Scalable Synthesis of Esp and Rhodium(II) Carboxylates from Acetylacetone and RhCl3·xH2O.

Rhodium(II) carboxylates are privileged catalysts for the most challenging carbene-, nitrene-, and oxo-transfer reactions. In this work, we address the strategic challenges of current organic and inorganic synthesis methods to access these rhodium(II) complexes through an oxidative rearrangement strategy and a reductive ligation reaction. These studies illustrate the multiple benefits of oxidative rearrangement in the process-scale synthesis of congested carboxylates over nitrile anion alkylation reactions, and the impressive effect of inorganic additives in the reductive ligation of rhodium(III) salts.

Nonclassical Mechanism in the Cyclodehydration of Diols Catalyzed by a Bifunctional Iridium Complex.

1,4- and 1,5-diols undergo cyclodehydration upon treatment with cationic N-heterocyclic carbene (NHC)-IrIII complexes to give tetrahydrofurans and tetrahydropyrans, respectively. The mechanism was investigated, and a metal-hydride-driven pathway was proposed for all substrates, except for very electron-rich ones. This contrasts with the well-established classical pathways that involve nucleophilic substitution.

Homogeneous Water Oxidation by Half-Sandwich Iridium(III) N-Heterocyclic Carbene Complexes with Pendant Hydroxy and Amino Groups.

Herein, we report three IrIII Cp* complexes with hydroxy- or amino-functionalized N-heterocyclic carbene (NHC) ligands that catalyze efficient water oxidation induced by addition of ceric ammonium nitrate (CAN). The pendant hydroxy or amino groups are very important for activity, and the complexes with heteroatom-functionalized NHC ligands show up to 15 times higher rates of oxygen evolution in CAN-induced water oxidation than a reference IrIII Cp* complex without heteroatom functionalization. The formation of molecular high-valent Ir intermediates that are presumably involved in the rate-determining step for water oxidation is established by UV/Vis spectroscopy and ESI-MS under turnover conditions. The hydroxy groups on the NHC ligands, as well as chloride ligands on the iridium center are proposed to structurally stabilize the high-valent species, and thereby improve the catalytic activity. The IrIII complex with a hydroxy-functionalized NHC shows the highest catalytic activity with a TON of 2500 obtained in 3 h and with >90 % yield relative to the amount of oxidant used.

Effect of the functionalisation route on a Zr-MOF with an Ir-NHC complex for catalysis.

A new iridium N-heterocyclic carbene (NHC) metallolinker has been synthesised and introduced into a metal-organic framework (MOF), for the first time, via two different routes: direct synthesis and postsynthetic exchange (PSE). The two materials were compared in terms of the Ir loading and distribution using X-ray energy dispersive spectroscopy (EDS), the local Ir structure using X-ray absorption spectroscopy (XAS) and the catalytic activity. The materials showed good activity and recyclability as catalysts for the isomerisation of an allylic alcohol.

Readily available ruthenium complex for efficient dynamic kinetic resolution of aromatic α-hydroxy ketones.

A ruthenium complex formed from commercially available [Ru(p-cymene)Cl2]2 and 1,4-bis(diphenylphosphino)butane catalyzes the racemization of aromatic α-hydroxy ketones very efficiently at room temperature. The racemization is fully compatible with a kinetic resolution catalyzed by a lipase from Pseudomonas stutzeri. This is the first example of dynamic kinetic resolution of α-hydroxy ketones at ambient temperature in which the metal and enzyme catalysts work in concert in one pot at room temperature to give quantitative yields of esters of α-hydroxy ketones with very high enantioselectivity.

Intramolecular cyclization of alkoxyaminosugars: access to novel glycosidase inhibitor families.

We report the synthesis of two novel families of iminosugars as glycosidase inhibitors involving an intramolecular cyclization between an N-alkoxyamino group and a latent aldehyde of a reducing sugar as the key step. Using this methodology we have prepared the hitherto unknown bicyclic polyhydroxylated N-(methoxy, benzyloxy)anhydroazepanes and N-benzyloxy-d-xylonojirimycin; all these novel compounds turned out to be moderate ß-glucosidase inhibitors in a pH-dependent manner.

Alkoxyamine-cyanoborane adducts: efficient cyanoborane transfer agents.

We report the synthesis of the hitherto unknown zwitterionic alkoxyamino cyanoboranes by reduction of O-alkyloximes with sodium cyanoborohydride; unprecedented cyanoboronated N-alkoxyformamidines were also isolated as by-products. Boronated alkoxyamines were found to be efficient cyanoborane transfer agents towards more basic amines, including aminosugars; they were also successfully transformed into neoglycoconjugates by the neoglycorandomization reaction with reducing sugars.