The Rieske dioxygenases are a group of non‐heme iron enzymes, which catalyze the stereospecific cis‐dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3‐bis(1‐methylimidazol‐2‐yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3‐bis(1‐methylimidazol‐2‐yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [FeII(PrL1)2](BPh4)2 (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [FeII(PrL1)2(MeOH)2](OTf)2 (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non‐heme iron(II) enzyme apocarotenoid‐15–15′‐oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non‐heme iron complexes [FeII(PrL1)2](OTf)2 (2) and [FeII(PrL1)2](BPh4)2 (3) were tested in olefin oxidation reactions with H2O2 as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis‐dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.

New chiral NCN-pincer palladium complexes containing bulky diphenylhydroxymethyl pyrrolidinyl moieties as chiral auxiliaries have been synthesized. Oxidative palladium addition to ligand 2 (2 ) 2,6-bis{[(S)-2-(diphenylhydroxymethyl)-1-pyrrolidinyl]methyl}-1-bromobenzene) initially yielded neutral arylpalladium bromide complex 3 in a moderate yield as a consequence of the bulky pyrrolidinyl functional groups. Performing the palladation reaction under microwave irradiation for only 5 min gave 3 in 79% yield. Abstraction of the bromide ion from 3 subsequently yielded the cationic complexes -coordination mode of the pincer framework is complemented by two rather long Pd-O interactions (2.622(2)-2.649(2) Å). Theoretical calculations (Mulliken population analysis and "atoms in molecules" analysis) confirmed that there is a coordinative interaction between the palladium and the oxygen atoms of both hydroxyl groups despite the long Pd-O distance. Complexes [4]PF 6 and [4]BF 4 catalyze the aldol condensation between R-methyl isocyanoacetate and various aromatic aldehydes with enhanced regio-(up to 70%) and stereoselectivity (up to 42% ee) for the cis-oxazolines. These observations are in contrast to prior literature results on other pincer systems, where the trans-oxazolines were the main product, and point to a deeper chiral cavity pointing away from palladium toward the coordinated isocyanoacetate substrate.

In situ resolution of the rapidly racemising diphosphine BIPHEP and its relatives with the cationic Rh complex of (S,S)-bicyclonona-2,6-diene permits the asymmetric hydrogenation of dehydroamino esters.

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A series of mononuclear iron(II) and zinc(II) complexes of the new chiral Py(ProMe) 2 (5) are reported. They all show a meridional NN′N coordination of the Py(ProMe) 2 ligand. The bis-chloride derivatives 1 and 2 represent neutral isostructural five-coordinated complexes with a distorted geometry around the metal center. Unusual sevencoordinate iron(II) complexes 3 and 4 having a pentagonal bipyramidal geometry were obtained using weakly coordinating triflate anions. The reaction of Zn(OTf) 2 with the Py(ProMe) 2 ligand afforded complex 5 with a distorted octahedral geometry around the zinc center. All complexes were formed as single diastereoisomers. In the case of complexes 3−5, the oxygen atoms of both carbonyl groups of the ligand are also coordinated to the metal. The stereochemistry of the coordinated tertiary amine donors in complexes 3−5 is of opposite configuration as in complexes 1 and 2 as a result of the planar penta-coordination of the ligand Py(ProMe) 2 . Complexes 1, 2, and 5 have an overall Λ-configuration at their metal center, while the Fe(II) ion in complexes 3 and 4 has the opposite ∆-configuration (crystal structures and CD measurements). The magnetic moments of iron complexes 1, 3, and 4 correspond to that of high-spin d 6 Fe(II) complexes. The solution structures of complexes 1−5 were characterized by means of UV−vis, IR, conductivity, and CD measurements and their electrochemical behavior. These studies showed that the coordination environment of 1 and 2 observed in the solid state is maintained in solution. In coordinating solvents, the triflate anion (3, 5) or water (4) co-ligands of complexes 3−5 are replaced by solvent molecules with retention of the original pentagonal bipyramidal and octahedral geometry, respectively.