Dongtao Liu

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>99 %) 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 (4 equiv) 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 (2 equiv) 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.

Stereoselective Copolymerization of Unprotected Polar and Nonpolar Styrenes by an Yttrium Precursor: Control of Polar-Group Distribution and Mechanism

Styrene underwent unprecedented coordination-insertion copolymerization with naked polar monomers (ortho-/meta-/para-methoxystyrene) in the presence of a pyridyl methylene fluorenyl yttrium catalyst. High activity (1.26×106  g molY-1  h-1 ) and excellent syndioselectivity were observed, and high-molecular-weight copolymers (24.6×104  g mol-1 ) were obtained. The insertion rate of the polar monomers could be adjusted in the full range of 0-100 % simply by changing the loading of the polar styrene monomer. Strikingly, the copolymers had tapered, gradient, and even random sequence distributions, depending on the position of the polar methoxy group on the phenyl ring and thus on its mode of coordination to the active metal center, as shown by tracking the polymerization process and DFT calculations.

Immortal ring-opening polymerization of ε-caprolactone by a neat magnesium catalyst system: an approach to obtain block and amphiphilic star polymers in situ

Catalyst systems obtained from the inexpensive, ligand-free and commercially available MgnBu2 and alcohols were used for the ring-opening polymerization (ROP) of e-caprolactone (e-CL) under mild conditions. The catalytic system of MgnBu2/Ph2CHOH showed very high activity as compared with the system of MgnBu2/Ph3COH, which applied a more bulky methanol derivative. Interestingly, in the presence of excess amount of alcohol (Ph2CHOH), i.e., varying the OH-to-Mg ratio in a wide range from 10 : 1 to 800 : 1, the system MgnBu2/Ph2CHOH still remained highly active, and produced up to 800 polycaprolactone (PCL) chains per Mg center, suggesting a “living immortal” polymerization mode. The molecular weights of the obtained PCLs are accurately controlled when the ratio of [CL]0/[Mg]0 changed from 500 to 8000 together with narrow molecular weight distributions. Moreover, diblock PCL-b-PLA copolymers with narrow PDIs have been facilely achieved. Furthermore, the allyl- and propargyl-functionalized diphenylmethanols could be employed as the chain transfer agents (CTA) in this system for in situ construction of allyl- and propargyl-functionalized PCLs that were facilely modified further to PCLs with multiple functionality as building blocks for amphiphilic and topological microstructured PCLs via coupling and click reactions.

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).

Rapid Syndiospecific (Co)Polymerization of Fluorostyrene with High Monomer Conversion

Fluoromonomers are difficult to polymerize through a coordination mechanism owing to the strong chelation between fluorine and catalysts and the electron-deficient double-bond. We report herein the unprecedented polymerization of para-fluorostyrene (pFS) with excellent activity (1.12×107  g molLn-1 h-1 ), distinguished syndioselectivity (rrrr >99 %) and high conversion (98.4 %) using rare-earth-metal catalysts bearing a pyridyl methylene fluorenyl ligand. DFT calculations reveal polar fluorine loses overwhelming coordination priority to the active central metal ion due to the sterically bulky and electron-donating CGC-ligand, thus its power of poisoning the active species is dramatically weakened. Based on this, copolymerization of pFS and styrene (St) has been successfully achieved with high activity and controllable pFS insertion. Conversely, the unlinked half-sandwich rare-earth-metal system shows relatively lower activity, because both the transition-states and intermediates incorporate a μ1 -F chelated pFS.