Synthesis, structure, dynamics, and selective methylation of platinum and palladium diphosphametallacyclobutane complexes

Article abstract of DOI:10.1021/om3005367

Treatment of M(dppe)Cl₂ (M = Pd, Pt) or Pt((R,R)-Me-DuPhos) Cl₂ with IsHPCH₂PHIs (1; Is = isityl = 2,4,6-(i-Pr) ₃C₆H₂) and 2 equiv of NaOSiMe₃ gave the mononuclear diphosphametallacyclobutane complexes M(dppe)(IsPCH ₂PIs) (M = Pd (2), Pt (3)), or Pt((R,R)-Me-DuPhos)(IsPCH ₂PIs) (4). Dynamic processes involving phosphorus inversion and rotation about the P-C(Is) bonds in 2-4 were characterized by variable-temperature NMR spectroscopy, which suggested that each existed as a single C₂-symmetric diastereomer in solution, consistent with their solid-state structures determined by X-ray crystallography. The MiniPhos derivative IsMePCH₂PMeIs (5) was prepared as a 5.5/1 rac/meso mixture by sequential arylation and methylation of Cl₂PCH ₂PCl₂. Alternatively, the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) mediated alkylation of secondary phosphines in the presence of NaOSiMe₃ to yield selectively meso-5 either from PHMe(Is) and CH₂I₂ or from 1 and MeI. Recrystallization and chromatography yielded diastereomerically enriched rac-5 and meso-5. Treatment of M(dppe)(OTf)₂ (M = Pd, Pt) or Pt((R,R)-Me-DuPhos)(OTf)₂ with meso-5 gave the dications meso-[M(diphos)(IsMePCH₂PMeIs)][OTf] ₂ (M(diphos) = Pd(dppe) (6), Pt(dppe) (8), Pt((R,R)-Me-DuPhos) (10)). Similar reactions of rac-5 yielded the dications rac-[M(diphos)(IsMePCH ₂PMeIs)][OTf]₂ (M(diphos) = Pd(dppe) (7), Pt(dppe) (9)) and a 1/1 mixture of the C₂-symmetric diastereomers [Pt((R,R)-Me-DuPhos)(IsMePCH₂PMeIs)][OTf]₂ (11a,b). Treatment of 2 and 3 with 2 equiv of methyl triflate gave the dications 6-9 as ca. 1/1 meso/rac mixtures, and methylation of 4 selectively gave one of the C₂-symmetric diastereomers, 11a. These alkylations proceeded via the observable monomethylated intermediates [M(diphos)(IsMePCH₂PIs)][OTf] (12-14).

Full text of DOI:10.1021/om3005367

Article
pubs.acs.org/Organometallics
Synthesis, Structure, Dynamics, and Selective Methylation of
Platinum and Palladium Diphosphametallacyclobutane Complexes
Timothy W. Chapp,† Adam J. Schoenfeld,† Matthew D. Sanderson,† Cory L. Chang,† David S. Glueck,*,†
James A. Golen,‡ Curtis E. Moore,‡ and Arnold L. Rheingold‡
†6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States
‡Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
S
* Supporting Information
ABSTRACT: Treatment of M(dppe)Cl2 (M = Pd, Pt) or Pt((R,R)-
Me-DuPhos)Cl2 with IsHPCH2PHIs (1; Is = isityl = 2,4,6-(i-
Pr)3C6H2) and 2 equiv of NaOSiMe3 gave the mononuclear
diphosphametallacyclobutane complexes M(dppe)(IsPCH2PIs) (M
= Pd (2), Pt (3)), or Pt((R,R)-Me-DuPhos)(IsPCH2PIs) (4).
Dynamic processes involving phosphorus inversion and rotation
about the P−C(Is) bonds in 2−4 were characterized by variable-
temperature NMR spectroscopy, which suggested that each existed
as a single C2-symmetric diastereomer in solution, consistent with their solid-state structures determined by X-ray
crystallography. The MiniPhos derivative IsMePCH2PMeIs (5) was prepared as a 5.5/1 rac/meso mixture by sequential
arylation and methylation of Cl2PCH2PCl2. Alternatively, the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) mediated
alkylation of secondary phosphines in the presence of NaOSiMe3 to yield selectively meso-5 either from PHMe(Is) and CH2I2 or
from 1 and MeI. Recrystallization and chromatography yielded diastereomerically enriched rac-5 and meso-5. Treatment of
M(dppe)(OTf)2 (M = Pd, Pt) or Pt((R,R)-Me-DuPhos)(OTf)2 with meso-5 gave the dications meso-[M(diphos)-
(IsMePCH2PMeIs)][OTf]2 (M(diphos) = Pd(dppe) (6), Pt(dppe) (8), Pt((R,R)-Me-DuPhos) (10)). Similar reactions of
rac-5 yielded the dications rac-[M(diphos)(IsMePCH2PMeIs)][OTf]2 (M(diphos) = Pd(dppe) (7), Pt(dppe) (9)) and a 1/1
mixture of the C2-symmetric diastereomers [Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2 (11a,b). Treatment of 2 and 3
with 2 equiv of methyl triflate gave the dications 6−9 as ca. 1/1 meso/rac mixtures, and methylation of 4 selectively gave one of
the C2-symmetric diastereomers, 11a. These alkylations proceeded via the observable monomethylated intermediates
[M(diphos)(IsMePCH2PIs)][OTf] (12−14).
Chart 1. Selected Metal Bis(phosphido) Complexes
INTRODUCTION
■
Terminal metal phosphido complexes are important inter-
mediates in catalytic reactions which form P−C bonds, such as
hydrophosphination of alkenes and phosphination of aryl or
alkyl halides,1 and in dehydrocoupling processes which lead to
P−element bond formation.2 Structure, bonding, and reactivity
in the M−PR2 functional group has been studied in detail.3
Complexes with two terminal phosphido groups, some of which
are stabilized by the chelate effect, are also known; some
examples are shown in Chart 1.4−6
However, mononuclear complexes of the simplest dianionic
bis(phosphido) ligand, (RPCH2PR)2−, have not been re-
ported.7 Such diphosphametallacyclobutanes are of interest by
analogy to the metallacyclobutanes shown to be intermediates
in olefin metathesis.8 We hypothesized that large R groups
would prevent the formation of μ-phosphido bridges9 and
would make these complexes preferentially adopt the C2-
symmetric conformation shown in Scheme 1, to avoid steric
overcrowding in the meso form. The diastereomers rac-E and
meso-E could interconvert by pyramidal inversion at the
phosphido stereocenters, which typically occurs rapidly.10
Methylation of the nucleophilic phosphido groups1d of E
would give the chelating bis(tertiary phosphine) complex F
(Scheme 1). This is attractive, because Imamoto has shown that
the P-stereogenic RMePCH2PMeR “MiniPhos” ligands are
valuable in asymmetric catalysis.11 If rac-E were present in
greater concentration than meso-E and/or underwent alkylation
more quickly, C2-symmetric rac-F might be the favored
Received: June 15, 2012
Published: July 30, 2012
© 2012 American Chemical Society
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Scheme 1. Potential Synthesis of MiniPhos Ligands via
Diphosphametallacyclobutanes
Figure 1. ORTEP diagram of Pd(dppe)(IsPCH2PIs) (2).
product. If a chiral ancillary ligand was used, this process could
be enantioselective, favoring one enantiomer of complexed
MiniPhos. Finally, steric crowding in the strained four-
membered ring of F might enable dissociation of the chelate
and, hence, catalytic turnover by conversion of F to E. To
investigate these possibilities, we report here studies of
platinum and palladium diphosphametallacyclobutane com-
plexes.
RESULTS AND DISCUSSION
■
Synthesis and Solid-State Structures of Platinum and
Palladium Diphosphametallacyclobutane Complexes.
Treatment of platinum and palladium dichloride precursors
with the known bulky bis(secondary phosphine)
IsHPCH2PHIs (1; Is = isityl = 2,4,6-(i-Pr)3C6H2)12 and 2
equiv of NaOSiMe3 gave the target bis(phosphido) complexes
M(dppe)(IsPCH2PIs) (M = Pd (2), Pt (3)) and the sparingly
soluble Pt((R,R)-Me-DuPhos)(IsPCH2PIs) (4) as air-sensitive
yellow crystalline solids (Scheme 2).
Figure 2. ORTEP diagram of Pt(dppe)(IsPCH2PIs) (3).
Scheme 2. Synthesis of Diphosphametallacyclobutane
Complexes 2−4
Figure 3. ORTEP diagram of Pt((R,R)-Me-DuPhos)((S,S)-
IsPCH2PIs) (4).
The crystal structures of complexes 2-4 are shown in Figures
1−3; see Table 1 and the Supporting Information for details. In
the solid state, the predicted sterically favored diastereomers
were observed: rac-2 and rac-3 and a C2-symmetric isomer of 4
(S,S configuration at the phosphido stereocenters), in which
the bulky isityl groups avoided the quadrants occupied by the
DuPhos phospholane methyl substituents.13
Complexes 2−4 adopted distorted-square-planar structures,
constrained by the bite angles of the dppe and Me-DuPhos
ligands and, more strikingly, by the 73° bite angle of the four-
membered diphosphametallacyclobutane ring (Table 2). The
phosphido P atoms were pyramidal, with angle sums of 314−
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Table 1. Crystallographic Data for Pd(dppe)(IsPCH2PIs) (2), Pt(dppe)(IsPCH2PIs) (3), Pt((R,R)-Me-DuPhos)(IsPCH2PIs)
(4), meso-[Pd(dppe)(IsMePCH2PMeIs)][OTf]2·Et2O (meso-6·Et2O), meso-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2·Et2O (meso-
8·Et2O), and rac-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2 (rac-9)
2
3
4
meso-6·Et2O
meso-8·Et2O
rac-9
formula
formula wt
space group
a, Å
C57H72P4Pd
987.43
C2/c
C57H72P4Pt
1076.12
C2/c
C49H76P4Pt
984.07
C2221
13.735(8)
17.118(8)
20.647(11)
90
C65H88F6O7P4PdS2
C65H88F6O7P4PtS2
C61H78F6O6P4PtS2
1404.32
1389.75
P65
1478.44
P61
P1
̅
33.225(9)
9.898(3)
18.448(4)
90
33.135(4)
9.8628(10)
18.4542(19)
90
13.4460(10)
13.4460(10)
66.635(7)
90
13.4616(2)
13.4616(2)
66.2129(15)
90
11.915(7)
13.515(8)
21.619(13)
73.777(7)
77.495(8)
68.875(9)
3092(3)
2
b, Å
c, Å
α, deg
β, deg
121.377(3)
90
121.312(2)
90
90
90
90
γ, deg
V, Å3
90
120
120
5180(2)
4
5152.5(9)
4
4854(4)
4
10433.2(15)
6
10391.2(3)
6
Z
D(calcd), g/cm3
μ(Mo Kα), mm−1
temp, K
1.266
1.387
1.347
1.327
1.418
1.508
a
0.517
2.883
3.053
4.122
5.767
2.507
100(2)
3.96
150(2)
3.75
100(2)
1.80
100(2)
4.96
100(2)
3.98
100(2)
4.68
b
R(F), %
b
Rw(F2), %
11.89
10.02
3.72
13.17
9.83
11.18
a
b
2
2
Cu Kα radiation was used. Quantity minimized: Rw(F2) = ∑[w(Fo2 − Fc2)2]/∑[(wFo )2]1/2; R = ∑Δ/∑(Fo), Δ = |(Fo − Fc)|, w = 1/[σ2(Fo ) +
(aP)2 + bP], P = [2Fc2 + Max(Fo ,0)]/3. A Bruker CCD diffractometer was used in all cases.
2
315° (compare to 328.5° for ideal tetrahedral coordination or
360° for trigonal-planar geometry).
configuration, giving rise to three diastereomers. However,
1
31P and H NMR spectra at room temperature showed only
one set of peaks for each complex. The 31P NMR spectra
(AA′XX′ patterns; Table 3) were consistent with the expected
square-planar structures and chemical shifts and coupling
constants observed for related Pt and Pd phosphido complex-
es.14,4d,9,3c
Table 2. Selected Bond Lengths (Å) and Angles (deg) for the
Diphosphametallacyclobutane Complexes
M(diphos)(IsPCH2PIs) (2−4)
M(diphos) (compd no.)
The room-temperature 1H NMR spectra of 2−4 included six
i-Pr Me signals and three i-Pr CH signals, indicating that the
two sides of the isityl groups were inequivalent (the Is aryl
proton signals overlapped with other peaks). For complexes 2
and 3, the dppe CH2 signals gave rise to complicated 1H NMR
multiplets (AA′XX′MM′NN′ spin systems); the 31P-decoupled
AA′XX′ patterns were successfully simulated using gNMR and
the JPP values were obtained from the 31P NMR spectra.15 The
Pd(dppe) (2) Pt(dppe) (3) Pt(Me-DuPhos) (4)
M−P(diphos)
M−P(Is)
P−M−P(diphos)
P−M−P(Is)
2.3747(7)
2.3554(8)
85.46(4)
2.3238(12)
2.3595(13)
85.53(6)
2.2803(9)
2.3464(10)
86.90(4)
72.48(4)
73.28(6)
73.43(4)
P−M−P(trans)
P−M−P(cis)
P−C−P
M−P(Is)−CH2
M−P−C(Is)
CH2−P−C(Is)
sum of angles P(Is)
172.06(2)
101.22(3)
96.26(17)
95.63(9)
172.71(4)
100.73(4)
97.0(3)
168.94(2)
100.51(4)
97.10(13)
94.74(7)
1
PCH2P H NMR signals of 2−4 were also complex multiplets.
1
94.84(17)
113.59(16)
105.94(18)
314.37(18)
In variable-temperature (VT) H NMR studies, heating a
112.15(8)
106.61(9)
314.39(9)
113.84(8)
106.66(8)
315.24(8)
toluene-d8 solution of Pt complex 3 resulted in coalescence of
the i-Pr signals to give spectra with three (instead of six) Me
peaks and two (instead of three) CH resonances. Similarly, the
dppe CH2 multiplet coalesced to a singlet. Measurement of the
coalescence temperatures and standard analysis provided
approximate free energies of activation at the coalescence
temperatures for the relevant dynamic process (Table 4).16 The
good agreement between the data obtained for these five
Solution Structures of the Diphosphametallacyclobu-
tane Complexes. Dppe complexes 2 and 3 could exist as
mixtures of rac and meso diastereomers, while the bis-
(phosphido) ligand in 4 could have an RR, RS, or SS
a
Table 3. 31P NMR Data for Diphosphametallacyclobutane Complexes 2−4
complex (compd no.)
δ(P1/P2) (JPt−P
)
δ(P3/P4) (JPt−P
)
J12
J13
J14
J34
b
Pd(dppe)(IsPCH2PIs) (2)
24.5
−159.5
−154.3 (819)
−156.3 (826)
15
0
−29
−13
−15
66
105
105
11
40
45
b
Pt(dppe)(IsPCH2PIs) (3)
39.1 (2101)
58.4 (1993)
c
Pt((R,R)-Me-DuPhos)(IsPCH2PIs) (4)
10
a
b
c
Data were obtained at 21 °C. The chemical shift standard was 85% H3PO4. Coupling constants are given in Hz. Toluene-d8. C6D6.
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1
make them equivalent and match the experimental observa-
tions.
Alternatively, if phosphido inversion was fast on the NMR
time scale, then planar structure G would be accessible
transiently (Chart 2). This analysis assumes that the puckered
Table 4. Variable-Temperature H NMR Data for
a
Diphosphametallacyclobutane Complexes 2−4
M(diphos) (compd
no.)
Δν
Tc
(K)
ΔGc⧧
resonance δ (ppm)
(Hz)
(kcal/mol)
Pd(dppe) (2)
i-Pr CH
p-Me
5.06, 4.70
1.42, 1.41
5.04, 4.84
1.89, 1.84
183
4
401
338
366
323
19
18
18
17
Chart 2. Planar Structures G Accessible via Phosphido
Inversion in dppe Complexes 2 and 3 (M = Pd, Pt) and
DuPhos Complex 4
Pt(dppe) (3)
i-Pr CH
100
22
dppe
CH2
o-Me
p-Me
1.71, 1.49
107
3
366
304
18
17
1.375,
1.369
o-Me
1.06, 0.96
5.42, 5.29
49
65
356
401
18
20
Pt((R,R)-Me-
DuPhos) (4)
i-Pr CH
o-Me
o-Me
1.69, 1.60
1.66, 1.49
43
88
346
401
17
20
a
The solvent was toluene-d8 for 3 and p-xylene-d10 for 2 and 4.
Chemical shifts, Δν values, and coupling constants are from slow-
exchange spectra at 21 °C. Estimated errors are different for each
resonance; “typical” errors are 5 Hz in Δν, 10 °C in Tc, and 0.5 kcal/
mol in ΔGc⧧.
different groups of signals suggested that the same process is
responsible in each case, with a barrier of about 18 kcal/mol.
Analogous VT NMR studies of Pd(dppe) complex 2 were
complicated by its partial decomposition on heating to yield the
known diphosphirane17 IsPCH2PIs in an apparent P−P
reductive elimination process (Scheme 3).18
dppe chelate, as commonly observed, can access a con-
formation in which the square plane of the molecule is a plane
of symmetry.19 Further, the P−Is groups must be able to reach
the position perpendicular to this plane, as shown. Then, the
molecular symmetry plane would make equivalent the o-i-Pr
Scheme 3. Thermal Decomposition of 2
groups above and below it, as well as the p-i-Pr Me groups.14
h
Finally, this plane, along with rotation about a C2 axis, would
make all the dppe CH2 hydrogens equivalent, matching the
experimental coalescence behavior. Thus, fast phosphido
inversion on the NMR time scale, via G, would be consistent
with all of the high-temperature NMR observations for Pt
complex 3. In contrast, fast rotation about the P−C(Is) bonds
would have no effect on the dppe CH2 1H NMR signals.
Therefore, we conclude that phosphorus inversion via a planar
transition state is the dynamic process responsible for the VT
NMR behavior of Pt complex 3.
At low temperature, the NMR observations require that both
P inversion and rotation about the P−C(Is) bonds in 3 is slow.
Inversion must be fast on the NMR time scale at high
temperature, but we cannot determine from the data if the
rotation process is fast or slow under these conditions.
However, indirect evidence on this point was obtained from
VT NMR analysis of DuPhos complex 4 (see below).
Nonetheless, coalescence phenomena similar to those for 3
were observed in 2 and 4, although for fewer groups of signals.
Analysis of these data (Table 4) showed that the barriers to the
dynamic processes involved (about 18 kcal/mol for 2 and 19
kcal/mol for 4) were very similar to that for 3.
Dynamic Processes in Diphosphametallacyclobutane
Complexes 2−4. What are the solution structures of 2−4, and
what dynamic process is responsible for these NMR
observations? An answer to these questions should also explain
why only one set of NMR signals was observed for each
complex, despite the potential presence of diastereomers. The
simplest explanation for the latter observations is that the solid-
state structures are maintained in solution and the other
possible isomers (meso for 2 and 3 or meso and R,R for DuPhos
complex 4) are not present in NMR-detectable concentrations.
Slow inversion on the NMR time scale at room temperature
1
means that the single set of 31P and H NMR signals observed
for 3 at room temperature cannot be an average spectrum
resulting from fast interconversion between rac and meso
diastereomers. Instead, it is most simply explained by the
dominant presence of one thermodynamically favored isomer,
likely the C2-symmetric one observed in the solid state.
Although the VT NMR behavior of Pd complex 2 was less well-
behaved, the similarity of the structures and spectra of 2 and 3
and their identical barriers for the dynamic processes suggest
that the same conclusions apply for 2.
1
For 4, this is consistent with the H NMR AA′MM′NN′
PCH2P signals, because these hydrogens would be inequivalent
in the meso isomer.
Likely dynamic processes include phosphido pyramidal
inversion and rotation about the P−C(Is) bonds.14b,c In dppe
complexes 2 and 3, slow rotation about the P−C(Is) bonds on
the NMR time scale would be consistent with the room-
temperature observation of inequivalent o-i-Pr groups. Fast
rotation on the NMR time scale at higher temperature would
The reduced symmetry of DuPhos complex 4 has significant
effects on related analyses. In particular, in planar structure 4G
(Chart 2), the presence of the chiral phospholane groups
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means that the i-Pr groups above and below the square plane of
the molecule are not equivalent, since, unlike the case for 2G
and 3G, this is not a symmetry plane. Therefore, rapid
phosphido inversion on the NMR time scale would not affect
the number of i-Pr Me and CH 1H NMR signals. In contrast, as
for 2 and 3, fast rotation about the P−C(Is) bonds in 4 at high
temperature would be consistent with the observed coalescence
behavior of the i-Pr signals. At room temperature, this process
must be slow on the NMR time scale, but we cannot determine
if P inversion is fast or slow under these conditions.
Scheme 4. Direct and Pt-Catalyzed Syntheses of MiniPhos
Derivative 5
a
Thus, in Pt(dppe) complex 3, the dynamic process
responsible for the VT NMR observations is P inversion,
while P−C(Is) rotation must be slow at room temperature, but
we cannot evaluate its rate at high temperature. The
conclusions are reversed for Pt(DuPhos) complex 4, in which
P−C(Is) rotation accounts for the coalescence behavior, but we
cannot tell directly if P inversion is fast or slow. The structural
similarity of these complexes and the near-identical barriers to
their dynamic processes suggest that their fluxional behavior is
the same. Thus, it is likely that both P inversion and P−C(Is)
rotation are slow on the NMR time scale in both 3 and 4 at low
temperature and fast at high temperature. In fact, these motions
might be correlated, and the measured barriers may correspond
to a composite process.
a
For the synthesis of 5 from Cl2PCH2PCl2, the dr (rac/meso ratio) was
5.5/1. The Pt-catalyzed formation of 5 was meso-selective. For the
synthesis of 5 from 1, dr = 1/2.2 and er (enantiomeric ratio) = 3.5. For
the synthesis of 5 from PHMe(Is), dr = 1/3.2 and er = 1.1.
Scheme 5. Synthesis of meso- and rac-MiniPhos Complexes
6−11
As for 3, slow P inversion in 4 at room temperature suggests
that a single set of NMR signals was observed for 4 because one
of its three possible diastereomers is favored in solution.
Although we did not investigate the absolute stereochemistry of
4, steric considerations suggest the C2-symmetric (S,S)-
IsPCH2PIs solid-state structure is maintained in solution.
Methylation of Bis(phosphido) Complexes 2−4:
Independent Synthesis and Structure of the Products.
These conclusions substantiated the first hypothesis of Scheme
1, that the preferred geometry of diphosphametallacyclobutane
complexes 2−4 would be C2-symmetric, not meso. With the
chiral ligand (R,R)-Me-DuPhos, one of the two possible C2-
symmetric diastereomers ((S,S)-IsPCH2PIs) also appeared to
be preferred strongly for 4. Would these structural preferences
lead to selective methylation (Scheme 1)?
To find out, we prepared the expected products of
methylation, the dications [M(diphos)(IsMePCH2PMeIs)]-
[OTf]2 (6−11). The bis(tertiary phosphine) IsMePCH2PMeIs
(5) was synthesized by three different methods (Scheme 4).
Sequential treatment of commercially available Cl2PCH2PCl2
with 2 equiv of IsMgBr/ZnCl2 and 2 equiv of MeMgBr gave a
5.5/1 mixture of rac- and meso-5. Recrystallization from acetone
gave highly enriched rac-5. A combination of recrystallization
and chromatography on the mixture of borane adducts rac- and
meso-IsMeP(BH3)CH2P(BH3)MeIs (5-BH3) enabled isolation
of enriched meso-5.20
Alternatively, alkylation of bis(secondary phosphine) 1 with
MeI was catalyzed by Pt((R,R)-Me-DuPhos)(Ph)(Cl) in the
presence of NaOSiMe3. The same Pt catalyst and base
mediated coupling of 2 equiv of PHMe(Is) with diiodo-
methane. Both reactions were meso-selective, with low
diastereoselectivity and enantioselectivity (Scheme 4); they
also led to the formation of byproducts (Experimental Section).
The dicationic complexes [M(diphos)(IsMePCH2PMeIs)]-
[OTf]2 (6−11) were prepared selectively by separate reactions
of meso-5 or rac-5 with the known triflate complexes
M(dppe)(OTf)2 (M = Pd, Pt)21 or Pt((R,R)-Me-DuPhos)-
(OTf)2 (Scheme 5).4d
The stereochemistry of complexed IsMePCH2PMeIs (5) in
these dications was identified by their characteristic AA′XX′
(rac) or ABXY (meso) 31P NMR spectra (Table 5). Methylation
led to the expected increases in JP−P and JPt−P coupling
constants as the bis(phosphido) ligands in 2−4 were
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a
Table 5. 31P NMR Data for Intermediates 12−14 and Cationic MiniPhos Complexes 6−11
J
13 b
b
complex (compd no.)
δ(P1/P2) (JPt−P
)
δ(P3/P4) (JPt−P
−89.6, −94.8
−103.9
)
J12
42
[J24]
J14 [J23]
J34
c
[Pd(dppe)(IsMePCH2PIs)][OTf] (12a)
[Pd(dppe)(IsMePCH2PIs)][OTf] (12b)
[Pt(dppe)(IsMePCH2PIs)][OTf] (13)
40.5, 35.0
22 [d]
d
48 [342]
[365]
12
d
c
40.5, 36.8−35.8
d
e
e
43.3 (1824),
40.1 (2644)
−87.4 (2246), −114.3 (764)
8
d [25]
73 [348]
d
[Pt((R,R)-Me-DuPhos)(IsMePCH2PIs)][OTf] (14)
68.0 (1710),
60.7 (2219)
−85.6 (2214), −113.6 (705)
11
6 [d]
64 [351]
26
meso-[Pd(dppe)(IsMePCH2PMeIs)][OTf]2 (6)
C2-[Pd(dppe)(IsMePCH2PMeIs)][OTf]2 (7)
meso-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2 (8)
C2-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2 (9)
55.4
−86.0
−71.3
22
20
7
7
375
358
333
320
79
75
54
57
56.6
1
44.4 (2333)
45.8 (2313)
−83.4 (1973)
−78.2 (1940)
−72.8 (1856), −76.4 (1997)
−6
−13
9 [7]
6
meso-[Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2 69.7 (2268),
(10)
5
318 [324] 53
69.0 (2198)
C2-[Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2
(11a)
71.4 (2253)
−58.8 (1932)
−76.9 (1969)
−38.9 (1959)
5
5
−13
307
49
65
C2-[Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2
(11b)
69.9 (2138)
48.8 (2312)
−14
303
23
,
f
[Pt(dppe)(dppm)][BPh4]2
5.7
−11.1
309.8
57.5
a
The chemical shift standard was 85% H3PO4. Coupling constants are given in Hz. Negative values of coupling constants were obtained from
simulation of AA′XX′ patterns; coupling constants in ABXY spin systems are absolute values. See ref 23 for comments on the signs of coupling
constants in related compounds. The solvent was CH2Cl2 for 12−14, CDCl3 for [Pt(dppe)(dppm)][BPh4]2, and CD2Cl2 for all other compounds.
b
c
The additional couplings J23 and J24 are included for ABXY spin systems (10, 12−14). Overlapping peaks from major and minor isomers 12a,b.
d
e
Not observed (in some cases due to broad signals). The broadness of the signals precluded unambiguous assignment of these small couplings,
f
which could be interchanged. Data for a related dicationic complex are included for comparison.
quaternized.9 The 1H NMR spectra of the PCH2P groups in 6−
11 could also be used to characterize the rac and meso
diastereomers. As in the free phosphines rac- and meso-5,22
these PCH2P hydrogens were equivalent in the C2-symmetric
rac isomers but showed significantly different chemical shifts in
the meso complexes. For example, in the 1H NMR spectrum of
meso-Pd complex 6 (CD2Cl2), the CH2 signals appeared at δ
6.27−6.17 and 3.93−3.85, respectively, with JHH = 16 Hz.
The 31P NMR spectra (AA′XX′ patterns) of the two C2-
symmetric diastereomeric DuPhos complexes 11a,b were
similar (Table 5), but their 1H NMR spectra differed: restricted
rotation about the P−C(Is) bonds in 11b gave rise to two Is
aryl signals, three i-Pr CH peaks, and six i-Pr Me signals. In
contrast, several of the analogous signals for 11a were broad,
but only one Is-Ar, two CH, and three Me peaks were observed.
Although we did not carry out NOESY studies to determine the
absolute stereochemistry of 11a,b or of their precursor 4, we
suppose that 11a contains (S,S)-MiniPhos, in which the bulky
Is substituents, as in 4, are oriented to avoid the quadrants
occupied by the DuPhos methyl groups. The expected greater
steric hindrance for (R,R)-11b would then be consistent with
the observed restricted rotation.
The crystal structures of the isomorphous Pd and Pt dppe
complexes meso-6·Et2O and meso-8·Et2O and of the Pt(dppe)
complex rac-9 (Figures 4−6 and Tables 1 and 6) confirmed the
stereochemical assignments. As anticipated by the presence of
the two bulky isityl groups and their forced proximity in the
meso isomers, the structures of 6 and 8 were distorted from
planarity. While the metal and three of the P atoms occupied
the square plane, P3 was more than 1 Å out of the plane in both
Figure 4. ORTEP diagram of meso-[Pd(dppe)(IsMePCH2PMeIs)]-
[OTf]2·Et2O (meso-6·Et2O). The anions and solvent are not shown.
cases. Note that these solid-state structures are not consistent
with the solution 31P NMR spectra (AA′XX′ spin systems),
which suggests more conformational flexibility in solution. In
contrast, in rac-9, Pt and all four P atoms were essentially
coplanar.
The structures of neutral precursors rac-2 and rac-3 and
dications meso-6 and meso-8 were remarkably similar (compare
the data in Tables 2 and 6), considering their differences in
charge, stereochemistry, and chelate ligands. The bite angles of
the dppe and four-membered-ring ligands showed little change
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Organometallics
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Scheme 6. Methylation of 2−4 with Methyl Triflate
Figure 5. ORTEP diagram of meso-[Pt(dppe)(IsMePCH2PMeIs)]-
[OTf]2·Et2O (meso-8·Et2O). The anions and disorder in an i-Pr group
(C33) are not shown.
These observations are most simply explained by diastereose-
lective methylation; we did not investigate potential dynamic
processes in these intermediates further.
The second alkylation was much slower, forming ca. 1/1
meso/rac mixtures of the dications [M(dppe)-
(IsMePCH2PMeIs)][OTf]2 (M = Pd (6, 7), Pt (8, 9)) after
several hours. Recrystallization of the 6/7 mixture gave a pure
sample of rac-7. In contrast, methylation of the DuPhos
complex 4 was more selective, yielding a ca. 25/1 mixture of C2-
symmetric [Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2
(11a) and meso-[Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)]-
[OTf]2 (10), along with small amounts of other unidentified
products. However, the other possible C2-symmetric diaster-
eomer 11b was not formed (Scheme 6).
Figure 6. ORTEP diagram of rac-[Pt(dppe)(IsMePCH2PMeIs)]-
[OTf]2 (rac-9). The disordered triflate anions are not shown.
CONCLUSION
■
The monomeric diphosphametallacyclobutane complexes re-
ported here showed the structural features anticipated from
their design; the C2-symmetric conformation of the bis-
(phosphido) ligand was favored over the meso form, resulting
in formation of a single isomer for dppe complexes 2 and 3.
Moreover, only one of the two possible C2-symmetric
diastereomers was observed for DuPhos complex 4. Although
methylation of the dppe complexes 2 and 3 was not
diastereoselective, that of DuPhos complex 4 led selectively
to one enantiomer of complexed MiniPhos, as desired. To
translate this stoichiometric reaction into an enantioselective
catalytic process requires dissociation of the chelate diphos-
phine product, which might be promoted with Pd or Ni instead
of Pt catalysts, and with bulkier chiral diphosphines, in order to
destabilize dications such as 11 further. Further investigations
of these ideas are in progress.
on methylation, suggesting that these constraints control the
geometries despite the expected effects of steric hindrance.
Similarly, bond lengths and angles in the diastereomeric Pt
complexes meso-8 and rac-9 were very similar, despite their
large steric differences. However, in contrast to the distorted-
square-planar solid-state structures of 6 and 8, Pt and all four P
atoms in 9 were essentially coplanar.
Methylation of 2−4: Selectivity. On treatment of
complexes 2-4 with 2 equiv of methyl triflate in CH2Cl2,
monomethylation occurred in minutes to give the intermediates
[M(diphos)(IsMePCH2PIs)][OTf] (12−14), which were
observed by 31P NMR spectroscopy (Scheme 6 and Table 5).
These cations could exist as mixtures of diastereomers, but only
one set of signals was observed at room temperature for Pt
complexes 13 and 14 and a 9/1 mixture for Pd complex 12.
Table 6. Selected Bond Lengths (Å) and Angles (deg) in the Dicationic Complexes meso-[M(dppe)(IsMePCH2PMeIs)][OTf]2
(M = Pd (6·Et2O), Pt (8·Et2O)) and rac-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2 (9)
complex
M−P (dppe)
M−P (Is)
P−M−P (dppe)
P−M−P (Is)
P−M−P (trans)
P−M−P (cis)
6·Et2O
8·Et2O
9
2.3328(14), 2.3501(13)
2.3316(15), 2.3197(14)
2.3352(17), 2.3239(16)
2.3203(13), 2.3706(13)
2.3203(16), 2.3578(14)
2.3524(17), 2.3511(17)
83.56(5)
83.60(5)
83.67(7)
73.43(5)
73.17(5)
72.06(6)
153.08(4), 172.08(5)
153.65(5), 172.36(6)
174.04(5), 174.08(5)
98.67(5), 103.22(5)
99.19(5), 103.22(5)
102.02(7), 102.25(6)
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Anal. Calcd for C31H56B2P2: C, 72.67; H, 11.02. Found: C, 72.78;
EXPERIMENTAL SECTION
■
1
H, 11.51. 31P{1H} NMR (CDCl3): δ −32.6, −34.9 (2/3 ratio). H
General Experimental Details. Unless otherwise noted, all
reactions and manipulations were performed in dry glassware under
a nitrogen atmosphere at 20 °C in a drybox or using standard Schlenk
techniques. Petroleum ether (bp 38−53 °C), CH2Cl2, ether, THF, and
toluene were dried over alumina columns similar to those described by
Grubbs.24 NMR spectra were recorded using Varian 300 or 500 MHz
NMR (CDCl3): δ 7.1 (d, J = 4, 4H, Ar, minor), 7.0 (d, J = 3, 4H, Ar,
major), 6.3 (broad dm, JPH = 393, 2H, P−H, minor), 5.9 (broad dm,
JPH = 393, 2H, P−H, major), 3.3 (m, 2H, Is CH, minor), 3.1 (br, 4H,
Is CH), 2.88 (m, 4H, Is CH, major), 2.6 (m, 2H, CH2, major), 2.4 (m,
2H, minor, CH2), 1.33 (d, J = 7, 4H, Is CH3 minor), 1.26 (d, J = 7, 4H,
Is CH3 minor), 1.243 (d, J = 7, 4H, Is CH3 major), 1.24 (d, J = 7, 4H,
Is CH3 minor), 1.2 (br d, J = 7, 4H, Is CH3 major), 1.08 (d, J = 7, 4H,
Is CH3 major). 13C{1H} NMR (CDCl3): δ 153.1 (quat, Ar, major),
153.0 (quat, Ar, minor), 122.74 (CH, Ar, minor), 122.68 (CH, Ar,
major), 119.4 (d, J = 56, quat Ar), 118.2 (d, J = 53, quat Ar, major),
34.32 (Is CHMe2, minor), 34.27 (Is CHMe2, major), 32.5 (br, Is
CHMe2), 24.7 (m, Is CH3), 24.0 (br, Is CH3), 23.6 (m, Is CH3), 20.1
(t, J = 20, CH2, minor), 19.7 (t, J = 20, CH2, major).
1
spectrometers. H or 13C NMR chemical shifts are reported vs Me4Si
and were determined by reference to the residual H or 13C solvent
1
peaks. 31P NMR chemical shifts are reported vs H3PO4 (85%) used as
an external reference. Coupling constants are reported in Hz, as
absolute values unless noted otherwise. Unless indicated, peaks in
NMR spectra are singlets. Instead of the expected quartet resonances25
in the 31P NMR spectra of the phosphine−borane, a poorly resolved
multiplet was observed. Elemental analyses were provided by
Quantitative Technologies Inc. Mass spectra were recorded at the
University of Illinois, Urbana−Champaign (http://www.scs.uiuc.edu/
∼msweb).
IsHPCH2PHIs (1).12 Piperazinomethyl polystyrene (1 g, 2.7 mmol/
g, 2.7 mmol, 4 equiv)30 and 1-BH3 (327 mg, 0.64 mmol, 1 equiv) were
slurried in toluene (ca. 20 mL) under N2. The mixture was stirred at
50 °C for 72 h, after which 31P NMR spectroscopy showed complete
deprotection to diphosphine 1 (δ −99.0, −99.2). The solvent was
removed under reduced pressure, the resin−phosphine mixture was
brought into the glovebox, and the phosphine was redissolved in
toluene; then the resin was removed by filtration through a frit. The
solvent was removed under reduced pressure to leave 291 mg (94%
yield) of clear thick oil.
Reagents were from commercial suppliers, except for these
compounds, which were made by the literature procedures:
Pt((R,R)-Me-Duphos)(Ph)(Cl),26 Pt(dppe)Cl2 and Pd(dppe)Cl2,27
Pt((R,R)-Me-DuPhos)Cl2,28 Pt(dppe)(OTf)2 and Pd(dppe)(OTf)2,21
4d
Pt((R,R)-Me-DuPhos)(OTf)2 and PHMe(Is).29
IsH(BH3)P(CH2)P(BH3)HIs (1-BH3). This synthesis of the diphos-
phine IsHP(CH2)PHIs (1) was modified from a literature procedure;
formation and isolation of the borane adduct is new.12 Under nitrogen,
a Schlenk flask was loaded with Mg powder (1.87 g, 76.8 mmol, 2
equiv, 50 mesh, Aldrich), which was then slurried in 5 mL of THF. A
solution of 2-bromo-1,3,5-triisopropylbenzene (21.8 g, 76.8 mmol, 2
equiv) in 30 mL of THF was added dropwise via cannula with stirring.
Two drops of 1,2-dibromoethane were added to initiate the reaction.
The mixture was gently refluxed for 1 h and then stirred for 14 h. The
resulting dark gray solution was transferred via cannula to a cooled
(−40 °C) solution of Cl2PCH2PCl2 (8.2 g, 38 mmol, 1 equiv) in 100
mL of THF. A solution of anhydrous ZnCl2 (20.9 g, 153.6 mmol, 4
equiv) in 500 mL of THF was added via cannula; a white solid
precipitated. The solution was stirred at −40 °C for 5 h. The mixture
was transferred via wide-bore cannula to a filter frit with a Celite bed
(3 cm high × 6 cm wide) and filtered under N2. The solid was washed
with two 100 mL portions of Et2O, and the solvent was removed from
the filtrate under reduced pressure.
The residue was redissolved in 200 mL of Et2O (at this stage, the
intermediate IsClPCH2PClIs could be observed by 31P NMR (δ 71.0,
64.2)) and the solution with some white precipitate was transferred via
filter cannula to a slurry of LiAlH4 (1.46 g, 38.4 mmol, 1 equiv) in
Et2O (ca. 20 mL) at 0 °C. The resulting mixture was stirred for 1 h
and then triethanolamine (5.6 mL, 42 mmol, 1 equiv) was injected via
wide bore syringe at 0 °C, producing some effervescence. The solution
was warmed to room temperature and was stirred vigorously
overnight, causing the residual gray solid to become very finely
divided. To this was added degassed H2O (ca. 40 mL), generating
minimal effervescence. The mixture was transferred via wide-bore
cannula to a filter frit with a Celite bed (3 cm high × 6 cm wide) and
filtered under N2. The gray solid was washed with two 100 mL
portions of Et2O, and the organic layer was separated from the
aqueous layer via cannula and dried over MgSO4. After cannula
filtration, the solvent was removed under reduced pressure to give 5.60
g (30% yield) of white solid.
Pd(dppe)(IsPCH2PIs) (2). To a slurry of Pd(dppe)Cl2 (33 mg,
0.058 mmol) in 5 mL of THF was added IsHPCH2PHIs (1; 29 mg,
0.059 mmol) in 5 mL of THF. The solution was cooled to −78 °C,
and then a solution of NaOSiMe3 (14 mg, 0.12 mmol, 2 equiv) in 5
mL of THF was added dropwise to the cooled solution over 10 min.
The solution turned canary yellow with the first addition of
NaOSiMe3. The solution was stirred for 1 h at −78 °C and was
then warmed to room temperature and stirred overnight; it became
orange-yellow. The solvent was removed under reduced pressure, and
the residue was brought into the glovebox and then dissolved in 2 mL
of toluene to give an orange solution, which was filtered through a
Celite pipet filter (0.5 cm wide × 2.0 cm high). The flask was rinsed
with two more 2 mL portions of toluene, and these extracts were
passed through the filter to give 6 mL of orange filtrate. The 31P NMR
spectrum showed the desired product (δ 24.5, −159 (86%)), residual
1 (δ −98, −99 (5%)), the diphosphirane IsPCH2PIs (δ −170 (3%)),17
and additional small quantities of unidentified impurities (δ 30, 28, 26,
−14, and −16 (totaling 5%)). The solvent was removed under
reduced pressure, and the orange residue was washed with three 1 mL
portions of petroleum ether to give a pale orange-yellow solid. The
solid was taken up in toluene and filtered a second time through a
Celite pipet filter (0.5 cm wide × 2.0 cm high) to give 34 mg (60%
yield) of the desired product containing the δ 30 impurity (3%) and a
small quantity of the diphosphirane (<1%). Recrystallization from
THF/petroleum ether at −30 °C gave 10 mg (18% yield) of yellow
powder. Note: if an excess of IsHPCH2PHIs was not used, the
solution became a deep brown-red, which was also generated from the
addition of NaOSiMe3 to Pd(dppe)Cl2. Once this colored solution
was generated, the addition of IsHPCH2PHIs to the solution did not
result in the formation of the yellow color associated with product 2.
We could not obtain spectroscopically pure bulk samples of 2;
therefore, elemental analysis was not possible. See the Supporting
Information for NMR spectra. HRMS (ESI): m/z calcd for
C57H73P4Pd (MH+) 987.3718, found m/z 987.3712. 31P{1H} NMR
(C7D8): δ 24.5 (PPh2, m), −159.5 (PIs, m). 1H NMR (C7D8): δ 8.17
(m, 4H, Ar), 7.14 (m, 4H, Ar), 7.09 (m, 2H, Ar), 6.99 (2H, Ar), 6.88
(m, 4H, Ar), 6.80 (m, 4H, Ar), 6.75 (m, 4H, Ar), 5.00 (m, 2H, Is CH),
4.63 (m, 2H, Is CH), 3.25 (m, 2H, CH2), 2.78 (septet, J = 7, 2H, Is
CH), 1.90 (br m, 2H, CH2), 1.74 (br m, 2H, CH2), 1.58 (d, J = 7, 6H,
Is CH3), 1.45 (d, J = 7, 6H, Is CH3), 1.29 (d, J = 7, 6H, Is CH3), 1.28
(d, J = 7, 6H, Is CH3), 1.02 (d, J = 7, 6H, Is CH3), 0.89 (d, J = 7, 6H,
Is CH3). 13C{1H} NMR (CDCl3): δ 154.2 (br, quat, Ar), 153.9 (br,
quat, Ar), 147.5 (quat, Ar), 140.8 (br d, J = 25, quat, Ar), 136.1 (br d, J
= 26, quat, Ar), 135.3 (m, CH, Ar), 134.3 (br d, J = 28, quat, Ar),
131.4 (d, J = 12, CH, Ar), 130.5 (CH, Ar), 129.2 (CH, Ar), 128.5
The solid was redissolved in 100 mL of petroleum ether, the
solution was cooled to 0 °C, and BH3(SMe2) (20 mL, 2.0 M in THF,
40 mmol, 2.66 equiv) was added via cannula with stirring. When the
mixture was warmed to room temperature, a white solid precipitated,
and the solvent was removed under reduced pressure. The solid was
recrystallized from THF/petroleum ether at −28 °C to give 4.59 g of
fine white solid (24% overall yield). Alternatively, we found that use of
a slight excess of IsMgBr (2.4 equiv) ensured complete 1,2-diarylation
of Cl2PCH2PCl2, but subsequent formation of IsH during the workup
hindered crystallization of 1-BH3. See the Supporting Information for
details.
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(CH, Ar), 128.2 (d, J = 6, CH, Ar), 125.4 (CH, Ar), 122.3 (CH, Ar),
120.2 (CH, Ar), 34.7 (Is CHMe2), 33.3 (br d, J = 20, Is CHMe2), 32.3
(br d, J = 43, Is CHMe2), 26.3 (CH2), 26.2 (Is CH3), 26.0 (m, CH2),
25.7 (Is CH3), 24.8 (Is CH3), 24.6 (Is CH3), 24.4 (Is CH3), 23.5 (Is
CH3).
chloride. X-ray-quality crystals were obtained by slow evaporation of a
toluene solution.
Anal. Calcd for C49H77P4Pt: C, 59.80; H, 7.78. Found: C, 56.02; H,
6.73. HRMS (FAB): m/z calcd for C49H77P4Pt (MH+) 983.4603,
found m/z 983.4591. 31P{1H} NMR (C6D6): δ 58.4 (P-DuPhos, m,
JPt−P = 1993), −156.3 (P-Is, m, JPt−P = 826). 1H NMR (C6D6): δ 7.18
(broad, 2H, Ar), 7.15−7.12 (m, 4H, Ar), 6.93−6.91 (m, 2H, Ar),
5.39−5.34 (m, 2H, i-Pr CH), 5.30−5.21 (m, 2H, i-Pr CH), 4.67−4.58
(m, 2H, P-CH2), 2.81 (sep, J = 7, 2H, i-Pr CH), 2.24−2.19 (m, 2H,
CH2), 2.02−1.93 (m, 2H, CH2), 1.81−1.71 (m, 2H, CH), 1.65 (dd, J
= 18, 7, 6H, CH3), 1.62 (d, J = 7, 6H, i-Pr CH3), 1.54 (d, J = 7, 6H, i-
Pr CH3), 1.51 (d, J = 7, 6H, i-Pr CH3), 1.50−1.42 (m, 4H, overlapping
CH2), 1.40 (d, J = 7, 6H, i-Pr CH3), 1.23 (d, J = 7, 6H, i-Pr CH3), 1.22
(d, J = 7, 6H, i-Pr CH3), 1.06−0.97 (m, 2H, CH), 0.55 (dd, J = 14, 7,
6H, CH3).
IsMePCH2PMeIs (5). Under nitrogen, a Schlenk flask was loaded
with Mg powder (802 mg, 33 mmol, 2 equiv, 50 mesh, Aldrich), which
was then slurried in THF (5 mL). To this was added dropwise a
solution of 2-bromo-1,3,5-triisopropylbenzene (9.354 g, 33 mmol, 2
equiv) in THF (30 mL) via cannula with stirring at 0 °C. Two drops
of 1,2-dibromoethane were added to initiate the reaction. The mixture
was warmed to room temperature and then stirred for 14 h. The
resulting dark gray solution was transferred via cannula to a cooled
(−40 °C) solution of Cl2PCH2PCl2 (3.597 g, 16.5 mmol, 1 equiv) in
THF (ca. 15 mL). A solution of anhydrous ZnCl2 (8.990 g, 66 mmol,
4 equiv) in THF (75 mL) was then added via cannula; a white solid
precipitated. The mixture was stirred at −40 °C for 5 h and then
warmed to room temperature and stirred for an additional 12 h. To
this mixture was added MeMgBr (2.5 mL of a 3.0 M solution in Et2O
(7.5 mmol) plus 27 mL of a 1.0 M solution in THF (34.5 mmol)) at 0
°C. The reaction mixture was warmed to room temperature and was
stirred for 1 h. 31P NMR spectroscopy showed 40% conversion to 5 (δ
−57.4 (major), −57.8 (minor)). After 2 h, little further conversion had
occurred; therefore, additional MeMgBr (20 mL of a 1.0 M solution in
THF (20 mmol)) was added. After 19 h, conversion was at 94%. After
the reaction mixture was stirred for an additional 24 h, the reaction was
complete by 31P NMR spectroscopy, giving 5 in a 5.5/1 ratio of
diastereomers.
The mixture was transferred via wide-bore cannula to a filter frit
with a Celite bed (3 cm high × 6 cm wide) and filtered under N2. The
solid was washed with three 30 mL portions of THF, and the solvent
was removed from the filtrate under reduced pressure to give a yellow
oil. The residue was redissolved in 100 mL of Et2O to give a cloudy
yellow solution. To this was added 30 mL of a degassed saturated
solution of aqueous NH4Cl; additional white solid precipitated in the
aqueous layer. An additional 30 mL of degassed distilled H2O was
added, and the two layers were stirred vigorously for 12 h. The yellow
organic layer was passed through a plug of silica (6.0 cm wide × 3.0 cm
high) under N2. The extraction−filtration process was repeated two
additional times with 50 mL of Et2O. The combined yellow extracts
were dried over MgSO4, and the solid was removed by filtration. The
solvent was removed under reduced pressure to give 7.583 g (90%
crude yield) of yellow oil.
A portion of the yellow oil (3.789 g) was recrystallized at −30 °C
from 10 mL of acetone to give an off-white solid. The yellow solution
was removed by pipet, and an additional 7 mL of acetone was added to
give a lighter yellow solution over a white solid. The mixture was
cooled to −30 °C for 30 min, and then the pale yellow solution was
removed by pipet. This process was repeated two more times until the
solution was colorless to give 1.191 g (31% yield) of white solid 5
almost exclusively as the rac diastereomer.
Pt(dppe)(IsPCH2PIs) (3). A solution of IsHPCH2PHIs (34 mg,
0.07 mmol) in 5 mL of THF was added to a slurry of Pt(dppe)Cl2 (43
mg, 0.07 mmol) and NaOSiMe3 (16 mg, 0.14 mmol, 2 equiv) in 5 mL
of THF; the solution turned a cloudy yellow. The mixture was stirred
for 1 h, at which point the 31P NMR spectrum showed mostly the
desired product along with some unreacted 1. The solvent was
removed under reduced pressure and the residue was washed with two
1 mL portions of petroleum ether. To the residue was added 3 mL of
toluene to give a yellow solution with a white precipitate. The solution
was filtered through a Celite pipet filter 0.5 cm wide by 3.0 cm high.
The solvent was removed from the filtrate to give 67 mg of yellow
solid. Recrystallization from THF/petroleum ether by solvent layering
at −28 °C gave 24 mg (34% yield) of yellow needlelike crystals.
We could not obtain satisfactory elemental analysis data for the air-
sensitive phosphido complexes 3 and 4, even accounting for their
potential oxidation. This problem has been encountered previously
with electron-rich phosphido complexes by us and others; see ref 4d
and ref 11 therein. See the Supporting Information for NMR spectra
of 2−4, which were also characterized as their methylated derivatives
6−11. Anal. Calcd for C57H72P4Pt: C, 63.62; H, 6.74. Calcd for
C57H72O2P4Pt: C, 61.78; H, 6.55. Found: C, 59.94; H, 6.35. HRMS
(FAB): m/z calcd for C57H73P4Pt (MH+) 1076.4311, found m/z
1076.4340. 31P{1H} NMR (C7D8): δ 39.1 (PPh2, m, JPt−P = 2101),
1
−154.3 (PIs, m, JPt−P = 819). H NMR (C7D8): δ 8.17 (m, 4H, Ar),
7.17 (m, 4H, Ar), 7.09 (m, 2H, Ar), 6.98 (d, J = 1.5, 2H, Ar), 6.88 (m,
4H, Ar), 6.80 (m, 4H, Ar), 6.73 (m, 4H, Ar), 5.04 (m, 2H, Is CH),
4.84 (m, 2H, Is CH), 4.28 (m, 2H, CH2), 2.80 (septet, J = 7, 2H, Is
CH), 1.79 (br m, 4H, CH2), 1.63 (d, J = 7, 6H, Is CH3), 1.41 (d, J = 7,
6H, Is CH3), 1.30 (d, J = 7, 6H, Is CH3), 1.29 (d, J = 7, 6H, Is CH3),
0.98 (d, J = 7, 6H, Is CH3), 0.89 (d, J = 7, 6H, Is CH3). 13C{1H} NMR
(C7D8): δ 154.6 (br, quat, Ar), 154.5 (br, quat, Ar), 137.2 (br, quat,
Ar), 135.4 (m, CH, Ar), 131.3 (d, J = 14, CH, Ar), 130.7 (CH, Ar),
129.2 (CH, Ar), 128.8 (CH, Ar), 128.4 (d, J = 10, CH, Ar), 128.3
(CH, Ar), 128.2 (d, J = 10, CH, Ar), 125.4 (CH, Ar), 122.5 (CH, Ar),
120.2 (CH, Ar), 34.7 (Is CHMe2), 32.4 (br m, Is CHMe2), 30.9 (br,
CH2), 29.0 (dd, J = 29, 17, CH2), 26.4 (Is CH3), 26.1 (Is CH3), 24.8
(Is CH3), 24.7 (Is CH3), 24.5 (Is CH3), 23.3 (Is CH3).
Pt((R,R)-Me-Duphos)(IsPCH2PIs) (4).
A solution of
IsHPCH2PHIs (1; 34 mg, 0.07 mmol) in 5 mL of toluene was
added to a slurry of Pt((R,R)-Me-DuPhos)Cl2 (40 mg, 0.07 mmol) in
5 mL of toluene. The mixture was cooled to −78 °C, and a solution of
NaOSiMe3 (16 mg, 0.14 mmol, 2 equiv) in 5 mL of toluene was added
via cannula; the mixture turned pale yellow. When it was warmed to
room temperature, the solution turned darker yellow, but 31P NMR
spectroscopy showed signals due to unreacted 1 and the desired
product. The toluene was removed under reduced pressure, and the
residue was redissolved in 10 mL of THF to give a clear yellow
solution that was stirred overnight to produce a yellow solution with
white precipitate. 31P NMR spectroscopy still showed a trace of
unreacted IsHPCH2PHIs, along with 4. Two additional portions of
Pt((R,R)-Me-DuPhos)Cl2 (5 mg, 0.009 mmol, then 3 mg, 0.005
mmol)) were added, stirring each time for 1 h, monitoring the
progress of the reaction by 31P NMR spectroscopy, until 1 was
consumed.
The solvent was removed under reduced pressure, and 7 mL of
toluene was added to the residue to give a yellow solution with a white
precipitate. The mixture was filtered through a Celite pipet filter (0.5
cm wide × 2 cm high) and eluted with 9 mL of toluene. The solvent
was removed from the filtrate under reduced pressure and the yellow
solid was washed with three 1 mL portions of petroleum ether to give
35 mg of yellow solid. An additional 20 mL of toluene was passed
through the Celite pipet filter until the eluting solution was pale
yellow, giving an additional 17 mg of yellow solid for an overall 75%
yield (52 mg total). This complex was only sparingly soluble at room
temperature in benzene, toluene, THF, chloroform, and methylene
To the other portion of yellow oil (3.749 g) in 7 mL of pentane was
added (BH3)SMe2 (8 mL of a 2.0 M solution in THF, 16 mmol). A
white precipitate formed, and the mixture was stirred overnight and
then filtered through an air-free frit. The white solid was washed with
two 10 mL portions of Et2O to give 1.71 g of the rac-enriched
monoborane adduct IsMe(BH3)PCH2PMeIs (31P NMR (CDCl3): δ
2.9 (broad), −58.2 (d, J = 87)). Deprotection of a small portion of this
material with morpholine (procedure described below) to give the free
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phosphine showed that the product was a 7.5/1 mixture of rac and
meso-5.
as PMe2Is(O) (see below); Pt((R,R)-Me-DuPhos)(Ph)(I) was also
observed.25 The solvent was removed under reduced pressure, and the
residue was extracted with 9/1 petroleum ether/THF (ca. 1 mL). The
extract was eluted over a silica pipet column with four 1 mL portions
of 9/1 petroleum ether/THF. The solvent was removed under
reduced pressure to give 13 mg (50% yield) of 5 as an oily residue
(3.2/1 meso/rac ratio) which contained unidentified impurities (31P
NMR: δ −42.5 (<1%), −61.1 (<0.5%)). For details on the scaleup of
this reaction and characterization data for PMe2Is(O), see the
Supporting Information.
Method 2 (from IsHPCH2PHIs (1) and MeI). A solution of
IsHPCH2PHIs (1; 27 mg, 0.06 mmol) in 1 mL of THF was added to
Pt((R,R)-Me-DuPhos)(Ph)(Cl) (3 mg, 0.006 mmol, 10 mol %), and
this solution was transferred to solid NaOSiMe3 (13 mg, 0.12 mmol, 2
equiv) to give a yellow solution, which was transferred to an NMR
tube. MeI (7 μL, 0.12 mmol, 2 equiv) was injected via microliter
syringe through a rubber septum; the solution turned pale yellow. The
31P NMR spectrum showed signals due to a mixture of 5 (δ −57.3,
−57.6, 29%), monoalkylated IsHPCH2PMeIs (δ −52.3 (d, J = 121),
−102.7 (d, J = 121), 56%), starting material 1 (δ −102.9, −103.9, 7%),
and another compound, perhaps overalkylated [IsMe2PCH2PMeIs][I]
(δ 18.8 (d, J = 128), −65.9 (d, J = 128), 8%). The reaction was
complete after 1.75 h. The solvent was removed under reduced
pressure, and the residue was extracted with three 1 mL portions of 9/
1 petroleum ether/THF. The collected extracts were passed through a
silica pipet column (0.5 cm wide × 3.0 cm high). The solvent was
removed under reduced pressure to give 12 mg (43% yield) of 5 (2.2/
1 meso/rac ratio) as a clear residue also containing an unidentified
impurity (31P NMR: δ −61.1 (10%)). For determination of the
enantioselectivity of these Pt-catalyzed reactions, see the Supporting
Information.
The yellow filtrate was concentrated to give a yellow oil, whose 31P
NMR spectrum (CDCl3) showed that it was IsMe(BH3)PCH2P-
(BH3)MeIs (5-BH3, δ 2.4 (broad)). A portion of the oil (∼300 mg)
was passed through a column of silica (2.5 cm wide × 14.0 cm high)
with 5% ethyl acetate in petroleum ether, and 14 10 mL fractions were
collected. The bulk of the material eluted in fractions 4−6 to give 20,
27, and 12 mg of product, respectively. The other fractions contained a
combined total of 19 mg. A final elution of the column with neat
EtOAc gave 43 mg of material. TLC analysis suggested that fraction 5
contained the most product; the 31P NMR spectrum (CDCl3) of this
material showed that it was the meso-enriched monoborane adduct
IsMe(BH3)PCH2PMeIs (δ 2.4 (broad), −59.2 (d, J = 139)). This
material (27 mg, 0.05 mmol) was dissolved in neat morpholine (ca.
0.75 mL) under N2 and transferred to an NMR tube. The mixture was
heated to 100 °C for 45 min, and then the morpholine was removed
under reduced pressure. To the residue was added 7 mL of 5% Et2O in
pentane to give a cloudy solution. The mixture was eluted through a
silica pipet column (0.5 cm wide × 3.0 cm high) to give 17 mg (65%
yield) of enriched meso-5 containing some rac-5 (11/1 ratio).
In attempts to optimize the synthesis and separation of rac- and
meso-5 (see the Supporting Information for details), we found that
selective precipitation of rac-enriched 5-BH3 was reproducible on a
large scale but was less efficient on a smaller scale. This precluded
effective rac/meso separation when BH3-THF was added to small
amounts of a 1/1 mixture of rac- and meso-5 obtained by thermal
epimerization. Similarly, because attempts to separate rac- and meso-5-
BH3 by chromatography were unsuccessful, meso-enriched 5 was best
obtained after selective precipitation or recrystallization of rac-5 or its
borane adduct.
Data for rac-5. Anal. Calcd for C33H54P2(acetone)0.5: C, 76.48; H,
10.60. Found: C, 76.35; H, 10.50. The white solid obtained by
recrystallization from acetone contained residual acetone, which was
observed by 1H NMR spectroscopy. Attempts to quantify the amount
of cocrystallized solvent were unsuccessful, since acetone appeared to
be lost on standing. HRMS (ES+): m/z calcd for C33H55P2 (MH+)
513.3779, found m/z 513.3773. 31P{1H} NMR (CDCl3): δ −52.1
(meso), −53.1 (rac) (81:1 rac/meso). 1H NMR (CDCl3): δ 7.03
(broad, 4H, Ar), 4.01−3.93 (m, 4H, i-Pr CH), 2.88 (sep, J = 7, 2H, i-
Pr CH), 2.54 (2H, P-CH2), 1.55 (t, J = 3, 6H, P-CH3), 1.28−1.23 (m,
36H, i-Pr CH3). 13C{1H} NMR (CDCl3): δ 155.2 (t, J = 7, quat, Ar),
150.1 (quat, Ar), 131.0 (t, J = 2, quat, Ar), 121.9 (t, J = 2, CH, Ar),
34.2 (i-Pr-CH), 31.2 (t, J = 11, i-Pr-CH), 29.9 (t, J = 20, P-CH2), 24.9
(i-Pr CH3), 24.81 (i-Pr CH3), 23.8 (d, J = 4, i-Pr CH3), 12.1 (t, J = 7,
P-CH3).
meso-[Pd(dppe)(IsMePCH2PMeIs)][OTf]2 (6). To a slurry of
Pd(dppe)(OTf)2 (34 mg, 0.04 mmol) in 7 mL of CH2Cl2 was added a
solution of meso-IsMePCH2PMeIs (22 mg, 0.04 mmol) in 5 mL of
CH2Cl2. The slurry turned homogeneous and pale yellow almost
immediately. The solution was stirred for 20 min, and then the solvent
was removed under reduced pressure. The residue was washed with
petroleum ether and then recrystallized from CH2Cl2 and petroleum
ether at 21 °C by solvent layering. A small quantity of orange residue
precipitated, leaving a pale yellow solution, which was removed with a
pipet. The solvent was removed under reduced pressure to leave 34
mg (84% yield) of pale yellow solid. Recrystallization from CH2Cl2/
Et2O at 21 °C by vapor diffusion gave yellow needlelike crystals for X-
ray analysis.
Anal. Calcd for C61H78F6O6P4PdS2: C, 55.69; H, 5.98. Found: C,
55.34; H, 6.36. HRMS (ES+): m/z calcd for C60H78F3O3P4PdS (M −
SO3CF3)+ 1165.3629, found m/z 1165.3721. 31P{1H} NMR
(CD2Cl2): δ 55.4 (m, P-dppe), −86.0 (m, P-MeIs). 1H NMR
(CD2Cl2): δ 7.82−7.77 (m, 2H, Ar), 7.72−7.65 (m, 10H, Ar), 7.64−
7.58 (m, 4H, Ar), 7.49 (td, J = 8, 2, 4H, Ar), 7.01 (d, J = 2, 4H, Ar),
6.27−6.17 (dm, J = 16, 1H, PCH2P), 3.93−3.85 (dm, J = 16, 1H,
PCH2P), 3.27−3.21 (m, 4H, i-Pr CH), 2.83 (sep, J = 7, 2H, i-Pr CH),
2.70−2.46 (broad m, 4H, dppe CH2), 1.88 (dd, J = 9, 2, 6H, P-CH3),
1.17 (dd, J = 7, 1, 12H, i-Pr CH3), 0.98 (d, J = 7, 12H, i-Pr CH3), 0.73
(d, J = 7, 12H, i-Pr CH3). 13C{1H} NMR (CD2Cl2): δ 155.4 (quat,
Ar), 154.9−154.7 (broad m, quat, Ar), 134.6 (broad, CH, Ar), 134.4
(broad, CH, Ar), 133.9−133.8 (broad m, CH, Ar), 133.6−133.5
(broad m, CH, Ar), 131.3−131.2 (broad m, CH, Ar), 131.1−131.0
(broad m, CH, Ar), 127.9 (d, J = 50, quat, Ar), 125.8 (d, J = 49, quat,
Ar), 124.1−124.0 (m, CH, Ar), 121.0−120.6 (m, quat, Ar), 120.0 (q,
JC−F = 321, CF3), 47.2−46.7 (m, PCH2P), 34.6 (i-Pr CH), 34.1−34.0
(m, i-Pr CH), 26.2−25.8 (m, PCH2CH2P), 25.6 (i-Pr CH3), 24.4 (i-Pr
CH3), 23.5 (d, J = 12, i-Pr CH3), 18.2−17.8 (m, PCH3).
Data for meso-5. Anal. Calcd for C33H54P2: C, 77.30; H, 10.62.
Found: C, 76.87; H, 9.82. 31P{1H} NMR (CDCl3): δ −52.1 (meso),
1
−53.1 (rac) (11/1 ratio). H NMR (CDCl3): δ 6.94 (broad, 4H, Ar),
3.91−3.84 (m, 4H, i-Pr CH), 2.83 (sep, J = 7, 2H, i-Pr CH), 2.60−
2.47 (m, 2H, P-CH2), 1.59 (t, J = 3, 6H, P-CH3), 1.22 (d, J = 7, 12H, i-
Pr CH3), 1.15 (d, J = 7, 12H, i-Pr CH3), 1.12 (d, J = 7, 12H, i-Pr
CH3). 13C{1H} NMR (CDCl3): δ 155.0 (t, J = 7, quat, Ar), 149.9
(quat, Ar), 131.2 (d, J = 6, quat, Ar), 121.8 (CH, Ar), 34.1 (i-Pr CH),
31.2 (d, J = 11, i-Pr CH), 30.2−29.7 (m, P-CH2), 24.8 (i-Pr CH3),
24.6 (i-Pr CH3), 23.8 (d, J = 2, i-Pr CH3), 13.3 (t, J = 5, P-CH3).
Pt-Catalyzed Synthesis of 5. Method 1 (from PHMe(Is) and
CH2I2). A solution of PHMe(Is) (25 mg, 0.1 mmol) in 1 mL of toluene
was added to Pt((R,R)-Me-DuPhos)(Ph)(Cl) (3 mg, 0.005 mmol, 5
mol %). The resulting solution was added to solid NaOSiMe3 (11 mg,
0.1 mmol, 2 equiv). The solution, now yellow, was transferred to an
NMR tube fitted with a septum, and CH2I2 (4 μL, 0.05 mmol, 2 equiv)
was injected via microliter syringe. A white precipitate formed, and the
reaction was monitored by 31P NMR spectroscopy. After 71 h the
reaction had stopped, giving 5 (δ −53.7, −53.9 (combined 48%)) as
well as a byproduct (δ 37.4, 36%) and unreacted PHMe(Is) (δ −109.2
(16%)). Additional NaOSiMe3 (5 mg, 0.04 mmol) and CH2I2 (2 μL,
0.04 mmol) were added to the reaction mixture. The reaction was
complete, as judged by 31P NMR spectroscopy after an additional 24 h
(95 h total), yielding a 2/3 mixture of 5 and the byproduct, identified
rac-[Pd(dppe)(IsMePCH2PMeIs)][OTf]2 (7). To a slurry of
Pd(dppe)(OTf)2 (34 mg, 0.04 mmol) in 4 mL of CH2Cl2 was
added a solution of rac-IsMePCH2PMeIs (rac-5; 22 mg, 0.04 mmol) in
5 mL of CH2Cl2. The slurry turned homogeneous and pale yellow
almost immediately. The solution was stirred for 20 min, at which time
31P NMR spectroscopy showed that the reaction was complete.
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Recrystallization from CH2Cl2/Et2O at 21 °C by vapor diffusion gave
41 mg (95% yield) of a pale yellow solid.
0.82 (broad m, 12H, i-Pr CH3). 13C{1H} NMR (CD2Cl2): δ 155.6
(quat, Ar), 154.3 (broad m, quat, Ar), 134.3 (CH, Ar), 133.8 (CH,
Ar), 133.5−133.4 (m, CH, Ar), 133.0−132.9 (m, CH, Ar), 130.8−
130.7 (m, CH, Ar), 130.3−130.2 (m, CH, Ar), 128.3 (d, J = 54, quat,
Ar), 126.0−124.8 (broad m, CH, Is), 124.8 (d, J = 58, quat, Ar), 121.1
(q, JCF = 321, CF3), 118.6−118.2 (m, quat, Ar), 52.1−51.6 (m,
PCH2P), 35.4−34.2 (broad m, i-Pr CH), 34.4 (i-Pr CH), 27.3−26.9
(m, CH2, PCH2CH2P), 25.8−24.0 (broad, i-Pr CH3), 23.6 (i-Pr CH3),
23.4 (i-Pr CH3), 21.9−21.7 (m, P-CH3).
meso-[Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2 (10). To
a solution of Pt((R,R)-Me-DuPhos)(OTf)2 (75 mg, 0.09 mmol) in 7
mL of CH2Cl2 was added meso-IsMePCH2PMeIs (meso-5; 46 mg, 0.09
mmol) in 5 mL of CH2Cl2. The solution was stirred for 20 min and
then concentrated under reduced pressure to ca. 2 mL to give a pale
yellow solution. An off-white solid was precipitated by the addition of
5−7 mL of petroleum ether. The solvent was removed by pipet, and
the solid was washed with three 0.5 mL portions of petroleum ether.
The solid was redissolved in 2 mL of CH2Cl2; 7 mL of petroleum
ether was layered on top, and cooling overnight at −45 °C resulted in
the formation of an off-white precipitate. 31P NMR spectroscopy
revealed a residual impurity (δ 61.3, 0.5%). Addition of 2 mg more of
IsMePCH2PMeIs in 2 mL of CH2Cl2 did not remove the impurity to
give the desired product. Removal of the solvent under reduced
pressure and washing with three 0.5 mL portions of petroleum ether
removed any residual phosphine. The solid was recrystallized again
from CH2Cl2 (3 mL) and petroleum ether (15 mL) by solvent layering
at −45 °C to give pale yellow needlelike crystals (103 mg, 86% yield)
suitable for elemental analysis.
Anal. Calcd for C61H78F6O6P4PdS2: C, 55.69; H, 5.98. Found: C,
55.26; H, 5.98. HRMS (ES+): m/z calcd for C60H78F3O3P4PdS (M-
CF3SO3)+ 1165.3609, Found m/z 1165.3623. 31P{1H} NMR
(CD2Cl2): δ 56.6 (m, P-dppe), −72.1 (m, P-MeIs). 1H NMR
(CD2Cl2): δ 7.76−7.72 (m, 2H, Ar), 7.68−7.63 (m, 8H, Ar), 7.49 (t, J
= 8, 2H, Ar), 7.38−7.33 (m, 4H, Ar), 7.23 (td, J = 8, 3, 4H, Ar), 7.04
(broad, 4H, Ar), 4.71 (t, J = 11, 2H, PCH2P), 3.32 (broad, 4H, i-Pr
CH), 3.07−2.93 (m, 2H, CH2), 2.90 (sep, J = 7, 2H, i-Pr CH), 2.77−
2.65 (m, 2H, CH2), 2.20−2.17 (br m, 6H, P-Me), 1.25 (d, J = 7, 12H,
i-Pr CH3), 1.24 (d, J = 7, 12H, i-Pr CH3), 1.02−0.96 (broad m, 12H, i-
Pr CH3). 13C{1H} NMR (CD2Cl2): δ 155.5 (quat, Ar), 154.1 (broad
m, quat, Ar), 134.4 (CH, Ar), 133.8−133.7 (m, CH, Ar), 133.6 (CH,
Ar), 133.0−132.9 (m, CH, Ar), 131.0−130.9 (m, CH, Ar), 130.3−
130.2 (m, CH, Ar), 128.3 (d, J = 47, quat, Ar), 126.0 (d, J = 49, quat,
Ar), 124.9 (broad, CH, Is), 121.2 (q, J = 321, quat, CF3), 119.3 (broad
d, J = 62, quat, Ar), 48.6−48.2 (m, PCH2P), 34.5 (overlapping, i-Pr
CH), 34.5 (broad, overlapping, i-Pr CH), 27.9−27.6 (m, PCH2CH2P),
26.4 (broad, i-Pr CH3), 24.8 (broad, i-Pr CH3), 23.5 (d, J = 20, i-Pr
CH3), 20.3−19.8 (m, P-CH3).
meso-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2 (8). To a solution of
Pt(dppe)(OTf)2 (82 mg, 0.09 mmol) in 7 mL of CH2Cl2 was added a
solution of meso-IsMePCH2PMeIs (meso-5; 46 mg, 0.09 mmol) in 5
mL of CH2Cl2. The solution was stirred for 5 min and then
concentrated under reduced pressure to ca. 2 mL. Addition of 7 mL of
Et2O resulted in the formation of a white precipitate. The solution was
allowed to stand until the solid settled and the solvent was removed
with a pipet. The white solid was washed with three 0.5 mL portions of
Et2O to give 99 mg of white solid (79% yield). Recrystallization at −45
°C from minimal CH2Cl2 and Et2O by solvent layering gave white
crystals suitable for X-ray crystallography and elemental analysis.
Anal. Calcd for C61H78F6O6P4PtS2: C, 52.17; H, 5.60. Found: C,
51.87; H, 5.78. HRMS (ES+): m/z calcd for C60H78F3O3P4PtS (M −
Anal. Calcd for C53H82F6O6P4PtS2: C, 48.51; H, 6.30. Found: C,
48.39; H, 6.21. ESI-MS: m/z calcd for C52H82F3O3P4PtS (M −
SO3CF3)+ 1161.4514, found m/z 1161.4545. 31P{1H} NMR
(CD2Cl2): δ 69.7 (dm, J = 325, JPt−P = 2268), 69.0 (broad dm, J =
318, JPt−P = 2198), −72.8 (ddd, J = 7, 53, 324, JPt−P = 1856), −76.4
1
(ddd, J = 9, 53, 318, JPt−P = 1997). H NMR (CD2Cl2): δ 8.00−7.88
+
SO3CF3 ) 1254.4216, found m/z 1254.4227. 31P{1H} NMR
(m, 4H, Ar), 7.29 (broad, 3H, Ar), 7.09 (broad, 1H, Ar), 6.49 (dm, J =
16, 1H, PCH2P), 4.35 (dm, J = 16, 1H, PCH2P), 3.22−2.98 (broad
overlapping m, 3H, DuPhos CH), 3.00 (sep, J = 7, 4H, i-Pr CH), 2.93
(sep, J = 7, 2H, i-Pr CH), 2.82−2.70 (broad m, 1H, DuPhos CH), 2.77
(dd, J = 4, 10, 3H, P-CH3), 2.68 (broad d, J = 9, 3H, P-CH3), 2.65−
2.50 (m, 3H, DuPhos CH2), 2.28−2.15 (m, 3H, DuPhos CH2), 1.99−
1.83 (m, 2H, DuPhos CH2), 1.61 (dd, J = 8, 20, 3H, DuPhos CH3),
1.40−1.22 (broad overlapping m, 18H, i-Pr CH3 and 6H, DuPhos
CH3), 1.29 (d, J = 7, 6H, i-Pr CH3), 1.24 (d, J = 7, 6H, i-Pr CH3), 1.10
(broad, 3H, i-Pr CH3), 1.00 (dd, J = 8, 18, 3H, DuPhos CH3), 0.57
(broad, 3H, i-Pr CH3). 13C{1H} NMR (CD2Cl2): δ 155.8 (quat, Ar),
155.2 (quat, Ar), 155.0 (broad, quat, Ar), 154.1 (broad, quat, Ar),
138.8 (dd, J = 29, 47, quat DuPhos P−C), 136.3 (dd, J = 28, 50, quat
DuPhos P−C), 135.1−135.0 (broad m, Ar, CH), 134.6−134.5 (broad
m, Ar, CH), 134.4−134.2 (broad m, CH, Ar), 133.9−133.7 (broad m,
CH, Ar), 125.6 (broad, CH, Ar), 124.7 (broad, CH, Ar), 122.3 (broad
dm, J = 49, quat, P-C), 121.2 (q, JCF = 321, CF3), 118.5 (broad dm, J =
138, quat P-C), 53.3−52.7 (m, P-CH2), 48.6 (d, J = 33, CH), 43.3 (d, J
= 36, CH), 40.6 (d, J = 28, CH), 39.7 (d, J = 34, CH), 37.9 (CH2),
36.4 (d, J = 6, CH2), 36.3 (CH2), 35.5 (d, J = 5, CH2), 34.6 (i-Pr CH),
34.4 (i-Pr CH), 32.5 (broad, i-Pr CH), 26.9 (broad dm, J = 40, i-Pr
CH3), 26.4 (broad, i-Pr CH3), 24.9 (broad dm, J = 87, i-Pr CH3), 23.5
(d, J = 6, i-Pr CH3), 23.4 (d, J = 5, i-Pr CH3), 21.6 (d, J = 35, P-CH3),
21.0 (d, J = 25, P-CH3), 18.9 (DuPhos CH3), 17.4 (d, J = 5, DuPhos
CH3), 15.8 (d, J = 3, DuPhos CH3), 14.5 (d, J = 2, DuPhos CH3).
rac-[Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2 (11a,b). To
a solution of Pt((R,R)-Me-DuPhos)(OTf)2 (91 mg, 0.11 mmol) in 5
mL of CH2Cl2 was added a solution of rac-IsMePCH2PMeIs (rac-5; 58
mg, 0.11 mmol) in 2 mL of CH2Cl2. The solution was stirred for 20
min. 31P NMR spectroscopy showed formation of a 1/1 mixture of
11a,b and a small quantity of residual Pt((R,R)-Me-DuPhos)(OTf)2.
Additional rac-IsMePCH2PMeIs (5 mg, 0.01 mmol) was added, the
solution was concentrated to ca. 1 mL, and the product was
precipitated by the addition of 5 mL of Et2O. The solvent was
removed by pipet, and the solid was washed with three 0.5 mL
portions of Et2O and dried under vacuum to give 138 mg (96% yield)
(CD2Cl2): δ 44.4 (m, P-dppe, JPt−P = 2333), −83.4 (m, P-MeIs,
1
JPt−P = 1973). H NMR (CD2Cl2): δ 7.80−7.76 (m, 2H, Ar), 7.73−
7.69 (m, 8H, Ar), 7.68−7.62 (m, 6H, Ar), 7.47 (td, J = 8, 3, 4H, Ar),
7.03 (d, J = 4, 4H, Ar), 6.64−6.55 (dm, J = 16, 1H, PCH2P), 4.18−
4.10 (dm, J = 16, 1H, PCH2P), 3.29−3.23 (m, 4H, i-Pr CH), 2.85
(sep, J = 7, 2H, i-Pr CH), 2.57−2.42 (m, 4H, dppe CH2), 1.95−1.92
(broad m, 6H, P-CH3), 1.17 (dd, J = 7, 2, 12H, i-Pr CH3), 0.97 (d, J =
7, 12H, i-Pr CH3), 0.73 (d, J = 7, 12H, i-Pr CH3). 13C{1H} NMR
(CD2Cl2): δ 155.4 (quat, Ar), 154.9−154.7 (broad m, quat, Ar), 134.5
(broad, 2 CH, Ar), 133.9 (d, J = 11, CH, Ar), 133.7 (d, J = 11, CH,
Ar), 131.1 (d, J = 11, CH, Ar), 130.8 (d, J = 11, CH, Ar), 127.6 (d, J =
50, quat, Ar), 125.3 (d, J = 59, quat, Ar), 124.09−124.01 (m, CH, Ar),
121.3 (q, JC−F = 321, CF3) 120.0−119.6 (m, quat, Ar), 49.7−49.1 (m,
PCH2P), 34.5 (i-Pr CH), 34.1 (filled-in d,31 J = 5, i-Pr CH), 25.9 (dd, J
= 36, 8, PCH2CH2P), 25.6 (i-Pr CH3), 24.4 (i-Pr CH3), 23.5 (d, J =
13, i-Pr CH3), 18.9−18.6 (m, PCH3).
rac-[Pt(dppe)(IsMePCH2PMeIs)][OTf]2 (9). To a solution of
Pt(dppe)(OTf)2 (86 mg, 0.1 mmol) in 5 mL of CH2Cl2 was added a
solution of rac-IsMePCH2PMeIs (rac-5; 49 mg, 0.1 mmol) in 2 mL of
CH2Cl2. The solution was stirred for 5 min and then concentrated
under reduced pressure to ca. 3 mL. Recrystallization by vapor
diffusion with CH2Cl2/Et2O at 21 °C resulted in the formation of a
white crystalline solid. The solvent was removed with a pipet, and the
solid was washed with three 1 mL portions of Et2O. The solid was
dried under vacuum to give 124 mg (92% yield) of the product.
Anal. Calcd for C61H78F6O6P4PtS2: C, 52.17; H, 5.60. Found: C,
51.87; H, 5.58. HRMS (ES+): m/z calcd for C60H78F3O3P4PtS (M -
-SO3CF3)+ 1254.4222, found m/z 1254.4231. 31P{1H} NMR
(CD2Cl2): δ 45.8 (m, JPt−P = 2312, P-dppe), −79.0 (m, JPt−P
=
1
1934, P-MeIs). H NMR (CD2Cl2): δ 7.73−7.68 (m, 2H, Ar), 7.64−
7.58 (m, 8H, Ar), 7.53−7.49 (m, 2H, Ar), 7.36−7.32 (m, 4H, Ar), 7.23
(td, J = 8, 3, 4H, Ar), 7.11−7.01 (broad, 4H, Ar), 5.11 (broad t, J = 12,
2H, PCH2P), 2.93 (sep, J = 7, 4H, i-Pr CH), 2.87−2.80 (m, 2H, i-Pr
CH), 2.76−2.63 (m, 4H, PCH2CH2P), 2.45−2.35 (br m, 6H, P-Me),
1.27 (d, J = 7, 12H, i-Pr CH3), 1.26 (d, J = 7, 12H, i-Pr CH3), 1.08−
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Organometallics
Article
of white solid. Recrystallization from CH2Cl2/Et2O by solvent layering
at −30 °C gave 100 mg (70% yield) of analytically pure white solid as
a mixture of diastereomers.
solid. NMR and mass spectral data for this mixture of 8 and 9 matched
results from independently prepared samples (see above).
Methylation of 4. Synthesis of C2-[Pt((R,R)-Me-DuPhos)-
(IsMePCH2PMeIs)][OTf]2 (11a). To a yellow slurry of Pt((R,R)-
Me-DuPhos)(IsPCH2PIs) (4; 10 mg, 0.01 mmol) in 1 mL of CH2Cl2
was added MeOTf (3 μL, 0.02 mmol, 2 equiv) via microliter syringe.
The yellow slurry became homogeneous and then pale yellow within 5
min of adding the MeOTf. The 31P NMR spectrum of the crude
reaction mixture suggested the presence of monomethylated [Pt-
((R,R)-Me-DuPhos)(MeIsPCH2PIs)][OTf] (14; δ 68.0 (ddd, J = 6,
11, 64, JPt−P = 1710), 60.7 (ddd, J = 11, 26, 351, JPt−P = 2219), −85.6
Anal. Calcd for C53H82F6O6P4PtS2: C, 48.51; H, 6.30. Found: C,
48.20; H, 6.37. ESI-MS: m/z calcd for C52H82F3O3P4PtS (M −
SO3CF3)+ 1162.4535, found m/z 1162.4536. The following NMR data
are for 11b, observed in the mixture with 11a (see below for data for
11a, prepared independently). 31P{1H} NMR (CD2Cl2): δ 69.9 (P-
1
DuPhos, m, JPt−P = 2138), −76.9 (P-Is, m, JPt−P = 1969). H NMR
(CD2Cl2): δ 7.95−7.92 (m, 2H, Ar), 7.92−7.87 (m, 2H, Ar,
overlapping 11a signal), 7.27 (broad, 2H, Ar, overlapping 11a signal),
7.23 (broad d, J = 3, 2H, Ar), 4.82 (apparent t, J = 11, 2H, PCH2P),
4.16 (broad sep, J = 6, 2H, i-Pr CH), 3.30−3.27 (broad m, 2H, CH),
3.08−3.02 (m, 2H, CH), 3.04 (sep, J = 7, 2H, i-Pr CH, overlapping
previous signal), 2.97 (sep, J = 7, 2H, i-Pr CH, overlapping 11a signal),
2.78 (broad, 2H, CH), 2.77−2.75 (m, 6H, P-Me), 2.61−2.51 (m, 4H,
CH2, overlapping 11a signal), 1.80−1.66 (m, 4H, CH2, overlapping
11a signal), 1.51 (d, J = 7, 6H, i-Pr CH3), 1.42 (d, J = 6, 6H, i-Pr CH3),
1.33 (d, J = 7, 6H, i-Pr CH3), 1.32 (d, J = 7, 6H, i-Pr CH3), 1.26 (d, J =
7, 6H, i-Pr CH3), 1.25 (d, J = 7, 6H, i-Pr CH3), 0.96 (dd, J = 20, 8, 6H,
CH3), 0.73 (dd, J = 17, 7, 6H, CH3). 13C{1H} NMR (CD2Cl2): δ
155.7 (quat, Ar), 154.7 (broad, quat, Ar), 153.4 (broad, quat, Ar),
135.7 (m, quat, Ar), 134.5 (m, CH, Ar), 133.5−133.3 (m, CH, Ar),
126.2−126.1 (m, CH, Ar), 125.4−125.3 (m, CH, Ar), 121.3 (q, J =
321, quat CF3), 120.8−120.0 (m, quat, Ar), 53.1 (apparent t, J = 31,
PCH2P), 40.7 (d, J = 32, CH), 39.0 (d, J = 29, CH), 36.9 (m, CH2),
36.6 (d, J = 6, CH2), 34.9 (i-Pr CH), 34.4 (i-Pr CH), 32.6 (i-Pr CH),
28.0 (i-Pr CH3), 25.3 (i-Pr CH3), 24.3 (i-Pr CH3), 23.47 (i-Pr CH3),
23.43 (i-Pr CH3), 23.4−23.2 (m, P-CH3), 18.3 (d, J = 4, DuPhos
CH3), 15.7 (DuPhos CH3).
(apparent dd, J = 6, 351, JPt−P = 2214), −113.6 (broad d, J = 64, JPt−P
=
705)). The mixture was allowed to stand overnight, and then the
solvent was removed under reduced pressure and the pale yellow
residue was washed with three 1 mL portions of petroleum ether.
Recrystallization from CH2Cl2/pentane at −30 °C gave 10 mg (77%
yield) of white crystalline solid. The same procedure was repeated on a
slightly larger scale (34 mg, 0.035 mmol of 4) to give 36 mg (80%
yield) of product after recrystallization from CH2Cl2/Et2O at −30 °C.
In four such experiments, a 25/1 mixture of C2-symmetric 11a (major
product) and meso-10 (minor) and two additional unidentified minor
products was formed. One of the unidentified products (δ 73.6 (dm, J
= 315), 71.8 (dm, J = 304), −59.8 (dm, J = 305), −60.1 (dm, J = 316),
∼9%) was retained while the other (δ 56.2 (dd, J = 374, 12), 55.9 (dd,
J = 385, 10)) appeared and then dissipated over the course of the
reaction.
ESI-HRMS: m/z calcd for C51H83P4Pt (MH − 2SO3CF3)+
1014.5098, found m/z 1014.4767. NMR data for 11a are as follows.
(see above for data for 11b, observed in a mixture with 11a). 31P{1H}
NMR (CD2Cl21): δ 71.4 (P-DuPhos, m, JPt−P = 2253), −58.8 (P-Is, m,
JPt−P = 1932). H NMR (CD2Cl2): δ 8.01−7.97 (m, 2H, Ar), 7.93−
7.89 (m, 2H, Ar), 7.27 (broad, 4H, Ar), 4.47 (apparent t, J = 11, 2H,
PCH2P), 3.63 (broad, 2H, i-Pr CH), 3.30−3.16 (m, 2H, CH), 2.97
(sep, J = 7, 4H, i-Pr CH), 2.78 (broad, 2H, CH), 2.65−2.57 (m, 2H,
CH2), 2.56−2.53 (m, 6H, P-Me), 2.44−2.33 (m, 2H, CH2), 2.08−2.00
(m, 2H, CH2), 1.74−1.69 (m, 2H, CH2), 1.58 (dd, J = 20, 7, 6H,
CH3), 1.45−1.36 (broad m, 6H, i-Pr CH3), 1.33−1.29 (broad m, 6H,
i-Pr CH3), 1.27 (d, J = 7, 24H, i-Pr CH3), 1.01 (dd, J = 17, 7, 6H,
CH3). 13C{1H} NMR (CD2Cl2): δ 156.0 (quat, Ar), 155.1 (broad,
quat, Ar), 153.6 (broad, quat, Ar), 137.1 (broad m, quat, Ar), 134.8
(m, CH, Ar), 134.4 (m, CH, Ar), 127.2 (broad, CH, Ar), 125.1 (broad,
CH, Ar), 122.6 (q, J = 322, CF3), 118.8−118.3 (m, quat, Ar), 49.7
(apparent t, J = 35, PCH2P), 46.6 (d, J = 33, CH), 38.7 (d, J = 31,
CH), 37.8 (CH2), 36.3 (d, J = 7, CH2), 34.5 (i-Pr CH), 32.4 (broad, i-
Pr CH), 28.0 (broad, i-Pr CH), 26.7 (i-Pr CH3), 26.6 (broad, i-Pr
CH3), 25.9 (broad, i-Pr CH3), 25.4 (broad, i-Pr CH3), 23.4 (i-Pr
CH3), 21.7−21.3 (m, P-CH3), 17.7 (d, J = 5, DuPhos CH3), 16.3
(DuPhos CH3).
Methylation of 2. Synthesis of rac-/meso-[Pd(dppe)-
(IsMePCH2PMeIs)][OTf]2 (6, 7). To an orange-red solution of
Pd(dppe)(IsPCH2PIs) (2; 47 mg, 0.048 mmol) in 1.5 mL of CH2Cl2
in an NMR tube was added MeOTf (11 μL, 0.1 mmol, 2 equiv). The
solution remained orange-red. The monomethylated product [Pd-
(dppe)(IsMePCH2PIs)][OTf] (12a, δ 40.5 (apparent dt, J = 342, 42),
35.0 (ddd, J = 48, 42, 22), −89.6 (m), −94.8 (ddd, J = 12, 22, 342))
was observed by 31P NMR spectroscopy within minutes after the
injection of MeOTf. Some additional peaks in the 31P NMR spectrum
were tentatively assigned to minor diastereomer 12b (δ 40.5 (dm, J =
365), 36.8−35.8 (m), −103.9 (dm, J = 365)). The ratio 12a/12b was
about 9/1. Formation of dications 6 and 7 was slower. The reaction
was incomplete after standing overnight. After addition of more
MeOTf (2 μL, 0.02 mmol), and standing overnight, the reaction was
complete, according to 31P NMR spectroscopy, which showed a 1.1/1
mixture of meso-6 and rac-7. Recrystallization from CH2Cl2/Et2O by
solvent layering at 21 °C gave 14 mg (29% yield) of an off-white solid
that was almost exclusively the rac diastereomer 7 (63/1 rac/meso
from integration of the 31P NMR dppe signals). NMR data for this
material matched that obtained for independently prepared 7 (see
above).
ASSOCIATED CONTENT
* Supporting Information
■
S
Text, tables, figures, and CIF files giving additional
experimental and crystallographic details and NMR spectra.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Methylation of 3. Synthesis of rac-/meso-[Pt(dppe)-
(IsMePCH2PMeIs)][OTf]2 (8, 9). To a yellow solution of Pt(dppe)-
(IsPCH2PIs) (3; 30 mg, 0.027 mmol) in 1.5 mL of CH2Cl2 in an
NMR tube was added MeOTf (6 μL, 0.054 mmol, 2 equiv). The
solution remained yellow. The monomethylated product [Pt(dppe)-
(IsMePCH2PIs)][OTf] (13, δ 43.3 (broad d, J = 73, JPt−P = 1824),
40.1 (ddd, J = 9, 25, 348, JPt−P = 2644), −87.4 (apparent d, J = 350,
JPt−P = 2246), −114.3 (broad, JPt−P = 764)) was observed by 31P NMR
spectroscopy within minutes. Formation of dications 8 and 9 was
slower. The reaction mixture was allowed to stand overnight, at which
time the reaction was complete, according to 31P NMR spectroscopy,
which showed a mixture of rac-9 and meso-8 that was slightly enriched
AUTHOR INFORMATION
Corresponding Author
*E-mail: Glueck@Dartmouth.Edu.
■
Notes
The authors declare no competing financial interest.
1
in the rac diastereomer (1.2/1 on the basis of integration of the H
ACKNOWLEDGMENTS
■
NMR PCH2P signals). The solvent was removed under reduced
pressure, and the residue was washed with three 1 mL portions of
petroleum ether. The residue was recrystallized twice at 21 °C, once
from CH2Cl2 (1 mL)/Et2O (5 mL) and once from THF (2 mL)/
petroleum ether (5 mL), to give 26 mg (68% yield) of pale yellow
We thank the National Science Foundation for support and the
Department of Education for a GAANN fellowship for T.W.C.
A.J.S. thanks the Beckman Foundation for a Beckman
Scholarship and Dartmouth College for a Dean of Faculty
5584
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P. Organometallics 1998, 17, 652−660. (b) Wicht, D. K.; Glueck, D. S.;
Liable-Sands, L. M.; Rheingold, A. L. Organometallics 1999, 18, 5130−
5140. (c) Wicht, D. K.; Kovacik, I.; Glueck, D. S.; Liable-Sands, L. M.;
Incarvito, C. D.; Rheingold, A. L. Organometallics 1999, 18, 5141−
5151. (d) Wicht, D. K.; Kourkine, I. V.; Kovacik, I.; Glueck, D. S.;
Concolino, T. E.; Yap, G. P. A.; Incarvito, C. D.; Rheingold, A. L.
Organometallics 1999, 18, 5381−5394. (e) Scriban, C.; Glueck, D. S.;
Golen, J. A.; Rheingold, A. L. Organometallics 2007, 26, 1788−1800;
Organometallics 2007, 26, 5124 (addition/correction). (f) Scriban, C.;
Glueck, D. S. J. Am. Chem. Soc. 2006, 128, 2788−2789. (g) Zhuravel,
M. A.; Glueck, D. S.; Zakharov, L. N.; Rheingold, A. L. Organometallics
2002, 21, 3208−3214.
Research Grant and a Zabriskie Fellowship. We thank
Dartmouth College for Presidential Scholarships to A.J.S. and
C.L.C.
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