Platinacycloalkane complexes containing [P,N] bidentate ligands: Synthesis and decomposition studies

Article abstract of DOI:10.1039/c3dt52798k

A new series of platinacyclopentanes (2a-2f) and platinacycloheptanes (3a-3f) of the type [Pt(N^P)(CH₂)_n] (n = 4, 6) were obtained by the reaction of [Pt(COD)(CH₂)_n] with the appropriate iminophosphine ligand (1a-1f). These complexes were characterised using a variety of spectroscopic and analytical techniques. X-ray structure analysis of complex 2a revealed a slightly distorted square planar geometry around platinum as a consequence of the ring strain imposed by the [P,N] chelate ring formed and the metallocycloalkane. Thermal decomposition analyses of the platinacycloalkanes revealed that the platinacyclopentanes are markedly stable, with the decomposition reaction requiring temperatures higher than 100 °C to occur. The major products obtained from the thermal decomposition reactions were 1-butene (for platinacyclopentanes) and 1-hexene (for platinacycloheptanes) . This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3dt52798k

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Platinacycloalkane complexes containing
[P,N] bidentate ligands: synthesis and
decomposition studies†
Cite this: Dalton Trans., 2014, 43,
5546
Tebello Mahamo,a,c John R. Moss,‡a Selwyn F. Mapolie,b Gregory S. Smith,*a
J. Chris Slootwegc and Koop Lammertsmac
A
new series of platinacyclopentanes (2a–2f) and platinacycloheptanes (3a–3f) of the type
[Pt(N^P)(CH2)n] (n = 4, 6) were obtained by the reaction of [Pt(COD)(CH2)n] with the appropriate imino-
phosphine ligand (1a–1f). These complexes were characterised using a variety of spectroscopic and
analytical techniques. X-ray structure analysis of complex 2a revealed a slightly distorted square planar
geometry around platinum as a consequence of the ring strain imposed by the [P,N] chelate ring formed
and the metallocycloalkane. Thermal decomposition analyses of the platinacycloalkanes revealed that the
platinacyclopentanes are markedly stable, with the decomposition reaction requiring temperatures higher
than 100 °C to occur. The major products obtained from the thermal decomposition reactions were
1-butene (for platinacyclopentanes) and 1-hexene (for platinacycloheptanes).
Received 7th October 2013,
Accepted 3rd February 2014
DOI: 10.1039/c3dt52798k
www.rsc.org/dalton
In these systems, the metallacyclic mechanism has been
favoured over the Cossee–Arlman mechanism used to explain
Introduction
Heterocycles containing a transition metal are an important the product distribution observed for late transition metal cata-
class of compounds, which have been studied as either lysts such as those based on nickel and palladium. However, a
catalysts1–5 or key intermediates in catalytic transformations of Cossee-type mechanism offers no reasonable explanation for
unsaturated molecules such as olefins6 and acetylenes.7,8
C6 or C8 α-olefin selectivity. Production of higher linear
Metallacyclobutanes, for example, are key intermediates in
olefin metathesis reactions9,10 while the good selectivity for
high-value α-olefins such as 1-hexene and 1-octene displayed
by ethylene oligomerization catalysts based on chromium
complexes has been attributed to the involvement of metalla-
cyclopentanes, -heptanes and -nonanes as key catalytic inter-
mediates.11–28 As such, metallacycles have achieved a trifecta
in terms of selective α-olefin production; all three of the
highest volume and highest value co-monomers (i.e. 1-butene,
1-hexene, and 1-octene) can be made selectively through this
route. For these reasons, metallacycles have been proposed
as significant intermediates in the trimerisation and tetra-
merisation of ethylene.29
α-olefins (up to C30) has also been proposed to proceed via an
extended metallacycloalkane mechanism.23 The preparation of
tantalum and titanium metallacycles by the reaction of precur-
sor complexes with ethylene and other simple olefins reported
by Schrock30 and Whitesides31,32 ultimately paved the way for
the construction of a catalytic process for ethylene dimeriza-
tion and oligomerization. The nature of supporting ligands in
these complexes plays an important role in the stability, reac-
tivity and catalytic activity.33,34 For instance, palladium com-
plexes with phosphine ligands have been successfully applied
in ethylene oligomerization and polymerization but complexes
with N-heterocyclic carbene ligands (NHC’s) have not found
such widespread use.35–37 This is likely due to the propensity
of metal alkyl complexes of NHC’s to decompose via alkyl-
imidazolium reductive elimination.33
The study of metallacyclopentane complexes containing
platinum,38–40 palladium41 and nickel42 has been reported.
Decomposition studies of a range of platinacycloalkanes by
Whitesides and co-workers revealed that the major products
in each case are α-olefins. The reaction is believed to occur
via β-hydride elimination, to generate a metal-hydride species,
followed by reductive elimination (Scheme 1).29 Because the
aDepartment of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701,
South Africa. E-mail: Gregory.Smith@uct.ac.za
bDepartment of Chemistry and Polymer Science, University of Stellenbosch,
Private Bag, Matieland, South Africa
cDepartment of Chemistry and Pharmaceutical Sciences, Faculty of Sciences,
VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
†CCDC 973798. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt52798k
‡Deceased.
5546 | Dalton Trans., 2014, 43, 5546–5557
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Scheme 1 Decomposition platinacyclopentanes.29
metal-hydride species is short-lived, it is expected that little
or no isomerisation of the α-olefin product should occur.30
Whitesides’ studies also showed that metallacyclopentanes
are markedly more thermally stable than analogous
Results and discussion
Preparation of platinacyclopentanes 2a–2f and
platinacycloheptanes 3a–3f
metallacycloheptanes.31,32,38–40 This may be as a consequence The reaction of [Pt(COD)Cl2] with the appropriate di-Grignard
of the constrained geometry of the metallacyclopentanes, reagent in THF gave platinacycloalkanes of the type [Pt(COD)-
which can hinder β-hydride elimination. Similar observations (CH2)n], n = 4, 6.38,43 The iminophosphine-containing platina-
have been made with chromacyclopentanes and chromacyclo- cycloalkanes were prepared by displacement of 1,5-cycloocta-
heptanes.26 The precise mechanism for the decomposition diene from [Pt(COD)(C4H8)] and [Pt(COD)(C6H12)] (Scheme 2)
reaction of metallacyclopentanes has not been conclusively by the appropriate iminophosphine ligands to give complexes
determined. Studies on platinum complexes indicate that 2a–2f and 3a–3f, respectively. The products were obtained as
although the elimination of a metal hydride is an important yellow or orange solids (2a–2f) or orange oils (3a–3f).
step in the thermal decomposition of dialkylplatinum(II) com-
1H NMR spectra of the complexes show an upfield shift of
plexes and larger platinacycles, other mechanisms such as 3,5- the imine proton signals from 8.98–9.05 ppm in the free
hydrogen transfer29 and intermolecular hydrogen transfer43 ligands to 8.13–8.43 ppm in the metal complexes. The observed
might also be involved. Theoretical studies with titanium upfield shift is attributed to back-bonding from the platinum
complexes suggest that despite the challenges presented by centre to the imine bond. These signals appear as singlets, in
constrained geometry of metallacyclopentanes, the step- contrast to the doublets observed for free ligands,47 due to the
wise β-hydride elimination/reductive elimination process conformational change of the ligand in order to facilitate
is still the most likely decomposition pathway for these coordination.49 Platinum satellites, with coupling constants in
complexes.44–46
Due to increased stability of platinacycloalkanes relative to of imine moiety of the ligands to the metal centre.
other metallacycloalkanes, their study can offer valuable Similar to other iminophosphine complexes, a downfield
the range of 3JHPt = 31.8–37.1 Hz, further support coordination
insights into the nature of transient species in catalytic pro- shift is observed from 4.64–4.87 ppm for the free ligands47 to
cesses such as ethylene oligomerization, that are proposed to 5.25–5.77 ppm for the platinacycles for the methylene protons
involve metallacycloalkanes as key intermediates. We pre- (N-CH2-R). This is due to the deshielding that occurs upon
viously reported a series of iminophosphine ligands 1a–1f coordination of the imine nitrogen to platinum. The methyl-
(Fig. 1), as well as their palladium dichloride and palladium ene protons (N-CH2-R) also show platinum satellites with a
methyl chloride complexes and the activity of these complexes 3JHPt = 15.1–17.0 Hz. The alkyl protons of the metallacycles
as pre-catalysts in ethylene oligomerization reactions47 and appear as multiplets in the region 0.72–1.91 ppm with the CH2
Suzuki–Miyaura coupling reactions.48 With the intent of protons adjacent to the metal centre being assigned to the
gaining access to further examples of platinacycloalkane most upfield resonance.
complexes, and to gain insight into the possible role played by
In the 13C NMR spectra, resonances for the imine carbons
supporting ligands in the reactivity of such compounds, we shift slightly downfield from between 160.3–161.4 ppm in the
have now prepared a series of platinacycloalkanes of the free ligands to between 161.6–163.4 ppm in the platinacycles.
general formula [Pt(P^N)(CH2)n] (n = 4, 6), based on these These signals appear as doublets, although the magnitude of
iminophosphine ligands. An investigation of the thermal the coupling constants is smaller compared to those of the
decomposition behaviour of these metallacycloalkanes was free ligands with a 3JCP in the range of 4.3–6.0 Hz for the plati-
also carried out.
nacycles compared to 21.1–23.4 Hz for the free ligands.
A downfield shift of up to 9.1 ppm is observed for the methyl-
ene carbon atoms (N-CH2-R) upon coordination. Resonances
for the carbon atoms of the carbocyclic fragment of the platina-
cycloalkanes are observed between 14.9 and 36.1 ppm. The
carbon atoms bonded to the metal centre (Pt-CH2–) resonate as
doublets as a result of coupling to the phosphorus nucleus of
the iminophosphine ligand.
The most shielded carbon atoms are those that are cis to
the phosphine group, Cd for the platinacyclopentanes 2a–2f
Fig. 1 General structure of iminophosphine ligands 1a–1f.
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Scheme 2 Synthesis of platinacyclopentanes 2a–2f and platinacycloheptanes 3a–3f.
and Cf for the platinacycloheptanes 3a–3f. These atoms appear Table 1 Selected bond ligands (Å) and angles (°) for 2a
2
as doublets at 14.9–17.3 ppm with a JCP coupling constant
Bond Lengths
Bond Angles
between 2.6–3.3 Hz. In contrast, the carbons coordinated trans
to the phosphine group (Ca) is the most deshielded, appearing
Pt(1)–C(1)
Pt(1)–C(4)
Pt(1)–N(1)
Pt(1)–P(1)
P(1)–C(18)
C(12)–C(13)
N(1)–C(12)
N(1)–C(5)
2.148(5)
2.052(5)
2.118(4)
2.2440(12)
1.831(5)
1.469(7)
1.281(6)
1.487(6)
C(4)–Pt(1)–N(1)
N(1)–Pt(1)–C(1)
C(4)–Pt(1)–C(1)
C(4)–Pt(1)–P(1)
C(1)–Pt(1)–P(1)
N(1)–Pt(1)–P(1)
176.77(18)
92.2(2)
84.6(2)
94.98(15)
176.78(14)
88.18(11)
2
as doublets at 32.7–36.1 ppm with coupling constants JCP
between 4.0–6.2 Hz, almost double the values observed for the
carbons cis to the phosphine group.
31P NMR spectra of the platinacycloalkanes reveal a down-
field shift of the phosphorus resonance from ca. −14 ppm in
the free ligands to 25.0–27.1 ppm in the complexes. These
signals are accompanied by platinum satellites with coupling
1
constants in the range JPPt = 1843–2066 Hz, similar to other N(1)–Pt(1)–P(1)–C(18)–C(13)–C(12) and the metallacycle Pt(1)–
platinacycloalkane phosphine complexes.50–54 In the IR C(1)–C(2)–C(3)–C(4), the complex displays a distorted square
spectra of the platinacycles, the imine stretching band is planar geometry around the metal centre. The iminophos-
observed in the region 1630–1635 cm−1, a slightly lower fre- phine ligand forms a puckered chelate ring with platinum,
quency compared to the free ligands where the imine absorp- with the benzyl moiety lying above the Pt(P^N)(C4H8) plane
tion band is seen between 1634–1636 cm−1. This confirms and a torsion angle Pt(1)–P(1)–C(18)–C(13) being 33.6(4)°. The
coordination of the imine nitrogen to platinum. This is in bite angles, N(1)–Pt(1)–P(1), C(4)–Pt(1)–C(1), C(4)–Pt(1)–P(1)
agreement with data reported for other transition metal imino- and N(1)–Pt(1)–C(1), around platinum deviate from the
phosphine complexes.6
expected 90° angles and this can be attributed to the ring
strain imposed by the two ring systems around the metal
centre (Fig. 2).
X-ray structural analysis
Crystals suitable for X-ray analysis were obtained by slow
A comparison of key bond lengths between complex 2a and
diffusion of hexane into a concentrated solution of complex 2a other platinacyclic and bisalkenyl complexes with mono- and
in DCM. Selected bond lengths and angles for complex 2a are bidentate phosphine ligands50–55 reveals important differences
presented in Table 1 and crystal data for the complex is listed between these complexes and the iminophosphine complex,
in Table 5. The X-ray crystal structure of 2a confirms the biden- 2a. Due to the different trans effects of phosphine and imine
tate coordination of the iminophosphine ligand to the metal donor groups, the bond lengths Pt(1)–C(1) and Pt(1)–C(4) are
centre. Due to the ring strain imposed by both the chelate ring different. As expected, Pt(1)–C(1), which is trans to the
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Fig. 2 The ORTEP plot of the molecular structure of 2a showing num-
bering scheme. All non-hydrogen atoms are shown as ellipsoids with
probability level of 30%.
phosphine group is slightly longer than Pt(1)–C(4), which
is trans to the imine moiety. Pt(1)–C(1) and Pt(1)–C(4) are
2.148(5) Å and 2.052(5) Å, respectively.
Thermal decomposition studies
Effect of temperature on product distribution of 2a. Prior to
investigating the thermal decomposition products for all the
iminophosphine platinacycloalkanes (2a–2f and 3a–3f), the
optimal conditions were determined using complex 2a. The
effect of temperature and time as well as the reaction kinetics
were studied using complex 2a. The effect of temperature on
the decomposition of 2a was studied by monitoring the
change in the 31P NMR spectra of 2a throughout the decompo-
sition process at 100 °C, 120 °C, 140 °C and 170 °C. The
results from this study were used to determine the amount of
time it takes for complete decomposition of 2a at each tem-
perature. In addition, the NMR study was used to shed light
on the nature of the platinum-containing fragment after
decomposition. Thus far, this fragment has been referred to as
the “Pt(0) species”39 in the literature.
Fig. 3 31P NMR spectra of complex 2a during heating at 140 °C,
(a) t0 h, (b) t11 h, (c) t27 h
.
Fig. 3 shows 31P NMR spectra of 2a over time at 140 °C. At that the temperature at which the decomposition reaction is
all temperatures, the spectra show a gradual decrease in the carried out has a significant influence on the hydrocarbon dis-
intensity of the resonance at 25.0 ppm (1JPPt = 1917 Hz). This tribution. As expected, the rate of reaction is significantly
decrease is accompanied by appearance and gradual increase higher at elevated temperatures but isomerisation and hydro-
of a new signal at 26.1 ppm (1JPPt = 2198 Hz). This result genation to internal olefins and n-alkanes is also prevalent.
reveals that only one phosphorus-containing compound is Decreasing the temperature from 170 °C to 120 °C resulted in
formed upon decomposition of 2a and the new phosphorus- an increase in the relative amount of 1-butene from 67% to
containing species is also a platinum complex, as evidenced by 91%. At 100 °C, however, no decomposition occurs, reflecting
the platinum satellites accompanying the new signal. Attempts the stability of platinacyclopentanes.38
to isolate this complex for full characterization were un-
successful due to its instability.
Under solvent free conditions (entry 5, Table 2) and in
toluene (entry 4, Table 2) the product distribution obtained is
After determining the time required for complete decompo- similar. These results indicate that the solvent could act as a
sition of 2a at each temperature, the reactions were scaled up hydrogen donor via C–H activation in the formation of satu-
(1.5 cm3 solutions) to determine the hydrocarbon product dis- rated hydrocarbons from the decomposition reaction. For-
tribution using GC-MS analysis. The results (Table 2) show mation of n-butane from the decomposition of 2a under
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Table 2 Thermal decomposition of complex 2aa
Entry
Temp. (°C)
Solvent
Time (h)
1-Buteneb
2-Butenesb
Butaneb
1
2
3
4
5
100
120
140
170
170
Toluene
Toluene
Toluene
Toluene
—
120
90
27
6
0
91
81
67
67
0
8
17
22
26
0
1
2
11
7
6
a Reactions done in triplicate. Error: 1%. b Amounts given as percentages.
solvent-free conditions, however, indicates that solvent is not techniques can be employed to investigate the kinetic behav-
the only available source of hydrogen atoms in this process. It iour of a reaction. Spectroscopic tools are particularly useful
is also possible that the hydrogen atoms could come from the because, in addition to reaction rates, they can provide struc-
C–H activation of coordinated ligands as has been proposed tural information about the reaction at a molecular level.56
by Whitesides,43 or platinum hydride species that may form as The kinetics of thermal decomposition of complexes 2a and 3a
intermediates or products in the reaction.
were followed using two procedures. In the first procedure,
Effect of time on product distribution for 2a. A time depen- samples were taken periodically, cooled in liquid nitrogen and
dence study in which the relative amounts of hydrocarbon pro- GC-MS analysis of the volatiles in solution was performed.
ducts obtained from the decomposition of 2a were compared Results were obtained by following the total concentration of
over time was carried out. The reactions were carried out at the hydrocarbon products relative to that of the internal stan-
170 °C for two reasons: (1) The rate of decomposition is higher dard (n-decane). In the second procedure, appearance of the
at higher temperatures, therefore appearance of products new peak at ∼26 ppm and the disappearance of the original
should be fast. (2) Effect of time on product isomerisation peak at ∼25 ppm in the 31P NMR spectra of the reactions were
and/or hydrogenation should be detected early. The reaction monitored. The results obtained using these two methods
was followed by analysis of the amounts of 1-butene, 2-butene were indistinguishable within experimental error. Kinetic data
and n-butane using GC-MS. The results (Fig. 4) show that the were collected for the decomposition of 2a and 3a at 140 °C
absolute amount of 1-butene obtained decreased. With pro- and at 170 °C.
longed heating, the relative amount of 1-butene decreased
The decomposition reactions were found to follow first-
from 90% after 1 h to 67% after 6 h, and the relative amounts order kinetics for approximately the first 30% to one half-life
of 2-butenes and n-butane increased. These results further of the decomposition reaction for both complexes. Beyond this
confirm that the primary products in the thermal decompo- point, the reaction kinetics showed deviations from first order
sition of platinacycloalkanes are α-olefins as has been pre- behaviour, indicating increasing involvement of products in
viously reported. Isomerisation and hydrogenation to internal the reaction mechanism, most likely the platinum-containing
olefins and saturated hydrocarbons are secondary processes. fragment as well as the occurrence of secondary reactions such
After complete decomposition, the major product was found as isomerisation and hydrogenation. The analysis presented
to be 1-butene, indicating that these secondary reactions occur herein is based on the results obtained over the first half life
at a slower rate than the production of 1-butene.
of the decomposition reaction. Rate constants derived from
Kinetic studies of thermal decomposition of 2a and 3a. the initial linear regions of the decomposition curves were cal-
Reaction kinetics is an important component in investigating culated according to Eqn (1) and are presented in Table 3.
reaction mechanisms.
A number of different analytical
lnðat=a0Þ ¼ ꢀkt
ð1Þ
where a = [Complex 2a] or [Complex 3a].
Table 3 Rate constants for the thermal decomposition of 2a and 3a in
toluene
Rate constanta (s−1
)
Rateb (M−1 s−1
)
Complex
140 °C
170 °C
140 °C
170 °C
2a
3a
2.90 × 10−5
1.50 × 10−4
4.31 × 10−7
2.02 × 10−6
(7.27 × 10−3
6.06 × 10−6
(2.18 × 10−2
(0.104 h−1
)
(0.525 h−1
)
(1.55 × 10−3
1.23 × 10−6
(4.44 × 10−3
)
)
)
9.00 × 10−5
(0.324 h−1
4.37 × 10−4
(1.58 h−1
)
)
)
a Rate constants in h−1 in parenthesis. b Reaction rates in M−1 h−1 in
parenthesis.
Fig. 4 Product composition (%) for the thermal decomposition of 5.1
over time.
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Fig. 5 Representative speciation (a) and first order (b) plots for the thermal decomposition of complex 2a at 140 °C and 170 °C.
Fig. 6 Representative speciation (a) and first order (b) plots for the thermal decomposition of complex 3a at 140 °C and 170 °C.
Fig. 5 shows the kinetic data plots for the decomposition temperature study using complex 2a and carrying out the reac-
reaction of 2a at 140 °C and 170 °C and Fig. 6 shows data plots tion in solution does not significantly effect selectively for
for the thermal decomposition of 3a. As expected, the rate of 1-butene. Finally, doing the reaction under the same conditions
decomposition at 170 °C is greater than that at 140 °C for both would allow for direct comparison of results between
complexes. 31P NMR data shows that at 140 °C complete complexes.
decomposition takes 29 h for 2a and 10 h for 3a. At 170 °C
The thermal decomposition of platinacyclopentanes 2a–2f
complete decomposition only takes 7 h for 2a and 2.5 h for 3a. (entries 1–6, Table 4) displays similar hydrocarbon product
The rate constants for decomposition of 2a and 3a at 140 °C profiles. The nature of the pendant R-group on the imine
are 0.104 h−1 and 0.324 h−1, respectively. At 170 °C the rate moiety of the ligand does not seem to have a significant
constant for the decomposition of 2a is 0.525 h−1, while impact on the outcome of the decomposition reaction. A
the rate constant for the decomposition of 3a is one order of similar observation is made with the platinacycloheptanes
magnitude higher (1.58 h−1). The decomposition of complex 3a–3f. A more noticeable effect is that of the size of the
3a (a seven-membered ring) was faster than that of 2a (a five- metallacyclic ring. It appears that the larger the ring size, the
membered ring) at both temperatures under investigation.39
greater the propensity for isomerisation and hydrogenation.
Thermal decomposition of complexes 2b–2f and 3a–3f. This can be attributed to the fact that, under similar reaction
Decomposition of the rest of the platinacycloalkane complexes conditions, larger metallacycles will decompose faster
in this study was carried out under the following conditions: than their smaller ring counterparts. This would therefore
140 °C, toluene, 27 h. Results of these reaction are presented allow for more secondary reactions to occur for the larger
in Table 4. These conditions were selected from the metallacycloalkanes.
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Table 4 Thermal decomposition of complexes 2a–2f and 3a–3fa
Internal
olefinsb,c
Entry
Complex
n
R
α-Olefinb
n-Alkanesb
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
4
4
4
4
4
4
6
6
6
6
6
6
Phenyl
4-Tolyl
2-Furfuryl
2-Thiophenyl
3-Pyridyl
Mesityl
Phenyl
4-Tolyl
2-Furfuryl
2-Thiophenyl
3-Pyridyl
Mesityl
81
85
71
76
80
84
50
63
56
54
52
58
17
11
20
13
13
11
33
27
29
35
28
20
2
4
9
11
7
5
17
10
15
11
20
22
9
10
11
12
a Reaction conditions: 0.02 M in toluene, 140 °C, 27 h. b Amounts given as percentages. c Mixture of cis and trans internal olefins.
step in the reaction. (3) Reaction temperature and reaction
time have a significant effect on the organic product distri-
bution. (4) The decomposition reaction follows first order
kinetics over the first half life of the decomposition process,
with deviation from first order behaviour thereafter.
Table 5 Crystal data for 2a
Formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C30H30NPPt
630.61
Triclinic
ˉ
P1
9.7744(13)
11.3517(15)
12.6780(16)
72.898(3)
67.960(3)
82.749(3)
1246.0(3)
2
α (°)
β (°)
Experimental
Materials and equipment
γ (°)
V (Å3)
All reactions were carried out under a nitrogen or argon atmos-
Z
Dc (g cm−3
)
1.681
5.713
phere using
a dual vacuum/nitrogen line and standard
µ (mm−1
)
Schlenk techniques unless otherwise stated. Solvents were
dried and purified by distillation under argon using a suitable
drying agent and stored under vacuum in a Teflon-valve
storage vessel. All commercially available chemicals were pur-
chased from either Sigma-Aldrich or Merck and used without
further purification. K2PtCl4 and PdCl2 were obtained from
Johnson Matthey. The ligands 1a–1f,47,48 [Pt(COD)(C4H8)],38,43
θ Range for data collection (°)
Limiting indices
1.80–28.34
−13 ≤ h ≤ 13
−15 ≤ k ≤ 15
−16 ≤ l ≤ 16
27 034
6180 (0.0549)
298
0.0448
0.0786
1.043
No. of reflns collected
No. of reflns unique (Rint
)
No. of params
R1
wR2
[Pt(COD)(C6H12)],38,43 2-Diphenylphosphinobenzaldehyde,57,58
Goodness of fit on F2
39,61
Pd(COD)Cl2,59 Pd(COD)MeCl,60 Pt(COD)Cl2
prepared using literature procedures.
were all
NMR spectra were recorded on a Varian Mercury-300 MHz
(1H: 300 MHz; 13C: 75.5 MHz; 31P: 121 MHz) or Varian Unity-
Conclusions
A new series of iminophosphine platinacyclopentanes and pla- 400 MHz (1H: 400 MHz; 13C: 100.6 MHz; 31P: 161.9 MHz)
tinacycloheptanes have been synthesised. Characterisation spectrometer. 1H NMR spectra were referenced internally
using several spectroscopic techniques confirmed that the using the residual protons in deuterated solvents (CDCl3:
iminophosphine ligands act as [P,N] bidentate donors to plati- δ 7.27; DMSO: δ 2.50) and values reported relative to the
num. This was further substantiated by the X-ray structure internal standard tetramethylsilane (δ 0.00). 13C NMR spectra
analysis of complex 2a which showed a slightly distorted were referenced internally to the deuterated solvent resonance
square planar geometry around platinum as a consequence of (CDCl3: δ 77.0; DMSO: δ 39.4) and the values are reported rela-
the ring strain imposed by the [P,N] bis-chelate ring formed tive to tetramethylsilane (δ 0.00). All chemical shifts are
and the metallocycloalkane. Thermal decomposition behav- quoted in δ (ppm) and coupling constants, J, in Hertz (Hz).
iour of the platinacyclopentanes was studied at different temp-
Melting points were determined on a Reichert-Jung Ther-
eratures and under both solvent free conditions and in movar hotstage microscope and are uncorrected. Infrared
solution. The results obtained show that: (1) Platinacyclopen- spectra were recorded on a Thermo Nicolete FT-IR instrument
tanes are markedly more stable than analogous platinacyclo- in the 4000–300 cm−1 range using KBr discs or CH2Cl2 solu-
heptanes. (2) The platinacycloalkanes decompose to give tions. Microanalyses were determined using a Fisons EA 1108
α-olefins as the primary, and major products, indicating that CHNO-S instrument. Mass spectra were recorded on a Waters
formation of a metal hydride intermediate is an important API Quatro Micro triple quadruple mass spectrometer (ESI,
5552 | Dalton Trans., 2014, 43, 5546–5557
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3
70 eV) at the University of Stellenbosch. GC analyses were per- 9.3 Hz; Ar-C), 129.4 (s; Ar-C), 129.6 (s; Ar-C), 129.7 (d, JCP
=
3
formed using a Varian 3900 gas chromatograph equipped with 1.7 Hz; Ar-C), 130.3 (d, JCP = 1.2 Hz; Ar-C), 131.5 (s; Ar-C),
2
3
an FID and a 50 m × 0.20 mm HP-PONA column (0.50 μm film 131.8 (s; Ar-C), 131.9 (d, JCP = 5.1 Hz; Ar-C), 132.2 (d, JCP
=
=
2
2
thickness). The carrier gas was helium at 40 psi. The oven was 2.6 Hz; Ar-C), 133.6 (d, JCP = 5.0 Hz; Ar-C), 134.1 (d, JCP
1
programmed to hold the temperature at 32 °C for 4 min and 7.9 Hz; Ar-C), 135.0 (d, JCP = 11.9 Hz; Ar-C), 138.1 (s; Ar-C),
then to ramp to 200 °C at 10° min−1 and hold for 5 min and 140.1 (d, JCP = 16.9 Hz; Ar-C), 162.2 (d, JCP = 5.1 Hz; C3).
then ramp to 250 °C at 10° min−1 and hold for 5 min. GC-MS 31P NMR (CDCl3): 26.2 (s, JPPt = 1920 Hz). ESI-MS: m/z 645.20
analyses for peak identification were performed using an [M + H]+, 589.44 [M − C4H8]+. Anal. Calc. For C31H32NPPt
Agilent 5973 gas chromatograph equipped with MSD and a (644.64): C, 57.76; H, 5.00; N, 2.17. Found: C, 57.79; H, 5.03;
60 m × 0.25 mm Rtx-1 column (0.5 μm film thicknesses). The N, 2.15.
2
3
carrier gas was helium at 0.9 ml min−1. The oven was pro-
Preparation of [Pt(C24H20NOP)(C4H8)] (2c). 2c was prepared
grammed to hold at 50 °C for 2 min and then ramp to 250 °C by the reaction of [Pt(COD)(C4H8)] (0.14 g, 0.40 mmol) and
at 10° min−1 and hold for 8 min.
(2-diphenylphosphanyl-benzylidene)-furan-2-ylmethyl-amine (1c)
(0.15 g, 0.40 mmol). The product was obtained as an orange
solid. (0.22 g, 87%). M.p. 146–148 °C (decomp). IR (KBr):
General procedure for the preparation of complexes 2a–2f
and 3a–3f
1
1630 cm−1 (νCvN, imine). H NMR (CDCl3): 0.86–0.88 (m, 4H;
3
The metallacycloalkanes were prepared from the reaction of Ha + Hd), 1.45–148 (m, 4H; Hb + Hc), 5.49 (s, 2H, JH–Pt
[Pt(COD)Cl2] with appropriate di-Grignard reagents to give 15.1 Hz; H5), 6.22 (dd, 1H, JHH = 1.9 Hz, 3.2 Hz; H3), 6.27 (d,
[Pt(COD)(CH2)n], where n = 4 or 6. After work-up, the 1,5- 1H, 3JHH = 3.2 Hz; H2), 7.08 (dd, 1H, 3JHH = 0.8 Hz, 1.8 Hz; H1),
=
3
cyclooctadiene was displaced by the iminophosphine ligands 7.24–7.41 (m, 14H; Ar-H), 8.15 (s, 1H, JH–Pt = 35.0 Hz; H6).
2
in a 1 : 1 reaction.
13C NMR (CDCl3): 15.8 (d, JCP = 2.8 Hz; Cd), 26.3 (s; Cc), 28.0
2
Preparation of [Pt(C26H22NP)(C4H8)] (2a). 2a was prepared (s; Cb), 33.9 (d, JCP = 5.8 Hz; Ca), 60.9 (s; C5), 110.2 (s; C3),
by the reaction of [Pt(COD)(C4H8)] (0.18 g, 0.50 mmol) and 111.7 (s; C2), 128.1 (d, JC–P = 9.7 Hz; Ar-C), 128.3 (d, JCP
benzyl-(2-diphenylphosphanyl-benzylidene)-amine (1a) (0.19 g, 11.0 Hz; Ar-C), 128.6 (d, JCP = 5.4 Hz; Ar-C), 129.7 (d, JCP
0.50 mmol), and the product was obtained as an orange solid 1.8 Hz; Ar-C), 130.2 (d, JCP = 1.4 Hz; Ar-C), 131.4 (s; Ar-C),
(0.26 g, 83%). X-ray quality crystals were obtained from slow 131.7 (s; Ar-C), 131.9 (d, JCP = 4.9 Hz; Ar-C), 132.0 (s; Ar-C),
diffusion of hexane into a concentrated solution of 2a in 132.3 (d, JCP = 2.7 Hz, Ar-C), 133.9 (d, JCP = 12.6 Hz; Ar-C),
1
1
=
=
2
3
3
3
3
1
2
2
dichloromethane. M.p. 164–167 °C (decomp). IR (KBr): 134.1 (s; Ar-C), 135.2 (d, JCP = 8.3 Hz; Ar-C), 138.7 (d, JCP
=
=
1631 cm−1 (νCvN, imine). H NMR (CDCl3): 0.79–0.84 (m, 4H; 16.4 Hz, Ar-C), 142.7 (s; C1), 150.4 (s; C4), 161.6 (d, JCP
1
3
3
Ha + Hd), 1.76–1.79 (m, 4H; Hb + Hc), 5.50 (s, 2H, JH–Pt
=
5.2 Hz; C6). 31P NMR (CDCl3): 25.3 (s, JPPt = 1904 Hz). ESI-MS:
16.4 Hz; H1), 6.88 (d, 2H, JHH = 7.8 Hz; Ar-H), 7.00 (d, 2H, m/z 621.17 [M + H]+, 564.50 [M − C4H8]+. Anal. Calc. For
3JHH = 7.1 Hz; Ar-H), 7.11–7.35 (m, 15H; Ar-H), 8.18 (s, 1H, C28H28NOPPt (620.58): C, 54.19; H, 4.55; N, 2.26. Found:
3
3JHPt = 35.1 Hz; H2). 13C NMR (CDCl3): 15.8 (d, JCP = 2.9 Hz; C, 54.41; H, 4.82; N, 2.36.
Cd), 28.0 (s; Cc), 29.7 (s; Cb), 33.9 (d; JCP = 5.7 Hz; Ca), 68.8 (s;
2
2
Preparation of [Pt(C24H20NPS)(C4H8)] (2d). 2d was prepared
C1), 127.3 (s; Ar-C), 128.1 (d, JCP = 9.0 Hz; Ar-C), 128.4 (s; by the reaction of [Pt(COD)(C4H8)] (0.13 g, 0.36 mmol) and
Ar-C), 128.7 (s; Ar-C), 129.4 (s; Ar-C), 129.8 (s; Ar-C), 130.3 (s; (2-diphenylphosphanyl-benzylidene)-thiophen-2-ylmethyl-amine
1
3
Ar-C), 131.5 (s; Ar-C), 131.8 (s; Ar-C), 131.9 (d, JCP = 4.9 Hz; (1d) (0.14 g, 0.36 mmol). The product was obtained as an
1
Ar-C), 133.6 (s; Ar-C), 133.9 (d, JCP = 12.6 Hz; Ar-C), 135.3 (d, orange solid (0.19 g, 81%). M.p. 127–129 °C (decomp). IR
1JCP = 8.3 Hz; Ar-C), 137.7 (s; Ar-C), 138.9 (d, JCP = 16.7 Hz; (KBr): 1630 cm−1 (νCvN, imine). 1H NMR (CDCl3): 0.80–0.83
2
Ar-C), 162.0 (d, JCP = 5.5 Hz; C2). 31P NMR (CDCl3): 25.0 (s, (m, 4H; Ha + Hd), 1.69–1.72 (m, 4H; Hb + Hc), 5.70 (s, 2H,
3
JPPt = 1894 Hz). ESI-MS: m/z 631.18 [M + H]+, 575.12 3JHPt = 16.4 Hz; H5), 6.38 (dd, 1H, JHH = 1.8 Hz, 3.0 Hz; H3),
3
[M − C4H8]+. Anal. Calc. For C30H30NPPt (630.62): C, 57.14; H, 6.45 (d, 1H, JHH = 3.2 Hz; H2), 7.14 (dd, 1H, JHH = 1.0 Hz,
3
3
3
4.80; N, 2.22. Found: C, 56.91; H, 4.83; N, 2.12.
1.8 Hz; H1), 7.28–7.47 (m, 14H; Ar-H), 8.21 (s, 1H, JHPt
=
Preparation of [Pt(C27H24NP)(C4H8)] (2b). 2b was prepared 36.4 Hz; H6). 13C NMR (CDCl3): 15.9 (d, JCP = 3.0 Hz; Cd), 25.9
2
by the reaction of [Pt(COD)(C4H8)] (0.18 g, 0.50 mmol) and (s; Cc), 27.8 (s; Cb), 36.1 (d, 2JCP = 5.9 Hz; Ca), 61.4 (s; C5), 123.5
1
(2-diphenylphosphanyl-benzylidene)-(4-methyl-benzyl)-amine (s; C3), 125.0 (s; C2), 128.0 (d, JCP = 10.1 Hz; Ar-C), 128.5 (d,
(1b) (0.20 g, 0.50 mmol), and the product was obtained as an 1JCP = 11.4 Hz; Ar-C), 128.9 (d, JCP = 4.8 Hz; Ar-C), 129.5 (d,
2
orange solid (0.24 g, 76%). M.p. 142–143 °C (decomp). IR 3JCP = 2.0 Hz; Ar-C), 130.9 (d, JCP = 1.8 Hz; Ar-C), 131.5 (s;
3
(KBr): 1634 cm−1 (νCvN, imine). 1H NMR (CDCl3): 0.87–1.01 Ar-C), 131.6 (s; Ar-C), 131.8 (d, JCP = 5.1 Hz; Ar-C), 132.1 (s;
3
3
1
(m, 4H; Ha + Hd), 1.74–1.79 (m, 4H; Hb + Hc), 2.31 (s, 3H; H1), Ar-C), 132.5 (d, JCP = 2.9 Hz, Ar-C), 134.2 (d, JCP = 11.6 Hz;
3
3
2
5.25 (s, 2H, JHPt = 15.8 Hz; H2), 6.99 (d, 2H, JHH = 7.1 Hz; Ar-C), 134.4 (s; Ar-C), 135.5 (d, JCP = 8.8 Hz; Ar-C), 137.9 (d,
Ar-H), 7.05 (d, 2H, JHH = 6.8 Hz; Ar-H), 7.17–7.34 (m, 14H; 2JCP = 16.0 Hz, Ar-C), 143.3 (s; C1), 151.6 (s; C4), 162.4 (d, 3JCP
=
3
Ar-H), 8.17 (s, 1H, JHPt = 34.8 Hz; H3). 13C NMR (CDCl3): 16.1 4.3 Hz; C6). 31P NMR (CDCl3): 25.7 (s, JPPt = 2066 Hz). ESI-MS:
3
(d, JCP = 3.1 Hz; Cd), 22.1 (s; C1), 28.0 (s; Cc), 30.3 (s; Cd), 33.1 m/z 637.13 [M + H]+, 581.08 [M − C4H8]+. Anal. Calc. For
2
(d; 2JCP = 6.0 Hz; Ca), 67.9 (s; C2), 125.5 (s; Ar-C), 127.2 (s; Ar-C), C28H28NPSPt (636.65): C, 52.82; H, 4.43; N, 2.20; S, 5.04.
1
1
128.0 (d, JCP = 8.8 Hz; Ar-C), 128.5 (s; Ar-C), 128.9 (d, JCP
=
Found: C, 53.01; H, 4.31; N, 2.17; S, 5.00.
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3
Preparation of [Pt(C25H21N2P)(C4H8)] (2e). 2e was prepared (m, 14H; Ar-H), 8.33 (s, 1H, JHPt = 34.7 Hz; H2). 13C NMR
by reacting [Pt(COD)(C4H8)] (0.13 g, 0.36 mmol) and (2-di- (CDCl3): 14.9 (d, 2JCP = 3.0 Hz; Cf), 26.2 (s; Ce), 28.1 (s; Cb), 32.3
phenylphosphanyl-benzylidene)-pyridin-3-ylmethyl-amine (1e) (s; Cd), 32.4 (s; Cc), 34.2 (d; 2JCP = 5.0 Hz; Ca), 65.4 (s; C1), 125.9
1
(0.14 g, 0.36 mmol). The product was obtained as an orange (s; Ar-C), 127.6 (d, JCP = 9.3 Hz; Ar-C), 127.9 (s; Ar-C), 128.4
solid (0.17 g, 76%). M.p. 139–142 °C (decomp). IR (KBr): (s; Ar-C), 128.6 (s; Ar-C), 129.0 (s; Ar-C), 129.4 (s; Ar-C), 129.9
1
2
1630 cm−1 (νCvN, imine). H NMR (CDCl3): 0.89–0.93 (m, 4H; (s; Ar-C), 130.7 (s; Ar-C), 131.3 (s; Ar-C), 132.0 (d, JCP = 5.1 Hz;
3
1
Ha + Hd), 1.41–146 (m, 4H; Hb + Hc), 5.69 (s, 2H, JH–Pt = 16.0 Ar-C), 133.6 (s; Ar-C), 134.6 (d, JCP = 12.2 Hz; Ar-C), 135.5 (d,
Hz; H6), 7.12 (1H, d, JHH = 7.3 Hz; Ar-H), 7.18–7.21 (5H, m; 1JCP = 9.1 Hz; Ar-C), 137.9 (s; Ar-C), 138.6 (d, JCP = 17.0 Hz;
3
2
Ar-H), 7.39–7.41 (4H, m; Ar-H), 7.51–7.53 (2H, m; Ar-H), Ar-C), 162.7 (d, JCP = 5.5 Hz; C2). 31P NMR (CDCl3): 26.8
3
7.60–7.62 (1H, m; Ar-H), 7.65–7.66 (1H, m; H3), 8.03 (1H, td, (s, JPPt = 1802 Hz). ESI-MS: m/z 659.34 [M + H]+, 575.20
3JHH = 2.0 Hz; 7.4 Hz, Ar-H), 8.30 (s, 1H; H4) 8.35 (1H, d, 4JHH
=
[M − C4H8]+.
3
2.1, Hz; H2), 8.43 (1H, s, JHPt = 35.7 Hz; H7), 8.56 (1H, dd,
Preparation of [Pt(C27H24NP)(C6H12)] (3b). 3b was prepared
by the reaction of [Pt(COD)(C6H12)] (0.25 g, 0.64 mmol) with
3JHH = 1.4 Hz, 5.0 Hz; H1). 13C NMR (CDCl3): 16.0 (d, JCP
=
2
2
2.8 Hz; Cd), 26.3 (s; Cc), 28.5 (s; Cb), 34.1 (d, JCP = 5.7 Hz; Ca), (2-diphenylphosphanyl-benzylidene)-(4-methyl-benzyl)-amine
1
64.4 (s; C6), 125.9 (s; C3), 126.5 (s; C), 129.1 (d, JCP = 12.3 Hz; (1b) (0.25 g, 0.63 mmol). The product was obtained as a brown
Ar-C), 130.4 (d, JCP = 1.6 Hz; Ar-C), 131.6 (d, JCP = 1.6 Hz; oil (0.29 g, 68%). IR (KBr): 1635 cm−1 (νCvN, imine). H NMR
3
3
1
2
Ar-C), 132.0 (d, JCP = 6.7 Hz; Ar-C), 132.8 (s; C5), 133.1 (d, (CDCl3): 0.76–0.89 (m, 4H; Ha + Hf), 0.95–1.37 (m, 8H;
1JCP = 12.4 Hz; Ar-C), 134.0 (s; Ar-C), 134.1 (s; Ar-C), 134.3 (s; Hb − He), 2.30 (s, 3H; H1), 5.45 (s, 2H, 3JHPt = 16.0 Hz; H2), 7.01
C4), 136.9 (d, JCP = 17.4 Hz; Ar-C), 137.2 (s; Ar-C), 139.4 (s; (dd, 1H, 3JHH = 1.2 H, 8.3 Hz; Ar-H), 7.11 (d, 1H; 4JHH = 1.7 Hz,
2
3
3
Ar-C), 149.7 (s; C2), 151.0 (s; C1), 162.1 (d, JCP = 5.3 Hz; C7). Ar-H), 7.14 (dd, 2H, JHH = 1.4 Hz, 7.2 Hz; Ar-H), 7.18 (m, 2H;
31P NMR (CDCl3): 25.7 (s, JPPt = 1886). ESI-MS: m/z 632.27 Ar-H), 7.30–7.44 (m, 12H; Ar-H), 8.13 (s, 1H, JPtH = 33.0 Hz;
3
[M + H]+, 575.36 [M − C4H8]. Anal. Calc. for C29H29N2PPd (631.61): H3). 13C NMR (CDCl3): 17.3 (d, JCP = 3.1 Hz; Cf), 21.7 (s; C1),
2
2
C, 55.15; H, 4.63; N, 4.44. Found: C, 55.20; H, 4.77; N, 4.39.
25.3, (s; Ce), 27.2 (s; Cb), 31.9 (s; Cd), 32.0 (s; Cc) 34.7 (d, JCP
=
Preparation of [Pt(C29H28NP)(C4H8)] (2f). 2f was prepared 6.0 Hz; Ca), 64.9 (s; C2), 125.5 (s; Ar-C), 127.2 (s; Ar-C), 128.0
1
1
using [Pt(COD)(C4H8)] (0.17 g, 0.48 mmol) and (2-diphenyl- (d, JCP = 8.8 Hz; Ar-C), 128.5 (s; Ar-C), 128.9 (d, JCP = 9.3 Hz;
3
phosphanyl-benzylidene)-(2,4,6-trimethyl-benzyl)-amine
(1f) Ar-C), 129.4 (s; Ar-C), 129.6 (s; Ar-C), 129.7 (d, JCP = 1.7 Hz;
(0.17 g, 0.40 mmol). The product was obtained as an orange Ar-C), 130.3 (d, JCP = 1.2 Hz; Ar-C), 131.5 (s; Ar-C), 131.8 (s;
3
2
3
solid (0.27 g, 85%). M.p. 172–175 °C (decomp). IR (KBr): Ar-C), 131.9 (d, JCP = 5.1 Hz; Ar-C), 132.2 (d, JCP = 2.6 Hz;
1635 cm−1 (νCvN, imine). H NMR (CDCl3): 0.81–0.92 (m, 4H, Ar-C), 133.6 (d, JCP = 5.0 Hz; Ar-C), 134.1 (d, JCP = 7.9 Hz;
1
2
2
1
Ha + Hd), 1.76–1.80 (m, 4H, Hb + Hc), 2.21 (s, 6H; H2 + H2′), Ar-C), 135.0 (d, JCP = 11.9 Hz; Ar-C), 138.1 (s; Ar-C), 140.1 (d,
2.40 (s, 3H; H1), 5.27 (2H, s, JH–Pt = 17.0 Hz; H3), 7.01 (d, 2H, 2JCP = 15.9 Hz; Ar-C), 162.2 (d, JCP = 5.1 Hz; C3). 31P NMR
3
3
3JHH = 7.6 Hz; Ar-H), 7.10 (d, 2H, JHH = 7.0 Hz; Ar-H), (CDCl3): 25.9 (s, JPPt = 1954 Hz). ESI-MS: m/z 671.63 [M + H]+,
3
3
7.21–7.30 (m, 12H, Ar-H), 8.20 (s, 1H, JH–Pt = 35.4 Hz; H4). 589.50 [M − C4H8].
Preparation of [Pt(C24H20NOP)(C6H12)] (3c). 3c was prepared
24.0 (s; C1), 27.6 (s; Cc), 29.9 (s; Cb), 32.7 (d; JCP = 5.9 Hz; Ca), by the reaction of [Pt(COD)(C6H12)] (0.25 g, 0.64 mmol) with
2
13C NMR (CDCl3): 15.8 (d, JCP = 3.0 Hz; Cd), 22.1 (s; C2 + C2′),
2
1
66.7 (s; C3), 126.3 (s; Ar-C), 128.0 (s; Ar-C), 128.8 (d, JCP
=
(2-diphenylphosphanyl-benzylidene)-furan-2-ylmethyl-amine
1
9.0 Hz; Ar-C), 129.0 (s; Ar-C), 129.5 (d, JCP = 9.1 Hz; Ar-C), (1c) (0.24 g, 0.64 mmol). The product was obtained as a dark-
129.6 (s; Ar-C), 129.9 (s; Ar-C), 130.0 (d, JCP = 1.4 Hz; Ar-C), orange oil (0.31 g, 77%). IR (KBr): 1632 cm−1 (νCvN, imine).
3
3
130.3 (d, JCP
=
1.5 Hz; Ar-C), 131.7 (s; Ar-C), 131.8 1H NMR (CDCl3): 0.72–0.75 (m, 4H; Ha + Hf), 1.31–1.39 (m,
2
3
3
(s; Ar-C), 132.0 (d, JCP = 5.3 Hz; Ar-C), 132.9 (d, JCP = 2.4 Hz; 8H; Hb − He), 5.77 (s, 2H, JHPt = 15.7 Hz; C5), 6.29 (dd, 1H,
Ar-C), 133.8 (d, JCP = 5.4 Hz; Ar-C), 134.4 (d, JCP = 9.3 Hz; 3JHH = 2.0 Hz, 3.1 Hz; H3), 6.34 (1H, d, JHH = 3.2 Hz; H2), 7.06
2
2
3
1
3
Ar-C), 134.8 (d, JCP = 12.1 Hz; Ar-C), 137.9 (s; Ar-C), 139.4 (1H, dd, JHH = 0.9 Hz, 2.0 Hz; H1), 7.24–7.42 (m, 14H; Ar-H),
(s, Ar-C), 142.2 (d, JCP = 16.5 Hz; Ar-C), 161.9 (d, JCP = 5.3 Hz; 8.16 (s, 2H, 3JHPt = 31.8 Hz; H6). 13C NMR (CDCl3): 15.1 (d, 2JCP
2
3
C4). 31P NMR (CDCl3): 26.7 (s, JPPt = 1843 Hz). ESI-MS: = 2.8 Hz; Cf), 24.3 (s; Ce), 24.9 (s; Cb), 31.4 (s; Cd), 31.5 (s; Cc),
m/z 672.23 [M + H]+, 617.16 [M − C4H8]+. Anal. Calc. For 33.7 (d, JCP = 4.9 Hz; Ca), 63.5 (s; C5), 109.6 (s; C3), 110.3 (s;
2
1
1
C31H32NPPt (672.70): C, 58.92; H, 5.39; N, 2.08. Found: C2), 127.7 (d, JCP = 10.0 Hz; Ar-C), 127.9 (d, JCP = 11.6 Hz;
Ar-C), 128.8 (d, JCP = 5.0 Hz; Ar-C), 129.5 (d, JCP = 1.4 Hz;
Preparation of [Pt(C26H22NP)(C6H12)] (3a). 3a was prepared Ar-C), 130.7 (d, JCP = 1.8 Hz; Ar-C), 131.1 (s; Ar-C), 131.5
by the reaction of [Pt(COD)(C6H12)] (0.25 g, 0.64 mmol) with (s; Ar-C), 131.7 (s; Ar-C), 131.9 (d, JCP = 5.1 Hz; Ar-C), 132.0 (s;
benzyl-(2-diphenylphosphanyl-benzylidene)-amine (1a) (0.24 g, Ar-C), 132.8 (d, JCP = 2.4 Hz, Ar-C), 134.0 (d, JCP = 12.3 Hz;
2
3
C, 58.97; H, 5.00; N, 2.01.
3
3
3
1
2
0.64 mmol). The product was obtained as a brown oil. (0.32 g, Ar-C), 134.7 (s; Ar-C), 135.6 (d, JCP = 8.1 Hz; Ar-C), 138.3 (d,
73%). IR (KBr): 1635 cm−1 (νCvN, imine). 1H NMR (CDCl3): 2JCP = 17.1 Hz, Ar-C), 143.1 (s; C1), 149.7 (s; C4), 162.6 (d, 3JCP
=
0.74–0.76 (m, 4H; Ha + Hf), 1.42–1.45 (8H, m; (Hb − He), 5.38 5.4 Hz; C6). 31P NMR (CDCl3): 26.4 (s, JPPt = 1860 Hz). ESI-MS:
(2H, s, JHPt = 16.8 Hz; H1), 7.08 (dd, 1H, JHH = 1.2 H, 8.3 Hz; m/z 649.69 [M + H]+, 565.41 [M − C4H8].
3
3
4
5
Ar-H), 7.11 (d, 1H, JHH = 1.8 Hz; Ar-H), 7.13 (dd, 2H, JHH
=
Preparation of [Pt(C24H20NPS)(C6H12)] (3d). 3d was pre-
1.6 Hz, JHH = 7.8 Hz; Ar-H), 7.21 (m, 1H; Ar-H), 7.39–7.51 pared by the reaction of [Pt(COD)(C6H12)] (0.25 g, 0.64 mmol)
3
5554 | Dalton Trans., 2014, 43, 5546–5557
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2
with (2-diphenylphosphanyl-benzylidene)-thiophen-2-ylmethyl- 1.8 Hz; Ar-C), 131.7 (s; Ar-C), 131.8 (s; Ar-C), 131.9 (d, JCP
=
=
3
2
amine (1d) (0.25 g, 0.64 mmol). The product was obtained as a 5.0 Hz; Ar-C), 133.1 (d, JCP = 2.6 Hz; Ar-C), 134.0 (d, JCP
dark-orange oil (0.30 g, 71%). IR (KBr): 1631 cm−1 (νCvN
,
5.1 Hz; Ar-C), 134.3 (d, 2JCP = 10.0 Hz; Ar-C), 134.6 (d, 1JCP = 11.9 Hz;
2
imine). 1H NMR (CDCl3): 0.76–0.80 (m, 4H; Ha + Hf), 1.26–1.43 Ar-C), 138.3 (s; Ar-C), 139.6 (s, Ar-C), 141.9 (d, JCP = 17.7 Hz;
(8H, m; Hb − He), 5.50 (2H, s, 3JHPt = 16.1 Hz; C5), 6.17 (1H, dd, Ar-C), 163.4 (d, JCP = 5.1 Hz; C4). 31P NMR (CDCl3): 26.7
3
3
3
4JHH = 2.0 Hz, JHH 3.2 Hz, H3), 6.23 (1H, d, JHH = 3.0 Hz, H2), (s, JPPt = 1863 Hz). ESI-MS: m/z 701.53 [M + H]+, 617.49
4
3
7.11 (1H, dd, JHH = 0.8 Hz, JHH = 1.8 Hz; H1), 7.30–7.39 (m, [M − C4H8].
14H; Ar-H), 8.17 (1H, s, JHPt = 33.8 Hz; H6). 13C NMR (CDCl3):
3
2
X-Ray structural analysis
17.1 (d, JCP = 2.9 Hz; Cf), 22.9 (s; Ce), 23.3 (s; Cb), 30.4 (s; Cd),
30.7 (Cc), 34.1 (d, JCP = 6.0 Hz; Ca), 63.9 (s; C5), 122.7 (s; C3), Single-crystal X-ray diffraction data for 2a was collected on a
124.0 (s; C2), 128.3 (d, JCP = 10.7 Hz; Ar-C), 128.6 (d, JCP
11.7 Hz; Ar-C), 129.1 (d, JCP = 4.8 Hz; Ar-C), 129.5 (d, JCP
1.8 Hz; Ar-C), 130.7 (d, JCP = 1.8 Hz; Ar-C), 131.3 (s; Ar-C), tion was carried out at 173(2) K. Temperature was controlled
131.6 (s; Ar-C), 131.8 (d, JCP = 5.4 Hz; Ar-C), 132.3 (s; by an Oxford Cryostream cooling system (Oxford Cryostat). Cell
2
1
1
=
=
Bruker KAPPA APEX II DUO diffractometer using graphite-
monochromated Mo-Kα radiation (χ = 0.71073 Å). Data collec-
2
3
3
3
3
1
Ar-C), 132.9 (d, JCP = 3.1 Hz, Ar-C), 134.2 (d, JCP = 12.1 Hz; refinement and data reduction were performed using the
Ar-C), 134.1 (s; Ar-C), 135.5 (d, JCP = 9.7 Hz; Ar-C), 137.9 (d, program SAINT.62 The data were scaled and absorption correc-
2
2JCP = 15.8 Hz, Ar-C), 142.3 (s; C1), 151.1 (s; C4), 163.0 (d, 3JCP
=
tions were performed using SADABS.63 The structure
5.1 Hz; C6). 31P NMR (CDCl3): 27.1 (s, JPPt = 1830 Hz). ESI-MS: was solved by direct methods using SHELXS-9764 and refined
by full-matrix least-squares methods based on F2 using
m/z 665.59 [M + H]+, 581.45 [M − C4H8].
Preparation of [Pt(C25H21N2P)(C6H12)] (3e). 3e was prepared SHELXL-9764 and using the graphics interface program
by the reaction of [Pt(COD)(C6H12)] (0.25 g, 0.64 mmol) with X-Seed.65,66 The programs X-Seed and POV-Ray67 were both
(2-diphenylphosphanyl-benzylidene)-pyridin-3-ylmethyl-amine used to prepare molecular graphic images. All non-hydrogen
(1e) (0.24 g, 0.64 mmol). The product was obtained as a brown atoms were refined anisotropically. All hydrogen atoms were
oil (0.27 g, 65%). IR (KBr): 1634 cm−1 (νCvN, imine). H NMR positioned geometrically with C–H distances ranging from
1
(CDCl3): 0.76–0.81 (m, 4H; Ha + Hf), 1.37–1.63 (m, 8H; Hb − He), 0.95 Å to 0.98 Å and refined as riding on their parent atoms,
3
3
5.38 (s, 2H, JHPt = 15.9 Hz; H6), 7.09 (1H, dd, JHH = 7.8 Hz, with Uiso(H) = 1.2–1.5Ueq(C). The structure was successfully
9.3 Hz; Ar-H), 7.15–7.24 (4H, m; Ar-H), 7.36–7.40 (4H, m; Ar-H), refined to the R factor 0.0238
7.53–7.57 (3H, m; Ar-H), 7.64–7.64 (1H, m; Ar-H), 7.70–7.72
3
Thermal decomposition reactions
(1H, m; H3), 8.09 (1H, td, JHH = 2.3 Hz; 7.8 Hz, Ar-H),
4
8.32–8.33 (m, 1H; H4), 8.36 (1H, JHH = 1.6 Hz, 5.4 Hz; H2), Thermolysis reactions were carried out in clean, dry, sealed
8.41 (1H, s, 3JHPt = 37.1 Hz; H7), 8.60 (1H, dd, d, 4JHH = 2.0, Hz; evacuated vertical Schlenk tubes of 1 cm o.d. and 10 cm
H1). 13C NMR (CDCl3): 16.8 (d, JCP = 3.3 Hz; Cf), 24.7 (s; Ce), lengths. Decomposition was accomplished by immersion of
2
2
25.4 (s; Cb), 31.4 (s; Cd), 31.7 (Cc), 33.5 (d, JCP = 5.6 Hz; Ca), the tube in a stirred oil bath set at the desired temperature.
67.2 (s; C6), 126.1 (s; C3), 126.4 (s; Ar-C), 129.7 (d, JCP = 12.2 Two procedures were used for the thermal decomposition
Hz; Ar-C), 130.9 (d, JCP = 1.8 Hz; Ar-C), 131.6 (d, JCP = 1.6 Hz; experiments were carried out under solvent free conditions.
1
3
3
2
Ar-C), 132.3 (d, JCP = 7.0 Hz; Ar-C), 132.6 (s; Ar-C), 133.5 (d, For solid complexes, a 20 mg sample was added to the tube
1JCP = 12.4 Hz; Ar-C), 133.9 (s; C4), 134.1 (s; Ar-C), 134.8 (s; C5), and dried under vacuum for at least 3 h before the tube was
2
136.7 (d, JCP = 16.9 Hz; Ar-C), 137.5 (s; Ar-C), 140.1 (s; Ar-C), sealed for thermolysis. For the oils, a 20 mg sample was dis-
148.9 (s; C2), 150.8 (s; C1), 161.9 (d, 3JCP = 6.0 Hz; C7). 31P NMR solved in dichloromethane and transferred into the tube. The
(CDCl3): 26.6 (s, JPPt = 1835 Hz). ESI-MS: m/z 660.61 [M + H]+, solvent was removed under vacuum, and the sample was dried
576.47 [M − C4H8].
for at least 3 h before sealing the tube for thermolysis. The
Preparation of [Pt(C29H28NP)(C6H12)] (3f). 3f was prepared decomposition products were extracted by adding cold toluene
by reaction of [Pt(COD)(C6H12)] (0.21 g, 0.54 mmol) with (0.5 ml) containing n-decane (20 μl) as the internal standard.
(2-diphenylphosphanyl-benzylidene)-(2,4,6-trimethyl-benzyl)-
For the thermal decompositions in solution, a 0.05 ml
amine (1f) (0.23 g, 0.54 mmol). The product was obtained as a aliquot of 0.02 M solution of each sample in toluene was
brown oil (0.23 g, 60%). IR (KBr): 1634 cm−1 (νCvN, imine). added to the tube by syringe. The tubes were connected to a
1H NMR (CDCl3): 0.79–0.93 (m, 4H; Ha + Hf), 1.80–1.91 (m, vacuum line and degassed using three freeze–thaw cycles and
8H; Hb − He), 2.26 (s, 6H; H2 + H2′), 2.43 (s, 3H; H1), 5.53 (2H, then sealed under vacuum. The tubes were then immersed in
s, 3JHPt = 16.4 Hz; H3), 7.07 (d, 2H, 3JHH = 7.8 Hz; Ar-H), 7.13 (d, a heated oil bath held at the desired constant temperature.
2H, 3JHH = 7.3 Hz; Ar-H), 7.33–7.42 (m, 12H; Ar-H), 8.17 (s, 1H, After the appropriate reaction time, the reaction was quenched
2
3JHPt = 35.0 Hz; H4). 13C NMR (CDCl3): 16.7 (d, JCP = 2.6 Hz; by immersion in liquid nitrogen. For the thermolysis in solu-
Cf), 24.3 (s; C2 + C2′), 24.9 (s; C1), 26.2 (s; Ce), 26.9 (s; Cb), 29.1 tion, the decomposition solutions were transferred to a liquid
(s; Cd), 29.4 (s; Cc), 33.3 (d, 2JCP = 6.2 Hz; Ca), 65.9 (s; C3), 127.3 nitrogen-cooled sample vial containing n-decane (20 μl) and
1
(s; Ar-C), 128.2 (s; Ar-C), 128.4 (d, JCP = 9.3 Hz; Ar-C), 129.2 (s; the sample was made up to a total volume of 0.5 ml.
1
Ar-C), 129.5 (d, JCP
=
9.1 Hz; Ar-C), 129.7 (s; Ar-C),
Decomposition products were analyzed by GC or GC-MS.
Products were identified by comparison of retention times to
3
3
129.9 (s; Ar-C), 130.1 (d, JCP = 1.8 Hz; Ar-C), 130.5 (d, JCP
=
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those of authentic commercial samples. Yields were deter- 14 W. J. van Rensburg, C. Grove, J. P. Steynberg, K. B. Stark,
mined by response relative to an internal standard (n-decane).
Response factors were obtained from authentic samples.
J. J. Huyser and P. J. Steynberg, Organometallics, 2004, 23,
1207.
15 C. N. Nenu, P. Bodart and B. M. Weckhuysen, J. Mol. Catal.
A: Chem., 2007, 269, 5.
NMR analysis of thermal decomposition
16 C. Temple, A. Jabri, P. Crewdson, S. Gambarotta,
I. Korobkov and R. Duchateau, Angew. Chem., Int. Ed., 2006,
45, 7050.
17 D. S. McGuinness, A. J. Rucklidge, R. P. Tooze and
A. M. Z. Slawin, Organometallics, 2007, 26, 2561.
18 D. S. McGuinness, D. B. Brown, R. P. Tooze, F. M. Hess,
J.-T. Dixon and A. M. Z. Slawin, Organometallics, 2006, 25,
3614.
A 0.02 M solution of complex 2a in toluene-d8 was prepared
and 0.85 ml aliquots of the solution were transferred to NMR
tubes fitted with J. Young valves and degassed using three
freeze–thaw cycles. The tubes were sealed under vacuum and
allowed to warm to room temperature. The NMR tubes were
then transferred to oil baths set at the required temperature
for each reaction. At appropriate intervals the reaction was
quenched by immersion in liquid nitrogen and 31P NMR
spectra were measured.
19 D. S. McGuinness, P. Wasserscheid, D. H. Morgan and
J.-T. Dixon, Organometallics, 2005, 24, 552.
20 S. J. Schofer, M. W. Day, L. M. Henling, J. A. Labinger and
J. E. Bercaw, Organometallics, 2006, 25, 2743.
21 W. J. van Rensburg, J.-A. van den Berg and P. J. Steynberg,
Organometallics, 2007, 26, 1000.
22 A. J. Rucklidge, D. S. McGuinness, R. P. Tooze,
A. M. Z. Slawin, J. D. A. Pelletier, M. J. Hanton and
P. B. Webb, Organometallics, 2007, 26, 2782.
23 A. K. Tomov, J. J. Chirinos, D. J. Jones, R. J. Long and
V. C. Gibson, J. Am. Chem. Soc., 2005, 127, 10166.
24 D. S. McGuinness, M. Overett, R. P. Tooze, K. Blann,
J.-T. Dixon and A. M. Z. Slawin, Organometallics, 2007, 26,
1108.
Acknowledgements
We gratefully thank the University of Cape Town, the National
Research Foundation (NRF) of South Africa, the Royal Nether-
lands Academy of Arts and Sciences (KNAW) for a Carolina
MacGillavry PhD Fellowship (T.M.) for financial support. We
thank the AngloPlatinum Corporation and Johnson Matthey
for the kind donation of metal salts. Dr Prinessa Chellan is
thanked for proof-reading and revising the manuscript.
25 J. R. Briggs, J. Chem. Soc., Chem. Commun., 1989, 674.
26 R. Emrich, O. Heinnemann, C. W. Jolly, C. Kruger and
G. P. J. Verhovnik, Organometallics, 1997, 16, 1511.
27 S. Kuhlmann, K. Blann, A. Bollmann, J.-T. Dixon, E. Killian,
M. C. Maumela, H. Maumela, D. H. Morgan, M. Pretorius,
N. Taccardi and P. Wasserscheid, J. Catal., 2007, 245,
279.
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