Phosphinimino-amino magnesium complexes: Synthesis and catalysis of heteroselective rop of rac -lactide

Article abstract of DOI:10.1021/om401056s

Alkane elimination reactions of phosphinimino-amine ligands HL ^1-8 ((2,6-Me₂-C₆H₃NH)C(Ph)i - CHPPh₂(NAr) (Ar = C₆H₅ (HL¹); 2,6-Me₂-C₆H₃

Full text of DOI:10.1021/om401056s

Article
pubs.acs.org/Organometallics
Phosphinimino-amino Magnesium Complexes: Synthesis and
Catalysis of Heteroselective ROP of rac-Lactide
Hongyan Xie,†,‡ Zehuai Mou,†,‡ Bo Liu,† Ping Li,§ Weifeng Rong,†,‡ Shihui Li,† and Dongmei Cui*,†
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, People’s Republic of China
‡University of Chinese Academy of Sciences, Changchun Branch, Changchun 130022, People’s Republic of China
§Jinzhou City Health School, Beijing Road 4-26, Jinzhou, Liaoning 121001, People’s Republic of China
S
* Supporting Information
ABSTRACT: Alkane elimination reactions of phosphinimino-amine ligands HL1−8 ((2,6-Me2-C6H3NH)C(Ph)
CHPPh2(NAr) (Ar = C6H5 (HL1); 2,6-Me2-C6H3 (HL2); 2,6-Et2-C6H3 (HL3); 2,6-iPr2-C6H3 (HL4); 2-OMe-C6H4 (HL5); 2-
Cl-C6H4 (HL6); 3-CF3-C6H4 (HL7); 4-MeO-C6H4 (HL8)) with MgnBu2, respectively, afforded a series of phosphinimino-amine-
based complexes L1−8MgnBu(THF) (1−8) by releasing butane. Complexes 1−8 are phosphinimino-amine-ligated THF-solvated
mono(alkyl)s, among which 1−4 adopt twisted tetrahedral geometries, whereas 5 contains a trigonal bipyramido geometry core.
Complexes 1−8 all display high activity for the ring-opening polymerization of rac-lactide. The molecular weights of the resulting
PLA are close to the theoretic values, and the molecular weight distributions are narrow. Moreover, these complexes show
medium to high heteroselectivity, which, interestingly, increases with the decrease of the ligand steric hindrance; thus, complex 1,
bearing a less bulky ligand, exhibits a heteroselectivity of Pr = 0.98, the highest value of a magnesium-based initiator achieved to
date. The kinetics study showed that the polymerization rate is first-order dependent on both monomer and initiator
concentrations, and the overall rate equation is −d[LA]/dt = 3.78 M−1 s−1 [LA][Mg].
Chart 1
INTRODUCTION
■
The development of environmentally benign and renewable
materials has become more and more urgent because of white
pollution and shortages of source and energy problems
encountered by our society.1 Polylactides (PLAs) are one of
the most promising biodegradable and biocompatible synthetic
materials arising from biosources, having been widely used in
packaging, agriculture, medicine, pharmaceutics, and tissue
engineering.1c,2 The applications are strongly dependent on the
microstructures of PLA.1e Ring-opening polymerization (ROP)
of lactide (LA) catalyzed by single-site catalysts has been
adopted as the most important manner in which to obtain
PLAs with tailor-made microstructures such as controllable
molecule weight and narrow molecule weight distribution as
well as stereoregularity when rac-LA or meso-LA is employed, in
particular, multiblocks and topological microstructures.3 There-
fore for the past decades, many efforts have been made to
develop novel organometallic complexes that facilitate enhanc-
ing catalytic activity and specific selectivity.4 β-Diketiminato
compounds (Chart 1, BDI) and their derivatives have been
widely used as “hard” donor ligands in the synthesis of
organometallic precursors,5 because they are monoanionic
chelating ligands having similar electronics to the cyclo-
pentadienyl anion, and their steric and electronic effects can
be swiftly tuned via choosing appropriate starting reagents.6
BDI-supported zinc7 and magnesium8 complexes, whether in
the dimeric or monomeric THF-solvate coordination mode,
have been proved to be highly active and heteroselective for the
ROP of rac-LA. Recently, modifying β-diketiminato frameworks
by replacing the carbon atoms in BDI with “large” and “soft”
phosphorus atoms to increase the steric bulk and lower the
electron density of the metal centers has led to generating
bis(phosphinimino)methane (Chart 1, BPI) and phosphinimi-
no-amine (Chart 1, PIA) ligands. The BPI-stabilized zinc
aryloxyl and triphenylmethoxyl complexes have been reported
Received: October 30, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 1. Synthesis of Ligands HL1−8
Scheme 2. Preparation of Complexes 1−8
to be highly active for ROP of rac-LA, although providing
atactic PLA.9 The coordination chemistry of PIA ligands to Li,
Pd, Ni, Sc, and Al metals has been investigated recently in
olefin polymerization and the ROP of ε-caprolactone;10
however, the analogous magnesium complexes have remained
unexplored. In addition, although aluminum, zinc, and
lanthanide-element-based complexes have been reported to
be highly active,11 and in some cases specifically selective,4f−h,12
abundant, cheap, and biobenign magnesium-based precursors
possessing high activity and specific selectivity are still
scarce.4c,13 Herein, we report the synthesis of magnesium
complexes bearing PIA ligands ((2,6-Me2-C6H3NH)C(Ph)
CHPPh2(NAr)), which exhibit unique structures and
excellent heteroselectivity for the ROP of rac-LA.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Complexes 1−6.
Compound I was generated by the condensation reaction of
2,6-dimethylaniline and acetophenone. Lithiation of compound
n
I by BuLi and further treatment with ClPPh2 gave compound
II. Staudinger reaction between compound II and the
corresponding azides afforded the PIA ligands HL1−8 (Scheme
1, HL′1−8 are the isomers).10a,11 In the H NMR spectrum of
1
HL1, two doublets at 4.68 (major) and 3.89 (minor) ppm are
arising from the methide proton CHPPh2; the methyl protons
CH3-Ph give two singlet signals at 1.91 (major) and 1.85
(minor) ppm; the singlet at 9.75 ppm can be attributed to a N-
H proton. In the 31P NMR spectrum, there are also two singlets
at 16.47 (major) and 14.72 (minor) ppm. These weak
resonances are attributed to the imine species (HL′1). The
amine species HL1 and imine species HL′1 exist in a HL1-to-
B
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
HL′1 ratio of 87:13 (Scheme 1). The ratio of amine-to-imine
species varies with the substituents; thus, HL2−5-to-HL′2−5 is
86:14 and HL6-to-HL′6 is 93:7, while HL7,8-to-HL′7,8 is 87:13.
Treatment of these ligands with 1.1 equiv of MgnBu2 afforded
the corresponding PIA-supported magnesium complexes
[L1−8MgnBu(THF)] (1−8) in 53−78% yields (Scheme 2).
Complexes 1−8 are soluble in THF and toluene but insoluble
in n-hexane. The NMR spectrum analyses of complexes 1−8
are informative for the formation of mono(alkyl) species. The
α-methylene protons of Mg-CH2(CH2)2CH3 give an AA′XX′
spin resonance centered at δ 0.28 (1), 0.26 (2), 0.18 (3), −0.11
(4), −0.30 (5), −0.06 (6), 0.27 (7), and 0.24 (8) ppm,
respectively, which are comparable to that in the BDI-MgnBu
complex.8b The methine proton CH-PPh2 gives a doublet
resonance (2JP−H = 20.6−24.5 Hz) due to coupling with the
phosphorus atom. The coupling constants of complexes 1−8
are comparable to the complexes PIA-Al (PIA = Ar-NC(Ph)
CHP(Ph2)N-Ar) and LZnEt (L = o-(OC(R)CHP(Ph2)
N)C6H4(3,5-Me2C3HN2)) (23−26 Hz).10a,14 For complex 5,
the methoxyl group −OCH3 shows a singlet at δ 3.25 ppm,
shifting downfield slightly compared to the free HL5 at δ 3.10
ppm in C6D6, suggesting the weak coordination of the
methoxyl oxygen to the central metal in solution.5f Complexes
1−8 reveal singlet resonances in their 31P NMR spectra at δ
33.28 (1), 29.35 (2), 30.01 (3), 31.55 (4), 31.71 (5), 34.66 (6),
34.09 (7), and 33.74 (8) ppm, respectively, however, which are
close to each other, suggesting the electronics around the
phosphorus atom in these molecules is similar.
Figure 2. X-ray structure of complex 5 (thermal ellipsoids at the 35%
probability level). Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Mg(1)−N(1) 2.202(4),
Mg(1)−N(2) 2.110(3), Mg(1)−C(27) 2.167(5), Mg(1)−O(1)
2.118(3), Mg(1)−O(2) 2.305(3), P(1)−N(2) 1.617(3); N(1)−
Mg(1)−N(2) 101.79(9), O(1)−Mg(1)−C(27) 108.76(12), N(2)−
Mg(1)−O(2) 71.36(12), C(27)−Mg(1)−O(2) 99.25(17), C(7)−
C(8)−P(1) 126.6(2).
the center of the tetrahedron. For complex 5, the Mg2+ ion σ-
bonds to an alkyl moiety, a coordinating N,N,O-tridentate
ligand, and a solvated THF molecule, generating a trigonal
bipyramidal geometry core. All the metal alkyl bond distances
Mg(1)−C(27) of these complexes (1, 2.130(3) Å; 2, 2.156(4)
Å; 3, 2.136(4) Å; 4, 2.134(3) Å; 5, 2.167(5) Å) fall in the
reasonable range of those reported in the literatures.8b,11f The
phosphinimine PN double-bond lengths (1.619(2) Å (1),
1.603(3) Å (2), 1.597(4) Å (3), 1.601(2) Å (4), 1.617(3) Å
(5)) are comparable to the PN bonds in PIA-Al complexes
[Me2Al(N(Ar)C(R)CHP(Ph2)N(Ar))] (av PN dou-
ble-bond length 1.62 Å) and in the other previously reported
literature,10a,15 which are also similar to that in the amino
isomer of the neutral PIA compound [(2,6-iPr2-C6H3NH)C-
(Me)CHP(Ph2)N(2,6-iPr2-C6H3)] (1.590(3) Å),16 but
longer than that in the localized imine isomer [(2,6-iPr2-
C6H3)NC(Me)CH2P(Ph2)N(2,6-Me2-C6H3)] (1.562(2)
Å),10c suggesting the partial delocalization of the electrons
over the NPCCN skeleton.17 The bond angle of N(1)−
Mg(1)−N(2), 101.79(9)° for 1, 96.14(11)° for 2, 96.20(14)°
for 3, 97.58(9)° for 4, and 93.11(13)° for 5, varies significantly
with the substituents of the ligands; the bigger the substituents,
the smaller the angle, which might be attributed to the steric
repulsion between the substituents and the alkyl ligand and the
coordinated THF molecule. Noteworthy was that the smaller
the N1−Mg1−N2 bond angle, the more open the environment
around the central metal ion, which affects significantly the
specific selectivity of the metal center (vide infra).
The solid-state structures of complexes 1−5 were established
by single-crystal X-ray diffraction analyses as shown in Figures
1, 2 (complexes 1, 5), and S1−3 (complexes 2−4) along with
the selected bond lengths and bond angles. Complexes 1−4 are
structural analogues, where the magnesium ion bonds to an
alkyl moiety, a THF molecule, and a PIA ligand in an N,N-
bidentate chelating mode, adopting a twisted tetrahedral
geometry. The ligand nitrogen atoms, THF oxygen atom, and
alkyl carbon atom occupy the apexes, while the Mg2+ ion sits in
ROP of rac-LA. The catalytic performances of complexes
1−8 toward the ROP of rac-LA in THF were investigated, the
representative polymerization results of which are summarized
in Table 1. Complexes 1−6 and 8 displayed similar catalytic
activity, suggesting that the substituents such as the bulky −iPr,
the electron-donating group −OMe, and the weak electron-
withdrawing group −Cl hardly affected the activity of the
initiators (Table 1, entries 1−8). However, by using complex 7,
the polymerization became sluggish, which might be attributed
Figure 1. X-ray structure of complex 1 (thermal ellipsoids at the 35%
probability level). Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Mg(1)−N(1) 2.093(2),
Mg(1)−N(2) 2.106(3), Mg(1)−C(27) 2.130(3), Mg(1)−O(1)
2.076(2), P(1)−N(2) 1.619(2); N(1)−Mg(1)−N(2) 101.79(9),
O(1)−Mg(1)−C(27) 108.76(12), C(7)−C(8)−P(1) 126.6(2).
C
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Table 1. ROP of rac-LA Initiated by Complexes 1−8
b
c
d
d
e
entry
cat
[LA]/[Mg]
temp (°C)
time (min)
conv (%)
Mn,cacld × 10−4
Mn, found × 10−4
Mw/Mn
Pr
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
200
200
200
200
200
300
200
200
300
300
300
100
50
25
25
25
25
25
25
25
25
25
25
0
10
10
94
95
95
96
96
96
73
93
88
trace
89
81
97
92
95
94
94
90
2.71
2.74
2.74
2.76
2.76
4.15
2.11
2.68
3.80
3.09
3.44
3.92
3.48
2.76
3.77
3.45
3.25
2.80
1.60
1.69
1.55
1.77
1.51
1.76
1.60
1.72
1.87
0.92
0.79
0.77
0.67
0.62
0.87
0.72
0.93
0.53
10
10
10
10
120
10
f
9
60
g
10
1440
30
11
12
3.84
1.17
0.70
1.32
4.10
5.41
6.77
10.37
13.25
8.99
3.55
1.17
2.11
4.21
5.08
6.47
8.50
10.01
2.28
1.63
1.59
1.70
1.59
1.58
1.45
1.54
1.38
0.96
0.98
0.93
0.93
0.92
0.91
0.92
0.90
0.90
0
30
h
13
25
25
25
25
25
25
25
10
14
15
16
17
100
300
400
500
800
1000
10
10
10
10
i
18
60
i
19
60
92
a
b
c
1
Polymerization conditions: THF 5 mL, [Mg]0 10 μmol. Determined by H NMR spectroscopy. Mn,cald = [LA]/[Mg] × 144.13 × conv (%) +
d
57.12(−nBu). Determined by size exclusion chromatography (SEC) against polystyrene standard. Mn values were obtained using a correction factor
for polylactides (0.58). Pr is the probability of racemic linkages between monomer units determined from the methine region of the homonuclear
decoupled H NMR spectrum. In toluene. In dichloromethane. [Mg]0 = 30 μmol, 20 min. [Mg]0 = 5 μmol, 60 min.
e
f
g
h
i
1
to the strong electron-withdrawing substituent −CF3 in the
molecule to reduce the electron density around the central
metal. The polymerization when complex 1 was chosen as the
initiator proceeded smoothly under various monomer-to-
initiator ratios ranging from 50 to 1000 to provide PLAs with
molecular weights close to the theoretic values and moderate
molecular weight distributions (Mw/Mn = 1.38−1.70) (Table 1,
entries 13−19), indicating a controlled process. In contrast to
their negligible effect on the catalytic activity, the substituents
aroused significant change to the specific selectivity of the
attached central metal. Complex 1, bearing the less bulky
ligand, exhibited the highest heteroselectivity for the polymer-
ization of rac-LA to give heterotactic PLA with a racemic
enchainment of monomer units of Pr = 0.92. When the
polymerization was carried out at a lower temperature (0 °C),
the selectivity increased up to Pr = 0.98, the highest value of a
magnesium-based catalyst achieved to date (Table 1, entry 12).
For complexes 2−4, the steric hindrance increased from the
complex 6 also displayed a higher specific selectivity because of
the smaller chloride-substituted ligand. As expected, complex 8
was highly heteroselective (Pr = 0.93, Table 1, entry 8), because
the methoxyl substituent is on the para position of the aromatic
ring, which hardly impacts the steric environment of the ligand.
The case of complex 5 was complicated: it has the smallest
N(1)−Mg(1)−N(2) bond angle of 93.11(13)°, which was the
main reason for its lowest selectivity (Pr = 0.62, Table 1, entry
5), while it also has a ligand with a methoxyl side arm
coordinating to the Mg2+ center that was designed to increase
the selectivity to mimic the role of THF (from the
polymerization medium). It has been demonstrated previously
through the amino−amino-bis(phenols) yttrium alkyl initiation
systems that the reversible coordination of the THF molecule
to the central metal active species facilitates the orientation of
the coordination of rac-LA and thus increases the hetero-
selectivity.4e,g,h,18a−c Thus, the low selectivity of complex 5
means that the interaction between the methoxyl group and
Mg2+, which is stronger and irreversible, is different from
THF.4e This could be proved further by performing the
polymerization in toluene and dichloromethane, whereupon
both the catalytic activity and heteroselectivity decreased
dramatically (Table 1, entries 9, 10). The end-group of a
PLA oligomer produced by complex 1 ([LA]0/[1]0 = 20, THF,
i
methyl-substituted ligand to the bulky Pr-substituted ligand
and the heterotactic selectivity dropped from 0.79 to 0.67
(Table 1, entries 2−4), which was in contrast to many
lanthanide-element-based complexes that display high hetero-
selectivity when bearing bulky ligands.4h,18 This might be
ascribed to the crystallographic geometry of the complexes
where the more bulkier the ligand, the more open the steric
environment around the central metal ion, due to the steric
repulsion (evidenced by the bite-angle N(1)−Mg(1)−N(2):
101.79(9)° for 1, 96.14(11)° for 2, 96.20(14)° for 3, and
97.58(9)° for 4, vide supra), which allows the coordination of
the rac-LA monomer to the initiation center more freely, to
result in a specifically irregular product. This could explain why
1
20 °C) was analyzed by its H NMR spectrum (Figure S30),
n
which revealed the resonances from a hydroxyl group and Bu
group (from the initiator), respectively, suggesting that the
ring-opening polymerization of rac-LA took place in the
coordination−insertion mechanism.
Kinetics Studies of Polymerization of rac-LA. Fixing the
initial concentration of monomer rac-LA at [LA]0 = 0.333 M,
D
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
polymerizations under various concentrations of complex 1
([Mg] = 0.834−2.09 mM) were performed in THF at 20 °C.
The conversions at different polymerization times were
the β-diketiminato Mg alkyl system (kp = 10.7 M−1 s−1, 25 °C
in dichloromethane)8b and the heteroscorpionate magnesium
alkyls [Mg(κ3-pbptamd)(CH2SiMe3)] and [Mg(κ3-tbptamd)-
(CH2SiMe3)] systems (1.73 and 1.27 M−1 s−1, 20 °C in
THF),19 but much higher than that for the magnesium alkoxide
(NNONNMg2)OEt system (3.9 × 10−3 M−1 s−1 in dichloro-
methane at 20 °C),20 positioning the current magnesium-based
initiators at top high activity, and moreover, with unprece-
dented high selectivity.
1
recorded according to H NMR spectroscopy analysis. The
results showed that the plots of ln[LA]0/[LA]t vs time are
linear in a wide range of [LA]0, indicating they proceeded with
first-order dependence on monomer concentration (Figure 3,
CONCLUSION
■
We have demonstrated that the phosphinimino-amine-stabi-
lized magnesium complexes are extremely active toward the
ROP of rac-LA to provide PLAs with controllable molecular
weights and narrow molecular weight distributions, in particular
a heterotacticity of up to Pr = 0.98, the highest value reported
to date by using a magnesium-based initiator. The change of
ligand steric hindrance and bulkiness seems to have a negligible
influence on the catalytic activity of these complexes but affects
the specific selectivity significantly: the smaller the steric
bulkiness of the ligand, the higher the selectivity of the attached
active magnesium center, because the repulsion of the large
substituents on the ligands leaves more open space for the
metal center to allow the monomer to coordinate to the active
centers more randomly. This work sheds new light on
designing catalyst precursors for specifically selective polymer-
izations and focuses on the geometry of the ligand generated
around the metal center.
Figure 3. First-order kinetic plots for rac-LA polymerizations versus
time in THF at 20 °C with different concentrations of complex 1 as
initiator ([LA]0 = 0.333 M, squares, [Mg] = 2.09 mM, kapp = 9.21 ×
10−3 s−1, R2 = 0.998; circles, [Mg] = 1.67 mM, kapp = 7.06 × 10−3 s−1,
R2 = 0.999; triangles, [Mg] = 1.25 mM, kapp = 5.05 × 10−3 s−1, R2 =
0.999; stars, [Mg] = 0.834 mM, kapp = 3.76 × 10−3 s−1, R2 = 0.997).
EXPERIMENTAL SECTION
■
General Methods. All operations were carried out under an
atmosphere of argon using standard Schlenk techniques or in a
nitrogen gas filled MBraun glovebox. Toluene, tetrahydrofuran, and n-
hexane were distilled under nitrogen from sodium/benzophenone.
Deuterated NMR solvents were purchased from Cambridge Isotopes,
dried over Na (for C6D6) and molecular sieves (for CDCl3), and
stored in the glovebox. Acetophenone, chlorodiphenylphosphine,
aniline, 2,6-dimethylaniline, 2,6-diethylaniline, 2,6-diisopropylaniline,
2-methoxyaniline, 2-choloaniline, 3-CF3C6H4, and 4-methoxyaniline
were obtained from commercial sources and distilled under nitrogen
prior to use. Compounds 2,6-Me2-C6H3NC(Me)Ph and 2,6-Me2-
C6H3NC(Ph)CH2PPh2 and all the azides21 were synthesized via a
modified procedure according to the literature. MgnBu2 was purchased
from Sigma-Aldrich. rac-Lactide (Aldrich) was recrystallized three
times in dry ethyl acetate.
the apparent rate constants kapp = (3.76−9.18) × 10−3 s−1).
Thus, the polymerization rate equation can be depicted as
−d[LA]/dt = kapp[LA], where kapp = kp[Mg]x and kp is the rate
constant. Plotting ln kapp vs ln[Mg] allowed us to determine the
order in initiator concentration from the slope of the fitted line,
x = 0.98, as shown in Figure 4 (R2 = 0.982). Eventually, the
polymerization of rac-LA initiated by complex 1 showed first-
order dependence on both monomer and initiator concen-
trations: −d[LA]/dt = k[LA][Mg]. The intercept of the
regression line deduces a polymerization rate constant of kp =
3.78 M−1 s−1 at 20 °C in THF, which is comparable to those for
Instruments and Measurements. Organometallic samples for
NMR measurements were prepared in NMR tubes and sealed with
paraffin film in the glovebox. 1H and 13C NMR spectra were recorded
1
on a Bruker AV400 (FT, 400 MHz for H, 100 MHz for 13C, 162
MHz for 31P) spectrometer. Homonuclear decoupled 1H NMR
spectra were recorded on a Bruker AV400 spectrometer. Elemental
analyses were performed at the National Analytical Research Centre of
the Changchun Institute of Applied Chemistry (CIAC). The number-
average molar mass (Mn) and the molecular weight distributions (Mw/
Mn) of the polymer were measured by size exclusion chromatography
(SEC) on a TOSOH HLC-8220 SEC instrument (column: Super
HZM-H × 3) at 40 °C using THF as eluent with a flow rate of 0.35
mL/min; the values were relative to polystyrene standards.
X-ray Crystallographic Studies. Crystals for X-ray analysis were
obtained as described in the preparations. The crystals were
manipulated in a glovebox. Data collections were performed at
−88.5 °C on a Bruker SMART APEX diffractometer with a CCD area
detector, using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). The determination of crystal class and unit cell parameters
was carried out by the SMART program package. The raw frame data
were processed using SAINT and SADABS to yield the reflection data
Figure 4. Plot of ln kapp versus ln[Mg] for the polymerization of rac-
LA with complex 1 as the initiator (THF, 20 °C, [LA]0 = 0.333 M).
E
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
file. The structures were solved by using the SHELXTL program.
Refinement was performed on F2 anisotropically for all non-hydrogen
atoms by the full-matrix least-squares method. The hydrogen atoms
were placed at calculated positions and were included in the structure
calculations without further refinement of the parameters.
ArH), 7.27−7.08 (m, 7H, ArH), 6.88−6.84 (m, 2H, ArH), 6.67−6.52
2
(m, 4H, ArH), 4.26 (d, JP−H = 23.7 Hz, 1H, PCH), 3.32 (s, 3H,
OCH3), 2.13 (s, 6H, C6H3(CH3)2). 31P NMR (162 MHz, CDCl3, 25
°C): δ 6.93 ppm (s). Anal. Calcd for C35H33N2OP: C, 79.52; H, 6.29;
N, 5.30. Found: C, 79.27; H, 6.22; N, 5.35.
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)NPh (HL1).
To a THF (25 mL) solution of 4.07 g (10 mmol) of 2,6-Me2-
C6H3NC(Ph)CH2PPh2 was added dropwise 1.43 g (12 mmol) of
PhN3. N2 evolution commenced immediately, and the mixture was
stirred at 50 °C for 24 h. Removal of THF under vacuum left a yellow,
oily solid. The solid was washed with 30 mL of hexane, and then the
suspension was stirred for 1 h at ambient temperature. Filtering,
washing with 2 × 20 mL of hexane, and evaporating the residual
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H4-2-Cl)
(HL6). Following a similar procedure to that described for the
preparation of ligand HL1, the ligand HL6 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 1.84 g (12 mmol) of (2-OMe-C6H4)N3 as a pale
1
yellow solid (4.66 g, 81%). H NMR (400 MHz, CDCl3, 25 °C): δ
10.22 (s, 1H, NH), 7.94−7.89 (m, 4H, ArH), 7.52−7.44 (m, 6H,
ArH), 7.23−7.06 (m, 6H, ArH), 6.87−6.75 (m, 4H, ArH), 6.63−6.52
2
1
solvents afforded HL1 as a pale yellow solid (4.28 g, 86%). H NMR
(m, 2H, ArH), 4.45 (d, JP−H = 22.7 Hz, 1H, PCH), 2.03 (s, 6H,
C6H3(CH3)2). 31P NMR (162 MHz, CDCl3, 25 °C): δ 5.97 ppm (s).
Anal. Calcd for C34H33ClN2P: C, 76.61; H, 5.67; N, 6.65. Found: C,
76.75; H, 5.61; N, 6.62.
(400 MHz, CDCl3, 25 °C): δ 9.75 (s, 1H, NH), 7.94−7.90 (m, 4H, o-
PPh2), 7.50−7.42 (m, 6H, o-C6H5, m-PPh2), 7.27−7.24 (m, 2H, p-
PPh2,), 7.20−7.18 (m, 3H, m,p-C6H5), 7.03−6.99 (m, 2H, m-
C6H3Me2), 6.87−6.79 (m, 5H, o,m,p-NC6H5), 6.64 (m, 1H, p-
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H4-3-
CF3) (HL7). Following a similar procedure to that described for the
preparation of ligand HL1, the ligand HL7 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 2.24 g (12 mmol) of (3-CF3-C6H4)N3 as a yellow
2
C6H3Me2), 4.68 (d, JP−H = 21.2 Hz, 1H, PCH), 1.91 (s, 6H,
C6H3(CH3)2). 31P NMR (162 MHz, CDCl3, 25 °C): δ 16.47 ppm (s).
Anal. Calcd for C34H31N2P: C, 81.90; H, 6.27; N, 5.62. Found: C,
81.72; H, 6.23; N, 5.65.
1
solid (4.73 g, 84%). H NMR (400 MHz, CDCl3, 25 °C): δ 9.17 (s,
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H3-2,6-
Me2) (HL2). Following a similar procedure to that described for the
preparation of ligand HL1, the ligand HL2 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 1.76 g (12 mmol) of (2,6-Me2-C6H3)N3 as a pale
1H, NH), 7.95−7.90 (m, 4H, ArH), 7.50−7.44 (m, 6H, ArH), 7.30−
7.05 (m, 6H, ArH), 6.99−6.77 (m, 6H, ArH), 4.77 (d, 2JP−H = 20.8 Hz,
1H, PCH), 1.83 (s, 6H, C6H3(CH3)2). 31P NMR (162 MHz, CDCl3,
25 °C): δ 3.48 ppm (s). 19F NMR (376 MHz, CDCl3, 25 °C): δ
−62.68 ppm (s). Anal. Calcd for C35H30N2F3P: C, 74.19; H, 5.34; N,
4.94. Found: C, 74.28; H, 5.30; N, 4.96.
1
yellow solid (4.48 g, 85%). H NMR (400 MHz, CDCl3, 25 °C): δ
9.97 (br, 1H, NH), 7.78−7.73 (m, 4H, ArH), 7.43−7.35 (m, 5H,
ArH), 7.27−7.25 (m, 2H, ArH), 7.21−7.12 (m, 4H, ArH), 6.87−6.68
(m, 5H, ArH), 6.61−6.56 (m, 1H, ArH), 4.72 (d, 2JP−H = 22.2 Hz, 1H,
PCH), 2.07 (s, 6H, C6H3(CH3)2), 2.00 (s, 6H, C6H3(CH3)2). 31P
NMR (162 MHz, CDCl3, 25 °C): δ 8.38 ppm (s). Anal. Calcd for
C36H35N2P: C, 82.10; H, 6.70; N, 5.32. Found: C, 81.95; H, 6.76; N,
5.28.
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H4-4-
OMe) (HL8). Following a similar procedure to that described for the
preparation of ligand HL1, the ligand HL8 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 1.79 g (12 mmol) of (4-OMe-C6H4)N3 as a
1
yellow solid (4.42 g, 84%). H NMR (400 MHz, CDCl3, 25 °C): δ
9.76 (s, 1H, NH), 7.93−7.88 (m, 4H, ArH), 7.48−7.40 (m, 5H, ArH),
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H3-2,6-
Et2) (HL3). Following a similar procedure to that described for the
preparation of ligand HL1, the ligand HL3 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 2.11 g (12 mmol) of (2,6-Et2-C6H3)N3 as a pale
7.26−7.09 (m, 7H, ArH), 6.82−6.77 (m, 4H, ArH), 6.64−6.61 (m,
2
2H, ArH), 4.69 (d, JP−H = 21.0 Hz, 1H, PCH), 3.69 (s, 3H, OCH3),
1.92 (s, 6H, C6H3(CH3)2). 31P NMR (162 MHz, CDCl3, 25 °C): δ
2.43 ppm (s). Anal. Calcd for C35H33N2OP: C, 79.52; H, 6.29; N, 5.30.
Found: C, 79.36; H, 6.23; N, 5.26.
1
yellow solid (4.65 g, 84%). H NMR (400 MHz, CDCl3, 25 °C): δ
Synthesis of L1MgnBu(THF) (1). To a hexane solution (3 mL) of
MgnBu2 (1.1 mL, 1 M, 1.1 mmol) was added dropwise HL1 (0.498 g, 1
mmol in 10 mL of THF) at room temperature. The mixture was
stirred for 2 h at room temperature to afford a clear yellow solution.
Evaporation of solvent gave crystalline solids, which were washed with
a small amount of hexane to remove impurities and dried in vacuo to
give yellow solids of complex 1 (0.475 g, 73%). Single crystals suitable
10.13 (br, 1H, NH), 7.73−7.68 (m, 4H, ArH), 7.42−7.34 (m, 5H,
ArH), 7.28−7.26 (m, 2H, ArH), 7.23−7.13 (m, 5H, ArH), 6.90−6.88
(m, 2H, ArH), 6.81−6.78 (m, 2H, ArH), 6.73−6.70 (m, 1H, ArH),
2
3
4.64 (d, JP−H = 22.3 Hz, 1H, PCH), 2.50 (q, JH−H = 7.6 Hz, 4H,
3
C6H3(CH2Me)2), 2.03 (s, 6H, C6H3(CH3)2), 0.92 (t, JH−H = 7.5 Hz,
6H, C6H3(CH2CH3)2). 31P NMR (162 MHz, CDCl3, 25 °C): δ −4.45
ppm (s). Anal. Calcd for C38H39N2P: C, 82.28; H, 7.09; N, 5.05.
Found: C, 81.98; H, 7.03; N, 5.07.
1
for X-ray analysis were obtained from a THF/hexane solution. H
NMR (400 MHz, C6D6, 25 °C): δ 7.92−7.87 (m, 4 H, o-PPh2), 7.42−
7.40 (m, 2H, ArH), 7.16 (m, 1H, ArH), 7.12−7.07 (m, 7H, ArH), 7.01
(m, 2H, ArH), 6.95−6.86 (m, 3H, ArH), 6.80 (m, 2H, ArH), 6.69 (m,
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H3-
2,6-iPr2) (HL4). Following a similar procedure to that described for
the preparation of ligand HL1, the ligand HL4 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 2.44 g (12 mmol) of (2,6-iPr2−C6H3)N3 as a pale
2
2H, ArH), 3.92 (d, JP−H = 22.9 Hz, 1H, PCH), 3.60 (m, 4H, THF),
2.17−2.10 (m, 8H, β-nBu and C6H3(CH3)2), 1.81 (m, 2H, γ-nBu), 1.24
3
(t, JH−H = 7.3 Hz, 3H, δ-nBu), 1.17 (m, 4H, THF), 0.29 (m, 2H,
1
yellow solid (4.72 g, 81%). H NMR (400 MHz, CDCl3, 25 °C): δ
α-nBu). 13C NMR (100 MHz, C6D6, 25 °C): δ 174.97 (s, N-C), 150.20
(C-Ar), 149.92 (d, JPC = 7.1 Hz, ipso-PPh2), 143.58 (d, JPC = 15.4 Hz,
ipso-PPh2), 133.90 (C-Ar), 133.28 (d, JPC = 9.6 Hz, C-Ar), 133.00 (C-
Ar), 132.77 (C-Ar), 131.34 (d, JPC = 2.6 Hz, C-Ar), 128.93 (C-Ar),
128.48 (C-Ar), 128.39 (C-Ar), 128.37 (C-Ar), 128.23 (C-Ar), 128.06
(C-Ar), 127.46 (C-Ar), 123.98 (d, JPC = 13.9 Hz, C-Ar), 122.76 (C-
Ar), 119.74 (C-Ar), 69.66 (d, JPC = 132.8 Hz, PCH), 68.55 (THF),
33.65 (δ-nBu), 32.34 (γ-nBu), 25.40 (THF), 19.88 (C6H3(CH3)2),
14.88 (β-nBu), 9.93 (α-nBu). 31P NMR (162 MHz, C6D6, 25 °C): δ
33.28 ppm (s). Anal. Calcd for C88H102Mg2N4O3P2: C, 76.91; H, 7.48;
N, 4.08. Found: C, 76.68; H, 7.42; N, 4.05.
10.35 (br, 1H, NH), 7.71−7.66 (m, 4H, ArH), 7.43−7.35 (m, 6H,
ArH), 7.42−7.29 (m, 2H, ArH), 7.21−7.14 (m, 4H, ArH), 6.91−6.89
(m, 2H, ArH), 6.80−6.78 (m, 3H, ArH), 4.56 (d, 2JP−H = 22.1 Hz, 1H,
3
PCH), 3.45 (sept, JH−3H = 6.9 Hz, 2H, CHMe2), 2.04 (s, 6H,
C6H3(CH3)2), 0.76 (d, JH−H = 6.9 Hz, 6H, C6H3(CH(CH3)2)2. 31P
NMR (162 MHz, CDCl3, 25 °C): δ −3.63 ppm (s). Anal. Calcd for
C40H43N2P: C, 82.44; H, 7.44; N, 4.81. Found: C, 82.56; H, 7.35; N,
4.77.
Synthesis of 2,6-Me2-C6H3NHC(Ph)CHP(Ph2)N(C6H4-2-
OMe) (HL5). Following a similar procedure to that described for the
preparation of ligand HL1, the ligand HL5 was isolated from the
Staudinger reaction of 4.07 g (10 mmol) of 2,6-Me2-C6H3N
C(Ph)CH2PPh2 and 1.79 g (12 mmol) of (2-OMe-C6H4)N3 as a
Synthesis of L2MgnBu(THF) (2). Following a similar procedure to
that described for the preparation of complex 1, complex 2 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
mmol) and HL2 (0.526 g, 1 mmol in 10 mL of THF) as a yellow solid
1
yellow solid (4.66 g, 81%). H NMR (400 MHz, CDCl3, 25 °C): δ
11.34 (s, 1H, NH), 7.88−7.83 (m, 4H, ArH), 7.49−7.41 (m, 5H,
F
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(0.359 g, 53%). Single crystals suitable for X-ray analysis were obtained
from a THF/hexane solution. H NMR (400 MHz, C6D6, 25 °C): δ
mmol) and HL5 (0.528 g, 1 mmol in 10 mL of THF) as a pale yellow
solid (0.531 g, 78%). Single crystals suitable for X-ray analysis were
obtained from a THF/hexane solution. 1H NMR (400 MHz, C6D6, 25
°C): δ 8.01−7.96 (m, 4H, o-PPh2), 7.30−7.28 (m, 2H, ArH), 7.16 (m,
1H, ArH), 7.11−7.10 (m, 5H, ArH), 6.92−6.74 (m, 7H, ArH), 6.67−
6.58 (m, 2H, ArH), 6.42−6.40 (m, 1H, ArH), 4.08 (d, 2JP−H = 24.5 Hz,
1H, PCH), 3.55 (m, 4H, THF), 3.25 (s, 3H, −OMe), 2.02 (s, 6H,
C6H3(CH3)2), 1.73 (m, 2H, β-nBu), 1.58 (m, 2H, γ-nBu), 1.38 (m, 4H,
1
7.87−7.86 (m, 4H, o-PPh2), 7.72−7.70 (m, 2H, ArH), 7.16 (m, 1H,
ArH), 7.11−7.05 (m, 5H, ArH), 7.02−6.95 (m, 2H, ArH), 6.95−6.90
(m, 1H, ArH), 6.86 (m, 4H, ArH), 6.82−6.75 (m, 1H, ArH), 6.71 (m,
2
1H, ArH), 3.70 (d, JP−H = 20.7 Hz, 1H, PCH), 3.15 (m, 4H, THF),
2.57 (s, 6H, PNC6H3(CH3)2), 2.13 (s, 6H, C6H3(CH3)2), 1.88 (m,
3
2H, γ-nBu), 1.34 (t, JH−H = 7.3 Hz, 3H, δ-nBu), 0.99 (m, 4H, THF),
0.26 (m, 2H, α-nBu). 13C NMR (100 MHz, C6D6, 25 °C): δ 176.01 (s,
N-C), 150.85 (C-Ar), 146.11 (d, JPC = 9.8 Hz, ipso-PPh2), 144.68 (d,
JPC = 16.0 Hz, ipso-PPh2), 136.34 (d, JPC = 6.3 Hz, C-Ar), 132.77 (d,
JPC = 9.1 Hz, C-Ar), 130.88 (d, JPC = 2.4 Hz, C-Ar), 128.72 (C-Ar),
128.69 (C-Ar), 128.57 (C-Ar), 128.54 (C-Ar), 128.44 (C-Ar), 128.15
(C-Ar), 127.94 (C-Ar), 127.59 (C-Ar), 122.49 (C-Ar), 122.44 (C-Ar),
68.87 (THF), 66.60 (d, JPC = 133.4 Hz, PCH), 33.99 (δ-nBu), 32.92
(γ-nBu), 24.90 (THF), 20.95 (C6H3(CH3)2), 20.58 (C6H3(CH3)2),
14.80 (β-nBu), 10.94 (α-nBu). 31P NMR (162 MHz, C6D6, 25 °C): δ
29.35 ppm (s). Anal. Calcd for C44H51MgN2OP: C, 77.81; H, 7.57; N,
4.12. Found: C, 77.63; H, 7.62; N, 4.08.
THF), 1.16 (t, 3JH−H = 7.2 Hz, 3H, δ-nBu), −0.30 (m, 2H, α-nBu). 13
C
NMR (100 MHz, C6D6, 25 °C): δ 174.94 (d, JPC = 3.1 Hz, N-C),
151.03 (d, JPC = 15.8 Hz, C-Ar), 149.25 (C-Ar), 143.71 (d, JPC = 15.2
Hz, C-Ar), 139.77 (d, JPC = 4.7 Hz, C-Ar), 133.61 (C-Ar), 132.70 (C-
Ar), 132.59 (d, JPC = 9.8 Hz, C-Ar), 131.76 (d, JPC = 2.5 Hz, C-Ar),
128.98 (d, JPC = 11.7 Hz, C-Ar), 127.67 (C-Ar), 127.38 (C-Ar), 123.02
(d, JPC = 43.4 Hz, C-Ar), 121.47 (d, JPC = 10.0 Hz, C-Ar), 118.71 (C-
Ar), 110.33 (C-Ar), 68.03 (THF), 62.06 (d, JPC = 120.7 Hz, PCH),
55.30 (OCH3), 33.36 (δ-nBu), 32.33 (γ-nBu), 25.59 (THF), 19.70
(C6H3(CH3)2), 14.81 (β-nBu), 8.01 (α-nBu). 31P NMR (162 MHz,
C6D6, 25 °C): δ 31.71 ppm (s). Anal. Calcd for C43H49MgN2O2P: C,
75.82; H, 7.25; N, 4.11. Found: C, 75.67; H, 7.19; N, 4.15.
Synthesis of L3MgnBu(THF) (3). Following a similar procedure to
that described for the preparation of complex 1, complex 3 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
mmol) and HL3 (0.554 g, 1 mmol in 10 mL of THF) as a yellow solid
(0.459 g, 65%). Single crystals suitable for X-ray analysis were obtained
Synthesis of L6MgnBu(THF) (6). Following a similar procedure to
that described for the preparation of complex 1, complex 6 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
mmol) and HL6 (0.533 g, 1 mmol in 10 mL of THF) as a pale yellow
solid (0.431 g, 63%). Single crystals suitable for X-ray analysis were
obtained from a THF/hexane solution. 1H NMR (400 MHz, C6D6, 25
°C): δ 7.97−7.92 (m, 4H, o-PPh2), 7.57−7.55 (m, 2H, ArH), 7.29−
7.27 (m, 1H, ArH), 7.19−7.16 (m, 2H, ArH), 7.10−7.07 (m, 5H,
ArH), 7.01−6.91 (m, 3H, ArH), 6.82−6.81 (m, 2H, ArH), 6.74−6.69
(m, 2H, ArH), 6.51−6.47 (m, 1H, ArH), 3.93 (d, 2JP−H = 22.4 Hz, 1H,
PCH), 3.32 (m, 4H, THF), 2.36 (s, 6H, C6H3(CH3)2), 1.89 (m, 2H,
β-nBu), 1.68 (m, 2H, γ-nBu), 1.21 (t, 3JH−H = 7.3 Hz, 3H, δ-nBu), 1.04
(m, 4H, THF), −0.06 (m, 2H, α-nBu). 13C NMR (100 MHz, C6D6, 25
1
from a THF/hexane solution. H NMR (400 MHz, C6D6, 25 °C): δ
7.87−7.82 (m, 4H, o-PPh2), 7.71−7.68 (m, 2H, ArH), 7.16 (m, 1H,
ArH), 7.11−7.05 (m, 5H, ArH), 7.00−6.97 (m, 5H, ArH), 6.94−6.90
2
(m, 1H, ArH), 6.87 (m, 4H, ArH), 6.72 (m, 1H, ArH), 3.66 (d, JP−H
= 20.6 Hz, 1H, PCH), 3.12 (m, 4H, THF), 2.92 (m, 2H, CH2Me),
2.58 (s, 6H, C6H3(CH3)2), 2.54 (m, 2H, CH2Me), 2.08 (m, 2H,
3
β-nBu), 1.83 (m, 2H, γ-nBu), 1.30 (t, JH−H = 7.3 Hz, 3H, δ-nBu),
0.97−0.92 (m, 10H, THF and CH2CH3), 0.18 (m, 2H, α-nBu). 13C
NMR (100 MHz, C6D6, 25 °C): δ 175.64 (s, N-C), 150.73 (C-Ar),
144.87 (C-Ar), 144.71 (d, JPC = 15.8 Hz, ipso-PPh2), 141.30 (d, JPC
=
°C): δ 174.92 (d, JPC = 2.5 Hz, N−C), 150.28 (C-Ar), 146.80 (d, JPC
=
6.2 Hz, ipso-PPh2), 132.76 (d, JPC = 9.0 Hz, C-Ar), 132.65 (C-Ar),
130.86 (d, JPC = 2.6 Hz, C-Ar), 128.65 (d, JPC = 8.8 Hz, C-Ar), 128.36
(C-Ar), 128.13 (C-Ar), 127.94 (C−Ar), 127.58 (C-Ar), 125.44 (d, JPC
= 3.0 Hz, C-Ar), 69.07 (THF), 66.67 (d, JPC = 133.1 Hz, PCH), 33.87
(δ-nBu), 32.87 (γ-nBu), 25.10 (CH2CH3), 24.82 (THF), 20.36
(C6H3(CH3)2), 14.77 (CH2CH3), 13.96 (β-nBu), 10.46 (α-nBu). 31P
NMR (162 MHz, C6D6, 25 °C): δ 30.01 ppm (s). Anal. Calcd for
C46H55MgN2OP: C, 78.12; H, 7.84; N, 3.96. Found: C, 77.89; H, 7.80;
N, 3.93.
6.6 Hz, C-Ar), 144.40 (d, JPC = 15.5 Hz, C-Ar), 134.44 (C-Ar), 133.50
(C-Ar), 133.19 (C-Ar), 132.76 (d, JPC = 9.6 Hz, C-Ar), 131.29 (d, JPC
= 2.1 Hz, C-Ar), 129.86 (C-Ar), 128.95 (C-Ar), 128.87 (C-Ar), 128.50
(C-Ar), 128.44 (C-Ar), 128.39 (C-Ar), 128.18 (C-Ar), 127.53 (C-Ar),
127.08 (C-Ar), 122.90 (C-Ar), 122.21 (d, JPC = 2.4 Hz, C-Ar), 68.09
(THF), 64.70 (d, JPC = 125.6 Hz, PCH), 33.63 (δ-nBu), 32.58 (γ-nBu),
25.01 (THF), 20.30 (C6H3(CH3)2), 14.78 (β-nBu), 9.81 (α-nBu). 31P
NMR (162 MHz, C6D6, 25 °C): δ 34.66 ppm (s). Anal. Calcd for
C42H46ClMgN2OP: C, 73.58; H, 6.76; N, 4.09. Found: C, 73.76; H,
6.70; N, 4.04.
Synthesis of L4MgnBu(THF) (4). Following a similar procedure to
that described for the preparation of complex 1, complex 4 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
mmol) and HL4 (0.582 g, 1 mmol in 10 mL of THF) as a pale yellow
solid (0.446 g, 61%). Single crystals suitable for X-ray analysis were
obtained from a THF/hexane solution. 1H NMR (400 MHz, C6D6, 25
°C): δ 7.75−7.70 (m, 4H, o-PPh2), 7.76 (m, 2H, ArH), 7.16 (m, 2H,
ArH), 7.06−6.88 (m, 12H, ArH), 6.75 (m, 1H ArH), 3.87 (m, 2H,
CHMe2), 3.69−3.58 (m, 5H, PCH and THF), 2.54 (s, 6H,
C6H3(CH3)2), 1.71−1.51 (m, 4H, β-nBu and γ-nBu), 1.25 (m, 10H,
Synthesis of L7MgnBu(THF) (7). Following a similar procedure to
that described for the preparation of complex 1, complex 7 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
mmol) and HL7 (0.566 g, 1 mmol in 10 mL of THF) as a pale yellow
solid (0.527 g, 73%). Single crystals suitable for X-ray analysis were
obtained from a THF/hexane solution. 1H NMR (400 MHz, C6D6, 25
°C): δ 7.86−7.81 (m, 4H, o-PPh2), 7.42 (s, 1H, ArH), 7.37−7.35 (m,
2H, ArH), 7.13−7.03 (m, 6H, ArH), 6.94−6.85 (m, 4H, ArH), 6.81−
6.75 (m, 3H, ArH), 6.68−6.65 (m, 1H, ArH), 3.92 (d, 2JP−H = 23.5 Hz,
1H, PCH), 3.63 (m, 4H, THF), 2.13−2.02 (m, 8H, β-nBu and
C6H3(CH3)2), 1.84−1.71 (m, 2H, γ-nBu), 1.21 (t, 3JH−H = 7.3 Hz, 3H,
δ-nBu), 1.12 (m, 4H, THF), 0.27 (m, 2H, α-nBu). 13C NMR (100
3
THF and CH(CH3)2), 1.14 (t, JH−H = 6.8 Hz, 3H, δ-nBu), 0.61 (d,
3JH−H = 6.8 Hz, 6H, CH(CH3)2), −0.11 (m, 2H, α-nBu). 13C NMR
(100 MHz, C6D6, 25 °C): δ 175.21 (N-C), 150.61 (C-Ar), 146.03 (d,
MHz, C6D6, 25 °C): δ 175.95 (d, JPC = 2.2 Hz, N-C), 151.22 (d, JPC
=
JPC = 6.4 Hz, C-Ar), 144.68 (d, JPC = 15.9 Hz, C-Ar), 142.51 (d, JPC
=
6.7 Hz, C-Ar), 150.18 (C-Ar), 143.50 (d, JPC = 15.3 Hz, C-Ar), 133.59
(d, JPC = 9.7 Hz, C-Ar), 133.07 (C-Ar), 132.94 (C-Ar), 132.17 (C-Ar),
132.12 (C-Ar), 132.10 (C-Ar), 129.64 (C-Ar), 129.05 (C-Ar), 128.82
(C-Ar), 128.30 (C-Ar), 127.87 (C-Ar), 123.34 (C-Ar), 120.35 (CF3),
115.62 (ipso-C6H4CF3), 69.50 (THF), 69.36 (d, JPC = 132.9 Hz,
PCH), 33.90 (δ-nBu), 32.61 (γ-nBu), 25.43 (THF), 20.08
(C6H3(CH3)2), 15.16 (β-nBu), 10.03 (α-nBu). 31P NMR (162 MHz,
C6D6, 25 °C): δ 34.09 ppm (s). 19F NMR (376 MHz, C6D6, 25 °C): δ
−62.44 ppm (s). Anal. Calcd for C43H46MgN2OPF3: C, 71.82; H,
6.45; N, 3.90. Found: C, 71.97; H, 6.39; N, 3.87.
10.4 Hz, C-Ar), 135.73 (C-Ar), 134.83 (C-Ar), 132.91 (d, JPC = 8.9
Hz, C-Ar), 132.53 (C-Ar), 130.82 (d, JPC = 2.3 Hz, C-Ar), 128.76 (d,
JPC = 13.3 Hz, C-Ar), 128.53 (C-Ar), 128.18 (C-Ar), 127.94 (C-Ar),
127.63 (C-Ar), 124.20 (d, JPC = 3.2 Hz, C-Ar), 123.84 (d, JPC = 3.7 Hz,
C-Ar), 122.70 (C-Ar), 69.40 (THF), 67.73 (d, JPC = 132.4 Hz, PCH),
33.39 (δ-nBu), 32.73 (γ-nBu), 28.73 (CH(CH3)2), 25.43 (CH(CH3)2),
25.19 (THF), 23.68 (CH(CH3)2), 20.27 (C6H3(CH3)2), 14.53
(β-nBu), 10.10 (α-nBu). 31P NMR (162 MHz, C6D6, 25 °C): δ
31.55 ppm (s). Anal. Calcd for C48H59MgN2OP: C, 78.41; H, 8.09; N,
3.81. Found: C, 78.64; H, 8.01; N, 3.78.
Synthesis of L5MgnBu(THF) (5). Following a similar procedure to
that described for the preparation of complex 1, complex 5 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
Synthesis of L8MgnBu(THF) (8). Following a similar procedure to
that described for the preparation of complex 1, complex 8 was
isolated from the metathesis reaction of MgnBu2 (1.1 mL, 1 M, 1.1
G
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mmol) and HL8 (0.528 g, 1 mmol in 10 mL of THF) as a pale yellow
solid (0.454 g, 67%). Single crystals suitable for X-ray analysis were
obtained from a THF/hexane solution. 1H NMR (400 MHz, C6D6, 25
°C): δ 7.94−7.89 (m, 4H, o-PPh2), 7.45 (m, 2H, ArH), 7.16 (m, 1H,
ArH), 7.12−7.10 (m, 6H, ArH), 7.07−6.99 (m, 2H, ArH), 6.96−6.87
(m, 3H, ArH), 6.83−6.81 (m, 2H, ArH), 6.72−6.68 (m, 1H, ArH),
1996, 8, 305. (f) Tschan, M. J. L.; Brule, E.; Haquette, P.; Thomas, C.
M. Polym. Chem. 2012, 3, 836.
(2) (a) Uhrich, K. E.; Cannizzaro, S. M.; Langer, R. S.; Shakesheff, K.
M. Chem. Rev. 1999, 99, 3181. (b) Kowalski, A.; Duda, A.; Penczek, S.
Macromolecules 2000, 33, 689.
(3) (a) Zhao, W.; Cui, D. M.; Liu, X. L.; Chen, X. S. Macromolecules
2010, 43, 6678. (b) Zhao, W.; Wang, Y.; Liu, X. L.; Chen, X. S.; Cui,
D. M. Chem. Asian J. 2012, 7, 2403. (c) Zhao, W.; Wang, Y.; Liu, X. L.;
Chen, X. S.; Cui, D. M.; Chen, E. Y. X. Chem. Commun. 2012, 48,
6375. (d) Stanford, M. J.; Dove, A. P. Chem. Soc. Rev. 2010, 39, 486.
(e) Jeske, R. C.; DiCiccio, A. M.; Coates, G. W. J. Am. Chem. Soc.
2007, 129, 11330. (f) Robert, C.; de Montigny, F.; Thomas, C. M.
Nat. Commun. 2011, 2, 6.
(4) (a) Luo, Y. J.; Li, W. Y.; Lin, D.; Yao, Y. M.; Zhang, Y.; Shen, Q.
Organometallics 2010, 29, 3507. (b) Zhang, Z. J.; Xu, X. P.; Li, W. Y.;
Yao, Y. M.; Zhang, Y.; Shen, Q.; Luo, Y. J. Inorg. Chem. 2009, 48, 5715.
(c) Chuang, H. J.; Chen, H. L.; Ye, J. L.; Chen, Z. Y.; Huang, P. L.;
Liao, T. T.; Tsai, T. E.; Lin, C. C. J. Polym. Sci., Part A: Polym. Chem.
2013, 51, 696. (d) Bakewell, C.; Cao, T. P. A.; Long, N.; Le Goff, X.
F.; Auffrant, A.; Williams, C. K. J. Am. Chem. Soc. 2012, 134, 20577.
(e) Zhang, Z. C.; Cui, D. M. Chem.Eur. J. 2011, 17, 11520.
(f) Arnold, P. L.; Buffet, J. C.; Blaudeck, R. P.; Sujecki, S.; Blake, A. J.;
Wilson, C. Angew. Chem., Int. Ed. 2008, 47, 6033. (g) Liu, X. L.; Shang,
X. M.; Tang, T.; Hu, N. H.; Pei, F. K.; Cui, D. M.; Chen, X. S.; Jing, X.
B. Organometallics 2007, 26, 2747. (h) Amgoune, A.; Thomas, C. M.;
Roisnel, T.; Carpentier, J. F. Chem.Eur. J. 2006, 12, 169.
(5) (a) Drouin, F.; Whitehorne, T. J.; Schaper, F. Dalton Trans. 2011,
40, 1396. (b) Li, D. F.; Li, S. H.; Cui, D. M.; Zhang, X. Q.
Organometallics 2010, 29, 2186. (c) Helou, M.; Miserque, O.; Brusson,
J. M.; Carpentier, J. F.; Guillaume, S. M. Macromol. Rapid Commun.
2009, 30, 2128. (d) Ayala, C. N.; Chisholm, M. H.; Gallucci, J. C.;
Krempner, C. Dalton Trans. 2009, 9237. (e) Chisholm, M. H.;
Phomphrai, K. Inorg. Chim. Acta 2003, 350, 121. (f) Dove, A. P.;
Gibson, V. C.; Marshall, E. L.; White, A. J. P.; Williams, D. J. Dalton
Trans. 2004, 570. (g) Sanchez-Barba, L. F.; Hughes, D. L.; Humphrey,
S. M.; Bochmann, M. Organometallics 2006, 25, 1012. (h) Chisholm,
M. H.; Huffman, J. C.; Phomphrai, K. J. Chem. Soc., Dalton Trans.
2001, 222.
(6) (a) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev.
2002, 102, 3031. (b) Cheng, M.; Moore, D. R.; Reczek, J. J.;
Chamberlain, B. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc.
2001, 123, 8738.
(7) (a) Cheng, M.; Attygalle, A. B.; Lobkovsky, E. B.; Coates, G. W. J.
Am. Chem. Soc. 1999, 121, 11583. (b) Chamberlain, B. M.; Cheng, M.;
Moore, D. R.; Ovitt, T. M.; Lobkovsky, E. B.; Coates, G. W. J. Am.
Chem. Soc. 2001, 123, 3229.
(8) (a) Chisholm, M. H.; Gallucci, J.; Phomphrai, K. Inorg. Chem.
2002, 41, 2785. (b) Chisholm, M. H.; Choojun, K.; Gallucci, J. C.;
Wambua, P. M. Chem. Sci. 2012, 3, 3445. (c) Chisholm, M. H.;
Choojun, K.; Chow, A. S.; Fraenkel, G. Angew Chem., Int. Ed. 2013, 52,
3264.
(9) (a) Wooles, A. J.; Cooper, O. J.; McMaster, J.; Lewis, W.; Blake,
A. J.; Liddle, S. T. Organometallics 2010, 29, 2315. (b) Hill, M. S.;
Hitchcock, P. B. Chem. Commun. 2003, 1758. (c) Hill, M. S.;
Hitchcock, P. B. Dalton Trans. 2003, 4570. (d) Hill, M. S.; Hitchcock,
P. B. J. Chem. Soc., Dalton Trans. 2002, 4694. (e) Aparna, K.; Ferguson,
M.; Cavell, R. G. J. Am. Chem. Soc. 2000, 122, 726.
2
6.63−6.61 (m, 2H, ArH), 3.89 (d, JP−H = 22.3 Hz, 1H, PCH), 3.58
(m, 4H, THF), 3.23 (s, 3H, OMe), 2.23 (s, 6H, C6H3(CH3)2), 2.11
(m, 2H, β-nBu), 1.81 (m, 2H, γ-nBu), 1.22 (m, 7H, THF and δ-nBu),
0.24 (m, 2H, α-nBu). 13C NMR (100 MHz, C6D6, 25 °C): δ 174.69 (d,
JPC = 2.1 Hz, N-C), 154.23 (C-Ar), 150.44 (C-Ar), 143.91 (d, JPC
=
15.7 Hz, C-Ar), 142.40 (d, JPC = 7.8 Hz, C-Ar), 134.65 (C-Ar), 133.75
(C-Ar), 133.21 (d, JPC = 9.5 Hz, C-Ar), 132.84 (C-Ar), 131.22 (d, JPC
= 2.1 Hz, C-Ar), 128.42 (C-Ar), 127.45 (C-Ar), 125.68 (d, JPC = 11.9
Hz, C-Ar), 122.70 (C-Ar), 114.42 (C-Ar), 69.29 (d, JPC = 132.8 Hz,
PCH), 68.57 (THF), 54.93 (OCH3), 33.69 (δ-nBu), 32.41 (γ-nBu),
25.38 (THF), 20.04 (C6H3(CH3)2), 14.91 (β-nBu), 9.80 (α-nBu). 31P
NMR (162 MHz, C6D6, 25 °C): δ 33.74 ppm (s). Anal. Calcd for
C43H49MgN2O2P: C, 75.82; H, 7.25; N, 4.11. Found: C, 75.72; H,
7.14; N, 4.07.
Polymerization of rac-Lactide. A typical procedure for polymer-
ization of rac-LA was performed in a 25 mL round flask in a glovebox.
To a stirred solution of rac-LA (0.288 g, 2 mmol) in 4 mL of THF was
added a THF solution (1 mL) of complex 1 (6.5 mg, 10 μmol, [LA]/
[Mg] = 200:1, [LA] = 0.4 mol/L). The polymerization took place
immediately at room temperature. The system became viscous in a few
minutes, was kept stirring for 10 min, and then was terminated by 0.5
mL of ethanol. The viscous solution was quenched by an excess
amount of ethanol, filtered, washed with ethanol, and then dried at 40
°C for 24 h in vacuo to give polymer product (0.271 g, 94%). The
molecular weight and the molecular weight distribution of the
resulting polymer were determined by GPC. The tacticity of the
PLA was calculated according to the methine region homonuclear
1
decoupling H NMR spectrum.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 13C, and 31P NMR spectra of all complexes, homonuclear
1
decoupling H NMR spectrum for resulting PLA, and X-ray
structures of complexes 2−4 as well as the crystallographic data
for complexes 1−5. This material is available free of charge via
the Internet at http://pubs.acs.org. Crystallographic data can
also be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif using accession codes CCDC-965841 (1), 965842
(2), 965843 (3), 965844 (4), and 965845 (5).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: dmcui@ciac.ac.cn. Fax: +86 431 85262774. Tel: +86
431 85262773.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(10) (a) Ma, W. A.; Wang, L.; Wang, Z. X. Dalton Trans. 2011, 40,
4669. (b) Chen, W.; Cai, Y.; Fu, X.; Liu, X.; Lin, L.; Feng, X. Org. Lett.
2011, 13, 4910. (c) Li, D. F.; Li, S. H.; Cui, D. M.; Zhang, X. Q. J.
Organomet. Chem. 2010, 695, 2781. (d) Li, D. F.; Li, S. H.; Wu, C. J.;
Yao, C. G.; Cui, D. M. Acta Polym. Sin. 2013, 649.
■
This work was partially supported by The National Natural
Science Foundation of China for project nos. 21374112,
2136114037, and 51321062.
(11) (a) Ma, H. Y.; Okuda, J. Macromolecules 2005, 38, 2665.
(b) Stevels, W. M.; Ankone, M. J. K.; Dijkstra, P. J.; Feijen, J.
Macromolecules 1996, 29, 6132. (c) Williams, C. K.; Breyfogle, L. E.;
Choi, S. K.; Nam, W.; Young, V. G.; Hillmyer, M. A.; Tolman, W. B. J.
Am. Chem. Soc. 2003, 125, 11350. (d) Chisholm, M. H.; Eilerts, N. W.;
Huffman, J. C.; Iyer, S. S.; Pacold, M.; Phomphrai, K. J. Am. Chem. Soc.
2000, 122, 11845. (e) Chisholm, M. H.; Eilerts, N. W. Chem. Commun.
REFERENCES
■
(1) (a) Yao, K. J.; Tang, C. B. Macromolecules 2013, 46, 1689.
(b) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. Rev.
2004, 104, 6147. (c) Drumright, R. E.; Gruber, P. R.; Henton, D. E.
Adv. Mater. 2000, 12, 1841. (d) Jeong, B.; Bae, Y. H.; Lee, D. S.; Kim,
S. W. Nature 1997, 388, 860. (e) Chiellini, E.; Solaro, R. Adv. Mater.
H
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1996, 853. (f) Wang, Y.; Zhao, W.; Liu, D. T.; Li, S. H.; Liu, X. L.; Cui,
D. M.; Chen, X. S. Organometallics 2012, 31, 4182. (g) Sung, C. Y.; Li,
C. Y.; Su, J. K.; Chen, T. Y.; Lin, C. H.; Ko, B. T. Dalton Trans. 2012,
41, 953. (h) Liu, Y. C.; Ko, B. T.; Lin, C. C. Macromolecules 2001, 34,
6196. (i) Kowalski, A.; Duda, A.; Penczek, S. Macromolecules 1998, 31,
2114.
(12) (a) Chen, H. Y.; Huang, B. H.; Lin, C. C. Macromolecules 2005,
38, 5400. (b) Chisholm, M. H.; Gallucci, J. C.; Phomphrai, K. Inorg.
Chem. 2005, 44, 8004. (c) Tang, Z.; Chen, X.; Pang, X.; Yang, Y.;
Zhang, X.; Jing, X. Biomacromolecules 2004, 5, 965. (d) Nomura, N.;
Ishii, R.; Akakura, M.; Aoi, K. J. Am. Chem. Soc. 2002, 124, 5938.
(13) (a) Song, S. D.; Ma, H. Y.; Yang, Y. Dalton Trans. 2013, 42,
14200. (b) Wang, L. Y.; Ma, H. Y. Macromolecules 2010, 43, 6535.
(c) Wheaton, C. A.; Hayes, P. G.; Ireland, B. J. Dalton Trans. 2009,
4832. (d) Huang, Y.; Hung, W. C.; Liao, M. Y.; Tsai, T. E.; Peng, Y. L.;
Lin, C. C. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 2318.
(e) Garces, A.; Sanchez-Barba, L. F.; Fernandez-Baeza, J.; Otero, A.;
Honrado, M.; Lara-Sanchez, A.; Rodriguez, A. M. Inorg. Chem. 2013,
52, 12691.
(14) Yu, X.-F.; Zhang, C.; Wang, Z.-X. Organometallics 2013, 32,
3262.
(15) (a) Johnson, K. R. D.; Hannon, M. A.; Ritch, J. S.; Hayes, P. G.
Dalton Trans. 2012, 41, 7873. (b) Johnson, K. R. D.; Hayes, P. G.
Organometallics 2011, 30, 58.
(16) (a) Masuda, J. D.; Walsh, D. M.; Wei, P. R.; Stephan, D. W.
Organometallics 2004, 23, 1819. (b) Masuda, J. D.; Wei, P. R.; Stephan,
D. W. Dalton Trans. 2003, 3500.
(17) (a) Rong, W. F.; Liu, D. T.; Zuo, H. P.; Pan, Y. P.; Jian, Z. B.; Li,
S. H.; Cui, D. M. Organometallics 2013, 32, 1166. (b) Liu, D. T.; Cui,
D. M. Dalton Trans. 2011, 40, 7755. (c) Li, S. H.; Cui, D. M.; Li, D. F.;
Hou, Z. M. Organometallics 2009, 28, 4814. (d) Wang, D.; Li, S. H.;
Liu, X. L.; Gao, W.; Cui, D. M. Organometallics 2008, 27, 6531. (e) Li,
S. H.; Miao, W.; Tang, T.; Dong, W. M.; Zhang, X. Q.; Cui, D. M.
Organometallics 2008, 27, 718.
(18) (a) Bouyahyi, M.; Ajellal, N.; Kirillov, E.; Thomas, C. M.;
Carpentier, J.-F. Chem.Eur. J. 2011, 17, 1872. (b) Ma, H.; Spaniol,
T. P.; Okuda, J. Inorg. Chem. 2008, 47, 3328. (c) Ma, H.; Spaniol, T.
P.; Okuda, J. Angew. Chem. 2006, 118, 7982. (d) Wang, H.; Ma, H.
Chem. Commun. 2013, 49, 8686.
(19) Sanchez-Barba, L. F.; Garces, A.; Fernandez-Baeza, J.; Otero, A.;
Alonso-Moreno, C.; Lara-Sanchez, A.; Rodriguez, A. M. Organo-
metallics 2011, 30, 2775.
(20) Breyfogle, L. E.; Williams, C. K.; Young, V. G.; Hillmyer, M. A.;
Tolman, W. B. Dalton Trans. 2006, 928.
(21) (a) Pilyugina, T. S.; Schrock, R. R.; Hock, A. S.; Muller, P.
Organometallics 2005, 24, 1929. (b) Liu, Q.; Tor, Y. Org. Lett. 2003, 5,
2571. (c) Murata, S.; Abe, S.; Tomioka, H. J. Org. Chem. 1997, 62,
3055. (d) Ugi, I.; Perlinger, H.; Behringer, L. Chem. Ber. Recl. 1958, 91,
2330.
I
dx.doi.org/10.1021/om401056s | Organometallics XXXX, XXX, XXX−XXX