197Au Moessbauer spectroscopic studies of cyclometalated golddimers containing 2-C6F4PPh2 ligands

Article abstract of DOI:10.1246/bcsj.82.1506

¹⁹⁷Au Mossbauer spectra have been measured on a series of homovalent and heterovalent dinuclear gold complexes containing the 2-C ₆F₄PPh₂ ligand. The correlation plot indicates that the electron densities of the

Full text of DOI:10.1246/bcsj.82.1506

1
506 Bull. Chem. Soc. Jpn. Vol. 82, No. 12, 1506–1509 (2009)
© 2009 The Chemical Society of Japan
197Au Mössbauer Spectroscopic Studies of Cyclometalated
Gold Dimers Containing 2-C F PPh Ligands
6
4
2
1
2
2
Martin A. Bennett, Nedaossadat Mirzadeh, Steven H. Privér,
3
2
Masashi Takahashi, and Suresh K. Bhargava*
1Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
2School of Applied Sciences (Applied Chemistry), RMIT University,
GPO Box 2476V, Melbourne, Victoria 3001, Australia
3Department of Chemistry, Toho University, 2-2-1 Miyama, Funabashi 274-8510
Received June 17, 2009; E-mail: suresh.bhargava@rmit.edu.au
197Au Mössbauer spectra have been measured on a series of homovalent and heterovalent dinuclear gold complexes
containing the 2-C6F4PPh2 ligand. The correlation plot indicates that the electron densities of the 6s and 6p orbitals of the
gold atoms in these complexes are less than those of their protio and 6-methyl analogs, reflecting the electron-
withdrawing property of the fluorine substituents.
2
The Mössbauer spectroscopy of gold was first investigated
C F PPh )(¬ -2-C F PPh )AuX] [X = Cl (5), Br (6), and I (7)];
6
4
2
6
4
2
about forty years ago1 and has since proved to be a powerful
technique for the determination of the structures and bonding in
inorganic and organometallic gold compounds in the solid
­3
this behavior resembles that of the dihalodigold(II) compounds
of C H -6-Me-2-PPh , but differs from that of the dihalo-
digold(II) compounds of 2-C H PPh , which undergo reductive
1
3
6
3
2
6
4
2
state, particularly for compounds that are either insoluble
coupling of the aryl groups to give digold(I) complexes
or unstable in solution.4
­8 197
Au Mössbauer spectroscopy has
[XAu(®-2,2¤-Ph PC H C H PPh )AuX].
14,15
Treatment of
2
6
4
6
4
2
2
also been successfully used in oxidation state determination
and structure elucidation of the dinuclear cyclometalated gold
[Au2Cl2(®-2-C6F4PPh2)2] (2) or [ClAu(®-2-C6F4PPh2)(¬ -2-
C F PPh )AuCl] (5) with silver nitrate or benzoate gives
6
4
2
9
compounds [Au (®-2-C H PR ) ] (R = Et and Ph), [Au (®-
the corresponding disubstituted oxyanion complexes [Au Y -
2 2
2
6
4
2 2
2
10
C H -6-Me-2-PPh ) ],
and [Au (®-C H -n-Me-2-AsPh ) ]
n = 5 and 6). It was shown that the isomer shift (IS) and
(®-2-C F PPh ) ] [Y = ONO (8) and OOCC H (9)] or [YAu-
6 4 2 2 2 6 5
6
3
2 2
2
6
3
2 2
11
2
(
(®-2-C F PPh )(¬ -2-C F PPh )AuY] [Y = ONO (10) and
6 4 2 6 4 2 2
quadrupole splitting (QS) values for [Au (®-C H -6-Me-2-
OOCC H (11)], respectively (Scheme 1).
2
6
3
6
5
PPh ) ] are larger than those reported for the analogous non-
Complexes 1­11 were analyzed by Mössbauer spectroscopy;
the spectra and parameters are shown in Figure 1 and Table 1,
respectively.
2
2
methylated protio compound, indicating that electron donation
from the methyl substituents increases the 6s electron density
of the gold atoms.9 The Mössbauer parameters reported
for the closely related arsenic analogs, [Au (®-C H -n-Me-
,10
The Mössbauer spectra of 1­4, 8, and 9 (Figure 1) each
consist of the expected well resolved quadrupole doublet,
showing that the two gold atoms in these complexes are
equivalent. In contrast, complexes 5­7, 10, and 11 each show a
pair of quadrupole doublets, confirming the presence of two
inequivalent gold centers. It is worth noting that the IS and QS
values for the dihalodigold(II) complexes 2­4, 8, and 9 are
much smaller than those of the digold(I) complex 1, consistent
2
6
3
2
-AsPh ) ] (n = 5 and 6), are smaller than those of the
2 2
corresponding phosphorus compounds, indicating that the
Au­As bond is less covalent than the Au­P bond in these
11
197
compounds. In this work, Au Mössbauer spectroscopy has
been applied to confirm the oxidation states of the gold atoms
in the homovalent and heterovalent dinuclear complexes
containing 2-C F PPh and to compare the derived parameters
5
,9­11
with the formation of higher oxidation states.
6
4
2
with those of the corresponding complexes containing 2-
The isomer shift and quadrupole splitting values for the
dinuclear gold(I) complex 1 are less than those of its protio
C H PPh or C H -6-Me-2-PPh .
6
4
2
6
3
2
9
and 6-methyl analogs {[Au (®-2-C H PPh ) ] (12) and
2
6
4
2 2
Results and Discussion
10
[
Au (®-C H -6-Me-2-PPh ) ] (13), respectively (Table 1)},
2 6 3 2 2
As described elsewhere,12 the dinuclear digold(I) 1 and
dihalodigold(II) complexes 2­4, containing ®-2-C F PPh ,
and decrease in the order 1 < 12 < 13. This decrease can be
attributed to the electron-withdrawing nature of the fluorine
substituents compared to hydrogen and methyl groups, which
affects the population of the 6s and 6p orbitals in the gold
atoms, resulting in smaller IS and QS values, respectively. The
electronic effect of fluorine is also evident from the smaller IS
and QS values for [Au Br (®-2-C F PPh ) ] (3) compared to
6
4
2
shown in Scheme 1, are made similarly and are structurally
similar to their ®-2-C H PPh counterparts, although the
6
4
2
fluorine substituents cause small contractions in the Au£Au
separations. Complexes 2­4 rearrange in toluene solution at
7
0 °C to heterovalent, gold(I)­gold(III) compouds [XAu(®-2-
2
2
6
4
2 2
Published on the web December 10, 2009; doi:10.1246/bcsj.82.1506

M. A. Bennett et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 12 (2009) 1507
F
F
F
F
PPh2
Au
Au
Ph P
F
F
2
F
F
1
PhICl2
F
F
F
F
F
F
F
F
F
F
F
F
PPh2
PPh2
Au
PPh2
Au
AgY
LiX
X
Au
X
Y
Au
Y
Cl
Au
Au Cl
Ph P
F
Ph P
2
F
Ph2P
F
2
F
F
F
F
F
F
F
F
F
Y = ONO2 (8), OOCC H (9)
2
X = Br (3), I (4)
6
5
∆
∆
F
F
F
F
F
F
F
Ph P
Ph P
Ph P
2
2
2
Y
Cl
X
F
AgY
Au
F
Au
F
Au
Au
Au
Au
Y
Cl
X
F
F
F
Ph P
Ph P
F
Ph P
F
2
2
2
F
F
F
F
F
F
F
F
F
Y = ONO2 (10), OOCC H (11)
5
X = Br (6), I (7)
6
5
Scheme 1. Oxidative addition reaction of dinuclear gold(I) complex, rearrangement of dinuclear gold(II) complexes, and preparation
of digold(II) and digold(I,III) oxyanion complexes.
those reported for its protio analog [Au2Br2(®-2-C6H4PPh2)2]
18). The same trend has also been observed in the digold(I,III)
states of the gold atoms in complexes 1­11 lie close to
similar oxidation states within the expected regions: +1 in 1,
(
I
III
complex 7 and its 6-methyl analog 15; the IS and QS values
+2 in 2­4, 8, and 9, and mixed-valence state Au ­Au in 5­7,
10, and 11.
2
for [IAu(®-2-C F PPh )(¬ -2-C F PPh )AuI] (7) are smaller
6
4
2
6
4
2
The AuI atoms in the mixed-valence Au –Au com-
pounds 5­7, 10, and 11 are located in the low IS and QS
region in the expected AuI area of the plot, indicating
the different chemical environment compared to the sym-
metric gold(I) dimers. There is no clear trend in the ordering
of the IS and QS values for complexes 5­7, 10, and 11 that
can be correlated to the hardness of the coordinated ligands.
I
III
than those found in the 6-methyl analog. A decrease in the QS
¹
1
value (6.50 mm s ) is also observed for the complex [Au I (®-
2
2
2
¹
1
-C F PPh ) ] (4) compared to that of 6.54 mm s in the protio
6 4 2 2
analog [Au I (®-2-C H PPh ) ] (17), whereas surprisingly the
2
2
6
4
2 2
IS value has not changed. The correlation plot for complexes
­11 is shown in Figure 2. Additional data, summarized in
1
Table 1, are taken from Refs. 9­11.
II
The correlation plot shows three distinct regions, corre-
This is in contrast to that observed in the Au complexes (see
I
II
III
sponding to Au , Au , and Au oxidation states. The oxidation
later).

1
508 Bull. Chem. Soc. Jpn. Vol. 82, No. 12 (2009)
197Au Mössbauer Studies of Gold Complexes
Figure 1. 197Au Mössbauer spectra for complexes 1­11 at 12 K.
Experimentally, the plot of QS against IS for the digold(II)
complexes falls in the intermediate region between those
obtained for the gold(I) and gold(III) plots. The gold atoms
containing the four-membered ring unit (complexes 5­7, 10,
III
and 11) lie in the Au region of the plot, close to the gold(III)
atoms containing similar chemical environments, and away
from the gold(III) atom containing the P­Au­X unit.
3
Among the gold(II)­gold(II) complexes 2­4, 8, and 9, the
values of IS increase in the order ONO < Cl < OOCC H <
2
6
5
Br < I, which is in agreement with the expectation based
on the softness of the ligand. This result is in contrast to
the observations for the dinuclear biphenyldiyl complexes
[
Au2X2(2,2¤-Ph2As-5-MeC6H3C6H3-5-Me-AsPh2)]
Br, and I) and also for the mononuclear organogold complexes
AuX(PPh )] (X = I, Br, Cl, OCOCH , N , CN, and CH ), in
(X = Cl,
[
3
3
3
3
3
,11
which the values of IS increase as the ligands become harder.
Experimental
Complexes 1­11 were prepared following a literature proce-
dure.12 Gold-197 Mössbauer spectra were acquired at Toho
University, Japan, on a Wissel Mössbauer spectrometer system
consisting of a MDU-1200 function generator, DFG-1200 driving
unit, MVT-100 velocity transducer and MVC-1200 laser calibrator.
The £-ray source (210 MBq) was prepared by neutron irradiation
Figure 2. Plot of QS against IS for dinuclear gold
complexes.
the Japan Atomic Energy Agency (JAEA). The absorber thickness
¹2
was 50­130 mg Au cm . Both the Mössbauer source and the
absorber were cooled to a temperature of 12 K in a cryostat
1
96
of a 40 mg disc of enriched metallic Pt in the JRR-4 reactor at

M. A. Bennett et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 12 (2009) 1509
Table 1. 197Au Mössbauer Parameters for Dinuclear Gold Complexes
IS/mm s 1
¹
QS/mm s¹1
Compound
Au oxidation state
[
[
[
[
[
[
[
Au2(®-2-C6F4PPh2)2] (1)
I
II
II
II
II
II
4.04
3.22
3.36
3.45
2.93
3.23
2.88
3.64
2.45
3.85
2.29
3.75
2.56
3.51
2.35
3.97
4.53
4.67
4.67
2.87
4.42
3.60
3.46
3.46
3.60
4.26
1.90
4.08
4.22
9.51
6.10
6.30
6.50
6.18
6.14
7.69
4.98
6.81
5.37
6.77
5.41
7.71
4.23
6.40
5.31
9.58
9.81
10.12
7.26
6.06
6.96
6.54
6.44
6.39
5.87
2.79
8.80
8.82
Au2Cl2(®-2-C6F4PPh2)2] (2)
Au2Br2(®-2-C6F4PPh2)2] (3)
Au2I2(®-2-C6F4PPh2)2] (4)
Au2(ONO2)2(®-2-C6F4PPh2)2] (8)
Au2(OOCC6H5)2(®-2-C6F4PPh2)2] (9)
2
ClAu(®-2-C6F4PPh2)(¬ -2-C6F4PPh2)AuCl] (5)
I (site A)
III (site B)
I (site A)
III (site B)
I (site A)
III (site B)
I (site A)
III (site B)
I (site A)
III (site B)
I
I
2
[
[
[
[
BrAu(®-2-C6F4PPh2)(¬ -2-C6F4PPh2)AuBr] (6)
2
IAu(®-2-C6F4PPh2)(¬ -2-C6F4PPh2)AuI] (7)
2
(O2NO)Au(®-2-C6F4PPh2)(¬ -2-C6F4PPh2)Au(ONO2)] (10)
2
(C6H5COO)Au(®-2-C6F4PPh2)(¬ -2-C6F4PPh2)Au(OOCC6H5)] (11)
[
[
[
[
Au2(®-2-C6H4PPh2)2] (12)a)
Au2(®-C6H3-6-Me-2-PPh2)2] (13)
Au2(®-2-C6H4PEt2)2] (14)
IAu(®-2-C6H3-6-Me-2-PPh2)(¬ -C6H3-6-Me-2-PPh2)AuI] (15)
b)
a)
I
2
b)
I (site A)
III (site B)
II
II
II
II
III (site A)
III (site B)
I
I
[
[
[
[
[
Au2I2(®-2-C6H4PEt2)2] (16)a)
Au2I2(®-2-C6H4PPh2)2] (17)
Au2Br2(®-2-C6H4PPh2)2] (18)
Au2I2(®-C6H3-6-Me-2-PPh2)2] (19)
a)
a)
b)
2
b)
Cl3Au(®-2-C6H3-6-Me-2-PPh2)(¬ -C6H3-6-Me-2-PPh2)AuCl] (20)
[
[
Au2(®-2-C6H4AsPh2)2] (21)a)
Au2(®-C6H3-5-Me-2-AsPh2)2] (22)
c)
a) Ref. 9. b) Ref. 10. c) Ref. 11.
incorporating a closed cycle refrigerator, and a pure Ge solid state
6
H. D. Bartunik, G. Kaindl, in Mössbauer Isomer Shifts,
1
6
detector was used for counting the £-rays. The data were
analyzed by least-squares methods and the isomer shifts are given
relative to the 1 Pt/Pt source at 12 K.
North-Holland, Amsterdam, 1978.
7
157.
8
M. Melnínk, R. V. Parish, Coord. Chem. Rev. 1986, 70,
H. Schmidbaur, C. Hartmann, F. E. Wagner, Hyperfine
97
This work was the result of a collaboration between RMIT
University, Australia and Toho University, Japan, and was
supported in part by the Inter-University Program for the Joint
Use of JAEA Facilities.
Interact. 1988, 40, 335.
9
M. Takeda, M. Takahashi, Y. Ito, T. Takano, M. A. Bennett,
S. K. Bhargava, Chem. Lett. 1990, 543.
1
0
S. K. Bhargava, F. Mohr, M. Takahashi, M. Takeda, Bull.
Chem. Soc. Jpn. 2001, 74, 1051.
K. Kitadai, M. Takahashi, M. Takeda, S. K. Bhargava,
11
References
M. A. Bennett, Bull. Chem. Soc. Jpn. 2006, 79, 886.
1
H. D. Bartunik, W. Potzel, R. L. Mössbauer, G. Kaindl,
12 M. A. Bennett, S. K. Bhargava, N. Mirzadeh, S. H. Privér,
J. Wagler, A. C. Willis, Dalton Trans. 2009, 7537.
Z. Phys. A: Hadrons Nucl. 1970, 240, 1.
2
249.
3
M. O. Faltens, D. A. Shirley, J. Chem. Phys. 1970, 53,
13 S. K. Bhargava, F. Mohr, M. A. Bennett, L. L. Welling,
A. C. Willis, Organometallics 2000, 19, 5628.
4
J. S. Charlton, D. I. Nichols, J. Chem. Soc. A 1970, 1484.
R. V. Parish, in Mössbauer Spectroscopy Applied to
14 M. A. Bennett, S. K. Bhargava, K. D. Griffiths, G. B.
Robertson, Angew. Chem., Int. Ed. Engl. 1987, 26, 260.
15 M. A. Bennett, S. K. Bhargava, D. C. R. Hockless, L. L.
Welling, A. C. Willis, J. Am. Chem. Soc. 1996, 118, 10469.
16 T. Takano, Y. Ito, M. Takeda, Radioisotopes 1980, 29, 341.
4
Inorganic Chemistry, ed. by G. J. Long, Plenum, New York, 1984.
H. Schmidbaur, J. R. Mandl, F. E. Wagner, D. F. Van de
Vondel, G. P. Van der Kelen, J. Chem. Soc., Chem. Commun. 1976,
70.
5
1