Different connectivities in supramolecular aggregates of trinuclear gold(I) complexes with the sacconi-ligand N(CH2CH2PPh2)3

Article abstract of DOI:10.1515/znb-1997-1206

Trichloro-[tris(2-(diphenylphosphanyl)ethyl)amine]-trigold(I) (1) has been prepared by treating the tripod ligand tris(2-(diphenylphosphanyl)ethyl)amine with three equivalents of chloro(dimethylsulfide)gold(I) in dichloromethane. Treatment of solutions of 1 in dichloromethane with potassium bromide or potassium iodide resulted in the formation of the tribromo (2) and triiodo (3) derivatives. All compounds were crystallized and X-ray structure analyses have been performed. Complexes 1 and 2 are isomorphous and crystallize in the rhombohedral space group R3?. An aggregation into layers through Au-X' contacts of 3.734 (X = Cl) and 3.711 ? (X = Br), but no Au-Au contacts were observed. Compound 3 on the other hand crystallizes in the monoclinic space group P2₁/c. The molecules are linked into strings through short intermolecular Au-Au contacts of 3.1072 ?.

Full text of DOI:10.1515/znb-1997-1206

Different C onnectivities in Supram olecular Aggregates of Trinuclear
GoId(I) Com plexes with the Sacconi-Ligand N(CH 2CH2PPh2)3
Johann Zank, Annette Schier, Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universität München,
Lichtenbergstrasse 4, D-85747 Garching, Germany
Z. Naturforsch. 52 b, 1471-1476 (1997); received October 13, 1997
(Triphosphane)gold(I) Complexes, Gold-Gold Contacts, Crystal Structure, Polynuclear Gold(I)
Complexes
Trichloro-[tris(2-(diphenylphosphanyl)ethyl)amine]-trigold(I) (1) has been prepared by
treating the tripod ligand tris(2-(diphenylphosphanyl)ethyl)amine with three equivalents
of chloro(dimethylsulfide)gold(I) in dichloromethane. Treatment of solutions of 1 in
dichloromethane with potassium bromide or potassium iodide resulted in the formation of
the tribromo (2) and triiodo (3) derivatives. All compounds were crystallized and X-ray struc-
ture analyses have been performed. Complexes 1 and 2 are isomorphous and crystallize in the
rhombohedral space group R3. An aggregation into layers through Au-X' contacts of 3.734 (X
= Cl) and 3.711 A (X = Br), but no Au-Au contacts were observed. Compound 3 on the other
hand crystallizes in the monoclinic space group P2i/c. The molecules are linked into strings
through short intermolecular Au-Au contacts of 3.1072 A.
Introduction
on ab initio calculations [10], the iodine compound
is expected to form the strongest gold-gold interac-
tions, while the bromide and the chloride should be
less prone to impose a similar structural pattern on
the packing.
Extensive research in several laboratories has
shown in recent years that most of the “simple”
gold(I) complexes of the type L-Au-X are actually
forming oligomeric or polymeric aggregates in the
solid state, the structures of which are determined
by A u-A u interactions [1 - 4]. The metal atoms
are generally taking up positions with equilibrium
interatomic distances around 3.0 A, and with the in-
termetallic approach perpendicular to the principal
axis of the individual molecules. The energy associ-
ated with a pair-wise aggregation amounts to ca. 7 -
11 kcal/mol [5 - 7] and is thus comparable to that of
a standard hydrogen bond, the most common mode
of supramolecular aggregation.
Previous investigations in this laboratory had fo-
cused initially on trinuclear gold(I) complexes of
tripodal ligands with short tentacles, which allowed
and even forced the metals into a close intramolecu-
lar approach. For HC(PPh2)3 [11] a trinuclear clus-
ter spanned by the ligand was obtained, but already
for RC(CH2PPh2)3 [12, 13] intermolecular contacts
dominate the aggregation. (NP3) is now used as the
basis for an extension of these earlier studies.
Preparation and Properties of the Ligand and its
Complexes
Following this concept we have now investigated
a set of complexes of a tripodal ligand (NP3) with
threefold symmetry first prepared by Sacconi and
his collaborators [8], which was used only once
in gold chemistry [9]. This ligand was expected to
form a framework with intermolecular connections
leading to layer-type aggregates. The halides Cl, Br,
and I were chosen as the counterions for gold(I), be-
cause they are sterically least demanding and give
room for a close approach of the metal atoms. Based
The ligand (NP3) was prepared following the
literature method given by Sacconi et al.: Tri-
ethanolamine is first converted into the trichloride
using thionyl chloride, followed by treatment with a
base. Upon reaction with potassium diphenylphos-
phide this trichloride finally affords the tripodal
molecule in an overall 60% yield.
Treatment of (NP3) with three equivalents of
chloro(dimethylsulfide)gold(I) in dichloromethane
* Reprint requests to Prof. Dr. H. Schmidbaur.
at room temperature leads to
a quantitative
0939-5075/97/1200-1471 $ 06.00
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1997 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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J. Zank et al. •Trinuclear Gold(I) Complexes with the Sacconi-Ligand
1472
liberation of dimethylsulfide within less than 2 h,
and the product (NP3)(AuCl)3 (1) can be isolated in
86% yield. The trinuclear complex is a colourless
crystalline solid, stable to air and moisture, which
decomposes on heating above 159 °C. It is soluble
in dichloromethane and crystallizes as a 1:1 solvate
on addition of pentane as shown by microanalytical
data.
N(CH2CH2PPh2)3
+
M^S-Au-Cl
N(CH2CH2PPh2AuCl)3
Fig. 1. Molecular structure of (NP3)(AuC1)3 (1) (ORTEP,
50% probability ellipsoids,o hydrogen atoms omitted).
Selected bond lengths [A] and angles [°]: Au-P
2.231(2), Au-Cl 2.285(2), Cl-Au-P 177.12(8), C-N-C
110.6(6). {Selected bond lengths [A] and angles [°] of
(NP3)(AuBr)3(2): Au-P 2.239(3), Au-Br 2.4022(13), Br-
Au-P 176.07(8), C-N-C 110.4(8)}.
1
N(CH2CH2PPh2AuBr)3
N(CH2CH2PPh2AuI)3
2
3
Scheme 1.
The trichloride can be converted into the
tribromide (NP3)(AuBr)3 (2) and triiodide
(NP3)(AuI)3(3) by metathesis with KBr or KI, re-
spectively, in a dichloromethane/water two-phase
system at room temperature. After 12 h of stir-
ring the yields are 84% (2) and 68% (3), re-
spectively. Crystals are obtained upon layering the
dichloromethane solutions with pentane.
The complexes were identified by elemental anal-
yses and mass spectrometric data. Solutions in
CDCI3 show the expected set of resonances in the
'H , 13C {1H} and 31P{ 1H } NMR spectra with only
small variations in the chemical shifts and multi-
plicities.
Attempts to generate the corresponding trigold-
oxonium tetrafluoroborate [(NP3)Au3 0 ]+ BF4~
using established methods [15, 16] failed, and
Fig. 2. View on to the layer structure of (NP3)(AuX)3 (X
= Cl, Br), 1 and 2. The molecules are aggregated through
intermolecular metal-halogen contacts of 3.734 (X = Cl)
and 3.711 Ä (X = Br).
experiments to produce
a
trimethyl complex
(NP3)(AuM e)3 by reaction of 1 with three equi-
valents of LiMe [17] were also unsuccessful.
in the unit cell. In the lattice, the threefold axis
passes through the nitrogen atom, and the three
arms of the tripodal ligand are symmetry-equivalent
(Fig. 1). The configuration of the central nitrogen
atom is pseudo-tetrahedral with angles C-N-C at
110.6(6) and 110.4(8)° for 1 and 2, respectively.
The ethylene bridges are in a strain-free single-trans
Crystal and Molecular Structures
Crystals of (NP3)(AuCl)3 (1), and (NP3)(AuBr)3
(2), are isomorphous and crystallize in the rhom-
bohedral space group R3 with 6 trinuclear units
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J. Zank et al. • Trinuclear Gold(I) Complexes with the Sacconi-Ligand
1473
Fig. 3. Molecular structure of (NP3)(AuI)3 (3) (ORTEP, Fig. 5. Chiral conformation adopted by 3 in the crystal
50% probability ellipsoids,o hydrogen atoms omitted).
- Selected bond lengths [A] and angles [°]: Aul-Pl
2.253(3), Aul-Il 2.5494(9), Au2-P2 2.262(3), Au2-
12 2.5716(9), Au3-P3 2.252(3), Au3-I3 2.5679(10),
Pl-Aul-Il 171.88(7), P2-Au2-I2 172.25(8), P3-Au3-I3
173.48(7).
(phenyl rings omitted for clarity).
exceptions to the general rule that L-Au-X com-
pounds aggregate through A u-A u' contacts, which
appear to be more strongly bonding than A u-X ' con-
tacts. However, because all these types of secondary
bonding are generally weak, they may be overruled
by other forces, like solvation (in solution) or pack-
ing (in the crystal). The latter is probably true also
for the present cases (1 and 2). A close inspection
of Fig. 2 shows that in the layers there is efficient
space filling like by pieces of a puzzle. A shift-
ing of the P-Au-Cl(Br) groups in one direction or
the other to allow A u-A u contacts instead of A u-
X' contacts would cause steric congestion in other
realms and thus be energetically unfavourable. The
arrangement of the (P-Au-X)2 units in 1 and 2 is of
the type frequently encountered in the correspond-
ing silver(I) or copper(I) compounds [18, 19], where
metal-metal bonding is much weaker owing i. e. to
the larger radius of silver as compared to gold [20]
and other properties affected by relativistic effects
[21].
Fig. 4. View of the supramolecular structure of 3. Forma-
tion of strings through intermolecular Au-Au contacts of
3.1072(7) A (only two of the three P-Au-I units participate
in the aggregation).
conformation and link the PPh2 groups to the nitro-
gen hub. The phosphorus atoms are in a tetrahedral
environment and are part of the linear coordina-
tion unit at the gold atoms with angles Cl-Au-P =
177.12(8) and Br-Au-P = 176.07(8)°. Like the bond
angles, the bond lengths show no anomalies.
Crystals of (NP3)(AuI)3 (3), are monoclinic,
space group P2i/c, with 4 formula units in the unit
cell. The individual molecules have no crystallo-
graphically imposed symmetry and the different
conformations of the three arms of the tripodal lig-
and lead to very significant deviations from the ide-
alized threefold symmetry (Fig. 3). Only two of the
three N-CH2-CH2-P units have the strain-free, stag-
gered, single-trans conformation, while the other
one is single-cis (N-C12-C11-PI). The configura-
tion at the nitrogen atom is rather flat with a sum of
In the crystals, the molecules of compounds 1 and
2 are aggregated into layers with the shortest inter-
molecular distances between the P-Au-X moieties
(X = Cl, Br; Fig. 2). The Au-X units form paral-
lelograms with A u-X ' contacts of 3.734 (X = Cl)
and 3.711 A (X = Br). These structures are two rare
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1474
Table I. Crystal data, data collection, and structure refinement for compounds 1, 2, and 3.
J. Zank et al. • Trinuclear Gold(I) Complexes with the Sacconi-Ligand
1
2
3
Crystal data
Formula
Mr
Crystal system
Space group
a (A)
b (A)
c (A)
a(°)
ß O
G^H-pAu^ChNPi
C42H42AU3I3NP3
1625.28
monoclinic
P2\/c
8.954(1)
27.108(2)
18.610(2)
90
98.43(1)
90
4468.3(8)
2.416
C42H42Au3Br3NP3
1350.93
rhombohedral
R3
17.208(1)
17.208(1)
28.721(3)
90
90
120
7365.3(10)
1.827
6
1484.31
rhombohedral
R3
17.263(1)
17.263(1)
29.318(3)
90
90
120
7566.5(10)
1.954
6
7 O
V(A3)
Pcalc (gem ' )
Z
4
F(000)
ju(Mo Ka) (cm-1)
3804
92.29
4128
112.01
2968
120.36
Data collection
T(°C)
Scan mode
-74
(j)
-90
UJ
-90
uj/9
hkl range
-21—»-2, 0—>21, -32—>35
0.62
4400
2959 [Rint = 0.0352]
2943
psi-scans
0.502/0.999
0— 10, 0—33,-22—22
0.62
9756
8483 [Kim = 0.0479]
8412
psi-scans
0.408/0.999
-21—>18,0—21, 0—^36
0.62
5216
3302 [Rm = 0.0320]
3282
psi-scans
sin(6»/A)max (A-1)
Measured reflections
Unique reflections
Refls. used for refinement
Absorption correction
0.496/0.999
Tmin ITjnax
Refinement
Refined parameters
H atoms (found/calcd.)
Final R values [I > 2cr(I)]
R \w
173
0/14
157
0/14
469
0/42
0.0410
0.0529
0.0431
wR2[b]
0.0964
0.1090
0.1335
(shift/error)max
/9fin(max/min) (eA-3)
o
< 0.001
4.284/-1.147tc]
< 0.001
5.203/-0.719[c]
< 0.001
2.035/- 1.809[dl
[a] R = r(IIF0l - IFcll)/riF0l;[b] wR2 = {[Ew (F20-F2c)2VS[w(F20)2] } {/2-, w = 1l[a2(F20) + (ap)2 + bp]-, p = {Fl + 2F“)/3;
a = 0.0590 (1), 0.0642 (2), 0.0326 (3); b = 177.28 (1), 315.78 (2), 66.73 (3);tc] see Experimental Section;™ residual
electron densities are located around the Au and I atoms.
the C-N-C angles at 343.5(8)° [average individual
is 3.1072(7) A and thus in the range typically cov-
angle 114.5(8)°, i.e. 4° larger than in 1 and 2], Most ered by aurophilic bonding [5 - 7]. This contact
other bond lengths and angles are as expected.
is clearly governing the supramolecular structure,
and this is not unexpected because theoretical cal-
culations predict that A u-A u bonding should be
strongest with polarizable, less electronegative sub-
stituents [10]. The “crossed” arrangement of the
P-Au-I units engaged in bonding (with a dihedral
angle I2-Au2-Au3'-I3' = 103.8°) is also known to
represent the energy minimum.
The marked differences in the crystal structures
of 1 and 2 on the one hand and 3 on the other
are clearly the consequence of a different type of
supramolecular aggregation: The molecules of com-
plex 3 are linked up into meandering strings through
short A u-A u contacts originating from two of the
three P-Au-I units (with Au2 and Au3, Fig. 4). The
atom triple P l-A u l-Il has no such contacts and
can be described as dangling free. The distance
Au2-Au3' (or its symmetry-equivalent Au2'-Au3)
Space-filling models of the lattice of complex 3
reveal that there is also an efficient phenyl stacking
which is probably strongly supporting the overall
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J. Zank et al. ■Trinuclear Gold(I) Complexes with the Sacconi-Ligand
1475
packing arrangement. Centers of inversion between
the meandering strings of molecules are relating
the components by symmetry. The chiral confor-
mation adopted by the molecules in the crystal is
thus present in two enantiomeric forms, repeated
by the relation imposed by the screw axis (Fig. 5).
Compound 3: (NP3)(AuC1)3 (100 mg, 0.074 mmol)
is dissolved in dichloromethane (10 ml) and a solution
of KI (370 mg, 2.22 mmol) in water (20 ml) is added.
After stirring this dichloromethane/water two-phase sys-
tem for 12 h the dichloromethane phase is dried with
MgSC>4 and filtered. After layering the dichloromethane
solution with pentane the crystallization of a colourless
needle-like product is observed. Yield 75 mg (62%), m.
p. 230 °C (decomp.). NMR (CDC13, 20 °C), 'H: 7.2 -
7.73 (m, 30 H, Ph); 2.68 (m, 6 H, N-CH2); 2.52 (m, 6 H,
P-CH2). 31P{‘H}: 33.5 (s). MS (FAB): m/z (%) = 1499
(42) [M+ - 1],
Experimental Part
General: All experiments were carried out if neces-
sary under dry, purified N2. Solvents were dried, distilled
and kept under N2. Glassware was oven-dried and filled
with N2. NMR spectra: Jeol GX 270 and GX 400 spec-
trometers; tetramethylsilane and phosphoric acid as ref-
erence compounds for 'H, l3C and 31P NMR (6 values in
[ppm], J values in [Hz]). Mass spectra: Finnigan MAT 90
C42H42AU3I3NP3 (1625.32 g/mol)
Calcd C 31.04 H 2.61 123.42 N 0.86%,
Found C 30.97 H 2.64 123.16 N 0.85%.
spectometer. Microanalyses\ In-house analysers (by com- Crystal Structure Determination
bustion). The ligand tris-[2-(diphenylphosphanyl)ethyl]-
amine (NP3) [8] and chloro(dimethylsulfide)gold(I) [14]
Specimens of suitable quality and size of com-
pounds 1, 2, and 3 were mounted in glass capil-
laries and used for measurements of precise cell
constants and intensity data collection on an Enraf
Nonius CAD4 diffractometer (Mo-ATQ radiation, A
= 0.71073 A). During data collection, three stan-
dard reflections were measured periodically as a
were prepared according to literature procedures.
Compound 1: NP3 (0.5 g, 0.77 mmol) is dissolved
in dichloromethane (20 ml) and (Me2S)AuCl (0.68 g,
2.29 mmol) is added at r. t. with stirring. Stirring is
continued for 2 h. The product precipitated as a white
solid after addition of pentane. Recrystallization from
dichloromethane/pentane gave colourless crystals. Yield general check of crystal and instrument stability.
0.91 g (86%), m. p. 159 °C (decomp.). NMR (CDC13, 20
°C), 'H: 7.52 - 7.74 (m, 30 H, Ph); 2.72 (m, 6 H, N-CH2);
2.61 (m, 6 H, P-CH2). '^ C h } : 133.1 (d, 2/(PC) = 13.5,
C2/6); 131.9 (d, 4/(PC) = 2.0, C4); 129.3 (d,V(PC) =
11.4, C3/5); 129.2 (d, '/(PC) = 59.7, Cl); 54.8 (s, N-C);
47.8 (d, '/(PC) = 7.3, P-C) .31P{1H}: 26.8 (s). MS (FAB):
m/z (%)= 1315 (19) [M+ - Cl],
No significant changes were observed for com-
pounds 2 and 3, whereas the data of compound
1 were corrected for decay (-5.8 %). Lp correc-
tion was applied and intensity data were corrected
for absorption effects. The structures were solved
by direct methods (SHELXS-86) and completed
by full-matrix least-squares techniques against F2
(SHELXL-93). The thermal motion of all non-
hydrogen atoms was treated anisotropically. All hy-
drogen atoms were placed in idealized calculated
positions and allowed to ride on their correspond-
ing carbon atoms with isotropic (CH2 of compound
1) or fixed isotropic contributions (UjS0(fiX) = 1.5
x Ueq of the attached C atom), respectively. The
high residual electron densities observed for com-
pounds 1 and 2 probably correspond to traces of
CH2C12 in the crystals (as also indicated by ele-
C42H42AU3CI3NP3 • CH2CI2 (1377.16 g/mol)
Calcd C 35.97 H 3.09 Cl 12.35 N0.98%,
Found C 35.43 H 3.08 Cl 13.7 NO.92%.
Compound 2: (NP3)(AuC1)3 (60 mg, 0.044 mmol) is
dissolved in dichloromethane (10 ml) and a solution of
KBr (160 mg, 1.32 mmol) in 10 ml of water is added. This
dichloromethane/water two-phase system is stirred for 12
h. The dichloromethane phase is dried using MgS04 and
filtered. A layer of pentane is then allowed to diffuse into
the dichloromethane solution resulting in the crystalliza-
tion of a colourless product. Yield 55 mg (84%), m. p. 149 mental analyses and spectroscopic data of the crys-
°C (decomp.). NMR (CDC13, 20 °C), 'H: 7.45 - 7.74 (m,
30 H, Ph); 2.64 (m, 6 H, N-CH2); 2.50 (m, 6 H, P-CH2).
31P{'H}: 28.9 (s). MS (FAB): m/z (%) = 1405 (100) [M+
-Br],
talline materials). Attempts to include the solvent
molecules in the refinements were not succesfull.
Further information on crystal data, data collec-
tion and structure refinement are summarized in
Table I. Important interatomic distances and an-
gles are given in the corresponding Figure Captions.
Anisotropic thermal parameters, tables of distances
C42H42Au3Br3NP3 •CH2C12 (1569.26 g/mol)
Calcd C 32.90 H 2.83 Br 15.2 N 0.89%,
Found C 31.62 H 3.24 Br 15.0 N 0.73%.
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J. Zank et al. •Trinuclear Gold(I) Complexes with the Sacconi-Ligand
and angles, and atomic coordinates have been de-
posited with Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaftlich-technische Infor-
mation mbH, D-76344 Eggenstein-Leopoldshafen.
The data are available on request on quoting CSD
No. 407785 (1), 407784 (2), and 407783 (3).
Acknowledgements
This work was supported by Deutsche Forschungs-
gemeinschaft and Fonds der Chemischen Industrie. The
authors are grateful to Mr. J. Riede for establishing the
X-ray data sets.
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