Air-stable iron complexes display good activity for CO2-epoxide cycloadditions and reactivity trends across family are reported.

Two lithium amine-bis(phenolate) and four chromium(III) amine-bis(phenolate) complexes have been prepared. The diprotonated tripodal tetradentate ligand precursors 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)[O(2)NO](BuMe); 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4,6-tert-butylphenol), H(2)[O(2)NO](BuBu); 2-pyridylamino-N,N-bis(2-methylene-4,6-methylphenol), H(2)[O(2)NN'](MeMe); and 2-pyridylamino-N,N-bis(2-methylene-4,6-tert-butylphenol), H(2)[O(2)NN'](BuBu); can be lithiated using n-butyllithium. Isolation of the Li(2)[O(2)NO](RR') compounds generates dimeric {Li(2)[O(2)NO](RR')}(2) (R = t-Bu, R' = Me in 1 and R = R' = t-Bu in 2) in the solid state as shown by single-crystal X-ray diffraction. The lithiated ligands were used to prepare a series of Cr(III) complexes. Monometallic complexes are obtained when prepared and purified under strictly anhydrous conditions, giving CrCl(THF)[O(2)NO](RR') (R = t-Bu, R' = Me in 3 and R = R' = t-Bu in 4). However, bimetallic Cr complexes are obtained upon recrystallization in air, where adventitious water reacts with the complex resulting in protonation of one of the phenolate groups of the ligand and generating hydroxide, which bridges two Cr(III) centres. Solid-state single-crystal X-ray diffraction studies of {CrCl[O(2)NN'](MeMe)}(mu-HO){CrCl[HO(2)NN'](MeMe)}, 5, and {CrCl[O(2)NN'](BuBu)}(mu-HO){CrCl[HO(2)NN'](BuBu)}, 6, were performed. The paramagnetic Cr(III) complexes were also characterized by UV-vis spectroscopy, mass spectrometry and magnetic measurements.

Lithium and sodium compounds supported by tetradentate amino-bis(phenolato) ligands, [Li2(N2O2(BuBuPip))] (1), [Na2(N2O2(BuBuPip))] (2) (where [N2O2(BuBuPip)] = 2,2'-N,N'-homopiperazinyl-bis(2-methylene-4,6-tert-butylphenol), and [Li2(N2O2(BuMePip))] (3), [Na2(N2O2(BuMePip))] (4) (where [N2O2(BuMePip)] = 2,2'-N,N'-homopiperazinyl-bis(2-methylene-4-methyl-6-tert-butylphenol) were synthesized and characterized by NMR spectroscopy and MALDI-TOF mass spectrometry. Variable temperature NMR experiments were performed to understand solution-phase dynamics. The solid-state structures of 1 and 4 were determined by X-ray diffraction and reveal tetrametallic species. PGSE NMR spectroscopic data suggests that 1 maintains its aggregated structure in CD2Cl2. The complexes exhibit good activity for controlled ring-opening polymerization of rac-lactide (LA) both solvent free and in solution to yield PLA with low dispersities. Stoichiometric reactions suggest that the formation of PLA may proceed by the typical coordination-insertion mechanism. For example, (7)Li NMR experiments show growth of a new resonance when 1 is mixed with 1 equiv. LA and (1)H NMR data suggests formation of a Li-alkoxide species upon reaction of 1 with BnOH.