Shihui Li

Highly isoselective coordination polymerization of ortho-methoxystyrene with β-diketiminato rare-earth-metal precursors.

Stereoselective coordination/insertion polymerization of the polar ortho-methoxystyrene has been achieved for the first time by using the cationic β-diketiminato rare-earth-metal species. High activity and excellent isoselectivity (mmmm>99u2009%) were acheived. The unmasked Lewis-basic methoxy group does not poison the Lewis-acidic metal center, but instead activates the polymerization through σ-π chelation to the active species together with the vinyl group, thus lower the coordination and activation energies as compared with those of styrene derivatives lacking the methoxy group.

Lutetium‐Methanediide‐Alkyl Complexes: Synthesis and Chemistry

The first four-coordinate methanediide/alkyl lutetium complex (BODDI)Lu2 (CH2 SiMe3 )2 (μ2 -CHSiMe3 )(THF)2 (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6-iPr2 C6 H3 ) (1) was synthesized by a thermolysis methodology through α-H abstraction from a Lu-CH2 SiMe3 group. Complex 1 reacted with equimolar 2,6-iPrC6 H3 NH2 and Ph2 C+O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu2 (CH2 SiMe3 )2 (μ2 -N-2,6-iPr2 C6 H3 )(THF)2 (2) and (BODDI)Lu2 (CH2 SiMe3 )2 (μ2 -O)(THF)2 (3). Treatment of 3 with Ph2 C=O (4u2005equiv) caused a rare insertion of Lu-μ2 -O bond into theC=O group to afford a diphenylmethyl diolate complex 4. Reaction of 1 with PhN=C=O (2u2005equiv) led to the migration of SiMe3 to the amido nitrogen atom to give complex (BODDI)Lu2 (CH2 SiMe3 )2 -μ-{PhNC(O)CHC(O)NPh(SiMe3 )-κ(3) N,O,O}(THF) (5). Reaction of 1 withtBuN=C formed an unprecedented product (BODDI)Lu2 (CH2 SiMe3 ){μ2 -[η(2) :η(2) -tBuN=C(=CH2 )SiMe2 CHC=NtBu-κ(1) N]}(tBuN=C)2 (6) through a cascade reaction of N=C bond insertion, sequential cyclometalative γ-(sp(3) )-H activation, C=C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1, PhN=C=O, and tBuN=C were elucidated by DFT calculations.

High trans-1,4 (co)polymerization of β-myrcene and isoprene with an iminophosphonamide lanthanum catalyst

Abstractβ-Iminophosphonamide ligated lanthanum bis(benzyl) complex (NPNDipp)La(CH2Ph-4-Me)2(THF) (NPNDipp = Ph2P(NC6H3iPr2-2,6)2), upon activation of AlEt3 and [Ph3C][B(C6F5)4], exhibited high catalytic activity and high trans-1,4 stereoselectivity for the polymerization of bio-sourced β-myrcene (MY). Based on which, a series of novel trans-1,4 regulated elastomers could be generated by random/block copolymerization of MY and isoprene (IP).

Renewable β-myrcene polymerization initiated by lutetium alkyl complexes ligated by imidophosphonamido ligand

Abstractβ-imidophosphonamido ligated lutetium alkyl complex (NPNDipp)Lu(CH2SiMe3)2(THF) (NPNDipp = Ph2P(NC6H3iPr2-2,6)2) with the activation of AliBu3 and [Ph3C][B(C6F5)4] exhibited high catalytic activity, medium syndio-(rr = 66%) but remarkably high 3,4-regioselectivity for the polymerization of β-myrcene (MY). In sharp contrast, high isotactic 3,4-polymyrcene (PMY) (mm = 95%) was obtained by the precursor (NPNEt)Lu(CH2SiMe3)2(THF) (NPNEt = PPh2(NC6H3iPr2-2,6)(NC6H4-Et-2)) with less bulky substituents on the N-aryl ring.

Highly syndioselective coordination (co)polymerization of isopropenylstyrene

Coordination (co)polymerization of para-isopropenylstyrene (pIPSt) and meta-isopropenylstyrene (mIPSt), initiated by scandium (Sc) based catalysts, afforded new type of products, bearing pendant isopropenyl groups with perfect syndiotacity (rrrr > 99%). Sc catalysts demonstrated overwhelming chemoselectivity towards the vinyl group over the isopropenyl moiety of isopropenylstyrene. Compared to the constrained-geometry Sc catalysts, having electron-donating pyridyl methylene fluorenyl ligands Flu′CH2Py (1, Flu′ = C13H8; 2, Flu′ = 2,7-tBu2C13H6, Py = C5H5N), the half-sandwich Sc catalysts containing electron-withdrawing substituents [3, C13H8SiMe3Sc(CH2SiMe3)2(THF); 4, C5Me4PhSc(CH2C6H4NMe2-o)2] showed much higher catalytic activity under identical conditions. The activity of 4 could be over 2164 kg molSc−1 h−1 at room temperature at a lower monomer concentration (1 mol L−1). Moreover, copolymerization of pIPSt and styrene (St) proceeded fluently in a pathway close to ideal copolymerization, with closely matched monomer reactivity ratios: rpIPSt = 1.05, rSt = 0.83. Therefore, a series of statically random copolymers with pendant unsaturated olefinic groups, ranging from 5% to 90%, were accessed. These pendant isopropenyl groups could be readily converted into epoxide and bromide moieties at mild reaction conditions.

Copolymerization of ethylene with styrene catalyzed by a scandium catalyst

Copolymerization of ethylene (E) and styrene (St) was successfully achieved by using a scandium catalyst to produce a series of pseudo-random copolymers. The incorporation content of the St monomer could be tuned from 16.1 mol% to 43.2 mol% swiftly through varying the St to E feeding mole ratio and polymerization time. The highest St content in the copolymer is lower than 50 mol% even at a feeding mole ratio as high as Stu2006:u2006E = 31u2006:u20061 due to the steric hindrance around the active metal center. This is consistent with the monomer reactivity ratios of rE = 14.7 and rst = 0.0036 calculated according to the Fineman–Ross equation. This catalytic performance was extended to other styrene derivatives, such as 4-methylstyrene, 4-tert-butylstyrene, 4-isopropenestyrene, 4-vinylphenyl dimethylsilane and 4-phenylethynylstyrene. The resulting E–St copolymers have no consecutive St sequences and show only one glass transition temperature varying from −21.2 °C to 18.2 °C with the St content. DFT simulation reveals the copolymerization mechanism.