Synthesis and Structure of C2-Symmetric, Doubly Bridged Bis(indenyl)titanium and -zirconium Dichlorides

Different routes for the construction of biologically active diversely functionalized bicyclo[3.3.1]nonanes: an exploration of new perspectives for anticancer chemotherapeutics

Cancer is the second most high-morbidity disease throughout the world. From ancient days, natural products have been known to possess several biological activities, and research on natural products is one of the most enticing areas where scientists are engrossed in the extraction of valuable compounds from various plants to isolate many life-saving medicines, along with their other applications. It has been noticed that the bicyclo[3.3.1]nonane moiety is predominant in most biologically active natural products owing to its exceptional characteristics compared to others. Many derivatives of bicyclo[3.3.1]nonane are attractive to researchers for use in asymmetric catalysis or as potent anticancer entities along with their successful applications as ion receptors, metallocycles, and molecular tweezers. Therefore, this review article discusses several miscellaneous synthetic routes for the construction of bicyclo[3.3.1]nonanes and their heteroanalogues in association with the delineation of their anticancer activities with few selective compounds.

Strategies for the Synthesis of Chiral Carbon-Bridged Group IV ansa-Metallocenes

This minireview provides a survey of the various synthetic approaches to chiral ansa-metallocenes of Ti, Zr, and Hf containing a carbon-based bridge. The individual strategies to install substitution patterns at either the cyclopentadienyl framework or the bridging unit are highlighted with focus on the progress made towards a direct preparation of single complex stereoisomers. The review further includes the discussion of potential problems such as the formation of undesired diastereomers, the threat of racemization of enantiopure material, and synthetic challenges originating from the synthesis, purification, and isolation of the target complexes. The review has been written with the goal in mind to facilitate the design and synthesis of new chiral ansa-metallocene derivatives for emerging research areas in asymmetric catalysis and organometallic chemistry.

Investigation of the formation of the [2(iohexol) + Mg]2+ complex and its fragmentation in electrospray ionization tandem mass spectrometry

RATIONALE

Mass spectrometry has been developed as one of the common tools for the analysis of the organometallic systems in the gas phase over decades. The study of the fragmentation of organics-metal complexes has attracted much attention since the interesting dissociation pathways exhibited by these compounds are usually different from the protonated analogues.

METHODS

In this work, iohexol complexed with different dications such as Mg²⁺ , Cu²⁺ and Zn²⁺ have been investigated by electrospray ionization (ESI) tandem mass spectrometry. Additionally, deuterium-labeling experiments and an analogue of iohexol were utilized to confirm the reaction mechanisms. A computational chemistry method was used to identify the coordination conformation between iohexol and metal ions in the gas phase. UV detection was also used to identify the interaction between iohexol and metal ions in the liquid phase.

RESULTS

A special gas-phase open-loop reaction of iohexol induced by Mg²⁺ , leading to the formation of [iohexol + Mg - H - HI - C₃ H₄ O]⁺ , was observed in the collision-induced dissociation of [2(iohexol) + Mg]²⁺ complexes. Moreover, theoretical calculation shows the proposed coordination configuration of iohexol/Mg²⁺ complexes. The Mg²⁺ could have tetrahedral coordination with two iohexol molecules.

CONCLUSIONS

The percent study is a case for better understanding the formation of a typical organic/metal complex and its gas-phase fragmentation reaction. In addition, it provides useful information for researchers working on analysis or structural elucidation of complicated compounds which contain the iohexol analogues. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of the stereochemistry of sugars on the selectivity of formation of carbohydrate-derived cyclopentadienyl and indenyl ligands

Interaction of lithium cyclopentadienide with a suitable partially protected alpha-D-allofuranose triflate, 4, epimer at C3 of glucose, gives as a major product, besides the expected glucose-cyclopentadiene, 5, a glucose-disubstituted cyclopentadiene, 6. This unprecedented behaviour, which does not occur with alpha-D-glucofuranose and other sugars, is tentatively explained by a complexation of LiCp and the oxygen atoms of the isopropylidene function of one molecule of 4 and one of 5, giving a termolecular structure as the result of a template effect. The results of other experiments, such as the use of MgCp2 in place of LiCp or the complexation of oxygen atoms by lithium triflate, which changed the selectivity of the reaction largely in favour of the monosubstitution product 5, support this hypothesis. When lithium indenide is reacted with 4, glucose-monosubstituted and glucose-disubstituted indenes, 8 and 9, respectively, are formed, and 9 is obtained with almost total diastereoselectivity. This result can also be rationalised by a stereoselective complexation of lithium, as shown by separate experiments and by molecular mechanics calculations. Methyltricarbonyl molybdenum(II) complexes have been synthesised and characterised from glucose-monosubstituted 5 and glucose-disubstituted 6 cyclopentadienes.

Enantioselective hydrogenations with chiral titanocenes

In this review article chiral titanocenes and their application for the enantioselective hydrogenations of different unsaturated compounds are discussed, with a special emphasis on the kinetics and the practicality of the developed systems. The nature of enantioselectivity and the hydrogenation mechanisms are reviewed as well. Catalyst immobilization and the different immobilization techniques are examined.