Coordination chemistry of 2,2-bis(diphenylphosphinomethyl)propionic acid

Article abstract of DOI:10.1016/j.ica.2007.08.032

The coordination chemistry of the diphosphine ligands 2,2-bis(diphenylphosphinomethyl)propionic acid, 1, and 2,2-bis(diphenylphosphinomethyl)propionate, 2, with copper(I), silver(I), gold(I), palladium(II) and platinum(II) is described. Structure determinations show that the carboxylic acid group in 1 can hydrogen bond to solvent molecules, to anions or to the carboxylic acid group of a neighboring complex, as in the complexes [MCl₂(1)] · 2DMSO (M = Pd or Pt), [Pt(1)₂](OTf)₂ or [Pd(NCMe)₂(1)](OTf)₂, respectively. The tridentate diphosphine-carboxylate ligand 2 forms oligomeric or polymeric complexes, such as [{Ag(2)}_n], [{PdCl(2)}_n] or [{PtMe(2)}_n].

Full text of DOI:10.1016/j.ica.2007.08.032

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 3301–3308
www.elsevier.com/locate/ica
Coordination chemistry of 2,2-bis(diphenylphosphinomethyl)
propionic acid
*
Chang-Qiu Zhao, Michael C. Jennings, Richard J. Puddephatt
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
Received 16 July 2007; accepted 18 August 2007
Available online 5 September 2007
Dedicated to Professor Bob Angelici in recognition of his distinguished contributions to inorganic chemistry.
Abstract
The coordination chemistry of the diphosphine ligands 2,2-bis(diphenylphosphinomethyl)propionic acid, 1, and 2,2-bis(diphenylphos-
phinomethyl)propionate, 2, with copper(I), silver(I), gold(I), palladium(II) and platinum(II) is described. Structure determinations show
that the carboxylic acid group in 1 can hydrogen bond to solvent molecules, to anions or to the carboxylic acid group of a neighboring
complex, as in the complexes [MCl2(1)] Æ 2DMSO (M = Pd or Pt), [Pt(1)2](OTf)2 or [Pd(NCMe)2(1)](OTf)2, respectively. The tridentate
diphosphine–carboxylate ligand 2 forms oligomeric or polymeric complexes, such as [{Ag(2)}n], [{PdCl(2)}n] or [{PtMe(2)}n].
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Diphosphine; Carboxylic acid; Palladium; Platinum; Copper; Silver; Gold
1. Introduction
through hydrogen bonding or it may be deprotonated to
form a hard, more labile carboxylate ligand which can par-
ticipate in self-assembly through dynamic coordination
chemistry [13–26]. The early research on mixed phos-
phine–carboxylic acid complexes used the simple deriva-
tives of diphenylphosphinobenzoic acid, diphenylphos-
phinoacetic acid or similar compounds, but there has been
recent interest in the design of more complex derivatives,
including carboxylic acid derivatives of diphosphine ligands
(Chart 1) [13–15]. This paper reports the coordination
chemistry of the new ligand 2,2-bis(diphenylphosphinom-
ethyl)propionic acid (1, Chart 1) with some Group 10 and
11 transition metal ions.
Tertiary phosphines, R3P, are strongly basic and are
excellent ligands for late transition metals [1–5], so many
derivatives have been prepared for use in transition metal
catalysts or metal extraction and associated processes
[6,7]. Bidentate phosphine ligands have been used in the
self-assembly of complex structures in coordination chemis-
try, either by acting as anchoring chelate ligands [8,9] or as
bridging ligands [10], and there is increasing interest in the
use of hybrid ligands containing both a phosphine and a
more weakly binding hard donor ligand in the synthesis
of macrocycles, polymers or network materials [11–22]. In
this regard, ligands containing both a tertiary phosphine
and a carboxylic acid group have great potential for build-
ing complex structures[13–15,17–21]. Thus the phosphine
can form a strong, more inert coordinate bond while the
carboxylic acid group can participate in self-assembly
2. Experimental
2.1. Synthesis and characterization by spectroscopic methods
NMR spectra were recorded using a Varian Mercury
400 or Inova 400 MHz NMR spectrometer. ESI-MS were
recorded using a Micromass LCT spectrometer in MeCN
solution.
*
Corresponding author.
E-mail address: pudd@uwo.ca (R.J. Puddephatt).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.08.032

3302
C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
(CDCl3), d(1H) = 0.86 [s, 3H, Me]; 2.39 [m, 2H,
O
O
PPh2
2J(HH) = 14 Hz, 2J(PH) = 5 Hz, CH2]; 2.47 [m, 2H,
2J(HH) = 14 Hz, 2J(PH) = 3 Hz, CH2]; 6.8–7.4 [m, 20H,
Ph]; d(31P) = À20.63 [s, P].
PPh2
HO
HO
PPh2
2.3.1. [CuI(1)] (3)
PPh2
PPh2
The ligand 1 (47 mg, 0.1 mmol) was added to CuI
(19 mg, 0.1 mmol) in MeCN (20 mL). A colorless clear
solution formed initially, then the product precipitated
from solution as a pale yellow solid, which was filtered,
washed with MeCN and ether, and dried under vacuum.
Yield: 94%. Anal. Calc. for C29H28CuIO2P2: C, 52.70; H,
4.27. Found: C, 52.26; H, 4.03%. Crystals were obtained
from hot MeOH/MeCN solution but were not suitable
for X-ray structure determination.
O
N
HO
PPh2
HO
O
O
1
OH
Chart 1. Some phosphine and diphosphine ligands with carboxylic acid
substituents.
2.3.2. [AuCl(1)] (4)
The ligand 1 (47 mg, 0.1 mmol) was added to a solution
of [AuCl(SMe2)] (29.5 mg, 0.1 mmol) in CH2Cl2 (3 mL) to
give a colorless solution. The solution was stirred for 1 h.,
then ether (10 mL) was added to precipitate the product as
a white solid, which was separated by filtration, washed
with ether, and dried under vacuum. Yield: 88%. Anal.
Calc. for C29H28AuClO2P2: C, 49.55; H, 4.01. Found: C,
49.54; H, 3.89%. NMR (CDCl3), d(1H) = 0.95 [br s, 3H,
Me]; 2.3–2.5 [br m, 4H, CH2]; 6.5–7.3 [m, 20H, Ph];
d(31P) = 26.4 [br s, P].
2.2. Bis(diphenylphosphinomethyl)propionic acid, 1
To an ice-cooled solution of diphenylphosphine (4.6 mL,
26.5 mmol) in dry THF (50 ml), was added dropwise a solu-
tion of n-BuLi (2.0 M solution in cyclohexane, 17.1 mL,
25.6 mmol). The red solution was stirred at 0 ꢁC for 1 h.
To this solution, was added dropwise methyl 2,2-bis(chloro-
methyl)propionate (2.45 g, 13.24 mmol) was added drop-
wise. The mixture was stirred at 0 ꢁC for 8 h, then
warmed to room temperature. Water (20 mL) was added
to the mixture, then the solvent THF was removed in vacuo.
The mixture was extracted with dichloromethane
(3 · 20 mL), the organic solution was washed with water
(3 · 20 mL), and dried over MgSO4. Evaporation of the sol-
vent yielded a yellow oil, which was added to a solution of
NaOH (4 g), EtOH (30 mL) and water (30 mL), and the
mixture was heated under reflux for 2 h. After cooling,
the mixture was acidified with aqueous HCl (2 M) until
pH 6. The mixture was then extracted with CH2Cl2, and
the extracts were washed with water, and dried over
MgSO4. The solvent was removed under vacuum, and the
residue was recrystallized from CH2Cl2–MeOH to afford
the product as white crystals. Yield 51%. Anal. Calc. for
C29H28O2P2: C, 74.03; H, 6.00. Found: C, 73.68; H,
2.3.3. [{Ag(2)}n] (5)
A mixture of ligand 1 (47 mg, 0.1 mmol) and Ag2O
(14 mg, 0.06 mmol) in MeCN (5 mL) and MeOH (3 mL)
was stirred for 15 h. The solution was filtered to remove
insoluble material, the volume of solvent was reduced to
ca. 1 mL under vacuum, and ether (10 mL) was added to
precipitate the product as a white solid. Yield: 83%. Anal.
Calc. for C29H27AgO2P2: C, 60.33; H, 4.71. Found: C,
59.84; H, 4.32%. NMR (CDCl3): d(1H) = 0.9 [br s, 3H,
Me]; 2.2–2.5 [br m, 4H, CH2]; 6.6–7.4 [m, 20H, Ph];
d(31P) = 25 [br, P].
2.3.4. [{Au(2)}n] (6)
The salt Li(2) (47.7 mg, 0.1 mmol) was added to a solu-
tion of [AuCl(SMe2)] (29.5 mg, 0.1 mmol) in CH2Cl2
(3 mL) to give a colorless solution. The solution was stirred
for 1 h, then filtered and ether (10 mL) was added to the fil-
trate to precipitate the product as a white solid, which was
filtered, washed with water, alcohol and ether and dried
under vacuum. Yield: 96 %. Anal. Calc. for C29H27AuO2P2:
C, 52.27; H, 4.08. Found: C, 51.96; H, 4.11%. NMR
(CDCl3), d(1H) = 0.88 [br s, 3H, Me]; 2.3–2.5 [br m, 4H,
CH2]; 6.5–7.5 [m, 20H, Ph]; d(31P) = 36.7 [br s, P].
1
5.57%. H NMR (CDCl3): d(1H) = 1.16 [s, 3H, Me]; 2.58
2
2
[m, 2H, J(HH) = 14 Hz, J(PH) = 2 Hz, CH2]; 2.63 [m,
2H, 2J(HH) = 14 Hz, 2J(PH) = 2 Hz, CH2]; 7.2–7.5 [m,
20H, Ph]; d (31P) = À22.17 [s, P].
2.3. Lithium 2,2-bis(diphenylphosphinomethyl)propionate,
Li(2)
To a solution of 1 (1.175 g, 2.5 mmol) in CH2Cl2 (5 mL)
was added dropwise a solution of LiOH Æ H2O (104.9 mg,
2.5 mmol) in MeOH (5 mL). The solution was stirred over-
night, then the solvent was evaporated to give the product
as a white solid, which was washed with ether and dried
under vacuum. Yield 99%. Anal. Calc. for C29H27LiO2P2:
C, 73.11; H, 5.71. Found: C, 73.23; H, 5.54%. NMR
2.3.5. [PdCl2(1)] (7)
A
solution of [PdCl2(COD)] (28.5 mg, 0.1 mmol)
CH2Cl2 (3 mL) was added to a solution of ligand 1
(47 mg, 0.1 mmol) in CH2Cl2 (3 mL). The mixture was stir-
red for 2 h, then the yellow solid precipitate was separated

C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
3303
by filtration, washed with CH2Cl2 and ether, and dried
under vacuum. Yield: 63 %. Anal. Calc. for
C29H28Cl2O2P2Pd: C, 53.77; H, 4.36. Found: C, 53.36; H,
4.18%. NMR (DMSO-d6–CDCl3): d(1H) = 0.87 [s, 3H,
Me]; 3.21 [m, 4H, CH2]; 7.8–8.6 [m, 20H, Ph];
d(31P) = 25.2 [s, PdP]. Crystals suitable for X-ray diffrac-
tion were obtained by recrystallization from DMSO/
MeCN/Et2O.
2.3.10. [PtMe(OH2)(1)](OTf) (12)
A solution of CF3SO3H (20 mg) in water (0.5 mL) was
added to a solution of [PtMe2(1)] (10 mg) in MeCN
(1 mL). The mixture was stirred for 15 min, then the solvent
was evaporated to give the product as a white solid, which
was washed with water, MeOH and ether and dried under
vacuum. Yield: 73%. Anal. Calc. for C31H33F3O6P2PtS: C,
43.92; H, 3.92. Found: C, 43.72; H, 4.06%. NMR (CD3CN):
d(1H) = 0.08 [m, 3H, J(PH) = 4, 7 Hz, J(PtH) = 53 Hz,
2
2.3.6. [PtCl2(1)] (8)
MePt]; 0.91 [s, 3H, Me]; 2.66 [dd, 2H, J(HH) = 14 Hz,
To a solution of [PtCl2(COD)] (32.4 mg, 0.1 mmol) in
CH2Cl2 (2 mL) was added a solution of ligand 1 (47 mg,
0.1 mmol) in CH2Cl2 (5 mL). The mixture was stirred over-
night, then the white solid precipitate was collected by fil-
tration, washed with CH2Cl2 and ether, and dried under
vacuum. Yield: 73%. Anal. Calc. for C29H28Cl2O2P2Pt: C,
47.29; H, 3.83. Found: C, 47.60; H, 4.02%. NMR
(DMSO-d6–CDCl3): d (1H) = 0.86 [s, 3H, Me]; 3.2–3.3
[m, 4H, CH2]; 7.8–8.6 [m, 20H, Ph]; d(31P) = 0.1 [s,
1J(PtP) = 4210 Hz, PtP].
2J(PH) = 9 Hz, CH2]; 2.68 [dd, 2H, 2J(HH) = 14 Hz,
2J(PH) = 8 Hz, CH2]; 2.78 [dd, 2H, 2J(HH) = 14 Hz,
2J(PH) = 6 Hz, CH2]; 2.80 [dd, 2H, 2J(HH) = 14 Hz,
2J(PH) = 6 Hz, CH2]; 7.3–7.8 [m, 20H, Ph]; d(31P) = 3.86
[m, 2J(PP) = 61 Hz, 1J(PtP) = 5255 Hz, PtP trans to O];
2
1
5.48 [m, J(PP) = 61 Hz, J(PtP) = 2044 Hz, PtP trans to
Me].
2.3.11. [{PtMe(2)}n] (14)
A solution of complex 11 (25 mg) in CD2Cl2 (0.6 mL)
was allowed to react over a period of 15 days, while the
course of the reaction was monitored by 31P NMR. After
1 day, peaks assigned to [PtMe(1)(l-2)PtMe2], 13, were
observed. NMR: d(31P) = 2.86 [m, 2J(PP) = 46 Hz,
1J(PtP) = 5152 Hz, PtP trans to O]; 4.89 [m,
2J(PP) = 46 Hz, 1J(PtP) = 2244 Hz, PtP trans to Me];
2.3.7. [Pd(NCMe)2(1)](OTf)2 (9)
To a suspension of [PdCl2(1)], 7 (129 mg, 0.2 mmol) in
acetonitrile (10 mL) was added AgOTf (110 mg,
0.42 mmol). The mixture was stirred for 15 h, the insoluble
solid (AgCl) was removed by filtration, volume of the fil-
trate was reduced to ca. 1 mL, and ether (10 mL) was
added to precipitate the product as a white solid, which
was separated, washed with ether and dried under vacuum.
Yield: 76 %. Anal. Calc. for C35H34F6N2O8P2PdS2: C,
43.92; H, 3.58; N, 2.93. Found: C, 43.39; H, 3.78; N,
3.01%. NMR (CD3CN–CDCl3): d(1H) = 1.18 [s, 3H, Me];
1.95 [s, 6H, MeCN]; 2.83 [dd, 2H, 2J(HH) = 15 Hz,
2J(PH) = 8 Hz, CH2]; 2.93 [dd, 2H, 2J(HH) = 15 Hz,
2J(PH) = 8 Hz, CH2]; 7.5–8.0 [m, 20H, Ph]; d(31P) = 31.1
[s, PdP].
1
5.12 [m, J(PtP) = 2250 Hz, 2PtP trans to Me]. After 15
days, the product appeared to be a mixture of oligomers
[{PtMe(2)}n] (14). The product was precipitated by addi-
tion of ether (2 mL). Yield: 35%. Anal. Calc. for
C30H30O2P2Pt: C, 53.02; H, 4.45. Found: C, 53.24; H,
4.33%. NMR: d(31P) = 2.83 [m, 2J(PP) = 50 Hz,
1J(PtP) = 5160 Hz, PtP trans to O]; 4.86 [m,
1
2J(PP) = 50 Hz, J(PtP) = 2250 Hz, PtP trans to Me].
2.3.12. [{PdCl(2)}n]
To a solution of Li(2) (48 mg, 0.1 mmol) in CH2Cl2
(5 mL) was added a solution of [PdCl2(COD)] (28.5 mg,
0.1 mmol) in CH2Cl2 (4 mL). The mixture was stirred for
2 h. The yellow solid which formed, was separated, washed
with water, methanol and ether and dried under vacuum.
Yield: 78%. Anal. Calc. for C29H27ClO2P2Pd: C, 56.98;
H, 4.45. Found: C, 56.35; H, 4.09%. NMR (CDCl3):
d(31P) = 18.8 [br]; 21.3 [br].
2.3.8. [Pt(1)2](OTf)2 (10)
A mixture of [Pt(EtCN)4](OTf)2 (35.7 mg, 0.05 mmol)
and ligand 1 (47 mg, 0.10 mmol) in acetonitrile (4 mL)
was warmed at 50 ꢁC for 10 min. The volume of the color-
less solution which formed was reduced to ca. 1 mL, and
ether (10 mL) was added to precipitate the product as a
white solid. Yield: 63%.
2.3.9. [PtMe2(1)] (11)
2.3.13. [{PtCl(2)}n]
To a solution of [Pt2Me4(l-SMe2)2] (0.05 mmol) in
CH2Cl2, (1 mL) was added a solution of ligand 1 (47 mg,
0.1 mmol) in CH2Cl2 (1 mL). The solution was stirred for
30 min., then concentrated to 0.5 mL and ether (10 mL)
was added to precipitate the product as a white solid, which
was separated, washed with ether and dried under vacuum.
Yield: 96%. Anal. Calc. for C31H34O2P2Pt: C, 53.52; H,
4.93. Found: C, 53.12; H, 4.66%. NMR (CD3CN–CDCl3):
d(1H) = 0.22 [m, 6H, J(PtH) = 69 Hz, MePt]; 1.17 [s, 3H,
Me]; 2.3 [m, 4H, CH2]; 7.5–8.0 [m, 20H, Ph];
d(31P) = 4.83 [s, J(PtP) = 2264 Hz, PtP].
This was prepared in a similar way from [PtCl2(COD)].
Yield 82%. Anal. Calc. for C29H27ClO2P2Pt: C, 49.76; H,
3.89. Found: C, 49.38; H, 3.70%. NMR (CDCl3):
d(31P) = 4.1 [br]; 5.8 [br].
2.4. X-ray structure determinations
Data were collected at 150 K using a Nonius Kappa-
CCD diffractometer with COLLECT (Nonius B.V.,
1998). The unit cell parameters were calculated and refined
from the full data set. Crystal cell refinement and data

3304
C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
Table 1
10 were grown from a solution in MeCN/CHCl3 by slow
diffusion of ether.
Crystal data and structure refinement for complexes 7 and 8 as DMSO
solvates
Complex
Formula
7 Æ 2DMSO
C33H40Cl2O4P2PdS2
804.01
150(2)
8 Æ 2DMSO
C33H40Cl2O4P2PtS2
892.70
150(2)
0.71073
3. Results and discussion
Formula weight
Temperature (K)
3.1. Synthesis and characterization of ligand 1 and its lithium
salt 2
˚
k (A)
0.71073
Crystal system
Space group
a (A)
triclinic
triclinic
ꢀ
ꢀ
P1
P1
The ligand 1 was prepared by reaction of the methyl
ester of 2,2-bis(chloromethyl)propionic acid with lithium
diphenylphosphide, followed by hydrolysis of the initial
product which is presumed to be the methyl ester, methyl
2,2-bis(diphenylphosphinomethyl)propionate, with sodium
hydroxide and acidification to give the desired ligand 1
(Scheme 1). The pure product 2,2-bis(diphenylphosphi-
nomethyl)propionic acid, 1, was obtained as a colorless
solid in 51% yield overall, without isolation or purification
of the intermediates (Scheme 1). In the 31P NMR spectrum,
ligand 1 gave a singlet resonance at d = À22.17(s), and in
˚
10.1153(2)
10.3271(2)
17.5809(5)
103.697(1)
96.259(1)
90.546(1)
1772.48(7)
2
1.506
0.918
8135/0/349
0.0497
0.1207
10.1892(2)
10.3810(2)
17.7404(4)
102.759(1)
96.590(1)
90.311(1)
1817.13(6)
2
1.632
4.246
8246/0/349
0.0484
0.1190
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg/m3)
l (mmÀ1
)
Data/restraints/parameter
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
1
the H NMR spectrum the methyl group gave a singlet at
1
d = 1.16. The H NMR resonances of the diastereotopic
CH2 groups were more complex, appearing as an [AB] mul-
tiplet, with geminal coupling 2J(HH) = 14 Hz, and with
further coupling to phosphorus.
reduction were carried out using DENZO (Nonius B.V.,
1998). The data were scaled using SCALEPACK (Nonius
B.V., 1998). The SHELXTL-NT V6.1 suite of programs was
used to solve the structures by direct methods. Subsequent
difference Fourier syntheses allowed the remaining atoms
to be located. The hydrogen atom positions were calculated
geometrically and were included as riding on their respec-
tive carbon atoms. Details of the crystal data and refine-
ments are in Tables 1 and 2.
Crystals of 7 Æ 2DMSO and 8 Æ 2DMSO were grown
from a solution in DMSO/MeCN by slow diffusion of
ether. Crystals of 9 Æ CHCl3 were grown from a solution
in MeCN/CHCl3 by slow diffusion of ether. Crystals of
The reaction of ligand 1 with butyllithium gave the cor-
responding lithium salt, lithium 2,2-bis(diphenylphosphi-
nomethyl)propionate, Li(2) (Scheme 2). The lithium salt
Li(2) was isolated as a white solid which was soluble in
chloroform. Its NMR spectra were similar to those of 1,
with minor differences in chemical shift values. For exam-
ple, the 31P NMR spectrum of Li(2) gave a singlet reso-
nance at d = À20.63.
3.2. Synthesis and characterization of complexes with
copper(I), silver(I) and gold(I)
The ligand 1 reacted with copper(I) iodide in acetonitrile
solution to give the complex [CuI(1)] (3), and with
[AuCl(SMe2)] to give [AuCl(1)] (4), with displacement of
SMe2 (Scheme 2). We were unable to isolate a correspond-
ing silver halide complex in pure form, but reaction of
Table 2
Crystal data and structure refinement for complexes 9 and 10
Complex
Formula
Formula weight
Temperature (K)
9 Æ CHCl3
10
C
36H35Cl3F6N2O8P2PdS2 C60H56F6O10P4PtS2
1076.47
150(2)
0.71073
triclinic
717.07
150(2)
˚
k (A)
0.71073
tetragonal
P4(3)2(1)2
14.3375(1)
14.3375(1)
29.3277(3)
90
PPh2
Cl
Crystal system
Space group
2 Ph2PLi
ꢀ
P1
˚
MeO
a (A)
13.7413(2)
13.7647(3)
14.0753(3)
73.850(1)
71.906(1)
62.029(1)
2207.00(7)
2
MeO
˚
- 2 LiCl
b (A)
PPh2
˚
Cl
c (A)
O
a (ꢁ)
b (ꢁ)
c (ꢁ)
O
90
90
NaOH
3
˚
PPh2
V (A )
6028.72(9)
4
1.580
2.579
5301/0/327
PPh2
H+
Z
Dcalc (Mg/m3)
1.620
0.845
12,666/0/493
HO
-
O
l (mmÀ1
)
PPh2
Data/restraints/
parameter
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
PPh2
O
1
O
2
0.0448
0.0999
0.0587
0.0779
Scheme 1. Synthesis of ligand 1.

C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
3305
PPh2
3.3. Synthesis and characterization of complexes with
palladium(II) and platinum(II)
PPh2
PPh2
LiOH
LiO
HO
- H2O
PPh2
Reaction of ligand 1 with [MCl2(COD)], M = Pd or Pt,
COD = 1,5-cyclooctadiene, occurred by displacement of
COD to give the corresponding complexes [MCl2(1)], (7,
M = Pd; 8, M = Pt) as shown in Scheme 3. The reaction
of 7 with silver triflate in acetonitrile solution gave the com-
plex [Pd(NCMe)2(1)](OTf)2, 9 (Scheme 3), with elimination
of insoluble silver chloride. The reaction of ligand 1 with
[Pt(NCEt)4](OTf)2 occurred with displacement of the pro-
pionitrile ligands to give the complex [Pt(1)2](OTf)2, 10
(Scheme 3). These complexes were sparingly soluble, but
most were sufficiently soluble to be characterized in solu-
tion by 1H and 31P NMR spectroscopy. For example, com-
plex 8 gave a broad singlet in the 31P NMR spectrum, with
O
1
O
Li(2)
Ag2O, M = Ag
[AuCl(SMe2)], M = Au
CuI or [AuCl(SMe2)]
PPh2
M
PPh2
M
X
O
HO
PPh2
n
PPh2
O
O
5, M = Ag
6, M = Au
3, M = Cu, X = I
4, M = Au, X = Cl
Scheme 2. Synthesis of Li(2) and coinage metal complexes 3–6.
1
ligand 1 with silver(I) oxide gave the carboxylate complex
[Ag(2)] (5). The related carboxylate complex of gold(I),
[Au(2)] (6), was prepared by reaction of Li(2) with
[AuCl(SMe2)], with elimination of lithium chloride and
dimethylsulfide (Scheme 2). We were not able to prepare
the copper(I) analog of 5 and 6 in pure form, nor were
we able to prepare complexes with different ratios of
diphosphine ligand 1 or 2 to M (M = Cu, Ag or Au).
The complexes 3–6 were sparingly soluble in common
organic solvents. The NMR spectra showed the expected
resonances but they were much broader than in the precur-
sor compounds 1 or Li(2), perhaps as a result of reversible
association in solution. The IR spectra of 3 and 4 con-
tained peaks due to m(OH) in the range 2610–2690 cmÀ1
and m(C@O) in the range 1675–1680 cmÀ1, indicating the
presence of hydrogen bonding associated with the carbox-
ylic acid groups [13–21]. The copper(I) complex 3 is less
soluble than the gold(I) complex 4, which could indicate
higher association of complex 3 through formation of
Cu2(l-I)2 units [27]. In the absence of an X-ray structure
determination, the nature of supramolecular association
of these complexes remains uncertain.
satellites due to coupling to 195Pt, with J(PtP) = 4210 Hz,
typical of complexes with cis-[PtCl2P2] coordination. The
broadness of the resonances for complexes 7, 8 and 10 is
tentatively attributed to reversible supramolecular oligo-
merization in solution, but the compounds were not suffi-
ciently soluble to allow a detailed study by variable
temperature NMR. The structures of complexes 7–10
(Scheme 3) were confirmed by X-ray structure
determinations.
The complexes 7 and 8 were crystallized as the DMSO
solvates, and they were isomorphous and isostructural.
The structures are shown in Fig. 1 and a comparison of
key structural parameters is given in Table 3. In each case,
the metal has the expected cis-MCl2P2 coordination,
M = Pd or Pt, and the 6-membered MP2C3 chelate ring
has the chair conformation (Fig. 1). The M–P distances
are slightly shorter and the angle P–M–P is correspond-
ingly slightly greater for M = Pt than for M = Pd (Table
3). There is a hydrogen bond between the carboxylic acid
group and a DMSO solvate molecule, with O(7)Á Á ÁO-
˚
(24A) = 2.599(4) and 2.616(7) A in 7 and 8, respectively
(Fig. 1, Table 3).
O
[Pt(NCEt)4](OTf)2
P
P
P
P
P
P
(OTf)2
OH
HO
Pt
HO
O
O
1
10
[MCl2(COD)]
P
P
NCMe
Cl
Cl
AgOTf
MeCN
M
(OTf)2
M
HO
HO
NCMe
P
P
O
O
7, M = Pd
8, M = Pt
9
Scheme 3. Synthesis of complexes 7–10 (P = PPh2).

3306
C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
Fig. 2. Structure of the dimer of cations [Pd(NCMe)2(1)]2+ in complex 9.
Selected bond parameters: Pd–N(11) 2.091(2); Pd–N(21) 2.103(2); Pd–P(2)
˚
2.2414(6); Pd–P(1) 2.2534(7) A; N(11)–Pd–N(21) 85.88(9); N(11)–Pd–P(2)
88.80(6); N(21)–Pd–P(1) 92.19(7); P(2)–Pd–P(1) 93.14(2)ꢁ; O(7)Á Á ÁO(6A)
˚
2.653(3) A.
ally anti and there is a 2-fold symmetry axis containing the
platinum atom which makes the diphosphine ligands crys-
tallographically equivalent (Fig. 3a). In complex 10, each
carboxylic acid group forms a hydrogen bond to a triflate
anion, with O(16)Á Á ÁO(32) = O(16A)Á Á ÁO(32A) = 2.748
Fig. 1. Structures of (a) complex 7 Æ DMSO, and (b) complex 8 Æ DMSO.
˚
(8) A (Fig. 3b).
The reaction of ligand 1 with [Pt2Me4(l-SMe2)2] gave
the dimethylplatinum(II) complex [PtMe2(1)], 11 (Scheme
4). One methylplatinum group was easily cleaved from
Individual cations in complex 9 have a similar structure
as in 7, with palladium(II) centers having the cis-PdN2P2
coordination, and with the 6-membered chelate ring in
the chair conformation (Fig. 2). However, in complex 9
each carboxylic acid group forms a pairwise hydrogen
bond with a neighboring molecule, thus creating a supra-
molecular dimer (Fig. 2), with distances O(7)Á Á ÁO(6A) =
˚
O(7A)Á Á ÁO(6) = 2.653(3) A.
The platinum center in complex 10 is more distorted
from square planar stereochemistry and the 6-membered
chelate rings are considerably more twisted, when com-
pared to complex 8 (Fig. 3). These effects appear to arise
because of steric congestion between phenyl substituents
of the two diphosphine ligands in complex 10. The carbox-
ylic acid groups on the two diphosphine ligands are mutu-
Table 3
˚
Bond lengths [A] and angles [ꢁ] for complexes 7 Æ 2DMSO and 8 Æ 2DMSO
7 Æ 2DMSO, M = Pd
8 Æ 2DMSO, M = Pt
M–P(1)
M–P(2)
M–Cl(1)
M–Cl(2)
P(2)–M–P(1)
Cl(2)–M–Cl(1)
P(1)–M–Cl(2)
P(2)–M–Cl(1)
O(7)Á Á ÁO(24A)
2.244(1)
2.234(1)
2.358(1)
2.337(1)
93.67(4)
91.39(4)
87.72(4)
87.21(4)
2.599(4)
2.230(1)
2.220(2)
2.353(2)
2.342(2)
94.72(6)
88.67(7)
88.69(6)
87.94(6)
2.616(7)
Fig. 3. The structure of complex 10: (a) an individual cation, with phenyl
groups omitted for clarity; (b) the complete structure with phenyl groups
and hydrogen bonded triflate groups included. Selected bond parameters:
˚
Pt–P(2) 2.347(1); Pt–P(1) 2.360(1) A; P(2)–Pt–P(2A) 93.26(8)ꢁ; P(2)–Pt–
˚
P(1) 87.60(5)ꢁ; P(1)–Pt–P(1A) 93.38(7)ꢁ; O(16)Á Á ÁO(32) 2.748(8) A. Sym-
metry transformations used to generate equivalent atoms: A, y + 1, x À 1,
Àz.

C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
3307
complex 11 by triflic acid to give methane and the aqua
P
P
complex [PtMe(OH2)(1)], 12 (Scheme 4). The carboxylic
acid group in 11 was less reactive than triflic acid, but it
did react slowly over a period of several days to cleave a
methylplatinum group. The initial product is proposed to
be the binuclear complex 13 and then further reaction
occurred to give oligomeric complexes 14 (Scheme 4).
The complexes 11–14 were characterized by their spec-
troscopic properties. For example, complex 11 gave a sin-
gle methylplatinum resonance in the 1H NMR, and a
single resonance in the 31P NMR at d(31P) = 4.83, with
characteristic coupling 1J(PtP) = 2264 Hz, in the range
expected for a phosphorus atom trans to a methyl group
[12,28]. The less symmetrical complex 12 gave two reso-
nances in the 31P NMR, one with a low value of the cou-
pling constant 1J(PtP) = 2044 Hz, for the phosphorus
trans to methyl, and the other with a much higher value
of 1J(PtP) = 5255 Hz, for the phosphorus trans to the oxy-
gen atom of the aqua ligand. The oligomeric complex 14
appears to form by stepwise intermolecular elimination of
methane as shown in Scheme 4. In the 31P NMR, there
are a series of overlapping resonances with 1J(PtP) ca.
2250 Hz and another series with 1J(PtP) ca. 5160 Hz, which
are assigned to phosphorus atoms trans to methyl and oxy-
gen, respectively [12,28,29].
Cl
Cl
+
LiO
M
O
2
- LiCl, COD
P
M
P
P
O
Cl
P
n
M
O
O
Cl
15, M = Pd
16, M = Pt
O
Scheme 5. P = PPh2. Oligomeric chloro derivatives of palladium and
platinum.
4. Conclusions
The ligand 2,2-bis(diphenylphosphinomethyl)propionic
acid, 1, acts primarily as a chelating diphosphine ligand
in neutral solution. An indication of the low tendency of
the carboxylic acid group to coordinate (with deprotona-
tion) is illustrated by the reaction of [PdCl2(1)] with silver
triflate in acetonitrile solution to give the cationic complex
[Pd(NCMe)2(1)]2+, in which the ligand 1 did not undergo
deprotonation. The carboxylic acid group in complexes
of 1 took part in hydrogen bonding. However, the familiar
dimerization by self-association between pairs of carbox-
ylic acid units was observed only in the complex
Very
sparingly
soluble
oligomeric
complexes
[{MCl(2)}n], 15, M = Pd; 16, M = Pt, were prepared by
reaction of the salt Li(2) with the complexes [MCl2(COD)],
with elimination of LiCl and 1,5-cyclooctadiene, as shown
in Scheme 5. The complexes were isolated in analytically
pure form but they were insufficiently soluble to give good
NMR spectra, so the proposed structures are tentative.
P
P
Me
Me
P
P
OH2
Me
HOTf
H2O
Pt
Pt
HO
(OTf)
HO
O
O
O
11
12
- CH4
P
Me
P
P
Pt
Me
Me
HO
O
Pt
P
O
13
P
Me
O
O
Pt
P
P
P
P
O
Me
Me
O
HO
P
Pt
Pt
O
n
Me
14
Scheme 4. Methylplatinum complexes.

3308
C.-Q. Zhao et al. / Inorganica Chimica Acta 361 (2008) 3301–3308
[Pd(NCMe)2(1)]2+. In other cases, the carboxylic acid
group in 1 formed a hydrogen bond to a solvent molecule
or to a triflate anion. Thus, as seen also in related studies,
there is a fine balance between the different possible modes
of hydrogen bonding, and so it is difficult to predict the
nature of the supramolecular association [15].
[4] M.M. Rahman, H.-Y. Liu, K. Eriks, A. Prock, W.P. Giering,
Organometallics 8 (1989) 1.
[5] T. Li, A.J. Lough, R.H. Morris, Chem. Eur. J. 13 (2007) 3796.
[6] B.M. Trost, M.R. Machacek, A. Aponick, Acc. Chem. Res. 39 (2006)
747.
[7] A.N. Turanov, V.K. Karandashev, A.N. Yarkevich, T.A. Orlova,
A.V. Kharitonov, E.N. Tsvetkov, Russ. J. Gen. Chem. 69 (1999)
1061.
The ligand 1 can be deprotonated by base to give the
corresponding carboxylate anion 2, which appears to act
as a bridging tridentate diphosphine–carboxylate ligand
in all cases studied. The complexes formed are oligomeric
or polymeric in nature and so definitive structural charac-
terization of these complexes of 2 proved to be difficult.
An interesting case was discovered in the case of the com-
plex [PtMe2(1)], which underwent slow intermolecular
elimination of methane to give the oligomeric complex
[{PtMe(2)}n] (Scheme 4).
[8] S. Leininger, B. Olenyuk, P.J. Stang, Chem. Rev. 100 (2000) 853.
[9] Z. Qin, M.C. Jennings, R.J. Puddephatt, Inorg. Chem. 42 (2003)
1956.
[10] M.J. Irwin, J.J. Vittal, G.P.A. Yap, R.J. Puddephatt, J. Am. Chem.
Soc. 118 (1996) 13101.
[11] P. Lange, A. Schier, H. Schmidbaur, Inorg. Chim. Acta 235 (1995)
263.
[12] S.F. Hoseini, M. Mohamadikish, K. Kamali, F.W. Heinemann, M.
Rashidi, Dalton Trans. (2007) 1697.
[13] M.B. Smith, S.H. Dale, S.J. Coles, T. Gelbrich, M.B. Hursthouse,
M.E. Light, P.N. Horton, CrystEngComm. 8 (2006) 140.
[14] M.R.J. Elsegood, M.B. Smith, P.M. Staniland, Inorg. Chem. 45
(2006) 6761.
[15] M.B. Smith, S.H. Dale, S.J. Coles, T. Gelbrich, M.B. Hursthouse,
M.E. Light, P.N. Horton, CrystEngComm. 9 (2007) 165.
[16] A.D. Burrows, R.W. Harrington, M.F. Mahon, S.J. Teat, Eur. J.
Inorg. Chem. (2003) 1433.
Acknowledgements
We thank the NSERC (Canada) for financial support.
R.J.P. thanks the Government of Canada for a Canada
Research Chair.
[17] S.M. Kuang, P.E. Fanwick, R.A. Walton, Inorg. Chim. Acta 338
(2002) 219.
[18] P.P. Phadnis, S. Dey, V.K. Jain, M. Nethaji, R.J. Butcher, Polyhe-
dron 25 (2006) 87.
Appendix A. Supplementary material
[19] F. Refosco, F. Tisato, G. Bandoli, E. Deutsch, Dalton Trans. (1993)
2901.
[20] V. Ravindar, H. Schumann, H. Hemling, J. Blum, Inorg. Chim. Acta
240 (1995) 145.
[21] F. Mohr, M.C. Jennings, R.J. Puddephatt, Angew. Chem. 116 (2004)
987.
[22] G. Jia, N.C. Payne, J.J. Vittal, R.J. Puddephatt, Organometallics 12
(1993) 4771.
[23] Z. Qin, M.C. Jennings, R.J. Puddephatt, Chem. Eur. J. 8 (2002) 735.
[24] Z. Qin, M.C. Jennings, R.J. Puddephatt, K.W. Muir, Inorg. Chem. 41
(2002) 5174.
[25] Z. Qin, M.C. Jennings, R.J. Puddephatt, Chem. Commun. (2002) 354.
[26] Z. Qin, H.A. Jenkins, S.J. Coles, K.W. Muir, R.J. Puddephatt, Can.
J. Chem. 77 (1999) 155.
[27] P. Aslanidis, P.J. Cox, S. Divanidis, A.C. Tsipis, Inorg. Chem. 41
(2002) 6875.
[28] P. Nair, C.P. White, G.K. Anderson, N.P. Rath, J. Organomet.
Chem. 691 (2006) 529.
CCDC 654076, 654077, 654078 and 654079 contain the
supplementary crystallographic data for 7, 8, 9 and 10.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-
mail: deposit@ccdc.cam.ac.uk. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2007.08.032.
References
[1] R.C. Bush, R.J. Angelici, Inorg. Chem. 27 (1988) 681.
[2] S. Ikuta, P. Kebarle, G.M. Bancroft, T. Chan, R.J. Puddephatt, J.
Am. Chem. Soc. 104 (1982) 5899.
[29] R.G. Peters, S. White, D.M. Roddick, Organometallics 17 (1998)
4493.
[3] O. Kuhl, Coord. Chem. Rev. 249 (2005) 693.