Ring Opening Polymerization and Copolymerization of Cyclic Esters Catalyzed by Group 2 Metal Complexes Supported by Functionalized P–N Ligands

Abstract

We report the preparation of alkali and alkaline earth (Ae) metal complexes supported by 2-picolylamino-diphenylphosphane chalcogenide [(PhP(=E)NHCH(CHN)] [E = S (1-H); Se (2-H)] ligands. The treatment of the protic ligand, 1-H or 2-H, with alkali metal hexamethyldisilazides at room temperature afforded the corresponding alkali metal salts [M(THF)(PhP(=E)NCH(CHN)] [M = Li, E = S (3a), Se (3b)] and [{M(THF) (PhP(=E)NCH(CHN)}] [M = Na, E = S (4a), Se (4b); M = K, E = Se (5b)] in good yield. The homoleptic Ae metal complexes [κ-(PhP(=Se)NCH(CHN)Mg(THF)] (6b) and [κ-{(PhP(=Se)NCH(CHN)}M(THF) ] (M = Ca (7b), Sr (8b), Ba (9b)] were synthesized by the one-pot reaction of 2-H with [KN(SiMe)] and MI in a 2:2:1 molar ratio at room temperature. The molecular structures of the protic-ligands 1-H and 2-H, as well as complexes 3a,b-5a,b and 6b-9b were established using single-crystal X-ray analysis. The Ae metal complexes 6b-9b were tested for ring-opening polymerization (ROP) of racemic lactide ( rac-LA) and copolymerization of rac-LA and ε-caprolactone (ε-CL) at room temperature. In the ROP of rac-LA, the calcium complex 7b exhibited high isoselectivity, with P = 0.89, whereas both the barium and strontium complexes showed lower isoselectivity with P = 0.78-0.62. In the copolymerization of rac-LA and ε-CL, both barium and strontium complexes proved to be efficient precatalysts for the formation of the block copolymer rac-LA-CL, but the reactivity of 9b was found to be better than that of 8b. All the polymers were fully characterized using differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography analyses. Kinetic studies on the ROP reaction of LA confirmed that the rate of polymerization followed the order Ba ≫ Sr ≈ Ca.

Hydroboration, Cyanosilylation, and Sequential Cyanosilylation and Hydroboration of Carbonyl Compounds in the Presence of a TiIV Amido Complex as an Efficient Catalyst

“…1 H (400 MHz), 31 P{ 1 H} (161.1 MHz), and 13 C{ 1 H} NMR (100 MHz) spectra were recorded with a BRUKER AVANCE III-400 spectrometer. [36] All the solvents were distilled from sodium metal prior to use. Ligand [(C 5 H 4 N)CH 2 NHP(=Se)Ph 2 ] (L 1 H) was prepared according to the literature procedure.…”

“…Ligand [(C 5 H 4 N)CH 2 NHP(=Se)Ph 2 ] (L 1 H) was prepared according to the literature procedure. [36] All the solvents were distilled from sodium metal prior to use. Ti(NMe 2 ) 4 was purchased from Sigma-Aldrich and used as received.…”

“…[36] Treatment of tetrakis(dimethylamido)titanium(IV) [36] Treatment of tetrakis(dimethylamido)titanium(IV)…”

“…2-Picolylamino-(diphenylphosphinoselenoic)amide ligand (L 1 H) and 1,1-diphenyl-N-(phenyl-2-fluoro)phosphinoselenoic amide (L 2 H) were prepared according to a procedure described in the literature. [36] Treatment of tetrakis(dimethylamido)titanium(IV)…”

Comparative Experimental and Theoretical Study of Mg, Al and Zn Aryloxy Complexes in Copolymerization of Cyclic Esters: The Role of the Metal Coordination in Formation of Random Copolymers

“…Due to the contrasting physical properties of polylactide (PLA) and poly-ε-caprolactone (PCL), random copolymers of LA and εCL have generally proved useful for the development of polymer materials with desired mechanical characteristics and biodegradation rate [ 33 , 34 , 35 , 36 , 37 , 38 ]. However, the inherent difference in reactivity of LA and εCL usually leads to the formation of diblock or gradient copolymers, since in most cases LA was polymerized primarily [ 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. Occasionally, only PLA was formed when the mixtures of LA and εCL were used as a comonomer feed [ 46 , 47 ].…”