Synthesis, Characterization of Methoxyl-bridged Aluminium-lithium Heterobimetallic Complex and Catalysis for the Ring-opening Polymerization of ε-Caprolactone†

doi:10.7503/cjcu20140849

Abstract

Abstract:

The methoxyl-bridged aluminium-lithium heterobimetallic complex [(L)Al(μ₂-OMe)Li(THF)₃]₂(1) was synthesized and structurally characterized. Reaction of 2,6-bis(3,5-bis-t-butyl-2-hydroxybenzyl)-4-t-butyl phenol(H₃-L) with n-BuLi and Al(CH₃)₃ in a molar of ratio 1:1:1 in THF provides methyl-aluminium-lithium phenoxide [(L)Al(CH₃)Li]. Oxidation of the phenoxide by O₂ in air gives target product 1 in quantitative yield. Catalysis by complex 1 for ring-opening of ε-caprolactone(ε-CL) was studied. Experimental results indicate that complex 1 could catalyze ε-CL with high conversion and narrow polydispersity even in an air atmosphere.

Key words: Methoxyl, Heterobimetallic complex, Catalysis, ε-Caprolactone, Ring-opening polymerization, Polycaprolactone

CLC Number:

O631

TrendMD:

WANG Lei, YANG Li, GAO Chengyong. Synthesis, Characterization of Methoxyl-bridged Aluminium-lithium Heterobimetallic Complex and Catalysis for the Ring-opening Polymerization of ε-Caprolactone^†[J]. Chem. J. Chinese Universities, 2015, 36(4): 794.

Figures/Tables 6

Scheme 1 Synthetic routes of complex 1

Table 1 Crystal data and refinement parameters for complex 1

Empirical formula	C₅₃H₇₉AlLiO₇	Density/(g·cm^-3)	1.370
Formula weight	865.110	F(000)	944
Temperature/℃	293(2)	Crystal size/mm³	0.26×0.17×0.08
Crystal system	Triclinic	θ/(°)	2.25—23.64
Space group	P $1 ˉ$	Index range	-12≤h≤13
a/nm	1.167(6)		-15≤k≤15
b/nm	1.419(8)		-14≤l≤19
c/nm	1.725(9)	Observed reflns	2684
α/(°)	73.543(6)	Data/restr.	7948/30
β/(°)	82.226(7)	GOF	0.911
γ/(°)	84.430(6)	Parameter	572
Volume/nm³	2.710(30)	I>2σ(I)	R₁=0.0864, wR₂=0.1857
Z	2	Peak and hole/(e·nm^-3)	307, -287
μ/mm^-1	0.083

Table 1 Crystal data and refinement parameters for complex 1

Empirical formula	C₅₃H₇₉AlLiO₇	Density/(g·cm^-3)	1.370
Formula weight	865.110	F(000)	944
Temperature/℃	293(2)	Crystal size/mm³	0.26×0.17×0.08
Crystal system	Triclinic	θ/(°)	2.25—23.64
Space group	P $1 ˉ$	Index range	-12≤h≤13
a/nm	1.167(6)		-15≤k≤15
b/nm	1.419(8)		-14≤l≤19
c/nm	1.725(9)	Observed reflns	2684
α/(°)	73.543(6)	Data/restr.	7948/30
β/(°)	82.226(7)	GOF	0.911
γ/(°)	84.430(6)	Parameter	572
Volume/nm³	2.710(30)	I>2σ(I)	R₁=0.0864, wR₂=0.1857
Z	2	Peak and hole/(e·nm^-3)	307, -287
μ/mm^-1	0.083

Table 2 Selected bond lengths(nm) and bond angles(°) for complex 1

Al1—O1	0.171(5)	Al1—O7	0.174(5)	Li1—O6	0.196(14)
Al1—O2	0.172(4)	Li1—O5	0.194(13)	Li1—O4	0.203(13)
Al1—O3	0.173(5)	Li1—O7	0.194(13)
O1—Al1—O2	113.2(2)	O1—Al1—O7	111.4(2)	O5—Li1—O7	112.9(6)
O1—Al1—O3	106.9(2)	O2—Al1—O7	103.2(2)	O5—Li1—O6	105.6(6)
O2—Al1—O3	113.9(2)	O3—Al1—O7	108.2(2)	O7—Li1—O6	118.9(7)

Fig.1 Molecular structure of complex 1 with ellipsoids given at the 30% probability level Methyl carbon atoms of the tert-butyl groups and all of the hydrogen atoms are omitted for clarity.

Fig.2 1H NMR spectrum of complex 1

Table 3 Ring-opening polymerization of ε-caprolactone catalyzed by complex 1a

Entry	n(ε-CL):n(Complex)	Time/h	Temperature/℃	Conversity(%)^f	$M n, calcd g$	$M n, obsd h$	PDI
1^a^,^c	100:1	36	80	42.1	4800	n.dⁱ	n.d.
2^a^,^c	100:1	36	100	>99	11300	5500	1.53
3^a^,^c	250:1	36	100	>99	28200	5300	1.36
4^a^,^d	100:1	24	100	97.0	11100	4300	1.23
5^b^,^c	100:1	36	100	>99	11300	4800	1.37
6^b^,^c	250:1	36	100	>99	28200	7600	1.54
7^b^,^d	100:1	24	100	98.1	11100	4100	1.20
8^a^,^c^,^e	100:1	36	100	Trace

Table 3 Ring-opening polymerization of ε-caprolactone catalyzed by complex 1a

Entry	n(ε-CL):n(Complex)	Time/h	Temperature/℃	Conversity(%)^f	$M n, calcd g$	$M n, obsd h$	PDI
1^a^,^c	100:1	36	80	42.1	4800	n.dⁱ	n.d.
2^a^,^c	100:1	36	100	>99	11300	5500	1.53
3^a^,^c	250:1	36	100	>99	28200	5300	1.36
4^a^,^d	100:1	24	100	97.0	11100	4300	1.23
5^b^,^c	100:1	36	100	>99	11300	4800	1.37
6^b^,^c	250:1	36	100	>99	28200	7600	1.54
7^b^,^d	100:1	24	100	98.1	11100	4100	1.20
8^a^,^c^,^e	100:1	36	100	Trace

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