Insertion of acrylonitrile into palladium methyl bonds in neutral and anionic Pd(II) complexes

Article abstract of DOI:10.1021/ja044119+

The reactions of a series of Pd(II) methyl compounds of general formula LPd(NCCH₃)CH₃, where L is a bulky phenoxydiazene or phenoxyaldimine ligand with the polar olefin acrylonitrile (AN), are reported. The compounds react with an excess of AN to give the products of 2,1 insertion into the Pd-Me bond, yielding dimers and/or trimers which feature bridging α-cyano groups. The reactions were studied by low temperature ¹H NMR spectroscopy, revealing an initial formation of compounds featuring N-bound AN, which isomerized to an (unobserved) π-bound species that rapidly underwent 2,1 insertion into the Pd-Me bond. Intermediate oligomeric complexes retaining a Pd-Me function were observed at low [AN] in these reactions. Under pseudo first-order conditions, k_obs values of 8.5 × 10^-5 to 2.68 × 10^-3 M^-1 (-22°C to 10°C, 100 equiv of AN) and activation parameters of ΔH^? = 14.4(5) kcal mol^-1 and ΔS ^? = -19(5) eu were obtained in one case. Comparison of the overall rates of insertion between two LPd(NCCH₃)CH₃, differing in the overall charge on the supporting ligand L, showed that the complex bearing a negatively charged ligand reacts with AN twice as fast as one with no anionic charge. The rates of insertion in both of these complexes are significantly faster than reported rates for analogous reactions in cationic Pd(II) derivatives, indicating that increasing the negative charge on the complex enhances the rate of AN insertion. These results provide fundamental mechanistic insights into a crucial reaction for incorporation of polar comonomers into alpha olefins via a coordination polymerization mechanism.

Full text of DOI:10.1021/ja044119+

Published on Web 01/25/2005
Insertion of Acrylonitrile into Palladium Methyl Bonds in
Neutral and Anionic Pd(II) Complexes
Laurent F. Groux,† Thomas Weiss,‡ Dastigiri N. Reddy,† Preston A. Chase,†
Warren E. Piers,*,† Tom Ziegler,† Masood Parvez,† and Jordi Benet-Buchholz§
Contribution from the Department of Chemistry, UniVersity of Calgary,
2500 UniVersity Dr. N. W., Calgary, Alberta, Canada T2N 1N4, Bayer AG,
Bayer Chemicals AG, BCH-R&D-I1, 51368 LeVerkusen, Germany, and Bayer AG,
Bayer Industry SerVices, X-ray Laboratory, Q18, 51368 LeVerkusen, Germany.
Received September 27, 2004; E-mail: wpiers@ucalgary.ca
Abstract: The reactions of a series of Pd(II) methyl compounds of general formula LPd(NCCH3)CH3, where
L is a bulky phenoxydiazene or phenoxyaldimine ligand with the polar olefin acrylonitrile (AN), are reported.
The compounds react with an excess of AN to give the products of 2,1 insertion into the Pd-Me bond,
yielding dimers and/or trimers which feature bridging R-cyano groups. The reactions were studied by low
temperature 1H NMR spectroscopy, revealing an initial formation of compounds featuring N-bound AN,
which isomerized to an (unobserved) π-bound species that rapidly underwent 2,1 insertion into the Pd-
Me bond. Intermediate oligomeric complexes retaining a Pd-Me function were observed at low [AN] in
these reactions. Under pseudo first-order conditions, kobs values of 8.5 × 10-5 to 2.68 × 10-3 M-1 (-22 °C
to 10 °C, 100 equiv of AN) and activation parameters of ∆H‡ ) 14.4(5) kcal mol-1 and ∆S‡ ) -19(5) eu
were obtained in one case. Comparison of the overall rates of insertion between two LPd(NCCH3)CH3,
differing in the overall charge on the supporting ligand L, showed that the complex bearing a negatively
charged ligand reacts with AN twice as fast as one with no anionic charge. The rates of insertion in both
of these complexes are significantly faster than reported rates for analogous reactions in cationic Pd(II)
derivatives, indicating that increasing the negative charge on the complex enhances the rate of AN insertion.
These results provide fundamental mechanistic insights into a crucial reaction for incorporation of polar
comonomers into alpha olefins via a coordination polymerization mechanism.
insertion mechanism,4 direct evidence for this is rare and some
of these examples5 involve monomers in which the polar
Introduction
While tremendous success in the controlled polymerization
of aliphatic olefins by homogeneous, single-site catalysts has
been attained in the past 15 years,1 the development of
organotransition metal compounds capable of incorporating
comonomers with polar functions remains a significant challenge
in polymerization catalysis.2 Currently, polymers or copolymers
integrating polar monomers are prepared via relatively uncon-
trollable radical or anionic initiation polymerization processes.3
While polymers that incorporate polar groups have useful
properties, it is likely that even more functional materials could
be discovered if the stereo and regiocontrol bestowed by single
site catalysts could be deployed in an effective coordination
polymerization process for these monomers.
function is relatively far-removed from the olefinic locus of
insertion. Polar monomers such as acrylates or vinyl halides,
in which the polar group is directly bonded to the olefinic moiety
to be inserted, are the most desirable polar monomers but
provide several challenges to be overcome if a coordination
insertion process is to be viable (Scheme 1). The first obstacle
involves the preference of binding for the substrate; for olefin
insertion to take place, it is clear that the olefinic moiety must
bind at some point to the metal center. Since the catalysts for
olefin polymerization are generally electrophilic in nature, there
is a tendency for polar monomers to preferentially bind the metal
through the polar function in a σ bonding mode. Thus, there
must at least be an equilibration to the π bound form involving
the olefin function, if not a clear preference for π bonding, in
order for insertion to take place at appropriate rates. Assuming
a π bound complex from which insertion can take place is
While there have been some late metal based catalysts that
are reportedly able to incorporate polar monomers via an
† Department of Chemistry, University of Calgary.
‡ Bayer AG, Bayer Chemicals AG, BCH-R&D-I1.
(4) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc. 1996, 118,
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J. A. Macromolecules 2003, 36, 8584. (d) He, X.; Yao, Y.; Luo, X.; Zhang,
J.; Liu, Y.; Zhang, L.; Wu, Q. Organometallics 2003, 22, 4952. (e)
Britovsek, G. J. P.; Gibson, V. C.; Spitzmesser, S. K.; Tellman, K. P.;
White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 2002, 1159.
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R. H.; Bansleben, D. A. Science 2000, 287, 460. (b) Diamanti, S. J.; Ghosh,
P.; Shimizu, F.; Bazan, G. C. Macromolecules 2003, 36, 9731.
§ Bayer AG, Bayer Industry Services, X-ray Laboratory.
(1) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. ReV. 2000, 100,
1253. (b) Coates, G. W. Chem. ReV. 2000, 100, 1223.
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(b) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479.
(3) Kulich, D. M.; Kelly, P. D.; Pace, J. E. In Encyclopedia of Polymer Science
and Engineering; Mark, H. F., Bikales, N. M., Overberger, C. G., Menges,
G., Krochwitz, J. I., Eds.; Wiley: New York, 1985; p. 388. (b) Hirai, H.;
Gotah, H. In. Polymeric Materials Encyclopedia; Salamone, J. C., Ed.;
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9
1854
J. AM. CHEM. SOC. 2005, 127, 1854-1869
10.1021/ja044119+ CCC: $30.25 © 2005 American Chemical Society

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
Scheme 1
Acrylonitrile (AN) is a particularly challenging polar comono-
mer given its high tendency to polymerize via radical10 or
anionic11 processes. Indeed, there are several transition metal
complexes that have been reported to be active for the
polymerization of AN,12 but in only a handful of cases has the
mode of polymerization been elucidated. In these cases,
anionic13 or radical14 mechanisms have been shown to be
operative, while some reports invoke enchainment via a group
transfer mechanism.15 Furthermore, the nitrile function is a
relatively good donor and though complexes of AN exhibiting
bonding via the olefinic π electrons are known,16 N-bound
isomers are energetically competitive, particularly for hard
metals. Little is known regarding the barrier to isomerization
between N-bound and π-bound17 AN isomers,18 and when
N-bound complexes dominate, insertion is precluded.19 When
π bonding is accessible, kinetically or thermodynamically,
products consistent with 2,1 AN insertion into M-P20 or M-C21
bonds have led authors to invoke this as a mechanistic possibility
but direct observation of these reactions has not, to our
knowledge, been reported.
accessible, the next challenge involves control of the regio-
chemistry of insertion. Vinyl monomers with polar groups
generally exhibit a tendency to undergo kinetic 2,1 insertion,
since the polarity of the 4-centered transition state disfavors
electron withdrawing groups in the â position.6 These 2,1
products, however, may undergo isomerization to the 1,2 isomer
with the polar group now on the â carbon and facile â-PG
elimination processes often ensue,7,8 poisoning the catalyst
toward further reactivity.9 In other instances, the polar group
simply forms a stable chelate to the metal from the â position,
blocking the vacant coordination site necessary to take up further
equivalents of monomer. In yet another scenario, the polar group
can facilitate oligomerization of catalyst sites by binding to the
vacant site of a separate catalyst molecule. All of these
proclivities have a tendency to preclude further steps in a
polymerization reaction. Finally, even if one can design a
catalyst that effectively binds the polar monomer through the
olefin and regioselectively inserts the monomer to an alkyl with
an a polar group that is relatively stable toward isomerization
or oligomerization processes, a final challenge is likely to be
encountered. The electron withdrawing nature of the polar group
tends to raise the barrier toward its migration to a coordinated
olefin since it is significantly less nucleophilic than an unfunc-
tionalized alkyl ligand. Thus, while it may be possible to exert
some control on the insertion of the polar comonomer into M-C
bonds, subsequent insertions of aliphatic olefins or polar
comonomers may be prohibited by the presence of the polar
substituents, even if it is nonchelating.
While suitable catalysts for AN enchainment via a coordi-
native mechanism are currently not known, computational
investigations22 point to certain key characteristics one might
expect in a candidate catalyst. To encourage a π bonding mode
involving the olefinic function of the monomer, softer late
transition metal-based catalysts would be more effective than
(10) Matyjaszewski, K.; Jo, S.; Paik, H.-J.; Shipp, D. A. Macromolecules 1999,
32, 6431. (b) Barboiu, B.; Percec, V. Macromolecules 2001, 34, 8626. (c)
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(13) See Schaper, F.; Foley, S. R.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
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C.; Spaniol, T. P.; Okuda, J. Angew. Chem. Int. Ed. 1999, 38, 227.
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K.; Daniels, J. A.; Jennings, J. R. Coord. Chem. ReV. 1982, 44, 149.
(17) Throughout, the term “π-bound” refers to AN bonded via the olefinic π
electrons; in principle, bonding via the π electrons of the CtN triple bond
is possible, but unlikely.16
(18) Rosenblum, M.; Turnbull, M. M.; Begum, M. K. J. Organomet. Chem.
1987, 321, 67.
(19) Yang, K.; Lachicotte, R. J.; Eisenberg, R. Organometallics 1998, 17, 5102.
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Organometallics 1999, 18, 2747.
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18, 5381.
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Organometallics 1998, 17, 1257.
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metallics 2002, 21, 4432. (d) Yang, S.-Y.; Szabo, M. J.; Michalak, A.;
Weiss, T.; Piers, W. E.; Jordan, R. F.; Ziegler, T. J. Am. Chem. Soc. 2004,
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(9) Intermediates in Scheme 1 that contain â-hydrogens could also potentially
undergo â-hydrogen elimination, forming Heck-type products; for simplicity
(and because this chemistry is unobserved in the systems presented herein)
these reactions are not depicted in Scheme 1.
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J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1855

A R T I C L E S
Chart 1
Groux et al.
Scheme 2
the harder early metal systems known to polymerize olefins.
Indeed, it is well-recognized that late metal catalysts, such as
Brookhart’s cationic diimine nickel and palladium catalysts,4
or Grubbs’ neutral salicylaldiminato nickel catalysts5,23 (Chart
1), offer significantly greater “functional group tolerance” than
do, for example, the cationic group 4 metallocenium family of
catalysts. In comparing the Brookhart and Grubbs classes of
catalysts, Deubel and Ziegler have shown that the catalysts
incorporating the second row metal palladium actually favor π
bonding over σ bonding for AN since the greater separation in
the ns/np and nd levels (n ) 4,5) allows for more effective
back-bonding to the AN than in the nickel compounds where n
) 3.22c Furthermore, since the N-bound σ binding mode has a
strong electrostatic component, the cationic Brookhart catalysts
more strongly favor this detrimental bonding mode than the
neutral Grubbs systems.22c In fact, it was shown that for the Pd
salicylaldiminato catalysts, π bonding is expected to be the
favored mode of bonding for AN. The calculations also show
that, for the π bound isomer of the AN complex, the barrier to
insertion into an M-C bond is comparable to that found for
ethylene, suggesting that the insertion of AN might be experi-
mentally observable in such systems.24
Given the above discussion, we have targeted neutral pal-
ladium complexes incorporating bulky salicylaldiminato donors
and closely related ligands incorporating a diazene function
(Chart 1) as good candidates for studying AN insertion into
metal alkyl bonds. Furthermore, extending the idea that neutral
catalysts are more likely to engage in π bonding than cationic
derivatives, we have developed a negatively charged25 version
of the Grubbs salicylaldiminato ligand framework to compare
with the neutral versions. These ligands use established motifs
for engendering polymerization activity, such as the 2,6-
diisopropyl aryl substituent on the imine nitrogen, and a tert-
butyl group ortho to the phenoxy donor, to provide a poly-
merization-relevant environment for this model study. We find
that 2,1 insertion of AN in these complexes is facile and present
results that corroborate some of the predictions of theory, but
at the same time underscore that some of the problems presented
in Scheme 1 are significant. The computational results men-
tioned above notwithstanding, Jordan and co-workers have found
that several cationic Pd methyl complexes also undergo these
reactions, indicating that π-bound AN complexes are also
accessible in these systems, although the N-bound isomers
dominate as determined by spectroscopic methods. Their results
are described in a companion paper26 and comparisons are made
when appropriate.
Results and Discussion
Ligand and Palladium Complex Syntheses. The bulky
diazene27 (a series) and salicylaldiminato5,23,28 (b series) ligands
were prepared according to literature procedures using the
appropriate amine/aldehyde or phenol/diazonium salt precursors
and converted to their alkali metal salts using standard reagents
and procedures. The synthesis of the salicylaldiminato ligand
c, bearing an anionic group, is outlined in Scheme 2. Bromi-
nation of 3-tert-butyl-2-hydroxy-benzaldehyde29 in the para
position was accomplished using Br230 and the crude solid was
reacted with 2,6-diisopropylaniline in methanol to prepare the
brominated salicylaldimine in 54% yield. Protection of the
phenolic group with a trimethylsilyl group via deprotonation
with NaH and quenching with ClSiMe3 gave the silyl ether as
a yellow solid in quantitative yield after evaporation of all the
volatiles. The anionic BF3 group was installed using a procedure
recently reported by Fro¨hn,31 involving lithium-halogen ex-
change by reaction with one equivalent of n-BuLi in cold THF
(-78 °C, yellow solution) followed by quenching with an excess
of B(OMe)3 and letting the mixture warm to room temperature
(23) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben,
D. A.; Day, M. W. Organometallics 1998, 17, 3149. (b) Connor, E. F.;
Younkin, T. R.; Henderson, J. I.; Waltman, A. W.; Grubbs, R. H. Chem.
Commun. 2003, 2272.
(24) Insertion of other polar monomers into Pd-CH3 bonds have been
observed: see refs 4a, 4b and Kang, M.; Sen, A.; Zakharov, L.; Rheingold,
A. L. J. Am. Chem. Soc. 2002, 124, 12080.
(25) The use of ligands with discrete negative charges has been shown to impart
novel reactivity in several recent studies: (a) Komon, Z. J. A.; Bu, X.;
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X.; Bazan, G. C. J. Am. Chem. Soc. 2000, 122, 12379. (c) Lee, B.-Y.;
Bazan, G. C.; Vela, J.; Komon, Z. J. A.; Bu, X. J. Am. Chem. Soc. 2001,
123, 5352. (d) Kim, Y. H.; Kim, T. H.; Lee, B.-Y.; Woodmansee, D.; Bu,
X.; Bazan, G. C. Organometallics 2002, 21, 3082. (e) Lee, B. Y.; Bu, X.;
Bazan, G. C. Organometallics 2001, 20, 5425. (f) Stradiotto, M.; Cipot,
J.; McDonald, R.; J. Am. Chem. Soc. 2003, 125, 5618. (g) Cipot, J.;
Wechsler, D.; Stradiotto, M.; McDonald, R.; Ferguson, M. J. Organome-
tallics 2003, 22, 5185. (h) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc.
2001, 123, 5100. (i) Lu, C. C.; Peters, J. C. J. Am. Chem. Soc. 2002, 124,
5272. (j) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 8870.
(k) Held, A.; Mecking, S.; Chem.-Eur. J. 2000, 6, 4623. (l) Bauers, F. M.;
Mecking, S. Macromolecules 2001, 34, 1165. (m) Soula, R.; Broyer, J. P.;
Llauro, M. F.; Tomov, A.; Spitz, R.; Claverie, J.; Drujon, X.; Malinge, J.;
Saudemont, T. Macromolecules 2001, 34, 2438. (n) Soula, R.; Novat, C.;
Tomov, A.; Spitz, R.; Claverie, J.; Drujon, X.; Malinge, J.; Saudemont, T.
Macromolecules 2001, 34, 2022.
(26) Wu, F.; Foley, S. R.; Burns, C. T.; Jordan, R. F. J. Am. Chem. Soc. 2005,
127, 1841.
(27) Schro¨der, D. L.; Keim, W.; Zuideveld, M. A.; Mecking, S. Macromolecules,
2002, 35, 6071. See also (b) Hashida, Y.; Landells, R. G. M.; Lewis, G.
E.; Szele, I.; Zollinger, H. J. Am. Chem. Soc. 1978, 100, 2816. (c) von
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W.; Hui, H. C.; Kolesnikov, A.; Li, Y.; Luong, C.; Martelli, A.; Radika,
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1856 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
Scheme 3
reaction of alkali metal salts of the ligands and (COD)Pd(Cl)-
Me32 as shown in Scheme 3. Acetonitrile was condensed (-78
°C) onto a mixture of the deprotonated ligand and one equivalent
of (COD)Pd(Cl)Me. After the solution was warmed to room
temperature and stirred for a few hours, filtration gave a clear,
bright yellow solution from which pure compounds 1-NCCH3
were isolated as light yellow solids after removal of the solvent
in vacuo. The main difference between the neutral complexes
1a,b-NCCH3 and the anionic 1c-NCCH3 is their solubility
properties, 1a,b-NCCH3 being completely soluble in hexanes,
while 1c-NCCH3 needing more polar solvents to dissolve.
Compounds 1-NCCH3 are stable as solids when stored under
inert atmosphere and low temperature, but exhibit a tendency
to decompose at room temperature in solvents other than
acetonitrile, depositing Pd(0). Typically, solutions of compounds
1-NCCH3 were kept at -78 °C and NMR spectra measured at
Figure 1. Crystalmaker diagram of the structure of the phenolic form of
borate functionalized ligand c. Selected bond distances (Å): C(1)-O(1),
1.360(2); C(11)-N(1), 1.280(2); C(4)-B(1), 1.601(3); B(1)-F(1), 1.402(2);
B(1)-F(2), 1.426(3); B(1)-F(3), 1.403(2); F(1)-K(1), 3.1533(15); F(2)-
K(1), 2.6570(13); F(3)-K(1), 4.376. Selected bond angles (deg): O(1)-
C(1)-C(2), 119.84(14); C(1)-C(2)-C(11), 121.16(16); C(2)-C(11)-N(1),
122.67(15); C(11)-N(1)-C(12), 122.08(14). Selected torsion angles
(deg): O(1)-C(1)-C(2)-C(11), 0.2(2); C(1)-C(2)-C(11)-N(1), -3.4(3);
C(11)-N(1)-C(12)-C(13),-79.2(2);C(11)-N(1)-C(12)-C(17),-106.59(19).
(almost colorless). Addition of water immediately formed the
boronic acid and hydrolyzed the O-Si bond. The crude product
was dissolved in methanol whereupon treatment with an aqueous
solution of KHF2 converted the boronic acid to the potassium
trifluoroborate salt, which was recrystallized from an acetone/
pentane solution and isolated in 56% yield. Stirring equimolar
mixtures of the ligand and 18-crown-6 in toluene for 24 h
followed by removal of the volatiles yielded pure [K-18-Crown-
6][4-BF3-t-BuG(OH)] as a beige solid. It was then deprotonated
with 1.2 equivalent of KOtBu in a CH3CN solution at room
temperature. The ligand and all the intermediates were com-
pletely characterized by NMR spectroscopy, elemental analysis
and in the case of the proteo ligand c (X ) H, Scheme 2) by
X-ray diffraction studies.
The molecular structure of the proteo ligand c is shown in
Figure 1; benzene molecules (1.5) and water cocrystallized with
in the centro-symmetric P-1 space group. The structure shows that
the potassium cation is strongly bonded by the six oxygens of
the crown ether (average K-O distance: 2.87(7) Å) and a water
molecule). A fluorine atom (F2) also comes to close contact
with the potassium (K1-F2 distance: 2.6570(13) Å) while the
two other fluorine atoms are much further away (more than 3.15
Å). As a result, boron-fluorine distances are not equivalent,
B1-F2 distance being elongated (B1-F2: 1.426 Å > B1-F1
≈ B1-F3: 1.402 Å). Metrical parameters in the rest of the
structure are normal. The diisopropylphenyl group is roughly
perpendicular to the phenolic group and the acidic proton of
the phenol function is oriented toward the nitrogen of the imine.
Palladium methyl complexes incorporating these ligands and
stabilized by coordinated acetonitrile can be prepared via
1
-20 °C to prevent decomposition. The H NMR signals for
the isopropyl group, as well as the Pd-Me moiety provide good
spectroscopic handles to confirm the preparation of the com-
plexes. When the ligands are not coordinated to the metal center,
only one doublet is observed for the CH(CH3)2; upon coordina-
tion to the Pd, the rotation of the aryl group is hindered and
two separate doublets are observed. The signals for the Pd-
CH3 group are found characteristically at higher field at 0.0
and -0.1 ppm for 1a,b-NCCH3, respectively and slightly further
upfield at -0.22 ppm for anionic 1c-NCCH3. In nOe experi-
ments, enhancement in the aryl isopropyl methines was observed
upon irradiation of the palladium methyl group, while no
enhancement in the tert-butyl group was seen. This indicates
that in these compounds the Pd-methyl occupies the site trans
to the phenoxide oxygen. Assignment of this structure is
consistent with the results of Ziegler and co-workers, who have
shown computationally that the isomer with Me trans to the
phenoxide is the most stable isomer.
Crystallographic analysis of the structures of 1a-NCCH3 and
1b-NCCH3 confirm that the methyl groups occupy the position
trans to the phenoxy donor in these compounds. Both 1a-
NCCH3 and 1b-NCCH3 crystallize with two independent
(32) Preparation of (COD)Pd(Me)Cl: Ru¨lke, R. E.; Ernsting, J. M.; Spek, A.
L.; Elsevier: C. J.; van Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem.
1993, 32, 5769.
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1857

A R T I C L E S
Groux et al.
Table 1. Selected Bond Distances (Å) and Angles (deg) of 1a-NCCH3 and 1b-NCCH3
parameter
1a-NCCH3
parameter
1b-NCCH3
Pd(1)-C(27)
2.021(4)
1.978(3)
2.050(3)
2.018(4)
1.285(4)
1.136(5)
Pd(1)-C(1)
2.004(5)
2.013(3)
2.062(3)
2.001(4)
1.292(6)
1.132(6)
Pd(1)-N(1)
Pd(1)-O(1)
Pd(1)-N(3)
N(2)-N(1)
N(3)-C(28)
Pd(1)-N(1)
Pd(1)-O(1)
Pd(1)-N(2)
C(8)-N(1)
N(2)-C(25)
O(1)-Pd(1)-N(1)
N(1)-Pd(1)-C(27)
C(27)-Pd(1)-N(3)
N(3)-Pd(1)-O(1)
O(1)-Pd(1)-C(27)
N(1)-Pd(1)-N(3)
Pd(1)-O(1)-C(1)
O(1)-C(1)-C(2)
C(1)-C(2)-N(2)
C(2)-N(2)-N(1)
N(2)-N(1)-Pd(1)
90.36(12)
95.47(17)
88.88(17)
85.60(13)
173.03(17)
173.92(14)
125.9(2)
123.4(3)
127.1(4)
124.6(3)
127.2(3)
O(1)-Pd(1)-N(1)
N(1)-Pd(1)-C(1)
C(1)-Pd(1)-N(2)
N(2)-Pd(1)-O(1)
O(1)-Pd(1)-C(1)
N(1)-Pd(1)-N(2)
Pd(1)-O(1)-C(2)
O(1)-C(2)-C(7)
C(2)-C(7)-C(8)
C(7)-C(8)-N(1)
C(8)-N(1)-Pd(1)
91.66(13)
93.40(18)
87.92(19)
87.19(14)
173.98(18)
176.92(15)
127.7(3)
122.4(4)
124.3(4)
130.5(4)
122.6(3)
Pd(1)-N(1)-C(15)-C(16)
Pd(1)-N(1)-C(15)-C(20)
N(2)-N(1)-C(15)-C(16)
N(2)-N(1)-C(15)-C(20)
-82.9(4)
96.0(4)
92.6(4)
Pd(1)-N(1)-C(13)-C(14)
Pd(1)-N(1)-C(13)-C(18)
C(8)-N(1)-C(13)-C(14)
C(8)-N(1)-C(13)-C(18)
78.6(4)
-99.2(4)
-98.4(5)
83.7(5)
-88.5(5)
Figure 2. Crystalmaker diagram of the structure of 1a-NCCH3. See Table
1 for selected metrical data.
Figure 4. Crystalmaker diagram of the structure of 1c-PMe3. See Table 2
for selected metrical data.
marginally better donor; corresponding increases in the Pd-
CH3 and Pd-NCCH3 distances are observed.
Ligand substitution reactions using PMe3 or CO occur rapidly
to produce the complexes 1-L; in the case of CO, insertion to
form the acyl complexes 2-CO is facile. The phosphine
complexes were fully characterized for identification purposes
in experiments described below and are generally much more
stable than the acetonitrile adducts toward deposition of Pd(0)
Figure 3. Crystalmaker diagram of the structure of 1b-NCCH3. See Table
1 for selected metrical data.
1
molecules in the unit cell, along with solvents of crystallization,
but the metrical parameters within the two molecules do not
differ significantly. Figure 2 shows the structure of 1a-NCCH3,
while Figure 3 shows that of 1b-NCCH3; Table 1 gives a
comparison of selected metrical parameters for the two related
compounds. For both, the coordination environment around the
Pd center is square planar with minimal distortion, the largest
angle being the N(1)-Pd-CH3 angle due to the sterically bulky
N-aryl group. The Pd-O and Pd-N bonds are slightly shorter
in the diazene complex 1a-NCCH3, indicating this ligand is a
in solution. In addition to characteristic resonances in the H
NMR spectra, they exhibit peaks in the 31P NMR spectra in the
regions around -3 ppm for L ) PMe3. The X-ray structure of
complex 1c-PMe3 was obtained and demonstrates that the ligand
bearing the anionic borate center coordinates the Pd similarly
to the parent ligand; the molecular structure is shown in Figure
4, while pertinent metrical data are given in Table 2. Aside from
the presence of the -BF3K(18-crown-6) moiety and the
substitution of CH3CN for PMe3, the structure is geometrically
identical and metrically quite similar to that observed for 1b-
9
1858 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
Table 2. Selected Bond Distances (Å) and Angles (deg) of
Scheme 4
1c-PMe3
parameter
1c-PMe3
Pd(1)-C(1)
2.041(5)
2.093(3)
2.097(3)
2.2273(13)
1.296(5)
1.602(7)
1.412(7)
1.386(8)
1.387(7)
2.716(3)
2.905(4)
3.125(4)
89.27(13)
92.36(17)
85.41(15)
93.07(9)
177.08(19)
176.50(11)
129.0(3)
122.5(4)
125.0(4)
130.4(4)
122.9(3)
-99.7(4)
79.9(5)
Pd(1)-N(1)
Pd(1)-O(1)
Pd(1)-P(1)
C(8)-N(1)
C(5)-B(1)
B(1)-F(1)
B(1)-F(2)
B(1)-F(3)
K(1)-F(1)
K(1)-F(2)
K(1)-F(3)
O(1)-Pd(1)-N(1)
N(1)-Pd(1)-C(1)
C(1)-Pd(1)-P(1)
P(1)-Pd(1)-O(1)
O(1)-Pd(1)-C(1)
N(1)-Pd(1)-P(1)
Pd(1)-O(1)-C(2)
O(1)-C(2)-C(7)
C(2)-C(7)-C(8)
C(7)-C(8)-N(1)
C(8)-N(1)-Pd(1)
Pd(1)-N(1)-C(13)-C(14)
Pd(1)-N(1)-C(13)-C(18)
C(8)-N(1)-C(13)-C(14)
C(8)-N(1)-C(13)-C(18)
the lithium salt of the ligand and (COD)Pd(Cl)Me using AN as
the solvent (Scheme 4). These observations all suggest that the
R-cyano group is a stronger Lewis base than the free nitrile
groups present, enthalpically favoring oligomerization.
79.5(5)
-100.9(5)
NCCH3 (Figure 3). Slight elongation of the Pd-C, N and O
bonds is observed in 1c-PMe3, but this may be due to the greater
steric presence of the PMe3 ligand in comparison to the more
rodlike acetonitrile donor rather than any electronic perturbation
caused by the anionic substituent.
While sparingly soluble in aromatic solvents, the products
of these reactions were soluble in chlorinated solvents such as
methylene chloride. The 1H NMR spectra, however, were
exceedingly complex due to the presence of both dimers and
trimers (and possibly higher oligomers), each with the potential
to consist of a mixture of diastereomers given that the R cyano
carbon is chiral. Similar diastereomeric mixtures for dimers of
chiral R-cyano Pd alkyls have been observed previously.34
The features of the spectra for the neutral compounds 3a and
3b were quite similar, particularly in the region associated with
the isopropyl methine resonances, suggesting a similar constitu-
The carbonyl derivatives were prepared to acquire a quantita-
tive measure of the effect of the ligand on the π back-donating
capacity of the palladium center. The reactions were monitored
by 1H NMR spectroscopy, which showed that compounds 1b,c-
CO rapidly formed at low temperature and then more slowly
converted to the acyl carbonyl compound 2 over the course of
a few hours. Carbonyl stretching frequencies for the coordinated
CO ligand in compounds 2-CO were 2088 cm-1 for 2b-CO
and 2085 cm-1 for anionic compound 2c-CO. A comparison
between the latter two indicates that the effect of the anionic
BF3 group on the electron density at Pd is not profound, but
measurable. In comparison to cationic Pd complexes incorporat-
ing a hard NN donor set, these compounds are considerably
more electron rich, since νCO values of ∼2120-2130 cm-1 are
observed in the cationic systems.26,33
Insertion of Acrylonitrile Into Pd-Me Bonds. The aceto-
nitrile adducts of compounds 1 all react with an excess of pure,
dry AN to afford products that were determined to be oligomers
of the product of 2,1 insertion in which the R-cyano alkyl group
coordinates to the Pd center of another molecule (Scheme 4).
In NMR tube reactions, free acetonitrile was apparent in the
medium. Reactions were carried out in THF at room temperature
and the products were isolated via evaporation of the volatiles
and washed before analysis by NMR spectroscopy and mass
spectrometry. Alternatively, the oligomeric product mixture
containing the diazene ligand a could be generated directly from
1
tion for these mixtures. In the H NMR spectrum of salicyla-
ldiminato derivative 3b, the region associated with the aldimine
proton (∼7.5 ppm) is quite informative. Five singlets are evident,
a 1:1:1 group of three and another 1:1 group of two at
approximately half the intensity of the first group. We tentatively
assign the less intense pair to a 1:1 mixture of syn and anti
dimers. In the case of a trimeric structure, because of the
identical constitution of the three chiral centers, there are only
two diastereomeric pairs of enantiomers possible, one in which
the relative stereochemistry for each center is the same, and
one in which two are the same and one is opposing. In the
former (RRR/SSS), a C3 axis exchanges the homotopic ligand
environments and one singlet for the aldimine proton would be
1
expected in the H NMR spectrum. In the RRS/SSR pair,35
however, the Pd centers cannot be exchanged by any symmetry
operation and so three aldimine resonances in a 1:1:1 ratio is
expected. Since this is what is observed, it appears that trimer
formation in these systems is diastereoselective for this pair of
enantiomers. Interestingly, the 1H NMR spectrum for the anionic
compound 3c was somewhat simplified, and only two prominent
(33) Carfagna, C.; Gatti, G.; Martini, D.; Pettinari, C. Organometallics 2001,
20, 2175. (b) Carfagna, C.; Formica, M.; Gatti, G.; Musco, A.; Pierleoni,
A. Chem. Commun. 1998, 1113. (c) Binotti, B.; Carfagna, C.; Gatti, G.;
Martini, D.; Mosca, L.; Pettinari, C. Organometallics 2003, 22, 1115.
(34) Ruiz, J.; Rodriguez, V.; Lopez, G.; Casabo, J.; Molins, E.; Miravitlles, C.
Organometallics 1999, 18, 1177.
(35) This diastereomer is identical to the RSR/SRS and SSR/RSS pairs.
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1859

A R T I C L E S
Groux et al.
Figure 5. Left: experimental and simulated FD mass spectrum of 3a
(Pd3C90H129N9O3) Right: experimental and simulated ESI mass spectrum
of dimeric 3c (Pd2C54H70N4O2B2F6K).
aldimine peaks in an approximately 1:1 ratio were observed,
suggesting that two diastereomeric dimers dominate the solution
chemistry of this species.
The NMR spectroscopic evidence for the assignment of main-
ly dimers and trimers for compounds 3 was augmented by mass
spectrometry data, which showed strong parent peaks corre-
sponding to the trimer for 3a (M+ ) 1703, FD MS) and dimer
for the anionic complex 3c (M- ) 1195, ESI MS).36 Figure 5
shows the parent peaks for these two compounds along with
the simulated spectra based on the expected isotopic distribution,
showing excellent agreement in both cases. In the spectrum for
3a, peaks at M ) 1137 and 567 indicate the presence of the
dimer and monomer, respectively; likely the monomer arises
from fragmentation. The spectrum for the anionic complex 3c
Figure 6. Crystalmaker diagram of the structure of the trimer of 3a. Top,
the full molecule; bottom, the Pd3 core of the molecule. See Table 3 for
selected metrical data.
Table 3. Selected Bond Distances (Å) and Angles (deg) of 3a
parameter
3a
3a
3a
Pd(1)
Pd(2)
Pd(3)
Pd-C
2.058(6)
1.979(5)
2.012(4)
2.005(6)
1.279(7)
2.073(7)
1.998(6)
2.022(5)
2.000(6)
1.285(8)
2.069(6)
1.960(6)
2.030(4)
2.008(6)
1.278(8)
Pd-Nligand
Pd-O(1)
contains no evidence for trimeric species but a peak at M+
)
Pd-Ncyanoalkyl
N-Nligand
508 is indicative of a monomer fragment. The lack of evidence
for the trimer is consistent with the solution NMR data which
indicate that in 3c the dimeric diasteromers dominate.
O-Pd-Nligand
88.33(19)
95.3(2)
88.0(2)
90.7(2)
95.0(3)
88.6(2)
85.8(2)
90.1(2)
94.2(2)
87.9(2)
Nligand-Pd-C
X-ray quality crystals were obtained from solutions of the
diazene complex 3a and analysis provided further confirmation
of the assignments made on the basis of the NMR and MS data
described above. The structure is shown in Figure 6 and selected
metrical data is given in Table 3. The structure shows that
insertion of AN has occurred with 2,1 regiochemistry, producing
R-cyano propyl ligands that occupy the position trans to the
phenoxy donor at each Pd center. Trimerization occurs through
the lone pair of the R-cyano group. As suggested by the NMR
spectroscopy for 3b, the diastereomer observed for 3a in the
solid state is the RRS/SSR pair, rendering the Pd centers
heterotopic. Despite their chemical inequivalence, the metrical
parameters associated with each center are quite similar, and in
C-Pd-Ncyanoalkyl
Ncyanoalkyl-Pd-O
O-Pd-C
Nligand-Pd-Ncyanoalkyl
Pd-O-Cipso(O)
O-Cipso(O)-Cipso(N)
Cipso(O)-Cipso(N)-N
Cipso(N)-N-Nligand
N-Nligand-Pd
88.6(2)
87.76(19)
175.0(2)
177.9(2)
125.4(3)
121.6(4)
129.5(4)
123.1(5)
129.0(4)
174.5(5)
176.6(7)
103.2(4)
174.5(2)
175.3(2)
122.4(3)
121.7(3)
126.9(3)
122.1(5)
126.2(4)
177.6(6)
176.3(7)
104.6(4)
174.4(2)
176.3(2)
126.1(4)
122.2(4)
129.0(4)
125.6(6)
126.3(5)
174.8(6)
176.0(7)
101.6(4)
Pd-Ncyanoalkyl-C
Ncyanoalkyl-C-CPd
Pd-C-CN
addition are comparable to those found for 1a-NCCH3 (Table
1). The Pd-C bonds are slightly longer than that observed in
1a-NCCH3, likely a reflection of the greater steric bulk of the
R-cyano alkyl group vs methyl.
Treatment of mixtures 3 with one equivalent of PMe3 or PPh3
based on Pd resulted in breaking of the dimers and trimers into
(36) The parent peak for 3c indicates loss of two 18-crown-6 molecules and
one potassium ion is facile. Attempts to obtain ESI data for the neutral 3b
mixture were unsuccessful, but we assume on the basis of the similarity in
the NMR data that the conclusions regarding the composition of oligomers
3a can be extended to the salicylaldimine compounds 3b.
9
1860 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
phosphine stabilized monomers 3-PR3 as shown in Scheme 4,
significantly simplifying the NMR spectra since now a single
species dominates in solution. In the case of PMe3, addition of
more than one equivalent of phosphine resulted in formation
of Pd(0) species, so careful control of the phosphine stoichi-
ometry is necessary in these reactions. Diagnostic patterns for
the R-cyanopropyl group were found in the signal for the R-CH-
(CN) moiety, which coupled to the two diastereotopic methylene
protons as well as the phosphine phosphorus atom, and the signal
for the methyl group which exhibited coupling only to the
methylene protons, appearing as a pseudo triplet. 31P NMR
chemical shifts were in the range expected for PMe3 or PPh3
complexes of a Pd alkyl complex with these ligands, suggesting
that the alkyl group maintains its position trans to the phenoxy
donor.
NMR Investigations of the Reactions of 1-NCCH3 with
AN. The complexities of AN insertion reactions are summarized
in Scheme 1; the reaction is further complicated in the case of
compounds 1-NCCH3 due to the dissymmetry of the ligand
donor, which creates the possibility of geometric isomers.
However, in the presence of excess donor, interconversion of
these isomers should be rapid37 and in the discussion below,
we assume that this is the case, given that for the most part a
large excess of AN is employed. Thus, although insertion of
AN into the Pd-Me bonds of compounds 1-NCCH3 presumably
leads to products with the R-cyanoalkyl group trans to the imine
function of the ligand, these are not observed and isomerize
rapidly to the more thermodynamically stable isomer with the
alkyl trans to the phenoxy donor.
Figure 7. (a) Concentration vs Time plot for 1b-n-AN and 4b-n-AN (10
equiv of AN, 3.1 °C). (b) Concentration vs Time plot for 1b-n-AN and
4b-n-AN (190 equiv of AN, 3.1 °C).
To gain further insight into the details concerning the reaction
of AN with compounds 1-NCCH3, the reaction of 1b-NCCH3
was examined by variable temperature 1H NMR spectroscopy.
Similar experiments with the diazene complex 1a-NCCH3 and
the anionic 1c-NCCH3 indicated a qualitatively identical
reaction course; for practical reasons (solubility issues, more
spectroscopic information) we focus on the experiments utilizing
1b-NCCH3 in the following discussion.
Scheme 5
When 1b-NCCH3 is reacted with 1.0 equiv of AN at -80
°C in CD2Cl2, signals for both free and bound NCCH3 are
observed, and two resonances at -0.26 and -0.30 ppm indicate
the presence of two Pd-Me containing species in solution. The
region for the AN vinyl protons shows two sets of resonances,
one for free AN and one due to N-bound AN, shifted only by
∼0.2 ppm upfield of the resonances for free AN. Typically,
π-bound AN exhibits more severely shifted resonances for these
protons,16,38 and no signals for π-bound AN are observed in
any of these experiments. The relative intensities of the Pd-
Me signals indicate that the ratio of 1b-NCCH3 to 1b-n-AN is
about 1:1 at -80 °C. When the sample is warmed to -30 °C,
the ratio of 1b-NCCH3 to 1b-n-AN changes slightly and a third
Pd-Me species appears (∼10% total); since it is in this
temperature regime and above that insertion of AN ensues, we
assign this peak, which intensifies as the equivalency of AN
used decreases to 0.5, to the Pd-Me containing dimers 4b-L
shown in Scheme 5. Although free AN and acetonitrile are
present, this dimer forms because the R cyano group is the most
basic nitrile group in the system. Further warming results in
consumption of all the AN in the system and formation of
dimers and trimers 3a. When only 0.5 equiv of AN are used,
4b-n-NCCH3 can also be identified among the final products.
(37) While four coordinate complexes of Ni(II) are subject to rapid isomerization
via tetrahedral intermediates, analogous Pd(II) compounds are generally
more resistant to isomerization in the absence of excess donor ligand;
however, interchange of these isomers by an associative mechanism is facile
when such donor is present. (b) Jun, H.; Young Jr., V. G.; Angelici, R. J.
Organometallics 1994, 13, 2444. (c) Wakatsuki, Y.; Yamazaki, H.; Grutsch,
P. A.; Santhanam, M.; Kutal, C. J. Am. Chem. Soc. 1985, 107, 8153.
(38) See for example: Albano, V. G.; Castellari, C.; Cucciolito, M. E.; Panunzi,
A.; Vitagliano, A. Organometallics 1990, 9, 1269.
When 1b-NCCH3 is reacted with a 10-190-fold excess of
AN at -78 °C, the equilibrium at the top of Scheme 5 shifts
completely to 1b-n-AN; all of the acetonitrile present is free
1
by H NMR spectroscopy. As these samples are warmed to
temperatures where product formation is observed, the Pd-Me
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1861

A R T I C L E S
Groux et al.
Table 4. Observed Rate Constants for the Reactions of
Compounds 1 with AN
5
AN
kobs
(
×
10-
)
1
complex
(equiv)
T (°
C)
(M-
)
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1b-NCCH3
1c-NCCH3
1c-NCCH3
20
20
20
20
20
100
100
100
100
100
10
40
60
80
190
20
-22.8
-15.0
-5.0
3.1
4.83
13.0
39.3
95.8
193
8.5
18.2
9.8
-22.8
-15.0
-5.0
3.1
65.8
123.0
267.5
75.5
108.3
117
120.8
127.2
215
9.8
3.1
3.1
3.1
3.1
3.1
3.1
3.1
100
316.8
signal for 1b-n-AN begins to diminish, while that for the dimer
4b-n-AN increases to a maximum and then disappears as the
reaction approaches completion. At low concentrations of AN,
the waxing and waning of 4b-n-AN is more prominent; a typical
concentration vs time plot for the Pd-Me containing species is
shown in Figure 7a. However, at high loadings of AN, 4b never
comprises more than 5% of the total concentration of Pd-Me
present (Figure 7b).
Observed rate constants for the disappearance of Pd-Me can
be evaluated by integration of the signals for both 1b-n-AN
and 4b-n-AN and constructing pseudo first-order plots on the
basis of the disappearance of total [Pd-Me].39 These plots are
linear over the course of the reaction, and kobs may be evaluated
as a function of [AN]; values for kobs in all of these experiments
are collected in Table 4. A plot of kobs vs [AN] (Figure 8a)
shows saturation behavior, with saturation being reached at about
100 equiv of AN at 3.1 °C. These results may be interpreted
on the basis of the mechanism depicted in Scheme 6. In the
presence of an excess of AN, formation of 1b-n-AN is
essentially quantitative and upon warming to the temperature
regime where product formation ensues, 1b-n-AN is in equi-
librium with the (unobserved) π bound isomer 1b-p-AN with
an equilibrium constant Keq. This species undergoes rapid
insertion to give the transiently stable insertion product, which
rapidly coordinates AN and in the process isomerizes to 3b-n-
AN. This species can undergo oligomerization to dimers and
trimer 3b, or react with 1b-n-AN to give the dimeric intermedi-
ate Pd-Me complex 4b-n-AN, which we observe spectroscopi-
cally. As the concentration of this species builds up, it can react
with free AN to generate one equivalent of 3b-n-AN, which
forms product, and one equivalent of 1b-n-AN and re-enters
the reaction scheme. As the concentration of AN increases, then,
the persistence of 4b-n-AN diminishes.
Figure 8. (a) Plot of kobs vs [AN] in the reaction of 1b-n-AN with AN.
(b) Plot of 1/kobs vs 1/[AN] in the reaction of 1b-n-AN with AN.
Scheme 6
not necessarily allow for straightforward evaluation of Keq and
kins.40 Clearly, however, at high [AN], where the concentration
build-up of 4b-n-AN is negligible over the course of the
reaction, and the equilibrium between 1b-n-AN and 1b-p-AN
is saturated, kobs approaches kins. By evaluation of kobs at various
temperatures under near saturation conditions (100 equivalents
of AN), an Eyring plot (Figure 9) can be constructed and the
activation parameters of ∆H‡ ) 14.4(5) kcal mol-1 and ∆S‡ )
-19(5) eu for kins extracted. This corresponds to a ∆G‡ of ∼20.2
Although an inverse plot of 1/kobs vs 1/[AN] (Figure 8b) is
linear, the complicated nature of the reaction scheme presented
in Scheme 6 (in particular the effect of 4b-n-AN on the
equilibrium Keq) muddies the interpretation of this plot and does
(39) Treatment of the data in this way is a simplification given that formation
and involvement of the dimer 4b-n-AN modifies the order in [Pd-Me]
somewhat. However, pseudo first order plots constructed by monitoring
the disappearance of only 1b-n-AN exhibit curvature, while inclusion of
the Pd-Me signal for 4b-n-AN leads to linear plots.
(40) Wilkins, R. G. The Study of Kinetics and Mechanisms of Reactions of
Transition Metal Complexes; Alyn and Bacon, Inc., Boston, 1974; pp 26-
31.
9
1862 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
imparts a positive influence on the kinetics of AN insertion into
the Pd-Me bond. These observations were corroborated by the
experiment outlined in Scheme 7, a competition experiment
designed to give a direct comparison of the relative rates of
insertion of AN into the Pd-Me bonds of 1b-NCCH3 and 1c-
NCCH3 by setting up a competition for 1 equiv of AN and the
two complexes. To distinguish between the two, complex 1b-
NCCH3 was selectively deuterium labeled in the Pd-Me
position, yielding d3-1b-NCCH3. A 1:1 mixture of this species
and 1c-NCCH3 was treated with one equivalent of AN (0.5
equiv based on total Pd) and allowed to form a complex mixture
of unreacted compounds 1, product oligomers d3-3 and mixed
dimers 4. These mixtures were then treated with 2 equiv of PMe3
to yield the more simple mixture shown to the right of Scheme
7. As shown in Figure 10, the ratio of d3-3b-PMe3 to d3-1b-
2
PMe3 was determined by H NMR spectroscopy to be 0.39:
Figure 9. Eyring plot for the disappearance of 1b-n-AN under saturation
conditions at various temperatures.
0.61, while the ratios of d3-1b-PMe3 to 1c-PMe3 and d3-3b-
PMe3 to 3c-PMe3 were found to be 0.67:0.33 and 0.42:0.58 by
31P NMR spectroscopy. These assignments were possible since
each of these compounds were made and identified separately
as described above in Schemes 3 and 4.
kcal mol-1 at 25 °C. Although the ∆S‡ value is subject to
considerable experimental uncertainty, given the narrow tem-
perature range we were able to access, it is comparable to that
reported by Brookhart et al. (-14(7) eu) for the insertion of π
bound methyl acrylate into the Pd-Me bond of a cationic
diimine complex akin to that shown in Chart 1.4b The overall
Taking the average of the ratios obtained shows that the
insertion of AN into the Pd-Me bond of the complex containing
the borate functionalized ligand occurs with an overall rate
roughly 1.6× as fast as the insertion into the Pd-Me bond of
the conventional neutral catalyst. This is consistent with the ratio
of kobs obtained by direct monitoring of the two reactions as
described above.
barrier is slightly higher than that calculated (17.6 kcal mol-1
)
by Ziegler et al.22d and that found by Brookhart et al. for the
insertion of methyl acrylate (17.4 kcal mol-1) in the cationic
compounds.4b Interestingly, in some of Brookhart’s systems,
O-bound methyl acrylate was observed at low temperatures, but
for this carbonyl containing monomer, the isomerization to the
π-bound species necessary for insertion has a comparable or
slightly lower barrier than that for insertion. In the AN system,
it appears that isomerization of 1b-n-AN to 1b-p-AN is rate
limiting.41 Given the differences in coordination geometry for
these two polar monomers (i.e., bent for the O-bound methyl
acrylate vs linear for the N-bound AN) this is not too surprising.
Relative Rates of Insertion in Neutral vs. Anionic Com-
plexes. The effect of charge on the overall rate of insertion is
of interest in designing compounds that exhibit facile insertion
rates. For example, while the character of the reactions of
cationic Pd-Me complexes, where N-bound AN is even more
thermodynamically favored, appears to be similar to these
reactions, overall insertion rates are somewhat slower.26 Given
this trend, complexes bearing an anionic charge should encour-
age π-bonding (i.e., increase Keq) and increase the overall rate
of insertion.
These experiments do not identify the reason for the increased
macroscopic rate of insertion vis-a`-vis improved access to the
π-bound isomer of the AN complex (Keq), or an enhanced
migratory insertion rate (kins), but do illustrate that the concept
of using anionically charged catalysts to improve reactivity
toward polar comonomers is moderately successful. Computa-
tional results suggest that the largest effect of increasing the
negative charge on the complex should have a positive effect
on Keq, but increase the barrier to insertion.22e Since we are
unable to reliably deconvolute these two parameters from the
data at hand, we cannot comment on the most likely origin of
the higher rates observed for the anionic compound 1c-NCCH3.
However, we note that based on the nCO stretches in compounds
2b,c-CO, the change in electron density at the metal center is
slight upon introduction of the BF3K(18-crown-6) group and
thus perhaps the effect on Keq would be expected to be minimal.
The observation of larger rates for kobs under near saturation
conditions (AN ) 100 equiv) suggests that the insertion rate
may be inherently larger for the complex supported by borate
bearing ligand c in comparison to its noncharged analogue. In
any case, the result is encouraging in light of the apparently
modest effect on the electron density at the metal that the
positioning and nature of the anionic group (BF3) has in this
case. Situating the anionic group in a position closer to the metal
center may lead to enhanced effects in this regard.
The ionic nature of compound 1c-NCCH3 made monitoring
the reaction with AN somewhat more technically challenging
than for the neutral 1b-NCCH3 as described above, but we were
able to obtain values for kobs under nonsaturation (20 equivalents
of AN) and near-saturation (100 equiv) conditions. In both cases,
the observed rate constants were nearly twice as large as those
observed for the neutral complex under identical conditions
(Table 4), showing that the ligand bearing the anionic group
Conclusions. The development of catalysts capable of
incorporating polar comonomers, and particularly acrylate
derivatives, requires a detailed understanding of the factors that
favor π-coordination of these monomers and insertion via a
conventional four centered coordination mechanism. It appears
based on this and other studies22,26 that the barriers to insertion
for such monomers are not the crux of the problem, but that
(41) Little is known about the mechanism of this isomerization, but it appears
to be influenced by the presence of free [AN], suggesting it is associative
in character. A pathway involving bimolecular species with bridging AN
ligands is conceivable, since complexes with such bridging AN ligands
are known.41b,c Further studies on the nature of this isomerization process
are underway. (b) Johmann, F.; tom Dieck, H.; Kruger, C.; Tsay, Y. H. J.
Organomet. Chem. 1979, 171, 353. (c) Massaux, M.; le Bihan, M.-T.;
Chevalier, R. Acta Cryst. Sect. B 1977, 33, 2084.
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1863

A R T I C L E S
Scheme 7
Groux et al.
sertion to give R-cyanopropyl derivatives that readily associate
to give dimers and trimers via the R-cyano groups. Furthermore,
we have shown that incorporation of an anionically charged group
into the salicylaldiminato ligand framework can enhance the
overall insertion rate for AN, although the effect is modest in
the system studied. New generation negatively charged ligands
are being explored in an attempt to increase this rate enhance-
ment further.
While we have demonstrated that it is possible to observe 2,1
insertion of AN into Pd-carbon bonds, this is just the first chal-
lenge in developing a transition metal catalyst capable of copoly-
merizing AN and related monomers with, for example, ethylene.
The dimers and trimers formed after insertion are quite robust
and although they can be ruptured with strong donors such as
PMe3, they do not react with ethylene or carbon monoxide under
conditions where they do not decompose first. Furthermore, pre-
liminary experiments utilizing compounds 3a,b-PR3 indicate
that these species are also unreactive toward small molecules
that might be expected to undergo insertion into the Pd-R-cyan-
opropyl bond. Thus, while a first insertion of AN can be ob-
served and enhanced by going from cationic to neutral to anionic
complexes, subsequent chain growth reactions appear to become
more energetic challenging as the charge on the metal increases.
Interestingly, Jordan and co-workers have observed insertion
of CO into an R-cyanoalkyl derived from AN insertion into the
Pd-Me bond of a cationic complex with a strongly electron
donating N2 ligand set,26 suggesting that a subtle balance of
charge, or an ability to modulate the charge at the metal may
prove a useful strategy for further catalyst design modification.
Figure 10. 2H (top) and 31P{1H} (bottom) NMR spectra for the competition
experiment depicted in Scheme 7.
the dominance of coordination of polar functions (both in the
monomer and in the products of insertion) must be overcome
to give insertion a chance to occur with any degree of efficiency.
To this end, we have shown that neutral Pd(II) methyl com-
pounds, while favoring N-bound acrylonitrile, undergo isomer-
ization to the π-bound isomer22 which undergoes rapid 2,1 in-
Experimental Section
General Procedures. All operations were performed under a purified
argon atmosphere using glovebox or vacuum line techniques. Toluene,
9
1864 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
Table 5. Crystal Data, Data Collection and Structure Refinement Parameters
anionic l
1a-NCCH3
1b-NCCH3
1c-PMe3
3a
formula
C35H54BF3KNO7.
1.5 C6D6 ‚ 0.5
H2O
C29H43N3OPd.
0.5 n-hexane
C26H36N2OPd.
0.22 CH2Cl2
C39H65BF3KNO7P
Pd. 1.5 CH3CN
C90H128N9O3Pd3
x CH2Cl2
cryst color/habit
dimensions, mm
symmetry
space group
a, Å
beige block
0.20 × 0.15 × 0.09
triclinic
yellow needle
0.40 × 0.03 × 0.01
triclinic
yellow needle
0.20 × 0.06 × 0.04
orthorombic
Pbcn
23.574(2)
14.380(3)
yellow block
0.14 × 0.11 × 0.10
triclinic
yellow block
0.10 × 0.10 × 0.02
monoclinic
P 21/c
23.5116(12)
17.1359(8)
P -1
P -1
P -1
8.5510(10)
10.112(2)
26.361(5)
91.776(5)
98.641(5)
99.773(10)
2217.1(7)
2
13.9617(12)
14.0737(11)
17.2592(14)
93.220(4)
110.871(3)
98.433(3)
3112.9(4)
4
14.004(4)
16.841(5)
21.172(6)
85.573(17)
80.042(16)
88.58(2)
b, Å
c, Å
31.490(4)
27.4042(14)
R, deg
â, deg
113.717(2)
γ, deg
volume, Å3
Z
10675(3)
16
1.288
Nonius KappaCCD
173(2)
4903(2)
4
1.308
Nonius KappaCCD
173(2)
10108.5(9)
4
1.119
Siemens P4
153(2)
D(calcd) (g cm-1
diffractometer
T (K)
)
1.249
Nonius KappaCCD
173(2)
1.230
Siemens P4
153(2)
λ, Å (Mo KR)
µ, mm-1
scan type
0.71073
0.18
ω scan
27.5
-11 e h e 11
-13 e k e 13
-34 e l e 34
18589/10103
multiscan method
0.964, 0.984
0.048, 0.104
1.00
0.71073
0.621
ω scan
31.53
-20 e h e 20
-20 e k e 20
-24 e l e 24
47987/19140
SADABS
0.670673, 1.00000
0.0496, 0.0898
0.765
0.71073
0.757
ω scan
25.0
-28 e h e 27
-17 e k e 17
-37 e l e 37
17626/9370
multiscan method
0.863, 0.970
0.045, 0.109
1.06
0.71073
0.553
ω scan
27.5
-18 e h e 18
-21 e k e 21
-27 e l e 27
40813/21810
multiscan method
0.927, 0.947
0.063, 0.125
1.09
0.71073
0.573
ω scan
28.00
-31 e h e 31
-22 e k e 22
-36 e l e 36
115473/24308
SADABS
0.548361, 1.00000
0.0816, 0.1919
0.939
θ
max, °
h,k,l range
refl collected/ind.
absorption correction
T (min, max)
R, wR2
GOF
Hexane, and THF were dried and purified by passing through activated
alumina and Q5 columns42 or have been purchased dry form Aldrich.
Dichloromethane and acetonitrile were dried over CaH2 and distilled
under reduced pressure. Deuterated NMR solvents: d2-dichloromethane
(CD2Cl2), d3-acetonitrile (CD3CN), and d-chloroform (CDCl3) were
suspended in THF (50 mL) at -20 °C and transferred onto a basic
solution of sodium phenolate in ethanol/water prepared by dissolving
the phenol (20 mmol) in a minimum amount of ethanol and adding
NaOH (10 g, 250 mmol) dissolved in 100 mL water. The reaction
mixture was warmed to 25 °C and stirred for 15 h obtaining a system
with two phases. Hexane (50 mL) was added. The organic layer was
separated washed first with 3 M HCl and then successive portions of
water until neutralized. The organic phase was dried with Na2SO4 and
all volatiles removed under high vacuum. The dye was isolated by flash
chromatography (silica gel, hexane/CH2Cl2 3/1). A pure compound was
obtained by crystallization from methanol at -20 °C which was dried
in high vacuum over P2O5. Yield: 70%. Mp.: 82 °C. 1H NMR
(CDCl3): δ (ppm) 13.2 (1H, OH), 7.80 (s, 1H, ArH), 7.50 (s, 1H, ArH),
7.25-7.32 (m, 3H, ArH), 3.05 (septet, 2H, 3JH-H ) 7.8 Hz, i-Pr CH),
1
2
dried and distilled over CaH2. H, H, 13C, and 31P NMR 1D and 2D-
experiments were performed on Bruker AC-200, AMX-300, DRV-400,
DPX400, and DRX700 spectrometers. Data are given in ppm using
1
the residual solvent signals or internal TMS for calibration of the H,
2H, and 13C spectra. 31P spectra were referenced to external H3PO4.
Elemental analyses were performed in the microanalytical laboratory
of the Department of Chemistry (University of Calgary) or at the Bayer
Industry Sevices laboratory for element- and water analysis (Bayer AG,
Leverkusen). IR spectra were recorded on a Nicolet NEXUS 470 FT-
IR spectrometer using KBr plates and given in reciprocal centimeters
(cm-1). UV-Vis-Spectra were recorded on a Varian Cary 4 spectrom-
eter at 25 °C. X-ray crystallography was performed on suitable crystals
coated in paratone or perfluoropolyether oil and mounted on a Nonius
KappaCCD diffractometer (University of Calgary) or a Siemens P4
diffractometer equipped with a SMART-CCD-1000 area detector, a
MACScience Co. rotating anode, and a Siemens LT2 low-temperature
device (Bayer AG). Crystal data and refinement details are given in
Table 5. Field desorption mass spectrometry (FD-MS) analyses were
carried out with a MAT 900 double focusing magnetic sector instrument
(ThermoFinnigan Inc., San Jose, CA, USA/ThermoFinnigan MAT
GmbH, Bremen, Germany) equipped with PATRIC-detector, while
Electron spray ionization mass spectrometry (ESI-MS) analyzes were
carried out on a Bruker Esquire 3000 instrument equipped with an
Agilent model 1100 LC source. (COD)Pd(Me)Cl32 was prepared by
literature procedures.
3
1.49 (s, 9H, t-BuH), 1.37 (s, 9H, t-BuH), 1.20 (d, 12H, JH-H ) 7.8
Hz, i-Pr CH3). 13C{1H} NMR (CDCl3): δ (ppm) 149.8 (Ar), 148.5
(Ar), 141.3 (Ar), 140.2 (Ar), 137.9 (Ar), 136.9 (Ar), 128.6 (Ar CH),
128.2 (Ar CH), 127.7 (Ar CH), 123.7 (Ar CH), 35.4 (t-Bu C), 34.3
(t-Bu C), 31.4 (t-Bu CH3), 29.5 (t-Bu CH3), 27.9 (i-Pr CH), 23.7 (i-Pr
CH3,). Anal. for C26H38N2O: C, 79.0; H, 10.4; N, 6.9; Calcd: C, 79.14;
H, 9.71; N, 7.10.
Synthesis of Lithio-2,4-Di-tert-butyl-6-[2,6-diisopropyl-phenyla-
zo)phenolate [N2,O]Li. The azo dye, [N2,OH], (14.2 mmol) was
dissolved in 150 mL THF and cooled to -78 °C. n-BuLi (2.7 M
solution in heptane, 5.8 mL, 15.6 mmol) was added and the reaction
mixture was stirred for 1 h at -78 °C. After being warmed to 25 °C,
all of the volatiles were removed under high vacuum, and the residue
was dissolved in 60 mL n-hexane. The pure compound was obtained
by crystallization at -20 °C. After isolation and drying under high
vacuum, it could be used without any further purification. Yield:
quantitative.
Synthesis of 2,4-Ditert-butyl-6-[2,6-diisopropyl-phenylazo)phenol
[N2,OH]. 2,6-diisopropylaniline (20 mmol), isoamylnitrite (2.9 g, 3.4
mL, 25 mmol) and BF3‚OEt2 (3.1 g, 2.8 mL, 22 mmol) were mixed in
CH2Cl2 (200 mL) at -10 °C. Within 1 h, the diazonium salt precipitated
and was isolated by filtration at -10 °C. The diazonium salt was then
Synthesis of 5-Bromo-3-tert-butyl-2-hydroxy-benzaldehyde). Bro-
mine (8.025 g, 50.2 mmol) in 15 mL of 1,2-dichloroethane was added
over 2 h to a stirred solution of 3-tert-butyl-2-hydroxy-benzaldehyde
(9.0 g, 50.2 mmol) in 25 mL of 1,2-dichloroethane at 0 °C. Further
stirring (1 h) and removal of the volatiles yielded crude 5-bromo-3-
(42) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1865

A R T I C L E S
Groux et al.
tert-butyl-2-hydroxy-benzaldehyde (12.65 g, 98% yield) as a beige solid.
CH3). Anal. for C23H30BF3KNO: C, 63.79; H, 7.09; N, 2.75. Calcd:
C, 62.30; H, 6.82; N, 3.16.
Purification can be achieved by chromatography (silica gel, hex/ethyl
1
acetate). H NMR (CDCl3): δ (ppm) 11.74 (s, 1H, OH), 9.82 (s, 1H,
Synthesis of [K-18-Crown-6][4-BF3-t-BuG(OH)]. [4-KBF3-t-BuG-
(OH)] (252 mg, 0.568 mmol) and 18-Crown-6 (150 mg, 0.568 mmol)
were stirred in toluene (15 mL) for 24 h. Removal of the solvent gave
pure [K-18-crown-6][4-BF3-t-BuG(OH)] in quantitative yield. 1H NMR
(CD3CN): δ (ppm) 13.22 (s, 1H, OH), 8.35 (s, 1H, imine H), 7.62 (s,
1H, ArH), 7.39 (s, 1H, ArH), 7.22 (m, 3H, ArH), 3.55 (s, crown ether),
3.05 (septet, 2H, 3JH-H ) 6.88 Hz, i-Pr CH), 1.46 (s, 9H, t-BuH), 1.16
(d, 12H, 3JH-H ) 6.88 Hz, i-Pr CH3). 13C{1H} NMR (CD3CN): δ (ppm)
170.49 (CdN), 159.35 (C-OH), 147.95 (C-N), 140.08 (C-iPr), 135.39,
126.19, 124.29, 70.99 (crown ether), 35.43 (t-Bu C), 30.15 (t-Bu CH3),
29.05 (i-Pr CH), 23.84 (i-Pr CH3). Anal. for C35H54BF3KNO7: C, 59.08;
H, 7.52; N, 1.75. Calcd: C, 59.40; H, 7.69; N, 1.98.
Synthesis of [K-18-Crown-6][4-BF3-t-BuG(OK)]. [[K-18-Crown-
6][4-BF3-t-BuG(OH)] (601 mg, 0.849 mmol) and KOtBu (125 mg, 1.02
mmol) were stirred in acetonitrile (30 mL) for 1.5 h. Crude product,
obtained by removal of the solvent, was dissolved in 2 mL THF, then,
ca. 20 mL of Et2O was added to precipitate the deprotonated ligand.
Filtration and washing with 2 portions of Et2O (30 mL) gave pure
[K-18-crown-6][4-BF3-t-BuG(OK)].
4
4
imine H), 7.59 (d, 1H, JH-H ) 2.44 Hz, ArH), 7.52 (d, 1H, JH-H
)
2.40 Hz, ArH), 1.41 (s, 9H, t-BuH). 13C{1H} NMR (CDCl3): δ (ppm)
196.94 (CdO), 160.17 (C-OH), 141.10 (C-tBu), 136.95, 133.58,
121.65 (C-CHO), 111.11 (C-Br), 34.90 (t-Bu C), 28.98 (t-Bu CH3).
Anal. for C11H13BrO2: C, 51.59; H, 5.11. Calcd: C, 51.38; H, 5.10.
Synthesis of 4-Bromo-2-tert-butyl-6-[(2,6-diisopropyl-phenylimino)-
methyl]-phenol. 5-Bromo-3-tert-butyl-2-hydroxy-benzaldehyde (3.0 g,
11.7 mmol) and 2,6-diisopropylaniline (2.76 g, 15.5 mmol) were stirred
in 20 mL of methanol for 24 h at room temperature. Removal of all
the volatiles and purification by column (silica gel, hexanes) yielded
pure 4-Bromo-2-tert-butyl-6-[(2,6-diisopropyl-phenylimino)-methyl]-
phenol as a bright yellow solid (2.70 g, 56% yield). 1H NMR (CDCl3):
4
δ (ppm) 13.70 (s, 1H, OH), 8.25 (s, 1H, imine H), 7.51 (d, 1H, JH-H
4
) 2.44 Hz, ArH), 7.33 (d, 1H, JH-H ) 2.48 Hz, ArH), 7.21 (s, 3H,
ArH), 3.00 (septet, 2H, 3JH-H ) 6.88 Hz, i-Pr CH), 1.50 (s, 9H, t-BuH),
1.21 (d, 12H, 3JH-H ) 6.88 Hz, i-Pr CH3). 13C{1H} NMR (CDCl3): δ
(ppm) 166.06 (CdN), 159.75 (C-OH), 145.79 (C-N), 140.53 (C-
tBu), 138.75 (C-iPr), 133.24, 132.29, 125.65, 123.35, 119.78 (C-
CdN), 110.14 (C-Br), 35.23 (t-Bu C), 29.20 (t-Bu CH3), 28.15 (i-Pr
CH), 23.62 (i-Pr CH3). Anal. for C23H30BrNO: C, 66.17; H, 7.42; N,
3.22. Calcd: C, 66.34; H, 7.26; N, 3.36.
Synthesis of 1a-NCCH3. The lithium salt [N2,O]Li (1.75 g, 4.38
mmol) was dissolved in acetonitrile (20 mL) at 0 °C and transferred to
(COD)Pd(Me)Cl (1.16 g, 4.38 mmol) dissolved in acetonitrile (20 mL)
at 0 °C. The mixture was stirred for 15 min at 0 °C and for another 3
h at 25 °C. All volatiles were then removed under high vacuum and
the residue was extracted with n-hexane. The solution was concentrated
and the compound crystallized within 2 days at -20 °C. Yield: 1.76
g, 72%. Dp: 120-123 °C. 1H NMR (CDCl3): δ (ppm) 7.49 (d, 4JH-H
Synthesis of (5-Bromo-3-tert-butyl-2-trimethylsilanyloxy-ben-
zylidene)-(2,6-diisopropyl-phenyl)-amine. THF (120 mL) was con-
densed onto a mixture of 4-bromo-2-tert-butyl-6-[(2,6-diisopropyl-
phenylimino)-methyl]-phenol (3.4 g, 8.17 mmol) and KH (0.5 g, 12.5
mmol) and stirred for 1 h at room temperature. The mixture was then
cooled to 0 °C. SiMe3Cl (2 mL, 15.7 mmol) was added; the resultant
mixture was stirred for another hr at room temperature and filtered.
All of the volatiles were removed under high vacuum to obtain the de-
4
) 2.6 Hz, 1H, ArH), 7.38 (d, JH-H ) 2.6 Hz, 1H, ArH), 7.38 (d,
4JH-H ) 2.6 Hz, 1H, ArH), 7.2 (m, 3H, ArH), 2.32 (s, 3H, CH3CN),
3
1.48 (s, 9H, t-BuH), 1.32 (d, JH-H ) 7.0 Hz, 6H, i-Pr CH3), 1.25 (s,
3
9H, t-BuH), 1.09 (d, JH-H ) 7.0 Hz, 6H, i-Pr CH3), 0.00 (s, 3H,
1
sired product as a pale yellow solid in quantitative yield. H NMR
Pd-Me). 13C{1H} NMR (CDCl3): δ (ppm) 155.7, 140.6 (Ar CH), 130.7
(Ar CH), 129.1 (Ar CH), 127.0 (Ar CH), 123.1 (Ar CH), 119.0
(CH3CN), 35.8 (t-Bu C), 33.9 (t-Bu C), 31.1 (t-Bu CH3), 29.6 (t-Bu
CH3), 27.6 (i-Pr CH), 24.5 (i-Pr CH3), 22.6 (i-Pr CH3), 4.5 (CH3CN),
-5.7 (Pd-CH3). IR: 3069 (w), 2959 (s), 2906 (m), 2886 (m), 1616,
1482, 1456, 1391, 1360, 1323, 1271, 1253, 1227, 1145. MS (FD)[%]
(toluene): 555 [100, M+]. Anal. for C29H43N3OPd: C, 62.6; H, 7.7;
N, 6.9; calcd. C, 62.64; H, 7.79; N, 7.56.
4
(CDCl3): δ (ppm) 8.42 (s, 1H, imine H), 8.21 (d, 1H, JH-H ) 2.88
4
Hz, ArH), 7.55 (d, 1H, JH-H ) 2.88 Hz, ArH), 7.13 (m, 3H, ArH),
2.95 (septet, 2H, 3JH-H ) 6.81 Hz, i-Pr CH), 1.42 (s, 9H, t-BuH), 1.17
3
(d, 12H, JH-H ) 6.81 Hz, i-Pr CH3), 0.24 (s, 9H, Si(CH3)). 13C{1H}
NMR (CDCl3): δ (ppm) 157.99 (CdN), 154.47 (C-O), 148.87 (C-N),
143.87 (C-tBu), 137.45 (C-iPr), 133.40, 129.56 (C-CdN), 128.27,
124.16, 122.92, 114.91 (C-Br), 35.07 (t-Bu C), 30.21 (t-Bu CH3), 27.80
(i-Pr CH), 23.58 (i-Pr CH3), 1.74 (Si(CH3)3). Anal. for C26H38BrNOSi:
C, 64.17; H, 8.02; N, 2.73. Calcd: C, 63.92; H, 7.84; N, 2.87.
Synthesis of 1b-NCCH3. The sodium salt of the bulky salicylaldi-
minato ligand (0.236 g, 0.55 mmol) and (COD)Pd(Me)Cl (0.145 g,
0.55 mmol) were weighed into a round-bottom flask in a glovebox,
placed on a frit assembly and transferred to the vacuum line. Acetonitrile
(10 mL) was condensed onto the solids at -78 °C and the reaction
was warmed to room temperature. Upon warming, the yellow solution
became turbid and was allowed to stir for an additional 3 h. The reaction
was filtered, and the solids washed until the filtrate was colorless. The
solvent was then removed in vacuo and the sample was isolated as a
light yellow solid, which was pure by NMR spectroscopy. (0.250 g,
Synthesis of (5-trifluoroborate-3-tert-butyl-2-trimethylsilanyloxy-
benzylidene)-(2,6-diisopropyl-phenyl)-amine [4-KBF3-t-BuG(OH)].
To a solution of (5-bromo-3-tert-butyl-2-trimethylsilanyloxy-ben-
zylidene)-(2,6-diisopropyl-phenyl)-amine (0.5 g, 1.02 mmol) in THF
(50 mL) at -78 °C, was added n-BuLi (0.7 mL of a 1.6 M solution in
hexanes, 1.13 mmol). After the mixture was stirred at the same
temperature for 2 h, B(OMe)3 (2 mL, 17.8 mmol) was added dropwise
and the mixture was allowed to warm to room temperature over a 30
min period. Water (10 mL) was then added and the solution stirred for
another 30 min. The mixture was extracted with Et2O and the volatiles
of the organic part were removed under vacuum. The residue was
dissolved in methanol (30 mL) and an aqueous solution of KHF2 (1
mL, 0.39 g/mL) was added. After the mixture was stirred for 1 h, all
of the volatiles were removed. The product was extracted with acetone
and dried under high vacuum overnight, washed with pentane, and dried.
Pure product (450 mg, 54% yield) was obtained after recrystallization
from an acetone/pentane solution. 1H NMR (CD3CN): δ (ppm) 13.24
(s, 1H, OH), 8.33 (s, 1H, imine H), 7.60 (s, 1H, ArH), 7.39 (s, 1H,
ArH), 7.17 (m, 3H, ArH), 3.00 (septet, 2H, 3JH-H ) 6.88 Hz, i-Pr CH),
1
91% yield). H NMR (CDCl3): δ (ppm) 7.67 (s, 1H, imine H), 7.35
(d, 1H, 3JH-H ) 7.11 Hz, ArH), 7.20 (m, 3H, ArH), 6.97 (d, 1H, 3JH-H
3
) 7.95 Hz, ArH), 6.39 (t, 1H, JH-H ) 7.46 Hz, ArH), 3.47 (septet,
3
2H, JH-H ) 6.81 Hz, i-Pr CH), 2.29 (s, 3H, NCCH3), 1.49 (s, 9H,
t-BuH), 1.30 (d, 6H, 3JH-H ) 6.81 Hz, i-Pr CH3), 1.10 (d, 6H, 3JH-H
)
6.81 Hz, i-Pr CH3), -0.10 (s, 3H, Pd-CH3). 13C{1H} NMR (CDCl3):
δ (ppm) 168.31 (C-O), 166.10 (CdN), 147.91 (N-C), 141.30 (C-
iPr), 134.35, 131.17, 126.30, 123.20, 122.99 (C-tBu), 119.27 (C-
CdN), 117.91 (CtN), 111.80 (Ar CH), 35.22 (t-Bu C), 29.52 (t-Bu
CH3), 27.68 (i-Pr CH), 24.84 (i-Pr CH3), 22.73 (i-Pr CH3), 2.88 (CH3-
CN), -5.15 (Pd-CH3). Anal. for C26H36N2OPd: C, 62.34; H, 7.21; N,
5.88. Calcd: C, 62.58; H, 7.27; N, 5.61.
3
1.46 (s, 9H, t-BuH), 1.15 (d, 12H, JH-H ) 6.88 Hz, i-Pr CH3). 13C-
{1H} NMR (CD3CN): δ (ppm) 169.74 (CdN), 159.65 (C-OH), 147.50
(C-N), 139.63 (C-iPr), 135.57, 135.08, 134.90, 125.92, 123.97,
118.50, 35.27 (t-Bu C), 30.04 (t-Bu CH3), 28.76 (i-Pr CH), 23.62 (i-Pr
Synthesis of 1b-PMe3. PMe3 (0.102 mmol) was condensed onto a
frozen THF solution (25 mL) of 1b-NCCH3 (51 mg, 0.102 mmol).
The mixture was warmed to room temperature and stirred for 2 h.
9
1866 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
Filtration and evaporation of all the volatiles gave pure 1b-PMe3 as a
1H NMR (CD2Cl2): δ (ppm) 7.87 (s, 1H, imine H), 7.45 (s, 1H, ArH),
7.18 (m, 3H, ArH), 7.01 (s, 1H, ArH), 3.52 (crown ether), 3.03 (septet,
2H, 3JH-H ) 6.53 Hz, i-Pr CH), 1.99 (free CH3CN) 1.41 (s, 9H, t-BuH),
1.18 (d, 6H, JH-H ) 6.68 Hz, i-Pr CH3), 0.99 (d, 6H, JH-H ) 6.69
Hz, i-Pr CH3), 0.05 (s, 3H, Pd-CH3). Traces of 2c-CO are also found
in this spectrum.
1
yellow solid (38 mg, 70% yield). H NMR (CD2Cl2): δ (ppm) 7.91
(d, 3JH-P ) 11.98 Hz, 1H, imine H), 7.28 (dd, 3JH-H ) 7.18 Hz, 4JH-H
) 1.80 Hz, 1H, ArH), 7.18 (m, 3H, ArH), 6.95 (dd, 3JH-H ) 7.78 Hz,
4JH-H ) 1.62 Hz, 1H, ArH), 6.39 (t, 3JH-H ) 7.51 Hz, 1H, ArH), 3.27
3
3
3
2
(septet, 2H, JH-H ) 6.83 Hz, i-Pr CH), 1.44 (d, JH-P ) 10.24 Hz,
3
9H, PCH3), 1.42 (s, 9H, t-BuH), 1.20 (d, 6H, JH-H ) 6.88 Hz, i-Pr
Synthesis of 2b-CO. 1b-NCCH3 (25 mg, 0.051 mmol) in CD2Cl2
was frozen, evacuated and exposed to an atmosphere of CO. The
mixture was kept at -78 °C and 1H NMR spectrum taken at 0 °C after
3
3
CH3), 1.05 (d, 6H, JH-H ) 6.88 Hz, i-Pr CH3), -0.42 (d, JH-P
)
3.88 Hz, 3H, Pd-CH3). 13C{1H} NMR (CD2Cl2): δ (ppm) 168.05 (C-
O), 166.73 (CdN), 147.82 (N-C), 141.16 (C-iPr), 140.61 (C-tBu),
135.54, 131.36, 125.89, 123.18, 119.39 (C-CdN), 111.82, 35.24 (t-
Bu C), 29.09 (t-Bu CH3), 27.75 (i-Pr CH), 24.78 (i-Pr CH3), 22.45
1
2 h. H NMR (CD2Cl2): δ (ppm) 7.96 (s, 1H, imine H), 7.40 (dd,
4
3JH-H ) 7.42 Hz, JH-H ) 1.84 Hz, 1H, ArH), 7.21 (m, 3H, ArH),
7.05 (dd, 3JH-H ) 7.85 Hz, 4JH-H ) 1.83 Hz, 1H, ArH), 6.43 (t, 3JH-H
1
2
3
(i-Pr CH3), 15.1 (d, JC-P ) 31.7 Hz, PCH3), -4.28 (d, JC-P ) 13.7
Hz, Pd-CH3). 31P{1H} NMR (CD2Cl2): δ (ppm) -3.73. Anal. for
(C27H42NOPPd): C, 60.17; H, 7.97; N, 2.52. Calcd: C, 60.73; H, 7.93;
N, 2.62.
) 7.60 Hz 1H, ArH), 3.28 (septet, 2H, JH-H ) 6.85 Hz, i-Pr CH),
2.68 (s, 3H, OdCCH3), 1.99 (free CH3CN), 1.33 (s, 9H, t-BuH), 1.33
3
(d, 6H, i-Pr CH3), 1.11 (d, 6H, JH-H ) 6.83 Hz, i-Pr CH3). 13C{1H}
NMR (CD2Cl2): δ (ppm) 218.74 (Pd-CO), 184.44 (free CO), 174.22
(Pd-COCH3), 167.11 (CdN), 165.10 (C-O), 150.80 (N-C), 140.90
(C-tBu), 139.66 (C-iPr), 134.91, 132.37, 126.72, 123.74, 119.50 (free
CH3CN), 114.72 (C-CdN), 39.18 (Pd-COCH3), 35.14 (t-Bu C), 29.13
(t-Bu CH3), 28.12 (i-Pr CH), 24.84 (i-Pr CH3), 22.92 (i-Pr CH3), 2.14
(free CH3CN). IR (KBr pellets; cm-1): 2088 (νCO, coord CtO), 1733
(νCO, acyl-CdO), 1610 (νCN, CdN).
Synthesis of 1b-CO. 1b-NCCH3 (25 mg, 0.051 mmol) in CD2Cl2
was frozen, evacuated and exposed to an atmosphere of CO. The
mixture was kept at -78 °C and 1H NMR spectrum taken at -60 °C.
3
1H NMR (CD2Cl2): δ (ppm) 7.90 (s, 1H, imine H), 7.33 (d, JH-H
)
7.24 Hz, 1H, ArH), 7.21 (m, 3H, ArH), 7.00 (d, 3JH-H ) 7.99 Hz, 1H,
3
3
ArH), 6.43 (t, JH-H ) 7.56 Hz 1H, ArH), 3.01 (septet, 2H, JH-H
)
6.64 Hz, i-Pr CH), 1.99 (free CH3CN) 1.36 (s, 9H, t-BuH), 1.16 (d,
Synthesis of 2c-CO. 1c-NCCH3 (22 mg, 0.025 mmol) in CD2Cl2
was frozen, evacuated and exposed to an atmosphere of CO. The
mixture was kept at -78 °C and 1H NMR spectrum taken at 0 °C after
3
3
6H, JH-H ) 6.75 Hz, i-Pr CH3), 0.97 (d, 6H, JH-H ) 6.69 Hz, i-Pr
CH3), 0.06 (s, 3H, Pd-CH3). Traces of 2b-CO are also found in this
spectrum.
1
2 h. H NMR (CD2Cl2): δ (ppm) 7.95 (s, 1H, imine H), 7.60 (s, 1H,
3
Synthesis of 1c-NCCH3. The dipotassium salt of ligand c (312 mg,
0.42 mmol) and (COD)Pd(Me)Cl (111 mg, 0.42 mmol) were weighed
into a round-bottom flask in the glovebox, placed on a frit assembly,
and transferred to the vacuum line. Acetonitrile (25 mL) was condensed
onto the solids at -78 °C and the reaction was warmed to room
temperature. Upon warming, the yellow solution became turbid and
was allowed to stir for an additional 2 h. The reaction was filtered,
and the solvent was removed in vacuo. The product was isolated as a
light yellow solid, which was pure by NMR spectroscopy (320 mg,
ArH), 7.19 (m, 4H, ArH), 3.56 (crown ether), 3.31 (septet, 2H, JH-H
) 6.78 Hz, i-Pr CH), 2.67 (s, 3H, OdCCH3), 1.98 (free CH3CN), 1.36
(s, 9H, t-BuH), 1.33 (d, 6H, 3JH-H ) 6.80 Hz, i-Pr CH3), 1.10 (d, 6H,
3JH-H ) 6.83 Hz, i-Pr CH3). 13C{1H} NMR (CD2Cl2): δ (ppm) 220.63
(Pd-CO), 174.61 (Pd-COCH3), 167.69 (CdN), 163.96 (C-O), 151.36
(N-C), 139.92 (C-iPr), 138.22, 137.02, 126.39, 123.60, 123.20,
118.72, 70.19 (crown ether), 39.41 (Pd-COCH3), 34.98 (t-Bu C), 29.51
(t-Bu CH3), 28.08 (i-Pr CH), 24.90 (i-Pr CH3), 22.96 (i-Pr CH3), 2.15
(free CH3CN). IR (KBr pellets; cm-1): 2085 (νCO, coord CtO), 1724
(νCO, acyl-CdO), 1603 (νCN, CdN).
1
88% yield). H NMR (CDCl3): δ (ppm) 7.68 (s, 1H, imine H), 7.62
(s, 1H, ArH), 7.23 (s, 1H, ArH), 7.16 (m, 3H, ArH), 3.57 (1, 24H,
Synthesis of 3a. [N2,O]Li (1.5 mmol) was dissolved in acrylonitrile
(10 mL) and transferred to a solution of (COD)Pd(Me)Cl (1.5 mmol)
in acrylonitrile (5 mL) at 0 °C. The resulting suspension was stirred
for 15 h at 25 °C. After removal of all volatiles the residue was extracted
with toluene and filtered; the toluene was removed and replaced by
n-hexane. A pure reddish-purple compound was obtained by crystal-
lization at -20 and -78 °C. Yield: 74%. Mixture of diastereomers:
3
crown ether), 3.50 (septet, 2H, JH-H ) 6.81 Hz, i-Pr CH), 2.26 (s,
3H, NCCH3), 1.49 (s, 9H, t-BuH), 1.25 (d, 6H, 3JH-H ) 6.33 Hz, i-Pr
3
CH3), 1.05 (d, 6H, JH-H ) 6.99 Hz, i-Pr CH3), -0.22 (s, 3H, Pd-
CH3). 13C{1H} NMR (CDCl3): δ (ppm) 167.86 (C-O), 166.60 (Cd
N), 148.44 (N-C), 141.61 (C-iPr), 138.05, 136.48 (C-BF3), 125.80,
122.94, 118.77 (C-CdN), 117.68 (CtN), 69.94 (crown ether), 35.05
(t-Bu C), 29.86 (t-Bu CH3), 27.49 (i-Pr CH), 24.89 (i-Pr CH3), 22.70
(i-Pr CH3), 2.86 (CH3CN), -5.89 (Pd-CH3). Anal. for C38H59BF3KN2O7-
Pd: C, 52.89; H, 6.76; N, 3.09. Calcd: C, 52.52; H, 6.84; N, 3.22.
Synthesis of 1c-PMe3. PMe3 (0.078 mmol) was condensed on a
frozen THF solution (25 mL) of 1c-NCCH3 (68 mg, 0.078 mmol).
The mixture was warmed to room temperature and stirred for 2 h.
Filtration and evaporation of all the volatiles led to the isolation of
crude 1c-PMe3 as a yellow solid (48 mg, 68% yield). 1H NMR (CD2-
3
1H NMR (CDCl3): δ (ppm) 7.1-7.4 (ArH) 3.60 (septet, JH-H ) 6.7
3
Hz, i-Pr CH), 3.46 (septet, JH-H ) 6.7 Hz, i-Pr CH), 3.33 (septet,
3JH-H ) 6.7 Hz, i-Pr CH), 3.15 (septet, 3JH-H ) 6.7 Hz, i-Pr CH), 3.06
3
3
(septet, JH-H ) 6.7 Hz, i-Pr CH), 2.87 (septet, JH-H ) 6.7 Hz, i-Pr
CH), 2.14 (m, CH3CH2), 1.95 (m, CH3CH2), 1.59 (d, 3JH-H ) 6.7 Hz,
i-Pr CH3), 1.47 (d, 3JH-H ) 6.7 Hz, i-Pr CH3), 1.38 (m, CH3CH2), 1.32
3
3
(d, JH-H ) 6.7 Hz, i-Pr CH3), 1.28 (d, JH-H ) 6.7 Hz, i-Pr CH3),
1.25 (s, t-BuH), 1.24 (s, t-BuH), 1.23 (s, t-BuH), 1.22 (s, t-BuH), 1.19
(s, t-BuH), 1.14 (s, t-BuH), 1.11 (d, JH-H ) 6.7 Hz, i-Pr CH3), 1.00
3
3
Cl2): δ (ppm) 7.89 (d, JH-P ) 12.33 Hz, 1H, imine H), 7.46 (s, 1H,
3
ArH), 7.18 (m, 3H, ArH), 7.06 (s, 1H, ArH), 3.55 (s, crown ether),
(t, JH-H ) 5.4 Hz, CH3), 0.91 (dd, CHCN), 0.88 (dd, CHCN), 0.61
3.30 (m, 2H, i-Pr CH), 1.44 (d, 2JH-P ) 10.24 Hz, 9H, PCH3), 1.42 (s,
(dd, CHCN), 0.42 (t, JH-H ) 5.4 Hz, CH3). MS (FD)[%] (toluene):
3
3
9H, t-BuH), 1.19 (d, 6H, JH-H ) 6.52 Hz, i-Pr CH3), 1.04 (d, 6H,
1703 [100, M+, trimer], 1137 [20, dimer], 567[20, monomer]. IR: 2235
3
3JH-H ) 6.42 Hz, i-Pr CH3), -0.48 (d, JH-P ) 2.91 Hz, 3H, Pd-
(s, νCN). UV-vis [toluene]: λmax: 501 nm; ꢀ: 56135. Anal. for
(C30H43N3OPd)n: C, 63.5; H, 7.8; N, 7.2; Calcd. C, 63.43; H, 7.63; N,
7.40.
CH3). 13C{1H} NMR (CD2Cl2): δ (ppm) 167.34 (CdN), 167.28 (C-
O), 148.27 (N-C), 141.40 (C-iPr), 138.75, 137.91, 135.99, 125.51,
122.99, 118.61 (C-CdN), 70.05 (crown ether), 35.12 (t-Bu C), 29.46
(t-Bu CH3), 27.65 (i-Pr CH), 24.83 (i-Pr CH3), 22.46 (i-Pr CH3), 15.15
Synthesis of 3a-PPh3. The oligomer Pd complex 3a (0.82 g, 0.48
mmol) was dissolved in 10 mL n-hexane at 25 °C. Triphenylphosphine
(excess) in 20 mL n-hexane was added and after 15 min a precipitate
was observed. The mixture was stirred for 15 h and the reddish-brown
precipitate was isolated by filtration and was dried in high vacuum.
Yield: 1.2 g, 86%. 1H-1H-COSY (C6D6): δ (ppm) 8.1-8.2 (m, ArH),
7.92 (s, ArH), 7.71 (s, ArH), 7.1-7.3 (m, ArH), 4.24 (septet, 1H, 3JH-H
1
2
(d, JC-P ) 31.46 Hz, PCH3), -4.59 (d, JC-P ) 14.2 Hz, Pd-CH3).
31P{1H} NMR (CD2Cl2): δ (ppm) -3.85. Anal. for (C39H65NO7PBF3-
KPd): C, 50.84; H, 6.98; N,1.51. Calcd: C, 51.80; H, 7.25; N, 1.55.
Synthesis of 1c-CO. 1c-NCCH3 (22 mg, 0.025 mmol) in CD2Cl2
was frozen, evacuated and exposed to an atmosphere of CO. The
mixture was kept at -78 °C and 1H NMR spectrum taken at -70 °C.
3
) 6.8 Hz, i-Pr CH), 3.74 (septet, 1H, JH-H ) 6.8 Hz, i-Pr CH), 2.58
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1867

A R T I C L E S
Groux et al.
3
3
(dd, 1H, JH-H ) 12.0, JH-P ) 5.0 Hz, CH2-CHCN), 1.61 (d, 6H,
29.46 (t-Bu CH3), 28.02 and 27.76 (i-Pr CH), 25.86, 24.93, 22.60 and
22.10 (i-Pr CH3), 24.93 (CH(CN)CH2), 14.59 (CH(CN)CH2CH3), 10.27
(d, 2JC-P ) 9.46 Hz, Pd-C). Anal. for (C39H59N2O7BF3KPd)n: C, 52.71;
H, 6.60; N, 3.40. Calcd: C, 53.16; H, 6.75; N, 3.18.
3JH-H ) 6.8 Hz, i-Pr CH3), 1.42 (s, 9H, t-BuH), 1.31 (d, 3H, JH-H
)
3
3
6.8 Hz, i-Pr CH3), 1.18 (d, 3H, JH-H ) 6.8 Hz, i-Pr CH3), 1.01 (m,
1H, CH3CH2), 0.94 (s, 9H, t-BuH), 0.65 (m, 1H, CH3CH2), 0.53 (t,
3H, 3JH-H ) 6.4 Hz, CH3CH2). 1H-13C-HSQC (CDCl3): δ (ppm) 154.0
(C-O), 149.5 (C-N), 142.9 (C-t-Bu), 142.5 (C-i-Pr), 141.3 (C-i-Pr),
140.7 (C-i-Pr), 136.8 (C-t-Bu), 136.2 (Ar CH., PPh3), 136.0 (Ar CH.,
PPh3), 135.8, 131.9, 131.0 (Ar CH., PPh3), 130.6, 123.9, 123.6, 35.3
(t-Bu C), 33.9 (t-Bu C), 31.2 (t-Bu CH3), 29.7 (t-Bu CH3), 29.0 (i-Pr
CH), 25.2 (i-Pr CH3), 24.9 (i-Pr CH3), 24.0 (CH-CN), 22.9 (i-Pr CH3),
22.7 (i-Pr CH3), 14.4 (CH2CHCN), 0.77 (CH3). 31P{1H} NMR
(CDCl3): δ (ppm) 30.4 ppm. IR: 2192 cm-1 (νCN). MS(FD) (tolu-
ene): M+(829, correct isotope pattern).
Synthesis of 3c-PMe3. PMe3 (0.026 mmol, 1 eq) was added to a
frozen CD2Cl2 solution of anionic oligomer mixture 3c (23 mg, 0.026
mmol). The mixture was warmed to room temperature and the NMR
1
3
tube shaken for 5 min. H NMR (CD2Cl2): δ (ppm) 7.89 (d, JH-P
)
12.85 Hz, 1H, imine H), 7.51 (s, 1H, ArH), 7.20 (m, 3H, ArH), 7.09
(s, 1H, ArH), 3.54 (s, crown ether), 3.27 (septet, 3JH-H ) 6.58 Hz 2H,
i-Pr CH), 1.62 (d, 2JH-P ) 10.64 Hz, 9H, PCH3), 1.43 (s, 9H, t-BuH),
1.38 (m, 1H, (CH(CN)CH2CH3), 1.29, 1.25, 1.07 and 0.98 (d, 12H,
3JH-H ) 6.72 Hz, i-Pr CH3), 1.22 and 1.03 (m, 2H, (CH(CN)CH2CH3),
0.34 (t, 3JH-H ) 7.04 Hz, 3H, (CH(CN)CH2CH3). 13C{1H} NMR (CD2-
Cl2): δ (ppm) 168.09 (CdN), 166.13 (C-O), 147.17 (N-C), 142.27
and 141.50 (C-iPr), 138.67 (Ar C-H), 137.81 (Ar C-tBu), 136.91
(Ar C-H), 129.32 (d, 3JC-P ) 6.03 Hz, CtN), 128.35 (C-BF3), 126.58
(Ar C-H), 123.44 (Ar C-H), 118.70 (C-CdN), 70.03 (crown ether),
35.04 (t-Bu C), 29.63 (t-Bu CH3), 28.08 and 27.87 (i-Pr CH), 25.63
and 25.16 (i-Pr CH3), 24.54 (CH(CN)CH2), 22.42 and 22.05 (i-Pr CH3),
14.30 (CH(CN)CH2CH3), 14.21 (d, 1JC-P ) 30.11 Hz, PCH3), 5.82 (d,
2JC-P ) 9.46 Hz, Pd-C). 31P{1H} NMR (CD2Cl2): δ (ppm) -5.68.
Competition Experiment (Scheme 7). d3-1b-NCCH3 (11 mg,
0.0219 mmol, 1 eq) and 1c-NCCH3 (19 mg, 0.0219 mmol, 1 eq) were
dissolved in CH2Cl2 (0.7 mL). Acrylonitrile (116 mg of a 1% w/w
CH2Cl2 solution, 0.0219 mmol, 1 eq) was then added and the NMR
tube was shaken and allowed to stand for 20 min. at room temperature.
The solution was frozen in liquid nitrogen, the tube evacuated and PMe3
was added via gas transfer (19.1 mL at 42.4 mmHg and 23 °C, 0.438
mmol, 2 eq). The mixture was warmed to room temperature and shaken
for 1-2 min. 2H and 31P NMR specta were recorded unlocked at -20
°C and referenced using naturally abundant deuterated solvent (2H) or
external H3PO4 in CD2Cl2 (31P). The experiment was repeated to confirm
the reproducibility of the results. 2H NMR (CH2Cl2): δ (ppm)
(integration first experiment, integration second experiment, assignment)
0.30 (1.00, 1.00, d3-3b-PMe3), -0.47 (1.56, 1.55, d3-1b-PMe3). 31P
NMR (CH2Cl2): δ (ppm) (integration first experiment, integration
second experiment, assignment) -3.73 (0.68, 0.85, d3-1b-PMe3), -3.89
(0.36, 0.38, 1c-PMe3), -5.29 (0.73, 0.74, d3-3b-PMe3), -5.68 (1.00,
1.00, 3c-PMe3).
Synthesis of 3b. Dry acrylonitrile (136 mg, 2.56 mmol) was added
to a stirred solution of 1b-NCCH3 (319 mg, 0.64 mmol) in THF (25
mL) at -78 °C. The solution was stirred for 2 h while warming to
room temperature. The volatiles were removed in vacuo and the sample
1
was isolated as an orange solid (305 mg, 93% yield). H NMR (CD2-
Cl2): δ (ppm) 7.59, 7.54, 7.53, 7.52, and 7.50 (5 s, imine H), 7.32-
7.15 (m, ArH), 7.00-6.89 (m, ArH), 6.45-6.30 (m, ArH), 3.73, 3.58,
3.53, 3.36, 3.36, 3.11, 3.02 (m, 3JH-H ) 6.5-6.9 Hz, i-Pr CH), 1.37 (s,
t-BuH), 1.30-0.90 (m, i-Pr CH3 and Pd-CH(CN)CH2), 0.65 (m, CH-
(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ (ppm) 166.61, 165.94,
165.85, 165.66 and 165.17 (CdN and C-O), 147.27, 147.23, 146.98
(N-C), 141.53-140.90 (C-i-Pr), 133.51-123.15 (Ar CH and CN),
119.07, 118.78, and 118.52 (C-tBu and C-CdN), 113.01, 112.93,
and 112.60 (Ar CH), 35.22 and, 35.13 (t-Bu C), 29.46-28.75 (t-Bu
CH3), 27.78-27.58 (i-Pr CH), 26.01-24.79 (i-Pr CH3), 23.43-22.13
(i-Pr CH3), 14.90-14.10 (CH3CH2CH(CN)), 10.32-8.43 (CH3CH2CH-
(CN)). Anal. for (C27H36N2OPd)n: C, 63.43; H, 7.18; N, 5.59. Calcd:
C, 63.46; H, 7.10; N, 5.48.
Synthesis of 3b-PMe3. PMe3 (0.045 mmol, 1 eq) was added to a
frozen CD2Cl2 solution of neutral oligomer mixture (23 mg, 0.045
mmol). The mixture was warmed to room temperature and the NMR
1
tube was shaken for 5 min. H NMR (CD2Cl2): δ (ppm) 7.91 (d, 1H,
3JH-P ) 12.3 Hz, imine H), 7.33 (d, 1H, 3JH-H ) 7.35 Hz, ArH), 7.22
(m, 3H, ArH), 6.97 (dd, 1H, 3JH-H ) 7.88 Hz, 4JH-H ) 1.74 Hz, ArH),
3
3
6.44 (t, 1H, JH-H ) 7.51 Hz, ArH), 3.23 (septet, 2H, JH-H ) 6.84
2
Hz, i-Pr CH), 1.63 (d, 9H, JH-P ) 10.73 Hz, PCH3), 1.41 (s, 9H,
t-BuH), 1.30, 1.26, 1.08 and 0.99 (4d, 12H, 3JH-H ) 6.88 Hz, i-Pr CH3),
1.45 (m, 1H, (CH(CN)CH2CH3), 1.22 and 1.05 (m, 2H, (CH(CN)CH2-
CH3), 0.35 (t, 3H, 3JH-H ) 7.10 Hz, (CH(CN)CH2CH3). 13C{1H} NMR
(CD2Cl2): δ (ppm) 167.51 (CdN), 167.05 (C-O), 146.70 (N-C),
142.03 and 141.28 (C-i-Pr), 140.53 (Ar C-tBu), 135.54 (Ar C-H),
NMR Tube Reactions of 1-NCCH3 with Acrylonitrile. 1a-NCCH3
(20 mg) was dissolved at -78 °C in CD2Cl2 (650 µL). Acrylonitrile
was then transferred to the NMR tube (1-20 eq) and the tube
transferred to a pre-cooled NMR probe. Several 1H NMR-experiments
have been carried out for complex 1a-NCCH3 at different temperatures
in CD2Cl2 to examine the exchange of acetonitrile by acrylonitrile and
insertion of acrylonitrile into Pd-Me. The exchange of acetonitrile by
acrylonitrile (AN) was monitored by observing the signals of coordi-
3
132.24 (Ar C-H), 128.91 (d, JC-P ) 6.23 Hz, CtN), 126.97 (Ar
C-H), 123.65 (Ar C-H), 119.46 (C-CdN), 112.97 (Ar C-H), 35.19
(t-Bu C), 29.29 (t-Bu CH3), 28.14 and 27.99 (i-Pr CH), 25.53 and 25.09
(i-Pr CH3), 24.55 (d, 3JC-P ) 2.90 Hz, CH(CN)CH2), 22.42 and 22.08
1
nated AN and free AN.43 Free AN at -30 °C: H NMR (CD2Cl2): δ
(i-Pr CH3), 14.26 (CH(CN)CH2CH3), 14.17 (d, JC-P ) 30.76 Hz,
1
PCH3), 6.05 (d, JC-P ) 8.92 Hz, Pd-C). 31P{1H} NMR (CD2Cl2): δ
2
(ppm) 6.33 (d, 3JHH ) 17.9 Hz, 1 H, CH2), 6.18 (d, 3JHH ) 11.9 Hz, 1
H, CH2), 5.77 (dd, 3JH-H ) 17.9, 11.9 Hz, 1 H, CHCN). 13C{1H} NMR
(CD2Cl2): δ (ppm) 130.1 (CH2), 117.1 (CHCN), 107.3 (CHCN).
N-Coordinated AN at -30 °C: 1H NMR (CD2Cl2): δ (ppm) 6.58 (d,
3JH-H ) 17.9 Hz, 1H, CH2), 6.45 (d, 3JH-H ) 12.1 Hz, 1H, CH2), 5.97
(ppm) -5.29.
Synthesis of 3c. Dry acrylonitrile (38.3 g, 0.72 mmol) was added
to a stirred solution of 1c-NCCH3 (157 mg, 0.18 mmol) in THF (25
mL) at -78 °C. The solution was stirred for 2 h during which room
temperature was reached. All the volatiles were then removed in Vacuo
and the sample was isolated as an orange solid (122 mg, 77% yield).
1H NMR (CD2Cl2): δ (ppm) 7.49 and 7.47 (s, imine H), 7.42 - 7.12
3
(dd, JH-H ) 17.9, 12.1 Hz, 1H, CHCN). 13C{1H} NMR (CD2Cl2): δ
(ppm) 142.2 (CH2), 106.0 (CHCN), 119.1 (CHCN). During the
exchange proton signals of free acetonitrile at 2.0 ppm have been
observed. For comparison in 1a-NCCH3 at -30 C: 1H NMR (CD2-
Cl2): δ (ppm) 2.35 (CH3CN). No insertion reaction was observed in
CD2Cl2 at -30 °C when a ratio of AN: 1a-NCCH3 ) 20 was used.
Upon warming to higher temperatures, the disappearance of 1a-n-AN
was monitored over time by observing the decrease of the Pd-Me signal
intensity at 0.0 ppm. Similar reactions were studied with 1b-NCCH3
3
(m, ArH), 7.07 (s, ArH), 3.52 (s, crown ether), 3.26 (t, JH-H ) 6.65
Hz, i-Pr CH), 3.20-2.80 (m, i-Pr CH), 1.33 (s, t-BuH), 1.26, 1.22,
1.04 and 0.95 (m, i-Pr CH3), 1.30 and 1.18 (m, CH(CN)CH2CH3), 0.97
and 0.84 (t, 3JH-H ) 6.80 Hz, CH(CN)CH2CH3), 0.53 (t, 3JH-H ) 7.08
Hz, CH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ (ppm) 165.69 (Cd
N), 164.92 (C-O), 147.03 (N-C), 141.85 and 141.60 (C-iPr), 138.05
(Ar C-tBu), 137.09 (Ar C-H), 136.93 (Ar C-H), 133.84 (C-BF3),
129.01 and 128.38 (CtN), 127.06 (Ar C-H), 123.69 (Ar C-H), 123.48
(Ar C-H), 117.88 (C-CdN), 70.02 (crown ether), 34.94 (t-Bu C),
(43) Rosenblum, M.; Turnbull, M. M., Begum, M. K. J. Organomet. Chem.
1987, 321, 67.
9
1868 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Insertion of Acrylonitrile into Palladium Methyl Bonds
A R T I C L E S
(12 mg, 1-190 eq AN, total volume: 700 µL) and with 1c-NCCH3
(21 mg, 1-100 eq AN, total volume: 700 µL). Below -30 °C, the
acetonitrile ligand is completely replaced by N-bound AN when more
20 eq of AN, or more, are present in solution to form 1b-n-AN and
1c-n-AN, respectively, whereas insertion into the Pd-Me bound is
observed above -30 °C.
Kinetic Studies of AN Insertion in the Pd-Me Bond: Complex
1b-NCCH3 or 1c-NCCH3 (0.024 mmol. 12 and 21 mg respectively)
was dissolved in CD2Cl2 at -78 °C. A CD2Cl2 solution of acrylonitrile
(1 to 190 eq) was then syringed to the NMR tube (total volume: 700
µL) and the tube transferred to a NMR probe set at different temperature
from -22.8 to +9.8 °C. The temperature in the probe was measured
accurately using a thermocouple device. Disappearance of the total [Pd-
Me], which include 1-n-AN as well as a new species identified as 4-n-
AN, was used to monitor the reaction at set temperatures and amounts
of AN. The obtained kobs are listed in Table 4.
1b-n-AN at -60°C 1H NMR (CD2Cl2): δ (ppm) 7.66 (s, 1H, imine
3
H), 7.23 (d, JH-H ) 7.0 Hz, 1H, ArH), 7.14 (m, 3H, ArH), 6.92 (d,
3
3JH-H ) 7.0 Hz, 1H, ArH), 6.47 (d, JH-H ) 17.8 Hz, 1H, n-bound
3
3
AN), 6.29 (d, JH-H ) 12.6 Hz, 1H, n-bound AN), 6.23 (d, JH-H
)
18.5 Hz, free AN), 6.09 (d, 3JH-H ) 13.0 Hz, free AN), 5.97 (dd, 3JH-H
) 17.8, 12.6 Hz, 1H, n-bound AN), 5.77 (dd, JH-H ) 17.9, 11.9 Hz,
free AN), 3.23 (septet, JH-H ) 6.58 Hz, 2H, i-Pr CH), 1.99 (s, 3H,
3
3
Acknowledgment. This paper is dedicated to Professor John
E. Bercaw on the occasion of his 60th birthday. Funding for
this work was provided by Bayer Polymers (Leverkusen). The
authors thank Prof. Richard Jordan (Chicago) for stimulating
discussions and for sharing unpublished work prior to publica-
tion; we also thank Dr. Miklos Szabo (University of Calgary)
for his insights. T. W. would like to thank Dr. Matthias Jank
and Dr. Joachim Wesener for technical support and helpful
discussions concerning NMR and MS measurements. L.F.G.
would like to thank the Natural Science and Engineering
Research Council of Canada and the Alberta Ingenuity Fund
for postdoctoral fellowships and Prof. Hans Vogel and Dr. Dean
McIntyre (Biological Sciences, University of Calgary) for the
use of their 400 MHz NMR spectrometer and technical
assistance with the kinetic experiments.
free CH3CN), 1.36 (s, 9H, t-BuH), 1.19 and 0.97 (d, 3JH-H ) 6.52 Hz,
6H, i-Pr CH3), -0.25 (s, 3H, Pd-Me). 13C{1H} NMR (CD2Cl2): δ
(ppm) 167.17 (CdN), 165.53 (C-O), 146.85 (N-C), 142.02 (n-bound
AN), 140.60 (C-iPr), 140.15 (Ar C-H), 138.26 (free AN), 137.81
(Ar C-tBu), 136.86 (Ar C-H), 134.48 (Ar C-H), 126.27 (Ar C-H),
123.10 (Ar C-H), 118.66 (Pd-NC), 117.94 (free CH3CN), 117.46 (free
AN), 111.91 (C-CdN), 107.27 (free AN), 106.21 (Pd-NCC), 35.01
(t-Bu C), 28.66 (t-Bu CH3), 27.38 (i-Pr CH), 24.62 and 22.15 (i-Pr
CH3), 2.28 (free CH3CN), -4.87 (Pd-C).
1c-n-AN at -60°C 1H NMR (CD2Cl2): δ (ppm) 7.62 (s, 1H, imine
H), 7.42 (s, 1H, ArH), 7.14 (m, 4H, ArH), 7.05 (s, 1H, ArH), 6.47 (d,
3
3JH-H ) 17.4 Hz, 1H, n-bound AN), 6.34 (d, JH-H ) 12.6 Hz, 1H,
3
3
n-bound AN), 6.23 (d, JH-H ) 18.3 Hz, free AN), 6.09 (d, JH-H
)
13.0 Hz, free AN), 5.97 (dd, 3JH-H ) 17.4, 12.6 Hz, 1H, n-bound AN),
5.77 (dd, JH-H ) 18.3, 11.9 Hz, free AN), 3.52 (crownether), 3.29
(septet, JH-H ) 6.68 Hz, 2H, i-Pr CH), 1.99 (s, 3H, free CH3CN),
3
3
1.39 (s, 9H, t-BuH), 1.20 and 1.04 (d, 3JH-H ) 6.62 Hz, 6H, i-Pr CH3),
-0.30 (s, 3H, Pd-Me). 13C{1H} NMR (CD2Cl2): δ (ppm) 166.80 (Cd
N), 166.16 (C-O), 147.52 (N-C), 141.72 (n-bound AN), 141.18 (C-
iPr), 138.19 (free AN), 137.44 (Ar C-tBu), 136.10 (Ar C-H), 128.50
(Ar C-H), 123.02 (Ar C-H), 118.10 (Pd-NC), 117.75 (free CH3CN),
117.42 (free AN), 108.20 (C-CdN), 107.36 (free AN), 106.66 (Pd-
NCC), 69.95 (crownether), 34.98 (t-Bu C), 29.24 (t-Bu CH3), 27.78
(i-Pr CH), 24.76 and 22.30 (i-Pr CH3), 2.29 (free CH3CN), -5.34 (Pd-
C).
Supporting Information Available: ORTEP diagrams for the
structurally characterized compounds (borate bearing ligand, 1a-
NCCH
3, 1b-NCCH3, 1c-PMe3, and 3a, 5 pages, print/PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA044119+
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1869