Protonolysis of a toluidinoalkyl platinum(II) complex derived from the insertion of the C=C bond into the Pt-NHR (amido) bond: the role of amine in Pt-catalyzed hydroamination of acrylonitrile

Article abstract of DOI:10.1039/b108234p

The complex Pt{2,6-(R2PCH2)2C6H3}(OTf) [R = Ph (1a), Cy (1b)] catalyzes the hydroamination of acrylonitrile with p-toluidine to produce CH2(CN)CH2NH(Tol-p), exclusively. In the catalyzed reactions, platinum intermediates were detected by NMR spectroscopy. The p-tolylamido platinum complex Pt{2,6-(Ph2PCH2)2C6H3}{NH(Tol-p)} (4), containing the pincer ligand, was synthesized from the reaction of 1a and NaNH(Tol-p). Complex 4 reacted with acrylonitrile to yield the regiospecific insertion product Pt{2,6-(Ph2PCH2)2C6H3}{CH(CN)CH2NH(Tol-p)} (5), quantitatively. Reaction of 5 with HX (X = Cl, OTf) generated free acrylonitrile, p-toluidine and Pt{2,6-(Ph2PCH2)2C6H3}X. Reacting 5 with a proton source having a non-coordinating counter anion, [NH3(Tol-p)]BPh4, also produced free acrylonitrile along with a cationic amine complex [Pt{2,6-(Ph2PCH2)2C6H3}{NH2(Tol-p)}]⁺. On the other hand, reaction of 5 with [NH3(Tol-p)]BPh4 in the presence of excess p-toluidine (ca. 30 equiv.) generated the hydroaminated product CH2(CN)CH2NH(Tol-p), predominantly. Treatment of 5 with [NH2Me2]BPh4 in the absence of amine bases also released the hydroaminated product. These results apparently reveal that the amine substrate plays a critical role in driving the catalytic cycle.

Full text of DOI:10.1039/b108234p

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Protonolysis of a toluidinoalkyl platinum(II) complex derived from
the insertion of the C᎐C bond into the Pt–NHR (amido) bond:
᎐
the role of amine in Pt-catalyzed hydroamination of acrylonitrile
Jung Min Seul and Soonheum Park*
Department of Chemistry, Dongguk University, Kyongju 780-714, Korea.
E-mail: shpark@mail.dongguk.ac.kr
Received 11th September 2001, Accepted 19th December 2001
First published as an Advance Article on the web 14th February 2002
The complex Pt{2,6-(R2PCH2)2C6H3}(OTf ) [R = Ph (1a), Cy (1b)] catalyzes the hydroamination of acrylonitrile
with p-toluidine to produce CH2(CN)CH2NH(Tol-p), exclusively. In the catalyzed reactions, platinum intermediates
were detected by NMR spectroscopy. The p-tolylamido platinum complex Pt{2,6-(Ph2PCH2)2C6H3}{NH(Tol-p)}
(4), containing the pincer ligand, was synthesized from the reaction of 1a and NaNH(Tol-p). Complex 4 reacted
with acrylonitrile to yield the regiospecific insertion product Pt{2,6-(Ph2PCH2)2C6H3}{CH(CN)CH2NH(Tol-p)} (5),
quantitatively. Reaction of 5 with HX (X = Cl, OTf ) generated free acrylonitrile, p-toluidine and Pt{2,6-(Ph2PCH2)2-
C6H3}X. Reacting 5 with a proton source having a non-coordinating counter anion, [NH3(Tol-p)]BPh4, also produced
free acrylonitrile along with a cationic amine complex [Pt{2,6-(Ph2PCH2)2C6H3}{NH2(Tol-p)}]ϩ. On the other hand,
reaction of 5 with [NH3(Tol-p)]BPh4 in the presence of excess p-toluidine (ca. 30 equiv.) generated the hydroaminated
product CH2(CN)CH2NH(Tol-p), predominantly. Treatment of 5 with [NH2Me2]BPh4 in the absence of amine bases
also released the hydroaminated product. These results apparently reveal that the amine substrate plays a critical role
in driving the catalytic cycle.
Introduction
Catalytic addition of N–H bonds to olefins mediated by late
transition metal complexes offers regioselective ways to prepare
biologically active compounds as well as industrial chemicals.1
Two different mechanistic pathways for these catalytic reactions
have been suggested. Milstein and co-workers2a have demon-
strated for the first time a catalytic system involving N–H bond
oxidative addition to an electron-rich metal center to yield a
hydrido amido complex [MH(NR2)], which proceeds via inser-
tion of a C᎐C bond into a metal–amide bond, followed by C–H
᎐
reductive elimination to give hydroaminated products.1,2 An
alternative, but more generally observed, pathway for high-
valent complexes may involve the nucleophilic attack of amine
on coordinated olefin, and then subsequent proton transfer to
generate hydroaminated products.1,3 Although many catalytic
hydroaminations of olefins have been reported so far, the mech-
anistic pathways for these catalytic systems have not been fully
understood. In this paper, the role of amines in platinum-
catalyzed hydroamination of olefins is discussed in terms of
their mechanistic features in microscopic reaction pathways.
For this study, platinum() complexes having terdentate P,C,P-
pincers have been employed, since the ligand inhibits both
phosphine dissociation and reductive elimination of the aryl
group.4 As a consequence, these types of complexes stabilized
with the rigid ligand framework offer regioselectivity in the
stoichiometric and catalytic reactions to be probed.5–8
Fig. 1 The 1H-NMR spectrum of a d6-benzene solution of 1b, at
ambient temperature, in the presence of an excess amount of
acrylonitrile shows resonance signals due to coordinated acrylonitrile
(marked with arrows).
Results and discussion
The complex Pt{2,6-(R2PCH2)2C6H3}(OTf ) [R = Ph (1a),
Cy (1b)] catalyzes the hydroamination of acrylonitrile with
p-toluidine to produce CH2(CN)CH2NH(Tol-p), exclusively
(eqn. 1). The reaction proceeds rather slowly (15 and 45%
Fig. 2 The 31P{1H}-NMR spectrum of the reaction mixture catalyzed
by 1a in the latter stages of the reaction shows that the solution mainly
contains three platinum species, 3a, 2a, and 5. The 195Pt satellites are
denoted 3aЈ, 2aЈ, and 5Ј.
(1)
DOI: 10.1039/b108234p
J. Chem. Soc., Dalton Trans., 2002, 1153–1158
This journal is © The Royal Society of Chemistry 2002
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yield with 1a and 1b, respectively; 2 days at 40 ЊC, 1.0 mol%
formation of 5 during the course of reaction was monitored
by the observation of a growing sharp single peak at δ 37.8
[Pt]). During the course of the reaction, two main species were
1
1
present in solution, as evidenced by H- and 31P{1H}-NMR
in the 31P{1H}-NMR spectrum. The H-NMR spectrum of 5
spectroscopy (see Fig. 1 and 2); one is an olefinic complex,
[Pt{2,6-(R2PCH2)2C6H3}(CH2CHCN)]OTf [R = Ph (2a), Cy
(2b)], and the other an amine complex, [Pt{2,6-(R2PCH2)2-
in d6-benzene shows the CH resonance of Pt–CH(CN)CH2-
NH(Tol-p) at δ 2.75 as a multiplet with platinum satellites
[2J(PtH) = 80 Hz]. The methylene protons of Pt–CH(CN)-
CH2NH(Tol-p) are observed to be diastereotopic, with reson-
ances at δ 3.08 and 3.45 as multiplets. The NH proton, the
assignment of which was confirmed on addition of D2O, was
observed at δ 3.52 as a multiplet. The addition of a strong
coordinating ligand such as triphenylphosphine or pyridine
into a d6-benzene solution of 5 resulted in no signal changes
C6H3}{NH2(Tol-p)}]OTf [R
= Ph (3a), Cy (3b)]. These
complexes were verified by independent preparation from the
reaction of the platinum triflates with acrylonitrile and
p-toluidine, respectively (see Experimental). In contrast to the
amine complexes, the olefinic complexes were not isolated in
the pure state due to their conversion into the corresponding
platinum triflate in the absence of acrylonitrile.9
1
in the H-NMR spectrum, indicating that N-chelation of the
In the reaction catalyzed by 1b, the amine complex 3b is pre-
dominantly observed; toluidine is favored over acrylonitrile in
the platinum coordination sphere (Keq = [3b][CH2CHCN]/
p-tolylaminoalkyl ligand to platinum in the complex can appar-
ently be excluded. Complex 5 was isolated from the d6-benzene
solution by reducing the volume of the solution under high
vacuum followed by the addition of n-hexane, giving a pale-
yellow powder. This complex can be synthesized on a prepar-
ative scale by the reaction of 4 with acrylonitrile in benzene (see
Experimental). It is worth noting that a d6-benzene solution of
5 was stable for 7 days at reflux temperatures. Even in the pres-
ence of an excess of acrylonitrile, the complex was intact for a
prolonged period of time at elevated temperatures, with no
formation of oligomeric or decomposed species. It was previ-
ously reported that Ir()- and Pt() anilide complexes having
monodentate tertiary phosphines undergo regiospecific inser-
[2b][NH2(Tol-p)] ≅ 3.1 at 21 ЊC: 2b ϩ NH2(Tol-p)
3b ϩ
CH2CHCN).10 However, in the reaction catalyzed by 1a,
the olefinic complex 2a, initially formed on addition of
acrylonitrile into a d6-benzene solution of 1a, immediately
disappeared to yield the amine complex 3a on subsequent
addition of p-toluidine into the solution. In the early stages of
this reaction, only the amine complex was observed in solution,
as monitored by the 31P{1H}-NMR spectroscopy. But in the
later stages, a small amount of olefinic complex, besides the
amine species, was observed along with the other platinum
species, which was identified as the insertion product 5 (vide
tion of the C᎐C bonds of norbonylene and acrylonitrile,
᎐
1
infra, see Fig. 2). The 31P chemical shifts and the J(195Pt–P)
respectively, into the M–N bond.2a,d In the previous studies,
however, the resulting anilinoalkyl complexes were unstable,
undergoing further C–H reductive elimination.
values in the 31P{1H}-NMR spectrum were very advantageous
for this study.
Thus, the p-tolylamido platinum complex Pt{2,6-(Ph2PCH2)2-
C6H3}{NH(Tol-p)} (4) was synthesized in the hope that an
amido complex bearing a PCP-pincer as an ancillary ligand
Protonolysis of complex 5
Since p-tolylaminoalkyl complex 5 can be isolated pure in the
solid state, further stoichiometric reactions with proton sources
were probed from the mechanistic viewpoint of catalytic
hydroamination of acrylonitrile with p-toluidine. Reaction of 5
with HX (X = Cl, OTf ) generated the corresponding platinum
complexes Pt{2,6-(Ph2PCH2)2C6H3}X, free acrylonitrile, and
p-toluidine, along with [NH3(Tol-p)]X. In the reaction with
a proton source having a non-coordinating counter anion,
[NH3(Tol-p)]BPh4, a cationic toluidine complex, [Pt{2,6-(Ph2-
PCH2)2C6H3}{NH2(Tol-p)}]ϩ was produced, along with free
acrylonitrile.15 These results can be indisputably explained by a
sequence of reactions involving preferential protonation at the
amine nitrogen rather than at the alkyl carbon in the platinum
complex, and then subsequent elimination of free acrylonitrile
with p-toluidine via deinsertion to give the observed products
(see Scheme 1). In the latter reaction, subsequent coordination
would undergo regioselective insertion of the C᎐C bond of
᎐
acrylonitrile into the Pt–N bond to give a stable platinum()
p-tolyaminoalkyl complex, whose protonolysis might provide
crucial mechanistic information on one of the key steps in the
catalytic hydroamination of olefins.
Preparation of p-tolylamido complex 4
Reaction of Pt{2,6-(Ph2PCH2)2C6H3}(OTf ) with an excess of
NaNH(Tol-p) (ca. 3 equiv.) in tetrahydrofuran afforded the
Pt() toluidinide complex Pt{2,6-(Ph2PCH2)2C6H3}{NH-
(Tol-p)} (4) in high yield (eqn. 2). The formulation of 4 can be
(2)
readily verified from the 1H- and 31P{1H}-NMR spectra. In the
1H-NMR spectrum of 4 in d6-benzene, the NH resonance of the
amide moiety NH(Tol-p) is observed at δ 3.06 as a broad signal
with platinum satellites [2J(PtH) = 14.0 Hz]. The methyl
resonance of the p-tolyl group exhibits a single peak at δ 2.26.
The resonance for the methylene protons (PCH2) is observed
at δ 3.63 as a pseudo-triplet, due to “virtual coupling”, with
platinum satellites (|2J(PH) ϩ 4J(PH)| = 9.0 Hz, 3J(PtH) =
26.2 Hz).11 This terminal amido complex of platinum() bear-
ing a PCP-pincer as an ancillary ligand is of particular interest
because such complex demonstrates that the metal–amide bond
should be selectively involved in stoichiometric reactions with
various substrates.12–14
Scheme 1
of the liberated p-toluidine to platinum afforded the cationic
species. In the reactions, either a hydroaminated product,
CH2(CN)CH2NH(Tol-p), or a vinylic amine (or imine), arising
from β-hydrogen elimination as a competing side product, was
not produced.16 These results are not consistent with the
observed catalytic reaction with the platinum triflates.
Taking account of reaction conditions in the catalytic
reactions, an excess of amine would act as a base, inhibiting
protonation at the amine nitrogen of the p-tolylaminoalkyl
ligand, thereby facilitating facile proton transfer at the alkyl
carbon to generate hydroaminated products. From this point of
view, we have tried the reaction of 5 with [NH3(Tol-p)]BPh4 in
Reaction of complex 4 with acrylonitrile
The platinum() amide
4 in d6-benzene slowly reacted
with acrylonitrile to yield the regioselective addition product
Pt{2,6-(Ph2PCH2)2C6H3}{CH(CN)CH2NH(Tol-p)} (5). The
reaction was not only highly selective, but also nearly quanti-
tative, as evidenced by the 1H- and 31P{1H}-NMR spectra. The
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J. Chem. Soc., Dalton Trans., 2002, 1153–1158

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Scheme 2
the presence of an excess amount of p-toluidine (ca. 30 equiv.).
As result, the hydroaminated product 2-cyanoethyl-
to form amido complexes can hardly be ruled out, the present
a
reaction may proceed via nucleophilic attack of amine on
the olefin pre-coordinated to platinum(). The nucleophilic
addition of amines on an olefin coordinated to platinum()18
and palladium()19 complexes is well known. Recently, it has
been reported that the nucleophilic attack of amine on coordin-
ated olefins on highly electrophilic dicationic palladium()
complexes leads to the formation of aminoalkyl complexes.20 In
the present study, it is noteworthy that complex 1b, whose metal
center is more basic than that of 1a, favors the π-olefinic com-
plex, displaying more effective catalytic activity (vide supra). A
plausible catalytic cycle for the observed hydroamination is
presented in Scheme 4.
In summary, the role of amine in catalytic hydroamination
of olefins has been demonstrated, for the first time, in terms
of mechanistic features in microscopic reaction pathways.
Although this fact has been perceived in generally observed
catalytic hydroamination of olefins, it has not yet been clearly
demonstrated at a molecular scale, probably due to scarcity of
amido complexes and their olefin addition derivatives.
(p-tolyl)amine CH2(CN)CH2NH(Tol-p) was predominantly
produced (67% yield) along with free acrylonitrile (33%) as
evidenced by NMR and GC/MS spectroscopy. Scheme 2
represents the observed reactions. These results indicate that
protonation is still competitive, occurring at both sites of the
amine nitrogen and the alkyl carbon, even in the presence of a
large excess of amine. In this reaction, however, the anilinoalkyl
complex 5, which is a stronger base than p-toluidine, favors
protonation at the amine nitrogen from [NH3(Tol-p)]BPh4 to
generate a transient alkylanilinium complex (A), which sub-
sequently undergoes deinsertion. This explanation implies that
the facile generation of the hydroaminated product in the reac-
tion obviously depends on the the pKa of the added ammonium
salt. Thus, treatment of 5 with the dimethylammonium salt
[NH2Me2]BPh4, which is a weaker acid than the corresponding
alkylanilinium complex, in the absence of base subsequently
produced 2-cyanoethyl(p-tolyl)amine (Scheme 3).
Experimental
General procedures
All preparations of air sensitive compounds were carried
out on a standard Schlenk line or in an inert atmosphere glove
box under argon. Tetrahydrofuran and diethyl ether were
freshly distilled from sodium–benzophenone ketyl under
nitrogen, and then stored over molecular sieves. Benzene
and n-hexane were distilled from sodium–benzophenone
ketyl with tetraglyme (tetraethylene glycol dimethyl ether).
CH2Cl2 was dried by refluxing over sodium hydride under
nitrogen. K2PtCl4 was supplied by Kojima Chemicals Co.,
Ltd., and used without purification. Potassium diphenyl-
phosphide, 1,5-cyclooctadiene, AgOTf, α,αЈ-dibromo-m-
xylene, CDCl3 and C6D6 were purchased from Aldrich
Chemical Company, and used as supplied. p-Toluidine was
purified by subliming in vacuo at 50 ЊC. All other reagents were
from various commercial companies. NaNH(Tol-p) was pre-
pared from the reaction of NaH and p-toluidine in refluxing
THF solution for 24 h, and isolated from diethyl ether.
[NH3(Tol-p)]BPh4 and [NH2Me2]BPh4 were prepared by reac-
tion of the respective chloride salts with NaBPh4 in H2O.
Scheme 3
These results apparently reveal that the amine plays a critical
role in driving the catalytic cycle. The amine substrate simul-
taneously acts as a base, deprotonating from a putative complex
A to lead to the formation of 5, in which facile proton transfer
occurs, in turn, at the alkyl carbon to generate the hydro-
aminated product (see Scheme 4). As a consequence, amines
inhibit reverse processes, i.e. deinsertion processes, in the cata-
lytic cycle. Protonolysis of the Pt–alkyl bond probably proceeds
via C–H elimination, preceded by protonation of the electron-
rich metal center.17
In the catalytic reactions, although a mechanism involving
amine coordination to platinum followed by N-deprotonation
J. Chem. Soc., Dalton Trans., 2002, 1153–1158
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Scheme 4
Pt{2,6-(Ph2PCH2)2C6H3}Cl4d and Pt{2,6-(Cy2PCH2)2C6H3}-
Pt{2,6-(Ph2PCH2)2C6H3}{NH(C6H4Me-p)} (4).
A
THF
(OTf ) (1b)21 were prepared as described in the literature.
IR spectra were recorded on a Bomem FT-IR spectrometer
(Michelson 100), from pressed KBr pellets. 1H-, 13C{1H}-,
31P{1H}- and 19F{1H}-NMR spectra were measured on a
Varian Gemini-2000 spectrometer, using the deuterium signal
of the solvent as an internal lock frequency. Chemical shifts for
1H and 13C{1H}-NMR are reported in ppm (δ) relative to TMS.
Chemical shifts for 31P{1H}- and 19F{1H}-NMR were measured
in ppm relative to external 85% H3PO4 (δ = 0) and perfluoro-
methylbenzene (δ = Ϫ63.73) (in a sealed capillary), respec-
tively. GC/MS analyses were performed using an HP 6890
gas chromatograph equipped with an HP 5973 MSD and an
HP-Ultra 1 column (crosslinked methyl silicone gum, 50 m ×
0.2 mm, 0.33 µm film thickness). Conductivity measurements
were obtained with a TOA conductivity meter (CM-40S).
Nitromethane was used as solvent in a cell containing platin-
ized electrodes (cell constant = 1.014 cmϪ1). Elemental analysis
was performed at the Korea Basic Science Institute in Seoul,
Korea.
solution of NaNH(Tol-p) (51 mg, 0.40 mmol) was slowly added
to a stirred solution of 1a (110 mg, 0.14 mmol) in THF. The
reaction mixture was stirred for 2 h. The color of the solution
gradually changed from colorless to deep green during the
course of the reaction. Removal of volatiles from the solu-
tion under high vacuum resulted in a deep-green residue, which
was washed with n-pentane (2 × 30 mL) to remove p-toluidine
and then extracted with dry benzene (2 × 10 mL) to give a
brownish green solution. The volume of the solution was
reduced to ca. 5 mL under high vacuum. Addition of n-pentane
(ca. 15 mL) to the concentrated solution resulted in a greenish
orange solution along with the formation of a small amount of
a brownish precipitate. After filtering off the precipitate, the
solvent was removed from the filtrate and the residue dried
in vacuo for 12 h to give an analytically pure greenish orange
compound. Yield 78 mg (72%). 1H-NMR (C6D6): δ 2.26 s (3H,
CH3), 3.06 br, s [1H, NH; 2J(PtH) = 14.0 Hz], 3.63 t [4H, CH2;
4
3
|2J(PH) ϩ J(PH)| = 9.0 Hz, J(PtH) = 26.2 Hz], 6.62 d [2H,
CH(Tol-p); 3J(HH) = 8.3 Hz], 6.81 d [2H, CH(Tol-p)], 7.0–7.8 m
(23H, Ph). 31P{1H}-NMR (C6D6): δ 30.7 s [1J(PtP) = 3013 Hz].
Anal. calc. for C39H35NP2Pt: C, 60.5; H, 4.55; N, 1.81; found: C,
60.9; H, 4.75; N, 1.61%.
Preparations
Pt{2,6-(Ph2PCH2)2C6H3}(OTf ) (1a). A mixture of Pt{2,6-
(Ph2PCH2)2C6H3}Cl (100 mg, 0.14 mmol) and AgOTf (43 mg,
0.17 mmol) was stirred in a mixed solvent (25 mL, THF–
CH2Cl2 4 : 1) for 2 h. After filtering off AgCl formed during the
course of the reaction, the solution volume was reduced to ca.
3 mL. Addition of n-hexane (ca. 20 mL) to the concentrated
solution gave an off-white precipitate, which was isolated by
filtration. Recrystallization of the precipitates from CH2Cl2–n-
hexane gave an analytically pure compound. Yield 105 mg
(90%). IR (KBr): ν(SO) = 1169, 1252 cmϪ1. 1H-NMR (CDCl3):
δ 3.83 t [4H, CH2; |2J(PH) ϩ 4J(PH)| = 9.4 Hz, 3J(PtH) = 25 Hz],
7.0–7.9 m (23H, Ph). 1H-NMR (C6D6): δ 3.26 t [4H, CH2;
|2J(PH) ϩ 4J(PH)| = 8.0 Hz, 3J(PtH) = 32 Hz], 7.0–7.9 m (23H,
Ph). 31P{1H}-NMR (CDCl3): 39.4 s [1J(PtP) = 3034 Hz].
31P{1H}-NMR (C6D6): δ 39.2 s [1J(PtP) = 3007 Hz]. 19F{1H}-
NMR (CDCl3): δ Ϫ79.02 s. ΛM = 66 ΩϪ1 cm2 molϪ1 (in MeNO3,
[Pt] = 1.0 × 10Ϫ3 mol). Anal. calc. for C33H27F3O3P2PtS: C, 48.5;
H, 3.33; S, 3.92; found: C, 48.4; H, 3.46; S, 3.62%.
Reaction of 4 with CH ᎐CHCN to yield Pt{2,6-(Ph PCH ) -
᎐
2
2
2 2
C6H3}{CH(CN)CH2NH(C6H4Me-p)} (5). To
a d6-benzene
solution of 4 (ca. 10 mg) in a 5 mm screw-capped NMR tube
(Wilmad, 528-TR) was added an excess of acrylonitrile (ca. 10
mg). The insertion product Pt{2,6-(Ph2PCH2)2C6H3}{CH-
(CN)CH2NH(Tol-p)} was quantitatively formed from the reac-
tion, although the reaction proceeded rather slowly (for ca. 3 h),
which was monitored by NMR spectroscopy. The product can
be isolated from the concentrated d6-benzene solution followed
by the addition of n-hexane. A preparative scale experiment for
this reaction was conducted in a glove box as follows. To a
benzene solution of 4 (100 mg, 0.13 mmol) was added an excess
of acrylonitrile (0.02 g, 0.38 mmol). The reaction mixture was
stirred for 6 h. The solution volume was reduced to ca. 5 mL
under high vacuum. Addition of n-hexane (ca. 20 mL) to
the concentrated solution gave a beige precipitate, which was
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J. Chem. Soc., Dalton Trans., 2002, 1153–1158

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isolated by filtration. Recrystallization of the precipitates from
CH2Cl2–n-hexane gave an analytically pure compound. Yield
1H-, 13C{H}- and 31P{1H}-NMR spectroscopy. In the 1H-NMR
spectrum at ambient temperature, the downfield-shifted olefinic
protons resonances of coordinated acrylonitrile were observed
as rather broad multiplets (Fig. 1). No couplings of the
1
98 mg (92%). IR (KBr): ν(CN) = 2248, 2172 cmϪ1. H-NMR
(C6D6): δ 2.20 s (3H, CH3), 2.75 m [1H, CH; 2J(PtH) = 80 Hz],
3.08 m (1H, CHa), 3.45 m (1H, CHb), 3.52 m (1H, NH), 3.66 t
[4H, CH2; |2J(PH) ϩ 4J(PH)| = 8.4 Hz, 3J(PtH) = 30.4 Hz], 6.00
1
coordinated acrylonitrile with 195Pt in the H- and 13C{1H}-
NMR spectra at ambient temperature were observed due to
the lability of the acrylonitrile complex. Variable-temperature
1H-NMR experiments in d8-toluene were attempted to detect
the 195Pt-satellites with no success. The corresponding signals
3
d [2H, CH(Tol-p); J(HH) = 8.4 Hz], 6.86 d [2H, CH(Tol-p)],
7.0–7.8 m (23H, Ph). 13C{1H}-NMR (C6D6): δ 3.92 t [Pt–
2
1
CH(CN)CH2NH(Tol-p); J(CP) = 10 Hz, J(PtC) = 429 Hz],
20.73 [Pt–CH(CN)CH2NH(Tol-p)], 47.53 t [P–CH2; |1J(PC) ϩ
3J(PC)| = 37.5 Hz], 49.61 t [Pt–CH(CN)CH2NH(Tol-p); 3J(CP)
= 3.8 Hz]. 31P{1H}-NMR (C6D6): δ 37.8 s [1J(PtP) = 2966 Hz].
Anal. calc. for C42H38N2P2Pt: C, 60.9; H, 4.63; N, 3.38; found:
C, 61.4; H, 4.46; N, 3.58%. NMR Assignments were made on
the bases of various NMR techniques: selective homonuclear
decouplings and COSY.
1
get even broader below Ϫ60 down to Ϫ85 ЊC. The H- and
13C{1H}-NMR data observed for the coordinated acrylonitrile
in the present complex are closely comparable to those of
π-olefinic acrylonitrile complexes of Pt() [PtMeL (CH ᎐
᎐
2
2
CHCN)]BF4 reported by Eisenberg et al.9a Attempts to isolate
complex 2b in the pure state were unsuccessful because of par-
tial decomposition into 1b; a d6-benzene solution prepared by
re-dissolving the isolated solid shows that the solution con-
tained both 2b and 1b in a 3 : 1 ratio, as evidenced by 31P{1H}-
NMR spectroscopy. On standing this solution in the absence of
Reaction of 5 with HCl to yield Pt{2,6-(Ph2PCH2)2C6H3}Cl,
CH ᎐CHCN and NH (C H Me-p). Reaction of 5 with HCl in
᎐
2
2
6
4
1
d -benzene generated Pt{2,6-(Ph PCH ) C H }Cl, CH ᎐CHCN
acrylonitrile, 2b slowly converted into 1b. For 2b: H-NMR
᎐
2
6
2
2
2
6
3
3
and p-toluidine (along with the byproduct, p-toluidineؒHCl
salt).
(C6D6): δ 5.88 d [CHcisHtrans; J(HH)cis = 12 Hz], 6.19 d [CHcis-
3
3
Htrans; J(HH)trans = 18 Hz], and 6.87 dd [CHCN; J(HH)cis =
3
12 Hz, J(HH)trans = 18 Hz]. 13C{1H}-NMR (C6D6): δ 106.9
(CH2CHCN), 118.3 (CH2CHCN), 143.0 (CH2CHCN).
31P{1H}-NMR (C6D6): δ 54.2 s [1J(PtP) = 2686 Hz].
Reaction of 5 with HOTf to yield 1a, CH ᎐CHCN and
᎐
2
NH2(C6H4Me-p). Reaction of 5 with HOTf in d6-benzene
generated Pt{2,6-(Ph PCH ) C H }(OTf ) (1a), CH ᎐CHCN
᎐
2
2
2
2
6
3
and p-toluidine (along with the byproduct, p-toluidineؒHOTf
salt).
Reaction of 1a with CH ᎐CHCN to generate [Pt{2,6-
᎐
2
(Ph PCH ) C H }(CH ᎐CHCN)](OTf ) (2a). To a d -benzene
᎐
2
2
2
6
3
2
6
solution of 1a (ca. 5 mg) in a 5 mm NMR tube was added
acrylonitrile (ca. 7 mg). The formation of [Pt{2,6-(Ph2PCH2)2-
Reaction of 5 with [NH3(C6H4Me-p)]BPh4 to yield [Pt{2,6-
(Ph2PCH2)2C6H3}{NH2(C6H4Me-p)}]؉ and CH ᎐CHCN. Reac-
C H }(CH ᎐CHCN)](OTf ) in solution was also supported
᎐
2
᎐
6
3
2
1
by H-, 13C{H}- and 31P{1H}-NMR spectroscopy. The NMR
data of 2a were similarly observed to those of complex 2b. The
isolation of this complex from the solution was unsuccessful
due to complete decomposition to 1a. For 2a: 1H-NMR (C6D6):
tion of 5 with [NH3(C6H4Me-p)]BPh4 in d6-benzene generated
free acrylonitrile and [Pt{2,6-(Ph2PCH2)2C6H3}{NH2(C6H4-
Me-p)}]ϩ. The formation of the cationic toluidine species has
been confirmed by the independent synthesis of the triflate
salt [Pt{2,6-(Ph2PCH2)2C6H3}{NH2(C6H4Me-p)}]OTf from the
reaction of 1a and p-toluidine (see the following experiment).
δ 5.22 d [CHcisHtrans; ;
3J(HH)cis = 12 Hz], 5.41 d [CHcisHtrans
3J(HH)trans = 18 Hz], 6.15 dd [CHCN; 3J(HH)cis = 12 Hz,
3J(HH)trans = 18 Hz]. 13C{1H}-NMR (CDCl3): δ 105.8 (CH2-
CHCN), 117.6 (CH2CHCN), 143.9 (CH2CHCN). 31P{1H}-
NMR (C6D6): δ 38.9 s [1J(PtP) = 2822 Hz].
[Pt{2,6-(Ph2PCH2)2C6H3}{NH2(C6H4Me-p)}]OTf (3a). Reac-
tion of 1a (30 mg, 0.036 mmol) and p-toluidine (19 mg, 0.18
mmol) in dichloromethane gave the cationic amine complex 3a,
which was isolated from CH2Cl2–diethyl ether. Yield 31 mg
(92%). IR (KBr): ν(NH) = 3362, 3469 cmϪ1, ν(SO) = 1152, 1264
Reaction of 5 with [NH3(C6H4Me-p)]BPh4 in the presence of
excess p-toluidine to produce CH2(CN)CH2NH(C6H4Me-p).
[NH3(Tol-p)]BPh4 (ca. 15 equiv.) was added to a d6-benzene
solution of 5 (ca. 10 mg) with p-toluidine (ca. 30 equiv.) in a
5 mm NMR tube. The hydroaminated product (ca. 67%) was
predominantly produced from the reaction, along with free
acrylonitrile, as evidenced by NMR and GC/MS spectroscopy.
For CH2(CN)CH2NH(Tol-p): GC/MS: m/z = 160, 120, 91.
1
cmϪ1. H-NMR (CDCl3): δ 2.25 s (3H, CH3), 3.93 t [4H, CH2;
|2J(PH) ϩ 4J(PH)| = 8.5 Hz, 3J(PtH) = 24 Hz], 5.84 br [2H, NH2;
2J(PtH) = 32 Hz], 6.07 d [2H, CH(Tol-p); 3J(HH) = 7.8 Hz], 6.58
d [2H, CH(Tol-p)], 7.0–7.9 m (23H, Ph). 31P{1H}-NMR
(CDCl3): δ 40.0 s [1J(PtP) = 2938 Hz]. 31P{1H}-NMR (C6D6):
δ 39.3 s [1J(PtP) = 2918 Hz]. ΛM = 86 ΩϪ1 cm2 molϪ1 (in MeNO3,
[Pt] = 1.0 × 10Ϫ3mol). 19F{1H}-NMR (CDCl3): δ Ϫ79.4 s. Anal.
calc. for C40H36NF3O3P2PtS: C, 51.9; H, 3.92; N, 1.51; S, 3.47;
found: C, 51.4; H, 4.01; N, 1.48; S, 3.32%.
Reaction of 5 with MeI to yield {2,6-(Ph2PCH2)2C6H3}PtI,
CH ᎐CHCN and amines. Reaction of 5 and MeI in d -benzene
᎐
2
6
slowly (for 12 h) generated Pt{2,6-(Ph2PCH2)2C6H3}I, acrylo-
nitrile, and a mixture of amines [p-toluidine (17%), N-methyl-
p-tolylamine (46%), N,N-dimethyl-p-tolylamine (37%)], which
were identified by NMR and GC/MS spectroscopy. For
Pt{2,6-(Ph2PCH2)2C6H3}I: 1H-NMR (C6D6): δ 3.55 t [4H, CH2;
[Pt(2,6-{Cy2PCH2)2C6H3}{NH2(C6H4Me-p)}]OTf (3b).
similar procedure as for complex 3a, using 1b (30 mg, 0.036
A
mmol) and p-toluidine (19 mg, 0.18 mmol) gave complex
3b. Yield 32 mg (94%). IR (Nujol): ν(NH) = 3364, 3470 cmϪ1
.
1H-NMR (CDCl3): δ 1.0–2.4 m (44H, Cy), 3.22 t [4H, CH2,
4
3
|2J(PH) ϩ J(PH)| = 9.0 Hz, J(PtH) = 25.4 Hz], 7.0–7.9 m
(23H, Ph). 31P{1H}-NMR (C6D6): δ 35.4 s [1J(PtP) = 2860
Hz]. GC/MS: p-toluidine [NH2(C6H4Me-p)]: m/z = 107, 106,
91. N-methyl-p-tolylamine [NHMe(C6H4Me-p)]: m/z = 121,
120, 106, 91. N,N-dimethyl-p-tolylamine [NMe2(C6H4Me-p)]:
m/z = 135, 120, 105, 91.
4
3
|2J(PH) ϩ J(PH)| = 8.8 Hz, J(PtH) = 20.0 Hz], 5.96 br [1H,
2
NH, J(PtH) = 34.0 Hz], 6.91 m (3H, Ph), 7.12 d [2H, CH2,
3J(HH) = 8.0Hz], 7.30 d [2H, CH2, 3J(HH) = 8.4 Hz]. 31P{1H}-
NMR (CDCl3): δ 47.9 [1J(PtP) = 2787 Hz]. 31P{1H}-NMR
(C6D6): δ 48.1 s [1J(PtP) = 2786 Hz]. 19F{1H}-NMR (CDCl3):
δ Ϫ79.5 s. Anal. calc. for C40H60NF3O3P2PtS: C, 50.6; H, 6.37;
N, 1.48; S, 3.38; found: C, 50.9; H, 6.71; N, 1.58; S, 3.25%.
Acknowledgements
Reaction of 1b with CH ᎐CHCN to generate [Pt(2,6-{Cy -
This work was supported by grant no. 2000-1-12200-002-1 from
the Basic Research Program of the Korea Science & Engineer-
ing Foundation. The authors are grateful to Mr J. G. Lee for
technical assistance.
᎐
2
2
PCH ) C H }(CH ᎐CHCN)]OTf (2b). To a d -benzene solution
᎐
2
2
6
3
2
6
of 1b (ca. 5 mg) in a 5 mm NMR tube was added acrylonitrile
(ca. 7 mg). The formation of 2b in solution was supported by
J. Chem. Soc., Dalton Trans., 2002, 1153–1158
1157

View Article Online
NMR spectra; the 1H-NMR resonances for [CH2CHCN]/[NH2-
(Tol-p)], and the 31P{1H]-NMR resonances for [3b]/[2b].
11 References for “virtual couplings”: (a) J. G. Verkade, Chem. Rev.,
1972, 9, 1; (b) P. S. Pregosin and R. Kunz, Helv. Chim. Acta, 1975,
58, 423; (c) A. W. Verstuyft, J. H. Nelson and L. W. Cary, Inorg.
Chem., 1976, 15, 732; (d ) P. S. Pregosin and R. W. Kunz, 31P- and
13C-NMR of Transition Metal Phosphine Complexes, Springer,
Berlin, 1979, p. 65.
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4 Examples of PCP-pincer complexes of group 10 metals: (a) H.
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13 For recent examples of monomeric amido complexes of late
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R. G. Bergman, J. Am. Chem. Soc., 1996, 118, 1092; (j) J. V. Cuevas,
G. Garcia-Herbosa, A. Munoz, S. Garcia-Granda and D. Miguel,
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5 Examples of C–X (X = H, C, O) activation by PCP-pincer
complexes: (a) B. Rybtchinski, A. Vigalok, Y. Ben-David and
D. Milstein, J. Am. Chem. Soc., 1996, 118, 12406; (b) M. E. Van der
Boom, H. B. Kraatz, L. Hassner, Y. Ben-David and D. Milstein,
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Chem., Int. Ed. Engl., 1997, 36, 625.
14 Recently, we have reported a rare example of a terminal dimethyl-
amido palladium() complex, Pd{2,6-(Ph2PCH2)2C6H3}(NMe2):
S. Y. Ryu, H. Kim, H. S. Kim and S. Park, J. Organomet. Chem.,
1999, 592, 194.
15 Treatment of 5 with MeI in d6-benzene also generated {2,6-
(Ph2PCH2)2C6H3}PtI, acrylonitrile, and a mixture of amines (see
Experimental).
6 Examples of aliphatic dehydrogenation by PCP-pincer complexes:
(a) F. Lie, E. B. Pak, B. Singh, C. M. Jensen and A. S. Goldman,
J. Am. Chem. Soc., 1999, 121, 4086; (b) M. Gupta, C. Hagen,
R. J. Flesher, W. C. Kaska and C. M. Jensen, Chem. Commun.,
1996, 2083; (c) M. Gupta, C. Hagen, W. C. Kaska, R. E. Cramer and
C. M. Jensen, J. Am. Chem. Soc., 1997, 119, 840.
7 Example of Stille coupling by PCP-pincer complexes: W. D. Cotter,
L. Barbour, K. L. McNamara, R. Hechter and R. J. Lachicotte,
J. Am. Chem. Soc., 1998, 120, 11016.
16 A recent theoretical study has revealed that the cleavage of the M–C
bond is rate determining for group 10 metals, and β-hydride
elimination is thought to be kinetically competing: H. M. Senn,
P. E. Blochl and A. Togni, J. Am. Chem. Soc., 2000, 122, 4098.
17 R. J. Angelici, Acc. Chem. Res., 1995, 28, 51.
18 (a) A. Panunzi, A. De Renzi, R. Palumbo and G. Paiaro,
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G. Paiaro, A. Panunzi and C. Pedone, Gazz. Chim. Ital., 1972, 102,
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Chem., 1973, 54, 399; (d ) A. De Renzi, B. Di Blasio, A. Panunzi,
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703.
8 Example of Heck coupling by PCP-pincer complexes: M. Ohff, A.
Ohff, M. E. Van der Boom and D. Milstein, J. Am. Chem. Soc., 1997,
119, 11687.
9 Precedents for the lability of Pt() complexes of acrylonitrile and
other α-olefins coordinated through the C᎐C bond, preventing the
19 (a) B. Akermark, J.-E. Backvall, L. S. Hegedus, K. Zetterberg,
K. Siirala-Hansen and K. Sjoberg, J. Organomet. Chem., 1974, 72,
127; (b) B. Akermark, J.-E. Backvall and K. Zetterberg, Acta Chem.
Scand., 1982, B36, 577.
᎐
observation of 195Pt-satellites in NMR spectra, exist: (a) K. Yang,
R. J. Lachicotte and R. Eisenberg, Organometallics, 1998, 17,
5102; (b) M. Fusto, F. Giordano, I. Orabona and F. Ruffo,
Organometallics, 1997, 16, 5981; (c) P. Ganis, I. Orabona, F. Ruffo
and A. Vitagliano, Organometallics, 1998, 17, 2646.
20 (a) C. Hahn, A. Vitagliano, F. Giordano and R. Taube,
Organometallics, 1998, 17, 2060; (b) C. Hahn, P. Morvillo and
A. Vitagliano, Eur. J. Inorg. Chem., 2001, 2, 419.
10 The equilibrium constant (Keq) was approximately calculated from
the integration ratios of the corresponding resonance peaks in the
21 S. Park, Bull. Korean Chem. Soc., 2000, 21, 1251.
1158
J. Chem. Soc., Dalton Trans., 2002, 1153–1158