Palladium(II) complexes with the bidentate iminophosphine ligand [Ph2PCH2C(Ph)=N(2,6-Me2C6H3 )]

Article abstract of DOI:10.1039/b102476k

A new iminophosphine ligand, [Ph₂PCH₂C(Ph)=N(2,6-Me₂C₆H₃ )] (HL), and the complexes [PdX₂(HL)], where X = Cl (1) and Br (2), [PdMeX(HL)], X = Cl (3) and Br (4), and [PdMe₂(HL)] (

Full text of DOI:10.1039/b102476k

View Article Online / Journal Homepage / Table of Contents for this issue
Palladium(II) complexes with the bidentate iminophosphine ligand
[Ph PCH C(Ph)᎐N(2,6-Me C H )]
᎐
2
2
2
6
3
Karl S. Coleman, Malcolm L. H. Green,* Sofia I. Pascu, Nicholas H. Rees, A. R. Cowley and
Leigh H. Rees
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford,
UK OX1 3QR
Received 16th March 2001, Accepted 18th September 2001
First published as an Advance Article on the web 1st November 2001
A new iminophosphine ligand, [Ph PCH C(Ph)᎐N(2,6-Me C H )] (HL), and the complexes [PdX (HL)], where X =
᎐
2
2
2
6
3
2
Cl (1) and Br (2), [PdMeX(HL)], X = Cl (3) and Br (4), and [PdMe2(HL)] (5) have been prepared and characterised.
Reaction of 2 with MeLi or KH leads to deprotonation of the neutral ligand to give [Pd2(µ-Br)2(LϪ)2], (6), where LϪ
is [Ph PCH᎐C(Ph)N(2,6-Me C H )]Ϫ. Similarly, reaction of 3 with KH and triphenylphosphine affords the neutral
᎐
2
2
6
3
complex [PdMe(PPh3)(LϪ)] (7). Insertion of CO into the Pd–Me bond has been investigated, as well as the catalytic
properties of [PdClMe(HL)] towards CO/ethylene copolymerisation. The crystal structures of HL, 1–3 and 5–7 have
been determined.
Introduction
Results and discussion
Transition metal complexes of hybrid ligands containing P and
N or O donor atoms are of interest1 since, with group 10
metals, such heteroditopic ligands can exhibit hemi-labile
character. Such behaviour has been exploited in homogeneous
catalysis and in the activation of small molecules, as the form-
ation and stabilisation of intermediate species is often facili-
tated.2,3 Ni complexes of P/O ligands have been investigated as
promising catalysts for the oligomerisation of olefins, as in the
Shell higher olefin process (SHOP).4,5 Similarly, group 10 tran-
sition metals with P- and N-based donor ligands have been
found to be active catalysts for polymerisation of ethene and
propene, giving rise to a new generation of polymers.6 Although
a variety of N/P ligand systems have been studied,7 only a small
number of bidentate N(sp2)–P(sp3) ligands, mainly oxazoline
and imidazolyl based, and transition metal complexes there-
of have been described.8–19 The synthesis and reactivity of
new N/P ligands and their coordination to late transition
metals continues to attract intrest owing to the possibility of
tailoring the steric and electronic properties of the different
donor groups. Recently, oxazoline-based N/P ligands, when
coordinated to Pd() centres, have shown some activity in
the copolymerisation of carbon monoxide and olefins, a reac-
tion typically confined to bidentate phosphine and imine
systems.13
Synthesis and characterisation of the ligand [Ph2PCH2C-
(Ph)᎐N(2,6-Me C H )] HL
᎐
2
6
3
The iminophosphine ligand [Ph PCH C(Ph)᎐N(2,6-Me C H )],
᎐
2
2
2
6
3
HL, was prepared in a two-step process, as shown in Scheme 1.
The arylimine [MeC(Ph)᎐N(2,6-Me C H )] was reacted with
᎐
2
6
3
lithium diisopropylamide (LDA) at Ϫ78 ЊC and, after stirring
for 1 h, a pre-cooled solution of Ph2PCl was added to afford
ligand HL as a white solid. HL was characterised by elemental
analysis, mass spectrometry (FABϩ) and 1H, 13C{1H} and
31P{1H} NMR spectroscopy using COSY, HSQC, HMBC,
1
NOESY and H{31P} experiments. NMR spectroscopy indi-
cated the presence of two species in solution, Tables 1 and 2.
The 31P{1H} NMR spectrum (CD2Cl2) exhibits two signals,
both singlets, at δ Ϫ14.4 and Ϫ19.8, in the ratio 85 : 15. This can
be attributed to the presence of the E and Z isomers. Although
no exchange broadening was detected in the room temperature
1H and 31P{1H} NMR spectra, the presence of exchange peaks
in the room temperature NOESY spectrum showed that the two
species were in slow exchange. The effects of exchange were
eliminated by cooling to Ϫ40 ЊC. From particular diagnostic
nOes, the major species was assigned to the E isomer (correl-
ations were observed between the signal for Me2C6H4N and
each of the signals for CH2
and PPh2-o) and the minor species
to the Z isomer (a correlation was observed between the
Me2C6H4N and Ph-o signals). Imines, and particularly N-aryl
imines, are known to isomerise in solution via a lateral shift
mechanism. This involves the shift of the substituent attached
to nitrogen from one side of the molecule to the other through a
linear transition state.20 The rate of E–Z isomerisation was
determined from variable temperature 31P{1H} NMR selective
inversion transfer experiments,21 and from the Eyring plot
the barrier to isomerisation was calculated to be 62.8 kJ molϪ1
(Fig. 1). This was further confirmed by line shape analysis.
Herein, we describe the synthesis and reactivity of a novel
iminophosphine ligand with a flexible backbone, HL, and the
preparation of the corresponding Pd() complexes. The activity
of the Pd() complexes toward the copolymerisation of CO and
ethylene is discussed.
Molecular structure of ligand HL
Crystals of HL, [Ph PCH C(Ph)᎐N(2,6-Me C H )], suitable for
᎐
2
2
2
6
3
single-crystal X-ray diffraction were obtained by slowly cooling
a toluene solution of the compound. An ORTEP view of the
3384
J. Chem. Soc., Dalton Trans., 2001, 3384–3395
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b102476k

View Article Online
Fig. 1 Estimation of the isomerisation barrier E/Z of ligand HL by an
Eyring plot: ∆H# = 62.8 kJ molϪ1; ∆S# = Ϫ17.9 × 10Ϫ3 kJ molϪ1 KϪ1 and
∆G# (273 K) = 67.68 kJ molϪ1. [Eyring plot: ln(K/T ) = Ϫ∆H#/RT ϩ
∆S#/R ϩ 23.76.]
Fig. 2 ORTEP diagram of the molecular structure of HL (major
isomer E).
Scheme 1 Synthesis of the neutral N/P ligand [(2,6-Me2C6H3)N᎐
᎐
C(Ph)CH2PPh2], HL.
molecular structure of HL is shown in Fig. 2, with selected bond
lengths and angles listed in Table 3. The C(1)–N(1) bond is
1.273(2) Å, consistent with significant double bond character
and the bond angles at both C(1) and N(1) atoms are indicative
of sp2 centres. The C(1)–C(2) bond of the backbone is 1.504(2)
Å, indicating a typical carbon–carbon single bond. The
phosphorus–phenyl P–C bond lengths are 1.818(2) and 1.829(2)
Å and the phosphorus–CH2 P–C bond length is 1.862(2) Å, as
expected for free tertiary phosphines. In the solid state, ligand
HL adopts the E isomer configuration. The E isomer is pre-
sumably the energetically favoured isomer for steric reasons,
this was supported by simple molecular mechanics calculations
using the CAChe software package.22 Similarly, E was the major
isomer in solution, as detected by NMR spectroscopy.
Scheme 2 Synthesis of compounds 1–3.
were prepared from the reaction of PdX2, where X = Cl and Br,
respectively, with 1 molar equivalent of ligand HL, as shown in
Scheme 2. Similarly, the neutral complex [PdMeCl(HL)] 3,
Palladium(II) complexes
where HL = [Ph PCH C(Ph)᎐N(2,6-Me C H )] was prepared
᎐
2
2
2
6
3
The metal complexes [PdX2(HL)], where X = Cl (1) and Br (2)
by reacting [PdMeCl(COD)] with HL in CH2Cl2 at room
J. Chem. Soc., Dalton Trans., 2001, 3384–3395 3385

View Article Online
Table 1 1H and 31P{1H} NMR data (CD2Cl2) of neutral ligand HL and complexes thereof (chemical shifts in ppm and coupling constants in Hz)a
HL(major)
—
—
HL(minor)
—
—
1
Cl
Cl
2
Br
Br
3
Cl
Me
4
Br
Me
5b
Me
Me
8c
MeCN
Me
9
X
Y
Cl
MeC᎐O
᎐
31P{1H}
1H
Me2C6H3N
Ϫ14.4
Ϫ19.8
43.8
43
40.9
40.3
21.3
42.5
22.3
o-Me
m-H
p-H
o-H
m-H
p-H
1.95
7.02
6.96
7.84
7.38
7.45
3.43
7.16
7.16
7.30
1.78
6.82
6.75
7.12
7.22
7.27
3.81
7.56
7.37
7.27
2.11
2.02
2.02
2.03
2.02
2.08
7.03
7.03
7.16
7.27
7.40
4.37
7.75
7.62
7.68
2.09
0.56
11.6
12.7
2.7
2.03
6.90
6.90
7.01
7.21
7.31
4.13
7.81
7.56
7.61
6.90
6.99
7.03
7.23
7.34
4.27
7.93
7.59
7.69
6.81
6.89
6.95
7.13
7.27
4.24
7.84
7.49
7.59
6.90
6.90
7.03
7.20
7.31
4.15
7.56
7.78
7.61
6.88
6.88
7.02
7.19
7.30
4.16
7.75
7.55
7.59
6.77
6.77
6.74
6.74
6.80
3.47
7.64
7.11
7.11
0.28
1.20
7.5
Ph
CH2–P
PPh2
o-H
m-H
p-H
Me
X
Y
Me
0.66
11.2
12.2
1.5
2.2
0.78
11.1
13.3
2.7
2.1
2.26
10.8
12.3
2.1
2JP–CH
2.6
7.5
1.6
0.9
1.1
7.5
12.8
13.2
3.0
12.9
12.9
3.0
2
3JP–Ph-o
4JP–Ph-m
5JP–Ph-p
3JP–Pd–Me
11.7
2.1
2.3
2.3
2.3
trans
cis
7.6
8.7
2.9
3.3
1.9
4JP–Pd–C–Me
1.3
a Assignments assisted by 1H, 13C{1H}, 31P{1H} NMR spectroscopy, using COSY, HSQC, HMBC (HL, 1–5, 8, 9), as well as NOESY and 1H{31P}
experiments (HL major and minor); ROESY (1–5), nOe difference experiments (3, 5, 9). b NMR data recorded in d8-toluene. c 11B NMR: δ Ϫ0.66, 19
NMR: δ Ϫ153.15.
F
Table 2 13C{1H} NMR data (CD2Cl2) of neutral ligand HL and complexes thereof (chemical shifts in ppm and coupling constants in Hz)a
HL(major)
—
—
HL(minor)
—
—
1
Cl
Cl
2
Br
Br
3
Cl
Me
4
Br
Me
5b
Me
Me
8
9
X
Y
MeCN
Me
Cl
MeC᎐O
᎐
Me2C6D6N
i
o
148.80
126.47
18.41
148.73
126.15
18.43
127.90
126.75
167.24
138.66
127.17
—
129.40
41.72
139.03
133.28
—
146.19
130.55
19.03
146.82
130.37
19.29
146.15
129.07
18.95
146.46
129.03
19.15
146.70
18.77
145.59
128.82
18.60
145.57
129.06
19.04
o-Me
m-H
p-H
128.39
123.31
166.26
139.17
128.30
128.49
130.54
32.28
138.26
133.07
128.86
129.27
128.05
127.46
182.16
133.17
127.29
128.84
131.99
48.11
126.39
133.47
129.77
133.16
127.88
127.22
181.37
133.00
127.21
128.65
131.75
48.94
126.71
133.43
129.50
132.92
127.75
125.63
174.94
135.47
127.03
128.57
130.90
47.61
129.31
133.44
129.54
131.96
127.68
125.60
174.97
135.41
126.94
128.49
130.80
47.60
128.81
133.34
129.49
131.91
127.52
126.62
176.88
133.78
128.64
128.98
132.06
47.92
127.01
133.42
129.97
132.87
2.24
127.85
125.61
174.68
135.55
127.01
128.62
131.04
45.75
127.67
133.18
129.65
131.93
N᎐C
174.94
134.02
᎐
Ph
i
o-H
m-H
p-H
129.83
45.12
CH2–P
PPh2
i
o-H
m-H
p-H
Me trans
CN
Me cis
CO
133.20
130.12
—
X
Y
9.43
119.42
Ϫ3.90
Ϫ4.73
Ϫ6.15
Ϫ9.19
19.00
225.58
5
29
5
55
11
13
<1
2J(P–C᎐N)
14
22
9
15
8
29
10
58
12
12
3
8
28
10
58
11
12
3
6
29
8
50
13
11
<1
8
28
8
61
13
11
3
11
17
22
4
31
8
57
12
12
<1
᎐
1J(P–CH )
2
3J(P–Ph-i)
1J(P–Ph-i)
16
20
7
15
20
2J(P–Ph-o)
14
3J(P–Ph-m)
4J(P–Ph-p)
<1
2J(P–Pd–Me cis)
7
115
2J(P–Pd–Me trans)
2J(P–Pd–C᎐O)
8
᎐
a Assignments assisted by 1H, 13C{1H}, 31P{1H} NMR spectroscopy, using COSY, HSQC, HMBC (HL, 1–5, 8, 9), as well as NOESY and 1H{31P}
experiments (HL major and minor); ROESY (1–5), nOe difference experiments (3, 5, 9). b NMR data recorded in d8-toluene.
temperature. The complexes 1–3 have been characterised by
mass spectrometry (FABϩ), elemental analysis and 1H, 13C{1H}
and 31P{1H} NMR spectroscopy using COSY, HSQC, HMBC,
ances of the Pd–Me protons were found at δ 0.66 as a doublet
with the coupling constant JP–Pd–Me = 2.9 Hz. In 3, the strong
methyl to PPh2-ortho nOe indicates that the methyl is co-
ordinated to the palladium cis to the phosphorus atom, which
was further confirmed by X-ray crystallography. Although lig-
and HL predominantly exists as the E isomer, a conformation
3
1
ROESY, nOe difference and H{31P} experiments. Full assign-
ment of the NMR data is presented in Tables 1 and 2. In the 1H
NMR spectrum of complex 3 recorded in CD2Cl2, the reson-
3386
J. Chem. Soc., Dalton Trans., 2001, 3384–3395

View Article Online
Table 3 Selected bond lengths (Å) and angles (Њ) for compounds HL, 1–3 and 5–7
Compounds
HL
Bond lengths
Bond angles
N(1)–C(11)
P(1)–C(41)
N(1)–C(1)
P(1)–C(31)
P(1)–C(2)
1.414(2)
1.829(2)
1.273(2)
1.818(2)
1.862(2)
1.504(2)
2.049(4)
2.2881(12)
1.288(5)
1.489(6)
1.834(5)
1.801(5)
2.1845(12)
2.3505(12)
1.445(6)
1.796(5)
2.081(2)
2.4169(5)
1.292(3)
1.831(3)
1.809(3)
2.2020(8)
2.4894(5)
1.451(3)
1.502(3)
1.800(3)
2.3798(9)
2.169(3)
1.815(3)
1.834(3)
1.297(4)
1.444(4)
2.1925(9)
2.062(4)
1.818(3)
1.509(5)
2.273(3)
2.185(8)
2.09(1)
C(1)–N(1)–C(11)
C(31)–P(1)–C(2)
C(31)–P(1)–C(41)
C(41)–P(1)–C(2)
N(1)–C(1)–C(2)
C(1)–C(2)–P(1)
N(1)–Pd(1)–P(1)
P(1)–Pd(1)–Cl(2)
P(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1)
121.1(2)
101.67(9)
103.64(8)
100.60(8)
125.0(2)
108.62(13)
83.63(10)
88.76(5)
173.57(5)
170.53(10)
94.92(10)
93.26(4)
C(1)–C(2)
1
2
3
5
6
7
Pd(1)–N(1)
Pd(1)–Cl(2)
N(1)–C(1)
C(1)–C(2)
C(2)–P(1)
P(1)–C(31)
Pd(1)–P(1)
Pd(1)–Cl(1)
N(1)–C(11)
P(1)–C(41)
Pd(1)–N(1)
Pd(1)–Br(2)
N(1)–C(1)
C(2)–P(1)
P(1)–C(31)
Pd(1)–P(1)
Pd(1)–Br(1)
N(1)–C(11)
C(1)–C(2)
P(1)–C(41)
Pd(1)–Cl(1)
Pd(1)–N(1)
P(1)–C(31)
P(1)–C(3)
C(2)–N(1)
N(1)–C(11)
Pd(1)–P(1)
Pd(1)–C(1)
P(1)–C(41)
C(3)–C(2)
N(1)–Pd(1)–Br(2)
N(1)–Pd(1)–Br(1)
Br(2)–Pd(1)–Br(1)
N(1)–Pd(1)–P(1)
P(1)–Pd(1)–Br(2)
P(1)–Pd(1)–Br(1)
170.51(6)
94.99(6)
93.68(2)
82.91(6)
88.98(3)
172.40(2)
Cl(1)–Pd(1)–P(1)
P(1)–Pd(1)–N(1)
P(1)–Pd(1)–C(1)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–C(1)
N(1)–Pd(1)–C(1)
176.46(4)
82.91(8)
90.8(1)
94.88(8)
91.5(1)
173.54(14)
Pd(1)–P(2)
Pd(1)–N(17)
Pd(1)–C(32)
Pd(1)–C(33)
P(2)–C(3)
P(2)–Pd(1)–N(17)
P(2)–Pd(1)–C(32)
N(17)–Pd(1)–C(32)
P(2)–Pd(1)–C(33)
N(17)–Pd(1)–C(33)
C(32)–Pd(1)–C(33)
80.2(2)
174.3(3)
95.5(4)
96.6(3)
175.8(4)
87.8(5)
2.045(11)
1.81(1)
1.84(1)
P(2)–C(9)
P(2)–C(15)
C(15)–C(16)
C(16)–N(17)
N(17)–C(18)
Pd(1)–Br(1)
Pd(1)–Br(1)Ј
Pd(1)–P(1)
Pd(1)–N(1)
P(1)–C(1)
P(1)–C(17)
P(1)–C(23)
C(1)–C(2)
C(2)–N(1)
C(3)–N(1)
Pd(1)–P(2)
Pd(1)–N(11)
Pd(1)–P(32)
Pd(1)–C(51)
P(2)–C(3)
1.84(1)
1.510(12)
1.300(11)
1.451(11)
2.4629(4)
2.5655(4)
2.2123(8)
2.039(3)
1.738(4)
1.820(4)
1.814(4)
1.379(4)
1.351(4)
1.424(4)
2.3276(7)
2.097(2)
2.2420(7)
2.143(3)
1.821(3)
1.756(2)
1.825(3)
1.363(4)
1.380(3)
1.410(3)
1.827(3)
1.836(3)
1.833(3)
Br(1)–Pd(1)–Br(1)Ј
Br(1)–Pd(1)–P(1)
Br(1)Ј–Pd(1)–P(1)
Br(1)–Pd(1)–N(1)
Br(1)Ј–Pd(1)–N(1)
P(1)–Pd(1)–N(1)
Pd(1)–Br(1)–Pd(1)Ј
Pd(1)–P(1)–C(1)
Pd(1)–N(1)–C(2)
Pd(1)–N(1)–C(3)
P(2)–Pd(1)–N(11)
P(2)–Pd(1)–P(32)
N(11)–Pd(1)–P(32)
P(2)–Pd(1)–C(51)
N(11)–Pd(1)–C(51)
P(32)–Pd(1)–C(51)
84.937(14)
93.77(2)
176.87(3)
173.09(8)
97.98(7)
83.62(8)
84.981(13)
102.03(11)
117.5(2)
116.9(2)
82.42(6)
102.48(3)
174.86(7)
167.37(7)
90.95(9)
P(2)–C(9)
83.95(7)
P(2)–C(26)
C(9)–C(10)
C(10)–N(11)
N(11)–C(12)
P(32)–C(33)
P(32)–C(39)
P(32)–C(45)
sterically unfavourable to chelation in a bidentate manner, the
metal complexes 1–3 are readily formed in high yield (ca. 70%).
The E and Z isomers are in equilibrium and addition of pal-
ladium halides leads to the formation of [PdX2(HL)] product,
probably with kinetic control. The structures of complexes 1–3
were determined by single crystal X-ray diffraction.
Reactivity
Reaction of the PdX2 compounds 1 and 2 with methyllithium
failed to afford the desired dimethyl complex cleanly (Scheme
3). For the case of the reaction of 2 with MeLi, three major
species were identified in the reaction mixture, the mono-
J. Chem. Soc., Dalton Trans., 2001, 3384–3395
3387

View Article Online
Scheme 3 Formation of complexes 4–6.
methyl, [PdMeBr(HL)] complex 4, the dimethyl complex
δ 1.20 (3JP–Pd–Me = 8.7 Hz) which was assigned to the Me group
[PdMe2(HL)] 5 and the dimeric species [Pd2(µ-Br)2(LϪ)2] 6.
Separation of 4 from the mixture of reaction products pro-
ceeded in very low yield, due to similar solubility in common
solvents with complexes 5 and 6. Compound [PdMeBr(HL)] 4,
was characterised by mass spectrometry (FABϩ), elemental
analysis and NMR spectroscopy (Tables 1 and 2). As observed
for [PdMeCl(HL)] 3, the 1H NMR spectrum of complex 4
(recorded in CD2Cl2) exhibits a doublet (3JP–Pd–Me = 3.3 Hz)
assignable to the Pd–Me protons cis to PPh2 at δ 0.78. The
presence in the 31P{1H} NMR spectrum, of a singlet at δ 40.3,
close to that observed in the corresponding spectrum of com-
plex 3, indicates the expected structural analogy between these
two mono-methyl derivatives of the neutral ligand [Ph2-
cis to PPh2. This assignment was based on the strong methyl to
PPh2-ortho nOe, and confirms that this particular methyl group
is co-ordinated to the palladium cis to the phosphorus atom
(Tables 1 and 2).
The formation of the complex [Pd2(µ-Br)2(LϪ)2] 6 (where LϪ
is [Ph PCH᎐C(Ph)N(2,6-Me C H )]Ϫ), as indicated by mass
᎐
2
2
6
3
spectrometry (FABϩ), elemental analysis and NMR spec-
troscopy, by reacting [PdBr2(HL)] 2 with 2 equivalents of MeLi,
clearly shows that the deprotonation of the CH2 of the ligand
backbone in 2 is favoured over the mono- or di-methylation of
the Pd() centre. Furthermore, the reaction of 2 with KH in
THF at Ϫ78 ЊC similarly forms the dimer [Pd2(µ-Br)2(LϪ)2] 6 in
high yield.
PCH C(Ph)᎐N(2,6-Me C H )].
The acidity of the backbone CH2 can be exploited to produce
the neutral complex [PdMe(PPh3)(LϪ)] 7, by addition of KH to
the PdMeCl complex 3 in the presence of PPh3, as shown in
Scheme 4. This template reaction is, to the best of our know-
ledge, unprecedented. The deprotonation of the co-ordinated
ligand backbone was confirmed by 1H NMR spectroscopy,
which showed a single (by integration) olefinic proton at δ 3.67
and the loss of the CH2 backbone resonance. Interestingly, the
ROESY spectrum shown in Fig. 3, indicates that ligand redistri-
bution has occurred and the methyl group is now positioned cis
to the nitrogen atom in the N/P ligand. This is confirmed by the
small coupling constant of 26 Hz between the two phosphorus
nuclei (Table 4). The proton resonances of the Pd–Me group
᎐
2
2
6
3
Complex [PdMe2(HL)] 5 was isolated by reacting [PdCl2-
(HL)] with excess Me2Zn at Ϫ78 ЊC (Scheme 3), as a highly air
and moisture sensitive compound, both in solution and the
solid state. In the presence of chlorinated solvents such as
CD2Cl2, formation of [PdMeCl(HL)] occurs rapidly, as the Me
group trans to PPh2 can be readily exchanged to form the more
stable mono-methylated derivative. It was previously found that
the mutual trans position of carbon and phosphorous ligands
in Pd() complexes leads to the weakening of the corresponding
Pd–C and Pd–P bonds.23 This could be responsible for the
instability of 5 towards formation of a mono-methylated
species. This could also occur as a consequence of the steric
hindrance between the xylyl group and the Me group cis to the
3
appear as a double-doublet at δ Ϫ0.57 with JP–Pd–Me = 3.9 Hz
1
3
imine moiety. For 5, the H NMR spectrum (in d8-toluene)
(coupling with PPh3) and JP–Pd–Me = 6.7 Hz (coupling with
exhibits a doublet at δ 0.28 (3JP–Pd–Me = 7.6 Hz) assignable to the
protons of the Me group trans to phosphorus and a doublet at
PPh2). The molecular structure of complex 7 was determined
by single crystal X-ray diffraction. The geometry of 7 is
3388
J. Chem. Soc., Dalton Trans., 2001, 3384–3395

View Article Online
Scheme 4 Reactions of the neutral complex 3, [PdMeCl(L)].
unexpected due to the predicted preference of alkyl groups to
be placed cis to the phosphine unit of the chelating ligand.23
A
possible explanation for the preferred geometry of 7, with the
metal-bound methyl group placed trans to PPh2 both in solu-
tion and solid state, could be the steric hindrance between PPh3
and the xylyl group of the imine moiety.
Complex [PdMeCl(HL)] 3 was also found to undergo
reactions with AgBF4 to give the cationic complex [PdMe-
(MeCN)(HL)][BF4] 8, shown in Scheme 4. This complex was
characterised by elemental analysis, mass spectrometry (FABϩ)
and NMR spectroscopy (Tables 1 and 2). NMR studies indi-
cated that the methyl group is positioned cis to the P atom.
The potential for inserting CO into the Pd–Me bond, the first
step in the CO/ethylene copolymerisation reaction, was tested
for the case of complexes 3 and 7 by NMR-scale reactions
performed in CD2Cl2 at room temperature, using ca. 2 bar CO.
In the case of [PdMe(PPh3)(LϪ)] 7, rapid CO insertion was
observed and the reaction proceeded to full conversion after
15 min. 1H NMR spectra of the reaction mixture showed a new
doublet assignable to Pd–CO–Me resonances at δ 2.34 with a
4
coupling constant JP–Pd–C–Me = 4.9 Hz. Also, the simultaneous
disappearance of the double-doublet at δ Ϫ0.57 corresponding
to the Pd–Me protons (trans to the ligand PPh2 and cis to PPh3)
was observed. 31P{1H} NMR spectroscopy confirmed complete
conversion of the starting material and formation of a mixture
of products. The absence of a signal assignable to the coordin-
ated PPh3 in the 31P{1H} NMR spectrum also suggests that this
ligand was displaced. However, decomposition to Pd metal
occurred after 2 h at room temperature, halting further investi-
gations and characterisation. By treating the complex 3,
[PdMeCl(HL)], with ca. 2 bar CO in an NMR tube at room
temperature, CO insertion into the Pd–Me bond cis to PPh2
occurred leading to the formation of the new complex,
1
[Pd(CO)MeCl(HL)] 9. H NMR spectroscopy of the reaction
mixture showed a doublet assignable to Pd–CO–Me protons at
4
δ 2.26 with coupling constant JP–Pd–C–Me = 1.3 Hz (Table 2).
1
Partial conversion (estimated by integration of the H NMR
spectrum to be ca. 70%) of the starting material was observed
after 24 h at room temperature. NMR experiments and solution
IR confirmed the proposed structure for complex 9 (Scheme 4).
Full assignments of the NMR spectra for complexes 1–9 are
presented in Tables 1, 2 and 4.
Molecular structures of the Pd(II) complexes
Fig. 3 500 MHz ROESY spectrum of complex 7 in CD2Cl2 (mixing
time = 250 ms).
Crystals of 1–3 and 6 suitable for single-crystal X-ray structural
J. Chem. Soc., Dalton Trans., 2001, 3384–3395
3389

View Article Online
Table 4 1H, 13C{1H} and 31P{1H} NMR data (CD2Cl2) of complexes 6 and 7 (chemical shifts in ppm and coupling constants in Hz)a
6
7
Y
X
Br
Ph3P
Me
PdBrLϪ
31P{1H}
54.4
31P{1H} 2JP–P = 26
PPh2
X
26.6
39.9
1H
13C{1H}
1H
13C{1H}
Me2C6D6N
i
o
150.73
136.47
19.88
i
o
150.69
o-H
2.15
o-H
2.32
135.57
19.85
127.17
122.62
177.23
142.09
126.86
127.89
126.86
77.50
136.56
132.43
128.34
129.04
133.96
134.52
128.29
130.17
17.25
30
50
22
39
13
10
2
86
49
o-Me
m-H
p-H
o-Me
m-H
p-H
m-H
p-H
6.70
6.70
127.50
124.94
178.87
137.53
127.32
128.07
128.21
72.64
133.58
133.18
128.73
131.22
m-H
p-H
6.85
6.68
N–C᎐
᎐
Ph
i
i
o-H
m-H
p-H
7.12
7.02
7.07
3.54
o-H
m-H
p-H
o-H
m-H
p-H
7.04
7.21
7.02
3.67
o-H
m-H
p-H
CH–P
PPh2
i
i
o-H
m-H
p-H
7.77
7.43
7.53
o-H
m-H
p-H
i
o-H
m-H
p-H
o-H
m-H
p-H
7.25
7.24
7.33
o-H
m-H
p-H
Y
o-H
m-H
p-H
7.28
7.18
7.33
Ϫ0.57
0.7
8.9
1.8
X
Me
Me
2J(P–CH)
3J(P–Ph-o)
4J(P–Ph-m)
5J(P–Ph-p)
8.6
12.8
2.5
2J(P–C–N)
1J(P–CH)
3J(P–Ph-i)
1J(P–Ph-i)
2J(P–Ph-o)
3J(P–Ph-m)
4J(P–Ph-p)
21
65
25
45
11
12
1
2J(P–CH)
PPh2
PPh2
PPh2
PPh2
PPh2
2J(P–C–N)
1J(P–CH)
3J(P–Ph-i)
1J(P–Ph-i)
2J(P–Ph-o)
3J(P–Ph-m)
4J(P–Ph-p)
2J(P–PdMe)
1J(P–Ph-i)
2J(P–Ph-o)
3J(P–Ph-m)
4J(P–Ph-p)
2J(P–PdMe)
3J(P–Ph-o)
4J(P–Ph-m)
5J(P–Ph-p)
3J(P–PdMe)
2.1
1.9
6.7
3J(P–CH)
X
X
X
X
X
0.7
8.3
2.2
1.9
3.9
3J(P–Ph-o)
4J(P–Ph-m)
5J(P–Ph-p)
3J(P–PdMe)
8
2
2
10
a Assignments assisted by 1H, 13C{1H}, 31P{1H} NMR spectroscopy, using COSY, HSQC, HMBC (6 and 7) as well as NOESY and 1H{31P}
experiments (7).
determination were obtained by slowly cooling a CH2Cl2
solution of each complex, whereas crystals of 5 and 7 were
grown from toluene and pentane, respectively. ORTEP
diagrams for HL and compounds 1–3 and 5–7 are presented in
Fig. 4–8 and their significant molecular parameters listed in
Table 3. Molecular structural determinations confirm that the
studied Pd() complexes exhibit the same structures in the solid
state and in solution.
Complex [PdCl2(HL)] 1, with the ORTEP view shown in
Fig. 4, is isostructural with complexes [PdBr2(HL)] 2, and
[PdMeCl(HL)] 3 (Fig. 5). In the solid state, all complexes are of
pseudo square planar geometry around the metal centre. For
1–3 and 5, the N–Pd–P bite angles are 83.63(10), 82.91(6),
82.91(8) and 80.2(2)Њ, respectively. The palladium–halogen
bond lengths are as expected for Pd() complexes, with the
longer metal–halogen bond trans to the phosphorus atom.11,13
In complex 3 (Fig. 5), the Pd–Me separation is 2.062(4) Å
with the methyl group located cis to the phosphorus atom,
as predicted by NMR for the solution species. In the case
of [PdMe2(HL)] 5, the Pd–C bond length for the methyl
group situated trans to phosphorus is 2.09(1) Å (Fig. 6). This
is somewhat longer than the Pd–C distance cis to PPh2
[2.045(11) Å], which we attribute to the greater trans-
influence of PPh2 compared to the aryl imine donor functional-
Fig. 4 ORTEP diagram of the molecular structure of complex 1
(isostructural with complex 2).
ity. In general, little variation in the bond lengths of the
structure of [Ph PCH C(Ph)᎐N(2,6-Me C H )] is observed
᎐
2
2
2
6
3
upon chelation to Pd(), although the carbon–nitrogen separ-
ation C᎐N does increase from 1.273(2) (in the free ligand) to
᎐
3390
J. Chem. Soc., Dalton Trans., 2001, 3384–3395

View Article Online
Fig. 5 ORTEP diagram of the molecular structure of complex 3.
Fig. 8 ORTEP diagram of the molecular structure of complex 7. The
molecule crystallises with one molecule of toluene (not shown).
separation in [PdMe(PPh3)(LϪ)] 7, of 1.363(4) Å. For com-
plexes 1–3 and 5, these distances were found to be 1.489(6),
1.502(3), 1.509(5) and 1.510(12) Å, respectively, close to the
value determined for the non-coordinated neutral ligand
[1.504(2) Å]. The shorter carbon–carbon bond of the ligand
backbone in compounds 6 and 7 is consistent with the form-
ation of a double bond as a result of the deprotonation
of the coordinated neutral ligand in the presence of a base.
In addition, the carbon(backbone)–nitrogen distances are
significantly greater in 6 [1.351(4) Å] and 7 [1.380(5) Å] than
those found in the free and coordinated neutral ligand
Fig. 6 ORTEP diagram of the molecular structure of complex 5.
[Ph PCH C(Ph)᎐N(2,6-Me C H )]. This is consistent with a
᎐
2
2
2
6
3
decrease in the C–N bond order as a result of deprotonation
and imine–enamine tautomerisation.
In the structure of 6, the Pd–Br distances trans to phos-
phorus are 2.5655(4) Å, somewhat longer than the correspond-
ing bonds cis to phosphorus of 2.4629(4) Å. The palladium and
bromine atoms form inorganic four-membered rings, distorted
from planarity, with a dihedral angle Pd1–Br1–Pd1Ј–Br1Ј of
130.08Њ. It was noted that the P–Pd–N bite angle found for 6,
83.62(8)Њ, is slightly larger than that found in complex 2,
[PdBr2(HL)], with the neutral ligand HL, 82.91(6)Њ. The geom-
etries around the palladium centres are essentially square-
planar in 6, and the molecule is folded and forms a ‘cavity’,
which accommodates the two molecules of CH2Cl2.
In the case of complex [PdMe(PPh3)(LϪ)] 7 containing the
anionic ligand [Ph PCH᎐C(Ph)N(2,6-Me C H )]Ϫ, the Pd–
᎐
2
2
6
3
Fig. 7 ORTEP diagram of the molecular structure of complex 6. The
molecule crystallises with two molecules of CH2Cl2 (not shown).
P(Ph2) bond [2.2420(7) Å] was found to be longer than that in
the neutral ligand [Ph PCH C(Ph)᎐N(2,6-Me C H )] com-
᎐
2
2
2
6
3
plexes 1–3 and 5. The Pd–C separation in 7 is 2.143(3) Å, with
the methyl group trans to the PPh2 moiety, which is larger than
the Pd–C bond in 3 [2.062(4) Å], where the Pd–Me group is cis
to phosphorus atom of the chelating ligand. This may account
for the greater reactivity of compound 7 towards CO insertion
into the Pd–C bond compared to compound 3.
1.288(5) in 1, 1.292(3) in 2, 1.297(4) in 3, and to 1.300(11) Å
in 5.
Molecular structures of 6 and 7, where the ligand is
[Ph PCH᎐C(Ph)N(2,6-Me C H )]Ϫ, were determined by single
᎐
2
2
6
3
crystal X-ray diffraction and their ORTEP diagrams are shown
in Fig. 7 and 8, respectively. Changes in the structure of the
ligand are reflected in the molecular parameters of the com-
plexes. The bond lengths determined for the C–C backbone in 6
and 7 were found to be considerably shorter than the corre-
sponding bonds determined in the neutral (free or coordinated)
ligand. For [Pd2(µ-Br)2(LϪ)2], 6, the C–C distance of the back-
bone is 1.379(4) Å, close to the corresponding carbon–carbon
Copolymerisation tests
Complexes [PdMeCl(HL)] 3 and [PdMe(PPh3)(LϪ)] 7 were
tested for their ability to catalyse the copolymerisation of ethyl-
ene and CO. Solutions of the compounds were stirred for 12 h
in CH2Cl2 at 90 ЊC in the presence of 40 bar 1 : 1 ethylene : CO
J. Chem. Soc., Dalton Trans., 2001, 3384–3395
3391

View Article Online
in a sealed Parr autoclave. No significant reduction in pressure
of the autoclave was observed during any of the runs.
were performed by the microanalytical laboratory of the
Inorganic Chemistry Laboratory, University of Oxford and
FABϩ mass spectra by the EPSRC National Mass Spectrometry
Service Centre, University of Wales, Swansea, UK.
The activity of 3 in the catalysis of CO/ethylene copolymer-
isation was tested using AgBF4 or Na[B{3,5-(CF3)2C6H3}4] as
co-catalysts. In both cases, grey solids were isolated, with prod-
uctivities of 634 g polymer (mol Pd)Ϫ1 hϪ1 (335 mg yield of
copolymer) and 358 g polymer (mol Pd)Ϫ1 hϪ1 (215 mg yield of
copolymer), respectively. The resultant products were charac-
terised by solution IR, 1H and 13C{1H} NMR spectroscopies in
a 1 : 1 mixture of 1,1,1,3,3,3-hexafluoroisopropanol and C6D6.
n
The reagents BuLi, MeLi, KH, [(COD)PdCl2], PdBr2 were
i
purchased from Aldrich and used as received. Ph2PCl, Pr2NH
and 2,6-Me2C6H3 were purchased from Strem and purified by
vacuum distillation before use. The imine [MeC(Ph)᎐N(2,6-
᎐
Me2C6H3)] was prepared as described below, and [(COD)Pd-
MeCl] was prepared as previously described.26
1
The H NMR spectra of the copolymers contained a single
band of resonances in the region δ 2.39–2.41 which can be
assigned to the methylene protons –[CH2–CH2–CO]n–. The
13C{1H} NMR spectra showed singlet resonances for the
methylene and carbonyl carbons at δ 35.3 and 212, respectively.
The presence of end-groups could not be unambiguously
detected by 1H or 13C{1H} NMR and the melting points of the
resulting copolymers were 249–259 ЊC, which suggests that n >
400.24,25 Notably, the NMR spectra of the resulting copolymers
did not show any detectable signals in the region expected for a
double insertion fault of ethylene into the copolymer. Spectro-
scopic data suggest the formation of a perfectly alternating
copolymer, probably with the formula CH3CH2C(O)[CH2CH2-
C(O)]nCH2CH2C(O)CH3.24,25 As a consequence of the poor
solubility of the copolymer in common organic solvents,
accurate molecular weight determinations were not obtained.
When [PdMe(PPh3)(LϪ)] was used as catalyst, a very small
amount of black powder was formed, whose infrared spectra
did not contain a carbonyl stretch characteristic of poly(C2H4-
alt-CO) at 1692 cmϪ1. Elemental analysis confirmed that mainly
Pd metal was isolated.
NMR
NMR spectra were recorded using either a Varian Mercury 300
(1H 300, 13C 75.5, 19F 282.3, 31P 121.6 MHz) or a Varian UNI-
TYplus (1H 500, 11B 160.4, 13C 125.7, 31P 202.4 MHz) spec-
trometer and are at room temperature unless otherwise stated.
The spectra were referenced internally relative to the residual
protio-solvent (1H) and solvent (13C) resonances relative to
tetramethylsilane (1H, 13C, δ = 0) or externally to BF3ؒEt2O (11B,
δ = 0), H3PO3 (31P, δ = 0) or CFCl3 (19F, δ = 0). Chemical shifts
(δ) are expressed in ppm and coupling constants (J) in Hz.
A solution of HL in d8-toluene was used for 31P selective
inversion transfer experiments. The temperature was calibrated
using a 100% methanol (<300 K) or ethylene glycol (>300 K)
sample. Data was acquired using a (180selective–τ–90non-selective
–
acquire) pulse sequence with proton decoupling during the
180selective pulse and the acquisition. The selective 180 pulse was
achieved using a Dante sequence and the choice of values of
τ was optimised to give the most points over the initial build up
of transferred saturation. A non-selective inversion recovery
experiment was used to estimate the spin–lattice relaxation
rates. The exchange rates were extracted from the data using
the program CIFIT21 and are summarised in the Eyring plot
(Fig. 1).
A probable reason for the inactivity of complex 7 is that the
PPh3 ligand is too strong a σ donor and therefore not displaced
by ethylene. Ligand displacement is regarded as a crucial step
before ethylene insertion into the initial Pd–acyl bond and,
hence, copolymerisation can occur.25
Preparations
[MeC(Ph)᎐N(2,6-Me C H )]. A mixture of acetophenone
᎐
2
6
3
Conclusions
(25.75 g, 21.45 mmol), 2,6-dimethylphenylamine (25.96 g, 21.45
mmol) and p-tolylsulfonic acid (1.37 g) in a round-bottom flask
fitted with a Soxhlet extractor containing about 20 g anhydrous
CaSO4 was refluxed in 200 mL toluene over three days. During
the reaction, the water was removed using activated molecular
sieves (4 Å). After removal of volatiles, the brown residue was
distilled under vacuum (10Ϫ3 bar), the unreacted starting
materials distilled up to 60 ЊC and the imine distilled between
160–166 ЊC as a yellow oil which solidified at room temperature
giving a yellow oily powder (21 g, overall yield 44%). Elemental
analysis (%) found (calculated): C 85.6 (86.0), H 7.5 (7.6), N 6.2
A novel route for the synthesis of a family of ligands with bulky
substituents at the N-donor and flexible backbone has been
demonstrated by the isolation and characterisation of the
neutral N/P ligand [Ph PCH C(Ph)᎐N(2,6-Me C H )].
᎐
2
2
2
6
3
Several group 10 metal halide and alkyl complexes of this
ligand have been prepared and fully characterised showing the
ability of the ligand to coordinate in a chelating bidentate fash-
ion. An initial study of the reactivity of the complexes, and of
their catalytic properties towards CO/ethylene copolymeris-
ation is described and further detailed studies are in progress.
(6.3); IR (CsI): νCN = 1640s cmϪ1
.
Experimental
[Ph PCH C(Ph)᎐N(2,6-Me C H )], HL. To a pre-cooled
᎐
2
2
2
6
3
i
solution of dry Pr2NH (2.26 g, 22.42 mmol) in 50 mL THF, a
General
n
1.6 M solution of BuLi in hexanes (1.43 g, 22.42 mmol) was
All manipulations of air and/or moisture sensitive materials
were performed under an inert atmosphere of pure Ar or dry
N2 using standard Schlenk line techniques or in an inert atmos-
phere dry box. Inert gases were purified firstly by passage
through columns filled with activated molecular sieves (4 Å)
and then either manganese() oxide suspended on vermiculite,
for the Schlenk line, or BASF catalyst, for the dry box. Celite
filtration aid was purchased from Fluka Chemie and oven-dried
at 150 ЊC prior to use. Solvents were pre-dried over activated
4 Å molecular sieves and then distilled from Na–K alloy (light
petroleum ether b.p. 40–60 ЊC, diethyl ether, pentane), from
sodium (toluene), from potassium (THF), or from calcium
hydride (dichloromethane), under N2. Deuterated NMR sol-
vents (Aldrich, Goss Scientific) were refluxed and distilled from
potassium metal (d8-toluene) or from calcium hydride
(CD2Cl2), distilled and degassed prior to use. Microanalyses
added dropwise at Ϫ78 ЊC. The mixture was allowed to warm
up to room temperature and stirred for 30 min for completing
the formation of LDA. A cold solution of dry imine
[MeC(Ph)᎐N(2,6-Me C H )] (5 g, 22.42 mmol) in 25 mL THF
᎐
2
6
3
was added dropwise at Ϫ78 ЊC under stirring. The mixture was
stirred for 2 h at Ϫ78 ЊC and the formation of the lithium salt of
the imine as a bright-yellow precipitate was observed, however
no isolation attempts have been made. A cold mixture of the
freshy distilled Ph2PCl (4.94 g, 22.42 mmol) and 25 mL THF
was transferred dropwise. After addition of Ph2PCl, the yellow
precipitate gradually disappeared and the solution colour
turned a lighter yellow. The mixture was stirred for 12 h at room
temperature followed by the removal of volatiles under reduced
pressure. The white residue was washed with 50 mL toluene and
the LiCl formed removed by filtration over Celite. The toluene
was removed under reduced pressure and the remaining solid
3392
J. Chem. Soc., Dalton Trans., 2001, 3384–3395

View Article Online
washed three times with 20 mL of cold pentane. White crystals
of HL (5.5 g, crude yield 60%) were formed from a 1 : 4 mixture
of toluene and pentane after storing at Ϫ20 ЊC overnight.
Elemental analysis (%) found (calculated): C 82.2 (82.5), H 6.6
(6.4), N 3.4 (3.4); IR (CsI): νCN = 1634s; FABϩ: 407 (40) [M]ϩ,
208 (100) [M Ϫ (Ph2PCH2)]ϩ.
4 and 5. Elemental analysis (%) found (calculated for 4):
C 56.8 (57.2), H 5.2 (4.8), N 2.1 (2.3); FABϩ: 594.9 (40)
[M Ϫ Me]ϩ; 513 (25) [M Ϫ Br Ϫ Me]ϩ; 609 (100) [M]ϩ.
6ؒCH2Cl2. Elemental analysis (%) found (calculated): C 53.8
(53.9), H 4.1 (3.9), N 2.1 (2.2); FABϩ: 1186 (20) [M]ϩ, 594 (85)
[M/2]ϩ.
[PdCl {Ph PCH C(Ph)᎐N(2,6-Me C H )}], 1. The ligand HL
Reaction of [PdBr {Ph PCH C(Ph)᎐N(2,6-Me C H )}] with
᎐
2 2 2 2 6 3
KH. The solids 2 [PdBr {Ph PCH C(Ph)᎐N(2,6-Me C H )}]
᎐
2 2 2 2 6 3
᎐
2
2
2
2
6
3
(1 g, 2.457 mmol) in 50 mL THF was added to a suspension of
PdCl2 (434 mg, 2.457 mmol) in 50 mL THF. The mixture was
stirred at room temperature overnight and 1.14 g (80% crude
yield) of 1 was formed (as a fine yellow powder). The product
was separated by filtration and recrystallised from a 1 : 4 mix-
ture of CH2Cl2 and pentane to give yellow crystals of 1 in near
quantitative yield. Elemental analysis (%) found (calculated): C
(100 mg, 1.5 mmol) and KH (5.94 mg, 1.5 mmol) were mixed in
a Schlenk tube and 50 mL cold THF was added at Ϫ78 ЊC
under stirring. The reaction mixture was left to reach room
temperature over 12 h. The volatiles were removed under
reduced pressure and the residue washed with 100 mL of
pentane to yield a dark grey solid. This compound was
extracted into 50 mL CH2Cl2 to give a purple solution and the
insoluble materials discarded. Removal of volatiles from the
purple solution yielded 75 mg of 6 as a purple solid (85% yield).
Recrystallisation from CH2Cl2 at Ϫ20 ЊC yielded plate-like
56.7 (57.5), H 4.5 (4.5), N 2.3 (2.4); IR (CsI): νCN = 1600 cmϪ1
FABϩ: 548.1 (100) [M Ϫ Cl]ϩ, 513.1 (15) [M Ϫ 2Cl]ϩ.
;
[PdBr {Ph PCH C(Ph)᎐N(2,6-Me C H )}], 2. The ligand HL
᎐
2
2
2
2
6
3
(765.5 mg, 0.5 mmol) in 50 mL THF was added dropwise to a
suspension of PdBr2 (500.3 mg, 0.5 mmol) in 50 mL THF. The
mixture was stirred at room temperature for 48 h. The orange
precipitate formed was separated by filtration, washed with 20
mL pentane and dried in vacuum to afford 0.89 g product in a
70% yield. Needle-like orange crystals were grown by the slow
diffusion of pentane at room temperature onto a concentrated
CH2Cl2 solution of 2 in a crystallisation bridge. Elemental
analysis (%) found (calculated): C 50.0 (49.9), H 4.0 (3.9), N 2.0
(2.1), Pd 15.6 (15.7); IR (CsI): νCN = 1584 cmϪ1; FABϩ: 594
(100) [M Ϫ Br]ϩ, 513 (15) [M Ϫ 2Br]ϩ, 672 (15) [M Ϫ H]ϩ.
green crystals of compound 6, [Pd (µ-Br) {Ph PCH᎐C(Ph)-
᎐
2 2 2
N(2,6-Me2C6H3)}2], crystallised with two molecules of
CH2Cl2.
[PdMe {Ph PCH C(Ph)᎐N(2,6-Me C H )}], 5. A solution of
᎐
2
2
2
2
6
3
Me2Zn (190 mg, 2 mmol, 2 M in THF) cooled to Ϫ78 ЊC was
added dropwise to a cold solution (Ϫ78 ЊC) of 1, [PdCl2-
{Ph PCH C(Ph)᎐N(2,6-Me C H )}], (100 mg, 0.17 mmol) in
᎐
2
2
2
6
3
50 mL THF. The mixture was left to reach room temperature
overnight, and a colour change from light yellow to brown was
observed. Volatiles were removed under reduced pressure
and a brown oily residue was obtained. This was extracted with
20 mL cold toluene which was then concentrated under reduced
pressure to 2 mL and layered with pentane (ca. 8 mL). Air
and thermally sensitive yellow crystals of complex 5, [PdMe2-
[PdMeCl{Ph PCH C(Ph)᎐N(2,6-Me C H )}], 3. To a mix-
᎐
2
2
2
6
3
ture of the ligand HL (387 mg, 0.945 mmol) and (COD)Pd-
MeCl (250 mg, 0.945 mmol) 100 mL toluene was added, whilst
stirring. The reaction mixture was stirred for 6 h at room tem-
perature. The resulting white solid was isolated by filtration,
washed with 20 mL cold pentane and the residual volatiles
removed under reduced pressure; 0.5 g product was isolated
(yield = 89%). Light yellow block-shaped crystals were obtained
after recrystallisation of the product from a 1 : 4 mixture of
CH2Cl2 and pentane at Ϫ20 ЊC. Elemental analysis (%) found
(calculated): C 61.2 (61.7), H 5.2 (5.2), N 2.5 (2.5); IR (CsI): νCN
= 1612 cmϪ1; FABϩ: 563.9 (10) [M]ϩ, 549.9 (80) [M Ϫ CH3]ϩ,
527.9 (100) [M Ϫ Cl]ϩ.
{Ph PCH C(Ph)᎐N(2,6-Me C H )}], (50 mg, 0.092 mmol, yield
᎐
2
2
2
6
3
= 54%) formed after storing the mixture at Ϫ20 ЊC for 48 h and
were isolated by filtration. Elemental analysis (%) found (calcu-
lated): C 65.3 (66.2), H 5.6 (5.9), N 2.0 (2.5); FABϩ: 528.1 (70)
[M Ϫ Me]ϩ, 513.1 (55) [M Ϫ 2Me]ϩ, 406.1 (30) [M Ϫ Pd Ϫ
2Me]ϩ.
[PdMe(PPh ){Ph PCH᎐C(Ph)N(2,6-Me C H )}], 7. The
᎐
3
2
2
6
3
solids 3, [PdMeCl{Ph PCH C(Ph)᎐N(2,6-Me C H )}] (100 mg,
᎐
2
2
2
6
3
0.177 mmol), KH (7.093 mg, 0.177 mmol) and PPh3 (46.46 mg,
0.177 mmol) were mixed in a Schlenk tube and 50 mL of THF
was added. The mixture was stirred at room temperature under
N2 for 12 h. A colour change from light yellow to orange
was observed. The solvent was removed under reduced pressure
and the resulting orange solid was washed with 20 mL of cold
pentane. Recrystallisation from a mixture of toluene and pen-
tane at 0 ЊC gave 90 mg (0.114 mmol, 64% yield) of orange
Reaction of [PdBr {Ph PCH C(Ph)᎐N(2,6-Me C H )}] with
᎐
2
2
2
2
6
3
MeLi. To a suspension of 2, [PdBr {Ph PCH C(Ph)᎐N(2,6-
᎐
2
2
2
Me2C6H3)}], (950 mg, 1.41 mmol) in 100 mL Et2O at Ϫ78 ЊC, a
cold solution of MeLi 1.57 M in Et2O (62.1 mg, 2.82 mmol) was
added dropwise. The reaction mixture was stirred for 15 min
at Ϫ78 ЊC and left to reach room temperature over 1 h. The
volatiles were removed under reduced pressure and the residue
washed with 100 mL warm petroleum ether (b.p. 40–60 ЊC) to
yield a red–brown solution (fraction 1) and a dark precipitate.
This precipitate was further washed with 50 mL CH2Cl2 to give
a purple solution (fraction 2) and LiBr, which was discarded.
Fraction 1. The volatiles were removed to give a small
amount of a brown solid which was recrystallised from toluene
crystals of complex 7, [PdMe(PPh ){Ph PCH᎐C(Ph)N(2,6-
᎐
3
2
Me2C6H3)}]. Elemental analysis (%) found (calculated): C 71.8
(71.4), H 5.4 (5.5), N 1.8 (1.8); FABϩ: 789.6 (70) [M]ϩ, 774.5
(25) [M Ϫ Me]ϩ, 527.7 (98) [M Ϫ PPh3].
[PdMe(CH CN){Ph PCH C(Ph)᎐N(2,6-Me C H )}][BF ], 8.
᎐
3
2
2
2
6
3
4
The complex 3, [PdMeCl{Ph PCH C(Ph)᎐N(2,6-Me C H )}],
᎐
2
2
2
6
3
to give a mixture of compounds 4, [PdMeBr{Ph PCH C(Ph)᎐
(120 mg, 0.454 mmol) and AgBF4 (88.47 mg, 0.454 mmol) were
mixed together in a Schlenk tube and 50 mL CH3CN added.
The mixture was stirred for 12 h in darkness at room temper-
ature. AgCl was removed by filtration over Celite and the vola-
tiles removed under reduced pressure to give 0.1 g (62% crude
yield) of white–yellow powder [PdMe(CH3CN){Ph2PCH2-
᎐
2
2
N(2,6-Me2C6H3)}], and 5, [PdMe {Ph PCH C(Ph)᎐N(2,6-
᎐
2
2
2
1
Me2C6H3)}], in a ratio of 2 : 3 by integration of the H NMR
spectrum thereof. Attempts to isolate either 4 or 5 from the
mixture were unsuccessful. These complexes were characterised
by 1H, 13C{1H} and 31P{1H} NMR spectroscopy (Tables 1
and 2).
C(Ph)᎐N(2,6-Me C H )}][BF ] 8. The solid was washed with
᎐
2
6
3
4
Fraction 2. The CH2Cl2 solution was concentrated to about
10 mL and stored at Ϫ20 ЊC. After 48 h green crystals of com-
pentane and recrystallised from CH2Cl2 and pentane to give 8
as a light-yellow microcrystalline powder. Elemental analysis
(%) found (calculated): C 56.0 (56.7), H 5.3 (4.9), N 4.2 (4.3), B
2.1 (1.7); IR (CsI): νCN = 1600 cmϪ1, νBF = 1100–1299 cmϪ1
(broad); FABϩ: 530.3 (100) [M Ϫ CH3CH Ϫ BF4]ϩ.
plex 6, [Pd (µ-Br) {Ph PCH᎐C(Ph)N(2,6-Me C H )} ] with two
᎐
2
2
2
2
6
3
2
molecules of CH2Cl2, were formed and isolated by filtration
(210 mg, 0.177 mmol, 50% yield).
J. Chem. Soc., Dalton Trans., 2001, 3384–3395
3393

View Article Online
Table 5 Crystallographic data for compounds HL, 1–3 and 5–7
HL
1
2
3
5
6a
7b
Chemical formula
Formula weight
Crystal system
Space group
C28H26NP
407.47
Monoclinic Monoclinic
C28H26Cl2NPPd C28H26Br2NPPd C29H29ClNPPd C30H27NPPd C29H27BrCl2NPPd C54H51NP2Pd
584.77
673.69
Monoclinic
P21/n
564.38
Monoclinic
Cc
537.92
Triclinic
P1
677.72
Monoclinic
C2/c
882.35
Triclinic
P1
P21/n
P21/n
Unit cell dimensions
a/Å
α/Њ
b/Å
13.402(5)
90
9.595(5)
92.423(5)
17.249(5)
90
2216.1(16) 2544.0
150
4
11.182(1)
90
22.663(1)
117.47(2)
11.314(1)
90
9.037(2)
90
13.944(3)
97.06(3)
20.419(4)
90
2553.5(9)
150
4
20.307(6)
90
10.905(5)
130.49(2)
15.256(7)
90
2569.3(6)
150
4
7.8590(7)
89.044(6)
9.2000(13)
84.199(8)
18.778(3)
70.296(7)
1271.4
150
2
0.81
11841
4630
28.0025(4)
90
11.62482(2)
121.2300(6)
19.8002(4)
90
5513.1
150
8
11.0390(9)
99.511(5)
12.1030(7)
106.438(4)
17.4530(14)
90.095(5)
2201.5
190
2
0.53
20284
6812
β/Њ
c/Å
γ/Њ
Volume/Å3
Temperature/K
Z
150
4
1.019
29609
4207
0.048
Absorption coefficient/mmϪ1 0.139
3.936
28729
5084
0.91
13025
2594
2.39
42409
5914
Reflections collected
Independent reflections
R(int)
27212
3906
0.027
0.060
0.03
0.08
0.04
0.03
Final R indices
R1
wR2
0.0476
0.0563
0.0246
0.0308
0.0868
0.0354
0.0564
0.1049c
0.0915c
0.0642c
0.0161d
0.0704e
0.0415d
0.0264d
a Crystallises with two molecules of CH2Cl2. b Crystallises with one molecule of CH3C6H5. c [I > 2σ(I )]. d [I > 3σ(I )]. e [I > 4σ(I )].
NMR-scale reaction between [PdMeCl{Ph PCH C(Ph)᎐
N(2,6-Me2C6H3)}] and CO. A yellow CD2Cl2 solution (0.55
was separated by filtration, washed with methanol and dried
under vacuum [yield poly(C2H4-alt-CO) 335 mg, 634 g product
(mol Pd)Ϫ1 hϪ1]. The same procedure was employed using 28 mg
᎐
2
2
mL) of complex 3, [PdMeCl{Ph PCH C(Ph)᎐N(2,6-Me C -
᎐
2
2
2
6
H3)}], (10 mg, 0.0177 mmol) maintained at Ϫ78 ЊC was
degassed and CO (<2 atm) admitted into an NMR tube fitted
with a Teflon valve before sealing. The mixture was allowed to
warm to room temperature and the 1H and 31P{1H} NMR spec-
tra were recorded after 5 min, which showed 20% conversion of
3 to 9. Further 1H and 31P{1H} NMR spectra recorded after 2 h
showed 50% conversion. After 24 h at room temperature, 70%
(0.05 mmol) of 3, [PdMeCl{Ph PCH C(Ph)᎐N(2,6-Me C H )}]
᎐
2 2 2 6 3
and Na[B{3,5-(CF2)2C6H3}4] (12.35 mg, 0.05 mmol) to generate
the catalyst [yield poly(C2H4-alt-CO) 215 mg, 358 g product
(mol Pd)Ϫ1 hϪ1] was isolated as a grey solid.
Infrared spectroscopy of the products showed the character-
istic carbonyl stretch of poly(C2H4-alt-CO) at 1692 cmϪ1. Fur-
thermore, 1H and 13C{1H} NMR spectroscopy of the products
are similar to those reported for catalysts based on Pd() com-
plexes of chelating diphosphines.24
The method described above was also applied using com-
pound 7 (10 mg, 0.0127 mmol) as the catalyst. In this case, 3 mg
of a black solid was formed whose IR spectra contained no CO
stretch characteristic of poly(C2H4-alt-CO) and was shown by
elemental analysis to contain mainly Pd metal.
1
conversion was estimated by integration of the H NMR spec-
trum. However, no significant reaction progress occurred after
one week at room temperature. The maximum conversion of 3
to 9 was therefore estimated to be 70%. Compound 9 was char-
acterised by solution IR recorded in CD2Cl2 (νCO = 1752 cmϪ1
,
1
νC᎐N = 1696 cmϪ1, νN–Ar = 1604 cmϪ1) and by H, 13C{1H} and
᎐
31P{1H} NMR spectroscopies (Tables 1 and 2).
NMR-scale reaction between [PdMe(PPh ){Ph PCH᎐C(Ph)-
Crystal structure determination
᎐
3
2
N(2,6-Me2C6H3)}] and CO. A red CD2Cl2 solution (0.55 mL) of
7, [PdMe(PPh ){Ph PCH᎐C(Ph)N(2,6-Me C H )}], (10 mg,
Sample preparation. Crystals of HL were grown by diffusion
of pentane into a toluene solution at Ϫ20 ЊC. Crystals of com-
pound 1 were grown from a 1 : 4 mixture of CH2Cl2 and pen-
tane at Ϫ20 ЊC. Crystals of compounds 2 and 3 were grown by
slow diffusion of pentane into concentrated CH2Cl2 solutions
(ratio pentane : CH2Cl2 ca. 1 : 1) at room temperature. Crystals
of 5 and 7 were formed in a 1 : 4 mixture of toluene and pen-
tane at Ϫ20 and 0 ЊC, respectively. Crystals of 6 were formed in
a concentrated CH2Cl2 solution stored at Ϫ20 ЊC. In all cases,
the crystals were isolated by filtration, and a specimen crystal
selected under an inert atmosphere, covered with polyfluoro-
ether, and mounted on the end of a glass fibre. Crystal data are
summarised in Table 5.
᎐
3
2
2
6
3
0.01266 mmol) maintained at Ϫ78 ЊC was degassed and CO
(<2 atm) admitted into an NMR tube fitted with a Teflon valve
before sealing. The mixture was allowed to warm to room
1
temperature and H and 31P{1H} NMR spectra recorded after
15 min to show complete insertion of CO in the Pd–Me bond.
1H NMR spectroscopy showed a signal (a doublet at δ 2.35,
4
with JP–Pd–C–Me = 4.95 Hz) which was assigned to acyl proton
resonances. In the 31P NMR spectra, the occurrence of a major
signal, a singlet at δ 28.3, was observed. No traces of starting
material were observed. Decomposition to Pd metal occurred
after 2 h at room temperature.
Copolymerisation tests
Data collection and processing. All data were collected at
150 K except for compound 7, data for which were collected
at 190 K, on an Enraf-Nonius DIP2000, except 6, data for
which were collected on a Nonius KappaCCD, with graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å), as summar-
ised in Table 5. The images were processed with the DENZO
and SCALEPACK programs.27
A mixture of Pd pre-catalyst, compound 3 [PdMeCl{Ph2-
PCH C(Ph)᎐N(2,6-Me C H )}], (25 mg, 0.044 mmol) and the
᎐
2
2
6
3
co-catalyst AgBF4 (8.64 mg, 0.044 mmol) in 50 mL CH2Cl2 was
transferred using a glove box into a dried 200 mL Parr auto-
clave fitted with a Teflon liner and equipped with a stirrer bar.
The autoclave was charged with 40 bar 1 : 1 C2H4 : CO mixture,
sealed, and allowed to reach 90 ЊC. The mixture was stirred at
this temperature for a further 12 h. Subsequently, the autoclave
was allowed to cool to room temperature before the remaining
C2H4–CO mixture was vented. The grey precipitate obtained
Structure solution and refinement. The crystal structures were
solved by direct methods using the programs SIR9228 (for com-
pounds HL, 1, 2 and 5–7) and SIR9729 (compound 3).
3394
J. Chem. Soc., Dalton Trans., 2001, 3384–3395

View Article Online
8 G. Minghetti, S. Stoccoro, M. A. Cinellu, A. Zucca, M. Manassero
and M. Sansoni, J. Chem. Soc., Dalton Trans., 1998, 4119.
9 M. A. Jalil, S. Fujinami, H. Senda and H. Nishikawa, J. Chem. Soc.,
Dalton Trans., 1999, 1655.
10 M. A. Jalil, S. Fujinami and H. Nishikawa, J. Chem. Soc., Dalton
Trans., 2001, 1091.
11 L. Crociani, G. Bandoli, A. Dolmella, M. Basato and B. Corain,
Eur. J. Inorg. Chem., 1998, 1811.
The structures of compounds HL, 1 and 2 were refined using
full-matrix least squares on all F 2 data using SHELXL-93;30 all
non-hydrogen atoms were refined anisotropically and hydrogen
atoms were included in calculated positions with isotropic
thermal parameters ca. 1.2 × (aromatic CH) or 1.5 × (Me) the
equivalent isotropic thermal parameters of their parent carbon
atoms, and allowed to ‘ride’ on their parent atoms during
refinement.
12 B. Crociani, S. Antonaroli, G. Bandoli, L. Canovese, F. Visentin and
P. Uguagliati, Organometallics, 1999, 18, 1137.
In the case of compounds 3 and 5–7, the refinement and
graphical calculations were performed using the CRYSTALS31
and CAMERON32 software packages. The structures were
refined by full-matrix least squares procedures on F. All non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were included in calculated
positions with isotropic thermal parameters, with the exception
of those on PdMe2 in 5, where they could not be located in a
Fourier map or positioned geometrically with confidence. A
Chebychev weighting scheme with the parameters 1.36, Ϫ1.45
and 0.870 was applied for compound 3, 1.70, Ϫ1.44 and 0.855
for compound 5, 1.94, Ϫ0.180 and 1.21 for 6 and 1.94, Ϫ1.82
and 1.38 for compound 7, as well as empirical absorption
corrections.33
13 P. Braunstein, M. D. Fryzuk, M. Le Dall, F. Naud, S. J. Rettig and
F. Speiser, J. Chem. Soc., Dalton Trans., 2000, 1067.
14 A. Aeby and G. Consiglio, J. Chem. Soc., Dalton Trans., 1999, 655.
15 A. Del Zotto, P. Di Bernardo, M. Tolazzi and P. L. Zanonato,
J. Chem. Soc., Dalton Trans., 1999, 979.
16 K. Selvakumar, M. Valentini, M. Worle, P. S. Pregosin and
A. Albinati, Organometallics, 1999, 18, 1207.
17 W. Clegg, S. Doherty, K. Izod, H. Kagerer, P. O’Shaughnessy and
J. M. Sheffield, J. Chem. Soc., Dalton Trans., 1999, 1825.
18 S. E. Watkins, X. Yang, D. C. Craig and S. B. Colbran, J. Chem.
Soc., Dalton Trans., 1999, 1539.
19 K. R. Reddy, K. Surekha, G. H. Lee, S. M. Peng and S. T. Liu,
Organometallics, 2000, 19, 2637.
20 H. Ahlbrecht and S. Fisher, Tetrahedron, 1970, 26, 2837.
21 A. D. Bain and J. A. Cramer, J. Magn. Reson., Ser. A, 1996, 118,
21.
22 Personal CAChe, Computer Aided Chemistry Molecular Modelling
Package, v. 4.1 for MacIntosh, Fujitsu, CAChe Scientific Ltd.,
Beaverton, OR, 1999.
CCDC reference numbers 171176–171182.
See http://www.rsc.org/suppdata/dt/b1/b102476k/ for crystal-
lographic data in CIF or other electronic format.
23 J. Vicente, J.-A. Abad, A. D. Frankland and M. C. Ramirez de
Arellano, Chem. Eur. J., 1999, 5, 3066.
24 E. Drent, J. A. M. van Broekhoven and M. J. Doyle, J. Organomet.
Chem., 1991, 417, 235.
25 E. Drent and P. H. M. Budzelaar, Chem. Rev., 1996, 96, 663.
26 F. T. Lapido and G. K. Anderson, J. Organomet. Chem., 1994, 13,
303.
27 Z. Otwinowski and W. Minor, Methods in Enzymology, ed. C. N.
Carter, Jr and R. M. Sweet, Academic Press, London, 1996, vol. 276,
p. 307.
28 A. Altomare, G. Cascarano, C. Giacovazzo and A. Guagliardi,
J. Appl. Crystallogr., 1993, 26, 343.
Acknowledgements
We thank the Balliol College for a Dervorguilla Scholarship
(S. I. P.), the Royal Society for a University Research Fellowship
(K. S. C.) and EPSRC for support.
References
1 S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000, 100,
1169.
2 E. Lindner, S. Pautz and M. Haustein, Coord. Chem. Rev., 1996, 155,
145.
29 A. Altomare, G. Carascano, C. Giacovazzo and A. Guagliardi,
SIR97, Program for Crystal Structure Solution, University of Bari,
Italy, 1997.
3 A. Bader and E. Lindner, Coord. Chem. Rev., 1991, 108, 27.
4 U. Klabunde, F. H. Kowaldt and R. Goddard, Angew. Chem.,
Int. Ed. Engl., 1978, 17, 466.
5 U. Klabunde and S. D. Ittel, J. Mol. Catal., 1987, 41, 123.
6 G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem.,
Int. Ed., 1999, 38, 428.
30 G. M. Sheldrick, SHELXL-93, Program for Crystal Structure
Refinement, Universität Göttingen, Germany, 1993.
31 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Better,
CRYSTALS, issue 10, Chemical Crystallography Laboratory,
Oxford, UK, 1996.
32 D. J. Watkin, C. K. Prout and L. J. Pearce, CAMERON, Chemical
Crystallography Laboratory, Oxford, UK, 1996.
7 S. D. Perera, B. L. Shaw and M. Thornton-Pett, J. Chem. Soc.,
Dalton Trans., 1992, 999.
33 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158.
J. Chem. Soc., Dalton Trans., 2001, 3384–3395
3395