A scandium
dication active species [(IPr)Sc(μ-CH2SiMe3)(μ-CH2CHMe2)Al
i
Bu2]2+[B(C6F5)4]2
– (IPr = (2,6-C6H3
i
Pr2NCH)2C) in situ generated from the reaction of
an N-heterocyclic carbene-ligated scandium trialkyl
complex (IPr)Sc(CH2SiMe3)3 (2) with 1–3 equiv of cocatalyst [Ph3C][B(C6F5)4] and an excess of Al
i
Bu3 exhibits unprecedentedly high activity
(up to 2.2 × 106 g·molSc
–1·h–1) and syndiotactic selectivity (rrrr > 99%) in the polymerization of o-methoxystyrene
(oMOS) and its silyloxy- or fluorine-substituted
derivatives, affording syndiotactic poly(oMOS)s and
their silyloxy or fluorine-substituted derivatives with ultrahigh
molecular weight (M
n up to 4.6 ×
106) and moderate molecular weight distributions (M
w/M
n = 1.37–2.21)
unavailable by the traditional catalysts. Based on in situ NMR spectroscopy, matrix-assisted laser desorption/ionization-time
of flight (MALDI-TOF) spectroscopy, and density functional theory
(DFT) calculations, a plausible coordination polymerization mechanism
has been proposed for the syndiotactic polymerization of oMOS by such a Sc dication active species.
A series of novel chiral nonmetallocene pincer-type rare-earth metal dialkyl complexes bearing the chiral monoanionic tridentate C 2 -symmetric 1,3-bis(oxazolinymethylidene)isoindoline (BOXMI-H) ligand (BOXMI)Ln(CH 2 SiMe 3 ) 2 1-3 (1: Ln = Sc, yield = 57%; 2: Ln = Lu, yield = 55%; 3: Ln = Y, yield = 62%) have been prepared in moderate yields via the acid-base reaction between the BOXMI ligand and rare-earth metal tri(trimethylsilylmethyl) complexes. The X-ray diffractions show that both of the complexes 1 and 2 contain one BOXMI ligand and two trimethylsilylmethyl ligands, adopting a distorted trigonal bipyramidal configuration. In the presence of a cocatalyst such as borate and AlR 3 , these complexes 1-3 exhibit high activities of up to 6.8 × 10 4 (g of polymer)/(mol Ln h) and high cis-1,4 selectivities of up to 97% in the polymerization of isoprene in toluene, yielding the cis-1,4-polyisoprenes with heavy molecular weights (M n of up to 710,000 g/mol) and bimodal molecular weight distributions (M w /M n = 2.0-4.5).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.