Group 15 elements heteroaromatics

As a caveat to the use of NICS values as the sole determinant of aromaticity, Sastry and co-workers <2003JMT(663)145> have examined the use of this parameter for a range of heteroaromatic systems, including phosphinine 1 and its monoprotonated form 16. Their conclusion is that NICS values should not be used as the sole criterion for aromaticity for heteroaromatic molecules containing group III and IV row main group elements. 

Direct replacement of the Cp2Zr unit in the zirconacyclopentadiene by main group elements such as PPh, S, and Se etc. provides an important route to the five-membered heteroaromatic cycles 54 (Scheme 11.22) [25]. Generally, the heteroatom compound... 

Similar to the reaction of zirconacyclopentadiene with main group dihalides EX2, the Cp2Ti unit in titanacyclopentadiene could also be replaced directly by main group elements to give five-membered heteroaromatic cycles. For example, titanacyclopentadiene 85, which was prepared by the homocoupling of 1,4-bis(trimethylsilyl)butadiyne, reacted with sulfur monochloride to give thiophene derivative 86 in a moderate yield, as shown in Scheme 11.33 [34]. 

Design of self-adapting N-heteroaromatic-substituted claw ligands as E /M" " (E = p-block element, M = main group metal)chargedspacers 97CB1365. 

This section deals with a few PES studies on molecules in which an element of the Group XIV is the heteroatom in a heteroaromatic compound78-80. 

Those donor atoms and/or groups are examined as donor centers in the problem of competitive coordination on which, due to the molecular structure of the ligand, the most favorable conditions are created for electrophilic attack by the metal, after taking into account the acceptor properties of the metal and the conditions of complex-formation reactions [19]. Such donor centers are mostly elements of a few main subgroups belonging to Groups V and VI of the Periodic Table, and also the unsaturated, aromatic, and heteroaromatic compounds which form the fundamentals of modern ligands (Chap. 2). 

Examples of efficient catalysts for the asymmetric hydrogenation of aromatic and heteroaromatic compounds are quite rare, even with hydrogenation procedures catalyzed by chiral Rh, Ru, and Ir complexes. Therefore an important breakthrough was by Rueping s group in 2006 the development of an enantioselective phosphoric acid-catalyzed partial reduction of quinoline derivatives [62]. This represents the first example of a metal-free reduction of heteroaromatic compounds. (/ )-(—)-9-phe-nanthryl-l,l -binaphthyl-2,2 -diyl hydrogenphosphate was selected as chiral element of choice to perform stereocontrol (97% ee. Scheme 15.29). 

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