Tungsten Oxo Alkylidene Complexes as Initiators for the Stereoregular Polymerization of 2,3-Dicarbomethoxynorbornadiene
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https://figshare.com/articles/dataset/Tungsten_Oxo_Alkylidene_Complexes_as_Initiators_for_the_Stereoregular_Polymerization_of_2_3_Dicarbomethoxynorbornadiene/2298538
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资源简介：
We have employed 2,3-dicarbomethoxynorbornadiene
(DCMNBD) as a
monomer to explore new tungsten oxo alkylidene complexes as initiators
for stereoregular ROMP (ring-opening metathesis polymerization). The
initiators include MAP (monoaryloxide pyrrolide) oxo alkylidene complexes
with the general formula W(O)(CHCMe2Ph)(Me2Pyr)(OAr)
(Me2Pyr = 2,5-dimethylpyrrolide, OAr = an aryloxide) and
W(O)(CHCMe2Ph)(OR)2 (OR = an aryloxide or OC(CF3)3), or PPh2Me or CH3CN adducts
thereof. We have found that MAP initiators yield cis,syndiotactic-poly(DCMNBD) as a consequence of stereogenic
metal control. In contrast, W(O)(CHCMe2Ph)(OR)2(L) initiators (where L = PPh2Me or acetonitrile) are
strongly biased toward formation of cis,isotactic structures, while W(O)(CHCMe2Ph)(OR)2 initiators
are strongly biased toward formation of cis,syndiotactic structures. Addition of B(C6F5)3 to W(O)(CHCMe2Ph)(Me2Pyr)(OR) species
leads to a dramatic increase in the rate of polymerization and to
an increase in the cis,syndiotacticity of the polymer
(if not already high), while addition of B(C6F5)3 to W(O)(CHCMe2Ph)(OR)2 initiators
leads to a dramatic increase in the rate of polymerization and to
the formation of highly cis,syndiotactic polymers.
All evidence supports the proposal that 16e W(O)(CHCMe2Ph)(OR)2(L) complexes can operate either through loss
of L to yield 14e W(O)(CHCMe2Ph)(OR)2 species
(which yield largely cis,syndiotactic-poly(DCMNBD))
or by directly reacting with DCMNBD to yield an 18e intermediate and
largely cis,isotactic-poly(DCMNBD). All polymerizations
by W(O)(CHCMe2Ph)(OR)2(L) and W(O)(CHCMe2Ph)(OR)2 initiators are proposed to operate
through some version of chain end control.
创建时间：
2016-02-17
