Reactions of Group III Biheterocyclic Complexes

Abstract

Group III alkyl complexes supported by a ferrocene diamide ligand (1,1'-fc(NSi(t)BuMe(2))(2)) have been found to be reactive toward aromatic N-heterocycles such as 1-methylimidazole and pyridines. These reactions were investigated experimentally and computationally. An initial C-H activation event is followed by a coupling reaction to form biheterocyclic complexes, in which one of the rings is dearomatized. In the case of 1-methylimidazole, the biheterocyclic compound could not be isolated and further led to an imidazole ring-opened product; in the case of pyridines, it transformed into an isomer with extended conjugation of double bonds. Mechanisms for both reactions are proposed on the basis of experimental and computational results. DFT calculations were also used to show that an energetically accessible pathway for the ring-opening of pyridines exists.

Ring opening of aromatic heterocycles by uranium complexes

“…The reaction of 6 mbi with quinoline was investigated in order to determine whether this substrate undergoes CeH activation, as observed with a scandium benzyl supported by the same ferrocene-diamide ligand [22], or alkyl transfer, as observed with isoquinoline and group 3 metal benzyl complexes [23]. Consequently, when 6 mbi was mixed with quinoline in hexanes, at room temperature, no toluene formation was observed after 15 h, ruling our CeH activation (Eq (2)).…”

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

“…[14][15][16] Our group has studied extensively the reactivity of group 3 metals and uranium alkyl complexes supported by diamide ligands towards heterocyclic aromatic compounds. [17][18] Benzyl complexes were found to ring open 1-methylimidazoles, [19][20][21][22][23] effect C-C coupling of pyridines, [24][25] and alkyl transfer to isoquinoline. [26][27] In those cases, the ligand framework was a ferrocenediamide that could support a weak donor-acceptor interaction between the metal in the ligand.…”

Beyond CH Activation with Uranium: A Cascade of Reactions Mediated by a Uranium Dialkyl Complex

“…This observation highlights the difference in the reactivity of the uranium complexes from that reported earlier for scandium complexes: [14,15] the scandium imidazolyl complex analogous to 2 mi cannot be generated in the absence of a base; therefore, a stronger Lewis base than 1-methylimidazole would be required to displace this ligand. Thermal-ellipsoid representation of 3 A (left, 50 % probability) and 3 B (right, 35 % probability); H atoms, solvent atoms, tBu methyl groups, and disordered counterparts were removed for clarity.…”

“…[10] Our interest in the reactions of electrophilic alkyl complexes [11,12] supported by a ferrocene (fc) diamide ligand with aromatic N heterocycles [13][14][15] prompted us to investigate the reactivity of the uranium dibenzyl complex 1-(CH 2 Ph) 2 ((NN fc )U(CH 2 Ph) 2 ; NN fc = 1,1'-fc(NSitBuMe 2 ) 2 ) [11,16] with imidazoles. It has been reported that actinide complexes are more reactive than analogous Group IV complexes towards aromatic N heterocycles, and that C À H activation occurs from neutral dialkyl complexes as opposed to the cationic alkyl complexes of group IV metals.…”

“…[26] The coupling of two imidazole rings dearomatizes one of them and poises it for ring opening, which presumably occurs because more stable structures with delocalized double bonds can be formed in this way. [14] We propose that the ringopening reaction leads to two intermediate isomer structures, A and B, which differ only with respect to the positions of their conjugated double bonds (Scheme 2). These intermediates A and B are transformed into the final products, 3 A and 3 B, through the migratory insertion [27][28][29][30][31] of the imidazolyl ring not involved in coupling.…”