Versatile Reactivity of β‑Diketiminato-Supported Yttrium Dialkyl Complex toward Aromatic N‑Heterocycles

The reactions of β-diketiminatoyttrium
dialkyl complex LY­(CH2Ph)2(THF) (1, L = [{N­(2,6-iPr2C6H3)­C­(Me)}2CH]−) with a series
of aromatic N-heterocycles
such as 2-phenylpyridine, benzothiazole, and benzoxazole were studied
and displayed discrete reactivity including C–H activation,
C–C coupling, ring-opening/insertion, and dearomatization.
The reaction of 1 with 2-phenylpyridine in 1:2 molar
ratio in THF at 30 °C for 14 days afforded a structurally characterized
metal complex, LY­(η2-N,C-C5H4NC6H4-2)­[C5H4N­(CH2Ph-4)­Ph] (2), in 73% isolated
yield, indicating the occurrence of phenyl ring C­(sp2)–H
activation and pyridine ring 1,4-addition/dearomatization. However,
when this reaction was done at 5 °C for 7 days, it gave the pyridine
ring 1,2-addition product LY­(η2-N,C-C5H4NC6H4-2)­[C5H4N­(CH2Ph-2)­Ph] (3) in
54% isolated yield. Further investigations revealed that complex 2 is the thermodynamic controlled product and complex 3 is the kinetically controlled product; 3 converted
slowly into 2, as confirmed by 1H NMR spectroscopy.
The equimolar reaction of 1 with benzothiazole or benzoxazole
produced two C–C coupling/ring-opening/insertion products,
LY­[η2-S,N-SC6H4NCH­(CH2Ph)2]­(THF) (4) and {LY­[μ-η2:η1-O,N-OC6H4NCH­(CH2Ph)2]}2 (5), in 84% and 78% isolated yields, respectively.