New catalyst for homocoupling of aryl halides based on nickel complexes with diazabutadiene ligands

Easy Entry into Reduced Ar‐BIANH2 Compounds: A New Class of Quinone/Hydroquinone‐Type Redox‐Active Couples with an Easily Tunable Potential

“…Compounds of the family bis(aryl)acenaphthenequinonediimine (Ar‐BIAN) ( 1 ; see Scheme ) have been known for some time,1–3 but have been brought to the general attention only in the 90s by Elsevier and his group 4. Since then, they have found widespread use mostly as ligands for transition metals and the corresponding complexes have been employed as catalysts for a wide variety of reactions, such as alkene hydrogenation,5 polymerization,6–11 copolymerization,12–18 aziridination,19 cyclopropanation,19 and epoxidation20 alkene‐CO copolymerization,21–24 alkyne coupling in the presence of halogens or organic halides and tin compounds25–27 or just tin compounds,28 selective semihydrogenation of alkynes29 and allenes,30 allylic aminations of olefins by nitroarenes in the presence of CO,31–33 the synthesis of pyrroles and oxazines from dienes, nitroarenes and CO,34 the reduction of nitroarenes to anilines by CO/H 2 O,35–37 the hydroamination of alkynes,38 the homo‐coupling of organic halides39 and their cross‐coupling reaction with organomagnesium, ‐zinc, and ‐tin reagents,40–44 the Suzuki–Miyaura cross coupling,45 the synthesis of 4‐quinolones and 2,3‐dihydroquinolones from 2′‐nitrochalcones and CO,46, 47 the synthesis of indoles from o ‐nitrostyrenes and CO,47, 48 the Heck arylation of olefins,49, 50 and oxidative Heck reaction,51, 52 the synthesis of dihydrofurans and dihydrobenzoxepines53 and N ‐acyl vinilogous carbamic acids,54 the cyclotrimerization of alkynes,55 the click reaction,56 the dimerization of vinyl ethers to acetals,57 and the diboration of α,β‐unsaturated carbonyl compounds 58. For some of these syntheses, the use of the Ar‐BIAN ligands was instrumental in achieving a high performance of the catalytic system.…”

Nickel/α‐diimine catalysts in C (sp2)–C (sp2) homocoupling: An underestimated and versatile ligand family

“…We started from a study of influence of variation of the conditions in a probe reaction-bromobenzene homocoupling-on the performance of the catalytic system (Table 1) using one of the best-performing ligands from our previous work (L Acen-dipp , Figure 1, C, R = 2,6-diisopropylphenyl). 18 The 0.75 equiv. loading of zinc dust (Table 1, entry 4) was generally enough for almost complete conversion of bromobenzene to biphenyl, although a larger excess (8 equiv.…”

“…Ligands L tOct , L Acen-dipp , L cC6 , and L cC12 , which gave the most active catalysts of homocoupling of 2-bromotoluene, were further considered to be the "first choice" ligands when a substrate with unknown reactivity is to be used with L tOct being a priori more preferable for ortho-unsubstituted aryl halides, whereas L cC6 and L cC12 worked better for mono-ortho-substituted ones. Next, we studied the scope of the reaction (Scheme 2) using various unsaturated halides and observed formation of homocoupling products containing bulky (5) electron-donating (11)(12)(13)(14), electron-withdrawing (7)(8)(9)(10)(15)(16)(17)(18), protecting (19,22,24), and reactive (23) groups. Aryl chlorides (2), iodides (18,19), and hetaryl (21,22) and vinyl (27) bromides were used as precursors.…”

“…13 Newer modifications of the nickel catalyzed C (sp 2 )-C (sp 2 ) homocoupling itself include the use of alternative reductants, 14 nickel sources, 15 bimetallic systems, 16 additives, 17 and ligands [14b,16b,18] including chiral ones. 19 Interestingly, the use of α-diimine ligands in nickelcatalyzed transformations in preparative organic chemistry has only been scarcely documented, 18,20 which is in striking contrast with enormous variety of nickel/α-diimine catalysts of olefin polymerization described in the literature. 21 Previously, we found 18 that α-diimines can be utilized as ligands in nickel-catalyzed homocoupling with advantages of low cost, low toxicity, and easy preparation allowing for variation of the structure in comparison with conventionally used phosphine 11 and bipyridyl 12 ligands.…”

Titanium-Mediated C–C Coupling of Imidoylstannanes for the Synthesis of Tetraaryl Diimines. Isolation of Titanium Iminoacyl and Ene-diamido Intermediates

“…Recent studies have shown that the substituents on the imine carbon atoms have significant electronic effects on the coordination properties and electronic structures. , Thus, the development of new approaches for the synthesis of C-substituted dimines are of great importance. In this context, several methods including cyanide ion and rare-earth-metal-mediated C–C coupling of aldimines for the synthesis of diimines have been developed . However, some of these methods suffer from drawbacks such as low isolated yields and limited substrate scopes.…”