Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes

Abstract

The influence of MgR2 and AlR3 additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s‐Bu2Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4‐ to 1,2‐ chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R3Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed. Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.

Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation

“…The K atoms bridge between two TMP units, forming strong K-N contacts [K1-N1, 3.052(2); K1-N2, 3.053(2) Å], with a bridging N1-K1-N2 angle of 146.72 (6) . Mg occupies a distorted trigonal planar site [N1-Mg1-N2 00 , 133.63(9); N1-Mg1-C20, 115.57 (14); N2 00 -Mg1-C20, 110.28 (14)], and the inner n-butyl appendages point alternately above and below the ring plane, in a similar fashion to that observed in the tetrameric polymorph 4. Interestingly, continuing the preinverse-crown notion (i.e., 5 contains basic, reactive n-butyl ligands which are capable of inducing arene deprotonation), hexameric 5 appears to represent the perfect template to produce the arene-ide inverse crowns 2a and 2b, as it is directly comparable in terms of aggregation state and conformation with all its n-butyl appendages still intact to deprotonate benzene or toluene.…”

“…Hexamer 5 features a 24-atom (KNMgN) 6 centrosymmetric ring, with two and three coordinate K and Mg centres respectively, although the K is positioned in relatively close proximity to one of the a-carbon atoms of the neighbouring n-butyl groups [K1-C20, 3.143(5); K1-C20 0 , 3.243(5)Å]. Mg occupies a distorted trigonal planar site [N1-Mg1-N2 00 , 133.63(9); N1-Mg1-C20, 115.57 (14); N2 00 -Mg1-C20, 110.28 (14)], and the inner n-butyl appendages point alternately above and below the ring plane, in a similar fashion to that observed in the tetrameric polymorph 4. Mg occupies a distorted trigonal planar site [N1-Mg1-N2 00 , 133.63(9); N1-Mg1-C20, 115.57 (14); N2 00 -Mg1-C20, 110.28 (14)], and the inner n-butyl appendages point alternately above and below the ring plane, in a similar fashion to that observed in the tetrameric polymorph 4.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Compared to the organolithium reagents commonly employed in these reactions, magnesiates (as well as other types of ate, most importantly zincates 1,21-45 ) can show advantages of superior functional group tolerance and application at ambient temperature and in ethereal solvents. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Compared to the organolithium reagents commonly employed in these reactions, magnesiates (as well as other types of ate, most importantly zincates 1,21-45 ) can show advantages of superior functional group tolerance and application at ambient temperature and in ethereal solvents.…”

“…Alkali metal magnesiates have recently seen increasing utilisation in key organic transformations such as metal-hydrogen exchange, metal-halogen exchange and nucleophilic addition reactions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Compared to the organolithium reagents commonly employed in these reactions, magnesiates (as well as other types of ate, most importantly zincates 1, ) can show advantages of superior functional group tolerance and application at ambient temperature and in ethereal solvents. Highlighting the synergistic reactivity inherent to these bimetallics, conspicuously homometallic magnesium compounds [dialkyls, R 2 Mg; Grignard (RMgX) or Hauser (R 2 NMgX) reagents] are oen inert in these same reactions, especially in aromatic functionalisations.…”

Structure and characterization for conterminously linked polymer of short‐chain epoxy resin with triallyl isocyanurate and bismaleimide

“…Finally, it should be noted that some authors propose an 1,4‐3,4 isomerization to explain the regioselectivity changes observed in the course of an alkyl lithium mediated anionic polymerization of diene conducted in the presence of magnesium dialkyls 41, 42…”