Structural and Synthetic Insights into Pyridine Homocouplings Mediated by a β‐Diketiminato Magnesium Amide Complex

Abstract

The reaction of [( Nacnac)Mg(TMP)] (1) with 4-subtituted pyridines proceeds via sequential regioselective metallation and 1,2-addition to furnish a range of symmetric 4,4'-R -2,2'-bipyridines in good yield, representing a new entry into bipyridine synthesis. Interestingly, the reaction of 1 with 2-OMe-pyridine led to formation of asymmetric bipyridine 6, resulting from the C6-magnesiation of the heterocycle followed by a C-C coupling step by addition to the C2 position of a second, non-metallated molecule, and subsequent elimination of [ NacnacMgOMe] (7). Synthesis combined with spectroscopic and structural analysis help rationalise the underlying processes resulting in the observed reactivity, and elucidate the key role that the sterically encumbered β-diketiminate ligand plays in determining regioselectivity.

Reaching Milestones in the Oxygenation Chemistry of Magnesium Alkyls: towards Intimate States of O2 Activation and the First Monomeric Well‐Defined Magnesium Alkylperoxide

“…The Mg−Mg separation is 2.999(2) Å, while Mg−O bonds lengths fall in a narrow range of 1.983–1.992 Å. The observed geometric parameters for 3 2 are essentially similar to that observed in the previously reported analogous compounds [( dipp BDI)Mg( μ ‐OR)] 2 . Compound 4 crystallizes in space group P as a monomeric moiety with a η 2 binding mode of the alkylperoxide ligand (Figure ).…”

“…Nevertheless, this issue is rather challenging due to the lack of univocal data concerning the coordination state of magnesium alkyl complexes in donor solvents. The formation of the Lewis acid‐base adducts between magnesium alkyls supported by β ‐diketiminates and various donor ligands is well‐documented in the solid state . In turn, in solution, the molecular dynamics and ligand exchange in [( dipp BDI)MgR(L)]‐type complexes were particularly nicely demonstrated by Chisholm and co‐workers .…”

“…The formation of the Lewis acid-base adducts betweenm agnesium alkyls supported by b-diketiminates and variousd onorl igands is well-documented in the solid state. [67][68][69] In turn, in solution,t he molecular dynamics and ligand exchange in [( dipp BDI)MgR(L)]-type complexes were particularly nicely demonstratedb yC hisholm and co-workers. [68] The authors showed that these complexes are kinetically labile and likelyr eact throughb othad issociative anda na ssociative (with the formation of the fifth-coordinate magnesium complex, Scheme3)i nterchange mechanism.…”

“…The four-coordinate metal cen-tres adopt distorted tetrahedral geometry.T he MgÀMg separation is 2.999(2) ,w hile MgÀOb onds lengths fall in an arrow range of 1.983-1.992 .T he observed geometricp arameters for 3 2 are essentiallys imilar to that observed in the previously reported analogousc ompounds [( dipp BDI)Mg(m-OR)] 2 . [10,11,53,54,67] Compound 4 crystallizes in space group P1 as am onomeric moiety with a h 2 binding mode of the alkylperoxide ligand ( Figure 4). The five-coordinate magnesium centre adopts distorted squarep yramidal geometry,a nd its coordination sphere is completed by two nitrogen atoms from the b-diketiminate ligand and the thf molecule.…”

Cobalt-Catalyzed Electrophilic Aminations with Anthranils: An Expedient Route to Condensed Quinolines

“…Furthermore, we have extended this new quinoline synthesis using aryl and heterocylic zinc pivalates 9 , which were prepared from the corresponding (hetero)aryl bromides by Mg- insertion in the presence of LiCl 14 ( 9a – 9g ), or by a directed metalation of heterocyclic substrates with TMP-bases (TMP = 2,2,6,6-tetramethylpiperidyl) 15 such as TMPZnOPiv·LiCl 16 or TMPMgCl·LiCl 17 ( 9h – 9n ), followed by transmetalation with Zn(OPiv) 2 . By using especially electron-rich organozinc pivalates, we have observed using our standard conditions, that after amination a cyclization occurs (via A and B in Table 2) leading to various condensed N-heterocyclic derivatives 10a – 10p .…”