Characterization and dynamics of [Pd(L-L)H(solv)]+, [Pd(L-L)(CH2CH3)]+, and [Pd(L-L)(C(O)Et)(THF)]+ (L-L = 1,2- CH2PBu2t)2C6H4 ): Key intermediates in the catalytic methoxycarbonylation of ethene to methylpropanoate

Article abstract of DOI:10.1021/om010938g

A detailed spectroscopic study has allowed the solution structure and dynamic properties of all the intermediates in the Pd-catalyzed methoxycarbonylation of ethene to be established. [Pd(L-L)H(solv)]⁺ 1 (L-L = 1,2-(CH₂PBu₂^t)₂C₆H₄ ; solv = MeOH, 1a; PrⁿOH, 1b; THF, 1c; EtCN, 1d) is static, and the two inequivalent P atoms do not become equivalent through solvent exchange over all the temperatures studied. [Pd(L-)(CH₂CH₃)]⁺, 2, contains a strong β-agostic C-H interaction which is remarkably stable and is not displaced even in strongly coordinating solvents such as EtCN. C_α and C_β of the ethyl group in 2 become equivalent via a stereospecific interchange involving [Pd(L-L)H(η²-C₂H₄)]⁺ without making the two P atoms equivalent; at higher temperatures these two inequivalent P atoms do become equivalent probably via a T-shaped intermediate. For [Pd(L-L)(C(O)Et)(solv)]⁺, 6, there is no β-agostic C-H interaction and multiple ¹³C-labeling of the C(O)Et group shows that the inequivalent P atoms become equivalent via movement of the intact C(O)Et group. The crystal structure of the related complex [Pd(L-L)(C(O)Et)Cl] cocrystallized with dibenzylacetone has been determined.

Full text of DOI:10.1021/om010938g

1832
Organometallics 2002, 21, 1832-1840
Ch a r a cter iza tion a n d Dyn a m ics of [P d (L-L)H(solv)]+,
[P d (L-L)(CH2CH3)]+, a n d [P d (L-L)(C(O)Et)(THF )]+
(L-L ) 1,2-(CH2P Bu t ) C6H4): Key In ter m ed ia tes in th e
2 2
Ca ta lytic Meth oxyca r bon yla tion of Eth en e to
Meth ylp r op a n oa te
William Clegg,† Graham R. Eastham,‡ Mark R. J . Elsegood,† Brian T. Heaton,*,§
J onathan A. Iggo,§ Robert P. Tooze,‡, Robin Whyman,§ and Stefano Zacchini§
Chemistry Department, University of Newcastle, Newcastle-upon-Tyne, U.K. NE1 7RU,
Ineos Acrylics, PO Box 90, Wilton, Middlesborough, Cleveland, U.K. TS90 8J E, and Chemistry
Department, University of Liverpool, Liverpool, U.K. L69 7ZD
Received October 30, 2001
A detailed spectroscopic study has allowed the solution structure and dynamic properties
of all the intermediates in the Pd-catalyzed methoxycarbonylation of ethene to be established.
[Pd(L-L)H(solv)]+ 1 (L-L ) 1,2-(CH2PBut )2C6H4; solv ) MeOH, 1a ; PrnOH, 1b; THF, 1c;
2
EtCN, 1d ) is static, and the two inequivalent P atoms do not become equivalent through
solvent exchange over all the temperatures studied. [Pd(L-L)(CH2CH3)]+, 2, contains a strong
â-agostic C-H interaction which is remarkably stable and is not displaced even in strongly
coordinating solvents such as EtCN. CR and Câ of the ethyl group in 2 become equivalent
via a stereospecific interchange involving [Pd(L-L)H(η2-C2H4)]+ without making the two P
atoms equivalent; at higher temperatures these two inequivalent P atoms do become
equivalent probably via a T-shaped intermediate. For [Pd(L-L)(C(O)Et)(solv)]+, 6, there is
no â-agostic C-H interaction and multiple 13C-labeling of the C(O)Et group shows that the
inequivalent P atoms become equivalent via movement of the intact C(O)Et group. The crystal
structure of the related complex [Pd(L-L)(C(O)Et)Cl] cocrystallized with dibenzylacetone
has been determined.
Sch em e 1
In tr od u ction
The methoxycarbonylation of ethene to form methyl-
propanoate (MP), using a palladium phosphine catalyst,
is currently being developed by Ineos Acrylics as part
of a novel two-stage route to methyl methacrylate
(MMA).1 This process employs a highly sterically hin-
dered diphosphine ligand and results in the formation
of MP with high turnover and selectivity (99.98%).2 We
have shown previously that the formation of MP em-
ploying this novel bis-phosphine ligand occurs via a
catalytic mechanism involving a Pd(II) hydride (A)
3
rather than the “methoxycarbonyl” cycle (B)
(see
Scheme 1). Herein, we report a detailed spectroscopic
analysis of the structure and dynamics of all the
intermediates [Pd(L-L)H(solv)]+, [Pd(L-L)(CH2CH3)]+,
and [Pd(L-L)(C(O)Et)(THF)]+ involved in the catalytic
cycle.
Resu lts a n d Discu ssion
* To whom correspondence should be addressed. E-mail: bth@
liverpool.ac.uk.
† University of Newcastle.
Syn th esis a n d Ch a r a cter iza tion of [P d (L-L)-
‡ Ineos Acrylics.
§ University of Liverpool.
3
(CH2CH3)]+, 2a . Previous work showed that [Pd(L-
Present address: Synetix, PO Box 1, Belasis Ave., Billingham,
Cleveland, U.K. TS23 1LB.
(1) New MMA Technology, European Chemical News, Oct 30-Nov
5, 2000; p 20.
(2) Clegg, W.; Eastham, G. R.; Elsegood, M. R. J .; Tooze, R. P.; Wang,
X. L.; Whiston, K. W. Chem. Commun. 1999, 1877.
(3) Eastham, G. R.; Heaton, B. T.; Iggo, J . A.; Tooze, R. P.; Whyman,
R.; Zacchini, S. Chem. Commun. 2000, 609.
L)H(MeOH)]+, 1a , is formed on oxidation of [Pd(L-
L)(dba)] [dba ) trans,trans-(PhCHdCH)2CO; L-L )
1,2-(CH2PBut ) C6H4, dtbpx] in MeOH in the presence
2 2
of an acid; the quantitative preparation of other ana-
logues, containing different solvent molecules, may be
10.1021/om010938g CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/26/2002

Catalytic Methoxycarbonylation of Ethene
Organometallics, Vol. 21, No. 9, 2002 1833
Ta ble 1. 31P NMR Da ta for [P d (L-L)H(solv)]+ a n d
[P d (L-L)CH2CH3]+ a t 193 K
Protonation of [Pd(L-L)(C2H4)] to give 2a has been
reported previously by Spencer et al.,4 but, unfortu-
nately, no NMR data were reported. Further support
for this formulation of 2a comes from examination of
both the 13C chemical shifts and C-H coupling con-
stants, obtained by reacting 1a with 13CH2dCH2 (1
equiv) in MeOH when two different isotopomers are
[Pd(L-L)H(solv)]+
[Pd(L-L)CH2CH3]+
1
2a
solvent
δP(A)
δP(B)
2J PP
δP(A)
δP(B)
2J PP
MeOH
nPrOH
THF
75.5
68.5
72.8
67.1
21.8
19.4
21.6
21.1
16.1
17
18.1
19.8
67.7
67.5
67.9
67.1
36.3
36.1
37.1
36.4
31.0
br
31.5
31.5
formed in the ratio 1:1, i.e., [Pd(L-L)(CH213CH3)]+, 2b,
EtCN
and [Pd(L-L)(13CH2CH3)]+, 2c. In the isotopomer 2b,
PA couples only with PB (the coupling with Câ is too
small to be resolved), and, hence, the expected signal is
more easily accomplished via the reaction shown in eq
1.
2
a doublet with J P(A)P(B) ) 31 Hz, as found in the
(i)
unenriched compound, 2a . For the isotopomer 2c, PB
couples with both PA [2J P(A)P(B) ) 31 Hz] and the trans
13C atom [2J P(B)C(R) ) 38 Hz], resulting in a doublet of
doublets. In solution, there is an equal amount of the
two isotopomers 2b and 2c, but, because 2c gives four
equally intense resonances and 2b only two, the inten-
sity of each of the resonances due to 2c is one-half the
intensity of each of the resonances due to 2b. Hence,
the resulting signal for PB is a multiplet consisting of
six lines, with relative intensities 1:2:1:1:2:1, as observed
in the experimental spectrum. In the 13C{1H} NMR
spectrum at 193 K, CR resonates at 31 ppm as a doublet
of doublets [2J C(R)P(B) ) 38 Hz, 2J C(R)P(A) ) 5 Hz], whereas
Câ gives a singlet at 8 ppm. Finally, in the proton-
coupled 13C NMR spectrum at 193 K, the resonance at
8 ppm appears as a quartet [1J C(â)H ) 124 Hz], and that
at 31 ppm as a triplet of doublets [1J C(R)H ) 158 Hz,
2J C(R)P(B) ) 38 Hz], in perfect agreement with our
assignments. In classical Pd-ethyl complexes,5 δ(CH3)
> δ(CH2), but for 2a -c δ(CH2) and δ(CH3) are at 31
and 8 ppm, respectively; this reversal of the CH2 and
CH3 chemical shifts between classical and nonclassical
metal-ethyl complexes is also found for [Pt(L-L)(CH2-
CH3)]+, which also contains a Câ-H agostic interaction.6
In this case [δCH2, 22.0; δCH3, 8.2], it was possible to
freeze out (145 K) the rotation of the CâH3 group and
[Pd(L-L)(O3SCF3)2] 8 [Pd(L-L)H(solv)]+ +
(ii)
HO3SCF3 (1)
solv ) PrnOH, 1b
) THF, 1c
) EtCN, 1d
(i)
+ MeOH followed by evacuation
+ solv (PrnOH, THF or EtCN)
(ii)
Consistent with our previous assignment of the in-
equivalent phosphorus atoms in 1a ,3 there is a signifi-
cant change in the value of δP(A) (trans to solvent) on
varying the solvent in 1a -d (see Table 1), whereas δP(B)
remains relatively unchanged. In all cases, on the NMR
time scale, there is no evidence for solvent exchange,
which would allow PA and PB to become equivalent, until
well above room temperature.
Previous work showed that 1a reacts immediately
with ethene and the product was formulated as shown
in eq 2. Using mono-13C-labeled ethene, it was possible
1
obtain two different values of J C(â)H in the 13C NMR
spectrum. In the 13C NMR of 2b-c, it was not possible,
even at 145 K, to freeze out the CâH3 rotation to obtain
the static isomer of 2. Nevertheless, this agostic interac-
tion is also supported by consideration of the values of
1J C(R)H, which are normally ca. 130 Hz for classical ethyl
complexes but increase to ca. 155 Hz when there is an
agostic interaction.7
to assign unambiguously the two inequivalent phospho-
rus resonances, and a reasonable assumption was to
assign the fourth coordination site in the palladium-
ethyl complex to MeOH. However, subsequent work on
analogous reactions with 1b-d suggests that the for-
mulation of the ethyl complex in eq 2 should be revised.
Thus, unlike 1a -d , there is little variation in the
chemical shifts of PA and PB with different solvents (see
Table 1), and this behavior is more consistent with
occupancy of the fourth coordination site in 2a being
due to a â-C-H interaction as shown below:
The NMR data reported in Table 1 also suggest that
the agostic interaction is retained in all the solvents
examined, even in a strongly coordinating solvent such
as EtCN. To confirm this, the reaction between [Pd(L-
L)H(EtCN)]+, 1d , and 13CH2dCH2 in EtCN has been
studied. The data in EtCN are very similar to those
obtained in MeOH (see Table 2), confirming the
(4) Conroy-Lewis, T. M.; Mole, L.; Redhouse, A. D.; Listen, S. A.;
Spencer, J . L. Chem. Commun. 1991, 1601.
(5) Osokada, K.; Ozawa, Y.; Yamamoto, A. J . Chem. Soc., Dalton
Trans. 1991, 759. Osakada, K.; Ozawa, Y.; Yamamoto, A. Bull. Chem.
Soc. J pn. 1991, 64, 2002. Drago, D.; Pregosin, P. S. J . Chem. Soc.,
Dalton Trans. 2000, 3191.
(6) Mole, L.; Spencer, J . L.; Carr, N.; G. Orpen, A. Organometallics
1991, 10, 49. Carr, N.; Mole, L.; Orpen, A. G.; Spencer, J . L. J . Chem.
Soc., Dalton Trans. 1992, 2653.
(7) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789.
Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983, 250, 395.

1834 Organometallics, Vol. 21, No. 9, 2002
Clegg et al.
Ta ble 2. NMR Da ta a t 193 K for
[P d (d tbp x)(CH2CH3)]+, 2a , in MeOH a n d EtCN
MeOH
EtCN
δP(A)
36.3
67.7
31.0
7.9
31.1
38.0
5
36.4
67.1
31.8
9.3
31.5
39.8
5.5
δP(B)
δC(R)
δC(â)
2J P(A)P(B)
2J P(A)C(R)
2J P(B)C(R)
1J C(R)H
1J C(â)H
158
124
157
a
a
Obscured by the solvent.
presence of the agostic interaction. This behavior is
unexpected, since agostic interactions are usually rela-
tively weak.
Dyn a m ics of [P d (L-L)(CH2CH3)]+, 2a . It has been
shown above that the methyl protons of the ethyl
substituent in 2a -c are equivalent on the NMR time
scale, even at 145 K, due to the very low-energy barrier
for the rotation of the methyl group. A similar behavior
has been observed by Spencer in the study of analogous
platinum complexes.6 The rotation can occur with or
without full dissociation of the agostic interaction, as
described by Green and Wong.8
In addition to the low-energy CâH3 rotation described
above, 2a -c undergo a higher energy exchange process
which still occurs below room temperature. The 31P{1H}
NMR spectra of a 1:1 mixture of 2b and 2c in MeOH
from 183 to 293 K are shown in Figure 1, and it is
important to note that the two resonances due to PA and
PB (see Scheme 2) change in a different way.
The resonance due to PA is always a well-resolved
doublet from 183 to 283 K and only starts to broaden
at 293 K. This should be contrasted with the behavior
of the resonance due to PB; from 183 to 233 K, it is
clearly a 1:2:1:1:2:1 multiplet, which starts to broaden
at 243 K. At 248 K there is complete coalescence, and
F igu r e 1. VT 31P{1H} NMR spectra of 2, which has been
prepared from 1a + 13CH2d12CH2 and contains 50% 13C at
both the CR and Câ positions: (a) PA resonance and (b) PB
resonance (see text for labeling scheme).
the ethyl-agostic complex and a hydride ethene com-
plex, which readily undergoes ethene rotation (see
Scheme 2). In some cases, the occurrence of such an
equilibrium has been proved experimentally.7,9 The
electronic and steric properties of the ligand signifi-
cantly influence the position of the equilibrium between
the ethene hydride and the agostic-ethyl complex
shown in Scheme 2, but the energy difference between
the two forms is usually quite small, and this explains
why the CR/Câ scrambling of the ethyl group occurs at
low temperature.
from 253 to 283 K, it becomes a doublet of doublets, with
av
2J PP ) 31 Hz and
J
) 19 Hz. Finally, at 293 K, the
PC
resonance due to PB starts to broaden again. The
mechanism responsible for the room-temperature broad-
ening will be discussed later. Consider now the mech-
anism responsible for the process occurring between 248
and 283 K, which clearly only affects the resonance due
to PB. It is possible to explain the observed changes by
an exchange process which scrambles the two carbons
of the ethyl group (see Scheme 2).
Above ca. 283 K, there is a gradual broadening of the
resonances due to PA and PB in 2a until at 353 K there
is only one resonance at 54 ppm; this coalescence is
concomitant with the appearance of resonances due to
1a as a result of the equilibrium shown in eq 3.
This interesting stereospecific interchange process can
only be detected in this case through the VT NMR
measurements on the monolabeled ethyl complex, and
in the fast exchange limit (ca. 263 K) between the two
av
isotopomers in Scheme 2,
J
) (38 + 0)/2 ) 19 Hz,
PC
MeOH
as observed experimentally. As expected for such a
process, the 13C{1H} resonances due to the methyl and
methylene groups both broaden and then coalesce (δ ca.
18) with increasing temperature. Spencer has shown
that for analogous platinum complexes6 the carbon
atoms of the ethyl group, which are inequivalent at low
temperature, also become equivalent on increasing the
temperature. It is usually accepted that the CR/Câ
scrambling process occurs via an equilibrium between
[Pd(L-L)CH2CH3]+
{
}
2a
+ + C2H4 (3)
[Pd(L-L)H(MeOH)]
1a
Nevertheless, there is a differential broadening of the
resonances due to 1a and 2a in this temperature region,
which suggests that PA and PB in 2a may become
(9) Werner, H.; Feser, R. Angew. Chem., Int. Ed. Engl. 1979, 18,
157.
(8) Green, M. L. H.; Wong, L. L. Chem. Commun. 1988, 677.

Catalytic Methoxycarbonylation of Ethene
Organometallics, Vol. 21, No. 9, 2002 1835
Sch em e 2
Sch em e 3
equivalent. Two different mechanisms can be proposed
in order to explain the equivalence of the P atoms of 2a
at high temperature (see Scheme 3). The first mecha-
nism, A, involves a non-dissociative intramolecular
rearrangement of 2a via a tetrahedral intermediate, and
the second mechanism, B, requires the reversible dis-
ruption of the strong agostic interaction to generate a
14-electron T-shaped intermediate, which allows inter-
conversion via a Y-shaped species. Spencer6 has pro-
posed this second mechanism in order to explain a
similar process in analogous platinum complexes. Romeo
et al.10 have claimed a dissociative mechanism involving
internal rearrangement of T-shaped intermediates for
explaining the cis-trans isomerization process in Pt-
(PR3)2(Me)2. The theoretical possibility of this mecha-
nism has been demonstrated by Thorn and Hoffman,11
who made quantomechanical calculations on model
platinum compounds. They calculated a very low activa-
tion energy for the T-Y interconversion, whereas all
the experimental data suggest a higher value. This
possibly stems from the very simplistic model adopted
in the calculation (i.e., [PtH(PH3)3]+), since Yamamoto’s
experimental work suggests a high activation energy
for this process.12
whereas in MeOH no hydride is present under the same
conditions. This result clearly shows the importance of
the solvent in determining the position of the equilib-
rium in eq 3. Moreover, the resonances due to 2a are
still well separated in both MeOH and EtCN at 293 K.
This lends further support to the conclusion that the
equilibrium in eq 3 and the process that makes the two
P atoms equivalent in 2a are independent.
R ea ct ivit y of [P d (L-L)H (MeOH )]+, 1a , w it h
High er r-Olefin s. The hydride, 1a , reacts in MeOH
with other R-olefins, i.e., propene, 1-hexene, and 1-hexa-
decene. All these olefins insert at low temperature into
the Pd-H bond and NMR spectroscopic experiments
clearly indicate that only one insertion product is
formed. By analogy with the reaction with ethene, these
compounds can be formulated as [Pd(L-L)(CH2C-
H2(CH2)nCH3)]+ (n ) 0, 3; 3, 4; 13, 5); only the linear
isomer is formed, and this is obviously preferred for
steric reasons. It is noteworthy that the catalytic system
based on [Pd(L-L)(dba)], using conditions similar to
those used for the methoxycarbonylation of ethene, is
also active for the methoxycarbonylation of these higher
R-olefins; significantly, only the linear ester is formed.
As found for the ethyl complex, 2a , the alkyl-agostic
complexes 3-5 exist in equilibrium with the hydride 1a :
It is also noteworthy that, on carrying out the same
experiment on the ethyl complex 2a in EtCN, the
solvento hydride complex [Pd(L-L)H(EtCN)]+, 1d , is
the main species present in solution even at 293 K,
MeOH
{
[Pd(L-L)(CH2CH2(CH2)nCH3)]+
n ) 0, 3; 3, 4; 13, 5
}
(10) Romeo, R.; Alibrandi, G. Inorg. Chem. 1997, 36, 4822.
(11) Thorn, D. L.; Hoffman, R. J . Am. Chem. Soc. 1978, 100, 2079.
(12) Yamamoto, A. J . Chem. Soc., Dalton Trans. 1999, 1027.
[Pd(L-L)H(MeOH)]+
CmH2m
m ) 3, 6, 16
+
(4)
1a

1836 Organometallics, Vol. 21, No. 9, 2002
Clegg et al.
Ta ble 3. Equ ilibr iu m Con sta n t (Keq) for Differ en t
Lin ea r r-Olefin s (Cm H2m ) (see eqs 3 a n d 4)
m
Keq at 193 K
Keq at 293 K
2
3
6
0
0
0
7.5 × 10-3
2.8 × 10-3
0.56
∞
16
0.77
The values of Keq calculated from the NMR data for
the equilibria shown in eqs 3 and 4 at different tem-
peratures are reported in Table 3. The position of the
equilibrium strongly depends on the chain length of the
olefin. At 293 K, the ethyl-agostic compound 2a is the
only product observed with ethene, whereas an ap-
preciable amount of the hydride 1a is present on using
propene. [Pd(L-L)H(MeOH)]+, 1a , is the main product
present in solution at 293 K with 1-hexene, and 1a is
the only product when 1-hexadecene is used. The fact
that the position of this equilibrium strongly depends
on the chain length of the alkyl substituent is probably
connected with the fact that L-L is a highly sterically
hindered ligand, which also contributes toward the very
high selectivity for the formation of methyl propanoate.
In the same context, it is noteworthy that 2a does not
react with excess ethene to give higher alkyl complexes.
Moreover, it has been reported that the catalysts used
for the formation of polyketones switch to the oligomer-
ization of ethene when the reaction is carried out in the
absence of CO;13 in contrast, there is no evidence for
ethene oligomerization using the catalytic system based
on L-L under the same conditions.
F igu r e 2. Molecular structure of [Pd(L-L)(C(O)Et)Cl], 7,
in its cocrystal with dba. Selected bond lengths (Å) and
angles (deg): Pd1-P1 2.4812(9), Pd1-P2 2.3177(8), Pd1-
Cl1 2.4135(9), Pd1-C1 2.010(4), P1-Pd1-P2 103.08(3),
Cl1-Pd1-C1 77.42(10), P1-Pd1-C1 158.56(11), P2-Pd1-
Cl1 158.37(3). Displacement ellipsoids are at the 50%
probability level.
the availability of the fourth coordination site of the
complex for occupancy by another ligand. The 31P{1H}
NMR spectrum of 7 consists of two doublets at δ 15.1
and 44.2 (2J PP ) 52.6 Hz), and the shift to lower field
observed for 6b is in accord with the substitution of an
anionic ligand, Cl-, by a neutral less basic molecule,
THF. Crystals of 7 suitable for X-ray analysis have been
obtained directly from the reaction mixture (see Figure
2), and a noteworthy feature of the structure is that 7
contains one of the longest Pd-phosphine bonds
(2.4812(9) Å) reported to date,14,15 trans to the acyl
ligand. The difference in the two Pd-P bond lengths,
0.163 Å, is due to the strong trans-influence of the acyl
compared to the chloride ligand. A similar effect, not
quite as marked, is seen in a previously reported series
of diphosphine complexes of palladium with acyl and
chloride ligands cis to each other, in which the Pd-P
bond trans to Cl ranges from 2.228 to 2.254 Å, and the
Pd-P bond trans to acyl ranges from 2.340 to 2.410 Å.16
Most square-planar complexes of palladium and plati-
num containing acyl and phosphine ligands adopt a cis
rather than a trans arrangement of these ligands, but
in platinum complexes the value of d(Pt-P) when trans
to acyl is always greater that the value of d(Pt-P) when
trans to Cl, H, Me, or P.17
Syn th esis a n d Ch a r a cter iza tion of [P d (L-L)-
(C(O)Et)(THF )]+, 6b. [Pd(L-L)(CH2CH3)]+, 2a , reacts
in MeOH under N2 with 1 equiv of CO to give the
hydride 1a and MP. This results from reaction of 2a
with CO to give [Pd(L-L)(C(O)Et)(MeOH)]+, 6a , fol-
lowed by rapid formation of the final products. This
process is too fast to follow by NMR, even at low
temperature, and thus it is not possible to distinguish
between alternative mechanistic possibilities such as
whether it proceeds by reductive elimination from the
[Pd(L-L)(C(O)Et)(MeOH)]+ complex, 6a , to give a ze-
rovalent palladium species first, and subsequently
Pd-H by protonation at Pd(0), or whether reductive
elimination and protonation proceed concertedly. Alter-
natively, it may be quite possible that the high basicity
of the Pd(0) intermediate, as a consequence of the use
of the very basic bis(di-tert-butylphosphine) ligand, is
responsible for fast protonation at Pd(0) and the high
stability of mononuclear Pd(L-L)H species.
To isolate and characterize the acyl complex, the
reaction has been performed in nonalcoholic solvents.
Thus, 2a reacts in THF at low temperature with 1 equiv
of CO, resulting in the formation of a new species which
shows two doublets at δ 36.3 and 83.4 (2J PP ) 40 Hz) in
the 31P{1H} NMR spectrum at 193 K. These NMR data
indicate that the new species contains two cis inequiva-
lent P atoms, in agreement with the formulation [Pd-
(L-L)(C(O)Et)(THF)]+, 6b. A related complex, [Pd(L-
L)(C(O)Et)Cl], 7, can be isolated from the reaction of
[Pd(L-L)(dba)] with EtC(O)Cl in Et2O, clearly showing
(14) Drago, D.; Pregosin, P. S.; Tschoerner, M.; Albinati, A. Chem.
Commun. 1999, 2279.
(15) Woo, T. K.; Pioda, G.; Rothlisberger, U.; Togni, A. Organome-
tallics 2000, 19, 2144.
(16) Koide, Y.; Bott, S. G.; Barron, A. R. Organometallics 1996, 15,
2213.
(17) Gerish, M.; Heinemann, F. W.; Bruhn, C.; Scholz, J .; Steinborn,
A. Organometallics 1999, 18, 564. Koh, J . J .; Lee, W. H.; Williard, P.
G.; Risen, W. M. J . Organomet. Chem. 1985, 284, 409. Ghilardi, C. A.;
Midollini, S.; Moneti, S.; Orlandini, A. J . Chem. Soc., Dalton Trans.
1988, 1833. Chen, J . T.; Huang, T. M.; Cheng, M. C.; Wang, Y.
Organometallics 1990, 9, 539. Wicht, D. K.; Glueck, D. S.; Liable-Sands,
L. M.; Rheingold, A. L. Organometallics 1999, 18, 5130. Powell, J .;
Horvath, M. J .; Lough, A. J . Chem. Soc., Dalton Trans. 1996, 1679.
You, Y. J .; Chen, J . T.; Cheng, M. C.; Wang, Y. Inorg. Chem. 1991, 30,
3261.
(13) Drent, E.; van Broekhoven, J . A. M.; Doyle, M. J . J . Organomet.
Chem. 1991, 417, 235. Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996,
96, 663.

Catalytic Methoxycarbonylation of Ethene
Organometallics, Vol. 21, No. 9, 2002 1837
Ta ble 4. NMR Da ta for th e Isotop om er s 6b-e of
Ta ble 5. NMR Da ta for [P d (d tbp x)(C(O)Et)(solv)]+
(solv ) THF , 6b; EtCN, 6f) a n d
[P d (d tbp x)(C(O)Et)(THF )]+ in THF a t 193 K
[P d (L-L)(13C(O)Et)(solv)]+ (solv ) THF , 6c; EtCN,
6g) a t 193 K
PA
PB
(a) NMR Chemical Shifts
36.3 83.4 232
(b) Coupling Constants (Hz)
CA
CB
CC
δ (ppm)
38.2
10.9
PA
PB
CA
40
84
17
23
23
23
40
84
23
17
23
3-4
a
CB
23
3-4
a
CC
a
1
1J C(B)H ) 133, J C(C)H ) 130.
EtCN
THF
δP(A)
20.2
49.4
233.2
40
92
13
36.4
83.4
232.0
40
83.9
17.0
To establish unambiguously the structure and ex-
change processes occurring for 6b in solution, 13C-
labeling of both the C(O) and/or Et groups within the
acyl group have been carried out. For [Pd(L-L)(13C(O)-
Et)(THF)]+, 6c (see below for labeling scheme) the two
31P resonances at δ 36.3 and 83.4 can be assigned to PA
and PB, respectively; both appear as doublets of doublets
δP(B)
δC(O)
2J P(A)P(B)
2J P(A)C
2J P(B)C
Noteworthy features include the following:
• The values for J CH are as expected for normal sp3
2
2
2
due to J P(A)P(B) ) 40 Hz, J P(A)C ) 84 Hz, and J P(B)C
)
1
17 Hz, and the much higher value of 2J PC clearly arises
from the trans-coupling with PA. The 13C{1H} NMR
spectrum of 6c has a resonance at δ ca. 232 due to the
C(O) group.18-20 The carbon spectrum is strongly tem-
perature dependent, because of a dynamic process (see
below). However, 6c is completely static at 173 K and
the C(O) resonance of the acyl group consists of a
doublet of doublets, due to trans-2J P(A)C ) 84.0 Hz and
cis-2J P(B)C ) 17.0 Hz.
carbons and are consistent with the absence of any
significant â-C-H agostic interaction.
• Occupancy by THF of the fourth coordination site
in [Pd(L-L)(C(O)Et)(THF)]+ is supported by the large
difference in 31P chemical shifts at 193 K when THF is
replaced by EtCN (see Table 5).
As far as we are aware, 6a -g are the first examples
in which a Pd-acyl complex containing a diphosphine
and a labile solvent molecule have been unambiguously
identified. Other authors have reported similar com-
plexes, but they contain CO instead of solvent. For
instance, Toth and Elsevier19 have reported that the
carbonylation of [Pd{(S,S′)-BDPP}(Me)(solv)]+ [(S,S′)-
BDPP ) (2S,4S)-2,4-bis(diphenylphosphino)pentane]
results in the formation of [Pd{(S,S′)-BDPP}(C(O)Me)-
(CO)]+ even on using a deficiency of CO. Moreover, they
report that the reaction of [Pd{(S,S′)-BDPP}(C(O)Me)-
Cl] with AgBF4 under N2 results in a 1:1 mixture of [Pd-
{(S,S′)-BDPP}(C(O)Me)(CO)]+ and [Pd{(S,S′)-BDPP}-
(Me)(solv)]+. It is also interesting to note that carbonyl-
ation of [Pd(dippe)(Me)(solv)]+ results in the analogous
species [Pd(dippe)(C(O)Me)(CO)]+;21 in direct contrast,
6a -g prefer solvent coordination rather than CO coor-
dination, even in the presence of free CO. This is a very
surprising experimental result, which is also interesting
from a theoretical point of view, and one for which we
have no obvious explanation.
A doubly 13C-enriched acyl can be obtained in
THF, THF/CH2Cl2, or EtCN on reaction of
a
1:1 mixture of [Pd(L-L)(13CH2CH3)]+, 2b , and
[Pd(L-L)(CH213CH3)]+, 2c, with 1 equiv of 13CO at 193
K. The products from this reaction are a 1:1 mixture of
the two isotopomers [Pd(L-L)(13C(O)13CH2CH3)(THF)]+,
6d , and [Pd(dtbpx)(13C(O)CH213CH3)(THF)]+, 6e (see
below for atom labeling).
Dyn a m ics of [P d (L-L)(C(O)Et)(THF )]+. VT 13C-
{1H} and 31P{1H} NMR spectra of this complex show
significant changes, and to obtain as much information
as possible on the mechanism(s) responsible for these
variations, we have examined the VT spectra of the
isotopomers 6a -e, which show consistent behavior.
The VT 13C{1H} NMR spectra in THF of the carbonyl
resonance in the acyl group of the mono-13C-enriched
isotopomer, 6c, are shown in Figure 3. At 193 K, this
resonance is a doublet of doublets (2J P(A)C(A) ) 84 Hz
The NMR data of all the isotopomers 6a -e at 193 K
in THF are consistent with their static structures and
are summarized in Table 4.
2
and J P(B)C(A) ) 17 Hz) due to the static structure,
whereas at 243 K it is a triplet; the triplet spacing (50
Hz) is unchanged at different magnetic fields and must
therefore arise from a time-averaged intraexchange
(18) Kacker, S.; Kim, J . S.; Sen, A. Angew. Chem., Int. Ed. 1998,
37, 1251. Brumbaugh, J . S.; Whittle, R. R.; Parvez, M. A.; Sen, A.
Organometallics 1990, 9, 1735. Kacker, S.; Sen, A. J . Am. Chem. Soc.
1995, 117, 10591.
(19) Toth, I.; Elsevier, C. J . J . Am. Chem. Soc. 1993, 115, 10388.
(20) Dekker: G. P. C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M. Organometallics 1992, 11, 1598.
(21) Fryzuk, M. D.; Clentsmith, G. K. B.; Retting, S. J . J . Chem.
Soc., Dalton Trans. 1998, 2007.

1838 Organometallics, Vol. 21, No. 9, 2002
Clegg et al.
F igu r e 3. VT 13C{1H} NMR of [Pd(L-L)(13C(O)Et)-
(THF)]+, 6c, in THF.
process which makes the cis- and trans-phosphorus
atoms become equivalent. This is substantiated in the
VT 31P{1H} NMR; the two sharp resonances at 173 K
F igu r e 4. VT 13C{1H} NMR of a 1:1 mixture of [Pd(L-
13
L)(13C(O)13CH2CH3)(THF)]+, 6d, and [Pd(L-L)(13C(O)CH2
CH3)(THF)]+, 6e, in CH2Cl2/THF.
-
(δ 36.4 and 83.4) broaden and coalesce to give a single
mean
resonance (δ ca. 59, compare with δP
60) at 256 K.
In addition, with increasing temperature, resonances
due to 2a start to appear as a result of the equilibrium
shown in eq 5.
slower for 9 than for 6b-e and supports the dissociative
mechanistic pathway.
+ a
[Pd(L-L)(C(O)Et)(THF)]
6b
+ + CO + THF (5)
[Pd(L-L)(CH2CH3)]
2a
Nevertheless, over a wide temperature range (153-
276 K) 31P resonances due to the presence of both the
acyl and ethyl complexes are clearly visible in all the
isotopomers studied. For the reaction in eq 5, there is
no spectroscopic evidence for the formation of [Pd(L-
L)Et(CO)]+ on variation of the ratio of Pd:CO e 1:4 over
the above temperature range.
Con clu sion s
In this paper, we have described different exchange
processes of the intermediates involved in the hydride
cycle of the catalytic methoxycarbonylation of ethene.
VT 13C{1H} NMR spectra of a 1:1 mixture of 6d and
6e in CH2Cl2/THF are shown in Figure 4. These spectra
are similar to those shown in Figure 3 and show
Both the formation of [Pd(L-L)(CH2CH3)]+, 2a , from
[Pd(L-L)H(MeOH)]+, 1a , and the formation of [Pd(L-
L)(C(O)Et)(MeOH)]+, 6a, involve facile equilibria, where-
as the methanolysis of 6a is an irreversible reaction and
is probably the rate-determining step. This conclusion
is supported by other authors who have studied the
methoxycarbonylation of higher R-olefins.22 Moreover,
whereas the hydride complex 1a is static over all the
temperatures studied, the ethyl and the acyl complexes
undergo a variety of intramolecular exchanges. In
particular, for both the ethyl and acyl complexes there
are exchange processes that equivalence the two P
atoms, whereas the two P atoms in the hydride complex
always remain inequivalent. Moreover, although this
process occurs below room temperature in the acyl
1
2
additional couplings due to J C(A)C(B) and J C(A)C(C) (see
Table 4). Of particular significance is the retention of
these additional couplings over a wide temperature
range. This shows that the intraexchange mechanism,
which makes the two inequivalent P atoms become
equivalent, must involve migration of the intact acyl
group.
Two different mechanisms could account for the above
spectroscopic changes. The first involves dissociation of
the solvent and rearrangement of the T-shaped inter-
mediate, and the second could involve an intraexchange
of the square-planar complex via a tetrahedral inter-
mediate. Reaction of [Pd(COD)(Me)Cl], 8, with L-L and
CO gives [Pd(L-L)(C(O)Me)Cl], 9 (eq 6). The 31P{1H}
NMR spectrum of 9 at 196 K consists of two sharp
doublets, whereas at 293 K they are broader but still
separated. This suggests that the exchange process is
(22) Saeyad, A.; Jayasree, S.; Damodaran, K.; Toniolo, L.; Chaudhari,
R. V. J . Organomet. Chem. 2000, 601, 100. Cavinato, G.; Toniolo, L.
J . Mol. Catal. 1981, 10, 161.

Catalytic Methoxycarbonylation of Ethene
Organometallics, Vol. 21, No. 9, 2002 1839
Syn th esis of [P d (L-L)Cl2]. EtC(O)Cl (2.60 g, 27.2 mmol)
was added via a syringe to a solution of [Pd(L-L)(dba)] (2.00
g, 2.72 mmol) in Et2O (100 mL). The solution turned from
orange to yellow in color immediately, and a yellow precipitate
began to form after 15 min. The reaction mixture was stirred
for a further 2 h before the precipitate was separated by
filtration and dried in a vacuum. Yield: 1.4 g (90%). Anal.
Calcd for C24H44Cl2P2Pd: C, 50.43; H, 7.70. Found: C, 50.39;
H, 7.65. 31P{1H} NMR (CH2Cl2, 293 K): 35.0 (s).
Syn th esis of [P d (L-L)H(MeOH)]+, 1a . [Pd(L-L)(dba)]
(100 mg, 0.136 mmol) and benzoquinone, BQ (29.4 mg, 0.272
mmol) were mixed as solids and degassed under vacuum. The
solids were partially dissolved under nitrogen in MeOH (2 mL),
and then CF3SO3H (60.5 µL, 0.680 mmol) was added via a
micropipet. The product was formed in a few minutes. 31P-
complex, it is not observed until 353 K in the ethyl
complex. The reasons for these dramatic differences
remain under investigation. In the case of exchange in
the acyl complex, we have unambiguously shown that
this process involves migration of the intact acyl group,
a process that, as far as we are aware, has not been
reported hitherto.
For the ethyl complex, two other low-temperature
exchange processes have been characterized, i.e., the
CâH3 rotation and the scrambling of the two C atoms of
the ethyl group; the latter is stereospecific since the two
P atoms remain inequivalent.
We have already shown3 the importance of the nature
of the bidentate ligand L-L in stabilizing the hydride
species [Pd(L-L)H(MeOH)]+, 1a . Herein, we have fully
characterized the first example of a stable acyl-solvento
complex containing a bidentate phosphine ligand. Also,
the formulation and dynamic behavior of the ethyl-
agostic complex is of interest. Although related com-
pounds have been characterized by Spencer,4,6 using
analogous ligands, our work shows that in
2
2
{1H} (MeOH, 293 K): 25.8 (d, J PP ) 17 Hz), 77.5 (d, J PP
)
17 Hz); 1H (MeOH, 293 K) -10 (dd, 2J PH ) 179.7 and 14.3 Hz).
Syn th esis of [P d (L-L)H(solv)]+ (solv ) P r n OH, 1b;
THF , 1c; EtCN, 1d ). [Pd(L-L)(O3SCF3)2] (100 mg, 0.125
mmol) was dissolved in MeOH (2 mL), and then, the solution
was dried in vacuum and the residue was dissolved in the
appropriate solvent (see Table 1).
Syn t h esis of [P d (L-L)(CH 2CH 3)]+, 2a . Ethene was
bubbled for a few seconds through a solution of [Pd(L-L)H-
(MeOH)]+ (0.136 mmol) in MeOH (2 mL). The solution turned
from brown-orange to brown-yellow immediately, and the
product was detected via NMR spectroscopy. For the studies
above room temperature, this sample was transferred to a 10
mm sapphire tube and pressurized with ethene (4 atm). 31P-
[Pd(L-L)(CH2CH3)]+, the â-agostic interaction is main-
tained even in strongly coordinating solvents. The
unique chemistry of these Pd/L-L complexes appears
to be determined by the highly restrictive steric de-
mands of L-L; this is also consistent with the reactivity
of 1a with higher olefins. Hence, the steric properties
of L-L are of paramount importance in determining the
high selectivity of the Ineos catalyst for the synthesis
of MP.
2
{1H} NMR (MeOH, 193 K): 36.3 (d, J PP ) 31 Hz), 67.7 (d,
2J PP ) 31 Hz).
Ch a r a cter iza tion of 2a via 13CH2dCH2 (syn th esis of 2b
a n d 2c). A brown-orange solution of [Pd(L-L)H(MeOH)]+
(0.136 mmol) in MeOH (2.5 mL, 25% CD3OD) was transferred
to a 10 mm NMR tube equipped with a connection for the high-
vacuum line. The tube was then frozen in liquid nitrogen and
evacuated. The liquid nitrogen bath was then removed and
the NMR tube put immediately into a dry ice/acetone bath, to
avoid the condensation of ethene. To this solution was added
1 equiv of 13CH2dCH2 through the high-vacuum line, then
frozen in the liquid nitrogen and sealed. 31P{1H} NMR (MeOH,
Exp er im en ta l Section
All reactions and sample manipulations were carried out
using standard Schlenk techniques under nitrogen and in
carefully dried solvents. 13C-enriched samples were prepared
using standard high vacuum line techniques. All NMR mea-
surements were performed on Bruker AMX200 and AMX400
instruments using commercial probes. The chemical shifts
were referenced to external H3PO4 (85% in D2O) for phospho-
rus and to internal TMS for carbon. High-temperature NMR
measurements were recorded using a 10 mm sapphire tube.
All the chemical products were purchased from Aldrich
Chemical Co., except [Pd(L-L)(dba)],2 [L-L],23 and [Pd(COD)-
(Me)Cl],24 which were prepared by published methods. 13CO
(99.8%) was purchased from Isotec Inc., and 13CH2dCH2 from
Aldrich Chemical Co. Most of the compounds reported below
have not been isolated because of their instability and/or
because on attempted crystallization, only oils were obtained.
Nevertheless, NMR measurements and detailed isotopic label-
ing experiments allow all of these compounds to be formulated
unambiguously.
2
2
193 K): 36.3 (d + dd, J PP ) 31 Hz, J PC ) 38 Hz), 67.7 (d,
2J PP ) 31 Hz). 13C{1H} NMR (MeOH, 193 K): 8 (s), 32 (dd,
2J PC ) 38 and 5 Hz).
Syn th esis of [P d (L-L)(CH2CH2CH3)]+, 3. A solution of
[Pd(L-L)H(MeOH)]+ (0.136 mmol) in MeOH (2.5 mL, 25%
CD3OD) in a 10 mm NMR tube equipped with a connection
for the high-vacuum line was frozen in liquid nitrogen and
evacuated. The liquid nitrogen bath was then removed and
replaced with a dry ice/acetone bath. To this solution was
added 2 equiv of propene through the high-vacuum line,
followed by cooling in liquid nitrogen and sealing. 31P{1H}
NMR (MeOH, 193 K): 37.8 (d, 2J PP ) 30.5 Hz), 67.6 (d, 2J PP
30.5 Hz).
)
Syn th esis of [P d (L-L)(O3SCF 3)2]. [Pd(L-L)Cl2] (1.50 g,
2.62 mmol) was dissolved in CH2Cl2 (100 mL) in a 250 mL
two-necked round-bottomed flask, and Ag(O3SCF3) (1.35 g, 5.24
mmol) was added. A white precipitate of AgCl was immediately
formed. The solution was further stirred for 1 h before
removing the precipitate by filtration. The volume of the
solution was, then, reduced in a vacuum to ca. 40 mL and the
product precipitated by addition of n-hexane (100 mL). The
solid was separated by filtration, washed with n-hexane (2 ×
50 mL), and dried in a vacuum. Yield: 1.8 g (86%). Anal. Calcd
for C26H44F6O6P2Pd S2: C, 39.08; H, 5.55. Found: C, 38.66;
H, 5.67. 31P{1H} NMR (CH2Cl2, 293 K): 78.2 (s).
Syn th esis of [P d (L-L)(CH2CH2(CH2)3CH3)]+, 4. To a
solution of [Pd(L-L)H(MeOH)]+ (0.136 mmol) in MeOH (2 mL)
was added 1-hexene (42.0 µL, 0.400 mmol) with a micropipet.
2
31P{1H} NMR (MeOH, 193 K): 38.6 (d, J PP ) 30.2 Hz), 67.7
2
(d, J PP ) 30.2 Hz).
Syn th esis of [P d (L-L)(C(O)Et)(THF )]+, 6b. A solution
of 2a (0.136 mmol) in MeOH (2 mL) was prepared as described
above and dried in a vacuum, and the residue was dissolved
in THF (2 mL, 25% d8-THF) under N2. The resulting solution
was stored in a dry ice/acetone bath, and its purity checked
via NMR spectroscopy. The solution was then transferred to
a 10 mm NMR tube equipped with a connection for the high-
vacuum line, frozen in liquid nitrogen, and evacuated on a
high-vacuum line. To this solution was added 1 equiv of CO
and the mixture shaken prior to recording the NMR spectrum.
(23) Moulton, J .; Shaw, B. L. Chem. Commun. 1976, 365.
(24) Rulke, E. R.; Ernsting, J . M.; Spek, A. L.; Elsevier: C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

1840 Organometallics, Vol. 21, No. 9, 2002
Clegg et al.
2
31P{1H} NMR (THF, 173 K): 32.5 (d, J PP ) 40.0 Hz), 79.9 (d,
Pd.C17H14O, Mr ) 827.73, triclinic, space group P1h, a )
10.2985(7) Å, b ) 11.3708(7) Å, c ) 19.5555(13) Å, R )
90.228(2)°, â ) 96.288(2)°, γ ) 115.134(2)°, V ) 2057.4(2) Å3,
Z ) 2, Fcalcd ) 1.336 g cm-3, Mo KR radiation, λ ) 0.71073 Å,
µ ) 0.63 mm-1, T ) 160 K; of 11 286 measured reflections
corrected for absorption, 7934 were unique, Rint ) 0.0333; R
) 0.0437 (I > 2σ), Rw ) 0.1093 (F2, all data), GOF ) 1.164,
465 parameters, final difference map extremes +0.92 and
2J PP ) 40.0 Hz).
Ch a r a cter iza tion of 6b via 13C-La belin g (syn th esis of
6c, 6d , a n d 6e). The monolabeled sample 6c was prepared in
the same way as 6b, using 13CO instead of 12CO. The doubly
13C-labeled samples 6d and 6e were prepared by addition of
13CO (1 equiv) to a 1:1 mixture of 2c and 2d . 6c 31P{1H} (THF,
2
2
2
173 K): 32.5 (dd, J PP ) 40 Hz, J PC ) 82.9 Hz), 79.9 (dd, J PP
) 40 Hz, 2J PC ) 18.2 Hz). 13C{1H} (THF, 173 K): 232 (dd, 2J PC
) 82.9 and 18.2 Hz). 6d 31P{1H} (THF/CH2Cl2, 173 K): 33.5
(ddd, 2J PP ) 39 Hz, 2J PC ) 83 and 23 Hz), 82.0 (ddd, 2J PP ) 39
Hz, 2J PC ) 18 and 23 Hz). 13C{1H} (THF/CH2Cl2, 173 K): 231.9
-1.06 e Å-3
.
Syn th esis of [P d (L-L)(Me)Cl], 9. To a solution of [Pd-
(COD)(Me)Cl] (1.00 g, 3.77 mmol) in CH2Cl2 (50 mL) was
slowly added L-L (0.39 g, 3.8 mmol) in CH2Cl2 (50 mL). The
solution was stirred at room temperature (4 h) and concen-
trated to ca. 30 mL. The product was precipitated by addition
of n-hexane (100 mL), separated by filtration, washed with
n-hexane (2 × 30 mL), and dried in a vacuum. Yield: 1.8 g
(88%). Anal. Calcd for C25H47ClPd: C, 54.45; H, 8.59. Found:
C, 54.39; H, 8.63. 31P{1H} NMR (CH2Cl2, 293 K): 49.0 (d, 2J PP
2
1
2
(ddd, J PC ) 83 and 18 Hz, J CC ) 23 Hz), 38.2 (q, J PC ) 23
Hz, 1J CC ) 23 Hz). 6e 31P{1H} (THF/CH2Cl2, 173 K): 33.5 (dd,
2
2
2
2J PP ) 39 Hz, J PC ) 83 Hz), 82.0 (dd, J PP ) 39 Hz, J PC ) 18
Hz). 13C{1H} (THF/CH2Cl2, 173 K): 231.9 (dd, J PC ) 83 and
2
3
18 Hz), 10.9 (d, J CC 3 Hz).
Syn th esis of [P d (L-L)(C(O)Et)(EtCN)]+, 6f. 6f was
prepared as for 6b, using EtCN instead of THF as the solvent.
2
) 30.5 Hz), 18.4 (d, J PP ) 30.5 Hz).
31P{1H} NMR (EtCN, 193 K): 20.2 (d, J PP ) 40 Hz), 49.4 (d,
Syn th esis of [P d (L-L)(C(O)Me)Cl], 8. [Pd(L-L)(Me)Cl]
(100 mg, 0.181 mmol) was dissolved in CH2Cl2 (2 mL) under
CO (1 atm). In these conditions, 9 is partially converted into
8. 31P{1H} NMR (CH2Cl2, 293 K): 17.6 (br), 45.6 (br).
2
2J PP ) 40 Hz).
Syn th esis of [P d (L-L)(13C(O)Et)(EtCN)]+, 6g. 6g was
prepared as for 6c, using EtCN instead of THF as the solvent.
31P{1H) (EtCN, 193 K): 20.2 (dd, J PP ) 40 Hz, J PC ) 92 Hz),
2
2
49.4 (dd, J PP ) 40 Hz, J PC ) 13 Hz). 13C{1H} (EtCN, 193 K):
2
2
Ack n ow led gm en t. The authors thank EPSRC for
a CASE award (to S.Z.) and for funding the NMR and
X-ray equipment. We also acknowledge one of the
referees for supportive comments.
2
233.2 (dd, J PC ) 92 and 13 Hz).
Syn th esis of [P d (L-L)(C(O)Et)Cl], 7. [Pd(L-L)(dba)] (30
mg, 0.04 mmol) was dissolved in Et2O (2 mL), and EtC(O)Cl
(3.8 mg, 0.04 mmol) was added via a micropipet. The solution
immediately changed from orange to yellow; removal of the
solvent followed by dissolution in Et2O and layering with
pentane gave yellow crystals, suitable for a single-crystal X-ray
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for complex 7. This material is available free of charge
via the Internet at http://pubs.acs.org.
study. 31P{1H} NMR (THF, 193 K): 15.1 (d, J PP ) 52.6 Hz),
2
44.2 (d, 2J PP ) 52.6 Hz). Crystal data for 7‚dba: C27H49ClOP2-
OM010938G