New facets of an old ligand: titanium and zirconium complexes of phenylenediamine bis(phenolate) in lactide polymerisation catalysis

Abstract

Phenylenediamine bis(phenolate) binds in the reduced dianionic form to titanium and zirconium alkoxides giving either mononuclear or bridging dinuclear complexes depending on the metal precursors; the fluxional mononuclear titanium complex is found to exhibit extremely high activity in polymerisation of rac-lactide in the melt.

Bis(aniline–phenolate) complexes of group 4 metals: Coordination chemistry and lactide polymerization catalysis

“…2. This geometry is typical of the complexes of the bis(imine-phenolate) ligands [15], and also of the tetradentate {ONNO} ligands such as Salans [16], Salophans [17], as well as the parent phenylenediamine bis(phenolate) [8] in which the N-donors are forced into a cisrelationship by the ligand skeleton. The common symmetry of complexes of this geometry is C 2 .…”

“…Hetereoleptic group 4 metal complexes have been explored to a lesser extent in comparison to complexes of other metals as catalysts for cyclic ester polymerization. Recently, we described the coordination chemistry of the tetradentate phenylenediamine bis(phenolate) ligand [8] around group 4 metals [9]. We found that it tends to bind in the "reduceddianionic" form giving either mononuclear [{ONNO}M(OR) 2 ] or dinuclear [{μ-ONNO}(M(μ-O-i-Pr)(O-i-Pr) 2 ) 2 ] complexes.…”

Heptacoordinated Molybdenum(VI) Complexes of Phenylenediamine Bis(phenolate): A Stable Molybdenum Amidophenoxide Radical

“…2 Thus, it can act, once partially or fully deprotonated, as a multidentate ligand to form complexes with Cu and Zn 2 as well as with Ti and Zr. 3,4 This potentially tetradentate ligand has rich electrochemical behavior and it can present five different oxidation states that are interrelated by one-electron transfer steps (see…”

Homopiperazine and Piperazine Complexes of ZrIV and HfIV and Their Application to the Ring‐Opening Polymerisation of Lactide

“…This structure is analogous to that recently reported by Kol for Ti IV and Zr IV phenylenediamine bis(phenolate) species. [11] However, this is the first example of such a structure with Hf IV . Selected bond lengths and angles for the Hf IV complexes are shown in Table 1.…”

“…[10] Kol has shown that a Zr IV complex of a tetradentate phenylenediamine bis(phenolate) affords heterotactic PLA under melt conditions. [11] The same group has also shown that dithiodiolate complexes with Zr IV are active for the production of hetereotactic PLA.…”