Preparation, structure and gold(I) complexation of p-xylylene-1,4- diphosphines

Article abstract of DOI:10.1515/znb-2005-0506

1,4-Dimethyl-2,5-di(phosphinyl)benzene (1) was prepared in high yield in a four-step synthesis from 1,4-dibromo-2,5-dimethyl-benzene. The intermediates with (Et₂N)₂P and Cl₂P groups (2, 3) with the corresponding substituti

Full text of DOI:10.1515/znb-2005-0506

Preparation, Structure and Gold(I) Complexation of
p-Xylylene-1,4-diphosphines
Stephan A. Reiter, Stefan D. Nogai, and Hubert Schmidbaur
Department Chemie, Technische Universita¨t Mu¨nchen,
Lichtenbergstraße 4, D-85747 Garching, Germany
Reprint requests to Prof. Dr. H. Schmidbaur. E-mail: H.Schmidbaur@lrz.tum.de
Z. Naturforsch. 60b, 511 – 519 (2005); received February 14, 2005
Dedicated to Professor Alfred Schmidpeter on the occasion of his 75th birthday
1,4-Dimethyl-2,5-di(phosphinyl)benzene (1) was prepared in high yield in a four-step synthesis
from 1,4-dibromo-2,5-dimethyl-benzene. The intermediates with (Et2N)2P and Cl2P groups (2, 3)
with the corresponding substitution pattern have been isolated and structurally characterized. All
three compounds (1 – 3) adopt a centrosymmetrical conformation with one of the P-X bonds of each
X2P group located in the ring plane while the other reaches out from this plane in a roughly per-
pendicular orientation. Distortions of the ring and its substituents from a standard planar hexago-
nal geometry are readily explained by invoking steric and inductive effects. The crystal structure of
1,4-dibromo-2,5-dimethyl-benzene has also been determined for reference purposes. Compound 1
was employed as a substrate for auration by tri(gold)oxonium salts of the type {[(R3P)Au]3O}BF4.
Hexanuclear complex salts of the type {[(R3P)Au]3P(C6H2Me2)P[Au(PR3)]3}(BF4)2 were obtained
in almost quantitative yield with R3P = tBu3P (4) and Ph3P (5). The former (4) has the higher ther-
mal stability, it could be crystallized and its structure determined. It features a conformation in which
the xylene plane bisects one of the Au-P-Au angles at both tetrahedrally coordinated central phos-
phorus atoms placing its methyl groups in sterically least hindered positions. Compound 5 is labile
in solution and shows rapid ligand exchange on the NMR time scale. The limited stability has also
been confirmed by mass spectrometry. Similar structural details and differences in stability were ob-
served in the related trinuclear gold complexes based on 1-naphthyl-phosphine, which were prepared
as reference materials using the same preparative procedure. Of the two compounds {(1-C10H7)-
P[Au(PR3)]3}BF4, with R3P = tBu3P (6) and Ph3P (7), the former is the more stable species. In the
solid state the cation approaches mirror symmetry in a conformation comparable to that of 4. Com-
pound 7 is thermally labile and shows a rapid ligand exchange in solution.
Key words: Primary Phosphines, Phenylene-1,4-diphosphines, Gold Complexes
Introduction
lene and 2,5-di(phosphinyl)-thiophene and -furan
[5 – 7]. In the course of these studies it has been
Primary phosphines RPH2 are attracting current in- noted that there is still a paucity of information on the
terest [1] owing to their synthetic potential a) for the efficient preparation and the properties of 1,4-di(phos-
preparation of new types of functional or chiral lig- phinyl)benzenes (A) with the most simple and obvious
ands [2], b) as substrates for hydrophosphination re- structural pattern for α,ω-ligation of benzene rings
actions [3] and c) for the construction of multidimen- via phosphorus atoms [8, 9].
sional frameworks [4]. Regarding the latter aspect,
polyfunctional primary arylphosphines with a rigid
skeleton are particularly useful for the design of chain-
like polymers or sheet-like layer structures with a vari-
ety of connectivity motifs which depend on the substi-
tution pattern of the parent aromatic hydrocarbon.
Ring-unsubstituted 1,4-di(phosphinyl)benzene was
first prepared by Wagner et al. in 1962, but for
quite some time its chemistry remained largely un-
explored [8]. The compound is a distillable liquid,
which could not be crystallized. Through the prepara-
tion and structural characterization of hexa- and even
In our own previous studies, work had focused on octa-nuclear gold(I) complexes it could be demon-
the chemistry of representative examples like 1,3,5- strated that the p-phenylene group of the substrate can
tri(phosphinyl)benzene, 1,8-di(phosphinyl)naphtha- act as a rigid plate-like unit connecting triangular or
c
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
square gold clusters by capping them with the phos-
phorus atoms [10]. In the absence of steric hindrance
by additional ring substituents, there is no conforma-
tional preference for the orientation of the phenylene
plane relative to the Au3 triangle or Au4 square as
shown by NMR spectroscopy in solution.
The present study therefore was initiated in order to
prepare a symmetrically substituted molecule, specifi-
cally the p-xylylene homologue, vic. 1,4-dimethyl-2,5-
di(phosphinyl)benzene (1). It was hoped that owing to
the reduced mobility of the –PH2 groups this homo-
logue should crystallize more readily than the parent
compound and allow the determination of its crystal
structure. It was further expected that its polynuclear
gold(I) complexes will exhibit a localized conforma-
tion of the xylylene unit.
The above structural expectations were based on ob-
servations with the corresponding p-phenylene com-
pounds with –SiH3 substituents [11– 16].
For the auration of the new diprimary phos-
phine 1, established methods could be employed
which were already used successfully in previous
studies with phenyl-, o-tolyl-, mesityl- and [2,4,6-
tri(tbutyl)phenyl]-phosphine, as well as 1,2- and
1,4-di(phosphinyl)- and 1,3,5-tri(phosphinyl)-benzene
[17– 21].
Scheme 1. Synthetic pathway to 1,4-dimethyl-2,5-di(phos-
phinyl)benzene (1).
In a complementary investigation 1-naphthyl-
phosphine, obtained in a parallel study [6], was also
triaurated and the product structurally characterized in
order to provide a reference compound with a more
pronounced steric effect of the aryl group (1-naphthyl).
Preparative Results
Scheme 2. Synthesis of the hexanuclear complexes 4 and 5.
The preparation of compound 1 is outlined in
Scheme 1. 1,4-Dibromo-2,5-dimethyl-benzene was
t
lithiated with four equivalents of BuLi in a tetrahy-
drofuran/pentane mixed solvent and the reaction mix-
ture subsequently treated with two equivalents of
bis(diethylamino)chlorophosphine. The product 2 was
isolated by crystallization from pentane in 59% yield
◦
(m.p. 89 C). Its conversion into the tetrachloride 3
Scheme 3. Synthesis of the trinuclear complexes 6 and 7.
The diprimary arylphosphine 1 was aurated by
was achieved in 93% yield by passing a stream of dry
hydrogen chloride into its solution in hexane. A crys-
◦
talline material (m.p. 66 C) was obtained upon crys- treating it with two different oxonium reagents
tallization from dichloromethane at −30 C. In the last {[(R3P)Au]3O}BF4 in dichloromethane at −78 ◦C
◦
step, compound 3 was reduced by an excess of LiAlH4 (R = tBu, Ph), (Scheme 2). The product 4 with
in diethylether to give a 92.5% yield of the target phos- the tBu3P ligands could be crystallized fr◦om di-
phine 1 which was isolated as a crystalline solid (from ethylether/acetone in 98.5% yield (m.p. 204 C with
diethylether at −30 ◦C, m. p. 51 ◦C).
decomposition). The analogous complex with Ph3P
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
513
ligands (5) was also obtained in high yield as a pale tion which would have indicated hindered rotation of
◦
yellow powder (m.p. 144 C with decomposition), but P(AuP)3 groups about the C-P(Au3) bonds. The 1H and
could not be crystallized.
1
13C{ H} NMR signals show no anomalies. No efforts
were made to completely analyze or assign all phenyl
and naphthyl resonances. The data are listed in the Ex-
perimental Section.
1-Naphthyl-phosphine [6, 22 – 27] was converted
into the corresponding trinuclear gold complexes (6,
7) using the same procedures (Scheme 3). While 6
(with the tBu3P ligands)◦was again readily crystallized
(98.3% yield, m.p. 142 C with decomposition), com-
pound 7 was received as a yellow powder (97.9% yield,
m. p. 123 ◦C with decomposition).
Crystal and Molecular Structures
1,4-Dibromo-2,5-dimethyl-benzene: The structure
of this precursor molecule (Scheme 1) was determined
in order to have reference data for the phosphines de-
rived thereof. Crystals (from ethanol) are monoclinic
(space group P21/n) with the unit cell containing Z = 4
molecules with no crystallographically imposed sym-
metry (Fig. 1). Except for the methyl hydrogen atoms
all atoms are largely coplanar with the representative
torsional angles all deviating less than 1◦ from 180◦.
Relative to the 120◦ standard, the endocyclic angles
at C2/C5 and C1/C4 are smaller by 3◦ and larger by
2◦ (average), respectively, as expected for electron-
donating methyl and electron-withdrawing bromo sub-
stituents [12, 16, 28 – 31]. The exocyclic angles indi-
cate a slight repulsion of neighbouring methyl and
bromo substituents (Caption to Fig. 1). The packing of
the molecules in the crystal shows no π-π stacking or
hydrogen phenyl embrace and appears to be governed
by intermolecular Br···Br contacts.
Analytical and Spectroscopic Data
Compounds 1 – 3 were characterized by microanal-
ysis, mass spectrometry and NMR spectroscopy. In
the EI mass spectra, the molecular ions were ob-
served with high intensity. The peaks featured the ex-
pected isotope patterns (3) and the fragments originat-
ing from the consecutive loss of hydrogen atoms (1).
The 31P{ H} NMR spectra showed singlet resonances
1
in the expected shift ranges, with the tetrachloride (3)
in the low-field region at δ = 159.8 ppm, the tetra-
amide (2) at δ = 93.0 ppm, and the tetra-hydride (1)
up-field at δ = −131.8 ppm (all in CD2Cl2 at 25 ◦C).
The 1H and 31P resonances of the –PH2 groups of com-
pound 1 appear as the A and X parts of an A2XX’A’2
multiplet, respectively, (with additional fine-structure
arising from weak couplings with the aryl hydrogen
atoms), which were not fully analyzed.
The gold complexes 4 – 7 gave satisfactory elemen-
tal analysis data. In the FAB mass spectra the mono-
(6) and dications (4) of the salts were detected as the
parent ions or with low intensity (7), while for 5 only
fragment ions could be registered. The 31P NMR spec-
tra showed significant differences for the complexes
with the tBu3P and Ph3P ligands, in that only the for-
mer featured the expected AX3 multiplicit◦ies (d, q) for
the PA(AuPX)3 groups in CD2Cl2 at 25 C. In these
spectra it was unnecessary to treat the coupling pat-
tern as based on an extended X3AA’X’3 spin sys-
tem, because the A-A’ coupling appears to be almost
◦
negligible. For 5 cooling to −80 C was required to
Fig. 1. Molecular structure of 1,4-dibromo-2,5-dimethyl-
benzene (ORTEP, 50% probability ellipsoids). Selected
obtain the doublet/quartet pattern. This phenomenon
indicated an exchange broadening of AuPR3 or PR3
groups in solution, which is slow for Bu3P, but rapid
for Ph3P ligands on the NMR time scale. In this con-
text it should be noted that complexes 5 and 7 were
found to have lower thermal stability than 4 and 6 both
◦
˚
bond lengths [A] and angles [ ]: Br1-C4 1.908(7), Br2-
C1 1.892(7), C2-C8 1.560(10), C5-C7 1.549(9); C1-C2-
C3 116.9(6), C2-C3-C4 120.3(6), C2-C1-C6 121.9(6), C3-
C4-C5 122.3(6), C4-C5-C6 117.0(6), C5-C6-C1 121.7(7),
Br1-C4-C5 120.5(5), Br1-C4-C3 117.2(5), Br2-C1-C2
119.8(5), Br2-C1-C6 118.3(5), C7-C5-C4 121.9(6), C7-C5-
t
as solids and in solution. However, there was no NMR C6 121.1(6), C8-C2-C1 122.4(6), C8-C2-C3 120.7(6). All
dihedral angles C-C-C-C/Br are very close to 0 or 180◦.
evidence for inequivalence of (AuPR3) groups in solu-
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
1,4-Bis[bis(diethylamino)phosphinyl]-2,5-dimeth- 1,4-Bis(dichlorophosphinyl)-2,5-dimethyl-benzene
yl-benzene (2): Crystals (from pentane at −30 ◦C) (3): Crystals (from dichloromethane at −30 ◦C)
are monoclinic (space group P21/c), with Z = 2 are monoclinic (space group P21/c), with Z = 2
centrosymmetrical molecules in the unit cell (Fig. 2). centrosymmetrical molecules in the unit cell (Fig. 3).
One of the four independent ethyl groups was found The conformation resembles that of compound 2.
disordered over two positions. The endocyclic C-C-C The endocyclic angles show only minor deviations
angles are large at C3, but small and equal at C1 and from 120◦, but the exocyclic angles P1-C2-C1 =
C2 reflecting the similarity of the electronegativities 124.16(12)◦ and P1-C2-C3 = 115.91(12)◦ are signif-
of C and P substituents. One of the two P-N bonds icantly different and indicate again (c.f. 2) a leaning
(P1-N2), and thus the nitrogen atom N2, lie roughly in over of the PCl2 groups towards the methyl group
the molecular plane [torsional angle N2-P1-C1-C3 = owing to the proximity of the hydrogen atom at C1 and
9.30(12)◦], while the second P-N bond (P1-N1) the in-plane chlorine atom Cl2 (the dihedral angles
reaches out from this plane [with a torsional angle Cl2-P1-C2-C1 and P1-C2-C3-C4 are only 4.22(14)◦
N1-P1-C1-C3 = 122.63(11)◦] (Fig. 2). The methyl and −4.9(2)◦, respectively).
carbon atoms deviate more strongly from the benzene
plane than in the dibromo precursor (above). These
distortions are clearly necessary to relieve steric
crowding. It is probably due to the proximity of the
hydrogen atom at C3 to the Et2N group which has
its N atom in the molecular plane (N2) that causes
an unexpected tilting of the C1-P1 bond towards the
methyl group [C3-C1-P1 = 122.17(10)◦].
Fig. 2. Top: Molecular structure of compound 2 projected
onto the xylene plane (ORTEP, 50% probability ellipsoids,
hydrogen atoms omitted; one ethyl group is disordered over
Fig. 3. Top: Molecular structure of compound 3 projected
perpendicular to the xylene plane (ORTEP, 50% probabil-
two positions). Bottom: Projection parallel to the xylene
ity ellipsoids). Bottom: Projection parallel to the xylene
plane (arbitrary radii, ethyl groups and hydrogen atoms
plane (arbitrary radii, hydrogen atoms omitted). Selected
◦
˚
omitted). Selected bond lengths [A] and angles [ ]: P1-C1
1.8422(13), P1-N1 1.6939(12), P1-N2 1.6956(13), C2-C4
1.5127(18); P1-C1-C2 119.46(10), P1-C1-C3 122.17(10),
C1-C2-C4 122.31(12), C3’-C2-C4 118.89(12). The center of
the xylene ring is a center of inversion.
◦
˚
bond lengths [A] and angles [ ]: P1-C2 1.8309(17), P1-
Cl1 2.0726(6), P1-Cl2 2.0553(6), C3-C4 1.514(2); P1-C2-C1
124.16(12), P1-C2-C3 115.91(12), C1’-C3-C4 119.67(14),
C2-C3-C4 122.03(15). The center of the xylene ring is a cen-
ter of inversion.
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
515
Fig. 5. Structure of the dication of compound 4 in the
4·(Et2O)2(Me2CO)2 solvate (ORTEP, 50% probability ellip-
soids, H atoms omitted for clarity). Selected bond lengths
◦
˚
[A] and angles [ ]: P1-Au1 2.3085(16), P1-Au2 2.3123(16),
P1-Au3 2.3129(15), P1-C2 1.822(6), C3-C4 1.519(8), C2-
C3 1.421(8); C2-P1-Au1 113.3(2), C2-P1-Au2 114.4(2),
C2-P1-Au3 112.4(2), Au1-P1-Au2 103.91(6), Au2-P1-Au3
105.37(6), Au1-P1-Au3 106.60(6), C2-C3-C4 121.8(6), P1-
C2-C3 122.7(4), P1-C2-C1 119.6(4), C4-C3-C1’ 119.8(6).
Fig. 4. Top: Molecular structure of compound 1 projected The center of the xylene ring is a center of inversion.
perpendicular to the xylene plane (ORTEP, 50% probability
◦
ellipsoids). Bottom: Projected parallel to the xylene plane
(4): Crystals (from diethylether/acetone at −30 C)
(arbitrary radii, xylene and methyl hyd◦rogen atoms omitted).
are monoclinic (space group P21/n) with two formula
units of the salt, four acetone and four diethylether
molecules in the unit cell: (4)2(Me2CO)4(Et2O)4. The
structure of the centrosymmetrical dication is shown
in Fig. 5. There are no unusual intermolecular contacts
between these dications and the anions or solvent
molecules. The phosphorus atoms of the precursor
molecule 1 are seen to be triply aurated attaining a
quasi-tetrahedral configuration with average Au-P-Au
and C-P-Au angles of 105.3◦ and 113.4◦, respectively.
The gold atoms are linearly two-coordinate with
conventional Au-P bond lengths. These structural
details are in agreement with results of structural
studies of other triply aurated primary phosphines. No
significant aurophilic bonding can be invoked due to
the large intermetallic distances [17 – 19].
˚
Selected bond lengths [A] and angles [ ]: P1-C1 1.8361(15),
P1-H11 1.28(2), P1-H12 1.29(3), C2-C4 1.533(2); P1-C1-C2
119.66(12), P1-C1-C3’ 121.08(12), C1-C2-C4 121.03(14),
C3-C2-C4 120.51(14). The center of the xylene ring is a cen-
ter of inversion.
1,4-Dimethyl-2,5-di(phosphinyl)benzene (1): Crys-
tals (from diethylether at −30 ◦C) are monoclinic
(space group P21/n) with Z = 2 centrosymmetrical
molecules in the unit cell (Fig. 4). The overall con-
formation of molecule 1 resembles that of 2 and 3,
but there are only minor signs of steric crowding. The
methyl carbon atoms reside in the molecular plane and
only the phosphorus atoms are slightly offset. Within
the molecular plane, the angles C1-C2-C4 and C2-
C1-P1 deviate from the 120◦ standard by only 1◦.
The leaning over of the (dichloro)phosphinyl group to-
wards the methyl group observed in 3 is not discernible
in 1, probably owing to the negligible steric effect of
the hydrogen atoms. The endocyclic angles are a lit-
tle larger at C3, but smaller and virtually equal at C1
and C2. The packing of the molecules in the unit cell
shows no evidence for hydrogen bonding or other non-
standard van der Waals interactions. This observation
is in agreement with previous findings.
The central xylene plane roughly bisects the an-
gle Au1-P1-Au2 thus placing each of its methyl sub-
stituents between a pair of [(tBu3P)Au] groups in order
to minimize steric pressure. As shown by NMR studies
in solution (above), this conformation is not fixed and
rapid rotation of the components about the P1-C2 axes
is possible (on the NMR time scale).
1-Naphthyl-tris{[tri(tbutyl)phosphine]gold(I)}phos-
1,4-Dimethyl-2,5-bis{tris[(tri(tbutyl)phosphine)-
phonium tetrafluoroborate, (6): Crystals (from di-
◦
gold(I)]phosphonio}benzene bis(tetrafluoroborate) ethylether/acetone at −30 C) are monoclinic (space
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
get compound 1 is obtained as a stable, colour-
◦
less, crystalline solid (m. p. 51 C), which is solu-
ble in most low-polarity solvents. Upon reaction with
tri[gold(I)]oxonium salts, it is converted in almost
quantitative yield into the corresponding hexanuclear
diquaternary phosphonium salts 4 and 5 (Scheme 2).
The complex 4 with the extremely bulky auxiliary lig-
and tBu3P shows significantly higher thermal stability
than complex 5 with the smaller Ph3P ligand, proba-
bly due to the efficient steric protection of the sensitive
parts of the dication. The analogous reactions with 1-
naphthyl-phosphine afford the trinuclear phosphonium
salts 6 and 7 (Scheme 3), of which the former – with its
tBu3P ligands – again shows higher thermal stability.
NMR spectroscopic studies at room temperature
have indicated that in dichloromethane solutions of the
Fig. 6. Structure of the cation of compound 6 (ORTEP, 50% more labile complexes 5 and 7 there is ligand mobil-
probability ellipsoids, hydrogen atoms omitted). Selected
ity which probably opens the decomposition pathway.
◦
˚
bond lengths [A] and angles [ ]: P1-Au1 2.3188(9), P1-Au2
2.2971(9), P1-Au3 2.3145(9), P1-C1 1.836(4); C1-P1-Au1
106.14(11), C1-P1-Au2 118.35(13), C1-P1-Au3 119.61(12),
Au1-P1-Au2 103.37(4), Au2-P1-Au3 103.03(3), Au1-P1-
Au3 104.45(3).
By contrast, no such process is observed for the ro-
bust complexes 4 and 6. For all four complexes (4 –
7) there is no NMR-evidence for hindered rotation of
the [(R3P)Au]3P units (with their local C3v symmetry)
about the P-C(arene) bonds connecting them to the flat
xylylene or naphthyl units (with local Cs symmetry).
Single crystal X-ray diffraction studies of com-
pounds 1 – 3 and their dibromo precursor have shown
that all four molecules have a center of inversion, ei-
ther imposed by crystal symmetry (1 – 3) or to a good
approximation (C6H2Me2Br2). Significant distortions
of the standard geometry are observed only for 2 with
its bulky P(NEt2)2 substituents. The PH2 groups in
1 are not sterically hindered and give freely access
for extensive complexation. The minor distortions of
the endocyclic angles of the central benzene ring in
molecules 1 – 3 show that carbon and phosphorus have
very similar electronegativity (“phosphorus, the carbon
copy” [32]).
The structures of the complexes 4 and 6 have
also been determined, for the former from a di-
ethylether/acetone solvate 4·(Et2O)2(Me2CO)2. The
[(R3P)Au]3P groups have a pseudo-tetrahedral con-
figuration attached to the flat xylylene and naphthyl
groups, respectively. The xylene plane bisects two of
the six Au-P-Au angles establishing inversion and mir-
ror symmetry for the dication of 4, while the naphthyl
plane bisects one of the three Au-P-Au angles generat-
group P21/c) with Z = 4 formula units in the unit
cell. The structure of the cation is shown in Fig. 6.
The geometry of the environment of the phosphonium
center is very similar to that in compound 4 and needs
no further comment. The plane of the naphthyl group
almost exactly bisects the angle Au1-P1-Au3 with
dihedral angles C9-C1-P1-Au1/Au3 of 58.7(3) and
−58.9(3)◦, respectively. This conformation places the
annealed benzene ring C5-C10 between two of the
three bulky [(tBu3P)Au] groups, very similar to the
conformation observed in compound 4 with respect to
the xylylene methyl groups. Neglecting the orientation
of the tBu groups, the structure of the cation in
compound 6 thus approaches very closely mirror
symmetry. However, in solution the three [(tBu3P)Au]
groups are NMR-equivalent and only one 31P signal is
observed for the tertiary phosphine ligands (in CD2Cl2
◦
at 25 C), suggesting free rotation of the naphthyl
“flag” around the P1-C1 “pole”.
Conclusions
In the preparative part of this work it has been
demonstrated that diprimary phosphines based on ing approximate mirror symmetry for the cation of 6.
the p-xylylene skeleton can readily be prepared in The two structures show efficient steric shielding of
high yield from 1,4-Br2-2,5-Me2-C6H2 following the the core units of the cations which explains the robust
four-step procedure shown in Scheme 1. The tar- nature of the two poly(gold)phosphonium salts.
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
517
Experimental Section
Compound 1: A solution of 3 (6.44 g, 20.9 mmol) in di-
ethylether (50 ml) was added slowly to a stirred suspension
of LiAlH4 (6.35 g, 167.3 mmol) in diethylether (200 ml) at
−78 ◦C. The reaction mixture was then allowed to warm to
room temperature and subsequently stirred for 12 h. After
General: All experiments were carried out in an at-
mosphere of dry nitrogen. Solvents were dried, distilled
and saturated with nitrogen; glassware was oven-dried and
filled with nitrogen. Standard equipment was used through-
out. The starting materials were commercially available
except for (Et2N)2PCl and the two oxonium salts which
were prepared following literature procedures [33 – 36].
MS: Finnigan MAT 90 (FAB, 4-nitro-benzyl alcohol); HP
5971A (EI, 70 eV). NMR: JEOL JNM-GX-270/400. Stan-
dards: TMS (1H, 13C), H3PO4 (85%, 31P), BF3·OEt2 (11B),
CFCl3 (19F).
◦
cooling to 0 C the mixture was treated with degassed wa-
ter (40 ml), stirred for 1 h and filtered. The residue was ex-
tracted with 2 × 50 ml of diethylether, the filtrate combined
with the extracts and dried over MgSO4. Evaporation of the
solvents in a vacuum left a residue which could be crystal-
◦
lized from diethylether at −30 C; colourless, air-sensitive
crystals, m.p. 51 ◦C, 3.29 g (92.5% yield). C8H12P2 (170.13):
calcd. C 56.48, H 7.11, P 36.41; found C 56.36, H 7.10,
◦
P 36.32. MS(EI): m/z 170 [M+]. NMR (CD2Cl2, 25 C),
Compound 2: A solution of C6H2Me2Br2 (12.0 g,
45 mmol) in THF (360 ml) was cooled to −78 ◦C and
treated dropwise with a solution of tBuLi in pentane (135 ml,
1.5 M, 203◦ mmol). The reaction mixture was allowed to
warm to 0 C and stirred for 1 h at this temperature. The
yellow solution turned into◦a pale yellow suspension, which
was again cooled to −78 C and treated with (Et2N)2PCl
(30.1 g, 143 mmol). The reaction mixture was allowed to
warm to room temperature and stirred for 12 h. Thereafter
all volatiles were removed in a vacuum and the residue ex-
tracted with 3 × 150 ml of pentane. The pentane extracts
were concentrated in a vacuum to a volume of 100 ml and
cooled to −30 ◦C to crystallize the product; colourless crys-
tals, 12.2 g (59.2% yield), m.p. 89 ◦C. C24H48N4P2 (454.61):
calcd. C 63.41, H 10.64, P 13.63; found C 62.98, H 10.66,
31P{ H}: δ = −131.8 (s); 13C{ H}: 138.9 (dd, J = 11.5
and 4.6, CMe), 136.4 (dd, J = 13.1 and 2.3, CH), 129.6 (d,
J = 10.0, CP), 21.4 (d, J = 10.0, Me); 1H: 7.29 (m, AA’XX’,
2H, HC), 3.82 (d, J = 204.3, 4H, H2P), 2.31 (s, 6H, Me).
1
1
Compound 4: A solution of the phosphine 1 (8.4 mg,
0.05 mmol) in dichloromethane (10 ml) was added slowly to
a solution of {[(tBu3P)Au]3O}BF4 (128.4 mg, 0.10 mmol)
◦
in the same solvent (20 ml) at −78 C with stirring. After
2 h the reaction mixture was warmed to room temperature,
concentrated to a volume of 5 ml in a vacuum, and pen-
tane (50 ml) was added to precipitate the product. The com-
pound crystallized as the solvate 4·(Et2O)2(Me2CO)2 from
acetone solution upon layering with diethylether at −30 ◦C.
The solvent can be removed in a vacuum; 133 mg (98.5%
yield), m.p. 204 ◦C with decomposition. C80H170Au6B2F8P8
(2735.40): calcd. C 35.13, H 6.26, P 9.06; found C 34.78,
H 6.16, P 9.17. MS(FAB) m/z 1282.0 (100%) [M2+]. NMR
P 13.26. MS(EI): m/z 454 [M+]. NMR (CD2Cl2, 25 C),
◦
1
1
31P{ H}: δ = 93.0 (s); 13C{ H}: 139.9 (d, J = 4.6, CP),
136.8 (d, J = 25.4, CMe), 133.2 (m, AXX’, CH), 44.0 (d,
J = 16.9, CH2), 20.8 (d, J = 13.9, MeC), 15.0 (s, MeCH2).
1H: 7.16 (m, AA’XX’, 2H, HC), 3.07 (m, 16H, CH2), 2.32 (s,
6H, MeC), 1.09 (t, J = 7.0, 24H, MeCH2).
◦
1
(CD2Cl2, 25 C), 31P{ H}: δ = 99.3 (d, J = 235.8, PAu),
−7.0 (q, J = 235.8, PAu3); 31P: 99.3 (2 × 28, 18 lines re-
2
3
2
solved, JPP 235.8 and JPH 13.9, PAu), −7.0 (qd, JPP
235.8 and JPH 13.9, PAu3); 13C{ H}: 141.0 (d, J = 22.3,
CP), 140.4 and 138.4 (2xm, AXX’, C-2,5 / C-3,6), 40.0 (d,
J = 13.8, CMe3), 32.7 (s, Me), 24.5 (d, J = 9.2, Mexyl); 1H:
7.95 (m, AA’XX’, 2H, CH), 2.64 (s, 6H, Mexyl), 1.53 (d,
J = 13.5, 162H, Me); 11B: −2.1 (s); 19F: −153.3 (s).
3
1
Compound 3: A solution of 2 (◦11.45 g, 25.2 mmol) in
hexane (500 ml) was cooled to 0 C and saturated with a
stream of gaseous HCl. The reaction mixture was stirred for
1 h and again saturated with HCl gas. This procedure was
repeated until the supernatant solution remained clear upon
further addition of HCl. The reaction mixture was allowed
to warm to room temperature and stirred for another 12 h
before the precipitate was removed by filtration and washed
with 2×100 ml of hexane. The filtrate and the extracts were
combined and the solvent evaporated in a vacuum. From a
solution of the residue in dichloromethane the product sep-
Compound 5: The preparation followed the procedure
given for 4 with 11.8 mg (0.07 mmol) of 1 and 205.6 mg
(0.14 mmol) of {[(Ph3P)Au]3O}BF4; 204.6 mg (95.3%
yield) of a yellow solid, m. p. 144 ◦C with decomposi-
tion. C116H98Au6B2F8P8 (3095.22): calcd. C 45.01, H 3.19,
P 8.01; found C 44.86, H 3.15, P 8.22. MS(FAB): m/z 720.4
[Au(PPh3)2+]. NMR (CD2Cl2, 25 C), 31P{ H}: δ = 46.5
◦
1
◦
arated upon cooling to −30 C; colourless crystals sensi-
(br. s, PAu), −19.1 (br. s, PAu3); [at −80 ◦C: 45.7 (d,
tive to oxidation and hydrolysis, 7.21 g (93% yield), m.p.
66 ◦C. C8H8Cl4P2 (307.91): calcd. C 31.21, H 2.62, P 20.12;
found C 31.21, H 2.69, P 19.90. MS(EI): m/z 308 [M+].
1
J = 258.1) / −20.4 (q, J = 258.1)]; 13C{ H}: 141.0 and
138.9 (2xm, AXX’, Cxyl), 139.4 (d, J = 24.6, CP), 134.5 (d,
J = 13.1), 132.3 (s), 129.9 (d, J = 51.9), and 129.8 (d, J =
◦
1
1
NMR (CD2Cl2, 25 C), 31P{ H}: δ = 159.8 (s); 13C{ H}:
142.5 (d, J = 59.2, CP), 139.1 (d, J = 34.8, CMe), 132.3 (d,
J = 13.0, CH), 19.7 (d, J = 25.4, CMe); 1H: 7.89 (m,
AA’XX’, 2H, HC), 2.67 (d, J = 3.3, 6H, MeC).
1
10.8, all Ph), 25.5 (d, J = 8.5, Me). H: 8.19 (m, AA’XX’,
2H, Hxyl), 7.68 – 7.32 (m, 90H, Ph), 2.78 (s, 6H, Me); 11B:
−2.1; 19F: −153.3.
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518
S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
Table 1. Crystal data, data collection and structure refinement of 1,4-Br2-2,5-Me2-C6H2 and compounds 1 – 4, and 6.
C6H2Me2Br2
1
2
3
4
6
Empirical formula
M
C8H8Br2
263.96
monoclinic
P21/n
6.2838(2)
7.7186(3)
17.3959(7)
95.368(1)
840.04(5)
2.087
C8H12P2
170.12
monoclinic
P21/n
6.2217(2)
11.0937(3)
6.4939(2)
98.032(1)
443.82(2)
1.273
C8H8Cl4P2
307.88
monoclinic
P21/c
7.4772(1)
11.2813(2)
7.5360(1)
110.257(1)
596.36(2)
1.715
C24H48N4P2
454.60
monoclinic
P21/c
7.9661(1)
9.9005(2)
17.5714(3)
102.729(1)
1351.77(4)
1.117
C94H202Au6B2F8O4P8 C46H88Au3BF4P4
2999.74
monoclinic
P21/n
1442.75
monoclinic
P21/c
Crystal system
Space group
˚
a [A]
13.2321(2)
17.2175(2)
26.4908(4)
102.5490(7)
5891.1(1)
1.691
12.1358(1)
23.9766(2)
19.4960(2)
104.6056(4)
5489.53(9)
1.746
˚
b [A]
˚
c [A]
β [◦]
3
˚
V [A ]
ρcalc [g cm−3
]
Z
4
2
2
2
2
4
F(000)
T [K]
504
143(2)
180
143(2)
308
143(2)
500
143(2)
2948
143(2)
2808
143(2)
Refls. measured
Refls. unique
Parameters
R1 [I ≥ 2σ(I)]
wR2a
31213
1932
93
0.058
10140
808
70
0.035
15954
1218
65
0.031
40221
3101
161
0.041
152951
9384
582
0.031
0.078
124856
10400
550
0.022
0.148
0.096
0.080
0.11
0.054
Weighting
scheme
a = 0.0349
b = 11.6627
a = 0.0652
b = 0.1866
a = 0.0503
b = 0.3455
a = 0.0551
b = 0.4837
a = 0.0255
b = 32.7801
a = 0.0194
b = 13.2669
1.495 / −0.956
−3
˚
σfin(max/min) [eA
]
1.451 / −0.832 0.259 / −0.363 0.282 / −0.459 0.305 / −0.405 1.772 / −1.180
a
2
wR2 = { [w(F −Fc2)2]/ [w(F 2)2]}1/2; w = 1/[σ2(Fo2)+(ap)2 +bp]; p = (F 2 +2F 2)/3.
∑
∑
o
o
o
c
Compound 6: The preparation followed the pro- monochromated Mo-Kα radiation. The structures were
cedure given for with 16.7 mg (0.10 mmol) of solved by a combination of direct methods (SHELXS-97)
4
1-naphthyl-phosphine and 135.6 mg (0.10 mmol) of and difference-Fourier syntheses and refined by full ma-
{[(tBu3P)Au]3O}BF4; 147.9 mg (98.3% yield) of colourless trix least-squares calculations on F2 (SHELXL-97) [37].
crystals, m.p. 142 ◦C with decomposition. C46H88Au3BF4P4 The thermal motion was treated anisotropically for all non-
(1442.79): calcd. C 38.29, H 6.15, P 8.59; found C 38.08, hydrogen atoms.
H 6.18, P 8.47. MS(FAB): m/z 1356.7 (100%) [M+].
One ethyl group in the structure of 2 is disordered over
1
NMR (CD2Cl2, 25 ◦C), 31P{ H}: δ = 99.5 (d, J = two sites with site occupation factors of 0.79 and 0.21, re-
1
236.0, PAu), −9.3 (q, J = 236.0, PAu3); 13C{ H}: 139.9 – spectively.
125.1 (naphthyl carbon atoms), 40.0 (d, J = 14.5, CMe3),
The hydrogen atoms of 1 were located and refined with
1
32.7 (d, J = 3.1, Me); H: 9.24 – 7.32 (m, naphthyl hydro- isotropic displacement parameters, those in C6H2Me2Br2, 2,
gen atoms), 1.52 (d, J = 13.5, Me); 11B: −2.1 (s); 19F: 3, 4 and 6 were calculated in ideal positions and refined after
−153.5 (s).
a riding model.
Absorption corrections were carried out for C6H2Me2Br2,
4 and 6 using DELABS, as part of the PLATON suite of pro-
grams [38]. Further information on crystal data, data collec-
tion and structure refinement is summarized in Table 1.
Displacement parameters and tables of interatomic dis-
tances and angles have been deposited with the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK. The data are available on request on quoting
CCDC 264182 – 264187.
Compound 7: The preparation followed the pro-
cedure given for with 20.5 mg (0.13 mmol) of
4
1-naphthyl-phosphine and 189.5 mg (0.13 mmol) of
{[(Ph3P)Au]3O}BF4; 203.3 mg (97.9% yield) of a yellow
◦
solid, m.p. 123 C with decomposition. C64H52Au3BF4P4
(1622.70): calcd. C 47.37, H 3.23, P 7.64; found C 46.98,
H 3.41, P 7.48. MS(FAB) m/z 1535.1 (21%) [M+]. NMR
1
(CD2Cl2, 25 ◦C), 31P{ H}: δ = 46.2 (br. s, PAu), −21.3 (br.
1
s, PAu3); 13C{ H}: 134.6 (d, J = 13.1), 132.3 (s), 129.9 (d,
J = 52.3), and 129.8 (d, J = 10.8) for Ph; 138 – 125.4 (naph-
thyl carbon atoms); 1H: 9.42 – 7.32 (m, phenyl and naph-
thyl); 11B: −2.1 (s); 19F: −153.4 (s).
Acknowledgements
Crystal structure determination: Specimens of suitable
This work was generously supported by Deutsche
quality and size of C6H2Me2Br2, 1, 2, 3, 4 and 6 were Forschungsgemeinschaft, Fonds der Chemischen Industrie
mounted on the ends of quartz fibers in inert perflu- and Deutscher Akademischer Austauschdienst. The authors
oropolyalkylether and used for intensity data collection are indebted to Degussa AG and Heraeus GmbH for the do-
on a Nonius DIP2020 diffractometer, employing graphite- nation of chemicals.
Unauthenticated
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S. A. Reiter et al. · Gold(I) Complexation of p-Xylylene-1,4-diphosphines
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