Comparison of the reactivity of platinum(II) and platinum(0) complexes with iminophosphine and phosphinocarbonyl ligands

Article abstract of DOI:10.1021/om2005113

Iminophosphines 2-(PPh₂)C₆H₄C(R)=NR′ (L) (R = H, Me; R′ = 2,6-Me₂C₆H₃ or 2,6-Prⁱ₂C₆H₃) react with Pt(II) precursors to form chelated P,N complexes [PtLX₂] (X = Me, Et, Cl), whereas with [Pt(C₇H₁₀)₃] (C₇H ₁₀ = norbornene) and other labile Pt(0) precursors coordination is via phosphorus and chelation is not observed. However, activation of the imine H or the methyl C-H bond of the ketoimine affords P,C metallacyclic hydride complexes [PtH(PPh₂C₆H₄C=NR′)L] and [PtH(PPh₂C₆H₄C(=NR′)CH₂)L], respectively. Under more forcing conditions the ketoimine complex undergoes a second metalation reaction, forming cis- and trans-bis-P,C-metallacyclic complexes. By contrast, reaction of the phosphinocarbonyl ligands 2-(PPh ₂)C₆H₄C(R)=O (L′) (R = H, Me) with Pt(II) precursors always affords bis-monodentate complexes [PtL′ ₂X₂] initially. Where X = Me, methane elimination occurs, forming five- (R = H) or six- (R = Me) membered P,C metallacyclic complexes, [PtMe(PPh₂C₆H₄CO)L′]. On heating, the second phosphinocarbonyl metalates, forming cis- and trans-bis-P,C-metallacyclic complexes. X-ray crystallography of the cis-metalla-β-diketone complex [Pt(PPh₂C₆H₄CO)₂] established the closeness of the carbonyl oxygen atoms, which readily capture H⁺ and other cations, forming stable complexes. These bis-chelate complexes also form readily from the reaction of the phosphinocarbonyls with [Pt(C₇H ₁₀)₃] via an intermediate norbornyl complex (R = H) or a 5,6-ring bis-chelate (R = Me) in which a hydride is transferred from one ketone to partially reduce the second ketone.

Full text of DOI:10.1021/om2005113

ARTICLE
pubs.acs.org/Organometallics
Comparison of the Reactivity of Platinum(II) and Platinum(0)
Complexes with Iminophosphine and Phosphinocarbonyl Ligands
Teresa F. Vaughan, David J. Koedyk, and John L. Spencer*
School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand
S Supporting Information
b
ABSTRACT: Iminophosphines 2-(PPh2)C6H4C(R)dNR0 (L) (R =
H, Me; R0 = 2,6-Me2C6H3 or 2,6-Pri2C6H3) react with Pt(II)
precursors to form chelated P,N complexes [PtLX2] (X = Me, Et, Cl),
whereas with [Pt(C7H10)3] (C7H10 = norbornene) and other labile
Pt(0) precursors coordination is via phosphorus and chelation is not
observed. However, activation of the imine H or the methyl CꢀH
bond of the ketoimine affords P,C metallacyclic hydride complexes
[PtH(PPh2C6H4CdNR0)L] and [PtH(PPh2C6H4C(dNR0)CH2)L],
respectively. Under more forcing conditions the ketoimine complex
undergoes a second metalation reaction, forming cis- and trans-bis-P,C-
metallacyclic complexes. By contrast, reaction of the phosphinocarbonyl
ligands 2-(PPh2)C6H4C(R)dO (L0) (R = H, Me) with Pt(II) pre-
cursors always affords bis-monodentate complexes [PtL02X2] initially. Where X = Me, methane elimination occurs, forming five- (R = H)
or six- (R = Me) membered P,C metallacyclic complexes, [PtMe(PPh2C6H4CO)L0]. On heating, the second phosphinocarbonyl
metalates, forming cis- and trans-bis-P,C-metallacyclic complexes. X-ray crystallography of the cis-metalla-β-diketone complex
[Pt(PPh2C6H4CO)2] established the closeness of the carbonyl oxygen atoms, which readily capture H+ and other cations, forming stable
complexes. These bis-chelate complexes also form readily from the reaction of the phosphinocarbonyls with [Pt(C7H10)3] via an
intermediate norbornyl complex (R = H) or a 5,6-ring bis-chelate (R = Me) in which a hydride is transferred from one ketone to partially
reduce the second ketone.
Chart 1
’ INTRODUCTION
Heterodentate ligands with both hard and soft donor atoms
have continued to attract interest due to their inherent
properties.1 Both iminophosphines and phosphinocarbonyl
ligands have proven interesting due to the combination of a hard
nitrogen or oxygen donor atom with a soft phosphorus donor.
On coordination to transition metals, this hard/soft combination
creates asymmetry in the metal orbitals, which then affects the
reactivity of a complex containing one of these ligands. This can
be illustrated by the difference in the trans influence of the
phosphorus donor atom compared to nitrogen or oxygen. For
example, in an iminophosphine complex the bond trans to the
phosphorus is longer than that trans to the nitrogen, indicating
the greater trans influence of phosphorus compared to the imine
donor functionality.2ꢀ5 The hard/soft combination also leads to
versatile coordination behavior with metal ions in different
oxidation states and the potential for hemilability.6
iminophosphine allows the modulation of the steric crowding
around the metal center through variation of the substituents on
the imine nitrogen.12 This is very useful for controlling the
catalytic activity and selectivity of complexes containing these
ligands.5 While a growing number of transition metal complexes
of iminophosphines have been reported,6,12ꢀ18 there has not
been a large amount of work published examining platinum
complexes containing these iminophosphines. In particular
While there are several examples in the literature of imino-
phosphines with different carbon backbones and substituents on
the nitrogen,3,7ꢀ9 this research focused on bidentate imino-
phosphines of the type in Chart 1, as they have shown poten-
tial as ligands in homogeneous catalysis.10,11 This type of
Received: June 14, 2011
Published: September 15, 2011
r
2011 American Chemical Society
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Scheme 1
To confirm the coordination of nitrogen to the platinum, the
1H NMR spectra were examined. In all cases the signal corre-
sponding to the proton in the CHdN group showed 195Pt
satellites (Figure 1). By contrast, this coupling was not observed
when the iminophosphine was acting as a monodentate ligand in
the reactions with tris(norbornene)platinum (see below). Also,
1
the CHdN signal in the H NMR spectra was no longer a
doublet, due to coupling to phosphorus, as it is in the free ligand.
Further confirmation that the nitrogen was coordinated to
platinum was found in the 1Hꢀ N heteronuclear multiple bond
15
correlation (HMBC) spectra of the complexes. In each case the
signal due to the nitrogen in the complex had shifted dramatically
from that of the free ligand. For example, the signal appeared at
ꢀ35.5 for a, while in complex 1a it appeared at ꢀ115.8 ppm
(Table 1). This significant low-frequency shift was consistent
with that seen when similar nitrogen ligands, such as methyl and
phenyl derivatives of 2,20-bipyridine and 1,10-phenanthroline,
coordinate to platinum(II).32,33 The change in chemical shift and
the observation of a correlation from the methyl ligands in
complexes 1a and 1b to the imine nitrogen confirmed that the
nitrogen was bound to the platinum.
iminophosphines with a methyl group attached to the carbon of
the imine group are notably rare.
2-(Diphenylphosphino)benzaldehyde is a structurally simple
bidentate P,O chelating ligand. A variety of coordination
modes have been reported for this ligand.8 First, it can act as a
monodentate phosphorus ligand.19 It can also act as a bidentate
chelating ligand, with the carbonyl portion bonded to the metal
through either a σ-bond from the oxygen or the π-system of the
carbonyl.19ꢀ21 This ligand has been observed to undergo chelate-
assisted oxidative addition of the CꢀH bond of the aldehyde
group with several late transition metals in low oxidation states to
give complexes containing a P,C chelate and a hydride ligand.21ꢀ24
While there have been a range of transition metal complexes of this
ligand reported,8,19ꢀ25 there has not been the same investigation
into the behavior of 2-(diphenylphosphino)acetophenone.26,27
While CꢀH activation is a common reaction for the
2-(diphenylphosphino)benzaldehyde ligand, before 2002 it had
not been observed for the iminophosphine ligands.28,29 Conse-
quently we were interested in exploring this metalation reaction
further in the iminophosphine ligand system, in particular, the
effect of replacing the imine/aldehyde proton with a methyl
group on the reactivity of both ligand systems toward CꢀH
activation. Thus, here we report the synthesis and reactivity of
previously unexplored platinum(II) and platinum(0) complexes
containing these ligands.
Complex 2a was synthesized via reaction of [PtEt2(COD)]
with the dimethylphenyl P,N ligand a and was crystallized from
Et2O, affording orange crystals of sufficient quality for single-
crystal X-ray diffraction analysis. Details of the structural solution
and refinement are given in Table 2, and key molecular para-
meters appear in Table 3. The molecular structure of 2a is shown
in Figure 2 and confirms the proposed structure, showing the
iminophosphine ligand acting as a chelating bidentate ligand.
The bite angle of the iminophosphine ligand (88.38(5)°) is
comparable to that reported for similar complexes of iminopho-
sphines with the same backbone including [PtMe2L] (86.8(1)°),
[PtCl2L] (88.39(8)°) (L = N-[{2-(diphenylphosphino)phenyl}
methylene]-[6,6-dimethyl-{1S-(1α,2β,5α)-bicyclo[3.1.1]heptane}]-
2-methaneamine),34 and [PdCl2(2-(PPh2)C6H4CHdN(C6H5))]
(86.34(8)°).16 The bond between the platinum and the carbon trans
to phosphorus (2.102(2) Å) is longer than that trans to nitrogen
(2.0546(18) Å). The Pt(1)ꢀP(1) bond length of 2.2543(5) Å is
comparable to that reported for [PtMe2L] (2.244(1) Å),34 and the
Pt(1)ꢀN(1) bond length of 2.140(2) Å is in the range found for
similar complexes where the imine is trans to a methyl group.30,34,35
Reaction of Pt(II) precursors with an excess of the P,N ligand
afforded products with only one P,N ligand coordinated to the
metal. Thus for the P,N ligands studied here, chelation is strongly
preferred over monodentate coordination when the metal is in
the +2 oxidation state. In contrast to the iminophosphine ligands,
the phosphinocarbonyl ligands d and e did not form chelated P,O
structures under any conditions investigated in this study.
The initial product of the reaction of the phosphinoaldehyde d
with [PtMe2(hexa-1,5-diene)] is the nonchelated intermediate
cis-[PtMe2(PPh2C6H4CHO)2] (4d), readily characterized by 1H
and 31P NMR spectroscopy (Scheme 2). In solution this complex
readily converts into the monometalated complex 5d with the
elimination of methane (observed at 0.22 ppm in the 1H NMR
spectra) and formation of a five-membered P,C metallacycle. The
31P NMR spectrum of 5d shows two doublets at 51.4 and 18.8
ppm (2JPP = 5.2 Hz) with 195Pt satellites. The small value of 2JPP
indicates a cis relationship between the phosphorus atoms, and
the high chemical shift of one signal is indicative of a five-
membered ring.36 Upon refluxing in toluene for 16 hours, a
second metalation takes place, affording a mixture of the cis and
trans isomers of 6d with two five-membered metallacyclic rings.
’ RESULTS AND DISCUSSION
Reactions with Pt(II) Precursors. Reaction of iminopho-
sphine ligands (aꢀc) with labile platinum(II) precursors such
as [PtX2(dialkene)] (X = Me, Et, Cl; dialkene = cycloocta-1,5-
diene (COD), hexa-1,5-diene) in equimolar ratios at room
temperature resulted in the formation of simple P,N bidentate
chelate complexes, [PtX2(PN)] (1aꢀ3c) (Scheme 1). Analo-
gous reactions have been reported previously.16,30 The new
Pt(II) complexes reported here were characterized by elemental
analysis, by detailed NMR spectroscopy, and, in the case of 2a, by
single-crystal X-ray diffraction. The complexes are air stable in
solution and in the solid state and were isolated as crystalline
solids. All are typical coordination complexes of square-planar
Pt(II) and display in their structural and spectroscopic properties
the pronounced difference in trans influence of trivalent phos-
phorus and sp2 imine nitrogen.
In each reaction, the formation of a platinum complex contain-
ing one of the iminophosphine ligands was confirmed by the 1H,
15N, and 31P NMR spectra recorded of the reaction mixture. The
31P NMR spectra showed that the signal due to phosphorus had
shifted 18ꢀ36 ppm downfield on coordination and had 195Pt
31
satellites (Table 1). The 195Ptꢀ P coupling constant in each
complex was found to vary depending on the ligand trans to the
phosphorus donor.31
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Table 1. Selected NMR Data of the Platinum Complexes
CRdN/O
13C/ppm (JPC/Hz)
compound
δ
31P/ppm
JPtP /Hz
δ1H/ppm (J/Hz)
JPtH/Hz
δ
JPtC/Hz
δ
15N/ppm
a
ꢀ14.0
ꢀ15.0
ꢀ9.3
ꢀ10.9
ꢀ2.7
21.8
21.8
24.0
22.2
22.2
23.4
2.4
8.90 (d, 5.6)
8.94 (d, 5.6)
1.77 (d, 1.5)
10.50 (d, 5.4)
2.02
ꢀ35.5
ꢀ37.3
ꢀ31.0
b
c
164.0
198.2
d
e
1a
1b
1c
2a
2b
2c
3a
3b
3c
4d
4e
5d
1921
1913
1892
1765
1755
1725
3668
3654
3679
1831
2067
2088
1558
2828
1888
2191
2901
1843
2114
2459
2823
3203
3242
3378
3545
3533
3543
3708
3851
1919
1870
1910
1817
2558
1797
2853
1898
3612
3997
4420
1696
1642
2972
1525
7.73
39
39
ꢀ115.8
ꢀ116.3
ꢀ112.6
8.15
1.35
166.8 (d, 5.9)
7.65
31
32
8.12
1.33 (d, 0.9)
8.33
ꢀ107.5
ꢀ160.3
111
109
2.9
8.39
2.5
2.02
171.3 (d, 6.8)
23.7
33.1
10.69 (d, 2.3)
1.86
51.4 (d, 5.2)
10.47 (d, 2.5)
232.5 (d, 133.0)
190.2 (d, 13.2)
1080
18.8 (d, 5.2)
33.4 (d, 10.8)
22.1 (d, 11.0)
10.5
5e
2.39
6c-cis-trans
2.45 (t, 8.2)
3.18 (t, 6.5)
99
79
13.7
a
a
6d-cis
6d+H+
47.8
45.2
250.5 (d, 108.8)
201.4
991
52
6e-cis-trans
18.0
2.60 (t, 6.3)
3.38 (dd, 7.3, 2.2)
8.94 (d, 2.6)
9.00 (d, 2.3)
1.78
82
93
17.5
a
a
a
7a
7b
7c
7e
8a
8b
8c
8e
9a
21.9
22.0
28.0
31.7
1.89
a
a
a
29.4
9.08
29.7
9.11
a
a
a
a
35.7
38.3
1.95
a
a
a
49.2 (m)
20.4 (d, 7.9)
49.6 (m)
22.9 (m)
28.6
9.60 (d, 2.8)
9b
9c
9e
9.28 (d, 2.1)
1.75
174.8
15.8
29.6 (d, 10.7)
17.1 (d, 10.7)
27.5
3.71 (t, 10.2)
95
a
a
10c
11c
12a
13d
1.66
35.9
1.87
42.4
9.11
45.0
10.59 (d, 2.7)
18.5
14e
41.0 (d, 8.1)
19.2 (d, 8.1)
4.16 (td, 8.0, 4.1)
3.68 (td, 9.4, 4.1)
98
88
199.8 (t, 6.0)
170.9 (d, 34.9)
a NMR data could not be obtained.
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Table 3. Selected Bond Distances (Å) and Angles (deg) for
Complex 2a
Pt(1)ꢀP(1)
Pt(1)ꢀN(1)
Pt(1)ꢀC(1)
Pt(1)ꢀC(3)
2.2543(5)
2.1400(16)
2.0546(18)
2.102(2)
N(1)ꢀC(5)
N(1)ꢀC(13)
P(1)ꢀC(15)
1.444(3)
1.283(3)
1.8260(18)
P(1)ꢀPt(1)ꢀN(1)
C(1)ꢀPt(1)ꢀC(3)
P(1)ꢀPt(1)ꢀC(1)
N(1)ꢀPt(1)ꢀC(3)
N(1)ꢀPt(1)ꢀC(1)
88.38(5)
87.50(8)
93.21(6)
91.51(7)
173.90(7)
P(1)ꢀPt(1)ꢀC(3)
C(5)ꢀN(1)ꢀC(13)
Pt(1)ꢀN(1)ꢀC(5)
Pt(1)ꢀN(1)ꢀC(13)
174.31(7)
113.78(16)
118.21(13)
127.96(14)
Figure 1. Low-field section of the 1H NMR spectrum of 1a.
identified by 1H and 31P NMR spectroscopy in solution.
Kurosawa et al. reported a similar investigation with less
sterically hindered ligands, and our observations are broadly
in accord with their findings.29
Table 2. Crystallographic Data
The initial formation of [Pt(P)(nb)2] (7a) and [Pt(P)2(nb)]
(8a) (P = a acting as a monodentate phosphorus ligand, nb =
norbornene) (Scheme 4) was observed in all of the reactions of a.
The signals for the complexes in the 31P NMR spectra of the
reactions appeared as singlets at 21.9 (1JPtP = 3203 Hz) and 29.4
ppm (1JPtP = 3533 Hz) for 7a and 8a, respectively (Table 1). This
is consistent with the 31P NMR data of the analogous complexes
with triphenylphosphine40 and that of [Pt(P)2(nb)] (where P =
2-(PPh2)C6H4CHdN((CH2)2C6H5)).29 The signals for the
2a
cis-6d C6H6
9b
3
chemical formula
formula weight
a, Å
C
31H34NPPt
C44H34O2P2Pt
851.74
13.6485(11)
18.4002(13)
14.5882(11)
90
C62H64N2P2Pt
1094.17
13.3764(5)
34.9788(12)
13.1827(5)
90
646.65
9.4923(4)
11.1549(4)
14.5403(8)
103.134(2)
104.928(2)
107.442(2)
1339.61(10)
2
b, Å
c, Å
α, deg
β, deg
112.622(4)
90
102.833(2)
90
1
CHdN group in the H NMR spectra did not have 195Pt
γ, deg
V, Å3
satellites, which were present in all of the platinum(II) com-
plexes where the ligands were acting as bidentate ligands.
Interestingly, no tris(phosphine) complex [Pt(P)3] was ob-
served in these reactions, even when carried out in a 1:3
complex/ligand ratio. This is in contrast with Kurosawa’s work,
where a tris(phosphine) complex was observed initially in the 1:3
reaction.29 We ascribe this to the greater bulk of the ligands used
in this study.
After one day all reactions showed the formation of a third
complex, which was identified as the hydride complex 9a. This
hydride complex was formed from the metalation of the CHdN
group on one of the ligands in 8a. The signal due to the hydride
ligand appeared in the 1H NMR spectra of the reaction mixture at
ꢀ2.83 ppm as a doublet of doublets with 195Pt satellites. The 2JPH
coupling constants of 176 and 29 Hz were consistent with the
hydride coupling to two different phosphorus nuclei, one in a cis
position and the other trans. The 31P signals of these phosphorus
nuclei appeared at 49.2 and 20.4 ppm; the high chemical shift
of the former signal is consistent with the formation of a five-
membered metallacycle. This type of reactivity of the CHdN
group has been reported twice in the literature in Pt com-
plexes29,41 and once in a Co complex.28
The reactivity pattern of ligand b with tris(norbornene)
platinum is identical to that of ligand a. Thus, the extra bulk of
the isopropyl groups did not interfere with the formation of the
hydride complex 9b. Crystals of a quality sufficient for use in X-ray
analysis were grown by the inward diffusion of hexane into a Et2O
solution of 9b in the presence of a small amount of cycloocta-1,5-
diene at 4 °C. Single-crystal X-ray crystallography confirmed the
proposed structure of 9b, showing metalation of one of the
iminophosphine ligands and monodentate coordination of the
other (Figure 3). Details of the structural solution and refinement
aregiven in Table2, and selected bondlengthsandangles are given
in Table 4. The platinum in this structure is disordered, occupying
3381.7(4)
4
6014.0(4)
4
Z
space group
P-1
C2/c
P21
T, K
121
118
118
dcalcd, g cmꢀ3
μ, cmꢀ1
R1 [I > 2σ(I)]a
wR2 (all data)a
1.603
1.673
1.208
5.316
4.283
2.422
0.021
0.045
0.049
0.057
0.145
0.094
2
a Definition of R indices: R1 = ∑ Fo| ꢀ |Fc /∑|Fo|; wR2 = [∑[w(Fo
ꢀ
Fc2)2]/∑[w(Fo ) ]]1/2
2 2
.
The 31P NMR spectrum of cis-6d has one singlet at 47.8 ppm with
195Pt satellites (Table 1). Similarly, d has been observed to
undergo chelate-assisted oxidative addition with [{IrCl(cod)}2]
to produce octahedral irida-β-diketones.37 Metalla-β-diketones
where the carbonyl groups are not stabilized by chelation have
also been prepared by Lukehart38 and Steinborn.39
In a similar manner e reacts readily with [PtMe2(hexa-1,5-
diene)] in chloroform to form a bis-monodentate intermediate
before reacting further to form a complex with one six-membered
ring metalated at the ketone methyl group, 5e (Scheme 3). The
31P chemical shifts are 33.4 and 22.1 ppm, the latter being typical
of phosphorus involved in a six-membered metallacycle.36
Further reaction in chloroform at reflux leads to doubly meta-
lated cis and trans isomers of 6e.
Reactions with Pt(0) Precursors. As catalysis with Pd and Pt
often involves both the 0 and +2 oxidation states of the metals, we
investigated the behavior of the iminophosphine and phosphino-
carbonyl ligands with Pt(0) precursors. Separate reactions of tris-
(norbornene)platinum(0) (norbornene = bicyclo[2.2.1]heptene)
and the ligands a, b, and c in 1:1, 1:2, and 1:3 ratios were carried
out. These reactions resulted in mixtures, and the products were
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Figure 2. ORTEP diagram of 2a showing 50% probability thermal ellipsoids. H-atoms have been omitted for clarity.
Scheme 2a
Scheme 3a
a Ar = C6H4C(CH3)dO.
a Ar = C6H4CHdO.
Scheme 4a
two different positions. Figure 3a shows the site with 85% occu-
pancy. When the platinum is occupying the other site, the ligands
switch coordination modes (Figure 3b), with the monodentate
ligand now chelated and vice versa. While the hydride ligand
was not found, given that the arrangement of the other ligands
around the platinum is square planar, its position can be inferred.
The bite angle of the metalated ligand is 79.2°. This is com-
parable to that reported by Kurosawa (82.1°)29 and that reported
in the Co complex containing a similar iminophosphine ligand
(79.1°).28
In the reaction of ligand c with tris(norbornene)platinum the
formation of the analogous hydride complex 9c was more facile
with a significant amount present in solution after one hour. This
complex was identified by the hydride signal at ꢀ4.17 ppm (2JPH
= 196, 28, 1JPtH = 1145 Hz) in the 1H NMR spectrum and two
signals in the 31P NMR spectrum at 28.6 and 15.8 ppm. The lack
of PP coupling for the two signals in the 31P spectrum and the
a (a) Ar = C6H4CHdN(2,6-Me2C6H3); (b) Ar = C6H4CHdN(2,6-
Pri2C6H3).
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Figure 3. (a) ORTEP diagram of 9b showing the platinum site with 85% occupancy. (b) ORTEP diagram of 9b showing the platinum site with 15%
occupancy. 50% probability thermal ellipsoids are shown. H-atoms have been omitted for clarity.
Table 4. Selected Bond Distances (Å) and Angles (deg) for
Complex 9b
Scheme 5a
Pt(1)ꢀP(1)
Pt(1)ꢀP(2)
Pt(1)ꢀC(1)
N(1)ꢀC(1)
N(1)ꢀC(20)
C(1)ꢀC(2)
2.305(2)
2.307(2)
2.087(7)
1.344(8)
1.424(9)
1.469(12)
C(2)ꢀC(3)
P(1)ꢀC(3)
N(2)ꢀC(50)
N(2)ꢀC(51)
C(50)ꢀC(49)
1.414(12)
1.797(8)
1.348(9)
1.391(12)
1.492(12)
P(1)ꢀPt(1)ꢀC(1)
P(1)ꢀPt(1)ꢀP(2)
P(2)ꢀPt(1)ꢀC(1)
Pt(1)ꢀC(1)ꢀN(1)
Pt(1)ꢀC(1)ꢀC(2)
79.2(2)
113.24(7)
166.5(2)
125.8(6)
117.2(5)
C(2)ꢀC(1)ꢀN(1)
C(1)ꢀN(1)ꢀC(20)
C(49)ꢀC(50)ꢀN(2)
C(50)ꢀN(2)ꢀC(51)
116.5(6)
121.3(6)
118.1(8)
116.9(7)
111.3(5)
magnitude of the 1JPtP confirm the cis geometry. In contrast to the
reactions of a and b this reaction proceeds to form the bis-chelate
complex 6c as a mixture of cis and trans isomers. However, this
reaction never goes to completion, and the reaction results in a
mixture of the two isomers of 6c and 9c.
a Ar = C6H4C(CH3)dN(2,6-Me2C6H3).
resonance at 42.4 ppm in the 31P NMR spectrum with JPtP
=
1
When c is reacted with tris(ethene)platinum, the bis- and
monoethene complexes [Pt(P)(C2H4)2] (10c) and [Pt(P)2-
4420 Hz. The chemical shift and coupling constant were consistent
with the 31P NMR data of [Pt(PPh3)3]45 and the tris(phosphine)
complex [Pt(2-(PPh2)C6H4CHdN((CH2)2C6H5))3].29 After
two hours the NMR spectra of the reaction mixture showed the
presence of unreacted ligand a and 9a only. In contrast, when b
and c were reacted in a similar manner with bis(cycloocta-1,5-
diene)platinum, only the hydride complexes and unreacted ligand
were observed.
In contrast to the reactions of the iminophosphine with
[Pt(nb)3], the 1:2 reaction with the phosphinocarbonyl d did
not proceed via the formation of detectable quantities of a
hydride complex. Instead, reaction over 20 h led to the observa-
tion of an intermediate norborn-2-yl complex of platinum 13d,
formed by the migration of the aldehyde hydrogen to
1
(C2H4)] (11c) are formed first (Scheme 5). The 31P and H
NMR data of these complexes are in accord with those reported
for analogous complexes with triphenylphosphine (Table 1).42ꢀ44
This reaction goes on to form 9c and then finally the cis and trans
isomers of 6c. It is important to note that this reaction always
contains a mixture of products, and heating the reaction resulted in
product degradation. Asfar astheauthorsare aware, this is theonly
complex containing two metalated iminophosphine ligands as well
as the only instance of a six-membered metallacycle formed from
metalation of this iminophosphine ligand.
When bis(cycloocta-1,5-diene)platinum was reacted with a,
the tris(phosphine) complex [Pt(P)3] (12a) was formed along
with the hydride complex 9a. The new complex displayed a single
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Scheme 6a
Table 5. Selected Bond Distances (Å) and Angles (deg) for
cis-6d C6H6
3
Pt(1)ꢀP(1)
Pt(1)ꢀC(1)
P(1)ꢀC(3)
2.3096(12)
2.073(5)
1.820(5)
C(1)ꢀC(2)
C(1)ꢀO(1A)
C(1)ꢀO(1B)
1.495(8)
1.333(15)
1.209(17)
P(1)ꢀPt(1)ꢀP(1)
C(3)ꢀP(1)ꢀC(10)
104.45(6)
106.1(2)
C(1)ꢀPt(1)ꢀC(1)
83.16(17)
a Ar = C6H4CHdO.
Scheme 7
disordered model in which one oxygen lies close to the plane and
the other is displaced from the plane by 0.64 Å refines well.
From the molecular structure it can be seen that there is
the potential for the two carbonyl oxygen atoms in cis-6d to co-
ordinate to another center. Reaction of cis-6d with the hydrocarbon
acid CH2(SO2CF3)2 confirmed this, forming the protonated
complex 6d+H+, where the proton is bound to the two oxygens
(Scheme 7). In the 1H NMR spectrum of this complex the shared
3
proton appears at 22.05 ppm with JPtH = 104.2 Hz, indicating
the proton is strongly bound.46 While the signal in the 31P NMR
spectrum has not shifted significantly (δ = 45.2 ppm), the 1JPtP
has increased (2114 Hz as opposed to 1843 Hz in the parent
compound). The ability of metalla-β-diketones of the type
[(CO)xM(RCO)(R0CO)]ꢀ to coordinate Lewis acids through
two carbonyl moieties has been investigated by Lukehart.38
Garralda and co-workers have extensively investigated the co-
ordination chemistry of irida-β-diketones.37
Figure 4. ORTEP diagram of cis-6d C6H6 showing 50% probability
thermal ellipsoids. H-atoms have been omitted for clarity. Occupancy of
O(1a) and O(1b) is 47% and 53%, respectively.
3
coordinated norbornene with the concomitant formation of a
five-membered metallacycle (Scheme 6). In agreement with the
proposed structure of the intermediate, both values of 1JPtP (1696
and 1642 Hz) are typical of 31P trans to carbon. Conversion of
13d to 6d occurs through the elimination of norbornene and
It is well known that the hydrogen atoms on a carbon in the
α-position to a carbonyl are particularly reactive, for example, in
ketoꢀenol tautomerism. This proved to be the case when e
was reacted with Pt(0) reagents. Thus the reaction of ketophos-
phine e with [Pt(nb)3] (2:1) in C6D6 at 20 °C under a nitrogen
atmosphere initially afforded a mixture of the mono- and bis-
norbornene complexes 8e and 7e in the presence of excess ligand
(Scheme 8). Interestingly, this reaction proceeded through the
short-lived hydride complex 9e, analogous to that seen in the
iminophosphine reactions, rather than a norbornyl intermedi-
ate as d does. Over two days a new complex forms with two
phosphine ligands that show very different chemical shifts (19.2
and 41.0 ppm, JPP = 8.1 Hz). This is indicative of the presence of
both five- and six-membered metallacyclic rings.36 The observation
1
hydrogen gas, the latter observed as a sharp singlet in the H
NMR spectrum at 4.62 ppm (in CDCl3). Over a period of several
days at room temperature orange-red and colorless crystals of
respectively the cis- and trans-bis-chelate complexes 6d form.
The X-ray crystal structure of cis-6d C6H6, isolated as a
3
benzene solvate in space group C2/c, confirms the structural
predictions based on the NMR data (Figure 4). Details of the
structural solution and refinement are given in Table 2, and
selected bond lengths and angles are given in Table 5. The
platinum atom lies on a crystallographic C2 axis and is coordi-
nated to two phosphorus atoms and to the two carbonyl carbons.
The nine atoms comprising the bis-chelate core of the molecule
are substantially coplanar, as are the attached phenyl rings. The
two oxygen atoms are bent out of the plane of the rings quite
noticeably, probably as a result of strong repulsive interactions
(apparent OꢀO separation 264 pm; sum of van der Waals radii
304 pm). However, there are significant anisotropic thermal
parameters associated with the oxygen atoms, suggesting that
their true position is not precisely defined by the refinement. A
1
of a signal in the H NMR spectrum at 2.19 ppm with 195Pt
satellites ascribed to a methyl group and a broad signal at
6.06 ppm assigned to a hydroxyl proton (confirmed by the addition
of D2O) suggests that this complex is the 5,6-bis-metallacycle 14e.
The partial reduction of the ketone function is achieved by the
hydride ligand that results from the metalation of the other ligand
to afford the six-membered metallacycle. The magnitude of 1JPtP
for both phosphorus nuclei suggests they are cis to each other
(Table 1).
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Scheme 8a
operating at 300 and 121 MHz for H and 31P spectra, respectively, a
Varian Unity Inova spectrometer operating at 500, 125, and 202 MHz
1
for H, 13C, and 31P spectra, respectively, and a Varian DirectDrive
1
1
spectrometer operating at 600 and 61 MHz for H and 15N spectra,
respectively. NMR spectra were recorded in deuterated benzene
(C6D6), unless stated otherwise. All direct-detected 1H and 13C
chemical shifts, δ (ppm), were referenced to the residual solvent peak
of the deuterated solvent.53 Indirectly detected 15N shifts were refer-
enced to the unified TMS scale with a Ξ ratio of 10.136767.54 31P NMR
spectra were measured with 1H-decoupling and referenced to 85%
H3PO4. Infrared spectra were obtained using a Perkin-Elmer Spectrum
One FT-IR spectrophotometer (resolution 4 cmꢀ1) in absorbance
mode, using pressed KBr discs. All spectral data were obtained at
ambient temperature, unless otherwise stated. Elemental analysis was
performed at the Campbell Microanalytical Laboratory at Otago Uni-
versity, Dunedin. Electrospray ionization mass spectroscopy was per-
formed by the GlycoSyn QC laboratory at Industrial Research Limited,
using a Waters Q-TOF Premier Tandem mass spectrometer.
a Ar = C6H4C(CH3)dO.
Synthesis of Iminophosphine Ligand 2-(PPh2)C6H4C-
(CH3)dN(2,6-Me2C6H3), c. This synthesis is based on the synthesis
of 2-(PPh2)C6H4C(CH3)dN(2,6-iPr2C6H3).55 Titanium tetrachloride
(3 mL, 1 mol Lꢀ1 in toluene, 3 mmol) was slowly added to a solution of
2-fluoroacetophenone (0.8 mL, 6.25 mmol) and 2,6-dimethylaniline (2 mL,
14.8 mmol) in toluene (4 mL) at 0 °C. The resulting solution was allowed
to warm to room temperature and stirred overnight. The suspension was
filtered through alumina and rinsed with ethyl acetate. The filtrate was
concentrated to an oil. As NMR spectra of the oil showed that the reaction
had not gone to completion, this oil was dissolved in toluene (4 mL), and
2,6-dimethylaniline (2 mL, 14.8 mmol) was added. The solution was cooled
to 0 °C, and TiCl4 (3 mL, 1 mol Lꢀ1 in toluene, 3 mmol) was added. The
resulting suspension was allowed to warm to room temperature and stirred
overnight. The reaction mixture was purified in the same manner as above to
yield the desired imine as a dark green oil (0.848 g, 56%).
A solution of this imine in Et2O (5 mL) was added to a solution of
potassium diphenylphosphide in THF. After stirring at room tempera-
ture for three hours ethyl acetate and water (5 mL each) were added.
The aqueous layer was removed, and the organic layer was washed with
brine (2 ꢁ 5 mL), dried over magnesium sulfate, filtered, and con-
centrated to a yellow oil. The crude product was purified by flash
chromatography (5% ethyl acetate in hexane) to give the iminopho-
sphine c as a yellow oil, which crystallized over two days (0.619 g, 24%).
1H NMR: δ/ppm 7.45 (ddd, 7.8, 4.5, 1.3 Hz, 1H, Ar-H), 7.38ꢀ7.29
(m, 5H, Ar-H), 7.07 (td, 7.8, 1.3 Hz, 1H, Ar-H), 7.02ꢀ6.86 (m, 10H, Ar-
H), 1.90 (s, 6H, 2 ꢁ Ar-CH3), 1.77 (d, JPH = 1.5 Hz, 3H, CH3).
13C NMR: δ/ppm 164.0 (s, CdN), 148.2 (s, Ar-C), 143.3 (d, JPC = 17.1
Hz, Ar-C), 140.7 (d, JPC = 10.5 Hz, Ar-C), 139.1 (d, JPC = 22.5 Hz,
Ar-C), 135.9 (s, Ar-C), 134.1 (d, JPC = 20.0 Hz, Ar-C), 129.4 (s, Ar-C),
128.9 (d, JPC = 2.9 Hz, Ar-C), 128.6 (d, JPC = 6.6 Hz, Ar-C), 128.4 (s,
Ar-C), 128.1 (s, Ar-C), 128.0 (s, Ar-C), 126.3 (s, Ar-C), 123.2 (s, Ar-C),
18.6 (d, JPC = 1.9 Hz, CH3), 18.5 (d, JPC = 5.8 Hz, Ar-CH3). 31P NMR:
δ/ppm ꢀ9.3 (s). 15N NMR: δ/ppm ꢀ31.0 (s). IR: νmax/cmꢀ1 1654
(CdN stretch). Analysis: C, 82.5; H, 6.5; N, 3.4 (C28H26NP requires C,
82.5; H, 6.4; N, 3.4).
When the same reaction is carried out in air, the major product
was cis and trans isomers of the bis-chelate 6e. These are readily
distinguished by the different magnitudes of 1JPtP. Furthermore,
if a solution of the cis-5,6-complex 14e is stirred in air, the ligand
that forms the five-membered ring rearranges, with the loss
of two hydrogen atoms, to form a second six-membered
metallacycle.
In this work three different coordination modes have been
observed when the iminophosphine ligands react with platinum.
Bidentate P,N binding was observed with platinum(II), while
both monodentate P coordination and the formation of a P,C
chelate were observed in the reactions with Pt(0) starting
materials. These results provide support for the proposal that
these ligands would display hemilabile behavior in platinum
catalysts going through 0 and +2 oxidation states. However,
the propensity to form stable P,C metallacyclic complexes could
severely limit catalyst lifetimes. In contrast, while a larger number
of coordination modes has been previously reported for the
phosphinocarbonyl ligands, only two modes of coordination
were observed in this research. Formation of a P,C chelate
through oxidative addition was observed with both Pt(II) and
Pt(0), as was coordination through the phosphorus alone. We
have also observed that the chelate-assisted oxidative addition of
a CꢀH bond in these ligands occurs more readily for the
phosphinocarbonyl ligands than for the iminophosphines.
’ EXPERIMENTAL SECTION
General Methods. All reactions were carried out using degassed
solvents and standard Schlenk techniques under a nitrogen atmosphere
unless stated otherwise. The starting materials used in this work were
obtained from Sigma-Aldrich except 2-fluoroacetophenone which was
obtained from Merck. The two iminophosphine ligands, a and b,12
2-diphenylphosphinobenzaldehyde, d,47 2-diphenylphosphinoaceto-
phenone, e,48 dichloro(hexa-1,5-diene)platinum,49 diethyl(cycloocta-
1,5-diene)platinum,50 bis(cycloocta-1,5-diene)platinum,51 and bis-
(trifluoromethylsulfonyl)methane52 were synthesized using standard
literature methods. Tetrahydrofuran (THF) and diethyl ether (Et2O)
were distilled under a nitrogen atmosphere from sodium benzophenone
ketyl immediately prior to use. All other solvents used were of analytical
grade and dried over molecular sieves. Nuclear magnetic resonance
(NMR) spectra were recorded using a Varian Unity Inova spectrometer
Synthesis of Dimethyl(hexa-1,5-diene)platinum. Dichloro-
(hexa-1,5-diene)platinum (0.348 g, 1.0 mmol, finely powdered) was
suspended in dry Et2O (5 mL). A solution of dimethylzinc (2 mL, 1 mol Lꢀ1
in toluene, 2 mmol) was added over 10 min. The mixture was stirred until
the last crystals of the starting material had dissolved. A solution of
ammonium chloride in water was added, and the mixture was stirred for
30 min. The organic layer was decanted, and the aqueous layer was
extracted with Et2O (5 mL). The organic fractions were combined and
dried over anhydrous sodium sulfate. The solvent was evaporated, leaving
a pale oil, which crystallized slowly. The crude product was sublimed at
50 °C and ∼0.5 mmHg, affording white crystals (0.260 g, 85%).
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1H NMR: δ/ppm 4.47 (m, 2H, 2 ꢁ dCH), 4.08 (d, 7.8, JPtH = 39 Hz,
2H, dCH2), 3.19 (q, 16.0 Hz, 2H, dCH2), 1.76 (m, 2H, CH2), 1.57
(m, 2H, CH2), 1.21 (s, JPtH = 84 Hz, 6H, 2 ꢁ Pt-CH3). 13C NMR: δ/
ppm 102.9 (s, JPtC = 44 Hz, dCH), 82.8 (s, JPtC = 42 Hz, dCH2), 30.7
(s, JPtC = 9 Hz, CH2), 9.9 (s, JPtC = 798 Hz, Pt-CH3). IR: νmax/cmꢀ1
3075, 3018 (sp2 CꢀH stretch), 2932, 2872 (sp3 CꢀH stretch), 956, 934
(alkene CꢀH bending). Analysis: C, 31.5; H, 5.4 (C8H16Pt requires C,
31.3; H, 5.3).
Synthesis of Tris(norbornene)platinum. The synthesis of
tris(norbornene)platinum reported here is based on the synthesis of
tris(styrene)platinum using a silane-reducing agent.56 Dichloro(hexa-
1,5-diene)platinum (10 g, 29 mmol, finely powdered) was added to a
stirred solution of norbornene (24 g, 260 mmol) in diethyl ether
(50 mL), followed by 2 mL of triethylsilane. The mixture was stirred
at room temperature for 30 min, after which a further 10 mL of triethylsilane
was added in 1 mL portions over one hour. At each addition of silane, the
temperature of the solution rose and a faint yellow color appeared, which
then slowly disappeared as the reaction proceeded. The solution was
saturated with product at ∼30 °C, and masses of fine crystals formed if
the solution became too cold. The reaction flask was cooled to 4 °C
overnight and then to ꢀ20 °C for a further day to complete crystallization.
The crystals were filtered at ꢀ5 °C, washed with cold hexane (3 ꢁ 5 mL),
and dried under vacuum for a short period (11.7 g, 84%).
then be deprotonated with DABCO or NaH to yield a pure sample of
cis-6d.
cis-6d. IR: νmax/cmꢀ1 1632 (CdO stretch).
Protonation of Complex 6d: Synthesis of 6d+H+. Complex cis-6d
(27.7 mg, 0.0358 mmol) was suspended in CH2Cl2 (10 mL), and
CHPh(SO2CF3)2 (10.0 mg, 0.0358 mmol) was added. An immediate
color change from red to yellow was observed along with the complete
dissolution of all solid 6d. The solvent was removed under vacuum, and
the product was recrystallized from CH2Cl2 and Et2O, forming yellow,
needle-shaped crystals (27.2 mg, 72%).
6d+H+. IR: νmax/cmꢀ1 1524 (CdO stretch). Analysis: C, 49.4, H, 3.2
(C47H34F6O6P2PtS2 requires C, 49.9; H, 3.0).
Reaction of Dimethyl(hexa-1,5-diene)platinum with Ligand e.
Dimethyl(hexa-1,5-diene)platinum (80 mg, 0.26 mmol) and ligand e
(170 mg, 0.56 mmol) were added to a Schlenk tube. The solids were
dissolved in CH2Cl2 (5 mL, degassed). The immediate formation of 4e
was quickly followed by the chelation of one of the ligands to form 5e.
Reaction of Dimethyl(hexa-1,5-diene)platinum with Ligand e:
Synthesis of cis-6e. Dimethyl(hexa-1,5-diene)platinum (80 mg, 0.261
mmol) and ligand e (165 mg, 0.543 mmol) were dissolved in CHCl3 and
refluxed for 72 h. The solvent was removed under vacuum, and the solid
was washed with toluene. The white microcrystalline solid was dissolved
in a minimum of CH2Cl2 and recrystallized by inward diffusion of Et2O.
This method produced exclusively the cis isomer.
The reaction produces byproduct that are solid at low temperature.
These may co-crystallize with tris(norbornene)platinum if a second or
third crop of crystals is sought. The product was purified by dissolving in
hexane along with a small crystal of norbornene, passing the solution
through a short column of alumina, and recrystallizing at low temperature.
Tris(norbornene)platinum crystallizes as fine white needles that entrain
the solvent in the mat of crystals. Slow crystallization affords larger crystals
that are easier to wash and dry. The NMR spectra of the crystals formed
were identical to those of samples produced by other methods.51
Reactions with Platinum(II) Complexes. Example Method
for Synthesis of Platinum(II) Complexes of Iminophosphine Ligands.
Diethyl(cycloocta-1,5-diene)platinum (47 mg, 0.13 mmol) and ligand a
(0.13 mmol) were combined in a Schlenk tube and dissolved in diethyl
ether (10 mL). The reaction was stirred at ambient temperature, and
after four hours the solution had turned dark orange. Orange crystals
suitable for single-crystal X-ray structure determination of 2a were
grown from the reaction mixture at ambient temperature. The complex
was isolated by filtration (62 mg, 74%). (See Supporting Information for
the details of the synthesis of 1aꢀ3c.)
cis-6e. IR: νmax/cmꢀ1 1629 (CdO stretch). HRMS: calcd for
C40H33O2P2Pt [M + H]+ m/z = 801.1583; found 801.1580. Analysis:
C, 60.2; H, 4.1 (C40H33O2P2Pt requires C, 59.9; H: 4.0).
Reactions with Platinum(0) Complexes. Reactions of Tris-
(norbornene)platinum(0) withLigandaor b. Tris(norbornene)platinum
and ligand a or b were reacted in a 1:1, 1:2, and 1:3 ratio. These syntheses
were carried out using 30 mg of tris(norbornene)platinum (0.063 mmol)
and the appropriate amount of ligand. The two solids were combined in an
NMR tube and dissolved in C6D6 (0.5 mL). The recorded 1H and 31P
NMR spectra initially showed the formation of complexes 7a and 8a or 7b
and 8b. After one day, the 1H and 31P NMR spectra showed the formation
of complex 9a or 9b.
Reactions of Tris(norbornene)platinum(0) with Ligand c. Tris-
(norbornene)platinum and ligand c were reacted in a 1:1, 1:2, and 1:3
ratio. These reactions were carried out using 28 mg of tris(nor-
bornene)platinum (0.059 mmol) and the appropriate amount of ligand.
The two solids were combined in an NMR tube and dissolved in C6D6
(0.5 mL). The recorded 1H and 31P NMR spectra initially showed the
formation of complex 7c and an extremely small amount of 8c. While the
1H and 31P NMR spectra recorded after one hour showed the formation
Reaction of Dimethyl(hexa-1,5-diene)platinum with Ligand d.
Dimethyl(hexa-1,5-diene)platinum (20 mg, 0.07 mmol) was dissolved
in CDCl3 (0.5 mL) in an NMR tube. Ligand d (39 mg, 0.13 mmol) was
added to the solution, rapidly forming complex 4d. The chelation of one
diphenylphosphinobenzaldehyde ligand to platinum followed, produ-
cing 5d. This complex was recrystallized from the inward diffusion of
Et2O into CH2Cl2, yielding orange crystals (42 mg, 80%).
1
of complex 9c, the H and 31P NMR spectra recorded after one day
showed the formation of a small amount of cis-6c. If the reaction is left at
room temperature over time, the amount of cis-6c increases and a
detectable amount of trans-6c is formed. However, the reaction never
goes to completion.
5d CH2Cl2. IR: νmax/cmꢀ1 1694 (CdO stretch, pendant CHO),
Reaction of Tris(ethene)platinum(0) with Ligand c: Synthesis of
Complexes 10c, 11c, and 6c. Under an atmosphere of ethene, tris-
(ethene)platinum (22 mg, 0.079 mmol) and ligand c (64 mg, 0.158
mmol) were combined in an NMR tube and dissolved in C6D6 (0.5 mL).
The 1H and 31P NMR spectra recorded initially showed the formation of
both 10c and 11c. After one day, there was only 11c present. Nitrogen
was bubbled through the sample to convert 11c to 9c. The sample was
then heated at 40 °C for five days to give both the cis and trans isomers of
the 6,6-metallacycle 6c. The cis isomer was the major product. The
solution was filtered through alumina and washed with hexane and
toluene to give a sample of the two isomers pure enough for spectros-
copy but not elemental analysis.
3
1618 (CdO stretch, coordinated CdO). Analysis: C, 54.4, H, 3.9
(C39H32O2P2Pt CH2Cl2 requires C, 54.9; H, 3.9).
3
Reaction of Dimethyl(hexa-1,5-diene)platinum with Ligand d:
Synthesis of 6d. Dimethyl(hexa-1,5-diene)platinum (80 mg, 0.261
mmol) and ligand d (165 mg, 0.569 mmol) were combined in a two-
necked flask, and toluene (20 mL) was added. The mixture was stirred at
room temperature for 16 h followed by reflux for 16 h. A microcrystalline
solid, containing mostly cis-6d and some trans isomer, precipitated from
the solution. The mixture was cooled and filtered through sintered glass.
The solid was washed with cold toluene and then hexane (143 mg, 71%).
Pure cis-6d can be isolated by reacting the crude material containing cis
and trans isomers with tetrafluoroboric acid or CH2(SO2CF3)2 in
dichloromethane to protonate the cis isomer exclusively. The trans
isomer can then be removed via filtration. The cis isomer can
Reaction of Bis(cycloocta-1,5-diene)platinum(0) with Ligand a, b,
or c. Bis(cycloocta-1,5-diene)platinum (13 mg, 0.031 mmol) and ligand
a, b, or c (0.093 mmol) were combined in an NMR tube and dissolved
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in C6D6 (0.5 mL). The initial NMR spectra of the reaction with a
showed the presence of the tris(phosphine) complex [Pt(P)3] (12a),
the hydride complex 9a, and unreacted ligand. After two hours only the
hydride complex 9a and free ligand a were present. In the reaction with b
or c only the hydride complex and unreacted ligand were observed in the
NMR spectra.
Reaction of Bis(cycloocta-1,5-diene)platinum(0) with Ligand b.
Bis(cycloocta-1,5-diene)platinum (53 mg, 0.13 mmol) and ligand b
(117 mg, 0.26 mmol) were dissolved in hexane (5 mL) to produce 9b,
which precipitated as a yellow powder. The yellow powder was dissolved
in Et2O with a drop of cycloocta-1,5-diene. Yellow block crystals suitable
for single-crystal X-ray structure determination were obtained from
inward diffusion of hexane at 4 °C.
Reaction of Tris(norbornene)platinum(0) with Ligand d. Tris-
(norbornene)platinum (100 mg, 0.21 mmol) and ligand d (128 mg,
0.44 mmol) were combined in a Schlenk tube. Toluene (7 mL, dry,
degassed) was added, and the mixture was stirred and then left to stand
for 20 h. Yellow crystals formed. The solvent was removed under vacuum,
and the residue was dried under vacuum for two hours to remove free
norbornene. NMR analysis showed a virtually pure sample of 13d,
although in solution the complex reacts to form cis-6d. After one week
complexes, and X-ray crystallographic files in CIF format for 2a,
cis-6d C6H6, and 9b. This material is available free of charge via
3
the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: +64 4 463 5119. Fax: +64 4 463 5241. E-mail: john.spencer@
vuw.ac.nz.
’ ACKNOWLEDGMENT
We thank Dr. Jan Wikaira at the University of Canterbury for
collecting the single-crystal X-ray data and Dr. John Ryan at
Victoria University of Wellington for measuring the 15N NMR
spectra. T.F.V. and D.J.K. would like to acknowledge the award of
Curtis Gordon Research Scholarships in Chemistry and VUW
Graduate awards.
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at room temperature, orange crystals of cis-6d C6H6 suitable for single-
3
crystal X-ray structure determination grew out of the reaction mixture.
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Reaction of Tris(norbornene)platinum(0) with Ligand e in Air:
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Nitrogen: Synthesis of 5,6-Metallacycle 14e. Tris(norbornene)platinum
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3
from the reaction of tris(norbornene)platinum and d in benzene. Yellow
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Et2O solution of 9b in the presence of a small amount of cycloocta-1,5-
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DABS program. The structures of 2a and cis-6d C6H6 were solved using
3
Patterson methods, and 9b was solved using direct methods using
SHELXS97 and refined using SHELXL97.57
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b
1aꢀ3c, 1H, 13C, 15N, and 31P NMR data for all of the platinum
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