Exploring steric effects in diastereoselective synthesis of chiral aminophenolate zinc complexes and stereoselective ring-opening polymerization of rac-lactide

Article

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Exploring Steric Eﬀects in Diastereoselective Synthesis of Chiral

Aminophenolate Zinc Complexes and Stereoselective Ring-Opening

Polymerization of rac-Lactide

Haobing Wang,^†Yang Yang,^†and Haiyan Ma*

Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, East China University of

Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China

S

* Supporting Information

ABSTRACT: A series of tridentate chiral aminophenol

proligands and corresponding zinc complexes, LZnX (L =

(S)-2-{[(1-R⁴-2-pyrrolidinyl)CH₂N(R³)-]CH₂}-6-R¹-4-R²-

C₆H₂O, X = N(SiMe₃)₂, R³= ⁿBu, R⁴= Bn: R¹= R²= Cl (1),

t

R¹= R²= Me (2), R¹= R²= Bu (3); X = N(SiMe₃)₂, R¹=

trityl, R²= Me: R³= n-octyl, R⁴= Bn (4), R³= Bn, R⁴= Bn

(5), R³= ⁿBu, R⁴= naphthalen-1-ylmethyl (6), R³= ⁿBu, R⁴=

ⁱPr (7); R¹= R²= cumyl, R³= Et, R⁴= Bn: X = N(SiMe₃)₂(8),

X = O^tBu (9), X = Et (10), X = Cl (11)), have been

synthesized. Complexes 4, 6, and 11 were obtained as

enantiopure products (4 and 6 as enantiopure a; 11 as

enantiopure b), while complexes 1−3, 5, and 7−10 as a pair of

diastereomers, but in diﬀerent ratios, which have been proved by X-ray diﬀraction and NMR spectroscopic studies. When

exposed to the ring-opening polymerization of rac-lactide, most of these complexes can eﬀectively produce PLAs with narrow

polydispersities, desirable molecular weights, and moderate to high isotacticities. The structure−selectivity relationships,

including the relationships of structure−synthesis diastereoselectivity and structure−polymerization stereoselectivity, have been

further investigated. Consistent trends of diastereoselectivity and stereoselectivity are observed with the variations of the R¹

group at the ortho-position of the phenolate ring and the R³group in the pyrrolidinyl moiety. The decrease of the steric bulkiness

of the R⁴group on the central amine has less inﬂuence on the diastereoselectivity, but leads to considerable loss of the

stereoselectivity, whereas the decrease of the steric bulkiness of the X group results in a reverse of the diastereoselectivity, but

shows no inﬂuence on the stereoselectivity. There is probably no direct relationship between the diastereoselectivity in complex

synthesis and the stereoselectivity of the complex toward the ROP of rac-LA. The stereocontrol of these complexes might largely

rely on the substituents in the ligand framework rather than their diastereomer ratios.

the metal center. Moreover, the prochiral nitrogen atom of an

amine moiety would turn into chiral after coordination,⁸which,

in combination with other inherent chirality within the ligand,

the helicity of the ligand wrapping the metal center, as well as

the stereogenic metal center in a four- or ﬁve-coordinate metal

complex, brings versatile distereoselective control in complex

synthesis, hence inﬂuencing the stereoselectivity in polymer-

ization. For instance, zinc complexes bearing achiral amino-

phenolate ligands reported by Tolman’s group (Chart 1, I)^3b

and our group (Chart 1, II)^3i,nare racemic mixtures both in

solution and in the solid state, despite the presence of the

stereogeneity at the amine donor and the metal center. When

other inherent chiral centers were introduced, mixtures of

diastereomers were obtained, as for the chiral aminophenolate

zinc complex III (Chart 1) reported by Mehrkhodavandi’s

group^3fand the aluminum complexes IV (Chart 1) reported by

INTRODUCTION

■

Aminophenols, as easily available, tunable, and even recyclable

compounds, have been widely used to stabilize Lewis acidic

metal centers,¹such as alkali metals,²alkaline earth metals and

Zn,³Al and In,⁴Ge and Sn,⁵rare earth metals,⁶as well as group

4 metals,⁷to provide active initiators for the catalytic ring-

opening polymerization (ROP) of lactides (LAs). The readily

adjustable nature of these compounds further allows systematic

studies concerning the steric and electronic eﬀects of ligands on

the activity and selectivity of the corresponding metal

complexes toward the ROP of rac-LA. Among a variety of

aminophenolate metal complexes, chiral complexes arising from

either achiral or chiral aminophenolate ligands have gained

considerable attention in the stereoselective polymerization of

rac-lactide, due to their potential in forming stereoregular PLAs

with controlled physical/mechanical properties.^{3p−r,4a,f,i,7h,i}

By serving as bridging linkers or terminal blocks, the amine

moieties in an aminophenolate ligand architecture play a key

role in establishing a speciﬁc coordination environment around

Received: February 15, 2016

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Chart 1

Scheme 1. Synthetic Route of Proligands L¹H−L⁸H

Chen’s group.^4bAll of these complexes showed low stereo-

selectivities for the ROP of rac-LA, possibly owing to the

presence of multiple catalytic species. Those racemic or

diastereomer mixtures also brought diﬃculties for under-

standing the detailed catalytic mechanisms. Very recently, Kol

and co-workers reported a series of alkyl aluminum complexes

bearing salan ligands assembled by a chiral 2,2′-bipyrrolidine

skeleton,^4jwhich were all obtained as single diastereomers

where the two N donors have identical conﬁgurations (Chart 1,

V). With chlorine atoms at the ortho- and para-positions of the

phenoxy rings, almost perfect heterotacticity (P_r> 0.98) was

achieved in the ROP of rac-LA by using the initiator in racemic

form, involving a proposed insertion/autoinhibition/exchange

mechanism. It was noted that the clear restraint of this

bipyrrolidine skeleton strongly supports the involvement of

well-deﬁned “chiral-at-metal” (single diastereomer) catalytic

species, which was proposed to be in favor of the stereoselective

polymerization of rac-lactide in this system. Such correlated

diastereoselectivity and stereoselectivity were also observed for

metal initiators bearing ligand frameworks beyond the amino-

phenolate ligands,^4a,15oparticularly the isoselective indium and

yttrium complexes reported by Mehrkhodavandi’s and Arnold’s

groups, all formed as homochiral diastereomers.

Our group has been interested in developing biocompatible

zinc and magnesium complexes stabilized by achiral and chiral

aminophenolate ligands for the ring-opening polymerization of

rac-lactide. Recently, we introduced a chiral pyrrolidinyl group

to the aminophenlate ligand framework, and enantiopure zinc

complexes S_CS_NR_NR_Zn-VI (Chart 1),^3p,qwere diastereoselec-

tively synthesized by a combination of the o-trityl group on the

phenoxy moiety, the benzyl group on the central amine, and

the N-ⁿbutyl group on the (S)-2-pyrrolidinyl ring, which also

showed high isoselectivity (P_m= 0.80−0.84). The variation of

the ligand substituents, however, led to the formation of

mixtures of diastereomers and lower isoselectivities in the ROP

of rac-LA.^3pWhile the issue of diastereomer persists in the

literature, to the best of our knowledge, no broadly suitable

strategy toward avoiding isomer interference has been put

forward to overcome this challenge. Besides, the tendency of

isoselectivity is likely beneﬁted from the enhanced content of

one speciﬁc diastereomer, but the relationship of the

diastereoselectivity of a complex and its performance in

stereoselective polymerization of rac-lactide is still unclear.

Herein, we optimized the catalyst’s structure by ﬁne-tuning the

substituents of the NNO-type chiral aminophenolate ligand,

resulting in a series of zinc complexes with a variety of

diastereomer ratios. Meanwhile, their catalytic activity and

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Scheme 2. Synthetic Route of Complexes 1−7

stereocontrol in the ROP of rac-LA as well as the structure−

diastereoselectivity−stereoselectivity relationships were further

investigated.

characterized by X-ray diﬀraction studies (vide post) (speciﬁc

isomer ratios, see Schemes 2 and 3).¹⁰

Besides the variation of ligand substituents, a variation of the

monodentate X group in this series of complexes LZnX was

also considered. Thus, proligand L⁸H with moderate steric

bulkiness was chosen for this purpose. As illustrated in Scheme

3, the tert-butoxide derivative 9 was prepared in a

straightforward manner by addition of tert-butanol to the in

situ generated complex 8 in toluene. Unexpectedly, the

resultant analytically pure product was found to have a diﬀerent

diastereomer ratio from that of the silylamido complex 8 [8

(a:b = 1:1.2) vs 9 (a:b = 1:2.3)]. The isopropoxide derivative

[(L⁸)ZnOⁱPr] (a:b = 1:3) was initially isolated as a yellow oily

RESULTS AND DISCUSSION

■

Synthesis and Characterization of Chiral Amino-

phenolate Zinc Complexes. According to the procedure

we reported previously,^3pthe chiral aminophenol proligands

L¹H−L⁸H were synthesized from (S)-prolinamide via alkyla-

tion, reduction, condensation−reduction, and Mannich reac-

tion as viscous oil or white powders in 37.1−77.1% yields

(Scheme 1). The stoichiometric reactions of L¹H−L⁸H with 1

equiv of Zn[N(SiMe₃)₂]₂at room temperature aﬀorded the

corresponding zinc silylamido complexes 1−8 (Schemes 2 and

3) in 40−69% yields. Being consistent with our previous

i

solid after treatment of 8 with PrOH in toluene, but its poor

crystallinity hampered the isolation of a pure product. An

attempt to synthesize this isopropoxide derivative by using

EtZnⁱOPr as the metal precursor was also unsuccessful; instead,

the zinc ethyl complex 10 was isolated but again with a diﬀerent

diastereomer ratio of a:b = 1:10. In THF, the two-step

reactions of proligand L⁸H with stoichiometric amounts of

KN(SiMe₃)₂and ZnCl₂in sequence yielded zinc chloride

complex 11 as an enantiopure complex. Zinc tert-butoxide

complex 9 could also be synthesized by a salt metathesis

reaction of zinc chloride complex 11 with KO^tBu, accompanied

by the formation of 1 equiv of KCl. However, the enantiopure

complex 11 did not lead to complex 9 as a single isomer;

complex 9 obtained via this method has exactly the same

diastereomer ratio as that obtained via the amine elimination

pathway, which indicates that the diastereoselectivity in

synthesis does not depend on the raw materials, but on the

structure of the target complex.

Scheme 3. Synthetic Route of Complexes 8−11

It was further found that, for all of those complexes with

diastereomers, the ratios of two isomers hardly changed when

conducted further recrystallization procedures. Moreover, the

variable-temperature ¹H NMR spectroscopic studies of

previously reported zinc complexes^3pof the same type

indicated that no obvious ﬂuxional behavior or dynamic

exchange process could be observed in broad temperature

ranges and the ratio of two diastereomers keeps constant

thoroughly (Figures S23 −S25). On the basis of these facts, it is

suggested that the ratio of two diastereomers of the obtained

complex is under a thermodynamical control of the reaction.

For a better understanding of the ligand structure−

diastereoselectivity relationship, the structures of complexes

1−11 and two previously reported zinc complexes 12 and 13^3p

of the same type as well as their diastereomer ratios are

work,^3palthough four stereogenic centers are present in the

structure, complexes 1−3, 5, 7, and 8 were obtained as a

mixture of two diastereomers, respectively,⁹whereas complexes

4 and 6 were obtained as enantiopure products. In the cases

where a mixture of diastereomers was obtained, the resonances

1

of two isomers in the H NMR spectrum were fully assigned

and the conﬁguration of each diastereomer could be identiﬁed

on the basis of the coupling constants of ArCH₂protons of the

ligand, via a comparison with those of the enantiopure

complexes, whose absolute conﬁgurations were further

1

summarized in Chart 2. Moreover, their corresponding H

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Chart 2. Diastereoselective Synthesis of Zinc Complexes Controlled by Substituent Eﬀects

1

Figure 1. Benzyl region of the H NMR spectra of zinc complexes 1, 2, 3, and 13 (C₆D₆, 400 MHz).

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1

Figure 2. Benzyl region of the H NMR spectra of zinc complexes 12, 13, 4, and 5 (C₆D₆, 400 MHz).

1

Figure 3. Benzyl region of the H NMR spectra of zinc complexes 6, 7, and 13 (C₆D₆, 400 MHz).

NMR spectra (only the benzyl region of the ligand) are

illustrated into groups in Figures 1−4 to support the

assignment of two diastereomers in each case. In order to

investigate the steric inﬂuence of one speciﬁc position, initially

the substituents of pyrrolidinyl and central amine moieties are

ﬁxed with R³being an n-butyl group and R⁴being a benzyl

group, respectively, and the ortho and para groups of the

phenoxy ring are changed gradually by size (Chart 2, 1, 2, 3,

and 13). When the ortho- and para-substituents are chlorine

atoms, as illustrated in Figure 1, complex 1 shows obviously

the ortho- and para-substituents of the phenoxy ring from

chloride (1) to methyl (2), tert-butyl (3), and trityl/Me (13),

as shown in Chart 2 and Figure 1, the ratio of two

diastereomers in these complexes increases gradually from a:b

= 1:3.2 to 1:2, 1:0.5, and 1:0. The decreasing content of

diastereomeric isomer b along with the increasing steric

bulkiness of the ortho-substituent of the phenoxy ring clearly

indicates that a bulkier ortho-substituent installed on the

phenolate platform would beneﬁt the diastereoselective syn-

thesis of isomer a.

Previously, we found that the formation of diastereomer b

can be completely suppressed by slightly increasing the steric

bulkiness of the pyrrolidinyl substituent (R³) from ethyl to n-

butyl [from 12 (a:b = 7:1) to 13 (enantiopure a); see Chart

1

two independent sets of signals in the benzyl region of the H

NMR spectrum. According to the coupling constant rules

obeyed by these complexes,^3p,qthe major component is in line

with the isomer b and thus the ratio of a:b is 1:3.2. Changing

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2].^3pIn this work, we proceeded to increase the size of R³from

n-butyl to n-octyl, and the NMR spectrum shows that complex

4 is still enantiopure (isomer a, Figure 2). With further

replacement of n-octyl by benzyl, however, the resultant

complex 5 shows to be a mixture of two diastereomers (a:b =

3:2) again, which, to some extent, indicates that only a

substituent of moderate size on the pyrrolidinyl nitrogen can

serve the purpose to produce enantiopure structure a.

crystal and reﬁnement data are reported in Tables S1 and S2

(see the SI). As shown by the molecular structures (Figures

5−8), all complexes have a monomeric structure in the solid

state, in which the zinc atom is four-coordinate by three donors

of the aminophenolate ligand and one silylamido group

adopting a distorted tetrahedron geometry around the metal

center. The related bond lengths and angles around the metal

center in these structures are close to one another, and the

selected data are listed in Table 1.

Diﬀerent R⁴groups such as 1-naphthalenylmethyl (6),

isopropyl (7), as well as benzyl (13) were introduced to

discuss the eﬀect of the steric hindrance of the central amine

moiety on the diastereoselective synthesis. As shown in Figure

3, the variation of R⁴from benzyl to 1-naphthalenylmethyl has

no inﬂuence on the diastereoselectivity and complex 6 is also

As depicted in Figure 6, two independent molecular

structures with diﬀerent absolute conﬁgurations and nearly

identical bond angles and lengths were obtained for complex 5,

which are just corresponding to the two diastereomers a and b.

However, it is not always possible to have two diastereomers in

one unit cell. For complexes 1, 3, and 7, only the molecular

structure of isomer a was determined in the solid state, despite

the moderate diastereomer ratios of 1 and 3. The molecular

structures of 1a, 3a, and 7a are very similar to one another

(Figure 5). In terms of stereochemistry, these structures

(isomer a) possess identical chirality at the zinc atom, which is

also consistent with that of enantiopure complex 13. Although

the corresponding orientations of substituents around the three

donor atoms of the tridentate ligand in these structures are also

identical, the descriptor assigned to the central amine nitrogen

atom or the pyrrolidinyl nitrogen atom could be diﬀerent due

to the involvement of a substituent of lower or higher priority.

Thus, for 5a/5b having a benzyl group on the pyrrolidinyl

nitrogen and 7a having an isopropyl on the central amine

nitrogen, diﬀerent absolute conﬁgurations are signed to them,

that is, 5a (S_CS_NS_NR_Zn), 5b (S_CS_NR_NS_Zn), and 7a (S_CR_NR_NR_Zn),

when compared with that of 1a, 3a, and 13 (S_CS_NR_NR_Zn).

Zinc ethyl complex 10 has a diastereomer ratio of a:b = 1:10.

As expected, the molecular structure of 10b with opposite

coordinate modes in the central amine moiety and the metal

center to those of the above isomers a was obtained (Figure 7).

The coordination geometry around the zinc center in 10b is

also a distorted tetrahedron, similar to those of the above

isomers a. When compared with Tolman and Hillmyer’s LZnEt

complex (L = 2,4-di-tert-butyl-6-{[(2′-dimethylaminoethyl)-

methylamino]-methyl}phenolate), we found that the bond

length and angles of 10b are similar to those of this complex

(Zn−C1 = 1.997(4), Zn−O1 = 1.956(2), Zn−N1 = 2.147(3),

Zn−N2 = 2.128(3) (Å); N1−Zn−N2 = 84.85(13), N1−Zn−

O1 = 93.32(12), N2−Zn−O1 = 99.76(12), C1−Zn−N1 =

117.82(16) (deg)).^3bHowever, the parameters of the above

isomers a quite resemble the structures of LZnEt (L = chiral

diaminophenoxy NNO aminophenolate ligand) reported by

Mehrkhodavandi’s group (Zn−C1 = 1.971(6), Zn−O1 =

1.927(3), Zn−N1 = 2.152(4), Zn−N2 = 2.185(5) (Å); N1−

Zn−N2 = 82.19 (15), N1−Zn−O1 = 95.54 (14), N2−Zn−O1

= 111.61 (16), C1−Zn−N1 = 124.5 (2) (deg)).^3fThe Zn−C40

distance of 1.983(3) Å is close to that of the usually observed

Zn(II)−alkyl bonds (1.93−2.00 Å).¹¹

1

entantiopure (isomer a, Chart 2). However, in the H NMR

spectrum of complex 7 with a isopropyl group on the central

amine, in addition to the dominant resonances of isomer a, a

small amount of isomer b could be observed (a:b = 10:1).

Compared to the crucial inﬂuence of the phenoxy ortho-

substituent (R¹), the impact of R⁴on the diastereoselectivity is

indistinctive, which is, however, consistent with its relatively far

location from the metal center.

For complexes 8−10 bearing the same aminophenolate

ligand, the inﬂuence of the X group of diﬀerent sizes/types has

been studied (Figure 4). The replacement of the bulky

Figure 4. Benzyl region of the ¹H NMR spectra of zinc complexes 8−

11 (C₆D₆, 400 MHz).

silylamino group in complex 8 by a tert-butoxy group does

not aﬀect much the diastereomer ratio (1:1.2 vs 1:2.3) of the

corresponding zinc complex 9. After introducing a relatively

small ethyl group, a sudden surge in the content of isomer b

(a:b = 1:10) is observed. It gives us a certain hint that the

reduction of the size of the X group would be favorable for the

generation of isomer b. As expected, the smallest chloride

group leads to the formation of enantiopure complex 11 in b

conﬁguration (Figure 4).

The molecular structure of enantiopure complex 11 (Figure

8) possesses the same conﬁguration as that of 10b, which

conﬁrms that complex 11 was obtained as the diastereomer b.

The bond angles involving Cl1 in 11 are relatively smaller than

the corresponding ones involving C40 in 10b, while the bond

lengths of N1−Zn1, N2−Zn1, O1−Zn1 in 11 are shorter than

those in 10b. All of these data indicate that the introduction of

the chloride group results in a tighter coordination of the

aminophenolate ligand around the zinc center in complex 11,

which is probably arising from the smaller size of the chlorine

From the above comparisons, it is clear that the steric

bulkiness of the ortho-substitutent (R¹) on the phenoxy ring,

the substituent (R³) on the pyrrolidinyl nitrogen atom, and the

X group play crucial roles in determining the diastereoselec-

tivity: the bulkier these substituents are, the higher the content

of diastereomer a will be.

Molecular Structures of 1a, 3a, 5a/5b, 7a, 10b, and 11.

X-ray quality crystals of 1a, 3a, and 10b were obtained from

saturated benzene solutions and of 5a/5b, 7a, and 11 were

obtained from mixed toluene/n-hexane solutions. Detailed

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Figure 5. Molecular structures of 1a, 3a, and 7a (ellipsoids drawn at the 30% probability, H atoms omitted for clarity).

eﬀectively initiate the ROP of rac-LA either as single

component initiators or in the presence of 2-propanol, giving

PLAs with moderate to high molecular weights and narrow to

Table 1. Selected Bond Lengths (Å) and Angles (deg) for

Structures 1a, 3a, 5a, and 7a

1a

3a

5a

7a

relatively broad molecular weight distributions (M_w/M_n

=

bond lengths

2.116(9)

2.128(12)

1.935(10)

1.868(8)

bond angles

116.3(4)

115.7(4)

97.1(3)

1.04−1.72). In agreement with our earlier observations, all

complexes exhibited lower catalytic activities in THF than in

toluene, especially for those bearing a bulky ligand, most

probably as a result of competitive coordination of the solvent

molecular to the zinc center.

Zn1−N1

Zn1−N2

Zn1−N3

Zn1−O1

2.1176(16)

2.1611(17)

1.9253(17)

1.9557(14)

2.151(5)

2.136(6)

1.926(5)

1.982(4)

2.183(5)

2.136(4)

1.950(5)

1.952(3)

The structure of the ancillary ligand has the most signiﬁcant

inﬂuence on the catalytic activity. Particularly, the substituent at

the ortho-position of the phenoxide unit of the ligand plays a

crucial role in determining the polymerization activity.

Complexes 1 and 2 with a small group (chloride or methyl,

respectively) at the ortho-position of the phenoxide moiety

exhibited the highest activities among this series of complexes.

High monomer conversions could be reached within 15 min

when the polymerization runs were carried out in toluene

(Table 2, runs 1 and 5). When the ortho-substituent of the

phenolate ring was changed to a tert-butyl (3) or trityl (13)

group, an obvious decrease in activity was observed (3, 75 min,

96%, run 9; 13, 180 min, 84%, run 37). Preliminary kinetic

study proved that, as illustrated in Figure 9, the apparent rate

constants decreased signiﬁcantly during the increased steric

hindered of ortho-substituents (1, k_{app(rac‑LA)}= 0.7078 min⁻¹; 2,

k_{app(rac‑LA)}= 0.4878 min⁻¹; 3, k_{app(rac‑LA)}= 0.1539 min⁻¹; 13,

k_{app(rac‑LA)}= 0.0404 min⁻¹). This is a reasonable result that

bulky groups located in the coordination sphere of the central

N3−Zn1−O1

N3−Zn1−N1

O1−Zn1−N1

N3−Zn1−N2

O1−Zn1−N2

N1−Zn1−N2

114.14(7)

126.79(7)

106.40(6)

123.97(7)

93.74(6)

84.44(6)

115.9(2)

121.4(2)

96.85(18)

128.5(2)

102.5(2)

83.9(2)

120.02(18)

122.07(19)

96.6(2)

131.1(4)

103.0(4)

85.1(4)

121.26(19)

104.57(15)

84.95(18)

atom as well as its electronic nature. Moreover, the Zn−Cl

bond distance in complex 11 is 2.1949(9) Å, slightly shorter

than the reported Zn−Cl bond lengths in complexes with an

analogous coordination environment (2.20−2.34 Å).¹²

Ring-Opening Polymerization of rac-LA with Com-

plexes 1−10. Except for the zinc chloride complex 11, which

was believed not to be active for the ROP of cyclic ester, all of

the synthesized zinc complexes 1−10 were evaluated as

initiators for the ROP of rac-LA in toluene and THF at

ambient temperature. The representative polymerization data

are summarized in Table 2. These zinc complexes can

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Figure 6. Molecular structures of 5a and 5b (ellipsoids drawn at the 30% probability, H atoms omitted for clarity).

catalytic activity. The substituent located in the pyrrolidinyl

amine moiety also plays an important role in inﬂuencing the

polymerization activity: the decreasing activity order of 13

(k_{app(rac‑LA)}= 0.0404 min⁻¹) > 4 (k_{app(rac‑LA)}= 0.0233 min⁻¹) >

5 (k_{app(rac‑LA)}= 0.0173 min⁻¹) is consistent with the increasing

steric hindrance of the substituent on the pyrrolidinyl nitrogen

atom (n-butyl < n-octyl < benzyl). The same tendency could be

observed when changing the substituent on the central amine

nitrogen atom from benzyl to 1-naphthalenylmethyl; complex 6

exhibited a considerably lower activity (k_{app(rac‑LA)}= 0.0140

min⁻¹) toward rac-LA polymerization than 13 (k_{app(rac‑LA)}

=

0.0404 min⁻¹). Unexpected, the introduction of 2-propyl to the

same position led to a dramatic drop of the activity of complex

7, which proved to be the least active (Table 2, run 25) initiator

among all the silylamido complexes in this work. At present, we

have no reasonable explanation to account for this unusual

phenomenon. By looking at the molecular structure of the

lactate model complex obtained from complex 13,^3qit is

tentatively suggested that the tertiary substitution mode of the

isopropyl methine carbon in complex 7 might bring certain

steric hindrance to the coordination sites of the active species

generated in the polymerization process.

Figure 7. Molecular structure of 10b (ellipsoids drawn at the 30%

probability, H atoms omitted for clarity). Selected bond lengths (Å)

and angles (deg): Zn1−C40, 1.983(3); Zn1−O1, 1.9297(16); Zn1−

N2, 2.152(2); Zn1−N1, 2.1421(19); O1−Zn1−C40, 128.06(10);

O1−Zn1−N2, 104.17(8); O1−Zn1−N1, 93.77(7); C40−Zn1−N2,

115.55(11); C40−Zn1−N1, 120.85(10); N1−Zn1−N2, 84.76(8).

The nature of the initiating group (X) inﬂuences both the

catalytic activity and the polymerization controllability. As

illustrated in Table 2, the isopropoxide complexes L¹⁻⁸ZnOⁱPr,

generated in situ from the reaction of silylamido complexes 1−8

with 2-propanol, exhibited signiﬁcantly higher activities than

their corresponding silylamido complexes for the ROP of rac-

LA both in toluene and in THF. Besides, the resulting polymers

initiated by the in situ generated isopropoxide group possess

more controlled molecular weights and relatively narrow

molecular weight distributions. For instance, using complex 4

as the initiator, the polymerization proceeded to 88%

conversion within 3 h in toluene (Table 2, run 13), giving

PLA with obviously high molecular weight compared with the

calculated value (M_n= 8.13 × 10⁻⁴g mol⁻¹, M_w/M_n= 1.26),

whereas high conversion of 92% was reached after 2 h in the

presence of 2-propanol (Table 2, run 14) under otherwise

identical conditions, and PLA with a smaller and more

controlled molecular weight (M_n= 3.32 × 10⁻⁴g mol⁻¹) and

a very narrow molecular weight distribution (M_w/M_n= 1.06)

was obtained. The polymerization behavior of complexes 8−10

was further investigated to compare the initiation eﬃciency of

Figure 8. Molecular structure of 11 (ellipsoids drawn at the 30%

probability, H atoms omitted for clarity). Selected bond lengths (Å)

and angles (deg): Zn1−O1, 1.877(2); Zn1−N1, 2.085(2); Zn1−N2,

2.080(3); Zn1−Cl1, 2.1949(9); O1−Zn1−N2, 110.90(10); O1−

Zn1−N1, 98.00(9); N2−Zn1−N1, 87.67(10); O1−Zn1−Cl1,

124.66(8); N2−Zn1−Cl1, 113.90(8); N1−Zn1−Cl1, 114.36(7).

metal tend to hinder the coordination/insertion of the

incoming monomer, and hence are not beneﬁcial to the

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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

a

Table 2. Polymerization of rac-LA Catalyzed by Zinc Complexes 1−10 and 13

b

c

d

e

run

cat.

feed ratio

solvent

temp. (°C)

time (min)

conv. (%)

M_c(× 10⁴)

M_n(× 10⁴)

PDI

P_m

1

2

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

200:1:0

200:1:1

200:1:0

200:1:1

200:1:0

200:1:1

tol

25

15

99

100

91

98

94

96

95

96

99

98

95

88

92

82

89

87

98

83

91

92

93

81

92

55

99

93

95

89

99

90

89

60

98

86

93

84

99

2.87

2.89

2.64

2.83

2.73

2.77

2.75

2.74

2.78

2.86

2.84

2.74

2.55

2.66

2.38

2.57

2.52

2.83

2.41

2.63

2.67

2.69

2.35

2.66

1.60

2.86

2.70

2.74

2.58

2.86

2.61

2.57

1.75

2.83

2.47

2.68

2.42

4.53

4.18

10.6

3.34

6.26

2.22

7.11

1.66

4.02

3.49

3.53

3.33

8.13

3.32

7.60

2.47

7.07

3.14

3.49

3.06

5.86

3.14

8.49

2.85

1.72

3.68

9.97

2.49

3.39

2.01

4.45

2.67

2.97

2.71

13.2

3.72

2.95

3.00

1.69

1.59

1.52

1.40

1.53

1.45

1.54

1.45

1.72

1.63

1.51

1.19

1.26

1.06

1.39

1.04

1.37

1.06

1.35

1.06

1.60

1.09

1.62

1.07

1.71

1.13

1.49

1.10

1.48

1.15

1.27

1.37

1.27

1.37

1.47

1.08

1.66

1.12

0.45

0.44

0.45

0.49

0.50

0.49

0.73

0.74

0.80

0.81

0.70

0.71

0.79

0.78

0.55

0.56

0.74

0.72

0.73

0.76

0.75

0.76

0.75

0.76

0.80

tol

5

3

1

THF

tol

20

4

1

5

2

15

6

2

tol

5

7

2

THF

tol

20

8

2

15

9

3

75

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

3

tol

20

3

THF

tol

150

45

3

4

3 h

2 h

7 h

5 h

10 h

2.5 h

8 h

5 h

15 h

3.5 h

15 h

7 h

30 h

7 h

80

4

tol

4

THF

tol

4

5

tol

5

THF

tol

5

6

tol

6

THF

tol

6

7

tol

8

tol

8

tol

25

8

THF

tol

120

40

8

9

40

9

THF

tol

90

10

12

13

48 h

360

90

tol

180

tol

90

2.85

a

b

c

[rac-LA]₀= 1.0 mmol·L⁻¹; feed ratio = [LA]₀/[M]₀/[ⁱPrOH]₀. Determined by ¹H NMR spectroscopy. M_n,calcd= [LA]₀/[M]₀× conv. % × 144.13

d

e

g·mol⁻¹+ 161; with the presence of isopropanol, M_n,calcd= [LA]₀/[M]₀× conv. % × 144.13 g·mol⁻¹+ 60. Determined by GPC. Determined by

analysis of all of the tetrad signals in the methine region of the homonuclear-decoupled H NMR spectrum.

1

Figure 9. ln([LA]₀/[LA]_t) vs time plots for the ROP of rac-LA catalyzed by zinc complexes 1−6 and 13 in toluene, [LA]₀/[Zn]₀/[ⁱPrOH]₀=

200:1:1, 25 °C).

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Article

diﬀerent groups. Complex 8 with a silylamido group showed a

lower activity than alkoxide initiators and produced PLA with a

high molecular weight and a broad molecular weight

distribution (Table 2, run 27). The polymerization initiated

by an isopropoxide group OⁱPr (8/2-propanol catalytic system)

gave more predictable M_nand narrow PDI than that initiated

by an O^tBu group (9). Zinc ethyl complex 10 showed the

lowest catalytic activity among all the complexes in this work

(Table 2, runs 33 and 35). To have some insight into the

polymerization mechanism operated by the zinc ethyl complex,

a typical polymer sample obtained by complex 10 (without

substituent at the ortho-position of the phenolate ring

signiﬁcantly aﬀects the ability of a catalyst to choose one

speciﬁc enantiomeric monomer. For instance, changing the

ortho-methyl in complex 2 (P_m= 0.60) to a tert-butyl group in 3

resulted in a signiﬁcant increase in polymer isotacticity (P_m=

0.74). This trend is maintained when further increasing the size

of the ortho-substituent of the phenolate ring: complex 13

containing an ortho-trityl group gave an even higher isotacticity

(P_m= 0.80, Table 2, run 37). Such a gradient change in

stereoselectivity is consistent with the previous observation

that, for rac-LA polymerization operated via a chain-end control

mechanism, the improvement of stereoselectivity normally

requires bulky substituents near the metal center. It is noticed

that the increasing trend of isoselectivity with the increase of

the steric bulkiness of the ortho-substituent is parallel to the

increasing trend of the diastereoselectivty in complexes

synthesis; that is, a complex which was more diastereose-

lectively synthesized also showed higher isoselectivity in the

ROP of rac-LA. Moreover, based on the fact that complex 1

obtained heterotactic-biased PLA from the ROP of rac-LA,

while the sterically comparable complex 2 yielded isotactic-

biased PLA, we, therefore, suggest that the stereoselectivity

switch herein is similar to that obtained for aluminum

complexes bearing salan ligands reported by Gibson’s group:

the extraordinary heteroselectivity obtained by a chloro-

substituted complex is probably an eﬀect of the electron-

withdrawing group.⁴ⁱ

i

addition of PrOH, run 33) was analyzed with the matrix

assisted laser desorption/ionization time-of-ﬂight mass spec-

trometry (MALDI-TOF MS), which indicated the presence of

polymer chains capped on one end with a −CH(CH₃)OH

group and on the other end with a HC(O)− terminus rather

than a CH₃CH₂− terminus (corresponding to the formula

H(OCHMeCO)_nH·K⁺with consecutive peaks separated by

increments of 144 or 72 Da; see in the SI, Figure S26). In

i

addition, the NMR tube reaction of complex 10 with PrOH

was monitored. Interestingly, no reaction was observed even at

70 °C upon standing for 24 h (SI, Figure S28). The MALDI-

TOF mass spectrum of the polymer sample obtained by

i

complex 10 with the addition of PrOH revealed the presence

i

of polymer chains end-capped by −CH(CH₃)OH and PrOC-

(O)− termini exclusively (SI, Figure S27). These facts may

suggest that the ROP of rac-LA catalyzed by zinc ethyl complex

10 probably involves a monomer activation mechanism, where

the zinc center serves as a Lewis acid and the impurities (H₂O,

The modiﬁcation of the substitute on the pyrrolidinyl N also

led to a signiﬁcant change in the stereoselectivity of the

corresponding catalyst. The replacement of an ethyl group in

the pyrrolidinyl moiety by an n-butyl group not only led to the

highly diastereoselective synthesis of complex 13 (Et: a:b = 7:1

(12); ⁿBu: enantiopure a (13)) but also resulted in an

i

etc.) or the added PrOH act as initiators.

Since Spassky et al. illustrated the highly isoselective

polymerization of rac-LA initiated by aluminum Schiﬀ base

complexes,¹³many aluminum complexes supported by salen-

based ligands acting as highly isoselective catalysts in the ROP

of rac-LA have been reported.¹⁴Beyond aluminum complexes,

not until very recently did some examples of other metals with

speciﬁc ligand frameworks aﬀord isotactic PLAs (P_m= 0.77−

0.94) from rac-LA,¹⁵which are in contrast to the relatively large

number of heteroselective catalysts with various ancillary ligand

architecture.¹⁶In this work, most of the complexes (2−10)

showed slight to high isoselectivities (P_m= 0.59−0.80) toward

the ROP of rac-LA. Previously, we suggested that the chiral zinc

complex 13 might realize the isoselective control in the

polymerization of rac-lactide via a cooperation mechanism of

predominated chain-end control and a peripheral enantiomor-

phic-site control mechanism.^3qIn this work, the microstructural

analysis of the resultant isotactic PLAs from rac-LA via

homodecoupled proton NMR spectroscopy indicated the

relatively small rmr signal in comparison with rmm, mrr, and

mrm signals, as well as the close integral ratio of rmm, mrr, and

mrm to 1:1:1 (see the SI, Figures S31−S38), which also

suggests the operation of a similar cooperative mechanism. It is

widely accepted that the stereoselectivity of a given catalyst

which operates via a chain-end control mechanism is highly

dependent on the structure of the ancillary ligand.¹Thus, we

put our research emphasis on the relationship of ligand steric

eﬀect and the stereoselectivity of the corresponding complex,

and intended to establish some correlation between the

diastereoselectivity in complex synthesis and the stereoseletivity

in the ROP of rac-LA.

enhancement of the isoselectivity (P_m= 0.77 for 12 vs P_m

=

0.81 for 13) toward the ROP of rac-LA.^3pThere was no

essential diﬀerence between the stereoselective behaviors of

enantiopure complexes 4 and 13 (Table 2, runs 13 and 37),

n

indicating that changing butyl to octyl at the pyrrolidinyl N

exerted little inﬂuence on the outcomes of the diastereose-

lective synthesis and the selective ROP of rac-LA. By further

increasing the size of the substituent at this position by

introducing a benzyl group, two diastereomers emerged again

in complex 5. Meanwhile, the corresponding stereoselectivity

decreased to P_m= 0.71. Therefore, the variation trends of the

diastereoselectivity in complex synthesis and the isoselectivity

of the complex in rac-LA polymerization are similar (12 < 13 =

4 > 5) again, which raises an important mechanistic question:

Does the isoselectivity of complexes rely heavily on the

diastereoselectivity?

With this question in mind, we set out to understand the

inﬂuence of the substituent at the central amine N as well as the

X group on the stereoselectivity. The steric bulkiness of the

substituent at the central amine N of the ligand was proved to

be another crucial factor aﬀecting the stereoselctivity of the

complex. There was a slight or negligible decrease of the

stereoselectivity when the benzyl group was replaced by a 1-

naphthalenylmethyl group (P_m= 0.80 for 13 vs P_m= 0.79 for

6). However, when a 2-propyl was introduced to the central

amine N, a dramatic decrease in the stereoselectivity toward the

ROP of rac-LA was witnessed for the corresponding complex 7

(P_m= 0.55), although this complex was obtained in high

diastereoselectivity (a:b = 10:1). As for complexes 8 and 9

possessing the same aminophenolate ligand but with diﬀerent

We investigated the inﬂuence of substituents of ancillary

ligands on the stereoselectivities of these complexes in the ROP

of rac-LA. The polymerization data indicated that the

J

DOI: 10.1021/acs.inorgchem.6b00378

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Article

initiating X groups as well as diﬀerent diastereomer ratios,

identical isoselectivities for the ROP of rac-LA were obtained

(P_m= 0.74−0.75), which is, however, reasonable since active

species bearing the same aminophenolate ligand and the same

“X” group (herein, X is O-polymeryl) are considered to be

formed in these two systems. Moreover, the moderate

isoselectivity achieved by complexes 8 and 9 with dominant b

isomers further implies that both the two diastereomers of a

given complex might possess quite similar stereoselectivity

toward the ROP of rac-LA. As indicated by the molecular

structures of these series of complexes, the parameters of two

diastereomers are indeed quite similar.^3pThe variation of the

diastereomer ratios in complexes 8−11 with the variation of the

X group promoted us to monitor the reactions of complex 7

with diﬀerent alcohols. The NMR tube reaction of complex 7

with i-PrOH and methyl 2-hydroxyisobutyrate indeed showed

the appearance of diastereomers in diﬀerent ratios (Figure

S29). Because of the overlapping of signals, the diastereomers

generated from complex 7 and i-PrOH could not be assigned

properly, whereas the reaction of complex 7 and methyl 2-

hydroxyisobutyrate clearly showed two diastereomers in a ratio

of a:b = 3:1. This value is comparable to that of complex 9

(1:2.3), but signiﬁcantly diﬀerent stereoselectivities were

obtained. Therefore, based on these facts, we would suggest

that, for this series of complexes, there is probably no direct

relationship between the diastereoselectivity in complex

synthesis and the stereoselectivity of the corresponding

complex toward the ROP of rac-LA. The diastereoselectivity

is mainly determined by the substituents at the ortho-position of

the phenolate ring and the central amine N, as well as the X

group, whereas the stereoselectivity in polymerization is mainly

controlled by the substituents at the ortho-position of the

phenolate ring, the central amine N, and the pyrrolidinyl N.

They share two common factors but are also inﬂuenced

signiﬁcantly by the third factor which is, however, less aﬀecting

to the other.

substituents in the ligand framework rather than their

diastereomer ratios.

EXPERIMENTAL SECTION

■

General Considerations and Material. All manipulations were

carried out under a dry argon atmosphere using standard Schlenk-line

or glovebox techniques. Toluene and n-hexane were reﬂuxed over

sodium benzophenone ketyl prior to use. Benzene-d₆and other

reagents were carefully dried and stored in a glovebox. rac-Lactide

(Aldrich) was recrystallized with dry toluene and then sublimed twice

under vacuum at 100 °C. K[N(SiMe₃)₂] and Zn[N(SiMe₃)₂]₂were

synthesized according to the literature method.³ⁱThe chiral amine

materials were prepared according to the reported literature with some

modiﬁcations (see the Supporting Information).^3p2-Propanol, tert-

butanol, and methyl 2-hydroxyisobutyrate were dried over calcium

hydride prior to distillation. All other chemicals were commercially

available and used after appropriate puriﬁcation. Glassware and vials

used in the polymerization were dried in an oven at 120 °C overnight

and exposed to a vacuum−argon cycle three times.

NMR spectra were recorded on a Bruker AVANCE-400

spectrometer at 25 °C (¹H: 400, 500 MHz; ¹³C: 100 MHz) unless

1

otherwise stated. Chemical shifts for H and ¹³C NMR spectra were

referenced internally using the residual solvent resonances and

reported relative to tetramethylsilane (TMS). Elemental analyses

were performed on a Carlo Erba EA-1106 instrument. Spectroscopic

analyses of polymers were performed in CDCl₃. Gel permeation

chromatography (GPC) analyses were carried out on a Waters

instrument (M1515 pump, Optilab Rex injector) in THF at 35 °C, at a

ﬂow rate of 1 mL·min⁻¹. Calibration standards were commercially

available narrowly distributed linear polystyrene samples that cover a

broad range of molar masses (4 × 10⁴< M_n< 4.4 × 10⁵g·mol⁻¹).

CCDC numbers 1450905 (10b), 1450906 (11), 1450907 (7a),

1450908 (5a/5b), 1450909 (3a), and 1450910 (1a) contain the

supplementary crystallographic data for this paper. These data can be

obtained free of charge from the Cambridge Crystallographic Data

Centre via www.ccdc.cam.ac.uk/data_request/cif.

Syntheses. (S)-2-{N-Benzyl-N-[(1-ⁿbutylpyrrolidin-2-yl)methyl]-

aminomethyl}-4,6-dichlorophenol (L¹H). Paraformaldehyde (0.600

g, 20.0 mmol) and 2,4-dichlorophenol (1.63 g, 10.0 mmol) were added

to a solution of (S)-N-benzyl-1-(1-ⁿbutylpyrrolidin-2-yl)methanamine

(2.18 g, 10.0 mmol) in ethanol (30 mL) at 90 °C within 12 h with

magnetic stirring. The mixture was cooled to ambient temperature and

concentrated under vacuum to give a red oil, which was puriﬁed by

column chromatography (silica gel 100 Merck, petroleum ether/ethyl

acetate = 5:1) to provide a dark red oil (2.18 g, 51.7%) after removal of

CONCLUSIONS

■

A series of zinc complexes 1−11, with a pair of diastereomers

or an enantiopure structure, supported by chiral tridentate

aminophenolate ligands were synthesized and structurally

characterized. X-ray diﬀraction and NMR studies demonstrated

that, via optimizing the steric bulkiness of the substituents in

the ligand framework as well as the X group, either the

diastereomer a or the diastereomer b could be diastereose-

lectively synthesized. In general, a bulky group in the ortho-

position of the phenoxy moiety, a moderate group at the

pyrrolidinyl N atom, and a benzyl group at the central amine N

atom would beneﬁt the diastereoselective synthesis of isomer a,

whereas the smallest X group could realize the diastereose-

lective synthesis of isomer b. In the presence or absence of an

external alcohol, complexes 1−10 acted as eﬀective initiators

for the ring-opening polymerization of rac-lactide, producing

PLAs with moderate to high isotacticities. Although for most of

these zinc complexes (1−6), their stereoselectivities are

corresponding to their diastereoselectivities, the exceptional

low isoselectivity of complex 7 and the moderate isoselectivity

of complexes 8 and 9 containing dominant isomers b imply that

there is probably no direct relationship between the

diastereoselectivity in complex synthesis and the stereo-

selectivity of the complex toward the ROP of rac-LA. The

stereocontrol of these complexes might largely rely on the

1

all the volatiles. H NMR (400 MHz, CDCl₃): δ 7.36−7.22 (m, 6H,

4

2

ArH), 6.90 (d, J = 2.4 Hz, 1H, ArH), 3.91 (d, J = 14.1 Hz, 1H,

ArCH₂N), 3.72 (d, ²J = 13.0 Hz, 1H, ArCH₂N), 3.61 (d, ²J = 14.1 Hz,

1H, ArCH₂N), 3.47 (d, J = 13.0 Hz, 1H, ArCH₂N), 3.16−3.04 (m,

2

1H, NCH₂− of pyrrolidinyl), 2.68−2.60 (m, 1H, NCH− of

pyrrolidinyl), 2.60−2.45 (m, 3H, NCH₂− of pyrrolidinyl and

NCH₂CH), 2.15−2.05 (m, 2H, NCH₂CH₂CH₂CH₃), 2.04−1.92 (m,

1H, −CH₂− of pyrrolidinyl), 1.72−1.61 (m, 2H, −CH₂− of

pyrrolidinyl), 1.49−1.34 (m, 3H, −CH₂− of pyrrolidinyl and NCH₂

3

CH₂CH₂CH₃), 1.33−1.18 (m, 2H, NCH₂CH₂CH₂CH₃), 0.89 (t, J =

7.3 Hz, 3H, NCH₂CH₂CH₂CH₃). ¹³C {¹H} NMR (100 MHz,

CDCl₃): δ 152.6, 136.2, 130.0, 128.9, 128.8, 128.1, 127.3, 125.0, 123.5,

121.8, (All ArC), 62.9 (ArCH₂N), 59.3 (ArCH₂N), 58.3 (NCH− of

pyrrolidinyl), 57.9 (NCH₂− of pyrrolidinyl), 55.4 (NCH₂CH), 54.2

(NCH₂CH₂CH₂CH₃), 31.0 (NCH₂CH₂CH₂CH₃), 30.2 (−CH₂− of

pyrrolidinyl), 22.7 (−CH₂− of pyrrolidinyl), 20.9 (NCH₂CH₂CH₂-

CH₃), 14.2 (NCH₂CH₂CH₂CH₃). Anal. Calcd for C₂₃H₃₀Cl₂N₂O: C,

65.55; H, 7.18; N, 6.65. Found: C, 65.53; H, 7.07; N, 6.52%.

(S)-2-{N-Benzyl-N-[(1-ⁿbutylpyrrolidin-2-yl)methyl]aminomethyl}-

4,6-dimethylphenol (L²H). The procedure was the same as that of

L¹H, except that 2,4-dimethylphenol (1.22 g, 10.0 mmol) was used to

1

aﬀord L²H as a viscous colorless oil (1.97 g, 51.8%). H NMR (400

MHz, CDCl₃): δ 10.63 (s, 1H, ArOH), 7.34−7.22 (m, 5H, ArH), 6.86

(s, 1H, ArH), 6.66 (s, 1H, ArH), 3.94 (d, ²J = 13.7 Hz, 1H, ArCH₂N),

K

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Inorganic Chemistry

Article

2

3.73 (d, J = 13.0 Hz, 1H, ArCH₂N), 3.52 (d, J = 13.7 Hz, 1H,

ArCH₂N), 3.39 (d, ²J = 13.0 Hz, 1H, ArCH₂N), 3.06 (ddd, ²J = 9.4, ³J

= 6.9, ³J = 2.9 Hz, 1H, NCH₂− of pyrrolidinyl), 2.61 (ddd, ²J = 11.6, ³J

(S)-2-{N-Benzyl-N-[(1-benzylpyrrolidin-2-yl)methyl]amino-

methyl}-4-methyl-6-tritylphenol (L⁵H). The procedure was the same

as that of L¹H, except that 4-methyl-2-tritylphenol (3.50 g, 10.0 mmol)

and (S)-N-benzyl-1-(1-benzylpyrrolidin-2-yl)methanamine (10.0

3

= 10.1, J = 6.2 Hz, 1H, NCH₂CH₂CH₂CH₃), 2.56−2.40 (m, 3H,

1

mmol) were used to aﬀord L⁴H as a white solid (4.80 g, 74.7%). H

NCH₂CH and NCH− of pyrrolidinyl), 2.23 (s, 3H, ArCH₃), 2.21 (s,

3H, ArCH₃), 2.11−1.91 (m, 3H, NCH₂CH₂CH₂CH₃and NCH₂− of

pyrrolidinyl and −CH₂− of pyrrolidinyl), 1.69−1.51 (m, 2H, −CH₂−

of pyrrolidinyl), 1.46−1.33 (m, 3H, −CH₂− of pyrrolidinyl and

NCH₂CH₂CH₂CH₃), 1.31−1.21 (m, 2H, NCH₂CH₂CH₂CH₃), 0.88

NMR (400 MHz, C₆D₆): δ 10.65 (s, 1H, ArOH), 7.61−7.51 (m, 6H,

ArH), 7.36 (d, ⁴J = 1.7 Hz, 1H, ArH), 7.22−7.05 (m, 14H, ArH), 7.01

3

4

(t, J = 7.3 Hz, 3H, ArH), 6.91−6.85 (m, 2H, ArH), 6.73 (d, J = 1.6

Hz, 1H, ArH), 3.71 (d, ³J = 13.6 Hz, 1H, ArCH₂N), 3.63 (d, ³J = 13.6

Hz, 1H, ArCH₂N), 3.35 (d, ³J = 13.6 Hz, 1H, ArCH₂N), 3.33 (d, ³J =

12.8 Hz, 1H, ArCH₂N), 3.02 (d, ³J = 13.6 Hz, 2H, ArCH₂N), 2.90 (d,

³J = 12.8 Hz, 1H, ArCH₂N), 2.68−2.58 (m, 1H, NCH₂− of

pyrrolidinyl), 2.29−2.18 (m, 3H,, NCH− of pyrrolidinyl and

(t, J = 7.3 Hz, 3H, NCH₂CH₂CH₂CH₃). ¹³C{¹H} NMR (100 MHz,

3

CDCl₃): 153.3, 137.2, 130.8, 130.1, 128.6, 127.9, 127.7, 127.2, 124.8,

121.5 (All Ar-C), 62.8 (ArCH₂N), 59.3 (ArCH₂N), 59.0 (NCH− of

pyrrolidinyl), 58.6 (NCH₂− of pyrrolidinyl), 55.4 (NCH₂CH), 54.4

(NCH₂CH₃), 31.2 (NCH₂CH₂CH₂CH₃), 30.5 (−CH₂− of pyr-

rolidinyl), 22.8 (−CH₂− of pyrrolidinyl), 21.6 (ArCH₃), 20.6

(NCH₂CH₂CH₂CH₃), 16.0 (ArCH₃), 14.0 (NCH₂CH₂CH₂CH₃).

Anal. Calcd for C₂₅H₃₆N₂O: C, 78.90; H, 9.53; N, 7.36. Found: C,

77.67; H, 9.08; N, 7.61%.

2

3

NCH₂CH), 2.15 (s, 3H, ArCH₃), 1.75 (dt, J = 9.2 Hz, J = 7.5 Hz,

1H, NCH₂− of pyrrolidinyl), 1.53−1.41 (m, 1H, −CH₂− of

pyrrolidinyl), 1.27−1.09 (m, 2H, −CH₂− of pyrrolidinyl), 1.07−0.96

(m, 1H, −CH₂− of pyrrolidinyl). ¹³C{¹H} NMR (100 MHz, C₆D₆): δ

154.9, 147.1, 140.8, 138.0, 134.9, 132.2, 131.7, 130.7, 129.6, 129.3,

129.0, 128.8, 128.5, 127.9, 127.8, 127.4, 126.1, 123.3 (All ArC), 64.3

(ArCPh₃), 62.4 (ArCH₂N), 60.3 (ArCH₂N), 59.9 (ArCH₂N), 59.5

(NCH− of pyrrolidinyl), 58.1 (NCH₂− of pyrrolidinyl), 54.5

(NCH₂CH), 30.5 (−CH₂− of pyrrolidinyl), 23.1 (−CH₂− of

pyrrolidinyl), 21.5 (ArCH₃). Anal. Calcd for C₄₆H₄₆N₂O: C, 85.94;

H, 7.21; N, 4.36. Found: C, 86.01; H, 7.20; N, 4.30%

(S)-2-{N-Benzyl-N-[(1-ⁿbutylpyrrolidin-2-yl)methyl]aminomethyl}-

4,6-di-tert-butylphenol (L³H). The procedure was the same as that of

L¹H, except that 2,4-di-tert-butylphenol (2.06 g, 10.0 mmol) was used

to aﬀord L³H as a viscous colorless oil (2.86 g, 61.5%). ¹H NMR (400

MHz, CDCl₃): δ 10.63 (s, 1H, ArOH), 7.34−7.22 (m, 5H, ArH), 7.20

(d, ²J = 2.3 Hz, 1H, ArH), 6.85 (d, ²J = 2.3 Hz, 1H, ArH), 3.99 (d, ²J =

13.5 Hz, 1H, ArCH₂N), 3.76 (d, ²J = 13.0 Hz, 1H, ArCH₂N), 3.55 (d,

²J = 13.5 Hz, 1H, ArCH₂N), 3.40 (d, ²J = 13.0 Hz, 1H, ArCH₂N), 3.06

(S)-2-{N-(Methyl-1-naphthyl)-N-[(1-ⁿbutylpyrrolidin-2-yl)methyl]-

aminomethyl}-4-methyl-6-titylphenol (L⁶H). The procedure was the

same as that of L¹H, except that 4-methyl-2-tritylphenol (3.50 g, 10.0

mmol) and (S)-N-(methyl-1-naphthyl)-1-(1-ⁿbutylpyrrolidin-2-yl)-

methanamine (10.0 mmol) were used to aﬀord L⁴H as a white solid

(3.12 g, 47.4%). ¹H NMR (400 MHz, CDCl₃): δ 10.30 (s, 1H, ArOH),

7.85 (d, ³J = 8.2 Hz, 1H, ArH), 7.81 (d, ³J = 7.7 Hz, 1H, ArH), 7.73 (d,

³J = 8.2 Hz, 1H, ArH), 7.46−7.35 (m, 2H, ArH), 7.34−7.29 (m, 1H,

2

3

(ddd, J = 9.3, J = 7.0, J = 2.6 Hz, 1H, NCH₂− of pyrrolidinyl),

2.67−2.57 (m, 1H, NCH− of pyrrolidinyl), 2.56−2.40 (m, 3H,

NCH₂CH and NCH₂CH), 2.11−1.91 (m, 3H, NCH₂CH₂CH₂CH₃

and −CH₂− of pyrrolidinyl), 1.71−1.53 (m, 3H, −CH₂− of

pyrrolidinyl), 1.44 (s, 9H, C(CH₃)₃), 1.42−1.33 (m, 2H, NCH₂-

CH₂CH₂CH₃), 1.27 (s, 9H, C(CH₃)₃), 1.32−1.18 (m, 2H, NCH₂-

CH₂CH₂CH₃), 0.88 (t, J = 7.3 Hz, 3H, NCH₂CH₂CH₂CH₃). ¹³C{¹H}

NMR (100 MHz, CDCl₃): 154.0, 140.7, 137.4, 135.8, 130.1, 128.6,

127.6, 124.0, 123.1, 121.8, (All Ar-C), 62.7 (ArCH₂N), 60.0

(ArCH₂N), 59.4 (NCH− of pyrrolidinyl), 58.6 (NCH₂− of pyr-

rolidinyl), 55.5 (NCH₂CH), 54.5 (NCH₂CH₂CH₂CH₃), 35.1

(C(CH₃)₃), 34.3 (C(CH₃)₃), 31.9 (C(CH₃)₃), 31.2 (−CH₂− of

pyrrolidinyl), 30.4 (C(CH₃)₃), 29.8 (NCH₂CH₂CH₂CH₃), 22.6

(−CH₂− of pyrrolidinyl), 21.0 (NCH₂CH₂CH₂CH₃), 14.2 (NCH₂-

CH₂CH₂CH₃). Anal. Calcd for C₃₁H₄₈N₂O: C, 80.12; H, 10.43; N,

6.03. Found: C, 80.31; H, 10.21; N, 6.00%.

4

ArH), 7.26−7.20 (m, 7H, ArH), 7.19−7.07 (m, 9H, ArH), 6.95 (d, J

= 1.6 Hz, 1H, ArH), 6.87 (d, ⁴J = 1.6 Hz, 1H, ArH), 4.06 (d, ²J = 13.0

Hz, 1H, ArCH₂N), 3.78 (d, ²J = 13.0 Hz, 1H, ArCH₂N), 3.68 (d, ²J =

2

13.4 Hz, 1H, ArCH₂N), 3.61 (d, J = 13.4 Hz, 1H, ArCH₂N), 2.83−

2.72 (m, 1H, NCH₂− of pyrrolidinyl), 2.53−2.44 (m, 2H, NCH− and

2

3

NCH₂− of pyrrolidinyl), 2.41 (dd, J = 13.4, J = 6.4 Hz, 1H, N,

NCH₂CH), 2.18 (s, 3H, ArCH₃), 2.15−2.06 (m, 1H, NCH₂CH₂CH₂-

CH₃), 1.84−1.72 (m, 2H, NCH₂CH₂CH₂CH₃and NCH₂CH), 1.33−

1.17 (m, 3H, −CH₂− of pyrrolidinyl), 1.16−1.04 (m, 4H, NCH₂-

CH₂CH₂CH₃), 0.99−0.87 (m, 1H, −CH₂− of pyrrolidinyl), 0.78 (t, ³J

= 7.0 Hz, 3H, NCH₂CH₂CH₂CH₃). ¹³C{¹H} NMR (100 MHz,

CDCl₃): δ 146.5, 131.5, 128.7, 128.6, 128.1, 127.0, 126.4, 125.6, 125.5,

125.3, 124.0 (All ArC), 63.9 (ArCPh₃), 63.6 (ArCH₂N), 60.1

(ArCH₂N), 59.8 (NCH− of pyrrolidinyl), 56.8 (NCH₂− of pyr-

rolidinyl), 56.0 (NCH₂CH), 54.1 (NCH₂CH₂CH₂CH₃), 30.5 (CH₂-

CH₂CH₂CH₃), 28.8 (−CH₂− of pyrrolidinyl), 22.2(−CH₂− of

pyrrolidinyl), 21.1 (ArCH₃), 21.0 (CH₂CH₂CH₂CH₃), 14.2 (CH₂-

CH₂CH₂CH₃). Anal. Calcd for C₄₇H₅₀N₂O: C, 85.67; H, 7.65; N, 4.25.

Found: C, 85.49; H, 7.61; N, 4.19%.

(S)-2-{N-Benzyl-N-[(1-ⁿoctylpyrrolidin-2-yl)methyl]aminomethyl}-

4-methyl-6-tritylphenol (L⁴H). The procedure was the same as that of

L¹H, except that 4-methyl-2-tritylphenol (3.50 g, 10.0 mmol) and (S)-

N-benzyl-1-(1-ⁿoctylpyrrolidin-2-yl)methanamine (10.0 mmol) were

used to aﬀord L⁴H as a white solid (4.30 g, 66.5%). H NMR (400

1

MHz, CDCl₃): δ 10.27 (s, 1H, ArOH), 7.36 (d, ³J = 4.4 Hz, 1H, ArH),

7.26−7.16 (m, 14H, ArH), 7.16−7.10 (m, 3H, ArH), 6.91 (d, ⁴J = 1.7

Hz, 1H, ArH), 6.87 (dd, ³J = 6.5 Hz, ⁴J = 2.8 Hz, 2H, ArH), 6.79 (d, ⁴J

= 1.7 Hz, 1H, ArH), 3.83 (d, ²J = 13.6 Hz, 1H, ArCH₂N), 3.54 (d, ²J =

13.6 Hz, 1H, ArCH₂N), 3.45 (d, ²J = 12.8 Hz, 1H, ArCH₂N), 3.27 (d,

²J = 12.8 Hz, 1H, ArCH₂N), 2.91 (ddd, ²J = 9.3, ³J = 7.2, ³J = 2.5 Hz,

(S)-2-{N-ⁱPropyl-N-[(1-ⁿbutylpyrrolidin-2-yl)methyl]amino-

methyl}-4-methyl-6-tritylphenol (L⁷H). The procedure was the same

as that of L¹H, except that 4-methyl-2-tritylphenol (3.50 g, 10.0 mmol)

and (S)-N-ⁱpropyl-1-(1-ⁿbutylpyrrolidin-2-yl)methanamine (10.0

2

3

1H, NCH₂− of pyrrolidinyl), 2.46 (td, J = 11.1, J = 5.8 Hz, 1H,

NCH₂(CH₂)₆CH₃), 2.37 (d, ³J = 10.1 Hz, 1H, NCH₂CH), 2.32−2.20

(m, 2H, NCH₂(CH₂)₆CH₃), 2.17 (s, 3H, ArCH₃), 1.95−1.85 (m, 2H,

NCH₂CH and NCH− of pyrrolidinyl), 1.60−1.49 (m, 1H, −CH₂− of

pyrrolidinyl), 1.47−1.37 (m, 2H, −CH₂− of pyrrolidinyl), 1.35−1.08

(m, 12H, NCH₂(CH₂)₆CH₃), 1.04−0.93 (m, 1H, −CH₂− of

1

mmol) were used to aﬀord L⁴H as a white solid (3.12 g, 47.4%). H

NMR (400 MHz, CDCl₃): δ 7.26−7.16 (m, 12H, ArH), 7.14−7.08

(m, 3H ArH), 6.88 (d, ⁴J = 1.8 Hz, 1H ArH), 6.73 (d, ⁴J = 1.7 Hz, 1H

ArH), 3.78 (d, ²J = 14.0 Hz, 1H, ArCH₂N), 3.55 (d, ²J = 14.0 Hz, 1H,

ArCH₂N), 3.06−2.97 (m, 1H, NCH₂− of pyrrolidinyl), 2.82−2.69 (m,

1H, NCH(CH₃)₂), 2.65−2.54 (m, 1H, NCH− of pyrrolidinyl), 2.40−

2.30 (m, 1H, NCH₂CH), 2.27−2.18 (m, 2H, NCH₂CH₂CH₂CH₃and

NCH₂− of pyrrolidinyl), 2.15 (s, 3H, ArCH₃), 2.07−1.94 (m, 2H,

NCH₂CH₂CH₂CH₃and NCH₂CH), 1.59−1.47 (m, 3H, −CH₂− of

pyrrolidinyl), 1.44−1.31 (m, H, −CH₂− of pyrrolidinyl), 1.31−1.12

(m, 4H, NCH₂CH₂CH₂CH₃), 0.87 (t, ³J = 7.2 Hz, 3H, NCH₂-

CH₂CH₂CH₃), 0.84 (d, ³J = 6.7 Hz, 6H, NCH(CH₃)₂). ¹³C{¹H}

NMR (100 MHz, CDCl₃): δ 154.6, 146.3, 133.6, 131.4, 130.6, 128.7,

127.0, 126.3, 125.3, 122.8 (All ArC), 63.4 (ArCPh₃), 63.0 (ArCH₂N),

55.5(NCH− of pyrrolidinyl), 55.5 (NCH₂− of pyrrolidinyl), 54.5

pyrrolidinyl), 0.88 (t, J = 7.0 Hz, 3H, NCH₂(CH₂)₆CH₃). ¹³C{¹H}

3

NMR (100 MHz, CDCl₃): δ 154.1, 146.3, 137.3, 133.8, 131.4, 131.0,

130.2, 129.2, 128.4, 127.4, 127.1, 126.6, 125.4, 122.8 (All ArC), 63.5

(ArCPh₃), 62.7 (ArCH₂N), 59.8 (ArCH₂N), 59.1 (NCH− of

pyrrolidinyl), 57.1 (NCH₂− of pyrrolidinyl), 55.6 (NCH₂CH), 54.2

(NCH₂(CH₂)₆CH₃), 32.1 (−NCH₂CH₂(CH₂)₅CH₃), 29.9 (−CH₂−

of pyrrolidinyl), 29.7, 29.5, 28.9, 27.6 (−CH₂− of ⁿoctyl), 22.9

(−CH₂− of pyrrolidinyl), 22.6 (−CH₂− of ⁿoctyl), 21.1 (ArCH₃), 14.3

n

(−CH₃of octyl). Anal. Calcd for C₄₇H₅₆N₂O: C, 84.89; H, 8.49; N,

4.21. Found: C, 84.95; H, 8.57; N, 4.27%.

L

DOI: 10.1021/acs.inorgchem.6b00378

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

(ArCH₂N), 53.1 (NCH(CH₃)₂), 49.5 (NCH₂CH₂CH₂CH₃), 31.2

(−CH₂− of pyrrolidinyl), 29.8 (NCH₂CH₂CH₂CH₃), 22.8 (−CH₂−

of pyrrolidinyl), 21.1 (ArCH₃), 21.0 (NCH₂CH₂CH₂CH₃), 18.7

(NCH(CH₃)₂), 15.3 (NCH(CH₃)₂), 14.3 (NCH₂CH₂CH₂CH₃). Anal.

Calcd for C₃₉H₄₈N₂O: C, 83.52; H, 8.63; N, 4.60. Found: C, 83.30; H,

8.73; N, 4.85%.

pyrrolidinyl), 2.50 (s, 3H, Ar−CH₃), 2.48−2.40 (m, 1H, NCH₂-

CH₂CH₂CH₃), 2.22 (s, 3H, Ar−CH₃), 2.12−2.03 (m, 1H, NCH₂-

CH₂CH₂CH₃), 1.91 (td, 1H, ²J = 13.2, ³J = 4.2 Hz, NCH₂− of

pyrrolidinyl), 1.78 (td, ²J = 11.6, ³J = 4.3 Hz, 1H, NCH₂− of

pyrrolidinyl), 1.53−1.41 (m, 1H, −CH₂− of pyrrolidinyl), 1.39−1.30

(m, 1H, −CH₂− of pyrrolidinyl), 1.28−1.14 (m, 2H, NCH₂CH₂CH₂-

3

(S)-2-{N-(Methyl-1-naphthyl)-N-[(1-ethylpyrrolidin-2-yl)methyl]-

aminomethyl}-4,6-dicumylphenol (L⁸H). The procedure was the

same as that of L¹H, except that 2,4-dicumylphenol (3.30 g, 10.0

mmol) and (S)-N-benzyl-1-(1-ethylpyrrolidin-2-yl)methanamine (10.0

CH₃), 1.14−1.04 (m, 2H, NCH₂CH₂CH₂CH₃), 1.00 (t, J = 7.8 Hz,

3H, NCH₂CH₂CH₂CH₃), 0.94−0.82 (m, 1H, −CH₂− of pyrrolidinyl),

0.57 (s, 18H, N(Si(CH₃)₃)₂), 0.46−0.36 (m, 1H, −CH₂− of

pyrrolidinyl). ¹³C{¹H} (100 MHz, C₆D₆): δ 164.7, 133.3, 133.1,

132.7, 131.9, 129.3, 129.1, 127.6, 121.5, 121.1 (All ArC), 67.1

(ArCH₂N), 64.9 (ArCH₂N), 60.6 (NCH− of pyrrolidinyl), 58.9

(NCH₂− of pyrrolidinyl), 55. 9 (NCH₂CH), 51. 1

(NCH₂CH₂CH₂CH₃), 31.8 (NCH₂CH₂CH₂CH₃), 25.5 (−CH₂− of

pyrrolidinyl), 21.3 (ArCH₃), 21.1 (ArCH₃), 20.7 (−CH₂− of

pyrrolidinyl), 18.0 (NCH₂CH₂CH₂CH₃), 14.7 (NCH₂CH₂CH₂CH₃),

7.5 (N(Si(CH₃)₃)₂). Anal. Calcd For C₃₁H₅₃N₃OSi₂Zn: C, 61.51; H,

8.82; N, 6.94. Found: C, 61.36; H, 8.82; N, 6.89%.

1

mmol) were used to aﬀord L⁸H as a white solid (4.30 g, 77.1%). H

NMR (400 MHz, CDCl₃): δ 10.23 (s, 1H, ArOH), 7.37 (m, 4H, ArH),

7.36−7.10 (m, 9H, ArH), 6.91 (d, 2H, ³J = 6.2 Hz, ArH), 6.74 (d, 2H,

2

⁴J = 1.8 Hz, ArH), 3.88 (d, J = 13.6 Hz, 1H, ArCH₂N), 3.56 (d, J =

12.8 Hz, 1H, ArCH₂N), 3.42 (d, ²J = 13.6 Hz, 1H, ArCH₂N), 3.21 (d,

²J = 12.8 Hz, 1H, ArCH₂N), 3.05−2.97 (m, 1H, NCH− of

pyrrolidinyl), 2.69−2.60 (m, 1H, NCH₂− of pyrrolidinyl), 2.44−

2.30 (m, 3H, NCH₂CH and CH₂CH₃), 2.10−2.00 (m, 1H, NCH₂− of

pyrrolidinyl), 2.00−1.90 (m, 1H, CH₂CH₃), 1.73 (s, 3H, C(CH₃)₂Ph),

1.70−1.65 (m, 1H, −CH₂− of pyrrolidinyl), 1.69 (s, 6H, C(CH₃)₂Ph),

1.65 (s, 3H, C(CH₃)₂Ph), 1.56−1.41 (m, 2H, −CH₂− of pyrrolidinyl),

[(L³)ZnN(SiMe₃)₂] (3). In a glovebox, the aminophenol L³H (0.697

mg, 1.50 mmol) was dissolved in toluene (3 mL) and was cannulated

to a solution of Zn[N(SiMe₃)₂]₂(0.655 g, 1.50 mmol) in n-hexane.

The reaction mixture was allowed to be stirred at room temperature

overnight. The solvent and volatile components were removed under

reduced pressure to aﬀord a white vesicular solid, which was then

recrystallized with n-hexane. The resulting colorless crystals were

washed with cold n-hexane three times and dried under vacuum to give

the target complex 3 in 49.9% (0.516 g) as a mixture of two

diastereomers in a 2:1 ratio. NMR spectroscopic data of 3a: ¹H NMR

3

1.12−1.02 (m, 1H, −CH₂− of pyrrolidinyl), 0.99 (t, J = 7.1 Hz, 3H,

NCH₂CH₃). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 153.7, 151.6,

140.1, 137.1, 135.4, 130.2, 128.7, 128.4, 128.1, 127.8, 127.5, 127.1,

127.0, 126.1, 126.0, 125.6, 125.0, 124.9, 122.0 (All Ar-C), 62.2

(ArCH₂N), 59.8 (ArCH₂N), 59.1 (NCH− of pyrrolidinyl), 58.1

(NCH₂− of pyrrolidinyl), 53.79 (NCH₂CH), 49.12 (NCH₂CH₃), 42.6

(C(CH₃)₂Ph), 42.2 (C(CH₃)₂Ph), 31.3 (C(CH₃)₂Ph), 31.3 (C-

(CH₃)₂Ph), 30.2 (−CH₂− of pyrrolidinyl), 22.6 (−CH₂− of

pyrrolidinyl), 13.9 (NCH₂CH₃). Anal. Calcd for C₄₂H₅₆N₂O₂: C,

83.52; H, 8.63; N, 5.00; Found: C, 83.32; H, 8.56; N, 4.65%.

4

(400 MHz, C₆D₆): δ 7.57 (d, J = 2.5 Hz, 1H, ArH), 7.05 (m, 3H,

4

ArH), 6.89−6.82 (m, 2H, ArH), 6.68 (d, J = 2.5 Hz, 1H, ArH), 4.36

(d, ²J = 12.2 Hz, 1H, ArCH₂N), 4.26 (d, ²J = 14.1 Hz, 1H, ArCH₂N),

[(L¹)ZnN(SiMe₃)₂] (1). In a glovebox, the aminophenol L¹H (0.632

g, 1.50 mmol) was dissolved in toluene (3 mL) and was added

dropwise to a solution of Zn[N(SiMe₃)₂]₂(0.580 g, 1.50 mmol) in n-

hexane (3 mL). The reaction mixture was stirred at room temperature

overnight, whereas a white precipitate was formed. After ﬁltration, the

collected white precipitate was washed with cold n-hexane (3 × 2 mL)

and dried under vacuum to aﬀord the target complex 1 in 49.5%

(0.480 g) as a mixture of two diastereomers in a 1:3.2 ratio (isomer

4.17 (d, J = 14.1 Hz, 1H, ArCH₂N), 3.36 (d, J = 12.2 Hz, 1H,

ArCH₂N), 3.16−3.08 (m, 1H, NCH− of pyrrolidinyl), 2.60−2.49 (m,

2H, NCH₂CH₂CH₂CH₃₃), 2.46−2.31 (m, 2H, NCH₂− of pyrrolidin-

2

yl), 2.23 (dd, J = 16.4, J = 10.3 Hz, 1H, NCH₂CH), 2.28−2.18 (m,

2

3

1H, −CH₂− of pyrrolidinyl) 2.09 (dd, J = 14.4, J = 4.2 Hz, 1H,

NCH₂CH), 2.00−1.91 (m, 2H, −CH₂− of pyrrolidinyl), 1.82 (s, 9H,

C(CH₃)₃), 1.61−1.51 (m, 1H, −CH₂− of pyrrolidinyl), 1.27 (s, 9H,

C(CH₃)₃), 1.26−1.14 (m, 2H, NCH₂CH₂CH₂CH₃), 1.13−1.02 (m,

1

3

1a:isomer 1b). NMR spectroscopic data of 1b: H NMR (400 MHz,

2H, NCH₂CH₂CH₂CH₃), 0.98 (t, J = 7.2 Hz, 3H), 0.60 (s, 18H,

4

N(Si(CH₃)₃)₂). ¹³C{¹H} NMR (100 MHz, C₆D₆): δ 165.2, 138.4,

135.0, 132.7, 132.4, 131.5, 129.2, 129.0, 127.2, 125.3, 120.1 (All ArC),

64.4 (ArCH₂N), 60.5 (ArCH₂N), 58.8 (NCH− of pyrrolidinyl), 56.2

(NCH₂− of pyrrolidinyl), 50.7 (NCH₂CH), 48.9 (NCH₂CH₂CH₂-

CH₃), 36.3 (C(CH₃)₃), 34.4 (C(CH₃)₃), 32.5 (C(CH₃)₃), 30.9

(NCH₂CH₂CH₂CH₃), 30.7 (C(CH₃)₃), 25.0 (−CH₂− of pyr-

rolidinyl), 21.3 (−CH₂− of pyrrolidinyl), 19.8 (NCH₂CH₂CH₂CH₃),

14.5 (NCH₂CH₂CH₂CH₃), 7.8 (N(Si(CH₃)₃)₂). Anal. Calcd For

C₃₇H₆₅N₃OSi₂Zn: C, 64.45; H, 9.50; N, 6.09. Found: C, 64.41; H,

9.39; N, 6.00%.

C₆D₆): δ 7.45 (d, J = 2.7 Hz, 1H, ArH), 7.13−7.10 (m, 3H, ArH),

3

4

7.01 (dd, J = 6.4, J = 2.8 Hz, 2H, ArH), 6.42 (d, J = 2.7 Hz, 1H,

ArH), 4.08 (d, ²J = 13.8 Hz, 1H, ArCH₂N), 3.83 (d, ²J = 12.7 Hz, 1H,

ArCH₂N), 3.61 (d, ²J = 13.8 Hz, 1H, ArCH₂N), 2.72 (d, ²J = 12.7 Hz,

1H, ArCH₂N), 2.57−2.49 (m, 2H, NCH₂CH₂CH₂CH₃), 2.48−2.34

(m, 2H, NCH₂− of pyrrolidinyl), 2.21−2.10 (m, 1H, NCH− of

pyrrolidinyl), 1.99 (dd, ²J = 13.2, ²J = 13.4 Hz, 1H, NCH₂CH), 1.79−

1.72 (m, 1H, −CH₂− of pyrrolidinyl), 1.66 (dd, ²J = 13.4, ³J = 4.7 Hz,

1H, NCH₂CH), 1.70−1.59 (m, 1H, −CH₂− of pyrrolidinyl), 1.36−

1.25 (m, 1H, NCH₂CH₂CH₂CH₃), 1.23−1.12 (m, 2H, NCH₂-

CH₂CH₂CH₃), 1.03 (t, ³J = 7.2 Hz, 3H), 1.01−0.94 (m, 1H,

NCH₂CH₂CH₂CH₃), 0.84−0.76 (m, 1H, −CH₂− of pyrrolidinyl),

0.53 (s, 18H, Si(CH₃)₃), 0.35−0.25 (m, 1H, −CH₂− of pyrrolidinyl).

¹³C {¹H} NMR (100 MHz, C₆D₆): δ 162.5, 132.7, 131.7, 130.8, 129.4,

129.3, 125.4, 124.9, 116.9 (All ArC), 67.3 (ArCH₂N), 65.3 (ArCH₂N),

59.7 (NCH− of pyrrolidinyl), 58.9 (NCH₂− of pyrrolidinyl), 56.1

(NCH₂CH), 51.1 (NCH₂CH₂CH₂CH₃), 32.0 (NCH₂CH₂CH₂CH₃),

25.3 (−CH₂− of pyrrolidinyl), 21.1 (NCH₂CH₂CH₂CH₃), 20.6

(−CH₂− of pyrrolidinyl), 14.7 (NCH₂CH₂CH₂CH₃), 7.4 (Si(CH₃)₃).

Anal. Calcd for C₂₉H₄₇Cl₂N₃OSi₂Zn: C, 53.90; H, 7.33; N, 6.50.

Found: C, 53.84; H, 7.24; N, 6.44%.

[(L⁴)ZnN(SiMe₃)₂] (4). In a glovebox, the aminophenol L⁴H (0.997

g, 1.50 mmol) was dissolved in toluene (3 mL) and was cannulated to

a solution of Zn[N(SiMe₃)₂]₂(0.580 g, 1.50 mmol) in n-hexane (3

mL). The reaction mixture was allowed to be stirred at room

temperature overnight. The solvent and volatile components were

removed under reduced pressure to aﬀord a white vesicular solid,

which was then recrystallized with a mixture of n-hexane and toluene.

The resulting colorless crystals were washed with cold n-hexane three

times and dried under vacuum to give a white solid 4 in 66.6% (0.856

1

g) as an enantiopure product. H NMR (400 MHz, C₆D₆): δ 7.87−

7.50 (m, 6H, ArH), 7.41 (d, ⁴J = 2.2 Hz, 1H, ArH), 7.15−7.07 (m, 8H,

4

[(L²)ZnN(SiMe₃)₂] (2). The procedure was the same as that of

complex 1, except that L²H (0.579 g, 1.50 mmol) and Zn[N-

(SiMe₃)₂]₂(0.580 g, 1.50 mmol) were used to aﬀord a white solid of 2

(0.541 g, 59.6%) as a mixture of two diastereomers in 1:2 (isomer

ArH), 7.02−6.88 (m, 6H, ArH), 6.39 (d, J = 2.2 Hz, 1H, ArH), 4.38

(d, ²J = 12.2 Hz, 1H, ArCH₂N), 4.25 (d, ²J = 14.2 Hz, 1H, ArCH₂N),

2

4.14 (d, J = 14.2 Hz, 1H, ArCH₂N), 3.27 (d, J = 12.2 Hz, 1H,

ArCH₂N), 3.05 (dt, 1H, ²J = 12.8, ³J = 6.5 Hz, NCH₂− of

pyrrolidinyl), 2.29 (dd, 1H, ²J = 13.3 Hz, ³J = 7.2 Hz, NCH₂CH), 2.06

(s, 3H, ArCH₃), 2.00−1.93 (m, 2H, NCH₂CH and NCH− of

pyrrolidinyl), 1.90−1.80 (m, 2H, NCH₂(CH₂)₅CH₂CH₃), 1.53−1.27

(m, 11H, NCH₂− of pyrrolidinyl and NCH₂(CH₂)₅CH₂CH₃), 1.27−

1.12 (m, 4H, −CH₂− of pyrrolidinyl and N(CH₂)₆CH₂CH₃), 0.94 (t,

1

2a:isomer 2b). NMR spectroscopic data of 2b: H NMR (400 MHz,

C₆D₆): δ 7.14−7.08 (m, 4H, ArH), 7.06 (s, 1H, ArH), 6.89−6.81 (m,

1H, ArH), 6.39 (s, 1H, ArH), 4.23 (d, ²J = 13.8 Hz, 1H), 4.08 (d, ²J =

2

12.2 Hz, 1H), 3.77 (d, J = 13.8 Hz, 1H), 3.07 (d, J = 12.2 Hz, 1H),

2.73−2.63 (m, 2H, NCH₂CH), 2.63−2.55 (m, 1H, NCH− of

M

DOI: 10.1021/acs.inorgchem.6b00378

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

³J = 6.9 Hz, 3H, N(CH₂)₇CH₃), 0.67−0.54 (m, 1H, −CH₂− of

pyrrolidinyl), 0.52−0.43 (m, 1H, −CH₂− of pyrrolidinyl), 0.36 (s,

18H, Si(CH₃)₃). ¹³C {¹H} NMR (100 MHz, C₆D₆): δ 165.2, 135.6,

134.9, 132.9, 132.7, 131.7, 129.2, 128.9, 128.5, 128.2, 127.9, 125.4,

120.9, 120.7 (All ArC), 64.8 (ArCPh₃), 63.7 (ArCH₂N), 59.7

(ArCH₂N), 58.4 (NCH− of pyrrolidinyl), 56.5 (NCH₂− of pyr-

rolidinyl), 48.9 (NCH₂CH), 48.4 (NCH₂(CH₂)₆CH₃), 32.6(NCH₂-

CH₂(CH₂)₅CH₃), 30.5 (N(CH₂)₂CH₂(CH₂)₃CH₃), 30.3 (N(CH₂)₃-

CH₂(CH₂)₂CH₃), 29.0 (−CH₂− of pyrrolidinyl) (N(CH₂)₄CH₂-

(CH₂)₂CH₃), 28.1 (N(CH₂)₅CH₂CH₂CH₃), 25.1 (−CH₂− of

pyrrolidinyl), 23.5 (N(CH₂)₅CH₂CH₂CH₃), 21.1 (ArCH₃), 19.9

(N(CH₂)₆CH₂CH₃), 14.7 (N(CH₂)₇CH₃), 7.6 (Si(CH₃)₃). Anal.

Calcd for C₅₃H₇₃N₂OSi₂Zn·0.5C₇H₈: C, 72.51; H, 8.29; N, 4.49;

Found: C, 72.19; H, 8.03; N, 4.01%.

ArH), 7.14−7.10 (m, 6H, ArH), 7.10−7.00 (m, 2H, ArH), 6.95 (t, ³J =

4

2

7.0 Hz, 1H, ArH), 6.66 (d, J = 2.0 Hz, 1H, ArH), 4.16 (d, J = 11.8

Hz, 1H, ArCH₂N), 3.13 (sept, ³J = 6.5 Hz, 1H, NCH(CH₃)₂), 2.92 (d,

²J = 11.8 Hz, 1H, ArCH₂N), 2.61−2.49 (m, 1H, NCH− of

pyrrolidinyl)), 2.19−2.13 (m, 1H, NCH₂CH₂CH₂CH₃), 2.10 (s, 3H,

ArCH₃), 2.07−1.95 (m, 1H, ArCH₂N), 1.66−1.57 (m, 1H,

NCH₂CH₂CH₂CH₃), 1.54 (d, 3H, ³J = 6.5 Hz, NCH(CH₃)₂),

1.29−1.15 (m, 3H, ArCH₂N and NCH₂CH₂CH₂CH₃), 1.07−1.00 (m,

3H, NCH₂CH₂CH₂CH₃and NCH₂− of pyrrolidinyl), 1.00 (t, ³J = 7.2

Hz, 3H, NCH₂CH₂CH₂CH₃), 0.94−0.79 (m, 2H, −CH₂− of

pyrrolidinyl), 0.70 (m, 1H, NCH₂− of pyrrolidinyl), 0.64 (d, J = 6.5

Hz, 3H, NCH(CH₃)₂), 0.54 (m, 1H, −CH₂− of pyrrolidinyl), 0.42−

0.34 (m, 1H, −CH₂− of pyrrolidinyl), 0.31 (s, 18H, Si(CH₃)₃)). ¹³C

{¹H} NMR (100 MHz, C₆D₆): δ 165.3, 135.4, 134.8, 133.2, 132.4,

132.3, 129.7, 128.9, 127.7, 126.0, 125.3, 121.7, 120.8 (All ArC), 64.9

(ArCPh₃), 64.8 (ArCH₂N), 55.2 (NCH− of pyrrolidinyl), 52.5

(NCH₂− of pyrrolidinyl), 51.7 (NCH₂CH), 49.8 (NCH(CH₃)₂),

46.7 (NCH₂CH₂CH₂CH₃), 30.0 (NCH₂CH₂CH₂CH₃), 24.9 (−CH₂−

of pyrrolidinyl), 22.4 (−CH₂− of pyrrolidinyl), 21.8 (NCH(CH₃)₂),

21.3 (Ar-CH₃), 21.2 (NCH(CH₃)₂), 18.9 (NCH(CH₃)₂), 14.5

(NCH₂CH₂CH₂CH₃), 12.9 (NCH₂CH₂CH₂CH₃), 7.2 (Si(CH₃)₃).

Anal. Calcd for C₄₅H₆₅N₂OSi₂Zn·C₇H₈: C, 71.16; H, 8.38; N, 4.79;

Found: C, 70.96; H, 8.40; N, 4.70%.

[(L⁵)ZnN(SiMe₃)₂] (5). The procedure was the same as that of

complex 4, except that L⁵H (0.835 g, 1.30 mmol) and Zn[N-

(SiMe₃)₂]₂(0.502 g, 1.30 mmol) were used to aﬀord colorless crystals

of 5 (0.821 g, 57.1%) as a mixture of two diastereomers in 3:2 (isomer

1

5a:isomer 5b). NMR spectroscopic data of 5a: H NMR (400 MHz,

C₆D₆): δ 7.64−7.48 (m, 7H, ArH), 7.37 (s, 1H, ArH), 7.14−6.95 (m,

12H, ArH), 6.95−6.86 (m, 6H, ArH), 6.45 (s, 1H, ArH), 4.50 (d, 1H,

²J = 12.5 Hz, ArCH₂N), 4.19 (d, 1H, ²J = 14.2 Hz, ArCH₂N), 3.99 (d,

1H, ²J = 14.2 Hz, ArCH₂N), 3.57 (d, 1H, ²J = 13.0 Hz, ArCH₂N), 3.39

(d, 1H, ²J = 12.5 Hz, ArCH₂N), 3.24 (d, 1H, ²J = 13.0 Hz, ArCH₂N),

3.21−3.11 (m, 1H, NCH₂− of pyrrolidinyl), 2.82−2.70 (m, 1H,

NCH− of pyrrolidinyl), 2.51−2.37 (m, 1H, NCH₂− of pyrrolidinyl),

2.34−2.21 (m, 1H, NCH₂CH), 2.05 (s, 3H, ArCH₃), 1.83 (dd, 1H, ²J

= 13.2, ³J = 3.2 Hz, NCH₂CH), 1.50−1.38 (m, 1H, −CH₂− of

pyrrolidinyl), 1.15 (td, 1H, ²J = 12.8, ³J = 6.9 Hz, −CH₂− of

pyrrolidinyl), 1.08−0.97 (m, 1H, −CH₂− of pyrrolidinyl), 0.69−0.57

(m, 1H, −CH₂− of pyrrolidinyl), 0.40 (s, 18H, Si(CH₃)₃). ¹³C {¹H}

NMR (100 MHz, C₆D₆): δ 164.3, 136.3, 135.8, 134.8, 132.2, 132.0,

131.7, 129.7, 129.4, 129.2, 127.9, 126.0, 125.6, 125.4, 120.8, 120.5 (All

ArC), 64.7 (ArCPh₃), 62.0 (ArCH₂N), 59.9 (ArCH₂N), 59.4

(ArCH₂N), 57.8 (NCH− of pyrrolidinyl), 48.9 (NCH₂− of pyr-

rolidinyl), 48.8 (NCH₂CH), 32.3 (−CH₂− of pyrrolidinyl), 25.4

(−CH₂− of pyrrolidinyl), 21.3 (ArCH₃), 7.8 (Si(CH₃)₃). Anal. Calcd

for C₅₂H₆₃N₃OSi₂Zn·C₇H₈: C, 73.83; H, 7.46; N, 4.38; Found: C,

73.54; H, 7.53; N, 4.37%.

[(L⁸)ZnN(SiMe₃)₂](8). The procedure was the same as that of

complex 4, except that L⁸H (0.840 g, 1.50 mmol) and Zn[N-

(SiMe₃)₂]₂(0.579 g, 1.50 mmol) were used to aﬀord colorless crystals

of 8 (0.477 g, 40.5%) as a mixture of two diastereomers in 1:1.2

(isomer 8a:isomer 8b). NMR spectroscopic data of 8b: ¹H NMR (400

2

MHz, C₆D₆): δ 7.67 (d, 1H, J = 2.6 Hz, ArH), 7.57−7.53 (m, 3H,

ArH), 7.42−7.38 (m, 2H, ArH), 7.30−7.24 (m, 2H, ArH), 7.10−7.04

2

(m, 7H, ArH), 6.79−6.76 (m, 2H, ArH), 4.25 (d, 1H, J = 13.9 Hz,

ArCH₂N), 3.90 (d, 1H, ²J = 13.9 Hz, ArCH₂N), 3.57 (d, 1H, ²J = 12.5

Hz, ArCH₂N), 3.16 (dt, 1H, ²J = 12.9, ³J = 8.6 Hz, NCH₂− of

2

pyrrolidinyl), 2.98 (d, 1H, J = 12.5 Hz, ArCH₂N), 2.73−2.62 (m,

1H), 2.42−2.33 (m, 1H, NCH₂CH₃), 2.29 (s, 3H, C(CH₃)₂Ph), 2.26−

2.20 (m, 1H, NCH₂CH₃), 2.10−1.99 (m, 2H, NCH− of pyrrolidinyl

and NCH₂CH), 1.87 (s, 3H, C(CH₃)₂Ph), 1.81 (dd, 2H, ²J = 8.6, ²J =

4.9 Hz, NCH₂CH), 1.75 (s, 3H, C(CH₃)₂Ph), 1.74 (s, 3H,

C(CH₃)₂Ph), 1.57−1.47 (m, 1H, NCH₂− of pyrrolidinyl), 1.17−

1.07 (m, 3H, −CH₂− of pyrrolidinyl), 0.72 (t, 3H, ³J = 7.2 Hz,

NCH₂CH₃), 0.60−0.54 (m, 1H, −CH₂− of pyrrolidinyl), 0.39 (s,

18H, Si(CH₃)₃). ¹³C {¹H} NMR (100 MHz, C₆D₆): δ 164.5, 153.2,

153.0, 138.1, 134.4, 134.0, 132.5, 132.3, 129.1, 129.0, 127.7, 127.4,

125.8, 124.8, 112.0 (All ArC), 63.5 (ArCH₂N), 60.4 (ArCH₂N), 59.2

(NCH− of pyrrolidinyl), 58.4 (NCH₂− of pyrrolidinyl), 50.1

(NCH₂CH), 49.0 (NCH₂CH₃), 43.3 (C(CH₃)₂Ph), 42.7

(C(CH₃)₂Ph), 34.2 (C(CH₃)₂Ph), 34.2 (C(CH₃)₂Ph), 32.0 (C-

(CH₃)₂Ph), 28.0 (C(CH₃)₂Ph), 25.0 (−CH₂− of pyrrolidinyl), 21.7

(−CH₂− of pyrrolidinyl), 14.0 (NCH₂CH₃), 7.7 (Si(CH₃)₃). Anal.

Calcd For C₄₅H₆₅N₃OSi₂Zn: C, 68.80; H, 8.34; N, 5.35. Found: C,

68.60; H, 8.08; N, 5.09%.

[(L⁶)ZnN(SiMe₃)₂] (6). The procedure was the same as that of

complex 4, except that L⁶H (0.988 g, 1.50 mmol) and Zn[N-

(SiMe₃)₂]₂(0.579 g, 1.50 mmol) were used to aﬀord colorless crystals

of 6 (0.624 g, 47.1%) as an enantiopure product. ¹H NMR (400 MHz,

2

C₆D₆): δ 8.34 (d, 1H, J = 8.6 Hz, ArH), 7.75−7.55 (m, 9H, ArH),

7.41 (d, 2H, ³J = 8.6 Hz, ArH), 7.24 (t, 2H, ³J = 7.6 Hz, ArH), 7.11−

2

6.86 (m, 9H, ArH), 6.11 (s, 1H, ArH), 4.97 (d, 1H, J = 14.6 Hz,

ArCH₂N), 4.57 (d, 1H, ²J = 14.6 Hz, ArCH₂N), 4.56 (d, 1H, ²J = 11.9

2

Hz, ArCH₂N), 3.17 (d, 1H, J = 11.9 Hz, ArCH₂N), 3.22−3.12 (m,

1H, NCH− of pyrrolidinyl), 2.38−2.22 (m, 1H, NCH₂− of

2

3

pyrrolidinyl), 2.21 (dd, 1H, J = 14.3, J = 3.6 Hz, NCH₂CH) 2.03−

1.88 (m, 3H, NCH₂CH and NCH₂CH₂CH₂CH₃), 1.94 (s, 3H,

ArCH₃), 1.74 (m, 1H, NCH₂− of pyrrolidinyl), 1.41−1.07 (m, 4H,

[(L⁸)ZnO^tBu] (9). In a glovebox, zinc complex [(L⁸)ZnN(SiMe₃)₂]

t

3

(8) (0.786 g, 1.00 mmol) was dissolved in toluene (5 mL). BuOH

NCH₂CH₂CH₂CH₃), 1.02 (t, 3H, J = 6.7 Hz, NCH₂CH₂CH₂CH₃),

(0.740 g, 1.00 mmol) was dissolved in n-hexane (2 mL) and added

dropwise to the solution of complex 8. The reaction mixture was

stirred at r.t. overnight. The solvent and volatile components were

removed under reduced pressure to aﬀord a white vesicular solid,

which was then recrystallized with a mixture of n-hexane and toluene

at room temperature. The resulting colorless crystals were washed with

cold n-hexane three times and dried under vacuum to give a white

solid in 49.1% (0.344 g) as a mixture of two diastereomers in 1:2.3

(isomer 9a:isomer 9b). NMR spectroscopic data of 9b: ¹H NMR (400

0.96−0.77 (m, 2H, −CH₂− of pyrrolidinyl), 0.51 (m, 2H, −CH₂− of

pyrrolidinyl), 0.41 (s, 18H, Si(CH₃)₃). ¹³C {¹H} NMR (100 MHz,

C₆D₆): δ 165.3, 135.1, 135.0, 134.9, 134.9, 133.1, 132.3, 132.2, 130.4,

129.9, 128.8, 127.9, 127.6, 126.7, 125.5, 125.3, 124.3, 121.3, 120.7 (All

ArC), 65.0 (ArCPh₃), 64.8 (ArCH₂N), 60.0 (ArCH₂N), 56.2 (NCH−

of pyrrolidinyl), 54.0 (NCH₂− of pyrrolidinyl), 48.8 (NCH₂CH), 48.3

(NCH₂CH₂CH₂CH₃), 31.2 (NCH₂CH₂CH₂CH₃), 24.9 (−CH₂− of

pyrrolidinyl), 21.2 (Ar-CH₃), 21.0 (−CH₂− of pyrrolidinyl), 19.3

(NCH₂CH₂CH₂CH₃), 14.6 (NCH₂CH₂CH₂CH₃), 7.6 (Si(CH₃)₃).

Anal. Calcd for C₅₃H₆₇N₂OSi₂Zn·0.5C₇H₈: C, 72.99; H, 7.70; N, 4.52;

Found: C, 72.83; H, 7.53; N, 4.36%.

4

MHz, C₆D₆): δ 7.62 (d, 1H, J = 2.4 Hz, ArH), 7.58 (m, 5H, ArH),

7.32 (d, 2H, ³J = 7.4 Hz, ArH), 7.22 (m, 4H, ArH), 7.08−6.98 (m, 4H,

4

2

[(L⁷)ZnN(SiMe₃)₂] (7). The procedure was the same as that of

complex 4, except that L⁷H (0.840 g, 1.50 mmol) and Zn[N-

(SiMe₃)₂]₂(0.579 g, 1.50 mmol) were used to aﬀord colorless crystals

of 7 (0.831 g, 69.0%) as a mixture of two diastereomers in 10:1

(isomer 7a:isomer 7b). NMR spectroscopic data of 7a: ¹H NMR (400

ArH), 6.66 (d, 1H, J = 2.4 Hz, ArH), 4.05 (d, 1H, J = 12.9 Hz,

ArCH₂N), 4.00 (d, 1H, ²J = 12.2 Hz, ArCH₂N), 3.32 (d, 1H, ²J = 12.9

Hz, ArCH₂N), 2.82 (d, 1H, ²J = 12.2 Hz, ArCH₂N), 2.23 (dd, 1H, ²J =

13.1, ³J = 5.9 Hz, NCH₂CH), 2.16 (s, 3H, C(CH₃)₂Ph), 1.82 (m, 2H,

NCH₂CH and NCH− of pyrrolidinyl), 1.80 (s, 3H, C(CH₃)₂Ph), 1.75

(s, 9H, OC(CH₃)₃), 1.73 (s, 3H, C(CH₃)₂Ph), 1.71 (s, 3H,

4

MHz, C₆D₆): δ 7.85−7.55 (m, 5H, ArH), 7.50 (d, J = 2.0 Hz, 1H,

N

DOI: 10.1021/acs.inorgchem.6b00378

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

C(CH₃)₂Ph), 1.68−1.57 (m, 4H, NCH₂− of pyrrolidinyl and

NCH₂CH₃), 1.46−1.37 (m, 1H, −CH₂− of pyrrolidinyl), 1.29−1.22

(m, 1H, −CH₂− of pyrrolidinyl), 1.04 (t, 3H, ³J = 7.0 Hz, NCH₂CH₃),

0.76 (m, 1H, −CH₂− of pyrrolidinyl), 0.41−0.33 (m, 1H, −CH₂− of

pyrrolidinyl). ¹³C {¹H} NMR (100 MHz, C₆D₆): δ 165.1, 153.3, 152.6,

138.1, 134.4, 134.3, 132.8, 132.4, 129.8, 129.0, 128.0, 127.6, 127.5,

126.9, 126.7, 125.9, 124.8, 121.4 (All ArC), 64.9 (ArCH₂N), 62.7

(ArCH₂N), 61.5 (NCH− of pyrrolidinyl), 51.1 (NCH₂− of pyr-

rolidinyl), 49.8 (NCH₂CH), 46.9 (NCH₂CH₃), 43.4 (OC(CH₃)₃),

42.9 (C(CH₃)₂Ph), 42.8 (C(CH₃)₂Ph), 36.3 (OC(CH₃)₃), 32.2

(C(CH₃)₂Ph), 31.9 (C(CH₃)₂Ph), 31.8 (−CH₂− of pyrrolidinyl),

27.8 (C(CH₃)₂Ph), 24.8 (−CH₂− of pyrrolidinyl), 20.4 (C(CH₃)₂Ph),

13.6 (NCH₂CH₃). Anal. Calcd For C₄₃H₅₆N₂O₂Zn: C, 73.96; H, 8.08;

N, 4.01. Found: C, 73.34; H, 8.16; N, 3.92%.

0.52−0.38 (m, 1H, −CH₂− of pyrrolidinyl). ¹³C {¹H}NMR (100

MHz, C₆D₆): δ 154.6, 152.3, 152.2, 140.7, 138.2, 136.2, 130.7, 128.9,

128.7, 128.4, 127.8, 127.6, 127.1, 126.7, 126.3, 125.4, 125.1, 123.2 (All

ArC), 62.6 (ArCH₂N), 60.1 (ArCH₂N), 59.5 (NCH− of pyrrolidinyl),

58.2 (NCH₂− of pyrrolidinyl), 53.9 (NCH₂CH), 49.4 (NCH₂CH₃),

43.2 (C(CH₃)₂Ph), 42.8 (C(CH₃)₂Ph), 31.6 (C(CH₃)₂Ph), 31.8

(C(CH₃)₂Ph), 30.9 (C(CH₃)₂Ph), 30.4 (C(CH₃)₂Ph), 29.6 (−CH₂−

of pyrrolidinyl), 23.2 (−CH₂− of pyrrolidinyl), 14.5 (NCH₂CH₃).

Anal. Calcd For C₃₉H₄₇ClN₂OZn: C, 70.90; H, 7.17; N, 4.24. Found:

C, 70.84; H, 7.10; N, 4.25%.

X-ray Crystallography. Single crystals of complexes 1, 3, 5, 7, 10,

and 11 were obtained from a mixture of toluene/n-hexane or benzene/

n-hexane solution by slow evaporation at room temperature or at −38

°C. The X-ray diﬀraction measurements were performed at room

temperature on a Bruker SMART APEX II diﬀractometer with

graphite-monochromated Mo−Kα (λ = 0.71073 Å) radiation. All data

of complexes were collected at 173 K, using the ω-scan techniques. All

structures were solved by direct methods and reﬁned using Fourier

techniques. An absorption correction based on SADABS was

applied.¹⁷All non-hydrogen atoms were reﬁned by full-matrix least-

squares on F²using the SHELXTL program package.¹⁸Hydrogen

atoms were located and reﬁned by the geometry method. The cell

reﬁnement, data collection, and reduction were done by Bruker

SAINT.¹⁹The structure solution and reﬁnement were performed by

SHELXS-97²⁰and SHELXL-97,²¹respectively. For further crystallo-

graphic data and details of measurements, see Table S1. Molecular

structures were generated using the ORTEP program.²²

[(L⁸)ZnEt] (10). In a glovebox, the aminophenol L⁸H (0.840 g, 1.50

mmol) was dissolved in toluene (2 mL) and was cannulated to a

solution of EtZnOⁱPr (0.231 g, 1.50 mmol) in n-hexane. The reaction

mixture was allowed to be stirred at room temperature overnight. The

solvent and volatile components were removed under reduced

pressure to aﬀord a white vesicular solid, which was then recrystallized

with a mixture of n-hexane and toluene. The resulting colorless crystals

were washed with cold n-hexane three times and dried under vacuum

to give a white solid 10 in 41.4% (0.406 g) as a mixture of two

diastereomers in 1:10 (isomer 10a:isomer 10b). NMR spectroscopic

1

4

data of 10b: H NMR (400 MHz, C₆D₆): δ 7.74 (d, 1H, J = 2.4 Hz,

ArH), 7.62 (d, 2H, ³J = 7.4 Hz, ArH), 7.52 (d, 2H, ³J = 7.4 Hz, ArH),

7.30−7.20 (m, 4H, ArH), 7.14−7.07 (m, 5H, ArH), 6.92 (dd, 2H, ³J =

6.3, ⁴J = 2.8 Hz, ArH), 6.87 (d, 1H, ⁴J = 2.4 Hz, ArH), 3.89 (d, 1H, ²J

Typical Polymerization Procedure. In a glovebox, an initiator

solution (0.5 mL, 10 mmol/mL) from a stock solution in toluene or

THF was injected sequentially to a series of 10 mL vials loaded with

rac-lactide (0.144 g, 1.00 mmol) and suitable amounts (0.5 mL) of the

same dry solvent. The mixture was stirred at room temperature and

quenched at the speciﬁc time intervals by adding an excess amount of

normal light petroleum ether. After being dissolved with dichloro-

methane, a small amount of an aliquot of the bulk solution was

withdrawn and dried under reduced pressure for monomer conversion

determination via ¹H NMR spectroscopy. The bulk solution was

slightly concentrated, and the polymer was precipitated from

dichloromethane via the addition of excess methanol. The collected

polymer sample was further dried in a vacuum oven at 60 °C for 16 h

to a constant weight for gel permeation chromatography (GPC) and

2

= 14.0 Hz, ArCH₂N), 3.44 (d, 1H, J = 12.3 Hz, ArCH₂N), 3.42 (d,

1H, ²J = 14.0 Hz, ArCH₂N), 2.70−2.64 (m, 1H, NCH₂− of

2

pyrrolidinyl), 2.60 (d, 1H, J = 12.3 Hz, ArCH₂N), 2.56−2.45 (m,

2H, NCH₂− of pyrrolidinyl and NCH₂CH₃), 2.37−2.28 (m, 1H,

NCH− of pyrrolidinyl), 2.22 (s, 3H, C(CH₃)₂Ph), 2.01 (s, 3H,

C(CH₃)₂Ph), 1.87 (s, 3H, C(CH₃)₂Ph), 1.85 (s, 3H, C(CH₃)₂Ph),

3

1.82−1.76 (m, 2H, NCH₂CH and NCH₂CH₃), 1.62 (dd, 1H, J =

12.7, J = 4.2 Hz, NCH₂CH), 1.52 (t, 3H, J = 8.1 Hz, ZnCH₂CH₃),

1.19−1.06 (m, 3H, −CH₂− of pyrrolidinyl), 0.97 (t, 3H, J = 7.0 Hz,

4

3

NCH₂CH₃), 0.58−0.45 (m, 1H, −CH₂− of pyrrolidinyl), 0.27−0.16

(m, 2H, ZnCH₂CH₃). ¹³C {¹H} NMR (100 MHz, C₆D₆): δ 165.1,

154.0, 153.4, 138.7, 134.3, 133.2, 132.1, 129.9, 128.7, 127.9, 126.9,

125.8, 125.7, 124.7, 123.0 (All ArC), 64.8 (ArCH₂N), 58.4 (ArCH₂N),

58.3 (NCH− of pyrrolidinyl), 53.0 (NCH₂− of pyrrolidinyl), 51.4

(NCH₂CH), 50.1 (NCH₂CH₃), 43.4 (C(CH₃)₂Ph), 43.1 (C(CH₃)₂-

Ph), 32.3 (C(CH₃)₂Ph), 31.9 (C(CH₃)₂Ph), 28.8 (C(CH₃)₂Ph), 26.4

(−CH₂− of pyrrolidinyl), 22.2 (−CH₂− of pyrrolidinyl), 14.3

(NCH₂CH₃), 14.2 (ZnCH₂CH₃), − 3.00 (ZnCH₂CH₃). Anal. Calcd

For C₄₁H₅₂N₂OZn: C, 75.26; H, 8.01; N, 4.28. Found: C, 75.19; H,

7.97; N, 4.22%.

1

¹H and homonuclear decoupled H NMR analyses.

In the cases where 2-propanol was used, the monomer solution was

treated ﬁrst with the solution of 2-propanol for 5 min, and then the

solution of initiator was injected to the mixture. Otherwise, the

procedures were the same.

ASSOCIATED CONTENT

■

[(L⁸)ZnCl](11). In a glovebox, K[N(SiMe₃)₂] (0.300 g, 1.50 mmol)

was added to a solution of L⁸H (0.840 g, 1.50 mmol) in THF (10

mL). The resulting mixture was stirred at r.t. for 2 h; then ZnCl₂

(0.218 g, 1.60 mmol) was added and the turbid solution was allowed

to be stirred for 24 h. The solvent was subsequently evaporated under

vacuum. The resultant residue was dissolved in toluene, and the

insoluble products were removed by ﬁlter. The resultant product in

solution was then recrystallized with a mixture of n-hexane and toluene

to aﬀord colorless crystals of 11 (0.675 g, 68.2%) as an enantiopure

S

* Supporting Information

The Supporting Information is available free of charge on the

ACS Publications website at DOI: 10.1021/acs.inorg-

chem.6b00378.

X-ray crystallographic data of complexes 1, 3, 5, 7, 10,

and 11 (CIF)

¹H and ¹³C NMR spectra of all complexes and

homonuclear decoupled ¹H NMR spectra of typical

polymer samples (PDF)

1

product. H NMR (400 MHz, C₆D₆): δ 7.79 (s, 1H, ArH), 7.59 (d,

3

2H, J = 7.6 Hz, ArH), 7.51 (d, 2H, J = 7.6 Hz, ArH), 7.25 (m, 4H,

ArH), 7.14−7.09 (m, 2H, ArH), 7.08−6.99 (m, 3H, ArH), 6.86−6.78

(m, 3H, ArH), 3.92 (d, 1H, ⁴J = 14.3 Hz, ArCH₂N), 3.73 (d, 1H, ⁴J =

4

14.3 Hz, ArCH₂N), 3.34 (d, 1H, J = 12.8 Hz, ArCH₂N), 3.15−3.01

AUTHOR INFORMATION

■

(m, 1H, NCH₂− of pyrrolidinyl), 2.59 (d, 1H, ⁴J = 12.8 Hz, ArCH₂N),

2.53−2.40 (m, 1H, NCH₂CH₃), 2.38−2.30 (m, 1H, NCH− of

pyrrolidinyl), 2.29 (s, 3H, C(CH₃)₂Ph), 2.25−2.14 (m, 1H, NCH₂− of

pyrrolidinyl), 2.05 (t, 1H, ⁴J = 12.6 Hz, NCH₂CH), 1.90 (s, 3H,

C(CH₃)₂Ph), 1.87 (s, 3H, C(CH₃)₂Ph), 1.84 (s, 3H, C(CH₃)₂Ph),

Corresponding Author

*E-mail: haiyanma@ecust.edu.cn. Fax/Tel.: +86 21 64253519.

Author Contributions

^†H. Wang and Y. Yang contributed equally.

2

3

1.79−1.66 (m, 1H, NCH₂CH₃), 1.53 (dd, 1H, J = 12.5, J = 3.1 Hz,

NCH₂CH), 1.25−1.06 (m, 2H, −CH₂− of pyrrolidinyl), 1.05−0.96

(m, 1H, −CH₂− of pyrrolidinyl), 0.92 (t, 3H, ³J = 6.8 Hz, NCH₂CH₃),

Notes

The authors declare no competing ﬁnancial interest.

O

DOI: 10.1021/acs.inorgchem.6b00378

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Angew. Chem., Int. Ed. 2015, 54, 14858−14861. (k) Chile, L.-E.;

Mehrkhodavandi, P.; Hatzikiriakos, S. G. Macromolecules 2016, 49,

909−919.

ACKNOWLEDGMENTS

■

This work is subsidized by the National Natural Science

Foundation of China (NNSFC, 21074032 and 21474028), and

the Fundamental Research Funds for the Central Universities

(WD1113011). All the ﬁnancial support is gratefully acknowl-

edged. H. Ma also thanks the very kind donation of a Braun

glovebox by AvH foundation.

(5) (a) Chmura, A. J.; Chuck, C. J.; Davidson, M. G.; Jones, M. D.;

Lunn, M. D.; Bull, S. D.; Mahon, M. F. Angew. Chem., Int. Ed. 2007, 46,

2280−2283. (b) Wang, L.; Kefalidis, C. E.; Sinbandhit, S.; Dorcet, V.;

Carpentier, J.-F.; Maron, L.; Sarazin, Y. Chem.Eur. J. 2013, 19,

13463−13478. (c) Wang, L.; Rosç a, S.-C.; Sinbandhit, S.; Poirier, V.;

Dorcet, V.; Roisnel, T.; Carpentier, J.-F.; Sarazin, Y. Dalton Trans.

2014, 43, 4268−4286.

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Q

DOI: 10.1021/acs.inorgchem.6b00378

Inorg. Chem. XXXX, XXX, XXX−XXX

Article Doi

Exploring steric effects in diastereoselective synthesis of chiral aminophenolate zinc complexes and stereoselective ring-opening polymerization of rac-lactide

DOI: 10.1021/acs.inorgchem.6b00378

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Full text of DOI:10.1021/acs.inorgchem.6b00378

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