An unusual hydrogen migration/C-H activation reaction with group 3 metals.

A novel hydrogen migration from the phenyl ring to the pyridine ring of an yttrium pyridyl complex supported by a 1,1'-ferrocene diamide ligand is reported. Density functional theory calculations were instrumental in probing the mechanism for this transformation.

Group 3 metal complexes of radical-anionic 2,2'-bipyridyl ligands.

A new method for generating group 3 metal complexes containing radical-anionic 2,2'-bipyridyl (bipy) ligands is described that relies on hydrogen-atom abstraction from dearomatized biheterocyclic complexes. This method does not involve electron transfer to neutral 2,2'-bipyridyl or salt metathesis between the lithium salt of the 2,2'-bipyridyl radical anion and group 3 metal halides. The new metal complexes were characterized by single-crystal X-ray diffraction, electron paramagnetic resonance, and absorption spectroscopy. Density functional theory (DFT) calculations were used to probe the electronic structure of these compounds. All these methods support the radical-anionic character of bipy in all bipy compounds presented.

Reactions of aromatic N-heterocycles with a lutetium benzyl complex supported by a ferrocene-diamide ligand.

A comparison between the reactivity behavior of two lutetium benzyl complexes supported by different ferrocene-diamide ligands towards aromatic N-heterocycles, such as 1-methylimidazole, isoquinoline, and pyridines, is presented. The two ferrocene-diamide ancillary ligands differ in their nitrogen-donor substituent: adamantyl for one and t-butyldimethylsilyl for the other. The synthesis and characterization of the adamantyl-derived complex 1(Ad)-DME are reported. The ring opening of 1-methylimidazole by the THF analogue of 1(Ad)-DME, 1(Ad)-THF, was observed, analogously to the ring opening of the same substrate by the lutetium benzyl complex supported by the silyl-substituted ligand. Also, analogous products were observed in the reactions with isoquinoline.

Dearomatization reactions of N-heterocycles mediated by group 3 complexes.

Group 3 (Sc, Y, Lu, La) benzyl complexes supported by a ferrocene diamide ligand are reactive toward aromatic N-heterocycles by mediating their coupling and, in a few cases, the cleavage of their C-N bonds. When these complexes reacted with 2,2'-bipyridine or isoquinoline, they facilitated the alkyl migration of the benzyl ligand onto the pyridine ring, a process accompanied by the dearomatization of the N-heterocycle. The products of the alkyl-transfer reactions act as hydrogen donors in the presence of aromatic N-heterocycles, ketones, and azobenzene. Experimental and computational studies suggest that the hydrogen transfer takes place through a concerted mechanism. An interesting disproportionation reaction of the dearomatized, alkyl-substituted isoquinoline complexes is also reported.

Reactions of group III biheterocyclic complexes.

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.