Dinuclear gold complexes of two simple but underutilized dicarbanionic ligand types

Article abstract of DOI:10.1515/znb-2009-11-1227

Both mono- and bisylide zwitterionic complexes of gold(I), [(C ₆F₅){PhCH(PPh₃)}Au] (4), [(C₆F ₅)₂(C₆H₄-p){CH(PPh ₃)}₂Au₂] (5) and [(C<

Full text of DOI:10.1515/znb-2009-11-1227

Dinuclear Gold Complexes of Two Simple but Underutilized
Dicarbanionic Ligand Types
Karolien Coetzee, Christoph E. Strasser, Stephanie Cronje, and Helgard G. Raubenheimer
Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1,
Matieland, 7602, Stellenbosch, South Africa
Reprint requests to Prof. Helgard G. Raubenheimer. Fax: +27 21 8083849. E-mail: hgr@sun.ac.za
Z. Naturforsch. 2009, 64b, 1449 – 1457; received October 6, 2009
Dedicated to Professor Hubert Schmidbaur on the occasion of his 75th birthday in recognition of his
numerous contributions to inorganic and organometallic chemistry
Both mono- and bisylide zwitterionic complexes of gold(I), [(C6F5){PhCH(PPh3)}Au] (4),
[(C6F5)2(C6H4-p){CH(PPh3)}2Au2] (5) and [(C6F5)2(C6H4-m){CH(PPh3)}2Au2] (6) were pre-
pared by THT substitution in [C6F5(THT)Au] (THT = tetrahydrothiophene) using deprotonated
mono- and bis-phosphonium salts. Lithiation of 4,4ꢀ-dibromo-2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-octafluoro-1,1ꢀ-
biphenyl and transmetallation with [Cl(Ph3P)Au] produced a dinuclear gold complex of octafluoro-
substituted biphenyl [[(PPh3)2(C6F4-C6F4)2Au2]] (8).
Key words: Gold(I), Bisylide Complexes, Octafluorobiphenyl, Ylide Structures,
Dinuclear Gold(I) Complexes
Introduction
In this communication we report on the preparation
and structure of dinuclear gold complexes employing,
firstly, zwitterionic phosphonium bisylides and, sec-
ondly, a dianionic fluorosubstituted biphenyl ligand.
For comparative purposes, three other and somewhat
related new crystal structures are also described.
For more than three decades ylide ligands have been
used by gold chemists to prepare a large variety of
complexes [1 – 3]. Groups that have featured promi-
nently are those of Schmidbaur [4], the Laguna broth-
ers [5], Fackler [6] and Vicente [7]. More recently,
phosphonium ylide complexes of gold (and other late
as well as early transition elements) have been used as
sources of carbene complexes [8], and in a recent Dal-
ton Perspective, Urriolabeitia [9] addresses the bond-
ing as well as redox properties of, amongst others, gold
ylide complexes from theoretical as well as practical
viewpoints. As far as we could ascertain, no dinuclear
gold complexes bearing phosphine bisylides have been
reported and, with certainty, no crystal structures of
such compounds or of any transition metals have been
authenticated.
Results and Discussion
Synthetic procedures
Colorless precursor phosphonium salts (1, 2 and 3,
Schemes 1 and 2) were formed by alkylation reactions
between mono- and bis(bromoalkyl)benzeneand triph-
enylphosphine [13, 14]. The choice of solvent is very
important for the formation of the bisphosphonium
Pentafluorophenyl is an important spectator lig-
and in gold chemistry [10], and it is surprising that
its extended 4,4ꢀ-dianionic variant, 2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-
octafluoro-1,1ꢀ-biphenyl, although synthetically useful
in organic chemistry and reported to form a gold(I)
complex [11], has been described as a ligand in only
one crystal structure determination wherein nickel is
the metal of choice [12].
Scheme 1.
c
0932–0776 / 09 / 1100–1449 $ 06.00 ꢀ 2009 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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K. Coetzee et al. · Dinuclear Gold Complexes
Fig. 1.
Scheme 2.
salts since strongly polar solvents such as nitroben-
zene, acetonitrile (used by us) and dimethylformamide
keep the formed monophosphonium salts in solution
allowing reaction with a second molar equivalent of
triphenylphosphine. Deprotonation effected ylide for-
mation.
Scheme 3.
complex by first converting the bisphosphonium bro-
mide into bisphosphonium tetrafluoroborate and then
deprotonating with one molar quantity of n-BuLi be-
fore reaction with [C6F5(THT)Au], was unsuccessful.
It produced a mixture of compounds from which solely
the salt 7 [20] (Fig. 1) was crystallized. The cationic
fragments in compounds 2 and 3 and 5 and 6, respec-
tively, differ only therein that two hydrogen atoms in
the former two are replaced by two isolobal C6F5Au
units in the latter two complexes.
To prepare compound 8 (Scheme 3) commer-
cial 4,4ꢀ-dibromo-2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-octafluoro-1,1ꢀ-bi-
phenyl was lithiated with n-BuLi at low tempera-
ture and the product then transmetallated in situ with
[Cl(Ph3P)Au]. Product 8 was obtained in pure form
by crystallization from the crude mixture and recrys-
tallization with diethyl ether to afford suitable crystals
for structure determination by X-ray diffraction. Dinu-
clear 8 was also characterized by NMR measurements,
elemental analysis and mass spectrometry.
Various methods were compared in our attempts
to prepare dinuclear ylide complexes of gold from
bisphosphonium salts. The biggest problem experi-
enced when successively deprotonating with n-BuLi
[15] and also when employing the Ag2O-method,
previously used for the preparation of carbene com-
plexes [16], was the formation of by-products that
could not easily be separated from the targeted
compounds. A similar complication emerged with
[(acac)(Ph3P)Au] [17], and the known compound
[{Me(CO)}2C(Ph3PAu)2] [18] was formed along with
the desired product and other mononuclear (acac)gold
and (ylide)gold compounds. The most successful pro-
tocol in our hands turned out to be one based on devel-
opmental work by Uso´n and coworkers [19]. The ap-
proach is illustrated for both monoylide (in Scheme 1)
and diylide formation (in Scheme 2). The ylide lig-
and substitutes Br− in [Br(C6F5)Au] upon formation
from the phosphonium salts. Complex 4 represents the
first example of a neutral gold compound stabilized by
C6F5 while also comprising an aromatic group adja-
cent to the ylide carbon atom. Using the same princi-
Spectrometric and spectroscopic characterization
Fragments observed in the EI-MS of 1 and ES-MS
ples, the method was extended to include the formation of 2, 3 and 6 confirmed the formation of the proposed
of the unique dinuclear complexes 5 and 6. Unreacted products. The molecular ions of 4, 5 and 8 were ob-
phosphonium salt was removed from the residue after served in their ES-MS spectra. For the latter, a scram-
stripping off the solvent by multiple extractions with bling of the gold ligands occurs in the mass spectro-
diethyl ether. An attempt to isolate only a mononuclear meter to form the homoleptic product (Ph3P)2Au+.
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K. Coetzee et al. · Dinuclear Gold Complexes
1451
It is interesting to note that the chemical shifts for
the ylide carbon atoms in 4, 5 and 6 adopt essentially
the same values, δ = 35.4, δ = 34.9 and 35.3 and δ =
35.6. The same carbon atoms in the precursor salts for
the preparation of these three complexes resonate up-
field at δ = 30.7 and 29.6 (5 and 6).
A single signal for the P atoms in compounds 1, 2
and 3 in their 31P NMR spectra confirms that the mul-
tiplets observed for the carbons of the PPh3 groups
of 2 and 3 result from the magnetic inequivalence of
these carbons (AAꢀXXꢀ spin system with JXXꢀ = 0 [21])
and not from the presence of impurities. The chemical
shifts of 2 and 3 were unequivocally assigned from 1H-
13C gHSQC NMR measurements.
In contrast to single resonances for 4 and 6, the two
singlet signals in the 31P NMR spectrum of 5 indicate,
like the 13C NMR spectra mentioned above, the for-
mation of diastereomeric compounds. Diastereomeric
structures are possible as a result of the two different
conformations (R and S) that each of the two chiral
centers (the two ylidic carbons) allow. These diastere-
omers give two different but very similar sets of NMR
signals for each type of carbon, proton or phosphorus
atom in the applicable spectra. The RR and SS isomers
are responsible for one set of signals and the meso RS
and SR isomers for another set. From the NMR spectra
(13C, 1H and 31P) it is evident that one set of diastere-
omers is preferably formed (60 %) to the other (40 %).
The 13C NMR spectra of 5 and 6 are again complicated
by the magnetic inequivalence of the carbon atoms of
the PPh3 groups similar to the spectra of 2 and 3. The
signals corresponding to the Ph3PAu fragments in 4, 5,
6 and 8 are normal.
Fig. 2. Molecular structure of 2; selected bond lengths and
˚
angles (A, deg): O1 ··· Br1 3.328(5), O1–H11 ··· Br1 155.5,
C7 ··· Br1 3.687(5), C7–H7A ··· Br1 172.9.
that contains O1 are well-defined, the other ethanol
molecule exhibits strong thermal motion and could not
be modeled satisfactorily. The dication is asymmet-
ric, and both CH2PPh3 groups at the central benzene
ring are in a UU configuration, meaning that they face
the same direction in respect of the C6 plane of the
ring. This orientation allows a short π ··· π contact
˚
of 3.570 A between the two benzene rings related by a
center of inversion (symmetry operator: 3/2−x, 3/2−
y, 1/2 − z). Other crystal structures that contain the
same dication as 2 are known to exhibit both UU [23]
and UD [24] orientations, and sometimes both ar-
rangements are observed in a single crystal [25]. Most
molecular structures in the UU orientation exhibit
π ··· π interactions of the central benzene ring with
˚
centroid distances between 3.623 and 3.701 A [23a],
markedly longer than in 2 · 2C2H6O.
Compound 3 (Fig. 3), the meta-substituted iso-
mer of 2, also crystallizes as 3 · 3C2H6O, with a
unique dication in the UU orientation and three
The C6F5Au group in the 13C NMR spectrum of 4
exhibits similar signals to those of the starting material
[(C6F5)(THT)Au] [22], but the multiplets are of low
intensity due to multiple JCF couplings. As a result of
this the signals for C1 and C4 in the spectrum of com-
pound 8 could not be observed, and in the spectra of 5
and 6 no signals were visible.
Molecular structures
Compound 2 crystallizes with two equivalents of
ethanol (Fig. 2) in the body-centered tetragonal space
group I41/a. The solvent molecules form hydrogen
bonds to bromide anions. The bromide Br1 is further
stabilized by C–H ··· Br contacts (H7A ··· Br1 dis-
Fig. 3. Molecular structure of 3. Two ethanol molecules
forming hydrogen bonds to Br2 have been omitted for clar-
˚
ity; selected bond lengths and angles (A, deg): O1 ··· Br1
3.266(2), O1–H11 ··· Br1 165.5, O2 ··· Br2 3.362(2), O2–
H21 ··· Br2 175.6, O3 ··· Br2 3.314(2), O3–H31 ··· Br2
156.9, C212 ··· O1 3.324(3), C212–H212 ··· O1 172.7,
C7 ··· Br1ꢀ 3.691(2), C7–H7A ··· Br1ꢀ 171.9.
˚
tance 2.69 A) involving pro-ylidic methylene groups.
While both bromide anions and the ethanol molecule
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1452
K. Coetzee et al. · Dinuclear Gold Complexes
Fig. 4. Molecular structure of 4; selected bond lengths
˚
and angles (A, deg): Au1–C1 2.098(3), Au1–C11 2.034(3),
Au1 ··· H112 2.73, C1–Au1–C11 178.45(14).
ethanol molecules in the asymmetric unit. The
chloro(pentafluorophenyl)auratesalt of this dication, 7,
(Fig. 1) has been reported [20]. Two ethanol solvent
molecules form hydrogen bonds with Br2 while the
ethanol that contains O1 forms a hydrogen bond to Br1
and associates via its oxygen atom with an aromatic
Fig. 5. Molecular structure of 6; selected bond lengths
˚
and angles (A, deg): Au1–C7 2.104(5), Au1–C11 2.038(6),
Au2–C8 2.079(6), Au2–C21 2.024(6), Au1 ··· H126 2.78,
Au2 ··· H8ꢀ 2.94 (symmetry transformations applied to gen-
erate equivalent atoms: 1 − x, 1 − y, 1 − z), Au2 ··· H236
2.68, Au2 ··· H8ꢀ–C8ꢀ 170.6.
˚
C–H unit (H212··· O1 2.38 A). The PPh3 moiety of
P1 forms a six-fold phenyl embrace (6PE) [26] with its
ꢀ
˚
symmetry-generated image (P1 ··· P1 6.055 A, sym-
metry operator ꢀ: 1 − x, 2 − y, 1 − z). As in the molec-
ular structure of 2 · 2C2H6O, a C–H ··· Br contact is
aromatic ring and C atoms attached thereto, thus plac-
ing the C6F5Au units on either side of this plane, too
far removed from each other for aurophilic interactions
to occur. The gold atom Au2 engages in a Au ··· H
interaction to H8ꢀ (symmetry operator: 1 − x, 1 − y,
ꢀ
ꢀ
˚
observed (H7A ··· Br1 2.71 A, symmetry operator :
1 −x, 1 −y, 1 −z).
˚
1 − z) measuring 2.94 A, effectively forming dimers
Complex 4 (Fig. 4) crystallized in the orthorhom-
bic crystal system, space group P212121. No aurophilic
interactions are present. The C11–Au1–C1 angle is
practically linear [177.7(5)◦] as expected for Au(I)
compounds. The Au(I)-aryl bond (to C6F5) is signifi-
in the solid state. Additionally, there are close contacts
between the ortho-hydrogen atoms of a PPh3 phenyl
˚
group and the gold centers (Au1··· H126 2.80 A,
˚
Au2 ··· H236 2.68 A). Contacts showing similar dis-
˚
tances have been observed in thione complexes of
Au(I) as well [28]. No 6PE interactions are formed
by either PPh3 group in 6. Only two other gold(I)
ylide complexes with AuC6F5 groups have been re-
ported by Uso´n et al., and they exhibit comparable
geometries [29]. The C8–Au2–C21 and C7–Au1–C11
bond angles deviate very slightly from linearity by 4◦
and 5◦, respectively. The phosphorus atoms in the
triphenylphosphonium units have tetrahedral symme-
try. π-Stacking ꢀof the pentafluorophenyl groups (dis-
cantly (0.05 A) shorter than the Au(I)-ylide bond. This
complex represents the simplest example of a coor-
dinated triphenylphosphonium ylide with an aromatic
side-chain and is also the first example of a mononu-
−
clear gold ylide complex that contains C6F5 as an
auxiliary ligand. The most important difference be-
tween the free [27] and coordinated ylide ligand is
˚
seen in the C–P separation that is 0.09 A shorter in
the free ylide owing to more double-bond character in
this bond. H112 exhibits a short contact to Au1 mea-
˚
˚
tance C14–C16 3.371 A, symmetry operator: 1 − x,
suring 2.73 A.
−y, 1 −z) determine the lattice arrangement.
In compound 6 (Fig. 5), the ylide substituents now
exhibit UD orientation relative to the central benzene
ring, but the whole molecule remains unique, and a
possible symmetry with a two-fold rotation axis is not
realized. No aurophilic contacts are formed by the gold
atoms due to steric requirements of the bulky triph-
Corresponding interatomic separations in all the
new ylide complexes [2, 3, 4, 6, 7 [20] and 9
(Fig. 6, [30])] of gold are remarkably similar (Table 1),
and representative values are displayed in Fig. 7.
Compound 8 (Fig. 8), the first gold and only the
enylphosphine groups that lie on opposite sides of the second dinuclear transition metal complex [12] of
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K. Coetzee et al. · Dinuclear Gold Complexes
1453
2a
3a
4b
6b
7a
9b
Table 1. Selected bond lengths
˚
(A) and angles (deg) in 2 – 4,
Distances
C6Hn–CP
6, 7, and 9 with estimated stan-
dard deviations in parentheses.
1.507(7), 1.516(3),
1.506(7) 1.520(3)
1.808(5), 1.811(2),
1.813(5) 1.816(2)
1.508(4)
1.789(3)
2.034(3)
2.098(3)
1.518(8), 1.507(5)
1.514(8)
1.777(6), 1.814(3)
1.781(6)
2.038(6), 2.008(4),
2.024(6) 2.3024(12)
2.104(5),
1.522(6)
1.788(4)
2.0040(4)
C6HnC–P
C6F5–Au
Au–CP
2.079(6)
Angles
C6F5–Au–CP
178.75(14) 176.0(2),
175.1(2)
C6Hn–C–P
113.8(4), 115.91(14), 113.0(2)
112.1(4) 116.52(15)
116.9(4), 115.0(2)
112.2(4)
114.6(3)
Dihedral angles
C6F5–Au–C–P
70.9
56.3
155(3),
119(3)
27(4),
−10(3)
78.4
a
C6F5–Au–C–C6Hn
−7.1
Phosphonium salt;
ylide compound.
b
C11 engages in an off-center π ··· π contact with its
symmetry-generated image (symmetry operator: 2 −
x, −y, −z) and the other tetrafluorophenylene group
forms contacts to the PPh3 phenyl substituent con-
taining C131. These π-stacking interactions are only
made possible by bending the P1–Au1–C11 angle
considerably. The best planes for the two benzene
rings of the octafluorobiphenyl linker are at an angle
of 62.1(3)◦. The rod-like molecules all arrange paral-
Fig. 6.
¯
lel to the [1 1 1] line in the crystal. The related com-
pound [(PPh3)(C6F5)Au] [31] exhibits similar Au–P
and Au–C distances.
Fig. 7. Representative values for
bond lengths.
Conclusion
Although practically ignored thus far in coordina-
tion chemistry, bisylides derived from m- or p-phen-
ylene-bis-[(triphenylphosphonio)methane] have now
been shown to form thermodynamically stable com-
plexes with the C6F5Au complex fragment. The iso-
lation and characterization of a 4,4ꢀ-dinuclear complex
of 2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-octafluoro-1,1ꢀ-biphenyl indicates
that gold, and certainly other metals as well, could
make use of this ligating binding unit to form a variety
of compounds in which more than one metal feature.
Fig. 8. Molecular structure of 8; selected bond lengths and
˚
angles (A, deg): Au1–P1 2.269(3), Au1–C11 2.04(1), P1–
Au1–C11 167.4(3), Au2–P2 2.275(3), Au2–C21 2.02(2),
P2–Au2–C21 177.8(3).
Experimental Section
the 4,4ꢀ-substituted 2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-octafluoro-1,1ꢀ-
biphenyl ligand to be characterized by X-ray diffrac-
tion, exhibits a considerably distorted C11–Au1–P1
angle of 167.4(3)◦ which can be assigned to pack-
ing forces rather than close sub-van der Waals con-
tacts to Au1. The tetrafluorophenylene unit containing
Reactions were carried out under argon using stan-
dard Schlenk and vacuum-line techniques. Tetrahydrofu-
ran and diethyl ether were distilled under N2 from sodium
diphenylketyl, n-pentane from sodium and CH2Cl2 and
methanol from CaH2. Melting points were determined on a
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1454
K. Coetzee et al. · Dinuclear Gold Complexes
Stuart Scientific Melting Point Apparatus SMP3 and are un- C5 and C6), 130.3 (m, o-Ph), 127.8 (m, C1 and C4), 117.1
corrected. Mass spectra were recorded on a VG Quattro (ESI, (d, 1J = 86.9 Hz, i-Ph), 29.6 (dm, 1J = 52.3 Hz, CH2). –
70 eV) or AMD 604 (EI, 70 eV) instrument, the infrared 31P NMR (CDCl3): δ = 28.1 (s, PPh3). – MS ((+)-ESI): m/z
spectra on a Perkin-Elmer 1600 Series FTIR instrument and (%) = 365 (49) [PPh3CHC6H4CH2]+, 314 (100) [P2Ph3Na–
NMR spectra on a Varian 300 FT or INOVA 600 MHz spec- 2H]2+, 262 (12) [PPh3]+. – C44H38Br2P2 (788.56): calcd.
trometer (δ reported relative to the solvent resonance or C 67.02, H 4.86; found C 67.31, H 4.92.
external reference 85 % H3PO4). Elemental analyses were
carried out by the Department of Chemistry, University of
Cape Town. Gold(I) starting materials, [(C6F5)(THT)Au]
[32 – 34], [Cl(PPh3)Au] [35] were prepared according to lit-
erature methods. All the other starting materials are commer-
cially available and were used without further purification.
1,3-Bis[(triphenylphosphonio)methyl]benzene dibromide (3)
Triphenylphosphine (9.88 g, 37.7 mmol, 25 % excess)
in acetonitrile (100 mL) was boiled under reflux until all
the triphenylphosphine had dissolved [13, 14]. To this clear
solution (3.97 g, 15.0 mmol) 1,3-bis(bromomethyl)benzene
in acetonitrile (100 mL) was added. The solution remained
clear and was boiled under reflux for 24 h. A white precipi-
tate (3.86 g, 36 %) formed which was filtered off and washed
with diethyl ether (3 ×20 mL) and dried under vacuum. The
preci◦pitate was recrystallized from hot ethanol. M. p. 237 –
239 C. – 1H NMR (CD2Cl2): δ = 7.77 (m, 6 H, p-Ph),
7.71 (m, 12 H, m-Ph), 7.60 (m, 12 H, o-Ph), 7.53 (m, 1 H,
Benzyltriphenyphosphonium bromide (1)
Triphenylphosphine (16.9 g, 64.3 mmol, 10 % excess) in
75 mL of diethyl ether was stirred until all the triphenylphos-
phine had dissolved. Benzyl bromide (9.99 g, 58.5 mmol) in
30 mL of diethyl ether was added dropwise to this solution.
The solution became cloudy and was stirred for 5 h at r. t. The
suspension was left for two days to precipitate. The precip-
itate (6.32 g, 30 %) was filtered off and dried in vacuo. The
salt was recrystallized from hot ethanol. Special precautions
were taken to destroy all benzyl bromide left in the flasks
and funnel with ammonium hydroxide since ◦benzyl bromide
is a powerful lachrymator. M. p. 294 – 296 C. – 1H NMR
(CDCl3): δ = 7.70 (m, 3 H, p-Ph), 7.63 (m, 6 H, o-Ph), 7.55
(m, 6 H, m-Ph), 7.14 (m, 1H, H4), 7.03 (m, 2 H, H2 and H6),
7.01 (m, 2 H, H3 and H5), 5.22 (d, 2J = 14.1 Hz, 2 H, CH2). –
13C NMR (CDCl3): δ = 134.9 (d, 4J = 2.5 Hz, p-Ph), 134.1
4
H5), 7.00 (m, 2 H, H4 and H6), 6.88 (d, JPH = 7.7 Hz,
1 H, H2), 5.23 (d, 2J = 15.1 Hz, 4 H, CH2). – 13C NMR
(CD2Cl2): δ = 135.5 (m, 4J = 1.3 Hz, p-Ph), 135.2 (m,
4J = 6.2 Hz, C5), 134.9 (m, 3J = 10.2 Hz, m-Ph), 131.8 (m,
3J = 8.6 Hz, C4 and C6), 130.5 (m, 2J = 13.1 Hz, o-Ph),
3
129.2 (m, 2J = 9.9 Hz, C1 and C3), 129.0 (m, J = 3.2 Hz,
C2), 118.0 (d, 1J = 86.3 Hz, i-Ph), 29.6 (d, 1J = 47.5 Hz,
CH2). – 31P NMR (CD2Cl2): δ = 23.4 (s, PPh3). – MS ((+)-
ESI): m/z (%) = 707 (70) [Br][Ph3PCH2C6H4CH2PPh3]+,
627 (70) [Ph3P=CHC6H4CH2PPh3]+, 315 (100) [P2Ph3Na–
H]2+. – C44H38Br2P2 (788.56): calcd. C 67.02, H 4.86;
found C 67.22, H 5.07.
3
3
(d, J = 9.7 Hz, m-Ph), 131.2 (d, J = 5.6 Hz, C2 and C6),
130.0 (d, 2J = 12.6 Hz, o-Ph), 128.6 (d, 4J = 3.3 Hz, C3 and
C5), 128.2 (d, 5J = 3.8 Hz, C4), 126.9 (d, 2J = 8.8 Hz, C1),
117.5 (d, 1J = 85.8 Hz, i-Ph), 30.7 (d, 1J = 46.2 Hz, CH2). –
31P NMR (CDCl3): δ = 23.8 (s, PPh3). – MS (EI, 70 eV): m/z
(%) = 353 (22) [PhCH2PPh3]+, 262 (100) [PPh3]+, 183 (66)
[PPh2]+, 108 (22) [PPh]+, 91 (9) [PhCH2]+. – C25H22BrP
(433.32): calcd. C 69.29, H 5.12; found C 69.38, H 5.00.
5
(Benzyl-triphenyl-λ -phosphorane)(pentafluorophenyl)gold
(4)
Benzyltriphenylphosphonium bromide (0.890 g, 2.10
mmol) and [(C6F5)(THT)Au] (0.920 g, 1.90 mmol) were
suspended in 20 mL of THF and stirred for 40 min at r. t.
NaH (0.240 g, 10.0 mmol) in 10 mL of THF was added
to deprotonate the phosphonium salt to the corresponding
1,4-Bis[(triphenylphosphonio)methyl]benzene dibromide (2)
Triphenylphosphine (11.7 g, 44.8 mmol, 25 % excess) in ylide. The suspension was stirred for 3 h at r. t. and filtered
◦
acetonitrile (100 mL) was boiled under reflux (80 C) un- through celite. The solvent was removed in vacuo and the
til all the PPh3 had dissolved, and 1,4-bis(bromomethyl)- residue extracted first with diethyl ether and subsequently
benzene (5.28 g, 20.1 mmol) in acetonitrile (100 mL) was with dichloromethane. Both fractions were dried in vacuo,
added [13, 14]. The solution became cloudy and was boiled yielding 1.08 g, 70 % of product. Crystals suitable for single
under reflux for 40 h. The colorless precipitate that formed crystal X-ray diffraction were obta◦ined from a solution of 5
◦
1
was filtered off and dried in vacuo (12.4 g, 80 %). These in CH2Cl2 at −20 C. M. p. 128 C (decomp.). – H NMR
colorless crystals were recrystallized from ◦hot chloroform (CDCl3): δ = 7.75 (m, 6 H, o-Ph), 7.63 (m, 3 H, p-Ph),
and dried again in vacuo. M. p. 330 – 332 C. – 1H NMR 7.50 (m, 6 H, m-Ph), 7.00 (m, 5 H, CHC6H5), 3.92 (d,
(CDCl3): δ = 7.69 (m, 6 H, p-Ph), 7.53 (m, 12 H, m-Ph), 2J = 13.6 Hz, 1 H, CHC6H5). – 13C NMR (CDCl3): δ =
7.43 (m, 12 H, o-Ph), 6.65 (s, 4 H, H2, H3, H5 and H6), 148.9 (ddm, 1J = 225.8 Hz, 3J = 26.2 Hz, o-C6F5), 138.7
4.62 (d, 2J = 13.6 Hz, 4 H, CH2). – 13C NMR (CDCl3): δ = (dm, 1J = 244.3 Hz, p-C6F5), 137.1 (dm, 1J = 232.2 Hz,
135.4 (br s, p-Ph), 133.9 (m, m-Ph), 131.7 (br s, C2, C3, m-C6F5), 134.2 (d, 3J = 8.9 Hz, m-Ph), 134.0 (d, 4J =
Unauthenticated
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K. Coetzee et al. · Dinuclear Gold Complexes
1455
7.3 Hz, C4), 133.3 (d, 4J = 2.9 Hz, p-Ph), 132.3 (m, i- ethyl ether and dichloromethane, filtered through anhydrous
C6F5), 130.2 (d, 3J = 8.0 Hz, C2 and C6), 129.4 (d, 2J = MgSO4 and dried in vacuo. The diethyl ether layer con-
11.7 Hz, o-Ph), 128.6 (d, 4J = 2.9 Hz, C3 and C5), 125.2 (d, tained the proposed compound (1.98 g, 60 %), and crystals
2
1J = 84.1 Hz, i-Ph), 124.9 (d, J = 3.8 Hz, C1), 35.4 (dm, suitable for single crystal X-ray diffraction studies were ob-
1J = 31.6 Hz, CHC6H5). – 31P NMR (CDCl3): δ = 26.2 (s, tained from a solution of 6 in CH2Cl2, layered with pentane
PPh3). – MS (EI, 70 eV): m/z (%) = 716 (3) [M]+, 459 (3) and stored at −10 C. M. p. 120 C (decomp.). – 1H NMR
[AuPPh3]+, 352 (100) [PhCHPPh3]+, 275 (6) [PPh3CH2]+, (CD2Cl2): δ = 7.70 (m, 12 H, o-Ph), 7.60 (m, 6 H, p-Ph),
262 (40) [PPh3]+, 183 (60) [PPh2]+, 167 (38) [C6F5]+, 91 7.46 (m, 12 H, m-Ph), 6.74 (m, 2 H, H2 and H5), 6.61 (m,
(24) [PhCH2]+. – C31H21F5AuP (716.10): calcd. C 51.97, 2 H, H4 and H6), 3.77 (d, 2J = 13.9 Hz, 2 H, AuCH). –
◦
◦
H 2.95; found C 51.86, H 2.78.
13C NMR (CD2Cl2): δ = 140.4 (t,4J = 4.8 Hz, C5), 134.5
(m, m-Ph), 133.7 (m, p-Ph), 132.3 (m, C4 and C6), 129.8
(m, o-Ph), 129.1 (m, C1 and C3), 126.9 (t, 3J = 5.5 Hz, C2),
125.4 (d, 1J = 84.4 Hz, i-Ph), 35.6 (d, 1J = 36.0 Hz, AuCH). –
31P NMR (CD2Cl2): δ = 25.6 (s, PPh3). – MS ((+)-ESI):
1,4-Bis[(triphenylphosphonio)methanido]benzene
bis(pentafluorophenyl)gold (5)
m/z (%) = 372 (100) [Ph3PCHC6H4CHPPh3 + CHCl3]2+
,
A suspension of phosphonium salt 2 (0.820 g, 1.04 mmol,
1 % excess) and [(C6F5)(THT)Au] (0.930 g, 2.06 mmol) in
20 mL of THF was stirred for 1 h at r. t. NaH (0.250 g,
10.4 mmol) in 10 mL of THF was added, and the mixture
stirred for 5 h at r. t., after which it was filtered through
celite. A brown filtrate was obtained and dried in vacuo.
The residue was extracted sequentially with diethyl ether
and dichloromethane, filtered through anhydrous MgSO4
358 (18) [Ph3PCH2C6H4CH2+3H]+. – C56H36F10Au2P2
(1354.77): calcd. C 49.65, H 2.68; found C 49.57, H 2.80.
4,4ꢀ-Bis-(triphenylphosphine)gold(I)-µ-2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-
octafluoro-1,1ꢀ-biphenyl (8)
A suspension of 4,4ꢀ-dibromo-2,3,5,6,2ꢀ,3ꢀ,5ꢀ,6ꢀ-octa-
and dried in vacuo. A brown solid stayed behind on the fluoro-1,1ꢀ-biphenyl (0.750 g, 1.60 mmol, 2 % excess) in
◦
MgSO4, which was insoluble in CH2Cl2, diethyl ether or 20 mL of diethyl ether was cooled down to −75 C, and
THF and was discarded. From the NMR spectra it was ev- 1.6 M n-BuLi (1.60 mL, 3.70 mmol) was added dropwise.
◦
ident that the dichloromethane extract contained the desired The mixture was stirred at −75 C for 10 min, whereafter
◦
compound, yield 1.29 g, 40 %. M. p. 135 C (decomp.). – the [Cl(Ph3P)Au] (1.57 g, 3.17 mmol) was added. The mix-
1H NMR ([D8]THF): δ = 7.83 (m, 24 H, m-Ph), 7.66 (m, ture was stirred at −75 C for another 10 min before the
◦
12 H, p-Ph), 7.52 (m, 24 H, o-Ph), 6.72, 6.68 (2 × br s, 2 temperature was slowly (over 1 h) raised to r. t. The suspen-
× 4 H, H2, H3, H5 and H6), 4.04, 4.00 (2×d, 1J = 13.5, sion was filtered through MgSO4 and the solvent removed
13.4 Hz, 2 × 2 H, AuCH). – 13C NMR ([D8]THF): δ = in vacuo. Compound 8 was recrystallized from a solution of
137.2, 137.0 (2 × m, C2, C3, C5 and C6), 135.3 (m, m-Ph), the crude m◦ixture in diethyl ether, yielding, 1.09 g, 60 %.
134.1 (br s, p-Ph), 131.4, 131.2 (2 × m, C1 and C4), 130.2 M. p. 106.7 C (decomp.). – 1H NMR (CD2Cl2): δ = 7.70
(m, o-Ph), 126.4, 126.5 (2 × dd, 1J = 85.3 Hz, 9J = 1.5 Hz, i- (m, 12 H, m-Ph), 7.60 (m, 6 H, p-Ph), 7.54 (m, 12 H, o-
Ph), 35.3, 34.9 (2 × m, AuCH). – 31P NMR ([D8]THF): δ = Ph). – 13C NMR (CD2Cl2): δ = 149.8 (dm, J = 228.4 Hz,
1
26.1, 26.3 (2× s, PPh3). – MS ((+)-ESI): m/z (%) = 1354 (15) C3 and C5), 144.7 (dm, 1J = 257.9 Hz, C2 and C6), 135.0
[M]+, 991 (100) [Ph3PCH(AuC6F5)C6H4CH2PPh3]+, 314 (d, 3J = 13.8 Hz, m-Ph), 132.3 (d, 4J = 2.5 Hz, p-Ph),
(15) [P2Ph3Na–2H]+. – C56H36F10Au2P2 (1354.77): calcd. 130.5 (d, 1J = 55.1 Hz, i-Ph), 130.0 (d, 2J = 11.3 Hz, o-
C 49.65, H 2.68; found C 49.55, H 2.81.
Ph). – 31P NMR (CD2Cl2): δ = 42.4 (s, PPh3). – MS ((+)-
ESI): m/z (%) = 1673 (10) [M + AuPPh3]+, 1215 (15)
[M+H]+, 721 (100) [(Ph3P)2Au]+, 459 (18) [AuPPh3]+. –
C48H30Au2F8P2 (1214.64): calcd. C 47.47, H 2.49; found
C 47.41, H 2.38.
1,3-Bis[(triphenylphosphonio)methanido]benzene
bis(pentafluorophenyl)gold (6)
The phosphonium salt 3 (0.810 g, 1.00 mmol) and
[(C6F5)(THT)Au] (1.10 g, 2.40 mmol) were suspended in
20 mL of THF and stirred for 1 h at r. t. A clear solution
formed to which NaH (0.250 g, 10.3 mmol) in 10 mL of THF
X-Ray structure determinations
Intensity data of 2, 3, 6, and 8 were collected at 100 K
was added. The mixture became light-yellow, and after stir- with a Bruker SMART Apex diffractometer [36], inten-
ring for 1 h the suspension became bright-orange. The mix- sity data of 4 were collected at 173 K with a Nonius
ture was stirred overnight as it was believed that the orange Kappa CCD diffractometer [37]. All experiments were con-
color resulted from free ylide. The next morning the suspen- ducted with graphite-monochromatized MoKα radiation (λ =
˚
sion was light-yellow again and was filtered over celite to 0.71073 A). Intensities were measured using the ω-scan
obtain a clear light-yellow filtrate. The solvent was removed mode (Nonius Kappa CCD: ϕ- and ω-scan mode) and were
in vacuo. The residue was extracted sequentially with di- corrected for Lorentz and polarization effects. The structures
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1456
K. Coetzee et al. · Dinuclear Gold Complexes
Table 2. Crystal structure data for 2 – 4, 6 and 8.
2
3
4
6
8
Formula
Mr
C44H38Br2P2 · 2C2H6O C44H38Br2P2 · 3C2H6O C31H21AuF5P
C56H36Au2F10P2 C48H30Au2F8P2
1354.7 1214.6
880.64
926.71
716.41
Crystal size, mm3
Crystal system
Space group
0.25×0.15×0.07
0.27×0.21×0.11
0.12×0.09×0.08 0.27×0.25×0.19 0.21×0.15×0.11
tetragonal
I41/a
triclinic
orthorhombic
P212121
9.761(2)
15.390(3)
17.025(3)
90
triclinic
P1
triclinic
P1
¯
¯
¯
P1
˚
a, A
36.774(4)
36.774(4)
12.672(3)
90
90
90
17136(5)
16
1.36
2.0
7264
10.6152(7)
11.8454(8)
18.686(2)
98.000(1)
93.938(1)
99.380(1)
2285.6(3)
2
13.319(2)
13.530(2)
14.453(2)
104.022(2)
107.468(2)
99.837(2)
2325.4(6)
2
11.935(3)
12.132(3)
15.224(3)
107.103(3)
97.704(4)
100.494(4)
2030.0(8)
2
˚
b, A
˚
c, A
α, deg
β, deg
90
90
2557.4(9)
4
1.86
γ, deg
3
˚
V, A
Z
Dcalcd, g cm−3
µ(MoKα ), cm−1
F(000), e
hkl range
1.35
1.9
960
1.93
6.4
1300
1.9
7.4
1156
5.9
1384
−47 to 48, −46 to 47,
−16 to 13
0.6673
45641
13, 15, −23 to 24
12, 19, 22
17, 17, 19
15, 16, 19
−1
˚
((sinθ)/λ)max, A
Refl. measured
Refl. unique
Rint
0.6664
26630
10552
0.0343
0.6492
5837
5837
0.0000
0.6666
26439
10600
0.0505
0.6664
22415
9206
0.0895
9445
0.1754
461
Param. refined
519
343
631
541
R(F)/wR(F2)a (all refl.) 0.1369 / 0.1659
0.0493 / 0.0912
0.0484, 0.1316
1.028
0.793 / −0.297
0.0337 / 0.0375
0.0154, 0
1.026
0.823 / −0.990
0.0657 / 0.0880
0.0389, 0
0.999
2.477 / −1.419
0.1075 / 0.1335
0.0466
0.990
2.048 / −0.248
Weighting factors a, b
0, 0
0.706
0.953 / −0.445
GoF (F2)b
−3
˚
∆ρfin (max / min), e A
a R = Σ||Fo|−|Fc||/Σ|Fo|, wR = [Σw(Fo −Fc2)2/Σw(Fo2)2]1/2, w = [σ2(Fo2)+(aP)2 +bP]−1, where P = (Max(Fo2,0)+2Fc2)/3; b GoF =
2
[Σw(Fo −Fc2)2/(nobs −nparam)]1/2
.
2
were solved by Direct Methods and refined by full-matrix grams [39]. The anisotropic displacement parameters of
least-squares or F2 using the SHELX-97 software pack- atoms C21, C25 and C26 in the crystal structure of 8 were
age within the X-Seed environment [38]. All non-hydrogen restrained with a DELU instruction.
atoms were refined with anisotropic displacement parame-
CCDC 749855 – 749859 contain the supplementary crys-
ters, and all hydrogens were placed in calculated positions. tallographic data for this paper. These data can be obtained
The figures are drawn with displacement ellipsoids at the free of charge from The Cambridge Crystallographic Data
50 % probability level; hydrogens not involved in close con- Centre via www.ccdc.cam.ac.uk/data request/cif.
tacts are omitted for clarity. Data and parameters of the crys-
Acknowledgement
tal structure determinations are shown in Table 2.
We thank the National Research Foundation (NRF) of
South Africa, the Alexander von Humboldt foundation (HGR
and SC) and Mintek (KC) for financial support.
In the crystal structure of 2 · 2C2H6O the disordered sol-
vent could not be modeled satisfactorily and was removed
using the SQUEEZE routine in the PLATON set of pro-
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