2022

Crystalline phosphino-functionalized mesoionic olefins (p-MIOs)

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 A. Merschel,  Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

Phosphino-functionalized mesoionic olefins (p-MIOs), (iMIC)CHR (iMIC = PhC{N(Dipp)}2C(PPh2)C, Dipp = 2,6-iPr2C6H3; R = H 4a or Ph 4b) derived from a 1,3-imidazole based mesoionic carbene (iMIC) are reported. The p-MIOs 4a (blue) and 4b (green) are crystalline solids and have been characterized by NMR spectroscopy and X-ray diffraction as well as analyzed DFT calculations. Calculated proton affinities of 4a (291.3 kcal/mol) and 4b (288.1 kcal/mol) support their remarkably basicity that exceed of classical NHCs. Treatment of 4a with (Me2S)AuCl (and AgOTf) affords the dinuclear gold compound [(4a)Au](X)2 (5-X) (X = Cl or OTf) with a short Au----Au distance of 3.130(2) Å for 5-Cl. Reaction of 4a with a main-group reagent PhBCl2 yields the boronium cation [(4a)BPhCl]Cl (6).

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Mesoionic Dithiolates (MIDts) Derived from 1,3-Imidazole-Based Anionic Dicarbenes (ADCs)

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 F. Ebeler,  Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

Mesoionic dithiolates Li(MIDts) as well as heteroleptic (MIDt)GeCl and homoleptic (MIDt)2Ge germylenes are reported as crystalline solids. The germylene (MIDt)2Ge features the highest-lying HOMO (−4.37 eV) and has the smallest HOMO-LUMO energy gap (2.82 eV) among the hitherto known germylenes. Insertion of GeCl2 into the Ge−Cl bond of (MIDt)GeCl affords the Ge−Ge catenation product (MIDt)GeGeCl3, a mixed-valence Ge(+1)/Ge(+3) compound.

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Advances and Recent Trends in Dipnictenes Chemistry

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L. Weber,* F. Ebeler, R. S. Ghadwal*

Dipnictenes are molecules comprising a double bond between two Group 15 elements (referred as pnictogens (Pn) = P, As, Sb, Bi). Over the last decades, the chemistry of dipnictenes has undergone a remarkable advance. This is largely because of the advancement of new ligand sets with distinct stereoelectronic properties. In general, classical dipnictenes are kinetically stabilized by the use of extremely bulky aryl or alkyl substituents. In recent years, numerous ligand frameworks featuring non-carbon donor substituents have also been introduced in dipnictenes
chemistry. Now a plethora of dipnictenes with divergent electronic structure, reactivity, and physical properties are known. Among carbon-donor substituents, stable N-heterocyclic carbenes (NHCs) and other singlet carbenes have also been used as potent Lewis bases to derive related unsaturated species. A comprehensive understanding of the structure, bonding, and reactivity of a whole series of dipnictenes (RPn=PnR) (R=a substituent) as well as the influence of substituents on the nature of these species will be instrumental for the advancement of the field, in particular to unveil the relevance of these molecules in materials science. The aim of this review is to outline recent advances in dipnictene chemistry with a special focus on their reactivity. The outcomes show that dipnictenes have emerged from simple laboratory curiosities to versatile and useful synthons in modern main-group chemistry, which is expected to evolve further.

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R. S. Ghadwal*

Molecules and materials with easily tunable electronic structures and properties are at the forefront of contemporary research. π-Conjugation is fundamental in organic chemistry and plays a key role in the design of molecular materials. In this Account, we showcase the applicability of N-heterocyclic vinyl (NHV) substituents based on classical N-heterocyclic carbenes (NHCs) for tuning the structure, properties, and stability of main-group species (E) via π-conjugation and/or π-donation...