Halide Anions as Ligands in Iron-Mediated Atom Transfer Radical Polymerization

Abstract

Halide anions have been used as complexing ligands in iron-mediated ATRP, in both direct and reverse ATRP. In direct ATRP, iron(II) bromide complexed with ammonium and phosphonium chloride, bromide, or iodide salts has been shown to catalyze the polymerization of both styrene and (meth)acrylates in a controlled manner under appropriate conditions. The experimental molecular weights increased linearly with monomer conversion and were close to the calculated values. The polymerization rates and polydispersities (Mw/Mn ) 1.1-1.4) were dependent on the monomer employed. Reverse ATRP, initiated by AIBN/FeBr3/onium salts, led to a controlled polymerization of both methyl methacrylate and methyl acrylate, while for styrene uncontrolled molecular weights and high polydispersities were obtained, presumably due to the involvement of the cationic polymerization. It is suggested that different iron complexes may be involved in ATRP, depending on the onium salt/FeBr3 ratio. Because of their ionic nature, the iron complexes could be removed easily from the reaction mixture by washing the polymerization mixture with water.

Iron(III) chloride/R‐Cl/tributylphosphine for metal‐catalyzed living radical polymerization: A unique system with a higher oxidation state iron complex

“…There was an attempt with FeBr 3 and AIBN in the presence of ammonium salts, in which the control failed presumably because of the occurrence of the cationic process by the Lewis acidic FeBr 3 . 20 Furthermore, the polymers obtained after the treatment of the reaction solution using acidic water became apparently colorless, which suggests that these simple ironbased catalysts are easily removable, in addition to the inherently less hazardous nature of the iron atom. Thus, the iron(III) complexes with phosphine ligands can induce the living radical polymerization of styrene under the appropriate conditions to give the polymers with controlled molecular weights.…”

“…[1][2][3][4][5][6][7] One of the most widely employed and efficient living radical polymerizations is the one based on a metal catalyst that generates the growing radical species from the carbon-halogen polymer terminal via the reversible redox reaction of the metal center. The various effective central metals, such as Ru(II), 8 Cu(I), [9][10][11] Ni(II), 12,13 Fe(II), [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] and so forth, give one electron upon the formation of the radical species from the dormant carbon-halogen covalent bond and thus should be basically in a low oxidation state.…”

“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Alternatively, iron(III) halides were employed in conjunction with similar ligands in the presence of a radical initiator like 2,2 0 -azobisisobutyronitrile (AIBN), in which Fe(III) was reduced to Fe(II) via the reaction with the initiating radical species (RÁ) along with the formation of an alkyl halide (RAX).…”

Living Radical Polymerization of Methyl Methacrylate with a Rhodium(III) Complex–Organic Halide System in Dimethyl Sulfoxide

“…2 Since then, systems based on other low-valent transitionmetal complexes of iron(II), [3][4][5][6][7][8][9][10][11][12][13][14][15][16] nickel(II), 17-21 rhodium(I), [22][23][24] and palladium(II) 25 have been found to be effective in similar living or controlled radical polymerizations. The transition-metal complex plays an indispensable role as a halogen carrier, through a series of consecutive reversible oxidation and reduction reactions involving single-electron transfers.…”

From UV to NIR light, photo-triggered 1,3 dipolar cycloadditions as a modern ligation method in solution and on surface

“…The employed metal must possess the ability to expand the coordination sphere and change the oxidation number. A variety of metals have been found to be suitable for ATRP such as Mo, 70 Fe, 71 Ni, 72 and Cu. 73 The corresponding nitrogen containing ligands (L) are required in order to stabilize the low oxidation state of the metal complex.…”