Monomeric and dimeric magnesium mono-BHT complexes as effective ROP catalysts

Phenoxide and alkoxide complexes of Mg, Al and Zn, and their use for the ring-opening polymerization of ɛ-caprolactone with initiators of different natures

“…Therefore, the number of aryloxide complexes of main group and transition metals has increased dramatically in recent years. ortho-Disubstituted bulky phenols, including 2,6-di-tert-butyl-4-methylphenol (butylated hydroxytoluene or BHT-H), have been used successfully to synthesize highly active catalysts for the ROP of rac-lactide, "-caprolactone and !-pentadecalactone (see Chen et al, 2012;Fang et al, 2012;Ivchenko et al, 2017;Nifant'ev et al, 2016Nifant'ev et al, , 2017aWilson et al, 2014Wilson et al, , 2015, and references therein) or cyclic phosphoesters (Nifant'ev et al, 2017c, 2018). We report herein the synthesis and structures of ISSN 2053ISSN -2296 # 2018 International Union of Crystallography Mg, Al and Zn complexes (Scheme 1) and present results on the ROP of "-caprolactone ("-CL) associated with these complexes.…”

“…Mg(BHT) 2 (THF) 2 itself (THF is tetrahydrofuran) is catalytically inactive but displays high catalytic activity in the polymerization of cyclic esters when activated by alcohols (e.g. Chen et al, 2012), whereas the [Mg(BHT)(OR)(THF) n ] 2 complexes (n = 0 or 1) do not require an initiator for the ROP process to occur (Nifant'ev et al, 2016(Nifant'ev et al, , 2017d. The reaction of either Mg(BHT) 2 (THF) 2 or Mg(BHT)(n-Bu)(THF) 2 with 1 molar equivalent of a primary alcohol allowed us to prepare dimeric complexes possessing definite compositions and established crystal structures [ Fig.…”

Structural diversity of polynuclear Mg x O y cores in magnesium phenoxide complexes

“…ortho-Disubstituted bulky phenols, including BHT-H (BHT-H is butylated hydroxytoluene or 2,6di-tert-butyl-4-methylphenol), have been used successfully to produce highly effective ROP catalysts. For example, the complexes (BHT) 2 Mg(THF) 2 (Calabrese et al, 1988; THF is tetrahydrofuran), n BuMg(BHT)(THF) 2 and [(-EtO)Mg-(BHT)(THF)] 2 (Nifant'ev et al, 2016), activated with alcohols, have demonstrated high efficiency in the ROP of lactide, "-caprolactone and !-pentadecalactone (Nifant'ev et al, 2016;Wilson et al, 2014Wilson et al, , 2015Fang et al, 2012;Chen et al, 2012). Using [(-RO)Mg(BHT)(THF)] 2 [R = Et or benzyl (Bn)] as examples, it has been demonstrated that activation with an alcohol is not necessary if both phenoxy and alkoxy groups are present within the same Mg complex (Nifant'ev et al, 2016(Nifant'ev et al, , 2017.…”

“…An attempt to synthesize another binuclear complex, i.e. [(BHT)Mg(-O-2-MeC 6 H 4 )(THF)] 2 , from the earlier described mononuclear complex [(BHT)Mg( n Bu)(THF) 2 ] (Nifant'ev et al, 2016) and 2-methylphenol (in a 1:1 molar ratio) resulted in the formation of the trinuclear complex {[(BHT)(THF)Mg] 2 (-OC 6 H 4 -2-Me) 4 Mg}, (II), which is poorly soluble in THF. Apparently, this reaction proceeds in a 3:4 molar ratio of [(BHT)Mg( n Bu)(THF) 2 ] and HO-2-MeC 6 H 4 (Scheme, middle, upper arrow).…”

“…Another approach was used in an attempt to synthesize the unknown complex [(BHT)Mg(-OCH 2 CH 2 NH 2 )(THF)] 2 , namely the reaction of (BHT) 2 Mg(THF) 2 (Calabrese et al, 1988) with an alcohol and the substitution of only one BHT ligand with an alkoxide anion (Nifant'ev et al, 2016). However, the reaction between (BHT) 2 Mg(THF) 2 and 2-aminoethanol (in a 1:1 molar ratio) resulted in the formation of the unusual tetranuclear complex Mg 4 (BHT) 2 (OCH 2 -CH 2 NH 2 ) 6 , (III), which is poorly soluble in THF.…”