Interaction of methylmercury(II) with the bifunctional ligand o-diphenylphosphinobenzoate, dpb. Synthesis and characterization of [(dpb)HgMe] and [(dpbo)HgMe], dpbo = o-diphenylphosphinoxidebenzoate

Article abstract of DOI:10.1016/S0022-328X(97)00713-4

The complex [(dpb)HgMe] (1) is obtained by reaction of MeHg(OH) with o-diphenylphosphinobenzoic acid (Hdpb); alternatively the solvate [(dpb)HgMe] · 0.5H₂O · 0.5C₅H₅N (1bis) can be prepared by reacting MeHgCl with Hdpb and pyridine. The derivative [(dpbo)HgMe] (2), where dpbo is o-diphenylphosphinoxidebenzoate, is formed by reaction of 1 or 1bis solutions with atmospheric oxygen. Crystal data for 1bis: monoclinic, space group P2/n, a =10.413(4), b = 9.831(3), c = 20.674(3) A, β = 102.51(3)°, Z = 2. Crystal data for 2: triclinic, space group P1, a = 11.535(2), b = 12.897(5), c = 13.275(7) A, α = 88.31(4), β = 73.65(4), γ = 85.27(4)°, Z = 2. In 1bis the mercury atom displays a distorted linear fashion, being coordinated to a methyl group and to the phosphorus atom of the dpb ligand. Two additional weaker linkages cause the packing in pairs of the molecules. In 2 the mercury is linearly linked to a methyl group and to an oxygen atom of the carboxylic group of the dpbo ligand. Also in this case the coordination around the mercury center is completed by two weaker additional bond interactions, which, involving the oxygen atoms of the adiacent moiety, determine the dimerization of the molecule. The multinuclear magnetic resonance spectra of 1 (or 1bis) which have been compared with those of the related complex [(PPh₃)HgMe](CF₃SO₃) (3) and of the solution containing 1 and CF₃SO₃H (molar ratio 1:1.5), do not seem to unambigously support a dimeric configuration of the complex in solution.

Full text of DOI:10.1016/S0022-328X(97)00713-4

Journal of Organometallic Chemistry 555 (1998) 255–262
Interaction of methylmercury(II) with the bifunctional ligand
o-diphenylphosphinobenzoate, dpb. Synthesis and characterization of
[(dpb)HgMe] and [(dpbo)HgMe],
dpbo=o-diphenylphosphinoxidebenzoate
Pierluigi Barbaro a, Carlo A. Ghilardi a,*, Stefano Midollini a, Annabella Orlandini a,
Jose` A. Ramirez b, Giancarlo Scapacci a
a Istituto per lo Studio della Stereochimica ed Energetica dei Composti di Coordinazione, CNR, Via Jacopo Nardi 39, 50132, Firenze, Italy
b Departamento de Quimica Inorganica, Uni6ersitat de Valencia, Dr. Moliner 50, 46100, Burjassot, Valencia, Spain
Received 10 October 1997
Abstract
The complex [(dpb)HgMe] (1) is obtained by reaction of MeHg(OH) with o-diphenylphosphinobenzoic acid (Hdpb); alterna-
tively the solvate [(dpb)HgMe] · 0.5H2O · 0.5C5H5N (1bis) can be prepared by reacting MeHgCl with Hdpb and pyridine. The
derivative [(dpbo)HgMe] (2), where dpbo is o-diphenylphosphinoxidebenzoate, is formed by reaction of 1 or 1bis solutions with
˚
atmospheric oxygen. Crystal data for 1bis: monoclinic, space group P2/n, a=10.413(4), b=9.831(3), c=20.674(3) A, i=
˚
(
102.51(3)°, Z=2. Crystal data for 2: triclinic, space group P1, a=11.535(2), b=12.897(5), c=13.275(7) A, h=88.31(4),
i=73.65(4), k=85.27(4)°, Z=2. In 1bis the mercury atom displays a distorted linear fashion, being coordinated to a methyl
group and to the phosphorus atom of the dpb ligand. Two additional weaker linkages cause the packing in pairs of the molecules.
In 2 the mercury is linearly linked to a methyl group and to an oxygen atom of the carboxylic group of the dpbo ligand. Also
in this case the coordination around the mercury center is completed by two weaker additional bond interactions, which, involving
the oxygen atoms of the adiacent moiety, determine the dimerization of the molecule. The multinuclear magnetic resonance
spectra of 1 (or 1bis) which have been compared with those of the related complex [(PPh3)HgMe](CF3SO3) (3) and of the solution
containing 1 and CF3SO3H (molar ratio 1:1.5), do not seem to unambigously support a dimeric configuration of the complex in
solution. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Methylmercury; Phosphine complexes; Crystal structure; NMR spectroscopy
1. Introduction
During our recent investigations about the interac-
tions of organomercury(II) ions with polydentate phos-
phines, we have found that the coordination of more
than one phosphorus atom to the metal center strongly
facilitates the cleavage of the Hg–C linkage (protonoly-
sis or symmetrization processes) [2,3].
Now here we report the synthesis and the structural
characterization of the complex [(dpb)HgMe] and of
the closely related [(dpbo)HgMe] one, where dpb and
dpbo are o-diphenylphosphinobenzoate and o-
diphenylphosphinoxidebenzoate, respectively (Scheme
1). The simultaneous presence in the dpb ligand of both
Most researches on the coordination chemistry of
methylmercury(II) have been aimed at the understand-
ing of its toxic effects on living organisms and at the
design of specific sequestering agents. Renewed interest
stems from the mechanism of the biological processes
of detoxification of this very dangerous organometallic
species [1].
* Corresponding author. Tel.: +39 55 243990; fax: +39 55
2478366; e-mail: ghilardi@cacao.issecc.fi.cnr.it
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00713-4

256
P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
a soft and an hard donor atom may be of interest,
because similar situation occurs in simple models for
the methylmercury-protein interaction such as methyl-
2.1.2. [(dbp)HgMe] · 0.5H2O · 0.5Py (1bis)
Pyridine (0.242 cm3, 3 mmol) was added to a solution
of methylmercury chloride (251 mg, 1 mmol) and Hdpb
(306.3 mg, 1 mmol) in ethanol (15 cm3). Addition of
water (20 cm3) and evaporation of ethanol under a
stream of nitrogen allowed the precipitation of the
complex. This was filtered, washed with water and
dried under vacuum at room temperature. Yield: 388
mg (68%). (Found: C, 47.35; H, 3.55; N, 1.15; Hg,
34.95; Calc. for C45H41Hg2NO5P2: C, 47.46; H, 3.63; N,
1.23; Hg, 35.22).
L
-cysteinatomercury(II) [4]. In the dbp case, the pres-
ence of P as soft donor atom in place of S, gives the
possibility of monitoring the complex behaviour in
solution through NMR.
Although the synthesis of [(PR3)HgMe]X complexes
had been reported in 1964 by Coates et al. [5], these
compounds have been scarcely investigated, maybe be-
cause of their propensity to undergo symmetrization
reactions [5,6]. As
a
matter of fact only
[(PMe3)HgMe]Cl [7] and [(PPh3)HgMe]NO3 [8] have
2.1.3. [(dbpo)HgMe] (2)
been properly characterized through H- and 13P-NMR
Hydrogen peroxide (36%, m/6) (0.5 cm3, 0.5 mmol)
was added at room temperature to a solution of the
complex 1 (260 mg, 0.5 mmol) in dichloromethane (10
cm3)/ethanol (2 cm3). The resulting solution was stirred
for 12 h, then all the solvent was removed under
vacuum. The solid was dissolved in dichloromethane
and the resulting mixture was filtered. Addition of ethyl
ether caused the precipitation of colorless crystals
which were collected as described for 1. Yield: 498 mg
(93%). (Found: C, 44.55; H, 3.25; Hg, 37.45. Calc. for
C20H17HgO3P: C, 44.74; H, 3.19; Hg, 37.36).
1
or X-ray analysis, respectively.
2. Experimental
All the reactions were performed under an atmo-
sphere of dry nitrogen. Solvents were purified and dried
by standard methods. O-diphenylphosphino benzoic
acid [9] and methylmercury triflate [2] were prepared by
the previously reported methods. The other starting
materials were reagent grade and were used without
further purification.
2.1.4. [(PPh3)HgMe](CF3SO3) (3)
A solution of triphenylphosphine (262 mg, 1 mmol)
in dichloromethane (10 cm3) was added to a solution of
[MeHg(DMSO)]CF3SO3 (442 mg, 1 mmol) in the same
solvent (10 cm3). n-hexane (15 cm3) was added to the
resulting solution and the solvent was evaporated under
a current of nitrogen until a colorless oil separated. The
solvent was decanted off and the oil was dissolved in
ethanol (10 cm3). Addition of n-heptane (10 cm3) and
slow evaporation of the solvent allowed the precipita-
tion of colorless crystals which were filtered, washed
with n-hexane and dried under a stream of nitrogen.
Yield: 524 mg (88%). (Found: C, 38.55; H, 3.05; Hg,
31.75. Calc. for C20H18F3HgO3PS: C, 38.31; H, 2.89;
Hg, 31.99).
2.1. Syntheses
2.1.1. [(dbp)HgMe] (1)
Methylmercury hydroxide (233 mg, 1 mmol) in water
(3 cm3) was added to a solution of Hdpb (306.3 mg, 1
mmol) in ethanol (10 cm3). The resulting solution was
stirred at room temperature for 10 min, then all the
solvents were removed under vacuum. The solid was
dissolved in dichloromethane (10 cm3), and the result-
ing solution was filtered. Addition of ethyl ether (60
cm3) caused the precipitation of colourless crystals.
These were filtered, washed with ethyl ether and dried
under a stream of nitrogen. Yield: 443 mg (85%).
(Found C, 46.35; H, 3.40; Hg, 38.45; Calc. for
C20H17HgO2P: C, 46.11; H, 3.29; Hg, 38.51).
2.2. Crystallography
Diffraction data of 1bis and 2 were collected at room
temperature on an ENRAF NONIUS CAD4 auto-
matic diffractometer. Unit cell parameters were deter-
mined by least-squares refinement of the setting angles
of 25 carefully centered reflections. Crystal data and
data collection details are given in Table 1. The intensi-
ties I as well as the standard deviations |(I) were
calculated by using the value of 0.03 for the instability
factor k [10]. The intensities were corrected for Lorentz-
polarization effects and an empirical absorption correc-
tion was applied using y scans [11].
All the calculations were carried out on a 486 IBM
personal computer, using the SHELXS86 [12], SHELXL93
Scheme 1. Structures of the ligands dpb (o-diphenylphosphinoben-
zoate) and dpbo (o-diphenylphosphinoxidebenzoate).

P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
257
Table 1
20% larger than those of the latter. The function mini-
Crystal data and structure refinement for 1bis and 2
2
2 2
mized during the refinement was Sw(ꢀFoꢀ −ꢀFcꢀ ) ,
where w is defined as 1/|2[(F2o)+(0.0406P)2+14.54P]
and 1/|2[(F2o)+(0.0685P)2+23.91P] in 1bis and 2, re-
spectively [P=(max(F2o, 0)+2Fc2)/3].
1bis
2
Formula
Formula weight
Temperature, K
C45H41Hg2NO5P2
1137.90
293(2)
C40H34Hg2O6P2
1073.79
293(2)
2.3. NMR measurements
˚
Wavelength, A
0.7107
0.7107
Crystal system
Space group
Monoclinic
P2/n
10.413(4)
9.831(3)
20.674(3)
90
102.51(3)
90
2066.2(11)
2
Triclinic
1
The H-, 13C{1H}- and 31P{1H}-NMR spectra were
(
P1
˚
a, A
11.535(2)
12.897(5)
13.275(7)
88.31(4)
73.65(4)
85.27(4)
1888.5(13)
2
recorded on a Bruker Avance DRX-500 spectrometer
operating at 500.132, 125.76 and 202.46 MHz, respec-
tively, and equipped with a variable temperature con-
˚
b, A
˚
c, A
h, deg
i, deg
k, deg
trol unit accurate to 90.1°C. H, 13C chemical shifts
1
are relative to tetramethylsilane, whereas 31P chemical
shifts are relative to external 85% H3PO4. 199Hg{1H}-
NMR spectra were recorded on a Bruker AC-200 spec-
trometer operating at 35.85 MHz. 199Hg chemical shifts
are relative to external 0.1 mol dm−3 Hg(ClO4)2 in 0.1
mol dm−3 HClO4. Downfield values of the chemical
shifts are reported as positive. The assignments of the
3
˚
Volume, A
Z
Density calc., g
1.829
1.888
cm−3
Absorption coeff., 75.5
82.5
cm−1
Absorption correc. 0.573–1.000
range
F(000)
Crystal size, mm
Theta range, q
Index ranges
0.320–1.000
1
1
signals resulted from 2D H COSY, 2D H NOESY
1094
1024
and proton detected 2D H, 13C and H, 31P correla-
tions using non-spinning samples. JHH and JPH cou-
pling constants were obtained from heteronuclear
decoupling experiments as well as from 1D-NMR spec-
tra. 2D-NMR spectra were recorded using pulse se-
quences suitable for phase-sensitive representations,
1
1
0.38×0.18×0.10
2.88–22.48
−115h510
05k510
05l522
0.50×0.30×0.10
2.52–22.48
−11Bh512
−135k513
05l514
Method
ꢀ–2q
1.03–8.24
Scan speed, deg
1.27–8.24
1
using TPPI. Double-quantum filtered H COSY experi-
min−1
ments [17] were recorded with 1024 increments of size
2K (with eight scans each) covering the full range (ca.
5000 Hz) in both dimensions. The 1H NOESY measure-
ments [18] were recorded with 1024 increments of size
2K (with 16 scans each) covering the full range (ca.
5000) in both dimensions and using a mixing time of
Scan width, deg
Background time
Standards
Reflections col-
lected
Independent reflec- 2694
tions
Refinement
method
0.7+0.35 tan q
Half the scan time
3 every 120 min
2774
0.8+0.35 tan q
4917
4917
1
Full matrix least-squares
0.8 s. The H, 13C correlations [19] were recorded using
on F2
the standard HMQC sequence with no decoupling dur-
ing acquisition, 1024 increments of size 2K (with 16
scans each) were collected covering 5000 Hz range in
F2 and 22 000 Hz range in F1. Standard pulse sequence
Data/restraints/
parameters
2694/0/88
4917/0/155
Goodness-of-fit on 1.039
0.925
F2
1
Final R [I\2|(I)] R1=0.037, wR2=0.084
R1=0.044,
wR2=0.11
R1=0.057,
wR2=0.12
was employed for the H, 31P correlations [20].
Final R [all data] R1=0.059, wR2=0.094
3. Results and discussion
The complex [(dbp)HgMe] is obtained from the
reaction of MeHg(OH) with Hdpb in water/ethanol
[13] and ORTEP [14] programs. Atomic scattering fac-
tors for neutral atoms were taken from ref. [15]. Both
Df % and Df ¦ components of anomalous dispersion were
included for all non-hydrogen atoms [16]. The struc-
tures were solved by heavy atom method and full-ma-
trix least-squares refinements were carried out on F2
with anisotropic thermal factors assigned to mercury
and phosphorus atoms. The phenyl rings were treated
as rigid bodies of D6h symmetry. Hydrogen atoms were
introduced in calculated positions, riding on their at-
tached carbon atoms with isotropic thermal parameters
solution.
Alternatively
the
solvate
[(dpb)-
HgMe] · 0.5H2O · 0.5Py can be prepared by reacting
MeHgCl with Hdpb and pyridine. The compound
which is soluble in common organic solvents such as
ethanol, dichloromethane, acetone, thf, slowly decom-
poses in solution, separating metallic mercury. The
complex [(dpb)HgMe] reacts in dichloromethane solu-
tion with [(DMSO)HgMe](CF3SO3) to form Hg metal
and untractable products. The complex very slowly
reacts with atmospheric oxygen to form the

258
P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
Fig. 1. Perspective view of the dimer [(dpb)HgMe]2. ORTEP drawing with 30% probability ellipsoids.
˚
phosphinoxide derivative [(dbpo)HgMe]. This latter can
be properly prepared through oxidation of [(dbp)Hg-
Me] by H2O2. The complex [(PPh3)HgMe](CF3SO3) was
prepared for comparison raisons by reaction of PPh3
with [(DMSO)HgMe](CF3SO3).
A). Therefore, we face a 2+2 coordination which
represent a common feature in the stereochemistry of
the mercury atom, made possible via overlap with
vacant 6p orbitals of the metal. The values of the
secondary bondings are effectively much larger than the
values of normal covalent Hg–O bond distances (2.00–
˚
2.35 A) [4,21], but are also appreciably shorter than the
3.1. Description of the structures
˚
sum of the Van der Waals radii (3.00 A [22], and 3.23
A [23,24]) and actually may be considered indicative of
some interactions.
As far as the distribution of the solvent molecules in
the latice is concerned, while pyridine does not show
any significative contact, the oxygen of the water
molecule displays hydrogen bonding interactions with
the oxygen (O(2)) of the carboxylic group not involved
in the interactions with the mercury atom. The value of
such contact, 2.88 A, is in between the values of twice
the Van der Waals radii of oxygen, as reported by
Pauling (2.84 A) [25] and by Bondi (3.04 A) [24].
It seems interesting to recall the structure of the
-cysteinate methylmercury hydrate [4], where a car-
boxylic group interacts with mercury atom forming a
six-membered ring, with an intra Hg..O contact match-
ing that found in our compound (2.85 A). It seems
˚
The molecular structure of 1bis may be described
as consisting of [(dbp)HgMe]2 dimers, the two
monomeric units being related by an inversion center,
˚
with a Hg..Hg separation of 4.616 A. Pyridine and
water solvent molecules are interspersed in the latice.
Fig. 1 shows the perspective view of the dimeric
unit and Table 2 reports selected bond distances and
angles.
In each half of the dimer the mercury is linked in a
slightly distorted linear fashion to a methyl group and
to the phosphorus atom of the phosphine group (Me–
Hg–P=165.8(3)°). Besides the two strong covalent
bonds there are additional linkages, which allow the
formation of the dimer. Indeed the two metal centers
are held together by two bridging oxygen atoms of the
carboxylic groups which display secondary interactions
with the mercury atoms (Hg...O(1%) 2.64, Hg...O(1) 2.84
˚
˚
˚
L
˚
anyway noteworthy that while in the phosphine ben-

P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
259
Table 2
Selected bond lengths (A) and angles (°) for 1bis
packing in pairs of molecules being achieved through
hydrogen bonding only between the oxygen and nitro-
gen atoms of the ligands.
˚
Hg–P
Hg–C(2)
Hg...O(1)
Hg...O(1%)
P–C(1,1)
P–C(1,2)
P–C(1,3)
O(1)–C(1)
2.413(3)
2.065(12)
2.842(6)
2.641(6)
1.824(5)
1.836(5)
1.799(5)
1.248(10)
1.251(11)
1.510(10)
The molecular structure of 2 (Fig. 2) consists of
[(dpbo)HgMe ]2 dimers, the two halves being linked
through mercury–oxygen bond interactions (Hg..Hg
˚
separation 4.142 A). As a matter of fact in each
monomer [(dpbo)HgMe] the metal atom is bonded to a
methyl unit and to one oxygen atom of the carboxylic
group in a slightly distorted linear fashion (Me–Hg–
O=169.2(5)°), the phosphorus atom being definitely
away from the mercury center. Also in this case the
coordination around each mercury atom is completed
by two weaker additional bond interactions, which
involve the oxygen atoms of the phosphinoxide and of
the carboxylic group of the adiacent molecule. Table 3
reports selected bond distances and angles of 2.
O(2)–C(1)
C(1)–C(6,1)
P–Hg–C(2)
P–Hg–O(1%)
C(2)–Hg–O(1%)
C(1,1)–P–C(1,2)
C(1,1)–P–C(1,3)
C(1,2)–P–C(1,3)
C(1,1)–P–Hg
C(1,2)–P–Hg
C(1,3)–P–Hg
C(1)–O(1)–Hg%
O(1)–C(1)–O(2)
O(1)–C(1)–C(6,1)
O(2)–C(1)–C(6,1)
165.8(3)
102.6(2)
91.4(4)
104.6(3)
108.8(3)
103.7(3)
114.1(2)
106.9(2)
117.4(2)
116.7(6)
124.9(9)
116.3(8)
118.8(8)
In both the structures the values of the bond dis-
tances involving mercury atom fit very well with the
values previously reported, both as strong covalent
[4,21] either as weak [26] interactions. In particular as
˚
concerns the Hg–P bond distance, (2.413(3) A) values
˚
of 2.37–2.40 A have been observed in structures con-
Symmetry transformations used to generate equivalent atoms: −x+
1, −y, −z+1.
taining nearly linear P–Hg–X units with P–Hg–X
angles in the range 158–166° [8,27].
The above structures highlight the better bonding
capabilities towards Hg(II) ions of the phosphine with
respect to the carboxilic group, provided the lone pair
on the phosphorus is available.
zoate complex the formation of the dimer occurs
through interactions involving the mercury atom, in the
cysteinato complex the metal atom does not present
any interactions with the neighbouring molecule, the
Fig. 2. Perspective view of the dimer [(dpbo)HgMe]2. ORTEP drawing with 30% probability ellipsoids.

260
P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
Table 3
3.2. NMR spectra
˚
Selected bond lengths (A) and angles (°) for 2
Selected NMR spectral data for the complex
[(dpb)HgMe] (1) are reported in Table 4. The corre-
sponding data for the complex [(PPh3)HgMe](CF3SO3)
(3) and for a solution containing [(dpb)HgMe] and
CF3SO3H (molar ratio 1:1.5) are also reported for
Hg(1)–C(1)
Hg(1)–O(1)
Hg(1)...O(4)
Hg(1)...O(6)
Hg(2)–C(3)
Hg(2)–O(4)
Hg(2)...O(1)
Hg(2)...O(3)
P(1)–O(3)
P(1)–C(1,3)
P(1)–C(1,2)
P(1)–C(1,1)
P(2)–O(6)
P(2)–C(1,5)
P(2)–C(1,6)
P(2)–C(1,4)
2.05(2)
2.086(7)
2.874(8)
2.732(8)
2.04(2)
2.101(7)
2.817(8)
2.814(8)
1.485(7)
1.806(5)
1.817(5)
1.855(5)
1.491(7)
1.815(5)
1.816(6)
1.836(5)
1.276(12)
1.216(13)
1.290(12)
1.215(13)
1.505(11)
1.480(11)
2
comparison. The values of the JHgH coupling constant,
as well as the 31P{1H} and 199Hg{1H} data, are consis-
tent with the coordination of the phosphorus atom to
the mercury in each case, but, while a static complex
forms even at room temperature in the presence of
triflic acid, a dynamic process takes place in the case of
1 and 3, the slow exchange limit being reached only at
198 K. This different dynamic behaviour can be at-
tributed to a rapid MeHg+ exchange among phosphine
ligands due to an associative pathway in the case of 1
and 3 (as previously reported for [(PMe3)HgMe]+ [7]),
whereas in the solution containing 1 and an excess of
triflic acid any free phosphine is clearly protonated and
thus uncoordinating. Indeed, traces of free phosphine
are likely present in solutions of 1 and 3 because of
exiguous decomposition processes [28], whilst we have
found that the addition of CF3SO3H to a solution of
[(PPh3)HgMe]+ analogously cancels out the exchange
process at room temperature.
O(1)–C(2)
O(2)–C(2)
O(4)–C(4)
O(5)–C(4)
C(2)–C(6,1)
C(4)–C(6,4)
C(1)–Hg(1)–O(1)
C(3)–Hg(2)–O(4)
O(3)–P(1)–C(1,3)
O(3)–P(1)–C(1,2)
C(1,3)–P(1)–C(1,2)
O(3)–P(1)–C(1,1)
C(1,3)–P(1)–C(1,1)
C(1,2)–P(1)–C(1,1)
O(6)–P(2)–C(1,5)
O(6)–P(2)–C(1,6)
C(1,5)–P(2)–C(1,6)
O(6)–P(2)–C(1,4)
C(1,5)–P(2)–C(1,4)
C(1,6)–P(2)–C(1,4)
C(2)–O(1)–Hg(1)
C(4)–O(4)–Hg(2)
O(2)–C(2)–O(1)
O(2)–C(2)–C(6,1)
O(1)–C(2)–C(6,1)
O(5)–C(4)–O(4)
O(5)–C(4)–C(6,4)
O(4)–C(4)–C(6,4)
169.2(5)
172.8(5)
110.4(4)
114.6(4)
103.6(3)
113.8(4)
104.7(3)
108.8(3)
110.6(3)
112.6(4)
102.3(3)
114.5(4)
105.0(3)
110.9(3)
119.9(6)
112.1(6)
125.1(10)
120.4(9)
114.5(8)
122.9(10)
121.5(9)
115.6(8)
1
The H- and 13C-NMR spectra of 1 and 1/triflic acid
have been investigated in greater detail. All the reso-
nances have unambiguously been assigned through 1D-
and 2D-NMR techniques (see experimental). The re-
sults are reported in Table 5. These data show that the
two phenyl phosphino rings are NMR equivalent in 1,
a single set of resonance being observed for all the ring
nuclei. This apparently rules out that, unlike in the
solid-state structure, a rigid chelate ring may exists in
the NMR time scale, involving the metal center, the
phosphorus atom and the carboxylate group in the
solution structure of 1. This seems consistent with a
weakening of the secondary interactions found in the
solid state due to the solvation process. Accordingly,
Table 4
Selected NMR spectral data for the dbp complexesa
Complex
Temp. (K)
1H (CH3)
31P{1H}
199Hg{1H}
b
[(dbp)HgMe] 1
295
198
0.92 (s with satell., br) 2JHgH=179
58.0 (br)
—
0.90 (d with satell.) 3JPH=7.0, 2JHgH=178
57.4 (s with satell.) 1JHgP=2665
1710 (d)
b
[(PPh3)HgMe](CF3SO3) 3
[(dbp)HgMe]/CF3SO3Hc
295
198
1.26 (s with satell., br) 2JHgH=177
57.4 (br)
—
1.13 (d with satell.) 3JPH=5.0, 2JHgH=177
55.9 (s with satell.) 1JHgP=1345
1747 (d)
295
1.14 (d with satell.) 3JPH=7.4, 2JHgH=175
65.9 (s with satell.) 1JHgP=1493
1725 (d)
a CD2Cl2 solutions 0.05 M. Abbreviations: br, broad; s, singlet, d, doublet. Chemical shifts in ppm, coupling constants in Hz.
b We were unable to record any signal in the 199Hg spectrum after 12 h long experiment.
c Mole ratio 1:1.5.

P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
261

262
P. Barbaro et al. / Journal of Organometallic Chemistry 555 (1998) 255–262
The Royal Society of Chemistry, Cambridge, 1993, p. 62 and
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the solution structure of 1 is likely better described in
terms of monomers than dimers. Analogous conclu-
sions can be drawn out for the complex obtained from
1 by the reaction with triflic acid. In addition, consider-
ing that: (i) the 31P{1H} and 199Hg{1H} parameters of
the 1/triflic acid solution closely resemble those
recorded for the cationic complex 3 at low temperature,
1
(ii) the down field shift of the H and 13C resonances of
the 1/triflic acid solution, as compared to those of 1,
can be attributed to a positive charge located on the
1
complex, (iii) the H(H2) and 13C(C2) signals appear as
sharp doublets, we identify the complex formed by the
addition of CF3SO3H to 1 as the CO2-protonated
cationic complex [(dpbH)HgMe](CF3SO3). Finally, it is
1
worth notice the remarkable difference in the JHgP
coupling constant found for the neutral complex 1
(2665 Hz) as compared to that found for 3 and for
[(dpbH)HgMe](CF3SO3) (1345 and 1493 Hz, respec-
tively). We attribute this difference to cationic nature of
the two latter compound, whose coupling constants fall
in the range normally observed for other phosphine
organomercury complexes [2,7,29].
1
The H- and 31P{1H}-NMR spectra of the complex 2
1
are straightforward: the methyl H signal is a singlet at
0.90 ppm with satellites (2JHgH=219 Hz) whereas the
31P resonance of the PꢀO group occurs at 30 ppm as a
singlet.
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4. Supplementary material
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Acknowledgements
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Maeda, S. Emura, Inorg. Chem. 1996 (1945) 35.
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Chem. Soc., Dalton Trans. (1993) 3235.
[28] Small amounts of Hg metal separate, after few minutes, into the
solutions.
We gratefully acknowledge the financial support of
EU for HCM program ‘Metals and Environmetal
Problems’ (1995–1997), through Grant ERBCHRX-
CT94-0632.
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