Acrylonitrile insertion reactions of palladium alkyl complexes that contain neutral or anionic bidentate phosphine ligands

Article abstract of DOI:10.1021/om060640w

The reactions of acrylonitrile (AN) with palladium alkyl complexes that contain bisphosphine ligands, P∧P = Ph₂P(CH₂) ₃PPh₂ (a, dppp), Me₂P(CH₂) ₂PMe₂ (b, dmpe), [Ph₂B(CH₂PPh ₂)₂]^- (c, Ph₂BP₂), were studied. (P∧P)PdMeCl (1a.b) reacts with [Li(Et₂O) _2.8][B(C₆F₅)₄] and AN to form N-bound AN adducts (P∧P)PdMe(NCCH=CH₂)+ (3a,b). 3b inserts AN to form [(dmpe)Pd(CHEtCN)]_nⁿ⁺ (4b). Sequential reaction of [ASN][(Ph₂BP₂)PdMe₂] (1c, ASN = 5-azoniaspiro[4.4]nonane) with [HNMe₂Ph] [B(C₆F ₅)₄] and AN affords the N-bound adduct (Ph ₂BP₂)PdMe(NCCH=CH₂) (3c), which reacts to form [(Ph₂NP₂)-Pd(CHEtCN)]_n (4c). IR data suggest that the Pd units of 4b,c are aggregated by PdCHEtCN...Pd bridges. 4b reacts with PPh₃ to form (dmpe)Pd(CHEtCN)(PPh₃) ⁺ (5b). 4c reacts with PMe₃ and with pyridine (py) to form (Ph₂BP₂)Pd(CHEtCN)(L) (L = PMe₃ (6c), py (7c)). The characterization of 5b, 6c, and 7c confirms the 2,1 AN insertion of 3b,c. The rate constants for AN insertion (k_obs,AN, 23°C) vary in the order 3c (1.12(3) × 10^-3 s^-1) > 3b (3.33(5) × 10^-5 s^-1) > 3a (no reaction). Electron-rich metal centers and incorporation of an anionic charge in the P∧P ligand promote insertion, probably by favoring formation of a reactive π-bound AN complex.

Full text of DOI:10.1021/om060640w

Organometallics 2006, 25, 5631-5637
5631
Acrylonitrile Insertion Reactions of Palladium Alkyl Complexes that
Contain Neutral or Anionic Bidentate Phosphine Ligands
Fan Wu and Richard F. Jordan*
Department of Chemistry, The UniVersity of Chicago, 5735 South Ellis AVenue, Chicago, Illinois 60637
ReceiVed July 14, 2006
The reactions of acrylonitrile (AN) with palladium alkyl complexes that contain bisphosphine ligands,
P∧P ) Ph2P(CH2)3PPh2 (a, dppp), Me2P(CH2)2PMe2 (b, dmpe), [Ph2B(CH2PPh2)2]- (c, Ph2BP2), were
studied. (P∧P)PdMeCl (1a,b) reacts with [Li(Et2O)2.8][B(C6F5)4] and AN to form N-bound AN adducts
n+
(P∧P)PdMe(NCCHdCH2)+ (3a,b). 3b inserts AN to form [(dmpe)Pd(CHEtCN)]n (4b). Sequential
reaction of [ASN][(Ph2BP2)PdMe2] (1c, ASN ) 5-azoniaspiro[4.4]nonane) with [HNMe2Ph][B(C6F5)4]
and AN affords the N-bound adduct (Ph2BP2)PdMe(NCCHdCH2) (3c), which reacts to form [(Ph2BP2)-
Pd(CHEtCN)]n (4c). IR data suggest that the Pd units of 4b,c are aggregated by PdCHEtCN- - -Pd bridges.
4b reacts with PPh3 to form (dmpe)Pd(CHEtCN)(PPh3)+ (5b). 4c reacts with PMe3 and with pyridine
(py) to form (Ph2BP2)Pd(CHEtCN)(L) (L ) PMe3 (6c), py (7c)). The characterization of 5b, 6c, and 7c
confirms the 2,1 AN insertion of 3b,c. The rate constants for AN insertion (kobs,AN, 23 °C) vary in the
order 3c (1.12(3) × 10-3 s-1) > 3b (3.33(5) × 10-5 s-1) > 3a (no reaction). Electron-rich metal centers
and incorporation of an anionic charge in the P∧P ligand promote insertion, probably by favoring formation
of a reactive π-bound AN complex.
Scheme 1
Introduction
The development of metal-catalyzed insertion polymerization
reactions of acrylonitrile (AN) is an attractive goal. Polyacry-
lonitrile (PAN) and AN copolymers are important materials with
diverse applications and are currently prepared by anionic or
radical polymerization.1 Hydrogenated nitrile butadiene rubbers
(HNBRs), which are in effect linear copolymers of ethylene
and AN, are prepared by radical copolymerization of butadiene
and AN followed by hydrogenation. Synthesis of these materials
by metal-catalyzed insertion polymerization/copolymerization
may provide improved control over polymer composition,
structure, and properties through tuning of the catalyst structure.2
Previously we investigated the reactions of AN with Pd
ethylene dimerization/polymerization catalysts that contain
bidentate N-donor ligands (N∧N).3 As shown in Scheme 1,
(N∧N)PdMe+ species that contain bis-imidazole, bis-pyridine,
or diimine ligands (N∧N) form N-bound (N∧N)PdMe(NCCHd
CH2)+ adducts (A). The bis-imidazole and bis-pyridine com-
plexes undergo 2,1 AN insertion to yield (N∧N)Pd(CHEtCN)+
products (C), which aggregate by PdCHEtCN- - -Pd bridging.
The diimine complex [{(2,6-iPr2-C6H3)NdCMeCMedN(2,6-i-
Pr2-C6H3)}PdMe(NCCHdCH2)][B(C6F5)4] does not insert AN
at 23 °C; however, Baird reported that the analogous B{3,5-
(CF3)2-C6H3}4- salt does undergo insertion to yield (N∧N)Pd-
(CHEtCN)(NCCHdCH2)+, which was characterized by ESI-
MS and partial NMR data.4 These insertions are presumed to
proceed via intermediate CdC π-bound AN adducts (B), which
were not observed. The overall insertion rates for (N∧N)PdMe-
(NCCHdCH2)+ species vary in the order N∧N ) bis-imidazole
> bis-pyridine > diimine, which parallels the order of electron-
richness at the Pd center based on νCO data for the corresponding
(N∧N)Pd{C(dO)Me}(CO)+ species. Isomerization of the N-
bound adducts A to the CdC π-bound adducts B is critical for
insertion, and highly electron-deficient (N∧N)PdMe(NCCHd
CH2)+ species for which the N-bound adduct is strongly favored
are poor candidates for insertion. In parallel work, Weiss, Piers,
and co-workers showed that (L∧L)PdMe(NCCH3) complexes
containing ancillary bidentate phenoxydiazene or phenoxyaldi-
* Corresponding author. E-mail: rfjordan@uchicago.edu.
(1) (a) Acrylonitrile Polymers. Kirk-Othmer Encyclopedia of Chemical
Technology, 4th ed.; Wiley: New York, 1991; Vol. 1, pp 370-411. (b)
Kirk-Othmer Encyclopedia of Chemical Technology Home Page. http://
www.mrw.interscience.wiley.com/kirk/ (accessed July 2006). (c) Wood, M.
E. Rubber Technol. 2001, 201. (d) Hashimoto, K.; Todani, Y. In Handbook
of Elastomers; Bhownick, A., Stephens, H. Eds.; Marcel Dekker: New York,
1988; Chapter 24, p 741. (e) Klingender, R. C. In Rubber Technology, 3rd
ed.; Morton, M., Ed.; Van Nostrand Reinhold: New York, 1987; p 488.
(2) (a) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479. (b) Ittel,
S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100, 1169. (c)
Simonazzi, T.; de Nicola, A.; Aglietto, M.; Ruggeri, G. In ComprehensiVe
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ment, pp 133-158.
(3) Wu, F.; Foley, S. R.; Burns, C. T.; Jordan, R. F. J. Am. Chem. Soc.
2005, 127, 1841.
(4) Stojcevic, G.; Prokopchuck, E. M.; Baird, M. C. J. Organomet. Chem.
2005, 690, 4349.
10.1021/om060640w CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/23/2006

5632 Organometallics, Vol. 25, No. 23, 2006
Wu and Jordan
mine ligands (L∧L) also form N-bound AN adducts, which
undergo 2,1 AN insertion to form (L∧L)Pd(CHEtCN) species
that dimerize and trimerize by PdCHEtCN---Pd bridging.5
Incorporation of an anionic -BF3 group on the ancillary L∧L
ligand increased the AN insertion rate, and both neutral and
anionic (L∧L)PdMe(NCCHdCH2) species insert faster than
(N∧N)PdMe(NCCHdCH2)+ species, again indicating that
increasing the negative charge at the metal center enhances the
overall AN insertion rate.
Figure 1. Ancillary ligands (P∧P) used in this work and νCO values
(in cm-1) for the terminal CO ligands in the corresponding [(P∧P)-
Pd{C(dO)Me}(CO)]n+ complexes (n ) 1 for a,b and 0 for c). The
n+
The [(N∧N)Pd(CHEtCN)]n species C formed in Scheme
νCO value for b is estimated from that for the corresponding dippp
1 do not react with ethylene or AN. However, [(N∧N)Pd-
(CHEtCN)]nn+ species that contain bis-imidazole ligands, which
are the strongest donors among the N∧N ligands studied, do
react with CO to form (N∧N)Pd(CHEtCN)(CO)+ complexes
(D). More interestingly, (bim)Pd(CHEtCN)(CO)+ (bim ) CH2-
(N-Me-imidazol-2-yl)2) undergoes slow, reversible CO insertion
to form (bim)Pd{C(dO)CHEtCN}(CO)+ (E), which demon-
strates that insertions into Pd-CHRCN bonds are possible.
However, this process is much slower than CO insertion of
(bim)PdMe(CO)+ species, which is normally very fast. This
difference in reactivity results from the electron-withdrawing
effect of the R-CN substituent in D.
complex.11
phosphorus donors versus nitrogen donors8a,b may labilize the
PdCHEtCN---Pd interactions in the insertion product aggregates
and promote insertions into Pd-CHEtCN bonds.
Results
Probe Complexes. “(P∧P)PdMen+” species (n ) 0 or 1)
containing the bidentate phosphine ligands Ph2P(CH2)3PPh2 (a,
dppp), Me2P(CH2)2PMe2 (b, dmpe), or [Ph2B(CH2PPh2)2]- (c,
Ph2BP2), which are shown in Figure 1, were studied in this work.
The electrophilic character of [(P∧P)PdMe]n+ (n ) 1 for a, b;
0 for c) species can be assessed by the νCO values for the
terminal CO ligands in the corresponding [(P∧P)Pd{C(dO)-
Me}(CO)]n+ complexes, which are listed in Figure 1.10a,11 On
the basis of these values, the electrophilic character of [(P∧P)-
PdMe]n+ is expected to vary in the order a > b > c. Ligands
a and c are more sterically demanding than b. Cationic/
zwitterionic [(P∧P)PdMe]n+ species based on a-c catalyze the
copolymerization of ethylene and CO, and (P∧P)PdMe-
(ethylene)+ complexes containing ligands a or b catalytically
dimerize ethylene.11a,12
These initial studies suggest that the key obstacles to
incorporation of AN in insertion polymerization/copolymeri-
zation reactions are: (a) slow overall AN insertion rates for
highly electrophilic catalysts due to the preference for N-
coordination over CdC π-coordination of AN; (b) the tendency
of LnM{CH(CN)CH2R} species to aggregate by MCH(CH2R)-
CN---M bridging, due to the high Lewis basicity of the R-CN
group; and (c) the low insertion reactivity of LnM{CH(CN)-
CH2R}(substrate)+ species due to the deactivating effect of the
R-CN group. Additionally, metal catalysts may initiate anionic
or radical AN polymerization.6,7
Generation of [(P∧P)PdMe(NCCHdCH2)]n+ Complexes
(3a-c). The reaction of (P∧P)PdMeCl (1a,b) with 0.5 equiv
of [Li(Et2O)2.8][B(C6F5)4] yields dinuclear [{(P∧P)PdMe}2(µ-
Cl)]+ complexes (2a,b) quantitatively (eq 1).13 Addition of
excess AN to 2a,b in the presence of 0.5 equiv of [Li(Et2O)2.8]-
[B(C6F5)4] results in quantitative formation of (P∧P)PdMe-
(NCCHdCH2)+ complexes (3a,b, eq 1).
The reaction of (dmpe)PdMe2 with [HNMe2Ph][B(C6F5)4]
quantitatively generates (dmpe)PdMe(NMe2Ph)+ and methane
within 10 min at -78 °C. Addition of AN results in quantitative
formation of 3b (eq 2).
To begin to address these issues, we have investigated the
reactivity of palladium methyl complexes that contain bidentate
phosphine ligands (P∧P). The softer character of phosphorus
donors compared to nitrogen donors8,9 may enhance CdC
π-complexation of AN and, therefore, increase the overall AN
insertion rate. Additionally, the stronger trans influence of
(5) 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,
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(6) (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.
The reaction of [ASN][(Ph2BP2)PdMe2] (1c, ASN ) 5-azo-
nia-spiro[4.4]nonane)10 with [HNMe2Ph][B(C6F5)4] at -78 °C,
followed by addition of excess AN and warming to -60 °C,
yields (Ph2BP2)PdMe(NCCHdCH2) (3c) cleanly (eq 3).
(7) For other examples of AN polymerization by metal complexes see:
(a) Jenkins, A. D.; Lappert, M. F.; Srivastava, R. C. J. Polymer Sci. B 1968,
6, 865. (b) Saegusa, T.; Horiguchi, S.; Tsuda, T. Macromolecules 1975, 8,
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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:
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Dalton Trans. 1999, 7, 1027.
1
The H and 13C NMR AN resonances of 3a-c are only
slightly shifted from the free AN positions. For example, the
1H NMR AN resonances for 3c (-60 °C, CD2Cl2) appear at δ
6.06 (d, J ) 12, 1H, Hcis), 5.78 (d, J ) 18, 1H, Htrans), and 5.39
(dd, J ) 18, 12; 1H, Hint), shifted upfield by <0.5 ppm from
(10) (a) Lu, C. C.; Peters, J. C. J. Am. Chem. Soc. 2002, 124, 5272. (b)
Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2001, 123, 5100.
(11) (a) Ledford, J.; Shultz, C. S.; Gates, D. P.; White, P. S.; DeSimone,
J. M.; Brookhart, M. Organometallics 2001, 20, 5266. (b) νCO for the
terminal CO ligand in (dmpe)Pd{C(dO)Me}(CO)+ could not be measured
due to significant decomposition at 23 °C. The νCO value quoted for b is
that of the analogous (dippp)Pd{C(dO)Me}(CO)+ complex (dippp ) 1,3-
bis(diisopropylphosphino)propane).
(8) (a) Crabtree, R. M. The Organometallic Chemistry of the Transitional
Metals, 3rd ed.; John Wiley & Sons: New York, 2001; pp 91-95. (b)
Spessard, G. O.; Miessler, G. L. Organometallic Chemistry; Prentice Hall:
Upper Saddle River, NJ, 1997; pp 131-135. (c) Dias, P. B.; Minas de
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(13) Shen, H.; Jordan, R. F. Organometallics 2003, 22, 1878.

Acrylonitrile Insertion Reactions of Pd Alkyl Complexes
Organometallics, Vol. 25, No. 23, 2006 5633
Scheme 2
cm-1) and 3b (2220 cm-1) are slightly lower than that for free
AN (2230 cm-1).17 The presence of AN was confirmed by the
ESI mass spectra of 3a,b, in which the (P∧P)PdMe(NCCHd
CH2)+ ions are the major cations observed.
Acrylonitrile Insertion of 3b. Complex 3a is stable at 23
°C for several days. No evidence for AN insertion of 3a was
observed up to 60 °C, at which temperature significant
decomposition occurred. In contrast, 3b undergoes 2,1 insertion
at 23 °C to afford (dmpe)Pd(CHEtCN)+, which is believed to
form as a mixture of [(dmpe)Pd(CHEtCN)]nn+ aggregate species
1
(4b, Scheme 2). H NMR monitoring experiments show that
3b is completely consumed within 2 days, but no free AN is
consumed in this reaction. No intermediates in the conversion
of 3b to 4b were observed by NMR. The observed first-order
rate constant for conversion of 3b to 4b determined by NMR
monitoring of the disappearance of the Pd-Me resonance of 3b
is kobs,AN ) 3.33(5) × 10-5 s-1 at 23 °C. This rate constant can
be expressed as kobs,AN ) k1k2/(k-1 + k2), making the steady-
state assumption for the unobserved π-complex intermediate
(Scheme 2). Compound 4b is stable in CD2Cl2 solution at 23
°C for at least 10 days.
The NMR spectra of 4b are complex. For example, the 31P
NMR spectrum of 4b contains five sets of resonances, indicating
the presence of five chemically inequivalent, unsymmetrical
dmpe environments. The ESI mass spectrum of 4b contains a
prominent signal for the (dmpe)Pd(CHEtCN)+ cation, but does
not contain signals for aggregated species. The IR νCN band
for 4b appears at 2218 cm-1. These results do not provide
definitive evidence for the structure of 4b. It is likely that 4b is
aggregated by PdCHEtCN---Pd bridges, as observed previously
for the (N∧N)Pd(CHEtCN)+ analogues and the structurally
characterized complex [(N∧O)Pd(CHEtCN)]3 (N∧O ) bulky
phenoxydiazene),3,5,18 but the aggregates dissociate under ESI-
MS conditions.
the corresponding free AN resonances. The 13C NMR AN
resonances of 3c appear at δ 141.8 (Cter), 120.3 (CN), and 105.2
(Cint), within 5 ppm of the corresponding free AN positions.
These data are consistent with N-coordination of the AN
ligand.3,14 In contrast, for CdC π-bound AN complexes, the
1H and 13C NMR AN resonances are normally shifted far upfield
from the free AN positions.15,16 The IR νCN values for 3a (2227
-
Although attempts to isolate 4b using B(C6F5)4 as the
counterion were unsuccessful, the corresponding B{3,5-(CF3)2-
-
C6H3}4 salt was isolated. The reaction of 1b with 1 equiv of
Na[B{3,5-(CF3)2-C6H3}4] and 10 equiv of AN in CH2Cl2 affords
(14) 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: Chem.
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.
(15) 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.
(16) Bryan, S. J.; Huggett, P. G.; Wade, K.; Daniels, J. A.; Jennings, J.
R. Coord. Chem. ReV. 1982, 44, 149.
(17) N-Coordination of AN or other nitriles is generally accompanied
by an increase in νCN. However, reduction of νCN upon N-coordination has
been reported for some cases and was typically ascribed to back-bonding
from metal d orbitals to the CN π* orbital. See ref 16 and: (a) Michelin,
R. A.; Mozzon, M.; Bertani, R. Coord. Chem. ReV. 1996, 147, 299. (b)
Strorhoff, B. N.; Lewis, H. C., Jr. Coord. Chem. ReV. 1977, 23, 1. (c) Ford,
P. C. Coord. Chem. ReV. 1970, 5, 75.
(18) (a) Culkin, D. A.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 9330.
(b) Ruiz, J.; Rodr´ıguez, V.; Lo´pez, G.; Casabo´, J.; Molins, E.; Miravitlles,
C. Organometallics 1999, 18, 1177. (c) Naota, T.; Tannna, A.; Kamuro,
S.; Murahashi, S. J. Am. Chem. Soc. 2002, 124, 6842. (d) Morvillo, A,;
Bressan, M. J. Organomet. Chem. 1987, 332, 337. (e) Oehme, G.; Rober,
K.; Pracejus, H. J. Organomet. Chem. 1976, 105, 127. (f) Falvello, L. R.;
Fernandez, S.; Navarro, R.; Urriolabeitia, E. P. Inorg. Chem. 1997, 36, 1136.

5634 Organometallics, Vol. 25, No. 23, 2006
Wu and Jordan
Scheme 3
and -0.20 ppm, which is consistent with the presence of three
inequivalent -CH(CN)CH2CH3 units. The major anion observed
in the ESI mass spectrum of 4c taken in the presence of
[Bu3(CH2Ph)N]Cl is [(Ph2BP2)Pd(CHEtCN)Cl]-. The IR spec-
trum of 4c contains a νCN band at 2215 cm-1, similar to the
value for 4b. These results suggest that 4c has an aggregated
structure but, as for 4b, do not provide convincing evidence
regarding this issue. Complex 4c is stable in CD2Cl2 solution
at 23 °C for at least 10 days.
Complex 4c does not react with PPh3, but does react with
PMe3 to form (Ph2BP2)Pd(CHEtCN)(PMe3) (6c, Scheme 3). The
1D and 2D NMR spectra of 6c confirm the presence of a Pd-
(CHEtCN) group. The IR νCN band for 6c appears at 2179 cm-1
,
ca. 36 cm-1 below the value for 4c. The reduction of νCN on
going from 4c to 6c is consistent with the aggregation of 4c by
PdCHEtCN---Pd bridging. The analogous pyridine adduct (Ph2-
BP2)Pd(CHEtCN)(py) (7c) is formed in a similar manner
(Scheme 3) and displays similar spectroscopic properties. These
results confirm the characterization of 4c as a 2,1 AN insertion
product.
Reactivity of 4b,c. Neither 4b nor 4c, nor their derivatives
5b, 6c, or 7c, react with excess AN at 23 °C in CD2Cl2 solution.
Also, 4b,c do not react with ethylene or CO (20 atm, 23 °C).
analytically pure [(dmpe)Pd(CHEtCN)][B{3,5-(CF3)2-C6H3}4]
(4b′) as a pale yellow solid in 63% yield.
To confirm the presence of a PdCHEtCN unit in 4b and hence
that 2,1 AN insertion occurs as proposed in Scheme 2, the
derivatization of 4b by Lewis base complexation was explored.
Complex 4b does not react with excess CH3CN or THF at 23
°C in CD2Cl2 solution. However, as shown in Scheme 2, 4b
reacts quantitatively with 1 equiv of PPh3 to yield (dmpe)Pd-
(CHEtCN)(PPh3)+ (5b, B(C6F5)4- salt). The 1H NMR spectrum
of 5b contains a multiplet at δ 1.81 for the PdCH(CN)CH2CH3
methine hydrogen, multiplets at δ 1.47 and 1.10 for the
diastereotopic PdCH(CN)CH2CH3 methylene hydrogens, and a
triplet at δ 0.89 for the PdCH(CN)CH2CH3 methyl group. The
COSY spectrum shows correlations between these resonances
that are consistent with the PdCH(CN)CH2CH3 structure. The
13C{1H} NMR spectrum of 5b contains a doublet (JCP ) 86
Hz) at δ 15.1 for the PdCHEtCN methine carbon. The 31P NMR
spectrum of 5b contains a PPh3 resonance with the expected
31P coupling at δ 28.1 (dd, J ) 367, 37), which is shifted
downfield from the free PPh3 position (δ -5.0). The ESI mass
spectrum of 5b contains a prominent signal for the cation of
Conclusion
(P∧P)PdMe+ complexes 2a,b and the zwitterionic species
(Ph2BP2)Pd(Me) (2c) form N-bound AN adducts 3a-c. The Cd
C π-bound isomers were not detected. The preference for
N-coordination over π-coordination of AN is consistent with
the poor back-bonding ability of these square-planar d8 Pd(II)
systems. (dmpe)PdMe(NCCHdCH2)+ (3b) and 3c undergo 2,1
insertion of AN. The observed first-order rate constants for AN
insertion vary in the order 3c > 3b > 3a (no reaction), which
parallels the order of the electron-richness of the Pd center, as
assessed by the νCO values in the corresponding [(P∧P)Pd{C(d
O)Me}(CO)]n+ species. In particular, the introduction of an
anionic charge in the backbone of the dppp ligand of 3a to give
3c dramatically increases the AN insertion rate. The increased
negative charge at Pd probably destabilizes the N-bound adduct
and favors isomerization to the reactive π-complex and,
therefore, promotes AN insertion. These results are consistent
with earlier studies of (N∧N)PdMe(NCCHdCH2)+ and (L∧L)-
PdMe(NCCHdCH2) species (L∧L ) bulky phenoxydiazene or
phenoxyaldimine ligand).3,5 Complexes 4b,c do not react with
AN, ethylene, or CO, which precludes AN polymerization or
copolymerization by these systems.
5b. The IR spectrum of 5b contains a νCN band at 2188 cm-1
,
similar to the νCN value observed for (bim)Pd(CHEtCN)(PPh3)+
(2192 cm-1).3 The reduction in νCN on going from 4b (2218
cm-1) to 5b (2188 cm-1) is consistent with the change from
the postulated bridging coordination of the Pd(CHEtCN) unit
in 4b to terminal coordination in 5b.
Attempts to isolate 5b using B(C6F5)4- as the counterion were
unsuccessful, but the corresponding B{3,5-(CF3)2-C6H3}4- salt
was isolated. The reaction of 4b′ with 1 equiv of PPh3 yields
[(dmpe)Pd(CHEtCN)(PPh3)][B{3,5-(CF3)2-C6H3}4] (5b′) as an
analytically pure, pale yellow solid.19
Acrylonitrile Insertion of 3c. Complex 3c also inserts AN
to yield [(Ph2BP2)Pd(CHEtCN)]n (4c, Scheme 3). The observed
first-order rate constant for AN insertion of 3c, kobs,AN ) 1.12-
(3) × 10-3 s-1 at 23 °C, is ca. 33 times greater than that for
3b. The 31P and 11B NMR spectra of 4c contain three major
sets of Ph2BP2 ligand resonances, implying the presence of three
inequivalent unsymmetrical (Ph2BP2)Pd environments. The 1H
NMR spectrum of 4c contains three triplets at δ 0.89, 0.34,
Experimental Section
General Procedures. All manipulations were performed under
purified nitrogen 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
and acrylonitrile (AN) were distilled from CaH2 and stored under
vacuum prior to use. PMe3 and pyridine were purchased from
Aldrich and dried over 4 Å molecular sieves. PPh3, CO, [Bu3(CH2-
Ph)N]Cl, and ethylene were purchased from Aldrich and used as
received. [HNMe2Ph][B(C6F5)4], [Li(Et2O)2.8][B(C6F5)4], and Na-
[B{3,5-(CF3)2-C6H3}4] were obtained from Boulder Scientific and
used as received. Compounds 1c,10a 1a,b, 2a,b,13 and (dmpe)-
20
PdMe2 were prepared by literature procedures.
(19) The molecular structure of 5b′ was confirmed by X-ray crystal-
lography. However, a detailed discussion of this structure is not warranted
due to disorder in the PCH2CH2P and CHEtCN units of the cation and the
CF3 units of the anion.
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

Acrylonitrile Insertion Reactions of Pd Alkyl Complexes
Organometallics, Vol. 25, No. 23, 2006 5635
determined by reference to the residual solvent peaks. 11B, 19F, and
31P chemical shifts were referenced to external neat BF3‚Et2O,
CFCl3, and H3PO4 respectively. Coupling constants are reported
in Hz. In the NMR assignments for AN, Hcis and Htrans refer to the
hydrogens that are cis and trans to Hint, respectively. NMR spectra
of B(C6F5)4 and B{3,5-(CF3)2-C6H3}4 salts contain anion reso-
nances at the free anion positions.21,22 Samples of CD2Cl2 solutions
of 2a,b and species generated in situ from 2a,b contain LiCl. NMR
spectra of species derived from [(dmpe)PdMe(NMe2Ph)][B(C6F5)4]
contain resonances for free NMe2Ph.23 NMR spectra of 3c and
species derived from this species contain resonances for free NMe2-
Ph and free [ASN]+ (ASN ) 5-azoniaspiro[4.4]nonane).24 NMR
spectra for species generated in the presence of excess AN contain
resonances for free AN.25
ESI-MS experiments were performed with a HP Series 1100
MSD instrument using direct injection via syringe pump (ca. 10-6
M solutions). For 4c, 6c, and 7c, [Bu3(CH2Ph)N]Cl (ca. 1.0 wt %)
was added to CH2Cl2 solutions of the samples to generate anionic
chloride complexes. 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. IR 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.
(Ph C2), 126.0 (Ph C4), 119.2 (Ph C3), 50.2 (NMe2Ph), 28.0 (dd,
J ) 30, 25; PCH2), 25.5 (dd, J ) 30, 9; PCH2), 13.2 (d, J ) 37,
PMe), 10.7 (d, J ) 17, PMe), 8.2 (dd, J ) 91, 7; PdMe). 31P{1H}
NMR (CD2Cl2, -60 °C): δ 37.5 (d, J ) 19), 15.4 (d, J ) 19).
[(dppp)PdMe(NCCHdCH2)][B(C6F5)4] (3a). A solution of
[{(dppp)PdMe}2(µ-Cl)][B(C6F5)4] (2a, 0.0088 mmol) and [Li-
(Et2O)2.8][B(C6F5)4] (0.0088 mmol) in CD2Cl2 (0.6 mL) was
generated in an NMR tube, and AN (0.13 mmol) was added by
vacuum transfer at -196 °C. The tube was warmed to -78 °C,
resulting in immediate formation of a slurry of a white solid in a
pale yellow supernatant. 1H NMR spectra showed that 3a had
formed quantitatively. Exchange of free and coordinated AN is fast
on the NMR chemical shift time scale at -60 °C. 1H NMR (CD2-
Cl2, -60 °C, in the presence of 0.19 M free AN): δ 7.52-7.33
(m, 20H, Ph), 6.25 (br d, J ) 17, Htrans of free and coordinated
AN), 6.11 (d, J ) 12, Hcis of free and coordinated AN), 5.67 (br,
Hint of free and coordinated AN), 2.57 (m, 2H, PCH2), 2.51 (m,
2H, PCH2), 1.82 (m, 2H, CH2), 0.35 (dd, J ) 7, 3; 3H, PdMe).
13C{1H} NMR (CD2Cl2, -60 °C, in the presence of 0.19 M free
AN): δ 138.4 (br, Cter of free and coordinated AN), 132.8 (d, J )
11), 132.6 (d, J ) 11), 131.5, 130.9, 129.5 (d, J ) 38), 128.9 (d,
J ) 11), 128.7 (d, J ) 11), 127.5 (d, J ) 57), 117.4 (br, CN of
free and coordinated AN), 107.0 (br, Cint of free and coordinated
AN), 26.8 (dd, J ) 34, 9; PCH2), 25.2 (d, J ) 22, PCH2), 17.9
(CH2), 10.5 (d, J ) 85, PdMe). 31P{1H} NMR (CD2Cl2, -60 °C):
δ 28.2 (d, J ) 54), -2.9 (d, J ) 54). The 13C NMR assignments
for AN were confirmed by a DEPT-135 experiment. The chemical
shifts for the coordinated AN at -60 °C in CD2Cl2 (δcoord) are
related to the observed weighted averages of the chemical shifts
(δaverage) for free (δfree) and coordinated (δcoord) AN and the mole
fractions of free (øfree) and coordinated (øcoord) AN by eq 4:
-
-
[(dmpe)PdMe(NMe2Ph)][B(C6F5)4]. An NMR tube was charged
with (dmpe)PdMe2 (7.8 mg, 0.027 mmol) and [HNMe2Ph]-
[B(C6F5)4] (21.8 mg, 0.027 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 (dmpe)PdMe(NMe2Ph)+ had formed
1
δaverage ) δfreeøfree + δcoordøcoord
(4)
quantitatively. H NMR (CD2Cl2, -60 °C): δ 7.39 (t, J ) 8, 2H,
m-Ph), 7.31 (d, J ) 8, 2H, o-Ph), 7.19 (t, J ) 8, 1H, p-Ph), 2.91
(s, 6H, NMe2Ph), 1.78 (m, 2H, PCH2), 1.54 (d, J ) 11, 6H, PMe),
1.46 (m, 2H, PCH2), 0.68 (d, J ) 8, 6H, PMe), 0.36 (d, J ) 7, 3H,
PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ 154.1 (Ph C1), 129.8
and are as follows: 1H NMR δ 6.31 (Htrans), 6.24 (Hcis), 5.54 (Hint);
13C NMR δ 140.3 (Cter), 118.0 (CN), 105.7 (Cint). ESI-MS: Major
cations observed [(dppp)PdMe(NCCHdCH2)]+ calcd m/z 586.1,
found 586.0; [(dppp)Pd(Me)]+ calcd m/z 533.1, found 532.9. IR
(neat): νCN ) 2227 cm-1
.
(20) de Graaf, W.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van Koten,
G. Organometallics 1989, 8, 2907.
(21) NMR data for free B(C6F5)4
[(dmpe)PdMe(NCCHdCH2)][B(C6F5)4] (3b) from 2b. This
complex was generated in CD2Cl2 (0.6 mL) from [{(dmpe)PdMe}2-
(µ-Cl)][B(C6F5)4] (2b, 0.020 mmol), [Li(Et2O)2.8][B(C6F5)4] (0.020
mmol), and AN (0.20 mmol) using the procedure for 3a. 1H NMR
spectra showed that 3b had formed quantitatively. Exchange of free
and coordinated AN is fast on the NMR chemical shift time scale
at -60 °C. 1H NMR (CD2Cl2, -60 °C, in the presence of 0.27 M
free AN): δ 6.29 (br, Htrans of free and coordinated AN), 6.15 (br,
Hcis of free and coordinated AN), 5.73 (br, Hint of free and
coordinated AN), 1.95 (m, 2H, PCH2), 1.69 (m, 2H, PCH2), 1.51
(d, J ) 11, 6H, PMe), 1.40 (d, J ) 9, 6H, PMe), 0.25 (dd, J ) 7,
3; 3H, PdMe). 13C{1H} NMR (CD2Cl2, -60 °C, in the presence of
0.27 M free AN): δ 138.9 (br, Cter of free and coordinated AN),
117.7 (br, CN of free and coordinated AN), 107.0 (br, Cint of free
and coordinated AN), 29.6 (dd, J ) 36, 22; PCH2), 24.4 (dd, J )
30, 8; PCH2), 12.6 (d, J ) 36, PMe), 11.9 (d, J ) 18, PMe), 1.9
(d, J ) 94, PdMe). 31P{1H} NMR (CD2Cl2, -60 °C): δ 42.5 (d,
J ) 24), 26.4 (d, J ) 24). The chemical shifts for the coordinated
AN at -60 °C in CD2Cl2 determined from the observed weighted
average chemical shifts for free and coordinated AN and the mole
fractions of free and coordinated AN as shown in eq 4 are as
follows: 1H NMR δ 6.49 (Htrans), 6.39 (Hcis), 5.89 (Hint); 13C NMR
δ 142.1 (Cter), 119.3 (CN), 106.2 (Cint). ESI-MS: Major cations
observed [(dmpe)PdMe(NCCHdCH2)]+ calcd m/z 324.0, found
324.0; [(dmpe)Pd(Me)]+ calcd m/z 271.0, found 271.0. IR (neat):
-
:
13C{1H} NMR (CD2Cl2): δ 148.5
(dm, J ) 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). 11B NMR (CD2Cl2): δ
-16.6 (s). 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). 11B NMR (CD2Cl2, -60 °C): δ -16.5
(s).
-
(22) NMR data for B{3,5-(CF3)2-C6H3}4
:
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).
(23) (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
(CD2Cl2, -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 3c,
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.
(24) NMR data for free [ASN]+: 1H NMR (CD2Cl2): δ 3.19 (m, 8H,
N(CH2CH2)2), 2.11 (m, 8H, N(CH2CH2)2). 13C{1H} NMR (CD2Cl2): δ 63.8
1
(N(CH2CH2)2), 22.3 (N(CH2CH2)2). H NMR (CD2Cl2, -60 °C): δ 3.06
(m, 8H, N(CH2CH2)2), 2.03 (m, 8H, N(CH2CH2)2). 13C{1H} NMR (CD2-
Cl2, -60 °C): δ 62.2 (N(CH2CH2)2), 21.3 (N(CH2CH2)2).
(25) NMR data for free AN: 1H NMR (CD2Cl2, 23 °C): δ 6.21 (d, J )
18, 1H, Htrans), 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,
νCN ) 2220 cm-1
.
[(dmpe)PdMe(NCCHdCH2)][B(C6F5)4] (3b) from [(dmpe)-
PdMe(NMe2Ph)][B(C6F5)4]. An NMR tube containing a solution
of [(dmpe)PdMe(NMe2Ph)][B(C6F5)4] (0.027 mmol) in CD2Cl2 (0.6
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).

5636 Organometallics, Vol. 25, No. 23, 2006
Wu and Jordan
mL) was cooled to -196 °C, and AN (0.023 mmol, ca. 0.85 equiv)
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
for 4b generated by this method are very similar to the data for 4b
generated from 2b.
[(dmpe)Pd(CHEtCN)]nn+ (4b′, B{3,5-(CF3)2-C6H3}4- salt). A
flask was charged with (dmpe)PdMeCl (1b, 0.11 g, 0.35 mmol)
and Na[B{3,5-(CF3)2-C6H3}4] (0.28 g, 0.32 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 (0.20 mL, 3.0 mmol) was added by
vacuum transfer. The flask was warmed to 23 °C, and the mixture
was stirred for 2 days to yield a slurry of a white solid in a yellow
supernatant. The mixture was filtered through Celite, and the filtrate
was dried under vacuum to afford a pale yellow solid (0.24 g, 63%).
Anal. Calcd for C42H34BF24NP2Pd: C, 42.47; H, 2.89; N, 1.16.
Found: C, 42.18; H, 3.05; N, 1.16. The NMR data for 4b′ are
very similar to the data for 4b, except for the anion resonances.
[(Ph2BP2)Pd(CHEtCN)]n (4c). An NMR tube containing a
solution of (Ph2BP2)PdMe(NCCHdCH2) (3c, 0.015 mmol) and AN
(0.66 mmol) in CD2Cl2 (0.6 mL) was maintained at 23 °C and
monitored periodically by NMR. The NMR signals associated with
3c disappeared after 2 h. The volatiles were removed under vacuum
to yield an off-white solid. The solid was redissolved in CD2Cl2
(0.6 mL). NMR and ESI-MS analyses showed that [(Ph2BP2)Pd-
(CHEtCN)]n (4c) was present. The NMR yield for 4c was 95%. In
a similar experiment with more frequent 1H NMR monitoring, the
first-order rate constant for conversion of 3c to 4c was determined
1
the NMR probe at -60 °C. A H NMR spectrum showed that
[(dmpe)PdMe(NCCHdCH2)][B(C6F5)4] (3b) had formed quanti-
tatively based on AN, i.e., 85% yield based on Pd. The NMR and
IR data for 3b generated by this method are nearly identical to
those for 3b generated from 2b. NMR data for coordinated AN:
1H NMR (CD2Cl2, -60 °C) δ 6.52 (d, J ) 18, 1H, Htrans of
coordinated AN), 6.41 (d, J ) 11, 1H, Hcis of coordinated AN),
5.91 (dd, J ) 18,11; 1H, Hint of coordinated AN); 13C{1H} NMR
(CD2Cl2, -60 °C) δ 143.0 (Cter of coordinated AN), 119.2 (CN of
coordinated AN), 105.4 (Cint of coordinated AN). The 13C NMR
assignments were confirmed by a DEPT-135 experiment. IR
(neat): νCN ) 2219 cm-1
.
(Ph2BP2)PdMe(NCCHdCH2) (3c). A solution of [ASN][(Ph2-
BP2)PdMe2] (1c, 11.8 mg, 0.0140 mmol) and [HNMe2Ph][B(C6F5)4]
(11.4 mg, 0.0140 mmol) in CD2Cl2 (0.6 mL) was generated in an
NMR tube at -78 °C and cooled to -196 °C, and AN (0.017 mmol,
1.2 equiv) was added by vacuum transfer. The tube was warmed
to -78 °C, resulting in the immediate formation of a clear, colorless
solution. The tube was transferred to an NMR probe at -60 °C.
1H NMR spectra showed that 3c had formed quantitatively. Separate
sharp 1H NMR resonances for free and coordinated AN were
from the disappearance of the PdMe 1H NMR resonance to be kobs
-
1
observed at -60 °C. H NMR (CD2Cl2, -60 °C): δ 7.36-7.05
(23 °C) ) 1.12(3) × 10-3 s-1 at 23 °C ([AN] ) 0.028 M, 1.2
equiv vs 3c). 1H NMR (CD2Cl2) of 4c: Major resonances δ 7.63-
6.30 (m, 90H, Ph), 2.04-1.07 (m, 19H, PCH2 and PdCH(CN)-
CH2), 0.89 (t, J ) 7, 3H, PdCH(CN)CH2CH3), 0.69 (m, 2H,
PdCH(CN)CH2), 0.34 (t, J ) 7, 3H, PdCH(CN)CH2CH3), -0.20
(t, J ) 7, 3H, PdCH(CN)CH2CH3). 31P{1H} NMR (CD2Cl2): Major
resonances δ 38.7 (d, J ) 45, 1P), 38.1 (d, J ) 45, 1P), 37.9 (d, J
) 45, 1P), 18.6 (d, J ) 45, 1P), 15.5 (d, J ) 45, 1P), 15.3 (d, J )
45, 1P). 11B NMR (CD2Cl2): Major resonances δ -13.8 (br), -14.3
(br), -15.2 (br). ESI-MS in CH2Cl2/[Bu3(CH2Ph)N]Cl, major anion
observed: [(Ph2BP2)Pd(CHEtCN) + Cl-] calcd m/z 772.2, found
(m, 20H, Ph), 6.82-6.60 (m, 10H, Ph), 6.06 (d, J ) 12, Hcis of
coordinated AN), 5.78 (d, J ) 18, Htrans of coordinated AN), 5.39
(dd, J ) 18, 12; Hint of coordinated AN), 1.91 (dd, J ) 15, 3; 2H,
PCH2), 1.76 (d, J ) 13, 2H, PCH2), -0.11 (d, J ) 7, 3H, PdMe).
13C{1H} NMR (CD2Cl2, -60 °C): δ 141.8 (Cter of coordinated
AN), 135.7 (d, J ) 33), 133.0 (d, J ) 52), 132.8 (d, J ) 11),
132.5 (d, J ) 11), 131.3, 130.9, 128.7, 128.6 (d, J ) 6), 127.5 (d,
J ) 11), 127.2 (d, J ) 11), 125.8, 121.7, 120.3 (d, J ) 13, CN of
coordinated AN), 105.2 (Cint of coordinated AN), 20.8 (br, PCH2B),
17.9 (CH2), 15.5 (br, PCH2B), 7.4 (d, J ) 87, PdMe). 31P{1H}
NMR (CD2Cl2, -60 °C): δ 38.9 (d, J ) 48), 14.1 (d, J ) 48). 11
NMR (CD2Cl2, -60 °C): δ -14.3.
B
772.2. IR (neat): νCN ) 2215 cm-1
.
[(dmpe)Pd(CHEtCN)(PPh3)][B(C6F5)4] (5b). Solid PPh3 (10.3
n+
-
[(dmpe)Pd(CHEtCN)]n (4b, B(C6F5)4 salt). An NMR tube
containing a solution of [(dmpe)PdMe(NCCHdCH2)][B(C6F5)4]
(3b, 0.039 mmol) and AN (0.16 mmol) in CD2Cl2 (0.6 mL) was
maintained at 23 °C and monitored periodically by NMR. The NMR
signals associated with 3b disappeared after 2 days. The volatiles
were removed under vacuum to yield a pale yellow solid. The solid
was redissolved in CD2Cl2 (0.6 mL). NMR and ESI-MS analyses
mg, 0.0390 mmol) was added to an NMR tube containing solid
n+
-
[(dmpe)Pd(CHEtCN)]n (4b, B(C6F5)4 salt, 0.0390 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 (dmpe)Pd(CHEtCN)(PPh3)+ (5b) had
formed quantitatively. 1H NMR (CD2Cl2): δ 7.66-7.50 (m, 15H,
PPh3), 2.08 (m, 2H, PCH2), 1.92 (m, 2H, PCH2), 1.85 (dd, J ) 11,
3; 3H, PMe), 1.81 (m, 1H, PdCH(CN)), 1.75 (dd, J ) 11, 3; 3H,
PMe), 1.47 (m, 1H, PdCH(CN)CH2), 1.10 (m, 1H, PdCH(CN)-
CH2), 0.90 (d, J ) 11, 3H, PMe), 0.77 (d, J ) 11, 3H, PMe), 0.50
(t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR (CD2Cl2): δ
134.4 (d, J ) 12, o-PPh3), 132.6 (d, J ) 3, p-PPh3), 129.9 (d, J )
10, m-PPh3), 128.4 (d, J ) 44, PPh3 Cipso), 128.1 (CN), 28.2-27.5
(m, PCH2CH2P), 25.3 (m, PdCH(CN)CH2), 15.8 (d, J ) 8, PdCH-
(CN)CH2CH3), 15.1 (d, J ) 86, PdCH(CN)CH2), 12.6 (d, J ) 23,
PMe), 12.0 (d, J ) 23, PMe), 11.7 (dd, J ) 26, 3; PMe), 10.7 (dd,
J ) 26, 3; PMe). The assignments of the PPh3 resonances are based
on the size of JP-C and are consistent with the trend observed in
free PPh3.26 31P{1H} NMR (CD2Cl2): δ 36.4 (dd, J ) 367, 32;
PCH2), 28.3 (dd, J ) 37, 32; PCH2), 28.1 (dd, J ) 367, 37; PPh3).
Key 1H-1H COSY correlations δ/δ: 1.81 (PdCH(CN))/1.47
(PdCH(CN)CH2); 1.81 (PdCH(CN))/1.10 (PdCH(CN)CH2); 1.47
(PdCH(CN)CH2)/1.10 (PdCH(CN)CH2); 1.47 (PdCH(CN)CH2)/0.50
(PdCH(CN)CH2CH3); 1.10 (PdCH(CN)CH2)/0.50 (PdCH(CN)-
n+
showed that [(dmpe)Pd(CHEtCN)]n species (4b) were present.
The NMR yield for 4b was 90%. In a similar experiment with more
frequent 1H NMR monitoring, the first-order rate constant for
conversion of 3b to 4b was determined from the disappearance of
the PdMe 1H NMR resonance to be kobs(23 °C) ) 3.33(5) × 10-5
1
s-1 at 23 °C ([AN] ) 0.028 M, 1.2 equiv vs 3b). H NMR (CD2-
Cl2) for 4b: Major resonances δ 2.26-2.03 (m, 3H, PCH2 and
PdCH(CN)), 2.03-1.72 (m, 4H, PCH2 and PdCH(CN)CH2), 1.72-
1.64 (m, 6H, PMe), 1.64-1.46 (m, 6H, PMe), 1.15-1.00 (m, 3H,
PdCH(CN)CH2CH3). 31P{1H} NMR (CD2Cl2): δ 49.1 (d, J ) 18,
1P), 48.8 (d, J ) 18, 1P), 48.7 (d, J ) 18, 1P), 47.3 (d, J ) 18,
5P), 47.0 (d, J ) 18, 1P), 46.8 (d, J ) 18, 5P), 46.4 (d, J ) 18,
1P), 45.4 (d, J ) 18, 1P), 44.3 (d, J ) 18, 1P), 43.7 (d, J ) 18,
1P). ESI-MS: Major cation observed (dmpe)Pd(CHEtCN)+ calcd
m/z 324.0, found 323.8. IR (neat): νCN ) 2218 cm-1
.
Alternatively, 3b was generated by the reaction of [(dmpe)PdMe-
(NMe2Ph)][B(C6F5)4] (0.022 mmol) with AN (0.13 mmol) in CD2-
Cl2 (0.6 mL). The conversion from 3b to 4b was monitored
periodically by NMR. The first-order rate constant for conversion
1
of 3b to 4b, measured from the disappearance of the PdMe H
(26) (a) Breitmaier, E.; Voelter, W. Carbon-13 NMR, 3rd ed.; VCH
Publishers: Weinheim, Germany, 1987; pp 247-254. (b) Mann, B. E. J.
Chem. Soc., Perkin Trans. 2 1972, 30.
NMR resonance, was kobs(23 °C) ) 3.5(1) × 10-5 s-1 at 23 °C
([AN] ) 0.18 M, 5 equiv vs 3b). The NMR, ESI-MS, and IR data

Acrylonitrile Insertion Reactions of Pd Alkyl Complexes
Organometallics, Vol. 25, No. 23, 2006 5637
1
CH2CH3). Key 1H-13C HMQC correlations δ 1H/δ 13C: 1.81
(PdCH(CN))/15.1 (PdCH(CN)); 1.47 (PdCH(CN)CH2)/25.3 (PdCH-
(CN)CH2); 1.10 (PdCH(CN)CH2)/25.3 (PdCH(CN)CH2); 0.50
(PdCH(CN)CH2CH3)/15.8 (PdCH(CN)CH2CH3). ESI-MS: Major
cations observed (dmpe)Pd(CHEtCN)(PPh3)+ calcd m/z 586.1,
Cl2): δ -15.0. Key H-1H COSY correlations δ/δ: 1.79 (Pd-
CH(CN))/1.38 (PdCH(CN)CH2); 1.38 (PdCH(CN)CH2)/0.54 (PdCH-
(CN)CH2CH3); 1.38 (PdCH(CN)CH2)/0.43 (PdCH(CN)CH2); 0.54
(PdCH(CN)CH2CH3)/0.43 (PdCH(CN)CH2). Key 1H-13C HMQC
correlations δ 1H/δ 13C: 1.97 (PCH2B)/25.2 (PCH2B); 1.97
(PCH2B)/20.6 (PCH2B); 1.79 (PdCH(CN))/14.1 (PdCH(CN)); 1.38
(PdCH(CN)CH2)/23.9 (PdCH(CN)CH2); 0.54 (PdCH(CN)CH2CH3)/
16.0 (PdCH(CN)CH2CH3); 0.43 (PdCH(CN)CH2)/23.9 (PdCH(CN)-
CH2). ESI-MS in CH2Cl2/[Bu3(CH2Ph)N]Cl, major anion ob-
served: [(Ph2BP2)Pd(CHEtCN) + Cl-] calcd m/z 772.2, found
found 586.0. IR (neat): νCN ) 2188 cm-1
.
[(dmpe)Pd(CHEtCN)(PPh3)][B{3,5-(CF3)2-C6H3}4] (5b′). A
flask was charged with (dmpe)PdMeCl (1b, 0.11 g, 0.34 mmol)
and Na[B{3,5-(CF3)2-C6H3}4] (0.29 g, 0.32 mmol), and CH2Cl2 (40
mL) was added at -78 °C by vacuum transfer. The pale yellow
slurry was warmed to 23 °C and vigorously stirred for 5 min. The
flask was cooled to -196 °C, and AN (0.20 mL, 3.0 mmol) was
added by vacuum transfer. The flask was warmed to 23 °C, and
the mixture was stirred for 2 days to yield a slurry of a white solid
in a pale yellow supernatant. A solution of PPh3 (85 mg, 0.32 mmol)
in CH2Cl2 (5.0 mL) was added by syringe. The mixture was stirred
for 10 h at 23 °C to afford a white slurry in a yellow supernatant.
The mixture was filtered through Celite, and the filtrate was dried
under vacuum to afford a pale yellow solid (0.30 g, 65%). Anal.
Calcd for C66H45BF24N3PPd: C, 49.69; H, 3.41; N, 0.97. Found:
C, 49.58; H, 3.60; N, 0.71. The NMR data for 5b′ are identical
with the data for 5b except for the anion resonances.
772.1. IR (neat): νCN ) 2179 cm-1
.
(Ph2BP2)Pd(CHEtCN)(C5H5N) (7c). Pyridine (0.14 mmol) was
added by vacuum transfer to an NMR tube containing [(Ph2BP2)-
Pd(CHEtCN)]n (4c, 0.014 mmol) in CD2Cl2 (0.6 mL) at -196 °C.
The tube was warmed to 23 °C and vigorously agitated, resulting
in a clear, colorless solution. After 30 min, the volatiles were
removed under vacuum, and the remaining off-white solid was
redissolved in CD2Cl2 (0.6 mL) to yield a colorless solution. NMR
spectra showed that (Ph2BP2)Pd(CHEtCN)(C5H5N) (7c) had formed
in 87% yield. 1H NMR (CD2Cl2): δ 8.21 (dd, J ) 5, 2; 2H, o-py),
7.60-6.94 (m, 24H, Ph and py), 6.87-6.61 (m, 10H, Ph), 1.99
(m, 4H, PCH2B), 1.25 (m, 1H, PdCH(CN)), 0.77 (m, 2H, PdCH-
(CN)CH2), 0.35 (t, J ) 7, 3H, PdCH(CN)CH2CH3). 13C{1H} NMR
(CD2Cl2): δ 151.2 (br, o-py), 137.8 (s, p-py), 136.0 (d, J ) 37),
135.1 (d, J ) 48), 134.6 (d, J ) 11), 134.0 (d, J ) 11), 132.4 (d,
J ) 9), 131.9 (d, J ) 9), 131.6 (d, J ) 10), 130.9 (s), 130.2 (d, J
) 16), 128.5 (d, J ) 5), 128.4 (d, J ) 6), 128.3 (d, J ) 11), 127.6
(d, J ) 8, CN), 126.5 (s), 125.3 (br, m-py), 122.4 (s), 24.1 (d, J )
4, PdCH(CN)CH2), 21.8 (br, PCH2B), 19.5 (d, J ) 90, PdCH(CN)),
17.4 (br, PCH2B), 15.9 (d, J ) 9, PdCH(CN)CH2CH3). Assuming
free rotation of the phenyl groups, there should be a total of 24
phenyl carbon signals. However, only 15 phenyl carbon signals
were observed, most likely because some are coincident due to the
distance of the phenyl group from the stereogenic center. 31P{1H}
NMR (CD2Cl2): δ 34.9 (d, J ) 48), 21.6 (d, J ) 48). Key 1H-13C
(Ph2BP2)Pd(CHEtCN)(PMe3) (6c). An NMR tube containing
a solution of [(Ph2BP2)Pd(CHEtCN)]n (4c, 0.015 mmol) in CD2-
Cl2 (0.6 mL) was cooled to -196 °C, and PMe3 (0.015 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 (Ph2BP2)Pd(CHEtCN)(PMe3)
1
(6c) had formed in 90% yield. H NMR (CD2Cl2): δ 7.58-7.10
(m, 20H, Ph), 6.67 (m, 10H, Ph), 1.97 (m, 4H, PCH2B), 1.79 (m,
1H, PdCH(CN)), 1.38 (m, 1H, PdCH(CN)CH2), 0.98 (dd, J ) 9,
2; 9H, PMe3), 0.54 (t, J ) 7, 3H, PdCH(CN)CH2CH3), 0.43 (m,
1H, PdCH(CN)CH2). 13C{1H} NMR (CD2Cl2): δ 136.6 (d, J )
34), 134.8 (d, J ) 11), 132.9 (d, J ) 10), 132.7 (d, J ) 10), 131.6
(d, J ) 4), 130.8 (d, J ) 2), 130.7 (d, J ) 2), 130.2 (s), 130.0 (d,
J ) 2), 128.8 (d, J ) 8), 128.4 (d, J ) 11), 128.3 (d, J ) 5), 128.2
(d, J ) 4), 126.5 (s), 122.2 (d, J ) 2), 25.2 (br, PCH2B), 23.9 (br
m, PdCH(CN)CH2), 20.6 (br, PCH2B), 16.0 (d, J ) 8, PdCH(CN)-
CH2CH3), 15.5 (d, J ) 25, PMe3), 14.1 (dd, J ) 87, 5; PdCH-
(CN)). Assuming free rotation of the phenyl groups, there should
be a total of 24 phenyl carbon signals. However, only 15 phenyl
carbon signals were observed, most likely because some are
coincident due to the distance of the phenyl group from the
stereogenic center. The CN resonance was not observed. 31P{1H}
NMR (CD2Cl2): δ 30.5 (dd, J ) 370, 53; PCH2), 19.0 (dd, J )
53, 33; PCH2), -21.0 (dd, J ) 370, 33; PMe3). 11B NMR (CD2-
HMQC correlations δ H/δ 13C: 1.25 (PdCH(CN))/19.5 (PdCH-
1
(CN)); 0.77 (PdCH(CN)CH2)/24.1 (PdCH(CN)CH2); 0.35 (PdCH-
(CN)CH2CH3)/15.9 (PdCH(CN)CH2CH3). 11B NMR (CD2Cl2): δ
-14.7. ESI-MS in CH2Cl2/[Bu3(CH2Ph)N]Cl, major anion ob-
served: [(Ph2BP2)Pd(CHCNEt) + Cl-] calcd m/z 772.2, found
772.1. IR (neat): νCN ) 2175 cm-1
.
Acknowledgment. This work was supported by the U.S.
Department of Energy (DE-FG02-00ER15036).
OM060640W