino (3), Me (4), and Ph (5)] are reported. DFT studies have identified the preferred structures for compounds 1-5 with the E-configuration being the most stable form for the N-phosphino-amidines, while the Z-conformation is preferred for the N-phosphino-guanidines something that highlights the potential of such systems to act as κ²-P,N-chelates. The differences in donor characteristics of 2-5 have been probed through the study of their corresponding P(v) selenide derivatives (6-9) and their complexes with the cis-RhCl(CO) (10-12) and cis-PdCl₂ (13-17) fragments. In line with the DFT studies both the amidines and guanidines are found to coordinate as κ²-P,N-chelates, with the latter being moderately weaker donor ligands. The molecular structures of compounds 3 and 4, together with those of the Rh and Pd complexes 10 and 15, respectively, have been determined in the solid state by X-ray crystallography, the latter confirming bidentate κ²-P,N-chelation. The Royal Society of Chemistry.

Full text of DOI:10.1039/b715736c

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PAPER
www.rsc.org/dalton | Dalton Transactions
N-Phosphino-amidines and -guanidines: synthesis, structure and P,N-chelate
chemistry†‡
a,b
Lise Baiget,a Andrei S. Batsanov,a Philip W. Dyer,*§ Mark A. Fox,a Martin J. Hanton,b
Judith A. K. Howard,a Philip K. Laneb and Sophia A. Solomona
Received 11th October 2007, Accepted 21st November 2007
First published as an Advance Article on the web 8th January 2008
DOI: 10.1039/b715736c
The syntheses of the cyclic N-phosphino-amidines and -guanidines Ph2PN(Pri)C(NPri2)N(Pri) (1) and
Ph2PN(c-Hex)C(R)N(c-Hex) [R = piperazino (2), morpholino (3), Me (4), and Ph (5)] are reported.
DFT studies have identified the preferred structures for compounds 1–5 with the E-configuration being
the most stable form for the N-phosphino-amidines, while the Z-conformation is preferred for the
N-phosphino-guanidines something that highlights the potential of such systems to act as
j2-P,N-chelates. The differences in donor characteristics of 2–5 have been probed through the study of
their corresponding P(V) selenide derivatives (6–9) and their complexes with the cis-RhCl(CO) (10–12)
and cis-PdCl2 (13–17) fragments. In line with the DFT studies both the amidines and guanidines are
found to coordinate as j2-P,N-chelates, with the latter being moderately weaker donor ligands. The
molecular structures of compounds 3 and 4, together with those of the Rh and Pd complexes 10 and 15,
respectively, have been determined in the solid state by X-ray crystallography, the latter confirming
bidentate j2-P,N-chelation.
and have found applications in many different transformations
Introduction
including olefin oligomerisation/polymerisation,8,16–18 asymmetric
hydrogenation,19 allylic substitution,20 hydrosilylation,21 and C–C
coupling reactions,22 for example.
Over the last decade the study of tricoordinate phosphorus
derivatives with one, two or three P–N bonds, (R2N)3−xPRꢀx, has
undergone somewhat of a renaissance. To a large extent interest
in such compounds has been driven by the ease of phosphorus–
nitrogen bond formation, something that facilitates the straight-
forward preparation of P(III) compounds with a diverse range of
steric demands, as well as providing a means for the introduction
of additional functionality or chirality remote from the P-centre.1–5
Furthermore, through judicious choice of substituents at nitrogen
it is possible to tune not only the Lewis basicity of the resulting
amidophosphines, but also their p-acceptor character, in a simple
and systematic fashion, while also opening up new reaction
pathways.6–9
An area in which P–N bond-forming reactions have proved
particularly versatile is in the synthesis of bidentate j2-P,E chelates
(E = O,10 P,11 S,12 Se13). Once coordinated, the heteroditopic
nature of these types of ligand has been used to engender both
control and selectivity in reactions occurring at metal centres.14,15
In this domain, phosphorus–nitrogen chelates (E = N) are
amongst the most widely studied of these types of scaffold
The obvious versatility of bidentate j2-P,N-ligands in coordi-
nation chemistry and catalysis means there is continued interest
in the development of increasingly structurally diverse systems.
With this in mind, it became apparent that the readily accessible
H–N-amidines and -guanidines make attractive building blocks
for the preparation of heteroditopic j2-P,N-ligands I and II,
respectively (Fig. 1), potentially providing a ready means of tuning
both their steric and electronic demands.23 A small number of
such compounds have been reported,24–26 although their molecular
structures and coordination chemistry have only briefly been
explored.27–31 Notably, though, related C-phosphino amidines have
been reported in detail by Coles and co-workers.32,33
aDepartment of Chemistry, Durham University, South Road, Durham, UK
DH1 3LE
Fig. 1 Selected isomeric forms of N-phosphino-amidines I and -guani-
dines II.
bDepartment of Chemistry, University of Leicester, University Road, Leices-
ter, UK LE1 7RH
† Dedicated to our colleague Prof. Ken Wade on the occasion of his 75th
birthday to mark his outstanding contributions to our understanding of
the relationships between structure and bonding across the periodic table.
‡ CCDC reference numbers 293165, 293166, 663533 and 663534 for 3, 4,
10 and 15, respectively. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b715736c
§ Present address: Department of Chemistry, Durham University, South
Road, Durham, UK DH1 3LE. E-mail: p.w.dyer@durham.ac.uk; Fax:
+44 (0)191 378 4737; Tel: +44 (0)191 334 2150
Here we describe the straightforward, high-yielding synthe-
ses of a number of variously-substituted N-diphenylphosphino-
amidines and -guanidines. Their donor characteristics have been
probed spectroscopically and a combination of computation and
X-ray diffraction studies employed to assess their structures. The
potential of these systems to act as j2-P,N-chelates with metals of
relevance to catalysis, namely Rh(I) and Pd(II), has been explored.
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Particular emphasis is placed upon understanding the effects of
the substitution pattern about the NCN skeleton.
guanidines 1–3. This may be caused by the influence of the NCN
C-substituent on the electronic properties of the P-donor moiety
or as a result of differences in conformation about the imine bond
between the guanidines 1–3 and the amidine 4. In contrast, the 31
P
Results and discussion
NMR spectrum of the benzamidine derivative 5 (R = c-Hex; Rꢀ =
Ph) is severely broadened at ambient temperature, but partially
sharpens on warming to 363 K. This presumably dynamic process
could not be fully frozen out even on cooling the sample to 233 K.
Synthesis and characterisation of N-phosphino-amidine and
-guanidines
Exploitation of the well-established reactivity of carbodiimides
towards lithium organyl and amide reagents provides ready access
to a host of P,N derivatives following reaction of the resulting
diazaallyl intermediates with halophosphine. In this way the N-
phosphino-amidines 1,2 and -guanidines 4,5 were prepared in
good yields (>70%) according to Scheme 1. A modification of
this strategy was used to prepare the 4-morpholinecarboxamidine
derivative 3 from commercially available N,N ꢀ-dicyclohexyl-4-
morpholinecarboxamidine in a ‘one-pot’ procedure (Scheme 1).
1
The 13C{ H} NMR spectra for compounds 1–5 are consistent
with acyclic structures where the Ph2P substituent is attached to
1
one nitrogen atom of the RNC(Rꢀ)NR moiety. The 13C{ H} NMR
spectra for 1–3 exhibits two sets of ortho-CH resonances for the
Ph2P substituent, whereas only one set of resonances is observed
for 4 and 5.24 Each of the compounds 1–4 displays a well-resolved
doublet resonance for the NCN carbon atom (Table 1). However,
a broad NCN resonance centred at 157.2 ppm is observed in the
13C NMR spectrum for benzamidine 5.
In order to try to understand the differences in the NMR data for
the guanidines 1–3, amidine 4 and benzamidine 5, X-ray studies on
3 and 4 and a DFT investigation on these and related compounds
were carried out.
X-Ray diffraction studies of N-phosphino-guanidine 3 and
-amidine 4
The results of X-ray diffraction studies (Table 2) confirm the
acyclic guanidine 3 (Fig. 2) and amidine 4 (Fig. 3) structures,
with no close inter-/intra-molecular contacts of the iminic N-
lone pair with the Ph2P fragment. Guanidine 3 is found to adopt
a formally Z configuration about the C–N double bond (cf.
its parent N,N ꢀ-dicyclohexyl-4-morpholinecarboxamidine, which
adopts an E arrangement).34 Both the C(1) and N(2) centres of 3
are trigonal-planar and lie in planes that form a dihedral angle of
66.0◦ precluding conjugation. Contrastingly the morpholine N(3)
centre is pyramidal, meaning that its lone pair is not involved
in delocalisation across the CN3 framework. The orientation of
the trigonal plane centred about N(2) and the inferred position
of the P-lone pair (torsion angle 7◦) are consistent with overlap
of the N(2) lone pair with one of the two degenerate r*(P–R)
MOs engendering some slight P–N(2) multiple bond character;6
the P–N(2) distance is shorter than a true P–N single bond by ca.
Scheme 1 (i) RꢀLi, Et2O, −78 ◦C to RT; (ii) Ph2PCl, Et2O, −78 ◦C to RT;
(iii) BunLi, Et2O, −78 ◦C to RT.
Compounds 2–5 were isolated as moderately air stable solids,
while the N,N ꢀ-diisopropyl derivative 1 was obtained as a viscous
oil, which proved to be extremely sensitive to protonolysis,
rapidly decomposing with the elimination of hydroxyphosphine-
containing species via P–N bond cleavage. Attempts to stabilise
1 by forming the corresponding P(V) derivatives by reaction
with elemental sulfur or selenium proved unsuccessful, giving
intractable mixtures of products in both cases.
0.07 A.35 The C(1)–N(1◦) bond distance is typical for a double bond
˚
The 31P{ H} NMR spectra of N-phosphino-guanidines 1–3
(not withstanding a 6.4 twist along its axis),35 while the N(2)–C(1)
and C(1)–N(3) distances are close to the standard non-conjugated
single bond distance.35a
In contrast to the molecular structure of guanidine 3, amidine
4 adopts an E configuration (Fig. 3), which is thus ideally
pre-disposed for metal j2-P,N-chelation. The amidine core has
1
and -amidine 4 each exhibit a single sharp resonance over the
temperature regime 233 to 323 K, at a chemical shift consistent
with an aminodiphenylphosphino moiety (Table 1).6 Note that the
31P NMR chemical shift of phosphino-amidine 4 is displaced to
lower frequency compared to those observed for the functionalised
Table 1 Selected NMR spectroscopic data for compounds 1–9a
d31P{ H}
d13C{ H} CN2
2JPC/Hz
d31P{ H}
|1JSeP|/Hz
1
b
1
c
1
b
1
2
3
4
5
+49.9d
+50.2
+49.8
+37.0
147.3e
154.8
153.6
155.7
157.2
21
21
21
1
—
—
6
7
8
9
+57.6
+56.3
+56.3
+67.3
772
775
749
753
+44.9 (m1/2 44 Hz)
9
a CDCl3, 298 K. NMR spectrometer frequencies: b 161.9 MHz; c 125.7 MHz; d 101.3 MHz; e 100.6 MHz.
1044 | Dalton Trans., 2008, 1043–1054
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◦
˚
Table 2 Selected bond distances (A), bond and dihedral angles ( )
3
10
4
15
10 (M = Rh)
15 (M = Pd)
P–N(2)
N(2)–C(1)
C(1)–N(1)
C(1)–N(3)
N(2)–P–C(24)
N(2)–P–C(18)
C(24)–P–C(18)
Mean X–N(2)–Y
Mean X–C(1)–Y
Mean X–N(3)–Y
C(1)–N(1)–C(2)
N(2) plane/C(1) plane
C(1) plane/N(1) plane
P–N(2)–C(1)–N(1)
N(2)–C(1)–N(1)–C(2)
1.7014(10)
1.4304(14)
1.2674(15)
1.4074(15)
107.38(5)
102.71(5)
99.20(5)
120.0
120.0
113.6
120.8(1)
66.0
6.4
1.739(2)
1.407(2)
1.306(2)
1.370(2)
102.90(8)
107.67(7)
101.58(8)
116.0
120.0
119.9
120.53(15)
30.2
23.8
1.721(3)
1.414(4)
1.270(4)
—
103.7(1)
103.9(1)
105.7(1)
119.3
120.0
—
119.8(2)
20.8
1.1
1.7115(14)
1.383(2)
1.301(2)
—
106.41(7)
106.43(7)
107.13(7)
119.9
120.0
—
118.38(14)
2.2
10.9
M–P
M–Cl(1)
M–Cl(2)
M–N(1)
2.1668(5)
2.4070(5)
—
2.1916(15)
1.804(2)
172.88(2)
76.25(4)
96.19(6)
—
99.24(4)
88.74(6)
—
171.11(7)
—
2.1644(4)
2.3913(4)
2.3212(4)
2.0727(14)
—
173.93(2)
81.90(4)
—
87.25(2)
102.54(4)
—
88.24(2)
—
M–C(30)
P–M–Cl(1)
P–M–N(1)
P–M–C(30)
P–M–Cl(2)
Cl(1)–M–N(1)
Cl(1)–M–C(30)
Cl(1)–M–Cl(2)
N(1)–M–C(30)
N(1)–M–Cl(2)
68.3(1)
4.6(1)
−25.4(2)
151.6(2)
179.1(2)
2.4(2)
169.60(14)
169.13(4)
156.2(2)
Fig. 2 Molecular structures of 3 (left) and 10·CDCl3 (right). Thermal ellipsoids are drawn at the 50% probability level.
Fig. 3 Molecular structures of 4 (left) and 15·CDCl3. Thermal ellipsoids are drawn at the 50% probability level.
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=
Table 4 Relative energies for various conformations for 1, 3, 4 and 5 in
localised C(1) N(1) and C(1)–N(2) bonds of 1.270(4) and
kcal mol−1
˚
1.414(4) A, respectively. As is the case for 3, the N(2) and C(1)
centres of 4 are trigonal-planar, but with a smaller interplanar
angle of 20.8◦ (cf. 3: 66.0◦). As a result of the significant
twist (19◦) between the trigonal plane centred on N(2) and the
inferred position of the r*(P–R) MO, there is a weakening of the
N(2)→P p-interaction and hence a slight elongation of the P–
1
3
4
5
1
3
4
5
Ea 2.21
Eb 0.00
Ec 0.90
Ed 6.26
2.29
0.80
1.35
3.00
0.43
0.52
2.50
0.00
2.75
0.00
6.95
3.96
Za
Zb
Zc
Zd
2.00
7.46
2.67
2.67
0.00
1.85
1.39
2.49
7.08
9.39
8.01
7.96
5.70
5.70
11.26
9.96
˚
N(2) (1.721(3) A) bond distance is observed relative to that for 3
˚
(1.7014(10) A).
The full geometries of the preferred conformers were then
computed for 1, 3, 4 and 5 (at the B3LYP/6-31G* level of theory)
and are listed in Table 4. Since both guanidines 2 and 3 are
structurally very similar, it has been assumed that the relative
energy trends for 3 will also apply to 2. The variations in the
relative energies between the model geometries (Table 3) and the
actual geometries (Table 4) indicate that the bulky cyclohexyl and
Pri2N groups impart a considerable influence on the preferred
conformations. The X-ray structures of 3 and 4 are in perfect
accord with the most stable forms identified computationally, i.e.
Za and Ed for 3 and 4, respectively. Examination of the relative
energy data for benzamidine 5 suggests that the Eb form is the
most stable conformation for 5. The preferred conformation for 1
also appears to be the Eb conformation, but here Za is only 2 kcal
mol−1 higher in energy.
The calculated HOMOs in the lowest energy minima of 1, 3,
4 and 5 all possess considerable lone-pair character at the P-
atom. Natural population analyses on each of these geometries
afford N–P Wiberg bond orders and charges at P that are all
similar with values of 0.8 and 1.1, respectively, consistent with the
molecular structures of 3 and 4 determined crystallograpically.
The HOMO-1 and HOMO-2 of each of these systems have
substantial contributions located at the nitrogen atoms of the
DFT studies of N-phosphino-amidines and -guanidines
As discussed above, it is well-established that both amidines
and guanidines may adopt a variety of different, potentially
interconverting isomeric configurations (Fig. 1).23,33 The stability
of each of the various arrangements and their rates of isomeri-
sation are intimately linked to the substitution pattern about
the NCN skeleton. Here, this is clearly reflected in the different
solid state molecular structures determined for the compounds
3 and 4, which are found to adopt Z and E conformations,
respectively. Since this current study seeks to assess the ability
of these variously-substituted N-phosphino-NCN derivates to
act as j2-P,N-chelating ligands, an understanding of the factors
that influence the structure they adopt is essential and has been
addressed computationally.
Initially, the structures of eight model compounds RN CR N-
ꢀ
=
(R)PPh2 (R = Me, Rꢀ = Me, Ph and NMe2) were explored at the
B3LYP/6-31G* level of theory, with the most stable arrangements
being identified in each case (Table 3, Fig. 4). The E-configuration
is computed to be the most stable form for the N-phosphino-
amidines, whereas the Z-conformation is the preferred geometry
for the N-phosphino-guanidines.
=
C N bonds. Together these data confirm the potential of these
compounds to act as j2-P,N-chelating ligands.
Elucidation of the origins of the differences in solution-state
dynamic behaviour of benzamidine 5 compared to that observed
for either amidine 4 or guanidines 1–3 is complex. Not only are
all the compounds subject to E/Z isomerisation of the C–N
multiple bond,23,32,33 but N-phosphino-amidines are also known to
be susceptible to intramolecular phosphatropic rearrangement.25
This latter process involves migration of the R2P moiety between
the two amidine N-atoms via a heterocyclic intermediate (Fig. 5),
with the magnitude of the free energy of activation (DG† ) having
been shown to be directly linked to the nature of the amidine
substituents R and Rꢀ. Since identification of the processes giving
rise to the differences in fluxional behaviour between 4 and
5 by variable temperature NMR spectroscopic studies proved
inconclusive, differences between these two compounds were
explored computationally.
Fig. 4 Eight conformations for N-diphenylphosphino-amidines and
-guanidines.
Table 3 Relative energies in kcal mol−1 for model geometries of
ꢀ
=
MeN C(R )N(Me)PPh2
Rꢀ
NMe2
Me
Ph
Rꢀ
NMe2
Me
5.37
6.65
11.96
9.84
Ph
Ea
Eb
Ec
Ed
1.15
0.54
4.00
4.90
3.51
0.00
4.50
3.03
1.07
0.00
3.19
4.65
Za
Zb
Zc
Zd
0.00
1.66
5.05
4.27
3.09
4.81
8.62
9.19
Fig. 5 Intramolecular phosphatropic rearrangement of N-phosphino-
amidines.24
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Initially, a comparison of the energy barriers for isomerisation
between the Zand E forms of both 4 and 5 were determined. Values
of 27.5 (4) and 24.2 (5) kcal mol−1 were obtained, which rule out
interconversion between these isomers for both compounds.
Next, it was of interest to explore the ease with which
intramolecular phosphatropic rearrangement may occur for 4
versus 5. The energy barriers for this process were computed for
4 and 5 and found to be 14.8 and 19.1 kcal mol−1, respectively,
assuming an Ea-conformation, Fig. 5, (something confirmed
crystallographically for 4) as the starting geometry, as this is
the most likely precursor to the phosphatropic rearrangement.
For comparison, an identical procedure was used to compute the
energy barrier for the rearrangement of the known benzamidine
‡
=
MeN C(Ph)N(Me)PPh2, which gave a value of DG = 24.0 kcal
mol−1 that is in excellent agreement with the experimentally deter-
mined value of 25 kcal mol−1.24 Since the structure of this latter
compound differs from that of 5 only in that it bears methyl rather
than cyclohexyl groups, it is likely that the lower barrier to rear-
rangement of 5 is steric in origin. However, it is clear that the small
difference inenergy for the phosphatropic rearrangementof4 com-
pared with that for 5 (DDG‡ = 4.3 kcal mol−1) cannot explain the
differences observed in the solution-state NMR spectra of 4 and 5.
Both the crystallographically- and computationally-determined
molecular structures of compounds 4 and 5 highlight the signif-
icant steric bulk about the NCN skeleton. This is likely to limit
free rotation in solution, particularly about the N–P bond, which
could give rise to the observed differences in the 31P NMR spectra
of 4 and 5. Thus, the barriers to rotation about the N–P axis
for both compounds 4 and 5 were estimated computationally,
assuming the Ea-conformation shown in Fig. 5 for both structures.
In each case, the barrier was found to be 7 kcal mol−1, a value
that is in broad agreement with those computed for the parent
aminophosphine H2NPH2 (5.78–9.38 kcal mol−1), obtained at
different levels of theory, and consistent with only slight P–N
multiple bond character.36 Clearly, since the rotational barrier
is identical for both 4 and 5, this again does not explain the
differences in their observed NMR spectra.
Scheme 2 (i) Se, CDCl3, RT, 1 h; (ii) 1/2 [RhCl(CO)2]2, CO, CDCl3, RT,
1 h; (iii) [PdCl2(MeCN)2], CH2Cl2, RT, 18 h.
from N or Se will induce a flattening about the P-centre and hence
augment it’s degree of s-character. In turn, this will give rise to
the larger magnitudes of 1JSeP observed.¶ Consequently, it is clear
from this study that varying the nature of the substituent on the
C-atom of the NCN skeleton (alkyl, aryl or amino) provides a
ready means of tuning the donor characteristics of this type of
P,N-chelating metal scaffold in a straightforward fashion.
In order to probe the donor characteristics of compounds 3–
5 when acting as chelating j2-P,N-ligands, their corresponding
[RhCl(CO)(j2-P, N )] (10–12) complexes were prepared through
reaction with half an equivalent of [RhCl(CO)2]2 under an
atmosphere of CO (Scheme 2). Each complex was isolated in near-
quantitative yield as an air-stable solid and as a single regioisomer,
Donor characteristics of N-phosphino-amidines and -guanidines
1
according to 13C and 31P NMR spectroscopy. The 31P{ H} NMR
Two complementary methods have been used to assess the
potential ligand characteristics of compounds 2–5. An estimate of
the Lewis basicity of the P-donor component of each compound
spectrum of complexes 10–12 features a sharp doublet resonance
to high frequency of that for the free ligands, with a 1JRhP coupling
constant of ca. 175 Hz (Table 5). Geometries in which P lies trans
1
can be made from the magnitude of the JSeP coupling constant
1
to Cl are suggested by 13C{ H} NMR spectroscopy, which presents
obtained from the corresponding selenides, 6–9, each of which
presents a single sharp resonance by 31P NMR spectroscopy
(Scheme 2, Table 1).¶37 The guanidinyl phosphine selenide deriva-
tives 6 and 7 display values of |1JSeP| of ca. 770 Hz, while those
from the Ph2P-functionalised amidines 8 and 9 are significantly
smaller, ca. 750 Hz, and comparable to Ph2P(Se)NEt2 (|1JSeP| =
746 Hz).6
a single carbonyl resonance for each complex at ca. d 185 ppm (d,
1JRhC ca. 75 Hz).8 Notably, no tractable product could be obtained
from the reaction of 1 with [RhCl(CO)2]2.
Phosphino-guanidine 3 adopts a Z configuration about the
imine bond in the solid-state (vide supra). As a result, in order for
3 to coordinate in a bidentate j2-P,N-fashion, a prior formal E/Z
isomerisation is required (Scheme 3). Thus, although spectroscopic
analysis of 10 was suggestive of a cis-[RhCl(CO)(3)] coordination,
it was of interest to probe the structure of the complex by X-ray
diffraction.
The molecular structure of the rhodium(I) complex 10·CDCl3
(Fig. 2, Table 2) confirms that 3 does indeed act as a j2-P,N-
chelate, consistent with the low barrier to Z/E isomerism of
the imine bond determined (vide supra) for these N-phosphino-
guanidines.32,38 The rhodium centre of 10 is near-square planar,
1
The significant divergence in the magnitudes of the JSeP
coupling constants between those for the guanidines (6,7) and
those for the amidines (8,9) is most readily explained in terms of
differences in geometry about P. For both 6 and 7 competition for
a vacant r*(P–R) MO of appropriate symmetry for back-bonding
¶ The greater the magnitude of 1JSeP, the greater the s-character of the
P-lone pair and hence the poorer its donating ability.
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Table 5 Selected NMR spectroscopic data for complexes 10–17a
1
b
1
c
d31P{ H}
1JRhP/Hz
d13C{ H} CN2
2JPC/Hz
mCOd/cm−1
10
11
12
13
14
15
16
+112.1
+124.9
+124.7
176
175
177
—
—
—
—
—
—
165.7
170
170.0
167.8
166.5
24
br
br
25
25
1994
1995
2000
—
—
—
—
—
—
+84.3 (m1/2 144 Hz)
+85.5 (m1/2 131 Hz)g
+108.0
168.9
br
+106.3 (m1/2 170 Hz)e
+95.1 (m1/2 254 Hz)
+81.2h
f
f
f
f
17
—
—
a CDCl3, 298 K. b 161.9 MHz. c 125.7 MHz. d KBr, CDCl3. e +106.3 : +95.1 = 8 : 1 at 298 K. f Not observed. g 75.8 MHz. h 101.3 MHz.
The similarity in the spectroscopic data between complexes 10–
12 is strongly suggestive of j2-P,N-chelation in each case.
Synthesis and characterisation of PdCl2 complexes 13–17
To further explore the coordination chemistry of compounds
1–5 a study of their PdCl2 complexes was undertaken. Here
the isoelectronic relationship between Rh(I) and Pd(II) facilitates
a direct comparison between the two different metal systems.
Reaction of compounds 1–5 with [PdCl2(MeCN)2] leads to the
formation of the corresponding [PdCl2(P,N)] complexes 13–17,
which are isolated as air-/moisture-stable yellow or orange solids
in excellent yields of typically >75% (Scheme 2). The exception
is [PdCl2(1)] (17), which forms cleanly according to 31P NMR
spectroscopy, but starts to decompose with the formation of
‘palladium black’ after ca. 1 h in solution.
Scheme 3
with a slight tetrahedral distortion (7.7◦ twist); the P-donor moiety
occupies a position trans to Cl, as predicted on the basis of relative
trans-influences. The metallacycle assumes a puckered envelope
˚
conformation, with the P atom being displaced by 0.81 A from the
RhN(1)C(1)N(2) plane. This non-planarity of the metallacycle is
responsible for the narrow P,N-bite angle of 76.25(4)◦ (cf. typically
83.0–87.7◦ in other [RhCl(CO)(P,N)]-type complexes with five-
membered j2-P,N-chelates39) and the slightly longer than usual
In solution the phosphino-guanidine derivatives [PdCl2(j2-P,N-
2,3)] (13,14) each display a single broad resonance at ca. d +85 ppm
1
by 31P{ H} NMR (298 K) spectroscopy, with the magnitude of
Dd (ca. +35 ppm) being consistent with the coordination of the
P-donor moiety to palladium (Table 2). On cooling to 233 K,
two resonances became apparent in each case at ca. d +90 and
+80 ppm in an approximately 1 : 8 ratio, respectively, which clearly
correspond to two Pd-bound P-species. On warming to 353 K the
31P NMR spectra of 13 and 14 both collapsed to a single sharp
resonance.
˚
Rh–N(1) distance (2.1916(5) A), which is typically in the range
2
35
˚
2.10–2.15 A for Rh←N(sp ) bonds.
There is a clear change in the bonding pattern and conformation
of 3 following its coordination with Rh(I). Partial bond delocali-
sation about the guanidine CN3 core ensues, which is reflected by
the pyramidalisation of the N(2) and the planarization of the N(3)
˚
=
centres. TheC(1) N(1)bondislengthenedby0.04A accompanied
The behaviour of the two amidine-derived palladium(II) com-
plexes 15 and 16 is quite different, again highlighting the influence
of the substituent on the NCN carbon atom. The methyl-
substituted phosphino amidine complex [PdCl2(j2-P,N-4)] (15) has
by an increase in twist to 23.8◦ (from 6.4◦ in 3), while both the
N(2)–C(1) and C(1)–N(3) bonds are shortened. The P–N(2) bond
is also weakened, as a result of the reduction in the N → P p-
1
interaction [3: 1.7014(10), 10: 1.739(2) A]. The cyclohexyl and
a static structure in solution (31P{ H} NMR d +108.0 ppm) be-
˚
morpholine substituents are in cis positions with respect to the
C(1) N(1) bond (Zanti), compared to the trans (Eanti) configuration
tween 233 and 363 K (Table 3). In contrast, its phenyl-substituted
counterpart [PdCl2(j2-P,N-5)] (16) behaves in a manner analogous
to that for complexes 13 and 14, exhibiting two broad resonances (d
+106, +95.1 ppm) at ambient temperature, with the two chemical
shifts being consistent with two Pd-bound phosphine species.
On cooling a sample of 16 to 233 K both resonances sharpen
significantly, while heating to 363 K causes these two peaks to
collapse to a broad single signal (d +103.0 ppm, m1/2 500 Hz).
In order to probe the origins of this dynamic behaviour,
the molecular masses of complexes 14 and 16 were determined
cryoscopically40 in solution. In both cases masses consistent with
monomeric structures [PdCl2(P,N)] were obtained. This rules
out any monomer–dimer interconversion in solution. Equally,
although the morpholine-substituted derivative 3 clearly acts as
=
observed in unbound 3.
From the IR spectra of the rhodium carbonyl complexes 10–
12 CO stretching frequencies of ca. 1996 cm−1 are obtained.
These values are indicative of ligands 2–5 being comparatively
weak Lewis bases,6,17 in agreement with the magnitudes of
1JSeP from their corresponding selenides (vide supra). Only small
differences (ca. 5 cm−1) are observed between the values of mCO
for the guanidine- (10,11) and amidine-based (12) complexes. This
indicates that in these cis-chelated complexes the N-donor moiety
=
( N–cHex in each case) that lies trans to the reporter carbonyl
ligand has the dominant influence on the C–O bonding, as may
be expected.
1048 | Dalton Trans., 2008, 1043–1054
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©

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a P,N-chelate with Rh(I) in complex 10, it is possible that this may
not be the case with Pd in complex 14, chelation through either
of the hard iminic N- or O-donor centres of the morpholine unit
also being possible. However, since identical dynamic behaviour
is observed with the piperazino derivative 13 that has no O-donor
functionality, this is clearly not the explanation. Furthermore,
since fluxionality is observed for both guanidine (13, 14) and
amidine complexes (16), exchange of N-imine and N-amine
donation can be eliminated.
and d8-toluene were distilled from P2O5 and subsequently handled
under nitrogen.
Palladium and rhodium salts were used on loan from
Johnson Matthey. All solid reagents were used as received.
Where appropriate liquid reagents were dried, distilled and
deoxygenated, while gases were passed through
a drying
column (silica/CaCO3/P4O10) prior to use.41 The complexes
[PdCl2(MeCN)2]42 and {RhCl(CO)2}2 were prepared according
43
to slight modifications of the literature procedures. Elemental
grey selenium (Aldrich), N,N ꢀ-diisopropylcarbodiimide (Aldrich),
N,N ꢀ-dicyclohexylcarbodiimide (Aldrich), N,N ꢀ-dicyclohexyl-
4-morpholinecarboxamide (Aldrich), Ph2PCl (Aldrich), PhLi
{solution in hexanes} (Aldrich), MeLi {solution in hexanes}
(Aldrich), were all used as received.
Consequently, despite the comparatively large chemical shift
difference between the two species being observed for complexes
13, 14 and 16, this temperature-dependent behaviour is largely
ascribed to conformational changes of the cyclohexyl substituents
at the ligand periphery combined with hindered rotation of
the phenyl substituent. This is consistent with the all-isopropyl-
substituted complex 17 presenting a static structure, with a single
Routine solution phase NMR spectra were collected on a Bruker
AM250, Varian Unity 300, or a Varian Inova 500 at ambient
probe temperatures (∼290 K). Variable temperature spectra were
collected on a Varian Inova 500. Chemical shifts were referenced to
residual protio impurities in the deuterated solvent (1H), 13C shift
of the solvent (13C), or external aqueous 85% H3PO4 (31P). For 1H
NMR spectra, 31P-coupled resonances were verified by running
1
sharp resonance being observed d +81.2 ppm in its 31P{ H} NMR
spectrum.
Since methyl-substituted amidine complex 15 does not exhibit
any dynamic behaviour in solution within the temperature range
233–363 K it was of interest to verify its structure. Thus, an X-
ray diffraction study was undertaken (15·CDCl3, Fig. 3, Table 2),
which confirms the expected P,N-chelation about a distorted
square planar Pd centre. The Pd, P, Cl(2) and N(1) atoms are
31
1H{ P} experiments. 13C NMR spectra were assigned with the
aid of DEPT-90, DEPT-135 and 1H–13C correlation experiments.
Chemical shifts are reported in ppm and coupling constants in Hz.
FAB (3-nitrobenzyl alcohol matrix) and EI mass spectra were
recorded on a Kratos Concept 1H instrument and are reported
in (m/z). Mass spectra were recorded either in Durham (ES:
Micromass Autospec; MALDI ToF: Applied Biosystems Voyager-
DE STR) or by the EPSRC National Mass Spectrometry Service
at the University of Wales, Swansea, (ES: Waters ZQ-4000) and
are reported in (m/z). The isotope distributions for all parent ion
peaks for metal complexes were verified via comparison with a
theoretical isotope pattern.
˚
coplanar, while Cl(1) lies out of their plane by 0.15 A. Both the
N(2) and C(1) centres retain their planarity upon complexation,
the interplanar angle dropping to 2.2◦ (cf. 20.8◦ (5)), while the twist
around the C(1) = N(1) bond increases only moderately, from 1.1◦
in 5 to 10.9◦ in 15. Thus the P,N-containing metallacycle of 15 is
much less puckered than in 10, adopting an envelope conformation
˚
with the Pd atom deviating by 0.27 A from the PN(2)C(1)N(1)
plane. Consequently, the P,N-bite angle of 15 (81.90(4)◦) is much
wider than that in 10, 76.25(4)◦.
Elemental analyses were performed by Mrs. J. Dostal, Chem-
istry Analytical Services Department, Durham University or Mr
S. Boyer, London Metropolitan University. Infrared spectra were
collected on Perkin Elmer 1600 or Spectrum1 spectrophotometers
using KBr discs or a solution cell fitted with KBr windows.
Summary
These studies have shown the utility of readily available amidines
and guanidines as building blocks for the straightforward
preparation of structurally diverse N-phosphino-amidines and -
guanidines. A combination of computational and spectroscopic
investigations has highlighted the impact of the substitution
pattern about the NCN backbone upon both their structure
and donor properties, with the guanidine series of compounds
being weaker donors. Irrespective of the conformation of the
various substituted N-phosphino-amidines and -guanidines, low
calculated barriers to E/Z isomerism permit their coordination
as strongly bound j2-P,N-chelates, despite comparatively weak
Lewis basicities. The application of P,N-ligands 1–5 in a number
of metal-catalysed transformations is on-going.
N,N,Nꢀ,Nꢀꢀ-Tetraisopropyl-N-diphenylphosphino-guanidine 1
◦
To a stirred, cooled (−78 C) solution of N,N ꢀ-diisopropyl-
carbodiimide (2.5 mL, 16.14 × 10−3 mol) in diethyl ether (200 mL)
was added dropwise BunLi (2.0 M, pentane, 8.1 mL, 16.14 ×
10−3 mol), and the vessel left to warm to RT over 1 h, to give an
opaque white solution. After re-cooling (−78 ◦C), an ethereal
solution (80 mL) of Ph2PCl (2.9 mL, 16.14 × 10−3 mol) was
added dropwise via cannula. The mixture was allowed to stir at
◦
−78 C for 1 h before being left to warm to RT, then stirred for
18 h, resulting in a yellow solution and white precipitate. Removal
of solvent under reduced pressure left a yellow oil. Addition of
CH2Cl2 (20 mL) followed by filtration and removal of all volatile
components in vacuo left 1 as a viscous yellow oil (4.52 g, 68%).
Attempts to purify 1 by distillation and column chromatography
lead to its decomposition; hence it was used without further
Experimental
All operations were conducted under an atmosphere of dry nitro-
gen using standard Schlenk and cannula techniques, or in a Saffron
Scientific nitrogen-filled glove box. All NMR-scale reactions were
conducted using Young’s tap valve NMR tubes. Bulk solvents were
freshly obtained from an Innovative Technologies SPS facility and
deoxygenated prior to use. CDCl3, d2-tetrachloroethane (TCE-d2)
1
purification. H (250.1 MHz, CDCl3) d: 7.44 (4H, br pseudo-t,
3JHH = 7.0, o-C6H5), 7.30 (6H, m, m- + p-C6H5), 3.82 (1H, m,
3
NCH), 3.60 (2H, m, NCH), 3.44 (1H, sept, JHH = 6.7, NCH),
1.10 (12H, br s, CH3), 1.05 (6H, br s, CH3), 0.90 (6H, br s, CH3);
Dalton Trans., 2008, 1043–1054 | 1049
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©

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1
2
13C{ H} (100.6 MHz, CDCl3) d: 147.3 (d, JPC = 20.7, C N),
139.6 (br d, 2JPC = 18, o-C6H5), 136.4 (br d, 2JPC = 18, o-C6H5),
131.9 (s, p-C6H5), 131.5 (d, 1JPC = 51, i-C6H5), 127.2 (br, m-C6H5),
50.4 (d, 4JPC = 5.5, =NCH), 47.5 (s, NCH), 45.9 (s, NCH), 24.2 (s,
=
C
1,1ꢀH C6H11 + OCH2CH2N), 3.19 (4H, m, OCH2CH2N), 1.83–
1
0.90 (20H, m, C6H11); 13C{ H} (125.7 MHz, C6D6) d: 153.6 (d,
2
=
JPC = 20.5, C N), 140.7 (br s, i-C6H5), 135.3 (br s, o-C6H5), 131.8
(br s, o-C6H5), 128.4 (br s, m- + p-C6H5), 67.0 (s, OCH2CH2N),
2
60.2 (d, JPC = 5.5, C1H-C6H11), 57.0 (s, C1H-C6H11), 50.1 (s,
CH3), 22.0 (s, CH3), 21.2 (s, CH3); 31P{ H} (101.3 MHz, CDCl3)
1
OCH2CH2N), 36.0 (br s, C2/2ꢀH2–C6H11), 33.9 (br s, C2/2H2–
d: + 49.9; MS (FAB+): 412 (MH)+.
ꢀ
C6H11), 27.5 (br s, C3/3H2–C6H11), 26.9 (br s, C4/4 H2–C6H11),
1
26.4 (br s, C4/4ꢀH2–C6H11), 25.7 (br s, C3/3ꢀH2–C6H11); 31P{ H}
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-piperidine-1-
carboxamidine 2
(125.7 MHz, C6D6) d: +49.8 (s); MS (FAB+): 478 (MH)+.
To a stirred, cooled (−78 ◦C) solution of piperidine (0.42 mL,
4.85 × 10−3 mol) in diethyl ether (15 mL) was added dropwise
BunLi (2.55 M, pentane, 1.9 mL, 4.85 × 10−3 mol), and the vessel
left to warm to RT over 2 h. After re-cooling (−78 ◦C), an ethereal
(25 mL), cooled solution of N,N ꢀ-dicyclohexylcarbodiimide (1.0 g,
4.85 × 10−3 mol) was added dropwise via cannula. The mixture was
allowed to warm to RT, then stirred for 2 h. Volatile components
were removed in vacuo. The resulting solid was dissolved in Et2O
(20 mL), cooled at −78 ◦C and Ph2PCl (0.87 mL, 4.85 × 10−3 mol)
was added dropwise, to give an opaque white solution. The mixture
was allowed to warm slowly to RT, then stirred for 18 h. The
solvents were removed under vacuum, hexane added and the
mixture filtered. Concentration and recrystallisation from hexane
afforded 2 as a white solid (1.70 g, 74%). Anal. Calc. for C30H42N3P
requires: C, 75.75; H, 8.90; N, 8.83. Found: C, 75.81; H, 8.99; N,
8.87. 1H (499.9 MHz, CDCl3) d: 7.50 (4H, br s, o-C6H5), 7.35 (6H,
m, m- + p-C6H5), 3.49 (1H, m, C1H C6H11), 3.40 (1H, m, C1ꢀH
C6H11), 3.03 (4H, m, C1H2 pip); 1.87–0.80 (26H, 4 overlapping m,
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-acetamidine 4
◦
To a stirred, cooled (−78 C) solution of N,N ꢀ-dicyclohexyl-
carbodiimide (1.0 g, 4.85 × 10−3 mol) in diethyl ether (25 mL)
was added dropwise MeLi (1.6 M, hexane, 3.0 mL, 4.85 ×
10−3 mol), and th◦ e vessel left to warm to RT over 1 h. After
re-cooling (−78 C), Ph2PCl (0.87 mL, 4.85 × 10−3 mol) was
added dropwise. The mixture was allowed to warm to RT, then
stirred for 18 h. The solvents were removed under vacuum, pentane
added and the solution filtered. Prolonged standing in pentane
gave rise to colourless crystals of 4 suitable for an X-ray structure
determination (1.65 g, 84%). Anal. Calc. for C26H35N2P requires:
C, 76.81; H, 8.68; N, 6.89. Found: C, 76.71; H, 8.64; N, 6.80.
1H (499.8 MHz, CDCl3) d: 7.53–7.27 (10H, m, C6H5), 4.02 (m,
1H, C1/1H-C6H11), 3.03 (1H, m, C1/1H-C6H11), 1.58 (3H, s, CH3),
1
2.02–1.21 (20H, m, CH2–C6H11); 13C{ H} (125.7 MHz, CDCl3) d:
1
155.7 (d, 2JPC 1, C N), 139.1 (d, JPC = 17, i-C6H5), 131.4 (d, JPC
=
=
20.23, o- or m-C6H5), 128.2 (d, JPC = 5, o- or m-C6H5), 128.1 (s,
p-C6H5), 58.5 (d, 2JPC = 17.5, C1ꢀH-C6H11), 57.4 (s, C1H-C6H11),
34.6 (s, C2H2–C6H11), 33.3 (d, 3JPC = 11.5, C2ꢀH2–C6H11), 26.8 (s,
1
2
C6H11 + pip); 13C{ H} (125.6 MHz, CDCl3) d: 154.8 (d, JPC
=
1
2
=
21, C N), 139.9 (d, JPC = 102, i-C6H5), 135.0 (d, JPC = 20, o-
C6H5), 131.3 (d, 2JPC = 16, o-C6H5), 129.8 (s, p-C6H5), 128.3 (br s,
C
3/3ꢀH2–C6H11), 26.3 (s, C4/4ꢀH2–C6H11), 26.1 (s, C4/4ꢀH2–C6H11),
2
3
1
m-C6H5), 59.8 (d, JPC = 5, C1H-C6H11), 56.6 (s, C1H-C6H11),
24.8 (s, C3/3ꢀH2–C6H11), 17.0 (d, JPC = 7 Hz, CH3); 31P{ H}
(161.90 MHz, CDCl3) d: +37.0; MS (EI): 406 (M), 329 (M-Ph),
221 (M-PPh2).
49.5 (s, C1H2 pip), 35.3 (br s, C2/2ꢀH2 C6H11), 33.2 (br s, C2/2ꢀH2–
C6H11), 26.7 (br s, C3/3ꢀH2–C6H11), 26.1 (s, C4/4ꢀH2–C6H11), 26.0 (s,
C
4/4ꢀH2–C6H11), 25.7 (s, C2H2–C5H10N), 25.2 (br s, C3/3ꢀH2–C6H11),
24.9 (s, C3H2–C5H10N); 31P{ H} (161.90 MHz, CDCl3) d: +50.2;
1
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-benzamidine 5
MS (ES+): 292.4 (M-PPh2)+.
◦
To a stirred, cooled (−78 C) solution of N,N ꢀ-dicyclohexyl-
carbodiimide (1.0 g, 4.85 × 10−3 mol) in diethyl ether (25 mL) was
added dropwise PhLi (2.0 M, Bu2O, 2.4 mL, 4.85 × 10−3 mol),
and the vessel left to warm to RT over 2 h. After re-cooling
(−78 ◦C), an ethereal, cooled solution (10 mL) of Ph2PCl (0.87 mL,
4.85 × 10−3 mol) was added dropwise via cannula. The mixture
was allowed to warm to RT, then stirred for 18 h. The volatile
components were removed under vacuum, hexane added and
the mixture filtered. Removal of the solvent in vacuo afforded
5 as a white solid (1.74 g, 83%) that was used without further
purification. Anal. Calc. for C31H37N2P requires: C, 79.45; H, 7.96;
N, 5.98. Found: C, 79.51; H, 8.00; N, 6.01. 1H (499.8 MHz, CDCl3)
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-4-
morpholinecarboxamidine 3
◦
To a stirred, cooled (−78 C) solution of N,N ꢀ-dicyclohexyl-4-
morpholinecarboxamide (9.43 g, 3.21 × 10−2 mol) in diethyl ether
(200 mL) was added dropwise BunLi (2.0 M, pentane, 16.1 mL,
3.21 × 10−2 mol), and the vessel left to warm to RT over 1 h, to give
an opaque white solution. After re-cooling (−78 ◦C), an ethereal
solution (80 mL) of Ph2PCl (5.8 mL, 3.21 × 10−2 mol) was added
dropwise via cannula. The mixture was allowed to stir at −78 ◦C for
1 h before being left to warm to RT, then stirred for 18 h, resulting
in a colourless solution with a thick white precipitate. Removal
of solvent under reduced pressure left a yellow oil. Addition, and
subsequent removal, of CH2Cl2 (50 mL) gave a yellow oily solid.
Dissolution of the oil in toluene and filtration through a glass frit
to remove the white solid, gave an orange solution. Concentration
and crystallisation at −30 ◦C gave colourless crystals of 3 suitable
for an X-ray structure determination (11.34 g, 74%). Anal. Calc.
for C29H40N3OP: C, 72.93; H, 8.44; N, 8.80%. Found: C, 72.99; H,
3
d: 7.57 (4H, pseudo-t, JHH = 16.0, o-(P)C6H5), 7.60–7.10 (9H,
m, C6H5), 7.08 (2H, d,3JHH = 8.0, o-C6H5), 3.15 (1H, m, C1,1ꢀH-
C6H11), 2.54 (1H, m, C1,1ꢀH-C6H11), 2.27 (2H, m, C6H11), 1.66–0.80
1
(18H, m, C6H11); 13C{ H} (125.6 MHz, CDCl3) d: 157.2 (d, 2JPC
=
1
3
=
9, C N), 138.9 (d, JPC = 15, i-(P)C6H5), 136.4 (d, JPC = 2, i-
C6H5), 132.6 (d, 2JPC = 21.5, o-(P)C6H5), 128.4 and 128.1 (s, o- +
3
m-C6H5), 127.9 (s, p-C6H5), 127.8 (d, JPC = 6.5, m-(P)C6H5),
127.4 (d, 4JPC = 2, p-(P)C6H5), 59.9 (d, 2JPC = 10, C1ꢀH-C6H11),
1
3
8.48; N, 8.86%. H (499.9 MHz, C6D6) d: 7.59 (4H, br pseudo-t,
58.8 (s, C1H-C6H11), 33.3 (d, JPC = 8.2, C2ꢀH2–C6H11), 34.7 (s,
3JHH = 7.0, o-C6H5), 7.09 (6H, m, m- + p-C6H5), 3.80–3.49 (6H, m,
C2H2–C6H11), 26.8 (s, CH2), 26.1 (s, CH2), 25.8 (s, CH2), 24.6 (s,
1050 | Dalton Trans., 2008, 1043–1054
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©

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1
1
CH2); 31P{ H} (161.9 MHz, CDCl3) d: +44.9 (br s, m1/2 = 44 Hz);
C6H11); 31P{ H} (161.9 MHz, CDCl3) d: +112.1 (d, 1JRhP = 176);
MS (FAB+): 608 (M − Cl)+; IR (KBr, CDCl3 solution): v(CO) =
1994 cm−1.
MS (ES+): 283.5 (M–PPh2)+.
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-selenide-piperidine-1-
carboxamidine 6
N,N ꢀ-Dicyclohexyl-N-diphenylphosphino-acetamidine rhodium
carbonyl chloride 11
A Young’s tap NMR tube was charged with Se (8 mg, 1.03 ×
10−4 mol), 2 (40 mg, 8.41 × 10−5 mol) and CDCl3 (0.75 mL). Com-
pound 6 was obtained quantitatively (by 31P NMR spectroscopy)
A Young’s tap NMR tube was charged with 4 (50 mg, 1.23 ×
10−4 mol), {Rh(CO)2Cl}2 (24 mg, 6.17 × 10−5 mol) and CDCl3
(0.75 mL). After 30 min, the solution was freeze/thaw degassed,
back-filled with an atmosphere of CO, sealed and left to stand at
RT for 1 h, resulting in a yellow solution. Complex 11 was obtained
quantitatively (by 31P NMR spectroscopy) as a single product
and subsequently isolated as a yellow–orange solid on removal of
solvent in vacuo (64 mg, 91%). Anal. Calc. for C27H35N2OPRhCl:
C, 56.60; H, 6.16; N, 4.89. Found: C, 56.68; H, 6.23; N, 4.99.
1H (499.9 MHz, CDCl3) d: 7.91–7.86 (4H, m, C6H5), 7.62–7.56
1
after 12 h at RT. 31P{ H} (161.9 MHz, CDCl3) d: +57.6 (s +
satellites, 1JSeP = 772).
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-selenide-4-
morpholinecarboxamidine 7
A Young’s tap NMR tube was charged with Se (8 mg, 1.03 ×
10−4 mol), 3 (41 mg, 8.58 × 10−5 mol) and CDCl3 (0.75 mL). The
tube was then sonicated for 18 h, affording 7 quantitatively (by 31
P
ꢀ
ꢀ
(6H, m, C6H5), 3.64 (1H, m, C1/1 H-C6H11), 3.24 (1H, br s, C1/1 H-
1
NMR spectroscopy). 31P{ H} (161.9 MHz, CDCl3) d: + 56.3 (s +
C6H11), 2.48 (3H, s, CH3), 2.27–0.81 (20H, m, C6H11); 13C{ H}
1
satellites, 1JSeP = 775).
(125.6 MHz, CDCl3) d: 181.3 (d, 1JRhC = 78.5, Rh-CO), 133.1 (d,
JPC = 14, o- or m-C6H5), 132.9 (bs, p-C6H5), 129.6 (d, JPC = 11, o- or
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-selenide-acetamidine 8
ꢀ
ꢀ
m-C6H5), 62.7 (s, C1/1 H-C6H11), 62.1 (br s, C1/1 H-C6H11), 32.9 (s,
CH2), 26.9 (s, CH2), 25.8 (s, CH2), 25.2 (s, CH2), 25.1 (s, CH2), 19.5
A Young’s tap NMR tube was charged with Se (8 mg, 1.03 ×
10−4 mol), 4 (50 mg, 0.1 × 10−3 mol) and CDCl3 (0.70 mL). Com-
pound 8 was obtained quantitatively (by 31P NMR spectroscopy)
1
(br s, CH3); 31P{ H} (161.9 MHz, CDCl3) d: + 124.9 (br d, 1JRhP
=
175.1); IR (KBr, CDCl3 solution): v(CO) = 1995 cm−1. Note,
1
after 12 h at RT. 31P{ H} (161.9 MHz, CDCl3) d: + 63.2 (s +
despite acquisition of spectra with long relaxation delay times, the
satellites, 1JSeP = 749).
=
C N carbon and ipso-C6H5 resonances could not be observed.
N,N ꢀ-Dicyclohexyl-N-diphenylphosphino-benzamidine rhodium
N,N ꢀ-Dicyclohexyl-N-diphenylphosphino-selenide-benzamidine 9
carbonyl chloride 12
A Young’s tap NMR tube was charged with Se (8 mg, 1.03 ×
10−4 mol), 5 (50 mg, 9.0 × 10−5 mol) and CDCl3 (0.80 mL). Com-
pound 9 was obtained quantitatively (by 31P NMR spectroscopy)
A Young’s tap NMR tube was charged with 5 (50 mg, 1.07 ×
10−4 mol), {Rh(CO)2Cl}2 (21 mg, 5.35 × 10−5 mol) and CDCl3
(0.75 mL). The tube was freeze/thaw degassed, back-filled with N2
and sealed. After 1 day, compound 12 was obtained quantitatively
(by 31P NMR spectroscopy) as a single product, which was isolated
as a brown waxy solid following removal of solvent under reduced
pressure (65 mg, 95%). Anal. Calc. for C32H37N2OPRhCl: C, 60.53;
H, 5.87; N, 4.41. Found: C, 60.80; H, 6.02; N, 4.55. 1H (499.9 MHz,
CDCl3) d: 7.94 (4H, m, C6H5), ꢀ7.60–7.46 (9H, m, C6H5), 7.22 (2H,
m, C6H5), 3.11 (1H, br s, C1/1 H-C6H11), 2.88 (3H, br s, C6H11),
1
after 12 h at RT. 31P{ H} (161.9 MHz, CDCl3) d: + 67.3 (s +
satellites, 1JSeP = 753).
N,N ꢀ-Dicyclohexyl-N-diphenylphosphino-4-
morpholinecarboxamidine rhodium carbonyl chloride 10
A Young’s tap NMR tube was charged with 3 (59 mg, 1.23 ×
10−4 mol), {Rh(CO)2Cl}2 (24 mg, 6.17 × 10−5 mol) and sealed.
CDCl3 (0.75 mL) was added and the tube freeze/thaw degassed,
back-filled with N2 and sealed. After 30 min, when gas evolution
had finished, the solution was freeze/thaw degassed, back-filled
with an atmosphere of CO, sealed and left to stand at RT for
1 h, resulting in a yellow solution. Layering hexane on top of
the CDCl3 solution, yielded crystals of 10 suitable for an X-ray
structure determination, after standing for 1 week (12 mg, 30%).
Anal. Calc. for C30H40N3O2PClRh.CDCl3: C, 48.71; H, 5.54; N,
5.50. Found: C, 48.82; H, 5.59; N, 5.45%. 1H (499.9 MHz, CDCl3)
d: 7.86 (4H, m, o-C6H5), 7.51 (6H, m, m- + p-C6H5), 3.73 (4H,
m, OCH2CH2N), 3.25 (6H, m, OCH2CH2N + C1/1H-C6H11), 2.74
1.74–0.56 (18H, m, C6H11); 13C{ H} (125.7 MHz, CDCl3) d: 187.3
1
=
(br, Rh-CO), 170.0 (br s, C N), 133.2 (d, JPC = 13.5, o- or m-
1
2
(P)C6H5), 132.1 (dd, JPC = 56, JRhC = 2, i-(P)C6H5), 132.0 (s,
C6H5), 130.5 (s, C6H5), 129.0 (d, JPC = 10.5, o- or m-(P)C6H5),
ꢀ
128.5 (br s, C6H5 +p-(P)C6H5), 64.2 (br s, C1/1 H-C6H11), 62.1 (br s,
ꢀ
C
1/1 H-C6H11), 34.5 (br s, CH2), 31.6 (s, CH2), 27.0 (br s, CH2),
25.8 (s, CH2), 24.9 (br s, CH2), 24.5 (s, CH2); 31P{ H} (161.9 MHz,
1
1
CDCl3) d: +124.7 (d, JRhP = 181.5); IR (KBr, CDCl3 solution):
v(CO) = 2000 cm−1.
N,N ꢀ-Dicyclohexyl-N-diphenylphosphino-piperidine-1-
carboxamidine palladium dichloride 13
1
(2H, m, C6H11), 1.77–0.61 (18H, 4 overlapping m, C6H11); 13C{ H}
(125.7 MHz, CDCl3) d: 188.1 (d, 1JRhC = 74, Rh-CO), 165.7 (dd,
2
2
2
=
JPC = 24, JRhC = 3.5, C N), 134.3 (d, JPC = 14.5, o-C6H5),
To a solution of 2 (460 mg, 0.98 × 10−5 mol) in CH2Cl2 (20 mL)
was added dropwise a solution of PdCl2(MeCN)2 (250 mg, 0.98 ×
10−5 mol) was dissolved in CH2Cl2 (20 mL) to give a very dark
orange solution. The mixture was stirred for 1 h. All volatile
components were removed in vacuo to afford 13 as a dark yellow–
brown solid, which was washed with diethyl ether (3 × 5 mL) and
132.2 (d, 4JPC = 2, p-C6H5), 132.0 (dd, 1JPC = 52.5, 2JRhC = 1.7, i-
C6H5), 128.7 (d, 3JPC = 12, m-C6H5), 66.4 (s, OCH2CH2N), 64.1 (s,
C1ꢀ H-C6H11), 62.0 (s, C1H-C6H11), 49.8 (s, OCH2CH2N), 33.7 (s,
ꢀ
ꢀ
ꢀ
C
2/2 H2–C6H11), 32.7 (s, C2/2 H2–C6H11), 26.9 (s, C3/3 H2–C6H11),
ꢀ
ꢀ
ꢀ
26.3 (s, C3/3 H2–C6H11), 25.3 (s, C4/4 H2–C6H11), 25.0 (s, C4/4 H2–
This journal is The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1043–1054 | 1051
©

View Article Online
ꢀ
ꢀ
dried in vacuo (489 mg, 77%). Anal. Calc. for C31H37N2PPdCl2
requires: C, 57.64; H, 5.77; N, 4.34. Found: C, 57.59; H, 5.60; N,
4.21. 1H (499.9 MHz, CDCl3) d: 7.97 (4H, m, o-C6H5), 7.61 (2H, m,
p-C6H5), 7.49 (4H, m, m-C6H5); 3.47–2.98 (6H, 3 overlapping m,
32.6 (s, C2/2 H2–C6H11), 31.5 (s, C2/2 H2–C6H11), 26.8 (s, CH2), 26.0
3
(s, CH2), 25.1 (s, CH2), 24.8 (s, CH2), 19.4 (d, JPC = 9.5, CH3);
31P{ H} (161.9 MHz, CDCl3) d: +108.0; MS (MALDI): 549 (M −
1
Cl)+.
ꢀ
C1,1 H-C6H11 + C1H2–C5H10N), 1.77–0.95 (26H, 4 overlapping m,
1
C6H11 + C5H10N); 13C{ H} (125.7 MHz, C6D6) d: 167.8 (d, 2JPC
=
=
=
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-benzamidine palladium
dichloride 16
4
=
25, C N), 134.6 (d, JPC = 13, o- or m-C6H5), 133.4 (d, JPC
1
3, p-C6H5), 129.0 (d, JPC = 13, o- or m-C6H5), 127.22 (d, JPC
To a solution of 5 (111 mg, 0.24 × 10−3 mol) in CH2Cl2 (10 mL) was
added a solution of PdCl2(MeCN)2 (61.50 mg, 0.24 × 10−3 mol) in
CH2Cl2 (10 mL), giving rise to a dark orange solution. The mixture
was stirred for 4 h. Volatile components were removed in vacuo and
the residue was washed with both hexane and Et2O, affording 16
as an orange solid (0.14 g, 92%). Anal. Calc. for C31H37N2PPdCl2:
C, 57.64; H, 5.77; N, 4.34. Found: C, 57.77; H, 5.89; N, 4.45. 1H
(499.9 MHz, CDCl3) d: 8.10 (2H, m, C6H5), 7.67–7.29 (13H, m,
C6H5), 3.01 (2H, br s, C6H11), 1.81–0.48 (20H, 4 overlapping m,
ꢀ
ꢀ
62, i-C6H5), 66.0 (s, C1/1 H-C6H11), 63.0 (s, C1/1 H-C6H11), 51.5
ꢀ
ꢀ
(s, C1H-C5H10N), 33.6 (s, C2/2 H2–C6H11), 32.6 (s, C2/2 H2–C6H11),
ꢀ
ꢀ
26.9 (s, C3/3 H2–C6H11), 26.5 (s, C3/3 H2–C6H11), 25.8 (s, C2H2–
ꢀ
ꢀ
C5H10N), 25.1 (br s, C4/4 H2–C6H11), 24.9 (s, C4/4 H2–C5H10N),
23.7 (s, C3H2–C5H10N); 31P{ H} (161.90 MHz, CDCl3) d: +84.4
1
(br s, m1/2 = 131 Hz); MS (MALDI): 617.5 (M–Cl)+.
N,N ꢀ-Dicyclohexyl-N-diphenylphosphino-4-
morpholinecarboxamidine palladium dichloride 14
C6H11); 13C{ H} (125.7 MHz, CDCl3) d: 134.1 (d, JPC = 12.5, o- or
1
m-(P)C6H5), 133.6 (s, p-(P)C6H5), 131.3 (s, C6H5), 130.1 (s, C6H5),
To a mixture of 3 (424 mg, 1.16 × 10−3 mol) and PdCl2(COD)
(321 mg, 1.12 × 10−3 mol) was added cold (−78 ◦C) CH2Cl2
(30 mL), the mixture then being left to stir and warm to RT over
18 h. Volatile components were removed under reduced pressure
to leave 14 as a yellow powder, which was washed with diethyl
ether (3 × 30 mL) and dried in vacuo (578 mg, 95%). Anal. Calc.
for C29H40N3OPCl2Pd: C, 53.18; H, 6.16; N, 6.42%. Found: C,
53.25; H, 6.22; N, 6.34%. 1H (301.2 MHz, CDCl3) d: 7.98 (4H, dd,
1
129.3 (d, JPC = 12, o- or m-(P)C6H5), 127.0 (d, JPC = 67 HZ,
ꢀ
i-C6H5), 126.9 (s, C6H5), 66.1 (s, C1/1 H-C6H11), 63.1 (s, C1/1ꢀH-
C6H11), 33.4 (s, CH2), 31.6 (s, CH2), 25.8 (s, CH2), 26.5 (s, CH2),
24.8 (s, CH2), 24.2 (s, CH2); only 1 ipso-C6H5 resonance could be
observed; 31P{ H} (161.9 MHz, CDCl3) d: +106.7; MS (MALDI):
1
610.5 (M − Cl)+.
N,N,Nꢀ,Nꢀꢀ-Tetraisopropyl-N-diphenylphosphino-guanidine
palladium dichloride 17
3JHH = 7.6, 3JPH = 6.4, o-C6H5), 7.64 (2H, dd, 3JHH = 7.5, 5JPH
=
2.3, p-C6H5), 7.52 (4H, dd, 3JHH = 7.6, 4JPH = 2.9, m-C6H5), 3.87–
3.71 (4H, m, OCH2CH2N), 3.51–3.03 (8H, m, OCH2CH2N +
C6H11), 1.69 (8H, m, C6H11), 1.48 (2H, m, C6H11), 1.39–0.90 (8H,
A Schlenk flask was charged with 1 (200 mg, 0.49 × 10−3 mol) and
PdCl2(COD) (139 mg, 0.49 × 10−3 mol). The vessel was cooled
to −78 ◦C and CH2Cl2 (30 mL) added. The mixture was allowed
to warm to RT over 6 h, whereupon the CH2Cl2 was removed
under reduced pressure to leave 17 as a yellow powder, which was
washed with diethyl ether (3 × 10 mL) and dried in vacuo (229 mg,
80%). Anal. Calc. for C25H38N3PPdCl2 requires: C, 50.98; H, 6.52;
1
m, C6H11); 13C{ H} (75.8 MHz, CDCl3) d: 166.5 (d, 2JPC = 24.5,
2
C
N), 134.5 (d, JPC = 13, o-C6H5), 133.6 (d, 4JPC = 3, p-C6H5),
=
129.1 (d, 3JPC = 12.5, m-C6H5), 126.9 (d, 1JPC = 62, i-C6H5), 66.5
(s, OCH2CH2N), 66.0 (s, C1ꢀ H-C6H11), 63.2 (s, C1H-C6H11), 50.2
(s, OCH2CH2N), 33.5 (s, CH2–C6H11), 32.6 (s, CH2–C6H11), 26.9
(s, CH2–C6H11), 26.4 (s, CH2–C6H11), 25.1 (s, CH2–C6H11), 24.7 (s,
1
N, 7.14%. Found: C, 51.01; H, 6.66; N, 7.12%. H (250.1 MHz,
1
CH2–C6H11); 31P{ H} (121.94 MHz, CDCl3) d: +84.6 (br s, m1/2
=
CDCl3) d: 7.98 (4H, m, o-C6H5), 7.57 (2H, m, p-C6H5), 7.40 (4H,
m, m-C6H5), 4.01 (m, 1H, NCH), 3.73 (3H, sept., 3JHH 7.6, NCH),
1.47 (6H, d, 3JHH 7.6, CH3), 1.30 (12H, m, CH3), 0.95 (6H, d, 3JHH
131 Hz); MS (FAB+): 618 (M − Cl)+, 583 (M-2Cl)+.
7.6, CH3); 13C{ H} (100.6 MHz, CDCl3) d: 169.6 (d, JPC 24.5,
=NC), 135.1 (d, 2JPC = 13.5, o-C6H5), 133.6 (d, 4JPC = 3, p-C6H5),
129.0 (d, 3JPC = 12.5, m-C6H5), 127.4 (d, 1JPC = 61, i-C6H5), 57.6
(s, NCH), 54.5 (s, NCH), 53.5 (s, NCH), 24.3 (s, CH3), 23.6 (d,
1
2
N,Nꢀ-Dicyclohexyl-N-diphenylphosphino-acetamidine palladium
dichloride 15
A solution of 4 (0.52 g, 1.28 × 10−3 mol) in CH2Cl2 (15 mL)
was added dropwise to a suspension of PdCl2(MeCN)2 (0.33 g,
1.28 × 10−3 mol) in CH2Cl2 (10 mL). The mixture was allowed to
stir for 18 h, the orange suspension turning to a yellow solution.
Removal of volatile components under reduced pressure afforded
an orange–yellow solid, which was washed with Et2O. Layering
hexane on top of a CDCl3 solution of 15 yielded suitable crystals
for an X-ray structure determination, after standing for 1 week.
(0.63 g, 84%). Anal. Calc. for C26H35Cl2N2PPdCDCl3: C, 46.05; H,
5.30; N, 3.98. Found: C, 45.88; H, 5.01; N, 3.76. 1H (499.9 MHz,
CDCl3) d: 8.00–7.97 (4H, m, o-C6H5), 7.67–7.64 (2H, m, p-C6H5),
5JPC = 12, CH3), 23.0 (s, CH3); 31P{ H} (101.3 MHz, CDCl3) d:
1
+81.2; MS (FAB+): 554 (M − Cl)+.
X-Ray crystallography
The single crystal X-ray diffraction experiments (Table 6) were car-
ried out for 3 and 10 on a Bruker APEX 2000 CCD diffractometer,
for 4 on a Rigaku R-Axis SPIDER IP diffractometer, and for 15
on a Bruker SMART 6000 CCD diffractometer, using Oxford
Cryrostream N2 cooling devices and graphite-monochromated
ꢀ
7.57–7.53 (4H, m, m-C6H5), 3.82 (1H, br s, C1/1 H-C6H11), 3.06
Mo-Ka radiation (k = 0.71073 A). The diffraction of 4 was
˚
ꢀ
(1H, br s, C1/1 H-C6H11), 2.83 (2H, br s, C6H11), 2.45 (3H, s, CH3),
extremely weak (mean I/r(I) < 2.8). The data were corrected
for absorption by semi-empirical method (on Laue equivalents)
for 3 and 10,44 by numerical integration (on crystal face-indexing)
for 15. The structures were solved by direct methods and refined
by full-matrix least squares against F2 of all reflections, using
1
1.82–0.81 (18H, m, C6H11); 13C{ H} (125.7 MHz, CDCl3) d: 168.9
(br s, C N), 133.9 (d, JPC = 12, o- or m-C6H5), 133.5 (d, 4JPC
=
=
=
3, p-C6H5), 129.3 (d, JPC = 12.5, o- or m-C6H5), 126.5 (d, 1JPC
64, i-C6H5), 62.2 (d, 2JPC = 3, C1ꢀ H-C6H11), 53.7 (s, C1H-C6H11),
1052 | Dalton Trans., 2008, 1043–1054
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The Royal Society of Chemistry 2008
©

View Article Online
Table 6 Crystal data and X-ray experimental details
3
4
10
15
CCDC deposition no.
Formula
Formula weight
T/K
293165
C29H40N3OP
477.61
663533
C26H35N2P
406.53
293166
663534
C30H40ClN3O2PRh·CDCl3
C26H35Cl2N2PPd·CDCl3
764.35
704.20
150
120
150
120
Crystal system
Space group (no.)
Monoclinic
P21/c (#14)
10.1116(5)
9.8929(4)
26.4573(12)
90.047(1)
2646.6(2)
4, 1.199
Orthorhombic
Pbca (#61)
19.450(2)
10.630(1)
22.218(2)
90
4593.6(8)
8, 1.176
0.13
Monoclinic
P21/c (#14)
21.4996(9)
9.3920(4)
16.7107(7)
103.496(1)
3281.1(2)
Monoclinic
P21/n (#14, non-standard)
8.0573(5)
22.988(2)
16.876(1)
98.13(1)
3094.3(4)
4, 1.512
1.10
˚
a/A
˚
b/A
˚
c/A
b/◦
3
˚
V/A
Z and qcalc/g cm−3
4, 1.547
0.93
l(Mo-Ka)/mm−1
0.13
Reflections collected, unique (Rint
)
21815, 5768 (0.025)
0.039, 0.114
36129, 4043 (0.136)
0.078, 0.153
16859, 7141 (0.028)
0.027, 0.067
53693, 13064 (0.055)
0.034, 0.084
R1 [I > 2r(I)] and wR2 (all data)a
2
1/2
a R1 = RꢁFo| − |Fcꢁ/R|Fo|; wR2 = {R[w(Fo − Fc2)2]/R[w(Fo2)2]}
.
the SHELXTL programs.45 All non-hydrogen atoms were refined
in anisotropic approximation, with hydrogen atoms ‘riding’ at
idealised positions.
CCDC reference numbers 293165, 663533, 293166 and 663534
for 3, 4, 10 and 15, respectively.
Notes and references
1 M. R. i. Zubiri and J. D. Woollins, Comments Inorg. Chem., 2003, 24,
189.
2 M. Alajar´ın, C. Lo´pez-Leonardo and P. Llamas-Lorente, Top. Curr.
Chem., 2005, 250, 77.
3 F. Agbossou, J.-F. Carpentier, F. Hapiot, I. Suisse and A. Mortreux,
Coord. Chem. Rev., 1998, 178–180, 1615.
4 B. L. Feringa, Acc. Chem. Res., 2000, 33, 346.
5 F. Dahan, P. W. Dyer, M. J. Hanton, M. Jones, D. M. P. Mingos, A. J. P.
White, D. J. Williams and A. -M. Williamson, Eur. J. Inorg. Chem.,
2002, 732.
6 P. W. Dyer, J. Fawcett, M. J. Hanton, R. D. W. Kemmitt and R. Padda,
Dalton Trans., 2003, 104.
7 A. D. Burrows, G. Kociok-Ko¨hn, M. F. Mahon and M. Varrone,
C. R. Chim., 2006, 9, 111.
8 C. E. Anderson, A. S. Batsanov, P. W. Dyer, J. Fawcett and J. A. K.
Howard, Dalton Trans., 2006, 5362.
9 P. W. Dyer, J. Fawcett, M. J. Hanton, D. M. P. Mingos and A.-M.
Williamson, Dalton Trans., 2004, 2400.
10 P. Braunstein, C. Frison, X. Morise and R. D. Adams, J. Chem. Soc.,
Dalton Trans., 2000, 2205.
11 A. Carter, S. A. Cohen, N. A. Cooley, A. Murphy, J. Scutt and D. F.
Wass, Chem. Commun., 2002, 858.
12 K. Hiroi and Y. Suzuki, Tetrahedron Lett., 1998, 39, 6499.
13 M. S. Balakrishna, R. Klein, S. Uhlenbrock, A. A. Pinkerton and R. G.
Cavell, Inorg. Chem., 1993, 32, 5676.
14 P. Braunstein and F. Naud, Angew. Chem., Int. Ed., 2001, 40, 680.
15 G. Helmchen and A. Pfaltz, Acc. Chem. Res., 2000, 33, 336.
16 F. Speiser, P. Braunstein and L. Saussine, Acc. Chem. Res., 2005, 38,
784.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b715736c
Computations
All ab initio computations were carried out with the Gaussian
03 package.46 The model and full geometries discussed here
were optimised using the B3LYP/6-31G* level of theory47,48 with
no symmetry constraints. Frequency calculations on these opti-
mised geometries have no imaginary frequencies. The electronic
structures were also computed at the same level of theory. The
energy barriers to phosphatropic rearrangement were estimated
by optimisation of the geometries with both N–P distances being
equivalent. The rotational barriers along the N–P bond were
calculated by fixing the C1–N2–P–C24 torsional angle at 30◦
angle intervals and optimised. The Z- and E-imine rearrangement
barriers were determined by fixing the N2–C1–N1–C2 dihedral
angle to 90◦ and the geometries otherwise fully optimised.
17 A. D. Burrows, M. F. Mahon and M. Varrone, Dalton Trans., 2003,
Acknowledgements
4718.
18 P. W. Dyer, J. Fawcett and M. J. Hanton, J. Organomet. Chem., 2005,
690, 5264.
The Universities of Durham and Leicester, the EPSRC, The
Lubrizol Corporation (MJH); Nuffield Foundation (PKL for
an Undergraduate Summer Studentship; PWD); the European
Union for a Marie Curie fellowship (LB) and The Royal Society
(PWD) are gratefully acknowledged for financial support. Johnson
Matthey is thanked for the loan of palladium and rhodium salts.
Dr A. M. Kenwright and Dr G. A. Griffith, Mrs C. F. Heffernan
and Mr I. H. McKeag are thanked for their assistance with
the acquisition and interpretation of NMR spectra. The EPSRC
National Mass Spectrometry Service at the University of Wales,
Swansea, is acknowledged for selected mass spectrometric data.
Prof. R. Re´au and Dr M. P. Coles are thanked for their scientific
input and useful discussions.
19 G. Xu and S. R. Gilbertson, Tetrahedron Lett., 2003, 44, 953.
20 C. Markert and A. Pfaltz, Angew. Chem., Int. Ed., 2004, 43, 2498.
21 H. Brunner and H. Weber, Chem. Ber., 1985, 118, 3380.
22 T. Schareina and R. Kempe, Angew. Chem., Int. Ed., 2002, 41, 1521.
23 M. P. Coles, Dalton Trans., 2006, 985.
´
24 E. E. Nifant’ev, V. V. Negrebetskii and M. K. Grachev, Russ. J. Gen.
Chem., 1991, 61, 1450.
25 V. V. Negrebetskii, L. Y. Bogel’fer, A. D. Sinitsa, V. I. Kal’chenko, V. S.
Krishtal and L. N. Markovskii, Russ. J. Gen. Chem., 1982, 52, 36.
26 K. Hartke and H.-M. Wolff, Chem. Ber., 1980, 113, 1394.
27 J. Mu¨nchenberg, A. K. Fischer, H. Tho¨nnessen, P. G. Jones and R.
Schmutzler, J. Organomet. Chem., 1997, 529, 361.
28 T. Chivers, K. McGregor and M. Parvez, Inorg. Chem., 1993, 32, 5119.
29 W.-K. Wong, C. Sun, T. Jiang, W.-T. Wong, F. Xue and T. C. W. Mak,
J. Chem. Soc., Dalton Trans., 1997, 693.
This journal is The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1043–1054 | 1053
©

View Article Online
30 G. Margraf, R. Pattacini, A. Messaoudi and P. Braunstein, Chem.
Commun., 2006, 3098.
31 S. P. Green, C. Jones, G. Jin and A. Stasch, Inorg. Chem., 2007,
46, 8.
32 J. Grundy, M. P. Coles, A. G. Avent and P. B. Hitchcock, Chem.
Commun., 2004, 2410.
33 N. E. Mansfield, J. Grundy, M. P. Coles, A. G. Avent and Peter B.
Hitchcock, J. Am. Chem. Soc., 2006, 128, 13879.
42 S. Komiya, Synthesis of Organometallic Compounds—A Practical
Guide, Wiley-Interscience, New York, 1998, pg. 285.
43 J. A. McCleverty and G. Wilkinson, Inorg. Synth., 1966, 8, 211.
44 G. M. Sheldrick, SADABS, version 2.10, Bruker AXS, Madison, WI,
USA, 2003.
45 G. M. Sheldrick, SHELXTL, version 6.14, Bruker AXS, Madison, WI,
USA, 2003.
46 Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S.
Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson,
W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian, Inc.,
Wallingford, CT, USA, 2004.
34 F. Bellucci, V. Bertolasi, V. Ferretti and G. Gilli, Acta Crystallogr., Sect.
C, 1985, C41, 544.
35 (a) F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen
and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, (Supplement, 1);
(b) G. Ha¨felinger and K. H. Kuske, in The Chemistry of the Amidines
and Imidates, ed. S. Patai and Z. Rappoport, Wiley, Chichester, 1991.
36 (a) A. V. Belyakov, A. Haaland, D. J. Shorokhov, V. I. Sokolov and
O. Swang, J. Mol. Struct., 1998, 445, 303; (b) A. E. Reed and P. v. R.
Schleyer, Inorg. Chem., 1988, 27, 3969.
37 N. G. Anderson and B. A. Keay, Chem. Rev., 2001, 101, 997; C.
Glidewell and E. J. Leslie, J. Chem. Soc., Dalton Trans., 1977, 527;
D. W. Allen and B. F. Taylor, J. Chem. Res. (S), 1981, 220; R. D.
Krosheefsky, R. Weiss and J. G. Verkade, Inorg. Chem., 1979, 18, 469;
D. W. Allen and B. R. Taylor, J. Chem. Soc., Dalton Trans., 1982, 51.
38 R. T. Boere´, V. Klassen and G. Wolmersha¨user, J. Chem. Soc., Dalton
Trans., 1998, 4147.
39 May 2007 update of the Cambridge Structural Database, see:F. H.
Allen and R. Taylor, Chem. Soc. Rev., 2004, 33, 463.
47 (a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648; (b) C. Lee, W. Yang
and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
40 E. P. Clark, Ind. Eng. Chem., Anal. Ed., 1941, 13, 820.
41 W. L. F. Armarego and D. D. Perrin, Purification of Laboratory
Chemicals, 3rd edn, Pergamon Press, New York, 1988.
48 (a) G. A. Petersson and M. A. Al-Laham, J. Chem. Phys., 1991, 94,
6081; (b) G. A. Petersson, A. Bennett, T. G. Tensfeldt, M. A. Al-Laham,
W. A. Shirley and J. Mantzaris, J. Chem. Phys., 1988, 89, 2193.
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