Synthesis and Single Crystal X‐ray Structures of Cationic Zinc β‐Diketiminate Complexes

Abstract

The cationic zinc complex [L1Zn][Al(OC(CF3)3)4] (1) (L1 = {[(2,4,6‐Me3–C6H2)NC(Me)]2CH}) bearing a weakly coordinating aluminate anion was obtained from reaction of L1ZnCl with Li[Al(OC(CF3)3)4]. In addition, base‐stabilized zinc cations [L1/2Zn(base)2][X] (2–5) (L2 = {[(2,6‐iPr2–C6H3)NC(Me)]2CH}; X = [Al(OC(CF3)3)4], [B(C6F5)4]) containing weakly coordinating anions and different Lewis bases (dimethylaminopyridine (dmap), tert‐butylpyridine (tBuPy)) were synthesized and structurally characterized. Moreover, the solid‐state structures of L1ZnMe (6) and the neutral base‐stabilized complexes tBuPy‐Zn(Cl)L1 (7) and base‐Zn(Me)L2 (base = dmap 8, tBuPy 9) are reported and compared with those of 2–5. Preliminary studies showed that 1 is catalytically activity in lactide polymerization at 160 °C.

Synthesis, Structure, and Catalytic Activity of Tridentate, Base‐Functionalized β‐Ketiminate Zinc Complexes in Ring‐Opening Polymerization of Lactide

“…Crystals of 12 suitable for single‐crystal X‐ray crystallography were obtained by slow cooling of a solution of 12 in CH 2 Cl 2 to –30 °C. Complex 12 adopts a dimeric structure in the solid state (Figure 5), in which the zinc atoms have a slightly distorted tetrahedral coordination geometry, as is typical for four‐coordinate zinc complexes 12c,14,27,30. This finding clearly illustrates the influence of the side‐arm donor, as both 1 and 2 adopt monomeric structures in the solid state.…”

“…Complexes 1 and 2 form monomeric structures in the solid state, and their central structural parameters are almost identical (Table 2). The zinc atoms in 1 and 2 adopt slightly distorted tetrahedral coordination geometries, as is typical for zinc complexes 12c,14,27,31. The Zn1–O1 [ 1 : 1.9675(7), 2 : 1.9815(8) Å], Zn1–N1 [ 1 : 2.0099(8), 2 : 2.0045(9) Å], and Zn1–N2 [ 1 : 2.1707(8), 2 : 2.1800(9) Å] bond lengths are comparable.…”

“…However, these cationic complexes converted 200 equiv. of lactide into polylactide within 8 min in bulk polymerization at 160 °C 27…”

Synthesis and X‐ray Crystal Structures of β‐Ketoiminate Complexes

“…We recently reported on the solid‐state structures of monomeric β‐ketoiminate complexes L2 Do1 Zn R ( R = Me, Et) . In contrast, complex L1 Do2 ZnEt was reported to form a tetrameric structure in the solid state .…”

Synthesis and X‐ray Crystal Structures of Homotrimetallic Zinc Bisureate Complexes

“…We are generally interested in the synthesis and solid‐state structures of homo‐ and heteroleptic zinc complexes containing N , N ′‐chelating β ‐diketiminates and amidinates, as well as of N , O ‐chelating ketoiminates and their potential capability to serve as catalyst in the ROP of rac ‐lactide Moreover, we recently reported on the synthesis and solid‐state structures of tethered bisamidinate alane complexes . These studies prompted our interest towards tethered bis(ureate) complexes and we herein report on reactions of the bis(urea) 1,4‐( t BuNHCONH) 2 ‐C 4 H 8 ( 1 ) with three zinc dialkyls Zn R 2 , yielding homotrimetallic zinc bis(ureate) complexes of the general type [RZn‐1,4‐( t BuNHCON) 2 ‐C 4 H 8 ] 2 Zn [ R = Me ( 2 ), Et ( 3 ), and n Pr ( 4 )].…”