Formation and properties of a novel dinuclear, cationic α-diimine palladium-based ethylene polymerization catalyst containing a Pd-Pd bond and bridging methylene and methyl groups

Article abstract of DOI:10.1021/om020673l

The compound PdMe₂(NΛN) (NΛN = ArN=CMeCMe=NAr, Ar = 2,6-C₆H₃(i-Pr)₂) reacts with the methide abstractors B(C₆F₅)₃, [Ph₃C][B(C₆F₅)₄], and [Ph₃C][CF₃SO₃] in the absence of ethylene to give the metal-metal-bonded, dinuclear, cationic complex [(NΛN)Pd(μ-CH₂)-(μ-Me)Pd(NΛN)]⁺, which is characterized by ¹H and ¹³C{¹H} NMR spectroscopy, mass spectrometry, and X-ray crystallography. This cationic complex, with the three counteranions, reacts with ethylene to produce the same type of low-density polyethylene produced by the known catalyst [PdMe(solvent)(NΛN)]⁺, formed by methide abstraction from PdMe₂(NΛN) by [H(Et₂O)₂][B{3,5-C₆H₃(CF₃ )₂}₄]. Indeed, reaction of the dinuclear species with ethylene results in conversion to the mononuclear [PdMe(solvent)(NΛN)]⁺, which appears to be the true catalytic species. The three weakly coordinating counteranions [BMe(C₆F₅)₃]^-, [B(C₆F₅)₄]^-, and [B{3,5-C₆H₃(CF₃)₂}₄] ^- differ little in their effects on the polymerization process, results consistent with the resting state for this catalytic system being the cationic ethylene complex [Pd(η²-C₂H₄)(～polymer) (NΛN)]⁺. Interestingly, activation by [Ph₃C][CF₃SO₃] gives a catalyst of considerably reduced potency, suggesting that the triflate anion is a better ligand in this system and does compete effectively for the active site on the metal.

Full text of DOI:10.1021/om020673l

Organometallics 2003, 22, 33-41
33
Articles
F or m a tion a n d P r op er ties of a Novel Din u clea r , Ca tion ic
r-Diim in e P a lla d iu m -Ba sed Eth ylen e P olym er iza tion
Ca ta lyst Con ta in in g a P d -P d Bon d a n d Br id gin g
Meth ylen e a n d Meth yl Gr ou p s
J ohn H. Brownie and Michael C. Baird*
Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6
Lev N. Zakharov and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received August 19, 2002
The compound PdMe2(N∧N) (N∧N ) ArNdCMeCMedNAr, Ar ) 2,6-C6H3(i-Pr)2) reacts
with the methide abstractors B(C6F5)3, [Ph3C][B(C6F5)4], and [Ph3C][CF3SO3] in the absence
of ethylene to give the metal-metal-bonded, dinuclear, cationic complex [(N∧N)Pd(µ-CH2)-
(µ-Me)Pd(N∧N)]+, which is characterized by 1H and 13C{1H} NMR spectroscopy, mass
spectrometry, and X-ray crystallography. This cationic complex, with the three counteranions,
reacts with ethylene to produce the same type of low-density polyethylene produced by the
known catalyst [PdMe(solvent)(N∧N)]+, formed by methide abstraction from PdMe2(N∧N)
by [H(Et2O)2][B{3,5-C6H3(CF3)2}4]. Indeed, reaction of the dinuclear species with ethylene
results in conversion to the mononuclear [PdMe(solvent)(N∧N)]+, which appears to be the
true catalytic species. The three weakly coordinating counteranions [BMe(C6F5)3]-, [B(C6F5)4]-,
and [B{3,5-C6H3(CF3)2}4]- differ little in their effects on the polymerization process, results
consistent with the resting state for this catalytic system being the cationic ethylene complex
[Pd(η2-C2H4)(∼polymer)(N∧N)]+. Interestingly, activation by [Ph3C][CF3SO3] gives a catalyst
of considerably reduced potency, suggesting that the triflate anion is a better ligand in this
system and does compete effectively for the active site on the metal.
Recent reports by Brookhart et al. of the use of aryl-
substituted R-diimine Ni(II) and Pd(II) catalysts for the
Ziegler-Natta polymerization of alkenes have initiated
intense interest in this area of catalysis.1,2 The catalysts
of interest, of the general type shown in Figure 1, are
formed by addition of 1 equiv of the strong acid
[H(Et2O)2][B{3,5-C6H3(CF3)2}4] to precursors of the type
PdMe2(N∧N) (N∧N ) aryl-substituted R-diimine); one
methyl group is removed as methane (eq 1).1
* To whom correspondence should be addressed. E-mail: bairdmc@
chem.queensu.ca. Fax: (613) 533-6669.
PdMe2(N∧N) + [H(Et2O)2][B{3,5-C6H3(CF3)2}4] f
[PdMe(OEt2)(N∧N)]+ +
(1) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414. (b) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.;
Brookhart, M. J . Am. Chem. Soc. 1996, 118, 11664. (c) J ohnson, L. K.;
Mecking, S.; Brookhart, M. J . Am. Chem. Soc. 1996, 118, 267. (d)
Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am. Chem.
Soc. 1998, 120, 888. (e) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem.
Rev. 2000, 100, 1169. (f) Arthur, S. D.; Bennett, A. M. A.; Brookhart,
M. S.; Coughlin, E. B.; Feldman, J .; Ittel, S. D.; J ohnson, L. K.; Killian,
C. M.; Kreutzer, K. A. U.S. Patent 5866663, Feb 2, 1999, to DuPont
(polymerizations). (g) Brookhart, M. S.; Ittel, S. D.; J ohnson, L. K.;
Killian, C. M.; Kreutzer, K. A.; McCord, E. F.; McLain, S. J .; Tempel,
D. J . U.S. Patent 5880241, May 3, 1999, to DuPont (polymer composi-
tions). (h) Brookhart, M. S.; J ohnson, L. K.; Killian, C. M.; Wang, L.;
Yang, Z.-Y., U.S. Patent 5880323, March 9, 1999, to DuPont (R-olefins).
(i) Arthur, S. D.; Bennett, A. M. A.; Brookhart, M. S.; Coughlin, E. B.;
Feldman, J .; Ittel, S. D.; J ohnson, L. K.; Killian, C. M.; Kreutzer, K.
A.; Parthasarathy, A.; Tempel, D. J . U.S. Patent 5886224, March 23,
1999, to DuPont (ligand compositions). (j) Arthur, S. D.; Brookhart,
M. S.; J ohnson, L. K.; Killian, C. M.; McCord, E. F.; McLain, S. J . U.S.
Patent 5891963, April 6, 1999, to DuPont (copolymers).
[B{3,5-C6H3(CF3)2}4]- + CH4 (1)
Key features of this type of catalyst are the presence
of a methyl ligand cis to a labile ether ligand and the
weakly coordinating counteranion [B{3,5-C6H3(CF3)2}4]-.
The mechanism of the polymerization process has been
much studied,1,3 and experimental evidence points inter
alia to a resting state in which an olefin is coordinated
to the active site of the catalyst (Figure 2).1 This is in
contrast to many early-transition-metal metallocene
(2) Mo¨hring, V. M.; Fink, G. Angew. Chem., Int. Ed. Engl. 1985,
24, 1001.
10.1021/om020673l CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/05/2002

34 Organometallics, Vol. 22, No. 1, 2003
Brownie et al.
Sch em e 1. Activa tion of 1 by Meth id e Abstr a ction
Rea ction s To Give Ca tion ic Ca ta lysts Con ta in in g
th e Cou n ter a n ion s [BMe(C6F 5)3]- (1-A), [B(C6F 5)4]-
(1-B), a n d [CF 3SO3]- (1-C) (S ) Solven t)
F igu r e 1. Conventional late-transition-metal ethylene
polymerization catalysts (M ) Ni, Pd; R ) H, Me; Ar )
substituted phenyl).
F igu r e 2. Catalyst resting state for palladium-based
catalysts.
To examine the effects of the anions [BMe(C6F5)3]-,
[B(C6F5)4]-, and [CF3SO3]- on the polymers produced,
we activated the compound PdMe2(N∧N) (N∧N ) ArNd
CMeCMedNAr, Ar ) 2,6-C6H3(i-Pr)2)1a with the meth-
ide abstractors B(C6F5)3, [Ph3C][B(C6F5)4], and [Ph3C]-
[CF3SO3], anticipating formation of the conventional
cationic, monomethyl palladium complex [PdMe(solvent)-
(N∧N)]+ as in Scheme 1. Instead we obtained the
unprecedented, metal-metal-bonded, dinuclear, cationic
complex [(N∧N)Pd(µ-CH2)(µ-Me)Pd(N∧N)]+, with bridg-
ing methylene and methyl units. We report here the
synthesis and characterization (NMR, MS, X-ray) of this
novel complex, in addition to its properties as an
ethylene polymerization catalyst precursor.
systems, where the resting state involves the coordina-
tion of the anion to the active site with the result that
the coordinating behavior of the counteranion has
considerable influence on both the activity of the
catalysts and the properties of the polymers obtained.4,5
While a great deal of research has focused on the
effects of modifying the cationic and the anionic com-
ponents of early-transition-metal polymerization cata-
lysts,6 relatively little has been done with respect to
the counteranions of late-transition-metal systems.1,7
Macchioni et al. have investigated the influence of
several anions on copolymerizations of styrene and
carbon monoxide using a Pd(II) bipyridyl complex,8
finding that the anions [B{3,5-C6H3(CF3)2}4]-, SbF6
,
-
PF6-, and BF4 were little different but that CF3SO3
-
-
Resu lts a n d Discu ssion
greatly hindered polymerization. To date, however, no
reports have examined anion effects in R-diimine Pd(II)
catalyst systems, and we therefore undertook a study
of a series of such catalysts containing various coun-
teranions.
Rea ction s of 1 w ith Meth yl-Abstr a ctin g Sp ecies.
Reactions of 1 in CD2Cl2 with an equimolar amount of
B(C6F5)3, [Ph3C][B(C6F5)4], or [Ph3C][CF3SO3] resulted
in all cases in effervescence and the formation of a deep
red solution. We anticipated that the reactions would
(3) (a) Shultz, L. H.; Brookhart, M. Organometallics 2001, 20, 3975.
(b) Tempel, D. J .; J ohnson, L. K.; Huff, R. L.; White, P. S.; Brookhart,
M. J . Am. Chem. Soc. 2000, 122, 6686. (c) Shultz, L. H.; Tempel, D. J .;
Brookhart, M. J . Am. Chem. Soc. 2001, 123, 11539.
1
proceed with 1:1 stoichiometries and that the H NMR
spectra would exhibit the resonances of the solvated
cation [PdMe(CH2Cl2)(N∧N)]+, including a Pd-Me reso-
nance (3H), two R-diimine backbone methyl resonances
(total of 6H relative to Pd-Me), and two isopropyl
methyl resonances (total of 24H relative to Pd-Me).1a
However, NMR monitoring of the reactions of 1 with
equimolar amounts of B(C6F5)3 and [Ph3C][B(C6F5)4]
indicated that only 0.5 equiv of each activator actually
reacted. For instance, with B(C6F5)3, a 19F NMR spec-
trum of the reaction mixture revealed the presence of
equal amounts of B(C6F5)3 and [BMe(C6F5)3]-, while a
1H NMR spectrum showed that 1 had completely
reacted but that only half of the expected amount of
[BMe(C6F5)3]- had formed. The expected Pd-Me reso-
nance (3H) was observed, but the pair of R-diimine
backbone methyl resonances were integrated for a total
of 12 hydrogen atoms (relative to Pd-Me), while the
isopropyl methyl resonances were integrated in total to
48 hydrogen atoms (relative to Pd-Me). Further inspec-
tion of the 1H NMR spectrum also revealed a two-
hydrogen resonance at δ 5.72 and a methane resonance
at δ 0.21, explaining the pronounced effervescence
observed in the initial stages of the reaction.
(4) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.
(5) See, for instance: (a) Chen, E. Y. X.; Marks, T. J . Chem. Rev.
2000, 100, 1391. (b) Rappe´, A. K.; Skiff, W. M.; Casewit, C. J . Chem.
Rev. 2000, 100, 1435. (c) Lohrenz, J . C. W.; Bu¨hl, M.; Weber, M.; Thiel,
W. J . Organomet. Chem. 1999, 592, 11. (d) Vanka, K.; Chan, M. S. W.;
Pye, C. C.; Ziegler, T. Organometallics 2000, 19, 1841. (e) Chan, M. S.
W.; Ziegler, T. Organometallics 2000, 19, 5182. (f) Lanza, G.; Fragala`,
I. L.; Marks, T. J . Organometallics 2001, 20, 4006. (g) Nifant’ev, I. E.;
Ustynyuk, L. Y.; Laikov, D. N. Organometallics 2001, 20, 5375. (h)
Vanka, K.; Ziegler, T. Organometallics 2001, 20, 905.
(6) For useful reviews see: (a) Mo¨hring, P. C.; Coville, N. J . J .
Organomet. Chem. 1994, 479, 1. (b) Gupta, V. K.; Satish, S.; Bhardwaj,
I. S. J . Macromol. Sci., Rev. Macromol. Chem. Phys. 1994, C34, 439.
(c) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (d) Bochmann, M.
J . Chem. Soc., Dalton Trans. 1996, 255. (e) Kaminsky, W.; Arndt, M.
Adv. Polym. Sci. 1997, 127, 143. (f) Alt, H. G.; Ko¨ppl, A. Chem. Rev.
2000, 100, 1205. (g) Coates, G. W. Chem. Rev. 2000, 100, 1223. (h)
Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. Rev. 2000, 100,
1253. (i) Angermund, K.; Fink, G.; J ensen, V. R.; Kleinschmidt, R.
Chem. Rev. 2000, 100, 1457. (j) Scheirs, J ., Kaminsky, W., Eds.
Metallocene-based Polyolefins; Wiley: Chichester, U.K., 1999.
(7) (a) Gates, D. P.; Svejda, S. A.; On˜ate, E.; Killian, C. M.; J ohnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320. (b)
Michalak, A.; Ziegler, T. Organometallics 1999, 18, 3998. (c) Michalak,
A.; Ziegler, T. Organometallics 2000, 19, 1850.
(8) Macchioni, A.; Bellachioma, G.; Cardaci, G.; Travaglia, M.;
Zuccaccia, C.; Milani, B.; Corso, G.; Zangrando, E.; Mestroni, G.;
Carfagna, C.; Formica, M. Organometallics 1999, 18, 3061.

A Cationic R-Diimine Palladium Catalyst
Organometallics, Vol. 22, No. 1, 2003 35
F igu r e 3. Calculated isotope distribution for C58H85N4Pd2 (left) (intensity (%) vs mass) and ESMS positive ion spectrum
of 2-A (right) (intensity (%) vs charge-to-mass ratio (Da/e)).
The 1H and 13C NMR chemical shifts and assignments
Sch em e 2. P ossible Rou te to a n d Str u ctu r e of
Dip a lla d iu m Sp ecies 2
of analytically pure 2 are given in the Experimental
Section. A variable-temperature 1H NMR study (-90
to 25 °C) indicated that 2 is symmetrical about the two
bridging units at temperatures as low as -90 °C, and
at no temperature was there evidence of a hydride
1
resonance. While assignments of the R-diimine H and
13C resonances are routine,1a unambiguous assignments
of the µ-CH2 and µ-CH3 1H and 13C resonances were
made using 2D 1H-13C HSQC (heteronuclear single
1
quantum coherence) and H-13C HMBC (heteronuclear
multiple bond coherence) methodologies. The 13C NMR
1
resonance at δ 129.74 correlates with the H NMR two-
hydrogen resonance at δ 5.72, while the 13C NMR
resonance at δ -46.44 correlates with the three-
hydrogen 1H NMR resonance at δ 0.04. The latter
resonance also shows a very weak long-range correlation
(HMBC) to the protons with a chemical shift of δ 5.72.
A 1H-13C HSQC DEPT experiment confirmed that the
resonances at δ 129.74 and -46.44 are to be assigned
to methylene and methyl groups, respectively, consist-
Essentially the same set of R-diimine-Pd complex 1H
resonances was also observed with the trityl reagent;
the absence of the resonance of [BMe(C6F5)3]- and the
presence of the resonances of 1,1,1-triphenylethane were
the only differences. Furthermore, when only 0.5 equiv
of either of the trityl activators was added to 1, the same
R-diimine-Pd product was obtained in ∼90% isolated
yield. These observations led to the hypothesis that a
bis(R-diimine-Pd) species was being formed, and this
was confirmed by an electrospray mass spectrum of an
aliquot taken from a reaction mixture. The mass
spectrum clearly exhibited a molecular ion base peak
of m/z 1051.72, corresponding to a molecular formula
of C58H85N4Pd2 (calculated mass 1051.09 amu) and with
an isotope distribution pattern identical with that
calculated for C58H85N4Pd2 (Figure 3). A dipalladium
complex could result if units of 1 and 1+ were to
combine, possibly as in Scheme 2, to give the cationic
complex [(N∧N)Pd(µ-Me)(µ-CH2)Pd(N∧N)]+ (2). The
molecular formula of 2 is precisely C58H85N4Pd2, and
the structure of this unusual µ-Me, µ-CH2 species was
confirmed by X-ray crystallography and by NMR spec-
troscopy.
1
ent with the integrations of the resonances in the H
NMR spectrum. Interestingly, both the methyl (δ 0.04)
and the methylene (δ 5.72) resonances exhibit through-
space 1H-1H NOESY correlations to the isopropyl
methyl protons of the R-diimine ligands, providing
further evidence for the structure proposed in Scheme
2.
1
The H and 13C NMR chemical shifts of δ 5.72 and
129.74 are consistent with a µ-methylene group bridging
1
a species with a metal-metal bond; typical H and 13C
NMR chemical shifts for this type of structure occur in
the ranges δ 5-11 and 110-210, respectively.9 Fur-
thermore, the highly shielded methyl resonance (δ
-46.44) finds precedent in the metal-metal-bonded
10
complexes (Me3P)3Ru(µ-CH2)2(µ-Me)Ru(PMe3)3 and
(9) (a) Herrmann, W. A. Adv. Organomet. Chem. 1982, 20, 159. (b)
Casey, C. P.; Audett, J . D. Chem. Rev. 1986, 86, 339. (c) Puddephatt,
R. J . Polyhedron 1988, 7, 767.
(10) Hursthouse, M. B.; J ones, R. A.; Malik, K. M. A.; Wilkinson,
G. J . Am. Chem. Soc. 1979, 101, 4128.

36 Organometallics, Vol. 22, No. 1, 2003
Brownie et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in 2-C
Bond Distances
Pd(1)-Pd(2)
Pd(1)-N(1)
Pd(1)-N(2)
Pd(1)-C(57)
Pd(1)-C(58)
2.6987(6)
2.081(4)
2.180(5)
1.982(6)
2.256(6)
Pd(2)-N(3)
Pd(2)-N(4)
Pd(2)-C(57)
Pd(2)-C(58)
2.093(5)
2.180(4)
2.022(6)
2.154(6)
Bond Angles
N(1)-Pd(1)-N(2)
75.19(18) N(3)-Pd(2)-N(4)
75.95(16)
C(57)-Pd(1)-C(58) 87.0(3)
C(57)-Pd(1)-N(1) 101.4(2)
C(57)-Pd(1)-N(2) 171.1(3)
N(1)-Pd(1)-C(58) 154.2(2)
C(57)-Pd(2)-C(58) 88.9(3)
N(3)-Pd(2)-C(58)
170.9(2)
C(57)-Pd(2)-N(4) 170.1(2)
C(58)-Pd(2)-N(4) 95.0(2)
N(2)-Pd(1)-C(58)
99.6(2)C C(57)-Pd(1)-Pd(2) 48.25(17)
Pd(1)-C(57)-Pd(2) 84.8(2)
Pd(2)-C(58)-Pd(1) 75.4(2)
C(57)-Pd(2)-N(3) 100.1(2)
C(58)-Pd(1)-Pd(2) 50.59(16)
C(57)-Pd(2)-Pd(1) 46.99(17)
C(58)-Pd(2)-Pd(1) 54.00(16)
consistent with the µ-methyl group being agostically
bound through a Pd-C-H-Pd linkage.
The geometry around Pd(2) is nearly square planar,
with an angle of 9.2(2)° between the C(57)-C(58)-Pd(2)
and the Pd(2)-N(3)-N(4) planes. In contrast, Pd(1) is
clearly not square planar, as an angle of 27.5(3)° is
formed between the N(1)-N(2)-Pd(1) and the Pd(1)-
C(57)-C(58) planes. Interestingly, C(57) (µ-CH2) is
0.286(9) Å below the Pd(1)-N(1)-N(2) plane, while
C(58) (µ-CH3) is above this plane by 0.972(9) Å. The
angle between the Pd(1)-C(57)-C(58) and Pd(2)-
C(57)-C(58) planes is 53.2(2)°. The Pd(1)-C(57)-Pd(2)
angle of 84.8(2)° is somewhat less acute than those of
most other µ-CH2 complexes with metal-metal bonds
(normal range 75-78°),9 but complexes containing a
µ-CH2 unit without a metal-metal bond tend to have
M-C-M angles in the range 89-123° and metal-metal
distances in the range 2.84-3.8 Å.9c Complex 2-C falls
outside of these parameters, indicating that a metal-
metal interaction probably exists. The Pd-Pd bond
distance of 2.6987(6) Å is similar to those of the
complexes Pd2(µ-dpm)2(SnCl3)Cl (dpm ) bis(diphenyl-
phosphino)methane) (2.644 Å),13a Pd2(µ-dpm)2Br2 (2.699
Å),13b and [Pd(dippe)(µ-CO)Pd(dippe)Me][BAr′4] (dippe
) 1,2-bis(diisopropylphosphino)ethane) (2.6886 Å)13c but
significantly shorter than that of the µ-CH2 complex
Pd2Cl2(µ-CH2)(µ-dpm)2, which does not contain a Pd-
Pd bond (Pd-Pd ) 3.171(2) Å).14
Previous reports have demonstrated similar bridging
arrangements between two metal systems and offer a
reasonable comparison to 2.10,15,16 Grubbs et al. have
reported a Ti/Pt heterobimetallic species with a Ti-Pt
bond and µ-CH3 and µ-CH2 groups.15 In the X-ray crystal
structure of this complex it was possible to refine the
position of the hydrogen atoms on the bridging methyl,
indicating a hydrogen agostically bound to the tita-
nium.15 Bond lengths (Ti-µ-Me ) 2.395(8) Å, Pt-µ-Me
) 2.122(8) Å) and angles (Ti-Me-Pt 75.6(2)°) similar
to those of complex 2-C were observed. The different
F igu r e 4. ORTEP plot of [Pd2(µ-CH2)(µ-Me)(N∧N)2][CF3-
SO3] (2-C) (30% thermal ellipsoids). The hydrogen atoms
and the [CF3SO3]- anion are omitted for clarity. Only one
position of the disorder at C(24) and C(25) is shown.
HOs3(CO)10(CH3),11 which exhibit µ-methyl 13C NMR
chemical shifts of δ -27.1 and -59.2, respectively.
In an attempt to further define the bonding of the
µ-CH2 and µ-CH3 groups with the palladium atoms,
1J C-H coupling constants were determined using a 2D
1H-13C HSQC coupled NMR experiment. The µ-
1
CH3 J C-H coupling constant was found to be 131 Hz, a
value inconsistent with a static agostic C-H-M inter-
1
action which would be expected to result in a J C-H
coupling in the range 60-90 Hz.12 Given the above-
mentioned symmetry about the Pd-Pd unit, either the
µ-CH3 group is bonded symmetrically or there is a very
rapid equilibration of the µ-CH3 group in solution
between the two palladium atoms. The µ-CH2 resonance
1
exhibits a J C-H coupling constant of 141 Hz, a normal
value for a µ-CH2 group in a metal-metal-bonded
system.9
Crystals of the triflate salt 2-C suitable for single-
crystal X-ray diffraction were obtained, and the struc-
ture was determined at 100 K; the molecular structure
of the dinuclear cation is shown in Figure 4, while
selected bond lengths and angles are listed in Table 1.
As can be seen, the structure consists of two Pd(N∧N)
units linked by a Pd-Pd bond (2.6987(6) Å) and two
bridging carbon atoms. One of the bridging carbon
atoms (C(57)) is bound symmetrically with the bond
distances Pd(1)-C(57) ) 1.982(6) Å and Pd(2)-C(57) )
2.022(6) Å, consistent with a µ-CH2 linkage.9 The other
bridging carbon (C(58)) is bound asymmetrically (Pd(1)-
C(58) ) 2.256(6) Å, Pd(2)-C(58) ) 2.154(6) Å), with
distances slightly longer than in related R-diimine Pd-
CH3 compounds3b and is presumably the µ-CH3 carbon.
Although low-temperature (100 K) diffraction data
unfortunately did not allow for refinement from the
electron density maps of the hydrogen atoms on either
of these carbon atoms, the asymmetry of C(58) is
(13) (a) Olmstead, M. M.; Benner, L. S.; Hope, H.; Balch, A. L. Inorg.
Chim. Acta 1979, 32, 193. (b) Holloway, R. G.; Penfold, B. R.; Colton,
R.; McCormick, M. J . J . Chem. Soc., Chem. Commun. 1976, 485. (c)
Fryzuk, M. D.; Clentsmith, G. K. B.; Rettig, S. J . J . Chem. Soc., Dalton
Trans. 1998, 2007.
(14) Klopfenstein, S. R.; Kluwe, C.; Kirschbaum, K.; Davies, J . A.
Can. J . Chem. 1996, 74, 2331.
(15) Ozawa, F.; Park, J . W.; Mackenzie, P. B.; Schaefer, W. P.;
Henling, L. M.; Grubbs, R. H. J . Am. Chem. Soc. 1989, 111, 1319.
(16) White, S.; Kalberer, E. W.; Bennett, B. L.; Roddick, D. M.
Organometallics 2001, 20, 5731.
(11) Calvert, R. B.; Shapley, J . R. J . Am. Chem. Soc. 1978, 100, 6544.
(12) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem.
1988, 36, 1.

A Cationic R-Diimine Palladium Catalyst
Organometallics, Vol. 22, No. 1, 2003 37
species, 1+ coordinates to 1 via activation of a methyl
C-H bond of 1. This is followed by hydride transfer to
the metal, resulting in a palladium bound through a
bridging methylene to the second palladium. Reductive
elimination of methane would then be followed by
coordination of the methyl group from the second
palladium to give the final product, 2. A similar obser-
vation has been made by Bochmann et al., who have
reported the formation of a µ-CH3, µ-CH2 dinuclear
zirconium complex by methane loss after methide
abstraction using [Ph3C][B(C6F5)4].18
Sch em e 3. P ossible Sequ en ce of Step s for th e
F or m a tion of 2
Generation of conventional mononuclear, catalytically
active, cationic complexes of the type [PdMe(S)(N∧N)]+
is typically achieved via procedures different from those
used in this study. Brookhart and others generally
synthesize the cationic palladium species in one of two
ways, via removal of the chloride from PdMeCl(N∧N)
with an alkali-metal borate salt in a coordinating
solvent, S, such as CH3CN and Et2O, or via protonation
of a methyl group from PdMe2(N∧N) in the same
coordinating solvents (eq 1).1,3b In both cases a solvent-
stabilized, mononuclear cationic species is formed rather
than a dipalladium complex such as 2. In an effort to
further understand the relationship between 2 and
1
mononuclear catalysts, we have carried out a H NMR
experiment in which 1 was activated with B(C6F5)3 and
[Ph3C][B(C6F5)4] in the presence of a large excess of
ethylene. The deep red 2 appears to be formed initially,
1
as a H NMR spectrum run immediately after activation
of 1 showed that 2 was present as ∼15% of the total
palladium at that point. However, the resonances of 2
disappeared within 10 min as the initially formed
orange-yellow color faded to yellow and low-density
polyethylene formed (see below). In a complementary
NMR experiment, preformed 2 was treated with a
smaller excess of ethylene and found to convert partially
to 1+; however, most of the ethylene was polymerized.
These experiments demonstrate clearly that the di-
nuclear 2 reacts with ethylene and converts to the
mononuclear catalytic complex 1+. While catalytic activ-
ity of 2 cannot be ruled out, the fact the polyethylene
formed is identical with that formed utilizing the
mononuclear catalyst seems to rule out catalysis by 2.
P olym er iza tion Rea ction s. For purposes of com-
parison, polymerizations by 1 activated with B(C6F5)3,
[Ph3C][B(C6F5)4], and [Ph3C][CF3SO3] were performed
in dichloromethane at 25 ( 2 °C under 1 atm of
ethylene. In a general procedure, the catalyst precursor
1 was dissolved in CH2Cl2 which had been saturated
with ethylene and then activated by addition of a
methide abstracting agent. In each case the solutions
turned from the deep red-brown of 1 to light yellow.
Polymerizations were run for varying periods of time
before being quenched with methanol. The solvents were
removed from the reaction mixtures under reduced
pressure, and the crude polymers were dissolved in
hexanes and the solutions passed through silica gel to
remove catalyst. The hexanes were then removed under
reduced pressure to leave colorless, viscous polymeric
materials. Information concerning conditions of the
bond lengths between the shorter Pt-Me bond and the
longer Ti-Me bond are very similar to the different
bond lengths between Pd(1)-C(58) and Pd(2)-C(58),
indicating the possible presence of an agostic metal-
hydrogen bond in 2-C.
Wilkinson et al. reported the diruthenium species
(Me3P)3Ru(µ-CH2)2(µ-Me)Ru(PMe3)3, in which µ-methyl
and µ-methylene groups bridge two ruthenium atoms
having a metal-metal bond.10 This complex has a
similar metal-metal bond distance (Ru-Ru ) 2.732(1)
Å) and bond lengths (Ru-CH3 ) 2.090(7) Å and Ru-
CH2 ) 2.109(7) Å) and angles (Ru-CH3-Ru ) 81.6(4)°
and Ru-CH2-Ru ) 80.8(4)°) for the bridging groups,
as observed in 2-C. Roddick et al. have recently reported
a Pt complex containing a bridging ethylidene.16 This
compound contains a Pt-Pt bond distance of 2.6540(8)
Å, which is marginally shorter than the Pd-Pd distance
in 2-C. This slightly shorter distance is expected when
comparing Pt and Pd complexes, due to the slightly
smaller Pt radius. The distances from Pt to the eth-
ylidene bridging carbon are similar to those in 2-C.
A possible route by which the dipalladium species 2
may form is shown in Scheme 3; the sequence is related
to a general mechanism for alkane C-H activation in
R-diimine platinum complexes.17 A cationic palladium
(17) (a) Zhong, H. A.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 2002, 124, 1378 and references therein. (b) Labinger, J . A.;
Bercaw, J . E. Nature 2002, 417, 507.
(18) Bochmann, M.; Cuenca, T.; Hardy, D. T. J . Organomet. Chem.
1994, 484, C10.

38 Organometallics, Vol. 22, No. 1, 2003
Brownie et al.
Ta ble 2. P olym er iza tion Resu lts
amt of (N∧N)PdMe2 amt of activator time yield
activity (kg of PE
branches per
1000 C
expt cat.
(mg, µmol)
(mg, µmol)
(h)
(g)
(mol of cat.-1 h-1
)
10-3Mw 10-3Mn Mw/Mn
1
2
3
4
5
6
7
8
9
1-A
1-A
1-A
1-B
1-B
1-B
1-C
1-C
1-C
15.0, 27.7
16.2, 29.9
15.2, 28.1
14.0, 25.9
14.8, 27.4
14.6, 27.0
13.4, 24.8
14.6, 27.0
16.3, 30.1
14.9, 29.1
16.1, 31.4
15.1, 29.5
25.1, 27.2
26.5, 28.8
26.1, 28.4
10.2, 26.0
11.1, 28.4
12.4, 31.6
0.5
1
1.5
0.5
1
1.5
0.5
1
1.06
2.24
2.64
1.14
2.19
2.89
0.87
1.66
2.36
77
75
63
88
80
71
70
61
52
31
54
70
27
77
94
9.5
9.3
9.3
27
43
59
23
65
79
4.7
4.1
4.9
1.13
1.25
1.19
1.17
1.18
1.18
1.5
91
98
97
104
99
90
100
90
98
2.27
1.91
1.5
polymerization experiments, conversions, and polymer
molecular weight data (GPC) are summarized in Table
2.
ethylene to a solution of this catalyst resulted in the
formation of polyethylene with an activity of 97 kg of
PE (mol of catalyst)-1 h-1, assuming that 2-A forms only
1 mol of mononuclear catalyst. The polymer formed had
a microstructure identical with those produced in
experiments 1-9 (Table 2) using 1+, as well as similar
molecular weights and a similar polydispersity index
as compared to the PE produced by 1-A (30 min: Mn )
36 000, Mw/Mn ) 1.15). The NMR experiments described
above, in which 1 was activated with B(C6F5)3 and
[Ph3C][B(C6F5)4] in the presence of a large excess of
ethylene and in which preformed 2 was exposed to lesser
amounts of ethylene, suggest strongly not only that
coordination of the ethylene inhibits the initial forma-
tion of the dinuclear species 2 but also that the latter
reacts with ethylene to form the mononuclear catalyst.
It thus seems that 2 is not the active catalyst during
the polymerization of ethylene by this catalyst system
but, rather, represents a high-energy resting state
associated with the catalytic system. We do not know
at this point if the µ-CH2 and the µ-CH3 groups are
incorporated into the polymer.
The 1H and 13C{1H} NMR spectra (CDCl3) of the
polymers formed by all three catalysts were essentially
identical with each other and with those of the highly
branched, low-density polyethylene formed by activation
of 1 by [H(Et2O)2][B{3,5-C6H3(CF3)2}4].1a Thus, the
catalytically active species investigated here are pre-
sumably identical both with each other and with the
well-studied catalyst containing the [B{3,5-C6H3(CF3)2}4]-
counteranion.1a
As can be seen from Table 2, activities of catalysts
1-A and 1-B and the molecular weights of the polymers
obtained from 1-A and 1-B vary only slightly, while the
activities of catalyst 1-C are somewhat lower and the
molecular weights of its polymers are significantly
lower. Thus, as anticipated, the most weakly coordinat-
ing anion, [B(C6F5)4]-, exhibits the highest activities and
produces the highest molecular weights, while the most
coordinating anion, triflate,19 has the lowest. All three
systems show a decrease in activity with time, which
can presumably be attributed to catalyst decomposition,
although the activities of the catalysts relative to each
other remain approximately constant with time. The
differences in activities are much smaller than those
observed in early-metallocene-based systems using the
[BMe(C6F5)3]- and [B(C6F5)4]- anions, where variations
as large as an order of magnitude have been observed
for activities in zirconocene systems.20
It was found that the molecular weights of the
polymers produced by catalysts 1-A and 1-B, which
contain the more weakly coordinating anions [BMe-
(C6F5)3]- and [B(C6F5)4]-, increased with time (Table 2,
experiments 1-6), while those produced by 1-C
([CF3SO3]-) remained essentially constant with time
(Table 2, experiments 7-9). In addition to the increase
in molecular weight with time, low polydispersities were
also observed for the [BMe(C6F5)3]- and [B(C6F5)4]-
systems. The behaviors of 1-A and 1-B thus implied the
existence of living polymers, as has been observed with
similar Pd R-diimine complexes.21
Su m m a r y. The compound PdMe2(N∧N) (N∧N )
ArNdCMeCMedNAr, Ar ) 2,6-C6H3(i-Pr)2) reacts with
the methide abstractors B(C6F5)3, [Ph3C][B(C6F5)4], and
[Ph3C][CF3SO3] in the absence of ethylene to give the
metal-metal-bonded, dinuclear, cationic complex [(N∧N)-
Pd(µ-CH2)(µ-Me)Pd(N∧N)]+, with bridging methylene
1
and methyl units. This complex is characterized by H
and 13C{1H} NMR spectroscopy, mass spectrometry, and
X-ray crystallography and is found to react with ethyl-
ene to form the same type of low-density polyethyl-
ene produced by the mononuclear catalysts formed by
methide abstraction from PdMe2(N∧N) by B(C6F5)3,
[Ph3C][B(C6F5)4], [Ph3C][CF3SO3], and [H(Et2O)2][B{3,5-
C6H3(CF3)2}4]. NMR experiments suggest strongly that
the dinuclear complex converts to a catalytic mono-
methyl palladium complex on reaction with ethylene
and is a previously unknown, high-energy species as-
sociated with the catalytic cycle.
The same cationic monomethyl palladium species
appear to be the catalyst involved with all four anions,
and the three weakly coordinating counteranions
[BMe(C6F5)3]-, [B(C6F5)4]-, and [B{3,5-C6H3(CF3)2}4]-
differ little in their effects on the polymerization process.
These results are consistent with the resting state for
all three systems being the cationic ethylene complex
[Pd(η2-C2H4)(∼polymer)(N∧N)]+ and are in contrast
with metallocene catalysts of the group 4 metals, where
the nature of the counteranions has a major impact on
the polymerization process. Interestingly, activation by
[Ph3C][CF3SO3] gives a catalyst of considerably reduced
potency, suggesting that the triflate anion is a better
Returning to 2, examination of the structure suggests
that a potential vacant site is present if an agostic
interaction exists between one Pd and the bridging
methyl group. Bulk polymerization of ethylene using
2-A was carried out, and it was found that addition of
(19) For evidence that triflate is a better coordinating ligand than,
for example, [B(C6H5)4]-, see: (a) Linert, W.; J ameson, R. F.; Taha, A.
J . Chem. Soc., Dalton Trans. 1993, 3181. (b) Linert, W.; Fukuda, Y.;
Camard, A. Coord. Chem. Rev. 2001, 218, 113.
(20) For examples see: J ia, L.; Yang, X.; Stern, C. L.; Marks, T. J .
Organometallics 1997, 16, 842.
(21) Gottfried, A. C.; Brookhart, M. Macromolecules 2001, 34, 1140.

A Cationic R-Diimine Palladium Catalyst
Organometallics, Vol. 22, No. 1, 2003 39
methane resonance at δ 0.21 was again present. In addition,
peaks for unreacted trityl borate and 1,1,1-triphenylethane
were observed. The same product was synthesized when only
half the amount of [Ph3C][B(C6F5)4] was added. 1H NMR of
Ph3CCH3 (25 °C, CD2Cl2): δ 2.17 (3H, s) [CH3], peaks in the
aromatic region overlap with those of 2. 1H NMR of [Ph3C]-
ligand in this system and does compete effectively for
the active site on the metal.
Exp er im en ta l Section
All experiments were carried out under purified argon using
standard Schlenk line techniques or an MBraun Labmaster
glovebox. Solvents were purified by standard methods and
distilled and degassed before use. Toluene-d8 and CD2Cl2 were
dried over Na/benzophenone and CaH2, respectively, and
vacuum-distilled prior to use. All 1H, 13C{1H}, and 19F NMR
1D spectra and all 2D COSY, HSQC, HMBC, NOESY, and
HSQC DEPT spectra (used for assignment and structural
determination) were run on Bruker AC 200 and Bruker Avance
400 spectrometers operating at 200 and 400 MHz, respectively.
Chemical shifts are referenced with respect to internal TMS
using residual proton or carbon resonances of the solvents for
1H and 13C{1H} spectra and external CFCl3 for 19F studies.
GPC data were obtained using a Waters Associates Model
GPC-2690 liquid chromatograph with separation columns
consisting of cross-linked polystyrene gel (µ-Styragel) with
various pore sizes: 100, 500, 1000, 10 000 Å. Calibration of
the instrument was performed using polystyrene standards
ranging in molecular weights from 2350 g/mol to 2 300 000
g/mol.
All chemicals, except as noted below, were purchased from
Aldrich and were purified as appropriate before use. The com-
pounds B(C6F5)3,22 [Ph3C][CF3SO3],23 H2PdCl4,24 CODPdCl2,25
CODPdMe2,26 (N∧N)PdMe2 (1),1a and N,N′-bis(2,6-diisopro-
pylphenyl)-1,4-diazabutadiene27 were synthesized according to
literature procedures. [Ph3C][B(C6F5)4] was purchased from
Asahi Glass Company Ltd., Tokyo. Polymerization grade
ethylene (99%+ purity) was purchased from Air Products and
was dried prior to use by passage through a column (3′ × 1”)
of 4A molecular sieves which had been dried under reduced
pressure while being heated above 100 °C and then cooled to
room temperature and purged with ethylene for 15 min prior
to use.
3
[B(C6F5)4] (25 °C, CD2Cl2): δ 8.27 (1H, t, J H-H ) 7.2 Hz,
3
p-C6H5), 7.88 (2H, t, J H-H ) 8.2 Hz, m-C6H5), 7.66 (2H, d,
3J H-H ) 8.0 Hz, o-C6H5).
Rea ction of 1.0 equ iv of 1 w ith 0.5 equ iv of B(C6F 5)3.
In a Schlenk flask, 58.3 mg of 1 (108 µmol) and B(C6F5)3 (27.6
mg, 53.9 µmol) were dissolved in 1.5 mL of CH2Cl2, resulting
in some effervescence and the formation of a deep red solution.
The CH2Cl2 solution was layered with 10 mL of pentanes and
cooled to -30 °C, yielding dark red crystals. The solvent was
removed by decantation, and the crystals were washed three
times with 3 mL of pentane to leave deep red crystals of 2-A
(77.5 mg, 91% yield). 1H NMR (25 °C, CD2Cl2): δ 7.22-7.10
3
(12H, m, N(C6H3)), 5.71 (2H, s, µ-CH2), 2.77 (4H, sept, J H-H
) 6.8 Hz, CH(CH3)2), 2.60 (4H, sept, 3J H-H ) 6.8 Hz, CH(CH3)2),
2.02 (6H, s, NC(CH3)), 1.95 (6H, s, NC(CH3)), 1.12 (12H, d,
3
3J H-H ) 6.8 Hz, CH(CH3)2), 1.06 (36H, d, J H-H ) 6.8 Hz,
CH(CH3)2), 0.46 (3H, br s, CH3B(C6F5)3-), 0.04 (3H, s, µ-CH3).
13C{1H} NMR (25 °C, CD2Cl2): δ 173.58, 171.09 (NdC(CH3)-
C′(CH3)dN), 144.98, 141.00 (Ar, Ar′: Cipso), 137.79, 137.25 (Ar,
Ar′: Co), 129.74 (µ-CH2), 127.57, 127.30 (Ar, Ar′: Cp), 124.23
(Ar, Ar′: Cm), 28.91 (CH(CH3)2), 28.65 (C′H(CH3)2), 23.98,
23.92, 23.78, 23.57 (CH(CH3)(C′H3) and C′H(CH3)(C′H3)),
20.63, 20.21 (NdC(CH3)C′(C′H3)dN), -46.44 (µ-CH3). 19F NMR
3
(25 °C, CD2Cl2): δ -134.27 (2F, d, J F-F ) 20.3 Hz, o-C6F5),
-166.45 (1F, t, 3J F-F ) 20.7 Hz, p-C6F5), -169.02 (2F, t, 3J F-F
) 21.4 Hz, m-C6F5). ESMS (m/z (relative intensity)): positive
ions 1059.70 (1.2), 1058.70 (4.1), 1057.71 (10.4), 1056.71 (16.7),
1055.72 (33.5), 1054.71 (36.9), 1053.72 (75.8), 1052.71 (71.5),
1051.72 (100), 1050.72 (85.4), 1049.72 (87.7), 1048.71 (74.6),
1047.72 (55.3), 1046.72 (23.3), 1045.71 (7.9), 1044.72 (2.2),
539.16 (5.0), 538.15 (8.1), 511.15 (13.8), 509.18 (19.9), 507.16
(15.8), 506.16 (9.4), 505.18 (5.0), 405.34 (8.0); calcd positive
ions for C58H85N4Pd2 1059.50 (1.2), 1058.49 (4.3), 1057.49
(10.0), 1056.49 (17.0), 1055.49 (33.4), 1054.49 (38.7), 1053.49
(74.5), 1052.49 (70.0), 1051.49 (100), 1050.49 (84.5), 1049.49
(85.8), 1048.49 (73.8), 1047.49 (53.5), 1046.49 (21.9), 1045.49
(7.5), 1044.49 (2.1); negative ions 528.98 (2.6), 528.01 (21.1),
NMR-Sca le Rea ction of 1 a n d B(C6F 5)3. In an NMR tube,
10.0 mg of 1 (18.5 µmol) and 10.0 mg of B(C6F5)3 (19.5 µmol)
were dissolved in 0.5 mL of CD2Cl2, resulting in some ef-
fervescence and the formation of a deep red solution. A 1H
NMR spectrum run immediately exhibited the following
resonances (25 °C, CD2Cl2): δ 7.22-7.10 (12H, m), 5.71 (2H,
s), 2.77 (4H, sept, 3J H-H ) 6.8 Hz), 2.60 (4H, sept, 3J H-H ) 6.8
527.03 (100), 525.98 (25.6); calcd negative ions for C19H3F15
529.02 (2.1), 528.01 (20.6), 527.01 (100), 526.01 (23.6). Anal.
Found for 77H88BF15N4Pd2: C, 58.27; H, 5.84; N, 3.46.
B
3
Hz), 2.02 (6H, s), 1.95 (6H, s), 1.12 (12H, d, J H-H ) 6.8 Hz),
C
3
1.06 (36H, d, J H-H ) 6.8 Hz), 0.46 (3H, br s), 0.04 (3H, s),
Calcd: C, 58.60; H, 5.62; N, 3.55.
0.21 (s, CH4). The same spectrum was produced when only
half the amount of B(C6F5)3 was added. The 19F NMR spectrum
exhibited peaks of unreacted B(C6F5)3 and of [BMe(C6F5)3]-.
19F NMR of B(C6F5)3 (25 °C, CD2Cl2): δ -129.1 (2F, br s,
o-C6F5), -144.7 (1F, br s, p-C6F5), -162.0 (2F, br s, m-C6F5).
19F NMR of [BMe(C6F5)3]- (25 °C, CD2Cl2): δ -134.27 (2F, d,
Rea ction of 1.0 equ iv of 1 a n d 0.5 equ iv of [P h 3C]-
[B(C6F 5)4]. By a procedure identical with that used in the
synthesis of complex 2-A, 35.6 mg of 1 (65.7 µmol) and 30.3
mg of [Ph3C][B(C6F5)4] (32.9 µmol) were dissolved in 1.5 mL
of CH2Cl2 in a Schlenk flask and layered with 10 mL of
pentanes and cooled to -30 °C, yielding dark red crystals. The
product was isolated as deep red crystals of 2-B (53.8 mg, 94%
3
3J F-F ) 20.3 Hz, o-C6F5), -166.45 (1F, t, J F-F ) 20.7 Hz,
3
p-C6F5), -169.02 (2F, t, J F-F ) 21.4 Hz, m-C6F5).
1
NMR-Sca le Rea ction of 1 a n d [P h 3C][B(C6F 5)4]. In an
NMR tube 6.1 mg of 1 (11.3 µmol) and 10.4 mg of [Ph3C]-
[B(C6F5)4] (11.3 µmol) were dissolved in 0.5 mL of CD2Cl2,
resulting in some effervescence and the formation of a deep
yield). H NMR (25 °C, CD2Cl2): cation peaks identical with
those of complex 2-A. 19F NMR (25 °C, CD2Cl2): δ -134.19
3
(2F, br s, o-C6F5), -164.87 (1F, t, J F-F ) 21.1 Hz, p-C6F5),
3
-168.69 (2F, t, J F-F 16.2 Hz, m-C6F5). Anal. Found for
1
red solution. A H NMR spectrum was recorded immediately
C
82H85BF20N4Pd2: C, 57.03; H, 5.05; N, 3.17. Calculated: C,
and was found to be identical with that observed above with
56.92; H, 4.95; N, 3.24.
trityl resonances substituted for that of [BMe(C6F5)3]-. The
Rea ction of 1.0 equ iv of 1 a n d 0.5 equ iv of [P h 3C]-
[CF 3SO3]. By a procedure identical with that used in the
synthesis of complex 2-A, 49.0 mg of 1 (90.6 µmol) and 17.8
mg of [Ph3C][CF3SO3] (45.3 µmol) were dissolved in 1.5 mL of
CH2Cl2 in a Schlenk flask and layered with 10 mL of pentanes
and cooled to -30 °C, yielding dark red crystals. 2-C was
isolated as a deep red crystalline material suitable for single-
crystal X-ray diffraction (48.2 mg, 89% yield). 1H NMR (25 °C,
(22) Pohlmann, J . L.; Brinckmann, F. E. Z. Naturforsch., B 1965,
20b, 5.
(23) Forbus, T. R., J r.; Martin, J . C. J . Org. Chem. 1979, 44, 313.
(24) Kauffman, G. B.; Tsai, J . H. S. Inorg. Synth. 1966, 8, 234.
(25) Drew, D.; Doyle, J . R. Inorg. Synth. 1972, 13, 47.
(26) Rudler-Chauvin, M.; Rudler, H. J . Organomet. Chem. 1977, 134,
115.
(27) tom Dieck, H.; Svoboda, M.; Greiser, T. Z. Naturforsch., B 1981,
36b, 823.
CD2Cl2): cation peaks identical with those of complex 2-A. 19
F

40 Organometallics, Vol. 22, No. 1, 2003
Brownie et al.
Ta ble 3. Cr ysta l Da ta a n d Da ta Collection a n d
Str u ctu r e Refin em en t Deta ils for 2-C
NMR (25 °C, CD2Cl2): δ 90.06. Anal. Found for C59H85F3N4O3-
Pd2S: C, 59.14; H, 7.24; N, 4.69. Calcd: C, 59.04; H, 7.14; N,
4.67.
formula, fw
temp
wavelength
cryst syst, space group
unit cell dimens
a
C59H85F3N4O3Pd2S, 1200.17
100(2) K
Gen er al P olym er ization P r ocedu r es. Compound 1 (∼15.0
mg, ∼28 µmol) was dissolved in 10 mL of CH2Cl2, and the
resulting deep red-brown solution was saturated with ethylene
for 10 min by bubbling ethylene through the stirred solution.
To this solution was then added a solution of 1.05 equiv of
activator (∼30 µmol) in 10 mL of CH2Cl2, resulting in the
formation of a clear yellow solution. Ethylene was continually
bubbled through the solution for the length of the polymeri-
zation (0.5, 1.0, or 1.5 h), at which point polymerization was
quenched by the addition of ∼20 mL of methanol. The reaction
temperature was monitored using a thermocouple immersed
into the polymerization solution, and the temperature was
maintained at 25 ( 2 °C by cooling in a water bath. The solvent
was removed from the crude polymer solution under reduced
pressure to leave a black oily residue, which was dissolved in
∼30 mL of hexanes and eluted through silica gel. The hexanes
were removed under reduced pressure to leave a viscous
colorless oil. Details of the polymerization experiments are
summarized in Table 2.
0.710 73 Å
orthorhombic, P212121
13.0389(8) Å
b
c
19.0498(14) Å
24.5120(17) Å
V, Z
6088.5(6) Å3, 4
cryst color, habit
density (calcd)
abs coeff
F(000)
red, block
1.309 Mg/m3
0.678 mm-1
2504
cryst size
θ range
index ranges
0.20 × 0.15 × 0.10 mm3
1.98-28.29°
-17 e h e 16, -14 e k e 24,
-31 e l e 32
no. of coll, indep rflns
abs cor
completeness to θ ) 28.29°
refinement method
39 145, 14 268 (Rint ) 0.0619)
SADABS
97.0%
full-matrix least squares on F2
14 268/0/648
no. of data/restraints/params
goodness of fit on F2
final R indicesa (I > 2σ(I))
R indicesa (all data)
abs struct param
1.165
R1 ) 0.0652, wR2 ) 0.1342
R1 ) 0.0735, wR2 ) 0.1379
0.03(4)
NMR Stu d y of th e Activa tion of 1.0 equ iv of 1 w ith
1.0 equ iv of B(C6F 5)3 in th e P r esen ce of Eth ylen e. A 7.5
mg portion of 1 (13.8 µmol) in an NMR tube was dissolved in
0.50 mL of CD2Cl2 to form a deep red-brown solution. The
solution was saturated with ethylene for ∼30 s, and a solution
of 7.4 mg of B(C6F5)3 (14.5 µmol) in 0.50 mL of CD2Cl2 was
added to the tube, resulting in the formation of a yellow
solution. A 1H NMR spectrum was obtained immediately and
exhibited weak resonances of complex 2-A in addition to new
resonances at δ 4.23 (s, ((N∧N)Pd[(CH2)nCH3](CH2dCH2)) and
2.34 and 2.21 (s, (NdC(CH3)C′(CH3)dN). The latter resonances
are similar to those observed by Brookhart et al. during low-
temperature NMR studies in which ethylene was added to a
solution of the cationic species 1+.1a A similar reaction of
[Ph3C][B(C6F5)4] with 1 under identical conditions yielded a
similar 1H NMR spectrum.
largest diff peak and hole
1.395 and -1.347 e Å-3
R1 )∑||Fo| - |Fc||/∑|Fo|; wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
;
a
w ) 1/[σ2(Fo2) + (aP)2 + bP], P ) [2Fc + max(Fo,0)]/3.
2
Sta r t/Stop /Sta r t P olym er iza tion s. Polymerizations were
performed identically with those listed above in the general
procedure. At 30 min, an aliquot of the active system was
removed from the polymerization reaction and quenched with
10 mL of methanol. The system was purged for 30 min with
argon, and then monomer addition was reinitiated by bubbling
ethylene through the solution. After a further 30 min, the
remaining solution was quenched with 10 mL of methanol.
The polymer samples were purified as before. 1-A: GPC (0.5
h) Mw ) 27 000, Mn ) 24 000, Mw/Mn ) 1.14; GPC (1.0 h) Mw
) 54 000, Mn ) 46 000, Mw/Mn ) 1.18. 1-B: GPC (0.5 h) Mw
)
NMR Stu d y of th e Rea ction of 2-A w ith Eth ylen e. To
a deep red solution of 2-A (14.3 mg, 9.06 µmol) in 0.5 mL of
CD2Cl2 in an NMR tube was added 1.5 mL (∼70 µmol) of
18 000, Mn ) 17 000, Mw/Mn ) 1.06; GPC (1.0 h) Mw ) 32 000,
Mn ) 29 000, Mw/Mn ) 1.12. The 1H NMR spectra of the
polymers were identical with those discussed above.
1
ethylene. The tube was shaken, and an H NMR spectrum was
X-r a y Cr ysta l Str u ctu r e Deter m in a tion . Diffraction
intensity data were collected with a Bruker Smart Apex CCD
diffractometer. Crystal data and data collection and refinement
parameters are given in Table 3. The space group was
determined from systematic absences in the diffraction data.
The structure was solved using direct methods, completed by
subsequent difference Fourier syntheses, and refined by full-
matrix least-squares procedures on reflection intensities (F2).
recorded. Further 1.5 mL aliquots of ethylene were added after
10 and 20 min, the reaction being monitored by 1H NMR
spectroscopy. Although the reaction mixture remained red and
the resonances of 2-A were observed throughout the experi-
ment, the resonances decreased in intensity as those of a new
species increased in intensity. The resonances of the new
complex are consistent with the formation of complex 1+
observed by Brookhart et al.1a New peaks: δ 7.45-7.33 (m,
Ar′), 2.75 (m, Ar′CH(CH3)2, overlapped by peak of 2-A), 2.34
and 2.21 (s, NdC(CH3)C′(CH3)dN). Although the resonance
of coordinated ethylene was not observed, this is not surprising
(see the Supporting Information of ref 1a). The resonances of
polyethylene1a were observed and increased in intensity after
each addition (see below).
SADABS absorption corrections were applied (Tmin/Tmax
)
0.81). All non-hydrogen atoms were refined with anisotropic
displacement coefficients. The hydrogen atoms were treated
as idealized contributions, except for the H atoms of the
bridging µ-CH2 and µ-CH3 groups, which were not found on
the F map and not included in refinement. In the structure of
2-C, two Me groups (the C(24) and C(25) atoms) and the O(1)
and F(1) atoms of the [CF3SO3]- group are disordered on two
positions with occupation multiplicity µ ) 0.65, 0.35 µ ) 0.51,
0.49, and µ ) 0.64, 0.36, respectively. Only one position for
these atoms is shown in Figure 4. The Flack parameter is
0.03(4); i.e., the given structure corresponds to the absolute
structure of 2-C. All software and source scattering factors are
contained in the SHELXTL (version 5.10) program package.28
The ORTEP plot of 2-C is shown in Figure 4.29
P olym er iza tion of Eth ylen e w ith 2-A. A 7.5 mg portion
of 2-A (4.75 µmol) was dissolved in 10 mL of CH2Cl2 at 25 °C,
generating a deep red color. Ethylene was then bubbled
through the solution for 30 min and, after ∼5 min, the deep
red solution had turned yellow. The reaction was quenched
after 30 min with 20 mL of methanol, and the solvent was
removed under reduced pressure. The crude polymer was
dissolved in 30 mL of hexanes and the solution passed through
silica gel, after which the solvent was removed under reduced
1
pressure to yield a clear, colorless, viscous oil (0.23 g). A H
(28) SHELXTL Version 5.10, Crystal Structure Analysis Package;
Bruker AXS, Madison, WI, 1998.
(29) Burnett, M. N.; J ohnson, C. K. ORTEP-III: Oak Ridge Thermal
Ellipsoid Plot Program for Crystal Structure Illustrations; Report
ORNL-6895; Oak Ridge National Laboratory, Oak Ridge, TN, 1996.
NMR spectrum was identical with that of the PE produced
above. GPC: Mw ) 42 000, Mn ) 36 000, Mw/Mn ) 1.15.
Activity: 97 kg of PE (mol of cat.)-1 h-1. Branches (per 1000
C): 106.

A Cationic R-Diimine Palladium Catalyst
Organometallics, Vol. 22, No. 1, 2003 41
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
details, including figures of 2-C showing complete numbering
schemes for the cation and anion and a thermal ellipsoid figure
and tables of positional and thermal parameters. This material
is available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank the Government of
Ontario (Ontario Graduate Scholarship to J .H.B.),
Queen’s University (Queen’s Graduate Award to J .H.B.),
and the Natural Sciences and Engineering Research
Council (Research Grant to M.C.B.) for funding this
research.
OM020673L