Carbon-carbon coupling in dinuclear cycloaurated complexes containing bridging 2-(diphenylphosphino)phenyl or 2-(diethylphosphino)phenyl. Role of the axial ligand and the fine balance between gold(II)-gold(II) and gold(I)-gold(III)

Article abstract of DOI:10.1021/om000773w

The reactions of the homovalent bis(benzoato) digold (II) complexes [Au^II₂ (O₂CPh)₂(μ-2-C₆H₄-PR₂) ₂] (R = Ph(1a), Et(1b)) with the anions CH₃^-, C₆F₅^-, and SCN^- were investigated. The behavior of the stability and isomerization of the homovalent digold(II) complexes [Au₂X₂(μ-2-C₆H₄PPh₂)₂] were found to be dependent on the nature of the axial ligand X. When X is a strongly electron-withdrawing anionic O-donor ligand, these compounds were found to be thermodynamically stable. NMR spectroscopic analysis are also reported.

Full text of DOI:10.1021/om000773w

Organometallics 2001, 20, 79-87
79
Ca r bon -Ca r bon Cou p lin g in Din u clea r Cycloa u r a ted
Com p lexes Con ta in in g Br id gin g
2-(Dip h en ylp h osp h in o)p h en yl or
2-(Dieth ylp h osp h in o)p h en yl. Role of th e Axia l Liga n d
a n d th e F in e Ba la n ce betw een Gold (II)-Gold (II) a n d
Gold (I)-Gold (III)
Martin A. Bennett,* David C. R. Hockless, A. David Rae, Lee L. Welling, and
Anthony C. Willis
Research School of Chemistry, Australian National University, Canberra,
Australian Capital Territory 0200, Australia
Received September 11, 2000
Reactions of the homovalent bis(benzoato)digold(II) complexes [AuII2(O2CPh)2(µ-2-C6H4-
PR2)2] (R ) Ph (1a ), Et (1b)) with the anions CH3-, C6F5-, and SCN- have been investigated.
Dimethylmagnesium gives the stable heterovalent complexes [AuI(µ-2-C6H4PR2)2AuIII(CH3)2]
(R ) Ph (2a ), Et (2b)), whereas (pentafluorophenyl)lithium gives the homovalent complexes
[AuII2(C6F5)2(µ-2-C6H4PR2)2] (R ) Ph (3a ), Et (3b)). On prolonged heating in toluene, the
latter rearrange to give predominantly dinuclear bis(pentafluorophenyl)digold(I) complexes
of the corresponding (2,2′-biphenylyl)bis(tertiary phosphines) [AuI (C6F5)2(µ-2,2′-R2PC6H4C6H4-
2
PR2)] (R ) Ph (4a ), Et (4b)), resulting from coupling of the C6H4PR2 units. Minor products
of these rearrangements are the zwitterionic heterovalent complexes [(C6F5)2AuIII(µ-2-C6H4-
PR2)2AuI] (R ) Ph (5a ), Et (5b)). The structure of 5a differs from that of 2a by rotation of
one of the bridging 2-C6H4PPh2 groups through 180°. Precursors to 4a /5a and 4b/5b have
been detected by 31P NMR spectroscopy and tentatively assigned the heterovalent structures
(C6F5)AuI(µ-2-R2PC6H4)AuIII(C6F5)(η2-2-C6H4PR2)] (R ) Ph (6a ), Et (6b)), in which one C6H4-
PR2 group bridges the two gold atoms while the other binds as a bidentate chelate ligand to
gold(III). The S-bonded bis(thiocyanato) complexes [AuII2(SCN)2(µ-2-C6H4PR2)2] (R ) Ph (8a ),
Et (8b)) formed from 1a or 1b and KSCN undergo C-C coupling more rapidly than the
C6F5 compounds to give [AuI (SCN)2(µ-2,2′-R2PC6H4C6H4PR2)] (R ) Ph (10a ), Et (10b)) via
2
the detectable heterovalent intermediates 9a or 9b, which are analogues of 6a and 6b. The
X-ray structures of complexes 2a , 3a , 4a , 4b, 5a , and 10b have been determined. The gold-
gold separations in 2a , 3a , and 5a are respectively 2.8874(4), 2.6139(4), and 2.931(1)/2.921-
(1) Å (for independent molecules), the shorter distance in 3a corresponding to a covalent
metal-metal bond. In 4a and 10b the torsion about the central C-C bond of the biphenyl
backbone results in a syn configuration for the Au-X (X ) C6F5, SCN) fragments and a
close intramolecular aurophilic contact between the gold atoms (r(Au...Au) ) 3.0688(8) Å
(4a ), 3.0853(9) Å (10b)), whereas in 4b the Au-C6F5 units adopt an anti configuration relative
to the biphenyl fragment, leading to a nonbonding gold-gold separation of 5.3469(7) Å. The
differences in behavior of digold(II) complexes [Au2X2(µ-2-C6H4PR2)2] as the axial anionic
ligand X is varied and the pathway of the intramolecular C-C coupling reaction are
discussed.
In tr od u ction
bis(ylides), [R2P(CH2)2]- (R ) Me, Et, Ph), have at-
tracted particular attention.4-9 Uniquely, however, the
digold(II) dihalide complexes containing 2-C6H4PR2
We have shown previously that the carbanions (2-
C6H4PR2)- (R ) Ph, Et) form digold(I) complexes [Au2(2-
C6H4PR2)2], in which two linearly coordinated gold(I)
atoms are held in close proximity. These compounds
undergo oxidative addition with halogens or dibenzoyl
peroxide to give the symmetrical digold(II) complexes
[Au2X2(2-C6H4PR2)2] (X ) Cl, Br, I, O2CPh), which
contain a pair of planar-coordinated gold(II) atoms
connected by a direct metal-metal bond.1-3 Gold(I) and
gold(II) complexes of similar geometry are formed by
many other 1,3-bifunctional ligands;4 those with
(1) Bennett, M. A.; Bhargava, S. K.; Griffiths, K. D.; Robertson, G.
B.; Wickramasinghe, W. A.; Willis, A. C. Angew. Chem., Int. Ed. Engl.
1987, 26, 258.
(2) Bennett, M. A.; Bhargava, S. K.; Griffiths, K. D.; Robertson, G.
B. Angew Chem., Int. Ed. Engl. 1987, 26, 260.
(3) Bennett, M. A.; Bhargava, S. K.; Hockless, D. C. R.; Welling, L.
L.; Willis, A. C. J . Am. Chem. Soc. 1996, 118, 10469.
(4) Articles by: Laguna, A. In Gold, Progress in Chemistry, Bio-
technology and Technology; Schmidbaur, H., Ed.; Wiley: Chichester,
U.K., 1999; Chapter 12, p 349. Fackler, J . P.; van Zyl, W. E.; Prihoda,
B. A. Ibid., Chapter 20, p 795.
10.1021/om000773w CCC: $20.00 © 2001 American Chemical Society
Publication on Web 12/02/2000

80 Organometallics, Vol. 20, No. 1, 2001
Bennett et al.
Sch em e 1
isomerize by coupling of the carbanions at the dimetal
center to give digold(I) complexes of the corresponding
2,2′-biphenylyl-substituted ligands, [Au2X2(µ-2-R2-
PC6H4C6H4PR2)] (Scheme 1). This reductive elimination,
in which a C-C bond is formed at the expense of two
Au-C bonds, occurs readily for X ) I, Br, Cl but not at
all for X ) O2CPh, O2CMe, ONO2; for R ) Ph, the first-
order rate constants for thermal isomerization decrease
in the order X ) I > Br . Cl.3 Since C-C coupling
seemed to be favored by less electron-withdrawing
anionic ligands, we have investigated the behavior of
AuII2(2-C6H4PR2)2 complexes containing the more co-
valently binding, electron-releasing anionic ligands CH3,
C6F5, and SCN. These studies have thrown light on the
likely pathway of the C-C coupling reaction.
F igu r e 1. Molecular structure of 2a with atom labeling.
Thermal ellipsoids show 30% probability levels; hydrogen
atoms have been omitted for clarity.
Sch em e 2
Resu lts
The new members of the Au2X2(C6H4PR2)2 series are
conveniently obtained by anation of the bis(benzoato)
complexes [Au2(O2CPh)2(µ-2-C6H4PR2)2] (R ) Ph (1a ),
Et (1b)), as outlined in Scheme 2.3 Attempts to prepare
the dimethyl compound by reaction of methyllithium
with either 1a or [Au2I2(µ-2-C6H4PR2)2] gave mainly the
digold(I) precursor [Au2(µ-2-C6H4PR2)2] as a result of
reduction. However, from reaction of 1a or 1b with a
slight excess of dimethylmagnesium, colorless solids of
empirical formula Au2(CH3)2(C6H4PR2)2 were isolated
1
in 70-80% yield. The H NMR spectra in CD2Cl2 show
a six-proton doublet resonance close to δ 0 due to the
Au-CH3 groups, and the highest mass peaks in the
FAB-mass spectra correspond in each case to the loss
of one methyl group from the unobserved parent ion.
The 31P{1H} NMR spectra consist of a pair of equally
intense doublets in the region δ 6-35 (2J PP ) 27.5 Hz),
arising from inequivalent phosphorus atoms, and thus
are inconsistent with a symmetrical digold(II) structure.
The spectroscopic data are, however, compatible with
the unsymmetrical structures 2a (R ) Ph) and 2b (R )
Et), and this conclusion has been confirmed by the
single-crystal X-ray structure of 2a , which is shown in
Figure 1 together with the atom labeling. Selected bond
distances and angles are given in Table 1.
The 2-C6H4PPh2 groups bridge a pair of gold atoms,
one of which, Au(1), is trivalent with approximately
planar coordination; the other, Au(2), is univalent and
its coordination geometry is close to linear. The methyl
groups on Au(1) are mutually trans, the Au-C bond
lengths (2.089(8) Å, 2.126(8) Å) being similar to those
observed for the trans-methyl groups in the monomeric
gold(III) complex [Au(CH3)3(PPh3)] (2.057(27)-2.168(22)
Å).10 Although the separation between the metal atoms
in 2a (2.8874(4) Å) is larger than that in the sym-
metrical digold(II) complexes [Au2X2(2-C6H4PR2)2] (2.593
(5) Grohmann, A.; Schmidbaur, H. In Comprehensive Organome-
tallic Chemistry II; Wardell, J ., Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 3, p 1.
(6) Fackler, J . P., J r. Polyhedron 1997, 16, 1.
(7) Schmidbaur, H.; Grohmann, A.; Olmos, M. E. In Gold, Progress
in Chemistry, Biochemistry and Technology; Schmidbaur, H., Ed.;
Wiley: Chichester, U.K., 1999; Chapter 18, p 648.
(8) Laguna, A.; Laguna, M. Coord. Chem. Rev. 1999, 193-195, 837.
(9) Laguna, M.; Cerrada, E. In Metal Clusters in Chemistry; Braun-
stein, P., Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim,
Germany, 1999; Vol. 1, p 459.

C-C Coupling in Dinuclear Cycloaurated Complexes
Organometallics, Vol. 20, No. 1, 2001 81
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [Au I,III2Me2(2-C6H4P P h 2)2] (2a )
Au(1)-P(2)
Au(1)-C(1)
Au(1)-C(3)
Au(1)‚‚‚Au(2)
2.347(2)
2.089(8)
2.055(7)
2.8874(4)
Au(2)-P(1)
Au(1)-C(2)
Au(2)-C(21)
P-C
2.308(2)
2.126(8)
2.053(7)
1.807(8)-1.840(8)
Au(2)-Au(1)-P(2)
Au(2)-Au(1)-C(2)
P(2)-Au(1)-C(1)
P(2)-Au(1)-C(3)
C(1)-Au(1)-C(3)
Au(1)-Au(2)-P(1)
80.86(5) Au(2)-Au(1)-C(1)
95.2(3)
93.8(2)
89.1(2)
174.9(3)
87.8(3)
92.6(2)
86.2(2)
96.0(2)
174.0(2)
87.2(3)
Au(2)-Au(1)-C(3)
P(2)-Au(1)-C(2)
C(1)-Au(1)-C(2)
C(2)-Au(1)-C(3)
81.81(5) Au(1)-Au(2)-C(21)
P(1)-Au(2)-C(21) 171.7(2)
Å (av) for R ) Ph, X ) I;2 2.5243(7) Å for R ) Et, X )
O2CPh3), the possibility of a donor-acceptor interaction
(Au(I)fAu(III)) clearly cannot be excluded. Dimethyl-
digold bis(ylide) complexes analogous to 2a have been
prepared,11,12 but no structures have been determined.
The closest analogue to 2a in the bis(ylide) series
appears to be the dibromo complex [AuI{µ-(CH2)2PPh2}2-
AuIIIBr2], in which the metal-metal distance is 3.061-
(2) Å.13
Examination in situ of the reaction mixture of 1a and
(CH3)2Mg by 31P{1H} NMR spectroscopy showed the
presence of a sharp singlet at δ 2.7 in addition to the
doublets due to 2a . After a few hours at room temper-
ature, the singlet had disappeared, leaving 2a as the
only phosphorus-containing product. The chemical shift
of the singlet is in the region expected for the sym-
metrical digold(II) complexes;3 hence, this peak may be
due to the symmetrical digold(II) precursor [(CH3)Au(µ-
2-C6H4PPh2)2Au(CH3)]. Attempts to cleave selectively
one of the methyl groups of 2a with benzoic acid led
only to the bis(benzoato)digold(II) complex together with
some digold(I) precursor.
F igu r e 2. Molecular structure of 3a with atom labeling.
Thermal ellipsoids show 30% probability levels; hydrogen
atoms have been omitted for clarity.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [Au II2(C6F 5)2(2-C6H4P P h 2)2] (3a )
Au(1)-P(1)
Au(1)-C(20)
Au(1)-C(37)
2.331(2)
2.088(8)
2.103(8)
Au(2)-P(2)
Au(2)-C(2)
Au(2)-C(43) 2.119(8)
P-C 1.790(9)-1.816(8)
2.323(2)
2.076(8)
Au(1)‚‚‚Au(2) 2.6139(4)
C-F
1.326(9)-1.35(1)
Au(2)-Au(1)-P(1)
Au(2)-Au(1)-C(37)
P(1)-Au(1)-C(37)
Au(1)-Au(2)-P(2)
Au(1)-Au(2)-C(43)
P(2)-Au(2)-C(43)
80.80(5)
168.3(2)
94.9(2)
83.89(6)
176.6(2)
93.1(2)
Au(2)-Au(1)-C(20)
93.3(2)
171.7(2)
91.9(3)
91.0(2)
174.5(2)
92.1(3)
P(1)-Au(1)-C(20)
C(20)-Au(1)-C(37)
Au(1)-Au(2)-C(2)
P(2)-Au(2)-C(2)
C(2)-Au(2)-C(43)
distances in these compounds (2.593 Å (av) and 2.5243(7)
Å, respectively), reflecting the effect of the less electron-
withdrawing C6F5 ligand in the axial position. The gold-
(II)-gold(II) distance is also less than those in the
closely related bis(ylide) complexes [Au2Y2{µ-(CH2)2-
PPh2}2] (2.677(1) Å for Y ) C6F5; 2.679(1) Å for Y )
CF3),14 as a consequence of the smaller size of the
bridging group in the (2-diphenylphosphino)phenyl
complex. The Au-C6F5 bond lengths in 3a (2.103(8),
2.119(8) Å) seem to fall in the range between those in
[Au2(C6F5)2{µ-(CH2)2PPh2}2] (2.145(8)-2.164(7) Å) and
those in [Au(C6F5)4]- (2.075(11)-2.084(11) Å).14
The lability of the axial pentafluorophenyl ligands is
similar to that of the anionic ligands in the parent
Au2X2(2-C6H4PR2)2 compounds.3 The 31P{1H} NMR
spectra of solutions in dichloromethane containing
approximately equal amounts of 3b and 1b, measured
as soon as possible after mixing, show an AB pattern
(δA 7.7, δB -2.5, J AB ) 66 Hz) attributable to the species
[(C6F5)Au(µ-2-C6H4PEt2)2(O2CPh)]. Mixtures of 3b and
[Au2I2(µ-o-C6H4PEt2)2] behave similarly, the mixed-
ligand species [(C6F5)Au(µ-2-C6H4PEt2)2AuI] being char-
Treatment of compound 1a with phenyllithium (2
equiv) gave a yellow solution whose 31P{1H} NMR
spectrum showed a sharp singlet at δ -1.1 and a pair
of doublets at δ 34.5 and 13.8 (2J PP ) 28.1 Hz) indicative
of the presence of the digold(II) complex [(C6H5)Au(µ-
2-C6H4PPh2)2Au(C6H5)] and its gold(I)-gold(III) isomer
[Au(µ-2-C6H4PPh2)2Au(C6H5)2]. Attempted isolation
caused gradual decomposition to unidentified species.
The bis(pentafluorophenyl)digold(II) complexes [Au2-
(C6F5)2(µ-2-C6H4PR2)2] (R ) Ph (3a ), Et (3b)) were
obtained in high yield as yellow, air-stable, crystalline
solids from the reaction of C6F5Li with 1a and 1b,
respectively. Both complexes show parent ion peaks in
their FAB-mass spectra and singlets in the region δ -6
to -8 in their 31P{1H} NMR spectra, no coupling to 19
F
being evident. The structure of 3a , determined by single-
crystal X-ray analysis, is shown in Figure 2 together
with the atom-labeling scheme; selected bond lengths
and angles are given in Table 2. The structure is similar
to those of [Au2I2(2-C6H4PPh2)2]2 and [Au2(O2CPh)2(2-
C6H4PEt2)2],3 the coordination geometry about each gold
atom being close to planar with the C6F5 groups lying
on the gold-gold axis. The gold(II)-gold(II) separation
in 3a , 2.6139(4) Å, is greater than the corresponding
acterized by an AB pattern at δA -3.5, δB -5.5 (J AB
67 Hz).
)
Although 3a and 3b are clearly more robust than
their methyl or phenyl analogues, they are not thermo-
dynamically stable. The changes that occur are outlined
in Scheme 3. When the solutions in d8-toluene were
heated to 90 °C, the 31P{1H} NMR spectra slowly
changed. After 5 h, the solution of 3a showed a pair of
(10) Stein, J .; Fackler, J . P., J r.; Paparizos, C.; Chen, H.-W. J . Am.
Chem. Soc. 1981, 103, 2192.
(11) Schmidbaur, H.; Franke, R. Inorg. Chim. Acta 1975, 13, 85.
(12) Schmidbaur, H.; Hartmann, C.; Riede, J .; Huber, B.; Mu¨ller,
G. Organometallics 1986, 5, 1652.
(13) Raptis, R. G.; Porter, L. C.; Emrich, R. J .; Murray, H. H.;
Fackler, J . P., J r. Inorg. Chem. 1990, 29, 4408.
(14) Murray, H. H.; Fackler, J . P., J r.; Porter, L. C.; Briggs, D. A.;
Guerra, M. A.; Lagow, R. J . Inorg. Chem. 1987, 26, 357.

82 Organometallics, Vol. 20, No. 1, 2001
Bennett et al.
Sch em e 3
F igu r e 3. Molecular structure of 5a (one of the two
independent molecules) with atom labeling. Thermal el-
lipsoids show 30% probability levels; hydrogen atoms have
been omitted for clarity.
gold(III) atom, which is therefore a monoanion, while
the phosphorus atoms of the 2-C6H4PPh2 groups are
attached to the linearly coordinated gold(I) atom, which
is therefore a monocation. The structure is similar to
that of the dimethyl compound 2a , except that one of
the bridging C6H4PPh2 ligands is rotated through 180°.
The separations between the gold atoms, 2.931(1) and
2.921(1) Å for the two independent molecules, are
significantly greater than that in the isomeric digold(II)
precursor 3a , but despite the absence of a formal
covalent bond, electrostatic and donor-acceptor interac-
tions may well be present. The Au-C6F5 distances
(2.081(10)-2.097(10) Å) are in the same range as those
in [Au(C6F5)4]-.14
The behavior of 3b on heating in d8-toluene was
similar to that of 3a . The first detectable intermediate,
which showed a pair of equally intense doublets in its
31P{1H} NMR spectrum at δ 42.3 and -53.1 (2J PP ) 13.4
Hz), transformed over a period of 48 h into two species
in a 1:7 ratio showing triplet 31P resonances at δ 32.9
and 30.9, the separation in each case being 6-7 Hz. The
more abundant species was characterized by X-ray
crystallography as [Au2(C6F5)2(µ-2,2′-Et2PC6H4C6H4-
PEt2] (4b); the minor compound is assumed to be the
corresponding zwitterionic complex [(C6F5)2AuIII(µ-2-
C6H4PEt2)AuI] (5b).
doublets at δ 44.0 and -61.8 (J PP ) 13.4 Hz) in addition
to the singlet due to unchanged starting material. Over
a further 20 h these peaks disappeared and were
replaced by approximate triplets at δ 36.3 and 32.8, the
separation in both cases being 6.3 Hz; after 48 h these
were the only observable signals, the ratio being 7:1.
The compounds responsible for these signals were
separated by fractional crystallization and identified by
X-ray crystallography. The main product was [Au2-
(C6F5)2(µ-2,2′-Ph2PC6H4C6H4PPh2)] (4a ), the bis(pen-
tafluorophenyl)digold(I) derivative of (2,2′-biphenylyl)-
bis(diphenylphosphine) (see below). The minor product
proved to be the unprecedented zwitterionic complex
[(C6F5)2AuIII(µ-2-C6H4PPh2)2AuI] (5a ), whose structure
is shown in Figure 3; selected bond lengths and angles
are listed in Table 3. The two C6F5 groups and both aryl
carbon atoms of the bridging 2-C6H4PPh2 group com-
plete approximately planar coordination about the
Prolonged heating of 5a in toluene did not form any
4a and the ratios of 4a to 5a , or of 4b to 5b, in their
mixtures did not change on heating; hence, the zwitter-
ionic complexes are not precursors to the 2,2′-biphenylyl
compounds.
The immediate precursors to 4a /5a and 4b /5b
could not be isolated, but the observation in each case
of a highly shielded 31P resonance at δ ca. -50 suggests
the presence of
a
chelate four-membered ring,

C-C Coupling in Dinuclear Cycloaurated Complexes
Organometallics, Vol. 20, No. 1, 2001 83
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles (d eg) for [(C6F 5)2Au III(µ-2-C6H4P P h 2)2Au I] (5a )
Au(1)-P(1)
Au(2)-C(2)
Au(2)-C(37)
Au(1)‚‚‚Au(2)
C-F
2.309(5)
2.101(12)
2.097(10)
2.931(1)
Au(1)-P(2)
Au(2)-C(20)
Au(2)-C(43)
P-C
2.308(5)
2.098(12)
2.081(10)
1.816(12)-1.836(13)
1.344(9)-1.356(11)
Au(3)-P(3)
Au(4)-C(52)
Au(4)-C(87)
Au(3)‚‚‚Au(4)
C-F
2.308(5)
2.093(12)
2.090(10)
2.921(1)
Au(3)-P(4)
Au(4)-C(70)
Au(4)-C(93)
P-C
2.320(5)
2.088(12)
2.087(10)
1.801(13)-1.828(11)
1.344(9)-1.356(11)
Au(2)-Au(1)-P(1)
P(1)-Au(1)-P(2)
Au(1)-Au(2)-C(20)
Au(1)-Au(2)-C(43)
C(2)-Au(2)-C(37)
C(20)-Au(2)-C(37)
C(37)-Au(2)-C(43)
86.4(1)
169.6(2)
91.3(4)
96.3(2)
88.9(4)
91.1(4)
169.1(2)
Au(2)-Au(1)-P(2)
Au(1)-Au(2)-C(2)
Au(1)-Au(2)-C(37)
C(2)-Au(2)-C(20)
C(2)-Au(2)-C(43)
C(20)-Au(2)-C(43)
83.2(1)
88.8(4)
94.6(2)
179.9(4)
91.4(4)
88.5(4)
Au(4)-Au(3)-P(3)
P(3)-Au(3)-P(4)
Au(3)-Au(4)-C(70)
Au(3)-Au(4)-C(93)
C(52)-Au(4)-C(87)
C(70)-Au(4)-C(87)
C(87)-Au(4)-C(93)
84.8(1)
168.3(2)
90.5(4)
93.2(2)
88.1(4)
92.7(4)
171.6(2)
Au(4)-Au(3)-P(4)
Au(3)-Au(4)-C(52)
Au(3)-Au(4)-C(87)
C(52)-Au(4)-C(70)
C(52)-Au(4)-C(93)
C(70)-Au(4)-C(93)
83.6(1)
89.4(4)
95.2(2)
179.2(4)
91.2(4)
88.0(4)
Sch em e 4
group. Clearly, there is an alternative arrangement 6c
(R ) Ph) in which C6F5 is trans to phosphorus and the
Au-C σ-bonds of the two C6H4PPh2 groups are trans to
each other. When complex 3a was heated in acetone
instead of toluene, the solution being exposed to labora-
tory light, a second pair of doublets at δ 40.1 and -64.0
(J PP ) 13.4 Hz) was frequently observed in addition to
the pair at δ 44.4 and -61.9. Both pairs of doublets
disappeared on continued heating as 4a and 5a were
formed. It seems likely that this second pair of signals
belongs to the alternative isomer 6c; of course, the
structural assignments for 6a and 6c could be reversed.
As shown in Scheme 3, the behavior of the bis-
(thiocyanato)digold(II) complexes is rather similar to
that of their bis(pentafluorophenyl) analogues, but the
changes occur more rapidly. Treatment of complexes 1a
and 1b with an excess of KSCN or LiSCN in acetone
immediately gave orange, light-sensitive precipitates,
which are assumed to be the S-bonded complexes [Au2-
(SCN)2(µ-2-C6H4PR2)2] (R ) Ph (8a ), Et (8b)). They show
singlets in their 31P{1H} NMR spectra and strong bands
in their IR spectra at ca. 2100 and 690 cm-1 assignable
to ν(CN) and ν(CS), respectively, of S-bonded thiocyan-
ate.18 Over a period of hours the solutions of 8a and 8b
in CH2Cl2 become colorless; the singlets disappear and
are replaced by a pair of doublets at δ 37-38 and δ -41
to -49 (J PP ) 11-12 Hz) and a singlet at δ ca. 53. The
nature of the species responsible for the latter resonance
is unknown, but the former can be assigned on the basis
of the evidence cited above to the gold(I)-gold(III)
structures 9a and 9b. Finally, all these signals are
replaced by singlets at δ 32.0 (R ) Ph) and 26.2 (R )
Et), which are due to the Au-SCN complexes of 2,2′-
biphenylylbis(diphenylphosphine) and its diethylphos-
phine analogue, [Au2(SCN)2{µ-2,2′-R2PC6H4C6H4PR2}
(R ) Ph (10a ), Et (10b)). These have been isolated, and
the structure of 10b has been determined by single-
crystal X-ray diffraction.
M(2-C6H4PR2).15 For example, the value of δP in [Pt(2-
C6H4PPh2)2] is -52.3,16 and similar or even more
shielded 31P resonances are found in related complexes
of other transition elements. The 31P NMR spectra of
the intermediates are consistent with dinuclear gold-
(I)-gold(III) species (6a , R ) Ph; 6b, R ) Et) in which
one C6H4PR2 acts as a bidentate chelate ligand to
planar-coordinated gold(III) and the other as a bridging
ligand from gold(III) to linearly coordinated gold(I). This
assignment is supported by the observation17 that the
dihalodigold(II) complexes containing the sterically
hindered bridging group 2-(diphenylphosphino)-6-me-
thylphenyl, [Au2X2{µ-2-(C6H3-6-Me)PPh2}2] (X ) Cl, Br,
I), rearrange spontaneously in solution above -20 °C
to isolable gold(I)-gold(III) complexes (Scheme 4) whose
31P NMR spectra resemble those of 6a and 6b and
whose structure, 7, has been established by X-ray
crystallography in the case of X ) I.
We make the arbitrary assumption that the ligand
arrangement about the gold(III) atom in 6a and 6b is
the same as that found in 7, i.e., with C6F5 trans to the
Au-C σ-bond of the four-membered ring and phospho-
rus trans to the Au-C σ-bond of the bridging C6H4PPh2
(15) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(16) Bennett, M. A.; Berry, D. E.; Bhargava, S. K.; Ditzel, E. J .;
Robertson, G. B.; Willis, A. C. J . Chem. Soc., Chem. Commun. 1987,
1613.
(17) Bhargava, S. K.; Mohr, F.; Bennett, M. A.; Welling, L. L.; Willis,
A. C. Organometallics, accepted for publication.
(18) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed.; Wiley-Interscience: New York,
1997; Part B, pp 116-121.

84 Organometallics, Vol. 20, No. 1, 2001
Bennett et al.
F igu r e 4. Molecular structure of 4a with atom labeling.
Thermal ellipsoids show 30% probability levels; hydrogen
atoms have been omitted for clarity. Selected interatomic
distances (Å) and angles (deg): Au(1)‚‚‚Au(2) ) 3.0688(8),
Au(1)-P(1) ) 2.278(3), Au(2)-P(2) ) 2.285(3), Au(1)-C(37)
) 2.02(1), Au(2)-C(43) ) 2.04(1); P(1)-Au(1)-C(37) )
168.0(4), P(2)-Au(2)-C(43) ) 172.3(4), Au(1)-Au(2)-P(2)
) 87.25(9), Au(2)-Au(1)-P(1) ) 89.54(9).
F igu r e 6. Molecular structure of 10b with atom labeling.
Thermal ellipsoids show 50% probability levels except for
hydrogen atoms, which are drawn as circles of small radius.
Selected interatomic distances (Å) and angles (deg): Au-
(1)‚‚‚Au(2) ) 3.0853(9), Au(1)-P(1) ) 2.256(3), Au(2)-P(2)
) 2.260(3), Au(1)-S(1) ) 2.332(4), Au(2)-S(2) ) 2.328(4),
S(1)-C(21) ) 1.63(2), S(2)-C(22) ) 1.66(2), N(1)-C(21) )
1.18(2), N(2)-C(22) ) 1.13(3); S(1)-Au(1)-P(1) ) 174.5-
(1), S(2)-Au(2)-P(2) ) 175.7(1), Au(2)-Au(1)-P(1) )
85.55(8), Au(1)-Au(2)-P(2) ) 85.97(9), Au(1)-S(1)-C(21)
) 98.0(6), Au(2)-S(2)-C(22) ) 96.2(7), S(1)-C(21)-N(1)
) 179(2), S(2)-C(22)-N(2) ) 177(3).
(Et)PC6H4C6H4P(Et)Ph}] (2.9924(9) Å).20 Exceptionally,
the torsion in 4b is in the opposite sense, causing the
gold atoms to adopt an anti rather than a syn orienta-
tion relative to the biphenyl backbone and to be sepa-
rated by 5.3469(7) Å. Presumably in 4b the relatively
weak aurophilic interaction is overcome by the lattice
energy associated with a more favorable packing ar-
rangement in the crystal.
In light of the results with the bis(pentafluorophenyl)
and bis(thiocyanato) complexes, we reexamined the
previously reported isomerizations of some of the dihalo
complexes.3 The 31P{1H} NMR spectrum of the solution
obtained by heating the iodo compound [Au2I2(µ-2-C6H4-
PEt2)2] at 50 °C in C6D6 for 4 h showed a pair of doublets
at δ 39.3 and -62.1 (J PP ) 12.6 Hz) in addition to
singlets due to the starting material at δ -11.7 and the
C-C coupled product at δ 27.0. Further heating caused
complete conversion into the 2,2′-biphenylyl compound.
In the isomerization of the [Au2X2(2-C6H4PPh2)2] com-
plexes, however, no corresponding intermediates could
be detected.
F igu r e 5. Molecular structure of 4b with atom labeling;
asterisked atoms are generated by the symmetry operation
1
-x, y,
/ - z. Thermal ellipsoids show 30% probability
2
levels; hydrogen atoms have been omitted for clarity.
Selected interatomic distances (Å) and angles (deg): Au-
(1)‚‚‚Au(1)* ) 5.3469(7), Au(1)-P(1) ) 2.271(2), Au(1)-
C(11) ) 2.056(7); P(1)-Au-C(11) ) 176.5(3).
The structures of [Au2X2(µ-2,2′-R2PC6H4C6H4PR2)] (X
) C6F5, R ) Ph, 4a ; X ) C6F5, R ) Et, 4b; X ) SCN, R
) Et, 10b) are shown in Figures 4-6, respectively,
together with the atom-labeling schemes. In all three
compounds, the bis(tertiary phosphine) bridges, through
phosphorus, a pair of linearly coordinated gold atoms.
The biphenyl backbone is twisted about the central C-C
bond, the dihedral angles between the planes of the
phenyl groups being 90° (4a ), 95° (4b), and 80° (10b).
In 4a and 10b this torsion brings the gold atoms into
fairly close contact; the separations, 3.0688(8) and
3.0853(9) Å, respectively, are in the range typical of
closed-shell, attractive (aurophilic) interactions in gold-
(I) complexes19 and are similar to those observed in
other members of the series, e.g. [Au2Br2(µ-2,2′-Ph2-
PC6H4C6H4PPh2)] (3.3013(5) Å),2 [Au2I2(µ-2,2′-Et2-
PC6H4C6H4PEt2)] (3.167(1) Å).3 and [Au2I2{µ-2,2′-Ph-
Discu ssion
The stability and isomerization behavior of the sym-
metrical, homovalent digold(II) complexes [Au2X2(µ-2-
C6H4PPh2)2] are strongly dependent on the nature of
the axial ligand X. These compounds appear to be
thermodynamically stable only when X is a strongly
electron-withdrawing anionic O-donor ligand such as
acetate, benzoate, or nitrate. When X is a strongly
(19) Schmidbaur, H. Gold Bull. 1990, 23, 11; Chem. Soc. Rev. 1995,
24, 391.
(20) Bennett, M. A.; Welling, L. L.; Willis, A. C. Unpublished work.

C-C Coupling in Dinuclear Cycloaurated Complexes
Organometallics, Vol. 20, No. 1, 2001 85
Sch em e 5
is sufficiently electrophilic, the aryl group can migrate
from gold(I) to gold(III) via a bridging intermediate or
transition state. For ligands (X) such as halide or
thiocyanate, the migration may be triggered by anion
dissociation, although this seems less likely for the
carbanion C6F5. Bis(benzoato)digold(II) complexes pos-
sess remarkably short, and presumably strong, metal-
metal bonds, e.g. 2.5243(7) Å in [Au2(O2CPh)2(µ-2-
C6H4PEt2)2]3 and 2.587(1) and 2.560(2) Å for independent
molecules of the bis(ylide) complex [Au2(O2CPh)2{µ-
(CH2)2PPh2}2];24 hence, for anionic oxygen-donor ligands
such as benzoate the heterovalent isomer may be
energetically inaccessible. In contrast, for carbanionic
ligands such as methyl, the heterovalent isomer is the
stable form but the gold(III) center is insufficiently
electrophilic to promote aryl migration.
electron-donating carbanion, such as methyl, the ho-
movalent compound isomerizes rapidly to the heterova-
lent gold(I)-gold(III) structure 2a , without disturbing
the arrangement of the bridging C6H4PPh2 ligands. This
behavior is undoubtedly associated with the high trans
influence of methyl; i.e., the methyl ligands weaken the
gold(II)-gold(II) bond by virtue of their competition for
6s-electron density.21 The same effect probably operates
in the bis(ylide) series: the high trans influence of alkyl
groups on the gold-gold and, more markedly, on the
axial gold-halide bonds is evident in the structures of
[Au2(X)(R){µ-(CH2)2PPh2}2] (R ) CH3, X ) Br;22 R )
C2H5, X ) I23). Further experiments will be required to
determine whether the methyl groups are transferred
in an intramolecular or intermolecular fashion.
Exp er im en ta l Section
Gen er a l P r oced u r es. Syntheses were carried out under
dry, prepurified nitrogen with use of standard Schlenk tech-
niques, although the isolated solid complexes were usually air-
stable. The following instruments were used for spectroscopic
measurements: Varian XL-200E (1H NMR at 200 MHz, 19F
NMR at 188.15 MHz, 31P NMR at 80.96 MHz), Varian Gemini-
300 BB (1H NMR at 200 MHz, 31P NMR at 121.44 MHz), VG
ZAB-2SEQ (high-resolution EI and FAB mass spectra), Perkin-
Elmer PE 683 and 1800 FT (infrared spectra as KBr disks,
Nujol mulls or polythene disks in the ranges 4000-400 and
4000-150 cm-1). The NMR chemical shifts (δ) are given in
ppm relative to TMS (1H), CFCl3 (19F), and 85% H3PO4, the
first being referenced to solvent. Elemental analyses were done
in-house.
We suggested previously3 that a key step in the
intramolecular C-C coupling reaction of [Au2X2(2-C6H4-
PR2)2] is migration of the metal-carbon bond of C6H4-
PPh2 between gold atoms to generate a heterovalent
intermediate and that the C-C coupling occurs by
reductive elimination of two metal-carbon σ-bonds at
the gold(III) center. Intermediates containing gold(I)
and gold(III) resulting from such a migration have now
been detected for the cases R ) Ph, Et, X ) C6F5, SCN
and R ) Et, X ) I and their structure established with
reasonable certainty. The proposed reaction sequence
leading to the C-C coupled product is depicted in
Scheme 3. The favored mode of reaction for the inter-
mediate is evidently intramolecular C-C coupling at the
gold(III) center; however, it is also possible for the
phosphorus atom in the four-membered ring to migrate
from gold(III) to gold(I) and for the anionic ligand X to
migrate from gold(I) to gold(III) to give the zwitterionic
species that has been isolated and characterized in the
case of X ) C6F5, R ) Ph. At least for X ) C6F5, this
species does not undergo reductive elimination and is
not an intermediate in the C-C coupling reaction.
It is noteworthy that the C-C coupling reaction in
[Au2X2(2-C6H4PR2)2] is observed only when the axial
anions (C6F5, NCS, I, Br, Cl) are intermediate in
electron-withdrawing ability between CH3 and C6H5 on
one hand and oxygen-donor ligands such as benzoate
on the other. We can account for this phenomenon on
the basis of our original assumption3 that each digold(II)
complex is potentially in equilibrium with a heterova-
lent isomer that is structurally similar to the isolated
dimethyl compound 2a (Scheme 5). If the gold(III) center
Sta r tin g Ma ter ia ls. The compound 2-BrC6H4PPh2 was
made initially either by the reaction of PhMgBr with 2-BrC6H4-
25
PCl2 or by the [PdCl2(NCMe)2]-catalyzed reaction between
2-BrC6H4I and Ph2PSiMe3;26 later we employed the more
convenient reaction of Ph2PCl with 1,2-BrC6H4Li, the latter
being generated from 1,2-C6H4Br2 and BuLi at -100 °C.27 The
compound 2-BrC6H4PEt2 was made either from 2-BrC6H4PCl2
and EtMgI3 or by the reaction of Et2PCl with 1,2-BrC6H4Li.28
Dimethylmagnesium was prepared by dioxane-induced dis-
proportionation of CH3MgI following the procedure described
for (Me3SiCH2)2Mg.29 The complexes [Au2(µ-2-C6H4PR2)2] and
[Au2(O2CPh)2(µ-2-C6H4PR2)2] (R ) Ph, Et) were made as
described previously.3
Dim eth yld igold (I,III) Com p lexes, [Au I,III2(CH3)2(µ-2-
C6H4P R2)2] (R ) P h (2a ), Et (2b)). A stirred solution of 1a
(94 mg, 0.086 mmol) or 1b (78 mg, 0.086 mmol) in toluene (20
mL) was cooled in dry ice and treated dropwise with an ether
solution of dimethylmagnesium (0.095 mmol) over 15 min. The
resulting yellow solution was stirred and warmed to room
temperature over 3 h. Solvents were removed in vacuo, and
the residue was extracted with hexane (2 × 10 mL). Suspended
salts were removed by centrifugation, and solvent was removed
in vacuo to leave the crude product as a colorless solid, which
was purified by crystallization from CH2Cl2/ethanol. Yields of
2a and 2b were 70-80%. X-ray-quality crystals of 2a were
obtained by layering a solution in CH2Cl2 with 95% ethanol.
2a : 1H NMR (CD2Cl2) δ 0.02 (d, J PH ) 2 Hz, CH3); 31P{1H}
NMR (CD2Cl2) δ 33.9 (d), 17.6 (d, J PP ) 27.8 Hz); FAB-MS
m/z 931 [M+ - 15]. Anal. Calcd for C38H34Au2P2: C, 48.22; H,
3.62. Found: C, 47.26; H, 3.20. 2b: 1H NMR (CD2Cl2) δ 0.26
(24) Porter, L. C.; Fackler, J . P., J r. Acta Crystallogr., Sect. C 1986,
42, 1128.
(25) Talay, R.; Rehder, D. Z. Naturforsch., B 1981, 36, 459.
(26) Tunney, S. E.; Stille, J . K. J . Org. Chem. 1987, 52, 748.
(27) Harder, S.; Brandsma, L.; Kanters, J . A.; Duisenberg, A.; van
Lenthe, J . J . Organomet. Chem. 1991, 420, 143.
(28) Hart, F. A. J . Chem. Soc. 1960, 3324.
(21) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
(22) Basil, J . D.; Murray, H. H.; Fackler, J . P., J r.; Tocher, J .;
Mazany, A. M.; Trczinska-Bancroft, B.; Knachel, H.; Dudis, D.; Delord,
T. J .; Marler, D. O. J . Am. Chem. Soc. 1985, 107, 6908.
(23) Murray, H. H.; Fackler, J . P., J r.; Trczinska-Bancroft, B.
Organometallics 1985, 4, 1633.
(29) Andersen, R. A.; Wilkinson, G. Inorg. Synth. 1979, 19, 262.

86 Organometallics, Vol. 20, No. 1, 2001
Ta ble 4. Cr ysta l a n d Refin em en t Da ta for Com p ou n d s 2a , 4a , 5a , 5b, 6a , a n d 10b
Bennett et al.
2a
3a
4a
4b
5a
10b
(a) Crystal Data
C48H28Au2F10P2
chem formula
C
38H34Au2P2
C48H28Au2F10P2
C32H28Au2F10P2
C48H28Au2F10P2‚
0.75C3H6O
1294.17
C22H28Au2N2P2S2
fw
946.57
1250.61
1250.61
1058.44
840.48
cryst syst
unit cell dimens
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
triclinic
monoclinic
monoclinic
monoclinic
monoclinic
monoclinic
9.414(2)
11.173(2)
16.567(2)
106.97(1)
94.32(2)
99.98(2)
1626.8(6)
P1h (No. 2)
1.93
11.856(3)
15.330(4)
23.551(5)
16.588(6)
12.275(5)
21.166(4)
18.403(1)
8.322(2)
22.104(2)
18.534(6)
21.930(6)
22.122(1)
9.685(3)
23.091(7)
11.999(4)
94.34(2)
90.76(2)
90.314(6)
93.04(2)
99.86(3)
4268(1)
P21/n (No. 14)
1.95
4309(2)
P21/c (No. 14)
1.93
3384.9(7)
C2/c (No. 15)
2.08
8979(4)
P21/n (No. 14)
1.915
2644(1)
P21/n (No. 14)
2.11
space group
Dc (g cm-3
Z
)
2
4
4
4
8
4
F(000)
color, habit
900.0
colorless, prism
2376.0
2376.0
1992.0
colorless, needle
4944.0
colorless, needle
1576.00
colorless, block
yellow, parallelepiped yellow, prism
cryst dimens (mm) 0.14 × 0.07 × 0.16 0.28 × 0.12 × 0.09
0.28 × 0.26 × 0.10 0.44 × 0.08 × 0.07 0.30 × 0.09 × 0.05 0.31 × 0.21 × 0.19
µ (cm-1
)
175.4 (Cu KR)
70.4 (Mo KR)
69.8 (Mo KR)
179.2 (Cu KR)
132.7 (Cu KR)
114.2 (Mo KR)
(b) Data Collection and Processing
diffractometer
X-radiation
T (°C)
Rigaku AFC6R
Cu KR
23(1)
Philips PW1100/20
Mo KR
Rigaku AFC6S
Mo KR
23(1)
Rigaku AFC6R
Cu KR
23(1)
Rigaku AFC6R
Cu KR
23(1)
Philips PW1100/20
Mo KR
23(1)
20(1)
scan mode
ω-2θ
ω-2θ
ω-2θ
ω-2θ
ω-2θ
ω-2θ
ω-scan width (deg) 1.10 + 0.30 tan θ
1.00 + 0.35 tan θ
50.0
0.80 + 0.34 tan θ
50.1
1.20 + 0.30 tan θ
120.1
1.20 + 0.30 tan θ
120
0.90 + 0.34 tan θ
55.0
2θmax (deg)
no. of rflns
unique
120.3
4824
7830
8039
2527
10 865
6271
obsd
abs cor
4529 (I > 3σ (I))
4874 (I > 3σ (I))
analytical
0.32-0.44
3500 (I > 3σ (I))
1829 (I > 2σ (I))
analytical
0.10-0.35
6406 (I > 3σ (I))
3480 (I > 3σ (I))
analytical
0.14-0.26
analytical
ψ-scan
ψ-scan
transmissn factors 0.11-0.37
0.78-1.00
0.315-0.515
(c) Structure Analysis and Refinement
struct soln
refinement
no. of params
weighting
scheme w
Patterson methods
559
direct methods
full-matrix least squares
380
559
208
385
275
[σ2(F) + (6.4 ×
10-5)F2]-1
3.5
[σ2(F) + (4 ×
10-8)F2]-1
3.2
[σ2(F) + (2.25 ×
10-6)F2]-1
3.8
[σ2(F) + (2.25 ×
10-4)F2]-1
2.9
[σ2(F) + (9 ×
10-4)F2]-1
5.4
[σ2(F) + (1 ×
10-4)F2]-1
4.6
R (obsd) (%)
R
w (obsd) (%)
4.7
2.8
2.4
3.5
7.4
4.2
GOF
3.79
1.73/-2.54
1.10
0.73/-0.52
1.48
1.67/-1.21
1.45
0.73/-0.61
1.49
2.1/-1.70
1.66
2.00/-1.34
max/min peak
in final
diff map (e Å-3
)
(d, J PH ) 2 Hz, AuCH3), 1.15 (sym 8-line pattern, PCH2CH3),
2.0-2.4 (overlapping m, PCH2); 31P{1H} NMR (CD2Cl2) δ 33.6
(d), 7.0 (d, J PP ) 27.5 Hz); FAB-MS m/z 739 [M+ - 15]. Anal.
Calcd for C22H34Au2P2: C, 35.03; H, 4.54. Found: C, 35.10; H,
4.79.
Attem p ted Rea ction of [Au I,III2(CH3)2(µ-2-C6H4P P h 2)2]
(2a ) w ith Ben zoic Acid . In an NMR tube, a solution of 2a
(13 mg, 0.014 mmol) in CD2Cl2 (0.6 mL) was treated with
benzoic acid (2 mg, 0.016 mmol) and the course of reaction
was monitored by 31P NMR spectroscopy. After 2 h a singlet
at δ 36.3 had appeared, presumably due to [Au2(µ-2-C6H4-
PPh2)2] formed by reductive elimination of ethane. After 24 h
a singlet at δ 4.6 due to the bis(benzoato) complex 1a was also
evident and, after 48 h, these two peaks, in a ratio of ca. 2:1,
had completely replaced those due to 2a .
yellow solution was filtered through Celite in air, and the
solvent was removed in vacuo. The crude product was purified
by passing a toluene solution down a short column of neutral
alumina and eluting with toluene/hexane. The solvent was
stripped, and the yellow residue was recrystallized from
toluene/hexane to give 3a or 3b in yields of 80-90%. X-ray-
quality crystals of 3a were obtained by diffusion of pentane
into a toluene solution. 3a : 19F NMR (CD2Cl2) δ -119.0 (m,
o-F), -160.0 (t, J ) 17 Hz, p-F), -161.0 (m, m-F); 31P{1H} NMR
(CD2Cl2) δ -6.1 (s), (d6-acetone) δ -5.1 (s), (C6H6) δ -5.7; FAB-
MS m/z 1249 (M+). Anal. Calcd for C48H28Au2F10P2: C, 46.10;
H, 2.26. Found: C, 46.43; H, 2.04. 3b: 1H NMR (C6D6) δ 0.83
(dt, PCH2CH3), 1.86 (m, CH2); 19F NMR (C6D6) δ -119.2 (d, J
) 24 Hz, o-F), -158.1 (t, J ) 21 Hz, p-F), -159.8 (t, J ) 23
Hz, m-F); 31P{1H} NMR (CD2Cl2) δ -7.8 (s), (d6-acetone) -6.1
(s), (C6D6) δ -7.9. Anal. Calcd for C32H28Au2F10P2‚0.5C6H14
:
A similar reaction in which 2a was treated with an excess
of benzoic acid gave, after 48 h, mainly 1a , a small amount of
[Au2(µ-2-C6H4PPh2)2], and a small amount of unidentified
decomposition products. There was no evidence for the forma-
tion of a methyl benzoato complex, [Au2(CH3)(O2CPh)(µ-2-C6H4-
PPh2)].
C, 38.16; H, 3.20; P, 5.62. Found: C, 38.17; H, 3.41; P, 5.42.
The 31P{1H} NMR spectrum of a CD2Cl2 solution containing
approximately equimolar amounts of 1b (δP 8.2) and 3b (δP
-7.8), measured soon after mixing, showed an AB quartet at
δ 7.7 and -2.5 (J PP ) 66 Hz) in addition to the original singlets;
the new species is presumed to be [Au2(O2CPh)(C6F5)(µ-2-C6H4-
PEt2)2], formed by anion scrambling.
Rea r r a n gem en t of [Au II2(C6F 5)2(µ-C6H4P R2)2] (R ) P h
(3a ), Et (3b)). These experiments were carried out either in
NMR tubes or in 10 mL Schlenk flasks that were shielded from
light. A typical preparative procedure is described.
A solution of 3a (ca. 30 mg) in d8-toluene (5 mL) was heated
at 90 °C, the progress of the rearrangement being monitored
by 31P NMR spectroscopy. The doublet of doublets assigned to
the intermediate [(C6F5)AuI(µ-2-Ph2PC6H4)AuIII(C6F5)(η2-2-
C6H4PPh2)] (see text) began to appear after 5 h. After 20 h,
Bis(p en ta flu or op h en yl)d igold (II) Com p lexes, [Au II
-
2
(C6F 5)2(µ-2-C6H4P R2)2] (R ) P h (3a ). Et (3b)). A solution of
C6F5Br (0.069 mL, 0.55 mmol) in ether (25 mL) was cooled in
dry ice and treated dropwise with a 1.6 M solution of n-
butyllithium in hexane (0.35 mL, 0.55 mmol). The mixture was
stirred at dry ice temperature for 1 h, and the resulting
solution of C6F5Li was treated over a 30 min period with a
solution of 1a (252 mg, 0.23 mmol) or 1b (208 mg, 0.23 mmol)
in toluene (50 mL), the temperature being maintained at ca.
-70 °C. After being stirred for a further 30 min, the mixture
was warmed to room temperature and was stirred for 3 h. The

C-C Coupling in Dinuclear Cycloaurated Complexes
Organometallics, Vol. 20, No. 1, 2001 87
singlets due to the C-C-coupled product [AuI (C6F5)2(µ-2,2′-
The structures of 2a and 3a were solved by heavy-atom
Patterson methods30 and those of 4a , 4b, and 10b by direct
methods (SIR 92).31 They were expanded by use of Fourier
techniques.32 Non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included at geometrically deter-
mined positions, which were periodically recalculated but not
refined. In the case of 10b, the terminal carbon atom C(18) of
an ethyl group was disordered over two sites, which were
assigned occupancy parameters of p and 1 - p; the parameter
p was refined to a final value of 0.66(2). C(18a) was assigned
a fixed isotropic B value equal to the Beq value of C(18).
Hydrogen atoms associated with the minor orientation of the
disordered ethyl group were not included. The neutral atom
scattering factors were taken from ref 33; ∆f ′ and ∆f ′′ values
and mass attenuation coefficients were taken from ref 34.
Anomalous dispersion effects were included in Fc.35 Calcula-
tions were performed with the teXsan crystallographic soft-
ware package;36 data reduction for 3a and 10b was performed
with XTAL 3.4.37
2
Ph2PC6H4C6H4PPh2)] (4a) and the zwitterionic complex [(C6F5)2-
AuIII(µ-C6H4PPh2)2AuI] (5a ) were observed and, after 48 h,
these were the only peaks present, in a ratio of 7:1. The solvent
was removed in vacuo, and the residue was dissolved in a few
milliliters of acetone. After several hours, X-ray-quality crys-
tals of 5a precipitated. The supernatant liquid was decanted
and evaporated to dryness; the residue was then taken up in
a few milliliters of benzene. Layering the solution with hexane
produced, after several hours, X-ray-quality crystals of 4a .
4a : 19F NMR (C6D6) δ -113.4 (d, J ) 28 Hz, o-F), -158.8 (t,
J ) 20 Hz, p-F), -162.3 (td, J ) 32 Hz, m-F); 31P{1H} NMR
(d8-toluene) δ 36.3 (approx t, J PF ) 6.3 Hz), (C6D6) 36.2, (d6-
acetone) δ 36.8. 4b: 19F NMR (C6D6) δ -116.5 (m, o-F), -161.4
(t, J ) 19.4 Hz, p-F), -166.0 (m, m-F); 31P{1H} NMR (C6D6) δ
32.8 (approx t, J PF ) 6.3 Hz), (d6-acetone) δ 34.2.
The procedure in the case of 3b was similar except that, in
d8-toluene, the coupled product [AuI (C6F5)2(µ-2,2′-Et2PC6H4C6H4-
2
PEt2)] (4b) was the almost exclusive product in the absence
of light. In acetone, no precautions being taken to exclude light,
a mixture of 4b and the presumed zwitterionic complex
[(C6F5)2AuIII(µ-C6H4PEt2)2AuI] (5b) was formed. X-ray-quality
crystals of 4b were obtained from dichloromethane/hexane.
4b: 19F NMR (C6D6) δ -114.7 (dt, J ) 29, 8.9 Hz, o-F), -158.9
(t, J ) 20 Hz, p-F), -162.5 (m, m-F); 31P{1H} NMR (C6D6) δ
30.9 (approx t, J PF ) 7.7 Hz). Anal. Calcd for C38H28Au2F10P2:
C, 36.31; H, 2.67; P, 5.85. Found: C, 36.65; H, 3.05; P, 6.15.
5b: 31P{1H} NMR (C6D6) δ 32.9 (approx t, J PF ) 6.6 Hz).
Bis(th iocya n a to)d igold (II) Com p lexes, [Au II2(SCN)2(µ-
2-C6H4P R2)2] (R ) P h (8a ), Et (8b)). Treatment of a solution
of 1a (306 mg, 0.028 mmol) or 1b (253 mg, 0.028 mmol) in
acetone (10 mL) with an excess of KSCN or LiSCN in acetone
(5 mL) caused immediate, quantitative precipitation of 8a or
8b as orange solids, which were separated by filtration and
washed with acetone. The solids appear to be unstable even
when stored under nitrogen at 0 °C in the absence of light.
8a : IR (cm-1, KBr) 2120 vs [ν(CN)], 694 vs [ν(CS)]; (polythene)
246 vs [Au-SCN]; 31P{1H} NMR (CD2Cl2) δ 0.0 (s). 8b: IR
(cm-1, KBr) 2126 vs, 2105 vs, (Nujol) 2128 s, 2116 s [ν(CN)];
1H NMR (CD2Cl2) δ 1.3 (dt, CH3), 2.1-2.8 (m, CH2); 31P{1H}
NMR (CD2Cl2) δ 0.85 (s).
The structure of 5a was solved by direct methods (SHELX
86).38 The unit cell contained disordered solvent regions, near
1
0, 0, 0 and /2, 0, 0 and their equivalent positions, which could
not be described properly. Their contributions to the structure
factors were defined with use of back Fourier transform
techniques.39,40 Satisfactory refinement was achieved on the
basis of an asymmetric unit containing two molecules of C48H28
-
Au2F10P2 related by a pseudo-translation about 0.00, 0.20, 0.48
with six disordered acetone molecules per unit cell. Only 6409
of the 10 498 independent reflections were considered reliable
(I > 3σ(I)); therefore, the comprehensive constrained least-
squares refinement program RAELS-9641 was used to mini-
mize the number of parameters required to describe the
structure (385 variables for 124 non-hydrogen atoms in the
asymmetric unit). The Au and P atoms were refined as
independent anisotropic atoms; all other atoms were refined
with constraints with rigid body thermal parametrization.40
Calculations were carried out with teXsan36 and RAELS-96.41
Su p p or t in g In for m a t ion Ava ila b le: Full crystallo-
graphic data for 2a , 3a , 4a , 4b, 5a , and 10b, including tables
of atomic coordinates, anisotropic displacement parameters,
and bond lengths and angles. This material is available free
of charge via the Internet at http://pubs.acs.org.
The 31P{1H} NMR spectrum of a solution measured im-
mediately after mixing 8b with [Au2I2(µ-2-C6H4PEt2)2] (δP
-11.6) in CH2Cl2 showed, in addition to the singlets due to
the components, an AB quartet at δ -3.2, -7.5 (J AB ) 70 Hz),
presumably due to [Au2(I)(SCN)(µ-2-C6H4PEt2)2] formed by
rapid anion scrambling.
OM000773W
(30) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C.
PATTY: The DIRDIF Program System; Technical Report of the
Crystallography Laboratory; University of Nijmegen, Nijmegen, The
Netherlands, 1992.
(31) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
435.
(32) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
de Gelder, R.; Israel, R.; Smits, J . M. M. The DIRDIF-94 Program
System; Technical Report of the Crystallography Laboratory; Univer-
sity of Nijmegen, Nijmegen, The Netherlands, 1994.
(33) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV.
(34) International Tables for Crystallography; Wilson, A. J . C., Ed.;
Kluwer Academic: Dordrecht, The Netherlands; Vol. C.
(35) Ibers, J . A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
(36) teXsan: Single-Crystal Structure Analysis Software, Version
1.8; Molecular Structure Corp., 3200 Research Forest Drive, The
Woodlands, TX 77381, 1997.
(37) Hall, S. R., King, G. S. D., Stewart, J . M., Eds. XTAL 3.4
Reference Manual; University of Western Australia; Lamb: Perth,
Australia, 1995.
(38) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick,
G. M., Kru¨ger, C., Goddard, R., Eds.; Oxford University Press: Oxford,
U.K., 1985; pp 175-189.
(39) Rae, A. D.; Baker, A. T. Acta Crystallogr. 1984, A40, C428
(supplement).
Rea r r a n gem en t of [Au II2(SCN)2(µ-2-C6H4P R2)2] (R ) P h
(8a ), Et (8b)). Solutions of 8a and 8b (25-50 mg) in CD2Cl2
and acetone were set aside at room temperature, and the
changes were monitored by 31P NMR spectroscopy. After 2 h
the singlets due to the starting materials had been replaced
by signals assigned to [(NCS)AuI(µ-2-C6H4PR2)AuIII(SCN)(η2-
2-C6H4PR2)] (R ) Ph (9a ), Et (9b)) and to [AuI (SCN)2(µ-2,2′-
2
R2PC6H4C6H4PR2)] (R ) Ph (10a ), Et (10b)). There were also
singlets at δ 53.8 (R ) Ph) and δ 53.3 (R ) Et) of unknown
origin. After 2 days, only the signals due to 10a and 10b
remained. Exposure of a solid sample of 8a to laboratory light
for 7 days also caused complete conversion to 10a . X-ray-
quality crystals of 10a were obtained by layering a CH2Cl2
solution with hexane. 9a : 31P{1H} NMR (CD2Cl2) δ 38.2 (d),
-49.3 (d, J PP ) 11.6 Hz). 9b: 31P{1H} NMR (CD2Cl2) 37.4 (d),
-41.3 (d, J PP ) 11.9 Hz). 10a : 31P{1H} NMR (CD2Cl2) δ 32.0
(s); 10b: IR (cm-1, KBr) 2122 vs [ν(CN)]; 31P{1H} NMR (CD2-
Cl2) δ 26.5 (s). Anal. Calcd for C22H28Au2N2P2S2: C, 31.44; H,
3.36; N, 3.33. Found: C, 31.93; H, 3.32; N, 3.06.
(40) Rae, A. D. Acta Crystallogr. 1975, A31, 560.
X-r a y Cr ysta llogr a p h y. The crystal and refinement data
for compounds 2a , 3a , 4a , 4b, 5a , and 10b are summarized in
Table 4.
(41) Rae, A. D. RAELS 96: A Comprehensive Constrained Least-
Square Refinement Program; Australian National University, Can-
berra, ACT, Australia, 1996.