Divalent Platinum Complexes of the Carbanion 2‑C
6
F
4
AsPh
2
:
Monodentate or Bidentate Coordination?
Nedaossadat Mirzadeh,
†
Steven H. Prive ́ r,
†
Martin A. Bennett,
‡
Jö rg Wagler,
§
and Suresh K. Bhargava*
,†
†
Centre for Advanced Materials & Industrial Chemistry, School of Applied Sciences, RMIT University, GPO Box 2476 V, Melbourne,
Victoria 3001, Australia
‡
Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia
§
Institut fü r Anorganische Chemie, Technische Universitä t Bergakademie, Freiberg D-09596, Germany
* S Supporting Information
ABSTRACT: The reaction of [PtI
2
(1,5-COD)] with 2-
LiC
6
F
4
AsPh
2
affords the planar platinum(II) fluoroaryl
complex [PtI(κC-2-C
6
F
4
AsPh
2
)(1,5-COD)] (7), in which
the arsenic atom is not coordinated to the metal atom.
Attempts to prepare the bis(chelate) complex [Pt(κ
2
As,C-2-
C
6
F
4
AsPh
2
)
2
] analogous to the known phosphorus compound
failed. Removal of iodide ion from 7 with TlPF
6
gave
[Pt(κ
2
As,C-2-C
6
F
4
AsPh
2
)(1,5-COD)]PF
6
(8), in which 2-
C
6
F
4
AsPh
2
is now coordinated as a bidentate ligand, giving a
four-membered chelate ring. Alternatively, protonolysis (with
triflic acid) of the methyl complex [PtMe(κC-2-C
6
F
4
AsPh
2
)(1,5-COD)] (15), which is obtained from 7 and dimethylzinc, gives
the triflate salt 16 of the same chelate cation. The chelate As,C ring in 8 is readily reopened when the complex is treated with
pyridine or with halide ions, forming respectively [Pt(py)(κC-2-C
6
F
4
AsPh
2
)(1,5-COD)]PF
6
(9) and [PtX(κC-2-C
6
F
4
AsPh
2
](1,5-
COD)] (X = Cl (10), Br (11), I (7)). The appearance of two pairs of olefinic COD resonances in the proton NMR spectra of 7,
10, 11, and 15 may indicate that there is restricted rotation about the Pt-κC-2-C
6
F
4
AsPh
2
bond; the additional signals are not
evident in the spectra of 8 or 16. Complexes 7 and 10 form the 1:1 adducts [PtX(μ-2-C
6
F
4
AsPh
2
)(1,5-COD)AuY] (X = Cl, Y = I
(12); X = Y = I (13); X = Y = Cl (14)) by attachment of gold(I) halides to their dangling arsenic atoms. In 12 the halides are
scrambled between platinum and gold. The X-ray structures of 7, 8, 9, 12, 15, and 16 are reported, and possible reasons for the
poorer chelating ability of 2-C
6
F
4
AsPh
2
in comparison with that of 2-C
6
H
4
PPh
2
are discussed.
■
INTRODUCTION
Ortho-metalated complexes containing the bidentate carbanion
[2-C
6
H
4
PPh
2
]
-
are known for most of the transition metals and
are usually prepared by C-H bond activation of coordinated
PPh
3
.
1
Other methods based on transmetalation of 2-
LiC
6
H
4
PPh
2
and on oxidative addition of 2-BrC
6
H
4
PPh
2
are
also known.
1
The resulting complexes are often mononuclear
and contain a four-membered M(κ
2
P,C-2-C
6
H
4
PPh
2
) chelate
ring, although examples are also known where the 2-C
6
H
4
PPh
2
group acts as a bifunctional bridging ligand spanning two metal
centers. For example, the reaction of 2-LiC
6
H
4
PPh
2
with
[PtCl
2
(SEt
2
)
2
] gives the mononuclear bis(chelate) complex cis-
[Pt(κ
2
P,C-2-C
6
H
4
PPh
2
)
2
](1), which dimerizes in refluxing
toluene to give [Pt
2
(μ-2-C
6
H
4
PPh
2
)
2
(κ
2
P,C-2-C
6
H
4
PPh
2
)
2
]
(2), derived by opening of half the available four-membered
chelate rings (Scheme 1).
Metal-perfluoroaryl complexes are usually much more stable
than their aryl counterparts and show distinctly different
chemistry.
2
Although the fluorine-substituted bis(chelate)
complex [Pt(κ
2
P,C-2-C
6
F
4
PPh
2
)
2
]
3
is prepared similarly to its
protio analogue, cis-[Pt(κ
2
P,C-2-C
6
H
4
PPh
2
)
2
], the former is
isolated as a cis/trans mixture that is converted into the more
stable trans isomer on heating and shows no tendency to
dimerize. The increased stability conferred by fluorine
substitution in the aromatic ring is also evident from the fact
that analogous nickel and palladium bis(chelate) complexes
trans-[M(κ
2
P,C-2-C
6
F
4
PPh
2
)
2
] (M = Ni, Pd) can be prepared,
3
whereas the protio analogues are unknown.
In contrast to the extensive range of ortho-metalated tertiary
phosphine species, relatively few examples of ortho-metalated
tertiary arsine species have been reported. Early work showed
that heating a solution of the iridium(I) complex [IrCl-
(AsPh
3
)
3
] gave the cyclometalated iridium(III) complex
[IrHCl(κ
2
As,C-2-C
6
H
4
AsPh
2
)(AsPh
3
)
2
].
4
More recently, treat-
ment of [AuBr(AsPh
3
)]
5
or [PtCl
2
(SEt
2
)
2
]
6
with LiC
6
H
3
-5-
Me-2-AsPh
2
has been reported to give the dinuclear gold(I)
complex 3 and a mixture of the dinuclear platinum(II)
complexes 4 and 5, respectively, as shown in Scheme 2.
Compound 4 is analogous to the phosphine compound 2,
whereas the lantern compound 5 has no known phosphine
analogue. The two isomeric diplatinum(II) complexes undergo
oxidative addition of halogens to give metal-metal-bonded
dihalodiplatinum(III) species (Scheme 3), and the photo-
Received: September 30, 2013
Published: December 5, 2013
Article
pubs.acs.org/Organometallics
© 2013 American Chemical Society 7451 dx.doi.org/10.1021/om400961z | Organometallics 2013, 32, 7451-7459