Reaction of vinyl chloride with late transition metal olefin polymerization catalysts

Article abstract of DOI:10.1021/ja029823+

The reactions of vinyl chloride (VC) with representative late metal, single-site olefin dimerization and polymerization catalysts have been investigated. VC coordinates more weakly than ethylene or propylene to the simple catalyst (Me₂bipy)PdMe⁺ (Me₂bipy = 4,4Κ-Me2-2,2Κ-bipyridine). Insertion rates of (Me₂bipy)Pd(Me)(olefin)⁺ species vary in the order VC > ethylene > propylene. The VC complexes (Me₂-bipy)Pd(Me)(VC)⁺ and (α-diimine)Pd(Me)(VC)⁺ α-diimine = (2,6-ⁱPr₂-C₆H₃) N=CMeCMe=N(2,6-ⁱPr₂-C₆H₃)) undergo net 1,2 VC insertion and β-Cl elimination to yield Pd-Cl species and propylene. Analogous chemistry occurs for (pyridine-bisimine)MCl₂/MAO catalysts (M = Fe, Co; pyridine-bisimine = 2,6-{(2,6-ⁱPr₂-C₆H₃) N=CMe}₂-pyridine) and for neutral (sal)Ni(Ph)PPh₃ and (P-O)Ni(Ph)PPh₃ catalysts (sal = 2-{C-(H)=N(2,6-ⁱPr₂-C₆H₃)} -6-Ph-phenoxide; P-O = {Ph₂PC(SO₃Na)=C(p-tol)O}), although the initial metal alkyl VC adducts were not detected in these cases. These results show that the L_nMCH₂CHCIR species formed by VC insertion into the active species of late metal olefin polymerization catalysts undergo rapid β-Cl elimination which precludes VC polymerization. Termination of chain growth by β-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization of VC.

Full text of DOI:10.1021/ja029823+

Published on Web 03/18/2003
Reaction of Vinyl Chloride with Late Transition Metal Olefin
Polymerization Catalysts
Stephen R. Foley, Robert A. Stockland, Jr., Han Shen, and Richard F. Jordan*
Contribution from the Department of Chemistry, The UniVersity of Chicago,
5735 South Ellis AVenue, Chicago, Illinois 60037
Received December 19, 2002; E-mail: rfjordan@uchicago.edu
Abstract: The reactions of vinyl chloride (VC) with representative late metal, single-site olefin dimerization
and polymerization catalysts have been investigated. VC coordinates more weakly than ethylene or
propylene to the simple catalyst (Me2bipy)PdMe+ (Me2bipy ) 4,4′-Me2-2,2′-bipyridine). Insertion rates of
(Me2bipy)Pd(Me)(olefin)+ species vary in the order VC > ethylene > propylene. The VC complexes (Me2-
bipy)Pd(Me)(VC)+ and (R-diimine)Pd(Me)(VC)+ (R-diimine ) (2,6-iPr2-C6H3)NdCMeCMedN(2,6-iPr2-C6H3))
undergo net 1,2 VC insertion and â-Cl elimination to yield Pd-Cl species and propylene. Analogous
chemistry occurs for (pyridine-bisimine)MCl2/MAO catalysts (M ) Fe, Co; pyridine-bisimine ) 2,6-{(2,6-
iPr2-C6H3)NdCMe}2-pyridine) and for neutral (sal)Ni(Ph)PPh3 and (P-O)Ni(Ph)PPh3 catalysts (sal ) 2-{C-
(H)dN(2,6-iPr2-C6H3)}-6-Ph-phenoxide; P-O ) {Ph2PC(SO3Na)dC(p-tol)O}), although the initial metal
alkyl VC adducts were not detected in these cases. These results show that the LnMCH2CHClR species
formed by VC insertion into the active species of late metal olefin polymerization catalysts undergo rapid
â-Cl elimination which precludes VC polymerization. Termination of chain growth by â-Cl elimination is the
most significant obstacle to metal-catalyzed insertion polymerization of VC.
Introduction
group of the monomer, are anticipated to be unimportant for
VC due to the weak tendency of halocarbons to coordinate to
The design or discovery of metal catalysts which are capable
of polymerizing or copolymerizing functionalized olefins by
insertion mechanisms, particularly CH2dCHX monomers with
functional groups directly bonded to the olefin unit, is a
challenging goal.1 While some success has been achieved in
the copolymerization of acrylates and vinyl ketones with
ethylene and propylene using palladium and nickel catalysts,2
general strategies for designing catalysts with high functional
group tolerance are lacking.
Vinyl chloride (VC) is a particularly attractive monomer for
insertion polymerization/copolymerization because PVC and VC
copolymers are important commercial materials,3 and because
many of the problems that complicate insertion polymerization
of polar monomers, such as coordination of the monomer to
the active species through the X group rather than the CdC
bond, and reaction of the catalyst with the C-X bond or X
metals and the low reactivity of the vinyl C-Cl bond.4,5
However, insertion polymerization of VC has never been
convincingly demonstrated.
In previous work, we found that group 4 metal catalysts react
with VC by two pathways: (i) radical polymerization initiated
by radicals derived from the catalyst, and (ii) net 1,2 insertion
followed by â-Cl elimination to yield metal chloride species
and olefins (eq 1).6 For example, radical VC polymerization is
initiated by (C5R5)2ZrMe2/MAO catalysts in the presence of
trace O2 and by (C5Me5)TiX3/MAO catalysts (X ) Cl or OMe;
low Al/Ti ratios, CH2Cl2 solvent) under anaerobic conditions.
In principle, radical polymerization can be avoided by the use
of redox inactive metals, anaerobic conditions, and radical
scavengers. The insertion/â-Cl elimination pathway is observed
for zirconocene catalysts under anaerobic conditions, (C5Me5)-
TiX3/MAO catalysts at high Al/Ti ratios, and (C5Me4SiMe2-
NtBu)MR+ “constrained geometry” catalysts (M ) Ti, Zr).
(1) (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.
(2) (a) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am. Chem.
Soc. 1998, 120, 888. (b) Johnson, L. K.; Mecking, S. F.; Brookhart, M. J.
Am. Chem. Soc. 1996, 118, 267. (c) Johnson, L.; Bennett, A.; Dobbs, K.;
Hauptman, E.; Ionkin, E.; Ittel, S.; McCord, E.; McLain, S.; Radzewich,
C.; Yin, Z.; Wang, L.; Wang, Y.; Brookhart, M. Polym. Mater. Sci. Eng.
2002, 86, 319. See also: (d) Stibrany, R. T.; Schulz, D. N.; Kacker, S.;
Patil, A. O.; Baugh, L. S.; Rucker, S. P.; Zushma, S.; Berluche, E.; Sissano,
J. A. Polym. Mater. Sci. Eng. 2002, 86, 325.
(3) (a) Odian, G. Principles of Polymerization; Wiley & Sons: New York,
1991; pp 308-310 and pp 712-713. (b) Vinyl Chloride and Poly
(Vinyl Chloride). Kirk-Othmer Encyclopedia of Chemical Technology, 3rd
ed.; Wiley & Sons: New York, 1983; Vol. 23, pp 865-936. (c) Kirk-
Othmer Encyclopedia of Chemical Technology Home Page. http://
www.mrw.interscience.wiley.com/kirk/ (accessed July 2002). (d) Alger, M.
Polymer Science Dictionary, 2nd ed.; Chapman Hall: New York, 1997;
pp 462-463.
(4) For reviews and recent studies of halocarbon complexes, see: (a) Kulawiec,
R. J.; Crabtree, R. H. Coord. Chem. ReV. 1990, 99, 89. (b) Huang, D.;
Bollinger, J. C.; Streib, W. E.; Folting, K.; Young, V., Jr.; Eisenstein, O.;
Caulton, K. G. Organometallics 2000, 19, 2281. (c) Huhmann-Vincent, J.;
Scott, B. L.; Kubas, G. J. Inorg. Chem. 1999, 38, 115. (d) Arndtsen, B. A.;
Bergman, R. G. Science 1995, 27, 1970.
(5) March, J. AdVanced Organic Chemistry; John Wiley and Sons: New York,
1985; pp 295-298.
(6) (a) Stockland, R. A., Jr.; Foley, S. R.; Jordan, R. F. J. Am. Chem. Soc.
2003, 125, 796. (b) Stockland, R. A., Jr.; Jordan, R. F. J. Am. Chem. Soc.
2000, 122, 6315. (c) Jordan, R. F.; Stockland, R. A., Jr.; Shen, H.; Foley,
S. Polym. Mater. Sci. Eng. 2002, 87, 39. (d) Jordan, R. F. Polym. Prepr.
(Am. Chem. Soc., DiV. Polym. Chem.) 2001, 42, 829. (e) Foley, S.; Jordan,
R. F. Abstr. Pap. Am. Chem. Soc. 2001, 222, 440-INOR. (f) Foley, S. R.;
Jordan, R. F. Abstr. Pap. Am. Chem. Soc. 2002, 223, 398-INOR.
9
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J. AM. CHEM. SOC. 2003, 125, 4350-4361
10.1021/ja029823+ CCC: $25.00 © 2003 American Chemical Society

Reaction of Vinyl Chloride with Catalysts
A R T I C L E S
Catalysts which undergo monomer insertion faster than â-Cl
elimination, or catalysts which undergo 2,1 VC insertion, will
be required to avoid this termination pathway.
Me2NCH2CH2NMe2) by methyl abstraction from (tmeda)PdMe2
with B(C6F5)3 in CD2Cl2.14 Complex 2 decomposes above
-50 °C.15
The facility of â-Cl elimination for group 4 metal catalysts
is not surprising given the strong driving force for this process
for early metals. For example, â-Cl elimination of a ZrCH2-
CHClR+ species is predicted to be exothermic by ca. 42 kcal/
mol, primarily due to the large difference between the Zr-Cl
(116 kcal/mol) and the Zr-Me (67 kcal/mol) bond strengths.7,8
In contrast, the driving force for â-elimination of heteroatom
groups from late transition metal species is anticipated to be
less than that for early metal catalysts due to the smaller
difference between M-X and M-C bond strengths.9 For
example, the Pt-Cl bond is estimated to be ca. 10 kcal/mol
stronger than the Pt-Me bond in (PEt3)2PtClX (X ) Cl, Me),
based on a calorimetric study.10 Indeed, several late metal alkyl
complexes which contain â-halogen substituents have been
Generation, Structure, and Dynamics of (Me2bipy)PdMe-
(CH2dCHCl)+ (3). Treatment of a CD2Cl2 solution of 2 with
VC at -78 °C generates the VC complex [(Me2bipy)PdMe-
(CH2dCHCl)][MeB(C6F5)3] (3, eq 3). For NMR characterization
experiments, 3 was generated using 0.9 equiv of VC to avoid
complications from associative intermolecular VC exchange
(vide infra). The low-temperature NMR spectra of 3 show that
the two halves of the Me2bipy ligand are inequivalent and
contain resonances for coordinated VC. The VC Hint 1H NMR
resonance is shifted 0.3 ppm downfield, and the Hcis and Htrans
resonances are shifted by an average of 0.6 ppm upfield from
the corresponding resonances of free VC.16 The 13C NMR
resonances for the coordinated VC (δ 102.7 (d, J ) 202, CHCl),
78.7 (t, J ) 168, CH2)) are shifted upfield by an average of
∆ ) 31 ppm. The shifts of the VC resonances establish that
the VC is coordinated through the CdC bond and not the
chlorine. Several other VC complexes have been characterized
previously, including the square-planar complexes (acac)PtCl-
(CH2dCHCl) and (acac)Rh(CH2dCHCl)2. The 13C NMR
resonances for the coordinated VC in these cases appear at much
higher field (∆ ) ca. 50 ppm) than for 3, reflecting the decreased
d-π* back-bonding in cationic 3.17
characterized, including PtCl5(CH2CH2Cl)2- 11
, (2,9-Me2phen)-
PtCl3(CH2CH2Cl),12 and Ir(CO)Br2(PMe2Ph)2(CH2CH2Br).13
The high oxidation states and absence of vacant coordination
sites presumably help to disfavor â-Cl elimination in these cases.
In this paper, we describe studies of the reaction of VC with
representative late metal, single-site olefin dimerization and
polymerization catalysts.6c-f
Results and Discussion
Generation of [(Me2bipy)PdMe(ClCD2Cl)][MeB(C6F5)3]
(2). To investigate the coordination and insertion chemistry of
VC with a simple late metal alkyl complex, we first studied
the reaction of VC with “(Me2bipy)PdMe+” (Me2bipy ) 4,4′-
Me2-2,2′-bipyridine). The precursor (Me2bipy)PdMe2 (1) is
prepared by displacement of cyclooctadiene (cod) from (cod)-
PdMe2 by Me2bipy (97%). Treatment of 1 with 1 equiv of
B(C6F5)3 (CD2Cl2, -78 °C) cleanly produces a new species
which is assigned as the methylene chloride adduct [(Me2bipy)-
PdMe(ClCD2Cl)][MeB(C6F5)3] (2, eq 2). The 1H and 13C NMR
spectra of 2 show that the two halves of the Me2bipy ligand
are inequivalent and contain MeB resonances at the free anion
positions (δ 0.31 and δ 8.9, respectively; CD2Cl2, -88 °C).
Resonances for coordinated CD2Cl2 are not observed in the low-
temperature 13C NMR spectrum of 2, so it is likely that fast
stereospecific solvent exchange occurs under these conditions.
Similarly, Baird prepared (tmeda)PdMe(ClCD2Cl)+ (tmeda )
The low-temperature 1H NMR spectrum of 3 contains a single
set of sharp resonances consistent with the presence of one
dominant isomer. The NOESY spectrum of 3 contains cross-
peaks between the Pd-Me and the VC Hcis and Hint resonances
(see eq 4 for assignments), which establishes that the CdC bond
is oriented perpendicular to the N-N-Pd-Me square plane,
as expected for a d8 square-planar olefin complex, and that the
Cl points away from the Pd-Me group, as illustrated in eq 4.18
This conformation is supported by the presence of a cross-peak
(14) Desjardins, S. Y.; Way, A. A.; Murray, M. C.; Adirim, D.; Baird, M. C.
Organometallics 1998, 17, 2382.
(15) (a) The decomposition products of 2 have not been fully characterized.
However, resonances for MeB(C6F5)2 are observed in the 1H and 19F NMR
spectra after decomposition, suggesting that C6F5- transfer from MeB(C6F5)3-
to Pd occurs. (b) For examples of C6F5- abstraction from MeB(C6F5)3- by
electrophilic cations, see: Dagorne, S.; Guzei, I. A.; Coles, M.; Jordan, R.
F. J. Am. Chem. Soc. 2000, 122, 274 and references therein. (c) Data for
MeB(C6F5)2: 1H NMR (CD2Cl2) δ 1.69 (s); 19F NMR (CD2Cl2) δ -128.4
(m), -146.7 (t, J ) 20, 2F), 160.7 (m, 4F). See: Qian, B.; Ward, D. L.;
Smith, M. R. Organometallics 1998, 17, 3070.
(7) This estimate assumes a Zr(IV)-olefin bond strength of 15 kcal/mol. See:
(a) Carpentier, J.-F.; Wu, Z.; Lee, C. W.; Stro¨mberg, S.; Christopher, J.
N.; Jordan, R. F. J. Am. Chem. Soc. 2000, 122, 7750. (b) Carpentier, J.-F.;
Maryin, V. P.; Luci, J.; Jordan, R. F. J. Am. Chem. Soc. 2001, 123, 898.
(8) Zr-C (67 kcal/mol) and Zr-Cl (116 kcal/mol) bond energies taken from:
Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.
(9) (a) Simoes, J. A. M.; Beauchamp, J. L. Chem. ReV. 1990, 90, 629. (b)
Bryndza, H. F.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw, J. E. J.
Am. Chem. Soc. 1987, 109, 1444.
(16) Data for free VC: 1H NMR (CD2Cl2, -73 °C) δ 6.30 (dd, J ) 14.5, 7.0,
1H, Hint), 5.51 (dd, J ) 14.5, 1.5, 1H, Htrans), 5.45 (dd, J ) 7.0, 1.5, 1H,
H
cis); 13C NMR (CD2Cl2, -73 °C) δ 125.4 (d, J ) 197, dCHCl), 117.8
(t, J ) 162, dCH2).
(10) Takhin, G. A.; Skinner, H. A.; Zaki, A. A. J. Chem. Soc., Dalton Trans.
1984, 371.
(17) (a) Jesse, A. C.; Gijben, H. P.; Stufkens, D. J.; Vrieze, K. Inorg. Chim.
Acta 1978, 31, 203. (b) Jesse, A. C.; Stufkens, D. J.; Vrieze, K. Inorg.
Chim. Acta 1979, 32, 87. (c) Ashley-Smith, J.; Douek, Z.; Johnson, B. F.
G.; Lewis, J. J. Chem. Soc., Dalton Trans. 1974, 128. (d) Alt, H. G.;
Engelhardt, H. E. J. Organomet. Chem. 1988, 346, 211. (e) Bigorgne, M.
J. Organomet. Chem. 1977, 127, 55.
(11) Halpern, J.; Jewsbury, R. A. J. Organomet. Chem. 1979, 181, 223.
(12) Fanizzi, F. P.; Maresca, L.; Pacifico, C.; Natile, G.; Lanfranchi, M.;
Tiripicchio, A. Eur. J. Inorg. Chem. 1999, 1351.
(13) Deeming, A. J.; Shaw, B. L. J. Chem. Soc. A 1971, 376.
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A R T I C L E S
Foley et al.
Figure 1. Variable temperature 1H NMR spectra of in situ generated (Me2-
bipy)PdMe(CH2dCHCl)+ (3; CD2Cl2 solvent). The bipy and vinyl regions
are shown. Assignments are based on the labeling scheme in eq 4 and were
determined by 2D NMR experiments: δ 8.42, H6′; 8.33, H6; 8.02, H3′;
7.96, H3; 7.50, H5; 7.43, H5′; 6.59, dCHCl; 5.01, dCHHtrans; 4.88,
dCHHcis. A deficiency of VC was used to avoid intermolecular VC
exchange. The chemical shift scale is in units of ppm.
Figure 2. 1H NMR spectra of (Me2bipy)PdMe(ClCD2Cl)+ (2) with added
VC (CD2Cl2, -80 °C). The bipy and vinyl regions are shown. (a) Free
VC, (b) 2 with 1.10 equiv of VC added, (c) 2 with 1.05 equiv of VC added,
(d) 2 with 0.90 equiv of VC added. Peak assignments: δ 8.41, H6′; 8.33,
between H6′ and Htrans and the absence of cross-peaks between
H6′ and Hcis or Hint. Warming a CD2Cl2 solution of 3 from -68
to -53 °C results in broadening of the VC, PdMe, and Me2-
bipy-H6′ resonances (Figure 1). These NMR line shape changes
are reversible, and the remaining Me2bipy resonances are
unaffected. The simplest explanation for these observations is
that an isomer of 3 in which the chloride points toward the Pd-
Me unit (3′) is present at low concentration (below the NMR
detection limit), and as the temperature is raised, rotation around
the Pd-VC bond occurs on the NMR time scale, resulting in
exchange of 3 and 3′. Because the structures of 3 and 3′ are
very similar, only the resonances for the hydrogens close to
the Pd-VC unit are sensitive to the VC conformation and are
affected by the fluxional process. Support for this explanation
is provided by the dynamic behavior of the analogous propylene
complex (vide infra).
H6; 8.02, H3′; 7.96, H3; 7.50, H5; 7.43, H5′; 6.59, dCHCl; 5.01, dCHHtrans
;
4.88, dCHHcis. The broadening of the VC and H6′ resonances is due to
associative VC exchange. The resonances at δ 8.33, 7.96, and 7.43 are due
to 2. The chemical shift scale is in units of ppm.
Generation and Properties of (Me2bipy)PdMe(CH2d
CHR)+ (R ) Me, H). To better understand the properties of
VC complex 3, the analogous propylene and ethylene adducts
were investigated. The reaction of 2 with propylene at -78 °C
yields (Me2bipy)PdMe(CH2dCHMe)+, which exists as a mix-
ture of two isomers (4/4′, 1.5/1 isomer ratio, eq 5). As illustrated
1
in Figure 3, the H NMR spectrum of 4/4′ at -73 °C contains
two sets of propylene, Pd-Me, and Me2bipy resonances
corresponding to the two isomers. Five of the Me2bipy aromatic
resonances are coincident for the two isomers, while the
remaining Me2bipy aromatic resonance, which is assigned to
the ortho-H adjacent to the propylene ligand (H6′), appears at
δ 7.80 for the major isomer and δ 8.30 for the minor isomer.
Warming the solution to -15 °C (above this temperature
insertion occurs) results in coalescence of the two sets of
resonances due to fast isomer exchange; this process is revers-
ible. The barrier for propylene rotation is ca. 11 kcal/mol.20
Thus, the solution behavior of 4 is similar to that of 3 with the
exception that both 4 and 4′ are directly observable. Addition
of excess propylene to 4/4′ at -88 °C in CD2Cl2 results in
coalescence of the 4 and 4′ resonances and of the free and
coordinated propylene resonances, due to fast associative
exchange of free and coordinated propylene.
Complex 3 undergoes fast intermolecular exchange of VC
by an associative mechanism, even at low temperature. The
NMR spectra of 3 in the presence of even a slight excess of
VC (CD2Cl2, -88 °C) display a single set of VC resonances at
the weighted average of the free and coordinated VC chemical
shifts (Figure 2). The Pd-Me and H6′ resonances broaden upon
addition of excess VC, which shows that intermolecular
exchange is accompanied by 3/3′ isomer exchange. However,
the remaining Me2bipy resonances remain sharp under fast
exchange conditions, showing that the entering VC takes the
same coordination site as the departing VC, as expected for a
square-planar d8 complex.19
(20) (a) Activation parameters for 4/4′ exchange were determined by simulation
of the 1H NMR spectra (Hint resonances) over the temperature range from
-92 to -26 °C. Values for ∆Gq evaluated at -33 °C are as follows. Major
to minor isomer, 11.1 kcal/mol; minor to major isomer, 10.7 kcal/mol. (b)
It is also possible that a small amount of free propylene formed by
dissociation from 4 (perhaps accompanying trace decomposition) could
produce the line shape changes in Figure 3. However, the VT NMR spectra
of a mixture of 3 + 0.75 equiv propene, which generates 0.75 equiv of 4
in the presence of excess 3 and ensures the complete absence of free
propylene, are identical to those of pure 4 between -80 and -23 °C. This
result confirms that the line shape changes are due to propylene rotation,
not intermolecular propylene exchange.
(18) Fusto, M.; Giordano, F.; Orabona, I.; Ruffo, F.; Panunzi, A. Organometallics
1997, 16, 5981.
(19) Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms; Brooks/
Cole: Montery, 1985; Chapter 2.
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Reaction of Vinyl Chloride with Catalysts
A R T I C L E S
exchange between free and coordinated propylene, but the
resonances for VC are sharp and appear at the free VC positions.
Similarly, treatment of a CD2Cl2 solution of 3 with 0.4 equiv
of ethylene at -88 °C results in the formation of 0.4 equiv of
5, leaving 0.6 equiv of 3 unreacted. The 1H NMR spectrum of
the mixture contains a normal spectrum of 5. However, only a
single set of VC resonances is observed, and the Pd-Me and
H6′ resonances of 3 are broadened. These results indicate the
0.4 equiv of free VC displaced by the ethylene exchanges rapidly
with the coordinated VC of 3 (as expected from above). Addition
of an additional 0.7 equiv of ethylene to this mixture results in
quantitative formation of 5. Only one ethylene resonance is
observed (δ 4.98, s), indicating that the 0.1 equiv of free ethylene
exchanges rapidly with the coordinated ethylene of 5 (as
expected from above). However, the VC resonances are sharp
and appear at the free VC positions.
The weaker coordination of the electron-poor olefin VC as
compared to the sterically similar propylene in the (Me2bipy)-
PdMe(olefin)+ system reflects the poor back-bonding properties
of the cationic Pd(II) center.22 For comparison, the same trend
in VC versus propylene binding strength was observed for solid
Ag(olefin)2+, while the opposite trend was observed for Ni-
{P(O-o-tolyl)3}2(olefin) and (acac)Rh(olefin)2, in which d-π*
back-bonding plays a more significant role.23
Figure 3. Variable temperature 1H NMR spectra of in situ generated (Me2-
bipy)PdMe(CH2dCHMe)+ (4/4′; CD2Cl2 solvent). The bipy and vinyl
regions are shown. Assignments are based on the labeling scheme in eq 5.
Major isomer: δ 8.32, H6; 8.00, H3 or H3′; 7.96, H3 or H3′; 7.80, H6′;
7.49, H5 or H5′; 7.44, H5 or H5′; 5.95, dCHMe; 4.87, dCH2; 4.54, dCH2.
Minor isomer: δ 8.32, H6; 8.30, H6′; 8.00, H3 or H3′; 7.96, H3 or H3′;
7.49, H5 or H5′; 7.44, H5 or H5′; 5.79, dCHMe; 4.56, dCH2; 4.47, dCH2.
The line shape changes are due to 4/4′ exchange.
VC Insertion of (Me2bipy)PdMe(CH2dCHCl)+ (3). The
reaction of 2 with VC was investigated in NMR experiments
using internal standards (eq 7). The reaction of 2 with a large
excess of VC (103 equiv) in CD2Cl2 at -78 °C, followed by
warming to room temperature for 30 min, results in complete
consumption of 2, consumption of 1.9 equiv of VC, and
formation of 1.8 equiv of propylene and 0.1 equiv of butenes
(cis and trans 2-butene and isobutylene). The 1H NMR spectrum
of the product mixture contains a predominant set of (Me2bipy)-
Pd resonances which integrate for 0.95 equiv versus starting 2
and are nearly identical to those of (Me2bipy)PdCl2, with the
exception that the Me2bipy ortho-H resonance is shifted slightly
upfield. In addition, resonances for the bis-ligand complex (Me2-
bipy)2Pd2+ (0.03 equiv vs 2) are observed; the identity of this
The ethylene complex (Me2bipy)PdMe(CH2dCH2)+ (5) is
generated by addition of ethylene to a CD2Cl2 solution of 2 at
-
species was confirmed by independent synthesis of the B(C6F5)4
salt.24 The 19F NMR spectrum contains predominant resonances
for free B(C6F5)3 (ca. 86% of total C6F5 species), which are
significantly broadened. These results show that the main
organometallic products of the reaction are (Me2bipy)PdCl2 and
1
-78 °C. The H NMR spectrum of 5 at -83 °C contains a
broad AA′XX′ pattern centered at δ 4.9 for the coordinated
ethylene. Complex 5 undergoes fast exchange with free ethylene
at -83 °C. The analogous Pt complex, [(tBu2bipy)PtMe(CH2d
CH2)][MeB(C6F5)3], was prepared previously by the reaction
of (tBu2bipy)PtMe2 and B(C6F5)3 in the presence of ethylene.21
Relative Olefin Binding Strengths in (Me2bipy)PdMe-
(olefin)+. Competition experiments establish that VC coordi-
nates more weakly to (Me2bipy)PdMe+ as compared to pro-
pylene or ethylene (eq 6). For example, addition of 1.04 equiv
of propylene to 3 at -73 °C results in complete displacement
of VC and formation of 4/4′. Only one set of resonances are
observed for the two isomers 4/4′ due to fast associative
(22) The poor back-bonding properties of L2PdR+ species are illustrated by the
high νCO values for the carbonyl ligands in (1,10-phenanthroline)Pd{C-
(dO)Me}(CO)+ (νCO ) 2128 cm-1) and (R-diimine)Pd{C(dO)Me}(CO)+
(νCO ) 2132 cm-1). Similar values are expected for (Me2bipy)Pd{C(dO)-
Me}(CO)+. (a) Rix, F. C.; Brookhart, M. J. Am. Chem. Soc. 1995, 117,
1137. (b) Burns, C. T.; Jordan, R. F. Abstr. Pap. Am. Chem. Soc. 2002,
224, 322-INOR. (c) Burns, C. T.; Jordan, R. F., unpublished results.
(23) (a) Quinn, H. W.; VanGilder, R. L. Can. J. Chem. 1971, 49, 1323. (b)
Cramer, R. J. Am. Chem. Soc. 1967, 89, 4621. (c) Tolman, C. A. J. Am.
Chem. Soc. 1974, 96, 2780.
(24) For other (Me2bipy)2Pd2+salts, see: (a) PF6 salt: Milani, B.; Anzilutti,
-
A.; Vicentini, L.; Santi, A.; Zangrando, E.; Geremia, S.; Mestroni, G.
Organometallics 1997, 16, 5064. (b) TfO- salt: Wehman, P.; Dol, G. C.;
Moorman, E. R.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Fraanje, J.;
Goubitz, K. Organometallics 1994, 13, 4856. (c) CF3COO- salt: Milani,
B.; Corso, G.; Zangrando, E.; Randaccio, L.; Mestroni, G. Eur. J. Inorg.
Chem. 1999, 11, 2085.
(21) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J. J. Chem. Soc., Dalton Trans.
1996, 1809.
9
J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003 4353

A R T I C L E S
Foley et al.
Scheme 1a
ligand exchange reactions in eqs ii and iii in Scheme 1, which
are the only significant reactions occurring below -30 °C. It is
also possible that 3 undergoes initial 2,1 insertion to give (Me2-
bipy)Pd(CHClCH2Me)+, which isomerizes by â-H elimination
and reinsertion to (Me2bipy)Pd(CHMeCH2Cl)+, which in turn
undergoes â-Cl elimination to yield the products of eq ii.
However, no evidence for the intermediates or possible chloro-
propylene byproducts from this indirect process was observed.
Above -30 °C, 6 consumes a second equiv of VC, and the
final products of eq 7 are formed. This stage is complete within
a few minutes at room temperature. These results are consistent
with eqs iv-vi in Scheme 1, in which Me/Cl exchange between
2+
-
{(Me2bipy)Pd(µ-Cl)}2 and MeB(C6F5)3 regenerates (Me2-
bipy)PdMe+, which in turn undergoes VC insertion and â-Cl
elimination. The chloro species (Me2bipy)PdCl+ and ClB(C6F5)3-
collapse to (Me2bipy)PdCl2 and B(C6F5)3.27
A key feature of Scheme 1 is that, although the equilibrium
in eq iii lies far to the right, the barrier for VC insertion of 3 is
much lower than that for propylene insertion of 4 (vide infra),
so that (Me2bipy)PdMe+ consumes VC faster than propylene.
The minor butene products are derived from propylene
insertion of 4, chain walking of the resulting (Me2bipy)Pd-
(butyl)+ species, and eventual butene loss. The bis-ligand
complex (Me2bipy)2Pd2+ is likely formed by decomposition of
the (Me2bipy)PdH+ species resulting from butene loss.28 The
yields of butenes and (Me2bipy)2Pd2+ increase at the expense
of the propylene and (Me2bipy)PdCl2 yields when the reaction
is conducted in the presence of lower VC charges. For example,
the reaction of 2 with 34 equiv of VC yields 1.3 equiv of
propylene, 0.36 equiv of butenes, 0.9 equiv of (Me2bipy)PdCl2,
a Pd ) (Me2bipy)Pd, ArF ) C6F5.
B(C6F5)3. Control experiments establish that the minor shifting
of the (Me2bipy)PdCl2 1H resonances and the broadening of
the B(C6F5)3 19F resonances result from interaction between
1
these species. The H and 19F NMR spectra of a pyridine-d5
solution (50 °C) of the solid remaining after removal of the
volatiles from the product mixture of eq 7 confirm that (Me2-
bipy)PdCl2 and B(C6F5)3 are present.
and 0.05 equiv of (Me2bipy)2Pd2+
.
Propylene and Ethylene Insertion of (Me2bipy)PdMe-
(olefin)+ Species. To confirm that VC insertion of 3 is faster
than propylene insertion of 4, the latter reaction was investigated
independently. The reaction of 4 with excess propylene was
monitored by low-temperature NMR. These experiments show
that no insertion occurs below -10 °C and that above this
temperature the propylene is catalytically dimerized.29 Similar
experiments establish that ethylene complex 5 inserts ethylene
only at ca. -23 °C; above this temperature, catalytic dimeriza-
tion to internal butenes occurs.22a,30 Thus, the insertion rate of
(Me2bipy)2Pd(Me)(olefin)+ species varies in the order: VC .
ethylene > propylene. These results are consistent with the
observations of Brookhart and Sen which demonstrate that the
rates of insertion of (R-diimine)PdMe(olefin)+ (R-diimine )
(2,6-iPr2-C6H3)NdCMeCMedN(2,6-iPr2-C6H3)) vary in the
order vinyl bromide > ethylene > propylene.2a,31,32 The higher
ground-state energies of the VC and vinyl bromide adducts, as
NMR studies were conducted to probe the mechanism of eq
7, and the results are summarized in Scheme 1. Low-temperature
NMR monitoring of the reaction of 3 with 34 equiv of VC shows
that 3 reacts slowly at -55 °C to produce the dinuclear
dicationic species {(Me2bipy)Pd(µ-Cl)}22+ (6, MeB(C6F5)3- salt)
and propylene. Gradual warming of the reaction mixture from
-55 to -30 °C over 2.5 h results in 80% conversion of 3 to 6.
The identity of 6 was confirmed by independent synthesis of
-
the B(C6F5)4 salt.25 Because propylene coordinates more
strongly than VC to (Me2bipy)PdMe+ (as confirmed above),
the propylene which is generated displaces VC from 3. Thus,
the NMR spectra show that a mixture of 3, 4, and 6 is present
until one-half of the Pd-Me groups are consumed, after which
point only 4 and 6 are present.26 These observations are
consistent with the net 1,2 VC insertion/â-Cl elimination and
(27) The minor unidentified B-C6F5 products observed by 19F NMR may result
from competing redistribution reactions of ClB(C6F5)3-, which is known
to be labile. For characterization and lability of ClB(C6F5)3-, see: (a) Zhou,
J.; Lancaster, S. J.; Walker, D. A.; Beck, S.; Thornton-Pett, M.; Bochmann,
M. J. Am. Chem. Soc. 2001, 123, 223. (b) Courtenay, S.; Stephan, D. W.
Organometallics 2001, 20, 1442. (c) Bosch, B. E.; Erker, G.; Fro¨lich, R.;
Meyer, O. Organometallics 1997, 16, 5449.
(28) In several experiments, traces of ethylene were also observed. The ethylene
is probably formed by VC insertion and â-Cl elimination of (Me2bipy)-
PdH+ species.
(29) A distribution of internal hexenes is produced which is similar to that
produced by {PhNdC(R)C(R)dNPh}NiBr2/MAO (R, R ) 1,8-naphth-diyl).
See: Svejda, S. A.; Brookhart, M. Organometallics 1999, 18, 65.
(30) These results are similar to the behavior of [(1,10-phenanthroline)Pd(Me)-
(CH2dCH2)][B{3,5-(CF3)2-C6H3}4]. Rix, F. C.; Brookhart, M.; White, P.
S. J. Am. Chem. Soc. 1996, 118, 4746.
(25) For representative examples of other halide-bridged dinuclear dicationic
Pd complexes, see: (a) Clater, M.; Hollis, T. K.; Overman, L. E.; Ziller,
J.; Zipp, G. G. J. Org. Chem. 1997, 62, 1449. (b) Pignat, K.; Vallotto, J.;
Pinna, F.; Strukul, G. Organometallics 2000, 19, 5160. (c) Neve, F.;
Ghedini, M.; Tiripicchio, A.; Ugozzoli, F. Organometallics 1992, 11, 795.
(26) The 1H NMR spectra of 3 and 4 are nearly identical except that Pd-Me
resonances occur at δ 0.91 (-63 °C) and 0.84 (-43 °C), respectively. Thus,
the Pd-Me resonance for the exchanging mixture of 3 and 4 gradually
shifts from δ 0.90 to δ 0.84 as the first 50% of Pd-Me groups are consumed
and thereafter remains constant at δ 0.84.
9
4354 J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003

Reaction of Vinyl Chloride with Catalysts
A R T I C L E S
Scheme 2a
intermediates in Scheme 2. At -80 °C, the VC adduct [(R-
diimine)PdMe(CH2dCHCl)][MeB(C6F5)3] was observed (60%).34
At -65 °C, this species reacts to produce [(R-diimine)Pd-
Cl(CH2dCHMe)][MeB(C6F5)3]; this conversion is complete
upon warming of the solution to -40 °C over 30 min. At 0 °C,
[(R-diimine)PdCl(CH2dCHMe)][MeB(C6F5)3] converts to
[{(R-diimine)Pd(µ-Cl)}2][MeB(C6F5)3]2, releasing free propyl-
ene. Sen has reported analogous chemistry with vinyl bromide.32
Reaction of (Pyridine-bisimine)MCl2/MAO Catalysts
(M ) Fe, Co) with VC. The active species in the catalysts
studied above are square-planar L2Pd(R)(olefin)+ cations. An
alternative possible approach to disfavoring â-Cl elimination
is to use metal catalysts with higher coordination numbers. To
probe this strategy, the reactions of VC with (pyridine-bisimine)-
MCl2/MAO catalysts (M ) Fe, Co; pyridine-bisimine ) 2,6-
{(2,6-iPr2-C6H3)NdCMe}2-pyridine) were examined.35 The
reaction of VC with (pyridine-bisimine)FeCl2/MAO (Al/Fe )
1000) in C6D6 at 25 °C results in the immediate production of
propylene. After 96 h at 25 °C, 42 equiv of VC per Fe is
consumed and converted to propylene.36 The reaction of
(pyridine-bisimine)CoCl2/MAO (Al/Co ) 1000) with VC under
similar conditions results in greater consumption of VC (220
equiv per Co after 96 h at 25 °C) and conversion to propylene.
No PVC was observed in these reactions. The mechanism of
these reactions was not examined in detail but is almost certainly
analogous to that observed earlier for zirconocene catalysts.6
The active LnM-Me species generated from the reaction of the
(pyridine-bisimine)MCl2 complex and MAO undergoes net 1,2
VC insertion and â-Cl elimination, generating a LnMCl species
which is re-alkylated by MAO (Scheme 3).37 VC insertion into
the LnMCH2CHClR+ intermediate does not compete with â-Cl
elimination. These results are consistent with the recent report
of Boone et al. that VC terminates {2,6-(o-tol-NdCMe)2-
pyridine}FeCl2/MAO-catalyzed ethylene polymerization by 1,2
insertion/â-Cl elimination.38
a Ar ) 2,6-iPr2-C6H3.
compared to the ethylene or propylene adducts, contribute to
the lower insertion barriers for vinyl halides.33
Reaction of (r-Diimine)PdMe+ with VC. The studies above
show that the simple (Me2bipy)PdMe+ model system readily
coordinates and inserts VC but that the resulting (Me2bipy)Pd-
(CH2CHMeCl)+ intermediate undergoes rapid â-Cl elimination
which precludes VC polymerization. One potential strategy for
circumventing â-Cl elimination is to use sterically bulky
catalysts. Accordingly, the reaction of Brookhart’s sterically
bulky (R-diimine)PdMe+ catalyst with VC was investigated (eq
8).31 The reaction of (R-diimine)PdMe2 with B(C6F5)3 and
excess VC (20 equiv) at -78 °C followed by warming to room
temperature for 24 h results in complete consumption of (R-
diimine)PdMe2 and formation of the dinuclear dicationic Cl-
bridged complex [{(R-diimine)Pd(µ-Cl)}2][MeB(C6F5)3]2 (0.35
equiv, 70%), (R-diimine)PdCl2 (0.15 equiv, 15%), and propylene
(0.8 equiv). The {(R-diimine)Pd(µ-Cl)}22+ dication was gener-
Reaction of Neutral Ni Catalysts with VC. Another possible
approach to circumventing â-Cl elimination is to use a neutral
catalyst in which the driving force for M-Cl bond formation
may be attenuated due to the reduced metal electrophilicity. To
probe this possibility, we investigated the reaction of VC and
ethylene/VC mixtures with several neutral nickel catalysts.
-
ated independently as the B(C6F5)4 salt and characterized by
NMR and ESI-MS. These observations are consistent with net
1,2 VC insertion and â-Cl elimination of the initially generated
(R-diimine)PdMe+ species and dimerization of the resulting (R-
diimine)PdCl+ product as shown in Scheme 2, analogous to
the reactivity observed for (Me2bipy)PdMe+. Evidently, re-
alkylation of the (R-diimine)PdCl+ product by MeB(C6F5)3- is
disfavored in this system by steric crowding.
(34) The reaction of (R-diimine)PdMe2 with B(C6F5)3 in the presence of VC
also produces a second species in 40% yield which was identified as the
dinuclear µ-CH2 complex [(R-diimine)Pd(µ-CH2)(µ-Me)Pd(R-diimine)]-
[MeB(C6F5)3]. This species was recently reported by Baird and is the
exclusive product of the reaction of (R-diimine)PdMe2 with 0.5 or 1 equiv
of B(C6F5)3 in the absence of olefin at room temperature. Key 1H NMR
features of this species at -80 °C include a distinctive singlet at δ 5.43 for
the µ-CH2 group and a singlet at δ -0.14 for the µ-CH3 group. We have
also generated [(R-diimine)Pd(µ-CH2)(µ-Me)Pd(R-diimine)][MeB(C6F5)3]
by the reaction of (R-diimine)PdMe2 with B(C6F5)3 at -80 °C and
confirmed the NMR and ESI-MS results reported by Baird. Baird reported
that this complex reacts with ethylene to partially form “(R-diimine)PdMe+”
which polymerizes the ethylene. We observed that [(R-diimine)Pd(µ-CH2)-
(µ-Me)Pd(R-diimine)][MeB(C6F5)3] reacts with VC at ca. 20 °C to yield
the same final products as (R-diimine)Pd(Me)(VC)+. See: Brownie, J. H.;
Baird, M. C.; Zakharov, L. N.; Rheingold, A. L. Organometallics 2003,
22, 33.
(35) (a) Small, B. L.; Bennett, A. M. A.; Brookhart, M. J. Am. Chem. Soc.
1998, 120, 4049. (b) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; Mctavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D.
J. Chem. Commun. 1998, 849. (c) Britovsek, G. J. P.; Bruce, V.; Gibson,
V. C.; Kimberley, B. S.; Maddox, P. J.; Mastroianni, S.; Mctavish, S. J.;
Redshaw, C.; Solan, G. A.; Stromberg, S.; White, A. J. P.; Williams, D. J.
J. Am. Chem. Soc. 1999, 121, 8728. (d) Small, B. L.; Brookhart, M.
Macromolecules 1999, 32, 2120. (e) Bennett, A. M. A. WO 98/27124
(DuPont); Chem. Abs. 1998, 129, 122973x.
Monitoring the reaction of (R-diimine)PdMe2, B(C6F5)3, and
VC by low-temperature NMR enabled observation of the
(31) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995,
117, 6414. (b) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.
Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686. (c) Gottfried, A. C.;
Brookhart, M. Macromolecules 2001, 34, 1140. (d) Schultz, L. H.; Tempel,
D. J.; Brookhart, M. J. Am. Chem. Soc. 2001, 123, 11539.
(32) Kang, M.; Sen, A.; Zakharov, L.; Rheingold, A. L. J. Am. Chem. Soc.
2002, 124, 12080.
(33) (a) Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118,
2436. (b) von Schenck, H.; Stro¨mberg, S.; Zetterberg, K.; Ludwig, M.;
Åkermark, B.; Svensson, M. Organometallics 2001, 20, 2813.
(36) (Pyridine-bisimine)FeCl2/MAO is moderately active for the polymerization
of propylene at -20 °C, but the activity is decreased at 0 °C. Small, B. L.;
Brookhart, M. Macromolecules 1999, 32, 2120.
9
J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003 4355

A R T I C L E S
Foley et al.
Scheme 3a
a M ) Fe, Co; Ar ) 2,6-iPr2-C6H3.
The neutral Ni-phenyl complex (sal)Ni(Ph)PPh3 (7) (sal )
2-{C(H)dN(2,6-iPr2-C6H3)}-6-Ph-phenoxide) is an active cata-
lyst for polymerization of ethylene, norbornene, and substituted
norbornenes and exhibits some tolerance of Lewis bases.39 The
reaction of 7 with excess VC in C6D6 at 50 °C was monitored
1
by H NMR using toluene as an internal standard. The results
are summarized in Scheme 4, and representative spectra are
shown in Figure 4. After 4 days, 1 equiv (vs 7) of VC is
consumed, and 1 equiv of styrene is produced. No further
consumption of VC is observed, and no PVC is produced. Over
the course of the reaction, the two iPr methyl 1H NMR signals
of 7 (δ 1.21, 1.12) disappear, and two broad iPr methyl signals
(δ 3.32, 2.19) corresponding to the paramagnetic complex (sal)-
Ni(Cl)(PPh3) (8) appear. Broad iPr methyl signals (δ 1.37, 1.15)
corresponding to the bis-ligand complex (sal)2Ni (9) grow in at
Figure 4. 1H NMR spectra (500 MHz, C6D6) of the reaction of (sal)Ni-
(Ph)PPh3 and VC in the presence of toluene (internal standard). (a) Before
any reaction takes place (t ) 0). (b) After 18 h at 50 °C. (c) After 4 d at
50 °C. Assignments: a, styrene; b, VC; c, toluene; d, resonances of 8; e,
iPr methyl resonances of 9; f, other resonances of 9.
i
later times. The total intensity of the Pr methyl signals for 7,
8, and 9 is constant over the course of the reaction, which
confirms good mass balance for the sal ligand. These observa-
tions are consistent with displacement of PPh3 by VC, net 1,2
VC insertion, and subsequent â-Cl elimination. The slow overall
reaction rate reflects the unfavorable displacement of PPh3 by
VC.40 The initial Ni product 8 disproportionates to 9 and (Ph3P)2-
NiCl2, which precipitates from solution.
Scheme 4
To confirm the identity of the Ni products, the reaction scale
was increased, and 8, 9, and (Ph3P)2NiCl2 were isolated as
described in the Experimental Section. Compounds 8 and 9 were
characterized by single-crystal X-ray diffraction, and the identity
of 9 was confirmed by alternate synthesis from (Ph3P)2NiCl2
and 2 equiv of Na[sal]. The identity of (Ph3P)2NiCl2 was
confirmed by powder X-ray diffraction. Attempts to synthesize
8 by the reaction of (Ph3P)2NiCl2 with 1 equiv of Na[sal]
produced mixtures of 8 and 9, consistent with the facile
disproportionation of 8.
The molecular structure of 8 is shown in Figure 5, and key
bond distances and angles are listed in Table 1. Compound 8 is
(37) The active species for (pyridine-bisimine)FeCl2/MAO is proposed to be
(pyridine-bisimine)Fe(R)(olefin)+. See: (a) Britovsek, G. J. P.; Gibson,
V. C.; Spitzmesser, S. K.; Tellmann, K. P.; White, A. J. P.; Williams, D.
J. J. Chem. Soc., Dalton Trans. 2002, 1159. (b) Deng, L.; Margyl, P.;
Ziegler, T. J. Am. Chem. Soc. 1999, 121, 6479. Activation of (pyridine-
bisimine)CoCl2/MAO has been proposed to involve alkylation/reduction
to (pyridine-bisimine)CoMe followed by conversion to either a Co(I) or a
Co(III) active species. See: (c) Gibson, V. C.; Humphries, M. J.; Tellmann,
K. P.; Wass, D. F.; White, A. J. P.; Williams, D. J. Chem. Commun. 2001,
2252. (d) Kooistra, T. M.; Knijnenburg, Q.; Smots, J. M. M.; Horton, A.
D.; Budzelaar, P. H. M.; Gal, A. W. Angew. Chem., Int. Ed. 2001, 40,
4719.
a distorted tetrahedral complex. The O-Ni-N bond angle is
constrained to 93.66(8)° by the chelation, while the O-Ni-Cl
(124.06(6)°) and N-Ni-Cl (119.36(6)°) angles are correspond-
ingly larger. The distances and angles associated with the (sal)-
Ni unit are similar to those for reported tetrahedral bis-
salicylaldiminato nickel complexes.41
Complex 9 crystallizes with two independent molecules in
the asymmetric unit, which have similar structures. The structure
of one molecule of 9 is shown in Figures 6 and 7, and key
(38) Boone, H.; Athey, P. S.; Mullins, M. J.; Philipp, D.; Muller, R.; Goddard,
W. A. J. Am. Chem. Soc. 2002, 124, 8790.
(39) (a) Younkin, T. R.; Conner, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs,
R. H.; Bansleben, D. A. Science 2000, 287, 460. (b) Wang, C.; Friedrich,
S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M.
W. Organometallics 1998, 17, 3149.
(40) Attempts to use a phosphine sponge (Ni(cod)2 or B(C6F5)3) to increase
reaction rates resulted in catalyst decomposition as evidenced by Ni(0)
plating on the reaction tubes.
(41) Fox, M. R.; Orioli, P. L.; Lingafelter, E. C.; Sacconi, L. Acta Crystallogr.
1964, 17, 1159.
9
4356 J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003

Reaction of Vinyl Chloride with Catalysts
A R T I C L E S
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
(sal)2Ni (9)
Ni(1)-O(1)
1.841(2)
1.843(2)
1.895(3)
1.894(3)
N(1)-C(1)
N(2)-C(14)
O(1)-C(7)
O(2)-C(20)
1.299(4)
1.299(4)
1.308(4)
1.300(4)
Ni(1)-O(2)
Ni(1)-N(2)
Ni(1)-N(1)
O(1)-Ni(1)-O(2)
O(1)-Ni(1)-N(2)
O(2)-Ni(1)-N(2)
160.4(1)
90.7(1)
93.7(1)
O(1)-Ni(1)-N(1)
O(2)-Ni(1)-N(1)
N(2)-Ni(1)-N(1)
93.5(1)
90.9(1)
153.9(1)
Scheme 5
are similar to those in the tetrahedrally distorted bis-salicylal-
diminato complex (tBuMesal-Et)2Ni (1.856, 1.899 Å; θ ) 22°).42
It is possible that the â-Ph group in the presumed (sal)Ni-
(CH2CHPhCl) intermediate in Scheme 4 accelerates â-Cl
elimination. Grubbs proposed that initiation of ethylene polym-
erization by 7 involves ethylene insertion into the Ni-Ph bond
of 7 followed by â-H elimination to generate a Ni-H species
and styrene.39a To explore the influence of the phenyl substitu-
ent, we investigated the reaction of ethylene/VC mixtures with
7 (eq i, Scheme 5). The reaction of 7 with 250 equiv of VC
under 100 psi of ethylene at 20 °C in toluene yields styrene
(not quantified). No polymer is formed. The reaction of 7 with
ethylene in the absence of VC under otherwise identical
conditions results in a high yield of solid polyethylene (TOF )
900/h, eq ii, Scheme 5). As independent experiments show that
VC does not insert into the Ni-Ph bond of 7 at 20 °C, a likely
mechanism for eq i in Scheme 5 is insertion of ethylene followed
by â-H elimination to generate styrene and the corresponding
Ni-H complex, which then undergoes net 1,2 VC insertion and
rapid â-Cl elimination. Thus, (sal)Ni(CH2CH2Cl) undergoes fast
â-Cl elimination even without the â-Ph substituent.
Figure 5. Molecular structure of (sal)Ni(Cl)PPh3 (8). Hydrogen atoms are
omitted.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
(sal)Ni(Cl)(PPh3) (8)
Ni(1)-O(1)
Ni(1)-N(1)
Ni(1)-Cl(1)
1.881(2)
1.953(2)
2.2059(8)
Ni(1)-P(1)
N(1)-C(1)
O(1)-C(7)
2.3257(8)
1.298(3)
1.302(3)
O(1)-Ni(1)-N(1)
O(1)-Ni(1)-Cl(1)
N(1)-Ni(1)-Cl(1)
93.66(8)
124.06(6)
119.36(6)
O(1)-Ni(1)-P(1)
N(1)-Ni(1)-P(1)
Cl(1)-Ni(1)-P(1)
102.92(5)
109.98(6)
105.46(3)
The sulfonated SHOP-type catalyst (P-O)Ni(Ph)PPh3 (10,
P-O ) {Ph2PC(SO3Na)dC(p-tol)O}) catalyzes ethylene po-
lymerization in a variety of media, including H2O/toluene, in
the presence of Rh(CH2dCH2)2(acac) as a phosphine sponge.43
The reaction of this catalyst system was briefly investigated by
1H NMR. The reaction of 10/0.5 Rh(CH2dCH2)2(acac) with
excess VC in acetone-d6 yields styrene (0.8 equiv) after 2.5 h
at 70 °C (eq 9). VC uptake could not be quantified due to
Figure 6. Molecular structure of (sal)2Ni (9). Hydrogen atoms are omitted.
1
broadening of the H NMR signals. GC-MS analysis of the
volatiles confirmed that styrene is the major volatile component.
No PVC was detected. These results are consistent with net
1,2 VC insertion and subsequent fast â-Cl elimination. The
reaction was repeated in the absence of VC, and no styrene
was generated. This control experiment shows that the styrene
(42) tBuMesal-Et ) 2-{C(H)dN(Et)}-4-Me-6-tBu-phenoxide; (a) Shkol’nikova,
L. M.; Knyazeva, A. N.; Voblikova, V. A. J. Struct. Chem. 1967, 8, 77.
(b) Knoch, R.; Elias, H.; Paulus, H. Inorg. Chem. 1995, 34, 4032.
(43) (a) Held, A.; Mecking, S. Chem.-Eur. J. 2000, 6, 4623. (b) Soula, R.; Broyer,
J. P.; Llauro, M. F.; Tomov, A.; Spitz, R.; Claverie, J.; Drujon, X.; Malinge,
J.; Saudemont, T. Macromolecules 2001, 34, 2438. (c) Soula, R.; Novat,
C.; Tomov, A.; Spitz, R.; Claverie, J.; Drujon, X.; Malinge, J.; Saudemont,
T. Macromolecules 2001, 34, 2022. (d) Held, A.; Bauers, F. M.; Mecking,
S. Chem. Commun. 2000, 301. (e) Bauers, F. M.; Mecking, S. Macromol-
ecules 2001, 34, 1165.
Figure 7. View of the core structure of 9 showing the distorted tetrahedral
geometry at Ni. The Ph substituents at C(6) and C(19), the 2,6-iPr2-phenyl
substituents at N(1) and N(2), and all H atoms are omitted.
bond distances and angles are listed in Table 2. Compound 9 is
a distorted square-planar complex. The angle between the
N-Ni-O planes defined by the two ligands (θ) is 28°. The
average Ni-O (1.846 Å) and average Ni-N (1.899 Å) distances
9
J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003 4357

A R T I C L E S
Foley et al.
in eq 9 does not arise by release of ethylene from Rh(CH2d
CH2)2(acac), followed by ethylene insertion and â-H elimination
of 10. In both cases, the formation of Rh(PPh3)2(acac) was
observed by 31P NMR.
catalysts, including sterically open and sterically crowded
square-planar cationic Pd catalysts, five-coordinate (pyridine-
bisimine)MCl2/MAO (M ) Fe, Co) catalysts, and neutral Ni
catalysts, undergo fast â-Cl elimination. Due to the facility of
â-Cl elimination for both early and late metal catalysts, insertion
polymerization of VC and related monomers will likely require
novel catalyst designs to favor 2,1 insertion or disfavor â-Cl
elimination. Our work on these themes will be reported in due
course.
Experimental Section
Conclusions
General Procedures. All reactions were performed under N2 or
vacuum using standard Schlenk techniques or in a N2-filled drybox.
Pentane, hexanes, toluene, and benzene were distilled from sodium/
benzophenone or purified by passage through columns of activated
alumina and BASF R3-11 oxygen removal catalyst. Toluene-d8 and
benzene-d6 were distilled from sodium/benzophenone. Dichloromethane,
chlorobenzene, dichloromethane-d2, and chlorobenzene-d5 were dried
over CaH2 and distilled. Nitrogen was purified by passage through
columns containing activated molecular sieves and Q-5 oxygen
scavenger. MAO (30% solution in toluene; MAO ) methylalumoxane)
was obtained from Albemarle. Dried MAO was prepared by drying a
sample of MAO (30% toluene solution) under vacuum for 12 h at 25
°C. B(C6F5)3 was obtained from Boulder Scientific and purified by
sublimation. Vinyl chloride (VC) was obtained from Aldrich and used
without further purification or received from Oxy Vinyl and dried over
molecular sieves. (cod)PdCl2 was purchased from Pressure Chemical
and used as received. The ligands R-diimine ((2,6-iPr2-C6H3)Nd
CMeCMedN(2,6-iPr2-C6H3)) and pyridine-bisimine (2,6-{(2,6-iPr2-
C6H3)NdCMe}2-pyridine) were obtained from Strem and used as
received. The complexes (R-diimine)PdMe2, (pyridine-bisimine)FeCl2,
and (pyridine-bisimine)CoCl2 were prepared by literature procedures.31,35
Elemental analyses were performed by Midwest Microlabs. ESI-
MS experiments were performed with a Hewlett-Packard Series
1100MSD instrument using direct injection via a syringe pump (ca.
10-6 M solutions). Good agreement between observed and calculated
isotope patterns was observed in all cases.
The studies described here enable several conclusions to be
made concerning the fundamental reactions of VC with late
metal catalysts and the prospects for polymerizing this and other
CH2dCHX monomers by insertion mechanisms.
(i) VC coordinates more weakly than ethylene or propylene
to the simple catalyst (Me2bipy)PdMe+, which parallels the trend
for monomer binding to the d0 model system (C5H4Me)2Zr-
(OtBu)+.44 The weak coordination of the electron-poor VC
reflects the predominance of the olefin-to-metal σ-donation and
the absence of significant d-π* back-bonding in these metal
olefin species. This trend is expected to be general for both
early and late metal catalysts.
(ii) Insertion rates of (Me2bipy)Pd(Me)(olefin)+ species vary
in the order VC > ethylene > propylene. This trend is consistent
with previous observations by Brookhart and Sen that insertion
rates of (R-diimine)Pd(Me)(olefin)+ species vary in the order
vinyl bromide > ethylene > propylene. The higher ground-
state energies of the VC and vinyl bromide adducts, as compared
to the ethylene or propylene adducts, contribute to the lower
insertion barriers for vinyl halides.
(iii) The sterically open VC complex (Me2bipy)Pd(Me)(VC)+
and the crowded complex (R-diimine)Pd(Me)(VC)+ undergo net
1,2 VC insertion and â-Cl elimination to yield Pd-Cl species
and propylene. Analogous chemistry occurs for (pyridine-
bisimine)MCl2/MAO (M ) Fe, Co) catalysts and for neutral
(sal)Ni(Ph)PPh3 and (P-O)Ni(Ph)PPh3 catalysts, although the
initial LnM(R)(VC)+ adducts were not detected in these cases.
Recent DFT calculations predict that 2,1 insertion is favored
over 1,2 insertion for the model systems {HNdCHCHdNH}-
Pd(R)(VC)+ (R ) Me, Et).33b,45 However, these calculations
also predict that the 2,1 insertion product, {HNdCHCHdNH}-
PdCHClCH2Et+, undergoes facile isomerization to {HNd
CHCHdNH}Pd(CH(Et)CH2Cl)+ via â-H elimination/reinsertion
and that the latter species undergoes facile â-Cl elimination.
Our low-temperature NMR studies of the (Me2bipy)Pd(Me)-
(VC)+ and (R-diimine)Pd(Me)(VC)+ systems did not provide
evidence for LnPd(CHClCH2CH3)+ intermediates or chloro-
propylene byproducts. Thus, if 2,1 insertion is the kinetic
pathway, isomerization of the initial insertion product to the
1,2 insertion product must be rapid and must occur without loss
of olefin from the presumed LnPd(H)(ClHCdCHMe)+ inter-
mediate.
NMR spectra were recorded at ambient temperature unless specified
1
otherwise. H and 13C chemical shifts are reported relative to SiMe4
1
and were determined by reference to the residual H and 13C solvent
resonances. 11B chemical shifts are reported relative to BF3(Et2O), and
19F chemical shifts are reported relative to CFCl3. Coupling constants
are given in Hz. NMR spectra for (Me2bipy)Pd salts containing the
MeB(C6F5)3- anion contain anion resonances which are nearly identical
to those of [NBu3CH2Ph)][MeB(C6F5)3] and are thus characteristic of
the free anion. Data for free MeB(C6F5)3-, H NMR (CD2Cl2, -83
1
°C): δ 0.33 (s). 13C NMR (CD2Cl2, -83 °C): 147.2 (d, J ) 242),
136.7 (d, J ) 237), 135.5 (d, J ) 247), 127.1 (br s, ipso-C6F5), 9.0 (q,
J ) 127, MeB). 11B NMR (CD2Cl2, -83 °C): δ -14.0 (br s). 19F
NMR (CD2Cl2, -83 °C): δ -132.2 (d, 6F, J ) 22, o-F), -162.5 (t,
3F, J ) 22, p-F), -165.3 (t, 6F, J ) 22, m-F). NMR spectra for
B(C6F5)4 salts contain resonances characteristic of the free anion.46
-
(cod)PdMe2.47,48 A Schlenk flask was charged with (cod)PdCl2 (997
mg, 3.50 mmol), and Et2O (40 mL) was added by cannula to form a
yellow suspension. The flask was cooled to -78 °C, and MeMgCl (2.35
mL, 3.0 M in THF, 7 mmol) was added dropwise. The reaction mixture
was stirred at -35 °C for 1 h, and the volatiles were removed under
vacuum at 0 °C. The resulting solid was extracted with pentane (40
mL) at 0 °C to yield a clear colorless extract. The volatiles were
removed from the extract at 0 °C under vacuum to yield (cod)PdMe2
as a white solid (480 mg, 56%). The product was used immediately
(iv) The LnMCH2CHClR species formed by VC insertion into
the LnMR active species of late metal olefin polymerization
(44) Jordan, R. F.; Stoebenau, E. J., III. Abstr. Pap. Am. Chem. Soc. 2002, 224,
284-INOR.
(45) (a) Philipp, D. M.; Muller, R. P.; Goddard, W. A., III; Storer, J.; McAdon,
M.; Mullins, M. J. Am. Chem. Soc. 2002, 124, 10198. See also: (b)
Michalak, A.; Ziegler, T. J. Am. Chem. Soc. 2001, 123, 12266.
(46) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G., Jr.; Jordan, R. F. J.
Am. Chem. Soc. 2001, 123, 8291.
(47) Calvin, G.; Coates, G. E. J. Chem. Soc. 1960, 2008.
(48) Rudler-Chauvin, M.; Rudler, H. J. Organomet. Chem. 1977, 134, 115.
9
4358 J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003

Reaction of Vinyl Chloride with Catalysts
A R T I C L E S
for subsequent reactions. (cod)PdMe2 decomposes at 25 °C in the solid
state or in solution and should be stored below -30 °C. 1H NMR (CD2-
Cl2): δ 5.40 (m, 4H, dCH), 2.60-2.34 (m, 8H, -CH2), 0.26 (s, 6H,
PdMe).
H5′), 5.93 (m, 1H, dCHMe), 4.74 (br s, 1H, dCH2), 4.58 (d, J )
15.4, 1H, dCH2), 2.58 (s, 3H, Me2bipy), 2.53 (s, 3H, Me2bipy), 1.97
(d, J ) 6.3, 3H, dCHMe), 0.86 (s, 3H, PdMe). 13C{1H} NMR (CD2-
Cl2, -88 °C; both isomers; selected JCH values taken from gated-{1H}
spectrum): δ 154.8 (C2 or C2′), 154.7 (C2 or C2′), 153.8 (C4 or C4′),
153.7 (C4 or C4′), 152.6 (C4 or C4′), 152.4 (C4 or C4′), 152.4 (C2 or
C2′), 152.2 (C2 or C2′), 146.9 (C6 or C6′), 146.1 (C6 or C6′), 145.9
(C6 or C6′), 144.5 (C6 or C6′), 127.8 (C5 or C5′), 127.4 (C5 or C5′),
127.2 (C5 or C5′), 127.1 (C5 or C5′), 123.4, (C3 or C3′), 123.3 (C3 or
C3′), 123.2 (C3 or C3′), 123.1 (C3 or C3′), 110.5 (d, JCH ) 155,
dCHMe), 109.8 (d, JCH ) 160, dCHMe), 79.8 (t, JCH ) 160, dCH2),
79.6 (t, JCH ) 161, dCH2), 21.3 (two peaks overlapped, Me2bipy),
21.2 (Me2bipy), 21.1 (Me2bipy), 20.7 (dCHMe), 20.6 (dCHMe), 13.3
(q, JCH ) 135, PdMe), 12.2 (q, J ) 136, PdMe), 9.3 (MeB).
(Me2bipy)PdMe2 (1). A Schlenk flask was charged with (cod)PdMe2
(245 mg, 1.00 mmol) and Me2bipy (162 mg, 1.00 mmol), and pentane
(20 mL) was added by cannula. The resulting yellow suspension was
stirred at 0 °C for 1 h and filtered to yield a yellow solid. The solid
was washed with pentane (3 × 10 mL) and dried under vacuum at 0
°C to yield (Me2bipy)PdMe2 as a bright yellow solid (276 mg, 88%).
1H NMR (CD2Cl2): δ 8.58 (d, J ) 5.5, 2H, H6), 7.87 (s, 2H, H3),
7.30 (d, J ) 5.5, 2H, H5), 2.47 (s, 6H, Me2bipy), 0.21 (s, 6H, PdMe).
13C NMR (CD2Cl2, -53 °C): δ 154.3 (s, C2), 149.3 (s, C4), 147.0 (d,
J ) 183, C6), 126.5 (d, J ) 161, C5), 122.2 (d, J ) 162, C3), 21.3 (q,
J ) 127, Me2bipy), -7.6 (q, J ) 125, PdMe). Anal. Calcd for C14H18N2-
Pd: C, 52.43; H, 5.62; N, 8.74. Found: C, 52.43; H, 5.60; N, 8.59.
Generation of [(Me2bipy)PdMe(ClCD2Cl)][MeB(C6F5)3] (2). An
NMR tube was charged with (Me2bipy)PdMe2 (0.021 g, 0.065 mmol)
and B(C6F5)3 (0.033 g, 0.065 mmol), and CD2Cl2 (0.5 mL) was added
by vacuum transfer at -196 °C. The tube was warmed to -78 °C and
transferred to a precooled NMR probe, and NMR spectra were recorded.
Complete conversion to 2 was observed. 1H NMR (CD2Cl2, -88 °C):
δ 8.23 (m, 2H, H6 & H6′), 7.94 (s, 1H, H3 or H3′), 7.89 (s, 1H, H3 or
H3′), 7.40 (m, 2H, H5 & H5′), 2.49 (s, 3H, Me2bipy), 2.45 (s, 3H,
Me2bipy), 0.98 (s, 3H, PdMe), 0.31 (br s, 3H, MeB). 13C NMR (CD2-
Cl2, -88 °C): δ 155.4 (d, 3JCH ) 9, C2 or C2′), 153.2 (m, C4 or C4′),
Generation of [(Me2bipy)PdMe(CH2dCH2)][MeB(C6F5)3] (5). The
procedure for 3 was followed with the substitution of ethylene for VC.
1H NMR (CD2Cl2, -83 °C): δ 8.31 (d, J ) 6, 1H, H6), 8.00 (s, 1H,
H3 or H3′), 7.94 (s, 1H, H3 or H3′), 7.80 (d, J ) 6, 1H, H6′), 7.49 (d,
J ) 5.4, 1H, H5 or H5′), 7.43 (d, J ) 5.4, 1H, H5 or H5′), 4.9 (m, 4H,
CH2dCH2; broad AA′XX′), 2.54 (s, 3H, Me2bipy), 2.47 (s, 3H, Me2-
bipy), 0.70 (s, 3H, PdMe), 0.32 (br s, MeB). 13C NMR (CD2Cl2, -83
2
2
°C): 154.9 (d, JCH ) 9, C2 or C2′), 154.3 (t, JCH ) 6, C4 or C4′),
152.9 (t, 2JCH ) 6, C4 or C4′), 152.2 (d, 2JCH ) 10, C2 or C2′), 146.3
(dd, J ) 180, 4; C6 or C6′), 145.2 (dd, J ) 180, 4; C6 or C6′), 128.1
(d, J ) 168, C5 or C5′), 127.5 (d, J ) 168, C5 or C5′), 123.6 (d, J )
164, C3 or C3′), 123.2 (d, J ) 163, C3 or C3′), 87.5 (br, CH2dCH2),
21.5 (qt, J ) 124, 5; Me2bipy), 21.4 (qt, J ) 124, 4; Me2bipy), 11.5 (q,
J ) 136, PdMe).
3
152.3 (m, C4 or C4′), 151.0 (d, JCH ) 10, C2 or C2′), 147.3 (d, J )
185, C6′), 146.5 (d, J ) 182, C6), 127.6 (d, J ) 166, C5′), 127.2 (d,
J ) 166, C5), 123.7 (d, J ) 163, C3′), 122.6 (d, J ) 163, C3), 21.1 (q,
J ) 129, Me2bipy), 21.0 (q, J ) 129, Me2bipy), 8.9 (br q, J ca. 126,
MeB), 5.2 (q, J ) 135, PdMe).
Analysis of Organometallic Products from the Reaction of
(Me2bipy)PdMe(ClCD2Cl)+ (2) and VC. An NMR tube containing
(Me2bipy)PdMe2 (10.0 mg, 0.0312 mmol), B(C6F5)3 (16.0 mg, 0.0312
mmol), C6Me6 (internal standard), and VC (115 equiv) in CD2Cl2 (0.5
mL) was warmed from -78 °C to room temperature over ∼1 min and
then maintained at room temperature for 3 days. The volatiles were
removed under vacuum, and the remaining solid was dissolved in
pyridine-d5 at 50 °C. C6F5H was added as a 19F internal standard to
quantify the B(C6F5)3 in the final solution. Yields versus 1: (Me2bipy)-
PdCl2, 70%; B(C6F5)3, 66%. 1H NMR (pyridine-d5, 50 °C): δ 8.63 (d,
J ) 5 Hz, 2H), 8.52 (s, 2H), 7.06 (d, J ) 5 Hz, 2H), 2.27 (s, Me, 6H).
Generation of [(Me2bipy)PdMe(CH2dCHCl)][MeB(C6F5)3] (3).
An NMR tube was charged with (Me2bipy)PdMe2 (0.011 g, 0.034
mmol) and B(C6F5)3 (0.018 g, 0.034 mmol), and CD2Cl2 (0.5 mL) and
VC (0.9 equiv) were added by vacuum transfer at -196 °C. The tube
was warmed to -78 °C and transferred to a precooled NMR probe,
and NMR spectra were recorded. 1H NMR (CD2Cl2, -73 °C): δ 8.41
(d, J ) 5.5, 1H, H6′), 8.33 (d, J ) 5.8, 1H, H6), 8.02 (s, 1H, H3′),
7.96 (s, 1H, H3), 7.50 (d, J ) 5.5, 1H, H5), 7.43 (d, J ) 5.4, 1H, H5′),
6.59 (dd, J ) 12.5, 5.4, 1H, dCHCl), 5.01 (dd, J ) 12.5, 1.8, 1H,
dCH2), 4.88 (dd, J ) 5.2, 2.2, 1H, dCH2), 2.54 (s, 3H, Me2bipy),
2.48 (s, 3H, Me2bipy), 0.89 (s, 3H, PdMe). 13C NMR (CD2Cl2, -88
°C): δ 155.0 (d, 2JCH ) 9, C2 or C2′), 154.5 (t, 2JCH ) 6, C4 or C4′),
152.8 (t, 2JCH ) 6, C4 or C4′), 152.1 (d, 2JCH ) 10, C2 or C2′), 147.4
(d, 1JCH ) 182, C6′), 146.3 (d, 1JCH ) 183, C6), 127.5 (d, 1JCH ) 162,
C5′), 127.4 (d, 1JCH ) 168, C5), 123.6 (d, 1JCH ) 158, C3′), 123.2 (d,
1
19F NMR (CD2Cl2): δ -130.4, -156.1, -162.6. These H and 19F
NMR data are identical to data for authentic (Me2bipy)PdCl2 and
B(C6F5)3 in pyridine-d5 at 50 °C.
(Me2bipy)PdCl2. A flask was charged with (cod)PdCl2 (1.1 g, 3.9
mmol), Me2bipy (0.71 g, 3.9 mmol), and CH2Cl2 (50 mL). The mixture
was stirred for 1 h at 25 °C, and a pale yellow precipitate formed. The
solid was collected by filtration and dried under vacuum to afford 4 as
a yellow solid (1.3 g, 94%). 1H NMR (CD2Cl2): δ 9.08 (d, J ) 6, 2H,
H6), 7.85 (s, 2H, H3), 7.35 (d, J ) 6, 2H, H5), 2.56 (s, 6H, Me2bipy).
13C{1H} NMR (CD2Cl2): δ 153.4, 150.3, 127.7, 123.6, 21.9; one
quaternary C was not detected.
1
1
1JCH ) 163, C3), 102.7 (d, JCH ) 202, dCHCl), 78.7 (t, JCH ) 168,
dCH2), 21.3 (q, 1JCH ) 129, Me2bipy), 21.1 (q, 1JCH ) 129, Me2bipy),
14.7 (q, JCH ) 137, PdMe).
1
Generation of [(Me2bipy)PdMe(CH2dCHMe)][MeB(C6F5)3] (4).
The procedure for 3 was followed with the substitution of propylene
Generation of [(Me2bipy)2Pd][B(C6F5)4]2. An NMR tube was
charged with (Me2bipy)PdCl2 (8.5 mg, 0.024 mmol), Me2bipy (4.3 mg,
0.024 mmol), AgOTf (12.1 mg, 0.047 mmol), and CD2Cl2 (0.5 mL)
and maintained at room temperature for 1 h. Solid [Li(Et2O)2.8]-
[B(C6F5)4] (40.6 mg, 0.047 mmol) was added, and the tube was
maintained at room temperature for 1 day. The mixture was filtered to
1
for VC. Isomer ratio at -73 °C: 1.5/1. H NMR (CD2Cl2, -73 °C,
major isomer): δ 8.32 (d, J ) 6, 1H, H6), 8.00 (s, 1H, H3 or H3′),
7.96 (s, 1H, H3 or H3′), 7.80 (d, J ) 5, 1H, H6′), 7.49 (d, J ) 5, 1H,
H5 or H5′), 7.44 (d, J ) 5, 1H, H5 or H5′), 5.95 (m, 1H, dCHMe),
4.87 (d, J ) 8.4, 1H, dCH2), 4.54 (d, J ) 15.5, 1H, dCH2), 2.54 (s,
3H, Me2bipy), 2.49 (s, 3H, Me2bipy), 1.92 (d, J ) 6.5, 3H, dCHMe),
1
yield a clear yellow solution of [(Me2bipy)2Pd][B(C6F5)4]2. H NMR
1
(CD2Cl2): δ 8.26 (d, J ) 6, 2H), 8.06 (s, 2H), 7.67 (m, 2H), 2.63 (s,
0.79 (s, 3H, PdMe). H NMR (CD2Cl2, -73 °C, minor isomer): δ
6H, Me). 19F NMR (CD2Cl2): δ -133.3, -163.5, -167.4. ESI-MS:
8.32 (d, J ) 5.6, 1H, H6), 8.30 (d, J ) 6, 1H, H6′), 8.00 (s, 1H, H3
or H3′), 7.96 (s, 1H, H3 or H3′), 7.49 (d, J ) 5, 1H, H5 or H5′), 7.44
(d, J ) 5, 1H, H5 or H5′), 5.79 (m, 1H, dCHMe), 4.56 (d, J ) 14.4,
1H, dCH2), 4.47 (d, J ) 8.0, 1H, dCH2), 2.54 (s, 3H, Me2bipy), 2.49
(s, 3H, Me2bipy), 1.94 (d, J ) 7.6, 3H, dCHMe), 0.78 (s, 3H, PdMe).
1H NMR (CD2Cl2, -23 °C, fast isomer exchange): δ 8.37 (d, J ) 6,
1H, H6), 8.05 (br s, 2H, H6′), 8.03 (s, 1H, H3 or H3′), 7.96 (s, 1H, H3
or H3′), 7.51 (d, J ) 5.5, 1H, H5 or H5′), 7.46 (d, J ) 5.3, 1H, H5 or
[(Me2bipy)2Pd]2+ calcd. m/z 237.1, found 237.1. B(C6F5)4 calcd. m/z
-
679.0, found 679.0.
[{(Me2bipy)Pd(µ-Cl)}2][B(C6F5)4]2. A flask was charged with (Me2-
bipy)PdCl2 (0.120 g, 0.332 mmol), AgPF6 (0.084 g, 0.33 mmol), and
CH2Cl2 (10 mL). Immediate precipitation of [{(Me2bipy)Pd(µ-Cl)}2]-
[PF6]2 and AgCl occurred. The mixture was stirred for 1 h, [Li(Et2O)2.8]-
[B(C6F5)4] (0.287 mg, 0.332 mmol) was added, and the mixture was
9
J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003 4359

A R T I C L E S
Foley et al.
stirred for an additional hour. The mixture was filtered, yielding a white
precipitate and a deep yellow filtrate. The filtrate was concentrated to
3 mL and cooled to -30 °C for 2 days, yielding a yellow microcrys-
talline solid which was collected by filtration (0.236 g, 73%). 1H NMR
(CD2Cl2): δ 8.12 (d, J ) 6, 2H), 7.86 (s, 2H), 7.46 (d, J ) 6, 2H),
2.63 (s, Me, 6H). 13C NMR (CD2Cl2): δ 157.4, 156.2, 149.5, 129.3,
125.2, 22.0. ESI-MS [{(Me2bipy)Pd(µ-Cl)}2]2+ calcd. m/z 326.0, found
N(2,6-iPr2-C6H3) (0.780 g, 1.93 mmol) was added. The mixture was
refluxed for 12 h to yield a clear orange-yellow solution. The volatiles
were removed under vacuum to yield an orange solid (1.12 g, 98%).
1H NMR (CD2Cl2): δ 7.40-7.25 (m, 6H), 3.07 (sept, J ) 7, 4H), 2.10
(s, 6H), 1.45 (d, J ) 7, 12H), 1.20 (d, J ) 7, 12H). 13C{1H} NMR
(CD2Cl2): δ 178.8, 141.1, 139.7, 129.1, 124.1, 29.7, 23.8, 23.7, 21.3.
Anal. Calcd for C28H40Cl2N2Pd: C, 57.79; H, 6.93; N, 4.81. Found:
C, 57.80; H, 7.18; N, 4.73.
-
325.8. B(C6F5)4 calcd. m/z 679.0, found 678.7.
Ethylene Insertion of [(Me2bipy)PdMe(CH2dCH2)][MeB(C6F5)3]
(5). An NMR tube was charged with (Me2bipy)PdMe2 (10.0 mg, 0.031
mmol) and B(C6F5)3 (16.0 mg, 0.031 mmol), and CD2Cl2 (0.6 mL)
and excess ethylene (ca. 30 equiv) were added by vacuum transfer at
-196 °C. The tube was warmed to -78 °C and placed in an NMR
probe precooled to -75 °C. The reaction was monitored from -75 to
20 °C. At -75 °C, [(Me2bipy)PdMe(CH2dCH2)][MeB(C6F5)3] (5) in
fast exchange with free ethylene was the only significant species in
solution. Ethylene insertion was observed at ca. -23 °C, resulting in
the disappearance of 5, the formation of propylene, and the formation
of a new species presumed to be [(Me2bipy)Pd(CH2CH3)(CH2dCH2)]-
[MeB(C6F5)3]. This species could not be definitively characterized at
this temperature due to the presence of propylene, excess ethylene, and
remaining 5. Warming to 10 °C resulted in complete conversion of the
ethylene to cis- and trans-2-butenes exclusively. Further warming to
20 °C resulted in conversion of the internal butenes to higher olefins.
Reaction of (r-Diimine)PdMe2/B(C6F5)3 and VC. An NMR tube
was charged with (R-diimine)PdMe2 (7.9 mg, 0.015 mmol) and B(C6F5)3
(7.5 mg, 0.015 mmol), and CD2Cl2 (0.6 mL) and excess VC (20 equiv)
were added by vacuum transfer at -196 °C. The tube was warmed to
-78 °C, resulting in a red solution. The tube was placed in an NMR
probe precooled to -80 °C, and the reaction was monitored from -80
to 20 °C. At -80 °C, the VC adduct, [(R-diimine)PdMe(CH2dCHCl)]-
Generation of [{(r-Diimine)Pd(µ-Cl)}2][B(C6F5)4]2. An NMR tube
was charged with (R-diimine)PdCl2 (15.0 mg, 0.026 mmol), AgPF6
(6.5 mg, 0.026 mmol), and CD2Cl2 (0.6 mL). The tube was maintained
at room temperature for 15 min, yielding an orange slurry. Solid
[Li(Et2O)2.8][B(C6F5)4] (22.3 mg, 0.026 mmol) was added, and the tube
was agitated for 15 min. The mixture was filtered to remove the white
precipitate, resulting in a clear orange solution of [{(R-diimine)Pd(µ-
1
Cl)}2][B(C6F5)4]2. H NMR (CD2Cl2): δ 7.40 (t, J ) 7.8, 4H, Hpara),
7.17 (d, J ) 7.8, 8H, Hmeta), 2.74 (sept, J ) 6.8, 8H, CHMe2), 2.24 (s,
12H, NdC(Me)), 1.28 (d, J ) 6.8, 24H, CHMe), 1.16 (d, J ) 6.8,
24H, CHMe). ESI-MS: [{(R-diimine)Pd(µ-Cl)}2]2+ calcd. m/z 546.2,
found 546.3.
Reaction of VC with (Pyridine-bisimine)FeCl2/MAO. An NMR
tube was charged with (pyridine-bisimine)FeCl2 (0.0011 g, 0.0018
mmol), dried MAO (0.105 g, 1.8 mmol), and toluene (internal standard),
and C6D6 (0.5 mL) and VC (20.3 mL at 419 mm and 25 °C, 0.46 mmol)
were added by vacuum transfer at -196 °C. The tube was warmed to
1
room temperature, and a H NMR spectrum was recorded within 5
min, which revealed the presence of propylene. The tube was maintained
at 25 °C for 96 h. A comparison of the integrals before and after the
96 h revealed that 16% of the VC was consumed and converted into
propylene (42 turnovers/Fe).
Reaction of VC with (Pyridine-bisimine)CoCl2/MAO. An NMR
tube was charged with (pyridine-bisimine)CoCl2 (0.0011 g, 0.0018
mmol), dried MAO (0.11 g, 1.9 mmol), and toluene (internal standard),
and C6D6 (0.5 mL) and VC (0.46 mmol) were added by vacuum transfer
at -196 °C. The tube was warmed to 25 °C, and a 1H NMR spectrum
was recorded within 5 min, which revealed the presence of propylene.
The tube was maintained at 25 °C for 96 h. A comparison of the
integrals before and after the 96 h revealed that 85% of the VC was
consumed and converted into propylene (220 turnovers/Co).
1
[MeB(C6F5)3], was observed (60%). H NMR of [(R-diimine)PdMe-
(CH2dCHCl)][MeB(C6F5)3] (CD2Cl2, -80 °C): δ 7.34 (m, 4H, meta-
H), 7.06 (m, 2H, para-H), 5.62 (br, 1H, VC Hint), 4.65 (br d, J ) 12,
1H, VC Htrans), 4.58 (br d, J ) 6, 1H, VC Hcis), 2.77 (m, 2H, CHMe2),
2.65 (m, 2H, CHMe2), 2.38 (s, 3H, NdCMe), 2.27 (s, 3H, NdCMe),
1.40 (d, J ) 7, 3H, iPr Me), 1.28 (d, J ) 7, 3H, iPr Me), 1.25 (m, 6H,
iPr Me), 1.14 (m, 12H, iPr Me), 0.55 (s, 3H, PdMe), 0.35 (MeB(C6F5)3).
19F NMR (CD2Cl2): δ -133.8, -164.3, -167.0. At -65 °C, this
species was converted to [(R-diimine)PdCl(CH2dCHMe)][MeB(C6F5)3].
The conversion was 28% complete after 30 min at -65 °C and was
100% complete after the tube was warmed to -40 °C over 30 min. 1H
NMR of [(R-diimine)PdCl(CH2dCHMe)][MeB(C6F5)3] (CD2Cl2, -30
°C): δ 7.35 (m, 4H, meta-H), 7.10 (m, 2H, para-H), 5.40 (m, 1H,
H2CdCHMe), 5.30 (d, J ) 16, 1H, propene Htrans), 4.32 (d, J ) 8, 1H,
propene Hcis), 3.00 (sept, J ) 7, 2H, CHMe2), 2.78 (sept, J ) 7, 2H,
CHMe2), 2.35 (s, 3H, NdCMe), 2.31 (s, 3H, NdCMe), 1.90 (d, J ) 6,
Reaction of (sal)Ni(Ph)(PPh3) (7) and VC. An NMR tube was
charged with (sal)Ni(Ph)(PPh3) (7, 11.1 mg, 0.0147 mmol) and toluene
(0.118 mmol; internal standard), and C6D6 (0.6 mL) was condensed
into the tube at -196 °C under vacuum. VC (0.118 mmol) was
condensed into the tube at -196 °C under vacuum. The tube was sealed,
allowed to warm to room temperature, and NMR spectra were recorded
periodically. No reaction between 7 and VC was observed at 25 °C.
The tube was heated to 50 °C in an oil bath. The orange solution turned
deep red over several hours. Over the course of 4 days, the NMR
resonances for VC and 7 decreased in intensity. Resonances corre-
sponding to styrene emerged, but no PVC resonances were observed.
By integrating against toluene as the internal standard, it was determined
that 1 equiv of VC (vs 7) was consumed and 1 equiv of styrene was
produced after 4 days at 50 °C. During the course of 4 days, as the
resonances for 7 disappeared, resonances for (sal)Ni(Cl)(PPh3) (8) and
i
i
H2CdCHMe), 1.47 (d, J ) 7, 3H, Pr Me), 1.45 (d, J ) 7, 3H, Pr
Me), 1.35 (d, J ) 7, 6H, iPr Me), 1.20 (d, J ) 7, 6H, iPr Me), 1.16 (d,
J ) 7, 6H, iPr Me), 0.40 (MeB(C6F5)3). 19F NMR (CD2Cl2): δ -133.6,
-164.8, -167.5. The tube was warmed to 0 °C for 15 min, and 20%
conversion of [(R-diimine)PdCl(CH2dCHMe)][MeB(C6F5)3] to [{(R-
diimine)Pd(µ-Cl)}2][MeB(C6F5)3]2 and free propylene was observed.
This species was generated independently as described below. After
24 h at 20 °C, [{(R-diimine)Pd(µ-Cl)}2][MeB(C6F5)3]2 (0.35 equiv,
70%), (R-diimine)PCl2 (0.15 equiv, 15%), and free propene (0.8 equiv)
were present.
i
then (sal)2Ni (9) appeared. The sum of the integrals of the Pr methyl
resonances for 7, 8, and 9 was constant during the reaction. The tube
was maintained at 50 °C for an additional 4 days. The resonances for
7 slowly decreased in intensity, while those for 8 increased in intensity,
and a green powder precipitated. The powder was analyzed by X-ray
fluorescence, which confirmed the presence of Cl, P, and Ni. The
powder was identified as (Ph3P)2NiCl2 by powder X-ray diffraction by
The reaction was repeated with 0.9 equiv of VC to facilitate
characterization of the intermediate VC and propene adducts at low
temperature with similar results. After 12 h at 20 °C, [{(R-diimine)-
Pd(µ-Cl)}2][MeB(C6F5)3]2 was the major species present (87%). VC
was completely consumed, and the propylene had been converted to
polypropylene by the remaining [(R-diimine)PdMe]+.
1
comparison of the pattern with that of an authentic sample. H NMR
(r-Diimine)PdCl2.49 A mixture of PdCl2 (342 mg, 1.93 mmol) and
CH3CN (100 mL) was refluxed for 2 h to yield an orange solution.
The solution was cooled to 25 °C, and (2,6-iPr2-C6H3)NdCMeCMed
(49) (a) Ishii, H.; Goyal, M.; Ueda, M.; Takeuchi, K.; Asai, M. Catal. Lett.
2000, 65, 57. (b) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskela¨, M.;
Rieger, B. Organometallics 2001, 20, 2321.
9
4360 J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003

Reaction of Vinyl Chloride with Catalysts
A R T I C L E S
Table 3. Crystallographic Data for (sal)Ni(Cl)(PPh3) (8) and
of VC (C6D6): δ 5.75 (dd, J ) 7.0, 14.5, 1H, Hint), 5.13 (d, J ) 14.5,
1H, Htrans), 4.80 (d, J ) 7.0, 1H, Hcis). H NMR of styrene (C6D6): δ
1
(sal)2Ni (9)
6.56 (dd, J ) 10.8, 17.6, 1H, Hint), 5.58 (d, J ) 17.6, 1H, Htrans), 5.10
(d, J ) 10.8, 1H, Hcis). Spectral data for 7-9 are given below.
Isolation of Organometallic Products from the Reaction of (sal)-
Ni(Ph)PPh3 (7) and VC. A flask was charged with a solution of
(sal)Ni(Ph)PPh3 (7, 0.273 g, 0.362 mmol) in benzene (20 mL), and
VC (200 mL at 760 mm and 25 °C, 8.2 mmol) was condensed in at
-78 °C under vacuum. The solution was stirred for 4 days at 50 °C,
cooled to room temperature, and the volatiles were removed under
vacuum. The resulting dark brown powder was taken up in hexanes
(20 mL), and the mixture was filtered to remove the (Ph3P)2NiCl2
precipitate. The filtrate was left to stand at 25 °C for 24 h, and red-
brown crystals of (sal)Ni(Cl)(PPh3) (8) precipitated and were separated
by filtration (44 mg, 17% vs 7). The filtrate was heated to 50 °C for
an additional 4 days and filtered to remove the (Ph3P)2NiCl2 precipitate
(total yield of (Ph3P)2NiCl2 ) 34 mg, 0.052 mmol, 14% vs 7). The
filtrate was condensed to 4 mL under vacuum and cooled to -36 °C.
Dark red crystals of (sal)2Ni (9) were obtained after 4 days (66 mg,
24% vs 7). Total isolated yield of 8, 9, and (Ph3P)2NiCl2 ) 55% versus
7. Compounds 8 and 9 were characterized by X-ray diffraction and 1H
8
9(hexane)
formula
cryst size (mm)
color/shape
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C43H41ClNNiOP
0.2 × 0.2 × 0.08
red-brown/fragment
triclinic
C106.7H104Ni2N4O4
0.17 × 0.15 × 0.12
red/fragment
monoclinic
P21/c
14.477(4)
14.703(4)
42.60(1)
P1h
10.322(2)
11.327(2)
16.646(3)
81.853(3)
80.372(3)
69.761(3)
1792.9(5)
2
99.574(5)
8941(4)
4
Z
µ (mm-1
)
0.695
0.473
diffractometer
radiation, λ (Å)
temp (K)
Bruker SMART APEX Bruker SMART APEX
Mo KR, 0.71073
Mo KR, 0.71073
100
100
θ range (deg)
data collected: h; k; l
no. of reflns
no. of unique reflns
structure solution
refinement
2.12-25.02
(12; -137; (19
9288
1.69-25.03
-15,17; (17; (50
44 655
15 762 (Rint ) 0.0498)
direct methods
FMLS on F 2
SADABS
90-100
15 762/0/1062
1.233
R1 ) 0.0714,
wR2 ) 0.1325
R1 ) 0.0877,
wR2 ) 0.1389
4717 (Rint ) 0.0212)
1
NMR. H NMR of 7 (C6D6): δ 8.01 (d, 1H), 6.20-7.75 (m, 31H),
Patterson
FMLS on F 2
SADABS
4.12 (sept, J ) 6.8, CHMe2, 2H), 1.21 (d, J ) 6.8, CHMe2, 6H), 1.13
1
(d, J ) 6.8, CHMe2, 6H). H NMR of 8 (C6D6): δ 3.32 (br, CHMe2,
abs corr
1
transmn range (%)
data/restraints/params
goodness-of-fit on F 2
89-100
6H), 2.19 (br, CHMe2, 6H). H NMR of 9 (C6D6): δ 7.18 (br, 14H),
5924/0/437
0.979
6.83 (br, 6H), 6.43 (br, 2H), 5.88 (br, 2H), 4.56 (br, CHMe2, 4H), 1.37
(br, CHMe2, 12H), 1.15 (br, CHMe2, 12H).
R indices (I > 2σ (I))a,b R1 ) 0.0393,
Generation of (sal)2Ni (9). An NMR tube was charged with Na[sal]
(11.7 mg, 0.0308 mmol) and (Ph3P)2NiCl2 (10.0 mg, 0.0152 mmol),
and C6D6 (0.6 mL) was condensed into the tube at -196 °C under
vacuum. The tube was sealed and allowed to warm to room temperature.
wR2 ) 0.0812
R1 ) 0.0479,
wR2 ) 0.0849
R indices (all data)a,b
a R1 ) ∑||Fo| - |Fc ||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo ) ]]1/2
,
2 2
1
After 30 min, the H NMR showed that 9 and free PPh3 had formed.
where w ) q/[σ2(Fo ) + (aP)2 + bP].
2
Reaction of (sal)Ni(Ph)(PPh3) (7) with VC and Ethylene. A 150
mL Fisher-Porter bottle was charged with (sal)Ni(Ph)(PPh3) (7, 0.010
g, 0.013 mmol) and toluene (20 mL) under nitrogen. The solution was
degassed, VC (250 equiv) was added, and the bottle was pressurized
with ethylene (100 psi). The ethylene pressure was maintained, and
the solution was stirred for 3 h at 20 °C. No physical change in the
solution was observed. The bottle was vented, and the contents were
poured into acidified MeOH (100 mL of a 1 M HCl solution), resulting
in a clear, colorless solution. GC-MS revealed that styrene was present,
but no R-olefins were detected. No polymer was formed.
The tube was warmed to 23 °C, and the solution became pale orange.
The tube was heated to 70 °C for 2.5 h to yield a slurry of a green
precipitate in a red supernatant. A 1H NMR spectrum showed that 0.18
mmol of styrene (0.8 equiv) was present. GC-MS confirmed the
presence of styrene. No PVC was observed.
X-ray Crystallography. X-ray data for 8 and 9 are summarized in
Table 3, and full details of the crystallographic analyses are given in
the Supporting Information. A disordered hexane molecule is present
in the lattice of 9; the disordered solvent atoms were modeled as carbon
atoms. Thermal ellipsoids are drawn at the 50% probability level.
Reaction of (sal)Ni(Ph)(PPh3) (7) and Ethylene. A 150 mL Fisher-
Porter bottle was charged with (sal)Ni(Ph)(PPh3) (7, 0.010 g, 0.013
mmol) and toluene (20 mL) under nitrogen. The solution was degassed,
and the bottle was pressurized with ethylene (100 psi). Ethylene pressure
was maintained, and the solution was stirred for 3 h at 20 °C, resulting
in the formation of a white precipitate. The bottle was vented, and the
reaction mixture was poured into acidified MeOH (100 mL of a 1 M
HCl solution). The solid precipitate was separated by filtration, washed
with MeOH, and dried under vacuum, yielding 0.85 g of white
Acknowledgment. This work was supported by the Edison
Polymer Innovation Corp. PVC Technology Consortium and
the Department of Energy (DE-FG02-00ER15036). We thank
Dr. Ian Steele (X-ray), Dr. Jin Qin (ESI-MS), and Edward
Stoebenau (NMR simulations) for technical assistance.
Supporting Information Available: Tables of X-ray crystal-
lographic data, atomic coordinates, bond lengths and bond
angles, and anisotropic thermal parameters for (sal)Ni(Cl)PPh3
(8) and (sal)2Ni (9) (TXT). This material is available free of
charge via the Internet at http://pubs.acs.org.
1
polyethylene, which was identified by H and 13C NMR.
Reaction of {Ph2PC(SO3Na)dC(p-tol)O}Ni(Ph)PPh3/Rh(CH2CH2)-
(acac) and VC. An NMR tube was charged with {Ph2PC(SO3Na)d
C(p-tol)O}Ni(Ph)PPh3 (0.019 g, 0.023 mmol), Rh(CH2CH2)2(acac) (3.0
mg, 0.012 mmol), and toluene (0.023 mmol; internal standard). Acetone-
d6 (0.5 mL) and then VC (0.92 mmol) were condensed in at -196 °C.
JA029823+
9
J. AM. CHEM. SOC. VOL. 125, NO. 14, 2003 4361