Combining alkali metals and zinc to harness heterometallic cooperativity in cyclic ester ring-opening polymerisation

Heterometallic cooperativity is an emerging strategy to elevate polymerisation catalyst performance. Here, we report the first heterotrimetallic Na/Zn₂ and K/Zn₂ complexes supported by a ProPhenol ligand, which deliver “best of both” in cyclic ester ring-opening polymerisation, combining the outstanding activity (Na/K) and good control (Zn₂) of homometallic analogues. Detailed NMR studies and density-functional theory calculations suggest that the Na/Zn₂ and K/Zn₂ complexes retain their heterometallic structures in the solution-state. To the best of our knowledge, the K/Zn₂ analogue is the most active heterometallic catalyst reported for rac-lactide polymerisation (k_obs = 1.7 × 10⁻² s⁻¹), giving activities five times faster than the Na/Zn₂ complex. These versatile catalysts also display outstanding performance in ε-caprolatone and δ-valerolactone ring-opening polymerisation. These studies provide underpinning methodologies for future heterometallic polymerisation catalyst design, both in cyclic ester polymerisation and other ring-opening (co)polymerisation reactions.

Cooperative heterotrimetallic Na/Zn₂ and K/Zn₂ complexes combine the excellent activities and control of the homometallic analogues, giving “best of both” in cyclic ester ring-opening polymerisation.     

An ab initio molecular orbital study of the grignard reagents CH3MgCl and [CH3MgCl]2: The Schlenk equilibrium

Ab initio molecular orbital calculations are used to study the modified Schlenk equilibrium: 2RMgCl (RMgCl)² MgR₂ + MgCl₂ Mg(Cl₂)MgR₂ with R=H and CH₃. In the absence of any solvents, calculations indicate that the formation of the various possible bridged dimers (RMgCl)₂ is substantially exothermic. However, using dimethylether as a model solvent, we show that the formation of the dimer (Me₂O)(CH₃)Mg(Cl₂)Mg(CH₃)(OMe₂) is exothermic only when entropic effects are included.     

Oxidative versus reductive additions: A 13C NMR study of H2, HX (X = Cl,Br, OR I), and Cl2 additions to some iridium(I) complexes

The ¹³C NMR spectra of a number of iridium complexes and of their adducts with H₂, HX, and Cl₂ (X = Cl, Br, I) are used to estimate the redox character of these additions. Rather than having the oxidative character expected, H₂ addition seems to be reductive. HX and Cl₂ additions are oxidative. Some of these complexes appear to have Lewis acid, rather than the expected Lewis base character.     

A convenient one-pot synthesis of 1,8-naphthyridones

In this paper, we disclose an efficient one-pot procedure for the preparation of substituted 1,8-naphthyridin-4-one analogues. Previous efforts to effect this type of transformation were complicated by the formation of benzene tricarboxylate. Via the use of excess base, the impurity formation was completely inhibited. This allowed for the clean preparation of the desired intermediate and subsequent formation of naphthyridone analogues in a single flask, which could then be crystallized directly from the reaction mixture in good yield and high purity.     

Pentakis(methoxycarbonyl)cyclopentadiene,a strong organic acid: Crystal and molecular structures of HC5(CO)2Me)5 and Li[C5(CO2Me)5](H2O)

Contrary to some previously depicted structures, the proton in HC₅(CO₂Me)₅ is bonded to two oxygens rather than to carbon; the lithium ion in Li[C₅(CO₂Me)₅] (H₂O) is tetrahedrally coordinated by two carbonyl oxygens from one C₅ anion, one from a second anion, and a water molecule.     

Synthesis of sodium tantalate nanorods by alkalide reduction

NaTaO3 nanorods were synthesized with high (>90%) yield by reduction of TaCl5 with THF solutions of the alkalide K+(15C5)2Na-, followed by product annealing under dynamic vacuum at 250 and 600 degrees C. In addition to the nanorods, the product is comprised of 5-10% approximately 10-nm diameter spheroidal NaTaO3 nanocrystals. The nanorods are generally longer than 500 nm, with some exceeding 1 mum, and 10-100 nm wide, with aspect ratios that vary between 10 and 20:1. Select area electron diffraction patterns of individual nanorods indicate that each nanorod is a single crystal with its axis oriented in the [010] direction.