An In-Depth Look at the Reactivity of Non-Redox-Metal Alkylperoxides.

Over the past 150 years, a certain mythology has arisen around the mechanistic pathways of the oxygenation of organometallics with non-redox-active metal centers as well as the character of products formed. Notably, there is a widespread perception that the formation of commonly encountered metal alkoxide species results from the auto-oxidation reaction, in which a parent metal alkyl compound is oxidized by the metal alkylperoxide via oxygen transfer reaction. Now, harnessing a well-defined zinc ethylperoxide incorporating a ß-diketiminate ligand, the investigated alkylperoxide compounds do not react with the parent metal alkyl complex as well as Et2 Zn to form a zinc alkoxide. Upon treatment of the zinc ethylperoxide with Et2 Zn, a previously unobserved ligand exchange process is favored. Isolation of a zinc hydroxide carboxylate as a product of decomposition of the parent zinc ethylperoxide demonstrates the susceptibility of the latter to O-O bond homolysis.

Oxygenation Chemistry of Magnesium Alkyls Incorporating ß-Diketiminate Ligands Revisited.

Despite the fact that extensive research has been carried out, the oxygenation of alkyl magnesium species still remains a highly unexplored research area and significant uncertainties concerning the mechanism of these reactions and the composition of the resulting products persist. This case study compares the viability of the controlled oxygenation of alkylmagnesium complexes supported by ß-diketiminates. The structural tracking of the reactivity of (N,N)MgR-type complexes towards O2 at low temperature showed that their oxygenation led exclusively to the formation of magnesium alkylperoxides (N,N)MgOOR. The results also highlight significant differences in the stability of the resulting alkylperoxides in solution and demonstrate that [(BDI)Mg(µ-η2 :η1 -OOBn)]2 (in which BDI=[(ArNCMe)2 CH]- and Ar=C6 H3 iPr2 -2,6) can be easily transformed to the corresponding magnesium alkoxide [(BDI)MgOBn]2 at ambient temperature, whilst [(F3 BDI)Mg(µ-OOtBu)]2 (in which F3 BDI=[(ArNCMe)2 CH]- and Ar=C6 H2 F3 -2,4,6) is stable under similar conditions. The observed selective oxygenation of (N,N)MgR-type complexes to the corresponding (N,N)MgOOR alkylperoxides strongly contradicts the widely accepted radical-chain mechanism for the oxygenation of the main-group-metal alkyls. Furthermore, either the observed transformation of the alkylperoxide [(BDI)MgOOBn]2 to the alkoxide [(BDI)MgOBn]2 as well as the formation of an intractable mixture of products in the control reaction between the alkylperoxide [(F3 BDI)MgOOtBu]2 and the parent alkylmagnesium [(F3 BDI)MgtBu] complex are not in line with the common wisdom that magnesium alkoxide complexes' formation results from the metathesis reaction between MgOOR and Mg-R species. In addition, a high catalytic activity of well-defined magnesium alkylperoxides, in combination with tert-butyl hydroperoxide (TBHP) as an oxygen source, in the epoxidation of trans-chalcone is presented.

Long-Acting Injectable Antipsychotics-A Review on Formulation and In Vitro Dissolution.

Long-acting injectable (LAI) neuroleptics constitute an effective therapeutical alternative for individuals suffering from persistent mental illness. These injectable pharmaceuticals help patients manage their condition better and improve long-term outcomes by preventing relapses and improving compliance. This review aims to analyse the current formulation aspects of LAI neuroleptics, with particular emphasis on analysis of drug release profiles as a critical test to guarantee drug quality and relevant therapeutical activity. While there is no officially approved procedure for depot parenteral drug formulations, various dissolution tests which were developed by LAI manufacturers are described. In vitro dissolution tests also possess a critical function in the estimation of the in vivo performance of a drug formulation. For that reason, thorough inspection of the in vitro-in vivo correlation (IVIVC) is also discussed.

Reactions of ZnR2 compounds with dibenzoyl: characterisation of the alkyl-transfer products and a striking product-inhibition effect.

The first systematic theoretical and experimental studies of reaction systems involving ZnR(2) (R=Me, Et or tBu) with dibenzoyl (dbz) as a non-innocent ligand revealed that the character of the metal-bonded R group as well as the ratio of the reagents and the reaction temperature significantly modulate the reaction outcome. DFT calculations showed four stable minima for initial complexes formed between ZnR(2) and dbz and the most stable structure proved to be the 2:1 adduct; among the 1:1 adducts three structural isomers were found of which the most stable complex had the monodentate coordination mode and the chelate complex with the s-cis conformation of the dbz unit appeared to be the least stable form. Interestingly, the reaction involving ZnMe(2) did not lead to any alkylation product, whereas the employment of ZntBu(2) resulted in full conversion of dbz to the O-alkylated product [tBuZn{PhC(O)C(OtBu)Ph}] already at -20 °C. A more complicated system was revealed for the reaction of dbz with ZnEt(2). Treatment of a solution of dbz in toluene with one equivalent of ZnEt(2) at room temperature afforded a mixture of the O- and C-alkylated products [EtZn{PhC(O)C(OEt)Ph}] and [EtZn{OC(Ph)C(O)(Et)Ph}], respectively. The formation of the C-alkylated product was suppressed by decreasing the initial reaction temperature to -20 °C. Moreover, in the case of the dbz/ZnEt(2) system monitoring of the dbz conversion over the entire reaction course revealed a product inhibition effect, which highlights possible participation of multiple equilibria of different zinc alkoxide/ZnEt(2) aggregates. Diffusion NMR studies indicated that dbz forms an adduct with the O-alkylated product, which is a competent species for executing the inhibition of the alkylation event.

Development of zinc alkyl/air systems as radical initiators for organic reactions.

This paper reports a series of comparative experiments on the activity of carbon- and oxygen-centred radical species in a model reaction of the radical addition of THF to imines mediated by a series of zinc alkyl/air reaction systems. The study strongly contradicts the notion that generally R˙ radicals are the initiating species in organic reactions mediated by R n M/air systems, and simultaneously demonstrates that oxygen-centred radical species are the key intermediates responsible for the initiation process. In addition, a new efficient RZn(L)/air initiating system for radical organic reactions exampled by a model reaction of radical addition of THF to imines is developed. Moreover, the isolation and structural characterization of the first zinc alkylperoxide supported by a carboxylate ligand, [Zn4(µ3-OOtBu)3(µ4-O)(O2CEt)3]2, as well as the novel octanuclear zinc oxo(alkoxide) aggregate with entrapped O-THF species, [Zn4(µ4-O)(µ3-2-O-THF)(O2CEt)5]2, provide clear mechanistic signatures for the mode of function of the RZn(O2CR')/air system.