Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex.

In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [Fe (O )(Bn3MC)] (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at -40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major Fe -OAr product 3. At the same time, the Fe (Bn3MC) (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [Fe (O)(L )] (2-syn)→2 [Fe (L )] (3)+[Fe (L )] (1)+H O.

Structural implications of the paramagnetically shifted NMR signals from pyridine H atoms on synthetic nonheme Fe=O complexes.

Oxoiron(IV) motifs are found in important intermediates in many enzymatic cycles that involve oxidations. Over half of the reported synthetic nonheme oxoiron(IV) analogs incorporate heterocyclic donors, with a majority of them comprising pyridines. Herein, we report H-NMR studies of oxoiron(IV) complexes containing pyridines that are arranged in different configurations relative to the Fe = O unit and give rise to paramagnetically shifted resonances that differ by as much as 50 ppm.

Catalytic intramolecular hydroamination of aminoallenes using titanium complexes of chiral, tridentate, dianionic imine-diol ligands.

Alkylation of d- or l-phenylalanine or valine alkyl esters was carried out using methyl or phenyl Grignard reagents. Subsequent condensation with salicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, or 5-fluorosalicylaldehyde formed tridentate, X2L type, Schiff base ligands. Chiral shift NMR confirmed retention of stereochemistry during synthesis.