Reactivity of a dimethylplatinum(II) complex with the bis(2-pyridyl) dimethylsilane Ligand: Easy silicon-carbon bond activation

Article abstract of DOI:10.1021/om3000136

The compound [PtMe₂(bps)] (1; bps = bis(2-pyridyl) dimethylsilane) undergoes easy oxidative addition with bromine, iodine, methyl iodide, or methyl triflate to give [PtBr₂Me₂(bps)], [PtI₂Me₂(bps)], [PtIMe₃(bps)], or [PtMe ₃(OH₂)(bps)][OTf], respectively. The complex [PtIMe ₃(bps)] is slowly hydrolyzed in solution, with cleavage of the pyridyl-silicon bonds, to give [PtIMe₃(py)₂] and (Me ₂SiO)_n. In contrast, oxidation of 1 with oxygen/CF ₃CH₂OH, hydrogen peroxide, or dibenzoyl peroxide/H ₂O occurs with cleavage of a methyl-silicon bond to give [PtMe(bps)-μ-{κ³N,N,O-OSiMe(2-C₅H ₄N)₂PtMe₃][CF₃CH ₂OB(C₆F₅)₃], [PtMe ₃{κ³N,N,O-(2-C₅H₄N) ₂SiMeO}], or [PtMe₃{κ³N,N,O-(2-C ₅H₄N)₂SiMeOH}][PhCOO], respectively. Mechanistic studies indicate that this methyl transfer from silicon to platinum occurs after oxidation to platinum(IV) and is induced by hydroxide attack at silicon.

Full text of DOI:10.1021/om3000136

Article
pubs.acs.org/Organometallics
Reactivity of a Dimethylplatinum(II) Complex with the Bis(2-
pyridyl)dimethylsilane Ligand: Easy Silicon−Carbon Bond Activation
Muhieddine Safa, Michael C. Jennings, and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
S
* Supporting Information
ABSTRACT: The compound [PtMe2(bps)] (1; bps = bis(2-pyridyl)-
dimethylsilane) undergoes easy oxidative addition with bromine, iodine,
methyl iodide, or methyl triflate to give [PtBr2Me2(bps)], [PtI2Me2(bps)],
[PtIMe3(bps)], or [PtMe3(OH2)(bps)][OTf], respectively. The complex
[PtIMe3(bps)] is slowly hydrolyzed in solution, with cleavage of the
pyridyl−silicon bonds, to give [PtIMe3(py)2] and (Me2SiO)n. In contrast,
oxidation of 1 with oxygen/CF3CH2OH, hydrogen peroxide, or dibenzoyl
peroxide/H2O occurs with cleavage of a methyl−silicon bond to give [PtMe(bps)-μ-{κ3N,N,O-OSiMe(2-C5H4N)2PtMe3]-
[CF3CH2OB(C6F5)3], [PtMe3{κ3N,N,O-(2-C5H4N)2SiMeO}], or [PtMe3{κ3N,N,O-(2-C5H4N)2SiMeOH}][PhCOO], respec-
tively. Mechanistic studies indicate that this methyl transfer from silicon to platinum occurs after oxidation to platinum(IV) and is
induced by hydroxide attack at silicon.
chemistry is complicated by the occurrence of Si−Me bond
activation.5 This paper gives a complete description of the
chemistry of the complex [PtMe2(bps)]. The ligand bps has
previously been used to form complexes of nickel, palladium,
and platinum, some of which are useful for formation of C−C
bonds by nickel- or palladium-catalyzed cross coupling.6
INTRODUCTION
■
There has been intense interest in carbon−hydrogen bond
activation by organoplatinum complexes, in a search for useful
catalysts and in order to gain a deeper understanding of
reactivity and mechanism in such reactions.1 Chelating
nitrogen-donor ligands are useful in C−H activation reactions
of the type shown in eq 1 (E = CH2, CO, NH), but not all such
RESULTS AND DISCUSSION
■
Synthesis and Structure of [PtMe2(bps)] (1). The
complex [PtMe2(bps)] (1) was prepared as an air-stable solid
by the reaction of [Pt2Me4(μ-SMe2)2]19 with bps, as shown in
1
eq 2. The H NMR spectrum of complex 1 contained a single
ligands give good reactivity.1−3 For example, when the
supporting ligand was di-2-pyridylmethane, the product of eq
1 was readily isolated, but when it was 2,2′-bipyridine, the
reactions were unsuccessful.3 It was argued that the twisting of
the pyridyl groups out of the square plane of the platinum(II)
center when LL = di-2-pyridylmethane, but not when LL = 2,2′-
bipyridine, was an important factor in determining reactivity
(Figure 1), and therefore that increasing the twist angle should
lead to increased reactivity.3 Introduction of a second
methylene bridge in the ligand increases the twist angle (Figure
1), but the seven-membered chelate ring formed by 1,2-bis(2-
pyridyl)ethane is not robust, and the easy dissociation of the
ligand from platinum makes it unsuitable as a supporting ligand
for C−H bond activation.4 A second way to increase the twist
angle is to introduce a larger single atom bridge between the 2-
pyridyl groups, and this paper describes the use of a
dimethylsilyl bridging group in the ligand bps = Me2Si(2-
C5H4N)2. A preliminary communication showed that the ligand
bps does give a larger twist angle (Figure 1) but that the
methylplatinum resonance at δ 0.71, with typical coupling
constant 2JPtH = 80 Hz,2−5 but two methylsilicon resonances at
δ 0.77 and 1.11. The nonequivalence of the methylsilicon
groups indicates that the ligand adopts a rigid-boat con-
formation (eq 2).
Received: January 6, 2012
Published: April 16, 2012
© 2012 American Chemical Society
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(2a, X = Br; 3a, X = I) according to eq 3. The complexes were
characterized by structure determination and by their 1H NMR
spectra.
The structures of complexes 2a and 3a are shown in Figure 3.
Complex 2a crystallized with some [PtBr3Me(bps)], with
Figure 1. Conformations of bis(pyridine) donors in platinum(II)
complexes and mean twist angles of the pyridyl groups from the
platinum(II) square plane: (a) (2-C5H4N)2CH2, 40°; (c) 1,2-(2-
C5H4N)2C2H4, 70°; (2-C5H4N)2SiMe2, 53°.
The structure of complex 1 is shown in Figure 2. It confirms
that the chelate ring is in the boat conformation, with one
Figure 3. Structures of complexes (a) 2a and (b) 3a. Selected bond
parameters for 3a (distances in Å and angles in deg): Pt−C(1),
2.079(8); Pt−C(2), 2.077(8); Pt−N(11), 2.210(6); Pt−N(25),
2.217(6); Pt−I(2), 2.6283(6); Pt−I(3), 2.6523(6); C(2)−Pt−C(1),
85.7(4); N(11)−Pt−N(25), 92.6(2); I(2)−Pt−I(3), 177.16(2);
C(19)−Si(17)−C(20), 115.3(4); C(19)−Si(17)−C(16), 114.9(4).
Figure 2. Structure of complex 1. Selected bond parameters (distances
in Å and angles in deg): Pt−C(1), 2.048(8); Pt−C(2), 2.043(8); Pt−
N(11), 2.121(7); Pt−N(25), 2.108(7); C(2)−Pt−C(1), 88.3(4);
N(25)−Pt−N(11), 90.7(2); C(19)−Si(17)−C(18), 109.7(4);
C(16)−Si(17)−C(20), 104.7(4).
disorder of equatorial methyl and bromide ligands, but 3a was
not disordered; therefore, its bond parameters are more
accurately determined.5 The structures are similar, and the
bps ligand is in the boat conformation in each case. The pyridyl
groups are twisted out of the Me2PtN2 plane by an average
value of 40° in 2a and 43° in 3a, compared to 53° in complex 1.
The lower twist, and hence flatter boat structure, in the
platinum(IV) complexes 2a and 3a appears to arise from steric
repulsion between bromide or iodide and the adjacent
methylsilicon group, aided by longer Pt−N distances than in
1. The distance Pt···C(19) is 3.52 Å in 1 but 4.80 Å in 3a, and
the angles C(19)−Si(17)−C(20) = 115.3(4)° and C(19)−
Si(17)−C(16) = 114.9(4)° in 3a are significantly distorted
methylsilicon group oriented below the square plane of the
platinum atom, with Pt···Si(17) = 3.25 Å. The angles about the
platinum and silicon atoms are close to the ideal values for
square-planar and tetrahedral centers, respectively, and so
indicate that there is little strain in the six-membered chelate
ring. The pyridyl groups are twisted by an average of 53° out of
the square plane of the platinum center.
Oxidative Addition Reactions with Bromine and
Iodine. Complex 1 reacted easily with bromine or iodine by
trans oxidative addition, to give the products [PtX2Me2(bps)]
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from tetrahedral, in order to relieve the Me···I repulsive
interaction. It is clear from Figure 2 that the preferred
orientation of the bps ligand in square-planar complexes must
distort in order to allow octahedral coordination in platinum-
(IV) complexes.6
The 1H NMR spectrum of complex 3a gave a single
resonance for the two methylplatinum groups at δ 2.31, with
2
the coupling constant JPtH = 71 Hz. However, in contrast to
complex 1, the two methylsilicon groups also gave a singlet
resonance at δ 0.76. The methylsilicon resonance became broad
on cooling to −80 °C but did not split, indicating very much
easier inversion of the chelate ring than in the square-planar
complex 1. This easy fluxionality of complex 3a, which must
involve boat inversion, can be understood in terms of the flatter
boat structure in comparison to the more rigid complex 1.
Oxidative Addition of Methyl Iodide or Triflate and
Hydrolysis of the bps Ligand. Complex 1 reacted rapidly
with methyl iodide to give [PtIMe3(bps)] (4), whose structure
Figure 4. Structure of [PtIMe3(C5H5N)2] (5). Selected bond
parameters (distances in Å): Pt−C(1), 2.05(1); Pt−C(2), 2.07(1);
Pt−N(11), 2.191(7); Pt−N(21), 2.197(7); Pt−I, 2.7917(9) Å.
1
was readily deduced from its H NMR spectrum; it contained
2
two methylplatinum resonances at δ 0.94, with JPtH = 72 Hz
2
(Me trans to I) and at δ 1.32, with JPtH = 68 Hz (Me trans to
N), and two methylsilicon resonances at δ 0.65 and 0.81. In this
case, inversion of the Pt(bps) boat conformation does not make
the methylsilicon groups equivalent. It is likely that the more
stable Pt(bps) boat conformation brings the syn-MeSi group
closer to the axial methylplatinum rather than to the larger
iodoplatinum group, as shown in Scheme 1. Complex 4 could
Scheme 1
Figure 5. NMR spectra during the reaction of complex 1 with CD3I in
1
1
CD2Cl2: (a) H NMR of complex 1 at −50 °C; (b) H NMR of 4′
after addition of CD3I at −50 °C; (c) 1H NMR of 4a/4b after 1 day at
2
20 °C; (d) H NMR of 4a/4b after 1 day at 20 °C. 195Pt satellite
spectra are indicated by *.
be isolated in pure form from the above reaction, but in
solution in moist CD2Cl2 it was slowly hydrolyzed over a
period of several days at room temperature to give the known
complex [PtIMe3(C5H5N)2] (5)7 and dimethylsiloxane poly-
mer (Me2SiO)n, by selective cleavage of the pyridyl−silicon
bonds (Scheme 1). The hydrolysis product (Me2SiO)n was
scrambling of MePt and CD3Pt groups was complete in several
hours at room temperature to finally give the roughly 2:1
mixture of 4b and 4a expected from statistical factors (Figure
5c). The 2H NMR spectrum (Figure 5d) confirmed the
assignment and showed that there was no exchange of CD3Pt
and MeSi groups. The scrambling of MePt and CD3Pt groups is
proposed to occur through cationic five-coordinate intermedi-
ates A and B (Scheme 2).9,10
The reaction of methyl triflate with complex 1 in acetone,
followed by recrystallization, gave the cationic aqua complex
[PtMe3(OH2)(bps)]+ as the triflate salt 6, whose structure is
shown in Figure 6. The Pt(bps) chelate rings are similar in
complexes 2, 3, and 6, with the pyridyl groups in 6 twisted out
of the C2PtN2 plane by an average of 42° with silicon syn to
C(1) (Figure 6). The aqua ligand hydrogen bonds to two
triflate anions in the dimeric structure, with O(4)···O(1B) =
2.71(1) and O(4)···O(2A) = 2.77(1) Å.
1
characterized by a broad methylsilicon resonance in the H
NMR spectrum at δ 0.1 and by a series of peaks in the ESI-MS
corresponding to (Me2SiO)n.8 The complex [PtI-
Me3(C5H5N)2] (5) crystallized during attempts to grow
crystals of its precursor complex 4 and was structurally
characterized (Figure 4). Although complex 5 has been
known for many years, its structure has not previously been
determined.7
The stereochemistry of the initial oxidative addition was
determined by monitoring the reaction of complex 1 with CD3I
at low temperature (Figure 5). Addition of CD3I at −50 °C led
to rapid trans oxidative addition to give complex 4a (Scheme 2,
Figure 5a,b), as shown by the absence of the axial
methylplatinum (trans to I) resonance of complex 4. The
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Scheme 2
Figure 7. 1H NMR spectra (400 MHz) of complex 6 in acetone-d6 at
(a) 20 °C, (b) −10 °C, and (c) −40 °C.
Scheme 3
equation to be ΔG⧧ = 56 kJ mol−1. At low temperature,
complex 6 is likely to be the major component, but minor peaks
could arise from the triflate complex 7 and the acetone complex
8, all of which are in rapid equilibrium at room temperature.
The ESI-MS of the isolated complex gave a major envelope of
peaks centered at m/z 472, as expected for the aqua complex
cation, and the corresponding complex prepared from 1-d6 and
CH3OTf gave the corresponding peak at m/z 478, as expected
for [PtMe(CD3)2(OH2)(bps)]+. If intermolecular methyl
group exchange occurred, peaks for all ions
[PtMen(CD3)3−n(OH2)(bps)]+ would be expected, and so the
experiment shows that the Me/CD3 exchange is intramolecular
(Scheme 3).9,10
Figure 6. Structure of complex 6. Selected bond parameters (distances
in Å): Pt(1)−C(1), 2.027(2); Pt(1)−C(14), 2.048(2); Pt(1)−C(15),
2.039(2); Pt(1)−N(1), 2.179(2); Pt(1)−N(2), 2.190(2); Pt(1)−
O(4), 2.179(2) Å. Hydrogen-bonding distances (in Å): O(4)···O(1),
2.71(1); O(4)···O(2), 2.77(1) Å.
1
The H NMR spectrum of complex 6 in acetone-d6 at room
temperature contained single resonances for the methylplati-
2
num groups at δ 1.21, with JPtH = 71 Hz, and for the
methylsilicon groups at δ 0.85. Since two MePt and two MeSi
resonances are expected for the structure of Figure 6, the
complex must be fluxional. At low temperature, each resonance
splits to give two major peaks along with some minor poorly
resolved ones, as shown in Figure 7. The very easy fluxionality
in this case is clearly due to the lability of the potential aqua,
acetone, and triflate ligands, which gives easy access to the
nonrigid five-coordinate intermediates C and D (Scheme 3).9,10
The free energy of activation is estimated from the Eyring
The reaction of complex 6 with methyl triflate in CD3CN
solution gave the complex [PtMe3(NCCD3)(bps)]OTf (9)
(Scheme 3), whose 1H NMR spectrum contained two
2
methylplatinum resonances at δ 0.93 (3H, JPtH = 76 Hz)
and 1.04 (6H, 2JPtH = 66 Hz) and two methylsilicon resonances
at δ 0.69 and 0.79, as expected for a rigid structure. Acetonitrile
is a better ligand than acetone for platinum, and ligand
dissociation from 9 is evidently slow on the NMR time scale.
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Reactions of Complex 1 with HCl. Complex 1 reacted
rapidly with excess HCl at −80 °C to give a transient
hydridoplatinum(IV) intermediate, 10, and then methane and
the product of protonolysis of both methylplatinum bonds,
[PtCl2(bps)] (11) (Scheme 4). Complex 10 was identified in
Scheme 4
the 1H NMR spectrum of the reaction mixture at −80 °C by its
hydridoplatinum resonance, which was seen at δ −20.64, with
1JPt−H = 1593 Hz, with parameters similar to those for several
similar complexes.1−4,11 Complex 10 was short-lived even at
low temperature and so could not be fully characterized. The
formation of complex 11 is expected to occur through
intermediates 10, [PtClMe(bps)], and [PtHCl2Me(bps)],1−4
but only 10 was positively identified. Complex 11 existed in a
rigid-boat conformation in solution, as shown by the presence
1
of two methylsilicon resonances at δ 0.90 and 1.45 in the H
NMR spectrum, and in the solid state, as shown by a structure
determination (Figure 8). This conformation of the bps ligand
is similar to that in complex 1 (Figure 2), with the pyridyl
groups twisted out of the square plane of the platinum center
by an average of 54°. There is a similarly short contact C(19)−
H···Pt = 2.93 Å, which partially blocks one potential axial
coordination site. The platinum(II) complex 11 was stable in
the presence of HCl in CD2Cl2 solution and did not undergo
cleavage of the silicon−carbon bonds at room temperature, in
contrast to the easy hydrolysis of the pyridyl−carbon bonds in
complex 4. Electrophiles usually give selectivity for aryl−silicon
over methyl−silicon bonds, and 2-pyridyl−silicon bonds can be
cleaved following initial nucleophilic attack at silicon.12
An Unexpected Methyl−Silicon Bond Cleavage
Reaction. The reaction of complex 1 with B(C6F5)3 in
CF3CH2OH was carried out in the presence of anisole, with the
aim of activating an aromatic C−H bond. However, the
reaction was found to occur according to Scheme 5, with the
anisole playing no role, to give complex 12.5 The reaction had
been expected to give initially [PtMe(bps){CF3CH2OB-
(C6F5)3}], and the cation [PtMe(bps)]+ was then expected to
react with anisole, in a way similar to that shown in eq 1.
However, although complex 12 does contain a [CF3CH2OB-
(C6F5)3]− anion and a square-planar platinum(II) center, with
the expected [PtMe(bps)]+ fragment, this platinum(II) frag-
ment is connected to an octahedral platinum(IV) center. The
platinum(IV) unit can be regarded as [PtMe3{κ3N,N,O-(2-
C5H4N)2SiMeO}], which then acts as a ligand for the
platinum(II) fragment, by coordination through the bridging
oxygen atom (Figure 9). The sum of the bond angles about this
bridging oxygen atom is 358°, indicating that the lone pair of
electrons on oxygen is involved in π bonding and so is not
stereochemically active. The original κ2-N,N-(2-C5H4N)2SiMe2
Figure 8. Structure of complex 11. Selected bond parameters
(distances in Å and angles in deg): Pt−Cl(1), 2.294(4); Pt−Cl(2),
2.296(3); Pt−N(11), 2.026(11); Pt−N(25), 2.022(11); Cl(1)−Pt−
Cl(2), 90.3(1); N(25)−Pt−N(11), 91.2(5); C(18)−Si(17)−C(19),
112.4(7); C(16)−Si(17)−C(20), 101.4(6). The space-filling model
below shows how the syn methylsilicon group lies close to the
platinum atom.
ligand in 1 was converted to the κ3-N,N,O-(2-C5H4N)2SiMeO−
ligand in 12, in a process which formally involves substitution
of a methyl by an oxide group at silicon. This was unexpected,
given that the 2-pyridylsilicon bond is much more reactive to
Scheme 5
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platinum bond.14−16 The hydroxoplatinum(IV) complexes are
basic, and they take part in strong hydrogen bonding or
undergo protonation to give [PtMe2(OH)(OH2)(LL)]+.14,15
A solution of complex 1 in acetone was stable to air, but a
solution in methanol was slowly oxidized over a period of
several hours according to Scheme 7. A complex with
Scheme 7
Figure 9. Structure of the cationic component of complex 12. Selected
bond parameters (distances in Å and angles in deg): Pt(1)−N(11),
2.134(6); Pt(1)−N(25), 2.001(6); Pt(1)−O(2), 2.028(5); Pt(1)−
C(1), 2.039(8); Pt(2)−N(31), 2.195(6); Pt(2)−N(45), 2.190(6);
O(2)−Pt(2), 2.244(5); C(3)−Pt(2), 2.043(8); C(4)−Pt(2),
2.047(8); O(2)−Si(37), 1.632(5); Si(37)−O(2)−Pt(1), 126.3(3);
Si(37)−O(2)−Pt(2), 99.8(2); Pt(1)−O(2)−Pt(2), 132.0(2); O(2)−
Si(37)−C(38), 119.2(3).
hydrolysis than the methyl−silicon bond in free silanes such as
Me3Si-2-C5H4N,12 as well as in complex 4 (Scheme 1), as
described above. The silicon−carbon bond activation evidently
occurred under conditions milder than those for many other
transition-metal-activated silicon−carbon bond cleavage reac-
tions.13 It was considered likely that the oxidation to give the
platinum(IV) unit in 12, and the origin of the oxide group,
arose from reaction with oxygen (Scheme 5).
essentially identical NMR parameters was formed rapidly
when complex 1 was treated with hydrogen peroxide in
methanol.5 Although these complexes were formed in high
yield in solution, as determined by monitoring the reactions in
CD3OD solution by 1H NMR, attempts to isolate the products
occurred with considerable amounts of decomposition. The 1H
NMR parameters for products of reactions in CD3OD are
consistent with either structure 13 or 14. The ESI-MS in
methanol contained a peak at m/z 456, corresponding to
[PtMe3(HOSiMe(2-C5H4N)2)]+, but this does not distinguish
between 13 or 14 as the more stable form, since they are likely
to be in equilibrium and only the cation will give a peak in the
ESI-MS. The corresponding product from the reaction of
complex 1 with 18O2/MeOH gave the corresponding peak in
the ESI-MS at m/z 458, confirming that the oxygen atom was
derived from dioxygen and not from methanol. The reaction of
complex 1 with dibenzoyl peroxide gave complex 15 (Scheme
7, Figure 10), which was sufficiently stable to be crystallized and
so could be characterized more definitively. It gave a peak in the
ESI-MS at m/z 456, as expected for the cation
[PtMe3(HOSiMe(2-C5H4N)2)]+.
The structure of complex 15 (Figure 10) confirms that the
methyl transfer from silicon to platinum has occurred to give a
trimethylplatinum(IV) complex. An unusual feature of the
structure is the tight association of the benzoate group, with the
distance Si(1)···O(2A) = 3.07(1) Å indicating a significant
secondary bonding interaction between the benzoate anion and
silicon, and the distance O(3)···O(1A) = 2.46(1) Å indicating a
strong hydrogen bond. The hydrogen atom between O(3) and
O(1A) (Figure 10) was tentatively located closer to O(3) than
to O(1A), but it could not be refined. A DFT calculation on the
simpler acetate complex (Figure 11) supports the presence of
an unsymmetrical hydrogen bond with PtO−H = 1.12 Å and
CO−H = 1.36 Å, thus supporting the formulation of 15 as
b e i n g c l o s e r t o [ P t M e 3 { κ 3 N , N , O - ( 2 -
C5H4N)2SiMeOH}]+[PhCO2]−, a rare example of a silanol
complex,17 than to [PtMe3{κ3N,N,O-(2-C5H4N)2SiMeO}]-
[PhCO2H], in each case with a strong hydrogen bond and
The NMR spectra showed that complex 12 was stable in
1
solution. The cation has only C1 symmetry, and the H NMR
spectrum contained four methylplatinum and three methyl-
silicon resonances. Individual assignments were confirmed by
recording the NOESY spectrum. Three equal-intensity
methylplatinum(IV) resonances occurred at δ 0.15 (2JPt−H
=
69 Hz), 1.17 (2JPt−H = 68 Hz), and 1.23 (2JPt−H = 78 Hz), and
the methylplatinum(II) resonance occurred at δ 0.64 (2JPt−H
=
75 Hz). The two methylsilicon resonances of the (bps)PtII unit
occurred at δ 0.95 and 1.63, while the single methylsilicon
resonance of the κ3N,N,O-(2-C5H4N)2SiMeO− ligand occurred
at δ 1.22. If the compound had undergone dissociation in
solution, the [PtMe3{κ3N,N,O-(2-C5H4N)2SiMeO}] unit
would give only two methylplatinum resonances in a 2:1
intensity ratio, since it would have Cs symmetry.
Oxidation of [PtMe2(bps)] with Peroxides and Air.
Dimethylplatinum(II) complexes [PtMe2(LL)], containing
chelating nitrogen-donor ligands LL, typically react with
hydrogen peroxide or with dioxygen in protic media (in the
presence of H2O or ROH) to give platinum(IV) complexes
[PtMe2(OH)2(LL)] or [PtMe2(OH)(OR)(LL)] (Scheme 6),
though oxygen is also known to give insertion into a methyl−
Scheme 6
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The 1H NMR spectrum, in the region of the MePt and MeSi
groups, of the product (14) of reaction of H2O2 with complex 1
in CD3OD solution is shown in Figure 12a. There are two
Figure 12. 1H NMR spectra (400 MHz, CD3OD) in the methyl
region for reactions of hydrogen peroxide with (a) complex 1 and (b)
complex 1-d6. 195Pt satellite spectra of the axial (PtMea) and equatorial
(PtMee) methylplatinum protons are shown as * and #, respectively.
The low-intensity triplet in (b) at δ 1.0 arises from ether impurity.
Figure 10. Structure of complex 15. Selected bond parameters
(distances in Å and angles in deg): Pt(1)−C(1), 2.050(5); Pt(1)−
C(2), 2.045(4); Pt(1)−C(3), 2.051(5); Pt(1)−N(1), 2.181(4);
Pt(1)−N(2), 2.168(4); Pt(1)−O(3), 2.237(3); Si(1)−O(3),
1.623(3); O(3)···O(1A), 2.46(1); Si(1)···O(2A), 3.07(1); Si(1)−
O(3)−Pt(1), 99.0(1); O(3)−Si(1)−C(4), 120.7(2).
2
methylplatinum resonances at δ 0.98 (6H, JPtH = 69 Hz,
2
PtMee) and 1.15 (3H, JPtH = 75 Hz, PtMea) and only one
methylsilicon resonance at δ 0.94 (3H, MeSi), as expected for
structure 14 (Scheme 7). A similar reaction with [Pt-
(CD3)2(bps)] (1-d6) gave the corresponding product [Pt-
1
(CD3)2Me{κ3N,N,O-(2-C5H4N)2SiMeO}] (14-d6), whose H
NMR spectrum is shown in Figure 12b. The equatorial
methylplatinum resonance of 14 (Figure 12a) is absent in this
spectrum, showing clearly that the methyl group transferred
from silicon occupies only the axial position in 14-d6, as shown
in Scheme 8. The reaction of 1-d6 with dibenzoyl peroxide
occurred in a similar way to give 15-d6 as the kinetic product,
but this complex underwent Me/CD3 exchange over a period of
about 2 days to give a 1:2 equilibrium mixture of 15-d6 and
15a-d6 (Scheme 8). It is likely that this scrambling reaction
Scheme 8
Figure 11. Calculated structures of adducts of complex 14 with (a)
H2O and (b) MeCO2H, including the calculated OH distances.
weaker Si···O secondary bond of the kind likely to be involved
in nucleophilic substitution at silicon.18 In contrast, a DFT
calculation suggests the product from hydrogen peroxide
oxidation is more reasonably regarded as [PtMe3{κ3N,N,O-(2-
C5H4N)2SiMeO}][H2O] than as [PtMe3{κ3N,N,O-(2-
C5H4N)2SiMeOH}]+[OH]−, with calculated hydrogen bond
distances PtO−H = 1.44 Å and HO−H = 1.06 Å (Figure 11).
These formulations are consisted with the expected series of
basicity MeO−
>
HO−
>
[PtMe3 {κ3 N,N,O-(2-
−
C5H4N)2SiMeO}] > PhCO2 . The low basicity of siloxanes is
usually attributed to π-donation from lone pairs on oxygen to
σ* orbitals of the R3Si unit.19 The products of oxidation of
complex 1 by H2O2 or O2/MeOH are therefore suggested to
have structure 14 rather than 13a or 13b, respectively (Scheme
7).
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occurs within a five-coordinate intermediate formed by
reversible dissociation of the silanol donor. There was no
CH3/CD3 exchange with the MeSi group, indicating that the
methyl group transfer to give 15 is irreversible. The ESI-MS of
14-d6 or 15-d6 in MeOH each contained a peak at m/z 462, as
expected for [Pt(CD3)2Me{κ3N,N,O-(2-C5H4N)2SiMeOH}]+.
The ease of the methyl group transfer to form complexes 14
and 15, without forming a Pt−Si bond, and the mutually trans
positions of the methyl and silanol units in the kinetically
controlled products, are unusual features of the reactions of
Scheme 8.13,20 A proposed mechanism is shown in Scheme 9.5
complete methyl transfer from silicon to platinum is
unfavorable because the Si−Me bond is stronger than the
Pt−Me bond.22 Two possible ways for rearrangement of
complex E are shown in Figure 14. The more favorable reaction
Scheme 9
The initial reaction is likely to occur by donation of electrons
2
from the filled 5dz orbital of the platinum(II) center of
complex 1 to the vacant σ*(O−O) orbital of the hydrogen
peroxide (Figure 13), which leads to oxidation of the platinum
Figure 14. Calculated relative energies and structures of platinum
complexes J and 14·H2O and potential reaction intermediates E and
G−I.
occurs by attack by hydroxide at silicon (F, Scheme 9) with
simultaneous methyl group transfer to platinum to give G.
Inversion of the chelate ring can occur to give H and then the
five-coordinate silicon compound I,23 with final rearrangement
gives the product 14·H2O (Scheme 9, Figure 14). The
hydroxide group might also attack at platinum to give J, the
product of simple oxidative addition (Figure 14),14 in a way
similar to that in reactions of complex 1 with halogens (eq 3),
but this is calculated to be less favorable and is not observed.
The key difference between the reactions of complex 1 with
halogens (eq 3) and hydrogen peroxide (Schemes 8 and 9) is
the much higher strength of the Si−O bond in comparison to
the Pt−O bond, with the hard oxygen-donor ligand which
favors attack by hydroxide at silicon rather than platinum.23 It is
noted that this reaction would normally be expected to occur
with cleavage of a pyridyl−silicon bond,12 as in the hydrolysis
of complex 4 (Scheme 1), and so the selectivity for cleavage of
the methyl−silicon bond must result from electrophilic
assistance from the adjacent platinum(IV) center.24
2
Figure 13. (left) Frontier orbitals, the filled 5dz orbital of complex 1,
and the vacant σ*(O−O) orbital of H2O2. (right) Calculated structure
of E (Scheme 9), with selected distances.
atom and cleavage of the O−O bond. A DFT calculation
predicts that this reaction is favorable and that there will be
strong hydrogen bonding between the incipient ion pair
[Pt(OH)Me2(bipy)]+OH− (E) (Figure 13), whose structure
may then also be considered as the aquated oxoplatinum(IV)
complex [Pt(O)Me2(bipy)]·OH2. In solution, a more exten-
sively solvated form is probable, and the theory indicates no
significant multiple-bond character in the Pt−O bond of E;
thus, it is better considered as Pt+-O− rather than PtO.21
Complex E is predicted to have a weak SiCH···Pt interaction
(Figure 13), which may be considered as an agostic bond, but
DISCUSSION AND CONCLUSIONS
■
The most unusual feature of the chemistry described above is
the easy methyl group transfer from silicon to platinum that
occurs during some oxidative addition reactions but not
others,5 and it is important to place this chemistry in a broader
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context. A reaction analogous to those discussed above is
observed in the methyl transfer from boron to platinum on
oxidation of the dimethylbis(2-pyridyl)borate complex shown
in eq 4 (R = Me, Ph, R′ = H, Me, Et, i-Pr).24 In the case of the
Scheme 11. Proposed Sequence of Reactions To Form
Complex 15 by Reaction of 1 with (PhCO2)2
boron ligand (eq 4), the alkyl transfer may be reversible and, in
reactions in alcohol solvents, the alkoxide group remains in the
product.24 However, in the case of the silicon ligand, bps, the
methyl transfer is not reversible (Schemes 2 and 3), and the
alkoxide group is not observed in the product 14 (Scheme 7).
The initial reaction of complex 1 with dibenzoyl peroxide is
expected to be [Pt(O2CPh)Me2(bipy)]+[PhCO2]−, with a
coordinated benzoate ligand, but the observed product is
complex 15, which contains no platinum−benzoate group
(Figure 10).5
With oxygen-donor ligands, associative substitution at silicon
and dissociative substitution at platinum(IV) are both expected
to occur easily, and so the thermodynamically preferred
product can be formed by displacement of the oxygen-donor
ligand from either silicon (Scheme 10) or platinum (Scheme
11). However, substitution at boron is likely to be slow, and so
the product is formed by kinetic control in the reaction of eq
4.12,24
The reactions of complex 1 with dioxygen in methanol are
expected to occur according to Scheme 10. The initial reaction
Scheme 10. Proposed Sequence of Reactions To Form
Complex 14 by Reaction of 1 with Dioxygen
In the proposed mechanisms of Schemes 9−11, it is
important that the methyl group transfer from silicon to
platinum is aided by attack of a hard oxygen-donor ligand at
silicon rather than at platinum(IV), and this is also likely to be
important in intermolecular transfer of alkylsilicon groups to
transition metals during stoichiometric or catalytic reac-
tions.13,22 The only case of oxidative addition using a reagent
with an R−O bond without accompanying methyl group
transfer was with methyl triflate (Figure 6, Scheme 3). In this
case, the methyl group transfer would lead to a
tetramethylplatinum(IV) center, with anunfavorable trans-
Me−Pt−Me linkage.25 Overall, the reactions described by
Vedernikov24 and in the present work (and preliminary
communication)5 give considerable new insight into how
alkyl transfer reactions to platinum(IV) and electrophilic
cleavage of alkyl−platinum(IV) bonds can occur.
EXPERIMENTAL SECTION
■
NMR spectra were recorded by using a Varian Mercury 400 and
Varian Inova 400 and 600 spectrometers. Chemical shifts are reported
relative to TMS. The ligand bps and the complexes cis-/trans-
[PtCl2(SMe2)2], [Pt2Me4(μ-SMe2)2], and [Pt2(CD3)4(μ-SMe2)2] were
prepared according to the literature.6,26 18O2 (97%) was purchased
from Aldrich.
gives a hydroperoxo complex cation, with methoxide anion, and
the hydroperoxo group reacts rapidly with a another 1 equiv of
complex 1 to give 2 equiv of a cationic hydroxoplatinum(IV)
complex with methoxide anion.14,15 The methoxide group then
attacks at silicon with methyl group transfer to platinum(IV),
and finally, the methoxo group is displaced from silicon by the
PtOH group to give the product 14 (Scheme 10). The unit of
14 present in the complex 12 (Scheme 5, Figure 9) is presumed
to be formed in an analogous way, but with trifluoroethanol in
place of methanol.
This mechanism can be compared with the proposed
mechanism of reaction with dibenzoyl peroxide, in which the
final step involves displacement of benzoate from platinum by
the SiOH group (Scheme 11).
X-ray Structure Determinations. Data were collected at −123
°C using a Nonius Kappa-CCD area detector diffractometer with
COLLECT software and with Mo Kα radiation (λ = 0.710 73 Å). The
unit cell parameters were calculated and refined from the full data set,
and data were refined using the standard software.27
DFT Calculations. Calculations were made using the Amsterdam
Density Functional program based on the Becke−Perdew functional,
with first-order scalar relativistic corrections.28
[PtMe2(bps)] (1). To a stirred solution of bis(2-pyridyl)-
dimethylsilane (0.75 g, 3.5 mmol) in ether (10 mL) was added
[Pt2Me4(μ-SMe2)2] (1.01 g, 1.75 mmol). The product precipitated
from solution as a pale brown solid, which was separated, washed with
ether (3 × 2 mL) and pentane (3 × 2 mL), and then dried under high
vacuum. Yield: 1.35 g, 88%. NMR in CDCl3: δ(1H) 0.71 (s, 6H, 2JPtH
=
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80 Hz, PtMe), 0.77 (s, 3H, SiMe), 1.11 (s, 3H, SiMe), 7.21 (t, 2H,
[Pt(H)ClMe2(bps)] (10) and [PtCl2(bps)] (11). To a solution of
[PtMe2(bps)] (0.010 g, 0.022 mmol) in CD2Cl2 (0.5 mL) in an NMR
tube at −80 °C was added a solution of HCl in CD2Cl2 (0.5 mL) at
−80 °C. The course of the reaction was monitored by NMR. NMR at
−80 °C for complex 10: δ(1H) −20.64 (s, 1H, 1JPtH = 1593 Hz, Pt-H),
3JHH = 5 Hz, H5), 7.55 (d, 2H, 3JHH = 7 Hz, H3), 7.67 (dd, 2H, 3JHH
=
5 Hz, 7 Hz, H4), 8.97 (d, 2H, 3JHH = 5 Hz, 3JPtH = 25 Hz, H6); δ(13C)
−20.0 (s, PtMe), −3.91 (s, SiMesyn), −1.74 (s, SiMeanti), 125.4, 130.4,
1
133.7, 152.4, 163.1 (py). The H NMR spectrum was essentially the
2
0.71 (s, 3H, SiMe), 0.81 (s, 3H, SiMe), 1.11 (s, 6H, JPtH = 65 Hz,
same at −50 °C. Anal. Calcd for C14H20N2PtSi: C, 38.26; H, 4.59; N,
6.37. Found: C, 38.53; H, 4.85; N, 6.33.
3
3
PtMe), 7.46 (dd, 2H, JHH = 5, 8 Hz, H5), 7.69 (d, 2H, JHH = 8 Hz,
H3), 7.96 (t, 2H, 3JHH = 8 Hz, H4), 9.31 (d, 2H, 3JHH = 5 Hz, 3JPtH = 18
Hz, H6), NMR at 20 °C for complex 11: δ(1H) 0.90 (s, 3H, SiMe),
[PtI2Me2(bps)] (3). To a stirred solution of [PtMe2(bps)] (0.200 g,
0.455 mmol) in CH2Cl2 (5 mL) was added excess iodine (0.012 g).
After 2 h the solvent was removed under vacuum to give the product
as a red solid, which was washed with pentane (3 × 3 mL) and ether
(3 × 3 mL) and dried under high vacuum. It was crystallized from
CH2Cl2/pentane. Yield: 0.265 g, 84%. NMR in CD2Cl2: δ(1H) 0.81 (s,
6H, SiMe), 2.39 (s, 6H, 2JPtH = 71 Hz, PtMe), 7.42 (dd, 2H, 3JHH = 5
Hz, 7 Hz, H5), 7.78 (d, 2H, 3JHH = 7 Hz, H3), 7.86 (t, 2H, 3JHH = 7 Hz,
1.45 (s, 3H, SiMe), 7.39 (dd, 2H, JHH = 5, 7 Hz, H5), 7.61 (d, 2H,
3
3JHH = 7 Hz, H3), 7.80 (t, 2H, 3JHH = 7 Hz, H4), 9.15 (d, 2H, 3JHH = 5
Hz, JPtH = 42 Hz, H6).
3
[PtMe(bps)-μ-{OSiMe(2-C5H4N)2PtMe3][CF3CH2OB(C6F5)3]
(12). To a solution of [PtMe2(bps)] (0.18 g, 0.45 mmol) in
CF3CH2OH (5 mL) was added a solution of B(C6F5)3 (0.23 g, 0.45
mmol) in CF3CH2OH (5 mL). The mixture was stirred for 2 days, the
volume of the solution was reduced to 2 mL, and the mixture was
cooled to 0 °C for 2 days to give colorless crystals of the product,
which were separated, washed with ether, and dried under high
vacuum. Yield: 0.128 g, 37%. NMR in acetone-d6: δ(1H) 0.15 (s, 3H,
3
3
H4), 9.36 (m, 2H, JHH = 5 Hz, JPtH = 22 Hz, H6). Anal. Calcd for
C14H20I2N2PtSi: C, 24.25; H, 2.91; N, 4.04. Found: C, 23.88; H, 2.77;
N, 4.32. The complex [PtBr2Me2(bps)] (2) was prepared similarly
from [PtMe2(bps)] (0.200 g, 0.455 mmol) and bromine but could not
be separated from [PtBr3Me(bps)]. Yield: 0.21 g. NMR for 2 in
CD2Cl2: δ(1H) 0.82 (s, 6H, SiMe), 1.25 (s, 6H, 2JPtH = 70 Hz, PtMe),
7.33 (dd, 2H, 3JHH = 5 Hz, 7 Hz, H5), 7.71 (d, 2H, 3JHH = 7 Hz, H3),
7.77 (t, 2H, 3JHH = 7 Hz, H4), 9.44 (m, 2H, 3JHH = 5 Hz, 3JPtH = 17 Hz,
H6). NMR for [PtBr3Me(bps)] in CD2Cl2: δ(1H) 0.83 (s, 6H, SiMe),
2
2JPtH = 69 Hz, PtMe), 0.64 (s, 3H, JPtH = 75 Hz, PtMe), 0.95 (s, 3H,
SiMe), 1.17 (s, 3H, 2JPtH = 68 Hz, PtMe), 1.22 (s, 3H, SiMe), 1.23 (s,
2
3H, JPtH = 78 Hz, PtMe), 1.63 (s, 3H, SiMe), 3.57 (q, 2H, CH2),
3
3
7.01−8.15 (12H, H3−H5), 8.49 (d, 1H, JHH = 5 Hz, JPtH = 20 Hz,
2
2.95 (s, 3H, JPtH = 68 Hz, PtMe), 7.42−7.95 (m, 6H, H3−H5), 9.15
H6), 8.60 (d, 1H, 3JHH = 5 Hz, 3JPtH = 20 Hz, H6), 8.72 (d, 1H, 3JHH
=
(m, 1H, 3JHH = 5 Hz, 3JPtH = 38 Hz, H6 trans to Br), 9.89 (m, 1H, 3JHH
5 Hz, 3JPtH = 21 Hz, H6), 8.96 (d, 1H, 3JHH = 6 Hz, 3JPtH = 65 Hz, H6
trans to O); δ(19F) −75 (br, 3F, CF3), −133 (br m, 6F, Ar−Fo), −164
(t, 3F, Ar−Fp), −168 (br, 6F, Ar−Fm). Anal. Calcd for
C47H39BF21N4O2Pt2Si2: C, 36.47; H, 2.54; N, 3.62. Found: C, 36.77;
H, 2.32; N, 3.62.
3
= 5 Hz, JPtH = 18 Hz, H6 trans to Me).
[PtIMe3(bps)] (4). To a solution of [PtMe2(bps)] (0.100 g, 0.228
mmol) in ether (10 mL) was added MeI (0.042 g, 0.30 mmol). After
30 min the product precipitated as a white solid, which was separated,
washed with pentane (3 × 5 mL), and dried under vacuum. Yield: 0.11
g, 82%. NMR in CD2Cl2: δ(1H) 0.65 (s, 3H, Si-Me), 0.81 (s, 3H, Si-
Me), 0.94 (s, 3H, 2JPtH = 72 Hz, Pt-Me), 1.32 (s, 6H, 2JPtH = 68 Hz, Pt-
Me), 7.35 (dd, 2H, 3JHH = 5 Hz, 7 Hz, H5), 7.79 (d, 2H, 3JHH = 7 Hz,
H3), 7.81 (t, 2H, 3JHH = 7 Hz, H4), 9.63 (d, 2H, 3JHH = 5 Hz, 3JPtH = 20
Hz, H6). Anal. Calcd for C15H23IN2PtSi: C, 30.99; H, 3.99; N, 4.82.
Found: C, 31.24; H, 3.72; N, 4.57.
[PtMe3{κ3N,N,O-(2-C5H4N)2SiMeO}] (14). To a solution of
[PtMe2(bps)] (0.010 g, 0.022 mmol) in CD3OD (1 mL) was added
excess hydrogen peroxide (0.01 mL, 30%). NMR in CD3OD: δ(1H)
2
0.94 (s, 3H, SiMe), 0.98 (s, 6H, JPtH = 69 Hz, PtMe), 1.15 (s, 3H,
2JPtH = 75 Hz, Pt-Me), 7.43 (dd, 2H, 3JHH = 5 Hz, 7 Hz, H5), 7.80 (d,
2H, 3JHH = 7 Hz, H3), 7.86 (t, 2H, 3JHH = 7 Hz, H4), 8.97 (d, 2H, 3JHH
= 5 Hz, 3JPtH = 20 Hz, H6). ESI-MS: m/z 456; calcd for 14 + H+ 456.
The complex decomposed on attempted isolation. A compound with
identical NMR properties was formed by reaction of [PtMe2(bps)]
with O2 in MeOH for 1 day. ESI-MS: m/z 456; calcd for 14 + H+ 456;
product from 18O2 gave m/z 458.
[PtI(CD3)Me2I(bps)] (4-d3). To a solution of [PtMe2(bps)] (0.010
g, 0.022 mmol) in acetone-d6 (1 mL), cooled to −78 °C, was added
CD3I (0.06 mL), and the reaction was monitored by 1H NMR
spectroscopy. NMR at −50 °C in acetone-d6: δ(1H) 0.73 (s, 3H,
SiMe), 0.87 (s, 3H, SiMe), 1.29 (s, 6H, 2JPtH = 69 Hz, PtMe), 7.52 (dd,
2H, 3JHH = 5 Hz, 7 Hz, H5), 7.99 (t, 2H, 3JHH = 7 Hz, H4), 8.07 (d, 2H,
[PtMe(CD3)2{κ3N,N,O-(2-C5H4N)2SiMeO}] (14-d6). This was
prepared in a similar way but using [Pt(CD3)2(bps)]. NMR in
CD3OD: δ(1H) 0.94 (s, 3H, SiMe), 1.15 (s, 3H, 2JPtH = 75 Hz, Pt-Me),
3
3
3JHH = 7 Hz, H3), 9.62 (d, 2H, JHH = 5 Hz, JPtH = 19 Hz, H6).
[PtIMe3(pyridine)2] (5). This complex was formed by hydrolysis of
complex 4 during recrystallization. NMR in CD2Cl2: δ(1H) = 1.20 (s,
3H, 2JPtH = 69 Hz, PtMe), 1.44 (s, 6H, 2JPtH = 70 Hz, PtMe), 7.44 (m,
4H, Hm), 7.88 (t, 2H, 3JHH = 7 Hz, Hp), 9.63 (d, 4H, 3JHH = 6 Hz, 3JPtH
= 19 Hz, Ho). The spectrum was identical with that of an authentic
sample.7
3
7.43 (dd, 2H, JHH = 5 Hz, 7 Hz, H5), 7.80 (d, 2H, 3JHH = 7 Hz, H3),
7.86 (t, 2H, 3JHH = 7 Hz, H4), 8.97 (d, 2H, 3JHH = 5 Hz, 3JPtH = 20 Hz,
H6).
[PtMe3{κ3N,N,O-(2-C5H4N)2SiMeOH}][PhCOO] (15). To a sol-
ution of complex 1 (0.050 g, 0.11 mmol) in acetone (10 mL) was
added dibenzoyl peroxide (0.030 g, 0.12 mmol). The mixture was
stirred for 2 h, and then the volume was reduced to 1 mL and pentane
(5 mL) was added to precipitate the product as a white solid, which
was separated, washed with ether (3 × 2 mL) and pentane (3 × 2 mL),
and dried under high vacuum. Yield: 0.046 g, 73%. NMR in CD2Cl2:
[PtMe3(OH2)(bps)][CF3SO3] (6). To a solution of complex 1
(0.010 g, 0.022 mmol) in acetone-d6 (1 mL) was added methyl triflate
(2.57 μL). NMR at 20 °C: δ(1H) 0.85 (s, 6H, SiMe), 1.21 (s, 9H, 2JPtH
= 71 Hz, PtMe), 7.73 (dd, 2H, 3JHH = 6, 7 Hz, H5), 8.12 (t, 2H, 3JHH
=
7 Hz, H4), 8.23 (d, 2H, JHH = 7 Hz, H3), 9.05 (d, 2H, JHH = 6 Hz,
3JPtH = 18 Hz, H6). The product was crystallized from acetone/
pentane. Yield: 0.009 g, 63%. ESI-MS: m/z 472; calcd for
[PtMe3(OH2)(bps)]+ m/z 472. Anal. Calcd for C16H25F3N2O4PtSSi:
C, 30.92; H, 4.05; N, 4.51. Found: C, 30.88; H, 3.84; N, 4.43. The
corresponding complex from 1-d6 and MeOTf gave ESI-MS m/z 478
(calcd for [PtMe(CD3)2(OH2)(bps)]+ m/z 478), with no evidence for
other ions [PtMen(CD3)3−n(OH2)(bps)]+ with n = 0, 2, 3.
3
3
2
δ(1H) 1.04 (s, 3H, SiMe), 1.05 (s, 6H, JPtH = 70 Hz, PtMe), 1.14 (s,
2
3H, JPtH = 75 Hz, PtMe), 2.12 (s, 1H, O−H), 7.37−7.95 (11H, Ph
and H3−H5), 8.58 (d, 2H, 3JHH = 5 Hz, 3JPtH = 20 Hz, H6). Anal. Calcd
for C21H26N2O3PtSi: C, 43.67; H, 4.54; N, 4.85. Found: C, 43.95; H,
4.42; N, 5.06.
[PtMe(CD3)2{κ3N,N,O-(2-C5H4N)2SiMeOH}][PhCOO] (15-d6).
To a solution of [Pt(CD3)2(bps)] (0.010 g, 0.022 mmol) in
acetone-d6 (1 mL) was added dibenzoyl peroxide (0.006 g, 0.024
mmol). The solution was transferred to an NMR tube, and the
[PtMe3(CD3CN)(bps)][CF3SO3] (9). This was prepared in a similar
way but using acetonitrile-d3 (1 mL) as solvent. NMR at −30 °C:
1
reaction was monitored by recording the H NMR spectrum with
2
δ(1H) 0.69 (s, 3H, SiMe), 0.79 (s, 3H, SiMe), 0.93 (s, 3H, JPtH = 76
time. Initially, the relative intensities of the resonances for MeSi (δ
1.04), MePt, trans-N (δ 1.05), and MePt, trans-O (δ 1.14) were 3:
(trace):3 but after 2 days at room temperature, the corresponding
relative intensities were 3:2:1.
Hz, PtMe), 1.04 (s, 6H, 2JPtH = 66 Hz, Pt-Me), 7.58 (dd, 2H, 3JHH = 6
Hz, 7 Hz, H5), 8.00−8.09 (m, 4H, H3, H4), 8.93 (d, 2H, 3JHH = 6 Hz,
3JPtH = 20 Hz, H6).
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Ed. 2008, 47, 7694. (g) Zhao, S.-B.; Wu, G.; Wang, S. Organometallics
2008, 27, 1030.
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystallographic data. This material is available
free of charge via the Internet at http://pubs.acs.org.
(11) (a) De Felice, V.; De Renzi, A.; Panuzzi, A.; Tesauro, D. J.
Organomet. Chem. 1995, 488, C13. (b) Stahl, S. S.; Labinger, J. A.;
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R. J. Organometallics 2006, 25, 1583. (f) Werner, M.; Wagner, C.;
Steinborn, D. J. Organomet. Chem. 2009, 694, 190.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: pudd@uwo.ca.
(12) (a) Itami, K.; Yoshida, J.-I. Synlett. 2006, 157. (b) Brown, R. S.;
Slebocka-Tilk, H.; Buschek, J. M.; Ulan, J. G. J. Am. Chem. Soc. 1984,
106, 5979.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
We thank the NSERC (Canada) for financial support.
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Article
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