Diphenylacetylene stabilised alkali-metal nickelates: synthesis, structure and catalytic applications

Abstract

Whilst low-valent nickelates have recently been proposed as intermediates in Ni-catalysed reactions involving polar organometallics, their isolation and characterisation is often challenging due to their high sensitivity and reactivity. Advancing...

NMR detection of the strained metallacycles in organolithiums: theoretical study

“…Chemical shifts and 1 J CLi spin-spin coupling constants were calculated for all other complexes using a WP04/aug-pcSseg-1 level of theory, providing the best balance between accuracy and time consumption. 27 Since the experimental investigations of organolithiums are most commonly performed with the use of 6 Li-enriched substrates, 12 the main discussion will be provided for 13 C- 6 Li spin-spin coupling constants. At the same time, the higher natural abundance of the 7 Li isotope (92.41%) makes NMR measurements with this nucleus more convenient (despite its higher quadrupole moment of −0.0406 barn).…”

“…5-and 6-membered metallacycles are more extensively studied, however no systematic data on the change of 1 J CLi upon titration with strong ligands is provided. It is a pity that having suitable compounds at their disposal, most authors did not measure low temperature 13 C NMR or did not quantify the spin-spin coupling constants. The experimental data on this matter, which we were able to find, is given in Scheme 4.…”

“…The latter is arguably the most fascinating feature of organolithiums: the implementation of additives, such as ligands or metal-containing species, or the simple act of changing the solvent allows to enhance the reaction rate, control regioselectivity and open up new reaction pathways. 12,13 For instance, as a monomer methyllithium is more basic than phenyllithium by more than 10 pK a units in the gas phase. However, at a high dilution in tetrahydrofuran, methyllithium is only little more reactive and at 0.5 M concentration, it is even of inferior reactivity due to the higher aggregation state in solutions (Scheme 1a).…”

Organolithium aggregation as a blueprint to construct polynuclear lithium nickelate clusters

“…13,14 In this context, the coordination of polar organometallics to Ni(0)-olefin complexes can afford highly reactive heterobimetallic nickelates, 15 and we have recently assessed the rich co-complexation chemistry of Ni(COD) 2 (COD = 1,5cyclooctadiene) with various organo-alkali-metal compounds such as aryl-lithiums and lithium acetylides. [16][17][18][19] In several cases, additional molecules of organolithium are readily incorporated within the nickelate structure, but not coordinated directly to Ni(0), and this feature has also been observed with lithium halides 17 and alkali-metal alkoxides. 17,20 Lithium nickelates with Li:Ni ratios of 1 : 1, 2 : 1 and 3 : 1 have now been documented, [15][16][17][18][19] and we sought to exploit the high aggregation ability of aliphatic lithium acetylides to access new classes of lithium nickelates with higher Li : Ni ratios.…”

“…[16][17][18][19] In several cases, additional molecules of organolithium are readily incorporated within the nickelate structure, but not coordinated directly to Ni(0), and this feature has also been observed with lithium halides 17 and alkali-metal alkoxides. 17,20 Lithium nickelates with Li:Ni ratios of 1 : 1, 2 : 1 and 3 : 1 have now been documented, [15][16][17][18][19] and we sought to exploit the high aggregation ability of aliphatic lithium acetylides to access new classes of lithium nickelates with higher Li : Ni ratios.…”