Synthesis, structure, and reactions of binuclear gold(I) complexes containing two different bridging ligands

Article abstract of DOI:10.1021/ic010272i

The binuclear cycloaurated compounds [Au₂(μ-C₆H₃-2-PPh₂-n-Me) ₂] (n = 5, 1a; n = 6, 1b) react with the digold-(I) complexes [Au₂(μ-S₂CNⁿBu₂)₂] an

Full text of DOI:10.1021/ic010272i

Inorg. Chem. 2001, 40, 4271-4275
4271
Synthesis, Structure, and Reactions of Binuclear Gold(I) Complexes Containing Two
Different Bridging Ligands
Suresh K. Bhargava* and Fabian Mohr
Department of Applied Chemistry, RMIT University, GPO Box 2476V,
Melbourne, Victoria 3001, Australia
Martin A. Bennett,* Lee L. Welling, and Anthony C. Willis
Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
ReceiVed March 12, 2001
The binuclear cycloaurated compounds [Au2(µ-C6H3-2-PPh2-n-Me)2] (n ) 5, 1a; n ) 6, 1b) react with the digold-
(I) complexes [Au2(µ-S2CNnBu2)2] and [Au2(µ-dppm)2](PF6)2 to give heterobridged dinuclear complexes [Au2-
(µ-C6H3-2-PPh2-n-Me)(µ-S2CNnBu2)] (n ) 5, 5a; n ) 6, 5b) and [Au2(µ-C6H3-2-PPh2-n-Me)(µ-dppm)]PF6, (n )
5, 9a; n ) 6, 9b), respectively. Complex 5a exists in the solid state as an infinite zigzag chain of dimeric units
with intramolecular Au-Au separations of 2.8331(3) and 2.8243(3) Å for independent molecules and intermolecular
Au-Au separations of 3.0653(3) and 3.1304(3) Å. Both 5a and 5b undergo oxidative addition with halogens to
give the heterovalent, gold(I)-gold(III) compounds [XAuI(µ-2-Ph2PC6H3-n-Me)AuIIIX(η2-S2CNnBu2)] [n ) 5,
X ) Cl (6a), I (8a); n ) 6, X ) Cl (6b), Br (7b), I (8b)]. Compound 8a has been shown by X-ray crystallography
to contain a gold(III) atom coordinated in a planar array by bidentate, chelating di-n-butyldithiocarbamate, iodide,
and the σ-aryl carbon atom, together with a gold(I) atom that is linearly coordinated by the phosphorus atom of
the arylphosphine and by iodide. The intramolecular gold-gold distance of 3.2201(3) Å indicates little or no
interaction between the metal atoms. In contrast to the behavior of the homobridged complexes 1a and 1b, the
heterobridged dithiocarbamate complexes 5a and 5b give structurally similar products on reaction with halogens,
irrespective of the position of the ring methyl substituent. Crystal data for [Au2(µ-C6H3-2-PPh2-5-Me)(µ-S2CNn-
Bu2)] (5a): triclinic, space group P1h (No. 2), with a ) 11.3398(1), b ) 15.9750(2), c ) 16.4400(3) Å, R )
91.0735(9), â ) 109.3130(7), γ ) 90.7666(8)°, V ) 2809.47(6) Å3, and Z ) 4. Crystal data for [IAuI(µ-2-Ph2-
PC6H3-5-Me)AuIIII(η2- S2CNnBu2)] (8a): triclinic, space group P1h (No. 2), with a ) 8.6136(2), b ) 9.3273, c )
21.1518(4) Å, R ) 84.008(1), â ) 84.945(1), γ ) 75.181(1)°, V ) 1630.54(6) Å3, and Z ) 2.
Introduction
isolated depending on the conditions.5-14 In contrast to the
numerous homobridged dinuclear gold(I) compounds, relatively
few heterobridged analogues are known. Ligand combinations
include phosphorus bis(ylides) with bis(diphenylphosphino)-
methanide [Ph2PCHPPh2]-,15 dppm,16 alkylxanthates,17 pyridine-
2-thiolate,18 phosphoniodithioformate,19 and dithiocarbamates.20
Compounds containing the combinations dppe/i-mnt,21 dppm/
A wide variety of binuclear compounds containing two gold-
(I) atoms held in close proximity by a pair of bifunctional ligands
is known. Examples of such ligands include dtc,1,2 dppm,3
(2-pyridyl)dimethylphosphine,4 methylenethiophosphinate,5 and
phosphorus bis(ylides).6,7 The digold(I) complexes characteristi-
cally undergo oxidative additions with halogens, pseudohalo-
gens, and, in the case of the bis(ylides), alkyl halides to give
either metal-metal bonded digold(II) compounds or heterova-
lent gold(I)-gold(III) compounds; sometimes both can be
(8) Schmidbaur, H.; Wohlleben, A.; Wagner, F. E.; van de Vondel, D.
F.; van der Kelen, G. P. Chem. Ber. 1977, 110, 2758-2764.
(9) Fackler, J. P., Jr. Polyhedron 1997, 16, 1-17.
(10) Calabro, D. C.; Harrison, B. A.; Palmer, G. T.; Moguel, M. K.; Rebbert,
R. L.; Burmeister, J. L. Inorg. Chem. 1981, 20, 4311-4316.
(11) Fackler, J. P., Jr.; Trzcinska-Bancroft, B. Organometallics 1985, 4,
1891-1893.
(12) Raptis, R. G.; Porter, L. C.; Emrich, R. J.; Murray, H. H.; Fackler, J.
P., Jr. Inorg. Chem. 1990, 29, 4408-4412.
(13) Laguna, A.; Laguna, M. Coord. Chem. ReV. 1999, 193-195, 837-
856.
(14) Laguna, M.; Cerrada, E., In Metal Clusters in Chemistry; Braunstein,
P., Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, 1999;
Vol. 1, p 459, and references therein.
* To whom correspondence should be addressed.
(1) A° kerstro¨m, S. Ark. Kemi 1959, 14, 387-401.
(2) Abbreviations: dtc ) dithiocarbamate, R2NCS2-; dppm ) bis-
(diphenylphosphino)methane; dppe ) bis(diphenylphosphino)ethane;
2-
i-mnt ) 1,1-dicyanoethylene-2, 2′-dithiolate, S,S′-S2C2(CN)2
.
(3) Schmidbaur, H.; Wohlleben, A.; Schubert, U.; Frank, A.; Huttner, G.
Chem. Ber. 1977, 110, 2751-2757.
(4) Inoguchi, Y.; Milewski-Mahrla, B.; Schmidbaur, H. Chem. Ber. 1982,
115, 3085-3095.
(5) Mazany, A. M.; Fackler, J. P., Jr. J. Am. Chem. Soc. 1984, 106, 801-
802.
(15) Schmidbaur, H.; Mandl, J. R.; Bassett, J. M.; Blaschke, G.; Zimmer-
Gasser, B. Chem. Ber. 1981, 114, 433-440.
(6) Grohmann, A.; Schmidbaur, H. In ComprehensiVe Organometallic
Chemistry II; Wardell, J., Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon: Oxford, 1995; Vol. 3, p 1, and references therein.
(7) Schmidbaur, H.; Grohmann, A.; Olmos, M. E., In Gold, Progress in
Chemistry, Biochemistry and Technology; Schmidbaur, H., Ed.; John
Wiley & Sons: Chichester, 1999; pp 647-746.
(16) Bardaj´ı, M.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Laguna, M.
Organometallics 1994, 13, 3415-3419.
(17) Bardaj´ı, M.; Jones, P. G.; Laguna, A.; Laguna, M. Organometallics
1995, 14, 1310-1315.
(18) Bardaj´ı, M.; Connelly, N. G.; Gimeno, M. C.; Jones, P. G.; Laguna,
A.; Laguna, M. J. Chem. Soc., Dalton Trans. 1995, 2245-2250.
10.1021/ic010272i CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/14/2001

4272 Inorganic Chemistry, Vol. 40, No. 17, 2001
Bhargava et al.
Table 1. Elemental Analyses and 31P{1H} NMR Data for Heterobridged Gold Complexesa
Anal. [calcd (found)]
b
color
% C
% H
% N
% other
δP
[AuI2(µ-C6H3-2-PPh2-5-Me)(µ-S2CNnBu2)] (5a)
orange
yellow
yellow
brown
pale
38.45 (38.08)
36.34 (36.53)
35.57 (35.96)
29.80 (30.03)
35.57 (35.91)
4.03 (4.09)
3.79 (4.15)
3.73 (3.70)
3.13 (3.39)
3.73 (3.93)
1.60 (1.52)
1.46 (1.68)
1.48 (1.59)
1.24 (1.54)
1.48 (1.58)
3.54 (3.14) (P)
3.23 (3.09) (P)
6.78 (6.63) (S)
22.49 (22.78) (I)
7.50 (7.29) (Cl)
38.4c
39.6c
32.5
36.7
32.5
[AuI2(µ-C6H3-2-PPh2-6-Me)(µ-S2C NnBu2)]‚CH2Cl2 (5b)
[AuI,III2Cl2(µ-C6H3-2-PPh2-5-Me)(µ2-S2CNnBu2)] (6a)
[AuI,III2I2(µ-C6H3-2-PPh2-5-Me)(µ2-S2CNnBu2)] (8a)
[AuI,III2Cl2(µ-C6H3-2-PPh2-6-Me)(µ2-S2CNnBu2)] (6b)
yellow
brown
orange
pale
yellow
pale
[AuI,III2Br2(µ-C6H3-2-PPh2-6-Me)(µ2-S2CNnBu2)] (7b)
[AuI,III2I2(µ-C6H3-2-PPh2-6-Me)(µ2-S2CNnBu2)] (8b)
[AuI2(µ-C6H3-2-PPh2-5-Me)(µ-dppm)]PF6 (9a)
32.51 (32.75)
29.80 (30.14)
nm
3.41 (3.36)
3.13 (3.32)
nm
1.35 (1.39)
1.24 (1.10)
-
15.45 (15.22) (Br)
22.49 (22.39) (I)
nm
33.9
36.2
37.5d
[AuI2(µ-C6H3-2-PPh2-6-Me)(µ-dppm)]PF6 (9b)
44.09 (43.71)
3.20 (3.27)
-
10.34 (10.74) (P)
37.2d
yellow
a Abbreviations: nm ) not measured. b In CD2Cl2 at 23 °C. c In CDCl3 at 23 °C. d δ (P,C-ligand); δ (dppm) 32.3 (δA), 32.7 (δB), JAB ) 59,
JAC ) 8, JBC ) 308 Hz (9a), δ (dppm) 32.2 (δA), 32.6 (δB), JAB ) 56, JAC ) 7, JBC ) 300 Hz (9b).
Scheme 1
Experimental Section
General Procedures. Most syntheses were performed under dry
argon with the use of standard Schlenk techniques, although the solid
gold complexes, once isolated, were air-stable. Solvents were dried by
standard procedures, distilled, and stored under nitrogen.
Physical Measurements. The following instruments were used for
spectroscopic measurements: Varian XL-200E (1H at 200 MHz, 31P
at 80.96 MHz), Varian Gemini 300 (1H at 300 MHz), Bruker Aspect
2000 (31P at 80.96 MHz), VG ZAB-2SEQ [high-resolution EI (electron
impact) and FAB (fast atom bombardment) mass spectra], Micromass
Platform 2 [electrospray (ES) mass spectra], Perkin-Elmer PE 683
(infrared spectra as KBr disks in the range 4000-400 cm-1), and
Perkin-Elmer FT 1800 (infrared spectra as polyethylene disks in the
range 400-150 cm-1). The NMR chemical shifts (δ) are given in ppm
relative to TMS (1H) and 85% H3PO4 (31P) and referenced either to
residual solvent signals (1H) or externally (31P). Coupling constants
(J) are given in hertz. Elemental analyses were performed by the
Microanalytical Laboratory of the Research School of Chemistry at
the Australian National University. Elemental analyses and 31P NMR
chemical shifts are collected in Table 1. Simulation of the 31P{1H} NMR
spectra of 9a and 9b was carried out with MestRe-C 2.3 NMR
processing and simulation software.25
i-mnt,22 dppm/dtc,22 and dppm/1,3-propanedithiolate23 are also
known. These compounds also undergo oxidative addition
reactions with halogens to give metal-metal bonded binuclear
gold(II) compounds.16-19 We have shown24 that the products
obtained by oxidative addition of halogens (X2 ) Cl2, Br2, I2)
to the binuclear cycloaurated complexes [Au2(µ-C6H3-2-PPh2-
n-Me)2] (n ) 5, 1a; n ) 6, 1b) differ depending on the position
of the ring methyl substituent, as outlined in Scheme 1. In both
series, the first isolable products are the homobinuclear digold-
(II) complexes 2a and 2b. The former isomerize slowly by
intramolecular C-C coupling to give digold(I) complexes 3,
whereas, in the 6-methyl series, the complexes 2b isomerize
rapidly above -20 °C to the heterobinuclear gold(I)-gold(III)
complexes 4, which do not undergo subsequent C-C coupling.
We wished to find out whether heterobridged digold(I) com-
plexes containing one bridging C6H3-2-PPh2-n-Me ligand and
a different bridging ligand, such as dtc or dppm, could be
isolated and if their oxidative addition behavior also would
depend on the placement of the ring methyl group. The results
of this study are reported here.
Starting Materials. The compounds [Au2(µ-C6H3-2-PPh2-n-Me)2]
(n ) 5, 1a; n ) 6, 1b),24 [Au2(µ-S2CNnBu2)2],1 [Au2(µ-dppm)2]Cl2,3
26
and PhICl2 were prepared by literature procedures.
Digold(I) Complexes, [Au2(µ-C6H3-2-PPh2-n-Me)(µ-S2CNnBu2)]
(n ) 5, 5a; n ) 6, 5b). A solution or suspension of 1a or 1b (214 mg,
0.23 mmol) in dichloromethane (20 mL) was treated with a solution
of [Au2(µ-S2CNnBu2)2] (182 mg, 0.23 mmol) in dichloromethane (5
mL) and stirred for 30 min at room temperature. Concentration of the
pale green solution in vacuo and addition of hexane gave air-stable
orange (5a) or yellow (5b) solids in yields of 316 mg (80%) and 275
mg (68%), respectively. Crystals of 5a suitable for X-ray diffraction
were obtained from dichloromethane/methanol. 5a. 1H NMR (CDCl3):
δ 0.9 (t, CH3 of nBu), 1.3 (sxt, CH2 of nBu), 1.8 (qnt, CH2 of nBu), 2.3
n
(s, C6H3CH3), 3.9 (q, CH2 of Bu), 6.8-7.7 (m, arom). EI-MS: m/z
874 (M+), 605, 342. IR (KBr disk): 1576 cm-1 [ν(CdN)]. 5b. 1H NMR
n
n
(CDCl3): δ 0.9 (t, CH3 of Bu), 1.4 (sxt, CH2 of Bu), 1.8 (qnt, CH2
n
n
of Bu), 2.6 (s, C6H3CH3), 3.9 (q, CH2 of Bu), 6.8-7.7 (m, arom).
EI-MS: m/z 874 (M+), 676, 605. IR (KBr disk): 1568 cm-1
[ν(CdN)].
(19) Bardaj´ı, M.; Laguna, A.; Laguna, M. J. Organomet. Chem. 1995, 496,
245-248.
(20) Bardaj´ı, M.; Connelly, N. G.; Gimeno, M. C.; Jime´nez, J.; Jones, P.
G.; Laguna, A.; Laguna, M. J. Chem. Soc., Dalton Trans. 1994, 1163-
1167.
Gold(I)-Gold(III) Complexes, [XAu(µ-2-Ph2PC6H3-n-Me)AuX-
(η2-S2CNnBu2)] [n ) 5, X ) Cl (6a), I (8a); n ) 6, X ) Cl (6b), Br
(7b), I (8b)]. To a solution of 5a or 5b (50 mg, 0.057 mmol) in
dichloromethane (10 mL) at -70 °C was added a solution of iodine,
(21) Davila´, R. M.; Elduque, A.; Staples, R. J.; Harlass, M.; Fackler, J. P.,
Jr. Inorg. Chim. Acta 1994, 217, 45-49.
(22) Tang, S. S.; Chang, C. P.; Lin, I. J. B.; Liou, L. S.; Wang, J. C. Inorg.
Chem. 1997, 36, 2294-2300.
(25) Cobas, C.; Cruces, J.; Sardina, F. J. MestRe-C, NMR processing and
simulation software, Universidad de Santiago de Compostela, Spain,
2000.
(26) Lucas, H. J.; Kennedy, E. R., In Organic Syntheses; Wiley: New York,
1955; Collect. Vol. III, p 482.
(23) Davila´, R. M.; Elduque, A.; Grany, T.; Staples, R. J.; Fackler, J. P.,
Jr. Inorg. Chem. 1993, 32, 1749-1755.
(24) Bhargava, S. K.; Mohr, F.; Bennett, M. A.; Welling, L. L.; Willis, A.
C. Organometallics 2000, 19, 5628-5636.

Binuclear Gold(I) Complexes
Inorganic Chemistry, Vol. 40, No. 17, 2001 4273
Table 2. Crystallographic Data for Compounds 5a and 8a
5a
8a
chem formula
fw
space group
a (Å)
b (Å)
c (Å)
C28H34Au2NPS2
873.61
C28H34Au2I2NPS2
1127.42
P1h (no. 2)
8.6136(2)
9.3273(2)
21.1518(4)
84.008(1)
84.945(1)
75.181(1)
1630.54(6)
2.296
P1h (no. 2)
11.3398(1)
15.9750(2)
16.4400(3)
91.0735(9)
109.3130(7)
90.7666(8)
2809.47(6)
2.065
R (deg)
â (deg)
γ (deg)
V (Å3)
Dc (g cm-3
)
Z
4
2
µ (cm-1
λ (Å)
)
106.92
0.7107
200(1)
3.35
111.08
0.7107
200(1)
2.97
T (°K)
R (obsd data) %a
[I > 2σ (I)]
Rw (obsd data) %b
[I > 2σ (I)]
3.37
3.38
a R ) ∑|F0| - |Fc|/∑|F0|. b Rw ) [∑w(|F0| - |Fc|)2/∑wF0 ]1/2, where
2
w ) 1/[σ2(F0)].
Figure 1. Molecular structure of [AuI2(µ-C6H3-2-PPh2-5-Me)(µ-S2CNn-
Bu2)] (5a) with atom labeling; ellipsoids show 30% probability levels.
Hydrogen atoms have been omitted for clarity.
bromine, or PhICl2 (0.06 mmol) in dichloromethane (5 mL), causing a
color change to deep red (I2) or orange (Br2, PhICl2). The mixture was
stirred at low temperature for 30 min, allowed to warm to room
temperature, and stirred for a further 30 min. Hexane was added, and
the solutions were evaporated under reduced pressure until the products
began to precipitate. The orange or yellow solids were isolated by
filtration and washed with hexane. The yields of 6a, 8a, and 6b-8b
were ca. 70%. Crystals of 8a suitable for X-ray diffraction were obtained
from dichloromethane/methanol. FAB-MS: m/z 979 (M+-Cl), 747, 472,
306 (6a); 1025 (M+-I) (8a); 979 (M+-Cl), 747, 472, 306 (6b); 1025
(M+-Br) (7b); 1198 (M+), 1071, 943, 747, 471, 275 (8b).
Table 3. Selected Bond Distances (Å) and Angles (Deg) in
[AuI2(µ-C6H3-2-PPh2-5-Me)(µ-S2CNnBu2)] (5a)a
Au(1)‚‚‚Au(2)
Au(1)-P(1)
Au(1)-S(1)
Au(2)-C(2)
2.8331(3) Au(1)‚‚‚Au(4)
2.264(2) Au(2)-S(2)
2.316(2) C(20)-N(1)
2.039(6)
3.0653(3)
2.338(2)
1.354(7)
S(1)-Au(1)-P(1)
S(2)-Au(2)-C(2)
S(1)-C(20)-S(2)
178.20(6) P(1)-C(1)-C(2)
174.6(2) Au(1)-S(1)-C(20)
127.4(4) Au(1)-P(1)-C(1)
121.5(5)
110.0(2)
113.0(2)
Au(2)-Au(1)-Au(4) 166.35(1) Au(1)-Au(2)-Au(3) 148.33(1)
Digold(I) Complexes, [Au2(µ-C6H3-2-PPh2-n-Me)(µ-dppm)]PF6
(n ) 5, 9a; n ) 6, 9b). A solution or suspension of 1a or 1b (50 mg,
0.053 mmol) in dichloromethane (15 mL) was treated with a solution
of [Au2(µ-dppm)2]Cl2 (65 mg, 0.053 mmol) in dichloromethane (5 mL).
The mixture was either heated to reflux for 1 h (9a) or stirred for 30
min at room temperature (9b). The solution was evaporated to dryness
under reduced pressure, and the residue taken up in acetone (5 mL).
The product was precipitated in ca. 80% yield by addition of a
concentrated solution of NH4PF6 in acetone. 9a. 1H NMR (CDCl3): δ
2.3 (s, CH3), 3.9 (t, sepn ) 10 Hz, CH2), 6.9-7.7 (m, arom). ES-MS:
Au(1)-Au(2)-S(2)
Au(1)-Au(2)-C(20) 113.7(2)
91.06(4) Au(1)-Au(2)-C(2) 93.1(2)
a In the second, independent molecule Au(3)‚‚‚Au(4) ) 2.8243(3),
Au(2)‚‚‚Au(3) ) 3.1304(3); other distances and angles are similar to
those given in the Table.
Results
The digold(I) complexes [Au2(µ-C6H3-2-PPh2-n-Me)2] (n )
5, 1a; n ) 6, 1b) react with an equimolar amount of the dtc
complex [Au2(µ-S2CNnBu2)2] in dichloromethane at room
temperature to give the heterobridged digold(I) compounds [Au2-
(µ-C6H3-2-PPh2-n-Me)(µ-S2CNnBu2)] (n ) 5, 5a; n ) 6, 5b)
as orange or yellow solids, respectively, which are stable to air
and moisture and show strong luminescence when exposed to
UV light (Scheme 2). Their EI-mass spectra show a parent-ion
molecular peak, and their 31P{1H} NMR spectra contain the
singlet expected for equivalent phosphorus atoms. The molecular
structure of 5a determined by single crystal X-ray diffraction
is shown in Figure 1; important bond lengths and angles are
listed in Table 3. In each molecule, two linearly coordinated
1
m/z 1053 (M+). 9b. H NMR (CDCl3): δ 2.7 (s, CH3), 4.1 (t, sepn )
10 Hz, CH2), 6.9-7.7 (m, arom). ES-MS: m/z 1053 (M+).
X-ray Crystallography. The crystal and refinement data for
complexes 5a and 8a are summarized in Table 2. Data reduction was
performed according to ref 27. Both structures were solved by heavy-
atom Patterson methods,28 and refined by use of teXsan.29 In 5a there
are two independent molecules in the asymmetric crystallographic unit,
one n-butyl group in each unit being disordered. Hydrogen atoms were
included at geometrically determined positions, which were periodically
recalculated but not refined. Methyl hydrogen atoms were oriented to
best-fit peaks in difference electron density maps. The neutral atom
scattering factors were taken from ref 30; ∆f ′ and ∆f ′′ values and
mass attenuation coefficients were taken from ref 31.
n
gold(I) atoms are bridged by Bu2dtc and C6H3-2-PPh2-5-Me
(P,C). As also observed in the binuclear gold(I)-dtc com-
pounds,32,33 the molecules pack in the crystal to generate an
infinite zigzag chain of gold atoms. The intramolecular Au-
Au separations for the two independent molecules in the
asymmetric unit, 2.8331(3) and 2.8243(3) Å, are similar to those
in [Au2(µ-2-C6H4PPh2)2] [2.8594(3) Å]34 and [Au2(µ-C6H3-2-
(27) Otwinowski, Z.; Minor, W., In Methods in Enzymology; Carter, C.
W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; 276,
p 307-326.
(28) 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, The Netherlands, 1992.
(29) teXsan: Single-Crystal Structure Analysis Software, Molecular Struc-
ture Corp., 3200 Research Forest Drive, The Woodlands, TX 77381,
1997.
(31) International Tables for Crystallography; Kluwer Academic: Dor-
drecht, The Netherlands, 1992; Vol. C.
(32) Hesse, R.; Jennische, P. Acta Chem. Scand. 1972, 26, 3855-3864.
(33) Heinrich, D. D.; Wang, J. C.; Fackler, J. P., Jr. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1990, 46, 1444-1447.
(30) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; Kynoch Press: Birmingham, England, 1974; Vol. IV.

4274 Inorganic Chemistry, Vol. 40, No. 17, 2001
Bhargava et al.
Scheme 2
Scheme 3
Figure 2. Molecular structure of [AuI,III2I2(µ-C6H3-2-PPh2-5-Me)(µ2-
S2CNnBu2)] (8a) with atom labeling; ellipsoids show 30% probability
levels. Hydrogen atoms have been omitted for clarity.
PPh2-6-Me)2] [2.861(2) Å],24 and are significantly greater than
n
those in [Au2(µ-S2CNR2)2] [2.76,32 2.782(1) Å33 for R ) Pr,
Et, respectively]. Evidently, the intramolecular Au-Au distance
in 5a is dictated mainly by the less compact P,C bridging ligand.
The intermolecular Au-Au separations, 3.0653(3) and 3.1304-
(3) Å, are slightly greater than those in [Au2(µ-S2CNEt2)2]
[3.004(1) Å] but much less than those in [Au2(µ-S2CNnPr2)2]
(3.40 Å).32
Treatment of 5a or 5b with 1 mole equiv of PhICl2, Br2, or
I2 in dichloromethane at -70 °C gives deep orange or red
solutions, which fade on warming to room temperature, and
from which yellow or orange adducts of empirical formula
[Au2X2(C6H3-2-PPh2-n-Me)(S2CNnBu2)] [n ) 5, X ) Cl (6a),
I (8a); n ) 6, X ) Cl (6b), Br (7b), I (8b)] can be isolated by
addition of hexane (Scheme 3). These compounds show singlet
31P{1H} NMR resonances, the shieldings (Table 1) of corre-
sponding compounds in the 5- and 6-methyl series being very
similar and decreasing in the order I > Br > Cl. With the
exception of 8b, the mass spectra do not show a parent ion
peak; the highest mass peak generally corresponds to the loss
of one halide ion.
An X-ray diffraction study has shown that 8a is a heterovalent
gold(I)-gold(III) complex, and the similarity of their spectro-
scopic properties indicates that 6a, 6b, 7b, and 8b have
comparable structures. The molecular structure of 8a is shown
in Figure 2, together with atom numbering; selected bond lengths
and angles are listed in Table 4. The trivalent gold atom, Au-
(2), is coordinated in a planar array by a bidentate, chelate S2-
CNnBu2 group, the carbon atom of a bridging C6H3-2-PPh2-5-
Me group, and iodide; the iodide is cis to the σ-bonded carbon
atom. The univalent gold atom, Au(1), is coordinated linearly
by iodide and the phosphorus atom of the bridging C6H3-2-
PPh2-5-Me group. The separation between the gold atoms,
3.2201(3) Å, suggests that they interact only weakly, if at all.
The Au(III)-S distance trans to iodide, 2.337(2) Å, is close to
that observed in [AuIII(η2-S2CNnBu2)2][AuIBr2], [2.332(9) Å],35
whereas that trans to the σ-bonded carbon, 2.388(2) Å, is
significantly greater, as expected on the basis of trans influence
considerations. The asymmetrical binding of the η2-S2CNnBu2
Table 4. Selected Bond Distances (Å) and Angles (Deg) in
[AuI,III2I2(µ-C6H3-2-PPh2-5-Me)(µ2-S2CNnBu2)] (8a)
Au(1)‚‚‚Au(2)
Au(1)-P(1)
Au(1)-I(1)
Au(2)-C(2)
C(20)-S(1)
3.2201(3)
2.256(2)
2.5663(5)
2.049(6)
1.728(7)
Au(2)-S(1)
Au(2)-S(2)
Au(2)-I(2)
C(20)-N(1)
C(20)-S(2)
2.337(2)
2.388(2)
2.6015(5)
1.323(8)
1.711(7)
P(1)-Au(I)-I(1)
S(1)-Au(2)-S(2)
S(1)-C(20)-S(2)
173.01(4)
74.85(6)
113.3(4)
C(2)-Au(2)-I(2)
Au(1)-P(1)-C(1)
P(1)-C(1)-C(2)
93.2(2)
115.3(2)
121.4(4)
group in 8a may be responsible for the slightly larger S-C-S
angle of 113° in this compound compared with that in [AuIII(η2-
S2CNnBu2)2][AuIBr2] (109°). The angle subtended at Au(2) by
the four membered S2CNnBu2 group (75°) is similar to that in
[AuIII(η2-S2CNnBu2)2][AuIBr2] and in complexes of the same
ligand with copper(III)36 and nickel(II).37 Other bond lengths
and angles are unexceptional.
The far IR spectra of 6a and 6b each show a strong band in
the region of 330 cm-1 assignable to ν(AuI-Cl); the correspond-
ing ν(AuI-Br) band in the spectrum of 7b is observed at 234
cm-1. Bands at similar positions are found in the spectra of
tertiary phosphine-gold(I) complexes.38-40 The band due to
ν(AuIII-Cl) in the spectrum of complexes 6a and 6b could not
be located.
Reaction of 1a or 1b with [Au2(µ-dppm)2]Cl2 and subsequent
addition of NH4PF6 gives the ionic, heterobridged digold(I)
complexes [Au2(µ-C6H3-2-PPh2-n-Me)(µ-dppm)]PF6 (n ) 5, 9a;
n ) 6, 9b) (Scheme 4). From the 31P{1H} NMR spectra it is
apparent that the PF6- counterion forces the equilibrium to the
right by selectively precipitating the heterobridged cation. The
electrospray mass spectra of 9a and 9b show molecular peaks
for both cation and anion. The 1H NMR spectra show a triplet
(separation 10 Hz) for the methylene protons and a singlet for
(36) Beurskens, P. T.; Cras, J. A.; Steggerda, J. J. Inorg. Chem. 1968, 7,
810-813.
(37) Bonamico, M.; Dessy, G.; Mariani, C.; Vaciago, A.; Zambonelli, L.
Acta Crystallogr. 1965, 19, 619.
(34) Bennett, M. A.; Bhargava, S. K.; Griffiths, K. D.; Robertson, G. B.;
Wickramsinghe, W. A.; Willis, A. C. Angew. Chem., Int. Ed. Engl.
1987, 26, 258-260.
(35) Beurskens, P. T.; Blaauw, H. J. A.; Cras, J. A.; Steggerda, J. J. Inorg.
Chem. 1968, 7, 805-810.
(38) Coates, G. E.; Parkin, C. J. Chem. Soc. 1963, 421-429.
(39) Jones, A. G.; Powell, D. B. Spectrochim. Acta, Part A 1974, 30, 563-
570.
(40) Williamson, D. R.; Baird, M. C. J. Inorg. Nucl. Chem. 1972, 34, 3393-
3400.

Binuclear Gold(I) Complexes
Inorganic Chemistry, Vol. 40, No. 17, 2001 4275
Scheme 5
Discussion
Figure 3. Observed (top) and simulated (bottom) 31P{1H} NMR
spectrum of 9a, where δA 32.3, δB 32.7, δC 37.5, JAB ) 59, JAC ) 8,
and JBC ) 308 Hz.
When two homobridged digold(I) complexes are mixed in
solution, an equilibrium with the heterobridged species is set
up immediately. The latter can be isolated if it is favored by
the equilibrium and if it precipitates selectively. Of the systems
we have examined with 1a and 1b, only di-n-butyldithiocar-
bamate and dppm (in the presence of PF6-) give isolable
heterobridged products.
Scheme 4
Addition of halogens to the S2CNnBu2 complexes initially
forms very dark solutions that may contain digold(II) intermedi-
ates, but these rapidly isomerize to gold(I)-gold(III) isomers,
as has also been observed in [Au2(µ-S2CNEt2)2].35,46,47 Com-
plexes 6a, 8a, and 6b-8b represent the first fully characterized
examples of heterovalent gold(I)-gold(III) complexes derived
from the oxidative addition to heterobridged digold(I) com-
pounds. In contrast to our results, addition of halogens to the
heterobridged dibenzyldithiocarbamato bis(ylide) complex 10
gives homobinuclear digold(II) complexes 11, as shown in
Scheme 5. These can only be converted into a gold(I)-gold-
(III) complex by treatment with [Ag(OClO3)(PPh3)] to remove
the halide, and it was not possible to distinguish between the
two structural possibilities, 12a and 12b, for the resulting
product.16 The only general conclusion from these results,
considered together, seems to be that coordination of a tertiary
phosphine tends to favor the gold(I)-gold(III) arrangement
relative to the gold(II)-gold(II) alternative. It is also noteworthy
that, in the halogenation of the heterobridged complexes 5a and
5b, isomerization from the presumed digold(II) product (Scheme
3) occurs with equal ease in the 5- and 6-methyl series, in
contrast to the behavior of the homobridged complexes 2a and
2b (Scheme 1). Qualitatively, this difference can be ascribed
to two factors: (1) the clear preference for the heterobinuclear
product induced by dithiocarbamate, except when bis(ylide) is
present as co-ligand, and (2) steric destabilization of the digold-
(II) homobridged P,C species caused by the presence of two
methyl substituents close to the axial halide ligands.
the methyl protons, in the expected ratio of 2:3, in addition to
the aromatic protons. The clearest evidence for the heterobridged
formulation comes from the 31P{1H} NMR spectra, which
display essentially two AB patterns with an additional, much
smaller coupling, as illustrated in Figure 3 for complex 9a. The
spectrum can be simulated to give the coupling constants
JAB ) 59 Hz, JAC ) 8 Hz, and JBC ) 308 Hz, the nuclei being
labeled as shown in Scheme 4. The corresponding values for
9b are: JAB ) 56 Hz, JAC ) 7 Hz, and JBC ) 300 Hz. The
magnitude of JBC is similar to that found in dinuclear gold(I)
complexes of the type [Au2X2L2] [L ) Ph2PCH2CHEtOPPh2],
for which values of 346 and 338 Hz have been reported,
depending on the anionic ligand (X) present.41 In addition, JBC
is also similar in magnitude to the P-P coupling constants
observed for mutually trans tertiary phosphines in planar d8 and
octahedral d6 complexes of the later transition metals.42 The
coupling constant of 59 Hz between the inequivalent phosphorus
atoms of µ-dppm is similar in magnitude to those derived from
the spectra of diplatinum(I) complexes [Pt2X2(µ-dppm)2] (X )
Cl, Br, I) and their derivatives.43-45 Attempts to obtain X-ray
quality crystals of 9a or 9b have been unsuccessful so far. In
efforts to obtain other heterobridged digold(I) complexes
containing µ-C6H3-2-PPh2-n-Me (n ) 5, 6), we either recovered
starting materials (in the case of [Au2(µ-S2CPEt3)2]) or obtained
equilibrium mixtures (in the case of [Au2(µ-i-mnt)2]).
Acknowledgment. We thank Ms. Vesna Lukic (work
experience student) for experimental assistance and the Aus-
tralian Government for the award of an APA Scholarship to
F.M.
Supporting Information Available: Details of the X-ray structure
determinations in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
(41) Bayler, A.; Schier, A.; Schmidbaur, H. Inorg. Chem. 1998, 37, 4353-
4359.
(42) Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition Metal
Phosphine Complexes; Springer: Berlin, 1979.
IC010272I
(43) Brown, M. P.; Puddephatt, R. J.; Rashidi, M.; Seddon, K. R. J. Chem.
Soc., Dalton Trans. 1977, 951-955.
(44) Grossel, M. C.; Batson, J. R.; Moulding, R. P.; Seddon, K. R. J.
Organomet. Chem. 1986, 304, 391-423.
(46) Blaauw, H. J. A.; Nivard, R. J. F.; van der Kerk, G. J. M. J. Organomet.
Chem. 1964, 2, 236-244.
(47) Kita, H.; Itoh, K.; Tanaka, K.; Tanaka, T. Bull. Chem. Soc. Jpn. 1978,
51, 3530-3533.
(45) Blau, R. J.; Espenson, J. H.; Kim, S.; Jacobson, R. A. Inorg. Chem.
1986, 25, 757-763.