Lead calix[n]arenes (n = 4, 6, 8): structures and ring opening homo-/co-polymerization capability for cyclic esters. Issue 42 (6th October 2021)

• Record Type: Journal Article
• Authors: Xing, Tian; Prior, Timothy J.; Redshaw, Carl
• Is Part Of: Dalton transactions. Volume 50:Issue 42(2021)
• Page Start: 15140
• Page End: 15152
• Publication Date: 2021-10-06
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d1dt02790e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Multi-metallic lead calix[4, 6 and 8]arenes have been structurally characterized and employed in the ring opening polymerization of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and r -lactide; the copolymerization of ε-CL and δ-VL was also conducted. Abstract : Reaction of [LiPb(O i Pr)3 ]2 (generated in situ ) with either p-tert -butylcalix[4]areneH4 (L 4 H4 ) or p-tert -butylcalix[6]areneH6 (L 6 H6 ) resulted in the heterometallic lithium/lead complexes [Pb4 Li2 (L 4 )4 H6 (MeCN)3 ]·4.5MeCN (1 ·4.5MeCN) and [Pb8 Li10 Cl2 (L 6 H2 )3 (L 6 )(OH)2 (O)2 (H2 O)2 (MeCN)4 ]·14MeCN (2 ·14MeCN), respectively. Use of the dimethyleneoxa-bridged p-tert -butyltetrahomodioxacalix[6]areneH6 (L 6′ H6 ) with five equivalents of [Pb(O i Pr)2 ] afforded [Pb13 (L 6′ )3 O4 ( i PrOH)]·11MeCN (3 ·11MeCN). Use of the larger p-tert -butylcalix[8]areneH8 (L 8 H8 ) with [Pb(O t Bu)2 ] or {Pb[N(TMS)2 ]} (TMS = SiMe3 ) afforded the products [Pb12 (L 8 )2 O4 ]·8.7C7 H8 (4 ·8.7C7 H8 ) or [Pb6 (SiMe3 )2 (L 8 )O2 Cl2 ] (5 ), respectively. Reaction of {Pb[N(TMS)2 ]} (generated in situ from (Me3 Si)2 NH, n BuLi and PbCl2 ) with L 6 H6 afforded, after work-up (MeCN), the mixed-metal complex [Pb10 Li2 (L 6 )2 (OH)Cl(O)4 ]·9.5MeCN (6 ·9.5MeCN). Reaction of distilled {Pb[N(TMS)2 ]} (six equivalents) with L 8 H8 resulted in the complex [Pb12 (L 8 )2 O4 ]·12MeCN (7 ·12MeCN). Complexes 1–7, Pb(O i Pr)2 and [Pb(N(TMS)2 )2 ] have been screened for their potential to act as pre-catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) and the copolymerization thereof. Generally, the lithiated complexes 1 and 2 exhibited better activities than the other pre-catalysts screened herein. For ε-CL and δ-VL, moderate activity at 130 °C over 24 h was observed for 1–7 . In the case of the co-polymerization of ε-CL with δ-VL, 1–7, Pb(O i Pr)2 and [Pb(N(TMS)2 )2 ] afforded reasonable conversions and high molecular weight polymers. The systems 1–7, Pb(O i Pr)2 and [Pb(N(TMS)2 )2 ] also proved to be active in the ROP of the rac -lactide ( r -LA); the activity trend was found to be 1 > 2 ≈ Pb(O i Pr)2 ≈ [Pb(N(TMS)2 )2 ] > 4 > 5 ≈ 6 ≈ 7 > 3 .