(Benz)Imidazolin-2-iminato Aluminum, Zinc, and Magnesium Complexes and Their Applications in Ring Opening Polymerization of ε-Caprolactone

Abstract

Synthesis and characterization of a new family of aluminum, magnesium, and zinc complexes supported by (benz)­imidazolin-2-iminato ligands are reported herein. Under different reaction conditions, (benz)­imidazolin-2-imine ligands reacted with metal alkyl precursors to afford the corresponding complexes, displaying mononuclear, binuclear, and trinuclear structures. Reaction in 1:1 stoichiometry at room temperature afforded the simple Lewis acid–base adducts, which exhibited distorted tetrahedral geometries around the metal centers, whereas high temperature reactions gave rise to dimeric complexes, with each metal bridging two (benz)­imidazolin-2-imine ligands to form a four-membered metallacycle ring at the center of the complexes. The catalytic ring opening polymerization (ROP) of ε-caprolactone was studied using these complexes as precatalysts in the presence of isopropanol, and very high activities were observed, affording high/medium molecular weight poly­(ε-caprolactone) products with low polydispersity indices. Detailed kinetic studies revealed that the polymerizations proceeded in a living manner and molecular weights of the polymers could be precisely controlled.

Aluminium alkyl complexes supported by imino-phosphanamide ligand as precursors for catalytic guanylation reactions of carbodiimides

“…37,38 However, aluminium alkyl complexes with the imidiazoline-2-iminato ligand were only recently studied by the research groups of Inoue, 35,36 Masuda 39 and Eisen. 40 Recently, we developed an N-heterocyclic imine-based imino-phosphanamide ligand-supported yttrium complex [{NHI R P(Ph)N-Dipp}Y{NSiMe 3 } 2 ] (iPr, Me), where the ligand upon metalation is bonded with the yttrium ion in a monoanionic fashion similar to that of amidinate ligands. 41 The two donor nitrogen atoms attached to the phosphorus atom are completely different and it is interesting to note that this system is amenable to stereoelectronic modulation through substitution at the phosphorus and nitrogen centers.…”

“… 37,38 However, aluminium alkyl complexes with the imidiazoline-2-iminato ligand were only recently studied by the research groups of Inoue, 35,36 Masuda 39 and Eisen. 40 …”

Isoselective Polymerization of rac‐Lactide by Aluminum Complexes of N‐Heterocyclic Carbene‐Phosphinidene Adducts

“…These findings confirm that the polymerization proceeds via a coordination‐insertion mechanism. Furthermore, heating toluene solutions of 4 a and 4 b up to 80 °C for 6 h did not lead to cleavage of the P−H bond (Figures S37–S40), e.g., by methane (CH 4 ) elimination as observed for related imidazolin‐2‐imine‐aluminum complexes [50] . These observations indicate that the (NHC)PH ligands are not degraded and are therefore able to sustain a potential stereocontrol during the polymerization process.…”

“…Furthermore,h eating toluene solutionso f4a and 4b up to 80 8Cf or 6hdid not lead to cleavage of the PÀH bond (Figures S37-S40), e.g.,b ym ethane (CH 4 )e limination as observed for relatedi midazolin-2-imine-aluminum complexes. [50] These observations indicate that the (NHC)PH ligands are not degraded and are therefore able to sustain ap otential stereocontrol during the polymerization process. Accordingly, the high stereoselectivity achieved with catalysts 4a and 4b can have various reasons: In addition to conventional chainend control (CEC), in whicht he insertion of either LLA or DLA is controlled by the chirality of the previously enchained monomer,t he ligand might cooperativelyi nducee nantiomorphic site control (ESC), effecting the stereoselectivity of the catalysts ystem.…”

Recent Advances of Imidazolin-2-iminato in Transition Metal Chemistry

“…Recently Zn(II) complexes bearing different Im R Nand analogous benzimidazolin-2-iminato ligands have been reported. [125][126] Scheme 26. appeared as a triplet at δH 1.58 and 1.26 ppm respectively. The molecular structure of 45 was confirmed by single-crystal X-ray diffraction analysis, which revealed that the geometry of central metal is distorted trigonal planar with the shortest Zn-N distance (1.974(2) Å) reported so far.…”