N-Donor stabilized tin(ii) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAsviathe activated monomer mechanism

Abstract

α-iminopyridine ligands L1 (2-(CH=N(C6H2-2,4,6-Ph3))C5H4N), L2 (2-(CH=N(C6H2-2,4,6-tBu3))C5H4N) and L3 (1,2-(C5H4N-2-CH=N)2CH2CH2) differing by the steric demand of the substituent on the imine CH=N group and by a number of donating nitrogen atoms...

Tin(ii) cations stabilized by non-symmetric N,N′,O-chelating ligands: synthesis and stability

“…While the signals ranging from −523.2 to −469.0 ppm were assigned to the [ L 1–6 SnCl] + cations, the signals ranging between δ = −101.1 and −57.7 ppm correspond to the related [SnCl 3 ] − anions. 8–15 The chemical shifts of the [ L 1–6 SnCl] + cations are in accordance with those of related bis(imino)pyridine-stabilized chlorostannyliumylidenes (range of −482.4 to −411.7 ppm), containing tetra-coordinated tin centers. 7,9 This clearly indicates the coordination of both nitrogen and also oxygen donor atoms in solutions of 1–6 .…”

“…Roesky et al observed a Lewis base mediated ionization of SnCl 2 and reported the synthesis of [(DIMPY)SnCl] + [SnCl 3 ] − , where DIMPY is 2,6-[(Me)CN(C 6 H 3 -2,6-iPr 2 )] 2 C 5 H 3 N. 7 This approach has become universal for obtaining a wide range of tin( ii ) cations with a general formula [D → SnX] + (D = Lewis base, X = halide or pseudohalide) (Chart 1, A–G ). 8–15…”

“…Many N-donor ligands such as α-iminopyridines, 8 bis(imino)pyridines, 9 bis(α-iminopyridines) 10 and N-heterocyclic imines 11 were then used as Lewis bases for the ionization of SnCl 2 . In addition to the N-donor ligands, also O-donor ligands have been used for this concept.…”

“…After Müller et al obtained [(tol) 3 Sn] 2+ in an attempt to recrystallize a stannylium cation in toluene (Chart 1, H ), 15 a significant progress has recently been made in the field of tin( ii ) dications [D → Sn] 2+ . This field is represented by the synthesis of bipy, 16 bis(α-iminopyridine) 10,17 and crown-ether 12 stabilized tin( ii ) dications (Chart 1, I–K ).…”

Syntheses of polylactides by means of tin catalysts

“…Finally, a recent publication of Novák et al discussing the usefulness of the cationic Sn(II) complexes (Schemes 26-28) as catalysts for ROPs of LLA should be mentioned. 160 In the title and in the section "Discussion" those authors claim that these cationic catalysts initiate an activated monomer mechanism. However, MALDI TOF mass spectra and NMR spectroscopic end group analyses were missing.…”