Synthesis, characterization, and electrochemical relationships of dinuclear complexes of platinum(II) and platinum(III) containing ortho-metalated tertiary arsine ligands

Article abstract of DOI:10.1021/ic0498790

Reaction of 2-Li-4-MeC₆H₃AsPh₂ with [PtCl₂(SEt₂)₂] gives two isomeric dinuclear platinum(II) complexes, one containing a half-lantern structure with two chelating and two bridging C₆H₃-5-Me-2-AsPh₂ ligands, [Pt₂(κ²As,C-C₆H ₃-5-Me-2-AsPh₂)₂(μ-κAs,κC-C ₆H₃-5-Me-2-AsPh₂)₂], and the other, a full-lantern with four bridging C₆H₃-5-Me-2-AsPh ₂ ligands, [Pt₂(μ-κAs,κC-C ₆H₃-5-Me-2-AsPh₂)₄]. The lantern structure of the latter is retained in the dihalodiplatinum(III) complexes that are formed by oxidative addition of chlorine, bromine, or iodine to the isomeric mixture. The dichloro derivative undergoes metathesis reactions with silver or sodium salts, yielding the corresponding cyano, thiocyanato, cyanato, and fluoro species. The structures of all complexes have been determined by single-crystal X-ray analysis. The oxidative addition products have Pt-Pt distances in the range 2.65-279 A (cf. 2.89 A in the lantern diplatinum(II) structure), consistent with the presence of a Pt-Pt bond. Electrochemical data lead to the conclusion that an initial rapid one-electron process and subsequent chemical reactions produce the dihalodiplatinum(III) lantern structure when mixtures of the lantern and half-lantern complexes are oxidized by halogens. The electrochemical data also explain why chemical reduction of the dihalodiplatinum(III) complex produces only the lantern diplatinum(II) complex.

Full text of DOI:10.1021/ic0498790

Inorg. Chem. 2004, 43, 7752−7763
Synthesis, Characterization, and Electrochemical Relationships of
Dinuclear Complexes of Platinum(II) and Platinum(III) Containing
Ortho-Metalated Tertiary Arsine Ligands
Martin A. Bennett,†,‡ Suresh K. Bhargava,*,† Alan M. Bond,§ Alison J. Edwards,‡ Si-Xuan Guo,§
Steven H. Prive´r,† A. David Rae,‡ and Anthony C. Willis‡
School of Applied Sciences (Applied Chemistry), RMIT UniVersity, GPO Box 2476V,
Melbourne, Victoria 3001, Australia, Research School of Chemistry,
Australian National UniVersity, Canberra, A.C.T. 0200, Australia, and School of Chemistry,
Monash UniVersity, PO Box 23, Clayton, Victoria 3800, Australia
Received January 30, 2004
Reaction of 2-Li-4-MeC6H3AsPh2 with [PtCl2(SEt2)2] gives two isomeric dinuclear platinum(II) complexes, one containing
a half-lantern structure with two chelating and two bridging C6H3-5-Me-2-AsPh2 ligands, [Pt2(κ2As,C-C6H3-5-Me-2-
AsPh2)2( As,
µ
-
κ
κC-C6H3-5-Me-2-AsPh2)2], and the other, a full-lantern with four bridging C6H3-5-Me-2-AsPh2 ligands,
[Pt2( As,κC-C6H3-5-Me-2-AsPh2)4]. The lantern structure of the latter is retained in the dihalodiplatinum(III) complexes
µ-κ
that are formed by oxidative addition of chlorine, bromine, or iodine to the isomeric mixture. The dichloro derivative
undergoes metathesis reactions with silver or sodium salts, yielding the corresponding cyano, thiocyanato, cyanato,
and fluoro species. The structures of all complexes have been determined by single-crystal X-ray analysis. The
oxidative addition products have Pt−Pt distances in the range 2.65−2.79 Å (cf. 2.89 Å in the lantern diplatinum(II)
structure), consistent with the presence of a Pt
−Pt bond. Electrochemical data lead to the conclusion that an initial
rapid one-electron process and subsequent chemical reactions produce the dihalodiplatinum(III) lantern structure
when mixtures of the lantern and half-lantern complexes are oxidized by halogens. The electrochemical data also
explain why chemical reduction of the dihalodiplatinum(III) complex produces only the lantern diplatinum(II) complex.
Scheme 1
Introduction
Treatment of 2-LiC6H4PPh2 or 2-Li-4-MeC6H3PPh2 with
[PtCl2(SEt2)2] gives monomeric bis(chelate) complexes [Pt-
(κ2P,C-C6H3-5-R-2-PPh2)2] (R ) H, Me)1,2 which isomerize
slowly in refluxing toluene to the dinuclear species [Pt2(κ2P,C-
C6H3-5-R-2-PPh2)2(µ-κP,κC-C6H3-5-R-2-PPh2)2] (Scheme 1).3
Since there appears to be only one well-authenticated
* To whom correspondence should be addressed. E-mail: suresh.
bhargava@rmit.edu.au.
† RMIT University.
‡ Australian National University.
example of a complex containing a four-membered arsenic-
carbon chelate ring, [IrHCl(κ2As,C-C6H4AsPh2)(AsPh3)2],
which is formed by isomerization of [IrCl(AsPh3)3],4 we were
interested to see whether arsenic analogues of the phosphorus
monomeric and dimeric species could be made. Unexpect-
edly, the work has revealed the existence of a novel, lantern-
§ Monash University.
(1) (a) 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. (b) Bennett, M. A.; Bhargava, S. K.; Ke, M.; Willis, A. C. J.
Chem. Soc., Dalton Trans. 2000, 3537.
(2) Bennett, M. A.; Bhargava, S. K.; Prive´r, S. H. Unpublished work.
(3) Messelha¨user, J.; Bennett, M. A.; Bhargava, S. K.; Ditzel, E. J.;
Robertson, G. B.; Willis, A. C.; Berry, D. E. Presented at the XIIIth
International Conference on Organometallic Chemistry, Turin, Sep-
tember 4-9, 1988.
(4) Bennett, M. A.; Milner, D. L. J. Am. Chem. Soc. 1969, 91, 6983.
7752 Inorganic Chemistry, Vol. 43, No. 24, 2004
10.1021/ic0498790 CCC: $27.50
© 2004 American Chemical Society
Published on Web 10/28/2004

Dinuclear Complexes of Platinum Arsine Ligands
Scheme 2
shaped diplatinum(II) complex that contains only bridging
As,C ligands, whose P,C-analogue has never been detected.
Oxidative addition of halogens affords dihalodiplatinum(III)
complexes that retain the lantern structure, and electrochemi-
cal studies have enabled some of the mechanistic details of
the reactions to be elucidated.
Results
Ligand Synthesis. Since there is no convenient probe
analogous to 31P NMR spectroscopy available for tertiary
arsine complexes, we chose to study compounds derived
from the reagent 2-Li-4-MeC6H3AsPh2 containing a useful
1H NMR indicator group. The required precursor, 2-Br-4-
MeC6H3AsPh2, can be obtained by the reaction of 2-Br-4-
MeC6H3AsCl2 with PhMgBr, following the literature proce-
dure for the preparation of 2-BrC6H4AsPh2 from 2-BrC6H4-
AsCl2.5 A convenient alternative, which avoids the synthesis
of the dichloroarsine from 2-bromo-4-methylaniline, employs
the [PdCl2(MeCN)2]-catalyzed reaction of 3-bromo-4-iodo-
toluene with (trimethylsilyl)diphenylarsine (Scheme 2); the
latter reagent is easily prepared in high yield from the
reaction of Me3SiCl with LiAsPh2.6 It is worth noting that
the reaction of Scheme 2 is complete after ca. 2 h at 90 °C,
whereas the corresponding reaction of 2-BrC6H4I with Me3-
SiPPh2 is reported to require 100 h at 70 °C.7
Platinum(II) Complexes. The reaction of 2-Li-4-MeC6H3-
AsPh2 with [PtCl2(SEt2)2] in ether at -30 °C gave a yellow
solid with the empirical formula [Pt(MeC6H3AsPh2)2] in ca.
40% yield (Scheme 3). The 1H NMR spectrum in the
aromatic methyl region showed a pair of equally intense
singlets at δ 1.93 and 1.98 accompanied by a singlet at δ
2.18 of approximately the same intensity, thus suggesting
the presence of at least two species. Slow crystallization from
CH2Cl2/MeOH afforded crystals of two distinct compounds,
which were shown by X-ray crystallography to be isomeric
dinuclear platinum(II) complexes. As shown in Figure 1, the
major isomer 1 is structurally similar to its phosphorus
analogue; two of the C6H3-5-Me-2-AsPh2 groups behave as
chelate ligands, while the other two bridge the metal atoms.
Figure 1. Molecular structure of [Pt2(κ2As,C-C6H3-5-Me-2-AsPh2)2(µ-
κAs,κC-C6H3-5-Me-2-AsPh2)2] (1). Ellipsoids show 30% probability levels.
Hydrogen atoms have been deleted for clarity.
We refer to this as a half-lantern structure. In contrast, in
the minor isomer 2, all four C6H3-5-Me-2-AsPh2 groups span
the platinum atoms to give a lantern-type structure (Figure
2) that is similar in basic geometry to [Pt2(pop)4]4- (pop )
µ-P,P-pyrophosphite, P2O5H22-)8 and to many platinum(II)
dimers containing the donor atom sets S-S and N-S.9 Both
isomers exhibit strong green-yellow luminescence in the
solid state under UV irradiation. In contrast to the phosphorus-
based system,1,2 no evidence was found for a monomeric
species [Pt(κ2As,C-C6H3-5-Me-2-AsPh2)2].
1
In the H NMR spectrum of the mixture, the singlet at δ
2.18 is assigned to the methyl protons of the equivalent
bridging C6H3-5-Me-2-AsPh2 groups of 2, while the singlets
at δ 1.93 and 1.98 belong to the inequivalent C6H3-5-Me-
2-AsPh2 groups of 1. It is not known which corresponds to
the chelate and which to the bridging ligands. The ratio of
1 to 2 in typical preparations was ca. 2:1, as estimated by
integration, although heating the mixture in refluxing toluene
caused complete conversion into 2. The 1H NMR spectrum
of the mixture also shows a 4H singlet at δ 7.90 with 195Pt
satellites (JPt-H ) 58.4 Hz), which is well separated from
the other aromatic multiplets and can be assigned to the
aromatic protons ortho to the Pt-C bond. Coupling constants
Scheme 3
Inorganic Chemistry, Vol. 43, No. 24, 2004 7753

Bennett et al.
Scheme 4
1
Table 1. Aromatic Methyl and Ortho-Proton H NMR Data for
Diplatinum(II) and Diplatinum(III) Complexes of the Type
[Pt2X2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]a
X‚‚‚X
δ (Me)
δ (Hortho) (3JPt-H
)
X absent in (2)
Cl‚‚‚Cl (3)
2.18
2.19
2.16
2.12
2.23
2.22
2.17
2.18
7.90 (58.4)
8.32 (35.0)
8.49 (37.9)
8.90 (42.8)
8.60 (46.9)
7.79 (37.7)
7.90 (37.4)
8.04 (29.4)
Br‚‚‚Br (4)
I‚‚‚I (5)
NC‚‚‚CN (6)
SCN‚‚‚NCS (7)
OCN‚‚‚NCO (8)
F‚‚‚F (9)b
Figure 2. Molecular structure of [Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (2).
Ellipsoids show 30% probability levels. Hydrogen atoms have been deleted
for clarity. Asterisks denote atoms related by inversion symmetry.
a In CDCl3. b In CD2Cl2.
of a similar magnitude have been reported for the ortho-
proton of a η1-C6H4 group in cycloplatinated complexes
containing deprotonated 6-(1-methylbenzyl)-2,2′-bipyridine,
e.g., [PtCl{2-C6H4(CHMe)C5H3NC5H4N}].10 The fast atom
bombardment (FAB) mass spectrum of the mixture shows a
parent-ion peak corresponding to the dimer. The structures
of 1 and 2 are discussed in more detail below.
Platinum(III) Complexes. Addition of iodobenzene dichlo-
ride to a mixture of isomers 1 and 2 in CH2Cl2 gave
quantitatively an orange solid which showed only one methyl
1H NMR signal at δ 2.19 and a 4H singlet at δ 8.32 with
195Pt satellites (JPt-H ) 35.0 Hz) assignable to the ortho-
aromatic protons. Structural analysis of a crystal obtained
from CH2Cl2/MeOH showed the compound to be the
platinum(III)-platinum(III) lantern complex [Pt2Cl2(µ-
κAs,κC-C6H3-5-Me-2-AsPh2)4] (3) derived by oxidative ad-
dition of chlorine across the dinuclear unit of 2 (Scheme 4);
the same compound also formed over a period of days from
a solution of 1 and 2 in CH2Cl2 and, more rapidly, in CHCl3
or CCl4. Complex 1 evidently isomerizes under the reaction
conditions (probably via 1+, according to the electrochemical
studies), leading to 3 as the sole product. Zinc dust reduction
of 3 regenerates 2 free from 1.
to 3 as brick red and purple solids, respectively, by addition
of bromine or iodine to complex 2. Similar oxidative
additions are known for other diplatinum(II) lantern com-
plexes.8,9 Both compounds can also be obtained by anion
exchange from 3. Methyl iodide reacted over a period of
days with a solution of 2 in the dark to give 5; in laboratory
light the reaction was complete in 2-3 h. The highest mass
peak in the FAB mass spectra of 3-5 corresponds to the
loss of one halide ion. A strong band at 203 cm-1 in the IR
spectrum of 3 may be due to ν(PtCl), but the assignment is
tentative because there is strong ligand absorption in the
region of 500-150 cm-1.
Treatment of 3 with AgCN, NaSCN, NaNCO, or AgF gave
the corresponding dicyano-, bis(thiocyanato)-, bis(cyanato)-,
and difluorodiplatinum(III) complexes [Pt2X2(µ-κAs,κC-
C6H3-5-Me-2-AsPh2)4] (X ) CN (6), NCS (7), NCO (8),
and F (9)) as yellow solids, which were identified on the
basis of single-crystal X-ray studies (see below) and spec-
troscopic data. The highest peak in the electron ionization
(EI) mass spectra of 6-8 corresponds to the loss of one anion
while the parent ion was observed for 9. The solid-state IR
spectra of 6-8 each show a ν(CN) band in the 2100-2200
cm-1 region. In the case of 7, the broad ν(CN) band at 2086
cm-1 is suggestive of N-bonded thiocyanate, a feature that
is confirmed by the X-ray diffraction study (see below).
Criteria based on ν(CS), δ(NCS), or ν(M-NCS)11 could not
be applied because of numerous overlapping bands in the
appropriate regions.
The corresponding complexes [Pt2X2(µ-κAs,κC-C6H3-5-
Me-2-AsPh2)4] (X ) Br (4), I (5)) were obtained similarly
(5) (a) Jones, E. R. H.; Mann, F. G. J. Chem. Soc. 1955, 4472. (b) Cochran,
W.; Hart, F. A.; Mann, F. G. J. Chem. Soc. 1957, 2818. (c) Levason,
W.; McAuliffe, C. A. Inorg. Synth. 1976, 16, 184. (d) Talay, R.;
Rehder, W. Z. Naturforsch., B: Chem. Sci. 1981, 36, 451.
(6) Fenske, D.; Teichert, H.; Pokscha, H.; Renz, W.; Becher, H. Monatsh.
Chem. 1980, 111, 177.
(7) Tunney, S. E.; Stille, J. K. J. Org. Chem. 1987, 52, 748.
(8) (a) Zipp, A. P. Coord. Chem. ReV. 1988, 84, 47. (b) Roundhill, D.
M.; Gray, H. B.; Che, C. M. Acc. Chem. Res. 1989, 22, 55. (c)
Sweeney, R. J.; Harvey, E. L.; Gray, H. B. Coord. Chem. ReV. 1990,
105, 23.
The 1H NMR spectra of complexes 4-9 show the
characteristic 195Pt-coupled resonance for the ortho proton
3
in the region of δ 8 (see Table 1), the magnitude of JPt-H
2
(29.4-46.9 Hz) being ca.
/ of that observed in the
3
diplatinum(II) precursor 2. A similar relationship holds for
(9) (a) Woollins, J. D.; Kelly, P. F. Coord. Chem. ReV. 1985, 65, 115. (b)
Umakoshi, K.; Sasaki, Y. AdV. Inorg. Chem. 1994, 40, 187.
(10) Romeo, R.; Plutino, M. R.; Scolaro, L. M. Inorg. Chim. Acta 1997,
265, 225.
(11) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 5th ed.; John Wiley: New York, 1997; Part B,
pp 116-121.
7754 Inorganic Chemistry, Vol. 43, No. 24, 2004

Dinuclear Complexes of Platinum Arsine Ligands
1JPt-P in the diplatinum(II) complexes, [Pt2(pop)4]4-
and [Pt2(pcp)4],4- and their oxidative addition products,
[Pt2X2(pop)4]4- and [Pt2X2(pcp)4]4- (pcp ) [CH2{P(O)
OH}2]2-).12 In the case of planar platinum(II) and octahedral
platinum(IV) complexes, PtX2L2 and PtX4L2, the correspond-
ing trend in coupling constants such as 1JPt-P and 2JPt-CH is
3
generally attributed to the change in s-character of the Pt-L
bonding orbital in the two oxidation states.13,14 The magnitude
of 3JPt-H in complexes 3-9 is also sensitive to the nature of
the axial ligand X, ranging from 29.4 Hz (X ) F) and 35.0
Hz (X ) Cl) to 42.8 Hz (X ) I) and 46.9 Hz (X ) CN).
The presence of a covalent Pt-F bond in complex 9 was
confirmed by the 19F NMR spectrum in CD2Cl2, which shows
a singlet at δ -228.6 with two sets of 195Pt satellites (1JPt-F
2
) 492 Hz, JPt-F ) 192 Hz). The NMR parameters are
comparable with those of the few well-characterized fluo-
1
roplatinum complexes, the JPt-F values being intermediate
between those reported for Pt(II) and Pt(IV); cf. [PtIIF(PEt3)3]-
BF4 (250 Hz),15 trans-[PtIIF(PEt3)2(PPh3)]ClO4 (215 Hz),16
trans-[PtIIPhF(PPh3)2] (399 Hz),17 and [Me3PtIVF]4 (708 Hz).18
There was no evidence for the formation of a mixed oxi-
dation state complex [Pt2II,IIICl(µ-κAs,κC-C6H3-5-Me-2-
AsPh2)4] from solutions of equimolar amounts of 2 and 3.
Attempts to prepare a thiocyanato Pt2(II,III) species from
solutions of 2 and 7 also failed. In contrast, linear chain
Pt2(II,III) complexes of pop and dithioacetate, K4[Pt2X(pop)4]
(X ) Cl, Br, I) and [Pt2I(S2CMe)4] are readily formed.8b,9
The aromatic rings of the bulky AsPh2 groups possibly hinder
bridging of halide or thiocyanate between pairs of dimeric
units.
Figure 3. Molecular structure of [Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]
(3).20 Ellipsoids show 30% probability levels. Hydrogen atoms have been
deleted for clarity. Asterisks denote atoms related by inversion symmetry.
in Figures 1 and 2; selected bond lengths and angles are listed
in Tables S1 and S2, respectively. In both complexes the
coordinated arsenic atoms are mutually cis. The coordination
geometry about each metal atom is close to planar in 2 but
that in 1 is more distorted. The small bite angle of the four-
membered rings in 1 (69.7(3)° (av)) is similar to that of many
κ2P,C-C6H4-2-PPh2 complexes19 and is associated with a
widening of the As-Pt-As angles to ca. 106°. Correspond-
ing metal-ligand bond lengths in the bridging groups of 1
and 2 and the chelate groups of 1 do not differ significantly.
As expected, the Pt-As bond lengths in 1 and 2 are ca. 0.15
Å greater than the Pt-P bond lengths in [Pt2(κ2P,C-C6H4-
2-PPh2)2(µ-κP,κC-C6H4-2-PPh2)2], although the Pt‚‚‚Pt sepa-
ration in 1 (3.4208(3) Å) is only slightly greater than that in
[Pt2(κ2P,C-C6H4-2-PPh2)2(µ-κP,κC-C6H4-2-PPh2)2] (3.3875(4)
Å).3 The shorter Pt‚‚‚Pt separation in 2 (2.8955(4) Å) is
presumably a consequence of the four bridging groups; it
falls between those observed in similar lantern structures
containing N-S or S-S bridging groups such as 4-meth-
ylpyridine-2-thiolate and dithiocarboxylates (2.68 Å and
2.76-2.86 Å, respectively) on one hand and P-P bridging
groups such as pop (2.92-2.98 Å) on the other.8,9
In an effort to prepare sterically less hindered complexes
containing µ-κAs,κC-C6H4-2-AsMe2, we treated 2-LiC6H4-
AsMe2 with [PtCl2(SEt2)2]. Analysis of the resulting orange-
yellow solid showed the expected formulation, [Pt(C6H4-
1
AsMe2)2] (10), but its H NMR spectrum at 23 °C showed
broad multiplets for the aromatic and AsMe2 resonances that
did not sharpen when the solution was cooled to -80 °C.
Treatment of 10 with PhICl2 gave the expected oxidative
addition product, [Pt2Cl2(C6H4AsMe2)4] (11) as an orange
solid whose 1H NMR spectrum also showed broad aromatic
and AsMe2 resonances. Both 10 and 11 appeared to be
dimeric in ca. 0.2 M CH2Cl2 solution by vapor pressure
osmometry, but we could not obtain satisfactory mass spectra
or crystals adequate for an X-ray diffraction study. We
suspect that 10 and 11 may consist of a mixture of rapidly
interconverting oligomers in solution.
X-ray Crystallographic Determinations. The structures
of the isomeric diplatinum(II) complexes 1 and 2 are shown
The diplatinum(III) complexes 3-9 all have similar lantern
structures20 derived from addition of a pair of halide or
(12) King, C.; Roundhill, D. M.; Dickson, M. K.; Fronczek, F. R. J. Chem.
Soc., Dalton Trans. 1987, 2769.
(19) For platinum(II), see: (a) Clark, H. C.; Hine, K. E. J. Organomet.
Chem. 1976, 105, C32. (b) Rice, N. C.; Oliver, J. D. J. Organomet.
Chem. 1978, 145, 121. (c) Scheffknecht, C.; Rhomberg, A.; Mu¨ller,
E. P.; Peringer, P. J. Organomet. Chem. 1993, 463, 245. (d) Clark, H.
C. S.; Fawcett, J.; Holloway, J. H.; Hope, E. G.; Peck, L. A.; Russell,
D. R. J. Chem. Soc., Dalton Trans. 1998, 1249. (e) Bennett, M. A.;
Dirnberger, T.; Hockless, D. C. R.; Wenger, E.; Willis, A. C. J. Chem.
Soc., Dalton Trans. 1998, 271. (f) Bennett, M. A.; Berry, D. E.;
Dirnberger, T.; Hockless, D. C. R.; Wenger, E. J. Chem. Soc., Dalton
Trans. 1998, 2367. (g) Bender, R.; Bouaoud, S.-E.; Braunstein, P.;
Dusausoy, F.; Merabet, N.; Raya, J.; Rouag, D. J. Chem. Soc., Dalton
Trans. 1999, 735.
(13) Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition Metal
Phosphine Complexes; Springer: Berlin, 1979; p 23
(14) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV. 1973,
10, 335 and references therein.
(15) Dixon, K. R.; McFarland, J. J. J. Chem. Soc., Chem. Commun. 1972,
1274.
(16) Cairns, M. A.; Dixon, K. R.; McFarland, J. J. J. Chem. Soc., Dalton
Trans. 1975, 1159.
(17) Nilsson, P.; Plamper, F.; Wendt, O. F. Organometallics 2003, 22, 5235.
(18) Cross, R. J.; Haupt, M.; Rycroft, D. S.; Winfield, J. M. J. Organomet.
Chem. 1999, 587, 195.
Inorganic Chemistry, Vol. 43, No. 24, 2004 7755

Bennett et al.
Table 2. Crystal and Refinement Data for Complexes 1-9
1
2
3
4
5
formula
C76H64As4Pt2‚
1.5CH2Cl2
1794.61
C76H64As4Pt2‚
2CH2Cl2
1837.05
C76H64As4Cl2Pt2‚
4CH2Cl2
2077.85
C76H64As4Br2Pt2‚
4CH2Cl2
2166.62
C76H64As4I2Pt2‚
2CH2Cl2
2090.88
fw
crystal system
space group
a, Å
b, Å
c, Å
triclinic
P1h
monoclinic
P21/n
11.8523(1)
19.3514(2)
14.8829(2)
triclinic
P1h
triclinic
P1h
monoclinic
P21/c
13.9842(1)
13.0891(1)
39.8723(3)
12.0083(1)
12.9967(1)
23.1465(2)
91.6097(3)
96.7525(3)
110.253(4)
3356.45(5)
2
12.5394(2)
12.7062(2)
13.5404(3)
97.7853(9)
98.1840(10)
115.2438(9)
1884.53(6)
1
12.5730(1)
12.7721(1)
13.5519(1)
97.4468(5)
98.2516(6)
115.0814(4)
1906.5(3)
1
R, deg
â, deg
105.9379(5)
91.6151(3)
γ, deg
V, Å3
3282.3
2
7295.35(9)
4
Z
color, habit
cryst dimens (mm)
yellow block
0.40 × 0.26 × 0.14
1.776
6.283
15358 (0.047)
9237
green rod
0.37 × 0.11 × 0.07
1.859
6.6467
9585 (0.063)
5141
orange needle
0.16 × 0.09 × 0.05
1.831
5.85
8655 (0.057)
4906
red block
0.25 × 0.20 × 0.18
1.888
6.761
11150 (0.039)
9053
black needle
0.33 × 0.04 × 0.04
1.904
6.67
12843 (0.09)
10083
D
calc (g cm-3
)
µ (mm-1
)
no. indep reflns (Rint
no. of obsd refln
[I > 3σ(I)]
)
no. of params refined
784
393
433
434
277
R(F)
0.026
0.027
0.032
0.035
0.039
Rw(F)
F
0.028
0.59/-0.83
0.029
1.06/-1.30
0.036
0.88/-1.07
0.040
2.05/-3.28
0.054
1.65/-1.59
max/Fmin (e Å-3
)
6
7
8
9
formula
fw
C78H64As4N2Pt2‚
4CH2Cl2
2058.98
C78H64As4N2Pt2S2
C78H64As4N2O2Pt2‚
2CH2Cl2
1921.11
2[C76H64As4F2Pt2]‚
CH2Cl2‚H2O
3513.36
1783.38
crystal system
space group
a, Å
b, Å
c, Å
triclinic
P1h
monoclinic
C2/c
27.1169(3)
17.9852(3)
17.0499(3)
monoclinic
P21/c
13.8368(1)
13.0378(1)
40.5832(2)
monoclinic
P21/n
26.1349(1)
12.9746(1)
38.4786(3)
12.5155(1)
12.7912(1)
13.5105(2)
97.6692(5)
98.6654(5)
114.1778(5)
1904.15(4)
1
R, deg
â, deg
97.1223(6)
91.1694(2)
94.3806(2)
γ, deg
V, Å3
6425.44(18)
4
7319.74
4
13009.59(15)
4
Z
color, habit
cryst dimens (mm)
yellow plate
0.30 × 0.20 × 0.19
1.795
5.721
8746 (0.05)
7137
yellow needle
0.36 × 0.05 × 0.05
1.843
6.507
7358 (0.06)
4143
yellow plate
0.44 × 0.07 × 0.03
1.743
5.807
12849 (0.037)
9512
yellow plate
0.26 × 0.11 × 0.03
1.793
D
calc (g cm-3
)
µ (mm-1
)
6.407
no. indep reflns (Rint
no. of obsd refln
[I > 3σ(I)]
)
23024 (0.07)
12068a
no. of params refined
453
397
839
1559
R(F)
0.023
0.022
0.024
0.027
Rw(F)
F
0.025
0.84/-0.87
0.025
0.90/-0.81
0.026
1.07/-0.89
0.027
0.79/-0.89
max/Fmin (e Å-3
)
a [I g 2σ(I)].
pseudohalide groups along the axis of 2. The structure of
the dichloro complex 3 is shown in Figure 3. Selected bond
lengths and angles in complexes 3, 4, 6, and 7 are listed in
Table S2; those for complexes 5, 8, and 9 are given in Table
S3. As is evident from the crystal and refinement data in
Table 2, the CH2Cl2 solvates of the dichloro, dibromo, and
dicyano complexes, 3, 4, and 6, are isomorphous (space
group P1h, Z ) 1), as are the CH2Cl2-solvated diiodo- and
bis(cyanato)-complexes 5 and 8 (space group P21/c, Z ) 4).
In contrast, the bis(thiocyanato) complex 7 is not solvated
by CH2Cl2 and belongs to a different space group (C2/c, Z
) 4), while two molecules of the difluoro complex (9a and
9b) (P21/n, Z ) 4) are associated with one CH2Cl2 molecule
and one water molecule (the basis of the identification is
further discussed in Appendix S1). The Pt-Pt distances in
3-9 depend on the nature of the axial ligand X and are
significantly shorter than that in the parent complex 2,
consistent with the presence of a discrete single bond between
the 5d7 metal centers.
The Pt-Pt distances are shortest for the difluoride 9 (9a,
2.6530(4) Å; 9b, 2.6524(4) Å) and for complexes 7 and 8
containing N-bonded NCS and NCO (2.6870(3), 2.6772(2)
Å, respectively) and longest for the C-bonded dicyano
complex 6 (2.7910(2) Å). A similar trend can be seen in the
diplatinum(III) complexes containing pop; the shortest Pt-
Pt distance occurs in the N-donor acetonitrile complex
[nBu4N]2[Pt2(pop)4(NCMe)2] (2.676(1) Å),21 while the longest
(20) The metal-metal vectors are generally not exactly perpendicular to
the plane of the Pt and the four attached atoms, as can be seen from
the range of metal-metal attached atom angles in Tables S2 and S3.
(21) Che, C. M.; Mak, T. C. W.; Miskowski, V. M.; Gray, H. B. J. Am.
Chem. Soc. 1986, 108, 7840.
7756 Inorganic Chemistry, Vol. 43, No. 24, 2004

Dinuclear Complexes of Platinum Arsine Ligands
occurs in the methyl iodide oxidative addition product K4-
[Pt2(I)(Me)(pop)4]‚2H2O (2.782(1) Å).22 The distances in the
dihalo complexes are essentially equal for the dichloride (3)
and dibromide (4) (2.7444(5) and 2.7457(1) Å, respectively)
and are slightly greater in the diiodide (5) (2.752(1) Å); they
are also similar to the Pt-Pt distances in corresponding
lantern complexes derived from pop and pcp, e.g., 2.7500-
(3) Å in K4[Pt2Cl2(pcp)4]‚8H2O (12),12 2.695(1) Å in
K4[Pt2Cl2(pop)4]‚2H2O (13),23 2.723(4) Å in K4[Pt2Br2-
(pop)4]‚2H2O (14),24 2.716(1) Å in [nBu4N]4[Pt2Br2(pop)4]
(15),25 2.754(1) Å in K4[Pt2I2(pop)4]‚2H2O (16),25 and
2.742(1) Å in K2[nBu4N]2[Pt2I2(pop)4] (17).25
The Pt-halide distances in 3-5 and 9 are ca. 0.15-0.20
Å longer than the distances found in [PtX6]2-, reflecting the
high trans-influence of the Pt-Pt bond. The Pt-Cl distance
in 3 (2.4884(16) Å) is also significantly greater than those
in 12 (2.442(1) Å)16 or 13 (2.407(2) Å),23 perhaps reflecting
the greater bulk and stronger electron-donating ability of the
bridging As-C ligand relative to those of pop. There is a
similar trend in the Pt-I distances (5, 2.779(1) Å; 16, 2.742-
(1) Å;25 17, 2.721(1) Å25). Complex 9 is unique in that there
are no analogous lantern-type dimers containing terminal
fluoride ligands; an unsupported dimer containing R-dioxi-
mato ligands has been reported,26 although no characteriza-
tion details are given. The Pt-F distances (see Table S3) in
9 (9a, 2.139(4), 2.100(4) Å; 9b, 2.172(5), 2.128(4) Å for
the two independent molecules in the asymmetric unit) lie
in the range found for the platinum(II) salt [PtF(PEt3)3]BF4
(2.043(7) Å)27 and the platinum(IV) complex [PtMe3F]4
(2.251(6) Å)18 in which fluoride is trans to a ligand of high
trans-influence; the Pt-F distances in platinum(IV) com-
plexes containing mutually trans-fluorides are much shorter,
e.g. 1.930(2) Å in trans-[nBu4N]2[PtF2(C2O4)2]28 and 1.938(10),
1.943(10) Å in trans-[PtF2(py)4][BF4]2‚H2O.29
Crystalline 7 and 8 contain N-bonded thiocyanate and
cyanate, respectively; in both cases, as commonly observed
in mononuclear complexes of these ligands, the Pt-N-C
bond angles deviate markedly from linearity (7, 164.8(4)°;
8, 146.2(3)°, 166.1(5)°). In contrast to 7, the pop analogue
contains S-bonded thiocyanate in the solid state.30 The Pt-N
distances in 7 and 8, and the Pt-C distances in 6, are all
longer than those found in typical cyanato-, thiocyanato-,
and cyano-platinum(II) complexes, respectively, again re-
flecting the high trans-influence of the Pt-Pt bond. The Pt-
Figure 4. Cyclic voltammogram obtained for oxidation of a 1.0 mM
solution of complex 2 at a 1 mm diameter GC working electrode in
dichloromethane (0.1 M Bu4NPF6) at a scan rate of 1000 mV s-1
.
As and Pt-C distances in the diplatinum(II) complexes 1
and 2 are, separately, not significantly different (ca. 2.43-
2.47 Å, 2.02-2.05 Å, respectively). Oxidative addition to
form the diplatinum(III) complexes 3-9 produces little effect
on the Pt-As distances but does lead to a significant
lengthening in the Pt-C distances to ca. 2.10-2.13 Å.
Electrochemical Oxidation of [Pt2(µ-κAs,κC-C6H3-5-
Me-2-AsPh2)4] (2). Three processes are detected for the
voltammetric oxidation of 2 in dichloromethane (0.1 M Bu4-
NPF6). The first process, labeled 1 in Figure 4, is chemically
and electrochemically reversible with a reversible formal
potential (Ef0) of -165 ( 5 mV vs Fc/Fc+ at both glassy
carbon and platinum disk electrodes. This process is as-
signed31 to the structurally conserved 20/+ couple (eq 1).
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] h
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ + e- (1)
The second and third oxidation processes (labeled 2 and 3
in Figure 4) are irreversible and have peak potentials (Eopx)
near 1.0 and 1.5 V vs Fc/Fc+. The irreversibility suggests
that a gross structural change accompanies more extensive
oxidation to a diplatinum(III) complex. The overall reaction
scheme is consistent with eq 2.
-
-
[Pt2(II,II)] y- e z [Pt2(II,III)]+ y- e z
+ e-
+ e-
[Pt2(III,III)]2+ f electroactive product (2)
(22) Che, C. M.; Mak, T. C. W.; Gray, H. B. Inorg. Chem. 1984, 23, 4386.
(23) Che, C. M.; Herbstein, F. M.; Schaefer, W. P.; Marsh, R. E.; Gray,
H. B. J. Am. Chem. Soc. 1983, 105, 4604.
(24) Clark, R. J. H.; Kurmoo, M.; Dawes, H. M.; Hursthouse, M. B. Inorg.
Chem. 1986, 25, 409.
(25) Alexander, K. A.; Bryan, S. A.; Fronczek, F. R.; Fultz, W. C.;
Rheingold, A. L.; Roundhill, D. M.; Stein, P.; Watkins, S. F. Inorg.
Chem. 1985, 24, 2803.
(26) Baxter, L. A. M.; Heath, G. A.; Raptis, R. G.; Willis, A. C. J. Am.
Chem. Soc. 1992, 114, 6944.
(27) Donath, H.; Avtomonov, E. V.; Sarraje, I.; von Dahlen, K. H.; El-
Essawi, M.; Lorberth, J.; Seo, B. S. J. Organomet. Chem. 1998, 559,
191.
(28) Uttecht, J. G.; Na¨ther, C.; Preetz, W. Z. Anorg. Allg. Chem. 2002,
628, 2847.
Cyclic voltammograms obtained after a one-electron bulk
oxidative electrolysis of 2 at a platinum electrode using a
controlled potential of +170 mV vs Fc/Fc+ (between
processes 1 and 2) exhibit exactly the same three processes
shown in Figure 4. However, while processes 2 and 3 remain
oxidative, reversible process 1 is now reductive and corre-
sponds to the reaction 2+/0 instead of 20/+ as was the case
prior to bulk electrolysis. Thus, a stable lantern 2+ species
exists on the voltammetric and bulk electrolysis time scales
(29) Drews, H. H.; Preetz, W. Z. Anorg. Allg. Chem. 1997, 623, 509.
(30) Che, C. M.; Lee, W. M.; Mak, T. C. W.; Gray, H. B. J. Am. Chem.
Soc. 1986, 108, 4446.
(31) Bennett, M. A.; Bhargava, S. K.; Boas, J. F.; Boere´, R. T.; Bond, A.
M.; Edwards, A. J.; Guo, S. X.; Hammerl, A.; Pilbrow, J. R.; Prive´r,
S. H.; Schwerdtfeger, P. To be submitted for publication.
Inorganic Chemistry, Vol. 43, No. 24, 2004 7757

Bennett et al.
is noted that the potential of reduction peak 1 is very similar
to the reduction peak potential of complex 2+ and that in
multicycling experiments with 1, the process now assigned
to the reaction 20/+ has the same characteristics as those
detected with bulk solutions of pure 2. Additionally, after a
one-electron bulk oxidative electrolysis at a controlled
potential of +400 mV vs Fc/Fc+, cyclic voltammograms have
the same number of peaks and same peak potentials to those
formed after bulk electrolysis of 2. That is, processes 4 and
5 disappear with only reversible process 2+/0 being detected
(now reductive) along with oxidative processes 2 and 3 at
very positive potentials (see Figure 4).
When the scan rate is increased to 10 V s-1, the oxidation
process is chemically reversible (coupled homogeneous
chemical isomerization reactions are now insignificant). The
0
Figure 5. Cyclic voltammogram for oxidation of 1.0 mM solution of
complex 1 at a 1 mm diameter GC working electrode in dichloromethane
Ef value of 150 ( 5 mV obtained at fast scan rates from
the average of the oxidation and reduction peak potentials
confirms that complex 1 is thermodynamically more difficult
to oxidize than 2 by about 300 mV. A theoretical rationaliza-
tion of the differences in potential will be presented in future
work.31
The ladder square scheme32-34 mechanism, summarized
in eq 5, is consistent with the cyclic voltammetry and bulk
electrolysis experiments
(0.1 M Bu4NPF6) at a scan rate of 500 mV s-1
.
and is also accessible by the action of very mild chemical
oxidants such as Fc+.31 In contrast, very powerful chemical
oxidants would be required to reach oxidation states beyond
the mixed-valent Pt2(II,III) species. Iodine would certainly
not be a sufficiently powerful oxidizing agent to doubly
oxidize 2 to 22+ but is predicted to enable 2+ to be formed
along with I- and hence enable the lantern structured [Pt2I2-
(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] complex 5 to be formed
by a reaction sequence of the kind presented in eqs 3a-c.
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] + 1/2I2 h
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ + I- (3a)
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ + I- f
[Pt2I(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (3b)
where X and X+ are intermediates of unknown structure.
Simulations, rotating disk electrode, and electron paramag-
netic resonance data in support of eq 5 will be presented in
a forthcoming paper.31 This scheme implies that chemical
oxidation of half-lantern 1 will generate 2+, thus explaining
why the overall oxidative additive reactions commencing
with either 1 or 2 or mixtures produce dihalodiplatinum(III)
complexes containing the lantern structure present in 2+.
Complex 1 also exhibits a second chemically irreversible
oxidation process at 1500 ( 5 mV at a scan rate of 500 mV
s-1. In view of the close proximity to the solvent limit, the
details of the second process could not be elucidated, but it
probably represents the oxidation of 1+/X+/2+ to a transient
Pt2(III,III) dinuclear or other electroactive complexes as has
been assumed to occur when 2 is oxidized at very positive
potentials (see eq 2). Like 2, 1 is not detected to undergo
reduction under voltammetric conditions, even at potentials
as negative as -3000 mV.
2[Pt2I(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] f
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] +
[Pt2I2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (3c)
The failure to detect the proposed intermediate [Pt2I(µ-
κAs,κC-C6H3-5-Me-2-AsPh2)4] is consistent with rapid dis-
proportionation (eq 3c). Overall, this series of reactions
corresponds to a net oxidative addition (eq 4).
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] + I2 h
[Pt2I2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (4)
Electrochemical Oxidation of [Pt2(κ2As,C-C6H3-5-Me-
2-AsPh2)2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)2] (1). Crystals of
1 were manually separated from the mixture of 1 and 2 to
provide low concentrations of pure 1. A cyclic voltammo-
gram of 1 (Figure 5) at a scan rate of 500 mV s-1 contains
an oxidation peak at about 200 mV, which is approximately
300 mV more positive than that for the 2 f 2+ process.
Three reduction processes at about 100, -60, and -200 mV
(vs Fc/Fc+), labeled 4, 5, and 1, respectively, also are
observed in the reverse scan. Thus, it is proposed that
complex 1 is initially oxidized to 1+, which, in a two-step
process, forms complex 2+. In support of this hypothesis, it
Electrochemical Reduction of [Pt2Cl2(µ-κAs,κC-C6H3-
5-Me-2-AsPh2)4] (3). A cyclic voltammogram of complex
(32) Bond, A. M.; Keene, F. R.; Rumble, N. W.; Searle, G. H.; Snow, M.
R. Inorg. Chem. 1978, 17, 2847.
(33) Bond, A. M.; Hambley, T. W.; Snow, M. R. Inorg. Chem. 1985, 24,
1920.
(34) Evans, D. H. Chem. ReV. 1990, 90, 739.
7758 Inorganic Chemistry, Vol. 43, No. 24, 2004

Dinuclear Complexes of Platinum Arsine Ligands
Figure 7. Electronic spectra of 0.25 mM complex 3 in dichloromethane
(0.1 M Bu4NPF6) before electrolysis (s), after reductive electrolysis at
-1500 mV (- -), and after oxidative electrolysis at +70 mV (‚‚‚).
electrolysis (Figure 6a) was now present as a primary
oxidation process (Figure 6b).
Oxidative bulk electrolysis of the reduced species at a
potential of 70 mV vs Fc/Fc+ re-formed complex 3;
voltammograms obtained before and after the bulk electroly-
sis reductive-oxidative sequence were very similar (8% loss
of complex 3 estimated). However, despite the inherent
complexity of the reaction scheme implied by the voltam-
metric measurements, on the synthetic (bulk electrolysis) time
scale the reduction-oxidation cycle is close to chemically
reversible (loss of less than 10% of complex 3 detected per
cycle on the basis of voltammetric evidence) and corresponds
to eq 6. The electrochemical data are consistent with the
observation that chemical reduction of 3 with zinc dust gives
pure 2 (complete absence of 1).
Figure 6. Cyclic voltammograms obtained at a scan rate of 1000 mV s-1
with a 3 mm diameter GC working electrode for (a) reduction of 0.25 mM
3 in dichloromethane (0.1 M Bu4NPF6) over a wide potential range and (b)
cyclic voltammogram obtained in the oxidation potential range before (‚‚‚)
and after (s) reductive bulk electrolysis at -1500 mV (vs Fc/Fc+) with a
platinum basket electrode.
[Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] + 2e- h
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] + 2Cl- (6)
3 (Figure 6a) at a scan rate of 1000 mV s-1 exhibits a
reduction peak at -1390 mV vs Fc/Fc+ along with a shoulder
at less negative potential. When the scan direction is reversed,
an oxidation peak is observed at -115 mV, which is
attributed to the oxidation of one or more reduction products
since no oxidation process is detected when the potential is
initially scanned in the positive direction (Figure 6a).
However, the nature of the reductive component of the cyclic
voltammetry depends very much on the number of cycles
of the potential (Figure S1), the scan rate (compare Figure
6a and S1), and the electrode surface (Figure S2), implying
that the reduction mechanism is complex. In contrast, the
oxidative process coupled to the reduction step is essentially
independent of electrode surface (Figure S2). No evidence
for further reduction was detected in the negative potential
range (-1500 mV to solvent limit) at glasy carbon (-3000
mV), platinum, or gold electrodes.
In situ spectroelectrochemical studies undertaken at a
platinum gauze electrode are completely consistent with eq
6. The electronic spectrum of the reduction product (Figure
7) has absorption bands at 405 and 360 nm and closely
resembles that of complex 2. Moreover, oxidation at 70 mV
vs Fc/Fc+ leads to close to 100% recovery of the initial
spectrum for complex 3.
Neither reduction nor oxidation are believed to occur by
a single-step, two-electron transfer. Rather, the data imply
that one-electron intermediates are involved and that these
do not need to be the same for the reduction and oxidation
directions of eq 6. It is known that the oxidation of complex
2 in the absence of chloride produces 2+ as a stable entity.
In the presence of 2 equiv of halide (Cl- and Br-), the
reversible cyclic voltammogram for the 20/+ process (Figure
3) becomes an irreversible two-electron oxidative process
with all the characteristics noted after bulk reduction of 3 to
2 (eq 6, Figure 6b). Consequently, oxidation in the presence
of Cl- is assumed to be modified so as to occur via an ECE
type reaction scheme for which a plausible representative
example is given in eqs 7a-c.
The overall results obtained by bulk electrolysis are readily
interpreted. Cyclic voltammetric measurements made after
bulk electrolysis revealed that the chemically irreversible
oxidation process detected on reverse scans prior to bulk
Inorganic Chemistry, Vol. 43, No. 24, 2004 7759

Bennett et al.
3
value of JPt-H, and the shorter Pt-Pt distances (9, X ) F;
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] h
3
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ + e-(E) (7a)
3, X) Cl) correspond with smaller values of JPt-H. In this
limited series, the correspondence is not exact, e.g., the value
of 3JPt-H for X ) NCO (8) is higher and that of X ) Cl (3)
is lower than the values that would be expected on the basis
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ + 2Cl- h
[Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]-(C) (7b)
3
of the Pt-Pt separations. The magnitudes of JPt-H fall in
the order X ) CN > I > Br > NCS > NCO > Cl > F,
which is similar to, though does not correspond exactly with,
orders of trans-influence based on, for example, ν(PtH) and
[Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]- h
[Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] + e-(E) (7c)
1
1JPt-H in trans-[PtHX(PR3)2], JPt-P in [PtXMe(dppe)], and
2JPt-H in methylplatinum(II) complexes.14,38 Since the cou-
pling constants in these cases are known to be positive39,40
and decrease with increasing trans-influence, it seems likely
that 3JPt-H in complexes 2-9 is negative, as is also the case
Numerous disproportionation and related second-order
processes and other intermediates also could give rise to the
final product (complex 3). The reduction process also may
be postulated to proceed via ECE type schemes. Irrespective
of the details of the mechanism, in the presence of a ligand
such as Cl-, an overall two-electron oxidative addition-
reductive elimination sequence is available, whereas in the
absence of a coordinating ligand, one-electron oxidized 2+
is detected as a stable compound.31
3
for JP-H (cis) in methylplatinum(II) complexes.40
We have so far been unable to isolate mixed-valent
Pt2(II,III) species of the type [Pt2X(µ-κAs,κC-C6H3-5-Me-
2-AsPh2)4] (X ) anionic ligand). Although complexes of this
type are well-known with pop and other bridging ligands,
such as dithioacetate, the pop compounds are reported to
disproportionate readily in aqueous solution.9b,24 Such Pt2(II,III)
halide bridged intermediates are very likely to be associated
with the electrochemistry of 3. Interestingly, the electro-
chemical studies demonstrate that the mixed-valence cation
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ is stable and long-
lived in solution in the absence of halide ion; this may
provide access to a wider range of diplatinum(III) complexes
containing the As-C bridging system.
The electrochemical data enable the synthetic results in
this work to be fully rationalized, in particular, the exclusive
formation of the complexes 3-5 from oxidation of complex
1 or 2 with halogen (X2). In the case of the oxidation of 2,
no structural change need occur with respect to the Pt
bonding after an initial one-electron oxidation by X2 to
generate 2+ and X-. These products of the initial redox
process can then react with each other to produce a halide
adduct of the one-electron-oxidized product, as shown in eqs
3a and 3b, with X replacing I.
Discussion
Although there are many examples of quadruply bridged
diplatinum(II) and diplatinum(III) complexes with a lantern
geometry,8,9 complexes 2-8 represent the first examples
containing a tertiary arsine. Moreover, there is only one
previous example of a diplatinum(III) complex of this type
containing a carbon-donor ligand, [Pt2Cl2(µ-κO,κO-O2CMe)2-
(µ-κO,κC-CH2CO2)2]2-.35
The isolation of the dinuclear complexes 1 and 2 rather
than a mononuclear species [Pt(κ2As,C-C6H3-5-Me-2-As-
Ph2)2] and the conversion of 1 into the lantern dimer 2
demonstrate that the bridging µ-κAs,κC-mode is favored over
κ2-binding for ortho-metalated arylarsines. Isomerization
from κ2As,C- to µ-κAs,κC-binding requires dissociation of
the Pt-As bond; this process evidently occurs more readily
than that of the corresponding Pt-P bond, reflecting the
weaker Pt-As interaction and the greater size of arsenic
compared with phosphorus.
There is considerable similarity in the chemistry and
structures between the platinum complexes of µ-κAs,κC-
C6H3-5-Me-2-AsPh2 and those containing diarylformamidi-
nato (DArF) ligands. For example, the initially formed half-
lantern dinuclear complex Pt2(κ2N,N-DArF)2(µ-κN,κN-
DArF)2 isomerizes on heating to the lantern structure,
analogous to complexes 1 and 2, respectively.36 The corre-
sponding dichlorodiplatinum(III) and Pt2(II,III) mixed-valent
complexes have also been prepared.36,37
The intermediate [Pt2X(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]
may disproportionate, as shown in eq 3c for X ) I or, in the
case of the stronger oxidant chlorine, could undergo further
oxidation to give directly the final oxidative addition product
3 (eq 8).
[Pt2Cl(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] + 1/2Cl2 f
[Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (8)
The bond lengths to the axial ligands in complexes 3-9
clearly show that the Pt-Pt bond exerts a strong trans-
influence. Moreover, the effects of different axial ligands
In the case of oxidation of 1, according to the electrochemical
studies, isomerization of initially formed 1+ to 2+ provides
the opportunity to achieve the structural change needed to
ultimately give 3 (eqs 9a-c, then as in eq 3 or 7).
are reflected both in the Pt-Pt distances and in the values
3
of JPt-H
(
195Pt coupling to the ortho proton). The longest
Pt-Pt separation (6, X ) CN) corresponds to the largest
(35) Yamaguchi, J.; Sasaki, Y.; Ito, T. J. Am. Chem. Soc. 1990, 112, 4038.
(36) Cotton, F. A.; Matonic, J. H.; Murillo, C. A. Inorg. Chem. 1996, 35,
(38) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738.
(39) (a) McFarlane, W. Chem. Commun. 1967, 772. (b) Dean, R. R.; Green,
J. C. J. Chem. Soc. A 1968, 3047.
498.
(37) Cotton, F. A.; Matonic, J. H.; Murillo, C. A. Inorg. Chim. Acta 1997,
264, 61.
(40) Bennett, M. A.; Bramley, R.; Tomkins, J. B. J. Chem. Soc., Dalton
Trans. 1973, 166.
7760 Inorganic Chemistry, Vol. 43, No. 24, 2004

Dinuclear Complexes of Platinum Arsine Ligands
[Pt2(κ2As,C-C6H3-5-Me-2-AsPh2)2
n-hexane, and toluene were dried over sodium/benzophenone,
dichloromethane over calcium hydride, and methanol over 4 Å
(µ-κAs,κC-C6H3-5-Me-2-AsPh2)2] + 1/2X2 h
[Pt2(κ2As,C-C6H3-5-Me-2-AsPh2)2
1
molecular sieves. H NMR (200 MHz) and 13C NMR (50 MHz)
spectra were measured on a Varian Gemini 2000 spectrometer at
room temperature in acid-free CDCl3 or CD2Cl2. Chemical shifts
(δ) are given in ppm, internally referenced to residual solvent signals
(1H, δ 5.32 for CD2Cl2 and δ 7.26 for CDCl3; 13C, δ 77.0 for
CDCl3); multiplicities are quoted without 195Pt satellites. 19F NMR
(282 MHz) spectra were acquired on a Varian Unity Inova 300
spectrometer, internally referenced to CFCl3. Elemental analyses
were performed by the Microanalytical Unit at the Research School
of Chemistry, ANU, Canberra, on samples that had been dried at
50 °C in vacuo to remove residual solvent. The carbon analyses
for complexes containing nitrogen (6-8) were consistently low,
perhaps due to incomplete combustion. Mass spectral data were
obtained on a VG ZAB-2SEQ (FAB with NOPE as matrix) or HP
5970 MSD (EI) spectrometer. IR spectra in the ranges 4000-400
cm-1 and 400-30 cm-1 were obtained as KBr and polythene disks,
respectively, on a Perkin-Elmer Spectrum 2000 FT-spectrometer.
Molecular weights were determined on a Knauer vapor pressure
osmometer with ∼0.2 M CH2Cl2 solutions at 37 °C. Melting points
were measured on a Gallenkamp melting point apparatus in open
glass capillaries and are uncorrected. Me3SiAsPh2,6 3-Br-4-IC6H3-
Me,43 2-BrC6H4AsMe2,5c PhICl2,44 [PtCl2(SEt2)2],45 and [PdCl2-
(NCMe)2]46 were prepared by literature methods, and the ligand
(µ-κAs,κC-C6H3-5-Me-2-AsPh2)2]+ + X- (9a)
[Pt2(κ2As,C-C6H3-5-Me-2-AsPh2)2
(µ-κAs,κC-C6H3-5-Me-2-AsPh2)2]+ f
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ (via intermediate)
(9b)
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]+ + X- h
[Pt2X(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (9c)
According to the electrochemical data, reduction of 3 can
occur without the need for a structural change around the Pt
core in any of the intermediates to give finally 2 and X-.
The fact that chemical reduction of 3 with zinc dust produces
isomerically pure 2 also is therefore explained on the basis
of the electrochemical results.
Although oxidative additions to dinuclear metal complexes
have attracted much attention, little is known about their
mechanism.41,42 The present work indicates that the apparent
two-electron oxidation by halogens involves one-electron
changes, at least in the system studied. The fact that complex
2 is oxidized more readily than 1 can be correlated with the
shorter metal-metal separation in the former, which allows
formation of the stabilizing 5d7-5d7 interaction.
7
2-Br-4-MeC6H3AsPh2 was prepared by a modified literature
method, the details of which are given below.
Tetrabutylammonium hexafluorophosphate (Bu4NPF6) (GFS)
used as the supporting electrolyte was purified according to a
literature method.47 Electrochemical data were obtained with a BAS
model 100B electrochemical workstation. The auxiliary electrode
was always platinum gauze. The potential of the Ag/AgCl (CH2Cl2,
saturated LiCl) reference electrode was always calibrated against
that of the ferrocene/ferrocenium (Fc/Fc+) redox couple. The 1 mm
diameter glassy carbon (GC) or platinum voltammetric working
electrodes were polished and cleaned prior to use. For bulk
electrolysis, the working electrode was cylindrical platinum gauze.
Spectroelectrochemical studies were undertaken with a Cary 5 UV-
visible-NIR spectrophotometer interfaced to a BAS model 100A
electrochemistry system. A rectangular quartz cuvette (1 mm path
length) was used as the electrochemical cell with a platinum gauze
working electrode. All electrochemical studies were carried out at
20 ( 1 °C. Dichloromethane solutions were always purged with
solvent-saturated nitrogen gas.
Conclusions
In this study, we have prepared novel dinuclear Pt(II) and
Pt(III) complexes containing cyclometalated tertiary arsine
ligands, including the first fully characterized example of a
difluoro complex of diplatinum(III). Two isomers, [Pt2(κ2As,C-
C6H3-5-Me-2-AsPh2)2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)2] and
[Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4], have been structurally
characterized in the case of the Pt(II) oxidation state, and
the spontaneous isomerization from κ2As,C- to µ-κAs,κC-
binding mode was observed. Conversion to this binding mode
is promoted by heat, chemical, or electrochemical oxidation,
demonstrating that the lantern configuration is thermody-
namically favored. Electrochemical studies of the oxidation
of [Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] and the reduction
of [Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] provide insights
into the mechanisms associated with oxidative addition and
reductive elimination of dinuclear complexes. In particular,
the electrochemical data implicate the presence of mixed-
valent one-electron-oxidized or -reduced species as being
important intermediates in the overall two-electron chemical
oxidation/reduction pathways.
Crystals adequate for X-ray diffraction studies were grown by
layering a dichloromethane solution of the complex with methanol
(complexes 1-8) or n-pentane (complex 9). Selected crystal data
and details of data collection and structure refinement are in Table
2. Crystals were coated in viscous oil and mounted on fine drawn
glass capillaries, and data were collected at 200 K on a Nonius-
Kappa CCD diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). The data were measured by use of
COLLECT;48 the intensities of the reflections were extracted, and
the data reduced by use of the computer programs Denzo and
Experimental Section
(43) Bhargava, S. K.; Mohr, F.; Bennett, M. A.; Welling, L. L.; Willis, A.
C. Organometallics 2000, 19, 5628.
(44) Lucas, H. J.; Kennedy, E. R. Organic Synthesis; Wiley and Sons: New
York, 1955; Collect. Vol. 3, p 482.
(45) Kauffman, G. B.; Cowan, D. O. Inorg. Synth. 1960, 6, 211.
(46) Hartley, F. R.; Murray, S. G.; McAuliffe, C. A. Inorg. Chem. 1979,
18, 1394.
(47) Kissinger, P. T.; Heineman, W. R. Laboratory Techniques in Elec-
troanalytical Chemistry; Marcel Dekker: New York, 1984; p 481.
(48) COLLECT Software, Nonius BV, 1997-2001.
General Comments. All experiments involving organolithium
reagents were performed under an atmosphere of dry argon with
use of standard Schlenk techniques. Diethyl ether, tetrahydrofuran,
(41) Collman, J. P.; Hegedus, L.; Norton, R.; Finke, R. G. Principles and
Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; Chapter 5, pp 306-322.
(42) Fackler, J. P., Jr. Polyhedron 1997, 16, 1.
Inorganic Chemistry, Vol. 43, No. 24, 2004 7761

Bennett et al.
Scalepak.49 The structures were solved by direct methods (SIR9250
for 1, 2, and 4-9; SIR9751 for 3) and refined on F with use of
CRYSTALS52 or, in the case of the twinned crystal of 5, RAELS
2000.53 Calculations were performed with use of crystallographic
software packages teXsan,54 maXus,55 and CRYSTALS.52 The
neutral atom scattering factors were taken from ref 56. The mass
attenuation coefficients were those implemented in maXus.55
Nonroutine aspects of X-ray crystallographic determinations of 1-9
are detailed in Appendix S1.
Preparations. 2-Br-4-MeC6H3AsPh2. To a solution of 3-bromo-
4-iodotoluene (13.08 g, 44.0 mmol) and [PdCl2(NCMe)2] (0.28 g,
1.07 mmol) in toluene (30 mL) under argon, (trimethylsilyl)-
diphenylarsine (14.01 g, 46.3 mmol) was added, and the dark
solution was heated to ca. 90 °C for 2 h. To the cooled mixture,
chloroform (30 mL) was added, and the orange solution was washed
with saturated sodium bicarbonate solution, water, and brine. The
organic layer was separated and dried (MgSO4), and the solvent
was removed. The dark oil was chromatographed on a silica gel
column and eluted with 1:1 toluene/hexanes. Removal of the solvent
and recrystallization from ethanol gave white needles (14.25 g,
81%). 1H NMR: δ 2.32 (s, 3H, Me), 6.72 (d, JH-H ) 7.7 Hz, 1H,
aromatic H), 7.00 (dd, JH-H ) 0.9, 7.7 Hz, 1H, aromatic H), 7.43
(d, JH-H ) 0.9 Hz, 1H, aromatic H), 7.2-7.4 (m, 10H, aromatics).
13C NMR: δ 20.8, 128.5, 128.6, 128.7, 130.0, 133.2, 133.8, 134.6,
137.9, 139.0, 140.5. EI-MS (m/z): 398 [M]+. Anal. Calcd for
C19H16AsBr: C, 57.17; H, 4.04; Br, 20.02. Found: C, 57.36; H,
4.12; Br, 20.26.
Ratio 1:2 typically ca. 2:1. FAB-MS (m/z): 1666 [M]+. Anal. Calcd
for C76H64As4Pt2: C, 54.75; H, 3.87. Found: C, 54.64; H, 3.97.
[Pt2Cl2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (3). To a solution
containing a mixture of 1 and 2 (186 mg, 0.11 mmol) in CH2Cl2
(15 mL), iodobenzene dichloride (31 mg, 0.11 mmol) dissolved in
CH2Cl2 (5 mL) was added, causing an immediate color change from
yellow to orange. After the mixture was stirred for 10 min, the
solution was evaporated to dryness, and the residue was recrystal-
lized from CH2Cl2/hexanes to give 3 as an orange solid (187 mg,
96%). 1H NMR: δ 2.19 (s, 12H, Me), 6.3-7.2 (m, 48H, aromatics),
8.32 (s, JPt-H ) 35.0 Hz, 4H, aromatic H ortho to Pt-C). FAB-
MS (m/z): 1702 [M - Cl]+. IR: 203 cm-1 (Pt-Cl). Anal. Calcd
for C76H64As4Cl2Pt2: C, 52.52; H, 3.71; Cl, 4.08. Found: C, 52.04;
H, 3.66; Cl, 4.15.
[Pt2X2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (X ) Br, 4; I, 5). To
a solution of 2 (100 mg, 0.060 mmol) in CH2Cl2 (15 mL), 1 equiv
of halogen in CH2Cl2 (5 mL) was added. The yellow solution
immediately changed color and was stirred for 10 min. After
removal of the solvent, the residue was recrystallized from CH2Cl2/
hexanes to give the products in ca. 90% yield. Alternatively, 4 and
5 may be obtained by metathesis of a CH2Cl2 solution of 3 with an
excess of LiX in MeOH.
1
X ) Br, 4. H NMR: δ 2.16 (s, 12H, Me), 6.4-7.2 (m, 48H,
aromatics), 8.49 (s, JPt-H ) 37.9 Hz, 4H, aromatic H ortho to Pt-
C). FAB-MS (m/z): 1747 [M - Br]+. Anal. Calcd for C76H64As4-
Br2Pt2: C, 49.96; H, 3.53; Br, 8.75. Found: C, 49.78; H, 3.43; Br,
8.95.
Mixture of [Pt2(κ2As,C-C6H3-5-Me-2-AsPh2)2(µ-κAs,κC-C6H3-
5-Me-2-AsPh2)2] (1) and [Pt2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4]
(2). To a suspension of (2-bromo-4-methylphenyl)diphenylarsine
(1.11 g, 2.55 mmol) in diethyl ether (10 mL), BunLi (1.6 M, 1.6
mL, 2.56 mmol) was added to give a clear solution, which was
stirred for 1 h during which time a white precipitate formed. The
solvent was decanted from the precipitated solid, and diethyl ether
(20 mL) was added. The suspension was cooled to -30 °C and
treated with [PtCl2(SEt2)2] (0.51 g, 1.14 mmol). The mixture was
stirred for 30 min at -30 °C, then at room temperature overnight.
The solvent was decanted from the yellow solid, which was washed
with hexanes (2 × 10 mL) and MeOH (2 × 10 mL) and
recrystallized from CH2Cl2/MeOH to give a mixture of 1 and 2 as
a bright yellow-green solid (0.38 g, 40%). When the isomeric
mixture was refluxed in toluene for 24 h, 1 was completely
1
X ) I, 5. H NMR: δ 2.12 (s, 12H, Me), 6.3-7.2 (m, 48H,
aromatics), 8.90 (s, JPt-H ) 42.8 Hz, 4H, aromatic H ortho to Pt-
C). FAB-MS (m/z): 1792 [M - I]+. Anal. Calcd for C76H64As4I2-
Pt2: C, 47.52; H, 3.36; I, 13.21. Found: C, 47.90; H, 3.69; I, 13.21.
[Pt2X2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (X ) CN, 6; F, 9). To
a solution of 3 (100 mg, 0.058 mmol) in CH2Cl2 (40 mL), an excess
of AgX (ca. 0.2-0.3 mmol) was added. The mixture was stirred
in the dark for 3 days. The pale yellow, turbid solution was filtered
through Celite, hexanes added, and the solution evaporated.
Complexes 6 and 9 precipitated as a pale yellow solids in yields of
90 and 72%, respectively.
1
X ) CN, 6. H NMR: δ 2.23 (s, 12H, Me), 6.2-7.2 (m, 48H,
aromatics), 8.60 (s, JPt-H ) 46.9 Hz, 4H, aromatic H ortho to Pt-
C). EI-MS (m/z): 1692 [M - CN]+. IR: 2123 cm-1 (CN). Anal
Calcd. for C78H64As4N2Pt2: C, 54.49; H, 3.75; N, 1.63. Found: C,
52.79; H, 3.73; N, 1.99.
1
converted into 2. H NMR: δ 1.93 (s, 3H, Me of 1), 1.98 (s, 3H,
Me of 2), 2.18 (s, 6H, Me of 2), 6.2-7.5 (m, 48H, aromatics of 1
and 2), 7.90 (s, JPt-H ) 58.4 Hz, 4H, aromatic H ortho to Pt-C).
1
X ) F, 9. H NMR (CD2Cl2): δ 2.18 (s, 12H, Me), 6.5-7.2
(m, 48H, aromatics), 8.04 (s with 195Pt satellites, JPt-H ) 29.4 Hz,
4H, aromatic H ortho to Pt-C bond). 19F NMR (CD2Cl2): δ -228.6
(49) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C.
W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol.
276, pp 307-326.
(50) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(51) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(52) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.; Cooper,
R. I. CRYSTALS, Issue 11; Chemical Crystallography Laboratory:
Oxford, England, 2001.
(53) Rae, A. D. RAELS 2000: A ComprehensiVe Constrained Least-Square
Refinement Program; Australian National University: Canberra, ACT,
Australia, 0200.
(54) teXsan: Single-Crystal Structure Analysis Software, Version 1.8;
Molecular Structure Corp.: The Woodlands, 1997.
(55) Mackay, S.; Gilmore, C. J.; Edwards, C.; Stewart, N.; Shankland, K.
maXus Computer Program for the Solution and Refinement of Crystal
Structures; Nonius, The Netherlands, MacScience, Japan, and the
University of Glasgow, 2000.
(s with 195Pt satellites, JPt-F ) 492 Hz, JPt-F ) 192 Hz). EI-MS
(m/z): 1703 [M]+. Anal. Found: C, 53.51; H, 3.82; F, 2.24. C76H64-
As4F2Pt2 requires: C, 53.53; H, 3.78; F, 2.23.
1
2
[Pt2X2(µ-κAs,κC-C6H3-5-Me-2-AsPh2)4] (X ) NCS, 7; NCO,
8). To a solution of 3 (100 mg, 0.058 mmol) in CH2Cl2 (40 mL),
an excess of NaX (ca. 0.3-0.4 mmol) in MeOH (20 mL) was added.
The orange solution turned yellow and was stirred for 10 min. The
solvent was removed in vacuo, CH2Cl2 (20 mL) was added, and
the turbid solution was filtered through Celite. Addition of hexanes
and evaporation of the solution caused 7 and 8 to precipitate as
yellow solids in yields of ca. 90%.
X ) NCS, 7. 1H NMR: δ 2.22 (s, 12H, Me), 6.3-7.1 (m, 48H,
aromatics), 7.79 (s, JPt-H ) 37.7 Hz, 4H, aromatic H ortho to Pt-
C). EI-MS (m/z): 1723 [M - NCS]+. IR: 2086 cm-1 (br, NCS).
Anal. Calcd for C78H64As4N2S2Pt2: C, 52.53; H, 3.62; N, 1.57.
Found: C, 51.21; H, 3.73; N, 1.60.
(56) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
7762 Inorganic Chemistry, Vol. 43, No. 24, 2004

Dinuclear Complexes of Platinum Arsine Ligands
X ) NCO, 8. 1H NMR: δ 2.17 (s, 12H, Me), 6.3-7.2 (m, 48H,
aromatics), 7.90 (s, JPt-H ) 37.4 Hz, 4H, aromatic H ortho to Pt-
C). EI-MS (m/z): 1707 [M - NCO]+. IR: 2186 cm-1 (br, NCO).
Anal. Calcd for C78H64As4N2O2Pt2: C, 53.50; H, 3.68; N, 1.60.
Found: C, 52.67; H, 3.58; N, 1.77.
[Pt2Cl2(µ-κAs,κC-C6H4-2-AsMe2)4] (11). To a solution of 10
(0.103 g, 0.092 mmol) in CH2Cl2 (3 mL), a solution of iodobenzene
dichloride (26 mg, 0.095 mmol) in CH2Cl2 (3 mL) was added. The
orange solution immediately reddened and was stirred for 15 min.
The mixture was evaporated to dryness, the orange residue was
dissolved in CH2Cl2, and hexanes were added. On evaporation of the
[Pt2(µ-κAs,κC-C6H4-2-AsMe2)4] (10). To a solution of (2-
bromophenyl)dimethylarsine (0.816 g, 3.12 mmol) in diethyl ether
(20 mL), BunLi (1.6 M, 1.95 mL, 3.12 mmol) was slowly added.
The clear solution became turbid and then clear again. It was stirred
for 30 min and cooled to -30 °C. It was treated with [PtCl2(SEt2)2]
(0.620 g, 1.38 mmol), and the mixture was stirred for 30 min at
this temperature, and then at room temperature overnight. The
solvent was removed in vacuo, and CH2Cl2 (20 mL) was added.
Filtration of the solution through Celite, addition of hexanes, and
evaporation caused precipitation of 10 as a yellow-orange solid
(0.743 g, 96%). 1H NMR: δ 0.5-2.2 together with multiplets at δ
0.88 and 1.25 due to hexanes (m, 9H, Me and hexanes), 6.2-8.2
(m, 4H, aromatics. Anal. Found: C, 35.72; H, 3.94; mol wt 1120.
C32H40As4Pt2.0.33C6H14 requires: C, 35.87; H, 4.17; mol wt 1115
(CH2Cl2).
1
solution, 11 precipitated as an orange solid (0.803 g, 73%). H
NMR: δ 0.5-2.2 together with multiplets at δ 0.88 and 1.25 due
to hexanes (m, 9H, Me and hexanes), 6.2-8.0 (m, 4H, aromatics).
Anal. Found: C, 32.69; H, 3.89; Cl, 6.08; mol. wt. 1218. C32H40As4-
Cl2Pt2 requires: C, 32.42; H, 3.40; Cl, 5.98; mol wt 1185 (CH2Cl2).
Supporting Information Available: X-ray crystallographic data
in CIF format for complexes 1-9, appendix S1 containing details
of nonroutine aspects of the X-ray crystallographic determinations
of 1-9, Figures S1 and S2 providing voltammograms for reduction
of 3 at different electrode surfaces and scan rates, and Tables S1-
S3 containing selected bond lengths. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC0498790
Inorganic Chemistry, Vol. 43, No. 24, 2004 7763