Ligand properties of tri(2-thienyl)- and tri(2-furyl)phosphine and -arsine (2-C4H3E)3P/As (E = O, S) in gold(I) complexes

Article abstract of DOI:10.1515/znb-2003-0806

Tri(2-thienyl)- and tri(2-furyl)phosphine and -arsine (L) have been introduced as ligands to gold(I) chloride and acetate (AuX). Structural studies have shown that in the 1:1 complexes of the type L-Au-X the gold atoms are bound exclusively to the phosphorus/arsenic centers without any intra- or intermolecular approach of the donor atoms of the three heterocycles towards the metal atoms. Intermolecular aurophilic bonding is found in the crystals of the [tri(thienyl)phosphine]gold acetate complex, but is absent in crystals of the chloride complexes. The phosphines L have been quaternized with methyl iodide and the resulting phosphonium salts [LMe]I structurally characterized to provide reference data as to the preferred configurational and conformational motifs. The mass spectra of the gold complexes indicate a high stability of the dinuclear cationic species [(LAu)₂X]⁺ with X = Cl, OAc for all ligands L.

Full text of DOI:10.1515/znb-2003-0806

Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
and -arsine (2-C4H3E)3P/As (E = O, S) in Gold(I) Complexes
Uwe Monkowius, Stefan Nogai, and Hubert Schmidbaur
Anorganisch-chemisches Institut der Technischen Universita¨t Mu¨nchen,
Lichtenbergstraße 4, D-85747 Garching, Germany
Reprint requests to Prof. Dr. Schmidbaur. E-mail: H.Schmidbaur@lrz.tum.de
Z. Naturforsch. 58b, 751 – 758 (2003); received May 7, 2003
Tri(2-thienyl)- and tri(2-furyl)phosphine and -arsine (L) have been introduced as ligands to gold(I)
chloride and acetate (AuX). Structural studies have shown that in the 1:1 complexes of the type
L-Au-X the gold atoms are bound exclusively to the phosphorus/arsenic centers without any intra-
or intermolecular approach of the donor atoms of the three heterocycles towards the metal atoms.
Intermolecular aurophilic bonding is found in the crystals of the [tri(thienyl)phosphine]gold acetate
complex, but is absent in crystals of the chloride complexes. The phosphines L have been quaternized
with methyl iodide and the resulting phosphonium salts [LMe]I structurally characterized to provide
reference data as to the preferred configurational and conformational motifs. The mass spectra of the
gold complexes indicate a high stability of the dinuclear cationic species [(LAu)2X]+ with X = Cl,
OAc for all ligands L.
Key words: Gold Complexes, Heteroarylphosphines/arsines, Furylphosphines/arsines,
Thienylphosphines/arsine, Phosphines, Arsines
Introduction
With one phosphorus and three sulfur atoms, tri(2-
thienyl)phosphine is a potential tetradentate ligand
with all donor centers in close proximity. However,
very little is known about the structural chemistry of
its metal complexes [7, 10 – 12, 20, 24 – 26] and of the
products obtained in its simple nucleophilic substitu-
tion reactions [7, 10]. For tri(2-furyl)phosphine the lig-
and properties are more predictable owing to the larger
differences between the soft phosphorus and the hard
oxygen donor functions. With gold(I) as an acceptor,
the former will clearly be the donor center of choice.
The present report is an account of preparative and
Tertiary phosphines R3P with heterocyclic sub-
stituents R have attracted considerable interest at dif-
ferent stages of the development of “tailor-made” lig-
ands for Transition and Main Group Elements [1,2]
or as auxiliary components in organic synthesis [3 –
6]. Tri(2-thienyl)phosphine was among the first pro-
totypes to be synthesized in the late 1950ies in stud-
ies by Issleib and Brack [7], preceded only by early
work on 2-thienyl-dichlorophosphine and its hydroly-
sis and oxidation products [8]. Tri(2-furyl)phosphine
was prepared by Japanese workers for the first time structural studies of four gold(I) complexes of the type
in 1966 [9]. The results of the preparative studies (2-C4H3E)3P-Au-X with a) E = S and X = chloride
[4, 7, 10– 12], and of extensive kinetic [2, 5, 6, 13 – 16] (1), b) E = S and X = acetate (2), c) E = O and X =
and spectroscopic investigations [17– 23] suggested chloride (4), and d) E = O and X = acetate (5). In all
differences of the inductive and electronic effects of the cases the gold atom is two-coordinate and bound solely
phenyl, 2-thienyl and 2-furyl substituents [7, 10, 11] to the phosphorus atom showing the superior donor
ascribed intermittently to the d(π)-p(π) interactions properties of the phosphorus center for soft acceptor
between the (hetero)arene systems and central phos- centers of low (+1) charge. As a reference for the ge-
phorus atom [11, 14, 17, 20]. However, straightforward ometry of fully quaternized compounds, the structures
steric and electronegativity effects appear to be suf- of the methylation products, the phosphonium salts
ficient to account for most experimental observa- [(2-C4H3S)3PMe]+I−, 3, and [(2- C4H3O)3PMe]+I−,
tions [20]. The 2-furyl group appears to act as the 6, have been determined. Also for comparison, tri(2-
most electron-withdrawing substituent among the tri- furyl)- and tri(2-thienyl)arsine have been prepared and
(hetero)arylphosphines [5, 12, 14,15].
used as ligands for AuCl. These arsines were first syn-
c
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U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
complex 4 in good yields (95.0%). The product was
crystallized from dichloromethane/pentane. The chlo-
ride 4 can be converted into the acetate 5 by metath◦e-
sis with silver acetate in dichloromethane at −32 C
(56.5% yield) (Scheme 1). However, this product is un-
stable both as a solid and in solution and could not be
crystallized.
Quaternization of (2-C4H3O)3P with excess methyl
iodide in toluene at reflux temperature gives the phos-
phonium salt [MeP(2-C4H3O)3]+ I−, 6, in good yield
(76.1%) (Scheme 1) [19]. The single crystals grown
from acetonitrile/diethylether were light-brown and
contained some excess iodine, as also confirmed by
disorder phenomena in the crystal structure determi-
nation.
As observed for the tri(2-thienyl)phosphine deriva-
tives (1 – 3, above), the 31P NMR signals of the tri(2-
furyl)phosphinecompounds 4 – 6 are shifted downfield
very considerably as compared to the resonance of the
free ligand [−77.39 ppm in CD2Cl2 at 25 ◦C]. The shift
difference is 49.37 ppm for 4, 42.63 ppm for 5, and
61.62 ppm for 6. This leaves no doubt that all deriva-
tives are products of the reaction at the phosphorus
center.
Tri(2-thienyl)arsine and tris(2-furyl)arsine are ob-
tained in low yield (28.4 and 47%, respectively) from
three equivalents of mono-lithiated thiophene or fu-
ran and arsenic(III) chloride in tetrahydrofuranas pale-
yellow viscous liquids [eq. (1)]. The thienyl compound
solidifies as a glass on cooling, while the furyl a◦na-
logue can be crystallized from diethylether at −78 C.
Scheme 1.
thesized in 1935 and 1948, respectively, from 2-furyl
and 2-thienyl mercury chloride and arsenic trichloride
[27– 30]. Nothing is known about their reactivity and
donor properties towards Transition and Main Group
Elements.
Preparative Results
Tri(2-thienyl)phosphine (2-C4H3S)3P is readily ob-
tained in good yield via the Grignard route em-
ploying 2-bromothiophene, magnesium and phospho-
rus trichloride in diethylether at −20 ◦C [7]. It is
also commercially available. Its 1:1 complexes with
gold(I) chloride can be prepared using (tetrahydrothio-
phene)gold(I) chloride in tetrahydrofuran. The cyclic
thioether is liberated in the reaction, which gives high
yields of a colorless, crystalline product (1, 95.4%
◦
yield, m. p. 192 C). This complex can be converted
into the corresponding acetate (2) by metathesis with
silver acetate in dichloromethane (84.5% yield, m.p.
100 ◦C, decomposition) (Scheme 1).
Upon coordination to gold(I) salts, the 31P NMR
signal of the ligand [(2-C4H3S)3P, −45.61 ppm in
◦
dichloromethane at 25 C] is shifted downfield very
(2-C4H3S)3As reacts with (tetrahydrothiophene)
significantly [1: −6.39 ppm, 2: −12.32 ppm, in the
same solvent]. For 1 and 2 the shift differences are thus
as much as 39.22 and 33.29 ppm, respectively, indicat-
ing ligation to the phosphorus atom.
Quantitative quaternization of (2-C4H3S)3P was
achieved with an excess of methyl iodide in tetrahydro-
furan at room temperature (94.4% yield) (Scheme 1)
[14,19,22]. The colorless product (3) crystallizes from
acetone. The 31P NMR spectrum of 3 also shows a
large downfield shift of no less than 50.14 ppm to
4.53 ppm as compared to the free ligand.
◦
gold chloride in dichloromethane at −78 C to give the
product (C4H3S)3AsAuCl, 7, which crystallizes from
dichloromethane/pentane in high yield (94.3%, m.p.
144 ◦C).
Mass spectrometry
The mass spectra (FAB mode) of the gold com-
plexes show similar patterns which confirm the pro-
posed composition of the products through the ap-
pearance of the molecular ions. Interestingly how-
Tri(2-furyl)phosphine (2-C4H3O)3P is commer- ever, the chloride complexes 1, 4 and 7 show the
cially available. Its reaction with (tetrahydrothio- di(gold)chloronium cations [(LAu)2Cl]+ as the ions
phene)gold(I) chloride in tetrahydrofuran afforded of highest mass in high abundance. This result is in
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U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
753
agreement with the high stability of cationic element-
centered gold clusters of the general type [E(AuL)n]+
[31]. In the present case with E = Cl, L = (2-C4H3S)3P,
(2-C4H3O)3P or (2-C4H3S)3As, and n = 2, species
with narrow angles Au-Cl-Au and short aurophilic Au-
Au contacts are characteristic for species formed from
LAuCl molecules and LAu+ cations. The results sug-
gest that the arsines can also function as the stabiliz-
ing ligand in these cations. Salts of this type have not
yet been isolated in crystalline form. Other cations of
high abundance are [L2Au]+ and [LAu]+. Dinuclear,
acetate-bridged cations are also observed for com-
Fig. 1. Molecular structure of 1 (ORTEP [36] draw-
plexes 2 and 5.
ing with 50% probability ellipsoids). Selected bond
In the mass spectra of the phosphonium salts 3 and
6, the cations are by far the most prominent parent
peaks.
◦
˚
lengths [A] and angles [ ]: Au1-Cl1 2.2894(12), Au1-P1
2.2315(12), P1-C11 1.796(4), P1-Au1-Cl1 177.89(4), C11-
P1-Au1 115.13(15), C21-P1-Au1 111.10(16), C31-P1-Au1
111.94(15), C21-P1-C11 105.4(2), C31-P1-C11 104.3(2),
C21-P1-C31 108.5(2).
Structural Studies
[Tri(2-thienyl)phosphine]gold(I) chloride, [(C4H3
S)3P-Au-Cl], 1, crystallizes in the triclinic space group
¯
P1 with two formula units in the unit cell. The asym-
metric unit contains one molecule which has no sub-
van-der-Waals contacts with neighboring units (Fig. 1).
The gold atom is attached solely to the phospho-
˚
rus atom with an Au-P distance of 2.2315(12) A,
and to the chlorine atom with an Au-Cl distance of
˚
2.2894(12) A. The coordination is linear with the an-
gle Cl-Au-P at 177.89(4)◦. With the three sulfur atoms
oriented away from the gold atom and with the three
C-P-Au angles all larger than the tetrahedral standard
[111.10(16)– 115.13(15)◦], there is no evidence for
gold-sulfur coordination. There is also no indication
for dimerization via aurophilic contacts. This result
is in agreement with the crystal structure of (triph-
enylphosphine)gold(I) chloride [32], which also fea-
tures monomeric units, and suggests similar steric and
electronic effects of phenyl and thienyl substituents (in
combination with a trans chloride ligand).
Fig. 2. Structure of dimeric complex 2 (ORTEP draw-
ing with 50% probability ellipsoids, H-atoms omitted for
clarity). Only one orientation of the disordered thienyl
˚
substituent is shown. Selected bond lengths [A], an-
gles and torsion angles [◦]: Au1-Au1’ 2.2170(8), Au1-
P1 2.2170(8), Au1-O1 2.072(3), Au1-Au1’ 3.0136(2),
P1-Au1-O1 174.86(8), C11-P1-Au1 111.14(12), C21-P1-
Au1 108.66(11), C31-P1-Au1 118.28(12), P1-Au1-Au1’-
P1’ 100.6, O1-Au1-Au1’-O1’ 102.1.
with maximum attainable symmetry, and – taking also
into account the disorder phenomenon – may be con-
sidered virtually random or co-determined by packing
forces.
Complementary to the three large Au-P-C an-
gles (above), the three C-P-C angles are consis-
tently smaller than the tetrahedral standard [104.3(2)–
108.5(2)◦] showing that the complexation has not in-
duced a perfect tetrahedral arrangement of the atoms
[Tri(2-thienyl)phosphine]gold(I) acetate, [(2-C4H3
at the phosphorus atom. One of the three thiophene S)3P-Au-OC(O)CH3], 2, crystallizes in the monoclinic
rings in complex 1 is disordered over two positions space group C2/c with Z = 8 formula units in the
with equal occupation factors (in Fig. 1 only one ori- unit cell. The asymmetric unit contains one molecule
entation is shown). The overall conformation of the with a linear coordination of the gold atom [Au-P
◦
˚
phosphine is neither close to mirror symmetry nor to 2.2170(8), Au-O1 2.072(3) A; P-Au-O1 174.86(8) ].
propeller symmetry, which are the two conformations However, these monomers are clearly associated into
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U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
Fig. 3. Molecular structure of 4 (ORTEP drawing with
˚
50% probability ellipsoid◦s). Selected bond lengths [A], an-
Fig. 4. Asymmetric unit in the structure of 3 (ORTEP
gles and torsion angles [ ]: Au1-Cl1 2.2864(11), Au1-P1
2.2159(11), P1-C11 1.787(5), P1-Au1-Cl1 178.12(4), C11-
P1-Au1 112.88, C21-P1-Au1 111.90(16), C31-P1-Au1
114.56(15), C11-P1-C31 103.3(2), C21-P1-C11 107.3(2),
C21-P1-C31 106.2(2), Au1-P1-C11-C12 −6.2(6), Au1-
P1-C21-C22 0.6(6), Au1-P1-C31-O3 1.9(4).
drawing with 50% probability ellipsoids, H-atoms omit-
˚
ted for clarity). Selected bond lengths [A], angles and tor-
sion angles [◦]: P1-C1 1.784(3), P1-C11 1.764(4), P1-C21
1.770(3), P1-C31 1.770(3), C11-P1-C1 108.36(17), C21-
P1-C1 109.53, C31-P1-C1 111.60(16).
˚
Compared with the data for the thienyl analogue 1,
this result suggests slightly poorer donor properties of
the tri(2-furyl)phosphine ligand in 4. The correspond-
ing acetate 5 could not be crystallized.
pairs via aurophilic bonding [Au-Au’ 3.0136(2) A,
dihedral angles P-Au-Au’-P’ 100.6◦, O1-Au-Au’-O1’
102.1◦] (Fig. 2). With one thienyl substituent also dis-
ordered, the configuration of the phosphine ligand in
2 is very similar to that in 1, and yet only complex
2 shows dimerization. This result shows that the elec-
tronic influence of the anion X is a very significant fac-
tor in establishing aurophilic bonding between L-Au-
X molecules. With the influence of L constant in 1 and
2, X is determining the building (or not building) of
dimers.
In order to obtain structural data of genuinely quat-
ernized tri(2-thienyl)- and tri(2-furyl)phosphine com-
pounds for comparison, the derivatives 3 and 6 were
also investigated.
Methyl-tri(2-thienyl)phosphonium iodide, 3, crys-
¯
tallizes in the triclinic space group P1 with Z = 4
formula units in the unit cell. The asymmetric unit
thus contains two independent cations and anions
(Fig. 4). Bond lengths and angles of the two cations are
very similar. The P-C(methyl) bonds are significantly
longer than the P-C(thienyl) bonds as expected for car-
bon atoms with different hybridization. The valence
angles at the phosphorus atoms are all close to the
tetrahedral standard indicating virtually complete hy-
bridization (sp3 for P) as a reaction to quaternization.
By contrast, complexation by AuCl or AuOC(O)CH3
(in 1 and 2) left the C-P-C angles well below 109◦. The
orientation of the thienyl rings of the cations does not
approach any symmetrical arrangement and appears to
be largely random.
This result is confirmed by the structure of the furyl
analogue of complex 1: [Tri(2-furyl)phosphine]gold(I)
chloride, [(C4H3O)3P]AuCl, 4, crystallizes in the
monoclinic space group P21/n with Z = 4 molecules
in the unit cell. Although the ligand L in 4 with oxy-
gen instead of sulfur as the heteroatom can be consid-
ered smaller than that in 1, the crystals are also built of
monomeric units which show no tendency to aggregate
(Fig. 3). The gold atom is in a standard linear coor-
dination [P-Au-Cl 178.12(4)◦; Au-P 2.2159(11), Au-
˚
Cl 2.2864(11) A] and entertains no oxygen contacts.
The phosphine ligand of 4 shows no disorder of furyl
substituents, and the overall conformation approaches
mirror symmetry (the mirror plane containing Cl, Au
Methyl-tri(2-furyl)phosphonium iodide, 6, crystal-
and P and bisecting the C11-Au-C21 angle). The di- lizes in the tetragonal space group P4/ncc with Z =
hedral angles Au-P-C11-C12 and Au-P-C21-C22 are 16 formula units in the unit cell. The configuration
−6.2(6) and +0.6(6)◦, respectively, and Au-P-C31-O3 of the phosphonium center of the cation is distorted
is 1.9(4)◦. All Au-P-C angles are larger than the tetra- tetrahedral with C-P-C angles spreading over the broad
hedral standard [111.90(16)– 114.56(15) ◦], and all C- range between 105.60(14) and as much as 116.11(15) ◦
P-C angles are smaller [103.3(2)– 107.3(2)◦].
for C1-P1-C11 (Fig. 5). All of these angles are larger
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U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
755
Fig. 5. Structure of the cation in crystals of 6 (ORTEP draw-
ing with 50% probability ellipsoids). Selected bond lengths
◦
˚
Fig. 6. Molecular structure of 7 (ORTEP drawing with
[A] and angles [ ]: P1-C1 1.779(3), P1-C11 1.763(3), P1-
C21 1.771(3), P1-C31 1.762(3), C11-P1-C1 116.11(15),
C21-P1-C1 107.55(14), C31-P1-C1 109.60(14), C1-P1-
C21-O22 176.8(2), C11-P1-C21-O22 51.2(3), C31-P1-
C21-O22 −63.5(2).
50% probability ellipsoids, H-atoms omitted for clar-
◦
˚
ity). Selected bond lengths [A] and angles [ ]: Au1-
Cl1 2.2834(10), Au1-As1 2.3284(4), As1-C11 1.901(4),
Cl1-Au1-As1 176.93(3), C11-As1-Au1 110.95(13), C21-
As1-Au1 113.82(12), C31-As1-Au1 118.48(12), C11-As1-
C21 105.94(19), C11-As1-C31104.03(18), C21-As1-C31
102.39(16).
than those in the AuCl complex (above) suggesting a
much stronger acceptor character of Me+ as compared
to AuCl. The four P-C bond lengths are all very similar
X the gold atoms are attached exclusively to the phos-
phorus centers. There is no evidence for homoleptic
structures [L2Au]+[AuX2]− in solution or in the solid
state. While the two chloride complexes (1 and 4)
are monomers in the crystal, the acetate 2 is present
as a dimer with significant intermolecular aurophilic
bonding.
The FAB mass spectra of the complexes show the
dinuclear cations [(LAu)2X]+ (X = Cl, OAc) in high
abundance suggesting extra stability of these compact
species due to efficient intra-ionic aurophilic interac-
tions. This structural motif has already been confirmed
for several other examples with standard trialkyl- and
triarylphosphine ligands [31].
Tri(2-thienyl)- and tri(2-furyl)arsine have been pre-
pared successfully via an organolithium route, but
yields were found to be low owing to side-reactions.
Both arsines were used as ligands for AuCl, but
only the tri(2-thienyl)arsine complex was found to
be a sufficiently robust compound to allow ana-
lytical, spectroscopic and structural characterization.
The data show no anomalies. The mass spectrum of
(C4H3S)3AsAuCl, 7, is again dominated by the dinu-
clear cation [(LAu)2Cl]+ indicating that the arsine lig-
and L is also an efficient donor to stabilize this chloro-
nium species.
˚
[1.762(3)– 1.779(3) A]. The dihedral angles C1-P1-
C21-O22 176.8(2)◦, C11-P1-C21-O22 +51.2(3)◦ and
C31-P1-C21-O22 −63.5(2)◦ indicate an approach to
mirror symmetry, but the deviations are larger than
found in the AuCl complex of the same phosphine
(4). The iodide anions are disordered over three dif-
ferent sites and the total occupancy indicates a non-
stoichiometric cation/anion ratio of 1/1.1. This result
explains the light brown color of the crystals, which
also indicates the contents of iodine, probably as tri-
iodide anions.
Crystals of [Tri(2-thienyl)arsine]gold chloride, 7
are monoclinic, space group P21/c, with Z = 4
molecules in the unit cell, and thus not isomorphous
with the phosphine analogue 1. Two of the three thienyl
substituents are disordered over two rotatory orienta-
tions each (Fig. 6). The Au-As and Au-Cl distances
are not anomalous, and the configuration at the ar-
senic atom is close to tetrahedral with all C-As-C an-
gles smaller (average 104.12◦) and all Au-As-C angles
larger than the tetrahedral standard (average 114.42◦).
Discussion and Conclusions
Tri(2-thienyl)- and tri(2-furyl)phosphine (L) were
employed as ligands for gold(I) chloride and acetate.
In model quaternization reactions, tri(2-thienyl)-
From the 31P NMR data it is immediately obvious and tri(2-furyl)phosphine were converted into the
that in the resulting heteroleptic 1:1 complexes L-Au- methylphosphonium salts (3 and 6) using an excess of
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U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
Table 1. Crystal data, data collection, and structure refinement of 1 – 6.
1
2
3
4
5
6
Empirical formula
M
C12H9AuClPS3 C14H12AuO2PS3 C13H12IPS3
C12H9AuClO3P C13H12IO3P·I0.10 C12H9AsAuClS3
512.76
Triclinic
¯
P1
536.35
Monoclinic
C2/c
422.28
Triclinic
¯
P1
464.58
Monoclinic
P21/n
9.7253(1)
12.4449(2)
11.1625(2)
90
387.02
Tetragonal
P4/ncc
20.4104(1)
20.4104
14.2572(2)
90
556.71
Monoclinic
P21/c
Crystal system
Space group
˚
a/A
9.0833(1)
9.0939(1)
10.4493(2)
112.8596(8)
102.7816(7)
98.1767(7)
750.220(19)
2.270
23.3435(3)
10.0027(2)
17.6489(2)
90
126.7145(8)
90
9.4955(1)
12.1118(2)
14.3116(2)
81.4286(8)
88.0477(9)
80.5240(6)
1606.27(4)
1.747
9.4214(1)
13.2064(2)
14.7627(2)
90
˚
b/A
˚
c/A
α/◦
β/◦
γ/◦
92.4088(6)
90
90
90
124.6795(6)
90
3
˚
V/A
3303.48(9)
2.157
1349.81(4)
2.286
6939.33(9)
1.731
1510.50(3)
2.448
ρ
calc/g cm−3
Z
2
8
4
4
16
4
F(000)
µ(Mo-Kα ) (cm−1
T/K
480
104.84
143
2032
93.82
143
824
24.65
143
864
112.10
143
2998
24.74
143
1032
124.83
143
)
Refls. measured
Refls. unique
Rint
20784
3241
0.034
47908
3053
0.057
42192
6982
0.033
37499
3090
0.050
155893
3265
0.043
42159
3442
0.046
Refined parameters
Restraints
189
12
209
0
325
0
199
0
172
0
201
0
R1[I ≥ 2σ(I)]
0.0257
0.0674
a = 0.0315
b = 1.7801
1.326 / −1.275
0.0216
0.0560
a = 0.0166
b = 8.1973
0.769 /−0.888
0.0359
0.1030
a = 0.0488
b = 2.2327
0.0267
0.0637
a = 0.0037
b = 6.0070
0.0310
0.0724
a = 0.0157
b = 11.5911
0.754 / −0.381
0.0245
0.0596
a = 0.0127
b = 3.0870
1.1145 / −1.189
wR2a
Weighting scheme
−3
˚
σfin(max/min)/eA
1.323 / −1.015 1.031 / −0.981
awR2 = {Σ[w(Fo2 −Fc2)2]/Σ[w(Fo2)2]}1/2;w = 1/[σ2(Fo2)+(ap)2 +bp]; p = (F2 +2F2)/3.
o
c
methyl iodide. The structures of 3 and 6 have been solution of (C4H8S)AuCl (0.175 g, 6.20 mmol) in tetrahy-
drofuran (15 ml) at −78 ◦C with stirring. After 2 h the
determined. In the phosphonium cations, the central
solvent is removed in a vacuum at room temperature. The
residue is crystallized from CH2Cl2/n-pentane; colorless
crystals, m.p. 192 ◦C, 0.303 g (95.4% yield), soluble in
CH2Cl2, CHCl3, C4◦H8O, sparingly soluble in diethylether.
atom reaches an almost perfect tetrahedral configura-
tion. By contrast, in the gold(I) complexes the ligands
still have much smaller C-P-C angles as compared to
the tetrahedral standard, indicating the rather low ac-
ceptor character. This result is in agreement with the
31P NMR data, where the largest downfield shifts are
observed for both phosphines upon quaternization with
MeI (50.14 ppm for 3 and 61.62 ppm for 6). The shift
differences for 1 and 4 are only 39.22 and 49.37 ppm,
respectively.
1
NMR (CD2Cl2, 20 C) 31P{ H} −6.39, s; 1H 7.26 – 7.85
1
(ABCX); 13C{ H}: 129.35, 131.09, 135.66, and 138.69,
all d (J 14.3, 74.2, 5.2, and 14.8 Hz). MS(FAB): m/z 984.8
(19.1) [(LAu)2Cl]+; 757.0 (4.9) [L2Au]+; 511.9 (5.4) [M]+;
477.0 (100) [LAu]+. Analysis found C 31.13, H 2.24, P
6.59, Cl 7.54; calcd. C 31.02, H 1.95, P 6.67, Cl 7.63.
[Tri(2-thienyl)phosphine]gold acetate (2): Compound 1
(0.200 g, 0.620 mmol) is reacted with a slurry of silver ac-
etate (0.103 g, 0.620 mmol) in dichloromethane (15 ml) at
Experimental Section
◦
All experiments were carried out routinely in an at-
mosphere of dry nitrogen. Glassware was oven-dried and
filled with nitrogen, and solvents were dried and satu-
rated with nitrogen. Standard equipment was used through-
out. Reactions with silver salts were carried out in
flasks covered with aluminium foil. Tri(2-thienyl)- and
tri(2-furyl)phosphine are commercially available (Aldrich).
(Tetrahydrothiophene)gold chloride was prepared following
a literature procedure [33].
−78 C for 2 h with stirring. The reaction mixture is fil-
tered and the filtrate concentrated in a vacuum. The product
is finally precipitated from a small volume of the solution by
the addition of pentane. Colorless needles, m.p. 100 ◦C (de-
composition), 0.282 g (84.8% yield). NMR (CD2Cl2, 20 ◦C)
1
31P{ H}: −12.32, s; 1H: 7.26 – 7.85, m, ABCX; 1.97, s,
1
Me; 13C{ H}: 176.71, s, CO2; 129.30, 131.04, 135.61, and
138.73, all d (J 13.84, 77.64, 5.38, and 15.37 Hz); 23.61, s,
Me. MS(FAB): 756.6 (5.6) [L2Au]+; 476.8 (57.7) [LAu]+.
[Tri(2-thienyl)phosphine]gold chloride (1): Tri(2- Analysis found C 31.61, H 2.27, P 5.73, Au 37.60; calcd. C
thienyl)phosphine (0.200 g, 6.20 mmol) is added to a 31.29, H 2.44, P 5.76, Au 36.65.
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U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
757
◦
Methyl-tri(2-thienyl)phosphonium iodide (3): This com- at 0 C with stirring. The mixture is allowed to warm to
◦
pound was prepared previously from the phosphine and 20 C and stirring is continued for 30 min. before a solu-
methyl iodide in benzene [14, 19,◦22]. m.p. 183 ◦C. Comple- tion of arsenic trichloride (5.0 g, 28 mmol) in tetrahydrofuran
1
1
mentary data: NMR (CDCl3, 20 C), 31P{ H}: 4.53, s. H: (20 ml) is added dropwise with stirring. After 12 h the reac-
1
3.34, d, J 13.9 Hz, Me; 7.45, 8.12, 8.22, m, ABCX. 13C{ H}: tion mixture is quenched with water (50 ml). The lower layer
16.43, d, J 62.3, Me; 119.43, 130.87, 139.52, and 142.36, is separated and the solvent evaporated to leave a residue
all d (J 112.1, 16.1, 5.7, and 12.5 Hz). MS(FAB) m/z 294.7 which is taken up in chloroform (10 ml) and washed with
(100) [M]+.
the same volume of water. The aqueous phase is extracted
with chloroform and the combined organic phase is dried
over Na2SO4. Evaporation of the solvent and kugelrohr dis-
tillation (220 ◦C/0.9 mbar) gives a yellow oil, which solidifies
to a glass upon cooling; 3.41 g (28.4% yield). NMR (CDCl3,
[Tri(2-furyl)phosphine]gold chloride (4): As described
for complex 1, compound 4 is prepared from (tht)AuCl
(0.200 g, 0.620 mmol) and the ligand (0.144 g, 0.620 mmol)
in thf (15 ml) at −78 ◦C. Work-up after 2 h gives 0.273 g of
4 (95.0% yield), colorless crystals, m.p. 175 ◦C (decomposi-
1
20 ◦C), 1H: 7.16, 7.35, 7.59, ABC. 13C{ H}: 127.82, 131.13,
134.46, and 138.28, all s. MS(FAB) m/z 324 [M]+.
1
tion). 31P{ H} NMR (thf, 20 ◦C): −28.52, s. 1H (CD2Cl2):
6.58, 7.18, 7.82, m, ABCX. 13C{ H} (CD2Cl2): 112.04,
1
Tri(2-furyl)arsine: As described for (2-C4H3S)3As, the
compound is prepared from furan (10 g, 0.15 mol), n-
butyllithium (75 ml, 1.6 m, 0.12 mol) and AsCl3 (5.0 g,
28 mmol) in a total of 75 ml of tetrahydrofuran. Kugelrohr
distillation at 160 ◦C/0.9 mbar gives 3.58 g of an oily product
(47% yield), which crystallizes from diethylether at −78 ◦C.
125.54, 141.55, and 150.53, all d (J 6.2, 17.7, 67.6, and
4.7 Hz). MS(FAB) m/z 893.1 (32) [(LAu)2Cl]+; 464.0 (2)
[M]+; 429.0 (92) [LAu]+; 164.9 (100) [R2P]+. Analysis
found C 28.24, H 1.83, Au 38.1, Cl 6.78; calcd. C 28.11,
H 1.77, Au 38.41, Cl 6.91.
1
NMR (CDCl3, 20 ◦C), 1H: 6.44, 6.71, 7.66, ABC. 13C{ H}:
[Tri(2-furyl)phosphine]gold acetate (5): As described for
complex 2, compound 4 (0.273 g, 0.588 mmol) is converted
into compound 5 using silver acetate (0.103 g, 0.620 mmol)
in dichloromethane (15 ml) at −78 ◦C. The mixture is kept
at −32 ◦C for 1 week and filtered. Evaporation of the filtrate
leaves a frozen foam, which is taken up in dichloromethane
and reprecipitated as a siroup by addition of pentane. Drying
in a vacuum leaves again a frozen foam of the product, which
cannot be crystallized. The product decomposes at room tem-
perature and must be kept below −32 ◦C for prolonged stor-
110.52, 120.05, 146.86, and 150.50, all s. MS(FAB) m/z
276 [M]+.
[Tri(2-thienyl)arsine]gold chloride (7): As described for
1, the compound is prepared from (tht)AuCl (0.20 g,
0.62 mmol) and the arsine (0.20 g, 0.62 mmol) in
dichloromethane (7 ml). Colorless crystals, m.p. 144 ◦C;
0.326 g (94.3% yield). NMR (CDCl3, 20 ◦C) 1H: 7.20, 7.52,
1
7.73, ABC. 13C{ H}: 128.56, 130.36, 133.92, and 136.76,
all s. MS(FAB) m/z 1075.7 (40.6) [(LAu)2Cl]+; 844.1 (9.4)
age; 0.162 g (56.5% yield). NMR (CD2Cl2, 20 ◦C), 31P{ H}:
1
[L2Au]+; 520.5 (100) [LAu]+.
−35.26, s. 1H: 1.97, s, Me; 6.57, 7.21, 7.82, ABCX, m.
Crystal structure determinations: Specimens of suitable
quality and size of 1, 2, 3, 4, 6 and 7 were mounted on
the ends of quartz fibres in inert perfluoropolyalkylether
and used for intensity data collection on a Nonius DIP2020
diffractometer, employing graphite-monochromated Mo-Kα
radiation. The structures were solved by a combination of
direct methods (SHELXS-97) and difference-Fourier syn-
theses and refined by full matrix least-squares calculations
on F2 (SHELXL-97) [34]. The thermal motion was treated
anisotropically for all non-hydrogen atoms. The hydrogen
atoms were calculated in ideal positions and allowed to ride
on their parent atoms with fixed isotropic contributions ex-
cept for those of 4 which were located and refined with
isotropic displacement parameters. Further information on
crystal data, data collection and structure refinement are sum-
marized in Table 1. One thienyl group each in 1 and 2 and two
in 7 are disordered over two sites by a rotation of the ring of
180◦ about the C-P axis. The occupation factors for the pre-
dominantly occupied positions are 0.5, 0.560, 0.62 (S22) and
1
13C{ H}: 23.41, s, Me; 111.99, 125.64, 141.33, all d, (J 9.34,
25.95, 1.73 Hz); 150.48, s; 176.48, s, CO2. MS(FAB) m/z
916.0 (15.6) [(LAu)2OAc]+; 660.4 (39.3) [L2Au]+; 488.6
(1.6) [M]+; 428.7 (97.6) [LAu]+; 165.0 (100) [R2P]+. The
compound was too unstable for a reliable microanalysis.
Methyl-tri(2-furyl)phosphonium iodide (6): As described
for compound 3, the salt is obtained from the phosphine
(0.085 g, 0.380 mmol) and an excess of methyl iodide
(0.5 ml, 1.14 g, 8.1 mmol) in toluene (5 ml) under reflux
for 2 h [19]. Recrystallization from acetonitrile/diethylether
gives light brown rods, m. p. 138 ◦C; 0.108 g (76.1% yield).
NMR (CDCl3, 20 C), 31P{ H}: −16.27, s. 1H: 3.09, d, J
◦
1
15.1 Hz, Me; 7.73, 7.78, 7.99, br. m, ABCX; 13C{ H}: 9.35,
1
d, J 62.80 Hz, Me; 113.27, 130.82, 130.84, and 153.38, all
d (J 10.4, 23.4, 144.3, 8.8 Hz). MS(FAB) m/z 247.1 (100)
[M]+; 180.1 (2.1) [R2MeP]+; 165.1 (3.6) [R2P]+. Analysis
found C 40.23, H 3.19, I 35.38; calcd. C 41.74, H 3.23, I
33.92.
Tri(2-thienyl)arsine: Thiophene (12 g, 0.14 mol) is dis- 0.68 (S32), respectively. One of the iodide positions of 6 is
solved in tetrahydrofuran (50 ml) and treated with a 1.6 M disordered over two sites with occupation factors of 0.20 and
solution of n-butyllithium in n-hexane (75 ml, 0.12 mol) 0.16, respectively. Referring the full occupancy for this spe-
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758
U. Monkowius et al. · Ligand Properties of Tri(2-thienyl)- and Tri(2-furyl)phosphine
cial position (0.5), there is an occupational deficit. Absorp-
tion corrections for all structures were carried out using DE-
LABS, as part of the PLATON suite of programs [35]. Dis-
placement parameters and tables of interatomic distances and
angles have been deposited with the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK. The data are available on request on quoting CCDC
210532 – 210537 [37].
Acknowledgements
This work was generously supported by Deutsche
Forschungsgemeinschaft, Fonds der Chemischen Industrie,
Volkswagenstiftung, and Heraeus GmbH.
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