Showing papers by "Georgina M. Rosair published in 2021"
TL;DR: In this article, air and moisture-stable polymetallic Ti and Zr amino acid-derived amine bisphenolate (ABP) complexes were synthesized and fully characterised, including X-ray crystallographic studies.
Abstract: Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates of different nuclearity. The steric bulk on the pendant arm of the ligand was found to play a critical role in establishing the nuclearity of the aggregated complex. Sterically, less-demanding groups, such as H or Me, facilitated the formation of tetrametallic Ti clusters, bridged by carboxylate groups, while increased steric bulk (tBu) led to the formation of binuclear μ-oxo-bridged species. The isolated complexes were employed as catalysts for the ring opening polymerisation (ROP) of rac-lactide. Overall, the Ti catalysts were all active with the smaller, bimetallic Ti aggregates exhibiting relatively faster rates. A monometallic, bis(ABP) Zr complex was found to exert remarkable ROP activity, albeit with limited control over the tacticity and molecular weight distribution of the polymer. A further oxo-bridged Zr cluster was shown to display a previously unprecedented trimetallic structure and achieved a moderate rate in the ROP of rac-lactide.
4 citations
TL;DR: In this article, a novel angular trinuclear Co(III)-Co(II)−Co(III) mixed-valence Schiff base complex of formula [{(μ-L)(μ-N3)CoIII(N3)}2CoII(H2O)2]⋅MeOH⋆1.5H2
3 citations
TL;DR: A series of amine bisphenol (ABP) pro-ligands featuring amino acid ester pendant arms were prepared in this article, which allowed the facile incorporation of chiral amino acids into the ABP scaffold with minimal racemisation.
Abstract: A series of amine bisphenol (ABP) pro-ligands featuring amino acid ester pendant arms were prepared. Optimisation of the synthetic method allowed the facile incorporation of naturally occurring, chiral amino acids into the ABP scaffold with minimal racemisation. Reaction of the pro-ligands (LH2) with Pd(OAc)2, in the presence of amines, led to the formation of complexes with an unprecedented pincer-like O,N,O coordination mode around the PdII centre. The complexations in the presence of trialkylamines (NR3) afforded a mixture of LPdNR3 and LPdNHR2 species. The latter was shown to form via an ambient-temperature C–N cleavage involving unstable Pd(OAc)2(NHR2)2 intermediates. Using pyridine as base eliminated this dealkylation and resulted in the exclusive formation of LPd(py) complexes in high yields. In total, seven novel PdII ABP complexes were prepared, exhibiting distorted square-planar geometries with the asymmetric ligand moieties orientated towards the metal centre. The air- and moisture-stable LPd(py) complexes were successfully employed as catalysts in two types of C–C coupling reactions. The Suzuki–Miyaura coupling of 4′-bromoacetophenone and phenylboronic acid reached high yields (up to 81%), while a scope of further alkyl bromides was also efficiently converted using low catalyst loadings (1 mol%) and mild temperatures (40 °C). Furthermore, a Pd–pyridine complex achieved high activity in the Mizoroki–Heck coupling of styrene and 4′-bromoacetophenone.
2 citations