Synthesis and Dynamic Behavior of Chiral NNO‐Scorpionate Zinc Initiators for the Ring‐Opening Polymerization of Cyclic Esters. Issue 15 (22nd January 2016)

• Record Type: Journal Article
• Authors: Honrado, Manuel; Otero, Antonio; Fernández‐Baeza, Juan; Sánchez‐Barba, Luis F.; Garcés, Andrés; Lara‐Sánchez, Agustín; Rodríguez, Ana M.
• Other Names: Pettinari C. guestEditor.
• Is Part Of: European journal of inorganic chemistry. Issue 15/16(2016)
• Page Start: 2562
• Page End: 2572
• Publication Date: 2016-01-22
• Subjects: Chirality -- Scorpionates -- Polymerization -- Zinc -- Cyclic esters; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201501347
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : The reaction of chiral alcohol–scorpionate compounds bpzbeH [bpzbeH = 1, 1‐bis(3, 5‐dimethylpyrazol‐1‐yl)‐3, 3‐dimethyl‐2‐butanol] or bpzteH [bpzteH = 2, 2‐bis(3, 5‐dimethylpyrazol‐1‐yl)‐1‐ para ‐tolylethanol] with [ZnR2 ] (R = Me, Et, CH2 SiMe3 ) in a 1:2 molar ratio afforded the dinuclear chiral zinc alkyls [Zn(R)(κ 2 ‐NNµ‐O)Zn(R)2 ] (1 –4 ) [κ 2 ‐NNµ‐O = bpzbe, R = Me (1 ), Et (2 ), CH2 SiMe3 (3 ); bpzte, R = Et (4 )]. Subsequent alcoholysis or thioalcoholysis reaction with ArEH (1 equiv.; E = O, S; Ar = 2, 6‐C6 H3 Me2 ) yielded the chiral dinuclear mixed alkyl–alryl oxides/thioaryl oxides [(ZnR)2 (κN:κN‐µ‐O)(µ‐EAr)] (5 –12 ) [κN:κN‐µ‐O = bpzbe, E = O, R = Me (5 ), Et (6 ), CH2 SiMe3 (7 ); bpzte, E = O, R = Et (8 ); bpzbe, E = S, R = Me (9 ), Et (10 ), CH2 SiMe3 (11 ); bpzte, E = S, R = Et (12 )]. The alcoholysis reaction of the previously reported monoalkyls [Zn(Me)(κ 3 ‐NNO)] or [Zn(R)(κ‐NNµ‐O)]2 with ArOH (1 equiv., Ar = 2, 6‐C6 H3 Me2 ) afforded the chiral aryl oxides [Zn(OAr)(κ 2 ‐NNµ‐O)]2 (13 –14 ) [κ 2 ‐NNµ‐O = bpzbe (13 ); bpzte (14 )]. The X‐ray crystal structures of3, 5, 6, and14 confirmed a dinuclear structure in all cases with the alkoxide of the heteroscorpionates in a µ‐bridging mode between the Zn II centers. Variable‐temperature NMR spectroscopic studies were carried out to study their dynamic behavior in solution. Complexes1 –9 and12 can act as single‐component initiators for the ROP of ε‐CL andl ‐/ rac ‐LA, and afforded materials with low molecular weights and narrow monomodal molecular weight distributions. MALDI‐TOF mass spectra confirmed that for5 –8 the initiation occurred through nucleophilic attack by the alkoxide group, rather than the alkyl group, on the lactide monomer. Furthermore, inspection of the kinetic parameters showed propagations with a pseudo‐first‐order dependence on monomer and catalyst concentrations. Microstructural analysis of poly( rac ‐lactide) revealed that the mixed alkyl/aryl oxide‐substituted initiators exert a moderate level of heteroselectivity ( P s = 0.66). Abstract : A new series of chiral dinuclear trisalkyl‐ and alkyl–aryl oxide‐containing zinc heteroscorpionates complexes, namely, [Zn(R)(κ 2 ‐NNµ‐O)Zn(R)2 ] and [(ZnR)2 (κN:κN‐µ‐O)(µ‐OAr)], respectively, has been synthesized. Their dynamic behavior has been studied. Both families act as single‐component living initiators for the ring‐opening polymerization of ε‐CL andl ‐/ rac ‐LA.