Magnesium and Zinc Complexes Supported by N,N,O Tridentate Ligands: Synthesis and Catalysis in the Ring-Opening Polymerization of rac-Lactide and α-Methyltrimethylene Carbonate

Article abstract of DOI:10.1002/ejic.201600441

A series of racemic biphenyl- or binaphthyl-based aminophenols were treated with 1 equiv. of Mg[N(SiMe₃)₂]₂or Zn[N(SiMe₃)₂]₂to provide eight heteroleptic magnesium and zinc silylamido complexes (Mg, 1a–5a; Zn, 1b, 3b, 5b). Single-crystal X-ray diffraction studies on typical magnesium complex 5a and zinc complexes 1b, 3b, and 5b showed a tridentate chelating mode of the ligand and a distorted tetrahedral geometry around the metal center. All of these complexes proved to be efficient initiators for the ring-opening polymerization of rac-lactide in toluene and THF. Microstructure analysis of the resultant poly(rac-lactide) samples by homonuclear-decoupled¹H NMR spectroscopy revealed heterotacticities ranging from 0.45 to 0.69. These complexes were also applied as initiators in the polymerization of racemic α-methyltrimethylene carbonate in toluene and exhibited moderate to high regioselectivities; the most regioregular polymer was obtained with magnesium complex 4a (X_reg= 0.93).

Full text of DOI:10.1002/ejic.201600441

DOI: 10.1002/ejic.201600441
Full Paper
Ring-Opening Polymerization
Magnesium and Zinc Complexes Supported by N,N,O Tridentate
Ligands: Synthesis and Catalysis in the Ring-Opening
Polymerization of rac-Lactide and α-Methyltrimethylene
Carbonate
[
a]
[a]
Miao Huang and Haiyan Ma*
Abstract: A series of racemic biphenyl- or binaphthyl-based lactide in toluene and THF. Microstructure analysis of the result-
aminophenols were treated with 1 equiv. of Mg[N(SiMe ) ] or ant poly(rac-lactide) samples by homonuclear-decoupled 1
H
3
2 2
Zn[N(SiMe ) ] to provide eight heteroleptic magnesium and NMR spectroscopy revealed heterotacticities ranging from 0.45
3
2 2
zinc silylamido complexes (Mg, 1a–5a; Zn, 1b, 3b, 5b). Single- to 0.69. These complexes were also applied as initiators in the
crystal X-ray diffraction studies on typical magnesium complex polymerization of racemic α-methyltrimethylene carbonate in
5
a and zinc complexes 1b, 3b, and 5b showed a tridentate toluene and exhibited moderate to high regioselectivities; the
chelating mode of the ligand and a distorted tetrahedral geom- most regioregular polymer was obtained with magnesium com-
etry around the metal center. All of these complexes proved to plex 4a (Xreg = 0.93).
be efficient initiators for the ring-opening polymerization of rac-
Introduction
hanced thermal properties.[8–10] Nevertheless, the generally low
activity of aluminum initiators restricts their practical applica-
tions to some extent. Under these circumstances, the high ac-
tivity of magnesium and zinc species, coupled with the nontox-
icity and low cost of these elements, attracted our attention.
Although the stereoselectivity control in the ROP of rac-LA initi-
ated by magnesium and zinc initiators is still not well estab-
lished, it is expected that these elements will provide good po-
tential to afford highly isoselective and active initiators, since a
few magnesium complexes with high heteroselectivity and zinc
complexes with high hetero-/isoselectivity towards the ROP of
rac-LA have been reported. For instance, magnesium complexes
bearing phosphinimino amine ligands showed high heterose-
Polylactides (PLAs) and poly(α-methyltrimethylene carbonate)s
[
P(α-MeTMC)s], as important biodegradable and biocompatible
polymers, are considered to be ideal alternatives to petroleum-
[
1,2]
based plastics.
The applications of these polymers are inti-
mately related to their microstructures, and the ring-opening
polymerization (ROP) of the corresponding cyclic monomers in
racemic form catalyzed by metal-based initiators is the most
efficient route to obtain PLAs and P(α-MeTMC)s with predicta-
ble molecular weights, narrow molecular weight distributions,
[
3,4]
and stereo-/regiotacticities.
Hence, designing well-defined
metal catalysts to prepare PLAs or P(α-MeTMC)s with specific
architectures has become a major focus of attention in recent
years.
[
51]
lectivity (P = 0.98). Zinc ꢀ-diketiminate complexes exhibited
r
[
52]
high heteroselectivity (P = 0.87), and amido-oxazolinate zinc
silylamido complexes showed high isoselectivity (Pm = 0.91).
r
A large number of metal complexes based predominantly
[
53]
[
5–7]
[8–15]
(
but not exclusively) on alkali metals,
aluminum,
Currently, more and more efforts are being devoted to the de-
velopment of new stereoselective zinc and magnesium initia-
tors, particularly those that can produce isotactic PLAs from rac-
LA.
[
16,17]
[18–20]
[21,22]
[23–35]
iron,
zinc,
titanium,
zirconium,
magnesium,
[
30–42]
[43–46]
[47–50]
calcium,
and trivalent lanthanides
have
been reported to be effective catalysts/initiators for the ROP of
lactides. Among them, aluminum complexes, especially those
supported by salen-type ligands and their derivatives, exhibit
satisfactory isoselectivities toward rac-lactide (rac-LA) polymeri-
zation, which is highly desired for obtaining PLAs with en-
Polycarbonates are another type of biobased aliphatic poly-
esters. Various discrete metal complexes have been employed
[
54–57]
in the ROP of trimethylene carbonate (TMC),
but the po-
lymerization of similar chiral cyclic carbonates, such as α-
MeTMC, has seldom been explored. Yasuda and co-workers re-
ported the ROP of (R)-α-MeTMC catalyzed by various types of
initiators, such as AlEt –H O, Sn(Oct) , [(C Me ) Sm(thf) ], and
[
a] Shanghai Key Laboratory of Functional Materials Chemistry and
Laboratory of Organometallic Chemistry, East China University of Science
and Technology,
3
2
2
5
5 2
2
1
30 Meilong Road, Shanghai 200237, P. R. China
[58]
[
(C Me ) SmMe(thf)], in toluene.
Rare earth metal alkoxides
5
5 2
E-mail: haiyanma@ecust.edu.cn
or aryloxides [“Ln(OiPr) ”; Ln(OAr) , Ar = 2,6-di-tert-butyl-4-
3
3
http://webmanage.ecust.edu.cn/s/230/t/262/a/57290/info.jspy
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejic.201600441.
methylphenolate; Ln = La, Dy, Y] were also reported for the
polymerization of this monomer, which afforded polycarbon-
Eur. J. Inorg. Chem. 2016, 3791–3803
3791
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
ates with high molecular weights and moderate polydispersi- tained biphenyl- and binaphthyl-based aminophenols are color-
ties.[ [(BDIiPr)ZnN(SiMe ) ] can also effectively initiate the ROP less crystalline solids, which were characterized via H and
59]
1
13
C
3
2
[
60]
[63]
of α-MeTMC and shows high regioselectivity (Xreg > 0.98). We NMR spectroscopy and elemental analysis.
reported a series of magnesium silylamido complexes bearing
biphenyl-based iminophenolate ligands, which showed moder-
ate activities for the ROP of α-MeTMC, affording regioregular
[
61]
polymers (Xreg = 0.65–0.86).
Nevertheless, in comparison
with catalyst systems for rac-LA polymerization, those involved
in α-MeTMC polymerization are still rather limited.
Previously, we synthesized a series of magnesium and zinc
silylamido complexes supported by racemic binaphthyl-based
iminophenolate ligands, which showed moderate heteroselect-
5
Scheme 2. Synthesis of proligand L H. (a) LiAlH
HOAc, 70 °C. (c) Et N, THF, room temp.
4
n
, THF, reflux. (b) (HCHO) , HBr,
ivities toward the polymerization of rac-LA (P = 0.72–0.84) and
r
3
moderate to high regioselectivities toward the polymerization
[
62]
of racemic α-MeTMC (Xreg = 0.78–0.98).
The NMe group on
2
The heteroleptic magnesium silylamido complexes 1a–5a
the binaphthyl ring of these complexes is dissociated from the
metal center in solution, and this is considered to weaken the
chiral induction effect of the binaphthyl moiety during the po-
lymerization. Therefore, in this work we synthesized an array of
magnesium and zinc complexes derived from relatively flexible
aminophenolate ligands based on two types of chiral back-
bones (racemic dimethylaminobiphenyl and dimethylaminobi-
naphthyl backbones), which proved to wrap around the metal
center in a more efficient manner. Detailed data concerning
their catalytic behavior toward the polymerization of rac-LA and
racemic α-MeTMC are presented.
were prepared by reaction of Mg[N(SiMe ) ] with 1 equiv.of
3
2 2
–5
the corresponding aminophenol proligands L1 H in toluene at
ambient temperature via an amine-elimination route
[
64]
(Scheme 3).
Colorless crystalline solids were obtained after
recrystallization from toluene/n-hexane at room temp. Al-
though these magnesium complexes have two stereogenic cen-
ters (the skeleton N atom and the metal center) in addition to
the chiral biphenyl or binaphthyl moiety, only a pair of enantio-
mers was formed, as evidenced by the appearance of a single
set of resonances corresponding to the stoichiometric struc-
tures of these complexes.
Similar reactions of proligands L1–5H with Zn[N(SiMe ) ]
3
2 2
were carried out to synthesize the corresponding zinc com-
plexes (Scheme 3). Zinc silylamido complexes 1b, 3b, and 5b
Results and Discussion
[
64]
The synthetic strategies for the biphenyl-based aminophenol could be isolated as colorless solids in moderate yields. Unex-
1
–4
2,4
proligands L H are summarized in Scheme 1. The synthesis pectedly, the reactions of equimolar amounts of L H and
of N′,N′-dimethyl-1,1′-biphenyl-2,2′-diamine was based on a Zn[N(SiMe
) ] gave a mixture of mono- and bis-ligated com-
3 2 2
modified procedure.[ Then acetylation of this diamine fol- plexes. Exhaustive fractional crystallization failed to afford the
61]
lowed by reduction with LiAlH afforded the corresponding N- target heteroleptic zinc silylamido complexes in pure form. Sim-
4
ethyl-N′,N′-dimethyl-1,1′-biphenyl-2,2′-diamine (see Supporting ilar to the magnesium complexes, no diastereomers could be
1
Information). N-Ethyl-N′,N′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-di- observed in the H NMR spectra of these zinc complexes.
1
amine was synthesized similarly (see Supporting Information).
The H NMR spectra of magnesium complexes 1a–5a and
Coupling reactions of these two N-ethyl-substituted amines zinc complexes 1b, 3b, 5b in C D at room temperature demon-
6
6
with different benzyl bromide derivatives yielded the target strate that the N(CH ) group in the ligand framework is well
3
2
dimethylaminobiphenyl-based aminophenol proligands L1 H. coordinated to the metal center in these complexes. For in-
–4
1
Similar synthetic strategies were adopted to obtain the binaph- stance, in the H NMR spectra, the sharp signal of the N(CH )
3
2
5
1
thyl-based aminophenol proligand L H (Scheme 2). All the ob- protons of the free ligand L H appears at δ = 2.09 ppm, while
1
4
Scheme 1. Synthesis of proligands L H–L H. (a) Ac
temp.
2
O, HOAc, CH
2
Cl
2
, room temp. (b) LiAlH
3792
4 n 3
, THF, reflux. (c) (HCHO) , HBr, HOAc, 70 °C. (d) Et N, THF, room
Eur. J. Inorg. Chem. 2016, 3791–3803
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Scheme 3. Synthesis of magnesium and zinc silylamido complexes.
two signals of N(CH ) protons of complex 1a are observed at Crystallographic Studies
3
2
δ = 2.46 ppm and 1.60 ppm, with one resonance shifted signifi-
cantly to the high-field region. Similar phenomena are also ob- Single crystals of magnesium complex 5a and zinc complexes
1
served in the H NMR spectra of 2a–5a and 1b, 3b, 5b in C D . 1b, 3b, and 5b suitable for X-ray structure determination were
6
6
Therefore, it is conceivable that these magnesium and zinc obtained from saturated solutions in n-hexane/toluene at room
complexes have the same configuration in solution as in the temperature. The crystallographic data and refinement of these
solid state (see below). This is in contrast to our previously re- complexes are listed in Table 1, and the ORTEPs of the molecu-
ported binaphthyl-based iminophenolate magnesium com- lar structures of these complexes are shown in Figures 1, 2, 3,
plexes, for which dissociation of the amino group was wit- and 4.
[
62]
nessed in solution,
and implies the formation of a less flexi-
As shown in Figure 1, complex 5a has a monomeric structure
ble complex geometry in this work.
in the solid state in which the magnesium center is fourfold
Table 1. Crystallographic data and refinement for 5a, 1b, 3b and 5b.
5a
1b
3b
5b
Empirical formula
Formula weight
T [K]
C
55
H
67MgN
3
OSi
2
C
47
H
63
N
3
OSi
2
Zn
C
55
H
81
N
3
OSi
2
Zn
55 67 3 2
C H N OSi Zn
907.66
293(2)
866.60
293(2)
807.55
140(2)
921.78
140(2)
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
0.26 × 0.21 × 0.13
triclinic
P1¯
0.20 × 0.12 × 0.10
triclinic
0.24 × 0.13 × 0.08
triclinic
0.243 × 0.211 × 0.134
triclinic
P1¯
P1¯
P1¯
12.278(2)
15.122(3)
17.749(3)
97.615(4)
100.073(4)
111.948(3)
2937.9(9)
2
13.2300(18)
13.3702(18)
15.751(2)
13.0326(16)
14.5796(18)
16.981(2)
12.252(8)
15.016(10)
17.599(12)
98.158(13)
99.532(14)
112.005(11)
2886(3)
α [°]
80.986(3)
82.522(3)
66.010(2)
2507.2(6)
104.916(2)
103.356(2)
104.166(2)
2870.4(6)
ꢀ
[°]
γ [°]
3
V [Å ]
Z
ρ
2
2
2
calcd. [Mg/m3]
0.980
0.106
932
1.070
0.570
864
1.067
0.505
996
1.045
0.502
968
Absorption coeff. [mm–1]
F (000)
θ range [°]
Data collection (hkl)
Reflections collected/unique 17405/11500
R (int)
1.69 to 26.00
–10 to 15, ±18, ±21
1.31 to 30.78
–18 to 19, ±19, –22 to 17
25780/15378
0.0790
1.53 to 27.00
±16, ±18, –21 to 15
22000/12411
0.0366
1.70 to 25.05
–12 to 14, –17 to 16, –20 to 15
15325/10136
0.0814
0.0352
Max. / min. transmission
Data/restrains/parameters
Goodness of fit on F
1.0000 / 0.0962
11500/14/572
1.036
0.9452 / 0.8945
15378/0/500
0.906
0.9607 / 0.8883
12411/31/576
1.073
1.00000 / 0.2654
10136/24/572
0.965
2
Final R ,wR
1
2
[I > 2σ(I)]
0.0582, 0.1472
0.1081, 0.1687
0.333/–0.266
0.0672, 0.1247
0.1633, 0.1423
0.447/–0.385
0.0561, 0.1683
0.0787, 0.1963
0.661/–0.609
0.0814, 0.1926
0.1454, 0.2202
1.104/–1.029
R
1
, wR (all data)
2
Δρmax./min. [e Å–3
]
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3
3 2
Figure 3. ORTEP of the molecular structure of [(L )ZnN(SiMe ) ] (3b). Thermal
ellipsoids are drawn at 50 % probability. Selected bond lengths [Å] and an-
gles [°]: Zn1–O1 1.917(2), Zn1–N1 2.153(3), Zn1–N2 2.146(3), Zn1–N3 1.940(2);
O1–Zn1–N3 121.18(10), O1–Zn1–N2 93.13(9), N3–Zn1–N2 116.06(11), O1–
Zn1–N1 95.11(9), N3–Zn1–N1 118.64(10), N2–Zn1–N1 108.35(10).
5
3 2
Figure 1. ORTEP of the molecular structure of [(L )MgN(SiMe ) ] (5a). Thermal
ellipsoids are drawn at 50 % probability. Selected bond lengths [Å] and an-
gles [°]: Mg1–O1 1.9245(16), Mg1–N1 2.228(2), Mg1–N2 2.202(2), Mg1–N3
.036(2); O1–Mg1–N3 120.87(9), O1–Mg1–N2 98.94(8), N3–Mg1–N2 115.37(8),
2
O1–Mg1–N1 92.19(7), N3–Mg1–N1 116.62(8), N2–Mg1–N1 109.51(8).
1
Figure 2. ORTEP of the molecular structure of [(L )ZnN(SiMe
3
)
2
] (1b). Thermal
5
Figure 4. ORTEP of the molecular structure of [(L )ZnN(SiMe
3
)
2
] (5b). Thermal
ellipsoids are drawn at 50 % probability. Selected bond lengths [Å] and an-
gles [°]: Zn1–O1 1.918(2), Zn1–N1 2.152(3), Zn1–N2 2.132(3), Zn1–N3 1.933(3);
O1–Zn1–N3 123.31(11), O1–Zn1–N2 95.97(10), N3–Zn1–N2 118.92(12), O1–
Zn1–N1 92.26(10), N3–Zn1–N1 114.53(11), N2–Zn1–N1 107.52(11).
ellipsoids are drawn at 50 % probability. Selected bond lengths [Å] and an-
gles [°]: Zn1–O1 1.935(4), Zn1–N1 2.208(4), Zn1–N2 2.158(5), Zn1–N3 1.945(4);
O1–Zn1–N3 122.68(19), O1–Zn1–N2 96.26(18), N3–Zn1–N2 115.64(19), O1–
Zn1–N1 93.54(17), N3–Zn1–N1 116.93(19), N2–Zn1–N1 108.09(17).
coordinated by three heteroatom donors of the tridentate li- sponding angles around the metal center vary to a great extent
[
62]
gand and one bis(trimethylsilyl)amido group in a distorted tet- in comparison to those in the ref. . Moreover, widening of the
rahedral geometry. In contrast to the iminophenolate ana- dihedral angle of the binaphthyl moiety in 5a [79.2(7)° vs.
[
62]
[62]
logues, the R configuration of the binaphthyl moiety in the 75.7(4) in ref. ] is also observed. All these features suggest
a
ligand leads exclusively to the R configuration of the magne- that the variation of the ligand skeleton from iminophenolate
sium center, and the S configuration to the S configuration. to aminophenolate does have a significant impact on the struc-
a
The Mg1–N2 [2.202(2) Å] and Mg1–N3 [2.034(2) Å] bond lengths tural parameters of the complex.
in complex 5a are comparable to those in the iminophenolate
As depicted in Figures 2, 3, and 4, zinc complexes 1b, 3b,
magnesium analogue bearing the same substituents on the and 5b are also four-coordinate with three heteroatom donors
phenoxide ring [4a in ref.[62], 2.243(6) Å, 2.008(5) Å]. The corre- of the tridentate ligand and one bis(trimethylsilyl)amido group,
Eur. J. Inorg. Chem. 2016, 3791–3803
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in contast to the binaphthyl-based iminophenolate zinc ana-
Compared with the previously reported biphenyl- or binaph-
logue, in which the NMe group of the iminophenolate ligand thyl-based iminophenolate magnesium analogues, the activities
2
[
62]
is not coordinated to zinc center even in the solid state.
of this series of magnesium complexes are significantly im-
Moreover, in comparison with the three-coordinate imino- proved. At 50 °C in toluene, 200 equiv. of lactide monomer
phenolate zinc analogue, the corresponding bond lengths be- could be converted within 40–60 min by magnesium com-
tween the zinc center and the central nitrogen atom in com- plexes 1a–5a, while ca. 120–300 min were need to convert the
plexes 1b, 3b, and 5b are somewhat elongated [2.152–2.206 Å same amount of monomer by the iminophenolate magnesium
vs. 1.969(2) Å], as are the bond lengths between the zinc center analogues at 50 °C or 70 °C.[61,62] This is a general trend for
and the silylamido nitrogen atom [1.933–1.945 Å vs. 1.861(2) Å]. metal complexes bearing aminophenolate versus iminophenol-
The dihedral angles of the biphenyl or binaphthyl moiety are ate ligands.[65–68]
70.1(1), 76.0(4), and 78.1(6)° for 1b, 3b, and 5b respectively, and
As depicted in Table 2, the backbone of the ancillary ligand
are closely related with the rotational hindrance of the back- has a remarkable influence on the catalytic activity of these
bone moiety. Similar to magnesium complex 5a, the R configu- magnesium complexes. In toluene, binaphthyl-based amino-
a
ration of the biphenyl or binaphthyl moiety in the ligand leads phenolate magnesium complex 5a with o,p-cumyl groups on
to the R configuration of the zinc center, and the S configura- the phenolate ring exhibits higher catalytic activity than bi-
a
tion leads to the S configuration.
phenyl-based magnesium complexes 1a and 3a with the same
substituents on the phenolate ring; moreover, complex 1a
shows slightly higher activity than complex 3a with two addi-
tional methyl groups substituting the biphenyl backbone. For
Ring-Opening Polymerization of rac-Lactide
All of the magnesium complexes 1a–5a and zinc complexes 1b, example, complex 5a achieves 94 % monomer conversion
b, 5b are capable of initiating the ROP of rac-LA in the pres- within 30 min in the presence of 2-propanol in toluene at room
3
ence/absence of 2-propanol, producing PLAs with high molecu- temp. (Run 19), whereas complexes 1a and 3a are less active.
lar weights and relatively broad molecular weight distributions High monomer conversions are achieved within 60 min for 1a
(
M /M = 1.16–1.74) in both THF and toluene. Representative (Run 3, 99 %) and within 90 min for 3a (Run 11, 95 %) under
w n
polymerization data are summarized in Table 2.
identical conditions. However, this activity order is reversed in
Table 2. ROP of rac-LA initiated by magnesium and zinc complexes.
/[iPrOH][a]
Solvent
T [°C]
t [min]
Conversion[b] [%]
M
n,calcd. (104)
[c]
M
[d]
(104)
M
/M
[d]
P
r
[e]
Run
Cat.
[LA]
0
/[M]
0
n
w
n
1
2
3
4
5
6
7
8
9
1a
200:1:0
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
toluene
toluene
toluene
thf
25
50
25
25
25
50
25
25
25
50
25
25
25
50
25
25
25
50
25
25
25
50
25
25
25
50
25
25
25
50
25
25
25
930
60
60
30
10
40
20
20
10
60
90
30
10
40
20
20
10
28
90
99
88
89
87
97
88
92
89
95
90
91
84
85
94
93
85
94
85
98
86
87
85
85
76
92
82
80
91
97
71
96
–
–
–
–
2.59
2.85
2.53
2.76
2.51
2.79
2.53
2.65
2.56
2.74
2.59
2.62
2.42
2.45
2.71
2.68
2.45
2.71
2.45
2.82
2.48
2.51
2.45
2.45
2.19
2.65
2.36
2.30
2.62
2.79
2.04
2.76
4.50
2.36
10.9
4.24
1.38
1.76
1.90
2.33
2.17
1.93
2.12
2.25
1.51
1.69
3.20
2.54
4.64
3.21
9.30
2.53
2.16
2.41
5.00
2.09
4.13
1.98
3.89
1.75
3.42
1.93
12.2
3.36
1.40
1.38
1.62
1.66
1.55
1.48
1.50
1.52
1.53
1.44
1.64
1.68
1.56
1.56
1.74
1.40
1.42
1.41
1.54
1.42
1.55
1.43
1.57
1.43
1.51
1.35
1.55
1.39
1.62
1.59
1.45
1.16
0.49
0.47
0.66
0.69
0.47
0.45
0.58
0.62
0.51
0.53
0.65
0.65
0.47
0.47
0.60
0.60
0.51
0.49
0.65
0.62
0.53
0.51
0.58
0.57
0.49
0.47
0.58
0.56
0.53
0.53
0.58
0.55
thf
2a
3a
4a
5a
1b
3b
5b
toluene
toluene
thf
thf
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
toluene
toluene
thf
thf
toluene
toluene
thf
thf
toluene
toluene
thf
40
30
30
20
thf
toluene
toluene
thf
300
180
480
30
300
240
480
30
300
180
420
40
thf
toluene
toluene
thf
thf
toluene
toluene
thf
thf
0 0
= 0.005 M /[M] ) × 144.13 × % conversion. [d] Determined by GPC,
. [b] Determined by 1H NMR spectroscopy. [c] Mn,calcd. = ([rac-LA]
[
a] [rac-LA]
0
= 1.0
M
, [M]
0
–
1
1
Waters M515 pump, 25 °C, 1 mL min , PS standards. [e] Probability of forming a new r diad, determined by homonuclear-decoupled H NMR spectroscopy.
Eur. J. Inorg. Chem. 2016, 3791–3803 www.eurjic.org © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3795

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THF, in which complex 3a is the most active catalyst. It seems tion of the NMe2 group in biphenyl-based iminophenolate
that the influence of the ligand backbone is predominantly magnesium complex could be observed on treatment with
electronic rather than steric. In toluene, the electron-withdraw- 2 equiv. of thf, and the binaphthyl-based iminophenolate mag-
ing effect of the backbone may increase the Lewis acidity of nesium analogue exits with a dissociated NMe
group even in
These results indicate clearly stronger coordination
monomer and therefore enhancement of the activity. However, of the NMe group to the magnesium center in 2a relative to
2
[
61,62]
the metal center, which is favorable for the coordination of
C D .
6 6
2
in THF, the solvent molecules compete with the monomer to the iminophenolate analogues, and this is then suggested to
coordinate to the magnesium center. In this case, the increase be a crucial factor leading to the above-mentioned discrepancy
in Lewis acidity would make the competition more serious, and between the polymerization behaviors of these two systems.
thereby lead to a decrease in activity.
Notably, the competition for coordination to the metal center
between the NMe group and monomer still exists, although
2
Besides the ligand backbone, the substituents, particularly
that at the ortho position of the phenoxide unit, also play an
important role in determining the catalytic activity. Magnesium
complexes bearing an o-trityl substituent on the phenolate ring
the NMe group completely dissociates from the metal center
2
in THF, which decreases the catalytic activity to some extent.
Compared with magnesium complexes 1a–5a, zinc com-
display higher catalytic activity than those with an o-cumyl sub- plexes 1b, 3b, and 5b show significantly lower catalytic activi-
[
61]
stituent.
By using complex 1a with an o-cumyl substituent ties toward the ROP of rac-LA in both solvents. This is normal
as the initiator, a monomer conversion of 99 % can be achieved but in contrast to our previous report on the binaphthyl-based
within 60 min at room temp. (Run 3), whereas complex 2a with iminophenolate analogue, in which the three-coordinate zinc
a sterically bulkier o-trityl group gives 97 % conversion within complex shows higher activity than the corresponding magne-
0 min under otherwise the same conditions (Run 7). Similarly, sium complex in toluene.[62] We attribute this difference to the
2
complex 4a also exhibits higher catalytic activity than complex stable coordination of the NMe group to the zinc center in 1b,
2
3
a. Likely, the introduction of sterically bulkier groups, espe- 3b, and 5b. When a solution of typical zinc complex 1b in C D
6 6
1
cially at the ortho position of the phenoxide oxygen atom, was treated with 1 equiv. of thf, the H NMR spectrum showed
might protect more efficiently the active metal center from ag- that all the resonances remained unchanged (see Figure S3). It
is conceivable that, for this series of complexes, the interaction
gregation and therefore lead to an increase in activity, as is
observed for most of the reported catalyst systems.[
69,70]
2
of the NMe group with the zinc center may be stronger and
In our previous work,[61,70] when the polymerization was car-
less influenced by thf, which accounts for the normal activity
trend observed for these complexes.
ried out in THF, a significant enhancement of the activity to-
ward rac-LA polymerization was observed for magnesium com-
plexes bearing biphenyl-based iminophenolate ligands, espe-
cially for those bearing o-trityl-substituted ligands (monomer
conversions up to 94 % within 1.5–2 min in THF at room temp.
vs. 93–95 % within 120 min in toluene at 70 °C). Moreover, the
addition of 2-propanol led to a remarkable decrease of the cata-
As shown in Table 2, in contrast to the magnesium com-
plexes, the variation of the ligand backbone leads to the same
activity order of 5b > 1b ≥ 3b in both solvents. Probably it is
related to the difference in Lewis acidity between the two ele-
ments. Moreover, zinc complexes also show increased activities
in thf and in the presence of alcohol.
[
61]
lytic activity in THF. However, the enhancement of the activ-
The PLAs produced by magnesium and zinc silylamido com-
ity is not so apparent for the binaphthyl-based iminophenolate plexes have broad polydispersities (M /M = 1.40–1.74) and M
w n n
magnesium complexes, and the addition of 2-propanol to the values that are smaller or larger than the theoretical ones. Two
polymerization mixture in THF also has no obvious influence possibilities are normally suggested to account for this: the use
[
62]
on the activity of these complexes.
abnormal, and are observed neither for most of the magnesium nucleophilic than alkoxides, leads to relatively slow initiation
Such trends are quite of a metal silylamide as the initiator, which is known to be less
[
35,71,72]
and zinc complexes reported in literature
nor for magne- with respect to chain propagation; and inter-/intramolecular
sium complexes 1a–5a in this work. Therefore, we hypothesize transesterification takes place as a side reaction resulting in the
that the aminophenolate ligand framework may lead to some formation of macrocycles and chains with a broad molecular
different structural features to complexes 1a–5a in solution weight distribution. Even in the presence of 2-propanol, the
compared with their biphenyl- or binaphthyl-based imino- obtained PLAs still have broad molecular weight distributions
phenolate analogues. To prove this assumption, 2 equiv. of thf (M /M = 1.16–1.59), and in most of the cases the M values
w
n
n
were added to a solution of complex 2a in C D and the mix- are slightly lower than the theoretical ones. All these results
6
6
1
ture was monitored by H NMR spectroscopy. Two sets of reso- indicate that the ROP of rac-LA by these magnesium and zinc
1
complexes is not well controlled and may have involved trans-
esterification to a considerable extent.
nances could be identified in the H NMR spectrum. One be-
longs to complex 2a (ca. 60 %), and the other set could be
assigned to a new structure with a dissociated NMe2 group,
The initiation mechanism with the addition of 2-propanol
since only one singlet is found for the NMe group (see Fig- was investigated by monitoring the NMR-scale reaction of com-
2
ure S1). The ratio of these two structures remains constant on plex 1a and 2-propanol (1:1) in C D . Free HN(SiMe ) was re-
6
6
3 2
1
standing overnight at ambient temperature. On increasing the leased quantitatively (δ = 0.09 ppm); neither free proligand L H
amount of thf to about 4 equiv., the percentage of the new nor 2-propanol could be observed in the H NMR spectrum.
1
species increases to about 90 % and a small amount of complex All these features support the generation of the magnesium
1
2
a is still detectable (see Figure S2). Nevertheless, easy dissocia- isopropoxide species “[L MgOiPr]”, probably in aggregated form
Eur. J. Inorg. Chem. 2016, 3791–3803
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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(
see Figure S4). On further addition of 20 equiv. of rac-LA to the Ring-Opening Polymerization of α-MeTMC
above C D solution, the active oligomer was produced within
6
6
a short period according to the assignments reported in litera- This series of magnesium and zinc complexes also proved to be
[
62,70]
1
ture.
was dissociated from the active metal center, since only one temperature, and gave poly(α-MeTMC)s with high molecular
The H NMR spectrum indicated that the NMe group active initiators for the ROP of α-MeTMC in toluene at room
2
singlet was displayed at δ = 2.48 ppm (see Figure S5).
weights and moderate to high regioselectivities.
On the basis of these results, kinetic studies on rac-LA poly-
As shown in Table 3, the magnesium complexes 1a–5a are
merization were carried out in toluene. For [LA] = 1.0
M
and highly active toward α-MeTMC polymerization as single-compo-
, a linear relationship between nent initiators in toluene at room temperature. The structure of
ln([LA] /[LA] ) and time can be observed (see Figure S6). The the ancillary ligand has a significant influence on the catalytic
0
[
1a] = [iPrOH] = 5.0, 3.3, 2.5, 2 m
M
0
t
plot of kapp versus [1a] also has a linear relationship (see Fig- activity. Magnesium complexes with an o-trityl substituent on
ure S7). The polymerization shows first-order dependence on the phenolate ring show remarkably higher catalytic activity
both monomer and initiator concentrations, which further im- than those with an o-cumyl substituent. For example, magne-
plies that the concentration of active species remains un- sium complex 4a with an o-trityl substituent can effectively po-
changed during the entire polymerization, although transesteri- lymerize 200 equiv. of α-MeTMC at room temperature, and a
fication reactions occur.
monomer conversion of 93 % could be achieved within 5 min
1
The H NMR spectrum indicates that the purified oligomer (Table 3, Run 4), whereas the monomer conversion is 91 %
(
obtained with [rac-LA] /[1a] /[iPrOH] = 20:1:1) is capped by within 40 min for complex 3a with an o-cumyl substituent
0
0
0
an isopropyl ester and a hydroxyl group on the two chain ends (Table 3, Run 3). In addition, the introduction of two methyl
(
see Figure S8). The ESI-TOF mass spectrum of the same sample groups in the biphenyl skeleton decreases the catalytic activity
exhibits a series of peaks with m/z of 72n + 60 (iPrOH) + 23 of complex 3a to a great extent. With complex 1a as the initia-
+
(
Na ) (see Figure S9), which further confirms the above conclu- tor, a conversion of 92 % can be reached within 10 min in tolu-
sion. It is therefore suggested that the magnesium isopropoxide ene, whereas complex 3a shows much lower activity in toluene
1
species “[L MgOiPr]” generated in situ by the reaction of the with a monomer conversion of up to 91 % in 40 min. Such
metal silylamido complex 1a and 2-propanol initiates the po- an influence is not observed for complex 4a with an o-trityl-
lymerization of rac-LA by a coordination/insertion mechanism, substituted ligand. Moreover, the activity order of 1a > 5a > 3a
which leads to the formation of linear PLAs with isopropyl ester for magnesium complexes with o,p-cumyl substituents on the
and hydroxyl termini.
phenolate ring implies that the influence of the ligand back-
All the magnesium and zinc silylamido complexes exhibit at- bone may be both electronic and steric, whereby the electron-
actic selectivity in toluene and a certain heteroselectivity in THF. withdrawing effect is beneficial, and steric bulk is unfavorable.
Compared with the biphenyl- or binaphthyl-based imino-
phenolate analogues, the heteroselectivities of magnesium magnesium analogues,
Compared with the previously reported iminophenolate
[
61,62]
the activities of magnesium com-
complexes 1a–5a are slightly lower (P = 0.58–0.69 vs. 0.67– plexes 1a–5a are significantly improved relative to those of the
r
[
61,62]
0.77),
but the heteroselectivities of zinc complexes 1b, 3b, biphenyl-based series (conversion of 85–95 % within 5–40 min
and 5b are notably lower (P = 0.55–0.58 vs. 0.80–0.83).
[
62]
This at room temp. vs. 90–95 % within 60–180 min at 70 °C), but are
r
may also be related to the stronger coordination of the NMe2 comparable to those of the binaphthyl-based analogues (con-
group to the metal center in the aminophenolate complexes of version of 91–94 % within 10–20 min). It seems that the varia-
this work. The influence of the ligand backbone on the stereo- tion of the ligand framework from iminophenolate to amino-
selectivity of the corresponding complexes is not conclusive, phenolate is more favorable for the biphenyl-based system.
whereby magnesium complexes 1a, 3a and 5a with o,p-cumyl Such a variation may enhance the electrophilicity of the metal
substituents on the phenolate ring show slightly higher prefer- center and thereby increase the catalytic activity. In the binaph-
ence for heterotactic dyad enchainment.
thyl-based system, the increase in steric bulk of the ligand may
Table 3. ROP of racemic α-MeTMC initiated by magnesium and zinc complexes in toluene.[a]
Conversion[b] [%]
M
n,calcd. (104)
[c]
M
[d]
(104)
M
/M
[d]
X
reg
[e]
T
g
[f]
[°C]
Run
Cat.
[α-MeTMC]
0
/[M]
0
/[iPrOH]
t [min]
n
w
n
1
2
3
4
5
6
7
8
9
1a
2a
3a
4a
5a
1b
1b
3b
3b
5b
5b
200:1:0
200:1:0
200:1:0
200:1:0
200:1:0
200:1:0
200:1:1
200:1:0
200:1:1
200:1:0
200:1:1
10
5
40
5
10
150
120
300
180
180
120
92
94
91
93
85
92
92
90
91
95
90
2.13
2.18
2.11
2.16
1.97
2.13
2.13
2.09
2.11
2.20
2.09
7.92
6.25
6.35
7.36
6.47
6.94
5.23
7.87
5.99
8.07
5.55
1.74
2.05
1.64
1.99
1.67
1.75
1.34
1.61
1.44
1.75
1.41
0.81
0.90
0.88
0.93
0.89
0.83
0.81
0.82
0.82
0.83
0.83
7.83
10.87
10.54
9.18
10.87
10.87
9.84
8.48
10.54
10.22
8.47
1
1
0
1
0 0 0
a] : [α-MeTMC] /[M] ) × 116.05 × % conversion. [d] Deter-
= 1.0 M; in toluene, at 25 °C. [b] Determined by 1H NMR spectroscopy. [c] Mn,calcd. = ([α-MeTMC]
[
1
3
mined by GPC. [e] Xreg is the percentage of head-to-tail/tail-to-head linkages in the polymer chain, determined by C NMR spectroscopy. [f] Determined by
DSC.
Eur. J. Inorg. Chem. 2016, 3791–3803
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counteract the positive electronic influence arising from such initiator reported to date. Both the substituents and the ligand
a framework variation, and no obvious change of the activity backbone exert a remarkable influence on the regioselectivity
occurs.
of these complexes. The introduction of an o-trityl group in the
aminophenolate ligands leads to magnesium complexes show-
ing higher regioselectivity. The selectivity order of 1a < 3a <
Similar to the trend observed for rac-LA polymerization, zinc
complexes 1b, 3b, and 5b exhibit significantly lower catalytic
activity in comparison with magnesium complexes. Two to six
hours were needed for the zinc complexes to convert 200 equiv.
of monomer to high conversions of 90–95 %, whereas high
monomer conversions could be achieved by the corresponding
5a indicates that the backbone of the ligand influences the
regioselectivity of the corresponding magnesium complex steri-
cally. The same order is also valid for the zinc complexes.
The regioselectivities of this series of magnesium complexes
magnesium complexes after 5–40 min under otherwise the toward α-MeTMC polymerization are generally higher than
identical conditions. Since only one zinc complex was obtained those of the related iminophenolate magnesium analogues,
[
62]
previously,
nolate and the aminophenolate systems is impossible. The regioselectivity of 0.98 was previously achieved by the bi-
a thorough comparison between the iminophe- while a reverse trend is observed for zinc complexes. A high
[
62]
higher activity of the binaphthyl-based iminophenolate zinc naphthyl-based iminophenolate zinc complex,
whereas the
complex compared to complex 5b suggests that a similar trend regioselectivities of zinc complexes 1b, 3b, and 5b are obvi-
to that found for magnesium complexes may also hold.
ously lower (Xreg = 0.81–0.83). It is conceivable that the in-
creased steric bulk of these aminophenolate ligands relative to
their iminophenolate counterparts are beneficial for the magne-
sium center but not for the zinc center toward the regioselect-
ive polymerization of α-MeTMC.
The influence of the ligand backbone on the activity of these
zinc complexes is similar to that of the magnesium complexes,
with an activity order of 1b > 5b > 3b. For instance, with bi-
phenyl-based zinc complex 1b as the initiator, a monomer con-
version of 92 % can be reached within 150 min (Table 3, Run
Moreover, although the regioselectivities of these complexes
vary to some extent, the glass transition temperatures T of the
6); binaphthyl-based zinc complex 5b gives 95 % monomer
g
resultant polymers are quite similar (Table 3). Similar to our
previous work, no obvious relationship could be established
conversion within 180 min under otherwise the same condi-
tions (Table 3, Run 10), whereas complex 3b shows the lowest
activity among them, and only gives 90 % conversion within
between the regioregularity and the T value.
g
300 min (Table 3, Run 8).
Compared with zinc silylamido complexes, the of zinc com-
plex/2-propanol systems 1b/, 3b/, and 5b/2-propanol exhibit
higher catalytic activity for the polymerization of α-MeTMC. For
example, 3b/2-propanol can convert 91 % of lactide monomer
to PLA within 180 min in toluene (Table 3, Run 9), whereas the
yield is only 90 % after 300 min with complex 3b alone (Table 3,
Run 8). The same trend is also found for zinc complexes 1b and
Conclusions
Several monomeric magnesium and zinc complexes derived
from biphenyl-or binaphthyl-based aminophenol proligands
were synthesized. X-ray diffraction studies demonstrated that
both magnesium complex 5a and zinc complexes 1b, 3b, 5b
have a four-coordinate metal center in the solid state. All com-
5
b.
To better understand the polymerization mechanism of α- plexes efficiently catalyzed the polymerization of rac-LA and ra-
1
MeTMC, the H NMR spectrum of a purified oligomer sample cemic α-MeTMC under mild conditions. For rac-LA polymeriza-
prepared with [α-MeTMC] /[1b] /[iPrOH] = 20:1:1 was deter- tion, the catalytic activity order is Mg > Zn, and all complexes
0
0
0
mined. The resonances at δ = 1.22 ppm and 4.98 ppm can be are more active in the presence of 2-propanol and in thf. The
ascibed to the –OCH(CH ) end group, while the resonances at structure of the ancillary ligand has a remarkable impact on the
3
2
4.36, 3.68, 1.28 ppm are characteristic peaks of the other chain catalytic behavior of the corresponding complex. Among them,
terminus [–OCH CH CH(CH )OH] (see Figure S10). All these fea- biphenyl-based magnesium complex 2a with an o-trityl group
2
2
3
tures indicate that the polymer is end-capped with hydroxyl on the phenolate ring is most active, and magnesium complex
[
61,62]
and isopropyl ester groups,
which were further comfirmed 1a bearing a ligand with the same backbone but an o-cumyl
by ESI-TOF mass spectrometry (Figure S11). Likely due to en- group is the most heteroselective (P = 0.69). For α-MeTMC
r
hanced transesterification reactions, oligomers end-capped polymerization, magnesium complexes are significantly more
with isopropyl group on both ends are also detected.
active than zinc complexes in toluene. Magnesium complexes
[
60]
According to the literature,
microstructures of typical 2a and 4a with an o-trityl group exhibit higher activity than the
poly(α-MeTMC)s were analyzed by 13C NMR spectroscopy. Four other complexes. These complexes display moderate to high
signals at 154.88, 154.4, 154.01, and 153.95 ppm can be ob- regioselectivity, and the highest value (Xreg = 0.93) is obtained
served, which are assigned to carbonyl groups of different envi- with magnesium complex 4a.
ronments [O–C(O)]. The regioselectivity of a given complex to-
ward α-MeTMC polymerization can be obtained by calculating
the relative intensity of the resonance at δ = 154.4 ppm in the
total carbonyl region. As shown in Table 3, magnesium complex
Experimental Section
4
a exhibits the highest regioselectivity (Xreg = 0.93) among
Materials and Methods: All manipulations were performed under
these magnesium and zinc complexes (Xreg = 0.81–0.90; see a dry argon atmosphere by using standard Schlenk-line or glove-
Figure S12), and it is also the most regioselective magnesium box techniques. Toluene and n-hexane were heated to reflux over
Eur. J. Inorg. Chem. 2016, 3791–3803
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sodium benzophenone ketyl prior to use. [D ]Benzene was carefully
ArH), 3.99 (d, J = 13.4 Hz, 1 H, ArCH ), 3.92 (d, J = 13.4 Hz, 1 H,
6
2
[
73]
dried and stored in the glove box. Mg[N(SiMe ) ] ,
ArCH ), 2.56–2.31 (m, 2 H, NCH CH ), 2.13 (s, 3 H, ArCH ), 2.12 [s, 6
3
2 2
2
2
3
3
[
74]
[75]
13
Zn[N(SiMe ) ] ,
2-bromomethyl-4,6-dicumylphenol,
and 2- H, N(CH ) ], 0.49 (t, J = 7.0 Hz, 3 H, NCH CH ) ppm. C NMR (CDCl3,
were synthesized accord- 100 MHz): δ = 153.5, 150.8, 147.9, 146.1, 140.1, 133.5, 133.3, 132.4,
3
2 2
3 2 2 3
[75]
bromomethyl-4-methyl-6-tritylphenol
ing to literature methods. Racemic 4-methyl-1,3-dioxan-2-one (α-
methyltrimethylene carbonate, α-MeTMC) was synthesized by fol-
lowing a literature procedure.[ rac-LA (Aldrich) was recrystallized
from dry toluene and then sublimed twice under vacuum at 80 °C.
131.2, 130.1, 129.5, 128.8, 128.4, 127.9, 126.9, 126.2, 125.1, 122.2,
121.9, 121.1, 119.0 (all Ar C), 63.3 (ArCH ), 59.7 (ArCPh ), 45.1
2
3
58]
(NCH CH ), 43.5 [N(CH ) ], 21.0 (ArCH ), 11.1 (NCH CH ) ppm.
2
3
3 2
3
2
3
C H N O (602.82): calcd. C 85.68, H 7.02, N 4.65; found C 85.60, H
43 42 2
2
-Propanol was dried with calcium hydride prior to distillation. All
7.01, N 4.45.
other chemicals were commercially available and used after appro-
priate purification. Glassware and vials used in the polymerization
were dried in an oven at 120 °C overnight and exposed to a vac-
uum/argon cycle three times.
2
-{[N-ethyl-N-(2′-dimethylamino-6,6′-dimethyl-1,1′-biphenyl-2-
3
yl)amino]methyl}-4,6-dicumyl-phenol (L H): This compound was
prepared in an analogous manner to that described for L H, except
that N-ethyl-N′,N′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diamine
1
NMR spectra were recorded with Bruker AVANCE 400 and Varian
(2.15 g, 8.00 mmol) and 2-bromomethyl-4,6-dicumylphenol (3.39 g,
1
13
3
3
00 spectrometers at 25 °C ( H: 300 MHz, 400 MHz; C: 100 MHz)
8.00 mmol) were used to afford proligand L H as an off-white solid
1
13
1
unless otherwise stated. Chemical shifts for H and C NMR spectra
(1.24 g, 25.3 %), m.p. 75–77 °C. H NMR (CDCl , 300 MHz): δ = 8.85
3
were referenced internally using the residual solvent resonances (s, 1 H, ArOH), 7.36–7.21 (m, 5 H, ArH), 7.16 (dd, J = 9.0, 4.8 Hz, 5 H,
and reported relative to TMS. Elemental analyses were performed
with an EA-1106 instrument. Spectroscopic analyses of polymers
ArH), 7.09 (t, J = 6.6 Hz, 5 H, ArH), 6.80 (d, J = 7.4 Hz, 1 H, ArH), 6.69
(s, 1 H, ArH), 6.58 (d, J = 8.2 Hz, 1 H, ArH), 3.93 (d, J = 13.4 Hz, 1 H,
ArCH ), 3.83 (d, J = 13.4 Hz, 1 H, ArCH ), 2.62–2.43 (m, 2 H,
were performed in CDCl . Gel permeation chromatography (GPC)
3
2
2
was carried out with a Waters 1515 Breeze instrument in thf at
NCH CH ), 2.10 [s, 6 H, N(CH ) ], 2.02 (s, 3 H, ArCH ), 1.87 (s, 3 H,
2 3 3 2 3
–
1
35 °C, at a flow rate of 1 mL min . Calibration standards were com- ArCH ), 1.76–1.59 [s, 6 H, C(CH ) Ph], 1.55 [s, 3 H, C(CH ) Ph], 1.49
3 3 2 3 2
1
3
mercially available narrowly distributed linear polystyrene samples [s, 3 H, C(CH ) Ph], 0.57 (t, J = 7.0 Hz, 3 H, NCH CH ) ppm. C NMR
3
2
2
3
3
that cover a broad range of molar masses (6 × 10 < Mn
6
<
(CDCl , 100 MHz): δ = 153.4, 151.6, 151.5, 150.8, 148.6, 138.9, 138.6,
3
× 105 g mol ). Differential scanning calorimetric (DSC) curves
–1
137.8, 136.5, 134.4, 131.2, 127.7, 127.4, 127.3, 127.0, 126.7, 125.6,
125.5, 125.3, 124.3, 124.2, 123.5, 121.0, 120.4, 117.2 (all ArC), 59.7
(ArCH ), 45.5 (NCH CH ), 43.0 [N(CH ) ], 42.3 [C(CH ) Ph], 41.7
were taken with a PerkinElmer Pyris 1 instrument. All samples were
cooled to –50 °C and heated to 60 °C for the first scan. After being
kept for 3 min, they were again cooled to –50 °C, and heated to
2
2
3
3 2
3 2
[C(CH ) Ph], 31.1 [C(CH ) Ph], 30.7 [C(CH ) Ph], 20.6 (ArCH ), 19.9
3
2
3 2
3 2
3
–
1
6
0 °C for the second cycle. The heating rate was 10 °C min .
(ArCH ), 10.6 (NCH CH ) ppm. C H N O (610.88): calcd. C 84.55, H
3 2 3 43 50 2
8
.25, N 4.59; found C 84.23, H 8.59, N 4.16.
2
-{[N-ethyl-N-(2′-dimethylamino-1,1′-biphenyl-2-yl)amino]-
1
methyl}-4,6-dicumylphenol (L H): A solution of 2-bromomethyl-
,6-dicumylphenol (3.39 g, 8.00 mmol) in dry thf (20 mL) was added
2-{[N-ethyl-N-(2′-dimethylamino-6,6′-dimethyl-1,1′-biphenyl-2-
yl)amino]methyl}-4-methyl-6-tritylphenol (L H): This compound
to a stirred solution of N-ethyl-N′,N′-dimethyl-1,1′-biphenyl-2,2′-di- was prepared in an analogous manner to that described for L H,
4
4
1
amine (1.92 g, 8.00 mmol) in dry thf (15 mL), and then a solution
of triethylamine (1.68 mL) in dry thf (5 mL) was added dropwise
and a precipitate formed. The reaction mixture was stirred for 1 h.
After filtration, the solvent of the filtrate was removed under vac-
uum to give a sticky solid. The crude product was purified by flash
chromatography within several minutes on a 5 cm silica gel column
except that N-ethyl-N′,N′,6,6′-tetramethylbiphenyl-2,2′-diamine
(2.15 g, 8.00 mmol) and 2-bromomethyl-4-methyl-6-tritylphenol
4
(3.54 g, 8.00 mmol) were used to afford proligand L H as an off-
white solid (2.34 g, 69.6 %), m.p. 90–93 °C. 1H NMR (CDCl3,
400 MHz): δ = 8.76 (s, 1 H, ArOH), 7.29–7.22 (m, 1 H, ArH), 7.22–7.03
(m, 17 H, ArH), 6.92–6.83 (m, 2 H, ArH), 6.71 (s, 2 H, ArH), 6.47 (d,
(
pretreated with NEt ) with petroleum ether/ethyl acetate in gradi- J = 8.1 Hz, 1 H, ArH), 4.02 (d, J = 13.6 Hz, 1 H, ArCH ), 3.85 (d, J =
3
2
[63]
ent polarity as the eluent.
off-white solid (3.19 g, 68.4 %), m.p. 43–45 °C. H NMR (CDCl ,
4
The pure product was obtained as an
13.4 Hz, 1 H, ArCH ), 2.49–2.28 (m, 2 H, NCH CH ), 2.13 (s, 3 H,
2
2
3
1
ArCH ), 2.09 [s, 6 H, N(CH ) ], 1.98 (s, 3 H, ArCH ), 1.83 (s, 3 H, ArCH ),
3
3
3 2
3
3
13
00 MHz): δ = 8.90 (s, 1 H, ArOH), 7.32–7.22 (m, 8 H, ArH), 7.20–7.14
0.46 (t, J = 7.0 Hz, 3 H, NCH CH ) ppm. C NMR (CDCl , 100 MHz):
2 3 3
(m, 5 H, ArH), 7.12–7.05 (m, 3 H, ArH), 6.94 (d, J = 7.0 Hz, 1 H, ArH), δ = 153.5, 150.6, 148.3, 146.0, 138.6, 137.9, 136.3, 133.2, 131.1, 131.0,
6
.87 (t, J = 7.3 Hz, 1 H, ArH), 6.70–6.66 (m, 2 H, ArH), 3.94 (s, 2 H,
130.2, 128.5, 128.0, 127.4, 127.1, 126.7, 125.9, 124.9, 123.6, 122.2,
ArCH ), 2.62–2.44 (m, 2 H, NCH CH ), 2.15 [s, 6 H, N(CH ) ], 1.66 [s,
120.4, 117.3 (all Ar C), 63.1 (ArCH ), 59.6 (ArCPh ), 45.3 (NCH CH ),
2
2
3
3 2
2
3
2
3
6
H, C(CH ) Ph], 1.53 [s, 6 H, C(CH ) Ph], 0.53 (t, J = 6.8 Hz, 3 H,
43.2 [N(CH ) ], 20.9 (ArCH ), 20.6 (ArCH ), 19.9 (ArCH ), 11.0
(NCH CH ) ppm. C H N O (630.87): calcd. C 85.67, H 7.35, N 4.44;
2 3 45 46 2
3
2
3 2
3 2 3 3 3
13
NCH CH ) ppm. C NMR (CDCl , 100 MHz): δ = 153.2, 151.6, 151.5,
2
3
3
1
1
1
50.8, 148.2, 139.7, 139.2, 134.6, 133.3, 132.2, 131.4, 128.1, 127.8, found C 85.17, H 7.02, N 4.62.
27.4, 126.7, 125.8, 125.6, 125.3, 124.9, 124.5, 121.9, 121.1, 121.0,
2
-{[N-ethyl-N-(2′-dimethylamino-1,1′-binaphthyl-2-yl)amino]-
18.5 (all Ar C), 59.2 (ArCH ), 45.8 (NCH CH ), 43.3 [N(CH ) ], 42.4
2
2
3
3 2
5
methyl}-4,6-dicumylphenol (L H): This compound was prepared
in an analogous manner to that described for L H, except that N-
ethyl-N′,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine (2.72 g,
[C(CH ) Ph], 41.8 [C(CH ) Ph], 31.1 [C(CH ) Ph], 30.2 [C(CH ) Ph], 10.7
3 2 3 2 3 2 3 2
1
(NCH CH ) ppm. C H N O (582.83): calcd. C 84.49, H 7.96, N 4.81;
2
3
41 46 2
found C 84.67, H 8.24, N 4.42.
8
.00 mmol) and 2-bromomethyl-4,6-dicumylphenol (3.39 g,
5
2
-{[N-ethyl-N-(2′-dimethylamino-1,1′-biphenyl-2-yl)amino]-
8.00 mmol) were used to afford proligand L H as an off-white solid
methyl}-4-methyl-6-tritylphenol (L H): This compound was pre- (4.74 g, 86.7 %), m.p. 165–167 °C. 1H NMR (CDCl , 300 MHz): δ =
2
3
1
pared in an analogous manner to that described for L H, except
8.94 (s, 1 H, ArOH), 7.95 (d, J = 8.9 Hz, 1 H, ArH), 7.86 (d, J = 8.1 Hz,
that 2-bromomethyl-4-methyl-6-tritylphenol (3.54 g, 8.00 mmol) 1 H, ArH), 7.77 (dd, J = 8.5, 3.7 Hz, 2 H, ArH), 7.62 (d, J = 8.9 Hz, 1
2
was used to afford proligand L H as an off-white solid (3.33 g,
H, ArH), 7.39 (dt, J = 8.1, 3.7 Hz, 1 H, ArH), 7.31–7.14 (m, 10 H, ArH),
1
6
9.1 %), m.p. 165–168 °C. H NMR (CDCl , 400 MHz): δ = 8.91 (s, 1 7.05 (m, 6 H, ArH), 6.76 (d, J = 8.5 Hz, 1 H, ArH), 6.66 (d, J = 1.8 Hz,
3
H, ArOH), 7.36–7.03 (m, 20 H, ArH), 6.94 (d, J = 7.1 Hz, 1 H, ArH),
.86–6.81 (m, 2 H, ArH), 6.71 (s, 1 H, ArH), 6.57 (d, J = 8.2 Hz, 1 H,
1 H, ArH), 4.08 (d, J = 13.1 Hz, 1 H, ArCH ), 3.85 (d, J = 13.1 Hz, 1 H,
2
6
ArCH ), 2.49 (q, J = 7.1 Hz, 2 H, NCH CH ), 2.10 [s, 6 H, N(CH ) ],
2
2
3
3 2
Eur. J. Inorg. Chem. 2016, 3791–3803
www.eurjic.org
3799
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
1
3
1
1
1
6
.64 [s, 6 H, C(CH ) Ph], 1.45 [s, 6 H, C(CH ) Ph], 0.38 (t, J = 7.1 Hz,
J = 2.4 Hz, 1 H, ArH), 6.96–6.93 (m, 3 H, ArH), 6.91 (d, J = 7.9 Hz, 1
H, ArH), 6.87–6.83 (m, 2 H, ArH), 6.81–6.71 (m, 3 H, ArH), 6.61 (d, J =
3
2
3 2
1
3
H, NCH CH ) ppm. C NMR (CDCl , 100 MHz): δ = 153.2, 151.6,
2
3
3
51.5, 149.7, 146.3, 139.0, 134.8, 134.5, 133.8, 133.5, 131.7, 129.4, 8.3 Hz, 1 H, ArH), 4.50 (d, J = 15.0 Hz, 1 H, ArCH ), 3.91 (d, J =
28.8, 128.8, 127.8, 127.8, 127.5, 127.3, 126.7, 126.2, 125.6, 125.5, 15.1 Hz, 1 H, ArCH ), 2.98–2.75 (m, 2 H, NCH CH ), 2.48 [s, 3 H,
25.3, 125.2, 124.4, 124.2, 123.0, 122.9, 121.7, 120.8, 120.3 (all Ar C),
2
2
2
3
N(CH ) ], 2.17 [s, 3 H, C(CH ) Ph], 1.81 [s, 3 H, C(CH ) Ph], 1.80 [s, 3
3 2 3 2 3 2
0.1 (ArCH ), 46.0 (NCH CH ), 43.1 [N(CH ) ], 42.4 [C(CH ) Ph], 41.7 H, C(CH ) Ph], 1.58 [s, 3 H, N(CH ) ], 1.33 (s, 3 H, ArCH ), 1.31 [s, 3
2
2
3
3 2
3 2
3 2
3 2
3
[
C(CH ) Ph], 31.1 [C(CH ) Ph], 30.9 [C(CH ) Ph], 11.5 (NCH CH ) ppm.
H, C(CH ) Ph], 1.30 (s, 3 H, ArCH ), 0.48 (t, J = 6.9 Hz, 3 H, NCH CH ),
3 2 3 2 3
3
2
3 2
3 2
2
3
13
C H N O (682.95): calcd. C 86.18, H 7.38, N 4.10; found C 85.63, H
0.39 [s, 9 H, Si(CH ) ], –0.03 [s, 9 H, Si(CH ) ] ppm. C NMR (C D ,
49
50
2
3 3 3 3 6 6
7
.41, N 3.90.
100 MHz): δ = 162.4, 154.4, 153.5, 146.3, 140.7, 140.3, 138.3, 135.9,
1
1
5
3
34.5, 133.9, 132.0, 129.6, 128.7, 128.5, 128.1, 127.9, 127.4, 126.7,
26.2, 126.1, 126.1, 125.6, 124.0, 122.8, 118.5 (all ArC), 57.5 (ArCH2),
0.2 (NCH CH ), 45.5 [N(CH ) ], 42.8 [C(CH ) Ph], 42.6 [C(CH ) Ph],
1
1
[
(L )MgN(SiMe ) ] (1a): The proligand L H (0.583 g, 1.00 mmol)
3
2
was added slowly to a solution of Mg[N(SiMe ) ] (0.345 g,
.00 mmol) in toluene (15 mL). The solution was stirred overnight
at room temp. The resultant solution was filtered to remove a trace
amount of impurities and the solvents evaporated to dryness under
vacuum for several hours to give a foamlike material. Recrystalliza-
3
2 2
2
3
3 2
3 2
3 2
1
1.7 [C(CH ) Ph], 31.5 [C(CH ) Ph], 27.2 (NCH CH ), 20.4 (ArCH ), 19.9
3
2
3 2
2
3
3
(ArCH ), 6.5 (SiCH ) ppm. C H MgN OSi (794.56): calcd. C 74.07,
3 3 49 67 3 2
H 8.50, N 5.29; found C 73.51, H 8.63, N 4.80.
4
tion from toluene/hexane afforded colorless crystals of complex 1a
212 mg, 27.7 %), m.p. 166–167 °C. H NMR (C D , 400 MHz): δ =
[(L )MgN(SiMe ) ] (4a): A similar method was employed to that
described for 1a. L H (0.631 g, 1.00 mmol) was treated with
3
2
1
4
(
6
6
7
.62 (s, 1 H, ArH), 7.47 (d, J = 7.8 Hz, 2 H, ArH), 7.28 (t, J = 7.7 Hz, 2
Mg[N(SiMe ) ] (0.345 g, 1.00 mmol) in toluene (15 mL) at room
3
2 2
H, ArH), 7.19 (d, J = 8.3 Hz, 1 H, ArH), 7.14–7.09 (m, 1 H, ArH), 7.06
temp. to give a foamlike material. Recrystallization from toluene/
(d, J = 7.4 Hz, 2 H, ArH), 7.00 (d, J = 2.4 Hz, 1 H, ArH), 6.97–6.91 (m, hexane afforded colorless crystals of complex 4a (240 mg, 29.5 %).
2
H, ArH), 6.81 (m, 5 H, ArH), 6.67 (d, J = 8.3 Hz, 1 H, ArH), 6.60 (d,
Because 4a is very air sensitive, a poor elemental analysis was ob-
1
J = 7.5 Hz, 1 H, ArH), 6.44 (d, J = 7.5 Hz, 1 H, ArH), 4.43 (d, J =
tained, m.p. 184–186 °C. H NMR (C D , 400 MHz): δ = 7.39 (d, J =
6
6
1
1
2
5.0 Hz, 1 H, ArCH ), 3.85 (d, J = 15.1 Hz, 1 H, ArCH ), 3.05–2.92 (m,
1.8 Hz, 1 H, ArH), 7.32 (d, J = 7.6 Hz, 6 H, ArH), 7.18 (d, J = 7.6 Hz,
2
2
H, NCH CH ), 2.84–2.72 (m, 1 H, CH CH ), 2.46 [s, 3 H, N(CH ) ], 1 H, ArH), 7.12 (d, J = 7.5 Hz, 1 H, ArH), 7.05 (d, J = 7.1 Hz, 1 H, ArH),
2
3
2
3
3 2
.17 [s, 3 H, C(CH ) Ph], 1.82 [s, 3 H, C(CH ) Ph], 1.81 [s, 3 H,
6.99 (t, J = 7.6 Hz, 5 H, ArH), 6.96–6.87 (m, 4 H, ArH), 6.84 (t, J =
7.0 Hz, 2 H, ArH), 6.79 (d, J = 7.2 Hz, 1 H, ArH), 6.61 (d, J = 8.2 Hz,
3
2
3 2
C(CH ) Ph], 1.60 [s, 3 H, N(CH ) ], 1.31 [s, 3 H, C(CH ) Ph], 0.42 [br.
3
2
3 2
3 2
s, 9 H, Si(CH ) ], 0.29 (t, J = 6.9 Hz, 3 H, NCH CH ), –0.01 [br. s, 9 H,
1 H, ArH), 4.54 (d, J = 15.7 Hz, 1 H, ArCH ), 4.11 (d, J = 15.7 Hz, 1 H,
3
3
2
3
2
13
Si(CH ) ] ppm. C NMR (C D , 100 MHz): δ = 162.5, 154.2, 153.5,
ArCH ), 3.06 (q, J = 7.0 Hz, 2 H, NCH CH ), 2.46 [s, 3 H, N(CH ) ],
3
3
6
6
2
2
3
3 2
1
1
1
4
3
46.2, 141.0, 136.6, 136.3, 135.0, 134.8, 134.2, 134.0, 129.6, 129.5, 2.27 (s, 3 H, ArCH ), 1.64 [s, 3 H, N(CH ) ], 1.39 (s, 3 H, ArCH ), 1.37
3 3 2 3
28.2, 127.3, 127.3, 127.0, 126.2, 126.1, 126.0, 125.7, 125.6, 124.2, (s, 3 H, ArCH ), 0.68 (t, J = 7.0 Hz, 3 H, NCH CH ), –0.07 [s, 18 H,
3
2
3
13
22.4, 119.8 (all ArC), 57.4 (ArCH ), 51.5 (NCH CH ), 47.4 [N(CH ) ], Si(CH ) ] ppm. C NMR (C D , 100 MHz): δ = 162.6, 147.7, 146.7,
2
2
3
3 2
3 3
6 6
4.2 [N(CH ) ], 42.8 [C(CH ) Ph], 42.6 [C(CH ) Ph], 31.7 [C(CH ) Ph],
141.1, 140.9, 139.0, 137.8, 134.7, 134.3, 133.1, 132.6, 131.8, 129.9,
129.7, 129.3, 129.0, 128.9, 128.5, 127.3, 125.6, 125.5, 125.0, 123.2,
120.9, 118.9 (all Ar C), 64.0 (ArCH ), 56.5 (ArCPh ), 49.8 (NCH CH ),
3
2
3 2
3 2
3 2
1.5 [C(CH ) Ph], 27.1 (NCH CH ), 6.2 (SiCH ) ppm. C H MgN OSi
3
2
2
3
3
47 63
3
2
(766.51): calcd. C 73.65, H 8.28, N 5.48; found C 73.50, H 8.27, N
2
3
2
3
5
.24.
48.1 [N(CH ) ], 44.6 (ArCH ), 21.4 (ArCH ), 20.6 (ArCH ), 20.1
3 2 3 3 3
(
7
NCH CH ), 6.3 (SiCH ) ppm. C51H MgN OSi (814.56): calcd. C
2 3 3 63 3 2
5.20, H 7.80, N 5.16; found C 75.44, H 7.66, N 4.33.
2
[
(L )MgN(SiMe ) ] (2a): A similar method was employed to that
3
2
2
described for 1a. L H (0.603 g, 1.00 mmol) was treated with
Mg[N(SiMe ) ] (0.345 g, 1.00 mmol) in toluene (15 mL) at room
5
[(L )MgN(SiMe ) ] (5a): A similar method was employed to that
temp. to give a foamlike material. Recrystallization from toluene/ described for 1a. L H (0.683 g, 1.00 mmol) was treated with
3
2 2
3 2
5
hexane afforded colorless crystals of complex 2a (202 mg, 25.7 %).
Because 2a is very air sensitive, a poor elemental analysis was ob-
Mg[N(SiMe ) ] (0.345 g, 1.00 mmol) in toluene (15 mL) at room
temp. to give a foamlike material. Recrystallization from toluene/
3 2 2
1
tained, m.p. 239–241 °C. H NMR (C D , 400 MHz): δ = 7.38 (s, 1 H,
hexane afforded colorless crystals of complex 5a (392 mg, 45.2 %),
6
6
1
ArH), 7.34–7.28 (m, 7 H, ArH), 7.02–6.88 (m, 10 H, ArH), 6.87–6.81 m.p. 145–148 °C. H NMR (C D , 400 MHz): δ = 7.62–7.48 (m, 8 H,
6
6
(
1
m, 4 H, ArH), 6.66 (d, J = 8.1 Hz, 2 H, ArH), 6.50 (dd, J = 8.5, 2.0 Hz,
ArH), 7.36 (t, J = 7.6 Hz, 2 H, ArH), 7.09–7.00 (m, 2 H, ArH), 6.94 (t,
J = 7.5 Hz, 1 H, ArH), 6.79 (d, J = 7.6 Hz, 2 H, ArH), 6.71 (t, J = 7.6 Hz,
1 H, ArH), 6.59 (t, J = 7.1 Hz, 1 H, ArH), 6.37 (t, J = 7.1 Hz, 1 H, ArH),
H, ArH), 4.54 (d, J = 15.9 Hz, 1 H, ArCH ), 4.06 (d, J = 15.9 Hz, 1 H,
2
ArCH ), 3.20–3.10 (m, 1 H, NCH CH ), 3.02–2.92 (m, 1 H, CH CH ),
2
2
3
2
3
2
.43 [s, 3 H, N(CH ) ], 2.27 (s, 3 H, ArCH ), 1.67 [s, 3 H, N(CH ) ], 0.46
6.25–6.17 (m, 4 H, ArH), 4.61 (d, J = 15.1 Hz, 1 H, ArCH ), 4.02 (d,
3
2
3
3 2
2
1
3
(t, J = 6.9 Hz, 3 H, NCH CH ), –0.05 [s, 18 H, Si(CH ) ] ppm. C NMR
J = 15.1 Hz, 1 H, ArCH ), 2.88–2.83 (m, 1 H, CH CH ), 2.67–2.62 [m,
2
3
3 3
2
2
3
(
C D , 100 MHz): δ = 162.7, 147.6, 146.6, 141.6, 136.4, 135.8, 135.2, 4 H, NCH CH and N(CH ) ], 2.15 [s, 3 H, C(CH ) Ph], 1.87 [s, 3 H,
6 6 2 3 3 2 3 2
1
1
35.1, 135.0, 133.0, 131.8, 129.6, 129.6, 127.3, 126.4, 126.3, 126.0, C(CH ) Ph], 1.85 [s, 3 H, C(CH ) Ph], 1.54 [s, 3 H, N(CH ) ], 1.35 [s, 3
3 2 3 2 3 2
25.0, 122.9, 121.1, 120.3 (all ArC), 64.0 (ArCH ), 56.5 (ArCPh ), 51.0
H, C(CH ) Ph], 0.41 [br. s, 12 H, NCH CH and Si(CH ) ], –0.09 [s, 9
2
3
3 2 2 3 3 3
13
(NCH CH ), 50.2 [N(CH ) ], 43.8 (ArCH ), 21.2 (NCH CH ), 6.0 (SiCH )
H, Si(CH ) ] ppm. C NMR (C D , 100 MHz): δ = 162.5, 154.0, 153.5,
3 3 6 6
2
3
3 2
3
2
3
3
ppm. C H MgN OSi (786.50): calcd. C 74.83, H 7.56, N 5.34; found
C 74.32, H 7.16, N 4.55.
144.8, 140.8, 136.2, 135.8, 135.4, 134.3, 132.1, 131.8, 131.2, 129.6,
129.3, 129.3, 128.5, 128.2, 127.6, 127.5, 127.4, 126.9, 126.7, 126.6,
49
59
3
2
1
1
4
2
7
26.6, 126.32, 126.26, 125.90, 125.87, 125.80, 125.75, 125.6, 124.0,
22.7, 118.9 (all Ar C), 57.9 (ArCH ), 50.3 (NCH CH ), 46.1 [N(CH ) ],
3
[
(L )MgN(SiMe ) ] (3a): A similar method was employed to that
3
2
3
2
2
3
3 2
described for 1a. L H (0.795 g, 1.00 mmol) was treated with
Mg[N(SiMe ) ] (0.345 g, 1.00 mmol) in toluene (15 mL) at room
temp. to give a foamlike material. Recrystallization from toluene/
hexane afforded colorless crystals of complex 3a (542 mg, 68.3 %),
5.1 [C(CH ) Ph], 42.7 [C(CH ) Ph], 31.8 [C(CH ) Ph], 31.5 [C(CH ) Ph],
3
2
3 2
3 2
3 2
3
2 2
7.3 (NCH CH ), 6.9 (SiCH ) ppm. C H MgN OSi (866.63): calcd. C
2
3
3
55 67
3
2
6.23, H 7.79, N 4.85; found C 76.53, H 8.33, N 4.62.
1
1
1
m.p. 156–158 °C. H NMR (C D , 400 MHz): δ = 7.58 (d, J = 2.0 Hz,
[(L )ZnN(SiMe ) ] (1b): The proligand L H (0.583 g, 1.00 mmol)
6
6
3 2
1
7
H, ArH), 7.48 (d, J = 8.0 Hz, 2 H, ArH), 7.29 (t, J = 7.7 Hz, 2 H, ArH),
.11 (t, J = 7.2 Hz, 1 H, ArH), 7.04 (d, J = 8.0 Hz, 1 H, ArH), 6.99 (d,
was added slowly to a solution of Zn[N(SiMe ) ] (0.386 g, 1.0 mmol)
in toluene (15 mL). The solution was stirred overnight at room temp.
3
2 2
Eur. J. Inorg. Chem. 2016, 3791–3803
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3800 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
The resultant solution was filtered to remove a trace amount of 126.1, 125.9, 125.8, 125.7, 125.6, 124.0, 121.5, 118.8 (all Ar C), 59.3
impurities and the solvent evaporated to dryness under vacuum
(ArCH ), 51.4 (NCH CH ), 46.9 [N(CH ) ], 42.8 [C(CH ) Ph], 42.7
2
2
3
3 2
3 2
for several hours to give a foamlike material. Recrystallization from [C(CH ) Ph], 31.7 [C(CH ) Ph], 31.5 [C(CH ) Ph], 27.3 (NCH CH ), 6.4
3
2
3 2
3 2
2
3
toluene/hexane afforded colorless crystals of complex 1b (235 mg,
(SiCH ) ppm (for clarity, solvent signals are not indicated in the NMR
3
1
2
9.1 %), m.p. 128–130 °C. H NMR (C D , 400 MHz): δ = 7.62 (s, 1 H,
spectroscopic data). C H N OSi Zn·0.6hexane: calcd. C 73.36, H
6
6
55 67
3
2
ArH), 7.47 (d, J = 7.8 Hz, 2 H, ArH), 7.28 (t, J = 7.6 Hz, 2 H, ArH), 7.21
d, J = 8.3 Hz, 1 H, ArH), 7.10–7.03 (m, 3 H, ArH), 7.06–6.90 (m, 3 H,
ArH), 6.85–6.75 (m, 5 H, ArH), 6.70 (d, J = 8.2 Hz, 1 H, ArH), 6.64 (d,
J = 7.5 Hz, 1 H, ArH), 6.50 (d, J = 7.6 Hz, 1 H, ArH), 4.58 (d, J =
7.92, N 4.38; found C 73.26, H 7.50, N 4.04.
(
X-ray Diffraction: Suitable single crystals of complexes 1b, 3b, 5a,
and 5b for X-ray diffraction analysis were obtained from saturated
solutions in toluene/hexane at room temperature. Diffraction data
were collected with a Bruker Smart 1000 CCD diffractometer with
1
1
2
4.9 Hz, 1 H, ArCH ), 3.88 (d, J = 14.9 Hz, 1 H, ArCH ), 3.14–3.03 (m,
2
2
H, NCH CH ), 2.89–2.79 (m, 1 H, CH CH ), 2.47 [s, 3 H, N(CH ) ],
2
3
2
3
3 2
graphite-monochromated Mo-K (λ = 0.71073 Å) radiation. All data
α
.16 [s, 3 H, C(CH ) Ph], 1.82 [s, 3 H, C(CH ) Ph], 1.81 [s, 3 H,
3
2
3 2
were collected at 140 or 293 K by using the ω-scan technique. All
structures were solved by direct methods and refined by Fourier
C(CH ) Ph], 1.60 [s, 3 H, N(CH ) ], 1.39 [s, 3 H, C(CH ) Ph], 0.41 [s, 9
3
2
3 2
3 2
H, Si(CH ) ], 0.28 (t, J = 6.9 Hz, 3 H, NCH CH ), –0.03 [s, 9 H, Si(CH ) ]
3
3
2
3
3 3
techniques. An absorption correction based on SADABS was ap-
ppm. 13C NMR (C D , 100 MHz): δ = 163.0, 154.2, 153.5, 147.5, 141.7,
6
6
[76]
plied.
All non-hydrogen atoms were refined by full-matrix least-
1
1
36.9, 136.7, 135.3, 134.6, 134.3, 134.2, 129.3, 129.2, 128.2, 127.3,
26.93, 126.88, 126.0, 126.0, 125.8, 125.7, 125.6, 124.1, 121.1, 119.5
2
[77]
squares methods on F by using the SHELXTL program package.
Hydrogen atoms were located and refined by geometric method.
(
all ArC), 58.8 (ArCH ), 52.8 (NCH CH ), 48.2 [N(CH ) ], 46.5 [N(CH ) ],
2 2 3 3 2 3 2
The cell refinement, data collection, and reduction were done with
4
2
6
2.8 [C(CH ) Ph], 42.6 [C(CH ) Ph], 31.7 [C(CH ) Ph], 31.5 [C(CH ) Ph],
3 2 3 2 3 2 3 2
[78]
Bruker SAINT.
The structure solution and refinement were per-
7.2 (NCH CH ), 6.1 (SiCH ) ppm. C H N OSi Zn (807.59): calcd. C
2
3
3
47 63
3
2
[79]
formed with SHELXL-97 and SHELXL-2013. SQUEEZE was used for
9.90, H 7.86, N 5.20; found C 69.87, H 7.90, N 5.09.
5
a, 3b, and 5b, OLEX2 was used for 1b. Molecular structures were
[
80]
3
generated with ORTEP III.
For complex 1b: C47H N OSi Zn; tri-
63 3 2
[
(L )ZnN(SiMe ) ] (3b): A similar method was employed to that
3
2
3
clinic, P1¯; a = 13.2300(18), b = 13.3702(18), c = 15.751(2) Å; α =
0.986(3), ꢀ = 82.522(3), γ = 66.010(2)°; Z = 2. For complex 3b:
C H N OSi Zn; triclinic, P1¯; a = 13.0326(16), b = 14.5796(18), c =
described for 1b. L H (0.611 g, 1.00 mmol) was treated with
8
Zn[N(SiMe ) ] (0.386 g, 1.00 mmol) in toluene (15 mL) at room
3
2 2
55
81
3
2
temp. to give a foamlike material. Recrystallization from toluene/
1
6.981(2) Å; α = 104.916(2), ꢀ = 103.356(3), γ = 104.166(2)°; Z = 2.
For complex 5a: C55 67MgN OSi ; triclinic, P1¯; a = 12.278(2), b =
5.122(3), c = 17.749(5) Å; α = 97.615(4), ꢀ = 100.073(4), γ =
hexane afforded colorless crystals of complex 3b (596 mg, 71.4 %),
1
H
3
2
m.p. 131–135 °C. H NMR (C D , 300 MHz): δ = 7.58 (s, 1 H, ArH),
6
6
1
1
1
9
7
2
6
1
1
2
.48 (d, J = 7.3 Hz, 2 H, ArH), 7.29 (t, J = 7.7 Hz, 2 H, ArH), 7.08 (m,
H, ArH), 6.97–6.90 (m, 4 H, ArH), 6.86 (t, J = 8.8 Hz, 3 H, ArH),
.81–6.73 (m, 3 H, ArH), 6.63 (d, J = 8.2 Hz, 1 H, ArH), 4.63 (d, J =
4.9 Hz, 1 H, ArCH ), 3.95 (d, J = 14.9 Hz, 1 H, ArCH ), 3.08–3.02 (m,
11.948(3)°; Z = 2. For complex 5b: C H N OSi Zn; triclinic, P1¯; a =
55
67
3
2
2.252(8), b = 15.016(10), c = 17.599(12) Å; α = 98.158(13), ꢀ =
9.532(14), γ = 112.005(11)°; Z = 2.
2
2
H, CH CH ), 2.90–2.80 (m, 1 H, NCH CH ), 2.49 [s, 3 H, N(CH ) ], CCDC 1041588 (for 1b), 1041589 (for 3b), 1041590 (for 5a), and
2
3
2
3
3 2
.16 [s, 3 H, C(CH ) Ph], 1.82 [s, 3 H, C(CH ) Ph], 1.81 [s, 3 H,
1041591 (for 5b) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
3
2
3 2
C(CH ) Ph], 1.58 [s, 3 H, N(CH ) ], 1.40 (s, 3 H, ArCH ), 1.37 [s, 3 H,
3
2
3 2
3
C(CH ) Ph], 1.34 (s, 3 H, ArCH ), 0.49 (t, J = 7.0 Hz, 3 H, NCH CH ),
3
2
3
2
3
1
3
0
1
1
1
4
3
.38 [s, 9 H, Si(CH ) ], –0.01 [s, 9 H, Si(CH ) ] ppm. C NMR (C D ,
3 3 3 3 6 6
Typical Polymerization Procedure: In a Braun Labstar glove box,
00 MHz): δ = 162.8, 154.4, 153.5, 147.5, 141.1, 140.4, 138.3, 136.3,
34.7, 134.1, 132.3, 129.4, 129.0, 128.1, 127.4, 126.2, 126.0, 125.9,
25.6, 124.0, 121.5, 118.1 (all Ar C), 58.9 (ArCH ), 51.4 (NCH CH ),
initiator solution (0.5 mL, 0.01
sequentially into a series of 10 mL Schlenk tubes loaded with rac-LA
0.144 g, 1.00 mmol) or α-MeTMC (0.116 g, 1.00 mmol) and suitable
M) in THF or toluene was injected
2
2
3
(
6.3 [N(CH ) ], 42.8 [C(CH ) Ph], 42.6 [C(CH ) Ph], 31.7 [C(CH ) Ph],
3
2
3 2
3 2
3 2
amounts of dry solvent. Then, each Schlenk tube was taken out of
the glove box and immersed in an oil bath thermostatted at 25 °C
or 50 °C for polymerization. The reaction mixture was quenched at
appropriate time intervals by adding wet petroleum ether and then
1.4 [C(CH ) Ph], 27.2 (NCH CH ), 20.4 (ArCH ), 20.0 (ArCH ), 6.5
3
2
2
3
3
3
(
SiCH ) ppm. C H N OSi Zn (835.64): calcd. C 70.43, H 8.08, N 5.03;
3 49 67 3 2
found C 70.05, H 8.01, N 4.70.
1
5
extracted with CH Cl . Monomer conversion was monitored by H
[
(L )ZnN(SiMe ) ] (5b): A similar method was employed as that
2
2
3
2
5
NMR spectroscopy after removal of all the volatile substances of
the withdrawn aliquot. The bulk solution was treated with an excess
of methanol and the precipitated polymer was collected. The ob-
tained polymers were dried in a vacuum oven at 60 °C for 24 h.
described for 1b. L H (0.683 g, 1.00 mmol) was treated with
Zn[N(SiMe ) ] (0.386 g, 1.00 mmol) in toluene (15 mL) at room
3
2 2
temp. to give a foamlike material. Recrystallization from toluene/
hexane afforded colorless crystals as complex 5b (503 mg, 55.5 %),
1
m.p. 111–113 °C. H NMR (C D , 400 MHz): δ = 7.61–7.52 (m, 7 H,
6
6
In the cases in which 2-propanol was used, the solution of the
initiator was injected into the solution of the monomer in toluene
to which 2-propanol was added. Otherwise the procedures were
the same.
ArH), 7.50 (d, J = 8.2 Hz, 1 H, ArH), 7.36 (t, J = 7.5 Hz, 2 H, ArH),
7.18–7.09 (m, 1 H, ArH), 7.06–6.99 (m, 1 H, ArH), 6.94 (t, J = 7.4 Hz,
1 H, ArH), 6.80 (d, J = 7.7 Hz, 2 H, ArH), 6.71 (t, J = 7.7 Hz, 1 H, ArH),
6.59 (t, J = 7.7 Hz, 1 H, ArH), 6.37 (t, J = 7.2 Hz, 1 H, ArH), 6.28 (d,
J = 8.7 Hz, 2 H, ArH), 6.18 (t, J = 7.6 Hz, 2 H, ArH), 4.74 (d, J =
1
1
2
4.9 Hz, 1 H, ArCH ), 4.08 (d, J = 15.0 Hz, 1 H, ArCH ), 3.05–2.99 (m,
2
2
H, NCH CH ), 2.75–2.66 (m, 1 H, NCH CH ), 2.63 [s, 3 H, N(CH ) ], Acknowledgments
2
3
2
3
3 2
.14 [s, 3 H, C(CH ) Ph], 1.88 [s, 3 H, C(CH ) Ph], 1.86 [s, 3 H,
3
2
3 2
This work was subsidized by the National Natural Science Foun-
dation of China (NNSFC) (grant numbers 21074032 and
21474028), and the Fundamental Research Funds for the Cen-
C(CH ) Ph], 1.54 [s, 3 H, N(CH ) ], 1.46 [s, 3 H, C(CH ) Ph], 0.42 (t, J =
3
2
3 2
3 2
7.2 Hz, 3 H, NCH CH ), 0.40 [s, 9 H, Si(CH ) ], –0.07 [s, 9 H, Si(CH ) ]
2 3 3 3 3 3
13
ppm. C NMR (C D , 100 MHz): δ = 162.8, 154.0, 153.5, 146.0, 141.4,
6
6
1
1
36.7, 135.7, 135.5, 134.4, 132.0, 131.7, 130.5, 129.5, 129.4, 129.3, tral Universities (grant number WD1113011). All the financial
28.5, 128.2, 128.1, 127.6, 127.4, 127.2, 126.9, 126.8, 126.4, 126.2, support is gratefully acknowledged.
Eur. J. Inorg. Chem. 2016, 3791–3803
www.eurjic.org
3801
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Received: April 15, 2016
Published Online: July 14, 2016
Eur. J. Inorg. Chem. 2016, 3791–3803
www.eurjic.org
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