Polyhedron 20 (2001) 727– 740
www.elsevier.nl/locate/poly
Solution and solid state behaviour of binuclear mercury(II)
compounds containing cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane:
first X-ray structural characterisation of mercury(II) complexes
with two different chelating phosphines
Werner Oberhauser a, Thomas Stampfl a, Rainer Haid a, Christoph Langes a,
Christian Bachmann a, Holger Kopacka a, Karl-Hans Ongania b, Peter Brüggeller a,*
a
Institut für Allgemeine, Anorganische und Theoretische Chemie, Uni6ersität Innsbruck, Innrain 52a, 6020 Innsbruck, Austria
b
Institut für Organische Chemie, Uni6ersität Innsbruck, Innrain 52a, 6020 Innsbruck, Austria
Received 21 November 2000; accepted 22 January 2001
Abstract
Several novel binuclear HgII complexes of cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) have been
prepared and characterised by X-ray diffraction methods, NMR spectroscopy (199Hg{1H}, 31P{1H}, 1H), FAB mass spectrometry,
IR spectroscopy, elemental analyses and melting points. The tetrahedral coordination of both the HgII centres in the
homobimetallic compounds [Hg2L4(dppcb)] (L =Cl− (1), Br− (2), CN− (3), NO−
3 (4)), synthesised by the reaction of HgL2 with
dppcb, is indicated by their solution NMR parameters and is confirmed by the X-ray structures of 1–3. Though the Fermi contact
term is not always dominant in determining 1J(Hg,P), the NMR parameters are correlated to the changes in the bond lengths and
angles in 1–3. A comparison is given with correlations derived from similar complexes. The reaction of 4 with 2,2%-bipyridine
(bipy) or 1,10-phenanthroline (phen) leads to [Hg2(dppcb)(bipy)2](NO3)4 (5) and [Hg2(dppcb)(phen)2](NO3)4 (6). Also, for 5 and
6 the NMR data and FAB mass spectra are in agreement with tetrahedral HgII centres. The treatment of 4 with monophosphines
produces trans-[Hg2(NO3)2(dppcb)L%2](NO3)2 (L%=P(CH2Ph)3 (7), P(CH2CH2CN)3 (8), PPh3 (9)). In 7–9 the typical large
1
J(Hg,P) values are observed for the monophosphines compared with the corresponding parameters for chelating dppcb, which
are reduced due to the five-membered ring formation. In the reaction of 4 with the diphosphine Ph2PCH2PPh2 (dppm) and the
subsequent metathesis with LiAsF6, trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](AsF6)2 (10) is formed. The X-ray structure of 10
showing coordinated and dangling phosphorus atoms of dppm is the first complete characterisation of a HgII complex containing
two different chelating phosphines. Though in solution the dppm ligands are involved in fast intramolecular end-over-end
exchange, the solution structure of 10 corresponds to its solid state structure, which is indicated by unusual 1J(Hg,P) values.
Catalytic amounts of HgII convert trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](NO3)2 into trans-[Hg2(NO3)2(dppcb)(h1-PdppmO)2](NO3)2 (11), where dppmO is Ph2PCH2P(O)Ph2. The X-ray structure of 11 is the first complete characterisation of a HgII
compound consisting of chelating phosphine together with phosphinoyl moieties. The solid state structure and the solution NMR
parameters of 11 clearly show the presence of a dangling P(O)Ph2 group. The complexes 1–11 illustrate the tendency that
polydentate donor ligands often geometrically and entropically restrict the number of accessible structures for HgII. Especially, the
X-ray structures of 1 –3, 10, and 11 indicate the preference of HgII for tetrahedral and trigonal pyramidal coordinations in
compounds containing dppcb. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Mercury complexes; Tetraphosphine complexes; Diphosphine complexes; Bimetallic complexes; Tetrahedral
coordination
* Corresponding author. Tel.: +43-512-5075115; fax: + 43-512-5072934.
E-mail address: [email protected] (P. Brüggeller).
0277-5387/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 1 ) 0 0 7 0 8 - 2
728
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
1. Introduction
Investigation of the coordination chemistry of HgII is
complicated by the tolerance for many different coordination numbers and coordination geometries, where
coordination to a metal ion with favourable NMR
properties provides an additional means for characterising the dynamics of complexes in solution and correlating solution state spectra with solid state structures [1].
However, polydentate donor ligands restrict the number of accessible structures. Only recently, it has been
shown that the bidentate diphosphine Ph2PNHPPh2
(dppam) strongly favours a face-to-face coordination of
HgII [2]. The use of chelating agents for the coordination of HgII is important, since the initial step of the
HgC bond cleavage process is the induction of higher
coordination numbers by nature’s mercury detoxification catalysts [3–8]. Furthermore, evidence for new
classes of metal-binding motifs in enzymes, transcription factors, and regulatory proteins underscores the
need for structural insights about local HgII coordination environments [9].
In this paper several novel complexes of HgII with
the recently described [10,11] tetradentate phosphine
cis,trans,cis - 1,2,3,4 - tetrakis(diphenylphosphino)cyclobutane (dppcb) are presented. The compounds
[Hg2L4(dppcb)] (L= Cl− (1), Br− (2), CN− (3), NO−
3
(4)) correspond to structure type (a) in Scheme 1, which
is confirmed by the X-ray structures of 1–3. There is
wide interest [12–28] in complexes containing the core
HgL2P2 (P=triorganophosphine, L= anionic ligand)
comparable to one half of [Hg2L4(dppcb)]. A correlation of solution NMR parameters with changes in the
bond lengths and angles in 1–3 is observed and compared with earlier results. The isomorphous crystal
structures of 2 and 3 confirm that no crystal packing
Scheme 1. Structure types observed in compounds 1– 11. Structure (a) occurs in [Hg2L4(dppcb)] (L =Cl− (1), Br− (2), CN− (3), NO−
3 (4)),
structure (b) in [Hg2(dppcb)(bipy)2](NO3)4 (5), structure (c) in [Hg2(dppcb)(phen)2](NO3)4 (6), structure (d) in trans-[Hg2(NO3)2(dppcb)L%2](NO3)2
(L%= P(CH2Ph)3 (7), P(CH2CH2CN)3 (8), PPh3 (9)), structure (e) in trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](AsF6)2 (10), and structure (f) in
trans-[Hg2(NO3)2(dppcb)(h1-P-dppmO)2](NO3)2 (11).
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
effects are responsible for this correlation. The NMR
data and FAB mass spectra of [Hg2(dppcb)(bipy)2](NO3)4 (5) and [Hg2(dppcb)(phen)2](NO3)4 (6) are consistent with structure types (b) and (c) in Scheme 1,
where bipy and phen are 2,2%-bipyridine and 1,10phenanthroline, respectively. Recent interest in HgII
coordination by heterocyclic nitrogens stems from the
observation that the pharmacological activity of sulphamides is often enhanced by complexation with
metal ions [29].
The compounds trans-[Hg2(NO3)2(dppcb)L%2](NO3)2
(L% = P(CH2Ph)3 (7), P(CH2CH2CN)3 (8), PPh3 (9)) corresponding to structure type (d) in Scheme 1 are rare
examples of HgII complexes containing three coordinated phosphines [30– 34]. This structure is confirmed
by the X-ray structures of trans-[Hg2(NO3)2(dppcb)(h1dppm)2](AsF6)2 (10) and trans-[Hg2(NO3)2(dppcb)(h1P-dppmO)2](NO3)2 (11), consistent with structure types
(e) and (f) in Scheme 1, also showing HgII centres
coordinated by three phosphines, where Ph2PCH2PPh2
(dppm) and Ph2PCH2P(O)Ph2 (dppmO) are involved in
a monodentate fashion. The NMR parameters and
X-ray structures of 10 and 11 clearly indicate for the
first time that in HgII complexes with two different
chelating phosphines and NO−
3 anions, only three phosphorus atoms are coordinated in solution as well as in
the solid state.
2. Experimental
2.1. Reagents and chemicals
Reagent grade chemicals were used as received unless
stated otherwise. Trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) was purchased from Aldrich.
Ph2PCH2PPh2 (dppm), P(CH2Ph)3, P(CH2CH2CN)3,
and PPh3 were obtained from Strem. All other reagents
and solvents were received from Fluka. Solvents used
for NMR measurements and crystallisation purposes
were of purissimum grade quality. Na2PtCl4·4H2O was
also obtained from Fluka. HgCl2, HgBr2, Hg(CN)2,
and Hg(NO3)2·H2O were purchased from Merck.
2.2. Instrumentation
Fourier-mode 199Hg{1H}, 31P{1H}, and 1H NMR
spectra were obtained using Bruker AC-200 and DPX300 spectrometers (internal deuterium lock). Positive
chemical shifts are downfield from the standards:
aqueous Hg(ClO4)2 (2 mmol of HgO per cm3 of 60%
HClO4) for the 199Hg{1H} resonances, 85% H3PO4 for
the 31P{1H} resonances and TMS for the 1H
resonances.
729
2.3. Syntheses of Hg II complexes
A Schlenk apparatus and oxygen-free, dry Ar were
used in the syntheses of all the complexes. Solvents
were degassed by several freeze–pump –thaw cycles
prior to use. All reactions were carried out at room
temperature (r.t.) unless stated otherwise. [Pt2Cl4(transdppen)2] and dppcb were prepared as described earlier
[10].
2.3.1. [Hg2Cl4(dppcb)] (1)
HgCl2 (0.077 mmol, 0.021 g) was dissolved in 10 cm3
EtOH and a solution of dppcb (0.039 mmol, 0.031 g) in
5 cm3 CH2Cl2 was added with vigorous stirring. A
white precipitate immediately formed. The slurry was
stirred for 1 h. The mixture of solvents was completely
removed, the white residue was slurried with water and
then filtered off, washed with H2O and dried in vacuo.
A white powder was recrystallised from DMF. Yield
0.052 g (91%); m.p. dec. 300°C. Anal. Found: C, 46.8;
H, 4.0. Calc. for C52H44Cl4P4Hg2·2DMF: C, 47.0; H,
3.9%. A sample for X-ray diffraction with the composition C52H44Cl4P4Hg2·2DMF was crystallised from
DMF.
2.3.2. [Hg2Br4(dppcb)] (2)
Compound 2 was prepared in a manner analogous to
1, where HgBr2 (0.077 mmol, 0.028 g) dissolved in 10
cm3 MeOH was used. A white powder was recrystallised from DMF. Yield 0.058 g (90%); m.p. 316°C.
Anal. Found: C, 41.9; H, 3.7. Calc. for C52H44Br4P4Hg2·2DMF: C, 42.0; H, 3.5%. A sample for X-ray
diffraction with the composition C52H44Br4P4Hg2·
2DMF was crystallised from DMF.
2.3.3. [Hg2(CN)4(dppcb)] (3)
Compound 3 was prepared in a manner analogous to
1, where Hg(CN)2 (0.077 mmol, 0.020 g) dissolved in 10
cm3 MeOH was used. A white powder was recrystallised from DMF. Yield 0.041 g (74%); m.p. 252–
254°C. IR (KBr, cm − 1) w (CN): 2160. Anal. Found: C,
51.3; H, 4.0; N, 5.6. Calc. for C56H44N4P4Hg2·2DMF:
C, 51.6; H, 4.0; N, 5.8%. A sample for X-ray diffraction
with the composition C56H44N4P4Hg2·2DMF was crystallised from DMF.
2.3.4. [Hg2(NO3)4(dppcb)] (4)
Hg(NO3)2·H2O (0.11 mmol, 0.038 g) was dissolved in
4 cm3 H2O. To this solution, dppcb (0.055 mmol, 0.044
g) dissolved in 5 cm3 CH2Cl2 was slowly added. Then
EtOH was added with vigorous stirring until a clear
solution was obtained. After several minutes a white
precipitate was formed. The slurry was stirred for 3 h.
The volume of the solvent was reduced, and the white
residue was filtered off, washed with H2O, and dried in
vacuo. A white powder was recrystallised from DMF.
730
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
Yield 0.052 g (65%); m.p. 214– 215°C. IR (KBr, cm − 1)
was(NO3) 1586, 1574; ws(NO3) 1300, 1263, 1026; l(NO3)
756. Anal. Found: C, 43.1; H, 3.3; N, 3.9. Calc. for
C52H44N4O12P4Hg2: C, 43.3; H, 3.1; N, 3.9%.
2.3.5. [Hg2(dppcb)(bipy)2](NO3)4 (5)
Compound 4 (0.055 mmol, 0.080 g) was dissolved in
CH2Cl2:DMF (v/v = 6:1, 10 cm3) and 2,2%-bipyridine
(0.11 mmol, 0.017 g) was added with vigorous stirring.
Immediately the colour of the solution turned yellowish. After 30 min a white precipitate formed slowly. The
slurry was stirred for 8 h. The mixture of solvents was
completely removed and the yellowish residue was dissolved in 6 cm3 MeOH. Then Et2O was added with
vigorous stirring. The white precipitate was filtered off,
washed with Et2O and dried in vacuo. A white powder
was recrystallised from DMF. Yield 0.074 g (77%);
m.p. 195–197°C. FAB mass spectrum: m/z 1474.2
+
[Hg2(dppcb)(bipy)](NO3)+
2 , 1055.4 [Hg(dppcb)](NO3) .
IR (KBr, cm − 1) w(NO3) 1385. Anal. Found: C, 49.1; H,
3.6; N, 6.3. Calc. for C72H60N8O12P4Hg2: C, 49.3; H,
3.4; N, 6.4%.
2.3.6. [Hg2(dppcb)(phen)2](NO3)4 (6)
Compound 6 was prepared in a manner analogous to
5, where 1,10-phenanthroline·H2O (0.11 mmol, 0.022 g)
was used. A white powder was recrystallised from
DMF. Yield 0.072 g (73%); m.p. 178– 180°C. FAB
mass spectrum: m/z 1498.2 [Hg2(dppcb)(phen)](NO3)+
2 ,
1055.4 [Hg(dppcb)](NO3)+. IR (KBr, cm − 1) w(NO3)
1385. Anal. Found: C, 50.3; H, 3.4; N, 6.0. Calc. for
C76H60N8O12P4Hg2: C, 50.6; H, 3.4; N, 6.2%.
2.3.7. trans-[Hg2(NO3)2(dppcb)(P(CH2Ph)3)2](NO3)2 (7)
Compound 4 (0.034 mmol, 0.049 g) was dissolved in
CH2Cl2:DMF (v/v =3:1, 6 cm3), and P(CH2Ph)3 (0.068
mmol, 0.021 g) was added with vigorous stirring. The
colourless solution was stirred for 8 h. The volume of
the solution was reduced and Et2O was added. Then
the white precipitate was filtered off, washed with Et2O
and dried in vacuo. A white powder was recrystallised
from DMF. Yield 0.050 g (71%); m.p. 195– 197°C. IR
(KBr, cm − 1) was(NO3 coordinated) 1601, 1586; ws(NO3
coordinated) 1333, 1291, 1030; l(NO3 coordinated)
766; w(NO3 ionic) 1385. Anal. Found: C, 55.0; H, 4.4;
N, 3.0. Calc. for C94H86N4O12P6Hg2: C, 55.1; H, 4.2; N,
2.7%.
2.3.8.
trans-[Hg2(NO3)2(dppcb)(P(CH2CH2CN)3)2](NO3)2 (8)
Compound 8 was prepared in a manner analogous to
7, where P(CH2CH2CN)3 (0.068 mmol, 0.013 g) was
used. A white powder was recrystallised from DMF.
Yield 0.037 g (59%); m.p. 155– 156°C. IR (KBr, cm − 1)
was(NO3 coordinated): 1586, 1572; ws(NO3 coordinated)
1310, 1236, 1026; l(NO3 coordinated) 796; w(NO3
ionic) 1385; w(CN) 2248. Anal. Found: C, 45.8; H, 3.9;
N, 7.7. Calc. for C70H68N10O12P6Hg2: C, 46.0; H, 3.7;
N, 7.7%.
2.3.9. trans-[Hg2(NO3)2(dppcb)(PPh3)2](NO3)2 (9)
Compound 9 was prepared in a manner analogous to
7, where PPh3 (0.068 mmol, 0.018 g) was used. A white
powder was recrystallised from DMF. Yield 0.046 g
(69%); m.p. 221°C. IR (KBr, cm − 1) was(NO3 coordinated) 1586, 1574; ws(NO3 coordinated) 1300, 1277,
1026; l(NO3 coordinated) 796; w(NO3 ionic) 1385.
Anal. Found: C, 53.5; H, 3.9; N, 3.0. Calc. for
C88H74N4O12P6Hg2: C, 53.7; H, 3.8; N, 2.8%.
2.3.10. trans-[Hg2(NO3)2(dppcb)(p 1-dppm)2](AsF6)2 (10)
and trans-[Hg2(NO3)2(dppcb)(p 1-P-dppmO)2](NO3)2
(11)
Compound 4 (0.069 mmol, 0.100 g) was dissolved in
CH2Cl2:DMF (v/v =10:1, 10 cm3), and dppm (0.138
mmol, 0.053 g) was added with vigorous stirring. The
yellowish solution was stirred for 2 h. The mixture of
solvents was completely removed and the residue was
dissolved in 10 cm3 MeOH. Then a solution of LiAsF6
(0.345 mmol, 0.068 g) in 5 cm3 MeOH was added with
stirring. A white precipitate formed immediately. The
white precipitate was filtered off, washed with H2O and
dried in vacuo. A white powder was recrystallised from
CH2Cl2. Yield 0.112 g (66%); m.p. 242°C. IR (KBr,
cm − 1) was(NO3) 1586, 1572; ws(NO3) 1310, 1277, 1024;
l(NO3) 796. Anal. Found: C, 49.6; H, 3.7; N, 1.4. Calc.
for C102H88As2F12N2O6P8Hg2: C, 49.7; H, 3.6; N, 1.1%.
A sample for X-ray diffraction with the composition
C102H88As2F12N2O6P8Hg2 was crystallised from
CH2Cl2 –MeOH –THF at 8°C.
trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](NO3)2
(0.136
mmol, 0.300 g) was dissolved in DMF:H2O (v/v =10:1,
10 cm3) and catalytic amounts of Hg(NO3)2·H2O were
added with vigorous stirring. After 1 min H2O was
added and a white precipitate formed immediately. The
white precipitate was filtered off, washed with H2O and
dried in vacuo. Colourless crystals were recrystallised
from CHCl3 –DMF –MeOH. Yield 0.036 g (11%); m.p.
208–210°C. The IR parameters are analogous to 10
except for the additional presence of w(NO3 ionic) at
1385 cm − 1. Anal. Found: C, 53.3; H, 4.5; N, 2.7. Calc.
for C102H88N4O14P8Hg2·DMF·1.2H2O·2MeOH: C,
53.5; H, 4.4; N, 2.9%. A crystal of this sample was
suitable for X-ray diffraction.
2.4. X-ray data collection, structure determination and
refinement
Details of the crystals and data collections are summarised in Tables 1 and 2. The empirical absorption
corrections were based on „-scans of nine reflections
(= 78–102°, 360° scans in 10° steps in „) [35]. All
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
731
Table 1
Crystallographic data for [Hg2L4(dppcb)] (L =Cl− (1), Br− (2), CN− (3))
Empirical formula
Colour
Habit
Crystal size (mm)
Unit cell dimensions
a (A, )
b (A, )
c (A, )
i (°)
V (A, 3)
Diffractometer
Crystal system
Space group
Z
Reflections collected
Independent reflections
Observed reflections
Rint
Completeness (%)
Number of parameters
Goodness-of-fit on F 2
Largest difference peak ((e A, −3))
Final R indices (observed data)
R1 (on F)
wR2 (on F 2)
Transmission
T (K)
1
2
3
C52H44Cl4P4Hg2·2DMF
colourless
prismatic
0.7×0.6×0.6
C52H44Br4P4Hg2·2DMF
colourless
prismatic
0.6×0.5×0.5
C56H44N4P4Hg2·2DMF
colourless
prismatic
0.5×0.5×0.4
13.333(3)
13.270(3)
23.095(5)
13.130(3)
19.212(4)
16.700(3)
106.17(3)
90.22(3)
2909.7(11)
5682(2)
Siemens P4 (Mo Ka radiation, …-scans)
monoclinic
monoclinic
P21/c
P21/n
4
2
11 304
12 877
9387
6476
5557
3165
0.022
0.024
99 (q= 2.08–25.00°)
99 (q =1.96–27.50°)
653
327
0.980
0.976
1.04
0.74
monoclinic
P21/n
2
11 939
5538
4117 (I\3|(I))
0.017
99 (q =1.99–26.04°)
430
1.001
0.62
0.0347
0.0789
0.641–0.969
163
0.0233
0.0534
0.395–1.000
163
0.0344
0.0684
0.601–0.987
173
13.237(3)
13.130(3)
16.603(3)
91.59(3)
2884.5(11)
Table 2
Crystallographic data for trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](AsF6)2 (10) and trans- [Hg2(NO3)2(dppcb)(h1-P-dppmO)2](NO3)2 (11)
Empirical formula
Colour
Habit
Crystal size (mm)
Unit cell dimensions
a (A, )
b (A, )
c (A, )
i (°)
V (A, 3)
Diffractometer
Crystal system
Space group
Z
Reflections collected
Independent reflections
Observed reflections
Rint
Completeness (%)
No. parameters
Goodness-of-fit on F 2
Largest difference peak (e A, −3)
Final R indices (observed data)
R1 (on F)
wR2 (on F 2)
Transmission
T (K)
10
11
C102H88As2F12N2O6P8Hg2
colourless
prismatic
0.5×0.2×0.1
C102H88N4O14P8Hg2·DMF·1.2H2O·2MeOH
colourless
prismatic
0.5×0.4×0.1
11.946(2)
31.062(6)
14.336(4)
106.99(1)
5087.4(19)
Siemens P4 (Mo Ka radiation, …-scans)
monoclinic
P21/c
2
11 031
9401
4168
0.035
99 (q = 1.98–28.00°)
631
1.031
0.89
23.620(4)
20.532(5)
22.449(7)
107.69(1)
10 372(4)
monoclinic
C2/c
4
9389
8339
4040 (I\3|(I))
0.041
99 (q =2.09–28.00°)
637
0.998
0.98
0.0554
0.1296
0.566–1.000
193
0.0561
0.1260
0.427–1.000
173
732
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
structure determination calculations were carried out
using SHELXTL NT 5.10 including SHELXS-97 [36] and
SHELXL-97 [37]. Final refinement on F 2 was carried out
with anisotropic thermal parameters for all non-hydrogen atoms except for the disordered DMF solvent
molecule in the case of 11. For 1, 2, 10, and 11 the
hydrogen atoms were included using a riding model
with isotropic U values depending on the Ueq of the
adjacent carbon atoms. In the case of 3 the hydrogen
atoms were located and isotropically refined with U
fixed.
3. Results
3.1. Crystal structures of [Hg2L4(dppcb)] (L = Cl− (1),
Br− (2), CN− (3))
In order to characterise definitely complexes of the
type [Hg2L4(dppcb)], the solid state structures of 1 –3
were determined by X-ray crystallography. They are
further novel examples of HgII centres showing tetrahedral coordinations by two phosphino groups and two
anions [12–28] and clearly indicate that these homobimetallic dimers correspond to structure type (a) in
Scheme 1. The crystal structure of 1 contains four
discrete [Hg2Cl4(dppcb)] molecules and eight DMF
molecules per unit cell. The crystal structures of 2 and
3 are isomorphous, consisting of two discrete
[Hg2L4(dppcb)] (L= Br− (2), CN− (3)) molecules and
four DMF molecules per unit cell. Compounds 2 and 3
are located on centres of symmetry. Views of 1 –3 are
given in Figs. 1–3. Table 3 contains selected bond
distances and bond angles.
The three structures show distorted tetrahedral coordinations of the HgII centres. In the case of 1 the
cyclobutane ring is nearly planar, where the dihedral
angle between the planes through C(1), C(2), C(4) and
C(2), C(3), C(4) is 177.8°. This folding of the cyclobutane ring is very small compared with the corresponding parameter of 145.6° in non-coordinating dppcb [10].
Furthermore, the cyclobutane ring of 1 shows a rectangular distortion, where the C(1)C(4) and C(2)C(3)
bond lengths of 1.608(9) and 1.595(9) A, belonging to
the five-membered rings are larger than the C(1)C(2)
and C(3)C(4) bond lengths of 1.544(8) and 1.542(9) A, ,
respectively. This is indicative of strain within the fivemembered rings. Nevertheless, these cyclobutane bond
lengths of 1 are typical of the usual range of 1.545–
1.607 A, [10,11,38– 40]. The strain of the five-membered
rings is partly released by ‘envelope’-folding (see Fig.
1(b)), leading to folding angles of 140.8 and 139.9° for
the five-membered rings containing Hg(1) and Hg(2),
respectively. This produces a Hg···Hg separation of
7.028(1) A, . The small P(1)Hg(1)P(4) and
P(2)Hg(2)P(3) chelate angles of 82.54(6) and
81.60(6)° are also a consequence of the five-membered
ring constraints. Nevertheless, the Cl(1)Hg(1)Cl(2)
and Cl(3)Hg(2)Cl(4) angles of 113.03(7) and
110.54(6)° remain nearly ideal. However, the variation
of the HgP bond lengths of 2.470(2)–2.6286(18) A, is
larger than in the two crystal modifications of
[HgCl2(PPh3)2] ranging from 2.462(2) to 2.532(4) A,
[17,21]. As a consequence the HgCl bond lengths vary
from 2.3941(19) to 2.5526(17) A, in 1, but only from
2.491(7) to 2.559(2) A, in [HgCl2(PPh3)2].
The X-ray structures of 2 and 3 fulfil the criteria of
analogous ligands coordinated to the same metal, the
same coordination number and geometry, isomorphous
crystal lattices and equal experimental conditions, and
therefore allow comparison of 2 and 3, where no interference with possible packing effects can be present
[41–43]. Figs. 2 and 3 clearly show the isomorphous
structures of 2 and 3. In both cases, owing to crystallographic constraints produced by the centres of symmetry, the cyclobutane rings are completely planar.
However, in 2 and 3 too , the cyclobutane rings show
rectangular distortions, where the C(1)C(2) bond
Fig. 1. (a) View of [Hg2Cl4(dppcb)] (1), showing the atom labelling
scheme; (b) view of [Hg2Cl4(dppcb)] (1) with the cyclobutane plane
perpendicular to the projection plane. For clarity only the first atoms
of the phenyl rings are shown.
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
733
The chelate angle in 2 is significantly larger than the
corresponding parameter of 80.5(1)° in [HgBr2(cis-dppen)], where cis-dppen is the chelating diphosphine
cis-1,2-bis(diphenylphosphino)ethene [22]. Compared
with 1, the HgP bond lengths of 2.5480(17) and
2.5315(17) A, are significantly different in 2. They are
significantly shorter than the analogous parameter of
2.572(2) A, in [HgBr2(cis-dppen)]. This leads to the
significantly longer Hg(1)Br(1) bond of 2.5537(9) A, in
2 than of 2.545(2) A, in [HgBr2(cis-dppen)]. However,
the Hg(1)Br(2) bond lengths of 2.5972(9) A, in 2 and
2.560(2) A, in [HgBr2(cis-dppen)] remain identical
within statistical significance.
In 3 the variation of the HgP bond lengths of
2.5426(9) and 2.5171(10) A, is smaller than the corresponding variation of 2.589(5) and 2.434(5) A, in
[Hg(CN)2(PPh3)2] [22]. However, both significantly different HgC bonds of 2.131(4) and 2.171(4) A, are
shorter in 3 than the analogous bonds of 2.19(2) and
2.27(3) A, in [Hg(CN)2(PPh3)2]. The CN bond lengths
of 1.121(6) and 1.119(5) A, in 3 and 1.13(3) A, in
Fig. 2. (a) View of [Hg2Br4(dppcb)] (2), showing the atom labelling
scheme. (b) View of [Hg2(CN)4(dppcb)] (3), showing the atom labelling scheme. The orientations of the phenyl rings in
[Hg2Br4(dppcb)] (2) and [Hg2(CN)4(dppcb)] (3) clearly indicate their
isomorphous structures.
length of 1.615(7) A, in 2 and the C(3)C(4) bond length
of 1.587(4) A, in 3 belonging to the five-membered rings
are significantly larger than the corresponding parameters for C(1)C(2A) of 1.562(8) A, in 2 and for
C(3)C(4A) of 1.557(4) A, in 3. Comparable to 1, this is
indicative of strain within the five-membered rings.
Also, in 2 and 3 the cyclobutane bond lengths remain
typical of the usual range of 1.545– 1.607 A, [10,11,38–
40]. This strain in 2 and 3 is again released by ‘envelope’-folding of the five-membered rings (see Fig. 3).
However, the folding angles of 159.8° in 2 and 158.6° in
3 are indicative of smaller ‘envelope’-foldings compared
with 1. This leads to significantly larger Hg···Hg separations of 7.627(1) A, in 2 and 7.598(1) A, in 3, and
significantly larger P(1)Hg(1)P(2) chelate angles than
in 1 of 84.13(5)° in 2 and 83.01(3)° in 3. Also, in 2 and
3 the Br(1)Hg(1)Br(2) angle of 104.57(3)° and the
C(1)Hg(1)C(2) angle of 108.15(15)° remain nearly
ideal.
Fig. 3. (a) View of [Hg2Br4(dppcb)] (2) with the cyclobutane plane
perpendicular to the projection plane. (b) View of [Hg2(CN)4(dppcb)]
(3) with the cyclobutane plane perpendicular to the projection plane.
For clarity only the first atoms of the phenyl rings are shown.
734
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
Table 3
Selected bond lengths (A, ) and angles (°) for [Hg2L4(dppcb)] (L = Cl−
(1), Br− (2) and CN− (3))
Compound 1
Bond lengths
Hg(1)P(1)
Hg(1)P(4)
Hg(2)P(2)
Hg(2)P(3)
Hg(1)Cl(1)
Hg(1)Cl(2)
Hg(2)Cl(3)
Hg(2)Cl(4)
P(1)C(1)
P(2)C(2)
P(3)C(3)
P(4)C(4)
C(1)C(2)
C(1)C(4)
C(2)C(3)
C(3)C(4)
2.5127(18)
2.536(2)
2.470(2)
2.6286(18)
2.5210(18)
2.4026(18)
2.5526(17)
2.3941(19)
1.852(7)
1.853(6)
1.840(7)
1.834(7)
1.544(8)
1.608(9)
1.595(9)
1.542(9)
Bond angles
Cl(2)Hg(1)P(1)
Cl(1)Hg(1)Cl(2)
P(1)Hg(1)Cl(1)
Cl(2)Hg(1)P(4)
P(1)Hg(1)P(4)
Cl(1)Hg(1)P(4)
Cl(4)Hg(2)P(2)
Cl(3)Hg(2)Cl(4)
P(2)Hg(2)Cl(3)
Cl(4)Hg(2)P(3)
P(2)Hg(2)P(3)
Cl(3)Hg(2)P(3)
C(11)P(1)C(1)
C(21)P(1)C(1)
C(11)P(1)Hg(1)
C(21)P(1)Hg(1)
C(1)P(1)Hg(1)
C(31)P(2)C(2)
C(41)P(2)C(2)
C(31)P(2)Hg(2)
C(41)P(2)Hg(2)
C(2)P(2)Hg(2)
C(51)P(3)C(3)
C(61)P(3)C(3)
C(51)P(3)Hg(2)
C(61)P(3)Hg(2)
C(3)P(3)Hg(2)
C(71)P(4)C(4)
C(81)P(4)C(4)
C(71)P(4)Hg(1)
C(81)P(4)Hg(1)
C(4)P(4)Hg(1)
C(2)C(1)C(4)
C(2)C(1)P(1)
C(4)C(1)P(1)
C(1)C(2)C(3)
C(1)C(2)P(2)
C(3)C(2)P(2)
C(4)C(3)C(2)
C(4)C(3)P(3)
C(2)C(3)P(3)
C(3)C(4)C(1)
C(3)C(4)P(4)
C(1)C(4)P(4)
131.22(6)
113.03(7)
102.31(6)
118.00(6)
82.54(6)
103.90(6)
137.75(6)
110.54(6)
103.05(6)
115.69(6)
81.60(6)
100.07(6)
104.3(3)
108.8(3)
113.1(2)
116.9(2)
102.0(2)
107.5(3)
105.5(3)
119.1(2)
111.4(2)
103.6(2)
105.4(3)
108.7(3)
115.3(2)
118.7(2)
99.8(2)
109.9(3)
106.0(3)
117.1(2)
113.9(2)
101.9(2)
89.4(4)
116.9(5)
117.7(4)
90.5(5)
113.9(4)
117.7(4)
90.0(5)
114.3(5)
118.4(4)
90.1(5)
115.5(4)
118.0(4)
Compound 2
Bond lengths
Hg(1)P(1)
Hg(1)P(2)
2.5480(17)
2.5315(17)
Table 3 (Continued)
Hg(1)Br(1)
Hg(1)Br(2)
P(1)C(1)
P(2)C(2)
C(1)C(2) a
C(1)C(2)
2.5537(9)
2.5972(9)
1.846(6)
1.863(6)
1.562(8)
1.615(7)
Bond angles
P(1)Hg(1)P(2)
P(2)Hg(1)Br(1)
P(1)Hg(1)Br(1)
P(2)Hg(1)Br(2)
P(1)Hg(1)Br(2)
Br(1)Hg(1)Br(2)
C(11)P(1)C(1)
C(21)P(1)C(1)
C(11)P(1)Hg(1)
C(21)P(1)Hg(1)
C(1)P(1)Hg(1)
C(31)P(2)C(2)
C(41)P(2)C(2)
C(31)P(2)Hg(1)
C(41)P(2)Hg(1)
C(2)P(2)Hg(1)
C(2) aC(1)C(2)
C(2) aC(1)P(1)
C(2)C(1)P(1)
C(1) aC(2)C(1)
C(1) aC(2)P(2)
C(1)C(2)P(2)
84.13(5)
114.50(5)
126.83(5)
121.66(4)
105.60(5)
104.57(3)
109.6(3)
106.5(3)
116.4(2)
111.8(2)
106.70(18)
108.8(3)
103.4(3)
115.6(2)
115.1(2)
106.67(19)
89.9(4)
116.1(4)
119.4(4)
90.1(4)
120.1(4)
118.2(4)
Compound 3
Bond lengths
Hg(1)C(1)
Hg(1)C(2)
Hg(1)P(1)
Hg(1)P(2)
P(1)C(3)
P(2)C(4)
C(1)N(1)
C(2)N(2)
C(3)C(4) a
C(3)C(4)
2.131(4)
2.171(4)
2.5426(9)
2.5171(10)
1.836(3)
1.865(3)
1.121(6)
1.119(5)
1.557(4)
1.587(4)
Bond angles
C(1)Hg(1)C(2)
C(1)Hg(1)P(2)
C(2)Hg(1)P(2)
C(1)Hg(1)P(1)
C(2)Hg(1)P(1)
P(1)Hg(1)P(2)
C(11)P(1)C(3)
C(21)P(1)C(3)
C(11)P(1)Hg(1)
C(21)P(1)Hg(1)
C(3)P(1)Hg(1)
C(31)P(2)C(4)
C(41)P(2)C(4)
C(31)P(2)Hg(1)
C(41)P(2)Hg(1)
C(4)P(2)Hg(1)
N(1)C(1)Hg(1)
N(2)C(2)Hg(1)
C(4) aC(3)C(4)
C(4) aC(3)P(1)
C(4)C(3)P(1)
C(3) aC(4)C(3)
C(3) aC(4)P(2)
C(3)C(4)P(2)
108.15(15)
113.09(13)
121.87(10)
123.17(13)
106.62(10)
83.01(3)
109.07(14)
106.44(16)
116.56(12)
111.08(10)
107.34(10)
108.37(14)
102.14(15)
115.19(12)
116.44(12)
107.05(10)
175.8(5)
171.6(4)
89.0(2)
115.6(2)
119.1(2)
91.0(2)
119.5(2)
117.8(2)
a
Symmetry transformations used to generate equivalent atoms:
−x, −y, −z.
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
Table 4
Hg{1H} and
199
735
31
P{1H} NMR data for 1–11 a
Compound
1
2
3
4
5
6
7
8
9
10
11 d
l(Hg)
l(P)
1217t
1668t
1655t
2076dt
2075dt
2127dt
2050tt
2112dt
6.44
−1.45
7.20
11.90
17.00
15.90
26.60d
27.70d
27.90d
27.20t
24.40d
b
1
J(Hg,P) b
2938
2457
1417
4333
3922
3979
1881
2300
2081
2022
2329
l(P) c
1
49.30t
44.50t
43.90t
18.70t
32.80t
5532
5840
5976
2859
6520
J(Hg,P) c
2
J(P,P)
102
107
116
63
109
a
J values in Hz. d, doublet; t, triplet; dt, doublet of triplets; tt, triplet of triplets. Spectra were run at 298 K. The following solvents were used:
DMF (1, 2, 4–9, 11) and CH2Cl2 (3 and 10).
b
Dppcb.
c
Monophosphine (7–9); h1-dppm (10); h1-P-dppmO (11).
d
l(P) (phosphineoxide) = 27.50.
[Hg(CN)2(PPh3)2]
significance.
are
identical
within
statistical
3.2. In6estigation of 1 – 11 in the solution state
The 199Hg{1H} and 31P{1H} NMR parameters of
compounds 1 –11 are summarised in Table 4. The
NMR data for 1–4 are consistent with structure (a) in
Scheme 1, showing four equivalent phosphorus atoms.
This means that the differences in HgP bond lengths
observed in the X-ray structures of 1 – 3 are equalised in
solution at room temperature. On cooling no further
splitting of the NMR signals occurs and the peaks are
only broadened. The trend of the l(P) values for 1–3
(see Table 4) is the same as for [HgL2(cis-dppen)],
where l =3.1 for L= Cl−, − 2.0 for L=Br−, and 7.2
for L = CN− [22]. The same is true for the 1J(Hg,P)
values for 1–3 (see Table 4) and [HgL2(cis-dppen)],
showing 3103 Hz for L=Cl−, 2547 Hz for L= Br−,
and 1525 Hz for L=CN−. In the series 1 – 4 the
31
P{1H} NMR resonance of 4 at 11.90 occurs at the
lowest field and the 1J(Hg,P) parameter of 4333 Hz is
the largest observed. This is in agreement with the same
trend for a series of [HgL2(PPh3)2] complexes, where L
is an anion [22,24]. l(Hg) of 1217 for 4 is shifted
towards a higher field compared with l(Hg) of 2517 for
the face-to-face complex [Hg2(HN2O3)2(NO3)2(Ph2PNHPPh2)2], also containing coordinated NO−
3 [2]. The
structure of 4 is confirmed by the presence of the IR
bands typical of coordinated NO−
3 [2,44] (see above).
The l(Hg) values of 1668 for 5 and 1655 for 6 are
shifted to lower fields compared with 4, which is characteristic of the occurrence of further chelate rings [7].
The same trend is observed for the l(P) parameters,
where the 1J(Hg,P) couplings of 5 and 6 are similar to
4 (see Table 4). Together with the presence of only one
−1
, typical of
IR band in the NO−
3 regions at 1385 cm
,
these
data
are
in
agreement
with
structures
ionic NO−
3
(b) and (c) in Scheme 1 for 5 and 6, respectively. This
tetrahedral coordination of HgII is also in line with the
fact that polydentate nitrogen donor ligands often induce higher coordination numbers than the classic linear arrangement [5].
Compounds 7–9 show the characteristic further
l(Hg) downfield shift compared with 4–6 (see Table 4)
as a consequence of the coordination of three phosphines per HgII centre [32–34]. Also, the occurrence of
the 199Hg{1H} NMR signals of 7–9 as doublets of
triplets is in agreement with structure (d) in Scheme 1.
The phosphorus resonances of dppcb in 7–9 occur at
higher fields than the resonances for the monophosphines. Since the same is observed for HgII complexes
contain-ing cis-dppen [22], this effect is related to the
distorted geometry of these HgII compounds induced by
the chelating phosphines. This is confirmed by the fact
that the 1J(Hg,P) values for the monophosphines in
7–9 are also more than twice as large compared with
the corresponding parameters for dppcb. Obviously, the
geometrical restraints of chelating, five-membered ring
forming phosphines like dppcb and cis-dppen markedly
reduce the binding overlap of their phosphorus orbitals
with HgII centres. In the case of 8 the occurrence of
w(CN) at 2248 cm − 1 clearly indicates the absence of
coordination of the nitrile groups [45]. The compounds
7–9 show only single isomers due to steric constraints.
It seems likely that only the trans isomers corresponding to structure (d) in Scheme 1 are formed, since the
X-ray structures of the comparable complexes 10 and
11 also reveal the trans isomers. This is confirmed by
the same preference of the trans isomer in the square
planar compound trans-[Pd2Cl2(dppcb)(PMePh2)2](BF4)2 [11].
736
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
The 199Hg{1H} NMR spectrum of 10 consists of a
triplet of triplets indicating that four phosphorus atoms
are coordinated to one HgII centre. This is in agreement
with structure (e) in Scheme 1, where the phosphorus
atoms of dppm are involved in an end-over-end exchange. This process is fast compared with the NMR
time scale at room temperature, but no new features
were obtained by low-temperature NMR measurements, due to the precipitation of 10. Accordingly, the
31
P{1H} NMR signals of the two different phosphorus
nuclei in 10 occur as triplets. However, the 1J(Hg,P)
value of 2022 Hz for dppcb in 10 is smaller than the
analogous parameter of 2859 Hz for dppm. Since
1
J(Hg,P) of dppcb is already reduced due to five-membered ring formation (see above), the unusual high
value for dppm in 10 indicates that no stable four-membered ring is present, which should lead to a further
reduction of the 1J(Hg,P) value as a consequence of the
very unfavourable overlap of the phosphorus orbitals
with the HgII centre. Thus, 10 is better formulated as
structure (e) in Scheme 1, with no stable four-membered ring. An analogous formulation has been found
for [Hg(h2-dppe)(h1-dppm)]2 + due to the same reasons,
where dppe is 1,2-bis(diphenylphosphino)ethane and
the 1J(Hg,P) parameters are 2822 Hz for dppm and
2456 Hz for dppe [32].
Compound 11 can be obtained via catalytic oxidation
of
trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](NO3)2
by
2+
2+
Hg . Increasing the amount of Hg
converts dppm
into Ph2P(O)CH2P(O)Ph2, which dissociates from the
HgII centre. As in 7 – 9, the 199Hg{1H} NMR spectrum
of 11 is a doublet of triplets consistent with structure (f)
in Scheme 1 and non-coordinating phosphinoyl groups.
Obviously, all l(Hg) values of 7 – 11 (see Table 4) are in
agreement with three coordinated phosphorus atoms
per HgII atom. The phosphorus resonance of dppcb in
11 occurs at a higher field than the resonance for the
phosphino group of dppmO, where its 1J(Hg,P)
parameter of 6520 Hz is nearly three times as large
compared with the corresponding parameter of 2329
Hz for dppcb. Both effects can again be explained by
the geometrical restraints of chelating dppcb (see
above). The 2J(P,P) value of 109 Hz for 11 is similar to
the same parameters of 102– 116 Hz for 7 – 9, but
considerably larger than the value of 63 Hz in 10. This
is in line with the fact that 2J(P,P) decreases with
increasing coordination ability of dppm versus the
monophosphines and dppmO [46].
The 1H NMR resonances (CH2Cl2-d2) for the aromatic protons in 1 – 11 occur at 6.5– 8.2. Broad 1H
NMR signals of the cyclobutane protons are observed
at 4.2–4.6. In 7, 8, 10, and 11 the CH2 resonances occur
at 2.0–2.3. For 1–11 the integrated intensities are in
agreement with the proposed structures.
3.3. Crystal structures of trans-[Hg2(NO3)2(dppcb) (p 1-dppm)2](AsF6)2 (10) and trans-[Hg2(NO3)2(dppcb) (p 1-P-dppmO)2](NO3)2 (11)
In order to characterise definitely 10 and 11, their
solid state structures were determined by X-ray crystallography.
Though
the
X-ray
structure
of
[Hg(dppe)2](O3SCF3)2 is known [47], the complete characterisation of 10 is the first reported for a HgII complex containing two different chelating phosphines.
Compound 11 is the unique example of a fully determined HgII compound consisting of chelating phosphine together with phosphinoyl moieties. The X-ray
structures of both 10 and 11 clearly indicate that not
only their solution but also their solid state structures
correspond to structure types (e) and (f) in Scheme 1,
respectively. The crystal structure of 10 consists of two
discrete trans-[Hg2(NO3)2(dppcb)(h1-dppm)2]2 + cations
and four (AsF6)− anions per unit cell. Trans[Hg2(NO3)2(dppcb)(h1-dppm)2]2 + is located on a centre
of symmetry and one phenyl ring is disordered. The
crystal structure of 11 contains four discrete trans[Hg2(NO3)2(dppcb)(h1-P-dppmO)2]2 + cations, eight
(NO3)− anions, four molecules of DMF, 4.8 molecules
of H2O, and eight molecules of MeOH per unit cell.
Trans-[Hg2(NO3)2(dppcb)(h1-P-dppmO)2]2 + is also located on a centre of symmetry. The ionic (NO3)− anion
and the DMF molecule are disordered. Views of the
cations of 10 and 11 are given in Figs. 4 and 5. Table
5 contains selected bond distances and bond angles.
The structures of 10 and 11 are nearer to distorted
trigonal pyramidal than to tetrahedral coordinations of
the HgII centres (see Figs. 4 and 5). Both in 10 and 11
the Hg(1) atoms show only small distances from the
planes through P(1), P(2), and P(3) of 0.325 and 0.294
A, , respectively. Therefore, these planes can be regarded
as the basal planes of the trigonal pyramids with the
monodentate (NO3)− groups at the apices. Further
interactions are negligible: in 10 the Hg(1)···O(2) and
Hg(1)···P(4) separations are 3.071 and 3.754 A, , respectively, and in 11 the Hg(1)···O(2) and Hg(1)···O(4)
distances are 3.035 and 3.192 A, , respectively. In 10 and
11, due to crystallographic constraints produced by the
centres of symmetry, the cyclobutane rings are completely planar. Within statistical significance the CC
bond lengths of the cyclobutane rings are identical (see
Table 5) and typical of the usual range of 1.545–1.607
A, [10,11,38–40]. In contrast to 1–3, this is indicative of
reduced strain within the five-membered rings, moving
from a tetrahedral coordination in 1–3 to a trigonal
pyramidal in 10 and 11. The ‘envelope’-foldings of the
five-membered rings of 147.5° in 10 and 146.7° in 11 are
located in between the corresponding values for 1–3
(see above). As a consequence the same is true for the
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
737
analogous parameters for 1–3 and also to the value of
83.0(1)° in [Hg(dppe)2](O3SCF3)2 [47]. In 10 and 11 the
significantly different chelating HgP bonds are significantly longer than the HgP bonds belonging to h1dppm and h1-P-dppmO, respectively: in 10 Hg(1)P(1)
is 2.522(3) A, , Hg(1)P(2) 2.555(3) A, , and Hg(1)P(3)
2.409(3) A, , and in 11 the corresponding parameters are
2.510(3), 2.595(3), and 2.411(4) A, . In both cases the
chelating HgP bond lengths are similar to the significantly different HgP bond lengths of 2.512(4) and
2.613(4) A, in [Hg(dppe)2](O3SCF3)2 [47]. They are also
comparable to the HgP bond lengths of 2.500(3)–
2.534(3) A, in the trigonal planar compound tris(tri-pmethoxyphenylphosphine)mercury(II)
diperchlorate
[31] and to the significantly different HgP bond
lengths of 2.527(4) and 2.547(4) A,
in the
[Hg(PMe2Ph)4]2 + cation [48]. Within statistical significance the Hg(1)O(1) distances for the coordinated
(NO3)− groups of 2.482(9) A, in 10 and 2.499(9) A, in 11
are identical with the analogous parameter of 2.507(4)
A, in [Hg(NO3)2(PPh3)2] [22,24]. The NO bond lengths
for the coordinated (NO3)− groups in 10 and 11 are
normal [22,24].
3.4. Comparison of the solid state and solution structures
of 1 – 3, 10, and 11
Fig. 4. (a) View of the cation of trans-[Hg2(NO3)2(dppcb)(h1dppm)2](AsF6)2 (10) with the cyclobutane plane perpendicular to the
projection plane. (b) View of the cation of trans[Hg2(NO3)2(dppcb)(h1-P-dppmO)2](NO3)2 (11) with the cyclobutane
plane perpendicular to the projection plane. For clarity only the first
atoms of the phenyl rings are shown.
Fig. 5. View of the cation of trans-[Hg2(NO3)2(dppcb)(h1-PdppmO)2](NO3)2 (11) showing the ‘envelope’-folding of the five-membered ring.
Hg···Hg separations of 7.282(1) A, in 10 and 7.292(1) A,
in 11. The P(1)Hg(1)P(2) chelate angles of 82.82(10)°
in 10 and 81.13(10)° in 11 are comparable to the
In the crystal structures of 1–3, 10, and 11 no
intermolecular contacts below 3.0 A, have been observed. This means that as a first approximation the
forces on the molecule in solution are of the same order
as those in the solid [49]. The PHgP chelate angles of
82.07° (mean value) in 1, 84.13(5)° in 2, and 83.01(3)°
in 3 are correlated with the ‘envelope’-folding angles of
140.4° (mean value) in 1, 159.8° in 2, and 158.6° in 3.
Thus, a larger ‘envelope’-folding produces a smaller
chelate angle. Furthermore, smaller chelate angles lead
to larger LHgL angles: 111.79° (mean value) for
L =Cl− (1), 104.57(3)° for L =Br− (2), and
108.15(15)° for L = CN− (3). Obviously, the solid state
structures of 1 –3 are determined by the ‘steric pressure’
[6] of dppcb, where releasing the strain of the five-membered rings results in larger ‘envelope’-foldings, but also
in larger deviations from ideal tetrahedral coordinations at the HgII centres. This subtle energetic balance
strongly influences the structures of 1–3. Nevertheless,
the solution 1J(Hg,P) parameters for 1–3 are in agreement with the trend for a series of [HgL2(PPh3)2] and
[HgL2(cis-dppen)] complexes, where L are the
analogous anions [22,24]. It seems likely, that in the
cases 1–3 the 1J(Hg,P) values are mainly a consequence
of the specific electronic demands of L.
The oxidation of one phosphorus atom of dppm in
the cation of 10 forming the cation of 11 has only little
influence on their solid state structures (see Fig. 4).
738
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
Table 5
Selected bond lengths (A, ) and angles
[Hg2(NO3)2(dppcb)(h1-dppm)2](AsF6)2
(10)
[Hg2(NO3)2(dppcb)(h1-P-dppmO)2](NO3)2 (11)
Table 5 (Continued)
(°) for
and
transtrans-
Compound 10
Bond lengths
Hg(1)P(1)
Hg(1)P(2)
Hg(1)P(3)
Hg(1)O(1)
P(1)C(1)
P(2)C(2)
P(3)C(3)
O(1)N(1)
O(2)N(1)
O(3)N(1)
P(4)C(3)
C(1)C(2)a
C(1)C(2)
2.522(3)
2.555(3)
2.409(3)
2.482(9)
1.882(9)
1.855(10)
1.817(11)
1.198(14)
1.213(14)
1.238(15)
1.857(11)
1.536(15)
1.573(14)
Bond angles
P(1)Hg(1)P(2)
P(1)Hg(1)P(3)
P(2)Hg(1)P(3)
O(1)Hg(1)P(1)
O(1)Hg(1)P(2)
O(1)Hg(1)P(3)
C(11)P(1)C(1)
C(21)P(1)C(1)
C(11)P(1)Hg(1)
C(21)P(1)Hg(1)
C(1)P(1)Hg(1)
C(31)P(2)C(2)
C(41)P(2)C(2)
C(31)P(2)Hg(1)
C(41)P(2)Hg(1)
C(2)P(2)Hg(1)
C(51)P(3)C(3)
C(61)P(3)C(3)
C(51)P(3)Hg(1)
C(61)P(3)Hg(1)
C(3)P(3)Hg(1)
N(1)O(1)Hg(1)
O(1)N(1)O(2)
O(1)N(1)O(3)
O(2)N(1)O(3)
C(71)P(4)C(3)
C(81)P(4)C(3)
C(2) aC(1)C(2)
C(2) aC(1)P(1)
C(2)C(1)P(1)
C(1) aC(2)C(1)
C(1) aC(2)P(2)
C(1)C(2)P(2)
P(3)C(3)P(4)
82.82(10)
138.01(9)
133.26(10)
84.2(3)
85.2(3)
114.7(3)
106.1(5)
109.4(5)
109.8(4)
119.3(4)
104.1(3)
108.5(5)
107.0(6)
118.4(4)
112.1(4)
103.6(3)
110.1(5)
107.9(5)
113.1(4)
108.4(4)
109.6(4)
113.4(8)
120.5(12)
118.3(12)
121.0(13)
101.4(6)
102.2(6)
90.8(8)
115.9(8)
117.7(7)
89.2(8)
115.2(8)
119.3(7)
108.3(6)
Compound 11
Bond lengths
Hg(1)P(1)
Hg(1)P(2)
Hg(1)P(3)
Hg(1)O(1)
P(1)C(1)
P(2)C(2)
P(3)C(3)
O(1)N(1)
O(2)N(1)
2.510(3)
2.595(3)
2.411(4)
2.499(9)
1.811(12)
1.832(11)
1.815(12)
1.206(13)
1.231(16)
O(3)N(1)
P(4)O(4)
P(4)C(3)
C(1)C(2)a
C(1)C(2)
1.228(17)
1.404(14)
1.816(11)
1.579(13)
1.587(14)
Bond angles
P(1)Hg(1)P(2)
P(1)Hg(1)P(3)
P(2)Hg(1)P(3)
O(1)Hg(1)P(1)
O(1)Hg(1)P(2)
O(1)Hg(1)P(3)
C(11)P(1)C(1)
C(21)P(1)C(1)
C(11)P(1)Hg(1)
C(21)P(1)Hg(1)
C(1)P(1)Hg(1)
C(31)P(2)C(2)
C(41)P(2)C(2)
C(31)P(2)Hg(1)
C(41)P(2)Hg(1)
C(2)P(2)Hg(1)
C(51)P(3)C(3)
C(61)P(3)C(3)
C(51)P(3)Hg(1)
C(61)P(3)Hg(1)
C(3)P(3)Hg(1)
N(1)O(1)Hg(1)
O(1)N(1)O(3)
O(1)N(1)O(2)
O(3)N(1)O(2)
O(4)P(4)C(71)
O(4)P(4)C(81)
O(4)P(4)C(3)
C(71)P(4)C(3)
C(81)P(4)C(3)
C(2) aC(1)C(2)
C(2) aC(1)P(1)
C(2)C(1)P(1)
C(1) aC(2)C(1)
C(1) aC(2)P(2)
C(1)C(2)P(2)
P(3)C(3)P(4)
81.13(10)
139.77(10)
134.19(10)
91.5(2)
81.3(2)
109.9(2)
105.8(5)
108.1(5)
108.1(4)
118.6(4)
105.6(3)
113.0(5)
106.2(6)
117.7(4)
109.6(4)
103.3(4)
108.5(5)
106.2(6)
110.6(5)
109.0(5)
111.8(4)
110.6(9)
115.8(15)
122.3(12)
121.4(13)
112.7(8)
112.8(7)
113.2(7)
104.5(6)
105.8(5)
89.2(7)
115.9(7)
119.2(8)
90.8(7)
117.5(7)
117.6(8)
112.0(6)
a
Symmetry transformations used to generate equivalent atoms:
−x, −y, −z.
Also, in this case the P(1)Hg(1)P(2) chelate angles of
82.82(10)° in 10 and 81.13(10)° in 11 are correlated with
the ‘envelope’-folding angles of 147.5° in 10 and 146.7°
in 11. Though the effect is small, for the trigonal
pyramidal coordinations of 10 and 11 as well, a larger
‘envelope’-folding leads to a smaller chelate angle. The
mean values of the chelating HgP bond lengths of
2.539 A, in 10 and 2.553 A, in 11 are nearly identical.
Within statistical significance the HgP bonds belonging to h1-dppm and h1-P-dppmO, respectively, of
2.409(3) A, in 10 and 2.411(4) A, in 11 are the same.
These differences of chelating HgP and Hg-h1-P bond
lengths correspond nicely to the solution 1J(Hg,P) values for dppcb of 2022 Hz in 10 and 2329 Hz in 11,
which are smaller than the analogous parameters for
W. Oberhauser et al. / Polyhedron 20 (2001) 727–740
h1-dppm and h1-P-dppmO, respectively, of 2859 Hz in
10 and 6520 Hz in 11. As mentioned above, this is
certainly a consequence of the reduced binding overlap
of the phosphorus orbitals of chelating phosphines with
HgII centres due to geometrical restraints. However, the
presence of an end-over-end exchange of h1-dppm in 10
forming a transient four-membered ring also reduces its
1
J(Hg,P) value compared with 11.
739
tane ring of dppcb produces PdII catalysts for
CO/ethene copolymerisation that are more efficient
than those of dppe by a factor of ten and comparable
to the industrial catalysts [52]. In homobimetallic complexes of RhI, two X-ray structures [53] clearly reveal
that dppcb induces the rare effect of mechanical coupling [54] and two different coordination sites are
formed in these dimers. Further work on this is in
progress.
4. Discussion
Emphasis has been given to the fact that the Fermi
contact term is not always dominant in determining
1
J(Hg,P) due to approximations or to contributions
from other coupling mechanisms that are larger than
expected [18]. As a possible consequence the 1J(Hg,P)
values are not consistent with the corresponding HgP
bond lengths. This is observed in 1 –3, where the mean
HgP bond lengths of 2.537 A, in 1, 2.5398 A, in 2, and
2.5299 A, in 3 are not in line with the corresponding
1
J(Hg,P) parameters (see Table 4). Furthermore, 31P
solid state NMR results for mercury– phosphine complexes reveal an anisotropy in the 199Hg31P J tensor,
which is comparable to the isotropic coupling constant,
being in the order of 70% [12,13,18,50]. Therefore, one
can conclude that mechanisms other than Fermi contact are operative and make substantial contributions
to the transmission of nuclear spin information between
199
Hg and 31P nuclei in these systems. Anisotropy is
clearly present in the solid state structures of 1 – 3, 10,
and 11, since all chelating HgP bond lengths are
significantly different in every complex (see Tables 3
and 5).
It seems likely that in all compounds, 1– 11, ‘envelope’-foldings of the five-membered rings are present,
which is confirmed by five X-ray structures. Also, in
complexes of HgII with bis[(2-pyridyl)methyl]amine the
five-membered chelating rings are each in an envelope
conformation [9]. Due to this release of strain, dppcb
prevents symmetrisation processes in the homobimetallic complexes 1–11 and no other HgII species are
formed. This happens in binuclear compounds of general formula [RHg(L-L)HgR]2 + (L-L = Ph2P(CH2)n PPh2, n=1–3), leading to the formation of the symmetrically substituted compounds, HgR2 and [Hg(L-L)2]2 +
[47]. The same effect occurs in [Hg(h2-dppe)
(h1-dppm)]2 + , where [Hg(h2-dppe)2]2 + and [Hg(h1dppm)2]2 + are produced [32].
The catalytic oxidation with Hg2 + leading to 11
could provide a simple method for the preparation of
dppmO. Only recently, the importance of heterodifunctional ligands derived from diphosphines or dppcb has
been emphasised [38,51]. Not only in the case of HgII
do the steric requirements of dppcb lead to new structural features. The decreased flexibility of the cyclobu-
5. Supplementary data
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos 152313, 152314, 152315,
152316, and 152317 for compounds [Hg2L4(dppcb)]
(L= Cl− (1), Br− (2), CN− (3)), trans-[Hg2(NO3)2(dppcb)(h1-dppm)2](AsF6)2 (10), and trans-[Hg2(NO3)2(dppcb)(h1-P-dppmO)2](NO3)2
(11),
respectively.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: + 44-1223-336033; email: [email protected] or www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
We thank the Fonds zur Förderung der wissenschaftlichen Forschung, Austria, for financial
support.
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