New bimetallic reactivity in Pt2II,III/Pt2 IV,IV transformation mediated by a benzene ring

Article abstract of DOI:10.1021/om901046p

A new Pt₂ ^II,II complex with the formula Pt ₂(TPAB)Me₄ (1), where TPAB = 1,2,4,5-tetrakis(5-(/p-C ₇H1₅Ph)-7-azaindol- l-yl)benzene, has been synthesized. This molecule has excellent solubility in common solvents, which enabled our investigation of its reactions with a variety of oxidants to form Pt2 ^IV,IV species and the reverse reactions of the Pt2^IV,IV species back to 1 via reduction. Despite the lack of direct Pt- ... -Pt interactions, the two Pt centers in 1 display distinct bimetallic cooperativity mediated by the central phenyl ring of the TPAB ligand. The most unusual finding is that the reactivity of 1 with MeOTf is highly dependent on the amount of molecular oxygen present in the reaction medium. In the absence Of O ₂, the reaction of 1 with MeOTf produced [Pt₂ ^IV,IV(TPAB)Me₆][OTf]₂ (6), while in the presence of O₂, complex 7, Pt₂^IV,IV(TP AB)Me₄(OTf)₂, was obtained. Compound 1 was found to react readily with O₂ at one atmosphere and ambient temperature to produce an insoluble and not yet fully characterized solid that further reacts with MeOTf to produce 7 quantitatively. NMR and single-crystal X-ray diffraction analyses established that the two Pt^IV centers in 6 are five-coordinate with a squarepyramidal geometry, while in 7 the two Pt ^IV centers are six-coordinate with an octahedral geometry. Most significantly, the central phenyl ring of the TPAB ligand was transformed to a cyclohexyldienyl in 7, while it remains unchanged in 6. Complex 1 also reacts readily with other oxidants such as CHCl₃, PhICl₂, Br ₂ (CBr₄), I₂, and H₂O₂ to produce Pt₂^IV,IV(TPAB)Me₄X₂ (X = Cl, 2; Br, 3; I,4; OH, 5). The structures of 2-5 are similar to that of 7, showing the generality of the central phenyl ring mediated oxidation of the Pt₂^IV,IV system. Complexes 2 and 7 can be reduced and converted back to complex 1 via reactions with BH₄-, as established by NMR experiments.

Full text of DOI:10.1021/om901046p

998 Organometallics 2010, 29, 998–1003
DOI: 10.1021/om901046p
New Bimetallic Reactivity in Pt2II,II/Pt2IV,IV Transformation Mediated
by a Benzene Ring
Shu-Bin Zhao, Qian Cui, and Suning Wang*
Department of Chemistry, Queen’s University Kingston, Ontario, K7L 3N6, Canada
Received December 6, 2009
A new Pt2II,II complex with the formula Pt2(TPAB)Me4 (1), where TPAB = 1,2,4,5-tetrakis(5-(p-C7-
H15Ph)-7-azaindol-1-yl)benzene, has been synthesized. This molecule hasexcellent solubility in common
IV,IV
solvents, which enabled our investigation of its reactions with a variety of oxidants to form Pt2
species and the reverse reactions of the Pt2IV,IV species back to 1 via reduction. Despite the lack of direct
Pt Pt interactions, the two Pt centers in 1 display distinct bimetallic cooperativity mediated by the
3 3 3
central phenyl ring of the TPAB ligand. The most unusual finding is that the reactivity of 1 with MeOTf
is highly dependent on the amount of molecular oxygen present in the reaction medium. In the absence
of O2, the reaction of 1 with MeOTf produced [Pt2IV,IV(TPAB)Me6][OTf]2 (6), while in the presence of
O2, complex 7, Pt2IV,IV(TPAB)Me4(OTf)2, was obtained. Compound 1 was found to react readily with
O2 at one atmosphere and ambient temperature to produce an insoluble and not yet fully characterized
solid that further reacts with MeOTf to produce 7 quantitatively. NMR and single-crystal X-ray
diffraction analyses established that the two PtIV centers in 6 are five-coordinate with a square-
pyramidal geometry, while in 7 the two PtIV centers are six-coordinate with an octahedral geometry.
Most significantly, the central phenyl ring of the TPAB ligand was transformed to a cyclohexyldienyl in
7, while it remains unchanged in 6. Complex 1 also reacts readily with other oxidants such as CHCl3,
PhICl2, Br2 (CBr4), I2, and H2O2 to produce Pt2IV,IV(TPAB)Me4X2 (X = Cl, 2; Br, 3; I, 4; OH, 5). The
structures of 2-5 are similar to that of 7, showing the generality of the central phenyl ring mediated
oxidation of the Pt2II,II system. Complexes 2 and 7 can be reduced and converted back to complex 1 via
reactions with BH4-, as established by NMR experiments.
Introduction
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Published on Web 12/31/2009
2009 American Chemical Society

Article
Scheme 1. C-Cl Activation by Pt2II,II(TTAB)Me4
Organometallics, Vol. 29, No. 4, 2010 999
afford selectively 5-bromo-3-(2-trimethylsilyl)ethynyl)pyri-
dine-2-amine. Treatment of the resultant pyridine substrate
successively with KOBut and HCl (37%) in tBuOH resulted
in 5-bromo-7-azainole.16b The subsequent coupling of
p-C7H15PhB(OH)2 with 5-bromo-7-azainole was realized
by using a Buchwald protocol.16c Condensation of the
resultant 5-(p-C7H15Ph)-7-azainole with 1,2,4,5-tetrabro-
mobenzene eventually give TPAB as a pale yellow powder
in ∼12% overall yield. The ligand displacement reaction
of TPAB with [PtMe2(μ-SEt2)]216d in THF preceded readily,
giving rise to 1 as a yellow solid in 78% yield, which is
soluble in most organic solvents including C6H6 and hexanes
because of the p-Ph-C7H15 moieties.
TPAB and complex 1 have been fully characterized by
NMR spectroscopic and elemental analyses. The structure of
TPAB determined by X-ray diffraction analysis (see Sup-
porting Information for details) is shown in Figure 1. The 1H
NMR spectrum of 1 shows one set of 1H signals for all of the
unique H atoms, indicating that it has the same structure as
that of Pt2II,II(TTAB)Me4 with C2h symmetry.
[P2O5H2]2-), which has a Pt Pt separation of ∼2.93 A with
˚
3 3 3
dinstinct bimetallic cooperativity.11 Bimetallic cooperativities
that confer distinct chemical reactivity or unusual selectivity are
largely restricted to species possessing or permitting direct
M
In contrast, bimetallic complexes with enforced long M
M interactions or bonds in previously known examples.12
3 3 3
M
3 3 3
˚
separation distances (>6 A) and distinct bimetallic chemical
cooperativities remain rare.2d,3e,12
We reported previously a Pt2 complex, Pt2II,II(TTAB)Me4
(TTAB = 1,2,4,5-tetrakis(7-azaindol-1-yl)benzene), that can
cleave C-Cl bonds readily at ambient temperature to form a
Reactivity of 1 with C-X Bonds, X2, and H2O2. Complex 1
reacts readily with 2e- oxidants such as C-Cl and C-Br bonds
and halogen molecules X2. Its reaction with C-Cl bonds is
PtIV species, Pt2IV,IV(κ3,3-TTAB)Me4Cl2, with the concomi-
2
tant dearomatization of the central phenyl ring (Scheme 1).13a
reminiscent of Pt2II,II(TTAB)Me4,13a producing Pt2IV,IV(κ3,3
-
The unusual reactivity of Pt2II,II(TTAB)Me4 toward C-Cl
bonds was attributed to the synergistic effects of the Pt2
II,II
TPAB)Me4Cl2 (2), quantitatively. Compound 2 also can be
obtained quantitatively by the reaction of 1 with PhI Cl2 in
core.13-15 The two Pt centers in Pt2II,II(TTAB)Me4 are sepa-
˚
3
C6D6. 1 also reacts readily with Br2 and I2 in the same manner,
producing compounds 3 and 4, respectively (Scheme 3). Note-
worthy is that excess Br2 tends to brominate the C3 positions of
the TPAB 7-azaindolyl moieties in 1. A better way to quantita-
tively generate 3 is treating 1 with excess CBr4 in C6H6. An
interesting finding is that treating 1 with H2O2 gives rise to the
dihydroxo complex 5, quantitatively (Scheme 3). These new
complexes were characterized by NMR spectroscopic and
elemental analyses. NMR data confirmed that the core in
2-5 is a cyclohexyl-1,4-dienyl moiety (see Supporting Informa-
tion), similar to that of Pt2IV,IV(TTAB)Me4Cl2.
rated by a phenyl ring with a long dPt
(6.89 A) that
Pt
3 3 3
prohibits direct Pt Pt interaction or bond formation.13a
3 3 3
Thus, the Pt2II,II(TTAB)Me4 complex was a unique example
demonstrating bimetallic cooperativity mediated by an aro-
II,II
matic ring. A related Pt2
derivative ligand has been reported recently by Song and co-
system based on a quinoline
II,II
workers.13b One drawback of the previous Pt2
systems is
their poor solubility in common solvents, which limits the scope
of the investigation. To overcome the insolubility of TTAB
complexes, we have developed synthetic methods to derivatize
the TTAB ligand, and a new ligand, 1,2,4,5-tetrakis(5-(p-
C7H15Ph)-7-azaindol-1-yl)benzene (TPAB), has been ob-
tained. In addition to the facile oxidation reactions by C-Cl
and C-Br bonds similar to the TTAB Pt2 complex shown in
Scheme 1, the new TPAB Pt2 complex displays unusual
reactivities with MeOTf and oxygen molecules that were not
observable for the TTAB complexes. The preliminary findings
are reported herein.
The high susceptibility of 1 toward oxidation was also
evident from cyclic voltammetric study, which showsþa/0n
irreversible oxidation peak at EP ≈ 0.13 V (vs FeCp2
)
in DMF (Figure 2), attributable to the oxidation of the
Pt(II) centers in 1. The free ligand TPAB and the related
mononuclear Pt(II) complex Pt(1,2-BAB)Me2 (1,2-BAB =
1,2-bis(7-azaindol-1-yl)benzene)17 do not display oxidation
peaks at such low potentials; thus the CV data provide
further support to the cooperativity of the two Pt(II) centers
mediated by the central phenyl ring.
Results and Discussion
II,II
Reactivity of 1 with MeOTf and O2. In addition to the 2e-
oxidation reactions described above, 1 also undergoes a
facile overall 4e- oxidation reaction with 2 equiv of MeOTf
(OTf=CF3SO3-, triflate) in benzene or THF under N2 to
produce the cationic complex 6, [Pt2IV,IV(TPAB)Me6][OTf]2,
instantaneously and quantitatively (Scheme 4, path a). Com-
plex 6 was fully characterized by NMR spectroscopic and
X-ray diffraction analyses. It should be noted that Pt2-
(TTAB)Me4 also reacts with MeOTf, but yields an insoluble
yellow product that precludes any structural study.
Syntheses of TPAB and Its Pt2
Complex 1. The syn-
thetic route to TPAB and its Pt2II,II complex (1) is shown in
Scheme 2, where 2-aminopyridine serves as a starting ma-
terial (see Supporting Information for details). Its bromina-
tion first gave 3,5-dibromopyridin-2-amine,16a which was
subsequently cross-coupled with trimethylsilylacetylene to
(12) Gavrilova, A. L.; Bosnich, B. Chem. Rev. 2004, 104, 349.
(13) (a) Song, D.; Sliwowski, K.; Pang, J.; Wang, S. Organometallics
2002, 21, 4978. (b) Tan, R.; Jia, P.; Rao, Y.; Jia, W.; Hadzovic, A.; Yu, Q.; Li,
X.; Song, D. Organometallics 2008, 27, 6614.
(14) Song, D.; Wang, S. Comments Inorg. Chem. 2004, 25, 1.
(15) (a) Tan, R.; Jia, P.; Rao, Y.; Jia, W.; Hadzovic, A.; Yu, Q.; Song,
D. Organometallics 2008, 27, 6614. (b) Song, D.; Jia, W.-L.; Wang, S.
Organometallics 2004, 23, 1194.
The crystal structure of 6 shown in Figure 3 contains
two five-coordinate PtIV centers with a square-pyramidal
geometry. Each Pt atom in 6 has a short contact distance
(16) (a) Majumdar, K. C.; Mondal, S. Tetrahedron Lett. 2007, 48,
6951. (b) Beard, C. D.; Lee, V. J.; Whittle, C. E. U.S. Patent 20060183758,
2006. (c) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J.
Am. Chem. Soc. 2005, 127, 4685. (d) Scott, D. J.; Puddephatt, R. J.
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Zhao, S.-B.; Song, D.; Jia, W.-L.; Wang, S. Organometallics 2005, 24, 3290.

1000 Organometallics, Vol. 29, No. 4, 2010
Zhao et al.
Figure 1. Structure of TPAB with 50% thermal ellipsoids and labeling scheme. The two orientations of the disordered heptyl group are
also shown.
Scheme 2. Syntheses of Ligand TPAB and Complex 1
Scheme 4. Reactivity of 1 with MeOTf
Figure 2. CV diagram of 1 showing the oxidation peaks in
DMF (vs FeCp2þ/0) with a scan rate of 75 mV/s.
Scheme 3. Reactivity of 1 toward C-Cl/Br Bonds and X2
Molecules
PtIV species are postulated as key intermediates in Shilov
chemistry.17-22 Despite a handful of examples of such mono-
nuclear species in the literature,17a,22 complex 6 to our
(19) (a) Brown, M. P.; Puddephatt, R. J.; Upton, C. E. E. J. Chem.
Soc., Dalton Trans. 1974, 2457. (b) Puddephatt, R. J. Angew. Chem., Int.
Ed. 2002, 41, 261. (c) Pawlikowski, A. V.; Getty, A. D.; Goldberg, K. I. J.
Am. Chem. Soc. 2007, 129, 10382, and reference therein.
(20) (a) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc.
˚
(2.53(1) A) with C(42) of the TPAB phenyl spacer, and the
2001, 123, 6423. (b) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J.
L. J. Am. Chem. Soc. 2001, 123, 6425. (c) Luedtke, A. T.; Goldberg, K. I.
Inorg. Chem. 2007, 46, 8496. (d) Kloek, S. M.; Goldberg, K. I. J. Am. Chem.
Soc. 2007, 129, 3460. (e) Khaskin, E.; Zavalij, P. V.; Vedernikov, A. N.
Angew. Chem., Int. Ed. 2007, 46, 6309. (f) Sangtrirutnugul, P.; Tilley, T. D.
Organometallics 2008, 27, 2223.
(21) Rendina, L. M.; Puddephatt, R. J. Chem. Rev. 1997, 97, 1735.
(22) (a) Hill, G. S.; Puddephatt, R. J. J. Am. Chem. Soc. 1996, 118,
8745. (b) Wick, D. D.; Goldberg, K. I. J. Am. Chem. Soc. 1997, 119, 10235.
˚
Pt Pt separation distance is 6.22(1) A. Five-coordinate
3 3 3
(18) (a) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879. (b)
Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. Angew. Chem, Int. Ed. 1998, 37,
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Article
Organometallics, Vol. 29, No. 4, 2010 1001
Figure 3. X-ray structures of the cation in 6 (top, H atoms
except those of the central phenyl ring are omitted for clarity)
and the central core of 6 (bottom).
Figure 5. Diagrams showing the structure of 7 (top, H atoms
except those of the central phenyl ring are omitted for clarity)
and its central core (bottom).
Figure 4. 1H NMR spectrum of complex 7 in C6D6.
knowledge is the first structurally characterized five-coordi-
nate dinuclear PtIV species. Steric protection exerted by the
TPAB ligand plays a crucial role in stabilizing the two
coordinatively unsaturated PtIV centers. Similar stabiliza-
tion of mononuclear five-coordinate Pt(IV) complexes has
been observed previously.17a
Figure 6. 1H NMR spectra showing the in situ generation of 7
(top) by treating 1 (bottom) successively with O2 and MeOTf in
C6D6. (a) Pure 1; (b) exposed to 1 atm O2 for 12 h; (c) exposed to 1
atm O2 for 3 days; (d) MeOTf added; (e) warmed to 60 °Cfor3min
(compare with the spectrum of pure compound 7 in Figure 4).
Another surprising finding is that TPAB adopts a 1,3-
N,N-chelating mode in 6 rather than the expected 1,2-N,N
chelate mode, indicating a chelating mode switching accom-
panying the 1 to 6 oxidation (Scheme 4, path a). The 1,2-
N,N-chelate mode has been observed in the mononuclear
elemental analyses confirmed that complex 7 is indeed an
analogue of 2-5 with a formula of Pt2IV,IV(κ3,3-TPAB)Me4-
(OTf)2, as shown in Figure 5. Each PtIV center in 7 has an
octahedral geometry, coordinated by two methyls (Pt-C =
five-coordinate PtIVMe3 analogue [Pt(1,2-BAB)Me3](OTf)17a
˚
˚
2.02(2) A, on average), two N atoms (Pt-N = 2.11(2) A, on
IV,IV
complexes previously.13,15b The pre-
˚
and the TTAB Pt2
average), one O atom from OTf (Pt-O = 2.151(16) A), and
ferential formation of the 1,3-N,N-chelate isomer of 6 from 1
must involve a Pt-N bond dissociation and reassociation
process, but the details are not understood yet.
one C atom from the cyclohexyldienyl ring (Pt-C(46) =
˚
2.12(2) A). The Pt Pt separation distance in 7 is 6.51(1) A.
˚
3 3 3
It is evident that 7 cannot be produced directly by MeOTf
The most intriguing and unusual reactivity of 1 is its reaction
with MeOTf in the presence of O2 that results in not only
complex 6 but also complex 7 (Scheme 4, path b) in benzene.
The yield of 7 increases with the increase of the amount of O2
used. The 1H NMR spectrum of 7 in C6D6 displays a singlet at
5.96 ppm with distinct 3JPt-H (36.5 Hz) and 4JPt-H (14.5 Hz)
coupling satellites that are characteristic of a cyclohexyl-1,4-
dienyl core (Figure 4).13a Single-crystal X-ray diffraction and
SN2 additions or simple radical processes involving Me
3
redicals.17,21 The unexpected formation of 7 is attributable to
O2 since the same species was not observed under O2-free
conditions (Scheme 4). Furthermore, because O2 does not react
with MeOTf, the Pt2 complex 1 must play a role in activating
O2. To further verify the role of O2, the reaction of 1 with O2 in
1
C6D6 was examined by H NMR spectroscopy (Figure 6).
Addition of O2 to the solution of 1 at ambient temperature

1002 Organometallics, Vol. 29, No. 4, 2010
Zhao et al.
observed, which may be attributed to the reduction of the
Pt(IV) centers(see FigureS18 inthe SupportingInformation).
II,II
In summary, a new soluble Pt2
complex 1 has been
obtained. Oxygen molecules have been found to have a
distinct impact on the reactivity of 1 with MeOTf and the
structure of the Pt2IV,IV product obtained. The possibility of
reductively converting Pt2IV,IV back to PtII2 has been demon-
II,II
strated, which has implications in the potential of this Pt2
system in catalytic bond activation/functionalization pro-
cesses such as dechlorination or oxygenation.
Experimental Section
All reactions were performed under N2 with the standard
Schlenk techniques unless otherwise noted. All starting materi-
als were purchased from Aldrich Chemical Co. and used without
further purification. THF, Et2O, and hexanes were purified
using the solvent purification system (Innovation Technology,
Inc.). Deuterated solvents C6D6, CD2Cl2, and THF-d8
(Cambridge Isotopes) were dried with CaH2. NMR spectra
were recorded on Bruker Advance 300, 400, or 500 MHz
spectrometers. 1H and 13C NMR chemical shifts were referenced
to the residual solvent peaks and have been reported in parts per
million (ppm). Cyclic voltammetry was performed using a BAS
CV-50 W analyzer with a scan rate of 100 mV/s to 1 V/s and a
typical concentration of ∼0.003 M in DMF using 0.10 M
tetrabutylammonium hexafluorophosphate (TBAP) as the sup-
porting electrolyte. Elemental analyses were performed by
Canadian Microanalytical Service, Ltd., Delta, British Columbia.
High-resolution mass spectra (HRMS) were obtained from a
Waters/Micromass GC-TOF EI-MS spectrometer. Synthetic
details and characterization data of starting materials for TPAB
and complexes 2-5, crystal data for TPAB, 6, and 7, and the
details for all NMR experiments are provided in the Supporting
Information.
Figure 7. 1H NMR spectra showing the clean conversion of 7 by
[Bu4N][BH4] to 1 in C6D6 at room temperature. (Bottom)
Spectrum of 7. (Top) Spectrum recorded 3 min after the addition
of [Bu4N][BH4]. For the spectrum of pure complex 1, see
Figure 6a.
causes a gradual formation of a yellow solid that is insoluble in
most organic solvents. The formation of the yellow solid is also
quantitative according to the disappearance of 1H NMR
signals of 1 after ∼3 days (Figure 6, a-c). Although the exact
nature of this yellow solid has not been established, elemental
analysis indicates that it contains oxygen. In addition, the
yellow precipitate reacts readily with excess MeOTf, resulting
in a clean and quantitative formation of complex 7, accom-
panied by the formation of MeOOMe (δ: 1H, 3.63 ppm; 13C,
∼61.6 ppm), identified by NMR (Figure 6, c-e; Figure S14 in
Supporting Information), thus suggesting that O2 is indeed
involved in the formation of 7. Recently, Goldberg, Britovsek,
and co-workers demonstrated that molecular O2 can directly
insert into a PtII-Me bond at room temperature, giving rise to
PtII-OOMe species.23 In our system, however, due to the high
Synthesis of TPAB. 1,2,4,5-Tetrabromobenzene (0.33 g,
0.84 mmol), 5-(p-C7H15Ph)-7-azaindole (1.1 g, 3.77 mmol),
CuI (0.18g, 0.95 mmol), 1,10-phenanthroline(0.30 g, 1.67 mmol),
Cs2CO3 (5.4 g, 16.6 mmol), and DMF (5.0 mL) were mixed
together and heated at 170 °C under an N2 atmosphere for 3 days.
After the reaction, the mixture was cooled to room temperature
and poured into water (80 mL). After extraction with ethyl
acetate (80 ꢀ 3 mL), the combined organic layers were washed
with water (40 mL ꢀ 2) and then dried with Na2SO4. After
removal of the solvent, the residue was purified by column
chromatography with ethyl acetate/hexanes (1:8) as eluent to
give the product as a white solid (0.44 g, 42% yield). Colorless
crystals of TPAB were obtained via slow evaporation of its
propensity of the Pt2II,II complex 1 toward oxidative transfor-
IV,IV
mation to Pt2 and the fact that all Pt-Me bonds in 7
remain intact, direct O2 insertion processes are unlikely in-
volved in the generation of complex 7.
Reductive Conversion of Complexes 7 and 2 to Complex 1.
The key feature of the new TPAB Pt2 system is the excellent
solubility of the Pt2IV,IV products, which makes it possible for
us to study their reduction back to 1. The reduction of 7 in
C6D6 withmetals such asZnandMg or insoluble hydridesalts
NaH and CaH2 proved ineffective, whereas excess
[Bu4N][BH4] converted 7 cleanly back to 1 within minutes at
room temperature in C6D6, along with the formation of H2
(Figure 7). A distinct high-field 1H signal (δ, -20.35 ppm with
1JPt-H ≈ 1464 Hz) attributable to22 PtIV-H was observed
when the reduction was carried out in CD2Cl2 at -50 °C
(Supporting Information, Figure S16). In a similar manner,
the dichloride complex 2 can also be converted back to 1
cleanly in C6D6 within ∼20 min at room temperature
1
CHCl3 solution. H NMR (400 MHz, 298.0 K, CDCl3) δ: 8.49
(d, 4J = 2.0 Hz, 4H), 8.43 (s, 2H), 8.04 (d, 4J = 2.0 Hz, 4H), 7.53
(d, 3J = 8.0 Hz, 8H), 7.29 (d, 3J = 8.0 Hz, 8H), 6.99 (d, 3J = 3.6
Hz, 4H), 6.43 (d, 3J = 3.6 Hz, 1H), 2.68 (t, 3J = 7.6 Hz, 8H), 1.68
(m, 8H), 1.39-1.32 (m, 32H), 0.92 (t, 3J = 6.8 Hz, 12H) ppm. 13
C
NMR δ: 147.84, 143.33, 142.29, 136.91, 133.71, 130.93, 129.73,
129.32, 129.19, 127.53, 127.40, 121.02, 101.72, 35.94, 32.16, 31.85,
29.66, 29.52, 23.01, 14.44 ppm. Anal. Calcd for C86H94N8: C
83.32, H 7.64, N 9.04, Found: C 82.78, H 7.58, N 8.94.
Synthesis of Pt2(TPAB)Me4 (1). TPAB (0.15 g, 0.12 mmol)
and [PtMe2(μ-SEt2)]2 (0.075 g, 0.12 mmol) werecombined inTHF
(8 mL) to afford a clear solution. The mixture was stirred
vigorously under N2 for 2 days at ambient temperature, resulting
in a yellow solution. After removal of the solvent under reduced
pressure, the residue was washed with dry Et2O/hexanes (1:2)
mixed solvents (0.5 mL ꢀ 3) to give the product 1 as a yellow
power (78% yield). 1H NMR (500 MHz, 298.0 K, C6D6) δ: 9.42
(d, 4J = 2.0 Hz, 4H), 7.78 (d, 3J = 3.5 Hz, 4H), 7.57 (d, 4J = 2.0
Hz, 4H), 7.33 (d, 3J = 8.0 Hz, 8H), 7.15 (d, 3J=8.0 Hz, 8H), 6.77
(s, 2H), 6.27 (d, 3J = 3.5 Hz, 4H), 2.62 (t, 3J=7.5 Hz, 8H), 1.67 (m,
8H), 1.43-1.38 (m, 44H), 1.03 (t, 3J = 7.0 Hz, 12H) ppm.
(Supporting Information, Figure S17). These reductions can
-
proceed beyond the stage of complex 1 due to excessive BH4
,
leading eventually to a dark solution consisting of the free
TPAB ligand and metallic Pt in a few days. In the CV diagram
of 2, a reversible reduction peak at -1.88 V (vs FeCp2þ/0) was
(23) (a) Grice, K. A.; Goldberg, K. I. Organometallics 2009, 28, 953.
(b) Taylor, R. A.; Law, D. J.; Sunley, G. J.; White, A. J. P.; Britovsek, G. J.
Angew. Chem., Int. Ed. 2009, 48, 5900.
(24) (a) Spek, A. L. Acta Crystallogr. 1990, A46, C34. (b) Spek, A. L.
PLATON, A Multipurpose Crystallographic Tool; Ultrecht University:
Ultrecht, The Netherlands, 2006.

Article
Organometallics, Vol. 29, No. 4, 2010 1003
13C NMR δ: 148.52, 144.44, 142.46, 138.83, 135.79, 132.10, 131.99,
131.77, 129.47, 127.77, 127.36, 103.17, 36.08, 32.40, 32.00, 29.80,
29.78, 23.26, 14.52, -20.87 ppm. Anal. Calcd for C90H106N8Pt2: C
63.96, H 6.32, N 6.63. Found: C 63.40, H 6.05, N 6.35.
evaporation of the solvent, the residue was washed with dry
Et2O and then dried under reduced pressure to give complex 7 as
pale white powder in 93% isolated yield. Colorless crystals of
complex 7 were obtained via slow evaporation of its C6H6
solution. 1H NMR (400 MHz, 298.0 K, C6D6) δ: 9.70 (m,
Synthesis of Pt2(TPAB)Me4Cl2 (2). Complex 1 (24 mg, 0.014
mmol) was dissolved with dry CHCl3 (0.5 mL) in a test tube in a
drybox, resulting in the immediate formation of complex 2.
After evaporation of the solvent, the residue was washed with
acetone to give complex 2 as a white powder in 96% isolated
yield. 1H NMR (400 MHz, 343.0 K, C6D6) δ: 10.69 (s, 2H), 9.25
(s, 2H), 8.39 (d, 3J = 3.2 Hz, 2H), 7.71 (d, 3J = 3.6 Hz, 2H), 7.66
(s, 2H), 7.52 (d, 3J = 8.0 Hz, 4H), 7.36 (d, 3J = 8.0 Hz, 4H), 7.13
3
4H), 7.70 (m, 4H), 7.64 (d, J = 1.2 Hz, 2H), 7.60-7.55 (m,
8H), 7.43 (d, 3J = 3.6 Hz, 2H), 7.22 (d, 3J = 8.0 Hz, 4H), 7.19 (d,
3J = 8.0 Hz, 4H), 6.32 (d, 3J = 3.6 Hz, 2H), 6.26 (d, 3J = 3.6 Hz,
2H), 5.96 (s, with satellites, 3JPt-H = 36.5 Hz, 4JPt2-H = 14.5 Hz,
2H), 2.65-2.55 (m, 8H), 2.33 (s, with satellites, JPt-H = 72.4
Hz, 6H for Pt-Me), 1.99 (s, with satellites, 2JPt-H = 76.4 Hz, 6H
for Pt-Me), 1.70-1.50 (m, 8H), 1.48-1.30 (m, 32H), 1.10-0.90
(m, 12H) ppm. Anal. Calcd for C92H106N8F6O6Pt2S2: C 55.58,
H 5.37, N 5.64. Found: C 55.68, H 5.43, N 5.60.
3
3
(d, J = 8.0 Hz, 8H), 6.51 (d, J = 3.2 Hz, 2H), 6.32 (s, with
satellites, 3JPt-H = 21.5 Hz, 4JPt-H = 8.2 Hz, 2H), 6.24 (d, 3J =
3.6 Hz, 2H), 2.62 (m, 8H), 1.98 (s, with satellites, 2JPt-H = 72.8
Hz, 6H for Pt-Me), 1.94 (s, with satellites, 2JPt-H = 72.4 Hz, 6H
X-ray Diffraction Anaylsis. Single crystals of the free ligand
TPAB were obtained from a CHCl3/hexanes solution, while
crystals of complexes 6 and 7 were obtained from benzene/
hexanes solutions. All crystals are marginal sizes. For complex 6
the crystal size is very small. For complex 7 the quality of the
crystals is very poor and the diffraction intensity is low, with
only about 20% of reflections that have intensity greater than
2σ. Data were collected on a Bruker Apex II single-crystal X-ray
diffractometer with graphite-monochromated Mo KR radia-
tion, operating at 50 kV and 30 mA, and at either ambient
temperature or 180 K. Data were processed on a PC with the aid
of the Bruker SHELXTL software package (version 5.10) and
corrected for absorption effects. All structures were solved by
direct methods. All three molecules have a crystallographically
imposed inversion center. The crystal lattice of TPAB contains 2
CHCl3 solvent molecules per molecule of TPAB, which were
refined successfully. In addition, one aliphatic chain of TPAB is
disordered. The disorder was modeled and refined successfully.
The crystal lattices of 6 contain disordered CH3CN solvent
molecules, which could not be modeled or refined. In addition,
the OTf anion in 6 also displays some degree of disorder. Hence,
to improve the quality of refinements, contributions from
solvent molecules and the anions in the crystal lattice of 6 were
removed by using the SQUEEZE routine of the Platon pro-
gram.24 One aliphatic chain in the asymmetric unit of 7 shows
severe disordering. Due to the lack of sufficient data to model
and refine the disorder, some of the C-C distances were fixed
using DFIX. Nonetheless, despite our best efforts and repeated
data collections, we were not able to obtain better data for
complex 7. The crystal structural data presented here are from
our best effort. For complexes 6 and 7 not all non-hydrogen
atoms were refined anisotropically due to the lack of sufficient
data. All hydrogen atoms were calculated and their contribu-
tions in structural factor calculations were included.
for Pt-Me), 1.69 (m, 8H), 1.40 (br, 32H), 1.01 (m, 12H) ppm. 13
C
NMR δ: 151.13, 143.10, 142.26, 138.04, 135.72, 135.10, 132.25,
131.67, 130.38, 129.88, 129.81, 129.58, 129.55, 127.83, 127.56,
127.34, 125.30, 123.94, 123.74, 119.08, 105.39, 103.44, 45.77,
36.01, 32.25, 32.22, 31.96, 31.86, 29.74, 29.70, 29.61, 29.60,
23.10, 14.53, 1.44 (Pt-Me), 1.35 (Pt-Me), -3.25 (Pt-Me) ppm.
Anal. Calcd for C90H106N8Cl2Pt2: C 61.39, H 6.07, N, 6.36.
Found: C 61.12, H 6.01, N 6.19. Compound 2 can also be
obtained by reacting 1 with PhI Cl2 (see Supporting In-
formation).
3
Synthesis of [Pt2(TPAB)Me6](OTf)2 (6). To a yellow C6H6
(1 mL) solution of Pt2(TPAB)Me4 (12 mg, 0.007 mmol) in a
5 mL test tube was added quickly neat MeOTf (1.9 μL, ∼2.2
equiv) via micropipet at ambient temperature in a drybox. A
yellow suspension was obtained in a few minutes while shaking
the solution vigorously. After evaporation of the solvent, the
residue was washed with dry Et2O and then dried under reduced
pressure to give complex 6 in 93% isolated yield. Crystals of
complex 3 were obtained via slow evaporation of its CH2Cl2
1
solution. H NMR (400 MHz, 298.0 K, CD2Cl2) δ: 8.76 (br,
6H), 8.57 (d, 4J = 1.6, 4H), 7.66 (d, 3J = 8.0 Hz, 8H), 7.52 (d,
3J = 3.6 Hz, 4 H), 7.45 (d, 3J = 8.0 Hz, 8H), 7.16 (d, 3J = 3.6 Hz,
=
4H), 2.78 (t, 3J = 7.6 Hz, 8H), 2.36 (s, with satellites, 2JPt-H
78.8 Hz, 6H for Pt-Meaxial), 1.75 (m, 8H), 1.51-1.20 (m, 32H),
1.00 (s, with satellites, JPt-H = 68.0 Hz, 12H for Pt-Mebasal),
2
3
0.91 (q, J = 7.6 Hz, 12H) ppm. 13C NMR δ: 146.67, 144.53,
140.63, 135.33, 124.25, 134.17, 132.90, 129.87, 127.84, 127.73,
127.29, 126.63, 108.78, 108.29, 35.91, 32.17, 31.87, 29.63, 29.51,
23.00, 17.88 (satellites, JPt-C = 754.6 Hz, Pt-Meaxial), 14.20,
1
1
-4.86 (satellites, JPt-C = 641.2 Hz, Pt-Mebasal) ppm. Anal.
Calcd for C94H112N8F6O6Pt2S2: C 55.94, H 5.59, N, 5.55.
Found: C 55.68, H 5.45, N 5.38.
Synthesis of [Pt2(TPAB)Me4(OTf)2] (7). A dry C6H6 solution
(3.0 mL) of Pt2(TPAB)Me4 (12 mg, 0.007 mmol) was allowed to
stand under one atmosphere of O2 in a Schlenk tube at ambient
temperature for 3 days, yielding a yellow suspension. MeOTf
(2.5 μL, ∼3 equiv) was then added quickly via microsyringe at
ambient temperature. After being shaken vigorously for about
10 s, the yellow suspension was warmed to 60 °C for 5 min,
resulting in a clear pale yellow solution. A large amount of
precipitates was produced upon cooling the solution. After
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada for financial
support and Dr. Ruiyao Wang for his assistance in X-ray
structure analyses.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.