Acrylonitrile insertion reactions of cationic palladium alkyl complexes

Article abstract of DOI:10.1021/ja044122t

The reactions of acrylonitrile (AN) with L₂PdMe ⁺ species were investigated; (L₂ = CH ₂(N-Me-imidazol-2-yl)₂ (a, bim), (p-tolyl) ₃CCH(N-Me-imidazol-2-yl)₂ (b, Tbim), CH ₂(5-Me-2-pyridyl)₂ (c, CH₂py′ ₂), 4,4′-Me₂-2,2′-bipyridine (d), 4,4′-^tBu₂-2,2′-bipyridine (e), (2,6- ⁱPr₂-C₆H₃)N=CMeCMe=N(2,6- ⁱPr₂-C₆H₃) (f)). [L ₂PdMe(NMe₂Ph)][B(C₆F₅)₄] (2a-c) and [{L₂PdMe}₂(μ-Cl)][B(C₆F ₅)₄] (2d-f) react with AN to form N-bound adducts L ₂Pd(Me)(NCCH=CH₂)⁺ (3a-f). 3a-e undergo 2,1 insertion to yield L₂Pd{CH(CN)Et}⁺, which form aggregates [L₂Pd{CH(CN)Et}]_nⁿ⁺ (n = 1-3, 4a-e) in which the Pd units are proposed to be linked by PdCHEtCN - Pd bridges. 3f does not insert AN at 23°C. 4a-e were characterized by NMR, ESI-MS, IR and derivatization to L₂Pd{CH(CN)Et}(PR₃)⁺ (R = Ph (5a-e), Me (6a-c)). 4a,b react with CO to form L₂Pd{CH(CN)Et}(CO) ⁺ (7a,b). 7a reacts with CO by slow reversible insertion to yield (bim)Pd{C(=O)CH-(CN)Et}(CO)⁺ (8a). 4a-e do not react with ethylene. (Tbim)PdMe⁺ coordinates AN more weakly than ethylene, and AN insertion of 3b is slower than ethylene insertion of (Tbim)Pd(Me)(CH ₂=CH₂)⁺ (10b). These results show that most important obstacles to insertion polymerization or copolymerization of AN using L₂PdR⁺ catalysts are the tendency of L ₂Pd{CH(CN)CH₂R}⁺ species to aggregate, which competes with monomer coordination, and the low insertion reactivity of L ₂Pd{CH(CN)CH₂R}(substrate)⁺ species.

Full text of DOI:10.1021/ja044122t

Published on Web 01/25/2005
Acrylonitrile Insertion Reactions of Cationic Palladium Alkyl
Complexes
Fan Wu, Stephen R. Foley, Christopher T. Burns, and Richard F. Jordan*
Contribution from the Department of Chemistry, The UniVersity of Chicago,
5735 South Ellis AVenue, Chicago, Illinois, 60637
Received September 27, 2004; E-mail: rfjordan@uchicago.edu
Abstract: The reactions of acrylonitrile (AN) with “L2PdMe+” species were investigated; (L2 ) CH2(N-Me-
imidazol-2-yl)2 (a, bim), (p-tolyl)3CCH(N-Me-imidazol-2-yl)2 (b, Tbim), CH2(5-Me-2-pyridyl)2 (c, CH2py′2),
4,4′-Me2-2,2′-bipyridine (d), 4,4′-tBu2-2,2′-bipyridine (e), (2,6-iPr2-C6H3)NdCMeCMedN(2,6-iPr2-C6H3) (f)).
[L2PdMe(NMe2Ph)][B(C6F5)4] (2a-c) and [{L2PdMe}2(µ-Cl)][B(C6F5)4] (2d-f) react with AN to form N-bound
adducts L2Pd(Me)(NCCHdCH2)+ (3a-f). 3a-e undergo 2,1 insertion to yield L2Pd{CH(CN)Et}+, which
form aggregates [L2Pd{CH(CN)Et}]nn+ (n ) 1-3, 4a-e) in which the Pd units are proposed to be linked by
PdCHEtCN- - -Pd bridges. 3f does not insert AN at 23 °C. 4a-e were characterized by NMR, ESI-MS, IR
and derivatization to L2Pd{CH(CN)Et}(PR3)+ (R ) Ph (5a-e), Me (6a-c)). 4a,b react with CO to form
L2Pd{CH(CN)Et}(CO)+ (7a,b). 7a reacts with CO by slow reversible insertion to yield (bim)Pd{C(dO)CH-
(CN)Et}(CO)+ (8a). 4a-e do not react with ethylene. (Tbim)PdMe+ coordinates AN more weakly than
ethylene, and AN insertion of 3b is slower than ethylene insertion of (Tbim)Pd(Me)(CH2dCH2)+ (10b).
These results show that most important obstacles to insertion polymerization or copolymerization of AN
using L2PdR+ catalysts are the tendency of L2Pd{CH(CN)CH2R}+ species to aggregate, which competes
with monomer coordination, and the low insertion reactivity of L2Pd{CH(CN)CH2R}(substrate)+ species.
Scheme 1
Introduction
Acrylonitrile (AN) homopolymers and copolymers and their
derivatives possess unique properties that are exploited in acrylic
fibers, nitrile rubbers, and other applications.1 Polyacrylonitrile
(PAN) and ethylene/AN copolymers are prepared commercially
by radical polymerization, and PAN can also be prepared by
anionic polymerization. The synthesis of AN polymers by
insertion polymerization using metal catalysts is an attractive
goal, because, as in conventional olefin polymerization, tuning
of the catalyst structure may enable greater control over polymer
structures and properties than is possible with radical or anionic
polymerization.2,3
A general scheme for the possible insertion polymerization
or copolymerization of AN is shown in Scheme 1. Several
challenges are immediately apparent. First, AN can coordinate
to metals through either the CN group or the CdC unit, or by
several bridging modes.4-6 Insertion polymerization catalysts
(1) (a) Acrylonitrile and Acrylonitrile Polymers. In Kirk-Othmer Encyclopedia
of Chemical Technology, 3rd ed.; Wiley & Sons: New York, 1983; Vol.
1, pp 414-456. (b) Kirk-Othmer Encyclopedia of Chemical Technology
Home Page. http://www.mrw.interscience.wiley.com/kirk/ (accessed June
2003). (c) Alger, M. Polymer Science Dictionary, 2nd ed.; Chapman Hall:
New York, 1997; pp 6-7.
(2) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479.
(3) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100, 1169.
(4) For representative N-bound AN complexes, see: (a) Albietz, P. J., Jr.; Yang,
K.; Lachicotte, R. J.; Eisenberg, R. Organometallics 2000, 19, 3543. (b)
Yang, Z.; Ebihara, M.; Kawamura, T. J. Mol. Catal. A: Chemical 2000,
158, 509. (c) Chin, C. K.; Chong, D.; Lee, S.; Park, Y. J. Organometallics,
2000, 19, 4043. (d) Davidson, J. L.; Ritchtzenhein, H.; Thiebaut, B. J. S.;
Landskron, K.; Rosair, G. M. J. Organomet. Chem. 1999, 592, 168. (e)
Fischer H.; Roth, G.; Reindl, D.; Troll, C. J. Organomet. Chem. 1993,
454, 133.
normally contain high valent, poor-back-bonding metal centers,
for which the N-bound mode will be favored. For example, an
N-bound AN ligand is present in the platinum R-diimine
complex (ArNdCHCHdNAr)Pt(Me)(NCCHdCH2)+ (Ar )
2-OSiiPr3-6-Me-C6H3),4a which is an analogue of the
classic {(2,6-iPr2-C6H3)NdCMeCMedN(2,6-iPr2-C6H3)}-
PdMe(L)+ catalyst.7 The requirement for N/π isomerization will
increase the overall insertion barrier in such cases. N/π-
9
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J. AM. CHEM. SOC. 2005, 127, 1841-1853
1841

A R T I C L E S
Wu et al.
isomerization was observed for CpFe(CO)2(AN)+.8 Nitriles are
known to inhibit ethylene polymerization by R-diimine cata-
lysts.3
Assuming that the CdC π complex can be accessed, AN
insertion can occur with either 1,2 or 2,1 regiochemistry to yield
LnMCH2CH(CN)R or LnMCH(CN)CH2R products, respectively.
Several examples of 2,1 AN insertion into LnM-H bonds are
known.9 For example, (Me2NCS2)Pd(PEt3)H reacts with AN at
low temperature to yield (Me2NCS2)Pd(PEt3){CH(CN)Me}.9a
Several examples of net 1,2 additions of LnM-H species to
the CdC bond of AN have been reported, which are believed
to proceed by radical mechanisms.10 Examples of net 2,1 AN
insertion into Pt-amido and Pt-phosphido bonds have also been
reported.11 AN insertions into metal-alkyl bonds have been
proposed as key steps in Ru-catalyzed AN dimerization, metal-
mediated coupling reactions involving AN, and other reactions,
but have not been directly observed to date.12
Figure 1. Ancillary ligands (L2) used in this work and νCO values (in cm-1
)
for the terminal CO ligands in the corresponding L2Pd{CdO)Me}(CO)+
complexes.
polymerization mechanism is either anionic or radical, few
systems have been studied in detail. For example, Cy3PCuMe
and (bipy)2FeEt2 each initiate the anionic polymerization of
AN.13j-o The major initiator in AN polymerization by Cy3-
Numerous metal complexes have been reported to polymerize
AN.13 While it is likely that in most of these cases the
PCuMe is PCy3, which is liberated from the Cu complex.14a
A
(5) For representative CdC-π-bonded AN complexes see (a) R´ıo, I. D.;
Gossage, R. A.; Hannu, M. S.; Lutz, M.; Spek, A. L.; Koten, G. V.
Organometallics 1999, 18, 1097. (b) Maekawa, M.; Munakata, M.; Kuroda-
Sowa, T.; Hachiya, K. Inorg. Chim. Acta 1994, 227, 137. (c) Felice, V.
D.; Albano, V. G.; Castellari, C.; Cucciolito, M. E.; Renzi, A. D. J.
Organomet. Chem. 1991, 403, 269. (d) Albano, V. G.; Castellari, C.;
Cucciolito, M. E.; Panunzi, A.; Vitagliano, A. Organometallics 1990, 9,
1269. (e) Tolman, C. A.; Seidel, W. C. J. Am. Chem. Soc. 1974, 96, 2774.
(6) Bryan, S. J.; Huggett, P. G.; Wade, K.; Daniels, J. A.; Jennings, J. R. Coord.
Chem. ReV. 1982, 44, 149.
transient iron hydride complex formed by â-H elimination of
(bipy)2FeEt2 was proposed to initiate AN polymerization by
(bipy)2FeEt2.14a Evidence for radical polymerization of AN by
(bipy)2FeEt2 has also been reported.14b
To identify and understand the chemical issues that underlie
the challenge of achieving metal-mediated AN insertion po-
lymerization, we are investigating the reactions of single-site
olefin polymerization catalysts with this substrate. Here we
describe studies of the reactions of representative cationic Pd-
(II) ethylene dimerization and polymerization catalysts with AN.
Parallel studies of the reactions of neutral and anionic Pd(II)
alkyl complexes with AN by Piers and co-workers are described
in a companion paper.15
(7) (a) Brookhart, M.; Leatherman, M. D.; Liu, W.; Williams, B. S. Polym.
Mater. Sci. Eng. 2004, 90, 79. (b) Shultz, L. H.; Tempel, D. J.; Brookhart,
M. J. Am. Chem. Soc. 2001, 123, 11539. (c) Gottfried, A. C.; Brookhart,
M. Macromolecules 2001, 34, 1140. (d) Tempel, D. J.; Johnson, L. K.;
Huff, R. L.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2000, 122,
6686. (e) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414.
(8) Rosenblum, M.; Turnbull, M. M.; Begum, M. K. J. Organomet. Chem.
1987, 321, 67.
(9) (a) Reger, D. L.; Garza, D. G. Organometallics 1993, 12, 554. (b) Herberich,
G. E.; Barlage, W.; Linn, K. J. Organomet. Chem. 1991, 414, 193. (c)
Deshpande, S. S.; Gopinathan, S.; Gopinathan, C. J. Organomet. Chem.
1989, 378, 103. (d) Gopinathan, S.; Unni, I. R.; Gopinathan, C. Polyhedron
1986, 5, 1921. (e) Otsuka, S.; Nakamura, A. J. Am. Chem. Soc. 1972, 94,
1886.
Results
+
Choice of Probe Complexes. Six representative “L2PdCH3
”
(10) (a) Anderson, D. J.; Eisenberg, R. Organometallics 1996, 15, 1697. (b)
Baddley, W. H.; Fraser, M. S. J. Am. Chem. Soc. 1969, 91, 3661. (c)
Lemsink, A. J.; Noltes, J. G. Tetrahedron Lett. 1966, 335.
(11) (a) Seul, J. M.; Park, S. J. Chem. Soc., Dalton Trans. 2002, 6, 1153. (b)
Park, S. Bull. Korean Chem. Soc. 2001, 22, 15. (c) Wicht, D. K.; Kovacik,
I.; Glueck, D. S.; Liable-Sands, L. M.; Incarvito, C. D.; Rheingold, A. L.
Organometallics 1999, 18, 5141. (d) Wicht, D. K.; Kourkine, I. V.; Lew,
B. M.; Nthenge, J. M.; Glueck, D. S. J. Am. Chem. Soc. 1997, 119, 5039.
(e) Cowan, R. L.; Trogler, W. C. J. Am. Chem. Soc. 1989, 111, 4750. (f)
Cowan, R. L.; Trogler, W. C. Organometallics 1987, 6, 2451.
catalysts, which contain the bidentate nitrogen L2 ligands a-f
in Figure 1, were studied in this work.16 Cationic “L2PdMe+”
species were generated as [L2PdMe(NMe2Ph)][B(C6F5)4] (2a-
c) or [{L2PdMe}2(µ-Cl)][B(C6F5)4] (2d-f) complexes as de-
scribed below. Ligands a-f were chosen to enable investigation
of how the electronic and steric properties of L2PdMe+ species
influence their reactivity with AN. The electrophilic character
of L2PdMe+ species is expected to vary in the order a,b < c,d,e
< f, based on the νCO values for the terminal CO ligands in the
corresponding L2Pd{C(dO)Me}(CO)+ complexes, which are
listed in Figure 1.17 Ligands b and f are sterically bulky while
a and c-e are not. L2PdMe(ethylene)+ species based on these
ligands catalyze the dimerization (a, c-e) or polymerization
(b, f) of ethylene.7,17 The ethylene insertion rates of L2PdMe-
(ethylene)+ species increase with increasing steric crowding and
electrophilic character at Pd (a < b < c , f).7,17
(12) (a) Yi, C. S.; Torres-Lubian, J. R.; Liu, N.; Rheingold, A. L.; Guzei, I. A.
Organometallics 1998, 17, 1257. (b) Depree, G. J.; Main, L.; Nicholson,
B. K. J. Organomet. Chem. 1998, 155, 281. (c) Janecki, T.; Pauson, P. L.;
Pietrzykowski, A. J. Organomet. Chem. 1987, 325, 247. (d) Bryndza, H.
E.; Calabrese, J. C.; Wreford, S. S. Organometallics 1984, 3, 1603. (e)
Healy, K. P.; Pletcher, D. J. Organomet. Chem. 1978, 161, 109. (f) Cooke,
M. P., Jr.; Parlman, R. M. J. Am. Chem. Soc. 1977, 99, 5222. (g) Otsuka,
S.; Nakamura, A.; Yoshida, T.; Naruto, M.; Ataka, K. J. Am. Chem. Soc.
1973, 95, 3180. (h) Fukuoka, A.; Nagano, T.; Furuta, S.; Yoshizawa, M.;
Hirano, M.; Komiya, S. Bull. Chem. Soc. Jpn. 1998, 71, 1409.
(13) (a) Jenkins, A. D.; Lappert, M. F.; Srivastava, R. C. Polymer Lett. 1968,
6, 865. (b) Saegusa, T.; Horiguchi, S.; Tsuda, T. Macromolecules 1975, 8,
112. (c) Gandhi, V. G.; Sivaram, S.; Bhardwaj, I. S. J. Macromol. Sci.,
Chem. 1983, A19, 147. (d) Billingham, N. C.; Lees, P. D. Makromol. Chem.
1993, 194, 1445. (e) Tsuchhara, K.; Suzuki, Y.; Asai, M.; Soga, K. Chem.
Lett. 1999, 891. (f) Siemeling, U.; Ko¨lling, L.; Stammler, A.; Stammler,
H.-G.; Kaminski E.; Fink, G. Chem. Commun. 2001, 1177. (g) Suh, M. P.;
Oh, Y.; Kwak, C. Organometallics 1987, 6, 411. (h) Mudalige, D. C.;
Rempel, G. L. J. Macromol. Sci., Chem. 1997, A34, 361. (i) Arndt, S.;
Beckerle, K.; Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. J. Mol. Catal. A:
Chem. 2002, 190, 215. (j) Yamamoto, A.; Ikeda, S. J. Am. Chem. Soc.
1967, 89, 5989. (k) Ikariya, T.; Yamamoto, A. J. Organomet. Chem. 1974,
72, 145. (l) Miyashita, A.; Yamamoto, T.; Yamamoto, A. Bull. Chem. Soc.
Jpn. 1977, 50, 1109. (m) Yamamoto, T.; Yamamoto, A.; Ikeda, S. Bull.
Chem. Soc. Jpn. 1972, 45, 1111. (n) Yamamoto, T.; Yamamoto, A.; Ikeda,
S. Bull. Chem. Soc. Jpn. 1972, 45, 1104. (o) Yamamoto, A. J. Chem. Soc.,
Dalton Trans. 1999, 7, 1027.
(14) (a) Schaper, F.; Foley, S. R.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
2114. (b) Yang, P.; Chan, B. C. K., Baird, M. C. Organometallics 2004,
23, 2752.
(15) Groux, L. F.; Weiss, T.; Reddy, D. N.; Chase, P. A.; Piers, W. E.; Ziegler,
T.; Parvez, M.; Benet-Buchholz, J. J. Am. Chem. Soc. 2005, 127, 1854.
(16) L2 ) CH2(N-Me-imidazol-2-yl)2 (a, bim), (p-tolyl)3CCH(N-Me-imidazol-
2-yl)2 (b, Tbim), CH2(5-Me-2-pyridyl)2 (c, CH2py′2), 4, 4′-Me2-2, 2′-
t
bipyridine (d, Me2bipy), 4, 4′-tBu2-2, 2′-bipyridine (e, Bu2bipy), and (2,
6-iPr2-C6H3)NdCMeCMedN(2, 6-iPr2-C6H3) (f, 2, 6-iPr2-diimine).
(17) Burns, C. T.; Jordan, R. F. Abstracts of Papers, 224th ACS National
Meeting, Boston, 2002, INOR-322.
9
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Acrylonitrile Insertion of Palladium Alkyl Complexes
A R T I C L E S
Generation of L2PdMe(NMe2Ph)+ and [{L2PdMe}2(µ-
Cl)]+ Species. The reaction of L2PdMe2 (1a-c) with [HNMe2-
Ph][B(C6F5)4] quantitatively generates L2PdMe(NMe2Ph)+ (2a-
c) and methane within 10 min at -78 °C (eq 1). The NMR
spectra of 2a-c show the presence of an unsymmetrical L2
ligand and a NMe2Ph ligand. Complexes 2a-c are stable at
-40 °C in CD2Cl2 but decompose to Pd0 at 23 °C (significant
Pd0 observed within 10 min).
Scheme 2
) 18, 12; 1H, Hint), ca. 0.3 ppm downfield from the corre-
sponding free AN resonances. The 13C NMR AN resonances
of 3a appear at δ 143.0 (Cter), 119.2 (CN) and 105.7 (Cint),
within 5 ppm of the corresponding free AN positions. Addition-
ally, the IR VCN values of two representative examples, 3a (2244
cm-1) and 3d (2247 cm-1) are ca. 15 cm-1 higher than that for
free AN (2230 cm-1). These data are similar to data for known
N-bound AN complexes, such as (C5Me5)Ir(η3-CHPhCHCH2)-
(NCCdCH2)+ (1H NMR: δ 6.56-6.35 (m); 13C NMR δ 143.4
(Cter), 120.4 (CN) and 106.2 (Cint); VCN 2259 cm-1), which was
characterized by X-ray diffraction.4c,6 In contrast, for CdC
π-bound AN complexes, the 1H and 13C NMR AN resonances
are normally shifted far upfield, and VCN is decreased, compared
to the free AN values.5,6 Therefore, it is clear that 3a-f contain
N-bound AN ligands. The presence of AN was confirmed by
the ESI mass spectra of 3d and 3f, in which the L2Pd(Me)-
(AN)+ ions are the major cations observed.
The chloride complexes L2PdMeCl (1d-f) were used as
precursors to L2PdMe+ species because they are more stable
than the corresponding L2PdMe2 compounds. The reaction of
1d-f with 0.5 equiv of [Li(Et2O)2.8][B(C6F5)4] yields dinuclear
[{L2PdMe}2(µ-Cl)]+ complexes 2d-f quantitatively (eq 2).7d,18
Complexes 2d-f are stable at 23 °C for several hours.
Acrylonitrile Insertion of 3a-e and Generation of [L2Pd-
n+
{CH(CN)Et}]n Species (4a-e). Complexes 3a-e undergo
2,1 insertion of the AN CdC bond at 23 °C to afford L2Pd-
{CH(CN)Et}+ products, which are formed as mixtures of [L2-
n+
1
Pd{CH(CN)Et}]n aggregate species (4a-e, Scheme 2). H
NMR monitoring experiments show that 3a-e are completely
consumed but no free AN is consumed in this reaction. No
intermediates in the conversion 3a-e to 4a-e were observed
by NMR. In contrast, 3f is stable at 23 °C for several days, and
there is no evidence for AN insertion in this case under these
conditions. The qualitative rates of AN insertion of 3a-e to
yield 4a-e, as assessed by NMR monitoring of the disappear-
ance of the Pd-Me resonance at 23 °C, vary in the order: 3b
(t1/2 ca. 6 min) > 3a (t1/2 ca. 1.5 h), 3c,d (t1/2 ca. 4 h) > 3f (no
reaction).
The NMR spectra of 4a-e are complex and show that several
Generation of N-Bound L2Pd(Me)(NCCHdCH2)+ Com-
plexes (3a-f). Addition of excess AN to 2a-c results in
quantitative displacement of NMe2Ph and formation of L2Pd-
(Me)(NCCHdCH2)+ complexes (3a-c, eq 1). 2a and 2c react
with AN at -60 °C within 5 min. In contrast, 2b requires a
higher temperature (-30 °C) and longer reaction time (30 min)
for complete displacement to occur due to the presence of the
bulky apical C(p-tolyl)3 substituent, which retards associative
substitution processes. Similarly, AN adducts 3d-f are gener-
ated quantitatively (5 min, 23 °C) by reaction of 2d-f with
excess AN in the presence of 0.5 equiv [Li(Et2O)2.8][B(C6F5)4]
(eq 2).
chemically inequivalent [L2PdCH(CN)Et]+ units are present in
1
each case. For example, the H NMR spectrum of 4a contains
three major sets of bim resonances implying the presence of
three inequivalent unsymmetrical (bim)Pd environments. This
spectrum also contains multiplets at δ 2.49 (1H), 2.22-1.78
(2H), 1.24-1.15 (3H) consistent with the presence of several
inequivalent -CH(CN)Et units. The ESI mass spectra of several
n+
examples (4a-c) show the presence of [L2Pd{CH(CN)Et}]n
ions (n ) 1-3). For example, three major cations are observed
in the ESI-MS of 4a, with molecular weights and isotope
patterns corresponding to (bim)Pd{CH(CN)Et}+, [(bim)Pd{CH-
(CN)Et}]22+ and {[(bim)Pd{CH(CN)Et}]33+[B(C6F5)4-]}. While
the detailed structures of 4a-e have not been established, it is
likely that the Pd units are linked by µ2-C,N-PdCHEtCN- - -
Pd bridges. The IR VCN bands for two representative cases, 4a
(2246 cm-1) and 4d (2249 cm-1), appear at slightly higher
frequency than those of free nitriles (e.g., CH3CH(CN)Et, 2238
1
The H and 13C NMR AN resonances of 3a-f are only
slightly shifted from the free AN positions. For example, the
1H NMR AN resonances for 3a (-60 °C) appear at δ 6.55 (d,
J ) 18, 1H, Htrans), 6.43 (d, J ) 12, 1H, Hcis) and 5.93 (dd, J
(18) Shen, H.; Jordan, R. F. Organometallics 2003, 22, 1878.
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A R T I C L E S
Wu et al.
cm-1).19 These values are similar to VCN values for the µ2-C,N
R-cyanoalkyl complexes [Pd2(C6F5)4{µ2-C,N-CHXCN}2]2- (X
) CN, 2250 cm-1; X ) CO2Me, 2240 cm-1).20 The VCN values
in such systems reflect the compensating effects of the presence
cm-1, ca. 56 cm-1 below the values for 4a,d. These VCN values
are similar to those for other complexes containing nonbridging
MCR2CN units,9,11,23 such as (bipy)Pd(CH2CN)2 (2194 cm-1),21d
(Me2NCS2)Pd(PEt3){CH(CN)Me} (2182 cm-1),9a and [cis-Ir-
(CO)2(CH2CN)2]- (2195 cm-1).24 The reduction in VCN on going
from 4a,d to 5a,d is consistent with the change from bridging
to terminal coordination of the PdCH(CN)Et unit.
of the metal at CR, which will reduce VCN, and coordination of
21
the metal at the CN nitrogen, which will increase VCN
.
Compounds 4a-e are stable in CD2Cl2 solution at 23 °C for at
least 10 days.
The analogous PMe3 adducts 6a-c are formed in a similar
manner (eq 3) and display similar spectroscopic properties.
-
Although attempts to isolate 4a-e using B(C6F5)4 as the
counterion were unsuccessful, [(Me2bipy)Pd{CH(CN)Et}]n
was isolated as the B{3,5-(CF3)2-C6H3}4 salt. The reaction
n+
-
of 1d with 1 equiv of Na[B{3,5-(CF3)2-C6H3}4] and 10 equiv
of AN in CH2Cl2 affords analytically pure [(Me2bipy)Pd{CH-
(CN)Et}][B{3,5-(CF3)2-C6H3}4] (4d′) as a yellow solid (81%).
The NMR spectra of 4d′ are very similar to those of 4d (with
the exception of the anion resonances) indicating that the
aggregation of the two species is similar. Further support for
the formulation of 4a-e as 2,1 insertion products is provided
by chemical derivatization experiments as discussed below.
Similar 2,1 AN insertion and aggregation by µ2-C,N-
PdCHEtCN- - -Pd bridging were observed for neutral and
anionic Pd alkyl complexes, and in one case the aggregation
mode was confirmed by X-ray diffraction.15
Attempts to isolate 5 or 6 using B(C6F5)4- as the counterion
were unsuccessful. However, 5d was isolated as the B{3,5-
(CF3)2-C6H3}4- salt. The reaction of 4d′ with 1 equiv of PPh3
in CH2Cl2 at 23 °C yields [(Me2bipy)Pd{CH(CN)Et}(PPh3)]-
[B{3,5-(CF3)2-C6H3}4] (5d′) as an analytically pure yellow
solid (74%). These results confirm the characterization of 4a-e
as 2,1 insertion products.
Generation of [L2Pd{CH(CN)Et}(CO)][B(C6F5)4] (7a,b).
As noted above, 4a-e do not react with AN at 23 °C. This
lack of reactivity arises because AN is not a sufficiently strong
Lewis base to break up the PdCHEtCN- - -Pd bridging units in
these aggregated cations. Similarly, 4a-e do not react with
ethylene at 23 °C (6 atm, 1 d; up to 25 atm for 4a). No evidence
for reaction of 4a with ethylene (6 atm) was observed up to 50
°C, at which temperature Pd0 formation was observed. To
determine if insertions into Pd-CH(CN)R bonds are possible,
the reactions of 4a-e with the potentially more reactive substrate
CO were explored.
Generation of [L2Pd{CH(CN)Et}(PR3)][B(C6F5)4] Deriva-
tives. To confirm the presence of a PdCH(CN)Et unit in 4a-e
and hence that 2,1 AN insertion occurs as proposed in Scheme
2, the reactions of 4a-e with Lewis bases were explored.
Complexes 4a-e do not react with excess AN, CH3CN or THF
at 23 °C in CD2Cl2 solution. However, as shown in eq 3, 4a-e
react quantitatively with 1 equiv of PPh3 (5 min, 23 °C) to yield
L2Pd{CH(CN)Et}(PPh3)+ cations 5a-e, which have been
characterized by multinuclear NMR and ESI-MS. Complex 5b
exists as two diastereomers due to the presence of two
stereogenic centers. Complex 5c also exists as two isomers, due
to slow inversion of the chelate ring, which likely has a boat
conformation similar to those in structurally characterized PdII
complexes containing related bidentate N-donor ligands.22 The
1H NMR spectra of 5a-e each contain a multiplet for the
PdCH(CN)CH2CH3 methine hydrogen, which couples to the two
methylene protons and phosphorus, multiplets for the diaste-
reotopic PdCH(CN)CH2CH3 hydrogens, and a triplet for the
Exposure of 4a,b to 6 atm of CO at 23 °C results in rapid (5
min) formation of the CO adducts L2Pd{CH(CN)Et}(CO)+
(7a,b, eq 4). In contrast, 4c-e do not react with CO under these
conditions. 7b exists as two diastereomers due to the presence
of two stereogenic centers. The 1H, 13C, and COSY NMR
spectra establish that 7a,b each contain an R-cyano-propyl
ligand. The Pd-CO 13C NMR resonance appears at δ 174 for
both 7a and 7b, close to the chemical shifts observed for the
analogous acetyl carbonyl complexes (bim)Pd{C(dO)Me}-
(CO)+ (δ 173) and (Tbim)Pd{C(dO)Me}(CO)+ (δ 172).17 The
IR VCO value for the terminal CO ligand of 7b (2132 cm-1) is
higher than that of (Tbim)Pd{C(dO)Me}(CO)+ (2118 cm-1),
which reflects the electron-withdrawing effect of the R-CN
substituent.17 For comparison, the VCO value for {(nhexyl)CH-
1
PdCH(CN)CH2CH3 methyl group. The H-1H COSY spectra
of 5a-e show correlations between these resonances that are
consistent with the PdCH(CN)CH2CH3 structure. The 13C{1H}
NMR spectra of 5a-e each contain a doublet (JCP ) 4-7 Hz)
in the range δ 10-16 for PdCH(CN)Et methine carbon. The
31P NMR spectra of 5a-e each contain a PPh3 resonance at ca.
δ 35, which is shifted downfield from the free PPh3 position (δ
-5.0). The IR VCN bands for both 5a and 5d appear at 2192
(N-Me-imidazol-2-yl)2}Pd(CHCl2)(CO) is 2144 cm-1 25
. The CO
ligand of 7a is labile, and decreasing the CO pressure to 1 atm
or below results in the regeneration of 4a. In contrast, 7b is
stable under 1 atm of CO for several hours.
(19) (a) Funabiki, T.; Hosomi, H.; Yoshida, S.; Tarama, K. J. Am. Chem. Soc.
1982, 104, 1560. (b) Odic, Y.; Pereyre, M. J. Organomet. Chem. 1973,
55, 273.
(20) Ruiz, J.; Rodr´ıguez, V.; Lo´pez, G.; Casabo´, J.; Molins, E.; Miravitlles, C.
Organometallics 1999, 18, 1177.
(21) For other examples see (a) Culkin, D. A.; Hartwig, J. F. J. Am. Chem. Soc.
2002, 124, 9330. (b) Naota, T.; Tannna, A.; Kamuro, S.; Murahashi, S. J.
Am. Chem. Soc. 2002, 124, 6842. (c) Morvillo, A,; Bressan, M. J.
Organomet. Chem. 1987, 332, 337. (d) Oehme, G.; Rober, K.; Pracejus,
H. J. Organomet. Chem. 1976, 105, 127. (e) Falvello, L. R.; Fernandez,
S.; Navarro, R.; Urriolabeitia, E. P. Inorg. Chem. 1997, 36, 1136.
(22) (a) Canty, A. J.; Minchin, N. J.; Skelton, B. W.; White, A. H. Aust. J.
Chem. 1992, 45, 423. (b) Newkome, G. R.; Gupta, V. K.; Theriot, K. J.;
Ewing, J. C.; Wicelinski, S. P.; Huie, W. R.; Fronczek, F. R.; Watkins, S.
F. Acta Crystallogr. 1984, C40, 1352. (c) Newkome, G. R.; Gupta, V. K.;
Taylor, H. C. R.; Fronczek, F. R. Organometallics 1984, 3, 1549.
CO Insertion of (bim)Pd{CH(CN)Et}(CO)+ (7a). Complex
7a undergoes slow CO insertion (23 °C, 2 d) to yield an
9
1844 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Acrylonitrile Insertion of Palladium Alkyl Complexes
A R T I C L E S
Scheme 3
equilibrium mixture of 7a and (bim)Pd{C(dO)CH(CN)Et)}-
(CO)+ (8a, eq 5). The equilibrium constant for CO insertion,
measured over a range of CO pressure (PCO) of 4 to 20 atm, is
Keq ) [8a][7a]-1PCO ) 0.050(2) atm-1 at 23 °C. At 6 atm
-1
CO pressure, a ca. 1/3 mixture of 8a and 7a is formed, whereas
at 20 atm of CO, a 1/1 mixture is formed. Complex 7b does
not insert CO under these conditions.
Complex 8a has been characterized by multinuclear NMR.
The Pd{C(dO)CH(CN)Et} acyl 13C resonance appears at δ 213,
close to the position observed for the acyl resonance in (bim)-
Pd{C(dO)Me}(CO)+ (δ 217).17 The 13C Pd{C(dO)CH(CN)-
Et} methine resonance appears at δ 56.4, ca. 40 ppm downfield
from the corresponding resonances of 5a, 6a, and 7a, as
expected due to the proximity of the carbonyl group.26 The Pd-
{C(dO)CH(CN)Et} methine 1H resonance occurs at δ 3.51 (dd),
ca. 1.7 ppm downfield from the corresponding resonances of
5a and 6a, and 0.7 ppm downfield from the corresponding
resonance of 7a. For comparison, the methine 1H resonance for
CH3C(dO)CH(CN)Et occurs at δ 3.70.27 These assignments
have been confirmed by experiments with 13CO.28
Exposure of 8a to vacuum results in regeneration of 4a,
confirming that the CO insertion of 7a (eq 5) and the CO
coordination of 4a (eq 4) are reversible. For comparison, (bim)-
Pd(Me)(CO)+ inserts CO much more rapidly (<1 min at 23
°C, ca. 1 atm) than 7a to yield (bim)Pd{C(dO)Me}(CO)+
quantitatively and irreversibly.17 Thus, the R-CN group clearly
inhibits but does not preVent the CO insertion.
acid (A) to cleave the aggregates to form potentially more
reactive monomeric [L2Pd{CH(CN-A)Et}+ species. The reac-
tion of 4a with B(C6F5)3 and 10 equiv of ethylene (0 °C, 20
min) generates [(bim)Pd{CH(CNB(C6F5)3)Et}(CH2dCH2)]-
[B(C6F5)4] (9a) quantitatively (eq 6). The 19F NMR spectrum
of 9a contains a set of resonances at δ -134.9, -156.9, and
-167.0 for the -CNB(C6F5)3 unit, which are in the range
observed for the nitrile adduct CH3CN-B(C6F5)3.29 The 1H and
13C NMR spectra of 9a contain resonances that are characteristic
of an R-cyano-propyl group. The ethylene 1H (δ 5.11) and 13
C
(δ 94.1) resonances of 9a both appear as broad singlets and are
shifted upfield from the free ethylene positions (1H: δ 5.38;
13C: δ 123.0; at -60 °C). Exchange of free and 9a-coordinated
ethylene is slow on the NMR time scale at 0 °C, which contrasts
with the fast ethylene exchange observed for (bim)Pd(Me)-
(CH2dCH2)+ at -60 °C.17 Ethylene exchange of 9a, which is
expected to occur by an associative mechanism, is probably
inhibited by the presence of the sterically bulky borane-capped
R-cyano-propyl group. Complex 9a decomposes to Pd0 over
several hours at 23 °C.
Complex 9a does not undergo ethylene insertion at 23 °C.
In contrast, (bim)Pd(Me)(CH2dCH2)+ inserts ethylene rapidly
above -10 °C.17 Therefore, the presence of the electron-
withdrawing R-CN-B(C6F5)3 substituent clearly inhibits inser-
tion of 9a.
Generation of [(bim)Pd{CH(CNB(C6F5)3)Et}(CH2dCH2)]-
[B(C6F5)4] (9a). As noted above, ethylene does not react with
4a-e at 23 °C. One possible approach to promoting the reaction
of [L2Pd{CH(CN)Et}]nn+ species with olefins is to use a Lewis
(23) (a) Ittel, S. D.; Tolman, C. A.; English, A. D.; Jesson, J. P. J. Am. Chem.
Soc. 1978, 100, 7577. (b) Ragaini, F.; Porta, F.; Fumagalli, A.; Demartin,
F. Organometallics 1991, 10, 3785. (c) Ros, R.; Bataillard, R.; Roulet, R.
J. Organomet. Chem. 1976, 118, C53. (d) Naota, T.; Tannna, A.; Murahashi,
S.-I.; J. Am. Chem. Soc. 2000, 122, 2960.
(24) Porta, F.; Ragaini, F.; Cenini, S. Organometallics 1990, 9, 929.
(25) Foley, S. R.; Shen, H.; Qadeer, U. A.; Jordan, R. F. Organometallics 2004,
23, 600.
(26) The 13C Pd{C(dO)CH(CN)Et} methine chemical shift of 8a (δ 56.4) agrees
reasonably well with the predicted value (δ 48.1) for CH3C(dO)CH(CN)-
Et, which is estimated using standard 13C NMR chemical shift additivity
rules. See Breitmaier, E.; Voelter, W. Carbon-13 NMR, 3rd ed.; VCH
Publishers: Weinheim, Germany, 1987; pp 313-325.
Comparative Ethylene and AN Coordination and Inser-
tion. The relative binding strength and insertion kinetics of
ethylene and AN were compared using the (Tbim)PdMe+
system, as shown in Scheme 3. The equilibrium constant for
(27) Itoh, T.; Fukuda, T.; Fujisawa, T. Bull. Chem. Soc. Jpn. 1989, 62, 3851.
(28) (a) The reaction of 4a with 13CO yields an equilibrium mixture of (bim)-
Pd{CH(CN)Et}(13CO)+ (7a-13C1) and (bim)Pd{13C(dO)CH(CN)Et}(13CO)+
(8a-13C2). The Pd{13C(dO)CH(CN)Et} methine 1H NMR resonance of 8a-
13C2 shows extra coupling not observed for 8a, due to the labeled acyl
carbonyl group. In addition, the Pd{13C(dO)CH(CN)Et} methine 13C NMR
resonance of 8a-13C2 is a doublet (δ 56.4, 1JCC ) 25). No 2JCC coupling is
observed between the Pd{13C(dO)CH(CN)Et} and Pd-13CO carbons. (b)
An unambiguous simulation of the Pd{13C(dO)CH(CN)Et} methine 1H
the reaction of 3b with ethylene to form 10b and AN, Keq
)
[10b][AN]/[3b][ethylene], was measured by 1H NMR between
-76 °C and -25 °C. Under these conditions, ethylene/AN
exchange (i.e., 3b/10b exchange) is slow on the NMR chemical
shift time scale. At -25 °C, Keq ) 6.3(1), and ethylene binding
is favored over AN coordination. For example, at this temper-
ature, the reaction of 3b with 130 equiv of AN and 20 equiv of
ethylene yields a ca. 1/1 equilibrium mixture of 3b and 10b.
The reverse reaction, i.e., addition of excess AN to 10b also
affords an equilibrium mixture of 10b and 3b. A van’t Hoff
2
NMR resonance of 8a-13C2 to acquire JCH is not possible because the
appearance of the simulated methine resonance is extremely sensitive to
the assigned chemical shift values for the diastereotopic CH2 hydrogens,
which cannot be obtained due to overlapping of these resonances with the
corresponding resonances of 7a-13C1. This complication reflects the second-
order character of the Pd{13C(dO)CH(CN)CH2CH3} spin system, which
results from the small chemical shift difference for the diastereotopic
methylene hydrogens. However, if the chemical shifts of the methylene
protons are taken as δ 1.92 and 1.91, the Pd{13C(dO)CH(CN)Et} methine
resonance is defined as ddd (JHH ) 13.2, 0.8; 2JCH ) 6.6). The 2JCH value
determined in this way is consistent with a two-bond C(dO)CH coupling
(29) Jacobsen, H.; Berke, H.; Do¨ring, T.; Kehr, G.; Erker, G.; Fro¨hlich, R.;
2
(cf. JCH ) 5.5 for acetone).
Meyer, O. Organometallics 1999, 18, 1724.
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1845

A R T I C L E S
Wu et al.
dimerization and polymerization catalysts, and the properties
of the R-CN-alkyl metal species that result from AN insertion
in these systems. The L2PdMe+ species 2a-f, which contain a
range of bidentate N-donor ligands (L2) with different steric
and electronic properties, coordinate AN to form N-bound L2-
Pd(Me)(AN)+ complexes 3a-f. The CdC π-bound isomers were
not detected. These observations are consistent with computa-
tional studies, which show that for the model system (HNd
CHCHdNH)Pd(Et)(AN)+, which is an analogue of 3f, the
N-bound form is ca. 13 kcal/mol more stable than the π-bound
isomer.32 The preference for N-coordination reflects the fact
that the σ-donation component dominates the Pd-olefin bonding
in L2Pd(Me)(olefin)+ species, due to the poor back-bonding
ability of the cationic d8 metal center, and the CdC bond of
AN is a poor donor due to the low HOMO energy.
L2PdMe(AN)+ species 3a-e undergo 2,1 AN insertion to
yield L2Pd{CH(CN)Et}+ species. These reactions likely proceed
by initial isomerization to the (unobserved) CdC π complexes
followed by migratory insertion, and therefore the overall AN
insertion rate will be determined by the energetics of the N/π
isomerization and the insertion rate of the π complex. The
strength of the Pd-N interaction and hence the stability of the
N-bound adducts should be enhanced as the net positive charge
on the metal center is increased. The overall insertion rates are
slower for the pyridine and diimine AN complexes 3c-f than
for the bim and Tbim complexes 3a,b, which is opposite to the
trend in insertion rates of the corresponding ethylene com-
plexes.7,17 IR νCO data for the terminal carbonyl ligands in L2-
Pd{CdO)Me}(CO)+ species (Figure 1) show that the metal
centers in the pyridine and diimine complexes are electron-poor
relative to those in the bim and Tbim complexes. Therefore,
the slower AN insertion rates of 3c-f can be ascribed to stronger
N-coordination of AN in these species. Steric crowding in 3f
may also disfavor the π complex and thereby contribute to the
absence of insertion in this case. It is interesting to note in this
context that calculated gas-phase barriers for insertion of the
model π complexes (HNdCHCHdNH)Pd(R)(AN)+ and (HNd
CHCHdNH)Pd(R)(ethylene)+ differ by only ca. 1-2 kcal/
mol.32,33
Figure 2. van’t Hoff plot for the equilibrium in Scheme 3.
plot of the Keq data (Figure 2) yields ∆H° ) -2.5(1) kcal/mol,
∆S° ) -6(1) eu for the equilibrium in Scheme 3. Using these
thermodynamic parameters, Keq is calculated to equal 4.4(3) at
0 °C.
The reaction of 3b to produce 4b is presumed to occur by
reversible N/π-isomerization, followed irreversible migratory
insertion and subsequent aggregation, as shown in Scheme 2.
The observed first-order rate constant for conversion of 3b to
1
4b measured by the disappearance of the Pd-Me H NMR
resonance of 3b, is kobs,AN ) 3.75(3) × 10-4 s-1 at 0 °C. Making
the steady-state assumption for the unobserved π-complex
intermediate, kobs,AN ) k1k2/(k-1 + k2) (see Scheme 2).30 For
comparison, the rate constant for ethylene insertion of 10b is
kins,) ) 11.0(2) × 10-4 s-1 at 0 °C.17
These results show that AN coordinates more weakly and,
overall, inserts more slowly than ethylene in the (Tbim)PdMe+
system. Nevertheless, AN can compete with ethylene for
insertion into (Tbim)PdMe+. Assuming that AN/ethylene ex-
change (i.e., 3b/10b exchange) is fast relative to insertion, the
relative rates of formation of (Tbim)Pd{CH(CN)Et}+ and
(Tbim)PdPr+ by reaction with AN and ethylene with (Tbim)-
PdMe+ are given by eq 7.31
The AN insertions of 3a-e occur with 2,1 regioselectivity;
i.e., Michael-type addition is observed. This regioselectivity is
consistent with computational results that show 2,1 insertion is
favored by ca. 5 kcal/mol for (HNdCHCHdNH)Pd(R)(AN)+
model species.32,33 The Cpz coefficient in the AN LUMO is
larger at the terminal carbon (C1) than the internal carbon (C2),
which favors migration of the alkyl to C1, and the M-CHRCN
bond is expected to be stronger than the M-CH2CHRCN bond
that would be formed by 1,2 insertion.
ESI-MS and NMR studies show that L2Pd{CH(CN)Et}+
species derived from AN insertion of 3a-e form robust [L2-
Pd{CH(CN)Et}]nn+ aggregates (4a-e). The structures of these
aggregates could not be determined, but IR data and literature
precedents strongly suggest that the monomer units are linked
by PdCHRCN- - -Pd bridges. These interactions are strong
because the PdCHRCN group is more electron-rich and hence
(kobs,AN)[AN]
rate of AN rxn
rate ethylene rxn
)
(7)
Keq(kins,))[ethylene]
For equal concentrations of AN and ethylene, this ratio is
estimated to be 7/93 at 0 °C, based on the extrapolated Keq value
and measured values of kobs,AN and kins,) at this temperature.
Discussion
The studies described above provide insights to the acryloni-
trile (AN) coordination and insertion reactions of L2PdR+ olefin
(30) The N/π-isomerization could occur intramolecularly as shown in Scheme
2 or by an associative mechanism involving free AN. However, the kobs,
A
N
value for 3b is essentially the same in the absence of free AN (i.e.,
when 3b is generated from 2b using a deficiency of AN) and in the presence
of 140 equiv of free AN, so possible associative N/π isomerization does
not influence the overall rate of insertion.
(31) As AN/ethylene exchange occurs by associative ligand substitution, the
rate will depend on the concentrations of free ethylene and AN. EXSY
studies show that the first-order rate constants for conversion of 3b to 10b
(1.8 × 10-2 s-1) and 10b to 3b (2.9 × 10-3 s-1) at -30 °C with [ethylene]
(32) (a) Philipp, D. M.; Muller, R. P.; Goddard, W. A., III; Storer, J.; McAdon,
M.; Mullins, M. J. Am. Chem. Soc. 2002, 124, 10198. (b) Deubel, D. K.;
Ziegler, T. Organometallics 2002, 21, 1603.
(33) (a) Deubel, D. K.; Ziegler, T. Organometallics 2002, 21, 4432. (b) von
Schenck, H.; Stro¨mberg, S.; Zetterberg, K.; Ludwig, M.; Åkermark, B.;
Svensson, M. Organometallics 2001, 20, 2813.
) 0.26 M and [AN] ) 1.4 M are much larger than the kobs,
and kins,)
AN
values determined at 0 °C. Thus, under typical conditions, AN/ethylene
exchange will be fast relative to insertion for the Tbim system.
9
1846 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Acrylonitrile Insertion of Palladium Alkyl Complexes
A R T I C L E S
more Lewis basic than a conventional nitrile, due to the presence
of the metal at CR. The PdCHRCN- - -Pd bridging is sufficiently
strong that neither AN nor ethylene break up the aggregates to
form L2Pd{CH(CN)Et}(monomer)+ complexes, and therefore
additional insertion reactions leading to polymerization or
copolymerization are not observed. In contrast, the binding
affinities of acetonitrile and ethylene to (phen)PdMe+ are nearly
equal,34 and L2Pd(R)(NCMe)+ species are effective catalysts
for ethylene polymerization, and ethylene/acrylate and olefin/
CO copolymerizations.7c,35 Complexes 4a-e do react with
phosphines to form L2Pd{CH(CN)Et}(PR3)+ complexes (5a-e
and 6a-c), which enabled definitive characterization of the 2,1
insertion regiochemistry. Complex 4a reacts with ethylene in
the presence of B(C6F5)3 to form (bim)Pd{CH(CNB(C6F5)3)-
Et}(CH2dCH2)+ (9a), but this species is resistant to insertion
due to the poor nucleophilicity and steric bulk of the borane-
capped cyanoalkyl group.
AN insertion should be competitive with ethylene insertion in
this and related systems.
Conclusions
The reactions of acrylonitrile (AN) with representative L2-
PdMe+ olefin dimerization and polymerization catalysts that
contain bidentate N-donor ligands (L2) have been studied to
probe the possibility of polymerizing this substrate by insertion
polymerization. L2PdMe+ species form N-bound L2Pd(Me)-
(AN)+ adducts that undergo 2,1 AN insertion to yield L2Pd-
{CH(CN)Et}+ products. These insertions likely proceed via
intermediate CdC π complexes, which, however, were not
detected. The ability of the N-bound isomers to isomerize to
the π complexes is critical for insertion, and highly electron-
deficient, sterically crowded LnMR+ species for which the
N-bound adduct is strongly favored over the π-complex, such
as 3f, are poor candidates for AN insertion. The L2Pd{CH(CN)-
Et}+ insertion products form robust aggregates by PdCHEtCN-
- -Pd bridging, due to the enhanced Lewis basicity of the
R-metalated nitrile group. The [L2Pd{CH(CN)Et}]nn+ aggregate
species studied here are not readily cleaved by ethylene or AN,
and therefore do not undergo further insertions of these
substrates. However, it should be possible to prevent aggregation
of this type by steric blocking using suitably designed ligands
or by site-isolation of active catalyst species on a support. The
bis-imidazole species (bim)Pd{CH(CN)Et}(CO)+ (7a) under-
goes reversible CO insertion to form (bim)Pd{C(dO)CH(CN)-
Et}(CO)+ (8a), but this process is disfavored both kinetically
and thermodynamically relative to CO insertion of (bim)Pd-
(Me)(CO)+, due to the electron-withdrawing effect of the R-CN
substituent. The low insertion reactivity of R-CN-substituted Ln-
MCHRCN species is the key obstacle to insertion polymeriza-
tion and copolymerization of AN.
n+
The two most electron-rich [L2Pd{CH(CN)Et}]n species
among those studied, 4a,b, react with CO to form L2Pd{CH-
(CN)Et}(CO)+ complexes 7a,b, whereas 4c-e do not. The
n+
reactivity of [L2Pd{CH(CN)Et}]n with CO is determined by
the lability of PdCHEtCN- - -Pd bridges and the ability of the
L2Pd{CH(CN)Et}+ unit to stabilize the coordinated CO by back-
bonding, both of which are enhanced by the strong donor
imidazole ligands of 4a,b. In the presence of excess CO, 7a
undergoes reversible CO insertion to form (bim)Pd{C(dO)-
CH(CN)Et}(CO)+ (8a), whereas 7b does not. The CO insertion
of 7a is disfavored both kinetically and thermodynamically
relative to CO insertion of the corresponding methyl complex
(bim)Pd(Me)(CO)+. These results are consistent with previous
studies of CO insertion into M-R bonds, which have shown
that electron-withdrawing substituents on the migrating R group
generally inhibit migration and destabilize the insertion product,
while electron-releasing substituents have the opposite effects.36
This trend has been ascribed to differences in bond strengths
(M-REWG > M-R) and differences in the basicity/nucleophi-
licity of the migrating group (R > REWG). It is also possible
that steric crowding inhibits insertion of 7a and especially 7b.
Nevertheless, the observation that 7a reversibly inserts CO
suggests that insertion reactions of suitably designed L2M{CH-
(CN)R}(olefin) species may also be possible.
Experimental Section
General Procedures. All manipulations were performed under
purified N2 or vacuum using standard Schlenk or high vacuum
techniques or in a nitrogen-filled drybox unless otherwise noted.
Nitrogen was purified by passage through columns of activated
molecular sieves and Q-5 oxygen scavenger. Chlorinated solvents were
distilled from CaH2, and acrylonitrile (AN) was distilled from CaCl2,
and these materials were stored under vacuum prior to use. PMe3 was
purchased from Aldrich and dried over 4 Å molecular sieves. PPh3,
CO, 13CO and ethylene were purchased from Aldrich and used as
received. [HNMe2Ph][B(C6F5)4], [Li(Et2O)2.8][B(C6F5)4], Na[B(3,5-
C6H3(CF3)2)4], and B(C6F5)3 were obtained from Boulder Scientific and
used as received. Compounds 1a,37 1b,c,17 1d,e and 2d,e,18 and 1f7e
were prepared by literature procedures.
Studies of ligand exchange equilibria and insertion kinetics
of (Tbim)Pd(Me)(AN)+ (3b) and (Tbim)Pd(Me)(ethylene)+
(10b) show that AN coordinates more weakly and, overall,
inserts more slowly than ethylene in the (Tbim)Pd(Me)+ system.
The slower insertion of 3b vs 10b reflects the requirement for
N/π isomerization of 3b. Nevertheless, the differences in
monomer binding and insertion rates are sufficiently small that
NMR spectra were recorded in sealed tubes on a Bruker AMX-500
spectrometer at ambient temperature unless otherwise indicated. 1H and
13C chemical shifts are reported versus Me4Si and were determined by
reference to the residual solvent peaks. 19F and 31P chemical shifts were
referenced to external neat CFCl3 and H3PO4, respectively. Coupling
(34) Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
(35) (a) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am. Chem.
Soc. 1998, 120, 888. (b) Brookhart, M.; Rix, F. C.; DeSimone, J. M.;
Barborak, J. C. J. Am. Chem. Soc. 1992, 114, 5894. (c) Done, M. C.; Ruther,
T.; Cavell, K. J.; Kilner, M.; Peacock, E. J.; Braussaud, N.; Skelton, B.
W.; White, A. J. Organomet. Chem. 2002, 607, 78.
(36) (a) Axe, F. U.; Marynick, D. S. J. Am. Chem. Soc. 1988, 110, 3728. (b)
Cotton, J. D.; Markwell, R. D. J. Organomet. Chem. 1990, 388, 123. (c)
Cotton, J. D.; Crisp, G. T.; Daly, V. A. Inorg. Chim. Acta 1981, 47, 165.
(d) Cross, R. J.; Gemmill, J. J. Chem. Soc., Dalton Trans. 1981, 2317. (e)
Cawse, J. N.; Fiato, R. A.; Pruett, R. L. J. Organomet. Chem. 1979, 172,
405. (f) Anderson, G. K.; Cross, R. J. Acc. Chem. Res. 1984, 17, 67. (g)
Kuhlmann, E. J.; Alexander, J. J. Coord. Chem. ReV. 1980, 33, 195. (h)
Calderazzo, F.; Noack, K. Coord. Chem. ReV. 1966, 1, 118. (i) Koga, N.;
Morokuma, K. J. Am. Chem. Soc. 1986, 108, 6136. (j) Ros, R.; Renaud,
J.; Roulet, R. J. Organomet. Chem. 1974, 77, C4.
-
constants are reported in Hz. NMR spectra of B(C6F5)4 salts contain
anion resonances at the free anion positions.38 NMR spectra of 3a-c
and species derived from these species contain resonances for free
(37) Byers, P. K.; Canty, A. J. Organometallics 1990, 9, 210.
-
:
13C{1H} NMR (CD2Cl2): δ 148.5 (dm, J
(38) NMR data for free B(C6F5)4
) 234, C2), 138.6 (dm, J ) 246, C4), 136.6 (dm, J ) 243, C3), 123.6 (br,
C1). 19F NMR (CD2Cl2): δ -133.2 (br s, 2F, o-F), -163.7 (t, J ) 23, 1F,
p-F), -167.6 (t, J ) 19, 2F, m-F). 13C{1H} NMR (CD2Cl2, -60 °C): δ
147.5 (dm, J ) 241, C2), 137.8 (dm, J ) 238, C4), 135.8 (dm, J ) 249,
C3), 123.6 (br, C1). 19F NMR (CD2Cl2, -60 °C): δ -133.7 (br s, 2F,
o-F), -163.0 (t, J ) 23, 1F, p-F), -167.0 (t, J ) 19, 2F, m-F).
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1847

A R T I C L E S
Wu et al.
NMe2Ph.39 Samples of CD2Cl2 solutions of 2d-f and species generated
in situ from 2d-f contain LiCl. NMR spectra for species generated in
the presence of excess AN contain resonances for free AN.40,41
ESI-MS experiments were performed with a HP Series 1100MSD
C2), 127.0 (C4 of NMe2Ph), 125.0 (imidazole C4), 122.3 (imidazole
C5), 122.2 (C3 of NMe2Ph), 121.9 (imidazole C5), 64.4 ((tolyl)3C),
56.0 (NMe2Ph), 50.4 (NMe2Ph), 45.0 (CH), 36.1 (imidazole NMe), 33.7
(imidazole NMe), 20.5 (tolyl Me), 4.5 (PdMe).
instrument using direct injection via a syringe pump (ca. 10-6
M
[(CH2py′2)PdMe(NMe2Ph)][B(C6F5)4] (2c). This complex was
generated quantitatively from (CH2py′2)PdMe2 (1c, 5.6 mg, 0.017 mmol)
and [HNMe2Ph][B(C6F5)4] (13.4 mg, 0.017 mmol) using the procedure
for 2a. Inversion of the chelate ring is slow on the NMR time scale at
-60 °C. 1H NMR (CD2Cl2, -60 °C): δ 8.20 (s, 1H, py′ H6), 7.63 (d,
J ) 8, 2H, o-Ph), 7.56 (d, J ) 8, 1H, py′ H4), 7.45 (t, J ) 8, 2H,
m-Ph), 7.39 (d, J ) 8, 1H, py′ H4), 7.31 (m, 2H, p-Ph and py′ H3),
7.22 (d, J ) 8, 1H, py′ H3), 5.97 (s, 1H, py′ H6), 5.08 (d, J ) 13.8,
1H, CH2), 4.22 (d, J ) 13.8, 1H, CH2), 2.95 (s, 3H, NMe2Ph), 2.90 (s,
3H, NMe2Ph), 2.27 (s, 3H, py′ Me), 1.86 (s, 3H, py′ Me), 0.91 (s, 3H,
PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ 153.7 (py′ C2), 152.5
(Ph C1), 151.8 (py′ C2), 151.3 (py′ C6), 149.4 (py′ C6), 139.7 (py′
C4), 139.2 (py′ C4), 134.2 (py′ C5), 133.1 (py′ C5), 129.2 (Ph C2),
126.9 (Ph C4), 124.2 (py′ C3), 124.0 (py′ C3), 121.6 (Ph C3), 54.7
(NMe2Ph), 49.7 (NMe2Ph), 46.5 (CH2), 17.8 (py′ Me), 17.7 (py′ Me),
5.4 (PdMe).
[{(2,6-iPr2-diimine)PdMe}2(µ-Cl)][B(C6F5)4] (2f).7d An NMR tube
was charged with (2,6-iPr2-diimine)PdMeCl (1f, 12.4 mg, 0.029 mmol)
and [Li(Et2O)2.8][B(C6F5)4] (26.3 mg, 0.029 mmol), and CD2Cl2 (0.6
mL) was added by vacuum transfer at -196 °C. The tube was warmed
to 23 °C resulting in slurry of a white solid in a an orange supernatant.
After 10 min, NMR spectra showed that 2f had formed quantitatively.
1H NMR (CD2Cl2): δ 7.34 (t, J ) 8, 2H, Ar H4), 7.26 (d, J ) 7, 4H,
Ar H3), 7.17 (t, J ) 8, 2H, Ar H4), 7.09 (d, J ) 8, 4H, Ar H3), 2.89
(septet, J ) 6, 4H, CHMe2), 2.75 (septet, J ) 6, 4H, CHMe2), 2.05 (s,
6H, NdCMe), 2.00 (s, 6H, NdCMe), 1.22 (d, J ) 7, 12H, CHMe2),
1.12 (d, J ) 7, 12H, CHMe2), 1.07 (d, J ) 7, 12H, CHMe2), and 1.00
(d, J ) 7, 12H, CHMe2), 0.41 (s, 6H, PdMe).
solutions). Good agreement between observed and calculated isotope
patterns was observed in all cases. In each case, the listed m/z value
corresponds to the most intense peak in the isotope pattern. Infrared
spectra were recorded on a Nicolet NEXUS 470 FT-IR spectrometer.
Unless otherwise noted, IR spectra were recorded for neat samples using
the Nicolet Smart Miracle ATR accessory after the evaporation of the
solvent.
The following procedure was used to quantity the CO in the
carbonylation reactions. A valved NMR tube containing the reaction
solution was attached to a vacuum line, the solution was frozen with
liquid nitrogen, the tube was evacuated, and the valve was closed. The
vacuum line was isolated from the pumping system and charged with
CO. The NMR tube valve was opened to allow CO into the tube and
then was closed. The amount of CO that was added to the tube was
determined from the decrease in CO pressure in the vacuum line.
[(bim)PdMe(NMe2Ph)][B(C6F5)4] (2a). An NMR tube was charged
with (bim)PdMe2 (1a, 4.0 mg, 0.013 mmol) and [HNMe2Ph][B(C6F5)4]
(10.0 mg, 0.013 mmol), and CD2Cl2 (0.6 mL) was added by vacuum
transfer at -78 °C. The tube was vigorously agitated resulting in a
pale yellow solution. The tube was maintained at -78 °C for 10 min
and then transferred to the NMR probe at -60 °C. NMR spectra showed
that 2a had formed quantitatively. 1H NMR (CD2Cl2, -60 °C): δ 7.85
(d, J ) 8, 2H, o-Ph), 7.44 (t, J ) 8, 2H, m-Ph), 7.30 (t, J ) 7, 1H,
p-Ph), 6.89 (s, 1H, imidazole), 6.88 (s, 1H, imidazole), 6.59 (s, 1H,
imidazole), 4.98 (s, 1H, imidazole), 4.13 (s, 2H, CH2), 3.66 (s, 3H,
imidazole NMe), 3.58 (s, 3H, imidazole NMe), 2.92 (s, 6H, NMe2Ph),
0.76 (s, 3H, PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ 152.9 (Ph
C1), 141.8 (imidazole C2), 140.7 (imidazole C2), 129.1 (Ph C2), 127.5
(Ph C4), 126.9 (imidazole C4), 125.6 (imidazole C4), 121.9 (Ph C3),
121.5 (imidazole C5), 121.4 (imidazole C5), 52.9 (NMe2Ph), 34.3
(imidazole NMe), 33.7 (imidazole NMe), 22.5 (CH2), 2.1 (PdMe).42
[(Tbim)PdMe(NMe2Ph)][B(C6F5)4] (2b). This complex was gener-
ated quantitatively from (Tbim)PdMe2 (1b, 11.0 mg, 0.018 mmol) and
[HNMe2Ph][B(C6F5)4] (14.7 mg, 0.018 mmol) using the procedure for
2a. 1H NMR (CD2Cl2, -60 °C): δ 7.84 (d, J ) 8, 2H, ortho NMe2Ph),
7.41 (t, J ) 8, 2H, meta-NMe2Ph), 7.28 (t, J ) 7, 1H, para-NMe2Ph),
7.01 (d, J ) 7, 6H, tolyl H2), 6.86 (s, 1H, imidazole), 6.80 (s, 1H,
imidazole), 6.60 (br s, 6H, tolyl H3), 6.50 (s, 1H, imidazole), 5.57 (s,
1H, CH), 5.24 (s, 1H, imidazole), 3.15 (s, 3H, imidazole NMe), 2.89
(s, 3H, imidazole NMe), 2.84 (s, 3H, NMe2Ph), 2.54 (s, 3H, NMe2Ph),
2.30 (s, 9H, tolyl Me), 0.30 (s, 3H, PdMe). 13C{1H} NMR (CD2Cl2,
-60 °C): δ 152.9 (C1 of NMe2Ph), 143.1 (imidazole C2), 143.0
(imidazole C2), 137.5 (tolyl Cipso), 137.4 (tolyl Cipso), 131.3 (br s, tolyl
C3), 129.2 (C2 of NMe2Ph), 128.3 (imidazole C4), 128.0 (br s, tolyl
[(bim)PdMe(NCCHdCH2)][B(C6F5)4] (3a). An NMR tube contain-
ing a solution of [(bim)PdMe(NMe2Ph)][B(C6F5)4] (2a, 0.013 mmol)
in CD2Cl2 (0.6 mL) was cooled to -196 °C and acrylonitrile (0.195
mmol) was added by vacuum transfer. The tube was warmed to -78
°C and vigorously agitated resulting in a pale yellow solution. The
tube was maintained at -78 °C for 10 min and then transferred to the
NMR probe at -60 °C. A 1H NMR spectrum showed that [(bim)-
PdMe(NCCHdCH2)][B(C6F5)4] (3a) had formed quantitatively. Sepa-
rate sharp 1H NMR resonances for free and coordinated AN were
observed at -60 and 23 °C. 1H NMR (CD2Cl2, -60 °C): δ 6.99 (d, J
) 1, 1H, imidazole), 6.97 (d, J ) 1, 1H, imidazole), 6.92 (d, J ) 1,
1H, imidazole), 6.86 (d, J ) 1, 1H, imidazole), 6.55 (d, J ) 18, 1H,
Htrans of coordinated AN), 6.43 (d, J ) 12, 1H, Hcis of coordinated
AN), 5.93 (dd, J ) 18, 12, 1H, Hint of coordinated AN), 4.08 (s, 2H,
CH2), 3.71 (s, 3H, NMe), 3.68 (s, 3H, NMe), 0.75 (s, 3H, PdMe). 13C-
{1H} NMR (CD2Cl2, -60 °C): δ 143.0 (Cter of coordinated AN), 140.1
(imidazole C2), 139.0 (imidazole C2), 126.1 (imidazole C4), 125.6
(imidazole C4), 122.1 (imidazole C5), 121.8 (imidazole C5), 119.2 (CN
of coordinated AN), 105.7 (Cint of coordinated AN), 34.6 (NMe), 33.7
(NMe), 22.7 (CH2), -2.7 (PdMe). The 13C NMR assignments for the
coordinated AN were confirmed by a DEPT-135 experiment. IR
(39) (a) NMR data for free NMe2Ph: 1H NMR (CD2Cl2): δ 7.20 (m, 2H, o-Ph),
6.72 (m, 2H, m-Ph), 6.67 (t, J ) 7, 1H, p-Ph), 3.03 (s, 6H, Me). 13C{1H}
NMR (CD2Cl2): δ 151.1 (C1), 129.3 (C2), 116.6 (C4), 112.8 (C3), 40.7
(Me). 1H NMR (CD2Cl2, -60 °C): δ 7.18 (m, 2H, o-Ph), 6.67 (m, 2H,
m-Ph), 6.63 (t, J ) 7, 1H, p-Ph), 2.88 (s, 6H, Me). 13C{1H} NMR (CD2-
Cl2, -60 °C): δ 150.2 (C1), 128.7 (C2), 115.8 (C4), 111.9 (C3), 40.3
(Me). (b) If excess [HNMe2Ph][B(C6F5)4] is used in the generation of 3a-
c, the excess HNMe2Ph+ undergoes fast H+ exchange with NMe2Ph and a
single set of NMe2Ph/HNMe2Ph+ resonances at the weighted average of
the chemical shifts of these species is observed.
(neat): VCN ) 2244 cm-1
.
[(Tbim)PdMe(NCCHdCH2)][B(C6F5)4] (3b). A solution of [(Tbim)-
PdMe(NMe2Ph)][B(C6F5)4] (2b, 0.018 mmol) in CD2Cl2 (0.6 mL) was
generated in an NMR tube, and AN (0.162 mmol) was added by vacuum
transfer at -196 °C. The tube was maintained at -30 °C for 30 min
to achieve complete displacement of NMe2Ph by AN. A 1H NMR
spectrum was obtained at -60 °C and showed that 3b had formed
quantitatively. Separate sharp resonances for free and coordinated AN
(40) NMR data for free AN: 1H NMR (CD2Cl2, 23 °C): δ 6.21 (d, J ) 18, 1H,
H
trans), 6.07 (d, J ) 12, 1H, Hcis), 5.67 (dd, J ) 18, 12.0, 1H, Hint). 13C-
{1H} NMR (CD2Cl2): δ 138.0 (Cter), 117.3 (CN), 108.2 (Cint). 1H NMR
(CD2Cl2, -60 °C): δ 6.24 (d, J ) 18, 1H, Htrans), 6.09 (d, J ) 12, 1H,
H
cis), 5.69 (dd, J ) 18, 12.0, 1H, Hint). 13C{1H} NMR (CD2Cl2, -60 °C):
δ 138.1 (Cter), 117.3 (CN), 107.2 (Cint).
1
were observed at -60 and 0 °C. H NMR (CD2Cl2, -60 °C): δ 6.99
(41) 13C NMR assignments for AN from Schumann, H.; Speis, M.; Bosman,
W. P.; Smits, J. M. M.; Beurskens, P. T. J. Organomet. Chem. 1991, 403,
165.
(d, J ) 8, 6H, tolyl H2), 6.83 (d, J ) 1, 1H, imidazole), 6.82 (d, J )
1, 1H, imidazole), 6.81 (d, J ) 1, 1H, imidazole), 6.77 (d, J ) 1, 1H,
imidazole), 6.51 (d, J ) 18, 1H, Htrans of coordinated AN), 6.50 (br d,
J ) 8, 6H, tolyl H3), 6.44 (d, J ) 12, 1H, Hcis of coordinated AN),
(42) Assignments of the imidazole C4 and C5 resonances are based on data in
Katritzky, A. R.; Pozharskii, A. F. Handbook of Heterocyclic Chemistry,
2nd ed.; Pergamon Publisher: New York, 2000; pp 108-112.
9
1848 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Acrylonitrile Insertion of Palladium Alkyl Complexes
A R T I C L E S
5.90 (dd, J ) 18, 12, 1H, Hint of coordinated AN), 5.65 (s, 1H, CH),
3.15 (s, 3H, NMe), 3.05 (s, 3H, NMe), 2.27 (s, 9H, tolyl Me), 0.33 (s,
3H, PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ 143.4 (imidazole C2),
142.5 (Cter of coordinated AN), 141.2 (imidazole C2), 137.6 (tolyl Cipso),
137.3 (tolyl Cipso), 131.4 (tolyl C3), 127.8 (tolyl C2),126.6 (imidazole
C4), 125.7 (imidazole C4), 123.0 (imidazole C5), 121.9 (imidazole C5),
118.0 (CN of coordinated AN), 105.7 (Cint of coordinated AN), 65.1
((tolyl)3C), 44.6 (CH), 35.3 (NMe), 34.5 (NMe), 20.5 (tolyl Me), -4.0
(PdMe).
(CMe3), 35.6 (CMe3), 29.8 (CMe3), 29.7 (CMe3), 2.9 (PdMe); reso-
nances for coordinated AN were not observed due to exchange
broadening.
[(2,6-iPr2-diimine)Pd(Me)(NCCHdCH2)][B(C6F5)4] (3f). This com-
plex was generated quantitatively in CD2Cl2 (0.6 mL) from 2f (0.014
mmol) in the presence of [Li(Et2O)2.8][B(C6F5)4] (0.014 mmol) and AN
(0.18 mmol) using the procedure for 3d. The NMR spectra contain
1
separate sharp resonances for free and coordinated AN at 23 °C. H
NMR (CD2Cl2): δ 7.34 (m, 6H, Ar), 6.19 (d, J ) 12, 1H, Hcis of
coordinated AN), 5.81 (d, J ) 18, 1H, Htrans of coordinated AN), 5.44
(dd, J ) 18, 12, 1H, Hint of coordinated AN), 2.95 (septet, J ) 7, 2H,
CHMe2), 2.89 (septet, J ) 7, 2H, CHMe2),2.24 (s, 3H, NdCMe), 2.23
(s, 3H, NdCMe), 1.37 (d, J ) 7, 6H, CHMe2), 1.34 (d, J ) 7, 6H,
CHMe2), 1.24 (d, J ) 7, 6H, CHMe2), 1.20 (d, J ) 7, 6H, CHMe2),
0.55 (s, 3H, PdMe). 13C{1H} NMR (CD2Cl2): δ 180.3 (NdC), 172.7
(NdC), 144.3 (Cter of coordinated AN), 140.7 (Ar C1), 140.6 (Ar C1),
138.6 (Ar C2), 138.0 (Ar C2), 129.3 (Ar C4),128.6 (Ar C4), 124.9 (Ar
C3), 124.6 (Ar C3), 120.5 (CN of coordinated AN), 104.5 (Cint of
coordinated AN), 29.5 (CHMe2), 29.3 (CHMe2), 23.8 (CHMe2), 23.7
(CHMe2), 23.4 (CHMe2), 23.0 (CHMe2), 21.8 (NdCMe), 20.1 (Nd
CMe), 7.4 (PdMe). ESI-MS: [(2,6-iPr2-diimine)PdMe(NCCHdCH2)]+
calcd. m/z 578.2, found 578.2.
[(CH2py′2)PdMe(NCCHdCH2)][B(C6F5)4] (3c). This complex was
generated quantitatively in CD2Cl2 solution from [(CH2py′2)PdMe(NMe2-
Ph)][B(C6F5)4] (2c, 0.017 mmol) and AN (0.527 mmol) using the
procedure for 3a. The 1H NMR spectrum contains separate sharp
resonances for free and coordinated AN at -60 °C and separate but
broad resonances for free and coordinated AN at 23 °C. 1H NMR (CD2-
Cl2, -60 °C): δ 8.22 (s, 1H, py′ H6), 8.17 (s, 1H, py′ H6), 7.66 (d, J
) 8, 1H, py′ H4), 7.63 (d, J ) 8, 1H, py′ H4), 7.40 (d, J ) 8, 1H, py′
H3), 7.38 (d, J ) 8, 1H, py′ H3), 6.55 (d, J ) 18, 1H, Htrans of
coordinated AN), 6.45 (d, J ) 12, 1H, Hcis of coordinated AN), 5.94
(dd, J ) 18, 12, 1H, Hint of coordinated AN), 4.72 (d, J ) 14.2, 1H,
CH2), 4.20 (d, J ) 14.2, 1H, CH2), 2.30 (s, 3H, py′ Me), 2.29 (s, 3H,
py′ Me), 0.88 (s, 3H, PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ
153.2 (py′ C2), 151.9 (py′ C6), 150.7 (py′ C2), 149.6 (py′ C6), 143.7
(Cter of coordinated AN), 140.6 (py′ C4), 140.2 (py′ C4), 134.8 (py′
C5), 134.3 (py′ C5), 125.1 (py′ C3), 124.6 (py′ C3), 119.7 (CN of
coordinated AN), 105.8 (Cint of coordinated AN), 45.8 (CH2), 18.0 (py′
Me), 17.9 (py′ Me), 0.9 (PdMe).
n+
-
[(bim)Pd{CH(CN)CH2CH3}]n (B(C6F5)4 salt, 4a). An NMR
tube containing a solution of [(bim)PdMe(NCCHdCH2)][B(C6F5)4] (3a,
0.013 mmol) and AN (0.182 mmol) in CD2Cl2 (0.6 mL) was maintained
at 23 °C and monitored periodically by 1H NMR. The NMR signals of
3a disappeared after 10 h. The volatiles were removed under vacuum
to yield a pale yellow solid. The solid was dissolved in CD2Cl2 (0.6
mL). NMR and ESI-MS analyses showed that [(bim)Pd{CH(CN)-
CH2CH3}]nn+ (4a) had formed quantitatively. 1H NMR (CD2Cl2) Major
resonances: δ 7.10 (d, J ) 1, 1H, imidazole), 7.05 (d, J ) 1, 1H,
imidazole), 7.03 (d, J ) 1, 1H, imidazole), 7.02 (d, J ) 1, 1H,
imidazole), 6.99 (d, J ) 1, 1H, imidazole), 6.93 (d, J ) 1, 1H,
imidazole), 6.91 (d, J ) 1, 1H, imidazole), 6.87 (d, J ) 1, 1H,
imidazole), 6.86 (d, J ) 1, 1H, imidazole), 6.83 (br s, 2H, imidazole),
6.82 (d, J ) 1, 1H, imidazole), 4.14 (s, 2H, CH2), 4.12 (s, 2H, CH2),
4.09 (s, 2H, CH2), 3.78 (s, 3H, NMe), 3.76 (s, 3H, NMe), 3.75 (s, 3H,
NMe), 3.74 (s, 3H, NMe), 3.69 (s, 3H, NMe), 3.68 (s, 3H, NMe), 2.49
(br m, 3H, PdCH(CN)), 2.22 (m, 1H, PdCH(CN)CH2), 2.13 (m, 1H,
PdCH(CN)CH2), 2.05 (m, 2H, PdCH(CN)CH2), 1.90 (m, 1H, PdCH-
(CN)CH2), 1.78 (m, 1H, PdCH(CN)CH2), 1.25-1.10 (m, 9H,
PdCH(CN)CH2CH3). Major cations observed in ESI-MS: (bim)Pd-
{CH(CN)CH2CH3}+ calcd. m/z 350.1, found 350.1; [(bim)Pd{CH(CN)-
CH2CH3}]22+ calcd. m/z 350.1, found 350.1; {[(bim)Pd{CH(CN)CH2-
[(Me2bipy)PdMe(NCCHdCH2)][B(C6F5)4] (3d). A solution of [{-
(Me2bipy)PdMe}2(µ-Cl)][B(C6F5)4] (2d, 0.0075 mmol) and 0.5 equiv
[Li(Et2O)2.8][B(C6F5)4] (0.0075 mmol) in CD2Cl2 (0.6 mL) was gener-
ated in an NMR tube, and AN (0.45 mmol) was added by vacuum
transfer at -196 °C. The tube was warmed to 23 °C, resulting in
immediate formation of a slurry of a white solid in a pale yellow
1
supernatant. H NMR spectra showed that 3d had formed in >95%
1
yield. The H NMR spectrum contains separate sharp resonances for
free and coordinated AN at -60 °C and separate but broad resonances
for free and coordinated AN at 23 °C. 1H NMR (CD2Cl2, -60 °C): δ
8.29 (d, J ) 7, 1H, bipy H6), 8.28 (d, J ) 6, 1H, bipy H6), 7.96 (s,
1H, bipy H3), 7.94 (s, 1H, bipy H3), 7.41 (d, J ) 6, 1H, bipy H5),
7.40 (d, J ) 7, 1H, bipy H5), 6.66 (d, J ) 18, Htrans of coordinated
AN), 6.52 (d, J ) 12, Hcis of coordinated AN), 6.03 (dd, J ) 18, 12,
Hint of coordinated AN), 2.51 (s, 3H, bipy Me), 2.49 (s, 3H, bipy Me),
0.94 (s, 3H, PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ 156.3 (bipy
C2), 153.1 (bipy C4), 152.5 (bipy C4), 151.8 (bipy C2), 147.9 (bipy
C6), 147.4 (bipy, C6), 143.8 (Cter of coordinated AN), 127.8 (bipy),
127.4 (bipy), 123.8 (bipy), 122.9 (bipy), 120.4 (CN of coordinated AN),
105.5 (Cint of coordinated AN), 21.4 (bipy Me), 21.3 (bipy Me), 2.8
(PdMe). ESI-MS: [(Me2bipy)PdMe(NCCHdCH2)]+ calcd. m/z 358.1,
CH3}]33+[B(C6F5)4]-} calcd. m/z 865.5, found 865.2. IR (neat): VCN
)
2246 cm-1
.
[(Tbim)Pd{CH(CN)CH2CH3}]nn+ (B(C6F5)4- salt, 4b). This species
was generated quantitatively from 3b (0.018 mmol) and AN (0.144
mmol) in 40 min at 23 °C using the procedure for 4a. The observed
first-order rate constant for conversion of 3b to 4b, determined from
found 358.0. IR (neat): VCN ) 2247 cm-1
.
1
the disappearance of the PdMe H NMR resonance, is kobs(23 °C) )
[(tBu2bipy)PdMe(NCCHdCH2)][B(C6F5)4] (3e). This complex was
generated quantitatively in CD2Cl2 (0.6 mL) from 2e (0.014 mmol) in
the presence of [Li(Et2O)2.8][B(C6F5)4] (0.014 mmol) and AN (0.39
2.06(4) × 10-3 s-1 at 23 °C ([AN] ) 2.6 M, 70 equiv excess vs 3b),
k
obs(0 °C) ) 3.75(3) × 10-4 s-1 at 0 °C ([AN] ) 0.82 M, 20 equiv
excess vs 3b), kobs(0 °C) ) 4.03(5) × 10-4 s-1 at 0 °C ([AN] ) 1.6 M,
140 equiv excess vs 3b), and kobs(0 °C) ) 4.5(2) × 10-4 s-1 at 0 °C
(no free AN; 3b generated from 2b and 0.7 equiv AN). 1H NMR (CD2-
Cl2) Major resonances: δ 7.14-7.10 (m, 6H, tolyl H2), 7.00-6.76
(m, 4H, imidazole H), 6.63-6.46 (m, 6H, tolyl H3), 5.90-5.72 (m,
1H, CH), 3.57-3.00 (m, 6H, imidazole NMe), 2.40-2.20 (m, 9H, tolyl
Me), 2.17-1.70 (m, 1H, PdCH(CN)), 1.53-0.81 (m, 5H, PdCH(CN)-
CH2 and PdCH(CN)CH2CH3). Key cations observed in ESI-MS:
(Tbim)Pd{CH(CN)CH2CH3}+ calcd. m/z 634.2, found 634.1; {[(Tbim)-
Pd{CH(CN)CH2CH3}]22+-(p-tolyl)3C+} calcd. m/z 983.3, found 983.1.
1
mmol) using the procedure for 3d. The H NMR spectrum contains
separate but broad resonances for free and coordinated AN at 23 °C.
1H NMR (CD2Cl2): δ 8.43 (d, J ) 6, 1H, bipy H6), 8.35 (d, J ) 6,
1H, bipy H6), 8.12 (d, J ) 2, 1H, bipy H3), 8.11 (d, J ) 2, 1H, bipy
H3), 7.61 (dd, J ) 6, 2, 1H, bipy H5), 7.60 (dd, J ) 6, 2, 1H, bipy
H5), 6.66 (br d, J ) 18, 1H, Htrans coordinated AN), 6.53 (d, J ) 12,
1H, Hcis of coordinated AN), 1.43 (s, 9H, CMe3), 1.42 (s, 9H, CMe3),
1.06 (s, 3H, PdMe); the Hint resonance for coordinated AN was not
observed due to exchange broadening and/or interference from the free
AN resonances. 13C{1H} NMR (CD2Cl2): δ 165.7 (bipy C2), 165.3
(bipy C2), 157.1 (bipy C4), 152.6 (bipy C4), 148.5 (bipy C6), 147.8
(bipy, C6), 124.4 (bipy), 124.0 (bipy), 120.1 (bipy), 119.1 (bipy), 35.6
n+
-
[(CH2py′2)Pd{CH(CN)CH2CH3}]n (B(C6F5)4 salt, 4c). This
species was generated quantitatively from 3c (0.017 mmol) and AN
(0.510 mmol) in 2 d at 23 °C using the procedure for 4a. H NMR
1
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1849

A R T I C L E S
Wu et al.
(CD2Cl2) Major resonances: δ 8.45-7.30 (m, 6H, py′), 4.90-4.60 (m,
1H, CH2), 4.50-4.20 (m, 1H, CH2), 2.50-2.20 (m, 6H, py′ Me), 2.20-
2.05 (m, 1H, PdCH(CN)), 2.00-1.40 (m, 2H, PdCH(CN)CH2), 1.40-
0.90 (m, 3H, PdCH(CN)CH2CH3). Major cations observed in ESI-
MS: (CH2py′2)Pd{CH(CN)CH2CH3}+ calcd. m/z 372.1, found 371.9;
[(Tbim)Pd{CH(CN)CH2CH3}(PPh3)][B(C6F5)4] (5b). This com-
pound was generated in 90% yield from 4b (0.018 mmol) and PPh3
(6.7 mg, 0.025 mmol) using the procedure for 5a. 5b exists as two
diastereomers. The diastereomer ratio was 3/1 after 5 min and reached
a constant value of 1/1 after 24 h at 23 °C. NMR data for major
diastereomer: 1H NMR (CD2Cl2): δ 7.60 (m, 6H, PPh3), 7.46 (m, 4H,
PPh3 and imidazole), 7.35 (m, 6H, PPh3), 7.12 (d, J ) 8, 6H, tolyl
H2), 6.94 (s, 1H, imidazole), 6.83 (d, J ) 8, 6H, tolyl H3), 6.28 (d, J
) 1, 1H, imidazole), 5.97 (s, 1H, imidazole), 5.35 (s, 1H, CH), 3.25
(s, 3H, NMe), 2.68 (s, 3H, NMe), 2.37 (s, 9H, tolyl Me), 1.70 (m, 1H,
PdCH(CN)CH2), 1.20 (m, 2H, PdCH(CN)CH2), 0.79 (t, J ) 8, 3H,
PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 144.9 (imidazole C2),
144.2 (imidazole C2), 139.3 (tolyl Cipso), 138.6 (tolyl Cipso), 134.8 (d,
J ) 11, o-Ph), 132.4 (tolyl C3), 132.3 (d, J ) 4, p-Ph), 129.7 (d, J )
11, m-Ph), 129.4 (imidazole C), 129.1 (tolyl C2), 128.2 (imidazole C),
127.7 (d, J ) 27, PPh3 Cipso), 125.9 (CN), 123.5 (d, J ) 3, imidazole
C), 121.6 (imidazole C), 66.0 ((tolyl)3C), 45.6 (CH), 36.8 (NMe), 33.7
(NMe), 25.6 (br s, PdCH(CN)CH2), 21.0 (tolyl Me), 15.3 (PdCH(CN)-
CH2CH3), 13.5 (br s, PdCH(CN)CH2). 31P{1H} NMR (CD2Cl2): δ 34.0
(s, PPh3). Key 1H-1H COSY correlations δ/δ: 1.70 (PdCH(CN)CH2)/
1.20 (PdCH(CN)CH2); 1.20 (PdCH(CN)CH2)/0.79 (PdCH(CN)CH2CH3).
2+
[(CH2py′2)Pd{CH(CN)CH2CH3}]2 calcd. m/z 372.1, found 371.9;
{[(CH2py′2)Pd{CH(CN)CH2CH3}]33+[B(C6F5)4]-} calcd. m/z 897.6,
found 897.8.
n+
-
[(Me2bipy)Pd{CH(CN)CH2CH3}]n (B(C6F5)4 salt, 4d). This
species was generated quantitatively from 3d (0.015 mmol) and AN
(0.430 mmol) in 2 d at 23 °C using the procedure for 4a. H NMR
1
(CD2Cl2) Major resonances: δ 8.46-7.90 (m, 4H, bipy), 7.56-7.34
(m, 2H, bipy), 2.76-2.47 (m, 7H, PdCH(CN) and bipy Me), 2.17-
1.64 (m, 2H, PdCH(CN)CH2), 1.44-1.11 (m, 3H, PdCH(CN)CH2CH3).
Major cation observed in ESI-MS: (Me2bipy)Pd{CH(CN)CH2CH3}+
calcd. m/z 358.1, found 358.0. IR (neat): VCN ) 2249 cm-1
.
n+
-
[(Me2bipy)Pd{CH(CN)CH2CH3}]n (B(3,5-C6H3(CF3)2)4 salt,
4d′). A flask was charged with (Me2bipy)PdMeCl (1d, 100 mg, 0.29
mmol) and Na[B(3,5-C6H3(CF3)2)4] (260 mg, 0.29 mmol), and CH2Cl2
(40 mL) was added at -78 °C by vacuum transfer. The pale yellow
slurry was vigorously stirred for 5 min at 23 °C. The flask was cooled
to -196 °C and AN (0.2 mL, 3.0 mmol) was added by vacuum transfer.
The flask was warmed to 23 °C and the mixture was stirred for 2 d to
yield a slurry of a white solid in a yellow supernatant. The mixture
was filtered through diatomaceous earth and the yellow filtrate was
dried under vacuum to afford a yellow solid (290 mg, 81%). Anal.
Calcd for C48H30BF24N3Pd: C, 47.18; H, 2.47; N, 3.44. Found: C,
47.35; H, 2.65; N, 3.38. The NMR data for 4d′ are very similar to the
data for 4d, with the exception of the anion resonances.43
Key H-13C HMQC correlations δ H/δ 13C: 1.70 (PdCH(CN))/13.5
(PdCH(CN)); 1.20 (PdCH(CN)CH2)/25.6 (PdCH(CN)CH2); 0.79 (PdCH-
(CN)CH2CH3)/15.3 (PdCH(CN)CH2CH3). NMR data for minor dias-
tereomer: 1H NMR (CD2Cl2): δ 7.80 (s, 1H, imidazole), 7.56 (m, 6H,
PPh3), 7.51 (m, 3H, PPh3), 7.29 (m, 6H, PPh3), 7.05 (d, J ) 8, 6H,
tolyl H2), 6.92 (s, 1H, imidazole), 6.64 (d, J ) 8, 6H, tolyl H3), 6.39
(d, J ) 1.4, 1H, imidazole), 5.89 (s, 1H, imidazole), 5.73 (s, 1H, CH),
3.17 (s, 3H, NMe), 3.00 (s, 3H, NMe), 2.31 (s, 9H, tolyl Me), 1.70 (m,
1H, PdCH(CN)CH2), 1.60 (m, 2H, PdCH(CN)CH2), 0.73 (t, J ) 8,
3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 144.6 (imidazole
C2), 144.4 (imidazole C2), 139.7 (tolyl Cipso), 138.4 (tolyl Cipso), 134.8
(d, J ) 11, o-Ph), 132.2 (d, J ) 4, p-Ph), 132.0 (tolyl C3), 129.6 (d,
J ) 11, m-Ph), 129.2 (imidazole C), 129.0 (tolyl C2), 128.4 (imidazole
C), 128.1 (d, J ) 40, PPh3 Cipso), 125.8 (CN), 123.4 (d, J ) 3, imidazole
C), 122.0 (imidazole C), 65.8 ((tolyl)3C), 46.1 (CH), 36.2 (NMe), 34.9
(NMe), 25.8 (PdCH(CN)CH2), 20.9 (tolyl Me), 15.0 (PdCH(CN)-
CH2CH3), 11.9 (d, J ) 7, PdCH(CN)CH2). 31P{1H} NMR (CD2Cl2):
δ 33.4 (s, PPh3). Key 1H-1H COSY correlations δ/δ: 1.70 (PdCH(CN)-
CH2)/1.60 (PdCH(CN)CH2); 1.60 (PdCH(CN)CH2)/0.73 (PdCH(CN)-
CH2CH3). Key 1H-13C HMQC correlations δ 1H/δ 13C: 1.70 (PdCH-
(CN))/11.9 (PdCH(CN)); 1.60 (PdCH(CN)CH2)/25.8 (PdCH(CN)CH2);
0.73 (PdCH(CN)CH2CH3)/15.0 (PdCH(CN)CH2CH3). ESI-MS: (Tbim)-
1
1
n+
-
[(tBu2bipy)Pd{CH(CN)CH2CH3}]n (B(C6F5)4 salt, 4e). This
species was generated quantitatively from 3e (0.028 mmol) and AN
1
(0.36 mmol) after 38 h at 23 °C using the procedure for 4a. H NMR
(CD2Cl2) Major resonances: δ 8.50-7.96 (m, 4H, bipy), 7.73-7.56
(m, 2H, bipy), 2.75-2.52 (m, 1H, PdCH(CN)), 2.22-1.64 (m, 2H,
PdCH(CN)CH2), 1.50-1.11 (m, 21H, CMe3 and PdCH(CN)CH2CH3).
Major cation observed in ESI-MS: (tBu2bipy)Pd{CH(CN)CH2CH3}+
calcd. m/z 442.1, found 442.0.
[(bim)Pd{CH(CN)CH2CH3}(PPh3)][B(C6F5)4] (5a). Solid PPh3 (3.3
mg, 0.013 mmol) was added to an NMR tube containing solid [(bim)-
n+
-
Pd{CH(CN)CH2CH3}]n (B(C6F5)4 salt, 4a, 0.013 mmol). The tube
was evacuated and CD2Cl2 (0.6 mL) was added by vacuum transfer at
-78 °C. The tube was vigorously agitated to yield an off-white solution
and was then warmed to 23 °C. After 5 min, NMR spectra showed
that (bim)Pd{CH(CN)CH2CH3}(PPh3)+ (5a) had formed in 90% yield.
1H NMR (CD2Cl2): δ 7.68 (m, 7H, o-Ph and imidazole), 7.57 (m, 3H,
p-Ph), 7.48 (m, 6H, m-Ph), 7.02 (m, 1H, imidazole), 6.40 (d, J ) 2,
1H, imidazole), 5.71 (d, J ) 2, 1H, imidazole), 4.26 (d, J ) 17, 1H,
CH2), 4.22 (d, J ) 17, 1H, CH2), 3.78 (s, 3H, NMe), 3.62 (s, 3H, NMe),
1.72 (ddd, JHH ) 12.9, 8.5; JHP ) 6.9, 1H, PdCH(CN)CH2), 1.30 (m,
2H, PdCH(CN)CH2), 0.67 (t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C-
{1H} NMR (CD2Cl2): δ 141.6 (imidazole C2), 141.0 (imidazole C2),
134.6 (d, J ) 11, o-Ph), 132.4 (d, J ) 3, p-Ph), 129.6 (d, J ) 10,
m-Ph), 128.2 (d, J ) 52, Ph Cipso), 128.0 (imidazole C4), 127.3
(imidazole C4), 123.8 (CN), 122.6 (d, J ) 2, imidazole C5), 122.0
(imidazole C5), 34.6 (NMe), 34.3 (NMe), 25.5 (PdCH(CN)CH2), 23.2
(CH2), 15.2 (PdCH(CN)CH2CH3), 13.2 (d, J ) 4, PdCH(CN)CH2). 31P-
{1H} NMR (CD2Cl2): δ 35.1 (s, PPh3). Key 1H-1H COSY correlations
δ/δ: 1.72 (PdCH(CN)CH2)/1.30 (PdCH(CN)CH2); 1.30 (PdCH(CN)-
CH2)/0.67 (PdCH(CN)CH2CH3). ESI-MS: (bim)Pd{CH(CN)CH2-
CH3}(PPh3)+ calcd. m/z 612.1, found 612.0. B(C6F5)4- calcd. m/z 679.0,
Pd{CH(CN)CH2CH3}(PPh3)+ calcd. m/z 896.2, found 896.2. B(C6F5)4
-
calcd. m/z 679.0, found 678.7.
[(CH2py′2)Pd{CH(CN)CH2CH3}(PPh3)][B(C6F5)4] (5c). This com-
pound was generated quantitatively from 4c (0.016 mmol) and PPh3
(4.2 mg, 0.016 mmol) using the procedure for 5a. 5c exists as two
diastereomers. The diastereomer ratio was 5/1 after 5 min and did not
1
change after 24 h at 23 °C. NMR data for major diastereomer: H
NMR (CD2Cl2): δ 9.12 (s, 1H, py′ H6), 7.75 (d, JHP ) 8, 1H, py′ H6),
7.61 (m, 8H, o-Ph and py′ H4), 7.48 (m, 6H, m-Ph), 7.35 (m, 5H, p-Ph
and py′ H3), 5.00 (d, J ) 14, 1H, CH2), 4.37 (d, J ) 14, 1H, CH2),
2.42 (s, 3H, py′ Me), 1.81 (ddd, JHH ) 12.1, 10.7; JHP ) 4.6, 1H,
PdCH(CN)CH2), 1.74 (s, 3H, py′ Me), 1.33 (m, 1H, PdCH(CN)CH2),
1.02 (m, 1H, PdCH(CN)CH2), 0.65 (t, J ) 7, 3H, PdCH(CN)CH2CH3).
13C{1H} NMR (CD2Cl2): δ 151.8 (py′ C2), 151.7 (d, J ) 2, py′ C6),
151.6 (py′ C2), 149.7 (py′ C6), 141.1 (py′ C4), 140.1 (py′ C4), 135.1
(d, J ) 2, py′ C5), 134.4 (py′ C5), 133.9 (d, J ) 11, o-Ph), 132.1 (d,
J ) 3, p-Ph), 129.3 (d, J ) 11, m-Ph), 126.8 (d, J ) 53, Ph Cipso),
125.6 (CN), 125.1 (d, J ) 2, py′ C3), 124.3 (py′ C3), 45.8 (CH2), 25.9
(PdCH(CN)CH2), 17.9 (py′ Me), 17.7 (py′ Me), 14.6 (PdCH(CN)-
CH2CH3), 12.1 (d, J ) 5, PdCH(CN)CH2). 31P{1H} NMR (CD2Cl2):
δ 34.0 (s, PPh3). Key 1H-1H COSY correlations δ/δ: 1.81 (PdCH(CN)-
CH2)/1.33 (PdCH(CN)CH2); 1.81 (PdCH(CN)CH2)/1.02 (PdCH(CN)-
CH2); 1.33 (PdCH(CN)CH2)/1.02 (PdCH(CN)CH2); 1.33 (PdCH(CN)-
found 678.7. IR (neat): VCN ) 2192 cm-1
.
(43) NMR spectra of B{3,5-C6H3(CF3)2}4- salts contain resonances at the free
anion positions. 1H NMR (CD2Cl2): δ 7.72 (s, 8H, H2), 7.55 (s, 4H, H4).
13C{1H} NMR (CD2Cl2): δ 162.1 (q, JCB ) 234, C1), 135.1 (C2), 129.2
(q, JCF ) 32, C3), 125.0 (q, JCF ) 273, CF3), 117.8 (m, C4). 19F NMR
(CD2Cl2): δ -62.8 (s). 11B NMR (CD2Cl2): δ -6.7 (s).
9
1850 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Acrylonitrile Insertion of Palladium Alkyl Complexes
A R T I C L E S
CH2)/0.65 (PdCH(CN)CH2CH3); 1.02 (PdCH(CN)CH2)/0.65 (PdCH(CN)-
CH2CH3). NMR data for minor diastereomer: H NMR (CD2Cl2): δ
120.3 (bipy), 120.2 (bipy), 36.1 (CMe3), 35.9 (CMe3), 30.2 (CMe3),
30.0 (CMe3), 24.6 (PdCH(CN)CH2), 15.9 (d, J ) 6, PdCH(CN)CH2),
15.0 (PdCH(CN)CH2CH3). 31P{1H} NMR (CD2Cl2): δ 40.7 (s, PPh3).
Key 1H-1H COSY correlations δ/δ: 2.00 (PdCH(CN)CH2)/1.66 (PdCH-
(CN)CH2); 2.00 (PdCH(CN)CH2)/1.41 (PdCH(CN)CH2); 1.66 (PdCH-
(CN)CH2)/1.41 (PdCH(CN)CH2); 1.66 (PdCH(CN)CH2)/0.76 (PdCH-
(CN)CH2CH3); 1.41 (PdCH(CN)CH2)/ 0.76 (PdCH(CN)CH2CH3). ESI-
MS: (tBu2bipy)Pd{CH(CN)CH2CH3}(PPh3)+ calcd. m/z 704.2, found
704.1.
1
8.51 (s, 1H, py′ H6), 7.66-7.21 (m, 20H, PPh3 and py′ H), 5.19 (d, J
) 13, 1H, CH2), 4.44 (d, J ) 13, 1H, CH2), 2.39 (s, 3H, py′ Me), 1.81
(m, 1H, PdCH(CN)CH2), 1.74 (s, 3H, py′ Me), 1.02 (m, 2H, PdCH-
(CN)CH2), 0.55 (t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR
(CD2Cl2): δ 151.5 (py′ C6), 150.3 (py′ C6), 141.0 (py′ C4), 140.0
(py′ C4), 133.8 (d, J ) 11, o-Ph), 132.1 (d, J ) 3, p-Ph), 129.3 (d, J
) 11, m-Ph), 126.6 (d, J ) 53, Ph Cipso), 125.4 (CN), 124.8 (d, J ) 2,
py′ C3), 124.3 (py′ C3), 46.4 (CH2), 22.9 (PdCH(CN)CH2), 17.9 (py′
Me), 17.7 (py′ Me), 14.5 (PdCH(CN)CH2CH3), 10.3 (d, J ) 5, PdCH-
(CN)CH2). The py′ C2 and C5 resonances were not observed. 31P{1H}
NMR (CD2Cl2): δ 34.2 (s, PPh3). ESI-MS: (CH2py′2)Pd{CH(CN)CH2-
CH3}(PPh3)+ calcd. m/z 634.2, found 633.9. B(C6F5)4- calcd. m/z 679.0,
found 678.7.
[(bim)Pd{CH(CN)CH2CH3}(PMe3)][B(C6F5)4] (6a). An NMR tube
containing a solution of [(bim)Pd{CH(CN)CH2CH3}]nn+ (B(C6F5)4- salt,
4a, 0.013 mmol) in CD2Cl2 (0.6 mL) was cooled to -196 °C and PMe3
(0.014 mmol) was added by vacuum transfer. The tube was warmed
to 23 °C and vigorously agitated resulting in an off-white solution.
After 5 min at 23 °C, NMR spectra showed that (bim)Pd{CH(CN)-
1
CH2CH3}(PMe3)+ (6a) had formed in 90% yield. H NMR (CD2Cl2):
[(Me2bipy)Pd{CH(CN)CH2CH3}(PPh3)][B(C6F5)4] (5d). This com-
pound was generated in 85% yield in 4 h at 23 °C from 4d (0.015
mmol) and PPh3 (3.8 mg, 0.015 mmol) using the procedure for 5a. 1H
NMR (CD2Cl2): δ 8.99 (br, 1H, bipy H6), 8.04 (s, 1H, bipy H3), 7.95
(s, 1H, bipy H3), 7.80 (m, 6H, o-Ph), 7.62 (m, 4H, p-Ph and bipy H5),
7.52 (m, 6H, m-Ph), 7.26 (d, J ) 6, 1H, bipy H6), 6.75 (d, J ) 6, 1H,
bipy H5), 2.61 (s, 3H, bipy Me), 2.39 (s, 3H, bipy Me), 1.99 (ddd, JHH
) 12.5, 6.3; JHP ) 10.2, 1H, PdCH(CN)CH2), 1.64 (m, 1H, PdCH-
(CN)CH2), 1.40 (m, 1H, PdCH(CN)CH2), 0.74 (t, J ) 7, 3H, PdCH-
(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 155.9 (bipy C2), 155.4 (bipy
C2), 154.6 (bipy C4), 153.8 (bipy C4), 151.0 (bipy C6), 149.8 (bipy,
C6), 135.1 (d, J ) 11, o-Ph), 133.0 (d, J ) 2, p-Ph), 129.9 (d, J ) 11,
m-Ph), 128.5 (bipy), 127.6 (d, J ) 53, PPh3 Cipso), 127.5 (bipy), 125.7
(CN), 124.1 (bipy), 124.0 (bipy), 24.5 (PdCH(CN)CH2), 21.7 (bipy
Me), 21.5 (bipy Me), 15.7 (d, J ) 6, PdCH(CN)CH2), 15.0 (PdCH-
δ 7.50 (s, 1H, imidazole), 6.98 (s, 1H, imidazole), 6.94 (d, J ) 1, 1H,
imidazole), 6.86 (d, J ) 1, 1H, imidazole), 4.17 (s, 2H, CH2), 3.75 (s,
3H, NMe), 3.72 (s, 3H, NMe), 1.93 (m, 1H, PdCH(CN)CH2), 1.53 (d,
J ) 11, 9H, PMe3), 1.46 (m, 2H, PdCH(CN)CH2), 1.03 (t, J ) 7, 3H,
PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 142.2 (imidazole C2),
141.7 (imidazole C2), 128.6 (imidazole C4), 126.8 (imidazole C4),
123.8 (CN), 122.8 (imidazole C5), 122.6 (d, J ) 4, imidazole C5),
34.5 (NMe), 34.4 (NMe), 25.6 (PdCH(CN)CH2), 23.2 (CH2), 15.6
(PdCH(CN)CH2CH3), 14.8 (d, J ) 35, PMe3), 9.0 (d, J ) 6, PdCH-
1
(CN)CH2). 31P{1H} NMR (CD2Cl2): δ -5.3 (s, PMe3). Key H-1H
COSY correlations δ/δ: 1.93 (PdCH(CN)CH2)/1.46 (PdCH(CN)CH2);
1.46 (PdCH(CN)CH2)/1.03 (PdCH(CN)CH2CH3). ESI-MS: (bim)Pd-
-
{CH(CN)CH2CH3}(PMe3)+ calcd. m/z 426.1, found 426.0; B(C6F5)4
calcd. m/z 679.0, found 678.7. IR (neat): VCN ) 2193 cm-1
.
1
(CN)CH2CH3). 31P{1H} NMR (CD2Cl2): δ 38.7 (s, PPh3). Key H-
[(Tbim)Pd{CH(CN)CH2CH3}(PMe3)][B(C6F5)4] (6b). This species
was generated in 95% yield in 5 min at 23 °C from [(Tbim)Pd{CH-
(CN)CH2CH3}]nn+ (B(C6F5)4- salt, 4b, 0.018 mmol) and PMe3 (0.018
mmol) using the procedure for 6a. 6b exists as two diastereomers. The
diastereomer ratio was 3/1 after 5 min and did not change after 24 h at
23 °C. NMR data for major diastereomer: 1H NMR (CD2Cl2): δ 7.54
(s, 1H, imidazole), 7.03 (d, J ) 8, 6H, tolyl H2), 6.86 (d, J ) 1, 1H,
imidazole), 6.85 (s, 1H, imidazole), 6.83 (d, J ) 1, 1H, imidazole),
6.62 (d, J ) 8, 6H, tolyl H3), 5.86 (s, 1H, CH), 3.27 (s, 3H, NMe),
3.16 (s, 3H, NMe), 2.33 (s, 9H, tolyl Me), 1.55 (m, 1H, PdCH(CN)-
CH2), 1.47 (m, 2H, PdCH(CN)CH2), 1.39 (d, J ) 10, 9H, PMe3), 1.10
(t, J ) 8, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 144.6
(imidazole C2), 144.5 (imidazole C2), 139.6 (tolyl Cipso), 138.4 (tolyl
1H COSY correlations δ/δ: 1.99 (PdCH(CN)CH2)/1.64 (PdCH(CN)-
CH2); 1.99 (PdCH(CN)CH2)/1.40 (PdCH(CN)CH2); 1.64 (PdCH(CN)-
CH2)/1.40 (PdCH(CN)CH2); 1.64 (PdCH(CN)CH2)/0.74 (PdCH(CN)-
CH2CH3); 1.40 (PdCH(CN)CH2)/0.74 (PdCH(CN)CH2CH3). ESI-MS:
(Me2bipy)Pd{CH(CN)CH2CH3}(PPh3)+ calcd. m/z 620.1, found 620.0.
IR (neat): VCN ) 2196 cm-1
.
[(Me2bipy)Pd{CH(CN)CH2CH3}(PPh3)][B(3,5-C6H3(CF3)2)4] (5d′).
A flask was charged with (Me2bipy)PdMeCl (1d, 100 mg, 0.29 mmol)
and Na[B(3,5-C6H3(CF3)2)4] (260 mg, 0.29 mmol), and CH2Cl2 (40 mL)
was added at -78 °C by vacuum transfer. The pale yellow slurry was
vigorously stirred for 5 min at 23 °C. The flask was cooled to -196
°C and AN (0.2 mL, 3.0 mmol) was added by vacuum transfer. The
flask was warmed to 23 °C and the mixture was stirred for 2 d to yield
a slurry of a white solid in a pale yellow supernatant. A solution of
PPh3 (75 mg, 0.29 mmol) in CH2Cl2 (5 mL) was added by syringe.
The mixture was stirred for 6 h at 23 °C to afford a white slurry in
yellow supernatant. The mixture was filtered through diatomaceous
earth and the yellow filtrate was dried under vacuum to afford a yellow
solid (320 mg, 74%). Anal. Calcd for C66H45BF24N3PPd: C, 53.41; H,
3.06; N, 2.83. Found: C, 53.57; H, 3.39; N, 2.85. The NMR data for
5d′ are identical with the data for 5d with the exception of the anion
resonances.43
[(tBu2bipy)Pd{CH(CN)CH2CH3}(PPh3)][B(C6F5)4] (5e). This com-
pound was generated in 90% yield in 1 h at 23 °C from 4e (0.026
mmol) and PPh3 (6.7 mg, 0.026 mmol) using the procedure for 5a. 1H
NMR (CD2Cl2): δ 9.09 (br, 1H, bipy H6), 8.17 (s, 1H, bipy H3), 8.09
(s, 1H, bipy H3), 7.81 (m, 7H, o-Ph and bipy H5), 7.63 (m, 3H, p-Ph),
7.53 (m, 6H, m-Ph), 7.34 (br, 1H, bipy H6), 6.92 (br, 1H, bipy H5),
2.00 (ddd, JHH ) 12.4, 10.2; JHP ) 6.2, 1H, PdCH(CN)CH2), 1.66 (m,
1H, PdCH(CN)CH2), 1.48 (s, 9H, CMe3), 1.41 (m, 1H, PdCH(CN)-
CH2), 1.30 (s, 9H, CMe3), 0.76 (t, J ) 7, 3H, PdCH(CN)CH2CH3).
13C{1H} NMR (CD2Cl2): δ 166.9 (bipy C2), 166.2 (bipy C2), 156.3
(bipy C4), 155.7 (bipy C4), 151.3 (bipy C6), 150.1 (bipy, C6), 135.1
(d, J ) 11, o-Ph), 133.0 (d, J ) 2, p-Ph), 129.9 (d, J ) 11, m-Ph),
127.6 (d, J ) 53, Ph Cipso), 125.1 (bipy), 123.9 (bipy), 122.6 (CN),
Cipso), 131.9 (tolyl C3), 129.5 (d, J ) 3, imidazole C), 128.9 (tolyl
C2), 126.8 (imidazole C), 126.5 (CN), 123.1 (d, J ) 4, imidazole C),
123.0 (imidazole C), 65.3 ((tolyl)3C), 46.2 (CH), 35.8 (NMe), 35.3
(NMe), 25.6 (PdCH(CN)CH2), 20.9 (tolyl Me), 15.7 (PdCH(CN)-
CH2CH3), 14.8 (d, J ) 34, PMe3), 9.1 (d, J ) 8, PdCH(CN)CH2). 31P-
1
{1H} NMR (CD2Cl2): δ -7.3 (s, PMe3). Key H-1H COSY correla-
tions δ/δ: 1.55 (PdCH(CN)CH2)/1.47 (PdCH(CN)CH2); 1.47
(PdCH(CN)CH2)/1.10 (PdCH(CN)CH2CH3). Key 1H-13C HMQC cor-
relations δ 1H/δ 13C: 1.55 (PdCH(CN))/9.1 (PdCH(CN)); 1.47 (PdCH-
(CN)CH2)/25.6 (PdCH(CN)CH2); 1.10 (PdCH(CN)CH2CH3)/15.7 (PdCH-
(CN)CH2CH3). NMR data for minor diastereomer: 1H NMR (CD2-
Cl2): δ 7.20 (s, 1H, imidazole), 7.08 (d, J ) 8, 6H, tolyl H2), 6.89 (s,
1H, imidazole), 6.84 (s, 1H, imidazole), 6.80 (s, 1H, imidazole), 6.65
(d, J ) 8, 6H, tolyl H3), 5.71 (s, 1H, CH), 3.19 (s, 3H, NMe), 3.15 (s,
3H, NMe), 2.33 (s, 9H, tolyl Me), 1.96 (m, 1H, PdCH(CN)CH2), 1.64
(m, 2H, PdCH(CN)CH2), 1.37 (d, J ) 10, 9H, PMe3), 1.15 (t, J ) 8,
3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 144.9 (imidazole
C2), 144.0 (imidazole C2), 139.4 (tolyl Cipso), 138.3 (tolyl Cipso), 132.0
(tolyl C3), 129.1 (imidazole C), 129.0 (tolyl C2), 127.3 (CN), 127.1
(imidazole C), 123.3 (d, J ) 3, imidazole C), 122.9 (imidazole C),
65.5 ((tolyl)3C), 46.0 (CH), 36.0 (NMe), 35.0 (NMe), 25.4 (PdCH-
(CN)CH2), 20.9 (tolyl Me), 15.4 (PdCH(CN)CH2CH3), 14.8 (d, J )
34, PMe3), 9.0 (d, J ) 8, PdCH(CN)CH2). 31P{1H} NMR (CD2Cl2): δ
9
J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1851

A R T I C L E S
Wu et al.
-7.7 (s, PMe3). Key 1H-1H COSY correlations δ/δ: 1.96 (PdCH(CN)-
CH2)/1.64 (PdCH(CN)CH2); 1.64 (PdCH(CN)CH2)/1.15 (PdCH(CN)-
CH2CH3). Key 1H-13C HMQC correlations δ 1H/δ 13C: 1.96 (PdCH-
(CN))/9.0 (PdCH(CN)); 1.64 (PdCH(CN)CH2)/25.4 (PdCH(CN)CH2);
1.15 (PdCH(CN)CH2CH3)/15.4 (PdCH(CN)CH2CH3). ESI-MS: (Tbim)-
(PdCH(CN)CH2)/1.92 (PdCH(CN)CH2); 1.92 (PdCH(CN)CH2)/1.21
(PdCH(CN)CH2CH3). Key H-13C HMQC correlations δ H/δ 13C:
2.83 (PdCH(CN))/16.4 (PdCH(CN)); 1.92 (PdCH(CN)CH2)/29.5 (Pd-
CH(CN)CH2); 1.21 (PdCH(CN)CH2CH3)/15.5 (PdCH(CN)CH2CH3).
The volatiles were removed under vacuum to yield a pale yellow solid.
The solid was dried under vacuum for 10 min and dissolved in CD2-
Cl2 (0.6 mL). NMR analysis showed that the solid was 4a. In a separate
experiment, 7a was formed under 6.7 atm CO pressure. The CO
pressure was decreased to 1 atm. NMR analysis showed that 7a was
completely converted to 4a.
1
1
Pd{CH(CN)CH2CH3}(PMe3)+ calcd. m/z 710.3, found 710.2; B(C6F5)4
-
calcd. m/z 679.0, found 678.7.
[(CH2py′2)Pd{CH(CN)CH2CH3}(PMe3)][B(C6F5)4] (6c). This spe-
cies was generated in 95% yield from [(CH2py′2)Pd{CH(CN)CH2-
n+
-
CH3}]n (B(C6F5)4 salt, 4c, 0.017 mmol) and PMe3 (0.017 mmol)
using the procedure for 6a. 6c exists as two isomers. The isomer ratio
was 3/1 after 5 min and did not change after 24 h at 23 °C. NMR data
for major isomer: 1H NMR (CD2Cl2): δ 8.92 (s, 1H, py′ H6), 8.20 (s,
1H, py′ H6), 7.72 (d, J ) 8, 1H, py′ H4), 7.68 (d, J ) 8, 1H, py′ H4),
7.44 (m, 2H, py′ H3), 4.82 (d, J ) 14, 1H, CH2), 4.29 (d, J ) 14, 1H,
[(Tbim)Pd{CH(CN)CH2CH3}(CO)][B(C6F5)4] (7b). This com-
pound was generated quantitatively from [(Tbim)Pd{CH(CN)CH2-
n+
-
CH3}]n (B(C6F5)4 salt, 4b, 0.018 mmol) and CO (0.558 mmol,
corresponding to ca. 6.7 atm at 23 °C) using the procedure for 7a. 7b
exists as two diastereomers. The diastereomer ratio was 4/3 after 5
min and reached a constant value of 1/1 after 2 h at 23 °C. 7b is stable
CH2), 2.40 (s, 3H, py′ Me), 2.34 (s, 3H, py′ Me), 1.90 (ddd, JHH
)
1
9.2, 6.6; JHP ) 11.9, 1H, PdCH(CN)CH2), 1.53 (d, J ) 11, 9H, PMe3),
1.31 (m, 1H, PdCH(CN)CH2), 1.19 (m, 1H, PdCH(CN)CH2), 0.98 (t,
J ) 7, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 153.0
(py′ C2), 151.5 (py′ C6), 150.9 (py′ C2), 149.5 (py′ C6), 141.1 (py′
C4), 141.1 (py′ C4), 135.0 (py′ C5), 134.8 (py′ C5), 126.2 (CN), 125.2
(py′ C3), 125.0 (d, J ) 3, py′ C3), 46.0 (CH2), 25.5 (PdCH(CN)CH2),
17.9 (py′ Me), 17.6 (py′ Me), 15.1 (PdCH(CN)CH2CH3), 14.0 (d, J )
35, PMe3), 9.4 (d, J ) 7, PdCH(CN)CH2). 31P{1H} NMR (CD2Cl2): δ
-5.4 (s, PMe3). Key 1H-1H COSY correlations δ/δ: 1.90 (PdCH(CN)-
CH2)/δ 1.31 (PdCH(CN)CH2); 1.90 (PdCH(CN)CH2)/1.19 (PdCH(CN)-
CH2); 1.31 (PdCH(CN)CH2)/1.19 (PdCH(CN)CH2); 1.31 (PdCH(CN)-
CH2)/0.98 (PdCH(CN)CH2CH3); 1.19 (PdCH(CN)CH2)/0.98 (PdCH(CN)-
CH2CH3). NMR data for minor isomer: 1H NMR (CD2Cl2): δ 8.37 (s,
1H, py′ H6), 8.17 (s, 1H, py′ H6), 7.70 (m, 2H, py′ H4), 7.45 (m, 2H,
py′ H3), 4.89 (d, J ) 14, 1H, CH2), 4.31 (d, J ) 14, 1H, CH2), 2.38
(s, 3H, py′ Me), 2.33 (s, 3H, py′ Me), 1.90 (m, 1H, PdCH(CN)CH2),
1.53 (d, J ) 11, 9H, PMe3), 1.16 (m, 2H, PdCH(CN)CH2), 1.01 (t, J
) 7, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 151.8 (py′
C6), 149.6 (py′ C6), 141.2 (py′ C4), 141.1 (py′ C4), 125.4 (py′ C3),
124.8 (py′ C3), 46.0 (CH2), 24.7 (PdCH(CN)CH2), 17.8 (py′ Me), 17.5
(py′ Me), 14.9 (PdCH(CN)CH2CH3), 13.4 (d, J ) 34, PMe3), 11.1
(PdCH(CN)CH2). The py′ C2, C5, and CN resonances were not
observed. 31P{1H} NMR (CD2Cl2): δ -6.5 (s, PMe3). ESI-MS: (CH2-
py′2)Pd{CH(CN)CH2CH3}(PMe3)+ calcd. m/z 448.1, found 447.9;
under 1 atm of CO. NMR data for diastereomer A: H NMR (CD2-
Cl2): δ 7.23 (d, J ) 1, 1H, imidazole), 7.10 (d, J ) 8, 6H, tolyl H2),
6.98 (d, J ) 1, 1H, imidazole), 6.96 (d, J ) 1, 1H, imidazole), 6.95 (d,
J ) 1, 1H, imidazole), 6.54 (d, J ) 8, 6H, tolyl H3), 5.83 (s, 1H, CH),
3.30 (s, 3H, NMe), 3.13 (s, 3H, NMe), 2.41 (m, 1H, PdCH(CN)CH2),
2.36 (s, 9H, tolyl Me), 1.67 (m, 2H, PdCH(CN)CH2), 1.15 (t, J ) 7,
3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ 173.7 (Pd-CO),
144.9 (imidazole C2), 142.5 (imidazole C2), 139.1 (tolyl Cipso), 137.7
(tolyl Cipso), 132.1 (tolyl C3), 129.0 (tolyl C2), 128.7 (imidazole C),
125.6 (imidazole C), 124.7 (imidazole C), 124.6 (CN), 123.9 (imidazole
C), 66.6 ((tolyl)3C), 45.7 (CH), 36.4 (NMe), 35.0 (NMe), 29.6 (PdCH-
(CN)CH2), 20.9 (tolyl Me), 15.6 (PdCH(CN)CH2CH3), 14.7 (PdCH-
(CN)CH2). Key 1H-1H COSY correlations δ/δ: 2.41 (PdCH(CN)CH2)/
1.67 (PdCH(CN)CH2); 1.67 (PdCH(CN)CH2)/1.15 (PdCH(CN)CH2CH3).
Key H-13C HMQC correlations δ H/δ 13C: 2.41 (PdCH(CN))/14.7
(PdCH(CN)); 1.67 (PdCH(CN)CH2)/29.6 (PdCH(CN)CH2); 1.15 (PdCH-
(CN)CH2CH3)/15.6 (PdCH(CN)CH2CH3). NMR data for diastereomer
1
1
1
B: H NMR (CD2Cl2): δ 7.12 (d, J ) 8, 6H, tolyl H2), 7.01 (d, J )
1, 1H, imidazole), 6.96 (d, J ) 1, 1H, imidazole), 6.95 (d, J ) 1, 1H,
imidazole), 6.88 (d, J ) 1, 1H, imidazole), 6.59 (d, J ) 8, 6H, tolyl
H3), 5.84 (s, 1H, CH), 3.35 (s, 3H, NMe), 3.10 (s, 3H, NMe), 2.58 (m,
1H, PdCH(CN)CH2), 2.37 (s, 9H, tolyl Me), 1.85 (m, 2H, PdCH(CN)-
CH2), 1.23 (t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2-
Cl2): δ 173.7 (Pd-CO), 144.6 (imidazole C2), 142.4 (imidazole C2),
139.0 (tolyl Cipso), 137.8 (tolyl Cipso), 132.1 (tolyl C3), 129.1 (tolyl C2),
128.8 (imidazole C), 125.0 (imidazole C), 124.6 (imidazole C), 124.1
(CN), 123.8 (imidazole C), 66.5 ((tolyl)3C), 45.8 (CH), 36.5 (NMe),
34.8 (NMe), 28.8 (PdCH(CN)CH2), 20.8 (tolyl Me), 15.3 (PdCH(CN)-
CH2CH3), 14.9 (PdCH(CN)CH2). Key 1H-1H COSY correlations δ/δ:
2.58 (PdCH(CN)CH2)/1.85 (PdCH(CN)CH2); 1.85 (PdCH(CN)CH2)/
1.23 (PdCH(CN)CH2CH3). Key 1H-13C HMQC correlations δ 1H/δ
13C: 2.58 (PdCH(CN))/14.9 (PdCH(CN)); 1.85 (PdCH(CN)CH2)/28.8
(PdCH(CN)CH2); 1.23 (PdCH(CN)CH2CH3)/15.3 (PdCH(CN)CH2CH3).
ESI-MS: Major cation observed: [(Tbim)Pd{CH(CN)CH2CH3}(CO)+-
CO] calcd. m/z 634.2, found 634.0. IR (CD2Cl2, under 1 atm CO): VCO
-
B(C6F5)4 calcd. m/z 679.0, found 678.7.
[(bim)Pd{CH(CN)CH2CH3}(CO)][B(C6F5)4] (7a). An NMR tube
containing a solution of [(bim)Pd{CH(CN)CH2CH3}]nn+ (B(C6F5)4- salt,
4a, 0.013 mmol) in CD2Cl2 (0.6 mL) was cooled to -196 °C and CO
(0.558 mmol, corresponding to ca. 6.7 atm at 23 °C) was added. The
tube was warmed to 23 °C to yield an off-white solution. After 5 min,
NMR spectra showed that (bim)Pd{CH(CN)CH2CH3}(CO)+ (7a) had
formed quantitatively.44 Separate resonances for free (δ 184.0) and
1
coordinated CO are present in the 13C NMR spectrum at 23 °C. H
NMR (CD2Cl2): δ 7.19 (d, J ) 1, 1H, imidazole), 7.14 (d, J ) 1, 1H,
imidazole), 7.09 (d, J ) 1, 1H, imidazole), 7.00 (d, J ) 1, 1H,
imidazole), 4.19 (d, J ) 18, 1H, CH2), 4.16 (d, J ) 18, 1H, CH2), 3.80
(s, 3H, NMe), 3.77 (s, 3H, NMe), 2.83 (m, 1H, PdCH(CN)CH2), 1.92
(m, 2H, PdCH(CN)CH2), 1.21 (t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C-
{1H} NMR (CD2Cl2): δ 174.2 (PdCO), 141.4 (imidazole C2), 140.1
(imidazole C2), 128.9 (imidazole C4), 125.8 (imidazole C4), 124.2
(CN), 124.0 (imidazole C5), 123.8 (imidazole C5), 35.1 (NMe), 34.6
(NMe), 29.5 (PdCH(CN)CH2), 23.2 (CH2), 16.4 (PdCH(CN)CH2), 15.5
(PdCH(CN)CH2CH3). Key 1H-1H COSY correlations δ/δ: 2.83
) 2132 cm-1
.
[(bim)Pd{C(dO)CH(CN)CH2CH3}(CO)][B(C6F5)4] (8a). An NMR
tube containing a solution of [(bim)Pd{CH(CN)CH2CH3}(CO)]-
[B(C6F5)4] (7a, 0.013 mmol) in CD2Cl2 (0.6 mL) and CO (0.558 mmol,
corresponding to ca. 6.7 atm at 23 °C) was maintained at 23 °C and
monitored periodically by NMR. The spectra showed that 7a was slowly
converted to (bim)Pd{C(dO)CH(CN)CH2CH3}(CO)+ (8a). After 2 d,
the [8a]/[7a] ratio reached a constant equilibrium value of 1/3. In a
similar experiment using 20 atm of CO, the equilibrium [8a]/[7a] ratio
(44) The imidazole 1H NMR resonance at δ 7.19 of complex 7a shifts slightly
upfield (<0.08 ppm), and the PdCH(CN) methine 13C NMR resonance at
δ 16.4 shifts slightly upfield (<0.7 ppm) when excess [HNMe2Ph][B(C6F5)4]
is present. These effects are attributed to partial protonation of the cyanide
group of 7a by HNMe2Ph+, which has been confirmed by control
experiments in which excess HNMe2Ph+ or NMe2Ph was added. To ensure
that the system is free of excess HNMe2Ph+, a slight excess (10%) of (bim)-
PdMe2 (1a) can be used in the activation process.
was 1/1 after 2 d. The equilibrium constant, Keq ) [8a][7a]-1PCO
)
-1
0.050(2) atm-1, was determined by six experiments, with PCO in the
range of 4 to 20 atm. Data for (bim)Pd{C(dO)CH(CN)CH2CH3)}-
(CO)+: 1H NMR (CD2Cl2): δ 7.07 (d, J ) 2, 1H, imidazole), 7.06 (d,
J ) 2, 1H, imidazole), 6.91 (d, J ) 2, 1H, imidazole), 6.83 (d, J ) 2,
1H, imidazole), 4.27 (s, 2H, CH2), 3.78 (s, 3H, NMe), 3.76 (s, 3H,
9
1852 J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005

Acrylonitrile Insertion of Palladium Alkyl Complexes
A R T I C L E S
NMe), 3.51 (m, 1H, Pd{C(dO)CH(CN)}), 1.91 (m, 2H, Pd{C(dO)-
CH(CN)CH2}), 1.07 (t, J ) 8, 3H, Pd{C(dO)CH(CN)CH2CH3}). 13C-
{1H} NMR (CD2Cl2): δ 212.8 (Pd{C(dO)CH(CN)}), 172.4 (PdCO),
142.0 (imidazole C2), 140.8 (imidazole C2), 128.6 (imidazole C4),
128.1 (imidazole C4), 127.2 (imidazole C5), 123.8 (imidazole C5),
123.3 (CN), 56.4 (CH(CN)CH2), 35.1 (NMe), 34.5 (NMe), 23.2 (CH2),
CH2dCH2), 4.19 (d, J ) 17.5, 1H, CH2), 4.16 (d, J ) 17.5, 1H, CH2),
3.76 (s, 3H, NMe), 3.73 (s, 3H, NMe), 2.30 (m, 1H, PdCH(CN)), 1.57
(m, 2H, PdCH(CN)CH2), 1.01 (t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C-
{1H} NMR (CD2Cl2, -60 °C): δ 140.4 (imidazole C2), 139.0
(imidazole C2), 136.7(dm, J ) 250, meta CNB(C6F5)3), 124.2 (imi-
dazole C), 123.8 (imidazole C), 123.2 (imidazole C), 123.0 (imidazole
C), 121.6 (CN), 94.1 (br, coordinated CH2dCH2), 34.8 (NMe), 34.5
(NMe), 22.6 (PdCH(CN)CH2), 22.5 (CH2), 14.8 (PdCH(CN)CH2CH3),
8.0 (PdCH(CN)). The ortho and para CNB(C6F5)3 13C resonances are
1
22.9 (CH(CN)CH2), 11.3 (CH2CH3). Key H-1H COSY correlations
δ/δ: 3.51 (Pd{C(dO)CH(CN)})/1.91 (Pd{C(dO)CH(CN)CH2}); 1.91
(Pd{C(dO)CH(CN)CH2})/1.07 (Pd{C(dO)CH(CN)CH2CH3}). Key
1
1H-13C HMQC correlations δ H/δ 13C: 3.51 (Pd{C(dO)CH(CN)})/
obscured by the B(C6F5)4 signals. 19F NMR (CD2Cl2, -60 °C): δ
-
56.4 (Pd{C(dO)CH(CN)}); 1.91 (Pd{C(dO)CH(CN)CH2})/22.9 (Pd-
{C(dO)CH(CN)CH2}); 1.07 (Pd{C(dO)CH(CN)CH2CH3})/11.3 (Pd-
{C(dO)CH(CN)CH2CH3}). The volatiles were removed under vacuum
to yield a pale yellow solid. The solid was dried under vacuum for 10
min, dissolved in CD2Cl2, and identified as 4a by NMR.
-134.9 (d, J ) 17, 2F, ortho-CNB(C6F5)3), -156.9 (t, J ) 22, 1F,
para-CNB(C6F5)3), -167.0 (t, J ) 22, 2F, meta-CNB(C6F5)3).
[(Tbim)PdMe(CH2dCH2)][B(C6F5)4] (10b). This species was
generated as described previously.17 1H NMR (CD2Cl2, -30 °C): δ
7.02 (d, J ) 8, 6H, tolyl H2), 6.91 (s, 1H, imidazole), 6.88 (s, 1H,
imidazole), 6.84 (s, 1H, imidazole), 6.61 (s, 1H, imidazole), 6.47 (d, J
) 8, 6H, tolyl H3), 5.77 (s, 1H, CH), 4.34 (AA′BB′, 4H, C2H4), 3.23
(s, 3H, NMe), 3.11 (s, 3H, NMe), 2.31 (s, 9H, tolyl Me), 0.16 (s, 3H,
PdMe).
[(bim)Pd{CH(CNB(C6F5)3)CH2CH3}(CH2dCH2)][B(C6F5)4] (9a).
Solid B(C6F5)3 (8.5 mg, 0.016 mmol) was added to an NMR tube
n+
-
containing solid [(bim)Pd{CH(CN)CH2CH3}]n (B(C6F5)4 salt, 4a,
0.016 mmol). The tube was evacuated and CD2Cl2 (0.6 mL) was added
by vacuum transfer at -78 °C. The tube was cooled to -196 °C and
CH2dCH2 (0.050 mmol) was condensed in via a gas bulb. The tube
was maintained at 0 °C in the NMR probe for 20 min. 19F NMR showed
Acknowledgment. This work was supported by Bayer
Polymers (Leverkusen) and the US Department of Energy (DE-
FG02-00ER15036). We thank Prof. Warren Piers, Prof. Tom
Ziegler, and Dr. Thomas Weiss for helpful discussions and for
sharing unpublished results prior to publication.
1
that free B(C6F5)3 had disappeared and H NMR spectra showed that
9a had formed quantitatively. Exchange of free and coordinated ethylene
is slow on the NMR time scale at -60 and 0 °C. 9a decomposes at 23
1
°C over several hours with formation of Pd0. H NMR (CD2Cl2, -60
°C): δ 7.07 (d, J ) 2, 1H, imidazole), 7.03 (s, 1H, imidazole), 6.82
(d, J ) 2, 1H, imidazole), 6.71 (d, J ) 2, 1H, imidazole), 5.11(br, 4H,
JA044122T
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J. AM. CHEM. SOC. VOL. 127, NO. 6, 2005 1853