Water addition to alkynes promoted by a dicationic platinum(II) complex

Article abstract of DOI:10.1021/om2007908

Dicationic platinum alkyne complexes were generated in situ by substitution of ethylene in [Pt(PNP)(C₂H₄)](BF₄) ₂ (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) with alkynes at low temperature. The dicationic acetylene complex readily adds water to form the platina-acetaldehyde complex [Pt(PNP)(CH₂CHO)]BF₄, which was analyzed by X-ray diffraction. ¹H and ³¹P NMR studies were performed to elucidate the mechanism of formation of [Pt(PNP)(CH ₂CHO)]BF₄. A reversible acid-base equilibrium between the platina-acetaldehyde and the corresponding η²-vinyl alcohol complex [Pt(PNP)(CH₂=CHOH)]²⁺ was observed. The complexes with terminal alkynes (propyne and 1-hexyne) gave with water a mixture of Markovnikov and anti-Markovnikov addition products [Pt(PNP){CH ₂C(O)R¹}]BF₄ and [Pt(PNP){C(O)CH ₂R¹}]BF₄ (R¹ = Me, n-Bu) in a ratio of 1:4. However, with tert-butyl- and phenylacetylene C-H bond activation occurred, yielding the σ-alkynyl complexes [Pt(PNP)(C≡CR ²)]BF₄ (R² = t-Bu, Ph). Complexes with internal alkynes R³C≡CR⁴ (R³ = Me; R⁴ = Me, n-Pr) react with water and form the corresponding β-ketonyl complexes [Pt(PNP){CHR³C(O)R⁴}]BF₄. Moderate regioselectivity was observed for 2-hexyne.

Full text of DOI:10.1021/om2007908

Article
pubs.acs.org/Organometallics
Water Addition to Alkynes Promoted by a Dicationic Platinum(II)
Complex†
Spring Carlisle, Angel Matta, Homer Valles, Jason B. Bracken, Mayra Miranda, Jinah Yoo,
and Christine Hahn*
Department of Physical Sciences, University of Texas of the Permian Basin, 4901 East University Boulevard, Odessa, Texas 79762,
United States
S
* Supporting Information
ABSTRACT: Dicationic platinum alkyne complexes were generated in situ by substitution of ethylene in [Pt(PNP)(C2H4)]-
(BF4)2 (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) with alkynes at low temperature. The dicationic acetylene complex
readily adds water to form the platina-acetaldehyde complex [Pt(PNP)(CH2CHO)]BF4, which was analyzed by X-ray diffraction.
1H and 31P NMR studies were performed to elucidate the mechanism of formation of [Pt(PNP)(CH2CHO)]BF4. A reversible
acid−base equilibrium between the platina-acetaldehyde and the corresponding η2-vinyl alcohol complex [Pt(PNP)(CH2
CHOH)]2+ was observed. The complexes with terminal alkynes (propyne and 1-hexyne) gave with water a mixture of
Markovnikov and anti-Markovnikov addition products [Pt(PNP){CH2C(O)R1}]BF4 and [Pt(PNP){C(O)CH2R1}]BF4 (R1 =
Me, n-Bu) in a ratio of 1:4. However, with tert-butyl- and phenylacetylene C−H bond activation occurred, yielding the σ-alkynyl
complexes [Pt(PNP)(CCR2)]BF4 (R2 = t-Bu, Ph). Complexes with internal alkynes R3CCR4 (R3 = Me; R4 = Me, n-Pr)
react with water and form the corresponding β-ketonyl complexes [Pt(PNP){CHR3C(O)R4}]BF4. Moderate regioselectivity was
observed for 2-hexyne.
alkynes in order to replace the traditional acid and the highly
toxic mercury catalysts.1 The first platinum(II)-catalyzed
hydration of alkynes was reported by Chatt and Duncanson
using Na2PtCl4·H2O as catalyst.2 Later, Jennings and co-
workers found that Zeise’s dimer and PtII halides efficiently
catalyze the hydration of unactivated alkynes.3 Terminal
alkynes were hydrated with Markovnikov selectivity and
unsymmetrical internal alkynes with moderate regioselectivity.
Atwood and co-workers have synthesized water-soluble
platinum(II) complexes containing sulfonated mono- and
bidentate phosphine ligands.4 Furthermore, platinum(IV)
chloride was shown to catalyze the hydration of various
alkynes at 1.38 MPa CO pressure.5 Also, for the study of
hydrative cyclizations of allenynes and trialkynes PtCl2 has
been frequently used as catalyst.6
INTRODUCTION
■
The hydration of alkynes is an important reaction to synthesize
aldehydes or ketones, because it is atom-economical and
inexpensive starting materials are used. With terminal alkynes
either Markovnikov or anti-Markovnikov products can be
formed, while with unsymmetrical alkynes two different
regioisomers can be expected (Scheme 1).
Scheme 1. Hydration of Terminal and Internal Alkynes
While various new gold complexes were reported more
recently as very efficient catalysts,7 there seem to be currently
In the last few decades increasing efforts have been made to
develop new transition-metal catalysts for the hydration of
Received: August 23, 2011
Published: November 14, 2011
© 2011 American Chemical Society
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no further efforts to design structurally new complexes of
platinum(II) and to study their catalytic activity, mechanistic
details, or reaction intermediates. Many questions concerning
transition-metal-catalyzed hydration of alkynes remain un-
answered. For example, the regioselectivity of the hydration of
unfunctionalized internal alkynes is still a challenge. The
catalytic anti-Markovnikov addition of water to terminal alkynes
to form aldehydes succeeded only with ruthenium catalysts.8
In analogy to our previous studies of electrophilic activation
of alkenes by coordination in dicationic platinum(II) com-
plexes of the type [Pt(PNP)(CHRCHR)](BF4)2 (PNP =
2,6-bis(diphenylphosphinomethyl)pyridine) and their reactions
with water and other weakly basic nucleophiles,9 we explored also
the activation of alkynes at the Pt(PNP)2+ complex fragment.
Since water addition to the coordinated C−C double bond gave
the stable β-hydroxyalkyl complexes [Pt(PNP)(CH2CHROH)]-
BF4 in a stoichiometric reaction, it was interesting to study
similarly the products resulting from water addition to the
coordinated C−C triple bond.
In this paper, we report the generation of dicationic
platinum(II) alkyne complexes of the type [Pt(PNP)(RC
CR′)](BF4)2 with acetylene and terminal and internal alkynes.
These complexes were reacted with water and gave platina-
acetaldehyde, ketonyl, acyl, or alkynyl σ complexes, which were
isolated and characterized by NMR, IR, and X-ray structure
analysis and studied in solution. These results provide not only
support for the relevant intermediates and reaction steps
suggested by Jennings and co-workers3 for the platinum(II)-
catalyzed alkyne hydration but also demonstrate the possibility
of the anti-Markovnikov addition of water to terminal alkynes
using a platinum(II) complex.
reaction conditions, but this time 15 equiv of water was added
to the solution of the ethylene complex prior to the addition of
acetylene. Water addition to the coordinated ethylene9 is very
slow at low temperature and is not a competing side reaction.
In contrast, the far more reactive acetylene complex [Pt(PNP)-
(C2H2)](BF4)2 (I) (eq 1) immediately reacts upon its
formation with the excess water provided in advance.12 This
prevents practically all unwanted side reactions. Under these
optimized conditions (eq 1) the platina-acetaldehyde complex
[Pt(PNP)(CH2CHO)]BF4 (1) was isolated in analytically pure
form.
The platina-acetaldehyde complex [Pt(PNP)(CH2CHO)]-
BF4 (1) was characterized by NMR and IR spectroscopy as well
1
as by X-ray crystal structure analysis. The H NMR spectrum
shows a characteristic doublet of triplets for the PtCH2 group at
δ 2.94 with platinum satellites. The triplet at δ 8.95 is diagnostic
for an aldehyde proton. In the 13C NMR spectrum a signal at δ
201.7 is observed for the carbonyl carbon atom. The IR bands
at ν
̃
1673 and 2722 cm−1 are assigned to the CO and C−H
stretching frequencies of the aldehyde functional group. Similar
IR bands were observed for the CO group in other platina-
acetaldehyde complexes.13,14
X-ray Structure Analysis of [Pt(PNP)(CH2CHO)]BF4
(1). Suitable crystals for X-ray structure analysis were obtained
by overlayering a solution of complex 1 in CH2Cl2 with diethyl
ether. An ORTEP drawing of the complex cation is shown
in Figure 1. The complex cation 1 has a square-planar coordination
RESULTS AND DISCUSSION
■
Reaction of [Pt(PNP)(C2H4)](BF4)2 with Acetylene and
Water. A common method to generate platinum(II) alkyne
complexes is the displacement of an alkene by the alkyne, since
the alkyne is a stronger donor ligand.10 When the ethylene
9
complex [Pt(PNP)(C2H4)](BF4)2 was reacted with an excess
of acetylene in CD2Cl2 at room temperature, the solution
turned immediately dark brown, indicating fast acetylene oligo-
or polymerization. The 1H NMR spectra of the reaction
solution showed a number of signals between 0 and 5 ppm,
which can be assigned to oligomerization products. This is not
unusual for platinum(II) complexes.10 The formation of un-
controlled oligomerization byproduct could be strongly reduced
by performing the reaction at lower temperature with only a
slight excess of acetylene. When 3 equiv of acetylene was added
to the ethylene complex in CH2Cl2 at −78 °C, the reaction
solution turned only light brown. After 15 min the reaction
mixture was warmed to room temperature and a light brown
solid was precipitated by addition of diethyl ether. However,
Figure 1. ORTEP drawing of the complex cation 1. Selected bond
lengths (Å) and angles (deg): Pt−P1 = 2.2693(9), Pt−P2 =
2.3033(10), Pt−N = 2.112(3), Pt−C1 = 2.132(3), C1−C2 =
1.410(6), C2−O = 1.218(5); P1−Pt−P2 = 165.90(3), N−Pt−P1 =
82.82(9), N−Pt−P2 = 83.15(9), N−Pt−C1 = 178.10(12), C1−Pt−
P1 = 95.34(10), C1−Pt−P2 = 98.70(10), Pt−C1−C2 = 102.2(2),
C1−C2−O = 126.7(4).
1
the H and 31P NMR spectra of the isolated product show the
formation of a mixture of compounds. A dicationic acetylene
complex could not be identified among them. This is not
surprising, since it is expected to be extremely reactive and can
easily undergo numerous side reactions. There are also no
examples known for isolated platinum acetylene complexes.11
However, in the 1H NMR spectrum of the compound
mixture a characteristic set of signals could be identified. It
suggests the formation of the platina-acetaldehyde complex
[Pt(PNP)(CH2CHO)]BF4 (1) as a result of reaction of the
coordinated acetylene with water which was adventitiously
present in solution. The reaction was repeated under the same
geometry with the η1-acetaldehyde ligand in the fourth posi-
tion. The Pt−C1 (2.132(3) Å) and C1−C2 (1.410(6) Å)
bond lengths are similar to those found in [Pt(PNP)-
15
{CH2CH2C6H2(OCH3)3}]SbF6 (2.157(9) and 1.421(16) Å;
cf. Table 1), indicating a Pt−C σ bond and a C−C single bond
type. The C2−O bond length of 1.218(5) Å is characteristic
for a C−O double bond, and the C1−C2−O angle of 126.7°
suggests the sp2 character of the C2 atom. These structural
features agree with the spectroscopic data.
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Table 1. Selected Bond Lengths (Å) and Angles (deg) of [Pt(PNP)(CH2CHO)]BF4 (1) and Those of Structurally Related
a
Complexes
Pt−C1
Pt−C2
C1−C2
C2−O
Pt−C1−C2
C1−C2−O
[Pt(PNP)(CH2CHO)]BF4 (1)
2.132(3)
2.081(9)
2.098(10)
2.121(9)
2.181(8)
2.157(9)
2.7937(3)
2.062(9)
2.222(9)
2.93
1.410(6)
1.45(1)
1.218(5)
1.41(1)
102.2(2)
70(1)
126.7(4)
121(1)
121.9(9)
n.a.
b
[PtBr(CH3)(dmphen)(CH2CHOH)]
c
[PtCl(acac)(CH2CHOH)]
1.387(5)
1.35(2)
1.297(12)
1.30(2)
76.3
d
[PtIII2(NH3)4{(CH3)3CCONH}2(CH2CHO)](NO3)3·H2O
113.5
e
[Pt(PNP)(CH2CH2)](BF4)2
2.180(6)
3.06(1)
1.359(10)
1.421(16)
71.8(4)
116.3(7)
f
[Pt(PNP){CH2CH2C6H2(OCH3)3}]SbF6
a
For the sake of uniformity the atom labeling was adopted for all complexes to that of complex 1 and may not agree with the original labeling.
b
c
d
e
f
dmphen = 2,9-dimethyl-1,10-phenanthroline.15 Reference 17. Reference 14. Reference 9. Reference 15.
It is interesting to compare the structure and bonding in
the coordinated vinyl alcohol in [PtBr(CH3)(dmphen)(CH2
CHOH)] is lengthened due to the relatively strong π back-
donation, which is expected for a relatively electron-rich five-
coordinate platinum(II) complex.
complex 1 with those of the following platinum complexes:
[PtBr(CH3)(dmphen)(CH2CHOH)],16a [PtCl(acac)(CH2
CHOH)],17 and [PtIII2(NH3)4{(CH3)3CCONH}2(CH2CHO)]-
(NO3)3 ·H2O14 (cf. Table 1), which display structural features
intermediate between vinyl alcohol π complex A and platina-
acetaldehyde σ complex C (Scheme 2). Structures A and C are
In contrast, the solid-state structure of [PtCl(acac)(CH2
CHOH)] reported by Cotton et al.17 displays a vinyl alcohol π
complex with a strong geometric bias to the intermediate
structure B (Scheme 2). In this structure the Pt−C2 bond
(2.222(9) Å) is significantly longer than Pt−C1 (2.098(10) Å).
The C2−O distance (1.29(12) Å) seems to be intermediate
between C−O single- and a double-bond lengths.18,19 The
C−C bond length of 1.387(5) Å of the vinyl alcohol in
[PtCl(acac)(CH2CHOH)] lies between the lengths ob-
served for the coordinated C−C double bonds in [PtBr(CH3)-
Scheme 2. Structural Relationship between Vinyl Alcohol
π Complex and Platina-Acetaldehyde σ Complex
9
(dmphen)(CH2CHOH)]16a and [Pt(PNP)(C2H4)](BF4)2
(cf. Table 1).
On the other hand, the platina-acetaldehyde σ complex
[PtIII2(NH3)4{(CH3)3CCONH}2(CH2CHO)](NO3)3·H2O re-
ported by Matsumoto14 represents essentially structure C but
with a bias to structure B. The Pt−C1 and Pt−C2 distances
(2.121(9) and 2.93 Å) are similar to those observed for
complex 1. The Pt−C1−C2 bond angle of 113.5° lies between
the values found for η 1 complexes 1 and [Pt(PNP)-
related through an acid−base equilibrium which was studied in
solution,13,14,16 while the intermediate structure B is considered
to be important in the mechanism of the alkyne hydration
(cf. Schemes 2 and 3; see discussion below).
The five-coordinate complex [PtBr(CH3)(dmphen)(CH2
CHOH)] is one of the few structurally characterized η2-vinyl
alcohol complexes of platinum16 and provides an example for
structure A (Scheme 2). The vinyl alcohol is coordinated with
essentially equal Pt−C1 and Pt−C2 bond lengths, as similarly
found for the π-coordinated ethylene in [Pt(PNP)(C2H4)]-
(BF4)2 (cf. Table 1).9 The C−C double bond (1.45(1) Å) of
15
{CH2CH2C6H2(OCH3)3}]SbF6 (cf. Table 1) and indicates
a σ-alkyl bond of the CH2 group. However, the C1−C2 bond
length in the PtIII complex at 1.35(2) Å is shorter than a C−C
single bond, while the C2−O distance (1.30(2) Å) appears
somewhat longer than a C−O double-bond length.
Scheme 3. Proposed Mechanism for the Formation of Complex 1, Where All Nonhighlighted Species Are Proposed
Intermediates
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A comparison of these structures may provide some insight
into the progress of the acid−base equilibrium of the vinyl
alcohol π complex and the platina-acetaldehyde σ-complex,
where complex 1 represents “pure” structure C.
NMR Studies of Complex 1 in Solution. According to
the mechanism for the alkyne hydration proposed by Jennings
and co-workers,3 it is suggested that the formation of complex 1
involves the nucleophilic addition of water to the in situ gene-
rated acetylene complex I (cf. Scheme 3). The β-hydroxonium
vinyl species II is most likely the primary addition product from
which the proton dissociates, and the η1-enol species III is
formed, which tautomerizes to the more stable platina-
acetaldehyde complex 1.
It was interesting to see if the proposed equilibrium reaction
can be shifted back by addition of HBF4 and if in this way the
dicationic acetylene π complex I can be generated back and
spectroscopically characterized. It should be noted that the
methanol addition to [Pt(PNP)(CH2CH2)](BF4)2 could
be completely reversed by addition of HBF4 to [Pt(PNP)-
(CH2CH2OCH3)]BF4.9
acidity of the corresponding vinyl alcohol PtIII complex is
expected. Similarly, intermediate IV should also display a
relatively high acidity due to the high positive complex charge,
and the equilibrium lies far on the side of complex 1. This
may explain the generally low stability of IV and the failure to
isolate it.
By addition of Na2CO3 to the mixture of complex 1 and
HBF4·Et2O the equilibrium was immediately shifted back to the
1
pure form of complex 1. The H NMR spectrum of this
solution showed the restored signals for complex 1. The similar
conversion of five-coordinate vinyl alcohol PtII π complexes to
the corresponding square-planar platina-acetaldehyde σ com-
plexes by addition of KOH was demonstrated by Panunzi16a
and De Felice16b previously.
While the addition of HCl to those square-planar platina-
acetaldehyde σ complexes regenerated the corresponding five-
coordinate vinyl alcohol PtII π complexes,15 the addition of HCl
to complex 1 resulted in the formation of [Pt(PNP)Cl]+ and
acetaldehyde (eq 2). This reaction is fast and complete after
To a solution of complex 1 in CD2Cl2 were added 3 drops of
HBF4·Et2O. In the 1H NMR spectrum the signal at δ 8.95 is no
longer observed and the characteristic doublet of triplets for the
PtCH2 group has shifted downfield from δ 2.94 to δ 3.78 and
2
the Pt−H coupling constant JPt−H has decreased from 108 to
81 Hz (see Figure S2 in the Supporting Information). This
indicates the formation of the η 2-enol complex IV rather
1
than the acetylene complex I, because very similar H NMR
data were observed for K[PtCl(acac)(CH2CHO)] and the
corresponding η2-enol complex (cf. Table 2).13b All attempts to
isolate the η2-vinyl alcohol intermediate IV, however, failed.
mixing (<1 min). In the 31P NMR spectrum a signal appears at
δ 21.5 which is similar to that of the iodo complex [Pt(PNP)I]+
(cf. Table 3), and in the 1H NMR spectrum a quartet at δ 9.73
and a doublet at δ 2.19 with 3JH−H = 2.7 Hz are observed, which
are in agreement with the signals of free acetaldehyde.
Table 2. Characteristic 1H NMR Data for Platina-
Acetaldehyde and Vinyl Alcohol Complexes (δ in ppm, J in Hz)
2
δ
3J
J
δ
Hc
Hab
Hab−Hc
5.5
8.1
5.5
8
Pt‑Hab
[Pt(PNP)(CHaHbCHcO)]+ (1)
2.94
3.78
3.28
3.89
108
81
8.95
Since the 1H NMR spectra of the mixture of complex 1 with
HBF4·Et2O are more or less obscured by large signals of the
diethyl ether, we decided to study the acid−base equilibrium of
complex 1 by 31P NMR. This should better show how many
different Pt(PNP) species are actually present in solution. 31P
NMR spectra were recorded upon subsequent addition of
5−200 μL of HBF4·Et2O to a solution of complex 1 in CD2Cl2
(see Figure S4 in the Supporting Information). After addition
of 5 μL of HBF4·Et2O the signal of complex 1 at δ 27.6
b
[Pt(PNP)(CHaHbCHcOH)]2+ (IV)
n.a.
a
K[PtCl(acac)(CHaHbCHcO)]
113
76
9.16
7.27
a
[PtCl(acac)(CHaHbCHcOH)]
a
b
Reference 13b. Not observed or hidden under signals of aromatic
protons.
When less HBF4·Et2O (1 drop) was added to complex 1, the
respective signals for the CHaHbCHcO moiety were shifted
only slightly (δH 8.48, δH 3.05) and the coupling constants
disappeared and two new characteristic signals at δ 34.0 (1JP−Pt
=
c
ab
also changed only slightly (2JPt−H = 97 Hz, 2JH
= 6.1 Hz; see
2487 Hz) and δ 29.4 (1JP−Pt = 2531 Hz) were observed in a
ratio of 3:2. After addition of further portions of HBF4·Et2O the
signal at δ 34.0 remained unchanged while the second signal
shifted slightly downfield and changed its intensity relative to
the first signal. At 35 μL of HBF4·Et2O the two species are
almost equally abundant, and at 200 μL of HBF4·Et2O the
second signal was observed at δ 30.2 with a decreased intensity.
A third small signal at δ 21.3 (1JP−Pt = 2554 Hz) appeared at
20 μL of HBF4·Et2O which increased in intensity with an
increasing amount of HBF4·Et2O. In order to attempt an
assignment for the observed signals, the 31P NMR data were
compared with those of known Pt(PNP) complexes.9,20 In
Table 3 the 31P NMR chemical shifts and corresponding
31P−195Pt coupling constants are given. A plot of these data is
shown in Figure S5 (Supporting Information), visualizing the
individual complex types.
ab−Hc
Figure S3 in the Supporting Information). The same trend was
also observed when K[PtCl(acac)(CH2CHO)] and the
corresponding η2-enol complex were mixed together in
solution.13b This suggests that complex 1 and intermediate IV
are involved in a similar dynamic acid−base equilibrium, where
1
Ha and Hb scramble rapidly on the H NMR time scale.
When the structural features of the different vinyl alcohol
complexes and their acid−base properties in solution are
compared, a trend of stability can be clearly seen. While the η2-
vinyl alcohol is stabilized in the five-coordinate PtII complex16
by strong π back-donation, the neutral vinyl alcohol complex
[PtCl(acac)(CH2CHOH)] behaves as a weak Brønsted acid
(pKa = 3.5) in aqueous solution.13 The dimeric platina-
acetaldehyde PtIII complex14 (cf. Table 1) was isolated from
strongly acidic solution. Therefore, even stronger Brønsted
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Table 3. 31P NMR Data for [Pt(PNP)R]n+ Complexes (δ in ppm,
J in Hz)
observed when a large excess of HBF4·Et2O was added to a
dichloromethane solution of the ethylene complex [Pt(PNP)-
(C2H4)](BF4)2.
[Pt(PNP)X]n+
δ
1JP−Pt
solvent ref
In another experiment ethylene was bubbled through a
[Pt(PNP)(CH2CH2)]2+
[Pt(PNP)(CH2CHMe)]2+
[Pt(PNP)(norbornene)]2+
[Pt(PNP)(CH2CHEt)]2+
41.7
40.8
40.7
39.3
2174 CD2Cl2
2268 CD2Cl2
2177 CD2Cl2
b
b
b
b
solution of complex 1 containing 200 equiv of HBF4·Et2O and
a
31P NMR spectrum was recorded (see Figure S4 in the
Supporting Information). This spectrum showed a new signal
at δ 39.6 (1JP−Pt = 2174 Hz) which could be assigned to the
ethylene complex [Pt(PNP)(C2H4)]2+. While the signal at δ
34.0 strongly decreased in intensity, the signal at δ 30.2 was not
visibly affected and became the most intense peak in the
spectrum. This can be interpreted by the substitution of the
acetylene by an ethylene molecule.
Reaction of [Pt(PNP)(C2H4)](BF4)2 with Terminal
Alkynes and Water. The reaction of [Pt(PNP)(C2H4)]-
(BF4)2 with terminal alkynes (propyne and 1-hexyne) and
water gave mixtures of the ketonyl and acyl complexes
[Pt(PNP){CH2C(O)R}]BF4 (2a, 3a) and [Pt(PNP){C(O)-
CH2R}]BF4 (2b, 3b) (R = Me, 2a,b; R = n-Bu, 3a,b); cf. eq 3.
2236 CD2Cl2/
CD3NO2
[Pt(PNP)(CH2CHPh)]2+
38.2
37.1
34.0
2328 CD2Cl2
2330 CD2Cl2
2432 CD2Cl2
2531 CD2Cl2
3003 CD2Cl2
3055 CD3OD
3052 CD2Cl2
3110 CD2Cl2
3020 CD2Cl2
3077 EtOH
c
[Pt(PNP)(CH2CHNaph)]2+
a
[Pt(PNP)(HCCH)]2+ (I)
d
d
b
a
Intermediates II−IV
29.4−30.2
32.8
[Pt(PNP)(CH2CHPhNHPh)]+
[Pt(PNP)(CH2CHNaphOMe)]+
[Pt(PNP)(CH2CHPhOH)]+
[Pt(PNP)(CH2CHPhOMe)]+
[Pt(PNP)(CH2CH2OMe)]+
[Pt(PNP)(CH2CHPhOEt)]+
[Pt(PNP)(CH2CHMeOH)]+
[Pt(PNP)(CH2CHMeNHPh)]+
31.1
31.0
b
b
b
c
30.3
29.9
29.7
29.4
3033 CD2Cl2
3060 CD2Cl2
2997 CD2Cl2
3029 CD2Cl2
3026 CD2Cl2
b
b
b
b
d
29.4
[Pt(PNP)(CH2CH2NHC6H4Cl-o)]+ 29.1
[Pt(PNP)(CH2CH2NHC6H4Me-p)]+ 29.1
[Pt(PNP){CH(CH2CH2CH3)C(O) 29.4
CH3}]+ (7b)
[Pt(PNP){CH(CH3)C(O)
28.9
3031 CD2Cl2
d
CH2CH2CH3}]+ (7a)
[Pt(PNP){CH(CH3)C(O)CH3)]+ (6) 28.7
3006 CD2Cl2
2866 CD2Cl2
d
d
[Pt(PNP){CH2C(O)
28.2
CH2CH2CH2CH3}]+ (3a)
[Pt(PNP){CH2C(O)CH3}]+ (2a)
[Pt(PNP)(CH2CHO)]+ (1)
[Pt(PNP)(E-CHCHPh)]+
[Pt(PNP)(E-CHCHNaph)]+
[Pt(PNP)(CCPh)]+ (4)
28.1
27.6
27.1
26.9
22.5
20.2
20.8
20.5
2851 CD2Cl2
2781 CD2Cl2
2922 CD3OD
2929 CD3OD
2576 CD2Cl2
2617 CD2Cl2
3252 CD2Cl2
3271 CD2Cl2
d
d
c
c
d
d
d
d
[Pt(PNP)(CCt-Bu)]+ (5)
[Pt(PNP){C(O)CH2CH3}]+ (2b)
[Pt(PNP){C(O)
CH2CH2CH2CH2CH3}]+ (3b)
[Pt(PNP)I]+
24.7
21.5
21.3
2487 CDCl3
2554 CD2Cl2
e
[Pt(PNP)Cl]+
d
d
[Pt(PNP)(BF4)]+
2554 CD2Cl2
The isomeric mixtures 2a,b and 3a,b were isolated in good
yields with a ketonyl/acyl ratio of about 1/4, respectively. The
terminal alkynes were somewhat less reactive than the
acetylene. Therefore, the reaction was performed at 0 °C
using 5 equiv of alkyne (cf. the Experimental Section).
a
b
c
Assumed species, see text and Scheme 3. Reference 9. Reference
d
e
20. This work. 31P NMR data not given in ref 9, only here.
The first signal at δ 34.0 might be assigned to the dicationic
acetylene complex I. The chemical shift and the 31P−195Pt
coupling constant are similar to those observed for the
dicationic alkene complexes (Table 3, Figure S5). Also the
fact that the chemical shift of this signal is not affected by the
concentration of HBF4 in solution supports the assignment.
Instead, the second signal could be assigned to the blend of
enol species II−IV being involved in the acid−base equilibrium
with complex 1. This is supported by the observed downfield
shift upon addition of increasing amounts of HBF4. It is also in
agreement with the changes which could be observed in the 1H
NMR spectrum. The chemical shift and the 31P−195Pt coupling
constant of this signal are between those for complex 1 and
dicationic π complexes (cf. Table 3 and Figure S5).
The respective complex mixtures 2a,b and 3a,b were
characterized by IR and NMR spectroscopy. In the IR
spectrum of 2a,b two CO stretching bands at ν
̃ 1626 and
1639 cm−1 were observed. Similar wavenumbers were reported
for other ketonyl21 and acyl22 PtII complexes. The H NMR
1
spectrum of 2a,b correspondingly showed two sets of signals.
For the acetonyl complex 2a a singlet for the methyl group
appeared at δ 1.28, and the triplet at δ 2.94 with characteristic
platinum satellites could be assigned to the PtCH2 group. A
triplet at δ 0.55 and a quartet at δ 2.09 were due to the ethyl
group of the acyl complex 2b. The 13C NMR spectrum showed
two signals at δ 214.6 and 219.1 for the two different carbonyl
groups in 2a,b, respectively. In the 31P NMR spectrum two
signals at δ 28.1 and δ 20.8 appeared in a ratio of 1:4. The first
signal had a chemical shift and 31P−195Pt coupling constant
similar to those observed for the platina-acetaldehyde complex
1 (cf. Table 3) and therefore could be assigned to the β-ketonyl
complex 2a. However, the signal for the acyl complex 2b was
The third signal at δ 21.3 which appeared only at higher
concentrations of HBF4 could be assigned to the tetrafluoro-
borato complex [Pt(PNP)(BF4)]+. Due to the relatively high
−
concentration of BF4 ions in solution the otherwise only
weakly coordinating anion may be able to bind at the platinum
center in an equilibrium reaction. This 31P NMR signal was also
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shifted more upfield and displayed a considerably larger
31P−195Pt coupling constant (cf. Table 3 and Figure S5). For
the complex mixture 3a,b similar NMR data were obtained (see
the Experimental Section).
Further structural evidence for the acetonyl complex 2a was
provided by protonolysis, whereby acetone was released upon
1
addition of concentrated HCl (cf. Scheme 4). The H NMR
Scheme 4. Protonolysis of the Complex Mixture 2a,b by HCl
Figure 2. ORTEP drawing of the complex cation 2b.23 Selected bond
lengths (Å) and angles (deg): Pt−P1 = 2.279(2), Pt−P2 = 2.284(3),
Pt−N = 2.131(8), Pt−C33 = 2.002(10), C33−C34 = 1.5001(11),
C34−C35 = 1.5000(11), C33−O = 1.200(15); P1−Pt−P2 =
163.61(9), N−Pt−P1 = 82.2(2), N−Pt−P2 = 81.4(2), N−Pt−C1 =
178.0(4), C1−Pt−P1 = 96.4(3), C1−Pt−P2 = 99.9(3), Pt−C33−C34 =
117.1(10), C34−C33−O = 121.6(13), C33−C34−C35 = 109.78(11).
spectrum of a solution of 2a,b in CD2Cl2 with added HCl
showed a singlet at δ 2.16 which can be assigned to acetone.
1
However, all H NMR signals of 2b appeared the same as
described above. The 31P NMR spectrum showed the signal of
[Pt(PNP)Cl]+ at δ 21.4, while the second signal at δ 21.7
(1JP−Pt = 3217 Hz) could be assigned to complex 2b (cf. Table 3).
The NMR signals of complex 2b in the HCl-containing solution
remained unchanged over at least 1 day. The inertness to
protonolysis reflects the relatively strong Pt−C bond in 2b, which
is much less polar than that in 2a.
The complex mixture 2a,b was recrystallized, and single
crystals suitable for X-ray structure analysis were obtained. The
crystal that was picked up was the anti-Markovnikov product
2b. An ORTEP drawing of the complex cation of 2b is shown
in Figure 2. The ethyl group of the acyl ligand is disordered,
and only one of the most probable positions of C34 and C35 is
depicted in Figure 2.23 The Pt−C33 bond length of 2.002(10) Å
is in the range (1.97−2.10 Å) found for other acyl complexes.24
In contrast to the terminal alkynes described above, phenyl-
and tert-butylacetylene do not add water to the coordinated C−
C triple bond under the same conditions. Instead, C−H bond
activation occurred and the corresponding alkynyl complexes 4
and 5 were formed (eq 4), which were isolated in good yield as
stable compounds. The IR spectrum showed a characteristic
and JC−Pt by ∼100 Hz26 (cf. the Experimental Section). For
2
complex 4 a 31P NMR signal is observed at δ 22.5 and for
complex 5 at δ 20.2.
With these different terminal alkynes three possible reaction
pathways in the presence of water have been demonstrated,
which are summarized in Scheme 5. The reaction paths are very
similar to those described earlier by Chisholm and Clark27 and
Belluco28 for the reaction of monocationic PtII alkyne
complexes with methanol. The way the coordinated terminal
alkyne may react depends on several parameters, such as
electronic conditions at the metal center, solvent, and the
substituent at the alkyne.
In each case the dicationic alkyne complex V was generated
in situ by substitution of ethylene (cf. Scheme 5). If the
substituent at the terminal alkyne is small or less bulky (R =
Me, n-Bu), the substituted carbon atom can be attacked by a
water molecule, presumably giving the η1-enol intermediate
VI, which tautomerizes to the ketonyl complex (2a, 3a:
Markovnikov products).
However, in the case of propyne and 1-hexyne the 1,2-
hydride shift is a more competitive path where either the
carbocationic intermediate VII or the η1-vinylidene species
VIII is thought to be formed. In any resonance structure
between VII and VIII the α-carbon atom is the electrophilic
center and is attacked by the water molecule. This leads to the
formation of an α-hydroxyalkenyl or an α-hydroxycarbene
̃
stretching band for the C−C triple bond at ν 2125 and 2123
cm−1 for the phenyl and tert-butyl derivatives 4 and 5,
respectively. Similar wavenumbers were reported for other
platinum(II) alkynyl complexes.22a,25 The 1H NMR spectra of 4
and 5 showed the corresponding signals for the phenyl and the
tert-butyl group (see the Experimental Section). The 13C NMR
signals for the alkynyl carbon atoms in complexes 4 and 5 are
observed at δ 75.9 and 59.2 for Cα and δ 114.5 and 124.5 for
Cβ, respectively. The 13C−195Pt coupling constants are greater
than those observed for the neutral bis-alkynyl platinum(II) com-
1
plexes trans-[Pt{P(n-Bu)3}2(CCAr)2]: JC−Pt by ∼300 Hz
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Scheme 5. Summary of the Reactions of [Pt(PNP)(HCCR)]2+ with Water
complex (IX or X) which tautomerizes to the acyl complex
(2b, 3b: anti-Markovnikov products).
alkyne which, in contrast to the enol VI, cannot further
tautomerize.32
The acyl complexes 2b and 3b seem to represent the first
examples for anti-Markovnikov addition of water to terminal
alkynes promoted by platinum(II). Although no catalytic anti-
Markovnikov hydration of terminal alkynes has been observed
with any platinum catalyst, the formation of 2b and 3b is not so
unusual with respect to earlier studies with monocationic PtII
alkyne complexes.27,28,32−35 Chisholm and Clark have
suggested a 1,2-hydride shift of terminal alkynes giving an
α-carbocationic intermediate such as VII to explain the
methanol addition at the α-carbon atom.27 Later Belluco
et al.35 were able to detect the η1-vinylidene complexes
[(CH3)(PPh3)2Pt(CCHR)]X in solution by NMR spec-
troscopy at low temperature; these were generated by
protonation of the corresponding alkynyl complexes. This
may support the proposed η1-vinylidene species VIII. Whether
the α-hydroxyalkenyl species IX or the α-hydroxycarbene
complex X is formed is unknown. Analogous monocationic
α-alkoxycarbene PtII complexes were prepared by alcohol
addition to a coordinated terminal alkyne and were isolated
and structurally characterized.33,34,36 The β-proton in the
monocationic α-alkoxycarbene PtII complexes is found to be
relatively acidic and can be removed by a base.34 In the
proposed dicationic α-hydroxycarbene complex X the acidity of
the β-proton might be enhanced due to the higher positive
complex charge and the equilibrium may probably be shifted
more to the side of the α-hydroxyalkenyl species IX. While no
stable α-hydroxycarbene complexes of platinum(II) have been
isolated (with the exception of dimeric acyl hydroxycarbene PtII
complexes reported by Steinborn and co-workers),37 those
of rhenium38 and other transition metals39 are well-known,
which can be generated by protonation of corresponding acyl
complexes. The latter reaction would exhibit the reverse
reaction to the formation of acyl complexes 2b and 3b from
intermediate X.
In the case of terminal alkynes with more bulky substituents
(R = Ph, t-Bu) the rearrangement to alkynyl complexes (4, 5)
by proton dissociation is the preferred path, where water acts as
a Brønsted base. Probably the water addition is kinetically
inhibited due to steric hindrance. In addition, the alkynyl
complexes 4 and 5 may be thermodynamically the most stable
species in the equilibrium system. For the phenyl derivative 4 π
conjugation may in addition contribute to the higher stability.
This is similar to the case for the alkene complexes
[Pt(PNP)(CH2CHR)]2+ (R = Ar), where vinylic deproto-
nation is preferred over nucleophilic addition of water or
alcohols, forming the very stable alkenyl complexes [Pt(PNP)-
((E)-CHCHR)]+.20
The suggested structures of the intermediates V−X are all
supported by results reported for closely related reactions with
platinum and other transition-metal complexes.27−42 Isolated
PtII complexes with terminal alkynes are extremely rare.29,30
The coordinated terminal alkyne is only reasonably stabilized in
electron-rich complexes, which are either anionic29 or five-
coordinate.30 In contrast, the dicationic alkyne complex V can-
not be easily trapped or detected, due to its high electro-
philicity, and reacts instantly either with a nucleophile or
rearranges upon its formation. Chisholm and Clark noted that
they were also not able to isolate monocationic PtII complexes
of terminal alkynes but have suggested them as reactive
intermediates.27
Similar to the first path (cf. Scheme 5), Markovnikov
addition of water to a series of terminal alkynes was observed
with the dimeric PtIII complex [PtIII2(NH3)4{(CH3)3CCONH}2-
(NO3)2](NO3)2, and the corresponding ketonyl complexes
were formed.31 In analogy to the η1-enol intermediate VI, η1-
vinyl ether complexes [(CO)(PPh3)2Pt{CHCR(OR′)]BF4
were isolated as a result of alcohol addition to the coordinated
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Studies by Michelin and co-workers have demonstrated the
addition of water to a cationic η1-vinylidene complex, forming
the α-hydroxycarbene PtII complex [(CH3)Pt(PPh3)2{C(OH)-
CH2R}]+, which was spectroscopically observed only in solution.35
The α-hydroxycarbene PtII complex was found to be unstable,
and one of the decomposition paths is C−C bond cleavage
resulting in the corresponding carbonyl complex and a
hydrocarbon due to the highly polarized Cα−Cβ bond. A
similar reaction path was observed by Bianchini et al., studying
the mechanism of the ruthenium-catalyzed anti-Markovnikov
addition of water to terminal alkynes in detail.40 However, the
acyl complexes 2b and 3b are stable even under acidic
conditions (see above) and do not decompose at room
temperature.
Further examples for simultaneous Markovnikov and anti-
Markovnikov addition of water to ruthenium alkynyl complexes
yielding a mixture of both ketonyl and acyl complexes were
reported by Onishi and co-workers.41
The conditions for a 1,2-hydride shift vs the formation of
alkynyl complexes from PtII complexes with terminal alkynes
vary, depending on the particular nature of the respective
complexes. For monocationic PtII alkyne complexes proton
dissociation is preferred over a 1,2-hydride shift when a polar
aprotic solvent instead of a protic solvent is used.27 In the case
of five-coordinate PtII complexes oxidative addition of the
terminal alkyne is observed upon heating, giving the
corresponding hydrido alkynyl PtIV complexes.30 So far it is
known for the dicationic PtII alkyne complexes V that the
nature of the substituent at the terminal alkyne determines
whether the proton dissociation or 1,2-hydride shift reaction
path is preferred. Other conditions remain to be explored.
Notable are the studies by Ogo and Fukuzumi where it was
shown that with a water-soluble iridium(III) complex all three
pathways can be tuned by adjustment of the pH of the aqueous
solution. Depending on the pH alkynyl, ketonyl, or acyl
complexes could be generated from a phenylacetylene IrIII
complex.42
The ketonyl complexes 6 and 7a,b were analyzed by 1H, 13C,
and 31P NMR spectroscopy.
1
The H NMR spectrum of 6 shows the characteristic signals
for the butanonyl group: a doublet at δ 0.85 and a singlet at δ
1.48 for the two different methyl groups with platinum satellites
of 50.5 and 11.0 Hz, respectively. A quartet for the α-proton
at δ 3.28 appears with platinum satellites of 117 Hz. In the
13C NMR spectrum the signal at δ 212.1 can be assigned to the
carbonyl group. The 31P NMR spectrum shows a signal at δ
28.7. Further structural evidence for the ketonyl complex 6 is
provided by treatment of a solution of this complex in CD2Cl2
1
with concentrated HCl (eq 7). In the H NMR spectrum the
Reaction of [Pt(PNP)(C2H4)](BF4)2 with Internal Alkynes
and Water. Furthermore, internal alkynes (2-butyne and
2-hexyne) were reacted with [Pt(PNP)(C2H4)](BF4)2 in the
presence of 15 equiv of water under conditions similar to those
described above for the reactions with the terminal alkynes
(eqs 5 and 6). The reaction with 2-butyne gave the
signals at δ 1.05 (triplet), 2.14 (singlet), and 2.46 (quartet) are
in agreement with 2-butanone. In the 31P NMR a signal appears
for [Pt(PNP)Cl]+ at δ 21.4.
The isolated ketonyl complexes 7a,b were characterized as a
product mixture. The presence of two different isomers can be
easily identified in the 31P NMR spectrum, where two signals
at δ 28.9 (7a) and δ 29.4 (7b) appear in a ratio of 4:1. In the
1H NMR spectrum a set of signals can be unambiguously
assigned to the major isomer 7a, while the signals for the minor
isomer 7b are partially overlapped by those of 7a (see the
Experimental Section). The signal set for the organic moiety of
7a consists of a multiplet at δ 3.35 with platinum satellites of
148 Hz for the PtCH group and a doublet at δ 0.88 for the α-
methyl group. Further signals in the region δ 0.5−2.0 belong to
the n-propyl group in 7a. In the 13C NMR spectrum for each iso-
mer a set of signals could be assigned (see the Experimental Section).
corresponding ketonyl complex 6, which was isolated in 85%
yield. With 2-hexyne the two regioisomers 7a,b in a ratio of 4/1
were formed, and the isomeric mixture was isolated in 89%
yield. The isomer 7a is more abundant due to less steric
interaction of the α-methyl group with the phenyl groups of the
PNP ligand in comparison to the other isomer 7b, having a
longer substituent at the α-carbon atom.
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were employed for sample screening and data collection, respectively,
for complexes 1 and 2b. A total of 45 data frames were taken at a
width of 0.3° with an exposure time of 20 s. Over 200 reflections were
centered, and their positions were determined. These reflections were
used in the autoindexing procedure to determine the unit cell. Suitable
cells were found and refined by nonlinear least-squares and Bravais
lattice procedures and are reported in Table S8 (Supporting
Information). The standard data collection procedure consists of the
collection of one hemisphere of data collected using ω scans, involving
collection over 1400 0.3° frames at fixed angles for ϕ, 2θ, and χ (2θ =
−28, 54.73°), while ω was varied. The total data collection was
performed for a duration of approximately 25 h at 110 K. All non-
hydrogen atoms of the asymmetric unit were refined with anisotropic
displacement parameters. All hydrogen atoms were calculated in ideal
positions. In the structure of complex 2b disorder was found for the
ethyl group in the acyl ligand and the solvent molecule (CH2Cl2). The
ethyl group is disordered over the two most probable positions C34−C35
and C34′−C35′ with relative occupancies of 76.1 and 23.9%, respectively.
The molecule of CH2Cl2 has full occupancy of 50%. In that molecule one
of the chlorine atoms is disordered over the two most probable positions
Cl(2) and Cl(2′) with occupancies of 31.7 and 18.3%. Bond restraints and
distances were applied to model the disorder.
General Procedure for the Synthesis of Complexes 1−7. The
ethylene complex [Pt(PNP)(C2H4)](BF4)2 (300 mg, 0.344 mmol)
was dissolved in 100 mL of CH2Cl2, and the solution was cooled to
−78 °C (when reacted with acetylene) or 0 °C (for all other alkynes).
Fifteen equivalents of water (93 μL, 5.2 mmol) was added to the
cold solution. Then, 3 equiv of acetylene (24 mL, 1.0 mmol) or
5 equiv of the substituted alkyne was added. The mixture was stirred
for 15 min at the respective temperature. The cooling bath was
removed, and the reaction solution was warmed to room temperature.
The volume of the solution was reduced to 10 mL, and the product
was precipitated with 100 mL of diethyl ether. The product was
filtered off, washed with diethyl ether, and dried under vacuum. For
further purification the product was recrystallized by dissolution in
CH2Cl2 and precipitation with diethyl ether.
The signals for the carbonyl groups appear at δ 215.5 for 7a and
at δ 212.0 for 7b.
Most likely as a result of steric interaction with the PNP
ligand the regioselectivity of the water addition to 2-hexyne is
slightly improved in favor of the 3-hexanonyl derivative 7a in
comparison to the catalytic hydration of 2-hexyne by Zeise’s
dimer or other PtII salts, where 3-hexanone and 2-hexanone
were obtained in a ratio of about 2/1.3
CONCLUSION
■
With these studies it has been shown that dicationic PtII alkyne
complexes can be generated by facile displacement of the
ethylene ligand in [Pt(PNP)(C2H4)]2+(cf. eq 1 and Scheme 5).
However, the dicationic alkyne complexes are too reactive and
therefore could not be isolated. The alkyne complexes readily
add water under very mild conditions in a relatively short
reaction time (eqs 1, 3, 5, and 6). In the case of terminal
alkynes three different reaction paths were observed, depending
on the substituent at the alkyne (cf. Scheme 5). With less bulky
substituents ketonyl and acyl complexes were obtained (i.e.,
Markovnikov and anti-Markovnikov products) in a ratio of 1/4
(eq 3), while for terminal alkynes with more bulky substituents
no water addition was observed. Instead alkynyl complexes
were formed by proton dissociation (eq 4). Internal alkynes
reacted by water addition and formation of the corresponding
ketonyl complexes (eqs 5 and 6). In the case of an unsym-
metrical alkyne moderate regioselectivity was observed in favor
of the isomer where the carbonyl function is located at the
carbon atom bearing the longer substituent (eq 6).
Studies are in progress addressing the isolation or detection
of dicationic alkyne and vinylidene Pt(PNP) complexes. Also,
other parameters such as solvent effects influencing the anti-
Markovnikov selectivity as well as conditions for a catalytic
alkyne hydration are of further interest.
[Pt(PNP)(CH2CHO)]BF4 (1). Yield: 226 mg (0.282 mmol, 82%).
Mp: 239 °C dec. Anal. Calcd for C33H30BF4NOP2Pt: C, 49.52; H,
3.78; N, 1.75. Found: C, 49.11; H, 3.37; N, 1.72. 1H NMR (250 MHz,
3
3
2
CD2Cl2): δ 2.94 (dt, 2H, JH−H = 5.5 Hz, JH−P = 5.5 Hz, JH−Pt
=
2+4
EXPERIMENTAL SECTION
108 Hz, PtCH2), 4.49 (ps t, 4H,
J
= 4.7 Hz, PCH2), 7.45−8.21
■
H−P
(m, 23H, Ph, py), 8.95 (t, 1H, JH2−H = 5.5 Hz, CHO). 13C NMR
3
General Considerations. The ethylene complex [Pt(PNP)-
(C2H4)](BF4)2 was prepared as described previsously.9 All reactions
were performed under an argon atmosphere. Atomic absorption grade
acetylene (dissolved) was used. The other alkynes were received from
Aldrich and were used without purification. CD2Cl2 and CD3NO2
were received from Aldrich and dried over 3 Å molecular sieves.
CH2Cl2 was dried over CaH2 and diethyl ether over sodium/benzo-
phenone. The solvents were distilled before use. The IR spectra were
recorded as neat solids on an FT Perkin-Elmer instrument. The
elemental analyses were performed by Columbia Analytical Services,
Tuscon, AZ. The NMR spectra were recorded on Bruker 250, 400, and
500 MHz (cryoprobe) instruments. The 1H NMR shifts were
referenced to the resonance of the residual protons. The 31P NMR
shifts were referenced to an external 85% H3PO4 standard. The
following abbreviations were used for NMR signals: s, singlet; d,
doublet; t, triplet; ps t, pseudotriplet; q, quartet, m, multiplet.
1
(62.89 MHz, CD2Cl2): δ 16.9 (t, JC−P < 3 Hz, JC−Pt = 530 Hz,
1+3
3+5
PtCH2), 45.5 (ps t,
J
= 16.9 Hz, PCH2), 123.3 (ps t,
J
=
C−P
C−P
1+3
5.5 Hz, 3,5-py), 126.2 (ps t,
J
= 29.0 Hz, Phi), 129.7 (ps t,
C−P
3+5
2+4
J
= 5.7 Hz, Phm), 132.6 (s, Php), 133.2 (ps t,
J
= 6.9 Hz,
C−P
C−P
2+4
Pho3), 140.9 (s, 4-py), 160.0 (ps t,
J
= 3.1 Hz, 2,6-py), 201.7
C−P
(t, JC−P = 3.0 Hz, JC−Pt = 54 Hz, CHO). 31P NMR (101.25 MHz,
2
CD2Cl2): δ 27.6 (1JP−Pt = 2781 Hz). IR ν (cm−1): 1052 (vs, BF4), 1671
̃
(m, CO), 2721 (w, CHO).
[Pt(PNP){CH2C(O)CH3}]BF4 (2a) and [Pt(PNP){C(O)CH2CH3}]BF4
(2b). Yield (combined): 220 mg (0.270 mmol, 78%). Anal. Calcd
for C34H32BF4NOP2Pt·(CH3CH2)2O: C, 51.36; H, 4.76; N, 1.58.
1
Found: C, 51.13; H, 5.10; N, 1.76. H NMR (250 MHz, CD2Cl2):
4
3
2a, δ 1.28 (s, 3H, JH−Pt = 7.0 Hz, CH3), 2.94 (t, 2H, JH−P = 6.2 Hz,
2JH−Pt = 109 Hz, PtCH2), 4.48 (ps t, 4H,
J
= 4.7 Hz, PCH2),
2+4
H−P
7.55−7.66 (m, 12H, Ph), 7.69−7.81 (m, 10H, Ph, 3,5-py), 8.06 (t, 1H,
3
3JH−H = 7.7 Hz, 4-py); 2b, δ 0.55 (t, 3H, JH−H = 7.4 Hz, CH3), 2.09
X-ray Structure Determination of [Pt(PNP)(CH2CHO)]BF4 (1)
and [Pt(PNP){C(O)CH2CH3}]BF4·0.5CH2Cl2 (2b)43−45. Details of
the X-ray experiments, data collection and reduction, and final
structure refinement calculations for complexes 1 and 2b are sum-
marized in Table S8 (Supporting Information). Crystals of complexes
1 and 2b were grown from CH2Cl2 solution by diffusion with diethyl
ether over several days at room temperature. Suitable crystals were
respectively selected and fixed to a nylon loop or a cactus needle,
which in turn was attached to a copper mounting pin. The mounted
crystals were then placed under a cold nitrogen stream (Oxford)
maintained at 110 K. A Bruker SMART 1000 three-circle X-ray
diffractometer with graphite-monochromated Cu Kα (λ = 1.541 84 Å,
40 kV, 40 mA) and Mo Kα radiation (λ = 0.70173 Å, 50 kV, 40 mA)
(q, 2H, 3JH−H = 7.3 Hz, CH2), 4.54 (ps t, 4H, 2+4JH−P = 5.0 Hz, PCH2),
7.55−7.66 (m, 12H, Ph), 7.69−7.81 (m, 10H, Ph, 3,5-py), 8.06 (t, 1H,
3JH−H = 7.7 Hz, 4-py). 13C NMR (100.61 MHz, CD2Cl2): 2a, δ 14.8
2
1+3
(t, JC−P = 4.0 Hz, PtCH2), 29.9 (s, CH3), 45.8 (ps t,
J
= 17.2
C−P
3+5
Hz, PCH2), 123.2 (ps t,
J
= 5.5 Hz, 3,5-py), 126.2 (ps t,
C−P
1+3
3+5
J
= 29.5 Hz, Phi), 129.5 (ps t,
J
= 5.6 Hz, Phm), 132.5
C−P
C−P
(s, Php), 133.3 (ps t, 2+4JC−P = 6.7 Hz, Pho), 140.7 (s, 4-py), 160.2 (ps
2+4
3
t,
J
= 3.0 Hz, 2,6-py), 214.6 (s, CO); 2b, δ 7.9 (s, JC−Pt
=
=
C−P
1+3
3
18 Hz, CH3), 44.9 (pst,
J
= 17.7 Hz, PCH2), 51.3 (t, JC−P
C−P
2
3+5
4.0 Hz, JC−Pt = 205 Hz, CH2), 123.0 (ps t,
J
= 5.6 Hz, 3,5-py),
C−P
127.7 (ps t, 1+3JC−P = 29.3 Hz, Phi), 129.5 (ps t, 3+5JC−P = 5.8 Hz, Phm),
2+4
132.4 (s, Php), 132.9 (ps t,
J
= 6.8 Hz, Pho), 141.0 (s, 4-py),
C−P
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dx.doi.org/10.1021/om2007908|Organometallics 2011, 30, 6446−6457

Organometallics
Article
2+4
2
1+3
159.4 (ps t,
J
= 3.0 Hz, 2,6-py), 219.1 (t, JC−P = 5 Hz, CO).
PtCH), 30.0 (s, CH3), 45.8 (ps t,
J
= 16.9 Hz, PCH2), 123.2
C−P
C−P
3+5
1+3
31P NMR (101.25 MHz, CD2Cl2): 2a, δ 28.1 (s, 1JP−Pt = 2851 Hz); 2b,
δ 20.8 (s, JP−Pt = 3252 Hz). IR ν
(ps t,
126.8 (ps t,
J
= 5.1 Hz, 3,5-py), 126.5 (ps t,
J
= 28.8 Hz, Phi),
C−P
C−P
1+3
3+5
(cm−1): 2a,b, 1626 (m, CO),
1
J
= 28.5 Hz, Phi′), 129.4 (ps t,
J
= 5.6 Hz,
̃
C−P
C−P
3+5
Phm), 129.5 (ps t,
(s, Php′), 133.2 (ps t,
J
= 5.6 Hz, Phm′), 132.3 (s, Php), 132.6
= 6.1 Hz, Pho), 133.9 (ps t,
1639 (m, CO).
C−P
2+4
2+4
J
J
=
=
[Pt(PNP){CH2C(O)(CH2)3CH3}]BF4 (3a) and [Pt(PNP){C(O)-
(CH2)4CH3}]BF4 (3b). Yield (combined): 268 mg (0.313 mmol,
91%). Anal. Calcd for C37H38BF4NOP2Pt·(CH3CH2)2O: C, 52.91;
H, 5.20; N, 1.51. Found: C, 52.52; H, 5.29; N, 1.71. 1H NMR
(500 MHz, CD3NO2): 3a, δ (CH2CH2CH2CH3 are hidden under the
C−P
C−P
2+4
2
7.1 Hz, Pho′), 140.6 (s, 4-py), 159.5 (ps t,
J
= 3.0 Hz, JC−Pt
C−P
33 Hz, 2,6-py), 212.1 (s, CO). 31P NMR (101.25 MHz, CD2Cl2):
1
δ 28.7 (s, JP−Pt = 3006 Hz).
[Pt(PNP){CH(CH3)C(O)CH2CH2CH3}]BF4 (7a) and [Pt(PNP){CH-
(CH2CH2CH3)C(O)CH3}]BF4 (7b). Yield (combined): 262 mg (0.306
mmol, 89%). Mp: 251 °C dec. Anal. Calcd for C37H38BF4-
NOP2Pt·(CH3CH2)2O: C, 52.91; H, 5.20; N, 1.51. Found: C, 52.90;
3
2
signals of 3b) 2.94 (t, 2H, JH−P = 6.3 Hz, JH−Pt = 110 Hz, PtCH2),
4.64 (ps t, 4H, 2+4JH−P = 4.6 Hz, PCH2), 7.59−7.68 (m, 12H, Ph), 7.74
3
(d, 2H, JH−H = 7.5 Hz, 3,5-py), 7.86−7.90 (m, 8H, Ph), 8.06 (t, 1H,
1
3JH−H = 7.5 Hz, 4-py); 3b, δ 0.63 (t, 3H, JH−H = 7.3 Hz, CH3), 0.76
3
H, 5.30; N, 1.66. H NMR (500 MHz, CD3NO2): 7a, δ 0.57 (t, 3H,
3
3
3JH−H = 9.1 Hz, CH3), 0.88 (d, 3H, JH−H = 8.2 Hz, JH−Pt = 57 Hz,
PtCCH3), 1.05 (m, 2H, CH2), 1.71 (m, 1H, OCCHaHb), 1.93
(m, 1H, OCCHaHb), 3.35 (m, 1H, 3JH−H = 8.2 Hz, 3JH−Pt = 148 Hz,
PtCH), 4.56 (d ps t, 2H, 3JH−H = 22.1 Hz, 2+4JH−P = 5.8 Hz, PCHaHb),
(m, 2H, CH2), 0.93 (m, 2H, CH2), 1.09 (m, 2H, CH2), 2.16 (t, 2H,
3JH−H = 7.5 Hz, COCH2), 4.70 (ps t, 4H,
J
= 4.8 Hz, PCH2),
2+4
H−P
3
7.59−7.68 (m, 12H, Ph), 7.74 (d, 2H, JH−H = 7.5 Hz, 3,5-py), 7.86−
7.90 (m, 8H, Ph), 8.06 (t, 1H, JH−H = 7.5 Hz, 4-py). 13C NMR
3
3
2+4
4.71 (d ps t, 2H, JH−H = 22.1 Hz,
J
= 5.6 Hz, PCHaHb),7.59−
H−P
(100.61 MHz, CD2Cl2): 3a, δ (CH3 not observed or overlapped by 3b
signal at 13.6), 14.2 (s, PtCH2), 22.1 (s, CH2), 26.1 (s, CH2), 43.1 (s,
7.72 (m, 14H, Ph, 3,5-py), 7.85−8.25 (m, 9H, Ph, 4-py); 7b, δ 0.48 (t,
3
1+3
3+5
3H, JH−H = 9.1 Hz, CH3), 0.55−2.50 (signals for CH2CH2 and O
CH2), 45.9 (ps t,
J
= 16.9 Hz, PCH2), 123.1 (ps t,
J
=
=
C−P
C−P
5.5 Hz, 3,5-py), 126.6 (ps t, 2+4JC−P = 29.7 Hz, Phi), 129.5 (ps t, 3+5JC−P
CCH3 overlapped by signals of 7a), 3.31 (m, 1H, PtCH), 4.52−4.76
(signals for 4H of PCHaHb overlapped by signals of 7a), 7.59−7.72
5.5 Hz, Phm), 132.6 (s, Php), 133.3 (ps t, 2+4JC−P = 6.8 Hz, Pho), 140.5
(s, 4-py), 160.2 (ps t, 2+4JC−P = 3.0 Hz, 2,6-py), 214.9 (s, CO); 3b, δ
(m, 14H, Ph, 3,5-py), 7.85−8.25 (m, 9H, Ph, 4-py). 13C NMR (100.62
3
MHz, CD2Cl2): 7a, δ 13.2 (s, CH3), 18.2 (s, CH2), 16.8 (t, JC−P
=
=
4
13.6 (s, CH3), 22.2 (s, CH2), 23.5 (s, JC−Pt = 18 Hz, CH2), 31.1 (s,
3
2
1
2 Hz, JC−Pt = 33 Hz, PtCHCH3), 22.5 (t, JC−P = 3 Hz, JC−P
1+3
3
CH2), 45.1 (ps t,
J
= 17.3 Hz, PCH2), 58.3 (t, JC−P = 3.8 Hz,
C−P
579 Hz, PtCH), 45.2 (ps t, 1+3JC−P = 17.1 Hz, PCH2), 45.4 s (s, CH2),
2JC−Pt = 188 Hz, COCH2), 123.0 (ps t, JC−P = 5.3 Hz, 3,5-py), 127.7
3+5
1+3
123.1 (ps t,
J
= 4.8 Hz, 3,5-py), 127.5 (ps t,
J
= 28.7 Hz,
3+5
C−P
C−P
(ps t, JC−P = 29.0 Hz, Phi), 129.6 (ps t,
J
= 5.7 Hz, Phm), 132.4
Phi), 127.8 (ps t, 1+3JC−P = 28.5 Hz, Phi′), 129.5 (ps t, 3+5JC−P = 5.5 Hz,
C−P
(s, Php), 133.0 (ps t, 2+4JC−P = 6.8 Hz, Pho), 140.9 (s, 4-py), 159.4 (ps
3+5
Phm), 129.6 (ps t,
J
= 5.5 Hz, Phm′), 132.4 (s, Php), 132.9 (s,
2+4
4
2
C−P
t,
J
= 3.0 Hz, JC−Pt = 33 Hz, 2,6-py), 218.1 (t, JC−P = 5.0 Hz,
Php′), 133.5 (ps t, 2+4JC−P = 6.1 Hz, Pho), 134.7 (ps t, 2+4JC−P = 7.2 Hz,
Pho′), 140.7 (s, 4-py), 160.2 (ps t, 2+4JC−P = 3.0 Hz, 2JC−Pt = 33 Hz, 2,6-
C−P
CO). 31P NMR (161.92 MHz, CD2Cl2): 3a, δ 28.2 (s, 1JP−Pt = 2866
1
Hz); 3b, δ 20.5 (s, JP−Pt = 3271 Hz).
py), 215.2 (s, CO); 7b, δ 13.5 (s, CH3), 22.7 (s, PtCH), 24.3 (s,
= 17.0 Hz,
C−P
[Pt(PNP)(CCC6H5)]BF4 (4). Yield: 230 mg (0.268 mmol, 78%).
1+3
CH2), 30.1 (s, CH3), 34.5 (s, CH2), 45.1 (ps t,
J
Mp: 277 °C dec. Anal. Calcd for C39H32BF4NP2Pt: C, 54.56; H, 3.76;
3+5
1+3
PCH2), 123.2 (ps t,
J
= 4.8 Hz, 3,5-py), 127.3 (ps t,
J
=
N, 1.63. Found: C, 53.77; H, 4.16; N, 1.65.46 1H NMR (250 MHz,
C−P
C−P
1+3
28.8 Hz, Phi), 127.7 (ps t,
J
= 28.4 Hz, Phi′), 129.3 (ps t,
C−P
2+4
CD2Cl2): δ 4.63 (ps t, 4H,
J
= 5.0 Hz, PCH2), 7.08−7.23
H−P
3
3+5
3+5
J
= 5.4 Hz, Phm), 129.8 (ps t,
J
= 5.3 Hz, Phm′), 132.5
C−P
C−P
(m, 5H, CPh), 7.54−7.63 (m, 12H, Ph), 7.84 (d, 2H, JH−H = 7.6 Hz,
(s, Php), 132.8 (s, Php′), 133.6 (ps t, 2+4JC−P = 6.2 Hz, Pho), 134.6 (ps t,
3
3,5-py), 7.98−8.07 (m, 8H, Ph), 8.13 (t, 1H, JH−H = 7.6 Hz, 4-py).
2+4
2+4
J
= 7.1 Hz, Pho′), 140.8 (s, 4-py), 160.1 (ps t,
J
= 3.0 Hz,
C−P
C−P
13C NMR (100.62 MHz, CD2Cl2): δ 43.9 (ps t,
J
= 16.9 Hz,
1+3
2,6-py), 212.0 (s, CO). 31P NMR (161.92 MHz, CD2Cl2): 7a,
C−P
2
1
PCH2), 75.9 (t, JC−2 P = 13.5 Hz, JC−Pt = 1325 Hz, PtCC), 114.5
1
1
δ 28.9 (s, JP−Pt = 3031 Hz); 7b, 29.4 (s, JP−Pt = 3026 Hz).
NMR Studies of Complexes 1, 2a,b, and 6 in Solution. To a
solution of 10 mg (0.011 mmol) of complex 1 in 0.5 mL of CD2Cl2
(a) 3 drops (∼ 30 mg, ∼ 0.18 mmol) and (b) 1 drop (∼ 10 mg, ∼
3
3+5
(t, JC−P = 3.0 Hz, JC−Pt = 372 Hz, PtCC), 123.5 (ps t,
J
=
=
C−P
5.8 Hz, 3,5-py), 126.6 (s, C6H5), 126.9 (s, C6H5), 127.5 (ps t, 1+3JC−P
3+5
30.0 Hz, Phi), 128.0 (s, C6H5), 129.5 (ps t,
131.1 (s, C6H5), 132.4 (s, Php), 133.1 (ps t,
J
= 5.8 Hz, Phm),
= 7.0 Hz, Pho),
C−P
2+4
J
1
C−P
0.062 mmol) of HBF4·Et2O (54% HBF4 in Et2O) were added. A H
2+4
2
141.1 (s, 4-py), 161.8 (ps t,
J
= 3.8 Hz, JC−Pt = 34 Hz, 2,6-py).
C−P
NMR spectrum was recorded of each respective solution.
To a solution of 10 mg of complex 1 in 0.5 mL of CD2Cl2
successively 5−200 μL portions (3−600 equiv) of HBF4·Et2O were
added. After each 5 μL (for the first 50 μL) and after 100, 150, and
200 μL were added to the solution, a 31P NMR spectrum was
recorded.
31P NMR (101.25 MHz, CD2Cl2): δ 22.5 (s, JP−Pt = 2576 Hz).
1
IR ν
̃
(cm−1): 1055 (vs, BF4), 2125 (m, CC).
[Pt(PNP){CCC(CH3)3}]BF4 (5). Yield: 222 mg (0.265 mmol, 77%).
Mp 238 °C (decomposition). Anal. Calcd for C37H36BF4NP2Pt: C,
53.00; H, 4.33; N, 1.67. Found: C, 51.63; H, 4.28; N, 1.67.46 1H NMR
2+4
(250 MHz, CD2Cl2): δ 1.16 (s, 9H, C4H9), 4.56 (ps t, 4H,
J
=
H−P
To the respective solutions of 10 mg of complexes 1, 2a,b, and 6 in
5.0 Hz, PCH2), 7.54−7.61 (m, 12H, Ph), 7.80 (d, 2H, 3JH−H = 7.7 Hz,
1
0.5 mL of CD2Cl2 a few drops of concentrated HCl were added. H
3
and 31P NMR spectra were recorded of each solution.
3,5-py), 7.95−8.04 (m, 8H, Ph), 8.11 (t, 1H, JH−H = 7.7 Hz, 4-py).
13C NMR (100.62 MHz, CD2Cl2): δ 29.6 (s, JC−Pt = 18 Hz,
3
1+3
C(CH3)3), 31.9 (s, C(CH3)3), 43.81 (ps t,
J
= 16.8 Hz, PCH2),
C−P
ASSOCIATED CONTENT
2
1
■
59.2 (t, JC−P = 16.8 Hz, JC−Pt = 1299 Hz, PtCC), 123.4 (ps t,
3+5
3
2
J
= 5.7 Hz, 3,5-py), 124.5 (t, JC−P < 3 Hz, JC−Pt = 363 Hz,
S
* Supporting Information
C−P
2+4
3+5
Figures giving the H,1H COSY NMR spectrum of complex 1,
1
PtCC), 128.0 (ps t,
J
= 30.0 Hz, Phi), 129.3 (ps t,
J
=
C−P
C−P
1H and 31P NMR spectra of complex 1 and HBF4·Et2O added,
5.8 Hz, Phm), 132.2 (s, Php), 133.2 (ps t, JC−P = 6.9 Hz, Pho), 140.8
2+4
2
(s, 4-py), 161.7 (ps t,
J
= 3.7 Hz, JC−Pt = 38 Hz, 2,6-py).
1
C−P
a
31P NMR data plot of Table 3, and H, 13C, and 31P NMR
31P NMR (101.25 MHz, CD2Cl2): δ 20.2 (s, JP−Pt = 2617 Hz). IR ν
̃
1
spectra of complexes 4 and 5, and a CIF file and table giving
crystallographic data and refinement details for complexes 1
and 2b. This material is available free of charge via the Internet
at http://pubs.acs.org.
(cm−1): 1051 (vs, BF4), 2123 (w, CC).
[Pt(PNP){CH(CH3)C(O)CH3}]BF4 (6). Yield: 242 mg (0.292 mmol,
85%). Mp: 244 °C dec. Anal. Calcd for C35H34BF4NOP2Pt·0.5-
(CH3CH2)2O: C, 51.34; H, 4.54; N, 1.62. Found: C, 51.31; H, 4.81;
N, 1.72. 1H NMR (250 MHz, CD2Cl2): δ 0.85 (d, 3H, 3JH−H = 6.6 Hz,
3JH−Pt = 50.5 Hz, CH3), 1.48 (s, 3H, JH−Pt = 11.0 Hz, CH3), 3.28
4
AUTHOR INFORMATION
■
(q, 1H, 3JH−H = 6.8 Hz, 2JH−Pt = 117 Hz, PtCH), 4.47 (m, 4H, PCH2),
7.53−8.04 (m, 23H, Ph, py). 13C NMR (100.62 MHz, CD2Cl2): δ 17.1
(s, 3JC−Pt = 34 Hz, PtCHCH3), 23.1 (t, 2JC−P = 3.0 Hz, 1JC−Pt = 578 Hz,
Corresponding Author
*E-mail: christhahn@gmx.net.
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dx.doi.org/10.1021/om2007908|Organometallics 2011, 30, 6446−6457

Organometallics
Article
coordinated acetylene takes place already at low temperature. Since the
ethylene/acetylene substitution is slow at −78 °C, complete
conversion can be achieved after warming to room temperature.
(13) (a) Tsutsui, M; Ori, M.; Francis, J. J. Am. Chem. Soc. 1972, 94,
1414−1415. (b) Hillis, J.; Francis, J.; Ori, M.; Tsutsui, M. J. Am. Chem.
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2900−2907.
(15) Cucciolito, M. E.; D’Amora, A.; Tuzi, A.; Vitagliano, A.
Organometallics 2007, 26, 5216−5223.
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ACKNOWLEDGMENTS
■
This work was supported by the donors of the Petroleum
Research Fund, administered by the American Chemical
Society (No. 48223-GB3), the Welch Foundation (No. AW-
0013), and the NSF-LSAMP program of the UT system. Dr.
Joseph H. Reibenspies, Dr. Christian Hilty, and Dr. Howard
Williams (Texas A&M University, College Station) are
acknowledged for the X-ray structure analyses and NMR
spectroscopy. Furthermore, we thank Dr. Thomas Ready
(Midland College) for his support.
DEDICATION
■
†Dedicated to Professor Rudolf Taube on the occasion of his
80th birthday.
(18) For comparison: C−O distances (1.385(6) and 1.404(6) Å)
found for ethanol molecules with an intermolecular H bond to an
amine: He, L.-M.; Hu, A.-X.; Cao, G.; Ye, J. J. Chem. Crystallogr. 2011,
41, 115−120.
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