Cationic methylpalladium(II) complexes containing bidentate N-O ligands as catalysts for the copolymerisation of CO and ethylene. Identification and isolation of intermediates from the stepwise insertion reactions, and subsequent detailed mechanistic interpretation

Article abstract of DOI:10.1039/a707199j

A series of cationic methylpalladium(II) complexes containing bidentate N-O ligands, of the general formula [PdMe(N-O)L]BF₄ (N-O = methyl picolinate, methyl 6-methylpicolinate, N,N-diisopropylpicolinamide, 6-methyl-N,N-diisopropylpicolinamide; L = PPh₃ or PCy₃) have been prepared and characterised. The solid-state structure of [PdMe(N-O)(PPh₃)]BF₄ (N-O = N,N-diisopropylpicolinamide), in comparison with that for the complex with N-O = methyl picolinate, indicates a significant lengthening of the Pd-P bond [Δ(Pd-P) = 0.018(3) A] possibly due to the presence of the more strongly co-ordinating N-O ligand. Complexes with L = PPh₃ were found to be active for the copolymerisation of CO and ethylene to give polyketone. The complexes [PdMe(N-O)(PPh₃)]BF₄ (N-O = methyl 6-methylpicolinate or diisopropylpicolinamide) have the highest catalytic activities (80 g polymer per g Pd per hour and 58 g polymer per g Pd per hour respectively, at 20°C). Examples of the complexes form simple acyl complexes when treated with CO at room temperature and pressure and the spectroscopic data of the resulting acetyl complexes are reported. The stepwise migratory insertion of CO and ethylene into the complex [PdMe(N-O)(PPh₃)]BF₄ (N-O = methyl picolinate) has been carefully monitored and the individual insertion products have been characterised. Insertion of ethylene into the Pd-acyl bond of [Pd(COMe)(N-O)(PPh₃)]BF₄ (N-O = methyl picolinate) affords one of the first examples of an isolable product from insertion of an unstrained alkene into a Pd-acyl bond. A detailed mechanism for the co-reaction of CO and ethylene catalysed by complexes containing chelate ligands with distinct donor groups is discussed and an explanation of the observed reaction behaviour provided. The proposed mechanism represents one of the most comprehensive interpretations of this important reaction.

Full text of DOI:10.1039/a707199j

View Article Online / Journal Homepage / Table of Contents for this issue
Cationic methylpalladium(II) complexes containing bidentate N᎐O
ligands as catalysts for the copolymerisation of CO and ethylene.
Identification and isolation of intermediates from the stepwise
insertion reactions, and subsequent detailed mechanistic
interpretation‡
Melinda J. Green,a George J. P. Britovsek,a Kingsley J. Cavell,*,†,a Frank Gerhards,a
Brian F. Yates,a Katrina Frankcombe,a Brian W. Skeltonb and Allan H. Whiteb
a Department of Chemistry, University of Tasmania, GPO Box 252C, Hobart 7001, Australia
b Department of Chemistry, University of Western Australia, Nedlands 6907, Australia
A series of cationic methylpalladium() complexes containing bidentate N᎐O ligands, of the general formula
[PdMe(N᎐O)L]BF4 (N᎐O = methyl picolinate, methyl 6-methylpicolinate, N,N-diisopropylpicolinamide, 6-methyl-
N,N-diisopropylpicolinamide; L = PPh3 or PCy3) have been prepared and characterised. The solid-state structure
of [PdMe(N᎐O)(PPh3)]BF4 (N᎐O = N,N-diisopropylpicolinamide), in comparison with that for the complex with
N᎐O = methyl picolinate, indicates a significant lengthening of the Pd᎐P bond [∆(Pd᎐P) = 0.018(3) Å] possibly due
to the presence of the more strongly co-ordinating N᎐O ligand. Complexes with L = PPh3 were found to be active
for the copolymerisation of CO and ethylene to give polyketone. The complexes [PdMe(N᎐O)(PPh3)]BF4
(N᎐O = methyl 6-methylpicolinate or diisopropylpicolinamide) have the highest catalytic activities (80 g polymer
per g Pd per hour and 58 g polymer per g Pd per hour respectively, at 20 ЊC). Examples of the complexes form
simple acyl complexes when treated with CO at room temperature and pressure and the spectroscopic data of the
resulting acetyl complexes are reported. The stepwise migratory insertion of CO and ethylene into the complex
[PdMe(N᎐O)(PPh3)]BF4 (N᎐O = methyl picolinate) has been carefully monitored and the individual insertion
products have been characterised. Insertion of ethylene into the Pd᎐acyl bond of [Pd(COMe)(N᎐O)(PPh3)]BF4
(N᎐O = methyl picolinate) affords one of the first examples of an isolable product from insertion of an unstrained
alkene into a Pd᎐acyl bond. A detailed mechanism for the co-reaction of CO and ethylene catalysed by complexes
containing chelate ligands with distinct donor groups is discussed and an explanation of the observed reaction
behaviour provided. The proposed mechanism represents one of the most comprehensive interpretations of this
important reaction.
With the introduction of Shell’s Carilon thermoplastic poly-
mers in 1995 the production of polyketone became an eco-
nomic reality. This initial success is likely to stimulate other
groups into looking for commercial opportunities with this
class of polymer.1 For example, new developments in this
area that have been recently reported include: the synthesis
of catalysts for the formation of alternating copolymers of
functionalised alkenes with CO,2 synthesis of stereoblock
polyketones,3 the use of alumoxanes as cocatalysts in poly-
ketone formation,4,5 and the application of bis(chelate)pal-
ladium complexes in the copolymerisation of CO with alkenes.6
The stepwise migratory insertion of CO and alkenes into
Pd᎐alkyl and Pd᎐acyl bonds are key steps in catalytic poly-
ketone formation. These insertion reactions have been
examined in some detail and the studies have provided
valuable information on mechanistic aspects of polyketone
formation.7–13 Very recently Vrieze and co-workers have also
investigated the stepwise insertion of CO with allenes.14 How-
ever, despite the range of studies undertaken the direct
observation of carbonyl alkyl and alkene acyl complexes and
their subsequent migratory insertion reactions is rare. Tóth
and Elsevier have investigated the reaction of CO with the
palladium complex [Pd(Me){(S,S)-BDPP}(solv)]BF4 [where
(S,S)-BDPP = (2S,4S)-2,4-bis(diphenylphosphino)pentane].15
They identified spectroscopically the square-planar cis-alkyl-
(carbonyl) complex [Pd(Me)(CO){(S,S)-BDPP}]BF4 which
they propose is an intermediate in the formation of the acyl
complex [Pd(COMe){(S,S)-BDPP}(CO)]BF4. By working at
very low temperatures Brookhart and co-workers10,11 have been
able to prepare the unstable cationic 1,10-phenanthroline
palladium complexes containing cis carbonyl alkyl, carbonyl
acyl, ethylene alkyl and ethylene acyl groups. The migratory
insertion reactions of these intermediates were monitored by
low-temperature NMR spectroscopy and energy barriers for
insertion were calculated.
The majority of the studies into stepwise insertion reactions
have been concerned with stoichiometric reactions of CO with
strained or bulky olefins; intermediates from the insertion of
alkenes into Pd᎐acyl complexes were generally only observable
if strained or bulky olefins were used. Furthermore, the systems
investigated were not reported as being catalytically active
for polyketone formation. In all studies it was found that
migratory insertion of alkenes into metal–acyl species results
in the formation of chelated alkyl/carbonyl species of the type
[PdCRHCRЈHC(O)RЉ]ϩ containing five-membered ring struc-
tures and in several cases six-membered chelates are formed
upon migratory insertion of a further CO unit.7–13,16,17 In a
preliminary communication we reported an active catalytic
system for CO/ethene copolymerisation, [PdMe(N᎐O)(PPh3)]-
BF4 1a (Fig. 1) (N᎐O = NC5H4CO2Me, methyl picolinate), for
which we were able to spectroscopically monitor the formation
of intermediates resulting from stepwise CO and ethene inser-
tion.12 We were also able to isolate and record a crystal structure
† E-Mail: Kingsley.Cavell@utas.edu.au
‡ Non-SI units employed: 1 atm = 101.325 kPa, 1 bar = 102 kPa.
Picolinate = 2-pyridinecarboxylate, picolinamide = 2-pyridinecarbox-
amide.
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144
1137

View Article Online
+ BF4
+ BF4
–
–
Me
Pd
Table 1 Selected IR data [ν(C᎐O)] for complexes 1a–5a and 1b–3ba
᎐
N
N
O
Me
Me
ν(C᎐O)/cmϪ1
᎐
Pd
OMe
OMe
Ph3P
O
Ph3P
Complex
Free ligand
Complex
∆ν(C᎐O)/cmϪ1
᎐
1a
2a
1a
1739, 1726
1735, 1724
1634
1630
1630
1739, 1726
1735, 1724
1634
1671
1672
1569
1572
1595
1673
1673
1569
68, 55
63, 52
65
58
35
66, 53
62, 51
65
2a
3a
4a
+ BF4
+ BF4
–
–
5a
Me
Pd
1bb
2bc
3bd
N
N
O
Me
Me
Pd
NPri2
NPri2
a In CH2Cl2 solution. b ν(C᎐O) PdCOMe 1721 cmϪ1
.
c ν(C᎐O) PdCOMe
Ph3P
O
R3P
᎐
᎐
1720 cmϪ1
.
d ν(C᎐O) PdCOMe 1707 cmϪ1
.
᎐
3a
4a PR3 = PPh3
5a PR3 = PCy3
Fig. 1 Cationic organopalladium complexes with bidentate N᎐O
ligands
+ BF4
+ BF4
–
–
R
R
O
N
O
N
CO
Me
Pd
Me
+ BF4
Pd
–
R
R
X
X
Me
L
Cl
Ph3P
Ph3P
O
N
O
Me
L
N
O
AgBF4
– AgCl
1
Pd
/
2
+
1b R = H, X = OMe
2b R = Me, X = OMe
3b R = H, X = NPri2
Pd
2
X
X
Scheme 1 Preparation of complexes 1a–5a
Scheme 2 Carbonylation of complexes 1a–3a
for the intermediate, 1c in Scheme 3, formed from the migratory
insertion of ethene into the metal–acyl bond. The complex has
a square-pyramidal structure with a chelating alkyl/carbonyl
ligand and a long Pd᎐O (ester carbonyl) bond [2.78(1) Å] in the
apical position.12 The only other example of an isolable com-
pound from the insertion of ethene into a Pd᎐acyl bond was
reported by Brookhart and co-workers.10,11
Herein we report details of the preparation and characteris-
ation of a series of cationic methylpalladium complexes, 1a–5a
(Fig. 1), containing the chelating N᎐O ligands methyl picolinate
(NC5H4CO2Me-2), N,N-diisopropylpicolinamide [NC5H4C(O)-
NPri2-2] and their 6-methyl derivatives. We also report their
reactions with CO and their application in the copolymeris-
ation of CO and ethene. The significance of the intermediates
identified during the copolymerisation reaction is discussed
with reference to the overall reaction mechanism. The detailed
mechanism proposed includes a discussion of possible isomeris-
ation processes occurring during the copolymerisation and pro-
vides an explanation of the observed reaction behaviour. The
solid-state structure of the complex [PdMe{C5H4NC(O)NPri2}-
(PPh3)]BF4, 3a, has been determined and is compared to that of
the related complex 1a.
The carbonylation of complexes 1a–3a to yield the acyl
complexes 1b–3b is complete and quantitative after 10–15 min
treatment with CO at room temperature and pressure (Scheme
2). The acyl complexes decompose in solution at room temper-
ature to Pd0 and unidentified organic products. Complex 1b has
been isolated in the solid state and stored overnight at 5 ЊC
without significant decomposition. The stability of the other
complexes was not investigated.
Selected spectroscopic data for the complexes 1a–3b are pre-
sented in Tables 1 and 2. From the IR spectra, a decrease in the
carbonyl stretching frequency [ν(C᎐O)] of the N᎐O ligands by
᎐
50–70 cmϪ1 is observed upon co-ordination of the carbonyl
oxygen. The changes in the carbonyl peaks may be used to
monitor the extent and rate of reaction of 1b→1c (see below).
The IR spectra of the two ester ligands (i.e. methyl picolinate
and methyl 6-methylpicolinate) exhibit two equally intense
peaks in the carbonyl stretching region (13 and 11 cmϪ1 apart
respectively) whether performed neat or in a CH2Cl2 solution.
A consideration of the carbonyl stretching region for similar
compounds indicates that this result is also observed for other
pyridine-based esters having a 2-substituted CO2R group (e.g.
ethyl picolinate).18 The reason for the existence of two carbonyl
stretching peaks is uncertain, but the effect disappears upon
co-ordination of the picolinate ligand (Table 1).
Results and Discussion
Preparation and characterisation of the complexes
[PdMe(N᎐O)L]BF4 and [Pd(COMe)(N᎐O)L]BF4
A comparison of the NMR data for the methyl complexes
1a–5a and related acyl complexes 1b–3b is provided in Table 2.
The Pd᎐methyl peaks moves downfield by approximately 1 ppm
1
Complexes 1a–5a were prepared by adding 2 equivalents of the
methyl picolinate or diisopropylpicolinamide ligand to a sus-
pension of [PdMe(PPh3)(µ-Cl)]2, with subsequent addition of
AgBF4 (Scheme 1). The reaction proceeds smoothly with high
yields, provided that the exact stoichiometric amount of AgBF4
is used.
in the H NMR and 30 ppm in the 13C NMR spectrum on
insertion of CO into the Pd᎐methyl bond. This is accompanied
by a small downfield shift in the 13C NMR carbonyl resonance
of the N᎐O ligand, and ≈10 ppm upfield shift of the 31P NMR
signal.
For the series of complexes 1a–1d, formed from the stepwise
It was anticipated that an amide N᎐O ligand may strengthen
the N᎐O chelate and thus provide a more stable complex. How-
ever, complexes 1a–5a are all unstable in solution, decomposing
to Pd0 and unidentified products within 1 d at room temper-
ature and the complexes 4a and 5a which both have the
6-methyl-N,N-diisopropylpicolinamide ligand are significantly
more unstable. It is evident that the presence of the methyl
group in the 6 position on the pyridine ring has a destabilising
influence probably due to steric interaction with the Pd᎐methyl
ligand.
insertion of CO and ethylene, regular changes in the IR carb-
onyl stretch [∆ν(C᎐O) = 55–83 cmϪ1] and 13C NMR carbonyl
᎐
signal [∆δ(C᎐O) = 6–12 ppm] are observed, corresponding to
᎐
the co-ordination/dissociation of the carbonyl groups of the
N᎐O ligand and the growing polymer chain (Table 3). From this
data it is clearly evident that the N᎐O ligand in 1d has reco-
ordinated after the reaction of 1c with further CO and that the
carbonyl group of the growing polyketone chain of 1d does not
co-ordinate to the palladium to form a six-membered chelate
(such chelates are known to be weak11). The 31P NMR reson-
1138
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144

View Article Online
Table 2 Selected 1H, 13C and 31P NMR data for complexes 1a–5a and 1b–3ba
13C NMR
1H NMR
δ(PdCH3 or
PdCOCH3)
[JHP in Hz]
δ(PdCH3 or
PdCOCH3)
[JCP in Hz]
δ(C᎐O)
N᎐O ligand
δ(C᎐O)
PdCOCH3
31P NMR
δ
᎐
᎐
Complex
1a
2a
3a
4a
5a
1b
2b
3b
1.09 [d, 1.4]
0.97
0.98
0.90
5.74
3.25
6.33
3.31
171.3
171.0
171.2
170.2
168.7
170.3
169.4
170.2
35.8
37.7
35.5
35.4
39.2
24.2
0.71
Ϫ7.59
2.25 [d, 1.7]
2.17
35.6 [d, 25.0]
37.0 [d, 28.2]
36.9 [d, 24.0]
221.0
221.5
224.5
25.4
1.97 (s), 2.29 [d, 1.8]b
24.1, 24.9b
a In CDCl3 solution. b Two isomers observed in 6:1 ratio.
Table 3 Comparison of spectral data for products from the stepwise insertion reactions
IR data,a ν(C᎐O)/cmϪ1 13C NMR,b δ(C᎐O)
31P NMRb δ
᎐
᎐
Compound
N᎐O Ligand
Acyl/alkyl
N᎐O Ligand
Acyl/alkyl
PPh3
Methyl picolinate
1726
1671
1672
1733
1670
165.3
171.3
170.3
164.2
171.2
1a
1b
1c
1d
35.8
24.2
36.2
24.7
1720
1637
1715
1715
221.0
232.4
221.0
206.8
a In CH2Cl2 solution. b In CDCl3 solution.
Fig. 2 Proton NMR spectra of the CO/ethylene insertion products
1a–1d [where a is the methoxy signal for the N᎐O ligand; b and d are the
methylene signals for the ethylene inserted products; c is the methyl
group initially co-ordinated to the palladium (which becomes the acyl
methyl then keto methyl)]
Fig. 3 View normal to the co-ordination plane for the complex 3a;
20% thermal ellipsoids are shown for the non-hydrogen atoms, hydro-
gen atoms having an arbitrary radius of 0.1 Å
ance of PPh3 shifts by 10 ppm on alternating insertions of CO
and ethylene. Fig. 2 shows the characteristic variation of the
methyl (c) and methylene signals (b and d) in the H NMR
spectra of the insertion products, while the methoxy signal (a)
of the N᎐O ligand remains virtually unchanged at δ ≈ 4
throughout.
together integrate for three protons (assigned to the acyl group)
and have integral ratios of 6:1. This is supported by the 31P
NMR spectrum of 3b which shows two peaks (at δ 24.1 and
24.9), also in a 6:1 ratio. It is likely that the major isomer is the
P trans N isomer.
1
Only one isomer of each of the methyl complexes 1a–5a is
observed in the NMR spectra. This is believed to be the P trans
N isomer for all complexes (see below). The NMR spectra of
the acyl complexes 1b and 2b also indicate that only one
isomer is present in each case. A similar neutral acyl complex,
[Pd(COMe)(NC5H4CO2-2){P(CH2Ph)3}], was found to exhibit
P trans N geometry,19 thus it is to be expected that complexes 1b
and 2b will have the same arrangement of ligands. Complex 3b
exists as both the P trans N and the P trans O isomers in a 6:1
ratio. Two peaks due to the methyl protons are observed in the
1H NMR spectrum of 3b, one at δ 2.29 and one at δ 1.97 which
Solid-state structures of 3a and 1c
Crystal structure determinations of complexes 1a20 and 3a
(Fig. 3) confirm that these complexes exist as the isomer with P
trans N in the solid state. This geometry is also preferred for
analogous neutral complexes [PdMe(PR3)(NC5H4CO2-2)].21
A
comparison of important bond lengths is shown in Table 4. The
only notable difference in the palladium co-ordination sphere
for the two complexes is the longer Pd᎐P bond for complex 3a
[2.226(2) Å] compared to complex 1a [2.208(3) Å]. A small
decrease in the size of the chelate angle (O᎐Pd᎐N) is observed
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144
1139

View Article Online
Table 4 Comparison of selected bond lengths (Å) and angles (Њ) for
complexes 1a, 3a and 1c
Table 5 Catalytic results for complexes 1a–5aa
Reaction
conditions
Complex 1a20
Complex 3a
Complex 1c
Results
TON g(PK) per g(Pd)
Catalyst
Run complex n/mmol T/ЊC t/h
Pd᎐P
Pd᎐N
Pd᎐C
Pd᎐O
2.208(3)
2.141(9)
2.02(1)
2.226(2)
2.122(4)
2.032(5)
2.173(4)
2.215(6)
2.19(1)
2.00(1)
2.78(1)a
2.16(2)b
1
2
1a
1a
2a
2a
2a
3a
3a
4ab
4a
4ac
4a
4a
5a
5a
0.097
0.093
0.104
0.090
0.092
0.103
0.098
0.102
0.103
0.093
0.103
0.103
0.103
0.097
20
20
20
20
20
20
40
65
20
20
40
20
20
40
1
20
1
41
115
103
75
146
0
21
2.180(7)
60
54
40
77
0
3
4
0.5
P᎐Pd᎐N
P᎐Pd᎐O
P᎐Pd᎐C
N᎐Pd᎐O
N᎐Pd᎐C
O᎐Pd᎐C
174.7(3)
99.9(2)
88.3(3)
74.8(4)
96.9(4)
170.3(2)
175.5(1)
100.1(1)
88.3(2)
76.6(1)
95.3(2)
170.3(2)
97.3(5)
169.5(3)
89.5(6)
91.6(6)
172.9(8)
81.4(7)
5
6
20
1
7
8
22.5
2
272
88
111
179
196
411
0
143
46
58
94
103
216
0
9
1
20
1
20
1
1
10
11
12
13
14
a Distance of axial contact between Pd and the oxygen of the N᎐O
ligand. b Bond distance for oxygen of the butanonyl ligand to
palladium.
0
0
a Catalytic conditions: 40 mL CH2Cl2; initial p(CO) = 20 bar; initial
p(CH2᎐᎐CH2) = 20 bar. b 50 mL CHCl3. c Initial p(CO) = 5 bar; initial
p(CH2᎐᎐CH2) = 25 bar.
+
MeO
PPh3
R
O
N
CO
Pd
polyketone
β-elimination,
R = H
1a R = Me
+
(n–1) CO
MeO
O
PPh3
R
Pd
n CH2=CH2
N
O
1b R = Me
+
MeO
O
O
PPh3
O
Pd
N
R
CH2=CH2
+
1d R = Me
R
O
N
Pd
O
PPh3
OMe
CO
1c R = Me
Fig. 4 View of the complex 1c normal to the co-ordination plane; 20%
thermal ellipsoids are shown for the non-hydrogen atoms, hydrogen
atoms having an arbitrary radius of 0.1 Å
Scheme 3 Proposed catalytic cycle for complex 1a showing the first
three isolated intermediates (1b–1d)
Copolymerisation of CO and ethylene
for complex 1a [74.8(4)Њ] compared with the picolinamide
ligand of complex 3a [76.6(1)Њ]. This seems to be compensated
for by a smaller N᎐Pd᎐C angle for complex 3a [95.3(2) cf.
96.9(4)Њ for complex 1a].
The methyl complex 1a and the CO and ethylene inserted
complex 1c (Fig. 4) have quite different arrangements of
ligands (with N trans P for 1a and N trans C for 1c) (Scheme 3).
The Pd᎐P bond distances are similar for the two complexes
[2.208(3) and 2.215(6) Å]. However, there is an increase in the
Pd᎐N bond length for complex 1c [2.19(1) Å] compared to 1a
[2.141(9) Å] consistent with the stronger trans influence of the
alkyl group relative to PPh3.
Complex 1c has a Pd᎐C bond length of 2.00(1) Å, which is
typical of those found in other alkene inserted complexes.9,16
However, the Pd᎐O bond distance [2.16(2) Å] of the chelat-
ing alkylketo group reflects the relative trans influence of
the PPh3 ligand, being significantly longer than those reported
by Markies et al.9 for complexes with bidentate nitrogen
ligands [р2.033(5) Å], but similar to the complex reported
by Brumbaugh et al. having two PPh3 ligands [2.114(6) Å].16
Bond lengths of the carbon–oxygen double bond in anal-
ogous complexes in the literature range from 1.236(8) to
1.249(6) Å9,16 which are close to the value found for complex 1c
[1.23(2) Å].
The results of the copolymerisation experiments are given in
Table 5, with activities expressed both as TON (i.e. moles of
substrate converted per moles of Pd) and also in g of poly-
ketone per g of palladium. Complexes 1a–4a are all active
catalysts for the copolymerisation of CO and ethylene, but
the activity is low in comparison with some reported
catalysts.4,5,22–28 Analysis of the solvent by GC after the removal
of all solid product showed the presence of only trace amounts
of oligomeric products when complexes 3a–5a were used. The
co-oligomers were identified by GC–MS and are identical to
those reported by Keim et al.,29 obtained using cationic
palladium catalysts with P᎐O ligands.
Under the conditions used, the activity of the complexes
towards polyketone formation decreases in the order: 4a >
2a > 1a > 3a ӷ (5a = 0). The 6-methyl substituent on the
pyridyl ring of the N᎐O ligand has an activating effect and both
complexes 2a and 4a are substantially more active than the
respective complexes with unsubstituted N᎐O ligands (1a
and 3a). The higher activity of complexes 2a and 4a can be
explained by sterically induced weakening of the Pd᎐N bond by
the 6-methyl substituent, facilitating isomerisation of the com-
plex during catalysis (see later discussion under Mechanism).
The 6-methyl substituent also leads to decreased stability in
1140
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144

View Article Online
+
+
+
MeOC
Ph3P
O
N
O
+
Me
N
O
MeOC
N
Pd
O
CO
Pd
Me
OC
N
Pd
isomerisation
Pd
PPh3
isomerisation
PPh3
Ph3P
1b
1a
migratory
insertion
migratory
insertion
+
Me
+
+
O
N
N
O
isomerisation
O
N
Pd
Pd
Pd
PPh3
O
MeOC
PPh3
PPh3
MeOC
1c
1b
Scheme 5 Mechanism for ethylene insertion
Scheme 4 Pathway for CO insertion
calculated value for the long apical Pd᎐O bond is 2.76 Å,
compared with 2.78(1) Å obtained in the experimental
work.
complexes 2a and 4a compared to complexes 1a and 3a.
Increasing the reaction temperature results in an increase in the
activity of complexes 3a (runs 6 and 7) and 4a (runs 8, 9 and
11), but the higher temperature also has a detrimental effect on
catalyst stability.
In contrast to complex 4a, which contains triphenylphos-
phine, the complex 5a containing the highly basic tricyclo-
hexylphosphine as a ligand has no observable catalytic activity.
The inhibitory effect of PCy3 in carbonylation reactions of
related neutral complexes has previously been noted.21 The pos-
sible reason for this effect is described below in the discussion
of the mechanism.
The only products observed from the carbonylation of
complexes 1a and 2a were the P trans N acyl complexes 1b
1
and 2b respectively, while H NMR and 31P NMR data sug-
gest that 3b is a 6:1 mixture of the trans and cis isomers. It is
difficult to account for the existence of the P cis N isomer of
3b when complexes 1b and 2b only have a trans geometry,
given the small differences in ligand environment of these
complexes. Calculations indicate that although the P cis N
isomer is the initial product of the CO migratory insertion
step, the P trans N acyl isomer is thermodynamically pre-
ferred (Scheme 4).31 A similar isomerisation process has been
observed previously by Markies et al. in the neutral PdII acyl
complexes [Pd(COMe)(bipy)X] (X = Cl or Br).9 They found
that irradiation of either of the inequivalent H6 protons of
Mechanism
Recently, we presented a preliminary report on the stepwise
migratory insertion of CO and ethylene into the catalytically
active complex 1a (Scheme 3).12 Reaction of CO with 1a yields
the acyl complex [Pd(COMe)(NC5H4CO2Me-2)(PPh3)]BF4 1b,
which has been identified spectroscopically. Subsequent reac-
tion of 1b with ethylene yields an isolable intermediate, [Pd-
(CH2CH2COMe)(NC5H4CO2Me-2)(PPh3)]BF4 1c, for which
the crystal structure was determined. This five-co-ordinate,
square pyramidal intermediate has the weakly interacting
methyl picolinate carbonyl oxygen in an apical position. The
methyl picolinate oxygen has apparently been displaced from
the square plane by the more strongly co-ordinating alkyl
carbonyl oxygen of the growing polyketone chain. In the solid
state, complex 1c exists only as the isomer having P cis N, in
contrast to complexes 1a and 1b (both P trans N). This result
shows clearly that isomerisation has also occurred during the
migratory insertion process, thus converting 1b into 1c. Add-
ition of further CO to intermediate 1c leads to formation of a
new acyl complex 1d. Spectroscopic evidence supports a P trans
N geometry for 1d (an analogue of 1b), which indicates that
isomerisation has again occurred during the migratory inser-
tion of CO into the Pd᎐alkyl bond.
1
bipy resulted in the disappearance of the H NMR signal of
the other. Such isomerisation processes are common for
square-planar complexes.4,32
It was noted above that more strongly co-ordinating
phosphines such as tricyclophosphine deactivate complexes of
type 1a. From experimental data alone this behaviour is hard
to explain. It may be expected that a stronger donor phos-
phine would further weaken the trans ligand and in fact pro-
mote the catalytic reaction. That this does not happen may
be understood by further reference to the ab initio modelling
studies. Calculations show that more strongly co-ordinating
phosphines such as PCy3 deactivate complexes of this type
by preventing the necessary isomerisation of the complex
during reaction with CO and ethylene.30 A low energy
pathway for isomerisation which proceeds via a weakening
or elongation of the Pd᎐P bond was identified. If this
elongation is impeded, i.e. by strong co-ordination of
the phosphine (as in the case of a more basic phosphine)
the barrier to isomerisation becomes too great. If isomeris-
ation cannot take place then migratory insertion cannot
proceed.
The proposed mechanism for the copolymerisation of CO
and ethylene catalysed by complexes of type 1a–4a is presented
in Scheme 3. The first step, the carbonylation of the methyl-
palladium complex to give an acyl complex, occurs readily for
all complexes and is therefore not the rate-determining step in
the cycle. The second CO insertion reaction is much slower than
the first (2 h versus 10 min for completion at room temperature
and 1 atm pressure). The slower reaction is probably due to the
energy required to break the stronger butanonyl chelate in
complex 1c which occurs during insertion of the second CO.
However, the slowest step in the overall reaction is ethylene
insertion into the palladium–acyl bond (ca. 3 h), which is gen-
erally believed to be the rate-determining stage in polyketone
formation.33 It is interesting to consider the stepwise insertion
process as a competitive switching of one carbonyl donor for
another in which firstly one chelate co-ordinates strongly and
then the other.
This study of the stepwise insertion of CO and ethylene
demonstrates that isomerisation is a general step in the
copolymerisation reaction with complex 1a as the catalyst. Such
a pathway is likely to be pertinent to other systems containing
chelate ligands with different donor groups. Supporting evi-
dence for the detailed mechanism comes from a recent theor-
etical study in which the model cationic complex, [Pd(CH3)-
(HN᎐CHCHO)(PH )]ϩ was investigated.30,31 Ab initio calcu-
᎐
3
lations indicate that the lowest energy pathway for the carbon-
ylation of the model complex occurs via a five-co-ordinate,
square pyramidal intermediate (akin to the isolated complex
1c) with trans-cis isomerisation (of P and N) preceding the
insertion step (Scheme 4).30,31 A similar low energy pathway
involving trans → cis isomerisation of the P and N ligands
was also noted for the insertion of ethylene into the resulting
Pd᎐acyl bond (Scheme 5).31 Importantly, the predicted struc-
ture of the intermediate formed following ethylene insertion
is a square pyramidal complex directly analogous to 1c. The
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144
1141

View Article Online
Synthesis and characterisation of ligands and complexes
Experimental
N,N-Diisopropylpicolinamide. This compound was prepared
by an adaption of the synthesis given for N,N-diisopropyl-
nicotinamide by Swain and Naegele.38 Picolinic acid (6.16 g, 50
mmol) and freshly distilled thionyl chloride (18 mL, 250 mmol)
was refluxed for 1 h. Excess SOCl2 was removed by vacuum
distillation to leave a burgundy solid. To this was added dry
benzene (30 mL), pyridine (8 mL, 100 mmol) and diisoprop-
ylamine (21 mL, 150 mmol). The reaction mixture was refluxed
for 15 min and left to stir overnight. This mixture was filtered
and the residue washed with benzene. The filtrate was made
basic with aqueous NaOH and the aqueous layer extracted with
three portions of diethyl ether. The combined extracts were
washed with water and dried over MgSO4. After removal of the
solvent the remaining brown liquid was fractionally distilled
under vacuum. The first fraction (a pale yellow solid) was col-
Reagents
All reagents were used as received unless otherwise stated. High
purity nitrogen was further dried and deoxygenated over 4 Å
molecular sieves and BASF R 3-11 catalyst at 135 ЊC. Manipu-
lations of all complexes were carried out using carefully dried
glassware employing standard vacuum line and Schlenk tech-
niques under a dry nitrogen atmosphere. All solvents were dried
and purified by standard methods and freshly distilled under
nitrogen before use. Methyl 6-methylpicolinate was prepared by
the method given by Mathes et al.34 The compound [PdMeCl-
(COD)] was prepared by the method described by Rülke et
al.35 The dimeric complex [PdMe(µ-Cl)PPh3]2 was prepared
according to the method of Ladipo and Anderson,36 with the
exception that CH2Cl2 was used as the solvent instead of
benzene. The complex [PdMe(µ-Cl)(PCy3)]2 was prepared by
a similar method to that employed for [PdMe(µ-Cl)(PPh3)]2.
However, the reaction was much slower, needing 20 h to
reach completion. The precipitate was too fine to collect by
filtration, therefore it was washed with 5 × 5 mL hexane and
dried under vacuum. The product was a very pale yellow
powder insoluble in all common solvents (yield: 93%)
(Found: C, 52.51; H, 8.35. Calc. for C19H36ClPPd: C, 52.28;
H, 8.32%).
lected at 72–78 ЊC (10Ϫ2 atm) and recrystallised from heptane to
1
give a white solid. IR (CH Cl ): ν(C᎐O) 1634 cmϪ1. H NMR
᎐
2
2
(200 MHz, CDCl3): δ 8.58 (ddd, 1 H, J = 4.9, J = 1.7, J = 1.1,
C5H4N), 7.77 (dt, 1 H, J = 7.7, J = 1.7, C5H4N), 7.44 (td, 1 H,
J = 7.7, J = 1.1, C5H4N), 7.30 (ddd, 1 H, J = 7.6, J = 4.9, J = 1.1,
C5H4N), 3.83 (spt, J = 6.6, 1 H, NCH), 3.56 (spt, 1 H, J = 6.6,
NCH), 1.57 [d, 6 H, J = 6.6 Hz, CH(CH3)2], 1.18 [d, 6 H,
J = 6.6 Hz, CH(CH3)2]. 13C NMR (50 MHz, CDCl3): δ 168.6
(C᎐O), 156.5, 148.6, 136.9, 123.6, 121.8 (C H N), 50.7 (NCH),
᎐
5
4
Nuclear magnetic resonance spectra were recorded at 22 ЊC
(unless otherwise indicated) on a Bruker AM-300 spectrometer
at 300.13 (1H), 75.48 (13C) and 121.50 MHz (31P) or a Varian
Gemini-200 spectrometer at 199.98 MHz (1H). Chemical
shifts (δ) are reported in ppm relative to internal SiMe4 (1H,
13C), or to external 85% H3PO4 (31P). Infrared (IR) spectra
were recorded in absorbance units on a Bruker IFS-66
FTIR spectrometer; KBr disks and CH2Cl2 or CDCl3 solu-
tions were used in the mid IR range (400–4000 cmϪ1). Micro-
analyses were performed by the Central Science Laboratory,
University of Tasmania, using a Carlo Erba EA1108 Elemental
Analyser.
46.0 (NCH), 20.7 [CH(CH3)2], 20.5 [CH(CH3)2].
6-Methyl-N,N-diisopropylpicolinamide. The method of Swain
and Naegele for the synthesis of N,N-diethylpicolinamide
hydrochloride was used.38 Thus 6-methylpicolinic acid (5.46 g,
40 mmol) in 30 mL toluene was heated to 80 ЊC in the presence
of diisopropylamine (14.44 g, 140 mmol). At this temperature
P2O5 (9.3 g, 65 mmol) was added in three portions, each 10 min
apart. After refluxing overnight, the dark brown reaction mix-
ture was treated with base (10% by weight NaOH solution), and
extracted with a 1:1 solution of diethyl ether and toluene. The
dark brown solid isolated from these extracts was recrystallised
several times with hexane to give a white solid. IR (CH2Cl2):
1
ν(C᎐O) 1630 cmϪ1. H NMR (200 MHz, CDCl3): δ 7.64 (t, 1
Crystallography
᎐
H, J = 7.7, C5H3N), 7.20 (d, 1 H, J = 7.7, C5H3N), 7.12 (d, 1 H,
J = 7.7, C5H3N), 3.78 (spt, J = 6.6, 1 H, NCH), 3.55 (spt, 1 H,
J = 6.6, NCH), 2.56 (s, 3 H, C5H3NCH3), 1.56 [d, 6 H, J = 6.6,
CH(CH3)2], 1.18 [d, 6 H, J = 6.6 Hz, CH(CH3)2]. 13C NMR (75
Structure determination. A unique data set was measured
at ≈295 K within the limit 2θmax = 50Њ using an ENRAF-
Nonius CAD-4 diffractometer (2θ/θ scan mode; graphite ‘single
crystal’ monochromator; Mo-Kα radiation, λ = 0.710 73 Å);
5859 independent reflections were obtained without signifi-
cant crystal decomposition, 3325 with I > 3σ(I) being con-
sidered ‘observed’ and used in the full-matrix least-squares
refinement (nv = 397) after Gaussian absorption correction,
and solution of the structure by the heavy-atom method.
Anisotropic thermal parameters were refined for the non-
hydrogen atoms; (x, y, z, Uiso)H were included constrained at
appropriate trigonal or tetrahedral sites. Difference map
residues were modelled on dichloromethane of solvation,
site occupancy set at 0.5 after trial refinement (final |∆ρmax| 0.4
e ÅϪ3). Conventional residuals R (Σ∆|F|/Σ|Fo|), RЈ (Σw∆2/
MHz, CDCl ): δ 168.6 (C᎐O), 157.2, 155.5, 136.6, 122.7, 118.2
᎐
3
(C5H3N), 50.2 (NCH), 45.5 (NCH), 24.0 (C5H3NCH3), 20.2
{N[CH(CH3)2]2}.
Preparation of complexes 1a–5a. The preparation of complex
1a was reported earlier.20 Complexes 2a–5a were prepared simi-
larly by reacting 2 equivalents of the N᎐O ligand and AgBF4
with 1 equivalent of [PdMeL(µ-Cl)]2 (L = PPh3 or PCy3) in
CH2Cl2 at room temperature. Crystals suitable for an X-ray
structure determination of 3a were obtained by layering diethyl
ether onto a CH2Cl2 solution of 3a at room temperature.
[Pd(Me)(PPh3)(NC5H3CO2Me-2-Me-6)]BF4 2a. Yellow solid
(Found: C, 51.13; H, 4.50; N, 2.37. Calc. for C27H27BF4NO2-
¹
¹
2
2
²
²
Σ|Fo| ) on |F| were 0.039, 0.038 [S = Σw∆ /(n Ϫ p) = 1.6]
at convergence (∆/σmax,mean = 0.1, 0.004), statistical weights
derivative of σ2(I) = σ2(Idiff) ϩ 0.0004σ4(Idiff) being used. Com-
putation used the XTAL 3.2 program system implemented by
S. R. Hall,37 neutral-atom complex scattering factors being
employed.
PPdؒ0.2CH2Cl2: C, 51.15; H, 4.32; N, 2.19%). IR (CH2Cl2):
1
ν(C᎐O) 1672 cmϪ1. H NMR (200 MHz, CDCl3): δ 8.09–8.02
᎐
(m, 3 H, C5H3N), 7.67–7.27 (m, 15 H, C6H5), 3.81 (s, 3 H,
OCH3), 2.80 (s, 3 H, C5H3NCH3), 0.97 (s, 3 H, PdCH3). 13C
NMR (75 MHz, CDCl ): δ 171.0 (C᎐O), 163.0, 146.7, 140.7,
᎐
3
134.7–129.4, 126.0 (C6H5 and C5H3N), 55.7 (OCH3), 26.5
(C5H3NCH3), 3.25 (PdCH3). 31P NMR (121 MHz, CDCl3):
δ 37.7.
Crystal data. C31H36BF4N2OPPdؒ0.5CH2Cl2, M = 719.29,
orthorhombic, space group Pbca, a = 18.788(7), b = 18.993(4),
c = 18.700(7) Å, U = 6673(4) Å3 (‘calibrated’ on {9 9 9}), Dc
(Z = 8) = 1.432 g cmϪ3, F(000) = 2936, µMo = 7.3 cmϪ1, (yellow)
specimen, 0.32 × 0.45 × 0.21 mm, A*min,max = 1.16, 1.22.
CCDC reference number 186/879.
[Pd(Me)(PPh3)(NC5H4CONPri2-2)]BF4 3a. Yellow solid
(yield: 87%) (Found: C, 55.22; H, 5.20; N, 4.17. Calc. for
C31H36BF4NOPPdؒ0.5CH2Cl2: C, 55.01; H, 5.36; N, 4.14%).
IR (CH Cl ): ν(C᎐O) 1569 cmϪ1. 1H NMR (300 MHz, CDCl3):
᎐
2
2
See http//www.rsc.org/suppdata/dt/1998/1137/ for crystallo-
graphic files in .cif format.
δ 8.63 (br m, 1 H, C5H4N), 8.44 (br m, 1 H, C5H4N), 8.01 (br
m, 1 H, C5H4N), 7.88 (br m, 1 H, C5H4N), 7.7–7.4 (m, 15 H,
1142
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144

View Article Online
C6H5), 4.58 (br m, 1 H, NCH), 3.55 (br m, 1 H, NCH), 1.39 [br
s, 6 H, CH(CH3)2], 0.98 [br s, 9 H, CH(CH3)2 and PdCH3]. 13
7.88 (s, 1 H, C5H4N), 7.7–7.3 (m, 17 H, C6H5 and C5H4N), 3.93
C
(s, 3 H, OCH3), 3.17 (t, 2 H, J = 6.0, PdCH2CH2), 2.41 (s, 3 H,
COCH3), 1.72 (dt, 2 H, J = 6.0, J = 2.7 Hz, PdCH2CH2). 13C
NMR (75 MHz, CDCl3): δ 232.4 (COMe), 164.2 (CO2Me),
152.2, 145.8, 138.9, 134.1–128.7, 127.7 (C6H5 and C5H4N), 53.3
(OCH3), 51.0 (PdCH2CH2), 27.8 (COCH3), 23.0 (PdCH2). 31P
NMR (121 MHz, CDCl3): δ 36.2.
NMR (75 MHz, CDCl ): δ 171.2 (C᎐O), 151.5, 149.0, 141.9,
᎐
3
135.5–128.8, 127.4 (C6H5 and C5H4N), 54.2, 49.1 (NCH),
21.5, 19.9 [NCH(CH3)2], 6.33 (PdCH3). 31P NMR (121 MHz,
CDCl3): δ 35.5.
[Pd(Me)(PPh3)(NC5H3CONPri2-2-6-Me)]BF4 4a. Yellow
1
solid (yield: 90%). IR (CH Cl ): ν(C᎐O) 1572 cmϪ1. H NMR
[Pd(COCH2CH2COMe)(NC5H4CO2Me-2)(PPh3)]BF4
1d.
᎐
2
2
(200 MHz, CDCl3): δ 8.10 (t, 1 H, J = 7.8, C5H3N), 7.7–7.4 (m,
17 H, C6H5 and C5H3N), 4.38 (br m, 1 H, NCH), 3.57 (br m,
1 H, NCH), 2.82 (s, 3 H, C5H3NCH3), 1.4–1.1 {m, 12 H,
[CH(CH3)2]2}, 0.90 (d, 3 H, J = 2.3 Hz, PdCH3). 13C NMR (75
Yellow CDCl solution. IR (CH Cl ): ν(C᎐O) 1715 cmϪ1 (PdCO
᎐
3
2
2
and COMe), 1670 cmϪ1 (CO2Me). 1H NMR (300 MHz,
CDCl3): δ 8.71 (s, 1 H, C5H4N), 8.3 (m, 2 H, C5H4N), 7.96 (m,
1 H, C5H4N), 7.8–7.3 (m, 15 H, C6H5), 3.93 (s, 3 H, OCH3),
2.86 (t, 2 H, J = 4.8, CH2CH2COMe), 2.18 (t, 2 H, J = 4.8 Hz,
PdCOCH2CH2), 2.07 (s, 3 H, COCH3). 13C NMR (75 MHz,
CDCl3): δ 221.0 (PdCO), 206.8 (COMe), 171.2 (CO2Me), 145.2,
141.6, 134.2–127.9, 127.7 (C6H5 and C5H4N), 55.8 (OCH3), 44.0
(d, J = 24 Hz, PdCOCH2), 37.9 (CH2COMe), 29.6 (PdCOCH3).
31P NMR (121 MHz, CDCl3): δ 24.7.
MHz, CDCl ): δ 170.2 (C᎐O); 161.9, 151.9, 140.1, 134.2–128.6,
᎐
3
122.3 (C6H5 and C5H3N), 53.4, 47.7 (NCH), 26.3 (C5H3NCH3),
20.7, 19.7 [NCH(CH3)2], 3.31 (PdCH3). 31P NMR (121 MHz,
CDCl3): δ 35.4.
[Pd(Me)(PCy3)(NC5H4CONPri2-2-6-Me)]BF4 5a. Yellow
solid (yield: 95%) (Found: C, 49.00; H, 7.70; N, 3.44. Calc. for
C32H56BF4NOPPdؒ1.25CH2Cl2: C, 48.99; H, 7.23; N, 3.44%),
IR (CH Cl ): ν(C᎐O) 1595 cmϪ1. 1H NMR (200 MHz, CDCl3):
Copolymerisation of CO and ethylene
᎐
2
2
δ 8.02 (t, 1 H, J = 7.3, C5H4N), 7.57 (t, 2 H, J = 7.6 Hz), 3.87
[br m, 2 H, N(CH)2], 2.79 (s, 3 H, C5H4NCH3), 2.1–1.1 {br m,
45 H, C6H11 and [CH(CH3)2]2}, 0.71 (s, 3 H, PdCH3). 13C NMR
A solution of the appropriate complex (0.01 mmol) in CH2Cl2
(40 mL) was transferred to a 350 mL V4A steel autoclave, which
was equipped with a glass inlet and a magnetic stirring bar. For
experiments at higher temperatures, the autoclave was heated in
an oil bath and the temperature allowed to equilibrate before
pressurising the vessel. With continuous stirring, the autoclave
was pressurised with 20 bar CO and then ethylene until a total
pressure of 40 bar was reached. After allowing the reaction to
proceed for the appropriate time the excess gases were vented,
and the product mixture filtered to remove polyketone which
was washed with CH2Cl2, dried and weighed. The filtrate
was analysed by GC. The polyketone has a strictly alternating
structure as confirmed by 13C NMR (CF3CO2H–C6D6) and
microanalysis.
(75 MHz, CDCl ): δ 168.7 (C᎐O), 161.1, 153.4, 140.1, 127.3,
᎐
3
120.1 (C), 52.1, 46.7 (NCH), 32.5–25.6 (C6H11 and C5H4NCH3),
20.7 {N[CH(CH3)2]2}, Ϫ7.59 (PdCH3). 31P NMR (121 MHz,
CDCl3): δ 39.2.
Carbonylation of complexes 1b–3b. The acyl complexes 1b–3b
were prepared by bubbling CO for 10–15 min through a CH2Cl2
or CDCl3 solution of complexes 1a–3a. The yields appear to be
quantitative on the basis of NMR spectroscopy. The prepar-
ation of complex 1b has been previously reported.20
[Pd(COMe)(PPh3)(NC5H3CO2Me-2)]BF4 1b. IR (CH2Cl2):
1
ν(C᎐O) 1721 cmϪ1 (PdCOMe), 1673 cmϪ1 (CO2Me). H NMR
᎐
(300 MHz, CDCl3): δ 8.16 (br s, 1 H, C5H3N), 7.70–7.43 (m,
15 H, C6H5), 3.99 (br s, 3 H, OCH3), 2.25 (d, 3 H, J = 1.7 Hz,
COCH3). 13C NMR (75 MHz, CDCl3): δ 221.0 (PdCO), 170.3
(CO2Me), 150.2, 145.3, 141.3, 134.1–127.7 (C6H5 and C5H3N),
55.5 (OCH3), 35.6 (d, J = 25 Hz, COCH3). 31P NMR (121 MHz,
CDCl3): δ 24.2.
Acknowledgements
We would like to acknowledge the support of the Australian
Research Council in particular for the salary of G. J. P. B. and a
scholarship for M. J. G. We also thank the Central Science
Laboratory, University of Tasmania for the use of their facil-
ities and expertise, and Johnson Matthey for their generous
loan of palladium chloride.
[Pd(COMe)(PPh3)(6-Me-NC5H3CO2Me-2)]BF4
2b.
IR
(CH Cl ): ν(C᎐O) 1720 cmϪ1 (PdCOMe), 1673 cmϪ1 (CO2Me).
᎐
2
2
1H NMR (300 MHz, CDCl3): δ 8.13–7.28 (m, 18 H, C6H5 and
C5H3N), 3.83 (s, 3 H, OCH3), 2.70 (s, 3 H, C5H3NCH3), 2.17 (s,
3 H, COCH3). 13C NMR (75 MHz, CDCl3): δ 221.5 (PdCO),
169.4 (CO2Me), 161.7, 146.1, 141.3, 139.4–125.8 (C6H5 and
C5H3N), 55.4 (OCH3), 37.0 (d, J = 28.2 Hz, COCH3), 26.7
(C5H3NCH3). 31P NMR (121 MHz, CDCl3): δ 25.4.
References
1 E. Drent, Eur. Pat. Appl., 229,408, 1986; U.S. Pat., 4,778,279, 1988.
2 S. Kacker, Z. Jiang and A. Sen, Macromolecules, 1996, 29, 5852.
3 M. Brookhart and M. Wagner, J. Am. Chem. Soc., 1996, 118, 7219.
4 Y. Koide, S. G. Bott and A. R. Barron, Organometallics, 1996, 15,
2213.
[Pd(COMe)(PPh3)(NC5H4CONPri2-2)]BF4 3b. IR (CH2Cl2):
ν(C᎐O) 1707 cmϪ1 (PdCOMe), 1569 cmϪ1 (CON). H NMR
1
᎐
(300 MHz, CDCl3): δ 8.31 (t, 2 H, J = 7.8, C5H4N), 7.93 (s, 1 H,
C5H4N), 7.74–7.43 (m, 17 H, C6H5 and C5H4N), 4.62 (br m, 1 H,
NCH), 3.55 (br m, 1 H, NCH), 2.29 (d, J = 1.8 Hz), 1.97 (s)
(peak integral 6:1, 3 H, COCH3), 1.7–0.9 {br m, 12 H,
[CH(CH3)2]2}. 13C NMR (75 MHz, CDCl3): δ 224.5 (PdCO),
170.2 (CO2Me), 150.3, 140.9, 134.1–126.0 (C6H5 and C5H4N),
53.4, 48.3 (NCH), 36.9 (d, J = 24 Hz, PdCOCH3), 20.8, 19.6
[NCH(CH3)2]. 31P NMR (121 MHz, CDCl3): δ 24.9, 24.1 (peak
integrals 1:6).
5 Y. Koide and A. R. Barron, Macromolecules, 1996, 29, 1110.
6 B. Milani, L. Vincentini, A. Sommazzi, F. Garvassi, E. Chiarparin,
E. Zangrando and G. Mestroni, J. Chem. Soc., Dalton Trans., 1996,
3139.
7 M. Brookhart, F. C. Rix, J. M. DeSimone and J. C. Barborak, J. Am.
Chem. Soc., 1992, 114, 5894.
8 R. van Asselt, E. E. C. G. Gielens, R. E. Rülke, K. Vrieze and
C. J. Elsevier, J. Am. Chem. Soc., 1994, 116, 977.
9 B. A. Markies, D. Kruis, M. H. P. Rietveld, K. A. N. Verkerk,
J. Boersma, H. Kooijman, M. T. Lakin, A. L. Spek and G. van
Koten, J. Am. Chem. Soc., 1995, 117, 5263.
10 F. C. Rix and M. Brookhart, J. Am. Chem. Soc., 1995, 117, 1137.
11 F. C. Rix, M. Brookhart and P. S. White, J. Am. Chem. Soc., 1996,
118, 4746.
12 M. J. Green, G. J. P. Britovsek, K. J. Cavell, B. W. Skelton and
A. H. White, Chem. Commun., 1996, 1563.
13 R. E. Rülke, V. E. Kaasjager, D. Kliphuis, C. J. Elsevier, P. W. N. M.
van Leeuwen, K. Vrieze and K. Goubitz, Organometallics, 1996, 15,
668.
Carbon monoxide and ethylene insertion products. The prep-
aration and selected spectroscopic data of complexes 1b–1d has
been reported earlier.12,20 The spectroscopic data are reported
here in full for complexes 1c and 1d.
[Pd(CH2CH2COMe)(NC5H4CO2Me-2)(PPh3)]BF4 1c. Yellow
solid (Found: C, 52.71; H, 4.18; N, 2.14. Calc. for C29H29-
BF4NO3PPd: C, 52.48; H, 4.40; N, 2.11%). IR (CH2Cl2):
14 J. H. Groen, C. J. Elsevier, K. Vrieze, W. J. J. Smeets and A. L. Spek,
Organometallics, 1996, 15, 3445.
15 I. Tóth and C. J. Elsevier, J. Am. Chem. Soc., 1993, 115, 10 388.
ν(C᎐O) 1733 cmϪ1 (CO2Me), 1637 cmϪ1 (PdCH2CH2COMe).
᎐
1H NMR (300 MHz, CDCl3): δ 9.1–8.1 (br m, 1 H, C5H4N),
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144
1143

View Article Online
16 J. S. Brumbaugh, R. R. Whittle, M. Parvez and A. Sen, Organo-
metallics, 1990, 9, 1735.
17 G. P. C. M. Dekker, A. Buijs, C. J. Elsevier, K. Vrieze, P. W. N. M.
van Leeuwen, W. J. J. Smeets, A. L. Spek, Y. F. Wang and C. H.
Stam, Organometallics, 1992, 11, 1937.
18 The Aldrich Library of FT-IR Spectra, ed. C. J. Pouchert, Aldrich
Chemical Company, Inc., 1985.
19 H. Jin, K. J. Cavell, B. W. Skelton and A. H. White, J. Chem. Soc.,
Dalton Trans., 1995, 2159.
20 G. J. P. Britovsek, K. J. Cavell, M. J. Green, F. Gerhards, B. W.
Skelton and A. H. White, J. Organomet. Chem., 1997, 533, 201.
21 J. L. Hoare, K. J. Cavell, R. Hecker, B. W. Skelton and A. H. White,
J. Chem. Soc., Dalton Trans., 1996, 2197.
22 E. Drent, J. A. M. Van Broekhoven and M. J. Doyle, J. Organomet.
Chem., 1991, 417, 235.
23 G. J. P. Britovsek, W. Keim, S. Mecking, D. Sainz and T. Wagner,
J. Chem. Soc., Chem. Commun., 1993, 1632.
24 Z. Jiang and A. Sen, Macromolecules, 1994, 27, 7215.
25 V. L. K. Valli and H. Alper, J. Polym. Chem., 1995, 33, 1715.
26 F. Benetollo, R. Bertani, G. Bombieri and L. Toniolo, Inorg. Chim.
Acta, 1995, 233, 5.
27 E. Lindner, R. Schreiber, T. Schneller, P. Wegner and H. A. Mayer,
Inorg. Chem., 1996, 35, 514.
28 S. Y. Desjardins, K. J. Cavell, H. Jin, B. W. Skelton and A. H. White,
J. Organomet. Chem., 1996, 515, 223.
29 W. Keim, H. Maas and S. Mecking, Z. Naturforsch., Teil B, 1995, 50,
430.
30 K. E. Frankcombe, K. J. Cavell, R. B. Knott and B. F. Yates,
unpublished work.
31 K. Frankcombe, Ph.D. Thesis, University of Tasmania, 1997.
32 G. K. Anderson and R. J. Cross, Chem. Soc. Rev., 1980, 9, 185.
33 E. Drent and P. H. M. Budzelaar, Chem. Rev., 1996, 96, 663.
34 W. Mathes, W. Sauermilch and T. Klein, Chem. Ber., 1953, 86, 584.
35 R. E. Rülke, J. M. Ernsting, A. L. Spek, C. J. Elsevier, P. W. N. M.
van Leeuwen and K. Vrieze, Inorg. Chem., 1993, 32, 5769.
36 F. T. Ladipo and G. K. Anderson, Organometallics, 1994, 13, 303.
37 S. R. Hall, H. D. Flack and J. M. Stewart (Editors), The XTAL 3.2
Reference Manual, Universities of Western Australia, Geneva and
Maryland, 1992.
38 A. P. Swain and S. K. Naegele, J. Am. Chem. Soc., 1957, 79, 5250.
Received 6th October 1997; Paper 7/07199J
1144
J. Chem. Soc., Dalton Trans., 1998, Pages 1137–1144