Reactivity of Scorpionate-Anchored Yttrium Alkyl Complex toward Organic Nitriles

The mixed TpMe2/Cp-supported yttrium monoalkyl
(TpMe2)­CpYCH2Ph­(THF) (1) reacted
with 1 equiv of PhCN in THF at room temperature to afford the imine–enamine
tautomer (TpMe2)­CpY­(N­(H)­C­(Ph)CHPh)­(THF) (2) and the insertion product (TpMe2)­CpY­(NC­(CH2Ph)­Ph)­(THF) (3), in 61% and 12% isolated yields,
respectively. 2 further reacted with PhCN in toluene
at 120 °C to give the N–H bond addition product (TpMe2)­CpY­(N­(H)­C­(Ph)­NC­(Ph)CHPh) (4). Treatment
of 1 with 1 equiv of anthranilonitrile produced the dimer
[(TpMe2)­CpY­(μ-NHC6H4CN)]2 (5). The monomer product (TpMe2)­CpY­(NHC6H4CN)­(HMPA) (6) can be obtained through
the coordination of HMPA (hexamethylphosphoric triamide). The reaction
of 5 with 1 in THF at room temperature gave
the cyano group insertion product [(TpMe2)­CpY­(THF)]2(μ-NHC6H4C­(CH2Ph)N)
(7). However, this reaction under the heating conditions
gave an unexpected rearrangement product, (TpMe2)­CpY­(THF)­(η2-NHC6H4C­(CH2Ph)NH)
(8). 5 further reacted with o-aminobenzonitrile at 120 °C to afford the nucleophilic addition/cyclization
product TpMe2Y­[κ3-(4-NH(C8N2H4)­(2-NHC6H4)]­(HMPA) (9), accompanied with the elimination of the
Cp ring. These results indicated that the yttrium alkyl complex exhibits
high activity toward organic nitriles and reveals some unusual transformations
during the insertion process. All these new complexes were characterized
by elemental analysis and spectroscopic methods, and their solid-state
structures were also confirmed by single-crystal X-ray diffraction
analysis.