Mono- and diphosphine platinum(0) complexes of methylenecyclopropane, bicyclopropylidene, and allylidenecyclopropane

Article abstract of DOI:10.1021/om200630z

The syntheses of the first platinum complexes with η²- bicyclopropylidene ligands are reported herein. Complexes of the formula [Pt(L)(P-P)] (L = η²-bicyclopropylidene, η²- methylenecyclopropane, P-P = Ph₂P(CH₂)₃PPh ₂, Cyp₂P(CH₂)₂PCyp₂, ^tBu₂P(CH₂)₂P^tBu ₂, ^tBu₂PCH₂(o-C₆H ₄)CH₂P^tBu₂) were synthesized by addition of the free alkene to ethene precursor complexes. Bicyclopropylidene underwent a ring-opening reaction with both Pt(0) and Pt(II) complexes to form allylidenecyclopropane, and the first allylidenecyclopropane complexes were synthesized, some of which underwent a rearrangement to form η²:σ²-metallacyclo-3-pentene complexes. Mixed alkene complexes [Pt(C₂H₄)(L)(PR₃)] (L = η²-bicyclopropylidene, η²-methylenecyclopropane, PR₃ = PPh₃, PCy₃) and bis-methylenecyclopropane complexes [Pt(MCP)₂(PR₃)] (PR₃ = PPh ₃, PCy₃) were synthesized by the addition of the free alkene to bis-ethene precursors.

Full text of DOI:10.1021/om200630z

ARTICLE
pubs.acs.org/Organometallics
Mono- and Diphosphine Platinum(0) Complexes of
Methylenecyclopropane, Bicyclopropylidene, and
Allylidenecyclopropane
Sarah A. Hoyte* and John L. Spencer*
School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand
S Supporting Information
b
ABSTRACT: The syntheses of the first platinum complexes
with η2-bicyclopropylidene ligands are reported herein. Com-
plexes of the formula [Pt(L)(PꢀP)] (L = η2-bicyclopropyli-
dene, η2-methylenecyclopropane, PꢀP = Ph2P(CH2)3PPh2,
t
t
Cyp2P(CH2)2PCyp2, Bu2P(CH2)2PtBu2, Bu2PCH2(o-C6H4)-
CH2PtBu2) were synthesized by addition of the free alkene to
ethene precursor complexes. Bicyclopropylidene underwent a
ring-opening reaction with both Pt(0) and Pt(II) complexes to
formallylidenecyclopropane, and thefirst allylidenecyclopropane
complexes were synthesized, some of which underwent a re-
arrangement to form η2:σ2-metallacyclo-3-pentene complexes.
Mixed alkene complexes [Pt(C2H4)(L)(PR3)] (L = η2-bicyclopropylidene, η2-methylenecyclopropane, PR3 = PPh3, PCy3) and bis-
methylenecyclopropane complexes [Pt(MCP)2(PR3)] (PR3 = PPh3, PCy3) were synthesized by the addition of the free alkene to bis-
ethene precursors.
’ INTRODUCTION
phosphines not only stabilize transition metal complexes, but
also allow the coordination of only one alkene ligand, thus
preventing possible oligomerization reactions. The diphosphines
used in this research were 1,3-bis(diphenylphosphino)propane
(dppp), 1,2-bis(dicyclopentylphosphino)ethane (dcyppe), 1,2-
bis[(di-tert-butylphosphino)methyl]benzene (dbpx), and 1,2-
bis(di-tert-butylphosphino)ethane (dbpe). Ethene complexes
were chosen as suitable precursors due to the ease of displace-
ment of the ethene ligand and the simplicity of the NMR spectra
of both the free and coordinated ethene, which facilitates the
monitoring of the reactions. A range of methods were used to
synthesize the various ethene complexes, the choice of method
dictated by the diphosphine ligand. The complexes [Pt(C2H4)
(dbpx)] and [Pt(C2H4)(dbpe)] were synthesized by adding the
diphosphine to [Pt(C2H4)3], generated in situ from [Pt(1,5-
cyclooctadiene)2] ([Pt(COD)2]).9 This method was unsuitable
for the synthesis of [Pt(C2H4)(dppp)], as the coordination of a
second dppp ligand to form [Pt(dppp)2] is very facile. Instead,
the ethene complex was generated by the reduction of [PtCl2-
(dppp)] under an ethene atmosphere using NaBH4. While the
reaction of dcyppe with [Pt(C2H4)3] yielded [Pt(C2H4)(dycppe)],
problems with purification meant that this was not a viable synthesis
method. The NaBH4 method was attempted, but was not success-
ful. Instead, [Pt(C2H4)(dycppe)] was synthesized by the reduction
of [PtCl2(dcyppe)] using sodium amalgam. Complexes of 1,
Bicyclopropylidene (BCP) and methylenecyclopropane (MCP)
belong to a class of alkenes that contain cyclopropyl rings with
exocyclic double bonds. These alkenes have a rich chemistry and are
active toward transition metal catalysts, particularly those of the
group 10 metals.1ꢀ4 However, the isolation of transition metal
complexes containing these alkenes in η2-coordination has not
received as much focus as their reactivity. Only a handful of η2-MCP
complexes have been reported to date,5ꢀ8 while there have been just
two of η2-BCP, both of first-row transition metals.7,8 A better
understanding of the coordination chemistry of these interesting
alkenes could provide valuable insight into their reactivity patterns.
Despite the lack of isolated complexes, MCP and BCP are expected
to be good ligands toward transition metals, with their high-lying
HOMOs capable of effectively donating electron density into empty
metal orbitals,2,7 while alleviation of strain in the highly strained
cyclopropyl rings upon coordination is a strong driving force for the
formation of stable complexes. As platinum(0) is a strong π-donor,
capable of effective back-donation, it is ideal for making the first late
transition metal complexes of BCP. The successful synthesis of the
Pt(0) complex [Pt(MCP)(PPh3)2] is a strong indication of the
viability of such complexes.5
’ RESULTS AND DISCUSSION
[Pt(L)(PꢀP)] Complexes. A range of Pt(0) complexes con-
taining chelating diphosphine auxiliary ligands were used as
precursors. These complexes were chosen because chelating
Received: July 13, 2011
Published: September 21, 2011
r
2011 American Chemical Society
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2-bis(diphenylphosphino)ethane (dppe) were considered, as these
would have made a good comparison for the dppp complexes.
However, [Pt(C2H4)(dppe)] could not be synthesized from
[Pt(C2H4)3] due to the facile formation of [Pt(dppe)2], while
reduction methods yielded only [Pt3H3(dppe)3]+. This is because
the intermediate hydride complex in the reduction is dimeric for
dppe, rather than monomeric as for dppp.10,11 While the synth-
esis of [Pt(C2H4)(dppe)] using sodium naphthalenide has been
reported, this method did not involve the isolation of the pure
ethene complex, which meant that this synthesis was not suitable
for the NMR-scale studies undertaken here.12
Methylenecyclopropane was made by the reaction of methallyl
chloride with sodium amide and potassium tert-butoxide,13 while
the synthesis of bicyclopropylidene made use of the Kulinkovich
reaction to produce cyclopropylcyclopropanol, which was then
converted to the bromide followed by dehydrobromination to
produce the alkene.14 BCP and MCP complexes were synthe-
sized via the displacement of the ethene ligand from the pre-
cursor complexes. This was done by dissolving the ethene com-
plex in either toluene or d6-benzene and adding an excess of the
appropriate alkene, producing the diphosphine complexes
[Pt(BCP)(PꢀP)] (1) and [Pt(MCP)(PꢀP)] (2) (PꢀP = dppp
(a), dcyppe (b), dbpe (c), dbpx (d)) (Scheme 1).
Scheme 1. Synthesis of [Pt(BCP)(PꢀP)] and
[Pt(MCP)(PꢀP)]
Whereas BCP is an easily handled liquid, MCP is a gas at room
temperature, with a boiling point of 10 °C. For this research, it
was deemed most practical to use MCP by cooling a glass syringe
and then rapidly injecting a small amount of the liquid alkene into
the reaction vessel. The formation rates of the complexes were
dependent on both the size of the alkene and the size of the
diphosphine ligand. MCP, with only one cyclopropyl ring (cPr),
coordinated more rapidly than BCP, with two rings. The steric
Table 1. Selected NMR Data of [Pt(L)(PꢀP)]a
2
2
1
1
compound
δP
1JPtꢀP JPꢀP
δH cPr JPtꢀH
δ
H dCHR JPtꢀH δC cPr JPtꢀC
δ
C dCR2 JPtꢀC
δ
C dCHR JPtꢀC
BCP
MCP
ACP
1.18
0.90
0.93
0.85
3.33
110.61
131.06
129.33
5.46
6.58
2.94
2.64
2.28
8.82
103.49
136.88
[Pt(BCP)(dppp)]
1a 9.29
2932
1.29
66.0
23.1
34.25
410.8
1.18
37.7
b
[Pt(BCP)(dcyppe)] 1b 70.77 2731
1.5ꢀ1.4
1.57
10.43 23.1
33.76
31.77
424.6
428.9
b
b
[Pt(BCP)(dbpe)]
[Pt(BCP)(dbpx)]
[Pt(MCP)(dppp)]
1c 97.43 2798
9.89
23.7
1.31
1d 43.31 2983
1.34
61.2
32.0
33.0
9.87
22.5
29.27
42.67
38.25
36.81
456.3
455.4
501.0
511.4
0.99
2a 11.73 3275 42
trans dCH2 1.65
2.63
2.40
2.39
2.12
3.78
3.41
3.43
65.3 10.08 25.9
60.5 12.30 23.0
60.6 11.82 24.5
56.2 11.41 25.0
25.29
22.35
23.54
173.4
169.0
171.6
11.35 2975
trans dCR2 1.32
trans dCR2 1.95
trans dCH2 1.80
trans dCR2 1.89
trans dCH2 1.79
trans dCH2 1.60
trans dCR2 1.60
trans dCHR 1.3ꢀ0.8
82.5
b
[Pt(MCP)(dcyppe)] 2b 75.03 2751 63
b
70.83 3107
[Pt(MCP)(dbpe)]
[Pt(MCP)(dbpx)]
[Pt(ACP)(dppp)]
2c 100.84 2807 66
99.15 3167
33.6
60.0
b
2d 49.25 3362 30
43.74 3025
33.61
537.6
27.83
164.2
b
b
b
b
b
b
b
b
b
b
3a 10.34 3293 39
67.8
62.1
9.67
3003
trans dCR2
b
b
b
b
b
b
[Pt(ACP)(dcyppe)] 3b 69.97 3153 ꢀ59 trans dCHR
68.60 2771
3c 96.40 2848 62
96.39 3196
trans dCR2
b
b
[Pt(ACP)(dbpe)]
trans dCR2 1.5
trans dCHR 1.0
62.0 10.60 17.7
9.47 15.5
41.43
533.1
44.72
165.5
[Pt(C2H4)(dppp)]
[Pt(C2H4)(dcyppe)]
[Pt(C2H4)(dbpe)]
[Pt(C2H4)(dbpx)]
13.76 3340
2.68
2.38
2.41
2.20
60.0
58.0
59.4
57.3
31.85
23.18
24.95
27.20
216.0
227.4
229.0
217.0
75.44 3170
102.54 3230
50.10 3493
a δ values are given in ppm and J values in Hz. All spectra were measured in C6D6 at room temperature. b NMR data could not be obtained.
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ARTICLE
131.0 to 33ꢀ43 ppm for 2. The methylene carbon was typically
∼15 ppm upfield of the cPr carbon, except for in 2d, where the
difference was only 5.8 ppm. For comparison, the methylene
chemical shift differed from that of the parent ethene ligand
by 0.6ꢀ6.6 ppm. A stronger PtꢀC bond is formed to the cyclo-
propyl carbons in 1 and 2 than to the methylene carbons in 2
and the parent ethene complexes. This is evidenced by the
lower 1JPtꢀP of the P trans to the cyclopropyl carbons and the
higher 1JPtꢀC coupling constants of these carbons and is a result
of the decrease in strain energy of the cPr rings by rehybridiza-
tion upon coordination.15ꢀ19
For the double-bond carbons in 1, the line shape was character-
istic of a “false AA0X” spin system (A, A0 = 31P, X = 13C) with 195Pt
satellites due to both the magnetic inequivalence of the two
chemically equivalent carbons when one was 13C and the two
31P atoms having the same chemical shift (Figure 1b).20,21 The
double-bond carbons in 2, however, were ABX systems with 195Pt
satellites, as the two 31P atoms were in different chemical
environments.21 These 13C NMR peaks, and the 31P NMR spectra
of 2, indicate that the alkene ligands do not rotate at room
temperature when coordinated, as rotation would result in the
two 31P atoms becoming equivalent.
X-ray quality crystals of 1a were grown by recrystallization
from toluene, and an X-ray crystal structure was obtained
(Figure 2). The BCP CdC bond length increased from
1.304(2) Å in the free alkene to 1.427(3) Å in 1a, an increase
of 9.4%.22 This was greater than the 7.4% increase observed
for [Co(BCP)(η5:η1[2-(di-tert-butylphosphanyl-P)ethyl]cyclo-
pentadienyl)], which had a CdC bond length of 1.401(5) Å.8
The bond length of 1a was closer to that of the comparable CꢀC
bond in bicyclopropyl (1.487(4) Å, differing from 1a by 0.06 Å)
than to the CdC bond length of free BCP (differing from 1a by
Figure 1. (a) 31P NMR spectrum of 2a. (b) 13C NMR spectrum of the
double-bond carbons of 1a.
c
0.123 Å).23 The two Pr rings in 1a were bent by 36.02° and
37.14° away from the plane of the double bond. The correspond-
ing angles in the cobalt complex were 39.33° and 41.04°, while in
bicyclopropyl the rings were at 54.72° to the central CꢀC bond.
bulk of the substituents on the phosphine ligands had a more
significant effect on the formation rates. Complexes of dppp
formed most rapidly, with the reaction occurring almost instantly
at room temperature. Complexes of dcyppe reacted more slowly,
c
There was a decrease in the Pr ring angle centered on the
double-bond carbon atom from 63.3(1)° to 61.40(14)° and
61.37(15)° upon coordination and a concomitant shortening of
the distal ring bond from 1.539(2) Å to 1.516(3) and 1.519(3) Å.
This effect was greater in the Co complex, with angles and distal
bond lengths of 61.15° and 1.499(12) Å, respectively. The
increase of the CdC bond length, the out-of-plane bend of the
cPr rings, and the shortening of the ring bond and angle were all
indicative of the large degree of back-donation and subsequent
rehybridization of the double-bond carbon atoms upon
coordination.8,24
The dppp backbone adopted a chair conformation, with a
PꢀPtꢀP angle of 96.762(19)°. A recent search of the Cambridge
Crystallographic Database showed that of 81 dppp complexes
with one or two platinum atoms, 86% adopted a chair conforma-
tion and 9% adopted a boat, while 5% were not sufficiently
resolved to determine the conformation. Four of the 81 com-
plexes were Pt(0) species, and of the four, three were trigonal-
planar complexes. All four Pt(0) complexes had dppp in a chair
conformation.25ꢀ27 These complexes had PꢀPtꢀP angles of
90.99ꢀ97.76°, with that of 1a falling at the top end of the range.
Allylidenecyclopropane: Formation and Coordination
Chemistry. It was found that when BCP reacted with
[Pt(C2H4)3], a ring-opening reaction occurred to form the 1,3-
diene, allylidenecyclopropane (ACP) (Scheme 2). This reaction
also occurred with [Pt(COD)2], [PtMe2(1,5-hexadiene)], and
t
forming overnight at room temperature. Both of the Bu phos-
phines required heating, overnight at 40 and 60 °C for 2c and 2d,
respectively, and for up to 6 days at 60 °C for 1c and 1d. The
dependence of reaction rate on steric bulk points to an associative
exchange mechanism.
The magnitude of the platinumꢀphosphorus 1JPtꢀP coupling
constants in the 31P NMR spectra of 1 and 2 showed that the
alkenes were in η2-coordination. In the BCP complexes, 1JPtꢀP
values were between 2731 and 2983 Hz (Table 1), ∼450 Hz less
than those in the parent ethene complex. The 31P NMR spectra
of 2 had second-order ABX (A, B = 31P, X = 195Pt) peak patterns
due to the asymmetry of the alkene and the rigid coordination
1
geometry (Figure 1a). The JPtꢀP values could be used to
distinguish the P trans to the cPr group from that of the P trans
to the methylene in the MCP complexes, as the two coupling
constants were comparable to those of 1 and the parent ethene
complexes, respectively.
The 13C NMR spectra also clearly showed that the alkenes
were in η2-coordination. The cyclopropyl double-bond carbons
showed large 1JPtꢀC values, 410ꢀ456 Hz for 1 and 455ꢀ538 Hz
1
for 2 (Table 1), while the methylene carbon in 2 had JPtꢀC
values several hundred Hz less (164ꢀ173 Hz). There was also a
c
large upfield shift of the Pr double-bond carbon resonances
upon coordination, from 110.6 to 29ꢀ34 ppm for 1 and from
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Scheme 3. Synthesis of [Pt(ACP)(PꢀP)]
Scheme 4. Synthesis of [Pt(ACP)(dbpe)]
of BCP and [Pt(COD)2] to solutions of [Pt(C2H4)(dbpe)],
followed by heating at 40 °C, was used to synthesize 3c (Scheme 4).
With 10% [Pt(COD)2] present, the reaction reached 97% com-
pletion after heating overnight. The formation of 3c still occurred
when no detectable [Pt(COD)2] was present; however, this reac-
tion only reached 88% completion after 13 days. [Pt(ACP)(dbpx)]
could not be synthesized, likely due to the bulk of the phosphine
ligand making coordination of the alkene unfavorable.
Figure 2. ORTEP diagram of 1a showing 50% probability thermal
ellipsoids. H atoms have been omitted for clarity.
It was found that when both ACP and BCP were present in the
reaction mixture, ACP complexes formed initially. However, the
ACP ligand in 3a was slowly displaced by BCP over several hours
at room temperature to generate 1a. For the dbpe complexes, 3c
was the only product at 40 °C, while at 60 °C, 3c formed initially
before continued heating over several days produced 1c. It was
unclear whether this would also happen for the dcyppe com-
plexes, as 3b underwent a rearrangement that reached comple-
tion too rapidly for displacement to occur (see below). From this
we inferred that the complexes of the less bulky ACP were the
kinetic products, while the BCP complexes, which had a degree
of extra stabilization afforded by alleviation of strain in the second
cyclopropyl ring, were the thermodynamic products.
Scheme 2. Synthesis of Allylidenecyclopropane from
Bicyclopropylidene
[Pt(norbornene)3]. One previous instance of the formation of
ACP from BCP has been reported, occurring in the reaction of
BCP with [Pd(OAc)2] and PPh3.28 The proposed mechanism
for this reaction involved the addition of a palladium hydride
across the BCP double bond, followed by a cyclopropylmethyl to
homoallyl rearrangement and terminated by β-hydride elimina-
tion. Under the reported conditions, ACP went on to react with
another molecule of BCP to form various oligomers. However,
no oligomerization reactions were observed with the above Pt
complexes, even after several days at 60 °C.
As there were no published reports of any transition metal
chemistry with ACP, the formation of Pt-diphosphine complexes
containing ACP ligands was investigated. A solution of ACP was
produced for these reactions by dissolving a few crystals of
[PtMe2(1,5-hexadiene)] in either CDCl3 or C6D6 under inert
atmosphere and adding a small amount of BCP. The reaction
could then be monitored by NMR for completion, typically
reaching ∼95% after 5 days. The solution was then used without
further purification.
All ACP complexes exhibited second-order ABX 31P NMR
spectra similar to the corresponding MCP complexes, with 1JPtꢀP
couplings for both phosphine environments within 40 Hz of
those in 2 (Table 1). The 1H NMR peak of the internal double-
bond proton had a large upfield shift from 6.6 ppm in free ACP to
2
3.4ꢀ3.8 ppm in 3 (Table 2). The magnitudes of the JPtꢀH
coupling constants of these protons, 62ꢀ68 Hz, were typical of
coordination through this bond. The protons of the terminal
double-bond have chemical shifts much closer to those in the free
alkene. Both the 1H and 31P NMR data indicated that ACP was
coordinated via the internal rather than the terminal double-
bond, as would be expected given the stabilization afforded by the
alleviation of ring strain in the cPr ring upon coordination.
1
The JPtꢀC coupling constants of the internal double-bond
carbons of 3c further indicated that the alkene had coordinated
via this bond. The coupling constant for the cyclopropyl carbon
was 533 Hz, while that of the methyne was 166 Hz, both of which
were within 20 Hz of the corresponding value for 2c (Table 1).
The chemical shifts of the carbons of the terminal double-bond
were also much closer to those of the free alkene than the internal
The first transition metal complexes of allylidenecyclo-
propane (3a and 3b) formed immediately upon addition of the
ACP solution to the parent ethene complex [Pt(C2H4)(PꢀP)]
(PꢀP = dppp, dcyppe) (Scheme 3). ACP could also be gen-
erated in situ fromsmall amounts of [Pt(COD)2], and the addition
c
double-bond carbons (Table 2). In 3c, the Pr double-bond
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1
Table 2. H and 13C NMR Data of [Pt(ACP)(PꢀP)]a
δC
δH
internal dCHR
compound
ACP
dCH2
terminal dCHR
internal dCHR
dCR2
cPr
dCH2
terminal dCHR
cPr
115.19
120.18
136.88
129.33
2.64
5.18
5.05
5.04
4.69
4.85
4.37
4.98
4.64
6.49
6.58
0.93
2.28
b
0.85
b
b
b
b
b
b
b
b
[Pt(ACP)(dppp)]
[Pt(ACP)(dcyppe)]
[Pt(ACP)(dbpe)]
3a
3b
3c
6.47
6.11
6.20
3.78
1.3ꢀ0.8
2JPtꢀH = 67.8 Hz
3.41
2JPtꢀH = 62.1 Hz
3.43
2JPtꢀH = 62.0 Hz
b
b
102.71
147.52
44.72
41.43
10.6
9.47
1.5
1.0
a δ values are given in ppm and J values in Hz. All spectra were measured in C6D6 at room temperature. b NMR data could not be obtained.
Scheme 5. Rearrangement of [Pt(ACP)(PꢀP)] to Form
Scheme 6. Synthesis of [Pt(BCP)(C2H4)(PR3)]
Metallocyclopentene Complexes
previously reported Pt metallacycles, the CH2 groups directly
carbons had an AA0X line shape with 195Pt satellites similar to
those of the BCP complexes. This was due to the two phosphorus
atoms in this complex coincidentally having the same chemical
shift.21 The effect could be seen throughout the carbon spectrum,
with all of the resonances of the ACP ligand showing AA0X line
shapes. It would be expected that the ACP ligands in 3a and 3b
would have ABX spectra (with 195Pt satellites) similar to the
corresponding MCP complexes, as the phosphorus atoms have
different chemical shifts. However, due to the short lifetimes of
these complexes, 13C NMR data could not be obtained.
Complexes 3a and 3b were unstable in solution, undergoing a
rearrangement to form the metallacyclic complexes 4a and 4b
(Scheme 5). The rearrangement proceeded more rapidly for the
dcyppe complex 3b, with significant amounts of 4b present
within 5 min of addition of the ACP solution and the reaction
proceeding to completion after 3 h. For the dppp complex 3a, the
metallacycle appeared in the 31P NMR after 3 h, reaching 96%
completion after 7 days.
2
bonded to the metal had δH at 2.8ꢀ3.2 ppm with JPtꢀH
=
1
68ꢀ92 Hz and δC at 31ꢀ41 ppm with JPtꢀC = 603ꢀ787
Hz,32,44 while the Ir metallacycles had 2.4ꢀ3.0 and ꢀ2ꢀ13
ppm for δH and δC, respectively.41 The NMR data of both the
PtꢀCH2 groups (δH = 2.9ꢀ3.2 ppm, 2JPtꢀH = 62ꢀ73 Hz, δC =
29ꢀ39, 1JPtꢀC = 297ꢀ450 Hz) and the PtꢀCR3 groups (δC =
1
32ꢀ33, JPtꢀC = 959 Hz for 4b) in 4 agree well with the
literature. The NMR data of the double-bond carbons and
their attached protons (δH = 5.3ꢀ6.4 and δC = 131ꢀ154) also
compared favorably to the literature values (δH = 5.0ꢀ5.6 and
δC = 135.9ꢀ151.3 ppm).32,41,44
The rearrangements of 3 to 4 appear to be the first instances of
the formation of η2:σ2-metallacyclopentene complexes from
η2:π-diene complexes. Previously reported η2:σ2-metallacyclo-
pentenes were formed either directly upon addition of the 1,3-
diene to a metal precursor32ꢀ34,37ꢀ39,44ꢀ46 or by rearrangement
of an η4:π-diene complex, generally initiated by the addition of a
species such as a Lewis base.35,36,41,43
[Pt(L)2(PR3)] Complexes. Precursor complexes containing
two ethene ligands and one phosphine ligand were also investi-
gated. Bis-ethene complexes were chosen due to the possibility
that oligomerization or isomerization reactions similar to the
formation of ACP from BCP might occur. Complexes of the type
[M(L)(BCP)(PR3)] (M = Ni, Pd, L = electron-deficient alkene,
PR3 = tert-butyldiisopropylphosphine, tris(o-phenylphenyl)pho-
sphite) have been proposed as intermediates in the palladium-
and nickel-catalyzed [3+2] co-cyclization of BCP with various
alkenes, but were not isolated.47 Bis-BCP complexes have also
been postulated to be intermediates in the nickel-catalyzed
[3+2+2] co-cyclizations.48
The formation of metallacyclo-3-pentenes from 1,3-dienes
is well established. There are two possible binding modes for
these ligands: the η4:σ2,π mode, where the double bond is
also coordinated to the metal, common for early transition
and actinide metals,29ꢀ31 and the planar η2:σ2 mode. Planar
metallacyclopentene complexes are considered to be inter-
mediates in ring-flipping mechanisms of η4-diene
complexes,32 and complexes with η2:σ2-metallacyclopentene
ligands formed from various 1,3-dienes have been reported for
Fe,33,34 Co,35 Mo,36 W,36 Rh,32,37ꢀ39 Ir,40ꢀ43 Pt,32,44 Ge,45
and Mg.46 The NMR data of 4 were consistent with a planar
1
η2:σ2-metallacyclopentene structure. The JPtꢀP coupling
When BCP was added to [Pt(C2H4)2(PR3)], the product was
[Pt(C2H4)(BCP)(PR3)] (5) (PR3 = PPh3 (a), PCy3 (b))
(Scheme 6). For the bulkier PCy3, complex 5b was stable with
an excess of BCP. However, 5a was stable in solution only when 1
constants of 4 (1784ꢀ1856 Hz) were comparable to those of
[Pt(CH2CPhdCHCdCMe2)(dppe)] (1818 and 1842 Hz),
which showed that there were PtꢀC σ-bonds in 4.32 In the
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Scheme 7. Synthesis of [Pt(MCP)(C2H4)(PR3)] and
[Pt(MCP)2(PR3)]
equiv of BCP was used. When more than 1 equiv was used,
[Pt(BCP)(PPh3)2] began to form after 40 min and was the only
phosphine-containing product after 24 h. The formation of a bis-
BCP complex did not occur with either of the phosphines used in
this work. This was likely due to the steric constraints of having
the two alkenes in a planar coordination geometry as occurs with
platinum(0).49 The double-bond carbons of the BCP ligand had
similar chemical shifts (29ꢀ30 ppm) and 1JPtꢀC (431ꢀ483 Hz)
to those in 1, indicating that it was in η2-coordination (Table 3).
The 1JPtꢀP coupling constants in both mixed alkene complexes
were ∼330 Hz lower than those of the parent bis-ethene
complexes, showing the same decrease in 1JPtꢀP upon coordina-
tion of BCP as was seen for the diphosphine complexes.
Despite the large excesses of MCP used, both the mixed alkene
[Pt(C2H4)(MCP)(PR3)] (6) and the bis-MCP [Pt(MCP)2(PR3)]
(7) (PR3 = PPh3 (a), PCy3 (b)) complexes were always formed in a
closed system (Scheme 7). The bis-MCP complexes 7 are the first
examples of Pt-MCP complexes with more than one MCP ligand.
When PPh3 was used, the product ratio was 80:20 bis-MCP:mixed
alkene. The ratio changed to 30:70 in favor of the mixed complex
when PCy3 was used, with the bulkier phosphine hindering but not
preventing the coordination of the second MCP ligand. When ethene
was allowed to diffuse out of the reaction, complex 7a was formed in
90% yield. Yields could be improved and complex 7b formed
selectively when inert gas was bubbled through the reaction mixture.
The mixed alkene complexes 6 became the major products when
ethene was bubbled through the solution. However, the mixed alkene
complexes were much less stable than the bis-MCP complexes, as
large amounts of ethene regenerated the bis-ethene complexes, while
in the presence of free MCP, 7 formed.
1
The mixed etheneꢀMCP complexes had JPtꢀP couplings
within 10 Hz of the etheneꢀBCP complexes 5 (Table 3). 13C
NMR data could not be obtained for these complexes due to their
1
instability. However, their H NMR spectra showed similar
chemical shifts and 2JPtꢀH for the ethene ligands to 5. The bis-
MCP complexes 7 had 1JPtꢀP several hundred Hz lower than the
parent ethene complex and more than 150 Hz lower than the
mixed alkene complex (Table 3). The MCP methylene reso-
nances in the 1H NMR were also at lower chemical shifts than in
the mixed complex and had lower 2JPtꢀH (50ꢀ55 Hz), closer to
those of the ethene rather than the MCP ligand in 6. Both the
carbon and proton NMR data showed that the two MCP ligands
were in the same chemical environment on the NMR time scale.
While this could be due to rotation of the ligands, it was
considered more likely that the ligands were arranged either
head-to-head or tail-to-tail. The X-ray crystal structure of 7a
showed that in the solid state the two MCP ligands were tail-to-
tail (Figure 3).
The MCP carbonꢀcarbon double-bond length was increased
by 5.7% upon coordination, from 1.332(1) Å in free MCP to
1.408(5) Å in 7a.50 In [Rh(MCP)2(acac)], the only other MCP
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using Mo Kα radiation. Data were reduced using Bruker SAINT
software. Absorption correction was performed using the SADABS
program. The structures were solved using OLEX2 running SHELXS97
and SHELXL97.57,58 The positions of all hydrogen atoms were calcu-
lated during refinement.
Synthesis of [Pt(BCP)(dppp)] (1a). [Pt(C2H4)(dppp)] (0.162
g, 0.28 mmol) was dissolved in toluene (3.5 mL). Bicyclopropylidene
(0.052 mL, 0.56 mmol) was added, and the solution stirred for 30 min.
The solvent was removed in vacuo, yielding an off-white solid
([Pt(BCP)(dppp)], 158 mg, 0.23 mmol, 82%). Crystals of [Pt(BCP)-
(dppp)] were grown by slow recrystallization from hot toluene.
1H NMR (δ, C6D6): 7.57(m, 8H, o-C6H5), 7.04(m, 8H, m-C6H5),
6.98(m, 4H, p-C6H5), 2.13(m, 4H, PꢀCH2), 1.51(m, 2H, CH2),
c
1.29(m, JPtꢀH = 66.0 Hz, 4H, Pr-endo), 1.18(d, 4.4, JPtꢀH = 37.3
c
Hz, 4H, Pr-exo). 13C NMR (δ, C6D6): 136.79(m, i-C6H5), 132.92(m,
o-C6H5), 129.54(s, p-C6H5), 128.35(s, m-C6H5), 34.25(m, JPꢀC = 73.3,
ꢀ9.1, JPꢀP = 24.5, JPtꢀC = 409.4 Hz, dCR2), 28.51(m, PꢀCH2), 20.93(m,
CH2), 8.82(s, JPtꢀC = 23.1 Hz, cPr). 31P NMR (δ, C6D6): 9.29(s, 1JPtꢀP
=
2932 Hz). m/z = [M + H]+ calcd for C33H35P2194Pt 687.1841; found
687.1849. Anal. Calcd for C33H34P2Pt: C 57.64; H 4.98. Found: C 57.76;
H 4.96.
Figure 3. ORTEP diagram of 7a showing 50% probability thermal
ellipsoids. H atoms have been omitted for clarity.
Synthesis of [Pt(MCP)(dppp)] (2a). [Pt(C2H4)(dppp)] (87 mg,
0.14 mmol) was dissolved in toluene (1 mL). A large excess of
methylenecyclopropane was added, and the solution stirred for 30 min.
The solvent was removed in vacuo, yielding an off-white solid
complex characterized by X-ray diffraction, the bond lengths
were 1.405(19) and 1.440(19) Å, representing increases of 5.4%
and 8.1%, respectively. The increase in MCP bond length upon
coordination was much greater than the 1.5% increase in ethene
CdC bond length in the related complex [Pt(C2H4)(C2F4)-
(PCy3)].51,52 The C2F4 bond increased by 10.0% upon
coordination.53 The cyclopropyl rings in 7a were bent by
35.49° and 35.86° away from the plane of the double bond, a
greater angle than those in the Rh complex (26.48° and 27.79°).
Given the strain of the cPr ring, it would be expected that there
was a stronger bond from the platinum to the ring double-bond
carbon than to the methylene carbon. This was evidenced by the
shorter PtꢀC distance to the cPr carbon (2.087(3) and 2.093(3)
Å) than to the methylene (2.130(3) and 2.123(3) Å). The PtꢀP
bond length was 2.3028(7) Å, shorter than that in [Pt(C2H4)-
(C2F4)(PCy3)], which had a PtꢀP distance of 2.343(2) Å.
1
([Pt(MCP)(dppp)], 79 mg, 0.13 mmol, 92%). H NMR (δ, C6D6):
7.77(t, 9 Hz, 4H, o-C6H5ꢀP1), 7.51(t, 8.5 Hz, 4H, o-C6H5ꢀP2),
7.05(m, 8H, m-C6H5), 7.00(m, 4H, p-C6H5), 2.63(dd, JPꢀH = 7.7, 4.5,
JPtꢀH = 65.3 Hz, 2H, dCH2), 2.17(m, 4H, PꢀCH2), 1.65(d, 6.5, JPtꢀH
=
33.0 Hz, 2H, cPr-exo), 1.59(m, 2H, CH2), 1.32(d, 9.5, JPtꢀH = 82.5 Hz,
c
2H, Pr-endo). 13C NMR (δ, C6D6): 138.36(m, i-C6H5ꢀP1), 136.88-
(m, i-C6H5ꢀP2), 133.17(m, o-C6H5ꢀP1), 132.84(m, o-C6H5ꢀP2),
129.44(m, p-C6H5), 128.36(m, m-C6H5), 42.67(dd, JPꢀC = 57.3, 5.0,
JPtꢀC = 455.4 Hz, dCR2), 28.84(m, PꢀCH2), 25.29(dd, JPꢀC = 36.4, 4.9,
JPtꢀC = 173.4 Hz, dCH2), 20.95(m, CH2), 10.08(d, JPꢀC = 3.8, JPtꢀC
=
=
c
1
25.9 Hz, Pr). 31P NMR (δ, C6D6): 11.76(AB, JPꢀP = 41.5, JPtꢀP
3275 Hz, P2, trans = CH2), 11.35(AB, JPꢀP = 41.5, 1JPtꢀP = 2975 Hz, P1,
trans = CR2). m/z = [M + H]+ calcd for C31H33P2194Pt 661.1684; found
661.1678. Anal. Calcd for C31H32P2Pt: C 56.28; H 4.87. Found: C 56.47;
H 4.86.
’ EXPERIMENTAL SECTION
General NMR Synthesis of [Pt(L)(PꢀP)] (L = BCP (1), MCP
(2), PꢀP = dcyppe (b), dbpx (c), dbpe (d)). [Pt(C2H4)(PꢀP)]
(20ꢀ50 mg) was dissolved in C6D6 (0.5 mL) and placed in an NMR
tube. An excess of the alkene was added. For PꢀP = dbpx, the reactions
were heated at 60 °C for up to 6 days, for PꢀP = dcyppe, the reactions
occurred overnight at RT, and for PꢀP = dbpe the reaction was heated
overnight at 40 °C. Yields by NMR ranged from 96% to 100%.
General NMR Synthesis of [Pt(ACP)(PꢀP)] (3) and
[Pt(CH2CHdCHC(CH2)2)(PꢀP)] (4) (PꢀP = dppp (a), dcyppe
(b)). A few crystals of [PtMe2(1,5-hexadiene)] were placed in an NMR
tube, and CDCl3 (0.5 mL) was added. BCP (0.2 mL, 18.7 mmol) was
added, and the reaction left for 3 days, after which all of the BCP had
reacted to form ACP. [Pt(C2H4)(PꢀP)] (30ꢀ100 mg) was placed in an
NMR tube, and C6D6 (0.5 mL) added. A solution of ACP (0.1 mL, 27 M
solution in CDCl3) was added, resulting in the immediate formation of
[Pt(ACP)(PꢀP)]. After several hours, the complex rearranges to form
General Considerations. All reactions were carried out using
degassed solvents and standard Schlenk techniques under either a
nitrogen or argon atmosphere, unless otherwise stated. Starting materi-
als were purchased from Sigma-Aldrich and used without further
purification unless otherwise stated. Bicyclopropylidene,14 methylene-
cyclopropane,13 [PtCl2(dppp)],54 [Pt(C2H4)(dbpx)],9 [Pt(C2H4)
(dbpe)],9 [Pt(C2H4)2(PPh3)],55 and [Pt(C2H4)2(PCy3)]55 were syn-
thesized according to literature methods. The synthesis of dbpx was via
the deprotection of dbpx-borane56 using neat diethylamine, while
dcyppe was synthesized by the reaction of cyclopentylmagnesium
bromide with 1,2-bis(dichlorophosphino)ethane. Deuterated solvents
were purchased from Sigma-Aldrich and stored under a nitrogen atmo-
sphere. NMR spectra were measured on Varian Unity Inova 300 and 500
MHz and Varian DirectDrive 600 MHz NMR spectrometers, with
chemical shift values δ referenced to the residual solvent peaks for 1H
and 13C{1H} and to 85% H3PO4 for 31P{1H}. Elemental analyses were
performed by the Campbell Microanalytical Laboratory, University of
Otago, New Zealand. Electrospray ionization mass spectra were per-
formed by the GlycoSyn QC laboratory at Industrial Research Limited
using a Waters Q-TOF Premier Tandem mass spectrometer. Calculated
NMR spectra were obtained from gNMR spectral simulation program,
version 5.0.6.0, written by P. H. M. Budzelaar, IvorySoft 2006. X-ray
diffraction data were collected on a Bruker SMART CCD diffractometer
[Pt(CH2CHdCHC(CH2)2)(PꢀP)] (91ꢀ93%).
Synthesis of [Pt(ACP)(dbpe)] (3c). [Pt(C2H4)(dbpe)] (100 mg,
0.185 mmol) was dissolved in C6D6 (0.5 mL) and placed in an NMR
tube. BCP (0.02 mL, 1.87 mmol) was added, and the solution heated at
40 °C for 13 days. [Pt(ACP)(dbpe)] fromed, 88% by NMR. X-ray
quality crystals were grown by slow recrystallization from hot toluene.
1H NMR (δ, C6D6): 6.20(dt, 16.2, 9.6 Hz, 1H, dCHR), 4.98(m,
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1H, dCH2), 4.64(m, 1H, dCH2), 3.43(m, JPtꢀH = 62.0 Hz, 1H, dCHR),
1.7ꢀ1.5(m, 9H, CH2), 1.5ꢀ0.9(m, 19H, cPr and CH2). 31P NMR (δ,
C6D6): 27.97(s, 1JPtꢀP = 2978 Hz).
c
t
1.9ꢀ1.5(m, 6H, PꢀCH2 and Pr), 1.16(d, 12.5 Hz, 9H, Bu), 1.15(d,
12.5 Hz, 9H, tBu), 1.03(d, 12.0 Hz, 9H, tBu), 1.02(d, 12.5 Hz, 9H, tBu),
Synthesis of [Pt(MCP)2(PPh3)] (7a). [Pt(C2H4)2(PPh3)] (70mg,
0.14 mmol) was suspended in hexane (5 mL). An excess of MCP
was added, and the reaction stirred for 15 min. Hexane was added to
dissolve the remaining solid. The solution was cooled to ꢀ78 °C for an
hour, after which the supernatant was decanted off, leaving an off-white
solid. Solid was 90% [Pt(MCP)2(PPh3)], 10% [Pt(MCP)(C2H4)
(PPh3)]. X-ray quality crystals of [Pt(MCP)2(PPh3)] were grown by
recrystallization from hexane containing a few drops of MCP. 1H NMR
(δ, C6D6): 7.52(m, 6H, o-C6H5), 7.00(m, 9H, m- and p-C6H5), 2.39(d,
4.0, JPtꢀH = 55.0 Hz, 4H, dCH2), 1.31(m, 4H, cPr). 13C NMR (δ, C6D6):
138.81(d, 39.1, JPtꢀC = 26.9 Hz, i-C6H5), 134.22(m, o-C6H5), 129.83(d, 2.4 Hz,
m-C6H5), 128.35(s, p-C6H5), 54.05(d, 16.3, JPtꢀC = 352.9 Hz, dCR2),
c
1.0(m, 2H, Pr). 13C NMR (δ, C6D6): 147.52(t, JPꢀC = 4.6, JPꢀP
=
ꢀ34.3, JPtꢀC = 56.4 Hz, dCHR), 102.71(t, JPꢀC = 8.6, JPꢀP = ꢀ25.3,
JPtꢀC = 42.9 Hz, dCH2), 44.72(dd, JPꢀC = 38.1, 2.0, JPꢀP = ꢀ57.7, JPtꢀC
165.5 Hz, dCHR), 41.43(m, JPꢀC = 70.3, 2.3, JPꢀP = 65.8, JPtꢀC
=
=
533.1 Hz, =CR2), 36.51(dd, JPꢀC = 12.8, 4.6, JPꢀP = ꢀ27.1, JPtꢀC = 46.8
Hz, PꢀCR3), 35.75(dd, JPꢀC = 11.5, 5.1, JPꢀP = ꢀ24.3, JPtꢀC = 44.0 Hz,
PꢀCR3), 35.50(dd, JPꢀC = 13.2, 3.4, JPꢀP = ꢀ31.2, JPtꢀC = 53.8 Hz,
PꢀCR3), 34.81(dd, JPꢀC = 14.5, 5.4, JPꢀP = ꢀ31.2, JPtꢀC = 60.0 Hz,
PꢀCR3), 30.5ꢀ29.5(m, CH3), 26.43(t, 35.8, JPtꢀC = 12.7 Hz, PꢀCH2),
25.22(t, 18.0, JPtꢀC = 10.4 Hz, PꢀCH2), 10.60(t, JPꢀC = 3.3,
JPꢀP = ꢀ10.4, JPtꢀC = 17.7 Hz, cPr), 9.47(t, JPꢀC = 2.0, JPꢀP = ꢀ8.9,
c
38.94(s, JPtꢀC = 100.3 Hz, dCH2), 7.79(s, JPtꢀC = 24.5 Hz, Pr).
c
JPtꢀC = 15.5 Hz, Pr). 31P NMR (δ, C6D6): 96.40(AB, JPꢀP
=
31P NMR (δ, C6D6): 22.30(s, 1JPtꢀP = 2932 Hz).
62.2, 1JPtꢀP = 2848 Hz), 96.39(AB, JPꢀP = 62.2, 1JPtꢀP = 3196 Hz). m/z =
[M + H]+ calcd for C24H49P2194Pt 593.2936; found 593.2946 [M + H+].
Synthesis of [Pt(BCP)(C2H4)(PPh3)] (5a). [Pt(C2H4)2(PPh3)]
(20 mg, 0.039 mmol) was dissolved in hexane (2 mL) under an ethene
atmosphere. BCP (3.6 μL, 0.34 mmol) was added, and the reaction
stirred for 5 min. The solution was cooled to ꢀ78 °C for an hour, after
which the supernatant was decanted off, leaving a white solid
([Pt(BCP)(C2H4)(PPh3)], 15 mg, 0.027 mmol, 70%). 1H NMR
(δ, C6D6): 7.52(m, 6H, o-C6H5), 7.00(m, 9H, m- and p-C6H5),
2.71(s, JPtꢀH = 51.0 Hz, 4H, dCH2), 1.2ꢀ0.8(brs, 8H, cPr). 13C NMR(δ,
Synthesis of [Pt(MCP)2(PCy3)] (7b). [Pt(C2H4)2(PCy3)] (12 mg,
0.023 mmol) was placed in an NMR tube under an ethene atmosphere,
and C6D6 (0.5 mL) added. A large excess of MCP was added, and
Ar bubbled through the solution for 5 min. [Pt(MCP)2(PCy3)] formed,
1
99% by NMR. H NMR (δ, C6D6): 2.27(d, 6.0 JPtꢀH = 50.0 Hz,
4H, dCH2), 2.21(d, 8.5, JPtꢀH = 24.0 Hz, 3H, PꢀCH), 1.88(d, 12.0 Hz,
6H, CH2), 1.65(dd, 13.0, 2.0 Hz, 6H, CH2), 1.55(d, 12.0 Hz, 3H, CH2),
1.47ꢀ1.29(m, 11H, cPr and CH2), 1.13(m, 6H, CH2), 1.03(m, 6H, CH2).
13C NMR (δ, C6D6): 48.45(brd, 28.3, JPtꢀC = 385.6Hz, dCR2), 36.72(d,
21.1, JPtꢀC = 26.9 Hz, PꢀCH), 32.0(m, dCH2), 30.34(s, JPtꢀC = 18.2 Hz,
CH2), 28.02(d, 10.2 Hz, CH2), 26.90(s, CH2), 7.20(s, JPtꢀC = 25.0 Hz,
cPr). 31P NMR (δ, C6D6): 23.21(s, 1JPtꢀP = 2695 Hz).
C6D6): 134.61(d, 43.1, JPtꢀC = 25.5 Hz, i-C6H5), 134.22(d, 12.4, JPtꢀC
=
18.2 Hz, o-C6H5), 129.88(d, 2.4 Hz, m-C6H5), 128.36(s, p-C6H5),
54.84(d, 2.9, JPtꢀC = 102.2 Hz, dCH2), 30.16(d, 16.3, JPtꢀC = 431.5 Hz,
dCR2), 9.2ꢀ6.8(brs, cPr). 31PNMR(δ, C6D6):23.17(s,1JPtꢀP = 3094 Hz).
Synthesis of [Pt(BCP)(C2H4)(PCy3)] (5b). [Pt(C2H4)2(PCy3)]
(63 mg, 0.12 mmol) was dissolved in hexane (3 mL) under an ethene
atmosphere. An excess of BCP (0.02 mL, 1.9 mmol) was added, and the
solution stirred for 30 min. The solution was reduced to approximately
0.5 mL and cooled to ꢀ78 °C. After an hour, the supernatant was
decanted, leaving a pale yellow solid ([Pt(BCP)(C2H4)(PCy3)], 53 mg,
0.091 mmol, 76%). 1H NMR (δ, C6D6): 2.68(s, JPtꢀH = 50.0 Hz,
4H, dCH2), 2.03(d, 10.0, JPtꢀH = 23.0 Hz, 3H, PꢀCH) 1.86(d, 12.5 Hz,
6H, CH2), 1.64(d, 11.0 Hz, 6H, CH2), 1.54(d, 12.5 Hz, 3H, CH2),
’ CONCLUSION
A range of η2-complexes of bicyclopropylidene and methyle-
necyclopropane of the formula [Pt(L)(PꢀP)] were synthesized
with various diphosphine ligands. Mixed alkene complexes of
BCP and MCP of the type [Pt(C2H4)(L)(PR3)] were synthesized
from the bis-ethene precursor. These complexes are similar to the
proposed intermediates in the palladium- and nickel-catalyzed [3
+2] co-cyclization of BCP with various alkenes.47 While bis-MCP
complexes could be synthesized, bis-BCP complexes were not
formed, most likely due to steric constraints. These complexes
are the first examples of late transition metal complexes of bicyclo-
propylidene as well as the first bis-methylenecyclopropane com-
plexes of platinum.
It was found that when BCP was reacted with a number of
Pt(0) and Pt(II) complexes, a ring-opening reaction occurred to
form allylidenecyclopropane. The coordination chemistry of
ACP was also explored, with the synthesis of the diphosphine
complexes [Pt(ACP)(PꢀP)]. Some of the ACP complexes
underwent a rearrangement reaction to form η2:σ2-metallacy-
clopentene complexes, the first examples of the first instances of
the formation of η2:σ2-metallacyclopentene complexes from
η2:π-diene complexes, rather than from η4:π-diene complexes.
This work is the first exploration of the transition metal chemistry
of allylidenecyclopropane.
c
1.35(qm, 13.0 Hz, 6H, CH2), 1.17ꢀ1.05(m, 11H, Pr and CH2),
1.02(quintt, 13.0, 3.0 Hz, 6H, CH2). 13C NMR (δ, C6D6): 50.65(d, 1.9,
JPtꢀC = 101.8 Hz, dCH2), 36.46(d, 20.6, JPtꢀC = 26.0 Hz, PꢀCH),
30.27(s, JPtꢀC = 17.8 Hz, CH2), 29.08(s, JPtꢀC = 482.9 Hz, dCR2),
27.93(d, 10.1 Hz, CH2), 26.82(s, CH2), 8.30(brs, JPtꢀC = 23.8 Hz, cPr).
31P NMR (δ, C6D6): 25.27(s, 1JPtꢀP = 2976 Hz).
Synthesis of [Pt(MCP)(C2H4)(PPh3)] (6a). [Pt(C2H4)2(PPh3)]
(10 mg, 0.019 mmol) was dissolved in hexane (1.5 mL) under an ethene
atmosphere. An excess of MCP was added, and the solution flushed with
C2H4 for 5 min. The volume was reduced to ∼0.5 mL, and the solution
cooled to ꢀ78 °C for an hour. The supernatant was decanted off, leaving
pale white crystals. [Pt(MCP)(C2H4)(PPh3)] formed, 47% by NMR.
1H NMR (δ, C6D6): 7.52(m, 6H, o-C6H5), 7.01(m, 9H, m- and p-
C6H5), 2.61(s, JPtꢀH = 56.0 Hz, 4H, C2H4 dCH2), 2.58(d, 6.5, JPtꢀH
=
c
61.5 Hz, 2H, MCP dCH2) 1.64(brd, 7.5, JPtꢀH = 60.0 Hz, 2H, Pr),
c
1.55(d, 5.5, JPtꢀH = 34.0 Hz, 2H, Pr). 31P NMR (δ, C6D6): 23.58(s,
1JPtꢀP = 3085 Hz).
’ ASSOCIATED CONTENT
Synthesis of [Pt(MCP)(C2H4)(PCy3)] (6b). [Pt(C2H4)2(PCy3)]
(12 mg, 0.023 mmol) was placed in an NMR tube under an ethene
atmosphere, and C6D6 (0.5 mL) added. An excess of MCP was added,
and the solution flushed with C2H4 for 5 min. [Pt(MCP)(C2H4)
(PCy3)] formed, 94% by NMR. In the presence of excess MCP,
[Pt(MCP)2(PCy3)] forms overnight. 1H NMR (δ, C6D6): 2.52(d,
6.3, JPtꢀH = 61.2 Hz, 2H, MCP dCH2), 2.49(s, JPtꢀH = 48.1 Hz, 4H,
C2H4 dCH2), 2.20(m, 3H, PꢀCH), 1.90(d, 12.0 Hz, 6H, CH2),
S
Supporting Information. Text giving experimental methods
b
and characterization data for 1bꢀd, 2bꢀd, 3a,b, 4, [Pt(C2H4)-
(dppp)], [PtCl2(dcyppe)], and [Pt(C2H4)(dcyppe)]. X-ray crystal-
lographic files in CIF format for [Pt(BCP)(dppp)] (1a) and
[Pt(MCP)2(PPh3)] (7a). This material is available free of charge
via the Internet at http://pubs.acs.org.
5422
dx.doi.org/10.1021/om200630z |Organometallics 2011, 30, 5415–5423

Organometallics
ARTICLE
’ AUTHOR INFORMATION
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Corresponding Author
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’ ACKNOWLEDGMENT
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We thank Dr. Jan Wikaira at the University of Canterbury for
collecting the single-crystal X-ray data.
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