Electron deficient zinc complexes: Enhanced lactide polymerization activity achieved through rational ligand design

Article abstract of DOI:10.1016/j.jorganchem.2012.01.004

Modification of a neutral bis(phosphinimine) pincer ligand, whereby alkyl groups were placed at the P and N positions of the phosphinimine moieties, has been performed. A cationic zinc-lactate complex of this ligand displays enhanced activity relative to

Full text of DOI:10.1016/j.jorganchem.2012.01.004

Journal of Organometallic Chemistry 704 (2012) 65e69
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Electron deficient zinc complexes: Enhanced lactide polymerization activity
achieved through rational ligand design
*
Craig A. Wheaton, Paul G. Hayes
Department of Chemistry and Biochemistry, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, Canada T1K 3M4
a r t i c l e i n f o
a b s t r a c t
Article history:
Modification of a neutral bis(phosphinimine) pincer ligand, whereby alkyl groups were placed at the P
and N positions of the phosphinimine moieties, has been performed. A cationic zinc-lactate complex of
this ligand displays enhanced activity relative to the previous generation catalyst for the polymerization
of rac-lactide.
Received 6 October 2011
Received in revised form
5 January 2012
Accepted 6 January 2012
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Zinc
Phosphinimine
Poly(lactic acid)
Ring-opening polymerization
Cationic
1. Introduction
alkyl complexes thereof proved to be relatively poor catalysts [6a].
Substantial improvements in activity were realized by employing
Interest in the use of poly(lactic acid) (PLA) as an eco-friendly
commodity polymer has grown substantially over the past
decade [1]. This is because lactide (LA) feedstocks are derived from
renewable resources, while PLA is biodegradable. This interest has
promoted increasingly intensive research in the area of LA poly-
merization catalysis [2]. While organocatalysts [3] and a wide
variety of metal-based catalysts [4] have been developed, much
work has been specifically devoted to the preparation of alkoxides
of Zn(II) and the alkaline earth metals (most commonly Mg(II) and
Ca(II)). Prior to 2009, virtually all such LA polymerization catalysts
were neutral complexes stabilized by formally anionic ancillary
ligands, and this continues to be the focus of most recent work [5].
Recently, however, we have pursued cationic zinc complexes for LA
polymerization catalysis [6].
Since our initial reports, there have been several other accounts
of cationic Zn(II), Mg(II) and Ca(II) complexes used for the ROP of LA
[7], but these tend to suffer drawbacks ranging from poor activity to
poor control to ill-defined polymerization mechanisms. A notable
exception is a cationic calcium complex recently reported by
Mountford and co-workers, which displays both excellent control
and activity for the ROP of rac-LA at ambient temperature [8].
Our initial foray into the field utilized a mono(phosphinimine)
ancillary ligand with a rigid dibenzofuran (dbf) backbone, but zinc-
a bis(phosphinimine) pincer ligand [6b]. Further tuning of the steric
bulk gave the ligand 4,6-(p-iPrPheN]PPh2)-dbf (LPipp), from which
the first cationic metal complex capable of rapid and controlled LA
polymerization at ambient temperature was produced [6c]. These
preceding studies clearly demonstrate catalyst activity is highly
dependent on both ligand steric bulk and the Lewis acidity of the
metal center.
Herein we report our next generation cationic zinc catalyst, in
which the ligand scaffold has been modified by installation of alkyl
substituents on the phosphinimine groups (Scheme 1). Specifically,
ethyl replaces phenyl at P and benzyl replaces paraisopropylphenyl
(Pipp) at N. This was expected to render the metal center more
sterically accessible, while simultaneously providing better modera-
tion of metal center Lewis acidity by enhancing the electron donating
capacity of the ligand. Such a less electropositive metal center was
targeted in hopes of achieving a level of Lewis acidity somewhere
between that of our previous cationic zinc catalysts and the more
commonly studied neutral zinc catalysts. The effect of these modifi-
cations has been studied, with the major outcome being a marked
enhancement in polymerization activity, as discussed below.
2. Results and discussion
Preparation of the bis(phosphine) precursor dbf(PEt2)2 was
targeted due to its reduced bulk relative to the known dbf(PiPr2)2
and dbf(PPh2)2 analogs. Efficient dilithiation of dibenzofuran was
* Corresponding author. Tel.: þ1 403 329 2313; fax: þ 1 403 329 2057.
E-mail address: p.hayes@uleth.ca (P.G. Hayes).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.01.004

66
C.A. Wheaton, P.G. Hayes / Journal of Organometallic Chemistry 704 (2012) 65e69
Methylzinc complex 1 was effortlessly prepared by reacting [LH]
[B(m-(CF3)2eC6H3)4] with ZnMe2 at ambient temperature for 1 h, to
afford a pure white powder in 90% yield. A single peak in the 31P
{1H} NMR spectrum (
d 46.6, CD2Cl2) is indicative of symmetry-
related phosphinimines in solution. The ZnCH3 resonates in the
1H NMR spectrum at
zinc complexes [6].
d
ꢀ0.95, which is typical of cationic methyl-
Synthesis of zinc-lactate complex 2 was performed by reaction
of [LH][B(m-(CF3)2eC6H3)4] with EtZn(methyl- -lactate) in toluene
L
solvent at 100 ꢁC for 60 min. This proved much more efficient than
the preparation of our previous Znelactate complexes [6c], with
95% yield of crystalline material achieved without the need for
further purification. Notably, complex 2 was synthesized in an
overall yield of 64% in four steps from dibenzofuran. Characteristic
peaks of the lactate moiety appear in the 1H NMR spectrum at
d
4.66 (CH), 3.69 (OeCH3), and 1.41 (CeCH3). Despite the presence
of the asymmetric lactate moiety, a single resonance is observed at
ambient temperature in the 31P{1H} NMR spectrum (
d
46.8).
At ꢀ60 ꢁC, the spectrum displays two distinct peaks (
d 46.8, 46.3),
indicating a fluxional process which we propose is a simple intra-
molecular rearrangement involving rotation of the lactate moiety.
Large single crystals of complex 2suitable for X-ray diffractionwere
grown from CH2Cl2 solvent, and the solid-state crystal structure was
determined(Fig. 2). Asexpected, the ancillary ligand coordinates tothe
metal center in a tridentate fashion and the methyl-lactate moiety
binds in a bidentate manner, resulting in a 5-coordinate, dis-
torted trigonal bipyramidal geometry. The phosphinimine groups
[Zn(1)eN(1) ¼ 2.013(1) Å, Zn(1)eN(2) ¼ 2.009(2) Å] and the formally
anionic oxygen atom [Zn(1)eO(2) ¼ 1.923(2) Å] prove to be the
strongest donors, occupying the equatorial sites. The sum of angles
Scheme 1. Synthesis of zinc-alkyl (1) and zinc-lactate (2) complexes of a bis(phos-
phinimine) pincer ligand (Ar ¼ m-(CF3)2eC6H3).
achieved using 2.0 equiv of tBuLi, rather than significant excesses of
secBuLi or nBuLi employed in previous reports (see ESI) [9]. This
novel bis(phosphine) compound exhibits one sharp signal in the
31P{1H} NMR spectrum (C6D6) at
d
ꢀ19.01.
Synthesis of L from dbf(PEt2)2 and benzyl-azide under standard
Staudinger conditions [10] was highly exothermic and proceeded to
completion within minutes at ambient temperature. Work-up is
straightforward and efficient, with high yield of analytically pure
crystalline material produced by simple addition of excess pentane to
the reaction mixture. A single peak appears in the 31P{1H} NMR
spectrum (C6D6) at
d 14.4. Single crystals of L were grown from
a toluene solution of the compound at ꢀ35 ꢁC, and an X-ray crystal
structure was obtained (Fig. 1). The PeN bond lengths are similar to
those of related bis(phosphinimine) ligands [P(1)eN(1) ¼ 1.568(1) Å;
P(2)eN(2) ¼ 1.550(2) Å] [6c,11].
As demonstrated in our previous work, and in the work of
Bochmann et al. [12], the synthesis of cationic zinc complexes is
most effectively performed by first protonating the ligand with an
appropriate Brønsted acid. Reaction of
L
with [H(OEt2)2]
[B(m-(CF3)2eC6H3)4] rapidly generated [LH][B(m-(CF3)2eC6H3)4],
which was isolated in 96% yield as an analytically pure light yellow
powder.
Fig. 2. X-ray crystal structure of the cation of 2, with hydrogen atoms omitted for
clarity and thermal ellipsoids drawn at the 30% probability level. Selected bond
distances (Å) and angles (ꢁ): Zn(1)eN(1), 2.013(1); Zn(1)eN(2), 2.009(2); Zn(1)eO(2),
1.923(2); Zn(1)eO(3), 2.173(1); Zn(1)eO(1), 2.525(1); P(1)eN(1), 1.608(2); P(2)eN(2),
1.605(1); N(1)eZn(1)eN(2), 131.35(6); N(1)eZn(1)eO(2), 109.06(6); N(2)eZn(1)eO(2),
116.10(6); O(1)eZn(1)eO(3), 168.57(5); N(1)eZn(1)eO(3), 108.05(6); N(1)eZn(1)e
O(1), 83.25(5).
Fig. 1. X-ray crystal structure of L with hydrogen atoms omitted and thermal ellipsoids
drawn at the 30% probability level. Selected bond distances (Å) and angles (ꢁ): P(1)e
N(1), 1.568(1); P(2)eN(2), 1.550(2); N(1)eC(17), 1.462(2); N(2)eC(28), 1.448(3); P(1)e
N(1)eC(17), 117.1(1); P(2)eN(2)eC(28), 126.9(1).

C.A. Wheaton, P.G. Hayes / Journal of Organometallic Chemistry 704 (2012) 65e69
67
Fig. 4. Plot of Mn versus conversion for the polymerization of rac-LA catalyzed by
complex 2 ([LA]0/[2] ¼ 200, [LA]0 ¼ 1 M, CH2Cl2, 25 ꢁC). Theoretical molecular weights
are represented by the straight line.
Fig. 3. Plot of ln[LA] versus time for polymerization of 200 equiv rac-LA. [LA]0 ¼ 1 M,
CD2Cl2, 25 ꢁC.
about these positions is 356.5(1)ꢁ. Correspondingly, the neutral
oxygen-donors occupy the axial sites, wherein the interaction
with the lactate carbonyl lies within the expected range
[Zn(1)eO(3) ¼ 2.173(1) Å], while that of the dbf oxygen is relatively
long [Zn(1)eO(1) ¼ 2.525(1) Å]. The angle between these groups is
distorted somewhat from the ideal 180ꢁ [O(1)eZn(1)e
O(2) ¼ 168.57(5)ꢁ], presumably due to steric repulsion of a nearby
benzyl group. Interestingly, the interaction with the dbf oxygen is
0.189(5) Å longer than that observed in our previous generation
catalyst [LPippZnLactate][B(m-(CF3)2eC6H3)4] [6c], which we attribute
to decreased Lewis acidity of the metal center.
The efficacy of both complexes for ROP of rac-LA was investi-
gated, and unsurprisingly complex 1 was inactive. However,
complex 2 is extremely active for the polymerization of rac-LA,
giving 90% conversion of 200 equiv of monomer to atactic PLA
(Pr ¼ 0.50) in less than 20 min at 25 ꢁC. Examination of the reaction
kinetics by in situ NMR studies revealed well-behaved first-order
monomer consumption with an observed rate constant of
1.88(1) ꢂ 10ꢀ3 sꢀ1 and no notable induction period (Fig. 3). This rate
is greater than the related complex of LPipp by a factor of 2.2
(measured under identical conditions) [6c]. Furthermore,
a MALDI-ToF mass-spectrum was obtained for a polymer sample
prepared from a 2% catalyst loading. Mass peaks are consistent with
polymer chains bearing a methyl-lactate end group (He[OCH(Me)
CO]neOCH(Me)CO2Me), indicating a coordination-insertion mech-
anism rather than a cationic process. However, peaks are separated
by 72 amu, suggesting appreciable rates of transesterification. The
lack of stereochemical control is not due to an epimerization
GPC analysis of PLA samples prepared at various catalyst load-
ings of
([LA]0/[2] ¼ 100 and 200), good molecular weight control was
achieved, yielding PLAs with relatively low polydispersity
2
was undertaken. At higher catalyst loadings
a
(1.24e1.25) and Mn values that closely match theoretical values
(Table 1). Further reduction of catalyst loading ([LA]0/[2] ¼ 300,
400, and 500) resulted in significantly lower than expected Mn and
higher polydispersities (PDI
¼
1.39e1.43). We attribute this
decreased control to appreciable rates of intermolecular trans-
esterification. Catalyst decomposition is an unlikely cause of
broadened PDIs at lower catalyst concentration, as we have found 2
to consume additional monomer at a similar rate after complete
consumption of the initial portion of rac-LA. Specifically, after
polymerization of 200 equiv of rac-LA for a duration of 90 min
(w15 half-lives), addition of a further 200 equiv of monomer
resulted in continued polymerization, giving PLA with molecular
weights similar to those measured for single step polymerization of
400 equiv (Table 1).
In an attempt to improve our understanding of the polymeri-
zation process, a variety of samples were prepared under identical
conditions ([LA]0 ¼ 1 M, [LA]0/[2] ¼ 200) and quenched at different
stages of completion. A plot of Mn versus conversion gives a curve
rather than the expected straight line (Fig. 4). During the early
stages (40e60% conversion) the polymerization is well controlled
(PDI ¼ 1.11e1.13), while in the latter stages, the Mn values begin to
drop off relative to the expected values, with a concomitant
increase in Mw and PDI (see ESI). An increase in the rate of inter-
molecular transesterification relative to propagation account for
increased PDIs in the later stages of polymerization. The cause of
decreasing Mn is less obvious, but most likely attributed to intra-
molecular transesterification. Such catalyst back-biting would give
rise to a lower molecular weight fraction that may be lost upon
work-up of the polymer. To verify, GPC studies of an unpurified
polymer sample ([LA]0/[2] ¼ 100, [LA]0 ¼ 1 M, CH2Cl2, 25 ꢁC) were
undertaken, indicating the presence of a substantial amount of low
molecular weight oligomer (Mn ¼ 1.25 kg molꢀ1; PDI ¼ 1.03). The
high molecular weight portion closely matched the corresponding
purified polymer sample (Mn ¼ 18.9 kg molꢀ1; PDI ¼ 1.16). This
observation suggests intramolecular transesterification to be
a major cause of lower than expected molecular weights.
process, as we have observed that 2 polymerizes L-LA to give
isotactic PLLA.
Table 1
Molecular weight data for PLA samples prepared using different concentrations of
catalyst 2.a
[LA]0/[2] Time
Isolated
Calc. Mn
Mn
Mw
PDI
b
c
(min) yield (%) (kg molꢀ1
)
(kg molꢀ1
)
(kg molꢀ1
)
100
200
300
400
500
400d
20
30
45
60
75
90
90
96
96
92
71
99
13.1
27.8
41.6
53.1
51.3
57.2
10.2
18.9
17.3
19.7
23.4
20.0
12.6
23.5
24.2
28.3
31.0
31.5
1.25
1.24
1.39
1.43
1.32
1.57
a
[LA]0 ¼ 1 M, CH2Cl2, 25 ꢁC.
b
c
Calculated using Mn ¼ [([LA]0/[2]) ꢂ 144.13 ꢂ conversion]þ104.1.
3. Conclusions
Molecular weights determined by GPC in THF at 40 ꢁC, and corrected by the
accepted MarkeHouwink parameter of 0.58 due to the use of PS standards [13].
d
In summary, a modified bis(phosphinimine) ligand has been
Sequential polymerization of two portions of 200 equiv of rac-LA, the second
portion being added after 60 min.
prepared, which bears alkyl substituents at both the P and N

68
C.A. Wheaton, P.G. Hayes / Journal of Organometallic Chemistry 704 (2012) 65e69
positions. From this, cationic zinc-alkyl (1) and zinc-lactate (2)
complexes were efficiently prepared. Complex 2 is among the most
active yet observed for ROP of lactide by a cationic metal complex.
This result further demonstrates the efficacy of cationic zinc species
for this process, and highlights the necessity of a strongly electron-
donating ligand to stabilize the highly electropositive metal.
However, relatively poor molecular weight control remains an
issue, which future studies will aim to address.
19F{1H} NMR (CD2Cl2):
(s). Anal. Calcd. (%) for C67H55BF24N2OP2Zn: C: 53.71; H: 3.70; N:
1.87; found: C: 53.35; H: 3.54; N: 2.20.
d
ꢀ62.84 (s). 11B{1H} NMR (CD2Cl2):
ꢀ6.61
d
4.1.4. [LZnOCH(Me)CO2Meþ][B(m-(CF3)2eC6H3)4ꢀ] (2)
LH (400 mg, 282 mmol) and ethylzinc-lactate (55.7 mg,
282 mmol) were dissolved in 5 mL of bromobenzene and sealed in
a glass bomb. The solution was heated to 100 ꢁC for 1 h and cooled
to ambient temperature. The solution was transferred to a glass vial
and concentrated to 2 mL in vacuo. Addition of 4 mL of pentane
caused the precipitation of the product as a pale yellow powder.
The supernatant was decanted and the solid was washed with a 1:1
benzene/pentane mixture (2 mL) and pentane (2 ꢂ 2 mL) and dried
in vacuo, giving 282 mg of the compound. The combined super-
natant and washings were reduced to dryness and redissolved in
1 mL of bromobenzene. A further 141 mg of the compound was
isolated from this solution in the same manner as described above,
giving 2 in an overall yield of 95% (423 mg, 267 mmol). 1H NMR
4. Experimental
4.1. Synthesis of compounds
4.1.1. 4,6-(BneN]PEt2)2dbf (L)
A solution of benzyl-azide (177 mg, 1.33 mmol) was added
dropwise to a stirring solution of dbf(PEt2)2 (218 mg, 0.633 mmol)
in benzene (2 mL). The resulting yellow solution was left to stand at
ambient temperature for 30 min. The solution was concentrated to
a volume of 1 mL, and 10 mL of pentane was added, causing the
solution to become cloudy. Cooling to ꢀ35 ꢁC for 19 h resulted in
the formation of yellow crystals. The mother liquor was decanted
and the crystals were washed with pentane (3 ꢂ 1 mL) and dried in
vacuo, giving L in 80% yield (279 mg, 0.503 mmol). 1H NMR (C6D6):
(CD2Cl2):
d
8.35 (dt, 2H, 3JHH ¼ 7.7 Hz, 4JHH ¼ 1.2 Hz, 1,9-dbf), 7.73 (s,
8H, o-BArF4), 7.61 (td, 2H, 3JHH ¼ 7.7 Hz, 4JPH ¼ 2.4 Hz, 2,8-dbf), 7.55
3
3
(s, 4H, p-BArF4), 7.48 (ddd, 2H, JPH ¼ 9.5 Hz, JHH ¼ 7.7 Hz,
4JHH ¼ 1.2 Hz, 3,7-dbf), 7.18e7.08 (ov m, 6H, m- þ p-CH2Ph),
7.05e6.98 (ov m, 4H, o-CH2Ph), 4.66 (q, 1H, 3JHH ¼ 6.8 Hz, OCH(CH3)
CO2CH3), 3.98 (d, 4H, 3JPH ¼ 23.1 Hz, CH2Ph), 3.69 (s, 3H, OCH(CH3)
CO2CH3), 2.45e2.24 (ov m, 8H, PCH2CH3), 1.41 (d, 3H, 3JHH ¼ 6.8 Hz,
3
3
d
8.24 (dd, 2H, JPH ¼ 11.0 Hz, JHH ¼ 7.6 Hz, 3,7-dbf), 7.88 (d, 4H,
3JHH ¼ 7.1 Hz, o-CH2Ph), 7.56 (d, 2H, JHH ¼ 7.6 Hz, 1,9-dbf), 7.40
3
(t, 4H, 3JHH ¼ 7.7 Hz, m-CH2Ph), 7.22 (t, 2H, 3JHH ¼ 7.3 Hz, p-CH2Ph),
OCH(CH3)CO2CH3), 1.04 (q, 6H, JPH ¼ 7.5 Hz, JHH ¼ 7.5 Hz,
3
3
3
4
3
3
7.13 (td, 2H, JHH ¼ 7.6 Hz, JPH ¼ 1.1 Hz, 2,8-dbf), 4.73 (d, 4H,
3JPH ¼ 18.4 Hz, CH2Ph), 2.10e1.85 (ov m, 8H, PCH2CH3), 0.95
PCH2CH3), 0.98 (q, 6H, JPH ¼ 7.5 Hz, JHH ¼ 7.5 Hz, PCH2CH3). 31P
{1H} NMR (CD2Cl2):
d
46.8 (s). 19F{1H} NMR (CD2Cl2):
d
ꢀ62.8 (s). 11
B
(dt, 12H, JPH ¼ 16.8 Hz, JHH ¼ 7.6 Hz, PCH2CH3). 31P{1H} NMR
{1H} NMR (CD2Cl2):
d
ꢀ6.6 (s). Anal. Calcd. (%) for
3
3
(C6D6):
d
14.43. Anal. Calcd. (%) for C34H40N2OP2: C: 73.63; H: 7.27;
C70H59BF24N2O4P2Zn: C: 53.00; H: 3.75; N: 1.77; found: C: 53.13; H:
3.92; N: 2.09.
N: 5.05; found: C: 73.47; H: 7.00; N: 5.12.
4.1.2. [LHþ][B(m-(CF3)2eC6H3)ꢀ4 ] (LH)
4.2. X-ray crystallography data
L (320 mg, 0.577 mmol) and [H(OEt2)þ2 ][B(m-(CF3)2eC6H3)4ꢀ]
(584 mg, 0.577 mmol) were combined in a 20 mL glass vial with
2 mL of benzene. The resulting mixture was stirred briefly, giving
a clear red solution, and left to stand for 5 min. Addition of 2 mL of
pentane resulted in precipitation of a red oil. The supernatant was
decanted, the oil was washed with pentane (3 ꢂ 2 mL) and dried in
vacuo, affording LH as a pale yellow powder in 96% yield (783 mg,
4.2.1. Crystal data for L
C34H40N2OP2, FW ¼ 554.62, crystal size 0.32 ꢂ 0.32 ꢂ 0.12,
triclinic, space group Pꢀ1, a ¼ 10.863(1)3 Å, b ¼ 11.126(2) Å,
c ¼ 13.923(2) Å,
a
¼ 72.388(1)ꢁ,
b
¼ 88.627(2)ꢁ,
g
¼ 69.792(1)ꢁ,
V ¼ 1499.1(3) Å3, Z ¼ 2, Dc ¼ 1.229 g cmꢀ3, F(000) ¼ 592, Mo K
a
radiation (
l
¼ 0.71073 Å), T ¼ 173(2) K,
m
¼ 0.174 mmꢀ1. 20286
0.552 mmol). 1H NMR (CD2Cl2):
d
8.26 (d, 2H, 3JHH ¼ 7.3 Hz, 1,9-dbf),
reflections, 6118 unique (Rint ¼ 0.0225) were used in all calcula-
7.75 (br s, 8H, o-BArF4), 7.65e7.50 (ov m, 8H, p-BArF4 þ 3,7-
dbf þ 2,8-dbf), 7.26e7.10 (ov m, 10H, o- þ m- þ p-CH2Ph), 5.45
(br s, 1H, NH), 4.03 (d, 4H, 3JHH ¼ 16.5 Hz, CH2Ph), 2.50e2.15 (ov m,
tions. R1 (I > 2
s
(I)) ¼ 0.0357, wR2 (I > 2 (I)) ¼ 0.0940.
s
4.2.2. Crystal data for 2
3
3
8H, PCHaHbCH3), 1.10 (dt, 12H, JPH ¼ 18.9 Hz, JHH ¼ 7.6 Hz,
C70H59BF24N2O4P2Zn,
FW
¼
1586.31,
crystal
size
PCH2CH3). 31P{1H} NMR (CD2Cl2):
d
39.53 (s). 19F{1H} NMR (CD2Cl2):
0.52 ꢂ 0.33 ꢂ 0.27, triclinic, space group Pꢀ1, a ¼ 15.019(2) Å,
d
ꢀ62.82 (s). 11B{1H} NMR (CD2Cl2):
d
ꢀ6.60 (s). Anal. Calcd. (%) for
b ¼ 15.453(2) Å, c ¼ 16.072(2) Å,
a
¼ 104.979(1)ꢁ,
b
¼ 101.291(1)ꢁ,
C66H53BF24N2OP2: C: 55.87; H: 3.77; N: 1.97; found: C: 55.74; H:
3.87; N: 2.26.
g
¼ 95.363(1)ꢁ, V ¼ 3492.5(8) Å3, Z ¼ 2, Dc ¼ 1.508 g cmꢀ3
,
F(000) ¼ 1612, Mo K
a
radiation (
l
¼ 0.71073 Å), T ¼ 173(2) K,
m
¼ 0.512 mmꢀ1. 47,147 reflections, 14,217 unique (Rint ¼ 0.0184)
4.1.3. [LZnCHþ3 ][B(m-(CF3)2eC6H3)ꢀ4 ] (1)
were used in all calculations. R1 (I > 2
s
(I)) ¼ 0.0340, wR2
A 1.2 M solution of dimethylzinc in toluene (120
mL, 144 mmol)
(I > 2
s
(I)) ¼ 0.0904.
was added to a solution of LH (200 mg, 141 mmol) in bromo-
benzene (1 mL). The solution was left to stand for 1 h, then 2 mL of
pentane were added, precipitating the product as a red oil. The
supernatant was decanted, the material was washed with pentane
(3 ꢂ 1 mL) and then dried in vacuo, giving 1 as an off-white powder
Acknowledgments
P.G.H. thanks NSERC, CFI, Canada School of Energy and Envi-
ronment and GreenCentre Canada for financial support. C.A.W.
acknowledges NSERC and the Alberta Ingenuity Fund (Alberta
Innovates) for student awards. Thanks to Yun Yang of GreenCentre
Canada for GPC measurements.
in 90.0% yield (190 mg, 127 mmol). 1H NMR (CD2Cl2):
d
8.34 (dt, 2H,
3JHH ¼ 7.7 Hz, JHH ¼ 1.1 Hz, 1,9-dbf), 7.73 (br s, 8H, o-BArF4), 7.64
(td, 2H, 3JHH ¼ 7.7 Hz, 4JPH ¼ 2.4 Hz, 2,8-dbf), 7.56 (br s, 4H, p-BArF4),
7.53 (ddd, 2H, 3JPH ¼ 10.4 Hz, 3JHH ¼ 7.7 Hz, 4JHH ¼ 1.1 Hz), 7.19e7.13
(ov m, 6H, m- þ p-CH2Ph), 7.07e7.01 (m, 4H, o-CH2Ph), 4.00 (d, 4H,
4
Appendix. Supplementary data
2
3
3JPH ¼ 19.2 Hz, CH2Ph), 2.30 (dq, 8H, JPH ¼ 11.8 Hz, JHH ¼ 7.7 Hz,
3
3
PCH2CH3), 1.07 (dt, 12H, JPH
¼
18.7 Hz, JHH
¼
7.6 Hz,
46.60 (s).
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2012.01.004.
PCH2CH3), ꢀ0.95 (s, 3H, ZnCH3). 31P{1H} NMR (CD2Cl2):
d

C.A. Wheaton, P.G. Hayes / Journal of Organometallic Chemistry 704 (2012) 65e69
G.W. Coates, J. Am. Chem. Soc. 123 (2001) 3229e3238;
69
References
(d) M. Chisholm, J. Gallucci, K. Phomphrai, Chem. Commun. (2003) 48e49;
(e) H. Chen, H. Tang, C. Lin, Macromolecules 39 (2006) 3745e3752;
(f) G. Labourdette, D.J. Lee, B.O. Patrick, M.B. Ezhova, P. Mehrkhodavandi,
Organometallics 28 (2009) 1309e1319;
(g) A. Garces, L.F. Sanchez-Barba, C. Alonso-Moreno, M. Fajardo, J. Fernandez-
Baeza, A. Otero, A. Lara-Sanchez, I. Lopez-Solera, A. Maria Rodriguez, Inorg.
Chem. 49 (2010) 2859e2871;
(h) F. Drouin, P.O. Oguadinma, T.J.J. Whitehorne, R.E. Prud’homme, F. Schaper,
Organometallics 29 (2010) 2139e2147;
(i) C.K. Williams, L.E. Breyfogle, S.K. Choi, W. Nam, V.G. Young, M.A. Hillmyer,
W.B. Tolman, J. Am. Chem. Soc. 125 (2003) 11350e11359;
(j) E.L. Marshall, V.C. Gibson, H.S. Rzepa, J. Am. Chem. Soc. 127 (2005)
6048e6051.
[1] (a) D.R. Dodds, R.A. Gross, Science 318 (2007) 1250e1251;
(b) R. Gross, B. Kalra, Science 297 (2002) 803e807;
(c) Y. Kimura, Polym. J. 41 (2009) 797e807.
[2] For selected recent reviews see: (a) M.J. Stanford, A.P. Dove, Chem. Soc. Rev. 39
(2010) 486e494;
(b) C.A. Wheaton, P.G. Hayes, B.J. Ireland, Dalton Trans. (2009) 4832e4846;
(c) H.R. Kricheldorf, Chem. Rev. 109 (2009) 5579e5594;
(d) J. Wu, T. Yu, C. Chen, C. Lin, Coord. Chem. Rev. 250 (2006) 602e626;
(e) O. Dechy-Cabaret, B. Martin-Vaca, D. Bourissou, Chem. Rev. 104 (2004)
6147e6176.
[3] For selected examples see: (a) S. Koeller, J. Kadota, A. Deffieux, F. Peruch,
S. Massip, J.-M. Leger, J.-P. Desvergne, B. Bibal, J. Am. Chem. Soc. 131 (2009)
15088e15089;
[6] (a) C.A. Wheaton, B.J. Ireland, P.G. Hayes, Organometallics 28 (2009)
1282e1285;
(b) C.A. Wheaton, P.G. Hayes, Dalton Trans. 39 (2010) 3861e3869;
(c) C.A. Wheaton, P.G. Hayes, Chem. Commun. 46 (2010) 8404e8406.
[7] (a) Y. Sarazin, B. Liu, T. Roisnel, L. Maron, J.-F. Carpentier, J. Am. Chem. Soc. 133
(2011) 9069e9087;
(b) C. Bonduelle, B. Martín-Vaca, F.P. Cossío, D. Bourissou, Chem.dEur. J. 14
(2008) 5304e5312;
(c) L. Zhang, F. Nederberg, J. Messman, R. Pratt, J. Hedrick, C. Wade, J. Am.
Chem. Soc. 129 (2007) 12610e12611;
(d) F. Nederberg, E. Connor, M. Moller, T. Glauser, J. Hedrick, Angew. Chem. Int.
Ed. 40 (2001) 2712e2715.
(b) Y. Sarazin, V. Poirier, T. Roisnel, J.-F. Carpentier, Eur. J. Inorg. Chem. (2010)
3423e3428;
(c) J. Börner, U. Flörke, K. Huber, A. Döring, D. Kuckling, S. Herres-Pawlis,
Chem.dEur. J. 15 (2009) 2362e2376.
[4] For selected examples see: (a) A. Pietrangelo, S.C. Knight, A.K. Gupta, L.J. Yao,
M.A. Hillmyer, W.B. Tolman, J. Am. Chem. Soc. 132 (2010) 11649e11657;
(b) A. Otero, J. Fernandez-Baeza, A. Lara-Sanchez, C. Alonso-Moreno,
I. Marquez-Segovia, L.F. Sanchez-Barba, A.M. Rodriguez, Angew. Chem. Int. Ed.
48 (2009) 2176e2179;
[8] M.G. Cushion, P. Mountford, Chem. Commun. 47 (2011) 2276e2278.
[9] (a) G. Asensio, A.B. Cuenca, M.A. Esteruelas, M. Medio-Simon, M. Olivan,
M. Valencia, Inorg. Chem. 49 (2010) 8665e8667;
(b) M. Kranenberg, Y.E.M. van der Burgt, P.C.J. Kamer, P.W.N.M. van Leeuwen,
K. Goubitz, J. Fraanje, Organometallics 14 (1995) 3081e3089.
[10] (a) A. Charafeddine, W. Dayoub, H. Chapuis, P. Strazewski, Chem.dEur. J. 13
(2007) 5566e5584;
(b) S. Bräse, C. Gil, K. Knepper, V. Zimmermann, Angew. Chem. Int. Ed. 44
(2005) 5188e5240.
[11] B.J. Ireland, C.A. Wheaton, P.G. Hayes, Organometallics 29 (2010) 1079e1084.
[12] (a) M.D. Hannant, M. Schormann, M. Bochmann, J. Chem. Soc. Dalton Trans.
(2002) 4071e4073;
(c) A.F. Douglas, B.O. Patrick, P. Mehrkhodavandi, Angew. Chem. Int. Ed. 47
(2008) 2290e2293;
(d) H.Y. Ma, T.P. Spaniol, J. Okuda, Angew. Chem. Int. Ed. 45 (2006)
7818e7821;
(e) A.P. Dove, V.C. Gibson, E.L. Marshall, H.S. Rzepa, A.J.P. White, D.J. Williams,
J. Am. Chem. Soc. 128 (2006) 9834e9843;
(f) Z.Y. Zhong, P.J. Dijkstra, J. Feijen, J. Am. Chem. Soc. 125 (2003)
11291e11298.
[5] For selected examples see: (a) V. Poirier, T. Roisnel, J.-F. Carpentier, Y. Sarazin,
Dalton Trans. (2009) 9820e9827;
(b) M. Hannant, M. Schormann, D. Hughes, M. Bochmann, Inorg. Chim. Acta
358 (2005) 1683e1691.
(b) M.H. Chisholm, N.W. Eilerts, J.C. Huffman, S.S. Iyer, M. Pacold,
K. Phomphrai, J. Am. Chem. Soc. 122 (2000) 11845e11854;
(c) B.M. Chamberlain, M. Cheng, D.R. Moore, T.M. Ovitt, E.B. Lobkovsky,
[13] T. Biela, A. Duda, S. Penczek, Macromol. Symp. 183 (2002) 1e10.