Platinum(II) phosphonate complexes derived from endo-8-camphanylphosphonic acid

Article abstract of DOI:10.1016/j.ica.2011.05.013

The reactions of cis-[PtCl₂L₂] [L = PPh₃, PMe₂Ph or L₂ = Ph₂P(CH₂) ₂PPh₂ (dppe)] with endo-8-camphanylphosphonic acid (CamPO₃H₂) and A

Full text of DOI:10.1016/j.ica.2011.05.013

Inorganica Chimica Acta 375 (2011) 228–235
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Platinum(II) phosphonate complexes derived from endo-8-camphanylphosphonic
acid
a
a
a
Meto T. Leach a, William Henderson a, , Alistair L. Wilkins , Joseph R. Lane , Ryland G. Fortney-Zirker ,
⇑
Mark M. Turnbull b,1, Brian K. Nicholson a
a Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
b Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of cis-[PtCl2L2] [L = PPh3, PMe2Ph or L2 = Ph2P(CH2)2PPh2 (dppe)] with endo-8-camphanyl-
phosphonic acid (CamPO3H2) and Ag2O in refluxing dichloromethane gave platinum(II) phosphonate
complexes [Pt(O3PCam)L2]. The X-ray crystal structure of [Pt(O3PCam)(PPh3)2]ꢀ2CHCl3 shows that the
bulky camphanyl group, rather than being directed away from the platinum, is instead directed into a
pocket formed by the Pt and the two PPh3 ligands. This allows the O3P–CH2 group to have a preferred
staggered conformation. The complexes were studied in detail by NMR spectroscopy, which demon-
strates non-fluxional behaviour for the sterically bulky PPh3 and dppe derivatives, which contain inequiv-
alent phosphine ligands in their 31P NMR spectra. These findings are backed up by theoretical calculations
on the PPh3 and PPhMe2 derivatives, which show, respectively, high and low energy barriers to rotation of
the camphanyl group in the PPh3 and PPhMe2 complexes. The X-ray crystal structure of CamPO3H2 is also
reported, and consists of hydrogen-bonded hexameric aggregates, which assemble to form a columnar
structure containing hydrophilic phosphonic acid channels surrounded by a sheath of bulky, hydrophobic
camphanyl groups.
Received 6 February 2011
Accepted 9 May 2011
Available online 17 May 2011
Keywords:
Platinum
Phosphonic acid
Phosphonate complexes
X-ray crystal structure
NMR spectroscopy
Theoretical calculations
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
(PhCO2)6(H2O)3]Cl with CamP(O)(OH)2 in the presence of Et3N
[5]. In these compounds, the bulky camphanyl group contributes
Previously, we reported the synthesis of endo-8-camphanyl-
phosphonic acid [CamP(O)(OH)2] by the oxidation of the
to a substantial hydrocarbon sheath around the inorganic core of
the aggregate. This structural motif was also seen in the polymeric
calcium salt of the corresponding phosphinic acid, CamPH(O)(OH),
which has a columnar structure comprising a hydrophilic, inor-
ganic core surrounded by a sheath of camphanyl groups [6].
1
corresponding phosphinic acid [CamPH(O)(OH)] [1,2]. Such orga-
nophosphorus acids are of potential interest for their coordination
chemistry, with the camphanyl group providing a readily-incorpo-
rated, bulky, chiral, and hydrophobic group. However, since the
discovery of CamP(O)(OH)2, relatively few studies have utilised
this phosphonic acid. The methyl ester CamP(O)(OMe)2, formed
by methylation of CamP(O)(OH)2 with CH2N2, forms a complex
O
OH
P
with
uranyl
nitrate,
UO2(NO3)2(CamP(O)(OMe)2)2
[2].
CamP(O)(OH)2 has also been utilised in the synthesis of a variety of
iron(III) phosphonate clusters. For example, reaction of
CamP(O)(OH)2 with the oxo-bridged iron-carboxylate aggregate
OH
1
[Fe3(
nuclear iron-phosphonate aggregate [Fe4(
l
3-O)(tBuCO2)6(H2O)3]Cl and pyridine (py) yielded the tetra-
3-O)(tBuCO2)4(Cam-
In this paper, we report the synthesis and characterisation of
some platinum(II) phosphine complexes of CamP(O)(OH)2. To date,
relatively few platinum(II) complexes containing bidentate chelat-
ing phosphonate ligands have been reported. A series of plati-
num(II) phosphine complexes [Pt(O3PR)L2] derived from
PhP(O)(OH)2 and MeP(O)(OH)2 were prepared by reaction of cis-
[PtCl2L2] [e.g. L = PPh3, PMePh2 or L2 = Ph2P(CH2)nPPh2 (n = 2, 3,
4)] with the phosphonic acid in refluxing dichloromethane in the
presence of silver(I) oxide as a base and halide-abstracting reagent
[7]. The same methodology has been extended to analogous
l
PO3)3(py)4] [3] whilst the same reaction in the absence of
pyridine yielded nonanuclear [Fe9O4(tBuCO2)13(CamPO3)3] [4]. An
even larger dodecanuclear aggregate [Fe12
(PhCO2)14)(CamPO3H)6] was prepared by reaction of [Fe3(
(
l
2-O)4(
l
l
3-O)4
3-O)
⇑
Corresponding author. Fax: +64 7 838 4219.
E-mail address: w.henderson@waikato.ac.nz (W. Henderson).
1
Present address: Department of Chemistry, Clark University, Worcester, MA
01610-1477, USA.
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.05.013

M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
229
Table 1
ferrocenyl–phosphonate
complexes
[Pt{O3P(CH2)nFc}(PPh3)2]
Bond lengths (Å) and selected bond angles (°) for 8-camphanylphosphonic acid 1.
Estimated standard deviations are in parentheses.
(Fc = Fe(C5H4)(C5H5); n = 0, 1, 2) and Fe{C5H4PO3Pt(PPh3)2}2 [8]
and to the fluorinated derivatives [Pt(O3PCH2CH2Rf)(PPh3)2]
(Rf = n-C4F9 or n-C6F13) and [Pt(O3PC6H4R)(PPh3)2] (R = p-F, p-CF3
or p-n-C6F13) [9]. More widely, platinum(II) complexes with phos-
phonate ligands have attracted some interest for their biological
activity [10,11], though there are very few studies in contrast to
related complexes containing phosphate ligands, because of the
significance of the latter to the interactions of platinum-based anti-
cancer drugs with DNA [12–15].
P(1)–O(2)
P(1)–O(3)
C(1)–C(6)
C(1)–C(2)
C(2)–C(3)
C(3)–C(10)
C(4)–C(5)
C(5)–C(6)
1.511(5)
1.548(6)
P(1)–O(1)
P(1)–C(8)
C(1)–C(7)
C(2)–C(8)
C(3)–C(4)
C(3)–C(9)
C(4)–C(7)
1.534(6)
1.762(8)
1.521(11)
1.555(11)
1.576(11)
1.522(12)
1.529(12)
1.538(12)
1.521(12)
1.532(10)
1.520(12)
1.541(11)
1.547(12)
O(1)–P(1)–C(8)
O(3)–P(1)–C(8)
O(1)–P(1)–O(3)
106.4(3)
104.0(4)
110.8(3)
O(2)–P(1)–C(8)
O(1)–P(1)–O(2)
O(2)–P(1)–O(3)
112.2(3)
111.2(3)
111.9(3)
2. Results and discussion
2.1. X-ray structure of 8-camphanylphosphonic acid, CamP(O)(OH)2
(1)
The structure of 1 is comprised of hydrogen-bonded hexamers,
packed about the threefold axis. Three molecules are linked in a
ring by O(3)–H(03)ꢀ ꢀ ꢀO(2) interactions between adjacent
molecules, then these trimers are linked together by six
O(1)–H(01)ꢀ ꢀ ꢀO(2) interactions to form the hexameric unit which
contains a central cavity formed by the P@O and P–OH groups,
surrounded by the camphanyl groups (Fig. 2). The CamP(O)(OH)2
hexamers then stack upon each other to give a discontinuous
hydrophilic central core surrounded by the bulky hydrophobic
camphanyl groups, as shown in Fig. 3.
The camphanylphosphonic acid CamP(O)(OH)2 used in this
study was prepared by oxidation of the corresponding phosphinic
acid CamPH(O)(OH), itself prepared in high yield by the radical-
catalysed addition of hypophosphorous acid to camphene [2].
During attempts to prepare a strontium salt of CamP(O)(OH)2 by
reaction of strontium nitrate with CamP(O)(OH)2 and urea in
methanol/water, colourless hexagonal crystals of CamP(O)(OH)2
were obtained. In light of the interest in metal–phosphonate deriv-
atives of this compound, the X-ray structure of CamP(O)(OH)2 was
determined to investigate how the bulky hydrophobic camphanyl
groups might influence the hydrogen bond-directed structure.
The molecular structure together with the atom numbering
scheme are shown in Fig. 1, and selected bond lengths and angles
are given in Table 1. The P–CH2 bond distance in 1 [1.762(8) Å] is
similar, but slightly shorter, than other methylene–phosphonic
acids reported in the literature, such as FcCH2P(O)(OH)2
[1.805(1) Å] [16], (HO)2P(O)CH2CH2P(O)(OH)2 [1.7858(5) Å] [17],
and Me3SiCH2CH2P(O)(OH)2 [1.787(2) Å] [18]. The P@O double
bond length of 1 [1.511(5) Å] is comparable to those in the same
phosphonic acids, which are 1.513(1), 1.5016(4), and 1.505(1) Å,
respectively.
Structural studies on other phosphonic acids with organic sub-
stituents of modest steric bulk, such as FcCH2P(O)(OH)2 [16], Me3-
SiCH2CH2P(O)(OH)2 [18], p-CH3C6H4C(O)CH2CH2PO3H2 [19],
o-FC6H4CH2PO3H2 [20], and 2,4,6-iPr3C6H2PO3H2 [21] indicate that
a layered structure (containing RPO3H2ꢀ ꢀ ꢀH2O3PR) is a common
structural feature. However, for phosphonic acids containing bulky
groups, a small number of cage structures have been reported.
Thus, tBuPO3H2, when crystallised from CDCl3, has (like CamPO3H2
1)
a
hexameric cage structure [22], whilst 4-tBu-2,6-Mes2-
C6H2PO3H2 (Mes = 2,4,6-trimethylphenyl) crystallises as a mono-
hydrate in the form of a hydrogen-bonded tetramer [23]. In these
structures of bulky phosphonic acids, and also in the structure of
the calcium salt of CamPH(O)(OH) [6], there is a hydrophilic core
Fig. 1. Molecular structure of 8-camphanylphosphonic acid 1, showing the atom numbering scheme. Thermal ellipsoids are shown at the 50% probability level.

230
M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
Fig. 2. The hydrogen-bonded hexameric core of 8-camphanylphosphonic acid 1, showing the presence of a central cavity and a hydrophobic camphanyl exterior.
surrounded by a hydrophobic organic sheath, which maximises
separation of the hydrophilic inorganic part from the hydrophobic
organic part. This suggests that further studies into the chemistry
of metal–phosphonate derivatives of camphene-derived organo-
phosphorus acids are worthy of investigation for the possibility
of generating interesting structures.
tone. Synthesised in moderate yield, the crystalline platinacycles
2, 3, and 4 are stable both in air and in organic solvents such as
dichloromethane and methanol.
The attempted synthesis of the analogous 1,5-cyclo-octadiene
(cod) complex [Pt(O3PCam)(cod)] was unsuccessful; the reaction
of equimolar amounts of 1 and [PtCl2(cod)] with excess Ag2O in
refluxing dichloromethane afforded a large number of products
from 31P NMR spectroscopy, and no further investigations were
carried out.
2.2. Synthesis of platinum(II) phosphine complexes derived from 1
The general synthetic route to the 8-camphanylphosphonic
acid-derived Pt(II) complexes 2, 3, and 4 involves the reaction of
an excess of silver(I) oxide with equimolar quantities of the plati-
num dichloride complexes cis-[PtCl2L2] [L = PPh3, PPhMe2;
L2 = dppe (1,2-bis(diphenylphosphino)ethane)] and phosphonic
acid 1. The reaction proceeds in dichloromethane at reflux, with
complete reaction (as determined by 31P NMR) typically occurring
within a 36 h period. Upon completion, the unreacted silver oxide
and silver chloride (a byproduct of the reaction) are simply re-
moved by filtration.
2.3. NMR spectroscopic characterisation
The 31P{1H} NMR data of the platinum-phosphonate complexes
2 and 4, Table 2, are more complicated than the analogous methyl-
and phenyl-phosphonate complexes [Pt(O3PR)L2] (R = Me or Ph;
L = PPh3 or L2 = dppe) that have been previously reported [7]. In
the methyl- and phenyl-phosphonates the phosphine phosphorus
1
atoms are equivalent, giving a single peak with JPtP coupling. In
contrast, the donor phosphorus atoms (Px and Py, refer Table 2) of
the camphanyl analogues 2 and 4 are inequivalent, coupling to each
other to produce two doublets in the 31P{1H} NMR spectra. These
1
3
O
doublets are further spilt by JPtP and JPP coupling. The inequiva-
lence of the phosphine phosphorus atoms of 2 and 4 is also reflected
in the difference in the one-bond Pt–Px and Pt–Py coupling con-
stants which, for example, are 3732 and 3843 Hz for the PPh3 com-
plex 2. The inequivalence of the phosphine ligand environments of
2 and 4 is proposed to arise from the steric restriction produced by
replacement of a less bulky methyl or phenyl group by the sterically
bulky camphanyl group. This steric restriction prevents the free
rotation of the camphanyl group, which results in the phosphine li-
gands becoming inequivalent. This is supported by NOE studies of
complex 2, as well as theoretical studies (vide infra).
O
P
L
Pt
O
L
2; L = PPh3
3; L = PPhMe2
4; L2 = Ph2PCH2CH2PPh2 (dppe)
Platinacycles 2 and 4 are readily purified by recrystallisation
from chloroform/petroleum spirit whilst the purification of plati-
nacycle 3 was achieved by washing the crude product with ace-
In contrast, the 31P{1H} NMR spectrum of the PPhMe2 complex 3
shows a singlet for the phosphine ligands (with 3JPP coupling to the

M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
231
Fig. 3. Space-filling representation showing the unit cell packing of the hexameric hydrogen-bonded assemblies of CamP(O)(OH)2 1, with hydrophilic channels running
parallel to the crystallographic c-axis.
Table 2
31P{1H} NMR data for the platinum-phosphonate complexes 2, 3, and 4, together with the atom labelling scheme.
Px
d
Py
d
Pz
d
1JPx–Pt (Hz)
1JPy–Pt (Hz)
2JPx–Py (Hz)
2JPz–Pt (Hz)
3JPx/Py–Pz (Hz)
2
3
4
5.4 dd
7.5 dd
55.3 t
53.2 t
58.4 t
3732
3654
3730
3843
3654
3701
26
0
20
117
100
102
7
4
7
ꢁ20.9 d
ꢁ20.9 d
30.5 dd
31.0 dd
phosphonate phosphorus) indicating that even though the bulkyl
camphanyl group is present, the donor phosphine environments
are equivalent. In this case, it is proposed that the decreased steric
bulk of the PPhMe2 ligand permits free rotation to occur, making
the phosphine ligands equivalent. Both a bulky group on the phos-
phonate ligand (camphanyl) and bulky phosphine ligands are re-
quired to produce the steric interactions that result in
inequivalence of the phosphine donors.
not observed. The simplification of this doublet of doublet pattern
to an observed triplet-like pattern occurs as the result of the Pz–Px
and Pz–Py couplings being approximately equal. [Pt(O3PPh)(PPh3)2]
is reported to have a 2JPtP coupling constant of 27 Hz [7]; this is not
consistent with other JPtP coupling constants in this type of com-
plex and is therefore assumed to be an error.
2
One- and two-dimensional NMR studies were carried out to
fully assign the 1H and 13C NMR spectra of complex 2, discussed
below. The camphanyl regions of the 1H and 13C{1H} NMR spectra
of 3 and 4 were similar to those of 2, and were assigned by compar-
ison. Tables 3 and 4 summarise the 1H and 13C{1H} NMR spectra of
the platinum complexes, and Scheme 1 gives the atom labelling
scheme.
1
The magnitudes of the JPtP coupling constants, which lie be-
tween 3654 and 3843 Hz, are comparable with those of the
methyl- and phenyl-phosphonate analogues [7], and are consistent
with phosphine ligands trans to low trans-influence oxygen donor
1
groups [24]. Thus, [Pt(O3PMe)(PPh3)2] has JPtP 3848 Hz, and the
phenyl-phosphonate analogue [Pt(O3PPh)(PPh3)2] has 1JPtP
3877 Hz.
The 13C{1H} NMR spectrum of the camphanyl region of 2 com-
prised ten resonances, consisting of two methyl, three methine,
four methylene, and a quarternary resonance. The methylene
signal (d 27.9) which exhibited a large one-bond carbon to phos-
phorus coupling (J 121.9 Hz) is assigned to C8. The other three
The phosphonate phosphorus Pz appears as a distinctive triplet-
like pattern between d 53.2 (3) and 58.4 (4). It is worth noting that
the expected multiplicity for Pz, a doublet of doublet pattern, was

232
M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
Table 3
1H NMR dataa for the platinum-phosphonate complexes 2, 3, and 4, together with data for camphanylphosphonic acid 1.
Compound
Solvent
CamP(O)(OH)2 1b
CD3OD
[Pt(O3PCam)(PPh3)2] 2
CDCl3
[Pt(O3PCam)(PPhMe2)2] 3
CDCl3
[Pt(O3PCam)(dppe)] 4
CDCl3
H4
H3
H1
2.38 (br, s)
1.82 (m)
1.77 (br, s)
1.72 (mc)
1.65 (m)
1.66 (m)
1.60 (m)
1.32 (m)
1.20 (dt, 2J 9.7, 3J 1.7)
1.44 (m)
1.34 (m)
0.98 (s)
2.58 (br, s)
1.96 (br, m)
1.69 (br, s)
1.60 (d, 2J 12.2)
1.54 (br, m)
1.68 (br, sc)
1.47 (s)
2.75 (br, s)
2.01 (br, m)
1.74 (br, s)
1.61 (d, 2J 11.7)
1.59 (br, m)
1.67 (d, 2J 13.0)
1.56 (s)
2.49 (br, s)
1.84 (br, m)
1.56 (br, s)
1.66 (br, sc)
1.61 (br, m)
1.35 (d, 2J 10.6)
1.39 (s)
0
00
H8 /8
00
H7
H6
H6
H7
H5
H5
Me0
Me00
Ph
00
0
1.10 (s)
1.21 (s)
1.04 (s)
1.05 (d, 2J 9.8)
1.26 (m)
1.15 (d, 2J 11.1)
1.49 (br, m)
1.22 (br, m)
1.01 (s)
0.84 (d, 2J 10.6)
1.28 (br, m)
0.87 (br, m)
0.84 (s)
0
00
0
0.83 (br, m)
0.95 (s)
0.71 (s)
0.83 (s)
–
0.81 (s)
7.37–7.28 (m)
0.70 (s)
7.95–7.20 (m)
7.80–7.30 (m)
a
b
c
Refer Scheme 1 for atom numbering scheme; coupling constants J in Hz.
From Ref. [2].
Multiplicity not discernible.
Table 4
13C{1H} NMR dataa for the platinum-phosphonate complexes 2, 3, and 4, together with data for camphanylphosphonic acid 1.
Compound
Solvent
CamP(O)(OH)2 1b
CD3OD
[Pt(O3PCam)(PPh3)2] 2
CDCl3
[Pt(O3PCam)(PPhMe2)2] 3
CDCl3
[Pt(O3PCam)(dppe)] 4
CDCl3
C5
C9 (Me00)
21.0
22.3
20.1
22.0
20.5
22.2
20.2
22.1
C6
C8
25.6
24.8
24.8
24.7
25.2 (1JPC 138.3)
32.3
27.9 (1JPC 121.9)
32.4
28.6 (1JPC 122.0)
32.3
28.0 (1JPC 121.3)
32.2
C10 (Me0)
C7
C2
C4
C3
C1
37.8
37.1
37.0
37.1
38.3 (3JPC 14.1)
43.5 (3JPC 3.6)
46.0 (2JPC 3.9)
50.1 (4JPC 3.9)
37.5 (3JPC 13.1)
42.5 (3JPC 3.3)
46.1 (2JPC 3.4)
49.0c
37.6 (3JPC 13.0)
42.8 (3JPC 3.2)
46.4 (2JPC 3.1)
49.0c
37.5 (3JPC 13.9)
42.0 (3JPC 3.0)
46.2 (2JPC 3.2)
48.8c
a
b
c
Refer Scheme 1 for atom numbering scheme. Excluding aromatic resonances between ca. d 128 and 132, and alkyl groups of PPhMe2 and dppe. Coupling constants J in Hz.
From Ref. [2].
4JPC coupling not discernible.
H7''
H4
H7'
In the 13C–1H correlated NMR spectrum of 2 the crosspeaks
relating to the camphanyl carbon signals identified all proton res-
onances relating to the camphanyl moiety. Identification of many
of the resonances in the 1H NMR spectrum was possible by exam-
ination of H4 crosspeaks in the COSY45 spectrum. Consequently,
(b)
(a)
C7
C1
H3
Me'
H5'
C4
C5
C3
C8
H6'
C10
0
00
resonances belonging to H4 (d 2.58), H3 (d 1.96), H8 /8 (d 1.60,
C6
C2
C9
H5''
H1
00
00
0
1.54), H7 (d 1.68), H5 (d 1.26), and H7 (d 1.05) were readily iden-
tified. Remaining structural ambiguities were resolved by NOE dif-
ference spectroscopy. Particularly diagnostic are the NOE’s
H8''
P
P
Me''
H6''
H8'
observed from Me0 to H7 and to H3 [but not significantly from
00
Scheme 1. NMR atom labelling schemes (a) hydrogen atoms; (b) carbon atoms.
Me0 to H8 /8 ] indicating that H7 and H3 are on the same side of
0
00
00
the molecule, confirming the endo disposition of the –CH2PO3
0
methylene signals (d 20.1, 24.8 and 37.1) belonging to C5, C6 and
C7, respectively, are assigned by comparison with those chemical
shifts obtained for 8-camphanylphosphonic acid 1 (d 21.0, 25.6,
and 37.8, respectively). The methine signal (d 49.0), which does
group. Other NOEs of significance are those of H4 to H5 (but not
00
0
0
00
00
0
to H5 ), H7 to H6 (but not H6 ) and H3 to H7 (but not H7 ). The
remainder of the NOE data, along with the COSY spectrum, gave
the complete spectral assignment.
4
not couple to phosphorus, is assigned to C1 as JPC coupling is not
Interestingly, significant NOEs between H3 or H4 of the campha-
nyl and the ortho-phenyl protons (d 7.49–7.37) of the triphenyl-
phosphine ligand of 2 were observed. Although at first glance
these NOEs seem unlikely, construction of a molecular model of
2 reveals the close proximity of the triphenylphosphine ligand pro-
tons to the camphanyl protons H3 and H4, and therefore the possi-
bility of an enhancement. Further NOE studies of the three phenyl
regions (d 7.49–7.37, 7.36–7.28, and 7.25–7.13 signals present in
ratios of 2:1:2) indicate that the phenyl protons at d 7.49 to 7.37
are the ortho protons. That is, the irradiation of the meta protons
(d 7.25–7.13) results in an enhancement of both the ortho (d
observed. The other two methine signals (d 46.1 and 42.5) belong-
ing to C3 and C4, respectively, exhibiting two and three bond P–C
coupling (J 3.4 Hz and 3.3 Hz, respectively), are assigned by com-
parison with those chemical shifts obtained for 1 (d 46.0, d, J 3.9
and d 43.5, J 3.6, respectively). The assignment of quaternary car-
bon C2 (d 37.5) which is coupled to phosphorus (J 13.1 Hz) is con-
firmed by its absence in the DEPT experiment. Due to the
complexity of the aryl region of 2 the signals (d 131.5–124.4)
belonging to the phenyl rings of the triphenylphosphines were
not assigned.

M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
233
Fig. 4. Molecular structure of [Pt(O3PCam)(PPh3)2] 2ꢀ2CHCl3, showing the atom numbering scheme; thermal ellipsoids are at the 50% probability level, chloroform solvate
molecules are not shown, and ipso carbon atoms of the PPh3 ligands are shown as small circles.
slightly distorted from a square–planar geometry, with an angle
of 9.0° between the P(2)–Pt(1)–P(3) and O(1)–Pt(1)–O(2) planes.
A similar angle of 9.1° was observed in [Pt(O3PCH2Fc)(PPh3)2] [8]
(CSD refcode ODASUH), but the other six crystallographically char-
acterised examples of platinum(II) phosphonates are more regular,
for example [Pt(O3PPh)(PPh3)2] (CSD refcode SOYMIC), where the
corresponding angle is only 2.2° [7]. Other bond parameters for 2
are ordinary, and remarkably constant for all 8 known examples
of structurally characterised platinum(II) phosphonates, with P–O
1.56–1.58 Å, P@O 1.475–1.496 Å, O–P–O 100–102°, and O–Pt–O
71–72°.
It is noteworthy that the bulky camphanyl group is directed into
a ‘pocket’ formed by the two triphenylphosphine ligands and the
platinum atom. Rotation about the P–CH2 bond would orient the
camphanyl group away from the platinum, but at the expense of
eclipsing the CH2 C–H bonds with the P–O bonds, and the campha-
nyl PCH2–C bond with the P@O bond, which would be unfavour-
able. Instead, the complex adopts the observed staggered
conformation. Because of the asymmetric nature of the camphanyl
group, the two PPh3 ligands are inequivalent; restricted fluxional-
ity of the system maintains this inequivalence in solution, as ob-
served in the 31P{1H} NMR spectrum of the complex. It is worth
noting that [Pt(O3PCH2Fc)(PPh3)2] [8] has a similar arrangement
of the CH2Fc group, which also points into the Pt(PPh3)2 pocket,
but because of a plane of symmetry in this system, the PPh3 groups
remain equivalent.
Table 5
Selected bond lengths (Å) and selected bond angles (°) for [Pt(O3PCam)(PPh3)2]
2ꢀ2CHCl3. Estimated standard deviations are in parentheses.
Pt(1)–O(1)
Pt(1)–P(3)
Pt(1)ꢀ ꢀ ꢀP(1)
P(1)–O(2)
P(1)–C(1)
2.084(2)
Pt(1)–O(2)
Pt(1)–P(2)
P(1)–O(3)
P(1)–O(1)
2.088(2)
2.2423(12)
1.490(3)
1.580(3)
2.2316(10)
2.6825(11)
1.575(3)
1.811(4)
O(1)–Pt(1)–O(2)
O(2)–Pt(1)–P(3)
O(2)–Pt(1)–P(2)
O(3)–P(1)–O(2)
O(2)–P(1)–O(1)
O(2)–P(1)–C(1)
71.58(9)
98.80(7)
163.52(7)
115.20(14)
101.32(13)
107.70(16)
O(1)–Pt(1)–P(3)
O(1)–Pt(1)–P(2)
P(3)–Pt(1)–P(2)
O(3)–P(1)–O(1)
O(3)–P(1)–C(1)
O(1)–P(1)–C(1)
168.30(7)
93.27(7)
96.96(4)
114.27(14)
108.39(17)
109.62(16)
7.49–7.37) and para (d 7.36–7.28) proton resonances whereas irra-
diation of the ortho proton (d 7.49–7.37) gives an enhanced meta (d
7.36–7.28) proton signal along with an enhancement of the cam-
phanyl H4 signal.
2.4. X-ray structure of [Pt(O3PCam)(PPh3)2] 2ꢀ2CHCl3
In order to determine if there are any structural features that
might render the PPh3 groups of complex 2 inequivalent (vide su-
pra), an X-ray structure determination was carried out. Crystals
of the di-chloroform solvate were obtained from CHCl3–hexane.
The structure of the complex is shown in Fig. 4, with the atom
numbering scheme. Selected bond lengths and angles are given
in Table 5.
2.5. Theoretical studies
The complex crystallises as the di-chloroform solvate, both of
which form H-bonds to the P@O oxygen atom. The camphanyl
group showed some fluxionality with elongated ellipsoids [espe-
cially C(9) and C(10)], as shown in Fig. 4. The platinum centre is
In order to quantitatively rationalise the different NMR spectro-
scopic behaviour of the PPh3 and PPhMe2 complexes theoretical
calculations were carried out. Fig. 5 shows the density functional
theory potential energy curves for rotation of the camphanyl group

234
M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
60
50
40
30
20
10
0
zero filled to 512 increments in the F1 dimension and 32 scans
per increment. After transformation the data matrix was symmetr-
ised. 13C–1H correlation spectra were acquired with 1 K increments
in F2 and 128 increments zero filled to 1 K increments in F1 with
32 or 128 scans per increment. 31P{1H} NMR spectra were recorded
on a JEOL FX90Q spectrometer (36.23 MHz) in CHCl3 solution.
Chemical shifts are externally referenced to 85% H3PO4 (d 0.0)
and a glass capillary used to provide a lock signal.
Elemental microanalyses were carried out by the Campbell
Microanalytical Laboratory, University of Otago, Dunedin, NZ.
Melting points were recorded on a Reichert hot-stage apparatus
and are uncorrected. ESI mass spectra were recorded in methanol
solution on a Bruker MicrOTOF instrument that was calibrated
using a solution of sodium formate; a capillary exit voltage of
120 V was used).
(a)
-180 -150 -120 -90 -60 -30
0
30
60
90 120 150 180
O-P-C-C torsional angle / degrees
60
50
40
30
20
10
0
3.1. Synthesis of [Pt(O3PCam)(PPh3)2] (2)
(b)
8-Camphanylphosphonic acid
1 (0.06 g, 0.27 mmol), cis-
[PtCl2(PPh3)2] (0.21 g, 0.27 mmol), and an excess of silver(I) oxide
(0.17 g, 0.73 mmol) were added in succession to dichloromethane
(30 mL). After refluxing and stirring for 36 h the insoluble silver
salts were removed by filtration and the yellow solution evapo-
rated to dryness under reduced pressure. Recrystallisation of the
yellow oil from chloroform/petroleum spirits gave 2 as a colourless
needle-like crystalline solid that was dried under vacuum (0.15 g,
60%), mp 224–225 °C. Anal. Calc. for C46H47PtP3O3: C, 59.04; H,
5.06. Found: C, 58.18; H, 5.12%. C46H47PtP3O3 requires C, 59.04;
H, 5.06%. ESI-MS (positive ion); [M+H]+ m/z 936.2933 (calculated
for C46H48O3P3Pt m/z 936.2463; [M+Na]+ m/z 958.2741 (calculated
for C46H47NaO3P3Pt m/z 958.2741).
-180 -150 -120 -90 -60 -30
0
30
60
90 120 150 180
O-P-C-C torsional angle / degrees
Fig. 5. B3LYP/6-311+G(d,p) potential energy curves for rotation of the camphanyl
group about the O–P–C–C torsional angle in (a) [Pt(O3PCam)(PPh3)2] 2 and (b)
[Pt(O3PCam)(PPhMe2)2] 3.
3.2. Synthesis of [Pt(O3PCam)(PPhMe2)2] (3)
in complexes 2 and 3. Both compounds exhibit three distinct max-
ima and three distinct minima corresponding to the hydrogen
atoms of the CH2 group being either eclipsed or staggered relative
to the adjacent P@O and P–O groups. We find that the energetic
barrier for rotation of the camphanyl group in 3 is low, with the
three maxima just 9–13 kJ molꢁ1 higher than the global minimum.
Additional steric interactions due to the bulky PPh3 ligands in 2
greatly increase the energetic barrier for rotation of the camphanyl
group, to 55 kJ molꢁ1. This much higher energetic barrier will
greatly reduce the rate at which the camphanyl group rotates in
2 compared to 3 and thus supports the NMR and X-ray crystallo-
graphic observations.
Complex 3 was prepared by the method for 2, starting from cis-
[PtCl2(PPhMe2)2]. Purification of the crude reaction mixture was
achieved by removing the solvent under vacuum and washing
the resulting yellow solid with acetone (0.5 mL) to remove impuri-
ties, to give a white crystalline solid of 3 (yield 67%). Mp 233–
234 °C. Anal. Calc. for C26H39PtP3O3: C, 45.40; H, 5.72. Found: C,
45.35; H, 5.97%.
3.3. Synthesis of [Pt(O3PCam)(dppe)] (4)
Complex 4 was prepared by the method described for 2, starting
from [PtCl2(dppe)]. Purification of 4 was achieved by the recrystal-
lisation of the crude reaction mixture, a yellow oil, from chloro-
form/petroleum spirit at room temperature to give colourless
needle-like crystals of 4 in 70% yield. Mp >140 °C (decomp.).
3. Experimental
Camphanylphosphonic acid 1 was prepared as described previ-
ously [2]. Silver(I) oxide was used as supplied from BDH. The com-
plexes cis-[PtCl2(PPh3)2], cis-[PtCl2(PPhMe2)2], and [PtCl2(dppe)]
were prepared by reaction of [PtCl2(cod)] [25] (cod = 1,5-cyclo-oct-
adiene) with the stoichiometric amount of the phosphine in dichlo-
romethane, followed by precipitation of the product with
petroleum spirits (bp 40–60 °C) [26,27].
3.4. Theoretical calculations
The geometries of complexes 2 and 3 were optimised using the
B3LYP density functional method with the 6-311+G(d,p) basis set
for the H, C, O, and P atoms and the cc-pVTZ basis set and effective
core potential for the Pt atoms. The initial geometry for optimisa-
tion of 2 was taken from the corresponding X-ray crystal structure.
The crystal structure of 3 has not yet been determined, hence the
initial geometry was inferred using the orientation of the campha-
nyl group in 2 and the Pt(PMe2Ph)2 framework from other compa-
rable crystal structures of Pt(PMe2Ph)2 complexes [28–30]. The
potential energy curve for rotation of the camphanyl group in 2
and 3 (Fig. 5) was calculated by displacing the O–P–C–C dihedral
angle from ꢁ180° to +180° in 10° increments with all other
geometric parameters fixed at their optimised values. All density
1H (300.13 MHz) and 13C{1H} (75.47 MHz) NMR spectra were
recorded on a Bruker AC300P spectrometer in CDCl3 (unless other-
wise specified), with chemical shifts relative to CD(H)Cl3 (d 1H 7.26
and 13C 77.06). Scheme 1 shows the atom numbering scheme used
in NMR assignments. NOE difference spectra were measured on a
solution that had not been degassed and were acquired with an
irradiation time of 3 s, typically achieving 50–60% saturation of
the irradiated multiplet. Each multiplet was recorded in cycles of
16 scans for long term averaging. COSY45 NMR spectra were ac-
quired with 1K increments in the F2 dimension, 256 increments

M.T. Leach et al. / Inorganica Chimica Acta 375 (2011) 228–235
235
functional theory calculations were completed using GAUSSIAN 09,
Revision A.01 [31].
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.05.013.
3.5. X-ray crystal structure of 8-camphanylphosphonic acid (1)
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3.6. X-ray crystal structure of [Pt(O3PCam)(PPh3)2] 2ꢀ2CHCl3
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l(Mo Ka
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D
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Acknowledgements
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The authors thank the University of Waikato for financial sup-
port of this work, and Tania Groutso (University of Auckland) for
the collection of the data set of 2. Robert Appleby is thanked for
preparation of camphanylphosphonic acid.
Appendix A. Supplementary material
CCDC 787904 and 787903 for compounds (1) and (2), respec-
tively, contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.