A one-pot method has been developed for the oxidative cleavage of internal alkenes into aldehydes by using 0.5 mol% of the nonheme iron complex [Fe(OTf)2(mix-bpbp)] (bpbp=N,N'-bis(2-picolyl)-2,2'-bipyrrolidine) as catalyst and 1.5 equivalents of hydrogen peroxide and 1 equivalent of sodium periodate as oxidants. A mixture of diastereomers of the chiral bpbp ligand can be used, thereby omitting the need for resolution of its optically active components. The cleavage reaction can be performed in one pot within 20 h and under ambient conditions. Addition of water after the epoxidation, acidification and subsequent pH neutralization are crucial to perform the epoxidation, hydrolysis, and subsequent diol cleavage in one pot. High aldehyde yields can be obtained for the cleavage of internal aliphatic double bonds with cis and trans configuration (86-98%) and unsaturated fatty acids and esters (69-96%). Good aldehyde yields are obtained in reactions of trisubstituted and terminal alkenes (62-63%). The products can be easily isolated by a simple extraction step with an organic solvent. The presented protocol involves a lower catalyst loading than conventional methods based on Ru or Os. Also, hydrogen peroxide can be used as the oxidant in this case, which is often disproportionated by second- and third-row metals. By using only mild oxidants, overoxidation of the aldehyde to the carboxylic acid is prevented.

The limited availability of catalytic reaction components may represent a major hurdle for the practical application of many catalytic procedures in organic synthesis. In this work, we demonstrate that the mixture of isomeric iron complexes [Fe(OTf)2(mix-BPBP)] (mix-1), composed of Λ-α-[Fe(OTf)2(S,S-BPBP)] (S,S-1), Δ-α-[Fe(OTf)2(R,R-BPBP)] (R,R-1) and Δ/Λ-β-[Fe(OTf)2(R,S-BPBP)] (R,S-1), is a practical catalyst for the preparative oxidation of various aliphatic compounds including model hydrocarbons and optically pure natural products using hydrogen peroxide as an oxidant. Among the species present in mix-1, S,S-1 and R,R-1 are catalytically active, act independently and represent ca. 75% of mix-1. The remaining 25% of mix-1 is represented by mesomeric R,S-1 which nominally plays a spectator role in both C-H and C[double bond, length as m-dash]C bond oxidation reactions. Overall, this mixture of iron complexes displays the same catalytic profile as its enantiopure components that have been previously used separately in sp(3) C-H oxidations. In contrast to them, mix-1 is readily available on a multi-gram scale via two high yielding steps from crude dl/meso-2,2'-bipyrrolidine. Next to its use in C-H oxidation, mix-1 is active in chemospecific epoxidation reactions, which has allowed us to develop a practical catalytic protocol for the synthesis of epoxides.

Homogeneous metal complexes often display superior activity and selectivity in catalysis of chemical transformations. Heterogenization of these complexes by immobilization on solid supports has been used to facilitate recovery, but this is often associated with a decrease in catalytic performance. We here describe a novel approach of sizing and engineering the cavity structure of nanoporous materials as “nanoreactors” to assemble metal complexes by the “ship-in-the-bottle” synthesis to combine the best of homogeneous and heterogeneous catalysts. Catalysis occurred by free metal complexes in confined liquid in these nanoreactors, while the catalysts were recyclable as being heterogeneous at the macroscopic scale. Subnanometer tailoring of window sizes (0.5–3.7 nm) of the cavities (16–22 nm) allowed control over loading (6–70 mg-metal complex/g-support) and a high turnover frequency (40–600 h–1) for the hydrolytic kinetic resolution of 1,2-epoxyhexane. Most importantly, the ‘heterogeneous homogeneous catalysts’ showed enhanced thermal stability and were stable upon reuse approaching excellent turnover numbers of 100,000. We showed that engineering and sizing of nanoreactors is a powerful approach to control performance of confined catalysts, and this method is generally applicable in host–guest catalysis.

A convenient approach for the anchoring of S,S-BnTsDPEN ligands (S,S-N-tosyl-1,2-diphenylethylenediamine) to branched carbosilane scaffolds was investigated. It is based on a high-yielding reductive amination reaction between commercially available S,S-TsDPEN and readily accessible carbosilanes furnished with benzaldehyde terminal fragments. These molecularly enlarged ligands, bearing four S,S-BnTsDPEN units, and their simplified monomeric and ''dimeric'' analogues were evaluated in iron(III)-catalyzed asymmetric trans-stilbene epoxidation reactions using hydrogen peroxide as an environmentally benign oxidant. The catalytic investigations showed a large degree of variation in the activity and stereoselectivity of the series of DPEN catalysts. In combination with ESI-MS investigations, these data revealed an important role of the ligand orientation in determining the overall activity of the catalyst system. Accordingly, a suitable design of the molecularly enlarged ligands resulted in fully retained activity and selectivity in catalysis. Finally, a number of strategies for the recovery and reuse of the best performing carbosilane-tethered DPEN ligands were explored.

A method for the regioselective transformation of dienes to carbonyl compounds has been developed. Electron‐rich olefins react selectively to yield valuable aldehydes and ketones. The method is based on the catalyst [Fe(OTf)2(mix‐BPBP)] with an oxidant combination of H2O2 (1.0 equiv.) and NaIO4 (1.5 equiv.); it uses mild conditions and short reaction times, and it outperforms other olefin cleavage methodologies.