A dimeric gold(I) triphospholyl complex

Article abstract of DOI:10.1016/S0022-328X(01)01211-6

The reaction of 1-trimethylstannyl-3,5-di(tert-butyl)-1,2,4-triphosphol with PPh₃AuCl affords [(1,2,4-triphospholyl)Au(PPh₃)] (5) in high yield. NMR spectra of 5 are indicative for a highly dynamic compound in solution. The molecular structure of 5 in the solid state is that of the dimer [(1,2,4-triphospholyl)Au(PPh₃)]₂. Its most striking feature is a remarkable range of different metal-triphospholyl ligand bonds which create a pronounced asymmetric core of the molecule. The central Au-Au distance of 3.14 ? indicates a weak interaction of the metal atoms.

Full text of DOI:10.1016/S0022-328X(01)01211-6

Journal of Organometallic Chemistry 643–644 (2002) 357–362
www.elsevier.com/locate/jorganchem
A dimeric gold(I) triphospholyl complex
M. Hofmann, F.W. Heinemann, U. Zenneck *
Institut fu¨r Anorganische Chemie, Uni6ersita¨t Erlangen-Nu¨rnberg, Egerlandstraße 1, 91058 Erlangen, Germany
Received 17 July 2001; accepted 31 August 2001
Dedicated to professor Francois Mathey on the occasion of his 60th birthday
Abstract
The reaction of 1-trimethylstannyl-3,5-di(tert-butyl)-1,2,4-triphosphol with PPh3AuCl affords [(1,2,4-triphospholyl)Au(PPh3)]
(5) in high yield. NMR spectra of 5 are indicative for a highly dynamic compound in solution. The molecular structure of 5 in
the solid state is that of the dimer [(1,2,4-triphospholyl)Au(PPh3)]2. Its most striking feature is a remarkable range of different
metalꢀtriphospholyl ligand bonds which create a pronounced asymmetric core of the molecule. The central AuꢀAu distance of
,
3.14 A indicates a weak interaction of the metal atoms. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: NMR spectra; Triphospholyl; Ligand; Gold
1. Introduction
formation of an unpredictable |-complex dimer [4].
When investigating the chemistry of [(1,2,4-triphos-
pholyl)Cu(I)L] complexes [5], we found evidence for
several coexisting species. Most of them exhibit a re-
markable structural flexibility which causes a big mani-
fold of spectroscopic parameters, aspecially in NMR
spectroscopy. No unambiguous interpretation of the
data was thus possible, even the reversible formation of
dimers could not be ruled out. To get some insight into
possible d10-M(I)-1,2,4-triphospholyl dimer structures,
we reacted triorganylstannyl-1,2,4-triphosphol with
PPh3AuCl, as Au(I) is more likely to form stable dimers
than Cu(I).
Cp(PPh3)Au(I) (1) is known since 1967 [6]. In con-
trast to its Cu(I) analogue 2, 1 exhibits a fluxional
h1-bonded Cp ligand in solution (Scheme 1). In the
solid state, however, a tendency towards h3-co-ordina-
tion of Cp ligands of Au(I) has been observed, too [7].
AuꢀAu bonds are found regularly in Au(I) complex
dimers [8], but no simple models have been developed
Triorganylstannyl-1,2,4-triphosphol derivatives are
excellent starting materials for a high yield transfer of
the five membered heterocyclic ligand 1,2,4-triphospho-
lyl onto various MLn fragments [1]. Ease and repro-
ducibility of this reaction encouraged us to investigate
the specific contributions of the phosphorus atoms to
the reactivity of this phosphorus-rich cyclopentadienyl
(Cp) analogue. Principally, the phosphorus atoms sup-
ply three lone pairs to the triphospholyl ring and cause
a decrease of the frontier p-orbital energies as well as a
significant ring size expansion with respect to Cp. All
three aspects contribute to the properties of compounds
which contain a triphospholyl unit, aspecially if the
rings are complexed to a metal atom. In case of their
dominance, the triphospholyl ligand cannot be viewed
as a Cp analogue any longer, where the phosphorus
atoms just replace CR fragments as isovalent and
isolobal building blocks [2]. Exceptions of that sort are
[bis(1,2,4-triphospholyl)Mn], which exhibits a novel
electronic ground state for manganocene derivatives [3],
and new structural features have been observed for
[(1,2,4-triphospholyl)NiLL%] derivatives, including the
* Corresponding author. Tel.: +49-9131-8527464; fax: +49-9131-
8527376.
E-mail address: zenneck@chemie.uni-erlangen.de (U. Zenneck).
Scheme 1.
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01211-6

358
M. Hofmann et al. / Journal of Organometallic Chemistry 643–644 (2002) 357–362
Scheme 2.
yet to interpret the AuꢀAu interactions and the bond-
ing angles around the metal atoms in the solid state [9].
Goldꢀgold distances for molecular species have been
that of the dimer [(triphospholyl)Au(PPh3)]2 only
(Scheme 2, Fig. 1, Tables 1 and 2).
The most striking feature of dimer 5 is a remarkable
range of different metal–triphospholyl ligand interac-
tions. One of the ligands bridges the AuꢀAu unit by
one P atom (P(3)), whereas the other one fulfils the
same function by the two adjacent phosphorus atoms
P(5) and P(6). PꢀAu bonds of different lengths as well
as a warped orientation of the ligand planes with
respect to the AuꢀAu vector creates a distinctly asym-
metric core of the molecule. When compared to the
,
observed in the range of 2.50–4.00 A. Values of more
,
than 3 A might be viewed as weak or even non-bonding
interactions, while contacts below this are regarded as
bonds. Theoretical studies revealed a complex bonding
situation of oligonuclear gold compounds [10]. The
aurophilic attraction of gold atoms is caused by a
combination of correlation and relativistic effects [11].
,
literature values, the distance Au(1)ꢀAu(2)=3.14 A
2. Results
indicates a weak interaction of the metal atoms in the
range of 6 kcal mol−1 [12].
The reaction of 1-trimethylstannyl-3,5-di(tert-butyl)-
1,2,4-triphosphol (3) with PPh3AuCl (4) results in the
formation of the desired product 5 in 86% yield. Ac-
cording to the analytical data it contains the three
components 1,2,4-triphospholyl, PPh3, and gold in the
ratio 1:1:1.
In spite of their different interactions with the two
metal atoms, both triphospholyl ligands of 5 form
almost identical delocalized p-systems which are char-
acterized by constant PꢀC bonding distances. They
,
appear all in the small range of 1.74–1.76 A. Likewise,
the PꢀP bonds of the ligands have the same length as
5 is a stable orange compound. NMR spectra are
dominated by dynamic effects. At room temperature
1H- and 13C-NMR spectra indicate a symmetric chemi-
cal situation for the triphospholyl ligand. The 31P-
NMR lines are slightly broadened, but close to a fast
exchange limit case and form three lines in the ratio
1:1:2. No coupling between the different phosphorus
atoms of 5 is observable. The room temperature NMR
data are in line with a |-complexed anionic triphospho-
lyl ligand. Because of the broadening of all NMR lines
at low temperature, the compound is regarded to un-
dergo rapid exchange process which simplify the spec-
tra. This dynamic situation is in contrast to the only
known example of a dimeric |-complex of this ligand
[(1,2,4-triphospholyl)(PPh3)(NO)Ni]2 [4]. The 31P-NMR
signals of 5 not only broaden, but split to form several
new ones. No slow-exchange limit spectrum could be
obtained, however. This indicates a low-activated equi-
librium between different triphospholylꢀAu bonding
modes. As for the Cu(I) triphospholyl complexes, the
dynamic NMR spectra do not reveal details of the
dynamic processes or the involved species. FD MS
spectra exhibit peaks, which represent (triphospho-
lyl)Au(PPh3) as well as its dimer [(triphospho-
lyl)Au(PPh3)]2. Crystals suitable for X-ray structural
analysis could be obtained from a solution in n-hex-
ane–THF. The molecular structure in the solid state is
,
well (2.09 A). The observed p-electron delocalization is
in line with the solution NMR data at room tempera-
Table 1
,
Selected bond length (A) and angles (°) for 5
Bond lengths
Bond angles
Au(1)ꢀAu(2)
Au(1)ꢀP(5)
Au(1)ꢀP(7)
Au(1)ꢀP(3)
Au(2)ꢀP(3)
Au(2)ꢀP(6)
Au(2)ꢀP(8)
P(5)ꢀP(6)
P(2)ꢀP(3)
P(5)ꢀC(4)
P(6)ꢀC(3)
P(4)ꢀC(4)
P(4)ꢀC(3)
P(3)ꢀC(1)
P(2)ꢀC(2)
P(1)ꢀC(1)
P(1)ꢀC(2)
3.1395(9)
2.335(2)
2.300(2)
2.836(2)
2.339(2)
2.730(2)
2.295(2)
2.090(3)
2.092(3)
1.741(9)
1.725(9)
1.732(9)
1.764(9)
1.732(9)
1.732(9)
1.737(9)
1.763((9)
Au(1)ꢀP(3)ꢀC(1)
Au(1)ꢀP(3)ꢀP(2)
Au(1)ꢀP(3)ꢀAu(2)
P(2)ꢀP(3)ꢀC(1)
133.5(3)
85.41(10)
74.00(7)
104.1(3)
125.57(6)
126.68(6)
147.41(8)
99.80(7)
112.76(7)
111.79(8)
98.97(8)
148.97(9)
85.83(10)
116.41(12)
129.4(3)
97.8(3)
Au(1)ꢀAu(2)ꢀP(8)
Au(2)ꢀAu(1)ꢀP(7)
P(3)ꢀAu(2)ꢀP(8)
P(3)ꢀAu(2)ꢀP(6)
P(6)ꢀAu(2)ꢀP(8)
P(7)ꢀAu(1)ꢀP(3)
P(3)ꢀAu(1)ꢀP(5)
P(7)ꢀAu(1)ꢀP(5)
Au(2)ꢀP(6)ꢀP(5)
Au(1)ꢀP(5)ꢀP(6)
Au(2)ꢀP(6)ꢀC(3)
P(5)ꢀP(6)ꢀC(3)
P(6)ꢀP(5)ꢀC(4)
103.5(3)
130.1(3)
60.26(6)
45.73(5)
72.89(6)
128.3(3)
Au(1)ꢀP(5)ꢀC(4)
Au(1)ꢀAu(2)ꢀP(3)
Au(2)ꢀAu(1)ꢀP(3)
Au(2)ꢀAu(1)ꢀP(5)
Au(2)ꢀP(3)ꢀC(1)

M. Hofmann et al. / Journal of Organometallic Chemistry 643–644 (2002) 357–362
359
Fig. 1. (A) Molecular structure of 5 in the solid state; hydrogen atoms are omitted for clarity; (B) core of 5.

360
M. Hofmann et al. / Journal of Organometallic Chemistry 643–644 (2002) 357–362
Table 2
angle triphospholylꢀAuꢀPPh3ꢁP(5)ꢀAu(1)ꢀP(7) equals
149°, thus the deviation from linearity is ca. 31°. The
interaction of P(3) with Au(1) and Au(2) can be viewed
as a bridging bonding mode, where the lone pair is
oriented towards the space between the two Au atoms.
Again, the bridge is asymmetric, as the AuꢀP bonds
P(3)ꢀAu(1) and P(3)ꢀAu(2) differ in their length by
Crystal data and structure refinement of compound 5
Empirical formula
Formula weight
Solvent
C56H66Au2P8
1380.78
n-hexane–THF
Orange prism
200
Crystal habit
Temperature (K)
Crystal system
Space group
Triclinic
,
21%. The short one, P(3)ꢀAu(2)=2.339 A is almost the
(
P1
same as Au(1)ꢀP(5). As the central angle P(3)ꢀAu(2)ꢀ
P(8)=147.4°, Au(2) appears as a perturbed linear co-
ordinate metal atom as well.
Unit cell dimensions
,
a (A)
10.661(2)
14.426(3)
14.426(3)
80.03(2)
85.92(1)
69.22(1)
2852.5(9)
2
1.608
5.396
1360
0.38×0.20×0.10
,
b (A)
,
c (A)
Because of the aromaticity of the triphospholyl an-
ions, the ligand to metal interaction is dominated by
the P lone pairs. Taking a high s-character of the P lone
pairs [14] and the empty gold orbitals into consider-
ation, their overlap should not be very sensitive to-
wards tilting of such s-bonds. Such a non-directional
bonding mode has been observed for the ligand proper-
ties of bis(phospholyl)Fe derivatives with respect to
Pd(0) [15] and Ag(I) [16], already. The same effect may
contribute to the weaker Au–triphospholyl interactions
as well and promote the asymmetry of dimer 5.
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
Theta range for data collection (°) 1.97–27.00
Index ranges
−135h51
−185k517
−255l525
Reflections collected
Reflections with I\2|(I)
Independent reflections
Completeness to q
Absorption correction
Max/min transmission
Refinement method
14 078
8209
12 428 [Rint=0.0457]
27.00°: 99.7%
„-scan
3. Conclusions
0.163, 0.086
Besides of the pronounced s-character of the P and
Au atom orbitals which create the bonding molecular
orbitals of 5, they are somewhat diffuse and allow
significant deviations from the optimal arrangement of
gold atoms and triphospholyl ligands without too much
loss of interaction energy. As a consequence, the equi-
librium structure of 5 is supposed to form a shallow
energetic minimum, thus packing effects may influence
the observed molecular structure in the solid state
significantly and create the pronounced asymmetry of
the co-ordination core. The low activation energy for
the dynamic effects in solution is completely in line with
this interpretation, however, the data do not allow to
distinguish unambiguously between intramolecular re-
Full matrix least squares on
F2
Data/restraints/parameters
Final R indices [I\2|(I)]
R indices (all data)
12428/0/607
R1=0.0563, wR2=0.1182
R1=0.1010, wR2=0.1395
1.013
Goodness-of-fit on F2
Largest difference peak and hole
1639 and −2528
(e nm−3
)
ture and a hint on aromatic p6-systems. The heterocy-
cles are thus anionic and compensate the charge of the
Au(I) cations.
Besides the weak AuꢀAu interaction, both gold cen-
tres exhibit planar co-ordination spheres, which are
occupied by three phosphorus atoms (sum of angles:
359.7 and 360.0°, respectively). In contrast to a [tris-
arrangement processes or the participation of
a
monomer–dimer equilibrium.
(diphosphanylmethane)Au2]2+
(AuꢀAu=3.04
A)
,
derivative, however [13], the central PꢀAuꢀP bond an-
gles differ significantly from the symmetrical case 120°.
The PꢀAuꢀP angles of 5 cover the range of ca. 99–150°
for Au(1) as well as for Au(2).
4. Experimental
As indicated by the asymmetric core of the dimer, the
4.1. General considerations
metal to ligand distances of the doubly bridging ligand
,
,
Au(1)ꢀP(5)=2.335 A and Au(2)ꢀP(6)=2.730 A differ
by remarkable 17%. This big difference leads to the
assumption that the shorter one contributes the main
part of the bonding energy Au(1)ꢀtriphospholyl. This
opens the possibility to view the co-ordination sphere
of Au(1) as a perturbed linear unit. The corresponding
The experiments were conducted under a N2 atmo-
sphere by using standard Schlenk and cannula tech-
niques. Solvents were dried according to described
procedures and used freshly distilled from the drying
agent. PPh3AuCl (4) and (H3C)3Sn(P3Ct2Bu2) (3) were
prepared according to the literature [5,17].

M. Hofmann et al. / Journal of Organometallic Chemistry 643–644 (2002) 357–362
361
4.2. [Au(P3Ct2Bu2)(PPh3)]2 (5)
5. Supplementary material
Crystallographic data for the structure reported in
this paper have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 167423 for
compound 5. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
www:http://ccdc.cam.ac.uk).
0.841 g (1.7 mmol) of Au(PPh3)Cl is suspended in 25
ml of THF 0.673 g (1.7 mmol) of 1-trimethylstannyl-
3,5-di(tert-butyl)-1,2,4-triphosphol (3) in 25 ml of THF
is added at a temperature of −50 °C. The reaction
mixture is then stirred and allowed to warm up to room
temperature (r.t.) over night. The THF is removed in
vacuo. The residue is suspended in n-hexane, filtered,
washed with n-hexane, dried in vacuo, and the resulting
orange–red powder is dissolved in 10 ml of THF and a
few drops of n-hexane. Crystallization occurs over
night at −18 °C to yield 1.012 g (1.465 mmol, 86.2%)
of the target product 5.
Acknowledgements
This work was supported by the Deutsche
Forschungsgemeinschaft, the DFG-Graduiertenkolleg
Phosphorchemie als Bindeglied verschiedener chemis-
cher Disziplinen at the University of Kaiserslautern,
Germany and the Fonds der Chemischen Industrie. We
also thank Dr M. Moll for the measurement of vari-
able-temperature NMR spectra.
4.3. Spectroscopic data for (5)
1H-NMR (399.65 MHz, CD2Cl2, 20.1 °C): l=1.44
(s, 18H, CH3), 7.23–7.39 (m, 15H, C6H5). 13C{1H}-
NMR (100.40 MHz, CD2Cl2, 20.3 °C): l=204.9
(dpt=doublet of pseudo triplets, 1J(31P(3)13C)=32.2
Hz; _ 1J(31P(1)13C)+2J(31P(2)13C)=54.5 Hz, CRing);
134.34 (d, 2J(31P13C)=14.9 Hz, o-PhꢀC); 131.62 (s,
p-PhꢀC); 131.08 (d, 1J(31P13C)=46.3 Hz, i-PhꢀC);
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